| As the lightest engineering structural material,magnesium alloy has broad application prospects in aerospace,automobile,military and other fields.However,magnesium alloys have disappointing corrosion resistance,and the protective effect of a single protective coating is limited.The composite coating is the main research direction in the future.The existing magnesium alloy composite protective coating does not have self-healing ability,magnesium alloy in the service process may be knocked,scratched,environmental corrosion and lead to coating failure,resulting in magnesium alloy substrate directly exposed to the external environment and corrosion,which greatly restricts the further development of magnesium alloy.Therefore,the development of a composite protective coating with self-healing ability has important research significance for the surface protection and practical application of magnesium alloys.This paper takes AZ91 D magnesium alloy as the research point,two kinds of microcapsule self-healing systems loaded with corrosion inhibitor（8-hydroxyquinoline）and repair agent（epoxy resin）were designed.The influence of microcapsules on the corrosion resistance and repairability of magnesium alloy plasma electrolytic oxidation（PEO）epoxy composite coating was studied,the repair theory of the two microcapsules on the coating was explored.Microcapsules loaded with corrosion inhibitor 8-hydroxyquinoline（8-HQ）and repair agent epoxy resin（E-51）were prepared by in-situ polymerization.The micromorphology,chemical composition,thermal stability,corpuscle diameter and loading rate of microcapsules were explored by scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy,and thermogravimetric analyzer.The effects of the contents of core and wall materials,emulsifier concentration,acidification time and stirring speed on the morphology,particle size and loading rate of microcapsules were investigated.The microstructure and coating repair morphology of PEO epoxy composite coating modified by microcapsules were studied by SEM.The influence of microcapsule content on the corrosion resistance and repairability of self-healing composite coating was studied by cathodic hydrogen evolution and electrochemical methods,and the repair effect and repair mechanism of the coating were explored by combining with micro-area electrochemical methods.The conclusions are as follows :（1）The influence of process parameters on the morphology,corpuscle diameter and load rate of microcapsules are remarkable.The amount of core and wall material has the greatest influence on the morphology and load rate of microcapsules,and the corpuscle diameter of microcapsules is mainly controlled by the agitation rate.With the increase of emulsifier concentration and acidification time,the agglomeration of microcapsules decreased,the surface was smoother,the corpuscle diameter and distribution area decreased,and the load rate increased.When the emulsifier concentration increased to more than 5 % and the acidification time exceeded 30 min,the morphology,corpuscle diameter and load rate of microcapsules were no longer affected by the emulsifier concentration and acidification time.With the increase of the relative content of core material and stirring speed,the morphology of microcapsules is more regular,the surface is smoother,the corpuscle diameter and distribution area are reduced,and the load rate is increased.When the proportion of core to wall material is greater than 1 : 1 and the stirring speed is more than 800 rpm,some microcapsules are demulsification and the load rate is reduced.The final microcapsule loading rate was up to 64 %,and had good thermal stability below 200 °C.（2）Microcapsules loaded with corrosion inhibitor have good dispersion in epoxy coating,and PEO layer is more closely bonded to epoxy coating modified by microcapsules than magnesium alloy substrate.With the improve of the amount of microcapsules in the coating,the corrosion resistance of epoxy coating and PEO epoxy composite coating increased first and then decreased.The amount of microcapsules in the coating was 3 %,the protective ability of the coating was the best.Compared with the composite coating without microcapsules,the corrosion current density of the composite coating modified by microcapsules decreased by 61.78 %.After immersion in prefabricated defects,the defects of PEO epoxy composite coating modified by microcapsule were repaired,and the chelate film of 8-HQ and magnesium was formed.With the improve of microcapsule amount,the repair effect of the coating was stronger.The potential difference between the coating after repair and the coating surface was reduced by 19.54 %compared with that before repair,and the self-repairing efficiency of the coating was 64.43 %calculated by the corrosion current density.（3）The microcapsule loading rate of the obtained load repair agent was about 76 %,and it had good thermal stability below 251 °C.The repair performance of the self-healing coating is mainly affected by the amount of activator（Dimethyl Imidazole）and microcapsule in the epoxy coating.With the improve of the amount of activator in the coating,The self-healing ability of the coating is stronger.When the content of curing agent exceeds 6 %,the repair performance of the coating is no longer affected by the content of curing agent.With the improve of the amount of microcapsules in the coating,the self-healing ability and protective effect of the coating are also improved.When the content of microcapsules in the coating reaches 9 %,the scratch is basically completely repaired,and the resistance value of the coating is enhanced by two orders of magnitude compared with that before repair. |
