JP6639147B2 - Cu-Ti-based copper alloy sheet, method for producing the same, and current-carrying part - Google Patents

Description

The present invention relates to a Cu—Ti-based copper alloy sheet having excellent fatigue resistance characteristics suitable for current-carrying parts such as connectors, relays, and switches. In particular, the conventional Cu—Ti-based copper alloy sheet has a fatigue resistance level of 10 ^3. A plate material having improved 180 ° bending workability capable of improving fatigue resistance characteristics under severe conditions where the fatigue limit is reached in 〜１０10 ⁴ times and capable of responding to miniaturization of electronic components, and production thereof About the method. The present invention also relates to a current-carrying part using the copper alloy sheet as a material.

  Materials used for current-carrying parts constituting electric / electronic parts are required to have excellent "strength", "bendability", and "stress relaxation resistance". Also, especially for current-carrying parts having movable parts such as connectors, relays, and switches, “fatigue resistance characteristics” that can withstand repeated stress loads are important.

  The Cu-Ti-based copper alloy has the second highest strength among the copper alloys next to the Cu-Be-based copper alloy, and has a stress relaxation resistance superior to that of the Cu-Be-based copper alloy. Further, it is more advantageous than a Cu-Be-based copper alloy in terms of cost and environmental load. For this reason, a Cu-Ti based copper alloy (for example, C1990; Cu-3.2 mass% Ti alloy) is used as a substitute for some Cu-Be based copper alloys for connector materials and the like.

  In a Cu—Ti-based copper alloy, although the strength can be improved by utilizing the modulated structure (spinodal structure) of Ti, coarse granular precipitates are easily formed in the manufacturing process of the sheet material, and the grain boundaries are formed from the grain boundaries. However, there is a problem that an interfacial reaction phase is easily generated. FIG. 1 illustrates a metallographic photograph (SEM photograph) of a cross section perpendicular to the rolling direction of a conventional general Cu—Ti-based copper alloy sheet. A large number of granular precipitates represented by symbol A and a layered grain boundary reaction phase represented by symbol B are observed. Among these second phases, the grain boundary reaction phase has a great influence on fatigue properties and bending workability.

In order to improve the properties of Cu-Ti based copper alloys, studies have been made on controlling the state of formation of the second phase such as the above-mentioned granular precipitates and grain boundary reaction phases. For example, Patent Literature 1 discloses a Cu-Ti-based copper alloy in which inclusions having a diameter of 1 µm or more are ² to 41 pieces / 1000 µm ² (2 × 10 ^{3 to} 41 × 10 ³ pieces / mm ² ). . Patent Document 2 discloses a Cu—Ti-based copper alloy in which the area ratio of second phase particles having a diameter of 1 μm or more is 0 to 0.16%. Patent Document 3 discloses a Cu-Ti-based copper alloy in which the area ratio of the Cu-Ti-based compound present in the grains is larger than the area ratio of the Cu-Ti-based compound existing in the grain boundaries. Patent Document 4 discloses a Cu—Ti-based copper in which the number of second phase particles having a diameter of 0.5 μm or more is 0.04 to 0.11 / μm ² (4 × 10 ^{4 to} 11 × 10 ⁴ / mm ² ). The alloy is shown. Patent Document 5 discloses that in a cross section perpendicular to the plate thickness direction, the maximum width of the grain boundary reaction type precipitate is 0.5 μm or less, and the density of the granular precipitate having a diameter of 100 nm or more is 10 ⁵ / mm ² or less. A certain Cu-Ti-based copper alloy sheet is shown.

JP 2005-187885 A JP 2011-202218 A JP 2011-195883 A JP 2012-97308 A JP 2014-185370A

  A copper alloy plate material used for a spring material such as a connector is often used after being subjected to a 180 ° U-shaped bending. Particularly in consumer electronic devices, there is a growing need for improved durability when repeated insertion / extraction operations are repeated, and it is desired to evaluate fatigue resistance characteristics using a test piece having a shape close to a mounted component subjected to 180 ° U-shaped bending. I have. However, the evaluation of fatigue resistance properties of copper alloy sheet materials has so far been mainly based on evaluation of flat samples such as pulley tests and knife edge tests, and the durability reflecting the mounting shape as described above is sufficiently understood. It is not at present. In the future, further improvement in bending workability is also desired so as to cope with further downsizing of components.

According to the study of the inventors, in the test pieces having a shape close to a mounting component having a 180 ° U-shaped bent portion, the durability level of the conventional sheet materials of Cu-Ti alloys with approximately 10 ⁴ times from 10 ³ times It has been found that an evaluation method under a severe condition of applying a load such that the fatigue limit is reached is effective to meet the above-mentioned need for improving durability. Also, it was considered necessary to implement a 180 ° bending test method capable of more appropriately evaluating the bending workability when processing into a small component having a small width. Conventional second-phase control techniques including Patent Literatures 1 to 5 cannot sufficiently meet the above-described needs for improving durability and bending workability. The present invention relates to a bending process capable of improving the durability of a Cu—Ti-based copper alloy based on a strict evaluation criterion grasped by a test piece having a shape close to the mounted component as described above and capable of responding to miniaturization of the component. The purpose is to improve the performance.

According to the inventors' detailed research, in order to simultaneously provide the above-described severe durability and bending workability, it is necessary to limit the maximum width of a generated grain boundary reaction phase and to set a specific orientation difference. It has been found that it is extremely effective to limit the amount of the generated grain boundary reaction phase precipitated at the grain boundaries of the crystals. In addition, they have found that the following method is extremely effective as a manufacturing method for realizing it.
(I) In the hot rolling, a rolling reduction of 60% or more is obtained in a high temperature region of 920 ° C. or more, and a large shear force is applied to the entire material by increasing the friction between the material and the roll in the high temperature region to thereby increase the casting structure. Promotes the destruction / separation of the segregated phase and water-cools from the highest possible temperature.
(Ii) The maximum material reaching temperature of the aging treatment is set in the range of 400 to 700 ° C., and the aging treatment time is strictly controlled according to the aging treatment temperature.
The present invention has been completed based on such findings.

