JP2019002042A - Cu-Ni-Al-BASED COPPER ALLOY SHEET MATERIAL, MANUFACTURING METHOD THEREOF, AND CONDUCTIVE SPRING MEMBER - Google Patents

Abstract

To provide a high strength Cu-Ni-Al-based copper alloy sheet material excellent in surface smoothness of an etching processed surface.SOLUTION: There is provided a copper alloy sheet material having a chemical composition consisting of, by mass%, Ni:10.0 to 30.0%, Al:7.50% or less and Ni/Al≤15.00, Mg:0 to 0.30%, Cr:0 to 0.20%, Co:0 to 0.30, P:0 to 0.10%, B:0 to 0.05%, Mn:0 to 0.20%, Sn:0 to 0.40%, Ti:0 to 0.50%, Zr:0 to 0.20%, Si:0 to 0.50%, Fe:0 to 0.30%, Zn:0 to 1.00% and the balance Cu with inevitable impurities, number density of coarse Ni-Al-based precipitate particle with longer diameter of 5.0 μm or more in an observation surface in parallel to a sheet surface (rolling surface) of 5.0×10piece/mmor less and a KAM value measured by EBSD of 1.50 to 5.00°.SELECTED DRAWING: None

Description

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

  Cu-Ni-Al-based copper alloys can be strengthened by Ni-Al-based precipitates, and those containing Ni of, for example, about 10% by mass or more are whiter than general copper alloys. Presents a metallic appearance. This copper alloy is useful as a conductive spring member such as a lead frame or a connector or a nonmagnetic high-strength member.

  So far, various studies have been made to improve other characteristics (conductivity, workability, fatigue characteristics, stress relaxation characteristics, etc.) while utilizing the high strength characteristics of Cu-Ni-Al based copper alloys ( For example, Patent Documents 1 to 9).

JP-A 63-250434 JP-A 63-266033 Japanese Patent Application Laid-Open No. 64-52035 JP-A-1-149946 JP-A-5-311297 Japanese Patent Laid-Open No. 5-311298 JP-A-5-320790 JP-A-6-128708 International Publication No. 2012/081573

  With the downsizing and high density of electronic equipment, there is an increasing need for downsizing of conductive parts used in the electronic equipment. Small copper alloy parts with high dimensional accuracy are often produced through an etching process. In particular, the etched parts are often molded with resin. At that time, if there is a part where the surface profile after etching is deeply digged locally and the irregularities are large, air enters between the resin and the etched surface, forming a void, and the resin adhesion is remarkably high. descend. When the resin adhesiveness is lowered, it becomes a factor that causes an increase in the defect rate of parts. Therefore, in order to apply to an etching part that is used as a resin mold, it is important that the material can obtain an etched surface with as few asperities (good surface smoothness). A plate material of Cu-Ni-Al-based copper alloy is useful as a substrate for a high-strength conductive spring member because it exhibits excellent high-strength characteristics. However, the present situation is that a Cu—Ni—Al-based copper alloy sheet material having excellent etching properties that can be applied to precise resin mold conductive parts has not been developed.

  In addition, since the Cu-Ni-Al-based copper alloy has a high Ni content, the copper appearance has a light copper appearance among the copper alloys. In particular, when the Ni content effective for improving the strength of the Cu—Ni—Al based copper alloy is increased, a white metal appearance gradually appears. Cu-Ni-Al-based copper alloys, like other general copper alloys, may change color when exposed to high-humidity environments, but they have a beautiful white tone for applications that emphasize white tone surface appearance. It is also important to have excellent resistance to discoloration so as not to be damaged.

  An object of this invention is to provide the Cu-Ni-Al type copper alloy board | plate material which etchability is notably improved and is excellent also in discoloration resistance.

According to the inventors' research, the following was found.
(A) In order to increase the surface smoothness of the etched surface in a Cu—Ni—Al based copper alloy sheet, a texture state with a large KAM value obtained by EBSD (electron beam backscatter diffraction method) and coarse Ni -It is extremely effective to reduce the abundance of Al-based precipitate particles.
(B) In order to increase the KAM value, in the solution treatment performed before the aging treatment, a rapid heating is performed in a high temperature region to keep the recrystallized grain growth as much as possible, and then cold rolling is sufficient. It is effective to introduce strain into the. Further, in the final heat treatment to be performed finally, the formation of the Cottrell atmosphere is promoted by controlling the heating conditions so that the rate of temperature rise is not excessive, and the KAM value is increased by the lattice strain.
(C) In order to reduce the abundance of coarse Ni—Al-based precipitate particles, the solution treatment temperature (about 800 to 900 ° C.) of a general Cu—Ni—Al-based copper alloy in solution treatment is used. It is also effective to heat to a high temperature. However, if the crystal grains become coarse at that time, the above-mentioned improvement in KAM value cannot be expected. In this regard, in the upper process, the slab is heated at a higher temperature than before, and hot rolling is sufficiently performed in a higher temperature range than before to sufficiently remove coarse Ni-Al-based precipitates produced during casting. By decomposing into the above, it becomes possible to shorten the high temperature holding time of the solution treatment, and avoid the coarsening of the crystal grains.
(D) In order to improve the strength and obtain a white metallic appearance, it is effective to secure a Ni content of 10% by mass or more. In that case, excellent discoloration resistance can be realized by limiting the Al content to a predetermined value or less and controlling the Ni content to a predetermined value or less according to the Al content.
In the present invention, the manufacturing technology capable of simultaneously realizing “increase in KAM value” and “reduction of coarse Ni—Al-based precipitate particles”, and “high strength”, “white tone”, and “discoloration resistance” are provided. It was completed by finding a composition range that satisfies the requirements at the same time.

