Aluminium Solder Alloy Free from Si Primary Particles and Method for Producing It

Abstract

The invention relates to an ingot consisting of an aluminium solder alloy having in percentage by weight 4.5%≦Si≦12%; and optionally one or more of the following alloying constituents in percentage by weight: Ti≦0.2%, Fe≦0.8%, Cu≦0.3%, Mn≦0.10%, Mg≦2.0%, Zn_23 0.20%, Cr≦0.05%, with the remainder aluminium and unavoidable impurities, individually at most 0.05 wt %, in total at most 0.15 wt %, wherein boron is additionally provided as an alloying constituent, wherein the boron content is at least 100 ppm and the aluminium alloy is free from primary Si particles having a size of more than 20 μm. The invention further relates to an aluminium alloy product consisting of an aluminium alloy, to an ingot consisting of an aluminium alloy and to a method for producing an aluminium alloy.

Claims

1. An ingot for producing an aluminium alloy product by rolling consisting of an aluminium solder alloy having the following proportions as alloying constituents in percentage by weight:
4.5%≦Si≦12% and optionally one or more of the following proportions as alloying constituents in percentage by weight:
Ti≦0.2%,
Fe≦0.8%,
Cu≦0.3%,
Mn≦0.10%,
Mg≦2.0%,
Zn≦0.20%,
Cr≦0.05%, with the remainder aluminium and unavoidable impurities, individually at most 0.05 wt %, in total at most 0.15 wt %, wherein boron is additionally provided as an alloying constituent, wherein boron is added to the alloy such that the boron content is at least 100 ppm and the aluminium alloy is free from primary Si particles having a size of more than 20 μm, in particular 10 μm.

2. The ingot according to claim 1, wherein the aluminium alloy has the following Si content:
6%≦Si≦11%

3. The ingot according to claim 1, wherein the boron content is ≧140 ppm, preferably≧220 ppm, and/or ≦1000 ppm, preferably ≦800 ppm.

4. The ingot according to claim 1, wherein boron is added to the alloy dependent on one or more other alloying constituents.

5. The ingot according to claim 1, wherein boron is added to the alloy dependent on the Ti, Zr and/or V contents, in particular in such a way that the boron content corresponds to at least one times, to one and a half times, to two and a half times or to at least three times the amount of the sum of the Ti, Zr and V and Cr contents.

6. The ingot according to claim 1, wherein the aluminium solder alloy is composed of aluminium alloy type AA 4043, AA 4343, AA 4045, AA 4044 or AA 4104.

7. The ingot according to claim 1, wherein the aluminium solder alloy has a phosphorus content of at most 30 ppm, of at most 20 ppm or of at most 10 ppm.

8. An aluminium alloy product produced from an ingot according to claim 1 by rolling the ingot.

9. The aluminium alloy product according to claim 8, wherein the aluminium alloy product is formed as a cladding sheet or soldering foil.

10. An aluminium alloy product, at least partly consisting of an aluminium solder alloy having the following proportions as alloying constituents in percentage by weight:
4.5%≦Si≦12% and optionally one or more of the following proportions as alloying constituents in percentage by weight:
Ti≦0.2%,
Fe≦0.8%,
Cu≦0.3%,
Mn≦0.10%,
Mg≦2.0%,
Zn≦0.20%,
Cr≦0.05%, with the remainder aluminium and unavoidable impurities, individually at most 0.05 wt %, in total at most 0.15 wt %, wherein boron is additionally provided as an alloying constituent, wherein boron is added to the alloy such that the boron content is at least 100 ppm and the aluminium alloy is free from primary Si particles having a size of more than 20 μm, in particular 10 μm, and the aluminium alloy product is a strip and has at least one further layer consisting of aluminium or of another aluminium alloy.

11. The aluminium alloy product according to claim 10, wherein the strip is produced by roll cladding or composite casting.

12. The aluminium alloy product according to claim 10, wherein the aluminium alloy product is formed at least as one part of a soldered component, in particular of a heat exchanger.

