Aluminum alloy sheet for uncoated can lids

Abstract

Provided is an aluminum alloy sheet for uncoated can lids that includes scrap material from cans and has both high strength and high toughness. One embodiment of the present disclosure is an aluminum alloy sheet for uncoated can lids wherein the Si content is 0.10–0.60 mass%, the Fe content is 0.20–0.70 mass%, the Cu content is 0.10–0.40 mass%, the Mn content is 0.5–1.2 mass%, the Mg content is 1.1–4.0 mass%, and the 0.2% yield strength σ0.2, the tensile strength σB, and the average σfm of the 0.2% yield strength and the tensile strength satisfy expression (1-1).　(1-1) σfm / (σ0.2 / σB)≥380 MPa

Description

Unpainted aluminum alloy sheet for can lids CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This international application claims the benefit of Japanese Patent Application Nos. 2023-223496, 2023-223497, 2023-223498, and 2023-223499, filed with the Japan Patent Office on December 28, 2023, the entire disclosures of which are incorporated herein by reference.

[0002] The present disclosure relates to an unpainted aluminum alloy sheet for can ends.

[0003] In recent years, with the rise of environmental awareness, CO ２ There is a demand for aluminum alloy sheets with low CO emissions. ２ The compounding of new aluminum ingots in the casting process indirectly contributes significantly to these emissions.

[0004] The production of primary aluminum ingots uses a large amount of electricity during the smelting process and produces a large amount of CO ２ Therefore, reducing the amount of virgin aluminum used and increasing the horizontal recycling rate will reduce CO emissions in the manufacture of aluminum alloy sheets. ２ This will lead to reduced emissions.

[0005] Generally, CO generated when aluminum scrap is remelted and cast ２ It is said that waste emissions can be reduced to about one-thirtieth of that when producing virgin aluminum ingots. In particular, the production volume of aluminum alloy sheets for beverage cans used worldwide is extremely large, and further improving the horizontal recycling rate for these cans will have a significant impact on reducing the environmental impact.

[0006] Among these, can ends made of 5182 aluminum alloy (AA5182 alloy) have lower upper limits for the compositional specifications of Si, Fe, Cu, Mn, etc. than can bodies made of 3104 aluminum alloy (AA3104 alloy), making it difficult to incorporate scrap derived from can stock containing 3104 aluminum alloy.

[0007] For example, if can scrap (UBC: Used Beverage Can) generated in the market is blended as is, the weight ratio of the can body to the can lid will result in a higher content of 3104 aluminum alloy components, which will likely exceed the upper limit of the content of 5182 aluminum alloy, making it necessary to dilute the components with virgin metal.

[0008] Therefore, compared with the aluminum alloy sheet for can bodies, the aluminum alloy sheet for can ends uses a larger amount of virgin metal to adjust the composition to that of 5182 aluminum alloy, resulting in a low recyclability. Therefore, by changing the can ends to an alloy whose composition is easily blended with 3104 aluminum alloy, the virgin metal usage rate for can ends can be significantly reduced.

[0009] Patent Documents 1 to 5 disclose aluminum alloy sheets for can lids that have compositions relatively close to those of 3104 aluminum alloy, which has excellent recyclability.

[0010] Japanese Patent Application Laid-Open No. 2001-73106 Japanese Patent Application Laid-Open No. 9-070925 Japanese Patent Application Laid-Open No. 11-269594 Japanese Patent Application Laid-Open No. 2000-160273 Japanese Patent Application Laid-Open No. 2016-160511

[0011] The problem of using an alloy for can lids with a composition similar to that of 3104 aluminum alloy is that it reduces the pressure resistance of the can lid and the toughness of the material. The pressure resistance of a can lid is the internal pressure value when the can lid is inverted against the pressure inside the can, and is the resistance value when the internal pressure of the can increases unexpectedly due to a change in the external environment.

[0012] In particular, positively pressurized cans for beer and carbonated beverages require high pressure resistance. Generally, the stronger the material and the thicker the plate, the greater the pressure resistance. For this reason, the lids of positively pressurized cans are made of high-strength 5182 aluminum alloy, which contains a large amount of magnesium, a component that contributes to increased strength.

[0013] In contrast, if conventional 3104 aluminum alloy is used for can lids, the pressure resistance is significantly reduced, and there is a high risk that the lid will invert and leak contents if the internal pressure of the can suddenly increases. Furthermore, if the plate thickness is increased to increase the pressure resistance, this will result in an increase in the weight and cost of the lid.

[0014] Furthermore, the toughness of the material affects the formability and openability of the lid. If the material has low toughness, cracks may occur during molding, especially at the rivet and countersink areas of the lid. Furthermore, if the internal pressure of the can increases unexpectedly, cracks may occur at the score, increasing the risk of leakage of the can contents.

[0015] However, aluminum alloy sheets for can lids, which have chemical compositions relatively close to those of the conventional 3104 aluminum alloy, do not satisfy either or both of the above-mentioned two problems, i.e., material strength (i.e., pressure resistance of the lid) and toughness (i.e., formability and openability).

[0016] One aspect of the present disclosure is to provide an unpainted aluminum alloy sheet for can ends that contains scrap raw materials derived from can stock and yet has both high strength and high toughness after paint baking.

