JP7681978B2 - Composite wire and coated wire - Google Patents

Description

This disclosure relates to composite wires and coated wires.

Patent Document 1 discloses a copper-clad aluminum wire as a conductor wire, which includes a core wire and an outer sheath that covers the outer periphery of the core wire. A representative example of a copper-clad aluminum wire is a composite wire made of pure metal, as shown in Sample No. 31 in Table 3 of Patent Document 1. In this composite wire, the core wire is made of pure aluminum, such as electrical aluminum. The outer sheath that covers the core wire is made of pure copper, such as oxygen-free copper. Hereinafter, this composite wire may be referred to as a pure metal composite wire.

Patent Document 1 also discloses a composite wire having a core wire made of an aluminum alloy containing Fe as an additive element. Hereinafter, this composite wire may be referred to as an alloy composite wire. This alloy composite wire is obtained by subjecting an ingot or hot-rolled material made of the above aluminum alloy to a specific two-stage annealing process. The obtained alloy composite wire has higher tensile strength and higher elongation than a pure metal composite wire.

Japanese Unexamined Patent Publication No. 53-110082

A thinner composite wire is desired that is stronger and more flexible than the pure metal composite wire described above. Furthermore, a composite wire that is excellent in electrical conductivity and manufacturability is also desirable.

The inventors have found that when an aluminum alloy containing Fe as an additive element is subjected to the above-mentioned specific two-stage annealing, breakage is likely to occur during cold drawing after annealing. Therefore, no composite wire with a core wire made of an aluminum alloy containing Fe as an additive element and a wire diameter of less than 0.5 mmφ has been obtained.

Therefore, one of the objectives of this disclosure is to provide a thin composite wire that has excellent strength and elongation.

The composite wire of the present disclosure is a composite wire comprising a core wire and an outer sheath covering the outer periphery of the core wire, the core wire is made of an aluminum alloy containing 1.0% to 4.0% by mass of Fe with the balance being Al and unavoidable impurities, the outer sheath is made of pure copper or a copper alloy, and has a wire diameter of less than 0.2 mm.

The coated wire of the present disclosure is a coated wire comprising a conductor wire and an insulating coating that covers the outer periphery of the conductor wire, and the conductor wire is a composite wire of the present disclosure.

The composite wire and coated wire disclosed herein have excellent strength and elongation, and are thin.

FIG. 1 is a cross-sectional view showing an example of a composite wire according to an embodiment. FIG. 2 is a cross-sectional view showing another example of the composite wire according to the embodiment. FIG. 3 is a cross-sectional view illustrating an example of a covered wire according to the embodiment. FIG. 4 is a cross-sectional view showing another example of the covered wire according to the embodiment. FIG. 5 is a perspective view showing an outline of a coil made of a covered wire according to the embodiment.

[Description of the embodiments of the present disclosure]
First, the embodiments of the present disclosure will be listed and described.
(1) A composite wire according to one aspect of the present disclosure is a composite wire including a core wire and an outer sheath covering an outer periphery of the core wire, wherein the core wire is made of an aluminum alloy containing 1.0 mass% or more and 4.0 mass% or less of Fe with the remainder being Al and unavoidable impurities, the outer sheath is made of pure copper or a copper alloy, and has a wire diameter of less than 0.2 mm.

The composite wire of the present disclosure has a core wire made of an aluminum alloy containing Fe (iron) as an additive element, and is therefore superior in strength and elongation compared to the above-mentioned pure metal composite wire. Preferably, the composite wire of the present disclosure is stronger than the alloy composite wire described in Patent Document 1. In addition, the composite wire of the present disclosure is thinner than the above-mentioned alloy composite wire.

The reasons for the excellent strength and elongation are as follows.
The Fe in the aluminum alloy is present mainly as a compound containing Fe and Al (aluminum). The composite wire of the present disclosure has high strength due to the effect of improving strength by dispersion strengthening of the above compound. In addition, the size of the above compound is such that it is unlikely to become a starting point for cracking, as described below. Since breakage due to the above compound is unlikely to occur, the composite wire of the present disclosure has high elongation.

Furthermore, because Fe exists as the above-mentioned compound, the amount of Fe dissolved in Al is very small. Preferably, Fe is not substantially dissolved in Al. Compared to other aluminum alloys, such as aluminum alloys containing Mg and Si as additive elements, such an aluminum alloy can prevent the conductivity from decreasing due to the additive elements being dissolved in Al. From this point of view, the composite wire of the present disclosure also has excellent conductivity.

Furthermore, in the manufacturing process of the composite wire of the present disclosure, breaks originating from the above-mentioned compounds are unlikely to occur. Therefore, it is possible to mass-produce thin composite wires with a wire diameter of less than 0.2 mm. From this point of view, the composite wire of the present disclosure is also excellent in manufacturability.

When the composite wire disclosed in this disclosure is used as a conductor wire for coil wire, for example, it is possible to construct a small coil that is less likely to break even when subjected to vibration, etc.

(2) An example of the composite wire of the present disclosure is one in which the core wire has a structure in which a compound containing Fe and Al is dispersed, the particle size of the compound is 30 μm or less, and the ratio of the total number of particles of the compound having a particle size of more than 1 μm and not more than 3 μm to the total number of particles of the compound having a particle size of 30 μm or less is 5% or more and 20% or less.

In the above embodiment, the compound present in the core wire is a particle having a particle size of 30 μm or less, not a coarse particle exceeding 30 μm. Therefore, the effect of improving strength by dispersion strengthening of the compound is obtained well. In addition, particles having a particle size of 30 μm or less are unlikely to become the starting point of cracks. Furthermore, particles having a particle size of more than 1 μm and 3 μm or less contribute to promoting the softening of the core wire during the manufacturing process. The core wire is softened well by promoting softening. By reducing breakage and promoting softening, the above embodiment has better elongation.

Furthermore, particles with a particle size of 30 μm or less are unlikely to become the starting point of cracks during the manufacturing process. Therefore, breaks are unlikely to occur during wire drawing. Therefore, the above form has excellent manufacturability even when the wire diameter is 0.15 mm or less, or even thinner, 0.10 mm or less.

(3) An example of the composite wire of (2) above is one in which the ratio of the total number of particles having a particle size of more than 1 μm and not more than 2 μm to the total number of particles having a particle size of 30 μm or less in the compound is 5% or more and 15% or less.

Of the above compounds, particles with a particle size of more than 1 μm and less than 2 μm tend to promote the softening of the core wire. Therefore, the above form tends to further increase elongation.

(4) An example of a composite wire according to the present disclosure is one in which the ratio of the cross-sectional area of the outer skin to the cross-sectional area of the composite wire in a cross section cut along a plane perpendicular to the axial direction of the composite wire is 10% or more and 80% or less.

The above configuration, by providing an appropriate outer sheath, has excellent electrical conductivity and solder wettability, and is also easy to make lightweight.

(5) An example of a composite wire according to the present disclosure is one having a breaking elongation of 8% or more.

The above configuration is less likely to break even if subjected to vibration or bending with a small bending radius.

(6) An example of a composite wire of the present disclosure is one having a tensile strength of 200 MPa or more.

The above configuration is less likely to break even when subjected to vibration, etc.

(7) An example of a composite wire according to the present disclosure is one having a conductivity of 58% IACS or more.

The above form has excellent electrical conductivity. Therefore, the above form is suitable for use as a conductor wire.

(8) An example of a composite wire according to the present disclosure is one in which the cross-sectional shape of the composite wire cut along a plane perpendicular to the axial direction is non-circular.

The above configuration allows for a high degree of freedom in the cross-sectional shape.

(9) A coated wire according to one aspect of the present disclosure is a coated wire comprising a conductor wire and an insulating coating covering the outer periphery of the conductor wire, the conductor wire being any one of the composite wires described above in (1) to (8).

The coated wire of the present disclosure has excellent strength and elongation, and is thin. In addition, the coated wire of the present disclosure has excellent electrical conductivity and is easy to manufacture.

When the coated wire of the present disclosure is used, for example, as a wire material for coils, it is difficult to break even when subjected to vibrations, and a small coil can be constructed. In addition, the coated wire of the present disclosure has excellent elongation, making it easy to wind. Therefore, the coated wire of the present disclosure is easy to manufacture into coils.

[Details of the embodiment of the present disclosure]
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same reference numerals denote the same objects.

