Production of bauxite and aluminum oxide in the leading countries in the world in 2018 and 2019 and the current state of bauxite raw material reserves.
This chapter introduces advanced aluminum alloy matrix composites and their manufacturing processes. In the beginning, the state of the art is characterized and the general characteristics of aluminum and its practical applications are presented, starting with the history of aluminum. The current approximate distribution of bauxite resources in the world and the production of bauxite and alumina in the leading countries of the world, as well as the production of primary and secondary aluminum and the range of aluminum end products, are presented. Aluminum alloys intended for plastic deformation and castings, and composite materials in general and with a matrix of aluminum alloys in particular, have been characterized in general. Against this background, a detailed review of the results of the Author’s own research included in numerous projects and own publications on advanced composite materials, their production technology, their structure, and properties were done. The range of aluminum alloy matrices of composite materials was adequately characterized, which include AlSi12, AlSi7Mg0.3, AlMg1SiCu, AlMg3, AlMg5, and AlMg9, respectively. Composite materials tested in terms of manufacturing technology include three groups. The first group includes gas pressure infiltration with liquid aluminum alloys of suitably formed porous preforms. Porous frameworks as a reinforcement for pressure-infiltrated composite materials with a matrix of aluminum alloys are produced by three methods. Al2O3 powder with the addition of 30–50% carbon fibers is uniaxially pressed, sintered, and heated to thermally degrade the carbon fibers and create the required pore sizes. In the second case, the ceramic porous skeleton is produced with the use of halloysite nanotubes HNTs by mechanical milling, press consolidation, and sintering. A third method is SLS selective laser sintering using titanium powders. Another group of manufacturing technologies is the mechanical synthesis of the mixture of AlMg1SiCu aluminum alloy powder and respectively, halloysite nanotubes HNTs in a volume fraction from 5 to 15% or multi-wall carbon nanotubes MWCNTs in a volume fraction from 0.5 to 5%, and subsequent consolidation involving plastic deformation. The third group of analyzed materials concerns composite surface layers on substrates of aluminum alloys produced by laser feathering of WC/W2C or SiC carbides. The structure and properties of the mentioned composite materials with aluminum alloys matrices are described in detail. The chapter summary provides final remarks on the importance of advanced aluminum alloy composite materials in industrial development. The importance of particular groups of engineering materials in the history and the development of the methodology for the selection of engineering materials, including the current stage of Materials 4.0, was emphasized. The importance of material design in engineering design is emphasized. Concepts of the development of societies were presented: Society 5.0 and Industry 4.0. The own concept of a holistic model of the extended Industry 4.0 was presented, taking into account advanced engineering materials and technological processes. Particular attention was paid to the importance of advanced composite materials with an aluminum alloy matrix in the context of the current stage of Industry 4.0 of the industrial revolution. Growth in the production of aluminum, its alloys, and composites with its matrix was compared with that of steel. Despite the 30 times less production, aluminum is important due to its lower density. The challenges posed by the development in the Industry 4.0 stage, including the expectations of the automotive and aviation industry, force constant progress in the development of new materials with the participation of aluminum, including the composite materials with an aluminum alloy matrix presented in this chapter.
- Aluminum alloys matrix composite
- pressure infiltration
- halloysite nanotubes
- multi-wall carbon nanotubes
- additive manufacturing
- selective laser sintering
- mechanical synthesis
- laser feathering
- Industry 4.0
- Sustainable Development Goals
- materials science paradigm
- aluminum market
1. State-of-the-art and the general characteristics of aluminium and its practical applications
1.1 General characteristics of aluminum
Aluminum is a metal of very high technical importance [1, 2, 3, 4]. It occurs in nature in many minerals and is the third element (after oxygen and silicon) in terms of its share in the earth’s crust. It is, however, the second metal after iron in terms of technical applications. Its main ore is bauxite, from which pure Al2O3 oxide is produced, and then by electrolysis of the oxide dissolved in the molten cryolite (sodium fluoroaluminate), blast aluminum is obtained, which can be further refined.
Aluminum has an atomic number of 13 and an atomic mass of 26.9815. It does not show allotropes and crystallizes in a wall-centered regular network of A1 type with a parameter of 0.40408 nm. The melting point of aluminum is 660.37°C and the boiling point is 2494°C. The density of aluminum is 2.6989 g/cm3 at 20°C. Aluminum in the annealed condition is characterized by tensile strength 70–120 MPa, yield strength 20–40 MPa, elongation 30–45%, and narrowing 80–95%. Aluminum can be cold and hot worked plastic deformed. In the cold plastic deformed state with 60–80% degree of crushing, the tensile strength reaches 140–230 MPa, yield strength 120–180 MPa, hardness 40–60 HBW, with a reduced elongation 1.5–3%.
Aluminum is characterized by high electrical conductivity – 37.74 MS/m, constituting approx. 65% of the electrical conductivity of copper, and good thermal conductivity. The electrical conductivity is significantly reduced with increasing concentrations of impurities and impurities, mainly Fe and Si, as well as Cu, Zn, and Ti. These elements also reduce the plasticity but increase the strength properties. The Fe admixture hardly dissolves in aluminum, creating the brittle Al3Fe phase. On the other hand, Si shows low solubility and does not form any phases, it is in the free form. In the case of the simultaneous presence of Fe and Si, the Fe3Si2Al12 or Fe3Si2Al9 intermetallic phases occur. Their separations, especially at the grain boundaries, significantly reduce the plastic properties of aluminum.
Aluminum is highly resistant to corrosion. In the air, it is covered with a thin layer of Al2O3, which protects against atmospheric corrosion, water, concentrated nitric acid, numerous organic acids, and hydrogen sulfide. On the other hand, reducing acids HCl and HF, seawater, vapors, and mercury ions accelerate the corrosion of aluminum. In order to improve corrosion resistance, aluminum may be subjected to anodic oxidation (so-called anodization), i.e. an electrolytic process of producing an oxide coating, e.g. in a 10% sulfuric acid solution, combined with different colors of the metal surface.
Aluminum is extracted from ores in a complex process and, obviously, unknown throughout most of human history [5, 6, 7]. On the other hand, hydrated potassium-aluminum sulphate (KAl (SO4) 2 12 H2O) has been known for millennia as alum, or more precisely aluminum-potassium alum, which occurs naturally as a mineral in the form of granular, infiltrative clusters. Raids and efflorescence. It occurs in the weathering zone of clay rocks, coals containing pyrite, marcasite and other sulfides. It is also formed in the process of weathering igneous rocks rich in feldspar and feldspar, incl. in Uzbekistan in the Kara-kum desert, in Italy near Vesuvius, in the USA in Alaska and in Russia in Kamchatka. People have known alum since the 5th century BC and it was widely used for staining as early as antiquity . It was widely distributed in international trade relations in the Middle Ages due to its use in dyeing [8, 9, 10]. Aluminum was discovered in 1825 by Hans Christian Oersted [11, 12, 13], a Danish physicist. The results of his work were extended by Friedrich Wöhler [8, 13, 14], a German chemist. In 1854, both Robert Wilhelm Bunsen, a German chemist, and Henri Étienne Sainte-Claire Deville, produced aluminum for the first time by electrolysis. Electricity supply was ineffective at the time, so their methods could not be developed in industry. At that time, aluminum was extremely valuable, and therefore its price significantly exceeded that of gold. The situation in this respect continued until 1856, when Deville first began industrial production and not through the production of electrolytes , which he considered impractical at the time, so he switched to chemical methods in the same year. In 1884, world aluminum production reached 3.6 tons.
In 1886, Paul Héroult, French engineer and Charles Martin Hall, American engineer, independently developed a method of producing aluminum, which became the first large-scale production technology . Their process is still in use today and is known as the Hall-Héroult process (Figure 1) [15, 16]. This process and the process developed by Carl Joseph Bayer, an Austrian chemist, determined the wide dissemination of aluminum and its availability to the public, starting from 1889 (Figure 2) .
Digestion, in which bauxite is ground and slurried to caustic soda (NaOH) which is then pumped into large pressure fermentors where the caustic soda reacts with aluminum oxide minerals to form soluble sodium oxide Na[Al(OH)4];
Clarification, in which a sodium oxide solution is processed in cyclones to remove coarse particles; the remaining fluid is processed in thickeners where the flocculates are added to the solid agglomerates which are removed with fabric filters; the residue (red mud) is washed and discarded and the clarified solution (containing Na[Al(OH)4]) goes to the next step;
Precipitation – aluminum oxide nucleating agents are added to the clarified solution in order to facilitate the separation of larger agglomerated aluminum oxide crystals; product-size crystals are separated from the small crystals (recycled serve as nucleating agents) and washed to remove caustic residues; agglomerates are transferred to the next step.
Calcination – Na[Al(OH)4] agglomerates are placed in rotary kilns or stationary fluidized bed calciners at a temperature higher than 960°C, ensuring dehydration and obtaining commercial grade aluminum oxide.
Both these processes are still used in the production of aluminum and it is them that have made aluminum popular in industry and everyday life. The statue of Anteros, which was erected in 1893 at Piccadilly Circus in London, Great Britain, can be considered a symbol of the growing role of aluminum and is considered the first large work made of this material (Figure 3).
World aluminum production reached 6,800 metric tons in 1900. Figure 4 shows changes in the production volume and prices of aluminum in the years 1885–2020.
In the late nineteenth and early twentieth centuries, aluminum alloys began to be used more and more. The basis of modern aluminum production are the Bayer and Hall-Héroult processes, further enhanced in 1920 by Carl Wilhelm Söderberg, a Swedish chemist and his cooperators. In the twentieth century, the range of aluminum applications has significantly increased, including both in engineering and in construction, to gain use in aviation as a strategically important material during World War I. For these reasons, the importance of aluminum during the Second World War was even greater, to exceed 1,000,000 metric tons for the first time in 1941. After the war, since 1945, aluminum consumption has been increasing annually by another 10% for almost three decades, gaining popularity in construction applications, electrical cables, basic foil and the aerospace industry. In 1954, aluminum, ahead of copper, became the most widely produced non-ferrous metal, with world production increasing to 2,810,000 tons per year. In the second half of the 20th century, aluminum found its way into transport and packaging, although its production was critically assessed for environmental reasons, and as a result aluminum recycling developed. For example, in the United States, in the period from 1970 to 1980, the level of aluminum recycling increased 3.5 times, and by 1990 even 7.5 times. At the same time, mining and processing costs decreased and aluminum production increased, exceeding 10,000,000 metric tons per year for the first time in 1971. This was accompanied by a fall in aluminum prices since the beginning of the 1970s. In 1973, that price was US$ 2,130 per metric ton (1998 US price level). The launch of the production of beverage cans prompted a significant increase in aluminum production in the early 1970s, despite the fact that in the 1970s and 1980s the costs of primary aluminum production increased. However, it contributed to an increase in the share of secondary aluminum in the overall production, due to its significantly increased recycling. In the 1970s, aluminum became a stock exchange commodity. In the 1970s, aluminum production from the United States, Japan and Western Europe was gradually allocated to Australia, Canada, the Middle East, Russia and China, where it was cheaper, e.g. in view of favorable tax regulations in these countries. Production costs fell in the 1980s and 1990s. In the first decade of the 21st century, the total share of the BRIC countries (Brazil, Russia, India and China) increased from 32.6% to 56.5% in primary production and from 21.4% to 47.8% in primary consumption. China amassed a particularly large share of world production thanks to abundant raw materials, cheap energy and government incentives, and its share in consumption increased from 2% in 1972 to 40% in 2010. In the United States, this share decreased to 11%. In the United States, Western Europe, and Japan, most aluminum is used in transport, engineering, construction, and packaging. World production continues to increase, surpassing 50,000,000 metric tons in 2013 and surpassing a record 58,500,000 metric tons per year in 2015. World production has now exceeded more than 62,500,000 metric tons per year . Aluminum is produced in greater quantities than all other non-ferrous metals combined.
The basic raw material for the production of aluminum is bauxite [20, 21, 22]. Pierre Berthier the French geologist discovered bauxite in Provence, France in 1821. Bauxite is a sedimentary rock which contains a high aluminum content as mixture of few minerals i.e. gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(OH)), goethite (FeO(OH)) and hematite (Fe2O3), clay mineral kaolinite (Al2Si2O5(OH)) and also anatase (TiO2) and ilmenite (FeTiO3 or FeO.TiO2). Australia is the largest producer of bauxite, followed by China. Figure 5 shows the distribution of the main raw materials of bauxite in the world with the differences in their abundance. Table 1 presents the production of bauxite and aluminum oxide in the leading countries in the world in 2018 and 2019 and the current state of bauxite raw material reserves .
|Country (alphabetical order)||Bauxite Reserves||Bauxite||Aluminum oxide|
|World total (rounded)||30,000,000||327,000||370,000||131,000||130,000|
Aluminum is produced in many grades  with varying degrees of purity from 99.999 to 99.0%, a few examples of which are given below:
the purest one containing 99.995% Al is used in the production of chemical equipment and condenser films,
containing 99.8% Al is used for foils, cable coatings and plating,
containing 99.5% Al for electric wires,
containing 99% Al for everyday products.
