Copper alloy and component for electronic and electrical equipment

Abstract

To provide a copper alloy that exhibits superior strength and heat resistance and is usable stably even under high-temperature conditions, and a component for electronic and electrical equipment comprising the copper alloy.SOLUTION: A copper alloy contains 1.5 atom% or more and 2.7 atom% or less of Mg, further contains, as an additional element, one selected from Si of 1 atom% or more and 8 atom% or less and Zn of 5 atom% or more and 25 atom% or less, the balance being Cu and inevitable impurities. The number density of precipitate particles having an equivalent circle diameter of 10 nm or more and 50 nm or less is 75 particles / μm2 or more. Under the condition of holding at 400°C for 2 hours, the Vickers hardness H1 after heat treatment is at least 55% of the Vickers hardness H0 before heat treatment, and the Vickers hardness H0 before heat treatment is 160 HV or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a copper alloy suitable for use in home appliances, semiconductor parts such as lead frames, printed wiring boards, heat sinks, switch parts, bus bars, connectors, and other electric and electronic device parts, and to electric and electronic device parts made of this copper alloy. [Background technology]

[0002] Conventionally, copper or copper alloys having excellent electrical conductivity have been used for electronic and electric device components such as terminals, bus bars, lead frames, and heat dissipation members. In recent years, with the miniaturization of electronic devices, electric devices, etc., efforts are being made to make electronic and electric device parts, such as terminals of connectors, relays, lead frames, etc., used in these electronic devices, electric devices, etc., smaller and thinner. Furthermore, electronic devices and electric devices are sometimes used in high-temperature environments, such as the engine compartment of an automobile. For this reason, copper alloys with excellent strength and heat resistance are required as materials for constituting parts of electronic and electric devices.

[0003] Here, as copper alloys to be used for electronic and electric device parts such as terminals of connectors, relays, and lead frames, for example, Patent Document 1 proposes a Cu-Mg-Zn-B alloy. In this Cu-Mg alloy, solution treatment and precipitation treatment are performed to precipitate intermetallic compounds consisting of Cu and Mg, and precipitation hardening makes it possible to obtain relatively high electrical conductivity and strength.

[0004] Moreover, Patent Document 2 proposes a work-hardening copper alloy of a Cu-Mg supersaturated solid solution produced by subjecting a Cu-Mg alloy to solution treatment and then quenching it. This Cu-Mg alloy has an excellent balance of strength, electrical conductivity, and bendability, making it particularly suitable as a material for the above-mentioned electronic and electrical device parts. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 07-018354 [Patent Document 2] JP 2013-104096 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the Cu-Mg alloy described in Patent Document 1, many coarse intermetallic compounds mainly composed of Cu and Mg are dispersed in the matrix, and therefore there is a risk that the heat resistance will be insufficient. In addition, in the Cu-Mg alloy described in Patent Document 2, if the Mg content is increased to improve strength, there is a risk that the alloy will segregate during casting to form a non-uniform structure, resulting in a significant decrease in workability. Also, there is a risk that coarse precipitates will form during heat treatment, resulting in insufficient heat resistance.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a copper alloy which has excellent strength and heat resistance and can be stably used even in high-temperature environments, and electronic / electrical device parts made of this copper alloy. [Means for solving the problem]

[0008] In order to solve the above problems, the copper alloy of the first aspect of the present invention contains 1.5 atomic % or more and 2.7 atomic % or less of Mg, and further contains, as an additive element, any one of 1 atomic % or more and 8 atomic % or less of Si and 5 atomic % or more and 25 atomic % or less of Zn, with the balance being Cu and unavoidable impurities, and has a number density of precipitate particles having a circle equivalent diameter of 10 nm or more and 50 nm or less of 75 particles / μm 2 The Vickers hardness H1 after heat treatment under conditions of holding at 400°C for 2 hours is 55% or more of the Vickers hardness H0 before heat treatment, and the Vickers hardness H0 before heat treatment is 160 HV or more.

