Aluminum alloy fin material and manufacturing method thereof

Abstract

The fin material (1) is composed of a brazing sheet having a core material (2) and brazing filler metals (3) arranged on both sides of the core material (2). The core material (2) has a chemical composition comprising Si: 0.02-0.80 mass%, Fe: 0.02-0.80 mass% and Mn: 0.8-2.0 mass%, with the balance being Al and unavoidable impurities; and a crystal texture wherein the orientation density of one or more crystal orientations among Brass orientation, Copper orientation and S orientation is 20 times or more of that of a random orientation sample, and the orientation density of Cube orientation, CR orientation and P orientation is 10 times or less of that of a random orientation sample. The brazing filler metals (3) are composed of an Al-Si alloy containing Si: 6.0-13.0 mass% and Fe: 0.02-0.80 mass%. The coverage of each brazing filler metal (3) is 6% or more and 16% or less.

Description

Technical Field

[0001] The invention relates to an aluminum alloy fin material and a manufacturing method thereof. Background Art

[0002] Heat exchangers such as condensers, radiators, heater cores, and intercoolers are often constructed from aluminum alloys, which possess both high specific strength and high thermal conductivity. These heat exchangers sometimes feature corrugated fins. Heat exchangers with corrugated fins are manufactured, for example, by forming the fin material into the desired shape, combining it with other components, and then brazing it. The fins are made from a core material and brazing plates with brazing filler metal laminated on both sides of the core material.

[0003] In recent years, there has been a strong demand for lighter and smaller heat exchangers in various technical fields, such as the automotive field. To meet these demands, fin materials used in heat exchangers are also required to have a reduced thickness while maintaining strength.

[0004] To address this need, Patent Document 1, for example, describes an aluminum alloy brazing plate fin material. The core material comprises an aluminum alloy containing 0.05-0.8 mass% Si, 0.05-0.8 mass% Fe, and 0.8-2.0 mass% Mn, where the Si, Fe, and Mn contents satisfy the condition Si+Fe≤Mn, with the balance consisting of Al and inevitable impurities. The brazing filler metal comprises an Al-Si alloy containing 6.0-13.0 mass% Si, 0.05-0.8 mass% Fe, with the balance consisting of Al and inevitable impurities. The fin material of Patent Document 1 achieves improved strength after brazing heating by controlling the core material's metallographic structure to a specific state before and after brazing heating.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2016 / 147627 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] To improve heat exchange efficiency, the corrugated fins incorporated into heat exchangers are sometimes given complex shapes such as slits and louvers. To miniaturize heat exchangers, the slits and louvers must be smaller than ever before, requiring fin materials with superior formability.

[0010] However, strength and formability are in a trade-off relationship, and improving formability tends to reduce strength. From the perspective of achieving both high strength and excellent formability, the fin material of Patent Document 1 still has room for improvement.

[0011] The present invention has been made in view of the above background, and an object of the present invention is to provide an aluminum alloy fin material having excellent strength and formability and a method for manufacturing the same.

[0012] Technical solutions to problems

[0013] One embodiment of the present invention is an aluminum alloy fin material comprising a brazing sheet including a core material and brazing filler metals disposed on both surfaces of the core material.

[0014] The core material has:

[0015] A chemical composition comprising Si (silicon): 0.02 mass % to 0.80 mass %, Fe (iron): 0.02 mass % to 0.80 mass %, and Mn (manganese): 0.8 mass % to 2.0 mass %, with the balance being Al (aluminum) and unavoidable impurities; and

[0016] The crystal texture has an orientation density of at least one of the Brass, Copper, and S orientations that is more than 20 times that of the random orientation sample, and an orientation density of the Cube, CR, and P orientations that is less than 10 times that of the random orientation sample.

[0017] The brazing filler metal is composed of an Al-Si alloy containing 6.0 mass % or more and 13.0 mass % or less of Si and 0.02 mass % or more and 0.80 mass % or less of Fe.

[0018] The coverage of each brazing filler metal is 6% or more and 16% or less.

[0019] Another embodiment of the present invention is a method for manufacturing the aluminum alloy fin material according to the above embodiment, comprising:

[0020] a casting step of producing a core material block having a chemical composition comprising Si: 0.02 mass % or more and 0.80 mass % or less, Fe: 0.02 mass % or more and 0.80 mass % or less, and Mn: 0.8 mass % or more and 2.0 mass % or less, with the balance consisting of Al and unavoidable impurities, and a brazing filler metal block composed of an Al-Si alloy containing Si: 6.0 mass % or more and 13.0 mass % or less, and Fe: 0.02 mass % or more and 0.80 mass % or less;

[0021] a lamination step of arranging the brazing material blocks on both sides of the core material block to produce a cladding block;

[0022] a hot rolling step of hot rolling the clad block to produce a clad plate;

[0023] a first cold rolling step of cold rolling the clad plate;

[0024] Annealing step: the clad sheet after the first cold rolling step is subjected to annealing until the total diffusion amount M calculated by the following formula (1) becomes 1.0×10 -14 m 2 Above and 5.0×10 -12 m 2 Heating and annealing are performed under the following conditions; and

[0025] The second cold rolling step is to cold-roll the clad sheet after the annealing step.

