Electrical transport wire made of an aluminum alloy, having high electrical conductivity

Abstract

The invention relates to an electrical transportation wire made of aluminum alloy comprising aluminum, zirconium and unavoidable impurities, characterized in that said alloy comprises at least 80 parts by weight of zirconium in the form of precipitates (Al.sub.3Zr) per 100 parts by weight of zirconium in said aluminum alloy.

Claims

1. An electrical transportation wire made of aluminum alloy, wherein said electrical transportation wire comprises: aluminum, from 0.2% to 0.6% by weight of zirconium and from 0.25% to 0.4% by weight of iron, from 0.12% to 0.35% be weight of copper, and unavoidable impurities, said unavoidable impurities including Mn and Si, and wherein said alloy comprises at least 80 parts by weight of zirconium in the form of precipitates Al.sub.3Zr per 100 parts by weight of zirconium in said aluminum alloy, wherein the aluminum alloy has at most 0.08% by weight of Mn and at most 0.08% by weight of Si, and wherein said alloy has an electrical conductivity of at least 57% IACS, and wherein said electrical transportation wire comprises, at the surface, a porous layer of alumina hydroxide.

2. The electrical transportation wire as claimed in claim 1, wherein said aluminum alloy comprises from 0.2 to 0.5% by weight of zirconium.

3. The electrical transportation wire as claimed in claim 1, wherein the diameter of the zirconium precipitates Al.sub.3Zr ranges from 1 to 200 nm.

4. The electrical transportation wire as claimed in claim 1, wherein said aluminum alloy comprises from 0.25% to 0.35% by weight of iron.

5. The electrical transportation wire as claimed in claim 1, wherein said aluminum alloy comprises from 0.12% to 0.22% by weight of copper.

6. The electrical transportation wire as claimed in claim 1, wherein said zirconium precipitates Al.sub.3Zr are spherical.

7. The electrical transportation wire as claimed in claim 1, wherein the aluminum content of the aluminum alloy of the electrical transportation wire is at least 98.00% by weight.

8. The electrical transportation wire as claimed in claim 1, wherein the content of unavoidable impurities in the aluminum alloy of the electrical transportation wire is at most 1.10% by weight.

9. The electrical transportation wire as claimed in claim 1, wherein the unavoidable impurities is one or more of the following elements: Ag, Cd, Cr, Mg, Mn, Pb, Si, Ti, V, Ni, S and/or Zn.

10. The electrical transportation wire as claimed in claim 1, wherein it is obtained by implementing a heating stage iv) at a temperature of 400 to 500 C.

11. The electrical transportation wire as claimed in claim 1, wherein said electric transportation wire has a round-section diameter or a round-section equivalent diameter ranging from 2.25 mm to 4.75 mm.

12. The electrical transportation wire as claimed in claim 1, wherein at least said electrical transportation wire is, along with an elongated reinforcing component, included within an electric cable, forming an aerial cable for the transportation of energy.

13. The electrical transportation wire as claimed in claim 12, wherein the elongated reinforcing component is surrounded by said electrical transportation wire made of aluminum alloy.

14. The electrical transportation wire as claimed in claim 12, wherein the electrical transportation wire made of aluminum alloy is twisted around the elongated reinforcing component.

15. The electrical transportation wire as claimed in claim 12, wherein said electric cable further comprises an assembly of said electric transportation wires made of said aluminum alloy.

16. The electrical transportation wire as claimed in claim 15, wherein all of said electric transportation wires are wound around the elongated reinforcing component.

17. A process for the manufacture of an electrical transportation wire as claimed in claim 1, wherein said process comprises the following stages: i) forming a molten aluminum ahoy comprising aluminum, zirconium, unavoidable impurities and optionally an element chosen from copper, iron and theft mixture; ii) casting the molten alloy of stage i), in order to obtain an as-cast alloy; iii) rolling the as-cast alloy of stage ii), in order to obtain a rolled alloy; iv) heating the rolled alloy of stage iii), in order to obtain said electrical transportation wire made of aluminum alloy, said alloy comprising at least 80 parts by weight of zirconium in the form of precipitates (A13Zr) per 100 parts by weight of zirconium in said aluminum alloy; thereby forming the electrical transportation wire of claim 1.

