Growth Behaviors of Layered Double Hydroxide on Microarc Oxidation Film and Anti-Corrosion Performances of the Composite Film

Microarc oxidation (MAO) film has been widely used as an anti-corrosive film for Al alloys. However, it is still a big challenge to further improve its anti-corrosion performance due to the defects that form during the MAO process. In this study, for the first time, Ni-Al layered double hydroxide (LDH) was in-situ synthesized on the MAO film to seal its defects, which contributes to the corrosion resistance enhancement of MAO treated 6061 Al alloy. The growth of the LDH on MAO film is largely determined by the specific area, chemical composition, and crystalline structures of the alumina phase of the MAO film. More importantly, LDH nanoplates can grow into the micropores and microcracks in MAO film, and then gradually seal these structural defects. The anti-corrosion performance of MAO film during long-term immersion in NaCl solution also can be improved greatly via LDH treating because the defect-sealing effects of LDH can enhance the barrier property of both the porous and dense layers of MAO film, and then restrain the penetration of corrosive agents through the MAO film to the metal substrate.