Patent Application
20210079502
The present invention relates to an aluminum alloy fin material used for producing heat exchangers made of aluminum alloy, a method of producing the same, and a heat exchanger produced using the same.
Heat exchangers made of aluminum alloy are widely used as heat exchangers for automobiles such as a radiator, a heater, an oil cooler, an intercooler, and an evaporator and a condenser of an air-conditioner, and also as heat exchangers such as oil coolers of hydraulic equipment and industrial machinery. The fin material of such aluminum alloy heat exchangers is required to have a sacrificial anode effect for corrosion protection of a tube material the internal surface of which serves as a passage for working fluid (refrigerant), and is also required to have brazed joint performance such as preventing buckling deformation or erosion by solder at high temperature during braze-heating in producing a core thereof.
As aluminum alloy fin materials for satisfying such requirements, fin materials of aluminum alloys comprising Mn such as Al—Mn-based, Al—Mn—Si-based, and Al—Mn—Si—Cu-based alloys according to JIS-A3003 and JIS-A3203, for example, have been conventionally used. Furthermore, in order to impart the sacrificial anode effect to the aluminum alloy fin materials, a method of adding Zn, Sn, In. and the like thereto to make the aluminum alloy fin materials electrochemically negative has been used.
In recent years, because of demand for weight reduction of automobiles, thickness reduction of component materials is required also of automotive heat exchangers from viewpoints of energy savings and resource savings, and thickness reduction is accordingly expected for fin materials. Because thickness reduction of fin materials affects stiffness of a heat exchanger, fin materials having excellent strength after brazing are demanded, and aluminum alloys formed by adding Fe, Cu, and Zn to JIS-A3003 alloys have been proposed.
Patent Literature 1 discloses an aluminum alloy fin material for heat exchangers comprising: 1.0 to 2.0 mass % of Mn; 0.5 to 1.3 mass % of Si; 0.1 to 0.8 mass % of Fe; more than 0.20 mass % and 0.4 mass % or less of Cu; and 1.1 mass % or more and less than 2.0 mass % of Zn, with the balance being Al and inevitable impurities, in which the matrix of the aluminum alloy fin material has a recrystallized structure.
Patent Literature 2 discloses an aluminum alloy fin material for heat exchangers comprising: 1.0% (mass %, the same applies hereinafter) to 2.0% of Mn; 0.5% to 1.3% of Si; 0.1% to 0.8% of Fe; 0.21 to 0.5% of Cu; and 1.1% to 5% of Zn, in which the content ratio of Mn to Si (Mn %/Si %) is set to 1.0 to 3.5, and the content ratio of Zn to Cu (Zn %/Cu %) is set to 5 to 15. The aluminum alloy fin material further comprises one or two types selected from 0.05% to 0.3% of Zr and 0.05% to 0.3% of Cr, with the balance being Al and inevitable impurities, and the tensile strength thereof is 160 to 270 MPa.
Patent Literature 3 discloses a sagging resistant strip produced by a) a step of casting a melt comprising: 0.3 to 1.5% of Si; ≤0.5% of Fe; ≤0.3% of Cu; 1.0 to 2.0% of Mn; ≤0.5% of Mg, more preferably ≤0.3%; ≤4.0% of Zn; ≤0.5% of Ni; ≤0.3% each of dispersoid forming elements from the group IVb, Vb, or VIb; and 0.05% or less each of inevitable impurity elements in a total amount of 0.15% or less, with the balance being aluminum, so as to obtain an ingot, b) a step of preheating the ingot at a temperature of less than 550° C., preferably 400 to 520° C., more preferably 450 to 520° C., and especially 470 or more up to 520° C., so as to form dispersoid particles, c) a step of hot-rolling to obtain a strip, d) a step of cold-rolling the strip obtained at step (c) with a total reduction of 90% or more, and preferably >95% resulting in a strip having a first proof stress value, and then e) a step of subjecting the strip to a heat treatment to the delivery temper with the purpose to soften the material by a tempering without any recrystallization of the strip alloy, in such a way that a strip is obtained having a second proof stress value that is 10 to 50% lower, and preferably 15 to 40% lower than the first proof stress value obtained immediately after the cold-rolling at step (d), and having a 0.2% proof stress range of 100 to 200 MPa, more preferably 120 to 180 MPa, and most preferably 140 to 180 MPa. The sagging resistant strip has in the delivery temper a dispersoid particle density in the range of 1 to 20×106, preferably 1.3 to 0.5×106 particles/mm2, most preferably 1.4 to 7×106 particles/mm2 of particles having a diameter in the range of 50 to 400 nm.
