Heat exchanger core and method for manufacturing same

Abstract

A heat exchanger core (1) is provided with fins (2), tubes (3), and a braze fitting (4) that joins the fins (2) and the tubes (3). The fins (2) are formed from an aluminum alloy having a chemical composition containing 2.0 to 3.0 mass% of Si, 0.05 to 1.2 mass% of Fe, 0.25 mass% or less of Cu, 0.3 to 1.8 mass% of Mn, and 0.3 to 5.0 mass% of Zn, with the remainder being Al and unavoidable impurities. The tube (3) is made of an aluminum alloy extruded material containing more than 0.05% by mass and 0.6% by mass or less of Cu. A sacrificial anode layer (31) is formed on the outer surface of the tube (3). The natural electrode potential of the sacrificial anode layer (31), the natural electrode potential of the inner surface of the tube (3), the natural electrode potential of the weld leg in the brazed assembly (4), and the natural electrode potential of the fin (2) satisfy specific conditions.

Description

Technical Field

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

[0002] For example, parallel-flow heat exchangers made of aluminum alloy are used in automobile radiators, condensers, and evaporators incorporated into automobile air conditioners. These heat exchangers have a heat exchanger core composed of multiple tubes and fins configured to allow the flow of a heat transfer medium. In a parallel-flow heat exchanger core, the tubes and fins are alternately stacked and joined together via brazing joints.

[0003] In the past, heat exchanger core fins often used brazing sheets with brazing filler metal applied to at least one surface of the core material. Meanwhile, in recent years, the use of single-layer aluminum alloy materials capable of forming a brazed joint with a counterpart material has been proposed as fins.

[0004] For example, Patent Document 1 describes a fin material for a heat exchanger, which is composed of the following aluminum alloy and has a heat bonding function in a single layer at a temperature where the liquid phase fraction is greater than 5% and less than 35%. The aluminum alloy contains Si: 1.0 to 5.0 mass%, Fe: 0.01 to 2.0 mass%, and Mn: 0.05 to 2.0 mass%, and the balance is Al and unavoidable impurities.

[0005] Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 5698416 Summary of the Invention Problems to be solved by the invention However, as a method for improving the corrosion resistance of heat exchanger cores, a known method is to form a Zn spray coating on the outer surface of the tube, thereby making the outer surface of the tube function as a sacrificial anode facing the interior of the tube. However, when a tube with a Zn spray coating is combined with the heat exchanger fin material described in Patent Document 1, corrosion of the brazed joints and fin material progresses early, sometimes resulting in a reduction in the corrosion resistance of the heat exchanger core.

[0006] The present invention has been made in view of the above background, and an object of the present invention is to provide a heat exchanger core having excellent corrosion resistance and a method for manufacturing the same.

[0007] Technical solutions to problems One embodiment of the present invention is a heat exchanger core having: A fin having a chemical composition comprising 2.0% by mass or more and 3.0% by mass or less of Si (silicon), 0.05% by mass or more and 1.2% by mass or less of Fe (iron), 0% by mass or more and 0.25% by mass or less of Cu (copper), 0.3% by mass or more and 1.8% by mass or less of Mn (manganese), and 0.3% by mass or more and 5.0% by mass or less of Zn (zinc), with the balance being Al (aluminum) and unavoidable impurities; A pipe composed of an aluminum alloy extruded material containing Cu: more than 0.05 mass % and 0.6 mass % or less; and a brazing joint joining the fin to the tube, A sacrificial anode layer is formed on the outer surface of the tube, and the sacrificial anode layer has a lower natural electrode potential than the inner surface of the tube. The heat exchanger core satisfies the following four conditions: (1) the natural electrode potential of the inner surface of the tube is greater than +50 mV 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 less than +100 mV when the natural electrode potential of the weld leg in the brazed joint is used as a reference; (3) the natural electrode potential of the sacrificial anode layer is greater than -80 mV and less than +150 mV when the natural electrode potential of the fin is used as a reference; (4) the natural electrode potential of the fin is lower than the natural electrode potential of the weld leg, or the natural electrode potential of the fin is greater than the natural electrode potential of the weld leg and the absolute value of the potential difference between the natural electrode potential of the fin, the natural electrode potential of the weld leg and the average value of the natural electrode potential of the sacrificial anode layer and the natural electrode potential of the fin is less than 40 mV.

[0008] Another aspect of the present invention is a method for manufacturing a heat exchanger core according to the aforementioned aspect, wherein fins and tubes made of an aluminum alloy extruded material are alternately overlapped and assembled into an assembly, the assembly is heated, and brazed in an atmosphere containing zinc vapor to form the brazed joint between the fins and the tubes, and the sacrificial anode layer is formed on the outer surface of the tube. The fin has the following chemical composition: Si: 2.0 mass% or more and 3.0 mass% or less, Fe: 0.05 mass% or more and 1.2 mass% or less, Cu: 0 mass% or more and 0.25 mass% or less, Mn: 0.3 mass% or more and 1.8 mass% or less, and Zn: 0.3 mass% or more and 4.0 mass% or less, with the balance being Al and unavoidable impurities, and the aluminum alloy extruded material contains Cu: more than 0.05 mass% and 0.6 mass% or less.

[0009] Effects of the Invention The fins in the heat exchanger core are composed of an aluminum alloy having the specific chemical composition. By using at least 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 weld legs of the brazed joint, and the fins to meet all four of the aforementioned conditions, which were difficult to achieve in conventional heat exchanger cores. Furthermore, by setting the natural electrode potentials of various locations in the heat exchanger core to the aforementioned conditions, the corrosion resistance of the heat exchanger core can be improved.

[0010] Furthermore, in the heat exchanger core manufacturing method, after fins having the specific chemical composition are combined with tubes to form an assembly, the assembly is brazed in an atmosphere containing zinc vapor. The zinc vapor in the brazing atmosphere can moderately reduce 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 tube.

[0011] In this way, not only the specific fins are used, but also the assembly is brazed in an atmosphere containing zinc vapor. This allows the natural electrode potentials at various locations in the heat exchanger core to be adjusted to satisfy all four of the aforementioned conditions, which were not achievable with conventional heat exchanger cores. As a result, a heat exchanger core with excellent corrosion resistance can be easily obtained.

[0012] As described above, according to the above aspect, a heat exchanger core having excellent corrosion resistance and a method for manufacturing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. 4 is a top view of a heat exchanger core in an embodiment.

[0014] Figure 2 yes Figure 1 A partial enlarged view of .

[0015] Figure 3 is a cross-sectional view of a tube in the embodiment.

[0016] Figure 4 This is a perspective view of a microchip test body in an experimental example.

[0017] Figure 5 This is an explanatory diagram of a device for measuring the spontaneous electrode potential in an experimental example. DETAILED DESCRIPTION

[0018] (Heat exchanger core) The heat exchanger core comprises fins and tubes. Furthermore, brazed joints are formed between the fins and tubes to connect them. The heat exchanger core can also be configured as a so-called parallel flow heat exchanger core, in which fins and tubes are alternately stacked. Furthermore, in addition to the fins and tubes, the heat exchanger core may also include side plates that connect to the outermost fins of the multiple fins, headers mounted at both ends of the tubes, and the like.

[0019] Fins The fins of the heat exchanger core are composed of a single layer of an aluminum alloy having the following chemical composition: Si: 2.0% to 3.0% by mass, Fe: 0.05% to 1.2% by mass, Cu: 0% to 0.25% by mass, Mn: 0.3% to 1.8% by mass, and Zn: 0.3% to 5.0% by mass, with the balance consisting of Al and unavoidable impurities. The thickness of the fins can be appropriately set, for example, within the range of 0.04 mm to 0.15 mm.

