The effects of Sn addition（0, 0.5, 1.0, 2.0 and 3 wt%） on microstructure of Mg-4Zn-1.5Al alloy in cast and extruded states were investigated, and the mechanical properties of as-extruded Mg-4Zn-1.5Al-xSn studied. The experimental results showed that the as-cast Mg-4Zn-1.5Al alloy was composed of two phases α-Mg and Mg32（Al, Zn）49, while Sn-containing alloys consisted of α-Mg, Mg32（Al, Zn）49 and Mg2Sn phases, and Mg32（Al, Zn）49 was not detected after extruding due to that the most of them dissolved into the matrix during the homogenized treatment. The addition of Sn refined the grains of as-cast and as-extruded Mg-Zn-Al alloys obviously. It was noted that the basal texture intensity reduced with increasing Sn content significantly in as-extruded Mg-Zn-Al alloys. The tensile tests results indicated that Sn addition improve the tensile strength of the extruded alloys,while it had a harmful effect on the ductility. When the addition of Sn was 2 wt%, the ultimate tensile strength（UTS）, yield strength（YS） and elongation（εf） of the alloy were 280 MPa, 147 MPa and 17.4%, respectively.
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