The long-term corrosion performance and adhesion properties of 7B04 aluminum alloy/anodic film/epoxy primer system in acidic NaCl solution

The deterioration process and corrosion protective effect of 7B04 aluminum alloy/anodic film/epoxy primer system in acidic NaCl solution for 3024 h were investigated by optical/electron microscopes, electrochemical impedance spectroscopy (EIS), scanning Kelvin probe (SKP), and pull-off adhesion test. The results showed that the protective system of anodic film and epoxy primer can protect aluminum alloy from pitting corrosion after immersion for 2352 h. According to the response characteristics of EIS and SKP, different stages of the failure process could be identified. During the first 100 h of immersion, the water transport in the coating followed Fickian law, and the water diffusion coefficient was 2.03 x 10(-11) cm(2)/s, which demonstrated that the coating has good impermeability. Anodizing and coating treatment improved the open circuit potential and impedance of 7B04 aluminum alloy and made the distribution of Volta potential more uniform. The decreasing rate of wet adhesion strength was first fast and then slow, which was similar to the variation rule of coating resistance. The anodic film enhanced the adhesion between epoxy primer and substrate so that the failure nature of the adhesion test was mainly the cohesive failure of the epoxy primer.