SECM in situ investigation of corrosion and self-healing behavior of trivalent chromium conversion coating on the zinc

Abstract

The trivalent chromium conversion coating (CCC) is prepared on pure zinc, and the corrosion resistance of trivalent CCC is characterized by scanning electron microscopy (SEM), polarization curves and electrochemical impedance spectroscopy (EIS). The local corrosion and self-healing behavior of trivalent CCC at the initial stage of immersion corrosion are investigated in situ by scanning electrochemical microscopy (SECM). The results show that trivalent CCC has higher impedance value and lower corrosion current density as compared to pure zinc, and the coating has excellent corrosion protection for pure zinc. At the initial stage of corrosion (0−12h), the SECM feedback current of the trivalent CCC does not change significantly; after immersed for 24 h, the local current rises from 0.83 to 0.95, which can be explained that the trivalent CCC cracks locally and occurs local corrosion. In situ analysis of oxygen concentration at the scratch of trivalent CCC indicates that the addition of polyaniline can inhibit the oxygen reduction reaction, which hinders the corrosion process and improves the self-healing ability of trivalent CCC.