WO2007052424A1

WO2007052424A1 - Aluminum alloy foil excellent in strength and surface roughening resistance and method of production of the same

Info

Publication number: WO2007052424A1
Application number: PCT/JP2006/319085
Authority: WO
Inventors: Toshiya Anami; Pizhi Zhao; Takayuki Kobayashi
Original assignee: Nippon Light Metal Company, Ltd.
Priority date: 2005-11-04
Filing date: 2006-09-20
Publication date: 2007-05-10
Also published as: JP2007126717A; JP4701998B2; TW200730640A

Abstract

Aluminum alloy foil providing a high strength equal or better than that of A3004 alloy foil and excellent in surface roughening resistance and a method of production of the same are provided. Aluminum alloy foil having a chemical composition comprising Fe: 0.4 to 0.7 mass%, Mn: 0.05 to 0.3 mass%, Cu: 0.05 to 0.3 mass%, Mg: 0.8 to 1.3 mass%, Cr: 0.05 to 0.3 mass%, and a balance of Al and unavoidable impurities, with Si as one of the impurities being less than 0.3 mass%, having a tensile strength after final annealing of 155 MPa or more, and having a surface crystal grain size of 25 (μm or less. A method of production of aluminum alloy foil comprising the steps of: casting an alloy melt of the above chemical composition by a thin-gauge sheet continuous casting machine to obtain a thin slab, cold rolling the thin slab without a soaking treatment to obtain a foil, and treating the foil by final annealing, performing intermediate annealing during the cold rolling.

Description

DESCRIPTION

ALUMINUM ALLOY FOIL ^'EXCELLENT IN STRENGTH AND

SURFACE ROUGHENING RESISTANCE AND METHOD OF

PRODUCTION OF THE SAME

TECHNICAL FIELD

[0001] The present invention relates to an aluminum alloy foil high in strength and good in formability able to be used as a material for frozen food containers, ready-to-cook food containers, confectionary or bread containers, etc. and a method of production of the same.

BACKGROUND ART

[0002] As foil used as a material for frozen food containers, ready-to-cook food containers, confectionary or bread containers, etc., aluminum alloy, which is high in strength and good in formability, has been used. A container-use aluminum foil high in strength and good in formability, for example, an Al-Fe-based alloy foil etc. have been developed (Japanese Patent Publication (A) No. 2002-322530) . Further, as an alloy system high in strength, an Al-Mn-based 3003 alloy excellent in workability and corrosion resistance is being employed as container foil, but in this case as well, there is a limit to the amount of solid solution of Mn in DC casting and it was difficult to further improve the strength of the final annealing foil. Therefore, alloy foil having properties equivalent to 3003 alloy foil using the continuous casting and rolling method has also been proposed (Japanese National Publication (A) No. 11- 500787) .

[0003] Further, to compensate for the insufficient strength of 3003 alloy sheet, a method of production of aluminum alloy sheet excellent in drop impact resistance characterized by continuously supplying an alloy melt containing Si: 0.20% (wt%, same below) or less, Fe: 0.80% or less, Cu: 0.15% or less, and Mn: 0.20 to 1.50%, further containing as needed one or more of Mg: 5% or less, Cr: 1% or less, and Zn: 1% or less, and comprising a balance of Al and unavoidable impurities to the outer circumferences of a pair of rotating facing cooled casting molds to cast a cast sheet having a sheet thickness of 2 to 15 mm and cold rolling the obtained cast sheet to give a reduction rate after the final heating of 70% or more has been proposed (Japanese Patent Publication (A) No. 6 to 172906) .

[0004] However, the continuous casting and rolling method has a higher cooling rate of the castings compared with the DC casting method, so it may also be considered to cast a thin slab, cold roll it without going through a precipitation step, and adjust it to a predetermined thermal refining state by final annealing. However, with an Al-Mn-based alloy (3003 alloy) or an Al-Mn-Mg-based alloy (3004-based alloy) , the excessive solid solution Mn precipitates while competing with recrystallization at the time of final annealing, so the recrystallization is remarkably delayed and a sufficient recrystallized structure cannot be obtained at the general annealing temperature. As a result, the formability remarkably falls. On the other hand, if trying to obtain a sufficient recrystallized structure by raising the annealing temperature, coarse recrystallized grains end up being produced.

