Aluminum alloy brazing sheet to suppress warping during brazing.

Abstract

To provide a brazing sheet that can suppress warping during brazing.SOLUTION: An aluminum alloy-based brazing sheet according to the present invention has a four-layered structure in which a core material layer is laminated on an intermediate layer to constitute a laminated body and brazing materials are arranged on both surfaces in a lamination direction of the laminated body. The core material layer contains Mn, Si, Fe and Cu, in a specified range, the intermediate layer includes Zn, Mn, Si, Fe in a specific range, the brazing layer contains Si, Mg and Bi, in a specified range. Average crystal grain diameter ratios (an average crystal grain diameter of the intermediate layer / an average crystal grain diameter of the core material layer) of the core material layer and the intermediate layer subjected to brazing heat treatment are in a range of 0.5-1.5, and further a difference between a melting point (a solidus temperature) of the intermediate layer and a melting point (a solidus temperature) of the core material layer is 15°C or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aluminum alloy brazing sheet for suppressing warpage during brazing.

Background Art

[0002] Conventionally, many aluminum automotive heat exchangers have been manufactured using brazing joints. Advantages of brazing include the ability to join multiple joints simultaneously in a single heat treatment and high sealing performance. Brazing is performed using a brazing sheet formed by laminating a brazing material made of an Al-Si alloy with a lower melting point than other aluminum alloys and a non-brazing material. The brazing sheet is formed into various part shapes according to each heat exchanger, and then assembled and subjected to a brazing heat treatment to achieve a brazing joint. To obtain good brazing properties, during the brazing heat treatment, the members need to be close to each other mainly at the brazing melting temperature. Therefore, the precisely formed parts are assembled so as to generate as little clearance as possible.

[0003] The applicant of the present application has previously proposed, for example, a fluxless brazing method shown in Patent Document 1 below. In the technique described in this Patent Document 1, an Al-Si-based brazing material containing a predetermined amount of Mg and Si is clad on a core material to form an aluminum clad material. The Al-Si-based brazing material and the brazing object are brought into contact and adhered to each other in a non-oxidizing atmosphere without reduced pressure, and brazing is performed by heating to 559 to 620°C.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in recent years, with the miniaturization and weight reduction of heat exchangers, there has been a trend towards products with more complex structures, and consequently, the difficulty of brazing joints has been increasing. For example, in heat exchangers with a structure in which cup-shaped molded parts are stacked, the joining length per part is long, so there is a concern that brazing defects may occur if there is excessive clearance in even one part. In fact, brazing defects frequently occur in heat exchangers with such complex structures. When the inventors observed the defective joints after brazing heat treatment, they confirmed that the components were deformed in a warped manner. It is believed that this deformation caused the clearance between the components to widen, resulting in the defective joints.

[0006] Further investigation by the inventors revealed that the brazing sheet deforms by warping as the brazing wax melts. This deformation occurs because the molten wax penetrates the non-brazing material side in contact with the brazing material, causing the non-brazing material side between the brazing material and the non-brazing material to expand. Therefore, in a brazing sheet where brazing material is arranged on both sides and two or more non-brazing material layers are sandwiched between the two brazing materials (for example, a four-layer material, brazing material / intermediate layer / core material / brazing material), the wax penetration properties of each non-brazing material layer generally differ, so the expansion of the non-brazing material side interface is not necessarily the same for each layer. As a result of the expansion difference caused by the difference in wax penetration properties, the member deforms by warping so that the side where more wax penetrates becomes convex.

[0007] According to the inventor's research, in order to eliminate member deformation, the solution is to adjust the wax penetration properties of multiple non-brazing layers to be the same, thereby eliminating the difference in expansion. Specifically, it is believed that member deformation can be suppressed by (1) controlling the grain size just before wax penetration occurs (≒ grain size after brazing), which are material properties related to wax penetration, and (2) adjusting the difference in melting points between the intermediate layer and the core layer.

