US20040035505A1

US20040035505A1 - Pie plate sheet and method of manufacturing

Info

Publication number: US20040035505A1
Application number: US10/226,458
Authority: US
Inventors: Ali Unal; David Tomes
Original assignee: Alcoa Inc
Current assignee: Howmet Aerospace Inc
Priority date: 2002-08-23
Filing date: 2002-08-23
Publication date: 2004-02-26

Abstract

A monolithic container having a bottom wall, a sidewall interconnected to the bottom wall and extending upwardly and outwardly therefrom to define an open end of the monolithic container at an upper edge of the sidewall, the sidewall having a peripheral flange extending outwardly from the upper edge. The monolithic container formed from an aluminum alloy feedstock comprising: from about 0.05 to 0.55% by weight silicon, from 0.10 to about 0.50% by weight iron, from less than about 0.60% by weight copper, from about less than about 0.4% by weight manganese, from about 0.9 to about 1.8% by weight magnesium, with the balance being aluminum and impurities.

The aluminum alloy feed stock used to form the container has a gauge of less than about 0.008 inch.

Description

BACKGROUND OF THE INVENTION

The present invention relates to open-ended food containers such as pie plates and methods for manufacturing aluminum alloy sheet for use in such open-ended food containers. More particularly, the present invention relates to such open-ended food containers that are designed to be reusable or used on a premium product.

PRIOR ART

It is now conventional to manufacture open-ended aluminum food containers, such as plates and pans, from sheet stock. The sheet is first blanked into a circular configuration and stamped or pressed to form the final shape. The open-food container industry is continuously striving to reduce costs by developing an increasingly lighter weight container through reduced metal gauge in order to save costs through the use of less metal.

In the disposable container market, the strength of the container is increased by forming ribs of varying sizes and designs in the bottom panel and sides of a container. In addition, controlled wrinkles or folds are formed into the bottom panel, the side walls and the rim to increase the strength of the container. A common aluminum alloy that has been used in the art is Aluminum Association 3004.

However for some applications, the containers are manufactured for repeated use. For these applications, it is highly desirable that the containers have smooth surfaces that are relatively free of wrinkles, ribs or folds. For these applications, there is a need to provide an aluminum alloy stock that is stronger than 3004. Stronger alloys can be made into a thinner sheet than 3004 while still having the same rigidity and structural strength as a higher gauge 3004 sheet material.

For applications that require a smooth surface, there is also a need to provide a process for producing a higher strength aluminum alloy open-ended food container stock. Such a process would need to be simple enough that the processing costs do not defeat the favorable economics associated with reduction of the metal gauge.

It is accordingly an object of the present invention to provide a smooth-walled open-ended food container that is formed from a thinner gauge metal than conventional alloys.

It is another object of this invention to provide a process for producing a thinner gauge aluminum alloy stock for used in an open-ended food container that has the same rigidity and structural strength as conventional 3004/3005 stock but is thinner in metal gauge.

It is a more specific object of the invention to provide a process for commercially producing a aluminum alloy open-ended food container stock in a continuous process which can be operated economically and provide a product having equivalent or better metallurgical properties needed for making smooth-walled plates and pans.

These and other objects and advantages of the invention appear more fully hereinafter from a detailed description of the invention.

SUMMARY OF THE INVENTION

The aluminum alloy feed stock used to form the container has a gauge of less than about 0.009 inch.

Another embodiment of the invention is a method of manufacturing of aluminum alloy open-ended food container. The method comprising: (a) manufacturing food container stock in a a continuous in-line sequence, the manufacturing comprising: (1) providing an aluminum alloy feedstock from a composition comprising: from about 0.05 to 0.55% by weight silicon, from 0.10 to about 0.50% by weight iron, from less than about 0.60% by weight copper, from about less than about 0.4% by weight manganese, from about 0.9 to about 1.8% by weight magnesium, with the balance being aluminum and impurities; (2) hot rolling the aluminum alloy feedstock to hot reduce its thickness; (3) annealing and solution heat treating the hot reduced feedstock without intermediate cooling while maintaining the temperature of the hot reduced feedstock for a time and level sufficient to retain alloying elements in solution; and (4) rapidly quenching the heat treated feedstock to a temperature for cold rolling. The heat-treated feedstock is then shaped into an open-ended food container. Preferably, the open-ended food container has smooth walls.