The present invention discloses the following invention.
[1] Content by mass, Ni: 10.0 to 30.0%, Al: 7.50% or less and satisfying the following formula (1), Mg: 0 to 0.30%, Cr: 0 to 0 .20%, Co: 0 to 0.30%, P: 0 to 0.10%, B: 0 to 0.05%, Mn: 0 to 0.20%, Sn: 0 to 0.40%, Ti : 0 to 0.50%, Zr: 0 to 0.20%, Si: 0 to 0.50%, Fe: 0 to 0.30%, Zn: 0 to 1.00%, remaining Cu and inevitable impurities The number density of coarse Ni—Al-based precipitate particles having a major axis of 5.0 μm or more is 5.0 × 10 ³ particles / mm ² or less on the observation surface parallel to the plate surface (rolled surface). And KAM measured at a step size of 0.5 μm in the crystal grain when a boundary having a crystal orientation difference of 15 ° or more is regarded as a crystal grain boundary by EBSD (electron beam backscatter diffraction method). Copper alloy sheet but is 1.50 to 5.00 °.
Ni / Al ≦ 15.00 (1)
Here, the content value of the element represented by mass% is substituted for the element symbol in the formula (1).
[2] The copper alloy sheet according to [1], wherein the average crystal grain size in the sheet thickness direction defined in (A) below is 10.0 μm or less.
(A) On a SEM image in which a cross section perpendicular to the rolling direction (C cross section) is observed, a straight line in the plate thickness direction is randomly drawn, and an average cut length of crystal grains cut by the straight line is an average in the plate thickness direction. The crystal grain size is used. However, a plurality of straight lines that do not cut the same crystal grain repeatedly are randomly set in one or a plurality of observation fields so that the total number of crystal grains cut by the straight line is 100 or more.
[3] The copper alloy sheet according to the above [1] or [2], wherein the maximum height roughness Rz in the direction perpendicular to the rolling direction of the sheet surface (rolled surface) is 1.2 μm or less.
[4] The copper alloy sheet according to any one of [1] to [3], wherein the conductivity is 3.0 to 20.0% IACS.
[5] The copper alloy sheet according to any one of [1] to [4], wherein the tensile strength in the rolling direction is 800 MPa or more.
[6] The copper alloy sheet material according to any one of [1] to [5], wherein the sheet thickness is 0.015 to 0.50 mm.
[7] A conductive spring member using as a material the copper alloy sheet according to any one of [1] to [6].
[8] A step of heating and holding the slab having the above chemical composition at 1000 to 1150 ° C for 2 hours or more (slab heating step),
Rolling rate in a temperature range of 950 ° C. or higher: 65% or higher, rolling temperature in final pass: 800 ° C. or higher (hot rolling step)
Cold rolling process (cold rolling process),
Maximum material temperature T ₁ : Over 950 ° C., 1100 ° C. or less, Average heating rate from 900 ° C. to T ₁ : 50 ° C./s or more, Holding time in temperature range of 900 ° C. or more and T ₁ or less: 30 to A step of performing a solution treatment under a condition of 360 seconds (solution treatment step),
A step of aging treatment at 400 to 650 ° C. for 0.1 to 48 hours (aging treatment step);
A step of performing cold rolling at a rolling rate of 30 to 99% (finish cold rolling step),
Maximum heat treatment temperature T ₂ : 400 to 700 ° C., Maximum heating rate up to T ₂ : 200 ° C./s or less, Holding time at 400 to 700 ° C .: 10 to 300 seconds (finishing) Heat treatment process),
The manufacturing method of the copper alloy board | plate material which has these in said order.
[9] The method for producing a copper alloy sheet according to [8], wherein cold rolling is performed at a rolling rate of 80 to 98% in the cold rolling step.
[10] The method for producing a copper alloy sheet according to the above [8] or [9], wherein in the finish cold rolling step, the sheet thickness after the cold rolling is set to 0.015 to 0.50 mm.

  Among the above alloy elements, Mg, Cr, Co, P, B, Mn, Sn, Ti, Zr, Si, Fe, and Zn are optional additive elements. The major axis of the Ni—Al-based precipitate particles is determined as the diameter of the smallest circle surrounding the particles on the observation image plane. The number density of coarse Ni—Al-based precipitate particles can be determined as follows.

[How to determine the number density of coarse Ni-Al-based precipitate particles]
The surface of the plate (rolled surface) is electropolished to dissolve only the Cu substrate to prepare an observation surface that exposes the Ni—Al-based precipitate particles. The observation surface is observed with an SEM and observed on the SEM image. A value obtained by dividing the total number of Ni—Al-based precipitate particles having a major axis of 5.0 μm or more by the observed total area (mm ² ) is the coarse Ni—Al-based precipitate particle number density (pieces / mm ² ). . The total observation area is set to a total of 0.1 mm ² or more by a plurality of non-overlapping observation fields set at random. Ni—Al-based precipitate particles partially protruding from the observation field are counted if the major axis of the part appearing in the observation field is 5.0 μm or more. Whether the particles are Ni-Al-based precipitates is determined by irradiating an electron beam while aiming at the center of the particles, and using an EDX (energy dispersive X-ray analysis) apparatus attached to the SEM, Cu, Ni, and Al. Confirm by quantitative analysis with 3 elements. Particles having measured values of Ni: 15.0% or more and Al: 7.5% or more in mass% of these three elements are identified as “Ni—Al-based precipitates”.