[0008] This invention was made to solve these problems and aims to provide an aluminum alloy brazing sheet that can suppress warping during brazing. [Means for solving the problem]

[0009] (1) The aluminum alloy brazing sheet of this embodiment is a four-layer aluminum alloy brazing sheet in which a laminate is formed by laminating a core layer and an intermediate layer, and brazing material layers are arranged on both sides of the laminate in the lamination direction, wherein the composition of the core layer is, by mass%, Mn: 0.7~1.7%, Si: 0.1~1.0%, Fe: 0.05~0.5%, Cu: 0.05~0.8%, with the remainder being Al and unavoidable impurities, the composition of the intermediate layer is, by mass%, Zn: 1.5~8.0%, Mn: 0.3~1.3%, Si: 0.2~0.8%, Fe: 0.05~0.5%, with the remainder being Al and unavoidable impurities, and the composition of the brazing material layer is, by mass%, Si: 5.0~14.0%, Mg: 0.3~1.5% The material contains 0.05-0.25% Bi, with the remainder being Al and unavoidable impurities, the average grain size ratio (average grain size of the intermediate layer / average grain size of the core layer) after brazing heat treatment of the core layer and the intermediate layer is in the range of 0.5-1.5, and furthermore, the difference between the melting point (solidus temperature) of the intermediate layer and the melting point (solidus temperature) of the core layer is within 15°C. However, regarding the suppression of warping, if we assume that the aluminum alloy brazing sheet, which has been warped into an arc shape after brazing heat treatment, is placed on a plane so that it is convex upwards, and that the distance between the two points where both ends of the aluminum alloy brazing sheet in the longitudinal direction touch the plane is the length of the chord (L (mm)), and that the maximum height of the arched aluminum alloy brazing sheet from the plane is h (mm), then the curvature σ ( / mm) obtained by substituting these values ​​into the following formula is taken as the amount of warping (Z), then the relationship 0 ≤ Z ≤ 0.005 is satisfied. σ = {8 × h / (L 2 +4×h 2 )} [Effects of the Invention]

[0010] The present invention relates to an aluminum alloy brazing sheet in which brazing metal layers are arranged on both sides of a laminate formed by stacking a core layer and an intermediate layer. The composition of the core layer (Mn, Si, Fe, Cu) is specified, the composition of the intermediate layer (Zn, Mn, Si, Fe, Mg) is specified, and the composition of the brazing metal layer (Si, Mg, Cu, Bi) is specified. The average grain size ratio of the core layer and the intermediate layer after brazing heat treatment (average grain size of the intermediate layer / average grain size of the core layer) is in the range of 0.5 to 1.5. The difference between the melting point (solidus temperature) of the intermediate layer and the melting point (solidus temperature) of the core layer is within 15°C. Therefore, the amount of molten solder immersed in the core layer and the intermediate layer during brazing can be equalized, and a brazing sheet with less warping after brazing can be provided. Therefore, by using the brazing sheet of the present invention, it is possible to braze components with fine structures, such as fins, tubes, or cup-shaped molded members, without producing brazing defects. [Brief explanation of the drawing]

[0011] [Figure 1] A cross-sectional view showing a first embodiment of the aluminum alloy brazing sheet according to this embodiment. [Modes for carrying out the invention]

[0012] An example of an embodiment will be described in detail below with reference to the attached drawings. Note that, for convenience, the drawings used in the following description may show enlarged versions of key features to make them easier to understand.

[0013] Figure 1 shows the cross-sectional structure of an aluminum alloy brazing sheet according to the first embodiment of the present invention. In this form, the aluminum alloy brazing sheet A is constructed by laminating a core material layer 1 and an intermediate layer 2 to form a laminate 4, with a first brazing material layer 5 laminated on one side in the lamination direction (thickness direction) and a second brazing material layer 6 laminated on the other side in the lamination direction (thickness direction), resulting in a four-layer structure.

[0014] "Heartwood layer" The composition of the heartwood layer 1 contains, by mass%, Mn: 0.7 to 1.7%, Si: 0.1 to 1.0%, Fe: 0.05 to 0.5%, Cu: 0.05 to 0.8%, and the balance consists of Al and unavoidable impurities. In addition, when expressing the range of mass% using "~", unless otherwise specified, it shall be expressed as including the lower and upper limits. Therefore, as an example, 0.7 to 1.7% means a content of 0.7 mass% or more and 1.7 mass% or less.

