Paste composition for brazing

Abstract

To provide a paste composition for brazing that is suitable for brazing an aluminum alloy base metal or the like, excellent in brazing properties such as flowability and wettability on a base material surface of a brazing material, and capable of stably yielding desired bonding strength.SOLUTION: A paste composition for brazing contains a brazing material made of aluminum alloy powder, flux and butyl rubber. The brazing material contains 27 mass% or more and 30 mass% or less of Cu, and 4.0 mass% or more and 6.0 mass% or less of Si, and the rest comprises Al and an inevitable foreign matter. An oxygen content of the brazing material is less than 300 ppm. The flux contains CsF. The paste composition for brazing contains 10 pts.mass or more and 50 pts.mass or less of the flux based on 100 pts.mass of the brazing material, and contains 1 pt.mass or more and 15 pts.mass or less of the butyl rubber based on 100 pts.mass of the brazing material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a brazing paste composition, and particularly to a brazing paste composition that is suitable for brazing aluminum or aluminum alloy materials and has excellent brazing properties such as the flowability and wettability of the brazing filler metal on the surface of the base material. [Background technology]

[0002] Brazing has long been known as a method for joining metals, ceramics, etc. Brazing falls under the category of welding methods, and is a method of brazing using a brazing filler metal with a melting point lower than that of the objects to be brazed and at 450°C or higher. More specifically, the brazing filler metal applied to the surface of one base material is heated to a temperature at which the brazing filler metal melts but not the base material, and a thin film of the brazing filler metal diffuses to the joining surface with the other base material by capillary action, solidifying the brazing filler metal and joining the base materials together.

[0003] Among the brazing base materials mentioned above, the use of aluminum and aluminum alloy die-cast products has been increasing in a wide range of fields, such as automobiles and home appliances, due to their light weight. Furthermore, the importance of brazing has increased as these products have become more complex in shape, and brazing materials made of aluminum alloy powder are generally used for brazing aluminum alloys.

[0004] Against this background, in recent years, there has been active development of brazing filler metals made from aluminum alloy powder with lower melting points and improved flow and wettability that tend to deteriorate at lower temperatures, with the aim of suppressing oxide formation at the joint (fillet) and protecting the base material.

[0005] For example, Japanese Patent Laid-Open Publication No. 2007-83271 (Patent Document 1) discloses a brazing filler metal and a brazing method using the brazing filler metal, which is an aluminum alloy brazing filler metal slurry prepared by suspending, in a dispersion medium, a powdered aluminum alloy brazing filler metal having an average particle size of 10 to 100 μm and containing 23 to 37 mass % of Cu, 4 to 10 mass % of Si, with the remainder being Al and unavoidable impurities, and a fluoride-based flux containing 11 mass % or more of CsF as a solid content. The brazing filler metal suppresses the occurrence of defects such as brazing failure and provides sound joints with excellent wettability and corrosion resistance, and the brazing filler metal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-83271 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a powdered aluminum alloy brazing filler metal as described in Patent Document 1 is used in the form of a slurry to braze a base material made of an aluminum alloy or the like, the brazing properties, such as the flowability and wettability of the brazing filler metal on the surface of the base material, are not necessarily sufficient, and there are problems such as the joint portion (fillet) being broken after brazing or voids being formed inside the fillet, making it impossible to obtain sufficient joint strength.

[0008] Therefore, an object of the present invention is to provide a paste-like composition for brazing that is particularly suitable for brazing aluminum or aluminum alloys as base materials, and that has excellent brazing properties such as flowability and wettability of the brazing filler metal on the surface of the base material, so that the joint (fillet) after brazing is not broken or voids are not formed inside the fillet, and the desired joint strength can be stably obtained. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present inventors have conducted extensive research into the compositions and combinations of brazing filler metals made of aluminum alloy powder, fluxes, and binders used in brazing paste compositions. As a result, they have found that the above-mentioned problems can be effectively solved by using a brazing filler metal made of aluminum alloy powder with a particularly low oxygen content in combinations of brazing filler metals, fluxes, and binders having specific compositions and components, and have thus completed the present invention.

