WO2016039215A1 - 缶胴用アルミニウム合金板 - Google Patents
缶胴用アルミニウム合金板 Download PDFInfo
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- WO2016039215A1 WO2016039215A1 PCT/JP2015/074774 JP2015074774W WO2016039215A1 WO 2016039215 A1 WO2016039215 A1 WO 2016039215A1 JP 2015074774 W JP2015074774 W JP 2015074774W WO 2016039215 A1 WO2016039215 A1 WO 2016039215A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
- C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
Definitions
- the present invention relates to an aluminum alloy plate used for forming a can body of a two-piece can by performing DI (draw & ironing) forming, and in particular, aluminum for a can body suitable for performing secondary processing on a can wall after DI forming. It relates to an alloy plate.
- Cans that have been subjected to secondary processing such as embossing and diamond cut pattern on the can wall are used in the manufacturing stage including filling of the contents, the distribution stage after filling, the stage for consumers, etc.
- secondary processing such as embossing and diamond cut pattern on the can wall
- a hard and sharp foreign object repeatedly comes into contact with a portion deformed by processing, and the portion further undergoes plastic deformation.
- the thickness of the portion is locally reduced (constriction occurs) due to the secondary processing and subsequent plastic deformation, the portion where the thickness is reduced, such as when the can is impacted or a foreign object contacts the can wall.
- excessive stress is applied to the can, and the can wall may break, causing leakage of the contents.
- the evaluation method of Patent Document 1 assumes the actual situation that the can wall may be locally reduced in thickness by the secondary processing and subsequent plastic deformation, and the can wall may break due to excessive stress applied thereto. Not a thing. After the secondary processing, even when plastic deformation corresponding to conditions (small bending radius) more severe than the evaluation method of Patent Document 1 is applied to the can wall, the can wall is uniformly deformed, and the local plate thickness is reduced. Is required to be suppressed.
- the present invention has been made on the basis of such a demand, and the can wall after DI processing and baking processing is uniformly deformed by secondary processing and subsequent plastic deformation, and the local wall thickness reduction of the can wall is reduced.
- An object of the present invention is to provide an aluminum alloy plate for a can body that is suppressed.
- the aluminum alloy plate for a can body according to the present invention has Si: 0.1 to 0.5% by mass, Fe: 0.3 to 0.6% by mass, Cu: 0.1 to 0.35% by mass, Mn: It contains 0.5 to 1.2% by mass, Mg: 0.7 to 2.5% by mass, the balance is made of Al and inevitable impurities, and the yield strength after baking at 200 ° C. for 20 minutes is 240.
- a 0.2% proof stress increment (also referred to as work hardening ability in the present invention) when performing 90 ° V bending-bending at a bending radius of 0.1 mm is 10 MPa or more.
- the aluminum alloy may further contain one or more of Cr: 0.10% by mass or less, Zn: 0.40% by mass or less, and Ti: 0.10% by mass or less as necessary.
- the aluminum alloy plate for can bodies according to the present invention has excellent DI processability and secondary can wall when the can wall is subjected to secondary processing such as embossing and diamond cut pattern after DI processing and baking treatment. Shows workability.
- the aluminum alloy plate for can bodies according to the present invention has high work hardening ability, and when the can wall subjected to secondary processing is further subjected to plastic deformation, the can wall is uniformly deformed, and the local plate thickness Reduction (neck formation) is suppressed. For this reason, when the can is impacted or when a foreign object comes into contact with the can wall, it can be prevented that a large stress is locally applied to the can wall, the can wall can be prevented from breaking after filling, and leakage occurs. Can be prevented.
- Fe 0.3-0.6% by mass
- the Fe content is less than 0.3% by mass, unrecrystallized remains in the hot coil, so that the 45 ° ear becomes high at the time of DI molding, and the ear cut and the tear-off due to this tend to occur during ironing.
- the Fe content exceeds 0.6% by mass, the amount of Al—Fe—Mn intermetallic compound increases, and tear-off is likely to occur during ironing.
- cracks starting from the intermetallic compound are likely to occur during secondary processing of the can wall.
- Cu 0.1 to 0.35 mass
- Mn 0.5 to 1.2% by mass
- Mn content is less than 0.5% by mass
- the strength is insufficient and the pressure resistance of the can is insufficient.
- the Mn content exceeds 1.2% by mass
- the Al—Fe—Mn intermetallic compound increases, and tear-off is likely to occur during ironing.
- cracks starting from the intermetallic compound are likely to occur during secondary processing of the can wall.
