GB1575555A - Method of continuously producing aluminium alloy rod - Google Patents

Description

(54) METHOD OF CONTINUOUSLY PRODUCING ALUMINIUM ALLOY ROD (71) We, SOUTHWIRE COMPANY, a Corporation organised and existing under the laws of the State of Georgia, United States of America, of 126 Fertilla Street, Carrollton, Georgia 30117, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the continuous production of aluminium alloy rod.

6201 Aluminum Alloy is a high strength aluminum magnesium silicon alloy which in wire form and in the heat treated condition has a tensile strength of over 46,000 PSI, elongation greater than 3 percent, and an electrical conductivity greater than 52.5 percent IACS. In the past, 6201 Aluminum Alloy redraw rod and similar aluminum alloy redraw rods had been manufactured for commercial use by a plurality of separate steps which included direct chill (DC) casting an aluminum ingot, reheating the ingot to about 700" to 8500F, hot rolling the cast ingot to redraw rod and solutionizing the rod at a temperature of approximately 1000"F and water quenching the rod. The rod was then cold drawn to form wire, and the wire artificially aged at temperatures between 250 and 4500F. This procedure was capable of producing wire having tensile strength and electrical conductivity characteristics which are similar to or in excess of those for 6201 Aluminum.

The foregoing batch process or non-continuous casting process, of course, necessitated a plurality of separate steps both in time and space, as well as the use of highly specialized and expensive material handling equipment. Moreover, the separate steps that were required provided a substantial amount of time in which the aluminum could oxidize, yielding a rod product of relative dullness in finish and hardness in texture.

The hard rod was particularly difficult to draw down into wire, and the wire-drawing dies would tend to deteriorate rapidly.

An improved method for continuously casting and rolling 6201 Aluminum Alloy was described in U.S. Patent No. 3,613-767.

Briefly, the invention of U.S. Patent No.

3,613,767 comprised a method of continuously manufacturing aluminum base alloy rod, such as 6201 Aluminum Alloy. rod, without the necessity of reseating the ingot or the rod during the process. The bar emerging from a continuous casting machine is passed through a rolling mill, a quench tube, and then cooled in a continuous process. The heat of the cast bar emerging from the continuous casting machine is not dissipated and the bar temperature is maintained in the solutionizing temperature range of the metal as a rod is passed to the rolling mill. The rod is hot worked in the rolling mill and quenched immediately as it emerges from the rolling mill so that the time lapse from the point where the bar enters the rolling mill to where the rod is quenched to a temperature level below the crystallization temperature of the alloy metals is less than the time required for the alloy metals to precipitate to the grain boundaries of the metal. After the rod is quenched it is at a temperature below the temperature where immediate and substantial precipitation occurs. When the rod is subsequently cold drawn into wire it has an unusually high tensile strength and a relatively high electrical conductivity, and an unusually bright appearance. Thus, the major problems of separate handling between each of the steps in the prior art process were eliminated by the practice of the invention disclosed in U.S. Patent No. 3,613,767.

However, while the process of continu ously casting and rolling 6201 Aluminum Alloy described in U.S. Patent No. 3,613,767 was a great improvement over the prior art non-continuous batch process, it nevertheless created entirely new problems which were not associated with the batch processing system. Thus, as explained in Application Serial No. 2725/76 (Serial No. 1,509,132) of which this Application is for a Patent of Addition, the process of U.S. Patent No.

3,613,767 not only yielded a rod product that contained relatively large and deleteri ous precipitate compounds on the order of 20,000 angstrom units in size, but the relatively high casting rate that was required resulted in the presence of solidification shrinkage voids in the cast bar which rendered the product brittle and thus adversely affected the drawability and elongation characteristics thereof.

Accordingly, there was disclosed in the aforementioned Application Serial No.

