Acoustic emission analysis of the corrosion progress on coated aluminum alloy AA2024-T3 during exco tests

Localized corrosion is one of the most dangerous damages that can occur on metals, affecting the structure/component integrity. The early detection of such corrosion type is challenging for field applications, especially if a coted metal is used (e.g. coated aluminum alloys used in the aeronautical industry). In the present study the use of the Acoustic Emission technique (AE) is proposed to monitor the evolution of the localized corrosion, from the initial pitting that evolves to intergranular corrosion (IGC) prior to the material exfoliation (EFC). Coated (anaphoretic ecoating) aluminum alloy 2024-T3 coupons were exposed to the EXCO solution (ASTM G34) for different time spans, and characterized by optical microscopy to evaluate the degradation. The most relevant parameters that characterize the AE signals were identified, allowing to classify practically all intervals of activity (≈80-90%) into 4 well-differentiated classes. The time distribution of such classes is in good agreement with the different stages (mechanisms) of the corrosion process as identified by the microstructural characterization. The AE data analysis has revealed the promising potential of this technique to distinguish between the different steps of the corrosion process, and pave the way to the detection of localized corrosion on coated aluminum alloys.