Electrochemical Study on Corrosion Damage of 7B04 Aluminum Alloy/Anodic Film/Epoxy Coating System in a Simulated Marine Atmospheric Environment

This paper investigates the electrochemical characteristics of the 7B04 aluminum alloy/anodic film/epoxy coating system in a simulated marine atmosphere using electrochemical techniques and surface morphology measurements. The coating system underwent a periodic immersion test for 480 h to simulate the harsh service conditions in a marine environment. Three equivalent circuit models were proposed based on the analysis of the electrochemical failure mechanism of the coating system. Akaike information criterion and Bayesian information criterion were used to selectively choose models for different degradation stages of the coating system, revealing its electrochemical degradation characteristics. Two-stage aging kinetics and gamma models were proposed to describe the time-varying processes of electrochemical low-frequency impedance and corrosion trend, respectively. Ultimately, low-frequency impedance is identified as the most effective and rapid evaluation index for coating performance due to its strong correlation with corrosion trends. The aforementioned models and index provide a foundation for accurately identifying corrosion stages and effectively predicting the corrosion process.