  A KAM (Kernel Average Misoration) value can be obtained as follows.

[How to find KAM value]
The observation surface (removal depth from the rolling surface is 1/10 of the plate thickness) prepared by buffing and ion milling of the plate surface (rolled surface) was observed with an FE-SEM (field emission scanning electron microscope), and 50 μm. For a measurement region of × 50 μm, the KAM value in the crystal grain is measured by EBSD (Electron Beam Back Scattering Diffraction Method) when the boundary with an orientation difference of 15 ° or more is regarded as the crystal grain boundary at a measurement pitch of 0.5 μm. This measurement is performed on five randomly selected non-overlapping measurement regions, and the average value of the KAM values obtained in each measurement region is adopted as the KAM value for the plate material.

  The KAM value determined in each of the above measurement areas is a measurement of all crystal orientation differences between adjacent spots (hereinafter referred to as “adjacent spot orientation differences”) for electron beam irradiation spots arranged at a pitch of 0.5 μm. This is equivalent to extracting only the measured value of the adjacent spot orientation difference of less than 15 ° and obtaining the average value thereof. That is, the KAM value is an index representing the amount of lattice strain in the crystal grains, and it can be evaluated that the larger the value, the larger the strain of the crystal lattice.

The rolling rate from a certain sheet thickness t ₀ (mm) to a certain sheet thickness t ₁ (mm) is obtained by the following equation (2).
Rolling ratio (%) = (t ₀ −t ₁ ) / t ₀ × 100 (2)

  According to the present invention, a Cu-Ni-Al-based copper alloy plate material excellent in surface smoothness and discoloration resistance of an etched surface can be realized. Since this plate material has high strength and excellent resin adhesion when etched into a precision part, it is extremely useful as a material for high-strength conductive spring parts and precision resin-molded conductive parts. Moreover, it is useful for the component use which desires the external appearance of white tone.

[Chemical composition]
In the present invention, a Cu—Ni—Al based copper alloy is employed. Hereinafter, “%” regarding alloy components means “% by mass” unless otherwise specified.

  Ni is a main element constituting a matrix (metal substrate) of Cu—Ni—Al based copper alloy together with Cu. Further, a part of Ni in the alloy is bonded to Al to form particles of the second phase (Ni—Al-based precipitation phase), which contributes to improving the strength. As the Ni content increases, a white metal appearance is exhibited as compared with other general copper alloys. However, as with other copper alloys, when exposed to a high humidity environment, a thin oxide film is formed on the metal surface, and it may be discolored to the extent that it can be seen as the appearance. In that case, the beautiful white appearance is impaired. According to the study by the inventors, the discoloration resistance can be maintained high by securing the Al content as described below after setting the Ni content to 10.0% or more. Therefore, in the present invention, a Cu-Ni-Al-based copper alloy of 10.0% or more is targeted. It is more effective to set the Ni content to 15.0% or more. On the other hand, when the Ni content increases, the hot workability deteriorates. The Ni content is limited to 30.0% or less.

Al is an element that forms Ni—Al-based precipitates. 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. As a result of various studies, it is necessary to contain Al so as to satisfy the following formula (1).
Ni / Al ≦ 15.00 (1)
Here, the content value of the element represented by mass% is substituted for the element symbol in the formula (1).
On the other hand, when the Al content is excessive, hot workability is deteriorated. The Al content is limited to 7.50% or less.

  As other elements, Mg, Cr, Co, P, B, Mn, Sn, Ti, Zr, Si, Fe, Zn, and the like can be contained as necessary. The content ranges of these elements are Mg: 0 to 0.30%, Cr: 0 to 0.20%, Co: 0 to 0.30%, P: 0 to 0.10%, B: 0 to 0. 0.05%, Mn: 0 to 0.20%, Sn: 0 to 0.40%, Ti: 0 to 0.50%, Zr: 0 to 0.20%, Si: 0 to 0.50%, Fe : 0 to 0.30%, Zn: 0 to 1.00% are preferable.

  When including one or more of Mg, Cr, Co, P, B, Mn, Sn, Ti, Zr, Si, Fe, and Zn, the total content thereof should be 0.01% or more. Is more effective. However, if it is contained in a large amount, it adversely affects hot or cold workability and is disadvantageous in terms of cost. The total amount of these optional added elements is more preferably 1.0% or less, and may be 0.50% or less. Moreover, when a large amount of Sn is added in a Cu—Ni—Al based copper alloy, gravity segregation is likely to occur during melting. When performing continuous casting or semi-continuous casting using a vertical continuous casting machine, it is more preferable that the Sn content is in the range of 0 to 0.20% or less.

[Number density of coarse Ni-Al-based precipitate particles]
In the Cu-Ni-Al-based copper alloy, high strength is achieved by utilizing fine precipitation of Ni-Al-based precipitates. Usually, before fine Ni—Al-based precipitate particles contributing to high strength are aged, a treatment (solution treatment) for dissolving the existing coarse Ni—Al-based precipitates is performed. Is called. In the case of a Cu—Ni—Al-based copper alloy, it is common to perform solution treatment at about 850 ° C. to 900 ° C. as seen in Examples of Patent Documents 1-9. In order to increase the strength by precipitating fine Ni—Al-based precipitates, a sufficient effect can be obtained by solution treatment at such a temperature. However, it has been found that it is necessary to strictly limit the amount of coarse Ni—Al-based precipitate particles in order to provide excellent etching properties that can cope with high-definition etching. As a result of detailed examination, the number density of coarse Ni—Al-based precipitate particles having a major axis of 5.0 μm or more on the observation surface parallel to the plate surface (rolling surface) is 5.0 × 10 ³ particles / mm ² or less (in this case (Including the case where coarse Ni—Al-based precipitate particles are not present). The structure state in which the number density of coarse Ni—Al-based precipitate particles is reduced as described above can be realized, for example, by careful solution treatment according to the manufacturing process described later.

