Aluminium composite material for use in thermal flux-free joining methods and method for producing same

Abstract

Provided are embodiments of an aluminium composite material for use in thermal flux-free joining methods. The composite material has at least one core layer of an aluminium core alloy and at least one outer solder layer of an aluminium solder alloy. The aluminium solder alloy has the following composition in wt %: 6.5%Si13%, Fe1%, 230 ppmMg450 ppm, Bi500 ppm, Mn0.15%, Cu0.3%, Zn3%, and Ti0.30% with the remainder Al and unavoidable impurities individually at most 0.05%, in total at most 0.15% and the aluminium solder layer has an alkaline pickled or acid pickled surface. The invention further relates to a method for producing an aluminium composite material, a method for the thermal joining of components, and a thermally joined construction.

Claims

1. An aluminium composite material for use in thermal flux-free joining methods, comprising at least one core layer consisting of an aluminium core alloy; and at least one outer solder layer provided on one or both sides of the core layer consisting of an aluminium solder alloy; wherein the aluminium solder alloy has the following composition in wt %: 6.5%Si13%, Fe1%, 230 ppmMg450 ppm, Bi<500 ppm, Mn0.15%, Cu0.3%, Zn3%, Ti0.30%, Remainder Al and unavoidable impurities individually at most 0.05%, in total at most 0.15%; and wherein the aluminium solder layer has an alkaline pickled or acid pickled surface.

2. The aluminium composite material according to claim 1, wherein the aluminium solder alloy has an Mg content in wt % of 230 ppmMg400 ppm

3. The aluminium composite material according to claim 1, wherein the aluminium solder alloy has a Bi content in wt % of Bi280 ppm

4. The aluminium composite material according to claim 1, wherein the aluminium solder alloy meets the specifications of type AA 4045 or type AA 4343.

5. The aluminium composite material according to claim 1, wherein the aluminium solder alloy has an Mg content of at most 1.0 wt %, preferably 0.2%-0.6%, 0.05%-0.30% or less than 0.05 wt %.

6. The aluminium composite material according to claim 1, characterised in that the aluminium core alloy is an alloy of type AA3xxx, preferably of the type AA3003, of the type AA3005, or of the type AA3017 or the type AA6xxx, preferably of the type AA6063 or the type AA6060.

7. The aluminium composite material according to claim 1, wherein the average thickness of the aluminium composite material is from 0.05-6 mm, preferably from 0.2-3 mm.

8. A method for producing an aluminium composite material, in particular an aluminium composite material according to claim 1, the method comprising the steps of: providing at least one core layer consisting of an aluminium core alloy; and applying at least one outer solder layer consisting of an aluminium solder alloy on one or both sides of the core layer; wherein the aluminium solder alloy has the following composition in wt %: 6.5%Si13%, Fe1%, 230 ppmMg450 ppm, Bi<500 ppm, Mn0.15%, Cu0.3%, Zn3%, Ti0.30%, Remainder Al and unavoidable impurities individually at most 0.05%, in total at most 0.15% and wherein the aluminium composite material is pickled with an aqueous, alkaline or acid pickling solution.

9. A method according to claim 8, wherein an acid, aqueous pickling solution is used containing: at least one mineral acid and at least one complexing agent or at least one acid of the group of short-chain carboxylic acids and at least one complexing agent; or at least one complexing acid.

10. A method according to claim 9, wherein the concentrations of the mineral acids in the pickling solution have the following limits: H.sub.2SO.sub.4: 0.1%-20 wt %, H.sub.3PO.sub.4: 0.1%-20 wt %, HCl: 0.1%-10 wt %, HF: 20 ppm-3.0 wt %, and optionally at least one surfactant is contained in the pickling solution.

11. A method according to claim 8, wherein an alkaline pickling solution is used containing 0.01-5 wt % NaOH, which optionally has at least 0.5-3 wt % of an aqueous mixture of 5-40 wt % sodium tripolyphosphate, 3-10 wt % sodium gluconate, 3-8 wt % non-ionic and anionic surfactants, optionally 0.5-70 wt % sodium carbonate.

12. A method for thermally joining components, comprising the step of thermally joining at least one component comprising an aluminium composite material according to claim 1 to at least one additional component in a flux-free manner.

13. A method according to claim 12, wherein the flux-free thermal joining is carried out in a vacuum, in particular with a maximum pressure of 10.sup.5 mbar.

