EP2868757A1

EP2868757A1 - Copper-alloy wire rod and manufacturing method therefor

Info

Publication number: EP2868757A1
Application number: EP20130812970
Authority: EP
Inventors: Tsukasa Takazawa; Satoshi Teshigawara; Toshio Abe; Shuji Tomimatsu
Original assignee: Furukawa Electric Co Ltd
Current assignee: Furukawa Electric Co Ltd
Priority date: 2012-07-02
Filing date: 2013-07-02
Publication date: 2015-05-06
Anticipated expiration: 2033-07-02
Also published as: CN104169448B; EP2868757A4; KR101719888B1; JPWO2014007258A1; KR20150030188A; CN104169448A; EP2868757B1; WO2014007258A1; JP5840234B2

Abstract

{Problem to solve} To provide, at low cost, a copper alloy wire that is excellent in physical strength, elongation, and electrical conductivity, and that is suitable for the use in, for example, magnet wires.

{Means to solve} A copper alloy wire containing 0.5 mass% or more of Ag and 0.05 mass% or more of Mg, with the balance being Cu and unavoidable impurities, wherein the copper alloy wire has a tensile strength of 350 MPa or more and an elongation of 7% or more; and a production method.

Description

TECHNICAL FIELD

The present invention relates to a copper alloy wire and a method of producing the same, and more specifically the present invention relates to an extra-fine copper alloy wire for magnet wires and a method of producing the same.

BACKGROUND ART

Along with the development in electronic equipment, making the size of an electronic part smaller is in progress, and there is an increasing demand for extra-fine copper alloy wire (round wire) having a wire diameter of 0.1 mm or less. For example, a coil for micro speakers that is used in mobile phones, smart phones, and the like, is produced by working an extra-fine wire (a magnet wire) having a wire diameter of 0.1 mm or less by winding into a coil shape.
For this winding, toughness (elongation) is required as the workability capable of turn formation, and pure copper excellent in toughness has been conventionally used. However, although pure copper is excellent in electrical conductivity, due to its low physical strength, there is a problem that pure copper is low in resistance to fatigue that is accompanied by coil vibration.
In order to solve this problem, there is a proposal of a technique of using a high-concentration Cu-Ag alloy containing 2 to 15 mass% of Ag that can enhance the tensile strength almost without lowering the electrical conductivity (Patent Literature 1). Furthermore, in general, a metal or an alloy, which has been subjected to working, is enhanced in tensile strength and lowered in elongation; however, when this is subjected to heating at a certain temperature or higher, elongation is recovered again, while physical strength is lowered. Thus, there is a proposal of a technique of achieving a balance between physical strength and elongation even in a low-concentration alloy, by carrying out the heating at a temperature lower than or equal to the softening temperature (Patent Literature 2). However, this method is difficult to control the heating temperature and time period. In this regard, there is a proposal of a technique of performing a semi-softening treatment of achieving a balance between physical strength and elongation, by adding 0.05 to 0.2 mass% of Ag and 0.003 to 0.01 mass% of Zr into copper to widen the softening temperature range (Patent Literature 3).

CITATION LIST

PATENT LITERATURES

Patent Literature 1: JP-A-2009-280860 ("JP-A" means unexamined published Japanese patent application)
Patent Literature 2: Japanese Patent No. 3941304
Patent Literature 3: JP-B-4-77060 ("JP-B" means examined Japanese patent publication)

SUMMARY OF INVENTION

TECHNICAL PROBLEM

However, according to the demand for lengthening the service life of magnet wires and the demand for making magnet wires finer (with a wire diameter of 0.07 mm or less) as a result of making the size of electronic parts further smaller, further strength enhancement of copper alloy wires has been demanded. As described in Patent Literature 1, when the Ag content is increased in order to further increase the physical strength, rather, electrical conductivity is lowered. Furthermore, Ag is an element which enhances heat resistance, and makes it difficult to perform heating. Furthermore, since Ag is highly expensive, a noticeable increase in the cost is brought about. Also, since the general solid-solution-type highly electrically conductive alloy, as described in Patent Literature 2, has a narrow temperature range of realizing the semi-softening heat-treatment, it is difficult to realize stabilized performance. Furthermore, the method of performing a semi-softening treatment by adding a trace amount of Zr to a low-concentration Cu-Ag alloy (Patent Literature 3) can easily achieve a balance between elongation and physical strength; however, the method is insufficient in view of strength enhancement.
Furthermore, recently, the shape of magnet wires is not limited to round wires, and investigations have also been conducted on the employment of square wires and rectangular wires. Even in the cases of these square wires and rectangular wires, it is requested to employ a wire with a thickness that is thin to the extent of that corresponding to the wire diameter of the round wire.
The present invention was achieved in view of the problems in those conventional art, and it is an object of the present invention to provide, at low cost, a copper alloy wire that is excellent in physical strength, elongation, and electrical conductivity, and that is suitable for the use in, for example, magnet wires.

