Thermodynamic assessment of the Sn–Ag–Co system and solidification simulation of the ternary alloy

Sn–Ag solder alloy with minor addition of Co exhibit refined microstructure and improved shear strength. To understand the beneficial effects of Co, the constituent phase of selected Sn-rich Sn–Ag–Co ternary alloys and microstructures are investigated in both as-cast and long-term annealed states using SEM with EPMA. The results show that ternary solubility in the Co–Sn or Ag–Sn compound is negligible and no ternary phase observed. Furthermore, a thermodynamic assessment of the Sn–Ag–Co system is carried out based on those of the constituent binaries and experimental ternary data obtained in the present study as well as those reported in literatures. Solidification path of three typical alloys was simulated through the so-called Scheil–Gulliver model, which can well explain the microstructures.