Solidification behavior of Sn–9Zn–xAg lead-free solder alloys

Solidification behaviors of Sn–9Zn–xAg lead-free solder alloys, which vary with Ag content, are examined by using scanning electron microscopy, electron probe microanalysis, X-ray analysis, computer aided-cooling curve analysis and differential scanning calorimetry. The backscattered images and X-ray diffraction patterns indicate that with the addition of two silver intermetallic compounds; γ-Ag5Zn8 and ɛ-AgZn3, form in the expense of zinc phase. The solid fraction versus temperature relationship and microstructure analysis show that Sn–Zn eutectic structures appear following the formation of primary tin. It is concluded in this study that the complicated solidification process of Sn–9Zn–xAg alloys can be described as L (liquid) → L + γ-Ag5Zn8 → L + γ-Ag5Zn8 + ɛ-AgZn3 → L + γ-Ag5Zn8 + ɛ-AgZn3 + β-Sn → γ-Ag5Zn8 + ɛ-AgZn3 + β-Sn + eutectic (Sn + Zn).