JP4807757B2 - Clad material for discharge electrode, method for producing the same, and discharge electrode - Google Patents

Description

  The present invention relates to a discharge electrode of a fluorescent discharge tube used as a backlight of a liquid crystal display device, for example, and an electrode material thereof.

  In a liquid crystal display device, a small fluorescent discharge tube is used as a backlight. As shown in FIG. 3, the fluorescent discharge tube has a glass tube 51 in which a fluorescent film (not shown) is formed on an inner wall surface, and a discharge gas (rare gas such as argon gas and mercury vapor) is sealed therein. And a discharge electrode 52 constituting a pair of cold cathodes provided at both end portions inside the glass tube 51. The discharge electrode 52 includes a tube portion 53 having one end opened, and the other end of the tube portion 53 is closed by an end plate portion 54. One end of a shaft-like support conductor 55 sealed through the end of the glass tube 51 is welded to the end plate portion 54, and a lead wire 57 is connected to the other end of the support conductor 55. The support conductor 55 is generally formed of W (tungsten), and is usually laser welded to the discharge electrode 52.

  The discharge electrode 52 is conventionally made of pure Ni and has a size of about 1.5 mm in inner diameter, about 5 mm in total length, and a wall thickness of the tube portion 53 of 0.1 mm for a small fluorescent discharge tube such as a backlight. Degree. Such a discharge electrode is usually integrally formed by deep drawing a pure Ni thin plate having a thickness equivalent to the thickness of the tube portion.

  As described above, the discharge electrode for a fluorescent discharge tube is formed of pure Ni that has good moldability and is stable in terms of material, but has a problem that the lamp life is relatively short. That is, when the fluorescent discharge tube is turned on, a phenomenon (sputtering) occurs in which ions and the like collide with the electrode to release atoms from the electrode metal. The electrode metal is consumed by this sputtering, and the atoms of the released electrode metal are combined with mercury sealed in the glass tube, and mercury vapor in the glass tube is consumed. Conventionally, Ni forming an electrode metal has a problem that the discharge amount of the discharge tube is likely to be shortened because the amount of atomic emission during sputtering is large, that is, the sputtering rate is high and the consumption of mercury is large.

  For this reason, in recent years, as described in JP-A-2002-110085 (Patent Document 1), it has been attempted to form the discharge electrode with Nb (niobium) having a low sputtering rate. However, Nb is more expensive than Ni. Nb has a high melting point (2793 ° C.), and it is necessary to weld at a high temperature when welding with a support conductor of W (melting point 3653 ° C.), which is also a high melting point metal. For this reason, a strong oxide film is easily formed on the welded portion. If the discharge electrode to which the support conductor is welded is sealed in the glass tube with the oxide film attached, the oxide film is decomposed during discharge to generate oxygen. This oxygen reacts with the fluorescent film on the inner surface of the tube and degrades the fluorescent film. For this reason, the process of removing the oxide film formed on the electrode surface is required after welding of the support conductor.

Therefore, in recent years, as described in paragraph 0024 of JP-A-2002-289138 (Patent Document 2) and International Publication WO2005 / 048285 (Patent Document 3), the discharge electrode is formed in two layers, Attempts have been made to form the outer layer of Ni and the inner layer of Nb substantially contributing to the discharge. In Patent Document 3, as a method for manufacturing a discharge electrode having a two-layer structure, a base layer metal sheet formed of Ni and a surface layer metal sheet formed of Nb are pressure-welded, and a clad obtained by diffusion-annealing the pressure-contact material It is described that a blank material is collected from the material and deep-drawn into a cup shape.
JP 2002-110085 A JP 2002-289138 A International Publication WO2005 / 048285

  When manufacturing the clad material, it is necessary to subject the base layer and the surface layer of the pressure welding material to diffusion annealing, but since Nb is a material that is very easily oxidized, the pressure welding material is usually batch-annealed in a vacuum heating furnace. . That is, the pressure contact material is charged into a vacuum heating furnace, the inside of the furnace is evacuated, and then the temperature is raised to a predetermined temperature and held at that temperature. In this case, since the heating atmosphere is a vacuum, the rate of temperature increase is slow, and even if the holding time at the target annealing temperature is shortened, in the process of reaching the target annealing temperature or in the process of cooling from the target annealing temperature, 800 The time to be exposed to a high temperature range of ℃ or longer becomes longer. For this reason, the NiNb intermetallic compound produced | generated between the base layer and the surface layer necessarily grows. When the NiNb intermetallic compound layer is thin, there is no problem in the bondability between the two layers. However, when the intermetallic compound layer becomes thick to some extent, cracks occur during deep drawing, and the surface layer becomes the base layer during molding. It is impossible to follow the deformation of the material, and there is a risk that cracks will occur in the surface layer.

