JP7557658B2 - Aluminum alloy brazing sheet - Google Patents

Description

The present invention relates to an aluminum alloy brazing sheet. This application claims priority to Japanese Patent Application No. 2022-138306, filed on August 31, 2022, the contents of which are incorporated herein by reference.

Automotive heat exchangers, such as radiators, are used to cool the medium used to cool the engine, which becomes hot when the vehicle is running. The heat from the hot medium is transferred via the tubes to the fins by thermal transfer, so the medium is cooled. Meanwhile, the tubes and fins are heated and undergo thermal expansion. Here, one side of the tube is fixed to the header plate and the other side is fixed to the fins. For this reason, when the tube thermally expands, stress is concentrated at the root part of the tube at the longitudinal end of the header plate, which may cause cracks in the tube at the root part.

As a countermeasure, the structure of the heat exchanger has been modified. However, in cases where the structure of the heat exchanger cannot be modified, it has been reported that the progression of cracks can be suppressed by increasing the strength of the aluminum alloy used in the tubes.

As a technique for improving the strength and brazeability of aluminum alloys, for example, an aluminum alloy brazing sheet having a core material and a brazing material, as described in Patent Document 1 below, is known.
This brazing sheet specifies the amounts of Mn, Si, Fe, and Cu contained in the core material, and the amounts of Si and Fe contained in the brazing material. In addition, the area ratio of the intermetallic compounds containing Fe contained in the core material, which have an equivalent circle diameter of 1 to 100 μm, is specified to be 3% or less.
Also, as an aluminum alloy laminate excellent in fatigue properties, a clad material consisting of a core material and a sacrificial anticorrosive material is known, as described in the following Patent Document 2. In this clad material, the amounts of Si, Cu, Mn, Ti, and Fe contained in the core material are specified, and the area ratio of the Cube orientation in the 45° direction to the rolling direction in the texture of the core material is specified to be 10 to 15%.

JP 2013-234376 A Patent No. 5452027

Incidentally, in order to suppress the propagation of cracks by increasing the strength of the aluminum alloy, it is possible to improve the strength of a three-layer clad material used for a tube by adding Mg to the brazing material.
However, when Mg is added to the brazing material, it reacts first with the fluoride-based flux that is applied to remove the oxide film on the aluminum alloy when brazing a heat exchanger, generating magnesium fluoride, which deactivates the material and impairs brazing properties.
Therefore, a method of use that isolates Mg from the brazing surface is required, such as processing into a flat tube shape by electric resistance welding using an aluminum alloy. Therefore, there is a problem that aluminum alloys containing Mg cannot be used in heat exchangers that are configured to form flow paths in the tube itself and then brazed to seal the flow paths.

The present invention has been made to solve the above-mentioned problems, and aims to provide an aluminum alloy brazing sheet that is suitable for use in heat exchangers, etc., and that has excellent yield strength after brazing and a long life until fracture, and that is equipped with a core material, brazing material, and sacrificial anode material.

(1) This embodiment is an aluminum alloy brazing sheet in which a brazing material is bonded to one side of a core material made of an aluminum alloy, and a sacrificial anode material is bonded to the other side of the core material to which the brazing material is bonded, wherein the core material is made of an aluminum alloy containing, by mass%, 1.3 to 1.8% Mn, 0.6 to 1.1% Si, 0.6 to 1.3% Cu, and 0.05 to 0.3%, with the balance being Al and unavoidable impurities, and the brazing material contains, by mass%, Si: 6. the sacrificial anode material is made of an aluminum alloy containing, by mass%, 1.3 to 1.8% Mn, 0.4 to 0.9% Si, 2.0 to 8.0% Zn, and 0.05 to 0.3% Zr, with the balance being made of an aluminum alloy containing Al and unavoidable impurities; the distribution density of Al-Mn-Si intermetallic compounds having a circle equivalent diameter of 0.01 μm or more and 1.0 μm or less contained in the core material before brazing is 0.65 x 10 ⁶ particles/mm ² to 5.0 x 10 ⁶ particles/mm ² ; and the distribution density of Al-Zr intermetallic compounds having a circle equivalent diameter of 0.01 μm or more and 1.0 μm or less contained in the core material before brazing is 0.05 x 10 ⁶ particles/mm ² to 0.5 x 10 ⁶ particles/mm ² .

(2) In the aluminum alloy brazing sheet according to this embodiment, when the fracture life in a pulsating plane bending fatigue test of the aluminum alloy brazing sheet alone after the brazing heat treatment is X and the strain value at the initial stage of the test is Y, it is preferable that the relationship Y≧1.0× ¹⁰⁵ ×X ^(−0.30) is satisfied, the 0.2% yield strength of the aluminum alloy brazing sheet after brazing is 58 MPa or more, and the n value is 0.25 or more.
(3) In the aluminum alloy brazing sheet according to (1) or (2) of the present embodiment, it is preferable that the core material further contains, by mass%, one or more of Fe: 0.1-0.7%, Ti: 0.01-0.3%, Cr: 0.01-0.3%, and Zn: 0.05-1.0%.