[KAM value]
The inventors have discovered that the KAM value of a copper alloy sheet affects the surface smoothness of the etched surface. The mechanism is still unclear, but is presumed as follows. That is, the KAM value is a parameter correlated with the dislocation density in the crystal grains. When the KAM value is large, the average dislocation density in the crystal grains is high, and the local variation in the dislocation density is considered to be small. With regard to etching, it is considered that a place with a high dislocation density is preferentially etched (corroded). In a material having a high KAM value, since the entire material is uniformly in a high dislocation density, corrosion due to etching proceeds rapidly and local corrosion does not easily occur. It is speculated that such a progressing form of corrosion may have an advantageous effect on the formation of an etched surface with less unevenness.

  As a result of detailed examination, in the case of a Cu—Ni—Al-based copper alloy, by EBSD (electron beam backscattering diffraction method), in a crystal grain when a boundary having a crystal orientation difference of 15 ° or more is regarded as a crystal grain boundary, It was found that when the KAM value (described above) measured at a step size of 0.5 μm is 1.50 ° or more, the surface smoothness of the etched surface is remarkably improved. It is more preferable to adjust the KAM value to 1.90 ° or more. However, even if the KAM value is sufficiently high, it is difficult to stably obtain an excellent etching improvement effect unless the number density of coarse Ni—Al-based precipitate particles is reduced as described above. The upper limit of the KAM value is not particularly defined, but may be adjusted to a KAM value of, for example, 5.00 ° or less. You may adjust within the range of 4.00 degrees or less. A structure state having a high KAM value can be realized by devising solution treatment conditions, finish cold rolling conditions, and finish heat treatment conditions, for example, according to the manufacturing process described later.

[Average crystal grain size]
The fact that the average crystal grain size in the plate thickness direction in the cross section perpendicular to the rolling direction (C cross section) is also small is advantageous for forming an etched surface with few irregularities. As a result of the examination, the average crystal grain size of the C cross section defined in (A) above is preferably 10.0 μm or less, and more preferably 5.0 μm or less. The average crystal grain size does not need to be excessively refined, and may be adjusted within a range of, for example, 0.50 μm or more. The average crystal grain size can be controlled mainly by the solution treatment conditions.

〔Surface roughness〕
The plate surface (rolled surface) is preferably a plate material having a maximum height roughness Rz in the direction perpendicular to the rolling of 1.2 μm or less. Adjustment to such a surface roughness is advantageous in stably realizing an etched surface having excellent surface smoothness in a mass production line.

〔Conductivity〕
When used for current-carrying parts and heat-dissipating parts, higher conductivity is advantageous in terms of electrical conductivity and thermal conductivity. On the other hand, recently, when assembling conductive members, there is an increasing need to apply laser welding instead of soldering. In the case of welding, the lower the electrical conductivity, the lower the thermal conductivity, so that heat is less likely to escape and welding is easier. In order to meet the welding needs, it is advantageous that the electrical conductivity is 20% IACS or less. In the use of the conductive spring member to which the Cu—Ni—Al based copper alloy is applied, it is preferable that the conductivity is adjusted to 3.0 to 20.0% IACS in consideration of weldability. You may adjust within the range below 15.0% IACS.

〔Strength〕
Considering application to the conductive spring member, it is desirable that the tensile strength in the rolling direction is 800 MPa or more. It is more preferable that the tensile strength is higher than 1000 MPa, and the tensile strength can be adjusted to 1100 MPa or more. An excessive increase in strength is accompanied by an increase in the load in the cold rolling process, resulting in a decrease in productivity. It is preferable to adjust the strength level in a range where the tensile strength in the rolling direction is 1400 MPa or less.

〔Production method〕
The copper alloy sheet material described above can be produced by the following manufacturing process, for example.
Melting / Casting → Hot Rolling → Cold Rolling → (Intermediate Annealing → Cold Rolling) → Solution Treatment → Aging Treatment → Finish Cold Rolling → Finish Heat Treatment Although not described in the above process, After rolling, chamfering 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. If the Sn content is limited as described above, the risk of gravity segregation is avoided, and casting using a vertical continuous casting machine is possible as with other general copper alloys. In order to prevent oxidation of Si or the like, it is preferable to carry out in an inert gas atmosphere or a vacuum melting furnace.

[Casting heating]
The slab is heated and held at 1000 to 1150 ° C. for 2 hours or more. This heating can be carried out using a slab heating process during hot rolling. In general, slab heating of Cu-Ni-Al-based copper alloy is performed at a temperature of 950 ° C or lower, and in order to obtain a high-strength material having favorable characteristics, it is necessary to heat at a higher temperature. It wasn't. However, in the present invention, it is necessary to strictly limit the abundance of coarse Ni—Al-based precipitate particles in order to improve etching properties. As a technique for reducing the abundance of coarse Ni—Al-based precipitate particles, first, the above-described high temperature region is heated at the stage of the slab, and Ni—Al-based precipitates present in the cast structure are dissolved as much as possible. Is effective. When the temperature exceeds 1150 ° C., the portion having a low melting point in the cast structure becomes brittle, and cracking may occur in hot rolling. If the heating time in the above temperature range is less than 2 hours, the Ni—Al-based precipitate may not be sufficiently dissolved. In consideration of economy, it is desirable to set the heating time in the above temperature range within a range of 5 hours or less.

