CA2232436C - A method for making beverage can sheet - Google Patents

Abstract

An improved method for making beverage containers from aluminum alloys as well as can end and tabs therefore in which an aluminum alloy is strip cast and then subjected to one or more of a series of quenching and annealing operations. The present application also contemplates the manufacture of aluminum alloy can stock utilizing hot rolling immediately after strip casting to reduce the thickness of the feedstock, either with or without intermediate coiling of the feedstock.

Description

A METHOD FOR MAKING BEVERAGE CAN SHEET

Background of the Invention The present invention relates to a process for making aluminum alloy beverage containers, and more particularly, to a process for making such can ends and tabs for such containers allowing them to be produced more economically and efficiently.

PKior Art It is now conventional to manufacture beverage containers from aluminum alloys. An aluminum alloy sheet stock is first blanked into a circular configuration and then cupped.
The side wall are ironed by passing the cup through a series of dies having diminishing bores. The dies thus produce an iron-ing effect which lengthens the sidewall to produce a can body thinner in dimension than its bottom.

Thus, formability is a key characteristic of aluminum alloy to be used in manufacturing cans. Such cans are most frequently produced from aluminum alloys of the 3000 series.
Such aluminum alloys contain alloy elements of both magnesium and manganese. In general, the amount of manganese and magne-sium used in can body stock is generally present at levels less than about 1% by weight.

In the manufacture of such beverage containers, it has been the practice in the industry to separately form both a top lid of such cans and tabs for easy opening of such lids separately and using different alloys. Such lids and tabs are then shipped to the filler of the beverage can and applied once the containers has been filled by a filler. The requirements 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. One such alloy commonly used is alloy AA5182, an aluminum alloy containing relatively high amounts of magne-sium to provide the added strength necessary for can ends and tabs. AA5182 typically contains magnesium in an amount ranging from 4.4% by weight, thus adding to the cost of the alloy for can ends and tabs.

It has been proposed to employ, as the aluminum alloy used in the fabrication of can ends and tabs, alloy from the 3000 series, such as AA3104. Because such alloys generally have diminished strength as compared to AA5187, it has been necessary to employ can ends fabricated from AA3104 which have a greater thickness and thus are more expensive.

It is accordingly an object of the present invention to provide can end and tab stocks and can ends and tabs made therefrom which overcome the foregoing disadvantages.

It is more specifically an object of the present invention to provide can ends and tabs and a method for fabri-cating same in which use is made of aluminum alloys containing less alloying elements without sacrificing strength.

It is a more specific object of the present invention to provide can ends and tabs therefor and a method for fabri-cating them which can be employed with aluminum alloys contain-ing less than 2% magnesium without sacrificing the necessary strength of the can ends and tabs.

These and other objects and advantages of the inven-tion appear more fully hereiinafter from a detailed description of the invention.

Summary of the Invention The concepts of the present invention reside in the discovery that aluminum alloys containing lesser amounts of alloying elements can, nonetheless, be used in fabricating can ends and tabs without sacrificing strength by utilizing a fabrication process in which the aluminum alloy, preferably containing less than 2% by weight of magnesium as an alloying element, is formed into sheet stock for making can ends and tabs. In accordance with the practice of the invention, the aluminum alloy is strip cast between a pair of continuous moving metal belts to form a hot strip cast feedstock, and then the feedstock is rapidly quenched to prevent substantial pre-cipitation of aluminum alloying elements as intermetallic compounds.

It has been unexpectedly found that such a fabrica-tion process provides an aluminum alloy feedstock having equal or better metallurgical characteristics as compared to aluminum alloys conventionally used in forming can ends and tabs.

It has been found in accordance with the preferred embodiment of the present invention that the fabrication pro-cess can be applied to alloys of the 3000 series such as AA3104 without the need to increase the thickness of the can ends and tabs to achieve comparable strips. Without limiting the pres-ent invention as to theory, it is believed that the techniques of strip casting followed by rapid quenching provide an alloy sheet stock having improved strength by reason of its eutectic constituents which provide increased strengths. In addition, it is believed, once again, without limiting the present inven-tion as to theory, that formability of the sheet stock of this invention used in forming can ends and tabs is improved over aluminum alloys containing greater qualities of alloying ele-ments because it is unnecessary, in the practice of the inven-tion, to use an annealing step typically used by the prior art.
Thus, the present invention allows can ends and tabs to be produced from less expensive aluminum alloys without sacrific-___ ing the metallurgical properties of those more expensive alloys.

In one preferred embodiment of the invention, the sequence of steps of strip casting, quenching and rolling is preferably greater within a continuous, in-line sequence. That has a further advantage of eliminating process and material handling steps typically employed in the prior art. The strip casting can be used to produce a cast strip having a thickness less than 1.0 inches, and preferably within the range of 0.01 to 0.2 inches. In addition, in accordance with the most pre-ferred embodiment of the invention, the widths of the strip is narrow contrary to conventional wisdom. That facilitates ease of in-line threading and processing and allows production lines for the manufacture of can ends and tabs to be physically located with or as part of a can making facility. A filler location that has the further advantage of eliminating addi-tional handling and shipping costs, thus promoting the overall economics of a can making operation.

In accordance with another embodiment of the inven-tion, the aluminum alloy is strip cast between a pair of con-tinuous moving metal belts to form a hot strip cast feedstock, and then the feedstock is rapidly quenched to prevent substan-tial precipitation of aluminum alloying elements as intermetallic compounds. Thereafter, with or without addi-tional rolling, the quenched feedstock is annealed and rapidly quenched, also to prevent substantial precipitation of alloying elements. It has been found that the intermediate annealing and quenching steps substantially improve the formability of the feedstock while maintaining exceptionally high metallurgi-cal =
properties including ultimate tensile strength and yield strength.

It has been unexpectedly found that such a fabrica-tion process provides an aluminum alloy feedstock having equal or better metallurgical and formability characteristics as compared to aluminum alloys conventionally used in forming can ends and tabs.

It has been found in accordance with a preferred embodiment of the present invention that the fabrication pro-cess can be applied to alloys of the 3000 series such as AA3104 without the need to increase the thickness of the can ends and tabs to achieve comparable strips. Without limiting the pres-ent invention as to theory, it is believed that the techniques of strip casting followed by rapid quenching provide an alloy sheet stock having improved strength by reason of its solid solution and age hardening. In addition, it is believed, once again, without limiting the present invention as to theory, that form-ability of the sheet stock of this invention used in forming can ends and tabs is equal to or better than these DC-cast aluminum alloys containing greater quantities of alloying =
elements. Thus, the present invention allows can ends and tabs to be produced from less expensive aluminum alloys without sacrificing the metallurgical properties of those more expen-sive alloys. It has also been found that the intermediate anneal and quench steps promote the formability of the can end and tab stock without adversely effecting its strength.

In accordance with yet another embodiment of the invention, the aluminum alloy is strip cast, preferably between a pair of continuous moving metal belts, to form a hot strip cast feedstock, and then the feedstock is rapidly, with or without additional rolling, annealed and rapidly quenched to prevent substantial precipitation of alloying elements.

It has been found that the intermediate annealing and quenching steps substantially improve the formability of the feedstock while maintaining exceptionally high metallurgi-cal properties including ultimate tensile strength and yield strength. The omission of the first quenching step represents more efficient utilization of energy since it is not necessary to reheat the feed stock to the desired annealing temperature after it has been cooled by initial quenching. It has also been found that the omission of such a first quench step as described also makes it more possible to efficiently utilize the concepts of the present invention in a continuous in-line sequence of steps. That, in turn, provides substantial eco-nomic benefits in carrying out the method of the present inven-tion.

It has been unexpectedly found that such a fabrica-tion process provides an aluminum alloy feedstock having equal or better metallurgical and formability characteristics as compared to aluminum alloys conventionally used in forming can ends and tabs.

