Aluminum alloy heat exchanger

Abstract

To provide a heat exchanger capable of attaining brazability improvement effect by addition of Bi while restraining deterioration of corrosion resistance due to the addition of Bi.SOLUTION: An aluminum alloy heat exchanger 1 is manufactured by being joined by brazing with heat in an inert gas atmosphere without using flux. A refrigerant passage pipe 2 is made of a clad material prepared by cladding a core material with a sacrifice anode material 22. A fin 3 is made of a clad material prepared by cladding a core material with a brazing material consisting of an aluminum alloy containing Si and Bi. The sacrifice anode material 22 and the fin 3 are brought into contact with each other and joined by brazing. A pitting potential Ef of a surface of the fin 3 and a pitting potential Es of a surface of the sacrifice anode material 22 of the refrigerant passage pipe 2 have the following relations (1) to (3), (1) the pitting potential Ef≥the pitting potential Es, (2) the pitting potential Es≥-830 mV (vs Ag / AgCl), (3) the pitting potential Ef≥-780 mV (vs Ag / AgCl).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy heat exchanger in which refrigerant passage tubes and fins are brazed together in an inert gas without using flux. [Background technology]

[0002] Aluminum alloy heat exchangers, which are lightweight and have good thermal conductivity, are generally used as heat exchangers for automobiles. These heat exchangers are widely manufactured by, for example, using refrigerant passage pipes made by bending or pressing aluminum alloy plate material into tubular shapes, assembling the refrigerant passage pipes and components such as fins into a predetermined structure, and brazing them together using a fluoride flux in an inert gas atmosphere.

[0003] Furthermore, with the recent trend toward lighter automobiles, thinner heat exchanger materials are also required, which has led to challenges in increasing the strength of refrigerant passage pipe plates and ensuring formability, brazing ability, and corrosion resistance in thin-walled materials.

[0004] Regarding corrosion resistance, for example, the outer surface of an evaporator is exposed to a corrosive environment due to condensation during use. Similarly, the outer surface of a condenser is exposed to a corrosive environment due to road splash containing deicing salt while driving. If corrosion causes premature holes in the refrigerant passage pipes, refrigerant will leak and the heat exchanger will no longer function. Therefore, it is common to apply corrosion prevention treatment to the outer surface of the refrigerant passage pipes to extend the life of the heat exchanger.

[0005] Conventional methods for protecting the outer surfaces of refrigerant passage pipes from corrosion include a method in which a plate material clad on the outer surface with an Al-Zn alloy is formed into a flat tube as a sacrificial anode material (see Patent Documents 1 and 2, etc.), and a method in which an extruded multi-hole tube is used for the refrigerant passage pipe. These heat exchangers generally have a structure in which the outer surfaces of the refrigerant passage pipes are brazed using fin material clad with a brazing filler metal. Using fin material clad with a brazing filler metal eliminates the need to apply a separately prepared brazing filler metal to the outer surfaces of the refrigerant passage pipes.

[0006] Furthermore, to enable brazing of aluminum alloys, it is necessary to destroy the oxide film on the surface of the material, and conventionally, flux has been applied to the brazing area to destroy the oxide film. However, the use of flux not only requires a flux application process and a post-brazing cleaning process, but also has various disadvantages. Therefore, flux-free brazing methods that do not use flux have been investigated.

[0007] As brazing methods that do not use flux (flux-free), for example, vacuum brazing, which is carried out in a vacuum atmosphere by utilizing the oxide film destruction effect of Mg and other substances contained in the brazing filler metal, and methods that are carried out in an inert gas atmosphere such as a nitrogen gas atmosphere by utilizing the oxide film destruction effect of Mg and other substances contained in the brazing filler metal, have been developed.

[0008] It has been disclosed that in flux-free brazing in an inert gas, adding Bi to the brazing filler metal of an aluminum alloy clad material can further suppress oxidation of the surface during brazing, resulting in good brazability even in an inert gas atmosphere with a relatively high oxygen concentration.

[0009] On the other hand, it is known that the inclusion of Bi in aluminum alloys deteriorates their corrosion resistance. In flux-free brazing, adding Bi to the brazing filler metal is effective in improving brazing properties, but simply adding Bi to the brazing filler metal further deteriorates the self-corrosion resistance of the fins, which can lead to early fin loss due to corrosion and, as a result, reduced heat exchange performance. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-225061 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-16937 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the above background, and aims to provide a heat exchanger that can suppress the deterioration of corrosion resistance due to the addition of Bi while obtaining the effect of improving flux-free brazing due to the addition of Bi, that is, an aluminum alloy heat exchanger that can improve the brazing properties of flux-free brazing in an inert gas atmosphere and can prevent early loss of fin material due to corrosion, thereby improving corrosion resistance. [Means for solving the problem]

