Corrosion Behavior of Field-Exposed 7A04 Aluminum Alloy in the Xisha Tropical Marine Atmosphere

Atmospheric corrosion behavior of 7A04 aluminum alloy exposed to a tropical marine environment for 4 years was investigated by weight loss test, morphology observation, and electrochemical impendence spectroscopy (EIS). The results showed that the weight loss of 7A04 alloy in the log-log coordinates can be approximately fitted with two liner segments, in which the slope value of the second segment is significantly lower than that of the first segment. This was mainly attributed to the protectiveness of the corrosion product layer formed on the specimen exposed for 12 and 24 months, which was further confirmed by the EIS results. Corrosion rate presented a significant fluctuation during the exposure test which is due to the deterioration effect caused by chloride ions and time of wetness and the stabilization process of the corrosion product layer. Intergranular corrosion occurred on the 7A04 alloy and then transformed into exfoliation corrosion because of the synergetic effect of the hydrogen-assisted crack initiation and the wedge effect-induced matrix delamination.