14. A method according to claim 12, wherein the flux-free thermal joining is carried out in a protective gas atmosphere.

15. A thermally joined construction comprising at least one component comprising an aluminium composite material according to claim 1; and at least one additional component which in particular comprises aluminium or an aluminium alloy.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0154] In the drawing is shown in:

[0155] FIG. 1 shows a perspective representation of the solder test geometry for determining the solder capacities of the aluminium composite materials;

[0156] FIG. 2 shows a side view of the soldering test geometry;

[0157] FIG. 3a-c show overview diagrams of the solder results of different exemplary embodiments of the aluminium composite material with pickled surface as a function of the Mg contents of aluminium solder alloy and aluminium core alloy in the CAB method;

[0158] FIG. 4a-c show photos of a soldered exemplary embodiment of the aluminium composite material in the CAB method;

[0159] FIG. 5a, b show cuts of the solder points of exemplary embodiments of the aluminium composite material in a vacuum soldering method;

[0160] FIG. 6 shows a schematic sectional view of an exemplary embodiment of a method for producing a strip-shaped aluminium composite material; and

[0161] FIG. 7 shows in a sectional view, an exemplary embodiment of a thermally soldered construction in the form of a heat exchanger.

DETAILED DESCRIPTION OF THE INVENTION

[0162] In order to examine the advantages of the aluminium composite material according to the invention, a number of tests have been carried out with a specified solder test arrangement, as is perspectively represented in FIG. 1. The solder test arrangement essentially consists of three parts in total, a sheet metal 1, an angular sheet metal 2 and a contact sheet metal 3 for the angular sheet metal 2. With its closed end 2a, the angular sheet metal 2 rests on the contact sheet metal 3 arranged on sheet metal 1. Both leg ends 2b, in contrast, rest on the sheet metal 1 such that, as represented in the side view in FIG. 2, a variable gap results from the contact point of the leg ends 2b of the angular sheet metal 2 to the contact point of the closed end 2a on the contact sheet metal 3. The solder gap 4 is increasingly larger from the angular ends 2b to the closed end 2a of the angular sheet metal. The increasing solder gap 4 means it can be determined to what extent the solder properties of the aluminium composite material of the sheet metal 1 are changed with different surface treatment.

[0163] In particular, the wetting of the provided solder gap is assessed in the solder results. In this case, the following assessments have been indicated,

.Math. very good
good
sufficient
poor

[0164] The gap filling capacity together with the forms of the solder fillet being decisive for this. The tests, which showed a virtually complete inflow of the solder gap and a wide, smooth and pore-free solder fillet, were assessed with very good (.Math.). The tests, which did not lead to soldering of the components, were assessed with poor ().

[0165] The sheet metal 1 consists, in the present exemplary embodiment, of the respective tested aluminium alloy composite material which comprises a roll-clad aluminium solder alloy layer. The lengths of the legs of the angle 2 were 50 mm, the opening angle of the angular sheet metal being 35. The contact sheet metal 3 has a thickness of 1 mm such that the height difference from the closed end of the angular sheet metal to the leg end is 1 mm. The angular sheet metal 2 and the contact sheet metal 3 are not equipped with an aluminium solder layer.

[0166] Generally, the solderability is also always a function of the component design, for example geometry, gap size, etc., and also the furnace atmosphere in addition to the use of suitable solderable materials. The oxygen particle pressure and the moisture of the atmosphere play a role here. The represented solder tests in the CAB method have been carried out in a batch furnace under nitrogen flow. These solder results are comparable to those from industrial production using a continuous furnace.

[0167] The tests results are described below based on the compilation of test runs. In this case, a test run in the CAB method with different Mg contents of aluminium solder alloy and aluminium core alloy with different surface treatments are recorded in Table 1. Solder results for different alloy combinations have also been examined in the second test run in the CAB method, the aluminium solder alloys in particular comprising Bi. The alloy combinations and results for the second test run are reflected in Tables 2 and 3. Table 4 and 5 show additional test results from the CAB method. Subsequently, results from the vacuum soldering method are presented in the description for Table 6 and FIG. 5a, b.