(Hot rolling)
In hot rolling, it is important to obtain a sufficient rolling rate at a temperature higher than the general hot rolling temperature of a Cu—Ni—Al based copper alloy. Specifically, the rolling rate in a temperature range of 950 ° C. or higher is set to 65% or higher, and the rolling temperature in 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 exiting the work roll in that rolling pass. "Rolling ratio at 950 ° C. or higher temperature range" is the thickness before hot rolling and t ₀ (mm), the thickness of the rolling temperature resulting from the last rolling pass is 950 ° C. or higher t ₁ (Mm) is determined by substituting these into the following equation (2).
Rolling ratio (%) = (t ₀ −t ₁ ) / t ₀ × 100 (2)

  By obtaining a sufficient rolling ratio at a high temperature according to the above conditions, the decomposition of coarse Ni—Al-based precipitates resulting from the cast structure is promoted, and the holding time at a high temperature can be shortened in the solution treatment step. The total hot rolling rate may be, for example, 70 to 97%. After the hot rolling is finished, it is preferable to quench by water cooling or the like.

(Cold rolling)
Before the solution treatment, cold rolling is performed to adjust the plate thickness. If necessary, the step of “intermediate annealing → cold rolling” may be added once or a plurality of times. The rolling rate in cold rolling performed before the solution treatment (when performing intermediate annealing, the rolling rate in cold rolling after the last intermediate annealing) can be set to 80 to 98%, for example.

[Solution treatment]
The main purpose of the solution treatment is to sufficiently dissolve the Ni—Al-based precipitate (solution solution). In the present invention, however, the solution treatment is performed while suppressing the coarsening of the crystal grains in order to achieve a high KAM value. Is extremely important. Regarding the solid solution of the Ni—Al based precipitate, in order to improve the etching property, it is heated to a temperature higher than the solution treatment temperature (about 800 to 900 ° C.) of a general Cu—Ni—Al based copper alloy. Specifically, the maximum temperature T ₁ of the material is set in a range higher than 950 ° C. and not higher than 1100 ° C., and the holding time in the temperature range of 900 ° C. or higher and T ₁ or lower (the time during which the material temperature is in that temperature range) is 30 It is necessary to secure at least 2 seconds. However, as will be described later, this holding time is limited to 360 seconds or less.

  On the other hand, with regard to the improvement of the KAM value, it has been found that it is very effective to suppress the coarsening of crystal grains during the solution treatment. According to the inventors' investigation, it has been confirmed that a high KAM value can be obtained when recrystallized grains formed by solution treatment are made as fine as possible and then processed strain is applied by cold rolling. It was. In Cu-Ni-Al-based copper alloys, it is surmised that the effect of accumulating lattice strain (dislocations) is particularly prominent when cold rolling is performed in a recrystallized structure with a large grain boundary area. .

As described above, since it is necessary to perform the solution treatment at a higher temperature, it is necessary to devise measures for preventing the coarsening of crystal grains. One of them is “reduction of high temperature holding time”. Specifically, the holding time in a high temperature range of 900 ° C. or higher and T ₁ or lower may be limited to 360 seconds or shorter. As described above, since the solid solution of the Ni—Al-based precipitate is promoted in the slab heating and hot rolling processes, sufficient solution can be realized even in such a short heating time in the solution treatment process. It is. Furthermore, as another contrivance, it is extremely effective to increase the rate of temperature rise in the high temperature range. Specifically, the average temperature rising rate from 900 ° C. to T ₁ is controlled to 50 ° C./s or more. When rapid recrystallization is caused by rapid temperature rise, it is assumed that recrystallized grains are generated at many sites simultaneously and are difficult to grow into coarse recrystallization. In order to increase the rate of temperature increase in the high temperature range, it is effective to set the furnace temperature higher than the maximum material temperature T _{1 or} to increase the rotational speed of the fan to promote convection in the furnace. If the furnace temperature is raised too much, T ₁ may not be stabilized, and there may be a variation in crystal grain size and characteristics, and the rotational speed of the fan is limited in terms of equipment. It is realistic to set the average rate of temperature increase from 900 ° C. to T ₁ within a range of 100 ° C./s or less. In actual operation, the average rate of temperature rise can be controlled based on the “relationship between the in-furnace time and the material temperature” obtained in advance according to the plate thickness and the furnace temperature. The cooling rate may be a rapid cooling that can be realized by a general continuous annealing line. For example, the average cooling rate from 900 ° C. to 300 ° C. is desirably 100 ° C./s or more.

[Aging treatment]
Next, an aging treatment is performed to precipitate fine precipitate particles that contribute to the strength. The aging treatment conditions can be set in the range of 400 to 650 ° C. and 0.1 to 48 hours according to the target strength and conductivity.

[Finish cold rolling]
The final cold rolling performed after the aging treatment is referred to as “finish cold rolling” in the present specification. Finish cold rolling is effective in improving strength, KAM value, and surface smoothness. In the plate material used in this process, Ni-Al-based precipitate particles finely precipitated by aging treatment are distributed in a matrix having many grain boundaries obtained by avoiding coarsening of crystal grains by solution treatment. Have an organizational state. When final cold rolling is performed on a plate material having such a structure, crystal lattice distortion is likely to accumulate. A large amount of accumulated strain is presumed to be maintained as a high lattice strain even in the final plate material by appropriately performing the finishing heat treatment described later, and as a result, a plate material having a high KAM value can be obtained. In order to sufficiently exhibit the effect of such finish cold rolling, it is effective to set the finish cold rolling rate to 30% or more, and more effectively to 40% or more. The finish cold rolling rate may be set within a range of 99% or less. The final plate thickness can be set, for example, in a range of about 0.015 to 0.50 mm.

