JP2022025611A - Cu-Ni-Al SYSTEM COPPER ALLOY PLATE MATERIAL, MANUFACTURING METHOD THEREOF AND CONDUCTIVE SPRING MEMBER - Google Patents

Abstract

To remarkably improve the fatigue characteristics while maintaining discoloration resistance, in a high strength Cu-Ni-Al system copper alloy of a composition region exhibiting whitish metallic appearance.SOLUTION: The above problem is solved by a copper alloy plate material having a chemical composition satisfying, in mass%, Ni: 10.0 to 30.0%, Al: 1.00 to 6.50%, Ag: 0 to 0.50%, B: 0 to 0.10%, Co: 0 to 2.0%, Cr: 0 to 0.5%, Fe: 0 to 2.0%, Mg: 0 to 2.0%, Mn: 0 to 2.0%, P: 0 to 0.2%, Si: 0 to 2.0%, Sn: 0 to 2.0%, Ti: 0 to 2.0%, Zn: 0 to 2.0%, Zr: 0 to 0.3%, the remainder consisting of Cu and inevitable impurities, and Ni/Al≤9.0, in which an area rate of deposits having an area of 0.1 μm2 or larger is 2.0% or smaller in an observation surface parallel to the plate surface, and the Vickers hardness is 270 HV or larger.SELECTED DRAWING: Figure 3

Description

The present invention relates to a Cu—Ni—Al-based copper alloy plate material and a method for producing the same. Further, the present invention relates to a conductive spring member using the plate material.

The Cu—Ni—Al-based copper alloy can be increased in strength by the Ni—Al-based precipitate, and has a metallic appearance in which the color of copper is lighter than that of the copper alloy. This component-based copper alloy is useful as a conductive spring member such as a lead frame and a connector, and a non-magnetic high-strength member.

Conductive spring members such as connectors are required to have smaller and higher performance characteristics than ever before so that they can be miniaturized and highly integrated in electronic devices and the like that use them. In particular, the need for high durability is increasing because the repetitive load stress on the metal part increases due to the miniaturization of parts. In order to improve the durability of metal spring members such as connectors, it is important to improve the fatigue characteristics. On the other hand, in applications where the white surface appearance peculiar to Cu—Ni—Al copper alloys is emphasized, it is also important to have excellent discoloration resistance so that the beautiful white tone is not impaired.

So far, various studies have been conducted to improve various other characteristics while utilizing the high strength characteristics of Cu—Ni—Al-based copper alloys.
For example, Patent Document 1 describes Si in a Cu—Ni—Al-based copper alloy containing a predetermined amount of Si by a step of solution treatment at 700 to 1020 ° C. and aging treatment at 400 to 650 ° C. A technique for obtaining a material excellent in high strength, processability, and high conductivity by precipitating a γ'phase containing γ'phase with an average particle size of 100 nm or less has been shown. However, in the manufacturing process disclosed in Patent Document 1, sufficient improvement in fatigue characteristics cannot be expected.

Patent Document 2 discloses a technique for producing a plate material having an excellent "strength-bending workability balance" and excellent discoloration resistance in a Cu—Ni—Al-based copper alloy. In the manufacturing process, cold rolling strain is applied to the solution-treated material as necessary, and then the first aging treatment in a higher temperature range and the second aging treatment in a conventional general temperature range are applied. The method of continuously applying and is adopted. This two-step aging treatment makes it difficult for intergranular reaction-type discontinuous precipitation to occur, and at the same time, intragranular precipitation of fine second-phase particles that contribute to strength improvement occurs sufficiently, achieving an excellent strength-bending workability balance. It is said that it can be done. However, according to a recent study by the present inventors, although the production method of Patent Document 2 has an effect of suppressing discontinuous precipitation at the grain boundaries, when focusing on the abundance of grain boundary precipitates themselves, the effect is observed. The effect of reducing the abundance is limited, and sufficient improvement in fatigue characteristics is not observed.

Patent Document 3 discloses a technique for manufacturing a plate material having a high Young's modulus in a Cu—Ni—Al-based copper alloy. Specifically, cold rolling with intermediate annealing was performed under specific conditions, solutionization treatment was performed at a slow temperature rise rate, and finish cold rolling was performed under conditions where the rolling ratio was controlled to be low. Later, by applying aging treatment, a specific crystal orientation can be obtained, and a high Young's modulus can be realized. However, the manufacturing method of Patent Document 3 cannot sufficiently improve the fatigue characteristics.

In Patent Document 4, in a Cu—Ti copper alloy, which is an alloy system different from that of the present invention, the grain boundary reaction precipitation is suppressed by adopting the steps of solution treatment, precursor treatment, cold rolling, and aging treatment. The technology to be used is disclosed. However, since the Cu—Ni—Al-based copper alloy targeted by the present invention has a larger amount of alloy components added than the Cu—Ti-based copper alloy, the amount of grain boundary precipitates produced is also inherently large. Therefore, it is difficult to effectively reduce the amount of grain boundary precipitates only by applying the method of Patent Document 4, and more strict control of manufacturing conditions is required to improve the fatigue characteristics.

International Publication No. 2012/081573 Japanese Unexamined Patent Publication No. 2020-50923 Japanese Unexamined Patent Publication No. 2020-79436 Patent No. 6263333

Cu—Ni—Al-based copper alloys are useful alloys for conductive spring members such as connectors, but a method for improving fatigue characteristics that can sufficiently meet the needs for miniaturization of parts has not been established. An object of the present invention is to remarkably improve fatigue characteristics of a high-strength Cu—Ni—Al copper alloy plate while maintaining discoloration resistance.

