Copper conductors, stranded conductors and wires

Abstract

The present invention provides a copper conductor that promotes the bonding between the copper conductor and the terminal when terminals are joined to the copper conductor to form a terminald wire, and improves the tensile durability of the terminald wire. In the crystal orientation analysis of this copper-based conductor performed by electron backscattering diffraction at a cross-section perpendicular to the extension direction, the average of the first total area and the second total area in the first measurement region selected within the cross-section accounts for a proportion of the total area of ​​the grains contained in the first measurement region, i.e., the total cumulative rate, of 40% or more. The first total area is obtained by summing the areas of grains with crystal orientations within ±8° of the <011> crystal orientation, the <012> crystal orientation within ±8° of the <012> crystal orientation, and the <123> crystal orientation within ±8° of the <123> crystal orientation, relative to the first direction. The second total area is obtained by summing the areas of grains with crystal orientation groups <011>, <012>, and <123> crystal orientations relative to the second direction orthogonal to the first direction.

Description

[Technical Field]

[0001] This invention relates to a copper conductor, a stranded conductor, and an electric wire. [Previous Technology]

[0002] As for wires used in electrical products or automotive parts, copper conductors with high conductivity are used, and terminals are provided at both ends of the copper conductors. In particular, when ultrasonic waves are applied to connect the copper conductors at the ends of the wires to the terminals, copper conductors that are flexible and easily deformable by the output of ultrasonic waves are used.

[0003] As such a copper-based conductor, Patent Document 1 discloses a copper alloy bonding wire, characterized in that: the number of copper alloy grains per cross-sectional area is 50 to 250, the maximum grain size is less than 1 / 3 of the diameter of the bonding wire, and specific crystal orientations such as <100> are all unoriented by 40% or less. This provides the following effect: a copper alloy bonding wire is provided in which the leading edge of the bonding wire cannot be bent into a J-shape, and the cut end does not protrude from the cross-sectional area of ​​the bonding wire. [Prior Art Documents] (Patent Documents)

[0004] Patent Document 1: Japanese Patent Application Publication No. 2017-045924. [Summary of the Invention]

[0005] [Problem to be Solved by the Invention] When an ultrasonic wave is applied to bond a copper conductor at the end of an electrical wire to a terminal, if the copper conductor lacks flexibility, especially if a gap forms between the copper conductor and the terminal, the bonding strength between the terminal and the wire will be low, resulting in reduced tensile durability of the resulting terminald wire. Therefore, it is sought to obtain a copper conductor that exhibits high tensile durability when bonded to a terminal to form a terminald wire.

[0006] Regarding this point, the bonding wire described in Patent Document 1 is a copper alloy bonding wire with a wire diameter of 15 μm or more and 20 μm or less, and does not focus on copper conductors with a larger diameter. Furthermore, during ultrasonic bonding, the wire is made easier to deform by applying ultrasound, thereby promoting the bonding between the copper conductor and the terminal. However, there is still room for improvement in terms of improving the tensile durability of the terminal wire when the copper conductor is bonded to the terminal.

[0007] Therefore, the present invention addresses the aforementioned technical problems by providing a copper conductor, a stranded conductor using the copper conductor, and an electrical wire. When terminals are joined to the copper conductor to form a terminald wire, the copper conductor facilitates the connection between the copper conductor and the terminals, and improves the tensile durability of the terminald wire. [Technical Means for Solving the Problem]

[0008] The inventors dedicated themselves to research and discovered the following insights, which led to the completion of this invention: by increasing the proportion of grains with <011>, <012>, or <123> crystal orientations in the total area of ​​grains contained in the measurement region within the cross-section, the copper conductor will be easily deformed by applying ultrasound to the copper conductor when the copper conductor or stranded conductor is joined to the terminal to form a terminald wire. This reduces the gap at the joint between the copper conductor and the terminal or the gap inside the stranded conductor, thereby promoting the joint between the copper conductor and the terminal and improving the tensile durability of the terminald wire.

[0009] In order to achieve the above objective, the main components of the present invention are as follows. (1) A copper-based conductor, in the crystal orientation analysis performed by electron backscattering diffraction (EBSD) at a cross section perpendicular to the extension direction of the aforementioned conductor, after defining an orthogonal xy coordinate system in the aforementioned cross section, assuming that the direction on the x-axis is the first direction and the direction on the y-axis is the second direction, the crystal orientation within ±8° of the <011> crystal orientation is set as the <011> crystal orientation group, the crystal orientation within ±8° of the <012> crystal orientation is set as the <012> crystal orientation group, and the crystal orientation within ±8° of the <123> crystal orientation is set as the <123> crystal orientation group, the first crystal orientation selected in the aforementioned cross section In a measurement region, the average of the first total area and the second total area accounts for a proportion of the total area of ​​the grains contained in the first measurement region, that is, the total cumulative rate is 40% or more. The first total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group and the aforementioned <123> crystal orientation group relative to the aforementioned first direction. The second total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group and the aforementioned <123> crystal orientation group relative to the aforementioned second direction. (2) The copper conductor as described in (1) above, wherein when the aforementioned cross-section is divided into a central portion and an outer ring portion surrounding the aforementioned central portion, in the second measurement region selected within the aforementioned central portion of the aforementioned cross-section, the average of the first total area and the second total area accounts for a proportion of the total area of ​​the grains contained in the aforementioned second measurement region, that is, the total cumulative rate is 50% or more. The first total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group, and the aforementioned <123> crystal orientation group relative to the aforementioned first direction. The second total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group, and the aforementioned <123> crystal orientation group relative to the aforementioned second direction. (3) The copper conductor as described in (1) or (2) above, wherein the average crystal grain size of the grains present in the aforementioned cross-section is less than 20.0 μm. (4) A stranded conductor formed by stranding multiple copper-based raw material wires, wherein the copper-based raw material wires are composed of any one of the copper-based conductors described in (1) to (3) above. (6) An electrical wire formed by forming at least an insulating coating layer on the surface of the copper-based conductor described in (1), (2) or (3) above, or the stranded conductor described in (4) above. [Effects of the Invention]

[0010] According to the present invention, a copper conductor, a stranded conductor using the copper conductor, and an electric wire are provided, wherein when a terminal is joined to the copper conductor to form a terminald wire, the copper conductor can promote the joining between the copper conductor and the terminal and improve the tensile durability of the terminald wire.