[0010] That is, according to the present invention, there is provided a brazing paste composition comprising a brazing filler metal made of aluminum alloy powder, a flux, and butyl rubber as a binder, wherein the brazing filler metal contains 27 to 30 mass% Cu, 4.0 to 6.0 mass% Si, with the remainder being Al and unavoidable impurities, the oxygen content of the brazing filler metal is preferably less than 300 ppm, more preferably less than 200 ppm, the flux contains CsF, and the flux is contained in an amount of preferably 10 to 50 parts by mass, more preferably 20 to 40 parts by mass, per 100 parts by mass of the brazing filler metal, and the butyl rubber is contained in an amount of preferably 1 to 15 parts by mass, more preferably 2 to 10 parts by mass, per 100 parts by mass of the brazing filler metal.

[0011] In the present invention, in order for the brazing paste composition to exhibit better brazing properties, it is more preferable that the CsF content of the flux is 10 mass % or more and 100 mass % or less, and the volume average particle diameter (D 50 ) is preferably 20 μm or more and 150 μm or less.

[0012] As a result, the brazing paste composition of the present invention is particularly suitable for brazing aluminum or aluminum alloys as base materials, and has excellent brazing properties such as flowability and wettability of the brazing material on the surface of the base material, so that the joint (fillet) after brazing is not broken and voids are not formed inside the fillet, and the desired joint strength can be stably obtained.

[0013] The brazing paste composition of the present invention contains a brazing filler metal made of aluminum alloy powder, flux, butyl rubber as a binder, and a solvent for wetting them. The brazing paste composition of the present invention may also contain other additives such as dispersants, thickeners, antifoaming agents, and colorants depending on the application. [Effects of the Invention]

[0014] According to the present invention, there is provided a brazing paste composition comprising a brazing filler metal made of aluminum alloy powder, a flux, and butyl rubber as a binder, wherein the brazing filler metal contains 27 to 30 mass% Cu, 4.0 to 6.0 mass% Si, with the remainder being Al and unavoidable impurities, the oxygen content of the brazing filler metal is less than 300 ppm, and the flux contains CsF, and the flux is contained in an amount of 10 to 50 parts by mass relative to 100 parts by mass of the brazing filler metal, and the butyl rubber is contained in an amount of 1 to 15 parts by mass relative to 100 parts by mass of the brazing filler metal.

[0015] As a result, the brazing paste composition of the present invention is particularly suitable for brazing components whose base material is aluminum or an aluminum alloy, and has excellent brazing properties such as flowability and wettability of the brazing filler material on the surface of the base material, so that the joint (fillet) after brazing is not broken or voids are not formed inside the fillet, and the desired joint strength can be stably obtained, which is an excellent effect. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a SEM photograph of the aluminum alloy powder of the brazing filler metal of Example 1. [Figure 2] 3 is a photograph of evaluation samples 1, 2, and 3 showing the molten state of the brazing filler metal of the paste composition after brazing. [Figure 3] 3 is an optical microscope photograph of a cross section of evaluation sample 1 of the brazing filler metal with a melting state evaluation of "A" in FIG. 2. [Figure 4]3 is an optical microscope photograph of a cross section of evaluation sample 2 of the brazing filler metal molten state evaluation "B" in FIG. 2. [Figure 5] 3 is an optical microscope photograph of a cross section of evaluation sample 3 of the brazing filler metal molten state evaluation "C" in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0017] A brazing paste composition according to one embodiment of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the examples shown below, and various modifications are possible within the scope of the technical concept of the present invention.

[0018] <Brazing Paste Composition> The brazing paste composition of the present invention contains a brazing filler metal made of aluminum alloy powder, a flux, butyl rubber as a binder, and a solvent for wetting these to form a paste. The composition may also contain other additives such as dispersants, thickeners, antifoaming agents, and colorants, provided that the effects of the present invention are not impaired.

[0019] <Brazing material (powder)> The brazing filler metal (powder) used in the present invention is an aluminum alloy powder containing 27.0 to 30.0 mass% Cu, 4.0 to 6.0 mass% Si, and the remainder being Al and unavoidable impurities. Such a brazing filler metal (powder) has a lower melting point than aluminum and other aluminum alloy base materials, and not only can it suppress melting of the base materials to be joined, but also can achieve strong brazing because it joins aluminum to aluminum.

