The role of Zn precipitates and Cl− anions in pitting corrosion of Sn–Zn solder alloys

•We investigate the pitting behavior of Sn–Zn alloys in NaCl solution.•Applicable equivalent circuits are employed to analyze the development of pitting.•Coarsening Zn precipitates leads to increasing in pitting susceptibility.•Pitting development is strongly related to Cl− anions.•A pitting mechanism is proposed to elaborate the pitting process.

Electrochemical corrosion behavior of Sn–Zn solder alloys in aerated and quiescent 0.5 M NaCl solution was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques, aiming to assess the role of Zn precipitates and Cl− anions in pitting corrosion. The results reveal that increasing in Zn contents leads to increasing in pitting susceptibility, ascribed to the coarsening Zn precipitates with larger intergranular boundaries between Zn-rich precipitates and Sn matrix. The EIS results provide a quantitative description of the electrochemical interface behavior. The mechanism of pitting and the role of Cl− anions are discussed.