Aluminum alloy brazing sheet for heat exchanger

Abstract

To provide an aluminum alloy brazing sheet for a heat exchanger.SOLUTION: An aluminum alloy brazing sheet for a heat exchanger as an aluminum alloy brazing sheet including a skin material comprising aluminum alloy at least on one surface of a core material is such that: the core material contains by mass %, 0.5-1.5% Cu, and one kind or two kinds of 1.4-1.9% Mn and 0.6-1.1% Si, and comprises aluminum alloy having a composition of a balance inevitable impurity and Al; a distribution density of an AlCu-based compound existing in the core material and having an equivalent circle diameter of 0.01×10-3 mm to 1.0×10-3 mm is 0.05×106 to 0.3×106 pieces / mm2; tensile strength is in a range of 190-250 MPa; a value as a ratio of 0.2% proof strength to tensile strength (0.2% proof strength / tensile strength) is 0.90 or more; and tensile strength after brazing represents 150 MPa or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aluminum alloy brazing sheet for heat exchangers.

Background Art

[0002] A brazing sheet made of an aluminum alloy used for an automotive heat exchanger is a laminate in which a skin material made of an aluminum alloy for brazing is bonded to a core material for maintaining strength. Elements such as Si, Cu, and Mg are added to the core material, which is an Al-Mn-based alloy excellent in strength and corrosion resistance, for the purpose of increasing strength.

[0003] For example, as described in Patent Document 1 below, by specifying the Si content, Cu content, and Mn content and setting the number density of Al-Cu-Mn-based intermetallic compounds within a specific range, an aluminum alloy material for a heat exchanger that achieves high strength after brazing is known. Also, as described in Patent Document 2 below, an aluminum alloy brazing sheet having a three-layer structure in which an aluminum alloy brazing material is clad on one side of an aluminum alloy core material containing Cu and an aluminum alloy sacrificial material containing Zn and Mg is clad on the other side is known. Patent Document 3 below discloses an aluminum alloy brazing sheet including a core material, a brazing material of an Al-Si-based alloy provided on one surface thereof, and a sacrificial material provided on the other surface of the core material, in which the thicknesses of the brazing material and the sacrificial material are specified and the total clad ratio of the brazing material and the sacrificial material is specified.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a brazing sheet, when the above-described elements are added for the purpose of improving the strength after brazing, the strength before brazing also improves. If the strength before brazing is high, there is a problem that the desired shape cannot be obtained because the tube becomes too hard during tube forming by roll forming. For example, according to the technique described in Patent Document 1, a problem occurs in that the material strength becomes too high. According to the technique described in Patent Document 2, since Mg is added, there is a risk that the flux and Mg react during brazing joining using the flux, resulting in brazing defects. Further, according to the technique described in Patent Document 3, since Mg is added to the sacrificial material, there is a risk that the flux and Mg react during brazing joining using the flux, resulting in a decrease in brazability.

[0006] As a countermeasure against the above problems, there is a technique of imparting a low-temperature heat treatment for softening treatment after the final rolling of an aluminum alloy, and tempered materials such as H24 after low-temperature heat treatment are known. However, when an aluminum alloy added with the above-described elements is subjected to low-temperature heat treatment to obtain an H24 tempered material, not only the tensile strength (TS) but also the 0.2% proof stress (YS) decreases. For this reason, the springback during forming becomes small, and there has been a problem that the butt joint load required at the butt joint of the tube end by high-frequency welding cannot be obtained.

[0007] The present invention has been made to solve the above problems, and in a brazing sheet suitable for use in a heat exchanger or the like, without impairing the strength after brazing, the tensile strength (TS) of the material is lowered to a desired range, and then the 0.2% proof stress (YS) of the material is maintained high, and an object is to provide an aluminum alloy brazing sheet for a heat exchanger capable of obtaining a high (YS / TS) ratio.

Means for Solving the Problems

[0008] (1) The aluminum alloy brazing sheet for a heat exchanger according to one embodiment of the present invention is an aluminum alloy brazing sheet for a heat exchanger provided with a skin material made of an aluminum alloy on at least one surface of a core material, wherein the core material contains, by mass%, Cu: 0.5 to 1.5%, and contains one or two of Mn: 1.4 to 1.9% and Si: 0.6 to 1.1%, and has a composition of the balance inevitable impurities and Al, and the equivalent circle diameter existing in the core material is 0.01×10 -3 mm to 1.0×10 -3 mm, and the distribution density of the AlCu-based compound is 0.05×10 6 to 0.3×10 6 pieces / mm 2 and the tensile strength is in the range of 190 to 250 MPa, the value of (0.2% proof stress / tensile strength), which is the ratio of the 0.2% proof stress to the tensile strength, is 0.90 or more, and the tensile strength after brazing is 150 MPa or more.

