Brazing sheets for heat exchangers and joining structures for brazing sheets for heat exchangers, and heat exchangers

Abstract

To provide a brazing sheet for a heat exchanger effectively suppressing or preventing preferential corrosion of a fillet even when the fillet caused by adjacency to junction parts of respective brazing sheets contains copper and zinc, and improving corrosion resistance of the heat exchanger.SOLUTION: A brazing sheet 10A includes at least a core material 11, brazing material layers 12, 13 and an intermediate sacrificial layer 14. The brazing material layers 12, 13 are located on the outside of the brazing sheet 10A viewed from each of both surfaces of the core material 11, and the intermediate sacrificial layer 14 is laminated on at least one surface of the core material 11. Neither of the brazing material nor a sacrificial anode material contains copper (Cu). The core material 11 contains copper (Cu) within a range of 0.3-1.2 mass%. The thickness of the intermediate sacrificial layer 14 is equal to or less than 50 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a brazing sheet used for a member constituting a heat exchanger, a joining structure for joining the brazing sheets to each other, and a heat exchanger having the joining structure.

Background Art

[0002] A general heat exchanger usually includes tubes and fins, and has a configuration in which a plurality of fins are attached to the outer periphery of the tubes. As the material of the tubes, copper (Cu) or its alloy (referred to as "copper material" for convenience) has been used, but in recent years, aluminum (Al) or its alloy (aluminum material) has also been used. As the material of the fins, generally aluminum material is used.

[0003] [[ID=1,6]]In the manufacture of a heat exchanger, for attaching fins to the tubes, generally, brazing using a brazing material is used. If both the tubes and the fins are made of aluminum material, for example, a brazing sheet in which a brazing material layer is clad (coated) on at least one surface of a core material made of an aluminum alloy is used. Considering the corrosion resistance of the tubes and the fins, a brazing sheet in which a brazing material is clad on one surface of the core material and a layer (sacrificial layer) made of a sacrificial anode material is clad on the other surface is used.

[0004] As an example of a brazing sheet with a sacrificial layer clad, for example, the one disclosed in Patent Document 1 is known. Patent Document 1 discloses an aluminum alloy brazing sheet used for a passage component material of an automotive heat exchanger, especially a fluid (such as cooling water or refrigerant), and adjusts the components of the core material and the sacrificial anode material in order to achieve good brazing property, excellent strength and corrosion resistance after brazing.

[0005] In this brazing sheet, the content of silicon, iron (Fe), and manganese (Mn) in the sacrificial anode material is restricted to 0.15% by mass or less. This is to suppress the formation of Al-Mn-Si or Al-Fe-Mn-Si compounds and to suppress the decrease in strength after brazing. In addition, in this brazing sheet, the silicon content in the core material is restricted to 0.15% by mass or less, and copper is added to the core material in the range of 0.40 to 1.2% by weight. The reason for adding copper is to improve the strength of the core material and to increase the potential of the core material, thereby increasing the potential difference with the sacrificial anode layer and improving the corrosion protection effect due to the sacrificial anodic action.

[0006] Another example of a brazing sheet with a sacrificial layer is, for example, the one disclosed in Patent Document 2. Patent Document 2 also discloses an aluminum alloy brazing sheet used in automotive heat exchangers, particularly as a component of the fluid passage, which has sacrificial corrosion protection on both sides and a brazing function on one side, and further adjusts the composition of the brazing material as well as the core material and sacrificial anode material to prevent preferential corrosion of the joint.

[0007] In this brazing sheet, zinc (Zn) is added not only to the sacrificial anode material but also to the brazing material. Furthermore, copper is added to the brazing material in the range of 0.1 to 0.6 mass%, and copper is also added to the core material in the range of 0.05 to 1.2 mass%. The purpose of adding copper to each material is different: in the brazing material, it is to make the potential of the brazing material noble, and in the core material, it is to improve the strength of the core material. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2010-163674 [Patent Document 2] Japanese Patent Publication No. 2013-155404 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The brazing sheet disclosed in Patent Document 1 aims to improve strength and corrosion protection through sacrificial anodic action by adding copper to the core material. However, in this brazing sheet, the silicon content of both the sacrificial anode material and the core material is limited to 0.15% by mass or less, and the content of various metal elements other than copper in the core material is also specified in detail. As a result, the range of materials that can be used as the core material and sacrificial anode material is narrowed. Moreover, in this brazing sheet, the silicon content of the sacrificial anode material is restricted to a very small amount. Therefore, this sacrificial layer is not considered to have the function of a general brazing material.

[0010] In the brazing sheet disclosed in Patent Document 2, by adding copper along with zinc to the brazing material, not only is zinc concentrated at the brazed joint, but copper is also concentrated in the same way. Therefore, this concentration (inclusion) of copper is intended to prevent the potential of the joint from being excessively lowered by zinc. However, as a result of our diligent research, it has become clear that when copper and zinc are used together, the preferential corrosion effect of the sacrificial layer is reduced, resulting in a decrease in corrosion resistance.

[0011] For example, some types of heat exchangers include structures in which, when brazing sheets are joined together, the angle formed by the joining surfaces is acute. For convenience, if we refer to such a structure as an "acute-angle joint structure" and the non-joined surfaces adjacent to the joining surfaces of the brazing sheets as "non-joined adjacent surfaces," then in such an acute-angle joint structure, a fillet is formed between the non-joined adjacent surfaces that form an acute angle with each other. In this specification, this fillet is defined as solidified brazing material or sacrificial anode material that flowed out from the joining surface during joining.

[0012] In the brazing sheet disclosed in Patent Document 2, copper segregates on the fillet surface after brazing. The segregated copper functions as a cathode in the corrosion reaction, but the sacrificial layer surrounding the segregated copper on the fillet surface becomes nobler. As a result, the potential difference between the sacrificial layer and the core material decreases, reducing the function of the sacrificial layer (preferential corrosion). Depending on the circumstances, there is a risk of premature penetration due to intergranular corrosion of the core material.

[0013] The present invention was made to solve these problems, and aims to effectively suppress or prevent preferential corrosion of fillets, even when fillets formed adjacent to the joints between brazing sheets contain copper and zinc, thereby improving the corrosion resistance of the heat exchanger. [Means for solving the problem]

[0014] The brazing sheet according to this disclosure, in order to solve the above problems, is used in a heat exchanger and comprises a core made of an aluminum alloy, a brazing layer made of a silicon (Si)-containing aluminum alloy brazing material, and an intermediate sacrificial layer made of an aluminum alloy sacrificial anode material containing zinc (Zn) in the range of 0.5 to 6.0 mass% and silicon (Si) in the range of 3.0 to 11 mass%, wherein the brazing layer is located on the outside when viewed from both sides of the core, and the intermediate sacrificial layer is laminated on at least one side of the core, neither the brazing material nor the sacrificial anode material contains copper (Cu), the core contains copper (Cu) in the range of 0.3 to 1.2 mass%, and the thickness of the intermediate sacrificial layer is 50 μm or less.

[0015] Furthermore, the brazing sheet joining structure according to this disclosure is constructed using the brazing sheet having the above configuration, and the brazing sheet has joining surfaces that form a joint when joined to each other, and non-joined adjacent surfaces adjacent to the joining surfaces, and when the joining surfaces are joined to each other, a fillet is formed in the area between each of the non-joined adjacent surfaces that is adjacent to the joining surface, where the brazing material has flowed out from the joining surface and solidified.

[0016] Furthermore, the heat exchanger according to this disclosure has a brazing sheet joining structure as described above.

[0017] According to the above configuration, in a brazing sheet having a brazing material layer on its outer surface, an intermediate sacrificial layer made of a sacrificial anode material is placed between at least one brazing material layer and the core material, and the brazing material layer and the intermediate sacrificial layer do not contain copper, while the core material contains copper within a predetermined range. As a result, when the brazing material layers of the brazing sheet are joined together, copper diffuses from the core material through the intermediate sacrificial layer to the brazing material layer constituting the joint of the brazing sheet, and the copper from the core material also diffuses to the fillet formed adjacent to the joint, making it easier for copper to segregate at the fillet at the end.

[0018] Here, during bonding at high temperatures, the brazing material liquefies, but the intermediate sacrificial layer does not. Therefore, copper tends to segregate in the fillet, but zinc is present around the fillet at a suitable concentration due to the intermediate sacrificial layer. This creates a state where zinc is appropriately present around the fillet where copper segregates, enabling good sacrificial anodic action in the fillet. Furthermore, the copper does not hinder the appropriate potential reduction by zinc, thus achieving good sacrificial anodic action.

[0019] As a result, the risk of the preferential corrosion effect on the surrounding sacrificial anode material being reduced due to copper segregation, as in conventional methods, is avoided, and the risk of corrosion progressing from the fillet to the joint and causing a decrease in the joint strength can be effectively suppressed or prevented. This makes it possible to further improve the corrosion resistance of the joints of the heat exchanger. [Effects of the Invention]

[0020] In the present invention, with the above configuration, even when the fillet generated adjacent to the joint portion between the brazing sheets contains copper and zinc, the preferential corrosion of the fillet can be effectively suppressed or prevented, and the corrosion resistance of the heat exchanger can be made good, which has the effect described above.