18. The process as claimed in claim 17, wherein the heating of stage iv) is carried out at a temperature ranging from 300 to 500 C. for a period of time ranging from 100 to 500 hours.

19. The process as claimed in claim 17, wherein the process additionally comprises the following stage: v) cold working the electrical transportation wire of stage iv), in order to obtain an electrical transportation wire with the desired dimensions.

20. The process as claimed in claim 17, wherein the cooling during the casting stage ii) is carried out at a rate of at least 50 C./min, from the casting temperature down to 500 C.

21. The process as claimed in claim 17, wherein said process additionally comprises the following stage: vi) forming, by chemical conversion, a porous layer of alumina hydroxide at the surface of said electrical transportation wire.

22. The process as claimed in claim 21, wherein stage vi) is carried out by anodizing.

23. The process as claimed in claim 21, wherein said process additionally comprises, before stage vi), at least one of the following stages: a) degreasing the electrical transportation wire, and/or b) stripping the electrical transportation wire.

24. The process as claimed in claim 21, wherein said process additionally comprises, before stage vi), the following stage: c) neutralizing the electrical transportation wire.

25. The process as claimed in claim 21, wherein said process additionally comprises, after stage vi), the following stage: vii) plugging the pores of said porous layer of alumina hydroxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention will become apparent in the light of the examples which will follow with reference to the annotated figures, said examples and figures being given by way of illustration and without any limitation.

(2) FIG. 1 diagrammatically represents a structure, in cross section, of a first alternative form of an electric cable according to the invention.

(3) FIG. 2 diagrammatically represents a structure, in cross section, of a second alternative form of an electric cable according to the invention.

(4) FIG. 3 diagrammatically represents a structure, in cross section, of a third alternative form of an electric cable according to the invention.

(5) FIG. 4 represents a transmission electron microscopy (TEM) view of the electrical transportation wire made of aluminum alloy of the electric cable of the invention.

(6) FIG. 5 represents the curves of the electrical conductivity of the electrical transportation wire of the electric cable of the invention as a function of the heating time of stage iv) of the fourth subject matter of the invention for different heating temperatures.

DETAILED DESCRIPTION

(7) For reasons of clarity, the same components have been denoted by identical references. Likewise, only the components essential for the understanding of the invention have been represented diagrammatically, without observing a scale.

(8) FIG. 1 represents a first alternative form of a high voltage electrical transmission electric cable of the OHL type 100A according to the invention, seen in cross section, comprising three layers of an assembly 10A of metal strands 1A of aluminum alloy of the invention. These three layers surround a central elongated reinforcing component 20A. The constituent metal strands 1A of said layers have a round-shaped cross section.

(9) FIG. 2 represents a second alternative form of a high voltage electrical transmission electric cable of the OHL type 100B according to the invention, seen in cross section, comprising two layers of an assembly 10B of metal strands 1B of aluminum alloy of the invention. These two layers surround a central elongated reinforcing component 20B. The constituent metal strands 1B of said layers have a trapezoidal-shaped cross section.

(10) FIG. 3 represents a third alternative form of a high voltage electrical transmission electric cable of the OHL type 100C according to the invention, seen in cross section, comprising two layers of an assembly 10C of metal strands 1C of aluminum alloy of the invention. These two layers surround a central elongated reinforcing component 20C. The constituent metal strands 1C of said layers have a Z-shaped (or S-shaped, according to the orientation of the Z) cross section. The geometry of the Z-shaped strands makes it possible to obtain a surface virtually devoid of any interstices which may bring about accumulations of moisture and thus centers of corrosion.

