WO2003066926A1

WO2003066926A1 - Method of manufacturing aluminum alloy sheet

Info

Publication number: WO2003066926A1
Application number: PCT/US2003/003754
Authority: WO
Inventors: Leland Lorentzen; David C. Peters
Original assignee: Nichols Aluminum
Priority date: 2002-02-08
Filing date: 2003-02-07
Publication date: 2003-08-14
Also published as: US20040007295A1; AU2003215101A1

Abstract

A method for manufacturing aluminum sheet stock that includes hot rolling an aluminum alloy feedstock to a final thickness and then back-annealing ( or stress relieving or stabilizing ) the hot rolled feedstock to provide an intermediate temper.

Description

METHOD OF MANUFACTURING ALUMINUM ALLOY SHEET

FIELD OF THE INVENTION The present invention relates generally to casting of aluminum alloys an specifically to a continuous casting process for producing intermediate tempered aluminum alloy sheet.

BACKGROUND Conventional manufacturing of flat rolled finish gauge stock has used batch processes, which generally include an extensive sequence of separate or discrete steps. In a typical direct chill casting process, a large ingot is cast and cooled to ambient temperature. The cooled ingot is stored for inventory management. When an ingot is needed for further processing, it is first treated to remove defects such as segregation, pits, folds, liquation and handling damage by machining its surfaces. This operation is called scalping. Once the ingot has surface defects removed, it is heated at a required temperature for several hours to ensure that the components of the alloy are uniformly and properly distributed throughout the metallurgical structure and thereafter cooled to a lower temperature for hot rolling. While it is still hot, the ingot is subjected to breakdown hot rolling in a number of passes using reversing or non-reversing mill stands that serve to reduce the thickness of the ingot. After breakdown hot rolling, the ingot is typically supplied to a tandem mill for hot finishing rolling, after which the sheet stock is coiled and the roll air cooled and stored. The roll is then typically batch annealed. The coiled stock is then finished reduced to final gauge by cold rolling using unwinders, rewinders and single and/or tandem rolling mills. After the coiled stock is at final gauge, the roll is back-annealed (also called stress-relieved or stabilized) in a batch process. Batch processes typically used in the aluminum industry require about seventeen different material handling operations to move ingots and coils between what are typically fourteen separate processing steps. Such operations are labor intensive, consume energy, and frequently result in product damage, reworking of the aluminum and even wholesale scrapping of product. And, of course, maintaining ingots and coils in inventory also adds to the manufacturing cost.

Aluminum scrap is generated in most of the foregoing steps, in the form of scalping chips, end crops, edge trim, scrapped ingots and scrapped coils. Aggregate losses through such batch processes typically range from 25 to 40%. Reprocessing the scrap thus generated adds 25 to 40% to the labor and energy consumption costs of the overall manufacturing process.

It has been proposed, as described in U.S. Pat. Nos. 4,260,419 and 4,282,044, to produce aluminum alloy can stock by a minimill process which uses direct chill casting or minimal continuous strip casting. In the minimill process, consumer aluminum can scrap is remelted and treated to adjust its composition. In one process configuration, molten metal is direct chill cast followed by scalping to eliminate surface defects from the ingot. The ingot is then preheated, subjected to hot breakdown followed by continuous hot rolling, batch annealing and cold rolling to form the sheet stock. In another process configuration, the casting is performed by continuous strip casting followed by hot rolling, coiling and cooling. Thereafter, the strip is annealed and cold rolled. The minimill process as described above requires about ten material handling operations to move ingots and coils between about nine process steps. Like other conventional processes described earlier, such operations are labor intensive, consume energy and frequently result in product damage. Scrap is generated in the rolling operations resulting in typical losses throughout the process of about 10 to 15%. hi the minimill process, annealing is typically carried out in a batchwise fashion with the aluminum in coil form. Although a common practice in producing aluminum alloy flat rolled products has been to employ slow air cooling of coils after hot rolling (because the hot rolling temperature is high enough to allow complete or near complete recrystallization of the hot coils before the aluminum cools down), a furnace coil batch anneal must sometimes be used to effect complete or near complete recrystallization before cold rolling. Batch coil annealing, as typically employed in the prior art, requires several hours of uniform heating and soaking to achieve the anneal temperature. Alternatively, after breakdown cold rolling, prior art processes frequently employ an intermediate annealing operation prior to finish cold rolling to effect complete or near complete recrystallization. During slow cooling of the coils following annealing, some alloying elements, which had previously been dissolved in the aluminum matrix, precipitate, resulting in reduced strength attributable to solid solution hardening. Although U.S. Patents, 4,260,419 and 4,282,044 employ batch coil annealing, they suggest the concept of flash or continuous annealing in a separate processing line. In the separate processing line, the alloy is slowly cooled after hot rolling and then reheated as part of the flash annealing process. There is thus a need to provide a continuous, in-line process for producing aluminum alloy sheet, which avoids the unfavorable economics embodied in conventional processes of the type described above.

