Preparation And Performance Of MAO-UV Water-based Coating Composite Film On Magnesium Alloy

Magnesium alloys are known as green structural materials in the 21st century due to their lightweight,high specific strength and stiffness properties.However,due to their active chemical properties,the research on the corrosion resistance of magnesium and its alloys has always been paid attention to.Surface treatment techniques are often used to improve it.Micro-arc oxidation(MAO)technology is considered to be an efficient and simple surface treatment technology for magnesium alloys,which can comprehensively improve the corrosion resistan ce,wear resistance,and has closely adhesion with the metal matrix.However,during the oxidation process,high voltage on both sides of the film layer generates breakdown discharge micro arcs,which form discharge channels in the oxide layer.Eventually,a large number of blind micropores are uniformly distributed on the surface of the film layer.These micropores serve as channels for external corrosive media to enter and corrode the substrate,seriously reducing the corrosion resistance of the film layer.The article uses UV(Ultraviolet,UV)curable water-based coatings to replace traditional oily coatings to improve the corrosion resistance of the micro arc oxidation film by sealing the holes.The effects of surface porosity,UV curing time,UV coating thickness,and coupling agents on the performance of composite film layers were studied;The crosslinking and curing mechanism of waterborne UV polyurethane coatings was revealed using infrared spectroscopy(FTIR)analysis technology;The corrosion behavior and corrosion resistance mechanism of micro arc oxidation and waterborne UV polyurethane composite coatings were studied through electrochemical impedance spectroscopy and salt spray corrosion experiments.The specific research is as follows:(1)The crosslinking and curing process of waterborne UV polyurethane coatings was analyzed by using infrared spectroscopy technology,and the curing degree of UV coatings was studied by analyzing the absorption peak intensity of unsaturated C=C.The results indicate that the crosslinking curing of waterborne UV coatings is actually an unsaturated C=C fracture reaction,and when the thickness of the UV coatings is constant,there is a saturation value for the conversion of C=C double bonds with increasing curing time.At a UV coating thickness of 10μm and the curing time is 20 s,the degree of crosslinking and curing is the highest,and the conversion rate of C=C reaches saturation at 44.2%;(2)The influence of oxide film porosity and UV composite process on the interfacial adhesion of MAO-UV composite film was studied by using paint film adhesion tester and UMT TriboLab friction and wear tester.The results show that as the surface porosity of the oxide film increases,the adhesion between the MAO and water-based UV coating composite film layers first increases and then decreases.The adhesion of the film layer is best when the porosity is 15.698%;With the prolongation of curing time,the bonding strength between the composite film layers first increases and then decreases.When the porosity of the oxide film is 15.698%,the thickness of the UV coating is 10 μm,and the curing time is 20 s,the optimal crosslinking curing is achieved,and the interfacial bonding force of the composite film layer is about 21 N;The introduction of silane coupling agent through the substrate method can significantly improve the interfacial adhesion of the MAO-UV composite film layer,and the interfacial adhesion of the MAO-A-UV composite sample reaches 36 N;(3)The corrosion resistance of the composite film layer was studied through salt spray corrosion experiments and electrochemical analysis.The research results show that the influence of surface porosity and UV curing time of the oxide film on the corrosion resistance of the composite film layer is consistent with the influence of adhesion.Through studying the influence of UV coating thickness on the corrosion resistance of the composite film layer,it was found that the interface adhesion of MAO-UV to a certain extent affects the corrosion resistance of the film layer.At the best porosity of the oxide film,the UV coating thickness is about 10 μm.At a curing time of 20 s,the impedance modulus of the MAO-A-UV composite film prepared by the substrate method increased by two orders of magnitude compared to the MAO sample.After soaking for 15 days,the impedance modulus of MAO-A-UV was 5.49E6 Ω,which was one order of magnitude higher than the impedance modulus of MAO-UV of 3.15E5Ω.