HEAT EXCHANGER CORE AND METHOD FOR MANUFACTURING THE SAME

Abstract

A heat exchanger core (1) has fins (2), tubes (3), and brazed joints (4) connecting the fins (2) and the tubes (3). The fins (2) are made of an aluminum alloy having a chemical composition comprising Si: 2.0 to 3.0% by mass, Fe: 0.05 to 1.2% by mass, Cu: 0.25% by mass or less, Mn: 0.3 to 1.8% by mass, and Zn: 0.3 to 5.0% by mass, the remainder consisting of Al and unavoidable impurities. The tubes (3) are made of an extruded aluminum alloy material containing Cu: more than 0.05% by mass and 0.6% by mass or less. A sacrificial anode layer (31) is formed on the outer surface of the tubes (3).The natural electrode potential of the sacrificial anode layer (31), the natural electrode potential of the inner surface of the tubes (3), the natural electrode potential of the fillet welds in the brazed joints (4), and the natural electrode potential of the fins (2) meet specific conditions.

Description

Heat exchanger core and manufacturing method thereof

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

[0002] For example, parallel-flow heat exchangers made of aluminum alloys are used in automobile radiators and condensers and evaporators of air conditioners installed in automobiles. This type of heat exchanger has a heat exchanger core including multiple tubes and multiple fins configured to allow a heat transfer medium to flow through. In the core of the parallel-flow heat exchanger, the tubes and fins are alternately stacked and joined to each other by brazing.

[0003] While brazing sheets, which have a brazing material applied to at least one surface of a core material, have been widely used as fins for heat exchanger cores, it has been proposed in recent years to use single-layer aluminum alloy fins that can form a brazing joint with a mating material.

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

[0005] Patent No. 5698416

[0006] A known method for improving the corrosion resistance of a heat exchanger core is to form a Zn spray coating on the outer surface of the tube, causing the outer surface of the tube to function as a sacrificial anode for the inside of the tube. However, when the tube with the Zn spray coating is combined with the heat exchanger fin material of Patent Document 1, corrosion of the brazed joint and the fin material progresses early, which can lead to a decrease in the corrosion resistance of the heat exchanger core.

[0007] The present invention has been made in view of the above background, and aims to provide a heat exchanger core having excellent corrosion resistance and a method for manufacturing the same.

[0008] One aspect of the present invention is a fin having a chemical composition containing 2.0 to 3.0 mass% Si (silicon), 0.05 to 1.2 mass% Fe (iron), 0 to 0.25 mass% Cu (copper), 0 to 1.8 mass% Mn (manganese), 0.3 to 1.8 mass% Zn (zinc), and the balance being Al (aluminum) and unavoidable impurities; a tube made of an aluminum alloy extrusion material containing more than 0.05 to 0.6 mass% Cu; and a brazing joint joining the fin and the tube, wherein a sacrificial anode layer having a lower natural electrode potential than that of the inner surface of the tube is formed on an outer surface of the tube, (1) The natural electrode potential of the inner surface of the tube is +50 mV or more 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 less 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 more and +150 mV or less 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 potential of the fin, the natural electrode potential of the fillet, and the natural electrode potential of the sacrificial anode layer and the natural electrode potential of the fin is 40 mV or less.

[0009] Another aspect of the present invention is a method for manufacturing the heat exchanger core of the above aspect, comprising assembling an assembly by alternately stacking fins having a chemical composition containing 2.0 to 3.0 mass% Si, 0.05 to 1.2 mass% Fe, 0 to 0.25 mass% Cu, 0.3 to 1.8 mass% Mn, 0.3 to 4.0 mass% Zn, with the balance being Al and unavoidable impurities, and tubes made of an aluminum alloy extrusion material containing more than 0.05 to 0.6 mass% Cu, and heating the assembly and brazing the assembly in an atmosphere containing zinc vapor, thereby forming the brazed joints between the fins and the tubes and forming the sacrificial anode layers on the outer surfaces of the tubes.

[0010] The fins in the heat exchanger core are made of an aluminum alloy having the specific chemical composition. By using at least the fins having the specific chemical composition, the natural electrode potentials of the surface of the sacrificial anode layer, the inner surface of the tube, the fillet of the brazed joint, and the fins can be adjusted to satisfy all of the four conditions described above, which were difficult to achieve with conventional heat exchanger cores. By adjusting the natural electrode potentials of each portion of the heat exchanger core to the above-described conditions, the corrosion resistance of the heat exchanger core can be improved.

[0011] In the method for manufacturing a heat exchanger core, the fins having the specific chemical composition are assembled with the tubes to form an assembly, 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 the brazed joint. Furthermore, the zinc vapor in the brazing atmosphere can form a sacrificial anode layer on the outer surface of the tubes.

[0012] In this way, by not only using the specific fins but also brazing the assembly in an atmosphere containing zinc vapor, it is possible to adjust the natural electrode potential of each part of the heat exchanger core so that all four of the above conditions are satisfied, which was not possible with conventional heat exchanger cores. As a result, it is easy to obtain a heat exchanger core with excellent corrosion resistance.

[0013] As described above, according to the above-described aspect, it is possible to provide a heat exchanger core having excellent corrosion resistance and a method for manufacturing the same.

[0014] Fig. 1 is a plan view of a heat exchanger core in an example. Fig. 2 is a partially enlarged view of Fig. 1. Fig. 3 is a cross-sectional view of a tube in an example. Fig. 4 is a perspective view of a mini-core test specimen in an experimental example. Fig. 5 is an explanatory diagram of a measuring device for natural electrode potential in an experimental example.

[0015] (Heat Exchanger Core) The heat exchanger core has fins and tubes. Furthermore, brazing is formed between the fins and the tubes to join them. The heat exchanger core may be configured as a core of a so-called parallel flow heat exchanger, in which the fins and the tubes are alternately stacked. Furthermore, in addition to the fins and the tubes, the heat exchanger core may further include side plates joined to the outermost fins of the multiple 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 aluminum alloy containing the following chemical components: 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 the balance being Al and unavoidable impurities. The thickness of the fin can be set appropriately within a range of, for example, 0.04 to 0.15 mm.

[0017] The chemical composition of the fins and the reasons for their limitations will be explained below.

[0018] Si The fin contains 2.0% by mass or more and 3.0% by mass or less of Si as an essential component. By setting the Si content in the fin to 2.0% by mass or more, a molten liquid containing Al and Si can be generated by brazing heat, and a brazed joint can be formed between the fin 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 molten liquid generated by brazing heat can be increased, further improving brazing properties. If the Si content is less than 2.0% by mass, the amount of molten liquid generated by brazing heat is insufficient, which may result in deterioration of brazing properties.

