EP1647996B1 - Copper plated aluminum stranded cable and its fabrication method - Google Patents

Abstract

An aluminium cable electric conductor, incorporating at least one strand with a base of conducting wires (1) with a core (2) of aluminium coated with an intermediate layer (3) of copper which is coated with a superficial layer (4) of nickel, has the following characteristics : (A) the superficial layer of nickel has a thickness (E) of between 1.3 mu m and 3 mu m; (B) the superficial layer of nickel has sufficient continuity to resist a continuity test in a bath of polysulphur for at least 30 seconds without the appearance of zones of attack of the copper, visible at an enlargement of times ten. An independent claim is also included for the production of this conductor.

Description

The present invention relates to conductors made of aluminum or copper-plated and nickel-plated aluminum alloy. It relates more particularly to electrical cables comprising at least one core conductor made of aluminum or aluminum alloy covered with a layer of copper itself covered with a layer of nickel.

In the description and the claims which follow, the word "aluminum" broadly designates aluminum and its alloys. The word "conductor" refers to an elongated electrically conductive body, the length of which is large relative to its cross-section, and which is generally in the form of a wire.

Aluminum-based electrical conductors are widely used in the transportation of electrical energy. Aluminum-core electrical wires and cables may include a coating of insulating material, and single wires or strands may be assembled to form the conductive core of a cable.

In the transport and distribution of electrical energy, aluminum conductors can be used in the raw state, that is to say without special treatment of the conductor surface. However, it has already been planned to coat the aluminum conductor with a layer of nickel, so as to improve the electrical contact properties.

Nickel plated aluminum wire strand electrical cables have already been used for example in aeronautical applications. There are more than one hundred kilometers of such cables in some current airliners.

Compared to the traditional copper core cable solution, aluminum has the advantage of reducing weight: for the same electrical resistance, an aluminum conductor weighs about half the weight of a copper conductor.

Despite the weight gain, the applications of aluminum conductors in the aerospace industry have, however, remained in the minority, mainly because of lower conductivity, lower load at break, poorer performance in terms of flexibility, the presence of non-conductive oxides in the driver's area, and industrialization difficulties.

Thus, the document DE 196 33 615 A1 discloses the use of an aluminum wire having a copper coating on which is applied an outer layer of nickel.

The document FR 2,083,323 discloses an aircraft cable having copper coated aluminum wires itself coated with a nickel layer. Each conductor is isolated by one or more layers of plastic material.

The above documents do not specify the thickness and strength of the nickel layer, nor the interest and means to ensure both sufficient conductivity, sufficient breaking load, and sufficient flexibility for use. in difficult conditions and aggressive atmosphere.

The document US 3,915,667 A teaches to coat an aluminum conductor with an inner coating of tin or zinc, then with a copper-based layer, then with a nickel coating, and finally with an outer layer of tin or silver. The nickel interlayer has a thickness of between about 2.5 μm and 12.7 μm. It is not specified the interest of a resistant surface layer of nickel, nor the means to achieve it.

In the field of small diameter cables, there is a need to improve the compromise between the conductivity of the cable, its load at break, and its flexibility, so as to satisfy the conditions of use of the cables that must be passed in nonlinear sheaths and relatively long, without risk of deterioration or blockage. In addition, there is a need for long-term protection of such cables against the appearance of non-conductive oxides on the surface, under severe conditions of use, for example large and repeated temperature differences, aggressive atmospheres. Also, there is a need to ensure a good electrical connection of the conductors without damaging their structure by mechanical clamping.

The object of the invention is to propose a new structure of stranded cable for conduction of electric current having both a low electrical resistivity, good flexibility, a sufficiently large breaking load, good electrical contact properties, good anticorrosive properties for long-term use in aggressive conditions, and good capacities to absorb mechanical tightenings of electrical connection.

A problem is in particular to provide a protective nickel surface layer which has a satisfactory quality, both in sealing and in adhesion on the lower layer of the conductor, but which does not substantially disturb the other properties of the conductor such as electrical conductance , flexibility, weight, load at break.

