Effects of annealing treatment on microstructure and tensile behavior of the Mg-Zn-Y-Nd alloy

In the present study, the Mg-4Zn-0.6Y-0.5Nd alloy was hot extruded and annealed at 200°C, 225°C and 250°C for different time to optimize microstructure and mechanical properties. The results exhibit that the dual-size grain structure and linearly distributed secondary phase are the main feature of the as-extruded Mg-Zn-Y-Nd alloy, which can be described as the elongated grain is surrounded by the fine equiaxed grain. Moreover, the as-extruded alloy shows strong {011¯0} fiber texture feature, especially for the large elongated grains. The annealing treatment results in static recrystallization, which increases fine equiaxed grains but decreases large elongated grains. In addition, the equiaxed grains formed during the annealing treatment demonstrate relative random orientations, which weaken the {011¯0} fiber texture of the alloy. Moreover, during the annealing at 225°C and 250°C, the extension twins begin to form in the alloy and weaken the {011¯0} fiber texture of the alloy further. The annealing treatment has little influence on the linearly distributed secondary phase but promotes the coarsening of small precipitates at 250°C. The annealing treatment could increase the yield and ultimate strength, but the elongation decreases, especially at higher temperature. Such a variation can be ascribed to the evolution of texture, grain structure, twinning and precipitation during the annealing treatment.