Copper-based conductor, twisted wire conductor, and electric wire

Abstract

The purpose of the present invention is to provide a copper-based conductor with which, when a terminal is joined to a copper-based conductor to form an electric wire with a terminal, it is possible to promote joining with the terminal and enhance tensile durability of the electric wire with a terminal.　In the copper-based conductor, in a crystal orientation analysis by an electron backscatter diffraction method performed in a cross section perpendicular to an extension direction, in a first measurement area selected in the cross section, the total accumulation rate is 40% or more, the total accumulation rate being the ratio to the total area of crystal grains contained in the first measurement area of the average value of: a first total area obtained by adding the area of crystal grains having, with respect to a first direction, a <011> orientation group, which is a crystal orientation within a <011> orientation ± 8°, a <012> orientation group, which is a crystal orientation within a <012> orientation ± 8°, and a <123> orientation group, which is a crystal orientation within a <123> orientation ± 8°; and a second total area obtained by adding the area of the crystal grains having, with respect to a second direction orthogonal to the first direction, the <011> orientation group, the <012> orientation group, and the <123> orientation group.

Description

Copper-based conductors, stranded conductors and wires

[0001] The present invention relates to a copper-based conductor, a stranded conductor, and an electric wire.

[0002] Electric wires used in electrical appliances, automotive components, etc. are made of copper-based conductors with high conductivity, and terminals are provided on both ends. In particular, when ultrasonic waves are applied to join the copper-based conductor at the end of the electric wire to the terminals, copper-based conductors are used because they are soft and easily deformed by the ultrasonic output.

[0003] As an example of such a copper-based conductor, Patent Document 1 describes a copper alloy bonding wire that has 50 to 250 copper alloy crystal grains per cross-sectional area, the maximum grain size of which is 1 / 3 or less of the diameter of the bonding wire, and that is characterized by having no orientation with any specific orientation such as <100> being 40% or less.This is said to have the effect of preventing the tip of the bonding wire from bending into a J shape, and providing a copper alloy bonding wire whose cut end does not protrude beyond the cross-sectional area of ​​the bonding wire.

[0004] JP 2017-045924 A

[0005] When ultrasonic waves are applied to join a copper-based conductor at the end of an electric wire to a terminal, if the copper-based conductor lacks softness, a gap is formed, particularly between the copper-based conductor and the terminal, which reduces the bonding strength between the terminal and the electric wire and further reduces the tensile durability of the resulting electric wire with terminal. Therefore, there has been a demand for a copper-based conductor that has high tensile durability when a terminal is joined to the copper-based conductor to form an electric wire with terminal.

[0006] In this regard, the bonding wire described in Patent Document 1 relates to a copper alloy bonding wire having a wire diameter of 15 μm or more and 20 μm or less, and does not focus on copper-based conductors with a larger diameter than this. There was room for improvement in that the bonding wire should be made more susceptible to deformation by the application of ultrasonic waves during ultrasonic bonding, thereby promoting bonding between the copper-based conductor and the terminal, and increasing the tensile durability of the terminal-attached electric wire when the terminal is bonded to the copper-based conductor.

[0007] Therefore, the present invention has been made in consideration of the above problems, and has an object to provide a copper-based conductor that can promote bonding between the copper-based conductor and a terminal when the terminal is joined to the copper-based conductor to form an electric wire with terminal, and can increase the tensile durability of the electric wire with terminal, and a stranded conductor and an electric wire using the same.

[0008] As a result of extensive research, the inventors have discovered that by increasing the proportion of crystal grains having the <011> orientation, <012> orientation, or <123> orientation in the total area of ​​crystal grains included in the measurement region in the cross section, when a copper-based conductor or a stranded conductor is joined to a terminal by ultrasonic bonding to form an electric wire with terminal, the copper-based conductor can be easily deformed by applying ultrasonic waves to the copper-based conductor, thereby reducing voids that were present at the joint between the copper-based conductor and the terminal and voids that were present inside the stranded conductor, thereby promoting bonding between the copper-based conductor and the terminal and increasing the tensile durability of the electric wire with terminal, and have thereby completed the present invention.

[0009] In order to achieve the above object, the gist of the present invention is as follows: (1) A copper-based conductor, wherein in a crystal orientation analysis performed on a cross section perpendicular to the extension direction of the conductor by electron backscatter diffraction (EBSD) method, an xy orthogonal coordinate system is defined within the cross section, a first direction on the x-axis and a second direction on the y-axis are assumed, and crystal orientations within ±8° of the <011> orientation are defined as a <011> orientation group, crystal orientations within ±8° of the <012> orientation are defined as a <012> orientation group, and crystal orientations within ±8° of the <123> orientation are defined as a <123> orientation group, A copper-based conductor, wherein the total integration rate, which is the percentage of the average of a first total area obtained by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the first direction in a first measurement region selected within a cross section, and a second total area obtained by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the second direction, to the total area of ​​crystal grains included in the first measurement region, is 40% or more. (2) The copper-based conductor according to (1) above, wherein, when the cross section is divided into a central portion and an outer annular portion surrounding the central portion, in a second measurement region selected within the central portion of the cross section, a total integration rate, which is the ratio of the average of a first total area obtained by adding together the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group with respect to the first direction, and a second total area obtained by adding together the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group with respect to the second direction, to the total area of ​​crystal grains included in the second measurement region, is 50% or more. (3) The copper-based conductor according to (1) or (2) above, wherein the average crystal grain size within the cross section is less than 20.0 μm. (4) A stranded conductor formed by twisting together a plurality of copper-based element wires made of the copper-based conductor according to any one of (1) to (3) above. (5) An electric wire in which at least an insulating coating layer is formed on the surface of the copper-based conductor according to (1), (2), or (3) above, or the stranded conductor according to (4) above.

