Copper alloy

Abstract

To provide a Cu-Ni-Zn alloy that meets all of high proof stress, low Young's modulus, favorable solderability, low electrical conductivity, and a small difference between Young's modulus at room temperature and after heating in Young's modulus measurement using a resonance method.SOLUTION: A copper alloy contains Zn: 32 mass% or more and 45 mass% or less, Ni: more than 15 mass% and 30 mass% or less, Mn: 0.001 mass% or more and 7 mass% or less, 0.001 mass% or more and 0.45 mass% or less of at least one selected from the group consisting of Sn, Ag, Ti, Si, P, Cr, and Mg, and 0.2 mass% or less (including 0 mass%) of at least one selected from the group consisting of O, H, Bi, Pb, As, and Fe, the balance being Cu and unavoidable impurities, the alloy containing a β phase, and an arithmetic average value of an inscribed circle diameter of the β phase being less than 1000 nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to copper alloys. [Background technology]

[0002] Copper alloys have traditionally been used as conductive spring materials for devices such as relays, switches, and connectors. Among these copper alloys, Cu-Ni-Zn alloys (also called "nickel silver"), which have high strength and excellent corrosion resistance, are widely used. Patent Document 1 discloses an inexpensive Cu-Ni-Zn alloy with excellent stress relaxation properties. Patent Document 2 discloses a Cu-Ni-Zn alloy that has both strength and corrosion resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 62-243750 [Patent Document 2] Japanese Patent Application Publication No. 7-292427 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, advances in automotive peripheral monitoring technology and the increasing use of cameras in portable information terminals have led to a demand for cheaper, higher-performance cameras. These cameras employ a new technology in which the lens module is linearly driven by electromagnetic force and actively oscillates in response to vibrations in the housing. To enable this new technology, copper alloys are now required to have high yield strength, a low Young's modulus, good solderability, low electrical conductivity, and a small difference in Young's modulus between room temperature and after heating when measured using the resonance method.

[0005] In the prior art such as those disclosed in Patent Documents 1 and 2, no Cu-Ni-Zn alloy has been investigated that satisfies all of the following requirements: high yield strength, low Young's modulus, good solderability, low electrical conductivity, and a small difference in Young's modulus between room temperature and after heating when measured by the resonance method.

[0006] The present disclosure has been made in view of these circumstances, and one of its objectives is to provide a Cu-Ni-Zn alloy that satisfies all of the following requirements: high yield strength, low Young's modulus, good solderability, low electrical conductivity, and a small difference in Young's modulus between room temperature and after heating when measured by the resonance method. [Means for solving the problem]

[0007] Aspect 1 of the present invention is Zn: 32% by mass or more and 45% by mass or less, Ni: more than 15% by mass and not more than 30% by mass, Mn: 0.001 mass% or more and 7 mass% or less, One or more selected from the group consisting of Sn, Ag, Ti, Si, P, Cr, and Mg: 0.001% by mass or more and 0.45% by mass or less; and one or more selected from the group consisting of O, H, Bi, Pb, As, and Fe: 0.2 mass% or less (including 0 mass%), with the remainder consisting of Cu and inevitable impurities, The copper alloy contains a β phase, and the arithmetic mean value of the circumscribed circle diameter of the β phase is less than 1000 nm.

[0008] Aspect 2 of the present invention is Aspect 2 is the copper alloy according to aspect 1, wherein the area ratio of the β phase is 6.0 area % or more.

[0009] Aspect 3 of the present invention is A copper alloy according to aspect 1 or 2, wherein, in a top view of an indentation made by a regular square pyramidal indenter when a high-temperature Vickers hardness test is performed at a temperature of 500°C or higher but lower than the solvus temperature in accordance with Japanese Industrial Standard JIS Z2252-1991, the maximum distance between a rectangle formed by connecting four vertices of the indentation with straight lines and the outer periphery of the indentation is less than one-fifth the length of the longer of two diagonals of the indentation.

