| Hot dip galvanized steel sheet has excellent processing and using property, when in the dry environment, hot dip galvanized steel sheet has the good performance of corrosion protection. It is used in various fields of industry, and it is the important products of iron and steel materials. In the air the 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.Hexavalent chromium in the chromate is a highly toxic, substances, it is carcinogenic, teratogenic, It can not only induce gene mutation, but also could 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 meet the requirement of international and get the entry card of the market, the development of chrome-free 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-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 sodium molybdate and phosphoric acid 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 the test of lead acetate, neutral salt spray test, scratch immersion experiment and electrochemistry test. The silanes composite could become blace after a long time. 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 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, characterized the molecular structure and chemical component of the silanes composite passive film. The weight of the silanes composite passive film is2.27g·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 AE=0.13; but the ability of silanes composite which resistance to water is poor. |
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