aluminum alloy wire

Abstract

Use of a cable harness (30) arranged on a part that is bent, comprising a covered electrical wire (10) and an end region (31) bound to an end region of the covered electrical wire (10), wherein the covered electrical wire (10) as a conductor comprises an aluminum alloy wire (2), an aluminum alloy stranded wire (20) obtained by twisting together a plurality of the aluminum alloy wires (2), and a compressed wire obtained by compression forming of the aluminum alloy stranded wire (20), and comprising an insulating cover layer (3) on an outer environment of the conductor, wherein the aluminum alloy wire (2) used as a conductor contains not less than 0.1 and not more than 1.5 wt% Mg, more than 0.1 and not more than 2.0 wt% Si, not less than 0.05 and not more than 0.5 wt% Cu, and the remainder comprising Al and impurities.comprises and has a mass ratio of Mg / Si of 0.8 ≤ Mg / Si ≤ 3.5, an electrical conductivity of not less than 35% IACS and less than 58% IACS, a tensile strength of not less than 150 MPa and not more than 400 MPa and an elongation at break of not less than 2%, wherein at least Cu is precipitated in the aluminium alloy.

Description

Technical FieldThis invention relates to the use of a wire harness disposed on a part being bent, comprising an aluminum alloy wire used as a conductor for an electric wire, an aluminum alloy stranded wire, a covered electric wire comprising the alloy wire or the stranded wire as a conductor, a method for producing the aluminum alloy wire, and a method for producing the covered electric wire. More specifically, this invention relates to the use of a wire harness comprising an aluminum alloy wire having excellent bending properties, strength and electrical conductivity properties disposed on a part being bent.BACKGROUND OF THE INVENTIONConventionally, for a conductor structure of a transport equipment such as automobile or aircraft, or an industrial facility such as robot, a form called a wire harness in which a plurality of electric wires are end-bound is used. A material constituting a conductor for an electric wire of such a wire harness is mainly copper having excellent electric conductivity properties or a copper-based material such as copper alloy.With the recent rapid increase in the performance and capability of automobiles, and consequently with an increased number of various on-board electrical devices, control devices, and the like, the number of electrical wires used for these devices tends to increase. In recent years, weight reduction is strongly desired to improve the fuel efficiency of an automobile, an aircraft or the like for environmental reasons.In order to achieve weight reduction in electric wires, studies are being made on aluminum electric wires comprising, as conductors, aluminum whose specific gravity is about one third that of copper. Pure aluminum is inferior in bending properties to copper-based materials. For example, when the above-described aluminum electric wire is used for a part that opens or closes, such as a door, it is broken at an early stage and is therefore difficult to apply to such a part. On the other hand, Japanese Patent Laid-Open No. 2004-134212 (PTL 1) discloses an electric wire for an automobile wire harness including an aluminum alloy conductor having a strength higher than that of pure aluminum. PTL 2 discloses a conductor made of wires made of an aluminum alloy including 0.3 to 1.2 mass % of Si, a weight ratio Mg / Si of 0.8 to 1.8, not more than 500 ppm of Ti, and not more than 50 ppm of B, and a balance of Al and an impurity, solution heat treatment, quenching, and aging heat treatment. PTL 3 discloses an aluminum conductor wire made of an aluminum alloy including 0.1 to 1.0 mass % of Fe, 0.05 to 0.5 mass % of Cu, and 0.05 to 0.4 mass % of Mg, wherein the total amount of Cu and Mg is 0.3 to 0.8 mass %, and the balance is made of aluminum and impurities.List of ReferencesPatent LiteraturePTL 1: Japanese Patent Laid-Open No. 2004-134212PTL 2: DE 11 2007 002 585 T5PTL 3: EP 1 852 875 A1When reference is made hereinafter to an aluminium alloy wire, an aluminium alloy stranded wire, a covered electrical wire and a cable harness, this means the products mentioned in use according to the scope of the claims.SUMMARY OF THE INVENTIONTechnical ProblemHowever, the above-described conventional aluminum alloy electric wire does not necessarily have sufficient bending properties. Accordingly, development of an aluminum alloy electric wire having further improved bending properties is desired. Further, since a conductor for an electric wire is desired to have excellent electrically conductive properties and strength, there is a need for developing an aluminum alloy wire having excellent electrical conductivity and strength in addition to the bending properties.Accordingly, an object of this invention is to provide an aluminum alloy wire excellent in bending properties, strength and electrically conductive properties, which is suitable as a conductor for an electric wire, and an aluminum alloy stranded wire.Another object of this invention is to provide a covered electric wire excellent in bending property, strength and electrically conductive property, which is suitable as a wire harness, and a wire harness.It is a still further object of this invention to provide a method of manufacturing the above-described aluminum alloy wire and a method of manufacturing the above-described covered electric wire.Solution of the ProblemThe present inventors found that an aluminum alloy wire having excellent bending properties can be obtained by performing solution heat treatment with a wire-drawn material after (not necessarily immediately after) the wire drawing, which representatively represents a wire-drawn material having a final wire diameter. It has been particularly found that an aluminum alloy wire having high strength and electronic conductivity and excellent bending properties can be obtained when an aluminum alloy having a specific composition is used. Specifically, it has been found that by performing the solution heat treatment, an added element in the aluminum alloy can be sufficiently dissolved in the aluminum as a base material and strength can be improved by solid solution hardening, thereby improving bending properties. Moreover, it has been found that by performing aging treatment after the above-described solution heat treatment, the strength can be further improved by aging hardening, thereby further improving the bending properties. It has also been found that by setting a content of the above-mentioned added element in a specific range, lowering of the electric conductivity can be reduced by dissolution of the added element, thereby obtaining an aluminum alloy wire having high electric conductivity. Further, it has been found that by restraining the strength to some extent, an aluminum alloy wire having a good balance of strength and toughness can be obtained. This invention has been accomplished on the basis of these findings.A method of producing an aluminum alloy wire according to this invention comprises the following steps. 