[0017] In one embodiment of the present disclosure, the silicon (Si) content is 0.10 mass% or more and 0.60 mass% or less, the iron (Fe) content is 0.20 mass% or more and 0.70 mass% or less, the copper (Cu) content is 0.10 mass% or more and 0.40 mass% or less, the manganese (Mn) content is 0.5 mass% or more and 1.2 mass% or less, the magnesium (Mg) content is 1.1 mass% or more and 4.0 mass% or less, and a 0.2% proof stress σ ０．２ , tensile strength σ Ｂ , and the average value σ of 0.2% proof stress and tensile strength ｆｍ is an unpainted aluminum alloy sheet for can ends, which satisfies the following formula (1-1).

[0018] σ ｆｍ / (σ ０．２ / σ Ｂ ) ≧ 380 MPa (1-1) According to this configuration, it is possible to achieve both high strength and high toughness of the aluminum alloy sheet after paint baking while blending scrap raw material derived from can stock. That is, it is possible to blend a certain amount of 3104 aluminum alloy scrap for can bodies, and to reduce the virgin metal usage rate and CO ２ Furthermore, an unpainted aluminum alloy sheet for can ends can be obtained that can be used for positive pressure can ends, which require high pressure resistance.

[0019] The "unpainted aluminum alloy sheet for can ends" of the present disclosure is an alloy sheet (i.e., a bare material) that is to be used as an aluminum alloy sheet for can ends after painting. That is, the "aluminum alloy sheet for can ends" is obtained by painting the "unpainted aluminum alloy sheet for can ends" of the present disclosure.

[0020] 1A is a schematic perspective view of an Erichsen cup, and FIG. 1B is a schematic plan view of the Erichsen cup. FIG. 2 is a graph showing an example of measurement results of the sidewall height of the Erichsen cup. FIG. 3 is a graph showing the measurement results of the sidewall height of the Erichsen cup in the example. ２．２７ ×σ ｆｍ / (σ ０．２ / σ Ｂ 1 is a graph showing the relationship between the temperature and the breakdown voltage.

[0021] 1. Eriksen Cup.

[0022] Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the drawings.

[0023] [1. First embodiment] [1-1. Configuration] The unpainted aluminum alloy sheet for can ends of the present disclosure may be continuously painted as a coil on a painting line, or may be cut into sheets and then painted or laminated to form into lids. The unpainted aluminum alloy sheet for can ends of the present disclosure can be used for any application. Furthermore, the unpainted aluminum alloy sheet for can ends is not limited to applications as beverage can lids, and can be widely used for food can lids, etc.

[0024] <Composition> The unpainted aluminum alloy sheet for can ends (hereinafter also simply referred to as "alloy sheet") of the present disclosure contains aluminum (Al), silicon (Si), iron (Fe), copper (Cu), manganese (Mn), and magnesium (Mg).

[0025] The lower limit of the Si content is 0.10 mass%, preferably 0.20 mass%. If the Si content is less than 0.10 mass%, the amount of Si precipitated in the processing heat of cold rolling after hot rolling and solution treatment may decrease, and the strength of the alloy sheet after paint baking may be insufficient.

[0026] Furthermore, the average Si content standard of 3104 aluminum alloy specified in JIS-H-4000:2014 is 0.30% by mass, and the average Si content standard of 5182 aluminum alloy specified in JIS-H-4000:2014 is 0.10% by mass. Therefore, by setting the Si content to 0.20% by mass or more, a large amount of 3104 aluminum alloy scrap can be blended.

[0027] The upper limit of the Si content is 0.60 mass%, preferably 0.40 mass%. If the Si content exceeds 0.60 mass%, Mg ２ The amount of Si particles increases, and the toughness of the alloy sheet after paint baking decreases.

[0028] The lower limit of the Fe content is 0.20% by mass, preferably 0.30% by mass. The average Fe content of the 3104 aluminum alloy is 0.40% by mass, and the average Fe content of the 5182 aluminum alloy is 0.18% by mass. Therefore, by setting the Fe content to 0.30% by mass or more, a large amount of 3104 aluminum alloy scrap can be blended.

[0029] The upper limit of the Fe content is 0.70% by mass. If the Fe content exceeds 0.70% by mass, the amount of Al-Fe-Mn or Al-Fe-Mn-Si intermetallic compounds (i.e., second phase particles) increases. As a result, crack propagation paths are created, and the toughness of the alloy sheet after paint baking decreases.

[0030] The lower limit of the Cu content is 0.10 mass%, preferably 0.11 mass%, and more preferably 0.20 mass%. If the Cu content is less than 0.10 mass%, there will be insufficient Cu, which increases strength by solid solution or precipitation, and the average strength of the alloy sheet after paint baking will decrease. By precipitating Cu during the cold rolling process after hot rolling and solution treatment, the strength of the alloy sheet after paint baking will be significantly increased.

[0031] The average Cu content of the 3104 aluminum alloy is 0.15% by mass, and the average Cu content of the 5182 aluminum alloy is 0.075% by mass. Therefore, by setting the Cu content to 0.11% by mass or more, a large amount of 3104 aluminum alloy scrap can be blended.

