BACKGROUND OF THE INVENTION Aluminum sheets are used in many different applications, from automobiles to cans.

In many of these applications, a thin, yet strong, aluminum sheet is desired. To serve in a wide number of applications, an aluminum alloy product should have not only a high tensile and yield strength but also high formability to facilitate shaping, drawing, bending and the like, without cracking, tearing, excessive wrinkling or press loads.

In the beverage can industry, for example, the aluminum sheet is used as a can body, can end and tab stock. To produce can ends and tabs, the aluminum alloy sheet is first blanked into a circular configuration and then cupped. The side walls are ironed by passing the cup through a series of dies having diminishing bores. The dies thus produce an ironing effect which lengthens the sidewall to produce a can body thinner in dimension than its bottom. In the manufacture of complete"two-piece"aluminum beverage containers, it has been the practice in the industry to separately form the bodies, top ends and tabs. Such ends and tabs are then shipped to the filler of the beverage can and applied once the containers have been filled. The requirement for can ends and tabs are generally quite different than those for can bodies. In general, greater strength is required for can ends and tabs, and that requirement for greater strength has dictated that such can ends and tabs be fabricated from an aluminum alloy different from that used in can bodies.

In the automotive industry, there has been increasing emphasis on producing lower weight automobiles in order, among other things, to conserve energy. Since the body of most automobiles is comprised of aluminum alloy sheets, reducing the gauge of the sheets will provide a reduction in the weight of the automobile. However, in reducing the gauge of the sheet, one cannot sacrifice the strength of the sheet. To serve in a wide number of automotive applications, an aluminum alloy product needs to be formable and strong. In addition, the alloy should have high bending capability without cracking or severe surface roughening, since often the structural products are fastened or joined to each other by

hemming or seaming. Thus, an aluminum alloy sheet having strength and formability characteristics is needed.

Various aluminum alloys and sheet products have been considered for these various applications, including both heat-treatable and non-heat-treatable alloys. Heat treatable alloys offer an advantage in that the sheet products formed from these alloys can be produced at a low gauge, yet still meet the strength and formability requirements. Thus, less raw materials are needed to form the sheet.

Referring to Figure 6, precipitation hardening of the sheet products to realize desired strength and formability requirements is performed by two different heat treatments, namely solution heat treatment and precipitation hardening. The heat treating process for solution heat treatment includes the steps of (a) solutionizing heat treatment at a first temperature (To) above the solvus temperature (for the particular alloy composition) and below the solidus and liquidus temperatures (for that alloy composition) and eutectic melting point (to avoid partial melting of the alloy) to dissolve the alloying constituent (s) in the aluminum and (b) a rapid <BR> <BR> quenching to a second temperature (T, ) below the solvus to trap the constituent (s) in aluminum solid solution. In step (a), the alloy is maintained at the first temperature for a time sufficient to dissolve at least substantially if not entirely, soluble constituents (such as intermetallic compounds) into solid solution and to form a homogeneous solid solution. <BR> <BR> <P>Through solutionizing at least substantially all (e. g. , at least about 80% and more typically at least about 95%) of the soluble second phase particles are dissolved into solid solution.

When an alloy is in the form of a solid solution, the elements and compounds which form the alloy are absorbed, one into the other (or are homogeneous), in much the same way that salt is dissolved in a glass of water. The solution is then quenched to a lower temperature to create a supersaturated state or condition (for the form of the constituent in the quenched alloy). In other words, the form of the constituent in the alloy will have a concentration in the solid solution that is greater than the equilibrium value for the concentration of that form of the constituent at the particular temperature and alloy composition. In precipitation heat treatment, the alloy is heated to a third temperature (T2) higher than the second temperature and less than the solvus to control the rate that the constituent (s) diffuse out of solution and combine to form intermetallic precipitates. These precipitates distort the crystal lattice and act as obstacles to dislocation motion, thereby strengthening the material. Over time, these precipitates increase in size from (a) zones to (b) small clusters of aluminum and alloy

component atoms to (c) fine coherent particles to (d) coarse incoherent particles. The maximum strengthening occurs while these particles are still coherent with the aluminum matrix lattice. In either type of heat treatment, once the sheet is quenched the strength of the sheet can be increased by artificial aging, through additional thermal treatments such as paint bake treatments.

