The effects of yttrium addition on microstructure and mechanical properties of as-cast Mg-6Zn-3Cu-0.6Zr-xY（x=0,0.5, 1.0,1.5 and 2.0,mass fraction,%）（ZCK630+xY for short in this study）alloys were investigated by means of OM,XRD and SEM. The results show that the average grain size of Mg-Zn-Cu-Zr magnesium alloy is effectively reduced（from 57μm to 39μm）by Y addition.The analysis of XRD indicates the existence of I-phase（Mg3Zn6Y）and W-phase（Mg3Zn3Y2）in ZCK630 alloys with Y addition.The ultimate tensile strength of ZCK630 alloys is significantly deteriorated with increasing Y addition,which is possibly related to the continuous networks of intergranular phases and the increase of W-phase.
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