WO1995018876A1

WO1995018876A1 - Method and composition for castable aluminum alloys

Info

Publication number: WO1995018876A1
Application number: PCT/US1994/014895
Authority: WO
Inventors: David A. Tomes; Donald C. Mcauliffe; Mark S. Selepack
Original assignee: Golden Aluminum Company
Priority date: 1994-01-04
Filing date: 1994-12-30
Publication date: 1995-07-13
Also published as: AU1554695A

Abstract

The present molten aluminum base alloy composition contains about, by weight, 0.28 % Cu, 0.42 % Fe, 0.37 % Si, 1.15 % Mn, and 1.8 % Mg (20) and formed by continuous casting process (50). During casting, the heat extraction rate from the alloy composition is within the range of 10-26 °C/s (60). After solidification, the cast aluminum products contain at least 25 percent Al12(FeMn)3Si alpha-phase content (90).

Description

METHOD AND COMPOSITION FOR CASTABLE ALUMINUM ALLOYS

FIELD OF THE INVENTION The present invention relates to aluminum alloy compositions and processes for producing them. In particular, the present invention relates to continuously casting sheets, strips or slabs of aluminum alloys which exhibit reduced galling and tearoffs when subsequently fabricated into a final product such as aluminum containers.

BACKGROUND OF THE INVENTION

In the casting of aluminum and its alloys, particularly the casting of aluminum strips, sheets and slabs, it is desirable to control the physical properties of the cast, so that it can be used for its intended purpose. The physical properties of aluminum being cast can be controlled by manipulation of the alloy compositions. The term "aluminum," as used herein, refers to aluminum and alloys of aluminum, including, but not limited to alloys of aluminum containing iron, copper, silicon, magnesium, manganese, zinc, titanium, nickel and other materials.

Aluminum cast by various methods can be useful for the manufacture of worked aluminum products, such as in the manufacture of aluminum containers and the like. If the aluminum cast is aluminum strip stock useful in the manufacture of containers, the aluminum strip should be capable of withstanding the drawing and ironing processes commonly encountered in the fabrication of aluminum containers, such as beverage cans. In particular, the aluminum strip should possess relatively high tensile strength, relatively high yield strength, adequate percent elongation for ironing, low earing, and should be resistant to galling and resulting tearoffs or metal failure during drawing and ironing. As used herein, the term "galling" refers to scratching of the sidewall surfaces of a container during drawing and ironing. The term "tearoffs", as used herein, refers to a container body which must be forcefully removed from a punch or die because it would not release during drawing and ironing as a result of galling of the container body and oxide buildup on the punch and die. Reduction in the amount of galling and tearoffs reduces the amount of waste material generated by container manufacturing processes and reduces downtime. Minimizing the waste generated and downtime reduces production costs.

It is generally known that it is advantageous to use aluminum strip and the like which has a closely controlled

Al₁₂(FeMn)₃Si alpha-phase content in the manufacture of worked aluminum products such as drawn and ironed containers. The term "alpha-phase", as used herein, refers to the alpha-phase particle content of an aluminum cast. In general, aluminum in the (FeMn)Al₆ beta-phase can be transformed to the Al₁₂(FeMn)₃Si alpha-phase as a solid-state phase transformation. The alpha-phase particles of an aluminum cast are generally harder than particles in the beta- or other phases. For this reason, it has been observed that the alpha-phase particles assist in reducing the buildup or removing layers of oxides deposited by other phases present in the aluminum cast on the tools, dies and punches in drawing and ironing processes.

Development of the alpha-phase in aluminum casts has been obtained in semi-continuous casting processes. For example, it is known that aluminum ingots can be homogenized to obtain the transformation from the beta- to the alpha-phase. In a homogenization process, the temperature of the ingot can be raised to the point where the beta-phase of the ingot can undergo solid-state phase transformation to the alpha-phase. The ingots can then be hot and cold rolled in order to obtain sheets or strips, such as those useful in the manufacture of containers. Production of the alpha-phase in aluminum strips, sheets and slabs using semi-continuous casting processes, however, can be labor intensive and can require that the cast be handled numerous times. These processes also require the addition of numerous hot and cold rolling steps to reduce the gauge of the ingot to a sheet or strip. Moreover, homogenization to obtain the alpha-phase transformation in semi-continuous processes can require lengthy processing time and can be energy intensive, increasing production costs.

Because of the relative inefficiency and expense in the semi-continuous production of aluminum casts having a substantial alpha-phase content, it would be desirable to produce these casts using continuous casting processes. The continuous casting of aluminum can be accomplished in a number of processes, including roll casting, block casting and belt casting. In a continuous caster, such as the block caster disclosed in U.S. Patent No. 3,570,586, by Lauener, assigned to Lauener Engineering Ltd., molten aluminum is supplied from a tundish to a continuously moving mold assembly consisting of two synchronized, counter-rotating block chains traveling in the casting direction. Heat transfer from the molten aluminum to the chilling blocks of the block chain results in solidification of the aluminum and the formation of aluminum strip. After exiting the caster, the metal strip can be hot and/or cold rolled in order to produce a thin- gauge metal strip and to further refine the cast strip for its intended purpose. In addition, other treatment steps can be performed, such as annealing, to further develop desired physical characteristics.

