Brazing sheet, heat exchanger fin and heat exchanger

Abstract

To provide: a brazing sheet having excellent brazability and self corrosion resistance after brazing; a fin for heat exchanger; and a heat exchanger made of the brazing sheet.SOLUTION: A brazing sheet 1 has: a core material 2; and a brazing material 3 laminated on at least one face of the core material 2. The core material 2 has a specific chemical component. The brazing material 3 contains 3.0 to 13.0 mass% of Si, 0.8 to 7.0 mass% of Mg, 0.01 to 1.0 mass% of Bi, and the remainder consists of Al and inevitable impurities, and has a chemical component in which a ratio of the content of Bi with respect to a content of Mg is 0.3 or less. In the case where the brazing sheet 1 is heated to 600°C under a predetermined condition, and cooled immediately after reaching 600°C, a ratio of an area having Mg strength of 50000cps or more in an element mapping image of a surface of the brazing material 3 is 1% or more, wherein the element mapping image is acquired by using an electron probe micro analyzer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a brazing sheet, a heat exchanger fin, and a heat exchanger. [Background technology]

[0002] Taking advantage of properties such as being lightweight for a metal and having excellent thermal conductivity, aluminum alloys are used in automotive heat exchangers such as radiators, evaporators, heaters, condensers, etc. This type of heat exchanger has tubes for circulating a heat transfer medium such as water mixed with ethylene glycol-based antifreeze, water, ammonia, fluorocarbons, chlorofluorocarbons, alcohol, etc., and fins joined to the tubes by brazing to improve the heat exchange efficiency between the heat transfer medium and the outside air.

[0003] Conventionally, brazing of tubes and fins has often been performed by a flux brazing method, in which flux is applied to the area where the brazing joint is to be formed in advance, and the brazing is performed by utilizing the effect of the flux on the surface of the aluminum alloy. However, when using the flux brazing method, it is necessary to remove the flux residue after brazing, which increases manufacturing costs.

[0004] Therefore, to avoid the problems associated with the use of flux, the use of flux-free brazing, in which brazing is performed in an inert gas atmosphere without applying flux to the area where the brazing joint is to be formed, is being considered. In the flux-free brazing method, an element that has the effect of destroying the oxide film, such as Mg, is added to the brazing material, and the oxide film is destroyed by the aforementioned element during brazing heating, thereby forming the brazing joint.

[0005] For example, Patent Document 1 describes a fluxless brazing method for aluminum materials, in which brazing is performed using a brazing sheet in which a core material is clad with an Al-Si-Mg based brazing filler metal containing, by mass%, 5.0 to 13.0% Si and 0.1 to 3.0% Mg. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-215797 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been an increasing demand for further weight reduction in heat exchangers and other equipment incorporated in automobiles in order to reduce the weight of automobiles, and there is a strong demand for thinner heat exchanger fins while maintaining various properties such as strength, formability, brazeability, corrosion resistance, etc. However, when the thickness of the brazing sheet is reduced, the thickness of the brazing filler metal also becomes thinner, which poses a problem of an increased likelihood of a shortage of the amount of brazing filler metal used in brazing joints.

[0008] On the other hand, to improve brazing performance in flux-free brazing, one method is to add Bi to the brazing filler metal along with Mg to increase the fluidity of the brazing filler metal. However, adding Bi to the brazing filler metal reduces the self-corrosion resistance of the brazed fins, which can lead to early fin loss.

[0009] The present invention has been made in view of the above background, and aims to provide a brazing sheet that has excellent brazing properties and self-corrosion resistance after brazing, and a heat exchanger fin and a heat exchanger that are made of this brazing sheet. [Means for solving the problem]

[0010] One aspect of the present invention is a brazing sheet configured to enable brazing of aluminum materials in an inert gas atmosphere without using flux, a core material having a chemical composition comprising one or more of the following elements: Si (silicon): 0.02% by mass or more and 1.5% by mass or less; Fe (iron): more than 0% by mass and 1.5% by mass or less; Cu (copper): more than 0% by mass and 1.0% by mass or less; Mn (manganese): more than 0% by mass and 2.0% by mass or less; Mg (magnesium): more than 0% by mass and 1.2% by mass or less; and Zn (zinc): more than 0% by mass and 4.5% by mass or less; the remainder being Al (aluminum) and unavoidable impurities; a brazing filler metal laminated on at least one surface of the core material, the brazing filler metal having a chemical composition containing Si: 3.0% by mass or more and 13.0% by mass or less, Mg: 0.8% by mass or more and 7.0% by mass or less, and Bi (bismuth): 0.01% by mass or more and 1.0% by mass or less, with the remainder being Al and unavoidable impurities, and the ratio of the Bi content to the Mg content being 0.3 or less; The brazing sheet has the property that when the brazing sheet is heated to 600°C at an average heating rate of 15°C / min from 580°C to 600°C, and then cooled immediately after reaching 600°C, the proportion of the area where the Mg intensity is 50,000 cps (counts per second) or higher is 1% or higher in an elemental mapping image of the surface of the brazing material obtained using an electron beam microanalyzer.

[0011] Another aspect of the present invention is a heat exchanger fin made of the brazing sheet of the above aspect.

[0012] Furthermore, still another aspect of the present invention is a heat transfer device including: a tube configured to allow a heat transfer medium to flow; a fin joined to the tube via brazing, The fin comprises a core material having a chemical composition containing one or more elements selected from the group consisting of Si: 0.02% by mass or more and 1.5% by mass or less, Fe: more than 0% by mass and 1.5% by mass or less, Cu: more than 0% by mass and 1.0% by mass or less, Mn: more than 0% by mass and 2.0% by mass or less, Mg: more than 0% by mass and 1.2% by mass or less, and Zn: more than 0% by mass and 4.5% by mass or less, with the remainder being Al and unavoidable impurities; and a brazing filler metal laminated on at least one surface of the core material, The brazing filler metal has a chemical composition containing Si: 3.0% by mass or more and 13.0% by mass or less, Mg: 0.8% by mass or more and 7.0% by mass or less, and Bi: 0.01% by mass or more and 1.0% by mass or less, with the remainder consisting of Al and unavoidable impurities, and the ratio of the Bi content to the Mg content is 0.3 or less, The heat exchanger is such that in an elemental mapping image of the surface of the brazing filler metal obtained using an electron beam microanalyzer, the ratio of the area where the Mg intensity is 50,000 cps or more is 1% or more. [Effects of the Invention]

[0013] The brazing sheet includes a core material having the specific chemical composition and a brazing filler metal. Furthermore, the brazing sheet has a characteristic that, in an elemental mapping image of the surface of the brazing filler metal after heating under the specific conditions, the ratio of the area where the Mg intensity is 50,000 cps or higher is 1% or higher. A brazing sheet having such a configuration can improve self-corrosion resistance after brazing while ensuring the effect of improving brazability due to Bi.