(4) In the aluminum alloy brazing sheet according to any one of (1) to (3) of the present invention, the brazing material preferably further contains, by mass%, 3.5% or less of Zn.
(5) In the aluminum alloy brazing sheet according to any one of (1) to (4) of the present embodiment, the sacrificial anode material preferably further contains, by mass%, one or more of Fe: 0.1 to 0.7%, Ti: 0.01 to 0.3%, and Cr: 0.01 to 0.3%.

(6) It is preferable that the aluminum alloy brazing sheet described in any of (1) to (5) in this embodiment is applied as a tube for a heat exchanger to be brazed to a fin.

The present invention can provide an aluminum alloy brazing sheet that has excellent proof stress after brazing and can extend the fracture life.
By forming a tube from the aluminum alloy brazing sheet according to the present invention, it is possible to improve the yield strength and fracture life of the tube.

1 is a cross-sectional view showing a first embodiment of an aluminum alloy brazing sheet according to the present invention. 1 is a perspective view showing an example of a heat exchanger provided with tubes made of an aluminum alloy brazing sheet according to the present embodiment; FIG. 4 is a side view showing a state of a plane bending test carried out in the examples.

An example of an embodiment will be described in detail below with reference to the attached drawings. Note that the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand.

As an example, the aluminum alloy brazing sheet A of this embodiment is made of a clad material in which a brazing material 2 is bonded to one side of a core material 1 made of an aluminum alloy and a sacrificial anode material 3 is bonded to the other side, as shown in FIG.
In addition, the brazing sheet A can have a multi-layer structure of the core material 1 and the brazing material 2, and may also have a four-layer or five-layer structure in which a sacrificial anode material is provided between the core material 1 and the brazing material 2.

"Heartwood"
In this embodiment, the core material 1 is made of an aluminum alloy containing, by mass%, 1.3-1.8% Mn, 0.6-1.1% Si, 0.6-1.3% Cu, 0.05-0.3% Zr, with the remainder being Al and unavoidable impurities.
In addition, when the range of mass% described in this specification is expressed using "to", the range includes the lower limit and the upper limit unless otherwise specified. Thus, as an example, 1.3 to 1.8% means that the content is 1.3% or more and 1.8% or less.
In addition to the above-mentioned elements, one or more of the following may be added to the aluminum alloy constituting the core material 1: Fe: 0.1-0.7%, Ti: 0.01-0.3%, Cr: 0.01-0.3%, and Zn: 0.05-1.0%.

Mn: 1.3-1.8%
Mn is added in the above 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 also strengthens the Al-Mn system, Al-Mn-Si system, in the core material 1. It contributes to the precipitation of intermetallic compounds such as Al--Mn--Fe--Si and Al--Mn--Fe--Si compounds, and exerts a dispersion strengthening effect.
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 rollability is reduced. Preferably the amount is between 1.31 and 1.77%, more preferably between 1.43 and 1.77%.
Si: 0.6-1.1%
Silicon is added in the above range in order to improve the material strength of the core material 1. Silicon improves the material strength by solid solution strengthening, and also strengthens the Al-Mn-Si system, Al-Mn-Fe- It contributes to the precipitation of intermetallic compounds such as Si-based compounds, and exerts a dispersion strengthening effect.
If the Si content is less than 0.6%, the desired strength improvement effect cannot be obtained. If the Si content exceeds 1.1%, the melting point of the matrix of the core material 1 decreases, causing local melting during brazing. The Si content is preferably 0.61 to 1.09%, and more preferably 0.61 to 1.01%.

Cu: 0.6-1.3%
Cu is added 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 0.6%, the desired strength improvement effect cannot be obtained. %, the melting point of the parent phase of the core material 1 decreases, and there is a risk of local melting during brazing. Furthermore, if the Cu content exceeds 1.3%, there is a risk of corrosion resistance decreasing. The amount is preferably 0.61 to 1.28%, more preferably 0.68 to 1.11%.
Zr: 0.05-0.3%
Zr is added in the above range in order to improve the material strength of the core material 1. Zr improves the material strength of the core material 1 by solid solution strengthening, and also strengthens the Al-Mn-Si based compounds and Al- It contributes to the precipitation of Zr-based intermetallic compounds and exerts a dispersion strengthening effect.
If the Zr content is less than 0.05%, the desired strength improvement effect cannot be obtained. If the Zr content exceeds 0.3%, giant intermetallic compounds are generated during casting, and rollability is reduced. The amount is preferably from 0.05 to 0.29%, more preferably from 0.05 to 0.22%.

