EP1204787A2

EP1204787A2 - Method for continuous nickel-plating of an aluminium conductor and corresponding device

Info

Publication number: EP1204787A2
Application number: EP00953251A
Authority: EP
Inventors: Gabriel Colombier; Jean-Sylvestre Safrany; Bernard Loreau
Original assignee: Aluminium Pechiney SA
Current assignee: Rio Tinto France SAS
Priority date: 1999-07-22
Filing date: 2000-07-18
Publication date: 2002-05-15
Anticipated expiration: 2020-07-18
Also published as: WO2001007685A3; ES2238300T3; US6780303B2; US20020139685A1; ATE291111T1; DE60018764T2; FR2796656B1; WO2001007685A2; FR2796656A1; DE60018764D1; EP1204787B1

Abstract

A process for continuous nickel plating of an aluminum conductor, by electrolytically pre-treating the aluminum conductor to improve adherence of a nickel coat thereon by passing the aluminum conductor through a pre-treating bath in which is disposed an electrode connected to a first current source at a first voltage, for supplying to the aluminum conductor a pre-treating current, then electrolytically plating the pre-treated aluminum conductor with nickel in a plating bath in which is disposed an anode connected to a second current source at a second voltage, in which a nickel coat is deposited on the conductor by action of a nickel plating current In. At least the nickel plating current In is transmitted to the conductor through a mechanical electrical contact which contacts the conductor between the pre-treating bath and the plating bath, the pre-treating improving the contact properties of the conductor sufficient to permit the transmitting through the mechanical electrical conductor.

Description

CONTINUOUS NICKELING PROCESS OF AN ALUMINUM CONDUCTOR AND CORRESPONDING DEVICE

Field of the invention

The invention relates to conductors made of nickel-plated aluminum or aluminum alloy. It relates more specifically to the nickel plating processes of aluminum or aluminum alloy conductors, as well as the devices making it possible to implement them. The invention also relates to electric wires and cables with an aluminum or aluminum alloy core comprising at least one nickel-plated conductor.

The word "aluminum" is used in the broad sense of aluminum and its alloys. This will be the case throughout the text. The word "conductor" here designates an electrically conductive body, of elongated shape, the length of which is large compared to its transverse dimensions, such as a wire, a strip, a bar or a tube.

State of the art

Aluminum electrical conductors are widely used in the transport of electrical energy. These conductors are most often in the form of bars, flats, wires or cables.

Aluminum core electric wires and cables, which may include a coating of insulating material, are generally obtained from a continuously rolled "machine" wire, which is then drawn to the desired diameter. Unit wires or strands can then be assembled to form the conductive core of a cable.

In a large part of applications, such as 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 surface of the conductor, in addition to a brushing any parts of the conductor intended for establishing an electrical contact. For some applications, however, it is preferable to coat the aluminum conductor with a layer of nickel, so as to improve the electrical contact properties.

According to known methods of nickel plating, the conductor circulates in at least one electrolytic nickel plating tank. This tank is provided with a nickel electrode which acts as an anode and which, for this purpose, is connected to the positive terminal of an electrical supply. The conductor to be treated acts as a blank cathode and, for this, is electrically connected to the negative terminal of this supply.

In French application FR 2 526 052 (corresponding to American patent US 4 492 615), the applicant has proposed a process and a device for electrolytic nickel-plating on the passing of an aluminum conductor making it possible to reach running speeds of 300 m /minute. According to this method, the electrolytic current is transmitted to the conductor by a so-called liquid current socket, that is to say without mechanical contact, which avoids the drawbacks of mechanical current sockets, in particular electric arcs. More precisely, the conductor to be coated circulates in a first tank provided with a negatively polarized electrode, then in a second tank provided with a positively polarized electrode; an electric current then flows through the conductor as it passes through the tanks. The first tank contains an aqueous ionic solution capable of transmitting the electric current from the electrode to said conductor. The second tank contains the nickel plating bath.