[0010] According to the present invention, it is possible to provide a copper-based conductor that can promote bonding between the copper-based conductor and a terminal when the terminal is joined to the copper-based conductor to form an electric wire with terminal, and can increase the tensile durability of the electric wire with terminal, as well as a stranded conductor and an electric wire using the same.

[0011] FIG. 2 is a cross-sectional view schematically showing the height of a joint in an electric wire with a terminal in which a stranded conductor formed by twisting together a plurality of copper-based conductors of the present invention is joined to a flat portion of a terminal.

[0012] Hereinafter, preferred embodiments of the copper-based conductor of the present invention will be described in detail. In the component composition of the copper-based conductor of the present invention, "mass %" may be simply represented as "%".

[0013] In a crystal orientation analysis of the copper-based conductor according to the present invention by electron backscatter diffraction method performed on a cross section perpendicular to the extension direction of the conductor, an xy Cartesian coordinate system is defined within the cross section, and a first direction which is a direction on the x axis and a second direction which is a direction on the y axis are assumed. When crystal orientations within ±8° of the <011> orientation are defined as a <011> orientation group, crystal orientations within ±8° of the <012> orientation are defined as a <012> orientation group, and crystal orientations within ±8° of the <123> orientation are defined as a <123> orientation group, the copper-based conductor according to the present invention has a crystal orientation in a first measurement region selected within the cross section that is inclined from the <011> orientation relative to the first direction. The total concentration ratio (hereinafter sometimes referred to as "the total concentration ratio of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the first measurement region as a percentage of the total area of ​​crystal grains included in the first measurement region") is 40% or more. The first total area is calculated by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the second direction, and the second total area is calculated by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the second direction.

[0014] In the copper-based conductor of the present invention, the crystal orientation of the crystal grains appearing in the cross section is controlled by setting the total area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to 40% or more of the total area of ​​crystal grains included in the first measurement region in the cross section, thereby increasing the proportion of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group, which can be deformed with a smaller force when ultrasonic waves are applied, among the crystal grains appearing in the first measurement region in the cross section. Therefore, when a terminal is joined to the copper-based conductor by ultrasonic bonding to form an electric wire with terminal, by making the copper-based conductor more deformable, voids at the joint between the copper-based conductor and the terminal and voids inside the stranded conductor can be reduced, thereby facilitating bonding between the copper-based conductor and the terminal and improving the tensile durability of the electric wire with terminal.

[0015] The copper-based conductor according to the present invention can provide a copper-based conductor that has high tensile durability when a terminal is joined to the copper-based conductor to form a terminal-attached electric wire, as well as a stranded conductor and electric wire using the same. This makes it possible to easily deform the copper-based conductor and promote bonding with the terminal when producing a terminal-attached electric wire for use in electrical appliances or automobiles by ultrasonic bonding, thereby stably bonding the copper-based conductor and the terminal and thereby achieving a high-quality electric wire connection. Furthermore, because the copper-based conductor according to the present invention can be easily deformed by applying ultrasonic waves, it can also be suitably used as a bonding wire in which the wire is deformed and bonded to a semiconductor chip.

[0016] [1] Metal structure of copper-based conductor In the copper-based conductor according to the present invention, the total concentration ratio of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​crystal grains included in the first measurement region is 40% or more. Here, in order to make the copper-based conductor easily deformable by applying ultrasonic waves, it is important to control the crystal orientation of the crystal grains relative to the deformation direction of the copper-based conductor. In this regard, the inventors have found that by increasing the number of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group relative to the deformation direction of the copper-based conductor, the copper-based conductor can be easily deformed with a weak force. Here, if the total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the first measurement region is less than 40%, the concentration of crystal grains having other orientations will be relatively high, and a larger force will be required in the direction of deformation. Therefore, the total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the first measurement region is preferably 60% or more, more preferably 80% or more. On the other hand, the upper limit of the proportion of the total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the first measurement region is not particularly limited, and may be, for example, 100%.