[0009] (2) One embodiment of the present invention is the aluminum alloy brazing sheet for a heat exchanger according to (1), wherein the core material further contains, by mass%, one or more of Fe: 0.2 to 0.5%, Zn: 0.1 to 1.0%, Zr: 0.05 to 0.2%, Ti: 0.05 to 0.2%, and Cr: 0.05 to 0.2%. (3) One embodiment of the present invention is the aluminum alloy brazing sheet for a heat exchanger according to (1) or (2), wherein the skin material is made of an aluminum alloy and contains, by mass%, Si: 8.0 to 12.0%, Zn: 0 to 1.5%, and has a composition of the balance inevitable impurities and Al.

[0010] (4) One aspect of the present invention is the aluminum alloy brazing sheet for a heat exchanger according to (1) or (2), wherein the core material has the skin material on one surface, and on the surface without the skin material, by mass%, among Zn: 4.5 to 7.5%, Mn: 1.3 to 1.7%, Si: 0.4 to 0.8%, Zr: 0.05 to 0.2%, it contains one or more kinds, and has a second skin material made of an aluminum alloy having a composition of inevitable impurities and Al as the balance. (5) One aspect of the present invention is the aluminum alloy brazing sheet for a heat exchanger according to (3), wherein the core material has the skin material on one surface, and on the surface without the skin material, by mass%, among Zn: 4.5 to 7.5%, Mn: 1.3 to 1.7%, Si: 0.4 to 0.8%, Zr: 0.05 to 0.2%, it contains one or more kinds, and has a second skin material made of an aluminum alloy having a composition of inevitable impurities and Al as the balance.

Advantages of the Invention

[0011] The present invention can provide an aluminum alloy brazing sheet for a heat exchanger that can obtain a high (YS / TS) ratio while reducing the TS of the material to a desired range and maintaining the YS of the material high without impairing the strength after brazing.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] Hereinafter, with reference to the accompanying drawings, an example of an embodiment will be described in detail. Note that the drawings used in the following description may show the characteristic parts enlarged for the sake of clarity.

[0014] The aluminum alloy brazing sheet A for a heat exchanger according to this embodiment is, for example, as shown in FIG. 1, composed of a clad material in which a first skin material 2 is bonded to one surface of a core material 1 made of an aluminum alloy and a second skin material 3 is bonded to the other surface. The second skin material 3 is formed on the surface of the core material 1 on the side where the first skin material 2 is not present. Note that the brazing sheet A can have a multilayer structure for the core material 1 and the skin materials 2 and 3, and a four-layer structure or a five-layer structure such as providing a sacrificial anode material between the core material 1 and the skin material 2 may be used.

[0015] "Core material" In this embodiment, the core material 1 is made of an aluminum alloy containing Cu: 0.5 to 1.5% by mass%, and containing one or two of Mn: 1.4 to 1.9% and Si: 0.6 to 1.1%, with the balance being inevitable impurities and Al. Note that when expressing the range of mass% described in this specification using "~", unless otherwise specified, it means inclusive notation of the lower limit and the upper limit. Thus, for example, 0.5 to 1.5% means a content of 0.5% or more and 1.5% or less.

[0016] In addition to the above elements, for the aluminum alloy constituting the core material 1, one or more of Fe: 0.2 to 0.5% by mass%, Zn: 0.1 to 1.0%, Zr: 0.05 to 0.2%, Ti: 0.05 to 0.2%, and Cr: 0.05 to 0.2% can be appropriately selected and added.

[0017] Cu: 0.5 to 1.5% Cu is added so as to be in the above range in order to improve the material strength of the core material 1 by solid solution strengthening. If the Cu content is less than 0.5%, the desired strength improvement effect after brazing cannot be obtained. If the Cu content exceeds 1.5%, the desired precipitation state of the AlCu-based compound before brazing cannot be obtained, and since the amount of Cu in solid solution increases and the strength improves, the desired strength before brazing cannot be obtained.