Figure I shows an equilibrium phase diagram for a binary alloy of copper in aluminum. The temperature ranges at which various process steps such as annealing, precipitation heat treating and solution heat treating performed are shown in Figure I. As will be appreciated, the diagram has a solidus line 100 and a liquidus line 104 defining various phase regions, namely a solid phase region 108 (which includes phases of Al and the intermetallic compound CuAl2), a solid phase region At 112 (which includes phases that correspond to substitutional solid solutions of copper in aluminum), a solid/liquid phase region Al-L 116 (which includes phases that correspond to mixtures of the substitutional solid solution of copper in aluminum and liquid phase aluminum), and a liquid phase region L 120 (which includes phases that correspond to mixtures of liquid phase copper and aluminum). As will be appreciated, the mechanical properties of the alloy are influenced by the character of the particles of the transition phases formed in a specific sequence during precipitation hardening. In the precipitation hardening process, the upper limit of the solution heat treatment range of temperatures is below the eutectic melting point of the copper/aluminum alloy system and solidus and liquidus lines (for that alloy composition) and the lower limit is above the solvus temperature (for that alloy composition). The eutectic melting point 124 of about 1018°F is the melting point of an eutectic mixture (where the liquidus and solidus lines intersect) which is about 5.65 wt. % copper and 94.35 wt. % aluminum. This temperature range, for the copper in aluminum alloy system, as shown in Figure 1, is between about 900 and 1018°F and, moretypically, isbetween 950 and 1018°F.

Figure 2 shows a time-temperature-property phase diagram for a 7075 alloy, a 2017 alloy, a 6061 alloy and 6063 alloy. Figure 2 shows the time in which an alloy must be cooled and the critical temperature range over which the cooling must occur. The alloy should be cooled fast enough so that the line of cooling does not intercept the"c"or nose portions 200, 204, 208, and 212 of the corresponding curve 216, 220,224, and 228 for that alloy. In other words, in quenching the cooling line for the alloy (time vs temperature) does not intersect (or stays to the left of) the corresponding curve for the alloy. Each curve defines the

temperature/time regime where nucleation and precipitation of intermetallic precipitates occurs. For instance, the 7075 alloy, according to Figure 2, would have to be cooled from 750°F to below 390°F in less than 10 seconds. On the other hand, the 2017 alloy would have to be cooled from 920°F to below 450°F in less than 100 seconds. Thus, for different alloys, the time in which the metal should be cooled varies. In addition, for various alloys, the temperature range over which the alloy must be cooled also varies.

An example of the state of the art in producing solution heat treated sheets is described in U. S. Patent Numbers 5,772, 802 and 6,045, 632, incorporated herein by reference.

These patents describe a process for producing a solution heat treated sheet which requires the afuminum al) oy to be cast and run through a hot mill. During hot milling, the strip or sheet is cooled by a combination of water sprays and thermal transfer to the hot rolls, but the temperature is maintained above the solvus temperature. Once the cast alloy exits the hot mill as a sheet, the sheet is quenched to below the solvus temperature and cold rolled into a coil. Following the cold roll, the sheet is annealed at or reheated to a high temperature to accomplish the solution heat treatment of the sheet. The solution heat treated sheet is then quenched again and cold rolled to its final gauge and aged before use in its final application.

The problems with the art as it exists now is that the solution heat treatment phase, accomplished by a high temperature anneal, is an expensive undertaking, both in operating costs and capital equipment costs. As one of skill in the art recognizes, the energy consumed in and operating costs of reheating the sheet from a temperature below 400°F to the temperature of600°F to 1000 °F are enormous. In addition, the cost of the capital equipment, the furnace, the heating elements, and the second quench station all add cost to the final product. The high temperature anneal requires a period of time to reheat the sheet to at least or above the solidus temperature, the temperature below which the alloy is solid, and recrystallize the sheet, thus increasing the processing time for making the sheet. All of these factors add to the cost of the final product. When the final solution heat treated sheet sells for only pennies a pound, every item that adds to or subtracts from cost of the final product- even if it only translates into a savings of a penny a pound-will have a significant effect on the market.

