Aluminium-alumina composite material and its method of preparation

Abstract

The present invention relates to a composite material based on aluminium and alumina, its method of manufacture, and a cable comprising said composite material as an electrical conductor element.

Claims

1. A method for preparation of a composite material having a matrix of aluminum or aluminum alloy and particles of alumina dispersed in said matrix of aluminum or aluminum alloy, wherein said method comprises at least the following steps: i) placing in contact at least one elongated electrical conductor element of aluminum or of aluminum alloy comprising a layer of hydrated alumina with molten aluminum or a molten aluminum alloy, ii) forming a solid mass based on alumina and aluminum, and iii) breaking the layer of hydrated alumina inside the solid mass, in order to form a composite material comprising a matrix of aluminum or aluminum alloy and particles of alumina dispersed in said matrix of aluminum or aluminum alloy.

2. The method according to claim 1, wherein the layer of hydrated alumina has a thickness ranging from 4 to 20 p.m.

3. Method according to claim 1, wherein step i) is carried out by any one of the following methods: casting molten aluminum or a molten aluminum alloy onto said elongated electrical conductor element of aluminum or of aluminum alloy comprising a layer of hydrated alumina, or passing said elongated electrical conductor element of aluminum or of aluminum alloy comprising a layer of hydrated alumina continuously through a bath of molten aluminum or of a molten aluminum alloy.

4. The method according to claim 1, wherein step i) is carried out by casting molten aluminum or a molten aluminum alloy onto said at least one elongated electrical conductor element of aluminum or of aluminum alloy comprising a layer of hydrated alumina placed in a container and step iii) is an extrusion step.

5. The method according to claim 1, wherein step i) is carried out by continuous passing of said at least one elongated electrical conductor element of aluminum or of aluminum alloy comprising a layer of hydrated alumina through a bath of molten aluminum or of a molten aluminum alloy or by continuous casting of molten aluminum or a molten aluminum alloy onto at least one elongated electrical conductor element of aluminum or of aluminum alloy comprising a layer of hydrated alumina placed on a casting wheel, and step iii) is a rolling step.

6. Method according to claim 1, wherein said method further comprises a step iv) of shaping the composite material obtained in the preceding step iii) in order to obtain a composite material having the desired dimensions and shape.

7. The method according to claim 1, wherein said method further comprises, after step iii) or step iv), a heating step v).

8. The method according to claim 1, wherein said method furthermore comprises, prior to step i), a step i.sub.0) of formation of the layer of hydrated alumina by anodization.

9. The electrical cable, wherein said electrical cable comprises at least one composite material obtained according to the method of claim 1, said composite material having a matrix of aluminum or aluminum alloy and particles of alumina dispersed in said matrix of aluminum or aluminum alloy.

10. The electrical cable according to claim 9, wherein said cable is an OHL cable comprising an elongated reinforcement element and an assemblage of composite strands positioned around the elongated reinforcement element, each of the composite strands being said composite material.

11. The electrical cable according to claim 9, wherein said cable comprises at least one electrically insulating layer surrounding said composite material or the plurality of composite materials, said electrically insulating layer comprising at least one polymer material.

12. The electrical cable according to claim 9, wherein said composite material comprises from 1 to 10,000 ppm of alumina.

13. The electrical cable according to claim 9, wherein said composite material has an electrical conductivity of at least 45% IACS.

14. The electrical cable according to claim 9, wherein said composite material has a mechanical tensile strength ranging from 70 to 500 MPa.

15. The electrical cable according to claim 9, wherein the particles of alumina have a thickness of at least 0.1 m.

16. The electrical cable according to claim 9, wherein the particles of alumina have a mean size ranging from 0.5 to 10 m.

17. The electrical cable according to claim 9, wherein said composite material is a nonporous material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention will appear in light of the following examples with reference to the annotated figures, said examples and figures being given as an illustration and in no way as a limitation.

(2) FIG. 1 shows in schematic fashion a structure, in cross section, of a first variant of an electrical cable according to the invention.

(3) FIG. 2 shows in schematic fashion a structure, in cross section, of a second variant of an electrical cable according to the invention.

(4) FIG. 3 shows in schematic fashion a variant of a method of manufacture of a composite material according to the invention.

(5) FIG. 4 shows two images of a composite material obtained at the end of step ii) according to the method of the invention.

(6) FIG. 5 shows an image and a cross section of a composite material according to the invention obtained at the end of step iii) according to the method of the invention.

(7) FIG. 6 shows the interior of a composite material according to the invention obtained at the end of step iii) according to the method of the invention.

(8) For reasons of clarity, only the essential elements for the understanding of the invention have been shown in a schematic manner, and without regard to scale.

DETAILED DESCRIPTION

(9) FIG. 1 shows a first variant of an electrical cable 1 according to the invention, in cross section view, comprising a composite material 2 according to the first object of the invention or obtained according to the method in accordance with the second object of the invention and an electrically insulating layer 3 surrounding said composite material 2.