[Composite wire]
A composite wire 1 according to an embodiment will be described with reference to FIGS.
1 and 2 are cross-sectional views of a composite wire 1 according to an embodiment, taken along a plane perpendicular to its axial direction. Hereinafter, this cross section may be referred to as a transverse section. The axial direction corresponds to the longitudinal direction of the composite wire 1.

(overview)
The composite wire 1 of the embodiment includes a core wire 11 and an outer sheath 12. The outer sheath 12 covers the outer periphery of the core wire 11. The composite wire 1 is a copper-clad aluminum alloy wire in which the core wire 11 is made of an aluminum alloy and the outer sheath 12 is made of pure copper or a copper alloy.

In particular, in the composite wire 1 of the embodiment, the additive element of the aluminum alloy constituting the core wire 11 is Fe (iron). The wire diameter of the composite wire 1 is less than 0.2 mm.
The details will be explained below.

(Core wire)
<Constituent Materials>
The material of the core wire 11 is an aluminum alloy containing 1.0% by mass to 4.0% by mass of Fe, with the remainder being aluminum (Al) and unavoidable impurities. The content (mass %) of the additive element here is the mass ratio with the aluminum alloy being 100% by mass.

Since the aluminum alloy constituting the core wire 11 contains Fe as an additive element, the core wire 11 has excellent mechanical properties such as strength and elongation, and also has excellent electrical conductivity, as described below. As a result, the composite wire 1 including such a core wire 11 has excellent strength, elongation, and electrical conductivity.

The amount of Fe dissolved in Al is very small. Therefore, Fe exists in the aluminum phase, which is the parent phase, as a compound containing mainly Fe and Al. In particular, in the composite wire 1 of the embodiment, the compound exists as small and fine particles, not as coarse particles. The small and fine particles are dispersed in the parent phase, which improves the strength of the core wire 11. Thus, the composite wire 1 has excellent strength. In addition, the small and fine particles are unlikely to become the starting point of cracks, so that the core wire 11 is unlikely to break. Thus, the composite wire 1 has excellent elongation. Furthermore, since Fe is not dissolved in Al but exists as the compound, the decrease in electrical conductivity caused by Fe being dissolved in Al is easily suppressed. That is, the core wire 11 easily maintains the electrical conductivity of Al itself. In addition, since the compound is small, it is unlikely to obstruct the conductive path in Al. The composite wire 1 having such a core wire 11 has excellent electrical conductivity.

If the Fe content is 1.0 mass% or more, compounds containing Fe and Al are appropriately present. Therefore, the effect of improving strength by dispersion strengthening can be obtained well. The higher the Fe content, the higher the strength is likely to be. From the viewpoint of improving strength, the Fe content may be 1.2 mass% or more, 1.5 mass% or more, or 1.8 mass% or more. If the Fe content is 2.0 mass% or more, the strength is likely to be higher.

If the Fe content is 4.0% by mass or less, the compound containing Fe and Al is less likely to become coarse. It is also easy to prevent the total amount of the above compounds from becoming excessive. As a result, elongation and electrical conductivity are more likely to be high. The lower the Fe content, the more easily the coarsening of the above compounds and the excessive inclusion of the above compounds are prevented. From the viewpoint of improving elongation and electrical conductivity, the Fe content may be 3.8% by mass or less, 3.5% by mass or less, or 3.2% by mass or less. If the Fe content is 3.0% by mass or less, elongation and electrical conductivity are more likely to be high.

If the Fe content is 1.2% by mass or more and 3.8% by mass or less, 1.5% by mass or more and 3.5% by mass or less, and particularly 1.8% by mass or more and 2.2% by mass or less, the composite wire 1 has a good balance of strength, elongation, and electrical conductivity.

The total content of unavoidable impurities is, for example, 0.1% by mass or less.

<Organization>
The core wire 11 has a structure in which a compound containing Fe and Al is dispersed in a matrix. The particle size of the compound is preferably 30 μm or less. This is because the following effects (a) to (c) can be obtained.

(a) The above compounds are easily dispersed in the matrix. Therefore, the effect of improving the strength due to the dispersion strengthening of the compounds is effectively obtained. By having a dispersion strengthened structure due to the compounds, the composite wire 1 has excellent strength.
(b) The compounds are unlikely to become the starting point of cracks. In other words, the compounds having a particle size of 30 μm or less are unlikely to affect wire breakage. Since the compounds are unlikely to break, the composite wire 1 has excellent elongation. Breakage is unlikely to occur during the manufacturing process. Therefore, continuous wire drawing is possible, and the composite wire 1 has excellent manufacturability.
(c) The above compounds are unlikely to block the conductive paths in the Al, so that the composite wire 1 has excellent conductivity.

When the core wire 11 contains coarse particles of more than 30 μm consisting of a compound containing Fe and Al, the number of the above compounds present in the parent phase tends to be small when the Fe content is constant. Therefore, the above compounds tend to be unevenly distributed in the parent phase. Furthermore, the above coarse particles are equivalent to more than 15% of the wire diameter of the core wire 11. Such coarse particles tend to become the starting point of cracks and tend to obstruct the conductive path in the Al. The wire diameter of the composite wire 1 is the sum of the wire diameter of the core wire 11 and the thickness of the outer sheath 12. Therefore, the wire diameter of the core wire 11 is naturally less than 0.2 mm.

Of the compounds containing Fe and Al, the ratio of the _total number S3 of particles having a particle size of more than 1 μm and not more than 3 μm to the total number Sall of particles having a particle size of ₃₀ μm or less is preferably 5% or more and 20% or less. The inventors have found that particles having the above-mentioned specific particle size made of the above compound contribute to promoting the softening of the core wire 11 during the manufacturing process. By being well softened during the manufacturing process, the core wire 11 has excellent elongation. The composite wire 1 including such a core wire 11 has excellent elongation.

Hereinafter, compounds containing Fe and Al and having a particle size of more than 1 μm and not more than 3 μm may be referred to as small particles. The above compounds having a particle size of more than 1 μm and not more than 2 μm may be referred to as first particles. The above compounds having a particle size of more than 2 μm and not more than 3 μm may be referred to as second particles. The ratio of the total number of particles having a predetermined particle size to the total number of particles having a particle size of 30 μm or less, S _all , may be referred to as the compound ratio. The compound ratio in the small particles is calculated by (S ₃ /S _all )×100.

Here, it is preferable that the Fe in the aluminum alloy constituting the core wire 11 exists as a compound containing Fe and Al as much as possible. Furthermore, if all of the compounds in the aluminum alloy are fine, for example, with a particle size of 10 μm or less, or even 5 μm or less, the compounds are easily dispersed in the aluminum alloy. Therefore, an improvement in strength can be expected. However, if the particle size of all of the compounds is 1 μm or less, the core wire 11 is not sufficiently softened during the manufacturing process of the composite wire 1. As a result, the elongation is low.

In contrast, if the compound ratio in the small particles is 5% or more, the Fe in the aluminum alloy is appropriately present as small particles consisting of a compound containing Fe and Al. Therefore, the core wire 11 is well softened during the manufacturing process. The greater the compound ratio in the small particles, the easier it is to promote the softening of the core wire 11. Therefore, the elongation is likely to be high. From the viewpoint of improving elongation, the compound ratio may be 6% or more, 9% or more, or 12% or more.

If the proportion of the compound in the small particles is 20% or less, the decrease in strength and decrease in elongation caused by a large number of small particles is likely to be reduced. The smaller the proportion of the compound, the less the decrease in strength and decrease in elongation is likely to be. From the viewpoint of suppressing the decrease in strength and the decrease in elongation, the proportion of the compound may be 18% or less, 16% or less, or 14% or less.

Furthermore, among the above-mentioned small particles, the ratio of the total number _S2 of particles having a particle size of more than 1 μm and not more than 2 μm to the total number S _all of particles having a particle size of 30 μm or less is preferably 5% or more and 15% or less. That is, the core wire 11 preferably includes first particles made of a compound containing Fe and Al. Also, the total number of second particles is preferably less than the total number _S2 of the first particles. The first particles are easier to reduce the softening temperature than the second particles. Therefore, when the core wire 11 includes the first particles, the softening of the core wire 11 is easily promoted during the manufacturing process. Also, the first particles are smaller than the second particles, and therefore (1) they are easily dispersed, (2) they are less likely to become the starting point of cracks, and (3) they are less likely to obstruct the conductive path in Al. The composite wire 1 including such a core wire 11 has high elongation and is more excellent in strength and conductivity. The compound ratio in the first particles is calculated by ( _S2 / _Sall )×100.

