AU2015315865B2

AU2015315865B2 - Aluminum alloy sheet for can body

Info

Publication number: AU2015315865B2
Application number: AU2015315865A
Authority: AU
Inventors: Yuji Inoue; Kazuharu Masada
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2014-09-10
Filing date: 2015-08-31
Publication date: 2018-04-05
Anticipated expiration: 2035-08-31
Also published as: TWI593806B; TW201631173A; KR20170038908A; CN106661681A; JP5841646B1; AU2015315865A1; CN106661681B; JP2016056419A; WO2016039215A1

Abstract

Provided is an aluminum alloy sheet for can bodies that, through drawing/ironing (DI) and baking, gives a can wall which evenly deforms upon secondary processing and subsequent plastic deforming and is inhibited from locally decreasing in thickness. The aluminum alloy sheet has a composition which contains 0.1-0.5 mass% Si, 0.3-0.6 mass% Fe, 0.1-0.35 mass% Cu, 0.5-1.2 mass% Mn, and 0.7-2.5 mass% Mg, with the remainder comprising Al and unavoidable impurities. The aluminum alloy sheet has a proof stress, measured after 200°C × 20 min baking, of 240-290 MPa. When the aluminum alloy sheet is subjected to DI forming so that the can wall has a rate of work of 60-70% and subsequently to 200°C × 20 min baking and when this baked can wall is subjected to 1% stretching and then to 90° V bending in the circumferential direction of the can at a bending radius of 0.1 mm and to unbending, then this can wall has an increase in 0.2% proof stress of 10 MPa or greater.

Description

DESCRIPTION

ALUMINUM ALLOY SHEET FOR CAN BODY

Technical Field [0001]

The present invention relates to an aluminum alloy sheet used to form a can body of a two-piece can by a draw and ironing (DI) process. More particularly, the invention relates to an aluminum alloy sheet for a can body, that is suitable for applying secondary processing to a can wall after the DI process.

Background Art [0002]

To improve the design of aluminum cans, there is an increasing demand for applying secondary processing, such as embossing or diamond cut patterning, to can walls undergoing the DI process. Thus, an aluminum alloy sheet for a can body is required to demonstrate excellent secondary processability. Furthermore, to reduce environmental loads, aluminum alloy sheets for a can body and can walls produced after the DI process have been thinned.

For example, Patent Document 1 describes a thinned aluminum alloy sheet for a can body, that has excellent secondary processability for a can wall. The aluminum alloy sheet endures six or more fracture limit testing cycles when being repeatedly bent by 90° with a bending radius of 1.0 mm relative to the can wall while applying a stress of about 15% of 0.2% proof stress to the sheet.

Prior Art Document

Patent Document [0003]

Patent Document '1: JP 2005-248275 A

Disclosure of the Invention

Problems to Be Solved by the Invention [0004]

Cans having their can walls undergoing the secondary processing, such as embossing or diamond cut patterning, would be deformed due to the secondary processing. The deformed parts of the cans repeatedly come into contact with hard, sharp foreign matters from the outside, and further they might be subjected to plastic deformation in some cases, in manufacturing stages, including filling the contents into the cans, in distribution stages after the filling process, and in consumption stages after can products are passed to consumers. Suppose that a part of the can is locally thinned (or the can is recessed) due to the secondary processing and subsequent plastic deformation. Then, if the can receives an impact or foreign matter comes into contact with the can wall, the thinned part receives an excessive stress, causing the breakage of the can wall, leading to a leakage of the contents in some cases.

[0005]

An evaluation method adopted in the technique mentioned in

Patent Document 1 does not assume the fact that the can wall sometimes could be thinned locally due to the secondary processing and plastic deformation thereafter, and thereby the thinned part of the can wall receives an excessive stress, leading to the breakage of the can wall. Cans are required to have their can walls deformed uniformly and to suppress a local decrease in the thickness of the can wall even when applying the plastic deformation to the can wall on a stricter condition (with smaller bending radius) than the evaluation method of Patent Document 1 after the secondary processing.

The present invention has been made based on these requirements . It is an obj ect of the present invention to provide an aluminum alloy sheet for a can body, that allows a can wall formed after the DI process and baking process to be uniformly deformed in a secondary processing and a subsequent plastic deformation, and that can prevent a part of the can wall from being locally thinned.

Means for Solving the Problems [0006]

An aluminum alloy sheet for a can body according to the present invention includes : 0.1 to 0.5¾ by mass of Si; 0.3 to 0.6% by mass of Fe; 0.1 to 0.35% by mass of Cu; 0.5 to 1.2% by mass of Mn; and 0.7 to 2.5% by mass of Mg, with the balance being Al and inevitable impurities, wherein the aluminum alloy sheet has a proof stress of 240 to 290 MPa after being subjected to baking at 200°C for 20 minutes, and an increase of a 0.2% proof stress of the aluminum alloy sheet of a can wall (hereinafter referred to as a work hardenability) is 10 MPa or more, on conditions in which the aluminum alloy sheet is subjected to a DI process at a processing rate of the can wall of 60 to 70% to produce a can, followed by baking at 2 00°C for 2 0 minutes and then applying 1% stretch to the can wall of the can, when performing a 90° V bending-bending back process at a bending radius of 0.1 mm in a can peripheral direction.