[0018] Mn: 1.4 to 1.9% Mn is added within the above-mentioned range in order to improve the material strength of the core material 1. Mn improves the material strength of the core material 1 by solid solution strengthening, and in the core material 1, it contributes to the precipitation of intermetallic compounds such as Al-Mn-based, Al-Mn-Si-based, Al-Mn-Fe-based, and Al-Mn-Fe-Si-based, and exhibits a dispersion strengthening effect. If the Mn content is less than 1.4%, the desired strength improvement effect after brazing cannot be obtained. If the Mn content exceeds 1.9%, huge intermetallic compounds are generated during casting, and the manufacturability decreases. Si: 0.6 - 1.1% Si is added within the above-mentioned range in order to improve the material strength of the core material 1. Si improves the material strength by solid solution strengthening, and in the core material 1, it contributes to the precipitation of intermetallic compounds such as Al-Mn-Si-based and Al-Mn-Fe-Si-based, and exhibits a dispersion strengthening effect. If the Si content is less than 0.6%, the desired strength improvement effect after brazing cannot be obtained. If the Si content exceeds 1.1%, the melting point of the core material 1 is lowered, and it may be subject to brazing erosion from the brazing filler metal during brazing, resulting in poor bonding.

[0019] Fe: 0.2 - 0.5% Fe is preferably added within the above-mentioned range in order to improve the material strength of the core material 1. Fe improves the material strength of the core material 1 by solid solution strengthening, and in the core material 1, it contributes to the precipitation of intermetallic compounds such as Al-Fe-based, Al-Fe-Si-based, Al-Mn-Fe-based, and Al-Mn-Fe-Si-based, and exhibits a dispersion strengthening effect. Fe is contained as an impurity in the raw material of aluminum. In order to make the Fe content less than 0.2%, it is necessary to use a high-purity aluminum raw material, which is costly. If the Fe content exceeds 0.5%, huge intermetallic compounds are generated during casting, and the manufacturability decreases.

[0020] Zn: 0.1 - 1.0% Zn contributes to improving the fatigue resistance of the brazing sheet. When the Zn content is less than 0.1%, the desired effect cannot be obtained. When the Zn content exceeds 1.0%, the self-corrosion resistance of the core material 1 decreases.

[0021] Zr: 0.05 - 0.2% Ti: 0.05 - 0.2% Cr: 0.05 - 0.2% Zr, Ti, and Cr contribute to the solid solution strengthening of the core material 1 or the precipitation of intermetallic compounds such as AlZr-based compounds, AlTi-based, and AlCr-based compounds, and exhibit a dispersion strengthening effect. Therefore, it is preferable to add them within the above ranges to improve the material strength. If at least one of the Zr content, Ti content, and Cr content is less than 0.05%, the desired effect of improving the strength after brazing cannot be obtained. If at least one of the Zr content, Ti content, and Cr content exceeds 0.2%, large intermetallic compounds are generated during casting, resulting in a decrease in manufacturability.

[0022] "First skin material (brazing material)" In this embodiment, the first skin material (brazing material) 2 is made of an aluminum alloy containing Si: 8.0 - 12.0% by mass, with the balance being Al and inevitable impurities. In the aluminum alloy constituting the first skin material 2, in addition to the above-mentioned Si, Zn: 1.5% or less can be contained, but Zn does not necessarily need to be added. Therefore, the Zn content can be set to 0 - 1.5%. Si: 8.0 - 11.0% Si lowers the melting point of Al and is necessary for the first skin material 2 to become a brazing material when melting during brazing and brazing with other members. If the Si content is less than 8.0%, sufficient molten brazing material may not be generated, and there is a risk of poor brazing. If the Si content exceeds 11.0%, the amount of molten brazing material increases, and the supply amount of the brazing material increases. Therefore, there is a risk that the supply amount of the brazing material to unintended locations increases. Zn: 0 - 1.5% or less Zn lowers the potential of the brazing filler metal and has the effect of protecting the core material 1 by sacrificial anode action. If Zn is not added, the sacrificial anode effect of the brazing filler metal cannot be obtained. Therefore, in order to obtain the sacrificial anode effect, it is preferable to contain 0.1 to 1.1% of Zn. If the first skin material 2 contains more than 1.5% of Zn, the corrosion rate may increase and the corrosion resistance may decrease.

[0023] "Second skin material (sacrificial anode material)" In this embodiment, the second skin material (sacrificial anode material) 3 is an aluminum alloy containing, by mass%, one or more of Zn: 4.5 to 7.5%, Mn: 1.3 to 1.7%, Si: 0.4 to 0.8%, Zr: 0.05 to 0.2%, and the balance consisting of inevitable impurities and Al. Zn: 4.5 to 7.5% Zn lowers the potential of the second skin material 3 and protects the core material 1 by sacrificial anode action. If the Zn content is less than 4.5%, the desired sacrificial anode effect cannot be obtained. If the Zn content exceeds 7.5%, the corrosion rate may increase and the corrosion resistance may decrease.

