Wet on wet method and chrome-free acidic solution for the corrosion control treatment of steel surfaces

A process for anticorrosion treatment of bright metal surfaces, which are at least in part steel surfaces, comprising:

• 1) contacting metal surfaces that are not yet coated with an anticorrosion coating, said metal surfaces comprising at least one steel surface, with an acidic aqueous solution of a fluoro complex of at least one element M selected from the group consisting of B, Si, Ti, Zr and Hf;
• wherein:
• a) the aqueous solution comprises no more than 1 mg/l of organic polymer;
• b) the aqueous solution comprises 10 to 1000 mg/l of silicon in the form of silica particles with an average particle size of less than 1 μm,
• c) the aqueous solution comprises at least one component selected from the group consisting of:
• nitrate ions, copper ions, silver ions, vanadium ions, vanadate ions, bismuth ions, magnesium ions, zinc ions, manganese ions, cobalt ions, nickel ions, tin ions, a buffer system for the pH range from 2.5 to 5.5, aromatic carboxylic acids having at least two groups containing donor atoms, and derivatives of said carboxylic acids;
• 2) rinsing the metal surfaces after step 1);
• and
• 3) coating the metal surfaces with a cathodically depositable electro-dipcoating.

An acidic, chromium-free aqueous solution of a fluoro complex of at least one element M selected from the group consisting of B, Si, Ti, Zr and Hf, said aqueous solution having a pH value in the range from 2 to 5.5, and comprising:

• a) no more than 1 mg/l of organic polymer;
• b) 10 to 1000 mg/l of silicon in the form of silica particles with an average particle size of less than 1 μm;
• and
• c) one or more components selected from among:
• copper ions, silver ions, tin ions, bismuth ions, buffer systems for the pH range from 2.5 to 5.5, aromatic carboxylic acids with at least two groups containing donor atoms, and derivatives of said carboxylic acids.