Fe: 0.1-0.7%
Fe is added in the above 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 also improves the strength of the core material 1 by strengthening the Al-Fe system, Al-Fe-Si system, and the like. It contributes to the precipitation of intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Fe-Si compounds, and exerts a dispersion strengthening effect. The preferable content of Fe is 0.3% to 0.7%.
If the Fe content is less than 0.1%, it is necessary to use high-purity aluminum, which is costly. If the Fe content exceeds 0.7%, huge intermetallic compounds are generated during casting, which reduces rollability. The iron content is preferably 0.11 to 0.68%, and more preferably 0.11 to 0.51%. is more preferred.
Ti, Cr: 0.01-0.3%
Ti and Cr can be added within the above-mentioned ranges to improve the material strength of the core material 1. Ti and Cr precipitate as Al-Ti and Al-Cr intermetallic compounds, and strengthen the core material 1 by dispersion strengthening. Contributes to strength improvement. If the Ti and Cr contents are less than 0.01%, the desired strength improvement effect cannot be obtained. If the Ti and Cr contents exceed 0.3%, huge intermetallic compounds are formed during casting. This results in a decrease in rollability.

Zn: 0.05-1.0%
Zn is added in the above range in order to improve the fatigue life. It is desirable for the Zn content to be in the above range.
If the Zn content is less than 0.05%, the desired effect cannot be obtained. If the Zn content exceeds 1.0%, there is no problem in improving the fatigue life, but the corrosion resistance of the brazing sheet is reduced. The Zn content is preferably 0.05 to 0.90%, and more preferably 0.10 to 0.80%.

"Brazing material"
In this embodiment, the brazing material 2 is made of an aluminum alloy containing, by mass %, 6.0 to 13.0% Si, with the remainder being Al and unavoidable impurities.
The aluminum alloy constituting the brazing material 2 may contain Zn: 3.5 mass % or less in addition to the above-mentioned Si.
Si: 6.0-13.0%
Silicon is necessary to lower the melting point of aluminum and melt the brazing material 2 during brazing to become brazing material when brazing to other components. If the silicon content is less than 6.0%, sufficient molten brazing material may not be produced, which may result in poor brazing. If the silicon content exceeds 13.0%, brazing material may be eroded into the core material, which may result in poor brazing. The silicon content is preferably 6.2 to 12.5%, and more preferably 7.5 to 12.5%.
Zn: 3.5% or less Zn makes the potential of the brazing material less noble, and acts as a sacrificial anode to protect the core material 1 from corrosion. If Zn is not added, the brazing material cannot achieve the sacrificial anode effect. If the brazing material 2 contains more than 3.5% Zn, the corrosion rate may increase and the corrosion resistance may decrease. The Zn content is preferably 0.11 to 3.49%, and more preferably 0.56 to 2.00%.

"Sacrificial anode material"
In this embodiment, the sacrificial anode material 3 is made of an aluminum alloy containing, by mass%, 1.3 to 1.8% Mn, 0.4 to 0.9% Si, 2.0 to 8.0% Zn, and 0.05 to 0.3% Zr, with the remainder being unavoidable impurities and Al.
In addition to the above elements, one or more of the following may be appropriately selected and added to the aluminum alloy constituting the sacrificial anode material 3: Fe: 0.1-0.7%, Ti: 0.01-0.3%, and Cr: 0.01-0.3%.

Mn: 1.3-1.8%
Mn is added within the above range in order to improve the material strength of the sacrificial anode material 3. Mn improves the material strength of the sacrificial anode material 3 by solid solution strengthening, and also improves the Al-Mn system , and contributes to the precipitation of intermetallic compounds such as Al--Mn--Si and Al--Mn--Fe--Si.
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 rollability is reduced. Preferably the amount is between 1.32 and 1.78%, more preferably between 1.40 and 1.65%.
Si: 0.4-0.9%
Silicon is added in the above range in order to improve the material strength of the sacrificial anode material 3. Silicon improves the material strength by solid solution strengthening, and also strengthens the Al-Mn-Si system and Al- It contributes to the precipitation of intermetallic compounds such as Mn--Fe--Si, and exerts a dispersion strengthening effect.
If the Si content is less than 0.4%, the desired strength improvement effect cannot be obtained. If the Si content exceeds 0.9%, the melting point of the parent phase of the sacrificial anode material 3 decreases, and local melting occurs during brazing. The Si content is preferably 0.41 to 0.88%, and more preferably 0.41 to 0.79%.

Zn: 2.0-8.0%
Zn makes the potential of the sacrificial anode material 3 baser, and acts as a sacrificial anode to protect the core material 1 from corrosion. If the Zn content is less than 2.0%, the desired sacrificial anode effect cannot be obtained. If it exceeds 0.0%, the corrosion rate increases and the corrosion resistance may decrease. The Zn content is preferably 2.3 to 7.9%, and more preferably 3.50 to 6.96%. is more preferred.
Zr: 0.05-0.3%
Zr is added within the above range in order to improve the material strength of the sacrificial anode material 3. Zr improves the material strength of the sacrificial anode material 3 by solid solution strengthening, and also improves the strength of the sacrificial anode material 3 by strengthening the Al-Mn- It contributes to the precipitation of Si-based and Al-Zr-based intermetallic compounds, and exerts a dispersion strengthening effect.
If the Zr content is less than 0.05%, the desired strength improvement effect cannot be obtained. If the Zr content exceeds 0.3%, giant intermetallic compounds are generated during casting, and rollability is reduced. The amount is preferably 0.05 to 0.28%, more preferably 0.05 to 0.22%.