Commonly, a fin material for heat exchangers is formed in a corrugated shape, and is then assembled with a tube material to be joined together by brazing. Because the fin material joined together by brazing provides stiffness to the entire core and has a sacrificial anticorrosive effect to the tube material in externally corrosive environments, a joint failure significantly affects strength and corrosion resistance of the core. There are various factors of the joint failure, and examples of the factors include variations in fin height when the fin is formed in a corrugated shape and deformation of fin tops due to erosion during brazing.
In Patent Literature 1, an aluminum alloy is proposed as a high strength fin material in which Fe, Cu, and Zn are added to a JIS-A3003 alloy. However, there are problems that elongation of the material decreases because it is a recrystallized material, that variations in fin height is more likely to occur when the fin is formed in a corrugated shape, and that joint failure is more likely to occur when the fin is assembled with a tube and subjected to braze-heating.
In Patent Literature 2, an H1n material that is cold-rolled after intermediate annealing is split into strips while rolling oil comprising rolling abrasion powder remains on the surface of the material. Thus, the rolling abrasion powder is more likely to be accumulated in a slitter, which requires washing thereby causing reduction in workability.
In Patent Literature 3, when the sagging resistant strip is used as a fin material to be brazed to a tube material, there is a problem in that the corrosion resistance thereof is insufficient.
In view of these, it is an object of the present invention is to provide an aluminum alloy fin material for heat exchangers having excellent formability before brazing, excellent brazing properties, and excellent strength properties and corrosion resistance after brazing.
In order to solve the above-described problems, as a result of studies conducted on relations among brazing properties, strength properties, a sacrificial anode effect, chemical compositions, combinations of chemical compositions, strength properties of materials, and internal structures, for example, the inventors of the present invention found that strength after brazing can be increased while strength before brazing is reduced and also satisfactory brazing properties and corrosion resistance can be obtained by optimizing the amounts of Si, Cu, Mn, and Zn to be added and the matrix structure of the fin material, and has completed the present invention.
Specifically, the present invention (1) provides an aluminum alloy fin material for heat exchangers, the aluminum alloy fin material being made of aluminum alloy comprising: 1.00 to 1.60 mass % of Mn; 0.70 to 1.20 mass % of Si; 0.05 to 0.50 mass % of Fe; 0.05 to 0.35 mass % of Cu; and 1.00 to 1.80 mass % of Zn, with the balance being Al and inevitable impurities, in which
The present invention (2) provides the aluminum alloy fin material for heat exchangers of (1), in which the aluminum alloy further comprises 0.20 mass % or less of Zr.
The present invention (3) provides the aluminum alloy fin material for heat exchangers of (1) or (2), in which the aluminum alloy is an H2n (n is an integer selected from 2, 4, and 6) material.
The present invention (4) provides the aluminum alloy fin material for heat exchangers of any one of (1) to (3), in which total number density of an Al—Mn-based intermetallic compound and an Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy after brazing is 0.50×106 particles/mm2 or more, and a grain size thereof after brazing is 40 to 200 mm.
The present invention (5) provides a method of producing an aluminum alloy fin material for heat exchangers, the method comprising: without performing homogenization treatment, subjecting an ingot to hot-rolling by heating up to 400 to 500° C. to start the hot-rolling and completing the hot-rolling at 350° C. or less, the ingot being made of aluminum alloy comprising 1.00 to 1.60 mass % of Mn, 0.70 to 1.20 mass % of Si, 0.05 to 0.50 mass % of Fe, 0.05 to 0.35 mass % of Cu, and 1.00 to 1.80 mass % of Zn with the balance being Al and inevitable impurities; subsequently subjecting the hot-rolled material to cold-rolling in one or a plurality of passes, or subjecting the hot-rolled material to the cold-rolling in one or a plurality of passes and intermediate annealing performed one or more times between the passes of the cold-rolling; and subsequently subjecting the cold-rolled material to final annealing.
The present invention (6) provides a heat exchanger obtained by brazing the aluminum alloy fin material for heat exchangers of any one of (1) to (5), in which a grain size of aluminum alloy that forms a fin of the heat exchanger is 40 to 200 pm, and total number density of an Al—Mn-based intermetallic compound and an Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy is 0.50×106 particles/mm2 or more.