Another embodiment of the invention is a method of manufacturing of aluminum alloy open-ended food container. The method comprising: (a) manufacturing food container stock in a a continuous in-line sequence, the manufacturing comprising: (1) providing an aluminum alloy feedstock from a composition comprising: from about 0.05 to 0.55% by weight silicon, from 0.10 to about 0.50% by weight iron, from less than about 0.60% by weight copper, from about less than about 0.4% by weight manganese, from about 0.9 to about 1.8% by weight magnesium, with the balance being aluminum and impurities; (2) hot rolling and/or warm rolling the aluminum alloy feedstock to hot reduce its thickness in such a manner as to retain alloying elements in solid solution; (3) annealing and solution heat treating the hot reduced feedstock without intermediate cooling while maintaining the temperature of the hot reduced feedstock for a time and level sufficient to retain alloying elements in solution; and (4) rapidly quenching the heat treated feedstock to a temperature for cold rolling. The heat-treated feedstock is then shaped into an open-ended food container. Preferably, the open-ended food container has smooth walls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a pie plate of the present invention. [0014]
FIG. 2 is a flow chart showing the processing steps used to make the open-ended food container of the present invention. [0015]

DEFINITIONS

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 at the required temperatures. [0016]
The term “plate” as used herein is intended to mean metallic sheet products that are commonly used for culinary purposes. Typically, culinary plate will be a rolled product having a length that is much greater than its thickness or width. Pie plate, cookie sheet and pizza plate are examples of such plate products and they typically have a thickness from about 0.5 inches to about 6 inches, and is typically produced by direct chill casting or electromagnetic casting alone or in combination with hot rolling of an aluminum alloy. [0017]
The term “slab” is used herein to refer to an aluminum alloy having a thickness ranging from 0.375 inches to about 3 inches, and thus overlaps with an aluminum plate. [0018]
The term “pan” as used herein is intended to mean metallic sheet products. Typically plans will be a rolled product having a length that is much than its thickness or width. The term as used herein is intended to include culinary pans products, such as pie pans, cake pans, roasting pans, loaf pans, basting pans and non-culinary pans such as oil pans, litter pan and the like. The terms pan and plate are used interchangeably herein to refer to the same products. [0019]
The term “sheet” as used broadly herein is intended to embrace gauges sometimes referred to as “plate” as well as gauges intermediate to plate and foil, including those higher than 0.006 inch (typically “sheet) and thus overlaps with slab. [0020]
The term “slab” is used herein to refer to an aluminum alloy having a thickness ranging from 0.375 inches to about 3 inches, and thus overlaps with an aluminum plate. [0021]
The term “smooth walled” as used herein is intended to mean having a wall that is relatively free of intentional formed wrinkles, ribs or folds. [0022]
The term “solution heat treat” is used herein to mean that the alloy is heated and maintained at a temperature sufficient to dissolve soluble constituents into solid solution where they are retained in a supersaturated state after quenching. [0023]
The term “rapidly quench” is used herein to mean cool the material at a rate sufficient that substantially all of the soluble constituents, which were dissolved into solution during solution heat treatment, are retained in a supersaturated state after quenching. [0024]
The term “anneal” is used herein to mean a heating process that causes recrystallization of the metal to occur, producing uniform formability and assisting in earing control. Annealing time as referred to defines the total time required to heat up the material and complete the annealing. Furthermore, the term “flash annealing” as used herein refers to an annealing treatment or solution heat treatment that employs rapid heating of a strip as opposed to a slowly heating. [0025]

