Brazing composition, aluminum material provided with the brazing composition and heat exchanger

Abstract: The present invention is a brazing composition for brazing a tube made of aluminum or aluminum alloy and a fin made of aluminum or aluminum alloy when manufacturing a heat exchanger such as evaporators, condensers, radiators, etc., comprising a powder of Al-Si-Zn alloy and binder, wherein the content of Zn in the powder of Al-Si-Zn alloy is in a range of 10 to 55 wt%.

Description: This invention relates to an art used for a heat exchanger for automobiles such as evaporators, condensers, radiators, etc. Heat exchangers made of aluminum or an aluminum alloy material (hereinafter simply referred to as Al material) are manufactured through a steps of forming tubes or fins using brazing sheets clad with brazing materials, assembling them in a predetermined shape and brazing them. However, it is difficult to manufacture brazing sheets and its yield is low, so that this method is wasteful. In addition, waste processing thereof is costly, because brazing sheets are not suitable for recycling. Furthermore, it needs special techniques to manufacture tubes using brazing sheets. Also, brazing sheets are difficult to be processed to a fin and apt to damage jigs. In addition, brazing sheets are difficult to be processed to thin, so that it is also difficult to produce small and light heat exchangers. By the way, as a brazing material for brazing sheets, an Al-Si alloy is used (Japanese Patent Publication No.27037 (1983)). In addition, as another brazing material, Al-Si-Zn alloy is known, too (Japanese Patent Publication No.27037 (1983), Japanese Patent Laid-Open No. 151188 (1991)). The method of manufacturing blazing sheets by cladding a brazing material made of Al-Si∼Zn alloy thereon, however, is difficult, so that this method is not used in practice. JP-A-03114659 discloses a brazing mixture containing Al-Si-Zn alloy powder and a binder. JP-A-03230889 discloses an Al-Si-Zn-BE alloy brazing material. Moreover, When using Al-Si alloy as a blazing material, it is proposed to provide Zn film thereon in advance with a means such as flame spray coating, etc. for increasing corrosion resistance. Namely, this implies that a fin and a tube on which an Zn film is provided are blazed with the Al-Si alloy clad on the fin. But, this method includes complicated steps such as a step of providing a Zn film, so that this method is not preferable. Like this, in a prior art, if trying to keep a sufficient corrosion resistance, the manufacturing process becomes complicated and wasteful. Contrary to this, if trying to reduce manufacturing cost, its corrosion resistance goes down. It is an object of the present invention to provide a brazing composition enabling to manufacture a variety of products of which brazing cost is low and having excellent corrosion resistance. It is another object of the present invention to provide a heat exchanger of which manufacturing cost is low, size is small and weight is light. According to one aspect of the present invention, there is provided a brazing composition comprising a binder and an Al-Si-Zn-In-Be alloy powder wherein the content of Zn is in a proportion of 10 to 55 wt % of said alloy, the content of In is in a proportion of 0.001 to 0.1 wt % of said alloy, and the content of Be is in a proportion of 0.01 to 0.07 wt % of said alloy, optionally up to 15 % Si and up to 0.2 % Bi, balance Al. It is to be noted that it is preferable that the content of Zn is in a proportion of 10 to 40 wt %, more preferably 11 to 36 wt %, and further more preferably 12 to 25 wt % of said alloy. To effectively draw out the functions of the brazing material, it is preferable that the content of Si is in a proportion of 5 to 15 wt % (5 to 11 wt %, in particular) of said alloy. It is preferable that the content of In is in a proportion of 0.01 to 0.1 wt % of the alloy. Advantageously, the alloy contains Bi, and the content of Bi is in a proportion of 0.02 to 0.2 wt % of said alloy. Also, it is allowable that the alloy contains unavoidable impurities. Moreover, to effectively draw out the functions of the brazing material, it is preferable that an average particle diameter of the powder of Al-Si-Zn alloy is in a range of 10 to 200 µm (10 to 53 µm, in particular). The binder is used to provide the