Negative Voltage on Structure and Corrosion Resistance of Micro-arc Oxidation Coating on AZ31B Magnesium Alloy postprint

Abstract: Micro-arc oxidation (MAO) coatings were fabricated on AZ31B Mg-alloy in a Na2SiO3-NaOH-NaF aqueous solution by varying applied negative voltages with a bipolar asymmetric pulsing power. Then the effect of the applied negative voltage on the microstructure and corrosion resistance of MAO coatings were studied by SEM and polarization curves. The results show that a corrosion resistant coating can be obtained by an applied negative voltage 40 V for a duration 10~15 min. However, the surface morphology of the MAO coating exhibited obviously many microcracks when the applied negative voltage is above 60 V, resulting in a poor corrosion resistance. Therefore, the value of the negative voltage and the oxidation time should be carefully matched so that to prepare a MAO coating with appropriate compactness and corrosion resistance.