[0019] On the other hand, if the Si content is excessively high, the amount of melting of the fins during brazing heating may increase, which may result in a decrease in the strength of the fins. As a result, the shape of the heat exchanger core may not be maintained during brazing. In order to avoid such problems, the Si content is set to 3.0 mass% or less. From the same perspective, the Si content is preferably set to 2.9 mass% or less, more preferably 2.8 mass% or less, and even more preferably 2.7 mass% or less.

[0020] The preferred range of the Si content in the fin can be determined by any combination of the upper and lower limits of the Si content described above. For example, the preferred range of the Si content in the fin may be 2.1 mass% to 2.9 mass%, 2.2 mass% to 2.8 mass%, or 2.3 mass% to 2.7 mass%.

[0021] Fe The fin contains 0.05% by mass or more and 1.2% by mass or less of Fe as an essential component. A portion of the Fe dissolves in the Al matrix and acts to improve the strength of the fin. The remainder of the Fe is dispersed in the Al matrix as crystallized precipitates and acts to improve the strength of the fin at room temperature and high temperatures. Furthermore, Fe has the effect of refining the crystal grains of the fin. By refining the crystal grains of the fin, it becomes easier for the molten liquid to seep out from the grain boundaries during brazing heating, thereby improving brazing performance.

[0022] Therefore, by setting the Fe content in the fin to 0.05 mass% or more, the strength and brazability of the fin can be improved. From the viewpoint of further improving the strength and brazability of the fin, the Fe content in the fin is preferably 0.07 mass% or more, more preferably 0.10 mass% or more, even more preferably 0.13 mass% or more, and particularly preferably 0.15 mass% or more. If the Fe content in the fin is less than 0.05 mass%, the above-mentioned effects may be reduced.

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

[0024] The preferred range of the Fe content in the fin can be any combination of the above-mentioned upper and lower limits of the Fe content. For example, the preferred range of the Fe content in the fin may be 0.07% by mass to 1.0% by mass, 0.10% by mass to 0.8% by mass, 0.13% by mass to 0.6% by mass, or 0.15% by mass to 0.4% by mass.

[0025] Cu The fin may contain Cu as an optional component in an amount of 0% by mass or more and 0.25% by mass or less. Like Fe, Cu in the fin dissolves in the Al matrix to improve the strength of the fin. Similarly to Fe, Cu also refines the crystal grains of the fin. However, if the Cu content is excessively high, the amount of molten liquid generated from the fin during brazing heating may become excessively large, which may result in a decrease in strength at high temperatures. Furthermore, in this case, the natural electrode potential of the fin may become nobler, which may result in a decrease in the sacrificial corrosion protection effect of the heat exchanger core.

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

[0027] The fin contains 0.3 mass % to 1.8 mass % of Mn as an essential component. Some of the Mn forms an Al-Mn-Si intermetallic compound in the fin, improving the strength of the fin through dispersion strengthening. The remainder of the Mn dissolves in the Al matrix, improving the strength of the fin through solid solution strengthening.

[0028] By setting the Mn content in the fin to 0.3% by mass or more, the strength of the fin can be improved by dispersion strengthening and solid solution strengthening. Furthermore, by setting the Mn content in the fin to 0.3% by mass or more, the growth of crystal grains in the fin during brazing heat can be promoted, and the occurrence of deformation or buckling of the fin during brazing heat can be suppressed. From the viewpoint of further enhancing the effect of Mn in improving the strength of the fin and suppressing deformation during brazing heat, 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 may be reduced, and the fin may be more likely to deform or buckle during brazing heat.

[0029] On the other hand, if the Mn content is excessively high, coarse intermetallic compounds are likely to be formed during the manufacturing process of the fin. If rolling is performed while these coarse intermetallic compounds are present, pinholes may be more likely to occur. Furthermore, if the Mn content is excessively high, intermetallic compounds containing Mn and Si are more likely to be formed, and the amount of Si that can participate in the formation of the molten liquid is likely to be insufficient. As a result, there is a risk of a decrease in brazability. From the viewpoint of easily avoiding these problems, the Mn content is set to 1.8 mass% or less. From the same viewpoint, the Mn content is more preferably 1.7 mass% or less, even more preferably 1.6 mass% or less, and particularly preferably 1.5 mass% or less.

[0030] The preferred range of the Mn content in the fin can be determined by any combination of the upper and lower limits of the Mn content described above. For example, the preferred range of the Mn content in the fin may be 0.5% by mass to 1.7% by mass, 0.7% by mass to 1.6% by mass, or 0.9% by mass to 1.5% by mass.

[0031] Zn: The fin contains 0.3 mass% or more and 5.0 mass% or less of Zn as an essential component. Zn in the fin increases the amount of melt generated from the fin and has the effect of making the natural electrode potential of the fin less noble. By setting the Zn content in the fin to 0.3 mass% or more, preferably 0.5 mass% or more, more preferably 0.7 mass% or more, even more preferably 0.9 mass% or more, and particularly preferably 1.0 mass% or more, the natural 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 mass%, the natural electrode potential Ef of the fin may become excessively noble, which may result in a decrease in the sacrificial corrosion protection effect.

[0032] On the other hand, if the Zn content in the fin is excessively high, the natural electrode potential Ef of the fin becomes excessively noble, which may result in a decrease in the self-corrosion resistance of the fin. Furthermore, if the Zn content in the fin is excessively high, cracks may easily occur during the fin manufacturing process, which may result in a decrease in productivity. These problems can be easily avoided by setting the Zn content in the fin 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] The preferred range of the Zn content in the fin can be determined by any combination of the upper and lower limits of the Zn content described above. For example, the preferred range of the Zn content in the fin may be 0.5% by mass to 3.5% by mass, 0.5% by mass to 3.0% by mass, 0.7% by mass to 2.5% by mass, 0.9% by mass to 2.0% by mass, 0.9% by mass to 1.5% by mass, or 1.0% by mass to 1.5% by mass.

[0034] In addition to the essential components and Al described above, the fin may 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 fin may contain, as optional components, one or more elements selected from the group consisting of Zr: more than 0% by mass and not more than 0.3% by mass, Cr: more than 0% by mass and not more than 0.3% by mass, Ti: more than 0% by mass and not more than 0.3% by mass, and V: more than 0% by mass and not more than 0.3% by mass. These elements have the effect of promoting the growth of crystal grains in the fin during brazing heating. Therefore, by setting the Zr content, Cr content, Ti content, and V content in the fin within the respective specific ranges, it is possible to more effectively suppress the occurrence of deformation and buckling of the fin during brazing heating.

