LU83249A1 - PROCESS FOR MANUFACTURING ALUMINUM MACHINE WIRE - Google Patents

Description

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PROCESS OF MANUFACTURING WIRE MACHINE EH ALÜMIHIOM

The invention relates to a process for manufacturing aluminum rod which comprises precipitable alloy elements. This process "and especially applicable to aluminum for electric powertrain" although pae limited to this type of aluminum "which includes" as element · of precipitable alloy! 0.3 to 0.9 magnesium "0.25 to 0.79 i" of silicon and O to 0.60% of iron, the remainder of the metal being aluminum and impurities) t (it is ie of · elements in an amount of less than 0.05 d>) * percentages of the total weight. The machine wire as well known, is the starting product for the drawing or subsequent rolling where the eeotion of the aluminum wire is reduced. Thus, the wire rod has a diameter of 5 to 20 mm, preferably between J and 12 mm, and t λ tensile strength significantly lower than the final drawn product, for example for aluminum for electric pusher mentioned above, a resistance generally less than 250 Hevton / mm, in any case less than λ 300 l / mrn · As is well known, after drawing or rolling, the wire is subjected to a mat; ration in which precipitates of alloying elements which had still remained in solution are formed, and this maturation improves the mechanical and electrical characteristics of the wire.

The conventional process for producing wire rod in a: minium consists of a first stage of hot rolling, in which the wire rod is formed on crowns, followed by a discontinuous operation of dissolving and soaking the crowns; obtained after rolling & hot. In fact, after rolling and re-dicing of the crowns, the alloying elements are precipitated so that there are no longer any available for the ultimate maturation.

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Λ laugh. This is the reason why these elements are returned to 2.

iterated rolling solution, and are forced to remain in supersaturated solution by the soaking which follows immediately after.

This dissolution is costly in energy, and also requires that the production be carried out batchwise. Thus it has been proposed that the first stage of hot rolling ends at as high a temperature as possible, in order to keep a maximum of alloying elements in solution, and to dip the wire rod directly in continuous at the outlet of the rolling mill up to a quenching temperature, so as to keep these alloying elements in supersaturated solution.

4 at this quenching temperature, the mobility of the atoms is so low, that the metallographic structure remains frozen in the state oft it is (except for slow aging effects) <the alloying elements remaining in supersaturated solution remain in solution, the precipitates do not change, nor do dislocations. For a given alloy, the range of "quenching temperatures" therefore has an upper limit which is not a striated maximum limit. This maximum value is determined by a sufficient immobility of the atoms so as not to produce a substantial change in the metallographic structure within a duration of the magnitude of a continuous aluminum treatment process, i.e. the order magnitude of one minute. The maximum aooeptable value for each type of alloy is sufficient for those skilled in the art. For aluminum for electrical conductor mentioned above, the maximum quenching temperature can be set to 260 "C, although this limit is not an absolute limit · θη also proposed a first rolling step which i completes & as high a temperature as possible in order to keep a maximum of alloying elements in solution, followed by quenching in which the metal is worked, while taking care that the metal is worked during the period when it crosses the range of temperatures between the maximum quenching temperature and the minimum working & hot temperature. Despite the quenching, it was observed that the elements in solution precipitated during this time.

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thermo-mechanical operation. The amount of alloying elements remaining in solution for subsequent maturation was therefore much smaller and this appeared to be a drawback. Kais it had been observed that the wire rod thus obtained was such that, depending on whether the precipitation had been partial or total, the need for maturation after subsequent drawing was partly or totally eliminated. The disadvantage was therefore not one, and a wire rod was obtained with properties which made it possible to more easily satisfy the specifications prescribed for the mechanical characteristics of the drawn wire, while avoiding the costly step of ease. solution and providing a continuous process.

The object of the invention is to provide an alternative to the last process mentioned above, providing the same advantages, and thus providing additional freedom in the choice of the parameters of the process, in order to obtain the desired combinations of tensile strength. , duotility and, where appropriate, conductivity.

The process according to the invention comprises, as in the penultimate process mentioned above, a purely thermal operation, that is to say not accompanied by mechanical work, where "a bar of said aluminum (leaving, for example d '' a rolling mill and partially cooled, or from a continuous casting wheel, or coming out of an extrusion press) is quenched continuously until a quenching temperature, as determined above, and so as to produce a structure restored with alloying elements in Bursaturated solution. By "restored structure" is meant a metallographic structure where the grains B elongated by work hardening have reformed into a larger or less isotropic structure under the effect of heat, which is the structure obtained after hot rolling. There must also be a minimum j of supersaturation alloying elements, for example at least OJ $ 6 J of the precipitable elements at the solution temperature.

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The quenching is therefore fast enough and from a temperature high enough to achieve this goal.

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The process according to the invention is however characterized by a second thermo-mechanical step and downstream from the first in the same continuous operation, in which the bar is worked at maturation temperature, and by the fact that the maohi yarn thus obtained is then subjected, before any subsequent work, to a "maturation.

