Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
  • C22C9/06—Alloys based on copper with nickel or cobalt as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/02—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of metals or alloys
  • H01B1/026—Alloys based on copper

Definitions

• the present invention relates to a copper alloy material that is applied to an electric/electronic part, such as a connector or terminal material for an electric/electronic equipment, particularly a high-frequency relay or switch where high electrical conductivity is desired, or a connector or terminal material to be mounted on an automotive vehicle, and a lead frame.
• an electric/electronic part such as a connector or terminal material for an electric/electronic equipment, particularly a high-frequency relay or switch where high electrical conductivity is desired, or a connector or terminal material to be mounted on an automotive vehicle, and a lead frame.
• Corson copper for example, C70250
• Cxxxxx denotes types of copper alloys specified in CDA (Copper Development Association).
• a copper alloy has been desired which has an electrical conductivity higher than that of a conventional Corson copper, and a tensile strength and a bending property at the same level of those of the conventional Corson copper.
• CXXXXX denotes types of copper alloys specified in CDA (Copper Development Association).
• %IACS is a unit which indicates an electrical conductivity of a material
• IACS is an abbreviation of "International Annealed Copper Standard”.
• a connector or terminal having such a design concept is, in many cases, referred to as a bellows-bent (corrugated) connector or terminal. That is, there is a strong demand for the mounting and installation of terminals or connectors that are bent in a complicated manner in small parts.
• the material of connectors and terminals to be used is becoming thinner concomitantly with the size reduction. This trend is furthered from the viewpoint of weight reduction and resource saving. Thin materials are demanded to have higher mechanical strength as compared with thick materials, in order to maintain the same contact pressure.
• precipitation strengthening is promising, as a method of enhancing the mechanical strength without decreasing the electrical conductivity of the copper alloy material.
• This precipitation strengthening is a technique of: subjecting an alloy to which elements causing precipitation have been added, to a heat treatment at high temperature, to thereby cause solid-solution of these elements into the copper matrix, and then heat treating the alloy at a temperature lower than the temperature used for the solid solution, thereby precipitating the solid-solution elements.
• beryllium copper, Corson copper, and the like employ that strengthening method.
• the bending property and the mechanical strength are properties in an inconsistent relationship.
• a material high in the mechanical strength is poor in the bending property, while a material good in the bending property is, on the contrary, low in the mechanical strength.
• it is considered effective to increase the cold-rolling ratio; however, if the cold rolling ratio is increased, there is a tendency that the bending property is conspicuously deteriorated.
• beryllium copper, Corson copper, titanium copper, and the like, as precipitation type copper alloys have a well balance between bending property and mechanical strength.
• beryllium copper which is an additive element
• Corson copper or titanium copper generally does not have an electrical conductivity of 50 %IACS or higher.
• Examples of the applications where a high electrical conductivity of 50 %IACS or higher is required, include battery terminals and relay contacts to which high current is applied.
• materials having high electrical conductivity are generally excellent in the thermal conduction property as well, materials for the sockets or heat sinks of central processing units (CPU; integrated logic elements), which require heat emission properties, are also required to have high electrical conductivity.
• CPU central processing units
• Copper alloys which have mechanical strength, bending property, and electrical conductivity (thermal conductivity), and which utilize intermetallic compounds containing Co (cobalt) and Si (silicon), are increasingly attracting attention. Copper alloys containing Co and Si as essential elements, or techniques related to these, are known as shown below.
• Patent Literatures 1 to 6 all describe only on one kind (or one size) of intermetallic compound composed of Co and Si.
• other alloy systems particularly the so-called Corson copper which contains Ni and Si as essential additive elements, it is known that when two or more kinds of intermetallic compounds are dispersed in the copper alloy, the bending property and the like are improved.
• This technique is known in Patent Literatures 7 to 11.
• Patent Literature 1 has no description on the precipitate (compound) of Co and Si and has no description on mechanical strength or electrical conductivity.
• Patent Literature 2 has no description on performing a recrystallization treatment, and it is thought that the resultant alloy is poor in bending property.