[0020] The chemical composition of the fin and the reasons for its limitation are described below.

[0021] ·Si The fins contain Si in an amount of 2.0% by mass or more and 3.0% by mass or less as an essential component. By setting the Si content in the fins to 2.0% by mass or more, a molten metal containing Al and Si can be generated by brazing heating, and a brazed joint can be formed between the fins and the tubes. 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 metal generated by brazing heating can be increased, further improving the brazing properties. When the Si content is less than 2.0% by mass, the amount of molten metal generated by brazing heating is insufficient, which may lead to deterioration of the brazing properties.

[0022] On the other hand, if the Si content becomes too high, the amount of fin melted during brazing heating increases, potentially reducing the fin strength. As a result, the shape of the heat exchanger core may not be maintained during brazing. To avoid this problem, the Si content is set to 3.0% by mass or less. From the same perspective, the Si content is preferably set to 2.9% by mass or less, more preferably to 2.8% by mass or less, and even more preferably to 2.7% by mass or less.

[0023] When defining the preferred range of the Si content in the fin, the upper and lower limits of the Si content may be arbitrarily combined. For example, the preferred range of the Si content in the fin may be 2.1% by mass or more and 2.9% by mass or less, 2.2% by mass or more and 2.8% by mass or less, or 2.3% by mass or more and 2.7% by mass or less.

[0024] Fe The fins contain Fe as an essential component, at a concentration of 0.05% to 1.2% by mass. A portion of the Fe forms a solid solution in the Al matrix, increasing the strength of the fins. Furthermore, the remaining Fe forms crystals dispersed within the Al matrix, enhancing the strength of the fins at both room and high temperatures. Furthermore, Fe refines the fins' grain size. This refinement of the fins' grain size facilitates the molten metal's infiltration from the grain boundaries during brazing heating, improving brazing performance.

[0025] Therefore, by setting the Fe content in the fins to 0.05% by mass or greater, the strength and brazing properties of the fins can be improved. To further improve the strength and brazing properties of the fins, the Fe content in the fins is preferably 0.07% by mass or greater, more preferably 0.10% by mass or greater, even more preferably 0.13% by mass or greater, and particularly preferably 0.15% by mass or greater. If the Fe content in the fins is less than 0.05% by mass, the aforementioned effects may be reduced.

[0026] On the other hand, if the Fe content becomes too high, coarse intermetallic compounds are likely to form during casting, potentially reducing 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, further 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.

[0027] When defining the preferred range of the Fe content in the fin, the upper and lower limits of the Fe content can be arbitrarily combined. For example, the preferred range of the Fe content in the fin can be 0.07 mass% to 1.0 mass%, 0.10 mass% to 0.8 mass%, 0.13 mass% to 0.6 mass%, or 0.15 mass% to 0.4 mass%.

[0028] ·Cu The fins may contain Cu as an optional component in an amount of 0% by mass or more and 0.25% by mass or less. The Cu in the fins, like Fe, is solid-dissolved in the Al matrix, which has the effect of increasing the strength of the fins. In addition, like Fe, Cu has the effect of refining the grains of the fins. However, if the Cu content becomes too high, the amount of molten metal generated from the fins during brazing heating becomes too high, which may lead to a decrease in strength at high temperatures. In addition, in this case, the natural electrode potential of the fins increases, which may also lead to a decrease in the sacrificial corrosion protection effect in the heat exchanger core.

[0029] Therefore, by setting the Cu content in the fin to 0.25% by mass or less, a decrease in strength at high temperatures and a decrease in the sacrificial corrosion protection effect can be easily avoided. From the perspective of more reliably achieving this effect, the Cu content in the fin is preferably 0% by mass or more and 0.20% by mass or less, more preferably 0% by mass or more and 0.15% by mass or less, even more preferably 0% by mass or more and 0.10% by mass or less, particularly preferably 0% by mass or more and 0.05% by mass or less, and most preferably 0% by mass or more and 0.04% by mass or less.

[0030] ·Mn The fins contain Mn as an essential component, at a concentration of 0.3% to 1.8% by mass. A portion of the Mn forms an Al-Mn-Si intermetallic compound in the fins, enhancing the fin's strength through dispersion strengthening. The remainder of the Mn dissolves in the Al matrix, further enhancing the fin's strength through solid solution strengthening.

[0031] By setting the Mn content in the fin to 0.3% by mass or more, the strength of the fin can be improved through dispersion strengthening and solid solution strengthening. In addition, by setting the Mn content in the fin to 0.3% by mass or more, the growth of the grains of the fin during brazing heating can be promoted, and the deformation and bending of the fin during brazing heating can be suppressed. From the perspective of further improving the effect of increasing the strength of the fin and suppressing deformation during brazing heating brought by Mn, 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. When the Mn content is less than 0.3% by mass, the aforementioned effect is reduced, and it is possible that the deformation and bending of the fin will easily occur during brazing heating.

[0032] On the other hand, when the Mn content is too high, coarse intermetallic compounds are easily formed during the manufacturing process of the fin. If rolling is performed in a state containing such coarse intermetallic compounds, pinholes may be easily generated. In addition, if the Mn content becomes too high, intermetallic compounds containing Mn and Si are easily formed, and the amount of Si that can participate in the formation of the melt becomes insufficient. As a result, there is a possibility of reducing brazing properties. From the viewpoint of easily avoiding these problems, the Mn content is set to 1.8% by mass or less. From the same viewpoint, the Mn content is more preferably 1.7% by mass or less, further preferably 1.6% by mass or less, and particularly preferably 1.5% by mass or less.

[0033] When defining the preferred range of the Mn content in the fin, the upper and lower limits of the Mn content can be arbitrarily combined. For example, the preferred range of the Mn content in the fin can be 0.5% by mass or more and 1.7% by mass or less, 0.7% by mass or more and 1.6% by mass or less, or 0.9% by mass or more and 1.5% by mass or less.

[0034] ·Zn The fins contain Zn as an essential component in an amount of 0.3% by mass or more and 5.0% by mass or less. The Zn in the fins increases the amount of melt generated from the fins and reduces the natural electrode potential of the fins. By setting the Zn content in the fins to 0.3% by mass or more, preferably 0.5% by mass or more, more preferably 0.7% by mass or more, further preferably 0.9% by mass or more, and particularly preferably 1.0% by mass or more, the natural electrode potential Ef of the fins can be easily adjusted to a range that satisfies the aforementioned conditions. If the Zn content in the fins is less than 0.3% by mass, the natural electrode potential Ef of the fins may be excessively increased, potentially leading to a reduction in the sacrificial anti-corrosion effect.

[0035] On the other hand, if the Zn content in the fins becomes too high, the natural electrode potential Ef of the fins will be excessively reduced, which may lead to a decrease in the corrosion resistance of the fins themselves. In addition, if the Zn content in the fins becomes too high, cracks will easily occur during the fin manufacturing process, which may lead to a decrease in productivity. These problems can be easily avoided by setting the Zn content in the fins to 5.0% by mass or less, preferably 3.5% by mass or less, more preferably 3.0% by mass or less, further preferably 2.5% by mass or less, particularly preferably 2.0% by mass or less, and most preferably 1.5% by mass or less.

[0036] When defining the preferred range of the Zn content in the fin, the upper and lower limits of the Zn content can be arbitrarily combined. For example, the preferred range of the Zn content in the fin can be 0.5% by mass or more and 3.5% by mass or less, 0.5% by mass or more and 3.0% by mass or less, 0.7% by mass or more and 2.5% by mass or less, 0.9% by mass or more and 2.0% by mass or less, 0.9% by mass or more and 1.5% by mass or less, or 1.0% by mass or more and 1.5% by mass or less.

