Cu-Ag alloy wire

Abstract

The problem to be solved by the present invention is to provide a Cu-Ag alloy wire which has sufficient conductivity and high strength, and which can maintain high strength even when used for a long period of time in a heat-generating state. In order to solve the problem, this Cu-Ag alloy wire has a composition containing 1-6 mass% of Ag, with the remainder comprising Cu and unavoidable impurities, and is characterized by having a Cu phase as a parent phase and a plurality of Ag phases as second phases, when sigma ([mu] m2) is the cross-sectional area of a cross-section orthogonal to the longitudinal direction of the Cu-Ag alloy wire and D ([mu] m) is the diameter of a perfect circle having the same area as each Ag phase present in the cross-section, the Cu-Ag alloy wire satisfies formula (1) [numerical formula 1] # imgabs0 # (in formula (1), [pi] represents the circumferential ratio). The ratio of the number of Ag phases having a diameter D of less than 5 nm to the total number of Ag phases is 50% or more.

Description

Technical Field

[0001] The present invention relates to a Cu-Ag alloy wire. Background Art

[0002] Pure copper wires and copper alloy wires are used as wire materials for electric and electronic devices. In this application, alloy wires such as Cu-Sn based, Cu-Cr based, and Cu-Ag based are being used in place of pure copper wires. As technology has advanced, the single wire diameter has become thinner, and the strength of pure copper wires is insufficient. In recent years, especially in the case of high density and miniaturization of electronic devices, wires such as cables for connecting electric and electronic devices or speaker coils also tend to have a further thinner diameter. Therefore, among copper alloys, Cu-Ag alloy wires, which have an especially excellent balance between strength and conductivity, are mainly used.

[0003] In Patent Documents 1 and 2, a technique is disclosed for improving both the strength and conductivity of a Cu-Ag alloy wire by controlling the eutectic phase of Cu and Ag to a structure that extends into a filamentous shape. In Patent Document 1, a technique is shown in which recrystallization texture is developed by heat treatment during the process, and high strength is achieved in subsequent high processing. In addition, in Patent Document 2, it is shown that by controlling the cooling rate during alloy casting, crystal precipitates are crystallized finely and uniformly, and the alloy wire is strengthened.

[0004] However, in Patent Document 1, since appropriate wire drawing process conditions were not adopted before heat treatment, embrittlement of the material during heat treatment was aggravated. As a result, it was difficult to make the wire thinner, and it could not become a cost-competitive product due to the deterioration of its productivity. Furthermore, the exploration of the cooling rate in the casting step was also insufficient. In addition, in Patent Document 2, promoting precipitation by controlling the distribution of crystal precipitates and optimizing intermediate heat treatment was not explored, leaving room for further strengthening. In addition, in Patent Documents 1 and 2, the strength characteristics under a continuous heating state of the cable caused by Joule heat or vibration heat generated during energization in the cable for connecting electric and electronic devices were not disclosed.

[0005] [Prior Art Documents]

[0006] (Patent Documents)

[0007] Patent Document 1: International Publication No. 2007 / 046378

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2017-2337 Summary of the Invention

[0009] [Problems to be Solved by the Invention]

[0010] An object of the present invention is to provide a Cu-Ag alloy wire that has both high strength and high conductivity and can maintain high strength even when used for a long time under high-temperature heating caused by heat generation.

[0011] [Technical means for solving the problem]

[0012] To achieve the above object, the key structure of the present invention is as follows.

[0013] [1] A Cu-Ag alloy wire having the following composition, that is, containing 1% by mass or more and 6% by mass or less of Ag, and the balance being composed of Cu and inevitable impurities,

[0014] The aforementioned Cu-Ag alloy wire has a metal structure including a Cu phase as a matrix phase and a plurality of Ag phases as second phases,

[0015] When the cross-sectional area of the cross-section of the aforementioned Cu-Ag alloy wire orthogonal to the long side direction is set to σ, and the diameter of a perfect circle having the same area as each Ag phase existing on the aforementioned cross-section is set to D, the following formula (1) is satisfied

[0016] [Formula 1]

[0017]

[0018] (In formula (1), π represents the ratio of the circumference of a circle to its diameter)

[0019] Moreover, the proportion of the number of Ag phases having a diameter D of less than 5 nm with respect to the total number of Ag phases is 50% or more.

[0020] [2] The Cu-Ag alloy wire according to the above [1], wherein, in the aforementioned cross-section of the aforementioned Cu-Ag alloy wire,

[0021] The proportion of the number of Ag phases existing at the grain boundaries of the aforementioned Cu phase with respect to the total number of Ag phases is 15% or more and 35% or less.

[0022] [3] The Cu-Ag alloy wire according to the above [1] or [2], wherein the aforementioned composition further contains at least one sub-additive element selected from the group consisting of Sn, Mg, Zn, In, Ni, Co, Zr, and Cr in a range of 0.05% by mass or more and 0.3% by mass or less.

[0023] [4] The Cu-Ag alloy wire according to any one of the above [1] to [3], wherein the aforementioned Cu-Ag alloy wire is a round wire having a wire diameter of 0.01 mm or more and 0.08 mm or less.

[0024] [5] The Cu-Ag alloy wire according to any one of [1] to [3] above, wherein the Cu-Ag alloy wire is a flat wire having a substantially rectangular cross-sectional shape, and the substantially rectangular cross-sectional shape has a width of 0.02 mm or more and 0.32 mm or less and a thickness of 0.002 mm or more and 0.04 mm or less.

[0025] (Effects of the Invention)

[0026] According to the present invention, a Cu-Ag alloy wire can be provided, which has both high strength and high electrical conductivity, and can maintain high strength even when used for a long time under high-temperature heating caused by heat generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic longitudinal sectional view showing the metal structure when the Cu-Ag alloy wire of the present invention is cut along its long side direction, showing the metal structure after each manufacturing step.

[0028] Figure 2 It is a schematic longitudinal sectional view showing the metal structure when a conventional Cu-Ag alloy wire is cut along its long side direction, showing the metal structure after each manufacturing step.

[0029] Figure 3 It is a scanning transmission electron microscopy (STEM) photograph and a processed image of the Ag phase showing the distribution state of the Ag phase present in the cross-section of the Cu-Ag alloy wire.

[0030] Figure 4 It is a scanning transmission electron microscopy (STEM) photograph and a processed image of the grain boundary of the Ag phase showing the distribution state of the Ag phase present at the grain boundaries of the cross-section of the Cu-Ag alloy wire. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present inventors found that in a Cu-Ag alloy wire having a specified composition and manufactured through a manufacturing process including wire drawing, by rationalizing the manufacturing method, particularly the heat treatment conditions, a Cu-Ag alloy wire having excellent strength and heat resistance with a desired metal structure can be obtained, and the present invention was completed based on this finding.

[0032] Hereinafter, embodiments of the present invention will be described.

[0033] [1] Composition of the Cu-Ag Alloy Wire

[0034] <Necessary component>

[0035] The Cu-Ag alloy wire of the present invention contains Ag as an essential component in an amount of 1% by mass or more and 6% by mass or less.

