NO761870L - - Google Patents

Description

The present invention relates to an improvement of manufacturing processes for the production of conductors of Al/Mg/Si alloys. The relevant conductors are particularly suitable for the manufacture of insulated electrical cables and wires for installation in private houses, wires and cables for telecommunications, flexible cables and also cables for energy transmission.

In the case of aluminum alloy insulated cables it has

.been the greatest development in the areas of power transmission cables with a large or medium cross-section using so-called "A5/L" commercial aluminum for electrical applications, and which contains less than.0.5% total impurity content and is in a 3/4 hardness state.

When it comes to non-insulated power transmission cables where great mechanical strength is desired, different technical solutions are used. In France, either composite cables of aluminum and

steel or more generally uniform cables of age-hardened ALMELEC (or AGS/L) aluminum alloy, which usually contains 0.30 - 80% magnesium, 0.30 - 0.70% silicon and 0.15 - 0.35% iron.

In this case, the cables are made up of alloy wires in so-called

T8 structural state, which is produced by means of a transformation process which in sequence includes: solid solution formation, quenching, drawing and hardening.

Other manufacturing processes are also used, and among these can be mentioned the one that uses "5005" (designation used in the Aluminum Association) aluminum/magnesium alloy with wires in 4/4 hardness state and cable twisted without prior heat treatment.

It has also been contemplated to replace copper with aluminum or one of its alloys in other areas of use, namely as wires for electrical installations in residential buildings, wires and cables for telecommunications, winding wires, as well as flexible wires and cables. These applications require an electrical conductivity roughly equivalent to A5/L, mechanical properties better than A5/L and good wire drawability. The improved electrical properties are required either during the actual manufacture of the conductors or during their use. Cables for telecommunications thus include wires with a small diameter, e.g. 0.5 or 0.63 mm, which are first isolated and then assembled in groups of pairs or fours. Production of insulated wires for assembling such cables can e.g. is carried out by moving at a fast pace through machines that carry out the desired wire drawing and insulation.

Such a work process requires conductors with an improved combination of breaking strength and breaking elongation compared to the corresponding properties that can normally be achieved for conventional A5/L. Furthermore, excellent wire drawing ability at high speed is required as well as a high degree of uniformity for the final results obtained

material properties.

The purpose of the present invention is a method which makes it possible to achieve the above-mentioned properties in connection with an AGS/L-1egeration.

French patent document no. 2,053,838 describes a method for the production of installation cable from AGS/L, whereby blank rods with a diameter between 7.5 and 12 mm are produced by casting and rolling according to the PROPERZI process, and said rods are subjected to a homogenization -treatment for at least half an hour at a temperature between 500 and 580°C, followed by quenching in cold water and drying, after which the bars are drawn into wire by repeated drawing passes until the desired final diameter is achieved. Finally, a final heat treatment is carried out by exposing the material to a temperature of 250°C for two to four hours and a temperature of 550°C for a few seconds.

A breaking strength of between 15 and 18 hectobar, an elongation at break between 8 and 14% and a specific electrical resistance between 2.86 and 2.90 micro-ohms. cm. is achieved in this way.'These material properties are completely satisfactory, but the indicated process has the disadvantage that it requires a homogenization treatment which, on an industrial scale, would take 8 hours. This process is actually carried out in a caloporter-type gas-circulation furnace by treating portions consisting of coils or bundles of several tons, and complete treatment is achieved if the warning effect lasts at least half an hour throughout

the length of the wires that form each coil or bundle. Furthermore, the drying is carried out after the quenching in cold water by heating at 120°C for several hours. These work operations will be time-consuming and expensive.

From French patent no. 2,179,515, a simplified process is also known which makes it possible to achieve the same mechanical and electrical properties when drawing bar blanks in a raw conversion state, which means that they have come directly from a PROPERZI rolling, and this process also has the advantage that it facilitates the drawing process by reducing the breaking strength of the bar blank, which decreases from 20 - 23 hectobar to 15 hectobar for the rolled bar blanks. As a result, the thread can be drawn using machines designed for drawing A5/L. The beneficial effect of the heat treatment during PROPERZI rolling is produced by extending this rolling to a reduced diameter of e.g.

7.5 mm has been achieved.