[0037] The fin may contain, in addition to the aforementioned essential components and Al, elements such as Zr (zirconium), Cr (chromium), Ti (titanium), V (vanadium), Ni (nickel), Mg (magnesium), In (indium), and Sn (tin) as optional components.

[0038] Zr, Cr, Ti, V The fins may contain, as optional components, one or more elements selected from the group consisting of Zr (greater than 0% by mass and less than 0.3% by mass), Cr (greater than 0% by mass and less than 0.3% by mass), Ti (greater than 0% by mass and less than 0.3% by mass), and V (greater than 0% by mass and less than 0.3% by mass). These elements promote grain growth in the fins during brazing heating. Therefore, by setting the Zr, Cr, Ti, and V contents in the fins within the specified ranges, deformation and warping of the fins during brazing heating can be more effectively suppressed.

[0039] ·Ni The fins may contain Ni as an optional component in an amount exceeding 0% by mass and not exceeding 0.8% by mass. Ni forms intermetallic compounds in the fins, improving the strength of the fins after brazing through dispersion strengthening. On the other hand, excessive Ni content may reduce the corrosion resistance of the fins themselves. By limiting the Ni content in the fins to exceeding 0% by mass and not exceeding 0.8% by mass, the aforementioned problems can be easily avoided and the strength of the fins can be further improved.

[0040] Mg The fins may contain Mg as an optional component in an amount exceeding 0% by mass and below 0.1% by mass. Mg forms Mg2Si in the fins after brazing, which improves the fin strength through age hardening. On the other hand, if the Mg content becomes excessive, Mg and the flux may react during brazing with flux, potentially reducing brazing properties. By limiting the Mg content to above 0% by mass and below 0.1% by mass, this problem can be easily avoided and the fin strength can be further improved.

[0041] In, Sn The fins may contain, as optional components, one or two elements selected from the group consisting of In (in) exceeding 0% by mass and 0.03% by mass, and Sn (tin) exceeding 0% by mass and 0.1% by mass. Like Zn, Sn and In lower the potential of the fins. By setting the Sn and In contents in the fins within the specified ranges, the potential of the fins can be adjusted while avoiding a decrease in the fin's corrosion resistance, further improving the corrosion resistance of the aluminum structure.

[0042] The fin may contain one or more of the aforementioned arbitrary components. For example, the fin may have a chemical composition comprising 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 5.0 mass%, and Ti: more than 0 mass% to 0.30 mass%, with the balance being Al and unavoidable impurities.

[0043] In addition, the fin may have, for example, a chemical composition containing 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.

[0044] In addition, the fin may have, for example, a chemical composition containing 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.

[0045] In addition, the fin may also have the following chemical composition, for example, containing 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 balance being Al and unavoidable impurities.

[0046] Other elements The fins may contain elements other than the aforementioned essential and optional components, as long as they do not impair the aforementioned effects. Examples of elements that may be contained in the fins include Sr, Na, and rare earth elements. These elements, if their individual content is 0.05% by mass or less and their total content is 0.15% by mass or less, will not affect the aforementioned effects and can be treated as unavoidable impurities.

[0047] Fin manufacturing method The fins can be manufactured in various ways. For example, the fins can be made of an extended material by stretching, or a forged material by forging. Alternatively, the fins can be cast.

[0048] To improve brazing performance and strength, the fins are preferably made of ductile material. Ductile materials require greater processing during manufacturing than forged materials, castings, and the like, so second-phase particles are more easily sheared off during the manufacturing process. Therefore, fins made of ductile material can increase the amount of Si particles, Si-based intermetallic compounds, Al-based intermetallic compounds, and the like dispersed within the Al matrix. As a result, brazing performance and strength can be balanced.

[0049] When producing fins made of ductile material, continuous casting methods such as twin-roll continuous casting and twin-belt continuous casting can be employed. Compared to DC casting, continuous casting can increase the cooling rate during casting. Consequently, a large number of fine second-phase particles, such as Si particles, can be formed in the fins. Furthermore, by dispersing a large number of fine second-phase particles in the fins, the amount of molten metal formed during brazing heating can be increased, thereby improving brazeability.

[0050] When producing the fins using a twin-roll continuous casting and rolling method, the casting speed is preferably set to 0.5 m / min or higher and 3 m / min or lower. In the twin-roll continuous casting and rolling method, a casting speed of 0.5 m / min or higher can significantly increase the cooling rate during casting, making it easier to refine the second-phase particles in the fins. Furthermore, a casting speed of 3 m / min or lower allows the molten metal to be sufficiently cooled and solidified during casting.

[0051] The temperature of the molten metal during casting is preferably 650°C to 800°C, more preferably 680°C to 750°C. Setting the molten metal temperature to 650°C or higher, more preferably 680°C or higher, can prevent the formation of large crystals in the molten metal. Setting the molten metal temperature to 800°C or lower, more preferably 750°C or lower, allows the molten metal to be sufficiently cooled and solidified during casting.

[0052] The thickness of the rolled sheet obtained by the continuous casting method is preferably 2 mm or more and 10 mm or less, more preferably 4 mm or more and 8 mm or less. By preferably setting the thickness of the rolled sheet to 2 mm or more, more preferably 4 mm or more, a sound rolled sheet can be stably manufactured. In addition, by preferably setting the thickness of the rolled sheet to 10 mm or less, more preferably 8 mm or less, it is easy to wind the rolled sheet after casting onto a roller.

[0053] Rolled plates obtained by continuous casting can also be used directly as the fins. Furthermore, by adjusting the thickness and material type of the rolled plates through cold rolling and heat treatment, fins with the desired thickness and material type can be obtained. For example, the fins may have a material type indicated by the material type designation O, H1n, or H2n. To suppress corrosion during brazing, the fins preferably have a material type indicated by the material type designation H1n or H2n.

[0054] Furthermore, the fins made of an extended material can also be produced, for example, by performing an extension process on an ingot produced by DC casting. When producing an ingot by DC casting, the casting speed is preferably 20 mm / min or higher and 100 mm / min or lower, and more preferably 30 mm / min or higher and 80 mm / min or lower. In DC casting, by setting the casting speed preferably to 20 mm / min or higher, and more preferably to 30 mm / min or higher, the cooling rate during casting can be sufficiently increased, and the second phase particles in the fins can be easily refined. Furthermore, by setting the casting speed preferably to 100 mm / min or lower, and more preferably to 80 mm / min or lower, the molten metal can be sufficiently cooled and solidified during casting.

[0055] 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 this case, the cooling rate during casting can be sufficiently increased, and the second phase particles in the fins can be easily refined.

[0056] After an ingot is produced by DC casting, the ingot is extended, thereby obtaining a fin having a desired shape. For example, after a slab is produced by DC casting, the slab is rolled, thereby obtaining the fin consisting of a rolled plate having a desired thickness. As the rolling process, hot rolling and cold rolling can be appropriately combined. In addition, from before the rolling process to after the rolling process is completed, heat treatments such as homogenization and annealing can be performed as needed, and the material category of the fin can be adjusted. The fin can, for example, have a material category represented by the material category code O, H1n, or H2n. From the viewpoint of suppressing corrosion during brazing, the fin preferably has a material category represented by the material category code H1n or H2n.

[0057] Furthermore, after a billet is produced by DC casting, it is subjected to hot extrusion, thereby obtaining the fins made of extruded material having a desired cross-sectional shape. Prior to hot extrusion, the billet may be homogenized as needed. The billet is cast using a casting method such as hot top casting or GDC casting.

