Fine Microstructures Of Mg-Zn-Y Alloy

The development of heat resistant magnesium alloys with Zn as the main addition element and microcontent addition of rare earth elements is one of the forcus in magnesium research. Especially, icosahedral quasicrystal (Ⅰphase) can be formed with Y element addition. Therefore, the mechanical properties at root and elevated temperatures can be improved significantly. The formation conditions of I phase during solidification process and alloy composite have not been reported systematically. The author arms on this purpose, the Mg-6Zn-0.2Y (ZW60) and Mg-6Zn-1.1Y (ZW61) were prepared under conventional solidification, near equilibrium solidification and rapid solidification conditions, respectively. The microstructures are analyzed by the optical microscopy (OM), scanning electron microscopy (SEM), energy dispersion spectrum (EDS), transmission electron microscopy (TEM) and differential thermal analyzer (DTA), The formation conditions of phases in Mg-Zn-Y alloys are determined. The following conclusions can be draw:a. under conventional solidification condition, ZW60 alloy is consists of well-development dendritic a-Mg, lamellasome Mg4Zn7 and a few Mg3YZn6 phases at a-Mg grain boundaries, the formed sequence of the phases is:ZW61 alloy is consists of dendritic a-Mg and eutectic Mg3YZn6 phase, the formed sequence of the phases is:b. Under near equilibrium solidification condition, ZW60 alloy is consists of dendritic a-Mg, fishbone-like Mg4Zn7, and a few block Mg3YZn6, the formed sequence of the phases is similar to the alloy under conventional solidification condition, it is:c. Under rapid solidification condition, ZW60 ribbon is consists of equiaxed dendritic α-Mg,needle-like Mg-Zn intermetallic compound and spheric Mg3YZn6, Mg-Zn intermetallic compound and Mg3YZn6 phases are precipitions formedα-Mg supersaturated solid solution during cooling process. ZW61 alloy is consists of equiaxed dendriticα-Mg, a few needle-like Mg-Zn intermetallic compound and amount of spheric Mg3YZn6 phases, the particle size of icosahedral quasicrystal is 80-300nm.