[0014] Furthermore, since the heat exchanger fin is made of the brazing sheet, it has excellent brazing properties and also has excellent self-corrosion resistance after brazing.

[0015] The heat exchanger fins have a core material having the specific chemical composition and a brazing filler metal laminated on at least one side of the core material. Furthermore, in an elemental mapping image of the surface of the brazing filler metal, the ratio of the area where the Mg intensity is 50,000 cps or higher is 1% or higher. Therefore, the heat exchanger fins have excellent self-corrosion resistance.

[0016] As described above, according to the above-described aspects, it is possible to provide a brazing sheet having excellent brazability and self-corrosion resistance after brazing, and a heat exchanger fin and a heat exchanger made of this brazing sheet. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing a main part of a brazing sheet in Example 1. As shown in FIG. [Figure 2] FIG. 2 is a plan view of a heat exchanger according to a second embodiment, which is provided with fins made of brazing sheets. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a portion in the vicinity of the brazed joint in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] (Brazing sheet) The brazing sheet is configured so that aluminum materials (including pure aluminum and aluminum alloys) can be brazed in an inert gas atmosphere without using flux, i.e., the brazing sheet is configured so that brazing can be performed by a flux-free brazing method.

[0019] The brazing sheet has a core material and a brazing filler metal laminated on at least one side of the core material. That is, the brazing sheet may be composed of two layers: the core material and the brazing filler metal laminated on one side of the core material, or it may be composed of three layers: the core material and the brazing filler metal laminated on both sides of the core material. When brazing filler metals are laminated on both sides of the brazing sheet, the chemical components of one brazing filler metal and the other brazing filler metal may be the same or different from each other. The brazing sheet may also include layers other than the core material and the brazing filler metal.

[0020] The thickness of the brazing sheet can be appropriately set within the range of 30 μm to 600 μm. From the viewpoint of reducing the weight of the brazing sheet while ensuring excellent brazability and corrosion resistance after brazing, the thickness of the brazing sheet is preferably 30 μm to 400 μm, and more preferably 30 μm to 100 μm.

[0021] <Heartwood> The core material of the brazing sheet has a chemical composition that contains one or more of the following elements: Si: 0.02% by mass or more and 1.5% by mass or less; Fe: more than 0% by mass and 1.5% by mass or less; Cu: more than 0% by mass and 1.0% by mass or less; Mn: more than 0% by mass and 2.0% by mass or less; Mg: more than 0% by mass and 1.2% by mass or less; and Zn: more than 0% by mass and 4.5% by mass or less, with the remainder being Al and unavoidable impurities.

[0022] ·Si: 0.02 mass% or more and 1.5 mass% or less The core material may contain 0.02% by mass or more and 1.5% by mass or less of Si. Si in the core material has the effect of improving the strength of the core material. By making the Si content in the core material 0.02% by mass or more, the strength of the core material is improved, and the thickness of the brazing sheet can be more easily reduced.

[0023] On the other hand, if the Si content in the core material is excessively high, the core material's self-corrosion resistance may be reduced. In this case, the solidus temperature of the core material may be lowered, making the core material more likely to melt during brazing. These problems can be easily avoided by setting the Si content in the core material to 1.5 mass% or less, preferably 1.4 mass% or less, and more preferably 1.3 mass% or less.

[0024] Fe: over 0% by mass and up to 1.5% by mass The core material may contain Fe, but an excessively high Fe content is likely to cause the formation of Al-Fe-Si intermetallic compounds and Al-Fe-Mn intermetallic compounds in the core material. These intermetallic compounds are undesirable because they cause a decrease in self-corrosion resistance. By keeping the Fe content in the core material at 1.5 mass% or less, preferably 1.2 mass% or less, more preferably 0.9 mass% or less, and even more preferably 0.7 mass% or less, the formation of the aforementioned intermetallic compounds in the core material can be suppressed, and a decrease in self-corrosion resistance can be easily avoided.

[0025] Cu: More than 0 mass% and 1.0 mass% or less The core material may contain more than 0 mass% but not more than 1.0 mass% Cu. The Cu in the core material not only improves the strength of the core material but also increases the pitting potential of the core material. By adding Cu to the core material, the thickness of the brazing sheet can be made thinner while maintaining sufficient strength. Furthermore, when the brazing sheet is used as a heat exchanger fin, the balance between the pitting potential of the fin and the pitting potential of the tube can be adjusted to an appropriate range, improving self-corrosion resistance.

[0026] On the other hand, if the Cu content in the core material is excessively high, the core material becomes more susceptible to corrosion and becomes more susceptible to intergranular corrosion, which may lead to a decrease in self-corrosion resistance. From the viewpoint of more reliably avoiding such problems, the Cu content in the core material is preferably 1.0 mass% or less.

[0027] Mn: More than 0% by mass and up to 2.0% by mass The core material may contain more than 0% by mass and not more than 2.0% by mass of Mn. Mn in the core material improves the strength of the core material and has the effect of making the pitting potential of the core material more noble. By adding Mn to the core material, the thickness of the brazing sheet can be made thinner while ensuring sufficient strength. Furthermore, when the brazing sheet is used as a fin for a heat exchanger, the balance between the pitting potential of the fin and the pitting potential of the tube can be adjusted to an appropriate range, thereby improving self-corrosion resistance. From the perspective of further enhancing these effects, the Mn content in the core material is preferably 0.4% by mass or more, and more preferably 0.8% by mass or more.

[0028] On the other hand, if the Mn content in the core material is excessively high, the rollability of the core material may be reduced, making it difficult to produce a brazing sheet. This problem can be easily avoided by setting the Mn content in the core material to 2.0 mass% or less, preferably 1.7 mass% or less, and more preferably 1.4 mass% or less.