[0058] In the manufacturing method, raw aluminum ingots, intermediate alloys, and aluminum scrap can be used as the raw materials for casting. The aluminum scrap used as the raw material for casting includes, for example, discarded aluminum products, aluminum components separated from discarded products, and scraps and shavings generated during the manufacturing process of aluminum products and aluminum components. When using aluminum scrap as the raw material for casting, the aluminum scrap can be melted directly. Alternatively, the aluminum scrap can be melted after adjusting its size by cutting and compressing it. Furthermore, recycled aluminum ingots can be temporarily produced from the aluminum scrap and then used as the raw material for casting.

[0059] 〔Tube〕 The tubes in the heat exchanger core are formed of an aluminum alloy extruded material containing Cu: more than 0.05 mass % and 0.6 mass % or less.

[0060] As the tubes in the heat exchanger core, flat tubes, flat multi-hole tubes, and other tubes with a flat cross-sectional shape can be used. More specifically, the tubes only need to have a pair of flat wall portions spaced apart from each other and arranged opposite each other, and a connecting wall portion connecting the two ends of the flat wall portions in the width direction, and be 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 portion. In addition, the tubes may also have a partition portion that divides the internal space surrounded by the flat wall portion and the connecting wall portion into a plurality of heat transfer medium flow paths. In the heat exchanger core, the flat wall portion of the tube and the fin are joined via a brazing joint.

[0061] The cross-sectional shape of the tube perpendicular to the longitudinal direction is not particularly limited and can be various shapes such as rectangular, oval, etc. Furthermore, the cross-sectional shape of the heat transfer medium flow path is also not particularly limited and can be various shapes such as circular, oval, elliptical, triangular, and quadrilateral.

[0062] Regarding the chemical composition of the aluminum alloy extruded material constituting the tube, as long as the Cu content is within the specific range described above, it will suffice. For example, the aluminum alloy extruded material constituting the tube may have the following chemical composition, which contains Cu: more than 0.05% by mass and less than 0.6% by mass, with the remainder consisting of Al and unavoidable impurities. The Cu in the tube has the effect of increasing the strength of the tube. On the other hand, the Cu in the tube diffuses from the tube to the Zn spray coating and the brazed joint during brazing, and has the effect of increasing the natural electrode potential of these parts. Therefore, if the Cu content in the tube becomes excessive, 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 keeping the Cu content in the tube within the specific range described above, it is possible to ensure excellent corrosion resistance of the heat exchanger core and improve the strength of the tube.

[0063] Furthermore, in addition to Cu as an essential component, the tube may contain one or more elements as optional components. For example, the aluminum alloy extruded material constituting the tube may have a chemical composition comprising Cu: greater than 0.05 mass% and less than 0.6 mass%, and further containing, as optional components, one or more elements selected from the group consisting of Si: less than 0.7 mass%, Fe: less than 0.5 mass%, Mn: less than 1.2 mass%, and Ti: less than 0.3 mass%, with the balance being Al and unavoidable impurities. In addition, the aluminum alloy extruded material constituting the tube may have a chemical composition comprising Cu: more than 0.05 mass % and less than 0.6 mass %, and, as an arbitrary component, further comprising one or more elements selected from the group consisting of Si: more than 0.05 mass % and less than 0.7 mass %, Fe: more than 0.05 mass % and less than 0.5 mass %, Mn: more than 0.05 mass % and less than 1.2 mass %, and Ti: more than 0.01 mass % and less than 0.3 mass %, with the balance being Al and unavoidable impurities.

[0064] A sacrificial anode layer is formed on the outer surface of the tube. This sacrificial anode layer has a lower natural electrode potential than the inner surface of the tube. The sacrificial anode layer may be, for example, a Zn spray coating. The Zn film serving as the sacrificial anode layer is formed, for example, by allowing a portion of the Zn spray coating provided on the outer surface of the tube before brazing to remain after brazing.

[0065] Alternatively, the sacrificial anode layer may be, for example, a Zn-rich layer having a higher Zn concentration than the surrounding layer. The Zn-rich layer, serving as the sacrificial anode layer, is formed by, for example, Zn atoms contained in zinc vapor or a Zn spray coating diffusing from the outer surface of the tube toward the interior during brazing. It should be noted that when the sacrificial anode layer is a Zn-rich layer, the boundary between the Zn-rich layer and adjacent layers within the tube may not be clear. Even in such cases, the aforementioned effects can be achieved as long as the natural electrode potential Ets at the surface of the Zn-rich layer, serving as the sacrificial anode layer, satisfies the aforementioned conditions.

[0066] 〔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 greater than +50 mV 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 less than +100 mV when the natural electrode potential of the weld leg in the brazed joint is used as a reference; (3) the natural electrode potential of the sacrificial anode layer is greater than -80 mV and less than +150 mV when the natural electrode potential of the fin is used as a reference; (4) the natural electrode potential of the fin is lower than the natural electrode potential of the weld leg, or the natural electrode potential of the fin is greater than the natural electrode potential of the weld leg and the absolute value of the potential difference between the natural electrode potential of the fin, the natural electrode potential of the weld leg and the average value of the natural electrode potential of the sacrificial anode layer and the natural electrode potential of the fin is less than 40 mV.

[0067] 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 weld leg in the brazed joint, and the natural electrode potential Ef of the fin all satisfy the following four conditions.

[0068] (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.

[0069] (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 solder fillet is 100 mV or less.

[0070] (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 not less than -80 mV and not more than 150 mV.

[0071] (4) The natural electrode potential Ef of the fin is lower than the natural electrode potential Ej of the weld leg, or the natural electrode potential Ef of the fin is greater than the natural electrode potential Ej of the weld leg, and the absolute value of the potential difference Eav-Ef between the average Eav of the natural electrode potentials Ef of the fin, Ej of the weld leg, and Ets of the sacrificial anode layer and the natural electrode potential Ef of the fin is 40 mV or less. It should be noted that the average Eav of the natural electrode potentials of the fin, weld leg, and sacrificial anode layer is the arithmetic average of the natural electrode potentials Ef of the fin, Ej of the weld leg, and Ets of the sacrificial anode layer (i.e., (Ef + Ej + Ets) / 3).

[0072] This natural electrode potential relationship was difficult to achieve in conventional heat exchanger cores using fins made of a single-layer aluminum material that lacks the ability to form brazing sheets or brazed joints. A heat exchanger core that meets all four of the aforementioned conditions was achieved for the first time by setting the chemical composition of the aluminum alloy constituting the fins and tubes within the specified ranges described in the manufacturing method and then brazing in the presence of zinc vapor.

[0073] Under condition (1), by setting the natural electrode potential Eti of the inner surface of the tube to a potential that is 50 mV or higher (i.e., high) relative to the natural electrode potential Ets of the sacrificial anode layer, the sacrificial anode layer can function as a sacrificial anode relative to the inner surface of the tube, thereby suppressing corrosion inside the tube. If the potential difference Eti-Ets between the inner surface of the tube and the sacrificial anode layer is less than 50 mV, the sacrificial corrosion protection effect provided by the sacrificial anode layer becomes insufficient, and the interior of the tube is susceptible to corrosion. As a result, there is a risk of premature leakage of the heat transfer medium from the tube.

[0074] 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 solder leg in the brazed joint. By setting the potential difference Ets-Ej between the sacrificial anode layer and the solder leg to 100 mV or less, the potential balance between the sacrificial anode layer and the solder joint can be kept within the optimal range, and premature disappearance of the solder joint can be easily avoided. As a result, the fins can be prevented from falling off from the heat exchanger core. When the potential difference Ets-Ej between the sacrificial anode layer and the solder leg exceeds 100 mV, the solder joint is more susceptible to corrosion than other parts of the heat exchanger core, and the solder joint may disappear early. As a result, the fins may be easily separated from the heat exchanger core at an early stage.

