Enhancing strength and ductility of Mg-Zn-Gd alloy via slow-speed extrusion combined with pre-forging

Mg-1.58Zn-0.52Gd (wt.%) alloy was subjected to slow-speed extrusion at 350 °C and 400 °C combined with hot pre-forging. The extruded alloy without pre-forging exhibited a bimodal microstructure, consisting of fine dynamically recrystallized (DRXed) grains and coarse unDRXed grains elongated along the extrusion direction, and strong basal texture, while pre-forging changed the bimodal structure into fully DRXed microstructure with finer grains and weaker extrusion texture. The fine and homogeneous extruded microstructure in the pre-forged alloy was mainly ascribed to the combined effect of refined starting microstructure just before extrusion, continuous DRX mechanism during extrusion and pinning effect induced by fine Mg₃Zn₃Gd₂precipitates. The pre-forged alloy exhibited superior balance of strength and ductility, as well as yield asymmetry, to the non-forged alloy after extrusion. The pre-forged alloy extruded at 350 °C and 400 °C showed highly improved elongation of 27.9% and 34.8%, respectively, mainly due to the formation of fully DRXed microstructure with fine grains through suppressing the activity of {10 1¯ 1} contraction and {10 1¯ 1}-{10 1¯ 2} double twins during tensile deformation.