Method of producing copper alloy sheet for vehicle or electric / electronic component having excellent strength, electrical conductivity, and bendability, and copper alloy sheet produced thereby

Abstract

The present invention relates to: a copper alloy which is for a vehicle or an electric / electronic component, and has high strength, high electric conductivity, and excellent bendability; and a method for producing same.

Description

FIELD

[0001] The present disclosure relates to a method for producing a copper alloy sheet for an automobile component or an electrical and electronic component with excellent strength, electrical conductivity and bendability, and a copper alloy sheet produced thereby. More particularly, the present disclosure relates to a method for producing a copper-nickel-cobalt-silicon (Cu—Ni—Co—Si)-based copper alloy sheet and a copper alloy sheet produced thereby.DESCRIPTION OF RELATED ART

[0002] A copper alloy material used in automobiles or electrical / electronic components is required to have good electrical conductivity in order to suppress the generation of Joule heat caused by electric current, and at the same time to have high strength to withstand the stress applied thereto during assembly or operation of a device. In addition, the automobile or electrical / electronic components are generally manufactured in a form of the copper alloy sheet, and are formed by bending processing of the sheet. Thus, the components are also required to have excellent bendability.

[0003] For the high strength and high conductivity, the use of precipitation hardening copper alloys as the copper alloy for the automobile or electrical / electronic components in place of a solid solution phase strengthened copper alloys such as conventional phosphor bronze and brass is increasing. In the precipitation hardening copper alloy, the solution-treated supersaturated solid solution undergoes aging treatment, thereby uniformly dispersing fine precipitates to increase the strength of the alloy, and at the same time, an amount of dissolved elements in copper is reduced, thereby improving electrical conductivity. For this reason, the precipitation hardening copper alloy has excellent mechanical properties such as strength and elasticity and good electrical conductivity, that is, thermal conductivity.

[0004] Among the precipitation hardening copper alloys, a Cu—Ni—Si-based copper alloy commonly called Corson-based alloy is a representative copper alloy that has the tensile strength of 700 MPa and relatively high electrical conductivity of about 40% IACS, and strength, and bending workability. As such, active development thereof is currently underway in the industry. In this Corson-based alloy, strength and electrical conductivity may be improved by precipitating fine Ni—Si intermetallic compounds in the Cu matrix. However, when the Corson-based alloy is applied to the automobile or electrical / electronic components, the strength thereof is not sufficient. Thus, measures such as increasing the content of nickel (Ni) and silicon (Si) or adding magnesium (Mg), etc. are being taken. However, there is a problem that conductivity decreases while strength increases due to the addition of the additional elements. Recently, a copper-nickel-cobalt-silicon (Cu—Ni—Co—Si) alloy in which a portion of the content of the Ni of the Corson-based alloy is replaced with Co is being actively developed. However, it is significantly lacking in the physical properties required for materials for electrical and electronic components.

[0005] In Korean Patent Application Publication No. 10-2009-0122303, the bendability is improved by controlling the size and distribution of the second phase of the copper-nickel-cobalt-silicon (Cu—Ni—Co—Si) alloy, while the final physical properties are as follows: tensile strength: 800 MPa, and conductivity: about 40% IACS.

[0006] In Korean Patent Application Publication No. 10-2014-0056003, the nickel (Ni), cobalt (Co), and silicon (Si) contents are increased to secure the strength, and the distribution of precipitates and the orientation of crystallized deposits are controlled to achieve the physical properties such as a yield strength of 950 MPa and a conductivity of 40% IACS. However, when actually producing the alloy, when the total content of nickel (Ni) and cobalt (Co) exceeds 3.5% by weight, there is a high probability of cracking during hot-rolling due to coarse inclusions formed inside the ingot during the casting. In addition, increasing the contents of nickel (Ni) and cobalt (Co) may result in the improved strength, but significantly low bendability, so that there is a high possibility of cracks occurring during parts processing, making it unsuitable as a material for the electrical and electronic components.DISCLOSURETechnical Purpose

[0007] The present disclosure seeks to provide a method for producing a copper alloy sheet for an automotive or electrical and electronic component with excellent strength, electrical conductivity, and bendability, and a copper alloy sheet produced thereby.Technical Solution

[0008] The present disclosure provides a method for producing a copper alloy sheet for an automobile component and an electrical and electronic component, wherein the copper alloy sheet consists of 1.5 to 3.4 wt % nickel (Ni), 0.1 to 1.5 wt % cobalt (Co), 0.3 to 1.2 wt % silicon (Si), 0.1 to 0.8 wt % tin (Sn), 0.01 to 0.45 wt % chromium (Cr), the balance copper (Cu), and unavoidable impurities of a total content of 0.4 wt % or smaller, wherein the unavoidable impurities include at least one selected from a group consisting of Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr and Mn, wherein the method comprises: melting and casting 1.5 to 3.4 wt % nickel (Ni), 0.1 to 1.5 wt % cobalt (Co), 0.3 to 1.2 wt % silicon (Si), 0.1 to 0.8 wt % tin (Sn), 0.01 to 0.45 wt % chromium (Cr), the balance copper (Cu), and the unavoidable impurities of a total content of 0.4 wt % or smaller, thereby obtaining an ingot; hot-rolling the obtained ingot in a temperature range of 900° C. to 1040° C.; performing first cold-rolling of the sheet obtained in the previous step at a reduction ratio of 50% or greater; performing intermediate heat treatment of the sheet obtained in the previous step in a temperature range of 400° C. to 800° C. for 1 to 300 minutes; performing second cold-rolling of the sheet obtained in the previous step at a reduction ratio of 70% to 90%; solution-treating the sheet obtained in the previous step in a temperature range of 820° C. to 1000° C. for 20 to 300 seconds; performing finishing cold-rolling of the sheet obtained in the previous step at a reduction ratio of 10% to 50%; and performing a two-step aging treatment in which the product obtained in the previous step is subjected to aging treatment in a temperature range of 440° C. to 600° C. for 5 minutes to 300 minutes, followed by aging treatment in a temperature range of 350° C. to 440° C. for 1 hour to 30 hours.

[0009] In the method, contents of Ni, Co, and Si may satisfy 3.5≤(Ni+Co) / Si≤4.5.

[0010] In the method, contents of Ni and Co may satisfy Ni+Co≤3.5.

[0011] The solution-treated sheet may simultaneously satisfy following Relationships:5≤grain⁢ size⁢ (μm)×I⁢{2⁢00} / (I⁢{1⁢1⁢1}+I⁢{2⁢2⁢0}+I⁢{3⁢1⁢1})≤602≤grain⁢ size⁢ (μm)-I⁢{2⁢00} / (I⁢{1⁢1⁢1}+I⁢{2⁢2⁢0}+I⁢{3⁢1⁢1})≤1⁢9wherein each of I{111}, I{200}, I{220}, and I{311} denotes an integrated intensity of a diffraction peak of each of the crystal planes measured using X-ray diffraction.

[0013] In the method, wherein after the solution-treatment, the sheet obtained in the previous step may be cooled down at a rate of 20 to 40° C. / s.

[0014] In the method, in the second cold-rolling, a number of passes may be in a range of 5 to 10.

[0015] The present disclosure provides a copper alloy sheet for an automobile component and an electrical and electronic component produced in accordance with the method as described above.

