Influence of friction stir processing on microstructure and mechanical properties of AA6061 reinforced with Zr and Ni metallic particles

Friction stir processing (FSP) is considered as a prolific secondary processing method to enhance the properties of aluminium matrix composites (AMCs) by altering their microstructure. AA6061/(15 wt.%) Al3Zr and AA6061/(15 wt.%) Al3Ni AMCs were manufactured with the addition of zirconium (Zr) and nickel (Ni) powders to the molten AA6061 and followed by FSP. The change in microstructure of AMCs before and after FSP was analysed through optical and electron microscopies integrated with electron back-scattered diffraction. The cast AMCs exhibited clustered, sharp cornered particles with micropores near the particle-matrix interfaces and showed coarse-grained microstructure. Upon conducting FSP, the particle distribution was uniform along with the elimination of cast defects. The sharp cornered particles were fragmented into finely dispersed particles in the aluminium matrix. Significant grain refinement was observed on AMCs owing to the pinning effect of particles and severe deformation happened during FSP. FSP enhanced the accumulation of dislocations and resulted in modification microstructure, which favoured attaining a combination of ductility and tensile strength. The strength attained by the Al3Ni AMC was higher than that of Al3Zr AMC due to the existence of finely dispersed near round-shaped particles, which exhibited better load-bearing ability.