Mechanical and Microstructural Evaluation of AA6082-T61 Joints Produced by Ultrasonic Vibration Assisted Friction Stir Welding Process

Continuous improvement in the friction stir welding process (FSW) is still growing to improve the process capabilities and overcome certain drawbacks encountered in the process. Low welding speeds, high welding loads, and high torque needed are the main limitations of this process. Applying ultrasonic vibration is one of the versatile approaches that was proposed to tackle these issues. In this paper, a comparative study between the conventional friction stir welding process (CFSW) and the ultrasonic-assisted friction stir welding process (UAFSW) was conducted. The objective is to evaluate quantitively and qualitatively the influence of ultrasonic vibration waves on the weld surface quality, tensile strength, micro-hardness, microstructure, and weld formation of the joints. The results have demonstrated that ultrasonic vibration waves cause grain refinement action by 23.6% at the stirring zone (SZ) as well as its desirable role in enhancing the mechanical properties by a percentage up to 15% for ultimate tensile strength and eliminating weld defects, especially at high welding speed (120 mm/min). However, no profound effect was found for ultrasonic waves on the grain size in the thermomechanical affected zone (TMAZ) or the heat-affected zone (HAZ). A considerable reduction in the elongation % whether in CFSW or UAFSW compared to that of base metal was detected.