[0036] [Ag: 1% by mass or more and 6% by mass or less]

[0037] In the Cu-Ag alloy wire of the present invention, by making the content of Ag in the range of 1% by mass or more and 6% by mass, it has sufficient conductivity and high tensile strength, and can maintain high strength even when used for a long time in a heated state. If the content of Ag is less than 1% by mass, the precipitation of the Ag phase cannot occur sufficiently, and the desired metal structure cannot be obtained. Therefore, the tensile strength will decrease significantly. On the other hand, if the content of Ag exceeds 6% by mass, the conductivity will decrease significantly. In addition, even if the content exceeds 6% by mass, no further improvement in the tensile strength effect can be expected because the increase in the Ag content will correspondingly lead to an increase in cost.

[0038] In the Cu-Ag alloy wire of the present invention, Ag (silver) exists in a state of being dissolved in the matrix phase (the first phase), that is, the Cu phase, or in a state of being crystallized and precipitated as the second-phase Ag phase. The Ag dissolved in the Cu phase plays a role of solid solution strengthening, and the precipitated Ag phase becomes a fibrous Ag phase with a fibrous shape by wire drawing processing, playing a role of fiber strengthening. The Ag phase as the precipitate precipitates during cooling after casting and during aging heat treatment, etc. In the manufacturing method of the Cu-Ag alloy wire of the present invention described below, it mainly precipitates during the cooling step after casting, the first and second heat treatment steps.

[0039] <Optional additive component>

[0040] The Cu-Ag alloy wire of the present invention may also contain the following components as optional additive components.

[0041] [At least one sub-additive element selected from the group consisting of Sn, Mg, Zn, In, Ni, Co, Zr, and Cr: 0.05% by mass or more and 0.3% by mass or less respectively]

[0042] Furthermore, in the Cu-Ag alloy wire of the present invention, as optional additive components, it is preferable to further contain at least one component selected from the group consisting of Sn (tin), Mg (magnesium), Zn (zinc), In (indium), Ni (nickel), Co (cobalt), Zr (zirconium), and Cr (chromium), and each is contained in the range of 0.05% by mass or more and 0.3% by mass or less. These optional additive components exist either in a state of being dissolved in the matrix phase (the first phase), i.e., Cu, or as single-phase or crystallization precipitates of a ternary system or higher, and play the role of solid solution strengthening or fiber strengthening. Examples of crystallization precipitates of a ternary system or higher include Cu-Ag-Zr, etc. The single-phase or crystallization precipitates of a ternary system or higher of the sub-additive elements precipitate during cooling after casting and during aging heat treatment.

[0043] The content of each sub-additive element will be described below.

[0044] (Sn: 0.05% by mass or more and 0.3% by mass or less)

[0045] Sn (tin) is an element that increases the tensile strength. To exert this effect, the content of Sn is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of Sn is too high, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.18% by mass or less, further preferably 0.15% by mass or less, and particularly preferably 0.12% by mass or less.

[0046] (Mg: 0.05% by mass or more and 0.3% by mass or less)

[0047] Mg (magnesium) is an element that increases the tensile strength. To exert this effect, the content of Mg is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of Mg is too high, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.18% by mass or less, further preferably 0.15% by mass or less, and particularly preferably 0.12% by mass or less.

[0048] (Zn: 0.05% by mass or more and 0.3% by mass or less)

[0049] Zn (zinc) is an element that improves the tensile strength. To exert this effect, the content of Zn is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of Zn is excessive, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.25% by mass or less, further preferably 0.2% by mass or less, and particularly preferably 0.15% by mass or less.

[0050] (In: 0.05% by mass or more and 0.3% by mass or less)

[0051] In (indium) is an element that improves the tensile strength. To exert this effect, the content of In is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of In is excessive, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.18% by mass or less, further preferably 0.15% by mass or less, and particularly preferably 0.12% by mass or less.

[0052] (Ni: 0.05% by mass or more and 0.3% by mass or less)

[0053] Ni (nickel) is an element that improves the tensile strength. To exert this effect, the content of Ni is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of Ni is excessive, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.25% by mass or less, further preferably 0.2% by mass or less, and particularly preferably 0.15% by mass or less.

[0054] (Co: 0.05% by mass or more and 0.3% by mass or less)

[0055] Co (cobalt) is an element that improves the tensile strength. To exert this effect, the content of Co is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of Co is excessive, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.18% by mass or less, further preferably 0.15% by mass or less, and particularly preferably 0.12% by mass or less.

[0056] (Zr: 0.05% by mass or more and 0.3% by mass or less)

[0057] Zr (zirconium) is an element that improves the tensile strength and alleviates brittleness. To exert this effect, the content of Zr is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of Zr is excessive, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, further preferably 0.15% by mass or less, and particularly preferably 0.12% by mass or less.

[0058] (Cr: 0.05% by mass or more and 0.3% by mass or less)

[0059] Cr (chromium) is an element that improves the tensile strength. To exert this effect, the content of Cr is preferably 0.05% by mass or more, more preferably 0.07% by mass or more, further preferably 0.08% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, if the content of Cr is excessive, the conductivity may decrease significantly. Therefore, it is preferably 0.3% by mass or less, more preferably 0.18% by mass or less, further preferably 0.15% by mass or less, and particularly preferably 0.12% by mass or less.

[0060] [Sn, Mg, Zn, In, Ni, Co, Zr and Cr: The total is 0.05% by mass or more and 1% by mass or less]

[0061] From the perspective of more highly balancing the tensile strength and conductivity, Sn, Mg, Zn, In, Ni, Co, Zr and Cr preferably contain a total of 0.05% by mass or more and 1% by mass or less, and more preferably a total of 0.1% by mass or more and 0.5% by mass or less.

[0062] <The remainder: Cu and unavoidable impurities>

[0063] Excluding the above essential components and optional additive components, the remainder is Cu (copper) and unavoidable impurities. Cu is the matrix phase of the Cu-Ag alloy wire of the present invention and exists in a state where Ag or the like as an essential additive component is dissolved or crystallized out. The so-called unavoidable impurities are impurities at a content level that may inevitably be contained in the manufacturing process of the Cu-Ag alloy wire of the present invention. Examples of unavoidable impurities include Pb (lead), S (sulfur), P (phosphorus), etc.

[0064] [2] Metallic structure and shape of the Cu-Ag alloy wire

[0065] The Cu-Ag alloy wire of the present invention has a metal structure including a Cu phase as a matrix phase and a plurality of Ag phases as second phases. The Ag phases in the Cu-Ag alloy wire of the present invention become fibrous Ag phases by wire drawing as described above, and there are relatively large and coarse fibrous Ag phases (hereinafter, also referred to as "fibrous coarse Ag phases") and fine fibrous Ag phases (hereinafter, also referred to as "fibrous fine Ag phases").