[0032] The upper limit of the Cu content is 0.40 mass %. If the Cu content exceeds 0.40 mass %, the toughness of the alloy sheet after paint baking decreases.

[0033] The lower limit of the Mn content is 0.5 mass%, preferably 0.7 mass%, and more preferably 0.8 mass%. If the Mn content is less than 0.5 mass%, the amount of Mn that increases strength by solid solution or precipitation will be insufficient, and the average strength of the alloy sheet after paint baking will decrease.

[0034] The average Mn content of the 3104 aluminum alloy is 1.1 mass %, and the average Mn content of the 5182 aluminum alloy is 0.35 mass %. Therefore, by setting the Mn content to 0.7 mass % or more, a large amount of 3104 aluminum alloy scrap can be blended.

[0035] The upper limit of the Mn content is 1.2 mass%, preferably 1.0 mass%. If the Mn content exceeds 1.2 mass%, the amount of Al-Fe-Mn or Al-Fe-Mn-Si intermetallic compounds (i.e., second phase particles) increases. As a result, crack propagation paths are created, and the toughness of the alloy sheet after paint baking decreases.

[0036] The lower limit of the Mg content is 1.1% by mass. If the Mg content is less than 1.1% by mass, there will be insufficient Mg, which increases strength through solid solution, and the average strength of the alloy sheet after paint baking will decrease. By precipitating Mg during the cold rolling process after hot rolling and solution treatment, the strength of the alloy sheet after paint baking will be significantly increased.

[0037] The upper limit of the Mg content is 4.0% by mass, preferably 3.0% by mass. The average Mg content standard for 3104 aluminum alloy is 1.05% by mass, and the average Mg content standard for 5182 aluminum alloy is 4.5% by mass. Therefore, by setting the Mg content to 4.0% by mass or less, more preferably 3.0% by mass or less, it is possible to incorporate a large amount of 3104 aluminum alloy scrap while reducing the amount of additional Mg-containing raw material.

[0038] The alloy plate may contain titanium (Ti). The upper limit of the Ti content is preferably 0.10 mass%. By including Ti, the ingot structure of the alloy plate is refined. The alloy plate may also contain zinc (Zn). The upper limit of the Zn content is preferably 0.25 mass%. Furthermore, the alloy plate may also contain chromium (Cr). The upper limit of the Cr content is preferably 0.10 mass%.

[0039] The alloy plate may contain unavoidable impurities to the extent that the performance of the alloy plate is not significantly impaired. That is, the alloy plate contains Si, Fe, Cu, Mn, and Mg in the respective ranges described above, with the balance consisting of aluminum and unavoidable impurities. The balance may be understood to include aluminum and unavoidable impurities. The balance may include substances other than aluminum and unavoidable impurities. The upper limit of the total amount of unavoidable impurities is preferably 0.15% by mass.

[0040] <Material strength and pressure resistance> 0.2% yield strength σ of the unpainted aluminum alloy plate of the present disclosure ０．２ , tensile strength σ Ｂ , and the average value σ of 0.2% proof stress and tensile strength ｆｍ satisfies the following formula (1-1).

[0041] σ ｆｍ / (σ ０．２ / σ Ｂ ) ≧ 380 MPa (1-1) Empirically, the pressure resistance value of an aluminum alloy lid has a strong positive correlation with the value V of the following formula (3), which is expressed by the material strength of the aluminum alloy plate (i.e., the left side of formula (1-1)) and the plate thickness t.

[0042] V = t ２．２７ ×σｆｍ / (σ ０．２ / σ Ｂ ) ... (3) Therefore, the material strength of the alloy plate σ ｆｍ / (σ ０．２ / σ Ｂ ) is 380 MPa or more, a lid having a sufficient pressure resistance value after paint baking can be formed without significantly increasing the plate thickness.

[0043] The lower limit of the left side of the formula (1-1) (i.e., the value of the right side of the formula (1-1)) is more preferably 400 MPa. ｆｍ / (σ ０．２ / σ Ｂ ) is 400 MPa or more, the pressure resistance value of the lid after painting and baking can be further increased.

[0044] Furthermore, the alloy sheet of the present disclosure has a 0.2% yield strength σ after heat treatment at 270°C for 30 seconds. ０．２ , tensile strength σ Ｂ , and the average value σ of 0.2% proof stress and tensile strength ｆｍ It is preferable that the following formula (1-2) is satisfied: This makes it possible to form a lid having a sufficient pressure resistance value after painting and baking.

[0045] σ ｆｍ / (σ ０．２ / σ Ｂ )≧350 MPa (1-2) The lower limit of the left side of the formula (1-2) (i.e., the value of the right side of the formula (1-2)) is more preferably 380 MPa. ｆｍ / (σ ０．２ / σ Ｂ ) to 380 MPa or more, the pressure resistance value of the lid can be further increased.

[0046] 0.2% proof stress σ in formula (1-1), formula (1-2) and formula (3) ０．２ and tensile strength σ Ｂ is measured by the method specified in JIS-Z-2241: 2011. The plate thickness t is measured, for example, with a microgauge.

