Influence of heat treatment on mechanical properties and microstructure of the Al2024/SiC composite produced by multi-pass friction stir processing

Aluminium matrix nano-composites were produced by friction stir processing of an Al-Cu alloy at different number of passes with pre-inserted SiC particles. The metal matrix composites were supplementary heat treated to elucidate the effect of heat treatment on microstructural changes and mechanical properties. The samples were fabricated by two and four passes. The supplementary heat treatment consisted of annealing at 590 °C for 1 h and artificial aging at 180 °C for 8 h. Microstructural studies showed that fine and co-axial grains along with uniform distribution nano-particles were formed in the stir zone (SZ). The agglomerated nano-scale particles were also observed in the samples. Micro-hardness results presented that in the SZ-region, hardness decreased with increasing the number of passes in the samples that were not heat treated. However, hardness uniformly increased about 70 HV in the heat-treated samples. Wear mechanism in all of the samples was adhesive mechanism and the value of wear resistance increased about 170% in the heat-treated samples. The obtained results showed that the improvement of hardness and wear resistance in the heat-treated sample was related to the change in size and distribution of the S-phase precipitates in microstructure.