Electrical cable with improved resistance to galvanic corrosion

Abstract

The invention relates to an elongated electrically conductive copper-aluminum bimetal element, a cable comprising at least one such elongated electrically conductive element, a process for preparing said elongated electrically conductive element and said cable, and a device comprising such an electric cable and at least one metal connector.

Claims

1. An elongated electrically conductive element comprising: an aluminum or aluminum alloy core; and a copper or copper alloy layer surrounding said aluminum or aluminum alloy core, wherein the copper or copper alloy layer represents a volume greater than 30% of the volume of the elongated electrically conductive element, and wherein said element is capable of being obtained according to a process comprising at least one step i) of forming a copper of copper alloy layer around an aluminum or aluminum alloy core by continuous casting.

2. The element as claimed in claim 1, wherein the copper layer represents from 40% to 80% by volume, of the volume of the elongated electrically conductive element.

3. The element as claimed in claim 1, wherein the copper or copper alloy layer is the outermost layer of the elongated electrically conductive element.

4. The element as claimed in claim 1, wherein said element has an external diameter ranging from 0.01 to 30 mm.

5. The element as claimed in claim 1, wherein the copper or copper alloy layer is directly in contact with the aluminum or aluminum alloy core.

6. The element as claimed in claim 1, wherein the aluminum content of the aluminum alloy is at least 95.00% by weight.

7. The element as claimed in claim 1, wherein the copper content of the copper alloy is at least 95.00% by weight.

8. The element as claimed in claim 1, wherein said element has a reduction of at most 20%, in newtons, of the mechanical strength of the terminals in a tensile test, when it is subjected to an exposure to a salt spray of at least 50 h.

9. An electric cable, comprising at least one elongated electrically conductive element as defined in claim 1 and at least one polymer layer surrounding said elongated electrically conductive element.

10. The electric cable as claimed in claim 9, wherein the polymer layer is an electrically insulating layer.

11. The electric cable as claimed in claim 9, wherein the polymer layer comprises a polymer material chosen from crosslinked and non-crosslinked polymers, and polymers of inorganic type and of organic type.

12. The electric cable as claimed in claim 9, wherein the polymer layer does not comprise halogenated compounds and the cable is a HFFR cable.

13. A device comprising: an electric cable having at least one elongated electrically conductive element as defined in claim 1, and at least one polymer layer surrounding said elongated electrically conductive element; and at least one metal connector, wherein said metal connector is connected to said at least one elongated electrically conductive element.

14. The element as claimed in claim 1, wherein the metals used during step i) of forming a copper or copper alloy layer around an aluminum or aluminum alloy core by continuous casting are: for the copper or the copper alloy, in the liquid state, and for the aluminum or the aluminum alloy, in the liquid or solid state.

15. The element as claimed in claim 1, wherein the aluminum or the aluminum alloy is in the solid state, and step i) is a step i-1) during which copper or a copper alloy in the liquid state is cast on aluminum or an aluminum alloy in the solid state, or aluminum or aluminum alloy in the solid state is immersed in copper or a copper alloy in the liquid state.

16. The element as claimed in claim 1, wherein the aluminum is in the liquid state, and step i) is a step i-2) during which a hollow element made of copper or of copper alloy is preformed from copper or a copper alloy in the liquid state; then said hollow element is cooled; then the hollow element is filled with aluminum or an aluminum alloy in the liquid state; then the assembly obtained is cooled.

17. An elongated electrically conductive element comprising: an aluminum or aluminum alloy core; and a copper or copper alloy layer surrounding said aluminum or aluminum alloy core, wherein the copper or copper alloy layer represents from 45% to 70% by volume of the volume of the elongated electrically conductive element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically represents a structure, in cross section, of an electric cable according to the invention.

(2) FIGS. 2a and 2b show the elongated electrically conductive element B-45 in accordance with the invention (FIG. 2a) and by comparison the elongated electrically conductive element B-10 not in accordance with the invention (FIG. 2b);

(3) FIG. 3 is a micrograph cross section of the elongated electrically conductive element B-45 in accordance with the invention (FIG. 3a) and by comparison a micrograph cross section of the elongated electrically conductive element B-10 not in accordance with the invention (FIG. 2b), when these have undergone an exposure to salt spray for 48 h, 88 h, 176 h and 360 h; and

(4) FIG. 4 is a chart of the mechanical strength of the terminals in a tensile test (in newtons N) as a function of the exposure time to the salt spray (in hours) for the conductors A-0 (curve with circles), A-10 (curve with squares), A-30 (curve with triangles), A-45 (curve with lozenges), A-60 (curve with crosses) and A-100 (curve with dotted lines).

