Thermodynamic Calculation of Al-Gd and Al-Gd-Mg Phase Equilibria Checked by Key Experiments

The binary Al–Gd and the ternary Al–Gd–Mg systems were calculated using the Calphad method. It is demonstrated that previous interpretation of ternary liquidus temperatures below 700 °C must be related to other phase equilibria. The actual ternary liquidus temperatures are much higher, up to some 600 °C above the previous interpretation in literature. They are widely governed by the high-melting compounds Al Gd and Al Gd with liquidus surfaces stretching far into the ternary system. A small number of key experiments in this work confirmed the calculated liquidus temperature and the phase relations. The available experimental data in literature fit excellently with the calculation in the binary Al–Gd system. In the ternary Al–Gd–Mg system, which is shown in several sections of the phase diagram, a good agreement can be observed too, considering the necessary reinterpretation of the liquidus temperatures suggested by Rokhlin et al. Ternary solubilities were not found experimentally. The ternary compound Al GdMg (τ) forms in a ternary peritectic reaction at 761 °C.