| As a lightweight structural material,magnesium alloy is widely used because of its high specific strength,specific rigidity,good machinability and biocompatibility.However,the corrosion resistance of magnesium alloy is poor,and the protection layer is usually required during use.However,the coating will inevitably be damaged under severe service conditions,causing corrosion to initiate from the damage of the coating and accelerating the failure of the magnesium alloy.Protective coatings do not have self-healing properties,so the research on self-healing coatings that can release corrosion inhibitors on the surface of magnesium alloys has certain engineering and scientific application value.This paper takes AZ91D alloy as the research object.Through immersion experiments in different corrosion inhibitor solutions,the film formation mechanism of different corrosion inhibitors on the surface of magnesium alloys is studied.On this basis,two methods of vacuum impregnation of inorganic corrosion inhibitor modified plasma electrolytic oxidation(PEO)coating and octahydroxyquinoline(8HQ)-loaded mesoporous silica modified plasma electrolytic oxidation coating have realized the surface autonomy of magnesium alloy.The preparation of the repair coating,and the effect of corrosion inhibitor on the corrosion resistance and self-repairing of the PEO ceramic layer and the self-repairing mechanism of the coating were studied.Through scanning electron microscope(SEM),X-ray diffractometer(XRD)and X-ray photoelectron spectroscopy(XPS),the surface morphology of magnesium alloys after immersion in different corrosion inhibitors,vacuum immersion inorganic corrosion inhibitors and media loaded with 8HQ were studied.The effect of porous silica on the microstructure and phases of PEO coatings;through electrochemical testing methods combined with immersion experiments,the changes in the surface corrosion resistance of magnesium alloys after immersion in different corrosion inhibitors,vacuum immersion inorganic corrosion inhibitors and minus 8HQ were studied.of mesoporous silica on the corrosion resistance of the PEO ceramic layer.The self-repair efficiency and self-repair mechanism of the modified PEO ceramic layer were studied by micro-area electrochemistry.Sodium vanadate(NaVO3),sodium phosphate(Na3PO4),sodium stannate(Na2SnO3)and octahydroxyquinoline(8HQ)are used as film-forming corrosion inhibitors to form MgVO3,Mg3(PO4),MgSnO3·3 H2O and Mg(HQ)2 on the surface of magnesium alloy.sodium tungstate(Na2WO4)as an adsorbent corrosion inhibitor,hydrolyzed WO42-,[W7O24]6-,[W10O34]4-and corrosive Cl-Competitive adsorption occurs,which plays a role of protecting the matrix to a certain extent.The weight loss method and electrochemical results show that sodium vanadate has a better slow-release effect,and the higher corrosion-inhibiting effect comes from the integrity of the formed product film MgVO3.The PEO ceramic layer is modified by vacuum impregnation of inorganic corrosion inhibitors.The PEO ceramic layer is mainly composed of MgO,Al2O3 and Mg2Sn.The surface of the PEO ceramic layer modified by different corrosion inhibitors NaVO3,Na3PO4,Na2WO4 and Na2SnO3 forms a lamellar,Aggregate granular,slender needle-like and fine granular crystalline salt structure.The self-corrosion potential of the PEO ceramic layer modified by the inorganic corrosion inhibitor is positively shifted,the self-corrosion current density is reduced,and the corrosion resistance is improved.Among them,the self-corrosion current density of the PEO ceramic layer modified by sodium vanadate and sodium tungstate is respectively They are 2.768×10-8 A·cm-2 and 2.548×10-8 A·cm-2,with low self-corrosion current density and better corrosion resistance.The PEO ceramic layer is modified by mesoporous silica loaded with 8HQ,the surface discharge micropore diameter of the modified PEO ceramic layer is reduced to about 2-3μm,and the dispersion coefficient increases to 0.8814 after impedance fitting,and the surface is more uniform.The self-corrosion current density of the modified PEO ceramic layer is two orders of magnitude lower than that of the unmodified ceramic layer,which is 1.8887×10-7 A·cm-2,showing good corrosion resistance.The self-healing performance of the coating was evaluated by immersing the scratched modified PEO ceramic layer samples.There were no obvious corrosion pits and corrosion products at the scratches of the modified PEO ceramic layer.The introduction of corrosion inhibitors inhibits corrosion at scratches.The electric potential difference between the scratches of the modified PEO ceramic layer and the surface of the ceramic layer is reduced.The electric potential difference between the scratches of the PEO ceramic layer modified by sodium phosphate and the surface of the ceramic layer is the smallest 0.115V,and the self-repairing efficiency is the highest,which is 73.86%.The potential difference between the scratches of the PEO ceramic layer modified by the mesoporous silica loaded with 8HQ and the ceramic layer is 0.28V,and the self-repair efficiency is 36.36%. |
