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).