[0029] Mg: Over 0% by mass and up to 1.2% by mass The core material may contain more than 0% by mass and not more than 1.2% by mass of Mg. Mg in the core material has the effect of improving the strength of the core material. Furthermore, Mg in the core material diffuses to the surface of the brazing filler metal during brazing heating, improving brazability. Therefore, by adding Mg to the core material, the thickness of the brazing sheet can be made thinner while ensuring sufficient strength and brazability. From the viewpoint of further improving the strength and brazability of the brazing sheet, the Mg content in the core material is preferably 0.1% by mass or more, and more preferably 0.2% by mass or more.

[0030] On the other hand, if the Mg content in the core material is excessively high, the core material may become more susceptible to intergranular corrosion, which may lead to a decrease in self-corrosion resistance. By keeping the Mg content in the core material at 1.2 mass% or less, preferably 1.0 mass% or less, and more preferably 0.8 mass% or less, such problems can be easily avoided.

[0031] Zn: More than 0% by mass and 4.5% by mass or less The core material may contain more than 0% by mass and not more than 4.5% by mass of Zn. Zn in the core material has the effect of lowering the pitting potential of the core material and lowering the pitting potential of the surface of the brazing sheet after brazing heating. Therefore, by adding Zn to the core material, when the brazing sheet is used as a heat exchanger fin, the balance between the pitting potential of the fin and the pitting potential of the tube can be adjusted to an appropriate range, thereby improving self-corrosion resistance. From the viewpoint of further enhancing this effect, the Zn content in the core material is preferably 0.3% by mass or more, and more preferably 0.6% by mass or more.

[0032] On the other hand, if the Zn content in the core material is too high, the pitting potential of the core material will be excessively reduced, which may lead to a decrease in self-corrosion resistance. This problem can be easily avoided by setting the Zn content in the core material to 4.5 mass% or less, preferably 3.6 mass% or less, more preferably 2.7 mass% or less, and even more preferably 1.8 mass% or less.

[0033] In addition to the elements mentioned above, the core material may further contain one or more of the following elements: Cr (chromium): more than 0% by mass but not more than 0.3% by mass; Ti (titanium): more than 0% by mass but not more than 0.3% by mass; and Zr (zirconium): more than 0% by mass but not more than 0.3% by mass. These elements have the effect of adjusting the grain size of the core material and improving the strength of the core material by dissolving in the core material and solid-solution strengthening. Therefore, by adding these elements to the core material, the thickness of the brazing sheet can be made thinner while maintaining sufficient strength.

[0034] To further enhance these effects, the Ti, Cr, and Zr contents in the core material are each preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. On the other hand, if the Ti, Cr, and Zr contents in the core material are excessively high, coarse intermetallic compounds are likely to be formed, which may result in a decrease in the plastic workability of the core material. By setting the Ti, Cr, and Zr contents in the core material to 0.30% by mass or less, and more preferably 0.20% by mass or less, respectively, it is possible to easily avoid a decrease in plastic workability due to the formation of coarse intermetallic compounds.

[0035] V (vanadium): over 0% by mass and up to 0.30% by mass The core material may contain more than 0% by mass and not more than 0.30% by mass of V. V dissolves in the core material and has the effect of improving the strength of the core material through solid solution strengthening and the effect of improving the corrosion resistance of the core material. Adding V to the core material can further improve the strength and corrosion resistance of the core material. From the perspective of further enhancing these effects, the V content in the core material is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more.

[0036] On the other hand, if the V content in the core material is excessively high, coarse intermetallic compounds are likely to be formed, which may lead to a decrease in the plastic workability of the core material. By setting the V content in the core material to 0.30 mass% or less, preferably 0.20 mass% or less, it is possible to easily avoid a decrease in plastic workability due to the formation of coarse intermetallic compounds.

[0037] B (boron): more than 0 mass% and not more than 0.3 mass%, In (indium): more than 0 mass% and not more than 0.1 mass%, Sn (tin): more than 0 mass% and not more than 0.1 mass% The core material may further contain one or more of the following elements: B: more than 0% by mass but not more than 0.3% by mass; In: more than 0% by mass but not more than 0.1% by mass; and Sn: more than 0% by mass but not more than 0.1% by mass. These elements have the effect of lowering the pitting potential of the core material. Therefore, by adding these elements to the core material, it is possible to control the potential balance when the brazing sheet is used as a heat exchanger fin, thereby improving the corrosion resistance of the entire heat exchanger.

[0038] Inevitable impurities In addition to the elements mentioned above, the core material contains unavoidable impurities that are inevitably mixed in during the manufacturing process. The content of the elements that constitute unavoidable impurities is 0.05% by mass or less for each element, and the total content is 0.15% by mass or less.

[0039] <Brazing material> The brazing sheet has a chemical composition in which the brazing filler metal contains Si: 3.0% by mass or more and 13.0% by mass or less, Mg: 0.8% by mass or more and 7.0% by mass or less, and Bi: 0.01% by mass or more and 1.0% by mass or less, with the remainder consisting of Al and unavoidable impurities, and the ratio of the Bi content to the Mg content is 0.3 or less.

[0040] ·Si: 3.0 mass% or more and 13.0 mass% or less The brazing filler metal contains 3.0% by mass or more and 13.0% by mass or less of Si as an essential component. Si in the brazing filler metal has the effect of lowering the melting point of the brazing filler metal. By making the Si content in the brazing filler metal 3.0% by mass or more, brazing filler metal can be generated during brazing heating, and a brazed joint can be formed. From the viewpoint of increasing the amount of brazing filler metal formed during brazing heating and further improving brazing properties, the Si content in the brazing filler metal is preferably 5.0% by mass or more, and more preferably 7.0% by mass or more.

[0041] On the other hand, if the Si content in the brazing filler metal is excessively high, primary crystals of Si are likely to form in the brazing filler metal, which may make it difficult to produce a brazing sheet. This problem can be easily avoided by setting the Si content in the brazing filler metal to 13 mass% or less, preferably 12 mass% or less, and more preferably 11 mass% or less.

