Research Progress of double self-repairing corrosion Protective Coatings for magnesium Alloys

Magnesium alloy is the lightest metal structure material, and its density (about 1.8g/mm3) is only 2 / 3 of aluminum alloy and 1 / 4 of steel, so it has a broad application prospect in lightweight. Magnesium alloy has poor corrosion resistance, which limits its wide application in various fields. Micro-arc oxidation (Microarc Oxidation-MAO) technology has an advantage in improving the corrosion resistance of magnesium alloy by in-situ formation of oxide ceramic film on the surface of magnesium alloy. The porous structure of MAO film affects its long-term corrosion protection performance. The composite coating formed after sealing with polymer coating can significantly improve the corrosion protection performance of magnesium alloy MAO film. However, the coating will be mechanically damaged in practical application, which makes it lose its protective effect on the metal matrix. In order to solve the problem of corrosion protection failure caused by coating mechanical damage, the construction of self-repairing coating is one of the important ways.

Based on the MAO film loaded with corrosion inhibitor and disulfide bond modified polyurethane, Liang Jun, a researcher at Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, constructed a composite coating with dual self-repairing function on the surface of magnesium alloy. In this study, the micropores in the MAO film were used as container-loaded corrosion inhibitors, on the basis of which the disulfide bond modified polyurethane was sprayed to form a composite coating (MP-i). The results show that, compared with the composite coating without corrosion inhibitor (MP-0) and the modified polyurethane single coating loaded with corrosion inhibitor (Pmuri), the composite coating shows excellent self-repair ability and corrosion protection effect after damage, and is expected to meet the application requirements of long-term corrosion protection in the case of external damage.

The self-repairing function of the composite coating after damage is mainly realized by the joint action of the following two processes. Under the action of heat, the damage was repaired by dynamic disulfide bond cross-linking reaction and shape memory effect of modified polyurethane. In the porous MAO film where the coating is damaged, the corrosion inhibitor is released to the surface of magnesium alloy substrate to form Barrier, which can restrain the occurrence and development of matrix corrosion, thus winning the "time lag" for the effective self-repair of modified polyurethane. In addition, even if the composite coating is damaged and corroded, the MAO film as an intermediate layer can also isolate the corrosion products from the polyurethane coating, which is conducive to the free movement of the polyurethane chain segment and the gap closure of the coating, and provides favorable conditions for the dynamic cross-linking reaction of disulfide bonds, thus improving the self-repairing ability of the polymer coating.

The relevant research results are published on Chemical Engineering Journal. The research work is supported by the National Natural Science Foundation of China.