Abstract
The corrosion protection of electrodeposited cerium-based conversion coatings (CeCCs) on AA 2024-T3 with and without subsurface crevices was investigated. Coatings that were otherwise identical provided significant corrosion protection with or without crevices, as long as a post-treatment was employed after crevice formation. During salt spray exposure, impedance of crevice-free coatings increased from an initial value of ~50 kΩ-cm2 to ~60 kΩ-cm2 after 96 hours of exposure. In contrast, the impedance of coatings containing crevices doubled after 24 hours to ~100 kΩ-cm2. The impedance increase for crevice-containing coatings was associated with the build up of oxides / hydroxides in the crevices, which limited direct contact between the electrolyte solution and the substrate. Crevice-free coatings exhibited active corrosion protection even though no oxide build up was observed. For CeCCs with or without crevices, corrosion protection appeared to occur due to the formation of an interfacial layer between the coating and the substrate.
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