- Mg 0.7-2.5% by mass
- the Mg content is less than 0.7% by mass
- the strength is insufficient and the pressure resistance of the can is insufficient.
- the work hardening ability of the aluminum alloy plate is insufficient, and constriction is likely to occur during secondary processing of the can wall.
- the Mg content exceeds 2.5% by mass, the strength becomes excessive and tear-off is likely to occur during ironing.
- Cr 0.10 mass% or less
- Cr can be positively added within the above range, for example, by increasing the mixing ratio of scrap (such as scrap containing a large amount of Cr) into the raw material.
- scrap such as scrap containing a large amount of Cr
- the Cr content in the aluminum alloy is limited to the above range. Normally, the content of Cr inevitably contained is 0.050% by mass or less.
- Zn 0.40 mass% or less
- Ti 0.10% by mass or less
- Ti is added as necessary for the purpose of refining the ingot crystal grains. If the ingot structure is refined during casting, castability is improved and high-speed casting becomes possible. The effect is acquired by addition of 0.01 mass% or more.
- Ti is added in excess of 0.10% by mass, the filter is clogged quickly, and it becomes difficult for the molten metal to pass through the filter during casting, and eventually casting must be stopped. Therefore, the Ti content in the aluminum alloy is limited to the above range.
- an ingot refining agent Al-Ti-B having a mass ratio of Ti and B of 5: 1 is added to the melt before casting in the form of waffles or rods. B corresponding to the content ratio is inevitably added. Usually, the content of Ti inevitably contained is 0.050% by mass or less.
- Inevitable impurities other than the above elements are each 0.10% or less, preferably 0.05% or less, and a total of 0.30% or less, preferably 0.15% Even if it is, it does not disturb the effect of the present invention. Note that these elements are not only added if they do not exceed the above contents, but are actively added, not only when they are contained as inevitable impurities, but also intentionally increasing the mixing ratio of scraps containing these elements. Even if it is a case, the effect of this invention is not disturbed.
- the work hardening ability is ⁇ 2 ⁇ 1 If this work hardening ability ( ⁇ 2 ⁇ 1 ) is 10 MPa or more, the can wall is uniformly deformed by secondary processing and subsequent plastic deformation, and a local reduction in plate thickness of the can wall is suppressed.
- the work hardening ability is less than 10 MPa, the can wall is difficult to be uniformly deformed by the secondary processing and the subsequent plastic deformation, and the can wall is locally reduced in thickness and is likely to be constricted. For this reason, excessive stress is applied to the thinned portion such as when the can is impacted or a foreign object comes into contact with the can wall, and the can wall is ruptured and the contents are likely to leak.
- the aluminum alloy sheet according to the present invention can be produced by each process of casting, homogenizing heat treatment, hot rolling, and cold rolling. Intermediate annealing after hot rolling and finish annealing after cold rolling are not performed.
- the method for producing an aluminum alloy plate according to the present invention is particularly characterized in that cold rolling is performed under predetermined conditions. Hereinafter, each step will be described.
- an aluminum alloy may be cast by a known semi-continuous casting method such as a DC (Direct-Chill) method.
- homogenization heat processing is performed based on a conventional method.
- a two-stage homogenization heat treatment or a two-time homogenization heat treatment may be employed.
- the two-stage homogenization heat treatment here refers to holding the ingot at a high temperature for a predetermined time (first stage homogenization heat treatment), and then cooling to a temperature exceeding 200 ° C. without cooling to room temperature. This means holding for a predetermined time (second-stage homogenization heat treatment).
- the double homogenization heat treatment means that the ingot is kept at a high temperature for a predetermined time (first homogenization heat treatment), then cooled to a temperature of 200 ° C. or less including room temperature, and reheated to a predetermined homogenization. This means holding at the treatment temperature for a predetermined time (second homogenization heat treatment).
- hot rolling is continued without cooling the ingot temperature to less than 450 ° C, and the hot rolling is preferably finished at 300 ° C or higher.
- hot rolling is performed after heating to a higher temperature as necessary.
- the produced hot rolled material has a recrystallized structure.
- the subsequent cold rolling is performed with a tandem rolling mill. By performing cold rolling with a tandem rolling mill, the rolling rate in one pass sheet can be increased. Thereby, processing heat_generation
- the total rolling rate of cold rolling is 80-90%. This rolling rate is achieved by one pass through a tandem rolling mill. If the total rolling ratio in cold rolling is less than 80%, the strength of the aluminum alloy sheet is insufficient, and the pressure resistance of the can after DI molding and baking is insufficient. On the other hand, if the total rolling ratio exceeds 90%, the strength becomes excessive and an increase of 45 ° ears is caused, and the occurrence of ear breakage and tear-off due to this are likely to occur during ironing.
