| Zinc Electroplating Steel Sheet was widely used to protect the steel, specially prevented from the atmospheric corrosion. But in the moist environment, the galvanizing steel is easily corroded due to white products or changing color on the surface, which can affect the appearance of galvanized steel and decrease corrosion resistance. Chromate conversion coatings have been used widely to decrease the dissolution rate of zinc. However, the hexavalent chromium is a kind of extremely poisonous and carcinogenic material which has the mutagenic effect. To meet environmental friendly needs, the development and production of chromate-free pretreatment for zinc electroplating steel become more and more important.In the paper, inorganic/organic composite chromium-free passivating treatment was developed on the zinc electroplating steel sheet, which is nontoxic and non-polluted. Inorganic/resin, organic/single silane and organic/double silane compound handing system were preliminarily studied by the neutral salt spray test and electrochemical tests, and established inorganic/double silane composite passivating system as the main research system. The orthogonal experimental methods were used to determinate the formulation the inorganic/silane composite passivating system. And it was studied that the effects of coating thickness and curing temperature on the corrosion resistance of the treating coatings.Based on the experimental research and industrial production performance testing methods, the passivating film properties of inorganic/silane compound coating were tested. It was shown that silane compound coating is a dual-layer corrosion controlling process in electrochemical corrosion, with good heat resistance, alkali resistance and optimal paintability.The morphology of the inorganic/silane compound films was observed with Scanning Electron Microscope. The silane compound films are not micro-cracks, uniform and continuous on the surface morphology analysis, and surface crystallization from the layered structure into columnar structure. Passivation films can be observed in the section observation, the thickness is less than1μm.The characterization of the silane treating films was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS).The test results showed that silane treating films consisted mainly of organic functional groups including Si-OH, Si-O-Si, Si-O-Zn and other organic functional groups. |
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