13. A method for producing an ingot consisting of an aluminium solder alloy, wherein the ingot is utilizable for producing an aluminium alloy product by rolling, the method comprising the steps of: melting pure aluminium with unavoidable impurities, individually at most 0.05 wt %, in total at most 0.15 wt %, in a melting furnace, optionally adding one or more of the following proportions
Ti≦0.2%,
Fe≦0.8%,
Cu≦0.3%,
Mn≦0.10%,
Mg≦2.0%,
Zn≦0.20%,
Cr≦0.05%, to the alloy as further alloying constituents in percentage by weight in the melting furnace or are already at least partially contained in the pure aluminium, adding silicon to the alloy in the melting furnace until an Si content of 4.5 wt % to 12 wt % of the aluminium alloy has been reached, adding boron to the alloy such that the boron content is at least 100 ppm and the solidified aluminium alloy is free from primary Si particles having a size of more than 20 μm, in particular 10 μm, and casting an ingot.

14. The method according to claim 13, wherein the addition of further grain refiners, in particular grain refiners having titanium borides, is dispensed with.

15. The method according to claim 13, wherein the B content is set to 100 ppm, preferably 220 ppm, and/or 1000 ppm, preferably 800 ppm.

16. The method according to claim 13, wherein boron is added to the alloy dependent on the Ti, Zr and/or V contents, in particular in such a way that the B content corresponds to at least one times, to at least one and a half times, to at least two and a half times or to at least three times the amount of the sum of the Ti, Zr and V contents of the starting melt.

17. The method according to claim 13, wherein an aluminium solder alloy is produced from type AA4xxx, AA 4043, AA 4343, AA 4045, AA 4044 or AA 4104.

18. The method according to claim 13, wherein the aluminium solder alloy has a phosphorus content of at most 30 ppm, of at most 20 ppm or of at most 10 ppm.

19. A cladding sheet produced from an ingot according to claim 1, wherein the cladding sheet is sawed from the ingot.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0054] The invention is explained in more detail below on the basis of an exemplary embodiment and in conjunction with the figures.

[0055] In the drawings,

[0056] FIG. 1 shows in a sectional view a milled cast ingot with marked areas for determining the number of primary Si particles,

[0057] FIG. 2 is a micrograph of a comparison aluminium solder alloy having coarse primary Si particles of 20 μm or larger,

[0058] FIGS. 2a and 2b are micrographs of a comparison aluminium solder alloy at different magnifications,

[0059] FIGS. 3a and 3b are micrographs of an inventive aluminium solder alloy at different magnifications, according to an exemplary embodiment of the present invention,

[0060] FIGS. 4a and 4b are micrographs of a comparison aluminium solder alloy at different magnifications,

[0061] FIGS. 5a and 5b are micrographs of an inventive aluminium solder alloy at different magnifications, according to an exemplary embodiment of the present invention,

[0062] FIGS. 6a and 6b are micrographs of a comparison aluminium solder alloy at different magnifications,

[0063] FIGS. 7a and 7b are micrographs of a comparison aluminium solder alloy at different magnifications,

[0064] FIGS. 8a and 8b are micrographs of an inventive aluminium solder alloy at different magnifications, according to an exemplary embodiment of the present invention,

[0065] FIGS. 9a and 9b are micrographs of a comparison aluminium solder alloy at different magnifications,

[0066] FIGS. 10a and 10b are micrographs of an inventive aluminium solder alloy at different magnifications, according to an exemplary embodiment of the present invention,

DETAILED DESCRIPTION OF THE INVENTION

[0067] Firstly, a conventionally produced aluminium solder alloy was examined. The contents of the alloying constituents of the sample are specified in Table 1 in percentage by weight or ppm.

[0068] As can be seen from Table 1, the conventionally produced comparison alloy L1 has a content of approximately 10% silicon and 11 ppm of boron. The other constituents of the comparison alloy L1 can be found in Table 1.

