Research On Sealing Treatment And Properties Of Micro-arc Oxidation Film Of 7075 Aluminum Alloy

7075 aluminum alloy has a wide range of uses and has become an indispensable metal material in the process of modernization.It is used as a skin for aircraft in technological manufacturing materials,as a whole frame in the direction of automobiles,and as a deck in ships.etc.However,it is easily damaged in actual use,and MAO is born as an application of surface treatment technology.MAO technology comes from anodic oxidation.It not only has the advantages of strong bonding between the anodic oxide film and the substrate,but also has a simple operation process and little harm to the environment.It has broad prospects in practical applications.During the working process of MAO,after the voltage rises to the breakdown voltage,molten oxides are formed on the surface of the substrate,which continuously accumulate on the surface to form an inner dense layer and an outer loose layer.The high temperature and high pressure caused the oxide inside the MAO film to overflow,and then destroyed the dense layer structure.The overflowing molten Al2O3accumulated in the outermost layer,resulting in a porous structure.These holes provide access channels for corrosive media,such as H₂O,Cl^-,etc.to chemically react with them to accelerate corrosion.Therefore,the research focus of this paper is to find a suitable sealing agent to seal these micropores,improve its corrosion resistance,expand the use of 7075aluminum alloy,use silica sol,polyvinylidene fluoride,zirconium dioxide The sealing agent was used for sealing treatment.The surface micro-morphology of the samples after sealing was observed by SEM.The corrosion test of the samples after sealing was performed,and the surface after corrosion was observed to evaluate the effectiveness of the sealing effect.The main conclusions are as follows:（1）The 7075 aluminum alloy MAO film was prepared in the electrolyte of Na₂Si O₃,Na OH and Na F,and the pores were sealed by silica sol with concentrations of 5g/L,10g/L,15g/L and 20g/L.The MAO film layer of the hole was found to find the effect of the optimum concentration of silica sol on the performance of the 7075 aluminum alloy MAO film layer.The results show that when the concentration of silica sol is too low,the sealing effect of the micro-arc oxidation film is relatively poor.When the concentration is 20g/L,the surface of the sealing film is smooth,the film thickness is uniform,and the sealing effect is the best.（2）After micro-arc oxidation of 7075 aluminum alloy,polyvinylidene fluoride with concentrations of 2g/L,4g/L,6g/L,8g/L,10g/L and 12g/L was used for micro-arc oxidation.The aluminum alloy was used for sealing,and the MAO/PVDF composite film was prepared on the original micro-arc oxidation film.The study found that when the concentration of polyvinylidene fluoride was 8g/L,the sealing layer had the best compactness.The film thickness of 2g/L polyvinylidene fluoride after sealing is 12.4um,when the concentration increases to 8g/L,the film thickness increases to 24.8um,and the impedance value measured in3.5wt.%Na Cl solution is 4000Ω·cm²,the corrosion potential is-0.042V,and the current density is 6.50×10^-4A·cm^-2,which is 3 orders of magnitude lower than that of the film without PVDF sealing.In addition,when the concentration of the polyvinylidene fluoride solution is too low,the polyvinylidene fluoride content is small,the viscosity is small,and the adhesion to the film layer is weak,and there are micropores that are not completely closed.When the concentration of polyvinylidene fluoride is too large,the fluidity is poor,the adhesion with the film layer is reduced,and the hole sealing is incomplete.When the concentration is 8g/L,the sealed membrane layer has the best corrosion resistance and wear resistance.（3）In the electrolyte prepared without adding and adding different concentrations（2g/L,4g/L,6g/L）of Zr O₂,put the polished sample in the electrolyte for MAO treatment,using SEM,X-The effects of adding different concentrations of Zr O₂ particles on the structure,binding force and corrosion of the film were studied by ray diffractometer,binding force tester and electrochemical workstation.Experiments show that Zr O₂ peaks appear in the films prepared with different concentrations of Zr O₂ particles.The particles entering the MAO film have a good bond with the oxide film.With the increase of concentration,the pores and cracks of the film gradually decrease.In addition,the films added with Zr O₂ particles exhibited stronger wear resistance in sliding friction at room temperature.The electrochemical test results show that the micro-arc oxidation film prepared by adding Zr O₂ particles has better corrosion resistance.When the concentration is 4g/L,the comprehensive performance of the film is the best.