SUMMARY OF THE INVENTION The present invention comprises a method and apparatus suitable for accomplishing the method that significantly simplifies the process of making a solution heat treated sheet.

As used herein,"feedstock"refers to an ingot, bar, plate, slab, strip, and/or sheet. The method comprises continuously casing an aluminum alloy to produce a cast strip. Any apparatus which accomplishes continuous casting is appropriate for use with the present invention. Once the cast strip is formed, it is hot rolled and quenched during hot rolling to form the solution heat treated sheet. As used herein,"quenching"means any process used to lower the temperature of the cast strip through thermal transfer. In a typical quench, nucleation and precipitation of intermetallic precipitates is at least substantially inhibited to provide a supersaturated state or condition. The term"hot rolling"means any process to reduce the thickness of the strip at a temperature above about 400 degrees Fahrenheit. The phrase"during hot rolling"means any process or item occurring between point 1, as indicated on Figure 5, at time 1 and point 2 at time 2. With reference to Figure 5, the phrase "during hot rolling"refers temporally to the time interval beginning when a portion of strip 12 contacts the first roller 25 at point pl (or time tl) and ending when the same portion of the strip last contacts the final roller 23 at point p2 (or time t2) or spatially to the portion of the strip 12 extending from point pi to point p2.

Quenching before or during hot rolling can be accomplished in any number of ways.

Examples include without limitation submersion of the strip, sprays or mists directed onto the strip, sprays or mists directed onto the rollers of the hot mill stand or other object contacting the sheet, or any combination of the above. In addition to quench bars being placed in the hot mill stands or as a substitute for the quench bars, a separate quenching station can be placed between the hot mill stands. Quenching may also be accomplished by any other means to reduce the temperature of the cast strip so as to prevent precipitation.

In one embodiment of the invention, the cast strip is hot rolled and quenched during hot rolling more than once with varying reductions in temperature and gauge occurring in the various hot rolling/quenching steps. The apparatus which accomplishes the method of the present invention comprises a continuous caster, at least one hot mill stand, and at least one quenching apparatus before or in the at least one hot mill stand. Although any aluminum alloys can be used with the process, aluminum alloys that react well to a solution heat treatment process are, generally, aluminum alloys from the 2XXX series, 3XXX series,

6XXX series, and 7XXX series. The 2XXX, 6XXX and 7XXX series are most commonly used with solution heat treating processes.

The advantages of the present invention include less capital equipment costs and less operating costs since the present invention produces a solution heat treated sheet directly from the hot mill stand. Also, less process time is needed to produce a solution heat treated sheet according to the teachings of the present invention. In addition, the resultant sheet has the same or better characteristics than solution heat treated sheets produced in conventional processes. Thus, the sheet produced by the present invention has high formability and strength, as required for use in the applications described herein and other applications.

These and other objects, features, and advantages of the invention will become apparent from the following best mode description, the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS The figures which follow depict a preferred embodiment of the invention, and may depict various alternative embodiments. The invention is not limited to the embodiment or embodiments depicted herein since even further various alternative embodiments will be readily apparent to those skilled in the art. For the ease of the reader, like reference numerals in various drawing figures refer to identical structural elements or components.

Fig. 1 is a phase diagram for a copper in aluminum alloy with the vertical axis being temperature (degrees Celsius) and the horizontal axis being copper content (weight percent).

Fig. 2 is a time-temperature-property diagram for various aluminum alloys with the vertical axis being temperature (degrees Celsius) and the horizontal axis being time (seconds).

Fig. 3 is a flowchart depicting an embodiment of the present invention.

Fig. 4 depicts a perspective view of an apparatus according to an embodiment of the present invention.

Fig. 5 depicts the various junctures at which the present invention quenches during hot rolling.

Fig. 6 depicts the relationship between solution heat treatment and precipitation heat treatment, with the vertical axis being temperature and the horizontal axis being time.

DETAILED DESCRIPTION OF THE INVENTION At the outset, it should be understood that this invention comprises a method and apparatus for producing a solution heat treated sheet from various aluminum alloys. The description which follows describes a preferred embodiment of the invention, and various alternative embodiments. It should be readily apparent to those skilled in the art, however, that various other alternative embodiments may be accomplished without departing from the spirit or scope of the invention.

