Heat exchanger core, its manufacturing method and aluminum alloy material for fins

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 technology]

[0002] For example, parallel-flow heat exchangers made of aluminum alloys are used in radiators of automobiles and condensers and evaporators of air conditioners installed in automobiles. This type of heat exchanger has a heat exchanger core including a plurality of tubes and a plurality of 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] Conventionally, brazing sheets having a brazing material provided on at least one surface of a core material have been widely used as fins for heat exchanger cores, but in recent years, it has been proposed to use single-layer aluminum alloy materials as fins, which have the function of forming a brazing joint with a mating material.

[0004] For example, Patent Document 1 describes a fin material for heat exchangers that is 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 that has a thermal bonding function in a single layer 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] Patent No. 5698416 Summary of the Invention [Problem to be solved by the invention]

[0006] As a method for improving the corrosion resistance of a heat exchanger core, a method is known in which a Zn spray coating is formed on the outer surface of a tube to make the outer surface of the tube function as a sacrificial anode for the inside of the tube. However, when a tube provided with a 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 may 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 manufacturing method thereof. [Means for solving the problem]

[0008] One aspect of the present invention is a fin having a chemical composition containing 2.0 mass% or more and 3.0 mass% or less of Si (silicon), 0.05 mass% or more and 1.2 mass% or less of Fe (iron), 0 mass% or more and 0.25 mass% or less of Cu (copper), 0.3 mass% or more and 1.8 mass% or less of Mn (manganese), 0.3 mass% or more and 5.0 mass% or less of Zn (zinc), with the balance being Al (aluminum) and unavoidable impurities; A tube made of an aluminum alloy extrusion material containing Cu: more than 0.05% by mass and not more than 0.6% by mass; and a brazing joint for joining the fin and the tube, a sacrificial anode layer having a lower natural electrode potential than an 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 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 the steps of: 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, are alternately stacked to form an assembly; The method for manufacturing a heat exchanger core includes 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. Effect of the Invention

[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 heat exchanger core can adjust 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 to satisfy all of the four conditions that were difficult to achieve with conventional heat exchanger cores. By adjusting the natural electrode potentials of each part of the heat exchanger core to the above-mentioned state, the corrosion resistance of the heat exchanger core can be improved.

[0011] In the method for manufacturing the heat exchanger core, the fins having the specific chemical composition are assembled with the tubes to prepare 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, the natural electrode potential of each part of the heat exchanger core can be adjusted to satisfy all of the four conditions described above, which could not be achieved with conventional heat exchanger cores. As a result, a heat exchanger core with excellent corrosion resistance can be easily obtained.

[0013] As described above, according to the above-described aspects, it is possible to provide a heat exchanger core having excellent corrosion resistance and a manufacturing method thereof. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a plan view of a heat exchanger core according to an embodiment. [Diagram 2] FIG. 2 is a partially enlarged view of FIG. [Diagram 3] FIG. 3 is a cross-sectional view of a tube in the embodiment. [Figure 4]FIG. 4 is a perspective view of a mini-core specimen in an experimental example. [Diagram 5] FIG. 5 is an explanatory diagram of a measuring device for natural electrode potential in the experimental examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] (Heat exchanger core) The heat exchanger core has fins and tubes. In addition, 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 type heat exchanger in which the fins and the tubes are alternately stacked. In addition to the fins and the tubes, the heat exchanger core may further include a side plate joined to the outermost fin of the plurality of fins, headers attached to both ends of the tubes, and the like.

[0016] 〔fin〕 The fins of the heat exchanger core are composed of a single layer of aluminum alloy 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, and the remainder being Al and unavoidable impurities. The thickness of the fin can be appropriately set within a range of, for example, 0.04 mm to 0.15 mm.

[0017] The chemical composition of the fins and the reasons for their limitations will be described 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 making the Si content in the fin 2.0% by mass or more, a molten liquid containing Al and Si can be generated by brazing heat, and a brazing 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, and the brazing property can be further improved. If the Si content is less than 2.0% by mass, the amount of molten liquid generated by brazing heat is insufficient, which may lead to deterioration of brazing property.