SUMMARY OF THE INVENTION

These and other needs are addressed by the various embodiments and configurations of the present invention. The present invention is directed generally to the use of hot rolling and back annealing or in-line self-back-annealing during or after hot rolling to produce a desired intermediate temper aluminum alloy product. In one embodiment, the present invention provides a method for manufacturing of aluminum sheet stock. The method includes the steps of:

(a) casting an aluminum alloy feedstock from an aluminum alloy melt;

(b) hot rolling the aluminum alloy feedstock to a finished (or final) gauge to form a hot rolled feedstock; and (c) back-annealing at least one of the aluminum alloy feedstock and hot rolled feedstock to provide a desired intermediate temper. As used herein, "finished gauge" refers to the gauge selected for the aluminum alloy sheet product of the process, "hot rolling" refers to reducing the gauge of feedstock at a temperature of 400° F or greater, "cold rolling" to reducing the gauge of feedstock at a temperature of less than 400° F, "back annealing" to thermally induced softening of an aluminum alloy to produce at least substantially uniform, desired mechanical properties, typically meeting Aluminum Association limits. An "intermediate temper" provides a metal with mechanical properties elevated from those typical at a dead soft temper, and includes all tempers in between O and Hx9. Other terms used in the industry to refer to back annealing include "stress-relieving" and "stabilizing". In one process configuration, the back-annealed feedstock is immediately coiled and allowed cool to a temperature suitable for finishing operations such as leveling, slitting or painting.

The feedstock can be formed by any casting technique, such as continuous or direct chill casting. As will be appreciated, in continuous castmg the feedstock is formed by depositing molten aluminum alloy on an endless belt formed of a heat conductive material. The molten metal solidifies to form a cast strip. In the hot rolling step, the feedstock is rolled to a finish gauge. In one configuration, the hot rolled feedstock is free of cold rolling after the hot rolling step. No further reductions in gauge are generally required. Depending on the input gauge and the desired output gauge, the hot rolling step typically reduces the thickness of the aluminum alloy feedstock by from about 40 to about 99%.

In the back annealing step, the aluminum alloy feedstock and/or hot rolled feedstock is preferably only partially recrystallized. In a preferred configuration, the back-annealing step is performed by in-line heating of the hot rolled feedstock. In another configuration, back-annealing is performed during hot rolling. Back-annealing times, as referred to herein, define the total time required to heat up the material to a desired temperature and complete back-annealing.

In back annealing, the feedstock is preferably not fully annealed. In other words, the feedstock is not fully recrystallized. Typically, the degree of recrystallization of the feedstock is no more than about 60%. In many cases, the back annealed feedstock is free or substantially free (less than about 5% recrystallized) of recrystallization. To accomplish this result, back annealing is typically performed at a temperature within the range of about 700 to about 1000°F. This temperature range is generally at or above the exit temperature of the hot rolled feedstock from the hot rolling step.