The above-mentioned aluminum alloy can further contain one or more kinds of elements selected from 0.10% or less by mass of

Cr, 0.40% or less by mass of Zn, and 0.10% or less of Ti as appropriate .

Effects of the Invention [0007]

Accordingly, the aluminum alloy sheet for a can body in the present invention exhibits excellent DI processability and can-wall secondary processability when being subjected to a DI process and a baking process to produce a can, followed by applying secondary processing, such as embossing and diamond cut patterning, to a can wall of the can. The aluminum alloy sheet for a can body in the present invention has high work hardenability and causes a can wall to be uniformly deformed when the can wall undergoing the secondary processing is further subjected to plastic deformation, thereby suppressing the local decrease in the thickness of the can wall (or the formation of a recessed part) . With this arrangement, a large stress can be prevented from being locally applied to the can wall when the can receives an impact or foreign matter comes into contact with the can wall, which can suppress the breakage of the can wall after filling the contents into the can, thus preventing the leakage of the contents.

Brief Description of the Drawings [0008]

Fig. 1 is conceptual diagrams of a test for measuring a decrease rate of the cross-sectional thickness of a can wall after a 90°V bending-bending back process.

Fig. 2A is a diagram for explaining a step of a pressure capacity test for cans, while showing a side view of the can used in the pressure capacity test.

Fig. 2B is a diagram for explaining another step of the pressure capacity test for cans, while showing a side view of a main part of a pressure tester.

Fig. 2C is a diagram for explaining another step of the pressure capacity test for cans, while showing a plan view of the main part of the pressure tester.

Fig. 3A is a diagram for explaining another step of the pressure capacity test for cans, while showing a side view of the state of the can fixed to a holder.

Fig. 3B is a diagram for explaining another step of the pressure capacity test for cans, while showing a side view of the state of buckling of a can bottom due to internal pressure.

Mode for Carrying Out the Invention [0009]

An aluminum alloy sheet for a can body and a manufacturing method therefor according to the present invention will be described in detail below.

cChemical Composition of Aluminum Alloy>

(Si: 0.1 to 0.5% by mass)

When the Si content is less than 0.1% by mass, the earing height at 0 to 180°is increased during the DI process, and thus ears are broken during ironing, and because of this, tear-off tends to occur. On the other hand, when the Si content exceeds

0.5% by mass, unrecrystallized grains remain in a hot coil. Thus, the earing height at 45°becomes high during the DI process, and ears are broken during ironing, and because of this, tear-off tends to occur.

[0010] (Fe: 0.3 to 0.6% by mass) .

When the Fe content is less than 0.3% by mass, unrecrystallized grains remain in a hot coil. Thus, the earing height at 45°becomes high during the DI process, and ears are broken during ironing, and because of this, tear-off tends to occur. On the other hand, when the Fe content exceeds 0.6% by mass, the amount of Al-Fe-Mn based intermetallic compounds becomes large. During the ironing, tear-off tends to occur. During the secondary processing of the can wall, cracks tend to occur starting from the above-mentioned intermetallic compound. (Cu: 0.1 to 0.35% by mass)

When the Cu content is less than 0.1% by mass, the strength of the aluminum alloy sheet becomes inadequate, leading to insufficient pressure capacity of the can. On the other hand, when the Cu content exceeds 0.35% by mass, the strength of the aluminum alloy sheet becomes excessive, so that tear-off tends to occur during the ironing.

[0011] (Mn: 0.5 to 1.2% by mass)

When the Mn content is less than 0.5% by mass, the strength of the aluminum alloy sheet becomes inadequate, leading to insufficient pressure capacity of the can. On the other hand, when the Mn content exceeds 1.2% by mass, the amount of Al-Fe-Mn based intermetallic compounds becomes large, so that during the ironing, tear-off tends to occur. During the secondary processing of the can wall, cracks tend to occur starting from the above-mentioned intermetallic compound.

{Mg: 0.7 to 2.5% by mass)

When the Mg content is less than 0.7% by mass, the strength of the aluminum alloy sheet becomes inadequate, leading to insufficient pressure capacity of the can. Furthermore, the work hardenability of the aluminum alloy sheet also becomes insufficient, whereby a recessed part is more likely to occur on the can wall during the secondary processing. On the other hand, when the Mg content exceeds 2.5% by mass, the strength of the aluminum alloy steel becomes excessive, so that tear-off tends to occur during the ironing.

[0012] (Cr: 0.10% or less by mass)

When the Cr content is 0.10% or less by mass, Cr has no effects on the material properties of the aluminum alloy sheet and the can characteristics after the DI process. Although Cr is an inevitable impurity, Cr can also be positively added within the above-mentioned range, for example, by increasing a blending ratio of scraps (scraps containing a large amount of Cr and the like) in raw materials in order to achieve the reduction in cost.