Implementation Method

[0012] Hereinafter, a preferred embodiment of the copper-based conductor of the present invention will be described in detail. Furthermore, in the composition of the copper-based conductor of the present invention, sometimes "mass %" is simply indicated as "%".

[0013] In the copper-based conductor according to the present invention, in the crystal orientation analysis performed by electron backscattering diffraction (EBSD) at a cross-section perpendicular to the conductor's extension direction, after defining an orthogonal xy coordinate system within the cross-section, assuming the direction on the x-axis is the first direction and the direction on the y-axis is the second direction, crystal directions within ±8° of the <011> crystal direction are designated as the <011> crystal direction group, crystal directions within ±8° of the <012> crystal direction are designated as the <012> crystal direction group, and crystal directions within ±8° of the <123> crystal direction are designated as the <123> crystal direction group, in the first measurement region selected within the cross-section, the average of the first total area and the second total area... The percentage of the total area of ​​the grains contained in the first measurement region, also known as the total cumulative rate (hereinafter sometimes referred to as "the total cumulative rate of grains with <011>, <012> and <123> crystal group in the total area of ​​the grains contained in the first measurement region") is 40% or more. The first total area is obtained by summing the areas of grains with <011>, <012> and <123> crystal group relative to the first direction. The second total area is obtained by summing the areas of grains with <011>, <012> and <123> crystal group relative to the second direction.

[0014] In particular, in the copper-based conductor of the present invention, the total cumulative rate of grains having <011>, <012> and <123> crystal orientation groups in the total area of ​​grains included in the first measurement region in the cross section is set to 40% or more, thereby controlling the crystal orientation of the grains appearing in the cross section, and thereby increasing the proportion of grains having <011>, <012> and <123> crystal orientation groups among the grains appearing in the first measurement region in the cross section. The grains having <011>, <012> and <123> crystal orientation groups can be deformed with less force when ultrasound is applied. Therefore, when using ultrasonic bonding to join terminals to copper conductors to make terminald wires, the copper conductors become easier to deform, thereby reducing the gap at the joint between the copper conductor and the terminal or the gap inside the stranded conductor. As a result, the bonding between the copper conductor and the terminal is promoted, and the tensile durability of the terminald wires is improved.

[0015] The copper conductor according to the present invention provides a copper conductor, a stranded conductor using the copper conductor, and a wire, which exhibits high tensile durability when terminals are joined to the copper conductor to form a terminald wire. Therefore, when using ultrasonic bonding to manufacture terminald wires for electrical products or automotive interiors, the copper conductor can be easily deformed to facilitate bonding with the terminals, thus enabling stable bonding between the copper conductor and the terminals and facilitating high-quality wire connections. Furthermore, the copper conductor according to the present invention can be easily deformed by applying ultrasound, making it suitable for bonding wires that are deformed to be joined to semiconductor wafers.

[0016] [1] The metal structure of the copper conductor According to the copper conductor of the present invention, the total cumulative percentage of grains having the <011>, <012> and <123> crystal orientation groups in the total area of ​​the grains included in the first measurement region is 40% or more. Here, in order to make the copper conductor easy to deform by applying ultrasound, it is important to control the direction of deformation of the copper conductor to the direction of the crystal orientation of the grains. In this regard, the inventors have found that by increasing the number of grains having the <011>, <012> and <123> crystal orientation groups relative to the direction of deformation of the copper conductor, the copper conductor can be easily deformed with a weaker force. Here, if the total cumulative percentage of grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains included in the first measurement region is less than 40%, a greater force must be applied to the direction to be deformed because the cumulative percentage of grains with other crystal orientations is relatively higher. Therefore, the total cumulative percentage of grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains included in the first measurement region is preferably 60% or more, and more preferably 80% or more. On the other hand, there is no particular upper limit to the total cumulative percentage of grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains included in the first measurement region; for example, it can be 100%.

[0017] The cumulative percentage of the total area of ​​the grains contained in the first measurement region within the cross-section, representing the total area of ​​grains with crystal orientation groups <011>, <012>, and <123>, can be obtained, for example, from crystal orientation analysis data. This data is obtained by continuously measuring crystal orientation data using an EBSD detector (manufactured by TSL Ltd., OIM5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (manufactured by JEOL Ltd., JSM-7001FA), and then calculating (processing) the measured crystal orientation data using analysis software (manufactured by TSL Solutions Ltd., OIM Analysis). "EBSD" is an abbreviation for Electron BackScatter Diffraction, a crystal orientation analysis technique that utilizes reflected electron Kikuchi line diffraction, which is generated when electron beams are irradiated onto a copper-based conductor used as the measurement sample within a scanning electron microscope (SEM). The object of measurement is a surface formed by grinding and mirror polishing a cross section perpendicular to the extension direction of a copper conductor. The measurement area is a first measurement region selected within the cross section, but it can be the entire area of ​​the cross section. When a portion of the cross section is designated as the first measurement region, the measurement region can be, for example, 200 μm to 500 μm square. Grinding of the cross section can be performed using a cross section polisher (registered trademark), or by means of mirror polishing such as wet grinding, FIB, and slicing machines, regardless of the specific method used. Based on the obtained crystal orientation data, on the IPF map, two directions perpendicular to the length of the wire are selected and differed by 90° to define an orthogonal xy coordinate system. The direction on the x-axis is defined as the first direction and the direction on the y-axis as the second direction. Based on the chart-crystal direction obtained using analytical software, when the boundary with an azimuth difference of more than 15° from the adjacent measurement point is defined as the grain interface (grain boundary), the set of measurement points that are continuous within the range contained by the grain boundary is defined as the grain. That is, the crystal orientation within ±8° of the <011> crystal orientation can be defined as the <011> crystal orientation group, the crystal orientation within ±8° of the <012> crystal orientation can be defined as the <012> crystal orientation group, and the crystal orientation within ±8° of the <123> crystal orientation can be defined as the <123> crystal orientation group. At this time, for the first and second directions, the area ratio of each grain with the <011>, <012> and <123> crystal orientation groups in the total area of ​​the grains contained in the first measurement region is measured. At the same time, this measurement is usually performed 3 times (n=3) at different locations in the first measurement region, and the average area ratio of the grains with each crystal orientation group obtained from the 3 measurements is calculated.Then, based on the average area ratio of the crystal examples with each crystal orientation group for the first and second directions, the total cumulative rate of the grains with each crystal orientation group is calculated. By calculating the average of the first and second directions, the measured value of the proportion of the total cumulative rate of the grains with <011>, <012> and <123> crystal orientation groups in the total area of ​​the grains contained in the first measurement region can be obtained.