1. the step of forming a cast material by casting a molten aluminum alloy comprising not less than 0.1 and not more than 1.5 mass % of Mg, more than 0.1 and not more than 2.0 % of Si, not less than 0.05 and not more than 0.5 % of Cu, the balance comprising Al. 2. the step of forming a rolled material by rolling the above-described cast material. 3. the step of forming a wire-drawn material by wire-drawing the above-described rolled material. 4. the step of forming a heat-treated material by performing solution heat treatment on the above-described wire-drawn material.Through steps 1 to 4 shown above, an aluminum alloy wire having an electrical conductivity of not less than 35% IACS and less than 58% IACS, a tensile strength of not less than 150 MPa and not more than 400 MPa, and an elongation of not less than 2% is produced by the production method according to this invention. The obtained aluminum alloy wire is used as a conductor.An aluminum alloy wire according to this invention is obtained by the above-described manufacturing method. The aluminum alloy wire according to this invention is used as a conductor and includes not less than 0.1 and not more than 1.5 mass % of Mg, more than 0.1 and not more than 2.0% of Si, not less than 0.05 and not more than 0.5% of Cu, and the balance of Al and impurities. A mass ratio Mg / Si of Mg to Si satisfies 0.8≤Mg / Si≤3.5. This aluminum alloy wire (hereinafter referred to as Al alloy wire) has an electrical conductivity of not less than 35% IACS and less than 58% IACS, a tensile strength of not less than 150 MPa and not more than 400 MPa, and an elongation of not less than 2%.Since the Al alloy wire of this invention is a wire with which solution heat treatment is performed as described above, it has excellent strength and bending properties due to solid solution hardening. Moreover, the Al alloy wire according to this invention has a content of added elements in specific ranges and hence excellent electroconductive properties.Further, the present inventors have found that when a wire harness is attached to a device or the like, an excessively high strength of a conductor may cause breakage of the conductor in the vicinity of the boundary between the conductor and an end portion. Thus, it is desired that a wire constituting a conductor for an electric wire of a wire harness is excellent not only in strength but also in toughness. The Al alloy wire of this invention has a strength in the specific range as described above, suppressing the lowering of toughness due to an increased strength and also an increased toughness.As described above, since the Al alloy wire of this invention has excellent bending properties, strength, electrically conductive properties and toughness, it has sufficient properties desired for a wire harness and can be suitably used as a conductor for an electric wire of a wire harness. In particular, an electric wire having the Al alloy wire of this invention as a conductor is unlikely to be broken even if it is disposed on a part that is bent.This invention will be described in detail below. The contents of the elements are expressed in mass %.Al alloy wireCompositionAn Al alloy constituting the Al alloy wire of this invention is an Al-Mg-Si-Cu based alloy comprising 0.1 to 1.5% Mg (magnesium), more than 0.1 to 2.0% Si (silicon), and 0.05 to 0.5% Cu (copper). The Al alloy wire according to this invention comprises not less than 0.1% Mg, more than 0.1% Si and not less than 0.05% Cu, these elements being dissolved or precipitated in Al, and thus exhibits excellent bending properties and strength. Although the bending properties and strength of the Al alloy wire are improved as the Mg, Si and Cu contents are increased, the electric conductivity and toughness are lowered, and the breakage of the wire may occur, for example, in wire drawing. Thus, Mg is set to not more than 1.5%, Si to not more than 2.0%, and Cu to not more than 0.5%.Although Mg can greatly lower the electrical conductivity of the Al alloy wire, it is an element particularly effective for improving the bending properties and strength. In particular, Si is contained in the specific range together with Mg, thereby effectively achieving improved strength due to aging hardening. Cu is capable of improving the bending properties and strength without significantly lowering the electrical conductivity of the Al alloy wire. More preferred contents are not less than 0.2% and not more than 1.5% Mg, not less than 0.1% and not more than 1.5% Si, and not less than 0.1% and not more than 0.5% Cu. The mass ratio of Mg / Si of Mg to Si also satisfies 0.8≤Mg / Si≤3.5. when Mg / Si is less than 0.8, the bending properties and strength of the Al alloy wire cannot be sufficiently effectively improved, and when Mg / Si is over 3.5, the electric conductivity significantly decreases. More preferably, 0.8 ≤ Mg / Si ≤ 3.Further, the above-described Al alloy may contain at least one of Fe (iron) and Cr (chromium). While Fe can improve the bending properties and strength without significantly lowering the electric conductivity, the addition of excess Fe causes the deterioration of the workability, for example, in wire drawing. Thus, a preferable Fe content is not less than 0.1 and not more than 1.0%, and particularly not less than 0.2 and not more than 2.9%. Although Cr can greatly lower the electric conductivity, it is an element which is highly effective for improving the bending properties and strength. A preferable Cr content is not less than 0.01 and not more than 0.5%, and particularly not less than 0.05% and not more than 0.4%.Further, the above-described Al alloy preferably contains at least one of Ti (titanium) and B (boron). Ti and B are effective to make the crystal structure of the Al alloy finer in casting. A fine crystal structure can improve strength. While the Al alloy may contain B alone, the effect of making the crystal structure finer is further improved when the Al alloy contains Ti alone or more specifically contains Ti and B. For achieving the effect of making the crystal structure finer, it is preferable that the mass proportion of Ti is not less than 100 ppm and the mass proportion of B is not less than 10 ppm. However, when the proportion of Ti is over 500 ppm and the proportion of B is over 50 ppm, the above-described effect of making the crystal structure finer is saturated or the electric conductivity decreases, and therefore the proportion of Ti is preferably not more than 500 ppm and the proportion of B is not more than 50 ppm.PropertiesThe Al alloy wire of this invention, which is made of