[0026]

Mathematical formula 1

[0027]

[0028] Wherein, n in the above formula (1) is the number of intervals when the total heating time is divided into unit time Δt, and D0 is 1.37×10 -5 m 2 / s, Q is 123 kJ / mol, R is 8.3145 kJ / (mol·K), and T(k) is the heating temperature [K] at the start time of the kth interval.

[0029] Effects of the Invention

[0030] The aluminum alloy fin material (hereinafter referred to as "fin material") is composed of a brazing sheet having a core material and brazing filler metals disposed on both surfaces of the core material. Furthermore, the core material has the specific chemical composition and a crystal texture defined by the orientation density of each crystal orientation. By maintaining the specific chemical composition and crystal texture of the core material before brazing heating, the fin material exhibits excellent formability.

[0031] Furthermore, when the core material is heated for brazing, fine precipitates of the core material can be formed in the core material, thereby increasing the strength of the core material, that is, the strength of the fin.

[0032] Therefore, the fin material has excellent formability before brazing heating and high strength after brazing.

[0033] The fin material can be produced using the manufacturing method described above. In this manufacturing method, an annealing step is performed between the first and second cold rolling steps, wherein the cladding sheet is heated and annealed under conditions such that the total diffusion amount M falls within the specific range. By ensuring that the total diffusion amount M during the annealing step falls within the specific range, the crystal texture of the core material of the resulting fin material can be easily adjusted to the specific configuration. Therefore, the manufacturing method described above makes it possible to easily produce the fin material.

[0034] As described above, according to the above aspect, it is possible to provide an aluminum alloy fin material having excellent strength and formability and a method for manufacturing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a cross-sectional view of the aluminum alloy fin material in the embodiment. DETAILED DESCRIPTION

[0036] (Fin material)

[0037] The fin material is composed of a so-called double-sided brazing sheet having a core material and a brazing filler metal disposed on both sides of the core material. More specifically, the brazing sheet constituting the fin material can be composed of three layers: a core material and a brazing filler metal laminated on both sides of the core material. In addition, the brazing sheet constituting the fin material can have, for example, four or more layers including a core material, a brazing filler metal, and a layer composed of an aluminum alloy other than the core material and the brazing filler metal. Examples of layers that can be included in the brazing sheet include a skin material exposed on the outermost surface of the brazing sheet and an intermediate material between the core material and the brazing filler metal.

[0038] <Core material>

[0039] The core material has a chemical composition comprising Si: 0.02% to 0.80% by mass, Fe: 0.02% to 0.80% by mass, and Mn: 0.8% to 2.0% by mass, with the balance consisting of Al and unavoidable impurities; and a crystal texture in which the orientation density of at least one of the Brass, Copper, and S orientations is 20 times or more compared to a randomly oriented sample, and the orientation density of the Cube, CR, and P orientations is 10 times or less compared to a randomly oriented sample. The chemical composition and crystal texture of the core material, as well as the reasons for their limitations, are described below.

[0040] [Chemical composition]

[0041] Si (silicon): 0.02 mass% or more and 0.80 mass% or less

[0042] The core material contains Si as an essential component, ranging from 0.02% to 0.80% by mass. Si, along with Mn and Fe, forms Al-Mn-Si and Al-Mn-Si-Fe compounds in the core material after brazing and heating, increasing the strength of the core material through precipitation strengthening.

[0043] By setting the Si content in the core material to 0.02% by mass or greater, the amount of Al-Mn-Si compounds and the like formed in the core material can be sufficiently increased, thereby improving the strength of the core material after brazing heating. To further improve the strength of the core material after brazing heating, the Si content in the core material is preferably 0.04% by mass or greater. If the Si content in the core material is less than 0.02% by mass, the amount of Al-Mn-Si compounds and the like formed in the core material after brazing heating is insufficient, potentially reducing the strength of the core material after brazing heating.

[0044] On the other hand, if the Si content in the core material increases, the amount of Si dissolved in the core material increases, which can easily lead to a decrease in the core material's melting point. Furthermore, if the core material's melting point is excessively lowered, the brazing filler metal can corrode the core material during brazing heating, potentially causing the core material to melt. This problem can be easily avoided by limiting the Si content in the core material to 0.80% by mass or less, preferably 0.70% by mass or less, and more preferably 0.60% by mass or less.

[0045] Fe (iron): 0.02 mass% or more and 0.80 mass% or less

[0046] The core material contains Fe as an essential component, ranging from 0.02% to 0.80% by mass. Fe promotes the formation of Al-Mn-Si and Al-Mn-Si-Fe compounds in the core material, thereby increasing the strength after brazing and stabilizing the core material's crystal structure.

[0047] By increasing the Fe content in the core material to 0.02% by mass or more, the strength of the core material after brazing can be increased and the crystal structure can be stabilized. To enhance these effects, the Fe content in the core material is preferably 0.05% by mass or more. If the Fe content in the core material is less than 0.02% by mass, the amount of Al-Mn-Si and Al-Mn-Si-Fe compounds formed in the core material becomes insufficient, which may lead to a decrease in the strength of the core material after brazing.