Brief Description of the Drawings

[0021] [Figure 1] (A) is a schematic cross-sectional view showing the schematic configuration of a brazing sheet according to a representative embodiment of the present invention, and (B) is a schematic cross-sectional view showing the schematic configuration of the joint structure of the brazing sheet according to a representative embodiment of the present invention. [Figure 2] (A) to (C) are schematic cross-sectional views showing other configurations of the brazing sheet shown in FIG. 1(A). [Figure 3] (A) is a schematic cross-sectional view showing an example of a header of a plate fin type heat exchanger configured using the brazing sheet shown in FIG. 1, and (B) is an enlarged schematic partial cross-sectional view showing the joint structure of the brazing sheet included in the header shown in (A). [Figure 4] (A) is a schematic partial cross-sectional view showing an example of a parallel flow condenser (PFC) configured using the brazing sheet shown in FIG. 1, and (B) is an enlarged schematic partial cross-sectional view showing the joint structure of the brazing sheet included in the PFC shown in (A). [Figure 5] (A) is a schematic cross-sectional view showing an example of a header of a plate fin type heat exchanger configured using the brazing sheet shown in FIG. 4(B), and (B) is an enlarged schematic partial cross-sectional view showing the joint structure of the brazing sheet included in the header shown in (A). [Figure 6] It is a view showing the schematic configuration and the corrosion resistance test results of the brazing sheet according to an example, a comparative example or a reference example in the present invention. [Figure 7](A) is a graph showing the copper concentration at the joint of the brazing sheet according to Example 1, Comparative Example 1, and Reference Example shown in Figure 6, and (B) is a diagram schematically illustrating the position of the joint, which is the horizontal axis of the graph shown in (A). [Modes for carrying out the invention]

[0022] The brazing sheet according to this disclosure is a brazing sheet used in a heat exchanger and comprises an aluminum alloy core, a brazing layer made of an aluminum alloy brazing material containing silicon (Si), and an intermediate sacrificial layer made of an aluminum alloy sacrificial anode material containing zinc (Zn) in the range of 0.5 to 6.0 mass% and silicon (Si) in the range of 3.0 to 11 mass%, wherein the brazing layer is located on the outside when viewed from both sides of the core, and the intermediate sacrificial layer is laminated on at least one side of the core, neither the brazing material nor the sacrificial anode material contains copper (Cu), the core contains copper (Cu) in the range of 0.3 to 1.2 mass%, and the thickness of the intermediate sacrificial layer is 50 μm or less.

[0023] According to the above configuration, in a brazing sheet having a brazing material layer on its outer surface, an intermediate sacrificial layer made of a sacrificial anode material is placed between at least one brazing material layer and the core material, and the brazing material layer and the intermediate sacrificial layer do not contain copper, while the core material contains copper within a predetermined range. As a result, when the brazing material layers of the brazing sheet are joined together, copper diffuses from the core material through the intermediate sacrificial layer to the brazing material layer constituting the joint of the brazing sheet, and copper from the core material also diffuses to the fillet formed adjacent to the joint, and copper segregation is more likely to occur at the fillet at the end.

[0024] Here, during bonding at high temperatures, the brazing material liquefies, but the intermediate sacrificial layer does not. Therefore, copper tends to segregate in the fillet, but zinc is present around the fillet at a suitable concentration due to the intermediate sacrificial layer. This creates a state where zinc is appropriately present around the fillet where copper segregates, enabling good sacrificial anodic action in the fillet. Furthermore, the copper does not hinder the appropriate potential reduction by zinc, thus achieving good sacrificial anodic action.

[0025] As a result, the risk of the preferential corrosion effect on the surrounding sacrificial anode material being reduced due to copper segregation, as in conventional methods, is avoided, and the risk of corrosion progressing from the fillet to the joint and causing a decrease in the joint strength can be effectively suppressed or prevented. This makes it possible to further improve the corrosion resistance of the joints of the heat exchanger.

[0026] In the brazing sheet having the above configuration, the brazing layer may be laminated on one side of the core material, and the brazing layer may be laminated on the other side of the core material on top of the laminated intermediate sacrificial layer.

[0027] Furthermore, in the brazing sheet having the above configuration, the intermediate sacrificial layer may be laminated on both sides of the core material, and the brazing material layer may be laminated on these intermediate sacrificial layers.

[0028] Furthermore, the brazing sheet having the above configuration may further include a flux-containing layer containing a brazing flux material, or a magnesium-containing layer configured as a layer independent of the brazing material layer, wherein at least magnesium (Mg) is added to the brazing material, and the flux-containing layer or the magnesium-containing layer may be located on the outside when viewed from the intermediate sacrificial layer.

[0029] Furthermore, in the brazing sheet having the above configuration, the flux-containing layer or the magnesium-containing layer may be adjacent to the brazing material layer.

[0030] Furthermore, in the brazing sheet having the above configuration, the core material may be an aluminum alloy of the 3000 series, 5000 series, or 6000 series to which copper has been added within the above range, and the intermediate sacrificial layer may be an aluminum alloy of the 1000 series or 3000 series to which zinc has been added within the above range.

[0031] Furthermore, in the brazing sheet having the above configuration, the brazing material layer may be made of a 4000 series aluminum alloy.

[0032] Furthermore, the brazing sheet joining structure according to this disclosure is configured using the brazing sheet having the above configuration, wherein the brazing sheet has joining surfaces that form a joint when joined together, and non-joined adjacent surfaces adjacent to the joining surfaces, and when the joining surfaces are joined together, a fillet is formed between each of the non-joined adjacent surfaces, in the portion adjacent to the joining surface, where the brazing material has flowed out from the joining surface and solidified.

[0033] In the brazing sheet joining structure described above, the angle formed by each of the non-joined adjacent surfaces may be an acute angle.

[0034] Furthermore, the heat exchanger according to this disclosure may have any configuration having a brazing sheet joining structure as described above. The heat exchanger with the above configuration may be a plate fin stacked heat exchanger or a parallel flow condenser (PFC).

[0035] Hereinafter, typical embodiments of the present invention will be described with reference to the drawings. In the following, the same or corresponding elements will be denoted by the same reference numerals throughout all the drawings, and redundant explanations will be omitted.

[0036] [Brazing sheet] The brazing sheet according to this disclosure is made of an aluminum alloy used in heat exchangers. Specifically, for example, as shown in Figure 1(A), the brazing sheet 10A according to this disclosure comprises a core material 11, a brazing layer 12 and a brazing layer 13, and an intermediate sacrificial layer 14. In Figure 1(A), the brazing layers 12 and 13 are formed to be located on the outer surfaces of both sides of the brazing sheet 10A, with the brazing layer 12 located on the lower surface (first surface) of Figure 1(A) and the brazing layer 13 located on the upper surface (second surface) of Figure 1(A).

[0037] In Figure 1(A), the brazing alloy layer 12 is clad on one side (first side) of the core material 11. An intermediate sacrificial layer 14 is laminated on the other side (second side) of the core material 11, and the brazing alloy layer 13 is clad on the outside of this intermediate sacrificial layer 14. Therefore, the intermediate sacrificial layer 14 is positioned between the core material 11 and the brazing alloy layer 13. The core material 11, the brazing alloy constituting the brazing alloy layers 12 and 13, and the sacrificial anode material constituting the intermediate sacrificial layer 14 are all aluminum alloys.

[0038] In the brazing sheet 10A according to this disclosure, an intermediate sacrificial layer 14 and a brazing material layer 13 are laminated on the side of the core material 11 that will be the joining surface. By joining these joining surfaces together, a joint is formed in which the brazing sheets 10A are joined together. The structure in which the brazing sheets 10A are joined at their joining surfaces is the joining structure of the brazing sheet 10A according to this disclosure. The brazing sheet 10A according to this disclosure has non-joining adjacent surfaces adjacent to the joining surfaces. When the brazing sheets 10A are joined together to form a joining structure, the angles formed by each non-joining adjacent surface are acute angles.

[0039] Specifically, as shown in Figure 1(B), for example, the brazing sheet 10A joining structure 20 according to this disclosure is constructed by joining the joining surfaces 11a of the brazing sheet 10A together. The angle θ1 formed between the non-joined adjacent surfaces 11b adjacent to the joining surface 11a is not particularly limited, but a preferred example is an acute angle, i.e., less than 90° (θ1 < 90°). For the sake of explanation, the angle θ1 formed by each non-joined adjacent surface 11b constituting the joining structure 20 will be referred to as the "adjacent surface formation angle" and is shown as a dotted line in Figure 1(B).

[0040] As mentioned above, the preferred range for the adjacent surface forming angle θ1 is not particularly limited as long as it is an acute angle, i.e., less than a right angle (less than 90°). However, depending on various conditions such as the type of heat exchanger and the structure of the heat exchanger in which the brazing sheet 10A is used, it may be, for example, within the range of 40° to 80° (40°≦θ1≦80°), or within the range of 50° to 70° (50°≦θ1≦70°). Alternatively, for example, only the lower limit may be 15° or more (15°≦θ1), or 20° or more (20°≦θ1).

[0041] In the joining structure 20 according to this disclosure, when brazing sheets 10A are joined together to form a joint 21, a fillet 22 is formed between adjacent non-joined surfaces 11b, as shown in Figure 1(B). Heat exchangers include members or structures in which such a fillet 22 is formed, and in such members or structures, the adjacent non-joined surfaces 11b often form an acute angle. In this embodiment, this fillet 22 is defined as solidified brazing material that flowed out from the joining surface 11a during joining.

[0042] This disclosure provides an effective way to suppress or avoid preferential corrosion of the fillet 22 in a heat exchanger using a brazing sheet 10A. If the adjacent surface formation angle θ1 becomes too large, for example, when it approaches 180°, i.e., horizontal, it becomes structurally difficult for the fillet 22 to form. Also, if the adjacent surface formation angle θ1 is too small, depending on the structure of the heat exchanger, the non-joined adjacent surfaces 11b become closer to parallel, making it difficult for the fillet 22 to form. Therefore, a suitable example of the adjacent surface formation angle θ1 is an angle within the range of the upper and lower limits mentioned above, or an angle greater than the lower limit.

