Copper alloy joined body

Abstract

Provided is a joined body of an age-hardenable copper alloy in which an extremely high joining strength is achieved. The copper alloy joined body is constituted from a plurality of members of age-hardenable copper alloy diffusion-bonded to each other, and joining interfaces between the plurality of members remain therein. The copper alloy joined body is such that the beryllium content of the age-hardenable copper alloy is 0.7 wt% or less, and in a laser microscope image of a cross-section that includes the joining interfaces, the proportion of the total length of line segments corresponding to discontinuous regions relative to the total length of a joining interface line defined along the joining interfaces and positions that were joining interfaces is 3.5% or above. The discontinuous regions are defined as regions in which when a plurality of perpendicular lines are drawn at a pitch of 5 μm with respect to the joining interface line, three or more mutually adjacent perpendicular lines do not intersect with the remaining joining interfaces.

Description

Copper alloy joint

[0001] The present invention relates to a copper alloy joined body.

[0002] Hydrogen stations that refuel fuel cell vehicles and other vehicles are equipped with precoolers to enable the rapid supply of high-pressure hydrogen cooled to approximately −45°C. Rapidly filling the tank of a fuel cell vehicle or other vehicle with hydrogen can pose a risk due to adiabatic compression, resulting in a dangerous increase in tank temperature. Therefore, by cooling the hydrogen in a precooler before supplying it, the safe and rapid supply of high-pressure hydrogen to fuel cell vehicles and other vehicles is possible. Therefore, it is preferable to use a material for the heat exchanger, a key component of a hydrogen station precooler, that not only does not exhibit hydrogen embrittlement, but also has tensile strength sufficient to withstand high pressures and thermal conductivity sufficient to enable efficient cooling. Currently, stainless steels for high-pressure hydrogen, such as SUS316L (Ni equivalent material), are used for the heat exchangers of hydrogen station precoolers in order to avoid hydrogen embrittlement. However, there is still room for improvement in terms of tensile strength and thermal conductivity.

[0003] Beryllium copper, known as a material with high tensile strength and thermal conductivity, is suitable as a material for heat exchangers and has been confirmed to be free from hydrogen embrittlement even under high-pressure hydrogen. For example, Patent Document 1 (JP 9-87780 A) discloses a beryllium copper alloy for heat exchangers, although it is not intended for use in hydrogen stations, that has a Be content of 1.0 to 2.5%, a Ni and Co total content of 0.2 to 0.6%, and the balance being Cu and unavoidable impurities. Furthermore, Patent Document 2 (JP 2017-145472 A) discloses a beryllium copper alloy having a Be content of 0.20 to 2.70 wt %, a Co, Ni, and Fe total content of 0.20 to 2.50 wt %, and a Cu, Be, Co, Ni, and Fe total content of 99 wt % or more, which is said to have excellent hydrogen embrittlement resistance, tensile strength, and thermal conductivity. Beryllium copper alloys do not exhibit hydrogen embrittlement (i.e., they are resistant to hydrogen embrittlement), and in addition, they have a higher tensile strength (e.g., about 1.5 to 2.5 times) than stainless steel for high-pressure hydrogen and a higher thermal conductivity (e.g., about 7 to 16 times) than stainless steel. Therefore, the size of heat exchangers for high-pressure hydrogen can be made significantly smaller than those made of stainless steel (e.g., about one-fourth), which is not possible with low-purity copper or low-strength copper alloys.

[0004] Japanese Patent Application Laid-Open No. 9-87780 Japanese Patent Application Laid-Open No. 2017-145472

[0005] Heat exchangers for hydrogen station precoolers have a multilayer structure consisting of metal plates with slits or grooves to form flow paths for hydrogen and refrigerant. A widely used method for joining stainless steel plates for high-pressure hydrogen applications is diffusion bonding, in which a surface oxide film is sublimated and removed during a temperature increase to the joining temperature, followed by application of a contact pressure to the joining area at a temperature below the melting point. However, copper alloys (i) have a strong oxide film that is difficult to remove by simple temperature increase and pressure decrease, and / or (ii) even if the oxide film is removed before joining, it easily reforms on the joining surfaces (contact surfaces) during the temperature increase under high vacuum during the joining process (and the oxide film is difficult to sublimate even at temperatures close to the joining temperature). When such copper alloys are diffusion bonded using the same process, a certain level of joint strength is ensured, but it is difficult to obtain a structure and strength equivalent to that of the base material. In particular, in order to realize copper alloy members with extremely high strength as required for the above-mentioned high-pressure heat exchanger applications, it is necessary to subject age-hardenable copper alloys to solution treatment and aging treatment. However, there has been a problem in that diffusion-bonded bodies of age-hardenable copper alloys that do not have sufficient bonding strength cannot withstand the severe thermal shock and dimensional fluctuations that accompany the solution treatment and aging treatment, and break at the bonded joint.

[0006] The present inventors have now discovered that, when an age-hardenable copper alloy having a beryllium content of 0.7 wt % or less is selectively employed, the joining surfaces are finished to a predetermined flatness, the oxide film is removed, and then diffusion bonding (and homogenization treatment as necessary) is performed, solution treatment and aging treatment can be performed so that the ratio of the total length of discontinuous regions to the total length of the joining interface line in a cross-sectional observation image is 3.5% or more, and thereby a copper alloy joined body having extremely high joining strength can be provided.

[0007] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a joined body of age-hardenable copper alloys that achieves extremely high joining strength.