That is, in the present invention, Ti: 2.0 to 4.0%, Ni: 0 to 1.5%, Co: 0 to 1.0%, Fe: 0 to 0.5%, and Sn: 0% by mass. -1.2%, Zn: 0-2.0%, Mg: 0-1.0%, Zr: 0-1.0%, Al: 0-1.0%, Si: 0-1.0% , P: 0 to 0.1%, B: 0 to 0.05%, Cr: 0 to 1.0%, Mn: 0 to 1.0%, V: 0 to 1.0%. Copper alloy sheet material having a total content of Sn, Zn, Mg, Zr, Al, Si, P, B, Cr, Mn, and V of 3.0% or less, and a balance of Cu and unavoidable impurities In the observation plane parallel to the plate surface, the average crystal grain size is 3.0 to 25.0 μm, the maximum width of the grain boundary reaction phase is 1.5 μm or less, and from one intersection of the crystal grain boundaries. The grain boundary part up to the next intersection is defined as one “grain boundary seg When defining the bets ", the heading difference is not more than 60% the number ratio of the grain boundary segments 10% or more of the grain boundary reaction phases are present in excess of the width 0.5μm of grain boundary segments of the crystal is 35 to 55 ° A copper alloy sheet having a certain metal structure, a 0.2% proof stress in a rolling direction of 800 MPa or more, and a conductivity of 11.0% IACS or more is provided. The plate thickness can be, for example, 0.03 to 1.0 mm. In particular, a thin plate having a thickness of 0.05 to 0.3 mm is useful for reducing the size of the current-carrying parts.

  The copper alloy sheet has excellent 180 ° bendability. Specifically, when a bending test piece having a width of 1 mm whose longitudinal direction is the rolling direction (LD) and the direction perpendicular to the rolling direction (TD) is sampled and subjected to a 180 ° bending test according to the winding method of JIS Z2248: 2014. A material having a bending workability in which the value of the ratio MBR / t between the minimum bending radius MBR and the plate thickness t at which cracking does not occur is 1.0 or less for both LD and TD is a suitable object.

The azimuth difference between adjacent crystal grains can be obtained by measuring a crystal grain orientation distribution map (OIM image) based on an electron backscatter diffraction pattern (EBSP) (hereinafter, referred to as an EBSP method). Specifically, a grain orientation distribution map of an observation surface parallel to the plate surface (rolled surface) is measured by an EBSP method using a field emission scanning electron microscope (FESEM), and the crystal orientation difference is determined. By superimposing and displaying the boundaries of the crystal grains of 35 to 55 ° on the SEM image, the individual grain boundary segments in the SEM field of view are “grain boundaries of the crystal with a misorientation of 35 to 55 °”. Segment ".
The grain boundary reaction phase is a precipitation phase of a Cu-Ti-based intermetallic compound that grows in a layer form while forming a layer with the Cu phase from the crystal grain boundary of the Cu mother phase to the inside of the crystal grain, and β-Cu It is considered that the main component is the ₄ Ti phase. Since the grain boundary reaction phase exists along the crystal grain boundaries and alternately forms a layered structure with the Cu phase, it can be distinguished from other types of second phases in metallographic observation.
The maximum width of the grain boundary reaction phase and the number ratio of the number of the grain boundary segments in which the grain boundary reaction phase exceeding 0.5 μm exists among the grain boundary segments of the crystal having the misorientation of 35 to 55 ° are as follows. Can be determined.

(Specification method of maximum width of grain boundary reaction phase)
In SEM observation of an observation surface parallel to the plate surface, 12 observation visual fields in which a rectangular area of 200 μm × 200 μm (40000 μm ² ) can be set are randomly selected. In each observation visual field, for all the grain boundary reaction phases observed in the rectangular area (including the boundary), the length in the direction perpendicular to the crystal grain boundary was measured, and the maximum of the above measured values in all 12 visual fields was measured. The value is defined as the maximum width (μm) of the grain boundary reaction phase.

[Method of Identifying Number Ratio of Grain Boundary Segments in Which Grain Boundary Reaction Phase Exceeding 0.5 μm in Width Among Grain Boundary Segments with Orientation Difference of 35 to 55 °]
In SEM observation of an observation surface parallel to the plate surface, 12 observation visual fields in which a rectangular area of 200 μm × 200 μm (40000 μm ² ) can be set are randomly selected. In one observation visual field, among grain boundary segments that are wholly or partially present in a rectangular area (including a boundary), crystal grain boundary segments whose orientation difference is 35 to 55 ° are extracted by the EBSP method. Are referred to as “35-55 ° grain boundary segments”, and the number thereof is n ₀ (number). Among the 35 to 55 ° grain boundary segments, a grain boundary segment having a grain boundary reaction phase having a size exceeding 0.5 μm in a direction perpendicular to a crystal grain boundary in a rectangular region (including a boundary). The number n ₁ (pieces) is counted. This operation is performed for the above 12 visual fields, and when the total sum of n ₀ in all 12 visual fields is N ₀ (number) and the total sum of n ₁ is N ₁ (number), it is expressed as N ₁ / N ₀ × 100. This value is defined as "the number ratio (%) of grain boundary segments having a grain boundary reaction phase exceeding 0.5 [mu] m in grain boundary segments of a crystal having a misorientation of 35 to 55 [deg.].

As a method of manufacturing the copper alloy sheet, a copper alloy sheet having the above chemical composition, when hot-rolling, cold-rolling, solution treatment, when producing in the step having the steps of aging treatment in the above order,
In the hot rolling step, the heating temperature is set to 960 ° C or lower, and a lubricating liquid having a water content of 97.0% by mass or more is used in a rolling pass performed at 920 ° C or higher, and the total rolling ratio at 920 ° C or higher is 60% or more. And the final pass temperature of the hot rolling is set to Ts (° C.) or more in the following formula (1), and after the final pass, water cooling is started from a high temperature equal to or higher than Ts−100 ° C.
In the solution treatment step, the heating and holding temperature is in a range of 750 to 900 ° C,
In the aging treatment step, the maximum attained material temperature T _MAX (° C.) is set in the range of 400 to 700 ° C., and the holding time t _A (min) in the temperature range of 400 ° C. or more and T _MAX or less is defined by the following equation (2). Aging treatment is performed under the condition that the relationship of the X values to be satisfied satisfies the following equation (3).
A method for manufacturing a copper alloy sheet is provided.
Ts = 151.5 × ln [Ti] +620.5 (1)
Here, ln is the natural logarithm, and [Ti] is the Ti content of the alloy expressed in mass%.
X = exp ((694−T _MAX ) / 28) (2)
0.20 ≦ t _A /X≦1.0 (3)

  Further, the present invention provides a current-carrying component using the above-mentioned copper alloy sheet as a material.