  On the other hand, when the pressure welding material is diffusion-annealed using a continuous annealing furnace, the temperature rise to the target annealing temperature and the temperature drop after the annealing are rapid, and excessive growth of the NiNb intermetallic compound layer can be suppressed. In this case, the atmosphere in the furnace needs to be an Ar gas atmosphere practically. However, according to experiments by the inventors, in a normal Ar gas atmosphere (dew point of about -20 ° C), cracks may occur in the Nb layer at the time of deep drawing, and cracks remarkably occur especially when the molding conditions become severe. I understood it. Note that nitrogen gas and hydrogen gas cannot be used as the heating atmosphere gas. This is because nitrogen forms nitrides with Nb, and hydrogen is easily absorbed by Nb, both of which make the Nb layer brittle and deteriorate formability.

  The present invention has been made in view of such a problem, and provides a clad material excellent in deep drawability to a cup-shaped discharge electrode and a manufacturing method thereof, and also provides a discharge electrode formed by the clad material. With the goal.

A cladding material for a discharge electrode according to the present invention includes a base layer made of pure Ni or a Ni-based alloy containing Ni as a main component and a surface layer made of pure Nb, and the surface layer is interposed through a NiNb intermetallic compound layer. The oxygen content in the pure Nb that is diffusion bonded to the base layer and forms the surface layer is 550 ppm or less, and the thickness of the NiNb intermetallic compound layer is 8.0 μm or less.

  According to this clad material, since the surface layer is formed of pure Nb having an oxygen content of 550 ppm or less, the ductility is excellent. Further, since the surface layer is diffusely bonded directly to the base layer or through a NiNb intermetallic compound layer having a thickness of 8.0 μm or less, the bonding property between the base layer and the surface layer is excellent. Combined with this excellent bondability and excellent surface ductility, the clad material is excellent in deep drawability.

  The base layer and the surface layer are preferably diffusion annealed by continuous annealing in an Ar gas atmosphere having a dew point of −40 ° C. or less. By this continuous annealing, the base layer and the surface layer can be efficiently diffusion-bonded while easily suppressing the amount of oxygen absorbed in the surface layer to 550 ppm or less, and thus the productivity of the clad material is excellent.

  The base layer is preferably formed of a Ni-base alloy containing 1.0 mass% or more and 12.0 mass% or less of Nb and Ta alone or in combination, the balance being Ni and inevitable impurities. By adding a predetermined amount of Nb and Ta to Ni, the corrosion resistance against mercury vapor can be improved, and the durability of the discharge electrode can be improved.

  The surface layer preferably has a thickness of 20 μm to 100 μm. By setting the thickness of the surface layer to 20 μm or more and 100 μm or less, it is possible to ensure the same life as a discharge electrode formed entirely with pure Nb using a small amount of Nb. For this reason, the material cost of a clad material can be reduced and it is economical.

  In addition, the thickness of the surface layer is preferably 70% or less with respect to the total thickness of the base layer and the surface layer. By setting the thickness of the surface layer in this way, the base layer can act as a backup layer for the surface layer when the cup-shaped discharge electrode is formed. Thereby, it can prevent that the unevenness | corrugation resulting from a Luders belt | band | zone arises in the surface layer formed with Nb with a large yield point elongation, and can ensure favorable press-formability. When the thickness of the surface layer exceeds 70% of the total thickness, even if the base layer is provided as a backup layer, it becomes difficult to suppress the occurrence of the unevenness, and the press formability deteriorates. For this reason, the thickness of the surface layer is preferably 70% or less, more preferably 60% or less with respect to the total thickness.

