Electrochemical Behavior and Interfacial Delamination of a Polymer-Coated Galvanized Steel System in Acid Media.

The degradation behavior of polymer coatings is essential for their protective performance under various corrosive environments. Herein, electrochemical impedance spectroscopy (EIS) is employed to study the corrosion behavior and interfacial delamination of a polymer-coated metal system exposed to 0.1, 0.5, and 1 mol/L H2SO4 solutions at 50 °C. The electrochemical impedance spectra are analyzed using different equivalent circuits to derive the time dependence of the parameters of the coating, delaminated area, and interfacial processes. The phase angle at 10 Hz (θ10 Hz) is not appropriate in the case of higher delamination area ratio α, while θ10 kHz provides a rapid approach to evaluate the degradation of polymer-coated metal systems. The frequency of the phase angle at -45° (f-45°) leads to a wrong evaluation for higher α and can be no longer viewed as the breakpoint frequency. The frequency fp obtained by the changing rate of phase angle (CRPA) method is proposed to monitor the coating degradation and determine the breakpoint frequency with the consideration of dispersive number n. The frequency fEIS derived from fitting EIS spectra shows a good agreement with fp, which can contribute to clarify the evolution in the process of degradation.