However, when the Cr content exceeds 0.10% by mass, unrecrystallized grains remain in a hot coil. Thus, the earing height at 45“becomes high during the DI process, and ears are broken during ironing, and because of this, tear-off tends to occur. Therefore, the Cr content in the aluminum alloy is limited to the above-mentioned range. Note that normally, the Cr content inevitably contained is 0.050% or less by mass.

[0013] (Zn: 0.40% or less by mass)

When the Zn content is 0.40% or less by mass, Zn has no effects on the material properties of the aluminum alloy sheet and the can characteristics after the DI process. Although Zn is an inevitable impurity, Zn can also be positively added within the above-mentioned range, for example, by increasing a blending ratio of scraps (scraps of a cladding material for a heat exchanger and the like) in raw materials in order to achieve the reduction in cost. Note that normally, the Zn content inevitably contained is 0.30% or less by mass.

[0014] (Ti: 0.10% or less by mass)

Ti is added as needed for the purpose of refining slab crystal grains. When the slab microstructure is refined during casting, the castability is improved, enabling the high speed casting. This effect can be exhibited by addition of 0.01% or more by mass of Ti . On the other hand, when the content of added

Ti exceeds 0.10% by mass, clogging of a filter tends to occur at an early stage, which makes it gradually less likely for the molten metal to pass through the filter during the casting. Eventually, the casting must be halted. Therefore, the Ti content in the aluminum alloy is limited to the above-mentioned range. When adding Ti, a slab refining agent (Al-Ti-B) in which the ratio of the mass of Ti to that of B is set at 5:1 is added in the form of a waffle or a rod to the molten metal before casting, so that B is also added essentially in an amount corresponding to the content ratio. Note that normally, the Ti content inevitably contained is 0.050% or less by mass.

[0015] (Other Inevitable Impurities)

Regarding inevitable impurities (V, Na, Zr, Ni, Ca, etc.,) other than the above-mentioned elements, the content of each of these inevitable impurities maybe 0.10% or less, preferably 0.05% or less, and the total of these inevitable impurities is 0.30% or less, and preferably 0.15%. Even the inevitable impurities contained in such contents do not interrupt the effects of the present invention. Note that as long as their contents do not exceed the above-mentioned ranges, these elements can be contained not only as the inevitable impurities, but also as elements that are positively added by intentionally increasing the blending ratio of scraps containing these elements, which does not interrupt the effects of the present invention.

[0016]

Properties of Aluminum Alloy Sheet>

(Proof Stress after Baking: 240 to 290 MPa)

When the proof stress of an aluminum alloy sheet after baking at 200 °C for 20 minutes is less than 240 MPa, the strength of the aluminum alloy sheet becomes insufficient, leading to inadequate pressure capacity of a can produced after the DI process and the baking. On the other hand, when the proof stress of an aluminum alloy sheet after baking exceeds 290 MPa, the strength of the aluminum alloy sheet becomes excessive, causing a number of tear-off parts during the ironing, thus degrading the productivity of cans. Note that the strength of the aluminum alloy sheet after the baking is associated with the strength thereof before the baking. Thus, the aluminum alloy sheet with the high strength after the baking also has high strength before the baking (during the ironing).

[0017] (Work Hardenability: 10 MPa or More)

The term work hardenability as used in the present invention is defined as an increase in 0.2% proof stress of an aluminum alloy sheet of a can wall, on conditions in which the sheet is subjected to a DI process at a processing rate of the can wall of 60 to 70% to produce a can, followed by baking at 200 °C for 20 minutes and then applying 1% stretch (permanent stress) to the can wall, when performing a 90° V bending-bending back process at a bending radius of 0.1 mm in a can peripheral direction. Note that the processing rate in the DI process of 60 to 70% is a standard processing rate in a normal DI process for cans.

[0018]

The work hardenability is represented by a formula of σ₂

- σι, where σι is a 0.2% proof stress of the can wall obtained after the DI process and the baking, and σ₂ is a 0.2% proof stress of the can wall obtained after the stretch and V bending-bending back process. When the work hardenability (σ₂ - σ_χ) is equal to or more than 10 MPa, the can wall is uniformly deformed due to the secondary processing and the subsequent plastic deformation, which suppresses the local decrease in the thickness of the can wall. On the other hand, when the work hardenability is less than 10 MPa, the can wall is less likely to be deformed uniformly in the secondary processing and the subsequent plastic deformation, and the can wall locally decreases its thickness and tends to be recessed. Thus, when the can receives an impact or foreign matter comes into contact with the can wall, the thinned part receives an excessive stress, causing the breakage of the can wall, making it more likely to leak the contents.

[0019]

Manufacturing Method for Aluminum Alloy Sheet>

The aluminum alloy sheet in the present invention can be manufactured through respective steps of casting, homegenization heat treatment, hot rolling, and cold rolling processes. Note that intermediate annealing after the hot-rolling and finish annealing after the cold rolling are not carried out. The manufacturing method for the aluminum alloy sheet in the present invention is characterized in that particularly, the cold rolling is performed under a predetermined condition.

Each step will be described below.

[0020]

First, the aluminum alloy may be cast by a known semicontinuous casting method, such as a direct-chill (DC) casting method.