When manufactured on an industrial scale, it has nevertheless been found that the uniformity achieved for threads structurally transformed according to said patent document No. 2,179,515 is insufficient and far too dependent on the PfSOPERZI casting and the processing conditions for

rod blank a<y>AGS/L.

On this background, it is an object of the present invention

to indicate a method by which the above-mentioned disadvantages can be overcome, as all heterogeneous conditions with respect to the material structure and non-uniform material properties are eliminated for the bar blanks.

This method thus applies to continuous production

of billets of AGS/L-1 alloys whose composition can vary between 0.30 and 0.80% (preferably 0.30 - 0.60%) magnesium, between 0.30 and 0.70% (preferably 0.30 - 0 .60%) silicon and between 0.15 and 0.35% (preferably 0.15 - 0.25%) iron, while the other components correspond to those normally present in aluminum alloys for electrical applications. Manufacturing takes place starting from continuous casting and rolling, e.g. when using a PROPERZI machine, the material immediately after leaving the last section of the rolling mill is subjected to rapid cooling to a temperature below 150°C, whereupon a considerable precipitation of IV^Si from a supersaturated solid solution takes place.

It is actually known that the liquid metal fed to the casting wheel at around 700°C leaves said wheel as solidified metal in the form of a mainly trapezoidal ingot and shortly afterwards (about 1 min. later) runs into the rolling mill at a temperature which. varies between 400 and 500°C, in which the latter temperature is mainly the one at which the solid solution which

achieved during solidification, precipitates magnesium and silicon on sufficiently slow cooling. Since the rolling of the mainly trapezoidal billet (S ^1 n2240 ^mth2) until bar blanks with a diameter of 9.5 or 7.5 mm is obtained, is carried out in a relatively short time (of the order of 1 min.), and the temperature of the bar blanks leaving the rolling mill is between 250 and 300°C

depending on the casting and rolling conditions, it will be realized that several process functions take place in the rolling mill at the same time, namely: forming, cold working and dynamic structure formation as a result of deformation at high temperature and quenching starting from a more or less perfect state of solid solution,

mainly as a function of the inlet temperature for the ingot in question in the rolling mill. A rapid cooling of the type that e.g. is described in French patent application No. 74.05878 prevents any significant precipitation in rod blanks wound in coils. Such precipitation manifests itself in a high degree of non-uniformity with respect to electrical and mechanical properties in a billet coil with a weight substantially equal to or greater than 1 ton, in view of the different cooling rates on the outside and inside of the coil, and the the resulting non-uniformity will affect the final material properties achieved.

In the method according to the invention, the temperature of the ingot that runs into the rolling mill after leaving the casting wheel can be between 400 and 500°C, but is preferably chosen within the range 400 - 450°C.

During another process step, the wire ends are exposed accordingly

the invention for a thermal precipitation treatment for that purpose

to precipitate the intermetallic compound Nk^Si from the partially solid solution state obtained by said continuous casting, rolling and cooling. Such treatment is carried out on coils of staple material at temperatures between 220 and 280°C for a period of between 1 hour and 12 hours, depending on the temperature used.' Depending on these conditions, the precipitation effect for I^^Si is increased by another softening effect of the rod blank by structural recovery. The most important effect of this thermal treatment is the heterogenization of the partially solid solution produced by the rolling process and the subsequent rapid cooling of the bar blank. This heterogenization contributes to the softening of the bar blanks and, above all, to the reduction of the material hardness produced by cold working during the drawing process, which means that the heterogenization contributes to reducing the increase in the tensile strength of the drawn wire that takes place with the reduction of the wire cross-section. The pulling force will thus be reduced and the material's wire drawing ability clearly improved.

Furthermore, said heterogenization treatment will lead to the formation of an alloy which will probably have improved material properties by virtue of the presence of reversible dispersed compounds, due to the fine distribution of the previously mentioned I^k^Si constituents.

Such a heat treatment carried out on the bar blanks does not lead to

a state of recrystallization, which would have a devastating effect on the very special combination of fracture toughness and fracture union that is obtained after wire drawing and the final heat treatment, and which is a distinctive feature of the present invention.

Finally, a heating system of the above-mentioned type will not be used at all

manner destroy the high degree of uniformity with regard to material properties for said billet coils with a weight equal to or greater than 1 ton, said uniformity being written from the continuous cooling on the exit side of the rolling mill.