According to the present invention, an aluminum alloy fin material for heat exchangers having excellent formability before brazing, excellent brazing properties, and excellent strength properties and corrosion resistance after brazing can be provided.
An aluminum alloy fin material for heat exchangers according to the present invention is an aluminum alloy fin material for heat exchangers, the aluminum alloy fin material being made of aluminum alloy comprising: 1.00 to 1.60 mass % of Mn; 0.70 to 1.20 mass % of Si; 0.05 to 0.50 mass % of Fe; 0.05 to 0.35 mass % of Cu; and 1.00 to 1.80 mass % of Zn, with the balance being Al and inevitable impurities, in which
The aluminum alloy fin material for heat exchangers according to the present invention is made of aluminum alloy. In other words, the aluminum alloy fin material for heat exchangers according to the present invention is formed by the aluminum alloy.
The aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention comprises Mn. Mn together with Si forms an Al—Si—Mn-based intermetallic compound, thereby increasing the strength of the fin material before brazing and after brazing and also improving high-temperature buckling resistance and formability thereof. The Mn content in the aluminum alloy is 1.00 to 1.60 mass %. When the content of Mn in the aluminum alloy is within this range, the strength of the fin material before brazing and after brazing is increased, and also the high-temperature buckling resistance and the formability are improved. If the content of Mn in the aluminum alloy is less than this range, the effect of Mn becomes too small. If the content exceeds this range, the strength before brazing becomes too high, whereby the formability is reduced, coarse crystallization products are formed during casting, and rolling workability is adversely affected. Consequently, it is difficult to obtain a perfect sheet material.
The aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention comprises Si. Si together with Mn forms an Al—Si—Mn-based intermetallic compound, and thus an effect of increasing the strength of the fin material before brazing and after brazing can be expected. The Si content in the aluminum alloy is 0.70 to 1.20 mass %. When the Si content in the aluminum alloy is within this range, the strength of the fin material before brazing and after brazing increases. If the Si content in the aluminum alloy is less than this range, the effect of Si becomes too small. If the content exceeds this range, the melting point decreases, and local melting is more likely to occur during brazing.
The aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention comprises Fe. Fe increases the strength of the fin material before brazing and after brazing and also improves the formability thereof. The Fe content in the aluminum alloy is 0.05 to 0.50 mass %. When the content of Fe in the aluminum alloy is within this range, the strength of the fin material before brazing and after brazing is increased and the formability is improved. If the content of Fe in the aluminum alloy is less than this range, the effect of Fe becomes too small. If the content exceeds this range, Fe serves as a cathode for the aluminum base material, whereby the corrosion resistance is reduced.
The aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention comprises Cu. Cu increases the strength of the fin material before brazing and after brazing and also improves the formability thereof. The Cu content in the aluminum alloy is 0.05 to 0.35 mass %. When the content of Cu in the aluminum alloy is within this range, the strength of the fin material before brazing and after brazing is increased and the formability is improved. If the Cu content in the aluminum alloy is less than this range, the effect of Cu becomes too small. If the content exceeds this range, the potential of the fin material is positive, the sacrificial anode effect is reduced, and also the melting point decreases and local melting is more likely to occur during brazing.
The aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention comprises Zn. Zn makes the potential of the fin material negative, thereby imparting a sacrificial anode effect to the tube material. The Zn content in the aluminum alloy is 1.00 to 1.80 mass %. When the Zn content in the aluminum alloy is within this range, the sacrificial anode effect for the tube material is increased. If the content of Zn in the aluminum alloy is less than this range, the effect of Zn becomes too small. If the content exceeds this range, intergranular corrosion susceptibility increases, the melting point decreases, and local melting is more likely to occur during brazing.
The aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention may further comprise 0.20 mass % or less of Zr as necessary. Zr increases the strength of the fin material before brazing and after brazing and also increases the grain size thereof after brazing, thereby enhancing the high-temperature buckling resistance and brazing properties. When the content of Zr in the aluminum alloy is within this range, the strength of the fin material before brazing and after brazing is increased, and also the high-temperature buckling resistance and brazing properties are enhanced. If the content of Zr in the aluminum alloy exceeds this range, coarse crystallization products are formed during casting, which makes production of a perfect sheet material difficult.
