Preparation And Corrosion Resistance Of Fluorozirconate/C₉H₆INO₄S Composite Conversion Coating On Galvanized Steel

Because it is prone to white reust corrosion in the wet environment,galvanized layer must be treated.In order to enhance the corrosion resistance of galvanized steel,traditional chromate conversion treatment technology is usually adopted in industry.However,the world has prohibited the use cf chromate because of its high toxicity,which is harmful to human health and ecological balance.Therefore,the study of chromium-free conversion technology on galvanized steel has become a hot topic in contemporary world scientific research.In this paper,chromium-free conversion coating was prepared by using the conversion solution composed of the main salt-fluorozirconates,zinc organic corrosion inhibitors and auxiliary film-forming agents.The component of the conversion solution?K₂Zr F₆,C₉H₆IO₄S and H₃BO₃?and film formation conditions?p H,temperature and time?were studied by single factor experiment.The results showed that the optimumal film forming process is as follows:4g/L potassium fluorozirconate,0.06g/L7-iodine-8-hydroxy quinoline-5-sulfonic acid,3g/L boric acid,temperature of 35?,p H value of3.6 and reaction time of 30min.SEM,EDS,XPS,FT-IR,Tafel,EIS and NSS were adopted to analyze the morphology,elemental and matter compositions and corrosion resistance of the coating.The analysis results indicate that the compact and uniform conversion coating is an amorphous structure with a thickness about 8?m.The conversion coating,which is composed of elements of 0.02%C,10.10%O,4.83%F,73.98%Zn,10.89%Zr or of Zr F₄,Zr O₂ and zinc sulfonate complexes,made the corrosion potential of the sample increase by 71m V?from-1.252V to-1.181V?,the corrosion current reduce by 85.5%(from blank sample to 120h after treatment,the corrosion resistance of the galvanized steel has been greatly enhanced.