[0019] On the other hand, if the Si content is excessively high, the amount of melting of the fins during brazing heating may increase, leading to a risk of 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 viewpoint, the Si content is preferably set to 2.9 mass% or less, more preferably set to 2.8 mass% or less, and even more preferably set to 2.7 mass% or less.

[0020] In determining the preferred range of the Si content in the fin, the above-mentioned upper and lower limits of the Si content can be combined arbitrarily. 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 part of Fe dissolves in the Al matrix and acts to improve the strength of the fin. The remainder of Fe is dispersed in the Al matrix as crystallized matter and acts to improve the strength of the fin at room temperature and high temperature. 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 crystal grain boundaries during brazing heating, and the brazing property can be improved.

[0022] Therefore, by making the Fe content in the fin 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 lead to 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] In determining the preferred range of the Fe content in the fin, the above-mentioned upper and lower limits of the Fe content can be combined arbitrarily. 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 in an amount of 0% by mass or more and 0.25% by mass or less as an optional component. Cu in the fin has the effect of improving the strength of the fin by dissolving in the Al matrix in the same manner as Fe. Also, Cu has the effect of refining the crystal grains of the fin in the same manner as Fe. However, if the Cu content is excessively high, the amount of molten liquid generated from the fin during brazing heating becomes excessively large, which may lead to a decrease in strength at high temperatures. In addition, in this case, the natural electrode potential of the fin becomes noble, which may lead to a decrease in the sacrificial anticorrosion effect in 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 anticorrosion 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] Mn The fin contains 0.3 mass% to 1.8 mass% Mn as an essential component. A part of the Mn forms an Al-Mn-Si intermetallic compound in the fin, and has the effect of improving the strength of the fin by dispersion strengthening. The remaining Mn dissolves in the Al matrix, and has the effect of improving the strength of the fin by solid solution strengthening.

[0028] By making the Mn content in the fin 0.3% by mass or more, the strength of the fin can be improved by dispersion strengthening and solid solution strengthening. In addition, by making the Mn content in the fin 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 and 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, 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 effect is reduced, and the fin may be easily deformed or buckled 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 including these coarse intermetallic compounds, pinholes may be likely to be generated. In addition, if the Mn content is excessively high, intermetallic compounds containing Mn and Si are 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 causing a decrease in brazing properties. 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, further preferably 1.6 mass% or less, and particularly preferably 1.5 mass% or less.

[0030] In determining the preferred range of the Mn content in the fin, the above-mentioned upper and lower limits of the Mn content can be combined arbitrarily. 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. The 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 making the Zn content in the fin 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 becomes excessively noble, which may lead to a decrease in the sacrificial anticorrosion effect.

[0032] On the other hand, if the Zn content in the fin is too high, the natural electrode potential Ef of the fin becomes too noble, which may lead to a decrease in the self-corrosion resistance of the fin. Also, if the Zn content in the fin is too high, cracks may easily occur during the manufacturing process of the fin, which may lead to 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] In determining the preferred range of the Zn content in the fin, the above-mentioned upper and lower limits of the Zn content can be combined arbitrarily. 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 elements 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 an optional component, 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 specific ranges, respectively, 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, which is 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 has the effect of improving the strength of the fin after brazing by dispersion strengthening. On the other hand, if the Ni content is excessively high, the self-corrosion resistance of the fin may be reduced. 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] Magnesium The fin may contain Mg, which is an optional component, in an amount of more than 0% by mass and not more than 0.1% by mass. Mg forms Mg2Si in the fin after brazing, and has the effect of improving the strength of the fin by age hardening. On the other hand, if the Mg content is excessively high, when brazing is performed using a flux, Mg and the flux may react, which may lead to a decrease in brazeability. By setting the Mg content to more than 0% by mass and not more than 0.1% by mass, it is possible to easily avoid such problems and further improve the strength of the fin.

