One-Step Hydrothermal Process to Fabricate Hydrophobic Mg-Al Layered Double Hydroxide Coating on MAO-Coated AZ31 Magnesium Alloy and Its Durability

In order to improve the corrosion resistance of micro-arc oxidation (MAO) ceramic layer of AZ31 magnesium alloy, a hydrophobic Mg-Al layered double hydroxide (LDH) coating was prepared on its surface by a one-step hydrothermal method. The microstructure of the coating was characterized by scanning electron microscope, energy disperse spectroscopy, X-ray diffractometer, and Fourier transform infrared spectrometer. The wettability and corrosion resistance of the coating were studied by contact angle (CA) measuring instrument and electrochemical workstation. Meanwhile, the durability of the coating was evaluated by sandpaper abrasion, tape peeling and immersion test. The results showed that the hydrophobic Mg-Al LDH coating can be successfully prepared on the surface of MAO ceramic layer by one-step hydrothermal treatment with alkaline aluminum nitrate solution containing sodium laurate. The hydrophobic Mg-Al LDH coating sealed the inherent defects of MAO ceramic coating, resulting in significantly improved corrosion resistance. With the extension of sandpaper abrasion distance, tape peeling times, and immersion time, the CA of the coating shows a downward trend, and the coating gradually changed from hydrophobic to hydrophilic. However, after the durability test, the coating still has good corrosion resistance, and its corrosion current density was still lower than that of MAO ceramic layer.