Manufacturing method of copper alloy sheet material for automobiles or electrical / electronic parts having excellent strength, electrical conductivity and bending workability, and copper alloy sheet material manufactured from the same

Abstract

The present invention provides a copper alloy for automobiles or electric / electronic parts, which has high strength, high electrical conductivity and excellent bending workability, and a method for producing the same. [Solution] A manufacturing method of copper alloy sheet material for automobiles and electrical and electronic parts, comprising the steps of obtaining a predetermined ingot; hot rolling the obtained ingot in the temperature range of 900°C to 1040°C; first cold rolling the obtained sheet material with a rolling reduction of 50% or more; intermediate heat treating the obtained sheet material at 400°C to 800°C for 1 to 300 minutes; second cold rolling the obtained sheet material with a rolling reduction of 70% to 90%; solution treating the obtained sheet material at a temperature of 820°C to 1000°C for 20 to 300 seconds; finish cold rolling the obtained sheet material with a rolling reduction of 10% to 50%; and a two-stage aging treatment in which the obtained product is aged at a temperature of 440°C to 600°C for 5 minutes to 300 minutes, and then aged at a temperature of 350°C to 440°C for 1 to 30 hours.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a copper alloy sheet material for automobiles or electrical / electronic parts, which has excellent strength, electrical conductivity and bending workability, and the copper alloy sheet material produced therefrom, and in particular to a method for producing a copper-nickel-cobalt-silicon (Cu-Ni-Co-Si)-based copper alloy sheet material and the copper alloy sheet material produced therefrom. [Background technology]

[0002] Copper alloy materials used in automobiles or electrical / electronic parts require good electrical conductivity to suppress the generation of Joule heat when electricity is passed through them, as well as high strength to withstand the stresses applied during the assembly or operation of the equipment.In addition, automobiles or electrical / electronic parts are usually manufactured in the form of copper alloy sheets and are formed by bending, so they also require excellent bendability.

[0003] Due to their high strength and electrical conductivity, precipitation-hardened copper alloys are increasingly being used in automobiles and electrical / electronic components, replacing conventional solid-solution-hardened copper alloys such as phosphor bronze and brass. Precipitation-hardened copper alloys are made by aging a solution-treated supersaturated solid solution, which uniformly disperses fine precipitates, increasing the alloy's strength and reducing the amount of solute elements in the copper, improving electrical conductivity. This results in materials with excellent mechanical properties, such as strength and elasticity, as well as good electrical conductivity, i.e., thermal conductivity.

[0004] Among precipitation-hardened copper alloys, Cu-Ni-Si copper alloys, commonly known as Corson alloys, are a representative copper alloy with relatively high electrical conductivity, strength, and bendability, with a tensile strength of 700 MPa and an electrical conductivity of 40% IACS. These alloys are currently being actively developed in the industry. Corson alloys improve strength and electrical conductivity by precipitating fine Ni-Si intermetallic compounds in the copper matrix. However, due to insufficient strength for automotive or electrical / electronic components, approaches such as increasing the nickel (Ni) and silicon (Si) content or adding magnesium (Mg) have been adopted. However, the addition of additional elements increases strength but reduces conductivity. Recently, copper-nickel-cobalt-silicon (Cu-Ni-Co-Si) alloys, in which some of the Ni in Corson alloys is replaced with Co, have been actively developed. However, these alloys fall significantly short of the physical properties required for electrical / electronic components.

[0005] In Korean Patent Publication No. 10-2009-0122303, the size and distribution of the second phase in a copper-nickel-cobalt-silicon (Cu-Ni-Co-Si) alloy is controlled to improve bendability, but the final physical properties are only a tensile strength of 800 MPa and a conductivity of 40% IACS.

[0006] Korean Patent Publication No. 10-2014-0056003 increased the nickel (Ni), cobalt (Co), and silicon (Si) content to ensure strength, and controlled the precipitate distribution and crystal orientation to achieve a yield strength of 950 MPa and a conductivity of 40% IACS. However, when actually producing the alloy, if the total nickel (Ni) and cobalt (Co) content exceeds 3.5 wt%, coarse inclusions formed inside the ingot during casting increase the likelihood of cracking during hot rolling. Furthermore, while the increased nickel (Ni) and cobalt (Co) content ensures strength, the alloy suffers from significantly poor bending workability, increasing the likelihood of cracking during part processing, making it unsuitable for use in electrical and electronic components. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a method for producing a copper alloy sheet material for automobiles or electrical and electronic parts, which has excellent strength, electrical conductivity and bending workability, and a copper alloy sheet material produced by the method. [Means for solving the problem]

[0008] The present invention is directed to a sintered body containing, by weight, 1.5 to 3.4% nickel (Ni), 0.1 to 1.5% cobalt (Co), 0.3 to 1.2% silicon (Si), 0.1 to 0.8% tin (Sn), 0.01 to 0.45% chromium (Cr), the balance being copper (Cu), and unavoidable impurities of a total content of 0.4% or less, wherein the unavoidable impurities are selected from the group consisting of Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr, and Mn. A method for producing one or more copper alloy sheet materials for automobiles or electrical and electronic parts, the method comprising the steps of: melting and casting 1.5 to 3.4% nickel (Ni), 0.1 to 1.5% cobalt (Co), 0.3 to 1.2% silicon (Si), 0.1 to 0.8% tin (Sn), 0.01 to 0.45% chromium (Cr), the balance being copper (Cu), and unavoidable impurities having a total content of 0.4% or less to obtain an ingot; The method for producing a copper alloy sheet material for automobiles and electrical and electronic parts includes the steps of hot rolling the obtained ingot in a temperature range of 900°C to 1040°C; first cold rolling the sheet material obtained in the previous step at a rolling reduction of 50% or more; intermediate heat treating the sheet material obtained in the previous step at 400°C to 800°C for 1 to 300 minutes; second cold rolling the sheet material obtained in the previous step at a rolling reduction of 70% to 90%; solution treating the sheet material obtained in the previous step at a temperature of 820°C to 1000°C for 20 to 300 seconds; finish cold rolling the sheet material obtained in the previous step at a rolling reduction of 10% to 50%; and two-stage aging treatment in which the product obtained in the previous step is aged at a temperature of 440°C to 600°C for 5 minutes to 300 minutes, and then aged at a temperature of 350°C to 440°C for 1 hour to 30 hours.