[0010] A fourth aspect of the present invention is The copper alloy according to any one of Aspects 1 to 3, which is in the form of a plate or a microsphere with a diameter of 1 mm or less. [Effects of the Invention]

[0011] According to an embodiment of the present invention, it is possible to provide a Cu-Ni-Zn alloy that satisfies all of the following requirements: high yield strength, low Young's modulus, good solderability, low electrical conductivity, and a small difference in Young's modulus between room temperature and after heating when measured by the resonance method. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a transmission electron microscope image of the copper alloy of Example Test No. 1. [Figure 2] FIG. 2 is an example of an SEM image of the copper alloy surface of Example Test No. 1 after a high-temperature Vickers hardness test in accordance with Japanese Industrial Standard JIS Z2252-1991 at a temperature of 500° C. or higher but lower than the solvus temperature. DETAILED DESCRIPTION OF THE INVENTION

[0013] The inventors have conducted research from various angles in order to realize a Cu-Ni-Zn alloy that satisfies all of the following requirements: high yield strength, low Young's modulus, good solderability, low electrical conductivity, and a small difference in Young's modulus between room temperature and after heating when measured by the resonance method.

[0014] It is generally known that when a high-melting-point element, such as Ni, is dissolved in copper, the Young's modulus increases in proportion to the amount of dissolved element. In order to achieve a low Young's modulus, the inventors first came up with the idea of ​​generating a β-phase intermetallic compound of Ni and Zn to reduce the amount of dissolved Ni in copper.

[0015] On the other hand, the small difference in Young's modulus between room temperature and after heating in Young's modulus measurement by the resonance method is thought to indicate the following properties. If the dislocation density is non-uniform in a copper alloy used for a spring, depending on the number of vibrations of the spring and / or the generated stress, the vibration energy of the spring may be absorbed by the metal structure of the spring, causing an error in the spring displacement, which may result in fatigue fracture and / or heat damage. On the other hand, if the dislocation density is non-uniform in a sample used for measuring Young's modulus by the resonance method, the absolute value of Young's modulus will be smaller under compression than under tension, resulting in a decrease in the average Young's modulus (hereinafter also simply referred to as "Young's modulus") measured under compression and tension. However, after heating (for example, to 150°C), recovery (annihilation and / or rearrangement of dislocations) occurs in the case of a Cu-Ni-Zn alloy, and the difference in Young's modulus is eliminated. In other words, in order to suppress fatigue fracture and / or heat damage in springs, it is necessary to suppress non-uniformity in dislocation density, and to do so, it is necessary to reduce the difference in Young's modulus between room temperature and after heating.

[0016] As a result of intensive research by the present inventors, it was found that by using a predetermined component composition, it is possible to achieve high yield strength, low Young's modulus, good solderability, and low electrical conductivity, while also being able to reduce the difference in Young's modulus between room temperature and after heating when measuring the Young's modulus using the resonance method by precipitating fine β phases of a predetermined size. This is thought to be because, while in conventional technology non-uniformity in dislocation density occurs due to the movement and accumulation of dislocations, in this embodiment the fine β phase can block the movement of dislocations in the copper alloy, thereby suppressing non-uniformity in dislocation density. The following provides details of each requirement stipulated by the embodiment of the present invention.

[0017] <Component composition> Preferably, the copper alloy according to an embodiment of the present invention contains Zn: 32% by mass or more and 45% by mass or less, Ni: more than 15% by mass and 30% by mass or less, Mn: 0.001% by mass or more and 7% by mass or less, one or more elements selected from the group consisting of Sn, Ag, Ti, Si, P, Cr, and Mg: 0.001% by mass or more and 0.45% by mass or less, and one or more elements selected from the group consisting of O, H, Bi, Pb, As, and Fe: 0.2% by mass or less (including 0% by mass), with the balance being Cu and unavoidable impurities. Each component will be described in detail below.