In order to achieve the above object, the following inventions are disclosed in the present specification.
[1] In terms of mass%, Ni: 10.0 to 30.0%, Al: 1.00 to 6.50%, Ag: 0 to 0.50%, B: 0 to 0.10%, Co: 0. ~ 2.0%, Cr: 0 ~ 0.5%, Fe: 0 ~ 2.0%, Mg: 0 ~ 2.0%, Mn: 0 ~ 2.0%, P: 0 ~ 0.2% , Si: 0 to 2.0%, Sn: 0 to 2.0%, Ti: 0 to 2.0%, Zn: 0 to 2.0%, Zr: 0 to 0.3%, the balance is Cu and It is composed of unavoidable impurities, has a chemical composition satisfying the following formula (1), has an area ratio of 0.1 μm ² or more on the observation surface parallel to the plate surface, and has an area ratio of 2.0% or less. A copper alloy plate having a hardness of 270 HV or more.
Ni / Al ≤ 9.0 ... (1)
Here, the content value of the element represented by mass% is substituted in place of the element symbol in the formula (1).
[2] The copper alloy plate material according to the above [1], wherein the number density of coarse precipitate particles having a major axis of 1.0 μm or more is 3.0 × 10 ⁴ particles / mm ² or less on an observation surface parallel to the plate surface.
[3] The copper according to the above [1] or [2], wherein the number density of fine precipitate particles having a major axis of 5 to 50 nm is 1.0 × 10 ⁷ particles / mm ² or more on an observation surface parallel to the plate surface. Alloy plate material.
[4] The copper alloy plate material according to any one of the above [1] to [3], wherein the tensile strength in the direction perpendicular to rolling is 900 MPa or more.
[5] In terms of mass%, Ni: 10.0 to 30.0%, Al: 1.00 to 6.50%, Ag: 0 to 0.50%, B: 0 to 0.10%, Co: 0. ~ 2.0%, Cr: 0 ~ 0.5%, Fe: 0 ~ 2.0%, Mg: 0 ~ 2.0%, Mn: 0 ~ 2.0%, P: 0 ~ 0.2% , Si: 0 to 2.0%, Sn: 0 to 2.0%, Ti: 0 to 2.0%, Zn: 0 to 2.0%, Zr: 0 to 0.3%, the balance is Cu and A step of heating a slab composed of unavoidable impurities and having a chemical composition satisfying the following formula (1) at 1000 to 1150 ° C. (slab heating step).
A process of hot rolling under the condition that the rolling temperature in the final rolling pass is 800 ° C or higher, and then cooling under the condition that the average cooling rate from 700 ° C to 600 ° C is 40 ° C / s or higher (hot rolling). Process),
A step of performing a heat treatment for holding at 950 to 1100 ° C. for 30 to 360 seconds (solution treatment step) with a tension of 10.0 to 20.0 N / mm ² applied.
A step of subjecting the plate material after the solution treatment step to a heat treatment for holding at 700 to 900 ° C. for 10 to 300 seconds (first aging treatment step).
A process of cold rolling in a rolling ratio of 5 to 50% or less (aging cold rolling process),
A step of subjecting the plate material after the aging cold rolling step to a heat treatment for holding at 400 to 620 ° C. for 0.5 to 75 hours (second aging treatment step).
A method for producing a copper alloy plate material, wherein a plate material having an area ratio of a precipitate having an area of 0.1 μm ² or more and an area ratio of 2.0% or less on an observation surface parallel to the plate surface is obtained by a manufacturing process including.
Ni / Al ≤ 9.0 ... (1)
Here, the content value of the element represented by mass% is substituted in place of the element symbol in the formula (1).
[6] Between the hot rolling process and the solution treatment process,
A process of performing cold rolling with a rolling ratio of 50% or more (cold rolling process),
The method for producing a copper alloy plate material according to the above [5].
[7] A conductive spring member using the copper alloy plate material according to any one of the above [1] to [4] as a material.

As used herein, the "plate surface" is a surface perpendicular to the plate thickness direction of the plate material. The "plate surface" is sometimes called the "rolled surface". The "area ratio of precipitates having an area of 0.1 μm ² or more" can be obtained as follows.

[How to determine the area ratio of precipitates with an area of 0.1 μm ² or more]
The observation surface obtained by electrolytically polishing the plate surface under the following electrolytic polishing conditions and then subject to ultrasonic cleaning in ethanol for 20 minutes has no observation field with a magnification of 2000 times by FE-SEM (field emission scanning electron microscope). An observation image having an area S ₀ (μm ² ) is obtained by setting it at random. By processing the obtained image with image analysis software, the area of one independent precipitate region in the region corresponding to the precipitate (hereinafter referred to as “precipitate region”) is less than 0.1 μm ² . The total area S ₁ (μm ² ) of the total precipitate region excluding certain ones is obtained, and the value of (S ₁ / S ₀ ) × 100 is defined as the precipitate area ratio A (%) in this observation field. This operation is performed for five or more different visual fields that do not overlap, and the arithmetic mean value of the precipitate area ratio A of each visual field is obtained, and this is calculated as "area ratio (%) of precipitates having an area of 0.1 μm ² or more" of the plate material. ".
(Electropolishing conditions)
・ Electrolyte: Distilled water, phosphoric acid, ethanol, 2-propanol are mixed at 10: 5: 5: 1 ・ Liquid temperature: 20 ° C
・ Voltage: 15V
・ Electrolysis time: 20 seconds

As the Vickers hardness, the Vickers hardness of the plate surface of the plate material measured in accordance with JIS Z2244: 2009 can be adopted.

The "major axis" of a particle is defined as the diameter (μm or nm) of the smallest circle surrounding the particle. The "number density of coarse precipitate particles having a major axis of 1.0 μm or more" and the "number density of fine precipitate particles having a major axis of 5 to 50 nm" can be obtained as follows.

