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This study investigated the impact of NaAlO2 concentration in electrolytic solutions on micro-arc oxidation (MAO) coatings, focusing on their surface quality enhancement and corrosion resistance improvement. The surface morphology and microstructure of these coatings were assessed using scanning electron microscopy. Mechanical properties, such as hardness and wear resistance of MAO coatings, were tested. The hardness of the 6 g/L group was 411.2 HV. X-ray photoelectron spectroscopy examinations showed that MgAl2O4, CaMgP2O7, and MgSiO4 were the phases in the MAO coating. Antibacterial assessments were performed to evaluate the influence of NaAlO2 concentration, and the antibacterial rate of the 6 g/L group reached 97.08%. The hydrophilicity of the coatings was determined using water contact angle measurements, wherein the water contact angle of the 6 g/L was the lowest, at 58.25°. Corrosion resistance was evaluated with an electrochemical workstation. The findings revealed that the MAO coatings prepared with a NaAlO2 concentration of 6 g/L exhibited superior uniformity with fewer defects, enhanced corrosion resistance, and increased adhesive strength compared to other concentration groups. The 6 g/L NaAlO2 concentration MAO coating demonstrated the highest fitting coating resistance R3 (8.14 × 104 Ω∙cm2), signifying better corrosion resistance. [ABSTRACT FROM AUTHOR]

Micro-arc oxidation (MAO) process was conducted on ZK60 Mg alloy under an optimized two-step voltage-increasing mode to investigate the effects of duty cycle and frequency on the evolution and characteristics of the coatings. Scanning electron microscopy, electrochemical impedance spectroscopy, and other methods are used to characterize the microstructure and corrosion behavior of the coating. Voltage–time curves under different duty cycles and frequencies show that duty cycle and frequency have a great influence on the microstructure and performances of the coatings under two-step voltage-increasing mode. A higher current peak combined with a wider basic peak width can provide enough driving force and longer duration, which contributes to producing a thick and compact coating with good corrosion resistance. When the duty cycle was 30%, it is favorable for developing a compact and smooth MAO coating which exhibits good corrosion resistance. Too high duty cycle would make the coating poor in corrosion resistance due to the loose coating resulting from the excessive energy. When the frequency is 600 Hz, the coating growth is greater in both stages, which leads to a dense and uniform coating and results in a high thickness of 22.4 μm. The MAO coating with the best corrosion resistance can be conducted when the duty cycle is 30% and the frequency is 600 Hz. [ABSTRACT FROM AUTHOR]

The ZK60 deformed magnesium alloy is treated by micro‐arc oxidation (MAO) and processed in the optimized silicate–phosphate electrolyte system, which is controlled under the two‐step current‐decreasing mode. The mechanism of discharge in the MAO process is investigated using the voltage–time curve and morphology of the spark discharge at different durations. The microstructures of the coatings fabricated at different durations are investigated. The rules of the coating ingrowth and/or outgrowth, the formation mechanisms of micropores, and microcracks in the coatings are explored systematically. The corrosion resistance of the coatings is measured by electrochemical methods. Through the exploration of the mechanism, two types of micropores in the coating are summarized: the in situ discharge growth type and the pores‐sealed type, and also three types of microcracks. The results illustrate the changes of the elements on the surface of the coating and Mg, O, and Si are incorporated into the coating formation process. The specimens show the best corrosion resistance after the two‐step current‐decreasing mode treatment. [ABSTRACT FROM AUTHOR]

In this work, zinc-aluminum layered double hydroxides (Zn–Al LDHs) were prepared on the surface of micro-arc oxidized ZK60 magnesium (Mg) alloy by a hydrotreatment in a Zn(NO 3) 2 solution. Scanning electron microscopy, X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), laser scanning confocal microscopy and Fourier-transform infrared spectroscopy (FT-IR) were applied to analyze the coating characteristics. Ion exchange experiments were performed on the optimized LDHscoatings with 0.1 M methionine (Met) and cysteine (Cys) solution for 4 h at 60 °C. Methionine and cysteine were successfully inserted into the interlayer structure of LDHs. The LDHs-Met and LDHs-Cys coatings are distributed in a petal shape by hexagonal nanosheets, and their distributions on the surface of the MAO are dense and uniform. The porosity, surface roughness, hydrophilicity, and corrosion resistance of LDHs-Met and LDHs-Cys coatings are increased compared to MAO and MAO/LDHs coatings. The amino acids in the LDHs could play an influential corrosion inhibition role, improving the corrosion resistance of the MAO effectively. The ion exchange layer has a more substantial protective effect on the substrate and better biocompatibility than MAO and MAO/LDHs coatings. [Display omitted] • Zinc-aluminum layered double hydroxides (LDHs) were prepared on micro-arc oxidized (MAO) coatings. • Amino acids was loaded on MAO/LDHs coatings by hydrothermal treatment. • Corrosion resistance of coatings after ion exchange were increased. • Ion exchange coatings showed better biocompatibility than MAO/LDHs coatings. [ABSTRACT FROM AUTHOR]