Comparative Study of Techniques and Methods Used to Characterize Intergranular Corrosion in AA2024 Aluminum Alloy

Abstract

Three methodologies, i.e., optical microscope (OM) observations, analyses using tomography without synchrotron radiations, and mechanical tests, were used, and their relevancy compared to provide a quantitative description of the intergranular corrosion (IGC) damage. The study was performed on three plates of 2024 aluminum alloy, to take into account variations in the microstructure of the material, using two types of exposure conditions, i.e. continuous immersions and cyclic tests. The resolution of tomography was too low to allow an analysis at the scale of the elementary IGC defects. For thin plates with recrystallized grains, the corrosion damage corresponded mostly to intragranular corrosion, and OM observations were the most relevant technique to quantify correctly this damage. Thicker plates were mainly affected by IGC. Continuous immersion tests led to slightly branched IGC defects and low hydrogen uptake, and OM observations provided an accurate description of the IGC damage that corresponded mainly to a geometrical one. However, combining OM observations and mechanical tests was required for a full description of the IGC damage after cyclic tests that were associated with a strong branching of the IGC defects, i.e. geometrical damage, and significant hydrogen uptake, i.e., a non-negligible volume damage.