Effect of polarizations on Sn–Zn solders alloys in alkaline electrolyte

•Sn–9Zn solder was polarized at different scanning rates in 6M KOH.•Dissolution of Zn was found to dominate the initial corrosion reactions of Sn–9Zn.•Lamellar-like grooves were formed resulted from the preferential dissolution of Zn.•Presence of grooves act as weak spots that reduce the ultimate tensile strength. The corrosion properties of Sn–9Zn lead-free solder was studied through potentiodynamic polarization in 6M potassium hydroxide at different scanning rates. The corrosion rates of Sn–9Zn solder remained nearly constant at 2.1×10−4Acm−2 from scan rates of 2.0mVs−1 to 3.5mVs−1 before significantly increasing as the rates increased to higher than 3.5mVs−1. The morphological analysis showed that two distinctive structures of a lamellar-like groove and irregularly shaped corrosion product compounds co-existed on the solder surface after being polarized at different rates. In addition, phase and elemental analyses revealed the formation of mixed corrosion products of SnO, SnO2, and ZnO on the surface after polarization. Moreover, the ultimate tensile stress endured by the solder joint decreased by 26% after polarization.