Heat exchanger core and method for manufacturing the same

Abstract

To provide a heat exchanger core having excellent corrosion resistance, and a method for manufacturing the same.SOLUTION: A heat exchanger core 1 has a fin 2, a tube 3, and a brazing part 4 for bonding the fin 2 and the tube 3. The fin 2 is composed of an aluminum alloy having a chemical component comprising 2.0 to 3.0 mass% Si, 0.05 to 1.2 mass% Fe, 0.25 mass% or less Cu, 0.3 to 1.8 mass% Mn, 0.3 to 5.0 mass% Zn, and the balance Al with inevitable impurities. The tube 3 is composed of an aluminum alloy extrusion material containing more than 0.05 mass% and 0.6 mass% or less Cu. A sacrificial anode layer 31 is formed on the outer surface of the tube 3. A natural electrode potential of the sacrificial anode layer 31, a natural electrode potential of the inner surface of the tube 3, a natural electrode potential of the fillet in the brazing part 4, and a natural electrode potential of the fin 2 satisfy a specific condition.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a heat exchanger core and a method for manufacturing the same.

Background Art

[0002] For example, in a radiator of an automobile, a condenser and an evaporator of an air conditioner incorporated in an automobile, a parallel flow type heat exchanger made of an aluminum alloy is used. This type of heat exchanger has a heat exchanger core including a plurality of tubes configured to allow a heat transfer medium to flow therethrough and a plurality of fins. In the core of the parallel flow type heat exchanger, the tubes and the fins are alternately laminated and joined to each other through brazing.

[0003] Conventionally, as fins of a heat exchanger core, a brazing sheet provided with a brazing material on at least one surface of a core material has been widely used. On the other hand, in recent years, it has been proposed to use a single-layer aluminum alloy material having a function of forming a brazing joint with a mating material as a fin.

[0004] For example, Patent Document 1 describes a fin material for a heat exchanger made of an aluminum alloy containing Si: 1.0 to 5.0 mass%, Fe: 0.01 to 2.0 mass%, Mn: 0.05 to 2.0 mass%, with the balance being Al and unavoidable impurities, and having a single-layer heat bonding function at a temperature where the liquid phase ratio is 5% or more and 35% or less.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, a known method for improving the corrosion resistance of heat exchanger cores is to form a Zn thermal spray coating on the outer surface of the tube, thereby making the outer surface of the tube function as a sacrificial anode for the inside of the tube. However, when a tube with a Zn thermal spray coating is combined with the heat exchanger fin material described in Patent Document 1, the brazing joint and corrosion of the fin material progressed prematurely, sometimes leading to a decrease in the corrosion resistance of the heat exchanger core.

[0007] This invention has been made in view of the above background, and aims to provide a heat exchanger core with excellent corrosion resistance and a method for manufacturing the same. [Means for solving the problem]

[0008] One aspect of the present invention relates to a fin having a chemical composition containing Si (silicon): 2.0% to 3.0% by mass, Fe (iron): 0.05% to 1.2% by mass, Cu (copper): 0% to 0.25% by mass, Mn (manganese): 0.3% to 1.8% by mass, Zn (zinc): 0.3% to 5.0% by mass, with the remainder being Al (aluminum) and unavoidable impurities. A tube made of an aluminum alloy extruded material containing Cu: more than 0.05 mass% and 0.6 mass% or less, The fin and the tube are joined by a brazing joint, A sacrificial anode layer having a lower natural electrode potential than the inner surface of the tube is formed on the outer surface of the tube. The heat exchanger core satisfies the following four conditions: (1) the natural electrode potential of the inner surface of the tube is +50mV or higher when the natural electrode potential of the sacrificial anode layer is used as a reference; (2) the natural electrode potential of the sacrificial anode layer is +100mV or lower when the natural electrode potential of the fillet in the brazed joint is used as a reference; (3) the natural electrode potential of the sacrificial anode layer is -80mV or higher and +150mV or lower when the natural electrode potential of the fin is used as a reference; and (4) the natural electrode potential of the fin is lower than the natural electrode potential of the fillet, or the natural electrode potential of the fin is equal to or higher than the natural electrode potential of the fillet, and the absolute value of the potential difference between the average of the natural electrode potentials of the fin, the fillet, and the sacrificial anode layer and the natural electrode potential of the fin is 40mV or lower.

[0009] Another aspect of the present invention is a method for manufacturing a heat exchanger core according to the above-described aspect, The assembly is constructed by alternately stacking fins having a chemical composition containing Si: 2.0% to 3.0% by mass, Fe: 0.05% to 1.2% by mass, Cu: 0% to 0.25% by mass, Mn: 0.3% to 1.8% by mass, and Zn: 0.3% to 4.0% by mass, with the remainder being Al and unavoidable impurities, and tubes made of aluminum alloy extruded material containing Cu: more than 0.05% by mass and 0.6% by mass or less. The method for manufacturing a heat exchanger core involves heating the assembly and brazing the assembly in an atmosphere containing zinc vapor to form the brazed joint between the fins and the tube, and forming the sacrificial anode layer on the outer surface of the tube. [Effects of the Invention]

[0010] The fins in the heat exchanger core are made of an aluminum alloy having the specified chemical components. By using fins having the specified chemical components, the heat exchanger core can be adjusted to satisfy all four conditions that were difficult to achieve with conventional heat exchanger cores, such as the natural electrode potential of the surface of the sacrificial anode layer, the inner surface of the tube, the fillet of the brazed joint, and the fins. By setting the natural electrode potential of each part of the heat exchanger core to the above configuration, the corrosion resistance of the heat exchanger core can be improved.

[0011] Furthermore, in the method for manufacturing the heat exchanger core, an assembly is fabricated by combining fins having the specific chemical components with tubes, and then the assembly is brazed in an atmosphere containing zinc vapor. The zinc vapor in the brazing atmosphere can appropriately lower the natural electrode potential of the fins and brazed joints. In addition, the zinc vapor in the brazing atmosphere can form a sacrificial anode layer on the outer surface of the tubes.

[0012] Thus, by not only using the aforementioned specific fins, but also by brazing the assembly in an atmosphere containing zinc vapor, the natural electrode potential of each part of the heat exchanger core can be adjusted so that all four conditions, which could not be achieved with conventional heat exchanger cores, are met. As a result, a heat exchanger core with excellent corrosion resistance can be easily obtained.

[0013] As described above, according to the above embodiment, a heat exchanger core having excellent corrosion resistance and a method for manufacturing the same can be provided. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a plan view of the heat exchanger core in the embodiment. [Figure 2] Figure 2 is a magnified view of a portion of Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the tube in the embodiment. [Figure 4]Figure 4 is a perspective view of the mini-core test piece in the experimental example. [Figure 5] Figure 5 is an explanatory diagram of the natural electrode potential measuring device in the experimental example.

Mode for Carrying Out the Invention

[0015] (Heat exchanger core) The heat exchanger core has fins and tubes. Also, a brazed joint for joining both is formed between the fins and the tubes. The heat exchanger core may be configured, for example, as the core of a so-called parallel flow type heat exchanger in which fins and tubes are alternately laminated. In addition to the fins and tubes, the heat exchanger core may also be provided with side plates joined to the outermost fins among the plurality of fins, headers attached to both ends of the tubes, and the like.

[0016] 〔Fins〕 The fins of the heat exchanger core are composed of a single layer of an aluminum alloy having a chemical composition containing Si: 2.0 mass% or more and 3.0 mass% or less, Fe: 0.05 mass% or more and 1.2 mass% or less, Cu: 0 mass% or more and 0.25 mass% or less, Mn: 0.3 mass% or more and 1.8 mass% or less, Zn: 0.3 mass% or more and 5.0 mass% or less, with the balance being Al and inevitable impurities. The thickness of the fins can be appropriately set, for example, within the range of 0.04 mm or more and 0.15 mm or less.

[0017] Hereinafter, the chemical composition of the fins and the reasons for its limitation will be described.

[0018] ·Si The fins contain 2.0% to 3.0% by mass of Si as an essential component. By setting the Si content in the fins to 2.0% by mass or more, a melt containing Al and Si can be generated by brazing heating, allowing a brazed joint to be formed between the fins and the tube. The Si content is preferably 2.1% by mass or more, more preferably 2.2% by mass or more, and even more preferably 2.3% by mass or more. In this case, the amount of melt generated by brazing heating can be increased, further improving the brazing properties. If the Si content is less than 2.0% by mass, the amount of melt generated by brazing heating will be insufficient, which may lead to a deterioration in brazing properties.