[0048] On the other hand, if the Fe content in the core material increases, coarse crystals are likely to form in the core material block during the fin material manufacturing process when casting the core material block. Coarse crystals in the core material block may make it difficult to produce the fin material or reduce the formability of the fin material. By limiting the Fe content in the core material to 0.80% by mass or less, preferably 0.70% by mass or less, the formation of coarse crystals can be easily avoided.

[0049] Mn (manganese): 0.8 mass% or more and 2.0 mass% or less

[0050] The core material contains Mn as an essential component, at a concentration of 0.8% to 2.0% by mass. A portion of the Mn dissolves in the core material after brazing and heating, increasing its strength through solid solution strengthening. Furthermore, the remaining Mn, along with Si and Fe, forms Al-Mn-Si and Al-Mn-Si-Fe compounds in the core material, increasing the strength of the core material after brazing through precipitation strengthening.

[0051] By increasing the Mn content in the core material to 0.8% by mass or greater, the effects of solid solution strengthening and precipitation strengthening can be enhanced, thereby increasing the strength of the core material after brazing heating. To further increase the strength of the core material after brazing heating, the Mn content in the core material is preferably 1.0% by mass or greater. If the Mn content in the core material is less than 0.8% by mass, the amount of Mn dissolved in the core material after brazing heating and the amount of Al-Mn-Si compounds formed in the core material are insufficient, potentially reducing the strength of the core material after brazing heating.

[0052] On the other hand, if the Mn content in the core material increases, coarse crystals are likely to form in the core material block when the core material block is cast during the fin material manufacturing process. Coarse crystals in the core material block may make it difficult to produce the fin material or reduce the formability of the fin material. By setting the Mn content in the core material to 2.0% by mass or less, preferably 1.8% by mass or less, the formation of coarse crystals can be easily avoided.

[0053] Zn (zinc): 0.3% by mass or more and 3.0% by mass or less

[0054] In addition to Si, Fe, and Mn, which are essential components, the core material may also contain Zn as an optional component: 0.3% by mass or more and 3.0% by mass or less. By adding Zn in the specific range to the core material, the potential of the core material can be appropriately reduced, so that the core material after brazing, that is, the fins in the heat exchanger, can function as sacrificial anodes. As a result, the sacrificial corrosion protection effect of the fins can suppress the corrosion of components other than the fins in the heat exchanger, such as tubes, for a longer period of time. From the perspective of ensuring the sacrificial corrosion protection effect produced by the fins and improving the corrosion resistance of the fins themselves, the Zn content in the core material is preferably 0.5% by mass or more and 2.8% by mass or less, and more preferably 0.7% by mass or more and 2.7% by mass or less.

[0055] Other elements

[0056] The core material may contain trace amounts of elements other than the above elements, as long as they do not impair the above effects. Examples of elements that may be included in the core material include Mg (magnesium), Cr (chromium), Ti (titanium), Zr (zirconium), and Cu (copper). The content of these elements may be 0.05% by mass or less for each element, and 0.15% by mass or less for the total.

[0057] [Crystal texture]

[0058] The core material has the following crystal texture before brazing heating: the orientation density of at least one crystal orientation among Brass orientation, Copper orientation and S orientation is more than 20 times that of the random orientation sample, and the orientation density of Cube orientation, CR orientation and P orientation is less than 10 times that of the random orientation sample.

[0059] The above-mentioned crystal orientations are representative crystal orientations present in aluminum alloys. The degree of development of a crystal orientation can be represented by the magnitude of the orientation density. The higher the orientation density of a certain crystal orientation, the more developed the crystal orientation is. The orientation density of a crystal orientation can be calculated based on the diffraction intensity of the crystal orientation in the X-ray diffraction pattern. In addition, the magnitude of the orientation density is represented by the ratio of the orientation density of the corresponding crystal orientation in the sample to be measured, using the orientation density of the crystal orientation in a randomly oriented sample, i.e., a sample with a disordered distribution of crystal orientations, as a reference.

[0060] Among the aforementioned crystal orientations, Brass, Copper, and S orientations have the effect of increasing the work hardening index of aluminum alloys. Therefore, by ensuring that the orientation density of one or more of the Brass, Copper, and S orientations in the core material prior to brazing heating is at least 20 times the orientation density of the corresponding crystal orientation in the randomly oriented sample, the work hardening index of the core material prior to brazing heating can be increased. If the orientation density of each of the Brass, Copper, and S orientations in the core material prior to brazing heating is less than 20 times that of the randomly oriented sample, the effect of these crystal orientations on increasing the work hardening index may be reduced.

[0061] Furthermore, Cube, CR, and P orientations have the effect of reducing the work hardening index of aluminum alloys. Therefore, by ensuring that the orientation density of the Cube, CR, and P orientations in the core material before brazing heating is less than 10 times the orientation density of the corresponding crystal orientations in the randomly oriented sample, a reduction in the work hardening index of the core material before brazing heating can be avoided. If the orientation density of one or more of the Cube, CR, and P orientations in the core material before brazing heating is greater than 10 times that of the randomly oriented sample, these crystal orientations may lead to a reduction in the work hardening index.