[0012] In one aspect of the present invention, the refrigerant passage pipe and the fin are joined together without using flux. to An aluminum alloy heat exchanger that is brazed and joined, the refrigerant passage pipe is made of a pipe clad material in which one surface of a pipe core material made of an aluminum alloy is clad with a sacrificial anode material made of an aluminum alloy, and is formed into a tubular shape so that the sacrificial anode material is exposed on the outer surface side; The fin is made of a fin clad material in which one or both sides of a fin core material made of an aluminum alloy are clad with a fin brazing filler metal made of an aluminum alloy containing at least Si and Bi, the sacrificial anode material of the refrigerant passage pipe and the fin are in contact with each other and brazed together; In the aluminum alloy heat exchanger, the pitting potential Ef of the surface of the fin in a 5 mass % NaCl solution and the pitting potential Es of the surface of the sacrificial anode material of the refrigerant passage tube in a 5 mass % NaCl solution satisfy the relationship of the following formulas (1) to (3): Pitting corrosion potential Ef≧pitting corrosion potential Es (1) Pitting potential Es≧ -794 mV (vs Ag / AgCl) (2) Pitting potential Ef≧-780mV (vs Ag / AgCl) (3) [Effects of the Invention]

[0013] In the heat exchanger, the brazing filler metal of the fin clad material contains Bi. Therefore, excellent brazing properties can be obtained even when flux-free brazing is performed in an inert gas atmosphere during fabrication of the heat exchanger. Furthermore, the pitting potential Ef of the surface of the fin in the heat exchanger in a 5% by mass NaCl solution and the pitting potential Es of the surface of the sacrificial anode material of the refrigerant passage in a 5% by mass NaCl solution have the relationship shown in formulas (1) to (3). As demonstrated in the experimental examples described below, by ensuring all of these specific relationships, it is possible to improve the corrosion resistance of the fins and, ultimately, the corrosion resistance of the entire heat exchanger. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is an explanatory diagram showing the configuration of a heat exchanger in the first embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing the configuration of a cladding material for pipes in the first embodiment. [Figure 3] FIG. 2 is an explanatory diagram showing the configuration of a clad material for a fin in the first embodiment. [Figure 4] FIG. 10 is an explanatory diagram showing the configuration of a heat exchanger in a second embodiment. [Figure 5] FIG. 2 is an explanatory diagram showing the configuration of a heat exchanger test piece in an experimental example. DETAILED DESCRIPTION OF THE INVENTION

[0015] The refrigerant passage pipe in the heat exchanger is made of a core material (pipe core material) made of an aluminum alloy and a pipe clad material in which a sacrificial anode material made of an aluminum alloy is clad on one side of the core material, and is formed into a tubular shape so that the sacrificial anode material is exposed on the outer surface and the opposite surface of the sacrificial anode material is the inner surface (refrigerant passage side). The refrigerant passage pipe can be configured so that nothing is provided inside it, or a configuration can be adopted in which inner fins are added.

[0016] The side of the core material in the pipe clad material opposite to the side where the sacrificial anode is provided may be left bare, leaving the core material exposed, or a brazing filler metal (pipe brazing filler metal) may be provided. When a brazing filler metal is used, this brazing filler metal is used to braze the ends of the pipe clad material when it is formed into a tubular shape. Furthermore, when an inner fin is provided, it can also function as a brazing filler metal to join the inner fin. When the pipe core material does not have a brazing filler metal, for example, a structure with an inner fin inside can be adopted, and a clad material with brazing filler metal on both sides of the core material can be used as the inner fin. This inner fin can be sandwiched between the end joints of the refrigerant passage pipe, thereby obtaining a refrigerant passage pipe brazed together with the inner fin. While various other shapes are possible for the refrigerant passage pipe, it is essential that the sacrificial anode material be present at least on the outer surface of the tubular shape, as described above.

[0017] The fins are assembled to the outer surface of the refrigerant passage pipes and brazed. The fins are made of a core material (fin core material) made of an aluminum alloy and a fin clad material in which a brazing filler metal (fin brazing filler metal) made of an aluminum alloy containing Si and Bi is clad on one or both sides of the core material. Generally, the fins are corrugated to form a wave shape, and the peaks of the mountain-like shapes are abutted against the outer surface of the refrigerant passage pipes to be joined.

[0018] The fin clad material may have the brazing filler metal applied to only one side of the core material, or may have the brazing filler metal applied to both sides. At least when the fin is corrugated and disposed so as to span two adjacent refrigerant passage pipes, it is preferable to adopt a configuration in which the brazing filler metal is applied to both sides of the core material, and in this case, the fin brazing filler metal can be placed in contact with the outer surfaces of the refrigerant passage pipes during assembly.

[0019] The heat exchanger is obtained by assembling the refrigerant passage pipes and fins and brazing them together by heating them in an inert gas atmosphere without using a flux. Specifically, the heat exchanger assembly, which includes the refrigerant passage pipes, fins, and other components as needed, is brazed together by heating the assembly to 600°C for 3 minutes in an inert gas atmosphere such as nitrogen gas. The heat exchanger of the present application has excellent brazability and structural strength even without using a flux because the brazing filler metal for the fins contains Bi.

[0020] In the heat exchanger after brazing, as described above, the pitting potential Ef of the fins in a NaCl solution and the pitting potential Es of the surface of the sacrificial anode material of the refrigerant passage in a 5 mass % NaCl solution satisfy the relationships of the following formulas (1) to (3).