[0036] Ni: The fin may contain Ni in an amount of more than 0% by mass and not more than 0.8% by mass as an optional component. Ni forms an intermetallic compound in the fin and acts to improve the strength of the fin after brazing by dispersion strengthening. On the other hand, an excessively high Ni content may result in a decrease in the self-corrosion resistance of the fin. By setting the Ni content in the fin to more than 0% by mass and not more than 0.8% by mass, the strength of the fin can be further improved while easily avoiding the above-mentioned problems.

[0037] The fin may contain, as an optional component, more than 0 mass % and 0.1 mass % or less of Mg. Mg is contained in the fin after brazing. ２ The magnesium content of the fins is 0.1% by mass or less, and the magnesium content of the fins is 0.1% by mass or less. .... The magnesium content of the fins is 0.1% by mass or less, and the magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is 0.1% by mass or less. The magnesium content of the fins is

[0038] In, Sn The fin may contain, as optional components, one or two elements selected from the group consisting of In: more than 0 mass% and not more than 0.03 mass% and Sn: more than 0 mass% and not more than 0.1 mass%. Like Zn, Sn and In have the effect of making the potential of the fin less noble. By setting the Sn content and In content in the fin within the specific ranges, the potential of the fin can be adjusted while avoiding a decrease in self-corrosion resistance, and the corrosion resistance of the aluminum structure can be further improved.

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

[0040] The fin may also have a chemical composition containing, for example, Si: 2.0 mass% or more and 3.0 mass% or less, Fe: 0.05 mass% or more and 0.6 mass% or less, Cu: 0 mass% or more and 0.05 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, and Ti: more than 0 mass% and 0.30 mass% or less, with the remainder being Al and unavoidable impurities.

[0041] The fin may also have a chemical composition containing, for example, Si: 2.0 mass% or more and 3.0 mass% or less, Fe: 0.05 mass% or more and 0.6 mass% or less, Cu: 0 mass% or more and 0.04 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, and Ti: more than 0 mass% and 0.30 mass% or less, with the remainder being Al and unavoidable impurities.

[0042] The fin may also have a chemical composition containing, for example, Si: 2.2 mass% or more and 2.7 mass% or less, Fe: 0.13 mass% or more and 0.6 mass% or less, Cu: 0 mass% or more and 0.04 mass% or less, Mn: 0.7 mass% or more and 1.6 mass% or less, Zn: 0.9 mass% or more and 2.0 mass% or less, and Ti: more than 0 mass% and 0.30 mass% or less, with the remainder being Al and unavoidable impurities.

[0043] Other Elements The fin may contain elements other than the essential and optional components described above, provided that the effects described above are not impaired. Examples of elements that may be contained in the fin include Sr, Na, and rare earth elements. These elements do not affect the effects described above and can be treated as inevitable impurities as long as the content of each element is 0.05% by mass or less and the total content is 0.15% by mass or less.

[0044] The fin manufacturing method can take various forms. For example, the fin may be a wrought material obtained by wrought processing, a forged material obtained by forging processing, or a casting obtained by casting.

[0045] From the viewpoint of improving brazability and strength, the fin is preferably a wrought material. Since the degree of processing in the manufacturing process of a wrought material is greater than that of a forged material or a cast material, second-phase particles are easily fragmented during the manufacturing process. Therefore, the fin 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, the brazability and strength can be improved in a balanced manner.

[0046] When producing the fins made of wrought material, continuous casting methods such as twin-roll continuous casting and twin-belt continuous casting can be used. Continuous casting methods can achieve a higher cooling rate during casting than DC casting. Therefore, a large number of fine second-phase particles, such as Si particles, can be formed in the fins. Dispersing a large number of fine second-phase particles in the fins increases the amount of molten liquid formed during brazing heating, thereby improving brazeability.

[0047] When the fin is produced by a twin-roll continuous casting and rolling method, the casting speed is preferably 0.5 m / min or more and 3 m / min or less. In the twin-roll continuous casting and rolling method, by setting the casting speed to 0.5 m / min or more, the cooling rate during casting can be sufficiently increased, and the second-phase particles in the fin can be easily refined. Furthermore, by setting the casting speed to 3 m / min or less, the molten metal can be sufficiently cooled and solidified during casting.

[0048] The temperature of the molten metal during casting is preferably 650°C or higher and 800°C or lower, and more preferably 680°C or higher and 750°C or lower. By setting the temperature of the molten metal to preferably 650°C or higher, more preferably 680°C or higher, it is possible to avoid the formation of large crystals in the molten metal. Furthermore, by setting the temperature of the molten metal to preferably 800°C or lower, more preferably 750°C or lower, it is possible to sufficiently cool and solidify the molten metal during casting.

[0049] The thickness of the rolled plate obtained by the continuous casting method is preferably 2 mm to 10 mm, more preferably 4 mm to 8 mm. By making the thickness of the rolled plate preferably 2 mm or more, more preferably 4 mm or more, a sound rolled plate can be stably produced. Furthermore, by making the thickness of the rolled plate preferably 10 mm or less, more preferably 8 mm or less, the rolled plate after casting can be easily wound onto a roll.

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

[0051] Furthermore, the fin made of a wrought material may be produced, for example, by a method in which an ingot is produced by DC casting and then the ingot is subjected 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 fin can be easily refined. Furthermore, 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 the slab is produced by DC casting, the thickness of the slab is preferably 600 mm or less, more preferably 500 mm or less, in which case the cooling rate during casting can be sufficiently increased to easily refine the second-phase particles in the fins.

[0053] After producing an ingot by DC casting, the ingot can be subjected to a wrought process to obtain a fin having a desired shape. For example, after producing a slab by DC casting, the slab can be rolled to obtain the fin made of a rolled plate having a desired thickness. The rolling process may be performed by appropriately combining hot rolling and cold rolling. Furthermore, between before the rolling process and after the completion of the rolling process, heat treatments such as homogenization and annealing can be performed as necessary to adjust the quality of the fin. The fin may have a temper represented by, for example, a temper symbol O, H1n, or H2n. From the viewpoint of suppressing erosion during brazing, the fin preferably has a temper represented by a temper symbol H1n or H2n.

[0054] Furthermore, after producing a billet by DC casting, the billet can be subjected to hot extrusion to obtain the fin made of an extruded material having a desired cross-sectional shape. If necessary, the billet may be subjected to homogenization treatment before hot extrusion. The billet is cast by a casting method such as hot top casting or GDC casting.

[0055] In the above-described manufacturing method, virgin aluminum ingots, intermediate alloys, and aluminum scrap can be used as the casting raw material during casting. Examples of aluminum scrap used as the casting raw material include 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 aluminum scrap is used as the casting raw material, the aluminum scrap may be melted as is. Alternatively, the size of the aluminum scrap may be adjusted by cutting or compressing it before melting. Furthermore, recycled aluminum ingots may be produced from the aluminum scrap, and then the recycled aluminum ingots may be used as the casting raw material.