In a third process step which is covered by the method of the invention, a cold deformation is carried out by wire drawing, which can optionally be followed by a thermal thickening treatment carried out in a manner known within the present field, and preferably in a static heating oven, by heat treatment of material portions at temperatures between 220 and 280°C for between 1 and 9 hours, depending on the temperature. For certain applications which do not require an electrical conductivity greater than S8.5% IACS (p <^ 2.95^u -XL. cm) for flexible cables), the final heat treatment can advantageously be carried out continuously after the drawing process, e.g. by Joule heating or induction heating. The threads produced according to the method of the invention have as a distinctive feature that the elongation at break in the drawn state is significantly higher than the values that can normally be achieved with the alloy A5/L with 3/4 hardness, while at the same time a much higher mechanical strength is achieved ( breaking strength between 20

o;g?30 kg/mm 2, depending on the wire diameter).

The special features and advantages of the invention will be better understood on the basis of the examples of execution which will be given in the following, the first of these examples almost indicating the previously known background of the invention.

EXAMPLE 1

The purpose of this design example is to indicate what can be achieved by prior art with regard to the material properties s hetrogenite effect for bar blanks of AGS/L with a diameter of 9.5 mm and a composition: Fe : 0.29%

Say : 0.60%

Mg : 0.59%

Pressed to a diameter of 2.3 mm and heat-treated according to the known technique as described in French patent document No. 2,179,515, the bar blanks being manufactured by a PROPERZI-type process, but without continuous rolling and initial heat treatment.

The following results were obtained:

Large deviations in the material properties can be observed, due to the non-uniform conditions of alloying materials in the billet coil as a result of the self-annealing effect of the material in the central region of the coil. The corresponding values measured on the bar blanks were as indicated in the following table:

EXAMPLE 2

An aluminum alloy of AGS/L type and composition:

Fe : 0.20%

Say: 0.45%.

Mg : 0.51%

Was compared with the common contaminant content of aluminum for electrical applications,

This alloy |jrle cast, on a PROPERZI wheel and rolled in a corresponding rolling mill under the following working conditions:

- the temperature of the ingot on the outlet side of the wheel: 450°C

- the temperature of the ingot at the inlet to the rolling mill: 440°C

- the temperature of the thawing emulation: 65°C

- continuous cooling of the bar blank on the outlet side of the rolling mill. Bar blank temperature at the outlet from the cooler: 70°C. - coiling of the manufactured rod blank with a diameter of 9.5 mm into a coil of 1 tonne. The rod blank thus obtained had the following mechanical and electrical properties:

A noticeable hardening was observed as a result of the ripening process.

The billet coil was then subjected to a precipitation treatment for 8 hours at 230°C in an industrial oven, followed by slow cooling in undisturbed air.

After this heat treatment, the following material properties were achieved:

R = 18 kg/mm<2>

A * 10%

p = 2.940^u JL . cm

After drawing to different diameters in an industrial drawing machine, the following values were measured:

It has been found that the elongation at break remains high despite cold working.

The values stated in the table above for a diameter of 2.7 mm are average values calculated on the basis of material samples taken from all parts of bar blank coils of 1 tonne. J This sampling includes 14 sets of test pieces taken from the 14 rod blank coils that were produced.

The following table allows assessment of the achieved good uniformity for the material properties:

The 14 wire ropes with a diameter of 2.7 mm were then subjected to a final heat treatment for 3 hours at 250°C. The mechanical and electrical properties that were achieved and the corresponding variations were as indicated in the following table:

It will appear that there are favorable values and good uniformity" for the material values obtained.

EXAMPLE 3

______ /

■v.

An AGS/L-1egeration with composition:

Fe : 0.23%

Say :0.55%

Mg.: 0.59%

was produced (on aluminum bdsis, and with the usual impurities in aluminum for electrical applications) and cast, on a PROPERZi wheel and rolled in a corresponding rolling mill under the following working conditions:

Temperature of the ingot on the exit side of the casting wheel: 460°C

The temperature of the ingots on the entrance side of the rolling mill: 450°C The temperature of the rolling mills: 68°C

Continuously cooled wire on the exit side of the rolling mill

The temperature of the wire at the outlet from the cooling unit: 70°C

Coiling of the manufactured rod blank with a diameter of 9.5 mm

in coils of 1 tonne.

