Study On Microstructure And Mechanical Properties Of Die Casting Mg-Gd-Y-Zr Alloys

In this paper,developed a non-aluminum heat resistant die casting magnesium alloys were studied based on Mg-Gd-Y-Zr(GWK) alloys by die casting process of cold mould in cold chamber press.By using OM,SEM,XRD,EDS and mechanical properties test,the microstructure and mechanical properties of cold mould die casting GWK alloys have been investigated.In order to reduce the alloys costs,die casting GWC63K and GWZ631K alloys through adding Ca and Zn elements and then decreased the content of rare earth element Gd.Effects of the Ca and Zn elements on microstructure and mechanical properties of cold mould die casting GWK alloys.The microstructure and mechanical properties of GWK alloys were investigated and mechanism through solid solution,aging and solid solution+aging treatment.The experimental results indicate that prepared die casting GWK magnesium alloys by controlling the quality of liquid alloys and process parameters,and then obtained small grains structure.The befitting processing parameters obtained in the experiment are that the pouring temperature is 700℃,the mould temperature is 80～100℃and the injection velocity is 3.0m/s.The cold mould die casting Mg-xGd-3Y-0.5Zr (x=6,8,12wt.%) alloys microstructure consists ofα-Mg matrix and Mg₂₄ Y,Mg₅(GdY) phase,and most of Gd,Y rare earth elements along the grain boundary distribution.The Gd element contribute to increase strength and hardness,but decreased slightly the plastic of die casting.The results show that the mechanical properties of heat treatment cold mould die casting GW83K and GW123K alloys have higher than die casting.Heat treatment such as solid solution(400℃×2h),ageing(200℃×8h) and solid solution+ageing (400℃×2h+200℃×8h),and solid solution effect mechanical properties of alloys notable results.By solid solution treatment,mechanical properties of die casting GW123K alloy can reach:σ_b=269.4MPa,σ_s=251.0MPa,δ₅=4.2%and the alloy exhibited higher than die casting,and tensile strength,yield strength and elongation of the alloy has improved 18%,17%and 20%at room temperature respectively.Ca elements can significantly refined structure of GWK alloys,and Zn elements make the number of non-continuous rod or granular second phases increased of GWK alloys.The strength and plasticity of GWC63K and GWZ631K alloys are better than GW83K alloy's at room temperature,and have good high temperature mechanical properties.In order to decrease the cost of alloys,adding Ca and Zn elements and reducing rare earth element Gd content,which the development of new does not contain aluminum rare earth heat resistant die casting magnesium alloy is extremely important to explore the value.