[0020] The oxygen content of the brazing filler metal (powder) made of the aluminum alloy powder used in the present invention is preferably less than 300 ppm, more preferably less than 200 ppm. If the oxygen content of the brazing filler metal (powder) is 300 ppm or more, the brazing filler metal (powder) becomes difficult to melt, and the flowability of the brazing filler metal (powder) and its wettability to the base metal are also reduced.

[0021] The ideal lower limit for the oxygen content of brazing filler metal (powder) is 0 ppm, but considering production costs, a value of 100 ppm or higher is practically acceptable. The oxygen content of brazing filler metal (powder) can be measured using the inert gas fusion non-dispersive infrared absorption method (instrument name: HORIBA EMGA-920 oxygen / nitrogen analyzer, manufactured by Horiba, Ltd.).

[0022] The shape of the brazing filler metal (powder) made of aluminum alloy powder is not particularly limited, but it is preferably approximately spherical or true spherical. Furthermore, it is preferable that the brazing filler metal (powder) has few secondary particles and does not form fine satellite particles adhered to the surfaces of larger particles. When the brazing filler metal (powder) is approximately spherical or true spherical and does not have satellite particles, the specific surface area of ​​each particle is small, making it easier to keep the oxygen content of the brazing filler metal (powder) below 300 ppm.

[0023] The particle size of the brazing material (powder) is not particularly limited, but the volume average particle size (D 50 The volume average particle diameter (D) of the brazing material (powder) is preferably 20 μm or more and 150 μm or less, and more preferably 50 μm or more and 100 μm or less. 50 By making the average particle diameter (D) of the brazing filler metal (powder) 50 μm or more, it becomes easier to keep the oxygen content of the brazing filler metal (powder) below 300 ppm. 50 By making the thickness 100 μm or less, the thickness of the brazing paste composition applied can be reduced, and the brazing material (powder) can be uniformly dispersed in the applied paste composition.

[0024] In the present invention, in order to keep the oxygen content of the brazing filler metal (powder) to 300 ppm or less, it is preferable that the brazing filler metal (powder) contains 20 volume % or less of fine aluminum alloy powder having a particle size of 50 μm or less. In the present invention, in order to reduce the oxygen content of the brazing filler metal (powder) made of aluminum alloy powder, the aluminum alloy powder can be produced by, for example, atomization in an inert atmosphere.

[0025] <Flux> The flux used in the present invention contains CsF. The CsF content is preferably 10% by mass or more and 100% by mass or less, and more preferably 20% by mass or more and 90% by mass or less. Fluxes other than CsF that can be used in the present invention include KF and AlF3.

[0026] The amount of flux blended is preferably 10 to 50 parts by mass, and more preferably 20 to 40 parts by mass, per 100 parts by mass of brazing filler metal (powder). If the amount of flux blended per 100 parts by mass of brazing filler metal (powder) is less than 10 parts by mass, the oxide film on the base material (e.g., aluminum alloy) and the brazing filler metal (powder) cannot be sufficiently removed, making it difficult for the brazing filler metal to wet the base material and form a good fillet. This can result in the brazing filler metal being repelled by the base material and remaining on the base material surface as globules. On the other hand, if the amount of flux blended per 100 parts by mass of brazing filler metal (powder) exceeds 50 parts by mass, the excess flux will create voids within the fillet, reducing brazing strength.

[0027] <Binder> The brazing paste composition of the present invention contains butyl rubber as a binder. By including butyl rubber in the paste composition, the brazing material (powder) and flux are less likely to scatter even when the organic solvent volatilizes during heating, improving workability.

[0028] In addition, in the present invention, the use of butyl rubber as a binder improves brazing properties. This is thought to be because butyl rubber has the property of being difficult for air to pass through, protecting the brazing filler metal from small amounts of oxygen and moisture that remain even in an inert atmosphere during heating. Furthermore, because butyl rubber does not contain heteroelements, it does not produce corrosive gases even when thermally decomposed in an inert atmosphere. Maintaining an inert or reducing atmosphere suppresses oxidation of the brazing filler metal. Another advantage of butyl rubber is that it leaves less carbon residue than other resins.