• Patent Literature 3 shows, in the example section, that the electrical conductivity is a relatively low value of 30 %IACS or less.
• Patent Literature 4 describes a precipitation strengthening type alloy, but has no description on the specific compound or its size.
• Corson copper and Cu-Co-Si-based alloys differ from each other in the alloying elements, and have differences, for example, in different temperature of carrying out a solution heat treatment.
• Corson copper when the amount of Ni is 3 mass% or more, a solution heat treatment temperature of about 900°C is required; while, in the case of a Cu-Co-Si alloy, it has been known that at a solution heat treatment temperature of about 900°C, alloys having an amount of Co of about 1.0 to 1.2 mass% only can be sufficiently treated by a solution heat treatment.
• Corson copper having an amount of Ni of 3 mass% or more
• it is practically difficult to obtain an electrical conductivity of 20 %IACS or more and a copper alloy having high electrical conductivity cannot be obtained. That is, the Corson copper and the Cu-Co-Si alloys have significant differences in the solution heat treatment temperature or the properties of alloy, so there is a demand for a new technique which is not an extension of the conventional techniques.
• the inventors of the present invention found a specifically preferable relationship of those properties with the grain size, by dispersing a precipitate (compound) of two or more kinds in a Cu-Co-Si-based copper alloy, and controlling the size of such a precipitate (if necessary, including its density).
• a precipitate compound of two or more kinds in a Cu-Co-Si-based copper alloy
• the inventors attained the present invention. According to the present invention, there is provided the following means:
• a copper alloy material can be provided, which has an optimized grain size, which is high in electrical conductivity, high in mechanical strength, and excellent in bending property, and which is favorable for the use in electric/electronic parts, by controlling two or more kinds of precipitates (compounds) in a Cu-Co-Si alloy which exhibits a high electrical conductivity.
• the term "copper alloy material” means a product obtained after a copper alloy base material (herein, the "copper alloy base material” means a mixture of component elements of a copper alloy not having the concept of shape) is worked into a predetermined shape (for example, sheet, strip, foil, rod, or wire).
• a predetermined shape for example, sheet, strip, foil, rod, or wire.
• the term “copper alloy of matrix” means a copper alloy not having the concept of shape.
• the inventors of the present invention found, by studying keenly, that, in order to obtain a copper alloy material high in mechanical strength, high in electrical conductivity, and favorable in bending property, two or more kinds of precipitates (compounds) having different sizes are needed in a Cu-Co-Si-based alloy, and that it is important to control the grain size of the copper alloy of the matrix to 3 to 35 ⁇ m. Further, the inventors found that it is preferable to control the density of the precipitates (compounds) so as to control the grain size of the copper alloy of the matrix to 3 to 35 ⁇ m. Furthermore, the inventors found that, between two kinds of precipitates having different sizes, a giant (coarse) compound having an average particle diameter from 50 nm to 500 nm can be obtained preferably by appropriately setting the cooling speed in the production of an ingot.
• the electrical conductivity is 50 %IACS or more, and, with regard to the relationship between tensile strength and bending property, it is preferable that when the tensile strength is 550 MPa or more but less than 650 MPa, R/t ⁇ 0.5, in which R/t serves as an index for bending property; when the tensile strength is 650 MPa or more but less than 700 MPa, R/t ⁇ 1; when the tensile strength is 700 MPa or more but less than 750 MPa, R/t ⁇ 2; and when the tensile strength is 750 MPa or more but less than 800 MPa, R/t ⁇ 3.
• R/t means a result obtained by conducting a W bending test at a bending angle of 90° according to the "Standard test method of bend formability for sheets and strips of copper and copper alloys (JBMA T307)" of the Japan Copper and Brass Association Technical Standards, and is a value obtained by subjecting a sheet material cut out in a direction perpendicular to rolling, to a bending test under the condition of a predetermined bending radius (R), determining the R value of the limit at which any crack (breakage) does not occur at the top, and normalizing the value by the sheet thickness (t). In general, a smaller value of R/t gives more satisfactory bending property.
• the electrical conductivity of the copper alloy material is set at 50 %IACS or higher.