[0056] [Tubes] The tubes in the heat exchanger core are made of an extruded aluminum alloy material containing more than 0.05 mass % and not more than 0.6 mass % of Cu.

[0057] The tubes in the heat exchanger core may be pipe materials with a flat cross-sectional shape, such as flat tubes or flat multi-hole tubes. More specifically, the tubes have a pair of flat wall portions arranged facing each other with a gap therebetween and a connecting wall portion connecting both ends of the flat wall portions in the width direction, and are configured to allow a heat transfer medium to flow through a heat transfer medium flow path surrounded by the flat wall portions and the connecting wall portions. The tubes may further have partition walls that divide the internal space surrounded by the flat wall portions and the connecting wall portions into multiple heat transfer medium flow paths. In the heat exchanger core, the flat wall portions of the tubes and the fins are joined by brazing.

[0058] The cross-sectional shape of the tube perpendicular to the longitudinal direction is not particularly limited and may be various shapes such as rectangular, elliptical, etc. The cross-sectional shape of the heat transfer medium flow path is also not particularly limited and may be various shapes such as circular, elliptical, oval, triangular, rectangular, etc.

[0059] The aluminum alloy extrusion material constituting the tube may have a chemical composition in which the Cu content is within the specified range. For example, the aluminum alloy extrusion material constituting the tube may have a chemical composition in which Cu: more than 0.05 mass% but not more than 0.6 mass%, with the remainder consisting of Al and unavoidable impurities. The Cu in the tube has the effect of improving the strength of the tube. On the other hand, Cu in the tube diffuses from the tube to the Zn spray coating and brazed joint during brazing, thereby increasing the natural electrode potential of these parts. Therefore, if the Cu content in the tube is excessively high, the balance of the natural electrode potentials of the various parts of the heat exchanger core may be disrupted, resulting in a decrease in corrosion resistance. Therefore, by setting the Cu content in the tube within the specified range, the strength of the tube can be increased while ensuring excellent corrosion resistance of the heat exchanger core.

[0060] Furthermore, the tube may contain one or more elements as optional components in addition to Cu as an essential component. For example, the aluminum alloy extrusion material constituting the tube may have a chemical composition that contains more than 0.05 mass % and not more than 0.6 mass % Cu, and further contains, as optional components, one or more elements selected from the group consisting of not more than 0.7 mass % Si, not more than 0.5 mass % Fe, not more than 1.2 mass % Mn, and not more than 0.3 mass % Ti, with the balance being Al and unavoidable impurities. The aluminum alloy extrusion material constituting the tube may have a chemical composition that contains Cu: more than 0.05% by mass and 0.6% by mass or less, and further contains, as optional components, one or more elements selected from the group consisting of Si: 0.05% by mass to 0.7% by mass, Fe: 0.05% by mass to 0.5% by mass, Mn: 0.05% by mass to 1.2% by mass, and Ti: 0.01% by mass to 0.3% by mass, with the balance being Al and unavoidable impurities.

[0061] 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 sprayed coating. The Zn coating as the sacrificial anode layer is formed, for example, by a Zn sprayed coating provided on the outer surface of the tube before brazing, which remains after brazing.

[0062] The sacrificial anode layer may be, for example, a Zn-enriched layer having a higher Zn concentration than the surrounding area. The Zn-enriched layer as the sacrificial anode layer is formed, for example, by the diffusion of Zn atoms contained in zinc vapor or a Zn spray coating from the outer surface of the tube toward the inside during brazing. When the sacrificial anode layer is a Zn-enriched layer, the boundary between the Zn-enriched layer and the layer adjacent to the Zn-enriched layer in the tube may not always be clear. Even in such a case, the aforementioned effect can be obtained as long as the natural electrode potential Ets on the surface of the Zn-enriched layer as the sacrificial anode layer satisfies the aforementioned condition.

[0063] [Natural Electrode Potential] The heat exchanger core satisfies all of the following four conditions: (1) the natural electrode potential of the inner surface of the tube is +50 mV or more 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 less 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 more and +150 mV or less 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 potential of the fin, the natural electrode potential of the fillet, and the natural electrode potential of the sacrificial anode layer and the natural electrode potential of the fin is 40 mV or less.

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

[0065] Such a relationship in natural electrode potential is difficult to achieve with a conventional heat exchanger core obtained using, for example, a brazing sheet or fins made of a single layer of aluminum material that does not have the ability to form a brazed joint. A heat exchanger core that satisfies all of the above four conditions can only be achieved by adjusting the chemical composition of the aluminum alloy that constitutes the fins and tubes to fall within the specific ranges specified in the manufacturing method, and then performing brazing in the presence of zinc vapor.

[0066] In the condition (1), by setting the natural electrode potential Eti of the inner surface of the tube to a potential 50 mV or more higher (i.e., more noble) than the natural electrode potential Ets of the sacrificial anode layer, the sacrificial anode layer functions 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, there is a risk that leakage of the heat transfer medium from the tube will occur early.

[0067] The condition (2) defines 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 setting the potential difference Ets-Ej between the sacrificial anode layer and the fillet to 100 mV or less, the potential balance between the sacrificial anode layer and the brazed joint can be optimized, and early loss of the brazed joint can be easily avoided. As a result, detachment of the fins from the heat exchanger core can be suppressed. If the potential difference Ets-Ej between the sacrificial anode layer and the fillet exceeds 100 mV, the brazed joint may be more susceptible to corrosion than other portions of the heat exchanger core, which may result in early loss of the brazed joint. As a result, the fins may be more likely to detach from the heat exchanger core.

[0068] The condition (3) 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 fin. By setting the potential difference Ets-Ef between the sacrificial anode layer and the fin within the specified range, both the fin 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 fin is less than -80 mV, the sacrificial anode layer is more likely to corrode earlier than the fin. As a result, the sacrificial anode layer may be lost early, and 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 fin exceeds 150 mV, the fin may be more likely to corrode earlier than the sacrificial anode layer, which may result in early loss of the fin.

[0069] In order to satisfy the condition (4), it is sufficient to satisfy either one 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 (that is, the natural electrode potential Ef of the fin is more base than the natural electrode potential Ej of the fillet); and (4-2) the natural electrode potential Ef of the fin is equal to or higher 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 equal to or higher than -40 mV and equal to or lower than 40 mV.