[0009] According to the copper alloy of the first aspect of the present invention, the composition contains 1.5 atomic % or more and 2.7 atomic % or less of Mg, and further contains, as an additive element, any one of 1 atomic % or more and 8 atomic % or less of Si and 5 atomic % or more and 25 atomic % or less of Zn, with the balance being Cu and unavoidable impurities, so that the additive element is contained in the precipitate particles, and when the precipitate particles are formed, the additive element also needs to aggregate, which retards the growth of the precipitate particles and disperses fine precipitate particles. As a result, the number density of precipitate particles with a circle equivalent diameter of 10 nm to 50 nm was 75 particles / μm 2 Since it is considered to have a strength and heat resistance of at least 100%, it has excellent heat resistance and strength.

[0010] In addition, the Vickers hardness H0 before heat treatment is 160HV or more, so it is certainly excellent in strength. Furthermore, when the material is heat-treated at 400°C for two hours, its Vickers hardness H1 after heat treatment is at least 55% of its Vickers hardness H0 before heat treatment. This means that the hardness does not decrease even when the material is held at high temperatures, ensuring excellent heat resistance.

[0011] The copper alloy of the present invention in accordance with the second aspect is characterized in that, in the copper alloy of the first aspect of the present invention, when the point at which the precipitate particle has the maximum length is taken as the major axis and the point at which the precipitate particle has the maximum length in a direction perpendicular to the major axis is taken as the minor axis, the minor axis length L2 is 25 nm or less, and the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is 3 or more.

[0012] According to the copper alloy of the second aspect of the present invention, the size and shape of the precipitate particles are such that the minor axis length L2 is 25 nm or less, and the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is 3 or more. Therefore, fine precipitate particles having a high aspect ratio are dispersed, and the strength and heat resistance are particularly excellent.

[0013] The copper alloy of the third aspect of the present invention is characterized in that, in the copper alloy of the first or second aspect of the present invention, the O concentration is 2 massppm or less and the S concentration is 10 massppm or less. According to the copper alloy of the third aspect of the present invention, the O concentration is 2 massppm or less and the S concentration is 10 massppm or less, so that the reaction of Mg with O (oxygen) and S (sulfur) is suppressed, fine precipitate particles containing Mg can be sufficiently precipitated, and the strength and heat resistance are particularly excellent. In addition, the generation of magnesium oxide and magnesium sulfide can be suppressed, and the processability is particularly excellent.

[0014] A part for electronic / electrical devices according to a fourth aspect of the present invention is characterized in that it is made of the copper alloy according to any one of the first to third aspects of the present invention. According to the electronic / electrical device part of the fourth aspect of the present invention, since it is made of the copper alloy of any one of the first to third aspects of the present invention, it can exhibit excellent properties even in a high-temperature environment. Effect of the Invention

[0015] It is possible to provide a copper alloy that has excellent strength and heat resistance and can be stably used even in high-temperature environments, and electronic / electrical device parts made of this copper alloy. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is an explanatory diagram of precipitate particles in the copper alloy according to the present embodiment. [Diagram 2] FIG. 1 is a flow diagram of a method for producing a copper alloy according to an embodiment of the present invention. [Diagram 3] 1 is an observation photograph of precipitate particles in Example 3 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A copper alloy and an electronic / electric device part according to one embodiment of the present invention will be described below. The copper alloy of this embodiment contains 1.5 atomic % or more and 2.7 atomic % or less of Mg, and further contains, as an additive element, one of the following elements: 1 atomic % or more and 8 atomic % or less of Si, or 5 atomic % or more and 25 atomic % or less of Zn, with the balance being Cu and unavoidable impurities. Furthermore, in the copper alloy of this embodiment, it is preferable that the O concentration contained as the unavoidable impurities is 2 massppm or less, and the S concentration is 10 massppm or less.

[0018] In the copper alloy according to the present embodiment, as shown in FIG. 1, precipitate particles 12 containing Mg and additive elements are dispersed in a copper matrix 11, and the number density of the precipitate particles having a circle equivalent diameter of 10 nm to 50 nm is 75 particles / μm 2 This is said to be the above. Furthermore, in the copper alloy of this embodiment, as shown in FIG. 1, when the point at which the precipitate particle 12 has the maximum length is defined as the long axis and the point at which the precipitate particle has the maximum length in a direction perpendicular to the long axis is defined as the short axis, it is preferable that the short axis length L2 is 25 nm or less and the ratio L1 / L2 of the long axis length L1 to the short axis length L2 is 3 or more.