Next, after removing a region of a superficial layer of the casted slab with a heterogeneous microstructure by face milling, the slab was subjected to the homogenization heat treatment based on a standard method. At this time, either a two-stage homogenization heat treatment or twice homogenization heat treatments may be adopted. The term two-stage homogenization heat treatment as used herein means that a slab is kept at a high temperature for a predetermined time (first-stage homogenization heat treatment) , then cooled to a temperature exceeding 200°C but not to the room temperature, followed by stopping the cooling at the temperature, and kept at the temperature for a predetermined time (second-stage homogenization heat treatment). The term twice homogenization heat treatments as used herein means that a slab is kept at a high temperature for a predetermined time (first

0 homogenization heat treatment) , cooled to a temperature of 200 °C or lower, including the room temperature, and then reheated and kept at a predetermined homogenization processing temperature for a predetermined time (second homogenization heat treatment).

[0021] . After such a homogenization heat treatment, hot rolling is subsequently carried out without cooling the temperature of the slab to lower than 450°C, and preferably, the hot rolling is ended at a temperature of 300°C or higher. When performing the two-stage homogenization heat treatment, after the second-stage homogenization heat treatment, hot rolling is carried out by heating the slab at a high temperature as needed. The fabricated hot-rolled material has a recrystallized microstructure.

Subsequent cold rolling is carried out by use of a tandem rolling mill. The use of the tandem rolling mill in the cold rolling can increase a rolling reduction per pass. Thus, the amount of heat generated in the processing becomes larger, which promotes the dynamic recovery of the cold-rolled material and the recovery thereof after winding. Consequently, the can produced by applying the DI process and baking to the cold rolled material (aluminum alloy sheet in the present invention) improves its work hardenability of its can wall.

[0022]

The total rolling reduction of the cold rolling is set at 80 to 90%. This rolling reduction can be achieved by one pass through the tandem rolling mill. When the total rolling reduction in the cold rolling is less than 80%, the strength of the aluminum alloy sheet becomes insufficient, leading to inadequate pressure capacity of the can produced after the DI process and the baking.

On the other hand, when the total rolling reduction exceeds 90%, the strength becomes excessive, and the earing value of the 45° ears increases. Thus, the ears tend to be broken during the ironing, and because of this the tear off tends to occur.

[0023]

A winding temperature after the cold rolling is set in a range of 120 to 180 °C. By setting the winding temperature within the above-mentioned temperature range, the dynamic recovery of the aluminum alloy sheet (cold-rolled material) and the recovery thereof after the winding are promoted, thereby improving the work hardenability of the can wall of the final can product.

When the winding temperature is lower than 12 0°C, the effect of the recovery becomes insufficient, so that the can wall is less likely to be uniformly deformed by the secondary processing and the subsequent plastic deformation because of lacking work hardenability of the can wall. Thus, the can wall is locally thinned and tends to be recessed. The lower limit of winding temperature is preferably 150°C.

When the winding temperature exceeds 180°C, the aluminum alloy sheet is significantly softened by the heat generated in the processing, and thereby the aluminum alloy sheet is more likely to be cut during rolling. Consequently, the productivity of the aluminum alloy sheet could be reduced significantly, which is not preferable in terms of practical use.

[0024]

The coil after winding is held at a temperature of 120°C or higher for four hours or more. Thus, the recovery of the aluminum alloy sheet (cold rolled material) is promoted, thereby improving the work hardenability of the can wall in the can obtained after the DI process and baking. On the other hand, when the holding time at a temperature of 12 0 °C or higher is less than

4 hours, the recovery of the aluminum alloy sheet (cold rolled material) becomes insufficient, which does not contribute to the improvement in the work hardenability of the can wall.

Examples [0025]

Examples in which the effects of the present invention could be confirmed will be specifically described below by comparison with Comparative Examples that did not satisfy the requirements of the invention. However, the present invention is not limited to the Examples .

Aluminum alloys with compositions shown in Tables 1 and 2 were melted, and by using the aluminum alloys, slabs having a thickness of 600 mm were fabricated using the semicontinuous casting method (except for Comparative Example No. 12). A superficial layer of the slab was removed by face milling, followed by the homogenization heat treatment. Subsequently, the slab was hot-rolled. Thereafter, the hot-rolled material was subjected to cold-rolling (by the tandem rolling mill or single rolling mill) without application of the intermediate annealing to produce an aluminum alloy sheet of 0.30 mm in thickness, followed by winding of the sheet. Note that finish annealing was not performed after the cold rolling (except for Comparative Example No. 20) . In Comparative Example No. 12, casting was not able to be performed because of clogging of a filter.

Tables 1 and 2 mentioned the type of the rolling mill used for the cold-rolling, the total rolling reduction of the cold rolling, the winding temperature of the sheet after the cold-rolling, the holding time during which the wound coil was held at 120°C or higher, and the presence or absence and conditions of the finish annealing after the cold-rolling.