[0005] That is, if forming foil, obtained by using the continuous casting and rolling method to cast a melt of an Al-Mn-based alloy (3003 alloy) or Al-Mn-Mg-based alloy (3004-based alloy) into a thin slab, cold rolling it without going through a precipitation step, then adjusting it by final annealing to a predetermined thermal refining state, into a frozen food container, ready-to-cook food container, confectionary or bread container etc., there is the problem that the coarse crystal grains present on the foil surface will cause remarkable roughening of the surface after forming work (deterioration of surface roughening resistance) .

[0006] DISCLOSURE OF THE INVENTION

[0007] The present invention has as its object to eliminate the above conventional problems and provide an aluminum alloy foil providing a high strength equal to or better than 3004 alloy foil and excellent in surface roughening resistance and a method of production of the same .

[0008] To achieve the above object, according to the present invention, there is provided aluminum alloy foil having a chemical composition comprising:

Fe: 0.4 to 0.7 mass%,

Mn: 0.05 to 0.3 mass%,

Cu: 0.05 to 0.3 mass%,

Mg: 0.8 to 1.3 mass%,

Cr: 0.05 to 0.3 mass%, and a balance of Al and unavoidable impurities, with Si as one of the impurities being less than 0.3 mass%, the final annealed sheet having a tensile strength of 155 MPa or more and a surface crystal grain size of 25 μm or less .

[0009] Further, according to the present invention, there is provided a method of production of aluminum alloy foil comprising the steps of: casting an alloy melt of the above chemical composition by a thin-gauge sheet continuous casting machine to obtain a thin slab, cold rolling the thin slab without a soaking treatment to obtain a foil, and treating the foil by final annealing, performing intermediate annealing during the cold rolling .

[0010] The aluminum alloy foil of the present invention enables an excellent surface roughening resistance to be secured while raising the strength over the past in a material for frozen food containers, ready- to-cook food containers, confectionary or bread - A -

containers, etc.

BEST MODE FOR WORKING THE INVENTION [0011] According to the method of production of aluminum alloy foil of the present invention, at the time of casting a thin slab by a thin-gauge sheet continuous casting machine, an Al- (Fe ^• Mn) -Si-based compound uniformly and finely crystallizes in the slab and the Mn and Si in solid solution in the matrix phase Al precipitate at a high density as a submicron level Al- (Fe-Mn)-Si phase due to the intermediate annealing. [0012] The thus finely crystallized Al- ( Fe ^• Mn) -Si- based compound and the highly densely precipitating submicron level Al-(Fe-Mn)-Si phase inhibit the action of dislocation at the time of plastic deformation, so the final annealed foil exhibits a high value of tensile strength. Further, the finely crystallized and then rolled and cleaved Al- (Fe ^• Mn) -Si-based compound forms nuclei for recrystallization and cause the formation of high density recrystallized grains, so the result is aluminum alloy foil with a crystal grain size of the final foil surface of 25 μm or less and an excellent surface roughening resistance.

[0013] Further, the strain built up due to the cold rolling can be released by the intermediate annealing to obtain a softened state and to prevent edge cracking at the time of subsequent final cold rolling. [0014] The aluminum alloy foil of the present invention typically has a thickness of 40 to 200 μm. However, even if outside this range of thickness, the present invention can be applied to obtain a better effect.

[0015] The reasons for limiting the configuration of the aluminum alloy foil according to the present invention will be explained below. First, the significances of the alloy elements and the reasons for limitation of their content will be explained.

Fe: 0.4 to 0.7 mass% [0016] Fe crystallizes at the time of casting and forms an Al-Fe-based intermetallic compound. The Fe disperses into the matrix, so contributes to the improvement of the strength. Further, the Al- (Fe ^• Mn) -Si- based compound forms the nuclei for recrystallization, so the crystal grains are made finer. To obtain a sufficient dispersed state for giving the aluminum alloy foil a tensile strength of 155 MPa, the Fe content has to be made 0.4 mass% or more. However, if the Fe content exceeds 0.7 mass%, recycling of the material for the non- Fe-containing, highly useful 3003 alloy and 3004 alloy becomes difficult. Therefore, the Fe content is limited to 0.4 to 0.7 mass%. The preferable Fe content is 0.4 to 0.6 mass% .

Mn: 0.05 to 0.3 mass%

[0017] Mn contributes to solution strengthening and makes the recrystallized grains finer. To obtain these effects, the Mn content has to be made 0.05 mass% or more. However, if the Mn content is over 0.3 mass%, the supersaturated solid solution Mn will suppress the recrystallization at the time of annealing, so thermal refining at a suitable annealing temperature will become difficult. Therefore, the Mn content is limited to 0.05 to 0.3 mass%. The preferable Mn content is 0.05 to 0.19 mass% .