[0075] 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 to within the specific range, both the fin and the sacrificial anode layer can function as sacrificial anodes relative to the tube. When the potential difference Ets-Ef between the sacrificial anode layer and the fin is less than -80 mV, the sacrificial anode layer is likely to corrode earlier than the fin. As a result, there is a possibility of early disappearance of the sacrificial anode layer, and corrosion of the tube may proceed 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 150 mV, the fin is likely to corrode earlier than the sacrificial anode layer, and there is a possibility of early disappearance of the fin.

[0076] In order to satisfy the condition (4), it is sufficient to satisfy any 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 weld leg in the brazed joint (i.e., the natural electrode potential Ef of the fin is lower than the natural electrode potential Ej of the weld leg); and (4-2): the natural electrode potential Ef of the fin is greater than the natural electrode potential Ej of the weld leg and the potential difference Eav-Ef between the average Eav and the natural electrode potential Ef of the fin is greater than -40 mV and less than 40 mV.

[0077] By making the natural electrode potential of each part of the heat exchanger core satisfy the above-mentioned condition (4) in addition to the above-mentioned conditions (1) to (3), it is possible to easily avoid the early disappearance of the fins and to achieve the sacrificial corrosion protection effect for a long time.

[0078] As described above, by ensuring that the natural electrode potential of each portion of the heat exchanger core satisfies all of the four conditions, the balance of the natural electrode potential at each portion of the heat exchanger core can be adjusted to an optimal range. As a result, it is easy to prevent any portion of the sacrificial anode layer, fins, and brazed joints from corroding earlier than other portions, thereby improving the corrosion resistance of the heat exchanger core as a whole. From the perspective of more reliably achieving this effect, the heat exchanger core preferably satisfies the four conditions (1) to (3) and (4-1). From the same perspective, the natural electrode potential of the fins, when taken as a reference to the natural electrode potential of the weld leg, 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 fins and the natural electrode potential Ef of the weld leg is preferably -5 mV or less, more preferably -10 mV or less, and even more preferably -15 mV or less.

[0079] (Method for manufacturing heat exchanger core) The heat exchanger core is obtained by alternately overlapping fins having the following chemical composition and assembling tubes made of the following aluminum alloy extruded material into an assembly, wherein the chemical composition contains Si: 2.0 mass% or more and 3.0 mass% or less, Fe: 0.05 mass% or more and 1.2 mass% or less, Cu: 0 mass% or more and 0.25 mass% or less, Mn: 0.3 mass% or more and 1.8 mass% or less, Zn: 0.3 mass% or more and 4.0 mass% or less, with the balance consisting of Al and unavoidable impurities, and the aluminum alloy extruded material contains Cu: more than 0.05 mass% and 0.6 mass% or less, The assembly is heated and brazed in an atmosphere containing zinc vapor, thereby forming the brazed joint between the fin and the tube and forming the sacrificial anode layer on the outer surface of the tube.

[0080] 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, for information on the types and contents of elements contained in the fins before brazing, and their effects, please refer to the description of the fins in the heat exchanger core after brazing.

[0081] The structure of the tubes used in the heat exchanger core is identical to that of the tubes in the heat exchanger core after brazing, except that the sacrificial anode layer is not formed on the outer surface. Therefore, for information on the types and contents of elements contained in the tubes before brazing, and their effects, reference can be made to the description of the tubes in the heat exchanger core after brazing.

[0082] In the heat exchanger core manufacturing method, after the tubes and fins are alternately stacked to form an assembly, the assembly is heated and brazed in an atmosphere containing zinc vapor. More specifically, the brazing atmosphere can be, for example, a non-oxidizing gas atmosphere containing zinc vapor. Examples of non-oxidizing gases include nitrogen and argon. Alternatively, the brazing atmosphere can be a reduced-pressure atmosphere containing zinc vapor.

[0083] The heating temperature during brazing of the assembly is preferably set so that the liquid phase fraction 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 greater than 5% by mass and less than 35% by mass, and more preferably is set so that the liquid phase fraction of the fins is greater than 7% by mass and less than 25% by mass. By setting the liquid phase fraction of the fins during heating within the specified range, a decrease in the strength of the fins during heating can be suppressed, and a sufficient amount of molten liquid can be generated from the fins, allowing for easy formation of a brazed joint with the tube.

[0084] In addition, the holding time of the heating temperature during brazing of the assembly is preferably set so that the time for the liquid phase fraction of the fin to reach 5% by mass or more is 30 seconds or more and 3600 seconds or less, and more preferably so that the time for the liquid phase fraction of the fin to reach 5% by mass or more is 60 seconds or more and 1800 seconds or less. By setting the holding time during brazing within the specific range, the reduction in the strength of the fin during heating can be suppressed, and the molten liquid generated from the fin can be fully filled between the fin and the tube. It should be noted that during the joining of 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.

[0085] More specifically, for example, the heating temperature during brazing can be appropriately set within a range of 580°C to 620°C. Furthermore, the holding time for the heating temperature can be appropriately set within a range of, for example, 0 minutes to 10 minutes, preferably 30 seconds to 5 minutes. The holding time here refers to the time elapsed from the point at which the heating temperature reaches the desired temperature. If the holding time for the heating temperature is 0 minutes, heating can be terminated immediately after the heating temperature reaches the desired temperature, and cooling of the heat exchanger core can be initiated.

[0086] The aforementioned liquid phase fraction of the fin can be determined based on the equilibrium diagram at the desired temperature and the lever rule. The equilibrium diagram used to calculate the liquid phase fraction can be a known equilibrium diagram or one created using equilibrium diagram calculation software. For example, the thermodynamic calculation system "Thermo-Calc (registered trademark)" manufactured by Thermo-Calc Software AB can be used.

[0087] Alternatively, prior to brazing, flux may be pre-placed on the portion of the assembly where the brazed joint is to be formed, and then the assembly may be heated and brazed. Examples of the flux 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 chloride-based fluxes, which are compounds commonly used as fluxes for brazing aluminum.

[0088] In the manufacturing method, when the assembly is heated, a small amount of molten metal is generated from the fins. Due to surface tension, the molten metal gathers at the contact portion between the fins and the tubes, thereby forming a brazed joint having a weld leg between the fins and the tubes.

[0089] In addition, in the manufacturing method, brazing is performed in an atmosphere containing zinc vapor. In this way, by brazing in the presence of zinc vapor, a sacrificial anode layer can be formed on the surface of the tube. Moreover, the Zn atoms in the zinc vapor can easily dissolve in the molten liquid generated from the fins during the formation of the brazed joint. Therefore, by dissolving the Zn atoms in the molten liquid gathered at the abutment portion between the fins and the tube, the natural electrode potential of the brazed joint can be moderately reduced. In addition, since the molten liquid generated from the fins is extremely small, the molten liquid present at a position away from the abutment portion between the fins and the tube is not introduced into the abutment portion between the fins and the tube, but remains on the fins. Therefore, the Zn atoms in the molten liquid dissolved in the fins can easily diffuse into the interior of the fins, which can moderately reduce the natural electrode potential of the fins.

[0090] As described above, by using fins made of an aluminum alloy having the specific chemical composition described above and capable of forming a brazed joint in a single layer, and 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. As a result, the heat exchanger core can be more easily obtained.

[0091] In the manufacturing method, the method for generating zinc vapor during brazing is not particularly limited, and various methods can be used. For example, in the manufacturing method, zinc can be placed in a heating furnace used for brazing, and zinc vapor can be generated from the zinc in the heating furnace by heating during brazing. Alternatively, as described later, a Zn spray coating can be formed on the outer surface of the tube before brazing, and zinc vapor can be generated from the Zn spray coating during brazing.

