DE2602339A1 - PROCESS FOR CONTINUOUSLY CASTING A STRAND FROM AN ALUMINUM ALLOY - Google Patents

Description

PATENT LAWYERS

Dr.-lng. Wolff

H. Bartels

O C η OOO η Dipl.-Chem. Dr. Brandes L DUZOJ y Dr.-lng. hero

Dipl.-Phys. Wolff

D-7 Stuttgart 1, Lange Strasse 51

Tel. (0711) 29 0310 and 29 72 S5

Telex 07 22312 (patwod)

Telegram address:

Hx 07 22312 Wolff Stuttgart

PA Dr. Brandes: Headquarters Munich postal check account St <jt. 7211-700 Deutsche Bank AG, Stuttgart. 14 / 28S30

Office hours:

9-11.30 a.m., 1.30 p.m.-4 p.m.

except saturdays

20th January 1976

Our ref .: 124 931/487333 ers

Southv / ire Company, Carrollton, Georgia, USA

Process for the continuous casting of a strand
made of an aluminum alloy

Telephone information and

09831/0712 Orders are only available after written

Confirmation binding

INSPECTS

The invention relates to a method for continuously casting a strand of an aluminum alloy containing approximately 0.5 to O _r 9 percent by weight silicon and approximately 0.6 to 0.9 percent by weight magnesium, the molten alloy at a temperature above its melting point is poured into the casting groove of a casting wheel for continuous casting, a cast strand is formed from the molten metal by cooling the aluminum alloy in the casting wheel and this is dug out of the casting groove, then the strand is fed into a rolling mill and continuously into a hot-rolled strand at one temperature is rolled, which is above the temperature at which the alloy metals are deposited on the grain boundary of the aluminum base metal, and. then the hot-worked strand is quenched to a temperature range which is below the temperature range at which an instant, substantial precipitation of alloy metals takes place in such a way that the cooling of the cast metal, calculated from the start of the hot working to the end of the quenching, is within a sd short period is carried out that no significant deposition of the alloy metals takes place.

The aluminum alloy 6201 is an aluminum-magnesium-silicon alloy of high strength, those in the form of a wire and in a heat-treated state

2 has a tensile strength of more than 3220 kg / cm, an elongation of more than 3% and an electrical conductivity that is greater than 52.5 %, based on the international copper standard IACS. Strands made of 6201 aluminum intended for drawing processes, as well as similar strands made of aluminum alloys intended for drawing, have so far been produced by a number of different process steps.

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places where ti-a. an aluminum block by direct current melting is cast, the ingot is reheated to about 371 to 454 C, and the cast ingot becomes a for a drawing process is hot rolled, the strand bar is heat treated to a temperature of about 533 ° C is used to bring the constituents into solution (solution annealing), and is then quenched in water. The strand is cold drawn to produce a wire, and the wire is artificially aged at temperatures between 121 ° C and 232 ° C, this allows wires to be created, which have tensile strength and electrical conductivity, which are similar to or exceed the corresponding values of aluminum 6201.

This known method does indeed produce an acceptable product, such a piece process or discontinuously ongoing casting process only allows the production of a limited amount of strand material, i.e. a mill of a given size only produces a corresponding amount of strand, so that separately manufactured Strand lengths must be welded together in order to obtain a strand of greater length. When the rolling doll reheats and is rolled to form the strand, it is customary to sever the leading end of the strand as this is a smaller one Has goodness. Therefore, the known method results in a considerable amount of waste material. A Elongated strand made up of several lengths of individual strands that are manufactured in a piece process and welded together shows a poor grain structure at the welds. This will increase the tensile strength and conductivity impaired. In addition, it is practically impossible to ensure that the reheating and rolling are different Vialz dolls are given identical conditions. The welded together Strand lengths usually have different structural properties.

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The known piece process not only requires extremely careful handling of a strand in the solution annealing furnace to obtain such a uniform heat treatment as it is required to in a time consuming and an additional The process requires the establishment of a uniform product, but the additional disadvantage arises that this results in an additional period of time within which the aluminum can oxidize, as is the case when the ingot is cooled or reheated when the out the strand discharged from the rolling mill is cooled or reheated for the purpose of solution treatment and when the one brought into solution Strand is cooled after leaving the furnace. As a result, a strand is obtained in the known method, which is substantially oxidized making the strand relatively hard for subsequent drawing operations and which causes the strand shows a rather dull finish. In addition, a heavily oxidized and hard strand is more difficult to draw, and the drawing tools used wear out fast.

