Cu-Ni-Al copper alloy sheet material, method for manufacturing the same, and conductive spring member

Abstract

To impart a property of remarkably suppressing occurrence of smut generation during etching, in a high strength Cu-Ni-Al system copper alloy of a composition region exhibiting whitish metallic appearance.SOLUTION: 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%, Ga: 0 to 0.5%, Ge: 0 to 0.5%, In: 0 to 0.5%, 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 a copper concentration XCu in the deposits expressed by XCu(mass%)=[Cu / (Cu+Ni+Al)]×100 is 15 to 50 mass%, and the Vickers hardness is 300 HV or larger.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a Cu-Ni-Al copper alloy sheet material that exhibits excellent performance in suppressing smut generation during etching, and to a method for manufacturing the same. Furthermore, it relates to a conductive spring member using this sheet material. [Background technology]

[0002] Cu-Ni-Al copper alloys can be made high-strength due to Ni-Al precipitates, and they exhibit a lighter copper color and metallic appearance compared to other copper alloys. Copper alloys with this composition are useful as conductive spring components and non-magnetic high-strength components in lead frames, connectors, and other applications.

[0003] With the miniaturization and increased density of electronic devices, there is a growing need for smaller conductive spring components used in them. Further miniaturization of conductive spring components requires increased strength. Cu-Ni-Al copper alloys require the formation of a large amount of precipitates to achieve high strength. On the other hand, small conductive spring components, which require high dimensional accuracy, are often manufactured through an etching process. When etching copper alloys containing many precipitates, particles derived from the precipitates, which are difficult to dissolve in the etching solution, form smut (residual deposits on the material surface), leading to reduced etchability and contamination of the components. Furthermore, obtaining materials for thin-walled components often requires an increase in the number of passes and rolling load in the final cold rolling process, which increases the risk of decreased productivity and reduced yield due to edge breakage, fracture, etc.

[0004] To date, various studies have been conducted to improve other properties while taking advantage of the high strength properties of Cu-Ni-Al copper alloys. For example, Patent Document 1 describes a technique for obtaining a material with high strength, workability, and high conductivity by precipitating a Si-containing γ' phase with an average particle size of 100 nm or less in a Cu-Ni-Al copper alloy containing a predetermined amount of Si, through a process of solution treatment at 700 to 1020°C and aging treatment at 400 to 650°C. However, Patent Document 1 does not disclose any technique effective in suppressing the occurrence of smut.

[0005] Patent Document 2 discloses a technology for manufacturing a Cu-Ni-Al copper alloy sheet material that exhibits an excellent "strength-to-bendability balance" and excellent discoloration resistance. In this manufacturing process, a solution-treated material is subjected to cold-rolling strain as needed, followed by a first aging treatment at a higher temperature range and a second aging treatment at a conventionally common temperature range. This two-stage aging treatment is said to reduce the occurrence of grain boundary reaction-type discontinuous precipitation, while allowing sufficient intragranular precipitation of fine second-phase particles that contribute to strength improvement, thereby achieving an excellent strength-to-bendability balance. However, Patent Document 2 does not disclose any technology effective in suppressing the occurrence of smut.

[0006] Patent Document 3 discloses a manufacturing technique for Cu-Ni-Al copper alloy sheets with a high Young's modulus. Specifically, it describes how a specific crystal orientation can be obtained and a high Young's modulus achieved by performing cold rolling with intermediate annealing under specific conditions, solution treatment at a slow heating rate, and finish cold rolling under conditions where the rolling ratio is controlled to be relatively low, followed by aging treatment. However, Patent Document 3 does not disclose any techniques effective in suppressing the occurrence of smut.

[0007] Patent Document 4 discloses a manufacturing technique for Cu-Ni-Al copper alloy sheets with excellent etchability. The manufacturing process involves rapid heating during solution treatment, cold rolling after aging treatment, and then a finishing heat treatment performed while ensuring that the heating rate is not excessive. This results in a microstructure with a high KAM value, yielding a highly smooth etched surface. It is also taught that reducing the formation of coarse precipitates is effective in improving etchability. However, Patent Document 4 does not disclose any techniques effective in suppressing the occurrence of smut. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2012 / 081573 [Patent Document 2] Japanese Patent Publication No. 2020-50923 [Patent Document 3] Japanese Patent Publication No. 2020-79436 [Patent Document 4] Japanese Patent Publication No. 2019-2042 [Overview of the project] [Problems that the invention aims to solve]

[0009] Cu-Ni-Al copper alloys are useful for conductive spring components such as connectors, but no effective solution has been found for suppressing smut generation during etching. The object of the present invention is to provide a Cu-Ni-Al copper alloy sheet material that has a high strength level and significantly suppresses smut generation during etching compared to conventional materials. Furthermore, the present invention discloses a manufacturing process that is effective in reducing the load during the final cold rolling process when producing high-strength thin sheet materials. [Means for solving the problem]

[0010] The Ni-Al-based precipitates that contribute to the strengthening of Cu-Ni-Al-based copper alloys mainly consist of intermetallic compounds of Ni and Al, but Cu is also present in the precipitate particles. The inventors found that by increasing the Cu concentration in the Ni-Al-based precipitates, the occurrence of smut during etching can be significantly suppressed, and thus completed the present invention.

