JP2010236075A - Aluminum alloy sheet for can barrel, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for a can barrel, which can be formed into a can barrel having excellent sticking resistance and can expansibility even if being thinned, by covering both sides of the aluminum alloy sheet with a protective layer made from resin, and to provide a method for manufacturing the same. <P>SOLUTION: The aluminum alloy sheet is manufactured by: producing an ingot by melting an aluminum alloy comprising, by mass, 1.6-6.0% Mg, less than 0.5% Mn, 0.05-0.5% Si, 0.1-0.5% Fe, 0.05-0.3% Cu and the balance Al with unavoidable impurities, and casting the melted alloy; homogenizing the ingot by heat-treating it once at 450°C or higher but lower than 550°C; subsequently hot-rolling the ingot at a total reduction ratio of 99.2% or more without cooling it; and cold-rolling the hot-rolled plate without annealing it. In the central part in the sheet thickness direction of a cross-section of the aluminum alloy sheet, intermetallic compounds with the maximum length of 1 μm or more occupy more than 0.3% but less than 1.3% by an area rate, and the number of intermetallic compounds with the maximum length of 11 μm or more is 100 pieces/mm<SP>2</SP>or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a packaging container used for beverages and foods, and more particularly to an aluminum alloy plate formed on a body portion of a beverage can after film lamination on both sides and a manufacturing method thereof.

  Currently, as one of packaging containers used for beverages and foods, a bottomed cylindrical body (can body) whose bottom and side walls are integrated, and an upper surface sealed by an opening of the body A two-piece can comprising a disc-shaped lid (can lid) is known. As a material for such a can, an aluminum alloy plate is widely applied in terms of formability, corrosion resistance, strength, and the like. Among the two-piece cans manufactured with this aluminum alloy plate, the cylindrical portion of the cylindrical can having a height particularly like a beverage can has a lot of drawing and ironing called DI (Drawing and wall Ironing) molding. Often formed by step processing. In this way, the aluminum alloy plate is DI molded, then painted and baked, the opening diameter is reduced by necking (neck molding), and the edge of the opening is expanded outward by flanging (flange molding). Become the torso. Finally, the contents (beverage, food) are filled in the body, and the lid is wound around the opening and sealed. A can made by such a manufacturing method is called a DI can (hereinafter referred to as “can” as appropriate) and is widely distributed.

  Conventionally, in order to reduce the cost of beverages packaged with such aluminum alloy cans, cans that are packaging containers have been reduced in thickness as measures for reducing weight and reducing raw materials (aluminum alloys). As a result, the thickness of the side wall (thinnest part) of the current aluminum alloy can is about 0.100 to 0.110 mm in the aluminum alloy part excluding the coating film and the like. However, in such a thinned can, when a protrusion is brought into contact with and pressed against a thin side wall (circumferential surface), the tip penetrates the side wall and a hole (pin (Hall) may open and the contents may leak. Protrusion contact may include contact of hard foreign matter from the outside during manufacturing (filling contents, tightening the lid, passing through the transport system in the manufacturing process), distribution, and even when handled by consumers. Can be mentioned. Also in flanging, when the edge of the opening is expanded, a crack (flange crack) may occur at the end of the opening. Therefore, the material of the thinned can can prevent the occurrence of pinholes on the side walls and cracks in the flanges of the openings, that is, improve the piercing resistance and flange formability (can expandability) of the side walls. The development of aluminum alloy plates is underway.

  For example, in Patent Document 1, a can is DI-molded from a JIS 3104-H19 tempered plate, and the can is heat-treated in a washing and drying furnace at 270 ° C. or more to increase the elongation of the side wall, thereby causing pinholes and flange cracks. A technique for producing a can with less generation is disclosed. Further, in Patent Document 2, an aluminum alloy cold-rolled sheet containing a predetermined amount of Mn, Mg, Cu, Si, and Fe, and by controlling the distribution density and area ratio of an intermetallic compound of a predetermined size on the surface thereof, Techniques for improving (puncture resistance) and toughness are disclosed. In Patent Literature 3, aluminum alloy cold-rolled sheets containing a predetermined amount of Mn, Mg, Cu, Si, and Fe are subjected to DI molding at a predetermined processing rate and heat-treated at 210 to 250 ° C., whereby work hardening by DI molding is performed. And a technique for improving the puncture resistance by controlling the tensile strength. In Patent Document 4, a relatively large Al-Mn-Fe-Si-based crystallized substance is densely distributed by homogenizing an ingot obtained by casting an aluminum alloy containing a predetermined amount of Mn, Mg, Cu, Si, and Fe. Thus, a technique for imparting strength is disclosed.

  Also, in order to perform DI molding by dry processing without the use of coolant, films made of PET or the like are laminated on both sides of the aluminum alloy plate to prevent seizure due to tools such as ironing dies coming into contact with the aluminum alloy plate. Film laminate cans are also available. In Patent Document 5, an aluminum alloy obtained by casting, homogenizing, hot rolling, cold rolling, intermediate annealing, and secondary cold rolling an aluminum alloy containing a predetermined amount of Mg, Si, and Fe while suppressing the content of Mn. A technique is disclosed in which a thin plate can be formed by increasing the yield strength of a resin-coated aluminum alloy plate in which the plate is coated with a resin such as PET. In Patent Document 6, an aluminum alloy containing a predetermined amount of Mg, Mn, Cu, Si, Fe, and Ti improves strength and workability in the resin coating, and increases the work hardening index by heating in the resin coating. A technique for improving the puncture resistance at a predetermined value or more is disclosed.