[0018] (Zn: 32% by mass or more and 45% by mass or less) The Zn content is set to 32 mass% or more to improve mechanical properties and form the desired β phase. However, excessive Zn makes it difficult to ensure cold workability. Therefore, the Zn content is set to 45 mass% or less.

[0019] (Ni: More than 15% by mass and 30% by mass or less) The Ni content is set to more than 15 mass% (for example, 15.1 mass% or more) to improve mechanical properties, corrosion resistance, and form the desired β phase. On the other hand, excessive Ni makes it difficult to ensure cold workability. Therefore, the Ni content is set to 30 mass% or less.

[0020] (Mn: 0.001 mass% or more and 7 mass% or less) The Mn content is set to 0.001% by mass or more to improve mechanical properties, corrosion resistance, solderability, and to form the desired β phase. However, excessive Mn makes it difficult to ensure hot workability. Therefore, the Mn content is set to 7% by mass or less.

[0021] (One or more selected from the group consisting of Sn, Ag, Ti, Si, P, Cr, and Mg: 0.001% by mass or more and 0.45% by mass or less) Sn, Ag, Ti, Si, P, Cr, and Mg act as deoxidizers to reduce the oxygen content in the copper alloy, allowing the mechanical property-improving effects of Ni, Mn, and Zn, and the corrosion resistance-improving effects of Ni and Mg to be fully utilized. Therefore, the content of any one or more elements selected from the group consisting of Sn, Ag, Ti, Si, P, Cr, and Mg is set to 0.001% by mass or more. On the other hand, excessive amounts of these elements can deteriorate cold workability. Furthermore, solderability may be deteriorated and the desired β phase may not be formed. Therefore, the content of any one or more elements selected from the group consisting of Sn, Ag, Ti, Si, P, Cr, and Mg is set to 0.45% by mass or less, preferably 0.30% by mass or less.

[0022] (One or more selected from the group consisting of O, H, Bi, Pb, As, and Fe: 0.2 mass% or less (including 0 mass%)) O, H, Bi, Pb, As, and Fe are elements that can be unavoidably present as impurities and degrade various properties. Therefore, the content of any one or more elements selected from the group consisting of O, H, Bi, Pb, As, and Fe is set to 0.2 mass% or less. In this specification, "including 0% by mass" means that it includes embodiments in which it is not intentionally added, i.e., cases in which the content is below the level of unavoidable impurities (it does not exclude cases in which it is intentionally added).

[0023] The copper alloy according to the embodiment of the present invention preferably includes the above-described composition, with the balance being Cu and inevitable impurities. The inevitable impurities include elements that are introduced due to the conditions of raw materials, materials, manufacturing equipment, etc. For example, O, H, Bi, Pb, As, and Fe are elements whose content is usually lower and therefore considered inevitable impurities, but whose composition ranges are separately specified as described above. Therefore, in this specification, the "unavoidable impurities" that constitute the balance are a concept that excludes elements whose composition ranges are separately specified.

[0024] <β phase> The copper alloy according to the embodiment of the present invention satisfies the above-mentioned composition and contains a β phase (body-centered cubic crystal) having an arithmetic mean value of the circumscribed circle diameter of less than 1000 nm, thereby effectively blocking the movement of dislocations in the copper alloy. As a result, the difference between the Young's modulus at room temperature and after heating can be reduced in Young's modulus measurement by the resonance method. When the arithmetic mean value of the circumscribed circle diameter of the β phase is 1000 nm or more, the Bauschinger effect is promoted, and the stress generated in response to compressive strain is significantly lower than the stress generated in response to tensile strain, resulting in a larger difference between the Young's modulus at room temperature and after heating in Young's modulus measurement by the resonance method. The arithmetic mean value of the circumscribed circle diameter of the β phase is more preferably 750 nm or less, and even more preferably 500 nm or less. Figure 1 is a transmission electron microscope image of an example described later. As shown in Figure 1, the β phase can be confirmed as a gray to black particulate phase in the transmission electron microscope image. The arithmetic mean value of the circumscribed circle diameter of the β phase can be determined by, for example, randomly selecting 50 or more β phases observed in a transmission electron microscope image (accelerating voltage 200 kV, magnification 60,000 times) and taking the arithmetic mean of the circumscribed circle diameters of these.