[0029] Butyl rubber is a copolymer of isobutylene and isoprene monomers, and because the bonds between the isobutylene and isoprene monomers are linear, it has a structure that is easily decomposed by heat. Therefore, butyl rubber is easily decomposed by heat during the brazing process without being affected by the atmosphere inside the brazing furnace.

[0030] The amount of butyl rubber blended is preferably 1 part by mass to 15 parts by mass, and more preferably 2 parts by mass to 10 parts by mass, per 100 parts by mass of the brazing filler material (powder). If the amount of butyl rubber blended is less than 1 part by mass per 100 parts by mass of the brazing filler material (powder), the above-mentioned effects of the butyl rubber cannot be obtained, and if the amount of butyl rubber blended exceeds 15 parts by mass, carbon residue may remain after heating, resulting in a poor appearance.

[0031] <Solvent> The type of solvent used in the present invention is not particularly limited as long as it dissolves the binder. Known organic solvents such as aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohol solvents, ether solvents, ester solvents, ketone solvents, and glycol ether solvents may be used alone or in combination.

[0032] More specifically, examples of aliphatic hydrocarbon solvents include compounds such as pentane, hexane, heptane, cyclohexane, and methylcyclohexane, as well as mixtures of petroleum ether, isoparaffinic oil, and naphthenic oil. Examples of aromatic hydrocarbon solvents include compounds such as benzene, toluene, xylene, ethylbenzene, and naphthalene, as well as mixtures of white spirit. Examples of alcohol solvents include methanol, ethanol, propanol, isopropanol, and butanol. Examples of ether solvents include diethyl ether and tetrahydrofuran. Examples of ester solvents include ethyl acetate, propyl acetate, butyl acetate, acetic acid, pentyl, hexyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, hexyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, pentyl butyrate, hexyl butyrate, γ-butyrolactone, and ε-caprolactone. Examples of ketone solvents include acetone, methyl ethyl ketone, diethyl ketone, cyclohexanone, etc. Examples of glycol ether solvents include cellosolve, ethyl cellosolve, butyl cellosolve, methyl carbitol, ethyl carbitol, butyl carbitol, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether, dipropylene glycol monomethyl ether acetate, etc.

[0033] The amount of the solvent is not particularly limited, but is preferably 10 parts by mass or more and 50 parts by mass or less, and more preferably 10 parts by mass or more and 30 parts by mass or less, when the total amount of the brazing paste composition is 100 parts by mass. If the amount of the solvent is within this range, the paste composition can be easily applied to the base material and is less likely to drip after application.

[0034] <Base material> The brazing paste composition of the present invention can be widely used to join components whose base metal is aluminum or an aluminum alloy having a higher melting point than the brazing filler metal (powder) used. The multiple components to be joined may each have the same type of aluminum or aluminum alloy as their base metal, or may each have different types of aluminum or aluminum alloy as their base metal.

[0035] Suitable base materials for the brazing of the present invention include aluminum with a purity of 99.00% or higher, such as A1100 and A1050. Applicable aluminum alloys include, but are not limited to, Al-Mn alloys such as A3003 and A3004, Al-Mg alloys such as A5052, Al-Mg-Si alloys such as A6063, and Al-Zn-Mg alloys such as A7003 and A7020.

[0036] <Brazing method> A method for joining components whose base material is aluminum or an aluminum alloy using the brazing paste composition of the present invention includes at least an application step of applying the brazing paste composition of the present invention to the components to be joined, an assembly step of assembling the components, and a brazing step of heating to melt the brazing material (powder).

[0037] The method for applying the brazing paste composition is not particularly limited, and may be appropriately selected from known methods taking into consideration the shape of the members to be joined, the joining method, etc. For example, when joining the surfaces of plate-like members, the brazing paste composition may be applied to the surface of one member using a doctor blade or the like, and then the joining surface of the other member may be attached to the applied surface to assemble them. Furthermore, when joining the ends of plate-like or cylindrical members, where the joining surface is strip-shaped or linear, the plate-like or cylindrical member may first be assembled to the other members to be joined, and then the brazing paste composition may be applied to the joining portion using a syringe, dispenser, or the like.