the Al alloy having the specific composition as described above and with which the solution heat treatment is performed, has not only a high strength but also a high electric conductivity and elongation and satisfies the conditions of an electric conductivity of not less than 35% IACS, a tensile strength of not less than 150 MPa, and an elongation of not less than 2%. However, the Al alloy wire of this invention includes the added elements actively dissolved in the base material Al, and therefore, the extent to which the electroconductive properties can be improved is limited, and the Al alloy wire has an electric conductivity of less than 58% IACS. While a tensile strength of not less than 200 MPa may be more preferable, a conductor for an electric wire having only a high strength and a low toughness is not suitable for a wire harness, and for this reason, the Al alloy wire according to this invention has a tensile strength of not more than 400 MPa. When the tensile strength falls within the above-described range, the Al alloy wire according to this invention can exhibit a good balance of toughness and strength.The electric conductivity, tensile strength and elongation of the Al alloy wire may vary depending on the type or amount of elements added, the conditions for wire drawing, the conditions for solution heating, whether or not the aging treatment described later is performed, and the conditions for the aging condition. For example, when the amount of added elements is small, the electric conductivity and toughness can be improved, and when the amount of added elements is large, the strength and bending property can be improved. An example of the Al alloy wire according to this invention may be an Al alloy wire satisfying an electric conductivity of not less than 40% IACS and an elongation of not less than 10%.MoldThe Al alloy wire of this invention can have any of various wire diameters (diameters) by appropriately adjusting the drawing reduction (rate of reduction of cross section) at the time of wire drawing. For example, when the Al alloy wire is used as a conductor for an electric wire of an automobile wire harness, it preferably has a wire diameter of not less than 0.1 and not more than 1.5 mm.The Al alloy wire of this invention may also have any of various cross-sectional shapes depending on the nozzle shape at the time of wire drawing. The cross-sectional shape is representatively circular, but examples of other cross-sectional shapes include oval, polygonal shapes such as rectangular and hexagonal shapes, and the like.Al alloy stranded wireA stranded wire can be formed by stranding a plurality of the above-described Al alloy wires according to this invention. Even in wires having a small diameter, a wire (stranded wire) having high bending properties and strength can be obtained by stranded production. The number of the stranded wires is not particularly limited, and may be, for example, 7, 11, 19, or 37. After stranding the wires, the Al alloy stranded wire according to this invention can be compression-formed into a compressed wire. In this way, the wire diameter can be made smaller than that of the stranded wire, thereby contributing to a reduction in the size of the conductor.Covered Electrical WireThe Al alloy wire of this invention, the Al alloy stranded wire of this invention and the compressed wire as described above can be suitably used as conductors for electric wires. Depending on the intended use, they may each be used as they are as conductors or as a covered electric wire of this invention comprising an insulation covering layer provided on an outer periphery of the conductor. An insulation material constituting the above-described insulation covering layer can be appropriately selected. Examples of the insulating material may include polyvinyl chloride (PVC), non-halogen resin, material having excellent flame retardancy, and the like. The thickness of the insulation covering layer can be appropriately selected in consideration of the desired insulation strength, and is not particularly limited.Wire harnessThe covered electric wire described above can be suitably used as a part constituting the wire harness according to this invention. The wire harness according to this invention includes the covered electric wire described above and an end portion bonded to an end portion of the covered electric wire. The covered electrical wire is bonded via this end region to an object to which it is connected, for example with a device. The wire harness may also include a group of electric wires wherein a single plug is divided by a plurality of covered electric wires each having an end portion bonded thereto. The end portion may be in any of various shapes such as male type, female type, shrink type, weld type, and the like, and is not particularly limited. Moreover, a plurality of covered electric wires included in the above-described wire harness may be bonded together with a bonding tool or the like, thereby achieving excellent operability. Further, this wire harness can be suitably used in various fields where weight reduction is desired, particularly in an automobile where further weight reduction is desired to enhance fuel economy.Production MethodCasting StepIn the manufacturing method according to this invention, first, a cast material is formed on an Al alloy having the above-described specific composition. In the casting, any of continuous casting using a movable mold or a frame-shaped fixed mold, or ingot casting using a box-shaped fixed mold (hereinafter referred to as pin casting) may be used. The continuous casting can, in particular, rapidly solidify a molten material and hence give a casting material having a fine crystal structure. The use of such a cast material as a starting material facilitates the production of an Al alloy wire having a fine crystal structure, thereby achieving improved bending properties and strength due to the finer crystal. While the cooling rate can be properly selected, it is preferably not less than 20°C / s at a temperature in a range of 600-700°C, wherein the molten material is in both solid and liquid forms. For example, a continuous casting machine having a water-cooled copper mold, a forced water cooling mechanism or the like may be used to achieve the rapid solidification at the cooling rate as described above.When Ti and / or B are added, it is preferable that Ti and / or B is added immediately before the molten metal is poured into a mold so as to suppress the deposition of Ti and / or the like in a local area, thereby producing a cast material in which Ti and / or B is uniformly mixed, which is preferable.Rolling stepThen, the above-described cast material is (hot) rolled to form a rolled material. In particular, when the above-described casting step and rolling step are sequentially performed, hot rolling can be