[0016] The copper alloy sheet has a tensile strength of 850 MPa or greater, a bendability of R / t≤1.0 (180° bending) in both a direction parallel to a rolling direction and a direction perpendicular to the rolling direction, and an electrical conductivity of 40% IACS or greater.Technical Effects

[0017] The present disclosure provides the method for producing the copper alloy sheet for the automotive or electrical and electronic component with excellent strength, electrical conductivity, and bendability, and the copper alloy sheet produced thereby.DETAILED DESCRIPTIONS

[0018] When % is used as an expression of a content herein, it means weight %, unless otherwise indicated.

[0019] The present disclosure provides a method for producing a copper alloy sheet for an automobile or electrical and electronic component with improved strength, electrical conductivity and bendability simultaneously, and a copper alloy sheet for an automobile or electrical and electronic component produced thereby. Hereinafter, a method for producing a copper alloy sheet for the automobile or electrical and electronic component according to the present disclosure and the copper alloy sheet for the automobile or electrical and electronic component produced thereby will be sequentially described.

[0020] A method for producing a copper alloy sheet for an automobile component and an electrical and electronic component according to the present disclosure is provided, wherein the copper alloy sheet consists of 1.5 to 3.4 wt % nickel (Ni), 0.1 to 1.5 wt % cobalt (Co), 0.3 to 1.2 wt % silicon (Si), 0.1 to 0.8 wt % tin (Sn), 0.01 to 0.45 wt % chromium (Cr), the balance copper (Cu), and unavoidable impurities of a total content of 0.4 wt % or smaller, wherein the unavoidable impurities include at least one selected from a group consisting of Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr and Mn, wherein the method comprises: melting and casting 1.5 to 3.4 wt % nickel (Ni), 0.1 to 1.5 wt % cobalt (Co), 0.3 to 1.2 wt % silicon (Si), 0.1 to 0.8 wt % tin (Sn), 0.01 to 0.45 wt % chromium (Cr), the balance copper (Cu), and the unavoidable impurities of a total content of 0.4 wt % or smaller, thereby obtaining an ingot; hot-rolling the obtained ingot in a temperature range of 900° C. to 1040° C.; performing first cold-rolling of the sheet obtained in the previous step at a reduction ratio of 50% or greater; performing intermediate heat treatment of the sheet obtained in the previous step in a temperature range of 400° C. to 800° C. for 1 to 300 minutes; performing second cold-rolling of the sheet obtained in the previous step at a reduction ratio of 70% to 90%; solution-treating the sheet obtained in the previous step in a temperature range of 820° C. to 1000° C. for 20 to 300 seconds; performing finishing cold-rolling of the sheet obtained in the previous step at a reduction ratio of 10% to 50%; and performing a two-step aging treatment in which the product obtained in the previous step is subjected to aging treatment in a temperature range of 440° C. to 600° C. for 5 minutes to 300 minutes, followed by aging treatment in a temperature range of 350° C. to 440° C. for 1 hour to 30 hours.

[0021] First, the composition range of the components of the copper alloy sheet according to the present disclosure is as follows.(a) Nickel (Ni): 1.5 to 3.4%

[0022] Ni is an element that forms (Co,Ni)2Si precipitates to improve the strength and electrical conductivity characteristics of the copper alloy sheet. In order to fully exert its effect, the Ni content is set to 1.5% or greater. On the other hand, excessive Ni content forms precipitates and causes a decrease in electrical conductivity due to Ni remaining in a solid solution state in the base phase or causes collapse during bending due to the production of coarse precipitates. Therefore, the Ni content should be smaller than or equal to 3.4%.(b) Cobalt (Co): 0.1 to 1.5%

[0023] Co is an element that forms (Co,Ni)2Si-based precipitates to improve the strength and electrical conductivity characteristics of the copper alloy sheets, and has a high precipitation temperature, which improves the precipitation driving force at high temperatures. In order to fully exhibit this effect, it is desirable to secure a Co content of 0.1% or greater. However, when an excessively large amount of Co is added, Co which cannot form the precipitates with Si, acts as an impurity existing in a dissolved state in the copper matrix, or forms coarse precipitates at high temperatures, which has the effect of reducing strength and electrical conductivity. Therefore, it is desirable to control the Co content to 1.5% or smaller.(c) Silicon (Si): 0.3 to 1.2%

[0024] Si is an element necessary for the formation of (Co,Ni)2Si-based precipitates. In the copper alloy sheet according to the present disclosure, the total content of Ni, Co, and Si in the alloy does not become the precipitates due to the aging treatment, but exist in a dissolved state in the base phase to some extent. Ni, Co, and Si in a dissolved state slightly improve the strength of the copper alloy, but the effect thereof is smaller than that in the precipitated state. Further, Ni, Co, and Si in a dissolved state also causes a decrease in electrical conductivity. Therefore, it is preferable that the Si content is in a range of 0.3 to 1.2%.(d) Tin (Sn): 0.1 to 0.8%

[0025] The inventors of the present disclosure have found that Sn has the effect of increasing strength during the final aging treatment by reducing the supersaturated solid solution formation temperature of the alloy. In the precipitation hardening alloy, the solution-treatment is performed to dissolve the added elements in the copper matrix, and then the solution product is cooled down to form the supersaturated solid solution, followed by the aging treatment to precipitate the dissolved elements into fine sized precipitates in a uniform distribution to secure strength and electrical conductivity of the alloy. Therefore, as the amount of the additive elements dissolved in the copper matrix is larger, the distribution of precipitates more greatly increases during the aging treatment, thereby increasing the precipitation effect. In the copper alloy sheet according to the present disclosure, the tin of the content of 0.1 to 0.8% may lower a temperature at which the supersaturated solid solution is formed by about 20° C., compared to the copper-nickel-cobalt-silicon (Cu—Ni—Co—Si) alloy free of the added tin. In other words, when the solution-treatment is carried out at the same temperature, in the Sn-added alloy, a larger amount of elements may be dissolved into the solid solution, which allows higher strength to be obtained after the aging treatment. When tin is added at a content smaller than 0.1%, the effect of increasing the solid solution cannot be obtained, whereas when tin is added in excess of 0.8%, a large amount of tin remains in the matrix such that sufficient electrical conductivity cannot be secured.(e) Chromium (Cr): 0.01 to 0.45%

[0026] The inventors of the present disclosure have found that chromium (Cr) has an excellent effect in increasing the electrical conductivity. In the precipitation hardening alloys such as copper-nickel-silicon (Cu—Ni—Si) and copper-nickel-cobalt-silicon (Cu—Ni—Co—Si) alloys, after the solution-treatment, the elements dissolved in the matrix are discharged out of the matrix via long-term aging treatment to form the precipitates, which increases electrical conductivity. In this regard, since the precipitates are formed at a fraction of an equilibrium state relative to a given aging treatment temperature, a decrease in the equilibrium temperature of the copper is necessary to further increase electrical conductivity.