A ripening temperature is a temperature "in a range whose maximum is located at the maximum quenching temperature, as determined above, and the minimum is located at the minimum ripening temperature, as determined below * A maturation temperature, it is therefore a temperature at which the atoms remain frozen, apart from the aging phenomena which occur in a time greater than the duration of a continuous process, i.e. of the magnitude of order of a minute. However, when the structure is subjected to a work at maturation temperature, it is observed that the precipitation of the alloying elements during the work and during a subsequent maturation causes a metallographic structure to be obtained which, after work hardening, allows to obtain a very good quality of wire, and eliminates, in part or in whole, depending on whether or not there are still elements in supersaturated solution, the need for maturation, after drawing. This work at maturing temperature is preferably a rolling with reduction of the section.

For a given aluminum, the minimum aging temperature will be determined as indicated below. It is known that an aluminum of given composition, in the non-hardened state, but comprising alloying elements in supersaturated solution by solution treatment up to a quenching temperature, when it is subjected to maturation , will first see its resistance & traction go up to reach a maximum, and then go down. This is due to the fact that during maturation, the elements k 5.

of alloy ae precipitate while the already existing precipitates conglomerate. The first effect, which increases the tensile strength, dominates at the start, while the second effect, which decreases this resistance, dominates at the end. The minimum maturation temperature for a given aluminum with a given quantity of alloying elements in supersaturated solution, it is the temperature at which aluminum in the non-eoroui state reaches its maximum tensile strength after 3 days · (The éorouie structure arriving earlier at its maximum by the effect of the softening of the work hardened structure) · For the aluminum for electric pusher mentioned above, this minimum temperature is about 130 * C ·

Maturation, which follows this work at maturation temperature, can be done directly at the outlet of the instrument carrying out this work, for example by free cooling in ambient air of the wire rod which causes precipitation of all or a part of the jmoore alloy elements remaining in supersaturation · We can speak of a maturation, when a considerable part, for example half of the elements precipitable after quenching, precipitates during this maturation · 11 is however preferred to operate a total pre-precipitation, in order to eliminate any need for maturation after drawing or any alteration of the properties of the wire rod after its manufacture · When the temperature at the% output of the instrument, operating the work at maturation temperature, approaches the minimum maturation temperature, it is sometimes necessary that the cooling of the wire rod leaving the instrument be slowed down (compared to free cooling in ambient air) e n surrounding the wire with heat insulating elements, for example by forming wire rings which are enclosed in cIob containers which avoid cooling by air convection. One can also maintain the wire for a certain time at the exit temperature by heating, or even increase the exit temperature, provided that a subsequent maturation is carried out.

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The continuous bar used at the start of the first stage of the process can be a bar emerging from a hot forming operation, such as an extrusion press, a casting wheel. This hot shaping will preferably include a continuous rolled delivery of an aluminum rod directed towards the entrance of a rolling mill, and hot rolling by which the section of said type is reduced to form said bar · Fax "hot rolling ”Means rolling with restoration during the operation or immediately after, before subsequent soaking · Oven aluminum for electrical conductor mentioned above, cevi means rolling with exit temperature above 350 * C.

The entry temperature into the rolling mill will preferably be a temperature higher than the solution temperature, oe which means for aluminum for electrical conductor, a temperature higher than 470 ° C.

The invention is particularly applicable to aluminum for an electrical conductor, the composition of which is given above. In a preferred mode, a continuous process will be used, comprising, in enumeration from upstream to downstream, continuous casting, the introduction of the rod leaving the continuous stream in a first rolling mill at a temperature higher than λ 470 * C, the continuous rolling at a temperature above 350 * 0 to form a continuous bar, the continuous soaking of said bar at the outlet of the rolling mill, the introduction of said bar leaving the soaking in a second rolling mill at a temperature above 1J0 * C, continuous rolling at a temperature above 130 * C, and ripening by free cooling & ambient air. The inlet temperature of the second rolling mill is to be adjusted so as to obtain a temperature at the outlet of the rolling mill in the range of 155 to 185 ° C, preferably% 7.

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For example, an 11-Mg-Si dp type 6201 alloy was used having as composition t Mg t 0.60 d Si i 0.55% "P · * 0.18 JÉ {

Zn: 0.006 56 I Cu * 0.004 #; Mn * 0.015 & I * 0.001; T t 0.0 (

One can however use an aluminum richer or poorer in alloying elements, according to the price which one wants to pay or to save for an increase or decrease in quality, due to the composition, without for oela affecting the possibilities of the alloy to obtain a better quality of it, due to the process according to the invention. "This alloy, after leaving a continuous rolling wheel itself 2 in the form of a rod having a section of approximately 2000 ma, entered a temperature of 490 * C in a first rolling mill oontinuous at 9 steps from where it emerges in the form of a round bar with a diameter of 15 mm and at a single temperature of 430 * C. at this temperature most of the alloying elements are still in solution, since at the equilibrium state only about 20 of the magnesium and preoipitable silicon in the form of MggSi is then in the precipitated form.