[0025] In this embodiment, the area ratio of the β phase is preferably 6.0 area% or more, and more preferably 7.0 area% or more. This can further reduce the difference in Young's modulus between room temperature and after heating when measuring the Young's modulus using a resonance method. On the other hand, the area ratio of the β phase is preferably less than 20 area%. This can suppress, for example, deterioration of mechanical properties due to the β phase being connected in a striped pattern and promotion of the Bauschinger effect. The copper alloy according to the embodiment of the present invention may be, for example, an α phase (face-centered cubic crystal) other than the β phase. The above area ratio can be calculated, for example, by observing a transmission electron microscope image (accelerating voltage 200 kV, magnification 60,000 times, field area 1.9 μm × 2.2 μm) to determine the area of ​​the β phase.

[0026] <Other characteristics> In the copper alloy according to this embodiment, when an indentation made with a regular pyramidal indenter is made by performing a high-temperature Vickers hardness test in accordance with Japanese Industrial Standard JIS Z2252-1991 at 500°C or higher and lower than the solvus temperature, the maximum distance between the rectangle formed by connecting the four vertices of the indentation with straight lines and the outer ridge of the indentation is preferably less than 1 / 5, and more preferably 1 / 10 or less, of the longer of the two diagonals of the indentation. This results in good hot workability at the test temperature (500°C or higher and lower than the solvus temperature) due to the presence of a β phase, etc. The solvus temperature can be measured by a known method.

[0027] FIG. 2 shows an example of an SEM image of the copper alloy surface after a high-temperature Vickers hardness test in accordance with Japanese Industrial Standard JIS Z2252-1991 at 500°C or higher but lower than the solvus temperature in Example (Test No. 1) described later. In FIG. 2, the inner diamond corresponds to "a rectangle formed by straight lines connecting the four vertices of the indentation made by a square pyramidal indenter in a top view" 1 (shown by a dashed line), and the outer line corresponds to "the peripheral ridge of the indentation" 2 (shown by a solid line). Of the maximum distances d1 to d4 between the four straight lines L1 to L4 connecting the four vertices of the indentation and the corresponding peripheral ridge, the maximum distance is preferably less than 1 / 5 of the length of the longer of the two diagonals X1 to X2 (shown by dashed lines). This indicates that the copper alloy undergoes almost no more than sinking when pressed with an indenter, demonstrating its excellent hot workability. On the other hand, a material with poor hot workability exhibits resistance (i.e., work hardening) when pressed with an indenter, causing a rise around the indentation, and therefore not satisfying the above-mentioned preferable requirements.

[0028] The shape of the copper alloy according to the embodiment of the present invention is not particularly limited, and may be a plate, a minute sphere with a diameter of 1 mm or less, or another shape.

[0029] In this embodiment, "high yield strength" refers to a 0.2% yield strength of 750 MPa or more when a tensile test is carried out as in the examples described later. Preferably, the 0.2% yield strength is 1000 MPa or more.

[0030] In this embodiment, "low Young's modulus" refers to a Young's modulus of 150 GPa or less when measured by a resonance method at room temperature as in the examples described later. Preferably, the Young's modulus is 130 GPa or less.

[0031] In this embodiment, "good solderability" refers to a solder wetted area of ​​80% or more when the solderability is evaluated as in the examples described later, and preferably, the solder wetted area is 90% or more.

[0032] In this embodiment, "low conductivity" refers to a conductivity of 15% IACS or less when measured as in the examples described below, and preferably a conductivity of 10% IACS or less.