SOLUTION TO PROBLEM

The inventors of the present invention conducted thorough investigations on various copper alloys and heating conditions therefor, in order to develop a copper alloy wire that is superior in physical strength, elongation, and electrical conductivity than conventional alloy wires, and that is suitably used in magnet wires, and the like. As a result, the inventors have found that, when a Cu-Ag-Mg alloy wire is subjected to a semi-softening treatment, the resultant alloy wire is highly excellent in elongation and physical strength, and realization of characteristics by heating can be achieved readily. The inventors have found that, when Ag and Mg are added to Cu each at a predetermined content and this alloy is subjected to a semi-softening treatment, it is possible to obtained, at low cost, a copper alloy wire that is excellent in physical strength, electrical conductivity, and elongation, and that is suitable for the use in, for example, magnet wires. The present invention was completed based on those findings.
That is, the present invention provides the following means:

(1) A copper alloy wire containing 0.5 mass% or more of Ag and 0.05 mass% or more of Mg, with the balance being Cu and unavoidable impurities, wherein the copper alloy wire has a tensile strength of 350 MPa or more and an elongation of 7% or more.
(2) The copper alloy wire according to (1), which has a wire diameter (in the case of a round wire) or a wire thickness (in the case of a square wire or a rectangular wire) of 0.1 mm or less.
(3) The copper alloy wire according to (1) or (2), wherein the content of Ag is 0.5 to 4.0 mass%, and the content of Mg is 0.05 to 0.5 mass%.
(4) The copper alloy wire according to (1) or (2), wherein the content of Ag is 0.5 to 2.0 mass%, and the content of Mg is 0.05 to 0.3 mass%.
(5) The copper alloy wire according to any one of (1) to (4), further containing at least one selected from the group consisting of Sn, Zn, In, Ni, Co, Zr, and Cr in a content of the respective alloying element of 0.05 to 0.3 mass%.
(6) The copper alloy wire according to any one of (1) to (5), wherein the wire diameter or the wire thickness is 50 µm or less.
(7) A method of producing a copper alloy wire, containing the steps of:
- wire-working of subjecting a rough-drawn wire of a copper alloy containing 0.5 mass% or more of Ag and 0.05 mass% or more of Mg, with the balance being Cu and unavoidable impurities, to cold-working, to form a wire having a wire diameter or a wire thickness of 0.1 mm or less; and
- final-heating to bring the wire into a semi-softened state.
(8) The method of producing a copper alloy wire according to (7), wherein the heating temperature of the final-heating is from 300°C to 600°C.
(9) The method of producing a copper alloy wire according to (7) or (8), wherein in the wire-working, an intermediate heating is carried out in mid course of a plurality of cold-workings.

Herein, in the present specification, a semi-softened state means a state in which elongation of the copper alloy wire satisfies 7% to 30%. Also, a semi-softening treatment means a heating that brings about the semi-softened state. Furthermore, the semi-softening temperature range means a range of heating temperature that brings about a state in which elongation of the copper alloy wire after heating satisfies 7% to 30%. In this regard, a softening temperature means a heating temperature that brings about a state in which, in a copper alloy wire after heating, the tensile strength is no longer lowered. Referring to Fig. 3, the heating temperature at which the gradient of a drop curve of tensile strength becomes 0 (zero) is the softening temperature. The heating temperature range means the temperature range in which a desired physical strength is retained after heating, and within the semi-softening temperature range. However, if the copper alloy wire is subjected to heating at a high temperature exceeding this softening temperature (a temperature on the righter side with respect to the softening temperature in Fig. 3), tensile strength is slightly further lowered due to overheating.
On the other hand, a softened state means a recovered state in which elongation of a copper alloy wire is more than 30%. Furthermore, a softening treatment means a heating at a high temperature that brings about the softened state.
In the present invention, a wire means to include a square wire or a rectangular wire, in addition to a round wire. Thus, unless otherwise specified, the wire of the present invention collectively means a round wire, a square wire, and a rectangular wire. Herein, the size of the wire means, in the case of a round wire (the cross-section in the transverse direction (TD) is circular), the wire diameter φ (the diameter of the circle of the cross-section) of the round wire; in the case of a square wire (the cross-section in the transverse direction is square), the thickness t and the width w (each being the length of one side of the square of the cross-section and being identical to each other) of the square wire; and in the case of a rectangular wire (the cross-section in the transverse direction is rectangular), the thickness t (the length of a shorter side of the rectangle of the cross-section) and the width w (the length of a longer side of the rectangle of the cross-section) of the rectangular wire.

ADVANTAGEOUS EFFECTS OF INVENTION

Since the Cu-Ag-Mg alloy wire of the present invention is excellent in tensile strength, elongation, and electrical conductivity, the alloy wire is preferably suitable as, for example, a copper alloy wire for magnet wires. Furthermore, since the Cu-Ag-Mg alloy wire of the present invention can exhibit performance with a smaller amount of the Ag content as compared with conventional Cu-Ag alloy wires having large Ag contents, the wire can be produced at a lower cost. Also, according to the method of producing a Cu-Ag-Mg alloy wire of the present invention, since the temperature range for carrying out a semi-softening heating is wide, a stable Cu-Ag-Mg alloy wire can be produced, which is excellent in the performance, and which has less fluctuation in the performance.

BRIEF DESCRIPTION OF DRAWINGS

{Fig. 1}
Fig. 1 is a front view schematically showing the apparatus used in the test for measuring the number of repeating times at breakage in bending fatigue (the number of repeating times at breakage), which was conducted in the Examples.
{Fig. 2}
Fig. 2 is a diagram showing a comparison between a Cu-Ag alloy wire for comparison containing no Mg and the Cu-Ag-Mg alloy wire of the present invention containing Mg, in connection with the relationship between the Ag content and the tensile strength at the time of semi-softening.
{Fig. 3}
Fig. 3 is a diagram showing changes in the physical strength and elongation, upon subjecting a Cu-1%Ag-0.1%Mg round wire (herein, percent (%) means mass%; the same will be applied to hereinafter) with wire diameter 0.1 mm, to heating at any of various temperatures.

MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below.

[Alloy composition]

The copper alloy wire of the present invention contains 0.5 mass% or more (preferably 0.5 to 4.0 mass%) of Ag, and 0.05 mass% or more (preferably 0.05 to 0.5 mass%) of Mg, with the balance being Cu and unavoidable impurities.
By adding Ag to Cu, the physical strength can be enhanced almost without lowering the electrical conductivity. Furthermore, it can be made easier to carry out a semi-softening heating, by enhancing heat resistance. The Ag content is set to 0.5 mass% or more, preferably 0.5 to 4.0 mass%, and more preferably 0.5 to 2.0 mass%. If the content of Ag is too small, sufficient physical strength cannot be obtained. Also, if the Ag content is too large, electrical conductivity is lowered, and also it becomes excessively high cost. Moreover, the heating temperature becomes so high that heating cannot be carried out easily.
By adding Mg, an extra-fine magnet wire can be obtained, which has an enhanced tensile strength upon semi-softening and which is excellent in physical strength. Furthermore, the semi-softening temperature range is widened, and thereby that the heating temperature range is widened for obtaining the characteristics required for extra-fine magnet wires (a tensile strength of 350 MPa or more, and an elongation of 7% or more), to allow stable production. The Mg content is set to 0.05 mass% or more, preferably 0.05 to 0.5 mass%, and more preferably 0.05 to 0.3 mass%. If the Mg content is too small, the effects become insufficient for: enhancing the physical strength upon semi-softening; and extending the semi-softening temperature range. Furthermore, if the Mg content is too large, electrical conductivity is conspicuously lowered.
Alternatively, the copper alloy wire of the present invention may have an alloy composition containing Ag at a content of 0.5 mass% or more (preferably 0.5 to 4.0 mass%), Mg at a content of 0.05 mass% or more (preferably 0.05 to 0.5 mass%), and at least one selected from the group consisting of Sn, Zn, In, Ni, Co, Zr, and Cr at a respective content of 0.05 to 0.3 mass%, with the balance being Cu and unavoidable impurities.
The at least one element selected from the group consisting of Sn, Zn, In, Ni, Co, Zr, and Cr is an optional alloying element in the copper alloy according to the present invention. In the present invention, the contents of those elements are, respectively, 0.05 to 0.3%, and preferably 0.05 % to 0.2%. If this content is too small as the respective content, the effect of strength enhancement owing to the addition of any of these elements cannot be expected in most cases. Also, if this content is too large, since the lowering of the electrical conductivity is too large, the resultant copper alloy is inappropriate as a copper alloy wire, such as a magnet wire.
These elements each are a solid solution strengthening-type or precipitation strengthening-type element, and when any of these elements is/are added to Cu, physical strength can be enhanced without lowering the electrical conductivity to a large extent. As a result of this addition, the physical strength of the copper alloy wire itself is enhanced, and the resistance to bending fatigue is enhanced.

[Physical properties]

The tensile strength of the copper alloy wire of the present invention is set to 350 MPa or more, because, if the tensile strength is less than 350 MPa, the strength is insufficient when the diameter is made finer by wire-drawing, and the wire is poor in resistance to bending fatigue.
Furthermore, the elongation of the copper alloy wire of the present invention is set to 7% or more, because, if the elongation is less than 7%, the wire is poor in workability, and the resultant wire is occurred with defects, such as wire breakage, at the time of forming into a coil.

[Production method]

The production method of the copper wire of the present invention will be described.
As discussed above, the shape of the copper alloy wire of the present invention is not limited to a round wire, and may also be a square wire or a rectangular wire. Then, these will be described below.

[Production method of a round wire]

First, the method of producing a copper alloy round wire of the present invention is carried out by performing the steps, for example, of: casting; cold-working (cold-wire-drawing); intermediate heating (intermediate annealing); and final-heating (final-annealing), in this order. Herein, when a copper alloy wire having desired properties can be obtained without being subjected to any intermediate annealing, the intermediate annealing may be omitted.

[Casting]

Raw materials of Cu, Ag, and Mg are melted and cast in a casting machine having the interior (internal walls) preferably made of carbon, for example, in a graphite crucible. The atmosphere inside the casting machine at the time of melting is preferably selected to be a vacuum or an inert gas atmosphere, such as nitrogen or argon, in order to prevent occurrence of oxides. There are no particular limitations on the casting method, and use may be made, for example, of a transverse continuous casting machine or an upcast method. By means of such a continuous casting wire-drawing method, steps can be carried out continuously from casting to wire-drawing, and a roughly-drawn rod is cast with a diameter of generally about φ 8 to 23 mm.
In the case where no continuous casting wire-drawing method is utilized, a roughly-drawn rod having a diameter of generally about φ 8 to 23 mm is similarly obtained, by subjecting the billet (casting ingot) obtained by casting, to wire-drawing.

