Heat Exchanger, Use of an Aluminium Alloy and of an Aluminium Strip as well as a Method for the Production of an Aluminium Strip

Abstract

Provided is a heat exchanger, in particular for motor vehicles, with at least one exchanger tube of an aluminium alloy and with at least one component connected fluidically to the exchanger tube, wherein the exchanger tube and the component (14, 16) are connected to one another by way of a common soldered connection and wherein the component connected to the exchanger tube has a core layer of an aluminium alloy with the following composition: Si: max. 0.7% by weight, Fe: max. 0.70% by weight, Cu: max. 0.10% by weight, Mn: 0.9-1.5% by weight, Mg: max. 0.3% by weight, Cr: max. 0.25% by weight, Zn: max. 0.50% by weight, Ti: max. 0.25% by weight, Zr: max. 0.25% by weight, unavoidable impurities individually max. 0.05% by weight, altogether max. 0.15% by weight, the remainder aluminium.

Claims

1. A heat exchanger, in particular for motor vehicles, with at least one exchanger tube made of an aluminium alloy and with at least one component connected in fluid communication to the exchanger tube, wherein the exchanger tube and the component are connected to one another by way of a common brazed connection, wherein the component connected to the exchanger tube has a core layer of an aluminium alloy with the following composition: Si: max. 0.7% by weight, Fe: max. 0.7% by weight, Cu: max. 0.10% by weight, Mn: 0.9-1.5% by weight, Mg: max. 0.30% by weight, Cr: max. 0.25% by weight, Zn: max. 0.50% by weight, Ti: max. 0.25% by weight, Zr: max. 0.25% by weight, unavoidable impurities individually max. 0.05% by weight, in total max. 0.15% by weight, remainder aluminium.

2. The heat exchanger according to claim 1, wherein the aluminium alloy of the core layer has the following composition: Si: 0.50-0.7% by weight, Fe: 0.15-0.40% by weight, Cu: max. 0.03% by weight, Mn: 1.2 to 1.5% by weight, Mg: 0.01-0.10% by weight, Cr: 0.10-0.20% by weight, Zn: max. 0.10% by weight, Ti: max. 0.25% by weight, Zr: max. 0.25% by weight, unavoidable impurities individually max. 0.05% by weight, in total max. 0.15% by weight, remainder aluminium.

3. The heat exchanger according to claim 1, wherein the aluminium alloy of the core layer has a ratio of the Mn content to the Si content in the range of 1.7 to 3.

4. The heat exchanger according to claim 1, wherein the component connected to the exchanger tube is a manifold or a tubesheet.

5. The heat exchanger according to claim 1, wherein the component connected to the exchanger tube has a corrosion potential in accordance with ASTM G69 of −740 mV or baser.

6. The heat exchanger according to claim 1, wherein the exchanger tube is an extruded multi-chamber tube.

7. The heat exchanger according to claim 1, wherein the exchanger tube consists of an aluminium alloy of the type 3xxx.

8. The heat exchanger according to claim 1, wherein the common brazed connection of the exchanger tube and the component connected thereto was produced using a brazing material which has a Zn content of max. 0.50% by weight.

9. The heat exchanger according to claim 1, wherein the component connected to the exchanger tube has a clad brazing material layer of a brazing alloy, wherein the brazing alloy is an aluminium alloy with a Si content of 7 to 12% by weight and with a Zn content of max. 0.50% by weight.

10. A component, in particular a manifold or a tubesheet for a heat exchanger, produced from an aluminium alloy or an aluminium strip with a core layer of an aluminium alloy, wherein the component is designed to be connected in fluid communication to an exchanger tube of a heat exchanger, wherein the aluminium alloy has the following composition: Si: max. 0.7% by weight, Fe: max. 0.7% by weight, Cu: max. 0.10% by weight, Mn: 0.9-1.5% by weight, Mg: max. 0.30% by weight, Cr: max. 0.25% by weight, Zn: max. 0.50% by weight, Ti: max. 0.25% by weight, Zr: max. 0.25% by weight, unavoidable impurities individually max. 0.05% by weight, in total max. 0.15% by weight, remainder aluminium.

11. The component of claim 10, wherein the component is produced from the aluminium strip with a core layer of the aluminium alloy, wherein the aluminium strip has a brazing material layer, clad onto the core layer of a brazing alloy, and wherein the brazing alloy is an aluminium alloy with an Si content of 7 to 12% by weight and with a Zn content of max. 0.50% by weight.