[How to determine the number density of coarse precipitate particles]
The FE-SEM was obtained by electrolyzing the plate surface under the following electrolysis conditions to dissolve only the Cu substrate to expose the precipitate particles, and then subjecting the plate surface to ultrasonic cleaning in ethanol for 20 minutes. The value obtained by dividing the total number of precipitate particles having a major axis of 1.0 μm or more observed on the FE-SEM image by the total observed area (mm ² ) when observed by (electrolyzed scanning electron microscope) is the coarse precipitate. The particle number density of the particles (pieces / mm ² ). The total observation area shall be 0.1 mm ² or more in total based on a plurality of non-overlapping observation fields set at random. Precipitate particles partially protruding from the observation field of view are counted if the major axis of the part appearing in the observation field of view is 1.0 μm or more.
(Electropolishing conditions)
・ Electrolyte: Distilled water, phosphoric acid, ethanol, 2-propanol are mixed at 10: 5: 5: 1 ・ Liquid temperature: 20 ° C
・ Voltage: 15V
・ Electrolysis time: 20 seconds

[How to determine the number density of fine precipitate particles]
About the observation surface obtained by electropolishing the plate surface under the electropolishing conditions described in "How to determine the area ratio of precipitates with an area of 0.1 μm ² or more" and then performing ultrasonic cleaning in ethanol for 20 minutes. , FE-SEM (field emission scanning electron microscope) is used for observation at a magnification of 100,000 times, and an observation field is randomly set in which some or all of the particles having an area of 0.1 μm ² or more are not included in the field. For the observation field of view, the number of precipitate particles having a major axis of 5 to 50 nm among the particles in which the entire outline of the particles is visible is counted. This operation is performed for 10 or more observation fields where the regions do not overlap, and the value obtained by dividing the total N _TOTAL of the counts in all the observed fields by the total area of the observation field is converted into the number per 1 mm ² . Is the number density of fine precipitate particles (pieces / mm ² ).

The rolling ratio from a certain plate thickness t ₀ (mm) to a certain plate thickness t ₁ (mm) can be obtained by the following equation (2).
Rolling rate (%) = [(t ₀ -t ₁ ) / t ₀ ] x 100 ... (2)

According to the present invention, in a Cu—Ni—Al-based copper alloy plate material having a white metallic appearance in a composition range, it has high strength, fatigue characteristics are remarkably improved, and discoloration resistance is excellent. Things are now available.

The figure which illustrated the "Threshold" screen in the image analysis software. For Comparative Example No. 35, an FE-SEM observation image (upper) at a magnification of 2000 times and a mapping image (lower) showing the location of the “precipitate having an area of 0.1 μm ² or more” obtained by image processing the image (upper). ) Is illustrated. Regarding Example No. 6 of the present invention, an FE-SEM observation image (upper) at a magnification of 2000 times and a mapping image showing the location of the “precipitate having an area of 0.1 μm ² or more” obtained by image processing the image (upper). The figure exemplifying the lower row).

[Chemical composition]
The present invention targets Cu—Ni—Al-based copper alloys. Hereinafter, "%" regarding the alloy component means "mass%" unless otherwise specified.

Ni, together with Cu, is a major element constituting a matrix (metal base) of a Cu—Ni—Al-based copper alloy. Further, a part of Ni in the alloy combines with Al to form a Ni—Al-based precipitate, and the fine particles contribute to the improvement of strength. In order to obtain sufficient strength, it is desirable to secure a Ni content of 10% or more. Further, as the Ni content increases, a whiter metallic appearance is exhibited as compared with other general copper alloys. However, like other copper alloys, when exposed to a high humidity environment, a thin oxide film is formed on the metal surface, and the color may change to the extent that it can be seen from the outside. In that case, the beautiful white appearance is impaired. In particular, when discoloration resistance is important, it is more preferable to increase the Ni content to 12.0% or more and secure the Al content as described later. It is more effective to set the Ni content to 15.0% or more. On the other hand, when the Ni content is high, the hot workability deteriorates. The Ni content is limited to 30.0% or less and may be limited to 25.0% or less. Further, the Ni content may be controlled to 18.0% or more and 22.0% or less.

Al is an element that forms a Ni—Al-based precipitate. If the Al content is too small, the strength improvement will be insufficient. Further, the discoloration resistance can be improved by increasing the Al content as the Ni content increases. Furthermore, it was found that it is important to adjust the components so that the Ni / Al ratio does not become too high in order to improve the fatigue characteristics while obtaining a sufficient strength level. As a result of various studies, it is necessary that the Al content is 1.00% or more and the Ni / Al ratio satisfies the following formula (1). It is more preferable to satisfy the following equation (1)'.
Ni / Al ≤ 9.0 ... (1)
2.0 ≤ Ni / Al ≤ 8.0 ... (1)'
Here, the content value of the element represented by mass% is substituted in the place of the element symbol of the equations (1) and (1)'.
On the other hand, if the Al content is excessive, the hot workability deteriorates. The Al content is limited to 6.50% or less.

As other elements, Ag, B, Co, Cr, Fe, Mg, Mn, P, Si, Sn, Ti, Zn, Zr and the like can be contained, if necessary. The content range of these elements is Ag: 0 to 0.50%, B: 0 to 0.10%, Co: 0 to 2.0%, Cr: 0 to 0.5%, Fe: 0 to 2. .0%, Mg: 0 to 2.0%, Mn: 0 to 2.0%, P: 0 to 0.2%, Si: 0 to 2.0%, Sn: 0 to 2.0%, Ti : 0 to 2.0%, Zn: 0 to 2.0%, Zr: 0 to 0.3%. Further, the total amount of these optional additive elements is preferably 2.0% or less, and may be 1.2% or less, or 0.5% or less.

[Area ratio of precipitates with an area of 0.1 μm ² or more]
In the Cu—Ni—Al-based copper alloy targeted by the present invention, a second phase mainly composed of a Ni—Al-based intermetallic compound is likely to be generated. Of the second phase, particles finely deposited in crystal grains by aging treatment (“fine precipitates” described later) contribute to the improvement of strength. However, in this alloy system, discontinuous precipitation at the grain boundaries occurs during the aging treatment, and the grain boundary precipitates existing at the grain boundaries are a factor that hinders the improvement of the fatigue characteristics. In addition to the discontinuous precipitation at the grain boundaries, the second phase, which could not be sufficiently solid-dissolved by the solution treatment, and the precipitates generated by the continuous precipitation in the crystal grains are contained in the crystal grains. It may be coarsened to form micron-order coarse particles (“coarse precipitates” described below).

The inventors have conducted detailed studies on the size and amount of precipitates that affect fatigue properties in this alloy system. As a result, it was found that it is extremely effective to reduce the abundance of precipitates having an area of 0.1 μm ² or more observed in the metallographic structure. Specifically, by setting the texture state in which the area ratio of the precipitate having an area of 0.1 μm ² or more is 2.0% or less on the observation surface parallel to the plate surface, a remarkable improvement effect of fatigue characteristics can be obtained. .. It is more effective to set the area ratio of the precipitate having an area of 0.1 μm ² or more to 1.6% or less, and further to set it to 1.0% or less.

