ANTICORROSION TREATMENT SOLUTION AND USES

Abstract

The present invention relates to a solution that is free of chromium in all its oxidising states, comprising: - at least one chemical oxidising compound, - at least one aluminium complexing agent, - at least one corrosion inhibiting compound, and -optionally, a chemical sealant compound, the solution having a pH in the range from 1 to 5. The present invention also relates to a method for treating a metal surface, comprising the application, on the surface, of a solution as defined above. The present invention additionally relates to a coating of a metal surface that can be obtained by the method for treating a metal surface as defined above, to a metal surface comprising the coating and to the use of the solution in an anti-corrosion treatment of a metal surface.

Claims

1. A solution free of chromium in all its oxidation states, comprising at least one oxidizing chemical compound, at least one aluminum-complexing agent, at least one corrosion-inhibiting compound, and optionally a plugging chemical compound, said solution having a pH ranging from 1 to 5.

2. The solution as claimed in claim 1, in which the oxidizing chemical compound is chosen from the group comprising permanganate salts, molybdate salts, persulfate salts and hydrogen peroxide.

3. The solution as claimed in claim 1, in which the complexing agent is chosen from fluorinated salts and mixtures thereof, organic compounds chosen from the group comprising gluconates, citrates, oxalates, acetates and formates and a mixture of at least one fluorinated salt and of at least one of said organic compounds.

4. The solution as claimed in claim 3, in which the complexing agent is a fluorinated salt chosen from hexafluorozirconates, hexafluorotitanates, hexafluorosilicates and a mixture thereof.

5. The solution as claimed in any one of the preceding claims, in which the corrosion inhibitor is chosen from rare-earth metal, tungstate, vanadate, phosphate and cerium(III) salts, zirconium, titanium or silicon salts.

6. The solution as claimed in any one of the preceding claims, also comprising a plugging chemical compound based on phosphate ions, phosphonate ions or polyphosphate ions or iron ions.

7. The solution as claimed in claim 6, in which: the concentration of permanganate ion is between 0.01 and 0.45 mol/L, the concentration of phosphate ion is between 0.001 and 0.20 mol/l, and the concentration of complexing agent is between 0.001 and 0.15 mol/L.

8. The solution as claimed in claim 6, in which: the chemical compound comprising permanganate ions is potassium permanganate, the chemical compound comprising phosphate ions is chosen from potassium hydrogen phosphate, phosphoric acid and an iron salt, and the complexing agent is a mixture of hexafluorozirconic acid, hexafluorotitanic acid and hexafluorosilicic acid.

9. A process for treating a metal surface, comprising the application to said surface of a solution as defined in any one of claims 1 to 8.

10. The process as claimed in claim 9, also comprising a step of pretreating said metal surface.

11. The process as claimed in claim 10, in which said pretreatment step successively comprises the following steps alkaline degreasing of the surface, nitric pickling of said surface and hydrofluoric pickling of said surface, or alkaline degreasing of said surface and ferric sulfo-nitro pickling of said surface, or alkaline degreasing of said surface and basic soda pickling of said surface optionally under an ultrasonic field.

12. The process as claimed in any one of claims 9 to 11, in which said metal surface consists of aluminum or is an aluminum alloy.

13. A coating of a metal surface that may be obtained via the process for treating a metal surface as defined in any one of claims 9 to 11.

14. A metal surface comprising a coating as defined in claim 13.

15. The use of a solution as defined in any one of claims 1 to 8, in an anticorrosion treatment of a metal surface.

Description

EXAMPLES OR EMBODIMENTS

Example 1: Preparation of a Chemical Conversion Solution of the Invention

[0090] The production of a chemical conversion solution consists in dissolving in water several potassium permanganate, potassium hydrogen phosphate, cerium nitrate and hexafluorozirconic acid salts in the following proportions: [0091] 1.5 to 75 g/L of potassium permanganate KMnO.sub.4, [0092] 5 to 30 g/L of potassium hydrogen phosphate KH.sub.2PO.sub.4, [0093] 1.4 to 27 ml/L of 50% hexafluorozirconic acid, [0094] 1 to 10 g/L of cerium(III) nitrate.

[0095] The preparation is performed at 60° C. with a dissolution time for all the salts of about 1 hour.

Example 2: Treatment of a Metal Surface Made of Aluminum or Alloy Using The Chemical Conversion Solution of the Invention

[0096] The protocol for treating a part made of aluminum or aluminum alloy is composed of several steps: [0097] immersion of the part for few minutes (2-6 minutes) in an alkaline degreasing bath which is chosen from the various solutions existing in a surface treatment workshop, [0098] rinsing in a rack plating bath and then in a bath of demineralized water, [0099] immersion of the part for a few minutes (2-6 minutes) in an acidic pickling bath of composition available in surface treatment (ST) workshops, [0100] rinsing in a rack plating bath and then in a bath of demineralized water, [0101] immersion in the chemical conversion bath which is the subject of the present invention for a time of between 2 and 10 minutes depending on the alloy to be treated, [0102] rinsing in a rack plating bath and then in a bath of demineralized water.

LIST OF REFERENCES

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