There are three different types of primary aluminum, corresponding to different production methods:
commercially pure aluminum from the reduction of Al2O3 in the electrolyser, representing the majority of industrial production; it may contain up to 1% of impurities, and the purity very often exceeds 99.9%.
refined aluminum produced by electrorefining commercially pure aluminum in the cell layer; its purity ranges from 99.9% to 99.99 + %.
zone refined aluminum produced by zone refining and with the appropriate starting material and technique can produce metal with less than 1 ppm impurities.
This purity was obtained thanks to the zone refining of electrodeposited metal from organic baths.
Secondary aluminum is produced by remelting production scrap or obsolete equipment and is usually recovered as alloys. Even after remelting high-quality electrodes, the resulting “secondary pure aluminum” is less pure than the corresponding primary aluminum because contamination by other materials occurs.
Most of the impurities in primary aluminum come from raw materials (bauxite, soda, carbon). Therefore, their purity should be controlled, although it is also important to vary the chemical composition of individual shipments, even if they come from the same source, as they may differ in their composition, even by one order of magnitude.
Metallurgical aluminum grades (with limited purity) are used in the production of alloys and numerous everyday products, equipment for the food industry, for some electric cables, heat exchangers, in construction, for coatings of steel products, and in the form of foil – for food packaging. Refined aluminum (high purity) is used in electronics and electrical engineering and for the construction of special chemical apparatus.
1.2 General presentation of aluminum alloys
The relatively low strength properties of aluminum can be increased – even several times – by introducing alloying elements and heat treatment of the alloys [24, 25, 26, 27, 28, 29, 30]. Table 2 gives the general classification of aluminum alloys according to their chemical composition.
|Aluminum alloy series||Major alloy additives||Characteristic|
|1xxx||Lack (admixtures <1%)||Low strength properties and very high plasticity, making them susceptible to cold and hot forming; thanks to the high purity of the alloy, they are highly resistant to corrosion, and they are also characterized by high thermal and electrical conductivity|
|2xxx||Cu||Has an increased hardness compared to 1xxx, but the corrosion resistance is much lower|
|3xxx||Mn||Low strength, but susceptible to plastic deformation; they are very well weldable and corrosion resistant|
|4xxx||Si||High strength and corrosion resistance|
|5xxx||Mg||Corrosion resistance is even higher than for 4xxx|
|6xxx||Mg + Si||Corrosion resistant, shows good plasticity, medium mechanical strength|
|7xxx||Zn + Mg||Hard, high-strength aluminum alloys; they are characterized by the highest strength of all aluminum alloys, but also low corrosion resistance|
|8xxx||Others, no classification||Covers aluminum alloys which were not classified in the previous series|
Most generally – due to the method of manufacturing – aluminum alloys are divided into:
for plastic deformation,
Some of these alloys can be used both as cast and for plastic deformation.
The alloys for plastic deformation usually contain up to about 5% of alloying elements, most often Cu, Mg, Mn, sometimes also Si, Zn, Ni, Cr, Ti, or Li. Some of these alloys are used in a plastic worked or in recrystallization annealed state, and some are subjected to a precipitation hardening heat treatment. Aluminum alloys with a concentration of alloying elements greater than 5% can also be subjected to plastic deformation, under special conditions. Aluminum alloys can be shaped by various methods of plastic deformation and are supplied in the form of many metallurgical intermediates.
Cast aluminum alloys are mostly multi-component alloys with a high concentration – from 5 to 25% – of alloying elements, mainly Si, Cu, Mg, Zn, and Ni or their various combinations. Cast Al alloys are characterized by good fluidity and often low casting shrinkage. Alloys containing less than 5% alloying elements can also be used as cast. In general, aluminum alloys can be sand-molded, die-cast, pressure-cast, and lost wax methods although some of these methods are rarely used today.
1.3 General information on composite materials with aluminum alloys matrices
Advanced possibilities of shaping the properties of materials containing aluminum alloys are provided by the production of composites with an aluminum matrix (AMC), where the matrix most often used is not aluminum but aluminum alloys [31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45]. AMCs in relation to aluminum and its alloys show better physical and mechanical properties, including a very favorable strength-to-weight ratio, high strength and high modulus of elasticity, better fatigue strength, good ductility, low thermal expansion coefficient, good wear resistance and corrosion resistance and creep strength. Therefore, AMCs have found numerous applications, many times unrivaled in comparison with aluminum alloys, when high properties are required, e.g. in the automotive, aviation, manufacturing, armaments, energy and medicine industries [46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62].
Generally, a composite material, often simply referred to as a composite, is a combination of two or more materials (reinforcement members, fillers and binder constituting the matrix of the composite) differing in type or chemical composition on a macroscopic scale . Components of composite materials retain their identity because they do not completely dissolve in each other and do not combine into other elements, but interact together. Typically, these components can be physically identified and exhibit interfacing surfaces.
Composite materials are usually artificially produced to obtain properties that cannot be obtained separately by any of the components present. Composite materials are used to ensure appropriate mechanical properties, but also electrical, thermal, tribological, various environmental and other properties. Composite materials most often contain fibers or phase particles and are stiffer and stronger than the continuous matrix phase. The many reinforcement elements also provide good thermal and electrical conductivity and a lower coefficient of thermal expansion and/or good wear resistance. However, there are exceptions that can also occur in composite materials, such as rubber-modified polymers, where the discontinuous phase is more compliant and more ductile than the polymer, resulting in increased impact strength. Similarly, steel wires can be used to reinforce gray cast iron in truck and tractor brake drums.
In general, composite materials can be classified on two separate levels. This classification, although it may seem a bit eclectic, is of practical importance. The first level of classification concerns the matrix material, and in this case the analysis is limited to metals and their alloys, in particular aluminum and its alloys. At the second level (Figure 6) the classification concerns the geometrical features of the reinforcing materials which is presented in the Figure 7 also.
Composite materials based on non-ferrous metals, including aluminum, may contain dispersoid particles with a diameter of 10–250 nm. These particles, usually metal oxides, distributed in the matrix, affect the blocking of the dislocation movement and even if they are not coherent with the matrix, they influence its strengthening. These particles cannot dissolve in the matrix, although a low solubility may improve the adhesion of the dispersoids and the matrix. As Al2O3 does not dissolve in Al, the Al2O3 – Al system effectively enhances the dispersive hardening of such a composite material. There are numerous examples of this type of composite materials, including sintered aluminum powder SAP reinforced by Al2O3 in 14% and dispersion hardened nickel or iron alloys, oxide dispersion-strengthened ODS.
Powder metallurgy is a frequently used technology to produce metal matrix composite materials, and this distinct group of composite materials is labeled P/M MMCs (powder metallurgy metal – matrix composites) or P/M AMCs respectively for aluminum matrix.
In the case of composite materials with a non-ferrous matrix, including aluminum and its alloys, reinforced with large particles, due to the relatively large size of the reinforcing particles and the lack of their coherence with the matrix of non-ferrous metals, dispersive hardening cannot take place. These groups of composite materials, on the other hand, achieve a combination of functional properties resulting from the interaction of both the matrix and the particles of the second phase arranged therein, which often guarantee an increase in strength properties.
Fiber-reinforced composite materials are most often used to provide increased static and fatigue strength, including specific strength and stiffness, which is obtained by incorporating strong, stiff but usually brittle fibers into a soft but tough matrix. The matrix only transmits applied load to the fibers, which for the most part carry it. Composite materials of this group can show high strength properties both at room temperature and at elevated temperature.
Many reinforcement materials are used. Boron, metal and ceramic fibers are used to strengthen e.g. composite materials with a metal matrix, as well as with a composition corresponding to the intermetallic phases. The described fibers have gained a wide range of applications due to their very high utility values. However, it should be noted that their price varies by as much as 50,000 times. Glass fibers are used very commonly, although not in the case of composite materials with a non-ferrous metal matrix, because their relative specific cost (cost of 1 kg of material) ranges from 1 to 3. Aramid, carbon, ceramic oxide and an oxide fibers show very good performance properties, but at a high price, because the relative cost related to the cost of glass fibers ranges from about 15 for aramid and carbon fibers, although also not used in the case of composite materials with a non-ferrous metal matrix, to approx. 4500 for SiC fibers, which determines the limited use of these materials. In very special cases, however, sapphire fibers are used, where special reinforcing properties are required, as the relative price of this material exceeds 45,000.
Often, the fibers are stapled, their length does not exceed 10 mm, and they are arranged randomly in the matrix of composite materials, especially those with a polymer matrix.
Composite materials with a non-ferrous metal matrix including AMCs reinforced with continuous fibers are a class of materials with a wide range of applications due to their mechanical properties, wear resistance and thermal properties. It is possible to adapt their properties to requirements and provide increased strength, stiffness, thermal conductivity, abrasion resistance, fatigue strength and dimensional stability. These composite materials are non-flammable, do not evaporate under vacuum, and are resistant to organic liquids, including fuels and solvents. The matrix of these materials consists of monolithic alloys, usually light metals, including aluminum, but also heat-resistant superalloys. They are reinforced with boron, carbide, oxide and tungsten fibers in a continuous form, usually with a volume fraction of 10–70% in the composite material, produced in addition to materials with the same matrix reinforced with discontinuous fibers. Aluminum oxide particles are a cheap solution and are most often used when the metal matrix is cast, while the most common are silicon carbide and boron carbide particles as a reinforcement in the form of discontinuous but also continuous fibers, especially in aircraft structures (Table 3).
|Reinforcing fiber material||Manufacturing process||Application examples|
|Boron||Hot pressing of the fiber system between the metal foils||Tubular struts of the central part of the space shuttle hull, cold heat dissipator (diffuser) in the housings of electronic microchips of multi-layer plates, neutron radiation shielding material (e.g. in spent nuclear fuel storage facilities or containers for transporting such fuel), fan blades in turbo-jet engines, aircraft wing plating, aircraft landing gear components, bicycle frames, golf clubs; Due to the degradation of boron fibers above 480°C, high-temperature applications are impossible and manufacturing using casting or high temperature low pressure pressing|
|SiC||Investment casting, low pressure hot forming, superplastic forming with diffusion welding, isostatic hot pressing HIP, green tape production by winding fibers on films covering a rotating drum and their initial bonding to the film using a polymer resin, removed then in the volatilization (evaporation) process or by plasma spraying and subsequent pressure diffusion welding of several such cut tapes stacked at a temperature close to the melting point and pressure consolidation in an autoclave in a vacuum metal container, as well as in closed forms to give the required final shapes||Construction of aircraft elements, wings up to 3 m long, elements of portable bridges, small pressure vessel cylinders, bullet stabilizers, missile casings|
|Graphite||Vacuum diffusion welding of raw metal (aluminum) strips with longitudinally arranged fibers, diffusion rolling welding Rapi-Press, continuous pressing, direct metal infiltration process, casting||Very high strength components and stiffness, e.g. the mast of the Hubble cosmic telescope, thin-walled pipes of small and large diameters (up to 2 m), with complex shapes, produced with the near-net-shape technology|
|Al2O3||Casting||Pistons for internal combustion engines (Toyota)|
Various types of ceramics, e.g., Al2O3, SiC and B4C, are widely used to reinforce aluminum matrix composites. They show very good properties, such as high strength, high hardness, abrasion resistance.
Composite materials in metal-to-metal and metal-ceramic systems are produced using liquid and solid-phase technologies. Liquid-phase technologies are based on direct (in situ) methods, during which the fibrous structure of the composite is obtained by solidifying the alloy with unidirectional heat dissipation, and on indirect (ex situ) methods using foundry technologies, plastic processing and powder engineering.
The basic manufacturing processes for AMC on an industrial scale can be divided into the following groups:
Liquid state processes, including stir casting, extrusion casting, injection molding and in situ (reactive) process, ultrasonic assisted casting, vacuum infiltration, pressureless infiltration and dispersion methods;
Solid-state processes involving powder mixing followed by consolidation (powder metallurgy), friction by shot-assisted high-energy powder grinding, ion bonding by diffusion and vapor deposition techniques
Liquid–solid processes including composite casting, semi-solid molding.