[0017] The total concentration ratio of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group relative to the total area of ​​crystal grains included in the first measurement region in the cross section can be obtained, for example, from crystal orientation analysis data obtained by continuously measuring crystal orientation data using an EBSD detector (TSL, OIM5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (JEOL, JSM-7001FA), and calculating (processing) the measured crystal orientation data using analysis software (TSL Solutions, OIM Analysis). "EBSD" stands for Electron Backscatter Diffraction, and is a crystal orientation analysis technique that utilizes reflected electron Kikuchi diffraction that occurs when an electron beam is irradiated on a copper-based conductor, which is a measurement sample, in a scanning electron microscope (SEM). The measurement object is a mirror-finished surface of a cross section perpendicular to the extension direction of a single copper-based conductor, which is polished to a first measurement area selected within the cross section, but it may also be the entire range of the cross section. When a portion of the cross section is used as the first measurement area, the measurement area may be, for example, 200 μm to 500 μm square. The polishing of the cross section can be performed using a Cross Section Polisher (registered trademark) device, as well as wet polishing, or any means capable of achieving a mirror finish, such as an FIB or microtome, and the specific means is not limited. For the obtained crystal orientation data, two directions that are 90° apart in a direction perpendicular to the longitudinal direction of the wire are selected on the IPF map to define an x-y orthogonal coordinate system, and a first direction on the x-axis and a second direction on the y-axis are defined. From the chart-crystal direction obtained using analysis software, when the boundary where the orientation difference between adjacent measurement points is 15° or more is defined as the interface (grain boundary) of the crystal grain, the set of consecutive measurement points in the range surrounded by the grain boundary is defined as a crystal grain, and crystal orientations within ±8° of the <011> orientation can be defined as a <011> orientation group, crystal orientations within ±8° of the <012> orientation can be defined as a <012> orientation group, and crystal orientations within ±8° of the <123> orientation can be defined as a <123> orientation group.In this case, the area ratios of the crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​the crystal grains included in the first measurement region are measured for the first and second directions, and typically this measurement is performed three times (n = 3) at different locations in the first measurement region, and the average of the area ratios of the crystal grains having each orientation group obtained by the three measurements is calculated. Then, the total concentration ratio of the crystal grains having each orientation group is calculated from the average of the area ratios of the crystal grains having each orientation group in the first and second directions, and by calculating the average for the first and second directions, a measurement value of the total concentration ratio of the crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​the crystal grains included in the first measurement region can be obtained.

[0018] In addition, when the copper-based conductor according to the present invention has a cross section divided into a central portion and an outer ring portion surrounding the central portion, in a second measurement region selected within the central portion of the cross section, the average of a first total area calculated by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in a first direction and a second total area calculated by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in a second direction is preferably 50% or more. Therefore, by setting the total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to 50% or more of the total area of ​​crystal grains included in the second measurement region selected within the center of the cross section, the copper-based conductor becomes more easily deformed from the center, allowing the copper-based conductor to be deformed with less force. Therefore, the total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to 50% or more of the total area of ​​crystal grains included in the second measurement region selected within the center of the cross section is more preferably 60% or more, and even more preferably 80% or more.

[0019] Here, the "center of the cross section" in this specification refers to a region having the same center of gravity as the center of gravity of the cross section when observed perpendicular to the extension direction of the copper-based conductor, having an area of ​​1 / 9 of the cross section from this center of gravity, and having a similar shape to the cross section. For example, if the copper-based conductor is a round wire, the center (center of gravity) can be taken as the same center (center of gravity) as the center (center of gravity) of the circular cross section when observed perpendicular to the extension direction of the copper-based conductor, and the region can be a region within a concentric circle from this center (center of gravity) whose diameter is 1 / 3 of the cross section.

[0020] The total concentration ratio of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​crystal grains included in the second measurement region in the cross section can be determined, for example, by measuring the second measurement region at the center of the cross section using the same procedure as when the first measurement region is measured. That is, for the first and second directions, the area ratios of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​crystal grains included in the second measurement region are measured, and this measurement is usually performed three times (n = 3) at different locations in the second measurement region, and the average area ratio of crystal grains having each orientation group obtained from the three measurements is calculated. The total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group is calculated from the average of the area ratios of crystal grains having each orientation group in the first and second directions, and the average of the first and second directions is calculated to obtain a measurement value of the proportion of the total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the second measurement region. Here, the crystal orientation data used to calculate the total concentration of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the second measurement region may be data extracted from crystal orientation data obtained by electron backscatter diffraction (EBSD) performed on the second measurement region.

[0021] In the copper-based conductor according to the present invention, the average crystal grain size in the cross section is preferably less than 20.0 μm. This reduces the variation in the bonding when the copper-based conductor or a stranded conductor formed by twisting multiple copper-based conductors together is ultrasonically bonded to a terminal, thereby enabling more stable bonding. Therefore, the average crystal grain size in the cross section is more preferably 15.0 μm or less, and even more preferably 10.0 μm or less. On the other hand, the lower limit of the crystal grain size is not particularly limited, but may be 1.0 μm, for example, from the viewpoint of making the copper-based conductor easily deformable.

[0022] Here, the average crystal grain size of the crystal grains of the copper-based conductor can be determined by analyzing the crystal orientation data of the above-mentioned electron backscatter diffraction (EBSD) method, selecting the chart-grain size (diameter) of the analysis software with the entire cross section as the analysis target, and calculating the average crystal grain size using the area method. More specifically, when the boundary where the orientation difference with adjacent measurement points is 15° or more is defined as the interface (grain boundary) of the crystal grain, the average diameter of the crystal grains can be determined as the circle-equivalent diameter of the crystal grains when the cross-sectional area of ​​the crystal grains is calculated using the number of consecutive measurement points in the area surrounded by the grain boundary and the step size during measurement.

[0023] [2] Material of the Copper-Based Conductor The copper-based conductor is made of copper or a copper alloy. Here, the copper-based conductor may be a copper alloy containing small amounts of elements such as silver (Ag), chromium (Cr), zirconium (Zr), or tin (Sn). However, from the viewpoint of making the copper-based conductor easier to bend, it is preferably copper (Cu), more specifically, 99.00% by mass or more of pure copper. Among them, since the higher the copper content, the higher the electrical conductivity, tough pitch copper containing 99.90% by mass or more of copper (Cu) and inevitable impurities is preferred, and oxygen-free copper containing 99.96% by mass or more of Cu and 10 ppm or less of oxygen and inevitable impurities is more preferred.