  ADVANTAGE OF THE INVENTION According to this invention, in the Cu-Ti-type copper alloy sheet material, the durability judged by the severe evaluation method using the sample which has a 180-degree U-shaped bending part was able to be improved. In addition, to provide excellent bending workability that 180 ° bending with R / t = 1 can be performed in both LD and TD directions in a severe 180 ° bending test evaluated with a 1 mm wide test piece. Was completed. Therefore, the present invention contributes to improving the durability and reducing the size of current-carrying parts having movable parts such as connectors, switches and relays.

5 is an SEM photograph illustrating the metal structure of a general Cu—Ti-based copper alloy sheet. The figure which illustrated the shape of the test piece for evaluating durability. 4 is a graph illustrating the relationship between the number of times of applying a load and the rate of decrease in load.

《Alloy composition》
In the present invention, a Cu-Ti-based copper alloy in which Ni, Co, Fe, and other alloy elements are blended as necessary with the binary basic component of Cu-Ti is employed. Hereinafter, “%” regarding the alloy composition means “% by mass” unless otherwise specified.

  Ti is an element that contributes to an increase in strength and an improvement in stress relaxation resistance. Here, an alloy having a Ti content of 2.0% or more is targeted. More preferably, it is 2.5% or more. Excessive Ti content lowers the hot workability and cold workability, and also narrows the appropriate temperature range of the solution treatment. Therefore, the Ti content is set to 4.0% or less. It may be controlled to 3.5% or less.

  Since Ni, Co, and Fe form an intermetallic compound with Ti and contribute to improvement in strength, one or more of these can be added as necessary. In particular, in the solution treatment of a Cu-Ti-based copper alloy, since the intermetallic compound of these elements suppresses the coarsening of the crystal grains, the solution treatment in a higher temperature range becomes possible, and Ti is sufficiently reduced. This is advantageous in forming a solid solution. When one or more of these are added, it is more effective that the content of Ni is 0.05% or more, Co is 0.05% or more, and Fe is 0.05% or more. It is more effective to set the ratio to 1 or more, Co: 0.1% or more, and Fe: 0.1% or more. However, when Fe, Co, and Ni are excessively contained, coarse granular precipitates are easily formed, and the durability is reduced. Therefore, when one or more of Ni, Co, and Fe are added, the content is set to a range of Ni: 1.5% or less, Co: 1.0% or less, and Fe: 0.5% or less. Ni: 0.25% or less, Co: 0.25% or less, Fe: 0.25% or less may be managed.

  Since Sn has a solid solution strengthening action and a stress relaxation resistance improving action, Sn may be positively added as necessary. It is effective to secure a Sn content of 0.1% or more. However, excessive Sn content lowers castability and conductivity, so when Sn is contained, the content is set to 1.2% or less. It may be controlled within a range of 0.5% or less or 0.25% or less.

  Zn has the effect of improving the solderability and strength, and also has the effect of improving the castability. Therefore, Zn may be positively added as necessary. It is effective to ensure a Zn content of 0.1% or more, and it is more effective to set the Zn content to 0.3% or more. However, since excessive Zn content is likely to cause a reduction in conductivity and resistance to stress corrosion cracking, the Zn content is set to 2.0% or less, and is controlled to a range of 1.0% or less or 0.5% or less. Is also good.

  Since Mg has an action of improving stress relaxation resistance and an action of removing S, Mg may be positively added as necessary. It is effective to secure the Mg content of 0.01% or more, and it is more effective to set the Mg content to 0.05% or more. However, Mg is an element that is easily oxidized, and excessive addition may cause the castability to be impaired. Therefore, when Mg is contained, the content should be 1.0% or less and adjusted within the range of 0.5% or less. Is more preferred. Usually, the content may be set to 0.1% or less.

  Other elements include Zr: 1.0% or less, Al: 1.0% or less, Si: 1.0% or less, P: 0.1% or less, B: 0.05% or less, and Cr: 1.0%. % Or less, Mn: 1.0% or less, V: 1.0% or less. For example, Zr and Al can form an intermetallic compound with Ti, and Si can form a precipitate with Ti. Cr, Zr, Mn, and V easily form a high melting point compound with S, Pb and the like existing as unavoidable impurities, and Cr, B, P, and Zr have an effect of refining a cast structure, and are hot worked. It can contribute to improvement of the performance. When one or more of Zr, Al, Si, P, B, Cr, Mn, and V are contained, they are contained so that the total amount thereof is 0.01% or more in order to sufficiently obtain the effect of each element. It is effective.

  However, when Zr, Al, Si, P, B, Cr, Mn, and V are contained in a large amount, the hot or cold workability is adversely affected, and the cost is disadvantageous. Therefore, the total content of Sn, Zn, Mg and Zr, Al, Si, P, B, Cr, Mn, and V is desirably suppressed to 3.0% or less, preferably 2.0% or less or 1.0% or less. It can be regulated within the range of 0% or less, and may be controlled within the range of 0.5% or less. As a more reasonable upper limit regulation considering economy, for example, Zr: 0.2% or less, Al: 0.15% or less, Si: 0.2% or less, P: 0.05% or less, B: 0 Regulations of 0.03% or less, Cr: 0.2% or less, Mn: 0.1% or less, and V: 0.2% or less can be provided.

《Metal structure》
As shown in FIG. 1, “granular precipitates” and “grain boundary reaction phases” are observed in conventional general Cu—Ti-based copper alloy sheet materials. Although these second phases are also observed in the Cu—Ti-based copper alloy sheet according to the present invention, it is characterized in that the maximum width and the form of the “grain boundary reaction phase” are severely restricted as described below. is there. The strengthening mechanism of the Cu-Ti based copper alloy is mainly based on a modulation structure (spinodal structure). The modulated structure itself is not observed with an optical microscope or SEM unlike the precipitated phase.

(Granular precipitate)
Granular precipitates observed in the parent phase (matrix) of the Cu-Ti copper alloy include intermetallics such as Ni-Ti, Co-Ti, and Fe-Ti, depending on the type of alloy element to be added. Although a compound may be present, the α-phase, which is a Cu—Ti-based intermetallic compound, occupies most of the compound.