Problem

The nickel plating of the conductors however constitutes an additional operation, the aim of which is both to minimize the cost and to maximize the productivity. In the case of conductors in the form of a wire or cable, satisfactory costs and productivity are obtained by carrying out nickel plating of the elementary wires at high speed. However, certain markets, such as that of aeronautics, wish have nickel-plated aluminum wires with a diameter between 0.1 and 0.5 mm, and cables made up of such wires.

The method according to French application FR 2 526 052 makes it difficult to nickel satisfactorily, and with high productivity, wires of diameter less than 1 mm. Indeed, the Applicant has found that the quality of the nickel coating becomes insufficient when the running speed exceeds 20 m / minute. On the other hand, since the entire intensity of the nickel-plating current passes through the conductor to be treated, the risks of breaking the conductor during treatment increase unacceptably below 1 mm in diameter when, for a thickness of the layer given nickel, we try to keep the unwinding speed (and therefore the nickel plating current) at a high value. Furthermore, this solution imposes a current in the first tank equal to the nickel-plating current in the second tank. The very high surface densities of current reached cause a significant attack of the conductor in the first tank and, consequently, irregularities in the surface of the conductor which make it more fragile. Finally, it has been found, in use, that the life of the baths is relatively limited, in particular because of the large current flowing in the first bath and resulting in a significant deposit of precipitates.

In French application FR 2,646,174 (corresponding to American patent US 5,015,340), the applicant has proposed to resolve some of these drawbacks by using baths of identical composition, one for a first so-called activation step and the 'other for the next nickel plating step, which keeps the conductor submerged when switching from one tank to another. This solution certainly allows running speeds of the order of 130 m / minute, but it does not limit the intensity of the activation current to the strictly necessary values since it is imposed by the intensity of the nickel plating current. This solution does not solve the problems associated with the liquid outlet.

In French application FR 2 609 292 (corresponding to American patent US 4 741 811), the applicant also proposed to modulate the current density on along the conductor path by reducing the current density in the upstream part of the nickel-plating bath and / or downstream of the so-called activation bath and by adjusting the acidity of the nickel-plating bath to a pH value between 1 and 5. This modulation is obtained in practice by the use of series of electrodes and screens interposed between the electrodes and the conductor. This solution makes it possible to nickel wires of diameters between 0.51 and 0.15 mm, at running speeds of between 25 and 50 m / minute. However, this solution requires a complex device which requires precise adjustment of the dimensions and of the position of the components, which in addition may change over time.

In French application FR 2 650 696, a process has been proposed for continuously coating an aluminum-based conductor comprising a chemical pretreatment of the surface of the conductor in order to create attachment points in the form of microscopic metallic germs and the deposition of a metallic layer on the conductor by electrodeposition. The method and the device described in this document have the drawback of operating at reduced running speed (the immersion times are of the order of 20 to 24 seconds).

The Applicant has therefore sought means to obtain nickel-plated aluminum conductors with a diameter of less than 1 mm which avoid the drawbacks of the prior art while maintaining acceptable profitability and productivity, with the lowest possible investment costs. .

Description of the invention

The subject of the invention is a process for continuous nickel plating (or "passing") of an aluminum conductor.

More specifically, the process for nickel-plating an aluminum conductor according to the invention comprises a pre-treatment step P capable of promoting the adhesion of the nickel layer and a step of electrolytic nickel-plating N, and is characterized in what said preprocessing P is also able to confer on said driver sufficient contact properties to allow mechanical electrical contact and in that the nickel-plating current is transmitted to said conductor via a mechanical electrical contact on the part of the conductor resulting from the pretreatment step.

The electrolytic nickel-plating step N makes it possible to form, by electrodeposition, a uniform nickel layer on said conductor.

The Applicant has unexpectedly found that, thanks to the pretreatment operation, it is possible to use mechanical contacts on conductors of very small diameter and to pass all the nickel intensity through the conductor. by these contacts (also called "sockets"). It also observed that, surprisingly, this solution made it possible to reach running speeds clearly greater than 20 m / minute, as demonstrated by the example presented below.

The subject of the invention is also a device for continuous nickel plating (or "in the process") of an aluminum conductor.

Even if the invention relates mainly to aluminum conductors intended for electrical applications, it also applies to aluminum conductors intended for non-electrical uses, such as thermal uses (which exploit the high thermal conductivity of aluminum, such as a heat exchanger) or, possibly, essentially mechanical uses.

