Aluminum alloy plate for caps and method for manufacturing the same

Abstract

The present invention aims to provide an aluminum alloy plate for caps and a method for manufacturing the same. [Solution] The aluminum alloy plate for caps according to the present invention contains, by mass%, Mn: 0.85~1.10%, Mg: 0.85~1.35%, Si: 0.20~0.40%, Fe: 0.40~0.60%, Cu: 0.20~0.30%, Zn: 0.10~0.30%, Cr: 0.01~0.10%, Ti: 0.01~0.10%, V: 0.01~0.10%, with the remainder being non- This is an aluminum alloy sheet having a composition of avoidable impurities and Al, with a tensile strength of 200-230 MPa, yield strength of 140-200 MPa, elongation of 4% or more, and edge ratio of 5.5% or less after baking. The average value of the n-value at angles of 0°, 45°, and 90° relative to the rolling direction after baking is 0.150 or less, and the difference between the maximum and minimum values ​​of these n-values ​​is 0.005 or less.

Description

Technical Field

[0001] The present invention relates to an aluminum alloy sheet for caps and a method for manufacturing the same.

Background Art

[0002] In aluminum beverage cans, generally, Al-Mn-Mg alloys such as AA3004 and AA3104 are used for the can body, and Al-Mg alloys such as AA5182 are used for the can lid and tab. On the other hand, for aluminum beverage bottle cans, Al-Mn-Mg alloys such as AA3004 and AA3104 are used, and Al-Mg alloys such as AA5151 are used for the cap material. In the recycling of these aluminum alloys, the alloy composition of used aluminum cans (UBC: Used Beverage Can) will be an Al-Mn-Mg alloy because the above-mentioned alloys are mixed and melted. Therefore, the resulting UBC alloy composition material has a chemical composition that is easy to use as a raw material for the can body and bottle.

[0003] In the integrated processing process of UBC recycling, in the casting process, either a UBC melt obtained by directly melting UBC as an aluminum alloy melt or a melt obtained by mixing UBC, high-purity raw materials or master alloys, and aluminum scraps such as process end materials generated in the manufacturing process of aluminum alloy sheets and the can manufacturing process is used. The aluminum alloy obtained by casting these melts is called a UBC recycled material. When manufacturing an aluminum alloy sheet with a high UBC blending ratio, compared with the case of using virgin aluminum ingots, the amount of CO2 generation can be significantly suppressed, and the environmental load can be reduced.

[0004] For example, Patent Document 1 below discloses a technique for providing an aluminum alloy sheet excellent for a beverage can body by adjusting the composition of an aluminum alloy in consideration of the bottom formability and bottom strength of a beverage can and adjusting manufacturing conditions such as homogenization conditions and rolling conditions. Furthermore, Patent Document 2 discloses a technique for obtaining a gauge by casting a hot band in a first hot rolling step from a molten aluminum alloy of the 2000 series to 7000 series containing 30% or more recycled content, and then reducing the thickness by 50% through a second hot rolling step. Patent Document 3 discloses an aluminum alloy sheet for caps and a manufacturing method in which the content of Mn, Mg, Si, Fe, Cu, and Zn is specified, and tensile strength, yield strength, and ear ratio are set to specific values ​​by performing stabilizing annealing after cold rolling. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6850635 [Patent Document 2] Patent No. 6964770 [Patent Document 3] Japanese Patent Publication No. 2017-088951 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, because UBC recycled material contains a relatively high concentration of manganese, it is difficult to apply it to bottle cap materials. This is because the work hardening properties vary depending on the alloy system. If UBC recycled material is used with the current manufacturing process, problems arise such as changes in the strength of the area that undergoes deep drawing on the side wall of the cap, disrupting the strength balance of various parts of the cap. For this reason, UBC recycled material is currently hardly used for bottle caps.

[0007] In view of the above problems, the present inventors aim to provide an aluminum alloy sheet and a method for manufacturing the same, which have a composition system that allows the use of UBC recycled material and possesses characteristics suitable for use as a cap. [Means for solving the problem]

[0008] (1) The aluminum alloy plate for the cap in this embodiment has the following composition by mass%, containing Mn: 0.85~1.10%, Mg: 0.85~1.35%, Si: 0.20~0.40%, Fe: 0.40~0.60%, Cu: 0.20~0.30%, Zn: 0.10~0.30%, Cr: 0.01~0.10%, Ti: 0.01~0.10%, V: 0.01~0.10%, with the remainder being unavoidable impurities and Al. Apply at 190°C for 10 minutes to 1 hour. An aluminum alloy sheet for caps, characterized by having a tensile strength of 200-230 MPa after baking, a yield strength of 140-200 MPa after baking, an elongation of 4% or more after baking, an edge ratio of 5.5% or less, an average value of n-values ​​at angles of 0°, 45°, and 90° with respect to the rolling direction after baking of 0.150 or less, and a difference of 0.005 or less between the maximum and minimum values ​​of these n-values. (2) In the aluminum alloy plate for the cap of this embodiment, it is preferable that the yield strength reduction for each 10°C increase in the final annealing temperature during the recovery softening behavior at 270°C or higher when the final annealing temperature is varied is 6 MPa or less.

[0009] (3) The method for manufacturing the aluminum alloy plate for the cap of this embodiment involves casting an aluminum alloy ingot having the following composition by mass%, Mn: 0.85~1.10%, Mg: 0.85~1.35%, Si: 0.20~0.40%, Fe: 0.40~0.60%, Cu: 0.20~0.30%, Zn: 0.10~0.30%, Cr: 0.01~0.10%, Ti: 0.01~0.10%, V: 0.01~0.10%, with the remainder being unavoidable impurities and Al. After casting, a homogenization treatment is performed at 560~610°C, followed by a soaking treatment at 520~550°C, and the final pass of hot rolling is performed at a strain rate of 80~140s. -1 This is followed by cold rolling in multiple passes, intermediate annealing between passes at 380-550°C, final cold rolling at a rolling ratio of 20-45%, and stabilization annealing at 270-320°C after the final cold rolling. The objective is to obtain an aluminum alloy sheet for caps that, after baking at 190°C for 10 minutes to 1 hour, has a tensile strength of 200-230 MPa, a yield strength of 140-200 MPa, an elongation of 4% or more, an edge ratio of 5.5% or less, an average n-value of 0.150 or less at angles of 0°, 45°, and 90° relative to the rolling direction after baking, and a difference of 0.005 or less between the maximum and minimum n-values. It is characterized by the following. (4) In the method for manufacturing an aluminum alloy plate for a cap according to this embodiment, it is preferable to obtain an aluminum alloy plate for a cap in which the yield strength reduction amount per 10°C increase in the final annealing temperature during the recovery softening behavior at 270°C or higher when the final annealing temperature is varied is 6 MPa or less. 。

