Phase-field simulation of dynamic recrystallization in friction stir weld nugget zone of dissimilar Al/Mg alloys

In friction stir welding (FSW) of dissimilar Al/Mg alloys, the materials on both sides in weld nugget zone (WNZ) undergo extremely uneven high temperature and plastic deformation, resulting in a great difference in dynamic recrystallization (DRX) which determines the weld microstructure evolution. In this study, the multi-phase field model coupled with the dislocation density model is developed to conduct numerical simulation of DRX behavior in WNZ of Al/Mg alloys FSW with Mg placed on advancing side. It is found that during welding process, the grain size at the checking points in WNZ always decreases rapidly at first and then increases slowly to a stable value, while the dislocation density always increases first and then decreases to a stable level. After welding, the final grain size on Al's side is lower than that on Mg's side. As the welding speed decreases, the DRX becomes more intense, and the dislocation density curve fluctuates more frequently. The calculated final values of average grain size at both Al's and Mg's sides are in good agreement with the experimentally measured ones.