Exfoliation Corrosion of Extruded AA2024-T4 in the Industrial and Coastal-Industrial Environments

Exfoliation of extruded AA2024-T4 (UNS A92024) in the industrial and coastal-industrial environments was investigated by the field test and laboratory-accelerated test. Results show that the exfoliation corrosion was influenced by the alloy structure and the type of the atmospheric environment, especially the concentration of SO42- in the environment. In the field test, AA2024-T4 suffered slighter exfoliation in both environments than that in the coastal environments. The side wall with a thinner coarse-grain structure of extruded AA2024-T4 suffered more severe exfoliation than the bottom with a thicker coarse-grain structure after a 20-year exposure. Energy-dispersive spectroscopy (EDS) results show that the corrosion products of extruded AA2024-T4 exposed in both environments contained a small amount of S in addition to a large amount of Al and O. In the laboratory-accelerated test, both the critical relative humidity (RH) and induction period for exfoliation in the simulated coastal-industrial environments were higher and longer than those in the sodium sulfate (Na2SO4)-free simulated coastal environment. Exfoliation was hindered due to the existence of SO42- in Cl -containing environments.