Cu: 0.05 to 0.3 mass%

[0018] Cu contributes to solution strengthening. To obtain this effect, the Cu content has to be made 0.05 mass% or more. However, if the Cu content is over 0.3 mass%, the corrosion resistance is remarkable reduced. Therefore, the Cu content is limited to 0.05 to 0.3 mass%. The preferable Cu content is 0.05 to 0.2 mass%.

Mg: 0.8 to 1.3 mass%

[0019] Mg contributes to solution strengthening. In particular, to obtain a strength (tensile strength) equal to that of 3004 alloy, the Mg content must be made 0.8 mass% or more. However, if the Mg content is over 1.3 mass%, the excessive solution strengthening causes a drop in the rollability. Therefore, the Mg content is limited to 0.8 to 1.3 mass% .

Cr: 0.05 to 0.3 mass%

[0020] Cr has the action of suppressing the growth of recrystallized grains at the time of annealing. It causes the crystal grains after annealing to become finer, improves the formability, and raises the strength as effects. To obtain these effects, the Cr content must be made 0.05 mass% or more. However, if the Cr content is over 0.3 mass%, giant crystals are easily formed at the time of casting. Therefore, the Cr content is limited to 0.05 to 0.3 mass%.

Impurity Si: less than 0.3 mass%

[0021] Among the unavoidable impurities, in particular Si forms the intermetallic compound Mg₂Si with Mg and reduces the amount of solid solution Mg. In particular, if the content becomes 0.3 mass% or more, the solution strengthening due to the Mg is remarkably reduced. On top of this, if the Si content is over 0.3 mass%, a drop in the rollability is caused. Therefore, the Si content must be suppressed to less than 0.3 mass% .

Optional Ingredient Ti: 0.1 mass% or less [0022] Ti is not particularly necessary in the alloy of the present invention, but as an amount of entry from the scrap material used as the raw material for production of the alloy or as the amount of addition for increasing the fineness of the cast structure, 0.1 mass% or less is allowable.

[0023] The aluminum alloy foil of the present invention has a tensile strength after final annealing of 155 MPa or more. Due to this, it is possible to secure a high strength of more than the conventional 3004 alloy and obtain a container with a high durability against outside force.

[0024] The aluminum alloy foil of the present invention has a surface crystal grain size limited to 25 μm or less. Due to this, a foil with an excellent appearance free from surface roughening is obtained. [0025] The aluminum alloy foil according to the present invention is produced by the following method. However, the conditions other than those limited in the following explanation are preferable conditions and not limitative conditions.

Casting Conditions of Thin Slab

[0026] The thin slab used for production of the aluminum alloy foil of the present invention is cast by a thin-gauge sheet continuous casting machine. Thin-gauge sheet continuous casting machines include twin belt types and twin roll types. A twin belt continuous casting machine pours melt between a pair of rotating belts facing each other in the vertical direction and cooled by water to cause the melt to solidify by the cooling from the belt surfaces to form a slab, continuously draws out the slab from the opposite sides of the belts from the pouring side, and coils it up. A twin roll continuous casting machine pours melt between a pair of rotating rolls facing each other in the vertical direction and cooled by water to cause the melt to solidify by the cooling from the roll surfaces to form a slab, continuously draws out the slab from the opposite sides of the rolls from the pouring side, and coils it up. [0027] In the present invention, the cast slab preferably has a thickness of 3 to 15 mm. With this thickness, the solidification rate at the center of the sheet thickness is also fast, the structure is uniform, and, if the composition is in the range of the present invention, there are little coarse compounds, and an aluminum alloy foil having a high strength in the final annealed foil, having a surface crystal grain size of 25 μm or less, and excellent in formability can be obtained. [0028] If the thin slab has a thickness less than 3 mm, the amount of aluminum passing through the casting machine per unit time becomes too small and the casting becomes difficult. Conversely, if the thin slab has a thickness over 15 ram, coiling by the rolls is not longer possible, so a range of slab thickness of 3 to 15 mm is preferable.