The invention can also be applied to the nickel plating of aluminum products, such as aluminum wires, strips or tubes, intended to be brazed. In particular, the invention relates to the use of the method or the device according to the invention for nickel plating an aluminum product so as to allow it to be brazed. The nickel layer, with a thickness typically of the order of 1 μm, can allow the formation of a satisfactory brazed joint without having recourse to a specific brazing flux. The invention also relates to a method of manufacture of an assembled product, characterized in that it comprises the use of a nickel-plated aluminum product according to the invention. Said manufacturing process optionally includes a brazing operation of said nickel-plated aluminum product.

Description of the figures

Figure 1 schematically illustrates a first preferred embodiment of the nickel plating process according to the invention. In this embodiment, the pre-treatment step P is carried out electrolytically and is carried out with mechanical contact means common to those of the nickel-plating step N.

FIG. 2 schematically illustrates a second preferred embodiment of the invention according to which the pretreatment step P is configured in a liquid current socket.

FIG. 3 illustrates a mechanical contact means according to the invention comprising one or more wheels.

FIG. 4 illustrates another contact means according to the invention comprising three wheels.

Detailed description of the invention

The process for nickel-plating at least one aluminum conductor (1) according to the invention comprises a pretreatment step P capable of promoting the adhesion of a nickel layer and an electrolytic nickel-plating step N in which said nickel layer is deposited on said conductor by the action of a so-called nickel-plating current (I _n = L), and is characterized in that said pre-treatment P is also capable of imparting to said conductor (1) sufficient contact properties to allow mechanical electrical contact and in that the nickel-plating current (I _n = Ii) is transmitted to said conductor via an electrical contact mechanical (7), preferably immersed in a liquid (14), on the part (6) of the conductor (1) from the pre-treatment step P.

Said mechanical contact (7) preferably comprises at least one mechanical contact means by bearing (70) which typically comprises at least one grooved wheel or a sheave.

The contact properties are sufficient when it is possible to pass the full intensity of the nickel-plating current through mechanical contact without damaging the conductor. Typically, the mechanical contact must make it possible to pass a nickel-plating current of the order of 5 A for a wire of 0.15 mm in diameter when the running speed is 50 m / minute.

Mechanical electrical contact can be achieved, for example, using rollers, rollers, rubbing contacts or brushes.

The composition of the nickel-plating bath is advantageously as follows: 300 ± 30 g / 1 of Ni (NH ₂ SO ₃ ) ₂ (sulfamate), 30 ± 5 g / 1 of NiCl ₂ , 6H ₂ O, 30 ± 5 g / 1 of H ₃ BO ₃ .

The device for nickel-plating at least one aluminum conductor (or "treatment line") according to the invention comprises a nickel-plating tank (30) comprising a tank (2) capable of containing a nickel-plating bath (4) and at least one electrode (3) containing nickel, called anode, at least one power supply (5) for applying an electric voltage (Vi) between the anode and said conductor, and means (21, 22) for scrolling the, or each, conductor (1) in the nickel-plating bath (4), and is characterized in that it also comprises at least one pretreatment tank (40, 41, 42) comprising a tank (17, 43, 46 ) capable of containing a pre-treatment bath (16, 44, 47), and means for scrolling the, or each, conductor in the pre-treatment bath (16, 44, 47), and in that it comprises mechanical contact means (7, 13, 14) for applying said electrical voltage to the part (6) of the, or each, said conductor (1) resulting from the pre-stroke step ement P. Typically, the conductor in the raw state (10), coming from at least a first unwinder (22), passes successively through the treatment baths (40, 41, 42, 30) and is wound, in the nickel-plated state (11), on at least one second unwinder (21).

The pre-treatment stage is chosen to give the conductor sufficient contact properties to allow mechanical electrical contact on the latter.