A detailed classification can also be made, based on the type of reinforcement (continuous and discontinuous) (Table 4).
|With the participation of the liquid phase||Gravitational||In solid state||Diffusion welding|
|Hot rolling welding|
|Hot extrusion welding|
|Bonding||Bonding high-energy shaping|
|Hot pressing with the participation of the liquid phase|
|Methods of manufacturing composite materials based on aluminum alloys with discontinuous reinforcement|
|With the participation of the liquid phase||Methods of mixing metal in liquid state||In solid state||Powder engineering methods|
|Thixotropic manufacturing in the liquid–solid state|
|In situ generation methods:|
Table 5 compares additionally some of the methods mentioned.
|Method||Range of shape and size||Range of volume fraction||Damage to reinforcement||Cost|
|Stir casting||Wide range of shapes, larger size up to 500 kg||Up to 0.3||No damage||Least expensive|
|Squeeze casting||Limited by preform shape up to 2 cm height||Up to 0.5||Severe damage||Moderate expensive|
|Spray casting||Limited shape, large shape||0.3–0.7||Expensive|
|Powder engineering||Wide range, restricted size||Reinforcement fracture||Expensive|
During the last quarter of a century, the processes of mechanical alloying, known for a long time, have been used in the production of composite materials reinforced with particles, causing improvement in the structure and dispersion hardening of these materials and even distribution of hardening particles in the matrix [33, 47, 63, 64, 65]. The resulting nanocrystalline or submicrocrystalline structure improves the properties of newly developed composite materials [34, 37, 47, 53, 63, 65].
2. Description of the materials taken into account and the technologies used for their manufacturing
2.1 The range of matrices of aluminum alloy matrix composite materials presented in this chapter
This chapter presents a generalization of the results of numerous own studies and provides a detailed overview of the structure and properties and manufacturing technology of several AMCs selected for presentation due to their advanced manufacturing methods and unexpected properties and the resulting wide application possibilities.
Among these materials, there are basically three groups of such materials presented in this chapter, examined within the research projects [66, 67, 68, 69, 70, 71, 72, 73, 74] of the Author of this chapter and doctoral dissertations [75, 76, 77, 78, 79, 80] carried out under the supervision of the Author of this chapter. The details were published earlier [81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112]. The description in this chapter covers the main groups of composite materials presented in Table 6, as follows:
composite materials manufactured by gas-pressure infiltration with liquid aluminum alloys,
nanocomposite materials manufactured by mechanical synthesis of a mixture of aluminum alloy powder with HNTs or MWCNTs nanotubes and the press consolidation,
composite surface layers on the substrate of aluminum alloys as a result of laser feather by introducing carbides powder.
|No.||Matrix||Reinforcement||A form of reinforcement||Technology of manufacturing||Literature|
|1||AlSi12||Sintered Al2O3 powder with carbon fibers||Skeleton structure||Gas-pressure infiltration||[73, 74, 75]|
|2.||AlSi12||Sintered HNTs halloysite nanotubes with carbon fibers||Skeleton structure||Gas-pressure infiltration||[68, 70, 74, 78]|
|3||AlSi12||Selective laser sintering of titanium powder||Skeleton structure||Gas-pressure infiltration||[66, 70, 74, 80]|
|4||AlSi7Mg0.3||Selective laser sintering of titanium powder||Skeleton structure||Gas-pressure infiltration||[66, 70, 74, 80]|
|5||AlMg1SiCu||Halloysite HNTs nanotubes||Reinforcing by dispersive particles||Mechanical synthesis & press consolidation||[68, 76]|
|6||AlMg1SiCu||Multi-wall carbon nanotubes MWCNTs||Reinforcing by dispersive particles||Mechanical synthesis & press consolidation||[67, 79]|
|7||AlMg3||WC||Powder particles in remelted zone||Laser feather by introducing powder in remelted zone||[69, 70, 72, 77]|
|8||AlMg3||SiC||Powder particles in remelted zone||Laser feather by introducing powder in remelted zone||[69, 70, 72, 77]|
|9||AlMg5||WC||Powder particles in remelted zone||Laser feather by introducing powder in remelted zone||[69, 70, 72, 77]|
|10||AlMg5||SiC||Powder particles in remelted zone||Laser feather by introducing powder in remelted zone||[69, 70, 72, 77]|
|11||AlMg9||WC||Powder particles in remelted zone||Laser feather by introducing powder in remelted zone||[69, 70, 72, 77]|
|12||AlMg9||SiC||Powder particles in remelted zone||Laser feather by introducing powder in remelted zone||[69, 70, 72, 77]|
In the above-mentioned composite materials, aluminum alloys listed in Table 7 were used as the matrix.
|Aluminum alloys||Elements concentration, wt. %|
|AlSi12||10.0–12.0||Max 0.3||Max 0.03||0.2–0.4||0.25–0.32||0.08–0.15||—||rest|
|AlSi7Mg0.3||6.5–7.5||Max 0.15||Max 0.05||Max 0.10||0.25–0.45||0.08–0.15||V max 0.03|
|AlMg1SiCu||0.6||0.47||0.22||0.11||0.95||0.006||Cr 0.26; Zn 0.015|
2.2 Manufacturing technologies of porous skeletons as a reinforcement of pressure-infiltrated aluminum alloy matrix composite materials
In the case of the 1st composite material in question, porous Al2O3 ceramic skeleton was produced by sintering Alcoa Industrial Chemicals CL 2500 powder (Table 8) with the addition of 30, 40, or 50% by weight Sigrafil C10 M250 UNS carbon fibers from SGL Carbon Group (Figure 8) with the properties given in Table 9.
|Density, g/cm3||Particle diameter D50, μm||Share of other phases, wt%|
|Diameter, μm||Average length, μm||Density, g/cm3||Strength, GPa||Young’s modulus, GPa||Carbon content, wt. %|
Al2O3 powder was wet-milled in a ball mill for 5 minutes to break up powder agglomerates. In order to eliminate mutual electrostatic interactions and prevent agglomeration of carbon fibers, Dolapix CE 64 was used, introduced into the Al2O3 suspension. To facilitate subsequent compression, 1% water-soluble polyvinyl alcohol Moviol 18–8 was added to the mixture. The powder was then dried by freezing and sublimating water under reduced pressure and sieved through a 0.25 mm sieve. The polyvinyl alcohol was activated after the powder was moistened with distilled water and left for 24 h in a polymer foil bag. Then the powders were pressed uniaxially in a die with a diameter of 30 mm on a manual laboratory press “Nelke” and in a rectangular die with dimensions of 65x46 mm on a hydraulic plate press Fontune TP 400 at a pressure 100MPa, for 15 seconds. The pressed preforms were sintered in Gero tubular furnace in an air atmosphere with a flow of 20 l/min, with slow heating up to 800°C at a rate of 20°C/h, heating for 10 hours for complete thermal degradation of carbon fibers, heating up to 1500°C at a rate of 300°C/h, sintering for 2 h and cooling with the furnace. The sintered skeletons show larger pores after the carbon fiber degradation and of much smaller dimensions around the individual ceramic particles that were intentionally not densified to the maximum extent (Figure 9). As a result, the created ceramic skeleton is characterized by a system of interconnected pores, ensuring high permeability of 2.48–10.56 m2 · 10−13 and facilitates infiltration with liquid aluminum alloy.
Appropriate Al2O3 wettability by the liquid aluminum alloy was ensured by nickel coating the pores of the ceramic skeletons by using Atotech’s Futuron technology (Table 10) used to make metallic coatings on polymeric materials to create a tin and palladium layer on the surface.
|Treatment||Reagent||Temperature, °C||Time, min|
|Surface activation||Futuron Activator||Room temperature||1|
|Noviganth Activator AK II||40–45||3|
|Applying Ni-P coating by chemical electroless method||Noviganth PA Chemical Nickel||55||1.5|
The solution of Noviganth Activator AK II ensures the exchange of tin on the surface with metallic palladium, after which it is possible to apply a layer of the Ni-P alloy by the chemical electroless method. The internal surfaces of the ceramic skeletons were coated using a solution pumping device which used a spiral cooler in the shape of a copper coil to ensure the required temperature. The sintered porous skeletons were glued with the two-component adhesive “UHU plus endfest 300” to the aluminum rings, which could be infiltrated with the liquid AlSi12 alloy after heating in a furnace at 800°C. The sintered ceramic skeleton in a matrix coated with graphite and heated to 450°C, was infiltrated by the AlSi12 liquid alloy at 800°C using a punch in a Fontune TP 400 hydraulic plate press with a pressing speed of 17 mm/s and a maximum press pressure of 100MPa for 120 s. They were removed from the mold and cooled with a stream of compressed air.
In the second case of the composite materials analyzed in this chapter, the ceramic porous skeleton, which is the reinforcement of the composite, was manufactured with the use of halloysite nanotubes (HNTs) by their mechanical milling, press consolidation, and sintering. HNTs are provided by NaturalNano (USA), and their phase composition is shown in Table 11. The nanotubes are obtained from halloysite, which is a clay mineral of volcanic origin, which is characterized by high porosity, large specific surface, high ion exchange and easy chemical and mechanical processing. Halloysite is a mineral [Al2Si2O5 (OH)4·H2O] that occurs in three deposits in the world, including in Poland. At least 30% of naturally occurring resources are in the form of nanotubes in the shape of polyhedron, hollow inside as cylindrical objects of the diameter 40–200 nm and length of up to 1–2 μm. After properly insulation HNTs can be used in nanotechnology. The morphology and particle size distribution of the powders used are shown in Figure 10.
|Halloysite nanotubes||Halloysite nanotubes heated at 1100°C||Halloysite nanotubes heated at 1500°C|
|10||Loss on the kiln at 1025°C||15.58||0.24||0.04|
For the manufacturing of porous ceramic skeletons, a mixture of halloysite powder with a mass fraction of 30, 40, 50, 60, or 70% by weight, respectively, was mechanically dry milled with Sigrafil CIO M250 UNS carbon fibers from SGL Carbon Group, analogous to that used in the previous case. Additionally, the MA7050 micronized amide wax powder with a mass fraction of 1% was used as a lubricant, also reducing the adhesion between the powder material and the mill and milling media, as well as leveling the friction between the die walls and powder particles. The technology of manufacturing the porous skeleton was very similar to that described in the 1st case. The milling of the mixture of the above-mentioned components was performed with the use of a Fritsch Pulverisette 6 centrifugal ball mill for 15 min.
The fragmented and homogeneous powder mixture obtained in this way was formed by uniaxial cold pressing in closed dies, respectively, of circular (φ30 mm) or rectangular (12 × 35 mm) cross-section for 15 s on a LabEcon 600 Fontijne Grotnes hydraulic plate press. Preliminary tests allowed to set the pressing pressure as 50, 75, and 100 MPa. The degradation and sintering cycle of the moldings in the PRS 75 W high-temperature furnace by Czylok in the air atmosphere with the flow of 5 l/h was analogous to that in the first case, but the sintering temperature, determined on the basis of the analysis of the structure and mechanical and functional properties, is 1500°C for 1 h heating and an optimal share of HNTs of 70%. In this way, the structure of sintered porous mullite is obtained (Figure 11), which is subjected to pressure infiltration in the device shown schematically in Figure 12 with the AlSi12 alloy.
In the third and fourth cases of composite materials, selective laser sintering SLS was used for the manufacturing of a porous skeleton, divided into two main stages: design and manufacturing this skeleton (Figure 13).
In stage I, a given element is designed. The available specialized three-dimensional software allows for almost complete control and repeatability of the size and geometrical features of the designed elements, and also enables full control of the conditions of the manufacturing process. The design result is a three-dimensional computer-aided design CAD model in stereolithography STL format, showing the surface of the element by means of a triangle mesh. The smaller triangles are, the more precise the mapping of the surface is. By successively dividing the element into layers of a specific thickness, the optimal conditions for the manufacturing process are established, including laser power, scanning speed, layer thickness, distance between successive remelting paths, and the diameter of the laser beam. Software for Manufacturing Applications 3D Marcarm Engineering AutoFab, integrated with the Renishaw AM 125 machine, used for selective laser sintering, was used. The three-dimensional skeleton model was designed by CAD using unit cells of a defined structure and size and by subsequently multiplicating such unit cell to design a repetitive structure skeleton in which the pore size and wall thickness are fully designed by the designer, characterized by completely open pores.
On the basis of numerous technological experiments, the selection of “hexagon cross” unit cells (Figure 14) was made and the conditions for the manufacturing by selective laser sintering of porous titanium skeletons with a selected pore size of 250 μm (controlled unit cell dimensions 500 μm) and 350 μm (dimensions unit cell 600 μm). Experimentally, the relationship between the design arrangements and the actual pore dimensions was established (Figure 15).
