Effect Of Rare Earth Elements On Microstructure And Mechanical Properties Of Heat-resistant Magnesium Alloy

Magnesium alloy is one of the lightest metal structural materials in the industrial application, which has high specific strength,stiffness and excellent anti electromagnetic shielding performance It’s applications are widely focused on aviation, cars, electronics and other fields. The improving of heat-resistant performance of magnesium alloy becomes an important research field, in order to broaden the application of magnesium alloy in the field of aviation egine. Therefore, the development of a new magnesium alloy with high strength, heat resistance and low cost has important research value.This paper studied the best foundary technology of Mg-Y-Sm series magnesium alloys by optical microscope, X-ray diffractometer, scanning electron microscope and electron back scattering diffraction, starting with composition design. The effect of element Sm and Ce on the microstructure and mechanical properties of Mg-Y series alloys were reseached as the main emphasis. The optimal experimental based master alloys were selected and the added contents of element Sm were adjusted to optimize the properties of the alloys. The new type of heat-resistant magnesium alloy with best composite property was obtained in the end.The results show that, in the current experimental conditions, the optimum casting parameters of experimental magnesium alloy is obtained. Standing time is 25 min before refining. The pouring type, temperature and speed are bet type and smooth pouring in 730℃. The preheating temperature of the casting mould is 200℃.The grains of the alloys are refined obviously by the mixed addition of rare element Sm and Ce, but a large number of precipitated phases gather in the grain boundaries. The strength of grain boundaries are weaken. The continuous mesh precipitated phases formed by the addition of element Sm separately improve the tensile strength of the alloy by 48%. With the addition of element Zn, the yield strength is improved remarkable. The based master alloy with best properties is Mg-3Y-2.8Sm-2Zn-0.6Zr. The tensile strength, yield strength and elongation in the room temperature are 207.2MPa、127.1MPa and 10.9%, respectively.When the content of elment Sm is less than 3%, the grains of Mg-3Y-2Zn-0.6Zr-x Sm(x=1,2,3,3.5) series alloys are refined. Grain size is reduced gradually. The changing contents of element Sm improve the mechanical properties of the alloys by transforming the morphology and distrubution of precipitated phases in the grain boundaries from fracture side shape into continious net and strip structure. A new type heat-resistant magnesium alloy Mg-3.5Sm-3Y-2Zn-0.6Zr with best composite properties is obtained. The tensile strength and yield strength in the room temperature are 230.1 MPa and 131.9MPa, respectively. The tensile strength in 300℃ is 188.4MPa.