EIS and LEIS investigation of aging low carbon steel with Zn-Ni coating

Electrochemical Impedance Spectroscopic technique (EIS) and Local Electrochemical Impedance Spectroscopic technique (LEIS) have been used to investigate the corrosion behavior of zinc-nickel + chromate conversion coating on carbon steel. The measurements were conducted in chloride media, 0.6 M and 10 mM NaCl solutions with coating with and without artificial defect. An electrical equivalent circuit was proposed to analyze the EIS spectra in 0.6 M NaCl solution. LEIS was also performed in the vicinity of a scratch exposing the carbon steel to the corrosive solution. It was shown that the local impedance measurement was very useful to characterize in situ the electrochemical reactivity around a defect.