[0010] (5) In the method for manufacturing an aluminum alloy plate for a cap according to the present embodiment of (3) or (4) above, it is preferable to blend the molten aluminum alloy with used aluminum cans and aluminum scrap, which is a process offcut generated in the aluminum material manufacturing process and the can manufacturing process, when casting the aluminum alloy. [Effects of the Invention]

[0012] The present invention aims to provide an aluminum alloy sheet for caps and a method for manufacturing the same, which has a composition that allows the use of UBC recycled material, is suitable as an aluminum alloy sheet for caps, can be accurately shaped during cap forming by deep drawing or capping forming by screw forming, can be given the pressure resistance strength required for caps, and has excellent formability, sealing properties and pressure resistance.

[0013] According to the present invention's method for manufacturing aluminum alloy plates for caps, when using raw materials during the casting of the aluminum alloy, either molten UBC obtained by directly melting UBC can be used as the molten aluminum alloy, or molten metal produced through a recycling process in which UBC and aluminum scrap are mixed with high-purity raw materials or a master alloy and then remelted can be used. This makes it possible to effectively utilize UBC and aluminum scrap, improve recycling efficiency, and obtain an aluminum alloy plate that is excellent for use as a cap. [Brief explanation of the drawing]

[0014] [Figure 1] A plan view showing a first embodiment of an aluminum alloy plate for a cap according to the present invention. [Figure 2] An explanatory diagram showing the apparatus and process used in the hot rolling step when carrying out the manufacturing method according to the present invention. [Figure 3] A schematic diagram showing an example of a continuous annealing apparatus used in carrying out the manufacturing method according to the present invention. [Modes for carrying out the invention]

[0015] Hereinafter, based on the accompanying drawings, an example of an embodiment of the present invention will be described in detail, but the present invention is not limited to the embodiments described below. Note that in the drawings used in the following description, in order to make the features easier to understand, there are cases where the characteristic parts are enlarged and shown for convenience.

[0016] The aluminum alloy plate for a cap according to an embodiment of the present invention is an alloy plate obtained by hot rolling an ingot of an aluminum alloy obtained by a semi-continuous casting method and then cold rolling it, and is obtained, for example, as a strip-shaped alloy plate. FIG. 1 is a plan view showing an embodiment of the aluminum alloy plate for a cap according to the present invention. The aluminum alloy plate 1 for a cap shown in FIG. 1 is composed of a raw plate obtained by hot rolling an ingot obtained by a semi-continuous casting method and then cold rolling it, and is depicted in FIG. 1 as a strip-shaped plate material having a certain width and with the length direction oriented left and right. The rolling direction of this aluminum alloy plate 1 for a cap is the left-right direction shown in FIG. 1 (the length direction of the aluminum alloy plate 1 for a cap). For convenience, the direction of 0° with respect to the rolling direction means the left-right direction in FIG. 1, the direction of 45° with respect to the rolling direction means the direction of the arrow marked 45° shown in FIG. 1, and the direction of 90° with respect to the rolling direction means the direction of the arrow marked 90° shown in FIG. 1. In the aluminum alloy plate 1 for a cap, the direction of 90° with respect to the rolling direction, in other words, means the width direction of the strip-shaped aluminum alloy plate 1 for a cap (the up-down direction of the paper surface in FIG. 1).

[0017] The composition of the aluminum alloy plate for a cap according to this embodiment will be described. The aluminum alloy plate for the cap in this embodiment is made of an aluminum alloy containing, by mass%, Mn: 0.85~1.10%, Mg: 0.85~1.35%, Si: 0.20~0.40%, Fe: 0.40~0.60%, Cu: 0.20~0.30%, Zn: 0.10~0.30%, Cr: 0.01~0.10%, Ti: 0.01~0.10%, and V: 0.01~0.10%, with the remainder being unavoidable impurities and Al. Since this aluminum alloy composition includes the composition of UBC, recycled UBC material can be used. UBC recycled material refers to aluminum alloys obtained by casting from molten UBC, which is made by melting UBC as is, or from molten metal mixed with high-purity raw materials or a base alloy, along with aluminum scrap such as process offcuts generated during the manufacturing process of aluminum alloy sheets and can manufacturing processes.

[0018] The following explains the reasons for limiting the composition of the aluminum alloy plate for the cap according to this embodiment. In this specification, the content of each element described is in mass percent unless otherwise specified, and unless otherwise specified, ranges include upper and lower limits. For example, 0.85~1.10% means 0.85% or more and 1.10% or less. Similarly, when expressing ranges for temperature, time, etc., upper and lower limits are included unless otherwise specified. For example, 380~550°C means 380°C or more and 550°C or less, and 1~2 hours means 1 hour or more and 2 hours or less.

[0019] "Mn: 0.85~1.10%" Mn forms Al-Mn-Fe and Al-(Mn,Fe)-Si intermetallic compounds, and by becoming a crystalline and dispersed phase, it exhibits a dispersion hardening effect, thereby improving the tensile strength and yield strength of the aluminum alloy sheet used for the cap. If the Mn content is less than 0.85% by mass, the dispersion of intermetallic compounds becomes insufficient, preventing the desired hardening properties from being obtained, resulting in a decrease in tensile strength and yield strength. Furthermore, dilution of the Mn contained in the molten UBC becomes necessary, preventing a high UBC blending ratio, thus reducing the UBC blending ratio. When the Mn content exceeds 1.1% by mass, the proportion of intermetallic compounds increases, leading to a decrease in moldability. A Mn content in the range of 0.90 to 1.05% is more preferable.