[0011] Specifically, the above object is achieved by a copper alloy sheet having a chemical composition consisting of, 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%, Ga: 0 to 0.5%, Ge: 0 to 0.5%, In: 0 to 0.5%, 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 being Cu and unavoidable impurities, and satisfying the following formula (1), and having a Cu concentration X in the precipitate determined by the following formula (2) based on the analysis of the residue obtained by electrolytic extraction in a phosphoric acid aqueous solution with a concentration of 7 mol / L Cu is 15 to 50% by mass and the Vickers hardness is 300 HV or more. Ni / Al ≦ 9.0 …(1) Here, the content value of the element represented in mass% is substituted into the position of the element symbol in formula (1). X Cu (mass%) = [Cu / (Cu + Ni + Al)] × 100 …(2) Here, the value of the mass ratio of the element in the residue is substituted into the position of the element symbol in formula (2).

[0012] In the above sheet, the number density of fine precipitate particles with a major axis of 5 to 50 nm on an observation plane parallel to the sheet surface is preferably 1.0×10 7 particles / mm 2 or more. The half-value width of the X-ray diffraction peak of the {220} crystal plane on the sheet surface is preferably 0.5° or more. The number density of coarse precipitate particles with a major axis of 1.0 μm or more on an observation plane parallel to the sheet surface is preferably 3.0×10 4 particles / mm 2 or less.

[0013] The manufacturing method for the above-mentioned plate material involves a step of heating a cast slab having the above-mentioned chemical composition at 1000 to 1150°C (cast slab heating step), A process in which hot rolling is performed under conditions in which the rolling temperature in the final rolling pass is 800°C or higher (hot rolling process), A process of cold rolling with a rolling ratio of 80% or more (cold rolling process), The process involves holding the material at 950-1100°C for 30-360 seconds, followed by cooling under conditions where the average cooling rate from 900°C to 700°C is 110-150°C / s (solution treatment process). The process involves holding the material at 400-650°C for 0.5-75 hours, followed by cooling under conditions where the average cooling rate from 400°C to 300°C is 40-80°C / h (aging process). The process of cold rolling with a rolling ratio of 30% or more (final cold rolling process), The process involves holding the material at 400-700°C for 10-600 seconds, followed by cooling under conditions where the average cooling rate from 400°C to 300°C is 50-90°C / s (final heat treatment process). A method for manufacturing copper alloy sheets is provided, which involves a manufacturing process that includes the above steps in that order to obtain a sheet material having a Vickers hardness of 300 HV or more. In this case, it is preferable to obtain a sheet material having a Vickers hardness of 300 HV or more by a manufacturing process in which the M value of the following equation (4), which represents the relationship between the Vickers hardness H1 (HV) after the aging treatment step, the Vickers hardness H2 (HV) after the final cold rolling step, and the Vickers hardness H3 (HV) after the final heat treatment step, is between -0.2 and 1.2. M = (H2 - H1) / (H3 - H2) …(4) Furthermore, the present invention provides a conductive spring member made of the above-mentioned copper alloy plate material. Furthermore, the following inventions are disclosed in this specification. In mass%, Ni: 10.0~30.0%, Al: 1.00~6.50%, Ag: 0~0.50%, B: 0~0.10%, Co: 0~2.0%, Cr: 0~0.5%, Fe:0~2.0%, Ga:0~0.5%, Ge:0~0.5%, In:0~0.5%, Mg:0~2.0%, Mn:0~2.0%, P:0~0.2%, Si:0~2 When manufacturing a sheet material from a cast slab having a chemical composition consisting of 0.0%, Sn: 0~2.0%, Ti: 0~2.0%, Zn: 0~2.0%, Zr: 0~0.3%, with the remainder being Cu and unavoidable impurities, and satisfying formula (1) above, by a process that includes the above-mentioned steps of casting slab heating, hot rolling, cold rolling, solution treatment, aging treatment, final cold rolling, and final heat treatment, A method for manufacturing copper alloy sheets, wherein, when the Vickers hardness after the aging process is H1 (HV), the Vickers hardness after the final cold rolling process is H2 (HV), and the Vickers hardness after the final heat treatment process is H3 (HV), a manufacturing process is used to obtain a sheet material with a Vickers hardness H3 of 300 HV or more, by setting the M value of equation (4) above to be between -0.2 and 1.2.

[0014] In this specification, the "plate surface" refers to the surface perpendicular to the plate thickness direction of the plate material. The "plate surface" may also be referred to as the "rolling surface". The Vickers hardness described above can adopt the Vickers hardness of the plate surface of the plate material measured in accordance with JIS Z2244:2009. The half-value width of the X-ray diffraction peak of the {220} crystal plane on the plate surface is calculated by measuring the X-ray diffraction pattern of the plate surface under the conditions of Cu-Kα line, tube voltage 30 kV, and tube current 10 mA, and removing the Kα2 line by X-ray diffraction pattern analysis software. The "long diameter" of the particle is defined as the diameter (nm or μm) of the smallest circle surrounding the particle. The "number density of fine precipitate particles with a long diameter of 5 to 50 nm" and the "number density of coarse precipitate particles with a long diameter of 1.0 μm or more" can be obtained as follows, respectively.