Japanese Patent Publication No. 8-950 (Claim 1) JP 2007-197815 A (paragraphs 0015 to 0018, 0030, 0031) JP 2007-169767 (paragraphs 0017 to 0021, 0033, 0036) JP 2006-77296 A (paragraphs 0006, 0022) JP-A-9-287043 (paragraphs 0004, 0023 to 0026) JP 2001-3130 (paragraphs 0008 to 0020, 0029 to 0033)

  However, in the technique disclosed in Patent Document 1, the side wall thickness of the can is 0.16 mm or more and does not have the strength corresponding to the current side wall thickness of the can. And the technique disclosed by patent document 2 has improved the piercing-proof property by making the side wall thickness of a can more than 0.110 mm, and does not respond to thickness reduction. Moreover, since the technique disclosed in Patent Document 3 has a limited baking temperature range when painting a can, it is necessary to apply a coating material corresponding to the temperature. On the other hand, the technique disclosed in Patent Document 4 performs homogenization at a high temperature of 590 to 630 ° C. in order to crystallize a relatively large Al—Mn—Fe—Si-based crystallized product in an ingot. Furthermore, preheating at 400 to 550 ° C. is performed before hot rolling, and energy consumption is large.

  The technique disclosed in Patent Document 5 is inferior in productivity because cold work is performed in two steps with intermediate annealing in between. Also, bending / unbending workability and pressure strength are supported. It does not correspond to the puncture resistance, and there is a possibility that the intermetallic compound grows and is not sufficient because the temperature in the homogenization treatment is particularly high. Moreover, since the technique disclosed in Patent Document 6 does not prescribe the manufacturing conditions up to cold rolling as a conventional method, there is a large variation due to the manufacturing conditions.

  The present invention has been made in view of the above-described problems, and when formed into a thinned can, the aluminum alloy plate for a can body having sufficient puncture resistance on the side wall and can expandability on the opening. And it aims at providing the manufacturing method.

  In order to solve the above-mentioned problems, the present inventors have investigated the mechanism of generating pinholes when protrusions are pushed into the side walls of the can, and as a result, the following phenomena have been found. That is, when the dent is deformed in the shape of a mortar to the inside of the can centering on the portion where the projection is in contact, local thinning and shear bands are formed at the periphery of the center (the inclined surface of the mortar). A crack is generated from the end of the shear band (inner surface of the can), and the crack propagates along the shear band to break, and the amount of intermetallic compound in the thinned portion, particularly When there are many large intermetallic compounds, it is easy to break. Therefore, the present inventors have determined that the area ratio of the intermetallic compound in the aluminum alloy sheet and the number density of the large intermetallic compound, particularly between the metals in the center of the plate thickness where the large intermetallic compound tends to remain in the rolled sheet. It came to the thought which controls a compound.

  In addition, when DI is formed on the can body, resin coating is applied to the aluminum alloy plate to avoid seizure due to contact with the tool, so that intermetallic compounds are appropriately dispersed on the surface of the aluminum alloy plate to provide lubricity. Therefore, the intermetallic compound in the aluminum alloy sheet is greatly reduced. On the other hand, the moderately dispersed intermetallic compound has the effect of promoting recrystallization by self-annealing after hot rolling and improving the formability of the aluminum alloy sheet. As a result of research on methods for promoting recrystallization, the inventors have found a method for controlling the composition of aluminum alloy, particularly the contents of Mg and Mn.

That is, the aluminum alloy plate for a can body according to the present invention is an aluminum alloy plate for forming a can body by coating a resin on both sides, and Mg: 1.6 to 6.0% by mass, Mn: 0.00. Less than 5% by mass, Si: 0.05 to 0.5% by mass, Fe: 0.1 to 0.5% by mass, Cu: 0.05 to 0.3% by mass, the balance being Al and inevitable An area ratio of an intermetallic compound having a maximum length of 1 μm or more is less than 1.3% and less than 1.3%, and the maximum length is 11 μm or more. The number of intermetallic compounds is 100 / mm ² or less.

  Thus, by containing Mg and Cu in a predetermined range, the formability for producing the can body can be maintained while appropriately improving the strength of the aluminum alloy plate for the can body. Further, by containing Mg, Mn, Si, and Fe within a predetermined range, the intermetallic compound can be appropriately dispersed in the aluminum alloy plate for a can body. Furthermore, in the center part of the thickness of the aluminum alloy plate for the can body, the distribution of the intermetallic compound is restricted by the area ratio and the number density, thereby maintaining the formability and reducing the thickness of the can body to 0.110 mm or less. Even if it is molded, the puncture resistance and the can expandability can be improved.

  Furthermore, in the aluminum alloy plate for a can body according to the present invention, Mg contained in the aluminum alloy is preferably 1.6 to 4.0% by mass. By setting it as such Mg content, the can expandability in flanging can be improved further.