[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 0.03 mass% or less and Sn: more than 0 mass% and 0.1 mass% or less. 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 range, it is possible to adjust the potential of the fin while avoiding a decrease in self-corrosion resistance, and to further improve the corrosion resistance of the aluminum structure.

[0039] The fin may contain one or more of the optional components described above. For example, the fin may have 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 5.0% by mass, Ti: more than 0% by mass to 0.30% by mass, and 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 components 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. If the content of each of these elements is 0.05 mass% or less and the total content is 0.15 mass% or less, these elements do not affect the effects described above and can be treated as unavoidable impurities.

[0044] Fin manufacturing method The manufacturing method of the fin may 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 brazeability and strength, the fin is preferably a wrought material. The wrought material is processed to a greater extent in the manufacturing process than forged materials and castings, and therefore second phase particles are easily broken down in the manufacturing process. Therefore, the fin made of the wrought material can increase the number of Si particles, Si-based intermetallic compounds, Al-based intermetallic compounds, etc. dispersed in the Al matrix. As a result, the brazeability and strength can be improved in a well-balanced manner.

[0046] When producing the fin made of a wrought material, a continuous casting method such as a twin-roll continuous casting rolling method or a twin-belt continuous casting method can be used. The continuous casting method can increase the cooling rate during casting compared to the DC casting method. Therefore, a large number of fine second phase particles such as Si particles can be formed in the fin. By dispersing a large number of fine second phase particles in the fin, the amount of molten liquid formed during brazing heating can be increased, and brazing properties can be improved.

[0047] When the fin is produced by a twin-roll continuous casting and rolling method, the casting speed is preferably 0.5 m / min to 3 m / min. 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. In addition, 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 650° C. or higher, and more preferably 680° C. or higher, it is possible to avoid the formation of large crystals in the molten metal. By setting the temperature of the molten metal to 800° C. or lower, and 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 casting is preferably 2 mm or more and 10 mm or less, and more preferably 4 mm or more and 8 mm or less. 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. In addition, 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 around a roll.

[0050] The rolled plate obtained by the continuous casting method may be used as the fin as it is. The fin having the desired thickness and temper may be obtained by adjusting the thickness and temper of the rolled plate by cold rolling, heat treatment, etc. The fin may have a temper represented by temper symbol 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 symbol H1n or H2n.

[0051] The fin made of a wrought material may be produced, for example, by a method of producing an ingot by DC casting and then performing a wrought process on the ingot. When producing an ingot by DC casting, the casting speed is preferably 20 mm / min to 100 mm / min, more preferably 30 mm / min to 80 mm / min. In DC casting, the casting speed is preferably 20 mm / min or more, more preferably 30 mm / min or more, so that the cooling rate during casting can be sufficiently increased and the second phase particles in the fin can be easily refined. Moreover, the casting speed is preferably 100 mm / min or less, more preferably 80 mm / min or less, so that 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 is subjected to a stretching process to obtain a fin having a desired shape. For example, after producing a slab by DC casting, the slab is subjected to a rolling process 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. In addition, between before the rolling process and after the rolling process is completed, a heat treatment such as a homogenization process or an annealing process may be performed as necessary to adjust the quality of the fin. The fin may have a quality represented by, for example, quality symbol O, H1n, or H2n. From the viewpoint of suppressing erosion during brazing, the fin preferably has a quality represented by quality symbol H1n or H2n.

[0054] In addition, after preparing 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. Before the hot extrusion, the billet may be subjected to homogenization treatment as necessary. The billet is cast by a casting method such as hot top casting or GDC casting.

[0055] In the manufacturing method, new aluminum ingots, intermediate alloys, and aluminum scrap can be used as the casting raw material during casting. The aluminum scrap used as the casting raw material 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 scrap as the casting raw material, the aluminum scrap may be melted as it is. Also, the aluminum scrap may be cut or compressed to adjust the size of the aluminum scrap before melting. Furthermore, aluminum recycled ingots may be produced from the aluminum scrap, and then the aluminum recycled ingot may be used as the casting raw material.