TABLE-US-00001 TABLE 1 Solder result Mg Mg Solder alkaline content content Solder result pickled, solder core result alkaline fluoride- layer layer acid pickled, containing Sample (ppm) (ppm) pickled deoxidized deoxidation A Inv 282 409 .Math. .Math. B Comp 79 192 C Comp 78 3 D Comp 33 3 E Comp 46 1 F Inv 279 34 G Comp 181 12 .Math. H Comp 106 394 .Math. I Comp 33 9 J Comp 62 9 K Comp 53 11 L Comp 46 4 M Comp 181 9 .Math. N Comp 140 0 .Math. O Comp 84 3

[0168] Table 1 shows a compilation of the solder results of the first test run, which have been measured with the described test structure. The used aluminium solder alloys meet the specifications of the type AA4045 in connection with the Mg contents indicated in Table 1 in ppm in relation to the weight. In order to examine an additional influence of the Mg content of the core layer, different aluminium core alloys of the type AA 3003, whose Mg content is recorded in Table 1, have also been used in 0.8 mm with 10% solder cladding. The solder capacity has been examined as a function of the Mg content in connection with three differently pickled surfaces, as are described below.

[0169] The acid pickled surface has been produced by pickling in the dip method. A mixture of surfactants, sulphuric acid and hydrofluoric acid has been used. The temperature of the solution was 60 C. The concentration of sulphuric acid was 2.5 wt %. 400 ppm of fluoride was also used in the pickling solution. The contact time was 60 seconds.

[0170] The alkaline pickled surface was produced by pickling in the spraying method. A mixture of a degreasing agent and caustic soda was used. The temperature of the solution was 60 C. 2% of an aqueous mixture of 5-40 wt % sodium tripolyphosphate, 3-10 wt % sodium gluconate, 3-8 wt % non-ionic and anionic surfactants were used as degreasing agents. The concentration of the caustic soda was 1% in total. The contact time was 30 seconds.

[0171] Following the alkaline spraying treatment, deoxidation by means of an acid rinse was applied. Deoxidation containing either 5% nitric acid or 5% nitric acid with 200 ppm fluoride was used as deoxidation.

[0172] FIG. 3a-c show overview diagrams of the solder result of the exemplary embodiments of the aluminium composite material from Table 1 as a function of the Mg contents of the aluminium solder alloy and aluminium core alloy. FIG. 3a shows the aluminium composite materials with acid pickled surface, FIG. 3b the aluminium composite materials with alkaline pickled and deoxidized surface and FIG. 3c the aluminium composite materials with alkaline pickled surface deoxidized by adding fluorides.

[0173] A clear dependence of the solder result on the Mg content of the aluminium solder alloy can be recognised. Alloys with lower Mg contents below 90 ppm produce predominantly poor and merely sufficient solder results. Even though sufficient and good results are present in the range between 90 ppm and 300 ppm, a dependence of the results is to be expected on the absolute quantity of solder, the Mg content of the aluminium core alloy and the optional fluoride content in the pickle or in the deoxidation. For improved solder results even with different or low Mg contents of the aluminium core alloy and possibly even lower absolute quantities of the solder layer, the Mg content of the aluminium solder alloy is thus fixed at 230-450 ppm.

[0174] FIG. 4a-c show photos of the soldered exemplary embodiment N of the aluminium composite material from Table 1 with an Mg content of 282 ppm in the aluminium solder alloy. The good or very good solder results can be recognised for all surface treatments. In this case, FIG. 4a shows the acid pickled sample, FIG. 4b the alkaline pickled and deoxidized sample and FIG. 4c the alkaline pickled sample deoxidized by adding fluorides.

TABLE-US-00002 TABLE 2 Mg content Bi content Mg content Cu content Ti content solder solder core core core layer layer layer layer layer Sample (ppm) (ppm) (ppm) (wt %) (wt %) V1 235 <5 <5 0.17 0.013 V2 230 240 <5 0.17 0.013 V3 230 240 5 0.44 0.145 V4 230 240 800 0.004 0.008 V5 247 467 <5 0.17 0.013

TABLE-US-00003 TABLE 3 Results of slow soldering Results of quick soldering Thickness Alkaline Acid Alkaline pickled Acid pickled Sample (mm) Untreated pickled pickled Untreated 10 s 20 s 30 s 60 s 10 s 15 s 30 s 60 s V1 0.4 1.5 .Math. .Math. .Math. .Math. .Math. .Math. .Math. V2 0.4 1.5 .Math. V3 0.4 1.5 .Math. .Math. .Math. .Math. V4 0.4 .Math. .Math. .Math. .Math. .Math. .Math. .Math. 1.5 .Math. .Math. .Math. .Math. .Math. .Math. .Math. .Math. V5 0.4 1.5 .Math. .Math. .Math. .Math.