For this purpose, the invention proposes an electric conductor of the aluminum cable type comprising at least one strand based on conducting wires having an aluminum core covered with an intermediate layer of copper, the intermediate layer of copper being itself covered with a surface layer of nickel. The invention provides such a surface layer of nickel in a thickness of between about 1.3 μm and 3.0 μm, this superficial layer of nickel having sufficient continuity to withstand a polysulfide bath continuity test for at least 30 seconds without showing visible copper etching areas at 10x magnification.

The polysulfide bath continuity test is defined by the ASTM B298 standard established by the American Society for Testing Materials.

The details of this continuity test by polysulphide bath is given in the description which follows.

Preferably, the thickness of the nickel surface layer is between about 2 μm and 3 μm.

Good results can be obtained with a surface layer of nickel whose thickness is about 2.3 microns.

It will thus be possible to form a cable of seven strands of 10 or 15 wires each, the wires having a unit diameter of about 0.51 mm.

According to another application, it will be possible to constitute a cable comprising seven strands of 19 wires each, the wires having a unit diameter of about 0.275 mm.

According to another application, it will be possible to form a cable comprising a strand of 61 wires each having a diameter of about 0.32 mm.

According to another application, it may be a cable comprising a strand of 37 son of 0.32 or 0.25 mm in diameter.

According to another application, the cable may comprise a strand of 19 son of 0.30 or 0.25 or 0.20 mm in diameter.

To increase the mechanical resistance of the cable, in small diameters, it is advantageous to provide a nickel-plated copper alloy core wire, surrounded by six nickel-plated copper aluminum wires of about 0.25 or 0.20 mm in diameter.

The cable can be stranded according to one or more concentric strands or concentric strands, or concentric unilay. The strand or strands and / or the cable may then be covered with an insulating layer of polyimide, and an outer layer of polytetrafluoroethylene.

1. a) prévoir un fil d'ébauche à âme en aluminium recouverte d'une couche de cuivre représentant 10 % à 20 % en volume, de diamètre compris entre 2 fois et 5 fois le diamètre final désiré du fil,
2. b) dégraisser le fil d'ébauche,
3. c) procéder à un mordançage du fil d'ébauche à l'acide sulfamique,
4. d) déposer sur le fil d'ébauche une couche de nickel par électrolyse dans un bain d'électrolyse au sulfamate de nickel aqueux,
5. e) rincer le fil obtenu à l'eau déminéralisée,
6. f) tréfiler le fil obtenu en huile entière jusqu'au diamètre final,
7. g) toronner plusieurs fils ainsi obtenus en faisceaux de fils,
8. h) procéder à un recuit sous gaz neutre.

A difficulty is to achieve industrially, at low cost, the continuous layer of nickel, adherent and sealed. For this, the invention proposes a procedure for manufacturing copper-plated and nickel-plated wire comprising the following steps:

1. a) providing an aluminum core preform coated with a copper layer of 10% to 20% by volume, with a diameter of between 2 and 5 times the desired final diameter of the wire,
2. b) degrease the roughing wire,
3. c) etching the sulfamic acid strand,
4. d) depositing on the wire a nickel layer by electrolysis in an aqueous nickel sulfamate electrolysis bath,
5. e) rinse the wire obtained with demineralized water,
6. f) drawing the obtained wire into whole oil up to the final diameter,
7. g) stranding several yarns thus obtained in bundles of yarns,
8. h) annealing under a neutral gas.

This method makes it possible in particular to avoid the appearance of oxides at the interfaces between the layers, in particular under the nickel layer, which oxides may then cause, during the drawing, discontinuities in the nickel surface layer, and thus reduce the protective and contact properties of this layer.

During step h) of annealing under neutral gas, the neutral gas may advantageously be nitrogen.

And in addition, during the neutral gas annealing step h), the temperature can be about 250 ° C. for a period of at least about two hours.

Step d) is particularly critical. During this step, the temperature of the electrolysis bath can be maintained between about 55 ° C and 65 ° C, the pH of the electrolysis bath can be maintained between about 2.3 and 3.0, the current density can be between 10 and 16 amperes per square decimetre (A / dm ² ), and the nickel concentration can be kept below about 140 grams per liter in the electrolysis bath. This makes it possible to more surely achieve a conductor that satisfies the optical polysulfide bath protection test mentioned above.

To optimize the process, during step d), it is possible to predict that the temperature of the electrolysis bath is about 60 ° C., that the pH of the electrolysis bath is about 2.4, that the density current is about 15 to 16 amperes per square decimetre (A / dm ² ).

