To enhance the corrosion resistance of Mg-Li alloy, a composite coating system integrating plasma electrolytic oxidation (PEO) with solgel sealing treatment is developed. Two functionalized sepiolite microcontainers (sepiolite-Ce and sepiolite-BA) are constructed by loading cerium ions (Ce³⁺) via ion exchange and encapsulating barbituric acid (BA) through low-pressure impregnation. The microcontainers are subsequently incorporated into the coating surface through controlled sol-gel deposition process. UV-Vis and ICP-OES analyses reveal that both functionalized sepiolite microcontainers exhibited pH-responsive release characteristics under alkaline conditions. Electrochemical impedance spectroscopy (EIS) tests demonstrate that the inhibitor-containing composite coating has excellent long-term corrosion resistance and self-healing performance. After 240 h of immersion in a 0.5 wt.% NaCl solution, the low-frequency impedance modulus of the composite coating is four orders of magnitude higher than that of the pristine coating.

The advent of three-dimensional (3D) printed porous Mg alloys is considered a significant milestone in the development of metal-based degradable implants. However, the poor corrosion resistance of additively manufactured Mg alloys, along with the occurrences of inflammation and bacterial infections following implantation, pose critical challenges. In this study, two drug-loaded coatings were prepared within a porous Mg alloy using in situ incorporation and post-deposition of layered double hydroxides (LDHs) to enhance corrosion resistance, antibacterial properties, and biological compatibility combined with plasma electrolytic oxidation (PEO). The results revealed that in situ incorporation of LDH capsules effectively reduced the porosity of the PEO layer and improved the long-term corrosion resistance of the coating. The post-deposited LDH layer effectively sealed the PEO layer, demonstrating highly stable corrosion resistance during 7 d electrochemical impedance spectroscopy (EIS) test, with the impedance modulus at 10^–2 Hz stabilizing at 5 × 10⁵ Ω·cm². After soaking, the surface morphology of the in situ drug-loaded PEO coating exhibited more cracks and defects, whereas the PEO-LDH coating maintained a relatively dense morphology. Among the tested samples, the PEO-LDH coating showed the best performance in terms of corrosion resistance, cell proliferation and differentiation capabilities, and antibacterial efficacy (>99%). Its strong compatibility with the porous structure of 3D-printed Mg alloy highlights the potential of this coating system for biomedical applications. The design strategy proposed in this study offers valuable insights for future development of drug-loaded coatings for 3D-printed porous materials.

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.

In-situ growth of layered double hydroxide (LDH) has been considered a feasible method to further improve the corrosion protection of PEO coated Mg alloys, but the process is basically carried out in an autoclave. In this study, LDH was in-situ synthesized on PEO treated AM50 Mg by hydrothermal treatment at ambient pressure in the presence of chelating agents. Results indicated that the synergistic effect of sulfosalicylic acid (SSA) and ethylenediaminetetraacetic acid tetrasodium salt (EDTA) chelating agents is appropriate for Mg-Al LDH formation due to the sufficient quantity of highly stable Mg and Al complexes in the treatment bath. An appropriate hydrothermal treatment time was also revealed in this work, which can efficiently seal the pores and defects of PEO coating with a uniform LDH film. As a result, the corrosion protection of the coating was improved dramatically. The prolonged hydrothermal treatment is detrimental to the integrity of PEO layers. The influence of chelating agents on the LDH formation processes is supported by thermodynamic calculation of the equilibrium composition, and the formation mechanism of LDH film is discussed in depth.

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.