[0047] The pressure resistance of an aluminum alloy sheet is measured, for example, by the following procedure. A shell formed from an aluminum alloy sheet after paint baking is fixed to a jig and internal pressure is applied. The internal pressure is gradually increased, and the internal pressure value when the shell inverts (i.e., buckles) is taken as the pressure resistance value.

[0048] Specifically, a φ204 full-form (B64) shell mold is used to mold the shell. Internal pressure values ​​are measured using a Versatile Technology DV036E buckle and missile measuring machine. Specifically, after fixing the molded shell in place with a special jig, the internal pressure is increased using a program, and the internal pressure value is read when the shell inverts. For example, the internal pressure is increased at a rate of approximately 175 kPa / s, and when it reaches approximately 350 kPa to 400 kPa, the internal pressure is increased at a rate of 10 kPa / s.

[0049] <Toughness> It is known that the formability of the lid and the force required to open the score (i.e., opening force) are affected by the toughness of the aluminum alloy plate after paint baking.

[0050] (Number of repeated bending tests) A repeated bending test is one of the evaluation indexes for the toughness of an aluminum alloy sheet. For a given sheet thickness, the greater the number of repeated bending tests, the better the toughness of the aluminum alloy sheet. The aluminum alloy sheet of the present disclosure can achieve a good number of repeated bending tests after paint baking.

[0051] The repeated bending test is carried out according to the following procedure. For example, a test piece is cut into a strip shape with a width of 12.5 mm and a length of 200 mm, which is subjected to a heat treatment at 250°C for 30 seconds, simulating a paint baking process, and is then oriented so that the bending ridgeline is parallel to the rolling direction of the alloy plate. Both ends of this test piece are fixed with chucks, and a tension of 200 N is applied.

[0052] In this state, the test piece is repeatedly bent by rotating the other chuck 90° left and right, using a jig with a bending radius of 2.0 mm as a fulcrum, which is positioned 150 mm in the longitudinal direction of the test piece from the end of the test piece fixed to one of the immovable chucks, and the number of bends until the test piece breaks is measured.

[0053] The number of bending times is counted as one bending operation to either the left or right by 90° and one operation returning to the original position. If the wire breaks during bending, the angle Θ (0°-90°) is read and the number of repeated bending times N is calculated using the following formula (3). In formula (4), N ０ is the total number of times that the test piece was bent 90° to either the left or right and returned to the original 0° position from the 90° bent position until it broke.

[0054] N=N ０ +Θ / 90 ... (4) Repeated bending evaluation is more disadvantageous as the plate thickness increases, so it is necessary to correct for the standard plate thickness. Therefore, the number of repeated bending cycles Ns is calculated using the following formula (5) with a plate thickness of 0.245 mm as the standard, where t (mm) is the plate thickness of the test piece.

[0055] Ns = N × t / 0.245 (5) (Second Phase Particles) Toughness is affected by the distribution of second phase particles. In other words, the higher the density of second phase particles, the lower the toughness. In particular, when the content of Mg and Si is high, the distribution of Mg ２ As a result, Mg ２ The Si particles act as crack initiation points and propagation paths, which reduces toughness.

[0056] The unpainted aluminum alloy sheet of the present disclosure has an area of ​​0.3 μm on the sheet surface (L-LT surface) after heat treatment at 270 ° C. for 30 seconds. ２ More than Mg ２ The ratio of the total area of ​​Si particles is preferably 1.0% or less.

[0057] Mg ２ The area ratio of Si particles can be measured by the following method: The surface to be measured (i.e., the L-LT surface) of the measurement sample is mechanically polished to a mirror finish. The polishing depth is approximately 1% of the plate thickness of the measurement sample.

[0058] Next, the polished surface (i.e., L-LT cross section) is observed using a SEM (scanning electron microscope) to obtain 10 fields of view. When the magnification of the SEM is 500 times, the range of one field of view is 0.049 mm ２ (Total of 10 fields of view: 0.49 mm ２) and obtain a COMPO (backscattered electron composition) image. When the SEM magnification is 1000 times, the range of one field of view is 0.012 mm ２ (Total of 10 fields of view: 0.12 mm ２ ) and obtain a COMPO (backscattered electron composition) image.

[0059] The captured COMPO image is analyzed using the image analysis software ImageJ. Specifically, the most frequent value of the image brightness in 256 gradations is defined as the background brightness, and particles with brightness lower than the value obtained by subtracting 30 from the most frequent brightness are defined as Mg ２ It is determined to be a Si particle.

[0060] Determined Mg ２ Among the Si particles, 0.3 μm ２ The total area of ​​particles with an area of ​​0.3 μm or more was calculated and divided by the photographed area of ​​10 fields of view (i.e., the total photographed area), resulting in an area of ​​0.3 μm ２ More than Mg ２ The percentage of the total area of ​​the L-LT plane of the Si particles is calculated.

[0061] (Earing ratio) The number of repeated bending cycles is also affected by the texture, and the higher the concentration of Cube orientation, the better. The concentration of Cube orientation is reflected in the ear shape of an Erichsen cup 1 formed from an aluminum alloy sheet by the Erichsen test shown in Figures 1A and 1B.

