Study on Corrosion Resistance of LDH/Micro-Arc Oxidation Composite Superhydrophobic Coatings on AZ31 Magnesium Alloy

Because of some defects such as holes and cracks, the corrosion resistance of micro-arc oxidation coating needs to be improved by surface modification. In this paper, LDH/MAO film with a micro-/nano-structure is constructed on the surface of AZ31 magnesium alloy by controlling the composition and concentration of the hydrothermal solution. The superhydrophobic surface is successfully constructed by coating an OTES modifier on the surface of LDH/MAO film by the spin-coating method. The surface morphologies, contact angles, and corrosion resistance of composite coatings are tested. The results show that the OTES-LDH/MAO composite coatings of magnesium alloy can seal the defects in the MAO film well to achieve a superhydrophobic effect and better corrosion resistance. Compared with a MgO ceramic film, the water contact angle of OTES-LDH/MAO composite coatings is increased from 38° to 155°; the corrosion potential increases by 0.7 V, the corrosion current density and polarization resistance decreases and increases by four orders of magnitude, respectively; and the corrosion resistance becomes much higher than that of MAO film.