Mechanical properties and strengthening mechanism of medium and high volume fraction SiCp/Al composites

The medium and high volume fraction SiCp/Al composites were prepared by hot isostatic pressing powder metallurgy process with volume fractions of 35%, 45% and 55% using 2024 and 6061 aluminum alloys as the matrix, respectively. The effect of matrix alloy and SiC volume fraction on the mechanical properties of the composites was investigated. The results show that with the same SiC volume fraction, composites with 2024 aluminum alloy matrix have higher bending strength and elastic modulus, while composites with 6061 aluminum alloy matrix present higher fracture strain. Meanwhile, the mechanical properties of composites with 2024 and 6061 alumium alloy matrix present the same trend as SiC volume fraction increases. The bending strength increases at first and then decreases, with the maximum values of composites with volume fraction of 45% being 656.54 MPa and 548.00 MPa, respectively. However, the elastic modulus continuous increases and reaches maximum for SiCp/2024Al and SiCp/6061Al composites with volume fraction of 55% being 202 GPa and 188 GPa, respectively. The effect of differences in matrix alloys on mechanical properties is more significant at lower volume fractions, and increasing the volume fraction will weaken this difference. According to the theoretical formulas calculation, Orowan mechanism has negligible strengthening effect for the composites with micron-grade SiC particle.The strengthening effect of other types of reinforcement mechanisms can be enhanced on different levels with the increase of the volume fraction of the reinforcement, wherein the contribution of geometrically necessary dislocations and thermal mismatch reinforcement to the yield strength of materials is always dominant.