Dynamic Recrystallization and Dynamic Precipitation in AA6061 Aluminum Alloy During Friction Stir Welding

This paper investigated the mode of recrystallization in the nugget zone (NZ) of friction stir welding (FSW) joint of AA6061-T6. By correlating grain orientation spread results, kernel average misorientation (KAM) results, misorientation maps of grain boundaries (GBs) and selected area diffraction patterns of precipitates systematically, we found that continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX) both occurred. CDRX could be enhanced by decreasing feeding speed of FSW. The variation trend of fraction of low-angle grain boundaries in NZ indicated different contribution brought by CDRX and GDRX and also different combination form of heat input. KAM results can also act as indicator of the extent of dynamic recrystallization in the NZ of FSW, only under a constant feeding speed. The fine needle-shaped β'' precipitate disappeared in NZ and evolved to β' and equilibrium β-Mg2Si phase during FSW. Furthermore, the shape and orientation of β' or β phases could be changed by mutual interaction with dislocation movement, to different extent depended on CDRX.