[0175] Tables 2 and 3 show the compilation of the solder results of the second test run which has been measured with the described test structure. In this case, the alloy compositions of the aluminium solder alloy corresponded to type AA 4045 and those of the aluminium core alloy to the type AA 3xxx, aside from possible deviations in the concentrations for Mg, Bi, Cu and Ti, as they are indicated in Table 2. The core alloy of the tests V1, V2 and V5 corresponds to the specifications of the type AA 3003. The core alloy of the test V3 corresponds to a modified type AA 3017 with the Cu content and Ti content indicated in Table 2. For test V4, a core alloy with a modified type AA 3003 has been used with the additional Mg content indicated in Table 2.

[0176] The thermal joining method has been carried out in a batch furnace under protective gas with two different soldering cycles: slow soldering over a soldering cycle with an approx. 20 minute heating curve and a holding time between 600 C. and 610 C. of 8 mins for a sample thickness of 0.4 mm or of 10 mins for a sample thickness of 1.5 mm. The slow heating curve has been achieved by the sample being inserted at a furnace temperature of 400 C. into the batch furnace and then heated to the soldering temperature. An even shorter soldering cycle is used in the quick soldering, the sample being inserted into the already hot furnace, which was heated to the soldering temperature. The heating curve up to achieving the soldering temperature lasted, in this case, only 4 to at most 8 minutes. The holding time at 600 C. was 8 mins for a sample thickness of 0.4 mm or over 10 mins for a sample thickness of 1.5 mm. The indicated temperatures have been measured on a steel sample holder, on which the aluminium sample rested.

[0177] The thickness of the sample is the average thickness of the entire sheet metal or aluminium composite material; the average thickness of the solder layer was 7.5% of the indicated average thickness of the entire aluminium composite material.

[0178] The contact time of the samples in the pickle in the tests with slow soldering was 20 seconds for the alkaline treatment and 30 seconds for the acid treatment. In addition to the different alloy combinations, the contact time for the alkaline pickling and the acid pickling were varied for the quick soldering. The contact time is noted in Table 3 with 10, 15 or 20, 30 and 60 seconds. Untreated samples, which are not surface-conditioned further, have also been examined as a comparison.

[0179] Initially, it can be determined based on the results from Table 3 that the untreated samples deliver predominately poor or only sufficient solder results. By means of an alkaline or acid treatment of the surface, the solder result for most of the samples is decidedly improved. Of the untreated samples, only V4 shows very good results. The aluminium core alloy of sample V4 has a high Mg content of 800 ppm which improves the solder result.

[0180] It also seems to emerge from a comparison of the results for the different sample thicknesses that the thicker samples with 1.5 mm thickness in general solder better than the thinner samples with 0.4 mm thickness. However, this also relates to the fact that the thicker samples with the same relative solder proportion have a greater absolute thickness of the solder layer and thus a greater absolute quantity of aluminium solder alloy. Irrespective of the thickness of the sample, it can be stated that the alkaline or acid treatment of the surface decidedly improves the solder result for most samples.

[0181] For example, it can be concluded from a comparison of the samples V1, V2 and V5 that Bi in the aluminium solder alloy has a positive influence on the solder result. It is shown that in combination with the specific Mg content of the aluminium solder alloy and the alkaline or acid treatment of the surface even a Bi content of less than 500 ppm, preferably at most 280 ppm has a notable positive effect on the solder result. In particular, the ranges of 100 ppm-280 ppm and 200 ppm-280 ppm are mentioned as advantageous. Corresponding Bi contents are already sufficient to largely optimise the solder properties of the aluminium composite material without larger quantities of Bi having to be added.

[0182] It has also been shown for the samples V2 to V5 that, for the minimum contents of Bi, an alkaline pickled surface leads to notably improved solder results or even requires shorter contact times than with an acid treatment. The advantageous effect of Bi in the aluminium solder alloy is thus supported in a particular manner by an alkaline pickled surface.

[0183] In the tests, the contact time of the aluminium composite material in the pickling solution is preferably 10-40 seconds. For an alkaline pickling, the contact time is further preferably 10-30 seconds since, as is discernible from Table 2, the solder result does not develop significantly further with higher contact times. For an acid pickling, the contact time is further preferably 20-40 second, for samples with a Bi content from 100 ppm or 200 ppm a dip time for the acid treatment of more than 40 seconds is advantageous. For the production, in particular using spraying methods for pickling, contact times of in particular 1-60 seconds, preferably 2-40 seconds, further preferably 2-20 second are envisaged.

