Phase equilibria of the Sn–Zn–Cu ternary system

Phase equilibria of the Sn–Zn–Cu ternary system are of fundamental importance for the industrial applications of Sn–Zn-based solders. However, there is a lack of experimental information as regards the Sn–Zn–Cu phase equilibria. In this study, the isothermal sections of the Sn–Zn–Cu phase equilibria at 250, 230, and 210 °C were experimentally determined. In addition, the 180 °C isothermal section is proposed without experimental verification. Ternary Sn–Zn–Cu alloys were prepared and equilibrated at these three temperatures. The equilibrium phases in the annealed alloys were determined. No ternary compound was found, and no noticeable Sn solubilities were observed in the ε-CuZn5 phase. Isothermal sections at these three temperatures were constructed based on the ternary experimental results and the phase diagrams of the three constituent binary systems. In contrast to previous calculated results, it was observed that the molten Sn has tie-lines with the η-Cu6Sn5 phase and all the binary Cu–Zn compounds at 250 and 230 °C.