DETAILED DESCRIPTION OF THE INVENTION

The overall appearance of pie plate is similar to a conventional reusable pie plate having smooth walls and a heavier gauge wall thickness. The relatively wrinkle surfaces of [0026] pie plate 10 makes it easily distinguishable from disposable foil pie plates. Such disposable pie plates are designed for single use and are concerned to be lower quality pie plates.
Surprisingly, by following the teachings of this invention, an improved an improved [0027] pie plate 10 can be formed of from sheet of a new alloy sheet having a thickness of 0.008 or less. The new alloy composition comprises from about 0.05 to 0.55% by weight silicon, from 0.10 to about 0.50% by weight iron, from less than about 0.60% by weight copper, from about less than about 0.4% by weight manganese, from about 0.9 to about 1.8% by weight magnesium, with the balance being aluminum and impurities. Preferably, the levels of chromium, nickel and zinc are each kept below 0.05 wt. %.
Turing first to FIG. 1, there is illustrated a [0028] monolithic pie plate 10 having a bottom wall 12, a sidewall 14 and a rim or flange 16. Pie Plate 10 is formed of an aluminum alloy sheet by suitable shaping techniques such as by drawing or stamping. The gauge of the aluminum metal sheet used to form pie plate 10 is 0.008 inch or less. A thickness has low as 0.007 inch has been found to produce an acceptable product.
[0029] Sidewall 14 is outwardly slanting from the substantial flat bottom wall 12. Sidewall 14 is relatively free of wrinkles, ribs or folds that are commonly designed into a disposable pie container to provide strength. Thus sidewall 14 obtains its strength primarily from the metal thickness and composition of the metal. The thermal processing of the metal is less important if the metal is provided in an O-temper.
The [0030] peripheral flange 16 extends outwardly and is substantially parallel to bottom wall 12. Flange 16 is relatively free of wrinkles, ribs or folds that are designed into the form to provide strength. The outer most edge 18 of flange 16 is curled.
Turning next to FIG. 2, there is illustrated a flow chart showing the processing steps used to make the open-ended food container of the present invention. The process of the present invention thus involves a new method for the manufacture of aluminum alloy open-ended food container stock in a continuous in-line sequence. [0031]
The process includes the following process steps in one, continuous in-line sequence is generally disclosed in U.S. Pat. Nos. 6,102,102, 5,894,879, 5,655,593 and 5,514,228; the teachings of which are incorporated herein by reference. [0032]
The method includes a first forming a hot aluminum feedstock from the alloy of the present invention. The aluminum alloy used to form the feedstock has a composition which comprises from about 0.05 to 0.55% by weight silicon, from 0.10 to about 0.50% by weight iron, from less than about 0.60% by weight copper, from about less than about 0.4% by weight manganese, from about 0.9 to about 1.8% by weight magnesium, with the balance being aluminum and impurities. Preferably, the levels of chromium, nickel and zinc are each kept below 0.05 wt. %. This alloy is designed for the in-line processes and results in a higher than expected properties. [0033]
Referring now to the flow chat of FIG. 2, prior to forming the feedstock, the molten metal is delivered from a furnace to a metal degassing and filtering device to reduce dissolved gases and particulate matter from the molten metal. The feedstock may be formed by know forming techniques including but not limited to casting, EMC casting, DC casting slab casting, belt casting, twin belt casting, drag casting or strip casting. [0034]
During forming metal is formed into a feedstock having a gauge of about 0.080 to 0.120 inch. The width of the metal feedstock is not considered to be critical and it needs to be at least wide enough to produce an 8-inch pie pan. There are cost advantages to producing a feedstock having a width that is sufficiently wide so that the feedstock can be slit down stream in the process into two or more sections each being sufficiently wide be able to be formed into pie plate. It is conventional to manufacture aluminum plates and pans from sheet stock of aluminum in wide widths (for example, 60 inches). [0035]
Next, the feedstock is hot rolled to reduce its thickness. The hot rolling is accomplished at elevated temperature such as 650-920° F. The feedstock temperature is reduced during the hot rolling due to conduction of heat from the feedstock to the rolls. Typically, the hot rolling is performed on metal that enters the hot rolling stand at a temperature of about 900° F. and exits the hot rolling stand at a temperature of about 680-780° F. [0036]
Next, the hot reduced feedstock is warm rolled to further reduce its gauge. In an in-line process, the metal exiting the hot rolling stand is directed immediately to warm rolling without the metal being cooled to room temperature. For all practical purposes the exit temperature from hot rolling stand is approximately the same as the entrance temperature to the warm rolling stand. The feedstock temperature decreases during the warm rolling due to conduction of heat from the feedstock to the rolls. Typically, the warm rolling is performed on metal that enters the warm rolling stand at a temperature of about 680° F. and exits the hot rolling stand at a temperature of about 530° F. [0037]
After hot and warm rolling the feedstock is cold rolled to a final gauge. In an in-line process, the metal exiting the warm rolling stand is directed immediately to cold rolling without the metal being cooled to room temperature. For all practical purposes the exit temperature from warm rolling stand is approximately the same as the entrance temperature to the cold rolling stand. The feedstock temperature diminishes during the cold rolling due to conduction of heat from the feedstock to the rolls. Typically, the cold rolling is performed on metal that enters the cold rolling stand at a temperature of about 530° F. and exits the hot rolling stand at a temperature of about 300-450° F. [0038]
Typically, the final gauge is between 0.006 and 0.00124 inch. For pie plate applications, it is desirable from a cost-of-metal standpoint to make the final gauge as thin as possible and yet provide the strength and rigidity required to meet customer specifications. Typically, these specifications are designed so that the pie plate will not be damaged during normal handling operations. [0039]
After rolling to final gauge, the feedstock is coiled and then annealed. Typically, the coil is annealed at a temperature of 625° F. for at least 2 hours. [0040]
After annealing, the feedstock is leveled and then lubricated. The lubricated sheet is then recoiled and eventually formed into a pie plate by stamping or other similar forming operation. During forming operations the sheet is first blanked into a circular configuration and stamped. Sometimes this is performed in a single operation as described for example in U.S. Pat. No. 3,233,813. [0041]
Unexpectedly, the alloy sheet formed by this process has adequate support and rigidity for handling and baking pies and the like. For the alloy processed in the in-line continuous sequence, the resulting sheet has the desired rigidity and strength found in 0.009 inch sheet of other alloys manufactured in other systems. Thus the sheet can be down gauged and still provide the required strength and rigidity required during handling and baking of the pies. Down gauging the sheet reduces the cost of the metal used in each pie plate. [0042]
