PRELIMINARY METALLIZING TREATMENT OF ZINC SURFACES

The zinc- or zinc alloy coated surfaces, contact an aqueous solution (1) at up to 9 pH. In the novel process the solution (1) contains cations and/or compounds of a metal (A). The redox potential (Eredox) is measured at a metal (A) electrode, at given process temperature and cation concentration. In addition or alternatively, compounds of metal (A) in aqueous solution, are more anodic than the electrode potential (E Z n) of the zinc- (or zinc alloy-) coated steel surface in contact with aqueous medium (2). This solution (2), differs from solution (1) in that no cations and/or compounds of metal A are contained. The redox potential of cations and/or compounds of metal A in aqueous solution (1) is more anodic than the electrode potential E Z n of the zinc-coated steel surface in contact with aqueous solution (2). The difference is preferably +50 mV to +800 mV. The concentration of cations and/or compounds of metal A is preferably 0.001 M to 0.1 M. The metal A is iron, molybdenum, tungsten, cobalt, nickel, lead and/or tin. Iron(II) ions and/or iron(II) compounds especially, are used as cations and/or compounds of the metal A. The solution pH is preferably 2-4. It contains chelating complexing agents with oxygen- and/or nitrogen ligands. Examples detailed, include diverse ethanolamines, lower organic acids and their salts and stereoisomers. Further suitable polymer compounds are listed. The molar ratio of chelating agents to the concentration of cations and/or compounds of the metal A, preferably does not exceed 2 : 1, but is at least 1 : 5. Further details and variants of the process are included. Salient features include the used of accelerators in solution, e.g. oxoacids of phosphorus or nitrogen in specified states. Solution conditions are further elaborated. The solution contains preferably no more than 0.1 ppm of copper(II) cations. It includes tensides. The contact time between surface and solution is preferably in the range 1-10 s. The metal A is deposited to a thickness of preferably 1 - 50 mm/m 2>. Following contact, with or without rinsing and/or drying, the surface is passivated. Additional layers such as paints or paint systems are then added. Further layers are applied to the metal component made from the sheet, especially conversion layers and/or paints. An independent claim IS INCLUDED FOR the metal component produced from the treated sheet.