In a preferred process configuration, casting, hot rolling and back-annealing are combined in one continuous in-line operation for the production of aluminum alloy sheet stock. The term "flash annealing", as used herein, refers to an amieal that employs rapid heating of a moving strip as opposed to slowly heating a coil. The continuous operation in place of batch processing facilitates precise control of process conditions and therefore metallurgical properties. Moreover, carrying out the process steps continuously and in-line can eliminate costly materials handling steps, in-process inventory and thermal and material losses associated with starting and stopping the processes. Compared to conventional batch processes, the process of the present invention can be operated more economically to provide a product having equivalent, or superior metallurgical properties. By way of example, the batch processing technique involves fourteen separate steps while the minimill prior art processing involves about nine separate steps, each with one or more handling operations in between. In the in-line processing configuration, the present invention differs from the prior art by virtue of in-line flow of product through the fabrication operations (thereby allowing fewer separate steps) and the metallurgical differences that the in-line method is capable of producing.

These and other advantages will be apparent from the disclosure of the invention(s) contained herein.

The above-described embodiments and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a comparative plot of in-process thickness versus time for a conventional minimill versus an in-line or continuous process embodiment of the present inventions;

Fig. 2 is a comparative plot of temperature versus time for the in-line process embodiment of the present invention compared to two prior art processes;

Fig. 3 is a plot of the in-process temperature for the in-line process embodiment of the present invention;

Fig. 4 is a flow chart of the in-line process embodiment of the present invention; and Fig. 5 is a schematic illustration of the in-line plant configuration according to the present invention with casting throughout finish rolling at the hot mill.

DETAILED DESCRIPTION OF THE INVENTION Generally, the various processes of the present invention (which are referred to collectively as the "megamill process") hot roll to finish gauge and back anneal the fully hot rolled sheet, as necessary, to produce a desired intermediate temper. As used herein, a "back anneal" is conducted under conditions of time and temperature sufficient to soften, but not completely recrystallize, the hot rolled sheet to the desired temper. The back anneal is typically conducted at a temperature that is less than the recrystallization temperature for the particular alloy being treated. The sheet may be cast by any suitable technique, such as direct chill casting, electromagnetic casting, and continuous strip casting. The back anneal can be batch or continuous, with a continuous (or in line) back anneal being preferred. A process embodiment of the present invention will now be discussed with reference to Figures 4 and 5.

In step 400, an aluminum-containing material is melted in a furnace (not shown) to form molten metal 500. The molten metal is transferred from the furnace to a metal degassing and filtering device (not shown) to reduce dissolved gases and particulate matter from the molten metal. step 404, the degassed and filtered molten metal is cast to form cast feedstock 504. As used herein, the term "feedstock" refers to any of a variety of aluminum alloys in the form of ingots, plates, slabs and strips, delivered to the hot rolling step 408 at a desired temperature. An aluminum "ingot" typically has a thickness typically ranging from about 6 inches to about 36 inches. An aluminum "plate," on the other hand, herein typically refers to an aluminum alloy having a thickness from about 0.5 inches to about 6 inches. A "strip" refers to an aluminum alloy having a thickness ranging from about 0.375 inches to about 3 inches (which range overlaps with an aluminum plate). A "sheet" refers to an aluminum alloy in sheet form, typically having a thickness less than about 0.375 inches.

Ingots, slabs, plates, strips, and sheets are generally produced by direct chill casting, electromagnetic casting, or combinations thereof. Preferably, slabs and strips are produced by continuous casting techniques well known to those skilled in the art. Continuous casting can be effected by any suitable continuous casting device, such as a twin belt caster like those described in U.S. Patents 3,937,270; 5,363,902; 5,515,908; 5,564,491; and 6,102,102 (each of which is incorporated herein by reference), a drum caster like those described in U.S. Patents 5,616,190 or 4,411,707 (each of which is incorporated herein by reference); or a block caster like those described in U.S. Patent 5,469,912 (which is incorporated herein by reference). A continuous strip casting technique, which can be used in step 404, is illustrated in