TABLE-US-00001 TABLE 1 Sample Si Fe Cu Mn Mg Ti Cr Zn B P L1 SdT 10.2 0.07 <0.001 <0.005 <0.005 50 ppm <0.001 0.005 11 ppm 7 ppm

[0069] The following was carried out with the comparison alloy L1. Firstly, the alloy was conventionally produced based on a standard primary aluminium pig and silicon in foundry quality together with the use of grain refiners in the form of AlTiB bars, so that a typical boron content below 30 ppm was obtained. The melting temperature before the casting was approximately 750° C.

[0070] The ingot in the casting format 600 mm×200 mm was cast and milled, i.e. the outer shell, which is up to approximately 20 mm thick, was removed. A slice as illustrated in FIG. 1 was separated from the ingot milled in this way perpendicularly with respect to the casting direction. Area sections of 30 mm×20 mm were examined at three different places, namely in the middle of the ingot on the surface 2, at the height of one quarter of the ingot thickness 3, and in the centre of the ingot 4, for the presence of primary Si particles.

[0071] The area sections of 30 mm×20 mm were separated from the ingot slice at the places mentioned and embedded in an epoxy resin, in order to make sample handling easier. The embedded samples were then firstly smoothed manually using SiC paper and abrasive cloth or non-woven abrasive with a grain size of up to 2400. The duration of the smoothing processes was approximately 10 to 20 s with the various grain sizes. Subsequent semi-automatic polishing was carried out firstly with 6 μm and then with 3 μm of polycrystalline diamond suspension for 8 to 9 minutes in each case. Final polishing was carried out using an oxide polishing suspension with a grain size of 0.25 μm for approximately 2 to 5 minutes. The polished sections prepared in this way were evaluated under a reflected-light microscope at 100 times to 200 times magnification.

[0072] At the same time, different production parameter studies, for example different holding times, with or without argon gas flushing, and changes to the gas flushing mixture, were carried out with the comparison alloy L1. It was shown that irrespective of the above-mentioned parameters of the melt treatment, coarse primary Si particles were present in the rolled ingots. The results of the number and size of the primary Si particles of comparison alloy L1 are shown in Table 2. An accumulation of the primary Si particles having a size of up to 22 μm could be seen on the surface.

TABLE-US-00002 TABLE 2 Number of primary Si particles Average size of ¼ ingot Ingot the primary Si Sample Surface thickness centre particles (μm) L1 53 29 171 12-22

[0073] FIG. 2 shows a magnified view of the polished section of an ingot from the ingot centre from comparison alloy L1. In the polished section, it can be clearly identified that coarse primary Si particles are present which have a size of 20 μm and more. The area illustrated in FIG. 2 originates from the centre of the ingot. The magnified image in FIG. 2 has a size of approximately 500 μm×375 μm.

[0074] Corresponding tests were carried out on further exemplary embodiments. The composition of the exemplary embodiments is specified in Table 3. The test batches specified in Table 3 were melted in a tiltable, gas-fired crucible melting furnace with a holding capacity of approximately 800 kg. Commercially available aluminium standard pigs of the type with a degree of purity of 99.85 and single-piece silicon for metallurgical applications with a degree of purity of 98 to 99% were used with all test batches. The starting alloys were melted at approximately 800° C. and subsequently skimmed at 750° C. After a holding time of approximately 10 minutes, the melt was also cast into a rolled ingot format of 600 mm×200 mm via a short channel system in a continuous casting line in the vertical continuous casting process (DC casting).

[0075] In the case of the test batches, the addition of boron took place after the first skimming at 750 0C by adding an AlBS master alloy. After the master alloy had dissolved in the melt, the melt was again skimmed and cast after 10 minutes' holding time.

[0076] The addition of boron took place in several stages. Starting from a standard alloy without the addition of boron, the continuous casting was interrupted, the aluminium boron master alloy type AlBS was added to the alloy, stirred, skimmed and cast after 10 minutes' holding time.

[0077] With the addition of boron, it has been found that a part of the boron with the Ti, V and Zr present in the starting melt partly formed borides which deposited in the furnace.