If the compound ratio in the first particles is 5% or more, the effects of promoting softening, strengthening dispersion, reducing cracking, and ensuring conductive paths, as described above, are easily obtained. Since these effects are well obtained, the compound ratio may be 6% or more, 7% or more, or 8% or more. It is preferable that the compound ratio is 5% or more and that more than half of the small particles are first particles.

If the compound ratio in the first particles is 15% or less, the number of first particles is relatively small. Such a core wire 11 has better manufacturability than a core wire in which the compound ratio exceeds 15%. From the viewpoint of manufacturability, the compound ratio may be 14% or less, 13% or less, or 12% or less. The compound ratio may further be 10% or less.

Of the above-mentioned small particles, the ratio of the total number of second particles having a particle size of more than 2 μm and not more than 3 μm to the total number of particles S _all having a particle size of 30 μm or less is, for example, 1% or more and 10% or less. The compound ratio in the second particles may be 9% or less, 8% or less, 7% or less, or even 5% or less. Or, the compound ratio may be 0%. In other words, the core wire 11 does not need to include second particles as long as it includes first particles.

In particular, a composite wire 1 having a core wire 11 that is a compound containing Fe and Al, has a particle size of 30 μm or less, and contains small particles in the above-mentioned range, has a good balance of strength, elongation, and conductivity. Furthermore, when the core wire 11 contains the first particles of the small particles in the above-mentioned range, the strength, elongation, and conductivity are likely to be higher.

The particle size of the compound containing Fe and Al is measured as follows.
A cross section of the composite wire 1 is taken. The core wire 11 in the cross section is observed with a scanning electron microscope (SEM). Multiple fields of view are taken from the SEM observation image. The size of the field of view can be about 20 μm × 20 μm. The observation image of each field of view is subjected to image processing to approximate the compound to an ellipse. The major axis length of the approximated ellipse particle is taken as the particle size of the compound. Details of the measurement method will be described in the test example below.

For a compound containing Fe and Al, the compound ratio in a given particle size is determined as follows.
The compound is divided into predetermined particle size classes according to the particle size of the compound. The total numbers _S2 , _S3 , etc. of each class are calculated. The total number _Sall of all classes is also calculated. Then, ( _S2 / _Sall ) x 100, etc. are calculated.

(outer skin)
1 and 2, the outer sheath 12 is an annular region that continuously covers the outer periphery of the core wire 11 in the circumferential direction of the core wire 11. The material of the outer sheath 12 is pure copper or a copper alloy. The composite wire 1 having the outer sheath 12 made of a metal mainly composed of copper is superior in electrical conductivity, solder wettability, corrosion resistance, etc. to the composite wire 1 having only the core wire 11.

Here, pure copper contains 99.9% by mass or more of Cu (copper), with the remainder consisting of inevitable impurities. Pure copper is generally softer than copper alloys and has excellent electrical conductivity. Therefore, the composite wire 1 having an outer sheath 12 made of pure copper is easy to bend and has excellent flexibility, as well as excellent electrical conductivity. Specific examples of pure copper include oxygen-free copper, tough pitch copper, electrolytic copper, and phosphorus-deoxidized copper.

The copper alloy contains additive elements, with the remainder being Cu and unavoidable impurities, with Cu being the most abundant element. The additive elements include, for example, one or more elements selected from the group consisting of Zr (zirconium), P (phosphorus), Sn (tin), Ag (silver), and Fe. The total content of the additive elements is, for example, 0.01% by mass or more and 1% by mass or less. Copper alloys generally have greater strength than pure copper. Therefore, the composite wire 1 having an outer sheath 12 made of a copper alloy has greater strength.

(Hull ratio)
In the cross section of the composite wire 1, the ratio of the cross-sectional area _S12 of the outer skin 12 to the cross-sectional area _S1 of the composite wire 1 can be selected in the range of more than 0% to less than 100%. Hereinafter, the ratio of the cross-sectional area _S12 of the outer skin 12 to the cross-sectional area _S1 of the composite wire 1 may be referred to as the outer skin ratio. The outer skin ratio (%) is calculated by ( _S12 / _S1 )×100.

The skin ratio is, for example, 10% or more and 80% or less.
When the sheath ratio is 10% or more, the effect of improving the electrical conductivity by providing the sheath 12 can be satisfactorily obtained. The larger the sheath ratio, the more excellent the electrical conductivity of the composite wire 1. From the viewpoint of improving the electrical conductivity, the sheath ratio may be 12% or more, 15% or more, 18% or more, or 20% or more.

If the skin ratio is 80% or less, the weight increase due to the skin 12 is small. Therefore, the composite wire 1 is likely to be lightweight. The smaller the skin ratio, the lighter the composite wire 1 is. From the perspective of weight reduction, the skin ratio may be 70% or less, 60% or less, or 50% or less.

From the viewpoint of good electrical conductivity and weight reduction, the skin ratio may be 10% or more and 50% or less, 15% or more and 40% or less, or 15% or more and 35% or less.

The thickness of the outer sheath 12 is typically uniform along the circumferential direction of the core wire 11, as shown in Figures 1 and 2. The thickness of the outer sheath 12 is adjusted so that the outer sheath ratio falls within the above range.

(Interface condition between core wire and outer sheath)
In the composite wire 1 of the embodiment, it is preferable that a compound containing Al derived from the core wire 11 and Cu derived from the outer sheath 12 is substantially absent at the interface between the core wire 11 and the outer sheath 12. The compound containing Al and Cu becomes the starting point of cracks, thereby preventing the composite wire 1 from breaking. The compound containing Al and Cu is typically generated by heating a wire having a metal coating made of pure copper or a copper alloy to a temperature of 280° C. or higher in the manufacturing process of the composite wire 1. The above temperature may further be 300° C. or higher, or 400° C. or higher. Since the above compound is generated, it is preferable that heat treatment and hot working at a heating temperature of 280° C. or higher is not performed in the manufacturing process of the composite wire 1.

(Wire diameter)
The composite wire 1 has a small wire diameter of less than 0.2 mm. Such a composite wire 1 is suitable for a conductor wire that is desired to have excellent strength and elongation, excellent conductivity, and further small size and light weight. Examples of such a conductor wire include conductor wires for electric wires used in portable electronic devices and small electronic devices, and in particular conductor wires for coil wires. The wire diameter of the composite wire 1 may be 0.15 mm or less, 0.12 mm or less, or even 0.10 mm or less. In particular, if the composite wire 1 having a wire diameter of less than 0.1 mm, or even 0.08 mm or less is used as a conductor wire for coil wires, a smaller coil can be obtained. From the viewpoint of manufacturability, the wire diameter of the composite wire 1 may be, for example, 0.01 mm or more, or even 0.02 mm or more.

The wire diameter of composite wire 1 here is the diameter of the smallest circle that contains the outline of composite wire 1 in the cross section of composite wire 1. If composite wire 1 has a circular cross section as shown in Fig. 1, the wire diameter of composite wire 1 corresponds to the outer diameter of outer jacket 12. As will be described later, if composite wire 1 has a square cross section, the wire diameter of composite wire 1 corresponds to the length of the diagonal of the square.
In addition, in the square composite wire 1 having a diagonal length of less than 0.2 mm, the length of one side of the square is, for example, 0.03 mm or more and 0.14 mm or less.

(Cross-sectional shape)
The cross-sectional shape of the composite wire 1 can be appropriately selected. A typical cross-sectional shape is a circle as shown in FIG. 1. The cross-sectional shape of the composite wire 1 may be non-circular. Examples of non-circular cross-sectional shapes include curved shapes such as polygons and ellipses. Examples of polygons include a rectangle as shown in FIG. 2 and other shapes such as a hexagon. Examples of rectangles include a square. The composite wire 1 may be a round wire as shown in FIG. 1, a rectangular wire as shown in FIG. 2, or another irregular shape. In this way, the composite wire 1 has a high degree of freedom in terms of shape.

The cross-sectional shape of the core wire 11 is typically similar to the cross-sectional shape of the composite wire 1, as shown in Figures 1 and 2.

(characteristic)
The composite wire 1 of the embodiment satisfies at least one of the following: a tensile strength of 200 MPa or more, a breaking elongation of 8% or more, and an electrical conductivity of 58% IACS or more. It is preferable that the composite wire 1 satisfies two of the above three items, and more preferably satisfies all three items.