Precipitates with an area of 0.1 μm ² or more include both “grain boundary precipitates” and “intragrain precipitates”, but the area ratio in the metal structure is large for precipitates with an area of 0.1 μm ² or more. The portion is occupied by "grain boundary precipitates". Fatigue characteristics are particularly affected by the size and amount of grain boundary precipitates. Therefore, reducing the area ratio specified by the above-mentioned "Method for determining the area ratio of precipitates having an area of 0.1 μm ² or more" is extremely a means for improving the fatigue characteristics of the plate material of this alloy system. It is valid.

[Vickers hardness]
The Cu—Ni—Al-based copper alloy plate material of the present invention has been increased in strength by aging treatment. Vickers hardness can be adopted as an index for increasing the strength by aging treatment. In order to sufficiently meet the needs for miniaturization of the conductive spring member, it is desired that the Vickers hardness is 270 HV or more. It is more preferably 300 HV or more, further preferably 320 HV or more, and may be 330 HV or more.

[Number density of coarse precipitate particles with a major axis of 1.0 μm or more]
Coarse precipitate particles having a major axis of 1.0 μm or more occupy a part of the above-mentioned “area ratio of precipitates having an area of 0.1 μm ² or more”. When the area ratio of the precipitate having an area of 0.1 μm ² or more is large, the number density of the coarse precipitate particles having a major axis of 1.0 μm or more tends to increase. However, the coarse particles caused by the second phase remaining after the solution treatment and the coarse precipitates in the crystal grains generated by the coarse growth during the aging treatment do not have a great adverse effect on the fatigue characteristics. Rather, they cause a decrease in bending workability. Since coarse precipitate particles having a major axis of 1.0 μm or more do not contribute to the improvement of strength, it is desirable that the abundance thereof is small. The abundance density of coarse precipitate particles having a major axis of 1.0 μm or more is preferably 3.0 × 10 ⁴ particles / mm ² or less. Considering the use in which bending workability is important, the abundance density of coarse precipitate particles having a major axis of 1.0 μm or more is more preferably 0.3 × 10 ⁴ particles / mm ² or less, which is extremely small.

[Number density of fine precipitate particles with a major axis of 5 to 50 nm]
The fine precipitate particles having a major axis of 5 to 50 nm contribute to the improvement of strength by being dispersed in the matrix (metal substrate). Among them, those having a major axis of about 20 nm or more also contribute to the improvement of bending workability. The fine precipitate formed in the Cu—Ni—Al-based copper alloy of the present invention is a Ni—Al-based precipitate phase mainly composed of the intermetallic compound Ni ₃ Al. From the viewpoint of strength improvement and bending workability, the number density of fine precipitate particles having a major axis of 5 to 50 nm is preferably 1.0 × 10 ⁷ / mm ² or more. In particular, in order to stably obtain a fairly high strength level as a copper alloy, for example, the tensile strength in the direction perpendicular to rolling (TD) is 1000 MPa or more, the number density of fine precipitate particles having a major axis of 5 to 50 nm is set to 5. It is preferably .0 × 10 ⁷ pieces / mm ² or more, and may be 8.0 × 10 ⁷ pieces / mm ² or more.

[Tensile strength]
As a copper alloy plate material used as a material for conductive spring members that are becoming smaller and thinner, the tensile strength in the direction perpendicular to rolling (TD) is desired to be 900 MPa or more, and more preferably 950 MPa or more. Further, as shown in Examples described later, it is possible to adjust the tensile strength in the direction perpendicular to rolling to 1000 MPa or more or 1100 MPa or more, and it is possible to realize a strength level according to the application. Such a high-strength level copper alloy plate material, coupled with a white-like appearance, is also suitable as a substitute for an iron-based conductive spring member whose conductivity is originally lower than that of a copper-based material.

[Production method]
The copper alloy plate material described above can be produced, for example, by the following manufacturing process.
Melting / casting → slab heating → hot rolling → cold rolling → (intermediate annealing → cold rolling) → solution heat treatment → → 1st aging treatment → aging cold rolling → 2nd aging treatment Although not described in the above, after hot rolling, surface milling is performed as necessary, and after each heat treatment, pickling, polishing, or further degreasing is performed as necessary. Hereinafter, each step will be described.

[Melting / Casting]
The slab may be manufactured by continuous casting, semi-continuous casting, or the like. From the viewpoint of preventing the oxidation of Al, it is preferable to carry out the dissolution in the chamber under an atmosphere of an inert gas or under vacuum.

[Cast heating]
The slab is heated and held at 1000 to 1150 ° C. This heating can be carried out by utilizing the slab heating step at the time of hot rolling. Conventionally, slab heating of a Cu—Ni—Al-based copper alloy has often been performed at a temperature of 950 ° C. or lower. In the present invention, in the composition range where the Ni and Al contents are high, the crystal grains that promote continuous precipitation by aging treatment to sufficiently generate fine precipitates that contribute to strength in the crystal grains and inhibit the improvement of fatigue characteristics. It is necessary to suppress discontinuous precipitation at the boundary. For that purpose, it is effective to heat the slab to the above-mentioned high temperature to dissolve the coarse second phase existing in the cast structure as much as possible. However, if the temperature exceeds 1150 ° C., the portion of the cast structure having a low melting point becomes fragile, and there is a risk of cracking during hot rolling. It is more effective that the heating holding time in the above temperature range is 1.5 hours or more, and it is more effective that the heating holding time is 2 hours or more. Considering economic efficiency, it is desirable to set the slab heating time in the above temperature range within the range of 5 hours or less.