[0027] When 0.01 to 0.45% of chromium (Cr) is added, Cr reacts with Si even at low temperatures to form Cr—Si-based precipitates, thereby allowing a larger amount of Si remaining in the matrix to be discharged. In other words, the addition of Cr may further lower the solid solubility of the copper in the aging treatment temperature range, resulting in an increase in electrical conductivity. When a content of smaller than 0.01% of Cr is added, the effect of reducing the solid solubility of the copper cannot be obtained within the aging treatment temperature range, whereas when the Cr is added in excess of 0.45%, Cr elements grow into coarse inclusions due to the intrinsic tendency thereof to aggregate with each other. Thus, the desired strength is not achieved.(f) Weight ratio of Ni, Co, Si: 3.5≤(Ni+Co) / Si≤4.5

[0028] Even when the content of each of Ni, Co, and Si is controlled to be within the above range, the precipitates are not sufficiently formed unless the optimal weight ratio thereof at which an intermetallic compound is able to be formed is not met. Therefore, the maximum strength and electrical conductivity may not be secured. When the ratio of the contents of Ni, Co, and Si satisfies a following relationship, the best strength and electrical conductivity may be obtained.3.5≤(Ni+Co) / Si≤4.5

[0029] Even when the content range of each of Ni, Co, and Si as mentioned above is satisfied, the above Relationship may not be satisfied. In this case, tensile strength equal to or greater than 850 MPa, electrical conductivity equal to or greater than 40% IACS, and bendability of R / t≤1.0 cannot be obtained simultaneously. When the (Ni+Co) / Si ratio is smaller than 3.5, Si is dissolved in an excessive amount inside the matrix, resulting in a decrease in strength, electrical conductivity, and bendability. Conversely, when the (Ni+Co) / Si ratio is greater than 4.5, Ni and Co are dissolved in an excessive amount inside the matrix, such that a high fraction of precipitates cannot be obtained.(g)⁢ Ni+Co≤3.5

[0030] Even when the ratio of (Ni+Co) / Si as mentioned above is met, the above Relationship Ni+Co≤3.5 may not be satisfied. In this case, the tensile strength equal to or greater than 850 MPa and electrical conductivity equal to or greater than 40% IACS cannot be secured. When the Ni+Co content exceeds 3.5, there is a high possibility of cracking during hot-rolling due to the formation of coarse crystallized deposits during casting, and an excessive amount of Ni and Co is dissolved in the matrix, resulting in a decrease in electrical conductivity.(h) Unavoidable Impurities

[0031] In the copper alloy sheet according to the present disclosure, the unavoidable impurities are elements that may be optionally contained therein. The copper alloy sheet of the present disclosure may optionally contain one or more elements from the group consisting of Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr, and Mn as the impurities in a total amount of 0.4% by weight or smaller. Specifically, Ti has the effect of inhibiting the formation of coarse crystallized deposits by preventing the agglomeration of the crystallized deposits that are inevitably produced during casting solidification. Mg has the effect of improving stress relaxation ability, and Zn and Fe have the effect of improving the solderability and castability of the copper alloy sheets. Al, V, and Zr have the effect of improving strength thereof. P and Ca have a deoxidizing effect and are advantageous in improving hot workability.

[0032] However, when the total content of the above impurities in the copper alloy sheet of the present disclosure exceeds 0.4% by weight, this may cause side cracks during hot processing. Thus, the total content thereof should be controlled to be smaller than or equal to 0.4% by weight.

[0033] The method for producing the copper alloy sheet according to the present disclosure includes melting and casting 1.5 to 3.4 wt % nickel (Ni), 0.1 to 1.5 wt % cobalt (Co), 0.3 to 1.2 wt % silicon (Si), 0.1 to 0.8 wt % tin (Sn), 0.01 to 0.45 wt % chromium (Cr), the balance copper (Cu), and the unavoidable impurities of a total content of 0.4 wt % or smaller, thereby obtaining an ingot (=melting and casting step); hot-rolling the obtained ingot in a temperature range of 900° C. to 1040° C. (=hot-rolling step); performing first cold-rolling of the sheet obtained in the previous step at a reduction ratio of 50% or greater (=first cold-rolling step); performing intermediate heat treatment of the sheet obtained in the previous step in a temperature range of 400° C. to 800° C. for 1 to 300 minutes (=intermediate heat treatment step); performing second cold-rolling of the sheet obtained in the previous step at a reduction ratio of 70% to 90% (=second cold-rolling step); solution-treating the sheet obtained in the previous step in a temperature range of 820° C. to 1000° C. for 20 to 300 seconds (=solution-treatment step); performing finishing cold-rolling of the sheet obtained in the previous step at a reduction ratio of 10% to 50% (=finishing cold-rolling step); and performing a two-step aging treatment in which the product obtained in the previous step is subjected to aging treatment in a temperature range of 440° C. to 600° C. for 5 minutes to 300 minutes, followed by aging treatment in a temperature range of 350° C. to 440° C. for 1 hour to 30 hours (=two-step aging treatment step).

[0034] Although not described in detail herein, in the producing method, a person skilled in the art may perform face milling as necessary after the hot-rolling, and may perform acid-washing, polishing, or degreasing as necessary after each heat treatment.

[0035] Hereinafter, each of the major process steps is described in more detail.(1) Melting and Casting Step

[0036] The components of the above-mentioned composition are mixed with each other and melted. The melting is heated at 1250° C. to 1350° C. so that all raw materials may be melted. When the melting temperature is lower than 1250° C., the fluidity of the molten metal decreases, whereas when the melting temperature is higher than 1350° C., the solubility of oxygen and hydrogen in the molten metal increases, which may deteriorate the ingot quality.

[0037] Once the melting has been completed, the molten metal is stabilized while maintaining the same in the temperature range of 1180° C. to 1230° C. for 30 to 120 minutes. The molten metal stabilization condition may be appropriately determined by a person skilled in the art based on knowledge in the relevant field.

[0038] After the molten metal stabilization has been completed, ingot casting is performed. In the casting, the cooling rate of the ingot is in a range of 100° C. / min to 200° C. / min. When the cooling rate is lower than 100° C. / min, this is not practical in terms of a production cost, whereas when the cooling rate exceeds 200° C. / min, thermal stress occurs inside the ingot due to rapid cooling, resulting in cracks.

[0039] The melting and casting step as described above may be carried out in a general atmospheric melting furnace. For example, a high-frequency atmospheric melting furnace may be used. To prevent oxidation of some constituent elements such as Cr, Si, etc., it may be more preferable to carry out the step in an inert gas atmosphere or a vacuum melting furnace.(2) Hot-Rolling Step

[0040] The obtained ingot is rolled in a temperature range of 900° C. to 1040° C. After the hot-rolling of the copper alloy in accordance with the present disclosure has been completed, rapidly cooling is performed to prevent precipitates from being produced during the rolling.(3) First Cold-Rolling Step

[0041] The sheet obtained in the previous step is first cold-rolled at a reduction ratio of 50% or greater. In order to increase the driving force for the seed formation of the cube texture in the intermediate heat treatment step as described later, it is recommended that the reduction ratio be set to 50% or greater. When the reduction ratio is smaller than 50%, sufficient seeds of the cube texture as desired may not be formed in the subsequent intermediate heat treatment step. The seeds are fine recrystallized grains formed in the intermediate heat treatment step.(4) Intermediate Heat Treatment Step

[0042] The sheet obtained in the previous step is subjected to intermediate heat treatment in a temperature range of 400 to 800° C. for 1 to 300 minutes. When the intermediate heat treatment is performed within the above temperature range, recrystallized grains are partially formed, thereby forming the seeds of the cube texture.

[0043] In a typical production process of the copper alloy, the intermediate heat treatment step is a step of relieving the stress generated by dislocations accumulated inside the material such that the material may be rolled to the desired thickness more easily (with less force) in the cold-rolling as performed later.

[0044] However, unlike the above typical purpose, the purpose of the intermediate heat treatment in accordance with the present disclosure is to partially recrystallize the rolled texture formed by the cold-rolling after the hot-rolling to generate the recrystallized grains.