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

[0071] As described above, by satisfying all four of the above conditions for the natural electrode potentials of each portion of the heat exchanger core, the balance of the natural electrode potentials of each portion of the heat exchanger core can be adjusted within an optimal range. As a result, it is easy to avoid any portion of the sacrificial anode layer, the fin, or the brazed joint from corroding earlier than the other portions, thereby improving the corrosion resistance of the heat exchanger core as a whole. From the viewpoint of more reliably achieving this effect, it is preferable that the heat exchanger core satisfy the four conditions (1) to (3) and (4-1). From the same viewpoint, the natural electrode potential of the fin, when taken as the natural electrode potential of the fillet, is preferably −5 mV or less, more preferably −10 mV or less, and even more preferably −15 mV or less. That is, the potential difference Ef-Ej between the natural electrode potential Ej of the fin and the natural electrode potential Ef of the fillet is preferably −5 mV or less, more preferably −10 mV or less, and even more preferably −15 mV or less.

[0072] (Method for manufacturing heat exchanger core) The heat exchanger core is obtained by alternately stacking fins having a chemical composition containing Si: 2.0% by mass to 3.0% by mass, Fe: 0.05% by mass to 1.2% by mass, Cu: 0% by mass to 0.25% by mass, Mn: 0.3% by mass to 1.8% by mass, Zn: 0.3% by mass to 4.0% by mass, with the balance being Al and unavoidable impurities, and tubes made of an aluminum alloy extrusion material containing Cu: more than 0.05% by mass to 0.6% by mass, to form an assembly; heating the assembly; and brazing the assembly in an atmosphere containing zinc vapor to form the brazed joints between the fins and the tubes, and forming the sacrificial anode layer on the outer surfaces of the tubes.

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

[0074] The tubes used to fabricate the heat exchanger core have the same structure as the tubes in the brazed heat exchanger core, except that no sacrificial anode layer is formed on the outer surface. Therefore, the types, contents, and effects of elements contained in the tubes before brazing can be appropriately referred to the description of the tubes in the brazed heat exchanger core.

[0075] In the method for manufacturing a heat exchanger core, the tubes and fins are alternately stacked to form an assembly, and then the assembly is heated in an atmosphere containing zinc vapor to perform brazing. More specifically, the brazing atmosphere may be, for example, a non-oxidizing gas atmosphere containing zinc vapor. Examples of the non-oxidizing gas that can be used include nitrogen and argon. Alternatively, the brazing atmosphere may be a reduced-pressure atmosphere containing zinc vapor.

[0076] The heating temperature when brazing the assembly is preferably set so that the liquid phase ratio of the fins, i.e., the ratio of the mass of the molten liquid generated from the fins to the mass of the fins before brazing, is more preferably set to more than 5 mass% and not more than 35 mass%, and more preferably set to be 7 mass% or more and not more than 25 mass%. By setting the liquid phase ratio of the fins during heating within the above specific range, a sufficient amount of molten liquid can be generated from the fins and a brazed joint can be easily formed between the fins and the tube while suppressing a decrease in the strength of the fins during heating.

[0077] Furthermore, the holding time of the heating temperature when brazing the assembly is preferably set so that the time required for the liquid phase ratio of the fin to reach 5% by mass or more is 30 seconds or more and 3,600 seconds or less, more preferably 60 seconds or more and 1,800 seconds or less. By setting the holding time during brazing within the specific range, the molten liquid generated from the fin can be sufficiently filled between the fin and the tube while suppressing a decrease in the strength of the fin during heating. Note that, when joining the fin and the tube, the molten liquid is generated from the entire surface of the fin, so the length of the holding time can be set regardless of the area of ​​the brazed joint formed between the fin and the tube.

[0078] More specifically, for example, the heating temperature in brazing can be appropriately set within a range of 580°C or higher and 620°C or lower. Furthermore, the holding time at the heating temperature can be appropriately set within a range of, for example, 0 minutes or higher and 10 minutes or lower, preferably 30 seconds or higher and 5 minutes or lower. Here, the holding time refers to the time elapsed from the point at which the heating temperature reaches the desired temperature. When the holding time at the heating temperature is 0 minutes, heating can be immediately terminated and cooling of the heat exchanger core can be started after the heating temperature reaches the desired temperature.

[0079] The liquid phase ratio of the fin can be determined based on an equilibrium diagram at a desired temperature and the lever rule. A publicly known equilibrium diagram may be used as the equilibrium diagram used to calculate the liquid phase ratio, or an equilibrium diagram created using software for calculating equilibrium diagrams may be used. Examples of this type of software that can be used include the thermodynamic calculation system "Thermo-Calc (registered trademark)" manufactured by Thermo-Calc Software AB.

[0080] Alternatively, before brazing, a flux may be placed in advance on the portion of the assembly where the brazing joint is to be formed, and then the assembly may be heated to perform brazing. ４ , K. ２ AlF ５ , K. ２ AlF ５ ・H ２ O.K. ３ AlF ６ , AlF ３ , KZnF ３ and K. ２ SiF ６ Fluoride-based fluxes such as Cs ３ AlF ６ , CsAlF ４ ・2H ２ O, Cs ２ AlF ５ ・H ２ Compounds used as fluxes for brazing aluminum, such as cesium-based fluxes such as O and chloride-based fluxes, can be used.

[0081] In this manufacturing method, when the assembly is heated, a small amount of melt is generated from the fins, and this melt collects at the contact points between the fins and the tubes due to surface tension, forming a brazed joint with a fillet between the fins and the tubes.

[0082] In the manufacturing method, brazing is performed in an atmosphere containing zinc vapor. Thus, by performing brazing in the presence of zinc vapor, a sacrificial anode layer can be formed on the surface of the tube. Furthermore, Zn atoms in the zinc vapor can easily dissolve into the molten liquid generated from the fin during the brazing process. Therefore, the Zn atoms dissolve into the molten liquid collected at the contact point between the fin and the tube, thereby appropriately reducing the natural electrode potential of the brazed joint. Furthermore, because the amount of molten liquid generated from the fin is very small, the molten liquid present at a position away from the contact point between the fin and the tube remains on the fin rather than being drawn into the contact point between the fin and the tube. Therefore, the Zn atoms dissolved in the molten liquid of the fin easily diffuse into the interior of the fin, thereby appropriately reducing the natural electrode potential of the fin.

[0083] As described above, by using fins made of an aluminum alloy having the specific chemical composition 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 the brazed joint can be appropriately reduced, and a sacrificial anode layer can be easily formed on the outer surface of the tube, thereby making it easier to obtain the heat exchanger core.