[0029] The casting speed (slab extraction speed) is preferably 0.5 to 15 m/min. The solidification is preferably completed across the entire slab thickness between the belts or between the rolls. If the casting speed is less than 0.5 m/min, the casting takes too much time and the productivity falls, so this is not preferable. If the casting speed is over 15 m/min, the aluminum melt cannot be supplied fast enough and a predetermined shape of a thin slab becomes difficult to obtain.

[0030] The method of production of aluminum alloy foil of the present invention is characterized in the point of performing the intermediate annealing during the cold rolling. The intermediate annealing is performed by a batch furnace or a continuous annealing furnace. Performing it under the following conditions is preferable .

Intermediate annealing Conditions by Batch Furnace The holding temperature of the intermediate annealing by a batch furnace is preferably 300 to 400°C. If the holding temperature of the intermediate annealing is less than 300⁰C, a sufficient softened state cannot be obtained and in the subsequent cold rolling, edge cracking occurs causing the yield to drop. If the holding temperature of the intermediate annealing is over 400°C, the solid solution Mn in the matrix ends up precipitating as the coarse Al- (Fe -Mn) -Si-based compound at the time of the high temperature intermediate annealing, so the action of suppressing the coarsening of the recrystallized grains at the time of the final annealing is weakened, the crystal grain size of the final annealed foil surface ends up exceeding 25 μm, and the surface roughening resistance drops. Further, the solution strengthening by Mn also declines.

[0031] The holding time of the intermediate annealing by a batch furnace does not have to be particularly limited, but 1 to 5 hours in range is preferable. If the holding time of the intermediate annealing is less than 1 hour, the temperature of the coil as a whole remains uneven and there is a possibility that a uniform recrystallized structure cannot be obtained in the sheet, so this is not preferable. If the holding time of the intermediate annealing exceeds 5 hours, precipitation of the solid solution Mn proceeds, the solution strengthening by the Mn drops, and it becomes hard to stably secure a crystal grain size of the final annealed foil surface of 25 μm or less. Not only this, but treatment requires a long time and the productivity falls, so this is not preferable.

[0032] The rate of temperature rise and cooling rate at the time of intermediate annealing by a batch furnace are not particularly limited, but 30°C/hr or more is preferable. If the rate of temperature rise and cooling rate at the time of the primary intermediate annealing are less than 30°C/hr, precipitation of the solid solution Mn proceeds. Not only is this disadvantageous in stably securing a crystal grain size of the final annealed foil surface of 25 μm or less, but also treatment takes too much time and productivity drops, so this is not preferable .

Intermediate annealing Conditions by Continuous Annealing Furnace

[0033] The temperature of the intermediate annealing by a continuous annealing furnace is preferably 350 to 500⁰C. If less than 350⁰C, a sufficient softened state cannot be obtained. However, if the holding temperature is over 500⁰C, the possibility of the low melting point intermetallic compound locally melting and causing a drop in the mechanical properties becomes greater, so this is not preferable.

[0034] The holding time of the intermediate annealing by a continuous annealing furnace is preferably within 5 minutes. If the holding time of the continuous annealing is over 5 minutes, not only will the low melting point intermetallic compounds locally melt and cause a drop in the mechanical properties, but also the precipitation of the solid solution Mn will proceed, it will become difficult to stably secure a crystal grain size of the final annealed foil surface of 25 μm or less, the treatment will take too long, and the productivity will fall, so this is not preferable.

[0035] As to the rate of temperature rise and cooling rate at the time of the continuous annealing, the rate of temperature rise is preferably made 100°C/min or more. If the rate of temperature rise at the time of continuous annealing is less than 100°C/min, the treatment will take too much time and the productivity will fall, so this is not preferable.

Final Cold Rolling Rate 50 to 96%

[0036] The final cold rolling rate is preferably 50 to 96%. If the final cold rolling rate is less than 50%, there will be little strain energy built up due to the cold rolling, the recrystallized grains of the surface of the final annealed foil surface will end up with a size over 25 μm, and the surface roughening resistance will fall. If the final cold rolling rate exceeds 96%, edge cracking at the time of rolling will become conspicuous and the yield will fall.