[0045] The intermediate heat treatment is carried out in a temperature range of 400° C. to 800° C. for 1 minute to 300 minutes. When the heat treatment temperature is lower than 400° C. or the heat treatment time is smaller than 1 minute, the recrystallization does not occur sufficiently, such that the grain size and a ratio defined in the Relationship of the integrated intensity of the diffraction peak of each of the crystal planes {200}, {111}, {220} and {311} as described later cannot be obtained. When the heat treatment temperature exceeds 800° C. or the heat treatment time exceeds 300 minutes, the alloy components are dissolved at the same time as the grain grows, resulting in random orientations, such that the grain size and the ratio defined in the Relationship of the integrated intensity of the diffraction peak of each of the crystal planes {200}, {111}, {220} and {311} as described later cannot be obtained. Specific details thereof are disclosed in the texture control section below.(5) Second Cold-Rolling Step

[0046] The sheet obtained in the previous step is subjected to second cold-rolling at a reduction ratio of 70% or greater and at a rolling number (number of passes) of 5 to 10. In order to sufficiently dissolve the coarse (Co,Ni)2Si crystallized deposits and precipitates produced during the cooling and intermediate heat treatment after the hot-rolling, a high solution-treatment temperature and a long solution-treatment time are required. In particular, Co has high precipitation and dissolution temperatures. Thus, it is difficult to dissolve Co sufficiently to secure strength.

[0047] The inventors of the present disclosure have found that sufficient solubility may be obtained in the solution-treatment described later by micronizing and stretching the produced coarse (Co,Ni)2Si crystallized deposits and precipitates via introduction of appropriate rolling conditions. In the general rolling process, the target thickness is obtained at 2 to 3 rolling times, whereas in accordance with the present disclosure, the target thickness is obtained at the rolling times of 5 to 10. When the number of the rolling times is smaller than 5, it is impossible to refine the coarse (Co,Ni)2Si crystallized deposits and precipitates, so that sufficient dissolution does not occur in the solution-treatment described later. When the number of the rolling times is higher than 10, productivity decreases sharply, making it difficult to apply the method to actual mass production. In addition, when the rolling is performed 5 to 10 times whereas the reduction ratio is smaller than 70%, the refinement of the (Co,Ni)2Si crystallized deposits and precipitates is not achieved, and the driving force for recrystallization is reduced in the solution-treatment as described later, making it difficult to obtain the desired diffraction integrated intensity.(6) Solution-Treatment Step

[0048] The sheet obtained in the previous step is solution-treated in a temperature range of 820° C. to 1000° C. for 20 to 300 seconds. The main purpose of a conventional solution-treatment is only to re-dissolve solute elements into the matrix and to achieve recrystallization. However, in accordance with the present disclosure, the purpose of the solution-treatment further includes the formation of the recrystallized texture having the cube as the main orientation component.

[0049] The solution-treatment is carried out in a temperature range of 820° C. to 1000° C. When the solution-treatment temperature is too low, the recrystallization is incomplete, and the dissolution of solute elements becomes insufficient, so that sufficient strength and electrical conductivity cannot be obtained during the aging treatment as described later. On the other hand, when the solution-treatment temperature is too high, the grains become coarse, making it difficult to ultimately obtain a high-strength copper alloy sheet with excellent bendability. In addition, when the solution-treatment treatment is performed for smaller than 20 seconds in the above temperature range, the recrystallization does not occur, so that the cube texture cannot be formed. On the other hand, when the solution-treatment treatment is performed for greater than 300 seconds, the grain becomes coarse such that excellent bendability cannot be obtained.

[0050] After the solution-treatment has been completed, the sheet may be cooled down at a rate of 20 to 40° C. / s. Co has the high precipitation temperature. Thus, when the sheet is cooled at a rate of smaller than 20° C. / s after the solution-treatment, the dissolved Co solutes may be quickly discharged out of the matrix, making it impossible to secure sufficient strength in the aging treatment as described later. When the cooling rate exceeds 40° C. / s, internal stress in the sheet may occur such that deformation of the plate shape, such as plate bending, may occur.(7) Finishing Cold-Rolling Step

[0051] The sheet obtained in the previous step is subjected to the finishing cold-rolling at a reduction ratio of 10% to 50%. The strength of the sheet may be improved via the finishing cold-rolling. The reduction ratio in the finishing cold-rolling is in a range of 10% to 50%. When the reduction ratio is smaller than 10%, sufficient strength cannot be secured in the aging treatment step as described later because the precipitation driving force is insufficient. When the reduction ratio exceeds 50%, the strength may be improved, whereas the cube texture decreases, resulting in a significant decrease in bendability.(8) Two-Step Aging Treatment Step

[0052] The product obtained in the previous step is subjected to a first aging treatment in a temperature range of 440° C. to 600° C. for 5 to 300 minutes, followed by a second aging treatment in a temperature range of 350° C. to 440° C. for 1 hour to 30 hours.

[0053] Typically, aging treatment of the Cu—Ni—Si-based copper alloy is often performed with a single heat treatment in the temperature range of 400° C. to 450° C. where the strength increase effect due to the formation of the intermetallic compound is most noticeable.

[0054] However, in accordance with the present disclosure, the first aging treatment is carried out in the temperature range of 440° C. to 600° C., and the second aging treatment is carried out in the temperature range of 350° C. to 440° C.

[0055] The first aging treatment carried out in the temperature range of 440° C. to 600° C. is intended to impose an appropriate thermal history on the sheet while increasing Co—Si precipitation at high temperatures. When the aging temperature is lower than 440° C., Co—Si precipitates cannot be formed, whereas when the aging temperature is higher than 600° C., re-dissolution of the precipitates occurs. The Co—Si precipitate refers to (Co,Ni)2Si precipitate with a high content of Co.

[0056] The subsequent second aging treatment in the temperature range of 350° C. to 440° C. further improves strength and electrical conductivity by increasing the precipitation of Ni—Si that was not sufficiently precipitated in the first aging treatment. When the aging temperature is lower than 350° C., the aging time becomes increased such that productivity is significantly reduced, whereas when it exceeds 440° C., Ni—Si precipitates are not formed such that the strength and the electrical conductivity cannot be sufficiently secured. The Ni—Si precipitate refers to (Co,Ni)2Si precipitate with a high content of Ni.Copper Alloy Sheet Obtained by Producing Method According to the Present Disclosure.(1) Recrystallization Fraction

[0057] When the crystal structure processed by the rolling is heated to a certain temperature, the internal stress accumulated during the processing gradually decreases, such that new crystal nuclei without internal strain are generated in the original crystal grain with residual strain, and then gradually grow and thus replaces the original crystal grains. This phenomenon is called recrystallization. The grain created via this phenomenon are called a recrystallized grain. Unless otherwise defined, in the present disclosure, the grains formed via recrystallization in the intermediate heat treatment step are referred to as recrystallized grains.

[0058] The inventors of the present disclosure have found that the size and fraction of the recrystallized grains formed in the intermediate heat treatment process has increased the cubic fraction in the solution-treatment as described later.

[0059] According to the present disclosure, based on a observing result of the structure using SEM after etching a cross-section in a direction parallel to the rolling direction of an intermediate heat-treated specimen, when the area ratio of the recrystallized structure is in a range of 60% to 90%, the fraction of the crystal plane of the cube texture is high in the solution-treatment as described later, thereby improving bendability.