[0008] The present invention provides the following aspects. [Aspect 1] A copper alloy joined body comprising a plurality of age-hardenable copper alloy members diffusion-bonded together, wherein a bonded interface between the plurality of members remains, the age-hardenable copper alloy having a beryllium content of 0.7 wt % or less, and in a laser microscope image of a cross section including the bonded interface, the ratio of the total length of line segments corresponding to a discontinuous region to the total length of a bonded interface line defined along the bonded interface and the position of the former bonded interface is 3.5% or more, and the discontinuous region is defined as a region in which, when a plurality of perpendicular lines are drawn at 5 μm intervals to the bonded interface line, three or more adjacent perpendicular lines do not intersect with the remaining bonded interface. [Aspect 2] The copper alloy joined body according to Aspect 1, which has been subjected to solution treatment and aging treatment. [Aspect 3] The copper alloy joined body according to Aspect 1 or Aspect 2, wherein the strength of a joint of the copper alloy joined body is 70% or more of the strength of a base metal of the copper alloy joined body. [Aspect 4] The copper alloy joined body according to any one of Aspects 1 to 3, wherein the strength of the joint portion of the copper alloy joined body is 85% or more of the strength of the base metal of the copper alloy joined body. [Aspect 5] The copper alloy joined body according to any one of Aspects 1 to 4, including crystal grains of the age-hardenable copper alloy grown beyond the joint interface or the position of the former joint interface. [Aspect 6] The copper alloy joined body according to any one of Aspects 1 to 5, wherein the joint interface or the position of the former joint interface is free of residual components derived from materials other than the age-hardenable copper alloy. [Aspect 7] The copper alloy joined body according to any one of Aspects 1 to 6, wherein the strength of the base metal and the joint portion of the copper alloy joined body is 520 MPa or more. [Aspect 8] The copper alloy joined body according to Aspect 7, wherein the strength of the base metal and the joint portion of the copper alloy joined body is 690 MPa or more. [Aspect 9] The copper alloy joined body according to any one of Aspects 1 to 8, wherein the joint portion of the copper alloy joined body has a joint strength of 85% or more of the strength of the base metal of the copper alloy joined body at a temperature of -196°C. [Embodiment 10] The copper alloy joined body according to any one of embodiments 1 to 9, wherein the joint portion of the copper alloy joined body has a Charpy impact value of 15% or more of the Charpy impact value of the base material of the copper alloy joined body at each temperature of 25 ° C. and −196 ° C.[Aspect 11] The copper alloy joined body according to any one of Aspects 1 to 10, wherein the thermal conductivity of a base material including a joint portion of the copper alloy joined body is 209 W / mK or more. [Aspect 12] The copper alloy joined body according to any one of Aspects 1 to 11, wherein the electrical conductivity of a base material including a joint portion of the copper alloy joined body is 50 IACS% or more. [Aspect 13] The age-hardenable copper alloy is selected from the group consisting of beryllium copper 11 alloy (JIS alloy number C1751, EN material number CW110C, and UNS alloy number C17510), beryllium copper 10 alloy (EN material number CW104C and UNS alloy number C17500), beryllium copper CuCo1Ni1Be (EN material number CW103C), beryllium copper 14Z alloy (Be: 0.2 to 0.6 wt %, Ni: 1.4 to 2.4 %, Zr: 0-0.5 wt%, balance Cu and inevitable impurities), beryllium copper 50 alloy (Be: 0.2-0.6 wt%, Ni: 1.4-2.1 wt%, Ag: 0.1-0.3 wt%, Zr: 0-0.5 wt%, balance Cu and inevitable impurities), beryllium copper 10Zr alloy (Be: 0.4-0.7 wt%, Co: 2.0-2.8 wt%, Zr: 0-0.3 wt%, balance Cu and unavoidable impurities), chromium copper (UNS Alloy No. C18200), chromium zirconium copper (UNS Alloy No. C18510 and EN Material No. CW106C), zirconium copper (UNS Alloy No. C15000, EN Material No. CW120C), and Corson copper (EN Material Nos. CW109C, CW111C, UNS Alloy Nos. C19010, C70250, AMPCO944 (Ni:6 The copper alloy joined body according to any one of Aspects 1 to 12, wherein the copper alloy is at least one selected from the group consisting of AMPCO 940 (Ni: 1.5 to 3.0 wt%, Si: 0.5 to 1.5 wt%, Cr: 0.5 to 1.5 wt%, the balance Cu and unavoidable impurities), and AMPCO 940 (Ni: 1.5 to 3.0 wt%, Si: 0.5 to 1.5 wt%, Cr: 0.3 to 1.5 wt%, the balance Cu and unavoidable impurities). [Aspect 14] The copper alloy joined body according to Aspect 13, wherein the age-hardenable copper alloy is beryllium copper 11 alloy (JIS Alloy No. C1751, EN Material No. CW110C, and UNS Alloy No. C17510). [Aspect 15] The copper alloy joined body according to any one of Aspects 1 to 14, wherein the copper alloy joined body has a flow path space therein.

[0009] 1A is a diagram for explaining the experimental procedure for elemental analysis of oxide films formed on the surfaces of various copper alloys during heat treatment in a high vacuum furnace. The diagram conceptually illustrates the progression of oxidation, and also shows the positions of the open furnace surface and contact surface where elemental analysis was performed, as well as the appearance of the samples. 1B is a diagram for explaining the experimental procedure for elemental analysis of oxide films formed on the surfaces (pickled surface, open furnace surface, and / or contact surface) of various copper alloys during heat treatment in a high vacuum furnace. Specifically, XPS results are shown for beryllium copper 25 alloy, beryllium copper 165 alloy, beryllium copper 11 alloy, beryllium copper 10Zr alloy, beryllium copper 50 alloy, and chromium copper alloy. 1B is a diagram for explaining one aspect of a discontinuous region at a joint interface. Specifically, XPS results are shown for Corson copper AMPCO 940 and Corson copper AMPCO 944.

[0023] Figure 1 is a diagram for explaining another embodiment of a discontinuous region at a joint interface.

[0024] Figures 1a to 1d show laser microscope images of cross sections including a joint interface of copper alloy joined bodies produced through solution treatment and aging treatment in Examples 1a to 1d.

[0025] Figures 1a to 1d show laser microscope images of cross sections including a joint interface of copper alloy joined bodies produced through solution treatment and aging treatment in Examples 2a to 2f.

[0026] Figures 1a to 1d show laser microscope images of cross sections including a joint interface of copper alloy joined bodies produced through solution treatment and aging treatment in Examples 3 to 7b.

[0027] Figures 1a to 1d show laser microscope images of cross sections including a joint interface of copper alloy joined bodies produced through solution treatment and aging treatment in Examples 3 to 7b.

[0028] Figures 1a to 1d show laser microscope images of cross sections including a joint interface of copper alloy joined bodies produced through solution treatment and aging treatment in Examples 3 to 7b.

[0029] Figures 1b to 1c show an example of the first half of a series of steps for calculating the discontinuous region flow by image processing laser microscope images using image analysis software ImageJ.

[0029] Figures 1c to 1d show an example of the second half of a series of steps for calculating the discontinuous region flow by image processing laser microscope images using image analysis software ImageJ.

[0010] Copper alloy joined body The copper alloy joined body of the present invention is composed of multiple age-hardenable copper alloy members that are diffusion-bonded together, and is typically subjected to solution treatment and aging treatment. In this copper alloy joined body, a bonded interface between the multiple members remains. The age-hardenable copper alloy has a beryllium content of 0.7 wt % or less. In this copper alloy joined body, in a laser microscope image of a cross section including the bonded interface, the ratio of the total length of line segments corresponding to discontinuous regions to the total length of a bonded interface line defined along the bonded interface and the position of the former bonded interface is 3.5% or more. A discontinuous region is defined as a region in which, when multiple perpendicular lines are drawn to the bonded interface line at 5 μm intervals, three or more adjacent perpendicular lines do not intersect with the remaining bonded interface. In this way, when an age-hardenable copper alloy having a beryllium content of 0.7 wt % or less is selectively employed, a copper alloy joined body having extremely high joining strength can be provided by performing solution treatment and aging treatment (after performing homogenization treatment as necessary) so that the ratio of the total length of discontinuous regions to the total length of the joining interface line in a cross-sectional observation image is 3.5% or more.

[0011] As described above, when copper alloys (i) having a strong oxide film that is difficult to remove by simply heating under reduced pressure and / or (ii) which reform an oxide film even under high vacuum are diffusion-bonded by the same process, a certain level of bonding strength is ensured, but it is difficult to obtain a structure and strength equivalent to those of the base material. In particular, in order to realize copper alloy members with extremely high strength as required for the above-mentioned heat exchanger applications, it is necessary to subject the age-hardenable copper alloy to solution treatment and aging treatment. However, there is a problem that diffusion-bonded bodies of age-hardenable copper alloys cannot withstand the severe thermal shock and dimensional fluctuations that accompany the solution treatment and aging treatment, and are broken at the bonded joint.

[0012] In this regard, the above-described configuration of the present invention advantageously solves this problem and makes it possible to provide a copper alloy joint having extremely high joint strength. The reason for this, as revealed by the inventor's confirmation tests described below, is as follows. Specifically, an age-hardenable copper alloy having a beryllium content of 0.7 wt % or less is selectively used, the flatness and surface roughness of the joint surfaces are adjusted to be suitable for diffusion bonding, the oxide film on the joint surfaces is removed, and the joint interfaces of the copper alloy members are brought into close contact with each other and then subjected to pressure and temperature increase for diffusion bonding. In this case, the proportion of discontinuous regions (regions where the joint interface is interrupted) at the joint interface (or the former joint interface) formed in an age-hardenable copper alloy having a beryllium content exceeding 0.7 wt % increases, thereby reducing the remaining joint interface. As a result, a high-quality diffusion bond that can sufficiently withstand solution treatment and aging treatment is realized. In other words, the presence of discontinuous regions is thought to reduce the proportion of oxide at the interface, which contributes to improved joint strength.