  After finishing cold rolling, shape correction with a tension leveler can be performed as necessary. The elongation at the tension leveler may be in the range of 0.1 to 1.5%, for example.

[Finish heat treatment]
A final heat treatment is applied to the plate material to which the rolling strain is imparted by the finish cold pressure to increase the KAM value. This heat treatment is called “finish heat treatment” in the present specification. In the finish heat treatment, the maximum temperature T ₂ of the material is set to 400 to 700 ° C., and the holding time at 400 to 700 ° C. (the time during which the material temperature is in the temperature range) is set to 10 to 300 seconds. By maintaining in this temperature range, rearrangement of dislocations occurs, and solute atoms form a Cottrell atmosphere and form a strain field in the crystal lattice. This lattice distortion is considered to be a factor for improving the KAM value. However, in order to obtain the effect of increasing the KAM value, it is important to control so that the temperature rising rate does not become too large. It has been found that when the rate of temperature increase is excessively high, dislocations disappear easily during the temperature increase process, and the KAM value decreases. According to the study by the inventors, the maximum temperature increase rate up to T ₂ needs to be 200 ° C./s or less, and more preferably 160 ° C./s or less. The maximum rate of temperature rise corresponds to the maximum slope of the temperature rise curve up to temperature T ₂ in the graph with time on the horizontal axis and material temperature on the vertical axis.

When emphasizing the shape (flatness) of the plate, it is effective to perform this finishing heat treatment under tension. In that case, at least when the material temperature is at the maximum temperature T ₂ , a tension of 40 to 60 N / mm ² may be applied in the rolling direction of the plate.

  A copper alloy having the chemical composition shown in Table 1 was melted and cast using a vertical semi-continuous casting machine. The obtained slab was heated and held at the temperatures and times shown in Tables 2A and 2B, extracted, hot-rolled to a thickness of 5 to 15 mm, and cooled with water. The total hot rolling rate is 90 to 95%. The rolling rate in the temperature range of 950 ° C. or higher, the rolling temperature of the final pass, and the finished sheet thickness after hot rolling are shown in Tables 2A and 2B. . In some cases where cracking occurred during hot rolling, production was stopped at that point. After the hot rolling, the surface oxide layer was removed (faced) by mechanical polishing, and cold rolling was performed at the rolling rates shown in Tables 2A and 2B to obtain an intermediate product plate material for solution treatment. Each intermediate product plate was subjected to solution treatment, aging treatment, finish cold rolling, and finish heat treatment to obtain plate products (test materials) having thicknesses shown in Tables 2A and 2B.

The solution treatment was performed using a continuous annealing furnace under the conditions shown in Tables 2A and 2B. The surface temperature of the material in the plate is monitored by radiation thermometers installed at multiple locations in the furnace, and the time when the furnace temperature and plate speed are stable (steady state) based on the temperature measurement data- A temperature curve was prepared, and an average temperature increase rate from 900 ° C. to T ₁ was determined. Finish cold rolling was performed at the rolling rates shown in Tables 2A and 2B.
The aging treatment was performed under the condition of holding at 500 ° C. for 12 hours.
The finish heat treatment was carried out under the conditions shown in Table 2A and Table 2B by applying a tension of 50 N / mm ^{2 in} the rolling direction by a method of air cooling after continuously passing through a catenary furnace. The surface temperature of the material in the plate is monitored by radiation thermometers installed at multiple locations in the furnace, and the time when the furnace temperature and plate speed are stable (steady state) based on the temperature measurement data- A temperature curve was created, and the maximum rate of temperature increase up to temperature T ₂ was determined from the slope of the curve.

In Tables 2A and 2B, the “temperature” of the solution treatment is the above-mentioned maximum attained temperature T ₁ , “time” is the time during which the material temperature is in the range of 900 ° C. to T ₁ , and “≧ 900 ° C. heating rate” Represents the average rate of temperature rise from 900 ° C. to T ₁ , respectively. In addition, the “temperature” of the finish heat treatment is the maximum temperature T ₂ described above, the “time” is the time during which the material temperature is in the range of 400 to 700 ° C., and the “maximum heating rate” is the maximum heating rate up to T _2. Displayed respectively. However, in the case where the maximum temperature T ₂ was less than 400 ° C. in the finish heat treatment, the holding time at the maximum temperature T ₂ was shown in the “time” column.

  The following investigation was conducted for each specimen.

(Number density of coarse Ni-Al precipitate particles)
In accordance with the above-mentioned “How to obtain the number density of coarse Ni—Al-based precipitate particles”, an observation surface obtained by electropolishing the plate surface (rolled surface) is observed with an SEM, and Ni—Al-based precipitate particles having a major axis of 5.0 μm or more are observed. The number density of was determined. A solution prepared by mixing distilled water, phosphoric acid, ethanol, and 2-propanol in a ratio of 10: 5: 5: 1 was used as an electropolishing liquid for preparing the observation surface. The electrolytic polishing was performed under the conditions of a voltage of 15 V and a time of 20 seconds using an electrolytic polishing apparatus (ELECTROPOLISHER POWER SUPPLUY, ELECTROPOLISHER CELL MODULE) manufactured by BUEHLER.

