Phosphate-free Protective Nano-ceramic Coatings for Galvanized Steel Sheet with H_2O_2 Additive

摘要

Environmentally friendly anti-corrosion surface treatment reinforced by nano-ceramic metal oxide particles were developed as a protective layer for galvanized steel. The treatment bath is based on a nano-ceramic conversion coating composed of dilute hexafluorozirconic acid with small quantities of additive components containing H_2O_2. The corrosion resistance of treated substrate was compared to samples treated in phosphate conversion coating bath and in a hexafluorozirconic acid without the addition. The effect of other parameters such as pH solution and H_2O_2 concentration as oxidant on coating morphology were evaluated. Scanning electron microscopy/energy dispersive spectroscopy(SEM/EDS) was used to characterize the coating surface morphology. Utilizing DC polarization and salt spray test were performed on the treated substrate for studying the corrosion performance of the coatings. During surface examination, uniform distribution of Zr along the surface of all treated samples was observed. Results of corrosion tests showed that phosphate-free coating have a higher corrosion resistance than simple galvanized steel samples and provided long term corrosion performance comparable to that of phosphate.