  Furthermore, in the aluminum alloy plate for can bodies according to the present invention, the total of Si and Fe contained in the aluminum alloy may exceed 0.6% by mass. By setting it as such Si and Fe content, the amount of scraps used can be ensured and recyclability can be improved.

  Further, the method for producing an aluminum alloy plate for a can body according to the present invention comprises a casting step for melting and casting the aluminum alloy of the above components to form an ingot, and the ingot is 2 to 8 at 450 ° C. or more and less than 550 ° C. A soaking process that homogenizes by performing heat treatment for one time, a hot rolling process that hot-rolls the homogenized ingot without cooling it into a hot-rolled sheet, and this hot-rolled sheet A cold rolling process that performs cold rolling without annealing, the hot rolling process includes rough rolling and finish rolling, and the total rolling rate in the hot rolling process is 99.2% or more. And

  In this way, by restricting the heat treatment conditions for homogenization, the ingot intermetallic compound is suppressed from coarsening, and the total rolling rate in the hot rolling is set to a predetermined value or more to achieve hot rolling. It is possible to produce an aluminum alloy plate for a can body in which large intermetallic compounds are sufficiently crushed and a large number of large intermetallic compounds do not remain.

  According to the aluminum alloy plate for a can body according to the present invention, a DI can having sufficient piercing resistance and can expandability can be produced by resin coating even if it is thinned. It enables cost reduction and resource saving by thinning. And according to the manufacturing method of the aluminum alloy plate for can bodies which concerns on this invention, the aluminum alloy plate for can bodies which has the said effect can be manufactured with sufficient productivity.

It is a figure explaining an example of the method of producing the can body of DI can from the aluminum alloy plate for can bodies. It is sectional drawing which illustrates typically the measuring method of the piercing strength of a can body. (A), (b) is sectional drawing which illustrates typically the can expandability evaluation method of a can body.

  Hereinafter, the form for implement | achieving the aluminum alloy plate for can bodies which concerns on this invention (henceforth an aluminum alloy plate) is demonstrated.

  The aluminum alloy plate according to the present invention has Mg: 1.6 to 6.0 mass%, Mn: less than 0.5 mass%, Si: 0.05 to 0.5 mass%, Fe: 0.1 to 0.3 mass%. 5% by mass, Cu: 0.05 to 0.3% by mass, with the balance being made of an aluminum alloy composed of Al and inevitable impurities.

The aluminum alloy plate according to the present invention has an area ratio of an intermetallic compound having a maximum length of 1 μm or more at a central portion in the plate thickness direction of the cross section of more than 0.3% and less than 1.3%, and the maximum length The number of intermetallic compounds having a diameter of 11 μm or more is 100 / mm ² or less. The thickness of the aluminum alloy plate is preferably about 0.26 to 0.36 mm before resin coating. Hereinafter, each element which comprises the aluminum alloy plate which concerns on this invention is demonstrated.

[Components of aluminum alloy]
(Mg: 1.6-6.0% by mass)
Mg has an effect of improving strength by solid solution strengthening and an effect of increasing work hardening in an aluminum alloy, and further has an effect of increasing accumulated strain during hot rolling and promoting recrystallization by subsequent self-annealing. Therefore, the DI formability of the aluminum alloy plate is improved. If the Mg content is less than 1.6% by mass, the accumulated strain during hot rolling is insufficient, and a sufficient recrystallized structure cannot be stably obtained during self-annealing after hot rolling. Since the non-recrystallized portion (processed structure) tends to remain in the central portion in the width direction, an aluminum alloy plate having a non-uniform structure is formed, so that the DI formability deteriorates. Even when recrystallization is sufficient, when the aluminum alloy plate is formed on the can body, the side wall strength becomes low and the buckling strength and puncture resistance are insufficient. On the other hand, if the Mg content exceeds 6.0% by mass, the work hardening of the aluminum alloy plate becomes excessive. For this reason, defects such as tear-off (fuselage cracks) during ironing, wrinkles and streaks during necking, and cracks during flanging are likely to occur, each processing yield decreases, especially work hardening by necking As a result, defects during flanging become prominent. Therefore, the Mg content is set to 1.6 to 6.0 mass%, and 1.6 to 4.0 mass% is preferable in order to obtain particularly excellent moldability.

(Mn: less than 0.5% by mass)
Mn has an effect of improving the strength of the aluminum alloy, and when the aluminum alloy plate is formed on the can body, the side wall strength is increased to ensure buckling strength and puncture resistance. Mn forms Al—Mn—Fe—Si-based and Al—Mn—Fe-based intermetallic compounds in the aluminum alloy. These intermetallic compounds of a certain size become the core of recrystallization in an aluminum alloy, so that they are moderately dispersed to promote recrystallization by self-annealing after hot rolling, so that the aluminum alloy Although the DI moldability of the plate is improved, on the other hand, when the amount and size thereof are increased, the puncture resistance and the can expandability are lowered. When the Mn content is 0.5% by mass or more, a large amount of fine intermetallic compounds are precipitated in the ingot. Here, in the aluminum alloy plate according to the present invention, the temperature in the soaking heat treatment of the ingot is limited to a low range as described later so that the intermetallic compound is not greatly grown. On the contrary, the intermetallic compound inhibits recrystallization after hot rolling, so that the DI moldability deteriorates. Therefore, the Mn content is less than 0.5% by mass. In addition, in the aluminum alloy plate according to the present invention, since the strength and workability are improved by other additive elements such as Mg and the manufacturing method, the lower limit of the Mn content is not specified, but the above-described strength improvement effect is further improved. In order to give and to improve recyclability, it is preferable to set it as 0.3 mass% or more.

