| In this thesis,anodic oxide film with good corrosion resistance and adhesion was prepared on 6061 aluminium alloy surface by anodic oxidation method.The process conditions of phytic acid-sulfuric acid anodic oxidation were studied.The anodic oxide film was sealed by different sealing methods.The optimum sealing conditions were determined.The influence of the content of polyurethane modified acrylic resin(GS-58)in the electrolyte solution on the properties of the composite anodized film was discussed.A new passivation pretreatment process for aluminium and aluminium alloys based on aluminium anodization was designed,and its application test was carried out.The main research contents and results of this thesis were as follows:(1)An anodic oxide film was prepared on the surface of 6061 aluminum alloy by using an anodic oxidation method using a mixture of phytic acid and sulfuric acid as an electrolyte solution.The effects of oxidation voltage,oxidation time,oxidation temperature and electrolyte ratio on the performance of anodized film(corrosion resistance,adhesion,etc.)during anodizing were studied.The surface morphology and chemical composition of the oxide film were characterized by SEM and EDS.The optimum process conditions of phytic acid-sulfuric acid anodizing process were determined by experiments.The results show that the surface of phytic acid-sulfuric acid anodic oxide film has a small number of holes,which was conducive to the improvement of its corrosion resistance;In the neutral salt spray test,the corrosion resistance time was 168h;In the drip alkali corrosion test,the corrosion resistance time was 1.2min;In the pitting corrosion test of copper sulfate,the corrosion resistance time was 26min;In the adhesion test,the adhesion grade of the paint film was 1;The optimum process parameters of phytic acid-sulfuric acid anodization were obtained by experiment:oxidation voltage 18V,oxidation temperature 38~o C,oxidation time 20min,and the mass ratio of sulfuric acid to phytic acid in the electrolyte solution is 2.(2)The anodized film prepared by phytic acid-sulfuric acid anodizing process was sealed with hot water,nickel cobalt salt and cerium nitrate respectively.The surface morphology of the anodic oxide film after sealing treatment was characterized by SEM.The effects of different sealing treatment methods on the performance of the anodic oxide film were studied,and the sealing treatment process of phytic acid-sulfuric acid anodic oxide film was optimized.The results show that the surface of the anodized film prepared by phytic acid-sulfuric acid anodizing process was irregularly pitted after being sealed by hot water,after the nickel-cobalt salt was blocked,the surface of the film was covered by granular crystals,and the pores were reduced,after the cerium nitrate sealing treatment,crystal particle clusters appeared on the surface of the membrane;The corrosion resistance of the anodized film was improved after each sealing treatment,and the optimal time of hot water sealing treatment is 20min,and the optimal time of nickel-cobalt salt sealing treatment is25min,the optimum time of cerium nitrate sealing treatment is 25min.Among them,the corrosion resistance of the anodic oxide film after cerium nitrate sealing treatment was the best.In the pitting corrosion test of copper sulfate,the corrosion resistance time was 44min;In the adhesion test,the adhesion of the anodized film changed little after each sealing treatment,and the sealing treatment did not improve the adhesion of the oxide film layer,but only improved its corrosion resistance.(3)Based on the phytic acid-sulfuric acid anodizing process,a polyurethane modified acrylic resin(GS-58)was added to the electrolyte solution,and a series of anodized films were prepared on the surface of 6061 aluminum alloy by anodic oxidation.The composite system of phytic acid-sulfuric acid-polyurethane modified acrylic resin was studied.The surface morphology of composite anodized oxide film was characterized by SEM;The effects of different electrolyte solutions on the properties of composite anodic oxide films(corrosion resistance,adhesion,etc.)were investigated.The results show that with the increase of the content of polyurethane modified acrylic resin in the electrolyte solution,the resin particles gradually appear on the surface of the composite anodized film,and form an uneven adhesive cover finally;In the alkali corrosion test,the corrosion resistance time of phytic acid-sulfuric acid-polyurethane modified acrylic resin composite anodized film was2.6min;In the copper sulfate pitting test,the corrosion resistance time of film was 35min;In the paint adhesion test,the film adhesion level was 0,compared with the phytic acid-sulfuric acid anodic oxide film,the adhesion is greatly improved.The optimum process parameters of phytic acid-sulfuric acid-polyurethane modified acrylic resin anodizing were determined by experiments:oxidation voltage 18V,oxidation temperature 40~o C,oxidation time 20min,sulfuric acid 20g,phytic acid10g,polyurethane modified acrylic resin 15g.(4)A new type of aluminum and aluminum alloy passivation pretreatment process based on aluminum anodizing was designed and applied experimentally.The results show that the passivation film obtained by the new passivation pretreatment process for aluminium and aluminium alloys is uniform and colorful,the adhesion grade of passivation film was 0 in the paint adhesion test,the pressure cooker boiling test level was 0.In the neutral salt spray test,the new passivation film salt spray corrosiontimeandthesaltspraycorrosionresistancetimeofthe chromium-containing passivation film was 168h,which was longer than that of Khmet passivation film for 5h,BYG507 passivation film for 5h and manganese chromium-free passivation film for 24h on the market.In the copper sulfate pitting test,the corrosion resistance of the new passivation film is several times higher than that of the conventional chromium or chromium-free passivation film,showing excellent corrosion resistance and can meet certain market application requirements.The reagents used in the new aluminum and aluminum alloy passivation pretreatment process are phytic acid and sulfuric acid,chemical poisons such as fluorine ions,hexavalent chromium and other heavy metals are not used,which eliminates environmental pollution and uses low voltage,low current,electrolytic film formation at room temperature,film stability,economical;Passivation film is continuous,uniform,and color,easy to monitor in real time in actual production;This new aluminium and aluminium alloy passivation pretreatment process,which combines degreasing,washing and passivation in traditional process into one process,greatly simplifies the production process,improves production efficiency,reduces water consumption and wastewater discharge,energy saving and environmental protection,has a good application prospect. |
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