It would also be desirable to produce the alpha-phase in an aluminum cast during continuous casting as the molten aluminum is solidifying rather than subsequent to casting. In general, it is undesirable to provide high temperature homogenization steps to obtain the solid-state beta-phase transformation to the alpha-phase after continuously casting metal strips, sheets or slabs. Homogenization, heat soaking, annealing and the like can cause the formation of oxidation on the surface of the cast, deformation of the cast strip, sheet or slab, and can require more production time, space and equipment, increasing production costs. U.S. Patent No. 4,976,790, by McAuliffe et al., assigned to Golden Aluminum Company, discloses a continuous casting operation which produces an aluminum sheet which has improved yield strength and reduced earing. The aluminum sheet is produced using a block caster, and is subsequently treated by hot and cold rolling steps, and an annealing step after coiling of the strip. The strip produced contains a nominal of 60 percent SiFeMnAl₆ transformed alpha-phase. U.S. Patent No. 4,976,790, also discloses an aluminum alloy composition useful in the manufacture of containers. The aluminum alloy disclosed is a 5017 alloy with a composition having the following weight percent ranges: manganese—0.6 to 0.8; silicon—0.15 to 0.14; iron—0.3 to 0.7; copper—0.18 to 0.28; magnesium—1.3 to 2.2; trace materials—less than about 0.25, with the balance being aluminum.

While the alloys which are known can be used successfully in the manufacture of aluminum strips, sheets or slabs, such as those useful in the manufacture of aluminum containers, there is a need to provide other aluminum alloys and methods for casting them which reduce the costs of manufacturing.

SUMMARY OF THE INVENTION In accordance with the present invention, novel aluminum alloys and methods for continuously casting such alloys are provided. The aluminum alloys of the present invention exhibit reduced galling and resulting tearoffs when drawn and ironed, while possessing the strength and properties necessary to produce useful products. The present invention provides aluminum products which contain a substantial percentage of alpha-phase transformation and inexpensive methods for continuously casting such products. The present invention provides continuously cast aluminum strip, sheet or slab having relatively high tensile strength and formability required of aluminum strip, sheet or slab in the manufacture of containers. The present invention provides cast aluminum strip stock which assists in reducing the amount of waste material generated by metal-working processes and methods for continuously casting such aluminum strip stock. In accordance with the present invention, an aluminum alloy is provided which contains silicon in the range of from about 0.24 percent to about 0.5 percent by weight, copper in the range of from about 0.18 percent to about 0.4 percent by weight, iron in the range of from about 0.3 percent to about 0.7 percent by weight, manganese in the range of from about 0.7 percent to about 1.3 percent by weight, and magnesium in the range of from about 1.7 percent to about 2.6 percent by weight.

In accordance with the present invention, the aluminum alloy can be continuously cast into articles such as strips, sheets or slabs having at least about 25 percent Al₁₂(FeMn)₃Si alpha-phase. Moreover, the weight ratio of silicon to magnesium in the strips, sheets or slabs can range from about 1:3.5 to about 1:9 silicon:magnesium. The cast strips, sheets and slabs can be further manufactured into worked aluminum products, for example, aluminum containers through drawing and ironing processes. Furthermore, in accordance with the present invention, a method is provided which includes the steps of providing an aluminum alloy composition containing silicon and magnesium in the weight ratio range of from about 1:3.5 to about 1:9 silicon:magnesium in molten form in a mold cavity of a continuous caster, and extracting heat from the molten composition to obtain a cast having at least about 25 percent Al₁₂(FeMn)₃Si alpha-phase.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a block diagram illustrating one embodiment of the method of the present invention.

DETAILED DESCRIPTION The present invention includes alloy compositions and continuous casting processes which produce substantially high strength aluminum castings suitable for use in the manufacture of worked aluminum products. In particular, the aluminum castings can be useful in the fabrication of containers such as drawn and ironed articles or the like. More particularly, the aluminum castings can be strip stock suitable for use in the production of beverage cans, and can exhibit reduced galling and resulting tearoffs. The present invention provides a unique combination of an alloy composition and a continuous casting process for producing high strength aluminum casts having a substantial content of beta-phase which has been transformed into the alpha-phase. The physical characteristics and the microstructures of the casts can be dependent upon the alloy composition and the continuous casting process. The term "microstructure" as used herein, refers to the structure of the cast, including, but not limited to, cast phase composition, grain size, grain composition, crystalline structure and imperfections. In particular, while not intending the present invention to be constrained by theory, it is believed that the physical characteristics and the microstructure of the cast are dependent upon both the alloy composition and the heat extraction rate during casting. The aluminum alloys of the present invention can contain copper, silicon, iron, magnesium, manganese, trace amounts of other materials and the remainder aluminum. The phrase "trace amounts" as used herein, refers to materials present in the alloy compositions of the present invention in amounts less than about 0.05 weight percent ("wt%") . The alloys of the present invention can be continuously cast using conventional continuous casters, preferably block casters. If the aluminum is to be worked subsequent to casting, such as in drawing and ironing operations, it has been found that it can be advantageous to produce aluminum casts wherein a substantial amount of the cast has been transformed from the beta-phase into the alpha-phase. In particular, if the cast is to be used in modern container manufacturing, it can be advantageous to produce aluminum container strip stock containing a substantial alpha-phase transformed particle content. Modern methods of manufacturing aluminum containers having thin wall gauges require the production of thin, strong strips of aluminum container stock. Because the alpha-phase particles are harder than particles of other phases, casts containing substantial amounts of alpha-phase transformed particles can be more desirable for drawing and ironing applications than casts which contain little or no alpha-phase. In particular, it has been observed that casts having a substantial alpha-phase transformed particle composition deposit substantially minimal amounts of oxide on dies and punches used to work the sheet or strip. It should be noted that the preferred ranges stated herein generally refer to aluminum alloys suitable for manufacturing thin-wall beverage cans, which can be suited for containing beverages having little or no internal pressure from carbonation. The more general ranges stated herein generally refer to aluminum alloys suitable for manufacturing of beverage cans capable of containing beverages having greater internal pressure from carbonation. In accordance with the casting method and alloy compositions of the present invention, during continuous casting, solidifying aluminum which is predominantly present in the less stable (FeMn)Al₆ beta-phase can be transformed into the Al₁₂(FeMn)₃Si alpha-phase. The solid- state phase transformation of the cast from the beta-phase to the alpha-phase is referred to herein as "alpha-phase transformation." The amount of cast existing in the alpha- phase can be measured metallographically by applying an etching solution, such as hot sulfuric acid, to the cast cross-section. The etch has a tendency to darken and outline the alpha-phase of the cast, such that under magnification, it can be visually measured. While it is possible to produce alpha-phase transformation during other operations performed subsequent to casting but during the production of metal sheets, strips and slabs, it is preferred that the alpha-phase transformation occur during casting. Typically, in the aluminum casts produced using the continuous casting method and alloys of the present invention, at least about 25% or more of the cast can be transformed into the Al₁₂(FeMn)₃Si alpha-phase from the (FeMn)Al₆ beta-phase. In a preferred embodiment, during continuous casting, at least about 30% to 45% or more of the cast can be transformed into the Al₁₂(FeMn)₃Si alpha- phase from the (FeMn)Al₆ beta-phase.