It has been found in accordance with a preferred embodiment of the present invention that the fabrication pro-cess can be applied to alloys of the 3000 series such as AA3104 without the need to increase the thickness of the can ends and tabs to achieve comparable strengths. Without limiting the present invention as to theory, it is believed that the tech-niques of strip casting followed by rapid annealing and quench-ing provide an alloy sheet stock having improved strength by reason of solid solution and age hardening. Strip casting followed by a rapid anneal and quench step, either with or without hot rolling before annealing, facilitates the rapid processing of the feed stock so that precipitation of alloying elements of intermetallic compounds is substantially minimized.
In addition, it is believed, once again, without limiting the present invention as to theory, that formability of the sheet stock of this invention used in forming can ends and tabs is equal to or better than these DC-cast aluminum alloys contain-ing greater quantities of alloying elements. Thus, the present invention allows can ends and tabs to be produced from less expensive aluminum alloys without sacrificing the metallurgical properties of those more expensive alloys. It has also been found that the anneal and quench steps promote the formability of the can end and tab stock without adversely effecting its strength.

Brief Description of the Drawinas Fig. 1 is a schematic illustration of the continuous in-line sequence of steps employed in the practice of the first embodiment of the invention.

Fig. 2 is a schematic illustration of the continuous in-line sequence of steps employed in the practice of the second embodiment of the invention.

Fig. 3 is a schematic illustration of the continuous in-line sequence of steps employed in the practice of the third embodiment of the invention.

Fig. 4 is a schematic illustration of preferred strip casting apparatus used in the practice of the invention.
Fig. 5 is a generalized time-temperature transforma-tion diagram for aluminum alloys illustrating how rapid heating and quenching serves to eliminate or at least substantially minimize precipitation of alloying elements in the form of intermetallic compounds.

Fig. 6 is a schematic illustration showing a process utilizing a continuous in-line sequence of steps for producing aluminum alloy sheet stock.

Fig. 7 is a drawing of a blank produced with a convoluted die to control earing in accordance with the inven-tion.

Fig. 8 is a schematic illustration of two continuous sequences of steps employed in accordance with another embodi-ment of the invention.

Detailed Description of the Drawinas The sequence of steps employed in the embodiment of the invention are illustrated in Fig. 1. One of the advances of the present invention is that the processing steps for pro-ducing sheet stock can be arranged in two continuous in-line sequences whereby the various process steps are carried out in sequence. The practice of the invention in a narrow width (for example, 12 inches) make it practical for the present process to be conveniently and economically located in or adjacent to sheet stock customer facilities. In that way, the process of the invention can be operated in accordance with the particular technical and throughput needs for sheet stock users.

In the preferred embodiment, molten metal is delivered from a furnace not shown in the drawing to a metal degassing and filtering device to reduce dissolved gases and particulate matter from the molten metal, also not shown. The molten metal is immediately converted to a cast feedstock or strip 4 in casting apparatus 3.

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. Patent No.
3,937,270 and the patents referred to therein. In some appli-cations, it may be preferable to employ as the technique for casting the aluminum strip the method and apparatus described in U.S. Patent No. 5,564,491.

The strip casting technique described in the forego-ing U.S. Patent No. 5,564,491 which can advantageously be em-ployed in the practice of this invention is illustrated in Fig.
2 of the drawing. As there shown, the apparatus includes a pair of endless belts 10 and 12 carried by a pair of upper pulleys 14 and 16 and a pair of corresponding lower pulleys 18 and 20. Each pulley is mounted for rotation, and is a suitable heat resistant pulley. Either or both of the upper pulleys 14 and 16 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 18 and 20. Each of the belts 10 and 12 is an endless belt and is preferably formed of a metal which has low reactivity with the aluminum being cast.
Low-carbon steel or copper are frequently preferred materials for use in the endless belts.

The pulleys are positioned, as illustrated in Fig.
2, one above the other with a molding gap therebetween corre-sponding to the desired thickness of the aluminum strip being cast.

Molten metal to be cast is supplied to the molding gap through suitable metal supply means such as a tundish 28.
The inside of the tundish 28 corresponds substantially in width to the width of the belts 10 and 12 and includes a metal supply delivery casting nozzle 30 to deliver molten metal to the molding gap between the belts 10 and 12.

The casting apparatus also includes a pair of cooling means 32 and 34 positioned opposite that position of the endless belt in contact with the metal being cast in the molding gap between the belts. The cooling means 32 and 34 thus serve to cool belts 10 and 12, respectively, before they come into contact with the molten metal. In the preferred embodiment illustrated in Fig. 2, coolers 32 and 34 are posi-tioned as shown on the return run of belts 10 and 12, respec-tively. In that embodiment, the cooling means 32 and 34 can be conventional cooling devices such as fluid nozzles positioned to spray a cooling fluid directly on the inside and/or outside of belts 10 and 12 to cool the belts through their thicknesses. Further details respecting the strip casting apparatus may be found in U.S. Patent No. 5,564,491.
Returning to Fig. 1, the feedstock 4 from the strip caster 3 is moved through optional shear and trim station 5 into optional one or more hot rolling stands 6 where its thickness is decreased. Immediately after the hot rolling operation has been performed in the hot rolling stands 6, the feedstock is passed to a quenching station 7 wherein the feedstock, still at an elevated temperature from the casting operation, is contacted with a cooling fluid. Any of a variety of quenching devices may be used in the practice of the invention. Typically, the quenching station is one in which a cooling fluid, either in liquid or gaseous form, is sprayed onto the hot feedstock to rapidly reduce its temperature.
Suitable cooling fluids include water, air,.liquefied gases such as carbon dioxide or nitrogen, and the like. It is;
important that the quench be carried out quickly to reduce the temperature of the hot feedstock rapidly to prevent substantial precipitation of alloying elements from solid solution.

It will be appreciated by those skilled in the art that there can be expected some insignificant precipitation of intermetallic compounds that do not affect the final proper-ties. Such minor precipitation has no affect on those final properties either be reason of the fact that the intermetallic =
compounds are small and redissolved during the rapid annealing step in any case, or their volume and type have a negligible effect on the final properties. As used herein, the term "substantial" refers to precipitation which affects the final sheet properties.

In general, the temperature is reduced from a temperature ranging from about 600 to about 950 F to a tempera-ture below 550 F, and preferably below 450 F. The importance of rapid cooling following hot rolling is illustrated by Fig. 3 of the drawings, a generalized graphical representation of the formation of precipitates of alloying elements as a function of time and temperature. Such curves, which are generally known in the art as time-temperature transformation or "C" curves, show the formation of coarse and fine particles formed by the precipitation of alloying elements as intermetallic compounds as an aluminum alloy is heated or cooled. Thus, the cooling afforded by the quench operation immediately following hot rolling is effected at a rate such that the temperature-time line followed by the aluminum alloy during the quench remains between the ordinate and the curves. That ensures that cooling is effected sufficiently rapidly so as to substantially avoid the precipitation of such alloying elements as intermetallic compounds.

In a preferred embodiment of the invention, the feedstock is passed from the quenching step to one or more cold rolling stands 19 in which the feedstock is worked to harden the alloy and reduce its thickness to finish gauge. In the preferred practice of the invention, it is sometimes desirable, after cold rolling to age the cold roll strip at an elevated temperature, preferably at temperatures within the range of 300-375 F for about 1 to about 10 hours. Because the strip has been quenched immediately following low rolling so as to substantially minimize precipitation of alloying elements as intermetallic compounds, the cast strip has an unusually high level of solute supersaturation. Thus, the aging step causes the ultimate tensile strength and yield strength to increase along with formability.

Thereafter, the cast strip which has been aged can either be coiled until needed or it can be immediately formed into can ends and/or tabs using conventional techniques.

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 in the cold mill 19 as part of the in-line process. Thus, the use of the cold rolling step is an optional process step of the present inven-tion, 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.

It has become the practice in the aluminum industry to employ wider cast strip or slab for reasons of economy. In the preferred embodiment of this invention, it has been found that, in contrast to this conventional approach, the economics are best served when the width of the cast feedstock 4 is maintained as a narrow strip to facilitate ease of processing and enable use of small decentralized strip rolling plants.
Good results have been obtained where the cast feedstock is less than 24 inches wide, and preferably is within the range of 2 to 20 inches wide. By employing such narrow cast strip, the investment can be greatly reduced through the use of small, two-high rolling mills and all other in-line equipment. Such small and economic micromills of the present invention can be located near the points of need, as, for example, can-making facilities. That in turn has the further advantage of minimiz-ing costs associated with packaging, shipping of products and customer scrap. Additionally, the volume and metallurgical needs of a can plant can be exactly matched to the output of an adjacent micromill.