[0033] In this embodiment, "the difference between Young's modulus at room temperature and after heating is small when measured by the resonance method" means that when Young's modulus is measured by the resonance method as in the examples described later, the difference between Young's modulus at room temperature and after heating to 150°C is 5 GPa or less. Preferably, the difference in Young's modulus is 2 GPa or less.

[0034] In this embodiment, the tensile strength when subjected to a tensile test as in the Examples described later is preferably 850 MPa or more, more preferably 1000 MPa or more. Also, in this embodiment, the Vickers hardness when measured as in the Examples described later is preferably 200 HV or more, more preferably 300 HV or more. These factors result in a copper alloy with higher strength.

[0035] In this embodiment, the elongation when subjected to a tensile test as in the examples described later is preferably 8% or more, and more preferably 9% or more, thereby obtaining a copper alloy with excellent cold workability.

[0036] In this embodiment, after further cold rolling (from 0.25 mm thickness to 0.2 mm thickness) as in the examples described later, the difference in Young's modulus between room temperature and after heating at 150°C is preferably 10 GPa or less, more preferably 2 GPa or less, in Young's modulus measurement by a resonance method. This means that the copper alloy can be said to have more suppressed non-uniformity in dislocation density.

[0037] A method for producing a copper alloy according to an embodiment of the present invention includes: (A) preparing a copper alloy having the above-described composition; (B) a first heating step of heating the copper alloy to a solvus temperature +100°C or higher; (C) after the first heating step, a step of cooling to 100°C or less at an average cooling rate of 80°C / second or more; (D) a second heating step of heating to 350°C or higher and 550°C or lower after the cooling step; Includes: Each step will be described in detail below.

[0038] (A) Preparation of copper alloy First, a copper alloy (e.g., a copper alloy ingot) having the above-described composition is prepared by a known method. For example, the copper alloy having the above-described composition can be melted in a cryptor furnace under a charcoal cover and in the air, and then an ingot can be cast.

[0039] In order to facilitate obtaining a desired cooling rate in the cooling step described below, it is preferable to hot roll and / or cold roll the sheet to a thickness of 1 mm or less. When hot rolling is performed, it is preferable to heat the steel to a temperature of 500°C or higher but lower than the solvus temperature. At 500°C or higher but lower than the solvus temperature, the steel contains a β-phase and has improved hot workability if it has the above-mentioned chemical composition. More preferably, hot rolling is performed at a test temperature at which a high-temperature Vickers hardness test conforming to Japanese Industrial Standard JIS Z2252-1991 is performed at 500°C or higher but lower than the solvus temperature, and an indentation made with a regular square pyramidal indenter is formed. When viewed from above, the maximum distance between the rectangle formed by connecting the four vertices of the indentation with straight lines and the outer ridge of the indentation is less than 1 / 5 (even 1 / 10 or less) of the longer of the two diagonals of the indentation. After hot rolling, both surfaces may be chamfered as appropriate to remove oxide scale. When cold rolling, it is preferable to first heat the steel to a temperature 100°C above the solvus temperature (below the liquidus temperature) and then rapidly cool it in water to 100°C or below. This makes it easier to obtain a single α phase, improving cold workability. The solvus temperature and liquidus temperature can be measured by known methods.

[0040] (B) First heating step A copper alloy having the above-mentioned composition is heated to a temperature above the solvus temperature + 100°C (below the liquidus temperature). This results in a uniform α-phase. The holding time is not particularly limited and may be, for example, 10 seconds or more.

[0041] (C) Cooling process After the first heating step, the steel is cooled to 100°C or less at an average cooling rate of 80°C / sec or more. This allows the α-phase obtained above to be maintained. After the cooling step, cold rolling may be performed as appropriate before the second heating step described below.

[0042] (D) Second heating step After the first cooling step, the material is heated to 350°C or higher and 550°C or lower. This allows fine β phases to be formed. The holding temperature at 350°C or higher and 550°C or lower is preferably 30 minutes or longer. This allows the area ratio of the β phase to be increased.