[0013] It is known that highly reliable bonding can be achieved between stainless steel, pure copper, and other materials by diffusion bonding. Stainless steel has a dense chromium oxide coating on its surface that forms in the atmosphere and acts as a protective coating, providing strong weather resistance. However, this oxide coating sublimes when heated to temperatures exceeding 700°C under high vacuum. Therefore, it naturally removes during the heating process during diffusion bonding, easily providing an active stainless steel surface free of the oxide coating. Therefore, simply applying pressure at the bonding temperature allows for good bonding without leaving oxides or other foreign matter at the bonding interface. Furthermore, pure copper has a copper oxide (CuO) coating on its surface. However, this oxide decomposes during the diffusion bonding temperature, and oxygen diffuses into the copper matrix. This allows for good bonding without leaving oxides or other foreign matter at the bonding interface, similar to stainless steel.

[0014] Prior to the completion of this invention, the inventors of the present invention confirmed that while a certain level of bond strength was achieved when age-hardenable copper alloys were subjected to conventional diffusion bonding, the bond strength deteriorated and fracture often occurred when the resulting bonded bodies were subjected to solution aging treatment. This phenomenon was particularly pronounced with beryllium copper 25 alloy (JIS C1720), which is known to have the highest strength among age-hardenable copper alloys. The inventors suspected that this was due to an oxide film remaining on the bonding surface, which is not observed in stainless steel or pure copper. To clarify the mechanism behind the oxide film remaining, the inventors conducted the following experiment, as shown in FIG. 1A. Each alloy shown in FIGS. 1B and 1C was machined into a plate measuring 15 mm × 15 mm × 5 mm. The top and bottom surfaces of the resulting 15 mm × 15 mm test specimens 10 were then lapped to achieve a flatness of 0.1 mm or less and a surface roughness (RzJIS) of 0.8 μm or less. The oxide film was then removed by washing with 30% nitric acid immediately before testing. Three test specimens 10 were prepared for each alloy. 1A, one test piece 10 was placed in a bonding furnace in a state where it was exposed to the vacuum atmosphere in the furnace, and the other two test pieces 10 were stacked and in close contact (like the bonding surfaces in diffusion bonding). After undergoing the same heat treatment as during bonding under various reduced pressure conditions in the bonding furnace, the test pieces were removed, and the surface of the former that was in contact with the furnace atmosphere (hereinafter referred to as the "open surface" in the bonding furnace) and the surface of the latter that was in close contact with each other (hereinafter referred to as the "contact surface") were etched with argon, while the oxide film 12 on the surface was subjected to elemental analysis using an X-ray photoelectron spectroscopy analyzer (XPS, product name: Quantera SXM, manufactured by ULVAC-PHI, Inc.).

[0015] 1B and 1C show the measurement results of the oxide layer for each alloy after pickling, after heat treatment on the open surface in the furnace, and / or after heat treatment on the contact surface. From these results, it can be seen that the oxide layer was completely removed by pickling in all alloy tests, and that the oxide layer on the open surface in the furnace was 5 × 10 －５It can be seen that a very thick oxide film is formed even under a high vacuum of 100 Torr. The degree of oxide film formation on the bonding surface, which is a problem in bonding, was investigated by: i) Welding 5×10 alloys containing 0.7 wt % or less of beryllium (beryllium copper 11 alloy, beryllium copper 50 alloy, beryllium copper 10Zr alloy, chromium copper alloy, Corson copper AMPCO 940, and Corson copper AMPCO 944). －５ ii) when processed at the bonding temperature under a high vacuum of 1000 Torr (the vacuum level achieved during continuous evacuation with a diffusion pump), no oxide film is formed or only a very slight oxide film is formed, even for alloys with a beryllium content of 0.7 wt% or less, －１ At a vacuum of about Torr, oxygen can penetrate the contact surface and form an oxide film; and iii) alloys with a beryllium content exceeding 0.7 wt.% (beryllium copper 25 alloy and beryllium copper 165 alloy) have a 5 x 10 －５ It was confirmed that even when processed under a high vacuum of 100 Torr, an oxide film was formed due to oxygen penetrating the bonding surfaces. From these results, it was found that because beryllium has an extremely high affinity for oxygen, when the beryllium concentration is above a certain level, it is difficult to prevent the formation of an oxide film due to oxygen penetrating between the bonding surfaces, even if the bonding strength of the components is increased under a high vacuum, and that the beryllium content must be taken into consideration when selecting materials in order to prevent an oxide film from remaining on the bonding surfaces.

[0016] The age-hardenable copper alloy used in the copper alloy joined body of the present invention is not particularly limited as long as the beryllium content is 0.7 wt % or less, and it may also be beryllium-free (i.e., 0 wt %). Joined bodies using beryllium-copper alloys with a high Be content of more than 0.7 wt % (e.g., beryllium-copper alloy 25 (JIS alloy number C1720)) have a significant oxide film remaining on the joining surface, cannot withstand solution treatment and aging treatment, and fracture at the joint after solution treatment or aging treatment. However, by selectively using an age-hardenable copper alloy with a low Be content of 0.7 wt % or less for diffusion bonding, a copper alloy joined body that can withstand solution treatment and aging treatment and has extremely high joining strength can be realized. Examples of such age-hardenable copper alloys include beryllium copper 11 alloy (JIS alloy number C1751, EN material number CW110C, and UNS alloy number C17510), beryllium copper 10 alloy (EN material number CW104C and UNS alloy number C17500), beryllium copper CuCo1Ni1Be (EN material number CW103C), beryllium copper 14Z alloy, beryllium copper 50 alloy, beryllium copper 10Zr alloy, chromium copper (U Examples of suitable age-hardenable alloys include copper chromium zirconium (UNS Alloy No. C18200), copper chromium zirconium (UNS Alloy No. C18510 and EN Material No. CW106C), copper zirconium (UNS Alloy No. C15000, EN Material No. CW120C), and Corson copper (EN Material Nos. CW109C, CW111C, UNS Alloy Nos. C19010, C70250, AMPCO 944, and AMPCO 940), with beryllium copper 11 being the most preferred. These preferred age-hardenable alloys not only achieve extremely high bonding strength after solution aging, but also have excellent hydrogen embrittlement resistance and thermal conductivity, making them particularly advantageous as materials for heat exchangers in precoolers for hydrogen stations. The compositions of the various copper alloys mentioned above are shown in Table 1 below.

[0017]

[0018] As described above, in the copper alloy joined body of the present invention, the bonding interfaces between multiple members remain. The disappearance or retention of the bonding interfaces is determined by observing a cross section including the bonded portion of the copper alloy joined body with a laser microscope at a magnification of 200 to 1000 times (see, for example, Figures 3 to 5 described below). The disappearance / remaining of the bonding interfaces is determined by whether or not traces of the bonding surfaces of the copper alloy members before joining remain. In the copper alloy joined body of the present invention, in a laser microscope image of a cross section including the bonding interfaces, the ratio of the total length of the line segments corresponding to the discontinuous region to the total length of the bonding interface line defined along the bonding interface and the position of the former bonding interface is 3.5% or more. The cross section including the bonding interface is preferably a rectangular cross section with long sides of 1200 μm and short sides of 200 μm (where the long sides are parallel to the bonding interface and the short sides are perpendicular to the bonding interface). The term "bonding interface line" as used herein refers to a boundary line defined along the bonded interface and the location of the former bonded interface in a laser microscope image (preferably a depth-combined image obtained by a laser microscope) (cross-sectional observation image). The term "bonding interface line" refers to a single continuous line consisting of a residual line segment defined based on the remaining bonded interface and a virtual line segment defined by extrapolating the residual line segment to the area where the bonded interface has disappeared. In other words, the bonded interface line can be defined by connecting the line segments of the remaining bonded interface and extrapolating the residual line segments to the area where the bonded interface has disappeared to form a single continuous line. Therefore, in this specification, the term "bonding interface line" is used to distinguish it from the term "bonding interface."