[0020] "Mg: 0.85~1.35%" Mg has a solid solution hardening effect, enhancing work hardening during rolling, and, when present with Si and Cu, exhibits dispersion hardening and precipitation hardening effects, thereby improving the tensile strength and yield strength of aluminum alloy sheets for caps. If the Mg content is less than 0.85% by mass, sufficient tensile strength and yield strength cannot be obtained. Furthermore, dilution of the Mg contained in the molten UBC is necessary, and since the UBC blending ratio cannot be increased, the UBC blending ratio decreases. If the Mg content exceeds 1.35% by mass, the tensile strength and yield strength become too high, reducing the elongation of the aluminum alloy sheet for the cap, and also worsening its formability. A Mg content in the range of 0.90 to 1.30% is more preferable.

[0021] "Si: 0.20~0.40%" Si, together with Mg and other elements present, forms intermetallic compounds, improving the tensile strength and yield strength of the aluminum alloy plate for the cap through solid solution hardening, dispersion hardening, and precipitation hardening. If the Si content is less than 0.20% by mass, sufficient tensile strength and yield strength cannot be obtained. Furthermore, dilution of the Si contained in the molten UBC is necessary, and since the UBC blending ratio cannot be increased, the UBC blending ratio decreases. If the Si content exceeds 0.40% by mass, the tensile strength and yield strength become too high, reducing the elongation of the aluminum alloy sheet for the cap, and also worsening its formability. A Si content in the range of 0.22% to 0.38% is more preferable.

[0022] "Fe: 0.40~0.60%" Fe increases the amount of crystallization and precipitation of Al-Mn-Fe intermetallic compounds and refines the crystal grains, thereby improving the tensile strength, yield strength, and elongation of aluminum alloy plates for caps. If the Fe content is less than 0.40% by mass, sufficient elongation cannot be obtained due to grain coarsening, and dilution of the Fe contained in the molten UBC becomes necessary, making it impossible to increase the UBC blending ratio, thus lowering the UBC blending ratio. If the Fe content exceeds 0.60% by mass, large intermetallic compounds are more likely to crystallize during casting, leading to cracking during molding. A Fe content in the range of 0.40-0.55% is more preferable.

[0023] "Cu: 0.20~0.30%" Cu improves the tensile strength and yield strength of aluminum alloy plates for caps through solid solution hardening, precipitation hardening, and dispersion hardening. If the Cu content is less than 0.20% by mass, sufficient tensile strength and yield strength cannot be obtained, and dilution of the Cu contained in the molten UBC becomes necessary, making it impossible to increase the UBC blending ratio, thus lowering the UBC blending ratio. If the Cu content exceeds 0.30% by mass, the tensile strength and yield strength become too high, resulting in poor moldability. A Cu content in the range of 0.20-0.30% is more preferable. "Zn: 0.10~0.30%" Zn has the effect of refining precipitates containing Mg, Si, and Cu, thereby improving tensile strength and yield strength. If the Zn content is less than 0.10% by mass, the effect of improving tensile strength and yield strength is not obtained, and dilution of the Zn contained in the molten UBC becomes necessary, preventing a high UBC blending ratio, and thus the UBC blending ratio decreases. If the amount of Zn added exceeds 0.30% by mass, the tensile strength and yield strength become excessively high.

[0024] "Cr: 0.01~0.10%" Cr improves the tensile strength and yield strength of aluminum alloy plates for caps through solid solution strengthening, and also has the effect of delaying recrystallization and coarsening grains during annealing. If the Cr content is less than 0.01% by mass, recrystallization during the final annealing process begins prematurely, leading to a decrease in tensile strength and yield strength. Furthermore, dilution of the Cr contained in the molten UBC becomes necessary, preventing a high UBC blending ratio and thus reducing the overall UBC blending ratio. When the Cr content exceeds 0.10 mass%, the tensile strength and yield strength become excessively high, and the formability during cap formation by deep drawing decreases due to the formation of large intermetallic compounds and grain coarsening.

[0025] "Ti: 0.01~0.10%" Ti improves the tensile strength and yield strength of aluminum alloy plates for caps through solid solution strengthening, and also has the effect of delaying recrystallization and coarsening grains during annealing. If the Ti content is less than 0.01% by mass, recrystallization during the final annealing process begins prematurely, leading to a decrease in tensile strength and yield strength. Furthermore, dilution of the Ti contained in the molten UBC becomes necessary, preventing a high UBC blending ratio and thus reducing the overall UBC blending ratio. When the Ti content exceeds 0.10 mass%, the tensile strength and yield strength become excessively high, and the formability during cap formation by deep drawing decreases due to the formation of large intermetallic compounds and grain coarsening.

[0026] "V: 0.01~0.10%" V improves the tensile strength and yield strength of the aluminum alloy plate for the cap through solid solution strengthening, and also has the effect of delaying recrystallization and coarsening the crystal grains during annealing. If the V content is less than 0.01% by mass, recrystallization during final annealing begins prematurely, leading to a decrease in tensile strength and yield strength. Furthermore, dilution of the V contained in the molten UBC becomes necessary, preventing a high UBC blending ratio, thus reducing the UBC blending ratio. If the V content exceeds 0.10 mass%, the tensile strength and yield strength become excessively high, and the formability during cap formation by deep drawing decreases due to the formation of large intermetallic compounds and grain coarsening.

[0027] In this embodiment, the aluminum alloy plate for the cap preferably has a tensile strength (TS) of 200 to 230 MPa after baking in the rolling direction, a yield strength (0.2% yield strength: YS) of 140 to 200 MPa after baking in the rolling direction, an elongation (EL) of 4% or more after baking in the rolling direction, and an edge ratio of 5.5% or less. Baking is performed under conditions of 190°C for 10 minutes to 1 hour.

[0028] The tensile strength and yield strength of the material after baking affect the formability of the aluminum alloy sheet used for the cap during deep drawing and capping, and also affect the airtightness and pressure resistance of the bottle can after molding. If the tensile strength after baking is less than 200 MPa, the structural strength of the cap is insufficient, making it prone to leakage when subjected to impact and reducing its airtightness. In addition, the restraining force of the threaded part of the cap's side wall is weak, reducing its pressure resistance. Pressure resistance refers to the resistance to the cap being blown off due to the rise in temperature of the bottle can and the increase in internal pressure due to the fermentation of the contents. If the pressure is greater than 230 MPa, the forming load required to obtain the desired thread dimensions when forming the threads on the side wall of the cap placed over the bottle can increases, making it more difficult to obtain the desired dimensions and reducing formability. If the post-baking yield strength is less than 140 MPa, the structural strength of the cap is insufficient, making it prone to leakage when subjected to impact and reducing its airtightness. In addition, the restraining force of the threaded portion of the cap's sidewall is weak, reducing its pressure resistance. If it is greater than 200 MPa, the forming load required to obtain the desired thread dimensions when forming the threaded portion of the cap's sidewall over a bottle can increases, and it becomes more difficult to obtain the desired dimensions, reducing moldability.