In the practice of the invention, the hot rolling exit temperature is generally maintained within the range of 300 to 1000 F. Hot rolling is typically carried out in temper-atures within the range of 300 F to the solidus temperature of the feedstock.

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 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 cold rolling opera-tions 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 obtained whenthe hot rolling operation effects reduction in thickness within the range of 15 to 99% and the cold rolling effects a reduction within the range from 10 to 85%. As will be appreciated by those skilled in the art, strip casting carried out in accordance with the most preferred embodiment of the invention provides a feedstock which does not necessarily require a hot rolling step as outlined above.

As indicated, the concept of the present invention make it possible to utilize, as sheets stock for fabricating can ends and tabs, aluminum alloys containing smaller quanti-ties of alloying elements as compared to the prior art. As a general proposition, the concepts of the present invention may be applied to aluminum alloys containing less than 2% magne-_ sium. Representative of suitable aluminum alloys include the 3000 series of aluminum alloys such as AA3004 and AA3104.
Because of the unique combination of processing steps employed in the practice of the invention, it is possible to obtain strength levels with such low in aluminum content aluminum alloys that are equal to or better than the more expensive aluminum alloy heretofore used. In general, such alloys con-tain 0 to about 0.6% by weight silicon, from 0 to about 0.8% by weight iron, 0 to about 0.6% by wight copper, about 0.2 to 1.5%
by weight manganese, about 0.2 to 2% by weight magnesium and about 0 to about .25% by weight zinc, with the balance being aluminum with its usual impurities.

In general, such aluminum alloys treated in accor-dance with the practice of the present invention have ultimate tensile strengths and yield strengths greater than 50,000psi.

Having described the basic concepts of this embodi-ment of the present invention, reference is now made to the following examples which are provided by way of illustration and not by way of limitation to the invention.

Bxam l~ e 1 An aluminum alloy with the following composition is strip cast to a thickness of 0.080 inches:

~ ..................
~ .~
r ,::: . ,:. ;, .<: := .
':..:r..'.i3:: ..Se~.t~ . ~k, it= ..::..:%~:=r .
, . . ::.. ..=
i.. ' . ~f5:,: . ~'~~... v".....: . .;.
y ......:. . .?=.=::
t ik ~ yc,.~3i:, = =v J.:.: =
::f~:.=, r... . ~2:.. = ~~CR;;".ri4:;4k;=c=..:
Si 0.3 Fe 0.45 Cu 0.2 Mn 0.90 Mg 0.80 Aluminum and Balance impurities The hot cast strip was hot rolled to a thickness of 0.037 inches and then quenched with water. Thereafter, it was cold rolled to a finished gauge of 0.116 inches. The cast strip was then cooled and aged for several hours at 320 F. The ultimate tensile strength (UTS), yield strength (YS) and percent elonga-tion (%Elg) for the cast strip was determined and is set forth in Table 1.

Example 2 In this example, use was made of aluminum alloy having the following composition:

. ..~;, ;:=,::~:: k= ~ .s:<:.,;;,u::. =a . =
'>:' ~'=;~:~ .~''~~.:::=''~'.=''=.~'Y' ;t{:~.~in'~' ..:.sF =...:=.....:..~} .
~;~~:' ~'iit:iv:=~i '$:: +'ST:%}>:~:{' 4't2)tt~~.:v n~'rx<~}rf+i.iY..
v'{'.; ~ti.. -hq=.w'==' >' ~'.v..~v.ti'.i}t.=.;=....{,4~}:=i}5::.:A.v::..,.~~
}\~ih:1i.4,+y4 =
= ' .~. .
~ . : . = ... , .. r = : .. .. . .y,. v.:
.> : = ' ~'i"'r=K '.~1~~1 y; q\~ . = ... . ~~~ .hT=~t'+i:*
~S~'Z''~4\~~~::{'~~'r"'~'wviK:,.~.'v~ ~i::
= ..3~= . ~<W:::~.vi:i:::9,v =
Si 0.3 Fe 0.45 Cu 0.2 Mn 0.94 Mg 0.92 Aluminum and Balance Impurities In this example, the foregoing aluminum alloy was strip cast to a thickness of 0.080 inches and then subjected to fast air cool quenching. Thereafter, it was hot rolled to a finished gauge of 0.110 inches and stabilized at 320-340 F. Its properties are likewise set forth in Table 1.

Example 3 Using the same alloy as described in Example 2, the aluminum alloy strip cast to a thickness of 0.080 inches and subjected to water quenching. Thereafter, it was cold rolled to a finished gauge of 0.0110 inches and aged at 320-340 F for several hours. Its properties are likewise set forth in Table 1.

,. ..v ... .::: . ::.~:..:....v .. .
- . .::,;:~k. ;: =- ~:~~:~x<;~ n- ;~.: .}:, . , .}
;:A : . . . . . S.R.>.:il, ,' i~,'k,:: , k" ,~'' : =~..~ ;. k ; :. t ' ~=;;~-,~,<,Y:~4;~,, ,'4~
. . . , .:: ;k~õ~''~'~~r:~:;v~ ;;::'=:7~ '~;,: ".~ .3.:~ss~:skf:.~~.'',~... -~s: " k <:=~r~ .:k.".".'~,.
~ ~.}}4'= , 4:'Y= = $kti=' f..,:Ki'.n 4' : { ff '. .} :.} . i~y O.. nvt'. .cZ.=:,.k>'~ . ' :="{y ~~( f~~'." ~' -:~\.}:N..:;k:tfn'.}: }ik:KWiO'~~= ..k~+m' .=,.k:5:'J~i-w? v=,'"~ui }.4T:~:i:}j~ry-=y'~'ff'.p, ~~;$~ ,~= ,~=,y': . '~g ?.
i eii~-=i?i>i~:.:~.,v'y~,+,~.~,=~'.==-,,.,~,===,~:h#: .;;i=
Example 1 51.6 47.8 7.2 Example 2 55.8 52.8 6.5 Example 3 58.2 55.0 4.6 For purposes of comparison, there is set forth below Examples A & B using, in the case of comparative Example A, conventionally prepared aluminum alloy AA5182 having a finished gauge of 0.0112 inches and, in the case of Example B another, standard can lid aluminum. The compositions and the physical properties associated with them are set forth in the following table. The data shows that it is possible to employ in the practice of the invention, as the aluminum alloy for fabrica-tion of can lids and tabs, low-aluminum content aluminum alloy without any sacrifice in metallurgic properties.

T'ABLE 2 f . f:5~'' ,= ~ '; ~i':,',f=~~':=:k: '.~:.o :2 ' '~f'f~ti '' =}~''';:=
;?,:fi.x,,. = t : ,'.,:: ,';ii{;Y,;;;:. ~. . -: =.'+},.,t:.}'x.::.. . ' a$F:=
. õ , = y =~
:=: = v . a :.. ..
,=.i . . .~,ya :=}+:.'õ ;''w' ,i? .: ii:r,~}.'=?::?'r.:=<a'a.::, f t'k=+ :i:}.
.'S4+:'.,G: ~i:
u _ ~ .:.,r.=.S.}. ""~yr:>~ ~.. , ,y.,:.:r: h= : = ,;: }. .}i .. ,~r.õ :}..
'iii71: :' f <=. ~::8:;,=
-:. =.
- .. . ~:
::~:} I i'i0~
d: .== =V.
~;it4,:=' {f. .;. :ih'='}=k'...::':f.'=;'' i:;.~ ~ :r: .
.:= := = . . . "...= . .
-.,~.~,~,~~.:.''.~,/.:=> iY,;fo,l,. ,..:}5<,3~::. .,,:,=r . r<. ,.. .T ..}y.:r r:,..,..r.::::=...~=. i:
.::=.. .. .... ::. ...:. :. .::.:,c:v.....,c:f .:. tt=.. ':~a.=.:.:
:!i?::}:w::.,,.}.n :,::: = ,.,:,:::~,?.:;=:, '",i..,k;:.::5<:;k#.'=,-~:4'':.,''= :r:ic.S.ck=:.-'.=:.N}..! , ~~:i<3.~,.
..:. . .:: ...... . f '.;f .'~.:::'.-.'="::::}:...:.. . . . :. .. +r: -:
i~i.:T ..:::. .:.. .... . :': :':: i{:;.::=.
A 0.1 0.2 0.05 0.3 4.4- 53-56 46-49 6-9 4.6 B 0.15 0.40 0.17- 0.90- 1.07- 44-47 40-44 5-6 0.25 1.12 1.30 The second embodiment of the invention utilizing an intermediate anneal step is illustrated in Fig. 2. The strip casting operation in strip caster 3, the optional hot rolling 6 and quench 7 are the same as shown in Fig. 1.