Various thermal precipitation treatments were carried out on the rod blanks produced in this way. The following material properties were obtained:

It has been found that this heat treatment^Mar the following effects:

8 hours of treatment at 200°C produces a slight hardening as a result of the aging effectj

the treatments at 240°C and 260°C are manifested by a marked softening which is the result of overagingj

the treatment at 280°C corresponds to initiation of recrystallization.

Rod blanks corresponding to the five material states indicated in it

last drawn up table, is then drawn to a diameter of 3.0 mm and

the drawn rod blanks were then annealed* The following material properties were thereby achieved:

This particularly shows the impact of the heat treatments at

240 and 260°C on the hardening process during cold working and consequently on the drawability of the wire to be used. is produced.

The wires, drawn to a diameter of 3 mm corresponding to the five bar blank states indicated in the last table, were subjected to different thermal softening treatments, which made it possible to draw up function curves for & 2Q0 = f (R) and the number of alternating bends = f (R) in each' case. For a constant value of R = 16 kg/mm 2, the corresponding values for <A>200 °9 the number of alternating bends were as indicated in the following table:

It has been found that threads that were heat-treated for 8 hours at

240 or 260°C, after the achieved material softening gave the best compromise with regard to the finally achieved material properties„

EXAMPLE 4

Wire with diameters of 2.7 mm was obtained in the drawn state according to Example 2, further drawn down to a diameter of 2 mm and subjected to various final heat treatments at temperatures between 2<20 and 360°G for periods of time from 30 min. to 9 hours, with the aim of investigating the effect of the final . heat treatment. With the expression "effect" here is meant the biggest change of state that will make it possible to achieve the desired final material properties in industrial practice.

From the graphical representations of A200^ as a function of time and

temperature and R kg/mm 2 as a function of time and temperature,

it can be deduced as follows:

To obtain A200me-'-lom ^ 0<3 °9

R between 15 and 25 kg/mm<2> can e.g. the following heat treatments are used:

5 hours between 220 and 260°Cj

1 hour between 230 and 280°C.

These treatments have a very large effect and a high degree of reproducibility, which means that the treatments are well suited for use under industrial manufacturing conditions.

EXAMPLE 5

■ *,

Wire with a diameter of 2.7 mm was left in the drawn state obtained according to Example 2, further drawn down to a diameter of 0.5 mm and then subjected to various final heat treatments.

The mechanical and electrical properties obtained in this way are indicated in the following table:

EXAMPLE'6

Wire with a diameter of 0.5 mm was, in the drawn state according to example 5, continuously heat-treated in an electric annealing unit of the induction type at a feed rate of 600 m/min. The mechanical and electrical properties that were obtained for

two different settings of the annealing unit are indicated in the following t&bell:

Claims (4)

1. Process for the production of electrical conductors from Al/Mg/Si alloys, particularly for use in the form of wires or cables, the alloys containing 0.30 - 0.80% (preferably 0.30 - 0.60%) Mg , 0.30 - 0* 70% (preferably 0.30 - 0.60%) Si and 0.15 - 0.35% (preferably 0.15 - 0.25%) Fe, as well as other elements to the same extent as usually in aluminum for electrical applications, and is manufactured starting from an ingot produced by continuous casting on the circumference of a casting head and subsequent continuous rolling, during which the ingot is fed into a rolling mill at a temperature between 400 and 520°C and preferably not above 450°C, thereby obtaining a rod blank with a diameter of 7.5 - 9.5 mm; characterized 'in that, after leaving the rolling mill, said bar blank is quickly cooled to a temperature below 150°C and is then subjected to a conversion process which includes a combination of the following process steps: thermal precipitation treatment at a temperature between 220 and 280°C for a period of time between 1 and 12 hours} cold drawing until the final diameter is achieved; final thermal softening treatment at a temperature between 220 and 280°C for a period of between 1 and 9 hours. 2. Procedure as stated in claim 1, characterized in that the final thermal softening treatment is carried out continuously, preferably in an electric annealing unit of the induction or resistance type. 3. Procedure as stated in claim 1, characterized in that the final thermal softening treatment is omitted, and the manufactured conductors are retained in the state obtained during the cold drawing. 4. Electrical conductors, especially insulated wires and cables, manufactured as specified in claim 1, 2 or 3.