[0066] Fibrous coarse Ag phases also exist in the Cu-Ag alloy wires manufactured in the past, as Figure 2 shown, mainly derived from the coarse Ag phases crystallized and precipitated during cooling after casting. The fibrous fine Ag phases are characteristic Ag phases in the present invention, as Figure 1 shown, particularly derived from a large number of fine Ag phases (hereinafter, also referred to as "fine Ag phases") crystallized and precipitated by the first and second heat treatment steps described below. The fine Ag phases crystallized and precipitated by the first and second heat treatment steps are usually less than one ten-thousandth of the wire diameter at the time of precipitation, and thus, the ratio of the drawn fibrous fine Ag phases to the wire diameter is also the same. That is, the fibrous fine Ag phase refers to an Ag phase with a diameter D less than one ten-thousandth of the wire diameter and less than 5 nm when observed on the cross-section of the manufactured Cu-Ag alloy wire. On the other hand, the fibrous coarse Ag phase refers to an Ag phase with a diameter D exceeding one ten-thousandth of the wire diameter or 5 nm or more when observed in the same way. In addition, the diameter of the fibrous Ag phase refers to the diameter of a perfect circle having the same area as each fibrous Ag phase existing on the cross-section. In the Cu-Ag alloy wire of the present invention, in addition to the fibrous coarse Ag phase 2f, there are also a large number of fibrous fine Ag phases 3f, and thus, the tensile strength is significantly improved by the fiber strengthening effect.

[0067] <Number ratio of fibrous fine Ag phases>

[0068] The Cu-Ag alloy wire of the present invention is characterized in that when the cross-sectional area of the cross-section of the Cu-Ag alloy wire orthogonal to the long side direction is set to σ (μm 2 ), and the diameter of a perfect circle having the same area as each Ag phase existing on the cross-section (hereinafter, also simply referred to as "diameter of Ag phase") is set to D (μm), the following formula (1) is satisfied

[0069] [Formula 2]

[0070]

[0071] (In formula (1), π represents the circumference ratio)

[0072] Moreover, the proportion of the number of Ag phases with a diameter D of less than 5 nm relative to the total number of Ag phases is 50% or more.

[0073] The diameter of the Ag phase in the cross-section of the Cu-Ag alloy wire, i.e., the diameter of the cross-section of the fibrous Ag phase, satisfies the above formula (1) in a proportion of 50% or more of the total number of Ag phases. Thus, the tensile strength of the Cu-Ag alloy wire can be improved. When the proportion of fine Ag phases, i.e., fibrous fine Ag phases, at a level satisfying the above formula (1) is high, the number of Ag phases contained in the Cu-Ag alloy wire increases, and thus a Cu-Ag alloy wire with a high density of fibrous fine Ag phases can be obtained. Therefore, the proportion of the number of Ag phases with a diameter D satisfying formula (1) is 50% or more, preferably 60% or more. In this case, the interval between the fibrous fine Ag phases in the direction perpendicular to the wire drawing direction becomes narrower.

[0074] The above formula (1) is independent of the shape of the Cu-Ag alloy wire. Based on the cross-sectional area σ (μm 2 ) of the alloy wire, the diameter d (μm) of the circle with the cross-sectional area σ is calculated, and the proportion of the fibrous fine Ag phase with a diameter D that is one ten-thousandth or less of the diameter d is determined. The diameter of the fibrous fine Ag phase is affected by the final wire diameter d after wire drawing, and thus is expressed as a function of the cross-sectional area σ calculated based on the final wire diameter d.

[0075] In addition, the fibrous Ag phase preferably has an average diameter in the range of 0.5 to 10 nm when measured on a cross-section orthogonal to the long side direction. Moreover, in the Cu-Ag alloy wire of the present invention, depending on the final wire diameter, there may be fibrous Ag phases with a diameter of less than 0.5 nm. However, it is very difficult to detect and count the number of fibrous Ag phases with a diameter of less than 0.5 nm in the detection cross-section in the current technology, so it is set to 0.5 nm or more.

[0076] In addition, among the above-mentioned fibrous Ag phases, the average diameter measured on the cross-section of the fibrous coarse Ag phase and the fibrous coarse Ag phase is different depending on the final wire diameter of the Cu-Ag alloy wire as described above. However, the average diameter of the fibrous fine Ag phase is, for example, 0.5 nm or more and less than 5 nm, preferably 0.5 nm or more and 3 nm or less. On the other hand, the average diameter of the fibrous coarse Ag phase is, for example, more than 5 nm and 20.0 nm or less.

[0077] The number ratio of fibrous fine Ag phases can be measured by the following method. First, the cross section of the Cu-Ag alloy wire perpendicular to the long side direction is subjected to a thinning process of the sample by a focused ion beam (FIB) method. In this processing, for example, the acceleration voltage of the Ga ion beam is set to 30 kV using SIINT-3050TB (manufactured by SII NANOTECH). After processing, in order to remove damage to the sample, the acceleration voltage is set to, for example, 2 kV, and Ar ion milling is performed for 5 minutes. For the processed sample, a scanning transmission electron microscope (STEM) is used to observe the cross section orthogonal to the long side direction. Regarding STEM observation, for example, the acceleration voltage of the electron beam is set to 200 kV using JEM-ARM200F (manufactured by JEOL), and the observation area is set to a square with a side of more than 130 nm, and STEM bright field images and STEM dark field images (high angle scattering dark field images) are taken. When observing the cross section, the Ag phase exists continuously in the depth direction of the observation surface, so even fine precipitates less than 5 nm can be easily detected. In addition, the obtained STEM dark field image is processed using the image processing software "Image J (version v1.53k)", which can calculate the average diameter of the Ag phase and the number of Ag phases, and further calculate the number ratio of fibrous fine Ag phases. In addition, by confirming the presence of the Ag phase by performing elemental analysis using Energy Dispersive X-ray spectroscopy (EDX) attached to STEM in the area where the contrast that may be the Ag phase is confirmed, the presence of the Ag phase can be confirmed more accurately.

[0078] Regarding the specific order of image processing, as a practical example Figure 3 The order is explained for reference. First, from the dark field image ( Figure 3 Left) Middle selection, e.g. 400 to 800 nm 2 Any range of Figure 3 (a to c on the left) grayscale this image. Next, in the histogram of the brightness value of this image, use the high 3 to 6% as the threshold, binarize the low brightness side to white, and binarize the high brightness side to black ( Figure 3 a-1~c-1). Furthermore, after removing the black part of less than 10 pixels as noise, the remaining part is regarded as Ag phase precipitation ( Figure 3a-2 to c-2). Then, after calculating the number of pixels of each precipitate and converting it into an area, assuming that each precipitate is a perfect circle, the diameter is calculated from the area, and thus the diameter D of each precipitate, i.e., the Ag phase, can be obtained. Then, the total number of Ag-phase precipitates in the measurement range is counted, and the number in the range of formula (1) is counted and divided by the total number, thereby calculating the number ratio of the fibrous fine Ag phase.

[0079] In addition, the Ag phase present in the Cu-Ag alloy wire is preferably continuously distributed on the wire in the substantially long-side direction. That is, the Ag phase is preferably a fibrous Ag phase (fibrous coarse Ag phase, fibrous fine Ag phase). In the prior art, it has been confirmed by analysis techniques that the coarsely precipitated Ag phase crystallizes and elongates in the long-side direction by wire drawing and exists as a fibrous coarse Ag phase in the Cu-Ag alloy wire. In this specification, although the analysis results indicating fibrous are not shown, it can be reasonably understood that in the present invention, the minute Ag phase crystallized and precipitated during aging heat treatment, although different in size, also elongates in the long-side direction, for example, becoming a fibrous minute Ag phase with an aspect ratio of 100 or more, and exists in the Cu-Ag alloy wire of the present invention.

