Corrosion Performances Of Micro-Arc Oxidation Coatings On Az31B, Az80 And Zk60 Cast Mg Alloys

Micro-arc oxidation (MAO) technology is attractive for the surface treatment of Mg alloys for diverse applications because it can be used to form adherent coatings with superior wear and corrosion resistance. In the present study, the corrosion protective MAO coatings were prepared on the AZ31B, AZ80 and ZK60 cast magnesium alloy at a constant current mode in an alkaline silicate electrolyte. Analysis of the surface and cross-section morphology, phase composition and microstructures of the MAO coatings and these three kinds of substrates was conducted utilizing scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. The corrosion properties of the uncoated and MAO coated Mg alloys were investigated using advanced electrochemical methods including the open circuit potential (OCP) measurement and electrochemical impedance spectroscopy (EIS). To further characterize the protectiveness of the MAO coating, the scribed MAO coated AZ31B and ZK60 alloy coupons were exposed to the continuous salt spray corrosion testing (SSCT) for 168 h. The experimental results show that the phase composition, the thickness and the microstructure of MAO coatings on different kinds of Mg alloys did not show any differences between them. While the MAO coating provides the best robust protection on the ZK60 Mg alloy substrate in the aqueous salt solution and continuous salt spray environments, the corrosion resistance increased by nearly three orders of magnitude as compared to uncoated Mg alloy.