[0019] As shown in Figures 2A and 2B, a discontinuous region is defined as a region where, when multiple perpendicular lines are drawn at 5 μm intervals to the bonded interface line, three or more adjacent perpendicular lines do not intersect with the remaining bonded interface. That is, a discontinuous region may be a region where the bonded interface has completely disappeared, as shown in Figure 2A, resulting in three or more adjacent perpendicular lines not intersecting with the bonded interface. Alternatively, a discontinuous region may be a region where the bonded interface is intermittently interrupted, as shown in Figure 2B, resulting in three or more adjacent perpendicular lines not intersecting with the bonded interface. The former discontinuous region (Figure 2A) has no remnants or traces of the bonded interface, while the latter discontinuous region (Figure 2B) has remnants or traces of the bonded interface that do not intersect with three or more perpendicular lines. The presence of such a discontinuous region contributes to achieving extremely high bond strength. It is believed that the presence of the discontinuous region reduces the proportion of oxide at the interface, thereby contributing to improved bond strength. The ratio of the total length of the line segments corresponding to the discontinuous region to the total length of the bonded interface line is 3.5% or more, preferably 4.5% or more, more preferably 7.5% or more, and even more preferably 10% or more. The upper limit of the ratio of the total length of the line segments corresponding to the discontinuous region is not particularly limited, but is typically 80% or less, more typically 70% or less, even more typically 50% or less, and particularly typically 30% or less.

[0020] Therefore, the copper alloy joined body of the present invention has extremely high joint strength. That is, by setting the ratio of the total length of the discontinuous regions to the total length of the joint interface line in a cross-sectional observation image to 3.5% or more, crack initiation points are reduced or the crack propagation rate is reduced during a tensile test, resulting in extremely high joint strength. Specifically, the strength of the joint of the copper alloy joined body is preferably 70% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% of the strength of the base metal of the copper alloy joined body. This strength is assumed to be a value at 25°C, but achieving a strength within the above range even at −196°C is preferable in terms of maintaining joint strength even in extremely low temperatures such as liquid hydrogen or liquid oxygen. Therefore, the joint of the copper alloy joined body preferably has a joint strength of 85% or more, more preferably 90% or more, and even more preferably 95% or more of the strength of the base metal of the copper alloy joined body at a temperature of −196°C. Since a high strength of the joint of a copper alloy joined body is desirable, the upper limit of the strength is not particularly limited, and is typically 100% or less of the strength of the base metal of the copper alloy joined body. The above strength is typically the strength after solution aging treatment. The strength of the base metal and the joint of a copper alloy joined body can be measured by preparing a test piece conforming to ASTM E8M Specimen 3 so that the joint is located at the center of the test piece, and performing a tensile test on the test piece using a procedure conforming to ASTM E8M.

[0021] Furthermore, the joint of a copper alloy joined body preferably has a Charpy impact value of 15% or more, more preferably 25% or more, and even more preferably 60% or more, of the Charpy impact value of the base metal of the copper alloy joined body at temperatures of 25°C and -196°C. By having a Charpy impact value within the above range not only at room temperature but also at -196°C, the copper alloy joined body can maintain its desired performance even in extremely low temperature conditions such as liquid hydrogen or liquid oxygen. Since a high Charpy impact value of the joint of a copper alloy joined body is desirable, the upper limit is not particularly limited, but is typically 80% or less, more typically 70% or less, and even more typically 60% or less of the Charpy impact value of the base metal of the copper alloy joined body. The Charpy impact values ​​of the base metal and joint of a copper alloy joined body can be measured in accordance with JIS Z 2242:2018, according to the procedures in the Examples described below.

[0022] An oxide film may be present at the bonded interface of the copper alloy joined body of the present invention. The thickness of the oxide film is typically 0 nm to 5.0 nm, preferably 0 nm to 4.0 nm, more preferably 0 nm to 3.0 nm, even more preferably 0 nm to 2.0 nm, particularly preferably 0 nm to 1.5 nm, and most preferably 0 nm to 1.0 nm. Such a thin oxide film can withstand solution aging treatment, similar to a case where the bonded interface disappears, and a copper alloy joined body with extremely high bond strength can be obtained after aging treatment. The thickness of the oxide film at the bonded interface can be determined by observing a cross section including the bonded interface with a scanning transmission electron microscope (STEM), obtaining an elemental mapping image of the cross section by electron energy loss spectroscopy (EELS) / energy dispersive X-ray analysis (EDX), and comparing the STEM image with the EELS / EDX elemental mapping image to identify the oxide film and determine its thickness. The oxide film present at the bonding interface may be not only a layer-like film but also a particulate film (i.e., oxide particles), in which case the height of the oxide particles is also included in the thickness of the oxide film.

[0023] The copper alloy joined body of the present invention may contain crystal grains of an age-hardenable copper alloy that have grown beyond the joining interface or the position of the former joining interface (previous joining interface). That is, the copper alloy joined body of the present invention has a structure at the joining interface or previous joining interface in which crystal grains that were present at the joining surfaces of the copper alloy members before joining have been recombined and recrystallized after joining, and it can be observed that the joining interface does not remain as it was when the joining was first performed. When the copper alloy joined body has such a joining microstructure, the joining strength is improved.

[0024] In the copper alloy joined body of the present invention, it is preferable that the joined interface or the former joined interface (old joined interface) be free of residual components derived from materials other than the age-hardenable copper alloy, from the viewpoint of ensuring high joint strength equivalent to that of the base material and hydrogen resistance equivalent to that of the base material. Therefore, it is desirable that the copper alloy joined body of the present invention does not include a joining agent such as a brazing material. In other words, the copper alloy joined body of the present invention preferably consists only of the age-hardenable copper alloy and inclusions composed of oxides, carbides, and / or intermetallic compounds derived therefrom.

[0025] The strength of the base metal and joints of the copper alloy joined body after solution treatment is preferably 520 MPa or more, more preferably 690 MPa or more. Such a strength of the copper alloy joined body satisfies the standards required for high-strength applications, including applications as heat exchangers in precoolers for hydrogen stations. Since high strength is desirable, its upper limit should not be specified. However, the strength of the base metal and joints of the copper alloy joined body according to the present invention, after solution treatment, is typically 895 MPa or less. The strengths of the base metal and joints of the copper alloy joined body before and after solution treatment can be measured by preparing a test piece conforming to ASTM E8M Specimen 3 so that the joint is located at the center of the test piece, and performing a tensile test on the test piece using a procedure conforming to ASTM E8M.

[0026] It is desirable for the base material, including the joints of copper alloy joined bodies, to have high thermal conductivity. Because thermal conduction, like electrical conduction, is an energy transfer based on conduction electrons, there is a correlation between the two, known as the Wiedemann-Franz law, and thermal conductivity can be converted to electrical conductivity, which is more easily measured. The thermal conductivity (and its converted electrical conductivity) of the base material, including the joints of copper alloy joined bodies, is preferably 209 W / mK or higher (converted electrical conductivity of 50 IACS% or higher), more preferably 228 W / mK or higher (converted electrical conductivity of 55 IACS% or higher), and even more preferably 246 W / mK or higher (converted electrical conductivity of 60 IACS% or higher). Such high thermal conductivity is advantageous in that it provides extremely high heat exchange efficiency when used in heat exchangers (for example, the thermal conductivity of SUS316LNi equivalent, currently used in precooler heat exchangers due to its excellent hydrogen properties, is very low at 16 W / mK, resulting in poor heat exchange efficiency and operational difficulties). Since a high thermal conductivity is desirable, its upper limit should not be specified. However, the thermal conductivity of a base material including a joint portion of a copper alloy joint having a beryllium content of 0.7 wt % or less according to the present invention, which can ensure a strength of 520 MPa or more for the base material and the joint portion, is typically 280 W / mK or less.