The pre-treatment stage P is preferably carried out electrolytically, which makes it easier to control the pre-treatment as a function of the operating conditions of the treatment line. In this case, the pre-treatment tank (40) is provided with at least one electrode (15) and the device comprises an electrical supply (8) intended for the pre-treatment. The electric voltage V ₂ delivered by this supply can be alternating, continuous or pulsed, or a combination of these. The socket on the conductor is produced by a mechanical contact placed downstream of the pre-treatment tank (40). This mechanical outlet is advantageously common to that of the nickel plating step, as illustrated in FIG. 1, which makes it possible to simplify the device without causing an overload of the mechanical contact means (1, 13, 14) because the intensity of the pre-treatment current (I) is generally much lower than the intensity of the nickel-plating current (ï _\ ).

According to a first variant of the invention, the pretreatment step P comprises activation A in a strongly acidic or alkaline bath which allows, in particular, rapid dissolution of the surface oxides. Activation is carried out in an activation tank (40, 42) comprising a tank (17, 46) capable of containing the activation bath (16, 47), in which the conductor (1) runs. When the activation step is carried out electrolytically, the activation tank (40, 42) also comprises at least one electrode (15, 48) and the device comprises an electrical supply (8) intended for this activation. The electric voltage V ₂ delivered by this supply can be alternating, continuous or pulsed, or a combination of these.

According to a second variant of the invention, the pre-treatment step P comprises, in addition to an activation step A to dissolve in particular the oxides present on the surface of the conductor (1), a pre-nickel-plating step PN for coating the aluminum conductor (1) of a "primary" nickel deposit. The nickel-plating current (I _I ) is then transmitted to said conductor by means of mechanical contact means (7, 13, 14) on the part (6) of the conductor (1) coated with said primary nickel deposit.

The term "primary nickel deposition" means a layer of nickel, which is in the form of nodules, the equivalent thickness of which is significantly less than the target thickness of the final layer. It has been found preferable to aim for an equivalent thickness which is, on average, less than about 0.1 of the final thickness. Typically, the thickness of the final layer being approximately 1 μm, we will aim for an equivalent thickness of the pre-nickel plating layer of less than approximately 0.1 μm.

The pre-nickel plating is carried out in a tank (40, 41) comprising a tank (17, 43) capable of containing the pre-nickel plating bath (16, 44), in which the conductor (1) runs. The pre-nickel plating bath (16, 44) contains a nickel salt so as to coat the aluminum conductor with a primary nickel deposit when the conductor passes through this bath.

The pre-nickel plating step is preferably carried out electrolytically, which makes it easier to control the thickness of the layer as a function of the operating conditions of the treatment line. In this case, the pre-nickel plating tank (40, 41) is provided with at least one electrode (15, 45) containing nickel and the device comprises an electrical supply (8) intended for pre-nickel plating. The electric voltage V ₂ delivered by this supply can be alternating, continuous or pulsed, or a combination of these.

Advantageously, the pre-nickel plating step PN is, in whole or in part, combined with the activation step A, which makes it possible to considerably simplify the device. In a preferred variant of this embodiment, the pre-nickel plating and activation steps are carried out in conjunction with a liquid outlet. FIG. 2 illustrates a device which makes it possible to implement this variant of the invention. This device comprises an electrolytic activation tank (42) and an electrolytic pre-nickel plating tank (41), preferably close to each other and possibly adjacent, a first electrical supply (8) common to these two tanks , an electrolytic nickel-plating tank (30), a second electrical supply (5) and mechanical contact means (7, 13, 14) on the part (6) of the conductor (1) situated between the pre-nickel-plating tank ( 41) and the nickel-plating tank (30).

The first electrical supply (8) is preferably direct current, optionally modulated or pulsed; the positive terminal is connected to at least one electrode (45) submerged, in whole or in part, in the pre-nickel plating bath (44) and the negative terminal is connected to at least one submerged electrode (48), in whole or in part , in the activation bath (47). The current flows through the conductor (1) by a liquid current pickup effect. Thus, the same power supply (8) is used for activation and pre-nickel plating.

The second power supply (5) is direct current, possibly modulated or pulsed; the positive terminal is connected to at least one electrode (3) containing nickel immersed, in whole or in part, in the nickel-plating bath (4) and the negative terminal is connected to the part (6) of the conductor (1) located between the pre-nickel plating tank (41) and the nickel plating tank (30) by means of mechanical contact means (7, 13, 14).

