The present invention relates to a method for connecting a conductor comprising a base metal to a terminal element comprising copper.

The present invention further relates to a terminal assembly with a conductor comprising a base metal, and with a terminal element which is connected to the conductor and which comprises copper.

For weight and cost reasons, cable harnesses and plug-in connectors are increasingly being miniaturised in the automotive industry. The cable harnesses and the terminal elements in plug- in connections are traditionally produced from copper or a copper alloy. However, copper is very heavy and is relatively expensive. Therefore the focus in the automotive industry is increasingly on alternative conductor materials which are lighter and more economical than copper, for example conductors made of base metals.

However, when connecting conductors comprising a base metal to a terminal element which comprises copper, it is difficult to produce a reliable mechanical and electrical connection between conductors and terminal elements. On the one hand, mechanically connecting a conductor and a terminal assembly which consist of different metals or metal alloys is problematic, in particular in view of the strict requirements set for plug-in connectors in the automotive industry. These are exposed to high physical stresses and therefore have to withstand high forces. On the other hand, the connection of a terminal element comprising copper to a conductor comprising a base metal is electrochemically problematic because the point of contact of copper to the base metal is at risk of corrosion. Corrosion not only weakens the mechanical connection, but also makes it difficult to transport charge if the oxide layer formed is insulating.

The problem of the present invention is thus to reliably connect a conductor comprising a base metal to a terminal element comprising copper both mechanically and in an electrically conductive manner such that the terminal assembly made up of the conductor and the terminal element connected thereto satisfies the strict requirements for use in the automotive industry. The present invention solves this problem through a method for connecting a conductor comprising a base metal to a terminal element comprising copper, the conductor and/or the terminal element being coated, at least at the weld joint, with a copper alloy or a mixture comprising copper and at least one base metal, before the conductor and the terminal element are welded onto one another. The terminal assembly specified above solves the problem in that it includes a conductor comprising a base metal, and a terminal element which is welded to the conductor and which comprises copper, wherein the weld seam has a layer of a copper alloy or of a mixture comprising copper and at least one base metal.

The solution according to the invention improves the connection of a conductor comprising a base metal to a terminal element comprising copper, both in mechanical terms and in terms of the electrical conduction. By coating with a copper alloy or with a mixture comprising copper and at least one base metal, a connecting layer is applied at the weld joint, i.e. in the region in which the welding parts are joined together, i.e. in the weld seam. This connecting layer improves the connection of the conductor to the terminal element both mechanically and in terms of electrical conductivity. The coating protects the region of the conductor which is connected to the terminal element from the formation of an insulating corrosion layer which impedes the electron transport across the surface as a conductor current from the conductor onto the terminal element. The base metal is present together with copper in the applied coating, either in a mixture or a copper alloy, such that corrosion occurs, if at all, at most partially and not across the surface. Furthermore, the coating according to the invention improves the mechanical connection between the conductor and the terminal element because it improves the suitability for welding and the weld connection quality.

"Base metal" should be understood to be all metals which have, in the electrochemical voltage series, a standard electrode potential which is smaller than the standard electrode potential of hydrogen.

"Weld joint" should be understood to be the region in which the welded parts, the conductor and the terminal element in this case, are welded together. "Welding" should be understood to mean the permanent connection of components by applying heat and/or pressure. The "weld seam" is the location at which the parts are welded together.

The solution according to the invention can be further improved by the following individually advantageous embodiments which are able to be combined with one another as desired. These embodiments and the associated advantages shall be explored hereafter. The following features of the embodiments can be realised both with the method and with the terminal element according to the invention.

In a first embodiment of the method according to the invention and the terminal assembly according to the invention, the conductor comprises aluminium as the base metal. In this case, the conductor can consist of aluminium or an aluminium alloy. Aluminium has the advantage that it is very light, such that with aluminium wires it is possible to obtain a substantial reduction in the weight of the cable harness. Furthermore, aluminium can be processed well and is relatively inexpensive.