While not intending the present invention to be constrained by theory, it is believed by the inventors that the amount of alpha-phase transformation obtained during continuous casting is dependent upon the alloy composition. It has been found that aluminum alloys containing silicon, iron and manganese can be suitable for producing aluminum sheets, strips and slabs wherein a substantial percentage of cast can be transformed from the (FeMn)Al₆ beta-phase into the Al₁₂(FeMn)₃Si alpha-phase. In general, iron and manganese can be present in amounts sufficient to form a substantial amount of particles in the beta-phase. Typically, the combined weight percent of iron and manganese in the alloy can exceed about 1.1 wt%. Preferably, the weight percent of iron and manganese combined in the alloy can be within the range of about 1.1 wt% to about 1.65 wt%. More preferably, the weight percent of iron and manganese combined in the alloy can be within the range of about 1.4 wt% to about 1.64 wt%.

In the aluminum alloy compositions of the present invention magnesium can also be used for increasing the strength of the cast, and it is believed that magnesium also has an impact upon the formation of the alpha-phase from the beta-phase. In particular, when using magnesium in the alloy compositions of the present invention, it has been surprisingly found that to encourage the transformation of the beta-phase to the alpha-phase, the relative amounts of silicon and magnesium can be present within a certain weight ratio range. It has also been found that alloys containing silicon and magnesium in other weight ratio ranges produce casts having substantially little or no alpha-phase transformation. Moreover, it has been found that preservation of the correct weight ratio range of silicon:magnesium in the aluminum casts of the present invention preserves the alpha-phase transformation over a broad range of alloy compositions. This can be particularly important, because it allows manipulation of the cast composition to obtain desired physical or chemical characteristics without reducing the formation of the alpha-phase. In order to obtain aluminum sheets, strips and slabs wherein a substantial percentage of the cast can be transformed into the alpha-phase, silicon and magnesium can be present within a weight ratio range of about 1:3.5 to about 1:9, silicon:magnesium. Preferably, silicon and magnesium can be present within a weight ratio range of about 1:4 to about 1:6, silicon:magnesium, and more preferably can be present within a weight ratio range of about 1:4.5 to about 1:5.5, silicon:magnesium.

Generally, in the alloys of the present invention, the weight percentage of silicon can range from about 0.24 wt% to about 0.5 wt%,. the weight percentage of iron can range from about 0.3 wt% to about 0.7 wt%, the weight percentage of manganese can range from about 0.7 wt% to about 1.3 wt%, and the weight percentage of magnesium can range from about 1.7 wt% to about 2.6 wt%. In a preferred embodiment, the weight percentage of silicon can range from about 0.3 wt% to about 0.4 wt%, the weight percentage of iron can range from about 0.3 wt% to about 0.5 wt%, the weight percentage of manganese can range from about 0.9 wt% to about 1.2 wt%, and the weight percentage of magnesium can range from about 1.7 wt% to about 2 wt%. In a more preferred embodiment, the weight percentage of silicon can range from about 0.35 wt% to about 0.39 wt%, the weight percentage of iron can range from about 0.4 wt% to about 0.44 wt%, the weight percentage of manganese can range from about 1.1 wt% to about 1.2 wt%, and the weight percentage of magnesium can range from about 1.75 wt% to about 1.85 wt%. In the alloys of the present invention, other materials can be present which modify the physical properties of the cast so that it will be useful for its desired purpose. For example, in the alloys of the present invention, copper can also be present in substantial amounts. When added to the alloy compositions of the present invention, copper has been found to increase the strength of the cast. In general, in the alloys of the present invention, copper can be present in a weight percentage range of from about 0.18 wt% to about 0.4 wt%. Preferably, copper can be present in a weight percentage range of from about 0.2 wt% to about 0.3 wt%. More preferably, copper can be present in a weight percentage range of from about 0.26 wt% to about 0.3 wt%. It should be understood, however, that numerous other alloying metals can be present without affecting the substantial transformation of beta-phase to the alpha-phase. It should be further understood that additional elements and/or materials can be present in the alloys of the present invention in trace amounts. While not intending the present invention to be constrained by theory, the inventors believe that the alpha-phase transformation obtained during continuous casting is also dependent upon maintaining a desired heat extraction rate of the molten metal. In practice, however, it has been found that it can be difficult to maintain a constant heat extraction rate, therefore, the heat extraction rate should be kept within a range of the desired heat extraction rate. Typically, the heat extraction rate for the mold can be in the range of about 50°F (10°C) per second to about 80°F (26°C) per second. Preferably, the heat extraction rate for the mold can be in the range of about 50°F (10°C) per second to about 75°F (24°C) . More preferably, the heat extraction rate for the mold can be in the range of about 53°F (12°C) per second to about 75°F (24°C) per second.