For the variant illustrated in FIG. 2, it has been found advantageous to use the following composition for the activation and pre-nickel plating baths: 125 ± 15 g / 1 of nickel chloride (NiCl ₂ , 6 HO), 12.5 ± 2 g / 1 of orthoboric acid and 6 ± 2 ml / 1 of hydrofluoric acid.

The PN pre-nickel-plating and activation A stages can be carried out simultaneously, in the same bath (40) and with common electrodes (15) (and having the same polarization), as illustrated in FIG. 1 In this case, the pretreatment step operates a dual function of activation and pre-nickel plating. The bath activation / pre-nickel plating (16) is then able to operate the two treatments, for example by having a mixed composition which allows both satisfactory activation and sufficient pre-nickel plating. The Applicant has found that it is possible to effectively perform these two functions using a single bath. The following composition gave excellent results: 125 ± 15 g / 1 of nickel chloride (NiCl ₂ , 6 H ₂ O), 12.5 ± 2 g / 1 of orthoboric acid and 6 ± 2 ml / 1 d hydrofluoric acid.

In this variant, the first electrical supply (8) is direct current, optionally modulated or pulsed, the positive terminal being connected to the conductor (1) via the mechanical contact (7) and the negative terminal being connected to at least an electrode (15) submerged, in whole or in part, in said activation / pre-nickel plating bath (16). The second power supply (5) is direct current, possibly modulated or pulsed; the positive terminal is connected to an electrode (3) containing nickel immersed, in whole or in part, in the nickel-plating bath (4) and the negative terminal is connected to the part (6) of the conductor (1) located between the tank activation / pre-nickel plating (40) and the nickel plating tank (30) by means of mechanical contact means (7, 13, 14), preferably common to those of the first supply (8).

For conductors with a very small cross-section, in particular for wires with a diameter of less than 0.2 mm, it is preferable that the mechanical contact is immersed in a liquid (14) such as water or a neutral solution, so as to avoid fusion of the conductor at the mechanical contact. For this purpose, the device may include an intermediate tank (13), generally of small dimensions, containing the liquid (14) and the mechanical contact (7). The liquid (14) can optionally be cooled.

The Applicant has also noted that, in order to achieve high running speeds, it was preferable to use mechanical contact means which limit the friction between them and the conductor as much as possible because a high coefficient of friction can lead when the conductor melts even when the electrical contact is immersed in a liquid. It has been found particularly advantageous using mechanical contacts comprising at least one wheel, preferably grooved, in particular as illustrated in FIGS. 3 and 4. The use of contact wheels makes it possible in particular to avoid the problems of sparking and degradation of the surface of the conductor after treatment.

For the treatment of two or more conductors in parallel ("ribbon" treatment), the mechanical contact can comprise several parallel wheels rotating around a common axis (as illustrated in FIG. 3).

The mechanical rolling contact means (70) illustrated in FIG. 3, which corresponds to a preferred embodiment of the invention, comprises one or more wheels (71) rotating around an axle (73) whose axis central (75) is substantially perpendicular to said wheels (71). The (or each) wheel (71) is preferably provided with a groove (74) in which the conductor (6) rests, which in particular makes it possible to avoid variations in the position thereof. The electric current flows from the axle (73) to the conductor (6) via the wheel (71). The axle-wheel assembly (s) (70) can be immersed in a liquid (14). The contact means (70) may comprise a ring (72), typically made of graphite, to facilitate the rolling of the wheels (71) around the axle (73) and improve the electrical contact. This latter variant also avoids the need for a ball bearing. In the applicant's tests, the wheels (71) were made of copper (possibly nickel-plated) and the axle (73) was made of stainless steel.

The mechanical contact means illustrated in FIG. 4, which also corresponds to a preferred embodiment of the invention, comprises a set of at least three wheels (701, 702, 703) which cooperate to ensure satisfactory electrical contact on the (or each) driver (6). Preferably, each conductor comprises such means when several conductors are treated simultaneously. At least one of said mechanical contact means (7, 13, 14) comprises such contact means. Each wheel rotates around its own axis (731, 732, 733) and exerts a force (FI, F2, F3) on the driver. In practice, it is sufficient to adjust the effort exerted on the driver by moving only the central wheel (702). The three wheels can be immersed in a liquid (14).