After quenching, the feedstock may be rolled and stored until needed. Alternatively, it may be continuously passed to an optional cold rolling stand 15 and then to a flash annealing furnace 17 in which the feedstock, in either coil or strip form, is rapidly heated. That rapid annealing step provides an improved combination of metallic properties such as grain size, strength and formability. Because the feedstock is rapidly heated, substantial precipitation of alloying elements is likewise avoided. Thus the heating operations should be carried out to the desired annealing and recrystallization temperature such that the temperature-time line followed by the aluminum alloy does not cross the C-curves illustrated in Fig.
in such a way as to cause substantial precipitation.

Immediately following the heater 17 is a quench station 18 in which the strip is rapidly cooled or quenched by means of a conventional cooling fluid to a temperature suitable for cold rolling. Because the feedstock is rapidly cooled in the quench step 18, there is insufficient time to cause any substantial precipitation of alloying elements from solid solution.

In a preferred embodiment of the invention, the feedstock is passed from the quenching step to one or more cold WO 97/11205 PC''/US96/14877 rolling stands 19 in which the feedstock is worked to harden the alloy and reduce its thiclcness to finish gauge. In the preferred practice of the invention, it is sometimes desirable, after cold rolling to age the cold-rolled strip at an elevated temperature, preferably at temperatures within the range of 220-400 F for about 1 to about 10 hours. Because the strip has been quenched immediately following hot rolling so as to sub-stantially mini-mize precipitation of alloying elements as intermetallic com-pounds, the cast strip has an unusually high level of solute supersaturation. Thus, the aging step causes the ultimate tensile strength and yield strength to increase along with formability.

Thereafter, the strip which has been aged can either be coiled until needed or it can be immediately formed into can ends and/or tabs using conventional techniques.

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 in the cold mill 19 as part of the in-line process. Thus, the use of the cold rolling step is an optional process step of the present inven-tion, 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.

In the practice of the invention, the hot rolling exit temperature is generally maintained within the range of 300 to 1000 F. Hot rolling is typically carried out in temper-atures within the range of 300 F to the solidus temperature of the feedstock.

The annealing step in which the feedstock is sub-jected to solution heat treatment to cause recrystallization is effected at a temperature within the range of 600 to 1200 F for less than 120 seconds, and preferably 0.1 to 10 seconds.
Immediately following heat treatment, the feedstock in the form of strip 4 is water quenched to temperatures necessary to continue to retain alloying elements in solid solution, typi-cally at temperatures less than 400 F.

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 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 cold rolling opera-tions of the invention is not critical to the practice of the invention. In general, good results are obtained when the hot -rolling operation effects reduction in thickness within the range of 15 to 99% and the cold rolling effects a reduction within the range from 10 to 85%. As will be appreciated by those skilled in the art, strip casting carried out in accor-dance with the most preferred embodiment of the invention provides a feedstock which does not necessarily require a hot rolling step as outlined above.

As indicated, this embodiment of the present inven-tion make it possible to utilize, as sheets stock for fabricat-ing can ends and tabs, aluminum alloys containing smaller quantities of alloying elements as compared to the prior art.
As a general proposition, the concepts of the present invention may be applied to aluminum alloys containing less than 2%
magnesium. Represen-tative of suitable aluminum alloys include the 3000 series of aluminum alloys such as AA3004 and AA3104.
Because of the unique combination of processing steps employed in the practice of the invention, it is possible to obtain strength and formability levels with such low alloy content aluminum alloys that are equal to or better than the more expensive aluminum alloy heretofore used. In general, such alloys contain 0 to about 0.6% by weight silicon, from 0 to about 0.8% by weight iron, 0 to about 0.6% by weight copper, about 0.2 to 1.5% by weight manganese, about 0.2 to 2% by weight magnesium and about 0 to about .25% by weight zinc, with the balance being aluminum with its usual impurities.

Having described the basic concepts of this embodi-ment of the present invention, reference is now made to the following examples which are provided by way of illustration and not by way of limitation to the invention.

Exam~le 4 An aluminum alloy with the following composition was strip cast to a thickness of 0.090 inches:

... -,,.,= _ :. ..::~ ~ ,}<. ., . = = . :. A.=. ? = = :::,~::;;~, : -,.~, . <.:;.
;~. ... =. .
.=:,}=. .... v......; ...
.:rnL= :. .. ; .v'f'..::n.C ' ={::{n A }:;, : :~ }K: =:=..,= :. =}. =4{=.'+ :~ } ~~+ .:.'õ ..,v.}'. v:
Yv1.:::'.:
..., :.= .; . }=.
. .:.::.}r , . ::::.. .
. : >:.. .'4,= ;==.~'y:,.~ 4i'{:.}~,J}= =' , '= = ' =~' > '~!:.:2~.. :.~~:.' '~ ~~>=:
~' :.~~~~ :s~~ ::f'~'; ~'=.,' " ;;
'..;
;~ == ,:=.. ., . ..;
i:.. =: : . . = . ;;..}..~~ , :. =. ....:.: : :
~, ~..:,.. , ~.=~~5=' , =} .;~:; :.:::Y >.{
. ...i}:~:4:=:i=:tv:..iw:T:. .. . K=.:'i'~.+}Jh:}J4;~.K=:
Si 0.3 Fe 0.45 Cu 0.2 Mn 0.90 Mg 0.80 Aluminum and Balance Impurities The hot cast strip was then immediately rolled to a thickness of 0.045 inches and heated for five seconds at a temperature of 1000 F and immediately thereafter quenched in water. The feedstock was then rolled to a thickness of 0.0116 inches and stabilized at 320 F for two hours at finish gauge.
It had an ultimate tensile strength of 56,000 psi, a yield strength of 50,600 psi and 7.2% elongation.

The third embodiment of the invention is shown in Fig. 3 of the drawings and utilizes an annealing step prior to quenching. As before, the strip casting operation 3 and the optional hot rolling 6 operations are the same as described in relation to Figs. 1 and 2.

Immediately after the optional hot rolling operation has been performed in the hot rolling stands 6, the feedstock is passed to a annealing furnace 27 wherein the feedstock, still at an elevated temperature from the casting operation, is rapidly heated, as by flash annealing. That rapid annealing provides an improved combination of metallurgical properties such as grain size, strength and formability. Because the feed stock is rapidly heated, substantial precipitation of alloying elements is avoided.

Immediately following the annealing furnace 27 is a quench station 8 in which the feedstock is rapidly cooled or quenched by means of a conventional cooling fluid to a temperature suitable for cold rolling. Because the feedstock is rapidly cooled in the quench station 8, there is likewise insufficient time to cause any substantial precipitation of alloying elements from solid solution. It is important as before that the quench be carried out quickly to reduce the temperature of the hot feedstock rapidly to prevent substantial precipitation of alloying elements from solid solution.

The importance of rapid heating and quenchinq is illustrated by Fig. 3 of the drawings, a generalized graphical -representation of the formation of precipitates of alloying elements as a function of time and temperature. Thus, the heating effected in the annealing step and the cooling effected by the quench operation immediately following annealing is effected at a rate such that the temperature-time line followed by the aluminum alloy during the heating and quenching remains between the ordinate and the curves. That ensures that heating and cooling is effected sufficiently rapidly so as to avoid substantial precipitation of such alloying elements as intermetallic compounds.

