Effect of different Sn additions on microstructure and mechanical properties of as-cast Mg-6Zn-0.7Zr alloys were investigated by XRD （X-ray diffraction）

SEM （scanning electron microscope）

EDS （energy dispersive spectrum） and tensile testing. The results show that Sn exists in the Mg-6Zn-0.7Zr alloy in form of three types: dissolved in α-Mg matrix

formed Mg2Sn phases

and existed in the MgZn phase. The addition of Sn can refine the divorced MgZn eutectics. However

the increase of Sn leads to the coarseness of α-Mg dendritic

which indicates that magnesium alloys containing Sn are not suitable for the addition of Zr element. A minor addition of Sn can improve the tensile strength of as-cast Mg-6Zn-0.7Zr alloy. The tensile strength and elongation of Mg-6Zn-0.7Zr-0.5Sn alloy reach 242 MPa and 17%

respectively. Fractographic analysis demonstrates that the brittleness of the alloy increases when the Sn content is over 3%. It is expressed as a large number of dissociation stepped surface and river pattern on the fracture surface.