Tensile strength
If the tensile strength of the composite wire 1 is 200 MPa or more, the composite wire 1 has a strength superior to that of the above-mentioned pure metal composite wire. Preferably, the composite wire 1 has a strength superior to that of the above-mentioned alloy composite wire. The higher the tensile strength, the stronger the composite wire 1 is, and the less likely it is to break even when subjected to vibration or the like. From the viewpoint of improving strength, the tensile strength may be 205 MPa or more, 210 MPa or more, 215 MPa or more, or 220 MPa or more. The higher the Fe content of the core wire 11 and the higher the sheath ratio, the higher the tensile strength tends to be.

The higher the tensile strength of the composite wire 1, the more likely it is that the elongation will decrease. From the viewpoint of improving elongation, the tensile strength may be 320 MPa or less, or 300 MPa or less.

<stretch>
If the breaking elongation of the composite wire 1 is 8% or more, the composite wire 1 has excellent elongation. The higher the breaking elongation, the better the elongation of the composite wire 1 and the less likely it is to break even when subjected to vibration or bending with a small bending radius. Furthermore, the composite wire 1 is easy to bend and has excellent flexibility. From the viewpoint of improving elongation, the breaking elongation may be 9% or more, 10% or more, or 12% or more.

The higher the breaking elongation of the composite wire 1, the more likely it is that the tensile strength will decrease. From the perspective of improving strength, the breaking elongation may be 35% or less, or 30% or less.

In particular, if the tensile strength of the composite wire 1 is 200 MPa or more and 320 MPa or less, and the breaking elongation of the composite wire 1 is 8% or more and 35% or less, the composite wire 1 has high strength and high toughness.

<conductivity>
If the electrical conductivity of the composite wire 1 is 58% IACS or more, the composite wire 1 has excellent electrical conductivity and can be used well as a conductor wire. In applications where the conductor wire is used, the higher the electrical conductivity, the more preferable it is, and it may be 60% IACS or more, 61% IACS or more, or 62% IACS or more. The higher the proportion of the outer sheath, the higher the electrical conductivity tends to be. Depending on the proportion of the outer sheath, the electrical conductivity may be 65% IACS or more, 68% IACS or more, or 70% IACS or more.

The Fe content, sheath ratio, manufacturing conditions, etc. may be adjusted so that the tensile strength, breaking elongation, and electrical conductivity of the composite wire 1 fall within the above-mentioned ranges. Examples of manufacturing conditions include the cooling rate during the casting process, the degree of wire drawing, and softening conditions.

(Main actions and effects)
The composite wire 1 of the embodiment has a core wire 11 made of an aluminum alloy containing Fe as an additive element, and therefore has excellent strength and elongation. The composite wire 1 also has excellent electrical conductivity. Such a composite wire 1 can be suitably used as a conductor wire. Furthermore, although the composite wire 1 has a small wire diameter of less than 0.2 mm, it also has excellent manufacturability.

[Coated wire]
The coated wire 2 according to the embodiment will be described with reference to FIGS.
3 and 4 are cross-sectional views of the coated wire 2 according to the embodiment taken along a plane perpendicular to its axial direction. This cross-section corresponds to a cross-section taken along line III-III in FIG. 5, which will be described later. The axial direction corresponds to the longitudinal direction of the coated wire 2.

The coated wire 2 of the embodiment includes a conductor wire 20 and an insulating coating 25. The insulating coating 25 covers the outer circumference of the conductor wire 20. The conductor wire 20 is a composite wire 1 of the embodiment. Figure 3 shows a coated wire 2 having a circular cross-sectional shape. The composite wire 1 included in the coated wire 2 shown in Figure 3 is a round wire having a circular cross-sectional shape as shown in Figure 1. Figure 4 shows a coated wire 2 having a rectangular cross-sectional shape. The composite wire 1 included in the coated wire 2 shown in Figure 4 is a rectangular wire having a rectangular cross-sectional shape as shown in Figure 2.

The insulating coating 25 may be made of various electrical insulating materials, such as resins. When the coated wire 2 is a coil wire, the resin that makes up the insulating coating 25 may be, for example, polyimide, polyamideimide, polyesterimide, polyurethane, polyester, polyolefin, polyamide, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polytetrafluoroethylene, etc.

The insulating coating 25 may be a single layer or a multi-layer of two or more layers. The thickness of the insulating coating 25 may be selected depending on the magnitude of the current flowing through the conductor wire 20. The thickness of the insulating coating 25 may be, for example, 5 μm or more and 50 μm or less. As shown in Figures 3 and 4, the thickness of the insulating coating 25 is typically uniform along the circumferential direction of the conductor wire 20. Therefore, the cross-sectional shape of the coated wire 2 is similar to the cross-sectional shape of the conductor wire 20, i.e., the cross-sectional shape of the composite wire 1.

In addition, the coated wire 2 may have a self-lubricating layer or a self-adhesive layer, etc., as the outermost layer (not shown).

The conductor wire 20 substantially maintains the composition, structure, characteristics, wire diameter, etc. of the composite wire 1 of the embodiment. Therefore, the coated wire 2 of the embodiment has excellent strength and elongation. The coated wire 2 also has excellent conductivity. Such a coated wire 2 can be suitably used as an electric wire, for example, a coil wire. Since the coated wire 2 is thin, a small coil can be constructed. Furthermore, since the composite wire 1 constituting the conductor wire 20 has excellent manufacturability, the coated wire 2 also has excellent manufacturability.

[coil]
A coil 3 using a coated wire 2 will be described with reference to FIG.
The coil 3 includes a winding portion 30 made of the coated wire 2 of the embodiment. The winding portion 30 is formed by winding the coated wire 2 in a spiral shape. Fig. 5 illustrates the coil 3 using the coated wire 2 having a circular cross-sectional shape shown in Fig. 3 .

The number of turns of the winding section 30, the inner diameter of the coil 3, etc. can be selected appropriately.

The coil 3 is manufactured by winding the coated wire 2 of the embodiment. The coated wire 2 constituting the coil 3 substantially maintains the composition, structure, characteristics, wire diameter, etc. of the coated wire 2 before winding. Therefore, the coil 3 has excellent strength and elongation. The coil 3 also has excellent conductivity. Furthermore, the coil 3 is small because it is composed of the coated wire 2 having the conductor wire 20 with a wire diameter of less than 0.2 mm.

As described above, coil 3 is small, making it suitable for use as a voice coil, motor coil, or earphone coil in portable electronic devices or small electronic devices. In particular, coil 3 is not prone to breakage even when subjected to vibration, making it suitable for use as a voice coil that is easily subjected to vibration.

[Method of manufacturing composite wire]
The composite wire 1 of the embodiment can be produced, for example, by a composite wire production method including the following steps.
(First step) A continuously cast and rolled material is produced from an aluminum alloy containing 1.0 mass % or more and 4.0 mass % or less of Fe, with the balance being Al and unavoidable impurities.
The cooling rate in the continuous casting process is 0.5° C./sec or more.
(Second step) The above-mentioned continuously cast and rolled material, or a processed material having a predetermined wire diameter obtained by cold working the above-mentioned continuously cast and rolled material, is used as a core material, and a metal coating portion is formed to cover the outer periphery of the core material.
The metal coating portion is made of pure copper or a copper alloy.
(Third step) The composite material comprising the core material and the metal coating portion is subjected to cold wire drawing to produce a drawn wire material having a wire diameter of less than 0.2 mm.
(Fourth step) The drawn wire is subjected to a softening treatment.
The heating temperature in the softening treatment is less than 280°C.

The above-mentioned method for producing a composite wire is based on the following findings.
In order to increase the strength of the composite wire having a core wire and a sheath, the material of the core wire is preferably an aluminum alloy rather than pure aluminum. In order to obtain a composite wire having excellent strength and excellent electrical conductivity, the additive element of the aluminum alloy is preferably Fe rather than Mg, Si, etc. Furthermore, in order to obtain a composite wire having excellent elongation, it is preferable that the core wire can be well softened.

Patent Document 1 discloses that two-stage annealing at a temperature of 400°C or higher increases the size of compounds containing Fe and Al, facilitating the softening of the core wire. It is believed that if hot rolling is performed after this annealing, the compounds are more likely to increase in size, i.e., the softening of the core wire is more likely to be promoted during the softening treatment. However, since the compounds are large, and contain coarse particles, particularly those with a particle size of more than 30 μm, breaks are likely to occur from these coarse particles during wire drawing. Therefore, it is practically impossible to mass-produce thin composite wires with a wire diameter of less than 0.2 mm.

