Corrosion characterizations of Sn–9Zn–xS in acidic and alkaline solutions

The effects of S addition on the corrosion behaviors of Sn–9Zn solder alloy in the acidic and alkaline solutions were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) techniques, and weight loss test. The results show that 0.02–0.08 wt% S can enhance the corrosion resistance of Sn–9Zn solder alloy in both solutions, evidenced by much lower corrosion current density, higher impedance modulus, lower corrosion rate, and less weight loss. When the content of S is around 0.08 wt%, the solder alloy exhibits the best corrosion resistance in both solutions. SEM and XRD results show that the corroded surface of the S-containing Sn–9Zn solder alloy is mainly covered with shorter grooves and a more uniform ZnSn(OH)6 layer than that of Sn–9Zn without S when being exposed to the alkaline solution, which is favorable to provide better protection for the underlying solder alloy and improve its corrosion resistance. After being immersed in the acidic solution, Sn–9Zn–0.08S solder alloy shows more obvious and uniform intergranular corrosion characteristics, with a few shorter grooves and cracks on the corrosion surface compared to that of Sn–9Zn. The corrosion products formed on the exposed surface of Sn–9Zn–xS solder alloy in acidic conditions are SnO2, SnO, and Zn5(OH)8Cl2·H2O. The corrosion characterizations of Sn–9Zn–xS in acid and alkaline solutions were fully discussed, and the possible mechanisms were proposed.