The temperature of the various baths is generally chosen so that the ionic conductivity and the reactivity of the baths are sufficient. Typically, the temperature of the baths is between 45 and 60 ° C.

The method according to the invention may comprise additional steps, such as shaving and / or possible degreasing of the conductor in the raw state (10) before the activation and / or pre-nickel-plating step.

The conductor is typically made of an AA 1370 alloy, AA 1110 or AA 6101 according to the nomenclature of the Aluminum Association.

The invention also relates to cables comprising at least one elementary nickel-plated wire according to the invention. In particular, the process for manufacturing an aluminum electric cable can comprise a nickel-plating operation according to the invention of at least one of the elementary wires.

According to another variant of the invention, several conductors are treated simultaneously, in particular in the pre-treatment and nickel-plating baths. For this purpose, it is possible, for example, to have two or more conductors in parallel, which conductors can pass simultaneously from one tank to the next using individual scrolling means for each conductor or common to all of the conductors . In other words, the device comprises means for simultaneously scrolling two or more conductors in at least one of said treatment tanks. For example, plies of conductors from a series of separate unwinders circulate in parallel in said baths and, after treatment, are wound on a series of separate winders. The contact means (7, 13, 14) on the part of the conductors (6) resulting from the pre-treatment step may be, in whole or in part, common to these; for example, said means can comprise a strip of carbon material which can be brought into contact with all the conductors of a sheet.

The conductor (s) can pass horizontally, vertically or at a certain angle with respect to the horizontal.

Example

Tests were carried out on the wires with a diameter of 0.20 mm, according to the prior art and according to the invention.

In the tests corresponding to the prior art, the activation and nickel-plating currents were of the same intensity and came from a common supply configured as a liquid current socket (as described in application FR 2 646 174); screens were interposed between the nickel electrodes and the wire (as described in application FR 2 609 292). The activation and nickel-plating baths had the same composition, namely: 125 ± 15 g / 1 of nickel chloride (NiCl ₂ , 6 H ₂ O), 12.5 ± 2 g / 1 of orthoboric acid and 6 ± 2 ml / 1 hydrofluoric acid.

The tests according to the invention were carried out using a device similar to that of FIG. 2. The electrodes (48) of the activation tank (42) were made of graphite and the electrodes (45) of the pre-nickel plating tank (41) were made of nickel. The activation and pre-nickel plating baths had the following composition: 125 ± 15 g / 1 of nickel chloride (NiCl ₂ , 6 HO), 12.5 ± 2 g / 1 of orthoboric acid and 6 ± 2 ml / 1 hydrofluoric acid. The nickel-plating bath had the following composition: 300 ± 30 g / 1 of Ni (NH ₂ SO ₃ ) ₂ (sulfamate), 30 ± 5 g / 1 of NiCl ₂ , 6H ₂ O, 30 ± 5 g / 1 of H ₃ BO ₃ .

Table I below groups together the main treatment parameters used in these tests and certain characteristics of the treated yarns. The contact resistance was measured using a so-called "cross wire" method, at an intensity of 0.1 mA and with a pressing force of 0.2 N. The adhesion of the layer nickel on the wire was measured by winding the wire on its own diameter; she is considered as excellent if the nickel layer uniformly follows the deformation of the wire without detaching from the surface.

Table I

In the tests according to the prior art, it was not possible to carry out the treatment at a running speed as high as 80 m / min. In fact, at such a high speed, a "burn" of the deposit was observed, that is to say a non-adherent black deposit caused by too high a current density in the activation step.