In order to mass-produce a thin composite wire with a wire diameter of less than 0.2 mm, it is necessary to control the size of the compound containing Fe and Al to a size that is unlikely to become a starting point of cracks. Also, it is necessary to control the size of the compound to a size that can promote the softening of the core wire. The inventors have found that in order to control the size of the compound to such a size, it is preferable to set the cooling rate in the casting process to 0.5°C/sec or more depending on the Fe content. Also, it has been found that it is preferable not to heat the wire to a temperature at which the compound is likely to grow in size in the manufacturing process after continuous casting and rolling. For example, it has been found that it is preferable not to perform annealing, hot working, etc. at 400°C or more.
Each step will be explained below.

(First step)
The first step is a step of producing an aluminum alloy material that will be the raw material of the core wire 11 provided in the composite wire 1. This aluminum alloy material is a continuous cast and rolled material. For the composition of the aluminum alloy material, refer to the above-mentioned (Core Wire) <Constituent Materials> section. A known continuous casting and rolling apparatus can be used to produce the continuous cast and rolled material.

The cooling rate in the continuous casting process is preferably 0.5°C/sec or more. The cooling rate here is the rate at which the temperature of the molten metal reaches 300°C. If the cooling rate is 0.5°C/sec, the particle size of the compound containing Fe and Al will be 30μm or less. In addition, small particles of the compound having the above-mentioned specific particle size are generated. The generation of small particles can promote the softening of the core wire in the fourth step. If the particle size is 30μm or less, the above-mentioned effects (a) to (c) can be obtained.

The higher the Fe content, the easier it is to generate a compound containing Fe and Al. Therefore, it is preferable to adjust the cooling rate according to the Fe content. Depending on the Fe content, the cooling rate may be 0.8°C/sec or more, 1.0°C/sec or more, 1.5°C/sec or more, or 2.0°C/sec or more. The higher the cooling rate, the easier it is to make the compound finer. If the cooling rate is, for example, 3.0°C/sec or more, fine particles with a particle size of 5 μm or less are more likely to be produced. As a result, breaks are less likely to occur. Since breaks are less likely to occur, in the composite wire 1 of the embodiment, the upper limit of the Fe content can be made larger than the upper limit of the Fe content in the alloy composite wire of Patent Document 1. It is believed that if the cooling rate is 15°C/sec or less or 8°C/sec or less, the above-mentioned small particles are more reliably generated.

The wire diameter of the continuously cast and rolled material can be appropriately selected. For example, the wire diameter can be set to a value that makes it easy to form a metal coating portion in the next second process. The wire diameter can also be made thinner by cold working the continuously cast and rolled material. The processing applied to the continuously cast and rolled material is cold working, not hot working. Therefore, the size of the compound containing Fe and Al generated during the continuous casting process does not change substantially before and after cold working. In other words, the processed material after cold working substantially maintains the size of the compound in the continuously cast and rolled material before cold working.

(Second process)
The second step is a step of manufacturing a metal coating portion which is a material for the outer sheath 12 of the composite wire 1. A known method for manufacturing a copper coating for a composite wire can be used to manufacture the metal coating portion. For example, the metal coating portion can be formed by using a tape material or a pipe material made of pure copper or a copper alloy, or by providing a plating layer made of pure copper or a copper alloy. The tape material is, for example, attached vertically or wound around the outer periphery of the core material so as to be arranged in a cylindrical shape. The thickness of the metal coating portion, i.e., the thickness of the tape material and the thickness of the plating layer, can be adjusted according to the above-mentioned outer sheath ratio, the degree of wire drawing, and the like. When the outer sheath ratio is relatively large, for example, when the outer sheath ratio is 20% or more, or even 50% or more, a relatively thick metal coating portion can be easily provided by using a pipe material. For details of pure copper and copper alloy, please refer to the above-mentioned (Outer Sheath) <Constituent Materials> section.

A component in which the above-mentioned tape material, pipe material, etc. is arranged on the outer periphery of the core material may be subjected to a cold tightening process before cold drawing. For the tightening process, for example, a diameter reduction process using a fitting die, a diameter reduction roll, etc. can be used. By performing the above-mentioned tightening process cold rather than hot, the size of the compound containing Fe and Al in the core material does not substantially change before and after the second process.

(Third step)
The third step is a step of producing a drawn wire material having a wire diameter of less than 0.2 mm from a composite material having a core material made of the above-mentioned aluminum alloy and a metal coating portion made of pure copper or a copper alloy. The drawn wire material has a core wire made of the above-mentioned aluminum alloy and an outer sheath made of pure copper or a copper alloy. By performing cold wire drawing until the wire diameter becomes less than 0.2 mm, the strength of the drawn wire material is increased by work hardening. A known wire drawing device can be used to produce the drawn wire material.

Because the wire drawing process applied to the composite material is cold processing rather than hot processing, the size of the compound containing Fe and Al in the core wire provided in the drawn wire material does not substantially change before and after the third process.

Intermediate heat treatment can be performed during the wire drawing. The intermediate heat treatment is intended to reduce processing distortion that occurs during the wire drawing process. The heating temperature for the intermediate heat treatment can be, for example, 200°C or higher and 250°C or lower. If the heating temperature is 250°C or lower, the processing distortion can be reduced while the compounds containing Fe and Al are less likely to become coarse.

(Fourth step)
The fourth step is a step of subjecting the drawn wire produced in the third step to a softening treatment, which is a heat treatment, for the purpose of improving elongation.

The higher the heating temperature of the softening treatment, the higher the elongation of the wire after the softening treatment. In addition, the processing distortion is reduced, and the electrical conductivity of the wire after the softening treatment is also likely to be high. However, the strength of the wire after the softening treatment is likely to decrease. In addition, the higher the heating temperature, the more likely the compound containing Al and Cu described above is generated at the interface between the core wire 11 and the outer sheath 12. This compound is likely to become the starting point of cracks, and cracks are likely to occur at the interface between the core wire 11 and the outer sheath 12. Therefore, the heating temperature of the softening treatment is preferably a temperature at which a compound containing Al and Cu is not generated. Here, the core wire of the drawn wire material subjected to the softening treatment contains the above-mentioned small particles that are a compound containing Fe and Al. Therefore, even if the heating temperature of the softening treatment is relatively low, the drawn wire material can be well softened. Specifically, the heating temperature of the softening treatment is less than 280°C.

If the heating temperature for the softening treatment is less than 280°C, the drawn wire material can be well softened, and a composite wire 1 having high elongation and excellent strength and electrical conductivity can be obtained. The heating temperature is preferably 200°C or higher and 250°C or lower. The holding time for the heating temperature is, for example, 1 hour or higher and 24 hours or lower.

If the softening process is a continuous process, it is advisable to adjust the process conditions, such as the linear speed, the current value, and the atmospheric temperature inside the furnace, so that they correspond to the heating temperatures described above.

The softening treatment causes the Fe dissolved in the aluminum alloy to precipitate as a compound containing Fe and Al. Alternatively, the softening treatment causes the compounds already present in the aluminum alloy to become slightly larger. However, as described above, the heating temperature of the softening treatment is relatively low. Therefore, the particle size of the newly precipitated compounds is small. Specifically, the particle size satisfies 30 μm or less. In addition, the change in the particle size of the compounds already present is small. Therefore, the particle size after the change satisfies 30 μm or less. The distribution of the compounds in the continuously cast and rolled material does not change substantially except when a heat treatment is performed at a temperature close to the melting point of the aluminum alloy, in other words, a high-temperature heat treatment is performed. Therefore, the distribution of the compounds in the composite wire 1 after the softening treatment substantially maintains the distribution of the compounds in the continuously cast and rolled material. In addition, it is expected that the precipitation of Fe will result in higher electrical conductivity and higher strength.

[Method of manufacturing coated wire]
The covered wire 2 of the embodiment can be produced, for example, by forming an insulating cover 25 on the outer periphery of the composite wire 1 of the embodiment. The insulating cover 25 can be formed by using a known method for producing an electrical insulating layer.

[Coil manufacturing method]
The coil 3 described above can be manufactured, for example, by winding the coated wire 2 of the embodiment. A known coil manufacturing method can be used as the winding method of the coated wire 2. The coated wire 2 of the embodiment is not easily broken and is easily bent even when bent with a small bending radius. Since the wound portion is easily formed, the coil 3 is also excellent in manufacturability.