[0019] On the other hand, if the Si content is excessively high, the amount of fin melting during brazing heating may increase, potentially leading to a decrease in fin strength. As a result, the shape of the heat exchanger core may not be maintained during brazing. From the viewpoint of avoiding such problems, the Si content should be 3.0 mass% or less. From a similar viewpoint, the Si content is preferably 2.9 mass% or less, more preferably 2.8 mass% or less, and even more preferably 2.7 mass% or less.

[0020] In determining the preferred range for the Si content in the fins, the upper and lower limits of the Si content described above can be arbitrarily combined. For example, the preferred range for the Si content in the fins may be 2.1% by mass or more and 2.9% by mass or less, 2.2% by mass or more and 2.8% by mass or less, or 2.3% by mass or more and 2.7% by mass or less.

[0021] ·Fe The fins contain 0.05% to 1.2% by mass of Fe as an essential component. A portion of the Fe is dissolved in the Al matrix, improving the strength of the fins. The remaining Fe is dispersed in the Al matrix as a precipitate, improving the strength of the fins at both room temperature and high temperatures. Furthermore, the Fe has the effect of refining the crystal grains of the fins. By refining the crystal grains of the fins, the melt can more easily seep out from the grain boundaries during brazing heating, thereby improving brazing properties.

[0022] Therefore, by setting the Fe content in the fins to 0.05% by mass or more, the strength and brazing properties of the fins can be improved. From the viewpoint of further improving the strength and brazing properties of the fins, the Fe content in the fins is preferably 0.07% by mass or more, more preferably 0.10% by mass or more, even more preferably 0.13% by mass or more, and particularly preferably 0.15% by mass or more. If the Fe content in the fins is less than 0.05% by mass, it may lead to a decrease in the effects described above.

[0023] On the other hand, if the Fe content is excessively high, coarse intermetallic compounds are more likely to form during casting, which may lead to a decrease in the manufacturability of the fins. By setting the Fe content in the fins to 1.2% by mass or less, preferably 1.0% by mass or less, more preferably 0.8% by mass or less, even more preferably 0.6% by mass or less, and particularly preferably 0.4% by mass or less, the formation of coarse intermetallic compounds in the fins can be suppressed.

[0024] In determining the preferred range for the Fe content in the fins, the upper and lower limits of the Fe content mentioned above can be arbitrarily combined. For example, the preferred range for the Fe content in the fins may be 0.07% by mass or more and 1.0% by mass or less, 0.10% by mass or more and 0.8% by mass or less, 0.13% by mass or more and 0.6% by mass or less, or 0.15% by mass or more and 0.4% by mass or less.

[0025] ·Cu The fins may contain, as an optional component, 0% to 0.25% by mass of copper (Cu). The Cu in the fins, like Fe, dissolves in the Al matrix, improving the fin's strength. Furthermore, like Fe, Cu refines the fin's crystal grains. However, if the Cu content is excessively high, the amount of molten metal generated from the fins during brazing heating may become excessively large, potentially leading to a decrease in strength at high temperatures. In this case, the natural electrode potential of the fins may become nobler, potentially reducing the sacrificial corrosion protection effect in the heat exchanger core.

[0026] Therefore, by limiting the Cu content in the fins to 0.25% by mass or less, a decrease in strength at high temperatures and a decrease in sacrificial corrosion protection can be easily avoided. From the viewpoint of more reliably obtaining such effects, the Cu content in the fins is preferably 0% by mass or more and 0.20% by mass or less, more preferably 0% by mass or more and 0.15% by mass or less, even more preferably 0% by mass or more and 0.10% by mass or less, particularly preferably 0% by mass or more and 0.05% by mass or less, and most preferably 0% by mass or more and 0.04% by mass or less.

[0027] · Mn The fin contains, as an essential component, 0.3% by mass or more and 1.8% by mass of Mn. A portion of the Mn forms an Al-Mn-Si intermetallic compound within the fin, thereby improving the strength of the fin through dispersion strengthening. The remaining Mn is dissolved in the Al matrix, further improving the strength of the fin through solid solution strengthening.

[0028] By setting the Mn content in the fins to 0.3% by mass or more, the strength of the fins can be improved through dispersion strengthening and solid solution strengthening. Furthermore, by setting the Mn content in the fins to 0.3% by mass or more, the growth of crystal grains in the fins during brazing heating can be promoted, and the occurrence of deformation and buckling of the fins during brazing heating can be suppressed. From the viewpoint of further enhancing the effect of Mn on improving the strength of the fins and suppressing deformation during brazing, the Mn content is preferably 0.5% by mass or more, more preferably 0.7% by mass or more, and even more preferably 0.9% by mass or more. If the Mn content is less than 0.3% by mass, the above-mentioned effects will decrease, and there is a risk that deformation and buckling of the fins will occur more easily during brazing heating.

[0029] On the other hand, if the Mn content is excessively high, coarse intermetallic compounds are more likely to form during the manufacturing process of the fins. If rolling is performed while these coarse intermetallic compounds are present, there is a risk of pinhole formation. Furthermore, if the Mn content is excessively high, intermetallic compounds containing Mn and Si are more likely to form, and the amount of Si that can participate in the formation of the melt tends to be insufficient. As a result, there is a risk of a decrease in brazing properties. From the viewpoint of easily avoiding these problems, the Mn content should be 1.8% by mass or less. From a similar viewpoint, the Mn content is more preferably 1.7% by mass or less, even more preferably 1.6% by mass or less, and particularly preferably 1.5% by mass or less.

[0030] In determining the preferred range for the Mn content in the fins, the upper and lower limits of the Mn content mentioned above can be arbitrarily combined. For example, the preferred range for the Mn content in the fins may be 0.5% by mass or more and 1.7% by mass or less, 0.7% by mass or more and 1.6% by mass or less, or 0.9% by mass or more and 1.5% by mass or less.

[0031] · Zn The fin contains 0.3% to 5.0% by mass of Zn as an essential component. The Zn in the fin increases the amount of melt generated from the fin and has the effect of lowering the innate electrode potential of the fin. By setting the Zn content in the fin to 0.3% by mass or more, preferably 0.5% by mass or more, more preferably 0.7% by mass or more, even more preferably 0.9% by mass or more, and particularly preferably 1.0% by mass or more, the innate electrode potential Ef of the fin can be easily adjusted to a range that satisfies the above-mentioned conditions. If the Zn content in the fin is less than 0.3% by mass, the innate electrode potential Ef of the fin may become excessively noble, which may lead to a decrease in the sacrificial corrosion protection effect.

[0032] On the other hand, if the Zn content in the fins is excessively high, the natural electrode potential Ef of the fins may become excessively low, potentially leading to a decrease in the self-corrosion resistance of the fins. Furthermore, if the Zn content in the fins is excessively high, cracking may occur more easily during the manufacturing process of the fins, potentially leading to a decrease in productivity. These problems can be easily avoided by setting the Zn content in the fins to 5.0 mass% or less, preferably 3.5 mass% or less, more preferably 3.0 mass% or less, even more preferably 2.5 mass% or less, particularly preferably 2.0 mass% or less, and most preferably 1.5 mass% or less.

[0033] In determining the preferred range for the Zn content in the fins, the upper and lower limits of the Zn content described above can be arbitrarily combined. For example, the preferred range for the Zn content in the fins may be 0.5% by mass or more and 3.5% by mass or less, 0.5% by mass or more and 3.0% by mass or less, 0.7% by mass or more and 2.5% by mass or less, 0.9% by mass or more and 2.0% by mass or less, 0.9% by mass or more and 1.5% by mass or less, or 1.0% by mass or more and 1.5% by mass or less.

[0034] In addition to the essential components and Al mentioned above, the fins may also contain optional components such as Zr (zirconium), Cr (chromium), Ti (titanium), V (vanadium), Ni (nickel), Mg (magnesium), In (indium), and Sn (tin).

[0035] Zr, Cr, Ti, V The fins contain, as optional components: Zr: greater than 0% by mass and 0.3% by mass or less, Cr: greater than 0% by mass and 0.3% by mass or less, Ti: greater than 0% by mass and 0.3% by mass or less, and V: greater than 0% by mass and 0.3% by mass. below The material may contain one or more elements selected from the group consisting of the following. These elements have the effect of promoting the growth of crystal grains in the fins during brazing heating. Therefore, by keeping the content of Zr, Cr, Ti, and V in the fins within the aforementioned specific ranges, deformation and buckling of the fins during brazing heating can be more effectively suppressed.

[0036] · Limited The fin may contain Ni as an optional component in an amount exceeding 0% by mass and up to 0.8% by mass. Ni forms intermetallic compounds within the fin, improving the strength of the fin after brazing through dispersion strengthening. On the other hand, if the Ni content is excessively high, it may lead to a decrease in the self-corrosion resistance of the fin. By setting the Ni content in the fin to exceeding 0% by mass and up to 0.8% by mass, the aforementioned problems can be easily avoided while further improving the strength of the fin.