[0024] The copper alloy constituting the copper-based conductor preferably has an alloy composition containing at least one element selected from the group consisting of 0.1% by mass to 1.0% by mass of Ag, 0.1% by mass to 1.0% by mass of Cr, 0.1% by mass to 1.0% by mass of Zr, and 0.1% by mass to 1.0% by mass of Sn, with the remainder being Cu and unavoidable impurities.

[0025] When at least one of the contents of Ag, Cr, Zr, and Sn is 0.1% by mass or more, the tensile durability of the copper-based conductor can be improved. Therefore, even if the cross-sectional area of ​​the connection deformed by ultrasonic bonding is small, the electric wire can withstand the tensile load when handled without breaking. On the other hand, when at least one of the contents of Ag, Cr, Zr, and Sn exceeds 1.0% by mass, this can cause a decrease in the conductivity of the copper-based conductor. Therefore, when using a copper-based conductor as an electric wire, it is preferable to add the above elements at low concentrations. From this perspective, when the copper alloy contains Ag, the upper limit of the Ag content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less. When the copper alloy contains Cr, the upper limit of the Cr content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less. When the copper alloy contains Zr, the upper limit of the Zr content is more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less. When the copper alloy contains Sn, the upper limit of the Sn content is more preferably 0.7 mass % or less, and even more preferably 0.4 mass % or less.

[0026] The remainder other than the above elements are unavoidable impurities. The unavoidable impurities refer to impurities at a level that is inevitably mixed in during the manufacturing process. Depending on the content of the unavoidable impurities, they may be a factor in reducing the conductivity of the copper-based conductor, so it is preferable that the content of the unavoidable impurities is small.

[0027] Examples of inevitable impurities contained in copper-based conductors include elements such as aluminum (Al), beryllium (Be), cadmium (Cd), iron (Fe), magnesium (Mg), nickel (Ni), phosphorus (P), lead (Pd), silicon (Si), and titanium (Ti). Examples of inevitable impurities include small amounts of silver (Ag), chromium (Cr), zirconium (Zr), and tin (Sn) that do not satisfy the silver (Ag), chromium (Cr), zirconium (Zr), and tin (Sn) content requirements in the alloy composition of the copper alloy. The upper limit of the content of inevitable impurities is preferably 30 ppm or less in total of the above elements.

[0028] [3] Shape and uses of copper-based conductors The shape of a copper-based conductor is such that the cross section perpendicular to the extension direction of the copper-based conductor is circular or approximately circular, and its size can be selected appropriately depending on the amount of current required in the electrical appliance or automobile to be installed and the installation space.

[0029] When the copper-based conductor is made of a copper-based wire having a round wire shape, it is preferable that the diameter of the copper-based wire (round wire) is 0.13 mm or more, since a relatively high current can be passed through the copper-based wire. Also, it is preferable that the diameter of the copper-based wire (round wire) is 0.54 mm or less, since the copper-based conductor is easily deformed when ultrasonic waves are applied.

[0030] Furthermore, a stranded conductor can be formed by twisting together multiple copper-based wires made of the above-mentioned copper-based conductor, which can be easily bent, easily deformed when ultrasonic waves are applied, and has high bonding strength to a terminal. Here, the number of twists in the stranded conductor and the total cross-sectional area of ​​the stranded wire are not limited, but by twisting together copper-based conductors having the above-mentioned wire diameters in a number ranging from 7 to 171, it is possible to easily join terminals, etc. by ultrasonic bonding and to form a small-diameter stranded conductor that requires little installation space.

[0031] Furthermore, the copper-based conductor of the present invention is preferably used for an electric wire. More specifically, an electric wire can be formed by forming at least an insulating coating layer on the surface of the above-mentioned copper-based conductor or stranded conductor.

[0032] Here, the insulating coating layer is preferably a coating layer made of, for example, polyvinyl chloride, and the coating layer can be formed, for example, by extruding molten resin onto the surface of the copper-based conductor or the stranded conductor.

[0033] Furthermore, when the copper-based conductor according to the present invention is ultrasonically bonded to a terminal to obtain an electric wire with terminal, the height h of the joint is preferably in the range of 1 / 3 to 2 / 3, where the outer diameter (stranded outer diameter) of the stranded conductor before bonding is taken as 1. If the height h of the joint exceeds 2 / 3 of the stranded outer diameter, many voids that were present at the joint between the copper-based conductor and the terminal and inside the stranded conductor remain, reducing the tensile durability of the electric wire with terminal. Therefore, the height h of the joint is preferably 0.55 or less, more preferably 0.45 or less, where the outer diameter (stranded outer diameter) of the stranded conductor before bonding is taken as 1. On the other hand, if the height h of the joint is less than 1 / 3 of the stranded outer diameter, the cross-sectional area of ​​the stranded conductor becomes small, making it difficult to pass a predetermined current through the electric wire with terminal. In this case, the reduced cross-sectional area of ​​the joint also tends to result in insufficient tensile durability. Therefore, when the outer diameter of the stranded conductor before joining (stranded outer diameter) is taken as 1, the height h of the joint is preferably 0.34 or more, and more preferably 0.38 or more.