Compared to copper wires, conductors comprising aluminium or which consist of aluminium or an aluminium alloy, or conductors which comprise another base metal or consist of it or an alloy thereof, have poorer conductivity. In order to compensate for this, the conductor can have a conductor cross-section of 5 to 120 mm ² . For example, the conductor can have a cross-section of 6 to 80 mm ² , such as a conductor cross-section from 30 to 40 mm ² , for example. With such a conductor cross-section, sufficient conductivity is guaranteed while also making savings in weight.

In a further embodiment, the terminal element is coated. The terminal element can for example be a contact element of a plug-in connector. Such terminal elements or contact elements are usually produced in this way as stamped bent parts. Firstly, the outer contour of the terminal element is stamped out of a strip-shaped contact material, with several terminal elements being produced from one strip and still being connected to one another at first in a prestamped strip. In this stage in which the individual terminal elements, for example contact elements, are stamped out but are still connected to one another via the prestamped strip, the weld joint provided at the terminal element can be particularly easily coated, for example by the individual terminal elements of the strip being successively and continuously fed through a coating zone.

According to a further embodiment, the mixture which is applied according to the method according to the invention to the weld joint as a coating or which is present at the weld seam according to the terminal assembly according to the invention has at least one base metal selected from the group comprising zinc, aluminium, tin, iron, nickel, manganese and oxides of the aforementioned metals. In a different embodiment, coating is performed with a copper alloy or the weld seam has a copper alloy selected from the group comprising CuSn, CuZn _x Sn _y , CuFe, CuNiSi, CuAl _xy and brass. Such mixtures or copper alloys can be applied well onto a conductor comprising a base metal or a terminal element comprising copper, as coating materials. According to one embodiment, the copper alloy can be brass and the zinc content of the brass can be between 10 and 70%. For example, the zinc content of the brass can be between 20 and 40%, such as between 28 and 32%. Such brass coatings adhere well to a carrier substrate, for example to a surface comprising copper or a copper alloy. Furthermore, these brass coatings display good plastic deformability, which opens up multiple coating methods for coating them on the carrier substrate.

The brass coating can comprise lead and/or at least one further alloy element. The at least one further alloy element can be selected from the group of aluminium, iron, manganese, nickel, silicon and tin. In this manner, the brass to be applied, or the brass coating, can be individually adapted to the requirements for the contact arrangement according to the invention or substrate to be coated and/or the materials of the conductor to be connected and terminal element.

According to a further embodiment, a solid, preferably a powder is applied for coating. By "coating" here, we generally mean the application of a firmly adhering layer of formless material onto the surface of a carrier material. The layer which arises is the "coating". A coating with a solid coating material has the advantage that it can generally be carried out continuously, with the substrates to be coated, for example a terminal element, being fed successively through a coating zone.

In a further embodiment, the powder can have a particle size of up to 60 μηη. For example, the powder can have a particle size of 1 to 50 μηη, such as 1 to 35 μηη. Such particle sizes allow a uniform coating of sufficient thickness to be applied across the surface.

According to a further embodiment, the coating can be applied by means of thermal spraying. Thermal spraying comprises surface coating methods in which the coating materials are introduced in the form of spray particles into a gas jet, are accelerated in the gas jet and are hurled onto the surface of the component to be coated. In the process, a layer is formed by the spray particles being flattened when they impact on the component surface and mainly remain adhered by mechanical clamping. The gas jet is in this case generally heated, depending on the method, to temperatures at which the spray particles in the gas jet can be fused, surface-fused or joined by fusing. Thermal spraying has the advantage that the substrate surface, i.e. the conductor and/or the terminal element, is not surface-fused and is only thermally stressed to a very minor degree.

For example, the coating can be applied by means of cold gas spraying. Cold gas spraying is a coating method, in which the coating material is applied onto the carrier material at high speed. For this purpose, a heated process gas is accelerated by expansion in a nozzle and the coating material is injected into the gas jet. Due to the high speed, which can be the speed of sound, a firmly adhering layer can be formed even when there is no surface-fusing or joining by fusion of the coating material when impacting on the substrate. A coating by means of thermal spraying, for example by means of cold gas spraying, has the advantage that it can be performed continuously, by the gas jet, including the coating particles, being directed onto the zones which are to be coated. The components to be coated, for example terminal elements, can be guided successively through a stationary gas jet or the gas jet can be moved, one after the other, over the weld joints, which are to be coated, of individual conductors and/or terminal elements.

