Electrochemical behavior of deeply corroded 2024 aluminum alloy: insights from electrochemical and microscopy analyses

Metallic aircraft were extensively developed using Al-Cu (2XXX) aluminum alloys. Many of these aircraft are now displayed in aviation museums, and the deep corrosion layers that have grown over the years pose a challenge for museum curators dealing with atmospheric corrosion. The objective is to study the electrochemical behavior of synthetic deeply corroded layers formed on a 2024-T3 alloy. The corroded structures were produced by anodic polarization in NaCl solution and characterized by stationary and non-stationary electrochemical techniques at Open-Circuit Potential, as well as Scanning Electron Microscopy/Scanning Transmission Electron Microscopy (SEM/STEM) analyses. Electrochemical Impedance Spectroscopy (EIS) revealed two main electrochemical interfaces: a passive area that shrinks and disappears with corrosion progress, and an active area that grows and becomes predominant. During the pitting process, the dealloying of copper-based intermetallics induces the formation of pure Cu nanoparticles within the pits, along with a 200 nm-thick CuOx-doped aluminum oxide layer. This composite material enhances cathodic activity, thereby promoting pitting growth. These findings highlight the specific behavior of deeply corroded Al-Cu alloys, providing insights into the conservation of aged Al-Cu alloys.