Electrochemical behavior of Zn-xSn high-temperature solder alloys in 0.5 M NaCl solution

Abstract

Electrochemical behavior of Zn-xSn (x = 40 wt%,30 wt%,20 wt%) high-temperature lead-free alloys was investigated in aerated 0.5 M NaCl solution by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. OCP results show that the corrosion state of the alloys working surface reached a relatively dynamic equilibrium after the alloys were immersed in 0.5 M NaCl solution for 100 h. EIS analysis reveals that the total corrosion resistance Rt of alloys depended on the amount of Sn, and Zn-40Sn possessed the highest value 2228.2 Ω cm2. No passivation behavior was observed during corrosion process by potentiodynamic polarization measurement. The dominant corrosion products were confirmed as Zn5(OH)8Cl2·H2O, ZnO and Zn(OH)2. Moreover, the surface and cross-section morphology of corrosion product suggested that the corrosion layer was more homogeneous and denser for higher Sn-content, Zn-40Sn obtained the best protective layer from corrosion product. The results recommend that Zn-xSn high-temperature solder alloy with higher Sn content appears to be more attractive in terms of superior corrosion properties. The exact corrosion process was also discussed in detail.