[0021] Pitting corrosion potential Ef≧pitting corrosion potential Es (1) Pitting potential Es≧ -794 mV (vs Ag / AgCl) (2) Pitting potential Ef≧-780mV (vs Ag / AgCl) (3)

[0022] It has been reported that the inclusion of Bi in a fin brazing filler metal causes early fin corrosion and fin loss. However, by strictly restricting the relationship between the pitting potentials of each part so as to ensure all of the specific relationships shown in the above formulas (1) to (3), it is possible to prevent early fin loss due to corrosion, suppress corrosion of the refrigerant passage tubes, and further suppress corrosion at the joints between the refrigerant passage tubes and the fins, thereby preventing fin peeling, and maintaining the function of the heat exchanger for a long period of time.

[0023] On the other hand, if any one of formulas (1) to (3) is not satisfied, it becomes difficult to obtain these effects. More specifically, by satisfying formula (1), the refrigerant passage pipe achieves improved corrosion resistance of the outer surface (air side) in a general corrosive environment due to the sacrificial anode material, and the sacrificial anode material of the refrigerant passage pipe exerts a sacrificial anode effect on the fins, suppressing early corrosion of the fins. However, if formula (1) is not satisfied, the fins will corrode preferentially and disappear early, resulting in a decrease in the heat exchange performance of the heat exchanger.

[0024] Furthermore, by satisfying formula (2), the corrosion potential of the entire refrigerant passage tubes can be prevented from becoming less noble, the corrosion rate of the refrigerant passage tubes can be prevented from increasing, and early corrosion and perforation of the refrigerant passages in a corrosive environment can be prevented. However, if formula (2) is not satisfied, the self-corrosion resistance of the refrigerant passage tubes will deteriorate, and the sacrificial anode material will be lost early due to corrosion, causing fin peeling and reducing the heat exchange performance of the heat exchanger.

[0025] Furthermore, by satisfying formula (3), the fins can function as sacrificial anodes, thereby inhibiting corrosion of the refrigerant passages for a long period of time.If formula (3) is not satisfied, the fins' self-corrosion resistance will deteriorate, and the fins will quickly disappear due to corrosion, resulting in a decrease in the heat exchange performance of the heat exchanger.

[0026] To obtain a configuration that satisfies all of the above formulas (1) to (3), it is necessary to appropriately adjust the chemical composition of each of the refrigerant passage tubes and the fins and to appropriately select their combination. Preferred chemical composition and combinations will be described later, but in practice, it is necessary to measure the pitting potential of each part in the heat exchanger after brazing to confirm that the above specific relationships are met.

[0027] Next, the cladding material for pipes and the cladding material for fins will be described in more detail.

[0028] (Core material for clad fins (core material for fins)) The fin core material is preferably made of an aluminum alloy containing one or two of 0.6 to 2.0 mass % of Mn and 1.0 mass % or less of Mg.

[0029] Mn in the fin core material is expected to improve the strength of the core material and make the pitting potential of the core material more noble. Therefore, it is preferable that the fin core material contain 0.6 to 2.0 mass%, preferably 1.0 to 2.0 mass%, of Mn. If the Mn content of the fin core material is less than 0.6 mass%, the above-mentioned effects of Mn inclusion cannot be fully obtained. On the other hand, if the Mn content exceeds 2.0 mass%, it may become difficult to roll the clad material.

[0030] It is preferable to include Mg in the core material for fins because it is expected to improve the strength of the core material and promote the destruction of the oxide film by diffusing to the surface during brazing heating. On the other hand, because Mg increases the susceptibility of the core material to intergranular corrosion, it is preferable to limit the Mg content to 1.0 mass% or less.

[0031] Preferably, the fin core material further contains Cu: 0.2 mass % or less.

[0032] Cu in the fin core material improves the strength of the core material and functions to make the pitting potential noble (higher), and it is preferable to include Cu in the core material to adjust the balance of the pitting potential with the refrigerant passage. On the other hand, Cu increases the corrosion rate of the core material and also increases its susceptibility to intergranular corrosion, so its content is preferably limited to 0.2 mass% or less.

[0033] Preferably, the fin core material further contains one or both of Si: 0.7 mass % or less and Fe: 0.7 mass % or less.

[0034] Since Si in the fin core material functions to improve the strength of the core material, it is preferable to include Si in the core material. On the other hand, the Si content is preferably limited to 0.7% by mass or less to prevent deterioration of the core material's self-corrosion resistance and melting of the fin due to a drop in the solidus temperature during brazing. When Si in the fin brazing filler metal diffuses into the fin core material during brazing, the Si concentration becomes significantly higher than in the original state, which can cause the solidus temperature to drop too much, potentially resulting in melting of the fin core material during brazing. To avoid this, it is preferable to initially keep the Si content of the fin core material low (0.7% by mass or less).

[0035] The inclusion of Fe in the fin core material is preferable because it is contained as an impurity in the base metal and because it allows for adjustment of the crystal grain size during material production and brazing. However, Fe easily forms Al-Fe-Si and Al-Fe-Mn intermetallic compounds, which may reduce the self-corrosion resistance of the core material, so the Fe content is preferably limited to 0.7 mass% or less.

[0036] The fin core material may further contain Zn: 1.5 mass % or less.

[0037] Zn in the fin core material functions to lower the pitting potential of the fin surface after brazing heat, maintaining the surface pitting potential of the fin surface low after brazing heat, and can be included to adjust the balance with the pitting potential of the refrigerant passage. On the other hand, to ensure the self-corrosion resistance of the fin core material and obtain the heat exchange performance of the heat exchanger over a long period of time, it is preferable to limit the Zn content to 1.5% by mass or less. If the Zn content exceeds 1.5% by mass, the pitting potential of the fin becomes too noble, the self-corrosion resistance of the fin deteriorates, the fins may be lost early due to corrosion, and the heat exchange performance of the heat exchanger may be reduced. Therefore, the Zn content in the fin core material is more preferably 1.0% by mass or less.