After giving the model the appropriate size and structure, it is divided into layers with a predetermined thickness, with the number of layers corresponding to the number of layers of powder that will sinter until obtaining the accuracy of the model production depends on the laser power used: for low power 50 W it is ±20 μm in the XY plane, and for high power 200 W ± 100 μm in the XY plane with a layer thickness of 20 to 50 μm. Manufacturing conditions are transferred to the designed model in STL format to the machine software for selective laser sintering. The most favorable properties of titanium skeletons with the given pore sizes are provided by the arrangement of unit cells at an angle of 45° to the x axis of the coordinate system (Figure 11d).
In the second stage, the previously designed element is manufactured by the method of selective laser sintering, layer by layer, until the final product is obtained. Selective laser sintering is a complex thermophysical process, the course of which depends on the type of material, the characteristics of the laser and the environment, and the thickness of the powder layer, as previously stated, as well as the diameter of the laser spot, the distance between the laser spots and the distance between the laser paths (Figure 16).
In the case of porous materials, the laser power of 60 W was selected and, in addition to the II laser path, the diameter of the spot was smaller than the distance between the laser spots, marked as laser path I. The AM 125 system uses a YFL fiber laser with ytterbium-doped active material and a maximum power of 200 W. The AM 125 system is equipped with a vacuum chamber, which allows the use of a unique method of emptying the working chamber of the device in such a way that all gases are first pumped out of the working chamber, and then an inert gas such as argon or nitrogen is introduced, providing an operating environment in which the oxygen concentration does not exceed 100 ppm.
The technology of selective laser sintering can be treated as a modern technology of powder engineering, where the process of building an element begins with the distribution of the powder layer on a working table with position adjustable in relation to the z-axis. This layer acts as a substrate for the created object. The laser beam is guided along the surface of the powder in accordance with the previously entered and appropriately configured information concerning the successive layers of the cross-section of the spatial image of the object. Next, the working table with the powder is lowered by the height (layer thickness) set by the user, another thin layer of powder is spread, where the grains sintering, which takes place by surface melting of another layer of metal powder grains with the previously sintered layers of the manufactured element. Whether the powder is sintered or fused depends on the manufacturing conditions. The process involves sintering with a liquid phase. Successive layers of the cross-section are sintered together. The process is repeated until a coherent element is obtained. After the construction is completed and the temperature is lowered, the element is removed from the powder bed and subjected to a finishing treatment, depending on the application, e.g. sandblasting or grinding. The AM 125 device has a powder container with automatic valves delivering an additional portion of the powder during the entire process, and its excess after the distribution of the next layer in the working chamber is drained to the container, which can be easily and quickly dismantled and placed at the powder sieving or selection station thanks to which it is possible to reuse the powder in the next process.
For the production of porous titanium skeletons, titanium powder was used with the composition presented in Table 12 with the purity grade 2 and the grain size up to 45 μm with a spherical shape. The powder used for the tests also has a reduced oxygen concentration down to 0.14% (in titanium powders the average oxygen concentration is about 0.5%).
|Mass concentration of elements, %|
The technology of selective laser sintering allows the production of microporous titanium skeletons with completely open pores, with the full possibility of controlling the shape and size of these pores, and also allows the production of elements of any designed shape, which makes it very competitive in relation to other material manufacturing technologies of porous materials.
The mechanical properties of selectively laser-sintered titanium micro-skeletons depend on the spatial orientation with respect to the main axes of the applied external stress, the assumed pore size, the laser power, the size of the laser spot, and the path of the laser spot. The best mechanical properties of 36 MPa (tensile strength), 97 MPa (bending strength), and 125 MPa (compressive strength) are obtained after selective laser sintering according to spatial orientation 45° in relation to the x-axis, with a laser spot width of 50 μm, laser power 60 W, an assumed porosity of 50–60%, corresponding to a pore size of 250 μm, for the course of a laser spot for which the distance between the laser spots and the laser remelting paths in relation to the diameter of the laser spot is equal to or smaller than the diameter of the laser spot. The lowest mechanical properties of 8 MPa (tensile strength), 15 MPa (flexural strength), 14 MPa (compressive strength), respectively, are ensured by the 45° orientation in relation to the y axis and 45° in relation to the x-axis for the same pore size ∼250 μm. The smaller assumed pore size influences the greater the strength, and it varies from 8 MPa (tensile strength), 17 MPa (bending strength), 12 MPa (compressive strength) to 18 MPa, 43 MPa, 37 MPa, respectively, with a reduction the pore size from 450 μm to 250 μm. As the pore size decreases, the diameter of the laser spot also decreases from 90 to 50 μm, respectively, which helps to increase the strength. With the increase of the laser power from 50 W to 60 W, the mechanical properties increase, changing from 28 MPa (tensile strength), 72 MPa (bending strength), 74 MPa (compressive strength) to 36 MPa, 97 MPa, 125 MPa respectively. Using the same technological conditions for selective laser sintering, changing the ratio of the diameter of the laser spot to the value of the distance between the spots and paths of laser remelting from ≥1 to <1 results in more than double the strength of porous titanium.
The titanium porous elements after selective laser sintering were subjected to preliminary cleaning in isopropanol solution using an ultrasonic cleaner. After the excess powder was removed from the pores of the titanium skeleton, the specimens were digested with aqua regia for 1 hour using an ultrasonic bath to remove excess powder loosely attached to the titanium skeleton that had not been removed in the pre-treatment. Composite engineering materials, the model of which structure is shown in Figure 14a, were produced by pressure infiltration of microporous titanium skeletons produced by the selective laser sintering technology at a temperature of 800°C under a pressure of 2–3 MPa for 2 minutes in a manner analogous to the second case, using casting matrix material aluminum alloys, respectively AlSi12 in third case and AlSi7Mg0.3 in fourth case (Figure 17).
2.3 Manufacturing technologies by mechanical synthesis and subsequent plastic consolidation of aluminum alloy matrix composite materials
In cases 5 and 6, the composite materials were manufactured by mechanical synthesis and subsequent plastic consolidation of the mixture of aluminum alloy AlMg1SiCu powders as a matrix and reinforcement, respectively for variant 5 halloysite nanotubes HNTs as in variant 2 in the volume fraction of 5 to 15% and in the variant 6 multi-wall carbon nanotubes MWCNTs in the volume fraction of 0.5 to 5% (Figure 18).
By using the mechanical alloying method, it is possible to produce nanostructured composite materials with the controlled particle size of the reinforcing phase and their uniform distribution and resulting in increased mechanical properties. Air-atomized aluminum alloy powder with nominal particle size <63 μm was obtained from ECKA, Austria. Multiwalled carbon nanotubes MWCNTs with the properties given in Table 13 were supplied by Cheap Tubes (USA).
As before, the lubricant MA7050 was used for all powders as a process control agent PCA reducing the adhesion between the feed and mill material with a mass fraction of 1%. The four stations planetary ball mill Pulverisette 5 by the Fritsch Company was used for mechanical synthesis using high energy mechanical milling for 0.5 to 20 hours at 200 rpm. Detailed conditions are given in Table 14.
|1||Reinforcement’s concentration||5; 10; 15 wt.%||0.5; 2; 3.5; 5 wt.%|
|2||Time of milling||0.5; 1; 1.5; 2; 2.5; 3; 3.5; 4; 5; 6 h||0.5; 1; 1.5; 2; 3; 4; 5; 10; 15; 20 h|
|3||Ball material||AISI 420 quenched stainless steel|
|4||Ball diameter||20 mm|
|5||Ball-to-powder weight ratio||20:1|
In the case 5th, halloysite nanotubes had to be annealed prior to high-energy milling. A series of structural changes takes place in the halloysite, starting from dehydroxylation causing a metastable state, during heating of halloysite nanotubes at a temperature of ∼100°C, associated with the 1st endothermic reaction consisting in the release of adsorption water (about 2% by weight), through the transformation into a regular spinel phase, in the temperature range of 400–600°C (peak at 548°C), when the 2nd endothermic reaction occurs, associated with hydroxylation (OH- ions in the octaendric layer are exchanged for O2- ions (approx. 13% by mass), ending with the formation of mullite at a temperature close to 950°C as a result of an exothermic reaction associated with the reconstruction of the halloysite structure and the formation of the Si-Al spinel phase as a transition form [113, 114, 115] (15% by mass) . These phenomena are confirmed by the thermogravimetric analysis (Figure 19) performed with the use of a corundum crucible in the range it is 20–1000°C in the air atmosphere to which 0.5018 g of halloysite nanotubes was subjected. The halloysite nanotubes used for the tests were therefore annealed at the temperature of 100, 500 or 700°C (HNT100, HNT500 and HNT700).
As a result of high-energy mechanical milling, crushed and permanently bonded composite powders were manufactured. Composite powders obtained as a result of high-energy mechanical milling were then cold pressed in a mold with a seat diameter of 26 mm and pressure of 300 MPa, and then pressed at a temperature of 460–500°C using a graphite suspension in oil as a lubricant, without degassing, in a cover made of AlMg1SiCu alloy. Co-extrusion of cold-pressed powders of rod-shaped composite materials consisted of placing the molded part in a thick-walled sleeve closed on one side by a punch, and on the other – by a die with a forming hole. At elevated temperature, under the pressure of the punch, the material was extruded through the die opening, obtaining a rod with a circular cross-section and a diameter of 8 mm in the case of using HNTs or 6 mm in the case of using MWCNTs, respectively.
2.4 Manufacturing technologies of the composite layers on the substrates of aluminum alloy
All other cases 7–12 concern composite layers of several millimeters obtained on the surface of casting aluminum alloys containing 3–10% magnesium. The desired composite layer of the tested aluminum alloys was obtained as a result of smelting the surface of the elements with the high-power HPDL ROFIN DL020 diode laser and fusing ceramic powders directly into the liquid metal pool using a gravity feeder (Figure 20). This laser is characterized by a very high beam power density, up to 107 W/cm2, which means that the thermal impact on the surface of the element is limited, and thus causes only slight stresses and thermal deformations. The use of a diode laser for feathering ceramic powders into the surface layer of Al-Mg alloys allows for a predictable and repeatable way to obtain a composite layer on the surface of the analyzed aluminum alloys.
In order to minimize the power of the laser beam, shorten the time of the beam’s impact on the surface and reduce the absorption of surface radiation, e.g. by grinding, anodizing, or tarnishing with the use of etching chemicals. The use of a flux, e.g. lithium chloride, is preferred. If this flux is not used, it would be necessary to reduce the scanning speed and increase the power of the laser beam, which results in increased linear energy and can lead to structure’s changes in a larger volume of the material, making the technology less predictable and more difficult to control than with laser feathering using flux on surfaces of aluminum-magnesium alloys. The purpose of selecting and optimizing the technological conditions of laser feathering is to produce a surface durable composite layer of aluminum with embedded carbides, characterized by a high coefficient of friction without the need for additional heat and surface treatment. The surface of the elements before laser feathering was mechanically processed by grinding with sandpaper with a gradation of 60 μm and then covered with a lithium chloride-based flux under the trade name “AluFlux”. Lithium chloride powder was mixed with anhydrous ethyl alcohol in a ratio by volume of 1:5, resulting in a liquid suspension which was uniformly covered over the entire surface of the laser-processed part. The surface prepared in this way was dried for 30 minutes in a furnace at 50°C in order to evaporate the alcohol and moisture from the element surface. WC/W2C and SiC powders were selected for laser surface treatment, taking into account the wettability of their powders (Figure 21). The conditions of the laser surface treatment, including the scanning speed and power of the laser beam, the method of powder feeding, and the shape of the laser spot, were determined on the basis of numerical calculations of the Finite Elements Method FEM computer simulation. In the numerical model, the laser beam power ranging from 0.5 to 2.5 kW, the beam scanning speed ranging from 0.2 to 0.8 mm/s, and the method of feeding the feathered powder through a paste consisting of a mixture of water glass and powder, milled on the surface of two or three grooves with a depth of 0.5 and 1 mm and a gravity feeder with a speed depending on the density of the fed powder from 0.5 to 12 g/min. Table 15 presents the decided experimental technical conditions of the laser feathering process and basic information on the ceramic powders used. The method of feeding the feathering particles into the area of the molten metal pool by means of a gravity feeder at a speed of 1 g/min for SiC and 8 g/min for WC/W2C was selected. After the laser surface treatment, no other thermal or thermo-mechanical treatments were performed.