[0092] Preferably, a Zn spray coating is provided on the outer surface of the tube used in the manufacture of the heat exchanger core. After assembling the assembly using the tube having the Zn spray coating provided on the outer surface, brazing is performed, thereby allowing the Zn atoms in the Zn spray coating to diffuse into the tube and more easily forming a sacrificial anode layer on the outer surface of the tube. In addition, the Zn spray coating can generate zinc vapor by being heated during brazing. By the zinc vapor coming into contact with the fins and the brazed joints, the natural electrode potential of the fins and the brazed joints can be reduced. As a result of the above, the natural electrode potential of each part in the heat exchanger core after brazing can be more easily adjusted to within the specific range.

[0093] The amount of Zn deposited in the Zn spray coating provided on the outer surface of the pipe is not particularly limited, and can be, for example, from 3 g / m 2 Above and 9g / m 2 The following ranges are set appropriately.

[0094] 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. In this case, it is easier to adjust the natural electrode potential of each portion of the heat exchanger core after brazing to within the specific range.

[0095] It should be noted that the difference between the Zn content in the fins after brazing and the Zn content in the fins before brazing can be adjusted, for example, by adjusting the concentration of zinc vapor in the atmosphere during brazing. For example, if it is desired to increase the Zn content in the fins after brazing, it is sufficient to increase the concentration of zinc vapor in the atmosphere during brazing. Furthermore, the concentration of zinc vapor in the atmosphere during brazing can be easily adjusted, for example, by adjusting the total amount of zinc in the heating furnace. For example, if it is desired to increase the concentration of zinc vapor in the atmosphere during brazing, it is sufficient to increase the amount of zinc in the heating furnace and / or the amount of zinc sprayed coating provided on the outer surface of the tube.

[0096] Example (Example) Reference Figures 1 to 3 The heat exchanger core and the manufacturing method thereof are described in detail. Figure 1 as well as Figure 2 As shown, the heat exchanger core 1 of this example includes fins 2, tubes 3, and brazing joints 4 that join the fins 2 and tubes 3. The fins 2 are made of an aluminum alloy having the following chemical composition: 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 5.0 mass%, with the balance being Al and unavoidable impurities.

[0097] The tube 3 is made of an aluminum alloy extruded material containing Cu: more than 0.05 mass % and 0.6 mass % or less. Figure 2 As shown, a sacrificial anode layer 31 is formed on the outer surface of the tube 3, and the sacrificial anode layer 31 has a lower natural electrode potential than the inner 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 greater than +50 mV 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 less than +100 mV when the natural electrode potential of the weld leg in the brazed joint 4 is used as a reference; (3) the natural electrode potential of the sacrificial anode layer 31 is greater than -80 mV and less than +150 mV when the natural electrode potential of the fin 2 is used as a reference; (4) the natural electrode potential of the fin 2 is lower than the natural electrode potential of the weld leg, or the natural electrode potential of the fin 2 is greater than the natural electrode potential of the weld leg and the absolute value of the potential difference between the average value of the natural electrode potential of the fin 2, the natural electrode potential of the weld leg, and the natural electrode potential of the sacrificial anode layer 31 and the natural electrode potential of the fin is less than 40 mV.

[0098] like Figure 1As shown, the heat exchanger core 1 of this example has a plurality of fins 2 and a plurality of tubes 3, and is constituted as a so-called parallel flow type heat exchanger core in which the fins 2 and tubes 3 are alternately stacked. The fins 2 in the heat exchanger core 1 of this example are given a corrugated shape by stamping, as shown in FIG. Figure 2 As shown in FIG, the fin is composed of a plurality of fin tops 21 bent into a U shape and a fin middle portion 22 connecting the fin tops 21 to each other. Figure 3 As shown, the tube 3 is composed of an extruded multi-hole tube, which includes: a pair of flat wall portions 32 arranged opposite to each other with a gap; a connecting wall portion 33 connecting the two ends of the flat wall portion 32 in the width direction; and a partition wall portion 35 that divides the internal space surrounded by the flat wall portion 32 and the connecting wall portion 33 into a plurality of heat transfer medium flow paths 34. Figure 2 As shown, the fin tops 21 of the fins 2 and the flat wall portions 32 of the tubes 3 are joined via brazing joints 4 .

[0099] like Figure 1 As shown, the heat exchanger core 1 of this embodiment may also include a header 11 attached to both ends of the plurality of tubes 3, and side plates 12 joined to the outermost fins 2 in the stacking direction of the plurality of fins 2. The internal space of the header 11 is configured to allow heat transfer medium to flow through the heat transfer medium flow paths 34 of the tubes 3. The header 11 can distribute the heat transfer medium within the header 11 to the plurality of tubes 3, or combine the heat transfer medium discharged from the tubes 3 in the header 11.

[0100] Although not shown, the header box 11 and the tubes 3 are joined via a brazed joint. The method for joining the header box 11 and the tubes 3 is not particularly limited; a brazed joint may be formed using a known method. For example, a method can be employed in which the header box 11 before brazing is constructed from a brazing sheet comprising a core material and a brazing filler metal laminated on at least one surface of the core material, and the brazed joint 4 is formed using the brazing filler metal of the header box 11. Alternatively, a separate brazing filler metal may be disposed between the header box 11 and the tubes 3, and the brazed joint may be formed using this brazing filler metal.

[0101] In addition, the side plates 12 and the fins 2 are joined via brazing joints 4 .

[0102] The manufacturing method of the heat exchanger core 1 of this example is as follows. First, a stack is produced by alternately stacking fins 2 having the following chemical composition: 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; the aluminum alloy extruded material containing Cu: greater than 0.05 mass% to 0.6 mass%. A header 11 is attached to both ends of the tubes 3 in this stack, and side plates 12 are brought into contact with the outermost fins 2 of the plurality of fins 2 to form an assembly.

[0103] Next, the assembly is heated and brazed in an atmosphere containing zinc vapor. Figure 1 The heat exchanger core 1 is shown.

[0104] Next, the effects of this example will be described. The fins 2 in the heat exchanger core 1 of this example are made of an aluminum alloy having the specific chemical composition. By using at least the fins 2 having the specific chemical composition, the heat exchanger core 1 can obtain a heat exchanger core 1 in which the natural electrode potential of each part satisfies all of the aforementioned four conditions. Furthermore, by setting the natural electrode potential of each part in the heat exchanger core 1 to the aforementioned manner, the corrosion resistance of the heat exchanger core 1 can be improved.

[0105] In addition, in the manufacturing method of the heat exchanger core 1, after the fins 2 having the specific chemical composition are combined with the tubes 3 to produce an assembly, the assembly is brazed in an atmosphere containing zinc vapor. The zinc vapor in the brazing atmosphere can moderately reduce the natural electrode potential of the fins 2 and the brazed joint 4. In addition, the zinc vapor in the brazing atmosphere can form a sacrificial anode layer 31 on the outer surface of the tube 3. In this way, by using zinc vapor to adjust the potential of each part of the heat exchanger core 1, it is easy to obtain a heat exchanger core 1 in which the natural electrode potential of each part meets all of the aforementioned four conditions.

[0106] (Experimental example) In this example, an example of corrosion resistance evaluation using a microcore test body S1 simulating a heat exchanger core 1 is described. Note that the same symbols used in this example as those used in the previously described embodiments represent the same components as those in the previously described embodiments.

[0107] like Figure 4As shown, the microcore test body S1 includes two tubes 3 (3a, 3b) spaced apart from each other, and a fin 2 interposed between the two tubes 3. Furthermore, the flat wall portion 32 of the tube 3 abuts against the fin top 21 of the fin 2, forming a brazed joint 4 between the tube 3 and the fin 2.