[0015] [Method for obtaining the number density of fine precipitate particles] After electrolytic polishing the plate surface under the following electrolytic polishing conditions and then performing ultrasonic cleaning in ethanol for 20 minutes, for the observation surface obtained, randomly set observation fields where some or all of the particles with a long diameter of 1.0 μm or more are not included in the field of view. For the observation fields, count the number of precipitate particles with a long diameter of 5 to 50 nm among the particles whose entire contour is visible. Perform this operation for 10 or more non-overlapping observation fields, and the total N TOTAL divided by the total area of the observation fields is converted to the number per 1 mm 2 and this is used as the number density of fine precipitate particles (number / mm 2 ). (Electrolytic polishing conditions) · Electrolyte: Mix distilled water, phosphoric acid, ethanol, and 2-propanol in a volume ratio of 10:5:5:1 · Liquid temperature: 20 °C · Voltage: 15 V · Electrolytic time: 20 seconds

[0016] [Method for obtaining the number density of coarse precipitate particles] The plate surface was electropolished under the following electrolytic polishing conditions to dissolve only the Cu substrate, exposing the precipitate particles. After ultrasonic cleaning in ethanol for 20 minutes, the observation surface was observed using a FE-SEM (Field Emission Scanning Electron Microscope), and the total number of precipitate particles with a major axis of 1.0 μm or larger observed on the FE-SEM image was measured over the total observation area (mm²). 2 The value obtained by dividing by ) is the number density of coarse precipitate particles (particles / mm²). 2 The total observation area is 0.1 mm², consisting of multiple randomly selected, non-overlapping observation fields. 2 This concludes the procedure. Precipitated particles that partially extend beyond the observation field of view will be counted if the major axis of the portion visible within the observation field of view is 1.0 μm or larger. (Electrolytic polishing conditions) • Electrolyte: Distilled water, phosphoric acid, ethanol, and 2-propanol are mixed in a volume ratio of 10:5:5:1. • Liquid temperature: 20℃ Voltage: 15V ·Electrolysis time: 20 seconds

[0017] The rolling ratio from a certain plate thickness t0 (mm) to a certain plate thickness t1 (mm) can be determined by the following equation (3). Rolling ratio (%) = [(t0-t1) / t0] × 100 …(3) [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a sheet material in the Cu-Ni-Al copper alloy composition range that exhibits a white metallic appearance, having a very high strength level and significantly suppressing the occurrence of smut during etching compared to conventional materials. Furthermore, in the final cold rolling process to obtain such a high-strength thin sheet material, the phenomenon of work softening can be utilized, making it possible to reduce the rolling load. [Brief explanation of the drawing]

[0019] [Figure 1]This figure illustrates the appearance of the test specimen after etching (top row) and the appearance of the cellophane adhesive tape after peeling (bottom row) of the test material used in Example No. 1 of the present invention. [Figure 2] This figure illustrates the appearance of the test specimen after etching (top row) and the appearance of the cellophane adhesive tape after peeling (bottom row) of the test material used in Example No. 7 of the present invention. [Figure 3] This figure illustrates the appearance of the test specimen after etching (top row) and the appearance of the cellophane adhesive tape on which a peeling test was performed (bottom row) for the test material of Comparative Example No. 34. [Modes for carrying out the invention]

[0020] [Chemical composition] This invention focuses on Cu-Ni-Al copper alloys. Hereafter, "%" in relation to alloy components refers to "mass%" unless otherwise specified.

[0021] Ni, along with Cu, is a major element constituting the matrix (metal base) of Cu-Ni-Al copper alloys. Furthermore, some of the Ni in the alloy combines with Al to form Ni-Al precipitates, and these fine particles contribute to improved strength. To obtain sufficient strength, it is desirable to ensure a Ni content of 10% or more. Also, as the Ni content increases, the alloy exhibits a whiter metallic appearance compared to other common copper alloys. However, like other copper alloys, exposure to high humidity environments can cause a thin oxide film to form on the metal surface, resulting in noticeable discoloration. In such cases, the beautiful white appearance is lost. Especially when discoloration resistance is important, it is preferable to increase the Ni content to 12.0% or more and ensure the Al content as described below. A Ni content of 15.0% or more is more effective. On the other hand, high Ni content worsens hot workability. The Ni content should be limited to 30.0% or less, or even 25.0% or less. Alternatively, the Ni content may be controlled between 18.0% and 22.0%.

[0022] Al is an element that forms Ni-Al precipitates. If the Al content is too low, the improvement in strength will be insufficient. On the other hand, if the Al content is too high, the hot workability will be poor. Furthermore, by increasing the Al content in conjunction with the Ni content, the resistance to discoloration can be improved. After various studies, it has been found that the Al content should be in the range of 1.00 to 6.50%, and the Ni / Al ratio should satisfy the following equation (1). It is more preferable that the following equation (1)' is satisfied. Ni / Al ≤ 9.0 …(1) 2.0 ≤ Ni / Al ≤ 8.0 …(1)' Here, the elemental symbols in equations (1) and (1)' are replaced with the content values ​​of the element, expressed as mass percent.

[0023] Other elements such as Ag, B, Co, Cr, Fe, Ga, Ge, In, Mg, Mn, P, Si, Sn, Ti, Zn, and Zr may be included as needed. The content ranges for these elements are as follows: Ag: 0-0.50%, B: 0-0.10%, Co: 0-2.0%, Cr: 0-0.5%, Fe: 0-2.0%, Ga: 0-0.5%, Ge: 0-0.5%, In: 0-0.5%, Mg: 0-2.0%, Mn: 0-2.0%, P: 0-0.2%, Si: 0-2.0%, Sn: 0-2.0%, Ti: 0-2.0%, Zn: 0-2.0%, and Zr: 0-0.3%. Furthermore, the total amount of these optional additives should preferably be 2.0% or less, but may be 1.2% or less, or 0.5% or less.

