Effect of pause time on microstructure and corrosion resistance in AZ31 magnesium Alloy's micro-arc oxidation coating

Micro-arc oxidation (MAO) coatings are among the most effective methods for protecting Mg alloys against corrosion. However, the corrosion protection effect of MAO coatings for Mg alloys is unsatisfactory due to the formation of micropores and microcracks in these coatings. Many researchers have improved the microstructure and corrosion resistance through changing the electrical parameters, such as current density, oxidation time, frequency, duty cycle and power modes. This study is one of the first to examine the role of pause time following anodic and cathodic polarization in a MAO process for magnesium alloys. Anodic pause time, as opposed to its cathodic counterpart, augments the corrosion resistance of these alloys, as demonstrated by electrochemical impedance spectroscopy results. Specifically, an MAO-coated specimen subjected solely to anodic pause time exhibits a total impedance six times greater than a specimen undergoing only cathodic pause time, irrespective of identical coating thickness. These findings emphasize the detrimental effect of cathodic pause time on corrosion resistance and demonstrate the beneficial role of anodic pause time.