There are specific alloy compositions that react well to being subjected to a solution heat treatment process. They are, generally, aluminum alloys from the 2XXX series, 3XXX series, 6XXX series, and 7XXX series. The 2XXX, 6XXX and 7XXX series are most commonly used with solution heat treating processes. The range of chemical compositions for the 2XXX, 3XXX, 6XXX and 7XXX series is shown below in Table 1.

Table 1 Table of Chemical Compositions for Heat Treatable Alloys Element 2XXX Alloy 3XXX Alloy 6XXX Alloy 7XXX Alloy (weight (weight (weight (weight percent) percent) percent) percent) Silicon about 0-1.4 about 0-1.8 about 0. 15-about 0-0.6 2. 0 Iron about 0-1.5 about 0-1.0 about 0-1.0 about 0-1.5 Copper about 0.7-7. 0 about 0-0.9 about 0-1.2 about 0-3.0 Manganese about 0-1.4 about. 05-1. 8 about 0-1.2 about 0-1.0 Magnesium about 0-2.5 about 0-1. 5 about 0.2-2. 0 about 0-4.0 Zinc about 0 about 0-1. 0 about 0-2.5 about 3.0-9. 0 Zirconium about 0-0. 5 about 0.05 about 0 about 0-0. 5 Aluminum Remainder Remainder Remainder Remainder (with usual impurities) The 2xxx series alloys have copper as the principal alloying element. These alloys require solution heat-treatment to obtain optimum properties; in the heat-treated condition mechanical properties of these alloys are similar to, and sometimes exceed, those of mild steel. The 3xxx series alloys have manganese as the principal alloying elements. These alloys can provide moderate strength and good workability. The 6xxx series alloys contain

silicon and magnesium in approximate proportions to form magnesium silicide, which makes these alloys heat-treatable. The 7xxx series alloys have zinc as the major alloying element, which, when coupled with a smaller percentage of magnesium results in a heat-treatable alloy of very high strength.

Thus, any aluminum alloy with compositions in the ranges described in the above table are suitable for use with the present invention. Although it should be noted that aluminum alloys, other than those specifically listed above, may also be appropriate for use in the present invention.

Without wishing to be held to any particular theory, it is believed that the hardening effect of solution heat treatment is accomplished by casting the aluminum alloy at a temperature above the eutectic melting point of the aluminum alloy (and above the melting point or liquidus or solidus lines for that alloy composition) to dissolve the copper, magnesium, and other alloying elements in the aluminum. The strip output from the caster has a temperature above the solvus temperature and typically below the eutectic meltingpoint and liquidus and solidus lines. The alloy with the dissolved copper is rapidly quenched during hot rolling to trap the dissolved copper in an aluminum solid solution in a form that is supersaturated. Some of the copper and/or other alloying elements may nucleate and form intermetallic precipitates, such as CuAl2, which will precipitate out of the aluminum solid solution. For example, with reference to Figure 1, corresponding to a copper in aluminum alloy, quenching causes the solid solution to be in the Al and CuAl2 phase region 108 of the phase diagram. These precipitates distort the crystal lattice of the aluminum matrix and act as obstacles to dislocation motion, thereby strengthening the material. Maximum strengthening occurs while these particles are still coherent with the aluminum matrix lattice.

Thus, in order to produce a strong, yet formable solution heat treated sheet, one would wish to minimize substantially the precipitation of such precipitates and maintain the alloy elements dissolved in the aluminum matrix.

