EIS study of a self-repairing microarc oxidation coating

The self-repairing microarc oxidation (MAO) coating consisting of a bottom nanocrystalline layer covered by a top conversion ceramic coating was fabricated on 2024 Al alloy by a duplex process with surface mechanical attrition (SMAT) prior to microarc MAO treatment. A 20 μm thick nanocrystalline layer with average grain size of 52.8 nm was fabricated by SMAT, and on which covered by a top MAO coating of 5 μm. The self-repairing property caused by the formation of a dense passive film at the damaged regions contacting the bottom nanocrystalline layer enhances the corrosion reisitance of the SMAT-MAO coating.

Research highlights
► A nanocrystalline layer with grain size of 52.8 nm was fabricated by SMAT.
► SMAT-MAO coating consists of top ceramic coating and bottom nanocrystalline layer.
► SMAT-MAO coating shows self-repairing property.
► The improved corrosion resistance is due to the formation of passive film.
► The equivalent circuits and physical models are given.