IL47706A - Aluminium-based electrical conductors and their productio - Google Patents

Abstract

1525961 Aluminium alloy wires; heat treatment SOC DE VENTE DE L'ALUMINIUM PECHINEY 28 Aug 1975 [28 Aug 1974] 35512/75 Heading C7A An electrical conductor having a resistivity of # 2À88 micro-ohm/cm at 20‹C (i.e. < 60% I.A.C.S.), breaking strain 13-19 hecto bar and elongation # 5 % is formed from an alloy containing in wt per cent with the proviso that Al-Fe-Si alloys containing <0-24% Si must also contain Cu within the range specified. The alloy has been subjected to such treatment that the elements of the first and second groups above are at least substantially out of solution. The conductor is produced by subjecting a blank to reduction with a work-hardening figure of < 1000% followed by a final heat-treatment at 150-300‹C for a few minutes to 24 hours. Additionally an intermediate heat-treatment of 10 minutes to 10 hours at 180-250‹C may be applied during working. [GB1525961A]

Description

o-iis'M fieri *?χΰ ο·»οη o'^awn o*s* io Aluminium-based electrical conductors and their production * Φ SOCIETE DE VENTE DE L»ALUMINIUM PECHINEY C:- 45277 Pure aluminium has an excellent electrical conductivity, of the order of 65 of that of IACS standard pure annealed copper. However, its mecha ical qualities are considered inadequate for certain applications such as fine wire for telephones and domestic appliances, or insulated wire for windings and building installations; the standard grade designated by reference A5/L (A5 signifying according to French standard AFNOR A 57 101 an aluminium content of not less than 99.5/* and the symbol L recalling use in electrical applications) for example has a breaking strain of only 10 to 12 hbar associated with an elongation of 10 to 12%, or of 12 to 15 hbar with an elongation of 2 to 3% according to the final heat treatment, and a conductivity of 63 to 63-5 IACS.

The mechanical properties can be considerably improved by the addition of alloy elements but then the conductivity is greatly diminished.

The family of alloys often called "almelec" containing up to around 0.6% of Si and around 0.7% of Mg only has a conductivity of the order of 53 IACS, for a breaking strain of approximately 30 hbars, associated an elongation of around h%.

It is also known that the alloy elements which most depress conductivity are in the main the polyvalent metals with unsaturated electronic sub-strata and thai. their influence manifests itself particularly when they are in solid solution in the aluminium matrix and much less when they are precipitated out of solution.

Manganese, chromium, vanadium, zirconium, titanium and to -a lesser extent , silicon- are especially-trouble- some in this connection; magnesium, iron, nickel, cobalt and copper occupy an intermediate position while the influence of zinc is particularly low.

Thus, the essential problem in the domain of electrical conductors is to reconcile mechanical characteristics adequate for the intended application with the highest possible electrical conductivity. Such a result is generally obtained by means of a series of complex thermo-mechanical treatments which effect the precipitation of certain elements in the form of more or less fi e intermetalli compounds while maintaining certain others in solution in the matrix.

French specification no. SS8 520 of Trefileries et Laminoire due Havre (now: Trefimetaux) , no. 1 48 715 of Pechiney, no 2,009,027 of Southwire company, no. 2,078,562 of Fuji-Cenki, no. 2,105,/(2S of Olin Corporation and U.S. no. 2, 182,212 of A.B. Elektrokoppar, and/specificati ons nos. 5,665,216 and 5,668,019 of the Aluminium Company of America (Alcoa) describe alloy compositions and preparation processes which aim to solve this problem," but none of them enables one to obtain fine wire for domestic applications, telephone systems or windings meeting users' requirements with regard to the combination of a breaking strain which should attain 15 to 18 and even conductivity not lower than 60$ LACS and a behaviour which should pass various tests such as bending back and forth.

The applicants discovered that it was possible to obtain new types of aluininium-based electrical conductors 1 a breaking strain of between 13 and 19 hbars, associated with an elongation at least equal to 5 and a conductivity at least equal to 60$ IACS by combining alloy element additives, which in the opinion of the "Skilled man" are incompatible with good electrical conductivity and by using a simple and perfectly reproducible thermo-mechanical treatment which involves starting from a blank in which all the elements are in solid solution in the aluminium matrix and deforming this blank with a cold drawing value-defined by the ratio S - s where S s is the initial section of the blank and is the final section of the conductor - at least equal to 1000$ and preferably greater than 10 , 000 , and effecting a softening-precipitation treatment which enables one to bring out of solution most of the elements having an adverse influence on electrical conductivity but which are indispensable for raising the breaking strain.