[0080] <Ratio of the number of Ag phases at grain boundaries>

[0081] In addition, in the Cu-Ag alloy wire of the present invention, it is preferable that the ratio of the number of Ag phases present at the grain boundaries of the Cu phase to the total number of Ag phases (hereinafter, also referred to as "ratio of the number of Ag phases at grain boundaries") in the cross-section of the Cu-Ag alloy wire is 15% or more and 35% or less. By preferably making the ratio of the number of Ag phases at grain boundaries 15% or more, more preferably 20% or more, softening caused by coarsening of grains during heating is suppressed by the pinning effect, and as a result, a decrease in the tensile strength during heating can be suppressed. On the other hand, from the viewpoint of suppressing grain boundary cracking caused by excessive deviation of the second-phase particles toward the grain boundaries and the resulting decrease in tensile strength, it is preferable that the ratio of the number of Ag phases at grain boundaries is 35% or less.

[0082] The ratio of the number of Ag phases at grain boundaries is measured in the following order. For the measurement, by using the STEM bright-field image and STEM dark-field image obtained during the measurement of the ratio of the number of Ag phases described above, image processing is performed using the image processing software "Image J (version v1.53k)", and the ratio of the number of Ag phases at grain boundaries can be measured.

[0083] Regarding the specific image processing, as an actual measurement example Figure 4To illustrate the order, first, for the acquired STEM bright-field image, binarization processing is performed to determine the positions of grain boundaries. From the bright-field image ( Figure 4 left), an arbitrary range such as 400 to 800 nm 2 is selected ( Figure 4 left a to c), and this image is grayscale-converted. Second, in the histogram of the luminance values of this image, binarization is performed using the upper 10% as the threshold, making the high-luminance side white and the low-luminance side black. Among the black parts, for example, black parts that continue for 15 nm or more in the long-side direction and have a short-side length of 5 nm or less are determined as grain boundaries ( Figure 4 a-1 to c-1). In addition, for the STEM dark-field image, according to the order shown in the description of the measurement of the number ratio of Ag phases, the same range ( Figure 4 left a to c) is subjected to the extraction of Ag-phase precipitates. In addition, since in Figure 4 , the measurement is performed for the same range as the range for the measurement of precipitates in Figure 3 , Figure 3 is used in the description of the positions of the precipitates. An arbitrary range such as 400 to 800 nm 2 is selected from the STEM dark-field image ( Figure 3 left a to c), and this image is grayscale-converted. Second, in the histogram of the luminance values of this image, the luminance values of the upper 10% and the upper 2% are compared. When the difference is 25 or more, binarization is performed using the upper 2% as the threshold ( Figure 3 a-1 to c-1). At this time, the low-luminance side is made white and determined as the matrix phase, and the high-luminance side is made black. Furthermore, among the binarized black parts, those with 10 pixels or less are removed as noise, and the remaining part is determined as Ag-phase precipitates ( Figure 3 a-2 to c-2). By comparing the positions of the grain boundaries ( Figure 4 a-1 to c-1) and the positions of the Ag-phase precipitates ( Figure 3 a-2 to c-2), Ag phases where even a part of the linear shape representing the grain boundary coincides are regarded as precipitates on the grain boundary, and Ag phases that do not coincide at all are regarded as precipitates within the grain rather than on the grain boundary, thereby calculating the number ratio of Ag phases as precipitates on the grain boundary.

[0084] In addition, when measuring on a cross-section orthogonal to the long-side direction, the total number of Ag phases present per unit area of 1 μm 2 is, for example, 100 or more and 15,000 or less. From the viewpoint of improving the tensile strength, the total number of Ag phases is preferably 1,000 or more. On the other hand, from the viewpoint of the ease of setting manufacturing conditions, the total number of Ag phases is preferably 13,000 or less.

[0085] <Shape of Cu-Ag alloy wire>

[0086] The shape of the Cu-Ag alloy wire of the present invention is not particularly limited, and examples thereof include round wire, flat wire, etc.

[0087] The Cu-Ag alloy wire of the present invention is preferably a round wire having a wire diameter of 0.01 mm or more and 0.08 mm or less. As a conductor used in parts on the market, a high tensile strength and high conductivity material of an extremely fine wire of 0.01 mmφ or more and 0.08 mmφ or less is required. The lower limit of the wire diameter being 0.01 mmφ reflects the market demand. If further fineness is required in the future, it can be addressed by applying the Cu-Ag alloy wire of the present invention. When the wire diameter exceeds 0.08 mmφ, the size is large and it cannot function as an extremely fine wire.

[0088] In addition, the Cu-Ag alloy wire of the present invention is preferably a flat wire having a substantially rectangular cross-sectional shape, and the substantially rectangular cross-sectional shape has a width of 0.02 mm or more and 0.32 mm or less and a thickness of 0.002 mm or more and 0.04 mm or less. As a manufacturing method, for example, there is a method of rolling the above-mentioned round wire after drawing into a desired shape. The flat shape dimensions are preferably in the range of a plate width of 0.02 mm or more and 0.32 mm or less and a plate thickness of 0.002 mm or more and 0.04 mm or less for the same reasons as the upper and lower limits of the wire diameter. The plate width corresponds to the width direction of the roll, and the plate thickness corresponds to the direction between the rolls. A shape portion that maintains an arc while deforming remains at the non-contact portion of the roll at the end in the plate width direction. Here, the longest value in the cross-section of the flat wire is taken as the width, and the short value is taken as the thickness. In addition, compared with the round shape before being formed into a flat shape, the properties of the flat wire, such as strength and conductivity, do not change significantly.

[0089] [3] Manufacturing method of Cu-Ag alloy wire

[0090] The Cu-Ag alloy wire of the present invention can be manufactured, for example, by a manufacturing method including the following casting step [Step 1], post-casting cooling step [Step 2], first drawing step [Step 3], first heat treatment step [Step 4], second heat treatment step [Step 5], and second drawing step [Step 6].

[0091] Among these steps, in order to control the number ratio of fibrous fine Ag phases within the range specified in the present invention, it is particularly important to perform the post-casting cooling step [Step 2], the first heat treatment step [Step 4], and the second heat treatment step [Step 5] under appropriate conditions. In addition, in order to control the number ratio of Ag phases at the grain boundaries within the range specified in the present invention, it is particularly important to perform the post-casting cooling step [Step 2] under appropriate conditions.

[0092] (i) Casting step [Step 1]

[0093] In the method for manufacturing a Cu-Ag alloy wire of the present invention, first, a casting step is performed. In this casting step, raw materials and sub-additive elements are added so as to achieve a desired composition, and then casting and rolling are carried out to obtain a wire rod. From the viewpoint of manufacturing efficiency, in this step, it is preferable to use a belt-type continuous casting and rolling mill that combines a casting wheel and a belt, in which molten metal is continuously poured into an annular groove mold for casting and then continuously rolled, so that a wire rod can be obtained.