[0019] In addition, in the copper alloy of this embodiment, the Vickers hardness H1 after heat treatment under conditions of holding at 400°C for 2 hours is 55% or more of the Vickers hardness H0 before heat treatment, and the Vickers hardness H0 before heat treatment is 160 HV or more.

[0020] The reasons for specifying the component composition, precipitate particles, and characteristics of the copper alloy of this embodiment as described above will be explained below.

[0021] (Mg) Mg dissolves in the matrix 11 and generates precipitate particles 12 together with Cu and the additive elements. The precipitate particles 12 are dispersed in the matrix 11, thereby making it possible to improve the strength and heat resistance. If the Mg content is less than 1.5 atomic %, precipitate particles are not generated sufficiently, and the effect of improving strength and heat resistance may be insufficient, whereas if the Mg content exceeds 2.7 atomic %, a large amount of eutectic structure is formed during casting, and workability may be deteriorated. Therefore, in this embodiment, the Mg content is set within the range of 1.5 atomic % to 2.7 atomic %. In order to ensure that the above-mentioned effects are achieved, the lower limit of the Mg content is preferably 1.6 atomic % or more, and more preferably 1.7 atomic % or more. In order to reliably prevent a large amount of eutectic structure from being generated during casting, the upper limit of the Mg content is preferably 2.6 atomic % or less, and more preferably 2.5 atomic % or less.

[0022] (Additional element) Since the additive elements Si and Zn are contained in the precipitate particles 12, the additive elements (Si, Zn) also need to aggregate when the precipitate particles 12 are formed, so the growth of the precipitate particles 12 is delayed and the fine precipitate particles 12 are dispersed. This makes it possible to improve the strength and heat resistance. Here, if the Si content is less than 1 atomic % or the Zn content is less than 5 atomic %, the amount of additive element contained in the precipitate particles 12 is small, and there is a risk of the precipitate particles 12 becoming coarse. On the other hand, if the Si content exceeds 8 atomic % or the Zn content exceeds 25 atomic %, there is a risk of the manufacturability being significantly reduced. Therefore, in this embodiment, the content of the additive element Si is set within the range of 1 atomic % to 8 atomic %, and the content of Zn is set within the range of 5 atomic % to 25 atomic %.

[0023] In order to ensure the above-mentioned effects, the lower limit of the content of the additive element Si is preferably 2 atomic % or more, more preferably 4 atomic % or more, and the upper limit of the content of the additive element Si is preferably 7 atomic % or less, more preferably 6 atomic % or less. Furthermore, the lower limit of the content of the additive element Zn is preferably 8 atomic % or more, and more preferably 15 atomic % or more, and the upper limit of the content of the additive element Zn is preferably 24 atomic % or less, and more preferably 22 atomic % or less.

[0024] (O,S) If the content of O and S, which are inevitable impurities, becomes large, Mg reacts with O and S and is consumed, which may result in a failure to generate a sufficient number of precipitate particles 12. Furthermore, if a large amount of magnesium oxide or magnesium sulfide is generated, these may become inclusions and cause a decrease in workability. Therefore, in this embodiment, it is preferable that the O concentration is 2 massppm or less and the S concentration is 10 massppm or less. The O concentration is more preferably 1 massppm or less, and even more preferably 0.5 massppm or less. The S concentration is more preferably 7 massppm or less, and even more preferably 5 massppm or less. There is no particular lower limit for the O concentration and the S concentration.

[0025] (Number density of precipitate particles) In the copper alloy of this embodiment, the number density of the precipitate particles 12 having a circle equivalent diameter of 10 nm or more and 50 nm or less is 75 particles / μm 2 As a result of the above and the sufficient dispersion of the fine precipitate particles 12, it is possible to improve the strength and heat resistance. The number density of precipitate particles 12 having a circle equivalent diameter of 10 nm or more and 50 nm or less is 100 particles / μm 2 More preferably, 120 particles / μm 2 More preferably, it is 140 particles / μm or more. 2 More preferably, it is equal to or greater than this.