facilitated by using the heat accumulated in the casting material, high energy efficiency is achieved, and excellent productivity of the rolled material (continuous casting and rolling material) is achieved, compared to a case where a rolled material is manufactured by rolling a casting material generated by a batch casting method. When the cast material is a continuous cast material, rolling is then performed on the cast material having a fine crystal structure, thereby also producing the resultant rolled material (continuous cast and rolled material) having a fine crystal structure, which is preferable.Wire Drawing StepThen, with the above-described rolled material or continuously cast and rolled material, (cold) wire drawing is performed to form a wire-drawn material. The draw reduction can be appropriately selected depending on the desired wire diameter.In the course of wire drawing, intermediate heat treatment may be performed if appropriate to remove any stresses caused by the processing before the intermediate heat treatment, thereby improving the wire drawing workability after the intermediate heat treatment. The conditions for the intermediate heat treatment may be, for example, a heating temperature of 150-400° C. and a heating time of not less than 0.5 h. The conditions for the intermediate heat treatment may be the same as the conditions for the solution heat treatment described below.Strand Manufacturing StepWhile the resulting wire-drawn material having an end wire diameter can be used as a single wire in one form of the manufacturing method according to this invention, a stranded wire can be further formed by manufacturing a plurality of the above-described wire-drawn materials and forming a stranded wire by stranded manufacturing these wire-drawn materials. Further, in one form of the manufacturing method according to this invention, a compressed wire can be formed by the step of compression-forming the above-described stranded wire to form a compressed wire having a certain wire diameter. In the formation of the above-described stranded wire or compressed wire, the stranded wire or compressed wire may be subjected to solution heat treatment as described below, or the above-described stranded wire may be further formed after the solution heat treatment is performed on the above-described wire-drawn material, or after the wire-drawn material is subjected to aging treatment when the aging treatment is performed in addition to the solution heat treatment.Solution Heat StepThen, the solution heat treatment is performed with the above-described wire-drawn material having a final wire diameter or in the formation of a stranded wire with the wire-drawn materials before the strand formation or a stranded wire after the strand formation or in the formation of a compressed wire with a stranded wire before the compression or in a compressed wire after the compression. This solution heat treatment is mainly aimed at achieving solid solution curing and is carried out to improve the bending properties and strength by the solid solution curing.When an ingot material is used as a casting material, the solution heat treatment may be performed after both the casting and the above-described wire drawing. By performing the solution heat treatment on the ingot material, the added elements are sufficiently dissolved, thereby facilitating subsequent plastic processing such as rolling and wire drawing. Moreover, by further performing the solution heat treatment and aging treatment after the wire drawing, improved strength and bending properties can be obtained.The solution heat treatment is performed under conditions that allow the above-described specific added elements to dissolve in the base material Al to form a super saturated solid solution. For example, the wire-drawn material having a final wire diameter, the stranded wire, the compressed wire or the like as described above is heated to not less than 450° C. and then rapidly cooled. Specifically, the cooling may be performed at a cooling rate of not less than, for example, 50° C. / min. By setting the heating temperature to not less than 450° C., the added elements can be sufficiently dissolved in the base material Al in the Al alloy of the specific composition described above. In addition, by performing the rapid cooling at the high cooling rate as described above, it is possible to suppress the precipitation of the elements dissolved in the base material in the cooling step. The above-mentioned cooling rate can be realized by using a liquid refrigerant such as water or liquid nitrogen or by forcibly cooling such as air bubbles. In particular, the cooling state is preferably set such that the cooling rate is not less than 100° C. / min.A representative example of an atmosphere during solution heat treatment is the ambient atmosphere. By using other atmospheres having a lower oxygen content, for example, a non-oxidizing atmosphere, it is possible to suppress the formation of an oxide film on the surface of the wire to be treated due to the heat during the solution heat treatment. Examples of the non-oxidizing atmosphere include a vacuum atmosphere (reduced pressure atmosphere), an inert gas atmosphere such as nitrogen (N 2) or argon (Ar), a hydrogen-containing gas (e.g., hydrogen (H 2) alone or a mixed gas of hydrogen (H 2) and an inert gas such as N 2, Ar or helium (He)), and a reducing gas atmosphere such as carbon dioxide-containing gas (e.g., a mixed gas of carbon monoxide (Co) and carbon dioxide (Co 2)).Further, a continuous or batch heat treatment may be used in the solution heat treatment.Batch Type Heat TreatmentThe batch heat treatment is a treatment method in which heating is performed with an object to be heated enclosed in a heating boiler (atmospheric furnace such as box-shaped furnace). Although the passage per treatment is limited, the treatment method can easily control the temperature and manage the heat state of the entire object to be heated. In the batch heat treatment, the temperature of the atmosphere in the heating boiler may be adjusted so as to heat the object to be heated to a certain temperature.Continuous Heat TreatmentThe continuous heat treatment is a treatment method in which an object to be heated is continuously heated by continuously feeding objects into a heating boiler. The treatment method has, for example, the following advantages: 1. the object can be continuously heated and thus excellent operation is achieved; and 2. the wire to be heated can be uniformly heated in the longitudinal direction, thereby suppressing variations in the properties in the longitudinal direction of the wire. In particular, the continuous heat treatment can be suitably used when the solution heat treatment is applied to a long wire used for a conductor for an electric wire.Examples of the continuous heat treatment