[0062] Therefore, by achieving this specific crystal structure in the core material before brazing, the core material's work hardening index can be increased. Such a core material can be easily deformed through forming processes such as stamping. Furthermore, the core material's strength increases after deformation due to work hardening, making it easier to maintain the shape imparted by the forming process. As a result, fin materials equipped with this core material have excellent formability.

[0063] <Brazing filler metal>

[0064] The fin material has brazing filler metals on both sides of the core material. The brazing filler metals arranged on one side of the core material and the brazing filler metals arranged on the other side may have the same chemical composition or may have different chemical compositions from each other. The brazing filler metals are composed of an Al-Si alloy containing Si: 6.0% by mass or more and 13.0% by mass or less, and Fe: 0.02% by mass or more and 0.80% by mass or less. More specifically, the Al-Si alloy constituting the brazing filler metal may also have a chemical composition containing Si: 6.0% by mass or more and 13.0% by mass or less, and Fe: 0.02% by mass or more and 0.80% by mass or less, with the remainder being Al and unavoidable impurities.

[0065] Si: 6.0 mass% or more and 13.0 mass% or less

[0066] As an essential component, the brazing filler metal contains Si in an amount of 6.0% by mass or more and 13.0% by mass or less. The Si in the brazing filler metal has the effect of lowering the melting point of the brazing filler metal and improving the fluidity of the brazing filler metal. In addition, a portion of the Si in the brazing filler metal can diffuse into the core material during brazing heating, dissolve in the core material, or form Al-Mn-Si compounds together with the dissolved Mn in the core material. Moreover, through solid solution strengthening and precipitation strengthening, it has the effect of improving the strength of the core material after brazing.

[0067] By increasing the Si content in the brazing filler metal to 6.0% by mass or more, preferably 6.5% by mass or more, the brazing properties with the mating material can be improved, and the strength of the core material after brazing can be increased. If the Si content in the brazing filler metal is less than 6.0% by mass, the diffusion of Si from the brazing filler metal to the core material during brazing heating is insufficient, which may result in a decrease in the strength of the core material after brazing.

[0068] On the other hand, when the Si content in the brazing filler metal increases, the amount of Si diffused from the brazing filler metal to the core material during brazing heating increases. If the amount of Si diffused into the core material is too much, the Mn dissolved in the core material is consumed excessively due to the formation of Al-Mn-Si compounds and the like. As a result, the amount of Mn dissolved in the core material after brazing is insufficient, which may lead to a decrease in strength. Moreover, in this case, the amount of brazing filler metal generated during brazing heating is too much, which may lead to a decrease in its own corrosion resistance. These problems can be easily avoided by making the Si content in the brazing filler metal less than 13.0% by mass, preferably less than 12.0% by mass.

[0069] Fe: 0.02 mass% or more and 0.80 mass% or less

[0070] The brazing filler metal contains 0.02% to 0.80% by mass of Fe as an essential component. Fe in the brazing filler metal has the function of improving the fluidity of the brazing filler metal and improving its own corrosion resistance.

[0071] By setting the Fe content in the brazing filler metal to 0.02 mass % or more, preferably 0.05 mass % or more, and more preferably 0.10 mass % or more, the fluidity of the brazing filler metal can be improved, and the corrosion resistance thereof can be enhanced. If the Fe content in the brazing filler metal is less than 0.02 mass %, the fluidity of the brazing filler metal may be reduced.

[0072] On the other hand, if the Fe content in the brazing filler metal increases, coarse crystals are likely to form in the brazing filler metal block during the manufacturing process of the fin material when the brazing filler metal block is cast. Coarse crystals in the brazing filler metal block may make it difficult to manufacture the fin material or reduce the formability of the fin material. Such problems exist. These problems can be easily avoided by making the Fe content in the brazing filler metal 0.80% by mass or less, preferably 0.70% by mass or less, and more preferably 0.60% by mass or less.

[0073] Sr (strontium): 0.005 mass% or more and 0.050 mass% or less

[0074] In addition to the essential components Si and Fe, the brazing filler metal may also contain Sr as an optional component: 0.005% by mass to 0.050% by mass. Sr in the brazing filler metal improves its fluidity. Adding Sr to the brazing filler metal within this specific range further enhances brazing properties.

[0075] Other elements

[0076] The brazing filler metal may contain trace amounts of elements other than the above elements, as long as the above effects are not impaired. Examples of elements that may be contained in the brazing filler metal include Mg, Cr, Ti, Zr, and Cu. The content of these elements may be 0.05% by mass or less for each element and 0.15% by mass or less for the total.

[0077] <Thickness>

[0078] The thickness of the fin material can be appropriately set within a range of, for example, 40 μm to 140 μm.

[0079] <Coverage>

[0080] The coverage of each brazing filler metal in the fin material is 6% or higher and 16% or lower. By ensuring that the coverage of each brazing filler metal is 6% or higher, the amount of brazing filler metal generated during brazing heating can be increased significantly, and the diffusion of Si from the brazing filler metal into the core material can be appropriately increased. This results in improved brazing properties and increased core material strength after brazing. If the coverage of any brazing filler metal is less than 6%, insufficient brazing filler metal may lead to deteriorated brazing properties and reduced core material strength after brazing.

