Phase equilibria of the Mg–Gd–Zn system at 500 °C

Abstract

The phase equilibria of the Mg–Gd–Zn system at 500 °C in the region below 50 at% Gd were investigated with equilibrated alloys, by means of the electron probe microanalysis and X-ray diffraction. Nine stable ternary phases, τ1 to τ8 and W, were found and their composition ranges determined. The solubility of the third elements in binary phases was well determined. W was found to be isostructural to the binary GdMg3, while a very narrow two-phase field between GdMg3 and W was determined. The τ1 phase, with a composition range of Gd5.5–6.2Mg89.2–90.0Zn4.3–4.7, is identical to the X-phase (LPSO-14 H). The τ2 phase, with a composition range of Gd6.4–8.6Mg24.0–28.5Zn63.1–69.3, was identified to be the hexagonal Gd7.7Mg28.6Zn63.8 phase or the Z-phase in literature. The τ3 and τ5 phases were measured to have composition ranges of Gd10.4–10.7Mg24.0–24.5Zn64.8–65.5 and of Gd13.9–15.3Mg18.7–24.4Zn61.1–67.1, respectively, corresponding to the I-phase and the F-phase. A partial isothermal section in the region below 50 at% Gd was constructed.