• the electrical conductivity is more preferably 55 %IACS or more, and further preferably 60 %IACS or more, and it is preferable that the electrical conductivity is as high as possible, but the upper limit is generally approximately 75 %IACS.
• the tensile strength and the bending property (R/t) have the relationship described above. Further, the lower limit of the bending property (R/t) is 0.
• the copper alloy as mentioned herein is an example of the case where the intermetallic compound is one kind of compound containing Co and Si.
• Co and Si are added to copper, followed by subjecting to an adequate heat treatment, to give a so-called precipitation type copper alloy in which an intermetallic compound composed of Co and Si precipitates.
• a heat treatment method of developing the function of a precipitation type copper alloy is generally carried out by essentially performing the following two kinds of heat treatments.
• the first heat treatment is referred to as heat solution (or recrystallization) treatment or homogenization treatment, and this heat treatment is carried out at a relatively high temperature for a shorter time period.
• the second heat treatment is referred to as aging heat treatment or precipitation treatment, and this heat treatment is carried out at a temperature lower than the solution heat treatment temperature for a longer time period.
• the first heat treatment is carried out, by using a continuous annealing furnace which threads a rolled sheet of a copper alloy inside the heating furnace. This is because, when a sheet is heat treated at a high temperature in a state of being wound in a coil form, adhesion occurs, and because, when the cooling speed thereafter is slow, the elements made into a solid solution uncontrollably precipitate, to form a precipitate that does not contribute to mechanical strength. Further, since there is a concern about sheet breakage caused by threading inside the furnace at high temperature, a heat treatment in a short time period is carried out.
• the sheet of the copper alloy wound into a coil form is subjected to a heat treatment for a relatively long time period (specifically, several minutes to several ten hours) in a heating furnace that has been kept under temperature control, and thus the precipitate (compound) which is optimal for a solid phase diffusion treatment is sufficiently dispersed.
• the temperature for the solution heat treatment (the first heat treatment) is raised as high as possible, and thereby the amount of solute elements that are made into a solid solution in the copper matrix is increased.
• a precipitate (compound) is precipitated, by utilizing the difference in temperature from the aging heat treatment (the second heat treatment) performed thereafter, and thus the copper alloy is strengthened.
• the temperature of this solution heat treatment (the first heat treatment) is raised higher, the solid solution amount of the solute elements is increased (thereby, the amount of precipitate that precipitates upon the later second heat treatment is increased).
• the particle diameter becomes larger upon recrystallization as the temperature is raised higher; and, when the high temperature heat treatment is carried out as the first heat treatment so as to increase the amount of the solute elements as described above, bending property is deteriorated on the contrary.
• the intermetallic compound is one kind of compound containing Co and Si, it can be said that it is extremely difficult to satisfy all of high electrical conductivity, high mechanical strength, and satisfactory bending property.
• the inventors developed a technique of dispersing two or more kinds of intermetallic compounds having different sizes in a Cu-Co-Si-based alloy, to satisfy all of high electrical conductivity, high mechanical strength, and satisfactory bending property.
• a fine compound composed of Co and Si and having a size of 5 nm or more but less than 50 nm is a compound that contributes to precipitation strengthening.
• a coarse compound having a size from 50 nm to 500 nm is a compound that does not contribute to precipitation strengthening but exhibits effects at the time of high temperature solution heat treatment as described in the above. This coarse compound cannot be made into a solid solution in the copper matrix even in the high temperature solution heat treatment, and exists in the copper matrix. Therefore, even if grain growth occurs, the coarse compound becomes a barrier and causes a state in which grain boundary movement is difficult to occur. As a result, coarsening of the grain size is suppressed.
• a copper alloy In the case of a copper alloy, an ingot obtained by melting (making into molten) raw materials followed by solidifying, is used as a starting material, which is subjected to hot rolling and cold rolling, and various heat treatments, thereby a copper alloy material exhibiting desired properties is completed.
• a solution heat treatment is a treatment to make those intermetallic compounds into solid solution, again, in the copper matrix.
