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

A self-healing composite coating based on the dual-action of corrosion inhibitor M−16 embedded in micro-arc oxidation coating and self-healing polyurethanes is designed for corrosion protection of Mg alloy. [Display omitted] •1. A dual self-healing composite coating was prepared for Mg alloys.•2. The MAO coating was more suitable to carry the inhibitor than polymer coating.•3. The scratches of the composite coating were repaired by modified polyurethane.•4. MAO coating enhanced the self-healing performance of the polymer coating. 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.