[0015] "Heartwood layer" The reasons for limiting the composition of the component elements contained in the heartwood layer 1 are explained below. Mn: 0.7 to 1.7% Mn is added to precipitate as intermetallic compounds such as Al-Mn, Al-Mn-Si, Al-Mn-Fe, Al-Mn-Si-Fe in the structure to improve the material strength. If the content of Mn is less than the lower limit, the effect is insufficient, and if it exceeds the upper limit, huge intermetallic compounds (crystallized products) are generated during casting, resulting in a decrease in ductility. Si: 0.1 to 1.0% Si is added to improve the material strength by solid solution in Al and also to precipitate as intermetallic compounds such as Al-Mn-Si and Al-Mn-Si-Fe in the structure to improve the material strength. If the content of Si is less than the lower limit, the effect is insufficient, and if it exceeds the upper limit, the melting point of the material decreases.

[0016] Fe: 0.05 to 0.5% Fe is added to precipitate as intermetallic compounds such as Al-Mn-Fe and Al-Mn-Si-Fe in the structure to improve the material strength. If the content of Fe is less than the lower limit, the manufacturing cost increases, and if it exceeds the upper limit, huge intermetallic compounds (crystallized products) are generated during casting, resulting in a decrease in ductility. Cu: 0.05 to 0.8% Cu is added to dissolve in Al to improve the material strength. If the content of Cu is less than the lower limit, the effect is insufficient, and if it exceeds the upper limit, huge intermetallic compounds (crystallized products) are generated during casting, resulting in a decrease in ductility.

[0017] "Intermediate layer" The following explains the reasons for limiting the composition of the constituent elements contained in intermediate layer 2. Zn: 1.5~8.0% Zn is added to Al to form a solid solution, lowering the material's natural potential compared to other components, thereby improving the cladding's resistance to pitting corrosion through a sacrificial corrosion protection effect. If the Zn content is below the lower limit, the sacrificial corrosion protection effect is insufficient, while exceeding the upper limit results in an excessively lower potential and an increased rate of self-corrosion. Mn: 0.3~1.3% Mn is added to improve material strength by precipitating within the microstructure as intermetallic compounds such as Al-Mn, Al-Mn-Si, Al-Mn-Fe, and Al-Mn-Si-Fe. If the Mn content is below the lower limit, the effect is insufficient, and if it exceeds the upper limit, large intermetallic compounds (crystallized deposits) are formed during casting, reducing rollability.

[0018] Si: 0.2~0.8% Si is added to improve material strength by solid-solving in Al, and also by precipitating as Al-Mn-Si and Al-Mn-Si-Fe intermetallic compounds. If the Si content is below the lower limit, the effect is insufficient, and if it exceeds the upper limit, the melting point of the material decreases. Fe: 0.05~0.5% Fe is added to improve material strength by precipitating within the microstructure as intermetallic compounds such as Al-Mn-Fe and Al-Mn-Si-Fe. If the Fe content is below the lower limit, manufacturing costs increase, and if it exceeds the upper limit, large intermetallic compounds (crystallized deposits) are formed during casting, reducing rollability.

[0019] "Waxing layer" The following explains the reasons for limiting the composition of the constituent elements contained in the brazing layers 5 and 6. Si: 5.0~14.0% Si is added during brazing to form molten solder and create a fillet at the joint. If the Si content is below the lower limit, there will be insufficient molten solder. If the Si content exceeds the upper limit, the material becomes hard and brittle, making material manufacturing difficult, and coarse Si is generated to maintain the casting, reducing corrosion resistance. Mg: 0.3~1.5% Mg is added to reduce and decompose the oxide film (Al2O3) and improve bonding properties. If the Mg content is below the lower limit, the effect is insufficient, and if it exceeds the upper limit, the material strength becomes too high, making material manufacturing difficult, and the bonding properties decrease due to the dense formation of a MgO film on the material surface.

