Investigation On Grain Refinement And Aging In Mg-12Gd-3Y-0.5Zr Magnesium Alloy

As the lightest metallic structural material, magnesium alloys are attractive for manyapplications. However, the applications of magnesium alloys have been limited due to theirpoor plasticity and low strength. Mg-12Gd-3Y-0.5Zr(wt.%) magnesium alloy, whichexhibits excellent mechanical properties, has been investigated in this paper. Strengtheningtechniques including equal channel angular pressing (ECAP) at 400℃via route Bc, extrusion at 300℃with extrusion ratio of 9,ageing at 250℃were applied to theMg-12Gd-3Y-0.5Zr(wt.%) magnesium alloy.. The mechanical properties were tested by thetensile testing along the extrusion direction, and the microstructure has been investigatedusing optical microscopy(OM),scanning electron microscopy(SEM) and transmissionelectron microscopy(TEM). Texture development during deformation was analyzed bypole figure and orientation distribution function (ODF). The results showed that the as-castalloy contains two different phases: the majorαphase which is supersaturated Gd,Y solidsolution in Mg matrix, and Mg-Gd-Y eutectic compound; The microstructure waseffectively refined by ECAP. However, after 4 passes, the texture softening is dominantover the Strengthening due to grain refinement, as a result, the tensile yield stress(TYS)was reduced, while the ultimate tensile strength(UTS) and elongation were increased; After extrusion, the texture strengthening plays an important role in the mechanicalproperty. The YTS and UTS were increased but the elongation was decreased. After aging, the precipitations were network-like stripes with weak contrast, the YTS and UTS wereincreased, while the elongation was decreased. A good combination of high strength atroom temperature, is achieved for aged at 250℃for 12h after ECAPed for 4 passes andextruded, whose ultimate tensile strengths, tensile yield strengths were 367MPa and317MPa, respectively. And the highest elongation (19.3%) was obtained by extrusion afterannealing. The results showed that the combination of ECAP, extrusion and aging can beapplied to improve the strength and plasticity of Mg-12Gd-3 Y-0.5Zr(wt.%) magnesium.