[0018] Furthermore, according to the present invention, the copper-based conductor is preferably such that, when the cross-section is divided into a central portion and an outer ring surrounding the central portion, in a second measurement region selected within the central portion of the cross-section, the average of the first total area and the second total area accounts for a proportion of the total area of ​​the grains contained in the second measurement region, i.e., the total accumulation rate (hereinafter, sometimes referred to as "the total accumulation rate of grains having <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains contained in the second measurement region") is 50% or more. The first total area is obtained by summing the areas of grains having <011>, <012>, and <123> crystal orientation groups relative to the first direction, and the second total area is obtained by summing the areas of grains having <011>, <012>, and <123> crystal orientation groups relative to the second direction. When a copper-based conductor is deformed by applying ultrasound, it tends to deform in the direction of compression. Therefore, by setting the total cumulative percentage of grains with <011>, <012>, and <123> crystal groups in the second measurement region selected within the center of the cross-section to 50% or more, the copper-based conductor becomes easier to deform from its center, allowing for deformation with less force. Therefore, the total cumulative percentage of grains with <011>, <012>, and <123> crystal groups in the total area of ​​the grains included in the second measurement region is preferably 60% or more, and more preferably 80% or more.

[0019] Here, the "center of the cross-section" in this specification has the same center of gravity as the center of gravity of the cross-section when viewed perpendicular to the extension direction of the copper conductor, and is defined as a region with a shape similar to the cross-section having an area of ​​1 / 9 of the cross-section from that center of gravity. For example, when the copper conductor is a circular wire, it can also be defined as the same center (center of gravity) as the center of the circular cross-section when viewed perpendicular to the extension direction of the copper conductor, and is defined as a region within a concentric circle with a diameter of 1 / 3 of the cross-section from that center (center of gravity).

[0020] The cumulative percentage of grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​grains contained in the second measurement region within the cross-section can be calculated, for example, by taking the second measurement region, which is the center of the cross-section, as the measurement object and following the same steps as when the first measurement region is taken as the measurement object. That is, for the first and second directions, the area ratio of grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​grains contained in the second measurement region is measured. At the same time, this measurement is usually performed 3 times (n=3) at different locations in the second measurement region, and the average of the area ratio of grains with each crystal orientation group obtained from the 3 measurements is calculated. Then, based on the average area ratio of the crystal examples with each crystal direction group for the first and second directions, the total cumulative rate of the grains with each crystal direction group is calculated. By calculating the average for the first and second directions, a measured value can be obtained of the proportion of the total cumulative rate of the grains with <011>, <012>, and <123> crystal direction groups in the total area of ​​the grains contained in the second measurement region. Here, the crystal direction data used to calculate the total cumulative rate of the grains with <011>, <012>, and <123> crystal direction groups in the total area of ​​the grains contained in the second measurement region can be data extracted from the crystal direction data obtained by electron backscattering diffraction (EBSD) method performed on the second measurement region.

[0021] According to the copper-based conductor of the present invention, it is preferable that the average grain size of the grains present in the cross-section is less than 20.0 μm. This allows for the suppression of bonding deviations when ultrasonically bonding a copper-based conductor or a stranded conductor formed by stranding multiple copper-based conductors to a terminal, thus enabling a more stable bonding. Therefore, the average grain size of the grains present in the cross-section is preferably 15.0 μm or less, and more preferably 10.0 μm or less. On the other hand, there is no particular limitation on the lower limit of the grain size; for example, from the viewpoint of making the copper-based conductor easier to deform, 1.0 μm can be set as the lower limit.

[0022] Here, the average grain size of the copper conductor is determined by using the entire cross-section as the analysis object and selecting the chart-grain size (diameter) of the analysis software in the analysis of crystal orientation data obtained by the electron backscattering diffraction (EBSD) method. This allows the average grain size calculated by the area method to be set as the average grain size. More specifically, when the boundary with an azimuth difference of 15° or more from adjacent measurement points is defined as the grain interface, the number of consecutive measurement points within the area surrounded by the grain boundary and the measurement step size can be used to set the average diameter of the circle corresponding to the grain when calculating the cross-sectional area of ​​the grain.

[0023] [2] The raw material of the copper conductor is copper or copper alloy. Here, the copper conductor may be, for example, a copper alloy containing a small amount of elements such as silver (Ag), chromium (Cr), zirconium (Zr), and tin (Sn), but from the viewpoint that the copper conductor is easier to bend, copper is preferred, and more specifically, pure copper of 99.00% by mass or more. Among these, from the viewpoint that the higher the copper content, the higher the conductivity, it is preferred to be tough copper composed of copper (Cu) of 99.90% by mass or more and unavoidable impurities, and even more preferably oxygen-free copper composed of Cu of 99.96% by mass or more, oxygen of less than 10 ppm and unavoidable impurities.