(Si: 0.05-0.5% by mass)
Si is mixed into the aluminum alloy as a metal base impurity. When the Si content is less than 0.05% by mass, the required purity of the aluminum base metal used as a raw material increases and the cost increases. In addition, Si forms Al—Mn—Fe—Si intermetallic compounds and Mg—Si intermetallic compounds (Mg ₂ Si) in an aluminum alloy. Recrystallization after hot rolling is promoted to improve the DI formability of the aluminum alloy sheet. On the other hand, when the Si content exceeds 0.5% by mass, a large number of these intermetallic compounds are formed, and the puncture resistance and can expandability are reduced, or a large amount of Mg ₂ Si is formed. Thus, the amount of Mg solid solution in the aluminum alloy is insufficient. Therefore, the Si content is 0.05 to 0.5 mass%.

(Fe: 0.1-0.5% by mass)
Fe is mixed into the aluminum alloy as a metal impurity, and if the Fe content is less than 0.1% by mass, the required purity of the aluminum metal used as a raw material increases, and the cost increases. In addition, Fe forms Al-Mn-Fe-Si-based and Al-Mn-Fe-based intermetallic compounds in an aluminum alloy, and these intermetallic compounds are appropriately dispersed to allow recrystallization after hot rolling. Is promoted to improve the DI formability of the aluminum alloy sheet. On the other hand, if the Fe content exceeds 0.5% by mass, a large amount of these intermetallic compounds are formed, and the puncture resistance and can expandability deteriorate. Therefore, the Fe content is 0.1 to 0.5 mass%.

  As described above, Si and Fe are inevitably mixed in the aluminum alloy as metal impurities, and are contained to some extent in scrap and recycled metal. That is, recyclability is improved by using an aluminum alloy having a high Si and Fe content. Therefore, the total content of Si and Fe is preferably more than 0.6% by mass.

(Cu: 0.05 to 0.3% by mass)
Cu has an effect of improving the strength of the aluminum alloy, and when the aluminum alloy plate is formed on the can body, the side wall strength is increased to ensure buckling strength and puncture resistance. When the Cu content is less than 0.05% by mass, this effect is insufficient. On the other hand, if the Cu content exceeds 0.3% by mass, the work hardening of the aluminum alloy plate becomes excessive and the workability is lowered. Therefore, the Cu content is set to 0.05 to 0.3% by mass.

  In addition to the above, inevitable impurities may be contained. As unavoidable impurities, for example, Cr: 0.10% by mass or less, Zn: 0.50% by mass or less, Ti: 0.10% by mass or less, Zr: 0.10% by mass or less, B: 0.05% by mass The following will not affect the characteristics of the aluminum alloy sheet according to the present invention.

[Intermetallic compounds in aluminum alloy sheets]
(Area ratio of intermetallic compounds with a maximum length of 1 μm or more at the center in the thickness direction of the cross section: more than 0.3% and less than 1.3%)
The intermetallic compounds in the aluminum alloy sheet according to the present invention are mainly Al—Mn—Fe—Si intermetallic compounds, Al—Mn—Fe intermetallic compounds, and Mg—Si intermetallic compounds (Mg ₂ Si). (Hereinafter referred to as “intermetallic compound” as appropriate). When these intermetallic compounds having a certain size are appropriately dispersed, recrystallization by self-annealing after hot rolling is promoted, and the DI formability of the aluminum alloy sheet is improved. Specifically, in an aluminum alloy sheet, when the area ratio of an intermetallic compound having a maximum length of 1 μm or more is 0.3% or less, recrystallization after hot rolling is insufficient and a processed structure remains, and DI Formability deteriorates.

  On the other hand, excessive intermetallic compounds deteriorate puncture resistance and can expandability. As described above, the mechanism when the protrusion is pushed into the side wall of the can is that the peripheral edge of the center portion is depressed when it is recessed in the shape of a mortar toward the inside of the can with the protrusion in contact with the center. The thickness is reduced locally, and at the same time, a shear band is formed. Cracks are generated from the end of the shear band (inner surface of the can) and propagated along the shear band. Becomes a pinhole. Further, in flanging, when the aluminum alloy plate exceeds the forming limit, a shear band is generated in the vicinity of the end of the opening, local thinning progresses, cracks are generated, and flange cracking occurs. If an intermetallic compound having a certain size, specifically, a maximum length of about 1 μm or more is present at the end of the shear band, this intermetallic compound is likely to be a source of cracks.