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

[0057] As the tubes in the heat exchanger core, a tube material having a flat cross-sectional shape, such as a flat tube or a flat multi-hole tube, can be used. More specifically, the tubes have a pair of flat wall portions arranged opposite to each other with a gap therebetween, and a connecting wall portion connecting both ends in the width direction of the flat wall portions, and are configured to allow the heat transfer medium to flow through the heat transfer medium flow path surrounded by the flat wall portions and the connecting wall portions. The tubes may further have a partition portion that divides the internal space surrounded by the flat wall portions and the connecting wall portions into a plurality of 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 a rectangle, an oval, etc. The cross-sectional shape of the heat transfer medium flow path is also not particularly limited and may be various shapes such as a circle, an oval, an ellipse, a triangle, a square, etc.

[0059] The aluminum alloy extrusion material constituting the tube may have a chemical composition in which the Cu content is within the specific range. For example, the aluminum alloy extrusion material constituting the tube may have a chemical composition containing Cu: more than 0.05 mass% and not more than 0.6 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 spray coating and brazing joint during brazing, and has the effect of making the natural electrode potential of these parts nobler. 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 is impaired, which may lead to a decrease in corrosion resistance. Therefore, by setting the Cu content in the tube within the specific range, the strength of the tube can be increased while ensuring the excellent corrosion resistance of the heat exchanger core.

[0060] 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 Cu: more than 0.05 mass% and 0.6 mass% or less, and further contains, as optional components, 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, 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 or more and 0.7% by mass or less, Fe: 0.05% by mass or more and 0.5% by mass or less, Mn: 0.05% by mass or more and 1.2% by mass or less, and Ti: 0.01% by mass or more and 0.3% by mass or less, with the balance being Al and unavoidable impurities.

[0061] In addition, 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 part of the Zn sprayed coating provided on the outer surface of the tube before brazing remaining after brazing.

[0062] The sacrificial anode layer may be, for example, a Zn-enriched layer having a higher Zn concentration than the surroundings. The Zn-enriched layer as the sacrificial anode layer is formed, for example, by diffusing Zn atoms contained in zinc vapor or 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 be clear. Even in such a case, the above-mentioned 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 above-mentioned 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 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 higher than the natural electrode potential Ej of the fillet, and the absolute value of the potential difference Eav-Ef between the average Eav of the natural electrode potentials 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 of natural electrode potential is difficult to realize, for example, in a conventional heat exchanger core obtained by using fins made of a single layer of aluminum material that does not have the ability to form a brazing sheet or a brazed joint. A heat exchanger core that satisfies all of the above-mentioned four conditions can be realized only by setting the chemical composition of the aluminum alloy constituting the fins and tubes within the specific range shown in the above manufacturing method and performing brazing in the presence of zinc vapor during brazing.

[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 can function as a sacrificial anode for the inner surface of the tube, and corrosion inside the tube can be suppressed. 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 anticorrosion effect of the sacrificial anode layer becomes insufficient, and the inside of the tube is easily corroded. As a result, there is a risk that leakage of the heat transfer medium from the tube will occur easily at an early stage.

[0067] The condition (2) 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 brazing joint. By setting the potential difference Ets-Ej between the sacrificial anode layer and the fillet to 100 mV or less, the balance of the potential between the sacrificial anode layer and the brazing joint can be set within an optimal range, and early loss of the brazing joint can be easily avoided. As a result, the fin can be prevented from falling off from the heat exchanger core. If the potential difference Ets-Ej between the sacrificial anode layer and the fillet exceeds 100 mV, the brazing joint is more susceptible to corrosion than other parts of the heat exchanger core, and there is a risk that the brazing joint will be lost early. As a result, there is a risk that the fin will be easily detached from the heat exchanger core early.