[0060] When the proportion of the recrystallized structure after the intermediate heat treatment is smaller than 60%, each grain grows so as to have a random structure without a preferential orientation in the solution-treatment as described later. When the proportion of the recrystallized structure after the intermediate heat treatment exceeds 90%, the driving force for cube texture growth is reduced, making it impossible to obtain the desired texture.(2) Control of Grain Size and Texture

[0061] The X-ray diffraction pattern from the sheet surface (rolled surface) of the Cu—Ni—Co—Si copper alloy sheet is generally composed of diffraction peaks of four crystal planes: {111}, {200}, {220}, and {311}. The X-ray diffraction intensity of other crystal surfaces is relatively very small. Thus, the other crystal surfaces are negligible in terms of texture control. Among the above crystal planes, {200} is the so-called cube texture crystal plane. When the fraction of the cube texture crystal plane is high and the fraction of other crystal planes is low, non-uniform deformation is suppressed and bendability is improved. Herein, unless otherwise specified, the grains related to X-ray diffraction integrated intensity refer to grains produced in the sheet after the solution-treatment.

[0062] According to the method for producing the copper alloy sheet in accordance with the present disclosure, the size of the grains produced in the sheet after the solution-treatment ranges from 5 to 20 μm. When the grain size is within the above range, the bendability may be improved without reducing the strength. When the grain size is smaller than 5 μm, the elasticity of the material is reduced such that the spring characteristics are poor, making it difficult to apply the same to the components. When the grain size is greater than 20 μm, the strength decreases and the bendability also decreases.

[0063] However, in the copper alloy sheet, increasing the fraction of the cube texture while maintaining the appropriate grain size as described above is as difficult as simultaneously increasing the strength and the electrical conductivity which are mutually exclusive. More specifically, the method of forming the seed of the cube texture varies per each alloy composition, Thus, an appropriate method of forming the seed of the cube texture should be found. Even when the seed of the cube texture is successfully formed, a growth condition for the texture growth should be determined in order to grow the texture into a high percentage of the cube texture. This is a challenging task that requires a comprehensive understanding of all of ingredients, contents, and intermediate production processes. In other words, because the growth of the cube texture occurs at high temperatures, the grain size tends to become coarse. Even when such a production is successful, it is difficult to secure the physical properties of strength, high electrical conductivity, and bendability as described below that are targeted in accordance with the present disclosure, without hardening by rolling. This is because when the rolling processing rate is increased to secure the physical properties, the fraction of the cube texture decreases and the bendability is significantly reduced, whereas when the rolling processing is not introduced or the rolling processing rate is reduced to secure the bendability, the strength cannot be increased.

[0064] Nevertheless, the inventors of the present disclosure have surprisingly found that in the case of the copper alloy sheet according to the present disclosure, when the grain size and the fraction of the cube texture crystal plane after the solution-treatment simultaneously satisfy following two Relationships, non-uniform deformation is suppressed, and the bendability is improved.5≤grain⁢ size⁢ (μm)×I⁢{2⁢00} / (I⁢{1⁢1⁢1}+I⁢{2⁢2⁢0}+I⁢{3⁢1⁢1})≤602≤grain⁢ size⁢ (μm)-I⁢{2⁢00} / (I⁢{1⁢1⁢1}+I⁢{2⁢2⁢0}+I⁢{3⁢1⁢1})≤1⁢9wherein each of I{111}, I{200}, I{220}, and I{311} denotes an integrated intensity of a diffraction peak of each of the crystal planes measured using X-ray diffraction.

[0066] When a value of I{200} / (I{111}+I{220}+I{311}) as a ratio of the X-ray diffraction integrated intensity and the grain size after the solution-treatment fail to simultaneously satisfy following two Relationships, the bendability is rapidly deteriorated.

[0067] The above Relationships may be simultaneously satisfied when producing the copper alloy sheet according to the method for producing the copper alloy sheet according to the present disclosure as described above. In particular, the conditions of the intermediate heat treatment, the second cold-rolling, and the solution-treatment should be included within the conditions presented in the method for producing the copper alloy sheet in accordance with the present disclosure as described above.(3) Physical Properties of Copper Alloy Sheet Produced According to Producing Method in Accordance with the Present Disclosure

[0068] The copper alloy sheet in accordance with the present disclosure has the tensile strength equal to or greater than 850 MPa, the electrical conductivity equal to or greater than 40% IACS, while the bendability thereof is R / t≤1.0 in a 180-degree bending test in both a direction parallel to the rolling direction and a direction perpendicular to the rolling direction.

[0069] The strength of the copper alloy sheet in accordance with the present disclosure is presented as the tensile strength. The tensile strength of the copper alloy sheet in accordance with the present disclosure is greater than or equal to 850 MPa. When the tensile strength is smaller than 850 MPa, the sheet cannot withstand the stress applied thereto during assembly or operation of automobile parts or electrical and electronic components, and the contact pressure between the parts is lowered, which reduces the reliability. For this reason, the tensile strength of 850 MPa or greater is required.

[0070] The electrical conductivity of the copper alloy sheet in accordance with the present disclosure is greater than or equal to 40% IACS. In the automotive connector, the number of pins has increased from 50 to 70 to more than 120 in the dense manner. Thus, heat generation control is also an important issue. In this regard, when the electrical conductivity of the copper alloy material used for the automotive connector is lower than 40% IACS, it becomes difficult to properly control the heat generation. When the heat generation control is not sufficient, the lifespan of the device is reduced due to the high temperature heat produced from the components. Therefore, the electrical conductivity of the copper alloy material used for the automobile or electronic and electrical component is required to be equal to or higher than 40% IACS. The copper alloy sheet in accordance with the present disclosure may secure the electrical conductivity higher than or equal to 40% IACS via reduction in the solubility of the additive elements into the matrix due to Cr, optimization of the content ratio of Ni, Co, and Si, and the two-step aging treatment that maximizes the precipitation of (Co,Ni)2Si.

[0071] The bendability of the copper alloy sheet in accordance with the present disclosure is R / t≤1.0 (180° bending) in both the rolling direction and the direction perpendicular to the rolling direction. When the R / t value of bendability exceeds 1.0, bending cracks occur during bending of a narrow-width processed product, making it difficult to apply the sheet to miniaturized or complex-shaped processed products. For this reason, the bendability of R / t≤1.0 is required. Controlling the grain size and the texture as described above by controlling the conditions of the intermediate heat treatment, the second cold-rolling, and the solution-treatment in the producing method according to the present disclosures may allow the copper alloy sheet according to the present disclosure to have excellent strength and electrical conductivity and, at the same time, to have the bendability of / t≤1.0. The relationship for control of the grain size and the texture has been described above.EXAMPLESExamples 1 to 10

[0072] The specimens of Examples 1 to 10 were produced based on compositions as disclosed in Table 1. The producing method of the specimen is as described below.

[0073] According to each Example, based on the composition as shown in Table 1, the alloy elements including copper were mixed with each other on a 10 kg basis, and the mixture was melted in a high-frequency atmospheric melting furnace. After the melting has been completed, the molten metal was stabilized while maintaining the same at 1210° C. for 40 minutes, and an ingot with a thickness of 35 mm, a width of 140 mm, and a length of 200 to 250 mm was cast.

[0074] In order to remove defective parts such as shrinkage holes and for rapid cooling, the obtained ingot was cut by 30 mm at each of a bottom portion and a top portion thereof, and the middle portion of the ingot was subjected to hot rolling under the condition as shown in Table 2, and rapid cooling was performed thereon. After the hot-rolling, a thickness of 0.5 mm of each of both opposing surfaces thereof was cut away to remove the oxidized scale formed in both opposing surfaces thereof.

[0075] Subsequently, the first cold-rolling, the intermediate heat treatment, the second cold-rolling, the solution-treatment, the finishing rolling, and the final two-step aging treatment were performed according to the conditions as shown in Table 2.