[0094] (ii) Post-casting cooling step [Step 2]

[0095] After the wire rod is formed by the casting step [Step 1], a post-casting cooling step [Step 2] is carried out at a cooling rate of 60°C / second or more and 120°C / second or less. If the cooling rate is less than 60°C / second, the crystallization precipitation of coarse Ag phases will become excessive, so the crystallization precipitation of fine Ag phases in the first and second heat treatment steps [Steps 4 and 5] will be significantly reduced. On the other hand, if the cooling rate is higher than 120°C / second, it will prevent the solute (Ag) from accumulating at the grain boundaries, and the crystallization precipitation of Ag phases at the grain boundaries will decrease. Therefore, by carrying out the post-casting cooling step [Step 2] at 60°C / second or less, preferably 80°C / second or more and 120°C / second or less, due to insufficient diffusion caused by rapid cooling, a large amount of solute (Ag) will exist near the grain boundaries, thus promoting the crystallization precipitation of Ag phases at the grain boundaries that act as pinning particles.

[0096] (iii) First wire drawing step [Step 3]

[0097] Following the post-casting cooling step [Step 2], a first wire drawing step [Step 3] is carried out by cold wire drawing at a reduction ratio of 50% or more and 90% or less. If the reduction ratio is less than 50%, insufficient crystallization precipitation of fine Ag phases will occur during age heat treatment. In addition, if the reduction ratio is less than 50%, there is also a problem that pore defects will grow. On the other hand, if the reduction ratio exceeds 90, it will be difficult to carry out wire drawing at a high reduction ratio after the second heat treatment step [Step 5]. Therefore, from the viewpoints of promoting sufficient crystallization precipitation of fine Ag phases, suppressing pore growth, and fully ensuring the space for wire drawing in subsequent steps, the first wire drawing step [Step 3] is carried out at a reduction ratio of 50% or more and 90% or less.

[0098] Here, the "processing rate" is a value obtained by subtracting the cross-sectional area after processing from the cross-sectional area before wire drawing processing, dividing by the cross-sectional area before processing, and multiplying by 100, which is expressed as a percentage and is represented by the following formula.

[0099] [Processing rate] = {([Cross-sectional area before processing] - [Cross-sectional area after processing]) / [Cross-sectional area before processing]} × 100 (%)

[0100] The first wire drawing step [Step 3] can be carried out by a known method such as drawing wire drawing using a die. The first wire drawing process can be carried out in one pass or multiple passes until the target wire diameter is obtained.

[0101] (iv) First heat treatment step [Step 4]

[0102] Following the first wire drawing step [Step 3], the first heat treatment step [Step 4] is carried out. The first heat treatment step [Step 4] is to hold at a temperature in the range of 300 °C or more and 400 °C or less for 2 hours or more and 100 hours or less, and then cool to room temperature at a cooling rate of 90 °C / second or more. By holding at this specified temperature, the crystallization precipitation of the fine Ag phase is promoted. In addition, by quenching to room temperature, the residual stress derived from the difference in thermal expansion coefficient and the cooling rate difference between the Ag phase and the matrix phase obtained before this step is accumulated, thereby promoting the precipitation of the Ag phase in the subsequent second heat treatment step [Step 5]. When the holding temperature in the first heat treatment step [Step 4] is lower than 300 °C, the generation of the Ag phase as a precipitate cannot occur sufficiently. On the other hand, if the holding temperature of the first heat treatment step [Step 4] exceeds 400 °C, the crystallized Ag phase will become coarser and the number of generated Ag phases will also decrease, so it is impossible to obtain a sufficient amount of crystallization precipitation of the fine Ag phase. In addition, if the cooling rate in the first heat treatment step [Step 4] is slow, the difference in shrinkage amount between the Ag phase and the matrix phase will become smaller, and it is difficult to effectively accumulate strain. By carrying out the first heat treatment step [Step 4] at a temperature in the range of 300 °C or more and 400 °C or less and cooling at a cooling rate of 90 °C / second or more, the proportion of the number of fibrous fine Ag phases generated can be increased.

[0103] (v) Second heat treatment step [Step 5]

[0104] After the first heat treatment step [Step 4], a second heat treatment step [Step 5] is performed at a temperature higher than that of the first heat treatment step. The second heat treatment step [Step 5] is carried out at a temperature more than 25°C higher than the holding temperature of the first heat treatment step [Step 4], and is usually performed at a holding temperature in the range of 400 to 600°C for a holding time of 2 hours or more and 100 hours or less. In addition, regarding the cooling after holding at a specified temperature, in order to have good workability in the subsequent wire drawing step, it is desirable to cool naturally in the furnace after stopping heating. Performing the second heat treatment step [Step 5] at a higher temperature after the first heat treatment step [Step 4] promotes the precipitation and recrystallization of the remaining solid solution elements due to the effects of improved diffusion ability and the strain accumulated during cooling.

[0105] The holding times in the first heat treatment step and the second heat treatment step are preferably in the range of 10 hours or more and 100 hours or less in total. By performing the heat treatment in two stages, namely the first heat treatment step [Step 4] and the second heat treatment step [Step 5], a large number of fine Ag phases are generated, and after wire drawing, a high-density fibrous fine Ag phase is formed, resulting in high strength. In addition, by going through the second heat treatment step [Step 5], that is, the recrystallization step, the workability in the subsequent wire drawing step can be improved, and wire breakage during thinning can be prevented. When the holding temperature and holding time do not meet the above-specified conditions, insufficient precipitation occurs due to slow diffusion of the solute (Ag), so the crystallization precipitation of the Ag phase will decrease significantly. In addition, from the viewpoint of preventing surface quality deterioration such as oxidation caused by the heat treatment step, a peeling step may also be provided after the second heat treatment step [Step 5].

[0106] The above-mentioned first heat treatment step [Step 4] and second heat treatment step [Step 5] can be performed, for example, by known methods such as batch heat treatment, high-frequency heating, electric current heating, continuous heat treatment such as in-line heating, etc. To obtain the desired cooling rate, the cooling after the first heat treatment step [Step 4] is preferably spraying with a quenching liquid such as oil or water or immersion in these liquids, cooling by a jet of non-oxidizing gas, etc.

[0107] (vi) Second wire drawing step [Step 6]

[0108] After cooling after the second heat treatment step [Step 5], a second wire drawing step [Step 6] of cold wire drawing is performed at a reduction rate of 99.7% or more and 99.998% or less. If the reduction rate is less than 99.7%, the strength cannot increase sufficiently. On the other hand, it is technically difficult to make the reduction rate exceed 99.998%. Therefore, the second wire drawing step [Step 6] is carried out at a reduction rate of 99.7% or more and 99.998% or less.

[0109] The second wire drawing step can be carried out by using well-known methods such as wire drawing processing using a die. The second wire drawing process can be carried out in one pass or multiple passes until the target wire diameter is obtained.

[0110] In addition, the above manufacturing method is mainly a manufacturing method for round wires in a circular shape. In the case of manufacturing flat wires in a flat shape, it can be manufactured by rolling a round wire manufactured in a circular shape by the above manufacturing method to a specified thickness.

[0111] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, but includes all aspects included in the concept and claims of the present invention, and various changes can be made within the scope of the present invention.

[0112] Examples

[0113] Next, examples and comparative examples will be described. The present invention is not limited to these examples.

[0114] 1. Experiment 1: Manufacturing and evaluation of Cu-Ag alloy wires

[0115] Cu-Ag alloy wires of the examples and comparative examples were manufactured using the manufacturing methods described below.

