The microstructure of the as-cast Mg-5Sn-4Zn alloy with 0.5%

1.0%

1.5%and 2.5% Si additions was observed by XRD（X-ray diffraction）

SEM（scanning electron microscopy）.The results reveal that besides ofα-Mg and Mg

2

Sn phase

Mg

2

Si with the Chinese script shape can be observed in the Si containing alloys.Zn exists in the Mg

2

Sn and Mg

2

Si phase or dissolves inα-Mg matrix.Grain size in the alloy can be refined with increasing in Si content

and amounts of Mg

2

Si are increased.The tensile test at the ambient temperature reveals that the Si addition can result in the deterioration of the tensile properties.The compressive creep behavior of the Mg-Sn-Zn-Si alloy at 175 ℃ with loading of 55 MPa was also investigated.The results reveal that the Si addition is helpful for improving the compressive creep resistance of Mg-Sn-Zn alloy.