|1||Laser beam power, kW||1.8; 2.0; 2.2|
|2||Laser beam scanning speed, m/min||0.5|
|3||Spot size, mm||1.8 x 6.8|
|5||Protective gas flow, l/s||20|
|7||Powder particle size, μm||45–180||45–180|
|8||The amount of powder fed, g/min||1||8|
|9||Theoretical powder density, g/cm3||3.21||15.7|
|10||Melting point, °C||2730||2870|
3. Structure and properties of the composite materials with aluminum alloys matrices taken into account in this chapter
3.1 Structure and properties of the composite materials with reinforcement in form of skeletons infiltrated with aluminum alloys matrices
In the first case of composite materials obtained by infiltration of porous skeletons, it is them that largely determine the properties. Pressure infiltration of porous skeletons with liquid metal alloys is increasingly used in the production of metal-matrix composite materials [116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140]. The benefits of using this technology include near-net-shape mapping and high surface quality, the possibility of local product strengthening and the use of a wide range of matrix and reinforcement materials, high efficiency also at mass production scale with relatively low production costs [87, 88, 141]. The interest in using aluminum oxide as the backbone of this group of materials has increased significantly in the current two decades [88, 141, 142, 143, 144, 145]. In the case of composite materials with reinforcement in the form of skeletons and an infiltrated matrix of aluminum alloys, a metal-ceramic connection also plays an important role due to the lack of wettability of aluminum oxide by aluminum alloys [82, 83, 84, 87, 88, 141, 142, 143, 146, 147, 148, 149, 150, 151, 152, 153, 154]. It has been improved by applying Ni-P coatings on Al2O3. A small proportion of pores with small dimensions ensures that after infiltration a density close to theoretical, which increases with the increase of the Al2O3 proportion. It was confirmed that composite materials with aluminum alloy matrix can be manufactured by pressure infiltration of porous ceramic skeletons made of a mixture of carbon fibers and Al2O3 particles, and the distribution of the reinforcing phase in the matrix is uniform. The infiltration is complete, and the fracture is mixed because the matrix is plastically deformed around the reinforcing phase, while at the metal-ceramic interface, the fracture is brittle (Figure 22). The Ni-P layer has a continuous structure with a thickness that does not clog the pores of the sintered ceramic skeletons.
The hardness of composite materials reinforced with porous skeletons made of Al2O3 particles increases with the increase in the proportion of the ceramic phase, obtaining 48.88 and 51.74 HRA, respectively, with a 30% share of reinforcement covered by Ni-P, and without it, which is more than 2.5 times increase in relation to the matrix with a hardness of 19.19 HRA (Figure 23). The tensile strength of the composite material reaches its maximum value with 25% reinforcement and amounts to 299.07 MPa and 320.14 MPa, respectively, in the case of the material with the reinforcement not covered or covered with Ni-P respectively. It proves the desirability of covering the internal surfaces of porous frameworks with a Ni-P layer in order to improve Al2O3 wettability by the liquid aluminum alloy and to improve the metal-ceramic bond.
The abrasion resistance of these composite materials increases with the increase in the proportion of the ceramic phase, and composite materials are characterized by much lower wear than their matrix, and the smallest of them is the material with a 25% ceramic phase (Figure 23c). Potentiodynamic studies confirm that the corrosion resistance of composite materials reinforced with ceramic skeletons in this way increases with the increase of the reinforcing phase. The presence of the Ni-P coating applied to the surface of the ceramic, however, promotes corrosion acceleration compared to the cases where this coating is absent, although the corrosion resistance also improves in these cases along with the increase in the proportion of the ceramic phase.
Composite materials reinforced with porous ceramic skeletons obtained from Al2O3 particles or fibers consisting in their pressure infiltration with liquid AlSi12 alloy constituting the matrix provides the required structure, as well as mechanical properties and wear resistance much more favorable than the aluminum alloy constituting the matrix.
In the second case, composite materials are manufacturing using liquid AlSi12 alloy for infiltration of the skeleton from sintered mineral nanotubes obtained from halloysite. Halloysite, like other secondary layered silicates, such as kaolinite or montmorillonite, and in general aluminosilicates or aluminum silicates, can be used to produce alternative reinforcement of composite materials with a matrix of light metals, especially aluminum, reinforced with ceramic particles [155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168]. These minerals can be used to produce mullite 3Al2O3·2SiO2, among others by sintering, melting, or mechanical or chemical synthesis [169, 170, 171, 172, 173]. The mullite has good mechanical and physicochemical properties, meeting the requirements for porous skeletons as reinforcement for composite materials [174, 175, 176, 177]. The porous skeletons produced in this way are an alternative to preforms commonly used for the production of composites based on aluminum alloys by infiltration methods, which are ceramic skeletons or foams formed from particles or short fibers, with high porosity 60–90% [119, 163, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189]. They replace the particles of oxides, carbides, nitrides, graphite, carbon, boron, glass, Al2O3 and SiC fibers, intermetallic phases used in their production; fly ash microspheres and microgranules; Al2O3, SiC, SiO2 nanotubes; multi-walled carbon nanotubes, graphene and most often SiC and Al2O3 fibers. For economic reasons, it is beneficial to replace Al2O3 fibers with particles, which also increases the strength of infiltrated materials by approx. 35%, despite a slight reduction in abrasion resistance [84, 86, 87, 106, 148]. Halloysite in the form of NHTs can be an alternative for both economic and mechanical properties reasons. Among the sintered, porous ceramic skeleton, it is most preferable to sinter HNTs at 1500°C with the share of 70% HNTs, while the differentiation of the pressing pressure in the range of 50 to 100 MPa is of little importance (compare Figure 19). All composite materials analyzed here are characterized by an infiltrated structure with complete filling of the pores of the ceramic skeleton with the matrix alloy and good adhesion at the phase boundary of the ceramic reinforcement and the metallic matrix (Figure 24).
Composite materials manufactured according to the technology described as the second case are characterized by a structure of evenly interpenetrating phases with a contrasting structure. The matrix material is an α-solution with numerous precipitates of the coarse-crystalline β phase and fine precipitates of the iron-rich phase, while the reinforcement is an evenly distributed, continuous mineral phase in the form of irregularly shaped mullite. The strengthening of the above-mentioned composites in the form of fine-grained mullite and cristobalite occurs as a result of sintering mineral nanotubes and the accompanying series of structural changes. The gas-pressure infiltration of these ceramic skeletons leads to the diffusion dissolution of the cristobalite formed during sintering in the liquid aluminum alloy. As a result, the excess of silicon in the liquid solution crystallizes in the form of coarse precipitates, analogous to hypereutectoid Al-Si alloys. The relatively short infiltration time does not affect the dissolution of mullite in the liquid solution. The mechanical and functional properties of the discussed composite materials with HNTs reinforcement are the best in the case of sintering ceramic skeletons at 1500°C and at 70% HNTs (Figure 25).
The mentioned technology enables the manufacturing of composite materials with enhanced mechanical properties and wears resistance, significantly exceeding the functional properties of the alloy used as a matrix, providing the prospect of their implementation on structural elements, e.g. in the aviation and automotive industries.
The third and fourth cases of composite materials concern the use of microporous titanium skeletons manufactured by selective laser sintering with an adjustable pore size and their controlled spatial orientation as reinforcement, manufactured by pressure infiltration with liquid alloys AlSi12 or AlSi7Mg0.3, respectively.
Additive technologies have found a very wide application in numerous industries, including military, automotive, aviation, machine, household goods, but also in medicine, both for the production of solid and porous elements [128, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218]. Porous materials produced with this technology can be used as skeletons for the production of infiltrated composite materials with a matrix of aluminum alloys. The structure of these composite materials with aluminum alloys matrix and titanium skeleton reinforcement manufactured by additive technology does not contain any local voids and pores. It is made of a matrix corresponding to the chemical composition of the alloys used, respectively, AlSi12 or AlSi7Mg0.3 (Figure 26) inside the pores of a titanium skeleton with a size of 250–350 μm, which is a reinforcement with a shoulder thickness of 200–300 μm depending on the sintering conditions. The matrix and reinforcement composition was confirmed by X-ray diffraction (Figure 26i-k). The results of the X-ray diffraction tests of the structure AlSi12/Ti (Figure 26j) and AlSi7Mg0.3/Ti (Figure 26k) composite materials show that during infiltration, phases with the participation of individual elements of the composite material, such as Al, Si, may be formed as well as Ti, AlSi and the AlSiTi phase. The AlSiTi phase is formed in the area between the matrix material and the reinforcement (Figure 27), and its chemical composition differs from that of the reinforcement and the matrix, as Al, Ti, and Si were identified in the qualitative and quantitative EDS method. In the matrix material, Mg, Cu, Ni can also be identified, the concentration of which in the matrix is less than 1%.
The mechanical properties of pressure-infiltrated composite materials with a matrix of selected aluminum AlSi12 or AlSi7Mg0.3 casting alloys (Figure 28) depend on the spatial orientation with respect to the main axes of the titanium micro-skeleton produced by selective laser sintering, the size of the pores in the micro-skeleton and the sintering conditions, especially laser power and the size of the laser spot. The bending strength is 280–430 MPa, and the compressive strength is 480–600 MPa. The most advantageous mechanical properties: bending strength of 430 MPa and compressive strength of 600 MPa, these composite materials obtain after laser sintering of the skeleton with a laser power of 60 W, with a laser spot with a diameter of 50 μm, the distance between the laser spots and between laser remelting paths equal or smaller than the diameter of the laser spot when the spatial orientation is 45° to the x-axis and if the pore size is 200–250 μm with a porosity of approx. 50–60%.
Therefore, reinforcing the aluminum alloy with porous titanium skeletons has a positive effect on the mechanical properties of the analyzed composite materials. The AlSi12 alloy is characterized by a bending strength of about 170 MPa, while in the case of the AlSi12/Ti composite material, the maximum bending strength was obtained using a titanium skeleton with a porosity of 56%, obtaining a bending strength of about 400 MPa, and with a titanium skeleton with a porosity of 66%. strength of about 280 MPa was obtained. The strength of the AlSi12/Ti composite material compared to the strength of solid titanium (1682 MPa) is more than four times lower, however, compared to the strength of the AlSi12 alloy itself, it increases twice. The use of a titanium skeleton with lower porosity, i.e. a skeleton of greater strength, in the composite material with the AlSi12 alloy matrix, increases the bending strength by about 230 MPa compared to the matrix material, while when the skeleton with lower strength and higher porosity is used, the increase in bending strength is not so significant at about 110 MPa compared to the matrix material. In the case of a composite material with the AlSi7Mg0.3 matrix with the use of titanium skeletons, the increase in bending strength compared to the matrix material is approximately 100 and 130 MPa, respectively. When the same titanium skeletons and different matrix materials are used, the matrix bending strength has a dominant effect on the bending strength of composite materials, while if the same matrix materials are used, the strength of the composite material is mainly determined by the strength of the titanium matrix.
The comparison of the fracture structure of the aluminum alloys constituting the matrix of the composite materials discussed with the fracture structure of the composite material after bending tests shows significant differences. The breakthroughs of aluminum alloys are flat, with visible planes along which the material cracked, while in the case of composite materials, places characteristic of titanium are distinguished (Figure 29). The studies of the breakthrough of the AlSi12/Ti and AlSi7Mg0.3/Ti composite materials indicate that the combination of titanium and aluminum alloys is durable and does not break when the bending force is applied. The structure of the breakthroughs after the compression test is significantly different from the breakthroughs after bending. After the compression test, such a clear separation of the matrix material from the reinforcement material cannot be noticed, which is so clearly visible in the structure of breakthroughs after bending.
Micro-skeletal composite materials, manufactured by pressure infiltration with selected aluminum casting alloys AlSi12 or AlSi7Mg0.3 to give the final shape and geometric form, dedicated, among others for the automotive, machine-building, and aerospace industries, as well as for medical and dental applications.