- the coiling temperature after cold rolling is in the range of 120 to 180 ° C.
- the winding temperature By setting the winding temperature within the above temperature range, the aluminum alloy sheet (cold rolled material) can be dynamically recovered and recovered after winding, and work hardening of the can wall when it becomes the final can. Performance is improved. If the winding temperature is less than 120 ° C, the effect of recovery is insufficient, the work hardening ability of the can wall is insufficient, it is difficult to deform uniformly by secondary processing and subsequent plastic deformation, and the can wall is locally platen. The thickness decreases and constriction is likely to occur.
- the lower limit of the winding temperature is preferably 150 ° C. When the winding temperature exceeds 180 ° C., softening of the aluminum alloy plate due to processing heat generation becomes large, and plate breakage is likely to occur during rolling. As a result, the productivity of the aluminum alloy plate is greatly reduced, which is not practically preferable.
- the coil after winding is kept at a temperature of 120 ° C. or more for 4 hours or more. Thereby, the recovery of the aluminum alloy plate (cold rolled material) is promoted, and the work hardening ability of the can wall is improved in the can after DI molding and baking. On the other hand, when the holding time at a temperature of 120 ° C. or higher is less than 4 hours, the recovery of the aluminum alloy plate (cold rolled material) is insufficient and does not contribute to the improvement of the work hardening ability of the can wall.
- Tables 1 and 2 show the types of rolling mills used in cold rolling, the total rolling rate of cold rolling, the winding temperature after cold rolling, the time that the coil after winding is held at 120 ° C or higher, and cold rolling. The presence and conditions of the subsequent finish annealing were described.
- Example No. manufactured 1 to 19 and Comparative Example No. 1 The aluminum alloy plates 1 to 11 and 13 to 20 were used as test materials, and the proof strength after baking was measured as follows. Subsequently, Example No. 1 to 19 and Comparative Example No. 1 DI cans were produced using aluminum alloy plates 1 to 11 and 13 to 20. As a production method, a blank having a diameter of 140 mm was first punched from an aluminum alloy plate, and the blank was drawn to produce a cup having a diameter of 90 mm. The obtained cup is subjected to DI molding using a general-purpose aluminum can body forming machine (redraw, 1-draw iron, 2-draw iron, 3-draw iron). It was. The ironing rate of the third stretch was 40%.
- a general-purpose aluminum can body forming machine redraw, 1-draw iron, 2-draw iron, 3-draw iron
- This ironing rate is a severe condition compared with a general ironing rate of about 35 to 38%.
- a side view of the produced can (after trimming the opening) is shown in FIG.
- the can has an outer diameter of 66.3 mm, a height of 124 mm, a thickness of the thinnest wall of the can wall (height 60 mm from the bottom of the can) is 95 ⁇ m, and a processing rate of the same is 68.3% (initial thickness: 0.3 mm).
- 10,000 cans were continuously formed by the aluminum can body molding machine, and the ironing processability was evaluated in the following manner. Subsequently, using the molded can, the work hardening ability of the can wall, the cross-sectional plate thickness reduction rate after 90 ° V bending-bending of the can wall, and the pressure strength were measured as follows. The above results are shown in Table 3.
- the first and second test pieces were subjected to a tensile test in accordance with the provisions of JIS Z 2241 (2011 revised edition), and each 0.2% proof stress was obtained.
- the initial plate thickness of the second test piece was assumed to be 95 ⁇ m, similar to the first test piece.
- the 0.2% proof stress of the first test piece is ⁇ 1
- the 0.2% proof stress of the second test piece is ⁇ 2
- the difference between them ⁇ 2 ⁇ 1
- the 0.2% yield strength increment after processing was defined as the work hardening ability of the can wall. Those having a work hardening ability ( ⁇ 2 - ⁇ 1 ) of 10 MPa or more were evaluated as acceptable.
- the can wall is uniformly deformed during the secondary processing and subsequent plastic deformation, and the local reduction in thickness (constriction formation) of the can wall is suppressed.
- the can is subjected to an impact or a foreign object contacts the can wall, it is possible to prevent the can wall from being subjected to a large stress locally.
- the stretch which gives 1% permanent distortion performed in this measurement test simulates the secondary processing (embossing processing or diamond cut pattern processing) applied to the can wall.