[0038] The fin core material may contain up to 0.3 mass% of V, Cr, Zr, or B, and may further contain up to 0.1 mass% of In and Sn, as long as the essential effects are not impaired. It may also contain other unavoidable impurities.

[0039] Based on the above, it is preferable that the chemical composition of the core material for fins contains one or two of Mn: 0.6 to 2.0 mass% and Mg: 1.0 mass% or less, and the following optional elements: Cu: 0.2 mass% or less, Si: 0.7 mass% or less, Fe: 0.7 mass% or less, Zn: 1.5 mass% or less, V: 0.3 mass% or less, Cr: 0.3 mass% or less, Zr: 0.3 mass% or less, B: 0.3 mass% or less, In: 0.1 mass% or less, and Sn: 0.1 mass% or less, with aluminum and unavoidable impurities as the remaining elements.

[0040] (Fin clad brazing filler metal (fin brazing filler metal)) The fin brazing filler metal is preferably made of an aluminum alloy containing 5 to 13 mass % of Si and 0.02 to 0.50 mass % of Bi.

[0041] The Si content of the brazing filler metal for fins is preferably 5 to 13 mass % to obtain this effect. If the Si content of the brazing filler metal is less than 5%, the amount of melted brazing filler metal will be insufficient, resulting in an insufficient function as a brazing filler metal. On the other hand, if the Si content exceeds 13 mass %, primary Si crystals may crystallize, making sound manufacturing difficult.

[0042] The Bi content of the brazing filler metal for fins suppresses oxidation during brazing, enabling brazing without the use of flux. To fully obtain this effect, the Bi content is preferably 0.02% by mass or more. On the other hand, if the Bi content of the brazing filler metal exceeds 0.50% by mass, sound manufacturing may become difficult.

[0043] Preferably, the fin brazing filler metal further contains 1.5 mass % or less of Mg.

[0044] The Mg content of the brazing filler metal for fins can be added up to 1.5% to promote the destruction of the oxide film during brazing. If the Mg content of the brazing filler metal exceeds this range, it may become difficult to manufacture the product properly.

[0045] The fin brazing filler metal may contain 0.30 mass% or less of each of Fe, Mn, Cu, Cr, Zn, and Ti, as long as the essential effects are not impaired. It may also contain other unavoidable impurities.

[0046] Based on the above, the chemical composition of the fin brazing filler metal preferably contains 5 to 13 mass% Si, 0.02 to 0.50 mass% Bi, and the following optional elements: 1.5 mass% or less Mg, 0.30 mass% or less Fe, 0.30 mass% or less Mn, 0.30 mass% or less Cu, 0.30 mass% or less Cr, 0.30 mass% or less Zn, 0.30 mass% or less Ti, with aluminum and unavoidable impurities as the remaining elements.

[0047] (core material for pipe cladding materials) The core material of the pipe clad material (pipe core material) is made of an aluminum alloy and is not particularly limited. However, from the viewpoints of improving strength characteristics, corrosion resistance, productivity, and the like, it is preferable to use variously adjusted aluminum alloys.

[0048] The core material for the pipe is preferably made of an aluminum alloy containing one or more of 0.6 to 2.0 mass % of Mn, 1.0 mass % or less of Cu, and 1.0 mass % or less of Mg.

[0049] Mn in the core material for pipes improves the strength of the core material and makes the pitting potential of the core material more noble. To obtain this effect appropriately, the Mn content of the core material for pipes is preferably 0.6 to 2.0 mass%, more preferably 1.0 to 2.0 mass%. If the Mn content of the core material for pipes is less than 0.6 mass%, the above effect cannot be sufficiently obtained. On the other hand, if the Mn content exceeds 2.0 mass%, it may become difficult to roll the clad material.

[0050] Cu in the pipe core material improves the strength of the core material and functions to make the pitting potential noble (to increase), and can be included to adjust the balance of the pitting potential with the sacrificial anode material. On the other hand, Cu in the pipe core material diffuses into the sacrificial anode material during brazing heating, thereby reducing the potential difference with the sacrificial anode material and increasing the corrosion rate of the sacrificial anode material, so its content is preferably limited to 1.0 mass% or less.

[0051] Mg can be added to the pipe core material to improve its strength and promote the destruction of the oxide film by diffusing to the surface during brazing heating. On the other hand, to increase the susceptibility of the pipe core material to intergranular corrosion, the Mg content is preferably limited to 1.0 mass% or less.

[0052] The pipe core material preferably further contains one or both of 0.7 mass % or less of Si and 0.7 mass % or less of Fe.

[0053] The Si content in the pipe core material is preferably limited to 0.7 mass% or less to prevent deterioration of the self-corrosion resistance of the pipe core material.

[0054] It is preferable to allow the inclusion of Fe in pipe core materials because it is contained as an impurity in the base metal and because it can adjust the crystal grain size during material production and brazing. On the other hand, Fe easily forms Al-Fe-Si and Al-Fe-Mn intermetallic compounds, which may reduce the self-corrosion resistance of the core material, so it is preferable to limit the Fe content to 0.7 mass% or less.