(11) The central elongated reinforcing component 20A, 20B, 20C represented in FIGS. 1, 2 and 3 can, for example, be steel strands 2A, 2B, 2C or composite strands 2A, 2B, 2C of aluminum in an organic matrix.

(12) In alternative forms of embodiments represented in FIGS. 1 to 3, it is possible to modify the number of strands 1A, 1B, 1C of each layer, their shape, the number of layers or also the number of steel strands or composite strands 2A, 2B, 2C, and also the nature of the aluminum.

Preparation of an Electrical Transportation Wire Made of Aluminum Alloy According to the Process in Accordance with the Fourth Subject Matter of the Invention

(13) An alloy was prepared according to the process of the invention in the following way:

(14) Stage i): after having incorporated a master alloy of aluminum, zirconium, copper and iron in a molten bath of aluminum pure to more than 99.5% by weight, everything was mixed in order to homogenize the pure aluminum and the master alloy and to thus form a molten alloy.

(15) Stage ii): the molten alloy was subsequently cast in a cylindrical die in order to form a bar of an as-cast alloy which was solidified by cooling: the cylindrical bar formed had a diameter of 30 mm.

(16) Stage iii): the cylindrical bar, directly formed in the preceding stage, was rolled at a temperature of 25 C., in order to obtain a bar having a smaller diameter, namely a bar with a diameter of 10 mm.

(17) Stage iv): the bar from the preceding stage was heated in a conventional resistance furnace at 400 C. for 150 hours in order to form an electrical transportation wire made of aluminum alloy comprising aluminum, 0.3% of zirconium, 0.15% of iron and 0.001% of copper, said alloy comprising 80 parts by weight of zirconium in the form of precipitates per 100 parts by weight of zirconium in said alloy. The amount of zirconium in the form of precipitates in the electrical transportation wire made of aluminum alloy was determined using the phase diagram, by calculation of the amount of zirconium remaining in the solid solution (i.e. zirconium not being in the form of precipitates) on conclusion of stage iv).

(18) Stage v): finally, the electrical transportation wire from the preceding stage was cold drawn, in order to obtain an alloy wire of the invention (i.e. metal alloy strand) with a diameter of 3.5 mm.

(19) The aluminum alloy of the electrical transportation wire comprised at most 0.8% by weight of unavoidable impurities.

(20) FIG. 4 shows a transmission electron microscopy (TEM) view of the aluminum alloy as prepared above in bright field (BF) mode (FIG. 4a) and in dark field (DF) mode (FIG. 4b).

(21) Transmission electron microscopy (TEM) was carried out with a high resolution transmission electron microscope sold under the reference ARM 200S by Jeol.

(22) The diameter of the zirconium precipitates in the alloy was determined by TEM. To do this, a sample of alloy as prepared above was withdrawn, polished until an alloy thickness of approximately 100 m was obtained and electrochemically drilled in order to obtain a sample thickness transparent to electrons ranging from 50 to 100 nm approximately.

(23) It could thus be observed that the process in accordance with the invention and in particular the casting stage ii) and the heating stage iv) makes it possible to obtain a homogeneous dispersion of controlled microstructure of zirconium precipitates and in particular to obtain spherical zirconium precipitates with a diameter ranging from 1 to 100 nm approximately.

(24) In contrast, it has been found that, when the operating conditions of the casting stage ii) and/or of the heating stage iv) were not optimal (e.g., casting stage carried out at an excessively low temperature, that is to say at a temperature of less than 680 C., cooling rate during the casting stage too low, that is to say less than 50 C./min, heating stage carried out for an excessively long period of time, that is to say greater than 500 hours), the zirconium precipitates obtained on conclusion of stage iv) were coarse, in particular with a diameter of greater than 100 nm.

Tensile Strength of the Electrical Transportation Wire Made of Aluminum Alloy Prepared According to the Process in Accordance with the Fourth Subject Matter of the Invention

(25) Table 1 below shows the tensile strength (in MPa) of several electrical transportation wires made of aluminum alloy A1, A2, A3, A4 and A01, their electrical conductivity (in % IACS) and the loss of their mechanical properties after aging at 230 C. for 1 hour (i.e. loss of the tensile strength, in UTS).