12. A method for the production of an aluminium strip, with the following steps: casting a rolling ingot in the DC method from an aluminium alloy with the following composition: Si: max. 0.7% by weight, Fe: max. 0.7% by weight, Cu: max. 0.10% by weight, Mn: 0.9-1.5% by weight, Mg: max. 0.30% by weight, Cr: max. 0.25% by weight, Zn: max. 0.50% by weight, Ti: max. 0.25% by weight, Zr: max. 0.25% by weight, unavoidable impurities individually max. 0.05% by weight, in total max. 0.15% by weight, remainder aluminium. optionally homogenising the rolling ingot by means of an annealing treatment at a temperature in the range of 540° C. and 620° C. and a hold time at the target temperature between 4 and 12 hours, hot rolling the rolling ingot to form a hot strip, in particular to a hot strip thickness in the range of 2.0 to 10 mm, cold rolling the hot strip to a final thickness with optional intermediate annealing at a temperature in the range of 300° C. to 450° C. to form a cold strip, wherein the final thickness of the cold strip is in the range of 0.1 to 5 mm.

13. The method according to claim 12, wherein the method produces a roll-clad aluminium strip, in which the rolling ingot is provided with a cladding coat prior to hot rolling.

14. The method according to claim 13, wherein the cladding coat consists of a brazing alloy, wherein the brazing alloy is an aluminium alloy with a Si content of 7 to 12% by weight and with a Zn content of max. 0.50% by weight.

15. The method according to claim 13, wherein, after cold rolling, the roll-clad aluminium strip is soft-annealed at final thickness at a temperature in the range of 300° C. and 450° C. or finally annealed at a temperature in the range of 240° C. and 350° C.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0170] In the drawing:

[0171] FIGS. 1a and 1b show an exemplary embodiment of the heat exchanger as well as the use of an aluminium alloy or an aluminium strip; and

[0172] FIG. 2 shows exemplary embodiments of the method for the production of an aluminium strip.

DETAILED DESCRIPTION OF THE INVENTION

[0173] FIGS. 1a and 1b show an exemplary embodiment of the heat exchanger as well as the use of an aluminium alloy or an aluminium strip. FIG. 1a shows a schematic side view of the heat exchanger and FIG. 1b shows a section through the plane designated in FIG. 1a with “1b”.

[0174] The heat exchanger 10 has a plurality of exchanger tubes 12, whose ends are in each case connected to a first manifold 14 as well as to a second manifold 16. The manifolds 14, 16 thus in each case constitute a component connected to the exchanger tubes 12.

[0175] A medium flow 18 is introduced into the first manifold 14 during operation which is distributed to the exchanger tubes 12 and lastly flows through the manifold 16 out of the heat exchanger 10 again. A second medium flow flows towards the region of the exchanger tubes 12 during operation, said second medium flow comes into thermal contact with the outer surface of the exchanger tubes 12 as a result, such that a heat exchange occurs between the first and the second medium flow. In order to enlarge the surface that can be used for the heat exchange, fins 20 are arranged between the exchanger tubes 12 which are brazed in each case with the exchanger tubes 12.

[0176] The exchanger tubes 12 are extruded multi-chamber tubes which have a plurality of channels 22 such that the contact surface between the first medium 18 and the exchanger tubes 12 is increased and the heat exchange is thus improved. The exchanger tubes 12 consists of a low-alloyed aluminium alloy, for example of the type EN-AW 3102 and thus have a rather low corrosion potential.

[0177] The manifolds 14, 16 have a multi-layer structure with a core layer 24 and a clad brazing material layer 26. In addition, another clad corrosion protection layer 28 can also be provided on the inside of the manifolds 14, 16. The manifolds 14, 16 can in particular be produced from a clad aluminium strip that has a corresponding structure with a core layer, a clad brazing material layer and, if appropriate, a corrosion protection layer clad on the opposing side of the core layer.

[0178] The exchanger tubes 12 are hard-brazed with the manifolds 14, 16, with the material of the brazing material layer 26 acting as a brazing material. The brazing material layer 26 can in particular be an aluminium brazing alloy with a Si content of 7 to 12% by weight.