[0055] The pipe core material preferably further contains Ti: 0.01 to 0.30 mass %.

[0056] The Ti in the pipe core material is divided into high-concentration and low-concentration regions in the thickness direction of the core material, and these regions are distributed alternately in layers. The low-Ti concentration regions corrode preferentially over the high-Ti concentration regions. This has the effect of creating a layered corrosion pattern in the core material, which is expected to prevent corrosion from progressing in the thickness direction of the refrigerant passage tube and improve corrosion resistance. To achieve this effect, the Ti content of the pipe core material is preferably 0.01 to 0.30 mass%. If the Ti content of the pipe core material is less than 0.01 mass%, the above effect cannot be fully achieved. On the other hand, if the Ti content exceeds 0.30 mass%, large crystals may form, which may impair the formability of the refrigerant passage tube.

[0057] Furthermore, the pipe core material may contain 0.3 mass % or less of each of V, Cr, Zr, or B, provided that the essential effects are not impaired. It may also contain other unavoidable impurities.

[0058] Based on the above, it is preferable that the chemical composition of the pipe core material contains one or more of Mn: 0.6 to 2.0 mass%, Cu: 1.0 mass% or less, and Mg: 1.0 mass% or less, and the following optional elements: Si: 0.7 mass% or less, Fe: 0.7 mass% or less, and Ti: 0.01 to 0.30 mass%, with the remainder consisting of aluminum and unavoidable impurities.

[0059] (Sacrificial anode material for pipe cladding) The sacrificial anode material is preferably made of an aluminum alloy containing one or more of 0.7 mass % or less of Si, 0.7 mass % or less of Fe, and 1.5 mass % or less of Mn.

[0060] The Si content of the sacrificial anode material is preferably limited to 0.7 mass% or less because it functions to improve the strength of the sacrificial anode material. However, if the Si content is too high, the self-corrosion rate of the sacrificial anode material increases.

[0061] The Fe content of the sacrificial anode material is preferably 0.7 mass% or less because it functions to improve the strength of the sacrificial anode material. However, if the Fe content is too high, the self-corrosion rate of the sacrificial anode material increases.

[0062] Mn in the sacrificial anode material is preferably contained because it functions to improve the strength of the sacrificial anode material. On the other hand, if the Mn content is too high, the self-corrosion rate of the sacrificial anode material increases and the potential of the surface of the sacrificial anode material may become nobler, so the Mn content is preferably limited to 1.5 mass% or less.

[0063] The sacrificial anode material may further contain Zn: 4.5 mass % or less.

[0064] The Zn in the sacrificial anode material functions to make the pitting potential of the surface of the sacrificial anode material less noble after brazing heat, maintaining the pitting potential of the surface of the sacrificial anode material low after brazing heat and adjusting the balance with the pitting potential of the fin. On the other hand, if the Zn content is too high, the self-corrosion rate of the sacrificial anode material increases too much, so the Zn content is preferably limited to 4.5% by mass or less. More preferably, the Zn content is limited to 3.0% by mass or less, and even more preferably to 2.5% by mass or less.

[0065] Furthermore, the sacrificial anode material may contain 0.1 mass % or less of In, 0.1 mass % or less of Sn, 0.3 mass % or less of Ti, and 0.6 mass % or less of Mg, as long as the effects of the present invention are not impaired. It may also contain other unavoidable impurities.

[0066] In view of the above, it is preferable that the chemical composition of the sacrificial anode material contains one or more of 0.7 mass% or less of Si, 0.7 mass% or less of Fe, and 1.5 mass% or less of Mn, and contains 4.5 mass% or less of Zn as an optional element, with the remainder being aluminum and unavoidable impurities.

[0067] (Pipe clad brazing filler metal (pipe brazing filler metal)) The clad pipe material is preferably obtained by cladding a brazing filler metal for pipe made of an aluminum alloy containing 5.0 to 13.0 mass % of Si on the surface of the core pipe material opposite to the surface clad with the sacrificial anode material.

[0068] Si in a pipe brazing filler metal can lower the solidus temperature and generate a liquid phase during brazing, and to obtain this effect, the Si content is preferably 5 to 13%. If the Si content of the brazing filler metal is less than 5%, the amount of melted brazing filler metal will be insufficient, resulting in an insufficient function as a brazing filler metal. On the other hand, if the Si content exceeds 13 mass%, primary Si crystals may crystallize, making it difficult to manufacture properly.

[0069] The pipe brazing filler metal may further contain one or both of Mg: 1.5 mass % or less and Bi: 0.02 to 0.5 mass %.

[0070] The Mg content of the brazing filler metal for pipes can be up to 1.5% to promote the destruction of the oxide film during brazing. If the Mg content of the brazing filler metal exceeds this range, it may become difficult to manufacture the pipes properly.

[0071] Bi in pipe brazing filler metal is effective in suppressing oxidation during brazing, and to obtain this effect, it is preferable to add 0.02 mass% or more of Bi. On the other hand, if the Bi content exceeds 0.50 mass%, it may become difficult to manufacture the pipe brazing filler metal properly.