[0108] The tube 3 used in the preparation of the microcore test body S1 is specifically a flat porous tube made of an aluminum alloy extruded material having the chemical composition shown in Table 1. It should be noted that "Bal." in Table 1 is a symbol indicating the balance. The width of the tube 3 is 14 mm, the length is 40 mm, and the thickness of the flat wall portion 32, the connecting wall portion 33, and the partition portion 35 are all 0.35 mm. In addition, a Zn spray coating is pre-formed on the outer surface of the tube 3. The amount of Zn atoms attached in the Zn spray coating is about 8 g / m 2 .

[0109] The fins 2 used in the preparation of the microcore test piece S1 were specifically single-layer corrugated fins made of an aluminum alloy having the chemical composition shown in Table 1. The thickness of the fins 2 was 0.08 mm, the spacing between the fin tips 21 was 3 mm, and the height of the fins 2 was 10 mm. Of the two tubes 3, 11 fin tips 21 abutted the first tube 3a, and 12 fin tips 21 abutted the second tube 3b.

[0110] To produce the microcore test piece S1, the tubes 3 and fins 2 are first overlapped, and flux is applied to the contact areas between the tubes 3 and fins 2 to create an assembly. Ten of these assemblies are placed in a heating furnace, and zinc is placed around them. Furthermore, to trap zinc vapor around the assemblies, the ten assemblies and the zinc are covered with a covering. The assemblies are then heated in an inert gas atmosphere, generating zinc vapor from the zinc and Zn spray coating. Brazing of the assemblies is then performed in the presence of the zinc vapor. Through the above operations, the microcore test piece S1 is obtained.

[0111] The Zn content in the fins 2 of the resulting microcore test piece S1 is higher than the Zn content in the fins 2 before brazing due to contact with zinc vapor during brazing. For example, in the microcore test piece S1 of this example, the Zn content in the fins 2 after brazing can be set to 1.75 mass%, which is 0.27 mass% higher than the Zn content in the fins 2 before brazing. The Zn content in the fins 2 after brazing can be measured, for example, using an electron probe microanalyzer (EPMA). When using EPMA to measure the Zn content in the fins 2, specifically, a line analysis of the surface of the fins 2 is performed at the center of the microcore test piece S1, and the average value of the resulting Zn concentration distribution is used as the Zn content.

[0112] Table 2 shows the natural electrode potential and corrosion resistance of various parts of microcore test body S1. It should be noted that microcore test body R1 shown in Table 2 is a test body used for comparison with microcore test body S1. Microcore test body R1 has the same structure as microcore test body S1, except that a double-sided brazing sheet with brazing filler metal laminated on both sides of the core material is used as the fin 2. The chemical composition of the core material and brazing filler metal in the fin 2 of microcore test body R1 is shown in Table 1. In addition, the thickness of the double-sided brazing sheet before brazing was 0.08 mm, and the coverage of the brazing filler metal was 10% for each. In addition, the production method of microcore test body R1 is the same as that of microcore test body S1, except that a double-sided brazing sheet is used instead of the fin 2 made of a single layer of aluminum alloy. It should be noted that the Zn content in the fin of microcore test body 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.

[0113] The method for measuring the natural electrode potential and the method for evaluating the corrosion resistance shown in Table 2 are as follows.

[0114] Natural electrode potential Ets of the sacrificial anode layer 31 Fins 2 were removed from the brazed microcore test pieces S1 and R1, and the first tube 3a was removed. Within the sacrificial anode layer 31 of the tube 3a, the area between any brazed joint 4 and the adjacent brazed joint 4 was determined as the potential measurement area. Specifically, the potential measurement area was the area on the outer surface of the first tube 3a that faced the fins at one pitch.

[0115] After the potential measurement area is determined as described above, the portion outside the potential measurement area is covered with a sealant. Then, the natural electrode potential of the potential measurement area is measured as follows. Figure 5 The measuring device 5 shown in FIG. 1 includes: a first container 51 for containing a solution for immersing the tube 3; a second container 52 for containing a solution for immersing the reference electrode 54; a salt bridge 53 for electrically connecting the solution in the first container 51 and the solution in the second container 52; and an electrometer 55 for measuring and recording the potential of the potential measurement area relative to the reference electrode 54. Figure 5 , the shape of the tube 3 is schematically shown.

[0116] The spontaneous electrode potential was measured as follows. First, a 5% NaCl aqueous solution adjusted to pH 3 using acetic acid was prepared in a first container 51, and a saturated NaCl aqueous solution was prepared in a second container 52. The solution in the first container 51 and the solution in the second container 52 were then electrically connected via a salt bridge 53. The temperature of each solution was set to room temperature.

[0117] Next, the tube 3 and the reference electrode 54 are electrically connected to the electrometer 55. In addition, as the reference electrode 54, a saturated calomel electrode (so-called SCE) can be used, for example.

[0118] In this state, the potential measurement region M of the tube 3 is immersed while stirring the solution in the first container 51, and the reference electrode 54 is immersed in the saturated NaCl aqueous solution in the second container 52. This allows the natural electrode potential (unit: mV vs. SCE) of the potential measurement region M of the tube 3 to be measured with reference electrode 54 as the reference. The arithmetic mean of the natural electrode potentials of the potential measurement region M from 20 hours to 24 hours after the start of the measurement is then calculated as the natural electrode potential Ets of the sacrificial anode layer 31.

[0119] The natural electrode potential Eti of the inner surface of tube 3 The fins 2 are cut off from the brazed micro core test bodies S1 and R1, and the first tube 3a is removed. The flat wall portion 32a, the connecting wall portion 33, and the partition wall portion 35 not joined to the fin top 21 are cut off from the tube 3a, and the flat wall portion 32b (see Figure 4 ) is exposed. A potential measurement region is defined on this inner surface, and the portion outside the potential measurement region is covered with a sealant. The natural electrode potential in the potential measurement region is then measured using the same method as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained is defined as the natural electrode potential Eti of the inner surface of the tube 3.

[0120] Natural electrode potential Ef of fin 2 The first tube 3a and the fin tip 21 connected to the first tube 3a were removed from the brazed microcore test bodies S1 and R1. Next, a potential measurement area was established on the surface of the fin 2 connected to the second tube 3b, and the area outside the potential measurement area was covered with a sealant. The natural electrode potential in the potential measurement area was then measured using the same method as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained was designated as the natural electrode potential Ef of the fin 2.

[0121] Natural electrode potential Ej of the weld foot Fins 2 are removed from the brazed microcore test pieces S1 and R1, and the first tube 3a is removed. Next, the remaining fin tip 21 of the first tube 3a is face-cut so that both the solder leg of the brazed joint 4 and the fin tip 21 are exposed on a common plane. A potential measurement area is then defined on the exposed solder leg, and the portion outside the potential measurement area is covered with a sealant. The natural electrode potential of the potential measurement area is then measured using the same method as the natural electrode potential Ets of the sacrificial anode layer 31. The natural electrode potential thus obtained is referred to as the natural electrode potential Ej of the solder leg.

[0122] Corrosion resistance The microcore test pieces S1 and R1 obtained by the aforementioned method were covered with a sealant on the end faces of the tubes 3, the connecting wall portions 33 of the tubes 3, and the flat wall portions 32a not bonded to the fins 2. SWAAT testing was then conducted according to ASTM-G85-A3. The test period was either 20 days or 40 days. After the test, the microcore test pieces S1 and R1 were cleaned with acid, and their corrosion resistance was evaluated based on whether the tubes 3 penetrated and whether the fins 2 peeled off from the tubes 3.

