Dual self-healing composite coating on magnesium alloys for corrosion protection

In this work, a new self-healing composite coating for corrosion protection of magnesium (Mg) alloy, which is based on the dual actions of the corrosion inhibitor M-16 embedded in the micro-arc oxidation (MAO) coating and self-healing polyurethane (PU) modified by disulfide bonds, is developed. Electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) are used to study the anti-corrosion performance of the scratched and healed composite coatings immersed in 3.5 wt% NaCl solution. Results show that the porous MAO coating is suitable to carry inhibitor M-16 and the anti-corrosion performance of the scratched coating is significantly improved by the inhibitor embedded in the MAO coating. The scratched coating exhibits an excellent recovery of the anti-corrosion performance after the heat treatment, which is attributed to the cooperation of dynamic disulfide bonds and shape-memory effect of the self-healing PU coating. Furthermore, it is found that the inhibitor M-16 embedded MAO coating can enhance the repair ability and anti-corrosion performance of the PU coating when the corrosion product was pre-formed inside the scratch of the composite coating.