[0116] <Manufacturing method>

[0117] (Examples 1-1 to 1-11)

[0118] In the atmosphere, a raw material of Cu-1.0 mass% Ag was melted and cast into an ingot of a wire rod. Under the conditions shown in Table 1, a post-casting cooling step and a first wire drawing step were carried out. Then, under the conditions shown in Table 1, a first heat treatment step and a second heat treatment step were carried out, and after natural cooling in the furnace after the heating stop in the second heat treatment step, a second wire drawing step was carried out to obtain Cu-Ag alloy wires of Examples 1-1 to 1-11. In addition, for Example 1-9, which is a flat wire, it was temporarily made into a round wire and then formed into a flat wire with the dimensions shown in Table 5.

[0119] (Comparative Examples 1-1 to 1-11)

[0120] Among Comparative Examples 1-1 to 1-11, for Comparative Examples 1-1 and 1-2, the first heat treatment step and the second heat treatment step were not carried out. For Comparative Example 1-4, the second heat treatment step was not carried out. For Comparative Example 1-5, the first heat treatment was not carried out. Except for these, the manufacturing was carried out under the conditions shown in Table 1 in the same order as Examples 1-1 to 1-11 to obtain Cu-Ag alloy wires of Comparative Examples 1-1 to 1-11.

[0121] [Table 1]

[0122]

[0123] (Examples 2-1 to 2-11)

[0124] For the ingot obtained by melting a raw material of Cu-2.0 mass% Ag in the atmosphere and casting it into a wire rod, under the conditions shown in Table 2, a post-casting cooling step and a first wire drawing step are carried out. Then, under the conditions shown in Table 2, a first heat treatment step and a second heat treatment step are carried out, and after natural cooling in the furnace after the heating is stopped in this second heat treatment step, a second wire drawing step is carried out to obtain the Cu-Ag alloy wires of Examples 2-1 to 2-11. In addition, for Example 2-9 which is a flat wire, it is temporarily made into a round wire and then formed into a flat wire with the dimensions shown in Table 6.

[0125] (Comparative Examples 2-1 to 2-11)

[0126] Among Comparative Examples 2-1 to 2-11, for Comparative Examples 2-1 and 2-2, the first heat treatment step and the second heat treatment step are not carried out. For Comparative Example 2-4, the second heat treatment step is not carried out. For Comparative Example 2-5, the first heat treatment is not carried out. Except for these, the manufacturing is carried out under the conditions shown in Table 2 in the same order as Examples 2-1 to 2-11 to obtain the Cu-Ag alloy wires of Comparative Examples 2-1 to 2-11.

[0127] [Table 2]

[0128]

[0129] (Examples 3-1 to 3-11)

[0130] For the ingot obtained by melting a raw material of Cu-4.0 mass% Ag in the atmosphere and casting it into a wire rod, under the conditions shown in Table 3, a post-casting cooling step and a first wire drawing step are carried out. Then, under the conditions shown in Table 3, a first heat treatment step and a second heat treatment step are carried out, and after natural cooling in the furnace after the heating is stopped in this second heat treatment step, a second wire drawing step is carried out to obtain the Cu-Ag alloy wires of Examples 3-1 to 3-11. In addition, for Example 3-9 which is a flat wire, it is temporarily made into a round wire and then formed into a flat wire with the dimensions shown in Table 7.

[0131] (Comparative Examples 3-1 to 3-11)

[0132] Among Comparative Examples 3-1 to 3-11, for Comparative Examples 1-1 and 1-2, the first heat treatment step and the second heat treatment step were not performed. For Comparative Example 1-4, the second heat treatment step was not performed. For Comparative Example 1-5, the first heat treatment was not performed. Except for these, the Cu-Ag alloy wires of Comparative Examples 3-1 to 3-11 were manufactured under the conditions shown in Table 3 in the same order as in Examples 3-1 to 3-11.

[0133] [Table 3]

[0134]

[0135] (Examples 4-1 to 4-11)

[0136] Regarding the ingot obtained by melting a raw material of Cu-6.0 mass% Ag in the atmosphere and casting it into a wire rod, a post-casting cooling step and a first wire drawing step were performed under the conditions shown in Table 4. Subsequently, a first heat treatment step and a second heat treatment step were performed under the conditions shown in Table 4, and a second wire drawing step was performed after natural cooling in the furnace after the heating was stopped in the second heat treatment step, to obtain the Cu-Ag alloy wires of Examples 4-1 to 4-11. In addition, regarding Example 4-9 which is a flat wire, it was temporarily formed into a round wire and then formed into a flat wire with the dimensions shown in Table 8.

[0137] (Comparative Examples 4-1 to 4-11)

[0138] Among Comparative Examples 4-1 to 4-11, for Comparative Examples 4-1 and 4-2, the first heat treatment step and the second heat treatment step were not performed. For Comparative Example 4-4, the second heat treatment step was not performed. For Comparative Example 4-5, the first heat treatment was not performed. Except for these, the Cu-Ag alloy wires of Comparative Examples 4-1 to 4-11 were manufactured under the conditions shown in Table 4 in the same order as in Examples 4-1 to 4-11.

[0139] [Table 4]

[0140]

[0141] [Evaluation Method]

[0142] The Cu-Ag alloy wires of the above-mentioned manufactured Examples and Comparative Examples were evaluated using the following evaluation method.

[0143] [1] Tensile Test (Final Product of Manufacture)

[0144] A tensile test was carried out on a Cu-Ag alloy wire as a final manufactured product. Since the shape of the test piece was the original wire shape, it did not conform to Japanese Industrial Standards (JIS) Z2201. The test conditions were based on JIS Z2241 of Japan, and the averaged value (n = 2) of the measurement results was used as the result of the tensile strength.

[0145] The increase amount (MPa) of the tensile strength was calculated based on the tensile strength of the Cu-Ag alloy wires (Comparative Example 1-1, Comparative Example 2-1, Comparative Example 3-1, Comparative Example 4-1) manufactured by the conventional manufacturing method without the first heat treatment step and the second heat treatment step, and was used as the evaluation of the tensile test. The evaluation criterion was that an increase amount (MPa) of the tensile strength of 100 MPa or more higher was regarded as qualified (good), and in particular, an increase amount of 150 MPa or more higher was regarded as qualified (excellent).

[0146] [2] Tensile test (after reheat treatment)

[0147] As the tensile strength after long-term use in a heated state, a tensile test was carried out to measure the tensile strength when a heat treatment at 250 °C for 30 min was performed on the Cu-Ag alloy wire as a final manufactured product. The tensile test was carried out in the same manner as the above-mentioned "[1] Tensile test (final manufactured product)". In addition, regarding the above heat treatment conditions, if converted to the heating temperature during energization by the Larson-Miller parameter, that is, a heat treatment at about 80 °C, the treatment time would be much longer than the product life, and it can be regarded as measuring the Cu-Ag alloy wire after long-term use in a heated state.