[0027] The copper alloy joint including the joint was subjected to a strain rate of 5×10 －５ s －１ Within the range below (e.g., 5 × 10 －５ s －１ In a slow strain rate tensile (SSRT) test conducted at a strain rate of 5×10, the tensile strength in hydrogen gas is preferably 520 MPa or more, more preferably 690 MPa or more. This copper alloy joined body, including the joined portion, has excellent hydrogen embrittlement resistance and high tensile strength. This slow strain rate tensile test is conducted in accordance with ASTM-G-142. The slow strain rate tensile test may be conducted, for example, using a test piece of a regular shape (smooth test piece). In general, with a smooth test piece, hydrogen sensitivity is evaluated using the relative tensile strength (RTS) or relative reduction of area (RRA), which is obtained by dividing the tensile strength or reduction of area in hydrogen gas by the tensile strength or reduction of area in a reference gas that is not affected by hydrogen. In a slow strain rate tensile test of a smooth test piece, for example, a strain rate of 5×10－５ s －１ The test may be performed at a pressure of 95 MPa or higher. Assuming a 70 MPa-class FCV (fuel cell vehicle) or hydrogen station, this slow strain rate tensile test is performed at a hydrogen gas pressure of 95 MPa or higher. Higher hydrogen gas pressures increase the amount of hydrogen that penetrates into the material, making the test specimen more susceptible to the effects of hydrogen exposure, allowing for more appropriate evaluation of hydrogen embrittlement. In the tests related to this application, it is preferable to evaluate hydrogen characteristics using a standard-shaped test specimen (smooth test specimen) using relative tensile strength (RTS) or relative reduction of area (RRA). For example, a copper alloy joint may be cut out to prepare a test specimen conforming to ASTM E8M Specimen 4, with the joint positioned at the center of the test specimen.

[0028] In the copper alloy joined body including this bonded portion, when the tensile strength is 520 MPa or more, desirably 690 MPa or more, in the slow strain rate tensile test, the relative reduction of area RRA is preferably 0.8 or more, more preferably 0.9 or more. The tensile strength RTS is also preferably 0.8 or more, more preferably 0.9 or more. When the tensile strength of the copper alloy joined body including the bonded portion is within the above ranges in air at room temperature or under a hydrogen gas pressure of 95 MPa or more, and the RRA and RTS also satisfy the above ranges, this copper alloy joined body has high strength and excellent hydrogen embrittlement resistance, and is therefore particularly suitable for use as a heat exchanger in a precooler for a hydrogen station. Since a high tensile strength is desirable, no upper limit should be specified. However, the tensile strength of the copper alloy joined body according to the present invention, which has a beryllium content of 0.7 wt % or less, in a slow strain rate tensile test at room temperature in air or under a hydrogen gas pressure of 95 MPa or more, is typically 895 MPa or less.

[0029] The copper alloy joined body may have a flow path space therein. In this case, the flow path space can be used as an internal space for passing a medium such as hydrogen or a refrigerant. Therefore, the copper alloy joined body having the flow path space can be preferably used as a heat exchanger of a pre-cooler for a hydrogen station, which is desired to have a plurality of flow path spaces for passing hydrogen and a refrigerant, respectively.

[0030] The copper alloy joined body of the present invention can be produced by subjecting a plurality of age-hardenable copper alloy members to the following steps in sequence: smoothing the joining surfaces (optional step), removing oxide films, hot press bonding (diffusion bonding), homogenizing treatment (optional step), solution treatment, and aging treatment, as required. Specifically, the steps are as follows.

[0031] (a) Preparation of copper alloy members First, a plurality of age-hardenable copper alloy members to be used for joining are prepared. The age-hardenable copper alloy has a beryllium content of 0.7 wt % or less, and can be any of those described above. The top and bottom surface materials of the laminated joint produced as a heat exchanger are preferably rolled or forged materials, and rolled materials are preferably used for the multiple laminated materials other than the top and bottom surfaces, with or without cooling water channels inside.

[0032] For the copper alloy joined body of the present invention, it is preferable to use a copper alloy material that does not deteriorate under hydrogen. It is known that, for example, in cupronickel (Cu-10% to 30%), significant deterioration in hydrogen characteristics occurs when the Ni concentration is 20% or higher, and that significant deterioration in hydrogen characteristics also occurs in tough pitch copper (pure copper that has not been deoxidized). Therefore, when selecting a copper alloy for use in the copper alloy joined body of the present invention, it is desirable to perform a slow strain rate tensile test (e.g., in accordance with ASTM-G-142, using a smooth test piece at a displacement rate of 0.001 mm / sec (strain rate of 0.00005 / sec)) in both air and high-pressure hydrogen (e.g., in 95 MPa hydrogen), and compare the test results in air with those in high-pressure hydrogen to confirm that the copper alloy material does not deteriorate under hydrogen. For example, the copper alloy joined body of the present invention is preferably a copper alloy material that does not deteriorate under hydrogen at a strain rate of 5×10 －５ s －１ It is preferable that the steel sheet is made using a copper alloy member having an RRA (relative reduction of area) in hydrogen gas of 0.8 or more, as measured by a slow strain rate tensile test performed below, and more preferably 0.9 or more.

[0033] Here, the surfaces of the age-hardenable copper alloy members to be joined must have a flat surface with a flatness of 0.1 mm or less and an arithmetic mean roughness Ra of 3.0 μm or less. That is, as mentioned above, even if the oxide film on the surface of the joining member is removed, in order to prevent reoxidation of the joining surface during hot press joining (diffusion joining), it is necessary to ensure adhesion of the joining surface so that the number of oxygen atoms penetrating the joining surface is sufficiently small even in a high vacuum atmosphere. This adhesion can be ensured if the flatness and Ra are within the above ranges. When the members to be joined are rolled materials, they often satisfy the flatness and Ra within the above ranges, so no special smoothing process is required. On the other hand, if the flatness and Ra do not satisfy the above ranges, a flat surface with a flatness and Ra within the above ranges can be formed by polishing, cutting, and / or other techniques. Although the plate material may have curl, this is not a problem as long as the plate thickness precision is well adjusted and the flatness is 0.1 mm or less when the required load is applied during hot press bonding (diffusion bonding), ensuring the desired adhesion. The arithmetic mean roughness Ra is the surface roughness specified in JIS B 0601-2001. The arithmetic mean roughness Ra of a flat surface is 3.0 μm or less, preferably 1.0 μm or less, more preferably 0.50 to 1.0 μm, and even more preferably 0.10 to 0.50 μm. In this specification, flatness is a parameter defined in JIS B 0621-1984 as "the magnitude of deviation from a geometrically correct plane (geometric plane) of a planar shape," and refers to the value indicated by the width when an object is sandwiched between a pair of flat surfaces.

[0034] If necessary, prior to removing the oxide film in the next step, it is preferable to form grooves on the surfaces of the components to be joined, which will provide flow path spaces after joining. The grooves can be formed by various known methods, such as etching, pressing, and machining. In this way, the copper alloy bonded body can be used to manufacture a copper alloy bonded body having internal flow path spaces, as described above. For example, by alternately stacking and joining grooved and non-grooved copper alloy sheets, a copper alloy laminate having a large number of flow paths can be manufactured. A multilayer bonded body having such a configuration can be preferably used as a heat exchanger for a precooler for a hydrogen station, which is desired to have multiple flow path spaces for passing hydrogen and a refrigerant, respectively.

