Effect of intermetallics on the corrosion of Al 2024-T3 alloy in solutions with different chloride concentration

Abstract

Al 2024-T3 is an important alloy very prone to localized corrosion. In this investigation the effect of chloride concentration on the corrosion resistance of the Al 2024-T3 alloy has been studied, focusing on the dissolution of the intermetallics (IMCs). Sodium chloride solutions of two concentrations, 0.6 M and 0.01mM, were used as test electrolytes. During the investigation selected regions of polished samples had their IMCs analyzed by Scanning Electron Microscopy (SEM) and X-ray Energy Analysis (EDX) prior and after different immersion times in the two test electrolytes. The results showed that even in the lowest chloride concentration the electrolyte was highly corrosive to the Al-Cu-Mg IMCs leading to their partial dissolution and to the attack of the surrounding matrix after only one hour of immersion. On the other hand, the corrosion behavior of the Al-Cu-Mn-Fe IMCs was random, and no correlation could be established between corrosive attack and chloride concentration or time of immersion for this type of particle. Atomic Force Microscopy (AFM) analyses have indicated a stronger dissolution of the matrix in the more concentrated electrolyte. This seems to lead to a milder attack of the IMCs in this solution when compared to the less concentrated one, as indicated in the SEM images.