[Cold-working, intermediate annealing] (wire-working steps)

When this roughly-drawn rod is subjected to cold-working, the roughly-drawn rod is worked into a fine diameter wire having a diameter of φ 0.1 mm or less. Regarding this cold-working, it is preferable to perform cold wire-drawing.
The working ratio in this cold-working (wire-drawing) may vary depending on the target wire diameter, the copper alloy composition, and the heating conditions, and there are no particular limitations. The working ratio is generally set to 70.0 to 99.9%.
When this cold-working includes a plurality of cold-working steps, such as first cold-working (wire-drawing) and second cold-working (wire-drawing), intermediate annealing (intermediate heating) may be carried out in the mid course of the first cold-working and the second cold-working.
The heating method of performing the intermediate annealing may be roughly classified into a batch-type method and a continuous method. Since the batch-type heating requires a longer treatment time period and a larger cost, this method is rather poor in productivity. However, since it is easy to perform the control of temperature or retention time period, it is easy to perform the control of characteristics. On the contrary, since the continuous-type heating can carry out heating and the wire-drawing continuously, this is excellent in productivity. However, since it is necessary to perform this heating in a very short time period, it is necessary to precisely control the heating temperature and time period, to realize characteristics stably. Those heating methods have advantages and disadvantages as described above, and therefore, it is desirable to select the heating method according to the purpose.
In the case of the batch-type heating, for example, it is preferable to perform heating in a heating furnace in an inert atmosphere, such as nitrogen or argon, at 300°C to 600°C for 30 minutes to 2 hours.
Examples of the continuous-type heating include an electrically heating-type heating and an in-atmosphere running-type heating. The electrically heating-type heating is a method of: providing electrode rings in the mid course of the wire-drawing step; passing an electric current to the copper alloy wire that passes among the electrode rings; and performing heating by the Joule heat generated by the copper alloy wire itself. The in-atmosphere running-type heating is a method of: providing a vessel for heating in the mid course of wire-drawing; and performing heating by passing a copper alloy wire in the atmosphere of the vessel for heating that has been heated to a predetermined temperature (for example, 300°C to 600°C). For both of those heating methods, it is preferable to perform heating in an inert gas atmosphere, in order to prevent oxidation of the copper alloy wire. In the case of the continuous-type, since the heating time period is short, it is preferable to perform the heating at 300° to 700°c for 0.1 to 5 seconds.
By performing the intermediate annealing in the mod course of a plurality of cold-working steps, elongation of the wire thus obtainable can be recovered, and thereby workability can be enhanced. Also, Ag precipitation is accelerated by the intermediate annealing, and thus the physical strength and electrical conductivity of the wire thus obtainable can be further enhanced.

[Finish-annealing (also referred to as final-annealing)] (final-heating step)

The copper alloy wire that has been worked to a desired size (wire diameter) by the steps described above, is subjected to finish-annealing as the final-heating.
Examples of the heating method of conducting finish-annealing include, similarly to the intermediate annealing, a batch-type heating and a continuous-type heating.
At the time of this finish-annealing, the tensile strength and elongation in the wire after the final-heating may undergo slight changes, depending on the composition of copper alloy wire or the working ratio. Thus, in the present invention, the heating temperature and the heating retention time period for the finish-annealing are appropriately adjusted such that the elongation of the copper alloy wire obtainable by this final-heating would be 7 to 30%, preferably 10 to 20%.
The final-heating is carried out at a higher temperature when the heating time period is short, and is carried out at a lower temperature when the heating time period is long. In the case of the continuous-type heating, since the heating time period is short, it is preferable to perform the heating for 0.1 to 5 seconds at 300°C to 700°C. Furthermore, in the case of the batch-type heating, a longer heating time period can be employed, and it is preferable to perform the heating for 30 to 120 minutes at 300°C to 600°C.

[Production method of a rectangular wire]

Next, the method of producing a copper alloy rectangular wire of the present invention is the same as the method of producing a round wire described above, except for containing rectangular wire-working. Specifically, the method of producing a rectangular wire of the present invention is carried out by performing the steps, for example, of: casting; cold-working (cold wire-drawing); rectangular wire-working; and final-heating (final-annealing), in this order. It is also the same as the method of producing a round wire that the intermediate annealing (intermediate heating) is carried out in the mid course of the cold-working and the rectangular wire-working, if necessary. The conditions of the steps of working and heating, such as casting, cold-working, intermediate annealing, and final-annealing, as well as the preferred conditions thereof, are also the same as those for the method of producing a round wire.

[Rectangular wire-working]

Up to the steps before the rectangular wire-working, the production process is the same as that for the round wire, in which an ingot obtained by casting is subjected to cold-working (wire-drawing) to obtain a roughly-drawn rod having a round wire shape, and the roughly-drawn rod is further subjected to intermediate annealing if necessary. Regarding the rectangular wire-working, the round wire (roughly-drawn rod) thus obtained is subjected to cold rolling using a rolling machine, cold rolling using a cassette roller die, pressing, drawing, and the like. Through this rectangular wire-working, the transverse direction (TD) cross-section shape is worked into a rectangular shape, to obtain the shape of a rectangular wire. This rolling and the like are generally carried out in one to five passes. The reduction ratio in each pass and the total reduction ratio at the time of rolling and the like are not particularly limited, and may be appropriately set to obtain a desired rectangular wire size. Herein, the reduction ratio is the ratio of change in the thickness in the rolling direction upon performing the rectangular wire-working, and when the thickness before rolling is designated as t₁, and the thickness of the wire after rolling is designated as t₂, the reduction ratio (%) is represented by: {1 - (t₂/t₁)} × 100. For example, this total reduction ratio can be adjusted to 10 to 90%, and the reduction ratio in each pass can be adjusted to 10 to 50%. Herein, in the present invention, there are no particular limitations on the cross-section shape of the rectangular wire, but the aspect ratio is generally 1 to 50, preferably 1 to 20, and more preferably 2 to 10. The aspect ratio (represented by w/t as described below) is the ratio of a shorter side to a longer side in the rectangle that forms the transverse direction (TD) cross-section of a rectangular wire. In regard to the size of the rectangular wire, a rectangular wire thickness t is equal to the shorter side of the rectangle that forms the transverse direction (TD) cross-section, and a rectangular wire width w is equal to the longer side of the rectangle that forms the transverse direction (TD) cross-section. The rectangular wire thickness is generally 0.1 mm or less, preferably 0.07 mm or less, and more preferably 0.05 mm or less. The rectangular wire width is generally 1 mm or less, preferably 0.7 mm or less, and more preferably 0.5 mm or less.
When this rectangular wire is subjected to coil working in the thickness direction, high tensile strength, elongation and electrical conductivity can be exhibited, similarly to the round wire according to the present invention. Herein, subjecting a rectangular wire to coil working in the thickness direction means that a rectangular wire is wound into a coil shape while taking the width w of the rectangular wire as the width of the coil.

