Chromium (VI)-free conversion layer and method for producing it
AssigneeSurTec International GmbH
InventorsPatricia Preikschat, Rolf Jansen, Peter Hulser
Life of this patent
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Abstract
A chromium(VI)-free, chromium(III)-containing and substantially coherent conversion layer on zinc or zinc alloys presenting, even in the absence of further components such as silicate, cerium, aluminum and borate, a corrosion protection of approx. 100 to 1000 h in the salt spray test according to DIN 50021 SS or ASTM B 117-73 until first attack according to DIN 50961 Chapter 10; being clear, transparent and substantially colorless and presenting multi-colored iridescence; having a layer thickness of approx. 100 nm to 1000 nm; and being hard, adhering well and being resistant to wiping.
Claims28
A chromium(VI)-free, chromium(III)-containing and substantially coherent conversion layer on zinc or zinc alloys, characterised in that
- even in the absence of further components such as silicate, cerium, aluminum and borate it presents a corrosion protection of approx. 100 to 1000 h in the salt spray test according to DIN 50021 SS or ASTM B 117-73 until first attack according to DIN 50961 Chapter 10;
- it is clear, transparent and essentially colorless and presents multi-colored iridescence;
- it has a layer thickness of approx. 100 nm to 1000 nm;
- and
- it is hard. adheres well and is resistant to wiping.
A method for producing chromium(VI)-free conversion layers affording at least the corrosion protection of conventional chromium(VI)-containing yellow chromations, wherein
- a metallic surface, in particular one of zinc or zinc alloys, in particular with iron, is treated with a solution of at least one chromium(III) complex and at least one salt characterised in that
- the concentration of the chromium(III) complex is increased in comparison with a conventional trivalent blue chromation;
- and/or
- a chromium(III) complex is used having ligand replacement kinetics more rapid than the fluoride replacement kinetics in chromium(III)-fluorocomplexes.
A concentrate for producing a passivation solution for surfaces of zinc or zinc alloys, in particular ones with iron, wherein it substantially contains chromium(III) for a passivating component, characterised in that
- the chromium(III) is present in the form of at least one complex having ligand replacement kinetics more rapid than the fluoride replacement kinetics in chromium(III)-fluorocomplexes.
A passivation bath for passivating metal surfaces, in particular ones of zinc, cadmium or aluminum, or alloys of these metals among each other and/or with other metals, in particular with iron, characterised in that
- it substantially contains chromium(III) as a passivating component, wherein chromium(III) is present in a concentration of approx. 5 to 100 g/l.
Dependencies are inferred from the claim text.