In this study, oxide coatings with layered double hydroxide (LDH) nanosheets were prepared on AZ91 magnesium alloy by a one-step low-voltage microarc oxidation (MAO) process. The microstructure and composition of the coatings were characterized using SEM, EDS, XRD, FT-IR, and XPS. The corrosion protection performance of the coatings was evaluated by electrochemical analysis and hydrogen evolution tests. The results showed that oxide coatings with Mg-Al-LDH nanosheets are successfully produced by microarc oxidation at a voltage of less than 100 V. The coating with a higher density of Mg-Al LDH nanosheets exhibited enhanced corrosion resistance. Moreover, after modification with stearic acid, the coatings displayed high hydrophobicity and corrosion resistance.

Despite considerable advances in artificial bone tissues, the absence of neural network reconstruction in their design often leads to delayed or ineffective bone healing. Hence, we propose a multilayer hierarchical lithium (Li)-doped titanium dioxide structure, constructed through microarc oxidation combined with alkaline heat treatment. This structure can induce the sustained release of Li ions, mimicking the environment of neurogenic osteogenesis characterized by high brain-derived neurotrophic factor (BDNF) expression. During in vitro experiments, the structure enhanced the differentiation of Schwann cells (SCs) and the growth of human umbilical vein endothelial cells (HUVECs) and mouse embryo osteoblast progenitor cells (MC3T3-E1). Additionally, in a coculture system, the SC-conditioned media markedly increased alkaline phosphatase expression and the formation of calcium nodules, demonstrating the excellent potential of the material for nerve-induced bone regeneration. In an in vivo experiment based on a rat distal femoral lesion model, the structure substantially enhanced bone healing by increasing the density of the neural network in the tissue around the implant. In conclusion, this study elucidates the neuromodulatory pathways involved in bone regeneration, providing a promising method for addressing bone deformities.

Black oxide coatings on 6061 Al alloy were produced by plasma electrolytic oxidation (PEO) process in silicate- and phosphate-rich base electrolytes with addition of ammonium metavanadate (NH4VO3), respectively. The characteristics of PEO processes and resulting coatings were investigated. The thermal control properties of the coatings were measured. The corrosion protection performances of the coatings in an acidic environment were evaluated. Results show that the base electrolytes have significant influence on the PEO discharge behavior, coating characteristics and properties. There are more intensive discharges in silicate-rich electrolyte with addition of NH4VO3 (denoted as “Si–V″) than that in phosphate-rich electrolyte with addition of NH4VO3 (denoted as “P–V”), leading to higher thickness and more defects for the Si–V coating. Both Si–V and P–V coatings are characterized by black color in appearance due to the formation of V-containing compounds. However, the P–V coating has higher contents of V-containing compounds and therefore lower lightness and higher solar absorptance (αs) than the Si–V coating. In addition, the P–V coating exhibits better corrosion protection performance and color durability compared with the Si–V coating in acidic NaCl solution (pH = 3.1⁓3.3) due to the formation of AlPO4 in the coating. It is demonstrated that phosphate-rich base electrolyte with addition of NH4VO3 is a good candidate for getting stable black therm control coatings on Al alloy for practical applications in harsh environment.

In this work, a bright white oxide coating was successfully prepared on 6061 Al alloy by PEO process from an environmentally friendly and low-cost concentrated silicate electrolyte as an alternative for commonly used fluozirconate electrolyte. The characteristics of PEO processes and resulting coatings both in diluted and concentrated silicate electrolytes were investigated by using Optical Emission Spectrometer (OES), Scanning Electron Microscope (SEM), X-ray Energy Dispersive Spectrometer (EDS) and X-ray Diffraction Spectrometer (XRD). The thermal control properties of the coatings were evaluated by UV-VIS-NIR spectrophotometer and infrared emissivity spectrometer, respectively. The corrosion protection performances of the coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. Results show that the discharges in diluted silicate electrolyte are more pronounced than those in concentrated silicate electrolyte. The more intensive discharges in diluted silicate electrolyte are related to plasma electrochemical reactions at the material surface or at the metal-oxide interface, facilitating to a relatively dense structure and complex oxides including α-Al2O3, γ-Al2O3 and mullite. The weaker discharges in concentrated silicate are associated with the fast silicate anions deposition process, resulting in the formation of amorphous SiO2 with a porous microstructure and high thickness. The coating prepared in concentrated silicate electrolyte is characterized by a bright white color in appearance and has much lower solar absorptance (αs) of 0.159 and higher emissivity (ε) of 0.90 than the coating prepared in diluted silicate electrolyte with αs of 0.429 and ε of 0.79. However, the coating prepared in concentrated silicate electrolyte has a little inferior corrosion protection performance compared with that prepared in diluted silicate electrolyte due to the more porous microstructure.

In this study, the pure Al and binary Al–Ni alloys with Ni addition of 1, 3, 6, and 10 wt % were coated via micro arc oxidation (MAO) in a tetraborate and phosphate based electrolyte for 60 min. With increased Ni content, the color of MAO coating became darker due to increased Ni-containing compounds on the surface. The Ni played a negative effect on the coating growth, decreasing both the coating thickness and surface roughness. The coatings on the Al–Ni alloys were mainly composed of γ-Al2O3 and α-Al2O3, and the Ni facilitated the formation of α-Al2O3 in the coating. Nanoparticles of NiO were generated around the edge of discharge channels for Al–6Ni and Al–10Ni alloys after a certain oxidation time. All coatings exhibited a uniform and dense surface structure, with the outer layer being more compact than the inner layer. Many tiny pores were found in the inner layer. Despite the corrosion resistance was decreased, the anti-wear performance of MAO treated samples was improved with the increased Ni content in the matrix. While, the corrosion resistance of the coated samples decreased with the adding of Ni content in the matrix.

For Mg alloy, it is important to develop effective protection coatings against galvanic corrosion. In this work, the effects of plasma electrolytic oxidation (PEO) coating with and without a polyurethane (PU) top layer on the corrosion and galvanic corrosion (coupled with mild steel) behavior of AZ31 Mg alloy are investigated. The microstructure and compositions of the coatings were studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FT-IR). The corrosion and galvanic corrosion behavior of uncoated, PEO and PEO-PU coated AZ31 Mg alloys were evaluated by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) tests, respectively. Results showed that the PEO coating is characterized by many micropores in structure and the micropores are sealed by the PU top layer. The OCP, EIS and SECM tests revealed that the single PEO coating only slightly reduces the galvanic corrosion tendency and marginally improved the corrosion resistance, resulting in short-term galvanic corrosion protection for AZ31 Mg alloy. In contrast to the single PEO coating, the PEO-PU coating greatly improves the stability of the AZ31 Mg alloy to galvanic corrosion and provides much better long-term corrosion protection performance, which could effectively protect the substrate from galvanic corrosion. The galvanic corrosion processes of the AZ31 Mg alloy with PEO and PEO-PU coatings are also discussed. These results demonstrate that the sealing of PEO coating is essential to inhibit the galvanic corrosion between Mg alloy and other metals.