In this embodiment of the invention, the feedstock is passed from the quenching step to one or more cold rolling stands 19 in which the feedstock is worked to harden the alloy and reduce its thickness to finish gauge. In the preferred practice, it is sometimes desirable, after cold rolling to age the cold-rolled strip at an elevated temperature, preferably at temperatures within the range of 220-400 F for about 1 to about hours. Because the strip has been quenched immediately following annealing so as to substantially minimize precipita-tion of alloying elements as intermetallic compounds, the cast strip has an unusually high level of solute supersaturation.
Thus, the aging step causes the ultimate tensile strength and yield strength to increase along with formability.

-Thereafter, the strip which has been aged can either be coiled until needed or it can be immediately formed into can ends and/or tabs using conventional techniques.

As will be appreciated by those skilled in the art, it is possible to realize the benefits of this embodiment of the present invention without carrying out the cold rolling step in the cold mill 19 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.

In the practice of this embodiment, the hot rolling exit temperature is generally maintained within the range of 300 to 1000 F. Hot rolling is typically carried out in temper-atures within the range of 300 F to the solidus temperature of the feedstock.

The annealing step in which the feedstock is sub-jected to solution heat treatment to cause recrystallization is effected at a temperature within the range of 600 to 1200 F for less than 120 seconds, and preferably 0.1 to 10 seconds.
Immediately following heat treatment, the feedstock in the form of strip 4 is quenched to temperatures necessary to continue to retain alloying elements in solid solution, typically at tem-peratures less than 550 F.

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 this embodiment of the 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 cold rolling operations of the invention is not critical to the practice of the invention. In general, good results are ob-tained when the hot rolling operation effects reduction in thickness within the range of 15 to 99% and the cold rolling effects a reduction within the range from 10 to 85%. As will be appreciated by those skilled in the art, strip casting carried out in accordance with the most preferred embodiment of the invention provides a feedstock which does not necessarily require a hot rolling step as outlined above.

As indicated, the concept of the present invention make it possible to utilize, as sheets stock for fabricating can ends and tabs, aluminum alloys containing smaller quanti-ties of alloying elements as compared to the prior art. As a general proposition, the concepts of the present invention may be applied to aluminum alloys containing less than 2% magne-sium. Representative of suitable aluminum alloys include the 3000 series of aluminum alloys such as AA3004 and AA3104.
Because of the unique combination of processing steps employed in the practice of the invention, it is possible to obtain strength and formability levels with such low alloy content aluminum alloys that are equal to or better than the more expensive aluminum alloy heretofore used. In general, such alloys contain 0 to about 0.6% by weight silicon, from 0 to about 0.8% by weight iron, 0 to about 0.6% by weight copper, about 0.2 to 1.5% by weight manganese, about 0.2 to 2% by weight magnesium and about 0 to about .25% by weight zinc, with the balance being aluminum with its usual impurities.

Having described the basic concept of this embodiment, reference is now made to the following examples which are provided by way of illustration and not by way of limitation to the invention.

Examr)le 5 An aluminum alloy with the following composition was strip cast to a thickness of 0.090 inches:

-.. =. .:.. .
..;
~ = r. .,:N:;::: :.:' '; ' ~ ' ~.
.. . .'::
.:.
...: ~~ . ~~~. ...:..:
. :=.=.. ;:~ ' ,. ..
~ .:, .:. =.<:
. . .. :..... ' '~:.::.
... . . Y ' = õ3',.v,.. .f . .:...... =n .:. :....=.:: . .
:.:.:.:~....n:::=:... ::.C,.... .
si 0.3 Fe 0.45 Cu 0.2 Mn 0.90 Mg 0.80 Aluminum and Balance Impurities The hot cast strip was then immediately rolled to a thickness of 0.045 inches and heated for five seconds at a temperature of 1000 F and immediately thereafter quenched in water. The feedstock was then rolled to a thickness of 0.0116 inches and stabilized at 320 F for two hours at finish gauge.
It had an ultimate tensile strength of 56,000 psi, a yield strength of 50,600 psi and 7.2% elongation.

The concepts as described above all relate to the manufacture of can ends and tabs for aluminum alloy beverage containers which present different problems as compared to the manufacture of aluminum alloy can stock employed in the making of the side walls and bottoms of aluminum alloy beverage con-tainers. As is also described above, it is often times advan-tageous to employ continuous in-line sequences of the foregoing steps in the processing of aluminum alloy in the manufacture of aluminum alloy can stock.

In U.S. Patent No. 5,496,423 there is disclosed a new concept in the processing of aluminum alloys in the manufacture of aluminum can stock. It has been discovered that it is possible to combine casting, hot rolling, annealing, solution heat treating, quenching and cold rolling into one continuous, in-line operation in the production of aluminum alloy can body stock. One of the advantages afforded by the process of the foregoing application is that it is possible to operate the continuous, in-line sequence of steps at very high speeds, of the order of several hundred feet per minute. One of the disadvantages that has been discovered in connection with the process of the foregoing application is that the intermediate annealing step, which provides re-solution of soluble elements and earing control through recrystallization of the sheet, may be a limiting factor on the speed at which the process can be operated. Thus, as production speed increases, the continuous annealing furnace preferably used in the practice of the process disclosed in the foregoing application must be made longer and be run at higher energy levels, representing an increase in the cost of capital equipment and the cost in operating the process. It would, therefore, be desirable that the continuous annealing step be avoided.

It is possible to produce aluminum alloy sheet stock, and preferably aluminum alloy can body stock having desirable metallurgical properties by using, in one continuous sequence of steps, the steps of providing a hot aluminum alloy feedstock which is subjected to a series of rolling steps to rapidly and continuously cool the feedstock to the thickness and metallurgical properties without the need to employ an annealing step conventionally used in the prior art. In simi-lar prior art processes, such as that described in U.S. Patent No. 4,282,044, it has been suggested that aluminum alloy can body stock can be produced by strip casting, followed by roll-ing and coiling whereby the rolled feedstock in the form of coils is allowed to slowly cool. Thereafter, the coil is later annealed to improve the metallurgical properties of the sheet stock.

It has been found, in accordance with the present invention, that when the feedstock is rapidly cooled following casting, it is unnecessary to employ annealing steps to attain the desired metallurgical properties resulting from solution of soluble elements. Without limiting the present invention as to theory, it is believed that the rapid cooling effected by the continuous, in-line rolling operations is carried out in a sufficiently short period of time to prevent precipitation of alloying elements contained in the aluminum feedstock as inter-metallic compounds. That precipitation reaction is a diffusion-controlled reaction, requiring the passage of time.
Where the feedstock is rapidly cooled during rolling, there is insufficient time to permit the diffusion-controlled precipita--tion from occurring. That, in turn, not only facilitates in-line processing of the aluminum alloy to minimize the number of materials handling steps, so too does the rapid cooling prevent substantial precipitation of alloying elements, making it un-necessary to utilize a high temperature annealing step to attain the desired strength in the final can product.

The feedstock produced by the method of the present invention is characterized as being produced in a highly economical fashion without the need to employ a costly anneal-ing step. As will be understood by those skilled in the art, annealing has been used in the prior art to minimize earing.
It has been found, in accordance with the practice of this invention, that, the conditions (time and temperature) of hot rolling, the thickness of the alloy as strip cast and the speed at which it is cast can be used to control earing. For exam-ple, casting the aluminum alloy at reduced thickness is be-lieved to reduce earing; similarly, casting at higher speeds can likewise reduce earing. Nonetheless, where use is made of processing conditions which tend to yield an aluminum alloy strip having a tendency toward higher earing, that phenomenon can be controlled by means of an alternative embodiment.

In accordance with that alternative embodiment of the invention, the high earing that can occur on the feedstock can be compensated for by cutting the processed feedstock into non-circular blanks prior to cupping, using what has become WO 97/11205 PCTlUS96/14877 known in the art as convoluted die. The use of a convoluted die compensates for any earing tendencies of the sheet stock, by removing metal from those peripheral portions of the blank which would be converted to ears on cup-drawing. Thus, the convoluted die offsets any earing that would otherwise be caused by the omission of high temperature annealing.

