Characteristic And Mechanism Of Nugget Performance Evolution With Rotation Speed For High-Rotation-Speed Friction Stir Welded 6061 Aluminum Alloy

High-rotation-speed friction stir welding (HRS-FSW) can effectively reduce welding load and has a great application prospect in the field of in-situ fabrication and repair. FSW of 6061-T4 aluminum alloy plate was performed using 1000-6000 rpm rotation speeds in this study, and a detailed investigation on the characteristic and mechanism of the nugget zone (NZ) performance was conducted from aspects of experiment and simulation. The results indicate that the HRS-FSW causes the area with higher temperature and strain to transfer from the shoulder-affected zone to the pin-affected zone and the material flow to be enhanced on the retreating side of weld, leading to the improvements in the size and symmetry of the NZ. Increase of rotation speed to higher values favors the grain growth and phase dissolution and simultaneously tends to weaken the effect of plastic strain on further increase in dislocation density. The grain size is found to dominate the NZ hardness evolution with rotation speed. The evolution of NZ hardness roughly presents a Hall-Petch relationship with the grain size.