With reference to Figures 3,4, and 5, the method and apparatus of the present invention begins by melting 50 the chosen alloy in a furnace (not shown) to produce molten metal 60. The molten metal is then degassed and filtered 70 in a degassing and filtering device (not shown). This step reduces dissolved gases and particulate matter in the molten metal. The molten metal is then continuously cast 80 in a continuous casting apparatus 10

to form a cast feedstock 90. The cast feedstock employed in the practice of the present invention can be prepared by any of a number of continuous casting techniques well known to those skilled in the art, including twin belt casters like those described in U. S. Patent Number 3,937, 270, and the patents referred to therein. In some applications, it may be advantageous to employ the method and apparatus described in the following U. S. Patents: U. S. Patent Numbers 5,363, 902; 5,515, 908; 5,564, 491 and 6,102, 102. Other casters may also be employed. For example, drum casters, such as that described in U. S. Patent Numbers 5,616, 190 or 4,411, 707 or block casters, such as those described in U. S. Patent Numbers 5, 469, 912 maybe employed to produce a cast feedstock. Each of the aforementioned patents and patent applications are hereby incorporated by reference herein in their entireties. The cast feedstock 90 typically has a temperature of from about 700 to about 1100°F and a gauge of from about 0.500 to about 0.850 inches and more typically a gauge of from about 0.500 to about 0.800 inches. As will be appreciated, this temperature is generally above the solvus and below the eutectic melting point and liquidus and solidus lines. Thus, the temperature is above the lower limit of the solution heat treatment temperature regime and, sometimes, above the upper temperature limit for the regime.

From the continuous casting apparatus 10, the cast feedstock 90 is hot rolled and quenched 120 during hot rolling in one or more hot mill stands 20 to produce a hot rolled solution heat treated sheet 130. The hot rol l ing step is performed to reduce the thickness and temperature of the cast feedstock. Thickness reduction is performed by passing the feedstock through rollers having a desired interroller spacing, while temperature reduction is realized by a combination of heat transfer from the feedstock to the rollers and quenching. Depending on the desired final thickness of the sheet 130 and/or the temperature reduction needed to produce the desired feedstock 130 output temperature from the final hot mill stand, the feedstock 90 can be hot rolled and quenched 100 through more than one hot mill stand 21 and 22 to produce the (fully) hot rolled feedstock 130.

Quenching in the hot mill stand (s) can be accomplished in any number of ways such that a reduction in the temperature of the feedstock is accomplished. Examples include without limitation submersion of the feedstock, sprays or mists directed onto the feedstock, sprays or mists directed onto the rollers of the hot mill stand, or any combination of the above. Figure 4 shows quench bars 30 in the hot mill stand 22. It should be understood by

one of skill in the art that quench bars can be placed in any or all of the hot mill stands. In addition to the quench bars or as a substitute for the quench bars, a separate quenching station can be placed between the hot mill stands. Spraying or misting the hot rollers will cool down the metal rollers 23 that are typically used in a hot mill stand. Cooling down the metal rollers will, in turn, allow heat to be removed from the cast feedstock and transferred to the rollers.

In addition, as the thickness of the feedstock is reduced, it becomes easier to remove heat from the feedstock since the rollers have more surface area on which to work. Quenching may also be accomplished by any other means to reduce the temperature of the cast feedstock so as to inhibit nucleation and precipitation of intermetallic precipitates.

To realize the desired properties of the solution heat treated feedstock 130, the input and output parameters of the final hot rolling stand are carefully controlled. As can be seen from Figures 1 and 2, the input temperature and gauge of the hot rolled feedstock 110 and the time required to traverse the temperature range for solution heat treating are important.

Preferably, the input temperature of the hot rolled feedstock 110 is maintained at or below the upper temperature of the solution heat treatment range while the output temperature of the solution heat treated feedstock 130 is maintained at or below the lower temperature of the solution heat treatment range.

Quenching the alloy reduces the temperature of the feedstock by a range and over a time sufficient for the resultant feedstock to possess the properties of a solution heat treated feedstock. Suitable quenching fluids include water, air, gases such as carbon dioxide or nitrogen, lubricants used to cool the rolling mills, and the like or a combination of any of the above. The quench requirements for solution heat treatable alloys generally are an input temperature of about 700 to about 800°F, an input gauge of about 0.090 inches to about 0.180 inches, and a resident time of about 3 to 12 seconds. The quench requirements required for the specific alloys to be solution heat treated (or quenched) in a single hot mill stand are listed in Tables 2,3, 4, and 5. As will be appreciated, the quench variables may be performed once in the first, intermediate, or last hot mill stand or gradually among multiple hot mill stands by modifying the speed of the strip through the stands to realize the desired degree of quenching within the desired time period (s).