The electrolytic pre-nickel plating layer was in the form of nodules which did not cover the entire surface of the conductor. The Applicant has observed that it was not necessary for said primary nickel deposit (or "pre-nickel plating layer") to be uniform or for it to completely cover the surface of the conductor; it has proved sufficient to achieve an equivalent recovery rate corresponding to approximately 0.1 of the final thickness of the nickel layer. The Applicant has hypothesized that such a recovery rate confers a quality of electrical contact sufficient to allow the transmission by mechanical contact of high nickel plating current intensities without degrading the surface of the conductor and ensures a high adhesion of the layer of final nickel. Thus, the term "primary nickel deposition" means a layer of nickel whose thickness is typically, on average, about 0.1 μm. The nickel layer obtained according to the invention therefore has great adhesion and low electrical contact resistance.

Benefits

The invention makes it possible to nickel effectively, and with great productivity, wires of different diameters. In particular, it allows easy adjustment of treatment parameters to production conditions, thanks to the decoupling between the pre-treatment and nickel-plating stages. It is in particular possible to independently adjust the intensity of the pre-treatment and nickel-plating currents, and in particular to impose a low current intensity in the pre-treatment stage and high in the nickel-plating stage.

The invention makes it possible to benefit from the advantages of mechanical sockets, in particular the possibility of passing high intensities, and of avoiding the disadvantages thereof, in particular the propensity to form electric arcs which can damage the surface of the conductor.

The low intensity of the pretreatment current required according to the invention leads to a significantly slower aluminum enrichment of the pretreatment bath, which makes it possible to considerably reduce the frequency of replacement of this bath. The low intensity of the pre-treatment current also limits the dissolution of the metal and, consequently, the formation of roughness on the surface of the wire. In other words, the pre-treatment step according to the invention also makes it possible to confer on the surface of the conductor a defined roughness in order to obtain optimal mechanical properties.

Claims

1. A process for nickel-plating at least one aluminum conductor (1) comprising a pre-treatment step (P) capable of promoting the adhesion of a layer of nickel and an electrolytic nickel-plating step (N) in which said nickel layer is deposited on said conductor by the action of a so-called nickel-plating current (I _n = Ii), and characterized in that said pre-treatment (P) is also capable of imparting to said conductor (1 ) sufficient contact properties to allow mechanical electrical contact and in that the nickel-plating current I _n is transmitted to said conductor via a mechanical electrical contact (7) on the part (6) of the conductor (1 ) from the pretreatment step (P).

2. Method according to claim 1, characterized in that the pre-treatment step (P) is carried out electrolytically.

3. Method according to claim 1 or 2, characterized in that the pretreatment step (P) comprises an activation (A) in a strongly acidic or alkaline bath which allows, in particular, a rapid dissolution of the surface oxides.

Method according to any one of claims 1 to 3, characterized in that the pre-treatment step (P) comprises a pre-nickel plating step (PN) for coating the aluminum conductor (1) with a primary nickel deposit.

5. Method according to one of claims 1 or 2, characterized in that the pre-treatment step (P) comprises an activation (A) in a bath (47) strongly acidic or alkaline which allows, in particular, a dissolution rapid surface oxides and a pre-nickel plating step (PN) in a pre-nickel plating bath (44) which allows the aluminum conductor (1) to be coated with a primary nickel deposit, and in that the pre-nickel plating (PN) and activation (A) are carried out jointly, electrolytically, with a liquid outlet.

6. Method according to claim 5, characterized in that the activation bath (47) and the pre-nickel plating bath (44) have substantially the same composition.

7. Method according to one of claims 1 or 2, characterized in that the pre-treatment step (P) comprises an activation (A) in a strongly acidic or alkaline bath which allows, in particular, a rapid dissolution of the oxides surface and a pre-nickel plating (PN) step which makes it possible to coat the aluminum conductor (1) with a primary nickel deposit, and in that the pre-nickel plating (PN) and activation steps ( A) are carried out simultaneously in the same bath (16).

8. Method according to any one of claims 4 to 7, characterized in that said primary nickel deposit has an equivalent average thickness less than about 0.1 μm.

9. Method according to any one of claims 1 to 8, characterized in that the mechanical contact (7) is immersed in a liquid (14), optionally cooled, such as water or in a neutral solution.

10. Method according to any one of claims 1 to 9, characterized in that said mechanical contact (7) comprises at least one mechanical contact means by rolling (70).