Preferably, the method may comprise a step prior to _o ) calibrating the copper-plated aluminum roughing wire in size and hardness.

After such a calibration step a _o ), the copper-plated aluminum roughing wire may have, for example, a load at break less than or equal to 20 decaNewtons per square millimeter (daN / mm ² ) approximately, and an elongation of between 2 and about 3%. In this way, it is still avoided, during drawing, the appearance of gaps or discontinuities in the surface layer of nickel.

During step c), the sulfamic acid bath may advantageously have a concentration of about 40 grams per liter.

The initial diameter of the copper-plated aluminum roughing wire may be between about 1.2 and 0.8 mm. The nickel deposit is then carried out in a thickness of about 10 to 15 μm. And the final diameter of the coppered and nickel-plated aluminum wire is between 0.51 mm and 0.20 mm.

1. b1) dégraisser le fil d'ébauche par ultrasons,
2. b2) procéder à un dégraissage anodique du fil d'ébauche dans un bain contenant de la soude et des tensioactifs,
3. b3) rincer le fil d'ébauche à l'eau déminéralisée.

Preferably, step b) of degreasing the wire may comprise the steps:

1. b1) degreasing the roughing wire by ultrasound,
2. b2) anodic degreasing of the blank wire in a bath containing sodium hydroxide and surfactants,
3. b3) rinse the roughing wire with deionized water.

For wires of diameter less than or equal to 0.25 mm, the stranding step g) is preferably carried out before the annealing step h). On the other hand, for the wires of greater diameter, the annealing step h) is preferably carried out before the stranding step g).

• la figure 1 est une vue en perspective en coupe transversale d'un fil à âme en aluminium selon un mode de réalisation de la présente invention ;
• la figure 2 est une coupe transversale d'un toron à 19 fils de type concentrique vrai ;
• la figure 3 est une coupe transversale d'un toron à 19 fils de type concentrique unilay ;
• la figure 4 est une coupe transversale d'un toron à 7 fils ;
• la figure 5 est une vue en perspective en coupe transversale d'une ébauche de fil en aluminium cuivré à partir duquel on réalise le fil selon l'invention ;
• la figure 6 est une vue schématique générale d'un dispositif pour la fabrication du fil de la figure 1 selon un mode de réalisation de l'invention ;
• la figure 7 est une vue schématique du poste de nickelage dans l'installation de la figure 6 ;
• la figure 8 illustre les deux étapes d'un processus de test permettant de contrôler la qualité du fil obtenu ;
• la figure 9 est une vue d'un fil de bonne qualité ayant subi le test ; et
• la figure 10 est une vue d'un fil de mauvaise qualité ayant subi le test.

Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, with reference to the accompanying figures, in which:

• the figure 1 is a cross-sectional perspective view of an aluminum core wire according to an embodiment of the present invention;
• the figure 2 is a cross-section of a 19-wire strand of true concentric type;
• the figure 3 is a cross-section of a 19-wire strand of concentric type unilay;
• the figure 4 is a cross section of a 7-wire strand;
• the figure 5 is a cross-sectional perspective view of a blank of copper-plated aluminum wire from which the yarn according to the invention is made;
• the figure 6 is a general schematic view of a device for the manufacture of the wire of the figure 1 according to one embodiment of the invention;
• the figure 7 is a schematic view of the nickel plating station in the installation of the figure 6 ;
• the figure 8 illustrates the two steps of a test process to control the quality of the wire obtained;
• the figure 9 is a view of a good quality thread that has been tested; and
• the figure 10 is a view of a poor quality wire that has been tested.

We first consider the figure 1 , which illustrates the structure of a conductor wire 1 according to one embodiment of the invention. There is a core 2 of aluminum, covered with an intermediate layer 3 of copper, itself covered with a surface layer 4 of nickel.

The aluminum constituting the core 2 may be pure aluminum or an aluminum alloy. A 99.5% aluminum alloy having at most 0.10% silicon and at most 0.40% iron may be preferred.

In applications for the aviation industry or the automotive industry, the wire may have a final total diameter D _F of between about 0.51 mm and 0.20 mm. Other diameter values may however be used, depending on the characteristics sought.

