Abstract:The phase equilibria and compositions at the Mg-rich corner of the Mg-Zn-Al ternary system at 335 °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 α-Mg solid solution is not in equilibrium with the Mg₃₂(Al, Zn)₄₉ (τ) ternary intermetallic compound or q quasicrystalline phase, but only in equilibrium with one ternary intermetallic compound Al₅Mg₁₁Zn₄ (φ). The whole composition range of the φ phase was also obtained at 335 °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 α-Mg solid solution.

Key words: Mg-Zn-Al ternary system; isothermal section; τ intermetallic compound; solubility