WET ON WET METHOD AND CHROME-FREE ACIDIC SOLUTION FOR THE CORROSION CONTROL TREATMENT OF STEEL SURFACES

Anticorrosion treatment of bare metal surface, (partly) of steel, by contacting with acid aqueous solution (I) of boron, silicon, titanium, zirconium and/or hafnium fluoro-complex, rinsing with water and cathodic coating with electrodeposition paint uses (I) containing (a) not > 1 mg/l allyl- or vinyl-amine polymer and (b) nitrate, copper, silver, vanadium or vanadate, bismuth, magnesium, zinc, manganese, cobalt, nickel and/or tin ions, pH 2.5-5.5 buffer system, aromatic carboxylic acid (derivative) with not less than 2 groups containing donor atoms and/or sub-micron silica particles in wet-on-wet method. In corrosion protection treatment of bare metal surface, (partly) of steel, by contacting with an acid aqueous solution (I) of a fluoro-complex (II) of boron (B), silicon (Si), titanium (Ti), zirconium (Zr) and/or hafnium (Hf), rinsing with water and then cathodic coating with electrodeposition paint (III), (I) contains (a) not > 1 mg/l organic polymer with allylamine or vinylamine monomers and (b) component(s) selected from nitrate, copper, silver, vanadium or vanadate, bismuth (Bi), magnesium, zinc, manganese, cobalt, nickel and tin ions, buffer systems (IV) for pH 2.5-5.5, aromatic carboxylic acids (VA) with not less than 2 groups containing donor atoms or their derivatives (VB) and silica particles with an average particle size below 1 mu m; and (c) the metal surface is not dried after contact with (I) and before coating with (III). An independent claim is included for acid, chromium-free aqueous solution (IA) of a fluoro-complex (II) of element(s) M, selected from B, Si, Ti, Zr and Hf, with pH 2-5.5 for treating metal surfaces, which also contains other component(s) selected from tin ions, Bi ions, (IV), (VA) and (VB).