[0072] The brazing filler metal for pipes may contain 0.30 mass % or less of each of Fe, Mn, Cu, Cr, Zn, and Ti, as long as the original effects are not impaired. The brazing filler metal may also contain other unavoidable impurities.

[0073] Based on the above, the chemical composition of the pipe brazing filler metal preferably contains 5 to 13 mass% Si, and the following optional elements: 0.02 to 0.50 mass% Bi, 1.5 mass% or less Mg, 0.30 mass% or less Fe, 0.30 mass% or less Mn, 0.30 mass% or less Cu, 0.30 mass% or less Cr, 0.30 mass% or less Zn, 0.30 mass% or less Ti, and also contains aluminum and unavoidable impurities.

[0074] (Dimensions of clad material for fins) The thickness of the fin clad material can be 0.03 mm to 0.20 mm. When the thickness is 0.15 mm or less, the clad ratio of the brazing filler metal in the fin clad material (value for the brazing filler metal on one side, the same applies below) is preferably 7 to 20%, more preferably 8 to 15%. When the thickness exceeds 0.25 mm, the clad ratio of the brazing filler metal is preferably 5 to 15%.

[0075] Regardless of the thickness range of the fin clad material, if the clad ratio of the brazing filler metal is less than the above lower limit, the amount of flowing brazing filler metal during brazing may be insufficient, resulting in insufficient joining.If the clad ratio of the brazing filler metal exceeds the above upper limit, the amount of flowing brazing filler metal during brazing may be excessive, resulting in the fin core material or the mating material melting.

[0076] (Pipe clad material dimensions) The thickness of the cladding material for pipes can be 0.1 mm to 1.0 mm. When the thickness is 0.5 mm or less, the cladding ratio of the sacrificial anode material in the cladding material for pipes is preferably 5 to 30%, more preferably 10 to 30%. When the thickness is more than 0.5 mm, the cladding ratio of the sacrificial anode material is preferably 3 to 30%.

[0077] Regardless of the thickness range of the clad material for pipes, if the clad ratio of the sacrificial anode material is less than the above lower limit, the amount of Zn in the sacrificial anode material may decrease due to diffusion during brazing, increasing the pitting potential of the surface of the sacrificial anode material and making it difficult to obtain a sufficient sacrificial anode effect.If the clad ratio of the sacrificial anode material exceeds the above upper limit, it may become difficult to roll the clad material for pipes.

[0078] When a brazing filler metal is provided on the surface of the cladding material opposite the sacrificial anode material, and the thickness of the cladding material is 0.5 mm or less, the cladding ratio of the brazing filler metal is preferably 5 to 30%, more preferably 5 to 20%. When the thickness exceeds 0.5 mm, the cladding ratio of the brazing filler metal is preferably 3 to 30%.

[0079] Regardless of the thickness range of the clad material for pipes, if the clad ratio of the brazing filler metal is less than the above lower limit, the liquid phase may be insufficient during brazing, which may result in poor brazing properties.If the clad ratio of the brazing filler metal exceeds the above upper limit, it may become difficult to roll the clad material for pipes.

[0080] (Embodiment 1) An embodiment of an aluminum alloy heat exchanger will be described with reference to Figures 1 to 3. As shown in Figure 1, the aluminum alloy heat exchanger 1 of this embodiment is an aluminum alloy heat exchanger formed by alternately stacking and assembling refrigerant passage tubes 2 and fins 3, and then heating and brazing them in an inert gas atmosphere without using flux.

[0081] As shown in FIG. 2, the refrigerant passage tube 2 is made of a pipe clad material 20 in which one side of a pipe core material 21 made of an aluminum alloy is clad with a sacrificial anode material 22 made of an aluminum alloy and the other side is clad with a pipe brazing material 23, and is formed into a tubular shape so that the sacrificial anode material is exposed on the outer surface.

[0082] The fin 3 is made of a fin clad material 30 in which a fin core material 31 made of an aluminum alloy is clad on both sides with a fin brazing material 32 made of an aluminum alloy containing at least Si and Bi, and is corrugated to give it a wavy shape.

[0083] The heat exchanger 1 of this example is manufactured by brazing the assembled heat exchanger 1 as shown in FIG. 1 for 3 minutes at 600°C in an inert gas atmosphere furnace without applying flux, thereby joining the refrigerant passage tubes 2 and the fins 3.

[0084] (Embodiment 2) In this embodiment, the refrigerant passage pipe 2 in Embodiment 1 is changed to a refrigerant passage pipe 202 shown in Fig. 4. That is, the refrigerant passage pipe 202 is produced using a two-layer clad material (not shown) of a pipe core material 21 and a sacrificial anode material 22, without providing the pipe brazing material 23 in the pipe clad material 20 described above. Then, the refrigerant passage pipe 202 is formed into a tubular shape so that the sacrificial anode material 22 is exposed on the outer surface side, and an inner fin 4, which is clad with brazing material on both sides of the core material, is inserted inside the refrigerant passage pipe 202, so that the inner fin 4 is sandwiched by the joints of the refrigerant passage pipe 202, and the refrigerant passage pipe 202 is brazed with the brazing material of the inner fin 4. The rest of the configuration is the same as in Embodiment 1.

[0085] (Experimental example) Assuming the configuration of the heat exchanger of the first embodiment, heat exchanger test pieces for performance evaluation were prepared and various evaluations were carried out.