[0009] In the above manufacturing method, the contents of Ni, Co, and Si satisfy the condition 3.5≦(Ni+Co) / Si≦4.5.

[0010] In the above-mentioned manufacturing method, the content of Ni and Co satisfies Ni+Co≦3.5.

[0011] The solution heat treated plate material simultaneously satisfies the following formulas:

[0012] 5 ≦ Grain size (μm) × I{200} / (I{111}+I{220}+I{311}) ≦ 60

[0013] 2 ≦ Grain size (μm) - I{200} / (I{111}+I{220}+I{311}) ≦ 19

[0014] Here, I{111}, I{200}, I{220}, and I{311} are the diffraction integrated intensities of the diffraction peaks of each crystal plane measured by X-ray diffraction.

[0015] In the above manufacturing method, the plate material obtained in the previous step is cooled at a rate of 20 to 40° C. / s after solution treatment.

[0016] In the above manufacturing method, the number of passes during the second cold rolling is 5 to 10.

[0017] The present invention provides a copper alloy sheet material for automobiles and electric / electronic parts, which is produced by the above-mentioned method for producing a copper alloy material of the present invention.

[0018] The copper alloy sheet has a tensile strength of 850 MPa or more, bending workability of R / t≦1.0 (180° bending) in both the rolling method and the right-angle method, and an electrical conductivity of 40% IACS or more. [Effects of the Invention]

[0019] The present invention provides a method for producing a copper alloy sheet material for automobiles or electrical and electronic parts, which has excellent strength, electrical conductivity and bending workability, and the copper alloy sheet material produced by the method. DETAILED DESCRIPTION OF THE INVENTION

[0020] In this specification, when a content is expressed in %, it means % by weight unless otherwise specified.

[0021] The present invention provides a method for manufacturing a copper alloy sheet for automobiles or electrical and electronic parts, which has improved strength, electrical conductivity, and bending workability, and a copper alloy sheet for automobiles or electrical and electronic parts manufactured therefrom. Hereinafter, the method for manufacturing a copper alloy sheet for electrical and electronic parts according to the present invention and the copper alloy sheet for electrical and electronic parts manufactured therefrom will be described in order.

[0022] The method for producing a copper alloy sheet material according to the present invention comprises, by weight percent, 1.5 to 3.4% nickel (Ni), 0.1 to 1.5% cobalt (Co), 0.3 to 1.2% silicon (Si), 0.1 to 0.8% tin (Sn), 0.01 to 0.45% chromium (Cr), the balance being copper (Cu), and unavoidable impurities of a total amount of 0.4% or less, wherein the unavoidable impurities are Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr, and Mn. 1. A method for producing a copper alloy sheet material for automobiles or electrical and electronic parts, which is one or more selected from the group consisting of 1.5 to 3.4% nickel (Ni), 0.1 to 1.5% cobalt (Co), 0.3 to 1.2% silicon (Si), 0.1 to 0.8% tin (Sn), 0.01 to 0.45% chromium (Cr), the balance being copper (Cu), and a total of 0.4% or less of unavoidable impurities, by melting and casting an ingot; The process includes the steps of hot rolling the obtained ingot in the temperature range of 900°C to 1040°C; first cold rolling the plate material obtained in the previous step at a rolling reduction of 50% or more; intermediate heat treatment of the plate material obtained in the previous step at 400°C to 800°C for 1 minute to 300 minutes; second cold rolling of the plate material obtained in the previous step at a rolling reduction of 70% to 90%; solution treatment of the plate material obtained in the previous step at a temperature of 820°C to 1000°C for 20 seconds to 300 seconds; finish cold rolling the plate material obtained in the previous step at a rolling reduction of 10% to 50%; and a two-stage aging treatment step in which the product obtained in the previous step is aged at a temperature of 440°C to 600°C for 5 minutes to 300 minutes, followed by aging at a temperature of 350°C to 440°C for 1 hour to 30 hours.

[0023] First, the composition ranges of the component elements of the copper alloy sheet material according to the present invention are as follows.

[0024] (a) Nickel (Ni): 1.5-3.4%

[0025] Ni is an element that forms (Co,Ni)2Si precipitates and improves the strength and electrical conductivity of copper alloy sheets. To fully utilize this effect, the Ni content is set to 1.5% or more. However, excessive Ni content forms precipitates, and Ni remaining in solid solution in the matrix can reduce electrical conductivity or cause collapse during bending due to the formation of coarse precipitates. Therefore, the Ni content is limited to a range of 3.4% or less.

[0026] (b) Cobalt (Co): 0.1-1.5%

[0027] Co is an element that forms (Co,Ni)2Si-based precipitates to improve the strength and electrical conductivity of copper alloy sheets, and has a high precipitation temperature and the effect of improving the driving force for precipitation at high temperatures. To fully exert this effect, it is preferable to ensure a Co content of 0.1% or more. However, if the amount is excessive, Co that does not form precipitates with Si becomes an impurity present in a solid solution state in the copper matrix or forms coarse precipitates at high temperatures, which actually reduces strength and electrical conductivity. Therefore, it is preferable to control the Co content to 1.5% or less.

[0028] (c) Silicon (Si): 0.3-1.2%

[0029] Si is an element necessary for the formation of (Co, Ni)2Si-based precipitates. In the copper alloy sheet material according to the present invention, the Ni, Co, and Si in the alloy do not all become precipitates by aging treatment, but exist to some extent in a solid solution state in the matrix. The Ni, Co, and Si in the solid solution state slightly improve the strength of the copper alloy, but this effect is smaller than that in the precipitated state, and they also cause a decrease in electrical conductivity. Therefore, the Si content is preferably in the range of 0.3 to 1.2%.