According to a further embodiment, the conductor and the terminal element can be friction welded. For example, the conductor and the terminal element can be welded together by means of ultrasonic welding. This type of welding offers the advantage that it can be performed continuously, that it allows different materials to be connected to one another well, and that the tools in the welding region are only slightly heated. In addition, faster weldings are possible with these methods, so that the terminal assemblies according to the invention can be produced at faster rates.

Hereinafter, the solution according to the invention is explained in greater detail by way of example using advantageous embodiments with reference to the drawings. The developments and advantageous embodiments described therein are respectively independent of one another and can be combined with one another as desired.

The drawings show:

Fig. 1 a schematic longitudinal section of an electrical wire (A), a schematic cross-section of an electrical wire (B) and a schematic depiction of a terminal element before and during coating (C);

Fig. 2 a schematic cross-section of a terminal assembly according to the invention during and after welding of the conductor and the terminal assembly;

Fig. 3 a surface picture of a coating according to the invention according to one embodiment; and

Fig. 4 a surface picture of a coating according to the invention according to another embodiment. Hereafter, an embodiment of the method according to the invention is described with reference to Figs. 1 and 2.

The method serves to connect an electrical conductor 1 to a terminal element 2.

The electrical conductor 1 is depicted schematically in longitudinal section and in cross-section in the Figures. The conductor 1 is part of an electrical wire 3 and is located in an insulating cover 4. At one end, the cover 4 of the electrical wire 3 is removed, so that the conductor 1 is exposed at this end. The region of the exposed conductor 1 which is welded to the terminal element later is the weld joint 5 at the conductor.

The conductor 1 can comprise aluminium. For example, the conductor 1 can consist of aluminium or an electrically conductive aluminium alloy. The conductor 1 can have a conductor cross-section 6 from 5 to 120 mm ² , for example from 6 to 80 mm ² , such as 30 to 40 mm ² for example. Fig. 1 B shows a schematic cross-section of the electrical wire 3. It can be seen here that the conductor 1 in the exemplary embodiment has a round cross-section 6. The conductor

1 can however just as well have any n-sided, an oval or any other cross-section.

Fig. 1 C further schematically shows a terminal element 2. In the embodiment shown, a prestamped strip 7 is shown with terminal elements 2 which have been stamped in one piece out of a metal sheet, in a manner which makes them able to be handled.

In the figures, the terminal element 2 is only depicted schematically. The terminal element has a contact section 8 and a terminal section 9. The contact section 8 is the region with which the terminal element 2 is later electrically contacted by a mating plug element, for example as a part of an electrical plug connector. The terminal region 9 is the part with which the terminal element

2 is connected to the conductor 1. The terminal region 9 comprises a weld joint 10 at the terminal element, at which the terminal element 2 is welded to the electrical conductor 1.

The terminal element 2 comprising copper can for example be a contact element of a plug-in connector. In order to improve the welding of the terminal element 2 comprising copper to the conductor 1 comprising a base metal, a layer made up of a copper alloy or a mixture comprising copper and at least one base metal is applied according to the invention at least at a weld joint 5, 10, before the conductor 1 and the terminal element 2 are welded together. In the exemplary embodiment shown in the figures, the terminal element 2 is coated. For this purpose, in the embodiment shown the terminal section 9 of the terminal element 2 is coated at least in sections, in particular in the region of the weld joint 10 at the terminal element. The coating process is schematically depicted on the right side of Fig. 1. In the embodiment shown, a solid coating material 14 is applied, for example in the form of a powder having a particle size for example up to 60 μηι, such as a particle size from 1 to 50 μηι, e.g. a particle size from 1 to 35 μηη.

The coating 16 can be applied by means of thermal spraying. In the embodiment shown, the coating is applied by means of cold gas spraying. For this purpose, a gas jet 11 is introduced into a spray nozzle 12, heated up in the spray nozzle, accelerated and pressed out through the nozzle outlet 13.