The matrix of the aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention has a fibrous structure. When the matrix of the aluminum alloy has a fibrous structure, elongation thereof before brazing is improved and the formability is also improved. If the matrix of the aluminum alloy has a recrystallized structure, elongation thereof before brazing decreases and the formability deteriorates.
The tensile strength (tensile strength before brazing) of the aluminum alloy fin material for heat exchangers according to the present invention is 170 to 230 MPa. If the tensile strength of the aluminum alloy fin material before brazing is less than this range, it is difficult to maintain the shape thereof after forming. If the tensile strength exceeds this range, springback during forming increases, which makes it difficult to achieve a desired shape.
The aluminum alloy of the aluminum alloy fin material for heat exchangers according to the present invention is an H2n (n is an integer selected from 2, 4, and 6) material.
In the aluminum alloy fin material for heat exchangers according to the present invention, the matrix of the aluminum alloy has a fibrous structure and the chemical compositions in the aluminum alloy are set within the above-described ranges, whereby the grain size thereof after brazing can be controlled to be 40 to 200 μm. When the grain size of the aluminum alloy after brazing is 40 to 200 μm, and preferably 40 to 100 μm, the brazing properties are enhanced and the strength is increased while occurrence of erosion is prevented. Herein, braze-heating conditions for brazing are common braze-heating conditions at 580 to 610° C. for 1 to 10 minutes.
In the aluminum alloy fin material for heat exchangers according to the present invention, the contents of Si and Mn in the aluminum alloy are set within the above-described ranges and appropriate heat treatment described later is performed, whereby the total number density of an Al—Mn-based intermetallic compound and an Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy after braze-heating can be controlled to be 0.50×106 pieces/mm2 or more, and preferably 0.60×106 pieces/mm2 or more. The aluminum alloy fin material for heat exchangers according to the present invention comprises Si and Mn that are specified to appropriate contents and appropriate heat treatment described later is performed thereon, whereby the Al—Mn-based intermetallic compound and the Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 m are precipitated in the matrix. This contributes to enhancing the strength of the fin material due to the effect of pinning processing strain. The total number density of the Al—Mn-based intermetallic compound and the Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy after brazing is 0.50×106 pieces/mm2 or more, preferably 0.60×106 pieces/mm2 or more. If the circle-equivalent diameter of the precipitated intermetallic compounds is less than this range, the pinning effect decreases. If the circle-equivalent diameter exceeds this range, the pinning effect also decreases. If the number density of the precipitated intermetallic compounds is less than the above-described range, the strength decreases.
In the aluminum alloy fin material for heat exchangers according to the present invention, the matrix of the aluminum alloy has a fibrous structure, the chemical compositions in the aluminum alloy are set within the above-described ranges, and appropriate heat treatment described below is performed, whereby the grain size thereof after brazing is controlled to be 40 to 200 μm. Furthermore, the contents of Si and Mn in the aluminum alloy are set within the above-described ranges, and the appropriate heat treatment described later is performed, whereby the total number density of the Al—Mn-based intermetallic compound and the Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 m in the aluminum alloy after brazing is set to 0.50×106 pieces/mm2 or more, and preferably 0.60×106 pieces/mm2 or more. Consequently, the strength after brazing can be increased.
In the aluminum alloy fin material for heat exchangers according to the present invention, the tensile strength of the aluminum alloy after brazing is 150 to 180 MPa.
In the aluminum alloy fin material for heat exchangers according to the present invention, the Zn content in the aluminum alloy is set to 1.00 to 1.80 mass %, whereby self-corrosion resistance of the fin is enhanced.
A method of producing an aluminum alloy fin material for heat exchangers according to the present invention is a method of producing an aluminum alloy fin material for heat exchangers, the method comprising: without performing homogenization treatment, subjecting an ingot to hot-rolling by heating up to 400 to 500° C. to start the hot-rolling and completing the hot-rolling at 350° C. or less, the ingot being made of aluminum alloy comprising 1.00 to 1.60 mass % of Mn, 0.70 to 1.20 mass % of Si, 0.05 to 0.50 mass % of Fe, 0.05 to 0.35 mass % of Cu, and 1.00 to 1.80 mass % of Zn with the balance being Al and inevitable impurities; subsequently subjecting the hot-rolled material to cold-rolling in one or a plurality of passes, or subjecting the hot-rolled material to the cold-rolling in one or a plurality of passes and intermediate annealing performed one or more times between the passes of the cold-rolling; and subsequently subjecting the cold-rolled material to final annealing.