An improved method for continuously casting and rolling 6201 aluminum alloy is described in U.S. Patent 3,613,767. According to this process, a billet or billet of aluminum alloy, such as alloy 6201, is continuously produced without the need to reheat the billet or billet during the process. The strand emerging from a continuous casting machine is passed through a rolling mill and a quenching tube and then cooled in a continuous process. The heat of the strand exiting the continuous caster is not dissipated and the temperature of the strand is kept in the range of the solution temperature of the metal while the strand is fed to the rolling mill. ^The strand is hot-formed in the rolling mill, and immediately after the strand emerges from the rolling mill, the quenching is carried out, so that the period between the point in time in which the strand the

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-r-

Rolling mill enters until the point in time when the strand has a temperature below the crystallization temperature of the alloy metal is cooled is less than the period which is necessary for the deposition of the alloy metals at the grain boundaries of the metal. After quenching the strand it has a temperature which is lower than the temperature at which a more substantial precipitation occurs immediately Dimensions done. If the strand is then cold drawn into a wire, it has an unusually high tensile strength, a relatively high electrical conductivity and. an unusually light appearance. In this procedure according to U.S. Patent 3,613,767 are therefore the main problems of the separate Handling between the individual process steps out of the world.

Although the known method according to US Pat. No. 3,613,767 represents a significant advance over the known piece processes with regard to the continuous casting and rolling of the 6201 aluminum alloy, it presents entirely new problems which were not encountered in the known piece processes. Thus, since the method according to US-PS 3,613,767 the temperature ^d there i _n a rolling mill _as j incoming strand. should be _n the solution region of the metal held required that the molding process takes place at such a high speed that the cast strand leaves the casting machine can travel the short distance in the rolling mill so quickly that no substantial decrease in temperature takes place in the meantime. However, when the casting process is carried out at such a high speed, a condition known as "solidification shrinkage" develops in the mold. This condition has the consequence that voids or cracks form on the outer surface of the cast strand as it shrinks away from the walls of the casting mold during solidification. In addition, solidification shrinkage can cause voids inside the cast strand. EEIM subsequent rolling of a cast strand, ^ ^he such, by solidification

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Contains shrinkage caused voids, oxide inclusions are within the voids that are on the outer parts of the cast

/ included, strand are present, / causing the rolled strand to become brittle and the drawability of the strand is significantly reduced. In addition, the internal cavities cause internal microcracks, which significantly impair the elongation of the strand and thereby greatly impair the subsequent cold deformability of the strand affect.

Since the method of US Pat. No. 3,613,767 requires that the Cast strand removed from the casting wheel at extremely high temperatures is, there is also the disadvantage that any precipitation of alloy components that this takes place, leads to large precipitates that are of the order of magnitude of 20,000 Angstrom units. It has been shown that the presence of such large precipitates is unifying has an extremely deleterious effect on the physical properties of the finished product.

The invention also includes the knowledge that the solution temperature of the G201 alloy depends on the concentration of the alloy constituents present within the alloy varies, the change in the solution temperature being such that the higher the concentration, the smaller the range of the solution temperature is the alloy constituent. Therefore, the solution temperature can range between approximately 454 ° C and 616 C for the at Alloy 62Ol given permissible concentration range fluctuate. In the process of US Pat. No. 3,613,767 assumed that solution temperatures up to 538 ° C can be used for all purposes. In fact, using this method, the temperatures of the Rolling mill incoming strands are not set to values above

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Hold 504 ° C. Accordingly that is The method of US Pat. No. 3,613,767 does not for the continuous production of strands from the 6201 alloy suitable / when concentrations of the alloy constituents are in the range at which a solution temperature is in the upper part of the solution temperature range for the 6201 alloy results.

When we speak of heat-treatable aluminum alloys, we mean those aluminum alloys, which contain alloy components that have high solubility in aluminum in the solid state at high temperatures and have a low solid solubility in aluminum when cooled to room temperature. These alloys harden by precipitation of a second phase during the heat treatment, and the alloy components are thereby in Solution held that a rapid quenching of high temperatures takes place.

