Aluminum alloy plate for can cover

Abstract

One aspect of the present disclosure provides an aluminum alloy plate for a can lid in which the content of silicon (Si) is 0.27 mass% or more and 0.39 mass% or less, the content of iron (Fe) is 0.35 mass% or more and 0.55 mass% or less, the content of copper (Cu) is 0.17 mass% or more and 0.25 mass% or less, the content of manganese (Mn) is 0.75 mass% or more and 0.95 mass% or less, and the balance is aluminum and unavoidable impurities. The content of magnesium (Mg) is 2.2 mass% or more and 2.8 mass% or less, and the remainder is composed of aluminum (Al) and unavoidable impurities, or the aluminum (Al) and unavoidable impurities are contained, and in the 0-degree direction, the 45-degree direction and the 90-degree direction respectively with respect to the rolling direction, the thickness of the aluminum (Al) and the thickness of the unavoidable impurities are smaller than the thickness of the rolling direction. The minimum evaluation value Smin, which is the minimum value, is 370-410 MPa (inclusive), among evaluation values S calculated by the following mathematical formula (1) using 0.2% yield strength [sigma] 0.2, tensile strength [sigma] B, and the average value [sigma] fm of the 0.2% yield strength and the tensile strength. (1) S = [sigma] fm / ([sigma] 0.2 / [sigma] B).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This international application claims the benefit of Japanese Patent Application No. 2023-067371 filed in the Japan Patent Office on April 17, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to an aluminum alloy sheet for can ends. Background Art

[0004] In recent years, with growing environmental awareness, there has been a demand for aluminum alloy sheets that emit less carbon dioxide during the manufacturing process. The amount of new aluminum matrix metal added during the casting process indirectly impacts carbon dioxide emissions during the aluminum manufacturing process.

[0005] The production of new aluminum matrix metal consumes a lot of electricity in the refining process, resulting in a large amount of carbon dioxide emissions. Therefore, reducing the amount of new aluminum matrix metal mixed and increasing the same-grade recycling rate can help reduce carbon dioxide emissions in aluminum alloy plate manufacturing.

[0006] Generally speaking, the amount of CO2 emitted when aluminum scrap is remelted and cast can be reduced to approximately one-thirtieth of that when new aluminum base metal is produced. Given the enormous volume of aluminum alloy sheet used worldwide for beverage cans, further increasing the recycling rate at this level is crucial for reducing the environmental burden.

[0007] Among them, compared with the can body made of 3104 aluminum alloy (AA3104 alloy), the upper limit of the component specifications of silicon (Si), iron (Fe), copper (Cu), manganese (Mn), etc. in the can lid made of 5182 aluminum alloy (AA5182 alloy) is lower, so it is difficult to mix the scrap derived from the can material containing 3104 aluminum alloy.

[0008] For example, if can scrap (UBC: Used Beverage Can) generated on the market is mixed as is, based on the weight ratio of the can body to the can lid, it will contain more 3104 aluminum alloy components, and therefore will easily exceed the upper limit of the composition of 5182 aluminum alloy, requiring the use of new base metal to dilute the composition.

[0009] Therefore, compared to aluminum alloy sheets for can bodies, aluminum alloy sheets for can lids require more new base metal to adjust the composition to that of 5182 aluminum alloy, resulting in a lower recycling rate. Therefore, by changing the can lid to an alloy whose composition is easily mixed with 3104 aluminum alloy, the use of new base metal in the can lid can be significantly reduced.

[0010] Patent Documents 1 to 5 disclose aluminum alloy sheets for can lids, which have a composition relatively close to that of 3104 aluminum alloy and have excellent recyclability.

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-73106

[0014] Patent Document 2: Japanese Patent Application Laid-Open No. 9-070925

[0015] Patent Document 3: Japanese Patent Application Laid-Open No. 11-269594

[0016] Patent Document 4: Japanese Patent Application Laid-Open No. 2000-160273

[0017] Patent Document 5: Japanese Patent Application Laid-Open No. 2016-160511 Summary of the Invention

[0018] Problems to be solved by the invention

[0019] Using aluminum alloys with compositions similar to 3104 aluminum alloy for can lids can lead to reduced pressure resistance and toughness. The pressure resistance of a can lid refers to the internal pressure of the can when the lid bulges, and is the resistance to an unexpected increase in the internal pressure of the can due to changes in the external environment.

[0020] In particular, pressure tanks used for beer and carbonated beverages require high pressure resistance. Generally speaking, the higher the material strength and the thicker the plate, the higher the pressure resistance. Therefore, the lid of the pressure tank is made of high-strength 5182 aluminum alloy, which contains a large amount of magnesium (Mg).

[0021] In contrast, using conventional 3104 aluminum alloy for can lids significantly reduces pressure resistance, increasing the risk of the lid bulging and leaking contents if the internal pressure of the can unexpectedly increases. Furthermore, increasing the plate thickness to increase pressure resistance increases the weight of the lid and the cost of the lid.