In the method of producing an aluminum alloy fin material for heat exchangers according to the present invention, in accordance with a common procedure, an ingot of aluminum alloy having predetermined chemical compositions is casted, without subjecting the ingot to homogenization treatment, the ingot is subjected to the hot-rolling, to the cold-rolling in one or a plurality of passes or to the cold-rolling in one or a plurality of passes and the intermediate annealing performed one or more times between the passes of the cold-rolling, and to the final annealing, whereby the aluminum alloy fin material for heat exchangers having a predetermined thickness is obtained. At the hot-rolling, the hot-rolling is started at 400 to 500° C. to perform the hot-rolling, and the hot-rolling is completed at 350° C. or less. After performing the hot-rolling, the cold-rolling in one or a plurality of passes is performed, or the cold-rolling in one or a plurality of passes and the intermediate annealing one or more times performed during between the passes of the cold-rolling are performed, and then the final annealing is performed to obtain the aluminum alloy fin material for heat exchangers. At this time, by appropriately selecting a degree of processing in cold-processing, an annealing temperature, an annealing period of time, and a cooling speed after the annealing, for example, the matrix of the aluminum alloy that forms the fin material can have a fibrous structure. Herein, in order for the matrix of the aluminum alloy to have a fibrous structure, the temperature of the final annealing needs to be set lower than the temperature at which the aluminum alloy after the hot-rolling and the subsequent cold-rolling starts recrystallizing. Because this recrystallization start temperature of the aluminum alloy varies depending on chemical compositions of the aluminum alloy, a temperature at which the hot-rolling is started and a temperature at which the hot-rolling is completed, and the degree of processing at the cold-rolling after the hot-rolling, the temperature of the final annealing is set accordingly.
For identification of the structure of the aluminum alloy, polishing and etching are performed so that grain boundaries thereof can be observed, and the grain boundaries are observed with an optical microscope, whereby whether it is a recrystallized structure or a fibrous structure can be identified. If the grain boundaries can be clearly observed and a rolled structure in which the structure has been spread in a fibrous shape is not observed, it is identified as a recrystallized structure. If the grain boundaries are not clearly observed and the rolled structure is observed, it is identified as a fibrous structure. There is a case in which a recrystallized structure and a fibrous structure coexist. However, the case in which a recrystallized structure and a fibrous structure coexist is not preferable because the grain size after brazing partially increases and variations in mechanical properties increase.
A heat exchanger according to the present invention is a heat exchanger obtained by brazing the aluminum alloy fin material for heat exchangers according to the present invention, and the grain size of aluminum alloy that forms a fin of the heat exchanger is 40 to 200 μm, and the total number density of an Al—Mn-based intermetallic compound and an Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy is 0.5×106 pieces/mm2 or more.
The heat exchanger according to the present invention is produced by forming the aluminum alloy fin material for heat exchangers according to the present invention into a shape of a fin that forms a heat exchanger, and assembling the fin material with other members such as a tube material and a plate material that form the heat exchanger, and joining them together by brazing. In other words, the heat exchanger according to the present invention comprises the fin obtained by braze-heating the aluminum alloy fin material for heat exchangers according to the present invention and the other members such as the tube material and the plate material that form the heat exchanger.
The fin material of the heat exchanger according to the present invention is the aluminum alloy fin material for heat exchangers according to the present invention, in which the fin material of the heat exchanger has been braze-heated, and thus is made of aluminum alloy comprising: 1.00 to 1.60 mass % of Mn; 0.70 to 1.20 mass % of Si; 0.05 to 0.50 mass % of Fe; 0.05 to 0.35 mass % of Cu; and 1.00 to 1.80 mass % of Zn with the balance being Al and inevitable impurities.
The fin of the heat exchanger according to the present invention is the aluminum alloy fin material for heat exchangers according to the present invention, in which the aluminum alloy fin material for heat exchangers has been braze-heated, and thus has a high strength. The tensile strength of the fin of the heat exchanger according to the present invention is 150 to 180 MPa.