Fe: 0.1~0.7%
Fe is added in the above range in order to improve the material strength of the sacrificial anode material 3. In the sacrificial anode material 3, Fe is added in the Al-Fe system, Al-Fe-Si system, Al-Mn-Fe-Si system, , etc., and exerts a dispersion strengthening effect.
If the Fe content is less than 0.1%, it becomes an inevitable impurity and cannot be controlled. If the Fe content exceeds 0.7%, huge intermetallic compounds are generated during casting, and rollability is reduced. , preferably 0.11 to 0.68%, and more preferably 0.11 to 0.48%.
Ti, Cr: 0.01-0.3%
Ti and Cr can be added within the above-mentioned ranges to improve the material strength of the sacrificial anode material 3. Ti and Cr precipitate as Al-Ti and Al-Cr intermetallic compounds, and strengthen the sacrificial anode material by dispersion strengthening. It contributes to improving the strength of the anode material 3. If the Ti and Cr contents are less than 0.01%, the desired strength improvement effect cannot be obtained. If the Ti and Cr contents are more than 0.3%, huge This generates intermetallic compounds and reduces the rollability.

The aluminum alloy brazing sheet A described above is used for the purpose of brazing by placing it in an inert gas atmosphere for about 1 to 30 minutes at a brazing temperature in the manufacture of a heat exchanger or the like, for example, in a temperature range of about 590 to 620°C.
For example, it is used in assembling heat exchangers by stacking it with brazing components such as tubes and fins of various heat exchangers or molded bodies of various shapes. After assembling the tubes, fins, or molded bodies, the entire assembly is heated to the brazing temperature to melt the brazing material 2, and then cooled to room temperature to complete the brazing.

In the aluminum alloy brazing sheet A of this embodiment, in order to obtain a desired post-brazing yield strength, it is necessary to optimally distribute the Al-Mn-Si intermetallic compounds and the Al-Zr intermetallic compounds before brazing.
The optimum particle size for any intermetallic compound is a compound particle size of 0.01 μm or more and 1 μm or less.
If the particle size (circle equivalent diameter) of these intermetallic compounds is less than 0.01 μm, the Al-Mn-Si intermetallic compounds or Al-Zr intermetallic compounds are redissolved in the matrix during brazing, and the mechanical properties and fatigue life after brazing are reduced. Even if the particle size of the intermetallic compounds exceeds 1 μm, the mechanical properties and fatigue life after brazing are reduced.
Regarding the dispersion density, the Al-Mn-Si intermetallic compounds must be in the range of 0.65×10 ⁶ to 5.0×10 ⁶ particles/mm ² , and the Al-Zr intermetallic compounds must be in the range of 0.05×10 ⁶ to 0.5×10 ⁶ particles/mm ² .
The Al-Mn-Si intermetallic compounds are preferably in the range of 0.66×10 ⁶ to 2.36×10 ⁶ particles/mm ² , and more preferably in the range of 1.03×10 ⁶ to 2.06×10 ⁶ particles/mm ² .
The Al-Zr intermetallic compounds are preferably in the range of 0.14×10 ⁶ to 0.44×10 ⁶ particles/mm ² , and more preferably in the range of 0.14×10 ⁶ to 0.29×10 ⁶ particles/mm ² .

To observe intermetallic compounds, a cross section parallel to the rolling direction is polished with a cross-section polisher, and secondary electron images of the processed cross section are taken with a field emission scanning electron microscope (FE-SEM) at a magnification of x30,000, for example, and the average value is obtained. From the images taken, the circle equivalent diameter and distribution density of the intermetallic compound particles can be calculated.

The aluminum alloy brazing sheet A after brazing preferably has a relationship of Y≧1.0×10 ⁵ ×X ^(−0.30) , where X is the fracture life in a pulsating plane bending fatigue test of the brazing sheet alone and Y is the strain value at the initial stage of the test.
It is more preferable that the relationship be Y=1.0 to 2.0×10 ⁵ ×X ^{(−0.20 to −0.30)} .
Furthermore, it is preferable that the 0.2% yield strength of the aluminum alloy brazing sheet after brazing is 58 MPa or more and the n value is 0.25 or more. The yield strength is more preferably 60 MPa or more.
If the brazing sheet A has the above-mentioned post-brazing yield strength and n value, when a heat exchanger is manufactured by brazing fins to a tube made from the brazing sheet A, a radiator for an automobile heat exchanger that is subject to high temperatures can be constructed, and a radiator can be provided that has a tube with excellent fatigue characteristics that does not cause early cracks or the like in the tube even if the tube thermally expands due to heat from a high-temperature medium.
The n value is more preferably 0.28 or more and 0.35 or less, and most preferably 0.29 or more and 0.34 or less.