2725/76- (Serial No. 1,509,132) an improved process of continuously producing 6201 Aluminum Alloy rod which avoided the problems of solidification shrinkage and formation of massive precipitate particles associated with the process of U.S. Patent No. 3,613,767, and which further advantageously permitted rolling of the rod at a temperature within the upper portion of the solutionizing range for 6201 Aluminum Alloy. Essentially, the process of the aforementioned application was characterized in that the cast bar was removed from the casting mold at a temperature below 9400F (i.e., below the temperature at which any solidification shinkage would occur), preferably 8000F to 9400F, and then passed through a heater, positioned between the casting mold and the rolling mill, wherein the temperature of the bar would be increased, preferably in the range of 850"F to 1 1400F. Thus, a substantially superior product-was obtained, wherein the amount of magnesium silicide retained in solid solution in the aluminum matrix was substantially increased, and the ultimate tensile strength, elongation and electrical conductivity improved, as compared with products produced by the prior art processes.

It has now been found, in accordance with this invention, that the improved product obtained by the process of the aforementioned application does not depend upon the precise location of the heater disclosed therein; namely, between the casting mold and the rolling mill, but rather the heating step-may also be advantageously carried out subsequent to rolling. More particularly, the heater may be positioned between the rolling mill and the quenching apparatus, and the rolled rod passed therethrough so that its temperature is raised from the temperature at which it exits the rolling mill to an elevated temperature within the solutionizing range. Preferably, the temperature of the rolled rod is raised to from 7000F to 10500F.

Accordingly, there is provided pursuant to this invention a method of continuously producing an aluminum base alloy rod con taining from 0.5 to 0.9 weight percent silicon 0.6 to 0.9 weight percent magnesium and the remainder essentìally aluminum, comprising the steps of còntinuously casting molten metal' bf 'the- foregoing composition -in a continuous casting mold into a continuous cast bar and removing the bar from the mold at a temperature below 9400F, immediately rolling the bar in a rolling mill into continuous rod and removing the rod from the rolling mill at a temperature above 650"F, continuously quenching the rod to a temperature below the temperature at which immediate substantial precipitation of alloying metals occur, and further including the step of raising the temperature of the cast bar to an elevated temperature within the solutionizing temperature range at a point in the process intermediate the casting and quenching operations; characterized in that said step of raising the temperature of the cast bar is performed by passing the bar through a heater as the bar exits the rolling mill in rod form, and therein raising its temperature in the range of 7000F to 10500F.

Because some precipitation of the Mg2Si occurs in the rolling mill, the process of the present invention yields a final rod product having slightly superior properties as compared with the process of the aforementioned application, of which this application is for a Patent of Addition, simply because the post-heating step (i.e., subsequent to rolling) will counteract the effects of such precipitation. In this regard it is noted that when the rod exits the rolling mill at a temperature of about 700 F, only about 20% of the Mg2Si is retained in solid solution. Thus, the post-heating step increases the amount of Mg2Si in solid solution whereby the improved properties of the rod product may be obtained.

On the other hand, because the rod travels at higher speeds as it exits the rolling mill than the cast bar travels as it enters the mill, the heating necessarily takes place in a shorter period of time. Consequently, more heat energy is repired when practicing the post-heating operation of the present inven tion 'than is required with the preheating operation of the process of the aforementioned application. While induction heating is preferable, any suitable heating process may be utilized within the scope of the invention.

Fig. 1 is a schematic side elevational view of a casting machine, rolling mill, quenching tube, and coiler utilized in the procedure herein set forth.

Fig. 2 is a graphical representation of the effect of heat treating 6201 Aluminum Alloy by the present invention compared to prior art methods of preparing 6201 Aluminum Alloy.

Referring now to the drawings, Fig. 1 shows a casting machine 10, a heater 11,- a rolling mill 12, a quench assembly 13 and a coiler pipe. The process of the present invention comprises pouring molten metal from a furnace (not shown) into a casting wheel 1 0a of casting machine 10. The molten metal is cooled and solidified in casting wheel 10a and extracted as a solid bar 15.