[0043] In the brazing sheet 10A according to this disclosure, a non-joining adjacent surface 11b is set adjacent to the joining surface 11a. As described above, when the brazing sheets 10A are joined together, the angle (adjacent surface formation angle θ1) that the non-joining adjacent surface 11b forms with each other is, for example, an acute angle. Therefore, for example, as shown in Figure 1(B), the non-joining adjacent surface 11b may be inclined with respect to the joining surface 11a.

[0044] In the example shown in Figure 1(B), the non-joined adjacent surface 11b is inclined to form an angle θ2 with respect to the joined surface 11a. Therefore, when the joined surfaces 11a are joined together to form the joint 21, the non-joined adjacent surfaces 11b adjacent to each joined surface 11a form an acute adjacent surface formation angle θ1. For the sake of explanation, the inclination angle θ2 of the non-joined adjacent surface 11b with respect to the joined surface 11a will be referred to as the "adjacent surface inclination angle," and in Figure 1(B), it is shown as a dotted line along with the extension of the joined surface 11a.

[0045] The specific angle of the adjacent surface inclination angle θ2 is not particularly limited, but for example, as shown in Figure 1(B), if the shapes of the brazing sheets 10A that are joined together are symmetrical with respect to the joining surface 11a, then the adjacent surface formation angle θ1 will be twice the adjacent surface inclination angle θ2 (θ1 = θ2 × 2). Therefore, if the adjacent surface formation angle θ1 is acute, the adjacent surface inclination angle θ2 only needs to be less than 45°. However, the shape of the brazing sheets 10A does not need to be symmetrical, and depending on various conditions such as the type of heat exchanger or the structure of the heat exchanger, brazing sheets 10A of various shapes will be joined together at the joining surface 11a. Also, the adjacent surface formation angle θ1 does not necessarily need to be acute. Therefore, the adjacent surface inclination angle θ2 is not limited to less than 45°.

[0046] For example, there may be a joining structure 20 in which a brazing sheet 10A of a different shape is joined to the joining surface 11a of a substantially flat brazing sheet 10A at an angle. In this case, the non-joined adjacent surface 11b of the substantially flat brazing sheet 10A is not inclined with respect to the joining surface 11a, and is set as a different region on the brazing material layer 13. Therefore, the adjacent surface inclination angle θ2 may be 0° (θ2=0°). That is, the non-joined adjacent surface 11b may not be inclined with respect to the joining surface 11a and may be a different region of a continuous flat surface (see the joining structure of the parallel flow capacitor described later).

[0047] In the brazing sheet 10A joint structure 20 according to this disclosure, corrosion may progress in the directions shown by block arrows C1 and C2 in Figure 1(B). The direction of block arrow C1 is the corrosion direction progressing from the non-joint adjacent surface 11b (and non-joint surfaces not adjacent to the joint surface 11a (such as the surface opposite to the joint surface 11a)) toward the core material 11, and the direction of block arrow C2 is the corrosion direction progressing along the direction of the joint surface 11a in the joint portion 21 including the fillet 22.

[0048] Of these, corrosion progressing in corrosion direction C1 is suppressed (avoided or prevented) by the sacrificial anode action of the intermediate sacrificial layer 14 located on the inside (core material 11 side) when viewed from the brazing material layer 13 that constitutes the joint surface 11a. However, corrosion progressing in corrosion direction C2 may progress because zinc is concentrated in the fillet 22, causing the potential of the joint portion 21 including the fillet 22 to become too negative. In the brazing sheet 10A according to this disclosure, by including copper in the core material 11 within a predetermined range, and substantially excluding copper from the brazing material layers 12, 13 and the intermediate sacrificial layer 14, corrosion in corrosion direction C2 can be effectively suppressed (avoided or prevented).

[0049] The brazing sheet 10A according to this disclosure comprises a core material 11, brazing layers 12, 13 and an intermediate sacrificial layer 14, and the intermediate sacrificial layer 14 and the brazing layer 13 are located on the joint surface 11a side of the core material 11. It is not limited to the four-layer structure shown in Figure 1(A). For example, it may have a laminated structure of five or more layers, such as the brazing sheets 10B to 10D shown in Figures 2(A) to (C).

[0050] For example, the brazing sheet 10B shown in Figure 2(A) is similar to the brazing sheet 10A shown in Figure 1(A) in that a brazing layer 12a is laminated on one side (second side) of the core material 11, an intermediate sacrificial layer 14 is laminated on the other side (second side) of the core material 11, and a brazing layer 13 is located on the outside (second side) of the intermediate sacrificial layer 14, but it differs in that it also has a flux-containing layer 15.

[0051] More specifically, in the brazing sheet 10B, the second surface of the core material 11 is laminated (covered) with an intermediate sacrificial layer 14, a flux-containing layer 15, and a brazing material layer 13, while the first surface of the core material 11 is laminated (covered) with a brazing material layer 12a, a flux-containing layer 15, and a brazing material layer 12b. Therefore, the brazing sheet 10B shown in Figure 2(A) has a seven-layer laminated structure.

[0052] The flux-containing layer 15 may be any layer containing a known brazing flux material, as described later, and may be laminated adjacent to the brazing material layers 12 and 13. In the brazing sheet 10B shown in Figure 2(A), the second side has a two-layer laminated structure of brazing material layer 13 and flux-containing layer 15 from the outside, and the first side has a three-layer structure of brazing material layer 12b, flux-containing layer 15 and brazing material layer 12a from the outside, but the laminated structure of brazing material layers 12 and 13 including the flux-containing layer 15 is not limited to this. For example, the second side of the brazing sheet 10B may have a three-layer structure, or the first side may have a two-layer structure, or both the first and second sides may have a two- or three-layer structure, or the laminated structure of brazing material layers 12 and 13 and flux-containing layer 15 may have four or more layers.

[0053] Alternatively, the brazing sheet 10C shown in Figure 2(B) is similar to the brazing sheet 10A shown in Figure 1(A) in that it does not have a flux-containing layer 15, but has a core material 11, brazing layers 12, 13 and an intermediate sacrificial layer 14, but differs in that the intermediate sacrificial layer 14 is laminated not only on the second side of the core material 11 but also on the first side.

[0054] More specifically, in the brazing sheet 10C, the second surface of the core material 11 is laminated (covered) with an intermediate sacrificial layer 14 and a brazing layer 13, and the first surface of the core material 11 is also laminated (covered) with an intermediate sacrificial layer 14 and a brazing layer 12. Therefore, the brazing sheet 10C shown in Figure 2(B) has a five-layer laminated structure.

[0055] In other words, in the brazing sheet 10A shown in Figure 1(A), the intermediate sacrificial layer 14 is laminated on the second surface side of the core material 11, so the second surface can be said to be the bonding surface 11a. However, in the brazing sheet 10C shown in Figure 2(B), the intermediate sacrificial layer 14 is laminated on both sides of the core material 11, so both the first and second surfaces can be said to be the bonding surface 11a.

[0056] Alternatively, the brazing sheet 10D shown in Figure 2(C) is similar to the brazing sheet 10A shown in Figure 1(A) in that a brazing layer 12 is laminated on one side (second side) of the core material 11, an intermediate sacrificial layer 14 is laminated on the other side (second side) of the core material 11, and a brazing layer 13 is laminated on the outside (second side) of the intermediate sacrificial layer 14. However, it differs in that a magnesium-containing layer 16 is laminated on the outside of the brazing layers 12 and 13.

[0057] As described later, the magnesium-containing layer 16 is a "brazing material layer" in which at least magnesium (Mg) is added to the brazing material (preferably with bismuth (Bi) or the like added in addition to Mg). By providing such a magnesium-containing layer 16, it becomes possible to join the brazing sheets 10D together without using flux (so-called flux-free or flux-less).

[0058] Although not shown in the diagram, the laminated structures of the brazing sheets 10A to 10D shown in Figure 1(A) or Figures 2(A) to (C) can be combined as appropriate, and the order of lamination can also be changed. For example, the flux-containing layer 15 or magnesium-containing layer 16 may be located on the first or second surface of the five-layer brazing sheet 10C shown in Figure 2(B). Alternatively, in the brazing sheet 10B shown in Figure 2(A), the flux-containing layer 15 is located inside when viewed from the outermost brazing layer 13 or brazing layer 12b, but the flux-containing layer 15 may also be located on the outside.

[0059] Therefore, in the brazing sheets 10A to 10D according to this disclosure, the brazing layers 12 and 13 do not necessarily have to be the outermost layers (surface layers). The brazing layers 12 and 13 only need to be located on the outside when viewed from both sides of the core material 11. The intermediate sacrificial layer 14 only needs to be laminated on at least one of the two sides of the core material 11. The intermediate sacrificial layer 14 and the brazing layer 13 (or brazing layer 12) may be in direct contact, or other layers such as a flux-containing layer 15 may be interposed between them.

[0060] Furthermore, the flux-containing layer 15 or magnesium-containing layer 16 only needs to be located on the outside when viewed from the intermediate sacrificial layer 14. A typical example is that it needs to be located adjacent to the brazing material layers 12 and 13, as shown in Figure 2(A) or Figure 2(C). However, the flux-containing layer 15 or magnesium-containing layer 16 does not necessarily need to be in direct contact with the brazing material layers 12 and 13.

[0061] [Materials for brazing sheets] As described above, the brazing sheet 10A relating to this disclosure is made of an aluminum alloy, and the core material 11, brazing material, and sacrificial anode material are all made of an aluminum alloy. Specifically, the core material 11 may be any known aluminum alloy that can achieve the physical properties required depending on various conditions such as the type or structure of the heat exchanger, but in this disclosure, copper (Cu) is added (contained) in the range of 0.3 to 1.2 mass%.