[Test Example 1]
Tables 1 and 2 show the mechanical and electrical properties of a composite wire having a core made of an aluminum alloy containing Fe as an additive element and an outer sheath made of pure copper.

The aluminum alloys constituting the core wires have five different Fe contents: 1.0 mass%, 1.8 mass%, 2.0 mass%, 2.2 mass%, and 4.0 mass%. All of the aluminum alloys contain the above-mentioned Fe contents, with the remainder being Al and unavoidable impurities.
The core wires having an Fe content of 1.0 mass % are labeled No. 1 to No. 4.
The core wires having an Fe content of 1.8 mass % are labeled No. 5 to No. 8.
The core wires having an Fe content of 2.0 mass % are labeled No. 9 to No. 12.
The core wires having an Fe content of 2.2 mass % are labeled No. 13 to No. 16.
The core wires having an Fe content of 4.0 mass % are labeled No. 17 to No. 20.
The composite wires including the core wires No. 1 to No. 4 have the same Fe content in the core wires, but have different properties such as breaking elongation, as described below. This is also true for the composite wires including the core wires No. 5 to No. 20.

In all samples, the composite wire is a round wire with a circular cross-sectional shape. In addition, in all samples, the wire diameter of the composite wire is 0.05 mm (50 μm). However, in the cross section of the composite wire, the ratio of the cross-sectional area of the outer sheath to the cross-sectional area of the composite wire, i.e., the outer sheath ratio, is different. There are eight types of outer sheath ratios: 5%, 10%, 15%, 30%, 50%, 70%, 80%, and 85%. Each outer sheath is assigned the symbols No. 1 to No. 8 in order of the outer sheath ratio. The larger the outer sheath ratio, i.e., the larger the outer sheath number, the thicker the outer sheath and the smaller the wire diameter of the core wire.

Hereafter, the outer sheath number and core wire number will be combined in order and referred to as sample No. 4-14, etc.

(Samples No. 1-1 to No. 8-20)
The composite wire having the core wire made of the above-mentioned aluminum alloy is manufactured as follows.

Continuously cast and rolled material is manufactured from the above-mentioned aluminum alloy. For all samples, the cooling rate during the continuous casting process is 1°C/sec. The continuously cast and rolled material is in the form of a round bar with a wire diameter of 10 mm.

The above continuously cast and rolled material is subjected to cold wire drawing to produce a processed material with a wire diameter of 8 mm. The continuously cast and rolled material is not subjected to either heat treatment at a heating temperature of 280°C or higher or hot processing.

A metal coating made of pure copper is formed on the above processed material to manufacture the composite material. Here, a tape material made of oxygen-free copper or a seamless pipe material made of oxygen-free copper is used to form the metal coating. For samples with a relatively large outer sheath ratio, a seamless pipe material is used to form the metal coating. The thickness of the tape material and the seamless pipe material are adjusted according to the outer sheath ratio, etc.

The above composite material is subjected to cold wire drawing to produce a drawn wire material with a wire diameter of 0.05 mm. The above composite material is not subjected to either heat treatment at a heating temperature of 280°C or higher or hot processing.

A composite wire is obtained by subjecting the drawn wire material to a softening treatment. The heating temperature for the softening treatment is selected from the range of 200°C to 250°C. Here, the breaking elongation is used as an index, and the heating temperature is selected from the above temperature range so that the breaking elongation is a value selected from the range of 4% to 15%. The larger the breaking elongation, the higher the heating temperature. The same principle of using the breaking elongation as an index for selecting the heating temperature applies to the comparative samples described below. In this test, as shown in Tables 1 and 2, a composite wire with a breaking elongation of 4% or more was obtained.

(Sample No. 4-101 to No. 4-103)
As a comparative sample, the mechanical and electrical properties of a pure metal composite wire having a wire diameter of 0.05 mm are shown in Table 1. In the pure metal composite wires of Samples No. 4-101 to No. 4-103, the core wire is made of pure aluminum (pure Al), the outer sheath is made of pure copper, and the outer sheath ratio is 30%. Known manufacturing methods can be referred to for the basic manufacturing method of the pure metal composite wire. Specifically, continuous casting and rolling, cold wire drawing, and softening treatment are performed in this order. The heating temperature for the softening treatment is selected from the range of 300°C to 450°C.

(Samples No. 111 to No. 130)
As a comparative sample, a wire having a sheath ratio of 0% was used, and its mechanical and electrical properties are shown in Table 3. This wire is an aluminum alloy wire having no sheath, made of the above-mentioned aluminum alloy, and having a wire diameter of 0.05 mm.

The aluminum alloy wires of Samples No. 111 to No. 130 are manufactured as follows.
A continuous cast and rolled material is manufactured in the same manner as the manufacturing process of the core wire No. 1, etc. This continuous cast and rolled material is subjected to cold wire drawing to manufacture a drawn wire material having a wire diameter of 0.05 mm. This drawn wire material is subjected to softening treatment to obtain an aluminum alloy wire. The heating temperature for the softening treatment is selected from the range of 300°C to 450°C.

(Samples No. 131 to No. 134)
As a comparative sample, a wire having a sheath ratio of 100% was used, and its mechanical and electrical properties are shown in Table 3. This wire does not have a core wire made of an aluminum alloy, but is made of pure copper and is a pure copper wire with a wire diameter of 0.05 mm.

The pure copper wires of samples No. 131 to No. 134 can be manufactured by a known copper wire manufacturing method. Specifically, the steps are continuous casting and rolling, cold wire drawing, and softening treatment in that order.

(mechanical properties)
The mechanical properties referred to here are tensile strength (MPa) and breaking elongation (%). The tensile strength and breaking elongation are measured using a general-purpose tensile tester in accordance with JIS Z 2241:2011 "Metallic material tensile test method".

(Electrical characteristics)
The electrical property here is electrical conductivity (% IACS), which is measured by a bridge method.

The composite wires of samples No. 1-1 to No. 8-20, which have a core wire made of an aluminum alloy containing Fe as an additive element, and the pure metal composite wires of samples No. 4-101 to No. 4-103, which have the same breaking elongation, are compared. In this comparison, as shown in Tables 1 and 2, the composite wires of samples No. 1-1 to No. 8-20 have a higher tensile strength than the pure metal composite wires of samples No. 4-101 to No. 4-103. In addition, the composite wires of samples No. 1-1 to No. 8-20 have a breaking elongation of 4% or more. Many composite wires have a breaking elongation of 8% or more. This shows that a composite wire having a core wire made of an aluminum alloy containing 1.0 mass% to 4.0 mass% Fe and having a wire diameter of less than 0.2 mm, and even a thin composite wire of less than 0.1 mm in this case, can be obtained that has excellent strength and excellent elongation.

Hereinafter, attention will be focused on composite wires of samples No. 1-1 to No. 8-20.
As shown in Tables 1 and 2, these composite wires satisfy at least one of the following: tensile strength of 200 MPa or more, breaking elongation of 8% or more, and electrical conductivity of 58% IACS or more. Most of the composite wires with a sheath ratio of 10% or more satisfy two of the above three items. There are also many composite wires that satisfy all three items. This shows that it is possible to obtain a composite wire having a core wire made of an aluminum alloy containing 1.0% by mass or more and 4.0% by mass or less of Fe, a thin composite wire with a wire diameter of less than 0.2 mm, and further less than 0.1 mm in this case, which is excellent in strength and elongation as well as electrical conductivity.

Composite wires of samples No. 1-1 to No. 8-20 are compared with aluminum alloy wires of samples No. 111 to No. 130 shown in Table 3, which have the same Fe content and breaking elongation. From this comparison, it can be seen that the above composite wires have higher tensile strength than the above aluminum alloy wires, and are superior in strength. The reason for this is believed to be that the above composite wires have an outer sheath made of pure copper.

In particular, the tensile strength of the composite wire tends to be higher as the skin ratio increases. If the skin ratio is 10% or more, the tensile strength is 180 MPa or more. If the skin ratio is 15% or more, the tensile strength of many composite wires is 200 MPa or more. If the skin ratio is 15% or more and the Fe content is 1.8 mass% or more, the tensile strength of many composite wires is 220 MPa. Depending on the skin ratio, the tensile strength is 250 MPa or more.

Composite wires No. 1-1 to No. 8-20 are compared with aluminum alloy wires No. 111 to No. 130 shown in Table 3, which have the same Fe content. From this comparison, it can be seen that the composite wires have a higher electrical conductivity than the aluminum alloy wires, and are more excellent in electrical conductivity. This is thought to be because the composite wires have an outer sheath made of pure copper.