[0024] Mn: 1.3 to 1.7% Mn is added so as to be in the above range in order to improve the material strength of the second skin material 3. Mn improves the material strength of the second skin material 3 by solid solution strengthening and contributes to the precipitation of intermetallic compounds such as Al-Mn-based, Al-Mn-Si-based, Al-Mn-Fe-based, and Al-Mn-Fe-Si-based in the second skin material 3. If the Mn content is less than 1.3%, the desired strength improvement effect cannot be obtained. If the Mn content exceeds 1.8%, huge intermetallic compounds are generated during casting and the rollability decreases. Si: 0.4 to 0.8% Si is added so as to be in the above range in order to improve the material strength of the second skin material 3. Si improves the material strength by solid solution strengthening and contributes to the precipitation of intermetallic compounds such as Al-Mn-Si-based and Al-Mn-Fe-Si-based in the second skin material 3, and exhibits a dispersion strengthening effect. If the Si content is less than 0.4%, the desired effect of improving the strength after brazing cannot be obtained. If the Si content exceeds 0.8%, the melting point of the second skin material 3 decreases, and there is a risk of local melting during brazing.

[0025] Zr: 0.05 - 0.2% Zr is added in the above range to improve the material strength of the second skin material 3. Zr improves the material strength of the second skin material 3 by solid solution strengthening, and in the second skin material 3, it contributes to the precipitation of Al-Zr based intermetallic compounds and exhibits a dispersion strengthening effect. If the Zr content is less than 0.05%, the desired effect of improving the strength after brazing cannot be obtained. If the Zr content exceeds 0.2%, huge intermetallic compounds are generated during casting, and the manufacturability decreases.

[0026] The aluminum alloy brazing sheet A described above is used for the purpose of brazing by being placed in an inert gas atmosphere at a brazing temperature, for example, in a temperature range of about 590 - 620 °C for about 1 - 30 minutes when manufacturing a heat exchanger or the like. For example, it is applied to components of heat exchangers such as tubes and fins of heat exchangers with various configurations or molded bodies with various shapes. The brazing sheet A is used for assembling a heat exchanger in a form of being laminated with other brazing members. After assembling the tube, fin, or molded body, the whole is heated to the brazing temperature, the skin material 2 is melted, and then cooled to room temperature to complete the brazing.

[0027] In order to obtain the desired endurance after brazing, the brazing sheet A of the present embodiment needs to make the AlCu-based compound before brazing in the core material 1 in an optimal distribution state. The optimal distribution state of the AlCu-based compound is that the distribution density of the AlCu-based compound with a circle equivalent diameter of 0.01×10 -3 mm - 1.0×10 -3 mm existing in the core material 1 is in the range of 0.05×10 6 - 0.3×10 6 pieces / mm 2 Preferably, it is in the range. If the distribution density of the AlCu-based compound is below or exceeds the aforementioned range, it is impossible to obtain the material strength of the brazing sheet A before brazing as desired. A decrease in the precipitation amount of the AlCu-based compound means a large amount of dissolved Cu, and when the amount of dissolved Cu is large, the strength exceeds the desired material strength. In order to make the distribution density of the AlCu-based compound within the aforementioned range, it is important to control the conditions in the manufacturing method of the brazing sheet described later.

[0028] The brazing sheet A has a tensile strength in the range of 190 to 250 MPa, a value of (0.2% proof stress: YS / tensile strength: TS), which is the ratio of the 0.2% proof stress to the tensile strength, of 0.90 or more, and a post-brazing tensile strength of 150 MPa or more.

[0029] "Tensile strength (TS) of the brazing sheet: 190 - 250 MPa" When a heat exchanger tube is formed using the brazing sheet A, when the tube is manufactured by roll forming, since the brazing sheet A has appropriate strength, a desired shape can be surely obtained. If the tensile strength of the brazing sheet A is lower than 190 MPa, the butting strength during electric resistance welding is low, the tube is likely to buckle, and it becomes difficult to obtain an appropriate joint state. Conversely, if the tensile strength exceeds 250 MPa, it becomes difficult to obtain an accurate tube shape by roll forming. Also, when applied to a heat exchanger having a shape in which the tube is bent to form a flow path, the springback amount increases, and it becomes difficult to obtain an appropriate shape. Therefore, it is desirable that the tensile strength of the brazing sheet is in the range of 190 to 250 MPa, and more desirably in the range of 200 to 220 MPa.

[0030] "(0.2% proof stress: YS / tensile strength: TS) value is 0.90 or more" In the brazing sheet A, when forming a tube, if the (YS / TS) value is lower than 0.90, the butting strength during electric resistance welding will be low, and the tube will be prone to buckling, making it impossible to obtain a normal joint state. The (YS / TS) value is more preferably 0.95 or more.

[0031] "Tensile strength of the brazing sheet after brazing" The tensile strength of the brazing sheet after brazing is desirably 150 MPa or more. To obtain the required structural strength as a heat exchanger, the tensile strength of the brazing sheet after brazing needs to be 150 MPa or more, and more preferably 175 MPa or more.