[0062] Examples of aluminum alloys used as the core material 11 include, but are not limited to, the 3000 series (aluminum-manganese (Al-Mn) alloy), the 5000 series (aluminum-magnesium (Al-Mg) alloy), or the 6000 series (aluminum-magnesium-silicon (Al-Mg-Si) alloy) in the field of heat exchangers.

[0063] If we consider the aluminum alloy before the addition of Cu as the "base material" for convenience, then the base material may contain Cu as an unavoidable impurity. Even if Cu is present as an unavoidable impurity, its concentration only needs to be, for example, 0.2 mass% or less. However, aluminum alloys that already contain Cu at a concentration exceeding 1.2 mass%, such as 2000 series alloys, cannot be used as the base material for the core material 11.

[0064] In the brazing sheet 10A relating to this disclosure, if the Cu content (concentration) in the core material 11 is less than 0.3 mass%, there is a risk that Cu will not diffuse from the core material 11 to the fillet 22 at a sufficient concentration, as will be described later. Furthermore, if the Cu content in the core material 11 exceeds 1.2 mass%, depending on the strength of the sacrificial anodic effect of the sacrificial anode material, the susceptibility of the core material 11 to intergranular corrosion may increase, potentially making it impossible to effectively suppress the progression of corrosion.

[0065] The Cu content in the core material 11 can be within the range of 0.3 to 1.2 mass%, but a preferred example is a range of 0.3 to 0.7 mass%. That is, the upper limit of the Cu content can be 1.2 mass% or less, but depending on the conditions, it may be 0.7 mass% or less. If the Cu content is 0.7 mass% or less, even if the sacrificial anodic action of the sacrificial anode material is relatively weak, the risk of increased intergranular corrosion susceptibility of the core material 11 can be effectively suppressed.

[0066] In this disclosure, the aluminum alloy used as brazing material may contain silicon (Si), i.e., any aluminum-silicon (Al-Si) alloy. The Si content (concentration) in the brazing material is not particularly limited and should be within a range suitable for use as brazing material. Specifically, for example, the Si content in the brazing material can be in the range of 2.5 to 13 mass%, or it may be in the range of 3.5 to 12 mass%. If the Si content is too low, the Al-Si alloy may not function adequately as brazing material. On the other hand, if the Si content is too high, Si may diffuse into the core material 11 or the mating material, potentially causing melting of the brazing sheet 10A itself.

[0067] Al-Si alloys used as brazing materials may contain elements other than Si, as long as they do not affect their function as brazing materials. Furthermore, Al-Si alloys used as brazing materials may contain various elements as unavoidable impurities. However, Al-Si alloys used as brazing materials should not contain substantially any copper (Cu). "Substantially no Cu" means that Cu is not present in concentrations exceeding those of unavoidable impurities. The upper limit of the permissible concentration of unavoidable impurities varies depending on various conditions, but generally, it can be said to be less than 0.1 mass% of the entire Al-Si alloy.

[0068] Aluminum alloys used as sacrificial anode materials contain zinc (Zn) in the range of 0.5 to 6.0 mass% in order to exhibit sacrificial anode action. In other words, Al-Zn alloys can be cited as a typical example of the intermediate sacrificial layer 14. If the Zn content (concentration) in the sacrificial anode material is less than 0.5 mass%, it will not exhibit good sacrificial anode action. On the other hand, if the Zn content exceeds 6.0 mass%, the sacrificial anode action will proceed too quickly, causing the intermediate sacrificial layer 14 to disappear from the brazing sheet 10A, which may reduce the corrosion resistance of the brazing sheet 10A.

[0069] Furthermore, Al-Zn alloys used as sacrificial anode materials may contain elements other than Zn, as long as they do not affect the sacrificial anode action. Also, Al-Zn alloys used as sacrificial anode materials may contain various elements as unavoidable impurities. However, even in Al-Zn alloys used as sacrificial anode materials, substantially no Cu is contained. Substantially no Cu is contained means that, similar to Al-Si alloys used as brazing materials, Cu is not contained at a concentration exceeding that of unavoidable impurities, and generally, a concentration of less than 0.1 mass% in the entire Al-Zn alloy is sufficient. Alternatively, the upper limit of the concentration of unavoidable impurities may conform to the alloy composition specified in known standards such as JIS.

[0070] The type of aluminum alloy used as brazing material is not particularly limited, but typically, 4000 series (aluminum-silicon (Al-Si) alloy) can be used. Similarly, the type of aluminum alloy used as sacrificial anode material is not particularly limited, but typically, 1000 series (industrial pure aluminum) or 3000 series (aluminum-manganese (Al-Mn) alloy) can be used. For sacrificial anode material, a 1000 series or 3000 series aluminum alloy to which Zn has been added by known methods so that its content is within the range of 0.5 to 6.0 mass% may be used.

[0071] The brazing flux material can preferably be any flux material known in the field of brazing aluminum or its alloys (a material that removes oxide films from aluminum-based materials). Examples of the main components of the flux material include fluorides of metal elements in Group 1 or 2 of the periodic table, such as CsF, CaF2, NaF, LiF, and KF, but are not particularly limited. The flux-containing layer 15 only needs to be a layer containing such a brazing flux material, and in this embodiment, a layer can be made by mixing aluminum or its alloy powder with the brazing flux material.

[0072] Furthermore, the method for forming such a flux-containing layer 15 containing brazing flux material can also suitably utilize known methods and is not particularly limited. A typical example is Reference 1: TRILLIUM (R) ACTIVE BRAZING, Granges AB. <https: / / www.granges.com / globalassets / 09.-kampanjer / 01.-trillium / 05.-learn-more / granges _trillium_brochure_180124. pdf> The methods described in (searched November 5, 2020) can be cited.

[0073] For the magnesium-containing layer 16, which is a flux-free or fluxless brazing material, materials known in the field of aluminum or its alloys can be suitably used. Specifically, for example, examples include brazing materials containing 0.1 to 6% by mass of magnesium, as described in Reference 2: Japanese Patent Publication No. 3701847 (Japanese Patent Publication No. 2002-18570), or brazing materials containing 0.1 to 6% by mass of magnesium and 0.01 to 1% by mass of bismuth.

[0074] Furthermore, the contents of Reference 1, which describes typical configurations of brazing flux material and flux-containing layer 15, or Reference 2, which describes typical configurations of flux-free magnesium-containing brazing material and magnesium-containing layer 16, shall be incorporated into this specification by reference thereto.

[0075] [Copper diffusion associated with the joining of brazing sheets] In this disclosure, multiple brazing sheets 10A to 10D are joined together by overlapping their joining surfaces 11a and melting the brazing material and sacrificial anode material at a high temperature (e.g., 580°C or higher). For example, as shown in Figure 1(B), in the joining structure 20 of brazing sheet 10A, a fillet 22 is formed in the area adjacent to the joining surface 11a (joint portion 21) between the non-joining adjacent surfaces 11b by solidifying the sacrificial anode material that has flowed out from the brazing material layer 13 constituting the joining surface 11a.

[0076] When brazing sheets 10A (or brazing sheets 10B to 10D) are joined together, Zn diffuses from the intermediate sacrificial layer 14 located beneath the brazing material layer 13 that constitutes the joint surface 11a to the brazing material layer 13. Furthermore, Cu diffuses from the core material 11 to the brazing material layer 13 via the intermediate sacrificial layer 14. Therefore, the fillet 22 contains Zn originating from the intermediate sacrificial layer 14 and Cu originating from the core material 11.

[0077] The Cu concentration in the fillet 22 (joint 21) is higher than that of the core material 11 and the brazing layer 13 (and the intermediate sacrificial layer 14), and the Cu concentration distribution is such that it is substantially localized in the fillet 22. From the results of the examples and comparative examples described later, when the Cu concentration in the core material 11 is within a predetermined range, and the brazing layer 13 and the intermediate sacrificial layer 14 substantially do not contain Cu, the Cu of the core material 11 exhibits behavior in which it diffuses into the liquid phase of the joint 21 and the fillet 22 during bonding at high temperatures.

[0078] Since the liquid phase can contain a larger amount of Cu than the solid phase, when the liquid phase solidifies, the Cu is more likely to segregate at the fillet 22 at the end, which is the final solidification point. As a result, the fillet 22 has a higher potential than its surroundings, preventing penetration due to preferential corrosion of the joint 21. Here, the brazing sheet 10A is equipped with an intermediate sacrificial layer 14, which does not liquefy during bonding at high temperatures. Therefore, Zn can be present around the fillet 22 at a suitable concentration. This allows for even better resistance to corrosion around the fillet 22.

[0079] In the brazing sheet 10A bonding structure 20 according to this disclosure, the Cu concentration and Zn concentration in the fillet 22 are not particularly limited, however the Cu concentration should be 2.0 mass% or less, and the Zn concentration should be less than the Cu concentration. If the Cu concentration in the fillet 22 exceeds 2.0 mass%, aging precipitation of the intermediate compound phase containing Cu will occur in a shorter period compared to the lifespan of the heat exchanger. Since such precipitates function as cathodes in corrosion reactions, the corrosion current density in the fillet 22 increases, and the corrosion resistance around the fillet 22 may deteriorate significantly.

[0080] The inventors' experimental verification revealed a proportional relationship between the Cu concentration of the core material 11 (initial Cu concentration) and the Cu concentration of the joint portion 21 (fillet 22) in the joint structure 20. Therefore, if the Cu concentration of the core material 11 is 1.2 mass% or less, the Cu concentration of the fillet 22 is considered to be 2.0 mass% or less. On the other hand, the Cu concentration of the core material 11 only needs to be 0.3 mass% or more, in which case the Cu concentration of the fillet 22 in the joint structure 20 is considered to be 0.5 mass% or more. For this reason, the lower limit of the Cu concentration of the fillet 22 in the joint structure 20 should be equal to or greater than the Zn concentration, but preferably 0.5 mass% or more.