The 0.2% yield strength of the aluminum alloy brazing sheet A after brazing can be obtained by preparing JIS No. 5 test pieces from the aluminum alloy brazing sheet A after brazing parallel to the rolling direction, and conducting a tensile test on three pieces of each sample.
If the proof stress and n-value after brazing are less than 0.25, the fatigue life will be shortened, and when a heat exchanger is manufactured by brazing tubes and fins made from a brazing sheet, there is a risk of the tubes cracking early on.

Figure 2 shows an aluminum heat exchanger 4 in which a tube 6 is constructed using the brazing sheet A, and an aluminum alloy fin 5 is used as the material to be brazed. The fin 5 and tube 6 are assembled with a reinforcing material 7 and a header plate 8, and the aluminum alloy heat exchanger 4 for automotive applications can be obtained by brazing.

With a heat exchanger 4 having the configuration shown in Figure 2, even if a high-temperature medium flows inside the tubes 6, the tubes 6 expand due to the heat, and stress acts on the joint with the header plate 8, it is possible to provide a heat exchanger 4 that is less likely to crack or break at the joint with the header plate 8.

"Manufacturing method"
To manufacture the brazing sheet A described above, aluminum alloys having the desired compositions are manufactured to constitute the core material 1, brazing material 2, and sacrificial anode material 3. For example, the aluminum alloys for the core material 1, brazing material 2, and sacrificial anode material 3, each having the above-mentioned composition, are cast by a semi-continuous casting method.
The aluminum alloy for the core material 1 formed by casting can be subjected to homogenization treatment at a desired temperature of 400°C to 600°C for a treatment time in the range of 1 to 10 hours. This allows for a suitable dispersion state of intermetallic compounds to obtain the desired characteristics. If the homogenization treatment is performed under conditions outside the above-mentioned desired temperature and time, the desired dispersion state of intermetallic compounds cannot be obtained. More preferably, the conditions are 520°C to 590°C and a treatment time of 5 to 9 hours.

The aluminum alloy constituting the brazing material 2 may be subjected to homogenization treatment at 400° C. to 550° C. for 1 hour to 10 hours in order to improve machinability.
The aluminum alloy constituting the sacrificial anode material 3 may be subjected to homogenization treatment if necessary. When homogenization treatment is performed, the same treatment conditions as those for the aluminum alloy constituting the core material 1 are applied.

"Clad rolling"
The aluminum alloy for the core material 1, the aluminum alloy for the brazing material 2, and the aluminum alloy for the sacrificial anode material 3 prepared as described above are processed into plates by hot rolling, and then the aluminum alloy plates are stacked and clad rolled.
The clad ratio can be set, for example, as follows: brazing material: core material: sacrificial material = 5-20%: 60-90%: 5-20%. The clad rolling is performed by hot rolling. By this hot rolling, three layers of aluminum alloy can be joined.

"Cold rolling"
After the hot rolling, the brazing sheet A having the three-layer structure shown in FIG. 1 can be obtained by cold rolling to a desired thickness.
The cold rolling conditions are not particularly limited, but the reduction ratio per pass can be set to between 20% and 50%. If the reduction ratio is outside this range, the manufacturability of the cold rolling decreases.
"Heat treatment"
Heat treatment can be performed to continue rolling or to adjust the quality. For example, it can be performed at a temperature increase rate of 30 to 70°C/h, at 100 to 400°C, and for a treatment time of 2 to 15 hours. The heat treatment temperature here is lower than the homogenization temperature.
If a temperature exceeding the homogenization temperature is used, the desired dispersed state of the intermetallic compounds cannot be obtained in the core material 1 before brazing.

"Brazing"
The heat treatment conditions for brazing are not particularly limited, but can be, for example, heated at a temperature increase rate such that it takes 1 to 15 minutes to reach the target temperature from 450°C, held at the target temperature of 590 to 615°C for 1 to 20 minutes, and then cooled to 200 to 300°C at a rate of 50 to 110°C/min, and then air-cooled to room temperature.

Each of the brazing sheets No. 1 to No. 334 was constructed by combining a core material made of an aluminum alloy having the composition shown in Tables 1 to 12, a brazing material, and a sacrificial material.
For each aluminum alloy constituting the core material, brazing material, and sacrificial anode material shown in Tables 1 to 12, only the main components are shown, and the contents of inevitable impurities and aluminum constituting the remainder are omitted in the tables.
Aluminum alloys having the compositions shown in Tables 1 to 12 were produced by semi-continuous casting, and processed into plates having the compositions shown in Tables 1 to 12 by hot rolling. The core materials were then subjected to homogenization treatment at the homogenization treatment temperatures and for the homogenization treatment times shown in Tables 13 to 20.
The laminated material consisting of the plate-shaped core material, brazing material, and sacrificial anode material was clad-rolled in a hot rolling mill, and then cold-rolled in a cold rolling mill while being appropriately heat-treated, to obtain a brazing sheet having a thickness of 0.2 mm.