[0029] If the post-baking elongation is less than 4%, the risk of defects such as cracking occurs when forming the cap by deep drawing, and the moldability decreases. If the lug ratio is greater than 5.5%, the anisotropy is high, causing variations in the wall thickness of the cap sidewall in the circumferential direction, which can make it difficult to obtain the correct thread dimensions and may reduce moldability. This may also impair sealing and pressure resistance.

[0030] "Average value of n-values ​​at angles of 0°, 45°, and 90° relative to the rolling direction after baking." It is preferable that the average value of the n-value at angles of 0°, 45°, and 90° with respect to the rolling direction after baking is 0.150 or less.

[0031] The average n-value at angles of 0°, 45°, and 90° relative to the rolling direction after baking is an indicator of the balance between top surface strength and side wall strength after cap forming. A larger n-value indicates that the side wall is more work-hardened, and the difference between top surface strength and side wall strength is larger. When work hardening is significant, the forming load required to obtain the desired thread dimensions increases, similar to when the tensile strength and yield strength of the material are high. Furthermore, the effect of springback becomes greater, making it difficult to obtain thread dimensions and reducing formability. In addition, defects in thread shape are more likely to occur, which may reduce pressure resistance. Furthermore, even if the desired shape can be obtained by adjusting the molding load during thread forming of the cap's side wall, there is a possibility that pressure resistance may decrease due to the concentration of pressure on the top surface.

[0032] "The difference between the maximum and minimum n values ​​at angles of 0°, 45°, and 90° relative to the rolling direction after baking." It is preferable that the difference between the maximum and minimum n values ​​at angles of 0°, 45°, and 90° with respect to the rolling direction after baking is 0.005 or less.

[0033] The difference between the maximum and minimum n values ​​at angles of 0°, 45°, and 90° relative to the rolling direction after baking is an indicator of the variation in work hardening in the circumferential direction after cap molding. A large value indicates a large variation in sidewall strength in the circumferential direction. Significant variation makes it difficult to accurately impart thread dimensions to the sidewall of the cap in the circumferential direction, reducing moldability. Deformation may be greater in areas with low sidewall strength. The tensile strength and yield strength of the cap's sidewall are collectively expressed as the sidewall strength. However, if the material is small and difficult to evaluate, variations in strength can be determined by methods such as the Vickers hardness test.

[0034] The difference between the average, maximum, and minimum n values ​​at angles of 0°, 45°, and 90° relative to the rolling direction after baking is a parameter indicating the degree of work hardening, and is therefore largely influenced by the alloy composition, final rolling ratio, and final annealing conditions. Accordingly, in the manufacturing method of aluminum alloy sheets for caps described later, it is necessary to set conditions such as the final rolling ratio and final annealing conditions, in addition to the alloy composition, within the range described later.

[0035] "When the final annealing temperature is varied, the yield strength reduction for every 10°C increase in the final annealing temperature during recovery softening behavior above 270°C is 6 MPa or less." After cold rolling, a final stabilization annealing is performed, which involves holding the material in the temperature range of 270-320°C for several tens of minutes to several hours. Stabilization annealing allows for adjustment and stabilization of tensile strength and yield strength. Furthermore, by using a temperature higher than the baking temperature of 190°C, the influence of fluctuations in baking temperature on tensile strength and yield strength can be reduced. However, slight fluctuations in the heat treatment temperature can occur due to factors such as differences in distance from the heat source between the inner and outer circumference of the coil during final annealing, and the arrangement within the furnace, which can cause variations in tensile strength and yield strength within the material and between different material samples. For materials where the yield strength reduction per 10°C increase in final annealing temperature during recovery softening behavior above 270°C, when the final annealing temperature is varied, is greater than 6 MPa, there is a higher possibility that the tensile strength and yield strength specifications cannot be met when the heat treatment conditions fluctuate, thus reducing productivity. For materials where the yield strength reduction is 6 MPa or less, there is a higher probability that the specifications can be met even if variations in tensile strength and yield strength occur due to heat treatment factors, making it easier to ensure productivity. Therefore, it is preferable that the yield strength reduction per 10°C increase in final annealing temperature during recovery softening behavior above 270°C, when the final annealing temperature is varied, is 6 MPa or less.

[0036] By satisfying the aforementioned conditions and characteristics, UBC or recycled UBC materials such as aluminum scrap can be used as bottle cap materials. By appropriately selecting the manufacturing conditions described later, such as homogenization treatment, uniform heat treatment, annealing, and rolling rate, the formability of the cap and various post-forming properties can be optimized. In particular, by reducing the final rolling rate and setting the final annealing conditions to a relatively high temperature, stable properties can be obtained as an aluminum alloy sheet for caps while maintaining a low ear ratio.

[0037] When manufacturing caps from aluminum alloy sheets having the aforementioned characteristics, it is possible to mold caps that offer excellent formability during cap molding and capping, as well as superior airtightness and pressure resistance for bottle cans.

[0038] "Method for manufacturing aluminum alloy plates for caps" To manufacture the aluminum alloy plate for caps according to the present invention, a molten aluminum alloy satisfying the above-mentioned composition is prepared, an aluminum alloy ingot is obtained by a casting method using this molten aluminum alloy, and the surface of this ingot is machined. Next, the aluminum alloy ingot, after surface machining, undergoes homogenization and soaking treatment, followed by hot rolling, and then cold rolling to achieve the desired plate thickness, after which it is subjected to final stabilization annealing. Cold rolling is performed in multiple passes, with intermediate annealing between passes.