[0020] Bi: 0.05~0.25% Bi is added to improve the wettability of molten solder. If the Bi content is below the lower limit, the effect is insufficient, and if it exceeds the upper limit, large intermetallic compounds (crystallized deposits) are formed during casting, reducing rollability.

[0021] The average grain size ratio (average grain size of the intermediate layer / average grain size of the core layer) after brazing heat treatment of the core layer and intermediate layer is in the range of 0.5 to 1.5. The warping deformation of the brazing sheet during brazing is caused by the difference in expansion resulting from the difference in brazing penetration between the core layer 1 and the intermediate layer 2. Several factors contribute to the penetration of the brazing material, but the most important is considered to be the average grain size of the core layer 1 and the intermediate layer 2. The smaller the average grain size between core layer 1 and intermediate layer 2, the greater the amount of wax penetration. Conversely, if the average grain size is large, wax penetration is limited. Therefore, to suppress warping, it is important to reduce the difference in average grain size between core layer 1 and intermediate layer 2, that is, to reduce the expansion difference due to wax penetration. If the difference in average grain size between core layer 1 and intermediate layer 2 is large, the expansion difference will be large, causing warping deformation. For this reason, it is necessary to keep the ratio of average grain size between core layer 1 and intermediate layer 2 within a predetermined range. For this reason, it is preferable to set the value of the ratio of average grain size between core layer 1 and intermediate layer 2 (average grain size / average grain size of the core) in the range of 0.5 to 1.5.

[0022] The difference between the melting point (solidus temperature) of the intermediate layer and the melting point (solidus temperature) of the core layer is within 15°C. Besides the average grain size, solidus temperature is another factor that influences the wax penetration between core layer 1 and intermediate layer 2. As the solidus temperature decreases, wax penetration increases. Therefore, a large difference in solidus temperature between core layer 1 and intermediate layer 2 leads to a large difference in expansion, causing warping. For this reason, the difference in solidus temperature between intermediate layer 2 and core layer 1 needs to be smaller than a predetermined value (15°C).

[0023] To minimize the difference in average grain size between core layer 1 and intermediate layer 2, which have different compositions, it is important to make the material structure of core layer 1 and intermediate layer 2 as similar as possible before brazing. The material structure of the core layer 1 and the intermediate layer 2 before brazing can be controlled by the manufacturing conditions described below.

[0024] "Manufacturing conditions" There are no particular restrictions when preparing brazing layers 5 and 6, and they can be prepared based on the conditions for preparing brazing layers when manufacturing a general brazing sheet. To obtain the desired sheet by casting from molten aluminum alloy of the required composition, homogenization treatment and surface machining are performed under normal conditions, and the desired sheet thickness is achieved by hot rolling. There are no particular restrictions when preparing the core layer 1 and the intermediate layer 2, and they can be prepared based on the conditions used to prepare the core layer 1 and the intermediate layer 2 when manufacturing a general brazing sheet. In order to obtain the desired sheet material by casting from molten aluminum alloy of the required composition, a homogenization treatment is performed under normal conditions, followed by surface machining. However, it is preferable to appropriately determine the conditions for the homogenization treatment, depending on the combination of core layer 1 and intermediate layer 2, so as to minimize the difference in average grain size between core layer 1 and intermediate layer 2. Homogenization treatment is not necessarily required when producing the intermediate layer 2, but in the case of the core layer 1, homogenization treatment should be performed under appropriate conditions of 400°C to 600°C for 1 to 12 hours, depending on the composition.

[0025] "Clad rolling" As described above, the brazing material, core material, and intermediate layer are assembled, and then subjected to soaking treatment, hot rolling, and cold rolling. If necessary, intermediate annealing and final annealing are performed during cold rolling. The assembly, soaking treatment, and hot rolling should be carried out under the same conditions as when manufacturing a general brazing sheet.