[0078] In the case of the test batches, the comparison alloy of test V1 formed the starting alloy for the aluminium alloys according to the invention V2, V3, V4. The comparison alloys V5 and V8 formed the starting alloys for the alloys according to the invention in the tests V6, V7 and V9, respectively. It can be clearly identified in all alloys according to the invention that the proportion of Ti, Zr and V decreases due to the deposition of borides in the furnace.

[0079] In Table 3, in addition to details of the proportions of the alloying constituents in wt % (except for boron and Zr), the sum of the alloying constituents Ti, Zr, V and Cr is also specified, as well as the ratio of the content of boron to the sum of the specified alloying constituents.

[0080] The ingots produced from the compositions were examined similar to the test L1 with respect to the microstructure of the aluminium alloy and the presence of coarse silicon particles. The results are illustrated in FIGS. 2 to 10 in each case with two polished section views in different magnifications.

TABLE-US-00003 TABLE 3 Σ B/Σ Test B Zr (Ti, Zr, (Ti, Zr, No. Si Fe Cu Mg P Ti (ppm) V (ppm) Cr V, Cr) V, Cr) V1 Cmp 10 0.107 0.0012 <0.005 0.0005 0.036 3 0.0097 4 0.001 0.0471 0.01 V2 Inv 10 0.125 0.0012 <0.005 0.0004 0.003 150 0.0011 2 0.001 0.0053 2.83 V3 Cmp 10.1 0.122 <0.001 <0.005 0.0005 0.003 70 0.0062 3 0.001 0.0105 0.67 V4 Inv 9.97 0.132 <0.001 <0.005 0.0006 0.003 270 0.001 2 0.001 0.0052 5.19 V5 Cmp 9.93 0.085 0.0023 0.0013 0.0007 0.0032 6 0.0107 3 0.0006 0.0148 0.04 V6 Cmp 10.06 0.085 0.0012 0.0017 0.0006 0.0024 84 0.0079 2 0.0006 0.0111 0.76 V7 Inv 9.94 0.085 0.0014 0.0007 0.0006 0.0002 355 0.0006 1 0.0004 0.0013 27.31 V8 Cmp 10 0.12 0.0014 <0.005 <0.0005 0.0059 29 0.0087 4 0.001 0.016 0.18 V9 Inv 10 0.22 0.0016 <0.005 <0.0005 0.003 690 0.0022 2 0.001 0.0064 10.78

[0081] The polished section images of test no. V1 illustrated in FIGS. 2a and 2b come from a reference aluminium alloy which was produced without the addition of AlBS master alloys. The boron content is 3 ppm. The polished section images FIG. 2a and FIG. 2b clearly show that the ingot has numerous primary Si particles with a size of approximately 30 μm and more. The ingot has a coarse AlSi eutectic and shows long unbranched dendrites.

[0082] FIGS. 3a and 3b show only a few fine Si primary particles in the polished section images FIG. 3a and FIG. 3b of the aluminium alloy V2 according to the invention. These have a size of less than 10 μm. The AlSi eutectic is clearly formed more finely than in the reference test V1. Boron was added here by using an AlBS master alloy. Two hundred ppm of boron were added to the alloy, so that after holding in the furnace 150 ppm could be measured in the cast sample. The ratio of the boron content to the sum of Ti, Zr, V and Cr contents is 2.83 in the case of test no. V2. The dendrites are formed short and branched. It is assumed that already from a value of 100 ppm the effect of boron on the formation of primary Si particles is sufficient such that their size is at most 20 μm. Aluminium solder alloys having corresponding compositions are particularly well suited for providing very thin aluminium solder layers having good soldering properties and a low proneness to soldering defects.

[0083] In contrast to the V2 alloys according to the invention, test no. V3 after the addition of 100 ppm of boron shows a content of 83 ppm of boron in the cast sample. The polished section images of FIGS. 4a and 4b come from an ingot cast with the V3 aluminium alloy. Here and there, primary Si particles having a size above 20 μm can still be identified. The AlSi eutectic is, however, already formed more finely than with the V1 alloy without the addition of boron. The microstructure has long and unbranched dendrites of the primary aluminium phase.