[Hot rolling]
In hot rolling, the rolling temperature of the final pass is set to 800 ° C. or higher. The temperature of each rolling pass can be represented by the surface temperature of the material immediately after leaving the work roll at that rolling pass. After the rolling in the final pass is completed, forced cooling is started as soon as possible, and cooling is performed under the condition that the average cooling rate from 700 ° C. to 600 ° C. is 40 ° C./s or more. By terminating the hot rolling process under such conditions, it is possible to obtain a hot rolled material in which unnecessary precipitation is suppressed, which is the suppression of grain boundary precipitation in the second aging treatment step described later, that is, the above-mentioned description. It was found to be extremely effective in significantly reducing the "area ratio of precipitates having an area of 0.1 μm ² or more". From the viewpoint of stably achieving a final pass rolling temperature of 800 ° C. or higher in the operation of a mass production site, the plate thickness (finished plate thickness) after hot rolling is preferably in the range of, for example, 5 to 15 mm, preferably 7 to 15 mm. It is more preferable to set it in the range of.

Water cooling is generally used as the forced cooling means after hot rolling. For example, Patent Document 2 also describes that after hot rolling of a Cu—Ni—Al copper alloy, “quick cooling by water cooling or the like is preferable”. (Paragraph 0033). Water cooling can also be adopted in the present invention. However, in normal hot rolling performed at mass production sites, it is a facility limitation to strictly control the above-mentioned fast cooling rate over the entire plate width of a relatively thick hot-rolled plate having a plate thickness of 5 to 15 mm, for example. Therefore, it is not always easy, and the cooling rate required by the present invention has not been obtained by "quenching" by ordinary water cooling. Even in the technique of Patent Document 2, strict control to the high cooling rate as described above is not required. By using equipment with enhanced water cooling capacity, it is possible to achieve both a high final pass rolling temperature of 800 ° C or higher and a fast cooling rate of 40 ° C / s or higher.

[Cold rolling]
Before the solution treatment, cold rolling can be performed to adjust the plate thickness. If necessary, the process of "intermediate annealing → cold rolling" may be added once or multiple times. The rolling ratio in cold rolling before the solution treatment (in the case of intermediate annealing, the rolling ratio in cold rolling after the final intermediate annealing) can be, for example, 50% or more. The upper limit of the rolling ratio may be set in the range of, for example, 99.5% or less according to the capacity of the mill.

[Solution processing]
The main purpose of the solution treatment is to sufficiently dissolve the second phase of the Ni—Al system (solution formation) before the aging treatment. In the present invention, the temperature is higher than the solution treatment temperature (about 800 to 900 ° C.) of a general Cu—Ni—Al-based copper alloy. Specifically, the time for holding the material in the temperature range of 950 to 1100 ° C. is 30 to 360 seconds. When heated to such a high temperature range, the second phase can be sufficiently solid-dissolved even if the holding time is short as described above. The technique of Patent Document 2 also employs a method of performing a short-time solution treatment in a high temperature region. However, in the present invention, this solution treatment is applied to a material at 10.0 to 20.0 N / mm ² . Perform with high tension applied. It was found that following these solution treatment conditions is extremely effective in stably obtaining the effect of significantly improving fatigue characteristics. The mechanism is not always clear at this time, but it is considered that a recrystallized structure with moderate strain is formed by high temperature and short time solution treatment under high tension application, and the inside of the crystal grains is considered to be formed. It is speculated that the strain functions as the starting site of aging precipitation and promotes fine precipitation in the crystal grains, and as a result, the grain boundary reaction is suppressed and the fatigue characteristics are improved. If this tension is too low or too high, the amount of grain boundary precipitates will increase and the "area ratio of precipitates with an area of 0.1 μm ² or more" will increase, and it will not be possible to achieve a significant improvement in fatigue characteristics. Therefore, the inventors believe that the introduction of appropriate strain in the solution treatment functions as the core of intragranular precipitation.

The tension can be controlled by, for example, the driving force of the bridle rolls at both ends of the heating zone while passing through a continuous heat treatment furnace. The direction of tension is the rolling direction. The first aging treatment is performed following the solution treatment, but the first aging treatment can also be performed in the cooling process of the solution treatment. When cooling to around room temperature after the solution treatment, it is preferable to rapidly cool the product so that the average cooling rate from 900 ° C. to 300 ° C. is 100 ° C./s or more.

[1st aging process]
After the solution treatment, it is directly subjected to the first aging treatment without imparting processing strain due to cold rolling. The first aging treatment is carried out under the condition of holding at 700 to 900 ° C. for 10 to 300 seconds. It is considered that the recrystallized structure to which the strain is applied as described above is obtained by the solution treatment under the application of tension. When such a texture state is heated under the above conditions, a large number of continuous precipitation nuclei are formed in the crystal grains, which is effective in suppressing the formation of grain boundary precipitates in the second aging treatment as a result. It is presumed that it works for. After the heat retention of the first aging treatment, it is preferable to cool under the condition that the average cooling rate from 700 ° C. to 600 ° C. is 70 ° C./s or more. Since the first aging treatment is short, it is efficient to perform it in a continuous heat treatment furnace.

[Aging cold rolling]
Cold rolling is performed between the first aging treatment and the second aging treatment. This cold rolling is referred to as "aging cold rolling" in the present specification. This cold rolling can be the final cold rolling to obtain the final plate thickness. For example, it is preferable to finish the plate with a thickness of 0.03 to 0.5 mm. The rolling ratio in aging cold rolling needs to be in the range of 5 to 50%, more preferably in the range of 5 to 40%. By subjecting the material that has undergone the first aging treatment to this relatively light cold rolling, processing strain (that is, dislocation) is appropriately introduced, and continuous precipitation in the crystal grains is promoted by the second aging treatment. Will be done. If the rolling ratio of aging cold rolling is too high, the structure state has a large amount of grain boundary precipitates, and no significant improvement in fatigue characteristics can be expected.

[Second aging process]
Next, a "second aging process" is performed as the final aging process. The second aging treatment is carried out within the condition range of holding the material in the microstructured state after the above-mentioned aging cold rolling at 400 to 620 ° C. for 0.5 to 75 hours. Within this condition range, the aging condition at which the Vickers hardness is 270 HV or more can be set according to the target strength level. By the second aging treatment, a structure in which fine precipitates are dispersed in the crystal grains is obtained, and high strength is realized. At the same time, the formation of grain boundary precipitates is remarkably suppressed, and the structure state has a small "area ratio of precipitates having an area of 0.1 μm ² or more", and a remarkable improvement effect of fatigue characteristics can be stably obtained. It is desirable that the second aging treatment be performed in a nitrogen atmosphere using a batch heat treatment furnace.