[0026] "Cold rolling" When performing cold rolling, the reduction ratio per pass of cold rolling is controlled as follows. In cold rolling, if the thickness of the aluminum alloy brazing sheet material is 1 mm or more, the reduction ratio per pass shall be 25% or more, and if the thickness is less than 1 mm, the reduction ratio per pass shall be 10% or more. In cold rolling, if the reduction ratio per pass does not meet the specified value, strain will not be uniformly distributed between the core layer and the intermediate layer, resulting in differences in the average grain size after brazing in each layer.

[0027] "Material temperature during cold rolling" The material temperature during cold rolling should preferably be below 180°C. Cold rolling increases the material temperature, but only for a very short time. If the temperature exceeds 180°C, recrystallization nuclei are formed coarsely, resulting in a large difference in average grain size between the core and the intermediate layer. Therefore, it is preferable to keep the material temperature below 180°C during cold rolling.

[0028] "Final annealing" Although the objectives of this embodiment can be satisfied even without the final annealing load, loading the load allows for a smaller average grain size difference between the core layer 1 and the intermediate layer 2, and enables the stable acquisition of a small average grain size difference. When performing the final annealing, a heating rate of 30 to 70°C / h is desirable.

[0029] The final annealing temperature (T) should preferably be in the range of 200°C ≤ T ≤ 240°C. If the final annealing temperature (T) is within the range described above, subcrystalline grains that serve as nuclei for recrystallization can be uniformly generated, and the recrystallization rates of the core layer 1 and the intermediate layer 2 can be made uniform during the brazing heat treatment, thereby reducing the difference in average grain size after brazing. If the final annealing temperature (T) is below 200°C, the generation of subcrystalline grains is insufficient and the full effect cannot be obtained, and if it exceeds 240°C, a portion of the core layer 1 and the intermediate layer 2 will recrystallize, resulting in a difference in the average grain size after brazing.

[0030] The final annealing temperature (T) should preferably be in the range of 300°C ≤ T ≤ 400°C. If the final annealing temperature (T) is within the range described above, recrystallization by final annealing, which has a slower heating rate than brazing heat treatment, results in uniform recrystallization, thus stably reducing the difference in average grain size between the core layer 1 and the intermediate layer 2. If the final annealing temperature (T) is below 300°C, the non-brazing layer cannot complete recrystallization, and if it exceeds 400°C, secondary recrystallization occurs, resulting in non-uniform grains.

[0031] The aluminum alloy brazing sheet A, manufactured according to the process described above, is used for brazing when manufacturing heat exchangers, for example, by placing it in an inert gas atmosphere at a brazing temperature range of approximately 590-620°C for 1-30 minutes. For example, it is used in the assembly of heat exchangers by laminating it with brazing components such as fins, tubes, or cup-shaped molded bodies of various heat exchangers. After assembling the fins, tubes, or cup-shaped molded bodies, the entire assembly is heated to the brazing temperature, the brazing material layers 5 and 6 of the aluminum alloy brazing sheet A are melted, and then the brazing is completed by cooling to room temperature.

[0032] In this embodiment, the aluminum alloy brazing sheet A has an average grain size ratio (average grain size of the intermediate layer / average grain size of the core layer) of the core layer 1 and the intermediate layer 2 after brazing heat treatment in the range of 0.5 to 1.5, and the difference between the melting point (solidus temperature) of the intermediate layer 2 and the melting point (solidus temperature) of the core layer 1 is within 15°C. Therefore, even if the brazing material layers 5 and 6 melt and spread as solder, the warping of the core layer 1 and the intermediate layer 2 can be reduced. If the average grain size ratio (average grain size of the intermediate layer / average grain size of the core layer) after brazing heat treatment of the core layer 1 and the intermediate layer 2 is in the range of 0.5 to 1.5, and the difference between the melting point of the intermediate layer 2 and the melting point of the core layer 1 is within 15°C, the penetration of molten solder into the core layer 1 and the intermediate layer 2 can be made uniform. Furthermore, by reducing the difference between the melting point of the intermediate layer 2 and the melting point of the core layer 1, the difference in expansion can be reduced, thereby suppressing the warping of the aluminum alloy brazing sheet A during brazing. This means that in a heat exchanger constructed by brazing together components with complex and microscopic structures, the brazing process does not cause any changes in the clearance between the components. As a result, it becomes possible to perform brazing without causing joint defects, even in microscopic structures where the clearance between the components to be brazed is small. [Examples]