described above may include a direct electric heating method in which an object to be heated is heated by resistance heating (continuous electric heat treatment), an indirect electric heating method in which an object to be heated is heated by high-frequency electromagnetic induction (continuous heat treatment by high-frequency induction), and a furnace method in which an object to be heated is introduced into a heating boiler (tube furnace) set to a heating atmosphere and in which the object is heated by heat transfer.In the continuous heat treatment described above, for example, a sample is subjected to solution heat treatment by appropriately varying a plurality of control parameters, and properties (here, strength, electric conductivity, and elongation) of the sample and a temperature of the sample (measured by using, for example, a non-contact type temperature measuring device) at this time are measured. Correlation data between the parameter values and the measured data are created beforehand. On the basis of these correlation data, it is possible to adjust the above-mentioned control parameters to obtain a solution heat-treated material having desired properties (in this regard, strength: 150-400 MPa, electrical conductivity: 35-58% IACS and elongation: not less than 2%) and control the temperature, whereby the solution heat treatment is easily carried out by applying the continuous heat treatment. Examples of the control parameters for the electric heating method include a feed rate into the container (wire speed), a size of the object to be heated (wire diameter), a current value, and the like. Examples of the control parameters for the furnace method include the feed rate into the container (wire speed), a size of the object to be heated (wire diameter), a furnace size (diameter of a tube softening furnace), and the like.Aging treatmentThe manufacturing method according to this invention may further include the step of forming a heat-treated material (aging-treated material) by performing aging treatment on the solution heat-treated material (heat-treated material) with which the described solution heat treatment is performed. By performing the aging treatment after the solution heat treatment, the added elements are precipitated in the Al alloy, which allows the precipitate to precipitate in the Al alloy. The strength can be improved by precipitation hardening, i.e., aging hardening, and the electric conductivity can be improved by reducing the dissolved elements. Particularly when the Al alloy has a fine structure as described above, a structure in which the precipitate is uniformly dispersed can be easily formed. This further improves the strength to obtain an Al alloy wire having high strength and electric conductivity.While the continuous heat treatment as described above can be used as the aging treatment described above, the batch type heat treatment can also be used, whereby a sufficient heat treatment time can be maintained, whereby a precipitate can be sufficiently formed. In performing the aging treatment by the batch heat treatment, specific conditions may be, for example, a heating temperature not lower than 100° C. and a heating time not shorter than 0.5 h, and preferably a heating temperature of 100-250° C. and a heating time of 1-24 h. The aging treatment may also be performed in the ambient atmosphere or the low oxygen atmosphere described above.Covering stepThe covered electric wire according to this invention can be manufactured by the step of manufacturing the heat-treated material (one of the single wire, stranded wire, and compressed wire) with which the above-described solution heat treatment and optionally the aging treatment is performed, and forming the above-described insulation covering layer of an insulation material on an external environment of the heat-treated material.Further, a wire harness can be manufactured by bonding an end portion to an end portion of the obtained covered electric wire described above and by bonding a plurality of the covered electric wires each to an end portion.Advantageous Effects of the InventionThe Al alloy wire, the Al alloy stranded wire, the covered electric wire and the wire harness according to this invention exhibit excellent bending properties, strength and electrically conductive properties. The manufacturing method according to this invention is capable of manufacturing the above-described Al alloy wire or covered electric wire of this invention.Brief Description of the DrawingsFIG. 1 is a schematic cross-sectional view of a covered electric wire including an aluminum alloy wire according to the invention. FIG. 2 is a schematic cross-sectional view taken along line II-II of FIG. 1. FIG. 3 is a flow chart for explaining a method for manufacturing the covered electric wire of FIGS. 1 and 2. FIG. 4 is a schematic cross-sectional view of a covered electric wire comprising an aluminum alloy stranded wire of this invention. FIG. 5 is a schematic cross-sectional view showing a first modification of the electric covered wire of FIG. 4. FIG. 6 is a schematic cross-sectional view showing a second modification of the covered electric wire of FIG. 4. FIG. 7 is a flow chart for explaining a method of manufacturing the covered electric wire of FIG. 4. FIG. 8 is a schematic diagram showing a wire harness including the covered electric wire of this invention. FIG. 9 is an explanatory diagram for explaining a test method for inspecting bending properties.DESCRIPTION OF THE EMBODIMENTSEmbodiments of this invention will be described below with reference to the drawings. In the drawings shown below, identical or corresponding parts are denoted by identical reference numerals, and the description thereof will not be repeated.(First Embodiment)Referring to FIGS. 1 and 2, a covered electric wire including an aluminum alloy wire according to this invention will be described.As shown in FIGS. 1 and 2, a covered electric wire 10 according to an embodiment of this invention includes an aluminum alloy wire 2 (hereinafter, referred to as Al alloy wire 2) and an insulation covering layer 3 made of an insulation material covering an outer periphery of the aluminum alloy wire 2. The Al alloy wire 2 is composed of an Al-Mg-Si-Cu based alloy comprising 0.1-1.5% Mg, more than 0.1-2.0% Si and 0.05-0.5% Cu. Further, in an Al alloy wire 2, the mass ratio Mg / Si of Mg to Si is 0.8≤Mg / Si≤3.5, the electric conductivity is not less than 35% IACS and less than 58% IACS, the tensile strength is not less than 150 MPa and not more than 400 MPa, and the elongation is not less than 2%. The Al alloy wire 2 according to this invention comprises not less than 0.1% Mg, more than 0.1% Si and not less than 0.05% Cu, these elements being dissolved or precipitated in Al, and thus exhibits excellent bending properties and strength. Although the bending