Table 2 2xxx Alloy Table for Input Temperature and Quench Variables 2XXX Alloy Preferable More Preferable Even more Quench Time and Preferable Temperature Preferred about 10 seconds about 8 seconds about 6 seconds Maximum Time Preferred Input-about 700-Input-about 700-Input-about 700- Temperature 1100°F 1000°F 900°F Range Output-about 250 Output-about 250-Output-about 250- - 500°F 450°F 400°F Preferred from about 200°F from about 250°F to from about 300°F to Temperature to about 850°F or about 750°F or even about 650°F or even Drop even more more preferably more preferably preferably about about 550°F about 600°F 500°F Preferred Hot about 0. 90 to 0. 150 about 0. 100 to 0. 130 about 0. 110 to 0. 120 Mill Exit Gauge (inches) Table 3 3xxx Alloy Table for input Temperature and Quench Variables 3xxx Alloy Preferable More Preferable Even More Quench Time and Preferable Temperature Preferred about 12 seconds about 10 seconds about 8 seconds Maximum Time Preferred Input-about 700-Input-about 700-Input-about 700- Temperature Range 1100°F 1000°F 900°F Output-about 250-Output-about 250-Output-about 250- 500°F 450°F 400°F Preferred from about 200°F from about 250°F from about 300°F Temperature Drop to about 850°F or to about 750°F or to about 650°F or even more even more even more preferably about preferably about preferably about 500°F 550°F 600°F Preferred Hot Mill about 0.070 to about 0.075 to about 0.075 to Exit Gauge (inches) 0.180 0.150 0.140

Table 4 6xxx Alloy Table for Input Temperature and Quench Variables 6XXX Alloy Preferable More Preferable Even more Quench Time and Preferable Temperature Preferred about 12 seconds about 10 seconds about 8 seconds Maximum Time Preferred Input-about 700-Input-about 700-Input-about 700- Temperature 1100°F 1000°F 900°F Range Output-about 250 Output-about 250-Output-about 250- - 500°F 450°F 400°F Preferred from about 200°F from about 250°F to from about 300°F Temperature Drop to about 850°F or about 750°F or even to about 650°F or even more more preferably even more preferably about about 550°F preferably about 500°F 600°F Preferred Hot Mill about 0. 90 to 0. 150 about 0. 100 to 0. 130 about 0.110 to Exit Gauge 0.120 (inches) Table 5 7xxx Alloy Table for Input Temperature and Quench Variables 7XXX Alloy Preferable More Preferable Even more Quench Time and Preferable Temperature Preferred about 4 seconds about 3 seconds about 2 seconds Maximum Time Preferred Input-about 700-Input-about 700-Input-about 700- Temperature 1100 1000°F 900 °F Range Output-about 250 Output-about 250-Output-about 250- -500°F 450°F 400°F Preferred from about 200°F from about 250°F to from about 300°F Temperature Drop to about 850°F or about 750°F or even to about 650°F or even more more preferably even more preferably about about 550°F preferably about 500OF 600OF Preferred Hot Mill about 0.090 to about 0. 100 to 0. 175 about 0.120 to Exit Gauge 0.180 0.170 (inches)

The resultant quenched feedstock from the hot mill stand is a solution heat treated product which is immediately available for use or storage. For either purpose, the feedstock will likely be coiled by a coiling apparatus 40 to allow for ease in handling and transport.

The resultant feedstock has been found to have equal or better metallurgical and formability characteristics as compared to solution heat treated feedstocks produced according to the current art. The solution heat treated feedstock can then be artificially aged to produce a desired degree of nucleation and precipitation of intermetallic precipitates and desired precipitate size distribution.

It will be appreciated by those skilled in the art that there can be expected some small precipitation of intermetallic compounds that does not specifically affect the final properties.

Such minor precipitation has little or no affect on those final properties either by reason of the fact that the intermetallic compounds are of a volume and/or type, which have a negligible effect on the final properties. However, it is believed that the present invention as described herein substantially minimizes or inhibits the number and type of intermetallic precipitates that are formed in order to produce a fonnable, yet strong solution heat treated feedstock.