[0042] ·Mg: 0.8 mass% or more and 7.0 mass% or less The brazing filler metal contains 0.8% by mass or more and 7.0% by mass or less of Mg as an essential component. Mg in the brazing filler metal has the effect of destroying oxide films during brazing heating. By setting the Mg content in the brazing filler metal to 0.8% by mass or more, preferably 2.0% by mass or more, the oxide films present on the surface of the brazing filler metal and the surface of the mating material can be destroyed during brazing heating, and a brazed joint can be formed. If the Mg content in the brazing filler metal is less than 0.8% by mass, the oxide films may not be destroyed sufficiently, making it difficult to form a brazed joint.

[0043] On the other hand, if the Mg content in the brazing filler metal is excessively high, it may become difficult to manufacture the brazing sheet. This problem can be easily avoided by setting the Mg content in the brazing filler metal to 7.0 mass% or less, preferably 6.5 mass% or less.

[0044] ·Bi: 0.01 mass% or more and 1.0 mass% or less The brazing filler metal contains 0.01% by mass or more and 1.0% by mass or less of Bi as an essential component. Bi in the brazing filler metal reduces the surface tension of the brazing filler metal and increases the fluidity of the brazing filler metal. Bi in the brazing filler metal also inhibits oxidation of the brazing filler metal surface. Therefore, adding 0.01% by mass or more of Bi to the brazing filler metal can further improve brazing performance. From the viewpoint of further enhancing this effect, the Bi content in the brazing filler metal is preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.07% by mass or more. If the Bi content in the brazing filler metal is less than 0.01% by mass, there is a risk of deterioration of brazing performance.

[0045] On the other hand, if the Bi content in the brazing filler metal is excessively high, it may become difficult to manufacture the brazing sheet. This problem can be easily avoided by setting the Bi content in the brazing filler metal to 1.0 mass% or less, preferably 0.7 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.3 mass% or less.

[0046] Furthermore, the mass ratio of Bi to Mg in the brazing filler metal is 0.3 or less. By setting the Bi content in the brazing filler metal within the above-mentioned specific range and also setting the mass ratio of Bi to Mg within the above-mentioned specific range, Bi and Mg can be bonded to form an Mg-Bi compound on the surface of the brazing sheet after brazing. In this way, by forming an Mg-Bi compound on the surface of the brazing sheet after brazing, the amount of elemental Bi present on the surface of the brazing sheet can be reduced. As a result, the self-corrosion resistance of the brazing sheet can be improved.

[0047] From the viewpoint of further enhancing this effect, the ratio of the Bi content to the Mg content is preferably 0.1 or less, more preferably 0.07 or less, and even more preferably 0.05 or less. If the ratio of the Bi content to the Mg content is higher than 0.3, the amount of elemental Bi present on the surface of the brazing sheet after brazing increases, which may lead to a decrease in self-corrosion resistance.

[0048] Elemental mapping image of the surface after brazing heating The brazing sheet has the property that, when heated to 600°C at an average heating rate of 15°C / min from 580°C to 600°C and then cooled immediately after reaching 600°C, the ratio of the area where the Mg intensity is 50,000 cps or higher is 1% or more in an elemental mapping image of the brazing material surface obtained using an electron probe microanalyzer (EPMA). The area where the Mg intensity is 50,000 cps or higher in the elemental mapping image corresponds to the area where Mg-Bi compounds are present. Furthermore, in the area where Mg-Bi compounds are present, it is presumed that the amount of elemental Bi is small because Bi is bonded to Mg. The unit of Mg intensity, "cps," is the number of characteristic X-ray photons counted per second by the EPMA detector.

[0049] Therefore, a brazing sheet having the characteristics that the elemental mapping image after heating under the specific heating conditions, i.e., heating conditions simulating brazing heating, has the specific pattern, and exhibits high self-corrosion resistance after brazing heating. If the area ratio of the region where the Mg intensity is 50,000 cps or higher in the elemental mapping image after heating under the specific heating conditions is less than 1%, the amount of elemental Bi present on the surface of the brazing sheet after heating for brazing heating will be large, which may result in a decrease in self-corrosion resistance. From the perspective of further improving the self-corrosion resistance of the brazing sheet after heating for brazing heating, the area ratio of the region where the Mg intensity is 50,000 cps or higher in the elemental mapping image after heating under the specific heating conditions is preferably 5% or higher, more preferably 10% or higher, even more preferably 30% or higher, and particularly preferably 40% or higher.

[0050] In addition to the essential components described above, the brazing filler metal may contain one or more of the following elements: Na (sodium): more than 0% by mass and not more than 0.05% by mass; Sr (strontium): more than 0% by mass and not more than 0.05% by mass; Sb (antimony): more than 0% by mass and not more than 0.05% by mass; Zn: more than 0% by mass and not more than 8.0% by mass; Cu: more than 0% by mass and not more than 4.0% by mass; Fe: more than 0% by mass and not more than 1.0% by mass; and Mn: more than 0% by mass and not more than 1.0% by mass.

[0051] Na: more than 0 mass% but not more than 0.05 mass%, Sr: more than 0 mass% but not more than 0.05 mass%, Sb: more than 0 mass% but not more than 0.05 mass% The brazing filler metal may contain, as optional components, one or more of more than 0% by mass and not more than 0.05% by mass of Na, more than 0% by mass and not more than 0.05% by mass of Sr, and more than 0% by mass and not more than 0.05% by mass of Sb. These elements have the effect of refining Si particles in the brazing filler metal and improving the fluidity of the brazing filler metal. From the viewpoint of further enhancing this effect, the Na content, Sr content, and Sb content in the brazing filler metal are preferably each 0.003% by mass or more.

[0052] On the other hand, if the Na content, Sr content, or Sb content in the brazing filler metal is excessively high, the oxide film formed on the surface of the brazing filler metal during brazing heating is likely to become thick, which may lead to deterioration of brazing properties. This problem can be easily avoided by setting the Na content, Sr content, and Sb content in the brazing filler metal to 0.05 mass% or less, respectively. From the same perspective, it is more preferable that the Na content, Sr content, and Sb content in the brazing filler metal be 0.02 mass% or less, respectively.