[Production method of a square wire]

Furthermore, in the case of producing a square wire, it is enough to set the transverse direction (TD) cross-section to be a square (w = t), in the method of producing a rectangular wire.

[Another embodiment of the production method of a wire]

Another embodiment of the method of producing a copper alloy wire of the present invention may be a whole production process of first subjecting a roughly-drawn rod obtained by casting to first cold-working (wire-drawing); recovering elongation by intermediate annealing; further performing second cold-working (wire-drawing) to obtain a desired wire diameter or a desired wire thickness, and controlling a predetermined mechanical strength and elongation by final (finish) annealing. However, it is preferable to reduce the number of cold-working steps, from the viewpoints of energy consumption and efficiency.
The respective working ratios for these first and second cold wire-drawings vary depending on the target wire diameter or wire thickness, the copper alloy composition, and the conditions for the two heating of intermediate annealing and finish-annealing, and there are no particular limitations on the working ratios. However, generally, the working ratio for the first cold-working (wire-drawing) is set to 70.0 to 99.9%, and the working ratio for the second cold-working (wire-drawing) is set to 70.0 to 99.9%.

[Other embodiments of the production methods of a rectangular wire and a square wire]

Instead of the production methods described above, a sheet or a strip having a predetermined alloy composition is produced, and the sheet or strip is slit, to obtain a rectangular wire or square wire having a desired wire width.
This production process, for example, contains: casting; hot rolling; cold rolling; finish-annealing; and slitting. If necessary, the intermediate annealing may be carried out in the mid course of a plurality of cold rollings. Slitting may be carried out before the finish-annealing, if necessary.

[Heating temperature range]

Fig. 3 shows the changes in the physical strength (tensile strength) and elongation when a Cu-1%Ag-0.1%Mg round wire with diameter φ 0.1 mm is heated at various temperatures. When the round wire is heated at a temperature lower than the heating-enabling temperature range, the resultant wire is high in physical strength but not sufficient in elongation exhibited, thus defects occur at the time of coil forming. Furthermore, when the round wire is heated at a temperature higher than the heating-enabling temperature range, the resultant wire is high in elongation but conspicuously low in physical strength, thus, defects may occur at the time of coil forming or fatigue resistance may be deteriorated, resulting in shortening in the service life of the coil. From the above, it is understood that in order to obtain an extra-fine magnet wire excellent in characteristics, heating in an appropriate temperature range is required. In order to produce a copper alloy wire with stabilized performances by that semi-softening heating, it is preferable that the temperature range of the semi-softening heating is wide, and the copper alloy wire of the present invention realizes this.

[Wire diameter or wire thickness, use]

There are no particular limitations on the wire diameter or the wire thickness of the copper alloy wire of the present invention. The wire diameter or the wire thickness is preferably 0.1 mm or less, more preferably 0.07 mm or less, and even more preferably 0.05 mm or less. There are no particular limitations on the lower limit of the wire diameter or the wire thickness. At the current level of technique, the lower limit is generally 0.01 mm or more.
The use of the copper alloy wire of the present invention is not particularly limited. Examples of the use include an extra-fine magnet wire for use in speaker coils that are used in mobile telephones, smart phones, and the like.

EXAMPLES

The present invention will be described in more detail based on examples given below, but the invention is not meant to be limited by these.

[Examples and Comparative examples of round wires]