(10) FIG. 2 shows a second variant of a high-voltage electrical transmission electrical cable 4 of OHL type according to the invention, in cross section view, comprising three layers of an assemblage 5 of composite strands 6, each composite strand being constituted of a composite material according to the invention. These three layers 5 surround a central elongated reinforcement element 7. The composite strands 6 constituting said layers 5 have a Z-shaped cross section (or S-shaped, depending on the orientation of the Z). The central elongated reinforcement element 7 shown in FIG. 2 may be, for example, steel strands 8 or composite strands of aluminium in an organic matrix.

(11) In the embodiment shown in FIG. 2, it is possible to modify the number of composite strands 6 of each layer 5, their shape, the number of layers 5 or indeed the number of steel strands or composite strands 8.

(12) FIG. 3 shows a device 9 which can be used to manufacture a composite material according to the method in accordance with the invention. The device comprises a vat 10 designed to contain a bath of molten aluminium or of a molten aluminium alloy and transport means 11 serving to convey an elongated electrical conductor element comprising a layer of hydrated alumina 13 to said vat 10. At the end of step i), an elongated electrical conductor element of aluminium or of aluminium alloy comprising a layer of hydrated alumina and coated with molten aluminium or a molten aluminium alloy is directly cooled down at the exit from the vat 10, in particular with the aid of cooling means 12, to obtain a solid mass (step ii)). Then the solid mass is taken to rolling means 14 situated after the cooling means 12 in order to carry out step iii).

Preparation of Composite Materials According to the Invention and Obtained in Accordance with the Method According to the Invention

(13) An electrical conductor element of aluminium alloy, marketed under the brand Al1370 and comprising a layer of hydrated alumina of thickness around 6 m, was prepared in the following manner:

(14) Steps a), b), c): for these steps, an electrical conductor element of aluminium alloy Al1370 of diameter 2.97 mm was used. Said elongated electrical conductor element was scoured and degreased by dipping it into a solution of soda and surfactants, known as GARDOCLEAN and marketed by the CHEMETALL company (30-50 g/L of soda), at a temperature of around 40 to around 60 C., for a duration of around 30 seconds. Next, said elongated electrical conductor element was dipped into a solution of sulfuric acid (20% by weight of sulfuric acid in distilled water) to carry out the neutralization step c), at ambient temperature, for 10 seconds.

(15) Step i.sub.0): a layer of hydrated alumina of thickness around 6 m was formed around the electrical conductor element previously obtained by anodization, using a current density of around 60 A/dm.sup.2 and a voltage of around 22 V.

(16) Step i.sub.1): the pores of the layer of hydrated alumina were plugged.

(17) Step i): four electrical conductor elements such as those previously prepared were placed in contact with a molten aluminium alloy marketed under the brand Al1370 by casting said molten aluminium alloy onto said elongated electrical conductor elements.

(18) To do this, said elongated electrical conductor elements were therefore placed in a cylindrical mould.

(19) Step ii): the mould was cooled in air at around 20 C., to form a solid cylinder of diameter around 37 mm and length around 150 mm.

(20) Step iii): the cylinder was extruded at around 450 C. after having heated the cylinder for around two hours.

(21) Step iv): the composite material obtained in the preceding step iii) was rolled at 20 C. in order to obtain a composite material according to the invention, denoted as M.sub.1, or the composite material obtained in the preceding step iii) was wire-drawn to form a wire-drawn composite material M.sub.2.

(22) Step v): the rolled composite material M.sub.1 obtained in step iv) was annealed at 350 C. for 2 h to form a composite material M.sub.3 or the wire-drawn composite material M.sub.2 obtained in step iv) was annealed at 350 C. for 2 h to form a composite material M.sub.4.

(23) For comparison, the steps as described above were reproduced with an electrical conductor element of aluminium alloy marketed under the brand Al1370 and not comprising a layer of hydrated alumina (i.e. not according to the invention) to form respectively the non composite materials M.sub.1, M.sub.2, M.sub.3 and M.sub.4.

(24) Table 1 below illustrates the electrical conductivity (in % IACS), mechanical tensile strength (in MPa) and elongation at breaking (in %) results of the composite materials M.sub.1, M.sub.2, M.sub.3 and M.sub.4 of the invention and for comparison of the materials not comprising alumina (i.e. not according to the invention) M.sub.1, M.sub.2, M.sub.3 and M.sub.4.

(25) TABLE-US-00001 TABLE 1 Mechanical Elongation at Conductivity tensile strength breaking % IACS (in MPa) (in %) M.sub.1 59.6 187 2 M.sub.1 62.8 132 2 M.sub.2 58.7 194 2 M.sub.2 62.9 138 2 M.sub.3 61.3 96 19 M.sub.3 57 30 M.sub.4 60.7 100 24 M.sub.4 63.4 73 39

(26) The composite material of the invention therefore has an improved mechanical strength while guaranteeing a good electrical conductivity so as to be able to be used as an elongated electrical conductor element of an electrical and/or a telecommunications cable.

(27) FIG. 4 shows two photos of the composite material prior to the extrusion step iii) and FIG. 5 shows two photos of the composite material obtained after the extrusion step iii). FIG. 6 shows the dispersion of the particles of alumina (in grey) within the matrix of aluminium alloy.