Microstructure and mechanical properties of dissimilar pinless friction stir spot welded 2A12 aluminum alloy and TC4 titanium alloy joints

The microstructure and mechanical properties of dissimilar pinless friction stir spot welded joint of 2A12 aluminum alloy and TC4 titanium alloy were evaluated. The results show that the joint of Al/Ti dissimilar alloys can be successfully attained through pinless friction stir spot welding (FSSW). The joint can be divided into three zones (SZ, TMAZ and HAZ). The microstructure of joint in Al alloy side changes significantly but it basically has no change in Ti alloy side. At the same rotation speed, the maximum load of welded joints gradually rises with the increase in dwell time. At the same dwell time, the maximum load of the welded joint increases with the increase of the rotational speed. In addition, optimal parameters were obtained in this work, and they are rotation speed of 1500 r/min, plunge speed of 30 mm/min, plunge depth of 0.3 mm and dwell time of 15 s. The fracture mode of welded joints is interfacial shear fracture. The microhardness of the joint on the Al side distributes in a typical “W” type and is symmetry along the weld center, but the distribution of the microhardness on the Ti side has no obvious change.