[0086] <Production of clad materials for pipes> By semi-continuous casting, alloys for sacrificial anode materials, alloys for core materials, and alloys for brazing filler metals were produced, each having the chemical composition shown in Tables 1 to 3. Of the resulting ingots, the alloys for sacrificial anode materials and brazing filler metals were hot-rolled to the specified thickness at a starting temperature of 480°C without homogenization treatment. The alloy ingots for core materials were either not homogenized or homogenized at 500°C for 8 hours, and then faced to the specified thickness.

[0087] Next, the hot-rolled sacrificial anode alloy and brazing alloy were faced, and then the aluminum alloys were stacked in the combinations shown in Table 4. The resulting laminate was hot-rolled to a thickness of 3 mm at a starting temperature of 480°C, further cold-rolled, intermediate annealed at a temperature of 370°C, and then cold-rolled to obtain clad pipe materials of the specified thickness (Test Materials 1 to 11). The thickness was 0.2 mm or 0.4 mm, and the thickness of each test material is shown in Table 4. The clad ratio of each sacrificial anode alloy and brazing filler metal is also shown in Table 4.

[0088] [Table 1]

[0089] [Table 2]

[0090] [Table 3]

[0091] [Table 4]

[0092] <Production of clad material for fins> Fin core alloy ingots and brazing alloy ingots with the chemical compositions shown in Tables 5 and 6 were cast by semi-continuous casting. The brazing alloy ingots were hot-rolled to the specified thickness without homogenization at a starting temperature of 480°C. The fin core alloy ingots were either homogenized or homogenized at 500°C for 8 hours, then surface-ground to the specified thickness. The brazing alloy ingots were stacked on both sides of the fin core alloy ingot in the combination shown in Table 7, and hot-rolled at a starting temperature of 480°C to produce clad materials of the specified thickness. After cold rolling, intermediate annealing was performed at 300°C, followed by cold rolling to obtain fin clad materials (Test Materials 21 to 33) with thicknesses of 0.05 to 0.07 mm. The cladding ratio of the brazing alloy in the fin clad materials was 10% per side.

[0093] [Table 5]

[0094] [Table 6]

[0095] [Table 7]

[0096] <Preparation of heat exchanger test pieces> In simulating the heat exchanger of embodiment 1, as shown in FIG. 5, one corrugated fin 3 was assembled between the sacrificial anode materials 22 of two pipe clad materials 20 serving as refrigerant passage pipes, and brazing heating was applied at 585 to 630°C for 1 to 30 minutes in an inert gas atmosphere without using flux, to produce heat exchanger test pieces TP (test pieces 101 to 131).

[0097] Regarding the brazing properties of flux-free brazing, the fins were removed and visually inspected to see if fillets remained. It was confirmed that sufficient fillets remained in all test pieces, indicating an excellent brazing condition. Potential measurements and corrosion tests were then conducted using the following methods. The details of the test pieces and the test results are shown in Table 8.

[0098] <Potential measurement> The pitting potential of the heat exchanger test piece TP was measured in a 5 mass % NaCl aqueous solution at room temperature. The pitting potential of the surface of the sacrificial anode material 22 of the refrigerant passage pipe (pipe cladding material 20) was measured by masking all surfaces except the surface on the sacrificial anode material 22 side. The pitting potential of the surface of the fin 3 was measured by masking all surfaces except the surface of the fin 3.

[0099] <Corrosion test> The heat exchanger test piece TP was masked to expose only the fin 3 and the surface of the sacrificial anode material 22 joined to the fin 3 and the joint, and a spray test was performed using SWAAT (in accordance with ASTM G85) to evaluate the corrosion resistance.

[0100] After 1,000 hours of spray testing, a compressive load was applied across the width of the fins to observe how they collapsed, and the corrosion resistance of the fins was evaluated according to the following criteria: Fins were crushed by compression, but resistance was high, and the fins that were pushed out after the test were not destroyed or separated, and there was little progress in fin wear. A rating of "excellent" (◎) was given; fins that were crushed by compression and partially destroyed or separated after the test, resulting in partial progress in fin wear, were given a rating of "good" (○); fins that were not pushed out but were destroyed or separated by compression, resulting in progress in overall fin wear, were given a rating of "fair" (△); and fins that could not be evaluated for compression due to wear or falling off were rated "fail" (×).

[0101] Furthermore, after 1200 hours of spray testing, the maximum pitting depth of the refrigerant passage pipe (pipe cladding material 20) was 0.05 mm or less, which was rated as "excellent" (◎), 0.05 to 0.075 mm was rated as "good" (○), over 0.075 mm but no through holes were formed, which was rated as "fair" (△), and through holes were formed, which was rated as "fail" (×).

[0102] In both the evaluation of fin strength and maximum pitting depth, "excellent" (◎) was given 3 points, "good" (○) 2 points, and "fair" (△) 1 point, and the scores for fin strength and maximum pitting depth of the refrigerant passage were added together to form an overall evaluation score. However, if either one of them also had a "fail" (×), it was deemed to be unsuitable for practical use and the overall evaluation score was set to 0 points. In the overall evaluation, items with 2 points or more were judged to have practical corrosion resistance and were therefore rated as passing.