[0035] (b) Removal of Oxide Layer As mentioned above, an oxide layer exists on the surface of a copper alloy member. Therefore, the oxide layer present on the surface of the copper alloy member to be joined is removed. Removal of the oxide layer is preferably performed by washing the surface of the copper alloy member to be joined with an inorganic acid solution, as this effectively removes the oxide layer. Examples of inorganic acid solutions include nitric acid, sulfuric acid, a chemical polishing solution, hydrochloric acid, a Kirin's bath, and hydrofluoric acid, with nitric acid being particularly preferred. The chemical polishing solution is an acid obtained by adding hydrogen peroxide as an oxidizing agent to sulfuric acid, and the Kirin's bath is a mixed acid of sulfuric acid, nitric acid, and hydrochloric acid, and may also contain a small amount of sodium hydroxide. Examples of preferred mixture ratios for the Kirin's bath include sulfuric acid:nitric acid:hydrochloric acid = 61:4:4, 81:1:0.02, or 11:1:0.02. Alternatively, the oxide layer may be removed by mechanical polishing, or mechanical polishing and washing with an inorganic acid solution may be combined.

[0036] (c) Hot press bonding (diffusion bonding) A plurality of copper alloy members are bonded by hot press to form an intermediate bonded body. This bonding can be performed in accordance with the diffusion bonding method. For example, hot press bonding can be performed at a temperature of 1.0 × 10 －２ Torr (i.e., 1.0×10 －２Preferably, the hot pressing is carried out in a furnace (pressure lower than 1.0 × 10 Torr) at a temperature of 500 to 1050°C for 30 to 480 minutes, applying a pressure of 5.0 MPa or more (preferably 10 MPa or more). However, when the age-hardenable copper alloy does not contain Be (for example, Corson copper), the hot pressing is carried out at a pressure of 1.0 × 10 －１ A vacuum level equal to or higher than 1.0×10 Torr (i.e., 1.0×10 －１ This can be done in a furnace (pressure equal to or lower than 1000 Torr) at a temperature of 500 to 1050°C for 30 to 480 minutes, applying a pressure of 5.0 MPa or more. In any case, this hot pressing is performed so that the longitudinal deformation in the pressure direction during joining of the copper alloy members is preferably 0.5% to 35%, more preferably 0.5% to 30%, even more preferably 1% to 20%, and particularly preferably 2% to 8%. There is an appropriate combination of hot pressing temperature and pressure, and preferably, the pressure is 5.0 MPa to 20 MPa at temperatures above 840°C and below 1050°C, 2 MPa to 24 MPa at temperatures above 720°C and below 840°C, and 4 MPa to 50 MPa at temperatures above 600°C and below 720°C. The hot pressing time is preferably 15 to 480 minutes, more preferably 30 to 150 minutes, and even more preferably 30 to 60 minutes. The degree of vacuum in the furnace during hot pressing is preferably 1.0×10 －３ Torr or less, more preferably 1.0×10 －４ Torr or less, more preferably 5.0 x 10 －５ Torr.

[0037] In particular, when grooves are formed on the surface of the copper alloy member to provide a flow path space in the intermediate bonded body, it is preferable to carry out the hot pressing at a relatively low temperature and a relatively high pressure, since this allows control so that the crushing of the flow paths due to pressing can be minimized. －２ Torr (i.e., 1.0×10 －２ Torr), more preferably 1.0×10 －４ Torr (i.e., 1.0×10 －４In a furnace with a vacuum of 1000 psi (or less than 1000 psi), the heating is preferably carried out by: (i) applying a pressure of 1 MPa to 4 MPa at a temperature of more than 840°C and not more than 930°C for 30 to 480 minutes (preferably 30 to 60 minutes); or (ii) applying a pressure of 2 MPa to 8 MPa at a temperature of more than 720°C and not more than 840°C for 30 to 480 minutes (preferably 30 to 60 minutes); or (iii) applying a pressure of 4 MPa to 30 MPa at a temperature of more than 600°C and not more than 720°C for 30 to 480 minutes (preferably 30 to 60 minutes).

[0038] (d) Homogenization Treatment (Optional Step) When a groove is formed on the surface of the copper alloy member to provide a flow path space in the intermediate bonded body, and when hot pressing is performed at a relatively low temperature and a relatively high pressure, the intermediate bonded body is subjected to a homogenization treatment, preferably 1.0 × 10 －１ Torr (i.e., 1.0×10 －１ Preferably, homogenization is performed for 60 to 480 minutes at a temperature of 900 to 1050°C in a furnace (pressure lower than 1000 Torr) or in a nitrogen or other non-oxidizing gas atmosphere (inert atmosphere) (at normal pressure or reduced pressure). Homogenization is also called homogenization annealing, but the term "homogenization treatment" will be used in this specification. That is, when hot pressing is performed at a relatively low temperature and a relatively high pressure, a bonded interface is likely to remain. However, by performing homogenization treatment, the bonded interface can be reduced or eliminated, and extremely high bond strength can be achieved by undergoing subsequent solution treatment and aging treatment. That is, it is possible to achieve both suppression of flow channel collapse and high bond strength. The homogenization treatment is performed at a temperature of 1.0 × 10 －１ In an air atmosphere at a pressure lower than Torr, or at normal pressure or 1.0 x 10 －１The treatment is preferably carried out in an inert atmosphere such as nitrogen, reduced to a pressure lower than Torr. The homogenization temperature is preferably 900 to 1050°C, more preferably 930 to 1000°C, and even more preferably 960 to 990°C. The holding time at the homogenization temperature is 60 to 480 minutes, more preferably 60 to 360 minutes, and even more preferably 60 to 240 minutes. However, it goes without saying that the homogenization treatment may be carried out as needed even if grooves are not formed on the surface of the copper alloy member.

[0039] It is preferable that (c) hot press bonding (diffusion bonding) and (d) homogenization treatment are performed continuously by releasing the press load and raising the temperature without lowering the furnace temperature. In this way, after hot press bonding (diffusion bonding) is performed under temperature and pressure conditions that do not excessively crush the flow path space, hot press bonding (diffusion bonding) and homogenization treatment can be performed as a series of continuous operations at a temperature effective for homogenizing the structure without applying pressure that would crush the flow path space, which is advantageous not only from an improved reliability of the bonded portion but also from an economical point of view.

[0040] (e) Solution Treatment The intermediate joint body is subjected to solution treatment. This solution treatment is preferably carried out by heating the intermediate joint body at a temperature of 700 to 1100°C for 1 to 180 minutes in a furnace such as an atmospheric furnace, a non-oxidizing atmosphere furnace, or a salt bath furnace, followed by water cooling. The copper alloy used in the present invention is an age-hardenable alloy. By eliminating the bonding interface or adjusting the thickness of the oxide film at the bonding interface to a certain level, and then undergoing solution treatment and subsequent aging treatment, the desired tempering characteristics (e.g., high strength), particularly extremely high bonding strength, can be achieved. The optimum solution treatment temperature range varies somewhat depending on the alloy composition, but is preferably 700 to 1100°C, more preferably 800 to 1050°C, and even more preferably 900 to 1000°C. The actual holding time at the above solution treatment temperature is preferably 1 to 180 minutes, more preferably 5 to 90 minutes, and even more preferably 10 to 60 minutes.

[0041] (f) Aging Treatment The intermediate joint body that has been solution-treated is then subjected to aging treatment. The optimum temperature range for this aging treatment varies somewhat depending on the alloy composition, but it is preferable to perform aging treatment at 350 to 550°C for 30 to 480 minutes. As described above, age-hardenable alloys such as beryllium copper alloys can exhibit desired tempering characteristics (e.g., high strength), particularly extremely high joint strength, by undergoing solution treatment and aging treatment. The aging treatment temperature is preferably 350 to 550°C, more preferably 400 to 500°C, and even more preferably 450 to 480°C. The holding time at the aging treatment temperature is preferably 30 to 480 minutes, more preferably 30 to 300 minutes, even more preferably 60 to 240 minutes, and particularly preferably 90 to 180 minutes. From the viewpoint of suppressing oxidation, the aging treatment is performed at a temperature of 1.0 x 10 －１ Torr (i.e., 1.0×10 －１ It is preferable to carry out the process in a furnace under a non-oxidizing atmosphere such as nitrogen or the like.

[0042] The present invention is further illustrated by the following examples.