  On the shear band, if an intermetallic compound having a maximum length of 1 μm or more exists, the intermetallic compound becomes a source of stress concentration, microcracks or voids, and promotes the generation and propagation of cracks. Therefore, if the number density of the intermetallic compound is large in the whole area in the plate thickness direction including the surface, that is, in the surface of the aluminum alloy plate and inside the plate thickness direction, in the vicinity of the side wall and the opening of the can, the aluminum alloy plate When this is formed into a can body, pinholes and flange cracks are likely to occur.

  In the rolled plate, the intermetallic compound closer to the rolling surface, that is, the ingot surface is crushed during rolling and is more easily refined. That is, in the vicinity of the center in the thickness direction, larger intermetallic compounds tend to exist (residual) in large numbers. Therefore, in the aluminum alloy plate according to the present invention, the distribution of the intermetallic compound in the central portion in the plate thickness direction is regulated. When the area ratio of the intermetallic compound having a maximum length in this region of 1 μm or more is 1.3% or more, cracking is likely to occur when the aluminum alloy plate is formed on the can body, and the puncture resistance is deteriorated. Furthermore, flange cracking is likely to occur in flanging, and the can expandability deteriorates. From the above, the area ratio of the intermetallic compound having a maximum length of 1 μm or more is more than 0.3% and less than 1.3% in the center part in the plate thickness direction of the cross section of the aluminum alloy plate. The central portion in the plate thickness direction of the cross section specifically refers to a region at 55 to 70% of the plate thickness centering on the plate thickness direction center.

  Since these intermetallic compounds also have a lubricating effect during ironing, a sufficient amount is dispersed especially on the surface of the aluminum alloy plate, so that a tool such as an ironing die can be formed between the aluminum alloy plate and the die during DI forming. It is possible to prevent seizure. However, the aluminum alloy plate according to the present invention limits the distribution of intermetallic compounds to less than the amount that can prevent seizure during DI molding in order to improve the puncture resistance and can expandability. Therefore, as will be described later, the aluminum alloy plate according to the present invention is coated with a resin such as a film laminate before DI molding so as not to come into direct contact with the tool.

(Number density of intermetallic compounds having a maximum length of 11 μm or more at the center in the thickness direction of the cross section: 100 / mm ² or less)
The larger the size of the intermetallic compound, the easier it is for cracks to propagate, and when the maximum length is 11 μm or more, a small number leads to breakage. As described above, in the rolled sheet, there are many large intermetallic compounds in the vicinity of the center in the sheet thickness direction. Accordingly, the number of intermetallic compounds having a maximum length of 11 μm or more at the central portion in the thickness direction of the cross section of the aluminum alloy plate is set to 100 pieces / mm ² or less. The distribution of the intermetallic compound as described above is controlled by the contents of the Mg, Mn, Si, and Fe and the manufacturing conditions described later.

Application of a scanning electron microscope (SEM) is an example of the intermetallic compound detection means. Intermetallic compounds with a maximum length of 1 μm or more can be identified by contrast with the parent phase in the SEM composition (COMPO) image. Al—Mn—Fe—Si and Al—Mn—Fe intermetallic compounds are more It appears white, and the Mg—Si intermetallic compound appears blacker than the Al matrix. The intermetallic compound in the center part in the thickness direction of the cross section of the aluminum alloy plate is cut out of the aluminum alloy plate, and the cut surface including the rolling direction and the plate thickness direction is polished into a mirror surface to obtain an observation surface. A region at 55 to 70% of the plate thickness centered on the center in the plate thickness direction is observed. From this region, a plurality of visual fields are preferably observed and photographed in a total of 1 mm ² or more, and the area ratio and number density of the intermetallic compound having a specified size can be measured using an image processing apparatus or the like.

  Next, the manufacturing method of the aluminum alloy plate concerning this invention is demonstrated. The aluminum alloy plate according to the present invention comprises a casting process for melting and casting the aluminum alloy of the above components to form an ingot, a soaking process for homogenizing the ingot by a single heat treatment, and an ingot after this heat treatment. It is manufactured by a hot rolling process in which hot rolling is performed without cooling to obtain a hot rolled sheet, and a cold rolling process in which cold rolling is performed without annealing the hot rolled sheet. Below, the conditions of each process are demonstrated.

[Casting process]
First, an aluminum alloy is melted, cast by a known semi-continuous casting method such as a DC casting method, and cooled to below the solidus temperature of the aluminum alloy to form an ingot. The thickness of the ingot is preferably 500 mm or more in order to ensure productivity and a sufficient amount of rolling in the subsequent hot rolling. On the other hand, if an excessively thick ingot is used, ingot cracking is likely to occur and the casting yield is lowered. Therefore, the thickness is preferably 650 mm or less. Moreover, if the speed of casting or cooling is slow, a large amount of coarse intermetallic compounds crystallize in the ingot, and if it is too fast, ingot cracking is likely to occur and the casting yield is lowered. Therefore, in casting, it is preferable that a casting speed is 40 to 65 mm / min and a cooling speed is 0.5 to 1.5 ° C./second. This cooling rate is for the temperature of the central part of the ingot, that is, the temperature of the central part of the surface perpendicular to the casting direction, and the cooling rate from the liquidus temperature to the solidus temperature of the aluminum alloy. And In addition, the liquidus temperature and the solidus temperature of the aluminum alloy according to the present invention vary depending on the composition, respectively, and become low when the contents of Mg and Cu are large.

