Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Reexamination Certificate
2000-01-18
2002-02-26
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
C148S551000, C148S552000, C148S696000, C148S416000, C148S438000, C420S529000, C420S537000, C420S538000, C420S548000, C420S550000, C420S553000
Reexamination Certificate
active
06350532
ABSTRACT:
TECHNICAL FIELD
This invention relates to aluminum alloy sheet products and methods for making them. Specifically, this invention relates to a new aluminum alloy for household foil.
BACKGROUND ART
Household aluminum foils are often produced from alloys that are cast as ingots by a process commonly referred to as direct chill or DC casting. The ingots are generally hot rolled and then cold rolled. Multiple passes through the hot rolling mill and the cold rolling mill are required to produce a foil. Often, after the first pass through the cold rolling mill, the alloy is subject to an interanneal. Then the alloy is rolled to its final desired gauge and optionally annealed again to produce a household foil. A common final gauge of household foil is 0.00155 cm (0.00061 inches) although foil is generally considered to be any sheet less than about 0.0254 cm (0.01 inches).
An interanneal is usually performed after the first and/or the second cold rolling pass. The interannealing process is carried out in order to ensure easy rollability to the final, desired gauge. Without this interanneal, the sheet may incur an excessive amount of work hardening and make further rolling difficult, if not impossible.
Compositions of some alloys currently used to produce household aluminum foil from DC cast ingots, and selected properties of these alloys in the fully annealed state at a foil gauge of 0.00155 cm (0.00061 inches) are given below in Table 1 below.
TABLE 1
Nominal Composition and Selected
Properties of Annealed Foils
UTS
1
YS
2
Alloy
Si
Fe
Cu
Mn
(ksi)
(ksi)
Mullen
1100
0.06
0.45
0.12
—
10.7
5.9
14.1
1200
0.17
0.65
—
—
10.1
6.1
8.6
8111
0.57
0.57
—
—
10.7
6.8
12.7
8015
0.12
0.95
—
0.2
18
15
15
8006
0.22
1.58
—
0.43
18.5
13.4
1
Ultimate Tensile Strength
2
Yield Strength
Alloys commonly used for producing household aluminum foils include 1100 and 1200 type alloys. As evidenced by Table 1, these commonly used foil alloys tend to be weaker than alloys such as 8015 or 8006. While alloys 8015 or 8006 tend to have greater strength than the standard foil alloys, the high iron content in alloys 8015 and 8006 results in foils that are unsuitable for re-melting with aluminum beverage can scrap. Thus, the economical consideration of re-melting forces use of the lower strength/less resilient 1100 or 1200 alloys to produce household aluminum foil.
Alloys 8015 and 8006 yield a stronger foil because their properties do not deteriorate as rapidly as 1100 or 1200 alloys after annealing. Deterioration is slowed or stopped by the dispersoids produced in 8015 and 8006 alloys during the interanneal, and also by the manganese and copper that remain in solid solution. Alloys such as 1100 and 1200 can be easily work hardened to produce a relatively strong foil after cold rolling. Once these alloys are annealed, however, their yields strength decreases rapidly.
The principal reason for this rapid decrease in yield strength is that 1100 and 1200 alloys have little or no solution strengthening elements, such as copper or manganese, remaining in solution. Also, these alloys have very few dispersoids. For example, 1100 alloy typically has a particulate content of about 0.8%, while 1200 alloy has a 1.6% content, and 8111 has a 1.8% content.
In contrast, alloy 8006 typically has a particulate content of 3.5% and alloy 8015 has a content of 2.6%. Furthermore, 8015 alloy when produced on a continuous caster retains almost all of its manganese in solid solution to provide considerable solution strengthening. Thus, due to the large quantities of dispersoids fortified by elements in solid solution, these alloys are able to retain their strength to a much greater extent after annealing.
Another important aspect when considering aluminum alloys for producing household foils is the castability of that alloy. Typically, alloys with a wider freezing range and higher silicon content are easier to cast than alloys with narrow freezing ranges and low silicon content. For example, alloy 8015 has a narrow freezing range and is difficult to cast on a continuous caster. Finally, to prevent the formation of a dull surface due to magnesium oxidation, the amount of magnesium needs to be strictly limited.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an improved alloy suitable for the production of aluminum foil and a method for manufacture of the alloy.
According to one aspect of the invention there is provided a recyclable aluminum foil having a thickness of less than 0.0254 cm (0.01 inches) characterized in that said foil results from a continuous strip casting process and is made of an alloy containing 0.2%-0.5% Si, 0.4%-0.8% Fe, 0.1%-0.3% Cu, and 0.05%-0.3%Mn by weight, with the balance aluminum and incidental impurities, said foil containing at least 2% by weight of strengthening particulates and having at least 0.1% by weight of said copper and/or manganese retained in solid solution.
According to another aspect of the invention there is provided an alloy sheet having a thickness of less than 0.0254 cm (0.01 inches), characterized in that said sheet results from a continuous strip casting process and contains 0.2% -0.5%-Si, 0.4%-0.8%-Fe, 0.1%-0.3% Cu, and 0.1%-0.3% Mn by weight, with the balance aluminum and incidental impurities, having a yield strength of at least 10 ksi in the fully annealed condition.
According to yet another aspect of the invention there is provided a method of manufacturing a sheet of aluminum-based alloy, in which a sheet of alloy is cast by continuous strip casting to form a cast sheet less than 5 cm (2 inches) thick, the cast sheet is coiled, the coiled sheet is cold rolled to final gauge by a procedure involving several passes, the sheet being interannealed at a temperature in the range of 250 to 450° C. after a first pass and rolled to final gauge in one or more subsequent passes, characterized in that said alloy contains, by weight, at least 0.2% and up to 0.5% silicon, at least 0.4% and up to 0.8% iron, at least 0.1% and up to 0.3% copper, at least 0.1% and up to 0.3% manganese, and the balance aluminum and incidental impurities.
An important aspect of the present invention is thus a new aluminum alloy composition suitable for use as household foil having improved strength due to a larger quantity of dispersoids fortified by elements in solid solution. The invention also provides an economical method for the manufacture of a household aluminum foil made of this alloy using a continuous caster.
The alloy of the invention, unlike alloys typically used for the production of foil, can be continuously cast with an interanneal to yield foil with the formability and drawability of the 1100 and 1200 alloys while retaining the high strength characteristics of the 8015 and 8006 alloys. This is accomplished through a balanced strengthening mechanism in which the ratio of iron to silicon is adjusted such that at least about 2% of strengthening particulates are formed in the foil and at least 0.1% by weight of copper and/or manganese are retained in sold solution.
In summary, the present invention teaches a new aluminum based alloy composition for use as a household aluminum foil and a low cost method of manufacturing the foil. The present application retains the continuous casting and process properties of conventional alloys used for household foils, while exhibiting the strength properties of alloys having a higher iron content that are consequently less desirable in the recycling stream.
BEST MODES FOR CARRYING OUT THE INVENTION
The present invention provides a new aluminum alloy for use in household foil and a method of manufacture of such foil. The composition as described in this invention yields all of the desirable properties required for a household aluminum foil. The alloy is suitable for casting on a continuous caster followed by cold rolling of the alloy with an interanneal after a first pass of cold rolling. After being rolled to a final gauge, the resulting foil is stronger than the current household foils while retaining desirable recyclability attributes.
Broadly stat
Davisson Thomas L.
Montgrain Luc
Nadkarni Sadashiv
Pulliam Daniel
Alcan International Ltd.
Cooper & Dunham LLP
Katz Robert D.
Koehler Robert R.
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