| CHEN Gaohong,XIAO Jian,YANG Haodong,YU Mei.Effects of LDH Pretreatment and Sol-gel Sealing on Corrosion Resistance of Sulfuric Acid Anodized Aluminum Alloy Film[J],53(4):58-67 |
| Effects of LDH Pretreatment and Sol-gel Sealing on Corrosion Resistance of Sulfuric Acid Anodized Aluminum Alloy Film |
| Received:April 21, 2023 Revised:September 07, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.04.005 |
| KeyWord:aluminum alloy anodization sol-gel method sealing modify LDH corrosion resistance |
| Author | Institution |
| CHEN Gaohong |
School of Materials Science and Engineering, Beihang University, Beijing , China;Beijing Engineering Research Center of Advanced Aluminum Alloys and Applications, Beijing Institute of Aeronautical Materials, Beijing , China |
| XIAO Jian |
School of Materials Science and Engineering, Beihang University, Beijing , China |
| YANG Haodong |
School of Materials Science and Engineering, Beihang University, Beijing , China |
| YU Mei |
School of Materials Science and Engineering, Beihang University, Beijing , China |
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| Abstract: |
| Anodized oxidation is one of the most commonly used methods in surface pretreatment of aluminum alloy. After anodized oxidation, there is a porous layer outside the film that needs to be closed to improve the corrosion resistance. Traditional boiling water sealing has some problems, such as high energy consumption and unsatisfactory long-term protection performance. Therefore, it is necessary to develop new anodizing sealing methods. In this paper, a new LDH pretreatment sol-gel sealing process was developed to improve compactness, corrosion resistance and hydrophobicity of the oxide film. The microstructure and corrosion resistance of the aluminum alloy anodized oxide film sealed by LDH pretreatment sol-gel were studied to compare with the conventional boiling water sealing process. After oil removal, washing, light and other pretreatment, 2195 aluminum alloy was subject to sulfuric acid anodization. The test conditions of sulfuric acid anodization were as follows:oxidation in 200 g/L sulfuric acid solution at 17 V voltage for 45 min at 15 ℃. The anodized aluminum alloys were pretreated with LDH and then immersed in 0.1 mol/L Li2CO3 solution for 30 min at 50 ℃. After that, the sample was immersed in sol at 80 mm/min and soaked for 5 min and cured for 15 min at room temperature. The above curing process was repeated, and finally the sample was cured at 60 ℃ for 3 h. The microstructure of the oxide films was characterized by a field emission scanning electron microscope (Zeiss SUPRA55) and an atomic force microscope (MESP-RC) before and after sealing. A contact Angle tester (Attension Theta) was used to evaluate the hydrophobicity of the anodized oxide film. The corrosion resistance of anodized oxide film was studied by an immersion test and an electrochemical test. The electrochemical impedance spectroscopy (EIS) of the oxide film was measured by an electrochemical workstation (CHI660C) in neutral 3.5wt.% NaCl solution. The anodic oxide film of 2195 aluminum alloy was successfully sealed by sol-gel pretreatment with LDH. After LDH pretreatment, the surface of the film layer was covered by a dense layer of LDH, and the porous structure and pore defects disappeared. The oxide film sealed with LDH pretreatment sol gel had a more even surface and lower roughness than that sealed with boiling water, with a contact Angle of 92.3° and hydrophobicity. The results of immersion test showed that after 15 days in 3.5wt.% NaCl solution, |Z|0.01 Hz could still reach 6.79×106 Ω.cm2. The film had good long-term corrosion resistance, because the double lamellar LiAl-LDH grew on the surface of the aluminum oxide film of LDH, and the surface film was denser. The lamellar structure prevented the invasion of the corrosion solution. At the same time, there were more —OH groups on the surface of the film, which provided more reaction sites when the sol-gel was closed, promoting the combination between the sol-gel coating and the matrix. As a result, the invasion of the outside solution to the matrix was effectively blocked and the corrosion was delayed. In conclusion, LDH pretreatment sol-gel sealing can improve the density and surface hydrophobicity of aluminum alloy anodized oxide film, and effectively improve the corrosion resistance of the film. |
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