[Soaking process]
Before rolling the ingot, it is necessary to perform a homogenization heat treatment (soaking) at a predetermined temperature. By applying heat treatment to the ingot, internal stress is removed and solute elements segregated during casting are homogenized. On the other hand, this heat treatment grows the intermetallic compound deposited at the time of casting cooling or later, but in the aluminum alloy plate according to the present invention, the intermetallic compound is not grown excessively, and for reducing energy consumption, The heat treatment in the soaking process is performed once. Further, the ingot homogenized by this heat treatment is continuously subjected to a subsequent hot rolling step without cooling.

(Heat treatment: 450 ° C. or higher and lower than 550 ° C. for 2 to 8 hours)
In the soaking process, if the heat treatment temperature is less than 450 ° C., it is insufficient for homogenizing the ingot having the composition of the aluminum alloy sheet according to the present invention. On the other hand, when the heat treatment temperature is 550 ° C. or higher, the intermetallic compound grows excessively and remains after the subsequent hot rolling process and cold rolling process, and the resistance when the aluminum alloy sheet is formed into a can body. The piercing property and can expandability are reduced. Further, if the heat treatment time is less than 2 hours, the homogenization of the ingot may not be completed. On the other hand, even if the heat treatment is performed for more than 8 hours, further improvement of the effect cannot be obtained and productivity is lowered. Therefore, in the soaking process, the heat treatment is performed at 450 ° C. or higher and lower than 550 ° C. for 2 to 8 hours.

[Hot rolling process]
(Total rolling ratio: 99.2% or more)
The homogenized ingot is hot-rolled continuously from the soaking process. First, the temperature at the time of completion of the heat treatment in the soaking process is maintained, the ingot is roughly rolled, and the aluminum alloy hot-rolled sheet having a predetermined plate thickness is obtained by finish rolling. If the total rolling reduction (total rolling reduction) in hot rolling including rough rolling and finish rolling is less than 99.2%, a large amount of large intermetallic compounds are produced because the intermetallic compounds are not sufficiently crushed by hot rolling. It tends to remain. Therefore, the total rolling rate in hot rolling is 99.2% or more.

[Cold rolling process]
The aluminum alloy hot-rolled sheet is cold-rolled without being annealed to finish an aluminum alloy sheet having a predetermined thickness. The total rolling rate (cold working rate) in cold rolling is preferably 80 to 90%.

[DI can manufacturing method]
The aluminum alloy plate according to the present invention is produced in a can body of a DI can by performing film lamination by a known method. Below, with reference to FIG. 1, an example of the method of producing the can body of DI can from the aluminum alloy plate which concerns on this invention is demonstrated. First, in order to form a corrosion-resistant film on the aluminum alloy plate according to the present invention, for example, phosphoric acid chromate treatment is performed. Then, as a protective layer for the aluminum alloy plate, a film (not shown) made of a crystalline thermoplastic resin such as a polyester resin or a polypropylene resin is laminated on both sides to obtain a resin-coated aluminum alloy plate for a can body. By covering such a protective layer, the surface of the aluminum alloy plate does not come into contact with tools such as ironing dies, so it is possible to prevent seizure during DI molding and the occurrence of tear-off due to seizure, thereby reducing the molding yield. Can be improved.

  This resin-coated aluminum alloy plate for can body is punched into a disk shape (blanking), drawn into a shallow cup shape (cupping), and subjected to DI molding. That is, drawing and ironing are repeated a plurality of times to gradually increase the side wall to obtain a bottomed cylindrical shape having a predetermined bottom surface shape and side wall height. It is preferable that the plate | board thickness reduction | decrease rate (ironing process rate) of the side wall of a can body by these processes shall be 60 to 70%. Then, after removing the highly volatile lubricant applied during DI molding and heating for preventing the film from peeling off, the edges of the side walls (openings) are trimmed and trimmed. Next, the outer surface of the can body is painted and baked (baked). And an opening part is diameter-reduced (necking), the edge of an opening part is expanded outside (flanging), and it becomes a can body. When used for beverages and food applications, the contents (beverages and food) are filled into the can body from the opening, and a can lid produced in a separate process is wound around the opening and sealed (not shown). )

  As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. In addition, this invention is not limited to this Example.

[Sample preparation]
(Aluminum alloy plate)
An aluminum alloy having the composition shown in Table 1 was melted, and an ingot having a thickness of 600 mm was produced using a semi-continuous casting method. This ingot is homogenized by holding at the soaking temperature shown in Table 1 for 4 hours, and then continuously hot-rolled at the total rolling rate shown in Table 1 (rough rolling and finish rolling) without cooling. To give a hot rolled sheet. Further, this hot-rolled plate was cold-rolled to obtain an aluminum alloy plate having a plate thickness of 0.30 mm.

(Can body)
The obtained aluminum alloy plate was subjected to a phosphoric acid chromate treatment, and a polyethylene terephthalate resin film having a thickness of 16 μm was laminated on both surfaces. This film laminated aluminum alloy plate is cupped, DI-molded (ironing rate 65-70%), the opening is trimmed, outer diameter is about 66mm, height (can axial length) 124mm, film A bottomed cylindrical can body having a side wall thickness of about 0.1 mm. Furthermore, heat treatment was performed at 270 ° C. for 30 seconds assuming baking during coating to obtain a test material. The thickness of the side wall not including the film of the obtained specimen is measured and shown in Table 1.