11. Method according to any one of claims 1 to 10, characterized in that several conductors are treated simultaneously.

12. Method according to any one of claims 1 to 11, characterized in that the aluminum conductor (1) is made of an alloy chosen from AA 1370, AA 1110 or AA 6101 according to the nomenclature of the Aluminum Association .

13. A method of manufacturing an aluminum electric cable comprising a nickel-plating operation of at least one of the elementary wires according to the nickel-plating method of any one of claims 1 to 12.

14. Device for nickel-plating at least one aluminum conductor (1) for implementing the nickel-plating method according to any one of claims 1 to 12, said device comprising a nickel-plating tank (30) comprising a tank (2) able to contain a nickel-plating bath (4) and at least one electrode (3), called anode, containing nickel, at least one power supply (5) for applying an electric voltage (Vi) between the, or each , electrode (3) and said conductor (1), and means (21, 22) for passing the conductor (1) through the nickel-plating bath (4), said device being characterized in that it also comprises at least a pre-treatment tank (40, 41, 42) comprising a tank (17, 43, 46) capable of containing a pre-treatment bath (16, 44,

47), and means for passing the or each conductor (1) through the pre-treatment bath (16, 44, 47), and in that it comprises mechanical contact means (7, 13, 14) to apply said voltage to the part (6) of the, or each, said conductor (1) from the pre-treatment step (P).

15. Device according to claim 14, characterized in that the, or each, pre-treatment tank (40, 41, 42) is provided with at least one electrode (15, 45, 48) and in that the device comprises at least one power supply (8) for the pre-treatment (P).

16. Device according to claim 15, characterized in that the electrical voltage of the nickel-plating (5) and pre-treatment (8) supply is applied to the conductor (1) by means of the same said mechanical contact means (7, 13, 14).

17. Device according to any one of claims 14 to 16, characterized in that the mechanical contact means (7, 13, 14) comprise a tank (13) capable of containing a liquid (14) making it possible to immerse the contact mechanical (7).

18. Device according to any one of claims 14 to 17, characterized in that it comprises an activation tank (42) comprising a tank (46) capable of containing an activation bath (47) and at least one electrode (48), in that it comprises a pre-nickel plating tank (41) comprising a tank (43) capable of containing a pre-nickel plating bath (44) and at least one electrode (45), and in that that it includes at least one power supply _. (8) common for activation (A) and pre-nickel plating (PN).

19. Device according to claim 18, characterized in that the electrical supply of the activation (42) and pre-nickel-plating (41) tanks is configured in liquid current outlet via the conductor (1).

20. Device according to any one of claims 14 to 19, characterized in that it allows the nickel plating of several conductors simultaneously.

21. Device according to any one of claims 14 to 19, characterized in that it comprises means for simultaneously scrolling two or more conductors in at least one of said treatment tanks.

22. Device according to any one of claims 14 to 21, characterized in that said mechanical contact means (7, 13, 14) comprise at least one mechanical contact means by rolling (70).

23. Device according to claim 22, characterized in that the, or each, means of mechanical contact by rolling comprises one or more wheels (71) rotating around an axle (73) whose central axis (75) is substantially perpendicular to said wheels (71).

24. Device according to claim 23, characterized in that the or each wheel (71) comprises a ring (72), typically made of graphite, to facilitate the rolling of the wheels (71) around the axle (73) and improve electrical contact.

25. Device according to any one of claims 22 to 24, characterized in that at least one of said mechanical contact means (1, 13, 14) comprises a set of at least three wheels (701, 702, 703) which cooperate to ensure electrical contact on the conductor (6).

26. Device according to any one of claims 23 to 25, characterized in that the or each wheel is provided with a groove.

27. Use of the method according to any one of claims 1 to 13 or of the device according to any one of claims 14 to 26 for the nickel plating of an aluminum product, such as an aluminum strip or tube, so as to allow soldering of said product.

28. A method of manufacturing an assembled product characterized in that it comprises the use of a nickel-plated aluminum product according to the method of any one of claims 1 to 13 or using the device according to any of claims 14 to 26.

29. Method according to claim 28, characterized in that it comprises a brazing operation of said nickel-plated aluminum product.