The bar 15 is then continuously guided toward and through rolling mill 12 wherein the bar is lengthened and reduced in its cross-sectional area and emerges from rolling mill 12 as a wrought rod 17 at a temperature of about 7000F. Rod 17 is then continuously passed through heater 11 wherein the temperature of rod 17 is raised to about 1050"F.

After passing through heater 11, rod 17 enters quench assembly 13 wherein the temperature of the rod is rapidly lowered to a temperature below 4000F, generally to about 1500F after which the rod 17 enters the coiler pipe for coiling by means of a continuous coiling apparatus (not shown).

In more detail, the product produced in the practice of the present invention is the heat treatable aluminum alloy 6201. The metallurgical composition of the aluminum alloy 6201 is generally accepted to be as follows: silicon and magnesium are present in concentrations of from about 0.50 to about 0.90 weight percent, and from about 0.60 to about 0.90 weight percent, respectively. The range of silicon and magnesium present in alloys. processed by the method of this invention can be varied beyond the concentration ranges for alloying elements in 6201alloy, to from about 0.20 to about 1.30 weight percent and from 0.30 to about 1.40 weight percent, respectively, if desired.

The metal in its molten state is poured through a fiberglass screen into a holding pot maintained at a temperature above - 12000F, usually at about 12700F. From a holding pot, the metal is poured into a casting wheel 10a of casting machine 10 where it is cooled to a temperature of from about 8000F. to about 940"F and solidified into cast bar 15 at a rate at which solidification shrinkage will not occur. The cast bar is stripped from casting wheel 10a at a temperature of from about 8000F to about 940"F and passed to rolling mill 12 where the bar is hot formed and coated with a soluble oil solution with an oil concentration of about 40.0 percent and at a temperature below 2000F, usually at about 160"F. Rolling mill 12 includes a plurality of roll stands which compress the cast bar 15 alternatively from top to bottom and side to side, which functions to lengthen the cast bar and reduce the cross-sectionalarea of the cast bar, so that the bar is progressively formed into rod 17. The volume of the soluble oil concentration in rolling mill 12 is maintained at a level of about two-thirds the volume of oil in a typical continuous casting system for electrically conductive rod. The temperature and volume of the coolant applied to the rod in the rolling mill 12, and the temperature of the rod is at a level so that the rod is within the hot forming temperature range of 6201 Aluminum Alloy, which is usually about 650" F, so that the alloy metals do not precipitate from aluminum. Generally, the temperature of the rod exiting the rolling mill is about 7000F. The low volume of coolant applied to the rod in the rolling mill requires that a high concentration of lubricant be present in the coolant solution, an approximately 40 percent solution of lubricant fqr the present system as compared to an approximately 10 percent solution of lubricant for an electrically conductive rod system, and the flow is adjusted so that an approximately equal flow of coolant solution is provided to each roll stand.

Fig. 2 is a graphical comparison of differences between 6201 Aluminum Alloy rod solution heat treated by the method of the present invention and prior art methods.

Line 22 of Fig. 2 represents time in seconds.

Line 20a represents temperature in degrees Farenheit, line 20b represents conductivity as Percent of the International Annealed Copper Standard (IACS) and line 20c represents percent Mg2Si in solution. Line 23 is a plot of 6201 Aluminum Alloy wrought rod undergoing solution heat treatment by prior art methods and line 21, 21a and 21b represent the solution heat treatment of 6201 Aluminum Alloy wrought rod by the method of the present invention.

Fig. 2 is best understood by considering the following examples which are representative of the data which may be obtained from Fig. 2 and which data is representative of the distinct advantages which the method of the present invention has over prior art methods for solution heat treating 6201 Aluminum Alloy wrought rod.