[Evaluation]
In the evaluation, the distribution of intermetallic compounds was evaluated with an aluminum alloy plate, and the can rigidity (anti-piercing property) and the can expandability (flange formability) were evaluated with a can body (after heat treatment) by the following methods. In the preparation of the aluminum alloy plate, the hot rolling plate after hot rolling was evaluated for the recrystallization rate by the method shown below, and the evaluation criteria were not satisfied, that is, the unrecrystallized portion remained. However, since the DI formability is insufficient even if it is cold-rolled to an aluminum alloy plate, it is not suitable as an aluminum alloy plate for can bodies. Indicated by “−”.

(Recrystallization rate)
The self-annealed hot-rolled sheet is cut out so that the surface including the rolling direction and the plate thickness direction becomes the observation surface, resin-filled, the observation surface is polished as a mirror surface, and this mirror-finished surface is borofluorinated. The crystal grains were visualized by etching with a dilute aqueous solution of hydrogen acid, and the crystal grain structure was observed with an optical microscope. Specifically, a continuous photograph is taken in the thickness direction so that both surfaces of the hot-rolled sheet are included with an optical microscope, a straight line in the thickness direction is drawn on the photograph, and the length of the recrystallized grains on this straight line is determined. The recrystallization rate was calculated by calculating the percentage of the total length of recrystallized grains over the plate thickness relative to the thickness of the hot rolled plate. The evaluation is performed by observing the crystal grain structure at a total of three locations in the center and at both ends in the rolling width direction of the hot rolled plate, calculating the recrystallization rate, and hot rolling plate having a recrystallization rate of 90% or more at all three locations. As a pass, “◯” indicates that a hot-rolled sheet of less than 90% at one location is evaluated as “bad”, and the result is shown in Table 1.

(Intermetallic compound distribution)
An aluminum alloy plate is cut out and filled with resin, and the surface including the rolling direction and the plate thickness direction is polished to be a mirror surface to be a mirror surface, and this mirror surface is scanned with a scanning electron microscope (SEM). Twenty visual fields (total 1 mm ² ) were observed with a composition (COMPO) image at an acceleration voltage of 20 KV and a magnification of 500 times. The observation visual field was within a range of 0.19 mm in the thickness direction centering on the center in the thickness direction. A portion that appears whiter than the parent phase is regarded as an Al-Mn-Fe-Si intermetallic compound or an Al-Mn-Fe intermetallic compound, and a portion that appears blacker than the parent phase is regarded as an Mg-Si intermetallic compound. The total area of intermetallic compounds having a maximum length of 1 μm or more was determined by the treatment, and the area ratio was calculated. In addition, the number of intermetallic compounds having a maximum length of 11 μm or more was counted, and the number per unit area (number density) was calculated. Table 1 shows the area ratio and number density of the intermetallic compound at the center of the thickness of the cross section of the aluminum alloy plate.

(Can rigidity)
A load in the can axis direction was applied to the can body from the opening, and the maximum load until the can body was buckled and deformed was measured as the buckling strength. If this buckling strength is 1500 N or more, the can rigidity is evaluated as “◯”, and if it is less than 1500 N, the can rigidity is evaluated as “x”. The results are shown in Table 1.

(Puncture resistance)
As shown in FIG. 2, the can body was fixed and an internal pressure of 2.0 kgf / cm ² (= 196 kPa) was applied. On the side wall of the can body, a piercing needle whose tip is a hemispherical surface with a radius of 0.5 mm is placed at a position where the rolling direction of the aluminum alloy plate coincides with the can axis direction and the distance L = 60 mm in the can axis direction from the can bottom. It was stabbed perpendicularly to the side wall at a speed of 50 mm / min. Then, the load until the piercing needle penetrates the side wall is measured, and the obtained maximum load is defined as the piercing strength. The piercing strength is 40N or higher, and particularly 45N or higher has excellent piercing resistance. “◎”, 40N or more and less than 45N are evaluated as “good” as good puncture resistance, while less than 40N are evaluated as “good” as puncture resistance, and are shown in Table 1.

(Can expandability)
A four-stage die necking was applied to the opening of the can body so that the inner diameter of the opening was 57.3 mm. As shown in FIG. 3A, the can bottom was fixed to the can body, a can expanding jig was inserted from the opening and pushed toward the can bottom, and the edge of the opening was expanded outward. The diameter of the insertion portion of the jig and the rising R (D, R in FIG. 3) are 57.3 mm and 3.0 mm, respectively, and a lubricant (Castrol water-soluble plastic working oil No. 700) was applied. The jig was pushed into the can body until the end of the opening was broken, and the flange widths at three points (see FIG. 3B) were measured at locations other than ± 90 ° from the broken position of the opening. The flange width of 10 can bodies is measured for each specification of the test material, and the average value of 3 points x 10 is 2.5 mm or more, and the can expandability is particularly excellent when the flange width is 3.0 mm or more. “◎”, 2.5 mm or more and less than 3.0 mm are evaluated as “◯” as good can expandability, and less than 2.5 mm are evaluated as “×” as poor can expandability, and are shown in Table 1.