(Table 1)

Finish annealing

None

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(Table 2)

Cold-rolling	Finish [ annealing	None	None	None	None I	None	None	None	None	None	None	None	\| None	None	None	None	None	None	None	None	* JO CD X U o © ’Tt
Holding time at a temperature of 120°C or higher (h)	© 'Tt	4.4	md	O\ ’Tt	5.8	4.8	CD ’Tt	1 4.6	5.0	5.5	CD TO		5.5	Tt	* ©	* ©	* ©	0 *	* ©	* ©
Winding temperature (°C)	152	155	TO	159	991	158	154	\| 157	160	’Tt TO	© Γ—	1	164	153	* MD ©	MD MD	96*	* © 07	*06	90*
Total rolling j reduction (%)	Γ- ΟΟ	Γ- ΟΟ	Γ- ΟΟ	⁸⁷	87	Γ- ΟΟ	87	87	Γ- ΟΟ	87	87		71*	* Tt 07	Γ- ΟΟ	Γ- ΌΟ	OO oo	OO OO	Γ- ΟΟ	Γ- ΟΟ
Rolling mill	Tandem	\| Tandem	Tandem	\| Tandem	\| Tandem	\| Tandem	Tandem	1 Tandem	\| Tandem	Tandem	Tandem	1	Tandem	Tandem	Tandem	Tandem	Single*	Single*	Single*	Single*
Chemical component (mass%)	IV	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	! Balance	Balance	Balance	Balance
P			1	1	1	1	1	1	1	t		0.22*		1	1	i	1	1		1
Zn			!	!	t	1					E			1	!	1		e		1
Cr	1	1	1	1	1		1	1			* TO O		1	1		1	1		1	1
Mg	Tt	TO	1.50	1.54	1.46	1.48	1.52	1.48 '	0.64*	2.60*	MD	1.53	1.52	1.54	1.49	1.48	1.80	1.20	1.52	1.54
Mn	0.84	0.85	0.92	88Ό	0.84	0.85	0.25*	1.33*	0.93	0.75	MD 00 ©	0.89	0.84	00 oo ©	TO oo ©	0.84	© ©	0.72	0.88	0.87
Cu	0.23	0.23	0.25	0.24	0.02*	0.40*	6Γ0	8ΙΌ 1_	0.25	0.20	0.22	0.23	0.21	0.24	0.25	0.23	0.22	0.20	0.23	0.24
Fe	0.47	0.42	0.24*	0.66*	0.44	0.44	0.52	0.33	0.41	0.49	0.45	0.43	0.43	0.47	0.42	0.45	0.42	© xt ©	0.45	0.46
tt	0.03*	0.52*	0.31	Γ 0.35	0.33	0.34	0.36	0.31	0.32	0.35	0.34	0.33	0.35	0.33	0.31	0.34	0.29	© CD ©	0.33	0.32
No.	-		cd	’Tt	md	to	Γ—	00	07	o		Γ9	cd	Tt	MD	TO	t—	OO	07	© CM
Comparative Examples

nJ ue that did not satisfy the requirement of the present invention or value in which -rolling condition was defective to ι—I u

nJ >

* [0028]

The aluminum alloy sheets manufactured in Examples No. 1 to 19 and Comparative Examples No. 1 to 11 and 13 to 2 0 were used as samples, whose proof stresses after baking were measured in the following way.

Subsequently, the aluminum alloy sheets in Examples No. 1 to 19 and Comparative Examples No. 1 to 11 and 13 to 20 were used to fabricate DI cans. In a fabrication method, in each example, first, the aluminum alloy sheet was cut into a blank having a diameter of 140 mm, and the blank was drawn to fabricate a cup having a diameter of 90 mm. The obtained cup was subjected to a DI process by a general-purpose aluminum can-body forming machine (through four stages, including redrawing, first ironing, second ironing, and third ironing) to produce a DI can. Note that the ironing rate in the third ironing was set at 4 0%. This ironing rate was set as strict conditions, compared to a general ironing rate of about 35 to 38%.

Part (a) of Fig. 1 is a side view of a fabricated can (after trimming its opening). The fabricated can had an outer diameter of 66.3 mm, a height of 124 mm, the thickness of the thinnest part of a can wall (part located at a height of 60 mm from the can bottom) of 95 pm, and the processing rate of the same part of 68.3% (original thickness: 0.3 mm).

In each of Examples and Comparative Examples, 10,000 cans were continuously formed by the aluminum can-body forming machine, and were then evaluated for the ironing workability in the following way. Subsequently, the work hardenability of the can wall, a decrease rate of the cross-sectional thickness of the can wall after 90 °V bending-bending back process, and the pressure 5 capacity were measured using the formed cans in the following ways

The results mentioned above are shown in Table 3.