[0038] The brazing process may be carried out in a single heating step, or may be divided into a drying step in which the solvent in the brazing paste composition is evaporated, and a degreasing step in which the binder is also removed, and heating is carried out in stages. When a drying step is provided, the paste composition may be dried at room temperature or, as necessary, at a temperature of about 30°C to 200°C. If the paste composition is not dried, the solvent in the applied paste composition may bump, causing the applied paste composition to scatter.

[0039] Brazing by heating can be carried out using a brazing furnace such as a muffle furnace under atmospheric pressure in an inert gas atmosphere such as nitrogen, argon, helium, etc. A carbon muffle furnace is preferably used as the brazing furnace because it absorbs trace amounts of oxygen remaining in the inert gas.

[0040] The heating temperature for brazing may be any temperature at which the brazing material (powder) and flux melt but the base material does not melt. Specifically, the heating temperature is preferably 500°C or higher and 550°C or lower, and more preferably 520°C or higher and 545°C or lower. The heating time may be any time sufficient to completely melt the brazing material (powder) and distribute it over the entire joining surface. Specifically, the heating time is preferably 1 minute or higher and less than 1 hour, and more preferably 3 minutes or higher and less than 30 minutes. Note that the heating temperature for brazing usually refers to the temperature of the base material used for brazing. However, when brazing is performed using a brazing furnace such as a muffle furnace, the ambient temperature of the brazing furnace may be used instead, since the ambient temperature of the brazing furnace shows approximately the same temperature history as the base material. [Example]

[0041] 1. Preparation of a brazing paste composition The brazing paste composition according to one embodiment of the present invention and the brazing paste composition of the comparative example were produced using the following raw materials and conditions (see "Table 1"). [Example 1] <Brazing material (powder)> The raw materials were mixed to contain 29.5% Cu, 5.0% Si, and the remainder Al and unavoidable impurities. The mixture was placed in a ceramic crucible and melted at 800°C in an inert atmosphere to obtain a molten brazing filler metal. The resulting molten brazing filler metal was then atomized in an inert gas atmosphere to obtain a brazing filler metal (powder) made from aluminum alloy powder. The oxygen content of the resulting brazing filler metal (powder) was measured using an oxygen / nitrogen analyzer (instrument name: HORIBA EMGA-920 Oxygen / Nitrogen Analyzer, manufactured by Horiba, Ltd.) and found to be 160 ppm. An SEM image of the resulting powder is shown in Figure 1.

[0042] <Brazing Paste Composition> Next, 100 parts by mass of the brazing filler metal (powder) obtained above was mixed with 30 parts by mass of CF-7 powder (manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd., CsF:AlF3 molar ratio of 50:50 to 60:40) as a flux containing CsF, and further, a solution of 1 g of butyl rubber (Butyl 268, manufactured by JSR Corporation) dissolved in 4 g of petroleum ether was added as a binder and mixed in a mixer to prepare the brazing paste composition of Example 1.

[0043] [Example 2] A brazing paste composition of Example 2 was prepared under the same conditions as Example 1, except that an aluminum alloy powder containing 27.5 mass % of Cu was used.

[0044] [Example 3] A brazing paste composition of Example 3 was prepared under the same conditions as in Example 1, except that the blending amount of the flux was 15 parts by mass.

[0045] [Example 4] A brazing paste composition of Example 4 was prepared under the same conditions as in Example 1, except that the blending amount of flux was 45 parts by mass.

[0046] [Example 5] A brazing paste composition of Example 5 was prepared under the same conditions as in Example 1, except that the oxygen content of the aluminum alloy powder was adjusted to 290 ppm by an atomization process.

[0047] [Example 6] A brazing paste composition of Example 6 was prepared under the same conditions as in Example 1, except that the blending amount of the binder was 10 parts by mass.

[0048] [Comparative Example 1] A brazing paste composition of Comparative Example 1 was prepared under the same conditions as in Example 1, except that an aluminum alloy powder containing 25 mass % of Cu was used.

[0049] Comparative Example 2 A brazing paste composition of Comparative Example 2 was prepared under the same conditions as in Example 1, except that an aluminum alloy powder containing 31 mass % of Cu was used.