[0024] [Cu concentration in precipitate Cu ] It was found that by controlling the Cu concentration in the precipitate, smut generation during etching can be significantly suppressed while maintaining high strength. Although Cu is present in Ni-Al precipitates along with Ni and Al, the Cu concentration is increased compared to normal. Specifically, the Cu concentration in the precipitate is determined by equation (2) below based on the analysis of the residue obtained by electrolytic extraction in a 7 mol / L phosphoric acid aqueous solution. Cu The composition of the precipitate is controlled so that it is between 15 and 50% by mass. X Cu(mass%)=[Cu / (Cu+Ni+Al)]×100…(2) Here, the elemental symbol in equation (2) is replaced with the value of the mass percentage of that element in the residue.

[0025] The above X Cu to 15 mass% By doing so, a significant effect in suppressing smut formation is observed. Although the mechanism is not yet clear, it is presumed that the increased amount of Cu dissolved in the precipitate makes the precipitate more easily soluble in the etching solution (e.g., ferric chloride aqueous solution). Cu to 15 mass% Further improvements can be achieved by following the manufacturing method described below. Cu is 20 mass% It is more preferable that the above conditions are met. Cu 50 mass% If it exceeds X, it will become impossible to maintain high strength, so X Cu is 50 mass% You can adjust it within the following range: 45 mass% The following, or 40 mass% You may adjust it within the following range.

[0026] [Vickers hardness] For applications in small conductive spring components, high strength is advantageous. A Vickers hardness of 300 HV or higher is preferable, and 320 HV or higher is even more preferable. It is also possible to adjust the hardness to an extremely high level for a Cu-Ni-Al copper alloy, such as 340 HV or higher, or even 380 HV or higher. There is no specific upper limit for hardness, but it is usually sufficient to adjust it within the range of 450 HV or lower. The strength level can be adjusted by the chemical composition and the conditions set in the manufacturing process described later.

[0027] [Number density of fine precipitate particles with a major axis of 5-50 nm] Fine precipitate particles with a major axis of 5 to 50 nm contribute to improved strength by being dispersed in the matrix (metal substrate). In the Cu-Ni-Al copper alloy targeted by this invention, the fine precipitates formed are Ni-Al precipitates mainly composed of Ni and Al. From the viewpoint of improving strength, the number density of fine precipitate particles with a major axis of 5 to 50 nm is 1.0 × 10⁻⁶. 7 pieces / mm 2 It is preferable that the above is true, 2.5 × 10 7 pieces / mm 2 It is more preferable that the above is true. Typically, 5.0 × 10 10 pieces / mm 2 The adjustment should be made within the following range. Although Cu is also present in the particles of Ni-Al precipitates, the copper alloy plate material of the present invention achieves a suppression effect on smut generation by controlling the Cu concentration to a higher level as described above.

[0028] [Number density of coarse precipitate particles with a major axis of 1.0 μm or larger] To form a highly smooth etched surface through etching, it is advantageous to minimize the amount of coarse precipitates present. Specifically, the density of coarse precipitate particles with a major axis of 1.0 μm or larger is 3.0 × 10⁻⁶. 4 pieces / mm 2 Preferably, it is 1.0 × 10 4 pieces / mm 2 The following is more preferable:

[0029] [Half-width of X-ray diffraction peaks on the {220} crystal plane] The Cu-Ni-Al copper alloy sheet material according to the present invention has a half-width of the X-ray diffraction peak of the {220} crystal plane on the sheet surface of, for example, 0.5° or more. Such a copper alloy sheet material has sufficient lattice strain introduced, which is advantageous for obtaining high strength and a highly smooth etched surface.

[0030] [Manufacturing method] The copper alloy sheet material described above can be manufactured, for example, by the following process. Melting and casting → Slab heating → Hot rolling → Cold rolling → (Intermediate annealing → Cold rolling) → Solution treatment → Aging treatment → Final cold rolling → Final heat treatment Although not mentioned in the above process, surface milling is performed as needed after hot rolling, and pickling, polishing, or further degreasing is performed as needed after each heat treatment. The following describes each process.

[0031] [Melting and Casting] Cast slabs can be manufactured by continuous casting, semi-continuous casting, or the like. From the viewpoint of preventing oxidation of Al, it is preferable to perform the melting in a chamber under an inert gas atmosphere or under vacuum.

[0032] [Slab heating] The cast slab is heated and held at 1000-1150°C. This heating can be carried out using the cast slab heating process during hot rolling. Conventionally, cast slabs of Cu-Ni-Al copper alloys were often heated at temperatures below 950°C. In this invention, it is necessary to control the Cu concentration in the precipitate in a later process. To achieve this, it is effective to heat the cast slab to the above high temperature to solidify as much of the coarse second phase present in the cast structure as possible. However, if the temperature exceeds 1150°C, the parts of the cast structure with low melting points become brittle, and cracking may occur during hot rolling. It is more effective to heat and hold the slab for 1.5 hours or more within the above temperature range, and even more effective for 2 hours or more. Considering economics, it is desirable to set the cast slab heating time within the above temperature range to 5 hours or less.

[0033] [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 expressed by the surface temperature of the material immediately after it exits the work roll in that rolling pass. The above-mentioned high-temperature heating of the cast slab and hot rolling at 800°C or higher sufficiently reduces the amount of coarse second phase. This makes it possible to control the Cu concentration in the precipitate to an appropriate range in subsequent processes. In the hot-rolled sheet material, the number density of coarse second phase particles with a major axis of 5 μm or more on an observation surface parallel to the sheet surface is, for example, 10 particles / mm². 2It is desirable that the following conditions be met. From the viewpoint of stably achieving a final pass rolling temperature of 800°C or higher in mass production operations, the plate thickness after hot rolling (finished plate thickness) is preferably in the range of 5 to 20 mm, and more preferably in the range of 7 to 20 mm.