[0043] Examples 1a to 7b Copper alloy joined bodies were produced by the following procedure, and various evaluations were carried out.

[0044] (1) Preparation of copper alloys In each example, multiple copper alloy members were prepared, each consisting of the alloy type and composition shown in Table 2 and having the following configurations: - Two copper alloy round bars with a diameter of 80 mm and a length of 50 mm (Examples 1a to 1d and 6a to 7b) - Two forged materials (square bars or rectangular parallelepiped blocks) with dimensions of 160 mm x 280 mm and a length (thickness) of 50 mm (Examples 2a to 3) - Two forged materials (square bars or rectangular parallelepiped blocks) with dimensions of 150 mm x 220 mm and a length (thickness) of 25 mm and ten rolled materials (square plates) with dimensions of 150 mm x 220 mm and a thickness of 1.3 mm (Examples 4a and 4b) - Two forged materials (square bars or rectangular parallelepiped blocks) with dimensions of 50 mm x 50 mm and a length (thickness) of 40 mm and four rolled materials (square plates) with dimensions of 50 mm x 50 mm and a thickness of 1.3 mm (Example 5)

[0045] The surfaces used for joining each copper alloy member (hereinafter referred to as "joining surfaces") were processed by lathe turning, lapping, or the like to form flat surfaces having an arithmetic mean roughness Ra of less than 3.0 μm as measured in accordance with JIS B 0601-2001 and a flatness of 0.1 mm or less as measured in accordance with JIS B 0621-1984. The average values ​​of the arithmetic mean roughness Ra measured for the joining surfaces after surface treatment were as shown in Table 2. In the case of two copper alloy round bars or two forged materials (Examples 1a to 3 and 6a to 7b), the average value of the Ra at the joining surface of the upper bar and the Ra at the joining surface of the lower bar was used as the representative value of Ra shown in Table 2. In addition, in the case of two forged materials and ten or four rolled materials (Examples 4a, 4b, and 5), the average value of Ra at the upper plate joining surface and the average value of Ra at the lower plate joining surface at one joining position of the ten or four rolled materials were used as the representative value.

[0046] (2) Removal of Oxide Film The joining surfaces of each copper alloy member were washed with 30% nitric acid to remove the oxide film present on the joining surfaces.

[0047] (3) Hot Pressing In Examples 1a to 3 and 6a to 7b, the joining surfaces of two copper alloy round bars or two forged materials cleaned with nitric acid were directly butted together (without using a brazing filler metal), and hot-pressed in a vacuum furnace under the joining conditions shown in Table 2 to obtain intermediate joined bodies in the shape of round bars or square bars. In Examples 4a, 4b, and 5, the joining surfaces of two copper alloy cast materials (square bars) cleaned with nitric acid were butted together (without using a brazing filler metal) with 10 (Examples 4a and 4b) or 4 (Example 5) rolled copper alloy materials (square plates) interposed therebetween (without using a brazing filler metal), and hot-pressed in a vacuum furnace under the joining conditions shown in Table 2 to obtain intermediate joined bodies in the shape of square bars. The deformation amount ΔL during joining at this time was calculated by dividing the cumulative length of the copper alloy members in the joining direction before joining by L. ０ , the length of the sample in the joining direction after joining L １ As a result, the following equation is obtained: ΔL = [(L ０ -L １ ) / L ０ ] × 100, and the results are shown in Table 2. A plurality of tensile test pieces were prepared for each example to perform various evaluations.

[0048] (4) Homogenization Treatment (Only for Examples 1b to 1d, 2b to 2f, 6b, and 7b) In Examples 1b to 1d, 2b to 2f, 6b, and 7b, prior to the subsequent solution treatment, the intermediate joined bodies that had been subjected to the hot pressing were subjected to a homogenization treatment (high-temperature soaking) at the temperatures shown in Table 3 for 8 hours, followed by furnace cooling.

[0049] (5) Solution Treatment The intermediate joined body obtained in (2) or (3) above was subjected to solution treatment by holding the copper alloy joined body in a molten salt bath at 930°C for 5 minutes, followed by water cooling.

[0050] (6) Aging Treatment The solution-treated intermediate joint body was subjected to aging treatment. This aging treatment was carried out by subjecting the copper alloy joint body to 1×10 －１ The copper alloys were then held in a vacuum furnace at 450°C for 3 hours (Examples 1a to 5) or at 500°C for 2 hours (Examples 6a to 7b) in a vacuum furnace with a vacuum of 100 Torr, followed by furnace cooling. In this manner, copper alloy joined bodies in the shape of round or square bars were obtained, which had been tempered by solution treatment and aging treatment (Examples 1a, 2a, 3 to 6a, and 7a) or homogenization treatment, solution treatment, and aging treatment (Examples 1b to 1d, 2b to 2f, 6b, and 7b).

[0051] (7) Evaluation The intermediate joined bodies as joined by the hot press and the copper alloy joined bodies obtained by the aging treatment (hereinafter collectively referred to as joined body samples) were evaluated as follows.

[0052] <Bonding strength> Each bonded sample was processed to prepare a test specimen conforming to ASTM E8M Specimen 3 so that the bonded portion was located at the center of the test specimen. Tensile tests were performed on these test specimens at 25°C and / or -196°C in accordance with ASTM E8M to measure the tensile strength (bonding strength), and then the fracture position was confirmed. The results are shown in Tables 3 and 4.

[0053] <Observation of the Joint Cross Section with a Laser Microscope> A cross section containing the joint of a joined specimen, which had been further subjected to solution treatment and aging treatment after joining, was cut and polished. The observation specimen was a section adjacent to the section from which the tensile test specimen was cut, which had undergone the same joining heat treatment process. The resulting cross section was etched with a mixture of 30-36% hydrogen peroxide and 29% ammonia water. The microstructure of the joined specimen was then observed at 500x magnification with a laser microscope (Keyence, VK-X100) to confirm the remaining joint interface. These images were then processed using an automatic image stitching function to obtain an image for image analysis. The laser microscope images (depth-composite images obtained with the laser microscope) were arranged to fit a rectangular cross section with a long side of 1200 μm and a short side of 200 μm (where the long side was parallel to the joint interface and the short side was perpendicular to the joint interface). Figures 3 to 5 show cross-sectional photographs obtained for Examples 1a to 7b.

[0054] <Proportion of discontinuous region at bonded interface line> The obtained laser microscope image was analyzed using image analysis software ImageJ according to the following procedure to determine the proportion (%) of the total length of the line segments corresponding to the discontinuous region to the total length of the bonded interface line.