[0026] (Shape of precipitate particles) In the copper alloy of this embodiment, as shown in Fig. 1, when the maximum length of the precipitate particle 12 is defined as the major axis and the point at which the maximum length in the direction perpendicular to the major axis is defined as the minor axis, it is preferable that the minor axis length L2 is 25 nm or less and the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is 3 or more. That is, as shown in Fig. 1, the precipitate particle 12 is rod-shaped with a large aspect ratio and its minor axis length L2 is preferably 25 nm or less. By sufficiently dispersing the precipitate particles 12 having such a shape, it becomes possible to reliably improve the strength and heat resistance.

[0027] (Vickers hardness before and after heat treatment) In the copper alloy of this embodiment, when the Vickers hardness H1 after heat treatment under conditions of holding at 400°C for 2 hours is 55% or more of the Vickers hardness H0 before heat treatment, and the Vickers hardness H0 before heat treatment is 160 HV or more, the copper alloy has sufficient strength and heat resistance. The Vickers hardness H0 before the heat treatment is more preferably 180 HV or more, and even more preferably 210 HV or more. Furthermore, the Vickers hardness H1 after heat treatment under conditions of holding at 400° C. for 2 hours is more preferably 60% or more, and even more preferably 75% or more of the Vickers hardness H0 before heat treatment.

[0028] Next, an example of a method for producing the copper alloy according to this embodiment will be described with reference to the flow chart shown in FIG.

[0029] (Melting and casting process S01) First, Mg and additive elements (Si, Zn) are added to the molten copper obtained by melting the copper raw material to adjust the composition, and a molten copper alloy is produced. In addition, elemental elements, mother alloys, etc. can be used to add various elements. In addition, raw materials containing various elements may be melted together with the copper raw material. In addition, recycled materials and scrap materials of this alloy may be used. Here, the molten copper is preferably so-called 4NCu, which has a purity of 99.99 mass% or more, or so-called 5NCu, which has a purity of 99.999 mass% or more. Then, the molten copper alloy with the adjusted composition is poured into a mold to produce an ingot. In addition, when considering mass production, it is preferable to use a continuous casting method or a semi-continuous casting method.

[0030] (Hot processing process S02) Next, hot working is performed to shape the resulting copper alloy ingot into the desired size. The introduction of strain and dynamic recrystallization destroy the cast structure and increase the homogeneity of the material. To obtain sufficient homogeneity, a total working rate of 50% or more is desirable. It is preferable that this hot working step S02 is carried out in a non-oxidizing or reducing atmosphere.

[0031] (First solution heat treatment step S03) Next, a heat treatment is carried out for the purpose of solution treatment. Macroscopic segregation from the casting process remains, so there are some uneven concentrations of Mg and added elements (Si, Zn). If solution treatment is not performed sufficiently, sufficient precipitate particles will not be obtained in low-concentration areas after the final process, resulting in reduced hardness and heat resistance. Also, in high-concentration areas, partial melting of the material will occur if heat treatment is performed at a high temperature, so the solution treatment temperature should be 700°C or lower. To prevent precipitation during cooling, the cooling rate from the solution treatment temperature to 200°C should be 300°C / min or higher. The oxygen concentration in the atmosphere is preferably 0.01 to 200 volppm. Within this range, a thin oxide film of Mg is generated on the surface, which can prevent Mg from volatilizing from the surface, and at the same time, no scale, which is a strong oxide film, is generated, making surface cutting unnecessary. If the oxygen concentration is too high, oxidation will generate scale on the surface, which will require surface cutting, resulting in a decrease in product yield. Furthermore, since Mg is consumed by the oxide, sufficient precipitate particles cannot be obtained after the final process, and hardness and heat resistance will decrease. If the oxygen concentration is too low, a thin oxide film of Mg will not be generated on the surface, and Mg will volatilize from the surface, reducing the homogeneity of the material.

[0032] (Cold working process S04) Next, cold working is performed to form a desired shape. The working method is not particularly limited, but rolling, drawing, extrusion, groove rolling, etc. may be applied.

