In this paper, the influence of the Sn element on the melt viscosity, grain size, shrinkage, and tensile properties of the sub-rapidly solidified Mg-6Al-4Zn alloy was studied. The results showed that the melt viscosity of the Mg-6Al-4Zn alloy was greatly decreased because of the addition of Sn. As the content of Sn increased from 0 to 1.8 wt.%, the grain size of the alloy was refined, and the dendrite microstructure was changed to rose-shaped ones simultaneously. The decreased melt viscosity and refined microstructure were conductive to the feeding of melt, which contributed to the reduction in volume fraction of shrinkage. The volume fraction of shrinkage of the Mg-6Al-4Zn-1.2Sn alloy was reduced by 30.8%, compared with that of the alloy without Sn addition. Tensile properties of the Mg-6Al-4Zn-xSn alloys were increased firstly and then decreased with the augmented Sn content. The yield strength, ultimate tensile strength, and elongation of the alloy containing 1.2 wt.% Sn were 21.4%, 39.5%, and 259.0% higher than those of the alloy without Sn addition, respectively. The addition of Sn was considered to reduce the shrinkage of the sub-rapidly solidified Mg-6Al-4Zn magnesium alloy and thus improved its tensile properties. To identify the mechanism, the effect of Sn on the volume fraction of shrinkage was discussed from three aspects of melt viscosity, grain refinement, and volume fraction of eutectic phases.

本文研究了Sn元素对亚快速凝固Mg-6Al-4Zn合金的熔体粘度，晶粒度，收缩率和拉伸性能的影响。结果表明，由于添加了锡，Mg-6Al-4Zn合金的熔体粘度大大降低。当Sn的含量从0增加到1.8wt。％时，合金的晶粒细化，并且树枝状组织同时变为玫瑰形。熔体粘度的降低和细化的微观结构有助于熔体的进料，从而有助于降低收缩率。与不添加锡的合金相比，Mg-6Al-4Zn-1.2Sn合金的收缩体积分数降低了30.8％。Mg-6Al-4Zn- x的拉伸性能随着Sn含量的增加，Sn合金先增加后减少。含有1.2重量％的Sn的合金的屈服强度，极限抗拉强度和延伸率分别比不添加Sn的合金高21.4％，39.5％和259.0％。认为Sn的添加减少了亚快速凝固的Mg-6Al-4Zn镁合金的收缩并因此改善了其拉伸性能。为了确定机理，从熔体粘度，晶粒细化和共晶相的体积分数的三个方面讨论了Sn对收缩体积分数的影响。