In a further preferred embodiment, resulting favorable capacity and economics mean that small dedicated pie pan stock plants may conveniently be located at pie-making facilities, further avoiding packaging and shipping of pie plate stock and scrap web, and improving the quality of the open ended food container stock as seen by the can maker. [0043]
The feedstock employed in the practice of the present invention can be prepared by any of a number of casting techniques well known to those skilled in the art, including twin belt casters like those described in U.S. Pat. No. 3,937,270 and the patents referred to therein [0044]
The present invention contemplates that any one of the above physical forms of the aluminum feedstock may be used in the practice of the invention. In the most preferred embodiment, however, the aluminum feedstock is produced directly in either slab or strip form by means of continuous casting. [0045]
The feedstock is moved through optional pinch rolls into hot rolling stands [0046] 6 where its thickness is decreased. The hot reduced feedstock exits the hot rolling stands 6 and is then passed to heater.
Heater is a device which has the capability of heating the reduced feedstock to a temperature sufficient to rapidly anneal and solution heat treat the feedstock. [0047]
It is an important concept of the invention that the feedstock be immediately passed to the heater for annealing and solution heat treating while it is still at an elevated temperature from the hot rolling operation of mills. In 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 not only more efficient to heat the feedstock [0048] 4 immediately after hot rolling to effect anneal and solution heat treatment but it also provides much improved metallurgical properties over conventional batch anneal and equal or better metallurgical properties compared to off-line flash anneal. After cold rolling, the strip or slab is coiled an annealed at a temperature of about
As will be appreciated by those skilled in the art, it is possible to realize the benefits of the present invention without carrying out the cold rolling step as part of the in-line process. Thus, the use of the cold rolling step is an optional process step of the present invention, and can be omitted entirely or it can be carried out in an off-line fashion, depending on the end use of the alloy being processed. As a general rule, carrying out the cold rolling step off-line decreases the economic benefits of the preferred embodiment of the invention in which all of the process steps are carried out in-line. [0049]
It is an important concept of the present invention that annealing and then solution heat-treating immediately follow hot rolling of the feedstock [0050] 4 without intermediate cooling, followed by immediate quenching. The sequence and timing of process steps in combination with the heat treatment and quenching operations provide equivalent or superior metallurgical characteristics in the final product compared to ingot methods. In the prior art, the industry has normally employed slow air cooling after hot rolling. Only in some installations is the hot rolling temperature sufficient to cause annealing of the aluminum alloy before the metal cools down. It common that the hot rolling temperature is not high enough to cause annealing. In that event, the prior art has employed separate batch anneal steps before and/or after breakdown cold rolling in which the coil is placed in a furnace maintained at a temperature sufficient to cause recrystallization. The use of such furnace batch annealing operations represents a significant disadvantage. Such batch annealing operations require that the coil be heated for several hours at the correct temperature, after which such coils are typically cooled under ambient conditions. During such slow heating, soaking and cooling of the coils, some of the elements present in the aluminum that had been in solution in the aluminum are caused to precipitate (Mn, Cu, Mg, Si). That in turn results in reduced solid solution hardening and reduced alloy strength.
In contrast, the process of the present invention achieves recrystallization and retains alloying elements in solid solution for greater strength for a given cold reduction of the product. The use of the heater allows the hot rolling temperature to be controlled independently from the annealing step and solution heat treatment temperature. That in turn allows the use of hot rolling conditions that promote good surface finish and texture (grain orientation). In the practice of the invention, the temperature of the feedstock in the heater can be elevated above the hot rolling temperature without the intermediate cooling suggested by the prior art. In that way, recrystallization and solutionization can be effected rapidly, typically in less than 30 seconds, and preferably less than 10 seconds. In addition, by avoiding an intermediate cooling step, the anneal operation consumes less energy since the alloy is already at an elevated temperature following hot rolling. [0051]
In the practice of the invention, the hot rolling exit temperature is generally maintained within the range of 600° to 1000° F. while the anneal and solution heat treating are effected at a temperature within the range of 750° F. up to the solidus of the particular alloy. Times for annealing and solution heat treating range widely depending on composition, temperature, and nucleation site density, but generally can be made to fall within 1 to 120 seconds and preferably within 1-10 seconds. Immediately following heat treatment at those temperatures, the feedstock in the form of strip is rapidly quenched to a temperature necessary to retain alloying elements in solid solution and to cold roll (typically less than 300° F.). [0052]
As will be appreciated by those skilled in the art, the extent of the reductions in thickness effected by the hot rolling and cold rolling operations of the present invention are subject to a wide variation, depending upon the types of feedstock employed, their chemistry and the manner in which they are produced. For that reason, the percentage reduction in thickness of each of the hot rolling and cold rolling operations of the invention is not critical to the practice of the invention. However, for a specific product, practices for reductions and temperatures must be used. In general, good results are obtainable when the hot rolling operation effects a reduction in thickness within the range of 40 to 99% and the cold rolling effects a reduction within the range of 20 to 75%. [0053]
One of the advantages of the method of the present invention arises from the fact that the preferred embodiment utilizes a thinner hot rolling exit gauge than that normally employed in the prior art. As a consequence, the method of the invention obviates the need to employ breakdown cold rolling prior to annealing. [0054]
Without limiting the invention as to theory, it is believed that the process of the invention, and particularly the solution heat treatment followed by immediate quenching, causes a significant improvement in strength even though the aluminum has diminished alloy in element content. Discussions of reduced alloying elements contents may be found in U.S. Pat. Nos. 4,605,448, 4,645,544, 4,614,224, 4,582,541, and 4,411,707. [0055]
Having described the basic concepts of the invention, reference is now made to the following example. [0056]