[0030] (d) Tin (Sn): 0.1-0.8%

[0031] The present inventors have discovered that Sn has the effect of lowering the temperature at which a supersaturated solid solution of an alloy is formed, thereby increasing strength during final aging treatment. Precipitation-hardened alloys are alloys that ensure strength and electrical conductivity by forming a supersaturated solid solution by cooling after solution treatment, in which additive elements are dissolved in the copper matrix, and then aging treatment is carried out to precipitate the dissolved elements in a uniformly distributed, fine-sized particles. Therefore, the more additive elements are dissolved in the copper matrix, the greater the distribution of precipitates during aging treatment, and the greater the precipitation effect. In the copper alloy sheet material according to the present invention, the 0.1 to 0.8% tin contained reduces the temperature at which a supersaturated solid solution is formed by about 20°C compared to a copper-nickel-cobalt-silicon (Cu-Ni-Co-Si) alloy without tin. In other words, when solution treatment is performed at the same temperature, an alloy containing Sn can dissolve more elements, resulting in higher strength after aging treatment. If tin is added in an amount less than 0.1%, the effect of increasing the solid solubility cannot be obtained, and if it exceeds 0.8%, a large amount of tin remains in the matrix, making it impossible to ensure sufficient electrical conductivity.

[0032] (e) Chromium (Cr): 0.01-0.45%

[0033] The inventors have discovered that chromium (Cr) has an excellent effect in increasing electrical conductivity. In the case of precipitation-hardened alloys such as copper-nickel-silicon (Cu-Ni-Si) and copper-nickel-cobalt-silicon (Cu-Ni-Co-Si) alloys, prolonged aging after solution treatment expels elements dissolved in the matrix, forming precipitates, thereby increasing electrical conductivity. Since precipitates are formed at an equilibrium fraction for a given aging temperature, a reduction in the equilibrium temperature of copper is necessary to further increase electrical conductivity.

[0034] When chromium (Cr) is added in the range of 0.01 to 0.45%, Cr reacts with Si even at low temperatures to form Cr-Si precipitates, which further removes Si remaining in the matrix. In other words, the addition of Cr further reduces the copper solid solubility within the aging temperature range, thereby increasing electrical conductivity. Adding less than 0.01% Cr does not reduce the copper solid solubility within the aging temperature range. Adding more than 0.45% Cr causes the Cr element to solidify with itself, resulting in the growth of coarse inclusions, preventing the desired strength from being achieved.

[0035] (f) Weight ratio of Ni, Co, and Si: 3.5≦(Ni+Co) / Si≦4.5

[0036] Even if the Ni, Co, and Si contents are controlled within the aforementioned ranges, sufficient precipitates cannot be formed unless the optimum weight ratio for forming intermetallic compounds is achieved. As a result, the maximum strength and electrical conductivity cannot be achieved. The best strength and electrical conductivity can be achieved when the ratio of Ni, Co, and Si satisfies the following relationship:

[0037] 3.5≦(Ni+Co) / Si≦4.5

[0038] Even if the above-mentioned ranges for the contents of Ni, Co, and Si are satisfied, if the above-mentioned relationship is not satisfied, it will be impossible to simultaneously obtain a tensile strength of 850 MPa or more, an electrical conductivity of 40% IACS or more, and bending workability of R / t≦1.0. If the (Ni+Co) / Si ratio is less than 3.5, Si will be over-dissolved in the matrix, resulting in reduced strength, electrical conductivity, and bending workability. Conversely, if the ratio exceeds 4.5, Ni and Co will be over-dissolved, preventing the formation of a high fraction of precipitates.

[0039] (g) Ni+Co≦3.5

[0040] Even if the (Ni+Co) / Si ratio is satisfied, if the above relationship is not satisfied, it is impossible to ensure a tensile strength of 850 MPa or more and an electrical conductivity of 40% IACS or more. If the Ni+Co content exceeds 3.5, coarse crystals are formed during casting, which increases the possibility of cracks occurring during hot rolling, and excessive Ni and Co are over-dissolved in the matrix, resulting in a decrease in electrical conductivity.

[0041] (h) Inevitable impurities

[0042] In the copper alloy sheet according to the present invention, the unavoidable impurities are elements that can be selectively contained. The copper alloy sheet according to the present invention can contain one or more elements selected from the group consisting of Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr, and Mn as impurities in a total amount of 0.4 wt. % or less. Specifically, Ti has the effect of preventing the aggregation of crystallized particles that are inevitably generated during casting solidification, thereby suppressing the formation of coarse crystallized particles. Mg has the effect of improving stress relaxation resistance, and Zn and Fe have the effect of improving the solderability and castability of the copper alloy sheet. Al, V, and Zr have the effect of improving strength. P and Ca have a deoxidizing effect, which is advantageous for improving hot workability.

[0043] However, if the total amount of the above-mentioned impurities in the copper alloy sheet material of the present invention exceeds 0.4% by weight, side cracks will occur during hot working, so it is necessary to control the amount to 0.4% by weight or less.

[0044] As described above, the method for producing a copper alloy sheet according to the present invention includes the following steps: (1) melting and casting 1.5 to 3.4% nickel (Ni), 0.1 to 1.5% cobalt (Co), 0.3 to 1.2% silicon (Si), 0.1 to 0.8% tin (Sn), 0.01 to 0.45% chromium (Cr), the balance copper (Cu), and unavoidable impurities in a total amount of 0.4% or less to obtain an ingot (=melting and casting step); (2) hot-rolling the obtained ingot at a temperature range of 900°C to 1040°C (=hot-rolling step); (3) subjecting the sheet obtained in the previous step to a first cold-rolling at a rolling reduction of 50% or more (=first cold-rolling step); and (4) intermediate heat-treating the sheet obtained in the previous step at 400°C to 800°C for 1 to 300 minutes. (5) a step (= intermediate heat treatment step) of subjecting the plate material obtained in the previous step to a second cold rolling at a rolling reduction of 70% to 90% (= second cold rolling step); (6) a step (= solution treatment step) of subjecting the plate material obtained in the previous step to a solution treatment at a temperature of 820°C to 1000°C for 20 to 300 seconds (= solution treatment step); (7) a step (= finish cold rolling step) of subjecting the plate material obtained in the previous step to a rolling reduction of 10% to 50%; and (8) a two-stage aging treatment step (= two-stage aging treatment step) of aging the product obtained in the previous step at a temperature of 440°C to 600°C for 5 to 300 minutes, and then at a temperature of 350°C to 440°C for 1 to 30 hours.