  Further, the discharge electrode of the present invention has a tube portion whose one end is released and an end plate portion which closes the other end of the tube portion, and the tube portion and the end plate portion are integrally manufactured by press molding. The discharge electrode is formed of the clad material, and the inner layer of the tube portion and the end plate portion is formed of a surface layer of the clad material. This discharge electrode is formed by using the clad material having excellent deep drawability, so that it is excellent in productivity and a wasteful Nb amount that does not contribute to discharge is saved, thereby reducing the material cost. can do. In addition, since the base layer formed of pure Ni or the like exists on the outside of the end plate portion, the weldability with the support conductor is also good.

  Further, the method for producing a cladding material for a discharge electrode according to the present invention comprises stacking a base layer metal sheet made of pure Ni or a Ni base alloy containing Ni as a main component and a surface layer metal sheet made of pure Nb. A pressure welding process for producing a pressure welding material in which the base layer and the surface layer are pressure welded together, and the pressure welding material in an Ar gas atmosphere having a dew point of −40 ° C. or less in an annealing temperature range of 800 to 1100 ° C. for 15 seconds or more. , 120 seconds or less, and a diffusion annealing step for diffusion bonding the base layer and the surface layer.

  According to this manufacturing method, the oxygen content of the surface layer of the clad material can be easily reduced to 550 ppm or less despite the diffusion bonding of the base layer and the surface layer of the pressure welding material using a continuous annealing furnace. The thickness of the NiNb intermetallic compound layer generated between the surface layer and the base layer can be suppressed to 8.0 μm or less. For this reason, the clad material excellent in deep drawability can be manufactured easily, and the productivity is excellent.

  In this manufacturing method, the base layer can be formed of a Ni-based alloy including one or two of Nb and Ta in total of 1.0 mass% or more and 12.0 mass% or less, and the balance Ni and inevitable impurities. In addition, a finish rolling process may be provided in which finish rolling is performed on the diffusion annealed clad material to adjust the thickness of the clad material.

  FIG. 1 shows a cross-sectional view of a discharge electrode clad material according to an embodiment of the present invention. This clad material is made of pure Ni or a base layer 1 made of Ni-based alloy containing Ni as a main component and pure Nb. The surface layer 2 is roll-welded onto the base layer 1 and further diffusion bonded. The surface layer 2 is diffusion-bonded to the base layer 1 through a very thin NiNb intermetallic compound layer (not shown in FIG. 1) having a thickness of 8.0 μm or less. In FIG. 1, this NiNb intermetallic compound layer is not shown. . This point will be described in the description of the method for manufacturing the clad material described later.

  Pure Ni and Ni-based alloy (hereinafter collectively referred to as “Ni-based metal”) forming the base layer 1 have excellent oxidation resistance, excellent cold workability, and good deep drawability. . The Ni-based alloy has an Ni amount of 80 mass% or more, more preferably 85 mass% or more, and includes one or more alloy elements (for example, Nb, Mo, W, Ta, V, Ti) that are solid-solved with Ni, and the balance What consists of Ni and an unavoidable impurity is desirable. Ni-Nb alloy, Ni-Ta alloy, Ni-Nb-Ta alloy containing 1.0 to 12.0 mass% of Nb and Ta alone or in combination, and the balance being Ni and unavoidable impurities. Is more preferable. If Nb and Ta are added in this amount, the moldability is not impaired, and the corrosion resistance against mercury vapor is improved, and the durability of the electrode can be improved. A Ni-W alloy containing 2.0 to 10 mass% of W and substantially including Ni is more preferable. W, like Nb and Ta, can improve the corrosion resistance against mercury vapor. W can be added together with Nb and / or Ta in the above-mentioned content range, but in this case, the W amount is preferably stopped to about 6.0% or less.

  The surface layer 2 is formed of pure Nb, but it is preferable that the amount of oxygen, hydrogen, nitrogen, or the like that is easily absorbed (solid solution) by Nb is smaller. As will be described later, the clad material is industrially manufactured by stacking and pressing the metal sheets that are the materials of the respective layers, and then annealing the obtained pressure contact material in an Ar gas atmosphere. In addition, oxygen generated by decomposition of moisture contained in Ar gas at high temperature may be absorbed by Nb. When oxygen is absorbed and the amount of oxygen in Nb exceeds 550 ppm, the ductility of Nb is remarkably deteriorated, and accordingly, the deep drawability of the clad material is deteriorated. Therefore, in the present invention, the oxygen concentration in pure Nb forming the surface layer is limited to 550 ppm or less, preferably 400 ppm or less. Since pure Nb is produced by a vacuum melting method, the oxygen content in the produced pure Nb is about 200 ppm or less.