- the permanent distortion of 1% is larger than the permanent distortion applied to the can wall in the actual processing of the diamond cut pattern, and this stretch can be said to be considerably severer than the actual embossing and processing of the diamond cut pattern.
- the V bending-bending process simulates the plastic deformation that is accidentally applied to the can in the manufacturing stage including filling of contents, the distribution stage after filling, and the stage for consumers. .
- This V-bending-bending process can be said to be stricter than the evaluation method of Patent Document 1 (the bending radius is 1 mm) in that the bending radius is as small as 0.1 mm.
- test piece was embedded in a resin to prepare a sample for cross-sectional observation (see FIG. 1 (e)), and a bending-bending part at the center in the width direction of the test piece (broken line in FIG. 1 (e)) The cross section of the portion surrounded by) was observed, and the plate thickness reduction rate with respect to the original plate thickness (95 ⁇ m) was measured. The case where the cross-sectional thickness reduction rate was 5% or less was evaluated as acceptable.
- the rubber tube 6 extends downward through the base plate 2, is connected to a water conduit, and communicates with a water pressure pump through a water pressure gauge, a switching valve, and the like. (Neither shown).
- a hole 7 is formed in the base plate 2, and the hole 7 is connected to a vent pipe and communicates with a vacuum pump via a switching valve or the like (both not shown).
- the fixing members 4 and 4 are advanced and retracted by hydraulic cylinders (not shown).
- the pressure resistance test is performed as follows. (1) As shown in FIGS. 2A to 2C, after the can 8 having a height of 100 mm is trimmed in the opening and fitted into the holder 3 with the can bottom facing up, the fixing members 4 and 4 are advanced by a predetermined stroke. Let When the fixing members 4 and 4 reach a predetermined position (see FIG. 3A), the tips of the fixing members 4 and 4 hold the can wall of the can 8 from both sides at a position slightly below the O-ring 5 to hold the can 8 in the holder 3. Secure to. As a result, the inner wall of the can 8 is closely attached to the periphery of the O-ring 5, and the inside of the holder 3 (inside the can 8) is sealed except for the rubber tube 6 and the hole 7. (2) The vacuum pump is operated, the inside of the holder 3 (inside the can 8) is deaerated to 9.8 kPa (0.1 kgf / cm 2 ) or less through the hole 7, and then the vent line is closed.
- the water pressure pump is operated to supply water from the rubber tube 6 into the holder 3 (inside the can 8).
- the water pressure in the holder 3 (in the can 8) (measured by the water pressure gauge) rises almost in proportion to the elapsed time from the start of supply, and drops at the moment when buckling of the can bottom occurs.
- the maximum internal pressure when the can bottom buckling occurred was defined as the pressure resistance of the can.
- FIG. 3B shows the state when buckling of the can bottom occurs. The case where the pressure strength was 618 kPa or more (6.3 kgf / cm 2 or more) was evaluated as acceptable.
- the composition of the aluminum alloy plate, the yield strength of the aluminum alloy plate after baking, and the work hardening ability of the can wall are within the prescribed range of the present invention.
- Nos. 1 to 19 have excellent ironing workability, a small reduction rate of the cross-sectional plate thickness of the can wall after stretching and V bending-bending, and a high pressure strength.
- the small cross-sectional reduction rate means that the can wall is not locally reduced in thickness (the occurrence of constriction is suppressed), and the can wall is uniform by stretching and V bending-bending. It means that it has been transformed.
- any one of the component composition of the aluminum alloy plate, the yield strength of the aluminum alloy plate after baking, and the work hardening ability of the can wall is outside the specified range of the present invention.
- Nos. 1 to 11 and 13 to 20 satisfy any of the criteria of the present invention in terms of ironing workability, reduction rate of the cross-sectional thickness of the can wall, and pressure strength.
- Comparative Example No. Nos. 1 and 2 are inferior in ironing workability because the Si content is outside the specified range of the present invention.
- Comparative Example No. 3 and 4 are inferior in ironing workability because the Fe content is outside the specified range of the present invention. Comparative Example No. Nos.
- Comparative Example No. Nos. 6 and 10 have excessive Cu and Mg contents, respectively, so that the proof stress of the aluminum alloy plate after baking is excessive and the ironing workability is inferior.
- Comparative Example No. Nos. 8 and 11 are inferior in ironing workability because of excessive Mn and Cr contents.
- No. No. 12 could not be cast as described above because the Ti content was excessive.
