Effects of the second phase on hot tearing susceptibility of Mg-Zn-Y alloy

The effect of Y (1, 1.33 and 2 at%) additions on hot tearing behavior of Mg-1Zn alloy is studied in this work. The microstructure and the phase constitution of hot tearing regions of the alloys are observed by XRD, SEM and TEM. Based on the above observations, the effect of the second phase type of the alloys on the hot tearing susceptibility of Mg-Zn-Y alloy is discussed. The HTS of the investigated alloys is found as follows: MgZn1Y1 > MgZn1Y2 > MgZn1Y1.33. The experimental results show that formation of the second phases in Mg-Zn-Y alloys strictly depended on the Y/Zn atom ratio. When Zn/Y ratio changes from 1 to 0.75 and then becomes 0.5, the secondary phase changes from W-phase, LPSO phases to W + LPSO phase. The results indicate that the hot tearing susceptibility is the lowest when the Zn/Y ratio is 0.75, because the precipitation temperature of LPSO phase is not only higher than that of W-phase and also coherent with -Mg matrix and has better pinning effect on grain boundaries.