The copper of the intermediate layer 3 may advantageously represent 15% by volume of the wire. This leads to a wire having the following characteristics: a density at 20 ° C of about 3.60 kilograms per cubic decimeter, a resistivity of 2.78 × 10 ^-8 ohms per meter, a conductivity of 60% to 64% IACS, typically 62% IACS, a breaking load of 138 Newtons per square millimeter and a minimum elongation of 6%.

To achieve both satisfactory flexibility, and sufficient conductivity through a large cross section, the above son are stranded together by the usual techniques of forming cables.

For example, as shown on the figure 2 it is possible to produce a strand 5 of 19 wires, such as wire 1, in a concentric strand structure, the layers being of alternate directions. In another example, on the figure 3 a strand 6 of 19 wires, such as the wire 1, was made according to a strand structure unilay, the layers being of the same direction.

On the other hand, one will avoid a structure of the type strand unilay hexagonal, which can make more difficult or defective the electrical connection at the end of cable.

Smaller section structures may comprise seven-stranded strands 7 having a central strand 7a and six peripheral strands 7b-7g, as illustrated in FIG. figure 4 . The central strand 7a may be made of nickel-plated copper alloy, whereas the peripheral strands 7b-7g are made of copper-plated and nickel-plated aluminum like the wire 1 of the figure 1 . Mixed strands 7 are thus produced in which the load at break is increased by this structure and the conductivity is reduced simultaneously, to the detriment of the weight.

In the wire of the figure 1 , the thickness E of the surface layer 4 of nickel must be greater than 1.3 μm, failing which it is found that the surface layer 4 of nickel is not sufficiently continuous to provide a effective protection of the intermediate layer 3 of copper. It is not advantageous to make a nickel layer whose thickness is greater than about 3 μm, since this adversely affects the other properties of the conductor such as electrical conductance, flexibility, load at break, and this reduces substantially the speed of manufacture of the driver. Preferably, the thickness E of the surface layer 4 of nickel will be between about 2 μm and 3 μm, and a good compromise is obtained with a surface layer 4 whose thickness E is equal to about 2.3 μm.

In practice, cables will be made with different numbers of wires and strands depending on the range.

According to a first example, a cable may comprise 7 strands of 10 or 15 wires each, the wires having a unit diameter of about 0.51 mm.

In a second example, a cable is formed comprising seven strands of 19 son each, the son having a unit diameter of about 0.275 mm.

According to a third example, a cable is formed comprising a strand of 61 wires of about 0.32 mm in diameter.

In another example, the cable comprises a strand of 37 wires of about 0.32 or 0.25 mm.

In another example, the cable comprises a strand of 19 wires of about 0.30 or 0.25 or 0.20 mm, in a structure of Figures 2 or 3 .

Finally, the cables with smaller section will consist of a nickel-plated copper alloy core wire 7a, surrounded by six son 7b-7g of copper-plated and nickel-plated aluminum of 0.25 or 0.20 mm in diameter.

The strands can then be covered with an insulating layer of polyimide and an outer layer of polytetrafluoroethylene.

For the realization of a thread 1 as illustrated on the figure 1 , we started from a copper-plated aluminum blank wire 8 of larger diameter D _l as illustrated on the figure 5 , the diameter D ₁ of blank wire 8 being between 2 and 5 times the desired final diameter D _F of the wire, for example from 0.8 to 1.2 millimeters approximately. This allowed a fast, industrially economical treatment.

The roughing wire 8 was processed by an illustrated method on the figures 6 and 7 .

The roughing wire 8 consisted of an aluminum core 8a, covered with a copper surface layer 8b, the copper representing 15% by volume of the assembly.

We now consider the figure 6 , which schematically illustrates the general structure of a device for manufacturing a wire according to a method of the invention.

The roughing wire 8 passes firstly into an ultrasound device 9, which performs a first degreasing. The wire then passes into an anode degreasing tank 10, which performs anodic degreasing in a bath 11 which may for example contain sodium hydroxide and surfactants. In this way, it is ensured that the surface of the wire is free of oxides. The presence of such oxides would be unfavorable to subsequent drawing.

The wire then passes into a rinsing device 12, producing a rinsing of the wire with demineralised water.