[0034] [Cold rolling] Before solution treatment, the sheet thickness can be adjusted by cold rolling. If necessary, one or more "intermediate annealing → cold rolling" steps may be added. The rolling ratio in the cold rolling performed before solution treatment (or the rolling ratio in the cold rolling after the final intermediate annealing, if intermediate annealing is performed) can be, for example, 80% or more. The upper limit of the rolling ratio can be set within a range of, for example, 99.5% or less, depending on the mill's capacity.

[0035] [Solution treatment] In the solution treatment of the present invention, the material is heated to a higher temperature than the typical solution treatment temperature for Cu-Ni-Al copper alloys (approximately 800-900°C). Specifically, the material is held in the temperature range of 950-1100°C for 30-360 seconds. Heating to such a high temperature range allows for sufficient solid solution formation of the second phase even with the short holding time described above. In addition to the heating temperature and holding time mentioned above, it is important in the present invention to control the cooling rate after the solution treatment within a narrow range. Specifically, the average cooling rate from 900°C to 700°C should be in the range of 110-150°C / s. If the cooling rate in this temperature range is too slow, the effect of suppressing smut formation cannot be sufficiently obtained. On the other hand, if the cooling rate is too fast, it becomes difficult to stably obtain a structure with a sufficient amount of fine precipitates dispersed in subsequent processes, which is disadvantageous in achieving a very high strength level. It is hypothesized that when the cooling rate in the above temperature range after solution treatment is controlled to a narrow range of 110 to 150°C / s, numerous nuclei for fine precipitation are generated within the crystal grains during the cooling process, and the growth of precipitated particles proceeds appropriately, resulting in a "precursor microstructure" suitable for dispersing a large number of fine precipitates with high Cu concentration in subsequent processes. In actual operation, it is efficient to continue forced cooling until the temperature reaches a range of 10°C to 100°C, under cooling conditions where the average cooling rate from 900°C to 700°C is in the range of 110 to 150°C / s, and it is more preferable to continue forced cooling until the temperature reaches a range of 20°C to 50°C.

[0036] [Statute of limitations] Next, aging treatment is performed. After solution treatment, aging treatment can be performed directly on the microstructure in which the solution treatment process was completed, without introducing processing strain such as cold rolling. The aging treatment is carried out under conditions where the material is held at 400-650°C for 0.5-75 hours, and then the average cooling rate from at least 400°C to 300°C is 40-80°C / h. After that, it is preferable to continue cooling in the furnace until the temperature reaches a range of 10°C to 200°C, and more preferably until the temperature reaches a range of 20°C to 100°C. Strictly controlling the cooling conditions as described above is extremely effective in adjusting the Cu concentration of the precipitate to a predetermined range. If the cooling rate is too fast, it becomes difficult to secure a sufficient amount of fine precipitates after the final heat treatment described later, which is disadvantageous in obtaining high strength. If the cooling rate is too slow, the concentration of Cu dissolved in the precipitated phase decreases, making it difficult to obtain a sheet material with a high concentration of Cu in the precipitate after the final heat treatment described later, and the work softening effect is not sufficiently exerted in the final cold rolling process.

[0037] [Final cold rolling] After aging treatment, cold rolling is performed to the final target plate thickness. This cold rolling is referred to as "final cold rolling" in this specification. The purpose of final cold rolling is not only to adjust to the target plate thickness but also to impart rolling strain so that sufficient hardening occurs in the final heat treatment process. From the perspective of imparting rolling strain, the rolling ratio in final cold rolling should be 30% or more. A ratio of 50% or more is more effective. The upper limit of the rolling ratio depends on the capacity of the mill, but it is usually sufficient to set it within the range of 99% or less. The final plate thickness can be adjusted, for example, within the range of 0.01 to 0.50 mm.

[0038] Generally, the higher the cold rolling ratio, the greater the deformation resistance due to work hardening. For example, when finishing thin sheets with a thickness of 0.1 mm or less, an increase in the number of passes and material tearing tend to become problems. However, when cold rolling is applied to aged material according to the above manufacturing conditions, work hardening is significantly suppressed, and the above problems are greatly improved. The reason for this is not clear, but it is speculated that a precipitate with a high concentration of Cu is formed at the end of the aging treatment, and as Cu dissolves in the precipitate and the composition of the precipitate approaches that of the matrix phase, the precipitate particles become more likely to pseudo-dissolve during plastic deformation by rolling (i.e., when rolling strain is applied). As a result, even though it is a cold work, the increase in hardness is very small, or rather, the hardness decreases. This phenomenon is referred to as "work softening" in this specification.