[0032] Figure 2 shows an aluminum alloy heat exchanger 4 as an example in which the tube 6 is formed using the brazing sheet A and the fin 5 made of an aluminum alloy is used as the brazing target material. By incorporating the fin 5 and the tube 6 with the reinforcing material 7 and the header plate 8 and brazing them, an aluminum alloy heat exchanger 4 for automotive applications etc. can be obtained.

[0033] For the heat exchanger 4 having the configuration shown in Figure 2, if a high-temperature medium flows inside the tube 6, the tube 6 expands upon receiving heat, and stress acts on the joint portion with the header plate 8. In this case, it is possible to provide a heat exchanger 4 that is less likely to crack or break at the joint portion with the header plate 8 and has sufficient structural strength.

[0034] "Manufacturing method" To manufacture the above-mentioned brazing sheet A, aluminum alloys for constituting the core material 1, the first skin material (brazing material) 2, and the second skin material (sacrificial anode material) 3 of the target composition are manufactured respectively. For example, the aluminum alloy material for the core material 1, the aluminum alloy material for the first skin material 2, and the aluminum alloy material for the second skin material 3 of the above-mentioned respective compositions are cast by a semi-continuous casting method. For the core material 1 and the skin materials 2 and 3, after obtaining the casting material, homogenization treatment is performed. For the aluminum alloy materials for the skin materials 2 and 3, hot rolling is performed to adjust to the desired thickness, and it is bonded to the aluminum alloy material for the core material 1, and through hot rolling and cold rolling, a brazing sheet of the target thickness is obtained. Intermediate annealing and low-temperature annealing are performed during cold rolling to obtain the target brazing sheet.

[0035] "Homogenization treatment" For the aluminum alloy for the core material 1 formed by casting, homogenization treatment can be performed at a desired temperature of 500°C or higher and less than 600°C for a treatment time in the range of 3 hours to less than 12 hours. Through homogenization treatment, an appropriate distribution state of intermetallic compounds (dispersion particles) (mainly the distribution state of intermetallic compound particles such as AlMn-based, AlMnSi-based, and AlMnFeSi-based) can be obtained to obtain the desired mechanical properties before and after brazing.

[0036] When homogenization treatment is performed at a temperature lower than the above-mentioned desired temperature range, the dispersion state of the particles becomes fine and high-density dispersion, so the material strength increases, and the desired properties of the material cannot be obtained. On the other hand, when homogenization treatment is performed at a temperature exceeding the above-mentioned desired temperature range, the dispersion particles become coarse and sparse, so the strength after brazing tends to be lower than the desired strength. Regarding the homogenization treatment temperature, even within the above-mentioned temperature range, it is more preferable to perform it in the temperature range of 520°C to 590°C. For the first skin material 2, for example, when it is used as a brazing material, homogenization treatment may be performed in the range of 400°C to 550°C for 1 hour to 10 hours to improve machinability.

[0037] "Hot rolling of the skin material" The skin material is hot rolled to a predetermined thickness for bonding to the core material. The hot rolling conditions at this time are rolled under general conditions. The thickness of the skin material after hot rolling is appropriately determined according to the clad ratio. "Bonding" Combine a first skin material (brazing material) and a second skin material (sacrificial material) processed into a plate shape by rolling with a core material. The clad ratio is not particularly defined, but it is defined in the range of brazing material: core material: sacrificial material = 5 to 20%: 60 to 90%: 5 to 20%.

[0038] "Hot rolling" For an aluminum alloy material obtained by laminating a core material and a skin material, clad rolling can be performed using a hot rolling mill to produce a clad material. The conditions are not particularly specified, but it is preferable to perform hot rolling after heating the combination of the core material and the skin material to 400 to 500 °C. The plate material after hot rolling is wound into a coil, but it is necessary to adjust the temperature of the brazing sheet at the outermost periphery of the coil after hot rolling to 300 °C or higher and the cooling rate of the coil to 20 °C / h or lower. Preferably, the cooling rate is 5 to 20 °C / h. As a result, Cu dissolved in the core material 1 can grow an AlCu-based compound to a stable phase larger than the size of a GP zone or a metastable phase that generally contributes to precipitation strengthening, and the strength can be reduced compared to the solution strengthening. Since these AlCu-based compounds are redissolved in the matrix during brazing, Cu contributes to strength improvement in a dissolved state after brazing. As a result, it is possible to improve the tensile strength after brazing while reducing the tensile strength before brazing. When the temperature of the brazing sheet at the outermost periphery of the coil is 300 °C or lower, the desired distribution state of the AlCu-based compound cannot be obtained. Similarly, even if the cooling rate is outside this range, the distribution state of the AlCu-based compound cannot be obtained. However, even outside this range of the cooling rate, an equivalent distribution state of the AlCu-based compound can be obtained by adding low-temperature annealing described later. "Cold rolling" Perform cold rolling on the clad material after hot rolling. The cold rolling conditions are not particularly specified, but it can be carried out with a reduction rate per pass between 20 and 50%. If it is outside this range, the manufacturability decreases.

