Numerical simulation of friction stir lap welding of Al-to-Mg alloys under different lap configurations and pin lengths

The lap configurations and pin lengths have important influences on the joint quality and performance in Al-to-Mg friction stir lap welding (FSLW). But how these two factors affect the thermo-mechanical process in Al-to-Mg FSLW remains unclear. In this study, a computational fluid dynamics model considering the effects of local liquation, tool adhesive layer, tool tilt angle and pin thread is developed to analyze the FSLW process of Al-to-Mg with sheet thickness 3 plus 3 mm. The numerical simulation results are experimentally verified by the measured interface temperature and thermal mechanical affected zone profile. For pin length 3.8 mm, the Al/Mg configuration results in higher temperature and stronger material flow, so that intermetallic compounds (IMCs) are easy to form and joint strength is poor. The Al–Mg mixed region in Mg/Al configuration is mainly from the pin bottom to the lap interface, while that in Al/Mg configuration extends from the pin bottom to the position close to the top surface on the advancing side. In Mg/Al configuration, when the pin length increases, the peak temperature increases, the high-temperature region around the tool obviously expands and the tool can drive more materials to flow, which results in a larger Al–Mg mixed region, and the IMCs are more likely to be generated.