[0039] "casting" In the above-described casting process, it is preferable to use either molten UBC obtained by directly melting UBC, or molten alloy obtained by mixing UBC and aluminum scrap with high-purity raw materials or a master alloy, and to cast from these molten metals. Aluminum scrap generated in the manufacturing process of aluminum alloy sheets and in the can-making process refers to molten metal residue, ingot cuttings, rolled coil scraps, and punched-out scraps (skeleton) generated in the can-making process, which are inevitably produced during the integrated UBC recycling process. By manufacturing aluminum alloy plates for caps using UBC-recycled material containing UBC, CO2 emissions can be reduced and the environmental impact lowered compared to using new aluminum ingots.

[0040] The thickness of the ingot mentioned above can be, for example, about 500 to 600 mm. Next, the ingot is surface-machined, removing about 1 to 25 mm from its surface to create a surface-machined body. Note that surface machining may be performed after the homogenization treatment described later.

[0041] "Homogenization process" The machined surface prepared as described above is subjected to a homogenization treatment. Homogenization treatment is generally performed to homogenize microsegregation caused by the solidification of the molten metal, precipitate supersaturated solid solution elements, and transition the metastable phase formed by solidification to the equilibrium phase. In the homogenization process, the homogenization temperature should be within the range of 560 to 610°C. If the homogenization temperature is below 560°C, the reduction of fine precipitates will be insufficient, resulting in reduced moldability. If the homogenization temperature exceeds 610°C, there is a risk of the ingot melting. In the homogenization process, the time for maintaining the homogenization temperature (homogenization time) is preferably between 4 and 10 hours. If the homogenization time is less than 4 hours, homogenization may not proceed sufficiently. However, if the homogenization time is too long, it is ineffective and production efficiency decreases. From these perspectives, the preferred homogenization time is within the range of 4 to 10 hours. Because this homogenization process has a relatively long homogenization time, it is usually carried out by setting it up in a batch-type furnace.

[0042] "Soaking treatment" In this embodiment, the surface-machined material after homogenization is cooled to 520-550°C and held for a predetermined time for soaking before hot rolling is started. It is desirable that the holding time (soaking time) in the temperature range of 520-550°C be 1 hour or more. If the soaking temperature is below 520°C, the amount of Mn solid solution tends to decrease, making it easier to form 0-90° edges in the sheet material after hot rolling. However, the rolling load increases, potentially reaching the equipment limit, and the temperature drops due to the increase in the number of rolling passes, making it difficult to obtain a hot-rolled structure, thus reducing hot workability. If the soaking temperature exceeds 550°C, the surface quality of the sheet material after hot rolling deteriorates. This is because oxides of Al and Mg are formed on the material surface during hot rolling, impairing the metallic luster inherent in aluminum alloy sheets for caps. Furthermore, the homogenization treatment and soaking treatment may be performed continuously or intermittently.

[0043] "rolling" The sheet material, after soaking, is processed to a thickness of approximately 2-4 mm by hot rolling. The hot rolling process involves a final pass strain rate of 80-140 s. -1 It will be implemented within the scope of [the specified scope]. The strain rate in the final pass of hot rolling is 80s. -1 Below this value, temperature variations within the sheet metal during hot rolling become large, the recovery recrystallization behavior changes depending on the location in the sheet metal, forming a non-uniform structure and resulting in large variations in edge ratio within the product. -1 Beyond this point, the rolling load increases, and cracks develop at the edges of the sheet metal, making fracture more likely and making stable production difficult. After hot rolling, cold rolling is performed, followed by intermediate annealing. The cold rolling ratio before intermediate annealing is preferably 30% or more to obtain uniform grain size. Furthermore, from the viewpoint of preventing fracture during rolling, the cold rolling ratio is preferably less than 90%.

[0044] In the hot rolling process, for example, as shown in Figure 2, the sheet is first hot-rolled to a thickness of approximately 20 mm using a hot rough rolling mill 20, and then hot-rolled to a thickness of 2.0 to 3.6 mm using a hot finishing rolling mill 30. The hot roughing mill 20 shown in Figure 2 is a device that includes, for example, upper and lower work rolls 21 and 22, backup rolls 23 and 24, and transport paths 4 and 6 in which multiple transport rollers are arranged, and rolls the transported aluminum alloy sheet material 5 to the desired thickness by passing it between the work rolls 21 and 22.

[0045] In Figure 2, the hot rough rolling mill 20 can roll the aluminum alloy sheet material 5 to the required thickness and produce sheet material 7 by repeatedly supplying aluminum alloy sheet material 5 between the work rolls 21 and 22 from the transport paths 4 and 6 on both the front and rear sides of the work rolls 21 and 22 and sequentially rough rolling it. The hot finishing rolling mill 30 shown in Figure 2 is a single-mill reverse-type hot finishing rolling mill, and comprises, for example, upper and lower work rolls 31, 32 and backup rolls 33, 34, a reel-type feed and winding device 35 installed on the entry side of these rolls, and a reel-type feed and winding device 36 installed on the exit side. The hot finishing rolling mill 30 is a device that hot-finishes aluminum alloy sheets for caps to the desired thickness by repeatedly performing the following operations: feeding out the sheet material from the feed-winding device 35, passing it between the work rolls 31 and 32, and winding it up with the feed-winding device 36; and then passing the sheet material again from the feed-winding device 36 through the work rolls 31 and 32 and winding it up with the feed-winding device 35, and gradually adjusting the distance between the work rolls 31 and 32 with each rolling operation. After hot rolling, the material is cold-rolled to the desired thickness using a cold-rolling mill to obtain a cold-rolled material of the desired thickness. Cold rolling is performed in multiple passes, but the following intermediate annealing is carried out before the final cold rolling.

[0046] "Intermediate annealing" Intermediate annealing involves heating the cold-rolled sheet material using a continuous annealing apparatus at a heating rate of 10°C / second or more, holding it at a temperature in the range of 380-550°C for 30 seconds or less, and cooling it at a cooling rate of 10°C / second or more. This intermediate annealing allows the yield strength after annealing to be brought within a suitable range. If the annealing temperature is below 380°C, a uniform recrystallized structure cannot be obtained throughout, and if the temperature exceeds 550°C, oxidation of the sheet surface becomes significant, degrading the surface quality.

