Numerical simulation of thermomechanical behavior and mechanical property in HRFSW of Aluminum Alloy

High-rotational-speed friction stir welding (HRFSW) has gained significant attention in the field of friction stir welding due to its numerous advantages, including minimal workpiece deformation, low load requirements, rapid weld cooling, and improved mechanical properties with refined grains at the joint. This study conducted a HRFSW experiment on 1 mm thick 6061-T6 aluminum alloy sheets with stirring speeds ranging from 8,000 to 12,000 rpm and a constant transverse speed of 300 mm/min. During the HRFSW process, real-time temperature measurements were performed at the welded joint. A numerical analysis of the temperature and strain fields was conducted utilizing the coupled Eulerian–Lagrangian (CEL) method. A novel mathematical model of microhardness was introduced and incorporated into the CEL algorithm via a VUSDFLD subroutine to predict the mechanical properties of the welded joints. The results demonstrated that the peak temperature at the joint area during HRFSW increases with increasing penetration depth or rotational speed of the stirring tool. The observed asymmetry in the temperature field was attributed to variations in the strain distribution. Furthermore, peak strains consistently appeared in regions characterized by higher material flow rates. Physical experiments validated the established model, demonstrating its ability to accurately capture the variations in microhardness according to different microstructural features within the welded joint. This study provides a substantial understanding of the thermomechanical behavior of materials during the HRFSW process and contributes to the interpretation of microhardness distribution patterns and corresponding mechanisms in various regions of welded joints under different processing conditions.