The Effect of Rotational Speed on Microstructure and Mechanical Properties of Al/Ti Dissimilar Joint Produced by Refill Friction Stir Spot Welding

The microstructure and mechanical properties of Al/Ti dissimilar refill friction stir spot welding joints at different rotational speeds were studied. The grain size of each zone of the joint increases with increasing rotational speed. An interfacial layer with thickness less than 50 nm was formed at the interface. Combined with the numerical simulation results, the multiple effects of thermal and mechanical action on microstructure are explained. The microhardness of the aluminum alloy joint presents a ‘W’ shape distribution. The tensile strength increases firstly and then decreases with the increase in rotational speed. The joint strength of 6353 N is the highest at 1300 rpm. The sleeve stir zone fracture occurs at the interface, and the fracture mode is brittle fracture. The pin stir zone fracture occurs at the aluminum alloy, and the fracture mode is ductile mixed fracture.