Study on Failure Mechanism of Epoxy Aluminum Coating Immersed in 3.5% NaCl
YAN Rui1, WU Hang2 (1. Institute of Surface Engineering, Armored force Engineering Academy, Beijing 100072; 2. Department of Scientific Research, Armored force Engineering Academy, Beijing 100072)
Electrochemical corrosion behavior of epoxy aluminum coating immersed in 3.5 %NaCl solution was investigated using electrochemical impedance spectroscopy(EIS). SEM and EDX were also used to analyze the surface and cross section images of coating, and the failure mechanism of coating was discussed as well. The experimental results showed that corrosive species can penetrate into coatings and reach the coating/substrate interface promptly, causing the decrease of electro-resistance and the beginning of electrochemical corrosion at the coatings/metal interface. The coating was compact and continuous, while the blisters and cavities occured after corrosion. Blisters were formed by volume expansion of corrosion products, which are mainly oxides and chlorides of Fe and Al, and osmotic pressure created by corrosion species penetration.