Al-Ga-Zn System: Reassessments of the Three Binary Systems and Discussion on Possible Estimations and on Optimisation of the Ternary System

Some optimisations have already been carried out on the three experimentally well-known binary systems Al-Ga, Al-Zn and Ga-Zn. Nevertheless, we carried out our own binary assessments. Then, a first estimation of the Al-Ga-Zn ternary was calculated by a geometrical summation of the excess Gibbs energies of each mixture. But the comparison between some estimated isoplethal sections and experimental points was not satisfactory. We optimised again the Al-Ga system and made a second estimate of the ternary which was slightly more satisfactory. We then used it for the optimisation of the ternary. But to carry out the ternary optimisation, we had to reduce the Ga-Zn fcc interaction parameter. A first discussion about the impact of different sets of optimised binary coefficients, and about an adjustment for Ga-Zn fcc interaction parameter is proposed here. A second discussion points out the self-consistency between most of the ternary experimental data and, for some of the experimental points of the ternary phase diagram, the effect of pressure on experimental transformation temperatures is considered.