[0022] Furthermore, the toughness of the material affects the formability and opening properties of the lid. Low material toughness can lead to forming cracks in the rivet section and counter sink of the lid. Furthermore, when the internal pressure of the can unexpectedly increases, cracks may form in the scored section, increasing the risk of leakage. These cracks are particularly prone to developing along the rolling direction. Therefore, toughness that can withstand tensile and bending stresses perpendicular to the rolling direction is required.

[0023] However, aluminum alloy plates for can covers having a composition close to that of conventional 3104 aluminum alloy cannot solve the above two problems, i.e., cannot satisfy one or both of the material's strength (i.e., compressive strength of the cover) and toughness (i.e., formability and openability).

[0024] One aspect of the present disclosure preferably provides an aluminum alloy plate for can covers that can incorporate scrap raw materials derived from can materials while simultaneously achieving high strength and high toughness.

[0025] Solutions to the Problem

[0026] One embodiment of the present disclosure relates to an aluminum alloy sheet for can lids, wherein the content of silicon (Si) is 0.27 mass% to 0.39 mass% inclusive, the content of iron (Fe) is 0.35 mass% to 0.55 mass% inclusive, the content of copper (Cu) is 0.17 mass% to 0.25 mass% inclusive, the content of manganese (Mn) is 0.75 mass% to 0.95 mass% inclusive, the content of magnesium (Mg) is 2.2 mass% to 2.8 mass% inclusive, and the remainder consists of or contains aluminum (Al) and inevitable impurities, and wherein the aluminum alloy sheet has a 0.2% yield strength (σ) in the directions of 0°, 45°, and 90° relative to the rolling direction. 0.2 , tensile strength σ B , and the average values ​​of 0.2% yield strength and tensile strength σ fm Among the evaluation values ​​S calculated by the following mathematical formula (1), the minimum evaluation value S is the minimum value. min It is 370 MPa or more and 410 MPa or less.

[0027] S=σ fm / (σ 0.2 / σ B ) (1)

[0028] This structure allows the incorporation of scrap raw materials from can materials while simultaneously achieving high strength and toughness in the aluminum alloy sheet. Specifically, a certain amount of scrap 3104 aluminum alloy used for can bodies can be incorporated, thereby reducing the use of new base metal and carbon dioxide emissions. Furthermore, a highly formable aluminum alloy sheet for can lids, which requires high pressure resistance, can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of the repeated bending test.

[0030] Figure 2 This is an explanatory diagram of the L-ST cross section.

[0031] Figure 3Graph showing the relationship between the value V and the shell body compressive strength in the embodiment. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the accompanying drawings.

[0033] [1. First embodiment]

[0034] [1-1. Structure]

[0035] <Component>

[0036] The present invention discloses a method for producing an aluminum alloy sheet for can lids (hereinafter also referred to simply as "alloy sheet") containing aluminum (Al), silicon (Si), iron (Fe), copper (Cu), manganese (Mn), and magnesium (Mg).

[0037] The lower limit of the Si content is 0.27% by mass, preferably 0.30% by mass. If the Si content is less than 0.27% by mass, the amount of Si precipitated due to working heat during cold rolling after hot rolling and solution treatment may decrease, which may lead to insufficient strength of the alloy plate.

[0038] Furthermore, the average Si content of 3104 aluminum alloy specified in JIS-H-4000:2014 is 0.30 mass %. Therefore, by setting the Si content to 0.27 mass % or more, preferably 0.30 mass % or more, a large amount of 3104 aluminum alloy scrap can be mixed.

[0039] The upper limit of the Si content is 0.39 mass %, preferably 0.35 mass %. If the Si content exceeds 0.39 mass %, the Mg2Si particles increase, resulting in a decrease in the toughness of the alloy plate.

[0040] The lower limit of the Fe content is 0.35% by mass, preferably 0.40% by mass. The average Fe content of 3104 aluminum alloy is 0.40% by mass. Therefore, by setting the Fe content to 0.35% by mass or more, preferably 0.40% by mass or more, a large amount of 3104 aluminum alloy scrap can be mixed.

[0041] The upper limit of the Fe content is 0.55% by mass. If the Fe content exceeds 0.55% by mass, the Al-Fe-Mn or Al-Fe-Mn-Si intermetallic compounds (i.e., second phase particles) increase. As a result, crack propagation paths are generated, resulting in reduced toughness of the alloy plate.

[0042] The lower limit of the Cu content is 0.17% by mass, more preferably 0.20% by mass. If the Cu content is less than 0.17% by mass, insufficient Cu is present to increase the strength by solutionization or precipitation, thereby reducing the strength of the alloy plate. In addition, when cold rolling is performed after hot rolling and solution treatment, the strength of the alloy plate is significantly improved by precipitation of Cu.

[0043] Furthermore, the average value of the Cu component specification of the 3104 aluminum alloy is 0.15 mass %. Therefore, by setting the Cu content to 0.17 mass % or more, a large amount of 3104 aluminum alloy scrap can be mixed.

