At Room Temperature Hydrostatic Extrusion Of Mg-12gd-3y-0.5zr Alloy Microstructure And Mechanical Properties

Being the lightest metallic structural material,magnesium alloys are attractive for many applications.However,the use of magnesium alloys has been limited due to their poor plasticity and low strength.As a typical kind of magnesium alloys of Mg-RE series, Mg-12Gd-3Y-0.5Zr(wt.%)was investigated in this paper.Strengthening techniques including solution treatment at 525℃,hydrostatic extrusion at room temperature,ageing at 225℃were applied to the as-extruded alloys.The mechanical properties of the Mg-12Gd-3Y-0.5Zr(wt.%)alloys were tested by tensile testing along the extrusion direction,and their microstructure were investigated using optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The results show that with increase of hydrostatic extrusion ratio,the grain size of all materials gets smaller,the density of dislocations in the materials increases and their yield strength(YS)and ultimate tensile strength(UTS)increase.The elongation of the as-extruded materials decreases when the hydrostatic extrusion ratio increases,but in the solution-treated materials it increases.XRD analysis reveals that a planar texture structure exists in the original as-extruded materials.After hydrostatic extrusion and ageing processing,the original texture in the as-extruded materials was weakened gradually. Microstructure characterization demonstrated that the unaged solution-treated alloy contains three different phases:Gd,Y solid solution in Mg matrix,spheroidized Mg₅(GdY) compound and cuboid-shaped Mg₂Y₃Gd₂ compound.Besides these three different phases, the aged solution-treated alloy containsβ' precipitate which leads to the age hardening in the solution-treated materials.A kind of twinning structure of {11(?)1}＜(?)26＞type was observed in the hydrostatic extruded solution-treated materials,which was rarely reported in magnesium alloys.In our research,the best mechanical properties are achieved in the as-extruded material which was processed by hydrostatic extruded at room temperature with extrusion ratio of 1.15 and ageing at 225℃for 48 hours,and the YS,UTS and elongation of it is 301Mpa,373Mpa and 5.0%,respectively.