[0062] Specifically, it is suggested that the greater the relative sidewall height H in the 0° / 180° direction with respect to the rolling direction RD of the aluminum alloy plate of the Erichsen Cup 1, with respect to the sidewall height H in the 45° direction with respect to the rolling direction RD (i.e., the ear height), the higher the degree of accumulation of Cube orientation. That is, the aluminum alloy plate of the present disclosure includes those having a relatively large degree of accumulation of Cube orientation and a high sidewall height H in the 0° / 180° direction.

[0063] The relative sidewall height in the 0° / 180° direction to the sidewall height in the 45° direction can be evaluated using an index called earing balance. The procedure for measuring the earing balance will be described below.

[0064] The earing ratio is expressed by the left side of the following equation (2).

[0065] (h ０ｐ -h ４５ｐ ) / h ｖ ×100≧-7.0...(2) In formula (2), h ０ｐ is the average value of the maximum sidewall heights in the first region A1 around 0° and the second region A2 around 180° with respect to the rolling direction. The first region A1 is, for example, in the range of 0°±11° with respect to the rolling direction. The second region A2 is, for example, in the range of 180°±11° with respect to the rolling direction.

[0066] h ４５ｐ is the average value of the maximum sidewall heights in the third region A3 around 45°, the fourth region A4 around 135°, the fifth region A5 around 225°, and the sixth region A6 around 315° relative to the rolling direction.

[0067] The third region A3 is, for example, in the range of 45°±22° with respect to the rolling direction. The fourth region A4 is, for example, in the range of 135°±22° with respect to the rolling direction. The fifth region A5 is, for example, in the range of 225°±22° with respect to the rolling direction. The sixth region A6 is, for example, in the range of 315°±22° with respect to the rolling direction.

[0068] h ｖ is the average value of the minimum sidewall height in each of the seventh region A7 from 0° to 45°, the eighth region A8 from 45° to 135°, the ninth region A9 from 135° to 180°, the tenth region A10 from 180° to 225°, the eleventh region A11 from 225° to 315°, and the twelfth region A12 from 315° to 360° with respect to the rolling direction.

[0069] 2 is a graph showing an example of the measurement results of the sidewall height of an Erichsen cup. The angles shown in Fig. 2 are angles relative to the rolling direction. The distance from the center of the graph indicates the sidewall height.

[0070] In the figure, a to d are the maximum values ​​in the third area A3 to the sixth area A6, e and f are the maximum values ​​in the first area A1 and the second area A2, and g to l are the minimum values ​​in the seventh area A7 to the twelfth area A12.

[0071] The Erichsen cup 1 is formed, for example, under the conditions of a blank diameter of 57 mm and a punch diameter of 33 mm. The sidewall height of the Erichsen cup is measured using, for example, a Roncorder EC1550-H manufactured by Kosaka Laboratory Co., Ltd.

[0072] Specifically, a measurement probe is placed at the opening of the Erichsen cup with the rolling direction as the reference (0° / 180°), and the table on which the Erichsen cup is placed is rotated once to measure the height of the opening in the circumferential direction of 360°.

[0073] In an Erichsen cup formed by an Erichsen test after heat treatment at 250°C for 30 seconds, the degree of concentration of Cube orientation increases when formula (2) is satisfied, i.e., when the earing ratio is -7.0% or more. As a result, the number of repeated bending cycles of the alloy sheet can be increased.

[0074] The values ​​of the aluminum alloy sheet after paint baking are important for the above-mentioned properties, such as strength, pressure resistance, number of repeated bending cycles, area ratio of second-phase particles, and earing ratio. Therefore, when measuring these properties, the aluminum alloy sheet of the present disclosure is subjected to a heat treatment simulating paint baking, for example, at 230°C to 280°C for 30 seconds or less, and then measured using the above-mentioned method. Here, the "270°C-30 second" heat treatment refers to heat treatment performed according to a temperature rise curve in which the actual temperature is 220°C or higher 15 seconds after the start of the heat treatment and reaches 270±5°C at 30 seconds. Furthermore, the "250°C-30 second" heat treatment refers to heat treatment performed according to a temperature rise curve in which the actual temperature is 200°C or higher 15 seconds after the start of the heat treatment and reaches 250±5°C at 30 seconds. The equipment used is, for example, a large drawer-type dryer manufactured by Tojo Thermal Engineering Co., Ltd.

[0075] <Method for producing aluminum alloy sheet> The unpainted aluminum alloy sheet of the present disclosure can be produced, for example, as follows: First, an aluminum alloy having the composition of the unpainted aluminum alloy sheet of the present disclosure is subjected to a semi-continuous casting method (i.e., DC casting) according to a conventional method to produce an ingot.

[0076] Next, the surface of the ingot is chamfered. Thereafter, the ingot is placed in a soaking furnace and subjected to homogenization treatment. The temperature in the homogenization treatment is preferably, for example, 470°C or higher and 620°C or lower. The time for the homogenization treatment is preferably, for example, 1 hour or higher and 20 hours or lower.