  The thickness of the surface layer 2 is required to be about 20 μm from the consumption form of the discharge electrode. However, considering the balance with safety and the total thickness of the clad material, it is about 20 to 100 μm, preferably about 40 to 80 μm. do it. On the other hand, the entire thickness of the clad material is about 0.1 to 0.2 mm in order to ensure deep drawability. The thickness of the base layer 1 is appropriately set in order to ensure the overall thickness in consideration of the thickness of the surface layer 2, but about 20 to 50 μm is sufficient from the viewpoint of ensuring the weldability of the support electrode. It is. Furthermore, in order for the base layer 1 to act as a backup layer for preventing deformation of the surface layer 2 and to ensure good press formability during deep drawing, the thickness of the surface layer 2 is the total thickness of the surface layer 2 and the base layer 1. The thickness (total thickness of the clad material) is 70% or less, preferably 60% or less.

  FIG. 2 shows a cup-shaped discharge electrode formed by deep drawing using the clad material. The discharge electrode includes a tube portion 11 having one end opened and an end plate portion 12 that closes the other end. The end plate portion 12 is integrally formed with the tube portion 11. The inner layer of the discharge electrode is formed by the surface layer 2 of the clad material. When used as a discharge electrode, it is mainly the inner surface of the bottom of the discharge electrode that is consumed by the discharge, so by forming the inner layer of the discharge electrode with the surface layer 2, the discharge characteristics equivalent to those of the discharge electrode formed only with Nb, The amount of Nb used can be reduced while ensuring the service life of the fluorescent discharge tube. Moreover, the presence of the base layer 1 facilitates welding with the support conductor.

  The cup-shaped discharge electrode is deep-drawn by press molding using a disc-shaped blank material punched from the clad material as a molding material. In the blanking process of the blank material, for example, a part of the blank material is connected to the outer peripheral portion of the clad material via a connecting portion, and after a plurality of cup-shaped discharge electrodes are formed by deep drawing, the discharge electrode is formed from the connecting portion. You may make it isolate | separate.

  Here, a method for manufacturing the clad material will be described. First, an Nb sheet (surface layer metal sheet) that is the origin of the surface layer 2 is overlaid on the Ni base metal sheet (base layer metal sheet) that is the basis of the base layer 1 and roll-welded. That is, the overlapping material obtained by overlapping the Ni sheet and the Nb sheet is pressed through a pair of rolls. This pressure welding can be performed cold. The rolling reduction in roll pressing is usually about 50 to 70%. This manufacturing process is called a pressure welding process. By this pressure contact process, a pressure contact material in which the base layer and the surface layer are pressure contacted is obtained.

  Next, the pressure contact material is diffusion annealed at a temperature of about 800 to 1100 ° C., preferably 900 to 1050 ° C. This manufacturing process is called a “diffusion annealing process”. When the temperature is lower than 800 ° C., diffusion hardly occurs, and when the temperature exceeds 1100 ° C., the diffusion becomes remarkable, and the NiNb intermetallic compound layer formed at the interface between the base layer and the surface layer of the pressure contact material grows in a short time, and the thickness is 8 μm. It will be over. A thick NiNb intermetallic compound layer exceeding 8 μm is very brittle and easily cracked, so that the moldability of the clad material is deteriorated. The thickness of the NiNb intermetallic compound layer is preferably 6.5 μm or less. The time to be held in the temperature range of 800 to 1100 ° C. is preferably about 15 to 120 seconds. If it is less than about 15 seconds, when the target annealing temperature is about 800 ° C., the diffusion is insufficient and the bonding strength is lowered, and the formability of the clad material may be deteriorated. On the other hand, if it exceeds about 120 seconds, when the target annealing temperature is about 1100 ° C., the diffusion becomes excessive, the intermetallic compound grows significantly, the bonding strength decreases, and the formability may also deteriorate. A preferable target annealing temperature is about 900 to 1050 ° C.

