Effect of Reverse-threaded Pin on Mechanical Properties of Friction Stir Lap Welded Alclad 2024 Aluminum Alloy

In friction stir welding (FSW), tool geometry plays an important role in joint quality. In order to improve mechanical properties of friction stir lap welding (FSLW) joint, a tool with a reverse-threaded pin was designed in the present study. Using 2024-T4 aluminum alloy as the research object, tools with the full-threaded pin and reverse-threaded pin were used in FSLW. Results showed that, when using the same parameter combination, FSLW joint using the reverse-threaded pin owned bigger effective sheet thickness (EST), bigger lap width and better lap shear failure strength. Compared with the full-threaded pin, fracture mode of the FSLW joint changed from shear fracture mode to tensile fracture mode when the reverse-threaded pin was used. Fracture morphologies presented ductile fracture.