[0123] The meanings of the symbols shown in the "Fin peeling" column in Table 2 are as follows.

[0124] A: All fin tops are joined to the tubes B: A portion of the fin top peels off from the tube C: All fin tops peeled off from the tube In addition, the symbols shown in the "Pipe Penetration" column in Table 2 are as follows.

[0125] A: No corrosion of the through pipe occurs B: Corrosion of the through pipe occurs [Table 1] [Table 2] As shown in Table 1, the microcore test piece S1 comprises a single-layer fin 2 made of an aluminum alloy having the specified 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 at various locations within the microcore test piece S1 all satisfy the four conditions described above. Consequently, the microcore test piece S1 avoids premature loss of any of the sacrificial anode layer 31, the fin 2, or the brazed joint 4, exhibiting excellent corrosion resistance.

[0126] On the other hand, the microcore test body R1 having fins made of double-sided brazing sheets had poorer corrosion resistance than the microcore test body S1, and the fins peeled off from the tube 3 when the SWAAT test was continued for 20 days. In addition, if the SWAAT test of the microcore test body R1 was continued for 40 days, the fins completely peeled off from the tube 3, and corrosion that penetrated the tube 3 occurred. The following reasons can be considered as reasons for this. When brazing sheets are used as fins, the molten brazing material formed by melting the brazing material has high fluidity, so it is believed that the molten brazing material containing Zn atoms easily moves to the weld leg of the brazed joint. Therefore, it is believed that the Zn content in the brazed joint becomes excessive, and the natural electrode potential Ej of the brazed joint easily becomes too low.

[0127] Furthermore, it is believed that the molten brazing filler metal easily flows during brazing, which can lead to insufficient diffusion of Zn from the molten brazing filler metal into the core material. Consequently, the effect of the sacrificial anode layer formed on the surface of the fin after brazing is insufficient, and corrosion is likely to progress into the interior of the tube.

[0128] The heat exchanger core and the manufacturing method thereof involved in the present invention are described above based on the embodiments and experimental examples, but the specific methods of the heat exchanger core and the manufacturing method thereof involved in the present invention are not limited to the embodiments and experimental examples, and the structure can be appropriately changed within the scope without damaging the main purpose of the present invention.

[0129] For example, the heat exchanger core can adopt the following aspects [1] to [2].

[0130] [1] A heat exchanger core having: A fin having a chemical composition comprising 2.0 mass % to 3.0 mass % of Si, 0.05 mass % to 1.2 mass % of Fe, 0 mass % to 0.25 mass % of Cu, 0.3 mass % to 1.8 mass % of Mn, and 0.3 mass % to 5.0 mass % of Zn, with the balance being Al and unavoidable impurities; A pipe composed of an aluminum alloy extruded material containing Cu: more than 0.05 mass % and 0.6 mass % or less; and a brazing joint joining the fin to the tube, A sacrificial anode layer is formed on the outer surface of the tube, and the sacrificial anode layer has a lower natural electrode potential than the inner surface of the tube. The heat exchanger core satisfies the following four conditions: (1) the natural electrode potential of the inner surface of the tube is greater than +50 mV 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 less than +100 mV when the natural electrode potential of the weld leg in the brazed joint is used as a reference; (3) the natural electrode potential of the sacrificial anode layer is greater than -80 mV and less than +150 mV when the natural electrode potential of the fin is used as a reference; (4) the natural electrode potential of the fin is lower than the natural electrode potential of the weld leg, or the natural electrode potential of the fin is greater than the natural electrode potential of the weld leg and the absolute value of the potential difference between the natural electrode potential of the fin, the natural electrode potential of the weld leg and the average value of the natural electrode potential of the sacrificial anode layer and the natural electrode potential of the fin is less than 40 mV.

[0131] [2] A heat exchanger core according to [1], wherein the fin further contains one or more elements selected from the group consisting of Zr: greater than 0 mass % and less than 0.3 mass %, Cr: greater than 0 mass % and less than 0.3 mass %, Ti: greater than 0 mass % and less than 0.3 mass %, V: greater than 0 mass % and less than 0.3 mass %, Ni: greater than 0 mass % and less than 0.8 mass %, Mg: greater than 0 mass % and less than 0.1 mass %, In: greater than 0 mass % and less than 0.03 mass %, and Sn: greater than 0 mass % and less than 0.1 mass %.

[0132] In addition, the method for manufacturing the heat exchanger core can adopt the following methods [3] to [6].

[0133] [3] A method for manufacturing a heat exchanger core according to [1] or [2], wherein fins having the following chemical composition and tubes made of the following aluminum alloy extruded material are alternately stacked and assembled into an assembly, The chemical composition contains Si: 2.0 mass% or more and 3.0 mass% or less, Fe: 0.05 mass% or more and 1.2 mass% or less, Cu: 0 mass% or more and 0.25 mass% or less, Mn: 0.3 mass% or more and 1.8 mass% or less, Zn: 0.3 mass% or more and 4.0 mass% or less, and the balance is composed of Al and inevitable impurities, and the aluminum alloy extruded material contains Cu: more than 0.05 mass% and 0.6 mass% or less, The assembly is heated and brazed in an atmosphere containing zinc vapor, thereby forming the brazed joint between the fin and the tube and forming the sacrificial anode layer on the outer surface of the tube.

[0134] [4] A method for manufacturing a heat exchanger core according to [3], wherein the fin further contains one or more elements selected from the group consisting of Zr: greater than 0 mass % and less than 0.3 mass %, Cr: greater than 0 mass % and less than 0.3 mass %, Ti: greater than 0 mass % and less than 0.3 mass %, V: greater than 0 mass % and less than 0.3 mass %, Ni: greater than 0 mass % and less than 0.8 mass %, Mg: greater than 0 mass % and less than 0.1 mass %, In: greater than 0 mass % and less than 0.03 mass %, and Sn: greater than 0 mass % and less than 0.1 mass %.

[0135] [5] The method for manufacturing a heat exchanger core according to [3] or [4], wherein the assembly is assembled using the tube having a Zn spray coating provided on the outer surface.

[0136] [6] The method for manufacturing a heat exchanger core according to [3] or [4], 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.

Claims

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

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

3. A method for manufacturing a heat exchanger core, which is the method for manufacturing a heat exchanger core according to claim 1 or 2, In the manufacturing method, fins and tubes made of aluminum alloy extruded material are alternately stacked and assembled into an assembly. heating the assembly and brazing the assembly in an atmosphere containing zinc vapor, thereby forming the brazed joint between the fin and the tube and forming the sacrificial anode layer on the outer surface of the tube, The fin has the following chemical composition: Si: 2.0 mass% or more and 3.0 mass% or less, Fe: 0.05 mass% or more and 1.2 mass% or less, Cu: 0 mass% or more and 0.25 mass% or less, Mn: 0.3 mass% or more and 1.8 mass% or less, and Zn: 0.3 mass% or more and 4.0 mass% or less, with the balance being Al and unavoidable impurities, and the aluminum alloy extruded material contains Cu: more than 0.05 mass% and 0.6 mass% or less.

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 0.3 mass % or less, Cr: more than 0 mass % and 0.3 mass % or less, Ti: more than 0 mass % and 0.3 mass % or less, V: more than 0 mass % and 0.3 mass % or less, Ni: more than 0 mass % and 0.8 mass % or less, Mg: more than 0 mass % and 0.1 mass % or less, In: more than 0 mass % and 0.03 mass % or less, and Sn: more than 0 mass % and 0.1 mass % or less.

5. The method for manufacturing a heat exchanger core according to claim 3 or 4, wherein: The assembly is assembled using the tube having the Zn spray coating provided on the outer surface.

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

Images