[0081] On the other hand, if the coverage ratio increases, the amount of Si diffused from the brazing filler metal into the core material during brazing heating increases, which tends to consume the Mn dissolved in the core material. As a result, the strength-enhancing effect of solid solution strengthening decreases, potentially leading to a decrease in the strength of the core material after brazing. This problem can be easily avoided by setting the brazing filler metal coverage ratio to 16% or less, preferably 14% or less, and more preferably 12% or less.

[0082] <Work Hardening Index>

[0083] The fin material preferably has a work hardening index at the yield point of 0.07 or greater, more preferably 0.08 or greater. The work hardening index is an index that indicates the degree of increase in strength due to work hardening under the same strain applied. A larger work hardening index value indicates a greater increase in strength.

[0084] Fin materials having a work hardening index within this specific range can further increase the strength gains associated with forming processes such as stamping. Therefore, during forming, the fin material can be easily deformed into a desired shape, and after the forming process is completed, the resulting shape can be easily maintained. Thus, by having a work hardening index within this specific range, the formability of the fin material can be further improved.

[0085] The work hardening index of the fin material can be calculated by the following method. First, a No. 13B test piece specified in JIS Z2241: 2011 is selected from the fin material in such a way that the length direction is parallel to the rolling direction. Next, a tensile test is performed at room temperature according to the method specified in JIS Z2241: 2011. Then, based on the test force-strain curve obtained from the tensile test, the test force and plastic strain values ​​at the yield point and the test force value at the point where the plastic strain increases by 0.1% from the yield point are determined. Then, the work hardening index calculated by the two-point method using these values ​​is used as the work hardening index of the fin material.

[0086] More specifically, the work hardening index n of the fin material is a value calculated by the following formula (2) using the test force F1 (unit: N) and plastic strain e1 (unit: %) at the yield point and the test force F2 (unit: N) at the point where the plastic strain increases by 0.1% from the yield point.

[0087]

Mathematical formula 2

[0088]

[0089] (Manufacturing method of fin material)

[0090] The fin material is produced, for example, by a manufacturing method having the following steps: a casting step of producing a plurality of aluminum alloy ingots including a core material block serving as a core material and a brazing material block serving as a brazing material; a stacking step of arranging the brazing material blocks on both sides of the core material block to produce a cladding block; a hot rolling step of hot rolling the cladding block to produce a cladding plate; a first cold rolling step of cold rolling the cladding plate; an annealing step of heating and annealing the cladding plate after the first cold rolling step; and a second cold rolling step of cold rolling the cladding plate after the annealing step.

[0091] <Casting Process>

[0092] In the casting process, the method for producing the core material block and the brazing filler metal block is not particularly limited. For example, known casting methods such as semi-continuous casting can be employed. When producing the core material block by semi-continuous casting, for example, the casting can be performed such that the average cooling rate from the time the molten metal is supplied to the mold until solidification is 0.5°C / second or higher.

[0093] Furthermore, when producing the core block by semi-continuous casting, it is preferable to cool the core block so that the average cooling rate from the time the core block reaches 550°C to the time it reaches 200°C is 0.10°C / second or higher. By setting the average cooling rate of the core block within this specific range, excessive precipitation of Al-Mn-Si compounds and the like in the core block can be avoided. From the same perspective, it is more preferable to cool the core block so that the average cooling rate from the time the core block reaches 550°C to the time it reaches 200°C is 0.13°C / second or higher.

[0094] The core material block and the brazing material block obtained in the casting process can be directly provided to the stacking process as they are. In addition, the core material block and / or the brazing material block can be subjected to surface cutting, and after removing the ingot segregation layer formed on the surface, the core material block and the brazing material block are supplied to the stacking process. Moreover, in order to make the coverage of the fin material finally obtained a desired value, the core material block and / or the brazing material block can also be subjected to hot rolling to adjust their thickness. In the case of wanting to manufacture a fin material having a layer composed of aluminum alloys other than the core material and the brazing material, it is sufficient to make aluminum alloy ingots other than the core material block and the brazing material block in the casting process.

[0095] Homogenization process

[0096] The manufacturing method may further include a homogenization step of heating and homogenizing the core material block after the casting step and before the lamination step. In the homogenization step, for example, a holding temperature of 420°C or higher and less than 510°C and a holding time of 0.5 hours or higher and 12 hours or lower may be appropriately selected.

[0097] <Lamination process>

[0098] In the lamination process, the brazing filler metal blocks and, if necessary, the aluminum alloy ingots other than the brazing filler metal blocks are stacked on both sides of the core material block to produce the cladding block.

[0099] Hot rolling process

[0100] In the hot rolling process, the cladding block is hot rolled to join adjacent ingots in the cladding block and reduce their thickness. In this way, a cladding plate with brazing filler metal arranged on both sides of the core material can be obtained. In the hot rolling process, the cladding block is preheated to a temperature range of 420°C to 500°C, preferably 430°C to 490°C, and then hot rolled. By setting the rolling start temperature to the specific range, excessive precipitation of Al-Mn-Si compounds and the like into the core material in the cladding plate can be avoided, and adjacent ingots can be easily joined to each other. In this way, the amount of Mn dissolved in the core material can be sufficiently increased in the final fin material, thereby improving the formability of the fin material before brazing and improving the strength of the fin after brazing.