properties and strength of the Al alloy wire increase with increase in the Mg, Si and Cu contents, the electrical conductivity and toughness decrease, and the breakage of the wire may occur, for example, in wire drawing. Therefore, it is preferable to set Mg to not more than 1.5%, Si to not more than 2.0%, and Cu to not more than 0.5%.Next, a method of manufacturing the covered electric wire 10 illustrated in FIGS. 1 and 2 will be described with reference to FIG. 3.In the method for manufacturing the covered electric wire 10 according to this invention, a casting step (S 10) is first performed as shown in FIG. 3. Specifically, a cast material is formed of an Al alloy having the above-described composition. The casting material can be formed using any conventionally known method such as continuous casting using a movable mold or a frame-shaped fixed mold, die casting using a box-shaped fixed mold (hereinafter referred to as continuous casting), and the like.Subsequently, a rolling step (S20) is performed as shown in Fig. 3. In this step (S 20), the above-described cast material is (hot) rolled to form a rolled material. Preferably, the above-described casting step (S 10) and rolling step (S 20) are performed sequentially.Then, a wire drawing step (S 30) is performed as shown in FIG. 3. In this step (S30), the above-described rolled material (or continuously cast non-rolled material) is subjected to (cold) wire drawing to form a wire-drawn material. Any conventionally known method can be used as the method for wire drawing.Then, a solution heating step (S 40) is performed as shown in FIG. 3. In this step (S 40), solution heat treatment is performed on the above-described wire-drawn material. For example, the wire-drawn material is heated to not less than 450° C. in the ambient atmosphere and then rapidly cooled (for example, cooled at a cooling rate of not less than 50° C. / min), so that the added elements are dissolved in Al, which is the base material of the wire-drawn material, and a supersaturated solid solution is formed.Then, an aging treatment step (S 50) is performed as shown in FIG. 3. In this step (S 50), aging treatment is performed for, for example, a heating time of not shorter than 0.5 h at a heating temperature of not less than 100° C.Subsequently, a capping step (S 60) is performed as shown in FIG. 3. In this step (S 60), an insulation covering layer made of an insulation material is formed on the heat-treated material (aging-treated material) with which the above-described aging treatment is performed. Any conventional well-known method can be used as the method for forming the insulation covering layer. In this way, a covered electric wire 10 shown in FIGS. 1 and 2 can be obtained.(Second Embodiment)Referring to FIG. 4, a covered electric wire comprising an aluminum alloy wire of this invention will be described.As shown in FIG. 4, a covered electric wire 10 according to an embodiment of this invention includes an aluminum alloy stranded wire 20 formed by strandedly manufacturing a plurality of Al alloy wires 2 of this invention, and an insulation covering layer formed on an outer periphery of an aluminum alloy stranded wire 20. In the aluminum alloy stranded wire 20, the plurality of Al alloy wires 2 extend along a direction perpendicular to the sheet surface illustrated in FIG. 4 twisted together. While an insulating covering layer 3 is disposed on the outer periphery of the aluminum alloy stranded wire 20, the insulating covering layer 3 may be formed in intimate contact with an outer periphery surface of the aluminum alloy stranded wire 20 as shown in FIG. 4, or may be formed with a clearance formed between the outer periphery surface and an inner periphery surface of the insulating covering layer 3. Such a covered electric wire 10 can also provide excellent bending properties and strength as in the covered electric wire 10 shown in the first embodiment.As shown in FIG. 4, even in small-diameter wires (Al alloy wires 2), a wire (stranded wire) having high bending properties and strength can be obtained by twisting the wires together. The number of the Al alloy wires 2 that are twisted is not particularly limited. For example, as shown in FIG. 4, seven Al alloy wires 2 may be twisted together to form an aluminum alloy stranded wire 20. After the wires are twisted together, the aluminum alloy stranded wire 20 of this invention can also be compression formed into a compressed wire as described below. In this way, the wire diameter can be made smaller than that of the twisted one, thereby contributing to a size reduction of the conductor. While the Al alloy wire 2 may have a circular cross-sectional shape as shown in FIG. 4, it may also have any other shape. For example, the Al alloy wire 2 may have a polygonal cross-sectional shape (for example, a rectangular, triangular, or trapezoidal shape). Moreover, while the plurality of Al alloy wires 2 constituting the aluminum alloy stranded wire 20 may have the same diameter, Al alloy wires 2 having different diameters may be combined to obtain the aluminum alloy stranded wire 20. In the aluminum alloy stranded wire 20, the Al alloy wires 2 are preferably arranged centrosymmetrically in the cross section shown in FIG. 4 in view of the stability of strength and the like.Referring to FIG. 5, a first modification of a covered electric wire 10 shown in FIG. 4 will be described. Referring to FIG. 5, although the covered electric wire 10 has basically the same structure as the covered electric wire 10 of FIG. 4, it differs from the covered electric wire 10 of FIG. 4 in the number of Al alloy wires 2 constituting the aluminum alloy stranded wire 20. That is, the aluminum alloy stranded wire 20 constituting the covered electric wire 10 shown in FIG. 5 is formed by twisting 19 Al alloy wires 2. the covered electric wire 10 having such a structure can also provide the same effects as obtained by the covered electric wire 10 shown in FIG. 4.Referring to FIG. 6, a second modification of the covered electric wire 10 illustrated in FIG. 4 will be described. Referring to FIG. 6, the covered electric wire 10 has basically the same structure as the covered electric wire 10 illustrated in FIG. 4, although it differs from the covered electric wire 10 illustrated in FIG. 4 in that the aluminum alloy stranded wire 20 is compressed toward the center in a radial direction. Specifically, in an aluminum alloy stranded wire 20, the centrally positioned Al alloy wire 2 has a substantially hexagonal shape in cross section. Moreover, a plurality of (six in FIG. 6 ) Al alloy wires 2 arranged around an outer periphery of a centrally positioned Al alloy wire 2 have a substantially trapezoidal cross-sectional shape whose length of a side opposite to the center of the aluminum alloy stranded wire 20 is shorter than the length of a side opposite to an outer