Microstructure and mechanical properties of similar and dissimilar friction stir spot welded AA 5052 and AA 6061-T6 sheets

Friction stir spot welding is a newly developed spot welding method used for various applications. It can join a variety of materials and remarkably dissimilar materials. However, joining different materials or alloys utilizing conventional spot welds was prone to multiple problems. The present study has employed to join dissimilar aluminum alloys of AA5052 to AA6061-T6 by friction stir spot welding. The combinations of selected dissimilar materials were widely applied for automotive and transportation applications where lightweight structures are in demand. In order to control the heat conduction and thereby grain coarsening, AA 6061-T6 has been kept as a base sheet on the backing plate during joining. The joint was analyzed to observe the formed material mixing at the interface. The hardness distribution across the dissimilar welds obtained from the upper and lower sheets and the minimum hardness was measured in the HAZ. The fracture surface was analyzed through a scanning electron microscope. The joint strength was evaluated by tensile testing.