EXAMPLE

An alloy having the following composition is used in this example: [0057]

Metal Percent By Weight

Si 0.38

Fe 0.3

Cu 0.15

Mn 0.25

Mg 1.4
A cast strip having the foregoing composition was formed having a thickness of 0.080 inches to 0.120 inches. The strip as immediately hot rolled at a temperature between about 680° F. to 900° F. The strip entered the hot mill at about 900° F. and exited near the lower end the above temperature range. [0058]
Next the strip was immediately warm rolled at a temperature in the range of about 530° F. to about 680° F. The strip had a thickness of about 0.140 inches to 0.026 inches. The temperature of the strip as it exited the rolling mill was 530° F. [0059]
The strip was then cold rolled to effect a 55% reduction in thickness to form a sheet having a thickness of between 0.0006 inches and 0.0012 inches. Typically the sheet had a thickness of 0.0080 inches or less. [0060]
The strip was then coiled and annealed at a minimum temperature of about 625° F. for 2 hours. The strip was then leveled and lubricated and formed into a open ended container. The container was a smooth walled pie pan having a wall thickness of 0.0080 inches. [0061]
Surprisingly, the resulting pie pan had a high rigidity without homogenization that is similar to a pie pan formed from 3004 that has been homogenized. [0062]
What is believed to be the best mode of the invention has been described above. However, it will be apparent to those skilled in the art that numerous variations of the type described could be made to the present invention without departing from the spirit of the invention. The scope of the present invention is defined by the broad general meaning of the terms in which the claims are expressed.[0063]

Claims

What is claimed is:

1. A monolithic smooth-walled container having a bottom wall, a sidewall interconnected to said bottom wall and extending upwardly and outwardly therefrom to define an open end of said monolithic container at an upper edge of said sidewall, said sidewall having a peripheral flange extending outwardly from said upper edge, said monolithic container formed from an aluminum alloy feedstock comprising:

from about 0.05 to 0.55% by weight silicon,

from 0.10 to about 0.50% by weight iron,

up to about 0.60% by weight copper,

up to about 0.4% by weight manganese,

from about 0.90 to about 1.8% magnesium,

with the balance being aluminum and impurities.