[0184] Table 4 and 5 show further solder results from the CAB method using the aluminium composite material.

TABLE-US-00004 TABLE 4 Si Fe Cu Mn Mg Cr Ni Zn Ti Bi Core 0.0460 0.1976 0.4467 1.0908 0.1449 0.0696 0.0190 0.0265 Solder 10.0435 0.1774 0.0035 0.0128 0.0360 0.0012 0.0050 0.0025 0.0099 0.0420

TABLE-US-00005 TABLE 5 Thickness Alkaline Alkaline Alkaline Acid Acid Acid (mm) Untreated treatment 1 treatment 2 treatment 3 pickled 60 sec pickled 10 sec pickled 20 sec 0.63 + .Math. .Math. .Math. .Math. .Math. .Math. 1.20 + .Math. .Math. .Math. .Math. .Math. .Math.

[0185] The indicated thickness corresponds to the entire thickness of the aluminium composite material. The samples were inserted into the hot batch furnace and were at the solder temperature within 4 to 8 minutes. The nitrogen flow was 30 I/min. The samples with 0.63 mm thickness were soldered with a holding time of 8 mins at 600-610 C. The samples with 1.20 mm thickness were soldered with a holding time of 10 mins at 600-610 C. The samples marked as untreated were soldered as comparative samples in the delivery state of the rolling mill.

[0186] For the three alkaline treatments, the aluminium composite material was treated for 30 seconds with a pickle comprising the following constituents: at least 0.5-3 wt % of an aqueous mixture of 5-40 wt % sodium tripolyphosphate, 3-10 wt % sodium gluconate, 3-8 wt % non-ionic and anionic surfactants, optionally 0.5-70 wt % sodium carbonate with the addition of NaOH, the caustic soda concentration in the pickling solution being 1 wt % in total.

[0187] Following the alkaline treatment 1, deoxidation was carried out for 30 seconds with an HNO.sub.3 solution with a concentration of 2.5 wt %. Following the alkaline treatment 2, deoxidation was carried out for 30 seconds with an HNO.sub.3 solution with a concentration of 2.5 wt %, with the addition of 500 ppm F. For the alkaline treatment 3, in contrast, deoxidation was carried out for 15 seconds with an acid mixture of 2.5 wt % H.sub.2SO.sub.4 and 400 ppm HF and optionally surfactants.

[0188] The results from Table 5 show that the above-described combination of the conditioned surface and the specific composition of the aluminium solder alloy, in particular the balanced Mg content, enables very good solder results in flux-free protective gas soldering.

[0189] The test results from Table 5 were also reproduced to the extent of an industrial scale production. The material indicated in Table 4 with a total thickness of 0.63 mm was subjected to the above-described alkaline treatment 2, except that 600 ppm fluoride and a contact time of 8 seconds were provided. The material indicated in Table 4 with a total thickness of 1.2 mm was also tested on an industrial scale, the above-described acid treatment with the addition of 800 ppm fluoride was applied with a contact time of 6 seconds. Subsequent solder tests in the laboratory showed very good solder results for both thicknesses and treatments.

[0190] In order to demonstrate the solder capacity of the aluminium composite material in different solder methods, solder tests were also carried out in a vacuum. Flat samples of the aluminium composite material with the solder layers were placed on top of each other and joined. FIGS. 5a and 5b shows metallographic cuts through the solder points resulting in the vacuum method.

[0191] The composition of aluminium core alloy and aluminium solder alloy from the test in FIG. 5a is the composition already indicated in Table 4. The aluminium composite material has a thickness of 0.63 mm and was conditioned with the above-described alkaline treatment 2 with fluorides in the deoxidation. As can be recognised from the microstructure in FIG. 5a, a virtually complete material bond has developed during soldering. The solder result is assessed as very good. It is thus clear that the aluminium composite material shows very good solder quality both in vacuum soldering and in the flux-free CAB method and can be reliably joined.

[0192] FIG. 5b shows a further test result of a connection produced by means of vacuum soldering. The composition of aluminium core alloy and aluminium solder alloy are indicated in Table 6 in wt %.