With respect to the cast material, the Cu-Ag-Mg alloys in Examples according to this invention having the respective alloy composition, as shown in Table 1, each containing Ag at a content of 0.5 to 4.0 mass%, and Mg at a content of 0.05 to 0.5 mass%, with the balance being Cu and unavoidable impurities, and the copper alloys of Comparative examples having the respective alloy composition as shown in Table 1, were cast into roughly-drawn rods with diameters φ 10 mm, respectively, by a transverse-type continuous casting method. Those roughly-drawn rods were subjected to cold-working (wire-drawing) (the total working ratio of the following first and second cold-workings: 99.984%), intermediate annealing, and finish-annealing, to give round wire samples with final wire diameter φ 40 µm. The heating of the intermediate annealing and the finish-annealing were carried out by any manner selected from three patterns of batch annealing, electric current annealing, and running annealing, each under a nitrogen atmosphere. The intermediate annealing was carried out only once in the mid course of the first cold-working (wire-drawing) and the second cold-working (wire-drawing). As shown in Table 1, the intermediate annealing was conducted in some Examples, while not conducted in the other Examples. Furthermore, even if the appropriate heating temperature range as defined in the present invention is adopted, the balance between elongation and physical strength varies to a large extent, depending on the heating conditions. Thus, the heating conditions were adjusted such that the conditions would result in an elongation that was relatively close to 13 to 18%.
Other examples of the round wire were, respectively, produced in the same manner as above, except for using the Cu-Ag-Mg-(Sn, Zn, In, Ni, Co, Zr or Cr) alloys in Examples according to this invention having the respective alloy composition, as shown in Table 2, which contained, in addition to Ag and Mg, at least one optional alloying element selected from the group consisting of Sn, Zn, In, Ni, Co, Zr, and Cr, with the balance being Cu and unavoidable impurities, and the copper alloys of Comparative examples having the respective alloy composition as shown in Table 2.

[Examples and Comparative examples of rectangular wires]

Rectangular wire samples were produced in the same manner as the above round wires, except that, after the roughly-drawn rods were subjected to cold-working (wire-drawing) or after the intermediate annealing if conducted, rectangular wire-working was carried out, and then the finish-annealing was carried out. As shown in Table 3, some samples were subjected to the intermediate annealing, and the other samples were not subjected to the intermediate annealing. Furthermore, even if the appropriate heating temperature range as defined in the present invention is adopted, the balance between elongation and physical strength varies to a large extent, depending on the heating conditions. Thus, the heating conditions were adjusted such that the conditions would result in an elongation that was relatively close to 13 to 18%.
Regarding the rectangular wire-working, as shown in Table 3, a round wire before this working was worked by cold rolling into a rectangular wire such that the wire diameter φ (mm) was worked into a size of width w (mm) × thickness t (mm).

[Characteristics/Physical properties]