[0045] Although not described in detail in this specification, in the above-mentioned manufacturing method, those skilled in the art may perform facing after hot rolling as needed, and may perform acid washing, polishing, or degreasing after each heat treatment as needed.

[0046] Each major process step is described in more detail below.

[0047] (1) Melting and Casting Step

[0048] The components of the aforementioned composition are mixed and melted. The melting is performed at a temperature of 1250-1350°C so that all raw materials are melted. If the melting temperature is lower than 1250°C, the fluidity of the molten metal decreases, and if the melting temperature is higher than 1350°C, the solubility of oxygen and hydrogen in the molten metal increases, which impairs the quality of the ingot.

[0049] Once the melting is complete, the molten metal is stabilized by holding it at 1180°C to 1230°C for 30 to 120 minutes. The conditions for stabilizing the molten metal can be determined appropriately by a person skilled in the art based on knowledge in the field.

[0050] Once the molten metal stabilization process is complete, the ingots are cast. The cooling rate for the ingots during casting is 100°C / min to 200°C / min. A cooling rate of less than 100°C / min is not practical from a cost perspective, and a rate of more than 200°C / min causes thermal stress inside the ingot due to rapid cooling, resulting in cracks.

[0051] The melting and casting steps are performed in a general atmospheric melting furnace, such as a high-frequency atmospheric melting furnace. To prevent oxidation of some components such as Cr and Si, it may be preferable to perform the steps in an inert gas atmosphere or a vacuum melting furnace.

[0052] (2) Hot rolling step

[0053] The ingot obtained as described above is rolled in the temperature range of 900° C. to 1040° C. When hot rolling the copper alloy of the present invention, rapid cooling is carried out after the rolling is completed so as not to generate precipitates during the rolling.

[0054] (3) First cold rolling step

[0055] The plate material obtained in the previous step is subjected to a first cold rolling with a reduction of 50% or more. In order to increase the driving force for the formation of cube structure seeds in the intermediate heat treatment step described below, it is preferable to set the reduction to 50% or more. If the reduction is less than 50%, sufficient cube structure seeds will not be formed as desired in the subsequent intermediate heat treatment step. These seeds are fine recrystallized grains formed in the intermediate heat treatment step.

[0056] (4) Intermediate heat treatment step

[0057] The plate material obtained in the previous step is subjected to intermediate heat treatment at 400 to 800°C for 1 to 300 minutes. When intermediate heat treatment is performed within this range, recrystallized grains are partially formed and seeds of a cube structure are formed.

[0058] The intermediate heat treatment step in the typical copper alloy manufacturing process is a step to relieve stresses generated by electric potentials and the like accumulated in the material so that the material can be rolled to the desired thickness more easily (with less force) in the subsequent cold rolling.

[0059] However, the purpose of the intermediate heat treatment in the present invention is different from the usual purpose, and is to partially recrystallize the rolled structure formed by cold rolling after hot rolling, thereby generating recrystallized grains.

[0060] The intermediate heat treatment is performed at 400°C to 800°C for 1 to 300 minutes. If the heat treatment temperature is less than 400°C or the heat treatment time is less than 1 minute, recrystallization is insufficient, and the ratio defined in the relationship between the crystal grain size and the diffraction integrated intensities of the {200}, {111}, {220}, and {311} crystal planes described below cannot be obtained. If the heat treatment temperature is higher than 800°C or the heat treatment time is longer than 300 minutes, the alloy components are dissolved simultaneously with the growth of the crystal grains, resulting in random orientation, and this also makes it impossible to obtain the ratio defined in the relationship between the crystal grain size and the diffraction integrated intensities of the {200}, {111}, {220}, and {311} crystal planes described below. Specific details are disclosed in the section on texture control below.

[0061] (5) Secondary cold rolling step

[0062] The sheet material obtained in the previous step is subjected to a second cold rolling process with 5 to 10 rolling passes and a reduction of 70% or more. After hot rolling, a high solution temperature and a long solution time are required to fully dissolve the coarse (Co, Ni)2Si crystals and precipitates formed during cooling and intermediate heat treatment. In particular, Co has high precipitation and solution temperatures, making it difficult to dissolve it sufficiently to ensure strength.

[0063] The inventors discovered that by introducing appropriate rolling conditions and refining the resulting coarse (Co, Ni)Si crystals and precipitates and then stretching them, sufficient solid solubility can be achieved in the solution treatment described below. In a typical rolling process, the number of rolling passes is set to 2-3 to achieve the desired thickness, but in the present invention, the number of rolling passes is set to 5-10. If the number of rolling passes is less than 5, the coarse (Co, Ni)Si crystals and precipitates cannot be refined, and sufficient solid solution does not occur in the solution treatment described below. On the other hand, if the number of rolling passes is 10 or more, productivity decreases sharply, making it difficult to apply to actual mass production. Furthermore, even if rolling is performed 5-10 times, if the reduction rate is less than 70%, the (Co, Ni)Si crystals and precipitates are not refined, and the driving force for recrystallization in the solution treatment described below is reduced, making it impossible to obtain the desired diffraction integrated intensity.

[0064] (6) Solution treatment step

[0065] The sheet material obtained in the previous step is solution treated at a temperature of 820°C to 1000°C for 20 to 300 seconds. While the main objectives of conventional solution treatment are to redissolve the solute elements in the matrix and to recrystallize, the objective of the solution treatment in the present invention also includes the formation of a recrystallization texture with cubes as the main orientation component.