[0034] Here, the height h of the joint can be defined as the maximum height of the stranded conductor 1 from the surface 2a of the flat portion 2 of the copper terminal when observing a vertical cross section perpendicular to the longitudinal direction of the stranded conductor 1 of the electric wire with terminal (the extension direction of the copper-based conductor 10), as shown in Fig. 1. In the stranded conductor 1 shown in Fig. 1, a plurality of copper-based conductors 10 are twisted together in a spiral shape to form multiple layers around a central conductor wire 11 made of a single copper-based conductor 10, and therefore the cross section of the copper-based conductor 10 in the spirally twisted portion is substantially elliptical.

[0035] Furthermore, when a copper-based conductor according to the present invention is ultrasonically bonded to a terminal so that the terminal extends on one side of the joint and the stranded conductor extends on the other side of the joint, and a tensile test is performed by grasping the terminal on one side and the stranded conductor on the other side according to JIS Z2241, the conductor does not break at the joint and preferably has a measured tensile strength of 70 MPa or more. Because the copper-based conductor and the terminal are strongly bonded in this type of electric wire with terminal, the electric wire with terminal can have high tensile durability. Therefore, the tensile strength of the electric wire with terminal is preferably 100 MPa or more, and more preferably 150 MPa or more.

[0036] The material of the terminal to be joined to the copper-based conductor according to the present invention is preferably copper or a copper alloy. Here, from the viewpoint of use in applications involving the flow of large currents, it is more preferable to use pure copper, which has high conductivity, as the material of the terminal. Furthermore, from the viewpoint of using the terminal as a fitting portion by utilizing the springiness of the terminal material, it is more preferable to use a copper alloy, which has high strength, as the material of the terminal. Here, the material of the terminal may be the same as the material of the copper-based conductor described above, or may be the same material as the copper-based conductor.

[0037] [4] Example of a manufacturing method of a copper-based conductor Next, a description will be given of a manufacturing method of a copper-based conductor according to an embodiment. In the manufacturing method of a copper-based conductor according to an embodiment, the copper-based conductor is isotropically processed in the radial direction, particularly in the wiredrawing step, and a specific crystal orientation when viewed from a direction perpendicular to the longitudinal direction of the wire is controlled by two-stage current annealing in the subsequent first and second heat treatment steps, thereby increasing the total density, which is the ratio of the average value of the first and second total areas to the total area of ​​the crystal grains included in the first measurement region.

[0038] In the method for producing a copper-based conductor according to the embodiment, a casting step is first performed in which electrolytic copper is melted in a reducing atmosphere to obtain a cylindrical ingot called a billet.

[0039] After the casting process, an extrusion process is carried out in which the billet is processed into a round bar by hot extrusion.

[0040] The extrusion process is followed by a wiredrawing process, in which the round bar or wire rod obtained in the above process is drawn to a predetermined wire diameter. Preferably, the wiredrawing process includes a peeling process to remove surface defects that have occurred up to the above process. If necessary, the wire may be subjected to one or more heat treatment processes before the wiredrawing process in order to remove processing strain and to facilitate wiredrawing.

[0041] When a stranded conductor is formed after the wire drawing process, a stranding process may be performed in which a plurality of drawn copper-based conductors are twisted together to form a stranded conductor. At this time, the conductor may be compressed using a compression die, or the copper-based conductors may be twisted together without being compressed using a compression die.

[0042] The copper-based conductor or the stranded conductor is then subjected to a heat treatment process, which includes a first heat treatment process and a second heat treatment process, so that the total concentration ratio, which is the ratio of the average of the first and second total areas to the total area of ​​the crystal grains contained in the first measurement region, can be 40% or more.

[0043] In the first and second heat treatment steps, current annealing is performed by passing an electric current through the wire passing through a plurality of pulleys that function as electrodes. By performing current annealing in the first and second heat treatment steps, the temperature of the copper-based conductor or the stranded conductor can be raised in a short time. Therefore, after a large number of small crystal grains are simultaneously generated by recrystallization in the first heat treatment step, these crystal grains can be grown in the second heat treatment step. Therefore, the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the first measurement region can be increased.

[0044] In the first heat treatment process and the second heat treatment process, the temperature and time for heating the copper-based conductor or stranded conductor can be adjusted appropriately depending on characteristics such as the proportion of the area of ​​crystal grains having the desired <011> orientation group, <012> orientation group, and <123> orientation group.

[0045] For example, if the temperature at which the copper-based conductor or the stranded conductor is heated in the first heat treatment step is too high, the generation of crystal grains by recrystallization and the growth of crystal grains occur simultaneously, making it difficult to increase the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains exposed in the cross section of the copper-based conductor. Also, if the heating temperature in the first heat treatment step is too high, the crystal grains tend to become larger than necessary. On the other hand, if the temperature at which the copper-based conductor or the stranded conductor is heated in the first heat treatment step is too low, atomic rearrangement due to heating and the generation of crystal grains by recrystallization do not occur easily, making it difficult to increase the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains exposed in the cross section of the copper-based conductor. Here, by increasing the current flowing through the copper-based conductor or the stranded conductor in the first heat treatment process, the temperature to which the copper-based conductor or the stranded conductor is heated can be increased, and by decreasing the current flowing through the copper-based conductor or the stranded conductor in the first heat treatment process, the temperature to which the copper-based conductor or the stranded conductor is heated can be decreased.