3.2 Structure and properties of the aluminum alloy matrix composite materials manufactured by mechanical synthesis and subsequent plastic consolidation
In cases 5 and 6 for mechanical synthesis of the composite materials in a planetary mill (the so-called high-energy process) of AlMg1SiCu alloy powder and respectively nanotubes obtained from halloysite or MWCNTs carbon nanotubes, was used to produce the composite materials. In the initial stage of mechanical synthesis, the originally spherical particles are deformed, flattened, and have a lamellar shape. After 5 hours of mechanical milling, it was found out that most of the particles were equiaxed with no flake shaped particles present. Changes in the shape and size of the milled powders are caused by the welding of individual particles as a result of collisions with the milling media or the walls of the mill. The flattened particle conglomerates formed as a result of welding become significantly hardened, hard, and therefore prone to cracking. As the milling progresses, these particles become fragmented and reassembled, which ultimately affects the random orientation of the boundaries of the particles to be welded. The fact that the process has reached a steady-state is provided by the relatively equiaxial shape of the milled powder particles. In contrast to the milled powder of the AlMg1SiCu alloy, in the case of the powder of the composite material, it was found out that the deformed particles joined tightly, creating a morphologically homogeneous structure, free of pores and discontinuities. Despite the twice longer milling time, the powder of the AlMg1SiCu alloy consists of fine particles, which to a large extent form porous conglomerates with irregular, non-aligned shapes and sizes varying in a wide range from 10 to 200 μm. Extending the milling time results in a homogeneous distribution of the reinforcing particles, and it is also possible to produce powders with equiaxed particles. The influence of the presence of reinforcement subject to fracture under the conditions of mechanical alloying of the ductile aluminum matrix is given in the diagram of the successive stages during mechanical alloying (Figure 30). The examples of the corresponding structure for the case respectively 5 and 6 are given in Figure 31. Examples of correctly and incorrectly made rods in the stage of plastic consolidation are shown in Figure 32.
In the case of 5th, the composite materials with the AlMg1SiCu matrix are reinforced with nanotubes obtained from halloysite. The use of HNTs particles reduces the bulk density of the mixture with the matrix powder of the AlMg1SiCu alloy even by more than 50%, and this effect becomes present with the increase in the proportion of the reinforcing phase. Reinforcement material particles are characterized by a larger specific surface, irregular, often oblong shape, and form porous conglomerates, thus characterized by a much lower bulk density compared to globular AlMg1SiCu particles. In the case of mechanical milling of a plastic powder of an aluminum alloy with a brittle reinforcing phase in the form of halloysite nanotubes with a mass fraction of 15%, the increase of the bulk density takes place in 2 times shorter time than in the case of matrix powder. As a result of high energy milling, an equiaxial shape of the particles is obtained and an even distribution of fine reinforcing particles confirming that the process has reached a steady state. Further milling does not significantly affect the obtained structure and properties of the powders. In the initial stage, the particle size distribution is characterized by two peaks (Figure 33), because the tested powders are a mixture of particles with a significant difference in size (the aluminum alloy powder has a median of 62.30 μm, and halloysite nanotubes – 2.58 μm). The particle size of the powders undergoes continuous, non-linear changes during milling. As the milling time increases, the deformed particles are joined together and the peak on the particle size distribution curve becomes wider at the base, and then with the increase of the milling time and the associated increase in the proportion of large particles resulting from repeated welding, an asymmetric deviation is achieved. Due to the breakage of large particles, the asymmetry that has arisen gradually disappears. Eventually, the process reaches a steady state, corresponding to a balance between the powder particle aggregation and fragmentation mechanisms, which is represented by symmetrical or a narrow particle size distribution curve (Figure 33).
Mechanical synthesis, in addition to the effect on the morphology and structure of the manufactured composite powders, also affects their phase composition, and increasing the milling time also affects the generation of a large number of defects and results in the fragmentation of the crystal structure [219, 220, 221]. Already after several minutes of milling, low-angle reflections from mineral halloysite crystals disappear, leaving only reflections identified as α-Al on the diffraction patterns. Structural changes occur during annealing of halloysite [169, 222, 223, 224, 225, 226]. The interplanar distance of all halloysite powders is 0.72 nm, which proves permanent dehydration [113, 114]. Annealing of halloysite nanotubes at the temperature of 500–700°C causes disorder of their crystal structure, which with increasing temperature causes amorphization of halloysite as a result of disordering the packet structure [227, 228, 229, 230]. Mechanical high energy milling improves the distribution of HNT100 reinforcement particles in the AlMg1SiCu matrix, more advantageously than when using HNT500 and HNT700. With a short milling time, this ensures a homogeneous structure of the nanocomposite material with an even distribution of reinforcing particles without their agglomeration after consolidation. The consolidation of powders consists in their successive cold pressing and hot extrusion, resulting in a lack of discontinuities of the structure in the form of pores or cracks and obtaining a material with a very fine structure (Figure 34a), devoid of agglomerates of reinforcing particles. In the produced material, there are grains with a size of several nanometers (Figure 34b-d) in the structure of the solid solution of the AlMg1SiCu alloy in a metastable state (Figure 34e-h). There are also many regular, parallel, rhomboidal regions not exceeding a few nanometers (Figure 34e), which most likely constitute the Guinier–Preston zones with the concentration of Cu atoms [1, 231, 232, 233].
Based on the results of the X-ray phase analysis, the presence of only the matrix phase in the analyzed composite materials, i.e. solid aluminum solution (Figure 35).
In addition to the nanometric grains of the Alα solution (Figure 36a) in the matrix, there are precipitations of the Al2O5Si phase (Figure 36b) probably formed during mechanical milling and the intermetallic primary phases AlFe3 and Al4 (Fe, Cr, Mn) Si0.74 (Figure 36c) .
The high degree of plastic deformation caused by mechanical milling, nanometric fragmentation of the structure, and dispersion hardening with particles of halloysite and oxides results in an almost 3-fold increase in the microhardness of powders than before milling and despite its reduction by about 30% after plastic consolidation, the produced nanocomposite materials show microhardness 110–150 HV0.1 (Figure 37a), higher than the Mg1SiCu alloy. The introduction of HNTs particles into the Mg1SiCu alloy matrix using high-energy milling causes more than a twofold increase in the yield point under compression, because the yield point for compression with HNT100 nanotubes is 450–495 MPa at the test temperature of 25°C (Figure 37b), and at the test temperature of 225°C is 265–280 MPa depending on HNTs share. When using nanotubes HNT500 and HNT700, respectively, it is slightly smaller (Figure 37c). Figure 37f-j show the course of compression diagrams at various temperatures of 25–225°C. The tested nanocomposite materials show a characteristic “dimple fracture” [235, 236, 237, 238], sometimes also referred to as a ductile foveal fracture  (Figure 38). Nanocomposite materials reinforced with HNTs nanotubes are more resistant to frictional wear, as measured by changes in the surface layer related to permanent deformation, mainly weight loss [1, 240, 241], therefore they are characterized by a lower abrasion trace volume than the AlMg1SiCu alloy (Figure 37d,e). Nanocomposite materials reinforced with HNT100 halloysite nanotubes with a mass fraction of 15% are characterized by over 180% higher yield strength under compression, over 200% higher microhardness, and nearly 250% higher friction wear resistance compared to the AlMg1SiCu alloy, which is the matrix of the composite material.
In the case of 6th composite materials with AlMg1SiCu matrix reinforced with MWCNTs, the main problem during manufacturing is the homogeneous distribution of carbon nanotubes in the matrix material. Of the several methods of dispersing nanotubes in a metal matrix, such as mechanical milling, mixing in a turbulent mixer or mixing with an ultrasonic homogenizer, only high-energy mechanical milling leads to an homogeneous distribution of the reinforcement in the matrix material, without agglomerating the MWCNTs on the surface [242, 243, 244, 245, 246, 247, 248, 249, 250]. Carbon nanotubes can be placed between particles of a gas-atomized or spheroidal cold-alloyed aluminum alloy. After mechanical milling on the surface of the ground particles, no carbon nanotubes are present on the surface of any of the powders ground for 5 or more hours [95, 242, 244, 246, 251, 252, 253, 254, 255]. With the increased share of MWCNTs, the particle size decreases (Figure 39).
As a result of mechanical milling, the order of the structure of carbon nanotubes and the interaction between the reinforcement and the matrix are degraded as a result of breaking the sp2 bonds. The results of the Raman analysis confirm the defect of the structure and the amorphization of carbon nanotubes (Figure 40), indicating a reduction in the intensity of the G and G’ bands as well as an increase in the intensity of the D band, which is confirmed by the ID/IG and IG’/IG intensity factors ratios (Figure 40).
Carbon nanotubes during high-energy mechanical milling were dispersed and placed between deformed aluminum alloy particles, which increases the density of powders of nanocomposite materials (Figure 41a, b). The structure of the nanocomposite material with the matrix of the AlMg1SiCu aluminum alloy reinforced with MWCNTs is homogeneous (Figure 41c) with symmetrical, approximately spherical grains, with a size of about 50–70 nm. Carbon nanotubes show homogeneous dispersion and are strongly deformed (Figure 41d,e), which was revealed after complete removal of the matrix by etching with HCl (Figure 41f). However, literature reports [244, 251, 255, 256, 257, 258, 259, 260, 261, 262, 263] concerning the degree of degradation of carbon nanotubes are not unequivocal.
However, extending the milling time from 5 to 20 hours causes increased degradation of the structure of carbon nanotubes. It is accompanied by the amorphization of nanotubes, which is associated with a reduction in the intensity of the G ‘bands (Figure 40n-r). It has been found, however, that the structure of carbon nanotubes may even be completely destroyed. Regardless of the share of MWCNTs above 0.5% and the mechanical milling the time the manufactured materials show a brittle fracture (Figure 42). The structure of the fractures also shows the fine grain structure of the material.
Defective nanotubes are much more reactive, so during the next consolidation involving plastic deformation at elevated temperature, as a result of the interaction of carbon nanotubes with the AlMg1SiCu alloy matrix, in places where there are nanotube defects and amorphous areas on their surface, probably intercalation of aluminum atoms occurs between the carbon layers in MWCNTs. It is the direct cause of the following precipitation of Al4C3 carbides (Figure 43) with a diameter of approx. 5–10 nm and a length of 20–30 nm. The precipitation of these carbides was also confirmed by X-ray analysis (Figure 44). Information on the Al4C3 carbides precipitation is also available in the literature in many cases of composite materials involving carbon nanotubes [264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274]. However, neither X-ray structural analysis nor literature data indicate that Al4C3 is secreted directly as a result of mechanical synthesis by milling for up to 50 h .
The share of MWCNTs and the manufacturing conditions of nanocomposite materials have a relatively small effect on their density 2.56–2.57 g/cm3 (Figure 45a), in contrast to the microhardness (Figure 45b). The manufactured nanocomposite materials reinforced with carbon nanotubes are characterized by increased microhardness by up to 300% (Figure 45b), greater ultimate tensile strength by over 200% (Figure 45c,e-g) and five times higher frictional wear resistance to the unground AlMg1SiCu alloy, because with the increase of share of MWCNTs, the volume of the wear mark decreases (Figure 45d). The coefficient of friction of nanocomposite materials is not only lower than the coefficient of friction of materials made of the AlMg1SiCu alloy without MWCNTs, but also occurs in a much smaller range, which is also confirmed by the literature .
The reason for such a significant strengthening of nanocomposite materials with AlMg1SiCu alloy matrix, reinforced with MWCNTs carbon nanotubes, is dispersion nanostructured precipitates of Al4C3 carbide. Without the precipitation of these carbides, these positive effects would not exist. However, note that this carbide is highly hygroscopic and completely hydrolyzes in an aqueous medium to form aluminum hydroxide and gaseous hydrocarbons such as methane or acetylene, according to the reaction:
Similarly, the reaction with hydrochloric acid also causes decomposition of aluminum carbide according to the reaction:
It leads to a deterioration of the corrosion resistance of the composite materials and is a common factor contributing to mechanical failure. Even a small share of aluminum carbide destroys composite materials with the participation of aluminum and nano additives of allotropic forms of carbon in aggressive environmental conditions, and even in atmospheric conditions, causing uneven pitting corrosion. It limits the practical use of such composite materials . Al resistance to electrochemical corrosion improves with the formation of Al4C3 on the Al surface, which prevents the dissolution of the metal in the chloride-based solution [278, 279]. The practical use of such nanocomposite materials will therefore be possible only in cases where their surface will be tightly covered with appropriate, durable coatings that effectively prevent contact of the material surface with water and other aggressive environmental media that can be applied. It is obvious that the technological process of applying the coatings cannot dissolve Al4C3 carbides. This requires further detailed studies as well as the eventual application of other coatings described as preventing corrosion of various alloys and composite materials based on aluminum or its alloys  including also the polymeric ones [281, 282, 283, 284] and maybe it could be also possible to use the atomic layers deposition ALD technology while ensuring the required adhesion of such layers [285, 286, 287, 288].
3.3 Structure and properties of the composite layers on the substrates of aluminum alloy
In all other cases, 7th–12th, the result of the work carried out is to obtain a hard and abrasion-resistant composite surface layer by introducing tungsten carbide or silicon carbide powder, respectively, through the interaction of a laser beam on the surfaces of aluminum AlMg3, AlMg5, AlMg9 alloys. Due to the use of laser treatment, the surface of the aluminum material is characterized by a relatively low density, receives better mechanical and tribological properties. Laser technologies are now widely used in surface treatment not only in the treatment of aluminum alloys, but many other alloys [289, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, 317].