[0043] After the second heating step, the material may be cooled to room temperature, for example, by air cooling, etc. After cooling, cold rolling may be carried out as appropriate.

[0044] The method for producing a copper alloy according to an embodiment of the present invention may include other steps within the scope of the present disclosure, for example, a step of processing the copper alloy into a desired shape (e.g., microspheres of 1 mm or less). [Example]

[0045] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention. [Example]

[0046] Copper alloys having predetermined compositions were melted in a Cryptor furnace under a charcoal cover and in the atmosphere to obtain ingots with a thickness of 45 mm having the compositions shown in Test Nos. 1 to 12 in Table 1. After the surface of each ingot was chamfered, a 20 mm long x 3 mm wide x 6 mm high hot hardness test piece was taken from each ingot except for No. 10, and a high-temperature Vickers hardness test conforming to Japanese Industrial Standard JIS Z2252-1991 was performed using a high-temperature Vickers hardness microscope manufactured by INTESCO under the temperature conditions shown in Table 2. Then, when viewed from above in an indentation made by a regular square pyramidal indenter, the ratio R of the maximum distance between the rectangle formed by connecting the four vertices of the indentation with straight lines and the outer rim of the indentation to the length of the longer of the two diagonals of the indentation was determined. Separately from the high-temperature Vickers hardness test, each ingot was hot-rolled to a thickness of 15 mm under the same temperature conditions as the high-temperature Vickers hardness test. After hot rolling, it was quenched (quenched in water). After quenching, both sides were chamfered by 1 mm to a thickness of 13 mm, after which a first cold rolling (rough cold rolling) was performed to reduce the thickness to 4 mm except for Test No. 10, which was reduced to 1 mm. The results are shown in Table 2.

[0047] [Table 1]

[0048] [Table 2]

[0049] The results in Table 2 reveal the following: Test Nos. 1 to 3 and 9 to 12 satisfied the desired component composition of this embodiment while also satisfying the preferable requirement of R being less than 1 / 5 (less than 0.2), and therefore the hot rolling results and cold rolling results were good.

[0050] Test No. 4 contained 15 mass% or less Ni and was an α single-phase alloy. Due to the high concentration of Ni added, the high-temperature deformation resistance was high, and work hardening was saturated. As a result, R became 0.2 or more, and it is thought that the hot workability was reduced.

[0051] Test No. 5 contained Ni in excess of 30 mass %, which is thought to have caused the deterioration in cold workability.

[0052] Test No. 6 contained more than 45 mass % Zn, which is thought to have caused the deterioration in cold workability.

[0053] Test No. 7 had a Zn content of less than 32 mass% and was an α single-phase alloy. It had high high-temperature deformation resistance and saturated work hardening, resulting in an R of 0.2 or more, which is thought to have reduced hot workability.

[0054] In Test No. 8, the Mn content exceeded 7 mass %, which is thought to have promoted the generation of hydrogen voids and reduced the hot workability.

[0055] In the above, a high-temperature Vickers hardness test was conducted before the final shape, but even if a similar high-temperature Vickers hardness test was conducted after the fourth cold rolling described below, it is believed that the same result (R) would be obtained due to the inclusion of the β phase.

[0056] Hereafter, only copper alloys that had good hot rolling properties and cold rolling properties in Table 2 were evaluated. After the first cold rolling, all the alloys except for Test No. 10, which was already 1 mm thick, were heated to 900°C, held for 1 minute, and then quenched in water. After quenching in water, the alloys were subjected to a second cold rolling to a thickness of 1 mm.

[0057] After the second cold rolling, the copper alloy was heated to 900°C (i.e., the two-phase (α+β) region temperature +100°C or higher) in a salt bath furnace and held there for 30 seconds (corresponding to the "first heating step" in the manufacturing method of the copper alloy according to this embodiment), and then water quenched at an average cooling rate of 80°C / second or higher (corresponding to the "first cooling step" in the manufacturing method of the copper alloy according to this embodiment). After water quenching, the copper alloy was subjected to third cold rolling to a thickness of 0.75 mm.