[0044] The upper limit of the Cu content is 0.25 mass %. If the Cu content exceeds 0.25 mass %, the toughness of the alloy plate decreases.

[0045] The lower limit of the Mn content is 0.75 mass %, preferably 0.80 mass %. If the Mn content is less than 0.75 mass %, insufficient Mn is present to increase strength through solid solution or precipitation, resulting in a decrease in the average strength of the alloy plate.

[0046] Furthermore, the average Mn content of 3104 aluminum alloy is 1.1% by mass, while the average Mn content of 5182 aluminum alloy is 0.35% by mass. Therefore, by setting the Mn content to 0.75% by mass or more, more 3104 aluminum alloy scrap can be mixed in compared to the conventional 5182 aluminum alloy.

[0047] The upper limit of the Mn content is 0.95% by mass, preferably 0.90% by mass. If the Mn content exceeds 0.95% by mass, the Al-Fe-Mn or Al-Fe-Mn-Si intermetallic compounds (i.e., second phase particles) increase. As a result, crack propagation paths are generated, resulting in reduced toughness of the alloy plate.

[0048] The lower limit of the Mg content is 2.2% by mass. If the Mg content is less than 2.2% by mass, insufficient Mg is present to increase the strength by solid solution, resulting in a decrease in the average strength of the alloy plate. In addition, when cold rolling is performed after hot rolling and solution treatment, the strength of the alloy plate is significantly improved by precipitating Mg.

[0049] The upper limit of the Mg content is 2.8% by mass. The average Mg content of 3104 aluminum alloy is 1.05% by mass, and the average Mg content of 5182 aluminum alloy is 4.5% by mass. Therefore, by setting the Mg content to 2.8% by mass or less, a large amount of 3104 aluminum alloy scrap can be mixed, and the amount of additional Mg-containing raw materials can be reduced.

[0050] The alloy plate may contain titanium (Ti). The upper limit of the content of Ti is preferably 0.10 mass %. By containing Ti, the ingot structure of the alloy plate is refined. In addition, the alloy plate may contain zinc (Zn). The upper limit of the content of Zn is preferably 0.25 mass %. In addition, the alloy plate may contain chromium (Cr). The upper limit of the content of Cr is preferably 0.10 mass %.

[0051] The alloy plate may contain unavoidable impurities within a range that does not significantly impair the performance of the alloy plate. Specifically, the alloy plate contains Si, Fe, Cu, Mn, and Mg within the aforementioned ranges, with the remainder consisting of aluminum and unavoidable impurities, or containing aluminum and unavoidable impurities. The upper limit of the total amount of unavoidable impurities is preferably 0.15% by mass. The remainder may contain substances other than aluminum and unavoidable impurities.

[0052] <Material Strength and Compression Resistance>

[0053] Rolled aluminum alloy sheets exhibit material anisotropy, with strength varying between 0°, 45°, and 90° relative to the rolling direction. When pressure rises inside the tank, deformation begins in the direction with the lowest strength.

[0054] Therefore, the alloy plate of the present disclosure uses the 0.2% yield strength σ in the 0° direction, 45° direction, and 90° direction relative to the rolling direction. 0.2 , tensile strength σ B , and the average values ​​of 0.2% yield strength and tensile strength σ fm The evaluation value S(S) is calculated by the following mathematical formula (1): 0° 、S 45° , and S 90° ), the minimum evaluation value S as the minimum value min (=min(S 0° ,S 45° ,S 90° )) is greater than 370 MPa and less than 410 MPa.

[0055] S=σ fm / (σ 0.2 / σ B ) (1)

[0056] According to experience, the compressive strength of the cover formed by the aluminum alloy plate is equal to the minimum evaluation value S min There is a strong positive correlation between the value V of the following mathematical formula (2) and the plate thickness t.

[0057] V=t 2.27 ×S min (2)

[0058] Therefore, by setting the minimum evaluation value S of the alloy plate min By setting the pressure to 370 MPa or more, a cover having a sufficient pressure resistance can be formed without significantly increasing the plate thickness.

[0059] In addition, if the minimum evaluation value S min If the value exceeds 410 MPa, the material strength becomes too high, resulting in a decrease in toughness. This means that shear bands corresponding to the tensile and bending stresses generated in the material are more likely to form during the forming process, making forming cracks more likely. By setting the minimum evaluation value Smin below 410 MPa, a balance is achieved between material strength (i.e., the compressive resistance of the cover) and toughness (i.e., formability and opening properties).

[0060] The 0.2% yield strength σ in formula (1) 0.2 and tensile strength σ B The plate thickness t is measured using the method specified in JIS-Z-2241: 2011. For example, a micrometer is used to measure the plate thickness t.

[0061] For example, the compressive strength of an aluminum alloy sheet can be measured using the following steps: First, a housing formed from the aluminum alloy sheet is fixed to a fixture and internal pressure is applied. The internal pressure is then gradually increased, and the internal pressure at which the housing bulges (i.e., buckles) is used as the compressive strength.

