Experimental study and finite element analysis of degradation behavior of epoxy zinc-rich coating system under stress corrosion

This paper aims to study the effect of stress corrosion on the electrochemical behavior and corrosion mechanism of epoxy zinc-rich coating/steel substrate. The electrochemical impedance spectroscopy (EIS) was applied to characterize the corrosion behavior of the system under different stress conditions (& sigma;1 = 0MPa; & sigma;2 = 120MPa; & sigma;3 = 180MPa and & sigma;4 = 240 MPa), and appropriate equivalent circuits were established. Additionally, the von Mises stress distribution and potential distribution around the pitting pit at the coating-substrate interface were quantified by means of finite element analysis. The approach used different tensile strains and the depths of the pitting pit to relate the corrosion current density and corrosion rate to the corrosion process. The EIS results demonstrate that, given the same time, the failure time of the epoxy zinc-rich coating/steel substrate system with 240 MPa is shortened by 27.8% compared to the system without stress. Meanwhile, the finite element model confirms that the uneven potential distribution around the pitting pit is responsible for coating failure. In-depth profile of the corrosion rate shows an increasing trend over the distance from the opening. Then this local corrosion acceleration will cause further stress concentration, which in turn accelerates the corrosion process of the system.