Refill Friction Stir Spot Welding of 2198-T8 Aluminum Alloy

Refill friction stir spot welding (RFSSW) technology was used to weld 2 mm-thick 2198-T8 aluminum alloy in this work. As one of the most significant factors affecting the joint mechanical properties, effect of the tool rotating speeds on microstructure and mechanical properties of the RFSSW joint was mainly discussed. Results showed that keyhole could be successfully refilled after the RFSSW process. Due to the complicated movement of the tool components, different material flow behaviors could be obtained at the pin affected zone and sleeve affected zone, leading to different microstructures at the two regions. By undergoing through different heat cycle during welding, the secondary phase particles (Al2Cu) showed different morphologies and sizes at different regions. The lap shear failure load of the joint firstly increased and then decreased with increasing in the rotating speed. The maximum failure load of 9298 N was obtained when using 1600 rpm. All the joints showed lap-shear fracture mode.