The share of feathering carbides WC/W2C or SiC in the surface layer of the AlMg alloys depends on the conditions of the laser treatment. The largest share of the feathered WC/W2C powder occurs for the AlMg9 alloy when a laser beam power is 1.8 kW. The surface layer manufactured in this case is characterized by a uniform distribution of the embedded particles in the matrix at a depth of up to 150 μm (Figure 46a), analogous to the laser treatment of the AlMg5 alloy surface (Figure 46i, j). Increasing the power of the laser beam causes an increase in the depth of remelting zone (Figure 47a), which results in greater dispersion of the feathered particles in the remelted layer, and the accompanying increase in the intensity of convection movements in the liquid pool affects the displacement of a part of the powder to a depth of about 1.5 mm both in the case of AlMg9 alloy (Figure 46c, d) and AlMg5 alloy (Figure 46i, j). The AlMg3 alloy after laser feathering of tungsten carbide with 1.8 kW laser beam power into the surface of the AlMg3 alloy results in an even distribution of carbides both at a depth of up to 160 μm and at the bottom of the layer. On the other hand, increasing the power of the laser beam causes gaps between the individual particles at a distance of up to 100 μm (Figure 46d).
The smallest proportion of the feathered powder occurs for the AlMg3 alloy after laser feathering of SiC carbide powder with a laser beam power of 2.2 kW (Figure 46e). As a result of laser feathering with a beam power of 2.0 and 2.2 kW, the carbides are evenly distributed in the near-surface part of the layer at a depth of up to 100 μm (Figures 46e,g and 47b). The best results for laser feathering of silicon carbide are for the AlMg5 alloy (Figure 46k,l). Composite layers manufactured with a laser beam power of 2.0 and 1.8 kW contain evenly distributed embedded powder particles in the matrix of an aluminum alloy, including AlMg9 (Figure 46e,f), with the largest share of feathered SiC powder in the case of alloy fusion AlMg5 with 1.8 kW laser beam power (Figure 46h). Single carbides with an average diameter of 100 μm occur in the central part of remelting zone also at the maximum power of the laser beam of 2.2 kW (Figure 46k, l).
Structure studies with the use of transmission electron microscopy and X-ray phase analysis showed the presence of intermetallic phases and AlMg2, Al3Mg2, Mg5Al18, Mg2Si precipitates.
Among the AlMg3, AlMg5 and AlMg9 alloys, the AlMg9 alloy has the highest hardness (Figure 47f). The mechanical and tribological properties of the manufactured composite layers containing respectively WC/W2C or SiC carbides on the above-mentioned alloys largely depend on the power of the laser beam, because too high power adversely affects the properties of these layers (Figure 47f). As a result of laser feathering of carbide powder, the greatest increase in hardness occurs for the AlMg9 alloy using a 1.8 kW laser beam (Figure 47e, f). In the case of the two other alloys, the highest hardness occurs at this laser power, and increasing the laser power causes a slight reduction in the hardness of the surface layer (Figure 47e, f). The highest hardness of the layer is provided by laser feathering of the WC/W2C powder into the AlMg9 alloy matrix with a laser beam power of 1.8 kW (Figure 47e). The smallest increase in hardness is obtained when laser feathering SiC powder into the AlMg3 alloy matrix with a laser beam power of 2.2 kW (Figure 47f). Increasing the power of the laser beam causes an increase in the hardness with respect to the Al-Mg alloy substrate at a greater depth (Figure 47c, d). The maximum value of hardness is lower than for treatment made with a lower power of the laser beam (Figure 47c, d). The introduction of WC/W2C into the Al-Mg alloys matrix enables obtaining a higher hardness of the layers than in the case of laser feathering of SiC powder (Figure 47c-f).
Ball-on-disk abrasion resistance tests of the obtained composite layers as well as aluminum alloy without laser treatment showed a significant increase in abrasive wear resistance of surfaces obtained as a result of laser feathering of hard powders of WC/W2C and SiC carbides, respectively, into the remelted matrix of AlMg3 alloys, AlMg5 and AlMg9. The highest abrasive wear resistance among all alloys and laser feathering variants is obtained after laser feathering SiC powder into the AlMg9 alloy matrix with a laser beam power of 1.8 kW. The highest wear resistance among these alloys as a result of laser feathering of WC/W2C tungsten carbide powder is demonstrated by AlMg9 alloy after feathering with a laser beam power of 1.8 kW.
The developed technology can find numerous applications, including in the mechanical engineering, automotive and aviation industries.
4. Final remarks on the importance of advanced composite materials based on aluminum alloys in the development of Industry
4.1 The general importance of engineering materials and the technology of their manufacturing and processing
Already a dozen or so years ago, the concept of a half-life of detailed knowledge was introduced by analogy to the half-life of radioactivity . After this period, characteristic for a given area of knowledge, about 50% of detailed information in this area will be up-to-date, and the rest will become outdated due to new scientific and technological discoveries. It is a measure of increasing the level of general knowledge of engineering staff, enabling them to be quickly transferred to the practice of engineering design and product manufacturing as well as a wide application area. It is undeniable that in the area of engineering materials and the technology of their manufacturing and processing, the half-life of knowledge has been greatly shortened over the course of history and now reaches only a few years (Figure 48).
The development of natural materials, and with time predominantly engineering materials, has become the basic determinant of the development of material culture and human civilization in general, largely determining the level and quality of life of societies achieved. It should be realized that to manufacture any product that is accepted on the market, it is necessary to use properly selected engineering materials. Initially, for thousands of years, as described in publications, including own publications [319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337], but also a hundred years ago, the selection of materials was carried out by trial and error, which is considered the Materials 1.0 stage (Figure 48). To date, even in 80% of cases, materials are systematically tested according to the Materials 2.0 protocol [319, 320, 324, 333, 337, 338], after the concept is developed and its subsequent verification, and then the prototype is tested in laboratory conditions and only then tested and validated in real conditions. The impact of environmental conditions should be investigated and the product life cycle designed. In the case of the Materials 3.0 protocol, the procedure is similar, except that the use of IT tools at the concept development stage is characteristic of this stage. To design the target functionality, computational and simulation methods are used, e.g. using the principles of quantum physics and chemistry, methods of artificial intelligence, and databases. Nowadays, opportunities have opened up for the use of cyber-physical systems and big data, as well as advanced methods of artificial intelligence and machine learning, including artificial neural networks and fuzzy logic, and more and more often smart systems cooperating with people, which is the essence of the Materials 4.0 approach, which is now increasingly being implemented. It is accompanied by the application of materials on-demand, when not more than two decades ago, the principle of having to choose materials only from the assortment offered by material manufacturers was in force. The task set for the designer can now be formulated in the form of the question: “what can be used to create a product interesting for the customer on the market?” On the other hand, the approach that answers the question: “What can be manufactured from a material that is currently available or already known to us?” It is anachronistic. Numerous grades from among much more than 100,000 currently known and available engineering materials give new innovative potential in the implementation of products. It is impossible to correctly select engineering material for any practical application without the use of modern and highly developed Computer-Aided Design CAD tools and other Computational Material Science methods. There are two aspects to this approach. On the one hand, the material properties of each product are designed by the constructor and an appropriate engineering material should be produced that meets the requirements of a given application solution, and on the other hand, the availability of one of the ready materials having a set of properties according to the criteria should be analyzed, using the available material databases. The problem is extremely important considering that an average small car has at least 15,000 parts and a passenger aircraft may have 4.5 million or more elements. Of course, in each case, the right decision must be made regarding the selection of engineering material and the appropriate technological process. All engineering materials are in each case equivalent from the point of view of engineering design, provided that they meet a set of required criteria, and the basis for multi-criteria optimization is a set of the best functional and technological properties with the lowest possible manufacturing and processing costs, as well as the use of the material and the product manufactured of it, taking into account ecological aspects and the product life cycle. Product engineering design is essential and is not an activity extracted from the overall product manufacturing process, but an important element in satisfying market needs and at the same time is dependent on them.
Product engineering design is composed of three elements that cannot be separated and cannot exist autonomously (Figure 49) [3, 318, 319, 320, 324, 339, 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351], which include:
structural design, ensuring the shape and geometric features of the product,
material’s design, ensuring the required physicochemical and technological properties as well as product life cycle,
technological design, ensuring the manufacturing of products with the required properties, with the highest possible efficiency, the highest possible degree of automation and computer aiding, and the lowest manufacturing costs.
The functional properties of products, are including mechanical, physicochemical, thermal, magnetic, electrical, and optical properties, depending on the chemical composition and the cross-sectional structure and very often also the surface structure of the materials and the conditions of use of the products and their components. These conditions include also operate at high or low temperatures, in conditions of cyclic loads, as well as in an aggressive gaseous or liquid medium. Materials science deals with the assessment of the impact of the structure on the electronic, crystalline, micro, and macroscopic scale on the properties of materials, while material engineering covers the relationships between the structure, technological processes, and functional properties of materials used for numerous products and complex application systems, significantly determining the quality of life of modern societies. The materials science paradigm corresponds to an octahedron illustrating the 6xE rule (Figure 49b) [3, 318, 319, 320, 339, 340]. Expected operational functions of the product are ensured by designing the expected material, processed using the expected technology, in order to give the expected geometric characteristics and shape of the product, enabling the expected structure and deciding to obtain a set of expected properties of the designed product. The above-mentioned approach provides people with continuous access to products and consumer goods that directly affect the level and quality of life, climate, quality and potential of health protection, education, information exchange, and other aspects recognized by the United Nations as Sustainable Development Goals (Figure 50). It presents a deeply humanistic mission of the engineering community in order to activate the development of societies. For this reason, the real development of materials engineering, including nanotechnology and surface engineering, and the accompanying research, are an important determinant of present and future prosperity and high quality of life. Sustainable development of this area is therefore of great interest to societies.
4.2 The importance of engineering materials and technological processes in the context of the current stage of Industry 4.0 of the industrial revolution
All products of interest to customers, without exception, are made of engineering materials and cannot be built without them. The processes of using engineering materials and other resources such as energy, capital, and people to make products available using different machines and different technological processes organized according to a well-designed plan are called manufacturing. The development of manufacturing processes is closely related to the development of the material culture of societies, which was reflected in the Japanese approach of the Society from groups of people practicing hunting and harmoniously coexisting with nature, which was considered Society 1.0 to information and achieving the goals of Society 5.0 of the smart sustainable development, oriented to people, their well-being and high quality of life, and ensuring economic development, which goals are achieved by connecting cyberspace with the real world (Figure 51) [319, 320, 322, 352, 353, 354, 355, 356, 357].
In Europe, a few years earlier, the German concept of Industry 4.0 was developed, already popular in many countries around the world, and also presented in Author’s own works, describing the stages of the industrial revolution (Figure 52) [195, 293, 319, 320, 322, 323, 332, 333, 334, 335, 336, 337, 349, 350, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414].
The introduction of steam engines at the end of the 18th century, considered Industry 1.0, marked the beginning of the industrial revolution. The current stage of Industry 4.0 includes smart factories, supplied by smart suppliers, producing smart products. Physical production processes are monitored by manufacturing systems, making smart decisions, based on real-time communication with people, machines, and sensors, and based on experiments performed on the so-called “Digital twins” in virtual reality using the simulation of real conditions of operation and maintenance of manufactured products using cyber-physical systems (CPS), Internet of Things (IoT) and cloud computing, with the use of large data sets. In the classic Industry 4.0 model [319, 320, 322, 361, 367, 368, 369, 372, 373, 374, 375, 378, 379, 380, 381, 382, 387, 388, 389, 390, 391, 393, 395, 402, 415, 416] it was recognized that this stage of using the nine basic technologies described in the literature was achieved (Figure 53) [293, 319, 320, 323, 345, 346, 347, 348, 349, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415].
It turned out that this model is one-sided and requires a significant augmentation, mainly by taking into account engineering materials, technological manufacturing processes and technological machines, and not only complex cyber-physical systems and very advanced tools and information systems (Figure 54).