Using the plate material according to the present invention obtained as described above as a material, it is possible to perform processing including press forming processing and bending processing to obtain a highly durable conductive spring member.

A copper alloy having the chemical composition shown in Table 1 was melted and cast using a vertical semi-continuous casting machine. The obtained slabs were heated and held at the temperatures and times shown in Tables 2 and 3, then extracted, hot-rolled, and water-cooled. The total hot rolling ratio is 85-95%. The rolling temperature of the final pass, the average cooling rate from 700 ° C to 600 ° C, and the finished plate thickness after hot rolling are shown in Tables 2 and 3. For water cooling after hot rolling, a cooling facility with an increased amount of water was used so that a sufficient cooling rate could be obtained over the entire plate width. The average cooling rate from 700 ° C to 600 ° C is calculated from the plate surface temperature T ₀ (° C) immediately before the start of water cooling and the plate surface temperature T ₁ (° C) immediately after the end of water cooling, and the elapsed time t (s) during that period. did. In each example, it was confirmed that T ₀ was 700 ° C. or higher, T ₁ was 600 ° C. or lower, and no increase in surface temperature due to reheat from the central portion of the plate thickness was observed after the completion of water cooling. Therefore, the value obtained by deferring the calculated value of (T ₀ -T ₁ ) / t in 5 ° C increments (for example, if the calculated value is 68 ° C / s, the value converted to 65 ° C / s) is changed from 700 ° C to 600 ° C. The average cooling rates up to are listed in Tables 2 and 3. When this value is 40 ° C./s or more, it can be considered that a cooling rate of at least an average cooling rate of 40 ° C./s or more is secured from 700 ° C. to 600 ° C. during cooling.

In some examples (Nos. 37 to 39) in which cracks were generated by hot rolling, production was discontinued at that point. After hot rolling, the oxide layer on the surface was removed (face milled) by mechanical polishing, and cold rolling was performed to the plate thickness shown in Tables 2 and 3. In No. 47, intermediate annealing at 675 ° C. × 10 hours was carried out in the middle of this cold rolling step. Other than that, it is straight rolling without intermediate annealing. Each of the obtained cold-rolled materials was solution-treated using a continuous annealing furnace. The solution heat treatment was carried out under the conditions shown in Tables 2 and 3 while applying a predetermined tension to the plate in the in-core plate. Tension was controlled by the driving force of the bridle rolls on the entry and exit sides of the heating zone. The cooling after heating was water cooling under the condition that the average cooling rate from 900 ° C to 300 ° C was 100 ° C / s or more. After the solution treatment, except for some examples (No. 35, 47, 48), the first aging treatment described later was directly performed without applying cold rolling strain. In Nos. 35 and 48, after the solution treatment, the final cold rolling was performed to a plate thickness of 0.1 mm, and then the first aging treatment was performed. In No. 47, after the solution heat treatment, the final cold rolling was performed to a plate thickness of 0.1 mm, and then the film was directly subjected to the final aging treatment corresponding to the second aging treatment described later. In some of the above examples, the cold rolling performed immediately after the solution treatment is described in the table as "cold rolling before aging".

In the first aging treatment, after holding the temperature shown in Tables 2 and 3 for the time shown in the same table using a continuous annealing furnace, the average cooling rate from 700 ° C. to 600 ° C. is shown in the same table. It was water-cooled under the conditions that became the value. Then, except for some examples (No. 35 and 48), the final cold rolling was performed at the rolling ratios shown in Tables 2 and 3 to the final plate thickness shown in the same table. Since this cold rolling is performed between the first and second aging treatments, it is referred to as "aging cold rolling" in the present specification. In Nos. 35 and 48, cold rolling is not performed during aging.

Next, except for some examples (No. 35, 47, 48), the plate material after aging cold rolling was subjected to "second aging treatment", which is the final aging treatment. In Nos. 35 and 48, the plate material after the first aging treatment was directly subjected to the second aging treatment. Further, in No. 47, the plate material after cold rolling before aging was directly subjected to the final aging treatment. These final aging treatments were carried out using a batch type annealing furnace under the conditions of holding at the temperature described in the column of "second aging treatment" in Tables 2 and 3 for the time described in the same table. It was carried out in a nitrogen atmosphere, and the cooling was air cooling. In this way, plate material products (test materials) having the final plate thickness shown in Tables 2 and 3 were obtained. The following surveys were conducted on each test material.

(Area ratio of precipitates with an area of 0.1 μm ² or more)
Accelerate the observation surface prepared by electrolytic polishing and ultrasonic cleaning by FE-SEM (manufactured by JEOL Ltd .; JSM-7200F) according to the above "How to determine the area ratio of precipitates with an area of 0.1 μm ² or more". Observations were made at a voltage of 15 kV and an irradiation current of 14, and observation images were obtained for 5 different non-overlapping visual fields set at random. The image size was 1280 pixels × 960 pixels. The electropolishing was performed using an electropolishing apparatus (ElectroMet 4) manufactured by BUEHLER. The ultrasonic cleaning was performed for 20 minutes using an ultrasonic cleaning machine "BRANSONIC M2800-J". ImageJ (National Institutes of Health (NIH), Version 1.52a) was used as the image analysis software. The analysis condition by the software is to measure the number of pixels of the scale bar length of the captured FE-SEM image on the "Set Scale" screen displayed by sequentially selecting Analyze and Set Scale, and input it to Disstance in pixels. .. Subsequently, the length (μm) of the scale bar is input to the Known distance, the Pixel aspect ratio is set to 1.0, the Unit of length is set to μm, and the size of the precipitate is set so that the size of the precipitate can be recognized by the software. After that, on the "Resize Image Canvas" screen, the Wizard is set to 1280 pixels, the Height is set to 950 pixels, the Position is set to Top-Center, and the image of the FE-SEM image portion excluding the scale bar portion is displayed. After setting this scale and deleting the scale bar display part, the upper limit of the threshold value is 255 and the lower limit is the number ratio of pixels on the "Threshold" screen that is displayed by sequentially selecting Image, Adjust, and Thrashold. It was set to the value closest to 5%. FIG. 1 illustrates a "Threshold" screen. Specifically, the upper limit of the threshold value at the point P in FIG. 1 was set to 255, and the lower limit of the threshold value was set so that the value displayed at the place Q was the closest to 5%. After that, in the "Analyze Particles" screen of the software, Size is set to "0.10-Infinity" as a condition for excluding those having an area of one independent precipitate region of less than 0.1 μm ² . Furthermore, with Circularity set to 0.00-1.00 and Show set to MASK, particle analysis is performed by setting conditions in which only the items of Display resonances, Clear reacts, Summarize, and Particle areas are checked, and the field of view is described. The area ratio A of the precipitate having an area of 0.1 μm ² or more was determined. This operation was performed for five visual fields, and the arithmetic mean value of the precipitate area ratio A of each visual field was obtained, and this was defined as the "area ratio (%) of precipitates having an area of 0.1 μm ² or more" of the plate material.