[0033] Using aluminum alloys No. 1 to No. 47 for core, intermediate, or brazing purposes, having the compositions shown in Tables 1 and 2, and applying the manufacturing conditions shown in Table 3, a four-layer brazing sheet with the structure shown in Figure 1 was produced by cladding and rolling. The final thickness of each brazing sheet was 0.2 mm. Alloy ingots with compositions No. 1 to No. 47 for core material, intermediate layer, or brazing material, as shown in Tables 1 and 2, were obtained by casting from molten aluminum alloy. After homogenization treatment and hot rolling, brazing sheets of the respective final thicknesses were produced by cold rolling according to manufacturing methods A to J shown in Table 3. In Table 3, condition X indicates the reduction ratio (%) per pass at the stage of cold rolling with a sheet thickness of 1 mm or more, and condition Y indicates the reduction ratio (%) per pass at the stage of cold rolling with a sheet thickness of less than 1 mm. The upper limit temperature indicates the upper limit temperature (°C) during cold rolling, the final annealing temperature (°C) indicates the temperature when final annealing is performed, and - indicates that final annealing is not performed. In addition, the homogenization treatment conditions (HOMO conditions: temperature (°C), treatment time (hr)) for each sample are listed in Tables 4 to 6. - indicates a sample that has not undergone homogenization treatment.

[0034] Using sheet materials consisting of alloys No. 1 to No. 47 for core, intermediate layer, or brazing material, each having the composition shown in Tables 1 and 2, brazing sheets No. 1 to No. 74 shown in Tables 4 to 6 were prepared by applying either the cold rolling conditions or the final annealing conditions shown in Tables A to J. The average grain size ratio (average grain size of the intermediate layer / average grain size of the core layer) and its evaluation, solidus temperature difference (°C) and its evaluation, tensile strength (MPa) and its evaluation, corrosion resistance and its evaluation, and the overall evaluation results (overall evaluation) for each brazing sheet are shown in Tables 4 to 6.

[0035] For brazing sheets made from 0.2 mm thick final plates, rectangular specimens were cut out with dimensions of 120 mm in the RD direction (rolling direction) and 100 mm in the TD direction (transverse direction). A hole was drilled in the center of one of the shorter sides, and a rod was inserted to suspend the specimen. The specimens were then heated to 600°C at an average heating rate of 100°C / min to simulate brazing heat treatment. After reaching 600°C, they were air-cooled (rapidly cooled) to room temperature to obtain each test specimen.

[0036] "Evaluation Criteria" (Measurement of average grain size in the core and intermediate layers) The brazing sheets of each specimen were polished to the center of the thickness of each layer, and the crystal grains on the RD-TD plane were observed using EBSD (Electron Back Scattered Diffraction Pattern). From the obtained observation images, the average crystal grain size was measured by sectioning. For each specimen's brazing sheet, rough polishing was performed to expose the material up to the center of each layer's thickness. The exposed cross-section was then polished with 0.1 μm abrasive particles, followed by electropolishing to a mirror finish. A crystal orientation map of 800 μm × 400 μm field of view was obtained in the RD-TD section using SEM (Scanning Electron Microscope)-EBSD (Electron Back Scattered Diffraction). Regions surrounded by large-angle grain boundaries of 15° or more were considered as a single crystal grain, and the average crystal grain size was measured using the sectioning method with the orientation maps of 5 fields of view for each sample.