  As shown in Table 1, the test material No. Nos. 1 to 7 are examples in which the contents of the components of the aluminum alloy are within the scope of the present invention, and the heat treatment temperature in the soaking process is within the scope of the present invention, so that the intermetallic compound distribution is moderately distributed. In addition, since recrystallization after hot rolling was sufficiently promoted, a can body having a side wall thickness of 0.097 to 0.103 mm could be formed without causing cracks and the like. Furthermore, the can body molded from these test materials had sufficiently high strength, and good can rigidity, puncture resistance, and can expandability.

  On the other hand, specimen No. 8 to 17 are comparative examples that do not satisfy any of the requirements of the present invention. Specimen No. Since No. 8 had insufficient Mg content, recrystallization after hot rolling was insufficient, and an unrecrystallized portion remained in the central portion in the rolling width direction. On the other hand, the test material No. In No. 9, since the Mg content was excessive, work hardening was excessive and the can expandability decreased.

  Specimen No. Nos. 10 and 11 have an excessive amount of Mn, so that a large amount of intermetallic compounds are formed, and the intermetallic compounds become fine because the heat treatment temperature in the soaking process is within the range of the present invention. The recrystallization after hot rolling was inhibited. In particular, sample No. No. 10 had insufficient recrystallization due to insufficient Mg content. On the other hand, the test material No. 16 is a specimen No. As in 10, the Mg content is insufficient and the Mn content is excessive, but in the soaking process, the heat treatment temperature is higher than the range of the present invention, so that the intermetallic compound grows excessively and in large quantities, Although recrystallization after hot rolling was sufficiently promoted, these intermetallic compounds remained on the aluminum alloy plate without being refined even after cold rolling, so that the piercing resistance was lowered. Specimen No. 12 also has an excessive Mn content and an excessive Fe content, so that in the soaking process, a large number of intermetallic compounds are formed in large quantities even when the heat treatment temperature is within the range of the present invention. , Puncture resistance decreased.

Specimen No. No. 13 has an excessive Si content, so a large amount of Mg ₂ Si is formed and the amount of Mg solid solution in the aluminum alloy is insufficient, resulting in insufficient strength and sufficient can rigidity, puncture resistance, and can expandability. Could not be obtained. Specimen No. In No. 14, since the Cu content was excessive, work hardening was excessive, workability was insufficient, and can expandability was reduced. On the other hand, the test material No. In No. 15, the Cu content was insufficient (no addition), so the strength was insufficient, and the can rigidity and puncture resistance were not sufficiently obtained.

  Specimen No. No. 17, the components of the aluminum alloy are within the scope of the present invention, but in the soaking process, the heat treatment temperature is higher than the scope of the present invention, so that the intermetallic compound grows excessively, and hot rolling and cold Since many large intermetallic compounds remained after rolling, the puncture resistance decreased.

Claims (6)

It is an aluminum alloy plate for a can body that covers a protective layer made of resin on both sides and is formed into a can body,
Mg: 1.6 to 6.0 mass%, Mn: less than 0.5 mass%, Si: 0.05 to 0.5 mass%, Fe: 0.1 to 0.5 mass%, Cu: 0.05 Containing 0.3 mass%, the balance being formed of an aluminum alloy consisting of Al and inevitable impurities,
In the central part in the plate thickness direction of the cross section, the area ratio of the intermetallic compound having a maximum length of 1 μm or more is more than 0.3% and less than 1.3%, and the number of intermetallic compounds having a maximum length of 11 μm or more is 100 / Mm ² or less, an aluminum alloy sheet for a can body.   The aluminum alloy plate for a can body according to claim 1, wherein the content of Mg in the aluminum alloy is 1.6 to 4.0% by mass.   The aluminum alloy plate for can bodies according to claim 1 or 2, wherein the total content of Si and Fe in the aluminum alloy exceeds 0.6 mass%. A method for producing an aluminum alloy plate for a can body, which is formed on a can body by covering a protective layer made of a resin on both sides,
Mg: 1.6 to 6.0 mass%, Mn: less than 0.5 mass%, Si: 0.05 to 0.5 mass%, Fe: 0.1 to 0.5 mass%, Cu: 0.05 A casting process that contains ~ 0.3% by mass, the balance being Al and unavoidable impurities, melting and casting into an ingot;
A soaking process in which the ingot is homogenized by performing heat treatment for 2 to 8 hours once at 450 ° C. or more and less than 550 ° C .;
A hot rolling step in which the homogenized ingot is hot rolled without cooling to form a hot rolled plate;
A cold rolling step of cold rolling the hot rolled sheet without annealing,
The hot rolling step includes rough rolling and finish rolling, and the total rolling rate in the hot rolling step is set to 99.2% or more.   5. The method for producing an aluminum alloy plate for a can body according to claim 4, wherein the content of Mg in the aluminum alloy is 1.6 to 4.0 mass%.   The method for producing an aluminum alloy plate for a can body according to claim 4 or 5, wherein the total content of Si and Fe in the aluminum alloy exceeds 0.6 mass%.

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