• the solution heat treatment is a treatment carried out prior to an aging heat treatment, but upon the solution heat treatment, only coarse compounds remain behind, while others are made into a solid solution in the copper matrix.
• the aging heat treatment of the subsequent step allows precipitation of fine precipitates (compounds), but at this temperature, the size and density of the coarse compounds that have been exposed to a high temperature in the preceding heat treatment, do not change.
• the solution heat treatment and the aging heat treatment are carried out in this successive order, and another case where a cold rolling step is conducted between these heat treatments; however, in any of those cases, there is no change in the size and density of the coarse compounds upon the heat treatment steps.
• the compound A having an average particle diameter of 5 nm or more but less than 50 nm which is a compound that contributes to precipitation strengthening, is a compound that precipitates upon the aging heat treatment, to enhance mechanical strength.
• the compound A is preferably Co 2 Si, but may also contain a compound that does not fulfill the composition ratio of Co 2 Si (for example, CoSi, or CoSi 2 ).
• the average particle diameter of the compound A is 5 nm or more, the amount of precipitation hardening is sufficient, and when the average particle diameter is less than 50 nm, the mechanical strength is sufficient, without a loss of coherent strain.
• the size of the compound A is defined to be 5 nm or more but less than 50 nm, and a preferred size is from 10 nm to 30 nm.
• a preferred size is from 10 nm to 30 nm.
• the compound B is a compound that does not contain one of Co and Si or any of them, and the contribution of this compound to mechanical strength is small.
• the composition of the compound B include Co-x, Si-x, and x-y, in which x and y each represent an element other than Co and other than Si.
• the compound B When the average particle diameter of the compound B is from 50 nm to 500 nm, the compound B exhibits an effect of suppressing (pinning) the grain boundary movement at high temperature.
• the compound B is an incoherent compound since it has an average particle diameter of 50 nm or more, and in order to suppress the grain boundary movement of the copper alloy of the matrix, the average particle diameter of the compound B is preferably from 50 nm to 500 nm.
• the average particle diameter of the compound B is more preferably from 100 nm to 300 nm.
• the inventors confirmed by an observation of the texture after a solution heat treatment, that the grain growth is suppressed most effectively when the compound B is dispersed.
• the compound C is a compound that contains both of Co and Si and another element, and this compound also is small in contribution to mechanical strength.
• the difference between the compounds C and B is that the compound C has a composition, for example, Co-Si-x, or Co-Si-x-y, in which x and y each represent an element other than Co and other than Si.
• the compound C is one having a melting point higher than the solid solution temperature (that is, the melting point) of Co 2 Si.
• the average particle diameter of the compound C is preferably from 50 nm to 500 nm, to exhibit the same effect as the compound B.
• the average particle diameter of the compound C is more preferably from 100 nm to 300 nm.
• the compound B or C is present in a size of an average particle diameter of 5 nm or more but less than 50 nm, which is the same as the average particle diameter of the compound A.
• a compound which has an average particle diameter of 5 nm or more but less than 50 nm and which has a composition similar to that of the compound B or C when the elements, which have been once made into solid solution by a solution heat treatment, undergo precipitation, the elements substitute Co, which is a main element, and form compounds with Si, thereby contributing to enhancement of mechanical strength.
• the compound D is a compound composed only of Co and Si, and has the same components as those of the compound A.
• the compound D has a different size, and it also includes compounds that do not have the composition ratio of Co 2 Si (for example, CoSi, and CoSi 2 ).
• the compound D is different from the compound A in the following point. Since the size of the compound D is coarse, the time period is not sufficient for the compound D to be made into a solid solution in the matrix in the high temperature solution heat treatment of a short time period, and as a result, the compound D remains in the copper matrix and exhibits the function of suppressing grain growth. Although this compound D has an angular shape in many cases, but its particle size is defined as the average particle diameter.
• the average particle diameter of the compound D is also preferably from 50 nm to 500 nm.
• the average particle diameter of the compound D is more preferably from 100 nm to 300 nm.