In accordance with a preferred embodiment of the invention, the strip is fabricated by strip casting to produce a cast thickness less than 1.0 inches, and preferably within the range of 0.01 to 0.2 inches.

In another preferred embodiment, the width of the strip, slab or plate is narrow, contrary to conventional wis-dom; this facilitates ease of in-line threading and processing, minimizes investment in equipment and mini.mizes cost in the conversion of molten metal to can body stock.

The preferred process of the present invention involves a new method for the manufacture of aluminum alloy cups and can bodies utilizing the following process steps in one, continuous in-line sequence:

(a) In the first step, a hot aluminum feedstock is provided, preferably by strip casting; and (b) The feedstock is, in the preferred embodiment, subjected to rolling to rapidly and continu-ously cool the sheet stock to the desired thickness and attain the desired strength prop-erties.

The cooled feedstock can then be either formed into a coil for later use or can be further processed to form non-circular blanks by means of a convoluted die to effect earing control, in accordance with conventional procedures.

It is an important concept of this embodiment of the invention that the rolling of the freshly cast strip be ef-fected rapidly, before there is sufficient time for the diffusion-controlled reaction by which alloying elements are precipitated from solid solution as intermetallic compounds.

In that way, the process of the present invention makes it possible to omit high temperature annealing as is required in the prior art to effect solution of soluble alloying elements.
In general, the cast feedstock must be cooled to cold rolling temperatures in less than 30 second, and preferably in less than 10 seconds.

In a preferred embodiment, the overall process of the present invention embodies characteristics which differ from the prior art processes: ~

-(a) The width of the can body stock product is narrow;

(b) The can body stock is produced by utilizing small, in-line, simple machinery;

(c) The tendency of the non-annealed aluminum alloy to exhibit high earing is offset through the use of a convoluted die while achieving desir-able strength properties; and (d) The said small can stock plants are located in or adjacent to the can making plants, and therefore packaging and shipping operations are eliminated.

The in-line arrangement of the processing steps in a narrow width (for example, 12 inches) makes it possible for the process to be conveniently and economically located in or adja-cent to can production facilities. In that way, the process of the invention can be operated in accordance with the particular technical and throughput needs for can stock of can making facilities.

In the preferred embodiment of the invention as illustrated in Fig. 6, the sequence of steps employed in the practice of the present invention is illustrated. One of the advances of the present invention is that the processing steps for producing can body sheet can be arranged in one continuous line whereby the various process steps are carried out in sequence. Thus, numerous handling operations are entirely eliminated.

In the preferred embodiment, molten metal is delivered from a furnace 1 to a metal degassing and filtering device 2 to reduce dissolved gases and particulate matter from the molten metal, as shown in Fig. 1 The molten metal is immediately converted to a cast feedstock 4 in casting appara-tus 3. 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. Herein, an aluminum "ingot" typically has a thickness ranging from about 6 inches to about 30 inches, and is usually produced by direct chill casting or electromagnetic casting. An aluminum "plate", on the other hand, herein refers to an aluminum alloy having 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. 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. The term "strip" is herein used to refer to an aluminum alloy, typically having a thickness less than 0.375 inches. In the usual case, both slabs and strips are produced by continuous casting techniques well known to those skilled in the art.

The feedstock employed in the practice of this embodiment 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. Patent No. 3,937,270 and the patents referred to therein.
In some applications, it is preferable to employ as the technique for casting the aluminum strip the method and apparatus described in U.S. Patent Nos. 6,102,102, 5,515,908, and 5,564,491. The strip casting technique described in the foregoing U.S. patents which can advantageously be employed in the practice of this invention is illustrated in Fig. 4 of the drawing as described above.

The feedstock 4 is moved through optional pinch rolls 5 into one or more hot rolling stands 6 where its thick-ness is decreased. In addition, the rolling stands serve to rapidly cool the feedstock to prevent or inhibit precipitation of the strengthening alloying components such as manganese, copper, magnesium and silicon present in the aluminum alloy.
As will be appreciated by those skilled in the art, use can be made of one or more rolling steps which serve to reduce thickness of the strip 4 while simultaneously rapidly cooling the strip to avoid precipitation of alloying elements.
The exit temperature from the strip caster 3 varies within the range of about 700 F to the solidus temperature of the alloy.
The rolling operations rapidly cool the temperature of the cast strip 4 to temperatures suitable for cold rolling, generally below 350 F in less than 30 seconds, and preferably in less than 10 seconds, to ensure that the cooling is effected suffi-ciently rapidly to avoid or substantially minimize precipita-tion of alloying elements from solid solution. The effect of the rapidly cooling may be illustrated by reference to Fig. 5 of the drawing, showing the formation of intermetallic precipi-tates in aluminum as a function of temperature and time. It is importance in the practice of the present invention to rapidly cool the feedstock during the rolling operations so that the strip 4 is cooled along a temperature time line that does not intersect the curves shown on Fig. 5 of the drawing. The prior art practice of allowing a slow cool of, for example, a coil, results in a temperature time line which intersects those curves, maintaining that the slow cooling causes precipitation of alloying elements as intermetallic compounds.

The effect of the reductions in thickness likewise effected by the rolling operations are subject to wide varia-tion, depending upon the types of feedstock employed, their chemistry and the manner in which they are produced. For that reason, the percent reduction in thickness of the rolling -operations is not critical to the practice of the invention.
In general, good results are obtained when the rolling opera-tion effects a reduction in thickness within the range of 40 to 99 percent of the original thickness of the cast strip.

Alternatively, it is preferred to immediately cut blanks using a convoluted die and produce cups for the manufac-ture of cans instead of coiling the strip or slab 4. Convo-luted dies useful in the practice of the present invention are known to the art, and are described in U.S. Patent Nos.
4,711,611 and 5,095,733. Such dies are now conventional and well known to those skilled in the art. The convoluted dies used in the practice of this invention may be used to form a non-circular blank having the configuration shown in Fig. 7 which in turn can be used to form a cup having the configura-tion shown in the same Figure. Thus, the convoluted die can be used, where necessary, to minimize earing tendencies of the sheet stock.

As will be appreciated by those skilled in the art, it is also possible, before treating the sheet stock with a convoluted die, to coil the sheet stock.

The concepts of this embodiment of the present invention are applicable to a wide range of aluminum alloys for use as can body stock. In general, alloys suitable for use in the practice of the present invention are those aluminum alloys containing from about 0 to about 0.6% by weight silicon, from 0 to about 0.8% by weight iron, from about 0 to about 0.6% by weight copper, from about 0.2 to about 1.5% by weight manga-nese, from about 0.2 to about 4% by weight magnesium, from about 0 to about 0.25% by weight zinc, with the balance being aluminum with its usual impurities. Representative of suitable alloys include aluminum alloys from the 3000 and 5000 series, such as AA 3004, AA 3104 and AA 5017.

Having described the basic concepts of this embodiment of the invention, reference is now made to the following examples which are provided by way of illustration of the practice of the invention.

Examnle 6 A sheet of finish gauge can stock which was not annealed was formed into a cup using a conventional round die.
The earing was measured as 6.6%.

An adjacent sheet from the same processing (still without an anneal) was formed into a cup with a convolute cut edge on the blanking die. The earing was measured as 3.1%.
Example 7 A thin strip of metal 0.09 inch thick was cast at 300 feet per minute and immediately rolled in three passes at high speed from 0.090 inch thick to 0.0114 inch thick while decreasing in temperature during rolling from 900 F to 300 F.
The earing of the sheet so produced was 3.8%. The ultimate tensile strength of the sheet was 43,400 psi and the elongation 4.4%.

A variation of the continuous in-line operation for aluminum alloy can stock disclosed and claimed in United States Patent No. 5,356,495 in which use is made of two sequences of continuous, in-line operations. In the first sequence, the aluminum alloy feedstock is first subjected to hot rolling, coiling and coil self annealing and the second sequence in-cludes the continuous, in-line sequence of uncoiling, quenching without intermediate cooling, cold rolling and coiling. The process as described in the latter patent has the advantage of eliminating the capital costs of an annealing furnace while nonetheless providing aluminum sheet and can stock having strength associated with aluminum alloys which have been heat treated.