[0053] Zn: More than 0% by mass and up to 8.0% by mass The brazing filler metal may contain more than 0 mass% but not more than 8.0 mass% Zn as an optional component. Zn in the brazing filler metal has the effect of lowering the pitting potential of the brazing filler metal. By adding 8.0 mass% or less Zn to the brazing filler metal, the potential difference between the core material and the brazing filler metal can be made large enough to allow the brazing filler metal to function as a sacrificial anode for the core material.

[0054] Cu: More than 0 mass% and 4.0 mass% or less The brazing filler metal may contain Cu in an amount of more than 0 mass % and not more than 4.0 mass % as an optional component. Cu in the brazing filler metal adjusts the potential of the brazing filler metal, allowing the brazing filler metal to function as a sacrificial anode material. Adding not more than 4.0 mass % of Cu to the brazing filler metal can further improve the corrosion resistance of the core material after brazing. Furthermore, in this case, the melting point of the brazing filler metal can be lowered, further improving brazeability.

[0055] Fe: over 0% by mass and up to 1.0% by mass The brazing filler metal may contain more than 0 mass % and not more than 1.0 mass % of Fe as an optional component. Fe has the effect of adjusting the fluidity of the brazing filler metal and improving brazing properties.

[0056] Cr: more than 0% by mass and up to 0.3% by mass, Ti: more than 0% by mass and up to 0.3% by mass, Zr: more than 0% by mass and up to 0.3% by mass The brazing filler metal may contain, as optional components, one or more of more than 0 mass% but not more than 0.3 mass% Cr, more than 0 mass% but not more than 0.3 mass% Ti, and more than 0 mass% but not more than 0.3 mass% Zr. These elements have the effect of precipitating fine intermetallic compounds in the brazing filler metal and coarsening the crystal grains of the brazing filler metal before brazing.

[0057] In: more than 0 mass% and not more than 0.1 mass%, Sn: more than 0 mass% and not more than 0.1 mass% The brazing filler metal may contain one or two of more than 0% by mass but not more than 0.1% by mass of In and more than 0% by mass but not more than 0.1% by mass of Sn as optional components. These elements have the effect of lowering the pitting potential of the brazing filler metal. By adding 0.1% by mass or less of In and / or 0.1% by mass or less of Sn to the brazing filler metal, the potential difference between the core material and the brazing filler metal can be made large enough to allow the brazing filler metal to function as a sacrificial anode for the core material.

[0058] Inevitable impurities In addition to the elements mentioned above, the brazing filler metal contains unavoidable impurities that are inevitably mixed in during the manufacturing process of the brazing filler metal. The content of the elements as unavoidable impurities is 0.05% by mass or less for each element, and the total content is 0.15% by mass or less.

[0059] Cladding rate The cladding ratio of the brazing material in the brazing sheet, i.e., the ratio of the thickness of each brazing material to the overall thickness of the brazing sheet, is preferably 5% or more and 30% or less. By making the cladding ratio of the brazing material 5% or more, a sufficient amount of brazing material is formed during brazing heating, thereby further improving brazing properties. Furthermore, by making the cladding ratio of the brazing material 30% or less, preferably 20% or less, the ratio of the core material is appropriately increased, making it easier to manufacture the brazing sheet.

[0060] <Manufacturing method> The brazing sheet can be produced, for example, by a lamination process of producing a clad ingot by laminating a plurality of aluminum ingots, the aluminum ingots including a core ingot having the chemical components of the core material and a brazing material ingot having the chemical components of the brazing material and disposed on at least one side of the core ingot; a hot rolling process for producing a clad plate including a core material made of the core ingot and a brazing material made of the brazing material ingot and disposed on at least one surface of the core ingot by hot rolling the clad ingot; and a cold rolling step of subjecting the clad plate to one or more passes of cold rolling.

[0061] The method for producing the core ingot and brazing filler ingot to be subjected to the lamination step is not particularly limited, and various casting methods such as DC casting, CC casting, etc. After casting, these aluminum ingots may be subjected to the lamination step without heat treatment, or may be subjected to heat treatment such as homogenization treatment as necessary before being subjected to the lamination step.

[0062] In the lamination step, the aluminum blocks are stacked in a desired order to produce a clad block. The stacking order and number of layers of the aluminum blocks in the clad block may be appropriately set depending on the desired laminate structure and number of layers of the brazing sheet.

[0063] For example, to obtain a brazing sheet with a two-layer structure comprising a core material and a brazing filler metal layered on one side of the core material, the clad ingot can be made from two aluminum ingots: a core material ingot and a brazing filler metal layered on one side of the core material ingot. Similarly, to obtain a brazing sheet with a three-layer structure comprising a core material and a brazing filler metal layered on both sides of the core material, the clad ingot can be made from three aluminum ingots: a core material ingot and a brazing filler metal layered on both sides of the core material ingot.

[0064] <Hot rolling process> After the lamination step, a hot rolling step is performed in which the clad ingot is hot rolled. By hot rolling the clad ingot in the hot rolling step, a clad plate in which adjacent aluminum ingots are bonded together can be obtained. The hot rolling start temperature in the hot rolling step can be appropriately set, for example, within the range of 400°C or higher and 550°C or lower. Furthermore, after the hot rolling step, the clad plate may be heated and subjected to a homogenization treatment, if necessary.

[0065] <Cold rolling process> After the hot rolling step, a cold rolling step is performed in which the obtained clad plate is subjected to one or more passes of cold rolling. By cold rolling the clad plate, the thickness of the clad plate is reduced to the desired thickness. In this manner, a brazing sheet can be obtained. The number of passes and rolling conditions in the cold rolling step may be appropriately set depending on the configuration of the clad plate and the desired configuration of the brazing sheet. Furthermore, the clad plate or brazing sheet may be heated and annealed as necessary before, during, or after cold rolling. The heating temperature in the intermediate annealing can be appropriately set, for example, within the range of 150°C to 500°C.

[0066] (Heat exchanger fins) As described above, the brazing sheet can be brazed using a flux-free brazing method. Furthermore, because Bi is bonded to Mg on the surface of the brazing sheet after brazing heat, the brazing sheet has excellent self-corrosion resistance after brazing heat. Therefore, the brazing sheet is suitable as a heat exchanger fin. Among heat exchangers, automotive heat exchangers, such as evaporators and condensers installed in automobiles, are particularly susceptible to corrosion due to contact with condensation water and road splash. Because the brazing sheet has excellent self-corrosion resistance, it is also suitable as a fin for automotive heat exchangers used in such harsh environments.

