In-Situ Preparation of MgCr-LDH Nano-Layer on MAO Coating of Mg Alloy and Its Anti-Corrosion Mechanism

A highly corrosion-resistant and active-protection composite coating was prepared using layered double hydroxides (LDH) layer and micro-arc oxidation (MAO) to further improve the anti-corrosion property of Mg alloy. MgCr-LDH/MAO composite coating was prepared through in-situ growing LDH layer including NO3- on the surface of MAO coating. The morphology, composition and microstructure of the MgCr-LDH/MAO composite coating were characterized by XRD, XPS, FT-IR, SEM, and the interaction between LDH and original MAO coating was investigated. The anti-corrosion properties of the MgCr-LDH/MAO coating were tested through immersion in 3.5% NaCl (mass fraction) solution and electrochemical experiments. The results show that the LDHs form a dense sheet-like layer on the original MAO coating surface, which can effectively cover the inherent defects of MAO coating, and LDH layer is preferentially formed in the pores of original MAO coating. LDHs do not damage the original MAO coating during the growth process, and the adhesion of LDH layer and MAO layer are strong and stable. The composite coating shows the optimum corrosion protection, since MgCr-LDH layer growing on the original MAO coating can hinder the penetration of chloride ions and effectively adsorb a large number of NO3- to exchange Cr in corrosion solution.