[0037] · Mg The fin may contain, as an optional component, Mg in an amount exceeding 0% by mass and up to 0.1% by mass. Mg forms Mg2Si in the fin after brazing, and has the effect of improving the strength of the fin through age hardening. On the other hand, if the Mg content is excessively high, the Mg may react with the flux when brazing is performed using flux, which may lead to a decrease in brazing properties. By setting the Mg content to exceed 0% by mass and up to 0.1% by mass, it is possible to further improve the strength of the fin while easily avoiding this problem.

[0038] ·In, Sn The fin may contain, as an optional component, one or two elements selected from the group consisting of In: greater than 0% by mass and 0.03% by mass or less, and Sn: greater than 0% by mass and 0.1% by mass or less. Sn and In, like Zn, have the effect of lowering the potential of the fin. By keeping the Sn and In content in the fin within the specified range, the potential of the fin can be adjusted while avoiding a decrease in self-corrosion resistance, thereby further improving the corrosion resistance of the aluminum structure.

[0039] The fin may contain one or more elements from the aforementioned optional components. For example, the fin may have a chemical composition containing Si: 2.0% to 3.0% by mass, Fe: 0.05% to 1.2% by mass, Cu: 0% to 0.25% by mass, Mn: 0.3% to 1.8% by mass, Zn: 0.3% to 5.0% by mass, and Ti: greater than 0% to 0.30% by mass, with the remainder being Al and unavoidable impurities.

[0040] Furthermore, the fin may have a chemical composition consisting of, for example, Si: 2.0% to 3.0% by mass, Fe: 0.05% to 0.6% by mass, Cu: 0% to 0.05% by mass, Mn: 0.3% to 1.8% by mass, Zn: 0.3% to 5.0% by mass, and Ti: greater than 0% to 0.30% by mass, with the remainder being Al and unavoidable impurities.

[0041] Furthermore, the fin may have a chemical composition consisting of, for example, Si: 2.0% to 3.0% by mass, Fe: 0.05% to 0.6% by mass, Cu: 0% to 0.04% by mass, Mn: 0.3% to 1.8% by mass, Zn: 0.3% to 5.0% by mass, and Ti: greater than 0% to 0.30% by mass, with the remainder being Al and unavoidable impurities.

[0042] Furthermore, the fin may have a chemical composition consisting of, for example, Si: 2.2% to 2.7% by mass, Fe: 0.13% to 0.6% by mass, Cu: 0% to 0.04% by mass, Mn: 0.7% to 1.6% by mass, Zn: 0.9% to 2.0% by mass, and Ti: greater than 0% to 0.30% by mass, with the remainder being Al and unavoidable impurities.

[0043] Other elements The fins may contain elements other than the essential and optional components mentioned above, as long as they do not impair the effects described above. Examples of elements that may be contained in the fins include Sr, Na, and rare earth elements. If the content of each of these elements is 0.05% by mass or less, and the total content is 0.15% by mass or less, these elements can be treated as unavoidable impurities without affecting the effects described above.

[0044] • Fin manufacturing method The method for manufacturing the fins can take various forms. For example, the fins may be a wrought material obtained by drawing, or a forged material obtained by forging. Alternatively, the fins may be castings obtained by casting.

[0045] From the viewpoint of improving brazing properties and strength, it is preferable that the fins be made of a wrought material. Because wrought materials undergo a greater degree of processing during their manufacturing process compared to forged materials and castings, the second-phase particles are more easily fragmented during the manufacturing process. Therefore, fins made of a wrought material can have a larger number of Si particles, Si-based intermetallic compounds, Al-based intermetallic compounds, etc., dispersed in the Al matrix. As a result, brazing properties and strength can be improved in a well-balanced manner.

[0046] When manufacturing the fins made of wrought material, continuous casting methods such as the twin-roll continuous casting rolling method or the twin-belt continuous casting method can be employed. Continuous casting methods allow for a higher cooling rate during casting compared to DC casting methods. As a result, a large number of fine second-phase particles, such as Si particles, can be formed in the fins. By dispersing a large number of fine second-phase particles in the fins, the amount of molten metal formed during brazing heating can be increased, thereby improving brazing properties.

[0047] When manufacturing the fins using a twin-roll continuous casting and rolling method, it is preferable to set the casting speed to 0.5 m / min or more and 3 m / min or less. In the twin-roll continuous casting and rolling method, setting the casting speed to 0.5 m / min or more allows for a sufficiently high cooling rate during casting, making it easy to refine the second-phase particles in the fins. Furthermore, setting the casting speed to 3 m / min or less allows for sufficient cooling and solidification of the molten metal during casting.

[0048] Furthermore, the temperature of the molten metal during casting is preferably between 650°C and 800°C, and more preferably between 680°C and 750°C. By setting the temperature of the molten metal preferably above 650°C, and more preferably above 680°C, the formation of large crystals in the molten metal can be avoided. Also, by setting the temperature of the molten metal preferably below 800°C, and more preferably below 750°C, the molten metal can be sufficiently cooled and solidified during casting.

[0049] The thickness of the rolled sheet obtained by casting is preferably 2 mm to 10 mm, and more preferably 4 mm to 8 mm. By making the thickness of the rolled sheet preferably 2 mm or more, and more preferably 4 mm or more, sound rolled sheets can be stably manufactured. Furthermore, by making the thickness of the rolled sheet preferably 10 mm or less, and more preferably 8 mm or less, it becomes easier to wind the rolled sheet onto a roll after casting.

[0050] The rolled sheet obtained by the continuous casting method may be used as the fin as is. Alternatively, the rolled sheet can be subjected to cold rolling, heat treatment, or other methods to adjust its thickness and temper to obtain a fin with a desired thickness and temper. The fin may have a temper represented by temper symbols O, H1n, or H2n, for example. From the viewpoint of suppressing erosion during brazing, it is preferable that the fin has a temper represented by temper symbols H1n or H2n.

[0051] Furthermore, the fins made of a wrought material may be manufactured, for example, by producing an ingot by DC casting and then subjecting the ingot to a wrought process. When producing an ingot by DC casting, the casting speed is preferably 20 mm / min or more and 100 mm / min or less, and more preferably 30 mm / min or more and 80 mm / min or less. In DC casting, by setting the casting speed to preferably 20 mm / min or more, more preferably 30 mm / min or more, the cooling rate during casting can be sufficiently increased, and the second phase particles in the fins can be easily refined. Also, by setting the casting speed to preferably 100 mm / min or less, more preferably 80 mm / min or less, the molten metal can be sufficiently cooled and solidified during casting.

[0052] When producing a slab by DC casting, the slab thickness is preferably 600 mm or less, and more preferably 500 mm or less. In this case, the cooling rate during casting can be sufficiently increased, making it easy to refine the second phase particles in the fins.

[0053] After producing an ingot by DC casting, a fin with a desired shape can be obtained by drawing the ingot. For example, after producing a slab by DC casting, the fin can be obtained by rolling the slab to obtain a rolled plate with a desired thickness. The rolling process can be a combination of hot rolling and cold rolling as appropriate. In addition, heat treatment such as homogenization or annealing can be performed as needed between before and after the rolling process to adjust the temper of the fin. The fin may have a temper represented by temper symbols O, H1n, or H2n. From the viewpoint of suppressing erosion during brazing, it is preferable that the fin has a temper represented by temper symbols H1n or H2n.

[0054] Furthermore, after producing a billet in DC casting, the fins can be obtained by hot extrusion of the billet, thereby obtaining the fins made of extruded material having the desired cross-sectional shape. Before hot extrusion, the billet may be subjected to homogenization treatment as needed. The billet is cast using a casting method such as hot top casting or GDC casting.

[0055] In the above manufacturing method, new aluminum ingots, intermediate alloys, and aluminum waste can be used as casting raw materials during casting. Aluminum waste used as casting raw materials includes, for example, discarded aluminum products, aluminum parts separated from discarded products, and scraps and chips generated during the manufacturing process of aluminum products and aluminum parts. When using aluminum waste as a casting raw material, the aluminum waste may be melted as is. Alternatively, the aluminum waste may be cut or compressed to adjust its size before melting. Furthermore, recycled aluminum ingots may be produced from the aluminum waste, and then the recycled aluminum ingots may be used as casting raw materials.

[0056] 〔tube〕 The tubes in the heat exchanger core are made of an aluminum alloy extruded material containing Cu: more than 0.05% by mass and less than or equal to 0.6% by mass.