It has also been found that when horizontally casting, the effects of gravity on the molten metal and the tendency of the molten metal to shrink away from the upper mold surface as it solidifies can cause variations in the heat extraction rate. To account for these effects, it can be necessary to maintain different heat extraction rates for the upper and lower mold surfaces. In general, the heat extraction rate for the top mold can be in the range of about 60°F (15°C) per second to about 80°F (26°C) per second and for the bottom mold in the range of about 50°F (10°C) per second to about 70°F (21°C) per second. Preferably, the heat extraction rate for the top mold can be in the range of about 65°F (18°C) per second to about 75°F (24°C) per second and for the bottom mold in the range of about 50°F (10°C) per second to about 68°F (20°C) per second. More preferably, the heat extraction rate for the top mold can be in the range of about 68°F (20°C) per second to about 75°F (24°C) per second and for the bottom mold in the range of about 53°F (12°C) per second to about 66°F (19°C) per second. Because the desired heat extraction rate can be dependent upon the casting parameters, the desired heat extraction rate can be obtained by controlling the continuous casting parameters. The term "continuous casting parameters," as used herein, refers to a variety of measurable physical characteristics of the casting process, including, but not limited to, the casting speed, the metallostatic pressure in the tundish, or the temperature of the continuously moving mold. The continuous casting parameters can be modified by manipulating the controls of the continuous caster.

In addition to controlling the amount of the cast that transforms into the alpha-phase, the continuous casting parameters can also be adjusted to obtain a heat extraction rate which provides other desirable physical characteristics of the sheets, strips or slabs being cast. For example, it is generally desirable to obtain continually cast sheets, strips and slabs which contain substantially minimal surface porosity and substantially minimal centerline porosity. Moreover, it is generally desirable to control the interphase parameters of the cast, such as the inter-dendritic cell spacing, especially if the cast is to have a decorative finish applied to it. The term "surface porosity" of a cast refers to the porosity of a cast measured along the cast surface. Surface porosity can be measured, for example, by a zyglo deep penetrant inspection technique. In this technique, a penetrant is applied to the surface of the cast. After a period of time, a developer is also applied to the surface of the cast, and the cast surface is inspected under black light to determine if the penetrant, which is black light sensitive, will bleed-out through the developer. High surface porosity can be the result of gas being trapped in the molten aluminum during casting. High surface porosity can cause pinholes in the aluminum or failure of the aluminum during subsequent working, such as in drawing and ironing processes typically encountered in container manufacturing. In general, for most applications, such as the production of aluminum strip for use in the fabrication of containers, it is preferred to adjust the casting parameters to obtain a cast that has substantially minimal surface porosity. The term "centerline porosity", as used herein, refers to the internal porosity of the cast along its centerline. Centerline porosity can be measured by visual inspection of a magnified cross section of a cast strip, sheet or slab that has been cut in a direction transverse to the casting direction. Centerline porosity can be caused by casting conditions and/or the gas content in the molten aluminum being cast. If cooling during casting is too rapid, the exterior surfaces of the cast will cool more rapidly than the interior, leaving voids along its centerline or causing surface cracking. If cooling is too slow, however, the cast can break apart as it exits the casting region of the caster. High centerline porosity can result in failure of the aluminum cast during subsequent working, such as the deep drawing and ironing processes commonly encountered in the manufacture of containers. In general, for most applications such as the production of aluminum strip useful in the manufacture of containers, it is preferred to adjust casting parameters to produce a cast which has substantially minimal centerline porosity.

Determination of a desired heat extraction rate can also take into account the impact of the cooling rate upon the interphase parameters at the surface of the cast, particularly if the cast is to have a decorative finish applied to the surface, as in the manufacture of containers. As used herein, the term "interphase parameters" includes, but is not limited to, inter- dendritic cell spacing at the surface of the cast. The interphase parameters of a cast strip can be measured by visual inspection, for example, after electro-polishing and etching a sample of the cast surface. In the production of aluminum strip useful for the manufacture of aluminum containers, the inter-dendritic cell spacing between dendritic rings on the surface of the aluminum strip can have an impact on the decoration quality of the can. In a finished container, undesirable inter-dendritic cell spacing between dendritic rings on the surface of the cans can produce segregation streaks called "looper lines" or can result in the dulling of the finish of a container. In general, when casting aluminum strip useful in the manufacture of products such as containers, inter-dendritic cell spacing can be within the range of about 14 microns to about 46 microns. More particularly, the inter-dendritic cell spacing can be maintained within the range of about 15 microns to about 30 microns. Preferably, however, the inter-dendritic cell spacing can be maintained within the range of about 18 microns to about 27 microns.