powder of the alloy of the present invention on the surfaces of tubes, header pipes or the like. Preferably, the binder used tends to volatize under a brazing temperature. Advantageously, said binder is selected from a group of acrylic resins and methacrylic resins, and an average molecular weight thereof is in the range of 1,000 to 100,000. For example, polybutyl acrylate of which average molecular weight are in a range of 1,000 to 100,000 can be listed up. It is preferable that a blending ratio of the binder is in a proportion of 0.1 to 100 parts by weight of the powder of said alloy of 100 parts by weight. More particularly the blending ratio is in a proportion of 5 to 20 parts by weight of the powder of said alloy of 100 parts by weight. To provide the brazing composition of the present invention on surfaces of Al materials, various coating means are adopted in general, for example, spraying method, flow coater method, roll coater method, brushing method or the like. Using these means, the brazing composition of the present invention is coated such that the thickness after drying is in a range of 5 to 200 µm. The range of the thickness is preferably from 10 to 150 µm, and more preferably 10 to 60 µm. In particular, it is preferable that an amount of the coated powder of the alloy on a surface is in a range of 20 to 400 g/m 2 , in particular, 40 to 150 g/m 2 . For the solvents to be used when coating the powder of the alloy, aliphatic alcohols of which carbon number is in a range of 1 to 8 such as methanol, ethanol, propanol, butanol, isopropyl alcohol, pentanol and the like are listed up. Among them, the most preferable solvent is isopropyl alcohol. On a blending ratio of the binder and the solvent, it is preferable that a content of the solvent is in a proportion of 100 to 10,000 parts by weight of the binder of 100 parts by weight, in particular, a proportion of 500 to 2,000 parts by weight of the binder of 100 parts by weight. For brazing works, fluoride fluxes such as KF-AlF 3 , RbF-AlF 3 are used. These fluxes may be added beforehand into the brazing composition of the present invention. Needless to say, it is possible to use other fluxes than the above. For a blending ratio of these fluxes, it is preferable that a content of flux is in a proportion of 3 to 50 parts by weight of the powder of the alloy of 100 parts by weight. More particularly, a proportion of 10 to 30 parts by weight of the powder of the alloy of 100 parts by weight may be used. It is preferable that a flux is added beforehand into the brazing composition, but it can be added at brazing work. According to another aspect of the present invention, there is provided an aluminum or aluminum alloy material on which is provided a coating film layer comprising a brazing composition as mentioned above. The Al material on which the brazing composition of the present invention is coated may be a component for a heat exchanger, that is, a fin. However, it is preferable that the brazing composition of the present invention is coated on surfaces of a tube or a header pipe. By assembling a fin and a tube (and a header pipe, optionally) on which surface a brazing composition is coated to a preset shape, and joining them by flux brazing under a vacuum atmosphere or an inert gas atmosphere, a heat exchanger is produced. Accordingly, another aspect of the present invention provides a heat exchanger comprising: a tube made of aluminum or aluminum alloy; a coating layer provided on a surface of said tube, said coating film layer comprising a brazing composition as mentioned above, the heat exchanger further including a fin made of aluminum or aluminum alloy and wherein said tube and said fin are joined by flux brazing. The reasons why the powder of Al-Si-Zn-In-Be alloy is adopted by the present invention are as below. (1) This method enables to uniformly diffuse Zn which shows a sacrificial anode effect on the surface of a tube or a header pipe and increase corrosion resistance and pitting corrosion resistance of the tube or the header pipe. In case of using an Al-Si alloy powder instead of the powder of Al-Si-Zn-In-Be alloy, corrosion resistance and pitting corrosion resistance of the resultant tube or header pipe are inferior.Also, in case of using a mixed powder of Al-Si alloy powder and the Zn powder instead of the powder