[0057] As tubes in a heat exchanger core, tubing materials with a flat cross-sectional shape, such as flattened tubes or flattened multi-hole tubes, can be used. More specifically, the tube has a pair of flat wall sections arranged opposite each other with a gap between them, and a connecting wall section that connects both ends of the flat wall sections in the width direction, and is configured to allow the heat transfer medium to flow through the heat transfer medium flow path surrounded by the flat wall sections and the connecting wall section. Furthermore, the tube may also have partition walls that divide the internal space surrounded by the flat wall sections and the connecting wall section into multiple heat transfer medium flow paths. In a heat exchanger core, the flat wall sections of the tube and the fins are joined via brazing.

[0058] The cross-sectional shape of the tube perpendicular to its longitudinal direction is not particularly limited and can take various forms such as rectangular or oval. Similarly, the cross-sectional shape of the heat transfer medium flow path is not particularly limited and can take various forms such as circular, oval, elliptical, triangular, or square.

[0059] The chemical composition of the aluminum alloy extruded material constituting the tube may be such that the Cu content is within the specified range. For example, the aluminum alloy extruded material constituting the tube may have a chemical composition in which Cu is greater than 0.05% by mass and less than or equal to 0.6% by mass, with the remainder being Al and unavoidable impurities. The Cu in the tube has the effect of improving the strength of the tube. On the other hand, the Cu in the tube diffuses from the tube to the Zn thermal spray coating and brazed joint during brazing, and has the effect of nourishing the natural electrode potential of these parts. Therefore, if the Cu content in the tube is excessively high, the balance of the natural electrode potential of each part of the heat exchanger core may be disrupted, potentially leading to a decrease in corrosion resistance. Accordingly, by keeping the Cu content in the tube within the specified range, it is possible to increase the strength of the tube while ensuring excellent corrosion resistance of the heat exchanger core.

[0060] Furthermore, in addition to Cu as an essential component, the tube may contain one or more elements as optional components. For example, the aluminum alloy extruded material constituting the tube may contain Cu: more than 0.05 mass% and 0.6 mass% or less, and further contain one or more elements selected from the group consisting of Si: 0.7 mass% or less, Fe: 0.5 mass% or less, Mn: 1.2 mass% or less, and Ti: 0.3 mass% or less as optional components, with the remainder being Al and unavoidable impurities. Furthermore, the aluminum alloy extruded material constituting the tube may contain Cu: more than 0.05 mass% and 0.6 mass% or less, and may also contain, as an optional component, one or more elements selected from the group consisting of Si: 0.05 mass% to 0.7 mass%, Fe: 0.05 mass% to 0.5 mass%, Mn: 0.05 mass% to 1.2 mass%, and Ti: 0.01 mass% to 0.3 mass%, with the remainder being Al and unavoidable impurities.

[0061] Furthermore, a sacrificial anode layer having a lower natural electrode potential than the inner surface of the tube is formed on the outer surface of the tube. The sacrificial anode layer may be, for example, a Zn thermal spray coating. The Zn coating serving as the sacrificial anode layer is formed, for example, by a portion of the Zn thermal spray coating applied to the outer surface of the tube before brazing remaining after brazing.

[0062] Furthermore, the sacrificial anode layer may be, for example, a Zn-enriched layer with a higher Zn concentration than the surrounding area. The Zn-enriched layer as a sacrificial anode layer is formed, for example, by the diffusion of Zn atoms contained in zinc vapor or Zn thermal spray coating from the outer surface of the tube toward the interior during brazing. Note that when the sacrificial anode layer is a Zn-enriched layer, the boundary between the Zn-enriched layer and the layer adjacent to it in the tube may not be clearly defined. Even in such cases, the aforementioned effects can be obtained if the natural electrode potential Ets at the surface of the Zn-enriched layer as a sacrificial anode layer satisfies the aforementioned conditions.

[0063] [Natural electrode potential] The heat exchanger core satisfies all four of the following conditions: (1) the natural electrode potential of the inner surface of the tube is +50mV or higher when the natural electrode potential of the sacrificial anode layer is used as a reference; (2) the natural electrode potential of the sacrificial anode layer is +100mV or lower when the natural electrode potential of the fillet in the brazed joint is used as a reference; (3) the natural electrode potential of the sacrificial anode layer is -80mV or higher and +150mV or lower when the natural electrode potential of the fin is used as a reference; and (4) the natural electrode potential of the fin is lower than the natural electrode potential of the fillet, or the natural electrode potential of the fin is equal to or higher than the natural electrode potential of the fillet, and the absolute value of the potential difference between the average of the natural electrode potentials of the fin, the fillet, and the sacrificial anode layer and the natural electrode potential of the fin is 40mV or lower.

[0064] In other words, the innate electrode potential Ets of the sacrificial anode layer, the innate electrode potential Eti of the inner surface of the tube, the innate electrode potential Ej of the fillet in the brazed joint, and the innate electrode potential Ef of the fin all satisfy the following four conditions. (1) The potential difference Eti-Ets between the innate electrode potential Eti on the inner surface of the tube and the innate electrode potential Ets of the sacrificial anode layer is 50mV or more. (2) The potential difference Ets-Ej between the innate electrode potential Ets of the sacrificial anode layer and the innate electrode potential Ej of the fillet is 100mV or less. (3) The potential difference Ets-Ef between the natural electrode potential Ets of the sacrificial anode layer and the natural electrode potential Ef of the fin is between -80mV and 150mV. (4) The innate electrode potential Ef of the fin is lower than the innate electrode potential Ej of the fillet, or the innate electrode potential Ef of the fin is greater than or equal to the innate electrode potential Ej of the fillet, and the absolute value of the potential difference Eav-Ef between the average Eav of the innate electrode potential Ef of the fin, the innate electrode potential Ej of the fillet, and the innate electrode potential Ets of the sacrificial anode layer and the innate electrode potential Ef of the fin is 40mV or less. Note that the average Eav of the innate electrode potentials of the fin, fillet, and sacrificial anode layer is the arithmetic mean of the innate electrode potential Ef of the fin, the innate electrode potential Ej of the fillet, and the innate electrode potential Ets of the sacrificial anode layer (i.e., (Ef+Ej+Ets) / 3).

[0065] Such a relationship of natural electrode potential is difficult to achieve with conventional heat exchanger cores, for example, those obtained using fins made of single-layer aluminum material that does not have the ability to form brazing sheets or brazed joints. A heat exchanger core that satisfies all four of the aforementioned conditions can only be achieved by keeping the chemical composition of the aluminum alloy constituting the fins and tubes within the specific range shown in the manufacturing method, and by performing brazing in the presence of zinc vapor.

[0066] In condition (1) above, by setting the natural electrode potential Eti of the inner surface of the tube to a potential 50 mV or more higher (i.e., nobler) than the natural electrode potential Ets of the sacrificial anode layer, the sacrificial anode layer can be made to function as a sacrificial anode relative to the inner surface of the tube, thereby suppressing corrosion inside the tube. If the potential difference Eti-Ets between the inner surface of the tube and the sacrificial anode layer is lower than 50 mV, the sacrificial corrosion protection effect of the sacrificial anode layer becomes insufficient, and the inside of the tube becomes more susceptible to corrosion. As a result, leakage of the heat transfer medium from the tube may occur prematurely.

[0067] Condition (2) above specifies the potential difference Ets-Ej between the natural electrode potential Ets of the sacrificial anode layer and the natural electrode potential Ej of the fillet in the brazed joint. By keeping the potential difference Ets-Ej between the sacrificial anode layer and the fillet to 100mV or less, the potential balance between the sacrificial anode layer and the brazed joint can be kept within an optimal range, making it easy to avoid premature failure of the brazed joint. As a result, detachment of fins from the heat exchanger core can be suppressed. If the potential difference Ets-Ej between the sacrificial anode layer and the fillet exceeds 100mV, the brazed joint becomes more susceptible to corrosion than other parts of the heat exchanger core, and there is a risk that the brazed joint will fail prematurely. As a result, there is a risk that the fins will be more likely to detach prematurely from the heat exchanger core.

[0068] Condition (3) above defines the potential difference Ets-Ef between the natural electrode potential Ets of the sacrificial anode layer and the natural electrode potential Ef of the fins. By keeping the potential difference Ets-Ef between the sacrificial anode layer and the fins within the specified range, both the fins and the sacrificial anode layer can function as sacrificial anodes for the tube. If the potential difference Ets-Ef between the sacrificial anode layer and the fins is less than -80mV, the sacrificial anode layer is more susceptible to corrosion earlier than the fins. As a result, this may lead to the premature disappearance of the sacrificial anode layer, and the corrosion of the tube may progress starting from the corrosion of the sacrificial anode layer. On the other hand, if the potential difference Ets-Ef between the sacrificial anode layer and the fins exceeds 150mV, the fins become more susceptible to corrosion earlier than the sacrificial anode layer, which may lead to the premature disappearance of the fins.

