LOCALIZED CORROSION BEHAVIOR OF ALLOY-2090 - THE ROLE OF MICROSTRUCTURAL HETEROGENEITY

The pitting and intergranular corrosion behavior of alloy AA 2090 (Al-2Li-3Cu UNS A92090) in a 3.5 wt% NaCl solution was investigated. Two different types of pitting mechanisms were identified. The first type attributed to dissolution of the subgrain boundary phase T1. A direct correlation between increased subgrain boundary precipitation and increased subgrain boundary pitting was observed. The second type of pitting involved enhance local galvanic attack of the matrix material surrounding Al-Cu-Fe constituent particles. With this type of attack, large pits formed around constituents which occurred randomly throughout the plate. Associated with constituent particle pitting was a form of localized attack designated as continuous subgrain boundary dissolution. This form of corrosion was observed on all specimens used. It was only seen, however, ever, in regions adjacent to the largest pits on the specimen, suggesting the influence of an occluded (crevice) environment. Simulated crevice experiments revealed that an acidic crevice solution developed with time. This environment is suspected to contribute to the continuous subgrain boundary dissolution in the vicinity of the constituent particles.