One-step hydrothermal preparation of corrosion-resistant coatings with microsphere structure

Rapid corrosion rate is limiting the engineering application of magnesium alloys. In this paper, an attempt was made to produce a corrosion resistant coating on the surface of AZ91D magnesium alloy using hydrothermal method. The coating surface is covered with microspheres and has a dense structure, which effectively isolates the contact between the outside world and the substrate. The corrosion potential(E) raised from −1.57 V to −0.45 V compared to the bare sample. The corrosion current density and corrosion rate of the coating can be reduced by 6 orders of magnitude, and the polarization resistance raised by 6 orders of magnitude. The thickness of the coating is 45.4 μm at the moment, with a minimum of defects on the surface, resulting in excellent corrosion resistance in the immersion test. The coating also has good adhesion strength at 4B, which can expand the application range of magnesium alloy in corrosive environments.