[0069] In order to satisfy condition (4) above, it is sufficient to satisfy either of the following conditions: (4-1) the natural electrode potential Ef of the fin is lower than the natural electrode potential Ej of the fillet in the brazed joint (i.e., the natural electrode potential Ef of the fin is less virtuous than the natural electrode potential Ej of the fillet), or (4-2) the natural electrode potential Ef of the fin is equal to or greater than the natural electrode potential Ej of the fillet, and the potential difference Eav-Ef between the average Eav and the natural electrode potential Ef of the fin is between -40mV and 40mV.

[0070] By ensuring that the natural electrode potential of each part of the heat exchanger core satisfies not only conditions (1) to (3) but also condition (4), premature loss of the fins can be easily avoided, and a sacrificial corrosion protection effect can be maintained over a long period of time.

[0071] As described above, by ensuring that the natural electrode potential of each part of the heat exchanger core satisfies all four conditions, the balance of the natural electrode potentials of each part of the heat exchanger core can be adjusted to an optimal range. As a result, it is easy to avoid corrosion occurring earlier in any of the sacrificial anode layer, fins, and brazed joints than in other parts, thereby improving the corrosion resistance of the heat exchanger core as a whole. From the viewpoint of more reliably obtaining this effect, it is preferable that the heat exchanger core satisfies all four conditions: conditions (1) to (3) and condition (4-1). From a similar viewpoint, the natural electrode potential of the fins, relative to the natural electrode potential of the fillet, is preferably -5mV or less, more preferably -10mV or less, and even more preferably -15mV or less. That is, the potential difference Ef-Ej between the natural electrode potential Ej of the fins and the natural electrode potential Ef of the fillet is preferably -5mV or less, more preferably -10mV or less, and even more preferably -15mV or less.

[0072] (Method of manufacturing a heat exchanger core) The heat exchanger core is assembled by alternately stacking fins having a chemical composition containing Si: 2.0 mass% to 3.0 mass%, Fe: 0.05 mass% to 1.2 mass%, Cu: 0 mass% to 0.25 mass%, Mn: 0.3 mass% to 1.8 mass%, and Zn: 0.3 mass% to 4.0 mass%, with the remainder being Al and unavoidable impurities, and tubes made of aluminum alloy extruded material containing Cu: more than 0.05 mass% and up to 0.6 mass%, and stacking these fins on top of each other. The assembly is heated and brazed in an atmosphere containing zinc vapor to form the brazed joint between the fins and the tube, and the sacrificial anode layer is formed on the outer surface of the tube, thereby obtaining the brazed joint between the fins and the tube.

[0073] The chemical composition of the fins used in the fabrication of the heat exchanger core is the same as that of the fins in the heat exchanger core after brazing. Therefore, the types, content, and effects of the elements contained in the fins before brazing can be appropriately referred to in the description of the fins in the heat exchanger core after brazing mentioned above.

[0074] Furthermore, the configuration of the tubes used in the fabrication of the heat exchanger core is the same as that of the tubes in the heat exchanger core after brazing, except that a sacrificial anode layer is not formed on the outer surface. Therefore, the types, content, and effects of the elements contained in the tubes before brazing can be appropriately referred to in the description of the tubes in the heat exchanger core after brazing mentioned above.

[0075] In the method for manufacturing the heat exchanger core, the assembly is assembled by alternately overlapping tubes and fins, and then the assembly is heated in an atmosphere containing zinc vapor to perform brazing. More specifically, the atmosphere during brazing may be, for example, a non-oxidizing gas atmosphere containing zinc vapor. As a non-oxidizing gas, for example, nitrogen or argon can be used. Alternatively, the atmosphere during brazing may be a reduced-pressure atmosphere containing zinc vapor.

[0076] When brazing the assembly, the heating temperature is preferably set such that the liquidus ratio of the fins, that is, the ratio of the mass of the molten material produced from the fins to the mass of the fins before brazing, is greater than 5% by mass and less than or equal to 35% by mass, and more preferably between 7% by mass and 25% by mass. By keeping the liquidus ratio of the fins during heating within the specified range, a sufficient amount of molten material is produced from the fins while suppressing a decrease in the strength of the fins during heating, making it possible to easily form a brazed joint between the fins and the tubes.

[0077] Furthermore, when brazing the assembly, the holding time at the heating temperature is preferably set to 30 seconds to 3600 seconds, and more preferably to 60 seconds to 1800 seconds, such that the time during which the liquidus fraction of the fins is 5% by mass or more is 30 seconds to 3600 seconds. By setting the holding time during brazing within the specified range, the decrease in the strength of the fins during heating can be suppressed, while the molten liquid generated from the fins can be sufficiently filled between the fins and the tube. Note that when joining the fins and the tube, since molten liquid is generated from the entire surface of the fins, the length of the holding time can be set independently of the area of ​​the brazed joint formed between the fins and the tube.

[0078] More specifically, for example, the heating temperature in brazing can be appropriately set from a range of 580°C to 620°C. The holding time for the heating temperature can also be appropriately set from a range of, for example, 0 minutes to 10 minutes, preferably 30 seconds to 5 minutes. Here, the holding time refers to the elapsed time from the point when the heating temperature reaches the desired temperature. If the holding time for the heating temperature is 0 minutes, heating should be stopped immediately after the heating temperature reaches the desired time, and cooling of the heat exchanger core should begin.

[0079] The liquid phase fraction of the fins described above can be determined based on the lever rule, using an equilibrium phase diagram at a desired temperature. The equilibrium phase diagram used to calculate the liquid phase fraction may be a publicly known one, or one created using software for calculating equilibrium phase diagrams. Examples of such software include the thermodynamic calculation system "Thermo-Calc®" manufactured by Thermo-CalcSoftwareAB.

[0080] Alternatively, before brazing, flux may be applied to the part of the assembly where the brazed joint is to be formed, and then the assembly may be heated and brazed. As the flux, for example, compounds used as fluxes for aluminum brazing can be used, such as fluoride-based fluxes such as KAlF4, K2AlF5, K2AlF5·H2O, K3AlF6, AlF3, KZnF3, and K2SiF6, cesium-based fluxes such as Cs3AlF6, CsAlF4·2H2O, and Cs2AlF5·H2O, and chloride-based fluxes.

[0081] In the above manufacturing method, when the assembly is heated, a small amount of molten material is generated from the fins. This molten material collects at the contact point between the fins and the tube due to surface tension, thereby forming a brazed joint with a fillet between the fins and the tube.

[0082] Furthermore, in the above manufacturing method, brazing is performed in an atmosphere containing zinc vapor. By performing brazing in the presence of zinc vapor in this way, a sacrificial anode layer can be formed on the surface of the tube. Moreover, Zn atoms in zinc vapor can easily dissolve into the melt generated from the fins during the formation process of the brazed joint. Therefore, by dissolving Zn atoms into the melt that accumulates at the contact point between the fins and the tube, the innate electrode potential of the brazed joint can be appropriately lowered. Also, since the amount of melt generated from the fins is very small, the melt that exists at a distance from the contact point between the fins and the tube is not drawn into the contact point between the fins and the tube, but remains on the fins. Therefore, the Zn atoms dissolved in the melt of the fins can easily diffuse into the interior of the fins, and the innate electrode potential of the fins can be appropriately lowered.

[0083] As described above, by using fins made of an aluminum alloy having the specific chemical components and capable of forming a single-layer brazed joint, and by performing brazing in an atmosphere containing zinc vapor, the natural electrode potential of the fins and brazed joint can be appropriately lowered, and a sacrificial anode layer can be easily formed on the outer surface of the tube. As a result, the heat exchanger core can be obtained more easily.

[0084] In the above manufacturing method, the method for generating zinc vapor during brazing is not particularly limited and can take various forms. For example, in the above manufacturing method, zinc can be placed in a heating furnace used for brazing, and zinc vapor can be generated from the zinc in the heating furnace by heating during brazing. Alternatively, as will be described later, a Zn thermal spray coating can be formed on the outer surface of the tube before brazing, and zinc vapor can be generated from the Zn thermal spray coating during brazing.