periphery thereof. In each of the plurality of Al alloy wires 2 disposed on the outer periphery, a surface positioned to be opposed to the outer periphery of an aluminum alloy stranded wire 20 (the surface forming the relatively longer side of the trapezoid) has the shape of a curved surface that is convexly outward from a central side of the aluminum alloy stranded wire 20. Further, a region where adjacent ones of the plurality of Al alloy wires 2 disposed on the outer periphery are in contact with each other extends substantially linearly radially outward from the center of the aluminum alloy stranded wire 20 in cross section. In this way, in addition to the same effects as those obtained by the covered wire material 10 shown in FIG. 4, the wire diameter of the covered wire material 10 can be made smaller than that of merely twisting Al alloy wires 2 having a circular cross section, thereby contributing to a reduction in size of the conductor. If the diameter of the covered wire material 10 is the same, the proportion of the cross sections of the Al alloy wires 2 in the cross section of the covered wire material 10 can be further increased.Referring to FIG. 7, a method of manufacturing the covered electric wire 10 illustrated in FIG. 4 will be described. Referring to FIG. 7, from the molding step (S 10) to the wire drawing step (S 30) in FIG. 7, the same steps as the molding step (S 10) to the wire drawing step (S 30) in FIG. 3 are performed. A processing step (S 70) is then performed as shown in FIG. 7. Specifically, in this step (S 70), the wire-drawn materials obtained in the above-described step (S 30) are produced, and a stranded wire is formed by twisting these wire-drawn materials together. In this way, an aluminum alloy stranded wire 20 can be obtained. In one form of the method for manufacturing a covered electric wire of this invention, the above-described stranded wire may be compression-molded to form a compressed wire having a predetermined wire diameter.From the solution heating step (S 40) to the covering step (S 60) illustrated in FIG. 7, the same treatments as those from the step (S 40) to the step (S 60) illustrated in FIG. 3 are applied to the above-described stranded wire (or compressed wire). In this way, a covered electric wire 10 shown in FIG. 4 can be obtained.(Third Embodiment)Referring to Fig. 8, a wire harness according to this invention will be described.Referring to FIG. 8, a wire harness 30 in an embodiment of this invention includes a plurality of covered electric wires 10 of this invention and an end portion 31 bonded to an end portion of each covered electric wire 10. The end portion 31 may be formed by bonding an individual end portion to an end portion of each individual covered electric wire 10 and then fixing a plurality of the end portions to each other. Alternatively, the end portion 31 may be formed by forming a plurality of connection portions to which the respective end portions of the covered electric wires 10 may be bonded. Further, a plurality of wire harnesses 30 can be bound to each other as shown in FIG. 8, to form a larger wire harness. Sufficient hardenability can also be obtained in such a wire harness because of the excellent bending properties and strength of the covered electric wires 10 of this invention.(Examples)An Al alloy wire was produced and various properties of the Al alloy wire were examined. The Al alloy wire is produced according to the following procedure: melting → continuous casting and rolling → wire drawing (with intermediate heat treatment if desired) → formation of a stranded wire → solution heating (→ with aging treatment if desired).[Properties of Al alloy wire]The Al alloy wire is first manufactured. Pure aluminum (Al content not less than 99.7% by mass) is prepared as a base and melted. To the obtained molten metal (molten aluminum), the additive elements shown in Table 1 are added to obtain the contents shown in Table 1 to produce a molten Al alloy. The molten Al alloy with the components adjusted is desirably subjected to, for example, a treatment for removing hydrogen gas and / or a treatment for removing foreign substances as appropriate. Table 1 Table 110,550,320,1--0,02 (200 ppm)-1, 720,20,250,1--0,05 (500 ppm)-0, 830, 90,60,20,280,140,02 (200 ppm)0,005 (50 ppm)1,540, 90,60,2-0,30,02 (200 ppm)0,005 (50 ppm)1,551,510,50, 8-0,02 (200 ppm)0,005 (50 ppm)1,51010,050,010,01--0,02 (200 ppm)0,005 (50 ppm)5,010220,10,1----20,01030, 90,61--0,02 (200 ppm)0,005 (50 ppm)1,51042,530,2--0,02 (200 ppm)0,005 (50 ppm)0, 8A belt-wheel type continuous casting and rolling machine is used for performing continuous casting and rolling by continuously casting and hot-rolling the produced molten Al alloy to produce a wire rod of φ 9.5 mm (continuous cast and rolled material). For a sample comprising Ti or Ti and B, Ti particles or a TiB 2- wire are fed to the molten Al alloy immediately before casting to obtain the contents as shown in Table 1.The above-described wire rod is subjected to cold wire drawing to produce a wire-drawn material having a final wire diameter of φ0.3 mm or φ1 mm. A sample shown with "intermediate heat treatment" in Table 2 is subjected to the intermediate heat treatment (3 hours at 300°C or under the same conditions as in the solution heat treatment) as appropriate during wire drawing. The obtained wire-drawn material having a final wire diameter of φ0.3 mm or φ1 mm is subjected to solution heat treatment and optionally aging treatment under the heat treatment conditions shown in Table 2 to produce a heat-treated material (Al alloy wire).In the solution heat treatment shown in Table 2, electric heating refers to a continuous heat treatment in which heating by resistance heating is performed by directly electric heating the above-described wire-drawn material, and "induction heating" refers to a continuous heat treatment in which the above-described wire-drawn material is heated by high-frequency electromagnetic induction. Batch heat treatment using a boiler is applied to samples for which heating temperatures and heating times are shown in Table 2. In the continuous heat treatments, the above-described correlation data between control parameter values and measured data is previously created, the control parameters (linear velocity, current value, etc.) are set on the basis of these correlation data to obtain desired characteristics (electric conductivity, etc.), and the heat treatment is applied to each sample. As the aging condition, the batch heat treatment using a boiler is used. Table 2 Table 21No. NOheating electricallyAmbient Atmosphere16082No. NOInduction heatingAr is Ar--3Yes5303Ar is Ar14084Yes5301Ambient Atmosphere12085No. NO5305N 214024101No. NO5303Ar is Ar14012102No. NOheating electricallyAmbient Atmosphere1205103No. NOheating electricallyAmbient Atmosphere1205104No. NO5303Ar is Ar10016The