| Due to it’s excellent processing and using property, as well as the corrosion resistance in the dry environment, galvanized steel is used in various fields of industry, it is one of the important products of iron and steel materials. In the air of more than70%humidity, pure zinc is very easily corroded, on the galvanized surface it will form a chromate film of high chemical stability. This film is called passive film or conversion film, it can improve the corrosion resistance and increase surface gloss as well as antifouling. Hexavalent chromium in the chromate is a highly toxic, substances, it is carcinogenic, teratogenic, and also can induce gene mutation, so it had become a tremendous burden for the environment. In all of the world, the management and supervision of it are becoming more and more stringent. In order to sovle the polution problem of hexavalent chromium, meet the requirement of environmental protection and get the entry card of the market, the development of chrome-free passivation technology and the abandoning of the traditional chromate passivation technology had become the trend of the times in the area of metal passivation technology.A optimizing preparation technology of silanes composite passive film was obtained by orthogonal experiment on the hot-dip galvanized steel. KH-550and KH-560silanes, as the primary film-forming substances, were overlayed on hot-dip galvanized steel to produce a physical shielding film that could keep from corrosive substances. The silanes composite passive film was added to the fluorozirconate acid and vanadyl sulfate that play the role of the inhibitor。the film corrosion resistance benefited from the synergies of the shielding film and inhibitor improve.The corrosion resistance of the silanes composite passive film was tested by neutral salt spray test, scratch immersion experiment and electrochemistry test. The silanes composite passive film could endure neutral salt spray test for72h without any corrosion. The silanes composite passive film could increase the corrosion resistance of galvanized steel to protect from electrochemical corrosion reaction, because of the increasing impedance value and polarization resistance of the silanes composite passive film. The scratch immersion experiment confirmed the self-repairing performance of the silanes composite passive film. LSCM and SEM was tested to characterize the micro-morphology of the silanes composite passive film. The results show that the surface of the silanes composite passive film was complete, consecutive and compact. XRD, XPS, FTIR and rf-GD-OES characterized the molecular structure and chemical component of the silanes composite passive film. The weight of the silanes composite passive film is1.86g-m-2; The film could endure temperature200℃and20min without yellow stain; Adhesion of the silanes composite passive film passed grade1; The silanes composite passive film anti-finger print appeared△E=0.15; The average film surface resistance is0.19mΩ; The silanes composite passive film have good formability; The silanes composite passive film welding performance is excellent and could meet the A grade requirment in the " test method of spot welding zone".The research indicates that the forming process of silanes composite passive film consists of two phases:the first stage, after the hot-dip galvanized steel immersed in the silane composite solution, the inorganic and organic components in the solution adhere on the surface of galvanized steel rapidly, and fluorozirconate acid and galvanized steel react to form a passive film. When the galvanized steel was taken out from the solution, the surface of the galvanized steel will be attached by a hydrated adsorption layer with a certain thickness. The second stage, during the heat curing process, the water in the adsorption layer evaporated, the organic and inorganic film-forming composition in the adsorption layer attached to the surface of the galvanized steel in the way of physical adsorption or chemisorption and formed a passive film. In the heat curing process a series of chemical reactions happened in the zinc surface. That included the condensation reaction between silane and zinc surface hydroxyl, the hydroxyl condensation reaction between silane molecules and the polymerization between KH-560epoxy groups and KH-550amino. The chemical bond interconnection between silane molecules made the silane on the surface of galvanized steel form a dense and cross-linked silane film with a certain thickness, while the added inorganic corrosion inhibitor was coated in the film. The silanes composite passive film is so compact that it can protect from outside corrosive substances. When the silanes composite passive film was damaged the inorganic corrosion inhibitor could adsorb spontaneously on the breakage to repair the damage and reduce the corrosion rate.According to the characteristics of electrogalvanized steel, the preparation technology of the silanes composite passive film on the hot-dip galvanized steel was optimized to meet the electrogalvanized steel corrosion resistance needs. The result showed that the surface of the silanes composite passive film was complete, consecutive and compact on electrogalvanized steel. The silanes composite passive film could endure a neutral salt spray test for72h corrosion area less than5%. The scratch immersion experiment confirmed the self-repairing performance of the silanes composite passive film. It was verified by the electrochemical test that the silanes composite passive film had good corrosion resistance on electrogalvanized steel. Adhesion of the silanes composite passive film passed grade1; The result of T-bent test was IT; The film anti-finger print appeared△E=0.16; The film could endure temperature200℃and20min without yellow stain; The average film surface resistance is less than1mΩ.A optimizing preparation technology of the waterborne acrylic resin composite passive film was obtained by orthogonal experiment on the electrogalvanized steel. The resin composite passive film could endure a neutral salt spray test for72h corrosion area less than5%. It was verified by the electrochemical test that the resin composite passive film had good corrosion resistance on electrogalvanized steel. Adhesion of the resin composite passive film passed grade0; The result of T-bent test was1T; The resin composite passive film anti-finger print appearedd△E=0.15. The excellent performance of the resin composite passive film comes from the synergy of the different structural units of the resin composite passive film. In the process of the cured film, ammonium zirconium carbonate can induce the cross-linking reaction between hydroxyl and carboxyl groups in the molecular chain of the acrylic resin, it will form the interpenetrating network structure to improve the crosslink density and the compactness in the resin composite passive film, that will effectively stop the erosion from the external environment. When the resin composite passive film is broken, molybdate and phosphate will react with zinc and form the insoluble salts, and the adsorption of it on the breakage can play the role of corrosion inhibition and self-repairing. |
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