Mg - 5A1 -2Sr - xSb ( χ = 0,0.3,0.6,1.0 ) alloys were prepared by microalloying method of surface active elements Sb. The effects of Sb content on the microstrueture and mechanical properties of Mg-5A1-2Sr were studied by optical microscope, X-ray diffraction, scanning electron microscopy (SEM) and mechanical property testing ,etc. The results indicate that the as-cast microstructure of Mg -5A1 -2Sr alloy consists of dendrite ot-Mg, lamellar or divorced eutectic AlaSr which distributed along the grain boundaries or between dendrites, ternary bulky MggA13 Sr phase (T phase) and granular SbSr2 phase. With the increase of Sb content, the number of SbSr2 phase gradually increases and T phase gradually reduces. With 0.6% Sb addi tion, the mechanical properties of Mg -5A1 -2St alloy at room temperature and high temperature ( 150 ℃ ) are both improved,which attribute to the discontinuous distribution AlaSr phase and fine dispersed SbSr2 phase.%采用表面活性元素Sb微合金化的方法制备了Mg-5A1-2Sr-χSb（χ=0，0．3，0．6，1．0）合金，通过金相显微镜、X射线衍射仪、扫描电镜和力学性能测试等方法研究了sb含量对Mg～5A1—2Sr合金微观组织和力学性能的影响,结果表明，Mg-5A1-2Sr-χSb合金铸态组织主要由枝晶α-Mg、沿晶界或分布在枝晶闾的层状或离异共晶的Al4Sr相、块状三元Mg9Al3Sr相（T相）和颗粒状SbSr2相组成，随着Sb含量的增加，Sb-Sr，相的数量逐渐增多，T相逐渐减少，Sb的质量分数为0．6％时，断续分布的Al4Sr相和细小弥散分布的Sb-Sr，相能够提高Mg-5A1-2Sr合金的室温和高温（150℃）机械性能。
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