Microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr alloys

The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr (x=1, 2, 3, 4; normal mass fraction in %) alloys were investigated. In low Zn content, aside from the major second phase of Mg-24(Er, Y, Zn)(5), there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg-24(Er,Y,Zn)(5) phase decreases, but the Mg12Zn(Y, Er) phase and lamellar phases continuously increase. When Zn content reaches 4% (normal mass fraction), the Mg12Zn(Y,Er) phase mainly exists as large bulks, and some alpha-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mg12Zn(Y,Er) and Mg-24(Er,Y,Zn)(5) phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.