Optimization of rotation speed ratio in dual-rotation friction stir welding by finite element method

Dual-rotation friction stir welding (DR-FSW) is a new variant technique of friction stir welding. By adopting different rotation speeds for the pin and shoulder, the temperature gradient can be adjusted to help decrease overheat and the dissolution of the strengthening precipitates and produces good joints for some cases, such as thick plates. In this study, by thermal-mechanical coupling method, with the help of finite element software-DEFORM- 3D, the temperature field of workpieces in DR-FSW for an 80-mm-thick 5A06 aluminum alloy was simulated, and the temperature gradients at different rotation speed ratios were calculated and analyzed. Better process parameters could be concluded using optimization. In our simulation, the rotation ratio of 200 rpm for the shoulder and 400 rpm for the pin in the first group achieved the gentlest temperature gradient in thickness direction with a temperature difference between the upper and lower surfaces of less than 30 degrees C. The study represents a practical reference for choosing process parameters in the actual DR-FSW process.