Rare earth texture and improved ductility in a Mg-Zn-Gd alloy after high-speed extrusion

Mg-1.58Zn-0.52Gd (wt%) alloy was successfully extruded at high extrusion speed of 60 m/min, suggesting the much better extrudability than commercial AZ31 alloy. After high-speed extrusion (die-exit speed ≥24 m/min), the Mg-Zn-Gd alloy exhibited a fully recrystallized microstructure with fine Mg3Zn3Gd2 phase at grain boundaries (GBs) and within grain interiors and rare earth (RE) texture at the position between [21̅1̅4] and [21̅1̅2] parallel to the extrusion direction. The RE texture favored the operation of both basal slip and {101̅2} extension twins, thus leading to a highly improved ductility of ∼30%, which was twice than that of the AZ31 alloy. It is hypothesized that the segregation of Gd solutes at GBs greatly influences the recrystallization behavior and thus contributes to the formation of RE texture.