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

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 degrees C. Many Mg-5(Gd, Zn) phases are formed in the alloy annealed at 200 degrees C. Further upon increasing the annealing temperature, static recrystallization occurs and lamellar LPSO phase forms within the matrix. When the annealing temperature reaches 500vC, an obvious grain growth is observed, and Zn2Zr3 phases form. Meanwhile, the dominant texture component transforms from the basal texture (< 10<(1)over bar>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 degrees 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 degrees C is mainly due to the increase in secondary phase strengthening, while the decrement of the yield strength in the alloy annealed at 500 degrees 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.