[0024] The copper alloy constituting the copper-based conductor preferably has the following alloy composition, which contains at least one of Ag (0.1% to 1.0% by mass), Cr (0.1% to 1.0% by mass), Zr (0.1% to 1.0% by mass), and Sn (0.1% to 1.0% by mass), and the remainder consists of Cu and unavoidable impurities.

[0025] If the content of at least any one of Ag, Cr, Zr, and Sn is 0.1% by mass or more, the tensile durability of copper conductors can be improved. Therefore, even when the cross-sectional area of ​​the connection deformed by ultrasonic bonding is small, the wire can still withstand tensile loads without breaking. On the other hand, if the content of at least any one of Ag, Cr, Zr, and Sn exceeds 1.0% by mass, it may cause a decrease in the conductivity of copper conductors. Therefore, in order to use copper conductors as wires, it is preferable to add them at low concentrations. From this point of view, the upper limit of the Ag content when the copper alloy contains Ag is preferably 0.7% by mass or less, and more preferably 0.4% by mass or less. The upper limit of the Cr content when the copper alloy contains Cr is preferably 0.7% by mass or less, and more preferably 0.4% by mass or less. Regarding the Zr content in copper alloys containing Zr, the upper limit is preferably below 0.7% by mass, and more preferably below 0.4% by mass. Regarding the Sn content in copper alloys containing Sn, the upper limit is preferably below 0.7% by mass, and more preferably below 0.4% by mass.

[0026] The remaining portion other than the aforementioned elements is unavoidable impurity. Unavoidable impurities refer to impurities that are inevitably introduced during the manufacturing process. Since the content of unavoidable impurities may reduce the conductivity of copper-based conductors, it is preferable to have a low content of unavoidable impurities.

[0027] Unavoidable impurities contained in copper-based conductors include, for example, elements such as aluminum (Al), beryllium (Be), cadmium (Cd), iron (Fe), magnesium (Mg), nickel (Ni), phosphorus (P), lead (Pd), silicon (Si), and titanium (Ti). Furthermore, unavoidable impurities may also include small amounts of silver (Ag), chromium (Cr), zirconium (Zr), and tin (Sn) in the alloy composition of the aforementioned copper alloys, where the required content is not met. Moreover, the upper limit for the content of unavoidable impurities is preferably 30 ppm or less in total for the aforementioned elements.

[0028] [3] Shape and application of copper conductors The shape of copper conductors is a circular or slightly circular cross-section that is perpendicular to the extension direction of copper conductors. Its size can be appropriately selected according to the current required in the electrical products and automobiles to be wired and the wiring space.

[0029] Here, when the copper conductor is made of copper wire with a round shape, it is preferable from the viewpoint that a higher current can flow through the copper wire if the diameter of the copper wire (round wire) is 0.13 mm or more. In addition, it is preferable from the viewpoint that the diameter of the copper wire (round wire) is 0.54 mm or less if the copper conductor is easily deformed when ultrasonic waves are applied.

[0030] Furthermore, multiple strands of copper-based raw material wires composed of the aforementioned copper-based conductors can be twisted together to form a stranded conductor. In this case, a stranded conductor can be obtained that is easy to bend, easily deformable when ultrasonically bonded, and has high bonding strength to the terminals. Here, there is no limitation on the number of strands in the stranded conductor and the total cross-sectional area of ​​the stranded wire. A small-diameter stranded conductor can also be formed by twisting copper-based conductors of the aforementioned wire diameter with a number of strands ranging from 7 to 171. This allows for easy bonding using ultrasonic bonding and requires less wiring space.

[0031] Furthermore, the copper-based conductor of the present invention is preferably used for electrical wires. More specifically, it can be configured as an electrical wire having at least an insulating coating layer formed on the surface of the aforementioned copper-based conductor or stranded conductor.

[0032] Here, the material of the insulating coating is not particularly limited, but preferably it is a coating made of ethylene chloride, which can be formed by extruding molten resin onto the surface of a copper conductor or a stranded conductor.

[0033] Furthermore, according to the present invention, the copper conductor is preferably such that, when ultrasonically joined with a terminal to obtain a terminal wire, the height h of the joint is in the range of 1 / 3 or more and 2 / 3 or less when the outer diameter (stretched outer diameter) of the stranded conductor before joining is set to 1. If the height h of the joint exceeds 2 / 3 of the stranded outer diameter, more gaps will remain at the joint between the copper conductor and the terminal or inside the stranded conductor, thus reducing the tensile durability of the terminal wire. Therefore, the height h of the joint is preferably 0.55 or less, more preferably 0.45 or less, when the outer diameter (stretched outer diameter) of the stranded conductor before joining is set to 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 will be smaller, making it difficult to allow a specific current to flow in the terminal wire. In this case, the reduced cross-sectional area of ​​the joint will also easily lead to insufficient tensile durability. Therefore, when the outer diameter (stretching outer diameter) of the stranded conductor before joining is set to 1, the height h of the joint is preferably 0.34 or more, and more preferably 0.38 or more.

[0034] Here, as shown in Figure 1, when observing a longitudinal section perpendicular to the length direction (extension direction of the copper conductor 10) of the stranded conductor 1 of the attached terminal wire, the height h of the joint can be set as the maximum height of the stranded conductor 1 from the surface 2a of the flat plate portion 2 of the copper terminal. Furthermore, in the stranded conductor 1 shown in Figure 1, the stranded conductor 1 is formed by twisting multiple strands of copper conductor 10 into a spiral shape to form multiple layers around the center conductor wire 11 composed of a single strand of copper conductor 10. Therefore, the cross-section of the copper conductor 10 twisted into a spiral shape is slightly elliptical.

