| Aluminum and its alloys are widely used in all walks of life because of their superior properties.However,the chemical activity of amphoteric aluminum element is relatively high and it is prone to be corroded due to chemical reaction in acid and alkaline environment.Superhydrophobic technology inspired by nature can effectively block the immersion of corrosive liquids,protect the matrix and delay corrosion.At the same time,superhydrophobic technology has many advantages,such as anti icing,friction reduction,self-cleaning and so on,so it has a huge application prospect in aerospace industry,pipeline transportation,housing construction and other fields.Therefore,it is of great significance to study the superhydrophobic surface preparation technology of aluminum for prolonging the service life of aluminum products and expanding the application field of aluminum materials.In this paper,based on gradient composite electroless plating and low surface energy material modification composite technology,superhydrophobic composite coatings with uniform appearance,excellent corrosion resistance and close binding to matrix were successfully prepared on the surface of 6063 aluminum alloy.The preparation process and properties of typical samples were studied and analyzed.The main research work and results are as follows:(1)Auxiliary complexing agent screening and formulation optimization of acidic Ni-Cu-P electroless plating solution.Taking the stability of the plating solution,the porosity of the coating,the plating speed,and the adhesion of the coating as technical indicators,the effects of three auxiliary complexing agents on the plating effect of Ni-Cu-P electroless plating were explored and the final additives were determined.Based on the screening results of the effective components of the plating solution,the effects of each component of the plating solution on the plating effect were systematically investigated,and the best plating solution formulation and plating parameters were determined as follows: sodium hypophosphite 22.5g/L,nickel sulfate 30g/L,Copper sulfate 1g/L,sodium acetate 30g/L,sodium citrate 20g/L,complexing agent A 3.5g/L;initial bath p H of 6,plating temperature of 80?,plating time of 1.5h.(2)Preparation of hydrophobic surface by Ni-Cu-P/Cu-Ni-P gradient composite electroless plating/stearic acid modified composite technology.Gradient electroless copper plating was applied on Ni-Cu-P coating by activation and coupling processes respectively.The composite surface was modified with stearic acid.The influence of gradient electroless plating process,bath composition and plating parameters on gradient plating effect was studied by taking the appearance and surface hydrophobicity of the coating as evaluation indexes.The results show that the continuous deposition of copper on Ni-Cu-P coatings can be achieved by coupling magnesium alloys to obtain copper layers with special structures.Moreover,after stearic acid modification,the surface of the composite coating can be approached to reach the superhydrophobic effect.(3)Study on the influence of stearic acid modification on the hydrophobic effect of aluminum alloy gradient composite coating surface.Using the static contact angle and rolling angle of the composite coating as the screening indicators,the influence of stearic acid concentration,immersion temperature and treatment time on the hydrophobic effect of the composite coating surface was investigated,and the optimal surface modification process was determined: the concentration of stearic acid is 7.5g / L,the solution temperature is 50 ?,and the treatment time is 1h.Under the optimal treatment process,the surface contact angle of the composite coating is 155.8 ± 1 ° and the rolling angle is as low as 1.5 °.(4)Microstructure,composition analysis and corrosion resistance test of typical samples.SEM observation results show that: the surface of the composite coating is composed of micronlevel cones,micron-level cluster-like protrusions and nano-scale particles grown on the protrusions;EDS and XRD results show that the composite coating is a copper-nickel alloy with low phosphorus content.The results of FT-IR showed that the hydrophobic alkyl long chain of stearic acid had successfully acted on the outer surface of Cu.Full immersion corrosion test and electrochemical test show that the super-hydrophobic surface modification technology based on Ni-Cu-P/Cu-Ni-P gradient composite plating can significantly improve the corrosion resistance of the base aluminum alloy,and the corrosion rate is reduced by 90% compared to the substrate and the corrosion current density is reduced by 2 orders of magnitude. |
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