Numerical and experimental study on the thermal process, material flow and welding defects during high-speed friction stir welding

Friction stir welding (FSW) involves complex interactions between thermal, mechanical and geometric effects. The thermal process and material flow in the welding process significantly influence the microstructure evolution and the final mechanical properties of the joint. This paper aims to determine the influence of the thermal process and material flow on welding defects during high-speed FSW of an aluminum alloy. A thermal-fluid coupling model based on computational fluid dynamics is established, and related experiments are designed to verify the difference in the temperature distribution and the characteristics of the material flow. The results show that the calculation results can accurately describe the quasi-steady state heat-flux coupling state during FSW. In high-speed welding, the material produces a considerable strain rate. The contact friction stress of the tool decreases as the temperature of the material increases. The dynamic recrystallization phenomenon is more evident on the advancing side, but there are tiny void defects on the advancing side.