  As an annealing method that can easily satisfy the above-described diffusion annealing conditions, continuous annealing in which the heating atmosphere is an Ar gas atmosphere is recommended. The continuous annealing is performed using a continuous annealing furnace. In the continuous annealing furnace, Ar gas is supplied into the tunnel furnace so as to have a positive pressure (a pressure higher by about 0.0005 to 0.001 MPa than the atmospheric pressure), and the expected temperature distribution is along the length of the furnace. The temperature is controlled to obtain. By supplying a material to be treated (for example, a strip-shaped pressure contact material) to this continuous annealing furnace and transporting it at a predetermined transport speed in the length direction of the furnace, based on the transport speed and a pre-formed temperature distribution, A predetermined temperature and holding time can be imparted to the material to be treated.

  When performing the said continuous annealing, about the Ar gas supplied in this invention, the dew point shall be -40 degrees C or less, Preferably it is set to -45 degrees C or less. When the dew point exceeds −40 ° C., the moisture contained in the Ar gas increases, and oxygen produced by decomposition of this moisture under a high annealing temperature is absorbed by Nb. For this reason, the ductility of the surface layer deteriorates and the moldability of the clad material decreases. By setting the holding time in the temperature range of 800 to 1100 ° C. in an Ar gas atmosphere having a dew point of −40 ° C. or less to 15 to 120 seconds, the oxygen concentration of the surface layer of the cladding material can be stopped to 550 ppm or less. Ductility degradation can be suppressed.

  Diffusion annealing of the pressure contact material may be performed under vacuum. However, in order to reduce the oxygen content in the pure Nb forming the surface layer 2 to 550 ppm or less, it is desirable to adopt a heating and cooling method that satisfies the annealing conditions. As an example, the following vacuum heating method can be adopted. Using a vacuum chamber with a heating device in the chamber, the workpiece is stored in the vacuum chamber, the inside of the chamber is evacuated, and then the workpiece is quickly heated to a predetermined temperature and held by the heating device. When cooling, the heating is stopped and Ar gas is introduced into the vacuum chamber to quickly cool it. If diffusion annealing is performed under vacuum, the NiNb intermetallic compound layer is hardly formed between the base layer 1 and the surface layer 2, and the surface layer 2 can be directly diffusion bonded to the base layer 1.

  The clad material after diffusion annealing can be cold-finished as necessary. As a result, the thickness of the clad material can be adjusted. Moreover, in order to soften a material after finish rolling, you may anneal on the conditions similar to the said diffusion annealing as needed. The clad material manufactured as described above is slit to an appropriate width as necessary, and a blank material is punched from the slit band material, and the blank material is subjected to press molding.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limitedly interpreted by this Example.

  Samples of various cladding materials in which a surface layer formed of pure Nb was diffusion-bonded under various conditions to a base layer formed of pure Ni were manufactured in the following manner. Prepare pure Ni sheet (width 30mm, length 100mm, thickness 0.5mm) as the base layer and pure Nb sheet (width 30mm, length 100mm, thickness 0.15mm) as the base layer In addition, roll pressure welding was performed in a cold manner, thereby obtaining a pressure welding sheet having a thickness of 0.28 mm. The pressure contact sheet is passed through a continuous annealing furnace in an Ar gas atmosphere and subjected to diffusion annealing under various conditions shown in Table 1. Each of the obtained clad materials is cold-rolled, and each clad material has a thickness of 0. The thickness was adjusted to 15 mm (base layer thickness 0.114 mm, surface layer thickness 0.036 mm). In addition, some of the pressure contact sheets were subjected to batch annealing in a vacuum furnace under the conditions shown in Table 1, and the obtained clad material was cold-rolled so as to have the above thickness.

  A sample of each clad material produced as described above was embedded in resin, and the resulting resin block was polished so that the cross section of the embedded clad material was exposed on the surface. And about the sample of each clad material, the average thickness of the NiNb intermetallic compound layer produced | generated between the base layer and surface layer of the clad material was measured using the electron microscope (magnification 1000-3500 times). In addition, an analysis piece was collected from each clad material, and the oxygen content was measured with an oxygen-nitrogen analyzer (model number EMGA-520, manufactured by Horiba, Ltd.). Since the amount of oxygen in the base layer is as small as about 1 to 2 ppm, the measured amount of oxygen was taken as the amount of oxygen in the surface layer. These measurement results are also shown in Table 1.