[0085] It is preferable that the outer surface of the tubes used in the fabrication of the heat exchanger core is provided with a Zn thermal spray coating. After assembling the assembly using the tubes with the Zn thermal spray coating on their outer surface, brazing is performed to diffuse the Zn atoms in the Zn thermal spray coating into the tubes, making it easier to form a sacrificial anode layer on the outer surface of the tubes. Furthermore, the Zn thermal spray coating can generate zinc vapor when heated during brazing. This zinc vapor comes into contact with the fins and brazed joints, lowering the innate electrode potential of the fins and brazed joints. As a result, the innate electrode potential of each part of the heat exchanger core after brazing can be more easily adjusted to the specified range.

[0086] The amount of Zn deposited in the Zn thermal spray coating applied to the outer surface of the tube is not particularly limited, but for example, 3 g / m 2 More than 9g / m 2 You can set it as appropriate from the following range.

[0087] In the above manufacturing method, it is preferable that the Zn content in the fins after brazing is 0.1% by mass or more higher than the Zn content in the fins before brazing. In this case, the natural electrode potential of each part of the heat exchanger core after brazing can be more easily adjusted to the above-mentioned specific range.

[0088] The difference between the Zn content in the fins after brazing and the Zn content before brazing can be adjusted, for example, by the concentration of zinc vapor in the brazing atmosphere. For example, to increase the Zn content in the fins after brazing, the concentration of zinc vapor in the brazing atmosphere can be increased. Furthermore, the concentration of zinc vapor in the brazing atmosphere can be easily adjusted, for example, by the total amount of zinc placed in the heating furnace. For example, to increase the concentration of zinc vapor in the brazing atmosphere, the amount of zinc placed in the heating furnace and / or the amount of Zn thermal spray coating applied to the outer surface of the tube can be increased. [Examples]

[0089] (Examples) Examples of the heat exchanger core and its manufacturing method will be described with reference to Figures 1 to 3. As shown in Figures 1 and 2, the heat exchanger core 1 of this example has fins 2, tubes 3, and brazed joints 4 that join the fins 2 and tubes 3. The fins 2 are made of an aluminum alloy having a chemical composition containing Si: 2.0 mass% to 3.0 mass%, Fe: 0.05 mass% to 1.2 mass%, Cu: 0 mass% to 0.25 mass%, Mn: 0.3 mass% to 1.8 mass%, and Zn: 0.3 mass% to 5.0 mass%, with the remainder being Al and unavoidable impurities.

[0090] Tube 3 is made of an aluminum alloy extruded material containing Cu: more than 0.05 mass% and less than or equal to 0.6 mass%. As shown in Figure 2, a sacrificial anode layer 31 having a lower natural electrode potential than the inner surface of tube 3 is formed on the outer surface of tube 3. Furthermore, the heat exchanger core 1 satisfies the following four conditions: (1) the natural electrode potential of the inner surface of the tube 3 is +50mV or higher when the natural electrode potential of the sacrificial anode layer 31 is used as a reference; (2) the natural electrode potential of the sacrificial anode layer 31 is +100mV or lower when the natural electrode potential of the fillet in the brazed joint 4 is used as a reference; (3) the natural electrode potential of the sacrificial anode layer 31 is between -80mV and +150mV when the natural electrode potential of the fin 2 is used as a reference; and (4) the natural electrode potential of the fin 2 is lower than the natural electrode potential of the fillet, or the natural electrode potential of the fin 2 is equal to or greater than the natural electrode potential of the fillet, and the absolute value of the potential difference between the average of the natural electrode potentials of the fin 2, the fillet, and the sacrificial anode layer 31 and the natural electrode potential of the fin is 40mV or less.

[0091] As shown in Figure 1, the heat exchanger core 1 in this example has a plurality of fins 2 and a plurality of tubes 3, and is configured as the core of a so-called parallel flow type heat exchanger, with the fins 2 and tubes 3 stacked alternately. The fins 2 in the heat exchanger core 1 in this example are given a corrugated shape by press working, and as shown in Figure 2, they consist of a plurality of U-shaped curved fin tops 21 and fin intermediate parts 22 that connect the fin tops 21. The tubes 3, as shown in Figure 3, are made of extruded multi-hole tubes having a pair of flat wall portions 32 that are spaced apart and facing each other, a connecting wall portion 33 that connects the two ends of the flat wall portions 32 in the width direction, and a partition wall portion 35 that divides the internal space enclosed by the flat wall portions 32 and the connecting wall portion 33 into a plurality of heat transfer medium flow paths 34. As shown in Figure 2, the fin tops 21 of the fins 2 and the flat wall portions 32 of the tubes 3 are joined via brazing 4.

[0092] As shown in Figure 1, the heat exchanger core 1 in this example may have header tanks 11 attached to both ends of a plurality of tubes 3, and side plates 12 joined to the outermost fins 2 in the stacking direction of the plurality of fins 2. The internal space of the header tank 11 is configured to allow the heat transfer medium to flow through the heat transfer medium flow path 34 of the tubes 3. The header tank 11 can distribute the heat transfer medium within the header tank 11 to the plurality of tubes 3, or it can merge the heat transfer medium led out from the tubes 3 in the header tank 11.

[0093] Although not shown in the diagram, the header tank 11 and the tube 3 are joined via brazing. The method of joining the header tank 11 and the tube 3 is not particularly limited, and the brazing joint can be formed by known methods. For example, the header tank 11 before brazing can be constructed from a brazing sheet comprising a core material and brazing material laminated on at least one side of the core material, and the brazing joint 4 can be formed by the brazing material of the header tank 11. Alternatively, a separate brazing material may be placed between the header tank 11 and the tube 3, and the brazing joint can be formed by this brazing material.

[0094] Furthermore, the side plate 12 and the fin 2 are joined together via brazing 4.

[0095] The manufacturing method for the heat exchanger core 1 in this example is as follows. First, a laminate is made by alternately stacking fins 2 having a chemical composition containing Si: 2.0 mass% to 3.0 mass%, Fe: 0.05 mass% to 1.2 mass%, Cu: 0 mass% to 0.25 mass%, Mn: 0.3 mass% to 1.8 mass%, Zn: 0.3 mass% to 4.0 mass%, with the remainder being Al and unavoidable impurities, and tubes 3 made of aluminum alloy extruded material containing Cu: more than 0.05 mass% and 0.6 mass% or less. Header tanks 11 are attached to both ends of the tubes 3 in this laminate, and a side plate 12 is brought into contact with the outermost fin 2 among the multiple fins 2 to obtain an assembly.

[0096] Next, the assembly is heated and brazed in an atmosphere containing zinc vapor. Through these steps, the heat exchanger core 1 shown in Figure 1 can be obtained.

[0097] Next, the effects of this example will be explained. The fins 2 in the heat exchanger core 1 of this example are made of an aluminum alloy having the aforementioned specific chemical composition. By using at least the fins 2 having the aforementioned specific chemical composition, a heat exchanger core 1 can be obtained in which the natural electrode potential of each part satisfies all four conditions described above. Furthermore, by setting the natural electrode potential of each part of the heat exchanger core 1 to the aforementioned configuration, the corrosion resistance of the heat exchanger core 1 can be improved.

[0098] Furthermore, in the manufacturing method of the heat exchanger core 1, an assembly is fabricated by combining the fins 2 having the specific chemical components and the tubes 3, and then the assembly is brazed in an atmosphere containing zinc vapor. The zinc vapor in the brazing atmosphere can appropriately lower the natural electrode potential of the fins 2 and the brazed joints 4. In addition, the zinc vapor in the brazing atmosphere can form a sacrificial anode layer 31 on the outer surface of the tubes 3. In this way, by adjusting the potential of each part of the heat exchanger core 1 with zinc vapor, a heat exchanger core 1 can be easily obtained in which the natural electrode potential of each part satisfies all four of the aforementioned conditions.

[0099] (Example of experiment) This example describes how to evaluate corrosion resistance using a mini-core test specimen S1 that simulates the heat exchanger core 1. In this example, the same reference numerals used in the previously described examples indicate the same components as those used in the previously described examples.

[0100] As shown in Figure 4, the mini-core test specimen S1 has two tubes 3 (3a, 3b) spaced apart from each other, and a fin 2 interposed between the two tubes 3. The flat wall portion 32 of the tube 3 is in contact with the fin top portion 21 of the fin 2, and a brazed joint 4 is formed between the tube 3 and the fin 2.

[0101] The tube 3 used to prepare the mini-core test specimen S1 is specifically a flat, multi-hole tube made from an aluminum alloy extruded material having the chemical composition shown in Table 1. In Table 1, "Bal." indicates the remainder. The tube 3 has a width of 14 mm, a length of 40 mm, and the thickness of the flat wall section 32, connecting wall section 33, and partition wall section 35 is 0.35 mm. Furthermore, a Zn thermal spray coating is pre-formed on the outer surface of the tube 3. The amount of Zn atoms adhering to the Zn thermal spray coating is approximately 8 g / m². 2 That is the case.