As shown in Figure 4, in one embodiment of the present invention, three hot mill stands 20,21, and 22 are used. As will be appreciated, a continuous heater, such as a solenoidal flux heater, can be positioned between the caster and first hot mill stand or between stands to provide the desired input temperature into the first hot mill stand. Such a heater is discussed 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 stand one 20, the feedstock's gauge or thickness is reduced in a range of 40 % to 75% to a thickness range of preferably about 0.187 inches to 0.450 inches, more preferably, about 0.200 inches to 0.350 inches and even more preferably, about 0.230 inches to 0.270 inches, in stand one 20 and the feedstock's temperature is reduced from an input temperature of about 900°F to about 1100°F to an output temperature of no more than about 950 °F with the temperature drop being in the range of over 100°F. In stand two 21, the feedstock's gauge is further reduced in a range of 35 to 60% to a thickness range of preferably about 0.100 inches to 0.250 inches, more preferably, about 0.110 inches to 0.200 inches and even more preferably, about 0.120 inches to 0.180 inches and the feedstock's temperature is reduced from about 850°F to about 950°F to an

output temperature of no more than about 850 °F with the temperature drop being in the range of approximately 100 °F. Thus, going into the final hot mill stand 22, the temperature of the feedstock is at least about 700 °F. In the final hot mill stand of this embodiment, the gauge is again reduced in a range of 40 to 60% to a thickness range of preferably less than about 0.150 inches, more preferably, about 0.125 inches to 0.95 inches and even more preferably about 0.060 inches to about 0.075 inches, while the majority of the quenching and, consequently, the temperature drop, for this embodiment, occurs in the last stand. The feedstock is preferably quenched, in the last hot mill stand, through the use of quench bars 30 which direct water onto the hot mill rollers 23 such that the temperature drops from at least about 700 °F to no more than about 550 °F and even more preferably in a range of about 250-500°F. In one embodiment, the exit temperature of the feedstock is in the range of about 250-450 °F, and even more preferably, the exit temperature of the feedstock from the last hot mill stand is in the range of about 250-400 °F. The feedstock preferably spends no more than about 10 seconds in the last hot mill stand and even more preferably no more than about 6 seconds, depending on the nature of the alloy used in the process and on the speed of the belt of the apparatus through the hot mill stand, as shown in Table 2. With reference to Figure 5, the residence time in any hot mill stand is measured from the point that a portion of the feedstock first contacts the stand's rollers to the point that the same feedstock portion last contacts the stand's rollers. For the times listed in Table 2, the belt speed is approximately 25 to 30 feet per minute. As will be appreciated by one of ordinary skill in the art, the belt speed will necessitate adjustments in the other variables in Table 2 which are important in producing a solution heat treated feedstock according to the present invention. The feedstock then exits from the last hot mill stand at a temperature below 400 °F and is coiled by a coiling apparatus 40 for storage or transport. The feedstock can also be further processed, depending on the properties specified for the final product.

In another embodiment, not shown in a figure, two hot mill stands are used. In stand one, the thickness of the cast feedstock is reduced by approximately 65 % to a thickness range of preferably about 0.200 inches to 0.300 inches, more preferably, about 0.220 inches to 0.280 inches and even more preferably, about 0.240 inches to 0.280 inches, and the feedstock is quenched enough to reduce the temperature of the feedstock from the exit temperature of the casting apparatus, usually in the range of from about 900°F to 1100°F to

a range of approximately 700°F to 900°F. The cast feedstock then proceeds to the second hot mill stand where, as the last hot mill stand of this embodiment, the thickness of the feedstock is reduced by approximately 55% to a thickness range of preferably about 0.100 inches to 0.180 inches, more preferably, about 0. 110 inches to 0.160 inches and even more preferably, about 0.115 inches to 0. 150 inches, and the majority of the quenching and the temperature drop occurs. Again, the feedstock has a residence time in the last hot mill stand of no more than about 10 seconds, dependent on the alloy used, as shown in Table 2.

As will be appreciated by those skilled in the art, the extent of the reductions in thickness effected by the hot rolling and final rolling operations of the present invention 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 each of the hot rolling and final rolling operations of the invention is not critical to the practice of the invention. In general, good results are obtained when the hot rolling operation effects a cumulative reduction in thickness within the range of about 15 to 99% and the final rolling effects a reduction within the range from about 10 to 85%.