  Next, using the above clad materials, as shown in FIG. 2, a cup-shaped discharge electrode having an outer diameter of 1.1 mm, an inner diameter of 0.9 mm, and a tube length of 4 mm can be drawn in 10 steps without intermediate annealing. Deep drawing was performed through the processing, and the crack occurrence state of the cup-shaped discharge electrode after forming was visually observed. The results are also shown in Table 1. Since the base layer of the clad material is excellent in spreadability, the clad material of any sample could be molded up to the final step without causing cracks in the outer layer of the cup-shaped discharge electrode corresponding to the base layer of the clad material. On the other hand, as shown in the molding results in Table 1, some clad materials had cracks in the inner layer of the cup-shaped discharge electrode corresponding to the surface layer of the clad material. This crack is presumed that the surface layer of the clad material cannot follow the deformation of the base layer at the time of molding and is broken.

  As shown in Table 1, since the average thickness of the NiNb intermetallic compound layer was 6.5 μm or less in the clad material of the invention example and the oxygen content of the surface layer was 380 ppm or less, excellent deep drawability was obtained. It was. On the other hand, in the clad materials of Sample Nos. 4 and 5 in which the dew point of Ar gas was −35 ° C. or higher, the oxygen content of the surface layer was excessively over 700 ppm, the ductility of the surface layer was deteriorated, and the surface layer was cracked. . In addition, in the clad material of sample No. 3 annealed in a vacuum furnace, the time for holding at 800 ° C. or more was inevitably increased, and the intermetallic compound layer grew excessively, so that the deep drawability deteriorated.

The principal part sectional drawing of the clad material for discharge electrodes concerning embodiment of this invention is shown. It is a longitudinal cross-sectional view of the discharge electrode for fluorescent discharge tubes concerning embodiment of this invention. It is a principal part longitudinal cross-sectional view of the fluorescent discharge tube provided with the discharge electrode for conventional fluorescent discharge tubes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base layer 2 Surface layer 11 Pipe part 12 End plate part

Claims (8)

A base layer formed of pure Ni or a Ni-based alloy containing Ni as a main component, a NiNb intermetallic compound layer, and a surface layer formed of pure Nb;
The surface layer is diffusion bonded to the base layer via the NiNb intermetallic compound layer,
A cladding material for a discharge electrode, wherein an oxygen content in pure Nb forming the surface layer is 550 ppm or less, and a layer thickness of the NiNb intermetallic compound layer is 8.0 μm or less. The cladding material for a discharge electrode according to claim 1, wherein the base layer and the surface layer are diffusion-bonded by continuous annealing in an Ar gas atmosphere having a dew point of −40 ° C. or less.   3. The base layer according to claim 1, wherein the base layer includes one or two of Nb and Ta in a total of 1.0 mass% or more and 12.0 mass% or less, and is formed of a Ni-based alloy composed of the balance Ni and inevitable impurities. Clad material for discharge electrode. 4. The discharge electrode cladding according to claim 1, wherein the surface layer has a thickness of 20 μm or more and 100 μm or less, and 70% or less of the total thickness of the base layer and the surface layer. Wood. A discharge electrode in which one end is released and an end plate that closes the other end of the tube, and the tube and the end plate are integrally manufactured by press molding,
A discharge electrode in which the discharge electrode is formed by the cladding material according to any one of claims 1 to 4 , and an inner layer of the tube portion and the end plate portion is formed by a surface layer of the cladding material.   A base metal sheet made of pure Ni or a Ni-based alloy containing Ni as a main component and a surface layer metal sheet made of pure Nb are overlapped and press-contacted, so that the base layer and the surface layer are press-contacted. A pressure welding process for manufacturing the material, and holding the pressure welding material in an Ar gas atmosphere having a dew point of −40 ° C. or less in an annealing temperature range of 800 to 1100 ° C. for 15 seconds or more and 120 seconds or less, and diffusion bonding the base layer and the surface layer The manufacturing method of the clad material for discharge electrodes which has a diffusion annealing process. The base layer metal sheet, 1.0 mass% or more of one or two kinds of Nb and Ta in total, comprise less 12.0Mass%, formed by Ni-based alloy consisting of balance Ni and unavoidable impurities, claim 6 The manufacturing method of the clad material for discharge electrodes described in 2. The manufacturing method according to claim 6 , further comprising a finish rolling step of performing finish rolling on the diffusion-annealed clad material and adjusting a thickness of the clad material.

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