The yarn then passes into a tray 13 containing a sulfamic acid bath 14. The sulfamic acid concentration may advantageously be about 40 grams per liter. This provides a surface treatment of the copper layer, facilitating the subsequent adhesion of nickel.

The wire then passes into an electrolytic nickel deposition device 15, which provides a suitable deposition of a surface layer of nickel. The device will be described in more detail in relation to the figure 7 . The wire then passes into a second rinsing device 16, which rinses the wire with demineralised water.

The wire then passes into a wire drawing device 17, in which a complete oil drawing is carried out to the final diameter, that is to say in the range of about 0.51 - 0.20 mm in diameter.

Generally, wire drawing takes place at a different speed than previous treatments. It is therefore necessary to provide an intermediate step during which the wire is packaged in a coil after the rinsing step in the rinsing device 16, and the wire is coated with a film of whole oil which protects it until to a subsequent drawing treatment.

At the output of the wire drawing device 17, the wire passes through an oven 18 associated with a source of neutral gas 19 such as nitrogen, in which the wire is annealed under nitrogen at about 240 ° C. for about two hours. This gives a wire 1 output, as illustrated on the figure 1 .

The result obtained by this method may depend on the size and the structure of the blank wire 8. In order to overcome any size and structure dispersions, it is advantageous to carry out a preliminary step of calibrating the blank wire. 8, to give it a dimension and a hardness appropriate and constant. It is preferable to prefer a roughing wire having a breaking load of less than or equal to about 20 daN per mm ² , and an elongation of between about 2 and 3%, with a constant dimension selected from the range of diameters between three and a half. times and five times the desired final diameter of the wire.

We now consider the figure 7 , for the description of the device 15 carrying out the step of depositing the nickel layer by electrolysis.

The device comprises an internal overflow tank 20, containing the electrolysis bath 21 which discharges, as indicated by the arrow 22, into an external tank 23 which contains the internal tank 20. The liquid collected in the outer tank 23 is sent by pipes 24 in a storage tank 25, from which the liquid is returned to the inner tank 20 by a pump 26 and a pipe 27. A nickel metal reserve 28 is housed in the inner tank 20, inside the electrolysis bath 21. The blank wire 8 is moved and guided through the inner tank 20, in several passages, and comes out after depositing a layer of nickel on its surface. The nickel reserve 28 is electrically connected to the positive pole of an electric generator 29 whose negative pole is connected to the wire 8.

The electrolysis bath 21 contains nickel sulphamate in aqueous solution. Good results require permanent control of the concentration of the electrolysis bath 21. This is done by connecting the storage tank 25 to a water supply 30, to a purge line 31, to a source of sulfamic acid 32 The pH of the electrolysis bath 21 is controlled by a pH sensor 33 acting on a regulator which controls the operation of the corresponding valves to withdraw a quantity of liquid from the electrolysis bath 21 via the purge pipe 31, to add water by the water supply 30, and to add sulfamic acid by the sulfamic acid source 32.

In the tests carried out, the pH of the electrolysis bath was advantageously maintained between about 2.3 and 3.0, preferably close to 2.4.

The temperature of the electrolysis bath 21 was also regulated, by means of a temperature sensor 34 and heating means 35, so that the electrolysis bath was for example at a temperature of approximately 60 ° C.

The nickel sulfamate concentration in the electrolysis bath 21 was kept low, for example less than 140 grams per liter of nickel. Otherwise, the superficial layer of nickel would have been too hard, and would have poorly supported the subsequent drawing.

The electric generator 29 is adapted to regulate the electrolysis current density. In the tests carried out, the electrolysis current density has advantageously been maintained within a range of values of between 10 and 16 A / dm ² ; preferably between 15 and 16 A / dm ² .

By way of example, the following are the results of some tests which have been carried out with different conditions of electrolytic deposition, and the satisfactory or unsatisfactory quality of the wire obtained is indicated, j being the current density: Samples j pH Result 1 14 2.5 Well 2 14 2.95 acceptable 3 14 3.2 bad 4 14 3.55 bad 5 20 2.5 bad 6 22 2.5 bad 7 17 2.5 bad 8 11.2 2.5 acceptable 9 8.4 2.5 bad

A difficulty has been in determining the good, acceptable or poor quality of the nickel coating produced by the process.

