Method for passivating aluminum surfaces with flux - Patents.com

Abstract

To provide a method for passivating an aluminum surface having flux.SOLUTION: According to the method, an aluminum surface having flux is provided, and then a passivation solution is applied to the supplied aluminum surface. Consequently, a reaction between the passivation solution and the aluminum surface supplied with the flux forms a passive layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for passivating an aluminum surface with a flux. The present invention further relates to a heat exchanger manufactured by carrying out this method. The present invention further relates to a motor vehicle equipped with such a heat exchanger. [Background technology]

[0002] It is known that fluxes are used to braze aluminum parts. For example, heat exchangers can be made of aluminum and include components that are connected to each other by brazing during the manufacture of the heat exchanger. Automotive heat exchangers are typically brazed by the so-called CAB soldering method (controlled atmosphere brazing), which uses potassium aluminum fluoride as the flux. Summary of the Invention [Problem to be solved by the invention]

[0003] However, the fluoride-free nature of this flux can lead to aluminum corrosion. Furthermore, the fluoride-free nature of the flux can corrode the additives of the coolant received in the heat exchanger, resulting in the formation of large amounts of aluminum hydroxide, which can block or even close the coolant path in the heat exchanger. Due to the aluminum hydroxide formed, the electrical conductivity of the coolant can additionally increase, causing dangerous charges to be distributed to the vehicle through the cooling cycle that guides the coolant, or in the case of aqueous coolants, water electrolysis with the formation of explosive gases. This occurs particularly in electric vehicles that include fuel cells, such as hydrogen fuel cells or metal-air fuel cells.

[0004] The object of the present invention is to provide an improved or at least alternative method for passivating aluminum surfaces with flux, taking into account the above-mentioned problems. Aluminum components with high corrosion resistance should in particular be produced by such a method. [Means for solving the problem]

[0005] According to the invention, this object is solved by the subject matter of the independent claims. Preferred and further advantageous embodiments are the subject matter of the dependent claims.

[0006] The basic idea of ​​the present invention is therefore to combine the flux residues present on the aluminum surface after the soldering process with a passivating solution, thereby preventing the flux residues from interacting with the coolant guided through the heat exchanger during operation and, in addition, creating a corrosion-resistant passivation layer in the area of ​​the aluminum surface. In this way, a particularly low electrical conductivity of the coolant received in the heat exchanger, in particular less than 50 μS / cm or even less than 20 μS / cm, is achieved, and the formation of explosive gases in the coolant is avoided. Furthermore, a compact, passivated, corrosion-resistant aluminum surface is created. Therefore, complex removal of flux and soldering residues, which can lead to defects, is not required.

[0007] The method according to the invention serves to passivate an aluminum surface that has been provided with a flux, by which the aluminum surface is provided with a flux, and then a passivating solution is applied to the provided aluminum surface, so that a passivating layer is formed by reaction of the passivating solution with the provided aluminum surface.

[0008] Advantageously, after application of the passivating solution, the aluminum surface is passivated by heating and pressure, preferably in an autoclave, so that the reaction of the passivating solution with the flux-bearing aluminum surface is particularly effective, resulting in the formation of a particularly compact and therefore corrosion-resistant passivating layer.

[0009] According to a preferred embodiment, the aluminum surface is heated to a temperature above 100° C., preferably above 120° C. In this embodiment, the reaction of the passivating solution with the flux-carrying aluminum surface also takes place particularly effectively, resulting in the formation of a particularly compact and corrosion-resistant passivating layer.

[0010] The same applies to a further preferred embodiment in which the aluminum surface is pressurized with a pressure of more than 1 bar, up to a maximum of 2 bar. In this way, the reaction of the passivating solution with the flux-bearing aluminum surface also takes place particularly well, resulting in the formation of a particularly compact, corrosion-resistant passivation layer.

[0011] According to an advantageous embodiment, the flux provided is or comprises potassium aluminum fluoride, in which case a particularly compact passivation layer is formed in the region of the aluminum surface.

[0012] The passivation solution applied is preferably prepared by mixing a zirconium solution with a waterglass dispersion, in which case a particularly large amount of flux is bonded to the aluminum surface, forming a particularly compact and corrosion-resistant passivation layer in the area of ​​the aluminum surface.