With respect to the thus-obtained samples of the round wires and the rectangular wires, various characteristics were tested and evaluated.
The tensile strength (TS) and the elongation (EI) were measured, according to JIS Z2201 and Z2241.
The electrical conductivity (EC) was measured, according to JIS H0505.
Since the Ag content largely affects the total cost, the index of cost performance CP was defined, by taking the tensile strength 350 MPa as a criteria required for an extra-fine magnet wire in connection with workability and resistance to bending fatigue: $CP (MPa / mass %) = (Tensile strength of copper wire - 350) (MPa) / Ag content (mass %)$
The results are evaluated in the following criterion: CP ≥ 20 was rated as "⊙ (excellent)", 10 ≤ CP < 20 was rated as "○ (good)", 0 ≤ CP < 10 was rated as "Δ (slightly poor)", and CP < 0 was rated as "X (poor)".
Regarding the service life of a coil, the number of repeating times at breakage in bending fatigue was measured by the testing method as illustrated in Fig. 1, and the service life of the coil was evaluated based on the number of repeating times at breakage in bending fatigue. As illustrated in Fig. 1, a test specimen of a copper alloy wire sample with a wire diameter φ or wire thickness t of 0.04 mm (40 µm) was sandwiched between two dies, and a load was applied thereon by hanging a weight (W) of 20 g at the lower end of the specimen in order to suppress deflection (flexure) of the wire. In the case of the rectangular wire, the sample was mounted to be sandwiched between the two dies in the wire thickness direction (ND). The upper end of the specimen was fixed with a connecting jig. While having the specimen maintained in this state, the specimen was bended 90° on the left side and the right side, respectively, bending was repeatedly carried out at a speed of 100 times per minute, and the number of repeating times at breakage in bending was measured for each specimen, i.e. the respective sample. Regarding the number of repeating times in bending, one reciprocation of 1 → 2 → 3 in Fig. 1 was counted as one time, and the distance between the two dies was set to 1 mm so that the specimen of the copper alloy wire would not be compressed in the test. Determination of breakage was made such that the specimen was judged to be broken when the weight hung at the lower end of the specimen dropped. Furthermore, the radius of bending (R) was set to 1 mm, 4 mm or 6 mm, depending on the curvature of the dies. The results are evaluated in the following criterion: a specimen which gave the number of repeating times at breakage in bending of 201 times or more was rated as "⊙ (excellent)", a specimen with the number of repeating times at breakage in bending of 151 to 200 times was rated as "○ (good)", a specimen with the number of repeating times at breakage in bending of 101 to 150 times was rated as "Δ (slightly poor)", and a specimen with the number of repeating times at breakage in bending of less than 100 times was rated as "X (poor)".
The coil performance was evaluated in the following criterion: a sample with tensile strength less than 350 MPa or elongation less than 7% was rated as "X (poor)", a sample with tensile strength 350 MPa or more but less than 370 MPa and elongation 7% or more was rated as "○ (good)", and a sample with tensile strength 370 MPa or more and elongation 7% or more, and also electrical conductivity 75%IACS or more was rated as "⊙ (excellent)".
The comprehensive evaluation was judged from the above-described cost performance, service life of coil, and coil performance, and a sample excellent as a copper alloy wire for extra-fine coil at a low cost was rated as "⊙ (excellent)", while other samples were successively rated as "○ (good)", "Δ (slightly poor)", and "× (poor)", respectively.
The results of measurement of the characteristics and evaluation of the thus-produced samples of Examples according to this invention and samples of Comparative examples, are shown in Table 1 and Table 2 for round wires, and in Table 3 for rectangular wires, respectively.
In the following tables, 'Temp.' means the heating temperature, and 'Time period' means the heating time period. Further, 'Butch' means the butch-type annealing (heating), and 'Running' means the running-type continuous annealing (heating). Further, "Ex" means Example according to this invention, and "C ex" means Comparative example.
Furthermore, the relationship between the Ag content and the tensile strength at the time of semi-softening was analyzed for Cu-Ag alloy wires for comparison not containing Mg and the Cu-Ag-Mg alloy wires of the present invention containing Mg. The results are shown in Fig. 2.
From Fig. 2 and Table 1, when a comparison is made on the characteristics of the copper alloy wires containing the same amount of Ag, the copper alloy wires of the present invention containing Mg each have a higher physical strength than the copper alloy wires of Comparative examples not containing Mg. Furthermore, the copper alloy wires of the present invention are comparative and are excellent, to the conventional Cu-Ag alloy wires, in view of the balance between electrical conductivity and physical strength. It is understood from these results that the copper alloy wires of the present invention can exhibit performance that is equivalent to the high concentration Cu-Ag alloy wires of Comparative examples, at smaller Ag contents and lower cost. When attention is paid to the heating temperature, the Cu-Ag-Mg alloy wires produced according to the production method of the present invention can be heated at a temperature lower by approximately 50°C, as compared with Cu-Ag alloy wires of higher concentrations than the alloy wires of Comparative examples having physical strength of the same extent, and the cost required for the heating can be reduced to a large extent.
It is also understood that among the Examples according to this invention, copper alloy wires having 0.5 to 2 mass% of Ag and 0.05 to 0.3 mass% of Mg are excellent in both the cost performance and the coil performance, and have properties more suitable as extra-fine magnet wires.
On the contrary, copper alloy wires in which at least any one of the Ag content and the Mg content is insufficient as in Comparative examples 1 to 5, cannot obtain sufficient physical strength even by a semi-softening heating, and the resultant copper alloy wires cannot be used as extra-fine magnet wires. Furthermore, as can be seen from Comparative examples 6 to 15, the effect of enhancing the semi-softening characteristics by Mg addition cannot be obtained in most of the copper alloy wires having insufficient Mg contents such as less than 0.05 mass%. Among these, Comparative example 7, Comparative examples 9 to 12, and Comparative examples 14 and 15 are comparative examples of the alloy compositions respectively simulating the Patent Literature 1.
Furthermore, Comparative example 16 is a comparative example of an alloy composition simulating the Patent Literature 3, and Comparative example 17 is a comparative example of an alloy composition simulating the Patent Literature 2. However, those wires each have insufficient physical strength, and at least any one of the cost performance and the service life of coil is inferior. Thus, the resultant wires could not be used as extra-fine magnet wires.
Furthermore, Comparative example 18 is a comparative example which was subjected to none of intermediate annealing and finish-annealing; however, the resultant wire had insufficient elongation and could not be used as an extra-fine magnet wire.
From Table 2, it can be seen that tensile strength has been enhanced, when alloy wires corresponding alloy compositions of Cu-Ag-Mg are compared with (for example, Example 101 versus Example 2, and Example 102 versus Example 3), by adding at least one optional alloying element selected from the group consisting of Sn, Zn, In, Ni, Co, Zr, and Cr, to a Cu-Ag-Mg alloy.
Although not shown in the table, if the content of Sn among the optional alloying elements was too large, the results were obtained in inferior electrical conductivity.
Also, it can be seen from Table 3 that, in the case of rectangular wires as well, the similar results were obtained as in the case of round wires.

Table 4 shows the results of the influence on the formability into magnet wire, when the wire diameter was changed into various values, in the Cu-Ag-Mg alloy wires (round wires) of the present invention and Comparative examples and the Cu-Ag alloy wires (round wires) of Comparative examples. When the respective copper alloy wire of each test material was formed into a coil, a test that did not have any occurrence of defects, such as short circuits, was rated as "⊙ (excellent)"; a test that had short circuits occurring very rarely was rated as "○ (good)"; a test that had short circuits frequently occurring was rated as "Δ (slightly poor)"; and a test that could not be formed into a coil was rated as "× (poor)".

Table 4

	Wire diameter	Ag	Mg	Brakeage upon forming
	mm	mass%	mass%	Brakeage upon forming
Ex
	2	0.12	0.5	0.1	⊙
		0.1	0.5	0.1	⊙
		0.08	0.5	0.1	⊙
		0.06	0.5	0.1	⊙
		0.04	0.5	0.1	⊙
0.02		0.5	0.1	○
C ex 4	0.12	0.5	=	⊙
	0.1	0.5	=	○
	0.08	0.5	=	Δ
	0.06	0.5	=	Δ
	0.04	0.5	=	Δ
	0.02	0.5	=	X
Ex 11	0.12	1	0.1	⊙
	0.1	1	0.1	⊙
	0.08	1	0.1	⊙
	0.06	1	0.1	⊙
	0.04	1	0.1	⊙
	0.02	1	0.1	⊙
C ex 6	0.12	1	=	⊙
	0.1	1	=	⊙
	0.08	1	=	○
	0.06	1	=	○
	0.04	1	=	Δ
	0.02	1		×
Ex 20	0.12	2	0.1	⊙
	0.1	2	0.1	⊙
	0.08	2	0.1	⊙
	0.06	2	0.1	⊙
	0.04	2	0.1	⊙
	0.02	2	0.1	⊙
C ex 7	0.12	2	=	○
	0.1	2	=	○
	0.08	2	=	○
	0.06	2	=	○
	0.04	2	=	○
	0.02	2	=	○

From the results of Table 4, it is understood that, when a comparison was made with copper alloy wires having an equal level of Ag content, the Cu-Ag-Mg alloy wires according to the present invention could be molded into coils without undergoing short circuits, as compared with the Cu-Ag alloy wires of Comparative examples, even in the case in which the alloy wires of the present invention had smaller wire diameters.
Also in the case of rectangular wires, the similar results can be obtained as in the case of the round wires.

