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Abstract  

The Al-Zn-Ga ternary phase diagram was earlier established by thermodynamic modellization [1], but no experimental study appears to have been carried out on this system, except for measurements of mixing enthalpies in the liquid [2]. The present experimental study was carried out by thermal analysis and X-ray diffraction at various temperatures, using the isopletic cuts method. Four isopletic cuts were established and two others were partly studied in the Al-rich corner of the diagram. On these cuts, two isobaric ternary invariant reactions were determined: a eutectic reaction at 231C, and a metatectic reaction at 1231C. Evidence was found for the existence of a retrograde miscibility of Ga in a solid solution α′SS which protrudes into the ternary system starting from the Al-Zn binary up to a Ga concentration of about 30%*.

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Abstract  

The first part of this paper presented five experimental isopletic cuts in the Al-Zn-Ga ternary phase diagram. On these cuts, two isobaric ternary invariant reactions were determined and a significant retrograde miscibility of Ga in a α′SS solid solution was observed. In the second part, the two isobaric invariant reactions are studied more precisely. In particular, the composition of the invariant phases are given and the Ga miscibility in the αSS ternary solid solution is studied. Isothermal sections are established. The results confirm the existence of a vanishing point in the liquidus area, conjugated with a ternary critical point at about 290C. A general perspective shape of the equilibria in the diagram is proposed.

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