The as cast microstructure and mechanical properties of Mg-6Al-1Zn-0?7Si (wt-%) alloys modified by Sn and Sr additions are investigated and compared. The results indicate that adding 0?56 wt-%Sn to Mg-6Al-1Zn-0?7Si can refine the Chinese script shaped Mg 2 Si phase in the alloy, but the modification of the Mg 2 Si phase is not obvious. Oppositely, adding 0?027-0?086 wt-%Sr can effectively refine and modify the Chinese script shaped Mg 2 Si phase in the Mg-6Al-1Zn-0?7Si alloy. After adding 0?027-0?086 wt-%Sr, the morphology of the Mg 2 Si phase in the Mg-6Al-1Zn-0?7Si alloy changes from coarse Chinese script shape to fine granule and/or irregular polygonal shapes. Accordingly, the Sr containing alloys obtain the relatively higher tensile and creep properties than the Sn containing alloy. The difference of Sn and Sr additions in the modification and refinement of the Chinese script shaped Mg 2 Si phase in the Mg-6Al-1Zn-0?7Si alloy is possibly related to the different effects of the two elements on the undercooling degree.

The effects of small additions of Zr and Sr on the as cast microstructure and tensile properties of the Mg–4Y–1·2Mn–0·9Sc (wt-) magnesium alloy were investigated. The results indicate that small additions of Zr and/or Sr to the Mg–4Y–1·2Mn–0·9Sc alloy do not cause an obvious change in the morphology and size of the secondary phases. However, the grains of the Zr and/or Sr containing alloys are effectively refined. Among the Zr and/or Sr containing alloys, the grains of the alloy with addition of 0·5 wt-Zr+0·1 wt-Sr are found to be the finest, followed by the alloys with additions of 0·5 wt-Zr and 0·1 wt-Sr respectively. Furthermore, the tensile properties of the Mg–4Y–1·2Mn–0·9Sc alloy, especially the room temperature ductility, are improved by small additions of Zr and/or Sr. Among the Zr and/or Sr containing alloys, the alloy with addition of 0·5 wt-Zr+0·1 wt-Sr obtains the optimum tensile properties at room temperature and 300°C, and the tensile properties of the alloys with additions of 0·5 wt-Zr and 0·1 wt-Sr are similar.

The as cast microstructure and mechanical properties of the Mg-3Ce-1?2Mn-1Zn and Mg-4Y-1?2Mn-1Zn (wt-%) magnesium alloys were investigated and compared. The microstructural results indicate that the Ce containing alloy is mainly composed of a-Mg and Mg 12 Ce phases, while the Y containing alloy mainly consists of a-Mg and Mg 12 YZn phases. Furthermore, the Mg 12 Ce and Mg 12 YZn phases respectively exhibit quasi-continuous and continuous nets. The tensile and creep tests indicate that the tensile and yield strengths of the Y containing alloy are relatively higher than those of the Ce containing alloy, but the elongation of the former is a little lower than that of the latter. In addition, the creep properties of the Y containing alloy are much higher than those of the Ce containing alloy.