EXAMPLE I A wrought rod fabricated from 6201 Aluminum Alloy by the method of the present invention enters the solution heat treating step at zero (0) time, from lines 22, 21a, 21b and 21 at a temperature of 700"F, line 20a having an electrical conductivity of approximately 58.1% IACS and with line 20b approximately 20% of the Mg2Si present in the alloy already in solid solution. A wrought rod of 6201 Aluminum Alloy frabricated by prior art methods requires approximately 5 seconds of heating by induction heating to attain similar characteristics.

EXAMPLE 11 To obtain a 6201 aluminum alloy wrought rod having 60% of the Mg2Si present in the alloy in solid solution, an electrical conductivity of 50% IACS and a solutionizing temperature of 900"F requires induction heating of the rod for a period of from about one (1) second to about 2.75 seconds, with the average heating time required to obtain these properties being approximately 1.75 seconds. To obtain a rod having the same characteristics using prior art processing methods would require heat treatment time of about 11.66 seconds.

This is can be seen from the comparisons of Examples I and II and from the multiplicity of other examples which can be demonstrated by a study of Fig. 2 that the method of the present invention is clearly superior to the prior art methods in terms of processing times. Not only is this method superior to prior art methods in terms of processing efficiency, the properties of the 6201 alloy wrought rod so produced are also superior to the properties of 6201 alloy rod produced by prior art methods. Exemplary of the superior properties of 6201 alloy rod produced by the present invention are the following: A. The cast bar may be removed from the casting wheel at a lower temperature and consequently high temperature cracking, piping and central microcracking of the cast bar is substantially reduced thereby producing a better quality wrought rod.

B. Rod produced by the method of the present invention is in a highly annealed state and consequently is easier to draw into wire.

C. Precipitation of Mg2Si occurs during artificial aging of the wire drawn from the rod with the results being a more finely divided and more evenly distributed precipitate.

D. Rod produced by prior art methods not drawn within about six days of casting and rolling becomes brittle, however, rod produced by the method of the present invention has been stored from seven to eight weeks before being drawn into wire without becoming brittle.

For the purpose of clarity, heat treatable aluminum alloys as used in this specification shall mean those aluminum alloys which contain alloying elements which have a high solid solubility in aluminum at high temperatures and low solid solubility in aluminum when cooled to room temperature.

These alloys harden by precipitation of a second phase during heat treatment and the alloying elements are kept in solution by rapid quenching from high temperatures.

For the purpose of clarity, wrought aluminum alloys as used in this specification shall mean those aluminum alloys which contain alloying elements which have low solid solubility in - aluminum at high temperatures as well as at low temperatures. These alloys normally harden by work hardening which is a hardening mechanism which operates during cold working of the alloy.

WHAT WE CLAIM IS:- 1. A method of continuously producing an aluminum base alloy rod containing from 0.2 to 1.3 weight percent silicon, 0.3 to 1.4 weight percent magnesium and the remainder essentially aluminum, comprising the steps of continuously casting molten metal of the foregoing composition in a continuous casting mold in a continuous cast bar and removing the bar from the mold at a temperature below 940"F, immediately rolling the bar in a rolling mill into continuous rod and removing the rod from the rolling mill at a temperature above 6500F, raising the temperature of the cast bar by passing the bar through a heater as the bar exits from the rolling mill in rod form, and therein raising its temperature to a temperature in the range of 700"F to 10509F, and continuously quenching the rod to a temperature below the temperature at which immediate substantial precipitation of alloying metals occur.

2. The method according to claim 1 characterised in that the molten metal is cooled in the mold to a temperature of 800"F to 9400F.

3. The method according to claim 1 or 2 characterised by coating soluble oil on the bar as it is rolled, said soluble oil being at a temperature of less than 200"F.

4. A method of continuously producing an aluminum base alloy rod, substantially as herein described with reference to the accompanying drawings.

5. An aluminum base alloy rod produced by the method claimed in any of the pre

Claims (1)

1. ceding claims.