One-pot scalable in situ growth of highly corrosion-resistant MgAl-LDH/MBT composite coating on magnesium alloy under mild conditions

Current corrosion-resistant layered double hydroxide (LDH) coating on Mg alloy is usually in situ grown in autoclave by hydrothermal methods under high temperature and high-pressure conditions, which is unfavorable for industrial application. We report that an inhibitor (2-mercaptobenzothiazole, MBT) incorporated composite (MgAl-LDH/MBT) coating can be in situ deposited on bare AZ31 Mg alloy surface with the assistance of a chelating agent (ethylenediaminetetraacetic acid) under a relatively low temperature (95 °C) and ambient pressure by a one-pot method. The successful formation of LDH/MBT composite coating is confirmed by a series of characterizations, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). The corrosion resistance of the composite coating is evaluated by means of hydrogen evolution measurement, electrochemical impedance spectroscopy (EIS), Tafel polarization curves, and neutral salt spray test. The tests show that the LDH/MBT composite coating has a very low corrosion current density (1.73 10−8 A cm−2), an extremely high charge transfer resistance (2.336 MΩ cm2), and does not show any corrosion pits even after 15 d of exposure to a NaCl solution or 7 d of exposure to salt fog environment, manifesting the good and robust corrosion protection. Lastly, the deposition and corrosion protection mechanisms of the MgAl-LDH/MBT composite coating are also discussed and proposed based on the EDS characterization of the coating after long-time exposure.