[0029] (Table 3)

No.	Ironing workability	Work hardenability of can wall (MPa)	Decrease rate of the cross-sectional thickness of the can wall after 90°V bending-bending back process (%)	Proof stress after baking of the aluminum alloy sheet (MPa)	Pressure capacity kPa
Examples	1	P	12	4.7	262	671
2	P	12	4.6	244	626
3	P	13	3.6	252	646
4	P	17	3.2	264	678
5	P	21	3.0	267	684
6	P	23	2.8	273	701
7	P	23	2.6	274	701
8	P	26	2.1	283	725
9	P	28	1.9	278	713
10	P	31	1.7	284	727
11	P	33	1.5	287	737
12	P	34	1.2	289	742
13	P	24	2.6	270	692
14	P	23	2.4	266	681
15	P	23	2.3	275	706
16	P	26	2.5	275	704
17	P	26	2.0	274	702
18	P	22	2.6	273	700
19	P	23	2.5	271	694
Comparative Examples	1	F	21	2.7	279	715
2	F	18	4.5	272	698
3	F	22	4.2	279	716
4	F	23	4.4	277	710
5	P	19	3.4 '	237*	606*
6	F	25	2.2	296*	760
7	P	17	2.0	237*	608*
8	F	21	4.8	289	740
9	P	8*	5.6*	228*	584*
10	F	35	1.6	327*	838
11	F	20	3.9	269	689
12	.	-		-	-
13	P	24	2.3	236*	606*
14	F	18	2.2	293*	750
15	P	8*	5.9*	279	715
16	P	9*	5.2*	271	694
17	F	9*	6.5*	302*	774
18	P	5*	8.1*	263	674
19	F	6*	7.0*	292*	748
20	P	7*	5.7*	284	728

*Value deviating from the requirement of the invention [0030] (Proof Stress after Baking of Aluminum Alloy Sheet)

The samples (aluminum alloy sheets) were baked at 200 °C for minutes, and then specimens in conformity with JIS No. 5 were taken out of the samples in the direction parallel to the rolling direction. Then, a tensile test was performed on the specimens in accordance with JIS Z 2241 (revised in 2011) to measure a 0.2% proof stress of each specimen. Specimens having a 0.2% proof stress ranging from 240 to 290 MPa were rated as Pass (P). (Ironing Workability)

Examples or Comparative Examples in which three or less of

10,000 cans continuously formed had failures, such as tear-off, were rated as Pass (P), while other examples in which four or more of 10,000 cans had failures were rated as Fail (F).

[0031] (Work Hardenability of Can Wall)

The fabricated can was baked at 200 °C for 20 minutes, and then a JIS 13B specimen (first specimen) was taken out of the baked can along a circumferential direction of the can such that the center of the specimen in the width direction was located at a height of 6 0 mm from the can bottom, and the center of the specimen in the length direction is aligned with the rolling direction (0° direction).

On the other hand, the fabricated can was baked at 2 00°C for 2 0 minutes, and then a strip-shaped specimen with 2 0 mm width and 100 mm length was taken out of the baked can along a circumferential direction of the can such that the center of the specimen in the width direction was located at a height of 60 mm from the can bottom, and the center of the specimen in the length direction is aligned with the rolling direction (0° direction) (see part (a) of Fig. 1) . Thereafter, 1% stretch was applied to the strip-shaped specimen by a tensile tester (see part (b) of Fig. 1) . Then, the specimen was subjected to a 90°V bending process (see part (c) of Fig. 1) and subsequently a bending back process in an opposite direction (see part (d) of Fig. 1) by using a jig with a bending radius R at its tip end of 0.1 mm. A JIS 13B specimen (second specimen) was taken out of the strip-shaped specimen.

A part of the specimen undergoing the V bending-bending back process was positioned at the center of the JIS 13B specimen in the longitudinal direction.

Note that the first specimen and the second specimen differ from each other in that the former specimen did not receive 1% stretch and was not subjected to the V bending-bending back process, while the latter specimen received the stretch and was subjected to the process.

[0032]

Subsequently, the tensile test was performed on the first and second specimens in accordance with JIS Z 2241 (revised 2011) , whereby a 0.2% proof stress of each of the specimens was determined.

Here, the original thickness of the second specimen was set as pm, which was the same as that of the first specimen. The work hardenability of the can wall was defined as a difference between both 0.2% proof stresses, namely, (σ₂-σι) , where σ_χ is a 0.2% proof stress of the first specimen and σ₂ isa0.2% proof stress of the second specimen. That is, the work hardenability of the can wall was defined as an increase in the 0.2% proof stress after the stretch and V bending-bending back process . Specimens having the work hardenability (σ₂ - σι) of 10 MPa or more were rated as Pass . As mentioned above, the can wall with high work hardenability is deformed uniformly during the secondary processing and the subsequent plastic deformation, thereby suppressing the local decrease in the thickness of the can wall (the formation of the recessed part). This can prevent the large stress from being locally applied to the can wall when the can receives an impact, or foreign matter comes into contact with the can wall.

[0033]

Note that the stretch applied in the measurement test to create 1% permanent stress is to simulate the secondary processing (embossing or diamond cut patterning) to be applied to the can wall. Note that the 1% permanent stress is larger than a permanent stress actually applied to the can wall in the diamond cut patterning, and the stretch for this stress is said to be considerably strict, compared with that actually applied in the embossing or diamond cut patterning. The V bending-bending back process is to simulate the plastic deformation accidentally applied to the can in manufacturing stages, including filling the contents into the cans, in distribution stages after the filling process, in consumption stages after can products are passed to consumers, and the like. The V bending-bending back process is said to be a strict condition because of an extremely small bending radius of 0.1 mm, compared with that in the evaluation method mentioned in Patent Document 1 (with a bending radius of 1mm) .

