Microstructures and mechanical properties of Mg-10Gd-3Y-2Zn-0.5Zr alloy were investigated. Three kinds of phases including Mg, Mg3(GdYZn) and Mg12(GdY)Zn were found in the as-cast alloy. Two different patterns of the long-period stacking order (LPSO) phases including lamellar structure and block-like structure were observed in the homogenized alloy and both of them were identified as the phase of Mg12(GdY)Zn. After extrusion with ratio of 10:1 under 420°C, fine dynamic recrystallized grains were obtained and its average size was only about 4μm. The alloy exhibited excellent mechanical properties by hot extrusion and heat treatment. The ultimate tensile strengths of the as-extruded and peak-aged alloys were 415MPa and 480MPa, the tensile yield strength were 335MPa and 410MPa, the elongations were 16% and 13.5%, respectively. The high mechanical properties were mainly attributed to the combined effects of fine grains, LPSO phases and the dispersed precipitates.

The hot backward extrusion process of the Mg-Gd-Y-Zn-Zr magnesium alloy was investigated by both numerical simulation and experiments. An axisymmetric 2D rigid-plastic finite element model (FEM) was established to simulate the material flow during the extrusion process. The shapes of the dies were optimized in order to avoid severe stress concentration and obtain uniform deformation of the workpiece. After hot extrusion, the microstructures of the alloys were obviously refined, and the secondary phases which included many long-period stacking order (LPSO) phases precipitated in the matrix. The optimal comprehensive mechanical properties of the alloy have been obtained after extrusion and ageing at 200°C for 48h with the ultimate tensile strength of 434MPa, tensile yield strength of 375MPa and elongation of 4.5%, respectively. The good mechanical properties were mainly attributed to the fine microstructures and numerous precipitates in the matrix.

Magnesium wrought alloys are of special interest for structural components owing to their improved microstructures and mechanical properties by comparison with Mg cast parts. However, the market of Mg wrought alloys is still relatively small and one of the most important limitations for their application in areas such as aviation and spaceflight is that their strength is still not high enough to be widely used. Currently, more and more attention are paid to hydrostatic extrusion of Mg alloys because the extruded Mg alloys which exhibit extremely fine grains and high strength can be easily obtained by hydrostatic extrusion process. This review detailed the microstructures and mechanical properties of various wrought Mg alloys subjected to hydrostatic extrusion. Furthermore, numerical simulations and processing parameters optimization of the hydrostatic extrusion were also discussed. Finally, the current problems and development trends of hydrostatic extrusion of high-strength Mg alloys were also put forward.