The influence of grain structure and intergranular corrosion rate on exfoliation and stress corrosion cracking of high strength Al-Cu-Mg alloys

This paper describes the effects of differences in grain structure on the exfoliation corrosion of 2014 T651 and 2024 T351 plate. Samples of each material were exfoliated using an acidified, intermittent salt fog (MASTMAASIS) test. The corrosion was assessed by rating the surface appearance and by measuring the depths of attack. Constant load stress corrosion tests were performed in EXCO solution. The severity of both types of corrosion was related to the grain aspect ratio of the material, with the most advanced attack occurring on the mid-section of the plate and ranked in the order T/2>T/4>Surface. Intergranular corrosion velocities were shown to be closely correlated with the grain aspect ratio. The grain structure had a similar effect in both exfoliation and SCC, providing further evidence for a link between the two forms of corrosion. The role of the wrought microstructure was to allow the strain caused by voluminous corrosion products to develop slowly to form blisters rather than pitting or flaking the surface. (C) 1999 Elsevier Science Ltd. All rights reserved.