Indeed, the applicants discovered that certain additives in stable solid solution or in supersaturation augment the cold drawing capacity of the aluminium in such a way that the considerable disorder state energy - the result of a high cold reduction - leads to the rapid and fairly complete rejection of the elements in super-saturation and this takes place at a moderate temperature.

This phenomenon is also linked to the fact that lessens markedly with temperature. In addition, the applicants have found that these same soluble additives in aluminium exercise a powerful inhibiting effect oh its recrystallisation (without however preventing its progressive softening by restoration) accompanied by the precipitation of the elements in supersaturation.

The result of this is that the electrical conductivity is noticeably raised \hile the reduction of the breaking strain, associated with an increase in the breaking elongation, is more easily controlled.

The additive elements having an unfavourable effect on conductivity are precipitated in element form or in the form of complex intermetallic compounds as shown in micrographic observations.

The applicants also discovered that, in the course of processing the conductor to the dimensions appropriate to its intended use, it was possible to subject it to intermediate restorative heat treatment at a temperature of between 180°C and 250°C for a period of between 10 mins and 10 hours, permitting an increase of the industrially attainable deformation figure without significantly affecting the combinations of mechanical and electrical characteristics which would be obtained without this intermediate heat treatment.

The applicants also discovered that the alloys to which this process can be applied should include in combination: l) at least one element belonging to a first group of conductivity and whose solubility in the solid state in aluminium does not exceed 0.2 by weight at 250°.

This group covers in particular: copper, silicon, manganese, taken in a proportion of 0.25 to 1 by weight for Cu and Mn and 0.05 to 0.5 by weight for Si; 2) at least one element belonging to a second group of elements tending to form complex intermetallic compounds and which are only to a very limited extent soluble in the matrix. This second group covers: iron, nickel, cobalt, beryllium, boron and zirconium, taken at a proportion of 0.10 to 2$ by weight for Fe, Ni , Co. and 0.001 to 0.2 by weight for Be and B; 0.001 to 0.1$ by weight for Zr; 3) and possibly at least one additive element chosen from a third group of elements for increasing the cold drawing capacity of aluminium and having a solubility in the solid state at 250 °C in aluminium of at least 4%. This group covers magnesium and zinc, the usual impurities of aluminium forming the base of the alloy (generally 99.5$ Al) can in addition be present in their usual proportions.

As stated above, in the finished conductor wire, according to the process of the invention, the elements of the first two groups are almost entirely brought out of solution duriig the thermo-mechanical treatment.

In view of the cold drawing figure necessary for the utilisation of the process, the invention is especially well suited to the production of flexible wire with a diameter of between 3.5 and 0.05 mm but of course it- is not only limited to the field of wire. Indeed, from the same alloys and the same process it enables one to obtain any other form of conductor such as thin strips of between 0.005 and 3 mm n thickness, flexible cables obtained by grouping by all known methods, wire corresponding to th>e invention as well as insulated flexible wire and cable, the insulation being obtained by all known methods.

• The following examples will better illustrate the application of the invention.

Example 1: Billets 83 mm in diameter were prepared by semi-continuous casting in alloys designated A and B with the following compositions: alloy A was of the type A5/L, defined above, and taken as the reference alloy while alloy B was in conformity with the invention.

The billets were drawn at 350°C to 9.5 mm and then super-drawn to 0.5 mm, the conditions and results being shown below: Example 2 : 83 mm Diameter billets, designated C and D, were cast by the "still" method: i.e. by slow pouring of the molten metal contained in the melting vessel into the ingot mould which is initially inclined and then progressively straightened as it is filled. The compositions were as follows: alloy C was of the type A5/L defined above and taken as the reference alloy, while alloy D was in conformity with the invention.

Element group 1 2 Si Fe C 0.05 0. 2'i D 0.2k 0. 51 The billets were drawn at ¾50°C to 9· 5 mm and then super-drawn to 0. 5 mm, the conditions and results being shown below: Final heat R A P20 C m treatment 200 mm IACS h bar Example 3 The following alloys, designated E and F were cast by the continuous method on a wheel, and then the blank was immediately hot rolled on a SECIM train (new name for S idem) to a diameter of 12 mm. "E" was of the type A5/L defined above and taken as the reference alloy while the alloy "F" was in conformity with the invention.

Then the pieces were super-drawn to 0.5 mm, the conditions and results being as follows: Example hi The following alloys, designated E and G were cast by the continuous method on a wheel and then the blank was immediately hot rolled to a diameter of 12 mm. Alloy "G" was in conformity with the invention: Element group: - 1 2 Si Cu Fe The alloys were then super-drawn to 0.5 mm diameter the conditions and results "being as follows: Exam le 5 : The following alloys designated E and H ("H" being in conformity with the iirvent on) were cast by the con-ti'ttuous method, on a wheel, and then the blank was immediately hot rolled, to a diameter of 12 mm.