[0035] Furthermore, the copper conductor according to the present invention is preferably an ultrasonically bonded terminal wire in which the terminal extends on one side of the joint and the stranded conductor extends on the other side of the joint. When a tensile test is performed based on JIS Z2241 to fix the terminal on one side and the stranded conductor on the other side, the wire does not break at the joint, and the measured tensile strength is 70 MPa or more. In such a terminal wire, the terminal is firmly bonded to the copper conductor, thus exhibiting high tensile durability. Therefore, the tensile strength of the terminal wire is preferably 100 MPa or more, and more preferably 150 MPa or more.

[0036] Copper or a copper alloy is preferably used as the material joined to the copper-based conductor according to the present invention. Here, from the viewpoint of applications requiring the flow of large currents, pure copper with high conductivity is preferably used as the terminal material. Furthermore, from the viewpoint of utilizing the elasticity of the terminal material as a fitting part, a high-strength copper alloy is more preferably used as the terminal material. Here, the raw materials of the copper-based conductor described above can be used as the terminal material, or the same material as the copper-based conductor can be used.

[0037] [4] An Example of a Method for Manufacturing a Copper Conductor Next, a method for manufacturing a copper conductor according to an embodiment will be described. In the method for manufacturing a copper conductor according to an embodiment, isotropic processing is performed in the diameter direction of the copper conductor, especially in the wire drawing step, and in the subsequent first heat treatment step and second heat treatment step, a specific crystal orientation when viewed from a direction perpendicular to the length direction of the wire is controlled by two-stage electric annealing. In this way, the proportion of the average value of the first total area and the second total area in the total area of ​​the grains contained in the first measurement region, that is, the total accumulation rate, can be increased.

[0038] In the manufacturing method of the copper-based conductor of the embodiment, a casting step is first performed. In the casting step, electrolytic copper is melted under a reducing atmosphere to obtain a cylindrical ingot called a billet.

[0039] An extrusion step is performed after the casting step. In the extrusion step, the waste material is processed into a round bar state by hot extrusion.

[0040] A wire drawing step is performed after the extrusion step. In the wire drawing step, the round bar or thick wire obtained from the above steps is drawn until it reaches a specified wire diameter. Here, a peeling step to remove surface defects generated up to the above steps is preferably included in the wire drawing step. In addition, to facilitate wire drawing while removing processing strain, one or more heat treatment steps may be performed before the wire drawing step as needed.

[0041] When forming a stranded conductor after the wire drawing step, a stranding step can be performed, which involves twisting multiple strands of drawn copper conductor together to form a stranded conductor. At this time, a compression die can be used to make a compressed conductor, or the copper conductor can be directly stranded in a non-compressed state without using a compression die.

[0042] Subsequently, a heat treatment step is performed on the copper conductor or the stranded conductor. Here, as a heat treatment step performed on the copper conductor or the stranded conductor, a first heat treatment step and a second heat treatment step are performed. In this way, the proportion of the average of the first total area and the second total area in the total area of ​​the grains included in the first measurement region, that is, the total accumulation rate, can be set to 40% or more.

[0043] In the first and second heat treatment steps, an electric current-driven annealing process is performed, in which current flows through the wire passing between multiple pulleys that function as electrodes. By performing electric current-driven annealing in the first and second heat treatment steps, the copper conductor or stranded conductor can be heated in a short time. Therefore, after a large number of smaller grains are simultaneously generated due to recrystallization in the first heat treatment step, these grains are grown in the second heat treatment step. As a result, the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains contained in the first measurement region can be increased.

[0044] In the first heat treatment step and the second heat treatment step, the temperature and time for heating the copper conductor or stranded conductor can be appropriately adjusted according to the desired ratio of the area of ​​the grains having the <011> crystal group, the <012> crystal group and the <123> crystal group.

[0045] For example, if the temperature at which the copper conductor or stranded conductor is heated in the first heat treatment step is too high, the formation and growth of grains generated by recrystallization will occur simultaneously. Therefore, the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains exposed in the cross-section of the copper conductor will become difficult to increase. In addition, if the heating temperature in the first heat treatment step is too high, the grains will easily become unnecessarily large. On the other hand, if the temperature at which the copper conductor or stranded conductor is heated in the first heat treatment step is too low, it will become difficult to induce the rearrangement of atoms generated by heating and the formation of grains generated by recrystallization. Therefore, the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains exposed in the cross-section of the copper conductor will become difficult to increase. Here, the heating temperature of the copper conductor or stranded conductor can be increased by increasing the current flowing through the copper conductor or stranded conductor in the first heat treatment step, and the heating temperature of the copper conductor or stranded conductor can be decreased by decreasing the current flowing through the copper conductor or stranded conductor in the first heat treatment step.

[0046] Furthermore, if the heating time of the copper conductor or stranded conductor in the first heat treatment step is too long, it is easy to induce the growth of grains due to recrystallization. Therefore, the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains exposed in the cross-section of the copper conductor will not be easily increased. That is, by shortening the heating time of the copper conductor or stranded conductor in the first heat treatment step, excessive grain growth can be suppressed, thereby increasing the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains exposed in the cross-section of the copper conductor.

[0047] In the subsequent second heat treatment step, if the temperature at which the copper conductor or stranded conductor is heated is too low, it becomes difficult to induce grain growth due to recrystallization. Therefore, it becomes difficult to increase the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains exposed in the cross-section of the copper conductor. On the other hand, if the temperature at which the copper conductor or stranded conductor is heated is too high in the second heat treatment step, excessive grain growth will cause a decrease in deformation resistance, thus increasing the risk of wire breakage, which is undesirable. Here, the temperature at which the copper conductor or stranded conductor is heated can be increased by increasing the current flowing through it in the second heat treatment step, and the temperature at which the copper conductor or stranded conductor is heated can be decreased by decreasing the current flowing through it in the second heat treatment step.