(Grain boundary reaction phase)
The grain boundary reaction phase is a fragile portion and acts as a starting point or a propagation path of fatigue fracture or bending crack. Therefore, it is considered desirable that the generation amount of the grain boundary reaction phase be as small as possible. However, in order to improve the severe durability evaluated by the test piece having the 180 ° U-shaped bent portion and the severe 180 ° bending workability evaluated by the narrow test piece, it is necessary to simply generate the grain boundary reaction phase. It is not enough to simply reduce the number of cracks, and it is required to adopt a method of more effectively preventing the generation and propagation of cracks at the crystal grain boundaries. Therefore, regarding the generation and propagation of cracks, the inventors classified the crystal grain boundaries into “grain boundaries where the influence of the grain boundary reaction phase is large” and “grain boundaries where the influence of the grain boundary reaction phase is small”, and Investigations have been conducted based on the idea of restricting the grain boundary reaction phase existing in the "grain boundary where the influence of the phase is large". As a result, the "grain boundary of a crystal having a misorientation of 35 to 55 [deg.]" Can be taken as "a grain boundary having a large influence of the grain boundary reaction phase". Has been found to be extremely effective in stably improving the above-mentioned severe durability and bending workability. At the same time, it has been confirmed that it is also important to regulate the maximum width of the grain boundary reaction phase, that is, the maximum length in the direction perpendicular to the crystal grain boundary where the grain boundary reaction phase occurs.

Specifically, on the observation plane parallel to the plate surface, the number ratio of the number of the grain boundary segments in which the grain boundary reaction phase exceeding 0.5 μm exists among the grain boundary segments of the crystal having the misorientation of 35 to 55 °. Is 60% or less, which is extremely effective in improving the above-mentioned severe durability and bending workability. The smaller the above number ratio, the better, but it is difficult to reduce the number to 0%. Generally, a high improvement effect can be obtained in the range of 10 to 60%. Here, the grain boundary segment means a grain boundary portion from one intersection of a crystal grain boundary to an adjacent intersection. The width of the grain boundary reaction phase at a certain position on the grain boundary corresponds to the length of the grain boundary reaction phase measured in a direction perpendicular to the tangent to the grain boundary at that position. If a grain boundary reaction phase is present at the end of a given grain boundary segment (ie, at the intersection of the grain boundaries), the grain boundary reaction measured at a direction perpendicular to the tangent to the grain boundary at that end. The phase length is the width of the grain boundary reaction phase at the intersection with respect to the grain boundary segment. While moving the position on the grain boundary from one end to the other end of a certain grain boundary segment, and measuring the width of the grain boundary reaction phase generated in the grain boundary segment, the width of the grain boundary reaction phase becomes If there is a portion exceeding 0.5 μm, the grain boundary segment corresponds to “a grain boundary segment having a grain boundary reaction phase having a width of more than 0.5 μm”. However, with respect to a grain boundary segment in which a part of the grain boundary segment is cut at the boundary of the rectangular area provided in the above-described observation field, the grain boundary reaction is limited to a portion within the rectangular area (including the boundary). The phase width may be measured.
The specific method of measuring the number ratio of the grain boundary segments having a grain boundary reaction phase exceeding 0.5 μm among the grain boundary segments of the crystal having the misorientation of 35 to 55 ° is as described above.

It is also important that the maximum width of the grain boundary reaction phase be 1.5 μm or less on the observation plane parallel to the plate surface. If a grain boundary reaction phase having a size exceeding that size is present at any of the grain boundaries, it is difficult to sufficiently improve the durability and bending workability by a strict evaluation method. More preferably, the maximum width of the grain boundary reaction phase is 1.0 μm or less.
The specific method of measuring the maximum width of the grain boundary reaction phase is as described above.

(Average crystal grain size)
Finer crystal grains are advantageous for bending workability and fatigue resistance, but are disadvantageous for stress relaxation resistance. As a result of various studies, the average crystal grain size is desirably adjusted to a range of 3.0 to 25.0 μm, and may be controlled to 5.0 to 20.0 μm. The control of the average crystal grain size can be mainly performed by a solution treatment. Here, the average crystal grain size is determined by observing the metallographic structure on the observation surface parallel to the plate surface (rolled surface), by drawing a line perpendicular to the rolling direction with a visual field of 300 μm × 300 μm or more, and measuring the particle size of 100 or more crystal grains. Can be determined by the cutting method of JIS H0501.

"Characteristic"
〔conductivity〕
In order to be used for a current-carrying part, it is desirable to have a conductivity of 11.0% IACS or more, more preferably 12.0% IACS or more. The conductivity can be satisfied by the above-described chemical composition and metal structure.

〔Strength〕
The 0.2% proof stress of the LD is desirably 800 MPa or more, and more desirably 810 MPa or more. On the other hand, if the strength is excessively increased, cracks are likely to occur at the 180 ° U-shaped bent portion, which may be a factor of reducing durability. The 0.2% proof stress of the LD is preferably adjusted within a range of 1000 MPa or less. It may be managed in a range of 970 MPa or less or 930 MPa or less. The tensile strength of the LD is desirably in the range of 820 to 980 MPa.

[Bendability]
In consideration of the need for miniaturization of current-carrying parts, here, the bending workability of the sheet material is evaluated by a strict evaluation method using a narrow bending test piece. Specifically, when a 1 mm wide test piece is sampled from a plate material and subjected to a 180 ° bending test by the winding method of JIS Z2248: 2014, the ratio MBR between the minimum bending radius MBR and the plate thickness t at which cracking does not occur. Those having bending workability in which the value of / t is 1.0 or less in both the LD and TD directions are suitable targets. The “bending workability of LD” is bending workability evaluated in the longitudinal direction by a test piece of LD, and the bending axis is TD. The “bendability of TD” is the bendability evaluated by a TD test piece in the longitudinal direction, and the bending axis is LD.

(Fatigue resistance characteristics)
Generally, the fatigue resistance is evaluated by a flat test piece. Here, as described above, a test piece having a 180 ° U-shaped bent portion is used to grasp the durability closer to the mounted state. Specifically, for example, a method described in the following embodiment can be applied.

(Stress relaxation resistance)
Stress relaxation resistance is particularly important in applications such as automotive connectors. In the stress relaxation characteristic evaluation method described below, the stress relaxation rate when a test piece having a TD in the longitudinal direction is held at 200 ° C. for 1000 hours is preferably 5% or less, more preferably 4% or less.