[0047] Intermediate annealing is performed on the sheet material during the cold rolling process using a continuous annealing apparatus, the basic configuration of which is shown in Figure 3, with the heating rate, holding temperature, holding time, and cooling rate described above. Figure 3 shows an example of the basic configuration of a Continuous Annealing Line (CAL). In this example, the Continuous Annealing Line 40 pulls out a long aluminum alloy sheet 42 from a supply roll 41 and supplies it to a long furnace body 44 of several tens to 100 meters in length via a buffer device 43. The sheet is annealed under the aforementioned conditions while moving within the furnace body 44, and after annealing, the sheet 42 is pulled out from the furnace body 44 and wound onto a winding roll 47 via a buffer device 46. With this Continuous Annealing Line 40, since the sheet 42 passing through the furnace body 44 can be processed continuously and individually, intermediate annealing can be performed with more precise heating and cooling conditions than a batch-type annealing furnace.

[0048] "Final cold rolling" The final cold rolling is performed within the rolling ratio range of 20-45%. Selecting this range ensures appropriate work hardening and productivity. If the rolling ratio is less than 20%, stable production becomes difficult, and the work hardening of the sidewall during cap forming becomes too high. Conversely, if the rolling ratio exceeds 45%, the edge ratio becomes too large. By cold rolling, aluminum alloy sheets for caps with a thickness of 0.20 to 0.51 mm can be obtained.

[0049] "Stabilized annealing" After the final cold rolling, a final stabilizing annealing is performed at a temperature range of 270-320°C. A holding time of 1 to 10 hours is desirable. Stabilizing annealing allows for adjustment and stabilization of tensile strength and yield strength. If the stabilizing annealing temperature is below 270°C, the tensile strength and yield strength become too high, leading to a decrease in the formability of the cap. Also, the temperature becomes equivalent to the baking temperature, resulting in large variations in tensile strength and yield strength, and a decrease in productivity. If the stabilizing annealing temperature is higher than 320°C, both tensile strength and yield strength decrease significantly due to recrystallization, making it impossible to obtain the desired tensile strength and yield strength. By stabilizing annealing, an aluminum alloy plate for caps having the above-described characteristics can be obtained.

[0050] By the manufacturing method described above, an aluminum alloy sheet 1 for caps can be obtained that has a tensile strength of 200-230 MPa after baking, a yield strength of 140-200 MPa after baking, an elongation of 4% or more after baking, an edge ratio of 5.5% or less, an average n value of 0.150 or less at angles of 0°, 45°, and 90° with respect to the rolling direction after baking, and a difference of 0.005 or less between the maximum and minimum values ​​of these n values. The aluminum alloy plate 1 for caps described above excels not in formability during cap formation by deep drawing, but in formability during capping formation using screw forming, and the pressure resistance obtained therefrom. Furthermore, this aluminum alloy plate 1 for caps has excellent balance of n values ​​not only in the 0° direction, but also in the 45° and 90° directions, and also has the excellent characteristic of having a small difference between the maximum and minimum n values. [Examples]

[0051] The method for manufacturing an aluminum alloy plate for caps according to the present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. Aluminum alloys with the compositions shown in Table 1 below were melted, degassed, and filtered to form slabs with a thickness of 550 mm, a width of 1500 mm, and a length of 4.5 m, which were then cast by semi-continuous casting. Examples of samples No. 3, 5-9, and 11 shown in Table 1 were formulated by blending molten UBC aluminum alloy with used aluminum cans and aluminum scrap such as process offcuts generated during the aluminum material manufacturing process and can manufacturing process, in a total mass ratio of 80%. Next, after surface-machining the slab, it was subjected to a homogenization treatment using a furnace that can be used for both homogenization and soaking, followed by a soaking treatment. Next, the sheets were roughly rolled to a thickness of 20 mm using hot rough rolling, and then hot rolling was performed to a thickness of 2.7 mm using a single-mill reverse-type hot finishing rolling mill at the strain rate of the final pass shown in Table 1.

[0052] Next, the hot-rolled aluminum alloy sheet was cold-rolled in multiple passes to achieve a rolling ratio of 76-90%, and intermediate annealing was performed at the intermediate annealing temperatures shown in Table 1 during the cold-rolling process. The rolling ratio during the final cold-rolling was set to the conditions shown in Table 2, and after the final rolling, final annealing was performed at the temperatures shown in Table 2 to obtain multiple aluminum alloy sheet samples for caps with a thickness of 0.22 mm.

[0053] The obtained aluminum alloy plate samples for caps were subjected to baking at 190°C for 20 minutes as part of the paint curing process. After baking, the tensile strength, 0.2% yield strength, elongation, edge ratio, n-values ​​at angles of 0°, 45°, and 90° relative to the rolling direction, surface condition of the plate material, productivity, pressure resistance, and formability were evaluated. The measurement results and evaluation results are summarized in Table 2 below.

[0054] "Measurement of 0.2% yield strength" The 0.2% yield strength was measured according to the method specified in JIS Z 2241. Specifically, a sample was cut from each obtained specimen parallel to the rolling direction (0°) to create a test piece of JIS No. 5 shape, and a tensile test was performed at room temperature to measure the 0.2% yield strength. The tensile speed was set to 5 mm / min.

[0055] "Measurement of elongation" The elongation was measured according to the method specified in JIS Z 2241. Specifically, a sample was cut from each obtained specimen parallel to the rolling direction to create a JIS No. 5 shaped test piece, and a tensile test was performed at room temperature to measure the elongation. The elongation referred to here is the permanent elongation after fracture, expressed as a percentage of the original gauge length, based on JIS Z 2241.

[0056] "Ear rate" A cylindrical deep drawing test was performed on the obtained aluminum alloy sheet for the cap. An Erichsen testing machine was used for the cylindrical deep drawing test. The deep drawing conditions were: punch diameter: 33 mm (flat-head punch), drawing ratio: 1.75, and wrinkle-holding force: 5 kN. The side wall height of the cap was measured around the entire circumference at 2° angles relative to the rolling direction using a digital micrometer, and the edge ratio was calculated using the following formula. (Maximum height - Minimum height) ÷ Minimum height × 100 = Ear rate (%) Since the ear ratio showed almost no change before and after baking, the ear ratio was measured without baking.