[0179] The exchanger tubes 12 thereby form a coupled galvanic system with the manifolds 14, 16. Heat exchangers from the prior art posed the problem that the exchanger tubes were particularly strongly affected by corrosion due to their low corrosion potential whereby this could prematurely lead to leakages. This problem is remedied with the heat exchanger 10 in that an aluminium alloy with the following composition is used in the present case for the core layer 24 of the manifolds 14, 16: [0180] Si: 0.50-0.7% by weight, [0181] Fe: 0.15-0.40% by weight, [0182] Cu: max. 0.05% by weight, in particular max. 0.03% by weight, [0183] Mn: 1.2 to 1.5% by weight, [0184] Mg: max. 0.10% by weight, in particular 0.01-0.10% by weight, [0185] Cr: 0.10-0.20% by weight, [0186] Zn: max. 0.10% by weight, [0187] Ti: max. 0.25% by weight, [0188] Zr: max. 0.25% by weight, [0189] unavoidable impurities individually max. 0.05% by weight, in total max. 0.15% by weight, remainder aluminium.

[0190] Using this alloy composition, the core layer 24 has a lower corrosion potential than the exchanger tubes 12 such that said exchanger tubes are anodically protected by the manifolds 14, 16.

[0191] If the heat exchanger 10 is exposed to a corrosion-promoting environment, for example in the engine compartment of a motor vehicle, the corrosion firstly attacks the manifolds 14 and 16 and possibly the fins 20, while the exchanger tubes 12 that are more critical for the operation of the heat exchanger 10 are subjected only to low corrosion. As a result, the service life of the heat exchanger 10 can be extended.

[0192] Using the anodic protection of the exchanger tubes 12 by way of the manifolds 14, 16, the use of Zn-containing brazing materials, which were used in the prior art partly as corrosion protection for the exchanger tubes, can in particular also be dispensed with. The aluminium brazing alloy of the brazing material layer 26 accordingly preferably has a Zn content of max. 0.50% by weight, further preferably of max. 0.20% by weight. Diffusion of Zn in the heat exchanger which is difficult to control can hereby be prevented.

[0193] FIG. 2 shows an exemplary embodiment of a method for the production of an aluminium strip which can be used in particular for the production of the manifolds 14, 16 from FIGS. 1a and 1b.

[0194] In a first step 80, an alloy of the above-mentioned composition is cast for the core layer 24 in the DC method to form a rolling ingot. This rolling ingot is homogenised in a subsequent step 82 at a temperature in the range of 540° C. and 600° C. and a hold time at the target temperature of 4 to 12 hours. In an alternative exemplary embodiment of the method, the homogenisation step 82 can also be omitted.

[0195] If a clad aluminium strip is supposed to be produced, for example with a brazing material layer and/or a corrosion protection layer, a cladding packet is produced in a subsequent step 84 from the rolling ingot as the core layer and one or a plurality of cladding layers arranged over or under the core layer. The thickness of the cladding layers are in each case preferably between 5 and 20% of the overall thickness of the cladding packet.

[0196] The rolling ingot or the cladding packet is hot-rolled in a subsequent step 86, in particular to a thickness in the range of 3-7 mm. The rolling ingot or the cladding packet is pre-heated prior to the hot-rolling and preferably to a temperature in the range of 450-480° C. with a hold time at the target temperature of 3-10 h.

[0197] The possibly roll-clad hot strip is cold-rolled in a subsequent step 88, preferably to a final thickness of 1.0 to 2.5 mm. Intermediate annealing (recrystallisation annealing) can be carried out in an intermediate step 90 during the cold rolling at an intermediate thickness, preferably at a temperature in the range of 300 and 400° C.

[0198] After the cold rolling to the final thickness, a final annealing can optionally be carried out in a subsequent step 92. By way of soft-annealing at a temperature in the range 300-400° C., a material in the soft-annealed state O can be thereby achieved. Alternatively, a final annealing can also take place for a material in the state H24 at a temperature in the range 240-350° C.

[0199] Tests were carried out from which emerge the desired combination of a low corrosion potential with simultaneously good strength for components of the described alloy.

