Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg-Al layered double hydroxide coating

To further enhance the corrosion resistance of the porous micro-arc oxidation (MAO) ceramic layers on AZ31 magnesium alloy, superhydrophobic Mg-Al layered double hydroxide (LDH) coating was fabricated on MAO-coated AZ31 alloy by using in-situ growth method followed by surface modification with stearic acid. The characteristics of different coatings were investigated by XRD, SEM and EDS. The effect of the hydrothermal treatment time on the formation of the LDH coatings was studied. The results demonstrated that the micro-pores and cracks of MAO coating were gradually sealed via in-situ growing LDH with prolonging hydrothermal treating time. Electrochemical measurement displayed that the lowest corrosion current density, the most positive corrosion potential and the highest impedance modulus were observed for superhydrophobic LDH/MAO coating compared with those of MAO coating and LDH/MAO coating. Immersion experiment proved that the superhydrophobic LDH/MAO coating with the active anti-corrosion capability significantly enhanced the long-term corrosion protection for MAO coated alloy.