(KAM value)
FE-SEM (manufactured by JEOL Ltd .; JSM-7001) equipped with an EBSD analysis system for the observation surface whose removal depth from the rolled surface is 1/10 of the plate thickness in accordance with the above-mentioned “How to obtain KAM value” It measured using. The acceleration voltage of electron beam irradiation was 15 kV, and the irradiation current was 5 × 10 ⁻⁸ A. EBSD analysis software was manufactured by TSL Solutions; OIM Analysis was used.

(Average crystal grain size in the plate thickness direction)
The observation plane on which the cross section perpendicular to the rolling direction (C cross section) was etched to reveal the crystal grain boundary was observed with SEM, and the average crystal grain size in the plate thickness direction defined in (A) was determined.

(Surface roughness of the plate surface)
For the plate surface (rolled surface), the surface roughness in the direction perpendicular to the rolling direction was measured with a laser surface roughness meter, and the maximum height roughness Rz according to JIS B0601: 2013 was determined.

(conductivity)
The electrical conductivity of each test material was measured according to JIS H0505. Considering the use of lead frames, those with 3.0 to 20.0% IACS or higher were determined to be acceptable (conductivity; proper).

(Tensile strength)
A tensile test piece (JIS No. 5) in the rolling direction (LD) was taken from each test material, and a tensile test according to JIS Z2241 was performed with the number of tests n = 3, and the tensile strength was measured. The average value of n = 3 was defined as the result value of the test material. Considering the use of the conductive spring member, a material having a tensile strength of 800 Pa or more was determined to be acceptable (high strength characteristics; good).

(Surface roughness of etched surface)
As an etchant, ferric chloride 42 baume was prepared. The surface of one side of the test material was etched until the plate thickness was halved. About the obtained etching surface, the surface roughness of the rolling orthogonal direction was measured with the laser type surface roughness meter, and the maximum height roughness Rz according to JIS B0601: 2013 was determined. If Rz by this etching test is 2.5 μm or less, it can be evaluated that the surface smoothness of the etched surface is greatly improved as compared with the conventional Cu—Ni—Al based copper alloy sheet, which is extremely suitable for high-definition etching. Useful. Therefore, here, those having the Rz of 2.5 μm or less were determined to be acceptable (etching property: good). The Rz is more preferably 2.1 μm or less (etching property: excellent).

(Discoloration resistance)
A sample having a width of 10 mm and a length of 65 mm was taken from the test material, and the plate surface (rolled surface) was dry-polished with abrasive paper having a count of 1200 (grain size P1200 defined in JIS R6010: 2000) as a weathering test piece Was made. The weather resistance test was performed by exposing the test piece to an atmosphere of 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, and a color difference ΔE ^* _ab depending on L ^* a ^* b ^* display color defined in JIS Z8730: 2009 was determined. Those having a color difference ΔE ^* _ab of less than 5.0 can be judged to have good discoloration resistance as a conductive spring member. Therefore, it was determined that the color difference ΔE ^* _ab was less than 5.0 as acceptable (discoloration resistance: good). For reference, the weather resistance test was also performed under the same conditions for oxygen-free copper (C1020), 70-30 brass (C2600), and naval brass (C4622). 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 naval brass.
These results are shown in Tables 3A and 3B.

  Each of the plate materials of the present invention obtained by strictly controlling the chemical composition and production conditions in accordance with the above-mentioned regulations has a structure state in which the number density of coarse Ni—Al based precipitate particles is low and the KAM value is high. And the surface smoothness of the etched surface was excellent. Further, the surface roughness in the direction perpendicular to the rolling, electrical conductivity, tensile strength, and discoloration resistance were good.

  On the other hand, Comparative Example No. 31 has a low slab heating temperature and a low rolling rate in a temperature range of 950 ° C. or higher in hot rolling, so that coarse Ni—Al-based precipitate particles increase and the etching property is improved. It has not been. Since No. 32 has a high solution treatment temperature, the KAM value is low, the crystal grain size in the plate thickness direction is large, and the etching property is not improved. Since No. 33 has a low solution treatment temperature, coarse Ni—Al-based precipitate particles increase, and the etching property is not improved. Since No. 34 had a high slab heating temperature, cracking occurred during hot rolling, and the subsequent steps were stopped. In No. 35, since the slab heating time is short, coarse Ni—Al-based precipitate particles increase, and the etching property is not improved. In No. 36, since the hot rolling final pass temperature was low, coarse Ni—Al-based precipitate particles increased. Moreover, since the temperature increase rate in the high temperature region in the solution treatment was slow, the crystal grains before finish cold rolling became large, and the KAM value was insufficiently increased. Therefore, the etching property is not improved. In No. 37, since the Ni content was excessive, cracking occurred during hot rolling, and the subsequent steps were stopped. No. 38 had a low Ni content, so its conductivity exceeded 20.0% IACS, and it was also inferior in discoloration resistance. In No. 39, since the Al content was excessive, cracking occurred during hot rolling, and the subsequent steps were stopped. No. 40 has a high Ni / Al ratio, low tensile strength, and inferior discoloration resistance. In No. 41, gravity segregation occurred in the vertical continuous casting due to excessive Sn content, so cracking occurred during hot rolling, and the subsequent steps were stopped. In No. 42, since the solution treatment time was long, the crystal grains before finish cold rolling became large, and the KAM value was insufficiently increased. Therefore, the etching property is not improved. In No. 43, since the solution treatment time is short, coarse Ni—Al-based precipitate particles increase, and the etching property is not improved. No. 44 has a low finish cold rolling rate, so the KAM value is not sufficiently increased, and the etching property is not improved. Also, the surface roughness in the direction perpendicular to the rolling was poor. No. 45 was hot-rolled and had a low rolling ratio in a high temperature range and a high finishing heat treatment temperature, so that coarse Ni—Al-based precipitate particles increased and the KAM value was not sufficiently increased. Therefore, the etching property is not improved. In No. 46, the finish heat treatment temperature is low, so the KAM value is not sufficiently increased, and the etching property is not improved. No. 47 has a long finish heat treatment time, so the KAM value is not sufficiently increased, and the etching property is not improved. In No. 48, the finishing heat treatment time is short, so the KAM value is not sufficiently increased, and the etching property is not improved. No. 49 has a large maximum heating rate in the finish heat treatment, so that the KAM value is not sufficiently increased, and the etching property is not improved.