[0148] The evaluation of the tensile test was carried out by comparing the control Cu-Ag alloy wire manufactured by the conventional manufacturing method without the first heat treatment step and the second heat treatment step with the tensile strength after reheat treatment. Regarding the tensile strength after reheat treatment shown in Tables 5 to 8, the value obtained by subtracting the tensile strength after reheat treatment of the control Cu-Ag alloy wire (Comparative Example 1-1, Comparative Example 2-1, Comparative Example 3-1, Comparative Example 4-1) of the same composition from the measured tensile strength after reheat treatment was used as the evaluation of the tensile test. The evaluation criterion was that an increase of 100 MPa or more higher compared to the target Cu-Ag alloy wire was regarded as qualified (good), and in particular, an increase of 150 MPa or more higher was regarded as qualified (excellent).

[0149] [3] Measurement of conductivity

[0150] The conductivity was measured for two specimens out of each test piece in a thermostatic bath maintained at 20 °C (±1 °C) using the four-terminal method based on JIS H0505-1975 of Japan, and the average value (%IACS) was taken as the measured value. At this time, the distance between the terminals was set to 100 mm.

[0151] In the evaluation, in the case of Cu-1.0 mass% Ag, a conductivity of 75% IACS or more was regarded as qualified, and 80% IACS or more was regarded as excellent. In the case of Cu-2.0 mass% Ag, a conductivity of 70% IACS or more was regarded as qualified, and 75% IACS or more was regarded as excellent. In the case of Cu-4.0 mass% Ag, a conductivity of 60% IACS or more was regarded as qualified, and 65% IACS or more was regarded as excellent. In the case of Cu-6.0 mass% Ag, a conductivity of 50% IACS or more was regarded as qualified, and 55% IACS or more was regarded as excellent.

[0152] In addition, it has been conventionally known that the tensile strength of Cu-Ag alloy wires can be controlled by increasing or decreasing the Ag content, and Cu-Ag alloy wires with different strengths for each Ag content are used in different applications. Therefore, in the above evaluation criteria, different conductivity evaluation criteria are set for each Ag content.

[0153] [4] Microstructure Observation

[0154] Before the image analysis of the metal microstructure, microstructure observation was carried out by STEM in order to obtain STEM bright-field images and STEM dark-field images by a scanning transmission electron microscope (STEM). The measurement sample was obtained by thinning a cross-section perpendicular to the long side direction of the Cu-Ag alloy wire by the focused ion beam (FIB) method. In this processing, SIINT-3050TB (manufactured by SII Nanotech) was used, and the acceleration voltage of the Ga ion beam was 30 kV. After processing, in order to remove the damage of the specimen, the acceleration voltage was set to 2 kV, and Ar ion milling was carried out for 5 minutes. For the processed specimen, observation of a cross-section orthogonal to the long side direction was carried out using STEM (JEM-ARM200F, manufactured by JEOL Ltd.). The conditions for STEM observation were carried out at an acceleration voltage of the electron beam of 200 kV. The observation area was set to a square with a side length of 130 nm or more, and STEM bright-field images and STEM dark-field images (high-angle scattering dark-field images) of this range were taken.

[0155] [5] Calculation of the Number Ratio of Fibrous Fine Ag Phases

[0156] For the obtained STEM dark-field image, the binarization of the Ag phase as a precipitate and the calculation of its average diameter were performed as follows using the image processing software "ImageJ (version v1.53k)". First, an arbitrary range of 400 to 800 nm was selected from the dark-field image, and this image was grayscale-converted. Secondly, in the histogram of the brightness values of this image, with the upper 3 to 6% as the threshold, the low-brightness side was binarized to white and the high-brightness side was binarized to black. Furthermore, on the basis of removing black parts of 10 pixels or less as noise, the remaining parts were regarded as Ag-phase precipitates. After calculating the number of pixels of each precipitate and converting it to an area, assuming that each precipitate was a perfect circle, the diameter was calculated from the area, and thus the diameter D of each precipitate, i.e., the Ag phase, was obtained. Then, the total number of the Ag phase in the measurement range was counted, the number of the range of formula (1) was counted and divided by the total number, and thus the number ratio of the fibrous fine Ag phase was calculated. 2 For the obtained STEM bright-field image, binarization processing was performed using the image processing software "ImageJ (version v1.53k)" to determine the position of the grain boundaries. An arbitrary range of 400 to 800 nm was selected from the bright-field image, and this image was grayscale-converted. Secondly, in the histogram of the brightness values of this image, binarization was performed with the upper 10% as the threshold, making the high-brightness side white and the low-brightness side black. Among the black parts, the black parts with a length of 15 nm or more in the long side direction and a short side length of 5 nm or less were determined as the positions of the grain boundaries. In addition, for the STEM dark-field image, in the order shown in "[5] Calculation of the number ratio of fibrous fine Ag phases", the extraction of Ag-phase precipitates was performed using the image processing software "ImageJ". An arbitrary range of 400 to 800 nm of the dark-field image was selected.

[0157] [6] Calculation of the number ratio of the Ag phase at the grain boundaries

[0158] For the obtained STEM bright-field image, binarization processing was performed using the image processing software "ImageJ (version v1.53k)" to determine the position of the grain boundaries. An arbitrary range of 400 to 800 nm was selected from the bright-field image, and this image was grayscale-converted. Secondly, in the histogram of the brightness values of this image, binarization was performed with the upper 10% as the threshold, making the high-brightness side white and the low-brightness side black. Among the black parts, the black parts with a length of 15 nm or more in the long side direction and a short side length of 5 nm or less were determined as the positions of the grain boundaries. In addition, for the STEM dark-field image, in the order shown in "[5] Calculation of the number ratio of fibrous fine Ag phases", the extraction of Ag-phase precipitates was performed using the image processing software "ImageJ". An arbitrary range of 400 to 800 nm of the dark-field image was selected. 2 For the obtained STEM bright-field image, binarization processing was performed using the image processing software "ImageJ (version v1.53k)" to determine the position of the grain boundaries. An arbitrary range of 400 to 800 nm was selected from the bright-field image, and this image was grayscale-converted. Secondly, in the histogram of the brightness values of this image, binarization was performed with the upper 10% as the threshold, making the high-brightness side white and the low-brightness side black. Among the black parts, the black parts with a length of 15 nm or more in the long side direction and a short side length of 5 nm or less were determined as the positions of the grain boundaries. In addition, for the STEM dark-field image, in the order shown in "[5] Calculation of the number ratio of fibrous fine Ag phases", the extraction of Ag-phase precipitates was performed using the image processing software "ImageJ". An arbitrary range of 400 to 800 nm of the dark-field image was selected. 2For any range, grayscale this image. Next, in the histogram of the luminance values of this image, compare the luminance values of the top 10% and the top 2%, and when the difference is 25 or more, perform binarization using the top 2% as the threshold. At this time, make the low-luminance side white and determine it as the matrix phase, and make the high-luminance side black. Furthermore, among the black portions after binarization, remove those with 10 pixels or less as noise, and determine the remaining portions as Ag-phase precipitates. By comparing with the positions of the determined grain boundaries, consider the Ag-phase that overlaps even partially with the line representing the grain boundary as a precipitate on the grain boundary, and consider the Ag-phase that does not overlap at all as a precipitate within the grain rather than on the grain boundary, and count the number of Ag-phases on the grain boundary, and divide by the total number of Ag-phases in the entire measurement range, thereby calculating the proportion of the number of Ag-phases on the grain boundary.

