Sealing of micro-arc oxidation coating on magnesium alloy by embedding nanoparticles and depositing sub-micrometer sulfur-selenium film toward superior corrosion protection

Conventional micro-arc oxidation (MAO) coating on lightweight alloy displays innumerable micron-sized through-holes, severely restricting its corrosion protection in many industrial applications. To address this problem, we demonstrated a new strategy by creating a highly corrosion-resistant composite coating on magnesium alloy. The composite coating comprises a micrometer-scale MAO primer and a sub-micrometer-sized sulfur-selenium (S-Se) alloy top layer. The underlying MAO layer is incorporated with metal–organic framework (MOF) nanoparticles, including inhibitor-loaded zeolitic imidazolate framework-8 (ZIF-8) nano-containers. The thin S-Se film was fabricated by dip coating in a dimethylsiloxane-containing melt. The composite coating (S-Se/MOFs/MAO) with a thin thickness showed a tremendously increased charge transfer resistance and an ultralow corrosion current density down to 0.273 nA cm⁻², demonstrating remarkably superior corrosion protection in comparison with the unmodified and other MAO-based coatings reported to date. The origin of this unprecedented corrosion protection was mainly attributed to a combination of the inhibition by the released inhibitor and the structural integration resulting from the nanoparticle incorporation. Notably, the effective pore sealing via the strongly adhesive S-Se alloy thin film to the MgO layer through chemical bonding played an essential role in enhanced corrosion protection, supported by density functional theory calculation.