[0048] Furthermore, if the heating time of the copper conductor or stranded conductor is shortened in the second heat treatment step, excessive grain growth can be suppressed, so the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains exposed in the cross-section of the copper conductor can be adjusted to be higher. On the other hand, if the heating time of the copper conductor or stranded conductor is increased in the second heat treatment step, the grains will grow, so the proportion of the area of ​​grains with <011>, <012>, and <123> crystal groups in the total area of ​​grains exposed in the cross-section of the copper conductor will not easily become higher.

[0049] Furthermore, during the first and second heat treatment steps, when performing energized annealing, the temperature of the copper conductor or stranded conductor may rise instantaneously, making it difficult for the thermocouple to keep up with the response speed and thus difficult to control the correct temperature. Therefore, when setting the heat treatment conditions for energized annealing, the voltage, current value, wire speed, and electrode distance are set based on the actual total cumulative rate of the copper conductor after the heat treatment step and the above description, thereby obtaining a copper conductor with the desired total cumulative rate.

[0050] Preferably, an electrical wire is made by forming an insulating coating layer by extruding molten resin onto the surface of the stranded conductor thus obtained.

[0051] The embodiments of the present invention have been described above. However, the present invention also includes all embodiments encompassed within the concept and scope of the present invention, and various changes can be made within the scope of the present invention, without being limited to the embodiments described above. [Example]

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

[0053] (Production of Copper Conductors A to H) A casting step, an extrusion step, and a wire drawing step are performed on the copper-based material composed of the components shown in Table 1 to form a thick wire with a diameter of 8 mm. Then, a wire drawing step is further performed to process it into a round wire with the diameter shown in Table 1. Next, a first heat treatment step is performed using the conditions shown in Table 1. Here, for copper conductor H, whose heat treatment type is marked as "batch annealing," the heat treatment temperature is set to 500°C, and the holding time at the heat treatment temperature is set to 2 hours. Then, for copper conductors A to F, whose presence or absence of a second heat treatment step is marked as "yes" in Table 1, a second heat treatment step is performed using the conditions shown in Table 1 to obtain copper conductors. On the other hand, for copper conductors G and H, whose presence or absence of a second heat treatment step is marked as "no," only the first heat treatment step is performed to obtain copper conductors without performing the second heat treatment step.

[0054] (Examples 1-18 of the present invention and Comparative Examples 1-6) From the copper conductors A-H obtained above, a stranding step to form a stranded conductor is performed by stranding raw material wires composed of copper conductors of the types shown in Tables 4, 5, and 6, thereby obtaining a stranded conductor. Then, an insulating coating layer is formed by extruding molten resin composed of polyvinyl chloride onto the surface of the obtained stranded conductor to obtain an electrical wire.

[0055] [Various Measurement and Evaluation Methods] The copper-based conductors and stranded conductors of the present invention and comparative examples described above were used to evaluate the characteristics as shown below. The evaluation conditions for each characteristic are as follows.

[0056] [1] Composition analysis was performed using a luminescence spectrophotometer (manufactured by Shimadzu Corporation) to measure and analyze the flat sample made by pressing the coarse wire obtained in the wire drawing step of the above manufacturing stage. The measurement was performed with n=3, and the average value was calculated and shown in Table 1. Columns were set up to record the values ​​of elements that were intentionally added, and these elements were included in the total of unavoidable impurities when they were not intentionally added. Furthermore, if the detected amount of a component is less than 0.001% by mass, it is considered that the component is not present and is recorded as "-" in the table.

[0057] [2] Determination of the total cumulative rate of grains with <011>, <012> and <123> crystal orientation groups in the total area of ​​grains contained in the first measurement region When measuring the total cumulative rate of grains with <011>, <012> and <123> crystal orientation groups in the total area of ​​grains contained in the first measurement region, it can be performed as follows: After continuously measuring and collecting EBSD patterns using an EBSD detector (manufactured by TSL Ltd., OIM5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (manufactured by Japan Electronics Corporation, JSM-7001FA), the crystal orientation data obtained from the EBSD patterns is analyzed using analysis software (manufactured by TSL Solutions Ltd., OIM Analysis) to obtain crystal orientation analysis data. The object of measurement is a surface formed by grinding and mirror polishing a cross-section perpendicular to the extension direction of the copper conductor (or, in the case of a stranded conductor, one strand of copper conductor). The entire area of ​​the cross-section is defined as the first measurement region. Measurements are performed in increments of 0.5 μm. Subsequently, based on the obtained crystal orientation data, on the IPF map, two directions perpendicular to the length of the wire and 90° apart are selected to define an orthogonal xy coordinate system. The direction on the x-axis is defined as the first direction and the direction on the y-axis as the second direction. Based on the chart-crystal direction obtained using analytical software, when the boundary with a difference of more than 15° from the adjacent measurement point is defined as the grain interface (grain boundary), the set of measurement points that are continuous within the range contained by the grain boundary is defined as the grain. That is, the crystal orientation within ±8° of the <011> crystal orientation is defined as the <011> crystal orientation group, the crystal orientation within ±8° of the <012> crystal orientation is defined as the <012> crystal orientation group, and the crystal orientation within ±8° of the <123> crystal orientation is defined as the <123> crystal orientation group. At this point, for both the first and second directions, the area ratios (A1-A3, A5-A7) of the grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains contained in the first measurement region are measured at different locations within the first measurement region. This measurement is then performed three times (n=3), and the average of the three measurements is calculated. The total area ratio of the grains with <011>, <012>, and <123> crystal orientation groups is then calculated and set as the total cumulative rate (A4, A8). Subsequently, based on the measured values ​​of the total cumulative rates (A4, A8) calculated for the first and second directions respectively, the average of the total cumulative rates for the first and second directions ((A4+A8) / 2) is calculated and presented in Table 2.