- Comparative Example No. 13 since the total rolling rate of cold rolling was insufficient, the proof stress of the aluminum alloy sheet after baking was insufficient, and the pressure strength was inferior. Comparative Example No. In No. 14, the total rolling rate is excessive, so the proof stress of the aluminum alloy sheet is excessive and the ironing workability is inferior. Comparative Example No. No. 15 has a low winding temperature, insufficient dynamic recovery and recovery after winding, low work hardening ability of the can wall, and a large reduction rate of the sectional wall thickness of the can wall.
- Comparative Example No. No. 16 has insufficient holding time of the coil after winding at a temperature of 120 ° C. or more, recovery after winding is insufficient, work hardening performance of the can wall is not improved, and cross-sectional thickness of the can wall is reduced. The rate is large.
- Comparative Example No. Nos. 17 and 19 were cold rolled with a single rolling mill, so the winding temperature was low, dynamic recovery and recovery after winding were insufficient, the proof stress of the aluminum alloy plate was excessive, and ironing workability was Inferior.
- Comparative Example No. Nos. 17 and 19 have a low work hardening ability of the can wall and a large reduction rate of the cross-sectional plate thickness of the can wall. Comparative Example No.
- the alloy composition of 17 is based on the composition of the alloy e5 of the example of Patent Document 1.
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Abstract
Description
例えば特許文献1には、0.2%耐力の15%程度の応力を付加した状態で缶壁に対し曲げ半径1.0mmの90°繰り返し曲げを行ったときの破断限界サイクルが6サイクル以上で、かつ薄肉の、缶壁の二次加工性に優れた缶胴用アルミニウム合金板が記載されている。
本発明は、このような要請に基づいてなされたもので、DI加工及びベーキング処理後の缶壁が、二次加工及びその後の塑性変形により均一変形し、缶壁の局部的な板厚減少が抑制される缶胴用アルミニウム合金板を提供することを目的とする。
上記アルミニウム合金は、必要に応じて、さらにCr:0.10質量%以下、Zn:0.40質量%以下、Ti:0.10質量%以下のうち1種以上を含有することができる。
<アルミニウム合金の成分組成>
(Si:0.1~0.5質量%)
Si含有量が0.1質量%未満では、DI成形時において0-180°耳が高くなり、しごき加工時に耳切れ及びこれに起因するティアオフが生じやすい。一方、Si含有量が0.5質量%を超えると、ホットコイルに未再結晶粒が残存するため、DI成形時において45°耳が高くなり、しごき加工時に耳切れ及びこれに起因するティアオフが生じやすい。