[0039] [Final heat treatment] A final heat treatment is applied to the sheet material after the final cold rolling to increase its strength while controlling the Cu concentration of the precipitates. The final heat treatment is performed at 400-700°C, more preferably 420-700°C, held for 10-600 seconds, and then cooled from 400°C to 300°C at an average cooling rate of 50-90°C / s. It is presumed that this heat treatment results in a microstructure in which dislocations are less likely to move, as the solute atoms that were pseudo-dissolved during the final cold rolling precipitate finely. If the cooling rate is too slow, the Cu concentration in the precipitates decreases, making it difficult to stably obtain sheet material that is highly effective in suppressing smut formation. If the cooling rate is too fast, the precipitation from the pseudo-dissolved state cannot proceed sufficiently, and as a result, a high strength level cannot be obtained. In actual operation, under cooling conditions where the average cooling rate from 400°C to 300°C is in the range of 50 to 90°C / s, it is efficient to continue forced cooling until the temperature reaches a range of 10°C to 100°C, and it is more preferable to continue forced cooling until the temperature reaches a range of 20°C to 50°C.

[0040] Using the plate material obtained according to the present invention as described above, a conductive spring member with high dimensional accuracy can be obtained by performing processing including etching. [Examples]

[0041] Copper alloys with the chemical composition shown in Table 1 were melted and cast using a vertical semi-continuous casting machine. The resulting 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 rate was 85-95%. The rolling temperature of the final pass and the finished plate thickness after hot-rolling are shown in Tables 2 and 3. In some cases where cracking occurred during hot-rolling (Nos. 35, 37, 39), production was stopped at that point. After hot-rolling, the oxide layer on the surface was removed by mechanical polishing (surface grinding), and cold-rolling was performed at the rolling rates shown in Tables 2 and 3.

[0042] Each cold-rolled material obtained was subjected to solution treatment using a continuous annealing furnace equipped with a heating zone and a forced cooling zone under the conditions shown in Tables 2 and 3. After heating in the heating zone, where it was held at a predetermined temperature for a predetermined time, forced cooling was performed in the forced cooling zone by blowing nitrogen gas, which was circulated by a fan, onto the surface of the sheet material as it passed through the furnace. The cooling rate could be controlled by adjusting the convection intensity. During the process, the surface temperature T0 (°C) of the sheet material immediately before the start of forced cooling and the surface temperature T1 (°C) immediately after the end of forced cooling were measured. In each example, it was confirmed that T0 was 900°C or higher and T1 was 700°C or lower. Therefore, based on the cooling curve determined from the above T0, T1, and the sheet material passing speed, the average cooling rate from 900°C to 700°C was determined.

[0043] After solution treatment, aging treatment was performed directly without adding cold rolling strain. The aging treatment was carried out using a batch-type annealing furnace under the conditions of holding at the temperatures and for the times specified in Tables 2 and 3. The atmosphere was nitrogen. After heating and holding, the material was cooled in the furnace at a generally constant cooling rate until it was below 300°C. Next, final cold rolling was performed at the rolling ratios specified in Tables 2 and 3. Subsequently, the final heat treatment was performed using a continuous-type annealing furnace equipped with a heating zone and a forced cooling zone under the conditions shown in Tables 2 and 3. After heating in the heating zone, holding at a predetermined temperature for a predetermined time, forced cooling was performed in the forced cooling zone by blowing nitrogen gas, which was forcibly convected by a fan, onto the surface of the sheet material as it passed through. The cooling rate could be controlled by adjusting the convection strength. During sheet passing, the surface temperature T0 (°C) immediately before the start of forced cooling and the surface temperature T1 (°C) immediately after the end of forced cooling were measured. In each example, it was confirmed that T0 was 400°C or higher and T1 was 300°C or lower. Therefore, based on the cooling curve determined from the above T0, T1, and sheet metal speed, the average cooling rate from 400°C to 300°C was calculated. In this way, plate products (test specimens) with the final plate thicknesses shown in Tables 2 and 3 were obtained. The following investigations were conducted on each test specimen. In addition to the test specimens after the final heat treatment, "hardness" was also measured for materials after aging treatment and materials after final cold rolling.

[0044] (Cu concentration in precipitate Cu ) A sample was taken from the test material, and the surface oxide layer was removed by dry polishing using emery abrasive paper of grit 1000 (particle size P1000 as specified in JIS R6010:2000). Then, the matrix (metal base material) was dissolved by applying a voltage of approximately 2.0 V for 15 minutes in a 7 mol / L phosphoric acid aqueous solution at 25°C. The residue (precipitate) extracted into the solution was recovered by suction filtration using a filter with a pore size of 50 nm. At that time, the residue and filter were washed with pure water until the pH of the aspirated liquid became 6.2. The recovered residue was analyzed for Cu, Ni, and Al by ICP emission spectrometry, and the Cu concentration X in the precipitate was determined by the following equation (2) based on the analysis. CuThe following was determined. A mixed acid, consisting of equal volumes of nitric acid and hydrochloric acid, was used to dissolve the residue. X Cu (mass%)=[Cu / (Cu+Ni+Al)]×100…(2) Here, the elemental symbol in equation (2) is replaced with the value of the mass percentage of that element in the residue.

[0045] (Half-width of X-ray diffraction peaks on the {220} crystal plane) Using an X-ray diffractometer (Bruker AXS; D2 Phaser), the X-ray diffraction pattern was measured on the plate surface under the conditions of Cu-Kα rays, tube voltage of 30kV, and tube current of 10mA. After removing the Kα2 rays using the Kα2 removal function of X-ray diffraction pattern analysis software (Bruker AXS; DIFFRAC.EVA) with the conditions of "maximum: 1, intensity ratio: 0.5, minimum: 0", the full width at half maximum of the X-ray diffraction peaks of the {220} crystal plane was calculated.