[0062] Specifically, the housing was formed using a φ204 Fullform (B64) housing mold. Internal pressure was measured using a VERSATILE TECHNOLOGY DV036E Buckle & Missile Gauge. Specifically, after securing the formed housing with a dedicated fixture, the internal pressure was increased using a program, and the internal pressure reading was taken when the housing bulged. For example, the internal pressure was increased at a rate of approximately 175 kPa / s, and once it reached approximately 350 to 400 kPa, the internal pressure was increased at a rate of 10 kPa / s.

[0063] <Toughness>

[0064] It is known that the toughness of the aluminum alloy plate affects the formability of the cover body and the force required to open the opening of the scored portion (ie, the opening force).

[0065] (Number of repeated bending)

[0066] One of the evaluation indicators of the toughness of aluminum alloy plates is the repeated bending test. For plates of the same thickness, the greater the number of repeated bends, the better the toughness of the aluminum alloy plate.

[0067] The repeated bending test is carried out according to the following steps. Figure 1As shown, a strip-shaped test piece with a width of 12.5 mm and a length of 200 mm was arranged so that the direction of the bending ridge line R was parallel to the rolling direction D of the alloy plate. Both ends of the test piece were fixed with chucks, and a tensile force of 200 N was applied.

[0068] In this state, a clamp with a bending radius R of 2.0 mm, which is arranged along the length of the specimen and 150 mm away from the end of the specimen fixed on the fixed chuck on one side, is used as a fulcrum. The chuck on the other side is rotated 90° to the left and right, and the bending is repeated. The number of bends until the specimen breaks is measured.

[0069] The number of bends is counted as one operation of bending 90° to the left or right and returning to the original position. If the specimen breaks during bending, the angle θ (0°-90°) is read, and the number of repeated bends N is calculated using the following mathematical formula (3). In mathematical formula (3), N0 is the total number of operations of bending 90° to the left or right and returning from the 90° position to the original 0° position until the specimen breaks.

[0070] N=N0+θ / 90 (3)

[0071] In the repeated bending evaluation, the larger the plate thickness, the more disadvantageous it is, so it is necessary to use the reference plate thickness for correction. Therefore, taking the plate thickness of 0.235mm as the reference, the standardized repeated bending number N is calculated by the following mathematical formula (4): s In addition, t (mm) is the thickness of the specimen.

[0072] N s =N×t / 0.235 (4)

[0073] The standardized repeated bending number N of the aluminum alloy plate disclosed in the present invention is s It is preferably 14.0 times or more.

[0074] (Second phase particles)

[0075] Toughness is affected by strength and the distribution of second-phase particles. Specifically, the greater the strength and the higher the density of second-phase particles, the lower the toughness. In particular, high Mg and Si contents increase the likelihood of Mg2Si particles forming. Consequently, these particles become crack initiation points and propagation paths, reducing toughness.

[0076] like Figure 2 As shown by the oblique lines, the aluminum alloy plate disclosed herein has an area of ​​0.3 μm on the L-ST cross section located in the center of the width direction. 2 The ratio of the total area of ​​the above Mg2Si particles in the L-ST cross section is preferably 0.2% or less. Figure 2In the figure, L indicates the longitudinal direction, ST indicates the plate thickness direction, and LT indicates the width direction.

[0077] For example, the area ratio of Mg2Si particles can be measured by the following method. First, the measurement sample is cut and the surface to be measured (i.e., L-ST cross section) is mechanically polished to a mirror finish. Next, a scanning electron microscope (SEM) is used to observe the polished surface (i.e., L-ST cross section) to obtain ten fields of view. The acceleration voltage of the SEM is set to 15 kV, the magnification is set to 500 times, and the range of one field of view is set to 0.049 mm. 2 to capture the reflected electron component image (COMPO).

[0078] The captured COMPO images were analyzed using the image analysis software "ImageJ." Specifically, the brightness value that appeared most frequently among the 256 color levels in the image was defined as the background brightness, and particles with a brightness lower than the value obtained by subtracting 30 from the brightness value that appeared most frequently were identified as Mg2Si particles.

[0079] The calculated area of ​​the identified Mg2Si particles is 0.3 μm 2 The total area of ​​the particles above is divided by the imaging area of ​​ten fields of view (i.e., the total imaging area) to calculate the area of ​​0.3 μm 2 The ratio of the total area of ​​the above Mg2Si particles in the L-ST cross section.

[0080] <Intensity Anisotropy>

[0081] It is known that the toughness of materials with lower cold rolling reduction (hereinafter referred to as cold rolling ratio) is higher, while the strength of materials with higher cold rolling ratio is higher. In addition, the higher the cold rolling ratio, the higher the 0.2% yield strength σ at 90° to the rolling direction. 0.2 _ 90° 0.2% yield strength σ at 0° relative to the rolling direction 0.2_0° Therefore, the difference of 0.2% yield strength between the 0° direction and the 90° direction relative to the rolling direction, that is, the strength anisotropy, can be corresponded to the cold rolling rate of the material.