[0034] (Decrease Rate of the Cross-Sectional Thickness of the Can Wall after the 90°V Bending-Bending Back Process)

The fabricated can was baked at 200°C for 2 0 minutes, and then a strip-shaped specimen with 2 0 mm width and 10 0 mm length was taken out of the baked can along a circumferential direction of the can such that the center of the specimen in the width direction was located at a height of 6 0 mm from the can bottom, and the center of the specimen in the length direction is aligned with the rolling direction (0° direction) (see part (a) of Fig. 1) . Thereafter, 1% (nominal strain) stretch was applied to the strip-shaped specimen by a tensile tester (see part (c) of Fig. 1) . Then, the specimen was subjected to a 90° V bending process (see part (c) of Fig. 1) and subsequently a bending back process in an opposite direction (see part (d) of Fig. 1) by using a jig with a bending radius R at its tip end of 0.1 mm. The thus-obtained specimen was embedded in resin to fabricate a cross-section observation specimen (see part (e) of Fig. 1) . The cross section of a part of the center in the width direction of the specimen subjected to the bending-bending back process (part enclosed by a dashed line as shown in part (e) of Fig. 1) was observed to measure the decrease rate of the thickness of the specimen with respect to the original thickness thereof (95 pm) . Examples or Comparative Examples in which the decrease rate of the cross-sectional thickness of the can wall was 5% or less were rated as Pass.

[0035] (Pressure Capacity of Can)

While the internal pressure was applied to a baked can, a pressure capacity of the can, which was defined as the maximum internal pressure when the can bottom was buckled, was determined by using a hydraulic pressure tester (a hydraulic pressurization and depressurization buckling test device, manufactured by Ace

Tech Co., Ltd., trade name: WBT-500).

As shown in Figs. 2A to 2C, the pressure tester includes a base plate 2 mounted on a tester stand 1, a cylindrical holder placed on the base plate 2, and a pair of fixing members 4 and placed on both sides of the holder 3. An 0-ring 5 is arranged at an intermediate position in the height direction of the holder . A rubber tube 6 is disposed in the holder 2 . The rubber tube 6 extends downward through the base plate 2 and is coupled to a water flow pipe to communicate with a hydraulic pump via a water pressure gauge, a switching valve, and the like (any of these elements not shown) . A hole 7 is formed in the base plate 2 . The hole 7 is coupled to an air flow pipe to communicate with a vacuum pump via a switching valve or the like (any of these elements not shown) . The fixing members 4 and 4 move forward and backward by a hydraulic cylinder (not shown).

[0036]

The pressure test was performed as follows.

(1) As shown in Figs . 2Ato2C, a can 8 that had its opening trimmed to have a height of 100 mm was fitted into the holder 3 with the can bottom positioned on upper side. Then, the fixing members 4 and 4 are moved forward at a predetermined stroke. When the fixing members 4 and 4 reach a predetermined position (see Fig. 3A) , the tips of the fixing members 4 and 4 press the can wall of the can 8 from both sides thereof and slightly under the O-ring 5, so that the can 8 is fixed by the holder 3. Thus, the inner surface of the can wall of the can 8 is brought into intimate contact with the periphery of the O-ring 5, thereby sealing the inside of the holder 3 (the inside of the can 8) other than the rubber tube 6 and the hole 7.

(2) The vacuum pump is activated to degasify the inside of the holder 3 (inside of the can 8) through the hole 7 to 9.8 kPa (0.1 kgf/cm²) or less, and then the air flow pipe is closed.

[0037] (3) The hydraulic pump is activated to supply water from the rubber tube 6 into the holder 3 (i.e. , into the can 8) . The water pressure (measured by the water pressure gauge) in the holder 3 (in the can 8) increases substantially in proportion to an elapsed time after the start of supply of the water. The water pressure instantly decreases as buckling of the can bottom occurs. Here, the pressure capacity of the can is defined as the maximum internal pressure upon the occurrence of the buckling of the can bottom. Fig. 3B illustrates the state in which the buckling of the can bottom occurs.

Examples or Comparative Examples that had a pressure capacity of 618 kPa or more (6.3 kgf/cm² or more) were rated as

Pass.

[0038]

As can be seen from Tables 1 and 3, Examples No. 1 to 19 satisfied the requirements specified by the invention regarding the chemical composition of the aluminum alloy sheet, the proof stress of the aluminum alloy sheet after baking, and the work hardenability of the can wall. As a result, these examples exhibited the excellent ironing workability, the small decrease rate of the cross-sectional thickness of the can wall after the stretch and V bending-bending back process, and large pressure capacity. The expression small decrease rate of the cross-sectional thickness means that the can wall did not locally decrease its thickness (or could suppress the occurrence of any recessed part), i.e., that the can wall was uniformly deformed by the stretch and V bending-bending back process. In each of

Examples No. 1 to 19, the cold-rolling was performed under the conditions mentioned above.