"Production method"
The Cu-Ti-based copper alloy sheet having the above-described characteristics can be manufactured by a process including hot rolling, solution treatment, and aging treatment. More specifically, for example, the following steps can be exemplified.
`` Melting / Casting → Hot rolling → Cold rolling → Solution treatment → Aging treatment → Finish cold rolling → Low temperature annealing ''
Although not described in the above steps, soaking and heat treatment (or hot forging) are performed as necessary after melting and casting, and face milling is performed as necessary after hot rolling, After the heat treatment, pickling, polishing, or further degreasing is performed as necessary. Further, "intermediate cold rolling" may be added before "aging treatment" depending on the use. Hereinafter, each step will be described.

[Melting / Casting]
The slab may be manufactured by continuous casting, semi-continuous casting, or the like. In order to prevent oxidation of Ti, it is preferable to carry out in an inert gas atmosphere or a vacuum melting furnace.

(Hot rolling)
In hot rolling, a large rolling reduction is achieved at as high a temperature as possible, and a large shear force is applied to the entire material to promote the destruction / separation of the segregated phase in the cast structure. It is extremely effective to finish the process at a temperature equal to or higher than the steepness line and to perform water cooling from the highest possible temperature after the final pass.
The heating temperature before hot rolling is 960 ° C. or less. If it is higher than that, if there is a portion where the melting point is lowered due to the cast structure, the portion may be melted, which may cause hot cracking. The heating temperature range is preferably 930 to 960 ° C., and the heating time is preferably 2 hours or more. While the surface temperature of the material is 920 ° C. or more, a reduction of 60% or more, more preferably 65% or more, is given to the total rolling reduction. That is, the total rolling ratio at 920 ° C. or more is set to 60% or more, and more preferably 65% or more. Since the upper limit of the total rolling reduction at 920 ° C. or higher is limited by the capacity of the equipment and the like, it is not necessary to particularly define the upper limit. By obtaining a large workability in this temperature range, the concentrated portion of Ti which is likely to be generated between the dendrite trees of the casting structure is broken and divided, and the nucleus source which easily grows into coarse second phase particles is sufficiently eliminated. If the total rolling reduction at 920 ° C. or higher is less than 60%, a coarse grain boundary reaction phase is finally generated, and thus the strength, bending workability, and durability (fatigue resistance properties) of the material are sufficiently improved. It becomes difficult. Of the hot rolling passes performed in a temperature range of 920 ° C. or higher, it is more effective to set the rolling reduction (maximum rolling reduction) in the hot rolling pass having the largest rolling reduction to 15% or more. In particular, it is more preferable that the average value of the rolling reduction (average rolling reduction) in each hot rolling pass performed in a temperature range of 920 ° C. or more is 15% or more.

The final pass temperature of the hot rolling is Ts (° C.) or more in the following equation (1).
Ts = 151.5 × ln [Ti] +620.5 (1)
Here, ln means a natural logarithm, and the value of Ti content of the alloy expressed in mass% is substituted for [Ti].
This Ts is an index indicating the solid solubility line temperature (° C.) of the α phase in the Cu—Ti binary alloy, and is accurately approximated by the above equation (1). Normally, nucleation hardly occurs in a temperature region near the solid solubility line on a lower temperature side than the solid solubility line, but nucleation easily occurs in a temperature region when a processing strain is applied. Once nucleation occurs in that temperature range, subsequent growth is fast because of the high temperature. Therefore, in order to reduce the amount of coarse precipitates, it is extremely effective to terminate hot rolling at a temperature equal to or higher than Ts. The total rolling reduction in the hot rolling may be set in a range of 60% or more and 95% or less.
The rolling ratio from a certain plate thickness t ₀ (mm) to a certain plate thickness t ₁ (mm) is obtained by the following equation (4). The same applies to the rolling ratio in each step described later.
Rolling ratio (%) = (t ₀ −t ₁ ) / t ₀ × 100 (4)
The rolling reduction in one rolling pass is calculated by the above equation (4), where the thickness before the rolling pass is t ₀ (mm) and the thickness before the rolling pass is t ₁ (mm). Rolling rate (%).

In order to apply a large shearing force to the entire material in this high temperature range, it is extremely effective to increase the tensile stress component applied to the material surface by using the frictional force between the rolling roll and the material. all right.
Generally, in the rolling process, a tensile stress state occurs near the surface in contact with the roll, and a compressive stress state occurs near the center of the sheet thickness, and stresses in different directions are applied between the surface layer portion and the inside of the material. The tensile stress is mainly generated by the frictional force between the roll and the material. Since this frictional force causes a reduction in the life of the roll, the lubricating liquid is used in a normal hot rolling operation to reduce the frictional force. As the lubricating liquid for hot rolling, a water-soluble lubricating component (soluble oil) added to water by a few percent is generally used in terms of cooling ability and flame retardancy.
In order to realize the microstructure according to the present invention in which the presence of the coarse grain boundary reaction phase is severely restricted in the final sheet material, the frictional force is actively utilized to make the tensile stress generated near the surface of the material. Is very effective. Due to the increase in tensile stress, the difference in stress direction between the surface layer and the inside increases, and a large shearing force is applied to the entire material. This promotes destruction / separation of the segregated phase in the cast structure. As a result of various studies, according to the present invention, the use of a lubricating liquid in which the amount of a lubricating component is limited by adding a lubricating component such as soluble oil to water so that the water content is 97.0% by mass or more is used. It is very effective in obtaining a plate product in a textured state. It is more preferable to use a lubricating liquid having a water content of 98.0% by mass or more, more preferably 99.0% by mass or more. The lubricating liquid may have a water content of 100% (that is, water), or may be controlled to have a water content of, for example, 99.8% by mass or less. The water content in the lubricating liquid can be measured by a heat-drying moisture meter.

  In the cooling process after the end of the final hot rolling pass, it is necessary to prevent the formation of the second phase as much as possible. In the cooling process after the end of the final hot rolling pass, since no work strain is introduced, it can be considered that the formation of the second phase near the solid solubility line temperature hardly occurs. However, when the temperature difference from the solid solubility line becomes large, precipitation actively occurs. As a result of various studies, if the temperature is lower than the temperature expressed by Ts-100 ° C., the formation of the second phase may become a problem. Therefore, after the end of the final hot rolling pass, water cooling is started when the material surface temperature is higher than the temperature represented by Ts-100 ° C. As a water cooling method, a method of bringing a sufficient amount of cooling water into contact with the surface of a material on a table for transporting a hot-rolled material, a method of immersing a wound coil in a water tank, and the like can be adopted. With these water cooling methods, the average cooling rate from the water cooling start temperature to 200 ° C. can be set to 20 ° C./sec or more, and can be controlled to 50 ° C./sec or more. The water cooling start temperature is more preferably a high temperature equal to or higher than the temperature represented by Ts-50 ° C.