[0082] In order to obtain toughness that can ensure the formability of the cover, the alloy plate disclosed in the present invention preferably has a 0.2% yield strength σ from the direction of 0° relative to the rolling direction as calculated by mathematical formula (5). 0.2_0° Subtract the 0.2% yield strength σ in the direction 90° relative to the rolling direction 0.2_90° The obtained value D is -20 MPa or more. However, if the value D is set to -10 MPa or more, the cold rolling rate will decrease, which may lead to insufficient strength. Therefore, the value D of strength anisotropy is preferably -10 MPa or less.

[0083] D=σ 0.2_0° -σ 0.2_90° (5)

[0084] Regarding the 0.2% yield strength σ from the direction of 0° relative to the rolling direction 0.2_0° Subtract the 0.2% yield strength σ in the direction 90° relative to the rolling direction 0.2_90° The significance of the obtained strength anisotropy can be explained as follows from the perspective of material texture.

[0085] After hot rolling or annealing, the material is in a recrystallized state, with a high concentration of isotropic cube-shaped orientations. Plastic deformation caused by cold rolling then develops a rolling texture that deforms toward the cube-shaped orientation, with anisotropy along the rolling direction. Furthermore, as the cold rolling ratio increases, the grains become more elongated in the rolling direction, increasing the grain diameter at 0° relative to the rolling direction, while the change in grain diameter at 90° relative to the rolling direction is smaller than that at 0°.

[0086] The above texture changes caused by rolling are related to the 0.2% yield strength σ 0.2 The relationship between κ and d is expressed as Equation (6) with reference to the Hall-Petch formula. In Equation (6), κ is the resistance of the grain boundary to slip, and d is the grain diameter.

[0087] σ 0.2 ∝κ×d -1 / 2 (6)

[0088] The resistance κ has different values ​​when the tensile force is applied in the direction of 0° or 90° relative to the rolling direction. This is because as the cold rolling ratio increases, the concentration of anisotropic rolling texture increases along the rolling direction, causing the resistance to slip at the grain boundary to change depending on the tensile direction.

[0089] Furthermore, at 0° relative to the rolling direction, the grains elongate and increase in diameter as the cold rolling rate increases, whereas at 90° relative to the rolling direction, the change in grain diameter with the cold rolling rate is relatively small. The cumulative effect of these effects leads to strength anisotropy with increasing cold rolling rate.

[0090] <Method for Manufacturing Aluminum Alloy Plate>

[0091] The aluminum alloy plate of the present disclosure can be manufactured, for example, by the following method: First, an ingot is manufactured from an aluminum alloy having the composition of the aluminum alloy plate of the present disclosure using a semi-continuous casting method (ie, DC casting) according to a conventional method.

[0092] Next, the ingot is face milled on all four sides, removing the front and rear ends. The ingot is then placed in a soaking furnace for homogenization. The homogenization temperature is preferably, for example, 470°C to 620°C. The homogenization time is preferably, for example, 1 hour to 20 hours.

[0093] When the homogenization temperature is above 400°C, segregation of the ingot structure is easily eliminated. In addition, if the homogenization temperature is above 450°C, the Mg2Si particles can be re-solubilized, thereby improving the strength and toughness of the alloy plate. In addition, if the homogenization temperature is above 470°C, more preferably above 550°C, the re-solubilization of the Mg2Si particles can be promoted, thereby further improving the strength and toughness of the alloy plate. On the other hand, if the homogenization temperature is below 620°C, the aluminum alloy is less likely to undergo local melting.

[0094] When the homogenization treatment time is 1 hour or longer, the temperature of the entire slab becomes uniform, segregation in the ingot structure is easily eliminated, and Mg2Si particles are easily re-dissolved. The longer the homogenization treatment time, the more Mg2Si particles can be re-dissolved. However, when the homogenization treatment time exceeds 20 hours, the effect of the homogenization treatment becomes saturated.

[0095] After homogenization, the ingot is hot rolled. The hot rolling process consists of a rough rolling step and a finish rolling step. In the rough rolling step, the ingot is processed into a sheet with a thickness of approximately tens of millimeters through reversible rolling. In the finish rolling step, the sheet is reduced to a thickness of approximately several millimeters using, for example, a tandem rolling mill. The sheet is then coiled into a hot-rolled coil.

[0096] When the total reduction ratio of the finishing rolling is high, a recrystallized structure is formed after coiling, thereby increasing the concentration of the cube orientation. When the coiling temperature of the finishing rolling is high, a recrystallized structure is formed after coiling, thereby increasing the concentration of the cube orientation.

[0097] Furthermore, by subjecting the hot-rolled coil to solution treatment to re-dissolve Mg and other elements, a high-strength alloy plate can be obtained. For example, heat treatment (i.e., annealing) is performed in a continuous annealing furnace (CAL) to a target solid temperature of 440°C or higher for 30 seconds or longer, followed by forced cooling such as air cooling, effectively improving the strength of the alloy plate.

