Thermodynamic modelling of the Cu-Mg-Zn ternary system.

The quasibinary MgCu2-MgZn2 system was optimized with the program BINGSS. All phase diagram data and thermodynamic values available in the literature were critically assessed before the optimization. Experimental investigations by EDX of ternary Cu-Mg-Zn alloys were specifically performed to provide missing data of the Cu solubilities of the Mg-Zn phases. The Laves-phases C15 (MgCu2), C14 (MgZn2) and C36 (tau,Mg2CuZn3) existing in the Cu-Mg, Mg-Zn and Cu-Mg-Zn systems were described by the "Compound-Energy-Formalism" with Cu-Zn exchange, Mg(Cu1-xZnx) and a weak tendency for antistructure atom formation (Cu and Zn on the Mg sublattices, Mg on the Cu-Zn sublattices). The binary intermetallic phases MgZn, Mg2Zn3 and Mg2Zn11 are modelled to have Cu-Zn exchange on one sublattice. The Bragg-Williams description of ordering was extended to describe the ternary range of the beta CuZn phase. Estimates were made, where experimental data are not sufficient. Using the binary subsystems from the literature with small updates the Cu-Mg-Zn ternary system was calculated. In general, good agreement is obtained between calculations and experiments.