The most important thing is that manufacturing possible only in reality, thanks to the physical system and on the condition of using real materials, usually engineering ones. No product can be manufactured without materials. Therefore, they should be absolutely included in the current Industry 4.0 model, because obviously they are and were necessary for every stage of the industrial revolution from Industry 1.0 to Industry 4.0. The simplified approach in the classic Industry 4.0 model creates the erroneous impression that the progress concerns only technologies covering monitoring, control, coordination, and integration of information and communication technologies that make up cyber-physical systems (Figure 53), without the need to make real progress in the field of technological machines, manufacturing technologies and necessary engineering materials to manufacture any product. It is obviously not true and therefore an adequate model must take into account all these aspects [319, 320, 322, 332, 333, 334, 335, 336, 365, 417]. A far-reaching simplification is also reducing the technological issues only to additive manufacturing, as it was done in the classic Industry 4.0 model. Additive manufacturing cannot be treated as ruthlessly competing with many known and used for many years, and sometimes even millennia, technologies for manufacturing products, such as foundry, machining, plastic working, heat treatment, surface engineering, joining and welding, and assembly [319, 320, 322, 332, 333, 334, 335, 336, 337, 345, 346, 347, 348, 349, 364, 365]. The enormous technological progress that is taking place now and in the near future will not eliminate these technologies, so it is necessary to include them in the Industry 4.0 model. It should be noted that the systematic modernization and progress in the field of these technologies concerns their mechanization, robotization, and above all computer-aided engineering design and manufacturing within cyber-physical systems. It is obvious that the classic model of Industry 4.0 in fact concerns only the computerization of technological processes, therefore, instead of it, it was necessary to introduce the appropriate holistic augmented model of Industry 4.0 [319, 320, 418] leaving cyber-physical systems as one of the elements technology platform of this new model (Figure 53).
4.3 The importance of advanced composite materials with an aluminum alloy matrix in the context of the current stage of Industry 4.0 of the industrial revolution
The growing and more sophisticated requirements set by the conditions of the current stage of the Industrial Revolution, conventionally designated as Industry 4.0, also pose challenges to designers and manufacturers of engineering materials. They apply equally to the implementation of new engineering materials, technological processes of their manufacturing and processing, advanced methods of their design, as well as the application of nanotechnology and surface engineering in this area. Among engineering materials, world steel production remains extremely high (Figure 55), despite reports of a decline in production in some countries due to the SARS-CoV-2 coronavirus pandemic.
The Worldsteel Association published crude steel production data in August 2020. Compared to August 2019, world production was 0.6% higher, despite the pandemic. The lowest production level, amounting to 137 million tons, was recorded in April 2020. Since then, production has been increasing and in August it amounted to 156.2 million tons. However, there has been a reshuffle in the market. Production declines were recorded in the United States (−24.4%), Japan (−20.6%), Germany (−13.4%), Russia (−4.6%), India (−4.4%) and South Korea (−1.8%). From the beginning of the year, production decreased by 19% in North America, by 18.6% in the European Union, by 15.6% in South America, and by 4.5% in the former Soviet Union countries. Production in the dominant country, i.e. China, despite the pandemic, does not decrease, but even increases. China, as the largest steel producer in the world, produced 94.8 billion tons in August, 8.4% more than in the previous year. Comparing total production in the first eight months of 2020 and 2019, China grew by 3.7%. Increases in steel production also occurred in Vietnam (32.9% compared to August 2019 and 11.5% in total since the beginning of the year), in Turkey (22.9% compared to August 2019 and 0.6% in total since the beginning of the year), in Iran (14.6%) and Brazil (6.5%).
Compared to steel, aluminum alloys are significantly lighter, and at low temperatures are characterized by higher impact strength. Aluminum alloys are the preferred structural materials used, among others, for the manufacturing of cars, in the aerospace industry and mining machines, in the processing industry for various high-performance elements for various applications, due to their relatively low weight and favorable set of properties. Ecological considerations require the reduction of the total weight of cars, which indicates the need to produce many new components from aluminum alloys (Figure 55). The use of lightweight materials for the manufacturing of car components allows for compliance with increasingly stringent air pollution regulations. It is obvious that a car with a lower weight allows for lower and more economical fuel consumption, which clearly reduces the emission of exhaust gases, mainly carbon dioxide, into the atmosphere.
Annual global aluminum production is expanding (Figure 55) at a level almost 30 times lower than that of steel, although the aluminum market may also have changed due to the COVID-19 pandemic. In 2015–2020 years, the total aluminum production amounted to 374,840 tons, and thanks to the increase in production in China in 2020, the total world production increased by a few percent compared to 2018, when it was higher than in 2019. The dynamics of aluminum production in 2015–2020 is shown in Figure 54. For example, in 2017, primary aluminum was produced in 41 countries. The main producers were China (55%), Russia (6%), India (5%), Canada (5%) and the United Arab Emirates (4%) in order of decreasing aluminum production. The share of China in the global aluminum production is growing year by year.
The end-use rate of aluminum and its alloys in various application areas has been established for many years. Aluminum has gained a good position on the world market due to its significant share in increasing the fuel efficiency of vehicles and in relation to its use in ecological construction products and ecological packaging. An example are the main areas of application of aluminum and its alloys in the United States and Canada (Figure 56).
According to the International Trade Center (ITC), the value of the aluminum market and its products in 2018 amounted to USD 194.32 billion . It was estimated that the volume of the aluminum market in that year was 79 million tons, and it is estimated that aluminum consumption will increase with compound annual growth rate CAGR of 4.2% in the forecast period until 2025 . Aluminum is widely used for packaging and construction, and is also used in machinery and equipment, and in the electrical and consumer durables industries. The main area of application of aluminum is the automotive industry. Since aluminum is a light metal, it is used mainly in car bodies and engines parts, what is an essential factor in reducing car fuel consumption. It also applies to trucks, as, for example, the Ford plant launched the production of an all-aluminum F-150 trak’s body in 2015 , which reduced the weight of the truck by more than 300 kg, resulting in a significant improvement in fuel efficiency and reduced total operating costs. International agreements on fuel economy are influencing for increase the use of aluminum in the automotive industry around the world. The expected increase in the production first of all of electric vehicles, and also semi-autonomous and autonomous vehicles as well as self-driving cars and trucks will further strengthen the aluminum automotive market. This segment is estimated to grow at a CAGR of 4.3% by 2025. Aluminum is now widely used in smartphones, tablets, laptops, flat screen TVs, monitors and other consumer electronics products. According to estimates provided by the Global System for Mobile communications Association (GSMA), the number of mobile phone users worldwide will increase from 5.1 billion in 2018 to 5.8 billion in 2025. Therefore, the global smartphone and smart TV market will be subject to a CAGR growth of 8–10% in the forecast period until 2025, which will affect the increase in demand on the aluminum market. Aluminum is the second most used metal in construction after steel, and according to the World Bank, in 2016, the gross domestic product GDP of construction was 25.4%. Aluminum is widely used in windows, curtain walls, roofing and cladding, sunshades, solar panels, railings, shelves and other temporary structures. The growing construction activity around the world creates more and more opportunities for the aluminum market. However, there are differences in aluminum consumption by end-use category in high (HIC), low (LIC) and middle income countries (MIC). In low- and middle-income countries, aluminum is mainly used for the production of electrical systems and in the construction industry. In high-income countries the main areas of application are products in the transportation sector, including cars, commercial aircraft and railway stock.
It is estimated that the aluminum market will grow in CAGR above 3% in the forecast period until 2025, although earlier data even indicated an increase in aluminum consumption up to 120 Mt. with an average growth rate of about 4.1% per year. The global aluminum market is expected to grow by 6.5% CAGR to reach USD 235.8 billion in 2025. This means that the annual production of bauxite should increase to approx. 570 Mt., and of aluminum oxide to approx. 230 Mt. However, a diversified increase in the use of aluminum is expected in different geographic areas (Figure 57). The main driver of the global aluminum market is the growing construction activity in the Asia-Pacific region. In North America, the growing number of construction projects and growing investments in the United States and Canada are driving the market under study. This upward trend is likely to continue, depending on the financing of larger projects. On the other hand, the slowdown in the global automotive industry and the unfavorable conditions resulting from the COVID-19 outbreak are holding back market development, and earlier forecasts are obsolete. Therefore, it is estimated that the construction industry will dominate the global aluminum market in the coming years. The Asia-Pacific region will be the fastest growing in the world in this situation, due to rising consumption in China, India and Japan, with a growing population, rising middle-class income and urbanization. In fact, the Asia-Pacific region will generally dominate the global aluminum market. The electronics manufacturing market in this region will develop rapidly in the coming years due to the numerous Original Equipment Manufacturer OEMs, low cost and availability of raw materials and cheap labor, as well as cooperation with numerous entities in Germany, France and the United States in the field of production services and assembly. China is expected to be the world’s largest market for civil aircraft sales by 2040 among all countries, which will have a significant impact on the demand for aluminum. For example, China is expected to purchase new aircraft from Boeing by 2036 worth USD 1.1 trillion. The growing demand for aluminum is also significantly influenced by the growing demand for cargo transportation, therefore the production of commercial aircraft in Japan will continue to increase, including the production of new generation F-35A fighters and other military aircrafts. Thus, the demand for aluminum in the Asia-Pacific region will increase rapidly in the next two decades due to the rapidly expanding end-user industry.
Aluminum is the only material that more than covers its own collection costs in the consumer disposal stream and is 100% recyclable, retaining its properties for an indefinite period of time. More than 70% of the aluminum produced from the beginning of industrial use of aluminum has been recycled and is still used today. In view of the expected growth of the global aluminum market in 2025 to USD 235.8 billion, and the related expected increase in the production capacity of bauxite mines around the world, one should take into account the probable increase in the share of secondary aluminum from new scrap, proportional to the total consumption. However, the share of aluminum produced from old scrap may decline, as in countries with high economic growth, the share of aluminum used to build new infrastructure with long-term use is significant. It could undoubtedly have a negative impact on greenhouse gas emissions, unless the stricter requirements of the climate policy force an increase in the efficiency of aluminum smelters and the related reduction of energy consumption for aluminum production. Recycling aluminum saves over 90% of energy costs compared to primary production, and thus reduces the use of fossil fuels, including oil, the energy of which would be used to produce fresh aluminum. For the recovery of post-consumer scrap, it is important to diversify the end use of aluminum. For example, statistically, an average of 113,000 aluminum cans are recycled in the world every minute, and their value per year amounts to over USD 800 million. Aluminum used in cars and vehicles can be easily recycled. Many applications in the transport sector, but also in the electronics sector, have a much shorter real life-time and therefore they are more recyclable than electrical systems and construction applications. According to the Aluminum Association, more than half a million tons of aluminum used in cars are recycled annually .
The challenges posed by the developing industry in the Industry 4.0 stage and the expectations of the automotive and aviation industries force constant progress in the development of new materials using aluminum. The undoubted advantages of these materials include the density almost three times lower than that of steel, which is the main premise for applications in the area of transport. Newer and newer aluminum alloys with other alloying elements are being developed and implemented. Of course, there are also alloys of other elements in which aluminum is an alloying element. Aluminum matrix composite materials ACMs have a steady share of the systematically growing group of materials using aluminum. This chapter presents a generalization of the results of numerous own studies and provides a detailed overview of the structure and properties and manufacturing technology of several new AMCs selected for presentation due to their advanced manufacturing methods and unexpected properties and the resulting wide application possibilities (Figure 58).
composite materials manufactured by gas-pressure infiltration with liquid aluminum alloys, respectively, eutectic AlSi12 and hypoeutectic AlSi7Mg0.3, constituting the matrix, in which the reinforcement has a skeleton structure, obtained alternatively by sintering Al2O3 powder with the participation of carbon fibers enabling, after their removal, obtaining a porous structure, sintering mixtures of HNTs halloysite nanotubes with carbon fibers, after their removal, providing a porous mullite skeleton and selective laser sintering of titanium powder to obtain a skeleton with the porosity of at least 50% with pores with a size of 50–500 μm,
nanocomposite materials manufactured by mechanical synthesis using high-energy mechanical milling of a mixture of an aluminum alloy powder for plastic deformation AlMg1SiCu with alternatively halloysite HNTs nanotubes and multi-wall carbon nanotubes MWCNTs and the next two-stage press consolidation and subsequent cold pressing in the first order hot at an elevated temperature in order to produce bars of the assumed diameter,
composite surface layers on the substrate of aluminum alloys, alternatively AlMg3, AlMg5, AlMg9, manufactured by surface laser feathering by introducing powder, alternatively tungsten carbide WC/W2C or silicon carbide SiC with the use of fluxes as agents supporting the operation of the laser beam and facilitating the selective remelting of the aluminum alloys, without the need for additional heat and surface treatment.
The structure, technology, and properties of these materials were presented, as well as the application perspectives, especially in transport and biomedical devices, as well as in connection with the implementation of the Industry 4.0 stage of the Industrial Revolution.
The author would like to acknowledge for the cooperation in research realisation his former PhD students Dr Marek Kremzer, Dr Magdalena Kujawa, Dr Anna Achtelik-Franczak, Dr Błażej Tomiczek, Dr Magdalena Macek-Sroka, and Dr Wojciech Pakieła.