[0103] [Table 8]

[0104] As shown in Table 8, all of the heat exchanger test pieces 101, 102, 104, 105, 107, 108, 110, 111, 113, 114, 116, 117, 119 to 131 satisfied all of the relationships of the following formulas (1) to (3), and in the corrosion test, the fin strength was at or above a practically acceptable level, and no through holes were formed in the refrigerant passage pipes.

[0105] Pitting potential Ef of the fin surface ≧ Pitting potential Es of the sacrificial anode surface (1) Pitting potential Es of the sacrificial anode surface -794 mV (vs Ag / AgCl) (2) Pitting potential of fin surface Ef≧-780mV (vs Ag / AgCl) (3)

[0106] On the other hand, as shown in Table 8, the comparative specimens 103, 106, 109, 112, and 115 had a pitting potential on the surface of the sacrificial anode material of the refrigerant passage. -794The pitting potential of the fin was below -780 mV, and the overall corrosion rate was high, resulting in a decrease in the strength of the fin. Furthermore, the Zn concentration of the fin core material and the Zn concentration of the sacrificial anode material were both too high, resulting in a pitting potential of the fin below -780 mV, and a pitting potential of the surface of the sacrificial anode material below -780 mV. -794 Because the voltage was below 1000 mV, the overall corrosion rate was high and the self-corrosion rate of the fins was also high, resulting in a decrease in the strength of the fins.

[0107] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention. [Explanation of symbols]

[0108] 1 heat exchanger 2, 202 Refrigerant passage pipe 20 Cladding material for pipes 21 Core material for pipes 22 Sacrificial anode material 3 Fins 30 Cladding material for fins 31 Fin core 32 Fin brazing filler metal 4 inner fins

Claims

1. An aluminum alloy heat exchanger in which refrigerant passage pipes and fins are brazed together without using flux, the refrigerant passage pipe is made of a pipe clad material in which one surface of a pipe core material made of an aluminum alloy is clad with a sacrificial anode material made of an aluminum alloy, and is formed into a tubular shape so that the sacrificial anode material is exposed on the outer surface side; The fin is made of a fin clad material in which one or both surfaces of a fin core material made of an aluminum alloy are clad with a fin brazing filler metal made of an aluminum alloy containing at least Si and Bi, the sacrificial anode material of the refrigerant passage pipe and the fin are in contact with each other and brazed together; an aluminum alloy heat exchanger, wherein a pitting potential Ef of the surface of the fin in a 5 mass % NaCl solution and a pitting potential Es of the surface of the sacrificial anode material of the refrigerant passage tube in a 5 mass % NaCl solution satisfy the relationship expressed by the following formulas (1) to (3): Pitting corrosion potential Ef≧pitting corrosion potential Es...(1) Pitting corrosion potential Es≧-794mV (vs Ag / AgCl)...(2) Pitting corrosion potential Ef≧-780mV (vs Ag / AgCl)...(3)

2. 2. The aluminum alloy heat exchanger according to claim 1, wherein the fin core material is made of an aluminum alloy containing one or two of Mn: 0.6 to 2.0 mass % and Mg: 1.0 mass % or less.

3. 3. The aluminum alloy heat exchanger according to claim 2, wherein the fin core material further contains Cu: 0.2 mass % or less.

4. 4. The aluminum alloy heat exchanger according to claim 2, wherein the fin core material further contains one or both of Si: 0.7 mass % or less and Fe: 0.7 mass % or less.

5. 5. The aluminum alloy heat exchanger according to claim 2, wherein the fin core material further contains Zn: 1.5 mass % or less.

6. The aluminum alloy heat exchanger according to any one of claims 1 to 5, wherein the fin brazing filler metal is made of an aluminum alloy containing 5 to 13 mass% of Si and 0.02 to 0.50 mass% of Bi.

7. 6. The aluminum alloy heat exchanger according to claim 5, wherein the fin brazing filler metal further contains 1.5 mass % or less of Mg.

8. The heat exchanger according to any one of claims 1 to 7, wherein the pipe core material is made of an aluminum alloy containing one or more of Mn: 0.6 to 2.0 mass%, Cu: 1.0 mass% or less, and Mg: 1.0 mass% or less.

9. 9. The aluminum alloy heat exchanger according to claim 8, wherein the pipe core material further contains one or two of Si: 0.7 mass % or less and Fe: 0.7 mass % or less.

10. 10. The aluminum alloy heat exchanger according to claim 8, wherein the pipe core material further contains Ti: 0.01 to 0.30 mass %.

11. The aluminum alloy heat exchanger according to any one of claims 1 to 10, wherein the sacrificial anode material is made of an aluminum alloy containing one or more of 0.7 mass% or less of Si, 0.7 mass% or less of Fe, and 1.5 mass% or less of Mn.

12. 12. The aluminum alloy heat exchanger according to claim 11, wherein the sacrificial anode material further contains Zn: 4.5 mass % or less.

13. The aluminum alloy heat exchanger according to any one of claims 1 to 12, wherein the pipe clad material is obtained by cladding a pipe brazing filler metal made of an aluminum alloy containing Si: 5.0 to 13.0 mass % on a surface of the pipe core material opposite to a surface clad with the sacrificial anode material.

14. 14. The aluminum alloy heat exchanger according to claim 13, wherein the brazing filler metal for pipes further contains one or both of Mg: 1.5 mass% or less and Bi: 0.02 to 0.50 mass%.

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