Microstructure and texture evolution of an Mg-Gd-Y-Nd-Zr alloy during friction stir processing

Friction stir processing (FSP) was successfully applied to modify the microstructure and texture of an Mg-8Gd-5Y-1.1Nd-0.45Zr (wt.%) alloy. Two kinds of original alloys, i.e., solid solution (SS) alloy and aging (AG) alloy were used for a comparative study. The results show that the grains in SZ were greatly refined to 3-4 μm after FSP in both SS and AG alloys. However, the form of rare earth elements (either as solute or forming precipitates) in original alloys can largely influence the homogenization of grains. Uniform equiaxed grains were found in the former, whereas fine grain bands were formed in the latter. Relatively weak texture was formed in stir zone (SZ) of the Mg-Gd-Y-Nd-Zr alloy after FSP. The texture evolution in SZ is similar to many previous reports on FSW of AZ and ZK series Mg alloys. Both types of continuous and discontinuous dynamic recrystallizations (DRX) were observed in the transition region between SZ and base material in AG-FSP alloy.