[0013] According to a preferred embodiment, the zirconium silicate solution contains 0.1 g / L to 5 g / L of zirconium silicate, in which case a particularly large amount of flux is bonded to the aluminum surface, forming a particularly compact and corrosion-resistant passivation in the area of ​​the aluminum surface.

[0014] J The zirconium solution is preferably prepared by dissolving zirconium carbonate in a sulfuric acid solution with a pH value of 2 to 6, followed by neutralization with ammonia. In this way, a particularly large amount of flux is bonded to the aluminum surface, and a particularly compact, corrosion-resistant passivation layer is formed in this area.

[0015] According to a further preferred embodiment, the zirconium silicate solution contains sebacic acid in a concentration of 0.1 to 2%.

[0016] The zirconium silicate solution may further contain sebacic acid at a concentration of 0.1 to 2% and alternatively or additionally triethanolamine at a concentration of 0.05 to 0.5%. It is also contemplated that the zirconium silicate solution may contain other dicarboxylic acids, such as tartaric acid.

[0017] In a further preferred embodiment, the passivation solution contains tartaric acid. The passivation solution particularly preferably contains 3 to 5 grams of tartaric acid per liter of passivation solution. Such passivation solutions are particularly effective.

[0018] According to a further preferred embodiment, the zirconium silicate solution contains triethanolamine in a concentration of 0.05-0.5%. These two measures, alone or in combination, allow particularly large amounts of flux to be bound to the aluminum surface, forming a particularly compact and therefore corrosion-resistant passivation layer in the area of ​​the aluminum surface.

[0019] The zirconium silicate solution advantageously comprises at least one corrosion inhibitor with a share of 0.005 to 10% by weight, preferably 0.01 to 2.0% by weight, wherein the at least one corrosion inhibitor is selected from the group consisting of catechol-3,5-disulfonic acid disodium salt, diethylenetriaminepentaacetic acid, 8-hydroxy-(7)-iodoquinoline-sulfonic acid-(5), 8-hydroxy-quinoline-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-pyran-4-one, citrates, carboxylates, in particular oxalates, alkali salts of stearic acid, alkali salts of formic acid, alkali glyconates, sodium tetraborate, and pyrophosphate, or alternatively or additionally calcium gluconate. This embodiment forms a particularly corrosion-resistant passivation layer.

[0020] It is particularly preferred that the water glass dispersion contains water glass in a concentration of 5 to 25%. In this way, particularly large amounts of the flux are also bonded to the aluminum surface, creating a particularly compact, corrosion-resistant passivation layer in the area of ​​the aluminum surface.

[0021] According to a preferred embodiment, the waterglass dispersion contains calcium gluconate in a concentration of 0.5-2%. In this way, particularly large amounts of flux are also bonded to the aluminum surface, creating a particularly compact and corrosion-resistant passivation layer in this area.

[0022] According to an advantageous embodiment, the applied passivation solution contains hexafluorozirconate, and in this way particularly large amounts of flux also bond to the aluminum surface, creating in this region a particularly compact and corrosion-resistant passivation layer.

[0023] According to a further advantageous embodiment, the applied passivation solution contains ammonium vanadate instead of or in addition to the polyurethane dispersion. In this way, particularly large amounts of the flux also bond to the aluminum surface, creating a particularly compact and corrosion-resistant passivation layer in the area of ​​the aluminum surface.

[0024] Advantageously, the provided aluminum surface is part of a heat exchanger comprising several aluminum components connected to one another by at least one soldered joint, preferably by at least one brazed joint, so that the aluminum surface can be passivated easily and efficiently by introducing the passivating solution into the heat exchanger.

[0025] The invention further relates to a heat exchanger comprising several components made of aluminum connected to one another by at least one soldered joint, preferably by at least one brazed joint, the aluminum surface of at least one component being passivated by the method according to the invention, so that the above-mentioned advantages of the method according to the invention also apply to the heat exchanger according to the invention.

[0026] The invention further relates to a motor vehicle comprising such a heat exchanger.The above-mentioned advantages of the method according to the invention and of the heat exchanger according to the invention therefore also apply to the motor vehicle according to the invention.

[0027] Further important features and advantages of the invention emerge from the dependent claims, the drawings and the corresponding drawing description based on the drawings.

[0028] It goes without saying that the above features and characteristics described below can be used not only in specific combinations but also in other combinations or alone without departing from the scope of the present invention.