[0039] "Intermediate annealing" Intermediate annealing is applied to recrystallize and soften the core material. If the core material is not sufficiently softened during intermediate annealing, the strength of the brazing sheet before brazing will increase, and the desired pre-brazing characteristics cannot be obtained. Intermediate annealing can be carried out in the range of a heating rate of 30 to 70 °C / h, a temperature of 300 to 400 °C, and a treatment time of 3 h to 10 h. If the intermediate annealing temperature is less than 300 °C, the recrystallization of the core material cannot be completed, and the desired softening cannot be obtained. When the intermediate annealing temperature is higher than 400 °C, secondary recrystallization may occur, resulting in non-uniform recrystallized grains.

[0040] "Low-temperature annealing" Low-temperature annealing is carried out to obtain the desired tensile strength before brazing while maintaining the tensile strength after brazing. By performing this low-temperature annealing, Cu dissolved in the core material can be grown into an AlCu-based compound up to a stable phase larger than the size of GP zones and metastable phases that generally contribute to precipitation strengthening, and the strength can be reduced compared to the solution strengthening state. Since these AlCu-based compounds are re-dissolved into the matrix during brazing, Cu contributes to the strength improvement in a dissolved state after brazing. As a result, it becomes possible to improve the tensile strength after brazing while reducing the tensile strength before brazing. The annealing conditions for low-temperature annealing can be carried out in the range of heating to 150 to 300 °C at a heating rate of 30 to 70 °C / h and a treatment time of 0.5 h to 15 h.

[0041] If the temperature of the low-temperature annealing is less than 150 °C, the desired distribution state of the AlCu-based compound cannot be obtained, and the tensile strength of the material cannot be reduced. When annealing at a temperature exceeding 300 °C, the distribution of the desired size of the precipitated AlCu-based compound cannot be obtained, or the precipitated AlCu-based compound is re-dissolved into the matrix, so the tensile strength cannot be reduced. In addition, this low-temperature annealing is carried out promptly after the intermediate annealing. For example, it may be carried out by two-stage annealing in which after cooling to 150°C to 300°C in the cooling process after the intermediate annealing, heat treatment is performed for 0.5 to 15 h as the heat treatment.

[0042] "Cold rolling" The reduction ratio of cold rolling is carried out at 20% to 40%. When the reduction ratio of cold rolling is less than 20%, the amount of work hardening after annealing is small, and the desired (YS / TS) value cannot be obtained, and the (YS / TS) value becomes less than 0.90. When the reduction ratio of cold rolling is higher than 40%, the tensile strength of the brazing sheet before brazing becomes high and exceeds 250 MPa. The cold rolling conditions are not particularly specified, but it is preferably carried out within 1 to 3 passes from the intermediate annealing and the low-temperature annealing to the final plate thickness in terms of manufacturing.

[0043] In the case of the brazing sheet A obtained by the manufacturing method described above, since the tensile strength in the state before brazing is 190 to 250 MPa, it has sufficient butting strength when manufacturing a tube by electric resistance welding, and can obtain an appropriate joining state without buckling. Further, by having the above-mentioned tensile strength, an accurate tube shape can be obtained by roll forming, and even when applied to a heat exchanger having a shape in which the tube is bent to form a flow path, the springback amount is appropriate and an appropriate shape can be obtained. In addition, in the case of the brazing sheet A, since the AlCu-based compound is redissolved in the matrix by heating during brazing, the matrix can be strengthened, and when a heat exchanger is manufactured by brazing, the structural strength required for the heat exchanger can be obtained.

Example

[0044] The core material is made of an aluminum alloy with the composition shown in A1 to A24 of Table 1, the first skin material (brazing material) is made of an aluminum alloy with the composition shown in B1 to B3 of Table 1, and the second skin material (sacrificial anode material) is made of an aluminum alloy with the composition shown in C1 to C5 of Table 1. Using these, brazing sheets numbered 1 to 36 were produced by combining them as shown in Table 2. The first skin material was placed on one side of the plate-shaped core material, and the second skin material was placed on the other side of the core material. For each aluminum alloy constituting the core material, the first skin material (brazing material), and the second skin material (sacrificial anode material) shown in Table 1, only the main components are indicated, and the content of the inevitable impurities and aluminum constituting the balance is not described in Table 1.