[0067] (heat exchanger) The use of a heat exchanger having fins made of the brazing sheet is not particularly limited. For example, the heat exchanger may be used in applications that perform heat exchange using an aqueous heat transfer medium, such as a radiator, heater, intercooler, or oil cooler. The heat exchanger may also be used in applications that perform heat exchange using a non-aqueous heat transfer medium, such as an evaporator, condenser, or heater.

[0068] The heat exchanger may, for example, a tube configured to allow a heat transfer medium to flow; and fins joined to the tubes via brazing. The fin comprises a core material having a chemical composition containing one or more of the following elements: Si: 0.02% by mass or more and 1.5% by mass or less; Fe: more than 0% by mass and 1.5% by mass or less; Cu: more than 0% by mass and 1.0% by mass or less; Mn: more than 0% by mass and 2.0% by mass or less; Mg: more than 0% by mass and 1.2% by mass or less; and Zn: more than 0% by mass and 4.5% by mass or less; the remainder consisting of Al and unavoidable impurities; and a brazing material laminated on at least one side of the core material. The brazing filler metal has a chemical composition containing Si: 3.0% by mass to 13.0% by mass, Mg: 0.8% by mass to 7.0% by mass, and Bi: 0.01% by mass to 1.0% by mass, with the remainder consisting of Al and unavoidable impurities, and the ratio of the Bi content to the Mg content being 0.3 or less. In an elemental mapping image of the surface of the fin obtained using an electron beam microanalyzer, the ratio of the area where the Mg intensity is 50,000 cps or more is 1% or more.

[0069] The core material of the fins in the heat exchanger is composed of the core material of the brazing sheet. Furthermore, the brazing joints in the heat exchanger are mainly composed of the brazing material of the brazing sheet. Therefore, with the heat exchanger, the thickness of the fins can be easily reduced, and the overall mass of the heat exchanger can be easily reduced. Furthermore, the fins and tubes in the heat exchanger are sufficiently joined by the brazing joints.

[0070] Furthermore, the core material contains brazing material remaining on the core material during brazing heating. In an elemental mapping image of the surface of the brazing material obtained using an electron beam microanalyzer, the ratio of the area where the Mg intensity is 50,000 cps or more is 1% or more. As mentioned above, the area where the Mg intensity is 50,000 cps or more in the elemental mapping image corresponds to the area where an Mg-Bi compound is present. Therefore, the fins of the heat exchanger contain a small amount of elemental Bi and have excellent corrosion resistance.

[0071] The heat exchanger may be, for example, a parallel flow type heat exchanger including a heat exchanger core formed by alternately stacking tubes and fins, and headers arranged at one and the other longitudinal ends of the tubes in the heat exchanger core and connected to the tubes.

[0072] The tubes in the heat exchanger may be, for example, flat tubes having two flat wall portions arranged opposite to each other and joined to the fins, side wall portions connecting the edges of the flat wall portions, and heat transfer medium flow paths surrounded by the flat wall portions and the side wall portions. Alternatively, the tubes may be, for example, flat multi-hole tubes having two flat wall portions arranged opposite to each other and joined to the fins, side wall portions connecting the edges of the flat wall portions, and partition walls dividing the space surrounded by the flat wall portions and the side wall portions into a plurality of heat transfer medium flow paths.

[0073] The heat exchanger can be manufactured, for example, by the following method. First, heat exchanger components, including tubes and fins, are assembled to form a desired heat exchanger configuration to produce an assembly. This assembly is heated in an inert gas atmosphere and brazed. The assembly is held at a temperature of 585°C to 630°C for 1 minute to 30 minutes, and then cooled to room temperature to form a brazed joint between the fins and the tubes. From the viewpoint of forming an Mg-Bi compound on the brazed fin surfaces and improving corrosion resistance, it is preferable to perform brazing heating so that the average heating rate from 580°C to 600°C is 2°C / min to 30°C / min. [Example]

[0074] Example 1 An example of the brazing sheet will be described with reference to Fig. 1. The brazing sheet of this example is configured to enable brazing of aluminum materials in an inert gas atmosphere without using flux. As shown in Fig. 1, the brazing sheet 1 has a core material 2 and a brazing material 3 laminated on at least one side of the core material 2.

[0075] The core material 2 has a chemical composition containing one or more of the following elements: Si: 0.02% to 1.5% by mass, Fe: more than 0% to 1.5% by mass, Cu: more than 0% to 1.0% by mass, Mn: more than 0% to 2.0% by mass, Mg: more than 0% to 1.2% by mass, and Zn: more than 0% to 4.5% by mass, with the balance being Al and unavoidable impurities. The brazing filler metal 3 has a chemical composition containing Si: 3.0% to 13.0% by mass, Mg: 0.8% to 7.0% by mass, and Bi: 0.01% to 1.0% by mass, with the balance being Al and unavoidable impurities, and the ratio of the Bi content to the Mg content being 0.3 or less.

[0076] Furthermore, when the brazing sheet 1 is heated to 600°C at an average heating rate of 15°C / min from 580°C to 600°C, and then cooled immediately after reaching 600°C, the brazing sheet 1 has the property that, in an elemental mapping image of the surface of the brazing filler metal 3 obtained using an electron beam microanalyzer, the ratio of the area where the Mg intensity is 50,000 cps or higher is 1% or higher. The configuration and manufacturing method of the brazing sheet 1 of this example will be described in more detail below.

[0077] Specifically, the core material 2 used in this example has the chemical composition shown as alloy symbol A1 in Table 1. The brazing filler metal 3 used in this example has the chemical composition of any of alloy symbols B1 to B3 shown in Table 1. The symbol "Bal." in Table 1 indicates the balance.

[0078] [Table 1]

[0079] To produce the brazing sheet 1 of this example, first, a core ingot and a brazing filler ingot having the aforementioned chemical components are produced by semi-continuous casting (casting process). For the core ingot, the surface of the cast core ingot is chamfered to adjust the thickness of the core ingot. For the brazing filler ingot, the cast brazing filler ingot is hot-rolled at a starting temperature of 480°C, and then the surface of the brazing filler ingot is chamfered to adjust the thickness of the brazing filler ingot.