[0058] After the third cold rolling, the copper alloy was heated to 400°C and held there for 2 hours (corresponding to the "second heating step" in the manufacturing method of the copper alloy according to this embodiment). After the second heating step, the copper alloy was air-cooled to room temperature (corresponding to the "second cooling step" in the manufacturing method of the copper alloy according to this embodiment). After the second cooling step, the copper alloy was subjected to fourth cold rolling to a thickness of 0.25 mm to obtain each copper alloy. Various measurements were carried out on each copper alloy.

[0059] (β phase observation) Observation of the β phase was performed before the fourth cold rolling (after the second heating step and air cooling to room temperature). The copper alloy sheets were mechanically polished from 1 mm to 0.1 mm thick. Then, a thin film for transmission electron microscopy (TEM) was prepared using a Struers TenuPol-5 electrolytic polishing system with a 30% nitric acid / 70% sulfuric acid mixture as the electrolyte. Images of the thin film were taken using a Hitachi H-800 transmission electron microscope at an accelerating voltage of 200 kV and a magnification of 60,000 times. The area fraction of the β phase within a rectangular observation field of 1.9 μm × 2.2 μm was calculated. The area fraction was determined by placing a piece of tracing paper with a 1 mm grid on the TEM image, tracing over the β phase, and calculating the total area of ​​the β phase. This was then divided by 1.9 μm × 2.2 μm. As an example, Figure 1 shows a transmission electron microscope image of Test No. 1. In Figure 1, the black or gray particulate matter is finely dispersed β phase. The circumscribed circle diameter of the observed β phase was at most 500 nm or less, and it can be said that the arithmetic mean value of the circumscribed circle diameter of the β phase was also 500 nm or less. Similarly, the arithmetic mean value of the circumscribed circle diameter of the β phase was also 500 nm or less for the other samples. After observing the β phase, a fourth cold rolling was performed to reduce the thickness from 0.75 mm to 0.25 mm. However, after the fourth cold rolling, the α phase was preferentially subjected to elongation deformation, and the fine β phase was hardly deformed, so it is thought that the arithmetic mean value of the circumscribed circle diameter and the area ratio of the β phase remained unchanged.

[0060] (mechanical properties) JIS No. 5 tensile test specimens were machined so that the longitudinal direction was parallel to the rolling direction (LD) of the plate material, and tensile tests were conducted in accordance with JIS-Z2241 to measure tensile strength, yield strength, and elongation. Here, the yield strength was defined as the tensile strength equivalent to a permanent elongation of 0.2%.

[0061] (Conductivity measurement) The conductivity measurements were performed in accordance with the JIS standard for measuring the conductivity of non-ferrous metal materials, using the four-terminal method with a double bridge.

[0062] (Hardness measurement at room temperature) The hardness at room temperature was measured in accordance with the microhardness test method specified in JIS-Z2251, and Vickers hardness was measured with a test load of 500 g (4.9 N).

[0063] (solderability) Solderability was evaluated by the solder wettability area. A Rhesca Meniscograph solder wettability tester was used, and lead-free solder consisting of Sn-3%Ag-0.5%Cu was used. Before soldering, non-activated rosin-based flux α100 manufactured by Japan Alpha Metals was applied. The soldering temperature was 260°C, the solder immersion time was 5 seconds, the solder immersion depth was 10 mm, and the solder immersion speed was 5 mm / second. After soldering, the specimen was cleaned with alcohol and wiped dry. Then, tracing paper with a 1 mm grid was placed on the specimen, and the number of squares corresponding to the area of ​​the solder repellent was counted. Complete wetness was considered to be 100%.