[0084] The addition of 300 ppm of boron gave a boron content of 270 ppm in the cast sample in the case of the V4 test alloy. The polished section images of FIGS. 5a and 5b of the V4 test alloy show short branched dendrites and no Si primary particles in contrast to the V3 alloy. In addition, fine agglomerates of AIB particles could be detected (circle in FIG. 5b). The ratio of boron to the sum of the alloying constituents Ti, Zr, V and Cr was 5.19. The aluminium alloy from test V4 showed a very fine microstructure and is therefore very suitable for thin aluminium solder alloys.

[0085] In FIGS. 6a and 6b, again the polished section images of a comparison alloy VS are illustrated which has no addition of boron and hence only has a B content of 6 ppm. In the polished section image FIG. 6b, Si primary particles approximately 50 to 60 μm in size can be clearly identified. Furthermore, long dendritic structures in the polished section image can be identified as well as a coarse grain structure.

[0086] The AlSi eutectic of test alloy V6 still shows in the polished section images illustrated in FIGS. 7a and 7b long unbranched dendrites and individual Si primary particles having a size of approximately 60 μm. It shows that a boron content of approximately 84 ppm is not sufficient to obtain a significant decrease in the primary particles and a reduction in the number of the particles. At the same time, the effect on the grain refinement is relatively small with a boron content of 84 ppm, so that there is a coarse grain structure.

[0087] The aluminium alloy V7 of the exemplary embodiment from FIGS. 8a and 8b after the addition of boron has a B content of 355 ppm. The ratio of the boron content to the sum of the contents of Ti, Zr, V and Cr is 27.31 and is particularly big. The AlSi eutectic is, as FIG. 8b shows, lamellar in form and has no Si primary particles. The dendrites of the primary aluminium phase are short and branched, FIG. 8a. The grain size is further reduced compared to lower boron contents. Due to the small grain size and the absence of Si primary particles the aluminium alloy V7 is also well suited for producing aluminium solder products which have a very thin aluminium solder layer.

[0088] FIGS. 9a and 9b and FIGS. 10a and 10b show polished section images of the aluminium alloys according to test no. V8 and no. V9. The polished section images are more greatly magnified and show in FIGS. 9a and 10a, respectively, an area with a more coarse formation of the AlSi eutectic and an area with a fine AlSi eutectic in FIG. 9b and FIG. 10b.

[0089] FIGS. 9a and 9b show polished section images of a reference alloy V8 to which no boron was added to the alloy. The boron content is 29 ppm. The polished section images clearly show that Si primary particles of 30 μm in size are present in the microstructure. Numerous Si primary particles were detected. The dendrites are very long and indicate grain sizes in the range from 2 to 3 mm. The AlSi eutectic is also coarsely formed.

[0090] By contrast, FIGS. 10a and 10b show a clear change in the microstructure due to the addition of boron in the test alloy no. V9. The absence of Si primary particles, the formation of a small grain size and a lamellar formation of the AlSi eutectic are attributed to the boron content of the aluminium alloy of 690 ppm. The primary alpha-aluminium phases can also be identified as branched short dendrites, so that it can be assumed that the aluminium alloy V9 is very suitable for particularly thin aluminium solder alloys. The finer grain structure ensures better formability of an aluminium alloy product coated with a corresponding aluminium solder, while the absence of Si primary particles prevents “burning through” due to the formation of a local AlSi eutectic during the soldering process.

[0091] In this exemplary embodiment, the ratio of the boron content to the sum of the contents of Ti, Zr, V and Cr amounts to 10.78. By setting the ratio of the boron content to the sum of the contents of Ti, Zr, V and Cr to at least one times, to at least one and a half times, particularly preferably to at least two and a half times or to at least three times, the reliability of the production process during production of the alloy in relation to the properties presence of Si primary particles is increased, since it can hereby be ensured that the effect of the addition of boron is not disrupted by the formation of borides and their deposition in the furnace. The ratio can preferably rise to values of more than 5, 10 or 20, as the exemplary embodiments show.

[0092] 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.

[0093] 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.

[0094] 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.