For each of the brazing sheets No. 1 to No. 334 shown in Tables 1 to 12, measurements of intermetallic compounds before brazing, proof stress after brazing, n value, and fracture life were carried out as described below, and the results of these measurements are shown in Tables 13 to 20. Note that, as the brazing-equivalent heat treatment, the brazing-equivalent heat treatment was performed by heating from 450°C to 600°C over 10 minutes, holding at 600°C for 5 minutes, and then cooling to 300°C at 50°C/min, followed by air cooling to room temperature.
"Measurement of intermetallic compounds"
The core material of the manufactured aluminum alloy brazing sheet was subjected to a cross-section polisher processing on a cross section parallel to the rolling direction, and the intermetallic compounds were observed. Ten secondary electron images were obtained from the processed cross section at a magnification of ×30,000 using a field emission scanning electron microscope (FE-SEM). From the obtained images, the circle equivalent diameter and distribution density of the particles of the intermetallic compounds were calculated.
The Al--Mn--Si intermetallic compound and the Al--Zr intermetallic compound were distinguished based on the elements detected by elemental analysis using EDS.

In order to obtain the desired post-brazing yield strength, it is necessary to adjust the Al-Mn-Si intermetallic compounds and Al-Zr intermetallic compounds before brazing to an optimal distribution state. This was adjusted by adjusting the amounts of these elements added and the homogenization treatment conditions.
The particle size (circle equivalent diameter) of each of the intermetallic compounds was set to 0.01 μm or more and 1 μm or less.
The dispersion density of the intermetallic compounds was 0.65×10 ⁶ to 5.0×10 ⁶ particles/mm ² for the Al—Mn—Si intermetallic compounds, and 0.05×10 ⁶ to 0.5×10 ⁶ particles/mm ² for the Al—Zr intermetallic compounds.
If the particle size (circle equivalent diameter) of the intermetallic compound is less than 0.01 μm, the Al-Mn-Si intermetallic compound is redissolved in the matrix during brazing, and the mechanical properties and fatigue life after brazing are reduced. If the particle size of the intermetallic compound exceeds 1 μm, the mechanical properties and fatigue life after brazing are also reduced.

"Measurement of yield strength and n value (work hardening index) after brazing"
JIS No. 5 test pieces were taken from the brazed aluminum alloy brazing sheet parallel to the rolling direction, and the 0.2% proof stress was measured according to a method conforming to JIS Z2241, and the n value was calculated between nominal strains of 1% and 2% according to a method conforming to JIS Z2253 to calculate the average value. The proof stress and n value after brazing affect the fatigue life, and if the proof stress and n value after brazing are low, the fatigue life will be shortened and the tube will tend to break early.

"Break life"
A plane bending fatigue test was carried out on the rolled surface of the brazed aluminum alloy brazing sheet so that the rolling direction was the normal direction to the rolled surface. Figure 3 shows the state of the plane bending fatigue test.
The brazed aluminum alloy brazing sheet is processed into a test piece so that the longitudinal direction is parallel to the rolling direction, and both ends of the test piece are fixed by the chucks of a testing machine. A bending test is then performed in which the test piece is repeatedly bent along a metal pulley, which will be described later, so as to impart a predetermined bending strain.

The bending test was a pulsating fatigue test in which only one of the brazing materials of the aluminum alloy brazing sheet was subjected to tension. As shown in Fig. 3, the upper side of the aluminum alloy brazing sheet A was inserted between metal pulleys 10 and 11 arranged on the left and right with a gap between them, and the aluminum alloy brazing sheet A was clamped between the metal pulleys 10 and 11.
In the test, the upper side of the aluminum alloy brazing sheet A protruding above the metal pulleys 10 and 11 was repeatedly bent along the outer circumferential surface of the left pulley 10. In order to conduct a bending test in which the brazing material side was subjected to tension, in the brazing sheet A having a three-layer structure, the brazing material 2 was placed on the right side of Figure 3 with the core material 1 at the center, and the sacrificial anode material 3 was placed on the left side.

The fracture life (fatigue life) was measured when the initial strain was set to 10,000 μST. It is also desirable to satisfy the following relational expression when the initial strain is between 1,000 μST and 30,000 μST. In the following relational expression, X represents the fracture life and Y represents the value of the initial strain.
Y≧1.0×10 ⁵ ×X ^(-0.30)
The magnitude of the Y value affects fracture near the joint between the header plate and the tube of the heat exchanger. If the Y value is small and the X value is small, there is a risk of fracture occurring near the joint between the header plate and the tube when the heat exchanger is exposed to a thermal stress fatigue environment.
This relationship is a fact confirmed by experiments. Materials with small initial strain Y and short fracture life X do not conform to this formula and do not provide the desired fatigue life.

