Effect of heat treatments on friction stir processed aluminium surface composites

In this study, an age-hardenable Al-Zn-Mg-Cu alloy was reinforced with titanium carbide particles by a novel method and a surface composite synthesised by way of recursive friction stir processing (FSP). The effects of age hardening (T6) and retrogression and reaging (RRA) treatments on microstructural evolution, and mechanical properties were investigated. Compared to the base material, significant grain refinement and improved mechanical properties were noticed in the friction stir processed Al/TiC composite due to the homogenous distribution of reinforcement. During heat treatments, the presence of reinforcement inhibited the growth of grains during dynamic recrystallisation producing a microstructure with finer grains. The heat-treated composites exhibited better mechanical properties than as-fabricated composite due to combined effect of reinforcement and the precipitated phases.