Claims (10)

Content by mass: Ni: 10.0 to 30.0%, Al: 7.50% or less and satisfying the following formula (1), Mg: 0 to 0.30%, Cr: 0 to 0.20% , Co: 0 to 0.30%, P: 0 to 0.10%, B: 0 to 0.05%, Mn: 0 to 0.20%, Sn: 0 to 0.40%, Ti: 0 Chemistry consisting of 0.50%, Zr: 0-0.20%, Si: 0-0.50%, Fe: 0-0.30%, Zn: 0-1.00%, the balance Cu and inevitable impurities The number density of coarse Ni—Al-based precipitate particles having a major axis of 5.0 μm or more is 5.0 × 10 ³ particles / mm ² or less on an observation surface having a composition and parallel to the plate surface (rolling surface). The KAM value measured with a step size of 0.5 μm in the crystal grain when a boundary with a crystal orientation difference of 15 ° or more is regarded as a grain boundary by EBSD (electron beam backscatter diffraction method) is 1. A copper alloy sheet material of 50 to 5.00 °.
Ni / Al ≦ 15.0 (1)
Here, the content value of the element represented by mass% is substituted for the element symbol in the formula (1). The copper alloy plate material according to claim 1, wherein an average crystal grain size in the plate thickness direction defined in (A) below is 10.0 µm or less.
(A) On a SEM (scanning electron microscope) image in which a cross section perpendicular to the rolling direction (C cross section) is observed, a straight line in the plate thickness direction is randomly drawn, and an average cut length of crystal grains cut by the straight line is obtained. The average crystal grain size in the plate thickness direction is used. However, a plurality of straight lines that do not cut the same crystal grain repeatedly are randomly set in one or a plurality of observation fields so that the total number of crystal grains cut by the straight line is 100 or more.   The copper alloy sheet according to claim 1 or 2, wherein a maximum height roughness Rz in a direction perpendicular to the rolling direction of the sheet surface (rolled surface) is 1.2 µm or less.   The copper alloy sheet material according to any one of claims 1 to 3, wherein the conductivity is 3.0 to 20.0% IACS.   The copper alloy sheet according to any one of claims 1 to 4, wherein the tensile strength in the rolling direction is 800 MPa or more.   The copper alloy plate material according to any one of claims 1 to 5, wherein the plate thickness is 0.015 to 0.50 mm.   The electroconductive spring member which used the copper alloy board | plate material of any one of Claims 1-6 for the material. Content by mass: Ni: 10.0 to 30.0%, Al: 7.50% or less and satisfying the following formula (1), Mg: 0 to 0.30%, Cr: 0 to 0.20% , Co: 0 to 0.30%, P: 0 to 0.10%, B: 0 to 0.05%, Mn: 0 to 0.20%, Sn: 0 to 0.40%, Ti: 0 Chemistry consisting of 0.50%, Zr: 0-0.20%, Si: 0-0.50%, Fe: 0-0.30%, Zn: 0-1.00%, the balance Cu and inevitable impurities A step of heating and holding the slab having a composition at 1000 to 1150 ° C. for 2 hours or more (slab heating step),
Rolling rate in a temperature range of 950 ° C. or higher: 65% or higher, rolling temperature in final pass: 800 ° C. or higher (hot rolling step)
Cold rolling process (cold rolling process),
Maximum material temperature T ₁ : Over 950 ° C., 1100 ° C. or less, Average heating rate from 900 ° C. to T ₁ : 50 ° C./s or more, Holding time in temperature range of 900 ° C. or more and T ₁ or less: 30 to A step of performing a solution treatment under a condition of 360 seconds (solution treatment step),
A step of aging treatment at 400 to 650 ° C. for 0.1 to 48 hours (aging treatment step);
A step of performing cold rolling at a rolling rate of 30 to 99% (finish cold rolling step),
Maximum heat treatment temperature T ₂ : 400 to 700 ° C., Maximum heating rate up to T ₂ : 200 ° C./s or less, Holding time at 400 to 700 ° C .: 10 to 300 seconds (finishing) Heat treatment process),
The manufacturing method of the copper alloy board | plate material which has these in said order.
Ni / Al ≦ 15.00 (1)
Here, the content value of the element represented by mass% is substituted for the element symbol in the formula (1).   The method for producing a copper alloy sheet according to claim 8, wherein cold rolling is performed at a rolling rate of 80 to 98% in the cold rolling step.   The method for producing a copper alloy sheet according to claim 8 or 9, wherein in the finish cold rolling step, the sheet thickness after the cold rolling is set to 0.015 to 0.50 mm.