[0102] The fins 2 used in the fabrication of the mini-core test specimen S1 are specifically single-layer corrugated fins made of an aluminum alloy having the chemical composition shown in Table 1. The thickness of the fins 2 is 0.08 mm, the spacing between the fin tips 21 is 3 mm, and the height of the fins 2 is 10 mm. Of the two tubes 3, 11 fin tips 21 contact the first tube 3a, and 12 fin tips 21 contact the second tube 3b.

[0103] To prepare the mini-core test specimen S1, first, the tube 3 and fin 2 are stacked, and then flux is applied to the contact area between the tube 3 and fin 2 to create an assembly. Ten of these assemblies are placed in a heating furnace, and zinc is placed around the assemblies. Furthermore, to retain zinc vapor around the assemblies, the ten assemblies and the zinc are covered. Then, the assemblies are heated in an inert gas atmosphere, and while generating zinc vapor from the zinc and Zn thermal spray coating, the assemblies are brazed in the presence of zinc vapor. By doing so, the mini-core test specimen S1 can be obtained.

[0104] The Zn content in the fins 2 of the mini-core specimen S1 obtained in this way is higher than the Zn content in the fins 2 before brazing due to contact with zinc vapor during brazing. For example, in the mini-core specimen S1 of this example, the Zn content in the fins 2 after brazing can be set to 1.75 mass%, which is 0.27 mass% higher than the Zn content in the fins 2 before brazing. The Zn content in the fins 2 after brazing can be measured, for example, using an electron probe microanalyzer (i.e., EPMA). When measuring the Zn content in the fins 2 using EPMA, specifically, a line analysis of the surface of the fins 2 is performed at the center of the mini-core specimen S1, and the average value of the obtained Zn concentration profile is taken as the Zn content.

[0105] Table 2 shows the natural electrode potential and corrosion resistance of each part of the mini-core specimen S1. Note that the mini-core specimen R1 shown in Table 2 is a specimen for comparison with mini-core specimen S1. Mini-core specimen R1 has the same configuration as mini-core specimen S1, except that the fin 2 uses a double-sided brazing sheet with brazing material laminated on both sides of the core material. The chemical composition of the core material and brazing material in the fin 2 of mini-core specimen R1 is as shown in Table 1. The thickness of the double-sided brazing sheet before brazing is 0.08 mm, and the cladding ratio of the brazing material is 10% in both cases. The manufacturing method of mini-core specimen R1 is the same as that of mini-core specimen S1, except that a double-sided brazing sheet is used instead of a single-layer aluminum alloy fin 2. The Zn content in the fin of mini-core specimen R1 after brazing is 1.20% by mass, which is 0.28% by mass less than the Zn content in the core material of the fin before brazing.

[0106] The methods for measuring the natural electrode potential and evaluating corrosion resistance shown in Table 2 are as follows.

[0107] • Natural electrode potential Ets of the sacrificial anode layer 31 The fins 2 are removed from the brazed mini-core test specimens S1 and R1, and the first tube 3a is removed. In the sacrificial anode layer 31 of this tube 3a, the region between any one brazed joint 4 and the adjacent brazed joint 4 is identified, and this region is designated as the potential measurement region. That is, the potential measurement region is the region on the outer surface of the first tube 3a that faces a 1-pitch fin.

[0108] After identifying the potential measurement area as described above, the areas other than the potential measurement area are covered with sealant. Then, the natural electrode potential of the potential measurement area is measured as follows. The measuring device 5 shown in Figure 5 is used to measure the natural electrode potential. The measuring device 5 includes a first container 51 for holding a solution for immersing the tube 3, a second container 52 for holding a solution for immersing the reference electrode 54, a salt bridge 53 for electrically connecting the solution in the first container 51 and the solution in the second container 52, and an electrometer 55 for measuring and recording the potential of the potential measurement area relative to the reference electrode 54. In Figure 5, the shape of the tube 3 is schematically shown.

[0109] The measurement of the natural electrode potential is performed as follows: First, a 5% NaCl aqueous solution, whose pH has been adjusted to 3 using acetic acid, is prepared in the first container 51, and a saturated NaCl aqueous solution is prepared in the second container 52. Then, the solution in the first container 51 and the solution in the second container 52 are electrically connected via a salt bridge 53. The temperature of each solution is set to room temperature.

[0110] Next, the tube 3 and the reference electrode 54 are electrically connected to the electrometer 55. For example, a saturated calomel electrode (so-called SCE) can be used as the reference electrode 54.

[0111] In this state, the potential measurement region M of tube 3 is immersed while stirring the solution in the first container 51, and at the same time, the reference electrode 54 is immersed in the saturated NaCl aqueous solution in the second container 52. This allows the natural electrode potential (unit: mV vs SCE) of the potential measurement region M of tube 3, relative to the reference electrode 54, to be measured. The arithmetic mean of the natural electrode potential of the potential measurement region M from 20 hours to 24 hours after the start of measurement is defined as the natural electrode potential Ets of the sacrificial anode layer 31.

[0112] • The natural electrode potential Eti of the inner surface of tube 3 The fins 2 are removed from the brazed mini-core test specimens S1 and R1, and the first tube 3a is removed. From this tube 3a, the flat wall portion 32a not joined to the fin top portion 21, the connecting wall portion 33, and the partition wall portion 35 are surface-ground to expose the inner surface of the flat wall portion 32b (see Figure 4) joined to the fin top portion 21. A potential measurement area is set on this inner surface, and the parts other than the potential measurement area are covered with sealant. Then, the natural electrode potential of the potential measurement area is measured in the same manner as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential obtained in this way is taken as the natural electrode potential Eti of the inner surface of the tube 3.

[0113] • Fin 2 native electrode potential Ef After brazing, the first tube 3a and the fin top 21 joined to the first tube 3a are removed from the mini-core test specimens S1 and R1. Next, a potential measurement area is set on the surface of the fin 2 joined to the second tube 3b, and the area other than the potential measurement area is covered with sealant. Then, the natural electrode potential of the potential measurement area is measured in the same manner as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential obtained in this way is defined as the natural electrode potential Ef of the fin 2.

[0114] • Fillet's natural electrode potential Ej After brazing, the fins 2 are removed from the mini-core test specimens S1 and R1, and the first tube 3a is removed. Next, the fin tops 21 remaining on the first tube 3a are surface-ground so that both the fillet of the brazed joint 4 and the fin tops 21 are exposed on a common plane. Then, a potential measurement area is set on the fillet exposed by surface grinding, and the area other than the potential measurement area is covered with sealant. After that, the natural electrode potential of the potential measurement area is measured in the same manner as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential obtained in this way is defined as the natural electrode potential Ej of the fillet.

[0115] • Corrosion resistance After coating the end faces of tube 3, the connecting wall portion 33 of tube 3, and the flat wall portion 32a not joined to fin 2 of the mini-core test specimens S1 and R1 obtained by the method described above with sealant, a SWAAT test is performed in accordance with ASTM-G85-A3. The test period shall be either 20 days or 40 days. After cleaning the mini-core test specimens S1 and R1 with acid after the test, the corrosion resistance is evaluated based on whether or not there is penetration of tube 3 and whether or not there is delamination of fin 2 from tube 3.

[0116] The symbols shown in the "Fin Separation" column of Table 2 have the following meanings: A: All fin tips are joined to the tube. B: Some of the fin tips are detached from the tube. C: All fin tips are detached from the tube.

[0117] Furthermore, the symbols shown in the "Tube Penetration" column in Table 2 are as follows: A: No corrosion has occurred that penetrates the tube. B: Corrosion has occurred that penetrates the tube.

[0118] [Table 1]

[0119] [Table 2]

[0120] As shown in Table 1, the mini-core test specimen S1 has a single layer fin 2 made of an aluminum alloy having the specific chemical composition described above, and a tube 3 having a sacrificial anode layer 31 on its outer surface. Furthermore, the natural electrode potentials Ets, Eti, Ef, and Ej of each part of the mini-core test specimen S1 satisfy all four conditions described above. Therefore, the mini-core test specimen S1 can avoid premature disappearance of any of the sacrificial anode layer 31, fin 2, or brazed joint 4, and has excellent corrosion resistance.

[0121] On the other hand, minicore specimen R1, which has fins made of double-sided brazing sheets, exhibits inferior corrosion resistance compared to minicore specimen S1, and fin delamination from tube 3 occurs after 20 days of continuous SWAAT testing. Furthermore, after 40 days of continuous SWAAT testing of minicore specimen R1, the fins completely detach from tube 3, and corrosion penetrating tube 3 occurs. Possible reasons for this include the following: When brazing sheets are used as fins, the fluidity of the molten solder formed from the melted brazing material is high, making it easy for molten solder containing Zn atoms to move to the fillet of the brazed joint. This can lead to an excessively high Zn content in the brazed joint, and the natural electrode potential Ej of the brazed joint tends to become excessively low.