It has now been discovered that aluminum alloys and can stock can be produced by utilizing two different sequences of in-line continuous operation in which the first sequence includes a quenching step and the second sequence includes a rapid annealing step to provide aluminum alloy sheet stock and can stock having highly desirable metallurgical properties. It has been found that the rapid quenching in the first sequence of steps and the rapid heating followed by quenching in the second sequence of steps do not permit substantial precipita-tion of alloying elements present in the alloy and, thus, affords an aluminum alloy sheet and can stock having highly desirable metallurgical properties.

It is possible to combine casting, hot rolling and rapid quenching in a first continuous sequence of steps whereby the rapid quenching does not permit substantial precipitation of alloying elements from solid solution, thereby ensuring that the alloying elements remain in solid solution. Thereafter, in a second sequence of continuous, in-line steps, the aluminum alloy sheet can be flash annealed and rapidly quenched to ensure that alloying elements are in solid solution. The annealing followed by quenching in the second sequence of steps maximizes alloying elements in solid solution to strengthen the final product.

As used herein, the term "anneal" or "flash anneal"
refers to a heating process to effect recrystallization of the grains of aluminum alloy to produce uniform formability and to control earing. Flash annealing, as referred to herein, refers to a rapid annealing process which serves to recrystallize the aluminum grains without causing substantial precipitation of intermetallic compounds. Slow heating and cooling of the aluminum alloy are known to cause substantial precipitation of intermetallic compounds. Therefore, it is an important concept of the invention that the heating, flash annealing and quench-ing be carried out rapidly. 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 elimi-nates costly materials handling steps, in-process inventory and losses associated with starting and stopping the processes.

The process of the present invention thus involves a new method for the manufacture of aluminum alloy sheet and can body stock utilizing the following process steps in two con-tinuous, in-line sequences. In the first sequence, the follow-ing steps are carried out continuously and in-line:

(a) A hot aluminum feedstock is hot rolled to re-duce its thickness;

(b) The hot reduced feedstock is thereafter rapidly quenched without substantial precipitation of alloying elements such as manganese to a temperature suitable for cold rolling;

(c) The quenched feedstock is, in the preferred em--bodiment of the invention, subjected to cold rolling to produce intermediate gauge sheet ;
and (d) The feedstock is coiled for further processing.

Thereafter, in a second sequence, the following steps may be carried out continuously and in-line:

(a) The feedstock is uncoiled and, optionally, can be subjected to cold rolling if desired to further reduce the thickness of the stock;

(b) The feedstock is subjected to a flash anneal to effect recrystallization of the aluminum grains at a sufficiently rapid rate to avoid substan-tial precipitation of alloying elements as intermetallic compounds and, thereafter, the feedstock is subjected to a rapid quench, also effectedrapidly so as to substantially avoid precipitation of alloying elements as intermetallic compounds; and (c) The quenched feedstock is thereafter subjected to further cold rolling and coiling to finish gauge.

It is an important concept of the invention that the flash anneal and the quench operation be carried out rapidly to ensure that alloying elements, and particularly manganese, as well as compounds of copper, silicon, magnesium and aluminum, remain in solid solution. As is well known to those skilled in the art, the precipitation hardening of aluminum is a diffusion controlled phenomena which is time dependent. It is therefore important that the flash annealing and quenching operations of the second sequence of steps be carried out sufficiently rap-idly that there is insufficient time to result in substantial precipitation of intermetallic compounds of copper, silicon, magnesium, iron, aluminum and manganese. At the same time, the annealing and quenching operations of the second step likewise minimize earing. That is particularly important when the aluminum alloy is a can stock alloy since earing is a phenome-non frequently found in the formation of cans from can body stock in which the plastic deformation to which the aluminum alloy is subjected is non-uniform. Thus, minimizing precipita-tion of intermetallic compounds raises the strength, allows recrystallization to be done at a lighter gauge, minimizes finish cold work and thereby reduces earing.

In accordance with a preferred embodiment of the invention, the strip is fabricated by strip casting to produce a cast thickness less than 1.0 inches, and preferably within the range of 0.06 to 0.2 inches. In another preferred embodi-ment, the width of the strip, slab or plate is narrow, contrary to conventional wisdom. This facilitates ease of in-line threading and processing, minimizes investment in equipment and minimizes cost in the conversion of molten metal to the sheet stock.

The sequence of steps employed in this embodiment of the invention are illustrated in Fig. 8. One of the advances of the present invention is that the processing steps for pro-ducing sheet stock can be arranged in two continuous in-line sequences whereby the various process steps are carried out in sequence. The practice of the invention in a narrow width (for example, 12 inches) make it practical for the present process to be conveniently and economically located in or adjacent to sheet stock customer facilities. In that way, the process of the invention can be operated in accordance with the particular technical and throughput needs for sheet stock users.

In the preferred embodiment, molten metal is delivered from a furnace not shown in the drawing to a metal degassing and filtering device to reduce dissolved gases and particulate matter from the molten metal, also not shown. The molten metal is immediately converted to a cast feedstock 4 in casting apparatus 3.

The strip casting technique described in the forego-ing co-pending applications which can advantageously be em-ployed in the practice of this invention is illustrated in Fig.
4 of the drawing as described above. The feedstock 4 from the strip caster 3 is moved through optional shear and trim station into one or more hot rolling stands 6 where its thickness is decreased. Immediately after the hot rolling operation has been performed in the hot rolling stands 6, the feedstock is passed to a quenching station 7 wherein the feedstock, still at an elevated temperature from the casting operation, is con-tacted with a cooling fluid. Any of a variety of quenching devices may be used in the practice of the invention. Typi-cally, the quenching station is one in which a cooling fluid, either in liquid or gaseous form, is sprayed onto the hot feedstock to rapidly reduce its temperature. Suitable cooling fluids include water, liquified gases such as carbon dioxide or nitrogen, and the like. It is important that the quench be carried out quickly to reduce the temperature of the hot feedstock rapidly to prevent substantial precipitation of alloying elements from solid solution.

It will be appreciated by those skilled in the art that there can be expected some insignificant precipitation of intermetallic compounds that do not affect the final proper-ties. Such minor precipitation has no affect on those final properties either by reason of the fact that the intermetallic compounds are small and redissolve during the rapid annealing step in any case, or their volume and type have a negligible effect on the final properties. As used herein, the term "substantial" refers to precipitation which affects the final sheet properties.

In general, the temperature is reduced from a temperature ranging from about 600 to about 950 F to a tempera-ture below 550 F, and preferably below 450 F. Thereafter, the feedstock can be coiled usirig conventional coiling apparatus in a coiler 8. Alternatively, before coiling, the feedstock 4 can be subjected to cold rolling as an optional step prior to cooling.

The importance of rapid cooling following hot rolling is illustrated by Fig. 5 of the drawings, a generalized graphical representation of the formation of precipitates of alloying elements as a function of time and temperature. Such curves, which are generally known in the art as time/temperature-transformation or "C" curves, show the forma-tion of coarse and fine particles formed by the precipitation of alloying elements as intermetallic compounds as an aluminum alloy is heated or cooled. Thus, the cooling afforded by the quench operation immediately following hot rolling is effected at a rate such that the temperature-time line followed by the aluminum alloy during the quench remains between the ordinate and the curves. That ensures that cooling is effected suffi-ciently rapidly so as to avoid substantial precipitation of such alloying elements as intermetallic compounds.

Once coiled, the cooled feedstock can be stored until needed. The temperature of the feedstock has been previ-ously rapidly reduced in the quenching station 7 to prevent substantial precipitation of alloying elements and compounds thereof; hence the coil can be stored indefinitely.

.r.=..

