Microstructure and mechanical properties of directionally solidified alloys of Mg-9Zn-2Y

Samples of directionally solidified Mg-9Zn-2Y alloys have been obtained using vacuum induced directional solidification equipment. The metallographic structures and mechanical properties at room and high temperatures of the directionally solidified alloys have been investigated and compared with those of conventional casting alloys. The structures have consisted of columnar crystals with a specific orientation, and the parallel phases near the grain boundaries and inside the grains have quasi-crystals of I-Mg3Zn6Y. At room temperature, the maximum compressive resistance and section expansion ratio of the directionally solidified alloys have been 54 and 31% higher, respectively, than those of the conventional casting alloys. The peak stress of the directionally solidified alloys has found 238 MPa, which is 57% higher than that of the conventional casting alloys (152 MPa) at 200 °C with a strain rate of 0.1 s-1. In addition, the peak stress was 140 MPa at 300 °C with a strain rate of 0.1s-1, while it was only 84 MPa for the conventional casting alloys. Therefore, the directionally solidified alloys has higher strength and plasticity at room temperature and improved mechanical properties at a high temperature.