2. The monolithic smooth-walled container of claim 1 in which said composition further comprises:

from about 0.05 to 0.55% by weight silicon,

from 0.10 to about 0.50% by weight iron,

from less than about 0.60% by weight copper,

from about less than about 0.4% by weight manganese,

from about 0.9 to about 1.8% by weight magnesium,

with the balance being aluminum and impurities.

3. The monolithic smooth-walled container of claim 1 in which said composition further comprises:

up to 0.05% by weight chromium,

up to 0.05% by weight nickel, and

up to 0.05% by weight zinc.

4. The monolithic contain of claim 1 in which said aluminum alloy feed stock has a gauge of less than about 0.008 inch.

5. A method for manufacturing of aluminum alloy open-ended food container, said method comprising:

(a) manufacturing food container stock in a continuous in-line sequence, said manufacturing comprising:

(1) providing an aluminum alloy feedstock from a composition comprising:

from about 0.05 to 0.55% by weight silicon,

from 0.10 to about 0.50% by weight iron,

from less than about 0.60% by weight copper,

from about less than about 0.4% by weight manganese,

from about 0.9 to about 1.8% by weight magnesium,

with the balance being aluminum and impurities.

(2) hot rolling said aluminum alloy feedstock to hot reduce its thickness;

(3) annealing and solution heat treating said hot reduced feedstock without intermediate cooling while maintaining the temperature of said hot reduced feedstock for a time and level sufficient to retain alloying elements in solution; and

(4) rapidly quenching said heat treated feedstock to a temperature for cold rolling; and

(2) shaping said heat treated feedstock into an open-ended food container.

6. A method as defined in claim 4 wherein the feedstock is provided by continuous strip or slab casting.

7. A method as defined in claim 4 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 the endless belt is cooled when it is not in contact with the metal.

8. A method as defined in claim 4 which includes, as a continuous in-line step, cold rolling the quenched feedstock.

9. A method as defined in claim 4 in which includes the further step of forming pie pans from the cold rolled sheet stock.

10. A method as defined in claim 4 in which includes the step of coiling the cold rolled feedstock after cold rolling.

11. A method as defined in claim 9 wherein the coiling of the cold rolled sheet stock is in-line.

12. A method as defined in claim 4 wherein the hot reduced feedstock is heated to a temperature within the range of 680° F. up to the solidus temperature of the feedstock.

13. A method as defined in claim 4 wherein the annealing and solution heat treating is performed in-line at a temperature approximately the same as the hot rolling exit temperature for a period of time provided by a holding means.

14. A method as defined in claim 4 wherein the hot rolling of the feedstock is carried out at an exit temperature within the range of 680° F. to 780° F.

15. A method as defined in claim 4 wherein the warm rolling of the feedstock is carried out at a temperature within the range of 530° F. to 680° F.

16. A method as defined in claim 4 wherein the cold rolling of the feedstock is carried out at a temperature within the range of 300° F. to 4500° F.

17. A method as defined in claim 4 wherein the cold rolling step effects a reduction in the thickness of the feedstock of 20 to 75%.

18. A method for manufacturing aluminum alloy open-ended food container sheet comprising the following steps in continuous, in-line sequence:

(a) strip or slab casting a open-ended food container aluminum alloy to form an aluminum alloy strip or slab;

(b) hot rolling said strip or slab to reduce its thickness at a temperature within the range of about 680° F. to about 900° F.;

(c) warm rolling said strip or slab to reduce its thickness at a temperature within the range of about 530° F. to about 680° F.; and

(d) cold rolling said strip to final guage at a temperature within the range of about 300° F. to about 450° F.

19. A method as defined in claim 17 in which includes the step of coiling the aluminum alloy strip after cold rolling.

20. A method as defined in claim 17 in which includes the step of coiling the aluminum alloy strip after cold rolling and annealing said coil said strip at a temperature of at least 625° F. for at least 2 hours.

21. A method as defined in claim 17 wherein the width of the feedstock is less than 24 inches.

22. The method of claim 17 in which said aluminum alloy comprises:

from about 0.05 to 0.55% by weight silicon,

from 0.10 to about 0.50% by weight iron,

up to about 0.60% by weight copper,

up to about 0.4% by weight manganese,

from about 0.90 to about 1.8% magnesium,

with the balance being aluminum and impurities.