[0077] When the homogenization temperature is 400°C or higher, segregation of the ingot structure is easily eliminated. Furthermore, when the homogenization temperature is 450°C or higher, Mg ２ The homogenization temperature is 490°C or higher, preferably 550°C or higher, and the Mg ２ The re-dissolution of Si particles is promoted, and the strength and toughness of the alloy plate can be further improved. On the other hand, if the temperature in the homogenization treatment is 620°C or less, local melting of the aluminum alloy is unlikely to occur.

[0078] When the homogenization treatment time is 1 hour or more, the temperature of the entire slab becomes uniform, segregation of the ingot structure is easily eliminated, and Mg ２ The longer the homogenization time, the easier it is to redissolve the Si particles. ２ The Si particles can be redissolved. However, if the homogenization treatment time exceeds 20 hours, the effect of the homogenization treatment becomes saturated.

[0079] After the homogenization treatment, the ingot is subjected to hot rolling. The hot rolling process includes a rough rolling process and a finish rolling process. In the rough rolling process, the ingot is processed into a plate material having a thickness of about several tens of mm by reverse rolling. In the finish rolling process, the thickness of the plate material is reduced to about several mm by, for example, tandem rolling, and the plate material is wound into a coil to form a hot-rolled coil.

[0080] If the total reduction rate of the finish rolling is high, a recrystallized structure is formed after coiling, and the concentration of the Cube orientation can be increased. If the coiling temperature of the finish rolling is high, a recrystallized structure is formed after coiling, and the concentration of the Cube orientation can be increased.

[0081] Furthermore, a high-strength alloy sheet can be obtained by subjecting the hot-rolled coil to solution treatment to redissolve Mg, etc. For example, the strength of the alloy sheet can be effectively increased by performing heat treatment (i.e., annealing) at a target solid temperature of 440°C or higher for 30 seconds or longer using a continuous annealing furnace, followed by forced cooling by air cooling or the like.

[0082] Following the hot rolling, the plate material is cold rolled. In cold rolling, the hot rolled coil is rolled until the product plate thickness is reached. Cold rolling may be either single rolling or tandem rolling. In single cold rolling, rolling is preferably carried out in two or more passes.

[0083] By setting the finishing temperature of 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 increasing the strength of the alloy sheet. Furthermore, by setting the finishing temperature to 130°C or higher, the strength of the alloy sheet can be further increased.

[0084] The cold rolling reduction (i.e., the target total reduction) is preferably 80% or more. When the cold rolling reduction is 80% or more, the strength of the alloy sheet can be increased. The lower the cold rolling reduction, the more the Cube orientation remains. The cold rolling reduction is preferably 92% or less.

[0085] The cold rolling reduction ratio R (%) is the thickness t of the hot rolled sheet. ０ (mm), product thickness after cold rolling t １ (mm) is calculated using the following formula (6).

[0086] R = (t ０ -t １ ) / t ０ × 100 (6) The product thickness can be appropriately selected to obtain the desired pressure resistance. As shown in the above formula (3), the pressure resistance improves as the thickness increases. The product thickness is determined by the t ２．２７ ×σ ｆｍ / (σ ０．２ / σ Ｂ ) ≧ 14. As described above, the unpainted aluminum alloy sheet of the present disclosure can suppress an increase in sheet thickness in order to maintain high pressure resistance.

[0087] Furthermore, in the above-described method for producing an aluminum alloy sheet, annealing may be performed, for example, before or after cold rolling or between passes, as long as the effects of the unpainted aluminum alloy sheet of the present disclosure are exhibited.

[0088] The coil that has been cold-rolled to the product thickness may be subjected to surface degreasing, cleaning, and chemical conversion treatment in a coating line or the like. An unpainted aluminum alloy sheet is obtained by the above treatments. The unpainted aluminum alloy sheet coil is further coated with paint and then subjected to a paint baking treatment to obtain a painted aluminum alloy sheet.

[0089] Chemical solutions such as chromate-based and zirconium-based solutions are used in chemical conversion treatments. Epoxy-based and polyester-based paints are used. These can be selected according to the application. In the paint baking process, the coil is heated to a peak metal temperature (PMT) of 220°C to 270°C for approximately 30 seconds or less. The lower the PMT, the more the recovery of the material is suppressed, and the higher the strength of the alloy plate can be maintained.

[0090] [1-2. Effects] According to the embodiment described above in detail, the following effects can be obtained.

[0091] (1a) While blending scrap raw materials derived from can stock, it is possible to achieve both high strength and high toughness of the aluminum alloy sheet after paint baking. That is, it is possible to blend a certain amount of 3104 aluminum alloy scrap for can bodies, and to reduce the virgin metal usage rate and CO ２ Furthermore, an unpainted aluminum alloy sheet for can ends can be obtained that can be used for positive pressure can ends, which require high pressure resistance.

[0092] [2. Other Embodiments] Although the embodiments of the present disclosure have been described above, it goes without saying that the present disclosure is not limited to the above-described embodiments and can take on various forms.

[0093] (2a) In addition to the unpainted aluminum alloy plate of the above embodiment, the present disclosure also includes various forms such as a member made of this unpainted aluminum alloy plate and a method for manufacturing this unpainted aluminum alloy plate.