[0064] (Young's modulus measurement using the resonance method) A JE-HT manufactured by Nippon Technoplus was used for the measurements. The test specimen was arranged as follows: a metal plate 10 mm wide, 0.25 mm thick, and 45 mm long was placed so that the plate surface was horizontal. Two nodes that would become nodes during bending resonance were suspended by thin Invar wires. Bending vibration was induced by an electrostatic induction transducer installed on the underside of the metal plate, and the vibration of the metal plate was monitored by an adjacent non-contact sensor. A thermocouple was installed immediately adjacent to the test specimen, and the temperature measured by this thermocouple was taken as the actual temperature. The measurements were carried out in a metal chamber with nitrogen gas circulating. Young's modulus E was calculated using the following equation (1): f=1.028×10 6 ×t / L 2 ×√(2E / ρ) (1) where f is the resonant frequency, L (m) is the specimen length, and ρ is the density (g / m 3 ), and t is the plate thickness (m). The resonance frequency f was determined by sweeping the frequency at which the resonance was sharpest on an oscilloscope. The test specimens were 10 mm wide and were the same as those specified in the Japan Copper and Brass Association technical standards JCBA T308 "Test method for fatigue properties of thin plates and strips," JCBA T309 "Test method for stress relaxation by bending of thin plate strips," and JCBA T312 "Measurement method for bending deflection coefficient of plate strips using a cantilever beam," and were cut to a length of 45 mm. The above measurements were carried out after the fourth cold rolling and after the fifth cold rolling to a thickness of 0.25 mm to 0.2 mm. The results are shown in Table 3.

[0065] [Table 3]

[0066] The following can be seen from Table 3. The copper alloys of Test Nos. 1 to 3 and 12 met all the requirements specified in this embodiment, and therefore met all of the requirements of high yield strength, low Young's modulus, good solderability, low electrical conductivity, and a small difference in Young's modulus between room temperature and after heating (5 GPa or less) in Young's modulus measurement by the resonance method. Furthermore, Test Nos. 1 to 3 met the preferable requirement of a β phase area fraction of 7.0% or more, and therefore the difference in Young's modulus between room temperature and after heating was even smaller (2 GPa or less).

[0067] Test No. 9 had an insufficient Mn content of less than 0.001 mass %, and was therefore inferior in solderability.

[0068] Test No. 10 had an excessive Ti content of 3.1 mass parts, which resulted in poor solderability. It also did not have a β phase, and the Young's modulus measured by the resonance method showed a large difference between the Young's modulus at room temperature and after heating.

[0069] Test No. 11 had low yield strength due to insufficient Ni and Zn contents. [Explanation of symbols]

[0070] 1 A quadrilateral formed by connecting the four vertices of the indentation with straight lines 2. Outer ridge of the indentation

Claims

1. Zn: 32% by mass or more and 45% by mass or less, Ni: more than 15% by mass and not more than 30% by mass, Mn: 0.001% by mass or more and 7% by mass or less, One or more elements selected from the group consisting of Sn, Ag, Ti, Si, P, Cr, and Mg: 0.001% by mass or more and 0.45% by mass or less; and one or more elements selected from the group consisting of O, H, Bi, Pb, As, and Fe: 0.2% by mass or less (including 0% by mass), with the balance consisting of Cu and inevitable impurities; A copper alloy comprising a β phase, wherein the arithmetic mean value of the circumscribed circle diameter of the β phase is less than 1000 nm.

2. 2. The copper alloy according to claim 1, wherein the area ratio of the β phase is 6.0 area % or more.

3. 3. The copper alloy according to claim 1, wherein, in a top view of an indentation made by a regular square pyramidal indenter formed by performing a high-temperature Vickers hardness test in accordance with Japanese Industrial Standard JIS Z2252-1991 at a temperature of 500°C or higher but lower than the solvus temperature, the maximum distance between a rectangle formed by connecting four vertices of the indentation with straight lines and a peripheral ridge line of the indentation is less than 1 / 5 of the length of the longer of two diagonals of the indentation.

4. 3. The copper alloy according to claim 1 or 2, which is in the form of a plate or a microsphere having a diameter of 1 mm or less.

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