Corrosion Fatigue Behavior of 7A85 Aluminum Alloy Thick Plate in NaCl Solution

The S-N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not noticeable at high-cyclic-stress regions, but the effect was significant at low-stress region. Corrosion fatigue mechanism was discussed by corrosion morphology analysis, fracture surface analysis and microstructure characterization. It was found that the corrosion fatigue crack commonly initialed at the localized intergranular corrosion site. TEM analysis showed that the microstructures of 7A85-T7452 aluminum alloy were characterized by fine and homogeneously distributed matrix precipitates, as well as continually distributed anodic grain boundary precipitates. The types of microstructures are the reason for its intergranular corrosion susceptibility. The corrosion fatigue process of 7A85 aluminum alloy in 3.5 wt% NaCl solution can be divided into four stages: the crack initiation stage, the stable growth stage with low and high growth rate and the final rupture stage. The sodium chloride solution mainly affected the crack initiation stage and the stable growth stage with low growth rate, and when the crack growth rate reached a threshold, the effect was reduced.