Typically, the present feedstock 150 has a maximum thickness of about 0.10 inches; more typically, the maximum thickness is about 0.090 inches. The present feedstock 150 has a minimum thickness of about 0.025 inches; more typically, the minimum thickness is about 0.030 inches. It is known to those skilled in the art that this thickness will continue to decrease with time because of continuous down gauging.

In a preferred configuration of the present invention, the majority of the quenching occurs in the last hot mill stand, whether one or more hot mill stands are used. Thus, the input requirements to this last hot mill stand are particularly relevant. Applicants have found that the temperature range into the last hot mill stand should be in the range of about 700°F to 900°F, in order for the solution heat treatment, which primarily occurs in the last hot mill stand, to be effective. The gauge of the feedstock as it enters the last hot mill stand should be in the range of about 0.100 to 0.200 inches.

It should be recognized by one of ordinary skill in the art, however, the majority of the quenching and temperature drop can occur in any hot mill stand, between hot mill stands, or in front of the first hot mill stand, with a lower temperature roll following the quench and temperature drop. With reference to Figure 5, for example, quenching can be performed in

front of the initial hot mill rollers 25, by thermal transfer to one or both of the rollers 25, between rollers 25 and 24, by thermal transfer to one or both of the rollers 24, between rollers 24 and 23, and/or by thermal transfer to one or both of rollers 23.

It should be noted that the output from the last hot mill stand is a solution heat treated product with a finish gauge that can be immediately used in the application for which it was produced. Thus, the solution heat treatment is occurring in the hot mill stands, eliminating the need for any further annealing or quenching.

After the coiling step, the feedstock may be stored until needed for further processing 140, as described below. Options for further processing include: 1) aging 160 for a period of time of about 10 to 25 hours and a temperature range of about 270 °F to 400 °F ; or 2) coiling or aging 160 for a time period of about 6 to 25 hours and a temperature range of from about 270°F to 400°F with cold rolling 165 following the aging to reduce the gauge of the feedstock by about 20% to 70% and form an aluminum alloy sheet. Other types of processing, including but not limited to the batch stabilization described below or paint baking, may also performed on the solution heat treated feedstock 130, depending the application in which the feedstock will be used.

It is sometimes desirable, after rolling to final gauge, to batch stabilize the cold-rolled feedstock at an elevated temperature, preferably at temperatures within the range of 220- 400°F for about 6 to about 20 hours. This batch stabilization precipitates intermetallic compounds in a strengthening form, and also increases formability through recovery of the aluminum matrix. More preferably, the feedstock can be stabilize annealed at a temperature between 300 and 375 °F for between 10 and 20 hours. When the feedstockhas been quenched during the above process so as to substantially minimize precipitation of alloying elements as intermetallic compounds, the cast feedstock has an unusually high level of solute super saturation. Thus, the stabilizing step causes the ultimate tensile strength and yield strength to increase along with formability (as measured by percent elongation in a tensile test, for example).

Having described the basic concept of the present invention, reference is now made to the following examples provided by way of illustration only and should not be interpreted to limit the scope or spirit of the present invention.

Example 1 An aluminum alloy having a composition of 0.35 % Silicon, 0.65% Iron, 0.15 % copper, 0.45% Magnesium, 0.52% manganese, and the balance aluminum (with its usual impurities) was cast as a strip having a thickness of 0.75 inches using a continuous feedstock caster similar to that as substantially shown and described in U. S. Patent Numbers 5,515, 908; 6,102, 102 and 5,564, 491, all of which are hereby incorporated by reference.

The hot cast strip was then immediately hot rolled to a finish gauge thickness of 0.055 and quenched during hot rolling. The hot rolled strip was stabilized at 320°F for 18 hours.

The strip, when tested, had an ultimate tensile strength of 41,500 psi, a yield strength of 39,000 psi and 9. 1% elongation.

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein should not, however, be construed as limited to the particular forms disclosed, as these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the present invention. Accordingly, the detailed description of the invention should be considered exemplary in nature and not as limiting to the scope and spirit of the invention as set forth in the appended claims.