Conventional and swing friction stir spot welding of aluminum alloy to magnesium alloy

Swing friction stir spot welding (SFSSW) technology which is mainly consisted of two steps is applied to join AA5083 Al alloy to AZ31B Mg alloy in the present investigation. In addition, AA5083/AZ31B joints produced by conventional FSSW were obtained. Optical microscope, scanning electron microscope equipped with energy-dispersive X-ray spectroscope, and X-ray diffraction pattern were used to analyze the morphology and microstructure of different joints. Lap-shear tensile testing and microhardness measurements were conducted to evaluate the joint performance. Results show that the bonding area and the material mixing of the spot welds fabricated by SFSSW technology were both promoted in comparison with that made by conventional FSSW. The thickness of intermetallic compounds (IMCs) at the interface around the filled original keyhole was larger owing to more heat input. The bonding interface of SFSSWed joints was irregular, and the IMCs along the annular interface were thinner than that produced by conventional FSSW. The IMC structure in the interface layer of SFSSWed joints is spherical, which is different from the dendritic structure by conventional FSSW. Finally, IMCs were found in the weld zone through phase analysis by XRD and microhardness measurements of SFSSWed joints. The fracture modes and morphologies were different to two joints, and the lap-shear tensile load of SFSSWed joint was 72.95% larger than the conventional FSSWed joint.