(Cold rolling)
In consideration of the thickness of the final product, cold rolling can be appropriately performed at a stage before the solution treatment. A plurality of cold rollings with intermediate annealing may be performed. It is effective that the cold rolling reduction of the sheet material to be subjected to the solution treatment is 90% or more.

(Solution treatment)
The heat holding temperature of the solution treatment is in the range of 750 to 900 ° C. In this temperature range, the α phase can be sufficiently dissolved. If it exceeds 900 ° C., the crystal grains tend to be coarse. If the temperature is lower than 750 ° C., the solid solution of the α phase tends to be insufficient. The holding time at 750 to 900 ° C. may be set in the range of 5 sec to 5 min. The average crystal grain size of the final product can be adjusted by the holding temperature and holding time of the solution treatment. In the cooling process of the solution treatment, it is desirable to perform rapid cooling so that the average cooling rate from 550 ° C to 300 ° C is 100 ° C / sec or more.

(Aging treatment)
The aging treatment is performed by heating the material to a range of 400 to 700 ° C. In the Cu-Ti-based copper alloy, a remarkable strength increasing effect by the formation of a modulated structure (spinodal structure) can be obtained in this temperature range. However, this range overlaps with the temperature range where the grain boundary reaction phase is likely to be formed at the same time. For this reason, it has been difficult to suppress the formation of a grain boundary reaction phase in a conventional Cu-Ti-based high-strength copper alloy. As a result of detailed studies, the inventors have found that, as a Cu-Ti-based copper alloy material to be subjected to aging treatment, a structure in which a nucleus source that easily grows into coarse second-phase particles by the above-described hot rolling step has sufficiently disappeared. When the solution-treated material in the state is used, the maximum attained material temperature T _MAX (° C.) is set in the range of 400 to 700 ° C., and the holding time t _A (min) in the temperature range of 400 ° C. or more and T _MAX or less. And the X value defined by the following equation (2) are subjected to aging treatment under the conditions satisfying the following equation (3), so that the growth of the grain boundary reaction phase is remarkably suppressed, and the 0.2% proof stress is 800 MPa or more. Has been found to be able to increase the strength of the steel. The highest attained material temperature T _MAX (° C.) may be controlled in the range of 420 to 500 ° C.
X = exp ((694−T _MAX ) / 28) (2)
0.20 ≦ t _A /X≦1.0 (3)
Since precipitation of grain boundary reaction phase is in the hard tissue condition progresses, a relatively high temperature for a long time aging treatment but it is possible, depending on the ultimate maximum material temperature T _MAX, severely limits the aging time There is a need.

If the maximum attained material temperature T _MAX exceeds 700 ° C., or if the heating holding time t _A is longer than t _A /X≦1.0 in the equation (3), the grain boundary reaction phase is excessive. Therefore, a metal structure in which the precipitation form of the grain boundary reaction phase is optimized to the above-mentioned desired state cannot be obtained. In such a case, the durability and the 180 ° bending workability are not sufficiently improved. When the maximum attained material temperature T _MAX is lower than 400 ° C. or when the heating holding time t _A is short of 0.20 ≦ t _A / X in the equation (3), the strength is not sufficiently increased. Becomes Here, the heating holding time t _A (min) means a time when the material temperature is 400 ° C. or more and T _MAX (° C.) or less. In the conventional general hot working method of Cu-Ti based copper alloy, a nucleus source that easily grows into coarse second phase particles is not sufficiently eliminated, and therefore, such a material is specified in the present invention. When the aging treatment under the above-mentioned conditions is applied, even if it is possible to increase the strength in a relatively short aging treatment time, the durability and the 180 ° bending workability intended in the present invention are improved. Can not.
More preferably, the highest attained material temperature T _MAX is in the range of 420 to 550 ° C. Further, as for the t _A / X value in the expression (3), it is more preferable that the upper limit is t _A /X≦0.9, and that the lower limit is 0.4 ≦ t _A / X. preferable.
In order to minimize surface oxidation during the aging treatment, a hydrogen, nitrogen or argon atmosphere can be used.

(Finish cold rolling)
After the aging treatment, finish cold rolling can be performed, if necessary, for the purpose of adjusting the thickness or adjusting the strength level. The finish cold rolling rate may be adjusted, for example, in the range of 5 to 15%.

(Low temperature annealing)
After the finish cold rolling, low-temperature annealing can be performed for the purpose of reducing the residual stress of the sheet material, improving the bending workability, and improving the stress relaxation resistance by reducing the dislocations on the holes and slip surfaces. The conditions may be set in the range of a heating temperature of 150 to 430 ° C. and a heating time of 5 to 3600 sec. When the finish cold rolling is omitted, the low-temperature annealing is usually also omitted.

  Copper alloys shown in Table 1 were melted and cast using a vertical semi-continuous casting machine. The obtained slab was hot-rolled under various conditions shown in Table 2. A lubricating liquid was prepared by adding commercially available soluble oil to water. The moisture content of the lubricating fluid was measured using a heat-drying moisture meter (ML-50, manufactured by A & D). In some examples (No. 6), water was used as the lubricating liquid. The heating time of the slab was 4 hours. Water cooling after hot rolling was performed by immersing the obtained coil in a water tank. At this time, the average cooling rate from the water cooling start temperature to 200 ° C. was 50 ° C./sec or more. The total hot rolling reduction from the slab is about 90%. The average value of the rolling reduction in each rolling pass at 920 ° C. or higher (average rolling reduction at 920 ° C. or higher) was 15% or more in each of the examples of the present invention. After hot rolling, the surface oxide layer was mechanically polished to remove about 0.5 mm on both sides of the plate (face milling) to obtain a rolled plate having a thickness of 10 mm. Next, after performing cold rolling at a rolling reduction of 95 to 98%, a solution treatment was performed under the conditions shown in Table 3. After the heating and holding in the solution treatment, water cooling was performed, and the average cooling rate from 550 ° C to 300 ° C was set to 100 ° C / sec or more. Thereafter, finish cold rolling and low-temperature annealing were performed under the conditions shown in Table 3 to obtain a test material having a final plate thickness of 0.20 mm.

The following items were investigated for each test material.
(Average crystal grain size)
The plate surface (rolled surface) of the test material is polished and etched, and the surface is observed with an optical microscope. The grain size of 100 or more crystal grains is determined by a cutting method according to JIS H0501 in a 300 μm × 300 μm visual field. Measured by the method.

