Study on localized corrosion mechanism of 2195 Al-Li alloy in 4.0% NaCl solution (pH 6.5) using a three-electrode coupling system

Localized corrosion morphologies of 2195 Al-Li alloy with various heat treatment in 4.0% NaCl solution (pH 6.5) were investigated, and its corrosion mechanism was studied using a three-electrode coupling system of alpha (Al) substituting for the precipitate-free zone (PFZ), simulated bulk theta' (Al2Cu) and T1 (Al2CuLi). theta' acts as cathodic zone in the alloy. At the initial stage, T1 phase is active with respect to theta' and a (Al), and endures the main anodic current, indicating that anodic dissolution occurs on T1. However, its potential moves to positive direction with immersion time, due to dealloying of Li from T1. As a result, the main anodic dissolution occurs on alpha (Al) at a later stage. At this stage, as only T1 and alpha (Al) are coupled, T1 is cathodic to alpha (Al). In real 2195 alloy, T1 phase is very tiny, and anodic dissolution of T1 and PFZ occurs alternately. These results show that its intergranular corrosion or intersubgranular corrosion is caused by alternate anodic dissolution of T1 phase and PFZ along grain and subgrain boundaries.