Unpainted aluminum alloy sheet for can lid

Abstract

To provide an unpainted aluminum alloy sheet for a can lid capable of achieving both high strength and high toughness while blending a scrap raw material derived from a can material.SOLUTION: An uncoated aluminum alloy sheet for a can lid according to an aspect of the present disclosure contains 0.10 mass% or more and 0.60 mass% or less of Si, 0.20 mass% or more and 0.70 mass% or less of Fe, 0.10 mass% or more and 0.40 mass% or less of Cu, 0.5 mass% or more and 1.2 mass% or less of Mn, and 1.1 mass% or more and 4.0 mass% or less of Mg, wherein the 0.2% yield strength σ0.2, the tensile strength σB, and the average value of the 0.2% yield strength and the tensile strength σfm satisfy the following formula (1-1). σfm / (σ0.2 / σB)≥380 MPa (1-1)SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an aluminum alloy sheet for an uncoated can lid.

[0002] In recent years, due to the increasing environmental awareness, an aluminum alloy sheet with low CO2 emissions in the manufacturing process has been demanded. In the aluminum rolling process, the composition of the new aluminum ingot in the casting process indirectly contributes greatly to the CO2 emissions.

[0003] The production of new aluminum ingots uses a large amount of electricity in the smelting process, leading to a large amount of CO2 emissions. Therefore, reducing the amount of new aluminum ingot and increasing the horizontal recycling rate lead to a reduction in CO2 emissions in the production of aluminum alloy sheets.

[0004] Generally, it is said that the CO2 emissions when remelting and casting aluminum scrap can be reduced to about 1 / 30 of those when producing new aluminum ingots. In particular, the production volume of aluminum alloy sheets for beverage cans used worldwide is very large, and further improving the horizontal recycling rate has great significance for reducing the environmental burden.

[0005] Among them, the can lid formed of 5182 aluminum alloy (AA5182 alloy) has lower upper limits of component specifications such as Si, Fe, Cu, and Mn than the can body formed of 3104 aluminum alloy (AA3104 alloy), and it is difficult to blend the scrap derived from the can material mixed with 3104 aluminum alloy.

[0006] For example, if the can scrap (UBC: Used Beverage Can) generated in the market is directly blended, since it contains more components of 3104 aluminum alloy due to the weight ratio between the can body and the can lid, it is easy to exceed the upper limit of the components of 5182 aluminum alloy, and it becomes necessary to dilute the components with new ingots.

[0007] Therefore, the aluminum alloy sheet for can lids uses more virgin metal than the aluminum alloy sheet for can bodies and is adjusted to the composition of 5182 aluminum alloy, resulting in a low recycling rate. Therefore, by changing the alloy of the can lid to an alloy with a composition that is easy to blend with 3104 aluminum alloy, the virgin metal usage rate of the can lid can be greatly reduced.

[0008] In Patent Documents 1-5, an aluminum alloy sheet for can lids has been developed that is relatively close to the composition of 3104 aluminum alloy, which is excellent in recyclability.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0010] When the alloy for the can lid is made into a composition close to 3104 aluminum alloy, problems include a decrease in the pressure resistance of the can lid and the toughness of the material. The pressure resistance of the can lid is the internal pressure value when the can lid flips against the pressure inside the can, and it becomes the resistance value when the internal pressure of the can increases unexpectedly due to changes in the external environment.

[0011] In particular, positive pressure cans for beer and carbonated beverages require high pressure resistance. Generally, the higher the strength of the material and the thicker the plate thickness, the higher the pressure resistance. Therefore, a high-strength 5182 aluminum alloy containing a large amount of Mg is used for the lids of positive pressure cans.

[0012] On the other hand, when the conventional 3104 aluminum alloy is used for the can lid, the pressure resistance is significantly reduced, and there is a high risk that the lid will invert and the contents will leak when the internal pressure of the can suddenly increases. Also, if the plate thickness is made too thick to increase the pressure resistance, it will lead to an increase in the lid weight and the lid cost.

[0013] The toughness of the material affects the formability and openability of the lid. If the toughness of the material is low, forming cracks may occur especially in the rivet part of the lid. Also, when the internal pressure of the can suddenly increases, cracks may occur in the score part, increasing the risk of leakage of the can contents.

[0014] However, aluminum alloy sheets for can lids that are relatively close to the composition of the conventional 3104 aluminum alloy do not satisfy either one or both of the above two problems, namely the strength (pressure resistance of the lid) and toughness (formability and openability) of the material.