[0068] The condition (3) specifies 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 specific range, both the fin and the sacrificial anode layer can function as sacrificial anodes for the tube. When the potential difference Ets-Ef between the sacrificial anode layer and the fin is less than -80mV, the sacrificial anode layer is likely to corrode earlier than the fin. As a result, the sacrificial anode layer may be lost early, and the corrosion of the tube may progress starting from the corrosion of the sacrificial anode layer. On the other hand, when the potential difference Ets-Ef between the sacrificial anode layer and the fin exceeds 150mV, the fin is likely to corrode earlier than the sacrificial anode layer, and the fin may be lost early.

[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 (i.e., the natural electrode potential Ef of the fin is more negative 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 for a long period of time.

[0071] As described above, when the natural electrode potential of each part of the heat exchanger core satisfies all of the four conditions, the balance of the natural electrode potential of each part of the heat exchanger core can be adjusted within an optimal range. As a result, it is possible to easily prevent any part of the sacrificial anode layer, the fin, and the brazing joint from corroding earlier than the other parts, and improve the corrosion resistance of the heat exchanger core as a whole. From the viewpoint of more reliably obtaining such an effect, it is preferable that the heat exchanger core satisfies the four conditions of the conditions (1) to (3) and the condition (4-1). From the same viewpoint, the natural electrode potential of the fin when the natural electrode potential of the fillet is used as a reference 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 of manufacturing heat exchanger core) the heat exchanger core is an assembly in which 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 are alternately stacked to form an assembly; The assembly is heated and brazed in an atmosphere containing zinc vapor to form the brazed joint between the fin and the tube, and the sacrificial anode layer is formed on the outer surface of the tube.

[0073] The chemical composition of the fins used in the manufacture of the heat exchanger core is the same as that of the fins in the heat exchanger core after brazing. 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 heat exchanger core after brazing.

[0074] The configuration of the tubes used in the manufacture of the heat exchanger core is the same as that of the tubes in the heat exchanger core after brazing, 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 heat exchanger core after brazing described above.

[0075] In the method for manufacturing the 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. The brazing atmosphere may also be a reduced pressure atmosphere containing zinc vapor.

[0076] The heating temperature when brazing the assembly is preferably set so that the liquid phase rate of the fin, i.e., the ratio of the mass of the molten liquid generated from the fin to the mass of the fin 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 rate of the fin during heating within the specific range, a sufficient amount of molten liquid can be generated from the fin while suppressing a decrease in the strength of the fin during heating, and a brazing joint can be easily formed between the fin and the tube.

[0077] In addition, the holding time of the heating temperature when brazing the assembly is preferably set so that the time during which the liquid phase rate of the fin becomes 5 mass% or more is 30 seconds or more and 3600 seconds or less, and more preferably 60 seconds or more and 1800 seconds or less. By setting the holding time during brazing within the specific range, the melt generated from the fin can be sufficiently filled between the fin and the tube while suppressing the decrease in strength of the fin during heating. In addition, since the melt is generated from the entire surface of the fin when joining the fin and the tube, the length of the holding time can be set regardless of the area of ​​the brazing joint formed between the fin and the tube.

[0078] More specifically, for example, the heating temperature in brazing can be appropriately set within the range of 580°C or more and 620°C or less. The holding time of the heating temperature can be appropriately set within the range of, for example, 0 minutes or more and 10 minutes or less, preferably 30 seconds or more and 5 minutes or less. Here, the holding time refers to the elapsed time from the point when the heating temperature reaches the desired temperature. When the holding time of 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 time.

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

[0080] Alternatively, before brazing, flux may be placed on the portion of the assembly where the brazing joint is to be formed, and then the assembly may be heated to perform brazing. Examples of flux that can be used include 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 compounds used as fluxes for brazing aluminum, such as chloride-based fluxes.