[0046] Furthermore, if the time for heating the copper-based conductor or the stranded conductor in the first heat treatment step is too long, the growth of crystal grains generated by recrystallization is likely to occur, making it difficult to increase the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains appearing in the cross section of the copper-based conductor. In other words, by shortening the time for heating the copper-based conductor or the stranded conductor in the first heat treatment step, excessive crystal grain growth can be suppressed, thereby increasing the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains appearing in the cross section of the copper-based conductor.

[0047] In the subsequent second heat treatment step, if the temperature at which the copper-based conductor or the stranded conductor is heated is too low, the growth of crystal grains generated by recrystallization is difficult, making it difficult to increase the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains exposed in the cross section of the copper-based conductor. On the other hand, if the temperature at which the copper-based conductor or the stranded conductor is heated in the second heat treatment step is too high, excessive crystal grain growth reduces deformation resistance, increasing the risk of wire breakage, which is undesirable. Here, the temperature at which the copper-based conductor or the stranded conductor is heated can be increased by increasing the current flowing through the copper-based conductor or the stranded conductor in the second heat treatment step, and the temperature at which the copper-based conductor or the stranded conductor is heated can be lowered by decreasing the current flowing through the copper-based conductor or the stranded conductor in the second heat treatment step.

[0048] In addition, by shortening the heating time of the copper-based conductor or the stranded conductor in the second heat treatment step, excessive growth of crystal grains can be suppressed, and therefore the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains exposed in the cross section of the copper-based conductor can be adjusted to be high. On the other hand, by lengthening the heating time of the copper-based conductor or the stranded conductor in the second heat treatment step, the crystal grains grow, and therefore it becomes difficult to increase the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains exposed in the cross section of the copper-based conductor.

[0049] When current annealing is performed in the first and second heat treatment steps, the temperature of the copper-based conductor or the stranded conductor may rise instantaneously, making it difficult to accurately grasp the temperature because the response speed of the thermocouple cannot keep up. Therefore, when setting the heat treatment conditions for current annealing, a copper-based conductor with a desired total integration rate can be obtained by adjusting conditions such as voltage, current value, wire speed, and electrode distance based on the total integration rate of the actual copper-based conductor after the heat treatment step and the above description.

[0050] It is preferable to form an insulating coating layer on the surface of the stranded conductor thus obtained by extruding a molten resin, thereby producing an electric wire.

[0051] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention.

[0052] Next, in order to further clarify the effects of the present invention, examples of the present invention and comparative examples will be described, but the present invention is not limited to these examples of the present invention.

[0053] (Preparation of Copper-Based Conductors A to H) A copper-based material composed of the components shown in Table 1 was subjected to a casting process, an extrusion process, and a wiredrawing process to form a roughly drawn wire with a wire diameter of 8 mm. This was then further subjected to a wiredrawing process to form a round wire with the wire diameter shown in Table 1. Subsequently, a first heat treatment process was performed under the conditions shown in Table 1. For copper-based conductor H, for which the type of heat treatment is "batch annealing," the heat treatment temperature was 500°C, and the holding time at the heat treatment temperature was 2 hours. Subsequently, for copper-based conductors A to F, for which the presence or absence of the second heat treatment process is marked "Yes" in Table 1, a second heat treatment process was performed under the conditions shown in Table 1 to obtain a copper-based conductor. On the other hand, for copper-based conductors G and H, for which the presence or absence of the second heat treatment process is marked "No" in Table 1, only the first heat treatment process was performed without the second heat treatment process to obtain a copper-based conductor.

[0054] (Invention Examples 1 to 18 and Comparative Examples 1 to 6) A stranded conductor was obtained by a stranding step in which strands of wires made of copper-based conductors of the types shown in Tables 4, 5, and 6, among the copper-based conductors A to H obtained above, were twisted together to form a stranded conductor. Then, an insulating coating layer made of polyvinyl chloride was formed on the surface of the obtained stranded conductor, thereby obtaining an electric wire.

[0055] [Various Measurement and Evaluation Methods] The copper-based conductors and stranded conductors according to the present invention and comparative examples were used to carry out the following characteristic evaluations. The evaluation conditions for each characteristic were as follows.

[0056] [1] Component Analysis A sample obtained by pressing the rough wire obtained in the wire drawing process in the above-mentioned manufacturing stage into a flat plate was measured and analyzed using an optical emission spectrometer (manufactured by Shimadzu Corporation). Measurements were performed three times, and the average values ​​were calculated and shown in Table 1. Elements that were intentionally added are listed in their respective columns, and if they were not intentionally added, these elements were included in the total of unavoidable impurities. Note that if the detected amount of a component was less than 0.001% by mass, the component was considered not to be contained and was marked with "-" in the table.

