Study On Preparation And Properties Of Composite Coatings On Aeronautical Aluminum Alloy Surface

As a kind of high quality alloy with low density,high strength and good ductility,2024aviation aluminum alloy is widely used in the main structures such as frame spar,rib,skin and so on.In normal environment,the surface of aluminum alloy components will be oxidized by a layer of oxide film,which can inhibit the further corrosion of the substrate.However,the thickness uniformity of the film is poor and there exist many pores,so it is difficult to meet the requirements for aircraft corrosion resistance.In view of the above shortcomings,this paper studies two anticorrosion methods?silanization and electroless plating?in order to improve the corrosion resistance and prolong the service life of 2024 aviation aluminum alloy.Vinyl triethoxy silane?VTE?film was prepared on the surface of 2024 aviation aluminum alloy through impregnation method in silanization.The effects of silane content,ratio of alcohol to water,PH of solution and hydrolysis temperature on the corrosion resistance of silane film were studied and the optimum preparation process was determined through single factor experiments:the additive amount was 2 mL/100 mL of alcohol-water solution,the ratio of alcohol to water was 20:80,the PH of the solution was 4,and the hydrolysis temperature was 30?.In view of the defects of single silane film such as void and crack,VTES-TiO₂ composite film and VTES-MWCNTs composite membrane were prepared by adding TiO₂ and MWCNTs to the VTES hydrolysis solution under the optimum technology.The effects of different TiO2 and MWCNTs contents on the corrosion resistance of the composite film were studied,and the optimum concentration of TiO2 and MWCNTs was 3.0 g.L^-1 and 0.2 g.L^-1,respectively.The performances of VTES film,VTES-TiO₂composite membrane and VTES-MWCNTs composite membrane under the optimum technology were compared and studied.The results show that VTES silane film has good adhesive,hydrophobic and anticorrosive performance,and the addition of TiO₂ and MWCNTs can further improve the adhesive,hydrophobic and anticorrosive performance of the silane film,among which the VTES-MWCNTs composite film has the best performance.Ni-P coating was deposited on the surface of 2024 aeronautical aluminum alloy through electroless plating.The effects of plating temperature,plating time and plating bath PH on the deposition rate were studied through single factor experiment.The optimum process parameters were obtained as follows:the plating temperature was 85?,the plating time was60 min,and the PH value of the bath plating was 9.In order to reduce the void on the surface of Ni-P coating,Ni-P-MWCNTs composite coating and Ni-W-P ternary coating were deposited by adding MWCNTs and Na₂WO₄ to the Ni-P plating bath under the optimum technology.The effects of different MWCNTs and Na2WO4 contents on the deposition rate of the coating were studied respectively,and the optimum addition concentration of MWCNTs and Na₂WO₄ was 0.3 g.L^-1 and 15.0 g.L^-1.The Ni-P coating,Ni-P-MWCNTs composite coating and Ni-W-P ternary coating under the optimum technology were characterized and their performances were tested.The results showed that the surface of the coating was smooth and the size of the cell body was uniform.The addition of MWCNTs and Na₂WO₄ can reduce the voids on the surface of the coating and improve the adhesive,hydrophobic and anticorrosive performance of the coating,among which the Ni-W-P ternary coating has the best performance.