[0098] After hot rolling, the sheet metal is cold rolled. During cold rolling, the hot-rolled coil is rolled until the product thickness is reached. Cold rolling can be performed in a single-stand or continuous rolling mill. In single-stand cold rolling, rolling is preferably performed in multiple passes, two or more.

[0099] Furthermore, by setting the final temperature of the cold rolling in intermediate passes other than the final pass to 120°C or higher, Si, Cu, and Mg are finely precipitated and age-hardened, thereby improving the strength of the alloy sheet. Further increasing the final temperature to 130°C or higher further improves the strength of the alloy sheet.

[0100] The cold rolling ratio (i.e., the target total reduction ratio) is preferably 80% or higher. A cold rolling ratio of 80% or higher can improve the strength of the alloy sheet. A lower cold rolling ratio results in more retained cube orientation, so a cold rolling ratio of 92% or lower is preferred.

[0101] The cold rolling rate R (%) is calculated using the plate thickness t0 (mm) after hot rolling or solution treatment and the product plate thickness t1 (mm) after cold rolling using the following mathematical formula (7).

[0102] R=(t0-t1) / t0×100 (7)

[0103] The product plate thickness can be appropriately selected to obtain the desired compressive resistance. As shown in the above mathematical formula (2), the greater the plate thickness, the higher the compressive resistance. The product plate thickness can be selected based on the value V in mathematical formula (2), provided that the value V is greater than 13.0, preferably greater than 14.0. As described above, according to the aluminum alloy plate disclosed herein, it is possible to suppress the increase in plate thickness for maintaining high compressive resistance.

[0104] Coils that have been cold-rolled to product thickness are pre-coated in a coating line, etc. The surface of the cold-rolled coil is degreased, cleaned, and chemically converted, then coated and baked.

[0105] Chemical conversion treatments use chemical solutions such as chromates and zirconium. Epoxy and polyester coatings are used. These chemical solutions and coatings can be selected based on the intended application. During the coating bake process, the coil is heated at a peak metal temperature (PMT) between 220°C and 270°C for approximately 30 seconds or less. A lower PMT suppresses material recovery, maintaining the alloy sheet's strength.

[0106] [1-2. Effect]

[0107] According to the embodiments described above, the following effects can be obtained.

[0108] (1a) It is possible to mix scrap raw materials from can materials while achieving both high strength and high toughness in the aluminum alloy sheet. Specifically, a certain amount of scrap 3104 aluminum alloy used for can bodies can be mixed into the raw materials, thereby reducing the use of new base metal and carbon dioxide emissions. Furthermore, it is possible to obtain aluminum alloy sheets for can lids with high formability that can be used in positive pressure can lids requiring high pressure resistance.

[0109] [2. Other Implementations]

[0110] The embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above embodiments and can take various embodiments.

[0111] (2a) In addition to the aluminum alloy plate of the above-described embodiment, the present disclosure also includes various aspects such as a component formed of the aluminum alloy plate and a method for manufacturing the aluminum alloy plate.

[0112] (2b) The functions of one component in each of the above embodiments may be shared by multiple components, or the functions of multiple components may be integrated into one component. In addition, part of the structure of the above embodiment may be omitted. At least part of the structure of each of the above embodiments may be added to the structure of the other embodiments, or at least part of the structure of each of the above embodiments may be replaced with the structure of the other embodiments. In addition, all the modes included in the technical ideas determined by the statements in the claims are embodiments of the present disclosure.

[0113] [3. Example]

[0114] Hereinafter, the contents of the tests conducted to confirm the effects of the present disclosure and the evaluation results thereof will be described.

[0115] <Manufacturing of Aluminum Alloy Sheets>

[0116] As examples and comparative examples, aluminum alloy plates S1 to S8 shown in Tables 1 and 2 were produced. Specific production steps are described below.

[0117] First, an ingot containing the components (mass %) of alloy numbers 1 to 4 shown in Table 3, with the remainder consisting of aluminum and inevitable impurities, was produced by a semi-continuous casting method. The ingot contained 0.10 mass % or less of Ti, 0.25 mass % or less of Zn, 0.10 mass % or less of Cr, and 0.15 mass % or less of inevitable impurities.

[0118] Next, the ingot was face milled on all four sides, removing the front and rear ends. The ingot was then placed in a furnace and homogenized. The homogenization temperatures are shown in Table 1. Following homogenization, the ingot was removed from the furnace and immediately hot rolled to form a rolled sheet.

[0119] Furthermore, the hot-rolled sheets of S1-S6 and S8 were cold-rolled until the sheet thickness reached the CAL sheet thickness shown in Table 1. The sheets that had reached the CAL sheet thickness were then annealed in a continuous annealing furnace (CAL). The CAL temperatures during annealing are shown in Table 1. After annealing, the sheets were cooled to room temperature by air cooling. After cooling, the sheets were cold-rolled again. The target cold rolling ratios during cold rolling after annealing are shown in Table 1.