[0057] [2] Measurement of the total accumulation rate of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group relative to the total area of ​​crystal grains contained in the first measurement region. To measure the total accumulation rate of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group relative to the total area of ​​crystal grains contained in the first measurement region, continuous measurements were performed using an EBSD detector (TSL, OIM5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (JEOL, JSM-7001FA), to collect EBSD patterns. The crystal orientation data obtained from the EBSD patterns was then analyzed using analysis software (TSL, OIM Analysis) to obtain crystal orientation analysis data. The measurement target was a mirror-finished cross section of a copper-based conductor (or, in the case of a stranded conductor, a single copper-based conductor constituting the stranded conductor) perpendicular to the longitudinal direction, and the entire cross section was designated the first measurement area. Measurements were performed with a step size of 0.5 μm. Next, for the obtained crystal orientation data, two directions perpendicular to the longitudinal direction of the wire were selected on the IPF map, which were 90° apart, to define an x-y Cartesian coordinate system. Then, a first direction on the x-axis and a second direction on the y-axis were defined. Furthermore, when the boundary where the orientation difference with adjacent measurement points is 15° or more is defined as the interface (grain boundary) of a crystal grain from the chart-crystal direction obtained using analysis software, the set of consecutive measurement points in the area surrounded by the grain boundary is defined as a crystal grain, and the crystal orientations within ±8° of the <011> orientation are defined as the <011> orientation group, the crystal orientations within ±8° of the <012> orientation are defined as the <012> orientation group, and the crystal orientations within ±8° of the <123> orientation are defined as the <123> orientation group. At this time, for each of the first and second directions, the area proportions (A1 to A3, A5 to A7) of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains contained in the first measurement region were measured, and this measurement was performed three times at different locations within the first measurement region.The average of the three measurements was calculated, and the total area proportions of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group were calculated to obtain the total accumulation rate (A4, A8).Then, from the measured values ​​of the total accumulation rates (A4, A8) calculated for the first and second directions, the average of the total accumulation rates for the first and second directions ((A4 + A8) / 2) was calculated and shown in Table 2.

[0058] [3] Measurement of the total concentration ratio of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the second measurement region. The total concentration ratio of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the total area of ​​crystal grains included in the second measurement region was measured by taking the center of a circular cross section of a copper-based conductor when viewed in cross section, and defining a concentric region having a diameter one-third that of the first measurement region. Data for the second measurement region was extracted from the crystal orientation data obtained by the electron backscatter diffraction (EBSD) method described above, and the data for the first and second orientations were measured using the same procedure as for the first measurement region. For each of the first and second directions, the area ratios (B1 to B3, B5 to B7) of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​crystal grains included in the second measurement region were measured. This measurement was performed three times at different locations within the first measurement region, and the average of the three measurements was calculated. The total area ratio of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group was calculated as the total accumulation ratio (B4, B8). Then, from the measured values ​​of the total accumulation ratios (B4, B8) calculated for the first and second directions, the average of the total accumulation ratios for the first and second directions ((B4 + B8) / 2) was calculated and shown in Table 3.

[0059] [4] Measurement of the average grain size of crystal grains The average grain size of crystal grains present in the cross section of the copper-based conductor was determined by analyzing the crystal orientation data of the electron backscatter diffraction (EBSD) method described above, selecting the chart-grain size (diameter) of the analysis software with the entire cross section as the analysis target, and calculating the average grain size by the area method. The results are shown in Table 3.

[0060] [5] Evaluation of the height of the connection when the stranded conductor is ultrasonically bonded to a terminal. For the electric wire having the stranded conductor obtained above, 40 mm of the coating material was stripped off from the stranded conductor, and a flat terminal with a width of 10 mm, a depth of 40 mm, and a thickness of 2 mm was prepared. The stranded conductor was brought into contact with the flat portion of the copper terminal and ultrasonically bonded to obtain an electric wire with a terminal. The ultrasonic bonding was performed using ultrasonic waves with a frequency of 20 kHz for a bonding time of 0.4 s. The ultrasonic energy input was 20 kHz for a cross-sectional area of ​​3 sq (approximately 3.30 mm). ２ ) is used, the cross-sectional area is 5 sq (approximately 5.23 mm ２ ) is used, the cross-sectional area is 15 sq (approximately 13.75 mm ２ In this case, the unit sq means the area of ​​the conductor and is a unit used to describe electric wires (for example, the cross-sectional area of ​​the stranded conductor in a 3 sq electric wire is approximately 3 mm ２ (It is).

[0061] Two such electric wires with terminals were prepared, and parallel longitudinal cross sections along the longitudinal direction of the stranded conductors (extension direction of the copper-based conductor) were observed. The maximum height of the stranded conductor 1 from the surface 2 a of the flat portion 2 of the copper terminal shown in FIG. 1 was determined and taken as the height h of the joint. The average value of the height h of the joint of the two electric wires with terminals was taken as the measured value of the height h of the joint [mm].

[0062] When the measured value of the height h of the joint was in the range of 1 / 3 to 2 / 3 of the outer diameter (stranded outer diameter) of the stranded conductor before joining, the voids at the joint between the copper-based conductor and the terminal and inside the stranded conductor were small, and the copper-based conductor and the terminal were well joined. This was evaluated as "○ (good)." On the other hand, when the measured value of the height h of the joint was more than 2 / 3 of the outer diameter (stranded outer diameter) of the stranded conductor before joining, many voids at the joint between the copper-based conductor and the terminal and inside the stranded conductor remained, and the copper-based conductor and the terminal were not well joined. This was evaluated as "× (poor)." Furthermore, when the measured value of the height h of the joint was less than 1 / 3 of the outer diameter (stranded outer diameter) of the stranded conductor before joining, the cross-sectional area of ​​the stranded conductor was small, making it difficult to pass a predetermined current through the electric wire with terminal. This was evaluated as "× (poor)." In the examples of the present invention and the comparative examples, the evaluation was made with a grade of "good" as a passing level. The results are shown in Tables 4, 5 and 6.

