Influence of processing parameters on microstructure and mechanical performance of refill friction stir spot welded 7075-T6 aluminium alloy

Abstract

Refill friction stir spot welding (FSSW) is a solid state joining technology recently derived from conventional FSSW. In the present study, refill FSSW was performed in a 0·8 mm thick AA7075-T6 aluminium alloy with varying welding parameters (welding time and plunge depth). The influence of welding parameters on the microstructure and mechanical properties of the weld was investigated in terms of nugget thickness, hardness and overlap shear strength. The microstructural features and fracture mechanism were observed by optical microscopy and scanning electron microscopy. The results indicate that the nugget thickness increases with increasing welding time and plunge depth. Furthermore, melted films observed in the stir zone (SZ) were consistent with a maximum temperature of 470·9°C measured 2·6 mm away from the SZ. The overlap shear strength increases with the increase of weld time and plunge depth due to increasing nugget diameter.