From the data gathered from measuring the physical characteristics of the cast, one can determine whether the casting parameters can be modified to obtain a greater percentage of alpha-phase transformation or to obtain other desired physical properties of the cast. In general, however, it has been found that after a heat extraction rate has been determined which provides a substantial percentage of alpha-phase transformation, only a relatively small range of adjustments can be made to the casting parameters while maintaining the transformation of the beta-phase to the alpha-phase. The numerous casting parameters which can have an impact upon the heat extraction rate can be manipulated individually or in groups to provide the desired heat extraction rate. Casting parameters which can be monitored and controlled include, but are not limited to, the metallostatic pressure in the tundish of the caster, the incoming molten metal temperature, the mass of the mold and the mold temperature, the mold cooling fluid temperature and pressure, the mold cooling fluid composition, the thickness of the cast strip or sheet, the gap between the upper and lower mold surfaces, and the speed of the caster. The casts produced in the present invention exhibit relatively high tensile strength, relatively high yield strength and adequate formability for fabricating the cast into a useful product. Typically, the tensile strength of a cast produced by the present invention can be in the range of about 40,000 psi (275 MPa) to about 48,000 psi (331 MPa) . Preferably, the tensile strength of casts produced by the present invention can be in the range of about 41,000 psi (282 MPa) to about 46,000 psi (317 MPa). More preferably, the casts produced by the present invention can exhibit a tensile strength in the range of about 42,000 psi (289 MPa) to about 44,000 psi (303 MPa).

In general, the yield strength of a cast produced by the present invention can be in the range of about 35,000 psi (241 MPa) to about 45,000 psi (310 MPa). Preferably, the yield strength of casts produced by the present invention can be in the range of about 37,000 psi (255 MPa) to about 43,000 psi (296 MPa). More preferably, the casts produced by the present invention can exhibit a yield strength of about 39,000 psi (269 MPa) to about 41,500 psi (286 MPa) .

The percent elongation of a typical cast produced by the present invention can be in the range of about 2 percent to about 5 percent. Preferably, the percent elongation of casts produced by the present invention can be in the range of about 2.5 percent to about 4 percent. More preferably, the casts produced by the present invention can exhibit percent elongation in the range of about 2.8 percent to about 3.5 percent.

The casts produced in accordance with the present invention can also be characterized by their suitability for use in metal-working operations, such as the drawing and ironing processes commonly encountered in the manufacture of containers. For example, the casts of the present invention exhibit low earing and reduced galling resulting in reduced numbers of tearoffs during drawing and ironing processes in the fabrication of containers. The method and composition of the present invention are capable of producing continuously cast aluminum strip stock wherein the number of tearoffs observed during ironing can be less than about 1 per 10,000 cans manufactured. Preferably, the method and composition of the present invention are capable of producing continuously cast aluminum strip stock wherein the number of tearoffs observed during ironing can be less than about 1 per 25,000 cans manufactured. More preferably, the method and composition of the present invention are capable of producing continuously cast aluminum strip stock wherein the number of tearoffs observed during ironing can be less than about 1 per 100,000 cans manufactured.

The method of the present invention includes providing an aluminum alloy composition capable of obtaining a substantial percentage of alpha-phase transformation to a continuous caster, adjusting the casting parameters to provide a desired heat extraction rate, and casting the alloy to obtain a cast sheet, strip or slab, having a substantial percentage of alpha-phase transformation. In one embodiment of the method of the present invention, an aluminum alloy composition can be heated to produce molten alloy which is supplied to a tundish. The aluminum alloy in the tundish can contain amounts of copper, iron, silicon, magnesium, manganese, trace amounts of other materials, and the remainder aluminum. The alloy composition in the tundish can be obtained in a number of ways, including by melting substantially pure ingots (known as "prime") of the constituent metals, by melting used beverage cans ("UBC") , plant scrap, and other consumer scrap, or any combination thereof.

The molten alloy in the tundish can be provided to the continuously moving mold of a caster where heat transfer to the mold can cause the alloy to be solidified into sheets, strips or slabs. In one embodiment, the molten alloy can be solidified into strips, such as those useful in the manufacture of containers by deep drawing and ironing processes. During casting, the physical characteristics of the cast can be measured to determine the casting parameters that can be adjusted in order to obtain the desired heat extraction rate. For example, the alpha-phase content of the cast, the interphase parameters, the surface porosity and the centerline porosity can be measured. In response to the measurements, the casting parameters can be manipulated to obtain the desired heat extraction rate.

After exiting the caster, the cast sheet, strip or slab can be subjected to one or more finishing steps as would generally be performed during the continuous casting of sheets, strips or slabs, including, but not limited to, hot rolling, cold rolling and/or annealing either by batch, semi-continuous or continuous processes. While not intending the present invention to be constrained by theory, it is believed by the inventors that substantially minimal alpha-phase transformation occurs in the processing steps subsequent to the casting step.