[0045] Each aluminum alloy with the composition shown in Table 1 was melted by semi-continuous casting, and the core material was homogenized at 580 °C for 8 hours.

[0046] The first skin material (brazing material) and the second skin material (sacrificial anode material) with plate thicknesses corresponding to the clad ratio were prepared, and the core material and the first skin material (brazing material) or the core material, the first skin material (brazing material), and the second skin material (sacrificial anode material) were clad-rolled. The clad rolling conditions are not particularly specified, but it is carried out by heating the combination of the core material and the skin material to about 400 to 500 °C and then performing hot rolling. The temperature of the outermost periphery of the coil after hot rolling is 300 °C, and the cooling rate is as shown in Table 2. After hot rolling, cold rolling is carried out in multiple passes. Also, for the samples that were subjected to intermediate annealing during cold rolling and then low-temperature annealing, the conditions are described in the column of low-temperature annealing. The intermediate annealing was carried out by heating at 330 °C for 4 hours and then slowly cooling. After the intermediate annealing or low-temperature annealing, cold rolling with a total reduction ratio of 20 to 40% set by multiple passes was carried out.

[0047] As shown in Table 2, a brazing sheet with a total thickness of 0.2 mm was obtained by overlapping the core material, the first skin material (denoted as skin material 1 in Table 2: brazing material), and the second skin material (denoted as skin material 2 in Table 2: sacrificial anode material).

[0048] For each of the brazing sheets numbered from No. 1 to No. 36 shown in Table 2, as described below, the distribution density of the AlCu-based compound was determined, the tensile strength was determined, the value of (0.2% proof stress: YS) / (tensile strength: TS) was determined, and the tensile strength after brazing was determined.

[0049] "Measurement of AlCu-based Compound" Regarding the core material of the manufactured aluminum alloy brazing sheet, cross-section polishing was performed on a cross-section parallel to the rolling direction to observe the AlCu-based compound. For the processed cross-section, 10 secondary electron images were obtained at a magnification of ×5000 using a field emission scanning electron microscope (FE-SEM). From the obtained images, the equivalent circle diameter and distribution density of the AlCu compound particles were calculated. The discrimination of the AlCu-based intermetallic compound was based on the elements detected by performing elemental analysis by EDS. The distribution density of the AlCu-based intermetallic compound with an equivalent circle diameter of 0.01×10 -3 mm to 1.0×10 -3 mm was measured.

[0050] "Brazing-equivalent Heat Treatment" For each of the brazing sheets numbered from No. 1 to No. 36, the temperature was raised to 450°C in a nitrogen gas atmosphere, held for 5 minutes, then raised to 600°C in about 15 minutes, and held at 600°C for 5 minutes. Thereafter, it was cooled to 300°C at a cooling rate of 100°C / min, and then cooled to room temperature by air cooling. "Tensile Test" For each brazing sheet before brazing, the tensile strength and 0.2% proof stress were determined in accordance with JIS Z2241. "Formability" The formability was evaluated by forming the manufactured brazing sheet into a tube shape. After cutting the brazing sheet to a predetermined width, it was rolled into a pipe shape by roll forming, the end faces were butted together, and pressure welding was performed by high-frequency welding to manufacture a round pipe. The round pipe was further flattened by roll forming to produce a tube shape. When a tube shape of a desired dimension was obtained with the formed tube material, it was marked as ○. For example, when the desired shape could not be obtained, such as the displacement between the end faces at the tube butting position or the bulge of the tube after flattening, it was marked as ×. The composition of the aluminum alloy samples and the various measurement results described above are summarized in Tables 1 and 2 below.

[0051]

Table 1

[0052]

Table 2

[0053] The aluminum alloy brazing sheets (Examples) numbered 1 to 31 shown in Table 2 are composed of an aluminum alloy in which the core material contains Cu: 0.5 to 1.5% by mass and contains one or two of Mn: 1.4 to 1.9% and Si: 0.6 to 1.1%, and the balance is inevitable impurities and Al. The brazing sheets of these examples have a distribution density of AlCu-based compounds with an equivalent circle diameter of 0.01×10 -3 mm to 1.0×10 -3 mm of 0.05×10 6 to 0.3×10 6 pieces / mm 2 and have a tensile strength in the range of 190 to 250 MPa and a (YS / TS) value, which is the ratio of the 0.2% proof stress to the tensile strength, of 0.90 or more. The brazing sheets of these examples showed a tensile strength of 150 MPa or more after brazing.

