METHOD FOR PASSIVATING AN ALUMINUM SURFACE PROVIDED WITH A FLUX

Abstract

A method is provided for passivating an aluminum surface. According to the method, the aluminum surface is provided with a flux. A passivation solution is subsequently applied to the aluminum surface, such that a passivation layer is created by reaction of the passivation solution with the aluminum surface, which is provided with the flux.

Claims

1. A method for passivating an aluminum surface provided with a flux, the method comprising: (a) providing the aluminum surface provided with the flux; and (b) applying a passivation solution to the aluminum surface provided in step (a), such that a passivation layer is created by reaction of the passivation solution with the aluminum surface, which is provided with the flux.

2. The method according to claim 1, wherein the aluminum surface is passivated with heating and pressurizing, typically in an autoclave, after the application of the passivation solution.

3. The method according to claim 2, wherein the aluminum surface is heated to a temperature of more than 100° C., typically of more than 120° C.

4. The method according to claim 2, wherein the aluminum surface is pressurized with a pressure of more than 1 bar and maximally 2 bar.

5. The method according to claim 1, wherein the flux provided in step (a) comprises or is potassium-aluminum fluoride.

6. The method according to claim 1, wherein the passivation solution applied in step (b) is produced by mixing a zirconium-silicate solution with a water glass dispersion.

7. The method according to claim 6, wherein the zirconium-silicate solution contains 0.1-5 g/L of zirconium silicate.

8. The method according to claim 6, wherein the zirconium-silicate solution is produced by dissolving zirconium carbonate in a sulfuric acid solution with a pH value of 2 to 6 and subsequent neutralizing with ammonia.

9. The method according to claim 6, wherein: the zirconium-silicate solution contains sebacic acid with a concentration of 0.1 to 2%, and/or the zirconium-silicate solution contains triethanolamine with a concentration of 0.05 to 0.5%.

10. The method according to claim 6, wherein: the zirconium-silicate solution contains at least one corrosion inhibitor with a share of 0.005 to 10% by weight, typically 0.01 to 2.0% by weight, and the at least one corrosion inhibitor comprises catechol-3,5-disulfonic acid disodium salt, diethylene triamine pentaacetic acid, 8-hydroxy-(7)-iodchinolin-sulfonic acid-(5), 8-hydroxy-chinolin-5-sulfonic acid, mannitol, 5-sulfosalicylic acid, aceto-O-hydroxamic acid, norepinephrine, 2-(3,4-dihydroxyphenyl)-ethylamine, L-3,4-dihydroxyphenylalanine (L-DOPA), 3-hydroxy-2-methyl-pyrane-4-on, citrates, carboxylates, in particular oxylates, alkali salts of stearate, formate, glyconat, sodium tetraborate, pyrophosphoric acid, and/or calcium gluconate.

11. The method according to claim 6, wherein the water glass dispersion contains water glass with a concentration of 5 to 25%.

12. The method according to claim 6, wherein the water glass dispersion contains calcium gluconate with a concentration of 0.5 to 2%.

13. The method according to claim 1, wherein the passivation solution applied in step (b) contains hexafluorozirconic acid.

14. The method according to claim 1, wherein the passivation solution applied in step (b) contains polyurethane dispersions and/or ammonium vanadates.

15. The method according to claim 1, wherein the aluminum surface provided in step (a) is part of a heat exchanger, which comprises a plurality of components made of aluminum, which are connected to one another with at least one soldered joint, typically with at least one brazed joint.

16. The method according to claim 6, wherein the zirconium-silicate solution contains tartaric acid.

17. The method according to claim 1, wherein the passivation solution contains tartaric acid, in particular 5 to 30 grams of tartaric acid per liter of passivation solution.

18. A heat exchanger comprising: a plurality of components made of aluminum, which are connected to one another with at least one soldered joint, typically with at least one brazed joint, wherein the aluminum surface of at least one component is passivated with the method according to claim 1.

19. A motor vehicle comprising a heat exchanger according to claim 18.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The disclosure will now be described with reference to the drawings wherein:

[0031] FIG. 1 shows a heat exchanger according to an exemplary embodiment of the disclosure.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0032] FIG. 1 shows a simplified illustration of a heat exchanger 1 according to an exemplary embodiment of the disclosure, in particular for an electric motor vehicle. The heat exchanger 1 comprises a plurality of tubular bodies 2, which extend along a longitudinal direction L and through which a coolant K can flow. Along a stack direction S perpendicular to the longitudinal direction L, the tubular bodies 2 are arranged at a distance from one another. In the exemplary embodiment shown in FIG. 1, 16 tubular bodies 2 are shown in an exemplary manner. It goes without saying that a different number of tubular bodies 2 is also possible in alternatives.

[0033] The tubular bodies 2 are fluidically connected to a coolant distributor 4 for distributing the coolant K to the tubular bodies 2, and to a coolant collector 5 for collecting the coolant after the flow-through of the tubular bodies 2. For this purpose, the coolant distributor 4 and the coolant collector 5 have slots 4a, 5a for receiving the longitudinal ends 2b of the tubular bodies 2.

[0034] The coolant distributor 4 and the coolant collector 5 are arranged in the region of longitudinal ends 2b of the tubular bodies 2, which are located opposite one another along the longitudinal direction L. A rib structure 2a comprising ribs for guiding the coolant is provided in the tubular bodies 2, at which rib structure the inner surfaces of the tube walls of the tubular bodies 2 are furthermore supported.

