Novel neutral electrolytes were designed to substantially decrease porosity and increase barrier property of plasma electrolytic oxidation (PEO) coating on AM50 Mg surface. Presence of additives was effective in tuning coating microstructure and composition, leading to significantly enhanced corrosion and wear properties. 50% improvement in fatigue limit was detected for the optimized coating compared to conventional PEO coating. The low-porosity coating remained uncorroded after performing salt spray test for 1 month, and exposure 1 year in harsh South China Sea environment. This can be new strategy to evaluate coating lifespan and promote wide range of applications for Mg alloy.

A gradient coating containing collagen and inorganic strontium/calcium phosphate (Sr/CaP) was fabricated on plasma-electrolytically oxidised magnesium via one-step cathodic electrodeposition. First, Sr-doped dicalcium phosphate dihydrate and hydroxyapatite (DCPD and HA) was deposited, followed by a collagen/CaP layer. The morphological evolution, sequential degradation behaviour, and in vitro bio-properties of the coatings were investigated. The incorporation of collagen remarkably refined the morphology of the CaP, and a more aggregated nano-spherical morphology was observed with increasing collagen concentration. Sr could partially replace Ca in the CaP crystals. Collagen combined with CaP formed a relatively stable skeletal frame, which provided sufficient barrier properties and more sites for the re-precipitation of bone tissue, as well as a more promising proliferation and differentiation ability of osteoblasts. A gradient coating that matches the requirements of bone growth at various periods is suggested for implantation.

The influence of sodium dodecyl sulfate (SDS) on morphology and chemical composition of corrosion product layer formed on α-Mg matrix and cathodic Al-Mn intermetallic was systematically investigated by using FIB and TEM analysis for the first time to disclose the underlying inhibition mechanism. A porous corrosion bi-layer composed of crystalline MgO and Mg(OH)₂ was observed on both of α-Mg and Al-Mn intermetallic. It was found that a passive inner layer was deposited on α-Mg after immersion in SDS-containing NaCl solution, which can be ascribed to steady-state growth of magnesium and aluminum oxide under the protection of hydrophobic group of SDS. The inhibition mechanism of the inhibitor was mainly associated with formation of dense oxide layer on α-Mg matrix and preferential adsorption of SDS on the corrosion layer deposited on Al-Mn intermetallic.

In-situ incorporation of layered double hydroxides (LDH) nanocontainers into plasma electrolytic oxidation (PEO) coatings on AZ91 Mg alloy has been achieved in the present study. Fumarate was selected as Mg corrosion inhibitor for exchange and intercalation into the nanocontainers, which were subsequently incorporated into the coating. It was found that the thickness and compactness of the coatings were increased in the presence of LDH nanocontainers. The corrosion protection performance of the blank PEO, LDH containing PEO and inhibitor loaded coatings was evaluated by means of polarization test and electrochemical impedance spectroscopy (EIS). The degradation process and corrosion resistance of PEO coating were found to be greatly affected by the loaded inhibitor and nanocontainers by means of ion-exchange when corrosion occurs, leading to enhanced and stable corrosion resistance of the substrate.