Long-term atmospheric corrosion of aluminum alloy 2024-T4 in coastal environment: Surface and sectional corrosion behavior

The surface and sectional corrosion behavior of anodized 2024-T4 exposed for 7 and 20 years was investigated. After 7 years of exposure, mild exfoliation corrosion had partially occurred. Pitting and intergranular corrosion (IGC) coexisted in the unexfoliation corrosion area. Due to the continuous formation of corrosion products beneath the surface and their difficulty in being transported through the IGC channel, surface blisters were eventually formed. After 20 years, severe exfoliation corrosion had occurred on the entire surface and cracked corrosion products were partly covered by filamentous corrosion products Al(OH)₃. The formation of filamentous corrosion products is the interaction between the ventilated environment, the long-term weathering, and the agglomeration of the Al(OH)₃ particles. Interestingly, most of the continuously corroded grain boundaries with severe IGC on the longitudinal section were parallel to the extrusion direction. The grain orientation, high precipitates continuity at grain boundaries and weak restraint of material itself to the expansion of IGC products are the reasons for this phenomenon by EBSD, SEM, TEM and mechanical analyses.