Stress Corrosion Cracking Behavior of Al Li 2090-T83 in Artificial Seawater

Stress corrosion (SC) behavior of the alloy 2090-T83 (UNS A92090) was evaluated in artificial seawater (ASW) under constant immersion. For comparison, some tests were performed in a 3.5 wt% NaCl solution, and, as a reference, the cracking behavior was also studied in N₂ gas. Smooth specimens machined from a 4-mm thick sheet were tested in the longitudinal and in the long transverse direction using the constant-load and the slow strain rate (SSR) techniques. Both methods suggested that the alloy was susceptible to stress corrosion cracking (SCC), ASW being a much more aggressive solution for SCC than the NaCl solution. The SCC mechanism was studied using the SSR method. The effects of strain rate, deaeration of the solution, or electrode potential were examined. During SSR testing, either the corrosion potential or the current at constant potential was monitored. The fractured specimens were examined in a scanning electron microscope (SEM) equipped with a backscatter electron detector and an energy dispersive x-ray analysis system to distinguish various local cracking and corrosion morphologies. SEM and a transmission electron microscope were used for characterizing the microstructure of the alloy. The experimental observations suggest that SCC of 2090-T83 in ASW is a result of local anodic dissolution along subgrain boundaries and is primarily induced by the preferential dissolution of T1 (Al₂CuLi) precipitates. Al₆(Fe,Cu) constituents played a minor role in the SCC process.