The coating material 14 is injected into the gas jet 11 as a solid, for example a powder. The injected spray particles are accelerated in the gas jet 11 and applied onto the terminal section 9 of a terminal element 2. In this manner, the coating zone 15, within which the spray particles are applied onto the substrate, can be restricted to the desired regions of the terminal element 2.

A coating by means of thermal spraying, for example by means of the cold gas spraying shown in Fig. 1 , has the advantage that it can be performed continuously. To do so, for example, either the coating zone 15 of the nozzle 12 can be guided successively over the weld joints 10 (at the terminal element) of the terminal sections 9 of the terminal element 2 of the prestamped strip 7. Alternatively, the treatment zone 15 of the nozzle 12 could be stationary and the individual terminal elements 2 within a strip 7 can be successively guided through the coating zone 15 by their areas which are to be coated.

The coating material 14 can have a mixture comprising copper and at least one base metal. The base metal of the mixture can, for example, be selected from the group comprising zinc, aluminium, tin, iron, nickel, manganese and oxides of the aforementioned metals.

For example, the mixture can have alumina powder, zinc powder and copper powder. Such a mixture forms a well-adhering coating on a terminal element 2 as a carrier material. For example, Fig. 3 shows a picture of a scanning electron microscope of a coating of a mixture made up of 40% zinc powder (purity 96%), 30% alumina powder (purity 99.4%) and 30% copper powder (purity 99.5%). In the scanning electron microscope picture in Fig. 3 it can be clearly recognised that both copper and the base metals zinc and aluminium are contained, uniformly distributed, in the coating.

A further surface coating can be seen in the scanning electron microscope picture in Fig. 4. In this, instead of the abovementioned mixture, the powder of a brass alloy was applied, by means of cold gas spraying, onto a terminal element having CuSn0.15 base material. The brass powder has a copper content of 70%, a zinc content of 30% and has a particle size of smaller than <32 μηη. Fig. 4 also makes it clear that both copper and zinc are uniformly distributed in the coating as base metal and are applied on the carrier in a well adhering manner.

Instead of brass, it is also possible to use any desired other copper alloy comprising copper and a base metal. For example, a copper alloy selected from the group comprising CuSn, CuZn _x Sn _y , CuFe, CuNiSi, CuAl _xy can be applied. If coating takes place with brass, the applied brass can have lead or at least one further alloy element. The at least one further alloy element can be selected from the group of aluminium, iron, manganese, nickel, silicon and tin.

After the copper alloy or the mixture has been applied as the coating 16 at least at the weld joint 5 at the conductor and/or at the weld joint 10 at the terminal element, the weld joint 5 at the conductor and the weld joint 10 at the terminal element are brought together and the conductor 1 and the terminal element 2 are welded there. The welding process is depicted schematically in Fig. 2 by an arrow 17.

During welding, a terminal assembly 18 according to the invention is created, the weld seam 19 of which has a layer of a copper alloy or of a mixture comprising copper and at least one base metal.

The conductor 1 and the terminal element 2 can be friction-welded, for example welded by means of ultrasonic welding. For this purpose, a mechanical ultrasonic vibration is generated in the high-frequency range, generally from 20 to 35 kHz, and is introduced into the joining partners, in this case the conductor 1 and the terminal element 2. The high-frequency mechanical vibration leads to heating by boundary friction and results in a serration and hooking of the joining partners. As a result, a mechanically reliable connection can be generated between a conductor 1 comprising a base metal, for example aluminium, and a terminal element 2 comprising copper. The weld connection according to the invention is more reliable and capable of withstanding higher tractive and peeling forces than is the case with a direct welding without the coating according to the invention. List of reference signs:

1 Conductor

2 Terminal element

3 Electrical wire

4 Cover

5 Weld joint at the conductor

6 Conductor cross-section

7 Prestamped strip of terminal elements

8 Contact section

9 Terminal section

10 Weld joint at the terminal element

11 Gas jet

12 Nozzle

13 Nozzle outlet

14 Coating material

15 Coating zone

16 Coating

17 Welding process

18 Terminal assembly

19 Weld seam