Aluminum alloys are known as wrought aluminum alloys understood, the alloy components have a low ■ solid solubility in aluminum both at high Temperatures as well as at low temperatures. These alloys usually harden by machining, which is a hardening mechanism that occurs during cold working of the alloy.

From the above, it can be seen that the continuous casting and rolling of heat _{treatable aluminum strands from aluminum alloys such as' 6201 aluminum /} still requires considerable improvements.

The invention is therefore based on the object of creating a method of the type in question, by means of which in the

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continuous production of strands from 6201 aluminum alloy the problems of solidification shrinkage and the formation of massive, precipitated particles are avoided as they are occur in the process according to US Pat. No. 3,613,767, and in which it is also possible to use the strand in a temperature range to be rolled, which is within the upper part of the solution temperature ranges given for 6201 aluminum alloy.

In a method of the type mentioned at the outset, this object is achieved according to the invention in that the processes of casting the molten metal and lifting the strand out of the casting groove are carried out at such a speed and at such a temperature that no solidification shrinkage occurs, and that afterwards the Temperature of the strand, while it runs between the casting wheel and the rolling mill, is increased to a temperature which is above that temperature at which the alloy metals would be deposited on the grain boundaries of the aluminum green metal. In contrast to the teaching of the aforementioned US Pat. No. 3,613,767, the cast strand is excavated from the casting groove at a temperature which is less than 504 ° C., preferably at a temperature which is between 427 and 504 ° C. Thereafter, the temperature of the strand is increased, preferably to a value between 454 and 616 ° C ₁ by passing the strand through a heater, within which heat is transferred to the strand.

It should be noted that the method according to the invention enables the strand to be removed from the casting wheel at one temperature dissipate which is lower than the temperature at which any solidification shrinkage could occur, and that

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then the temperature to a value within the upper part of the solution range for 6201 aluminum alloy can be increased if so desired before the strand enters the mill. Accordingly, will Obtain a much better product than when using the known method according to the mentioned U.S. Patent 3,613,767 is the case.

The invention is illustrated below with reference to the drawing in FIG individually explained.

Show it:

Fig. 1 is a schematically drawn side view of a device for performing the procedure outlined here;

Fig. 2 is a ternary diagram for graphic

Representation of the solubility of magnesium, silicon and the intermetallic compound Magnesium silicide in aluminum different temperatures and

3 shows a graphic representation of the effect of the method according to the invention achieved heat treatment of 6201 aluminum alloy in comparison to a 6201 aluminum alloy produced according to the known method. ■

1 shows a casting machine 10, a heater 11, a roller mill 12, a pipe quenching device 13 and a winding device 14. In the method according to the invention, molten metal is in a (not shown) furnace in a casting wheel 10a of the casting machine 10 is cast. The melted

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Zene metal is cooled, solidified in the casting wheel 10a and is as a solidified strand 15 at a temperature below of 504 ° C from the casting wheel and passed to the heater 11 and through it, in which the solidified Strand 15 is continuously heated until the temperature of the strand is within the range of approximately 454 to 616 C. The heated strand 15 is then passed to the rolling mill 12 and through it. The product is lengthened in the rolling mill 15 and reduced in its cross-sectional area and leaves the rolling mill as kneaded strand 17. The strand 17 is passed through the pipe quenching device 13, which is the first Quenching tube 18 forming the quenching stage, feed rollers

19, a quench tube forming the second quenching stage

20, feed rollers 21 and a strand guide tube 22. The strand emerging from the strand guide tube 22 is wound into bobbins by the winding device. The quench liquid is fed from a sump 24 to a pump 23 which feeds the liquid under pressure to the quench tube 18 of the first stage. The quenching liquid is passed through the quenching tube 18 in a flow direction which corresponds to the direction of movement of the strand 17 and is fed via a line system to a cooling tower 26, v / o the quenching ^{liquid cools and from where} the cooled liquid is returned to the sump 24. A pump 27 receives quenching liquid from a sump 23 and feeds this under pressure to the quenching pipe 20 of the second stage. The quenching liquid of the second stage is passed through the quenching tube 20 in countercurrent to the advancing movement of the strand 17 and flows through a pipe system to a cooling tower 31, where the liquid is cooled and from where the liquid is returned to the sump 28 kept at certain temperatures during the quenching process.