As the tube material, a tube material is used that is obtained by forming, in the shape of a tube, a two-layer material consisting of an outer brazing material and a core material or a three to four-layer material having a brazing material or a sacrificial material arranged on the internal surface of the two-layer material, forming a brazing strip by disposing an inner fin formed of a bare fin or a clad fin, in which the inner fin has been formed in a corrugated shape into the tube consisting of the two to four-layer material, forming a circular tube by joining the side-end surfaces thereof by high-frequency welding, and forming this tube into a flat tubular shape by roll forming. As the tube material, a tube material is also used obtained by partially overlapping end portions of a sheet to each other or bending part of the sheet such that the part serves as an inner pillar of the tube, thereby forming the sheet into a flat tubular shape by braze-heating without welding.
Alternatively, an extruded flat multi-hole tube to the outer surface of which brazing material powder such as Si powder is applied may be joined to the fin material by brazing. Into the brazing material powder, powder having a flux composition, powder having a sacrificial anode effect, or a binder may be mixed. As the plate material, a plate on the core material of which a brazing material or a sacrificial anode material is cladded is used as necessary, and is formed in a desired shape to be used.
The core material of a brazing sheet used as the tube material is not limited to a particular one if it can be used for heat exchangers, and examples thereof include pure Al, an Al—Cu-based alloy, an Al—Mn-based alloy, an Al—Mn—Cu-based alloy, and an Al—Cu—Mn—Mg-based alloy.
As the composition of the brazing material, any alloy may be used if it has a melting point lower than that of the tube material or the plate material. Examples thereof include: aluminum alloy powder that comprises Si, such as an Al—Si-based alloy, an Al—Si—Zn-based alloy, and an Al—Si—Cu-based alloy; and a flux that comprises Si and forms a brazing material during brazing, such as K2SiF6.
Braze-heating conditions for brazing are not limited to particular ones if they are conditions used for normal braze-heating, and are normal braze-heating conditions at 580 to 610° C. for 1 to 10 minutes, for example. As for the cooling speed after brazing, the cooling speed from 550° C. to 450° C. is preferably 50 to 80° C./min. If the cooling speed is too slow, a Cu-based compound is more likely to be precipitated along grain boundaries, and intergranular corrosion is more likely to occur.
In the heat exchanger according to the present invention, the grain size of the aluminum alloy that forms the fin is 40 to 200 μm, and preferably 40 to 100 μm. When the grain size of the aluminum alloy that forms the fin is within this range, the strength of the fin increases.
In the heat exchanger according to the present invention, the total number density of an Al—Mn-based intermetallic compound and an Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy that forms the fin is 0.50×106 pieces/mm2 or more, and preferably 0.60×106 pieces/mm2 or more. When the total number density of the Al—Mn-based intermetallic compound and the Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy that forms the fin is within this range, the strength of the fin increases. The upper limit of the total number density of the Al—Mn-based intermetallic compound and the Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy that forms the fin is preferably 8.00×106 pieces/mm2 or less, more preferably 5.00×106 pieces/mm2 or less, and particularly preferably 3.00×106 pieces/mm2 or less.
The fin in the heat exchanger according to the present invention is the aluminum alloy fin material for heat exchangers according to the present invention, in which the aluminum alloy fin material for heat exchangers has been braze-heated. Thus, the heat exchanger according to the present invention is a heat exchanger the fin of which is made of aluminum alloy comprising: 1.00 to 1.60 mass % of Mn; 0.70 to 1.20 mass % of Si; 0.05 to 0.50 mass % of Fe; 0.05 to 0.35 mass % of Cu; and 1.00 to 1.80 mass % of Zn with the balance being Al and inevitable impurities, in which the grain size of the aluminum alloy that forms the fin is 40 to 200 μm, and the total number density of the Al—Mn-based intermetallic compound and the Al—Si—Mn-based intermetallic compound having a circle-equivalent diameter of 0.1 to 1.0 μm in the aluminum alloy that forms the fin is 0.50×106 pieces/mm2 or more.
Although the following specifically describes the present invention with reference to Examples, the present invention is not limited to Examples described below.
Ingots having chemical compositions given in Table 1 and Table 2 were casted by continuous casting. Without being subjected to homogenization treatment (with skipping homogenization treatment between casting and hot-rolling), these alloys were subjected to hot-rolling, cold-rolling, and final annealing, whereby sheets having a thickness of 0.05 mm (H2n materials) were prepared. At this time, by adjusting the final annealing temperature, structures of the aluminum alloy fin materials were adjusted. Furthermore, sheet materials that had been hot-rolled by the same method were cold-rolled, were subjected to intermediate annealing at a recrystallization completion temperature or more, and then were finishing cold-rolling, whereby comparative materials having a thickness of 0.05 mm (H14 materials) were prepared.