Fig. 5. The casting apparatus includes a pair of endless belts 508a,b, carried by a pair of upper pulleys 512a,b, and a pair of corresponding lower pulleys 516a,b. Each pulley 512a,b and 516a,b is mounted for rotation and is a suitable heat resistant pulley, Either or both of the upper pulleys 512a,b are driven by suitable motor means or like driving means not illustrated in the drawing for purposes of simplicity, The same is true for the lower pulleys 516a,b. Each of the belts 508a,b is an endless belt and is preferably formed of a metal that has low reactivity with the aluminum being cast. Stainless steel or copper is frequently preferred materials for use in the endless belts. The pulleys 512a,b and 516a,b are positioned, as illustrated in Fig. 5, one above the other with a molding gap therebetween corresponding to the desired thickness of the aluminum strip 504 being cast. Degassed and filtered Molten metal 500 to be cast is supplied to the molding gap through suitable metal supply means such as tundish 520. The inside of the tundish 520 corresponds substantially in width to the width of the belts 508a,b and includes a metal supply delivery casting nozzle 524 to deliver molten metal 528 to the molding gap between the belts 508a,b. The casting apparatus also includes a pair of cooling devices 532a-d positioned opposite that position of the endless belt in contact with the metal being cast in the molding gap between the belts. The cooling devices 532a-d cool the belts 508a,b, respectively, while they are in contact with the molten metal, h the preferred embodiment illustrated in Fig. 5, the cooling devices 532a-d are positioned as shown relative to the belts 508a,b, respectively, In that embodiment, the cooling devices 532a-d can be conventional cooling devices such as fluid nozzles positioned to spray a cooling fluid directly on the inside of belts 508a,b to cool the belts through their thicknesses.

The feedstock 504 from between the belts 508a,b is moved through optional pinch rolls 536a,b into hot rolling stands 540a-c, each including a pair of hot rolls 544a,b, where the thickness of the feedstock is progressively decreased. After exiting from the caster and pinch rolls, the feedstock has a thickness typically ranging from about 0.5 to about 1.5 inches, more typically from about 0.6 to about 1 inch, and even more typically from about 0.65 to about 0.80 inches and a temperature above the solvus temperature and below the eutectic melting point and solidus temperature of the alloy, typically ranging from about 700 to about 1160°F, and even more typically ranging from about 750 to about 1050°F. As will be appreciated, to provide a desired input temperature into the first hot rolling stand the cast feedstock 504 can be heated, preferably by a continuous or in line heater such as a solenoidal flux heater, after exit from the caster and before hot rolling as disclosed in U.S. Patents 5,985,058, 5,993,573, 5,976,279, and 6,290,785, each of which is incorporated herein by this reference. In the hot rolling stands 540a-c and in step 408, the cast feedstock 504 is reduced from the cast output gauge to a desired finish gauge. As will be appreciated by those skilled in the art the extent of the reductions in thickness effected by the hot rolling step 408 are subject to a wide variation, depending upon the types of alloys employed, their chemistry and the manner in which they are produced. For that reason, the percentage reduction in thickness of the hot rolling operation of the invention is not critical to the practice of the invention. However, for a specific product, known practices for reductions and temperatures must be used. Overall, the thickness of the cast feedstock is typically reduced by at least about 40%, more typically at least about 50%, and even more typically in the range of about 65% to about 99%. The gauge of the hot rolled feedstock 548 output from the last hot rolling stand 540c typically is no more than about 0.300 inches, more typically no more than about 0.200 inches, and even more typically ranges from about 0.180 to about 0.040 inches. In the multiple stand configuration in Figure 5, in the first stand 540 a the thickness is preferably reduced by from about 30% to about 70% to produce an output gauge of from about 0.200 to about 0.400 inches, in the second stand 540b the thickness is preferably reduced by from about 30% to about 70% to produce an output gauge of from about 0.075 to about 0.250 inches, and in the third and final stand 540c the thickness is preferably reduced by from about 30%) to about 70% to produce the output gauge noted previously. The output temperature of the (fully) hot rolled feedstock typically is at least about 250 °F and even more typically ranges from about 300 to about 1 ,000 °F. It is to be understood that the number of hot rolling stands illustrated in Fig. 5 is not limiting. As will be appreciated, the number of hot mill stands used in hot rolling step 408 will vary depending on the input cast feedstock gauge and the output (fully) hot rolled feedstock gauge or finish gauge desired.