The method of the present invention can be better understood by reference to Figure 1. Figure 1 is a block diagram illustrating one embodiment of the method of the present invention. In Figure 1, UBC, plant scrap, other consumer scrap, prime (copper, iron, manganese, magnesium and aluminum) , and silicon 10 can be provided to a furnace where it can be heated 20 to produce molten alloy composition containing about 0.28 wt% copper, about 0.42 wt% iron, about 0.37 wt% silicon, about 1.15 wt% manganese, about 1.80 wt% magnesium, trace amounts of other materials and the remainder aluminum. Typically, the molten alloy will be filtered to remove particulate matter and can then be supplied to a tundish 30. In general, the temperature of the molten alloy in the tundish can be about 1280°F (693°C) . The molten alloy in the tundish can then be inserted into the continuously moving mold cavity of a block caster 40 where heat transfer to the chilling blocks can cause the alloy to be solidified into sheets, strips or slabs. It is believed that the molten alloy enters the caster at a temperature of about 1250°F (677°C) . During casting, a sample of the cast can be taken for measuring its physical characteristics 50. From these measurements, it is possible to determine whether the casting parameters need to be adjusted in order to obtain the desired physical characteristics and the desired heat extraction rate for the cast 60. The heat extraction rate for the top mold can be in the range of about 68°F (20°C) per second to about 75°F (24°C) per second and the heat extraction rate for the bottom mold can be in the range of about 53°F (12°C) per second to about 66°F (19°C) per second. At these heat extraction rates, the temperature of the surface of the cast as it exits the casting region of the caster can typically be within the range of about 900°F (482°C) to about 1100°F (593°C) . If the casting parameters are not acceptable, the casting parameters can be adjusted 70. After the casting parameters are adjusted, the physical characteristics of the cast can be again sampled 50. This cycle of sampling the cast and adjusting casting parameters can continue until desired casting parameters are obtained. After exiting the caster 80, the cast sheet, strip or slab can be subjected to one or more batch, semi-continuous or continuous finishing steps 90, as would generally be performed during the casting of sheets, strips or slabs. including, but not limited to, hot rolling, cold rolling and/or annealing.

A number examples have been provided by the inventors which are illustrative of the alloy compositions of the present invention and methods for producing them.

COMPARATIVE EXAMPLE 1 Used beverage cans ("UBC") and ingots of pure aluminum, copper, iron, manganese and magnesium were added to a furnace and melted. Silicon was also added to the melt to give a melt composition of approximately 0.23 wt% silicon, 0.42 wt% iron, 0.28 wt% copper, 1.15 wt% manganese, 1.8 wt% magnesium, trace amounts of other materials and the remainder aluminum. The molten composition was provided to a tundish and supplied through a 19 millimeter tundish tip to the continuously moving mold of a block caster at a temperature of about 1260°F (682°C). The caster's controls were adjusted to provide a heat extraction rate of about 65°F (18°C) per second. After solidification, the cast slab was hot rolled, annealed, cold rolled, annealed a second time, and cold rolled a final time to about 0.0108 gauge.

By hot sulfuric acid etch testing the cast produced, it was determined that the alpha-phase transformation was approximately 45 percent. The cast was fabricated into containers using drawing and ironing processes. The cast exhibited an unacceptable amount of galling. Moreover, the cast had an unacceptable rate of tearoffs during ironing due to inclusions. Overall, the run could be characterized as unsuccessful.

EXAMPLE 2 UBC and ingots of pure aluminum, copper, iron, manganese and magnesium were added to a furnace and melted. Silicon was also added to the melt to give a melt composition of approximately 0.37 wt% silicon, 0.42 wt% iron, 0.28 wt% copper, 1.15 wt% manganese, 1.8 wt% magnesium, trace amounts of other materials and the remainder aluminum. The molten composition was provided to a tundish and supplied by a 19 millimeter tundish tip to the continuously moving mold of a block caster at a temperature of about 1260°F (682°C). The caster controls were adjusted to provide a heat extraction rate of about 65°F (18°C) per second. After solidification, the cast slab was hot rolled, annealed, cold rolled, annealed a second time, and cold rolled a final time to about 0.0108 gauge.

By hot sulfuric acid etch testing the cast produced, it was determined that the alpha-phase transformation was approximately 50 percent. The cast was fabricated into containers using drawing and ironing processes. Galling was observed to be within acceptable limits. Moreover, the cast had an acceptable rate of tearoffs during ironing. Overall, the run could be characterized as successful. EXAMPLE 3

UBC and ingots of pure aluminum, copper, iron, manganese and magnesium were added to a furnace and melted.

Silicon was also added to the melt to give a melt composition of approximately 0.37 wt% silicon, 0.42 wt% iron, 0.28 wt% copper, 1.15 wt% manganese, 1.88 wt% magnesium, trace amounts of other materials and the remainder aluminum. The molten composition was provided to a tundish and supplied by a 19 millimeter tundish tip to the continuously moving mold of a block caster at a temperature of about 1260°F (682°C). The caster controls were adjusted to provide a heat extraction rate of about

65°F (18°C) per second. After solidification, the cast slab was hot rolled, annealed, cold rolled, annealed a second time, and cold rolled a final time to about 0.0116 gauge.

By hot sulfuric acid etch testing the cast produced, it was determined that the alpha-phase transformation was approximately 50 percent. The cast was fabricated into containers using drawing and ironing processes. Galling was observed to be within acceptable limits. Moreover, the cast had an acceptable rate of tearoffs during ironing.

Overall, the run could be characterized as successful.

EXAMPLE 4

Silicon was also added to the melt to give a melt composition of approximately 0.37 wt% silicon, 0.42 wt% iron, 0.28 wt% copper, 1.15 wt% manganese, 2.0 wt% magnesium, trace amounts of other materials and the remainder aluminum. The molten composition was provided to a tundish and supplied by a 19 millimeter tundish tip to the continuously moving mold of a block caster at a temperature of about 1260°F (682°C) . The caster controls were adjusted to provide a heat extraction rate of about 65°F (18°C) per second. After solidification, the cast slab was hot rolled, annealed, cold rolled, annealed a second time, and cold rolled a final time to about 0.0120 gauge.