[0081] As mentioned above, in the conventional brazing sheet disclosed in Patent Document 2, the core material contains Cu in the range of 0.05 to 1.2 mass%, but in this brazing sheet, the brazing material also contains Cu in the range of 0.1 to 0.6 mass%. When the brazing material contains Cu in this way, the area around the fillet or the sacrificial anode layer becomes nobler, reducing the potential difference with the core material, thus decreasing the sacrificial corrosion protection performance (preferential corrosion action). Furthermore, since the conventional brazing sheet disclosed in Patent Document 2 does not have an intermediate sacrificial layer, the presence of Zn at a suitable concentration due to an intermediate sacrificial layer cannot be expected around the Cu segregated in the fillet.

[0082] In this disclosure, if the brazing sheet 10A has a bent portion, for example (see Figure 1(B), etc.), the dislocation density increases in that portion, so the diffusion of Cu is considered to be promoted (the diffusion coefficient becomes larger) compared to the surrounding area. In this disclosure, since the brazing sheets 10A to 10D have an intermediate sacrificial layer 14, when bonding at high temperatures, Cu diffuses from the core material 11 to the liquid phase via the solid intermediate sacrificial layer 14. If there are processed portions such as bends in the brazing sheets 10A to 10D, it is considered that the amount of Cu diffusion in the processed portion will be greatly affected compared to when the core material 11 and the liquid phase are in direct contact (see the comparison between Example 1 and the Reference Example described later).

[0083] Furthermore, Cu remains in the core material 11 in areas other than the joint 21. The core material 11 is nourished by containing Cu within a predetermined range, thereby increasing the potential difference with the intermediate sacrificial layer 14. This allows the sacrificial anode effect of the intermediate sacrificial layer 14 to be more effectively expressed. Additionally, adding Cu to the core material 11 improves its strength. This is advantageous for thinning the brazing sheet 10A and improving the pressure resistance of the heat exchanger.

[0084] Furthermore, as a method to suppress or avoid preferential corrosion of the joint without including Cu in the joint, it is conceivable to isolate it from the surroundings by painting or partially removing the brazing layer and intermediate sacrificial layer. However, such methods require additional steps of painting or partial removal of each layer, which leads to increased manufacturing costs, increased complexity or complication of the overall manufacturing process, and problems such as peeling and scattering of the paint film in the case of painting. In contrast, in this disclosure, the Cu concentration of the fillet 22 can be optimized simply by including Cu in the core material 11 and joining them, thus eliminating the need for additional steps and enabling easy manufacturing.

[0085] In this disclosure, the specific thickness of the brazing sheets 10A to 10D is not particularly limited, nor is the thickness of each layer constituting the brazing sheets 10A to 10D particularly limited. However, from the viewpoint of effectively suppressing or preventing preferential corrosion of the fillet 22, it is preferable to define an upper limit on the thickness of the intermediate sacrificial layer 14.

[0086] As is clear from the results of the examples described later (Comparative Examples 1 and 2, Examples 1 and 2, and Reference Examples), in the brazing sheets 10A to 10D according to this disclosure, if the core material 11 contains Cu in the range of 0.3 to 1.2 mass%, and the brazing material and sacrificial anode material do not contain Cu, then the provision of an intermediate sacrificial layer 14 can effectively suppress or prevent preferential corrosion of the fillet 22 (Examples 1 and 2 described later).

[0087] Here, even with a brazing sheet that does not necessarily have an intermediate sacrificial layer 14 (brazing sheet 10E in the reference example described later), the brazing material layer 13 also serves as the sacrificial anode material, thereby suppressing or preventing preferential corrosion of the fillet 22 in the joint structure 20 (reference example described later). However, by having an intermediate sacrificial layer 14 that does not liquefy during joining, when Cu is segregated to a high concentration in the fillet 22, Zn can be present around it at a suitable concentration. As a result, preferential corrosion of the fillet 22 can be effectively suppressed or prevented.

[0088] The brazing sheets 10A to 10D are equipped with an intermediate sacrificial layer 14, which allows the brazing material layer 13 (or brazing material layer 12), which is the surface layer of the brazing sheets 10A to 10D, to suppress the volatilization of Zn from the intermediate sacrificial layer 14 in the furnace. Furthermore, although the brazing material layer 13 (and brazing material layer 12) flows in the furnace, the intermediate sacrificial layer 14 itself, which is located inside the brazing material layer 13, does not flow. Therefore, the intermediate sacrificial layer 14 can function stably as a sacrificial anode material.

[0089] However, if the thickness of the intermediate sacrificial layer 14 is too large (too thick), the Cu diffusing from the core material 11 will have difficulty reaching the brazing layer 13 (or brazing layer 12). In this case, Cu will have difficulty diffusing into the liquid phase of the joint 21 and fillet 22, making it difficult to achieve the preferential corrosion prevention effect of the fillet 22 (Comparative Example 1 described later). On the other hand, if the thickness of the intermediate sacrificial layer 14 is too small (too thin), it may not be able to fully realize its function as a sacrificial anode material.

[0090] Furthermore, if the Cu concentration in the core material 11 is too low (too thin), Cu may not diffuse well to the brazing layer 13 via the intermediate sacrificial layer 14, potentially making it impossible to achieve preferential corrosion prevention of the fillet 22 (see Comparative Example 2 described later). On the other hand, if the Cu concentration in the core material 11 is too high (too concentrated), the presence of Cu ions may reduce corrosion resistance.

[0091] Therefore, by setting the Cu concentration in the core material 11 within the range of 0.3 to 1.2 mass%, as described above, and setting the upper limit of the thickness of the intermediate sacrificial layer 14 to 50 μm or less, it is possible to effectively suppress or prevent the risk of corrosion progressing from the fillet 22 to the joint 21, which could lead to a decrease in the joint strength of the joint 21.

[0092] The upper limit of the thickness of the intermediate sacrificial layer 14 is expected to be set based on a mathematical model. Specifically, for example, the diffusion of Cu from the core material 11 to the brazing layer 13 can be calculated using a solute concentration formula based on Fick's second law, and the thickness of the intermediate sacrificial layer 14 can be set based on this calculation result. However, as a result of our diligent research, it has become clear that it is difficult to calculate the thickness of the intermediate sacrificial layer 14 using a simple mathematical model.

[0093] When brazing sheets 10A to 10D are joined, the brazing material layer 13 melts and liquefies. Although the concentration of Cu diffused from the core material 11 remains almost constant in the liquid phase of the brazing material, once the brazing material solidifies, Cu tends to segregate on the surface of the solid phase brazing material (fillet 22, etc.). In such situations, predictions based on simple mathematical models become difficult. Therefore, in this disclosure, based on the specific lamination structure and joining conditions of the brazing sheets 10A to 10D, the diffusion coefficient D in the solute concentration equation based on Fick's second law is adjusted. Furthermore, when Cu diffuses into the brazing material layer 13, the Cu concentration at the boundary between the intermediate sacrificial layer 14 and the brazing material layer 13 is considered. This Cu concentration at the boundary is used in the solute concentration equation, and simulations are performed based on experimental results described later, thereby setting the upper limit of the thickness of the intermediate sacrificial layer 14 to 50 μm.

[0094] The lower limit of the thickness of the intermediate sacrificial layer 14 is not particularly limited; it should be thick enough to function as a sacrificial anode material between the brazing layer 13 and the core material 11. For example, 0.05 μm can be cited as the lower limit for which a sacrificial anode material using Zn can exhibit good corrosion resistance, but depending on the specific lamination structure of the brazing sheets 10A to 10D or the bonding conditions of the brazing sheets 10A to 10D, it may be less than 0.05 μm.

[0095] In the brazing sheets 10A to 10D relating to this disclosure, the cladding ratio of the brazing material and sacrificial anode material is not particularly limited and can be given within a general range. A general cladding ratio can be given, for example, in the range of 2 to 30 mass%, or it may be in the range of 3 to 20 mass%. Furthermore, the thickness of the brazing sheets 10A to 10D, as well as the respective thicknesses of the core material 11 and the brazing material layers 12 and 13 (excluding the thickness of the intermediate sacrificial layer 14), are not particularly limited and can be set appropriately depending on the configuration of the brazing sheet 10A or the type or components of the heat exchanger to be manufactured.

[0096] Furthermore, the method for evaluating the potential of the joint 21 including the fillet 22, the brazing layer 13, or the intermediate sacrificial layer 14 is not particularly limited, and known methods can be suitably used. Typically, a potentiostat / galvanostat can be used to measure the potential of a sample for potential measurement (for example, a brazing sheet 10A, or a core material 11, brazing layer 13, intermediate sacrificial layer 14, fillet 22 or joint 21, or an alloy with a composition simulating these), a counter electrode, and a reference electrode (for example, a silver / silver chloride (Ag / AgCl) electrode), and the sample is immersed in an electrolyte (for example, a 5% by weight sodium chloride (NaCl) solution) to measure the potential difference between the sample and the reference electrode.

[0097] The method for manufacturing the brazing sheet 10A according to this disclosure is not particularly limited, and known manufacturing methods can be suitably used. Specifically, for example, an aluminum alloy containing Cu in the range of 0.3 to 1.2 mass% is formed into a plate by a known method to form a core material 11, an intermediate sacrificial layer 14 is formed by cladding an aluminum alloy sacrificial anode material containing Zn to one side of the core material 11 by a known method, a brazing material layer 13 and a brazing material layer 12 are formed by cladding an aluminum alloy brazing material containing Si to the upper surface of the intermediate sacrificial layer 14 by a known method, and cladding an aluminum alloy brazing material to the other side of the core material 11 by a known method. In this disclosure, the conditions for manufacturing the brazing sheet 10A can be appropriately set according to the configuration of the brazing sheet 10A or the type or components of the heat exchanger to be manufactured.