• EDS energy dispersive spectrometer
• SEM transmission electron microscope
• the grain size of the copper alloy of the matrix is set within the range of 3 to 35 ⁇ m. This is because, when the grain size is 3 ⁇ m or more, recrystallization is sufficient, there is no risk that there could be mixed grains including unrecrystallization where insufficiently recrystallized portions are observed, and the bending property is favorable. Furthermore, when the grain size is 35 ⁇ m or less, the grain boundary density is high, the bending stress (applied strain) can be sufficiently absorbed, and the bending property is favorable.
• the grain size of the copper alloy is preferably from 10 to 30 ⁇ m.
• the electrical conductivity of the material is set to be 50 %IACS or more. This property is obtained, by precipitating an intermetallic compound of Co 2 Si by, for example, adjusting preferably the content of Co to 0.4 to 2.0 mass% and the content of Si to 0.1 to 0.5 mass%.
• the ratio of the dispersion densities of the compounds preferably to: 0.0001 ⁇ ⁇ (the dispersion density of the compound B + the dispersion density of the compound C + the dispersion density of the compound D)/the dispersion density of the compound A ⁇ ⁇ 0.1.
• the coarse compounds B, C, and D that suppress the grain boundary movement of the copper alloy of the matrix may be exist in two or more kinds of those together with the compound A, but the ratio of their dispersion densities is preferably 0.0001 ⁇ ⁇ (the dispersion density of the compound B + the dispersion density of the compound C + the dispersion density of the compound D)/the dispersion density of the compound A ⁇ ⁇ 0.1.
• the ratio of dispersion density is within this range, the effect of suppressing the grain boundary movement is high, and the proportion of the coarse precipitates (compounds) is small, which do not contribute to mechanical strength but which suppress movement. Thus, the purpose of high mechanical strength can be sufficiently achieved.
• the ratio of the dispersion density of the respective compounds is preferably: 0.0001 ⁇ ⁇ (the dispersion density of the compound B + the dispersion density of the compound C + the dispersion density of the compound D)/the dispersion density of the compound A ⁇ ⁇ 0.01, and more preferably: 0.0001 ⁇ ⁇ (the dispersion density of the compound B + the dispersion density of the compound C + the dispersion density of the compound D)/the dispersion density of the compound A ⁇ ⁇ 0.001. If the number of compounds B, C, and D (particularly, the total number of those) is too small, for example, deterioration in bendability of the resultant copper alloy material may occur due to grain coarsening, and the like.
• the mechanical strength is enhanced.
• the number of precipitates of the compound B, C, and D (particularly, the total number of these) is larger, that is, the (the dispersion density of the compound B + the dispersion density of the compound C + the dispersion density of the compound D) in the copper alloy material is higher, a copper alloy material can be obtained, which has a favorable bendability, with respect to mechanical strength enhancement.
• the amount of addition of Co is set at 0.4 to 2.0 mass%, since, when the amount of addition of Co is 0.4 mass% or more, a desired mechanical strength can be obtained, and, when the amount of addition of Co is 2.0 mass% or less, the solution heat treatment temperature is within an appropriate range and no production technique with an extremely high degree of difficulty is needed.
• Si since the stoichiometric ratio of Co 2 Si, which is the precipitation strengthening phase of this Cu-Co-Si alloy, is the ratio Co/Si nearly equals to 4.2, the range of the amount of addition of Si is set according to this ratio.
• the ratio (Co + x)/Si nearly equals to 4.2 (in which x is Fe, Ni, or Cr). Even in that case, there is no problem for practical use, as long as the ratio (Co + x)/Si nearly equals to 3.5 to 4.8.
• the copper alloy material of the present invention may contain elements other than Co and other than Si.
• Al, Ag, Sn, Zn, Mg, Mn, and In have a feature of being made into a solid solution in the copper matrix to strengthen the resultant alloy.
• the amount of addition of the elements is 0.05 mass% or more in total, the effect is obtained, and when the amount of addition is 1.0 mass% or less in total, the electrical conductivity is not inhibited.
• a preferred amount of addition is at least one of these elements in an amount of 0.2 to 0.4 mass% in total.