For reference, FIGS. 2 and 3 show the presence of an FE-SEM observation image (upper) at a magnification of 2000 times and a “precipitate having an area of 0.1 μm ² or more” obtained by image processing the image. An example is a mapping image (lower). FIG. 2 is Comparative Example No. 35, and FIG. 3 is the present invention Example No. 6. The length of the white scale bar shown at the bottom of the FE-SEM observation image corresponds to 10 μm.

(Number density of coarse precipitate particles)
According to the above "How to determine the number density of coarse precipitate particles", observe the observation surface prepared by electrolytic polishing and ultrasonic cleaning with FE-SEM, and determine the number density of coarse precipitate particles with a major axis of 1.0 μm or more. I asked. The electropolishing was performed using an electropolishing apparatus (ElectroMet 4) manufactured by BUEHLER. The ultrasonic cleaning was performed for 20 minutes using an ultrasonic cleaning machine "BRANSONIC M2800-J".

(Number density of fine precipitate particles)
According to the above "How to determine the number density of fine precipitate particles", the observation surface prepared by electrolytic polishing and ultrasonic cleaning was observed with FE-SEM (manufactured by JEOL Ltd .; JSM-7200F), and the major axis was 5. The number density (pieces / mm ² ) of fine second-phase particles having a diameter of about 50 nm was determined. The electropolishing was performed using an electropolishing apparatus (ElectroMet 4) manufactured by BUEHLER. The ultrasonic cleaning was performed for 20 minutes using an ultrasonic cleaning machine "BRANSONIC M2800-J".

(Fatigue strength)
Resonated by a fatigue tester (manufactured by Nippon Techno Plus Co., Ltd .; RF-RT) using a test piece (without drilling) with a width of 3 mm and a length of 15 to 25 mm, the width direction being the rolling direction and the longitudinal direction being the rolling perpendicular direction. A fatigue test was conducted by the method. The position of the laser spot for measuring the amplitude was set to a position 1 mm from the end of the test piece. When the Young's modulus reached 98% of the initial (pre-test) Young's modulus, it was determined that the material was "fatigue". Measurements were made with various stresses in increments of 20 MPa, and the maximum stress at which fatigue did not occur after ¹⁰⁷ times was defined as the fatigue strength (MPa). This operation was carried out 5 times with one test material, and the average value of the fatigue strength of 5 times (rounded to the nearest 1) was adopted as the fatigue strength of the test material. Those having a fatigue strength of 200 MPa or more are evaluated to have very excellent fatigue characteristics as a plate material of a high-strength Cu—Ni—Al alloy. For Young's modulus, a tensile test with a crosshead displacement speed vc of 0.02 mm / s was performed on a JIS No. 5 tensile test piece whose longitudinal direction was parallel to rolling, which was collected from the plate material, based on JISZ 2241: 2011. The strain and stress values are recorded every 0.1 seconds, and the regression line in the stress-strain orthogonal coordinate system is calculated by the minimum square method using all the strain and stress data recorded between 100 MPa and 400 MPa. It was the slope of the regression line when it was determined.

(Hardness)
The Vickers hardness of the plate surface was measured by a method according to JIS Z2244: 2009. The average value d (mm) of the diagonal lengths d ₁ and d ₂ of the formed indentation (indentation) is 2/3 or less of the sample plate thickness. The average value of 5 points excluding the value was adopted as the hardness of the test material.

(Tensile strength)
Tensile test pieces (JIS No. 5) in the direction perpendicular to rolling (TD) were collected from each test material, and a tensile test was performed in accordance with JIS Z2241 with the number of tests N = 3, and the tensile strength was measured. The average value of N = 3 was used as the performance value of the test material.

(Discoloration resistance)
A sample having a width of 10 mm and a length of 65 mm is taken from the test material, and the plate surface (rolled surface) is dry-polished with a polishing paper having a count of 1200 (grain size P1200 specified in JIS R6010: 2000) and then infiltrated with ethanol. A weather resistance test piece was prepared by wiping off the polishing powder with a Kimwipe (registered trademark) and drying it. The weather resistance test was carried out by exposing the test piece to an atmosphere having a temperature of 50 ° C. and a relative humidity of 95% for 24 hours. L ^* a ^* b ^* was measured on the surface of the test piece before and after the weather resistance test, respectively, and the color difference ΔE ^* _ab according to the display color was determined by L ^* a ^* b ^* specified in JIS Z8730: 2009. If the color difference ΔE ^* _ab is less than 5.0, it can be judged that the conductive spring member has good discoloration resistance. Therefore, those having a color difference ΔE ^* _ab of less than 5.0 were judged to be acceptable (discoloration resistance; good). For reference, weather resistance tests were also conducted on each plate material of oxygen-free copper (C1020), 70-30 brass (C2600), and Nepalese brass (C4622) under the same conditions. As a result, the color difference ΔE ^* _ab was 11.0 for oxygen-free copper, 10.5 for 70-30 brass, and 10.7 for Nepalese brass.
The results of these surveys are shown in Tables 4 and 5.