[0080] Next, a clad ingot is produced by stacking the brazing material ingots on both sides of the core ingot in the combination shown in Table 2 (lamination process). This clad ingot is hot rolled at a starting temperature of 480°C to obtain a clad plate with a thickness of 3 mm (hot rolling process). Next, the clad plate is cold rolled to reduce the thickness of the clad plate until it is thicker than the desired thickness of the brazing sheet.

[0081] The cold-rolled clad sheet is held at a temperature of 370°C for intermediate annealing, and then further cold-rolled to reduce the thickness of the clad sheet to 0.07 mm (cold-rolling step). Through the above steps, the brazing sheets (test materials S1 to S3) shown in Table 2 can be obtained.

[0082] The properties of the brazing sheet were evaluated as follows.

[0083] Evaluation of the distribution state of Mg-Bi compounds The test material is placed in a brazing furnace and heated in an inert gas atmosphere at a temperature increase rate of 15°C / min from 580°C to 600°C. When the temperature of the test material reaches 600°C, heating of the test material is stopped and the test material is cooled in the brazing furnace.

[0084] The surface of the brazing material in the test material removed from the brazing furnace is analyzed by EPMA. The EPMA analysis conditions are: acceleration voltage: 15 kV, probe current: 4 × 10 -7A, irradiation time: 10 ms, beam diameter: minimum, multiple measurement points are set in a square area with sides of 250 μm, with a pitch of 0.5 μm in the vertical and horizontal directions. Then, these measurement points are irradiated with an electron beam, and an elemental mapping image is created based on the obtained Mg intensity.

[0085] In the elemental mapping image obtained as described above, the ratio of measurement points where the Mg intensity is 50,000 cps or more to the total number of measurement points is taken as the area ratio of the region where the Mg intensity is 50,000 cps or more. The "EPMA analysis results" column in Table 2 shows the area ratio of the region where the Mg intensity is 50,000 cps or more for each test material.

[0086] Self-corrosion resistance The test material is placed in a brazing furnace and heated to 600°C in an inert gas atmosphere at a temperature increase rate of 15°C / min from 580°C to 600°C. When the temperature of the test material reaches 600°C, heating of the test material is stopped and the test material is cooled in the brazing furnace.

[0087] A rectangular evaluation area measuring 15 mm in length and 85 mm in width was set on the surface of the brazing filler metal of the brazed test material, and the rest of the test material was masked. A SWAAT test was then conducted according to ASTM G85, and the mass loss of the test material after 24 hours was measured, i.e., the difference between the mass of the test material before and after the SWAAT test. The mass loss for each test material is shown in the "Self-Corrosion Resistance" column of Table 2.

[0088] [Table 2]

[0089] As shown in Table 2, test materials S1 and S2 are composed of a core material having the specific chemical composition and a brazing filler metal. Therefore, by heating these test materials for brazing, an Mg-Bi compound can be formed on the surface of the brazing filler metal. Test materials with a sufficient amount of Mg-Bi compound formed on the surface of the brazing filler metal exhibit excellent self-corrosion resistance.

[0090] On the other hand, in the case of test material S3, the chemical composition of the brazing filler metal is outside the specific range, and therefore, the Mg-Bi compound is not sufficiently formed on the surface of the brazing filler metal after the brazing heat, and therefore test material S3 has inferior self-corrosion resistance after brazing compared to test materials S1 and S2.

[0091] Example 2 This example shows an example of a heat exchanger manufactured using the brazing sheet. Note that, among the symbols used in this example, the same symbols used in the previous examples represent the same components as those in the previous examples unless otherwise specified.

[0092] 2 and 3 , the heat exchanger 4 includes tubes 41 configured to allow a heat transfer medium to flow therethrough, and fins 43 joined to the tubes 41 via brazing joints 42. The fins 43 include a core material 431 having a chemical composition containing one or more elements selected from the group consisting of 0.02% by mass or more and 1.5% by mass or less of Si, more than 0% by mass and 1.5% by mass or less of Fe, more than 0% by mass and 1.0% by mass or less of Cu, more than 0% by mass and 2.0% by mass or less of Mn, more than 0% by mass and 1.2% by mass or less of Mg, and more than 0% by mass and 4.5% by mass or less of Zn, with the remainder being Al and unavoidable impurities;

[0093] The brazing filler metal 432 has a chemical composition containing 3.0 to 13.0% by mass of Si, 0.8 to 7.0% by mass of Mg, and 0.01 to 1.0% by mass of Bi, with the remainder being Al and unavoidable impurities, and the ratio of Bi to Mg is 0.3 or less. In an elemental mapping image of the surface of the brazing filler metal 432 obtained using an electron beam microanalyzer, the proportion of the area where the Mg intensity is 50,000 cps or more is 1% or more.

[0094] 2, the heat exchanger 4 of this example has a heat exchanger core 40 formed by alternately stacking tubes 41 and fins 43, and headers 44 disposed at one and the other longitudinal ends of the tubes 41 in the heat exchanger core 40 and connected to the tubes 41. That is, the heat exchanger 4 of this example is configured as a parallel flow type heat exchanger.

[0095] One end of the tubes 41 is connected to one header 44a of the two headers 44 (44a, 44b) in the heat exchanger 4. The header 44a is provided with a supply port 441 for supplying a heat transfer medium from the outside to the heat exchanger 4, and a discharge port 442 for discharging the heat transfer medium from the heat exchanger 4 to the outside. Although not shown in the figure, a partition plate that divides the internal space of the header 44a is provided between the supply port 441 and the discharge port 442 inside the header 44a. Therefore, the heat transfer medium that flows into the header 44a from the supply port 441 is distributed to the tubes 41 connected to the header 44a between one end 443a and the partition plate (not shown).

[0096] The other ends of the tubes 41 are connected to the other header 44b of the two headers 44. Each tube 41 is also in communication with the other tube 41 via the header 44b. Therefore, the heat transfer medium that flows from the supply port 441 into the header 44b via the header 44a and the tubes 41 joins together in the header 44b. The heat transfer medium that joins together in the header 44b is then distributed to the tubes 41 connected between the partition plate (not shown) of the header 44a and the other end 444a.

