Corrosion Resistance Enhancement of Micro-Arc Oxidation Ceramic Layer by Mg-Al-Co Layered Double Hydroxide Coating
Zhi Hu Wang, Ju Mei Zhang, Yan Li, Li Jing Bai, Guo Jun Zhang
Abstract
To improve the corrosion resistance of the ceramic layer prepared by micro-arc oxidation (MAO) on magnesium alloy, a hydrophobic Mg-Al-Co layered double hydroxide (LDH) coating was fabricated on MAO coated AZ31 magnesium (Mg) alloy by using a simple in-situ growth method. The results showed that the LDH film covered the MAO coating tightly, and it sealed the micro-pores and cracks in the MAO coating successfully. As a result, the LDH film increased the water contact angle of MAO coating from 10.35° to ∼137.21°, and the hydrophobic LDH/MAO composite coating increased the Ecorr of MAO coating from –1.47 to –1.39 V/SCE and decreased the Icorr by about two orders of magnitude. The electrochemical impedance spectroscopy results showed that the LDH/MAO composite coating achieved the largest dimension of capacitive loop and the highest impedance at low frequency compared to MAO coated and uncoated AZ31 Mg alloy. Therefore, the LDH/MAO composite coating could provide long-term protection for Mg substrate from corrosive environment due to its hydrophobic function, ion-exchange ability and barrier effect. This work has significant meaning to the applications of Mg alloys.