Process optimization and microstructure analysis in refill friction stir spot welding of 3-mm-thick Al-Mg-Si aluminum alloy

Novel ultra-high-strength aluminum alloys provide enormous lightweighting potential for modern car body design. However, joining such alloys can be challenging. Refill friction stir spot welding is a solid-state joining process that provides fundamental advantages compared to conventional joining technologies when welding aluminum alloys. This work presents refill friction stir spot welding for joining 3-mm-thick Al-Mg-Si alloys. The welded joints have been optimized for shear load condition by the design of experiment and analysis of variance. The results show that it is possible to obtain welds of relatively thick Al-Mg-Si alloys with good mechanical properties. Microstructure analyses show that rotational speed and plunge depth play important roles in the bonded width and hook height, which affect the mechanical performance of the joint.