Research Of Mg-Sn-Si Heat Resistance Magnesium Alloy

In order to improve the heat resistant properties of Mg alloys, base on Mg-4Si alloy,the effect of Sr and Pr addition on the microstructures and the modification and refiningmechanism of primary and eutectic Mg2Si phase were investigated by using the SEM,XRD and FWSEM. What’s more, Mg-Sn-Si heat resistance alloy were designed based onMg-4Si. The phase constituent and microstructure were investigated by using the SEM,XRD, respectively. The creep test of as as-extruded alloy has also performed, the fracturesurfaces were analyzed by using SEM. The important results are summarized as follows:The primary and eutectic Mg2Si phases were effectively modified by Sr addition.However, different amount of Sr are required for the two microstructures, i..e., the primaryand eutectic Mg2Si can effectively be modified by0.5%and1.0~2.0%Sr addition,respectively. The rare earth Pr can effectively modification and refine the primary Mg2Si inMg-4Si alloys, the primary Mg2Si can effectively modification by0.5%Pr addition, When2.0%Pr is added, the primary Mg2Si phases are mainly regular-shaped particles, theaddition of Pr should be controlled between1.0~2.0%.The microstructure of the Mg-3Sn-4Si-0.5Sr-0.5Bi alloy are mainly composed withα-Mg、Mg2Si、Mg2Sn、MgSnSr、Mg3Bi2phases. The alloys have the best mechanicalproperties after T5treatment at room temperature. The tensile strength, yield strength andelongation are154.5MPa,93.58MPa,5.7%, respectively. The as-extruded alloy ofMg-3Sn-4Si-0.5Sr-0.5Bi have the best mechanical properties after T5treatment at roomtemperature, the tensile strength, yield strength and elongation are245.5MPa,207.2MPa,8.1%, respectively.The as-extruded and T5technique(aging at200℃×12h) Mg-3Sn-4Si-0.5Sr-0.5Bialloys have the best creep performance at35MPa/150℃, the creep life, steady-state creeprate, total creep are145.7h,1.95×10-7s-1,15.75%and180.15h,1.17×10-7s-1,17.46%,respectively. The creep life, total creep increased23.66%,10.86%, respectively, comparedwith the as-extruded alloys. When the creep condition is150~175℃, the creep activation energy value of theas-extruded and aging-treated of as-extruded Mg-3Sn-4Si-0.5Sr-0.5Bi alloys areQ=94.54kJ/mol, Q=108.46kJ/mol, respectively. And the creep mechanism of the alloys arecontrolled by grain boundary diffusion at150~175℃. Hower, When the creep condition is175~200℃, the creep activation energy value of the as-extruded and aging-treated ofas-extruded Mg-3Sn-4Si-0.5Sr-0.5Bi alloys are Q=130.78kJ/mol, Q=139.73kJ/mol,respectively. And the creep mechanism of the alloys are controlled by dislocation climb at175~200℃.