[0081] In the manufacturing method, when the assembly is heated, a small amount of melt is generated from the fins, and the 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 zinc vapor can easily dissolve into the molten liquid generated from the fin during the process of forming the brazed joint. Therefore, the natural electrode potential of the brazed joint can be appropriately made less noble by the Zn atoms dissolving into the molten liquid collected at the abutment between the fin and the tube. In addition, since the amount of molten liquid generated from the fin is very small, the molten liquid present at a position away from the abutment between the fin and the tube is not drawn into the abutment between the fin and the tube and remains on the fin. Therefore, the Zn atoms dissolved in the molten liquid of the fin can easily diffuse into the inside of the fin, and the natural electrode potential of the fin can be appropriately made less noble.

[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 potentials of the fins and the brazed joints can be appropriately made less noble, 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 above-mentioned manufacturing method, the method of generating zinc vapor during brazing is not particularly limited, and various modes can be adopted.For example, in the above-mentioned 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.In addition, as described later, a method can be adopted in which a Zn spray coating is formed on the outer surface of the tube before brazing, and zinc vapor is generated from the Zn spray coating during brazing.

[0085] The outer surface of the tube used to manufacture the heat exchanger core is preferably provided with a Zn sprayed coating. After assembling the assembly using the tube with the Zn sprayed coating on its outer surface, brazing is performed, whereby the Zn atoms in the Zn sprayed coating are diffused into the tube, and a sacrificial anode layer can be more easily formed on the outer surface of the tube. Furthermore, the Zn sprayed coating can generate zinc vapor by being heated during brazing. This zinc vapor can be brought into contact with the fins and brazed joints to make the natural electrode potentials of the fins and brazed joints less noble. As a result of the above, the natural electrode potentials of each part of the heat exchanger core after brazing can be more easily adjusted to within the specific 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 More than 9g / m 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 0.1 mass % or more higher 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 within the specific 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 atmosphere during brazing. For example, if the Zn content in the fin after brazing is to be increased, the concentration of zinc vapor in the atmosphere during brazing can be increased. The concentration of zinc vapor in the atmosphere during brazing can be easily adjusted, for example, by the total amount of zinc placed in the heating furnace. For example, if the concentration of zinc vapor in the atmosphere during brazing is to be increased, 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. EXAMPLES

[0089] (Example) An embodiment of the heat exchanger core and a manufacturing method thereof will be described with reference to Fig. 1 to Fig. 3. As shown in Fig. 1 and Fig. 2, the heat exchanger core 1 of this embodiment 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 mass% to 3.0 mass% Si, 0.05 mass% to 1.2 mass% Fe, 0 mass% to 0.25 mass% Cu, 0.3 mass% to 1.8 mass% Mn, 0.3 mass% to 5.0 mass% Zn, and the balance being Al and unavoidable impurities.

[0090] The tube 3 is made of an aluminum alloy extrusion material containing Cu: more than 0.05 mass % and not more than 0.6 mass %. As shown in Fig. 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. In addition, the heat exchanger core 1 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 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 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 a plurality of fins 2 and a plurality of tubes 3, and is configured as a core of a so-called parallel flow type heat exchanger in which the fins 2 and the tubes 3 are alternately stacked. The fins 2 in the heat exchanger core 1 of this example are given a corrugated shape by press processing, and are configured of a plurality of fin apexes 21 curved in a U-shape and a fin intermediate portion 22 connecting the fin apexes 21 with each other, as shown in FIG. 2. In addition, the tubes 3 are configured as extruded multi-hole tubes having a pair of flat wall portions 32 arranged facing each other with a gap therebetween, a connecting wall portion 33 connecting both ends of the flat wall portions 32 in the width direction, and a partition portion 35 dividing the internal space surrounded 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 FIG. 2. The fin apex 21 of the fin 2 and the flat wall portion 32 of the tube 3 are joined via a brazing joint 4.

[0092] 1, the heat exchanger core 1 of this example may have a header tank 11 attached to both ends of a 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 in the header tank 11 to the plurality of tubes 3, or can join the heat transfer medium led out from 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 is no particular limitation on the method of 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 adopted in which the header tank 11 before brazing is made of a brazing sheet including a core material and a brazing material laminated on at least one side of the core material, and the brazing joint 4 is formed by the brazing material of the header tank 11. Also, 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] Moreover, the side plate 12 and the fins 2 are joined via brazing 4 .