• Zn has an effect of improving solder adhesiveness
• Mn has an effect of improving hot workability
• the addition of Sn and Mg has an effect of improving the stress relaxation resistance.
• Individual addition of Sn or Mg also provides the effect, but when those two elements are added, the elements exhibit the effect synergistically.
• the amount of addition is 0.1 mass% or more in total, the effect is provided, and when the amount of addition is 1.0 mass% or less, the electrical conductivity is not inhibited, and an electrical conductivity of 50 %IACS or more is secured.
• Sn/Mg ⁇ 1, excellent results on the stress relaxation resistance are obtained in many cases.
• the respective elements of Zn, Mn, Sn, and Mg also have the function of serving as x and y of the compounds B and C, the effect of suppressing grain boundary movement as the compounds B and C is exhibited.
• Fe, Cr, Ni, Zr, and Ti are elements that substitute Co to form compounds with Si, to contribute to enhancement of mechanical strength. That is, the respective elements of Fe, Ni, Cr, Zr, and Ti have a function of substituting a part of Co in the main precipitate phase to form a (Co, z) 2 Si compound (in which z is Fe, Ni, Cr, Zr, or Ti), thereby enhancing mechanical strength.
• the amount of addition when at least one of these elements is added in an amount of 0.05 mass% or more in total, the effect is exhibited, and when added in an amount of 1.0 mass% or less, the elements do not cause crystallization upon casting, or do not form intermetallic compounds that do not contribute to the mechanical strength.
• the elements of Fe, Cr, Ni, Zr, and Ti also have a function of serving as x and y of the compounds B and C, the elements exhibit the effect of suppressing the grain boundary movement as the compounds B and C. These elements exhibit almost the same effects when added in combination with two or more of those, or added singly.
• a preferred amount of addition is 0.5 to 0.8 mass% in total for at least one of these elements.
• the properties of the individual elements will not be inhibited.
• the unavoidable impurities in the copper alloy material for electric/electronic parts of the present invention include H, C, O, S, and the like.
• the copper alloy material of the present invention can be produced by, for example, the following steps.
• An outline of the main production steps for the copper alloy material of the present invention includes: melting ⁇ casting ⁇ homogenization treatment ⁇ hot rolling ⁇ face milling ⁇ cold rolling ⁇ solution heat treatment ⁇ aging heat treatment ⁇ final cold-rolling ⁇ low-temperature annealing.
• the aging heat treatment and the final cold-rolling may be in a reversed order.
• the low-temperature annealing (stress relief annealing) of the final step may be omitted.
• the steps can be carried out in a usual manner, except for the steps especially mentioned herein.
• the fact that the average cooling speed from the solid state temperature to 500°C, in the production of the copper alloy ingot, is 5 to 100°C/sec also contributes to the precipitation of the compound B, C, and D in appropriate sizes and amounts.
• this average cooling speed is from 5 to 100°C/sec, the compounds B, C, and D are appropriately formed, and as a result, the grain size of the copper alloy of the matrix can be adjusted to an adequate range.
• the solid state temperature is the temperature at which solidification is initiated, and since a temperature lower than 500°C falls in a temperature zone in which the compound A is precipitated, the lower limit of the temperature range is determined 500°C. If the cooling speed after the casting is too slow, the mechanical strength may be lowered, owing to an increase of coarse precipitates.
• the solution heat treatment temperature is preferably, when the amount of Co is 0.4 to 1.2 mass%, the temperature is 800°C to 950°C; when the amount is 1.0 to 1.5 mass%, the temperature is 900°C to 950°C; and when the amount is 1.3 to 2.0 mass%, the temperature is 900 to 1,000°C. Then, solution and recrystallization can be sufficiently carried out for the respective cases.
• the grain size of the copper alloy of the matrix is determined by the heat treatment at these temperatures. Further, it is preferable to conduct rapid cooling with the cooling speed of 50°C /sec or more from the solution heat treatment temperature. If the rapid cooling is not conducted, the element solution-heat-treated at the high temperature may precipitate.