Fe含有量が0.3質量%未満では、ホットコイルに未再結晶が残存するため、DI成形時において45°耳が高くなり、しごき加工時に耳切れ及びこれに起因するティアオフが生じやすい。一方、Fe含有量が0.6質量%を超えると、Al-Fe-Mn系金属間化合物が多くなり、しごき加工時にティアオフが生じやすい。また、缶壁の二次加工時に前記金属間化合物を起点とした割れが発生しやすくなる。
(Cu:0.1~0.35質量%)
Cu含有量が0.1質量%未満では強度が不足し、缶の耐圧強度が不足する。一方、Cu含有量が0.35質量%を超えると強度が過大となり、しごき加工時にティアオフが生じやすい。
Mn含有量が0.5質量%未満では強度が不足し、缶の耐圧強度が不足する。一方、Mn含有量が1.2質量%を超えると、Al-Fe-Mn系金属間化合物が多くなり、しごき加工時にティアオフが生じやすい。また、缶壁の二次加工時に前記金属間化合物を起点とした割れが発生しやすくなる。
(Mg:0.7~2.5質量%)
Mg含有量が0.7質量%未満では強度が不足し、缶の耐圧強度が不足する。また、アルミニウム合金板の加工硬化能が不足し、缶壁二次加工時にくびれが生じやすい。一方、Mg含有量が2.5質量%を超えると強度が過大となり、しごき加工時にティアオフが生じやすい。
Crは0.10質量%以下の含有量であれば、アルミニウム合金板の材料特性、DI成形後の缶特性に影響を及ぼさない。Crは不可避不純物であるが、コストダウンを図るため、例えば原料中へのスクラップ(Crを多く含有するスクラップ等)配合率を高くするなど、上記範囲内でCrを積極添加することもできる。しかし、Cr含有量が0.10質量%を超えると、ホットコイルに未再結晶が残存し、DI成形において45°耳が高くなり、しごき加工時に耳切れ及びこれに起因するティアオフが生じやすい。従って、アルミニウム合金中のCr含有量は上記範囲内に制限される。なお、通常、不可避的に含まれるCrの含有量は、0.050質量%以下である。
Znは0.40質量%以下の含有量であれば、アルミニウム合金板の材料特性、DI成形後の缶特性に影響を及ぼさない。Znは不可避不純物であるが、コストダウンを図るため、例えば原料中へのスクラップ(熱交換器用クラッド材のスクラップ等)配合率を高くするなど、上記範囲内でZnを積極添加することもできる。なお、通常、不可避的に含まれるZnの含有量は、0.30質量%以下である。
Tiは鋳塊結晶粒の微細化を目的に、必要に応じて添加される。鋳造時に鋳塊組織を微細化すると、鋳造性が向上して高速鋳造が可能となる。その効果は0.01質量%以上の添加により得られる。一方、Tiを0.10質量%を超えて添加すると、フィルターの目詰まりが早く、鋳造中に次第に溶湯がフィルターを通過しにくくなり、ついには鋳造を中止せざるを得なくなる。従って、アルミニウム合金中のTi含有量は上記範囲内に制限される。なお、Tiを添加する場合には、TiとBの質量比を5:1とした鋳塊微細化剤(Al-Ti-B)を、ワッフルあるいはロッドの形態で鋳造前の溶湯に添加するため、含有割合に応じたBも必然的に添加される。なお、通常、不可避的に含まれるTiの含有量は、0.050質量%以下である。
上記元素以外の不可避不純物(V、Na、Zr、Ni、Caなど)について、各々0.10%以下、好ましくは0.05%以下、且つ合計0.30%以下、好ましくは0.15%含まれていても、本発明の効果を妨げない。なお、これらの元素についても、前記含有量を超えなければ、不可避的不純物として含有される場合だけではなく、意図的にこれらの元素を含むスクラップの配合率を高めるなど、積極的に添加される場合であっても、本発明の効果を妨げない。
(ベーキング後の耐力:240~290MPa)
200℃×20分のベーキング後のアルミニウム合金板の耐力が240MPa未満では強度が不足し、DI成形及びベーキング後の缶の耐圧強度が不足する。一方、ベーキング後のアルミニウム合金板の耐力が290MPaを超えると強度が過大であり、しごき加工時にティアオフが多発し、生産性を低下させる。なお、ベーキング後の強度はベーキング前の強度と連動しており、ベーキング後の強度が大きいアルミニウム合金板は、ベーキング前(しごき加工時)の強度も大きい。
本発明では、缶壁の加工率が60~70%となるDI成形後、200℃×20分のベーキングを施した缶の缶壁に対し、さらに1%(永久歪み)のストレッチを加えた後、缶周方向に曲げ半径0.1mmで90°V曲げ-曲げ戻し加工を行ったときの0.2%耐力の増分を加工硬化能と定義する。なお、DI成形による加工率60~70%は、缶のDI成形において標準的な加工率である。
本発明に係るアルミニウム合金板は、鋳造、均質化熱処理、熱間圧延、及び冷間圧延の各工程で製造することができる。熱間圧延後の中間焼鈍及び冷間圧延後の仕上げ焼鈍は行わない。そして、本発明に係るアルミニウム合金板の製造方法は、特に冷間圧延を所定の条件で行う点に特徴がある。