TABLE-US-00001 TABLE 1 Alloy Si Fe Cu Mn Mg Cr Zn Ti Zr Al A 0.64 0.31 0.00 1.40 0.08 0.13 0.005 0.008 — Remainder B 0.62 0.26 0.00 1.37 0.20 0.00 0.001 0.006 — Remainder C 0.50 0.30 0.27 1.09 0.27 0.20 0.001 0.007 — Remainder D 0.59 0.29 0.00 1.34 0.06 0.13 0.01 — — Remainder E 0.60 0.28 0.02 1.41 0.06 0.12 0.00 — — Remainder F 0.59 0.30 0.00 1.35 0.07 0.12 0.01 — — Remainder EN-AW 4045 9.87 0.21 0.00 0.01 0.01 0.00 0.005 0.005 — Remainder

[0200] Table 1 shows the alloy compositions used in the tests (all weight information in % by weight). The alloys A and B from Table 1 are in accordance with the invention, with the alloy A corresponding to a preferred embodiment of the invention. Alloy C is a comparative alloy which is used as the core alloy in the heat exchanger field. The alloys D to F are in turn in accordance with the invention and correspond to a preferred embodiment of the invention. The brazing alloy of type EN-AW 4045 also indicated was used in the tests A-C and F for the brazing material cladding layer.

[0201] Roll-clad aluminium strips were produced using the method represented in FIG. 2, with the alloys A, B, C, D, E and F in each case having been used for the core layer and the alloy of type EN-AW 4045 mentioned in Table 1 in each case for the brazing material cladding coats in tests A, B, C and F. In the tests D and E, an alternative alloy of the type EN-AW 4343 was in each case used for the brazing material cladding coats, with 1% by weight of Zn also having been added to the brazing alloy in test E.

[0202] In the cases A-C, 60 kg batches of the alloys in question were in each case produced and cast in the DC casting method to form ingots in the cross section 335 mm×125 mm. In the cases D-F, batches of a number of tones of the alloy in question were in each case produced and cast in the DC casting process to form larger bars (cross section approx. 500×approx. 1500 mm). For the production of strip material, a brazing material ingot EN-AW 4045 or EN-AW 4343, respectively, was firstly rolled to the required thickness for a cladding layer of 7.5% of the total thickness. The core bars of the alloys A, B, C or D were subjected to homogenisation at a temperature of 575° C. and the core bars of the alloys E and F were subjected to homogenisation at a temperature of 600° C. for a hold time of 6 h. Cladding packets with a one-sided brazing material coat of 7.5% of the total thickness were produced thereafter with the pre-rolled brazing material coat. These were in each case pre-heated with a temperature of 470° C. and a hold time of at least 3 h and then hot-rolled to a thickness of 7.0 mm.

[0203] Cold-rolling with a plurality of passes to a final thickness of 1.5 mm (tests A-C and E) or 1.0 mm (test D) or 1.6 mm (test F) followed in each case. Soft-annealing to set a temper 0 state at a temperature of 350° C. (for the strips with the core layer alloys A and B) or of 320° C. (for the strip with the core layer alloy C) or of 400° C. (for the strips with the core layer alloys D to F) was then carried out, in each case with a hold time of 2 h.

[0204] From the strips with core layer alloys A and B, a strip section in each case with an intermediate thickness of 2.15 mm was also subjected to soft-annealing at 350° C. and a hold time of 2 h and then cold-rolled with a final reduction rolling degree of 30% to a final thickness of 1.5 mm in the temper state H14.

[0205] Samples were taken from the brazing material-clad strips produced in this way and subjected to brazing simulation in each case to test the properties in the brazed state which corresponds to a typical industrial brazing cycle. The samples were, for this purpose, heated at a heating rate of 0.9° C./s to a temperature of 600° C. and cooled after a hold time of 5 mins at a rate of 0.9° C./s.

[0206] The mechanical properties of the strips were determined on the samples. The measurement of the mechanical properties was in each case carried out prior to and after the brazing simulation and in each case in the rolling direction.

[0207] Table 2 below shows the results of the measurements of the mechanical properties. The first column indicates in each case the alloy composition of the core layer, the second column indicates in each case the state of the roll-clad strip from which the respective sample was taken. R.sub.p0.2, R.sub.m, A.sub.g and A.sub.50mm were in each case determined according to DIN EN ISO 6892-1/A224.