[0050] Comparative Example 3 A brazing paste composition of Comparative Example 3 was prepared under the same conditions as in Example 1, except that an aluminum alloy powder containing 3 mass % of Si was used.

[0051] Comparative Example 4 A brazing paste composition of Comparative Example 4 was prepared under the same conditions as in Example 1, except that an aluminum alloy powder containing 7 mass % of Si was used.

[0052] Comparative Example 5 A brazing paste composition of Comparative Example 5 was prepared under the same conditions as in Example 1, except that a non-CsF based Nocolok (registered trademark) Flux (manufactured by Solvay) was used as the flux.

[0053] Comparative Example 6 A brazing paste composition of Comparative Example 6 was prepared under the same conditions as in Example 1, except that the blending amount of flux was set to 7 parts by mass.

[0054] Comparative Example 7 A brazing paste composition of Comparative Example 7 was prepared under the same conditions as in Example 1, except that the blending amount of flux was set to 55 parts by mass.

[0055] [Comparative Example 8] A brazing paste composition of Comparative Example 8 was prepared under the same conditions as in Example 1, except that the oxygen content of the aluminum alloy powder was adjusted to 310 ppm by an atomization process.

[0056] Comparative Example 9 A brazing paste composition of Comparative Example 9 was prepared under the same conditions as in Example 1, except that the oxygen content of the aluminum alloy powder was adjusted to 500 ppm by an atomization process.

[0057] [Comparative Example 10] A brazing paste composition of Comparative Example 10 was prepared under the same conditions as in Example 1, except that the blending amount of the binder was set to 0 parts by mass.

[0058] [Comparative Example 11] A brazing paste composition of Comparative Example 11 was prepared under the same conditions as in Example 1, except that the amount of binder was changed to 0.5 parts by mass.

[0059] [Comparative Example 12] A brazing paste composition of Comparative Example 12 was prepared under the same conditions as in Example 1, except that the blending amount of the binder was changed to 20 parts by mass.

[0060] [Comparative Example 13] A brazing paste composition of Comparative Example 13 was prepared under the same conditions as in Example 1, except that ethyl cellulose was used as the binder.

[0061] 2. Evaluation of brazing paste composition <Measurement of brazing filler metal (powder) characteristics> (1) Volume average particle size The volume average particle diameter (D 50) indicates the particle diameter (μm) at 50% of the volume average particle diameter in the volume cumulative particle size distribution curve. The volume average particle diameter was measured using a laser diffraction / scattering particle size distribution measuring device (instrument name: Microtrac, manufactured by Microtrac-Bell). For example, the volume average particle diameter (D 50 ) means the particle size (μm) at a cumulative frequency of 50% in a volume cumulative particle size distribution curve in which the vertical axis is cumulative frequency (%) and the horizontal axis is particle size (μm).

[0062] (2) Measurement of oxygen content The oxygen content of the brazing filler metal (powder) made of aluminum alloy powder was measured using an oxygen / nitrogen analyzer (instrument name: HORIBA EMGA-920 oxygen / nitrogen analyzer, manufactured by Horiba, Ltd.).

[0063] <Evaluation of brazeability> (1) Preparation of brazed samples <Brazing> A 55 mm x 25 mm x 2 mm plate and a 50 mm x 20 mm x 2 mm plate of JIS aluminum wrought material A1050 were assembled in a T-shape, and 0.2 g of the paste composition of each example and comparative example was applied using a syringe to one side of the joint. 3 Brazing was carried out by holding the brazing temperature at 540°C for 5 minutes using a batch-type brazing furnace for aluminum adjusted to a temperature of 540°C / h.

[0064] (2) Brazeability evaluation After brazing was completed, the brazed portion of the T-shaped aluminum plates was visually and optically observed for the molten state of the brazing filler metal, its wettability to the base material (appearance), the formation of fillets (appearance), and voids inside the fillets, and evaluated according to the following criteria.

[0065] (1) Melting state of brazing material "A": Good spread, no discontinuities on both the coated and uncoated sides (see evaluation sample 1 in Figure 2) "B": The wax flow is slightly poor and breaks are visible (see evaluation sample 2 in Figure 2). "C": The brazing filler metal is not melted (see evaluation sample 3 in Figure 2).