[0029] Preferred exemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. [Brief explanation of the drawings]

[0030] [Figure 1] 1 shows a simplified example of a heat exchanger 1 according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] 1 shows a simplified example of a heat exchanger 1 according to the invention, in particular for an electric vehicle. The heat exchanger 1 comprises a plurality of tubular bodies 2 extending along a longitudinal direction L and through which a coolant K can flow. The tubular bodies 2 are arranged at a distance from one another along a stacking direction S perpendicular to the longitudinal direction L. In the example of FIG. 1, 16 tubular bodies 2 are shown in an exemplary manner, although it goes without saying that a different number of tubular bodies 2 is alternatively possible.

[0032] The tubular body 2 is fluidly connected to a coolant distributor 4 for distributing the coolant K to the tubular body 2 and to a coolant collector 5 for collecting the coolant after it has flowed through the tubular body 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 body 2.

[0033] The coolant distributor 4 and the coolant collector 5 are arranged in the region of the longitudinal end 2b of the tubular body 2, which is arranged opposite to each other along the longitudinal direction L. A rib structure 2a consisting of ribs for guiding the coolant is provided within the tubular body 2, and this rib structure 2a further supports the inner surface of the pipe wall of the tubular body 2.

[0034] The fluid path 3 through which the gas G, particularly the charge air, flows is formed by intermediate spaces provided between the tubular bodies 2 along the stacking direction S. The rib structure 3a (not completely shown in FIG. 1 for clarity) is provided in the fluid path 3 and includes ribs for guiding the gas G and supports the outer sides of the pipe walls of adjacent tubular bodies 2 in the stacking direction S.

[0035] The components of the heat exchanger 1, in the example of FIG. 1, are the tubular body 2, the rib structure 2a, 3a, the coolant distributor 4 and the coolant collector 5, and contain or consist of aluminum as a material.

[0036] As part of the manufacture of the heat exchanger 1, these individual components of the heat exchanger 1 are soldered, i.e., brazed, to each other at their respective contact points 10 by using potassium aluminum fluoride as a flux, thus connecting them to each other by a material bond. A different flux containing fluoride can also be used instead of potassium aluminum fluoride.

[0037] The tubular body 3 is brazed to the coolant distributor 4 and the coolant collector 5, so that there are contact points 10 between the respective tubular body 2 and the coolant distributor 4 and the coolant collector 5. As the rib structures 2a, 3a are brazed to the tubular body 3, such contact points 10 are also provided between the rib structure 3a and the tubular body 3.

[0038] The method of the invention will now be explained using the example of a heat exchanger 1.

[0039] After brazing the aluminum components of the heat exchanger 1 described above (by using a flux), these components are prepared for the method according to the invention, which means that the aluminum surfaces of the components are also provided in the area of ​​the contact points 11. During operation of the heat exchanger 1, the coolant flows through the tubular body 3, which consists of the rib structure 3a and the coolant distributors 4 and collectors 5, and thus comes into contact with the aluminum surfaces, which are passivated by the method according to the invention.

[0040] For this purpose, a passivating solution is applied to the provided aluminum surface, so that a passivating layer is produced by reaction of the passivating solution with the flux-provided aluminum surface. In the example of heat exchanger 1, this can be achieved by introducing the passivating solution into coolant distributor 4, into tubular body 2 and into coolant collector 5.

[0041] The passivation solution is , Ji It is prepared by mixing a rhenium solution with a waterglass dispersion.

[0042] The zirconium silicate solution contains 0.1 to 5 g / L of zirconium silicate. . The zirconium silicate solution is prepared by dissolving zirconium carbonate in a sulfuric acid solution with a pH value of 2 to 6, followed by neutralization with ammonia. Instead of the zirconium silicate solution, solutions of other fluoride-complexing elements, such as lanthanum, can also be used.

[0043] The zirconium silicate solution may further contain sebacic acid at a concentration of 0.1 to 2%, alternatively or in addition, triethanolamine at a concentration of 0.05 to 0.5%. It is also contemplated that the zirconium silicate solution may contain other dicarboxylic acids, such as tartaric acid.

[0044] The passivation solution may contain tartaric acid, for example, 3 to 5 grams of tartaric acid per liter of passivation solution.