[0098] [Brazing sheet bonding structure and heat exchanger] As described above, the brazing sheet 10A according to this disclosure can be used particularly suitably in the manufacture of heat exchangers. The joint structure 20 formed when the brazing sheet 10A according to this disclosure is applied to a heat exchanger is, as described above, a structure as illustrated in Figure 1(B), but more specifically, examples include a plate fin stacked heat exchanger having a structure as shown in Figures 3(A) and (B), a parallel flow condenser (PFC) having a structure as shown in Figures 4(A) and (B), or a stacked heat exchanger for an air-to-water heat pump having a structure as shown in Figures 5(A) and (B).

[0099] A plate-fin stacked heat exchanger, although not shown in the diagram, is a plate-fin stack having channels through which a first fluid, a refrigerant, flows, and heat exchange is performed between the first and second fluids by flowing air, a second fluid, between each plate-fin stack. The plate fins of this heat exchanger include a channel region having a plurality of first fluid channels through which the first fluid flows in parallel, and a header region having a header channel that communicates with each of the first fluid channels in this channel region.

[0100] In a plate-fin stacked heat exchanger, end plates, which have substantially the same shape as the plate fins in plan view, are provided on both sides of the stacking direction of the plate-fin stack. These pair of end plates and the multiple plate fins interposed between them are joined together by brazing while stacked. Figure 3(A) shows a schematic cross-section of the header portion of this plate-fin stack 30, with multiple plate fins 32 stacked on the end plate 31 located at the top of the figure.

[0101] The end plate 31 and the plate fin 32 each have openings, and when these plates are stacked to form a plate fin stack 30, a header opening 33 is formed. In the configuration shown in Figure 3(A), the first fluid, the refrigerant, flows in from the outside of the header opening 33 in the direction indicated by the block arrow in the figure, and further flows between the plate fins 32. As described above, each plate fin 32 is provided with a first fluid passage, so the refrigerant that flows between the plate fins 32 flows through the first fluid passage. In addition, the second fluid, the air, flows through the space formed between the plate fins 32 in a direction intersecting the direction of refrigerant flow (the direction of the first fluid passage). As a result, the air is cooled by the refrigerant.

[0102] Figure 3(B) is a partially enlarged view of the plate fin laminate 30 shown in Figure 3(A), schematically illustrating an example of the joining structure 20 of the brazing sheet 10A according to the present disclosure. In the example shown in Figures 3(A) and (B), the plate fins 32 are the brazing sheet 10A according to the present disclosure (see Figure 1(A)), and the joining structure 20 according to the present disclosure is the joining portion 21 located on the header opening 33 side. In Figure 3(B), the brazing material layer 13 on the joining surface 11a side (second surface side) of the plate fin 32, which is the brazing sheet 10A, is highlighted with hatching, and the fillet 22 is also highlighted with hatching.

[0103] At the joint 21 on the header opening 33 side, the joint surfaces 11a of the plate fins 32 are joined together, and a fillet 22 is formed between the non-jointed adjacent surfaces 11b adjacent to these joint surfaces 11a. In this disclosure, the core material 11 of the plate fins 32 contains Cu in the range of 0.3 to 1.2 mass%, and the brazing layers 12, 13 and intermediate sacrificial layer 14 in the plate fins 32 do not substantially contain Cu. Therefore, the fillet 22 contains Cu at a concentration higher than that of the core material 11, brazing layers 12, 13, and intermediate sacrificial layer 14, but less than 2.0 mass%. This effectively suppresses (avoids or prevents) preferential corrosion of the joint 21, thereby improving the corrosion resistance life of the plate fin stacked heat exchanger.

[0104] Specific examples of such plate-fin stacked heat exchangers are described, for example, in Japanese Patent Publication No. 2017-180856, Japanese Patent Publication No. 2018-066531, Japanese Patent Publication No. 2018-066532, Japanese Patent Publication No. 2018-066533, Japanese Patent Publication No. 2018-066534, Japanese Patent Publication No. 2018-066535, Japanese Patent Publication No. 2018-066536, etc., and the contents of these published publications are referred to herein and thus constitute part of the description herein.

[0105] In the joint structure 20 shown in Figure 3(B), the plate fin 32, which is the brazing sheet 10A, has a configuration with two stages of bending. That is, the non-joint adjacent surface 11b is inclined with respect to the joint surface 11a on the right side of the figure so as to form an acute adjacent surface inclination angle θ2, and furthermore, to the left of the non-joint adjacent surface 11b, there is a non-joint surface parallel to the joint surface 11a. However, the specific shape of the brazing sheet 10A is not limited to a shape with such two stages of bending, and may be a flat shape without bending, or a shape with a single stage of bending as schematically shown in Figure 1(B), or a shape with three or more stages of bending, or a shape with other three-dimensional structures such as curved sections. The specific shape of the brazing sheet 10A is appropriately determined according to various conditions such as the type or structure of the heat exchanger.

[0106] Furthermore, the specific configuration of the plate fin 32 shown in Figures 3(A) and 3(B) is not limited to the brazing sheet 10A shown in Figure 1(A), but may be any brazing sheet within the scope of this disclosure. For example, the plate fin 32 may be any of the brazing sheets 10B to 10D shown in Figures 2(A) to 2(C), or it may be a brazing sheet obtained by appropriately combining or modifying the laminated structure of these brazing sheets 10A to 10D.

[0107] A parallel flow condenser (PFC) is a heat exchanger widely used in car air conditioners (automotive air conditioning systems). It consists of multiple flat tubes arranged between a pair of header tubes, with corrugated fins for heat dissipation placed between these flat tubes. These header tubes, flat tubes, and corrugated fins are joined by brazing. Figure 4(A) shows a schematic cross-section of the connection between the header tube 41 and the flat tubes 42 in this PFC 40. Corrugated fins 43 are provided between the flat tubes 42, and these are also joined by brazing. The joining structure 20 according to this disclosure is the connection between the header tube 41 and the flat tubes 42, as shown in an enlarged view in Figure 4(B).

[0108] In the example shown in Figure 4(B), both the header pipe 41 and the flat pipe 42 are brazing sheets 10A, and for both the header pipe 41 and the flat pipe 42, the brazing material layer 13 on the joint surface 11a side (second surface side) is highlighted with hatching. The fillet 22 is also highlighted with hatching. Since the brazing material layer 13 of the flat pipe 42 is flat, the joint surface 11a and the non-joined adjacent surface 11b are set as different regions on a continuous single surface (the surface of the brazing material layer 13 or the second surface). Therefore, the flat pipe 42, as a brazing sheet 10A, has a flat shape without any bends.

[0109] The header pipe 41 has an opening for inserting the flat pipe 42 through it, and a joint surface 11a and an adjacent non-joining surface 11b are provided at this opening. In Figure 4(B), the joint surface 11a of the header pipe 41 is shown as a surface parallel to the joint surface 11a (outer surface) of the flat pipe 42, but it is not limited to this and may be a surface that is not parallel to the outer surface of the flat pipe 42. The opening of the header pipe 41 has a shape with a single bend in the brazing sheet 10A.

[0110] In the joint structure 20 shown in Figure 4(B), a fillet 22 is formed between the non-joint adjacent surface 11b of the header pipe 41 adjacent to the joint surface 11a and the non-joint adjacent surface 11b of the flat pipe 42 adjacent to the joint surface 11a. In this disclosure, the core material 11 of the header pipe 41 and the flat pipe 42 contains Cu in the range of 0.3 to 1.2 mass%, and the brazing layers 12, 13 and intermediate sacrificial layer 14 of the header pipe 41 and the flat pipe 42 do not substantially contain Cu. Therefore, the fillet 22 contains Cu at a concentration higher than that of the core material 11, brazing layers 12, 13, and intermediate sacrificial layer 14, but less than 2.0 mass%. This effectively suppresses (avoids or prevents) preferential corrosion of the joint 21, thereby improving the corrosion resistance life of the plate fin stacked heat exchanger.

[0111] Furthermore, the specific configurations of the header pipe 41 and flat pipe 42 shown in Figures 4(A) and 4(B) are not limited to the brazing sheet 10A shown in Figure 1(A), but may be any brazing sheet within the scope of this disclosure. For example, the header pipe 41 or flat pipe 42 may be any of the brazing sheets 10B to 10D shown in Figures 2(A) to 2(C), or it may be a brazing sheet obtained by appropriately combining or modifying the laminated structure of these brazing sheets 10A to 10D.

[0112] The manufacturing method for the joint structure 20 of such brazing sheets 10A to 10D is not particularly limited, and known brazing methods can be suitably used. For example, a known flux can be applied to the joint surface 11a of the brazing sheets 10A to 10D, and then heated in a nitrogen atmosphere furnace at a temperature of, for example, about 600°C. In particular, the Cu content in the fillet 22 (and joint portion 21) in the joint structure 20 according to this disclosure is not substantially affected by the detailed joining conditions.

[0113] As shown in Figure 5(A), the plate fin stack 34 constituting the stacked heat exchanger for the Air To Water heat pump has a basic configuration similar to that of the plate fin stack 30 of a typical plate fin stacked heat exchanger. However, as shown in Figure 5(B), the plate fins 35 constituting the plate fin stack 34 are configured such that both sides can serve as joining surfaces 11a. Therefore, in Figures 5(A) and (B), the brazing sheet 10C shown in Figure 2(B) (a configuration in which intermediate sacrificial layers 14 are laminated on both sides of the core material 11, and brazing layers 12 and 13 are located on the outside thereof) can be cited as the plate fin 35. For this reason, in Figures 5(A) and (B), the fillets 22 are formed not only on the joint 21 located on the header opening 33 side (inside), but also on the joint 21 located on the opposite side (outside) from the header opening 33.