tensile strength (MPa), electrical conductivity (% IACS), elongation (%), and bending properties were measured for each obtained heat-treated material having a final wire diameter of φ1.0 mm. The results are shown in Table 3.Tensile strength (MPa) and elongation (%, elongation at break) were measured according to JIS Z 2241 (Tensile Test Method for Metallic Materials, 1998) using a universal tensile strength testing machine. The electrical conductivity (% IACS) was measured by the bridge method.The bending properties were measured as follows. As shown in FIG. 9, a sample S (diameter: φ0.3 mm) was placed between a pair of opposed bolts m. With a weight w (load imposed: 100 g) imposed on one end of the sample S with the other end clamped with a lever 1 of the testing machine, bending with a bending radius R (= 15 mm) was imposed on the sample S along the vicinity of the mandrels m. The number of elongations until the sample S was broken was measured. The number of bends was counted, defining a 90° bend and the return bend as one. For example, when the sample is bent as indicated by the arrow in FIG. 9, the number of bends is 2.Table 3 Table 3129154328898224644102876233134215385964287401830256530542123549110180612895431022003230212251033303814059210438030141275As shown in Table 3, it is observed that an Al alloy wire excellent in bending property can be obtained by performing the solution heat treatment. In particular, samples 1 to 5, each composed of an Al-Mg-Si-Cu based alloy having the specific composition and with which the solution heat treatment was performed, exhibited excellent bending properties and strength. Each of Samples 1 to 5 also exhibited high electric conductivity and high elongation and satisfied the conditions of an electric conductivity of not less than 35% IACS and an elongation of not less than 2%. It is particularly observed that samples having a tensile strength of not less than about 250 MPa were obtained while having an electrical conductivity of not less than 40% IACS and an elongation of not less than 10%. Then, it is observed that strength and electric conductivity tend to be improved when the aging treatment is performed after the solution heat treatment.In contrast, each of the samples 101 and 102 which are not composed of an Al-Mg-Si-Cu-based alloy having the specific composition is observed to be inferior in bending properties and strength even though the wire-drawn material having a final wire diameter is subjected to solution heat treatment and aging treatment. On the other hand, it is observed that although the samples 103 and 104 having a large amount of Mg or Cu have high strength and excellent bending resistance, they have low elongation and also low electric conductivity.As described above, Al alloy wires each composed of an Al-Mg-Si-Cu based alloy having the specific composition and obtained by performing solution heat treatment on the wire-drawn material having a final wire diameter and optionally subjected to aging treatment are excellent not only in bending properties but also in strength, electroconductive property and toughness. Accordingly, these Al alloy wires are expected to be suitably used as conductors for electric wires for wire harnesses, particularly, as conductors for electric wires of automobile wire harnesses in which light weight is desired.Note that the aforementioned embodiments and examples can be appropriately modified without departing from the scope of this invention, and are not limited to the above-described structures. For example, the composition of the Al alloy, the wire diameter of the Al alloy wire, the conditions for solution heat treatment, and the like can be varied within specific ranges. Moreover, the Al alloy wires can be converted into a stranded wire or compressed wire.Industrial applicabilityThe covered electric wire according to this invention can be suitably used in applications where light weight as well as excellent bending properties and strengths are desired, for example, as electric wires for automobile wire harnesses. Any aluminum alloy wire and the aluminum alloy stranded wire according to this invention can be suitably used as the conductor of the above-described covered electric wire. The wire harness according to this invention can be suitably used, for example, in the wiring of an automobile. Any method of manufacturing an aluminum alloy wire according to this invention and method of manufacturing a covered electric wire according to this invention can be suitably used in manufacturing the aluminum alloy wire or the covered electric wire according to this invention as described above.List of Reference Numerals2: Aluminum alloy wire, 3: Insulation covering layer, 10: Covered electric wire, 20: Aluminum alloy stranded wire, 30: Wire harness, 31: End, 1: Lever, S: Sample, w: Weight, m: Mandrel, r: Bending radius.

Claims

Use of a wire harness (30) disposed on a part being bent, comprising a covered electric wire (10) and an end portion (31) bonded to an end portion of the covered electric wire (10), wherein the covered electric wire (10) comprises, as a conductor, one of an aluminum alloy wire (2), an aluminum alloy stranded wire (20) obtained by twisting a plurality of the aluminum alloy wires (2), and a compressed wire obtained by compression molding the aluminum alloy stranded wire (20), and comprising an insulation covering layer (3) on an outer periphery of the conductor, wherein the aluminum alloy wire (2) used as a conductor comprises not less than 0.1 and not more than 1.5 mass% of Mg, more than 0.1 and not more than 2.0 mass% of Si, A composition for producing an alloy according to the present invention is characterized in that the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the composition of the invention is not less than 0.05 and not more than 0.5 mass % of Cu and the balance comprising Al and impurities and having a mass ratio Mg / Si of Mg to Si of 0.8 ≤ Mg / Si ≤ 3.5, an electric conductivity of not less than 35% IACS and less than 58% IACS, a tensile strength of not less than 150 MPa and not more than 400 MPa and an elongation at break of not less than 2%, at least Cu being precipitated in the aluminum alloy.The use according to claim 1, wherein the aluminum alloy wire (2) further comprises at least one element of Fe and Cr, wherein the Fe content is not less than 0.1 and not more than 1.0 mass%, and the Cr content is not less than 0.01 and not more than 0.5 mass%.The use according to claim 1, wherein the aluminum alloy wire (2) further comprises at least one element of Ti and B, wherein a content of Ti is not more than 500 mass ppm and a content of B is not more than 50 mass ppm.The use according to claim 1, wherein the aluminum alloy wire (2) has a wire diameter of not less than 0.1 mm and not more than 1.5 mm.

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