[0076] Finally, a 0.1 mm thick sheet specimen was produced.Comparative Examples 1 to 25

[0077] In the Comparative Examples, specimens were produced by the method as disclosed in Table 2 and according to the composition as disclosed in Table 1, and evaluation tests were performed on the specimens as obtained in Examples 1 to 10 and ComparativeExamples 1 to 25TABLE 1Chemical composition of copper alloy(wt %)Ni + 3.5 ≤ (Ni + Co) / ExamplesCuNiCoSiSnCrImpuritiesCo ≤ 3.5Si ≤ 4.5Example 1Balance2.10.60.750.20.05—2.703.60Example 2Balance2.30.350.650.330.12Mn 0.152.654.08Example 3Balance1.80.750.630.150.07—2.554.05Example 4Balance1.90.470.580.210.21—2.374.09Example 5Balance2.440.950.90.550.3Zn 0.33.393.77Example 6Balance2.051.40.950.20.1—3.453.63Example 7Balance3.10.320.80.150.32—3.424.28Example 8Balance2.70.570.840.650.33—3.273.89Example 9Balance2.150.450.760.450.08P 0.052.63.42Example 10Balance2.350.860.80.250.22Ti 0.23.214.01ComparativeBalance1.21.40.60.10.1—2.604.33Example 1ComparativeBalance2.71.491.10.40.25—4.193.81Example 2ComparativeBalance2.40.750.720.230.15Al 0.53.154.38Example 3Mn 0.2ComparativeBalance2.560.650.60.150.35—3.215.35Example 4ComparativeBalance2.440.810.820.420.75—3.253.96Example 5ComparativeBalance1.860.550.570.520.13—2.414.23Example 6ComparativeBalance2.50.450.670.220.07—2.954.40Example 7ComparativeBalance2.450.470.650.350.25—2.924.49Example 8ComparativeBalance2.350.240.610.10.05—2.594.25Example 9ComparativeBalance2.760.640.780.350.11—3.404.36Example 10ComparativeBalance2.250.570.650.540.32P 0.052.824.34Example 11ComparativeBalance2.480.150.60.120.22—2.634.38Example 12ComparativeBalance2.10.750.750.10.1—2.853.80Example 13ComparativeBalance2.20.80.71.20.15V 0.13.004.29Example 14ComparativeBalance2.070.660.650.450.01—2.734.20Example 15ComparativeBalance2.80.691.30.20.2—3.492.68Example 16ComparativeBalance4.20.750.90.10.2—5.504.95Example 17ComparativeBalance1.61.70.620.10.09—5.323.3Example 18ComparativeBalance2.80.550.20.330.25—16.753.35Example 19ComparativeBalance2.50.660.80.030.1P 0.153.953.16Example 20ComparativeBalance2.010.760.750.20.3—3.692.77Example 21ComparativeBalance30.350.750.150.3—4.473.35Example 22ComparativeBalance2.40.850.80.30.2Al 0.24.063.25Example 23ComparativeBalance2.40.850.80.30.2Al 0.24.063.25Example 24ComparativeBalance2.40.850.80.30.2Al 0.24.063.25Example 25TABLE 2Two-step aging treatmentIntermediateSolution-SecondFirstheat PassSecondtreatmentSolution-First agingagingHot-rollingcold-treatmenttimes incold-temper-treatmentFinishingtreatmenttreatmenttemperaturerollingtemper-secondrollingature(° C.) coolingrollingtemperaturetemperature(° C.) ×reductionature(° C.) ×cold-reduction×ratereduction(° C.) ×(° C.) ×Examplestime(hr)ratio(%)time(min)rollingratio(%)time(sec)(° C. / sec)ratio(%)time(hr)time(hr)Example 1970 × 360450 × 60775 950 × 502030440 × 1400 × 5Example 2970 × 370420 × 120780 820 × 1202030460 × 1.5380 × 20Example 3970 × 380550 × 40990 980 × 302020440 × 2380 × 15Example 4970 × 360570 × 501075 950 × 602530480 × 1370 × 22Example 5970 × 365450 × 120685 950 × 802530460 × 1.5400 × 7Example 6970 × 375420 × 220590 850 × 2402535460 × 1.5410 × 3Example 7970 × 366600 × 12875 900 × 702540440 × 2380 × 12Example 8970 × 371750 × 5880 870 × 902530440 × 4400 × 6Example 9970 × 380500 × 100885 950 × 502045600 × 0.2380 × 15Example 10970 × 386400 × 2301086 950 × 452040550 × 0.5410 × 8Comparative970 × 365410 × 2801081 900 × 802040440 × 2400 × 6Example 1Comparative970 × 375450 × 80976 820 × 1502020440 × 2390 × 8Example 2Comparative970 × 365415 × 280980 830 × 2802520460 × 1.5380 × 10Example 3Comparative970 × 366720 × 10675 900 × 702035500 × 1380 × 10Example 4Comparative970 × 382750 × 4775 950 × 402035520 × 1400 × 5Example 5Comparative970 × 374310 × 275880 920 × 652035460 × 2380 × 15Example 6Comparative970 × 388420 × 140550 825 × 2802030460 × 2360 × 20Example 7Comparative970 × 385530 × 80285 870 × 902530550 × 0.5400 × 6Example 8Comparative970 × 355430 × 160775 700 × 2502040440 × 3430 × 3Example 9Comparative970 × 367700 × 20770 820 × 1601030440 × 2400 × 5Example 10Comparative970 × 359410 × 80785 950 × 1002570460 × 1.5380 × 7Example 11Comparative970 × 375480 × 60882 900 × 1002030380 × 13Example 12Comparative970 × 368435 × 155988 850 × 2002035440 × 2480 × 5Example 13Comparative970 × 376710 × 91090 900 × 902035500 × 1370 × 10Example 14Comparative970 × 389790 × 2885 950 × 602530440 × 2400 × 4Example 15Comparative970 × 360490 × 60880 950 × 602530460 × 1.5380 × 12Example 16Comparative970 × 380550 × 40790 980 × 302020440 × 2380 × 15Example 17Comparative970 × 380500 × 100685 950 × 603020600 × 0.5380 × 20Example 18Comparative970 × 375420 × 130785 880 × 903530440 × 2400 × 13Example 19Comparative970 × 380500 × 90685 950 × 502045600 × 0.7380 × 16Example 20Comparative970 × 330420 × 200590 850 × 2402535460 × 1.5410 × 3Example 21Comparative970 × 360900 × 501075 950 × 602530480 × 1370 × 22Example 22Comparative970 × 385400 × 23010861030 × 452040530 × 0.7420 × 6Example 23Comparative970 × 385400 × 2301086 950 × 152040530 × 0.7420 × 6Example 24Comparative970 × 385400 × 2301086 950 × 4002040530 × 0.7420Example 25During the production process of each specimen according to the Tables 1 and 2, the recrystallization ratio in the intermediate heat treatment step was calculated using EDAX's EBSD (Electron Backscatter Diffraction), and a size of the recrystallized grain after the solution-treatment was performed was measured using FEI's Quanta650FEG (FE-SEM). In a representative example, the size of the recrystallized grains measured in the solution-treatment step of Present Example 1 was 8 μm.

[0079] In addition, the integrated intensity of the X-ray diffraction peak was measured using an X-ray diffraction device. The integrated intensity of the X-ray diffraction peak of the {200}, {220}, {111}, and {311} crystal planes relative to the sample sheet surface (rolled surface) was obtained using the characteristic X-rays of Cu-Kai, the tube voltage of 40 kV and the tube current of 30 mA of the X-ray diffraction device. For example, the I{200} / (I{111}+I{220}+I{311}) diffraction peak integrated intensity ratio in the solution-treatment step of Example 1 as obtained in the above manner was 1.5.