[0095] The manufacturing method of the heat exchanger core 1 of this embodiment is, for example, as follows. First, 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 balance being Al and unavoidable impurities, and tubes 3 made of an aluminum alloy extrusion material containing Cu: more than 0.05 mass% to 0.6 mass% or less are alternately stacked to prepare a laminate. Header tanks 11 are attached to both ends of the tubes 3 in this laminate, and a side plate 12 is abutted against the fin 2 located at the outermost position among the multiple fins 2 to obtain an assembly.

[0096] Next, the assembly is heated and brazed in an atmosphere containing zinc vapor, whereby 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 in this embodiment are made of an aluminum alloy having the specific chemical components. By using at least the fins 2 having the specific chemical components, the heat exchanger core 1 can be obtained in which the natural electrode potentials of each portion satisfy all of the four conditions described above. By making the natural electrode potentials of each portion in the heat exchanger core 1 be in the above-mentioned mode, 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 components are combined with the tubes 3 to prepare 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 brazing 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, the potential of each part of the heat exchanger core 1 is adjusted by the zinc vapor, so that the heat exchanger core 1 in which the natural electrode potential of each part satisfies all of the above-mentioned four conditions can be easily obtained.

[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. Among the symbols used in this example, the same symbols as those used in the previous examples indicate the same components as those in the previous examples.

[0100] 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 that it is a remainder. The width of the tube 3 is 14 mm, the length is 40 mm, and the thicknesses of the flat wall portion 32, the connecting wall portion 33, and the partition portion 35 are all 0.35 mm. A Zn sprayed coating is formed in advance on the outer surface of the tube 3. The amount of Zn atoms attached in the Zn sprayed coating is approximately 8 g / m. 2 It 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 apexes 21 is 3 mm, and the height of the fins 2 is 10 mm. Of the two tubes 3, the number of fin apexes 21 that come into contact with the first tube 3a is 11, and the number of fin apexes 21 that come into contact with the second tube 3b is 12.

[0103] In producing the mini-core specimen S1, first, the tube 3 and the fin 2 are overlapped, and then flux is applied to the contact portion between the tube 3 and the fin 2 to produce an assembly. Ten of these assemblies are placed in a heating furnace, and zinc is placed around the assemblies. Furthermore, in order to retain zinc vapor around the assemblies, a cover is placed on the ten assemblies and the zinc. Thereafter, the assemblies are heated in an inert gas atmosphere, and while zinc vapor is generated from the zinc and Zn spray coating, the assemblies are brazed in the presence of zinc vapor. In this manner, the mini-core specimen S1 can be obtained.

[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. The Zn content in the fin 2 after brazing can be measured using, for example, an electron probe microanalyzer (that is, EPMA). When measuring the Zn content in the fin 2 using EPMA, specifically, a 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 part 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 a double-sided brazing sheet in which a brazing material is laminated on both sides of a core material is used as the fin 2. The chemical components of the core material and brazing material 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 material is 10%. The manufacturing method of the minicore specimen R1 is the same as the manufacturing method of the minicore specimen S1, except that a double-sided brazing sheet is 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 is 1.20 mass%, which is 0.28 mass% less than the Zn content in the core material of the fin before brazing.

[0106] The method for measuring the natural electrode potential and the method for 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 are cut off from the mini-core specimens S1 and R1 after brazing, and the first tube 3a is removed. In the sacrificial anode layer 31 of this tube 3a, a region between any one brazed joint 4 and the brazed joint 4 adjacent to the brazed joint 4 is specified, and this region is set as the potential measurement region. In other words, the potential measurement region is a region on the outer surface of the first tube 3a that faces one pitch of fins.

[0108] After the potential measurement area is specified as described above, the area other than the potential measurement area is covered with a sealant. Then, the natural electrode potential of the potential measurement area is measured as follows. A measuring device 5 shown in FIG. 5 is used to measure the natural electrode potential. The measuring device 5 has 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 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 FIG. 5, the shape of the tube 3 is shown typically.

