Method for coating metallic surfaces with a mixture containing at least two silanes

A process for coating a metallic surface that is clean, pickled, cleaned or pretreated or the metallic surface treated by any combination of cleaning, pickling and pre-treatment, with an aqueous, also comprising, if desired, organic solvent and other components, which is substantially or entirely free from chromium (VI) compounds, for the purpose of pretreatment prior to a further coating or for treatment, wherein said aqueous composition consists essentially of

• water;
• at least one hydrolyzable or at least partly hydrolyzed fluorine-free silane;
• at least one of a hydrolyzable or at least partly hydrolyzed fluorine-containing silane;
• and
• a film former comprising at least one of a monomer, oligomer, polymer or copolymer;
• wherein the ratio of component d) to silanes a) and b) in the composition range from 0.1:1 to 10:1,
• wherein the silanes a) and b) are water-soluble or become water-soluble by virtue of hydrolysis reactions or by chemical reactions prior to application to the metallic surface, wherein the fluorine free silane comprises at least one fluorine-free organosilane and at least one fluorine-free organofunctional silane, and wherein the fluorine-containing silane is at least one fluorine-containing organosilane;
• as said fluorine containing silane,
• said process comprising contacting the clean, pickled, cleaned or pretreated or the metallic surface treated by any combination of cleaning, pickling and pre-treatment with the aqueous composition to form an anticorrosive on the metallic surface and subsequently drying and, optionally curing the anticorrosive film,
• wherein the dried and optionally cured, anticorrosive film has a thickness in the range from 0.001 to 10 μm, wherein the hydrolyzed fluorine-free silane is selected from the group consisting of functional trialkoxysilane, aminosilane, ureidosilane, or a vinylsilane with bis-trialkoxysilane.