[0080] Using the size of the recrystallized grain and the I{200} / (I{111}+I{220}+I{311}) diffraction peak integrated intensity ratio as previously obtained, a value of the size of the recrystallized grain—I{200} / (I{111}+I{220}+I{311}) and a value of the size of the recrystallized grain×I{200} / (I{111}+I{220}+I{311}) in the solution-treatment step were determined. In the solution-treatment step of Example 1, the value of the size of the recrystallized grain—I{200} / (I{111}+I{220}+I{311}) was calculated as 6.5, and the value of the size of recrystallized grain×I{200} / (I{111}+I{220}+I{311}) was calculated as 12. The values calculated in the same manner in the remaining Examples and Comparative Examples are listed in Table 3.

[0081] When the specimens in Examples 1 to 10 and Comparative Examples 1 to 25 were produced, the tensile strength, electrical conductivity, and bendability of each obtained sample were evaluated in the following manner.Test Example(Tensile Strength)

[0082] The tensile strength was measured in the rolling direction using a tensile tester in accordance with JIS Z 2241. The results are shown in Table 3.(Bendability)

[0083] In order to measure the bendability, a fully close-contact bending test (180° fully close-contact U bending test) was conducted in a direction parallel to the rolling direction (bad way) and in a direction perpendicular to the rolling direction (good way). With the inwardly bending radius as R and the material thickness as t, a fully close-contact bending test (180° fully close-contact U bending test, R / t≤1.0 condition) was conducted in a direction parallel to the rolling direction (bad way) and in a direction perpendicular to the rolling direction (good way). Then, when no cracks were observed with an optical microscope, this was evaluated as O, whereas when cracks were observed with an optical microscope, this was evaluated as X. The results are shown in Table 3.(Electrical Conductivity)

[0084] All of the oxidized scales were removed by polishing the surface of the specimen. Then, the electrical conductivity of the specimen surface was measured at a frequency of 240 kHz using SIGMATEST from FORSTER. The results are shown in Table 3.TABLE 3Size ofSize ofrecrystallizedrecrystallizedRecrystallization grain (μm) ×grain (μm) −Presence orratio inI{200} / (I{111} + II{200} / (I{111} + IBendabilityabsence of hotintermediate{220} + I{311 }){220} + I{311 })TensileElectrical(180°, R / t ≤ 1.0)cracks in hot-heat treatmentin solutionin solutionstrengthconductivityBadGoodExamplesrolling stepstep (%)treatment steptreatment step(MPa)(% IACS)waywayExample 1Absent82126.586554OOExample 2Absent8326.49.887153OOExample 3Absent8037.710.185655OOExample 4Absent8553.216.285256OOExample 5Absent9020896243OOExample 6Absent7019.89.287352OOExample 7Absent7513.66.394042OOExample 8Absent6527.58.585554OOExample 9Absent7548.615.385252OOExample 10Absent8033.611.692342OOComparativeAbsent8010.84.276242OOExample 1ComparativeAbsent8528.89.681140OOExample 2ComparativePresent—00————Example 3ComparativeAbsent8518.79.377838OOExample 4ComparativeAbsent8218.96.970262OOExample 5ComparativeAbsent343.912.787552XXExample 6ComparativeAbsent7018.45.781056OOExample 7ComparativeAbsent7529.886451XXExample 8ComparativeAbsent7511.26.679554OOExample 9ComparativeAbsent7535.714.976656OOExample 10ComparativeAbsent6521.610.297238XXExample 11ComparativeAbsent6012.67.680243OOExample 12ComparativeAbsent7216.84.676442OOExample 13ComparativeAbsent8022.513.582038OOExample 14ComparativeAbsent8025.29.985234OOExample 15ComparativeAbsent8420.85.477543OOExample 16ComparativeAbsent83227.876032XOExample 17ComparativeAbsent7725.29.977135OOExample 18ComparativeAbsent8025.515.574529OOExample 19ComparativeAbsent80237.779545OOExample 20ComparativeAbsent702.210.884546XXExample 21ComparativeAbsent10011.255.886742XXExample 22ComparativeAbsent801176.588140XOExample 23ComparativeAbsent812.83.376449XOExample 24ComparativeAbsent83118.864.287945XXExample 25

[0085] As may be seen in the Table 3 above, it is identified that in Examples 1 to 10, each of the specimen has the tensile strength of 850 MPa or greater, the electrical conductivity of 40% IACS or greater, and R / t≤1.0 in the fully close-contact bending test (180° fully close-contact U bending test) conducted in a direction parallel to the rolling direction (bad way) and in a direction perpendicular to the rolling direction (good way). In other words, the specimens in Examples 1 to 10 have high strength, high conductivity, and excellent bendability.

[0086] On the other hand, in Comparative Example 1, the specimen had a low Ni content of 1.2%, such that both strength and electrical conductivity decreased in the specimen due to the influence of Si dissolved in the matrix.

[0087] In the specimen of Comparative Example 2, the total content of Ni and Co was too high at 4.19%, and thus Ni and Co were excessively dissolved in the copper matrix such that a high percentage of precipitates was not formed, and thus high strength and electrical conductivity were not obtained.

[0088] In the specimen of Comparative Example 3, the impurities Al and Mn contents exceeded 0.7%, that is, Al and Mn were added excessively, such that side cracks occurred during hot-rolling, making it impossible to produce a finished specimen.

[0089] In the specimen of Comparative Example 4, the (Ni+Co) / Si ratio was too high at 5.35, the Ni and Co remaining after forming the precipitates with Si were dissolved excessively, such that a high fraction of precipitates was not formed, but remain in the matrix, such that the strength and electrical conductivity were not secured.

[0090] In the specimen of Comparative Example 5, the Cr content was too high at 0.75%, resulting in low strength and cracking during the bending test due to the formation of coarse inclusions.

[0091] In the specimen of Comparative Example 6, under the intermediate heat treatment conditions: 310° C.×275 mins, the heat treatment was carried out at an excessively low temperature. Thus, there was not a sufficient recrystallization fraction to form a cube texture, such that the desired texture fraction could not be obtained in the solution treatment. As a result, cracks occurred in the bent area at R / t=1.0 during a 180° bending test in a direction parallel to the rolling direction (bad-way).

[0092] In the specimen of Comparative Example 7, the reduction ratio in the second cold rolling was 50% which was excessively low, such that the coarsened precipitates after the intermediate heat treatment were not sufficiently refined, resulting in low solubility in the solution-treatment and ultimately failing to secure sufficient strength. Because the sufficient recrystallization driving force was not obtained, a low cube texture fraction was obtained in the solution-treatment, and as a result, cracks occurred in the bent area during the bending test.

[0093] In the specimen of Comparative Example 8, the second cold-rolling was performed at two passes. As a result, the rolling was performed at too few passes such that the precipitates that became coarse after the intermediate heat treatment could not be sufficiently refined, resulting in low solubility in the solution-treatment, ultimately failing to secure sufficient strength.

[0094] In the specimen of Comparative Example 9, the specimen was produced by the heat treatment at an excessively low temperature of 700° C.×250 seconds as the solution-treatment condition. Due to the heat treatment at the low temperature, the alloy components such as Ni, Co, Si, and Cr were not completely dissolved in the matrix, making it impossible to secure strength in the final aging treatment.