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The molten metal treated in this device is, more precisely, one for heat treatment suitable aluminum alloy. If the product to be formed is a 6201 aluminum alloy, then extend the range of contained silicon is from approximately 0.5 to 0.9% and that of contained magnesium from approximately 0.6 up to about 0.9%. The range of alloy constituents of silicon and magnesium in this metal can exceed the for the 6201 alloy specified range beyond 0.2 to 1.3% and from 0.3 to about 1.4%, respectively, if desired. The metal is in a molten state poured through a fiberglass sieve into a crucible kept at a temperature of more than 649 ° C. from the tie, the metal is poured into the casting wheel 10a where the M is cooled and unites to form the cast strand 15. , solidified speed, which is chosen so that no solidification shrinkage occurs. The cast. Strand becomes from the casting compound 10a at a temperature of approximately 427 ° C Stripped or dug up to 504 ° C and runs to the heater 11 and through it, the temperature of the cast strand being increased to a value at which the alloy constituents go into solution. The heater 11 continuously supplies thermal energy to the strand in order to maintain the temperature of strand 15 from about 454 ° C to about 616 ° C increase, usually from around 510 ° C to 549 ° C or, depending on the alloy composition, from 549 C to approximately 616 ° C. After leaving the heater 11, the Cast strand to the rolling mill 12 and passed through it, in which the strand is hot deformed and coated with a coating is coated in soluble oil, its concentration to about 40% and its temperature to less than 93 ° C, usually around 71 ° C. The rolling mill 12 has a plurality of rolling stands, which alternate the cast strand from top to bottom and compress from the sides, making the strand

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lengthened and its cross-sectional area reduced, see above that the cast strand is progressively transferred into the strand 17 suitable for a subsequent drawing process will. The volume of the concentrate containing the soluble oil is kept in the rolling mill 12 at a value which is approximately 2/3 the volume, as is the case with a conventional, continuous casting system for strand of electrolytic copper Applies. The temperature and the volume of the coolant supplied to the strand in the rolling mill can be adjusted so that that when the strand 17 leaves the rolling mill 12, its temperature is so high that the strand is still in the for the hot working is suitable temperature range, usually above 343 C, so that the alloy metals have not separated from the aluminum. Due to the small volume supplied by the strand in the rolling mill Coolant requires a higher concentration of lubricant, approximately 40% compared to. about 10% for an electrolytic copper strand system, and the flow rate is adjusted so that approximately the same coolant flow is present at each roll stand.

Fig. 2 shows a ternary diagram which graphically shows the solubility of magnesium, silicon and magnesium silicide in Represents aluminum at various temperatures ranging from 440 ° C to 535 ° C.

A straight line shows the increase in the solubility of magnesium, silicon and magnesium silicide in the 6201 alloy with an increase in temperature to about 535 C. A location 42 on the straight line represents the amount of Magnesium, silicon and magnesium silicide are the result of a continuously cast strand of 6201 aluminum are in solution when the strand undergoes heat treatment according to the known process for continuous production cast aluminum alloy 6201;

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A digit 43 represents the amounts of magnesium, magnesium silicon and silicon used in the 6201-7 aluminum alloy remain in solution when a continuously cast strand of this alloy undergoes a heat treatment according to the is subjected to the method according to the invention. As from the As can be seen in the diagram of FIG. 2, sch for the in Solution held amount of magnesium silicide in the 6201 alloy, if this is continuously cast, rolled into a strand and heat-treated and if this is the process is used in accordance with the invention, an increase of 162%.

The following is an example of the improved properties that result from having a greater amount of magnesium silicide before aging and before. Precipitation process in the alloy matrix is in solution. A cast strand was continuously made using the process known for the 6201 alloy. The results were as follows: The tensile strength of the finished wire was 3212 kg / cm ** with an elongation of 8.3% and a conductivity of 52.5% _χ based on the international copper standard IACS. Proceeding from these properties as a basis, the temperature of the strand was then increased from 482 ° C. to 549 ° C. using the method according to the invention in an area between the casting machine and the inlet of the strand into the rolling mill. The strand was then rolled and made into wire. The physical properties of this strand produced by the process of the invention were:

Tensile strength 3571 kg / cm

Elongation 7.9%
Conductivity 52.5%.