以下、各工程について説明する。
次に、鋳塊表層の不均一な組織となる領域を面削にて除去した後、常法に基づき均質化熱処理を施す。このとき2段均質化熱処理又は2回均質化熱処理を採用してもよい。ここでいう2段均質化熱処理とは、鋳塊を高温に所定時間保持(1段目の均質化熱処理)した後、室温まで冷却せず、200℃を超える温度で冷却を止め、その温度に所定時間保持(2段目の均質化熱処理)することを意味する。また、2回均質化熱処理とは、鋳塊を高温に所定時間保持(1回目の均質化熱処理)した後、室温を含む200℃以下の温度にいったん冷却し、再加熱して所定の均質化処理温度に所定時間保持(2回目の均質化熱処理)することを意味する。
続く冷間圧延は、タンデム圧延機で行う。タンデム圧延機で冷間圧延を行うことで、1回の通板における圧延率を大きくすることができる。それにより、加工発熱が大きくなり、冷間圧延材の動的回復及び巻き取り後の回復が促進される。その結果、冷間圧延材(本発明に係るアルミニウム合金板)をDI成形及びベーキングを行った缶において、缶壁の加工硬化能が向上する。
巻き取り温度が120℃未満では、回復の効果が不十分であり、缶壁の加工硬化能が不足して、二次加工及びその後の塑性変形で均一変形しにくく、缶壁が局部的に板厚減少してくびれが生じやすい。巻き取り温度の下限は好ましくは150℃である。
巻き取り温度が180℃を超えると、加工発熱によるアルミニウム合金板の軟化が大きくなり、圧延中に板切れが生じやすくなる。その結果、アルミニウム合金板の生産性を大きく低下するので実用上好ましくない。
表1,2に示す組成のアルミニウム合金を溶解し、半連続鋳造法を用いて厚さ600mmの鋳塊を作製した(比較例のNo.12を除く)。この鋳塊の表層を面削し、均質化熱処理を施した後、続けて熱間圧延を行った。その後中間焼鈍を施すことなく、熱間圧延材に対し冷間圧延(タンデム圧延機又はシングル圧延機)を行い、板厚0.30mmのアルミニウム合金板とし、巻き取りを行った。冷間圧延後の仕上げ焼鈍は行わなかった(比較例のNo.20を除く)。なお、比較例のNo.12は、フィルターの目詰まりのため、鋳造ができなかった。
表1,2に冷間圧延で用いた圧延機の種類、冷間圧延の総圧延率、冷間圧延後の巻き取り温度、巻き取り後のコイルを120℃以上で保持した時間、冷間圧延後の仕上げ焼鈍の有無及び条件を記載した。
続いて、実施例No.1~19及び比較例No.1~11,13~20のアルミニウム合金板を用い、DI缶を作製した。作製方法として、まずアルミニウム合金板から直径140mmのブランクを打ち抜き、このブランクを絞り成形して直径90mmのカップを作製した。得られたカップに対し、汎用のアルミ缶胴成形機(再絞り、1伸目しごき、2伸目しごき、3伸目しごきの4段階で構成されるもの)にてDI成形を施し、DI缶とした。なお、3伸目のしごき加工率は40%とした。このしごき加工率は、一般的なしごき加工率である35~38%程度に比べ厳しい条件である。
作製した缶(開口部をトリミング後)の側面図を図1の(a)に示す。缶は外径が66.3mm、高さが124mm、缶壁の最薄肉部(缶底から60mmの高さ)の肉厚が95μm、同部の加工率が68.3%(当初板厚:0.3mm)であった。
前記アルミ缶胴成型機により、各実施例及び比較例とも10000缶を連続成形し、以下に示す要領でしごき加工性の評価を行った。引き続き、その成形した缶を用いて、缶壁の加工硬化能、缶壁の90°V曲げ-曲げ戻し加工後の断面板厚減少率、及び耐圧強度を、以下に示す要領で測定した。以上の結果を表3に示す。
供試材(アルミニウム合金板)に対し200℃×20分のベーキングを実施した後、圧延平行方向にJIS5号試験片を採取して、JIS Z 2241(2011年改定版)の規定に準じて引張試験を行い、0.2%耐力を測定した。この0.2%耐力が240~290MPaの範囲内のとき、合格と評価した。
(しごき加工性)
連続成形した10000缶のうち、ティアオフ等の不具合が生じた缶が3缶以下のものを合格(○)、4缶以上のものを不合格(×)と評価した。
作製した缶に200℃×20分のベーキングを実施した後、缶底からの高さ60mmの高さが幅方向の中心となり、圧延0°方向が長さ方向の中心となるように、缶の円周方向に沿ってJIS13号B試験片(第1試験片)を採取した。
また、作製した缶に200℃×20分のベーキングを実施した後、缶底からの高さ60mmの高さが幅方向の中心となり、圧延0°方向が長さ方向の中心となるように、缶の円周方向に沿って幅20mm×長さ100mmの短冊状試験片を切り出した(図1の(a)参照)。その短冊状試験片に対し、引張試験機にて1%のストレッチを加えた後(図1の(b)参照)、先端の曲げ半径Rが0.1mmの冶具を用いて、90°V曲げ加工を実施し(図1の(c)参照)、次いで、反対方向に曲げ戻す加工を実施した(図1の(d)参照)。この短冊状試験片からJIS13号B試験片(第2試験片)を採取した。V曲げ-曲げ戻し加工部はこのJIS13号B試験片の長さ方向中央に位置させた。