[0015] One aspect of the present disclosure aims to provide an unpainted aluminum alloy sheet for can lids that can achieve both high strength and high toughness after painting and baking while incorporating scrap raw materials derived from can materials.

Means for Solving the Problems

[0016] One embodiment of the present disclosure is an unpainted aluminum alloy sheet for can lids, wherein 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 the 0.2% proof stress σ 0.2 , the tensile strength σ B , and the average value σ fm of the 0.2% proof stress and the tensile strength satisfy the following formula (1-1). σ fm / (σ 0.2 / σ B )≧380MPa ···(1-1)

[0017] According to such a configuration, while blending scrap raw materials derived from can materials, it is possible to achieve both high strength and high toughness of the aluminum alloy plate after painting and baking. That is, a certain amount of scrap of 3104 aluminum alloy for can bodies can be blended, reducing the new ingot usage rate and CO2 emissions. Furthermore, an aluminum alloy plate for an unpainted can lid that can be used for applications such as positive pressure can lids that require high pressure resistance can be obtained.

[0018] Note that the "aluminum alloy plate for an unpainted can lid" of the present disclosure is an alloy plate (i.e., a bare material) that is used as an aluminum alloy plate for a can lid after undergoing painting. That is, by performing a baking treatment on the "aluminum alloy plate for an unpainted can lid" of the present disclosure, an "aluminum alloy plate for a can lid" can be obtained.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the drawings. [1. First Embodiment] [1-1. Configuration] The aluminum alloy plate for an unpainted can lid of the present disclosure may be continuously painted in the form of a coil at the painting line, or may be cut into sheet form and subjected to painting or lamination treatment to be formed into a lid. The aluminum alloy plate for an unpainted can lid of the present disclosure can be used for any application. Also, the aluminum alloy plate for an unpainted can lid is not limited to beverage can lid applications and can be widely used for food can lid applications and the like.

[0021] <Composition> The aluminum alloy sheet for an unpainted can lid of the present disclosure (hereinafter, also simply referred to as "alloy sheet") contains aluminum (Al), silicon (Si), iron (Fe), copper (Cu), manganese (Mn), and magnesium (Mg).

[0022] The lower limit of the Si content is 0.10% by mass, and 0.20% by mass is preferable. When the Si content is less than 0.10% by mass, the precipitation amount of Si in the processing heat of cold rolling after hot rolling and solution treatment decreases, and the strength of the alloy sheet after painting and baking may be insufficient.

[0023] Also, the average value of the Si component standard of the 3104 aluminum alloy standardized by JIS-H-4000:2014 is 0.30% by mass, and the average value of the Si component standard of the 5182 aluminum alloy standardized by 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 scrap of the 3104 aluminum alloy can be blended.

[0024] The upper limit of the Si content is 0.60% by mass, and 0.40% by mass is preferable. When the Si content exceeds 0.60% by mass, the Mg2Si particles increase, and the toughness of the alloy sheet after painting and baking decreases.

[0025] The lower limit of the Fe content is 0.20% by mass, and 0.30% by mass is preferable. The average value of the Fe component standard of the 3104 aluminum alloy is 0.40% by mass, and the average value of the Fe component standard 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 scrap of the 3104 aluminum alloy can be blended.

[0026] The upper limit of the Fe content is 0.70% by mass. When the Fe content exceeds 0.70% by mass, intermetallic compounds (i.e., secondary phase particles) in the Al-Fe-Mn system or the Al-Fe-Mn-Si system increase. As a result, crack propagation paths are generated, and the toughness of the alloy sheet after painting and baking decreases.

[0027] The lower limit of the Cu content is 0.10% by mass, preferably 0.11% by mass, and more preferably 0.20% by mass. When the Cu content is less than 0.10% by mass, there is insufficient Cu to increase the strength by solid solution or precipitation, and the average strength of the alloy sheet after painting and baking decreases. By precipitating Cu in the cold rolling process after hot rolling and solution treatment, the strength of the alloy sheet after painting and baking increases significantly.

[0028] Also, the average value of the Cu component standard of the 3104 aluminum alloy is 0.15% by mass, and the average value of the Cu component standard of the 5182 aluminum alloy is 0.075% by mass. Therefore, by setting the Cu content to 0.11% by mass or more, more scraps of the 3104 aluminum alloy can be blended.