[0037] (solidus temperature difference) The solidus temperatures of the core material and sacrificial material were measured using differential thermal analysis. A temperature difference of 10°C or less between the core material and sacrificial material was marked as ○, a temperature difference between 10°C and 15°C was marked as ○, and a temperature difference greater than 15°C was marked as ×. (Tensile strength measurement) After applying a heat treatment equivalent to brazing, samples were cut parallel to the rolling direction to prepare JIS No. 13B test specimens, and tensile tests were performed. At this time, measurements of 150 MPa or higher were marked with ○, 130 MPa or higher but less than 150 MPa with ○, and less than 130 MPa with ×. (corrosion resistance) The brazing material surface on the core side of the test specimen, which has undergone heat treatment equivalent to brazing, is masked, and the brazing material surface on the sacrificial material side is exposed. OY water (Cl-: 195 ppm, SO4) 2- :60ppm,Cu 2+ :1 ppm, Fe 3+ An immersion test was conducted using a solution of 30 ppm (the remainder being pure water). The test conditions consisted of a 16-hour cycle at room temperature followed by an 8-hour cycle at 88°C (without stirring), resulting in a total immersion time of 400 hours. Afterward, corrosion products were removed with chromic acid phosphate, and the corrosion depth of the test material was evaluated. A corrosion depth of less than 80 μm was marked with a circle (○), and a corrosion depth of 80 μm or more was marked with a cross (×).

[0038] (Evaluation of curvature) The brazing was evaluated by observing the appearance of the test material brazing sheets after the brazing heat treatment described above. The brazing sheets after the brazing heat treatment described above were placed horizontally on the measurement reference horizontal plane, and a photograph of the appearance of the brazing sheet from the side was taken. From this photograph, the maximum value of the warp of each test material brazing sheet was determined. For the measurement of warping, a curved plate sample is placed on a plane so that it is convex upwards. The length between the two points where the ends of the sample touch the plane is assumed to be the chord length L (mm), and the maximum height of the curved sample from the plane is assumed to be the arrow height h (mm). Under these assumptions, the curvature σ ( / mm) obtained by substituting the result into the following equation (1) was taken as the amount of warping (Z).

[0039] σ = {8 × h / (L 2 +4 × h 2)}…(Equation (1))

[0040] The warp evaluation results (= z mm) described in Tables 4 to 6 -1 ) where ○ indicates the result of evaluating that (0.002 < Z ≤ 0.005), ○○ indicates the result of evaluating that (0 ≤ z ≤ 0.002), and × indicates the result of evaluating that (0.005 < z). The non-welding material layer composition, manufacturing method, and measurement results described above are shown in Tables 1 to 6 below. (Total) In the items of warp evaluation, strength, and corrosion resistance, if there is one or more ×, it is judged as ×; if the corrosion resistance is ○, and the warp evaluation and strength are ○ and ○, it is judged as ○; if the warp evaluation and strength are ○ and ○○, it is judged as ○○; if the warp evaluation and strength are ○○ and ○, it is judged as ○○○; if the warp evaluation and strength are ○○ and ○○, it is judged as ◎. Hereinafter, Alloy No. and composition are shown in Tables 1 and 2, manufacturing conditions are shown in Table 3, and the above measurement results are shown in Tables 4 to 6.

[0041]

Table 1

[0042]

Table 2

[0043]

Table 3

[0044]

Table 4

[0045]

Table 5

[0046]

Table 6

[0047] As shown in Tables 4 to 6, an aluminum alloy brazing sheet containing Mn: 0.7-1.7%, Si: 0.1-1.0%, Fe: 0.05-0.5%, and Cu: 0.05-0.8% in the core layer, Zn: 1.5-8.0%, Mn: 0.3-1.3%, Si: 0.2-0.8%, and Fe: 0.05-0.5% in the intermediate layer, and Si: 5.0-14.0%, Mg: 0.3-1.5%, and Bi: 0.05-0.25% in the brazing layer, with an average grain size ratio in the range of 0.5-1.5 and a solidus temperature difference of 15°C or less, exhibited excellent strength and corrosion resistance, and showed minimal warping.

[0048] The alloy samples No. 24-31 shown in Table 4 are samples in which the composition of Mn, Si, Cu, or Fe in the core layer falls outside the desirable range described above. Of these samples, samples No. 24, 26, 28, 30, and 31 either resulted in reduced strength, precipitation of crystallized material, a high melting point, or high cost, making them unsuitable for manufacture, and thus preventing the production of the desired brazing sheet. Samples No. 25, 27, and 29 showed reduced strength. Furthermore, sample No. 31 requires high-purity raw materials to keep the Fe content low, resulting in an expensive brazing sheet.