[0094] (2b) The function of one component in the above embodiments may be distributed among multiple components, or the functions of multiple components may be integrated into one component. Also, part of the configuration of the above embodiments may be omitted. Furthermore, at least part of the configuration of the above embodiments may be added to, replaced with, or the like, the configuration of another of the above embodiments. Note that all aspects included in the technical idea identified by the wording of the claims are embodiments of the present disclosure.

[0095] 3. Examples The following describes the details of tests conducted to confirm the effects of the present disclosure and their evaluation.

[0096] <Production of Unpainted Aluminum Alloy Sheets> As examples and comparative examples, unpainted aluminum alloy sheets S1 to S10 shown in Tables 1 and 2 were produced. Specific production procedures are described below.

[0097] First, ingots containing the components (by mass%) of Alloy Nos. 1-9 shown in Table 3, with the balance consisting of aluminum and unavoidable impurities, were produced by semi-continuous casting. The balance may be understood to include aluminum and unavoidable impurities. The balance may also include substances other than aluminum and unavoidable impurities. The ingots contained 0.10% by mass or less of Ti, 0.25% by mass or less of Zn, 0.10% by mass or less of Cr, and 0.15% by mass or less of unavoidable impurities.

[0098] Next, the four sides of the ingot were chamfered. Thereafter, the ingot was placed in a furnace and subjected to homogenization treatment. The homogenization treatment temperature is shown in Table 1. After the homogenization treatment, the ingot was removed from the furnace, and immediately hot rolling was started to produce a rolled sheet.

[0099] The obtained rolled sheet was annealed. The annealing temperature was as shown in Table 1, and the annealing time was 30 seconds. After annealing, the rolled sheet was cooled to room temperature by air cooling. After cooling, the rolled sheet was subjected to cold rolling. The target total reduction in cold rolling was as shown in Table 1. The product sheet thickness after cold rolling (i.e., t1 in formula (6)) was set to a range of approximately 0.245±0.01 mm. During cold rolling and after final cold rolling, the final temperatures shown in Table 1 were applied. Unpainted aluminum alloy sheets S1-S10 were obtained by the above-mentioned treatment.

[0100]

[0101]

[0102]

[0103] <Evaluation of Unpainted Aluminum Alloy Sheets> (Tensile Properties) For the unpainted aluminum alloy sheets S1-S10, No. 5 test pieces defined in JIS-Z-2241:2011 were prepared from the aluminum alloy sheets after heat treatment at 270°C or 250°C for 30 seconds, which is a heat treatment simulating paint baking as described in the embodiments, and from the aluminum alloy sheets before this heat treatment. These test pieces extend in a direction forming an angle of 0° with respect to the rolling direction. Tensile tests were performed on these test pieces in accordance with JIS-Z-2241:2011 to measure 0.2% proof stress and tensile strength. 0.2% proof stress σ ０．２ and tensile strength σ Ｂ The measurement results and the average value σ of 0.2% yield strength and tensile strength ｆｍ are shown in Tables 1 and 2.

[0104] For the unpainted aluminum alloy plates S1-S10, the plate thickness was measured using a microgauge, and the value V (= t ２．２７ ×σ ｆｍ / (σ ０．２ / σ Ｂ )) was calculated. The calculation result of the value V and σ ｆｍ / (σ ０．２ / σＢ ) values ​​are shown in Table 2.

[0105] (Toughness) In the unpainted aluminum alloy plates of S1 to S10, the area of ​​0.3 μm2 after heat treatment at 270° C. for 30 seconds was measured by the measurement method described in the embodiment. ２ More than Mg ２ The ratio of the total area of ​​the L-LT plane of the Si particles (area ratio) was calculated. The measurement results are shown in Table 2.

[0106] For the unpainted aluminum alloy sheets S1-S10, the earing ratio after heat treatment at 250°C for 30 seconds was calculated from the measurement method described in the embodiment and the left side of equation (2). The results are shown in Table 2. In the table, "-" indicates that the measurement was not performed.

[0107] For the unpainted aluminum alloy sheets S1-S10, the number of repeated bending cycles after heat treatment at 250°C for 30 seconds was measured using the measurement method and formulas (4) and (5) described in the embodiment, and the normalized number of repeated bending cycles was calculated. The results are shown in Table 2. In the table, "-" indicates that the value was not measured.

[0108] (Scrap Blending Ratio) With respect to the compositions of the unpainted aluminum alloy plates S1 to S10, it was determined whether the possible blending ratio of 3104 aluminum alloy scrap was 50 mass % or more. The results are shown in Table 2.

[0109] In Table 2, unpainted aluminum alloy plates indicated as "≧50" can contain 50 mass% or more of 3104 aluminum alloy. The possible blending ratio of 3104 aluminum alloy scrap is determined based on Table 4.

[0110] Table 4 shows the relationship between the blending ratios of 3104 aluminum alloy and 5182 aluminum alloy and the average values ​​of the component specifications. The first row of Table 4 shows the average values ​​of the component specifications of 3104 aluminum alloy, and the second row shows the average values ​​of the component specifications of 5182 aluminum alloy.

[0111] For example, when the compounding 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%.