[0120] The rolled sheet after hot rolling in S7 was subjected to cold rolling without annealing. The target cold rolling ratios during cold rolling are shown in Table 1.

[0121] The product plate thickness after cold rolling of S1-S8 (ie, t1 in the mathematical formula (7)) is in the range of approximately 0.235±0.03 mm.

[0122] After cold rolling, the coating was applied to the surface of each S1-S8 sheet and a coating bake treatment was performed for approximately 30 seconds. The physical temperature (PMT) during the coating bake treatment is shown in Table 1. Through the coating bake treatment, aluminum alloy sheets of S1-S8 were obtained. Table 1 also shows the sheet thickness (i.e., product sheet thickness) of the aluminum alloy sheets of S1-S8, measured using a micrometer.

[0123] [Table 1]

[0124]

[0125] [Table 2]

[0126]

[0127] [Table 3]

[0128]

[0129] <Evaluation of Aluminum Alloy Plate>

[0130] (Tensile properties)

[0131] Three No. 5 test pieces specified in JIS-Z-2241: 2011 were each produced by slicing from aluminum alloy sheets S1 to S8. The longitudinal directions of the three test pieces extended at angles of 0°, 45°, and 90° to the rolling direction, respectively.

[0132] The above test pieces were subjected to a tensile test according to JIS-Z-2241:2011, and the 0.2% yield strength and tensile strength were measured. Tables 1 and 2 show the 0.2% yield strength σ 0.2 and tensile strength σ B The measurement results, as well as the average values ​​of 0.2% yield strength and tensile strength σ fm .

[0133] In addition, three evaluation values ​​S are calculated based on the measurement results of the tensile test at 0°, 45°, and 90° relative to the rolling direction and mathematical formula (1). The minimum value of the above evaluation values ​​S, that is, the minimum evaluation value S min As shown in Table 2.

[0134] (toughness)

[0135] For the aluminum alloy plates of S1 to S8, the measurement method described in the embodiment was used to measure the area of ​​0.3 μm. 2 The ratio of the total area of ​​the Mg2Si particles in the L-ST cross section (area ratio) was calculated. The measurement results are shown in Table 2.

[0136] For aluminum alloy plates of grades S1 to S8, the number of repeated bending times and the normalized number of repeated bending times were calculated according to the measurement method described in the embodiment and equations (3) and (4). The results are shown in Table 2.

[0137] (Intensity anisotropy)

[0138] The strength anisotropy (ie, the value D) of the aluminum alloy plates of S1 to S8 was calculated according to the mathematical formula (5) described in the embodiment. The results are shown in Table 2.

[0139] (Shell single body compressive strength)

[0140] The compressive strength of the aluminum alloy plates S1 to S8 was calculated according to the measurement method described in the embodiment. The results are shown in Table 2. The aluminum alloy plates S1 to S6 and S8 exhibited a high compressive strength of 550 kPa or more.

[0141] (Waste mixing ratio)

[0142] Regarding the compositions of the aluminum alloy plates S1 to S8, it was determined whether the possible mixing ratio of 3104 aluminum alloy scrap was 50% by mass or greater. The results are shown in Table 2.

[0143] The aluminum alloy plates marked with "≥50" in Table 2 indicate that 50% by mass or more of 3104 aluminum alloy can be mixed in. Furthermore, the possible mixing ratio of 3104 aluminum alloy scrap was determined based on Table 4.

[0144] Table 4 shows the correspondence between the mixing ratio and the average value of the composition specifications of the 3104 aluminum alloy and the 5182 aluminum alloy. The first row of Table 4 shows the average value of the composition specifications of the 3104 aluminum alloy, and the second row shows the average value of the composition specifications of the 5182 aluminum alloy.

[0145] For example, when the mixing ratio of 3104 aluminum alloy is 50 mass %, the average value of Si is 0.20 mass %, the average value of Fe is 0.29 mass %, the average value of Cu is 0.11 mass %, the average value of Mn is 0.7 mass %, and the average value of Mg is 2.8 mass %.

[0146] Therefore, when the ratios of the various components in the aluminum alloy sheet are equal to or greater than the aforementioned values ​​for Si, Fe, Cu, Mn, and Mg, the possible mixing ratio of the 3104 aluminum alloy sheet is 50% by mass or greater. As the mixing ratio of the 3104 aluminum alloy increases, the Si, Fe, Cu, and Mn contents increase, while the Mg content decreases. Aluminum alloy sheets in grades S1-S10 can contain 50% by mass or more of 3104 aluminum alloy scrap.