[0033] (Second solution heat treatment step S05) Next, heat treatment is performed again for the purpose of solutionization. In order to obtain a high-strength alloy by finely precipitating precipitate particles 12 consisting of Cu, Mg, and additive elements (Si, Zn), not only microscopic homogeneity but also high homogeneity from the surface to the entire inside of the material is required. For this reason, it is necessary to perform heat treatment multiple times at high temperatures to diffuse Mg and the additive elements. Since melting due to macroscopic segregation during casting is suppressed in the first solution heat treatment step S03, the solution heat treatment temperature in the second solution heat treatment step S05 is preferably 700° C. or higher and 800° C. or lower. In order to prevent precipitation during cooling, the cooling rate from the solution heat treatment temperature to 200° C. is preferably 300° C. / min or higher. The oxygen concentration in the atmosphere is preferably 0.01 to 200 volppm. Within this range, a thin oxide film of Mg is generated on the surface, which can prevent Mg from volatilizing from the surface, and at the same time, no scale, which is a strong oxide film, is generated, making surface cutting unnecessary. If the oxygen concentration is too high, oxidation will generate scale on the surface, which will require surface cutting, resulting in a decrease in product yield. Furthermore, since Mg is consumed by the oxide, sufficient precipitate particles cannot be obtained after the final process, and hardness and heat resistance will decrease. If the oxygen concentration is too low, a thin oxide film of Mg will not be generated on the surface, and Mg will volatilize from the surface, reducing the homogeneity of the material.

[0034] (Warm processing process S06) Next, warm working is performed. By performing warm working, it is possible to suppress uneven distribution of dislocations and promote fine precipitation while forming a desired shape. The temperature is preferably less than 200°C to prevent precipitation, and 50°C or higher to suppress uneven distribution of dislocations. There are no particular limitations on the processing method, but rolling, drawing, extrusion, groove rolling, etc. may be applied.

[0035] (Aging heat treatment process S07) Next, aging heat treatment is carried out for precipitation hardening. By carrying out this aging heat treatment, fine precipitate particles 12 are precipitated within the crystal grains, and high hardness is obtained. It is preferable to perform the heat treatment in a non-oxidizing or reducing atmosphere. The heat treatment temperature is preferably 200°C or higher and lower than 400°C. If the heat treatment temperature is lower than 200°C, the diffusion is insufficient and sufficient precipitates cannot be obtained. If the heat treatment temperature is 400°C or higher, coarse precipitates are formed, the number density of the precipitates decreases, and sufficient hardness and heat resistance cannot be obtained. In addition, recovery and recrystallization occur, resulting in a decrease in hardness.

[0036] The copper alloy of this embodiment is manufactured by the above-mentioned steps.

[0037] The electronic / electrical device part of this embodiment is obtained by processing the copper alloy of this embodiment into a predetermined shape.Specifically, it is used as home appliances, semiconductor parts such as lead frames, printed wiring boards, heat sinks, switch parts, bus bars, connectors, etc.

[0038] The copper alloy of this embodiment configured as described above contains 1.5 atomic % or more and 2.7 atomic % or less of Mg, and further contains, as an additive element, one of 1 atomic % or more and 8 atomic % or less of Si and 5 atomic % or more and 25 atomic % or less of Zn, with the balance being Cu and unavoidable impurities. Therefore, the additive element is contained in the precipitate particles, and when the precipitate particles are formed, the additive element also needs to aggregate, which retards the growth of the precipitate particles and disperses fine precipitate particles. As a result, the number density of precipitate particles with a circle equivalent diameter of 10 nm to 50 nm was 75 particles / μm 2 Since it is considered to have a strength and heat resistance of at least 100%, it has excellent heat resistance and strength.

[0039] Moreover, in the copper alloy of this embodiment, the Vickers hardness H1 after heat treatment under conditions of holding at 400°C for 2 hours is 55% or more of the Vickers hardness H0 before heat treatment, and the Vickers hardness H0 before heat treatment is 160HV or more. Therefore, the copper alloy is reliably excellent in strength and heat resistance, and is particularly suitable as a material for electronic and electric device parts used in high-temperature environments.

[0040] In the copper alloy of this embodiment, when the maximum length of a precipitate particle 12 is defined as the major axis and the point at which the maximum length in a direction perpendicular to the major axis is defined as the minor axis, if the minor axis length L2 is 25 nm or less and the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is 3 or more, fine precipitate particles 12 having a high aspect ratio are dispersed, and the strength and heat resistance are particularly excellent.

[0041] In the copper alloy of this embodiment, when the O concentration is 2 massppm or less and the S concentration is 10 massppm or less, the reaction of Mg with O (oxygen) and S (sulfur) is suppressed, fine precipitate particles containing Mg can be sufficiently precipitated, and the strength and heat resistance are particularly excellent. In addition, the generation of magnesium oxide and magnesium sulfide can be suppressed, and the processability is particularly excellent.