In particular, the greater the sheath ratio, the higher the electrical conductivity of the composite wire. If the sheath ratio is 15% or more, the electrical conductivity is 59% IACS or more. If the sheath ratio is 50% or more, the electrical conductivity is 70% IACS or more, and even 75% IACS or more.

However, the larger the sheath ratio, the higher the specific gravity, approaching the specific gravity of the pure copper wires of samples No. 131 to No. 134 shown in Table 3. Therefore, in order to obtain a lightweight composite wire with a good balance of strength, elongation, and conductivity, the sheath ratio is preferably 10% or more and 80% or less. In particular, composite wires with a sheath ratio of 30% or less have a specific gravity less than twice the specific gravity of the aluminum alloy wire mentioned above, 2.7, and are lightweight.

In addition, when comparing the composite wires of samples No. 1-1 to No. 8-20 that have the same sheath ratio and breaking elongation, it can be seen that the higher the Fe content, the higher the tensile strength. This comparison also shows that the lower the Fe content, the higher the electrical conductivity. Furthermore, it can be seen that a composite wire that satisfies the above three conditions can be obtained if the Fe content is 1.0 mass% or more and 4.0 mass% or less and the sheath ratio is 10% or more.

This test also demonstrated that it is possible to manufacture a thin composite wire having a wire diameter of less than 0.2 mm, which is equipped with a core wire made of an aluminum alloy containing 1.0% to 4.0% by mass of Fe. The manufacturing conditions are discussed in detail in Test Example 2 below.

[Test Example 2]
The manufacturing conditions of a composite wire having a core wire made of an aluminum alloy containing Fe as an additive element and an outer sheath made of pure copper, the structure of the core wire, and the interface state between the core wire and the outer sheath were investigated.

In this test, the following composite wires were produced. Except for sample No. 202, the basic manufacturing process was the same as that of sample No. 1-1 in Test Example 1. That is, continuous casting and rolling, cold wire drawing, formation of the metal coating, cold wire drawing, and softening treatment were carried out in that order. Details of the manufactured composite wires are described below.

<Common matters>
All the sample composite wires were round wires having a circular cross-sectional shape.
In all samples, the composite wire had a wire diameter of 0.1 mm.
In all samples, the skin percentage of the composite wire is 15%.

<Fe Content>
In the composite wire of sample No. 21, the Fe content in the core wire is 1.0 mass %.
In the composite wires of Samples No. 22, 23, and 202, the Fe content in the core wire was 2.0 mass %.
In the composite wire of sample No. 24, the Fe content in the core wire is 4.0 mass %.
In the composite wire of sample No. 201, the Fe content in the core wire is 0.5 mass %.
In the composite wire of sample No. 203, the Fe content in the core wire is 5.0 mass %.

<Manufacturing conditions>
<Cooling rate during continuous casting>
Except for sample No. 23, the cooling rate during the continuous casting process was 1° C./sec.
In sample No. 23, the cooling rate during the continuous casting process is 4° C./sec.

Anneal
For sample No. 202, the continuous cast and rolled material was subjected to two-stage annealing. The first annealing conditions were a heating temperature of 600° C. and a holding time of 10 hours. The second annealing conditions were a heating temperature of 400° C. and a holding time of 1 hour. Samples other than sample No. 202 were not subjected to the above two-stage annealing.

<Softening treatment>
Except for sample No. 201, the heating temperature for the softening treatment is selected from the range of 200° C. to 250° C. As in Test Example 1, the breaking elongation is used as an index, and the heating temperature is selected from the above range so that the breaking elongation is a value selected from the range of 4% to 15%. The larger the breaking elongation, the higher the heating temperature.
The heating temperature for the softening treatment of sample No. 201 was 350°C.

(Manufacturability)
The occurrence of wire breakage during cold drawing was investigated.
Here, a metal coating made of pure copper is formed, and then the composite material having this metal coating is subjected to cold wire drawing to produce a drawn wire material with a wire diameter of 0.9 mm. 100 kg of drawn wire material with a wire diameter of 0.9 mm is prepared. A drawn wire material with a final wire diameter of 0.1 mm is produced from the drawn wire material with a wire diameter of 0.9 mm. The number of wire breakages that occurred from the prepared 100 kg of drawn wire material to the time when the drawn wire material with the final wire diameter is obtained is checked. The number of wire breakages is divided by 100 kg to obtain the number of wire breakages per 1 kg of drawn wire material. The obtained ratio is defined as the wire breakage rate (times/kg). The wire breakage rate (times/kg) is shown in Table 4.

(Textural Observation)
For each sample composite wire obtained by softening a drawn wire material with a final wire diameter of 0.1 mm, the state of compounds present in the aluminum alloy constituting the core wire was examined. Also, the state of the boundary between the core wire and the sheath in each sample composite wire was examined.

<Compounds in aluminum alloys>
The aluminum alloy constituting the core wire of each composite wire sample contained compounds containing Fe and Al. The size of these compounds was examined as follows.

A cross section is taken of the composite wire of each sample. Three fields of view, each 19 μm x 24 μm in size, are taken from the core wire of the composite wire cross section. Each field of view is observed by SEM. The SEM observation image of each field of view is subjected to image processing to binarize the SEM observation image and approximate the compound containing Fe and Al to an ellipse. This image processing can be performed using known software, such as ImageJ. If known software such as ImageJ that has an ellipse conversion function is used, the binarized compound can be automatically converted to a best-fitting ellipse. The major axis length of each elliptical particle is determined. The major axis length of each particle is taken as the particle size of each particle made of the compound.

According to the particle size, each particle made of a compound containing Fe and Al is divided into five classes, namely, 1 μm or less, more than 1 μm and less than 2 μm, more than 2 μm and less than 3 μm, more than 3 μm and less than 30 μm, and more than 30 μm. The total number of particles is calculated for each class. The total number of particles in the five classes, S _all , is also calculated. Then, the ratio of the total number of each class to the total number, S _all , that is, the compound ratio is calculated. Here, the compound ratio of each class is calculated for each visual field. The compound ratio of each class is calculated by averaging the compound ratios of each class in the three visual fields. The compound ratio of each class is shown in Table 4.

Here, the above-mentioned compounds with particle sizes of 0.4 μm or less were excluded from the calculation of the number of particles, since they were assumed to be due to processing errors, etc. In other words, the number of compounds with particle sizes exceeding 0.4 μm was calculated.

By analyzing the components of the above-mentioned compound, it can be confirmed that it is a compound containing Fe and Al, typically an intermetallic compound of Fe and Al. For the component analysis, for example, an energy dispersive X-ray analyzer (SEM-EDX) attached to a SEM can be used.

<Interface condition between core wire and outer sheath>
A cross section was taken for each sample composite wire. The cross section of the composite wire was observed by SEM to check whether or not there were inclusions at the boundary between the core wire and the sheath. The results are shown in Table 5. If inclusions were present, the components of the inclusions were analyzed. For example, SEM-EDX or the like can be used for the component analysis.

In addition, in sample No. 201, which has an Fe content of 0.5%, a composite wire with a breaking elongation of 8% could not be obtained even when the heating temperature of the softening treatment was adjusted. Therefore, in sample No. 201, the results when the breaking elongation was 4% are shown in Table 5.

Furthermore, for the composite wires of each sample, the tensile strength (MPa) and electrical conductivity (%IACS) when the breaking elongation is 8% are shown in Table 4. For samples No. 21 and No. 22, the tensile strength (MPa) and electrical conductivity (%IACS) when the breaking elongation is 4%, 8%, 12%, and 15% are shown in Table 5. The measurement methods for tensile strength, breaking elongation, and electrical conductivity are the same as those in Test Example 1.

Hereinafter, samples No. 21 to No. 24 are collectively referred to as a specific sample group.
As shown in Table 4, in the specific sample group, Fe in the aluminum alloy constituting the core wire exists mainly as a compound containing Fe and Al, and the particle size of the compound is 30 μm or less. That is, in the specific sample group, there are no coarse particles of the compound having a particle size of more than 30 μm. On the other hand, in samples No. 202 and No. 203, there are coarse particles of the compound having a particle size of more than 30 μm.

One of the reasons why the compounds containing Fe and Al in the specific sample group do not contain the above-mentioned coarse particles is thought to be that the cooling rate during the continuous casting process is 0.5°C/sec or more. In this case, the cooling rate is 1°C/sec or more.