[0058] [3] Determination of the total cumulative percentage of grains with <011>, <012> and <123> crystal orientation groups in the total area of ​​grains contained in the second measurement region. The total cumulative percentage of grains with <011>, <012> and <123> crystal orientation groups in the total area of ​​grains contained in the second measurement region is determined by taking the center of the circular cross-section when observing the copper conductor, and setting the area of ​​concentric circles with a diameter of 1 / 3 relative to the first measurement region as the second measurement region. The first measurement region is selected from the crystal orientation analysis data obtained by the electron backscattering diffraction (EBSD) method. Using the same procedure as for the first measurement region, the area ratio (B1-B3, B5-B7) of grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains contained in the second measurement region was measured for each of the first and second directions. This measurement was performed three times (n=3) at different locations within the first measurement region, and the average of the three measurements was calculated. The total area ratio of grains with <011>, <012>, and <123> crystal orientation groups was then calculated and set as the total cumulative rate (B4, B8). Subsequently, based on the measured values ​​of the total cumulative rates (B4, B8) calculated for the first and second directions respectively, the average of the total cumulative rates for the first and second directions ((B4+B8) / 2) was calculated and presented in Table 3.

[0059] [4] Determination of the average grain size of the grains present in the cross-section of the copper conductor. In the analysis of crystal orientation data by the electron backscattering diffraction (EBSD) method described above, the entire cross-section is used as the analysis object and the chart-grain size (diameter) of the analysis software is selected. Then, the average grain size calculated by the area method is set as the average grain size. The results are shown in Table 3.

[0060] [5] Evaluation of the connection height when ultrasonically bonding stranded conductor to terminal For a wire having the stranded conductor obtained above, a stranded conductor with 40 mm of sheathing material stripped and a flat terminal with a width of 10 mm, a depth of 40 mm and a thickness of 2 mm are prepared. The stranded conductor is brought into contact with the flat portion of the copper terminal to perform ultrasonic bonding, thereby obtaining a terminald wire. The ultrasonic bonding is performed with an ultrasonic frequency of 20 kHz and a bonding time of 0.4 seconds. At this time, the input energy generated by the ultrasonic wave is set to 600 J when using a wire with a cross-sectional area of ​​3 sq (about 3.30 mm2), 1000 J when using a wire with a cross-sectional area of ​​5 sq (about 5.23 mm2), and 3000 J when using a wire with a cross-sectional area of ​​15 sq (about 13.75 mm2). Here, sq, as a unit, refers to the area of ​​a conductor and is a unit used for marking electrical wires (e.g., the cross-sectional area of ​​the stranded conductor in a 3 sq wire is approximately 3 mm2).

[0061] Make two of the attached terminal wires, observe the longitudinal sections that are parallel along the length direction of the stranded conductor (the extension direction of the copper conductor), and as shown in Figure 1, set the maximum height of the stranded conductor 1 from the surface 2a of the flat plate portion 2 of the copper terminal as the height h of the joint, and set the average value of the height h of the joint in the two attached terminal wires as the measured value of the height h of the joint [mm].

[0062] Regarding the measured value of the height h of the joint, if it is in the range of 1 / 3 to 2 / 3 when the outer diameter (stretched outer diameter) of the stranded conductor before jointing is set to 1, it is considered good and evaluated as "○ (Good)" because there are few gaps in the joint between the copper conductor and the terminal or in the interior of the stranded conductor, and the copper conductor and the terminal are well joined. On the other hand, if the measured value of the height h of the joint exceeds 2 / 3 when the outer diameter (stretched outer diameter) of the stranded conductor before jointing is set to 1, it is considered poor and evaluated as "× (Poor)" because there are many gaps in the joint between the copper conductor and the terminal or in the interior of the stranded conductor, and the copper conductor and the terminal are not well joined. Furthermore, on the other hand, when the measured value of the joint height h is less than 1 / 3 when the outer diameter of the stranded conductor before jointing (stretched outer diameter) is set to 1, it is considered undesirable to make the attached terminal wire due to the small cross-sectional area of ​​the stranded conductor, making it difficult to allow a specific current to flow. Therefore, it is evaluated as "× (unsatisfactory)". In the present invention example and comparative example, "○" is evaluated as a qualified level. The results are shown in Tables 4, 5 and 6.

[0063] [6] Tensile test and evaluation of terminal wire The tensile strength of the terminal wire is determined by preparing two test pieces of terminal wire and performing a tensile test on these test pieces with the terminal on one side and the stranded conductor on the other side fixed in accordance with JIS Z2241. The point where the terminal wire breaks is found, and the tensile strength Rm is obtained from the tensile test results. The average of the tensile strength Rm of the two terminal wires is set as the measured value of the tensile strength [MPa]. The test piece of the terminal wire has a joint with a length of 10 mm at the position where the terminal and the stranded conductor overlap, and the terminal extends 40 mm on one side of the joint and the stranded conductor extends 140 mm on the other side of the joint. Furthermore, the tensile strength of the terminal wire is set as the value calculated by dividing the force when the terminal wire breaks during the tensile test by the cross-sectional area of ​​the stranded conductor before the joint, which is a unit area.

[0064] Regarding the tensile test results, if the fracture points of both terminal wires are not at the joint and the measured tensile strength is 70 MPa or higher, the terminal wire is considered good and rated as "○ (Good)" because the copper conductor and the terminal are firmly bonded and the tensile durability of the terminal wire is high. On the other hand, if at least one terminal wire fractures at the joint or the measured tensile strength is less than 70 MPa, the terminal wire is considered poorly made and rated as "× (Poor)" because the bond between the copper conductor and the terminal is weak. In the present invention example and comparative example, "○" is rated as acceptable. The results are shown in Tables 4, 5, and 6.