[0046] (Number density of fine precipitate particles) Following the "Method for Determining the Number Density of Fine Precipitate Particles" described above, the observation surface prepared by electrolytic polishing and ultrasonic cleaning was observed using an FE-SEM (JEOL Ltd.; JSM-7200F), and the number density (particles / mm³) of fine second-phase particles with a major axis of 5-50 nm was determined. 2 The above electrolytic polishing was performed using an electrolytic polishing device (ELECTROPOLISHER POWER SUPPLUY, ELECTROPOLISHER CELL MODULE) manufactured by BUEHLER. The above ultrasonic cleaning was performed in ethanol for 20 minutes using an ultrasonic cleaner "BRANSONIC M2800-J".

[0047] (Hardness) The Vickers hardness of the board surface was measured according to the method compliant with JIS Z2244:2009. Seven measurements were taken at a test force F(N) such that the average value d(mm) of the diagonal lengths d1 and d2 of the formed indentation (indentation) was 2 / 3 or less of the sample board thickness. The average of the five values, excluding the maximum and minimum values, was adopted as the hardness of the test material.

[0048] In each example, the hardness H1 (HV) after aging treatment, the hardness H2 (HV) after final cold rolling, and the hardness H3 (HV) of the test material after final heat treatment were measured, and the manufacturability index M, expressed by the following formula (4), was determined. M = (H2 - H1) / (H3 - H2) …(4) The manufacturability index M represents the ratio of the "increase in hardness during final cold rolling" to the "increase in hardness after final heat treatment." A smaller value indicates that work hardening during final cold rolling has been effectively suppressed, resulting in better material strengthening. In other words, a smaller manufacturability index M indicates a lower load during final cold rolling in the strengthening process, which combines aging treatment, final cold rolling, and final heat treatment, and thus better manufacturability. After various studies, it has been determined that for this alloy system, if the manufacturability index M is 1.2 or less, high-strength sheet metal can be efficiently manufactured with a high yield using the above strengthening process. Note that if the hardness decreases due to final cold rolling, the manufacturability index M will be negative, and the load during that rolling process is considered to be particularly reduced. However, if the decrease in hardness during final cold rolling is too large, a considerably large increase in hardness during final heat treatment is required to ensure sufficient strength, which severely restricts the conditions for final heat treatment. Furthermore, if the material undergoes significant work hardening during the final cold rolling process and then softens during the final heat treatment, the manufacturability index M may become a large negative value, which is undesirable from the standpoint of reducing the load during the final cold rolling process. Considering the load balance in each process and the load reduction during the final cold rolling process, the M value expressed by equation (4) above is preferably in the range of -0.2 to 1.2.

[0049] (Smut generation amount) Test pieces approximately 10 mm wide and 40-60 mm long were cut from the test material, and their surfaces were subjected to etching tests using a spray etching apparatus. The etching solution was an aqueous solution of ferric chloride with a Baumé degree of 42 Bh. The solution temperature was 50°C, the spray pressure was 0.15 MPa, and the spray time was 120 seconds. After the etching test, the samples were washed with water and dried, and a "peeling test" was performed by applying cellophane adhesive tape according to JIS Z1522:2009 to the sample surface and then peeling it off. The smut generated by etching adhered to the sample surface after washing and drying. The amount of smut transferred to the surface of the cellophane adhesive tape peeled off in the peeling test (the degree of black staining on the tape) can be used to evaluate the smut generation suppression performance.

[0050] Figures 1 to 3 illustrate photographs of the appearance of test specimens after etching (top row) and photographs of the appearance of cellophane adhesive tape that underwent a peeling test on its surface (bottom row). Figure 1 is Invention Example No. 1, Figure 2 is Invention Example No. 7, and Figure 3 is Comparative Example No. 34. The results for two test specimens are shown for each. It can be seen that the occurrence of smut is significantly suppressed in the Invention Examples (Figures 1 and 2) compared to the Comparative Example (Figure 3). Here, the appearance of the test specimens after etching and the degree of black staining on the cellophane adhesive tape peeled off in the peeling test were observed visually, and compared with Comparative Example No. 34 (Figure 3), those that clearly showed a smut suppression effect were evaluated as ○ (smut suppression ability: good), those that showed a particularly remarkable smut suppression effect were evaluated as ◎ (smut suppression ability: excellent), and all others were evaluated as × (smut suppression ability: insufficient improvement). The results of these surveys are shown in Tables 4 and 5.

[0051] [Table 1]

[0052] [Table 2]

[0053] [Table 3]

[0054] [Table 4]

[0055] [Table 5]

[0056] All of the Cu-Ni-Al copper alloy plate materials of the present invention have high strength, and the Cu concentration in the precipitate is X Cu The smut content was in the range of 15-50% by mass, demonstrating excellent smut suppression performance. The manufacturability index M was also low, and manufacturability was good even in strengthening processes combining aging treatment, final cold rolling, and final heat treatment.

[0057] Among the comparative examples, Nos. 31-34, 40, and 41 showed that the Cu concentration in the precipitate was X because the manufacturing conditions fell outside the range specified by the present invention. Cu In this example, the temperature was lower than the range specified in the present invention, and the performance in suppressing smut generation could not be improved. Specifically, in Comparative Example No. 31, the slab heating temperature and the rolling temperature of the final hot-rolling pass were low. In No. 32, the solution treatment temperature was low. In No. 33, the average cooling rate from 900°C to 700°C in the solution treatment process was slow. In No. 34, the cooling rate from 400°C to 300°C in the aging treatment process was too slow. In No. 40, the rolling temperature of the final hot-rolling pass was low and the heating and holding time in the solution treatment was short. In No. 41, the average cooling rate from 400°C to 300°C in the final heat treatment process was slow.