The hot rolled feedstock 548 exits the last hot rolling stand 540c and is inputted into heater 552 for back annealing. The heater 552 is any suitable heating device, such as a transflux induction heater, a gas fired heater, an oil fired heater, and an electric furnace, that has the capability of heating the hot rolled feedstock 548 to a temperature sufficient to back-anneal the feedstock 548. Although the heater can be batch or continuous, a continuous heater is preferred. Preferably, the feedstock 548 is immediately passed to the heater 552 for back-annealing while the feedstock 548 is still at or near the output temperature from the last hot rolling stand 540c. The average temperature of the hot rolled feedstock 548 when the feedstock is inputted into the heater is maintained preferably at a temperature of no less than about 50 °F, more preferably no less than about 25 °F, and even more preferably no less than about 0 °F less than the output temperature from the last hot rolling stand 540c. The average temperature of the hot rolled feedstock 548 when the feedstock is inputted into the heater is typically at least about 400 °F, more typically at least about 425 °F, and even more typically ranges from about 450 to about 550 °F. hi contrast to the prior art teaching that slow cooling following hot rolling is metallurgically desirable, it has been discovered in accordance with the present invention that it is more efficient to heat the feedstock 548 immediately after hot rolling to effect annealing. In addition, the heating provided by heater 552 without intermediate cooling provides much improved metallurgical properties (grain size and formality) over conventional batch annealing and equal or better metallurgical properties compared to off-line flash annealing.

The process variables used in the back annealing step depend, of course, on the alloy and temper desired. Table I provides a listing of alloys by family and their respective chemical compositions.

TABLE 1 Table of Chemical Composition for Alloys

Although the concepts of the present invention are particularly applicable alloys from the 1000, 3000, 5000, 7000 and 8000 series, it is to be understood that the concepts are equally applicable to other aluminum alloys and/or alloys used in a wide variety of products. As will be appreciated, other alloys than those listed above can be treated by the process of the present invention to realize a desired intermediate temper.

Table JT provides a listing of specific alloys within the alloy families of Table I and provides, for each alloy and temper, the approximate feedstock thickness, the approximate ultimate tensile strength, the approximate yield strength, the approximate elongation percent (minimum in 2 inch or 4 inches in diameter), the approximate back anneal temperature range, and the approximate maximum percent recrystallization realized during back annealing. As will be appreciated, in a continuous back anneal the feedstock preferably has a residence time of no more than about 120 seconds, more preferably no more than about 30 seconds, and even more preferably from about 1 to about 10 seconds and in a batch back anneal the feedstock has a residence time of more than about 8 hours, more preferably no more than about 5 hours, and even more preferably from about 1 to about 3 hours. Generally, the back anneal temperature range is from about 600 to about 1 ,000 °F, more generally from about 700 to about 950 °F, and even more generally from about 700 to about 900 °F.

TABLE II

Process Parameters for Intermediate Tempers For (XXX, 3XXX, and 5XXX Alloys)

A number of observations are important in understanding Table H For the H2 Temper corresponding to various of the alloys listed above, limits for maximum ultimate tensile strength and minimum yield strength do not apply. The table specifies the properties applicable to the test specimens, and, since for plate 0.0500 inch or greater in thickness, the cladding material is removed during the preparation of the test specimens. The listed properties are therefore applicable to the core material only. Tensile and yield strengths of the composite plate are slightly lower depending on the thickness of the cladding. With reference to the "4D" appearing in the elongation column, "D" represents the specimen diameter. Processes such as flattening, leveling, or straightening coiled products subsequent to shipment by the manufacturer may alter the mechanical properties of the metal.