[0065] [7] In the comprehensive evaluation, if both of the two evaluation results regarding the height of the connection portion when the stranded conductor is ultrasonically joined to the terminal and the tensile test results of the wire attached to the terminal are rated as "○", then the comprehensive evaluation is rated as "○" because both the height of the connection portion to the terminal and the tensile test results of the wire attached to the terminal are excellent. On the other hand, if either of the two evaluation results regarding the height of the connection portion to the terminal and the tensile test results of the wire attached to the terminal is rated as "×", then the comprehensive evaluation is rated as "×" because at least one of these two characteristics is insufficient. The results are shown in Tables 4, 5 and 6.

[0066] [Table 1]

[0067] [Table 2] Metallic structure of copper conductors The proportion of the total area of ​​the grains contained in the first measurement region The area ratio of grains with the <011> crystal orientation group relative to the first direction (A1) [%] The area ratio of grains with the <012> crystal orientation group relative to the first direction (A2) [%] The area ratio of grains with the <123> crystal orientation group relative to the first direction (A3) [%] Area ratio relative to the total area in the first direction (A7= (A1+A2+A3) [%] The area ratio of grains with the <011> crystal orientation group relative to the second direction (A4) [%] The area ratio of grains with the <012> crystal orientation group relative to the second direction. (A5) [%] The area ratio of grains with the <123> crystal orientation group relative to the second direction. (A6) [%] Area ratio relative to the total area in the second direction (A8= (A4+A5+A6) [%] (A7+A8) / 2 [%] Copper conductor A 10 25 5 40 20 11 19 50 45 Copper conductor B 7 7 30 44 30 15 38 83 64 Copper conductor C 28 15 37 80 5 6 28 39 60 Copper conductor D twenty four 13 twenty two 59 13 33 4 50 55 Copper conductor E 1 25 52 78 8 4 66 78 78 Copper conductor F 17 28 28 73 16 27 27 70 72 Copper conductor G 10 20 twenty one 51 0 1 18 19 35 Copper conductor H 0 0 6 6 11 30 3 44 25 (Note) The underlined bold text in the table indicates situations outside the proper scope of the present invention.

[0068] [Table 3]

[0069] [Table 4]

[0070] [Table 5]-

[0071] [Table 6]

[0072] As shown in Tables 1-6, in Examples 1-18 of the present invention, the proportion of the area of ​​grains with <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains included in the first measurement region is controlled within a specific range. Therefore, when the stranded conductor and the terminal are joined by ultrasonic bonding to form a terminal wire, the height of the connection portion with the terminal and the tensile test results of the terminal wire are both excellent. Based on this, in Examples 1-18 of the present invention, by applying ultrasonic waves to the copper conductor, the copper conductor is easily deformed, and the gaps at the joint portion between the copper conductor and the terminal and the gaps inside the stranded conductor are reduced. This promotes the bonding between the copper conductor and the terminal and further improves the tensile durability of the terminal wire.

[0073] On the other hand, in Comparative Examples 1-6 and Examples 1-18 of the present invention, the proportion of the area of ​​grains having <011>, <012>, and <123> crystal orientation groups in the total area of ​​the grains included in the first measurement region was not controlled within a specific range. Therefore, in Comparative Examples 1-6, when a stranded conductor is joined to a terminal using ultrasonic bonding to form a terminal-attached wire, at least one of the height of the connection portion to the terminal and the tensile test results of the terminal-attached wire are poor. Based on this result, it can be seen that the tensile durability of the terminal-attached wires in Comparative Examples 1-6 is also poor. [Simplified Explanation of the Diagram]

[0011] Figure 1 is a cross-sectional view schematically showing the height of the joint portion of a terminal wire formed by joining multiple strands of copper conductors of the present invention to a flat portion of a terminal.

Claims

1. A copper-based conductor, comprising pure copper containing 99.90% by mass or more of copper, wherein in a crystal orientation analysis performed by electron backscattering diffraction (EBSD) at a cross-section perpendicular to the conductor's extension direction, after defining an orthogonal xy coordinate system within the cross-section, assuming the x-axis direction is a first direction and the y-axis direction is a second direction, crystal directions within ±8° of the <011> crystal direction are designated as the <011> crystal direction group, crystal directions within ±8° of the <012> crystal direction are designated as the <012> crystal direction group, and crystal directions within ±8° of the <123> crystal direction are designated as the <123> crystal direction group, in a first measurement region selected within the aforementioned cross-section, the average of the first total area and the second total area accounts for a cumulative rate of 40% or more of the total area of ​​the grains contained within the first measurement region. The first total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group, and the aforementioned <123> crystal orientation group relative to the aforementioned first direction. The second total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group, and the aforementioned <123> crystal orientation group relative to the aforementioned second direction.

2. The copper-based conductor as described in claim 1, wherein, When the aforementioned cross-section is divided into a central portion and an outer ring surrounding the aforementioned central portion, in the second measurement region selected within the aforementioned central portion of the aforementioned cross-section, the average of the first total area and the second total area accounts for a proportion of the total area of ​​the grains contained in the aforementioned second measurement region, that is, the total cumulative rate is 50% or more. The first total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group, and the aforementioned <123> crystal orientation group relative to the aforementioned first direction. The second total area is obtained by summing the areas of grains having the aforementioned <011> crystal orientation group, the aforementioned <012> crystal orientation group, and the aforementioned <123> crystal orientation group relative to the aforementioned second direction.

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

4. A stranded conductor formed by stranding multiple copper-based raw material wires, wherein the copper-based raw material wires are composed of the copper-based conductor described in claim 1.

5. An electrical wire having at least an insulating coating layer formed on the surface of a copper conductor as described in claim 1, 2 or 3 or a stranded conductor as described in claim 4.

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