All of the Cu—Ni—Al-based copper alloy plates of the examples of the present invention are excellent in strength, fatigue characteristics, and discoloration resistance. Of these, No. 13 had a metal structure having more coarse precipitates in the crystal grains than in other invention examples because the aging treatment time was relatively long in the composition having a relatively high Ni / Al. However, the area ratio of the precipitate having an area of 0.1 μm ² or more was kept low, and a remarkable improvement in fatigue characteristics was observed as compared with that of the comparative example.

Among the comparative examples, Nos. 31 to 36 and 41 to 48 are examples of copper alloys having a chemical composition satisfying the provisions of the present invention, in which a plate material is manufactured by a manufacturing process that does not meet the manufacturing conditions specified in the present invention. Specifically, No. 31 had a low slab heating temperature. In No. 32, the rolling temperature in the final hot rolling pass was low. No. 33 had a low solution treatment temperature. No. 34 had a small average cooling rate from 700 ° C. to 600 ° C. after the final pass of hot rolling. In No. 35, the final cold rolling was performed between the solution treatment and the first aging treatment. No. 36 had a short time for the first aging process. In No. 41, the solution treatment was performed at a conventional low tension level. No. 42 had a high rolling ratio in aging cold rolling. No. 43 had a high tension during the solution treatment. In No. 44, the temperature of the first aging treatment was high. In No. 45, the temperature of the first aging treatment was low. No. 46 had a long time for the first aging process. No. 47 has a small average cooling rate from 700 ° C to 600 ° C after the final pass of hot rolling, and after the cold rolling process with intermediate annealing, solution treatment is performed at a conventional low tension level. The process corresponding to the first aging treatment was not carried out. No. 48 has a small average cooling rate from 700 ° C to 600 ° C after the final hot rolling pass, and the final cold rolling is performed between the solution treatment at a low tension level and the first aging treatment, which are generally common in the past. rice field. In all of these examples, due to the formation of a large amount of grain boundary precipitates, the texture state was such that the area ratio of the precipitates having an area of 0.1 μm ² or more was large, and the improvement of the fatigue characteristics was insufficient.

Nos. 37 to 39 are examples in which production was discontinued at that point because cracks occurred during hot rolling. Of these, No. 37 had a slab heating temperature that was too high. No. 38 had too high Ni content. No. 39 had an too high Al content.

In No. 40, the Al content was low and the Ni / Al ratio was too high in the chemical composition, so that the discoloration resistance was inferior and the strength level was also low.

Claims (7)

By mass%, Ni: 10.0 to 30.0%, Al: 1.00 to 6.50%, Ag: 0 to 0.50%, B: 0 to 0.10%, Co: 0 to 2. 0%, Cr: 0 to 0.5%, Fe: 0 to 2.0%, Mg: 0 to 2.0%, Mn: 0 to 2.0%, P: 0 to 0.2%, Si: 0 to 2.0%, Sn: 0 to 2.0%, Ti: 0 to 2.0%, Zn: 0 to 2.0%, Zr: 0 to 0.3%, the balance is Cu and unavoidable impurities. It has a chemical composition that satisfies the following formula (1), has an area ratio of 0.1 μm ² or more on the observation surface parallel to the plate surface, and has a Vickers hardness of 2.0% or less. Copper alloy plate material with 270 HV or higher.
Ni / Al ≤ 9.0 ... (1)
Here, the content value of the element represented by mass% is substituted in place of the element symbol in the formula (1). The copper alloy plate material according to claim 1, wherein the number and density of coarse precipitate particles having a major axis of 1.0 μm or more on an observation surface parallel to the plate surface is 3.0 × 10 ⁴ particles / mm ² or less. The copper alloy plate material according to claim 1 or 2, wherein the number density of fine precipitate particles having a major axis of 5 to 50 nm is 1.0 × 10 ⁷ particles / mm ² or more on an observation surface parallel to the plate surface. The copper alloy plate material according to any one of claims 1 to 3, wherein the tensile strength in the direction perpendicular to rolling is 900 MPa or more. By mass%, Ni: 10.0 to 30.0%, Al: 1.00 to 6.50%, Ag: 0 to 0.50%, B: 0 to 0.10%, Co: 0 to 2. 0%, Cr: 0 to 0.5%, Fe: 0 to 2.0%, Mg: 0 to 2.0%, Mn: 0 to 2.0%, P: 0 to 0.2%, Si: 0 to 2.0%, Sn: 0 to 2.0%, Ti: 0 to 2.0%, Zn: 0 to 2.0%, Zr: 0 to 0.3%, the balance is Cu and unavoidable impurities. A step of heating a slab composed of and having a chemical composition satisfying the following formula (1) at 1000 to 1150 ° C. (slab heating step).
A process of hot rolling under the condition that the rolling temperature in the final rolling pass is 800 ° C or higher, and then cooling under the condition that the average cooling rate from 700 ° C to 600 ° C is 40 ° C / s or higher (hot rolling). Process),
A step of performing a heat treatment for holding at 950 to 1100 ° C. for 30 to 360 seconds (solution treatment step) with a tension of 10.0 to 20.0 N / mm ² applied.
A step of subjecting the plate material after the solution treatment step to a heat treatment for holding at 700 to 900 ° C. for 10 to 300 seconds (first aging treatment step).
A process of cold rolling in a rolling ratio of 5 to 50% or less (aging cold rolling process),
A step of subjecting the plate material after the aging cold rolling step to a heat treatment for holding at 400 to 620 ° C. for 0.5 to 75 hours (second aging treatment step).
A method for producing a copper alloy plate material, wherein a plate material having an area ratio of a precipitate having an area of 0.1 μm ² or more and an area ratio of 2.0% or less on an observation surface parallel to the plate surface is obtained by a manufacturing process including.
Ni / Al ≤ 9.0 ... (1)
Here, the content value of the element represented by mass% is substituted in place of the element symbol in the formula (1). Between the hot rolling process and the solution treatment process,
A process of performing cold rolling with a rolling ratio of 50% or more (cold rolling process),
5. The method for producing a copper alloy plate material according to claim 5. A conductive spring member using the copper alloy plate material according to any one of claims 1 to 4 as a material.

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