The alloys were then super-drawn to 0. 5 mm diameter the conditions and results being as follows: The association of a breaking strain at 18 h bar with an elongation of 10-11$ and. a conductivity virtually equal to 60$ IACS is particularly remarkable and by far exceeds anything achieved hitherto with aluminium-based conductor alloys.

In addition, examples ¾G and 5H show that the tolerances for temperature and duration of the final treatment are particularly wide as variations of 20°C for a given duration of l- hours, at constant temperature have practically no effect on the final result. This fact which is also exceptional is a guarantee of the ability to reproduce these results in industrial production.

Exam le 6: The following alloys, designated J and K and conforming to the invention, were cast by the semi-continuous method as in example 1 as 83 mm diameter billets, then dra\¾rn to a diameter of 9.5 mm and super-drawn to a diameter of 0.5 mm: , Element group 1 ' 2 3 Si Cu Fe Mg J 0.06 0.20 0.18 0.02 K 0.06 0.20 0.18 0.15 with the following results: Exam le 7' Billets of 83 mm diameter were cast by the semi-continuous method from alloy B of example 1 (Fe: 0.18 Si: 0.05; Cu: 0.48), drawn at 350 °C to a diameter of 9.5'iiim and then redrawn to a diameter of 2mm. A one-hour intermediate heat-treatment was effected at 230 °C in the first case and lh at 350°C in the second case, and the alloy was then super-drawn to a diameter of 0.5 mm the conditions and results being as follows: Example 8: 83 mm Billets were cast ("still" casting) from alloy D of example 2 (Fe: 0.51; Si: 0.24), drawn at 450°C to a diameter of 9.5 mm and then redrawn to a diameter of 2 mm. Intermediate heat treatment was applied for lh at 230 °C in the first case and for lh at 350°C in the second case, and the pieces were super-drawn to a diameter of 0.5 mm, the conditions and results being as follows: Intermediate Final heat R heat treatment treatment m A# Ψ C at 2 mm h bar 200 mm »/cm IACS at 0.5 mm lh at 230 °C lh at 260 °C 13 12.5 2.75 62.7 D lh at 350°C lh at 230 °C 11 10 2.73 63.

Examples 7 and 8 show that the intermediate heat treatment at 2 mm conducted for lh at 350 °C does not produce characteristics as favourable as when the temperature does not exceed 25 °C.

Exam le 9: Billets 83 mm in diameter were prepared by semi-continuous casting from the alloys in example 1 designated A and B. The billets were decrusted to a diameter of 81 mm and then drawn without preheating so as to obtain a flat bar of 40 x 5 mm; rolling was then carried out to a thickness of 0.15 mm and the following results were obtained:

Claims (3)

1. . Aluminium-based electrical conductors, in particular thin strips between 0 .005 mm and 3 mm in thickness, wire between 0 .050 mm and 3 · 5 mm in diameter, bare, insulated or grouped to form flexible cables, characterised in that they include in combination: a) at least one element belonging to a first group of precipitable elements which when in solution in the matrix have a considerable effect in lowering the electrical conductivity and whose solubility in the solid state in aluminium does not exceed 0 . 2$ by weight at 250 °C; and b) at least one element belonging to a second group of elements tending to form complex intermetallic compounds and which is only partially soluble in the matrix, the elements of these first two groups having been brought almost entirely out of solution during the thermo-mechan-ical treatment applied during production; and in that their resistivity is at the most equal to 2.88 micro-ohms per centimetre at 20°C (conductivity at least equal to 60# IACS), that their breaking strain is between 13 and 19 h bar and that their breaking elongation on a 200 mm test piece is at least equal to 5$ ·

2. . Aluminium-based electrical conductors according to Claim 1 , characterised in that they also include at least one additional additive element selected from a third group of elements which augment the work-hardening capacity of the aluminium and which have a. solubility in °

3. ) Aluminium-based electrical conductors according to Claim 1 or 2 characterised in that the elements of the first group are selected from copper, silicon and manganese; the elements of the second group are selected from iron, nickel, cobalt, beryllium, boron and zirconium; and the elements of the third group are selected from magnesium and zinc . ) Aluminium-based electrical conductors, according to Claim 3, characterised in that the proportions of the alloy elements are selected within the following limits: 0.25 - 1 by weight for copper and manganese 0.05 - 0.5/6 " " for silicon 0.10 - 2 " '» for iron, nickel and cobalt 0.001-0.2