of Al-Si-Zn-In-Be alloy, corrosion resistance and pitting corrosion resistance of the resultant tube or header pipe are inferior. (2) This method enables to provide necessary quantity of brazing material to necessary places. In this invention, an art such as cladding is not necessary, so that the manufacturing process becomes very simple. This reduces manufacturing cost. In particular, it becomes easy to provide a brazing material layer made of the Al-Si-Zn-In-Be alloy that is difficult to be clad. (3) This method enables to provide a various additives of powder (fluxes for brazing, for example) as necessary into a brazing material film as one. Furthermore, as the present invention does not need to use brazing sheets for manufacturing a heat exchanger, the manufacturing cost goes down. Also, as there is no need to use brazing sheets for manufacturing fins, resultant fins can be thin, and a resultant heat exchanger is small and light. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a figure showing an outline of a condenser brazed by the art of the present invention. EXAMPLES Next, concrete examples are explained. Using atomization under a dried nitrogen atmosphere, spherical powders of which average particle size was in a range of 10 to 45 µm in each composition shown in the following Table-1 were produced. Proportion (wt%) Average particle diameter Si Zn In Be Bi Al (µm) E-1 5.0 11.0 0.00 0.04 0.00 rest 10 E-5 10.0 15.0 0.00 0.03 0.00 rest 10 E-7 10.2 15.0 0.02 0.04 0.00 rest 30 E-9 10.0 20.0 0.02 0.02 0.04 rest 30 E-12 7.0 30.0 0.00 0.02 0.00 rest 40 E-14 12.0 30.0 0.02 0.03 0.00 rest 30 E-16 10.0 35.0 0.02 0.02 0.05 rest 20 E-20 6.0 11.0 0.00 0.02 0.15 rest 20 E-21 6.0 11.0 0.00 0.06 0.03 rest 20 E-24 6.0 11.0 0.05 0.02 0.00 rest 20 E-25 6.0 11.0 0.01 0.06 0.00 rest 20 E-26 10.0 15.0 0.00 0.01 0.00 rest 20 C-1 8.0 7.0 0.00 0.00 0.00 rest 30 C-2 8.0 5.0 0.01 0.00 0.00 rest 30 C-3 8.0 0.0 0.00 0.00 0.00 rest 30 Where, "E" means example of Embodiment and "C" means example for Comparison. For each example, 100 parts by weight of the above alloy powder, 10 parts by weight of binder (polybutyl acrylate of average molecular weight 10,000), 50 parts by weight of solvent (isopropyl alcohol) and 15 parts by weight of flux (KF-AlF 3 ) were mixed and stirred. Thus, samples of brazing composition were produced. Next, each of the above brazing composition was coated 30 µm in thickness (amount of alloy powder is 60 g/m 2 ) on a surface of extruded aluminum tube made of Al alloy of 2 mm in thickness, 20 mm in width and 500 mm in length. Also, each of the above brazing composition was coated 150 µm in thickness (amount of alloy powder is 300 g/m 2 ) on a part of a header pipe made of Al alloy in which the extruded aluminum tube would be inserted. Assembling these extruded aluminum tubes, header pipes and fins, brazing were conducted by keeping them for 5 minutes at about 600°C under dried nitrogen atmosphere, thus a condenser for automobile shown by Fig.1 was obtained. In this figure, number 1 is the fin, number 2 is the extruded aluminum tube and number 3 is the header pipe. Results of examinations of the heat exchanger on brazing rate, corrosion resistance, pitting corrosion resistance are shown in the following Table-2. Joining Rate Corrosion Resistance Pitting Corrosion Resistance E-1 99% ○ ○ E-5 99% ○ ○ E-7 99% ▵ o ○ E-9 100% ▵ o ○ E-12 99% ○ ○ E-14 99% ▵ o ○ E-16 100% ▵ o ○ E-20 100% ○ ○ E-21 100% ○ ○ E-24 99% ▵ o ○ E-25 99% ▵ o ○ E-26 99% ○ ○ C-1 97% ▵ X C-2 97% ▵ X C-3 97% X X C-4 93% X X C-5 93% ▵ ○ Where, "E" shows example of Embodiment and "C" shows example for Comparison. * In C-4, a mixed powder of 70 parts by weight of Al-Si alloy powder (Al: 92 wt%, Si: 8 wt%) of 30 µm in size and 30 parts by weight of Zn powder of 30 µm in size were used and processed similarly to the E-1. * In C-5, a brazing composition of Al-Si alloy powder (Al: 92 wt%, Si: 8 wt%) of 30 µm in size was coated on a surface of the extruded aluminum tube made of Al alloy on which Zn film was provided by flame spray coating, followed by flux brazing. * ○ in the column of "Corrosion Resistance" shows: "Only a little corrosion can be found on the tube". * ▵ shows "Light corrosion can be found on whole of the tube". * X shows "Very heavy corrosion can be found on whole of the tube". * o ○ in the column of "Pitting