TABLE-US-00002 TABLE 2 R.sub.p0.2 Thickness [N/ R.sub.m A.sub.g A.sub.50 mm Sample State [mm] mm.sup.2] [N/mm.sup.2] [%] [%] A Prior to brazing 1.5 52 127 19.9 26.0 simulation O temper A Prior to brazing 1.5 165 179 1.9 5.5 simulation H14 B Prior to brazing 1.5 52 128 20.2 26.4 simulation O temper B Prior to brazing 1.5 169 179 1.7 5.1 simulation H14 C Prior to brazing 1.5 68 152 17.8 22.4 simulation O temper A After brazing 1.5 47 129 18.6 22.9 simulation O temper A After brazing 1.5 46 130 19.0 23.1 simulation H14 B After brazing 1.5 47 134 14.9 15.7 simulation O temper B After brazing 1.5 47 138 18.2 21.3 simulation H14 C After brazing 1.5 51 148 14.8 20.7 simulation O temper D Prior to brazing 1.0 52 125 21.3 31.6 simulation O temper D After brazing 1.0 49 142 17.2 19.6 simulation O temper E Prior to brazing 1.5 52 121 22.5 33.8 simulation O temper E After brazing 1.5 45 132 20.2 25.6 simulation O temper F Prior to brazing 1.6 49 121 22.4 33.5 simulation O temper F After brazing 1.6 47 129 N/A N/A simulation O temper

[0208] The results in Table 2 show that comparable strengths can be achieved with the alloy according to the invention (samples A and B as well as D to F) as with standard alloys (sample C).

[0209] Corrosion tests were also carried out on the samples. To this end, the electrochemical corrosion potential was firstly measured in accordance with ASTM G69 against a saturated calomel electrode in an electrolyte of neutral 1 mole NaCl solution. The corrosion potential was in each case measured at the core layer.

[0210] The results of the measurements are reproduced in Table 3 below. The measurement was carried out in each case prior to and after the above-described brazing simulation.

TABLE-US-00003 TABLE 3 Corrosion potential prior Corrosion potential to brazing simulation after brazing Sample Temper state [mV] simulation [mV] A O −773 −759 A H14 −772 −759 B O −772 −758 B H14 −770 −761 C O −746 −727 D O −759 −742 E O −784 −757 F O −760 −747

[0211] The samples A and B as well as D to F deliver comparably good values for the corrosion potential. The proposed aluminium alloy with the lower Mg content of max. 0.10% by weight (corresponding to samples A and D to F) is preferred since an impairment of the brazeability in the CAB brazing process by a higher proportion of Mg can thereby be prevented. Similarly, a proportion of Mg of 0.04% by weight or more is preferred in order to thereby be able to better set the desired strength and the desired corrosion potential of the alloy. The sample corresponding to the comparative alloy C exhibits a corrosion potential clearly outside of the desired range.

[0212] An advantage of the alloy proposed for the core alloy is in particular the galvanic compatibility with typical alloys for exchanger tubes, in particular MPEs. In order to verify this galvanic compatibility, contact corrosion measurements were carried out in accordance with DIN 50919. For these measurements, the samples A, B and C were brought into contact in each case in an electrolyte with samples K from an extruded tube of the frequently used alloy EN-AW 3102. An acidified synthetic saline solution with a pH value between 2.8 and 3.0 in accordance with testing standard ASTM G85, Annex A3 was used as the electrolyte. Prior to the measurement, the samples A, B, C and K were in each case subjected to the above-described brazing simulation. The samples K of EN-AW 3102 have a corrosion potential in accordance with ASTM G69 of −742 mV in the braze-simulated state.

[0213] The contact corrosion measurement in accordance with DIN 50919 was carried out with the sample A, B and C on the unclad side, i.e. directly on the core layer. The galvanic compatibility was in each case assessed based on the direction of the measured current flow. Compatibility is then present when the current flow takes place from the sample for the component of the heat exchanger, e.g. of the tubesheet or of the manifold, towards the material of the exchanger tube, in particular the MPEs. In this case, the component (tubesheet/manifold) preferably dissolves and sacrifices itself for the exchanger tube (MPE).

[0214] In the case of the contact corrosion measurements, the combination of the sample A (O temper) with a sample K resulted in a mass loss of the sample K of 1.6 g/m.sup.2 and the combination of the sample B (O temper) with a sample K resulted in a mass loss of the sample K of 3.9 g/m.sup.2. In contrast, the mass loss of the sample K for the combination of the sample C (O temper) with a sample K was 34.4 g/m.sup.2. The samples A and B accordingly had a significantly better galvanic compatibility with the sample K than the comparative sample C, i.e. the corrosion of the sample K was significantly reduced by the combination with one of the samples A or B.

[0215] In conclusion, the previously described tests show that by using the alloy, which is proposed in the present case for the core layers of components connected to exchanger tubes, anodic protection of the exchanger tubes can be achieved such that the service life of the heat exchanger is notably extended. The corresponding components also have sufficient strength.

[0216] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0217] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0218] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.