[0066] Solution treatment is performed in the temperature range of 820°C to 1000°C. If the temperature is too low, recrystallization is incomplete and the solute elements are not dissolved sufficiently, so sufficient strength and electrical conductivity cannot be obtained during the aging treatment described below. On the other hand, if the temperature is too high, the crystal grains become coarse, making it difficult to finally obtain a high-strength copper alloy sheet material with excellent bending workability. Furthermore, if the heat treatment is performed for less than 20 seconds within the above temperature range, recrystallization does not occur, and a cube structure cannot be formed. On the other hand, if the heat treatment is performed for more than 300 seconds, the crystal grains become coarse, so that excellent bending workability cannot be obtained.

[0067] After solution treatment, the sheet material is cooled at a rate of 20 to 40°C / s. Because Co has a high precipitation temperature, if the material is cooled at a rate of less than 20°C / s after solution treatment, the dissolved Co solute is quickly re-extracted from the matrix, making it impossible to ensure sufficient strength during the aging treatment described below. If the cooling rate exceeds 40°C / s, stress is generated inside the sheet material, causing deterioration of the sheet shape, such as bending.

[0068] (7) Finishing cold rolling step

[0069] The plate material obtained in the previous step is finish cold rolled at a rolling reduction of 10% to 50%. Finish cold rolling can improve the strength level. The rolling reduction ratio for finish cold rolling is in the range of 10% to 50%. If the rolling reduction ratio is less than 10%, the precipitation driving force is insufficient, making it impossible to ensure sufficient strength in the aging treatment step described below. If the rolling reduction ratio exceeds 50%, the strength level improves, but the cube structure decreases and bending workability is significantly reduced.

[0070] (8) Two-stage aging treatment step

[0071] The product obtained in the previous step is subjected to a first aging treatment at a temperature range of 440°C to 600°C for 5 to 300 minutes, and then a second aging treatment at a temperature range of 350°C to 440°C for 1 to 30 hours.

[0072] Generally, aging treatment of Cu-Ni-Si based copper alloys is often carried out by a single heat treatment in the range of 400°C to 450°C, where the effect of increasing strength due to the formation of intermetallic compounds is most pronounced.

[0073] However, in the present invention, the primary aging treatment is carried out in the range of 440°C to 600°C, and the secondary aging treatment is carried out in the range of 350°C to 440°C.

[0074] The primary aging treatment, which is performed at a temperature between 440°C and 600°C, is intended to increase Co-Si precipitation at high temperatures and provide the sheet material with an appropriate thermal history. If the aging temperature is below 440°C, Co-Si precipitates are not formed, but if it exceeds 600°C, the precipitates re-dissolve. Co-Si precipitates refer to (Co,Ni)2Si precipitates, which have a high specific gravity of Co.

[0075] The subsequent secondary aging treatment at 350°C to 440°C increases the precipitation of Ni-Si, which was not sufficiently precipitated during the primary aging treatment, thereby further improving strength and electrical conductivity. If the aging temperature is below 350°C, the aging time becomes long and productivity decreases significantly, while if the aging temperature exceeds 440°C, Ni-Si precipitates are not formed, making it impossible to ensure sufficient strength and electrical conductivity. Ni-Si precipitates refer to (Co,Ni)2Si precipitates with a high specific gravity of Ni.

[0076] Copper alloy sheet material obtained by the manufacturing method according to the present invention

[0077] (1) Recrystallization fraction

[0078] When a crystalline structure processed by rolling is heated at a certain temperature, the internal stress accumulated by the processing gradually decreases, and new crystal nuclei without internal deformation are generated from the original crystal grains that still have deformation, and these nuclei gradually grow and confront the original crystal grains. This phenomenon is called recrystallization, and the particles generated by this phenomenon are called recrystallized grains. Unless otherwise defined, in the present invention, the crystal grains formed by recrystallization in the intermediate heat treatment step are called recrystallized grains.

[0079] The present inventors have found that the size and fraction of recrystallized grains formed in the intermediate heat treatment step increase the cube fraction in the solution treatment described below.

[0080] According to the present invention, when the end faces of a test piece that has undergone intermediate heat treatment that are parallel to the rolling direction are etched and the structure is observed using an SEM, if the area ratio of the recrystallized structure is 60% to 90%, the crystal plane fraction of the cube structure grows to a high level during the solution treatment described below, improving bending workability.

[0081] If the proportion of recrystallized structure after the intermediate heat treatment is less than 60%, the individual crystal grains will grow as a random structure without preferential orientation during the solution treatment described below. If the proportion of recrystallized structure exceeds 90%, the driving force for the growth of the cube structure will be reduced and the desired texture will not be obtained.

[0082] (2) Control of grain size and texture

[0083] The X-ray diffraction pattern from the sheet surface (rolled surface) of a Cu-Ni-Co-Si-based copper alloy sheet generally consists of diffraction peaks from four crystal planes: {111}, {200}, {220}, and {311}. The X-ray diffraction intensities of other crystal planes are relatively very small and therefore negligible from the perspective of texture control. Of these crystal planes, {200} is a so-called cube-structure crystal plane. When the fraction of cube-structure crystal planes is high and the fractions of other crystal planes are low, non-uniform deformation is suppressed and bending workability is improved. In this specification, unless otherwise specified, the crystal grains associated with the intensity of the X-ray diffraction integral refer to the crystal grains formed in the sheet after solution treatment.

[0084] According to the method for producing a copper alloy sheet of the present invention, the size of the crystal grains generated in the sheet after solution treatment is in the range of 5 to 20 μm. When the crystal grain size is within this range, the strength is not reduced and bending workability can be improved. When the crystal grain size is less than 5 μm, the elasticity of the material is reduced and the spring properties are poor, making it difficult to apply to parts. When the crystal grain size exceeds 20 μm, the strength is reduced and bending workability is also reduced.

[0085] However, in copper alloy sheets, achieving an appropriate crystal grain size and increasing the cube structure fraction is difficult, as it is similar to simultaneously increasing strength and electrical conductivity, which are mutually exclusive properties. More specifically, because the method for forming cube structure seeds varies depending on the alloy composition, it is necessary to find an appropriate method for forming cube structure seeds. Even if cube structure seeds are successfully formed, it is necessary to find the crystal grain growth conditions to grow a high cube structure fraction. This is a challenge that must be addressed by comprehensively understanding all components, contents, and intermediate formation processes. That is, because cube structure growth occurs at high temperatures, the crystal grain size tends to coarsen. Even if successful, it is difficult to achieve the physical properties of strength, high electrical conductivity, and bendability desired in the present invention without work hardening due to rolling. This is because increasing the rolling rate to ensure physical properties reduces the cube structure fraction and significantly reduces bendability. Conversely, not introducing rolling or reducing the rolling rate to ensure bendability does not increase strength.