[0045] The zirconium silicate solution further contains the corrosion inhibitor catechol-3,5-disulfonic acid disodium salt in a proportion of 0.01 to 2.0% by weight. However, the zirconium silicate solution may alternatively or additionally contain one or more of the following substances: disodium salt, diethylenetriaminepentaacetic acid, 8-hydroxy-(7)-iodoquinoline-sulfonic acid-(5), 8-hydroxy-quinoline-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-pyran-4-one, citrate, carboxylate, especially oxalate, alkali salt of stearic acid, alkali salt of formic acid, alkali gluconate, sodium tetraborate, pyrophosphate, or calcium gluconate.

[0046] The water glass dispersion contains water glass at a concentration of 5 to 25%. The water glass may be sodium silicate, lithium water glass, or potassium water glass. The water glass dispersion further contains calcium gluconate at a concentration of 0.5 to 2%.

[0047] The passivation solution may also contain hexafluorozirconate. It is also contemplated that the passivation solution may contain a polyurethane dispersion. The passivation solution may also contain ammonium vanadate.

[0048] After applying the passivating solution, the heat exchanger is introduced into a pressure cooker and the aluminum surface with the flux is passivated by applying heat and pressure, which heats the aluminum surface to a temperature above 120° C. The aluminum surface is further pressurized at a pressure above 1 bar, up to a maximum of 2 bar.

[0049] Other aluminum surfaces with flux can similarly be passivated in the manner described above.

Claims

1. a) providing an aluminum surface with a flux; and step b) applying a passivation solution to the aluminum surface provided in step a) to generate a passivation layer by reaction of the passivation solution with the aluminum surface having the flux, After application of the passivating solution, the aluminum surface is passivated by heating and applying pressure above 1 bar and up to 2 bar, the flux provided in step a) comprises or is potassium aluminum fluoride; The passivation solution applied in step b) is prepared by mixing a zirconium solution with a water glass dispersion, and the passivation solution contains 0.1 to 5 g / L of zirconium silicate.

1. A method for passivating an aluminum surface with a flux, comprising:

2. The aluminum surface is heated to a temperature above 100°C.

2. The method of claim 1.

3. the zirconium solution contains sebacic acid in a concentration of 0.1 to 2% by weight, and / or The zirconium solution contains triethanolamine at a concentration of 0.05 to 0.5% by weight.

3. The method according to claim 1 or 2, characterized in that

4. the zirconium solution comprises at least one corrosion inhibitor with a share of 0.005 to 10% by weight; The at least one corrosion inhibitor comprises catechol-3,5-disulfonic acid disodium salt, diethylenetriaminepentaacetic acid, 8-hydroxy-(7)-iodoquinoline-sulfonic acid-(5), 8-hydroxy-quinoline-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-pyran-4-one, citrate, oxalate, alkali salt of stearic acid, alkali salt of formic acid, alkali glyconate, sodium tetraborate, and / or pyrophosphate.

4. The method according to claim 1, wherein the

5. The water glass dispersion contains water glass at a concentration of 5 to 25% by weight.

5. The method according to claim 1, wherein the first and second electrodes are connected to a first electrode.

6. The water glass dispersion contains calcium gluconate at a concentration of 0.5 to 2% by weight.

6. The method according to claim 1, wherein the

7. The passivation solution applied in step b) contains hexafluorozirconic acid 7. The method according to claim 1, wherein the

8. the passivation solution applied in step b) contains a polyurethane dispersion and / or ammonium vanadate; 8. The method according to claim 1, wherein the

9. The aluminum surface provided in step a) is part of a heat exchanger (1) comprising several aluminum components (2, 2a, 3a, 4, 5), which are connected to one another by at least one brazed joint.

9. The method according to any one of claims 1 to 8, characterized in that

10. The zirconium solution contains tartaric acid 10. The method according to any one of claims 1 to 9, characterized in that

11. 2. The method of claim 1, wherein after application of the passivating solution, the aluminum surface is passivated by heat and pressure in a pressure cooker.

12. 3. The method of claim 2, wherein the aluminum surface is heated to a temperature above 120°C.

13. 5. The method of claim 4, wherein the zirconium solution contains at least one corrosion inhibitor with a share of 0.01 to 2.0% by weight.

14. Providing several components (2, 2a, 3a, 4, 5) made of aluminum connected to each other by at least one brazed joint; The aluminum surfaces of the components (2, 2a, 3a, 4, 5) are passivated by a method according to any one of claims 1 to 13. A method for manufacturing a heat exchanger (1), comprising:

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