Influence of multi-pass friction stir processing on wear behaviour and machinability of an Al-Si hypoeutectic A356 alloy

A356 is a widely used Al-Si alloy in automotive and aerospace industries for its good combination of mechanical and tribological properties. When these materials are to be considered for advanced engineering applications, machining becomes inevitable. However, presence of coarse and non-uniformly distributed silicon particles greatly influence the material properties imposing great challenge to its machinability. Our present work is focussed to improve the wear resistance and machinability of this alloy using multi pass friction stir processing (FSP). The wear behaviour of FSPed materials is characterised against metallic and abrasive medium and the machining studies are done by drilling experiments in dry condition. Under metallic wear condition, the wear resistance is maximum for the material subjected to 3 pass FSP and in case of abrasive wear, the maximum wear resistance is observed in 2 pass FSPed material. A decrease in both drilling force and surface roughness is observed with increase in FSP passes upto 2 pass beyond which they increased. Study on edge burr formation during drilling suggests that the entry and exit burrs are minimal for 3 pass FSPed material. A detailed investigation on the observed results is done in correlation with the microstructural evolution and mechanical properties.