[0086] Nevertheless, the present inventors have surprisingly found that in the case of a copper alloy sheet material according to the present invention, when the size of the crystal grains after solution treatment and the fraction of the crystal planes of the cube structure simultaneously satisfy the following two formulas, non-uniform changes are suppressed and bending workability is improved.

[0087] 5 ≦ Grain size (μm) × I{200} / (I{111}+I{220}+I{311}) ≦ 60

[0088] 2 ≦ Grain size (μm) - I{200} / (I{111}+I{220}+I{311}) ≦ 19

[0089] Here, I{111}, I{200}, I{220}, and I{311} are the diffraction integrated intensities of the diffraction peaks of each crystal plane measured by X-ray diffraction.

[0090] After solution treatment, if the grain size and the value of the ratio of the integrated X-ray diffraction intensities, I{200} / (I{111}+I{220}+I{311}), do not simultaneously satisfy the above formula, bending workability will rapidly deteriorate.

[0091] The above-mentioned relationship is satisfied when the copper alloy sheet is manufactured by the method for manufacturing the copper alloy sheet of the present invention. In particular, the conditions for the intermediate heat treatment, the second cold rolling, and the solution treatment must be within the conditions presented in the method for manufacturing the copper alloy sheet of the present invention.

[0092] (3) Physical properties of copper alloy sheet material produced by the production method of the present invention

[0093] The copper alloy material of the present invention has a tensile strength of 850 MPa or more, an electrical conductivity of 40% IACS or more, and a bending workability of R / t≦1.0 or less in a 180-degree bending test in both the rolling direction and the direction perpendicular to the rolling direction.

[0094] The strength of the copper alloy material of the present invention is represented by tensile strength. The tensile strength of the copper alloy material of the present invention is 850 MPa or more. If the tensile strength is less than 850 MPa, the copper alloy material cannot withstand the stress applied during assembly or operation of automobile parts or electric / electronic parts, resulting in a low contact pressure between parts and a decrease in reliability, and therefore a tensile strength of 850 MPa or more is necessary.

[0095] The electrical conductivity of the copper alloy material of the present invention is 40% IACS or more. In the case of automotive connectors, the number of pins has increased from 50 to 70 in the past to 120 or more, making heat generation control an important issue to be resolved. In this regard, in the case of copper alloy materials used as automotive connectors, if the electrical conductivity is less than 40% IACS, it becomes difficult to appropriately control heat generation. Insufficient heat generation control shortens the lifespan of the equipment due to high temperatures generated by components. Therefore, copper alloy materials used for automotive or electronic / electrical components are required to have an electrical conductivity of 40% IACS or more. The copper alloy material of the present invention ensures electrical conductivity of 40% IACS or more by reducing the solid solubility of additive elements in the matrix with Cr, optimizing the content ratio of Ni, Co, and Si, and performing a two-stage aging treatment that can maximize the precipitation of (Co,Ni)2Si.

[0096] The bending workability of the copper alloy material of the present invention is R / t≦1.0 (180° bend) in both the rolling direction and the direction perpendicular to the rolling direction. If the R / t value of the bending workability exceeds 1.0, bending cracks occur when bending narrow-width processed products, making it difficult to apply the material to small or complex-shaped processed products, and therefore a bending workability of R / t≦1.0 is required. The copper alloy material of the present invention has excellent strength and electrical conductivity and ensures bending workability of R / t≦1.0 by controlling the grain size and texture described above through control of the conditions of the steps of intermediate heat treatment, secondary cold rolling, and solution treatment in the manufacturing method of the present invention. The relationship between grain size and texture control can be determined by referring to the above content. [Example]

[0097] Examples 1 to 10 Test pieces of Examples 1 to 10 were produced with the compositions shown in Table 1. The method for producing the test pieces is described below.

[0098] According to each example, alloy elements including copper were blended based on 10 kg and melted in a high-frequency atmospheric melting furnace with the composition shown in Table 1. After melting was completed, the molten metal was stabilized by holding it at 1210°C for 40 minutes, and then ingots measuring 35 mm in thickness, 140 mm in width, and 200 to 250 mm in length were cast.

[0099] The resulting ingot was cut into 30 mm sections at the bottom and top to facilitate rapid cooling and remove defects such as shrinkage holes, and the middle ingot was then hot rolled under the conditions shown in Table 2 and rapidly cooled. After hot rolling, the ingot was chamfered to a thickness of 0.5 mm to remove the oxide scale formed on both surfaces.

[0100] Next, under the conditions shown in Table 2, the steel sheets were subjected to first cold rolling, intermediate heat treatment, second cold rolling, solution treatment, finish rolling and final two-step aging treatment.

[0101] Finally, plate specimens with a thickness of 0.1 t were produced.

[0102] Comparative Examples 1-2 5 For each comparative example, a test piece was produced using the composition shown in Table 1 and the method shown in Table 2, and evaluation tests were carried out in the same manner as for the test pieces obtained in Examples 1-10.

[0103] [Table 1]

[0104] [Table 2]

[0105] Meanwhile, in the process of manufacturing each test specimen according to Tables 1 and 2, the recrystallization ratio in the intermediate heat treatment step was calculated using EBSD (Electron Backscatter Diffraction) from EDAX Corporation, and the size of the recrystallized grains after the solution treatment was measured using a Quanta 650FEG (FE-SEM) from FEI Corporation. Typically, the size of the recrystallized grains measured in the solution treatment step of Example 1 was 8 μm.