(Precipitation form of grain boundary reaction phase)
After the plate surface of the test material is polished with a water-resistant abrasive paper having a count of 1500 (particle size P1500 specified in JIS R6010: 2000), the surface is polished by a vibration polishing method in order to prevent a polishing strain from being applied to the surface. I got Using FESEM (Field Emission Scanning Electron Microscope) manufactured by JEOL Co., Ltd., there is a grain boundary reaction phase having a width of more than 0.5 μm among the grain boundary segments of the crystal having a misorientation of 35 to 55 °. According to the method described in “Specifying the Number Ratio of Grain Boundary Segments to be Performed”, observation was performed on 12 randomly selected visual fields having a rectangular area of 200 μm × 200 μm (40000 μm ² ) using the SEM and the EBSP method. Of the grain boundary segments was determined. When observing the 12 visual fields, the maximum width of the grain boundary reaction phase was measured from the SEM image according to the above-mentioned “method of specifying the maximum width of the grain boundary reaction phase”, and 1.5 μm was measured based on the measured value of the maximum width. Was determined. In the SEM image, the grain boundary reaction phase is observed as a layered structure that grows from the crystal grain boundary to the inside of the grain, and the grain boundary reaction phase having a width of more than 0.5 μm can be clearly confirmed.

〔conductivity〕
The conductivity of each test material was measured according to JIS H0505.
[Tensile strength, 0.2% proof stress]
An LD tensile test piece (JIS No. 5) was collected from each test material, and a tensile test of JIS Z2241 was performed at n = 3, and the tensile strength and 0.2% proof stress were determined by the average value of n = 3.

[Bendability]
A bending test piece having a LD in the longitudinal direction and a bending test piece having a TD (each having a width of 1 mm) were sampled from the plate material of the test material, and subjected to a 180 ° bending test in accordance with the winding method of JIS Z2248: 2014. The bending radius R inside the bent portion was the same as the plate thickness t (R / t = 1). The cross section perpendicular to the bending axis of the test piece after the test was observed with an optical microscope at a magnification of 100 times to check for the occurrence of cracks on the outer surface of the 180 ° bent portion. A test piece in which cracking was not observed in this test is determined to have an MBR / t value of 1.0 or less. Both the LD and TD of each test material were tested with the number of tests n = 3, and x was evaluated when at least one of n = 3 was cracked (with cracks), and O was determined when no crack was generated. It was evaluated (no crack).

[Endurance times]
The test material was pressed to prepare a test piece having a shape close to an actual energized component, and was subjected to a fatigue test. FIG. 2 shows the shape of the test piece. This test piece corresponds to a material obtained by punching a material having a width of 1.4 mm with TD as a longitudinal direction from a plate having a thickness of 0.20 mm and performing a bending process including a 180 ° U-shaped bending. A load P was repeatedly applied to a position indicated by an arrow in FIG. The pushing amount was set to a displacement amount when an initial load of 20 N was applied. A load was repeatedly applied at the indentation amount, and the load was measured every 1000 times. The number of times the load became 50% or less of the initial load was defined as the number of times of durability. The reason that 50% of the initial load is used as a reference is that when the surface of the test piece is observed by SEM, cracks are observed in the test piece that has become 50% or less of the initial load. The number of tests was set to n = 5, and the worst durability count among them was adopted as the performance value of the plate. In this test, those having a durability of 10,000 times or more have remarkable durability in terms of repeated insertion / removal and switching operation as current-carrying parts mounted on electronic devices, compared to conventional general Cu-Ti based copper alloys. It can be judged that it has been improved.

(Stress relaxation rate)
A bending test piece (width: 10 mm) having a longitudinal direction of TD was sampled from each test material, and was arch-bent so that the surface stress at the center in the longitudinal direction of the test piece was 80% of 0.2% proof stress. Fixed in state. The surface stress is determined by the following equation.
Surface stress (MPa) = 6Etδ / L ₀ ²
However,
E: Modulus of elasticity (MPa)
t: thickness of sample (mm)
δ: Deflection height of sample (mm)
The stress relaxation rate was calculated from the bending habit after holding the test piece in this state at a temperature of 200 ° C. in the atmosphere for 1000 hours using the following equation.
Stress relaxation rate (%) = (L ₁ −L ₂ ) / (L ₁ −L ₀ ) × 100
However,
L ₀ : length of jig, that is, horizontal distance (mm) between sample ends fixed during the test
L ₁ : Sample length at the start of test (mm)
L ₂ : Horizontal distance between sample edges after test (mm)
A connector having a stress relaxation rate of 5.0% or less is evaluated as having high durability as a connector for a vehicle.
Tables 4 and 5 show these results.

  In the copper alloy sheet according to the present invention, no grain boundary reaction phase having a width exceeding 1.5 μm is observed, and among grain boundary segments of a crystal having a misorientation of 35 to 55 °, a grain boundary exceeding 0.5 μm in width is used. The number ratio of the grain boundary segments in which the reaction phase was present was 60% or less. All of these have excellent bending workability in which cracks do not occur in both LD and TD in 180 ° bending where 1 mm width and R / t = 1, and the number of durability in the above fatigue test is 10,000 or more. It exhibited durability. The electrical conductivity, 0.2% proof stress, bending workability, and stress relaxation rate were also good.