[0066] (2) Wettability to the base material (appearance) "A": The molten brazing material has spread throughout the joint. "B": The molten brazing material is spreading only around the applied area. "C": The brazing filler metal does not spread and is in the form of beads, or is not melted.

[0067] (3) Fillet formation (appearance) "A": A continuous fillet is formed on both the coated and non-coated sides, and the buildup is built up. "B": Fillet is formed but is broken "C": Fillet is not formed or is extremely small

[0068] (4) Voids inside the fillet "A": No or very few voids (see Figure 3) "B": Fine voids present (see Figure 4) "C": Large void size and many voids (see Figure 5)

[0069] Table 1 shows the composition of each brazing paste composition of Examples 1 to 6 and Comparative Examples 1 to 13 and the evaluation results of the brazing properties of each brazing paste composition. [Table 1]

[0070] <Consideration> Comparison of the brazing paste compositions of Examples 1 and 2 and Comparative Examples 1 and 2 revealed that the melting state of the brazing material was good when the Cu content in the brazing material (powder) was 27% by mass or more and 30% by mass or less. It is thought that when the Cu content was 25% by mass or less, the θ phase (CuAl2) precipitated, reducing the melting state of the brazing material, and when the Cu content was 30% by mass or more, the melting point became high, which is why the brazing material no longer melted at 540°C.

[0071] Comparing the brazing paste compositions of Example 1 with those of Comparative Examples 3 and 4, it was found that the melted state of the brazing material was improved when the Si content in the brazing material (powder) was 4% by mass or more and 6% by mass or less.

[0072] Comparison of the brazing paste compositions of Example 1 and Comparative Example 5 revealed that the inclusion of CsF as a flux improved the molten state of the brazing material and its wettability to the base material.

[0073] Comparing the brazing paste compositions of Examples 1, 3, and 4 and Comparative Examples 6 and 7, it was found that by using 10 to 50 parts by mass of flux per 100 parts by mass of brazing material (powder), the melted state of the brazing material is good and the occurrence of voids inside the fillet is suppressed.

[0074] Comparison of the brazing paste compositions of Examples 1 and 5 and Comparative Examples 8 and 9 revealed that the molten state of the brazing material was good when the oxygen content in the brazing material (powder) was less than 300 ppm.

[0075] Comparison of the brazing paste compositions of Examples 1 and 6 and Comparative Examples 10, 11, 12, and 13 revealed that the melted state of the brazing material was good when the blending amount of butyl rubber was 1 part by weight or more and 15 parts by weight or less.

[0076] From the above results, it was found that by using the brazing paste composition according to the examples of the present invention, aluminum materials or aluminum alloy materials can be brazed together satisfactorily. [Explanation of symbols]

[0077] 1. Aluminum alloy powder for brazing filler metal 2. Brazeability evaluation sample (JIS aluminum wrought material A1050) 3. Fillet 4...Void

Claims

1. A brazing paste composition comprising a brazing filler metal made of aluminum alloy powder, a flux, and butyl rubber, The brazing filler metal contains 27% by mass or more and 30% by mass or less of Cu, 4.0% by mass or more and 6.0% by mass or less of Si, and the remainder being Al and inevitable impurities, The oxygen content of the brazing filler metal is less than 300 ppm; the flux comprises CsF, and The flux is contained in an amount of 10 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the brazing filler metal, A brazing paste composition comprising the butyl rubber in an amount of 1 part by mass or more and 15 parts by mass or less relative to 100 parts by mass of the brazing filler metal.

2. 2. The brazing paste composition according to claim 1, wherein the brazing filler metal has an oxygen content of less than 200 ppm.

3. 2. The brazing paste composition according to claim 1, wherein the CsF content of the flux is 10% by mass or more and 100% by mass or less.

4. The brazing paste composition according to claim 1, wherein the butyl rubber is contained in an amount of 2 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the brazing filler metal.

5. 2. The brazing paste composition according to claim 1, wherein the flux is contained in an amount of 20 parts by mass or more and 40 parts by mass or less relative to 100 parts by mass of the brazing filler metal.

6. The brazing material has a volume average particle diameter (D ５０ 6. The brazing paste composition according to claim 1, wherein the average particle size is 20 μm or more and 150 μm or less.

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