[0106] Furthermore, the integrated intensities of X-ray diffraction peaks were measured using an X-ray diffractometer. The tube voltage of the X-ray diffractometer was 40 kV, the tube current was 30 mA, and Cu-Kα1 characteristic X-rays were used to determine the integrated intensities of the X-ray diffraction peaks of the {200}, {220}, {111}, and {311} crystal planes relative to the sample sheet surface (rolled surface). For example, in the solution treatment step of Example 1 obtained by the above-mentioned method, the integrated intensity ratio of the I{200} / (I{111}+I{220}+I{311}) diffraction peaks was 1.5.

[0107] Using the previously calculated recrystallized grain size and the ratio of the integrated intensity of the I{200} / (I{111}+I{220}+I{311}) diffraction peak, the value of the recrystallized grain size - I{200} / (I{111}+I{220}+I{311}) and the recrystallized grain size were calculated in the solution treatment step. × The value of I{200} / (I{111}+I{220}+I{311}) was determined. In the solution treatment step of Example 1, the value of the recrystallized grain size - I{200} / (I{111}+I{220}+I{311}) was 6.5, and the recrystallized grain size × The value of I{200} / (I{111}+I{220}+I{311}) is 12. Table 3 shows values ​​calculated in the same manner for other examples and comparative examples.

[0108] In the cases where test pieces were successfully produced from Examples 1 to 10 and Comparative Examples 1 to 25, the tensile strength, electrical conductivity and bending workability of the obtained samples were evaluated by the following methods.

[0109] Test Example (tensile strength) The tensile strength in the rolling direction was measured using a tensile tester in accordance with JIS Z 2241. The results are shown in Table 3.

[0110] (bending workability) To evaluate bending workability, a complete contact bending test (180° complete contact U-bend test) was conducted in the direction parallel to the rolling direction (bad way) and perpendicular to the rolling direction (good way). The bending radius was R and the material thickness was t. The complete contact bending test (180° complete contact U-bend test, R / t≦1.0 condition) was conducted in the direction parallel to the rolling direction (bad way) and perpendicular to the rolling direction (good way). The specimens were rated O if no cracks were observed under an optical microscope, and X if cracks were observed. The results are shown in Table 3.

[0111] (electrical conductivity) The surface of the test piece was polished and all oxide scale was removed using a FOERSTER SIGMATEST, and then the electrical conductivity of the surface of the test piece was measured at a frequency of 240 kHz. The results are shown in Table 3.

[0112] [Table 3]

[0113] As can be seen from Table 3, Examples 1 to 10 have a tensile strength of 850 MPa or more, an electrical conductivity of 40% IACS or more, and R / t≦1.0 or less in a 180° fully contact U-bend test in the direction parallel to the rolling direction (bad way) and in the direction perpendicular to the rolling direction (good way). That is, the test pieces of Examples 1 to 10 have high strength, high conductivity, and excellent bending workability.

[0114] On the other hand, in Comparative Example 1, the Ni content was as low as 1.2%, and therefore both the strength and electrical conductivity decreased due to the influence of Si dissolved in the matrix.

[0115] In Comparative Example 2, the sum of the Ni and Co contents was too high at 4.19%, and Ni and Co were over-dissolved in the copper matrix, preventing the formation of a high proportion of precipitates, resulting in failure to obtain high strength and electrical conductivity.

[0116] In Comparative Example 3, the impurities Al and Mn were excessively added at a content of 0.7% or more, and side cracks occurred during hot rolling, making it impossible to manufacture a finished test piece.

[0117] In Comparative Example 4, the (Ni+Co) / Si ratio was too high at 5.35, and the Ni and Co remaining after forming precipitates with Si were over-dissolved, failing to form a high fraction of precipitates and remaining in the matrix, making it impossible to ensure strength and electrical conductivity.

[0118] In Comparative Example 5, the Cr content was excessively added at 0.75%, and coarse inclusions were formed, resulting in low strength and cracks during bending tests.

[0119] In Comparative Example 6, the intermediate heat treatment was performed at 310°C for 275 minutes, which was too low a temperature, and the recrystallization ratio was insufficient to form a cube structure, and the desired texture fraction was not obtained in the solution treatment. As a result, cracks occurred in the bent portion at R / t = 1.0 during a 180° bending test in the direction parallel to the rolling direction (bad-way).

[0120] In Comparative Example 7, the secondary cold rolling reduction was too low at 50%, and the precipitates that had become coarse after the intermediate heat treatment were not sufficiently refined, the solid solubility decreased during the solution treatment, and sufficient strength could not be secured. Since a sufficient driving force for recrystallization was not obtained, the fraction of cube structures was low during the solution treatment, and as a result, cracks occurred in the bent portion during the bending test.

[0121] In Comparative Example 8, the secondary cold rolling was performed in two passes. As a result, the rolling was performed in an excessively small number of passes, and the precipitates that had become coarse after the intermediate heat treatment were not sufficiently refined, the solid solubility decreased during the solution treatment, and finally, sufficient strength could not be secured.

[0122] In Comparative Example 9, the test piece was produced by performing the heat treatment at a too low temperature, i.e., 700°C for 250 seconds as the solution treatment condition. Because the heat treatment was performed at a low temperature, alloying elements such as Ni, Co, Si, and Cr were not completely dissolved in the matrix, and as a result, the strength could not be ensured by the final aging treatment.

[0123] In Comparative Example 10, the cooling condition after the solution treatment was set to 10°C / sec, which was an excessively slow cooling rate, and as a result, the solute that had been dissolved in the matrix during the solution treatment was quickly re-extruded from the matrix during cooling due to the slow cooling rate, and as a result, sufficient strength could not be secured during the aging treatment.

[0124] In Comparative Example 11, the reduction ratio of the finish rolling was increased to 70% to prepare a test piece. Because the reduction ratio of the finish rolling was too high, the strength increased significantly, but the electrical conductivity and bending workability decreased. Cracks occurred in the bent portion during the bending test.

[0125] In Comparative Example 12, a test piece was produced by performing aging treatment solely under the secondary aging conditions without performing the primary aging treatment, resulting in insufficient precipitation and insufficient strength and electrical conductivity.