By hot sulfuric acid etch testing the cast produced, it was determined that the alpha-phase transformation was approximately 50 percent. The cast was fabricated into containers using drawing and ironing processes. Galling was observed to be within acceptable limits. Moreover, the cast had an acceptable rate of tearoffs during ironing. Overall, the run could be characterized as successful.

While it has been mentioned that the alloys of the present invention can be particularly useful in the manufacture of aluminum containers, it is anticipated by the inventors that the alloys of the present invention would be desirable for use in any metalworking application where high strength aluminum alloys are preferred, such as in the manufacture of automobile body components, airplane body components, boat components, building materials, aluminum blinds, etc. While various embodiments of the present invention have been described in detail, it is apparent that further modifications and adaptations of the invention will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.

Claims

What is claimed is:

1. An aluminum alloy, comprising silicon in the range of from about 0.24 wt% to about 0.5 wt%, copper in the range of from about 0.18 wt% to about 0.4 wt%, iron in the range of from about 0.3 wt% to about 0.7 wt%, manganese in the range of from about 0.7 wt% to about 1.3 wt%, and magnesium in the range of from about 1.7 wt% to about 2.6 wt%.

2. The aluminum alloy as claimed in Claim 1, comprising silicon in the range of from about 0.3 wt% to about 0.4 wt%, copper in the range of from about 0.2 wt% to about 0.3 wt%, iron in the range of from about 0.3 wt% to about 0.5 wt%, manganese in the range of from about 0.9 wt% to about 1.2 wt%, and magnesium in the range of from about 1.7 wt% to about 2 wt%.

3. The aluminum alloy as claimed in Claim 1, comprising silicon in the range of from about 0.35 wt% to about 0.39 wt%, copper in the range of from about 0.26 wt% to about 0.3 wt%, iron in the range of from about 0.4 wt% to about 0.44 wt%, manganese in the range of from about 1.1 wt% to about 1.2 wt%, and magnesium in the range of from about 1.75 wt% to about 1.85 wt%.

4. The aluminum alloy as claimed in Claim 1, comprising trace amounts of other materials and the remainder aluminum.

5. The aluminum alloy as claimed in Claim 1, wherein the combined weight percent of said iron and said manganese exceeds about 1.1 wt%.

6. The aluminum alloy as claimed in Claim 1, wherein the combined weight percent of said iron and said manganese is in the range of about 1.1 wt% to about 1.65 wt%.

7. The aluminum alloy as claimed in Claim 1, comprising silicon and magnesium in the weight ratio range of from about 1:3.5 to about 1:9 silicon:magnesium.

8. The aluminum alloy as claimed in Claim 1, wherein said aluminum alloy has a tensile strength in the range of from about 40,000 psi (275 MPa) to about 48,000 psi (331 MPa) .

9. The aluminum alloy as claimed in Claim 1, wherein said aluminum alloy has a yield strength in the range of from about 35,000 psi (241 MPa) to about 45,000 psi (310 MPa) .

10. The aluminum alloy as claimed in Claim 1, wherein said aluminum alloy has a percent elongation in the range of from about 2 percent to about 5 percent.

11. The aluminum alloy as claimed in Claim 6, comprising silicon and magnesium in the weight ratio range of from about 1:3.5 to about 1:9 silicon:magnesium.

12. A product comprising a continuously cast aluminum alloy article, comprising silicon and magnesium in the weight ratio range of from about 1:3.5 to about 1:9 silicon:magnesium and wherein said article comprises at least about 25 percent Al₁₂(FeMn)₃Si alpha-phase.

13. The product as claimed in Claim 12, wherein said continuously cast aluminum alloy article comprises a strip.

14. The product as claimed in Claim 12, wherein said continuously cast aluminum alloy article comprises a sheet.

15. The product as claimed in Claim 12, wherein said continuously cast aluminum alloy article comprises a slab.

16. The product as claimed in Claim 12, comprising iron and manganese in a combined weight percent which exceeds about 1.1 wt%.

17. The product as claimed in Claim 12, comprising iron and manganese in a combined weight percent in the range of about 1.1 wt% to about 1.65 wt%.

18. The product as claimed in Claim 12, comprising silicon in the range of from about 0.24 wt% to about 0.5 wt%, copper in the range of from about 0.18 wt% to about 0.4 wt%, iron in the range of from about 0.3 wt% to about 0.7 wt%, manganese in the range of from about 0.7 wt% to about 1.3 wt%, and magnesium in the range of from about 1.7 wt% to about 2.6 wt%.

19. The product as claimed in Claim 12, comprising silicon in the range of from about 0.3 wt% to about 0.4 wt%, copper in the range of from about 0.2 wt% to about 0.3 wt%, iron in the range of from about 0.3 wt% to about 0.5 wt%, manganese in the range of from about 0.9 wt% to about 1.2 wt%, and magnesium in the range of from about 1.7 wt% to about 2 wt%.

20. The product as claimed in Claim 12, comprising silicon in the range of from about 0.35 wt% to about 0.39 wt%, copper in the range of from about 0.26 wt% to about 0.3 wt%, iron in the range of from about 0.4 wt% to about 0.44 wt%, manganese in the range of from about 1.1 wt% to about 1.2 wt%, and magnesium in the range of from about 1.75 wt% to about 1.85 wt%.

21. The product as claimed in Claim 12, comprising silicon and magnesium in the weight ratio range of from about 1:4 to about 1:6 silicon:magnesium.