[0058] Cases No. 36, 38, and 42-44 are examples where the number density of fine precipitate particles was low and the intensity level corresponding to 300 HV was not reached due to the chemical composition or manufacturing conditions falling outside the range specified by the present invention. Specifically, in case No. 36, the Ni content was too low. In case No. 38, the Al content was low and the Ni / Al ratio was high. In case No. 42, the average cooling rate from 900°C to 700°C in the solution treatment process was too fast. In case No. 43, the cooling rate from 400°C to 300°C in the aging treatment process was too fast. In case No. 44, the cooling rate from 400°C to 300°C in the final heat treatment process was too fast.

[0059] Examples No. 35, 37, and 39 are cases where production was stopped at the point of cracking during hot rolling. Of these, No. 35 had too high a nickel content, No. 37 had too high an aluminum content, and No. 39 had too high a slab heating temperature.

[0060] (Number density of coarse precipitate particles) To obtain an etched surface with minimal irregularities and high smoothness, it is advantageous to have fewer coarse precipitates. Therefore, the number density of coarse precipitate particles in the plate material obtained in the present invention (test material after final heat treatment) was investigated using the following method. Following the "Method for Determining the Number Density of Coarse Precipitate Particles" described above, observation surfaces prepared by electropolishing and ultrasonic cleaning were observed using FE-SEM, and the number density of coarse precipitate particles with a major axis of 1.0 μm or larger was determined. The electropolishing was performed using an electropolishing apparatus (ELECTROPOLISHER POWER SUPPLUY, ELECTROPOLISHER CELL MODULE) manufactured by BUEHLER. The ultrasonic cleaning was performed in ethanol for 20 minutes using an ultrasonic cleaner "BRANSONIC M2800-J". As a result, it was confirmed that all of the examples of the present invention had a very low number density of coarse precipitates. The results are shown in Table 6.

[0061] [Table 6]

Claims

1. 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: 0-2.0%, Ga: 0-0.5%, Ge: 0-0.5%, In: 0-0.5%, Mg: 0-2.0%, Mn: 0-2.0%, P: 0-0.2%, The Cu concentration X in the precipitate is determined by formula (2) below, based on the analysis of the residue obtained by electrolytic extraction in a 7 mol / L aqueous phosphoric acid solution, and the following chemical composition satisfies equation (1) below: Si: 0-2.0%, Sn: 0-2.0%, Ti: 0-2.0%, Zn: 0-2.0%, Zr: 0-0.3%, with the remainder being Cu and unavoidable impurities. Ｃｕ A copper alloy sheet material having a composition of 20-50% by mass and a Vickers hardness of 300 HV or higher. Ni / Al≦9.0…(1) Here, the elemental symbol in equation (1) is replaced with the content value of the element, expressed as a mass percent. X Ｃｕ (Mass weight%) = [Cu / (Cu+Ni+Al)] × 100 … (2) Here, the elemental symbol in equation (2) is replaced with the value of the mass percentage of that element in the residue.

2. On the observation surface parallel to the plate surface, the number density of fine precipitate particles with a major axis of 5 to 50 nm is 1.0 × 10⁻⁶. ７ pieces / mm ２ The copper alloy plate material according to claim 1.

3. The copper alloy plate material according to claim 1 or 2, wherein the full width at half maximum of the X-ray diffraction peak of the {220} crystal plane on the plate surface is 0.5° or more.

4. A step of heating a cast slab at 1000 to 1150°C (cast slab heating step), wherein the chemical composition is as follows: 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%, Ga: 0 to 0.5%, Ge: 0 to 0.5%, In: 0 to 0.5%, 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%, with the remainder being Cu and unavoidable impurities, and satisfying the following formula (1). A process in which hot rolling is performed under conditions in which the rolling temperature in the final rolling pass is 800°C or higher (hot rolling process), A process of cold rolling with a rolling ratio of 80% or more (cold rolling process), The process involves holding the material at 950-1100°C for 30-360 seconds, followed by cooling under conditions where the average cooling rate from 900°C to 700°C is 110-150°C / s (solution treatment process). A process of holding the material at 400-650°C for 0.5-75 hours, followed by cooling under conditions where the average cooling rate from 400°C to 300°C is 40-80°C / h (aging process), A process of cold rolling with a rolling ratio of 30% or more (final cold rolling process), The process involves holding the material at 400-700°C for 10-600 seconds, followed by cooling under conditions where the average cooling rate from 400°C to 300°C is 50-90°C / s (final heat treatment process). A method for manufacturing a copper alloy sheet material according to claim 1, comprising a manufacturing process including the above steps in order, wherein a sheet material having a Vickers hardness of 300 HV or more is obtained. Ni / Al≦9.0…(1) Here, the elemental symbol in equation (1) is replaced with the content value of the element, expressed as a mass percent.

5. A method for manufacturing a copper alloy sheet material according to claim 4, wherein the M value of the following formula (4), which represents the relationship between the Vickers hardness H1 (HV) after the aging treatment step, the Vickers hardness H2 (HV) after the final cold rolling step, and the Vickers hardness H3 (HV) after the final heat treatment step, is between -0.2 and 1.2, thereby obtaining a sheet material having a Vickers hardness H3 of 300 HV or more. M=(H2-H1) / (H3-H2)...(4)

6. A conductive spring member made of a copper alloy plate material as described in any one of claims 1 to 3.

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