(26) A1, A2, A3 and A4 were manufactured according to the process of the invention as described in the example above, with different heating parameters according to the amount of zirconium present in them, and A01 was sold under the reference Al1120 by Nexans. A01 does not form part of the invention since it does not comprise zirconium.

(27) TABLE-US-00001 TABLE 1 Tensile strength Zirconium Copper Iron before Electrical content content content aging conductivity UTS Alloy (%) (%) (%) (MPa) (% IACS) (%) A01 0 0.17 0.27 229.8 59.1 18.2 A1 0.568 0.17 0.27 220.4 59.4 9.3 A2 0.487 0.17 0.27 225.3 59.3 6.7 A3 0.426 0.17 0.27 207.1 59.1 7.0 A4 0.349 0.17 0.27 221.8 59.5 8.6

(28) A1, A2, A3 and A4 were respectively obtained with the following heating parameters of stage iv): 400 C./300 hours, 400 C./250 hours, 400 C./220 hours and 400 C./180 hours.

(29) Thus, from table 1 illustrated above, it can be seen that the electrical transportation wires made of aluminum alloy manufactured according to the process in accordance with the invention exhibit good mechanical properties before and after aging and good electrical properties.

(30) In addition, the presence of the zirconium in the aluminum alloy makes it possible to reduce the loss in mechanical properties after aging, while guaranteeing good electrical properties.

Study of the Electrical Conductivity of the Electrical Transportation Wire Made of Aluminum Alloy as a Function of the Heating Time and of the Heating Temperature of the Fourth Subject Matter of the Invention

(31) FIG. 5 shows the electrical conductivity of the electrical transportation wire made of aluminum alloy of the invention as a function of the heating time of stage iv) of the process in accordance with the invention when stage iv) is carried out at a heating temperature of 450 C. (curve A), 400 C. (curve B) and 350 C. (curve C).

(32) The alloy used in this example was prepared as in the examples described above and comprised 0.35% of zirconium, 0.27% of iron and 0.17% of copper.

(33) It can thus be observed that the temperature and time parameters used during said stage iv) are interdependent and that they have a direct impact on the electrical conductivity of the alloy obtained. Examples of time/temperature pairs which make it possible, during stage iv), to form sufficient zirconium precipitates and thus to obtain a conductivity of at least 57% IACS include the following time/temperature pairs: 100 hours/450 C. approximately, 200 hours/400 C. approximately and 340 hours/350 C. approximately.

Preparation of an Electrical Transportation Wire Made of Aluminum Alloy According to the Process in Accordance with the Fifth Subject Matter of the Invention

(34) An electrically conducting component made of aluminum alloy A5 was prepared according to the process in accordance with the invention in the following way:

(35) Stage A): after having incorporated a master alloy of aluminum and zirconium in a molten bath of aluminum pure to more than 99.5% by weight, everything was mixed in order to homogenize the pure aluminum and the master alloy and to thus form a molten alloy.

(36) Stage B): the molten alloy was subsequently cast in a cylindrical die in order to form a bar of an as-cast alloy which was solidified by cooling: the cylindrical bar formed had a diameter of 30 mm.

(37) Stage C): the cylindrical bar, directly formed in the preceding stage, was rolled at a temperature of 25 C., in order to obtain a bar with a smaller diameter, namely a bar with a diameter of 10 mm.

(38) Stage D): the bar from the preceding stage was heated at 400 C. for 180 hours in order to form an electrical transportation wire made of aluminum alloy comprising aluminum and 0.35% of zirconium.

(39) Stage E): said electrical transportation wire from the preceding stage was cold drawn in order to obtain an alloy wire of the invention (i.e. metal alloy strand) with a diameter of 3.5 mm.