[0042] According to the electronic / electrical device part of this embodiment, since it is made of the copper alloy of this embodiment described above, it can exhibit excellent characteristics even in a high-temperature environment and can be used stably.

[0043] The copper alloy and the electronic / electrical device part according to the embodiment of the present invention have been described above, but the present invention is not limited thereto and can be appropriately modified within the scope of the technical idea of ​​the invention. In the above embodiment, an example of a method for producing a copper alloy has been described, but the method for producing a copper alloy is not limited to the one described in the embodiment, and an existing method may be appropriately selected to produce the copper alloy. EXAMPLES

[0044] The results of experiments carried out to confirm the effects of the present invention will be described below.

[0045] First, in the melting and casting process, a copper raw material consisting of oxygen-free copper (ASTM B152 C10100) with a purity of 99.99% by mass or more was prepared, and this was placed in an alumina crucible and melted in a high-frequency melting furnace in an Ar gas atmosphere. Mg and additive elements (Si, Zn) were added to the obtained molten copper. The obtained molten copper alloy was melted and poured into a carbon mold to produce an ingot. The size of the ingot was about 18 mm thick x about 22 mm wide x about 50 mm long.

[0046] In the hot rolling process, the obtained ingot was hot worked at 900°C until the thickness became 8 mm. If necessary, it was appropriately reheated. After the hot rolling, it was water-cooled. In order to remove the oxide film formed on the surface after the hot rolling, it was faced.

[0047] The first solution heat treatment step was performed under the conditions shown in Table 2. The cooling rate from the heat treatment temperature to 200°C was 500°C / min. As the cold working step, cold rolling was performed at the working ratio shown in Table 2. The second solution heat treatment step was performed under the conditions shown in Table 2. The cooling rate from the heat treatment temperature to 200°C was 1000°C / min. In the warm working process, the material heated to 100° C. was warm-rolled under the conditions shown in Table 2 to a plate thickness of 0.6 mm. The aging heat treatment step was carried out under the conditions shown in Table 2.

[0048] The copper alloys of the present invention and comparative examples obtained as described above were evaluated as follows. The evaluation results are shown in Tables 1 and 3.

[0049] (Alloy composition) Measurement samples were taken from the resulting ingots and component analysis was performed. Analysis of Mg and added elements (Si, Zn) was performed by inductively coupled plasma atomic emission spectrometry. Analysis of O and S was performed by infrared absorption spectrometry.

[0050] (Hot workability) The hot-worked materials in the above-mentioned hot working process were evaluated for the presence or absence of cracks. Those that broke were evaluated as "x", those that had minor cracks were evaluated as "△", and those that had no cracks were evaluated as "◯".

[0051] (Cold workability) The cold-worked materials were evaluated for the presence or absence of cracks in the above-mentioned cold working process. Those that broke were evaluated as "x", those that had minor cracks were evaluated as "△", and those that had no cracks were evaluated as "◯".

[0052] (Observation of precipitate particles) Observation of precipitate particles was carried out by the following method. The surface of the sample for evaluation and measurement was mechanically polished to a mirror finish, and then a thin film specimen was prepared using a focused ion beam processing device (Scios, manufactured by Thermo Fisher Scientific). The precipitate particles in the thin film specimen were observed using a transmission electron microscope (Titan G2 80-200, manufactured by Thermo Fisher Scientific). The circle-equivalent diameter was calculated from the area of ​​the observed precipitate particles, and the number density of precipitate particles having a circle-equivalent diameter of 10 μm or more and 50 μm or less was calculated. Observation was performed in three or more visual fields. In addition, the maximum length of all precipitate particles was defined as the major axis, and the point at which the maximum length in the direction perpendicular to this major axis was defined as the minor axis, and the minor axis length L2 and the ratio L1 / L2 of the major axis length L1 to the minor axis length L2 were measured. L1, L2 and L1 / L2 were each measured for 30 or more precipitates, and the average value was calculated. An example of the observation results (Example 3 of the present invention) is shown in Fig. 3. In Fig. 3, precipitate particles with a large ratio L1 / L2 of the major axis length L1 to the minor axis length L2 are confirmed.