[0112] Therefore, when the proportions of each component of the unpainted aluminum alloy sheet are equal to or greater than the above-mentioned values ​​of Si, Fe, Cu, Mn, and Mg, the possible blending ratio of 3104 aluminum alloy sheet is 50% by mass or more. As the blending ratio of 3104 aluminum alloy increases, the contents of Si, Fe, Cu, and Mn increase and the content of Mg decreases. The unpainted aluminum alloy sheets S1, S9-S10 can blend 50% by mass or more of 3104 aluminum alloy scrap.

[0113]

[0114] (Pressure resistance) The pressure resistance of the unpainted aluminum alloy sheets S1-S10 was measured after heat treatment at 270°C for 30 seconds by the measurement method described in the embodiment. The results are shown in Table 2. The unpainted aluminum alloy sheets S1 and S9-S10 showed a high pressure resistance of 550 kPa or more after heat treatment.

[0115] The value V (= t ２．２７ ×σ ｆｍ / (σ ０．２ / σ Ｂ )) and the breakdown voltage of the alloy plate is shown in Figure 3. From Figure 3, it was confirmed that there is a high correlation between the value V and the breakdown voltage. Therefore, σ on the left side of the formula (1-1) ｆｍ / (σ ０．２ / σＢ If the value of (a) is 350 MPa or more, a high pressure resistance of 550 kPa or more can be provided without a large increase in plate thickness.

[0116] The unpainted aluminum alloy sheet S1, which was subjected to a high homogenization temperature, exhibited significantly high pressure resistance. In addition, since the unpainted aluminum alloy sheet S1 was also subjected to a high annealing temperature after hot rolling, high strength and pressure resistance were obtained even with a small Mg content.

[0117] The unpainted aluminum alloys S1 and S10 are Mg after heat treatment. ２ The area ratio of Si particles was small, 1.0% or less. The unpainted aluminum alloy sheet S10, which was subjected to a higher homogenization treatment temperature, had a higher Mg content after heat treatment than the unpainted aluminum alloy sheet S9. ２The area ratio of Si particles was small.

[0118] Therefore, when comparing the unpainted aluminum alloy plate S9 and the unpainted aluminum alloy plate S10, although the pressure resistance of the aluminum alloy of S10 was nearly 25 kPa higher than that of the aluminum alloy plate S9, the number of repeated bending times was the same.

Claims

1. An aluminum alloy sheet for an uncoated can lid, wherein the silicon (Si) content is 0.10% by mass or more and 0.60% by mass or less, the iron (Fe) content is 0.20% by mass or more and 0.70% by mass or less, the copper (Cu) content is 0.10% by mass or more and 0.40% by mass or less, the manganese (Mn) content is 0.5% by mass or more and 1.2% by mass or less, the magnesium (Mg) content is 1.1% by mass or more and 4.0% by mass or less, and the 0.2% proof stress σ ０．２ , the tensile strength σ Ｂ , and the average value σ of the 0.2% proof stress and the tensile strength ｆｍ satisfy the following formula (1-1). An aluminum alloy sheet for an uncoated can lid. σ ｆｍ / (σ ０．２ / σ Ｂ ) ≧ 380 MPa ・・・(1-1) 2. The aluminum alloy sheet for an unpainted can lid according to claim 1, wherein the 0.2% proof stress σ after heat treatment at 270°C for 30 seconds ０．２ , the tensile strength σ Ｂ , and the average value σ of the 0.2% proof stress and the tensile strength ｆｍ satisfy the following formula (1-2): The aluminum alloy sheet for an unpainted can lid. σ ｆｍ / (σ ０．２ / σ Ｂ ) ≧ 350 MPa ··· (1-2) 3. An aluminum alloy sheet for an uncoated can lid according to claim 1 or claim 2, wherein on the plate surface after heat treatment at 270 ° C for 30 seconds, the area is 0.3 μm ２ or more of Mg ２ The ratio of the total area of Si particles is 1.0% or less, and the aluminum alloy sheet for an uncoated can lid.

4. An aluminum alloy sheet for an uncoated can lid according to claim 1 or claim 2, wherein in the circumferential direction of an Erichsen cup formed by an Erichsen test after heat treatment at 250°C for 30 seconds, the average value h of the maximum values of the side wall heights in the regions around 0° and around 180° with respect to the rolling direction ０ｐ and the average value h of the maximum values of the side wall heights in the regions around 45°, around 135°, around 225°, and around 315° with respect to the rolling direction ４５ｐ and the average value h of the minimum values of the side wall heights in the regions from 0° to 45°, from 45° to 135°, from 135° to 180°, from 180° to 225°, from 225° to 315°, and from 315° to 360° with respect to the rolling direction ｖ satisfy the following formula (2). An aluminum alloy sheet for an uncoated can lid. (h ０ｐ − h ４５ｐ ) / h ｖ × 100 ≥ −7.0 ··· (2) 5. An aluminum alloy sheet for an unpainted can lid according to claim 1 or claim 2, wherein the Si content is 0.20% by mass or more and 0.60% by mass or less, the Fe content is 0.30% by mass or more and 0.70% by mass or less, the Cu content is 0.11% by mass or more and 0.40% by mass or less, the Mn content is 0.7% by mass or more and 1.2% by mass or less, and the Mg content is 1.1% by mass or more and 3.0% by mass or less. An aluminum alloy sheet for an unpainted can lid.

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