[0095] In the specimen of Comparative Example 10, the cooling condition after the solution-treatment was the cooling rate of 10° C. / sec. Thus, the sheet was cooled at an excessively low rate. As a result, the solutes dissolved inside the matrix via the solution-treatment were quickly discharged out of the matrix during the cooling due to the slow cooling rate, and as a result, sufficient strength was not secured in the aging treatment.

[0096] In the specimen of Comparative Example 11, the specimen was produced by increasing the reduction ratio of the finished rolling to 70%. Thus, the reduction ratio of the finished rolling was too high, which resulted in a significant increase in the strength, but resulted in a decrease in electrical conductivity and bendability. During the bending test, cracks occurred in the bent area.

[0097] In the specimen of Comparative Example 12, the specimen was produced via a single aging treatment under the second aging condition without performing the first aging treatment. As a result, sufficient strength and electrical conductivity could not be obtained due to insufficient precipitation.

[0098] In the specimen of Comparative Example 13, the specimen was produced via the heat treatment at a high temperature of 480° C.×5 hrs as the second aging treatment condition. As a result, due to the high temperature, Ni—Si-based precipitates were not sufficiently formed, resulting in low values of both strength and electrical conductivity.

[0099] In the specimen of Comparative Example 14, the Sn content was excessively high at 1.2%. As a result, the Sn content remaining in the matrix even after the precipitation treatment was high, resulting in a low electrical conductivity value.

[0100] In the specimen of Comparative Example 15, the Cr content was too low at 0.01%, so that the dissolution reduction effect could not be obtained in the aging treatment, such that sufficient electrical conductivity was not secured.

[0101] In the specimen of Comparative Example 16, the Si content was too high at 1.3%, so that sufficient precipitates could not be obtained, and thus, sufficient strength and electrical conductivity were not secured.

[0102] In the specimen of Comparative Example 17, the condition failed to form precipitates because the Ni content was too high at 4.2%. Further, sufficient electrical conductivity was not secured due to the influence of Ni remaining in the matrix, and bendability was reduced due to the formation of coarse precipitates.

[0103] In the specimen of Comparative Example 18, the (Ni+Co) / Si ratio was high due to excessively high Co content of 1.7%, such that sufficient strength and electrical conductivity were not secured.

[0104] In the specimen of Comparative Example 19, due to a significantly low Si content of 0.2%, sufficient precipitates were not formed such that strength and electrical conductivity were not secured.

[0105] In the specimen of Comparative Example 20, the Sn content was too low at 0.03%. Thus, the effect of increasing the solubility was not achieved during the solution-treatment, and as a result, sufficient strength could not be obtained.

[0106] In the specimen of Comparative Example 21, the first cold-rolling reduction ratio was low at 30%, so that a sufficient area % of the recrystallized grain could not be obtained in the intermediate heat treatment. As a result, the bendability was significantly reduced because the value of the size of the recrystallized grain×I{200} / (I{111}+I{220}+I{311}) in the solution-treatment failed to meet the target value range.

[0107] In the specimen of Comparative Example 22, the intermediate heat treatment temperature was too high at 900° C., so that complete recrystallization occurred in the intermediate heat treatment. Ultimately, the value of the size of the recrystallized grain—I{200} / (I{111}+I{220}+I{311}) in the solution-treatment failed to meet the target value range. As a result, the bendability could not be secured.

[0108] In the specimen of Comparative Example 23, the grain growth occurred rapidly because the solution-treatment temperature was too high at 1030° C. Further, the value of the size of the recrystallized grain—I{200} / (I{111}+I{220}+I{311}) in the solution-treatment failed to meet the target value range. In the end, sufficient bendability was not secured.

[0109] In the specimen of Comparative Example 24, the strength could not be secured because Ni, Co, Si, and Cr were not sufficiently dissolved due to the short solution-treatment time. Further, the value of the size of the recrystallized grain×I{200} / (I{111}+I{220}+I{311}) in the solution-treatment failed to meet the target value range. Thus, the bendability was also not secured.

[0110] In the specimen of Comparative Example 25, the solution-treatment time was too long, so that the grains grew coarsely, and thus, sufficient bendability was not secured.

Claims

1: A method for producing a copper alloy sheet for an automobile component and an electrical and electronic component,wherein the copper alloy sheet consists of 1.5 to 3.4 wt % nickel (Ni), 0.1 to 1.5 wt % cobalt (Co), 0.3 to 1.2 wt % silicon (Si), 0.1 to 0.8 wt % tin (Sn), 0.01 to 0.45 wt % chromium (Cr), the balance copper (Cu), and unavoidable impurities of a total content of 0.4 wt % or smaller, wherein the unavoidable impurities include at least one selected from a group consisting of Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr and Mn,wherein the method comprises:melting and casting 1.5 to 3.4 wt % nickel (Ni), 0.1 to 1.5 wt % cobalt (Co), 0.3 to 1.2 wt % silicon (Si), 0.1 to 0.8 wt % tin (Sn), 0.01 to 0.45 wt % chromium (Cr), the balance copper (Cu), and the unavoidable impurities of a total content of 0.4 wt % or smaller, thereby obtaining an ingot;hot-rolling the obtained ingot in a temperature range of 900° C. to 1040° C.;performing first cold-rolling of the sheet obtained in the previous step at a reduction ratio of 50% or greater;performing intermediate heat treatment of the sheet obtained in the previous step in a temperature range of 400° C. to 800° C. for 1 to 300 minutes;performing second cold-rolling of the sheet obtained in the previous step at a reduction ratio of 70% to 90%;solution-treating the sheet obtained in the previous step in a temperature range of 820° C. to 1000° C. for 20 to 300 seconds;performing finishing cold-rolling of the sheet obtained in the previous step at a reduction ratio of 10% to 50%; andperforming a two-step aging treatment in which the product obtained in the previous step is subjected to aging treatment in a temperature range of 440° C. to 600° C. for 5 minutes to 300 minutes, followed by aging treatment in a temperature range of 350° C. to 440° C. for 1 hour to 30 hours.2: The method according to claim 1, wherein contents of Ni, Co, and Si satisfy 3.5≤(Ni+Co) / Si≤4.5.3: The method according to claim 1, wherein contents of Ni and Co satisfy Ni+Co≤3.5.4: The method according to claim 1, wherein the solution-treated sheet simultaneously satisfies following Relationships:5≤grain⁢ size⁢ (μm)×I⁢{2⁢00} / (I⁢{1⁢1⁢1}+I⁢{2⁢2⁢0}+I⁢{3⁢1⁢1})≤602≤grain⁢ size⁢ (μm)-I⁢{2⁢00} / (I⁢{1⁢1⁢1}+I⁢{2⁢2⁢0}+I⁢{3⁢1⁢1})≤1⁢9wherein each of I{111}, I{200}, I{220}, and I{311} denotes an integrated intensity of a diffraction peak of each of the crystal planes measured using X-ray diffraction.5: The method according to claim 1, wherein after the solution-treatment, the sheet is cooled down at a rate of 20 to 40° C. / s.6: The method according to claim 1, wherein in the second cold-rolling, a number of passes is in a range of 5 to 10.7: A copper alloy sheet for an automobile component and an electrical and electronic component produced in accordance with claim 1.8: The copper alloy sheet according to claim 7, wherein the copper alloy sheet has a tensile strength of 850 MPa or greater, a bendability of R / t≤1.0 (180° bending) in both a direction parallel to a rolling direction and a direction perpendicular to the rolling direction, and an electrical conductivity of 40% IACS or greater.

Images