[0055] (Operation procedure in ImageJ) - Step 1: Import the laser microscope image into the image analysis software ImageJ (see Figure 6A (a)). - Step 2: Cut out an area of ​​1200 μm x 200 μm that includes the bonded interface (this area is called the "region of interest"). - Step 3: Select the commands "Image" → "Type" → "16-bit" in that order to convert the image to "16-bit". - Step 4: Select the commands "Process" → "Filters" → "Gaussian Blur" in that order, and adjust the "Sigma (Radius)" value (for example, to 0.1) in the Gaussian blur function to reduce noise. Step 5: Select the commands "Image" → "Adjust" → "Threshold" in this order to adjust the threshold value and color the grain boundaries and bonded interfaces (see FIG. 6A(b)). At this time, the threshold value in the "Threshold" window is adjusted so that only the grain boundaries and bonded interfaces are selectively colored red (in this analysis, the threshold value was set to 140 or more), thereby selecting the areas corresponding to the grain boundaries and bonded interfaces. Step 6: With the grain boundaries and bonded interfaces colored, select the "Apply" command in the "Threshold" window to binarize the target area (see FIG. 6A(c)). Step 7: In the obtained binarized image, numerous perpendicular lines are synthesized at 5 μm intervals relative to the bonded interfaces (see FIG. 6B(d)). This perpendicular line synthesis can be performed using PowerPoint. Step 8: In the resulting composite image, areas where three or more adjacent perpendicular lines (i.e., a width of 10 μm or more) (at a 5 μm pitch) do not intersect with the remaining bonded interface are identified as discontinuous areas (see FIGS. 2A and 2B). Step 9: The image corresponding to the entire length (i.e., 1200 μm) of the bonded interface line defined along the bonded interface and the former bonded interface is enlarged, and discontinuous areas are visually selected. This discontinuous area selection is performed by adding measurement lines to each location identified as a discontinuous area in the enlarged image.Specifically, in ImageJ, select the commands [Edit] → [Add to Manager] → [ROI Manager] (or [Amalyze] → [Tools] → [ROI Manager]) in this order to launch the ROI Manager. Then, a straight line (see the icon shown in Figure 6B(e)) is drawn parallel to the bonded interface line in an area that contains three or more perpendicular lines (total width 10 µm) with a 5 µm pitch. A straight line is added by clicking [Add] in the ROI Manager window (Figure 6B(e)). In this way, multiple straight lines can be drawn. - Step 10: Click [Measure] in the ROI Manager window to automatically display the length of each straight line ( FIG. 6B(f) ). In this way, the total length of the line segments corresponding to the discontinuous region can be automatically calculated. - Step 11: Calculate the ratio of the total straight line length to the total length using the spreadsheet software Excel. That is, divide the obtained total length by the total length of the bonded interface line (i.e., 1200 μm) and multiply the result by 100 to calculate the ratio (%) of the total length of the line segments corresponding to the discontinuous region to the total length of the bonded interface line (i.e., 1200 μm).

[0056] <Charpy Impact Value> A Charpy impact test was performed in accordance with JIS Z 2242:2018 to measure the Charpy impact values ​​of the base metal and joint of the bonded specimen. The Charpy impact test was performed by processing the bonded specimen into a V-notch test specimen (55 mm long, 10 mm square cross section, V-notch at the center of the length, 45° notch angle, 2 mm notch depth, and 0.25 mm notch bottom radius) as specified in JIS Z 2242:2018, and measuring the Charpy impact value (absorbed energy) at 25°C or -196°C using a Charpy impact tester (Tokyo Koki Testing Instruments Co., Ltd., automatic Charpy impact tester CI-500D). The test specimen for measuring the Charpy impact value of the base metal was a V-notch formed in a base metal specimen separately prepared using the material used to fabricate the bonded specimen. On the other hand, the test specimens used to measure the Charpy impact value of the joints had a V-notch formed so that its tip was located at the joint interface of the joint. The test specimens with the V-notch tip located at the joint interface were prepared by first etching the joint sample with 30% nitric acid to identify the position of the joint interface, and then forming a V-notch so that the tip of the V-notch coincided with the position of the joint interface.

[0057] <Measurement of Electrical Conductivity and Conversion to Thermal Conductivity> The electrical conductivity (IACS%) of the bonded sample was measured at room temperature using an eddy current conductivity meter (product name: Hocking AutoSigma 3000DL, manufactured by GE Sensing & Inspection Technologies, Inc.) The obtained electrical conductivity was converted into thermal conductivity (W / mK) using a correlation equation based on the Wiedemann-Franz law.

[0058]

[0059]

[0060]

Claims

1. A copper alloy joined body comprising a plurality of age-hardenable copper alloy members that are diffusion-bonded together, wherein a bonded interface between the plurality of members remains, the age-hardenable copper alloy has a beryllium content of 0.7 wt% or less, and in a laser microscope image of a cross section including the bonded interface, the ratio of the total length of line segments corresponding to a discontinuous region to the total length of the bonded interface line defined along the bonded interface and the position of the former bonded interface is 3.5% or more, and the discontinuous region is defined as a region where, when a plurality of perpendicular lines are drawn at 5 μm intervals to the bonded interface line, three or more adjacent perpendicular lines do not intersect with the remaining bonded interface.

2. The copper alloy joined body according to claim 1, wherein the copper alloy joined body has been subjected to solution treatment and aging treatment.

3. A copper alloy joined body according to claim 1 or 2, wherein the strength of the joint portion of said copper alloy joined body is 70% or more of the strength of the base metal of said copper alloy joined body.

4. A copper alloy joined body according to claim 1 or 2, wherein the strength of the joint of said copper alloy joined body is 85% or more of the strength of the base metal of said copper alloy joined body.

5. A copper alloy joined body according to claim 1 or 2, which contains crystal grains of the age-hardenable copper alloy that have grown beyond the bonded interface or beyond the position of the former bonded interface.

6. A copper alloy joined body according to claim 1 or 2, wherein the joining interface or the former joining interface is free of residual components derived from materials other than the age-hardenable copper alloy.

7. A copper alloy joined body according to claim 1 or 2, wherein the strength of the base material and the joint of said copper alloy joined body is 520 MPa or more.

8. A copper alloy joined body according to claim 5, wherein the strength of the base material and the joint of said copper alloy joined body is 690 MPa or more.

9. A copper alloy joined body according to claim 1 or 2, wherein the joint of said copper alloy joined body has a joint strength of 85% or more of the strength of the base metal of said copper alloy joined body at a temperature of -196°C.

10. A copper alloy joined body according to claim 1 or 2, wherein the joint of said copper alloy joined body has a Charpy impact value of 15% or more of the Charpy impact value of the base metal of said copper alloy joined body at temperatures of 25°C and -196°C.

11. A copper alloy joined body according to claim 1 or 2, wherein the base material including the joining portion of said copper alloy joined body has a thermal conductivity of 209 W / mK or more.

12. A copper alloy joined body according to claim 1 or 2, wherein the electrical conductivity of the base material including the joint portion of said copper alloy joined body is 50 IACS% or more.

13. The age-hardenable copper alloy is selected from the group consisting of beryllium copper 11 alloy (JIS alloy number C1751, EN material number CW110C, and UNS alloy number C17510), beryllium copper 10 alloy (EN material number CW104C and UNS alloy number C17500), beryllium copper CuCo1Ni1Be (EN material number CW103C), and beryllium copper 14Z alloy (Be: 0.2 to 0.6 wt. %, Ni: 1.4 to 2. 4% by weight, Zr: 0-0.5% by weight, balance Cu and unavoidable impurities), beryllium copper 50 alloy (Be: 0.2-0.6% by weight, Ni: 1.4-2.1% by weight, Ag: 0.1-0.3% by weight, Zr: 0-0.5% by weight, balance Cu and unavoidable impurities), beryllium copper 10Zr alloy (Be: 0.4-0.7% by weight, Co: 2.0-2.8% by weight, Zr: 0-0.3% by weight, balance Cu and unavoidable impurities), Part Cu and unavoidable impurities), chromium copper (UNS alloy no. C18200), chromium zirconium copper (UNS alloy no. C18510 and EN material no. CW106C), zirconium copper (UNS alloy no. C15000, EN material no. CW120C), and Corson copper (EN material nos. CW109C, CW111C, UNS alloy nos. C19010, C70250, AMPCO944 ( 3. The copper alloy joined body according to claim 1, wherein the alloy is at least one selected from the group consisting of AMPCO940 (Ni: 6.5 to 7.5 wt %, Si: 1.5 to 2.5 wt %, Cr: 0.5 to 1.5 wt %, the balance being Cu and unavoidable impurities), and AMPCO940 (Ni: 1.5 to 3.0 wt %, Si: 0.5 to 1.5 wt %, Cr: 0.3 to 1.5 wt %, the balance being Cu and unavoidable impurities).

14. A copper alloy joined body according to claim 13, wherein the age-hardenable copper alloy is beryllium copper 11 alloy (JIS alloy number C1751, EN material number CW110C, and UNS alloy number C17510).

15. A copper alloy joined body according to claim 1 or 2, which has a flow path space therein.