Numerical simulation of bidirectional fluid-solid coupling in friction stir welding of aluminium and magnesium dissimilar alloys

Abstract During friction stir welding, the flow degree of metal materials and the welding temperature determine the microstructure and mechanical properties of the joint. This paper establishes a bidirectional fluid-solid coupling model for dissimilar friction stir welding of aluminum and magnesium alloys. Combining simulation results and experimental research, it quantitatively analyzes the distribution laws of the flow field, temperature field, and stress field during the welding process. The results show that in terms of temperature field distribution, the simulated temperature matches the thermal cycle curve of the measured temperature, with the welding temperature peak located in the rear area of the shoulder’s bottom. In addition, the temperature field on both sides of the weld is asymmetrically distributed, with the temperature on the aluminum side being higher than that on the magnesium side. In terms of flow field distribution, the material flowability decreases as the distance from the stirring head increases. Therefore, the material flow patterns around the stirring head and in areas farther from the stirring head are different. It was also found that the best material flow was at the bottom of the shoulder and the material flow rate was higher on the magnesium side than on the aluminium side. It is noteworthy that under the combined action of the stirring pin and the shoulder, the material mixing zone and the magnesium alloy shift towards the aluminum side. In terms of stress field distribution, the equivalent stress of the stirring head is distributed differently on the aluminum side and the magnesium side.