In the aluminum alloy brazing sheets of Examples 1 to 334 shown in Tables 1 to 12, the core material is made of an aluminum alloy containing, by mass%, 1.3 to 1.8% Mn, 0.6 to 1.1% Si, 0.6 to 1.3% Cu, 0.05 to 0.3% Zr, and the balance being made of Al and unavoidable impurities; the brazing material is made of an aluminum alloy containing 6.0 to 13.0% Si, and the balance being made of Al and unavoidable impurities; and the sacrificial anode material is made of an aluminum alloy containing 1.3 to 1.8% Mn, 0.4 to 0.9% Si, 2.0 to 8.0% Zn, 0.05 to 0.3% Zr, and the balance being made of Al and unavoidable impurities.
In addition, in the aluminum alloy brazing sheets of Examples No. 1 to No. 334, the distribution density of Al-Mn-Si intermetallic compounds having a circle equivalent diameter of 0.01 μm or more and less than 1.0 μm contained in the core material before brazing (abbreviated as distribution before brazing in the table) is 0.66 x 10 ⁶ pieces/mm ² to 2.36 x 10 ⁶ pieces/mm ² , and the distribution density of Al-Zr intermetallic compounds is 0.14 x 10 ⁶ pieces/mm ² to 0.44 x 10 ⁶ pieces/mm ² .

Therefore, the aluminum alloy brazing sheets of Examples No. 1 to No. 334 have a long fatigue life, excellent yield strength after brazing, and a large n value after brazing.
In addition, the aluminum alloy brazing sheets of Examples 1 to 334 have a 0.2% yield strength of 58 MPa or more and an n value of 0.28 or more after brazing. For example, the 0.2% yield strength was in the range of 58 to 96 MPa, and the n value was in the range of 0.28 to 0.35.
In addition, the brazing sheets of the examples have a relationship of Y≧1.0×10 5 ×X (−0.30), where ^X is the fracture life in a pulsating plane bending fatigue test of the aluminum alloy brazing sheet alone after brazing heat treatment, and Y is the strain value at the initial stage of the ^test .
For this reason, the aluminum alloy brazing sheets of Examples No. 1 to No. 334 can provide tubes with long fatigue life, and when joined to fins by brazing to form a heat exchanger, a heat exchanger with excellent durability can be provided.

In the brazing sheet of Comparative Example 1, since the Mn content of the core material was low, the desired number of dispersed particles of the intermetallic compound was not reached before brazing, and the strength after brazing was insufficient.
In the brazing sheet of Comparative Example 2, since the Mn content of the core material was high, huge intermetallic compounds were generated during casting, and it became impossible to continue rolling halfway through.
The brazing sheet of Comparative Example 3 had a low Si content in the core material, did not reach the desired number of dispersed particles before brazing, and had insufficient strength after brazing.
The brazing sheet of Comparative Example 4 was unsuitable for manufacturing a heat exchanger because the melting point was lowered due to the excessive addition of Si to the core material and excessive erosion occurred during brazing.

The brazing sheet of Comparative Example 5 had a low Cu content in the core material, resulting in insufficient strength after brazing.
The brazing sheet of Comparative Example 6 had an excessively high Cu content in the core material, which resulted in a drop in melting point and excessive erosion during brazing, making it unsuitable for producing heat exchangers.

The brazing sheet of Comparative Example 7 had a low Zr content, did not achieve the desired number of dispersed particles before brazing, and had insufficient strength after brazing.
The brazing sheet of Comparative Example 8 had an excessively high Zr content, and as a result, large intermetallic compounds were formed during casting, making it impossible to continue rolling.
The brazing sheet of Comparative Example 9 had a small amount of Si contained in the brazing material, and the amount of brazing material required for joining the respective components was insufficient, resulting in a problem with brazing properties.
In the brazing sheet of Comparative Example 10, the homogenization temperature was too low, so that the desired dispersed particle state was not obtained before brazing, and the strength after brazing was insufficient.
In the brazing sheet of Comparative Example 11, the homogenization temperature was too high, so that the desired dispersed particle state was not obtained before brazing, and the strength after brazing was insufficient.
The brazing sheet of Comparative Example 12 had a large amount of Si contained in the brazing material, which caused severe erosion of the core material and other components, resulting in problems with brazing properties.

The brazing sheet of Comparative Example 13 was a sample containing a small amount of Mn in the sacrificial anode material, and the desired strength after brazing was not obtained.
The brazing sheet of Comparative Example 14 was a sample containing too much Mn in the sacrificial anode material, and huge intermetallic compounds were formed during casting, making it impossible to continue rolling.
The brazing sheet of Comparative Example 15 is a sample containing a small amount of Si in the sacrificial anode material, and the desired strength after brazing was not obtained.
The brazing sheet of Comparative Example 16 was a sample containing too much Si in the sacrificial anode material, and the melting point was lowered, causing the sacrificial material to melt during brazing, making it unsuitable for manufacturing heat exchangers.