Final Annealing Conditions

[0037] The holding temperature of the final annealing is preferably 300 to 400⁰C. If the holding temperature of the intermediate annealing is less than 300⁰C, the predetermined temper refining cannot be obtained. If the holding temperature of the final annealing exceeds 400⁰C, coarsening of the recrystallized grains occurs, the final annealed foil surface ends up with a crystal grain size over 25 μm, and the surface roughening resistance falls. [0038] The holding time of the final annealing does not have to be particularly limited, but 1 to 5 hours in range is preferable. If the holding time of the intermediate annealing is less than 1 hour, the coil as a whole remains uneven in temperature and there is a possibility that a uniform recrystallized structure cannot be obtained in the middle of the sheet, so this is not preferable. If the holding time of the final annealing exceeds 5 hours, coarsening of the recrystallized grains occurs. Not only is this disadvantageous in stably securing a crystal grain size of the final annealed foil surface of 25 μm or less, but also treatment takes too much time and productivity drops, so this is not preferable.

[0039] The rate of temperature rise and cooling rate at the time of the final annealing are not particularly limited, but 30°C/hr or more is preferable. If the rate of temperature rise and cooling rate at the time of the primary intermediate annealing are less than 30°C/hr, precipitation of the solid solution Mn proceeds. Not only is this disadvantageous in stably securing a crystal grain size of the final annealed foil surface of 25 μm or less, but also treatment takes too much time and productivity drops, so this is not preferable. [0040] According to the method of the present invention, at the time of casting a thin slab by a thin- gauge sheet continuous casting machine, an Al- (Fe-Mn) -Si- based compound uniformly and finely crystallizes in the slab and the Mn and Si in supersaturated solid solution in the matrix phase Al precipitate at a high density as a submicron level Al-(Fe-Mn)-Si phase due to the intermediate annealing. [0041] The thus finely crystallized Al-(Fe-Mn)-Si- based compound and the highly densely precipitating submicron level Al-(Fe-Mn)-Si phase inhibit the action of dislocation at the time of plastic deformation, so the final annealed foil exhibits a high value of tensile strength.

[0042] Further, the finely crystallized and then rolled and cleaved Al- (Fe • Mn) -Si-based compound forms nuclei for recrystallization and cause the formation of high density recrystallized grains. In addition, the submicron Ie vel Al-(Fe-Mn)-Si phase precipitating at the time of intermediate annealing has the action of suppressing the coarsening of the recrystallized grains at the time of the final annealing. Therefore, the result is aluminum alloy foil with a crystal grain size of the final foil surface of 25 μm or less and an excellent surface roughening resistance.

[0043] As another effect of the intermediate annealing, the strain built up due to the cold rolling is released by the intermediate annealing thereby enabling a softened state to be obtained and enabling prevention of edge cracking at the time of the subsequent.

EXAMPLES

[0044] An aluminum alloy melt of each of the chemical compositions shown by Alloy Nos. 1 to 10 in Table 1 was cast by a twin belt continuous casting machine into a 10 mm thick thin slab. The balance of the chemical compositions not shown in Table 1 is comprised of aluminum and accompanying unavoidable impurities. Each obtained thin slab was cold rolled, without soaking, by the processes shown in Table 2 to a final thickness of 0.08 mm. The obtained foil was annealed by final annealing at 35O⁰C x 1 hour to obtain thermal refining of " 0 " . [0045] Table 1

[0046] Table 2

Table 2

[0047] Each alloy was investigated for rollability at the time of rolling and for the tensile strength of the final annealed material. The tensile strengths of the final annealed materials satisfied the required 155 MPa or more. Further, it is known that the formability, in particular the surface roughness resistance, is largely dependent on the crystal grain size at the final thermal refining, so the crystal grain size of the surface of the final annealed material was measured and a recrystallized grain size of 25 μm or less was deemed passing (not yet recrystallized is judged as failing) . The size of the recrystallized grains was measured by the cross cut method. The results are shown together in Table 3. [0048] Table 3 Table 3

[0049] Invention Examples 1 to 4 were all good in rollability and could be rolled to foil without problem. The tensile strengths were in the range of the present invention (155 MPa or more), while the crystal grain sizes of the foil surfaces were in the range of the present invention (25 μm or less) .

[0050] As opposed to this, Comparative Examples 5 to 12 were all poor in at least one of the rollability, tensile strength, and crystal grain size. [0051] That is, Comparative Example 5 was not subjected to the intermediate annealing during the cold rolling essential to the method of the present invention, so the strain built up due to the cold rolling was not released and a softened state could not be obtained. As a result, edge cracking occurred during the cold rolling and the rolling was suspended.

