Composition and method for the chromium-free pretreatment of aluminium surfaces

Abstract

Described herein is an aqueous, chromium-free composition for a pretreatment of aluminum surfaces, which includes at least one water-soluble phosphorus compound, at least one water-soluble zirconium compound, at least one water-soluble titanium compound, and at least one water-soluble molybdenum compound, a phosphorus compound content being in a range from 15 to 50 mg/l (calculated as phosphorus), a zirconium compound content being in a range from 400 to 600 mg/l (calculated as metal), a titanium compound content being in a range from 85 to 400 mg/l (calculated as metal), and a molybdenum compound content being in a range from 40 to 150 mg/l (calculated as metal). Also described herein are a corresponding method and a correspondingly pretreated component or strip.

Claims

1. An aqueous, chromium-free composition for a pretreatment of aluminum surfaces, which comprises at least one water-soluble phosphorus compound, at least one water-soluble zirconium compound, at least one water-soluble titanium compound, and at least one water-soluble molybdenum compound, a phosphorus compound content being in a range from 25 to 40 mg/l calculated as phosphorus, a zirconium compound content being in a range from 400 to 600 mg/l calculated as metal, a titanium compound content being in a range from 200 to 400 mg/l calculated as metal, and a molybdenum compound content being in a range from 40 to 150 mg/l calculated as metal, the aqueous composition having a pH at room temperature in a range from 2.0 to 5.0.

2. The aqueous composition according to claim 1, wherein the zirconium compound content is in a range from 450 to 540 mg/l calculated as metal, and the molybdenum compound content is in a range from 60 to 130 mg/l calculated as metal.

3. The aqueous composition according to claim 1, wherein a ratio of the individual phosphorus compound, zirconium compound, titanium compound, and molybdenum compound contents is in a range of (0.04 to 0.40):(1.4 to 5.8):1.0:(0.10 to 1.4) standardized to the titanium compound content.

4. The aqueous composition according to claim 1, further comprising free fluoride, wherein a free fluoride content is in a range from 40 to 100 mg/l, a total fluorine content is in a range from 1 to 2 g/l, the at least one zirconium compound comprises hexafluorozirconium acid, and the at least one titanium compound comprises hexafluorotitanic acid.

5. The aqueous composition according to claim 1, wherein the aqueous composition has a pH in a range from 3.0 to 4.0, free acid points in a range from 3.9 to 4.5, and total acid points of not more than 25.

6. The aqueous composition according to claim 1, which comprises in total not more than 1 mg/l of organic polymer.

7. The aqueous composition according to claim 1, which comprises not more than 300 mg/l of aluminum.

8. The aqueous composition according to claim 1, which comprises in total not more than 20 mg/l of elements selected from the group consisting of As, Ba, Cd, Co, Cu, Mn, Ni, Pb, Sb, Sn, Sr, V, and Ce.

9. The aqueous composition according to claim 1, wherein the phosphorus compound content is in a range from 30 to 38 mg/l calculated as phosphorus, the zirconium compound content is in a range from 470 to 520 mg/l calculated as metal, the titanium compound content is in a range from 350 to 380 mg/l calculated as metal, and the molybdenum compound content is in a range from 80 to 125 mg/l calculated as metal.

10. The aqueous composition according to claim 1, wherein a ratio of the individual phosphorus compound, zirconium compound, titanium compound, and molybdenum compound contents is in a range of (0.06 to 0.25):(1.4 to 3.5):1.0:(0.15 to 0.9) standardized to the titanium compound content.

11. The aqueous composition according to claim 1, which comprises in total not more than 0.5 mg/l of organic polymer.

12. A concentrate wherefrom by dilution with a suitable solvent and optionally adjustment of a pH with a suitable acid or base, an aqueous composition according to claim 1 is obtainable.

13. A method for a substantially chromium-free pretreatment of aluminum surfaces, which comprises contacting an optionally cleaned and rinsed surface consisting at least partly of aluminum or an aluminum alloy with an aqueous composition according to claim 1 and then optionally carrying out rinsing and/or drying.