In the back anneal, the time and temperature of the anneal are selected such that the alloy is not completely recrystallized. Preferably, the maximum recrystallization is no more than about 60%. Thus, the back am eal is conducted at a maximum temperature below the recrystallization temperature of the particular alloy. After back annealing, the annealed feedstock 556 is coiled on a coiler 560 to form a roll.

As will be appreciated by those skilled in the art, it is possible to realize the benefits of the present invention in providing intermediate tempers by eliminating the cold rolling and batch thermal operations dictated in the conventional manufacturing processes. In other words, in a preferred embodiment there is no further thickness reduction of the hot rolled feedstock 548, such as by cold rolling, after hot rolling and no further heat treatment of the annealed feedstock 556 after back annealing.

It is possible, and sometimes desirable, to employ appropriate automatic control apparatus; for example, it is frequently desirable to employ a temperature measuring device (not shown) in the heater 552 for metal temperature monitoring, a surface inspection device 564 for in-line monitoring of surface quality, and athickness measurement device 568 (which measures the output gauge of the fully hot rolled feedstock 548), conventionally used in the aluminum industry can be employed in a feedback loop for control of the process.

Preferably, back-annealing immediately follows hot rolling of the feedstock 504 to final thickness. "Immediately following" means that the time for a selected section of the feedstock to move from the last hot rolling stand 540c to the opening of the heater 552 is no more than about 60 seconds, more preferably no more than about 15 seconds, and even more preferably no more than about 10 seconds.

The sequence and timing of process steps-in combination with, the back-annealing operation can provide equivalent or superior metallurgical characteristics in the final product. In the prior art, the industry has normally employed slow air cooling after hot rolling. Only on some occasions are the hot rolling temperatures sufficient to allow annealing of the aluminum alloy before the metal cools down. It is common that the hot rolling temperature is not high enough to control back-annealing. In that event, the prior art employed separate batch thermal steps before and/or after cold rolling in which the coil is placed in a furnace or heater maintained at a temperature sufficient to cause recrystallization or final mechanical properties. The use of such furnace batch thermal operations represents a significant disadvantage. Such batch thermal operations require that the coil be heated for several hours at the correct temperature, after which such coils are typically cooled under ambient conditions. In contrast, the process of the present invention achieves final mechanical properties of the final product. The use of the heater 552 allows the hot rolling temperature to be controlled independently from the back-annealing temperature. That in turn allows the use of hot rolling conditions that can maximize surface finish and texture (grain orientation). In the practice of the invention, the temperature of the feedstock 548 in the heater 552 can be elevated above the hot rolling temperature (or output temperature of the hot rolled feedstock 548) without the intermediate cooling suggested by the prior art. In that way mechanical properties can be effected rapidly, typically in less than about 30 seconds, and preferably in less than about 10 seconds for a continuous or in line back anneal. In addition, by avoiding an intermediate cooling step, the back-annealing operation consumes less energy since the alloy is already at an elevated temperature leaving the final hot rolling stand 540c.

An advantage of the present invention arises from the fact that the preferred embodiment utilizes, as the finished gauge, a final hot rolling exit gauge rather than a cold rolling gauge as normally employed in the prior art. As a consequence, the method of the invention obviates the need to employ breakdown cold rolling- prior to back-annealing. In addition, the method of the present invention has, as a further advantage, the ability to produce a finished product where desired without the cold rolling step. These advantages are illustrated graphically by Figures 1-3.

Figure 1 shows the thickness of intermediate and final feedstock (vertical axis) versus processing days (horizontal axis) during manufacture for both the minimill and the megamill processes. The minimill process starts at about 0.75-inch thickness and takes 9 days. The megamill process starts at about 0.750-inch thickness and takes 4 days (most of which is 1 day for the melting cycle and two days for coil cooling). The individual vertical bars in Fig.

1 represent major processing and/or handling steps for the corresponding identified process.

