Thermodynamic assessment of the Au–Zn binary system

The phase diagram of the Au–Zn binary system may play an important role in developing new Au-base solders. In this paper, the Au–Zn binary system has been thermodynamically assessed with the CALPHAD method. Excess Gibbs energies of solution phases, liquid, fcc, hcp, and ϵ were formulated with the Redlich–Kister expression, while the intermediate phases were modeled with (Au,Zn)0.5:(Au,Zn)0.5 for β′, (Au)0.6:(Au,Zn)0.2:(Zn)0.2 for α1, (Au)0.64286:(Au,Zn)0.25:(Zn)0.10714 for α3, (Au,Zn)0.15385:(Au)0.15385: (Au,Zn)0.23077:(Zn)0.46153 for γ, and (Au)0.12:(Au,Zn)0.16:(Zn)0.72 for γ3, and the other phases including α2, ϵ′, Au5Zn3, γ2 and δ were treated as stoichiometric compounds according to their composition ranges. Based on the reported thermodynamic properties and phase boundary data, the thermodynamic parameters of these phases were optimized, which give a reasonable agreement between thermodynamic properties and phase diagram.