The brazing sheet of Comparative Example 17 was a sample containing a small amount of Zn in the sacrificial anode material, and the desired sacrificial anode function was not obtained, resulting in a problem in corrosion resistance.
The brazing sheet of Comparative Example 18 was a sample containing too much Zn in the sacrificial anode material, and the corrosion rate of the sacrificial material was so high that the core material could not be protected from corrosion, resulting in a problem in corrosion resistance.
The brazing sheet of Comparative Example 19 was a sample containing a small amount of Zr in the sacrificial anode material, and the desired strength after brazing was not obtained.
The brazing sheet of Comparative Example 20 was a sample containing too much Zr in the sacrificial anode material, and huge intermetallic compounds were formed during casting, making it impossible to continue rolling.

A comparison of Comparative Examples No. 1 to 20 with Example Nos. 1 to 334 reveals that it is important to specify the content of each element in the core material, brazing material, and sacrificial anode material, and to specify the distribution density of the Al-Mn-Si intermetallic compound and the distribution density of the Al-Zr intermetallic compound contained in the core material before brazing, as described above. Specifying the above-mentioned element contents and specifying the distribution density of the intermetallic compounds makes it possible to provide an excellent brazing sheet that has excellent yield strength after brazing, a large n value, and a long fracture life.
Furthermore, if a heat exchanger has tubes constructed using the above-mentioned brazing sheet and the tubes and fins brazed together, it is possible to provide a heat exchanger in which the tubes are less likely to crack even if they thermally expand due to the circulation of the heat transfer medium.

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, 10, 11...metal pulleys.

Claims (11)

An aluminum alloy brazing sheet in which a brazing material is bonded to one surface of a core material made of an aluminum alloy, and a sacrificial anode material is bonded to the other surface of the core material to which the brazing material is bonded,
the core material is made of an aluminum alloy containing, by mass%, 1.3 to 1.8% Mn, 0.6 to 1.1% Si, 0.6 to 1.3% Cu, 0.05 to 0.3% Zr, and the balance being Al and unavoidable impurities;
The brazing filler metal is made of an aluminum alloy containing, by mass%, 6.0 to 13.0% Si, with the balance being Al and unavoidable impurities;
the sacrificial anode material is an aluminum alloy containing, by mass%, 1.3 to 1.8% Mn, 0.4 to 0.9% Si, 2.0 to 8.0% Zn, and 0.05 to 0.3% Zr, with the balance being Al and unavoidable impurities;
the distribution density of Al-Mn-Si intermetallic compounds having a circle equivalent diameter of 0.01 μm or more and less than 1.0 μm contained in the core material before brazing is 0.65×10 ⁶ pieces/mm ² to 5.0×10 ⁶ pieces/mm ² ,
An aluminum alloy brazing sheet , characterized in that the distribution density of Al-Zr intermetallic compounds having an equivalent circle diameter of 0.01 μm or more and less than 1.0 μm contained in a core material before brazing is 0.05 x 10 ⁶ pieces/mm ² to 0.5 x 10 ⁶ pieces/mm ² . When the fracture life in a pulsating plane bending fatigue test of an aluminum alloy brazing sheet alone after brazing heat treatment is X and the strain value at the initial stage of the test is Y,
The relationship is Y≧1.0×10 ⁵ ×X ^(−0.30) ,
2. The aluminum alloy brazing sheet according to claim 1, characterized in that the aluminum alloy brazing sheet after brazing has a 0.2% yield strength of 58 MPa or more and an n value of 0.25 or more. The aluminum alloy brazing sheet according to claim 1 or 2, characterized in that the core material further contains, in mass percent, one or more of the following: Fe: 0.1-0.7%, Ti: 0.01-0.3%, Cr: 0.01-0.3%, Zn: 0.05-1.0%. The aluminum alloy brazing sheet according to claim 1, characterized in that the brazing material further contains 3.5% or less Zn by mass percent. The aluminum alloy brazing sheet according to claim 1 or 2, characterized in that the sacrificial anode material further contains, by mass%, one or more of the following: Fe: 0.1-0.7%, Ti: 0.01-0.3%, Cr: 0.01-0.3%. The aluminum alloy brazing sheet according to claim 3, characterized in that the sacrificial anode material further contains, by mass%, one or more of the following: Fe: 0.1-0.7%, Ti: 0.01-0.3%, Cr: 0.01-0.3%. The aluminum alloy brazing sheet according to claim 4, characterized in that the sacrificial anode material further contains, by mass%, one or more of the following: Fe: 0.1-0.7%, Ti: 0.01-0.3%, Cr: 0.01-0.3%. The aluminum alloy brazing sheet according to claim 1 or 2 is used as a tube for a heat exchanger to be brazed to a fin. The aluminum alloy brazing sheet according to claim 3 is used as a tube for a heat exchanger brazed to a fin. The aluminum alloy brazing sheet according to claim 4 is used as a tube for a heat exchanger brazed to a fin. The aluminum alloy brazing sheet according to claim 5 is used as a tube for a heat exchanger brazed to a fin.

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