Figure 2 compares typical in-process feedstock temperatures (vertical axis) versus processing time (horizontal axis) for three methods of producing common alloy stock, namely a direct chill casting process, the minimill process, and the megamill process, h the conventional ingot or DC casting process, there is a period for melting followed by a rapid cool during casting with a slow cool to room temperature thereafter. Once the scalping process is complete, the ingot is heated to a homogenization temperature before hot rolling. After hot rolling, the product is again cooled to room temperature. At this point, it is assumed in Figure 2 that the hot rolling temperature and slow cool were sufficient to anneal the product. However, in some cases, abatch anneal step of about 600°F is needed at about day 8 that extends the total process schedule an additional two days. The last temperature increase is associated with cold rolling. The cold rolled feedstock is then allowed to cool to room temperature. In the minimill process, there is again a period by melting, followed by rapid cooling during slab casting and hot rolling, with a slow cool to room temperature thereafter. Temperature is raised slightly by cold rolling and the cold-rolled feedstock is allowed to cool again slowly before being heated for back-annealing. After back-annealing, the cold rolled feedstock is cooled slowed to room temperature. In the megamill process of the present invention, there is a period for melting, followed by a rapid cool during strip casting. The cast strip is then hot rolled to final thickness . The in-line back-anneal step raises the temperature, and the hot rolled feedstock is immediately allowed to cool to room temperature. As can be seen from Fig. 2, the present invention differs substantially from the prior art in duration, frequency and rate of heating and cooling. As will be appreciated by those skilled in the art, these differences represent a significant departure from prior art practices for manufacturing aluminum common alloy sheet. Figure 3 plots feedstock temperature (vertical axis) against process step (vertical axis). The steps are melting, casting, hot rolling, back-annealing, and cooling. As can be seen from Figure 3, the feedstock temperature only drops below about 400 °F after the back- annealing step. This figure shows the high degree of thermal efficiency of the megamill process.

A number of variations and modifications of the invention can be used. It would be possible to provide for some features of the invention without providing others.

For example, in some applications the hot rolling temperature can be high enough to allow in-line self-back-annealing without the need for imparting additional heat to the hot rolled feedstock 548 by means of the heater 552 to raise the feedstock temperature. In that embodiment of the invention, it is unnecessary to employ the heater 552; the hot rolled feedstock 548 exiting the hot rolling stands 540 a-c is then coiled by means of coiler 560, with the same metallurgical properties as realized by the process configuration of Figure 5.

Referring again to Figure 4, the back-annealed feedstock can be subjected to further processing 412, depending on the desired end product. For example, the feedstock can be subjected to leveling 416, slitting 420, painting 428, or shearing to desired lengths.

Alternatively, the feedstock can be coiled and cooled to form coil sheet stock 424. As shown by step 432, other processing can be performed depending on the product.

The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention.

Moreover though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent pennitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.

Claims

What is claimed is:

1. A method for manufacturing of aluminum sheet stock, comprising: casting an aluminum alloy feedstock from an aluminum alloy melt; hot rolling the aluminum alloy feedstock to a finished gauge to form a hot rolled feedstock; and back-annealing at least one of the aluminum alloy feedstock and hot rolled feedstock to provide a desired intermediate temper.

2. A method as claimed in Claim 1, wherein the feedstock is formed by continuous strip or slab casting.

3. A method as claimed in Claim 1, wherein the feedstock is formed by depositing molten aluminum alloy on an endless belt formed of a heat conductive material whereby the molten metal solidifies to form a cast strip, and a portion of the endless bolt is cooled when the portion is not in contact with the metal.

4. A method as claimed in Claim 1, wherein, in the back annealing step, the at least one of the aluminum alloy feedstock and hot rolled feedstock is only partially recrystallized.

5. A method as claimed in Claim 1, wherein the hot rolled feedstock is free of cold rolling after the hot rolling step.

6. A method as claimed in Claim 1, wherein the hot rolling step reduces the thickness of the aluminum alloy feedstock by from about 40 to about 99%.

7. A method as claimed in Claim 1 , wherein the back-annealing step comprises the step of: in-line heating of the hot rolled feedstock to a temperature above the output temperature from the hot rolling step.