[0101] When preheating the core material block, it is preferred to preheat the core material block so that the holding time at the rolling start temperature is 0.5 hours or more and 12 hours or less. By setting the holding time within the specific range, excessive precipitation of Al-Mn-Si compounds and the like into the core material can be more reliably avoided. From the same point of view, it is preferred to preheat the core material block so that the time from the start of preheating to the reaching of the rolling start temperature is within 15 hours.

[0102] In addition, during the hot rolling process, it is preferred to perform hot rolling so that the temperature of the cladding sheet at the time when the reduction rate during hot rolling, that is, the reduction rate of the thickness of the cladding sheet relative to the thickness of the cladding block at the start of hot rolling, reaches 10% is 370°C to 450°C, and more preferably 380°C to 440°C. In addition, during the hot rolling process, it is preferred to perform hot rolling so that the temperature of the cladding sheet at the time of completion is less than 370°C, and more preferably 350°C or less. In addition, during the hot rolling process, it is preferred to perform hot rolling so that the time from the start of hot rolling to the completion is 60 minutes or less, and more preferably 40 minutes or less. By performing hot rolling under such conditions, excessive precipitation of Al-Mn-Si compounds and the like into the core material can be more reliably suppressed.

[0103] <First Cold Rolling Process>

[0104] The cladding sheet after the hot rolling process is supplied to the first cold rolling process without annealing. In the first cold rolling process, the cladding sheet obtained by the hot rolling process is cold rolled in one or more passes to reduce the thickness of the cladding sheet so that the thickness is thicker than the desired thickness of the fin material. When multiple cold rolling passes are performed in the first cold rolling process, annealing between passes is not performed. In the first cold rolling process, for example, the cold rolling can be performed in such a manner that the reduction rate, that is, the reduction rate (unit: %) of the thickness of the cladding sheet caused by the first cold rolling process relative to the thickness of the cladding sheet after the hot rolling process is 85.0% or more and 99.5% or less.

[0105] Annealing process

[0106] After the first cold rolling step is completed, an annealing step is performed to heat and anneal the clad sheet. In the annealing step, when the total diffusion amount M calculated by the following formula (1) is 1.0×10 -14 m 2 Above and 5.0×10 -12 m 2 The cladding plate was heated under the following conditions.

[0107]

Mathematical formula 3

[0108]

[0109] Wherein, n in the formula (1) is the number of intervals when the total heating time is divided by the unit time Δt, and D0 is 1.37×10 -5 m 2 / s, Q is 123 kJ / mol, R is 8.3145 kJ / (mol·K), and T(k) is the heating temperature (unit: K) at the start time of the kth interval.

[0110] When the cladding sheet is heated during the annealing process, aluminum atoms diffuse and the crystal lattice rearranges. By controlling the amount of aluminum atoms diffused during the annealing process within an appropriate range, the crystal texture of the core material in the cladding sheet after the annealing process can be controlled to a desired form, thereby achieving the desired crystal texture of the core material in the final fin material.

[0111] More specifically, the self-diffusion coefficient D of aluminum atoms is expressed by the following formula (3) using the temperature T (unit: K) of the cladding plate.

[0112] D=D0exp(-Q / RT)···(3)

[0113] Therefore, when the temperature T is constant, the diffusion amount of aluminum atoms can be calculated by multiplying the diffusion coefficient D calculated by the above formula (3) by the holding time. However, in an actual annealing process, the temperature may fluctuate, for example, from the start of heating to the point where the holding temperature is reached, or from the end of heating to the completion of cooling. In the above formula (1), the period from the start of annealing to the completion of annealing is divided into intervals of unit time Δt, and the total diffusion amount M is calculated by summing the product of the self-diffusion coefficient and the unit time Δt in each interval. Therefore, the above formula (1) can calculate the total diffusion amount M that takes into account the above-mentioned temperature fluctuations.

[0114] In this manufacturing method, by heating the cladding sheet so that the total diffusion amount M during the annealing step falls within the specified range, aluminum atoms can be appropriately diffused, developing Brass, S, and Copper orientations in the core material while suppressing the development of Cube, CR, and P orientations in the core material. As a result, the crystal texture of the core material in the final fin material can be achieved in the specified form.

[0115] The total diffusion amount M during the annealing process is less than 1.0×10 -14 m 2 In the case of , the development of Brass orientation, S orientation and Copper orientation is likely to become insufficient. In addition, when the total diffusion amount M is greater than 5.0×10 -12 m 2 Therefore, if the total diffusion amount M in the annealing process is outside the above-mentioned specific range, the formability of the fin material may be deteriorated.

[0116] When calculating the total diffusion amount M, the unit time Δt may be set to an appropriate value so that the difference between the cladding plate temperature at the start and end of each interval is sufficiently small. For example, the unit time Δt may be set to 1 minute.

[0117] <Second Cold Rolling Process>

[0118] In the second cold rolling step, the clad sheet after the annealing step is cold rolled in one or more passes to obtain a fin material of a desired thickness. When multiple passes are cold rolled in the second cold rolling step, no annealing is performed between passes.