[0114] In this disclosure, the core material 11 of the plate fin 35 contains Cu in the range of 0.3 to 1.2 mass%, and the brazing layers 12, 13 and intermediate sacrificial layer 14 of the plate fin 35 do not substantially contain Cu. Therefore, the fillet 22 contains Cu at a concentration higher than that of the core material 11, brazing layers 12, 13, and intermediate sacrificial layer 14, but less than 2.0 mass%. This effectively suppresses (avoids or prevents) preferential corrosion of the joint 21, thereby improving the corrosion resistance life of the plate fin stacked heat exchanger. Note that the configuration shown in Figures 5(A) and (B) is the same as the configuration shown in Figures 3(A) and (B) except for the formation positions of the plate fin 35 and the fillet 22, so its explanation is omitted.

[0115] As described above, the brazing sheet according to this disclosure is used in a heat exchanger and comprises an aluminum alloy core, a brazing layer made of an aluminum alloy brazing material containing silicon (Si), and an intermediate sacrificial layer made of an aluminum alloy sacrificial anode material containing zinc (Zn) in the range of 0.5 to 6.0 mass% and silicon (Si) in the range of 3.0 to 11 mass%. The brazing layer is located on the outside when viewed from both sides of the core, and the intermediate sacrificial layer is laminated on at least one side of the core. Neither the brazing material nor the sacrificial anode material contains copper (Cu), the core contains copper (Cu) in the range of 0.3 to 1.2 mass%, and the thickness of the intermediate sacrificial layer is 50 μm or less.

[0116] With this configuration, in a brazing sheet having a brazing material layer on its outer surface, an intermediate sacrificial layer made of a sacrificial anode material is placed between at least one brazing material layer and the core material, and neither the brazing material layer nor the intermediate sacrificial layer contains copper, while only the core material contains copper within a predetermined range. As a result, when the brazing material layers of the brazing sheet are joined together, copper diffuses from the core material through the intermediate sacrificial layer to the brazing material layer constituting the joint of the brazing sheet, and the copper from the core material also diffuses to the fillet formed adjacent to the joint, making it easier for copper to segregate at the fillet at the end.

[0117] Here, during bonding at high temperatures, the brazing material liquefies, but the intermediate sacrificial layer does not. Therefore, copper tends to segregate in the fillet, but zinc is present around the fillet at a suitable concentration due to the intermediate sacrificial layer. This creates a state where zinc is appropriately present around the fillet where copper segregates, enabling good sacrificial anodic action in the fillet. Furthermore, the copper does not hinder the appropriate potential reduction by zinc, thus achieving good sacrificial anodic action.

[0118] As a result, the risk of the preferential corrosion effect on the surrounding sacrificial anode material being reduced due to copper segregation, as in conventional methods, is avoided, and the risk of corrosion progressing from the fillet to the joint and causing a decrease in the joint strength can be effectively suppressed or prevented. This makes it possible to further improve the corrosion resistance of the joints of the heat exchanger. [Examples]

[0119] The present invention will be described in more detail based on examples, comparative examples, and reference examples, but the present invention is not limited thereto. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention. The various evaluation methods, etc., in the following examples, comparative examples, or reference examples were carried out as described below.

[0120] (Evaluation methods, etc.) [Bonded surface and non-bonded adjacent surface of brazing sheet] In the examples, comparative examples, or reference examples, as shown in Figure 6, a brazing sheet 10A with a four-layer structure including an intermediate sacrificial layer 14, or a brazing sheet 10E with a three-layer structure not including an intermediate sacrificial layer 14 was used. The thickness of both these brazing sheets 10A and 10E is 200 μm.

[0121] Furthermore, the joint surface and non-joined adjacent surface of the brazing sheet 10A were the surfaces (second surfaces) on the side of the brazing layer 13 adjacent to the intermediate sacrificial layer 14, and the joint surface and non-joined adjacent surface of the brazing sheet 10E were the surfaces on the side of the brazing layer 13 that also serves as the sacrificial anode material.

[0122] The angle between the joint surface and the adjacent non-joined surface varies slightly depending on the brazing sheet, but is basically around 30°±5° (within the range of 25-35°). When the joint surfaces are joined together, the angle formed by the adjacent non-joined surfaces is approximately 60°±10° (within the range of 50-70°).

[0123] [Elemental concentration analysis of the joint] Using an electron beam microanalyzer (EPMA), model EMPA-1600 manufactured by Shimadzu Corporation, the Cu concentration at the joint between brazing sheets 10A (or brazing sheet 10E) (the brazing sheet joint structure) was analyzed. As shown in Figure 7(B), the Cu concentration at the joint 21 was analyzed using the fillet 22 as the reference point (position: 0 mm) and along the direction of the joint surface 11a toward the opposite end of the fillet 22 (position: 0.7 mm) under the analysis conditions of an acceleration voltage of 15 kV, a beam diameter of 2 μm, a step interval of 2 μm, and an integration time of 1 second.

[0124] [Corrosion resistance test] The corrosion resistance of the brazing sheet joint structure was evaluated based on the SWAAT test (Sea Water Acidified Test) specified in ASTM G85-A3.

[0125] (Comparative Example 1) As shown in the top row of Figure 6, the brazing sheet 10A according to Comparative Example 1 has a four-layer structure comprising a core material 11, brazing layers 12 and 13, and an intermediate sacrificial layer 14 (see Figure 1(A)).

[0126] The core material 11 has a thickness of 116 μm, and the aluminum alloy used for the core material 11 is A3003 (3003-0.5% Cu, Mn-containing), which contains 0.5 mass% copper (Cu). The brazing layers 12 and 13 both have a thickness of 12 μm, and the brazing material used for the brazing layers 12 and 13 is an aluminum alloy (Al-10% Si) with 10 mass% silicon (Si) and the remainder being aluminum. The intermediate sacrificial layer 14 has a thickness of 60 μm, and the sacrificial anode material used for the intermediate sacrificial layer 14 is an aluminum alloy (Al-1% Zn) with 1% zinc (Zn).

[0127] Two brazing sheets 10A according to Comparative Example 1 were brazed at their joint surfaces 11a at 610°C to form a joint 21, thereby manufacturing the brazing sheet joint structure according to Comparative Example 1 (see Figure 1(B)).

[0128] The aforementioned corrosion resistance test was performed on the brazing sheet joint structure obtained in Comparative Example 1, and its corrosion resistance was evaluated. The results are shown in Figure 6. Furthermore, as described above, the Cu concentration of the joint 21 of the joint structure was analyzed. The results are shown in the solid line graph in Figure 7(A).

[0129] (Comparative Example 2) As shown in the second section of Figure 6, the brazing sheet 10E according to Comparative Example 2 has a three-layer structure that does not have an intermediate sacrificial layer 14 (it comprises a core material 11 and brazing layers 12, 13).

[0130] The core material 11 has a thickness of 160 μm, and the aluminum alloy used for the core material 11 is A3003 (3003-0.16%Cu, Mn-containing) which contains 0.16 mass% copper (Cu). The brazing layers 12 and 13 both have a thickness of 20 μm. Of these, the brazing material used for the brazing layer 12 covering the first surface is an aluminum alloy (Al-7.5%Si) with 7.5 mass% silicon (Si) and the remainder being aluminum, and the brazing material used for the brazing layer 13 covering the second surface is an aluminum alloy (Al-4%Si-4%Zn) with 4 mass% silicon (Si) and 4 mass% zinc and the remainder being aluminum. Therefore, the brazing layer 13 also serves as the sacrificial anode layer.

[0131] The brazing sheet joint structure according to Comparative Example 2 was manufactured in the same manner as in Comparative Example 1, except that the brazing sheet 10E according to Comparative Example 2 was used. A corrosion resistance test was performed on the obtained brazing sheet joint structure in the same manner as in Comparative Example 1. The results are shown in Figure 6.

[0132] (Example 1) As shown in the third section of Figure 6, the brazing sheet 10A according to Example 1 has a four-layer structure comprising a core material 11, brazing layers 12 and 13, and an intermediate sacrificial layer 14 (see Figure 1(A)).

[0133] The core material 11 has a thickness of 152 μm, and the aluminum alloy used for the core material 11 is the same copper-containing A3003 (3003-0.5% Cu, Mn-containing) as in Comparative Example 1. The brazing material layer 12 (first surface side) has a thickness of 18 μm, and the brazing material layer 13 (second surface side) has a thickness of 5 μm, and the brazing material used for these brazing material layers 12 and 13 is the same silicon-containing aluminum alloy (Al-10% Si) as in Comparative Example 1. The intermediate sacrificial layer 14 has a thickness of 25 μm, and the sacrificial anode material used for the intermediate sacrificial layer 14 is an aluminum alloy with 4% zinc (Zn) (Al-4% Zn).

[0134] Except for using the brazing sheet 10A according to Example 1, the brazing sheet joint structure according to Example 1 was manufactured in the same manner as in Comparative Example 1. A corrosion resistance test and an analysis of the Cu concentration of the joint 21 were performed on the obtained brazing sheet joint structure in the same manner as in Comparative Example 1. The results of the corrosion resistance test are shown in Figure 6, and the results of the Cu concentration analysis are shown in the dashed line graph in Figure 7(A).

[0135] (Example 2) As shown in the fourth section of Figure 6, the brazing sheet 10A according to Example 2 has a four-layer structure comprising a core material 11, brazing layers 12 and 13, and an intermediate sacrificial layer 14 (see Figure 1(A)).