[0054] Therefore, the brazing sheets of these examples can provide an aluminum alloy brazing sheet for a heat exchanger that can maintain the strength after brazing, lower the tensile strength of the brazing sheet as a material to a desirable range, maintain the 0.2% proof stress of the brazing sheet at a high level, and obtain a high (YS / TS) ratio. In addition, since the brazing sheet before brazing has appropriate strength, when forming the tubes of the heat exchanger by roll forming, the tubes have appropriate hardness, so that the desired tube shape can be obtained. Further, when forming the tubes for the heat exchanger by roll forming using the brazing sheets of these examples, the butt joint load required at the time of butting the tube ends can be obtained. Therefore, there is an effect that the tubes for the heat exchanger having the desired shape can be formed.

[0055] The brazing sheet No. 32 (comparative example) shown in Table 2 has a small number of AlCu-based compounds and low tensile strength, so the tensile strength after brazing also becomes low. When a heat exchanger is configured using the brazing sheet No. 32, the strength required as a heat exchanger cannot be ensured. The brazing sheet No. 33 (comparative example) has too much Cu content in the core material, resulting in too high tensile strength of the brazing sheet. When the tensile strength of the brazing sheet is too high, when manufacturing the tubes for the heat exchanger from the brazing sheet by roll forming, it may not be possible to form the desired shape.

[0056] The brazing sheet No. 34 (comparative example) had a faster cooling rate after hot rolling than desired, so the precipitation density of the AlCu-based compounds was low, the amount of Cu dissolved in the matrix increased, and the tensile strength became too high. The brazing sheet No. 35 (comparative example) did not undergo low-temperature annealing, so the precipitation density of the AlCu-based compounds was low, the amount of Cu dissolved in the matrix increased, and the tensile strength became too high. The brazing sheet No. 36 (comparative example) is a sample of quality H2n that was subjected to final annealing (200 °C × 5 hours) after cold rolling in order to reduce the tensile strength before brazing, but the (YS / TS) ratio is low, and when forming the tubes of the heat exchanger, forming defects occurred.

Explanation of Signs

[0057] A... Aluminum alloy brazing sheet, 1... Core material, 2... Brazing material, 3... Sacrificial anode material, 4... Heat exchanger, 5... Fin, 6... Tube, 8... Header plate.

Claims

1. An aluminum alloy brazing sheet having a skin material made of an aluminum alloy on at least one surface of a core material, wherein the core material is made of an aluminum alloy containing, by mass%, 0.5 to 1.5% of Cu, and containing one or two of 1.4 to 1.9% of Mn and 0.6 to 1.1% of Si, and having a composition of the balance inevitable impurities and Al, the distribution density of AlCu-based compounds having an equivalent circle diameter of 0.01×10 －３ mm to 1.0×10 －３ mm is 0.05×10 ６ to 0.3×10 ６ pieces / mm ２ and the tensile strength is in the range of 190 to 250 MPa, an aluminum alloy brazing sheet for a heat exchanger having a value of (0.2% proof stress / tensile strength), which is a ratio of 0.2% proof stress to tensile strength, of 0.90 or more.

2. Further, in the core material, by mass%, Fe: 0.2 to 0.5%, Zn: 0.1 to 1.0%, Zr: 0.05 to 0.2%, Ti: 0.05 to 0.2%, Cr: 0.05 to 0.2% The aluminum alloy brazing sheet for a heat exchanger according to claim 1, characterized by containing one or more of them.

3. The skin material is made of an aluminum alloy and contains, by mass%, Si: 8.0 to 12.0%, Zn: 0 to 1.5% The aluminum alloy brazing sheet for a heat exchanger according to claim 1 or claim 2, characterized by having a composition of the balance inevitable impurities and Al.

4. The core material has the skin material on one surface, and on the surface without the skin material, by mass%, Zn: 4.5 to 7.5%, Mn: 1.3 - 1.7%, Si: 0.4 - 0.8%, Zr: 0.05 - 0.2% The aluminum alloy brazing sheet for a heat exchanger according to claim 1 or claim 2, characterized by having a second skin material made of an aluminum alloy containing one or more of the above and having a composition of inevitable impurities and Al as the balance.

5. In the core material, the skin material is provided on one surface, and on the surface without the skin material, in mass%, Zn: 4.5 - 7.5%, Mn: 1.3 - 1.7%, Si: 0.4 - 0.8%, Zr: 0.05 - 0.2% The aluminum alloy brazing sheet for a heat exchanger according to claim 3, characterized by having a second skin material made of an aluminum alloy containing one or more of the above and having a composition of inevitable impurities and Al as the balance.

6. The aluminum alloy brazing sheet for a heat exchanger according to claim 1 or claim 2, showing a tensile strength of 150 MPa or more after brazing.

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