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Fig. 3 is a graph of the properties as they are when using the usual method of heat treatment and when using the inventive Method of continuously casting a strand of 6201 aluminum alloy. Here shows a curve 50 shows the relationship between conductivity and tensile strength of the made of 6201 aluminum alloy Wire using the conventional technique, and a curve 52 shows this relationship between conductivity and tensile strength for a wire made from 62Ol aluminum alloy is produced using the method according to the invention.

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Claims (13)

Claims Process for the continuous casting of a strand from an aluminum alloy containing about 0.5 to 0.9 weight percent silicon and about 0.6 to 0.9 weight percent Contains magnesium, the molten alloy at a temperature above its melting point Temperature is poured into the casting groove of a casting wheel for continuous casting by Cooling the aluminum alloy in the casting wheel from the molten metal. cast strand formed and this is dug out of the casting groove, then the strand is fed into a rolling mill and continuously hot-formed Strand is rolled at a temperature which is above the temperature at which the alloy metals are deposited at the grain boundaries of the aluminum base metal, and then the hot-worked strand a temperature range which is below the temperature range at which an instantaneous, substantial Precipitation of alloy metals takes place, is quenched in such a way that the cooling of the cast Metal, counted from the start of hot working to the end of quenching, in such a short period of time is carried out so that no significant deposition of the alloy metals takes place, characterized in that that the operations of pouring the molten metal and excavating the strand from the casting groove with such Speed and at such a temperature that no solidification shrinkage occurs and that thereafter the temperature of the strand, while it runs between the casting wheel and the rolling mill, increased to .eine temperature is, which is above the temperature at which the alloy metals at grain boundaries of the Would deposit aluminum base metal. 609831/0712 2. The method according to claim 1, characterized in that the excavation of the cast strand from the casting groove a temperature of less than 504 ° C is carried out and that increasing the temperature of the strand by passing it through a heater which transfers heat to the strand. 3. The method according to claim 2, characterized in that the alloy is cooled in the casting groove to a temperature between about 427 and 504 ° C. 4. The method according to claim 2, characterized in that the temperature of the cast strand after the passage through the heater is approximately 454 to 616 ° C. 5. The method according to claim 4, characterized in that the temperature of the cast strand after the passage the heater is approximately 454 ° to 510 ° C. 6. The method according to claim 4, characterized in that the · temperature of the cast strand after the passage through the heater is approximately 510 ° to 549 ° C. 7. The method according to claim 4, characterized in that the temperature of the cast strand after the passage through the heater is approximately 549 ° to 616 ° C. 8. The method according to claim 1, characterized in that the temperature of the cast strand at the beginning of the Warming temperature is approximately 454 ° to 616 ° C. 9. The method according to claim 8, characterized in that the temperature of the cast strand at the beginning of the Hot working is approximately 454 ° to 510 ° C. 609831/0712 10. The method according to claim 8, characterized in that the temperature of the cast strand at the beginning of the Hot working is approximately 510 ° to 549 ° C. 11. The method according to claim 8, characterized in that the temperature of the cast strand at the beginning of the Hot working is approximately 549 to 616 ° C. 12. The method according to claim 1 and one of claims 8 to 11, characterized in that the continuous rolling of the cast metal to form the warr Strand at a temperature which is above the temperature range at which the Alloy metals at the grain boundaries of the aluminum.; - Base metal deposit, is carried out in such a way that the strand is hot-rolled while the strand is coated at the same time with a soluble oil, which has a temperature of less than 93 ° C. 13. The method according to any one of claims 1 to 12, characterized in that that the continuous quenching of the strand to a temperature value which is below the Is the temperature range at which significant, instantaneous deposition of alloy metals takes place, and the complete cooling of the alloy from the start of the hot working to the end the quenching, takes place within a period of time in which no significant precipitation of the alloy metals takes place, be carried out in such a way that the hot-rolled strand immediately after its exit from the hot rolling facility on a Temperature of less than 204 C is quenched and that the period of time between entry into the hot rolling facility and the completion of quenching to a temperature less than 204 ° C for between 9 seconds and is 30 seconds. 609831/0712 Empty set