[0136] Except for the thickness of the core material 11 being 160 μm and the thickness of the intermediate sacrificial layer 14 being 17 μm, this is the same as the brazing sheet 10A according to Example 1 (the materials of the core material 11, brazing layers 12, 13 and intermediate sacrificial layer 14 are the same as in Example 1, and the thicknesses of the brazing layers 12, 13 are also the same as in Example 1).

[0137] The brazing sheet joint structure according to Example 2 was manufactured in the same manner as in Comparative Example 1, except that the brazing sheet 10A according to Example 2 was used. A corrosion resistance test was performed on the obtained brazing sheet joint structure in the same manner as in Comparative Example 1. The results are shown in Figure 6.

[0138] (Reference example) As shown in the bottom row (fifth row) of Figure 6, the brazing sheet 10E in the reference example has a three-layer structure that does not have an intermediate sacrificial layer 14 (it has a core material 11 and brazing layers 12, 13).

[0139] Except for the aluminum alloy used in the core material 11 being copper-containing A3003 (3003-0.5% Cu, Mn-containing) with the same copper concentration as Comparative Example 1, Example 1, or Example 2, the brazing sheet 10E is the same as that of Comparative Example 2 (the material of the brazing layers 12 and 13 is the same as that of Comparative Example 2, and the thickness of the core material 11 and the brazing layers 12 and 13 are also the same as those of Comparative Example 2).

[0140] Except for using the brazing sheet 10E according to this reference example, the brazing sheet joint structure according to the reference example was manufactured in the same manner as in Comparative Example 1. A corrosion resistance test and an analysis of the Cu concentration of the joint 21 were performed on the obtained brazing sheet joint structure in the same manner as in Comparative Example 1. The results of the corrosion resistance test are shown in Figure 6, and the results of the Cu concentration analysis are shown in the dotted line graph in Figure 7(A).

[0141] (Comparison of comparative examples, examples, and reference examples) As is clear from the corrosion resistance test results shown in Figure 6, in Example 1 or Example 2, no corrosion occurred in the fillet 22 of the brazing sheet joint structure, demonstrating that good corrosion resistance can be achieved.

[0142] On the other hand, as in Comparative Example 2, in the brazing sheet 10E where the intermediate sacrificial layer 14 is absent and the Cu concentration of the core material 11 is low, preferential corrosion occurs in the joint structure of the brazing sheet, as indicated by the arrows. Also, as in Comparative Example 1, even when the intermediate sacrificial layer 14 is present, preferential corrosion occurs in the joint structure of the brazing sheet, as indicated by the arrows, if its thickness is too large (too thick). As is clear from the comparison between Comparative Example 1 and Comparative Example 2, the degree of corrosion is greater in Comparative Example 1, where the intermediate sacrificial layer 14 is too thick.

[0143] The reference example shows that even with a three-layer brazing sheet 10E that does not have an intermediate sacrificial layer 14, corrosion does not occur in the fillets 22 in the brazing sheet's joint structure, and good corrosion resistance can be achieved. As is clear from the comparison between the reference example and comparative example 2, it is considered that if the Cu concentration in the core material 11 is too low, good corrosion resistance cannot be achieved.

[0144] As shown in Figure 7(A), when comparing the Cu concentrations of the joint 21 in Comparative Example 1, Example 1, and Reference Example, in Reference Example or Example 1, the Cu concentration is high in the fillet 22, while the Cu concentration is low in the joint 21 other than the fillet 22. In contrast, in Comparative Example 1, although a high Cu concentration is locally observed between 0.1 and 0.2 mm, the overall Cu concentration is around 0.2 mass%, and Cu is not concentrated (segregated) in the fillet 22.

[0145] Furthermore, comparing Example 1 and the Reference Example, it can be seen that Cu is more easily concentrated (segregated) in the fillet 22 in Example 1. In the Reference Example, which does not have an intermediate sacrificial layer 14, the Cu concentration is relatively high up to a position of about 0.3 mm, but in Example 1, which has an intermediate sacrificial layer 14, the Cu concentration is about 0.2 mass% in most of the joint 21 other than the fillet 22.

[0146] Thus, in the brazing sheet according to this disclosure, only the core material contains copper, the intermediate sacrificial layer and the brazing layer do not contain copper, and the thickness of the intermediate sacrificial layer is optimized. Therefore, when brazing layers of the brazing sheet are joined together, the copper from the core material diffuses into the fillet formed adjacent to the joint, making it easier for copper to segregate at the end fillet. However, zinc is present around the fillet at a suitable concentration due to the intermediate sacrificial layer. As a result, a state is achieved where zinc is appropriately present around the fillet where copper segregates, enabling a good sacrificial anode effect at the fillet. Furthermore, the copper does not hinder the appropriate potential reduction by zinc, thus achieving a good sacrificial anode effect.

[0147] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments and multiple variations are also included in the technical scope of the present invention. [Industrial applicability]

[0148] The present invention can be broadly and suitably used not only in the field of brazing sheets for heat exchangers having an intermediate sacrificial layer, but also in the field of heat exchangers using said brazing sheets. [Explanation of Symbols]

[0149] 10A~10E: Brazing sheet 11: Heartwood 11a: Joint surface 11b: Non-joined adjacent surface 12,12a,12b: Brazing material layer (non-jointed side) 13: Brazing layer (joint surface side) 14: Middle Sacrifice Layer 15: Flux-containing layer 16: Magnesium-containing layer 20: Joining structure of brazing sheet 21: Joint 22: Fillet 30: Plate fin laminate 31: End plate 32: Plate Fin 33: Header opening 34: Plate fin stack 35: Plate Fin 40: Parallel Flow Capacitor (PFC) 41: Header pipe 42:Flat tube 43: Corrugated fins

Claims

1. A brazing sheet having joining surfaces that form a joint when joined together, and non-joined adjacent surfaces which are flat surfaces adjacent to the joining surfaces, wherein when the joining surfaces are joined together, the angle formed by the respective flat non-joined adjacent surfaces is acute, and fillets are formed in the area between these non-joined adjacent surfaces adjacent to the joining surfaces, where sacrificial anode material has flowed out from the joining surfaces and solidified, and the brazing sheet is used in an acute-angle joint structure in a heat exchanger, the brazing sheet having joining surfaces that form a joint when joined together, and non-joined adjacent surfaces which are flat surfaces adjacent to the joining surfaces, the brazing sheet being used in an acute-angle joint structure in a heat exchanger, the brazing sheet having an acute-angle joint structurecing sheet having an acute-angle joint structure, the bracing sheet having an acute-angle joint structure, the bracing sheet having a joining surface that forms a joint when joined together, and non-joined adjacent surfaces which are flat surfaces adjacent to the joining surfaces, is a brazing sheet used in an acute-angle joint structure in a heat exchanger, the bracing sheet having an acute-angle joint structure, the bracing sheet having a joining surface that forms a joint when joined together, is an acute-angle structure, and fillets are formed between these non-joined adjacent surfaces which are adjacent to the joining surfaces, where sacrificial anode material has flowed out from the joining surfaces and solidified, is a brazing sheet used in an acute-angle joint structure in a heat exchanger, the bracing sheet having a joining surface that forms a joint when joined together, is an acute-angle structure, and The core material is made of aluminum alloy, A brazing material layer made of an aluminum alloy brazing material containing silicon (Si) in the range of 2.5 to 13% by mass, An intermediate sacrificial layer consisting of an aluminum alloy sacrificial anode material containing zinc (Zn) in the range of 0.5 to 6.0 mass%, Equipped with, On one side of the core material, the brazing layer is laminated, and on the other side of the core material, the brazing layer is laminated on top of the laminated intermediate sacrificial layer, or The intermediate sacrificial layer is laminated on both surfaces of the core material, and the brazing layer is laminated to these intermediate sacrificial layers. The brazing material does not contain copper (Cu) in a concentration exceeding that of unavoidable impurities, nor does it contain elements other than Si in a concentration exceeding that of unavoidable impurities. The sacrificial anode material does not contain copper (Cu) in concentrations exceeding those of unavoidable impurities, nor does it contain elements other than Zn in concentrations exceeding those of unavoidable impurities. The core material contains copper (Cu) in the range of 0.3 to 1.2% by mass. The thickness of the aforementioned intermediate sacrificial layer is 50 μm or less. Brazing sheet.

2. Furthermore, it is characterized by comprising a flux-containing layer made of a brazing flux material, or a magnesium-containing layer which is configured as a layer independent of the brazing material layer and to which at least magnesium (Mg) is added to the brazing material. The brazing sheet according to claim 1.

3. The flux-containing layer or the magnesium-containing layer is characterized by being adjacent to the intermediate sacrificial layer or the brazing layer. The brazing sheet according to claim 2.

4. The core material is an aluminum alloy of the 3000 series, 5000 series, or 6000 series to which copper has been added within the aforementioned range. The aforementioned intermediate sacrificial layer is characterized by having zinc added to a 1000 series or 3000 series aluminum alloy within the aforementioned range. A brazing sheet according to any one of claims 1 to 3.

5. The brazing layer is characterized by being a 4000 series aluminum alloy. A brazing sheet according to any one of claims 1 to 4.

6. The acute angle formed by each of the non-joined adjacent surfaces is characterized in that it is within the range of 40° to 80°. A brazing sheet according to any one of claims 1 to 5.

7. The brazing sheet described in any one of claims 1 to 6 is used, Joining structure of brazing sheets.

8. Having the brazing sheet joining structure described in claim 7, heat exchanger.

9. A plate-fin stacked heat exchanger or a parallel flow condenser (PFC) is characterized by being a plate-fin stacked heat exchanger or a parallel flow condenser (PFC). The heat exchanger according to claim 8.

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