One of the reasons why sample No. 202 contains the coarse particles mentioned above is thought to be that the two-stage annealing described above was performed. Here, heat treatment was performed at a heating temperature of 400°C or higher.

One of the reasons why sample No. 203 contains the above-mentioned coarse particles is thought to be that the Fe content in the above-mentioned aluminum alloy is high at 5 mass %.

The specific sample group is a compound containing Fe and Al, and contains many fine particles with a particle size of 1 μm or less, but also contains particles over 1 μm. Specifically, the compound ratio in small particles with a particle size of more than 1 μm and less than 3 μm is 5% to 20%. Among the small particles, the compound ratio in first particles with a particle size of more than 1 μm and less than 2 μm is 5% to 15%. Furthermore, more than half of the small particles are first particles, and first particles are always present. The compound ratio in second particles with a particle size of more than 2 μm and less than 3 μm is 0% to less than 5%. Therefore, it can be said that the specific sample group is the compound, does not contain the above-mentioned coarse particles, contains a certain amount of the above-mentioned small particles, and contains many fine particles.

Compare sample No. 22 and sample No. 23. Compared to sample No. 22, sample No. 23 has fewer small particles and more fine particles. One of the reasons for this is thought to be that the cooling rate during the continuous casting process in sample No. 23 is faster than the cooling rate in sample No. 22.

Compare samples No. 21, No. 22, No. 24, No. 201, and No. 203. From this comparison, it can be said that the greater the Fe content in the aluminum alloy that constitutes the core wire, the greater the number of small particles described above. Conversely, the smaller the Fe content, the greater the number of fine particles described above. From this, it can be said that the amount of Fe content affects the size of the particle size of the compound containing Fe and Al.

And, as shown in Table 4, the specific sample group has a smaller breakage rate than samples No. 202 and No. 203. Specifically, the breakage rate of the specific sample group is 0.1 times/kg or less, and even 0.05 times/kg or less, which is 1/20 or less of the breakage rate of sample No. 202. From this, it can be said that the composite wire of the specific sample group has excellent manufacturability even if the wire diameter is less than 0.2 mm.

One of the reasons why the breakage rate of the specific sample group is low is that the core wire in the specific sample group is a compound containing Fe and Al, and does not contain coarse particles with a particle size of more than 30 μm. It is believed that the above-mentioned coarse particles are likely to become the starting point of cracks when cold drawing is performed until the wire diameter becomes less than 0.2 mm, here 0.1 mm or less.

Comparing samples No. 21 to No. 24, the fewer the above-mentioned small particles, especially the fewer the second particles, of the compound containing Fe and Al, the lower the breakage rate. The composite wire of sample No. 23, which contains first particles but does not contain second particles, is less likely to break during cold drawing in the manufacturing process, and is therefore more manufacturable. One of the reasons for this is thought to be the high cooling rate in the continuous casting process in sample No. 23, as described above.

As shown in Table 4, the specific sample group has a composite wire with a breaking elongation of 4% or more, and even 8% or more, and at least one of a tensile strength of 200 MPa or more and an electrical conductivity of 58% IACS or more. Among the specific sample group, there is a composite wire with a breaking elongation of 8% or more, a tensile strength of 200 MPa or more, and an electrical conductivity of 58% IACS or more. In contrast, as shown in Table 5, sample No. 201 does not have a composite wire with a breaking elongation of 8% or more.

One of the reasons why the specific sample group has high elongation is thought to be that the core wire is a compound containing Fe and Al and contains the above-mentioned small particles in the specific range mentioned above. It is thought that the above-mentioned small particles contribute to promoting the softening of the core wire, thereby achieving high elongation even when the heating temperature for the softening treatment is a relatively low temperature of 250°C or less. The relatively low heating temperature for the softening treatment reduces the decrease in strength. Therefore, it is thought that the specific sample group is more likely to have high strength.

Sample No. 201 has few small particles. Therefore, even if the heating temperature for the softening treatment is 280°C or higher, and even higher than 300°C in this case, only a breaking elongation of about 4% was obtained. The reason for the small amount of small particles in Sample No. 201 is thought to be that the Fe content is low at 0.5 mass% or less.

Furthermore, as shown in the right column of Table 5, in the composite wires of samples No. 21 and No. 22, no inclusions were observed at the interface between the core wire and the sheath. In contrast, in the composite wire of sample No. 201, inclusions were observed. These inclusions are compounds containing Al and Cu. One of the reasons for the presence of inclusions at the interface between the core wire and the sheath in sample No. 201 is thought to be that the heating temperature of the softening treatment was high, at 280°C or higher, and in this case, 300°C or higher. It is thought that the high heating temperature of the softening treatment caused the Al derived from the core wire and the Cu derived from the sheath to form a compound.

From the above explanation, it has been shown that for a thin composite wire having a core wire made of an aluminum alloy containing Fe as an additive element, excellent in strength and elongation, and a wire diameter of less than 0.2 mm, it is preferable that the aluminum alloy satisfy the following conditions (a) to (c). In addition, in order for this composite wire to have excellent manufacturability, it is preferable that the manufacturing process of the composite wire satisfy the following conditions (A) and (B).

(a) The Fe content in the aluminum alloy is more than 0.5 mass % and less than 5 mass %, particularly 1.0 mass % or more and 4.0 mass % or less.
(b) The aluminum alloy is a compound containing Fe and Al, does not contain the above-mentioned coarse particles, and the compound ratio in the above-mentioned small particles is 5% or more and 20% or less.
(c) The above (b) is satisfied, and the proportion of the compound in the first particles is 5% or more and 15% or less.

(A) The cooling rate during the continuous casting process is 0.5° C./sec or more, and further 1° C./sec or more.
(B) After continuous casting and rolling, no heat treatment or hot working is carried out at a heating temperature of 280° C. or higher, further 300° C. or higher, or 400° C. or higher.

The composite wires of Samples No. 1-1 to No. 8-20 in Test Example 1 were manufactured under manufacturing conditions roughly equivalent to those of the specific sample group in Test Example 2, and are therefore considered to satisfy the above conditions (b) and (c).

The present invention is not limited to these examples, but is intended to include all modifications within the scope and meaning equivalent to the claims. For example, in the composite wires shown in Test Examples 1 and 2, the Fe content, the composition of the outer sheath, the outer sheath ratio, the wire diameter of the composite wire, the cross-sectional shape of the composite wire, etc. can be changed. For example, the cross-sectional shape of the composite wire may be non-circular, such as rectangular. Or, for example, the constituent material of the outer sheath may be a copper alloy.

REFERENCE SIGNS LIST 1 composite wire, 11 core wire, 12 outer sheath, 2 coated wire, 20 conductor wire, 25 insulating coating, 3 coil, 30 winding portion

Claims (8)

A composite wire comprising a core wire and an outer sheath covering an outer periphery of the core wire,
The core wire is made of an aluminum alloy containing 1.0% by mass or more and 4.0% by mass or less of Fe, with the remainder being Al and unavoidable impurities.
The material of the outer shell is pure copper or a copper alloy,
The core wire has a structure in which a compound containing Fe and Al is dispersed,
The particle size of the compound is 30 μm or less,
The wire diameter is less than 0.2 mm ,
The breaking elongation is 8% or more.
Composite wire. 2. The composite wire according to claim 1, wherein the ratio of the total number of particles having a particle size of more than 1 μm and not more than 3 μm to the total number of particles having a particle size of 30 μm or less among the compounds is 5% or more and 20% or less. The composite wire according to claim 2, wherein the ratio of the total number of particles having a particle size of more than 1 μm and not more than 2 μm to the total number of particles having a particle size of not more than 30 μm among the compounds is 5% or more and not more than 15%. A composite wire according to any one of claims 1 to 3, in which the ratio of the cross-sectional area of the outer skin to the cross-sectional area of the composite wire in a cross section cut along a plane perpendicular to the axial direction of the composite wire is 10% or more and 80% or less. 5. The composite wire according to claim 1, having a tensile strength of 200 MPa or more. 6. The composite wire according to claim 1, having an electrical conductivity of 58% IACS or more. 7. The composite wire according to claim 1, wherein a cross-sectional shape of the composite wire taken along a plane perpendicular to an axial direction of the composite wire is non-circular. A coated wire comprising a conductor wire and an insulating coating covering an outer periphery of the conductor wire,
The conductor wire is a composite wire according to any one of claims 1 to 7 .
Coated wire.

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