Liquidus projection and thermodynamic modeling of Sn–Zn–Cu ternary system

The ternary Sn–Zn–Cu system is of interest for the electronic solder applications. Its liquidus projection was experimentally determined and the system was thermodynamically modeled in this study. Sn–Zn–Cu alloys of various compositions were prepared. Differential thermal analysis was employed to determine the reaction temperatures and solidification sequences. The solidified samples were metallographically examined and the primary solidification phases were determined. There is no ternary compound. The primary solidification phases are the terminal solid solutions and binary intermetallic compounds, and they are Sn, η-Cu6Sn5, ɛ-Cu3Sn, γ-(Cu–Sn), β, Cu, γ-Cu5Zn8, δ-CuZn3, ɛ-CuZn5 and Zn. Thermodynamic modeling was developed from the models of the constituent binary systems and the experimental results from this study and those in the literature. The calculated isothermal sections and liquidus projection are in agreement with the experimental determinations. Six class II and one class III invariant reactions are found in the Sn–Zn–Cu system.