[0057] "Measurement of n-values ​​at angles of 0°, 45°, and 90° relative to the rolling direction after baking." Tensile tests were conducted according to the method conforming to JIS Z 2241, and the n-value was measured according to the method conforming to JIS Z 2253. Specifically, samples were cut from each obtained specimen at angles of 0°, 45°, and 90° relative to the rolling direction to create test pieces of JIS No. 5 shape. Tensile tests were then conducted at room temperature, and the n-value was measured for plastic strains in the range of 0.01 to 0.03. The tensile speed was set to 5 mm / min.

[0058] "Surface quality" The surface of the obtained aluminum alloy plate for the cap was evaluated as follows: if it turned white due to oxidation during annealing, it was marked as × (poor surface quality); if there was no change, it was marked as ○ (good surface quality).

[0059] "productivity" For the obtained aluminum alloy plates for caps, if the recovery softening behavior at temperatures above 270°C varied, the degree of softening was 6 MPa or less per 10°C, it was judged as ○ (good productivity), and if it was greater than 6 MPa, it was judged as × (poor productivity).

[0060] "Pressure resistance" The obtained aluminum alloy plates for the caps were printed and painted on both sides using conventional methods, and then caps were formed using a cap forming device. Then, 65°C hot water was filled into the screw-type aluminum bottle cans, and immediately after adding liquid nitrogen to the headspace, the caps were screwed onto the screw-type aluminum bottle cans using a well-known capping device, producing 10 bottle cans with caps filled with contents for each example and comparative example. The internal pressure of the bottle cans was approximately 0.9 MPa on average at room temperature. Next, using a well-known method, compressed air (nitrogen gas) was introduced into the aforementioned capped bottle cans to increase the internal pressure. The internal pressure was increased until the screwed-on cap flew off, or, if the cap did not flew off, until the capped aluminum bottle can burst. The internal pressure at the point when the cap flew off or the capped aluminum bottle burst was measured as the pressure resistance strength. If the measurement result was less than 1.2 MPa for even one can, it was evaluated as × (insufficient pressure resistance), and if all 10 cans were 1.2 MPa or higher, it was evaluated as ○ (good pressure resistance). The axial load of the pressure block of the capping device was set to 900 N.

[0061] The capping process using the aforementioned capping device will now be explained in detail. In a capping device, first, a cap is placed on the bottle. Then, an axial load is applied by the pressure block of the capping device, and the outer surface of the top of the cap is drawn downwards in the axial direction by the drawing molding section on the outer circumference of the pressure block, thereby reducing the diameter of the top of the cap and creating a stepped portion on the cap. It is known that by forming this stepped portion, the liner attached to the inner surface of the cap is pressed firmly against the mouth of the bottle, improving the airtightness of the bottle can. The distance from the top surface to the bend in the stepped section is called the drawing depth. (Drawing process) Next, two thread-cutting rollers press the side of the cap toward the center of the bottle can, forming a female thread on the side of the cap that aligns with the male thread of the bottle can. (Thread forming process) Finally, two hem-rolling rollers press the bottom edge of the cap towards the center of the bottle can, wrapping it around the lid (bulging part) of the bottle can. (Hem-rolling process) In the capping device, these processes are performed either in the order described or almost simultaneously. Furthermore, the settings for each part of the capping device were the same as those used during normal production, except for the axial load setting.

[0062] "Moldability" The obtained aluminum alloy plates for the caps were printed and painted using conventional methods, and then molded into the desired cap shape using the same process as the one used to evaluate the pressure resistance. Ten aluminum bottle cans with caps, filled with hot water, were then produced for each example and comparative example. The cans were measured, and the average value of the cans molded from conventional 5000 series aluminum alloy caps was defined as 1.65 mm. By comparing the cans to this value, those where all 10 cans had a can depth within ±5 / 100 mm were marked as ○ (pass), and those where even one can was outside ±5 / 100 mm were marked as × (fail). The measurement of the squeezing depth was taken as the average of 6 points (measured at 60° intervals) per can.

[0063] "Variation in ear rate" From the aluminum alloy plates for the caps obtained from the innermost and outermost circumferences of the fabricated coils, samples were taken from three locations in the plate width direction: the right end, the center, and the left end. A cylindrical deep drawing test was then performed under the conditions described above. The difference between the maximum and minimum values ​​of the ear ratios for a total of six samples was defined as the ear ratio variation. A value of 3.0% or less was marked as ○ (pass), and a value greater than 3.0% was marked as × (fail).

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] Examples of samples No. 1 to 12 shown in Table 1 are aluminum alloy plates for caps, containing, by mass%, Mn: 0.85 to 1.10%, Mg: 0.85 to 1.35%, Si: 0.20 to 0.40%, Fe: 0.40 to 0.60%, Cu: 0.20 to 0.30%, Zn: 0.10 to 0.30%, Cr: 0.01 to 0.10%, Ti: 0.01 to 0.10%, and V: 0.01 to 0.10%, with the remainder being unavoidable impurities and Al. The samples in these examples had a tensile strength (AB-TS) of 200-230 MPa after baking, a yield strength (AB-YS) of 140-200 MPa after baking, an elongation (AB-EL) of 4% or more after baking, and an ear ratio of 5.5% or less. In addition, the average n-values ​​at angles of 0°, 45°, and 90° relative to the rolling direction after baking were 0.150 or less, and the difference between the maximum and minimum n-values ​​was 0.005 or less.

[0068] More specifically, the example samples had a tensile strength (AB-TS) of 201-230 MPa after baking, a yield strength (AB-YS) of 142-199 MPa after baking, an elongation (AB-EL) of 4.2-12.0% after baking, and an ear ratio of 3.5-5.4%. Note that Example No. 3 is a sample obtained using molten aluminum alloy mixed with used aluminum cans and aluminum scrap such as process offcuts generated during the aluminum material manufacturing process and the can manufacturing process. In contrast, Example No. 4 is a sample obtained using molten aluminum alloy without used aluminum cans or aluminum scrap. From the comparison between the two, it can be seen that if the aluminum alloy has a nearly identical composition, the resulting aluminum alloy sheet will have almost the same properties whether or not used aluminum cans or aluminum scrap are incorporated into it. Examples No. 9 and No. 10 also involve the production of aluminum alloy sheets, and while the composition is almost identical, the difference lies in whether or not used aluminum cans or aluminum scrap are incorporated. As shown in Tables 2 and 3, equivalent properties were obtained.