14. The method according to claim 13, wherein the surface is contacted with the aqueous composition such as to result in a phosphorus addon calculated as P.sub.2O.sub.5 in a range from 8 to 17 mg/m.sup.2, a zirconium addon in a range from 1 to 6 mg/m.sup.2, a titanium addon in a range from 7 to 19 mg/m.sup.2, and a molybdenum addon in a range from 6 to 18 mg/m.sup.2, on the surface.

15. The method according to claim 13, wherein the surface is a surface of a strip and the surface is immersed in the aqueous composition for 5 to 10 seconds at 50 to 55° C.

16. The method according to claim 13, wherein the surface is first of all cleaned alkalinically or alkalinically and acidically, then thoroughly rinsed with water, and immersed in the aqueous composition.

17. A component or strip with a surface consisting at least partly of aluminum or an aluminum alloy, which is obtainable with a method according to claim 13 and optionally has been coated.

18. The component or strip according to claim 17, wherein its surface has a phosphorus addon calculated as P.sub.2O.sub.5 in a range from 8 to 17 mg/m.sup.2, a zirconium addon in a range from 1 to 6 mg/m.sup.2, a titanium addon in a range from 7 to 19 mg/m.sup.2, and a molybdenum addon in a range from 6 to 18 mg/m.sup.2.

19. The method according to claim 13, wherein the surface is first of all cleaned alkalinically or alkalinically and acidically, then thoroughly rinsed with water in a plurality of stages, and immersed in the aqueous composition.

20. A concentrate wherefrom by dilution with water and optionally adjustment of a pH with a suitable acid or base, an aqueous composition according to claim 1 is obtainable.

Description

EXAMPLES

(1) The inventive compositions IE1 to IE6 and also the noninventive compositions CE1 to CE4, as apparent from tab. 1, were produced as follows:

(2) First of all, an aqueous, acidic solution of a phosphorus compound was prepared. Solid ammonium heptamolybdate was added to this solution and dissolved. Next, the solution was rounded out with zirconium fluoride and titanium fluoride compounds, likewise present in aqueous solution.

(3) TABLE-US-00001 TABLE 1 X compound content in mg/l (Comp.) Ex. X = P Zr Ti Mo IE1 35 513 356 81 IE2 35 513 356 122 IE3 20 513 173 41 IE4 17 513 356 91 IE5 35 513 89 122 IE6 35 513 167 81 CE1 0 513 176 122 CE2 35 513 0 41 CE3 0 513 0 82

(4) Subsequently in each case an aluminum sheet cleaned alkalinically beforehand was immersed for 5 seconds at 50° C. in the corresponding composition, and was rinsed and dried.

(5) The addons of phosphorus (as P.sub.2O.sub.5), zirconium, titanium, and molybdenum were each determined by X-ray fluorescence (XRF) analysis (see tab. 2).

(6) The sheets were subsequently coated with a polyamino resin combination, using a 30 μm doctor blade. The coating material was then baked in an oven at 250° C. (max. temperature of sheets: 224° C.) for 45 seconds, to give a coating film thickness of 7 μm.

(7) In order to determine the coating adhesion on the respective aluminum sheet, two tests were conducted: a DIN EN 13523-7 T-bend test and a DIN EN ISO 2409 cross-cut test. These tests furnished the coating delamination values evident from tab. 2. The lower the value in question, the better the coating adhesion.

(8) TABLE-US-00002 TABLE 2 Coating delamination in test Addon of X in mg/m.sup.2 Y in % (Comp.) X = Y = T-bend Y = cross-cut Ex. P.sub.2O.sub.5 Zr Ti Mo test test IE1 14-15 2 15-16 13-14 2 0 IE2 11-14 2 11-13 11-13 2 0 IE3 11 5-6 11-12 8 2 2.5 IE4 11-12 4 18-19 10-11 8 0 IE5 12-15 4-5  8-10 13-14 9 0 IE6 16-17 2 13-14 17-18 7 2.5 CE1 <2 14-16 22-25 25-30 30 47.5 CE2  8-11  7-10 2  6-10 25 50 CE3 <2 22-27 2 16-25 51 82.5

(9) The significantly lower coating delamination (improved coating adhesion) in the case of the inventive compositions IE1 to IE6 by comparison with the noninventive compositions CE1 to CE3 in both the T-bend test and the cross-cut test is clearly apparent. The best results here are furnished by IE1 and IE2.