The Influence of Negative Voltage on Corrosion Behavior of Ceramic Coatings Prepared by MAO Treatment on Steel

In this study, the 10B21 steel was treated by micro-arc oxidation (MAO) in the electrolyte consisting of aluminate and phosphate to enhance its corrosion resistance. The effect of negative voltage on corrosion resistance of the MAO coating obtained has mainly been analyzed through their phase composition, microstructure, interfacial bonding strength, salt spray and electrochemical testing. The result indicates that with negative voltages applied to the MAO coating, Fe-Al transition layers arise between coating layer and matrix. Furthermore, different negative voltages bring forward different α-Al2O3 contents contained in the MAO coatings and when it reaches −100 V, the amount of α-Al2O3 appears as the largest. The surface porosity of the coating was also significantly decreased. In addition, the corrosion current density of the coating is only 3.64 μA·cm−2, which is two orders of magnitude lower than that of the substrate. After 72 h of salt spray corrosion, it is found that the coating substrate is less corroded when the negative voltage of 100 V is applied. Therefore, −100 V has been proven as the optimum performance for improving the corrosion resistance of 10B21 steel.