• the particles (compounds) precipitated upon this cooling are incoherent precipitates, which do not contribute to the mechanical strength, and which give an adverse effect to the characteristics, by contributing as nucleus forming sites in forming coherent precipitates in the subsequent aging heat treatment step (or the aging heat treatment step after the cold rolling step subsequent to the solution heat treatment), thereby to accelerate precipitation at the sites.
• the above-mentioned cooling speed means an average speed from the solution heat treatment temperature at high temperature to 300°C. At a temperature 300°C or lower, a significant change in the texture does not occur, and the cooling speed to this temperature may be set at a predetermined cooling speed.
• an aging heat treatment is carried out, to form compounds of Co and Si in the copper alloy.
• This heat treatment may also be carried out after the solution heat treatment, and even after a predetermined cold rolling is carried out after the solution heat treatment.
• the conditions for this aging heat treatment are preferably at a temperature of 500°C to 600°C for 1 to 4 hours, in the case of performing the aging heat treatment after the solution heat treatment but before the final cold-rolling; and preferably at a temperature of 450°C to 550°C for 1 to 4 hours, in the case of performing the aging heat treatment after the final cold-rolling after the solution heat treatment.
• the cooling speed after this aging heat treatment has a preferred range.
• the cooling speed is in the range of 20 to 100°C/hour, increase of the electrical conductivity is sufficiently achieved. If the cooling speed is faster than 100°C/hour, increase of the electrical conductivity is not achieved sufficiently; and if the cooling speed is slower than 20°C/hour, the target changes in the properties do not occur but only the heat treatment time is prolonged, which is not economical.
• the temperature range associated with the cooling speed is the range of cooling from the respective heat treatment temperature to 300°C.
• the target high electrical conductivity cannot be obtained; and if the lower limit of the temperature range is set at a much lower value than 300°C, there is no change in the obtained electrical conductivity.
• the cooling speed after the aging heat treatment can be adjusted by controlling the temperature at a heating furnace. Further, in the case where it is required to conduct a rapid cooling, the rapid cooling can be conducted by taking out the subject from a heating zone of the heating furnace and subjecting the subject to forced air cooling or water quenching.
• Alloys (Example Nos. 1 to 35, Comparative Example Nos. 101 to 128) containing elements as shown in Tables 1 and 2, with the balance of Cu and unavoidable impurities, were melted with a high-frequency melting furnace, followed by casting at a cooling speed of 5 to 100°C /sec, to obtain ingots, respectively, with thickness 30 mm, width 100 mm, and height 150 mm. At that time, a thermocouple was placed in the vicinity of the mold wall, and casting and melting were carried out to obtain the ingots, while measuring any time.
• the thus-prepared materials were subjected to any one of the following two processes, to produce test specimens of the final products.
• Process A (The solution heat treatment) - Aging heat treatment (at a temperature from 500 to 600°C for 2 to 4 hours) - Cold working (working ratio: 5 to 25%) *Then, according to the necessity, strain-relieving annealing was conducted at a temperature from 300 to 400°C for 1 to 2 hours.
• Process B (The solution heat treatment) - Cold rolling (working ratio: 5 to 25%) - Aging heat treatment (at a temperature from 450 to 550°C for 2 to 4 hours)
• each of Examples satisfied all of mechanical strength, electrical conductivity, and bending property, each at a high level in a well-balanced manner.
• the electrical conductivity (EC) was 50 %IACS or more, and in regard to the relationship between the tensile strength (TS) and the bending property (R/t), when TS was 550 MPa or more but less than 650 MPa, R/t ⁇ 0.5; when TS was 650 MPa or more but less than 700 MPa, R/t ⁇ 1; and when TS was 700 MPa or more but less than 800 MPa, R/t ⁇ 2, thus, a good balance was achieved, with each of the properties being at a high level.
• TS tensile strength
• R/t bending property
• Comparative Examples shown in Table 2 at least any one of the properties of mechanical strength, electrical conductivity, and bending property was not practical. Among those, Sample Nos. 101, 107 to 112, and 125 to 126 of Comparative Examples had the tensile strengths of less than 500 MPa, which did not reach a practical level.

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