In the second sequence of steps, when there is a need to provide finished alloy, the stored coil can then be subjected to the second continuous, in-line sequence of steps, also as shown in Fig. 8. The coil previously formed is placed in an uncoiler 13 from which it is passed to an optional cold rolling station 25 and then to a flash annealing furnace 17 in which the coil is rapidly heated. That rapid annealing step provides an improved combination of metallurgical properties such as grain size, strength and formability. Because the feedstock is rapidly heated, substantial precipitation of alloying elements likewise is avoided. Thus, the heating operation should be carried out to the desired annealing or recrystallization temperature such that the temperature-time line followed by the aluminum alloy does not cross the C-curves illustrated in Fig. 5 in such a way as to cause substaiztial precipitation. Immediately following the annealing furnace 17 is a quench station 15 in which the strip is rapidly cooled by means of a conventional cooling fluid to a temperature suitable for cold rolling. Because the feedstock is rapidly cooled in the quench step 15, there is insufficient time to cause any substantial precipitation of alloying elements from solid solution. That facilitates higher than conventional strength.
This reduces the amount of strengthening required by cold working, and less cold working reduces earing.

In the preferred embodiment of the invention,, the feedstock is passed from the quenching step to one or raore cold rolling stands 19 in which the feedstock is worked to harden the alloy and reduce its thickness to finish gauge. After cold rolling, the strip 4 is coiled to a coiler 21.

As will be appreciated by those skilled in the art, it is possible to realize the benefits of this embodiment of the present invention without carrying out the cold rolling step in the cold mill 19 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.

It is possible, and sometimes desirable, to employ appropriate automatic control apparatus; for example, it is frequently desirable to employ a surface inspection device for on-line monitoring of surface quality. In addition, a thick-ness measurement device conventionally used in the aluminum industry can be employed in a feedback loop for control of the process.

In the practice of this embodiment, the hot rolling exit temperature is generally maintained within the range of 300 to 1000 F. Hot rolling is typically carried out in temper-atures within the range of 300 F to the solidus temperature of the feedstock. The annealing and solution heat treatment is effected at a temperature within the range of 600 to 1200 F for less than 120 seconds, and preferably 0.1 to 10 seconds.
Immediately following heat treatment at those temperatures, the feedstock in the form of strip 4 is water quenched to tempera-tures necessary to continue to retain alloying elements in solid solution and to cold roll (typically less than 400 F).

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 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 cold rolling opera-tions 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 obtained when the hot rolling operation effects reduction in thickness within the range of 15 to 99% and the cold rolling effects a reduction within the range from 10 to 85%. As will be appreciated by those skilled in the art, strip casting carried out in accordance with the most preferred embodiment of the invention provides a feedstock which does not necessarily require a hot rolling step as outlined above. In those instances where the feedstock is produced by such strip casting techniques, the hot rolling step can be avoided alto-gether and, thus, is optional in the practice of the invention.

The concepts of the present invention are applicable to a wide range of aluminum alloys for use in a wide variety of products. In general, alloys from the 1000, 2000, 3000, 4000, 5000, 6000, 7000 and 8000 series are suitable for use in the practice of the present inveintion.

Having described the basic concepts of this embodiment, reference is now made to the following example which is provided by way of illustration of the practice of the invention. The sample feedstock was as cast aluminum alloy solidified rapidly enough to have secondary dendrite arm spac-ings below 10 microns.

Example 8 In Tests 1 and 2, an aluminum alloy having the composition set forth in Table 3 and a prior art example are each carried out by casting aluminum alloys using a twin belt strip caster in which the belts are cooled while they are not in contact with either molten metal or the cast metal strip to yield a cast metal strip having a thickness of 0.10 inches.
The cast stip is then processed as indicated in the Table for each of the examples to yield the products whose characteris-tics are set forth in Table 3. The prior art process illus-trated is that in U.S. Patent No. 4,292,044, except that the strip casting in the prior art process is carried out using the same technique as Tests 1 and 2. Table 3 also sets forth typical data for aluminum alloys having the composition set forth therein for AA3104 and AA5182 produced by the conven-tional ingot process in which the ingots have thicknesses of 26 inches. Can buckle strengths are set forth for all alloys except 5182, and have been corrected to 0.0112 inch gauge for ease of comparison.

The Tests illustrate the unexpected results produced by the present invention. Rapid quenching instead of slow cooling in accordance with the concepts of this invention results in significantly higher strength, either with or with-out hot rolling. The strengths obtained in the practice of this invention for low alloy content aluminum alloys approaches that of AA5182, a high alloy content aluminum alloy typically used for can lids and tabs, as the data shows. Not only does the process of the invention provide superior strength, it provides equivalent or lower earing as well.

WO 97/11205 PCTlUS96/14877 Invention Examples Typical Ingot Process r ' gr:::. >=r =. x=..: } ~kk:}:r<., . :=.. .:
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Si 0.30 0.26 0.39 0.18 0.10 Fe 0.29 0.33 0.44 0.45 0.20 Cu 0.27 0.20 0.23 0.20 0.05 Mn 0.95 0.59 0.97 1.00 0.35 Mg 0.93 0.84 0.96 1.10 4.50 Cast Gauge, inch 0.10 0.09 0.10 26 26 Hot Rolling 0 53% 46% 99% 99%
Cooling Quench Quench slow slow slow Anneal Type Rapid Rapid Rapid slow Slow Anneal Gauge, inch 0.031 0.025 0.027 0.110 0.110 Anneal Temp, F 1075 1000 930 650 650 Finish Gauge, inch 0.0106 0.0109 0.0116 0.0112 0.0108 Ultimate Strength, ksi 51.5 46.2 39.8 44.0 58.0 Yield strength, ksi 46.6 41.7 37.5 41.0 50.0 Elongation 8.1% 5.3% 1.2% 6.0% 8.0%
Cup Earing N/A 2.1% 3.4% 2.2% N/A
Can Buckle strength, psi N/A 100.7 78.5 93.0 N/A

It will be understood that various changes and modifications can be made in the details of procedure, formula-tion and use without departing from the spirit of the inven-tion, especially as defined in the following claims.

Claims (12)

The embodiments of the present invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of making aluminum alloy beverage containers by manufacturing an aluminum alloy sheet stock in a continuous, in-line sequence comprising the following steps:
(a) providing hot aluminum alloy feedstock in the form of ingots, plates, slabs and strips in a casting apparatus, wherein the exit temperature of the feedstock from the casting apparatus is from 371°C (700°F) to the solidus temperature of the alloy; and (b) hot rolling the feedstock to reduce its thickness and to rapidly cool the feedstock sufficiently to substantially avoid substantial precipitation of alloying elements in solid solution; wherein said hot rolling cools the temperature of the cast feedstock to below 177°C (350°F) in less than 30 seconds.

2. A method according to claim 1, wherein the cast feedstock is a strip having a thickness before hot rolling of less than 1.0 inch (25 mm).

3. A method according to claim 2, wherein the strip cast feedstock has a thickness before hot rolling of within the range of 0.01 to 0.2 inches (0.254 to 5.08mm).

4. A method according to any one of claims 1 to 3, wherein the rolling reduces the thickness of the feedstock by 40 to 99%.

5. A method according to claim 1, wherein the feedstock is rolled to about 0.0114 inch (2.90 mm).

6. A method according to any one of claims 1 to 5, wherein the rolling to cool the feedstock is carried out in less than 10 seconds.

7. A method according to any one of claims 1 to 6, wherein the aluminum alloy is a can body stock alloy.

8. A method according to any one of claims 1 to 7, wherein the feedstock is provided by strip casting which is carried out using a continuous belt caster comprising moving belts which are cooled before contacting molten aluminum.

9. A method according to any one of claims 1 to 8, wherein the feedstock is an aluminum alloy containing from 0 to 0.6% by weight silicon, from 0 to 0.8% by weight iron, from 0 to 0.6% by weight copper, from 0.2 to 1.5% by weight manganese, from 0.2 to 4% by weight magnesium, from 0 to 0.25%
by weight zinc, from 0 to 0.1 % by weight chromium with the balance being aluminum and its usual impurities.

10. A method according to claim 9, wherein the aluminum alloy feedstock is selected from AA 3004, AA 3104 and AA 5017.

11. A method according to any one of claims 1 to 10 which comprises the further step of forming cups from the cooled rolled feedstock by use of a convoluted blanking die.

12. A method according to any one of claims 1 to 11, wherein the rolled feedstock is coiled after rolling.