Effect of Thread and Rotating Speed on Material Flow Behavior and Mechanical Properties of Friction Stir Lap Welding Joints

This study focused on the effects of thread on hook and cold lap formation, lap shear property and impact toughness of alclad 2024-T4 friction stir lap welding (FSLW) joints. Except the traditional threaded pin tool (TR-tool), three new tools with different thread locations and orientations were designed. Results showed that thread significantly affected hook, cold lap morphologies and lap shear properties. The tool with tip-threaded pin (T-tool) fabricated joint with flat hook and cold lap, which resulted in shear fracture mode. The tools with bottom-threaded pin (B-tool) eliminated the hook. The tool with reverse-threaded pin (R-tool) widened the stir zone width. When using configuration A, the joints fabricated by the three new tools showed higher failure loads than the joint fabricated by the TR-tool. The joint using the T-tool owned the optimum impact toughness. This study demonstrated the significance of thread during FSLW and provided a reference to optimize tool geometry.