Experimental investigation and thermodynamic modeling of the Cu-Si-Zn system with the refined description for the Cu-Zn system

The isothermal section of the Cu-Si-Zn ternary system at 600 °C was experimentally determined with fifteen alloys by means of optical microscopy, X-ray diffraction, and the scanning electron microscopy with energy dispersive X-ray spectroscopy. At 600 °C, no ternary compounds were observed, and five three-phase equilibria were well determined. In particular, the longstanding controversy regarding the four three-phase equilibria in the Cu-rich corner involving the phases α, β, γ- Cu₅Zn₈, and κ- Cu₇Si was resolved experimentally in the present work. In an effort to provide a compatible thermodynamic description of the Cu-Si-Zn system for the multi-component Al-based thermodynamic database, the Cu-Zn system was remodeled using the CALPHAD approach with a new sublattice model Zn ₄(Cu,Zn)₁(Cu,Zn)₈ for the γ- Cu ₅Zn₈ phase. Besides, the temperature dependence of enthalpy of mixing was also taken into account for the liquid phase. Subsequently, a thermodynamic description of the Cu-Si-Zn system was obtained over the entire composition range based on the presently modeled Cu-Zn system and the experimental data from the literature and the present measurements. It is found that most reliable experimental data in this ternary system are satisfactorily reproduced by the present thermodynamic modeling.