なお、前記第1試験片と第2試験片は、前者が1%のストレッチとV曲げ-曲げ戻し加工を受けてなく、後者がそれらの加工を受けている点で異なる。
作製した缶に、200℃×20分のベーキングを実施した後、缶底からの高さ60mmの高さを幅方向の中心として、圧延0°方向が長さ方向の中心となるように、缶の円周方向に幅20mm×長さ100mmの短冊状試験片を切り出した(図1の(a)参照)。その短冊状試験片に対し、引張試験機にて1%(公称歪み)のストレッチを加えた後(図1の(b)参照)、先端の曲げ半径Rが0.1mmの冶具を用いて、90°V曲げ加工を実施し(図1の(c)参照)、次いで、反対方向に曲げ戻す加工を実施した(図1の(d)参照)。得られた試験片を樹脂に埋め込んで断面観察用試料を作製し(図1の(e)参照)、試験片の幅方向中央部の曲げ-曲げ戻し加工部(図1の(e)において破線で囲った部分)の断面を観察し、元の板厚(95μm)に対する板厚減少率を測定した。断面板厚減少率が5%以下の場合を合格と評価した。
水圧式の耐圧試験機(エーステック株式会社製の水圧式加減圧バックリングテスト装置、型式名WBT-500)を用いて、ベーキングを施した缶に内圧を負荷し、缶底がバックリングしたときの最大内圧を耐圧強度として求めた。
図2A~Cに示すように、耐圧試験機は、機台1上に設置されたベース板2と、ベース板2の上に設置された円筒状のホルダー3と、ホルダー3の両側に配置された一対の固定部材4,4を備える。ホルダー2の高さ方向中間位置にO-リング5が設置されている。ホルダー2の内部にゴムチューブ6が設置され、該ゴムチューブ6はベース板2を通って下に延び、通水管路に連結され、水圧計及び切換弁等を介して水圧ポンプに連通している(いずれも図示せず)。ベース板2に穴7が形成され、該穴7は通気管路に連結され、切換弁等を介して真空ポンプに連通している(いずれも図示せず)。固定部材4,4はそれぞれ図示しない油圧シリンダにより進退する。
(1)図2A~Cに示すように、開口部をトリミングして高さ100mmとした缶8を、缶底を上にしてホルダー3に嵌めた後、固定部材4,4を所定のストローク前進させる。固定部材4,4が所定位置に達すると(図3A参照)、固定部材4,4の先端が缶8の缶壁をO-リング5のやや下の位置で両側から押さえ、缶8をホルダー3に固定する。これにより、缶8の缶壁内面がO-リング5の周囲に密着し、ゴムチューブ6及び穴7の箇所を除き、ホルダー3内(缶8内)が密封される。
(2)前記真空ポンプを作動させ、穴7を通してホルダー3内(缶8内)を9.8kPa(0.1kgf/cm2)以下に脱気し、次いで前記通気管路を閉じる。
この耐圧強度が618kPa以上(6.3kgf/cm2以上)の場合を合格と評価した。
比較例No.1,2は、Si含有量が本発明の規定範囲外であるため、しごき加工性が劣る。比較例No.3,4は、Fe含有量が本発明の規定範囲外であるため、しごき加工性が劣る。比較例No.5,7,9は、それぞれCu,Mn,Mg含有量が不足しているため、ベーキング後のアルミニウム合金板の耐力が不足し、缶の耐圧強度が劣る。比較例No.6,10は,それぞれCu,Mg含有量が過剰なため、ベーキング後のアルミニウム合金板の耐力が過大で、しごき加工性が劣る。比較例No.8,11は、それぞれMn,Cr含有量が過剰なため、しごき加工性が劣る。なお、No.12はTi含有量が過剰なため、先に述べたとおり、鋳造ができなかった。
Claims (2)
- Si:0.1~0.5質量%、Fe:0.3~0.6質量%、Cu:0.1~0.35質量%、Mn:0.5~1.2質量%、Mg:0.7~2.5質量%を含有し、残部がAl及び不可避的不純物からなり、200℃×20分のベーキングを行った後の耐力が240~290MPaであり、缶壁の加工率が60~70%となるDI成形後200℃×20分のベーキングを施した缶の前記缶壁に、1%のストレッチを加えた後、缶周方向に曲げ半径0.1mmで90°V曲げ-曲げ戻し加工を行ったときの0.2%耐力の増分が10MPa以上であることを特徴とする缶胴用アルミニウム合金板。
- Cr:0.10質量%以下、Zn:0.40質量%以下、Ti:0.10質量%以下のうち1種以上を含有することを特徴とする請求項1に記載された缶胴用アルミニウム合金板。
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JP2005042165A (ja) * | 2003-07-22 | 2005-02-17 | Kobe Steel Ltd | 包装容器蓋用アルミニウム合金板およびその製造方法 |
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