[0039]

On the other hand, as can be seen from Tables 2 and 3,

Comparative Examples No. 1 to 11 and No. 13 to 2 0 deviated from the requirement specified by the invention regarding at least one of the chemical composition of the aluminum alloy sheet, the proof stress of the aluminum alloy sheet after baking, and the work hardenability of the can wall. As a result, in these comparative examples, one of the ironing workability, the decrease rate of the cross-sectional thickness of the can wall, and the pressure capacity did not satisfy the reference specified by the invention.

Comparative Examples No. 1 and 2 had the Si content deviated from the requirement specified by the invention, and thus were inferior in the ironing workability. Comparative Examples No. 3 and 4 had the Fe content deviated from the requirement specified by the invention, and thus were inferior in the ironing workability. In Comparative Examples No. 5, 7, and 9, the Cu content, the Mn content, and the Mg content were insufficient, respectively. Thus, Comparative Examples No. 5, 7, and 9 lacked the proof stress of the aluminum alloy sheet after baking, and thus were inferior in the pressure capacity of the can. In

Comparative Examples No . 6 and 10 , the Cu content and the Mg content were excessive, respectively. Thus, Comparative Examples No. 6 and 10 had excessive proof stress of the aluminum alloy sheet after baking, and thus were inferior in the ironing workability. In

Comparative Examples No. 8 and 11, the Mn content and the Cr content were excessive, respectively. Thus, Comparative Examples No. 8 and 11 were inferior in the ironing workability. Comparative

Example No. 12 had the excessive Ti content, and thus could not be subjected to casting as mentioned above.

[0040]

In Comparative Example No. 13, the total rolling reduction of the cold rolling was insufficient. Thus, Comparative Example

No. 13 lacked the proof stress of the aluminum alloy sheet after baking and was inferior in the pressure capacity. In Comparative Example No. 14, the total rolling reduction of the cold rolling was excessive . Thus, Comparative Example No. 14 had the excessive proof stress of the aluminum alloy sheet and was inferior in the ironing workability. In Comparative Example No. 15, the winding temperature was low; the dynamic recovery and recovery after the winding of the cold-rolled aluminum alloy sheet were insufficient,· the work hardenability of the can wall was low; and the decrease rate of the cross-sectional thickness of the can wall was large.

[0041]

In Comparative Example No. 16, the holding time of the wound coil at a temperature of 120°C or higher was insufficient; the recovery after winding of the aluminum alloy sheet was insufficient; the work hardenability of the can wall was not improved; and the decrease rate of the cross-sectional thickness of the can wall was large. In Comparative Examples No. 17 and 19, since the cold rolling was performed by the single rolling mill, the winding temperature was low; the dynamic recovery and recovery after the winding of the aluminum alloy sheet were insufficient; the proof stress of the aluminum alloy sheet was excessive; and the ironing workability was poor. In Comparative Examples No. 17 and 19, the work hardenability of the can wall was low, and the decrease rate of the cross-sectional thickness of the can wall was large. Note that the alloy composition of Comparative Example No. 17 was configured based on the composition of the alloy e5 mentioned in the example of Patent Document 1. In Comparative Example No. 18, since the cold rolling was performed by the single rolling mill, the winding temperature was low, and the dynamic recovery and recovery after the winding of the aluminum alloy sheet were insufficient. Thus, Comparative Example No. 18 had the low work hardenability of the can wall and the large decrease rate in the cross-sectional thickness of the can wall. In Comparative Example No. 20, since the cold rolling was performed by the single rolling mill, the winding temperature was low, and the dynamic recovery and recovery after the winding of the aluminum alloy sheet were insufficient. Thus, Comparative

Example No. 20 barely exhibited the effect of finish annealing and had the low work hardenability of the can wall and the large decrease rate in the cross-sectional thickness of the can wall.

[0042]

This application claims priority on Japanese Patent Application No. 2014-184681, filed on September 10, 2014, the disclosure of which is incorporated by reference herein.

Claims

1. An aluminum alloy sheet for a can body, comprising: 0.1 to 0.5% by mass of Si; 0.3 to 0.6% by mass of Fe; 0.1 to 0.35% by mass of Cu; 0.5 to 1.2% by mass of Mn; and 0.7 to 2.5% by mass of Mg, with the balance being Al and inevitable impurities, wherein the aluminum alloy sheet has a proof stress of 240 to 290

MPa after being subjected to baking at 200°C for 20 minutes, and an increase of a 0.2% proof stress of the aluminum alloy sheet of a can wall is 10 MPa or more, on conditions in which the aluminum alloy sheet is subjected to a DI process at a processing rate of the can wall of 60 to 70% to produce a can, followed by baking at 2 00°C for 2 0 minutes and then applying 1% stretch to the can wall of the can, when performing a 90° V bending-bending back process at a bending radius of 0.1 mm in a can peripheral direction.

2. The aluminum alloy sheet according to claim 1, further comprising one or more kinds of elements selected from 0.10% or less by mass of Cr, 0.40% or less by mass of Zn, and 0.10% or less of Ti .

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Fig. 2A

Fig.2B k

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Fig.2C

Fig. 3A

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Fig.3B