[0119] [Example]

[0120] The aluminum alloy fin material and its manufacturing method are described below with reference to embodiments. Specific aspects of the aluminum alloy fin material and its manufacturing method according to the present invention are not limited to those of the following embodiments and can be modified as appropriate without prejudice to the gist of the present invention.

[0121] like Figure 1 As shown, the fin material 1 of this example is composed of a brazing sheet comprising a core material 2 and brazing filler metals 3 disposed on both surfaces of the core material 2. The core material 2 has the following chemical composition: Si: 0.02% to 0.80% by mass, Fe: 0.02% to 0.80% by mass, and Mn: 0.8% to 2.0% by mass, with the balance consisting of Al and unavoidable impurities. Furthermore, the core material 2 has a crystal texture in which the orientation density of one or more of the Brass, Copper, and S orientations is 20 times or more compared to a randomly oriented sample, and the orientation density of the Cube, CR, and P orientations is 10 times or less compared to a randomly oriented sample. The brazing filler metals 3 are composed of an Al-Si alloy containing Si: 6.0% to 13.0% by mass, and Fe: 0.02% to 0.80% by mass. The coverage of each brazing filler metal 3 is 6% to 16%. Hereinafter, the structure and manufacturing method of the fin material 1 of this example will be described in more detail.

[0122] The chemical composition of the core material 2 used in this example is shown in Table 1. The chemical composition of the brazing filler metal 3 used in this example is shown in Table 2. The symbol "Bal." in Tables 1 and 2 indicates the remaining amount, and the symbol "-" indicates that the content of the element is below the detection limit of the spark discharge optical emission spectrometer.

[0123]

Table 1

[0124]

[0125]

Table 2

[0126]

[0127] When making the fin material 1 of this example, first, a core material block having the chemical composition shown in Table 1 and a brazing material block having the chemical composition shown in Table 2 are made by semi-continuous casting (casting process). For the core material blocks having the chemical composition shown in alloy symbol A1 and alloy symbols A3 to A6, the core material blocks after casting are kept at a temperature of 500°C for 8 hours for homogenization treatment. In addition, for the core material blocks having the chemical composition shown in alloy symbol A2, no homogenization treatment is performed. The surfaces of each core material block and brazing material block obtained in this way are surface cut to remove the segregation layer of the ingot. In addition, in this example, the brazing material block is hot rolled and the thickness of the brazing material block is adjusted so that the coverage of the final fin material becomes the desired value.

[0128] Next, the brazing filler metal blocks were stacked on both sides of the core material block in the combination shown in Table 3 to produce a cladding block (lamination step). The cladding block was preheated and then hot-rolled to produce a cladding plate (hot rolling step). The cladding plate was then cold-rolled to reduce its thickness to a thickness greater than the desired fin material thickness (first cold rolling step).

[0129] After the first cold rolling step, the clad sheet was heated and annealed under conditions such that the total diffusion amount M reached the values ​​shown in Table 3 (annealing step). The clad sheet was then further cold rolled to reduce its thickness to the values ​​shown in Table 3 (second cold rolling step). The above results in the fin material 1 (test materials S1 to S3) shown in Table 3.

[0130] In this example, for convenience, the brazing material 3 laminated on one surface of the core material 2 is referred to as the first brazing material 3a, and the brazing material 3 laminated on the other surface is referred to as the second brazing material 3b. The coverage rates of the first brazing material 3a and the second brazing material 3b are shown in Table 3.

[0131] Test materials S4 to S6 shown in Table 3 were used for comparison with test materials S1 to S3. The preparation method for test materials S4 to S6 was the same as that for test materials S1 to S3, except that the heating conditions in the annealing step were changed to cause the total diffusion amount M to deviate from the specified range.

[0132] The following describes a method for evaluating the crystal texture of the fin material 1 , a method for measuring the work hardening index, and a method for evaluating the strength of the fin after brazing.

[0133] <Crystal Texture Evaluation Method>

[0134] A 25 mm square test piece was taken from the center of the fin material 1, perpendicular to the rolling direction. The 25 mm x 25 mm surface of this test piece was polished until the thickness of the test piece was half the thickness of the fin material, exposing the core material 2. Next, the test piece was immersed in an etching solution composed of nitric acid, hydrochloric acid, and fluorine for 10 seconds to etch the surface of the core material 2.

[0135] Next, X-rays are irradiated onto the surface of the core material 2 of the test piece, and an X-ray diffraction measurement based on the reflection method is performed. Thus, a pole diagram of the surface of the core material 2 is obtained. Then, a three-dimensional analysis of the pole diagram of the core material 2 is performed by using the series expansion method of the spherical harmonic function, and the orientation density of each crystal orientation present in the core material 2 is calculated. For a randomly oriented sample, the same measurement and analysis are performed to calculate the orientation density of each crystal orientation present in the randomly oriented sample. In addition, as a randomly oriented sample, a sample in which the crystal orientation in a sample such as aluminum powder is not oriented in a specific direction can be used.

[0136] Then, the ratio of the orientation density of the core material 2 to the orientation density of the randomly oriented sample was calculated. The ratio of the orientation density of the crystal orientation of each test material was the value shown in Table 3.

