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.