On the other hand, in Comparative Examples Nos. 21 to 23, since the aging treatment time t _A was outside the range of the expression (3) and was excessive, the width of the crystal having the misorientation of 35 to 55 ° occupying the grain boundary segment. The proportion of those having a grain boundary reaction phase exceeding 0.5 μm was high, and the improvement in bending workability and durability was insufficient. In No. 24, the rolling was not performed at 920 ° C. or higher by hot rolling, and a coarse grain boundary reaction phase was formed by completing the final hot rolling pass at a temperature lower than Ts, which indicates the solid solubility line temperature. However, sufficient bending workability and durability could not be obtained. In No. 25, the aging temperature was too low, and in No. 28, the Ti content was too small. Was low. In No. 26, the aging temperature was too high, so that a grain boundary reaction phase having a width of more than 1.5 μm was formed, and the ratio of the grain boundary having a misorientation of 35 to 55 ° generated by the grain boundary reaction phase was also high. And the durability was low. In No. 27, the rolling reduction in the temperature range of 920 ° C. or more was insufficient in hot rolling, so that a grain boundary reaction phase having a width of more than 1.5 μm was formed, and the bending workability and durability were poor. In No. 29, since the Ti content was too large, cracks were generated by hot rolling, and the subsequent steps were stopped. No. 30 had an excessively high Fe content, No. 32 had an excessively high Co content, and No. 34 had an excessively high Ni content. It formed and was inferior in bending workability and durability. In No. 31, since the slab heating temperature in the hot rolling was too high, cracks occurred in the hot rolling due to local melting, and the subsequent steps were stopped. In No. 33, the rolling reduction in the temperature range of 920 ° C. or more was insufficient in hot rolling, so that a grain boundary reaction phase exceeding 1.5 μm in width was formed, and the aging treatment time t _A also deviated from the expression (3). Therefore, the ratio of grain boundaries having a misorientation of 35 to 55 ° produced by the grain boundary reaction phase was high, and the bending workability and durability were significantly inferior. In No. 35, since the solution treatment temperature was too high, the crystal grains became coarse, and as a result, sufficient bending workability and durability could not be obtained. In No. 36, since the final pass temperature of hot rolling was lower than Ts, a grain boundary reaction phase finally exceeding 1.5 μm in width was generated, and the bending workability and durability were poor. In No. 37, a lubricating liquid having a large amount of lubricating components (oil) was used as a lubricating liquid at the time of hot rolling, so that the destruction and fragmentation of concentrated Ti in the cast structure became insufficient, and finally a grain boundary reaction exceeding 1.5 μm in width. A phase was formed, resulting in poor bending workability and durability. In No. 38, the aging treatment time t _A was shorter than the expression (3) and was short, so that the strength was insufficient and the durability was low accordingly.

  FIG. 3 exemplifies the relationship between the number of endurance times and the load reduction rate for the inventive example No. 1 and the comparative example No. 21. It can be seen that the durability is greatly improved according to the present invention.

Claims (7)

In mass%, Ti: 2.0 to 4.0%, Ni: 0 to 1.5%, Co: 0 to 1.0%, Fe: 0 to 0.5%, Sn: 0 to 1.2% , Zn: 0 to 2.0%, Mg: 0 to 1.0%, Zr: 0 to 1.0%, Al: 0 to 1.0%, Si: 0 to 1.0%, P: 0 to 0% 0.1%, B: 0 to 0.05%, Cr: 0 to 1.0%, Mn: 0 to 1.0%, V: 0 to 1.0%, and among the above elements, Sn and Zn , Mg, Zr, Al, Si, P, B, Cr, Mn, and V, the total content of which is 3.0% or less, and a copper alloy sheet having a composition consisting of a balance of Cu and unavoidable impurities, On the observation plane parallel to the plane, the average crystal grain size is 3.0 to 25.0 μm, the maximum width of the grain boundary reaction phase is 1.5 μm or less, and from one intersection point of the crystal grain boundary to the next intersection point. When the grain boundary part of is defined as one "grain boundary segment" Has a metal structure misorientation is less than 60% the number ratio of the grain boundary segments 10% or more of the grain boundary reaction phases are present in excess of the width 0.5μm of grain boundary segments of the crystal is 35 to 55 °, A copper alloy sheet having a 0.2% proof stress of 800 MPa or more in the rolling direction and a conductivity of 11.0% IACS or more.   When a bending test piece having a width of 1 mm whose longitudinal direction is the rolling direction (LD) and the perpendicular direction to rolling (TD) is sampled and subjected to a 180 ° bending test according to the winding method of JIS Z2248: 2014, no crack occurs. The copper alloy sheet according to claim 1, wherein the copper alloy sheet has bending workability in which a value of a ratio MBR / t between the minimum bending radius MBR and the sheet thickness t is 1.0 or less for both LD and TD. In mass%, Ti: 2.0 to 4.0%, Ni: 0 to 1.5%, Co: 0 to 1.0%, Fe: 0 to 0.5%, Sn: 0 to 1.2% , Zn: 0 to 2.0%, Mg: 0 to 1.0%, Zr: 0 to 1.0%, Al: 0 to 1.0%, Si: 0 to 1.0%, P: 0 to 0% 0.1%, B: 0 to 0.05%, Cr: 0 to 1.0%, Mn: 0 to 1.0%, V: 0 to 1.0%, and among the above elements, Sn and Zn , Mg, Zr, Al, Si, P, B, Cr, Mn and V have a total content of 3.0% or less, and a copper alloy sheet having a composition consisting of a balance of Cu and unavoidable impurities is hot-rolled. Cold rolling, solution treatment, when producing in the process having the steps of aging treatment in the above order,
In the hot rolling step, the heating temperature is set to 960 ° C or lower, and a lubricating liquid having a water content of 97.0% by mass or more is used in a rolling pass performed at 920 ° C or higher, and the total rolling ratio at 920 ° C or higher is 60% or more. And the final pass temperature of the hot rolling is set to Ts (° C.) or more in the following formula (1), and after the final pass, water cooling is started from a high temperature equal to or higher than Ts−100 ° C.
In the solution treatment step, the heating and holding temperature is in a range of 750 to 900 ° C,
In the aging treatment step, the maximum attained material temperature T _MAX (° C.) is set in the range of 400 to 700 ° C., and the holding time t _A (min) in the temperature range of 400 ° C. or more and T _MAX or less is defined by the following equation (2). Aging treatment is performed under the condition that the relationship of the X values to be satisfied satisfies the following equation (3).
The method for producing a copper alloy sheet according to claim 1 .
Ts = 151.5 × ln [Ti] +620.5 (1)
Here, ln is the natural logarithm, and [Ti] is the Ti content of the alloy expressed in mass%.
X = exp ((694−T _MAX ) / 28) (2)
0.20 ≦ t _A /X≦1.0 (3)   4. The method for producing a copper alloy sheet according to claim 3, wherein in the hot rolling step, a total rolling reduction at 920 ° C. or more is set to 60% or more and 95% or less. 5.   5. The method of manufacturing a copper alloy sheet according to claim 3, wherein in the hot rolling step, a reduction ratio (maximum reduction ratio) in a hot rolling pass having the largest reduction ratio is 15% or more. The method for manufacturing a copper alloy sheet according to any one of claims 3 to 5, wherein, in the aging treatment step, a maximum attained material temperature T _MAX (° C) is set in a range of 420 to 500 ° C.   A current-carrying part using the copper alloy sheet material according to claim 1 as a material.