[0069] Comparative examples of samples No. 13 and 14 were samples in which the content of Si, Fe, Cu, Mn, Zn, Cr, Ti, and V was lower than the desirable range, and the content of Mg was higher than the desirable range, and were manufactured with a final rolling ratio set higher than the desirable rolling ratio. These samples had excessive softening, a large difference between the maximum and minimum n values ​​after baking, a high ear ratio, poor productivity, and reduced moldability. Comparative example of sample No. 14 had low yield strength after baking and poor pressure resistance. The comparative example of sample No. 15 is a sample in which the intermediate annealing temperature is lower than the desired temperature range, the final rolling ratio is higher than the desired rolling ratio range, and the final annealing temperature is lower than the desired temperature range. This sample had too much softening, too large a difference between the maximum and minimum n values ​​after baking, too high tensile strength and yield strength after baking, and a high ear ratio, resulting in poor productivity and moldability.

[0070] In the comparative example of sample No. 16, the intermediate annealing temperature was higher than the desired temperature range, resulting in a white surface and deterioration of surface quality. The comparative example of sample No. 17 was a sample whose final annealing temperature was higher than the desired range, resulting in low tensile strength and yield strength after baking, and poor pressure resistance and moldability. In the comparative example of sample No. 18, the homogenization and soaking temperatures were low, the hot rolling strain rate was low, and the final annealing temperature was high. As a result, the tensile strength and yield strength after baking were too low, leading to poor pressure resistance and formability, and a large variation in ear ratio. In the comparative example of sample No. 19, the final rolling ratio was lower than the desired range, resulting in an excessively high average n-value after baking, leading to poor productivity, pressure resistance, and moldability. Comparative example No. 20 was discontinued because the homogenization treatment and soaking temperatures were too high, resulting in poor material surface condition. In the comparative example of sample No. 21, the hot rolling strain rate was too high, causing cracks to form at the edges of the material, resulting in excessive rolling load on the machine and leading to the discontinuation of production. In the comparative example of sample No. 22, the final annealing temperature was lower than the desired range, and coupled with the high Si and Mg content, the amount of softening was excessive, resulting in poor productivity.

[0071] The comparative example of sample No. 23 was a sample in which the content of Cu, Mn, Zn, Cr, Ti, and V was higher than the desirable range. As a result, the hot rolling strain rate was low, the tensile strength and yield strength after baking became too high, the formability decreased, and the variation in ear ratio increased. Comparative example No. 24 had a higher-than-desirable Fe content, resulting in reduced moldability. Furthermore, the low content of Mg, Cr, Ti, and V led to insufficient tensile strength and yield strength after baking, and reduced pressure resistance. The comparative example of sample No. 25 was a sample with high content of Cr, Ti, and V, resulting in excessively high strength after baking and reduced moldability. The comparative example of sample No. 26 was a sample that did not contain Cr, Ti, or V, and after baking, the average n-value was high, the strength and yield strength after baking were low, the pressure resistance decreased, and the moldability also decreased. [Explanation of Symbols]

[0072] 1…Aluminum alloy sheet for caps, 20…Hot roughing mill, 30…Hot finishing mill, 40...Continuous annealing apparatus.

Claims

1. This is an aluminum alloy sheet for caps, comprising, by mass%, Mn: 0.85-1.10%, Mg: 0.85-1.35%, Si: 0.20-0.40%, Fe: 0.40-0.60%, Cu: 0.20-0.30%, Zn: 0.10-0.30%, Cr: 0.01-0.10%, Ti: 0.01-0.10%, V: 0.01-0.10%, with the remainder being unavoidable impurities and Al. The tensile strength after baking at 190°C for 10 minutes to 1 hour is 200-230 MPa, the yield strength after baking is 140-200 MPa, the elongation after baking is 4% or more, and the ear ratio is 5.5% or less. An aluminum alloy sheet for caps, characterized in that the average value of n-values ​​at angles of 0°, 45°, and 90° with respect to the rolling direction after baking is 0.150 or less, and the difference between the maximum and minimum values ​​of these n-values ​​is 0.005 or less.

2. The aluminum alloy plate for caps according to claim 1, wherein the yield strength reduction per 10°C increase in the final annealing temperature during recovery softening behavior above 270°C when the final annealing temperature is varied is 6 MPa or less.

3. After casting an aluminum alloy ingot having the following composition by mass%, Mn: 0.85-1.10%, Mg: 0.85-1.35%, Si: 0.20-0.40%, Fe: 0.40-0.60%, Cu: 0.20-0.30%, Zn: 0.10-0.30%, Cr: 0.01-0.10%, Ti: 0.01-0.10%, V: 0.01-0.10%, with the remainder being unavoidable impurities and Al, a homogenization treatment is performed at 560-610°C, followed by a soaking treatment at 520-550°C, and finally a hot rolling final pass at a strain rate of 80-140 s. －１ This is done by first performing cold rolling in multiple passes, then performing intermediate annealing between passes at 380-550°C, followed by final cold rolling at a rolling ratio of 20-45%, and finally stabilizing annealing at 270-320°C after the final cold rolling. A method for producing an aluminum alloy sheet for caps, characterized by obtaining an aluminum alloy sheet for caps that, after baking at 190°C for 10 minutes to 1 hour, has a tensile strength of 200 to 230 MPa, a yield strength of 140 to 200 MPa, an elongation of 4% or more, an ear ratio of 5.5% or less, and an average value of n-values ​​at angles of 0°, 45°, and 90° with respect to the rolling direction after baking of 0.150 or less, with the difference between the maximum and minimum values ​​of these n-values ​​being 0.005 or less.

4. The method for manufacturing an aluminum alloy sheet for caps according to claim 3, characterized in that an aluminum alloy sheet for caps is obtained in which the yield strength reduction amount per 10°C increase in the final annealing temperature during recovery softening behavior at 270°C or higher, when the final annealing temperature is varied, is 6 MPa or less.

5. A method for manufacturing an aluminum alloy plate for a cap according to claim 3 or 4, characterized in that, during the casting of the aluminum alloy, used aluminum cans and aluminum scrap, which is a process off-cut generated in the aluminum material manufacturing process and the can manufacturing process, are blended into the molten aluminum alloy.

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