[0159] [Table 5]

[0160]

[0161] As shown in Tables 1 and 5, in the case of a Cu-Ag alloy wire with an Ag content of 1.0 mass%, in Examples 1-1 to 1-11 where the proportion of the number of Ag-phases in Formula (1) is 50% or more, sufficient conductivity and a tensile strength higher than that of Comparative Example 1-1 (tensile strength: 920 MPa, tensile strength after reheat treatment: 720 MPa) were confirmed, and it was confirmed that the tensile strength was sufficiently high even after reheat treatment.

[0162] In addition, in Examples 1-1, 1-3 to 1-11 where the proportion of the number of Ag-phases on the grain boundary is 15% or more and 35% or less, a particularly high increase in tensile strength after reheat treatment was confirmed, and the tensile strength was excellent.

[0163] [Table 6]

[0164]

[0165] As shown in Tables 2 and 6, in the case of a Cu-Ag alloy wire with an Ag content of 2.0 mass%, in Examples 2-1 to 2-11 where the proportion of the number of Ag-phases in Formula (1) is 50% or more, sufficient conductivity and a tensile strength sufficiently high compared to Comparative Example 2-1 (tensile strength: 1020 MPa, tensile strength after reheat treatment: 860 MPa) were confirmed, and it was confirmed that the tensile strength was sufficiently high even after reheat treatment.

[0166] In addition, in Examples 2-1, 2-3 to 2-11 where the proportion of the number of Ag-phases on the grain boundary is 15% or more and 35% or less, a particularly high increase in tensile strength after reheat treatment was confirmed, and the tensile strength was excellent.

[0167] [Table 7]

[0168]

[0169] As shown in Tables 3 and 7, in the case of the Cu-Ag alloy wire with an Ag content of 4.0 mass%, in Examples 3-1 to 3-11 where the number ratio of the Ag phase in Formula (1) is 50% or more, sufficient conductivity and a tensile strength sufficiently high compared to Comparative Example 3-1 (tensile strength: 1235 MPa, tensile strength after reheat treatment: 1060 MPa) were confirmed, and it was confirmed that the tensile strength was sufficiently high even after reheat treatment.

[0170] In addition, in Examples 3-1, 3-3 to 3-11 where the number ratio of the Ag phase at the grain boundaries is 15% or more and 35% or less, a particularly high increase in the tensile strength after reheat treatment was confirmed, and the tensile strength was excellent.

[0171] [Table 8]

[0172]

[0173] As shown in Tables 4 and 8, in the case of the Cu-Ag alloy wire with an Ag content of 6.0 mass%, in Examples 4-1 to 4-11 where the number ratio of the Ag phase in Formula (1) is 50% or more, sufficient conductivity and a tensile strength sufficiently high compared to Comparative Example 4-1 (tensile strength: 1470 MPa, tensile strength after reheat treatment: 1270 MPa) were confirmed, and it was confirmed that the tensile strength was sufficiently high even after reheat treatment.

[0174] In addition, in Examples 4-1, 4-3 to 4-11 where the number ratio of the Ag phase at the grain boundaries is 15% or more and 35% or less, a particularly high increase in the tensile strength after reheat treatment was confirmed, and the tensile strength was excellent.

[0175] 2. Experiment 2: Fabrication and Evaluation of Cu-Ag Alloy Wires Containing Additive Elements

[0176] Except for adding the specified amounts of additive elements shown in Table 9, Cu-Ag alloy wires of Examples 5-1 to 5-8 and Comparative Example 5-1 were fabricated under the fabrication conditions shown in Table 9 in the same manner as in Examples 2-1 to 2-11 of Experiment 1, and evaluated in the same manner as in Experiment 1. In addition, Comparative Example 5-1 was used as a control for the tensile test.

[0177] [Table 9]

[0178]

[0179] [Table 10]

[0180]

[0181] As shown in Tables 9 and 10, in the case of a Cu-Ag alloy wire to which a sub-additive element is added in the range of 0.05% by mass or more and 0.30% by mass or less, in Examples 5-1 to 5-8 where the number ratio of the Ag phase is 50% or more in Formula (1), sufficient conductivity and a tensile strength sufficiently higher than that of Comparative Example 5-1 (tensile strength: 1060 MPa, tensile strength after reheat treatment: 900 MPa) were confirmed, and it was confirmed that the tensile strength was sufficiently high even after reheat treatment.

[0182] In addition, in Examples 5-1 to 5-8 where the number ratio of the Ag phase at the grain boundaries is 15% or more and 35% or less, a particularly high increase in the tensile strength after reheat treatment was confirmed, and the tensile strength was excellent.

[0183] [Table 11]

[0184]

[0185] In addition, as shown in Table 11, compared with Example 2-1 manufactured under the same conditions with the same Ag content of 2.0% by mass, in Examples 5-1 to 5-8 manufactured by adding a sub-additive element, both the tensile strength and the tensile strength after reheat treatment were high, and it was confirmed that the addition of the sub-additive element could improve both the tensile strength and the tensile strength after reheat treatment.

[0186] Reference numerals

[0187] 1 Cu phase

[0188] 2 Coarse Ag phase

[0189] 2f Fibrous coarse Ag phase

[0190] 3 Fine Ag phase

[0191] 3f Fibrous fine Ag phase

[0192] 10, 10a, 10b, 10c, 20, 20a, 20b Cu-Ag alloy materials

Claims

1. A Cu-Ag alloy wire has the following composition, that is, it contains 1% by mass or more and 6% by mass or less of Ag, and the balance is composed of Cu and inevitable impurities. The aforementioned Cu-Ag alloy wire has a metal structure including a Cu phase as a matrix phase and a plurality of Ag phases as second phases. When the cross-sectional area of the cross-section orthogonal to the long side direction of the aforementioned Cu-Ag alloy wire is set to σ (μm 2 ), and the diameter of a perfect circle having the same area as each Ag phase existing in the aforementioned cross-section is set to D (μm), the following formula (1) is satisfied [Formula 1] (In formula (1), π represents the ratio of the circumference of a circle to its diameter) Moreover, the proportion of the number of Ag phases with a diameter D of less than 5 nm to the total number of Ag phases is 50% or more.

2. The Cu-Ag alloy wire according to claim 1, wherein, In the aforementioned cross-section of the aforementioned Cu-Ag alloy wire, the proportion of the number of Ag phases present at the grain boundaries of the aforementioned Cu phase to the total number of Ag phases is 15% or more and 35% or less.

3. The Cu-Ag alloy wire according to claim 1, wherein, The aforementioned composition further contains at least one sub-additive element selected from the group consisting of Sn, Mg, Zn, In, Ni, Co, Zr, and Cr in the range of 0.05% by mass or more and 0.3% by mass or less, respectively.

4. The Cu-Ag alloy wire according to any one of claims 1 to 3, wherein The aforementioned Cu-Ag alloy wire is a round wire having a wire diameter of 0.01 mm or more and 0.08 mm or less.

5. The Cu-Ag alloy wire according to any one of claims 1 to 3, wherein The aforementioned Cu-Ag alloy wire is a flat wire having a substantially rectangular cross-sectional shape, and the substantially rectangular cross-sectional shape has a width of 0.02 mm or more and 0.32 mm or less and a thickness of 0.002 mm or more and 0.04 mm or less.

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