| 摘要 |
A dipping composition for the treatment of a chromatized or passivated zinc or zinc alloy coating deposited on a steel substrate is disclosed. The composition comprises titanic, acid esters, titanium chelates or mixtures thereof, organo- functional polysiloxanes and a solvent selected from the group consisting of organic solvents, preferably alcohols and hydro- carbons, water and mixtures thereof. The weight ratio of titanic acid esters to polysiloxanes in the composition is from about 1:1 to about 1:4. Using the composition, a coating having thickness of, for example, 4 to 6 microns can be applied using a dipping process, which coating is subsequently dried at 80.degree.C and burnt in at up to 250.degree.C. The coating so obtained provides corrosion protection times at least 5 to 10 times longer than those which may be achieved without it. In particular, it can be used to improve the corrosion resistance and durability of chromatized coatings obtained using chromium III compounds, which chromatizing, normally less durable than that obtained using chromium VI com- pounds, is preferred because of its lesser environmental impact.
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