[0122] Furthermore, the easy flow of molten solder during brazing is likely to result in insufficient diffusion of Zn from the molten solder to the core material. This is thought to lead to insufficient effectiveness of the sacrificial anode layer formed on the surface of the fins after brazing, making it easier for corrosion to progress into the interior of the tube.

[0123] Although embodiments of the heat exchanger core and its manufacturing method according to the present invention have been described above based on the examples and experimental examples, the specific embodiments of the heat exchanger core and its manufacturing method according to the present invention are not limited to the embodiments of the examples and experimental examples, and the configuration can be appropriately modified without impairing the spirit of the present invention.

[0124] For example, the heat exchanger core may take the following forms [1] to [2].

[0125] [1] A fin having a chemical composition containing Si: 2.0% to 3.0% by mass, Fe: 0.05% to 1.2% by mass, Cu: 0% to 0.25% by mass, Mn: 0.3% to 1.8% by mass, Zn: 0.3% to 5.0% by mass, with the remainder being Al and unavoidable impurities, A tube made of an aluminum alloy extruded material containing Cu: more than 0.05 mass% and 0.6 mass% or less, The fin and the tube are joined by a brazing joint, A sacrificial anode layer having a lower natural electrode potential than the inner surface of the tube is formed on the outer surface of the tube. A heat exchanger core that satisfies four conditions: (1) the natural electrode potential of the inner surface of the tube is +50mV or higher when the natural electrode potential of the sacrificial anode layer is used as a reference; (2) the natural electrode potential of the sacrificial anode layer is +100mV or lower when the natural electrode potential of the fillet in the brazed joint is used as a reference; (3) the natural electrode potential of the sacrificial anode layer is -80mV or higher and +150mV or lower when the natural electrode potential of the fin is used as a reference; and (4) the natural electrode potential of the fin is lower than the natural electrode potential of the fillet, or the natural electrode potential of the fin is equal to or higher than the natural electrode potential of the fillet, and the absolute value of the potential difference between the average of the natural electrode potentials of the fin, the fillet, and the sacrificial anode layer and the natural electrode potential of the fin is 40mV or lower.

[0126] [2] The fins further consist of Zr: greater than 0 mass% and 0.3 mass% or less, Cr: greater than 0 mass% and 0.3 mass% or less, Ti: greater than 0 mass% and 0.3 mass% or less, V: greater than 0 mass% and 0.3 mass% below The heat exchanger core described in [1] contains one or more elements selected from the group consisting of Ni: greater than 0 mass% and 0.8 mass% or less, Mg: greater than 0 mass% and 0.1 mass% or less, In: greater than 0 mass% and 0.03 mass% or less, and Sn: greater than 0 mass% and 0.1 mass% or less.

[0127] Furthermore, the method for manufacturing the heat exchanger core may take the forms shown in [3] to [6] below.

[0128] A method for manufacturing a heat exchanger core as described in [3], [1], or [2], The assembly is constructed by alternately stacking fins having a chemical composition containing Si: 2.0% to 3.0% by mass, Fe: 0.05% to 1.2% by mass, Cu: 0% to 0.25% by mass, Mn: 0.3% to 1.8% by mass, and Zn: 0.3% to 4.0% by mass, with the remainder being Al and unavoidable impurities, and tubes made of aluminum alloy extruded material containing Cu: more than 0.05% by mass and 0.6% by mass or less. A method for manufacturing a heat exchanger core, comprising heating the assembly and brazing the assembly in an atmosphere containing zinc vapor to form the brazed joint between the fins and the tube, and forming the sacrificial anode layer on the outer surface of the tube.

[0129] [4] The fins further consist of Zr: greater than 0 mass% and 0.3 mass% or less, Cr: greater than 0 mass% and 0.3 mass% or less, Ti: greater than 0 mass% and 0.3 mass% or less, V: greater than 0 mass% and 0.3 mass% below A method for manufacturing a heat exchanger core according to [3], comprising one or more elements selected from the group consisting of Ni: greater than 0 mass% and 0.8 mass% or less, Mg: greater than 0 mass% and 0.1 mass% or less, In: greater than 0 mass% and 0.03 mass% or less, and Sn: greater than 0 mass% and 0.1 mass% or less.

[0130] [5] The method for manufacturing a heat exchanger core according to [3] or [4], wherein the assembly is assembled using the tube having a Zn thermal spray coating on its outer surface. [6] The method for manufacturing a heat exchanger core according to [3] or [4], wherein the Zn content in the fin after brazing is 0.1% by mass or more higher than the Zn content in the fin before brazing. [Explanation of symbols]

[0131] 1 Heat exchanger core 2 fins 3 tubes 31 Sacrificial Anode Layer 4. Brazing

Claims

1. A fin having a chemical composition containing Si: 2.0% to 3.0% by mass, Fe: 0.05% to 1.2% by mass, Cu: 0% to 0.25% by mass, Mn: 0.3% to 1.8% by mass, Zn: 0.3% to 5.0% by mass, with the remainder being Al and unavoidable impurities, A tube made of an aluminum alloy extruded material containing Cu: more than 0.05 mass% and 0.6 mass% or less, The fin and the tube are joined by a brazing joint, A sacrificial anode layer having a lower natural electrode potential than the inner surface of the tube is formed on the outer surface of the tube. A heat exchanger core that satisfies the following four conditions: (1) The natural electrode potential of the inner surface of the tube is +50 mV or higher when the natural electrode potential of the sacrificial anode layer is used as a reference; (2) The natural electrode potential of the sacrificial anode layer is +100 mV or lower when the natural electrode potential of the fillet in the brazed joint is used as a reference; (3) The natural electrode potential of the sacrificial anode layer is -80 mV or higher and +150 mV or lower when the natural electrode potential of the fin is used as a reference; and (4) The natural electrode potential of the fin is lower than the natural electrode potential of the fillet, or the natural electrode potential of the fin is equal to or higher than the natural electrode potential of the fillet, and the absolute value of the potential difference between the average of the natural electrode potentials of the fin, the fillet, and the sacrificial anode layer and the natural electrode potential of the fin is 40 mV or lower.

2. The heat exchanger core according to claim 1, wherein the fins further contain one or more elements selected from the group consisting of Zr: greater than 0% by mass and 0.3% by mass or less, Cr: greater than 0% by mass and 0.3% by mass or less, Ti: greater than 0% by mass and 0.3% by mass or less, V: greater than 0% by mass and 0.3% by mass or less, Ni: greater than 0% by mass and 0.8% by mass or less, Mg: greater than 0% by mass and 0.1% by mass or less, In: greater than 0% by mass and 0.03% by mass or less, and Sn: greater than 0% by mass and 0.1% by mass or less.

3. A method for manufacturing a heat exchanger core according to claim 1 or 2, An assembly is constructed by alternately stacking fins having a chemical composition containing Si: 2.0% to 3.0% by mass, Fe: 0.05% to 1.2% by mass, Cu: 0% to 0.25% by mass, Mn: 0.3% to 1.8% by mass, and Zn: 0.3% to 4.0% by mass, with the remainder being Al and unavoidable impurities, and tubes made of aluminum alloy extruded material containing Cu: more than 0.05% by mass and 0.6% by mass or less. A method for manufacturing a heat exchanger core, comprising heating the assembly and brazing the assembly in an atmosphere containing zinc vapor to form the brazed joint between the fins and the tube, and forming the sacrificial anode layer on the outer surface of the tube.

4. The method for manufacturing a heat exchanger core according to claim 3, wherein the fins further contain one or more elements selected from the group consisting of Zr: greater than 0% by mass and 0.3% by mass or less, Cr: greater than 0% by mass and 0.3% by mass or less, Ti: greater than 0% by mass and 0.3% by mass or less, V: greater than 0% by mass and 0.3% by mass or less, Ni: greater than 0% by mass and 0.8% by mass or less, Mg: greater than 0% by mass and 0.1% by mass or less, In: greater than 0% by mass and 0.03% by mass or less, and Sn: greater than 0% by mass and 0.1% by mass or less.

5. A method for manufacturing a heat exchanger core according to claim 3, wherein the assembly is assembled using the tube having a Zn thermal spray coating on its outer surface.

6. The method for manufacturing a heat exchanger core according to claim 3, wherein the Zn content in the fin after brazing is 0.1% by mass or more higher than the Zn content in the fin before brazing.

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