Effect of annealing treatment on texture evolution, microstructure and mechanical properties of an extruded Mg-Gd-Zn-Zr alloy

Abstract

Texture evolution, microstructure and mechanical properties of an extruded Mg-10Gd-1Zn-0.4Zr alloy during annealing were investigated. A bimodal microstructure containing coarse deformed grains and fine dynamically recrystallized grains is observed when the annealing temperature is lower than 200 °C. Many Mg5(Gd, Zn) phases are formed in the alloy annealed at 200 °C. Further upon increasing the annealing temperature, static recrystallization occurs and lamellar LPSO phase forms within the matrix. When the annealing temperature reaches 500 °C, an obvious grain growth is observed, and Zn2Zr3 phases form. Meanwhile, the dominant texture component transforms from the basal texture (<101‾0> parallel to extrusion direction) to an abnormal texture (<0001> parallel to extrusion direction), which is attributed to the growth preference of the grains with abnormal texture. The alloy annealed at 200 °C possesses the optimal mechanical properties with the yield strength of 320 MPa, the ultimate strength of 368 MPa and elongation of 18.4 %. The contribution of each strengthening mechanism to the yield strength in annealed alloys is calculated quantitatively. Compared to the as-extruded alloy, the increment of the yield strength in the alloy annealed at 200 °C is mainly due to the increase in secondary phase strengthening, while the decrement of the yield strength in the alloy annealed at 500 °C is attributed to the reduction of grain boundary strengthening. This work sheds light on adjusting the texture and mechanical properties of the extruded Mg alloys via annealing treatment.