TABLE-US-00006 TABLE 6 Si Fe Cu Mn Mg Cr Ni Zn Ti Core 0.1382 0.3182 0.4294 1.1446 0.0022 0.0007 0.004 0.0025 0.1361 Solder 9.9562 0.1744 0.002 0.0087 0.0294 0.0013 0.0032 0.0136 0.0102

[0193] The core layer had a thickness of 0.42 mm and was in the state 0. The aluminium composite material was treated with an alkaline pickle comprising the following constituents:

[0194] At least 0.5-3 wt % of an aqueous mixture of 5-40 wt % sodium tripolyphosphate, 3-10 wt % sodium gluconate, 3-8 wt % non-ionic and anionic surfactants, optionally 0.5-70 wt % sodium carbonate, with the addition of NaOH, the caustic soda concentration in the pickling solution being in total 1 wt %. Following the pickle, deoxidation was carried out in an HNO.sub.3 solution with a concentration of 2.5 wt %, adding 400-600 ppm fluoride.

[0195] The aluminium solder alloy from FIG. 5b or Table 6 contains virtually no Bi. The solder capacity is thus effected in particular by the combination of the surface treatment with the composition of the alloys, in particular the specifically set Mg content of the aluminium solder alloy. The solder result from FIG. 5b is also assessed as very good.

[0196] Contrary to the expectation among experts, it is surprisingly possible, by combining the alkaline or acid pickle with the specific composition of the aluminium composite material, to join aluminium composite materials thermally in a vacuum without solders with more than 1% Mg having to be used.

[0197] In a synopsis with the results from the CAB method explained above concerning Table 1 to 5, it becomes clear that using the described aluminium composite material, process-reliable soldering is enabled in the different soldering methods, in particular both in the CAB method and in vacuum soldering.

[0198] An exemplary embodiment for a method for producing a strip-shaped aluminium composite material is represented in FIG. 6. In the manufacturing step A, the aluminium composite material is manufactured by simultaneous casting of different melts or by roll cladding. Subsequently, cold rolling B to final thickness is for example carried out, wherein at least intermediate annealing can take place during the cold rolling. Subsequently, the aluminium composite material is for example soft-annealed in the method step C. At least the aluminium solder alloy layer is subjected to surface treatment in method step D. Method step D is subsequently represented for a strip-shaped aluminium composite material.

[0199] The aluminium composite material located on a coil 5 is optionally subjected to a degreasing step 6. Subsequently, the aluminium composite material passes through the pickling step 7 in which it is for example guided through a bath with an aqueous acid pickling solution which has a complexing agent, in addition to an acid such that material erosion takes place on the aluminium solder alloy surface. The bath preferably consists of an aqueous sulphuric acid with 0.1%-20%, optionally at least one surfactant and one HF content of 20 ppm-600 ppm, preferably 300 ppm-600 ppm or 300 ppm-480 ppm.

[0200] Following a rinsing and drying step 8, the surface-treated aluminium composite material is wound to a coil 9. The described surface treatment step D can, however, also take place in a non-strip shaped manner or directly at the outlet of the production process, i.e. of the cold rolling or for example soft-annealing, provided a continuous furnace is used for this purpose.

[0201] An exemplary embodiment of a thermally joined construction is represented in FIG. 7 in plan view in the shape of a heat exchanger 10.

[0202] The fins 11 of the heat exchanger 10 usually consists of blank aluminium alloy strip or aluminium alloy strip coated on both side with an aluminium solder. The fins 11 are soldered to pipes 12 bent in a meandering shape such that a plurality of solder connection is required. It is thus particularly advantageous to use the aluminium composite material according to the invention since the particularly good solder results are achieved in the CAB method even without fluxing agents. The absent fluxing agent residues have a positive effect on the operation of the heat exchangers in comparison to heat exchangers soldered with fluxing agents.

[0203] The test results in particular showed that an aluminium composite material, which has a pickled surface of an aluminium solder alloy layer in connection with a specific Mg content, has very good properties with regard to its solder capacity in a flux-free joining thermal method carried out under protective gas, for example a CAB method and in thermal joining in a vacuum. Using the described aluminium composite material, it is thus possible to further optimise the solder properties without the use of fluxing agents while avoiding the disadvantages known from the prior art and to also reliably carry out different soldering methods with the same type of aluminium composite material.

[0204] All concentration information in the description, unless otherwise explicitly indicated, relates to the weight.

[0205] 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.

[0206] 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.

[0207] 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.