Experimental evidence of the Mg7(Zn, Ag)3 continuous solid solution in Mg-rich corner of Mg–Zn–Ag ternary system at 335 °C

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The phase constituents and compositions of a series of Mg–Zn–Ag ternary alloys held at 335 °C have been determined using X-ray diffraction and scanning electron microscopy assisted X-ray energy dispersive spectroscopy. The results indicate that a continuous solid solution, i.e., Mg7(Zn, Ag)3 phase exists stably in the Mg-rich corner at 335 °C, whose composition range is 65.1–76.9% Mg, 2.3–24.3% Zn, and 2.3–24.6% Ag (mole fraction), instead of the Mg3Ag phase reported in earlier studies. Moreover, the Mg7(Zn, Ag)3 phase is in equilibrium with the α-Mg solid solution in the Mg-rich corner, which is completely different with the presently accepted phase equilibria in the Mg–Zn–Ag ternary system. Additionally, Ag and Zn are simultaneously soluble in the α-Mg solid solution, and the maximum total solubility reaches approximately 3 at.%. Simultaneously, the c/a ratio of α-Mg decreases owing to the common solution of Ag and Zn.