[0053] (Vickers hardness) Test pieces were taken from the copper material for property evaluation, and the surfaces were mechanically polished using waterproof abrasive paper and diamond abrasive grains. Vickers hardness H0 was then measured at a test load of 0.1 kgf in accordance with the micro Vickers hardness test method specified in JIS Z 2244.

[0054] (Heat resistance evaluation) The heat treatment was carried out under the condition of holding at 400°C for 2 hours, and the Vickers hardness H1 after the heat treatment was measured using the procedure described above. Then, the ratio H1 / H0 of the Vickers hardness H0 before the heat treatment to the Vickers hardness H1 after the heat treatment was calculated.

[0055] [Table 1]

[0056] [Table 2]

[0057] [Table 3]

[0058] In Comparative Example 1, the Mg content was as low as 1.0 atomic %, and precipitate particles with an equivalent circle diameter of 10 nm to 50 nm were not formed, resulting in a significant decrease in Vickers hardness after heat treatment and insufficient heat resistance. In Comparative Example 2, the Si content was as low as 0.5 atomic %, and precipitate particles with an equivalent circle diameter of 10 nm to 50 nm were not formed, resulting in a large decrease in Vickers hardness after heat treatment and insufficient heat resistance.

[0059] In Comparative Examples 3 and 4, precipitate particles having an equivalent circle diameter of 10 nm to 50 nm were not sufficiently formed, and therefore the Vickers hardness was low before the heat treatment, and sufficient strength was not obtained.

[0060] In Comparative Example 5, precipitate particles having an equivalent circle diameter of 10 nm or more and 50 nm or less were not sufficiently formed, and therefore the Vickers hardness was significantly reduced after the heat treatment, and the heat resistance was insufficient. In Comparative Example 6, precipitate particles having an equivalent circle diameter of 10 nm or more and 50 nm or less were not sufficiently formed, and therefore the Vickers hardness was significantly reduced after the heat treatment, and the heat resistance was insufficient.

[0061] In Comparative Example 7, the Mg content was as high as 4.0 atomic %, and the specimen broke during hot working, so the subsequent steps and evaluation were discontinued. In Comparative Example 8, the Si content was as high as 9.0 atomic %, and the specimen broke during hot working, so the subsequent steps and evaluation were discontinued. In Comparative Example 9, the Zn content was as high as 50 atomic %, and the specimen broke during cold working, so the subsequent steps and evaluation were discontinued.

[0062] In contrast, in Examples 1 to 15 of the present invention, precipitate particles having a circle equivalent diameter of 10 nm to 50 nm were sufficiently formed, the Vickers hardness was sufficiently high and the strength was excellent before the heat treatment, and the Vickers hardness did not decrease significantly after the heat treatment, and the heat resistance was excellent.

[0063] As a result of the above confirmatory experiments, it was confirmed that the present invention can provide a copper alloy that is excellent in strength and heat resistance and can be stably used even in high-temperature environments.

Claims

1. The composition contains 1.5 atomic % or more and 2.7 atomic % or less of Mg, and further contains, as an additive element, one of 1 atomic % or more and 8 atomic % or less of Si and 5 atomic % or more and 25 atomic % or less of Zn, with the balance being Cu and unavoidable impurities; The number density of precipitate particles having a circle equivalent diameter of 10 nm or more and 50 nm or less is 75 particles / μm ２ That's all. A copper alloy characterized in that a Vickers hardness H1 after heat treatment under conditions of holding at 400°C for 2 hours is 55% or more of a Vickers hardness H0 before the heat treatment, and the Vickers hardness H0 before the heat treatment is 160 HV or more.

2. The copper alloy according to claim 1, characterized in that, when a point at which the precipitate particle has a maximum length is defined as a major axis and a point at which the precipitate particle has a maximum length in a direction perpendicular to the major axis is defined as a minor axis, a minor axis length L2 is 25 nm or less, and a ratio L1 / L2 of the major axis length L1 to the minor axis length L2 is 3 or more.

3. 2. The copper alloy according to claim 1, wherein the O concentration is 2 ppm by mass or less and the S concentration is 10 ppm by mass or less.

4. A part for electronic or electric equipment, comprising the copper alloy according to any one of claims 1 to 3.

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