Study On Preparation And Properties Of Aluminum Matrix Composites Reinforced By SiC Particles And Carbon Fibers

Aluminum alloys are widely used in industry and civil fields, because they have many excellent properties such as, light density, good thermal and electric conductivity, good oxidation resistance, good corrosion resistance and good plasticity, and easily to be machined. Using the different aluminum alloys with high strength as matrix, the discontinuously reinforced aluminum matrix composites are produced if they compound with the discontinuous materials such as, SiC, Al2O3, TiC particles with high hardness and elastic modulus or carbon fiber and graphite with solid lubricant effects. These discontinuous aluminum matrix composites can be made by variable manufacture technologies. In addition, they can furthest integrate their component properties advantages which make they have high strength, good thermal and electric conductivity and easily processing as the matrix aluminum alloys do. Besides, they may have high specific modulus, good wear resistance, and low expandability and dimension stability properties. Therefore, they are ones of advanced metal matrix composites, which have a most potentially wide application and have been used as structure materials in aerospace, automobile and other industries.In this paper, the pretreatment of SiC particles and carbon fibers are investigated, and SiCp/Al-Cu-Mg and Cf/Al-Cu composites are made by powder metallurgy and heat treatment, respectively. Their density, hardness, ultimate tensile strength and tribological properties are measured, the factors such as mechanical alloying technique, volume fraction of reinforcements and loads on their mechanical and wear properties are analyzed, and the wear mechanisms are discussed. The main results are therefore found as follows.To SiCp/Al-Cu-Mg composites, with the increase of the SiC particle volume fraction, their density increases, but their hardness and ultimate tensile strength increases first and then drops, as a result that 9%SiCp/Al-Cu-Mg composite has the optimize mechanical properties. The SiCp/Al-Cu-Mg composites have better wear resistance than the matrix alloy does. The wear rates of the composites are obviously lower than that of their matrix alloy, and they decrease with the increase of the SiC particle volume fraction.9%SiCp/Al-Cu-Mg and 12%SiCp/Al-Cu-Mg composites have the almost equal lowest wear rate values. The mechanical alloying technique improves the ultimate tensile strength of the AlCuMg matrix alloy, but it does not influence its density, hardness, wear rate and friction coefficient. On the other hand, the mechanical alloying technique enhances the density, hardness, ultimate tensile strength and friction coefficient of 9%SiCp/Al-Cu-Mg composite, but it does not influence its wear rate. The loads hardly affect the wear rate of SiCp/Al-Cu-Mg composites while somewhat change their friction coefficient, such as, the heavier load obviously raises that of 9%SiCp/Al-Cu-Mg and 12%SiCp/Al-Cu-Mg composites.To Cf/Al-Cu composites, their density drops with carbon fiber volume fraction (Vf) increasing, besides their hardness and ultimate tensile strength increases first and then decreases, of which 6% Cf/Al-Cu has the best ultimate tensile strength and the 9%Cf/Al-Cu has the best hardness. The wear rate of Cf/Al-Cu composites drops first and then increases with Vf of carbon fiber increasing, and the 6%Cf/Al-Cu composite has the lowest value. Furthermore, the wear rates of the composites are lower than that of the matrix alloy. The friction coefficient of Cf/Al-Cu composites drops with Vf of carbon fiber volume fraction augmenting. The AlCu matrix alloy and 6%Cf/Al-Cu composite have the equal maximum friction coefficient while the 12%Cf/Al-Cu composite has the minimum. The loads hardly affect the wear rates and friction coefficients of the composites, except that the heavier load enhances the friction coefficient of the 12%Cf/Al-Cu composite.The wear mechanism of SiCp/Al-Cu-Mg and Cf/Al-Cu composites is mainly adhesive mechanism. In additional, the oxidation mechanism inevitably exists because the aluminum matrix alloy is easily oxidized during the wearing process, resulting in that the abrasive mechanism exists in that of Cf/Al-Cu composites.