Table 5 shows the results, obtained: by heating Cu-Ag-Mg alloy wires according to the present invention, and Cu-Ag alloy wires and Cu-Ag-Mg alloy wires (each with an insufficient Mg content) for comparison, at any of various temperatures in the batch-type for 30 minutes; and measuring the heating temperature range, in which both a tensile strength of 350 MPa or more and an elongation of 7% or more can be obtained. It can be seen that, although the Cu-Ag-Mg alloy wires according to the present invention have lower Ag concentrations, the alloy wires have heating temperature ranges that are equal to or broader than those in conventional high concentration Cu-Ag alloy wires for comparison. From this, it is understood that, according to the present invention, a semi-softening treatment by which a Cu-Ag-Mg alloy wire obtainable can achieve a balance between elongation and physical strength as desired, can be carried out easily in a broader heating temperature range, and can be produced products having a stabilized performance.

Table 5

	Ag	Mg	Heating-enabling temperature range	Heating temperature tolerance width
	mass%	mass%	°C	°C
Ex 301	0.5	0.05	340 to 380	40
Ex 302	0.5	0.1	340 to 385	45
Ex 303	0.5	0.2	330 to 385	55
Ex 304	0.5	0.3	330 to 390	60
Ex 305	0.5	0.4	325 to 390	65
Ex 306	0.5	0.5	325 to 395	70
Ex 307	1	0.05	350 to 395	45
Ex 308	1	0.1	350 to 410	60
Ex 309	1	0.2	350 to 420	70
Ex 310	1	0.3	340 to 420	80
Ex 311	1	0.4	340 to 425	85
Ex 312	1	0.5	340 to 430	90
Ex 313	2	0.05	350 to 410	60
Ex 314	2	0.1	345 to 410	65
Ex 315	2	0.2	340 to 415	75
Ex 316	2	0.3	335 to 415	80
Ex 317	2	0.4	335 to 415	80
Ex 318	2	0.5	330 to 420	90
Ex 319	3	0.05	360 to 430	70
Ex 320	3	0.1	360 to 435	75
Ex 321	3	0.2	350 to 440	90
Ex 322	3	0.3	350 to 445	95
Ex 323	3	0.4	350 to 445	95
Ex 324	3	0.5	345 to 450	105
Ex 325	4	0.05	360 to 440	80
Ex 326	4	0.1	355 to 445	90
Ex 327	4	0.2	355 to 450	95
Ex 328	4	0.3	350 to 450	100
Ex 329	4	0.4	350 to 455	105
Ex 330	4	0.5	345 to 460	115
C ex 301	0.5	0	350 to 375	25
C ex 302	0.5	0.03	350 to 375	25
C ex 303	1	0	360 to 390	30
C ex 304	1	0.03	360 to 395	35
C ex 305	2	0	360 to 405	45
C ex 306	2	0.03	360 to 405	45
C ex 307	3	0	370 to 420	50
C ex 308	3	0.03	370 to 425	55
C ex 309	4	0	370 to 430	60
C ex 310	4	0.03	370 to 435	65

Claims

A copper alloy wire containing 0.5 mass% or more of Ag and 0.05 mass% or more of Mg, with the balance being Cu and unavoidable impurities, wherein the copper alloy wire has a tensile strength of 350 MPa or more and an elongation of 7% or more.
The copper alloy wire according to claim 1, which has a wire diameter or a wire thickness of 0.1 mm or less.
The copper alloy wire according to claim 1 or 2, wherein the content of Ag is 0.5 to 4.0 mass%, and the content of Mg is 0.05 to 0.5 mass%.
The copper alloy wire according to claim 1 or 2, wherein the content of Ag is 0.5 to 2.0 mass%, and the content of Mg is 0.05 to 0.3 mass%.
The copper alloy wire according to any one of claims 1 to 4, further containing at least one selected from the group consisting of Sn, Zn, In, Ni, Co, Zr, and Cr in a content of the respective alloying element of 0.05 to 0.3 mass%.
The copper alloy wire according to any one of claims 1 to 5, wherein the wire diameter or the wire thickness is 50 µm or less.
A method of producing a copper alloy wire, containing the steps of:
wire-working of subjecting a rough-drawn wire of a copper alloy containing 0.5 mass% or more of Ag and 0.05 mass% or more of Mg, with the balance being Cu and unavoidable impurities, to cold-working, to form a wire having a wire diameter or a wire thickness of 0.1 mm or less; and

final-heating to bring the wire into a semi-softened state.
The method of producing a copper alloy wire according to claim 7, wherein the heating temperature of the final-heating is from 300°C to 600°C.
The method of producing a copper alloy wire according to claim 7 or 8, wherein in the wire-working, an intermediate heating is carried out in mid course of a plurality of cold-workings.