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

[0085] The outer surfaces of the tubes used to fabricate the heat exchanger core are preferably provided with a Zn sprayed coating. By assembling the assembly using the tubes with the Zn sprayed coating on their outer surfaces and then performing brazing, the Zn atoms in the Zn sprayed coating can be diffused into the tubes, making it easier to form a sacrificial anode layer on the outer surfaces of the tubes. Furthermore, the Zn sprayed coating can generate zinc vapor when heated during brazing. When this zinc vapor comes into contact with the fins and brazed joints, it can lower the natural electrode potential of the fins and brazed joints. As a result, the natural electrode potential of each portion of the brazed heat exchanger core can be more easily adjusted to fall within the specified range.

[0086] The amount of Zn in the Zn thermal spray coating formed on the outer surface of the tube is not particularly limited, but is, for example, 3 g / m ２ 9g / m or more ２ It can be set appropriately from the following ranges.

[0087] In the manufacturing method, the Zn content in the fins after brazing is preferably higher by 0.1 mass % or more than the Zn content in the fins before brazing, which makes it easier to adjust the natural electrode potential of each portion of the heat exchanger core after brazing to fall within the specified range.

[0088] The difference between the Zn content in the fin after brazing and the Zn content in the fin before brazing can be adjusted, for example, by the concentration of zinc vapor in the brazing atmosphere. For example, if it is desired to increase the Zn content in the fin 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, if it is desired 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 spray coating provided on the outer surface of the tube can be increased.

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

[0090] The tube 3 is made of an extruded aluminum alloy containing more than 0.05% by mass and 0.6% by mass or less of Cu. As shown in Figure 2, a sacrificial anode layer 31 having a lower natural electrode potential than the inner surface of the tube 3 is formed on the outer surface of the tube 3. The heat exchanger core 1 also satisfies the following four conditions: (1) the natural electrode potential of the inner surface of the tube 3 is +50 mV or more 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 +100 mV or less when the natural electrode potential of the fillet at the brazed joint 4 is used as a reference; (3) the natural electrode potential of the sacrificial anode layer 31 is −80 mV or more and +150 mV or less 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 potential of the fin 2, the natural electrode potential of the fillet, and the natural electrode potential of the sacrificial anode layer 31 and the natural electrode potential of the fin is 40 mV or less.

[0091] As shown in FIG. 1 , the heat exchanger core 1 of this example has multiple fins 2 and multiple tubes 3. The fins 2 and tubes 3 are stacked alternately, forming a core for a so-called parallel-flow heat exchanger. The fins 2 in the heat exchanger core 1 of this example are formed into a corrugated shape by press working. As shown in FIG. 2 , the fins 2 are formed of multiple U-shaped fin crests 21 and fin intermediate sections 22 connecting the fin crests 21. As shown in FIG. 3 , the tubes 3 are formed of extruded multi-hole tubes each including a pair of flat wall sections 32 spaced apart from each other, a connecting wall section 33 connecting both ends of the flat wall sections 32 in the width direction, and a partition wall section 35 dividing the internal space surrounded by the flat wall sections 32 and the connecting wall section 33 into multiple heat transfer medium flow paths 34. As shown in FIG. 2 , the fin crests 21 of the fins 2 and the flat wall sections 32 of the tubes 3 are joined via brazing joints 4.

[0092] 1 , the heat exchanger core 1 of this example may include a header tank 11 attached to both ends of the plurality of tubes 3, and a side plate 12 joined to the outermost fin 2 in the stacking direction among 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 paths 34 of the tubes 3. The header tank 11 can distribute the heat transfer medium therein to the plurality of tubes 3, or can merge the heat transfer medium led out of the tubes 3 in the header tank 11.

[0093] Although not shown in the figure, the header tank 11 and the tubes 3 are joined via brazing. There are no particular limitations on the method for joining the header tank 11 and the tubes 3, and the brazing joint may be formed by a known method. For example, a method can be employed in which the header tank 11 before brazing is formed from a brazing sheet including a core material and a brazing material laminated on at least one surface of the core material, and the brazing joint 4 is 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 tubes 3, and the brazing joint may be formed by this brazing material.

[0094] The side plate 12 and the fin 2 are joined together via a brazing joint 4 .

[0095] The heat exchanger core 1 of this example is manufactured, for example, as follows. First, fins 2 having a chemical composition containing 2.0 to 3.0% by mass of Si, 0.05 to 1.2% by mass of Fe, 0 to 0.25% by mass of Cu, 0.3 to 1.8% by mass of Mn, and 0.3 to 4.0% by mass of Zn, with the remainder being Al and unavoidable impurities, are alternately stacked to form a laminate. Header tanks 11 are attached to both ends of the tubes 3 in the laminate, and side plates 12 are abutted against the outermost fins 2 of the multiple fins 2 to obtain an assembly.

[0096] Next, the assembly is heated and brazed in an atmosphere containing zinc vapor, thereby obtaining the heat exchanger core 1 shown in FIG.

[0097] Next, the effects of this embodiment will be described. The fins 2 in the heat exchanger core 1 of this embodiment are made of an aluminum alloy having the specific chemical composition. By using at least the fins 2 having the specific chemical composition, it is possible to obtain a heat exchanger core 1 in which the natural electrode potentials of each portion satisfy all of the four conditions described above. By setting the natural electrode potentials of each portion of the heat exchanger core 1 to the above-mentioned configuration, the corrosion resistance of the heat exchanger core 1 can be improved.

[0098] In addition, in the manufacturing method of the heat exchanger core 1, the fins 2 having the specific chemical composition are combined with the tubes 3 to form an assembly, 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. Furthermore, 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 the zinc vapor, it is possible to easily obtain a heat exchanger core 1 in which the natural electrode potential of each part satisfies all of the four conditions described above.

[0099] (Experimental Example) In this example, an example of evaluating corrosion resistance will be described using a mini-core specimen S1 simulating a heat exchanger core 1. Note that, among the symbols used in this example, the same symbols as those used in the previous examples indicate the same components, etc. as those in the previous examples.

[0100] As shown in Fig. 4, the mini-core 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 abuts against 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] Specifically, the tube 3 used to prepare the mini-core specimen S1 is a flat multi-hole tube made of an aluminum alloy extrusion material having the chemical composition shown in Table 1. In Table 1, "Bal." is a symbol indicating a remainder. The tube 3 has a width of 14 mm and a length of 40 mm, and the thicknesses of the flat wall portion 32, the connecting wall portion 33, and the partition wall portion 35 are all 0.35 mm. A Zn sprayed coating is formed in advance on the outer surface of the tube 3. The Zn atom deposition amount in the Zn sprayed coating is approximately 8 g / m ２ is.

[0102] Specifically, the fins 2 used to fabricate the mini-core specimen S1 are 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 crests 21 is 3 mm, and the height of the fins 2 is 10 mm. Of the two tubes 3, the number of fin crests 21 that abut on the first tube 3a is 11, and the number of fin crests 21 that abut on the second tube 3b is 12.