DETAILED DESCRIPTION

(5) FIG. 1 shows an electric cable (1) in accordance with the invention comprising an elongated electrically conductive element comprising an aluminum or aluminum alloy core (2) and a copper or copper alloy layer (3) surrounding said aluminum or aluminum alloy core (2); and a polymer layer (4) surrounding said elongated electrically conductive element (2, 3).

(6) Other features and advantages of the present invention will become apparent in light of the following examples with reference to the annotated figures, said examples and figures being given by way of nonlimiting illustration.

EXAMPLES

Example 1: Manufacturing of Elongated Electrically Conductive Elements in Accordance with the Invention and not in Accordance with the Invention

(7) In this example, three elongated electrically conductive elements A, B and C were compared with various volume contents of copper: an elongated electrically conductive element A: strand comprising 7 wires having a diameter of 0.302 mm, i.e. a total cross section of 0.5 mm.sup.2, an elongated electrically conductive element B: strand comprising 7 wires having a diameter of 0.674 mm, i.e. a total cross section of 2.5 mm.sup.2, and an elongated electrically conductive element C: single wire having a diameter of 1.45 mm, i.e. total cross section of 1.65 mm.sup.2.

(8) The volume contents of copper of each of the elongated electrically conductive elements A, B and C were: for the comparative elongated electrically conductive elements (i.e. not in accordance with the invention): 0% (pure aluminum) (conductors A-0, B-0, C-0), 10% (conductors A-10, B-10, C-10), 30% (conductors A-30, B-30, C-30) or 100% (conductors A-100, B-100, C-100), and for the elongated electrically conductive elements in accordance with the invention: 45% (conductors A-45, B-45, C-45), 60% (conductors A-60, B-60, C-60) or 80% (conductor C-80).

(9) The various conductors were prepared according to the following steps:

(10) i) a step of drawing at ambient temperature, so as to obtain aluminum wires (aluminum sold under the reference Al1350), aluminum wires coated with 10% by volume of copper relative to the total aluminum+copper volume (aluminum+copper sold under the reference CCA10), or copper wires (electrolytic copper sold under the reference ETP1);

(11) ii) a step of depositing copper on the CCA10 wires from step i), by electrodeposition in order to achieve the desired volume % of copper, said electrodeposition being carried out using:

(12) a copper plating bath based on methanesulfonic acid sold under the reference Copper Gleam RG10 which is a copper plating bath,

(13) a current density of 30 A/dm.sup.2 with a voltage of less than 5 volts,

(14) a temperature of the bath between 45 C. and 55 C., and

(15) a deposition rate of the order of 6 m/min;

(16) iii) a step of annealing copper-coated CCA10 wires at a temperature of 250 C., for 2 hours;

(17) iv) a stranding step for the conductors of A and B type;

(18) v) a step of cutting the strands or wires into 15 cm long samples;

(19) vi) a step of sheathing the samples with a heat-shrinkable polyolefin sheath having a crosslinking temperature at 105 C.; and

(20) vii) a step of crimping standard tin-plated copper eyelet terminals (connectors) at the ends of the samples.

(21) FIG. 2 shows the elongated electrically conductive element B-45 in accordance with the invention (FIG. 2a) and by comparison the elongated electrically conductive element B-10 not in accordance with the invention (FIG. 2b).

(22) FIG. 3 shows a micrograph cross section of the elongated electrically conductive element B-45 in accordance with the invention (FIG. 3a) and by comparison a micrograph cross section of the elongated electrically conductive element B-10 not in accordance with the invention (FIG. 2b), when these have undergone an exposure to salt spray for 48 h, 88 h, 176 h and 360 h.

(23) FIG. 4 shows the mechanical strength of the terminals in a tensile test (in newtons N) as a function of the exposure time to the salt spray (in hours) for the conductors A-0 (curve with circles), A-10 (curve with squares), A-30 (curve with triangles), A-45 (curve with lozenges), A-60 (curve with crosses) and A-100 (curve with dotted lines).

(24) From FIG. 4, it can be concluded that the mechanical strength of the terminals is significantly improved for the cables in accordance with the invention (volume content of copper greater than 30% of the volume of the conductor) even after 360 hours of salt spray. Thus, even though some corrosion is observed (cf. FIG. 3), the mechanical strength of the terminals is guaranteed over time, which is not the case for the mechanical strength of the comparative cables which drops after 60 hours of exposure (cf. conductor A-30).