[0147] [Table 4]

[0148] alloy Si Fe Cu Mn Mg 3104 0.30 0.40 0.15 1.10 1.05 5182 0.10 0.18 0.08 0.35 4.50 3104 Mixing Ratio Si Fe Cu Mn Mg 5％ 0.11 0.19 0.08 0.4 4.3 10％ 0.12 0.20 0.08 0.4 4.2 15％ 0.13 0.21 0.09 0.5 4.0 20％ 0.14 0.22 0.09 0.5 3.8 25％ 0.15 0.23 0.09 0.5 3.6 30％ 0.16 0.24 0.10 0.6 3.5 35％ 0.17 0.25 0.10 0.6 3.3 40％ 0.18 0.27 0.11 0.7 3.1 45％ 0.19 0.28 0.11 0.7 2.9 50％ 0.20 0.29 0.11 0.7 2.8 55％ 0.21 0.30 0.12 0.8 2.6 60％ 0.22 0.31 0.12 0.8 2.4 65％ 0.23 0.32 0.12 0.8 2.3 70％ 0.24 0.33 0.13 0.9 2.1 75％ 0.25 0.34 0.13 0.9 1.9 80％ 0.26 0.36 0.14 1.0 1.7 85％ 0.27 0.37 0.14 1.0 1.6 90％ 0.28 0.38 0.14 1.0 1.4 95％ 0.29 0.39 0.15 1.1 1.2 100％ 0.30 0.40 0.15 1.1 1.1

[0149] (evaluate)

[0150] Figure 3 The relationship between the value V of each of the aluminum alloy plates S1-S8 and the shell compressive strength is shown. Figure 3 As can be seen from the graph, there is a high correlation between the value V and the compressive strength. Therefore, the minimum evaluation value S min The alloy plate having a compressive strength of 370 MPa or more can have high compressive resistance at the same level as that of the alloy plate formed of the existing A5182 aluminum alloy without significantly increasing the plate thickness.

[0151] Although S1-S6 aluminum alloy sheets have lower Mg contents than S8, they still exhibit higher strength. Furthermore, S4-S6 aluminum alloy sheets undergo a higher homogenization temperature than S1-S3 aluminum alloy sheets, resulting in higher strength and a greater number of repeated bends, even at the same process and paint bake temperatures.

[0152] In addition, the lower the paint baking temperature (PMT), the higher the strength of the alloy plate. For example, when comparing S1-S3 and S4-S6, the lower the paint baking temperature, the higher the minimum evaluation value S. min .

[0153] In the aluminum alloys of S4-S6, the area ratio of Mg2Si particles is relatively small, less than 0.2%. The comparison between S1-S3 and S4-S6 shows that the area ratio of Mg2Si particles can be significantly reduced by increasing the homogenization temperature.

[0154] The number of repeated bendings also varies depending on the strength. By comparing S4-S6, which have a relatively small area ratio of Mg2Si particles and the same cold rolling rate, it can be seen that the increase in PMT leads to a decrease in strength, and the number of repeated bendings increases accordingly.

Claims

1. An aluminum alloy plate for can lids, characterized in that: In the aluminum alloy plate for can lids, The content of silicon (Si) is 0.27 mass % or more and 0.39 mass % or less, The content of iron (Fe) is 0.35 mass % or more and 0.55 mass % or less, The content of copper Cu is 0.17 mass % or more and 0.25 mass % or less, The content of manganese Mn is 0.75 mass % or more and 0.95 mass % or less, The content of magnesium Mg is 2.2 mass % or more and 2.8 mass % or less, and The remainder consists of aluminum Al and inevitable impurities, or contains aluminum Al and inevitable impurities. The 0.2% yield strength σ is used in the 0°, 45°, and 90° directions relative to the rolling direction. 0.2 , tensile strength σ B , and the average values ​​of 0.2% yield strength and tensile strength σ fm Among the evaluation values ​​S calculated by the following mathematical formula (1), the minimum evaluation value S is the minimum value. min 370 MPa or more and 410 MPa or less, S=σ fm / (s 0.2 / s B ) (1).

2. The aluminum alloy plate for can ends according to claim 1, wherein: 0.2% yield strength σ from the direction of 0° relative to the rolling direction 0.2 _ 0° Subtract the 0.2% yield strength σ in the direction 90° relative to the rolling direction 0.2 _ 90° The obtained value was -20 MPa or more and -10 MPa or less.

3. The aluminum alloy plate for can lids according to claim 2, wherein: In the L-ST cross section of the center in the width direction, the area is 0.3 μm 2 The ratio of the total area of ​​the above Mg2Si particles in the L-ST cross section is 0.2% or less.

4. The aluminum alloy plate for can lids according to claim 2 or claim 3, wherein: When a specimen cut into a strip with a width of 12.5 mm and a length of 200 mm is repeatedly bent 90° and returned to the 0° position in a direction parallel to the rolling direction until the specimen breaks, the number of bending operations at the time of breakage, i.e., the number of repeated bending operations N, is normalized by the thickness t of the specimen and the following mathematical formula (2). The normalized number of repeated bending operations N is obtained. s More than 14.0 times, N s =N×t / 0.235 (2)。

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