Effect of Yttrium on Hot Tearing Susceptibility of Mg-6Zn-1Cu-0.6Zr Alloys

The effect of Yttrium (Y) addition on hot tearing susceptibility of Mg-6Zn-1Cu-xY-0.6Zr (x = 0, 1, 2, 3) alloys was investigated using a constrained rod casting apparatus which monitored the hot tearing formation with a load sensor and a data acquisition system. The solidification characterization of the investigated alloys was studied through thermal analysis. The thermal analysis results revealed that as-cast Mg-6Zn-1Cu-xY-0.6Zr alloys are composed of primary alpha-Mg dendrites and several types of second phases, MgZnCu, MgZn2, Mg3YZn6 and/or Mg3Y2Zn3. The hot tearing susceptibility is affected by the addition of Y content that significantly decreases the hot tearing susceptibility of Mg-6Zn-1Cu-xY-0.6Zr alloys due to the grain refinement and high feeding capacity. In addition, the analysis of microstructures and fracture surfaces indicated that liquid film theory and feeding theory are mainly dominant on the hot tearing mechanisms.