[0063] [6] Tensile test and evaluation of electric wire with terminal The tensile strength of the electric wire with terminal was measured by preparing two test pieces of electric wire with terminal, each having a 10 mm long joint at the position where the terminal and the stranded conductor overlap, with the terminal extending 40 mm on one side of the joint and the stranded conductor extending 140 mm on the other side of the joint, and conducting a tensile test on these test pieces by grasping the terminal on one side and the stranded conductor on the other side, with reference to JIS Z2241. The location where the electric wire with terminal broke was identified, and the tensile strength R ｍ Calculate the tensile strength R of the two terminal-attached wires. ｍ The tensile strength of the electric wire with terminal was calculated by dividing the force at which the electric wire with terminal broke in a tensile test by the cross-sectional area of ​​the stranded conductor before joining as a unit area.

[0064] Regarding the results of the tensile test, if neither of the two electric wires with terminals broke at the joint and the measured tensile strength was 70 MPa or more, the copper-based conductor and the terminal were strongly joined, and the electric wires with terminals had high tensile durability. The results were evaluated as "Good (◯)." On the other hand, if at least one electric wire with terminal broke at the joint or the average tensile strength was less than 70 MPa, the bond between the copper-based conductor and the terminal was weak, and the electric wires with terminals had low tensile durability. The results were evaluated as "Poor (×)." In the examples of the present invention and the comparative examples, "Good" was used as a passing grade. The results are shown in Tables 4, 5, and 6.

[0065] [7] Overall Evaluation When both of the two evaluation results, the height of the connection portion when the stranded conductor was ultrasonically joined to the terminal and the results of the tensile test of the electric wire with the terminal, were evaluated as "Good," the overall evaluation was evaluated as "Good," since both the height of the connection portion with the terminal and the results of the tensile test of the electric wire with the terminal were excellent. On the other hand, when at least one of the two evaluation results, the height of the connection portion with the terminal and the results of the tensile test of the electric wire with the terminal, was evaluated as "Poor," the overall evaluation was evaluated as "Poor," since at least one of these two characteristics was insufficient. The results are shown in Tables 4, 5, and 6.

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] As shown in Tables 1 to 6, in Examples 1 to 18 of the present invention, the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​crystal grains included in the first measurement region was controlled within a predetermined range. Therefore, when a terminal-attached electric wire was constructed by joining a stranded conductor and a terminal by ultrasonic bonding, both the height of the connection with the terminal and the results of the tensile test of the terminal-attached electric wire were excellent. Therefore, in Examples 1 to 18 of the present invention, the copper-based conductor was easily deformed by applying ultrasonic waves to the copper-based conductor, thereby reducing voids that were present at the joint between the copper-based conductor and the terminal and voids that were present inside the stranded conductor, thereby promoting bonding between the copper-based conductor and the terminal and further improving the tensile durability of the terminal-attached electric wire.

[0073] On the other hand, in Comparative Examples 1 to 6 and Inventive Examples 1 to 18, the proportion of the area of ​​crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group to the total area of ​​crystal grains included in the first measurement region was not controlled within a predetermined range. Therefore, in Comparative Examples 1 to 6, when a terminal-fitted electric wire was constructed by joining a stranded conductor and a terminal by ultrasonic bonding, at least one of the height of the connection with the terminal and the results of a tensile test of the terminal-fitted electric wire was poor. As a result, the tensile durability of the terminal-fitted electric wires in Comparative Examples 1 to 6 was also poor.

[0074] REFERENCE SIGNS LIST 1 stranded conductor 10 copper-based conductor 11 central conductor wire 2 flat portion of terminal 2a surface of flat portion h height of joint

Claims

1. A copper-based conductor, wherein in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) on a cross section perpendicular to the extension direction of the conductor, an xy orthogonal coordinate system is defined within the cross section, and a first direction is a direction on the x axis and a second direction is a direction on the y axis, and when crystal orientations within ±8° of the <011> orientation are defined as a <011> orientation group, crystal orientations within ±8° of the <012> orientation are defined as a <012> orientation group, and crystal orientations within ±8° of the <123> orientation are defined as a <123> orientation group, in a first measurement region selected within the cross section, a first total area is calculated by adding together the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group with respect to the first direction; A copper-based conductor, wherein the total concentration rate, which is the ratio of the average of a second total area obtained by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group relative to the second direction to the total area of ​​crystal grains included in the first measurement area, is 40% or more.

2. A copper-based conductor as described in claim 1, wherein, when the cross section is divided into a central portion and an outer annular portion surrounding the central portion, in a second measurement region selected within the central portion of the cross section, a total integration rate, which is the ratio of the average of: a first total area calculated by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the first direction; and a second total area calculated by adding up the areas of crystal grains having the <011> orientation group, the <012> orientation group, and the <123> orientation group in the second direction, to the total area of ​​crystal grains included in the second measurement region, is 50% or more.

3. The copper-based conductor according to claim 1, wherein the average grain size of the grains present in the cross section is less than 20.0 μm.

4. A stranded conductor formed by twisting together a plurality of copper-based wires made of the copper-based conductor according to claim 1.

5. An electric wire in which at least an insulating coating layer is formed on the surface of the copper-based conductor according to claim 1, 2 or 3, or the stranded conductor according to claim 4.

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