[0052] Comparative Example 6 had an Mn content beyond the prescribed range of the present invention, so thermal refining was not possible at the annealing temperature of the prescribed range of the present invention and edge cracking occurred during cold rolling. Further, the supersaturated solid solution Mn suppressed the recrystallization at the time of annealing, so the structure remained not recrystallized. The tensile strength of the foil also became 240 MPa or unnecessarily high.

[0053] Comparative Example 7 had an Fe content lower than the prescribed range of the present invention, so the dispersion strengthening due to the Fe became insufficient and the tensile strength failed to reach the prescribed range of the present invention. [0054] Comparative Example 8 did not have the essential ingredient Mn of the present invention added to it, so the effect of Mn in increasing the fineness of the recrystallized grains could not be obtained. The crystal grain size ended up becoming 28 μm or beyond the prescribed range of the present invention. [0055] Comparative Example 9 did not have the essential ingredient Cu of the present invention added to it, so the solution strengthening action of Cu could not be obtained, and the tensile strength failed to reach the prescribed range of the present invention. [0056] Comparative Example 10 had a content of the impurity Si beyond the prescribed range of the present invention, so the intermetallic compound with Mg, that is, Mg₂Si, was formed resulting in deterioration of the rollability, the occurrence of edge cracking, and a drop in the amount of solid solution Mg thereby causing insufficient solution strengthening by the Mg and the tensile strength to fail to reach the prescribed range of the present invention.

[0057] Comparative Example 11 did not have the essential ingredient Cr of the present invention added to it, so the action of Cr in increasing the fineness of the crystals and its strengthening action became insufficient. The crystal grains had sizes of 33 μm or over the prescribed range of the present invention, and the tensile strength was 152 MPa, i.e., failed to reach the prescribed range of the present invention. [0058] Comparative Example 12 had an Mg content smaller than the prescribed range of the present invention, so the solution strengthening action of Mg was insufficient and the tensile strength was 132 MPa, i.e., failed to reach the prescribed range of the present invention .

INDUSTRIAL APPLICABILITY

[0059] According to the present invention, aluminum alloy foil, providing a high strength equal to or greater than that of 3004 alloy foil and excellent in surface roughening resistance, suitable as a material for frozen food containers, ready-to-cook food containers, confectionary or bread containers, etc. and a method of production of the same are provided.

Claims

1. Aluminum alloy foil having a chemical composition comprising:

Fe: 0.4 to 0.7 mass%,

Mn: 0.05 to 0.3 mass%,

Cu: 0.05 to 0.3 mass%,

Mg: 0.8 to 1.3 mass%,

Cr: 0.05 to 0.3 mass%, and a balance of Al and unavoidable impurities, with Si as one of the impurities being less than 0.3 mass%, having a tensile strength after final annealing of 155 MPa or more, and having a surface crystal grain size of 25 μm or less.

2. Aluminum alloy foil as set forth in claim 1, further containing Ti: 0.1 mass% or less.

3. Aluminum alloy foil as set forth in claim 1 or 2, having a thickness of 40 to 200 μm.

4. A method of production of aluminum alloy foil comprising the steps of: casting an alloy melt of a chemical composition as set forth in claim 1 or 2 by a thin sheet continuous casting machine to obtain a thin slab, cold rolling said thin slab without a soaking treatment to obtain a foil, and treating said foil by final annealing, performing intermediate annealing during said cold rolling.

5. A method of production as set forth in claim 4, characterized by performing said intermediate annealing in a batch furnace at 300 to 400⁰C.

6. A method of production as set forth in claim 4, characterized by performing said intermediate annealing in a continuous annealing furnace at 350 to 500⁰C.

7. A method of production as set forth in any one of claims 4 to 6, characterized in that said thin slab has a thickness of 3 to 15 mm.

8. A method of production as set forth in any one of claims 4 to I₁ characterized by coiling said thin slab into a roll, then performing said cold rolling.

9. A method of production as set forth in any one of claims 4 to 8, characterized by performing said cold rolling in two stages including a first stage of rolling said thin slab to a sheet having a thickness of 0.4 to 1.0 mm, then performing said intermediate annealing and then a second stage of rolling said cold rolled sheet to said foil.

10. A method of production as set forth in claim 9, characterized in that said second stage has a cold rolling rate of 50 to 96%.

11. A method of production as set forth in any one of claims 4 to 10, characterized by performing said final annealing at 300 to 400⁰C.

12. A method of production as set forth in any one of claims 4 to 11, characterized in that the aluminum alloy foil has a thickness of 40 to 200 μm.