(40) Stages a) and b): said electrical transportation wire made of aluminum of the preceding stage was stripped and degreased by immersing it in a solution of sodium hydroxide and surfactants sold under the Gardoclean reference by Chemetall (30 to 50 g/l of sodium hydroxide), at a temperature ranging from 40 to 60 C. approximately, for a period of time of approximately 30 seconds.

(41) Stage c): said electrical transportation wire made of aluminum from the preceding stage was then immersed in a sulfuric acid solution (20% by weight of sulfuric acid in distilled water) at ambient temperature (i.e. 25 C.) for 10 seconds.

(42) Stage F): a porous layer of alumina hydroxide was formed at the surface of the electrical transportation wire from the preceding stage by sulfuric acid anodizing (20% by weight of sulfuric acid in distilled water) at a temperature of 25 to 35 C., under the application of a current density of between 55 and 65 A/dm.sup.2. Said electrical transportation wire made of aluminum alloy which is obtained is thus covered with a porous layer of alumina hydroxide. The thickness of said porous layer of alumina hydroxide ranges from 8 to 10 m approximately.

(43) Stage vii): the pores of the porous layer of alumina hydroxide as formed in the preceding stage were plugged by immersing said electrical transportation wire from the preceding stage in hot water.

(44) The aluminum alloy A5 of the electrical transportation wire comprised at most 0.8% by weight of unavoidable impurities.

(45) The diameter of the zirconium precipitates was determined by the TEM method, as described in example 1, on the A5 alloy as prepared on conclusion of the wire drawing stage E) (i.e. before the stripping, degreasing, neutralizing, anodizing and plugging stages).

(46) The inventors of the present patent application were thus able to confirm that the process in accordance with the invention makes it possible to obtain a homogeneous dispersion of controlled microstructure of zirconium precipitates and in particular to obtain spherical zirconium precipitates with a diameter ranging from 1 to 20 nm approximately.

(47) The temperature stability (in C.) of several electrical transportation wires made of aluminum alloy A5, A6, A02 and A03, their electrical conductivity (as % IACS), their emissivity, their absorption, their diameter, the diameter and the section of the corresponding cables (in mm), intensity (in A) and the increase in intensity (in %) of the cables respectively comprising the electrical transportation wires made of aluminum alloy A03, A5 and A6, in comparison with the cable comprising the electrical transportation wire made of aluminum alloy A02, are shown in table 2 below.

(48) A6 was manufactured according to the process in accordance with the fourth subject matter of the invention and as described in the first example of the present patent application (with the following heating parameters of stage iv): 400 C./180 hours).

(49) It comprised aluminum and 0.35% of zirconium (said alloy did not comprise iron and copper). A6 did not comprise a porous layer of alumina hydroxide.

(50) A02 (pure aluminum) was sold under the reference Al1350 by Nexans. A02 did not comprise a porous layer of alumina hydroxide.

(51) A03 was manufactured from A02 by carrying out only stages a), b), c), F) and vii) described above in the present example. A03 thus comprised a porous layer of alumina hydroxide.

(52) A02 and A03 do not form part of the invention since they do not comprise zirconium.

(53) TABLE-US-00002 TABLE 2 A02 A03 A6 A5 Maximum temperature 80 C. 80 C. 210 C. 210 C. ( C.) Conductivity 62% 62% 60% 60% (% IACS) Emissivity 0.4 0.92 0.4 0.92 Absorption 0.85 0.5 0.85 0.5 Diameter of the wire 3.500 3.500 3.513 3.513 (mm) Diameter of the cable 31.50 31.50 32.52 31.52 (mm) Section (mm.sup.2) 346.46 346.46 357.67 357.67 Intensity (A) 1360 1549 2334 2688 Increase in intensity 13.91 71.59 97.68 (%)

(54) In addition to improved mechanical properties at a temperature of 210 C. in continuous use during a period ranging up to 40 years, the acceptable maximum intensity is particularly increased by virtue of the invention, as is shown by the calculations of table 2 above, carried out on round electrical transportation wires.