[0035] Fluid paths 3 for being flown through with a gas G, in particular charge air, are formed with intermediate spaces provided between the tubular bodies 2 along the stack direction S. A rib structure 3a (not completely shown in FIG. 1 for the sake of clarity), which comprises ribs for guiding the gas G and on which the outer sides of the tube walls of the tubular bodies 2 adjoining in the stack direction S are furthermore supported, is provided in the fluid paths 3.

[0036] The components of the heat exchanger 1, in the exemplary embodiment shown in FIG. 1, which are the tubular body 2, the rib structures 2a, 3a, the coolant distributor 4, and the coolant collector 5, comprise aluminum as material or consist of aluminum.

[0037] As part of the production of the heat exchanger 1, these individual components of the heat exchanger 1 are soldered to one another, namely brazed, at respective contact points 10 by using potassium-aluminum fluoride as flux, and are thus connected to one another with a substance-to-substance bond. Alternatively to potassium-aluminum fluoride, a different flux containing fluorides can also be used.

[0038] Said contact points 10 exist between the respective tubular bodies 2 and the coolant distributor 4 as well as the coolant collector 5, because the tubular bodies 3 are brazed to the coolant distributor 4 as well as to the coolant collector 5. Due to the fact that the rib structures 2a, 3a are brazed to the tubular bodies 3, such contact points 10 are also provided between the rib structures 3a and the tubular bodies 3.

[0039] The method according to the disclosure will be described below using the example of the heat exchanger 1:

[0040] After the brazing of the above-mentioned aluminum components of the heat exchanger 1—by using a flux—these components are provided for the method according to the disclosure. This means that the aluminum surfaces of said components are also provided in the region of the contact points 11. Due to the fact that coolant flows through the tubular bodies 3 comprising the rib structures 3a as well as the coolant distributor 4 and the coolant collector 5 during the operation of the heat exchanger 1, so that the coolant comes into contact with the aluminum surface, the aluminum surface is passivated with the method according to the disclosure.

[0041] For this purpose, a passivation solution is applied to the provided aluminum surfaces, so that a passivation layer is created by reaction of the passivation solution with the aluminum surfaces, which are provided with the flux. In the exemplary embodiment of the heat exchanger 1, this can be attained with introduction of the passivation solution into the coolant distributor 4, into the tubular bodies 2, and into the coolant collector 5.

[0042] The passivation solution is produced with mixing a zirconium-silicate solution with a water glass dispersion.

[0043] The zirconium-silicate solution contains 0.1-5 g/L of zirconium silicate. The zirconium-silicate solution is produced with dissolving zirconium carbonate in a sulfuric acid solution with a pH value of 2 to 6, subsequent neutralizing with ammonia. Alternatively to the zirconium-silicate solution, a solution of a different fluoride-complexing element, such as, for example, lanthanum, can also be used.

[0044] The zirconium-silicate solution can furthermore also contain sebacic acid with a concentration of 0.1 to 2% and, in the alternative or in addition, triethanolamine with a concentration of 0.05 to 0.5%. It is also conceivable that the zirconium-silicate solution contains other dicarboxylic acids, such as, for example, tartaric acid.

[0045] The passivation solution can contain tartaric acid. The passivation solution can contain, for example, 3 to 5 grams of tartaric acid per liter of passivation solution.

[0046] The zirconium-silicate solution additionally contains the corrosion inhibitor catechol-3,5-disulfonic acid disodium salt with a share of 0.01 to 2.0% by weight. It is also conceivable, however, that the zirconium-silicate solution, in the alternative or in addition, contains one or several of the substances disodium salt, diethylene triamine pentaacetic acid, 8-hydroxy-(7)-iodchinolin-sulfonic acid-(5), 8-hydroxy-chinolin-5-sulfonic acid, mannitol, 5-sulfosalicylic acid, aceto-O-hydroxamic acid, norepinephrine, 2-(3,4-dihydroxyphenyl)-ethylamine, L-3,4-dihydroxyphenylalanine (L-DOPA), 3-hydroxy-2-methyl-pyrane-4-on, citrates, carboxylates, in particular oxylates, alkali salts of stearate, formate, glyconat, sodium tetraborate, pyrophosphoric acid, or calcium gluconate.

[0047] The water glass dispersion contains water glass with a concentration of 5 to 25%. The water glass can thereby be sodium silicate, lithium water glass, or potassium water glass. The water glass dispersion furthermore contains calcium gluconate with a concentration of 0.5 to 2%.

[0048] The passivation solution can also contain hexafluorozirconic acid. It is also conceivable that the passivation solution contains polyurethane dispersions. The passivation solution can also contain ammonium vanadates.

[0049] After the application of the passivation solution, the heat exchanger is introduced into an autoclave, and the aluminum surfaces, which are provided with the flux, are passivated with heating and pressurization. The aluminum surfaces are thereby heated to a temperature of more than 120° C. The aluminum surfaces are furthermore pressurized with a pressure of more than 1 bar and maximally 2 bar.

[0050] Other aluminum surfaces, which are provided with flux, can likewise be passivated in the above-specified manner.

[0051] It is understood that the foregoing description is that of the exemplary embodiments of the disclosure and that various changes and modifications may be made thereto without departing from the spirit and scope of the disclosure as defined in the appended claims.