Corrosion Resistance" shows: "Only the surface of the tube is pitting corroded". * ○ shows "A little pitting corrosion can be found on the tube". * ▵ shows "Heavy pitting corrosion can be found on the tube". * X shows "Much penetrating pitting corrosion can be found on the tube". Furthermore, similarly to the above embodiment, the above brazing composition of 30 µm (amount of alloy powder: 60 g/m 2 ) was coated on a surface of the extruded aluminum tube made of Al winded in coil-shape, followed by being cut into a predetermined length. Next, assembling the extruded aluminum tube thus obtained, a header pipe and a fin, a condenser shown in Fig.1 was obtained similarly to the above embodiment. This heat exchanger was examined on joining rate, corrosion resistance and pitting corrosion resistance. As a result, the same results as Table-2 were obtained. These results show that the brazing composition of the present invention has excellent brazing property and superior corrosion resistance and pitting corrosion resistance. It is to be noted that all the brazing compositions containing Zn can not give superior corrosion resistance and pitting corrosion resistance. Namely, even if Zn is used, such a feature like this invention can not be obtained so far as the brazing composition is in a form of mixture of Al-Si alloy powder and Zn powder. In addition, however, it is not enough to use Al-Si-Zn-In-Be alloy, but the Zn content in the Al-Si-Zn-In-Be alloy must be such high as 10 to 55 wt%. Furthermore, it is not enough to use Al-Si-Zn-In-Be alloy of the above proportion, but the Al-Si-Zn-In-Be alloy must be powder. Described as above, the present invention enables to braze a tube made of aluminum and a fin made of aluminum alloy at a low temperature such as under 600°C, so that brazing work becomes easy and aluminum materials can avoid to be damaged by high temperature.

Claims: A brazing composition comprising a binder and an Al-Si-Zn-In-Be alloy powder wherein the content of Zn is in a proportion of 10 to 55 wt % of said alloy, the content of In is in a proportion of 0.001 to 0.1 wt % of said alloy, and the content of Be is in a proportion of 0.01 to 0.07 wt % of said alloy, optionally up to 15 % Si and up to 0.2 % Bi, balance Al apart from impurities. The brazing composition of Claim 1, wherein the content of Si is in a proportion of 5 to 15 wt % of said alloy. The brazing composition of Claim 1 or Claim 2 wherein said alloy contains Bi, and the content of Bi is in a proportion of 0.02 to 0.2 wt % of said alloy. The brazing composition of any preceding claim, wherein an average particle diameter of said powder of said alloy is in a range of 10 to 200 µm. The brazing composition of any preceding claim, wherein said binder tends to volatilize under a brazing temperature. The brazing composition of any preceding claim, wherein said binder is selected from a group of acrylic resins and methacrylic resins, and an average molecular weight thereof is in a range of 1,000 to 100,000. The brazing composition of any preceding claim, wherein a content of said binder is in a proportion of 0.1 to 100 parts by weight of said powder of said alloy of 100 parts by weight. The brazing composition of any preceding claim, further comprising a solvent, wherein a content of said solvent is in a proportion of 100 to 10,000 parts by weight of said binder of 100 parts by weight. The brazing composition of any preceding claim, further comprising a flux, wherein a content of said flux is in a proportion of 3 to 50 parts by weight of said powder of said alloy of 100 parts by weight. An aluminum or aluminum alloy material on which is provided a coating film layer comprising a brazing composition according to any preceding claim. A heat exchanger comprising: a tube made of aluminum or aluminum alloy; a coating film layer provided on a surface of said tube, said coating film layer comprising a brazing composition according to any of Claims 1 to 9, the heat exchanger further includes a fin made of aluminum or aluminum alloy and wherein said tube and said fin are joined by flux brazing.

Inventors: MOMOSAKI HIROTO, SAITO HITOSHI, TOHMA KEN, MOMOSAKI, HIROTO, SAITO, HITOSHI, TOHMA, KEN
Applicants: MITSUBISHI ALUMINIUM, MITSUBISHI ALUMINUM CO.,LTD.
Application year: 1995
Main classification: B23K35
IPC codes: B23K35, F28F1, F28F21