[0049] The samples using alloys No. 32-39 shown in Tables 4 and 5 are samples in which the composition of Mn, Si, Fe, or Zn in the intermediate layer falls outside the desirable range described above. These samples either have reduced strength, precipitate crystals, have a high melting point, or are expensive.

[0050] The samples using alloys No. 40-45 shown in Table 5 are samples in which the composition of Si, Mg, or Bi in the brazing layer falls outside the desirable range described above. These samples either precipitated coarse Si, caused problems during brazing, were too hard, precipitated crystals, or had high melting points, and in any case, they were unsuitable for manufacturing.

[0051] Of the samples shown in Table 5, samples No. 46 and 47 had alloy compositions within the desirable range, but the large solidus temperature difference resulted in poor warpage evaluation. Of the samples shown in Table 5, samples No. 48 to 52 were brazing sheets with excellent strength and corrosion resistance, and minimal warping. Of the samples shown in Tables 5 and 6, samples No. 53 to 56, while having alloy compositions within the desirable range, were either samples with a low reduction ratio under condition X, a low reduction ratio under condition Y, samples where the upper limit temperature during cold rolling was set too high, or samples where the temperature during final annealing was set too high, all under the manufacturing conditions shown in Table 3. In all of these cases, the average grain size ratio fell outside the desirable range, and the warpage evaluation was also poor. Samples No. 57-61 shown in Table 6 were brazing sheets with excellent strength and corrosion resistance, and minimal warping.

[0052] Samples No. 62-65 shown in Table 6 were samples whose crystal grain size ratio fell outside the desirable range and were brazed sheets with a high degree of warping. Samples No. 66-70 shown in Table 6 were brazing sheets with excellent strength and corrosion resistance, and minimal warping. Samples No. 71-74 shown in Table 6 are samples whose average crystal ratio falls outside the desirable range, resulting in larger warpage values. [Explanation of Symbols]

[0053] A...Aluminum alloy brazing sheet, 1...Core layer, 2...Intermediate layer, 4...Laminate, 5...First brazing layer, 6...Second brazing layer.

Claims

[Claim 1] An aluminum alloy brazing sheet having a four-layer structure, in which a laminate is formed by laminating a core layer and an intermediate layer, and brazing material layers are arranged on both sides of the laminate in the lamination direction, The composition of the core layer is, by mass%, Mn: 0.7-1.7%, Si: 0.1-1.0%, Fe: 0.05-0.5%, Cu: 0.05-0.8%, with the remainder being Al and unavoidable impurities; the composition of the intermediate layer is, by mass%, Zn: 1.5-8.0%, Mn: 0.3-1.3%, Si: 0.2-0.8%, Fe: 0.05-0.5%, with the remainder being Al and unavoidable impurities; the composition of the brazing layer is, by mass%, Si: 5.0-14.0%, Mg: 0.3-1.5%, Bi: 0.05-0.25%, with the remainder being Al and unavoidable impurities. An aluminum alloy brazing sheet that suppresses warping during brazing, characterized in that the average grain size ratio (average grain size of the intermediate layer / average grain size of the core layer) after brazing heat treatment of the core layer and the intermediate layer is in the range of 0.5 to 1.5, and further, the difference between the melting point (solidus temperature) of the intermediate layer and the melting point (solidus temperature) of the core layer is within 15°C. However, regarding the suppression of warping, if we assume that the aluminum alloy brazing sheet, which has been warped into an arc shape after brazing heat treatment, is placed on a plane so that it is convex upwards, and that the distance between the two points where both ends of the aluminum alloy brazing sheet in the longitudinal direction touch the plane is the length of the chord (L (mm)), and that the maximum height of the arched aluminum alloy brazing sheet from the plane is h (mm), then substituting these values ​​into the following formula to obtain the curvature σ ( / mm) and taking this as the amount of warping (Z), then the relationship 0 ≤ Z ≤ 0.005 is satisfied. σ = {8 × h / (L² + 4 × h²)}

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