Joint Formation and Mechanical Properties of 2060 Aluminum Alloy Refill Friction Stir Spot Welding Joint

Refill friction stir spot welding (RFSSW) was used to weld the 2060 aluminum alloy with 2 mm thickness. Joint formation, defect characteristics and mechanical properties were investigated. Results show that stir zone (SZ) is clarified into dynamic recrystallization zone (DRZ) and heat extruded zone (HEZ) due to different microstructural features. The size of void near the hook tip decreases with the increase of the plunge depth. Different hook morphologies are obtained under different plunge depths. The tensile-shear load of joint with the void defect initially decreases and then increases with increasing plunge depth. The mean loads of joints under different plunge depths are in the range of 5.1-5.8 kN. The void separates the hook from lap interface, so the cracks initiating from the hook propagate along the sleeve retreating path. The hook has a larger influence on the tensile-shear load of joint than void. All the tensile specimens present a shear-plug fracture mode.