Microstructures and Properties of As-Cast Mg92Zn4Y4 and Mg92Zn4Y3Gd1 Alloys with LPSO Phase

Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys with long period stacking ordered (LPSO) structure phases were prepared by conventional solidification process. By OM, SEM, EDS, XRD and TEM analysis the phases and 14H-LPSO structures of the two alloys were characterized. The results show that as-cast Mg-alloy with the atomic ratio of Zn/RE = 1 will lead to LPSO phase; adding of Gd element to Mg92Zn4Y4 alloy can facilitate the formation of LPSO phase, and its volume fraction increases from 12.1% to 30.4%; Mg dendrites are split and refined during the precipitation of LPSO phase formed at high temperature, resulting in that the average grain size of α-Mg decreases from 50 µm to 10 µm; the solidification microstructure of as-cast Mg92Zn4Y4 alloy is α-Mg solid solution + Mg12ZnY + Mg3Zn3Y2 + Mg-Y; In Mg92Zn4Y3Gd1 alloy, the as-cast microstructure is confirmed to be composed mainly of α-Mg solid solution, Mg12Zn(Y, Gd) and Mg3Zn3(Y, Gd)2; at room temperature, the compression ratio and the thermal conductivity of Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys are 12.4% and 15.5%, and 99.233 W·(m·K)−1 and 88.639 W·(m·K)−1, respectively.