[0137] <Method for measuring work hardening index>

[0138] A No. 13B test piece specified in JIS Z2241:2011 was taken from fin material 1 with its length direction parallel to the rolling direction. Next, a tensile test was performed at room temperature according to the method specified in JIS Z2241:2011. Based on the test force-strain curve obtained from the tensile test, the test force and plastic strain values ​​at the yield point, as well as the test force value at the point where the plastic strain increased by 0.1% from the yield point, were determined. These values ​​were then used to calculate the work hardening index using the two-point method. The work hardening index for each test material is the value shown in Table 3.

[0139] <Evaluation of Fin Strength After Brazing>

[0140] The strength of brazed fins can be evaluated based on the tensile strength of test materials heated under conditions simulating brazing heating. Specifically, fin material 1, cut into appropriate sizes, is placed in a brazing furnace and heated in a nitrogen atmosphere. Heating is completed when the furnace temperature reaches 600°C, and the fin material 1 is cooled within the furnace. After being removed from the brazing furnace and naturally cooled to room temperature, a No. 13B test specimen, as specified in JIS Z2241:2011, is taken from the fin material 1 with its length aligned with the rolling direction.

[0141] Using the test pieces thus prepared, a tensile test was performed at room temperature according to the method specified in JIS Z 2241: 2011. Table 3 shows the tensile strength after brazing of each test material.

[0142]

Table 3

[0143]

[0144] As shown in Tables 1 to 3, test materials S1 to S3 comprise a core material 2 having the aforementioned specific chemical composition and crystal texture, and a brazing filler metal 3 having the aforementioned specific chemical composition. Furthermore, the coverage of the brazing filler metal 3 in test materials S1 to S3 all fell within the aforementioned specific ranges. Test materials S1 to S3 with such a composition exhibited high work hardening indices, excellent formability, and excellent strength after brazing heating.

[0145] On the other hand, samples S4-S6 were annealed under conditions where the total diffusion amount M was greater than that of samples S1-S3. Consequently, during annealing, aluminum atoms in the core material of samples S4-S6 diffused excessively, reducing the orientation density of the Brass, S, and Copper orientations while promoting the development of the Cube, CR, and Copper orientations. As a result, the formability of samples S4-S6 was inferior to that of samples S1-S3.

Claims

1. An aluminum alloy fin material, comprising a brazing sheet comprising a core material and brazing filler metals disposed on both surfaces of the core material, wherein: The core material has: A chemical composition comprising: Si: 0.02 mass % or more and 0.80 mass % or less, Fe: 0.02 mass % or more and 0.80 mass % or less, and Mn: 0.8 mass % or more and 2.0 mass % or less, with the balance being Al and unavoidable impurities; and The crystal texture has an orientation density of at least one of the Brass, Copper, and S orientations that is more than 20 times that of the random orientation sample, and an orientation density of the Cube, CR, and P orientations that is less than 10 times that of the random orientation sample. The brazing filler metal is composed of an Al-Si alloy containing 6.0 mass % or more and 13.0 mass % or less of Si and 0.02 mass % or more and 0.80 mass % or less of Fe. The coverage of each brazing material is 6% or more and 16% or less, By making the crystal texture of the core material before brazing into a specific form, the work hardening index of the core material can be increased, and the fin material has a characteristic of having a work hardening index of 0.07 or more at the yield point.

2. The aluminum alloy fin material according to claim 1, wherein: The core material further contains Zn: 0.3 mass % or more and 3.0 mass % or less.

3. The aluminum alloy fin material according to claim 1 or 2, wherein: The Al—Si alloy constituting the brazing filler metal further contains Sr: 0.005 mass % or more and 0.050 mass % or less.

4. A method for producing an aluminum alloy fin material, the method for producing an aluminum alloy fin material according to any one of claims 1 to 3, wherein: The manufacturing method of the aluminum alloy fin material comprises: a casting step of producing a core material block having a chemical composition comprising Si: 0.02 mass % or more and 0.80 mass % or less, Fe: 0.02 mass % or more and 0.80 mass % or less, and Mn: 0.8 mass % or more and 2.0 mass % or less, with the balance consisting of Al and unavoidable impurities, and a brazing filler metal block comprising an Al-Si alloy containing Si: 6.0 mass % or more and 13.0 mass % or less, and Fe: 0.02 mass % or more and 0.80 mass % or less; a lamination step of arranging the brazing material blocks on both sides of the core material block to produce a cladding block; a hot rolling step of hot rolling the clad block to produce a clad plate; a first cold rolling step of cold rolling the clad plate; Annealing step: the clad sheet after the first cold rolling step is subjected to annealing until the total diffusion amount M calculated by the following formula (1) becomes 1.0×10 -14 m 2 Above and 5.0×10 -12 m 2 Heating and annealing are performed under the following conditions; and The second cold rolling step is to cold-roll the clad sheet after the annealing step. 【Mathematical formula 1】 ; Wherein, n in the formula (1) is the total heating time in unit time The number of intervals when t is divided, D0 is 1.37×10 - 5 m 2 / s, Q is 123kJ / mol, and R is 8.3145kJ / (mol K), and the value of T(k) is the heating temperature [K] at the start time of the kth interval.

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