Friction Stir Lap Welding Ti-6Al-4V Alloy Using a Threaded Pin by Simulation and Experimental Investigation

摘要

Commonly, the rotating tool during friction stir welding of Ti-6Al-4V alloy owns flat surfaces since serious tool wear always appears during welding. However, a tool with flat surface easily results into insufficient material mixing during friction stir lap welding process. In order to increase material mixing between the upper and lower sheets while welding Ti-6Al-4V alloy, a tool with a threaded pin was used in this work. The material flow behaviors at the lap interfaces using pins with and without threads were investigated. Results showed that when using the threaded pin, the maximum material flow velocity showed an obvious increase at the lap interface, which was beneficial to enhance the material mixing between upper and lower sheets. Even using the threaded pin, void-like defects appeared at joint bottoms using higher rotating speeds of 200 and 180 rpm, which were eliminated by decreasing the rotating speed to 150 rpm because of reduced temperature gradient along sheet thickness direction. The welding processes in this work were considered as below beta-transus temperature because no obvious lamellar structures were observed on all the joints. The maximum failure load of 20.23 KN was attained when using 200 rpm. The lap joints presented tensile fracture mode.