On each aluminum alloy fin material thus obtained, (1) the structure and (2) the tensile strength were evaluated. Furthermore, on each aluminum alloy fin material obtained as described above, the fin material was heated up to 600° C. in nitrogen gas as heating corresponding brazing, and then was cooled at a cooling speed of 60° C./min from 550° C. to 450° C. On each test piece thus obtained, (3) the tensile strength after heating corresponding to brazing, (4) the grain size, (5) the density of the precipitated intermetallic compound, and (6) the corrosion resistance were evaluated. On each aluminum alloy fin material obtained as described above, (7) the brazing properties were evaluated.
A surface of each H2n material was polished and then etched, and the state of the structure thereof was observed by observation of its microstructure with a microscope. If grains could be identified, it was determined that the material had a recrystallized structure. If grains were not clearly observed and if a rolled structure was observed, it was determined that the material had a fibrous structure.
After a JIS No. 5 test piece was formed, a tensile test was conducted at room temperature, and the tensile strength was measured. The resultant broken test pieces were brought into contact with each other, and the breaking elongation was measured.
(3) Tensile Strength after Heating Corresponding to Brazing
A tensile test was conducted on each sheet material after heating corresponding to brazing described above, and the tensile strength was measured.
A surface of each sheet material after heating corresponding to brazing described above was polished and then etched, the state of the structure thereof was observed by observation of its microstructure with a microscope, and the grain size was measured by a comparison method.
Each sheet material after heating corresponding to brazing described above was cut so that an L-ST section could be viewed, a smooth surface was formed thereon by polishing and ion milling, and the section was observed with a FE-SEM at an acceleration voltage of 1 kV The obtained photographic data was subjected to image analysis, and the circle-equivalent diameter and the number of the respective grains were measured.
On each sheet material after heating corresponding to brazing described above, a corrosion test in accordance with SWAAT of ASTM G85-A3 was conducted for 24 hours. The reduced weight and the corrosion form of each fin material after the test were evaluated. To a material in which self-corrosion of the fin was small and intergranular corrosion did not occur or was slight, “◯” was assigned. To a material in which self-corrosion of the fin was great or intergranular corrosion was apparent, “x” was assigned.
The fin material was formed in a corrugated shape. A sheet material (hereinafter, called “tube material”) including a core material for which a JIS-A3003 alloy was used and a brazing material for which a JIS-A4045 alloy was used and having a thickness of 0.23 mm was assembled therewith such that a surface of the brazing material was in contact with the fin tops. Fluoride-based flux having a concentration of 3% was applied to a surface of the tube material on the brazing material side, and then this assembly was subjected to braze-heating at 600° C. for 3 minutes in a nitrogen atmosphere to prepare a mini-core of a heat exchanger. On this mini-core, joints between the fin material and the tube material were visually checked, and brazing properties thereof were evaluated based on the presence or absence of buckling and melting in the fin. To a case in which neither buckling nor melting was found, “◯” was assigned. To a case in which buckling or melting was found, “x” was assigned.
As given in Table 3, all of the materials of No. 1 to No. 3 were H2n materials that satisfied specifications of the present invention, and the tensile strengths thereof were 170 to 230 MPa and the elongations thereof were 3% or more. Even when heated at 600° C., the grain sizes thereof were 40 μm or more, neither fin melting nor buckling was found, and the brazing properties thereof were excellent. The number densities of all of the intermetallic compounds having a circle-equivalent diameter of 0.1 to 1.0 μm after brazing were 0.50×106 pieces/mm2 or more, and the tensile strengths thereof were excellent strengths of 150 MPa or more. As for the corrosion resistance, it was found in the SWAAT test that both of the intergranular corrosion and the self-corrosion were slight.
By contrast, because the materials of No. 4 and 5 had excessively high Zn contents, the melting points thereof decreased and erosion occurred during brazing. Thus, it cannot be said that the brazing properties thereof were excellent, and the self-corrosion resistances were insufficient. The materials of No. 6 to 8 had a recrystallized structure, and thus elongations thereof were small and insufficient. As for the material of No. 8, the grain size thereof after brazing was large, and the tensile strength after brazing was insufficient.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-050712 | Mar 2018 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2019/010779 | Mar 2019 | US |
| Child | 17026178 | US |