[0126] In Comparative Example 13, the secondary aging treatment was performed at a high temperature of 480°C for 5 hours to produce a test piece. As a result, the high temperature did not allow sufficient formation of Ni-Si based precipitates, resulting in low strength and electrical conductivity.

[0127] In Comparative Example 14, the Sn content was added at an excessively high fraction of 1.2%, resulting in a high Sn content remaining in the matrix even after the precipitation treatment, and a low electrical conductivity value.

[0128] In Comparative Example 15, the Cr content was added at an excessively low level of 0.01%, and the effect of reducing the solid solubility during aging treatment was not obtained, and sufficient electrical conductivity could not be ensured.

[0129] In Comparative Example 16, the Si content was excessively added at 1.3%, and sufficient precipitates were not obtained, so sufficient strength and electrical conductivity could not be ensured.

[0130] In Comparative Example 17, the Ni content was excessively added at 4.2%, which prevented precipitates from forming. As a result, sufficient electrical conductivity could not be secured due to the influence of Ni remaining in the matrix, and bending workability was reduced due to the formation of coarse precipitates.

[0131] In Comparative Example 18, the Co content was excessively added at 1.7%, and the (Ni+Co) / Si ratio was high, so sufficient strength and electrical conductivity could not be ensured.

[0132] In Comparative Example 19, the Si content was significantly low at 0.2%, so that sufficient precipitates could not be formed, and strength and electrical conductivity could not be ensured.

[0133] In Comparative Example 20, the Sn content was added at an excessively low level of 0.03%, which resulted in the effect of increasing the solid solubility during solution treatment not being achieved, and as a result, sufficient strength was not obtained.

[0134] In Comparative Example 21, the reduction ratio of the first cold rolling was as low as 30%, and a sufficient area percentage of recrystallized grains was not obtained during intermediate heat treatment. As a result, the size of the recrystallized grains was reduced during solution treatment. × The value satisfying I{200} / (I{111}+I{220}+I{311}) was not obtained, and bending workability was significantly reduced.

[0135] In Comparative Example 22, the temperature of the intermediate heat treatment was too high at 900°C, causing complete recrystallization during the intermediate heat treatment. As a result, the recrystallized grain size -I{200} / (I{111}+I{220}+I{311}) was not obtained during the solution treatment, and bending workability could not be ensured.

[0136] In Comparative Example 23, the solution treatment temperature was 1030°C, which was too high, causing rapid grain growth and failing to obtain a value satisfying the recrystallized grain size -I{200} / (I{111}+I{220}+I{311}). As a result, sufficient bending workability could not be ensured.

[0137] In Comparative Example 24, the solution treatment time was short, and Ni, Co, Si, and Cr were not dissolved sufficiently, so that strength could not be ensured. × A value satisfying I{200} / (I{111}+I{220}+I{311}) could not be obtained, and bending workability could not be ensured.

[0138] In Comparative Example 25, the solution treatment time was too long, causing the crystal grains to grow coarse, and as a result, sufficient bending workability could not be ensured.

Claims

1. In weight percent, it consists of 1.5 to 3.4% nickel (Ni), 0.1 to 1.5% cobalt (Co), 0.3 to 1.2% silicon (Si), 0.1 to 0.8% tin (Sn), 0.05 to 0.45% chromium (Cr), the balance being copper (Cu), and unavoidable impurities totaling 0.4% or less; The method for producing a copper alloy sheet material for automobiles or electrical and electronic parts, wherein the unavoidable impurities are one or more selected from the group consisting of Mg, Al, P, Ca, Ti, V, Zn, Fe, Zr and Mn, The method comprises: (1) melting and casting 1.5-3.4% nickel (Ni), 0.1-1.5% cobalt (Co), 0.3-1.2% silicon (Si), 0.1-0.8% tin (Sn), 0.05-0.45% chromium (Cr), the balance copper (Cu), and unavoidable impurities totaling 0.4% or less to obtain an ingot; (2) hot rolling the obtained ingot at a temperature range of 900°C to 1040°C; (3) A step of first cold rolling the plate material obtained in step (2) at a rolling reduction of 50% or more; (4) A step of subjecting the plate material obtained in step (3) to intermediate heat treatment at 400°C to 800°C for 1 to 300 minutes; (5) A step of subjecting the plate material obtained in step (4) to a second cold rolling at a rolling reduction rate of 70% to 90%; (6) A step of subjecting the plate material obtained in step (5) to a solution treatment at a temperature of 820°C to 1000°C for 20 seconds to 300 seconds; (7) A step of finish cold rolling the plate material obtained in step (6) at a rolling reduction rate of 10% to 50%; and (8) A two-stage aging treatment is carried out on the product obtained in step (7) at a temperature of 440°C to 600°C for 5 minutes to 300 minutes, followed by aging at a temperature of 350°C to 440°C for 1 hour to 30 hours; The contents of Ni, Co, and Si (each meaning the content of each component element in weight percent) satisfy 3.5≦(Ni+Co) / Si≦4.5, The contents of Ni and Co (respectively meaning the contents of each component element in weight percent) satisfy Ni + Co ≦ 3.5; In the second cold rolling in step (5), the number of passes during the second cold rolling is 5 to 10, After the solution treatment in step (6), the copper alloy sheet is cooled at a rate of 20 to 40°C / s.

2. The manufacturing method according to claim 1, wherein the solution heat treated plate material simultaneously satisfies the following formulas: 5≦Crystal grain size (μm)×I{200} / (I{111}+I{220}+I{311})≦60 2≦grain size (μm)−I{200} / (I{111}+I{220}+I{311})≦19 Here, I{111}, I{200}, I{220}, and I{311} are the diffraction integrated intensities of the diffraction peaks of the respective crystal planes measured by X-ray diffraction.

3. A copper alloy sheet material for automobiles and electric / electronic parts, produced according to claim 1 or 2.

4. The copper alloy sheet according to claim 3, wherein the copper alloy sheet has a tensile strength of 850 MPa or more, bending workability of R / t≦1.0 (180° bending) in both the rolling direction and the direction perpendicular to the rolling direction (where R is the bending radius (mm) and t is the thickness (mm)), and an electrical conductivity of 40% IACS or more.

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