8. A method as claimed in Claim 1, wherein the back annealing step occurs at least one of during and immediately after hot rolling.

9. A method as claimed in Claim 1, wherein, in the back annealing step, the recrystallization of the at least one of the aluminum alloy feedstock and hot rolled feedstock is no more than about 60%.

10. A method as claimed in Claim 7, wherein, in the back annealing step, the hot rolled feedstock is heated to a temperature within the range of about 600 to about 900 °F.

11. A method as claimed in Claim 1 , wherein, in the back annealing step, the at least one of the aluminum alloy feedstock and hot rolled feedstock is heated to a temperature within the range of about 700 degree to about 1000°F.

12. A method as defined in Claim 1 wherein the exit temperature of the hot rolled feedstock from the hot rolling step ranges from about 300 to about 1000°F.

13. A method as claimed in Claim 1, wherein the residence time of a selected portion of the hot rolled strip in the back-annealing step is no more than about 120 seconds.

14. A method as claimed in Claim 13 , wherein the residence time is no more than about 10 seconds.

15. A method for manufacturing aluminum alloy sheet comprising the following steps in continuous, in-line sequence:

(a) continuously casting an aluminum alloy melt to form an aluminum alloy feedstock;

(b) hot rolling the aluminum alloy feedstock to form a hot rolled feedstock having an output temperature, wherein a thickness of the hot rolled feedstock is less than a thickness of the aluminum alloy feedstock;

(c) maintaining the temperature of the hot rolled feedstock at no less than about 50 °F less than the output temperature of the hot rolled feedstock; and

(d) heating the hot rolled feedstock to a temperature sufficient to back-anneal said hot rolled feedstock to form back-annealed feedstock, wherein a degree of recrystallization of the back-annealed feedstock after the back annealing step is no more than about 60%.

16. A method as claimed in Claim 15, wherein the hot rolled feedstock is free of quenching and cold rolling.

17. A method as claimed in Claim 15 , wherein the back annealed-feedstock is free of further annealing.

18. A method as claimed in Claim 15, wherein the hot rolled feedstock is at finished gauge.

19. A method as claimed in Claim 15, wherein the back-annealed feedstock has an intermediate temper.

20. A method as claimed in Claim 15, wherein the aluminum alloy feedstock is one of a IXXX, 3XXX, 5XXX, 7XXX, and 8XXX alloy.

21. A method for manufacturing aluminum shoot stock comprising the following steps in a continuous, in-line sequence:

(a) one of strip and slab casting an aluminum alloy on at least one endless belt to form an aluminum alloy strip; (b) hot rolling said strip to form a hot rolled strip having a thickness less than a thickness of the aluminum alloy strip; and

(c) immediately after hot rolling, heat treating said hot rolled strip at a temperature sufficient to provide a heat treated strip having an intermediate temper.

22. A method as claimed in Claim 21, wherein the hot rolled strip is free of quenching and cold rolling.

23. A method as claimed in Claim 21, wherein the heat treated strip is free of further annealing.

24. A method as claimed in Claim 21, wherein the hot rolled strip is at finished gauge after hot rolling is completed.

25. A method as claimed in Claim 21, wherein the back-annealed strip has an intermediate temper.

26. A method as claimed in Claim 21, wherein the aluminum alloy is one of a IXXX, 3XXX, 5XXX, 7XXX, and 8XXX alloy.

27. A method for manufacturing aluminum sheet stock comprising: (a) continuously casting an aluminum alloy by depositing a molten alloy on at least one endless belt formed of a heat conductive material, whereby the molten metal solidifies on said belt to form a cast strip;

(b) hot rolling said cast strip to form a hot rolled strip having a thickness less than a thickness of the cast strip, wherein the hot rolled strip thickness is at finish gauge; and (c) heat treating at least one of the cast strip and hot rolled strip to provide an intermediate temper to the at least one of the cast strip and hot rolled strip.

28. A method as claimed in Claim 27, wherein the steps are performed in a continuous, in-line sequence.