A polysulfide bath test according to ASTM B298 has been successfully used, with a specific optical examination, which provides an overall result of quality control of the coating, highlighting any gaps or microcracks in the nickel coating.

As illustrated on the figure 8 a sample of yarn 1 is first defatted by immersion in a suitable organic solvent such as benzene, trichlorethylene or a mixture of ether and alcohol for at least 3 minutes. It is then removed and dried by wiping with a soft, clean cloth. The wire sample 1 should be held in the tissue until the test is complete, and should not be touched by hand.

A concentrated solution of polysulfide is prepared by dissolving sodium sulphide crystals in deionized water until saturation at about 21 ° C and adding enough sulfur flower to obtain complete saturation, which can be controlled by the presence of an excess of sulfur when the solution has sat for at least 24 hours. The test solution was made by diluting a portion of the concentrated solution with deionized water to a specific gravity of 1.142 at 15.6 ° C. The sodium polysulfide test solution should have sufficient strength to fully blacken a section of copper wire within 5 seconds. The test solution will not be considered exhausted as long as it can blacken a piece of copper.

A solution of hydrochloric acid is prepared simultaneously by diluting the commercial hydrochloric acid with distilled water to a density of 1.088 measured at 15.6 ° C. A portion of the acid solution hydrochloric acid with a volume of 180 milliliters will be considered exhausted if it can not suppress in 45 seconds the silver discoloration due to immersion in the polysulfide.

To test the yarn, the sample of yarn 1 having a length of at least 114 mm was immersed for 30 seconds in a polysulfide bath 37 containing the above-described solution of sodium polysulfide maintained at a temperature of between 15.degree. 6 ° C and 21 ° C.

Then the wire sample 1 is rinsed with deionized water 38, and dried with a soft, clean cloth.

The sample of yarn 1 was immediately immersed for 15 seconds in a hydrochloric acid solution described above, then washed thoroughly with deionized water and dried with a clean, soft cloth.

Less than two hours after this treatment, the sample of wire 1 is examined, for example using a binocular loupe 41 in magnification x 10. No attention will be paid to the end zones of the wire sample. 1, that is, the areas within 12.7 mm of each end.

A sample of yarn 1 taken from a thread of good quality, illustrated in the photograph of the figure 9 does not show a visible mark of attack of the lower layer of copper by the polysulfide bath. It is estimated that an attack mark is visible when it has an area of at least 0.02 mm ² in magnification x 10 (corresponding to a spot of 0.01 mm side at magnification 1).

On the other hand, a sample of wire taken from a defective wire, as illustrated in the photograph of the figure 10 , has dark areas 42 which are evidence of a lack of sealing of the nickel surface layer, leaving an attack of the underlying copper by the polysulfide bath. This is how the threads of the samples in the table above were examined.

The electrical conductors according to the present invention may advantageously be used in all types of applications requiring a good compromise between conductivity, load at break, flexibility, weight, and long-term protection, especially in the aeronautics, in the automobile, and generally in all types of mobiles.

The present invention is not limited to the embodiments which have been explicitly described, but it includes the various variants and generalizations thereof within the scope of the claims below.

Claims (21)

1. Aluminum cable type electrical conductor comprising at least one stranded conductor based on conductive wires (1) with an aluminum core (2) coated with an intermediate layer (3) of copper itself coated by a surface layer (4) of nickel, characterized in that :

   - the surface layer (4) of nickel has a thickness (E) from about 1,3 µm to about 3 µm,

