Tensile Strength of Friction Stir Spot Welded Dissimilar AA5754-to-AZ31B Alloys

Friction stir welding (FSW) is a relatively new joining process. As a solid-state joining technique, FSW provides good potential for dissimilar materials, even for those considered to be "difficult" and "unweldable". As a variant, friction stir spot welding (FSSW) can have significant potential to replace riveting or resistant spot welding for aerospace and automotive applications. To date, limited work has been carried out on the FSSW of dissimilar material combinations. In this work, the tensile shear strength obtained is reported for a dissimilar 2-mm thick AA5754-to-AZ31 alloy system. The main process parameters investigated include tool rotation speed, tool plunge rate, dwell time and work-piece placement (i.e. either Al or Mg alloy on the top of the lap spot welds). The tensile shear strength is also compared with that obtained for similar AA5754-to-AA5754 and AZ31-to-AZ31 welds. Furthermore, the tensile shear strength is correlated with the joint geometrical dimensions and welding defects.