22. The product as claimed in Claim 12, wherein said continuously cast aluminum article has substantially minimal surface porosity.

23. The product as claimed in Claim 12, wherein said continuously cast aluminum article has substantially minimal center-line porosity.

24. The product as claimed in Claim 12, wherein said continuously cast aluminum article has inter-dendritic cell spacing within the range of from about 14 microns to about 46 microns.

25. The product as claimed in Claim 13, wherein said strip is capable of being formed into a drawn and ironed aluminum container. 26. The product as claimed in Claim 25, comprising silicon in the range of from about 0.35 wt% to about 0.39 wt%, copper in the range of from about 0.

26 wt% to about 0.3 wt%, iron in the range of from about 0.40 wt% to about 0.44 wt%, manganese in the range of from about 1.1 wt% to about 1.2 wt%, and magnesium in the range of from about 1.75 wt% to about 1.85 wt%.

27. A method, comprising the steps of providing an aluminum alloy composition comprising silicon and magnesium in the weight ratio range of from about 1:3.5 to about 1:9 silicon:magnesium in molten form in a mold cavity of a continuous caster, and extracting heat from said composition to obtain a cast comprising at least about 25 percent Al₁₂(FeMn)₃Si alpha-phase.

28. The method as claimed in Claim 27, further comprising the step of removing from said continuous caster an aluminum strip.

29. The method as claimed in Claim 27, further comprising the step of removing from said continuous caster an aluminum sheet.

30. The method as claimed in Claim 27, further comprising the step of removing from said continuous caster an aluminum slab.

31. The method as claimed in Claim 27, further comprising the step of measuring the physical characteristics of said cast.

32. The method as claimed in Claim 27, further comprising the step of subjecting said cast to at least one finishing step.

33. The method as claimed in Claim 27, wherein said cast comprises at least about 30 percent Al₁₂(FeMn)₃Si alpha- phase.

34. The method as claimed in Claim 27, wherein said step of extracting heat from said composition further comprises extracting heat from said composition within the range of from about 50°F (10°C) per second to about 80°F (26°C) per second.

35. The method as claimed in Claim 27, wherein said continuous caster comprises a block caster.

36. The method as claimed in Claim 27, wherein said composition comprises silicon in the range of from about 0.24 wt% to about 0.5 wt%, copper in the range of from about 0.18 wt% to about 0.4 wt%, iron in the range of from about 0.3 wt% to about 0.7 wt%, manganese in the range of from about 0.7 wt% to about 1.3 wt%, and magnesium in the range of from about 1.7 wt% to about 2.6 wt%.

37. The method as claimed in Claim 27, wherein said composition comprises silicon in the range of from about 0.3 wt% to about 0.4 wt%, copper in the range of from about 0.2 wt% to about 0.3 wt%, iron in the range of from about 0.3 wt% to about 0.5 wt%, manganese in the range of from about 0.9 wt% to about 1.2 wt%, and magnesium in the range of from about 1.7 wt% to about 2 wt%.

38. The method as claimed in Claim 27, wherein said composition comprises silicon in the range of from about 0.35 wt% to about 0.39 wt%, copper in the range of from about 0.26 wt% to about 0.3 wt%, iron in the range of from about 0.4 wt% to about 0.44 wt%, manganese in the range of from about 1.1 wt% to about 1.2 wt%, and magnesium in the range of from about 1.75 wt% to about 1.85 wt%.

39. The method as claimed in Claim 27, comprising providing iron and manganese in a combined weight percent which exceeds about l.l wt%.

40. The method as claimed in Claim 27, comprising providing iron and manganese in a combined weight percent in the range of about 1.1 wt% to about 1.65 wt%.

41. The method as claimed in Claim 35, wherein said continuous caster comprises top and bottom mold surfaces and said step of extracting heat from said composition further comprises extracting heat from said composition along said top mold surface within the range of from about 60°F (15°C) per second to about 80°F (26°C) per second and extracting heat from said composition along said bottom mold surface within the range of from about 50°F (10°C) per second to about 70°F (21°C) per second.

42. The method as claimed in Claim 28, further comprising the step of fabricating an aluminum container from said strip.

43. The method as claimed in Claim 31, further comprising the step of adjusting the casting parameters of said caster.

44. The method as claimed in Claim 32, wherein said finishing step comprises hot rolling.

45. The method as claimed in Claim 32, wherein said finishing step comprises cold rolling.

46. The method as claimed in Claim 32, wherein said finishing step comprises annealing.

47. The method as claimed in Claim 35, wherein said block caster comprises top and bottom mold surfaces and said step of extracting heat from said composition further comprises extracting heat from said composition along said top mold surface within the range of from about 60°F (15°C) per second to about 80°F (26°C) per second and extracting heat from said composition along said bottom mold surface within the range of from about 50°F (10°C) per second to about 70°F (21°C) per second.

48. The method as claimed in Claim 38, further comprising the step of removing from said continuous caster an aluminum strip having at least about 45 percent Al₁₂(FeMn)₃Si alpha-phase.

49. The method as claimed in Claim 42^*, wherein said step of fabricating an aluminum container from said strip comprises drawing and ironing.

50. The method as claimed in Claim 48, further comprising the step of fabricating an aluminum container from said strip.

51. The method as claimed in Claim 48, further comprising the step of manufacturing worked aluminum products from said strip.

52. The method as claimed in Claim 50, wherein said step of fabricating an aluminum container from said strip comprises drawing and ironing.