[0097] The heat transfer medium that flows into the tubes 41 from the header 44b joins together in the header 44a and is discharged from the discharge port 442.

[0098] The heat exchanger core 40 has a plurality of tubes 41 and a plurality of fins 43, and the tubes 41 and the fins 43 are alternately stacked. As shown in FIG. 3, the tubes 41 and the fins 43 are joined via brazing joints 42. The tubes 41 in this example are flat tubes having two flat wall portions arranged opposite each other and side wall portions connecting the edges of the flat wall portions. Although not shown in the figure, the tubes 41 in this example have a rectangular cross-sectional shape.

[0099] The fin 43 is made of the brazing sheet 1 after brazing, and has a core material 431 and a brazing material 432 laminated on both sides of the core material 431. The core material 2 of the brazing sheet 1 before brazing becomes the core material 431 of the fin 43 after brazing. Of the brazing material 3 of the brazing sheet 1 before brazing, the brazing material 3 that remains on the core material 2 during brazing heating becomes the brazing material 432 of the fin 43. The brazing joint 42 is connected to the brazing material 432 on the core material 431. The brazing joint 42 is mainly composed of the brazing material 3 of the brazing sheet 1 that gathers at the contact area between the fin 43 and the tube 41 during brazing heating, and has the same chemical composition as the brazing material 432.

[0100] In an elemental mapping image of the surface of the brazing filler metal 432 obtained using an electron beam microanalyzer, the ratio of the area where the Mg intensity is 50,000 cps or more is 1% or more. As described above, an Mg-Bi compound is formed in the brazing filler metal 432, and therefore the content of simple Bi in the brazing filler metal 432 is reduced. Therefore, the fins 43 of the heat exchanger 4 of this example have excellent self-corrosion resistance.

[0101] The above describes specific aspects of the brazing sheet, heat exchanger fin, and heat exchanger according to the present invention based on examples, but the specific aspects of the brazing sheet, heat exchanger fin, and heat exchanger according to the present invention are not limited to the aspects of the examples, and the configuration can be changed as appropriate within the scope that does not detract from the spirit of the present invention. [Explanation of symbols]

[0102] 1. Brazing sheet 2 Heartwood 3 Brazing filler metal

Claims

1. A brazing sheet configured to enable brazing of aluminum materials in an inert gas atmosphere without using flux, a core material having a chemical composition containing one or more elements selected from the group consisting of Si: 0.02% by mass or more and 1.5% by mass or less, Fe: more than 0% by mass and 1.5% by mass or less, Cu: more than 0% by mass and 1.0% by mass or less, Mn: more than 0% by mass and 2.0% by mass or less, Mg: more than 0% by mass and 1.2% by mass or less, and Zn: more than 0% by mass and 4.5% by mass or less, with the remainder being Al and unavoidable impurities; a brazing filler metal laminated on at least one surface of the core material, the brazing filler metal having a chemical composition containing Si: 3.0 mass% or more and 13.0 mass% or less, Mg: 0.8 mass% or more and 7.0 mass% or less, and Bi: 0.01 mass% or more and 1.0 mass% or less, with the balance being Al and unavoidable impurities, and the ratio of the Bi content to the Mg content being 0.3 or less; The brazing sheet has the property that when the brazing sheet is heated to 600°C at an average heating rate of 15°C / min from when it reaches 580°C to when it reaches 600°C, and when it is cooled immediately after it reaches 600°C, the ratio of the area where the Mg intensity is 50,000 cps or more in an elemental mapping image of the surface of the brazing material obtained using an electron beam microanalyzer is 1% or more.

2. 2. The brazing sheet according to claim 1, wherein the core material further contains one or more elements selected from the group consisting of Cr: more than 0 mass% and not more than 0.3 mass%, Ti: more than 0 mass% and not more than 0.3 mass%, and Zr: more than 0 mass% and not more than 0.3 mass%.

3. 3. The brazing sheet according to claim 1, wherein the brazing filler metal further contains one or more of the following elements: Na: more than 0% by mass and not more than 0.05% by mass; Sr: more than 0% by mass and not more than 0.05% by mass; Sb: more than 0% by mass and not more than 0.05% by mass; Zn: more than 0% by mass and not more than 8.0% by mass; Cu: more than 0% by mass and not more than 4.0% by mass; Fe: more than 0% by mass and not more than 1.0% by mass; and Mn: more than 0% by mass and not more than 1.0% by mass.

4. The brazing sheet according to any one of claims 1 to 3, wherein the brazing filler metal further contains one or more elements selected from the group consisting of Cr: more than 0 mass% and 0.3 mass% or less, Ti: more than 0 mass% and 0.3 mass% or less, and Zr: more than 0 mass% and 0.3 mass% or less.

5. The brazing sheet according to any one of claims 1 to 4, wherein the brazing filler metal further contains one or two elements selected from the group consisting of In: more than 0 mass% and 0.1 mass% or less and Sn: more than 0 mass% and 0.1 mass% or less.

6. A heat exchanger fin comprising the brazing sheet according to any one of claims 1 to 5.

7. a tube configured to allow a heat transfer medium to flow; a fin joined to the tube via brazing, The fin comprises a core material having a chemical composition containing one or more elements selected from the group consisting of Si: 0.02% by mass or more and 1.5% by mass or less, Fe: more than 0% by mass and 1.5% by mass or less, Cu: more than 0% by mass and 1.0% by mass or less, Mn: more than 0% by mass and 2.0% by mass or less, Mg: more than 0% by mass and 1.2% by mass or less, and Zn: more than 0% by mass and 4.5% by mass or less, with the remainder being Al and unavoidable impurities; and a brazing filler metal laminated on at least one surface of the core material, The brazing filler metal has a chemical composition containing Si: 3.0% by mass or more and 13.0% by mass or less, Mg: 0.8% by mass or more and 7.0% by mass or less, and Bi: 0.01% by mass or more and 1.0% by mass or less, with the remainder being Al and unavoidable impurities, and the ratio of the Bi content to the Mg content is 0.3 or less, A heat exchanger, wherein the ratio of an area where the Mg intensity is 50,000 cps or more in an elemental mapping image of the surface of the brazing filler metal obtained using an electron beam microanalyzer is 1% or more.

Images