Isothermal section of Mg-rich corner in Mg-Zn-Al ternary system at 335 °C

The phase equilibria and compositions at the Mg-rich corner of the Mg-Zn-Al ternary system at 335 degrees C were systemically investigated through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). It is experimentally testified that the alpha-Mg solid solution is not in equilibrium with the Mg-32(Al, Zn)(49) (tau) ternary intermetallic compound or q quasicrystalline phase, but only in equilibrium with one ternary intermetallic compound Al5Mg11Zn4 (phi). The whole composition range of the phi phase was also obtained at 335 degrees C, i.e., 52.5%-56.4% Mg, 13.6%-24.0% Al, 19.6%-33.9% Zn (mole fraction). The solubility of Al in the MgZn phase is remarkably more than that in the Mg7Zn3 phase, and the maximum is about 8.6% Al. Aluminum and zinc are simultaneously soluble in the alpha-Mg solid solution.