[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. 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. 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 it, 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 until the point 24 hours after the start of measurement is set as the natural electrode potential Ets of the sacrificial anode layer 31.

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

[0113] Fin 2 natural electrode potential Ef The first tube 3a and the fin top 21 joined to the first tube 3a are cut out 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 by the same method as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained is set as the natural electrode potential Ef of the fin 2.

[0114] Fillet natural electrode potential Ej The fins 2 are cut off from the mini-core specimens S1 and R1 after brazing, 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. Next, a potential measurement area is set on the fillet exposed by the chamfering, and the area other than the potential measurement area is covered with a sealant. Then, the natural electrode potential of the potential measurement area is measured by the same method as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained is the natural electrode potential Ej of the fillet.

[0115] Corrosion resistance In the mini-core specimens S1 and R1 obtained by the above-mentioned method, the end face of the tube 3, the connecting wall portion 33 of the tube 3, and the flat wall portion 32a not joined to the fin 2 are covered with a sealant, and then a SWAAT test is carried out by a method conforming to 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 tube 3 is penetrated and whether the fin 2 is peeled off from the tube 3.

[0116] The symbols shown 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] In addition, 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] [Table 1]

[0119] [Table 2]

[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. In addition, the natural electrode potentials Ets, Eti, Ef, and Ej of each part of the mini-core specimen S1 satisfy all of the four conditions. Therefore, the mini-core specimen S1 can avoid early disappearance of any of the sacrificial anode layer 31, the fin 2, or the brazing 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 has inferior corrosion resistance to the mini-core specimen S1, and the fins peel off from the tube 3 after 20 days of SWAAT testing. In addition, when the SWAAT test of the mini-core specimen R1 is continued for 40 days, the fins peel off completely from the tube 3 and corrosion penetrates the tube 3. The following reasons are considered to be the reasons for this. When the brazing sheet is used as the fin, the fluidity of the molten brazing material formed by melting the brazing material is high, so that the molten brazing material containing Zn atoms is thought to easily move to the fillet of the brazing joint. As a result, the Zn content in the brazing joint becomes excessively high, and the natural electrode potential Ej of the brazing joint is likely to become excessively low.

[0122] In addition, it is believed that the easy flow of the molten brazing material during brazing makes it difficult for Zn to diffuse from the molten brazing material to the core material, which leads to an insufficient effect of the sacrificial anode layer formed on the surface of the fin after brazing, and makes 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. However, 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 depart from the spirit of the present invention.

[0124] For example, the heat exchanger core may have the following aspects (1) to (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 not more than 0.6% by mass; and a brazing joint for joining the fin and the tube, a sacrificial anode layer having a lower natural electrode potential than an 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 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 producing the heat exchanger core may take the following aspects [3] to [6].

[0128] [3] A method for producing a heat exchanger core according to [1] or [2], 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, are alternately stacked to form an assembly; 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 tubes, and forming the sacrificial anode layer on the outer surface 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% 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.

[0130] [5] A method for manufacturing a heat exchanger core according to [3] or [4], wherein the assembly is assembled using the tube having a Zn sprayed coating on its outer surface. [6] A method for manufacturing a heat exchanger core described in [3] or [4], wherein the Zn content in the fin after brazing is 0.1 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% 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 mass% and not more than 0.6 mass%; and a brazing joint that joins the fin and the tube, 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; (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.

2. 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% 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.

3. A method for manufacturing a heat exchanger core according to claim 1 or 2, comprising the steps of: an assembly is assembled 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; 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 fin and the tube, and forming the sacrificial anode layer on the outer surface of the tube.

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

7. An aluminum alloy material for fins used in heat exchanger fins, An aluminum alloy material for fins having a chemical composition containing: Si: 2.5% 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 0.04% 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; and Ti: more than 0.3% by mass or less, with the remainder being Al and unavoidable impurities.

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