   - the surface layer (4) of nickel has sufficient continuity to resist a polysulfide bath (37) continuity test for at least 30 seconds without visible traces of attack (42) of the copper appearing at x10 magnification.
2. Conductor according to claim 1, characterized in that the thickness (E) of the surface layer (4) of nickel is from about 2 µm to about 3 µm.
3. Conductor according to claim 2, characterized in that the thickness (E) of the surface layer (4) of nickel is about 2,3 µm.
4. Conductor according to any one of claims 1 to 3, characterized in that it consists of a cable comprising seven stranded conductors each of 10 or 15 wires having an individual diameter of about 0,51 mm.
5. Conductor according to any one of claims 1 to 3, characterized in that it consists of a cable with seven stranded conductors each of 19 wires having an individual diameter of about 0,275 mm.
6. Conductor according to any one of claims 1 to 3, characterized in that it consists of a cable with stranded conductor of 61 wires having a diameter of about 0,32 mm.
7. Conductor according to any one of claims 1 to 3, characterized in that it consists of a cable with one stranded conductor of 37 wires having a diameter of about 0,32 mm or about 0,25 mm.
8. Conductor according to any one of claims 1 to 3, characterized in that it consists of a cable comprising one stranded conductor (5, 6) of 19 wires of about 0,30 mm or about 0,25 mm or about 0,20 mm.
9. Conductor according to any one of claims 1 to 3, characterized in that it comprises a central wire (7a) of nickel-plated copper alloy surrounded by six wires (7b-7g) of nickel-plated copper-plated aluminum with a diameter of about 0,25 mm or about 0,20 mm.
10. Conductor according to any one of claims 1 to 9, characterized in that the cable is stranded with one or more true concentric or unilay concentric wires or stranded conductors.
11. Conductor according to any one of claims 1 to 10, characterized in that the stranded conductor(s) and/or the cable are coated with an insulative layer of polyimide and an external layer of polytetrafluoroethylene.
12. Method for producing a conductor according to any one of claims 1 to 11, in which is provided a copper-plated and nickel-plated aluminum wire fabrication procedure including the following steps :

    a) providing a wire blank (8) with an aluminum core (8a) coated with a layer of copper (8b) representing 10% to 20% by volume, of diameter (D_l) from twice to five times the required final diameter (D_F) of the wire,

    b) degreasing the wire blank (8),

    c) etching the wire blank (8) using sulfamic acid (14),

    d) depositing on the wire blank (8) a layer of nickel by electrolysis in an electrolysis bath (21) containing aqueous nickel sulfamate, the temperature of the electrolysis bath (21) being maintained from about 55°C to about 65°C, the pH of the electrolysis bath (21) being maintained from about 2,3 to about 3,0, the current density (j) being from 10 A/dm² to 16 A/dm², the concentration of nickel being maintained at less than 140 grams per liter approximately in the electrolysis bath (21),

    e) rinsing the wire obtained with demineralized water,

    f) drawing the wire obtained in whole oil to the final diameter,

    g) stranding a plurality of the wires obtained in this way into bundles of wires,

    h) annealing in a neutral gas.
13. Method according to claim 12, characterized in that, in the neutral gas annealing step h), the neutral gas is nitrogen.
14. Method according to any of claim 12 or claim 13, characterized in that, in the neutral gas annealing step h), the temperature is maintained at about 250°C for at least about two hours.
15. Method according to any one of claims 12 to 14, characterized in that, in the step d), the temperature of the electrolysis bath (21) is about 60°C, the pH of the electrolysis bath (21) is about 2,4, and the current density is about 15 to 16 A/dm².
16. Method according to any one of claims 12 to 15, characterized in that it comprises a prior step a_o) of calibrating the copper-plated aluminum wire blank (8) in terms of dimensions and hardness.
17. Method according to any one of claims 12 to 16, characterized in that, after a calibration step a_o), when effected, the copper-plated aluminum wire blank (8) has a yield point less than or equal to about 20 daN/mm² and an elongation from about 2% to about 3%.
18. Method according to any one of claims 12 to 17, characterized in that, in the step c), the sulfamic acid bath has a concentration of about 40 grams per liter.
19. Method according to any one of claims 12 to 18, characterized in that the initial diameter (D_l) of the wire blank (8) of copper-plated aluminum is from about 1,2 mm to about 0,8 mm, the nickel is deposited to a thickness from about 10 µm to about 15 µm, and the final diameter of the copper-plated and nickel-plated aluminum wire (1) is from about 0,51 mm to about 0,20 mm.
20. Method according to any one of claims 12 to 19, characterized in that the step b) of degreasing the wire comprises :

    b1) degreasing the wire blank (8) by ultrasound,

    b2) anodically degreasing the wire blank (8) in a bath (11) containing soda and surfactants,

    b3) rinsing the wire blank (8) with demineralized water.
21. Method according to any one of claims 12 to 20, characterized in that, for wires of diameter less than or equal to 0,25 mm, the stranding step g) is carried out before the annealing step h), whereas for wires of greater diameter the annealing step h) is carried out before the stranding step g).

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