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This bar, which leaves at a speed of about 2.4 m / sec from the first rolling mill, is then directed towards the entrance to a second continuous rolling mill, the entrance of which is located at a distance of about 2 m from the exit of the first. Between the two, the bar passes through a tube 50 mm in diameter and one meter long, supplied with 1 counter-current refrigeration emulsion, the flow rate of which is adjusted so that the bar exits therein. a temperature of 220 * C. Other ways of quenching can also be used, for example by emulsion jets directed on the wire, provided that the temperature can be adjusted to the desired temperature.

The second continuous rolling mill has 4 steps with equal reduction, reducing the bar to the diameter of 9 * 5 mm of the machine wire, the wire leaving the rolling mill at a temperature of 175 * 0 and at a speed of approximately 6 m per second. This wire rod is then wound on a spool and placed in a refractory stone container. What is important is that the container is closed so as to avoid cooling by convection of the free air around the coil. In the case following this example, the cooling was of 2eC per hour.

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We will compare the properties obtained with a wire rod of the same composition, obtained by the conventional method, ie t continuous casting followed by continuous hot rolling, wound on coils which cool freely with ambient air, then setting in solution by keeping the coils for 8 hours in an oven at 550 ° C, then soaking the coils to a temperature of around 45 ° C.

These two types of mahine wire with a diameter of 9 * 5 ** "one according to the invention, the other according to the conventional method are then drawn, both up to 3 * 60 mm and up to 'at 3.15 µm, the drawn wire from the conventional method is then further matured for 5 hours at 16 ° C.

The comparative results are as follows:

According to the invention Conventional method H <T f B <T p

Pii machine 304 7 "75 31" 10 196 21

After drawing 3.60 mm 34B 5 31.30 295 4.5 34.9

After drawing 3.60 nm -t- maturation - - - 343 7.5 32.13

After wire drawing 3.15_nm 362 4.5 31.44 290 4 34.70

After wire drawing 3.15 "a + maturation - - - 350 7 31.95 2 H - tensile strength in Newton / mm (f - ductility (56) P - resistivity (mA mm ^ / m) The invention does not is not limited neither to the specific mode B of the operations given in the example, nor to the composition of the aluminum. It is also possible, without departing from the scope of the present invention, to use as aluminum with pitiful preei-4 alloying elements Al-Cu, Al-Cu-Mg, Al-ZnfcMg, Al-Zn-Mg-Cu and i Al-Mg-Si alloys.

Claims (11)

2. Method according to claim 1, characterized in that said maturation takes place during free cooling & ambient air of the wire rod immediately after the work V · at maturation temperature. 3. Method according to claim 1, characterized in that said maturation takes place during a slow cooling of the wire rod, immediately after working at maturation temperature. * 4 · A method according to claim 1, characterized in that said maturation is carried out by maintaining, by heating, the wire rod at a maturation temperature, immediately after working at maturation temperature. 3. Method according to any one of claims 1 to 4, characterized in that the working at maturing temperature is a rolling with reduction of the section. 6. Process according to any one of claims 1 to 5, characterized in that the continuous bar used at the start of said first step is a bar leaving an operation of confor-L hot mat ion. .10. »V 7. Method according to claim 6, characterized in that the hot shaping operation comprises a continuous casting delivering an aluminum rod directed towards the entrance of a rolling mill, and a hot rolling by which the seotion of said rod is reduced to form said bar. 6. Process according to Claim 7, characterized in that the temperature of entry of the rod into the rolling mill is a temperature higher than the solution temperature. "; S 9. Process according to any one of the preceding claims, characterized in that the aluminum used is an alloy Al-Cu, Al-Cu-Mg, Al-Zn-Mg, ï Al-Mg-Zn-Cu and Al-Kg -Yes. 10. Method according to one of the preceding claims, characterized in that the aluminum comprises 0.3 to 0.9 ί of magnesium, 0.23 to 0.73 of silicon and 0 λ 0.60 of iron, the remainder being tin aluminum and impurities. 11. The method of claim 10, characterized in that in said second step, the bar is worked at a temperature in the range from 130 * 0 & 260 * 0. 12. The method of claim 11, characterized in that the * bar is worked by continuous rolling, the wire rod exits at a temperature in the range from 133 to 183 * C, and being wound in a crown, and that this crown is then cooled in a closed container. 13. The method of claim 12, characterized in that the continuous bar used at the start of said first step is a bar leaving a continuous rolling mill where. aluminum is worked at a temperature ranging from a temperature above 470 ° C at the start of the rolling mill to a temperature above 350 * 0 at the end of the rolling mill. / <r7 ~ J ^ r _____