Experimental study on ultrasonic vibration enhanced friction stir welding

Ultrasonic vibration enhanced friction stir welding (UVeFSW) is a recent modification of conventional FSW, which transmits ultrasonic vibration directly into the localized area of the workpiece near and ahead of the rotating tool. In this study, high strength aluminium alloy (2A12-T4) test pieces were welded by using UVeFSW to investigate the effect of the ultrasonic vibration on the weld quality and efficiency. In all experiments, it is found that the ultrasonic vibration can enhance the plastic fluidity of the material around the tool pin since an additional deformation force and thermal action are superimposed. It turns to lower the yield strength of the material, and further to reduce the required Z-axial force and the torque of the main spindle. As a result, it can improve the weld morphology and/or avoid internal tunnel defect related to the lack of heat input caused by lower Z-axial force or high welding speed or low tool rotation speed. In addition, the tensile strength and the fracture elongation of the weld joint were also improved to some extent.