[0103] To prepare the mini-core specimen S1, first, the tube 3 and the fin 2 are stacked, and then a flux is applied to the contact area between the tube 3 and the fin 2 to prepare an assembly. Ten of these assemblies are placed in a heating furnace, and zinc is placed around the assemblies. Furthermore, a cover is placed over the ten assemblies and the zinc to allow zinc vapor to remain around the assemblies. The assemblies are then heated in an inert gas atmosphere, and the assemblies are brazed in the presence of zinc vapor while generating zinc vapor from the zinc and Zn spray coating. The mini-core specimen S1 can be obtained by the above steps.

[0104] The Zn content in the fin 2 of the mini-core specimen S1 obtained in this manner is higher than the Zn content in the fin 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 fin 2 after brazing can be set to 1.75 mass%, which is 0.27 mass% higher than the Zn content in the fin 2 before brazing. Note that the Zn content in the fin 2 after brazing can be measured using, for example, an electron probe microanalyzer (i.e., EPMA). When measuring the Zn content in the fin 2 using EPMA, specifically, line analysis of the surface of the fin 2 at the center of the mini-core specimen S1 is performed, 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 portion of the Minicore specimen S1. The Minicore specimen R1 shown in Table 2 is a specimen for comparison with the Minicore specimen S1. The Minicore specimen R1 has the same configuration as the Minicore specimen S1, except that the fin 2 is a double-sided brazing sheet in which a brazing filler metal is laminated on both sides of a core material. The chemical compositions of the core material and brazing filler metal in the fin 2 of the Minicore specimen R1 are 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 filler metal is 10%. The Minicore specimen R1 was produced in the same manner as the Minicore specimen S1, except that a double-sided brazing sheet was used instead of the fin 2 made of a single layer of aluminum alloy. The Zn content in the fin of the Minicore specimen R1 after brazing was 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 the corrosion resistance shown in Table 2 are as follows.

[0107] Natural electrode potential Ets of the sacrificial anode layer 31 The fins 2 were removed from the brazed mini-core specimens S1 and R1, and the first tube 3a was removed. In the sacrificial anode layer 31 of this tube 3a, a region between any one brazed joint 4 and the adjacent brazed joint 4 was identified, and this region was designated as the potential measurement region. In other words, the potential measurement region was the region facing one fin pitch on the outer surface of the first tube 3a.

[0108] After the potential measurement area is identified as described above, the area other than the potential measurement area is covered with a sealant. The natural electrode potential of the potential measurement area is then measured as follows. A measuring device 5 shown in FIG. 5 is used to measure the natural electrode potential. The measuring device 5 includes a first container 51 for containing a solution in which the tube 3 is immersed, a second container 52 for containing a solution in which the reference electrode 54 is immersed, a salt bridge 53 for electrically connecting the solution in the first container 51 with 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. Note that FIG. 5 shows a schematic shape of the tube 3.

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

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

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

[0112] Natural electrode potential Eti of the inner surface of the tube 3 The fins 2 were removed from the brazed mini-core specimens S1 and R1, and the first tube 3a was removed. The flat wall portion 32a, connecting wall portion 33, and partition wall portion 35, which are not joined to the fin tops 21, were then faced from this tube 3a to expose the inner surface of the flat wall portion 32b (see FIG. 4) joined to the fin tops 21. A potential measurement area was set on this inner surface, and the area other than the potential measurement area was covered with a sealant. The natural electrode potential of the potential measurement area was then measured using a method similar to that for the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained was designated as the natural electrode potential Eti of the inner surface of the tube 3.

[0113] Natural electrode potential Ef of fin 2 The first tube 3a and the fin top 21 joined to the first tube 3a are removed from the brazed mini-core 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 a sealant. Thereafter, the natural electrode potential of the potential measurement area is measured using a method similar to that for the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained is defined as the natural electrode potential Ef of the fin 2.

[0114] Fillet Natural Electrode Potential Ej: The fins 2 are removed from the brazed mini-core specimens S1 and R1, and the first tube 3a is removed. Next, the fin tops 21 remaining on the first tube 3a are chamfered so that both the fillet of the brazed joint 4 and the fin tops 21 are exposed on a common plane. A potential measurement area is then set on the exposed fillet, and the area other than the potential measurement area is covered with a sealant. The natural electrode potential of the potential measurement area is then measured using a method similar to that for the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained is designated as the fillet natural electrode potential Ej.

[0115] Corrosion Resistance After coating the end faces of the tubes 3, the connecting wall portions 33 of the tubes 3, and the flat wall portions 32a not joined to the fins 2 of the mini-core specimens S1 and R1 obtained by the method described above with a sealant, a SWAAT test is carried out using a method in accordance with ASTM-G85-A3. The test period is either 20 days or 40 days. After the test, the mini-core specimens S1 and R1 are washed with acid, and the corrosion resistance is evaluated based on whether the tubes 3 are penetrated and whether the fins 2 are peeled off from the tubes 3.

[0116] The symbols in the "Fin Peeling" column in Table 2 have the following meanings: A: All fin tips are bonded to the tube B: Some fin tips are peeled off from the tube C: All fin tips are peeled off from the tube

[0117] The symbols shown in the "Tube penetration" column in Table 2 are as follows: A: No corrosion has penetrated the tube. B: Corrosion has penetrated the tube.

[0118]

[0119]

[0120] As shown in Table 1, the mini-core specimen S1 has a single-layer fin 2 made of an aluminum alloy having the specific chemical composition 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 specimen S1 satisfy all four of the above conditions. Therefore, the mini-core specimen S1 can avoid early loss of the sacrificial anode layer 31, the fin 2, or the brazed joint 4, and has excellent corrosion resistance.

[0121] On the other hand, the mini-core specimen R1 having fins made of double-sided brazing sheets had inferior corrosion resistance compared to the mini-core specimen S1, and the fins peeled off from the tube 3 after 20 days of SWAAT testing. Furthermore, after 40 days of SWAAT testing of the mini-core specimen R1, the fins completely peeled off from the tube 3, and corrosion penetrated the tube 3. The following reasons are considered to be the reasons for this: When a brazing sheet is used as a fin, the fluidity of the molten brazing filler metal formed by melting the brazing filler metal is high, and therefore, the molten brazing filler metal containing Zn atoms is thought to easily migrate to the fillet of the brazed joint. This is thought to result in an excessively high Zn content in the brazed joint, which tends to result in an excessively low natural electrode potential Ej of the brazed joint.

[0122] Furthermore, it is believed that the easy flow of molten brazing filler metal during brazing can lead to insufficient diffusion of Zn from the molten brazing filler metal to the core material, which in turn leads to an insufficient effect of the sacrificial anode layer formed on the surface of the fin after brazing, making it easier for corrosion to progress to the inside of the tube.

[0123] The above describes aspects of the heat exchanger core and its manufacturing method according to the present invention based on examples and experimental examples, but the specific aspects of the heat exchanger core and its manufacturing method according to the present invention are not limited to the aspects of the examples and experimental examples, and the configuration can be changed as appropriate within the scope that does not detract from the spirit of the present invention.

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

[0125] [1] A fin having a chemical composition containing Si: 2.0% by mass or more and 3.0% by mass or less, Fe: 0.05% by mass or more and 1.2% by mass or less, Cu: 0% by mass or more and 0.25% by mass or less, Mn: 0.3% by mass or more and 1.8% by mass or less, Zn: 0.3% by mass or more and 5.0% by mass or less, with the balance being Al and unavoidable impurities; a tube made of an aluminum alloy extrusion material containing Cu: more than 0.05% by mass and 0.6% by mass or less; and a brazing joint joining the fin and the tube, wherein a sacrificial anode layer having a lower natural electrode potential than that of the inner surface of the tube is formed on an outer surface of the tube, (1) the natural electrode potential of the inner surface of the tube is +50 mV or more 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 less 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 more and +150 mV or less 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 potential of the fin, the natural electrode potential of the fillet, and the natural electrode potential of the sacrificial anode layer and the natural electrode potential of the fin is 40 mV or less.

[0126] [2] The heat exchanger core described in [1], wherein the fin further contains one or more elements selected from the group consisting of Zr: more than 0% by mass and not more than 0.3% by mass, Cr: more than 0% by mass and not more than 0.3% by mass, Ti: more than 0% by mass and not more than 0.3% by mass, V: more than 0% by mass and not more than 0.3% by mass, Ni: more than 0% by mass and not more than 0.8% by mass, Mg: more than 0% by mass and not more than 0.1% by mass, In: more than 0% by mass and not more than 0.03% by mass, and Sn: more than 0% by mass and not more than 0.1% by mass.

[0127] The method for manufacturing the heat exchanger core may take the following aspects [3] to [6].

[0128] [3] A method for manufacturing a heat exchanger core according to [1] or [2], comprising: assembling an assembly by alternately stacking fins having a chemical composition containing Si: 2.0% by mass or more and 3.0% by mass or less, Fe: 0.05% by mass or more and 1.2% by mass or less, Cu: 0% by mass or more and 0.25% by mass or less, Mn: 0.3% by mass or more and 1.8% by mass or less, Zn: 0.3% by mass or more and 4.0% by mass or less, with the balance being Al and unavoidable impurities, and tubes made of an aluminum alloy extrusion material containing Cu: more than 0.05% by mass and 0.6% by mass or less; heating the assembly and brazing the assembly in an atmosphere containing zinc vapor, thereby forming the brazed joints between the fins and the tubes, and forming the sacrificial anode layers on the outer surfaces of the tubes.

[0129] [4] The method for manufacturing a heat exchanger core described in [3], wherein the fin further contains one or more elements selected from the group consisting of Zr: more than 0 mass% and not more than 0.3 mass%, Cr: more than 0 mass% and not more than 0.3 mass%, Ti: more than 0 mass% and not more than 0.3 mass%, V: more than 0 mass% and not more than 0.3 mass%, Ni: more than 0 mass% and not more than 0.8 mass%, Mg: more than 0 mass% and not more than 0.1 mass%, In: more than 0 mass% and not more than 0.03 mass%, and Sn: more than 0 mass% and not more than 0.1 mass%.

[0130] [5] The method for manufacturing a heat exchanger core according to [3] or [4], wherein the assembly is assembled using the tubes having a Zn thermal spray coating on their outer surfaces. [6] The method for manufacturing a heat exchanger core according to [3] or [4], wherein the Zn content in the fins after brazing is 0.1 mass % or more higher than the Zn content in the fins before brazing.

Claims

1. A fin having a chemical composition containing Si: 2.0% by mass or more and 3.0% by mass or less, Fe: 0.05% by mass or more and 1.2% by mass or less, Cu: 0% by mass or more and 0.25% by mass or less, Mn: 0.3% by mass or more and 1.8% by mass or less, Zn: 0.3% by mass or more and 5.0% by mass or less, with the balance being Al and unavoidable impurities; a tube made of an aluminum alloy extrusion material containing Cu: more than 0.05% by mass and 0.6% by mass or less; and a brazing joint for joining the fin and the tube, wherein a sacrificial anode layer having a lower natural electrode potential than that of the inner surface of the tube is formed on the outer surface of the tube, (1) a natural electrode potential of the inner surface of the tube is +50 mV or more when the natural electrode potential of the sacrificial anode layer is used as a reference; (2) a natural electrode potential of the sacrificial anode layer is +100 mV or less when the natural electrode potential of the fillet in the brazed joint is used as a reference; (3) a natural electrode potential of the sacrificial anode layer is -80 mV or more and +150 mV or less 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 potential of the fin, the natural electrode potential of the fillet and the natural electrode potential of the sacrificial anode layer and the natural electrode potential of the fin is 40 mV or less.

2. The heat exchanger core of claim 1, wherein the fin further contains one or more elements selected from the group consisting of Zr: more than 0 mass% and not more than 0.3 mass%, Cr: more than 0 mass% and not more than 0.3 mass%, Ti: more than 0 mass% and not more than 0.3 mass%, V: more than 0 mass% and not more than 0.3 mass%, Ni: more than 0 mass% and not more than 0.8 mass%, Mg: more than 0 mass% and not more than 0.1 mass%, In: more than 0 mass% and not more than 0.03 mass%, and Sn: more than 0 mass% and not more than 0.1 mass%.

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

4. The method for manufacturing a heat exchanger core as described in claim 3, wherein the fin further contains one or more elements selected from the group consisting of Zr: more than 0 mass% and not more than 0.3 mass%, Cr: more than 0 mass% and not more than 0.3 mass%, Ti: more than 0 mass% and not more than 0.3 mass%, V: more than 0 mass% and not more than 0.3 mass%, Ni: more than 0 mass% and not more than 0.8 mass%, Mg: more than 0 mass% and not more than 0.1 mass%, In: more than 0 mass% and not more than 0.03 mass%, and Sn: more than 0 mass% and not more than 0.1 mass%.

5. A method for manufacturing a heat exchanger core according to claim 3 or 4, wherein the assembly is assembled using the tubes having a Zn thermal spray coating on their outer surfaces.

6. A method for manufacturing a heat exchanger core described in any one of claims 3 to 5, wherein the Zn content in the fins after brazing is 0.1 mass% or more higher than the Zn content in the fins before brazing.