[0029] The upper limit of the Cu content is 0.40% by mass. When the Cu content exceeds 0.40% by mass, the toughness of the alloy sheet after painting and baking decreases.

[0030] The lower limit of the Mn content is 0.5% by mass, preferably 0.7% by mass, and more preferably 0.8% by mass. When the Mn content is less than 0.5% by mass, there is insufficient Mn to increase the strength by solid solution or precipitation, and the average strength of the alloy sheet after painting and baking decreases.

[0031] Also, the average value of the Mn component standard of the 3104 aluminum alloy is 1.1% by mass, and the average value of the Mn component standard of the 5182 aluminum alloy is 0.35% by mass. Therefore, by setting the Mn content to 0.7% by mass or more, more scraps of the 3104 aluminum alloy can be blended.

[0032] The upper limit of the Mn content is 1.2% by mass, and 1.0% by mass is preferred. When the Mn content exceeds 1.2% by mass, intermetallic compounds (i.e., secondary phase particles) in the Al-Fe-Mn system or the Al-Fe-Mn-Si system increase. As a result, crack propagation paths are generated, and the toughness of the alloy sheet after painting baking decreases.

[0033] The lower limit of the Mg content is 1.1% by mass. When the Mg content is less than 1.1% by mass, there is insufficient Mg to increase the strength by solid solution, and the average strength of the alloy sheet after painting baking decreases. By precipitating Mg during cold rolling after hot rolling and solution treatment, the strength of the alloy sheet after painting baking increases significantly.

[0034] The upper limit of the Mg content is 4.0% by mass, and 3.0% by mass is preferred. The average value of the Mg component standard of the 3104 aluminum alloy is 1.05% by mass, and the average value of the Mg component standard of the 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 reduce the additional blending amount of the Mg-containing raw material while blending a large amount of scrap of the 3104 aluminum alloy.

[0035] The alloy sheet may contain titanium (Ti). The upper limit of the Ti content is preferably 0.10% by mass. By containing Ti, the ingot structure of the alloy sheet is refined. Further, the alloy sheet may contain zinc (Zn). The upper limit of the Zn content is preferably 0.25% by mass. Furthermore, the alloy sheet may contain chromium (Cr). The upper limit of the Cr content is preferably 0.10% by mass.

[0036] The alloy sheet may contain inevitable impurities within a range that does not significantly impair the performance of the alloy sheet. That is, the alloy sheet contains Si, Fe, Cu, Mn, and Mg within the above-mentioned ranges, and the balance consists of aluminum and inevitable impurities. The upper limit of the total amount of inevitable impurities is preferably 0.15% by mass.

[0037] <Material Strength and Pressure Resistance> The 0.2% proof stress σ of the unpainted aluminum alloy sheet of the present disclosure 0.2 , the tensile strength σ B , and the average value σ of the 0.2% proof stress and the tensile strength fm shall satisfy the following formula (1-1). σ fm / (σ 0.2 / σ B ) ≧ 380 MPa ···(1-1)

[0038] The pressure resistance value of the lid made of aluminum alloy has a strong positive correlation with the value V of the following formula (3) expressed empirically by the material strength of the aluminum alloy sheet (that is, the left side of formula (1-1)) and the plate thickness t. V = t 2.27 ×σ fm / (σ 0.2 / σ B ) ···(3)

[0039] Therefore, by the value of the material strength σ fm / (σ 0.2 / σ B ) being 380 MPa or more, it is possible to form a lid having a sufficient pressure resistance value after painting and baking without significantly increasing the plate thickness.

[0040] The lower limit of the left side of formula (1-1) (that is, the value on the right side of formula (1-1)) is more preferably 400 MPa. By setting the material strength σ fm / (σ 0.2 / σ B ) to 400 MPa or more, the pressure resistance value of the lid after painting and baking can be further increased.

[0041] Furthermore, the alloy sheet of the present disclosure preferably has 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 (1-2) after being heat-treated at 270°C for 30 seconds. Thereby, it is possible to form a lid having a sufficient pressure resistance value after painting and baking. σ fm / (σ 0.2 / σ B ) ≧ 350 MPa ···(1-2)

[0042] The lower limit of the left side of formula (1-2) (i.e., the value of the right side of formula (1-2)) is more preferably 380 MPa. The material strength σ after heat treatment fm / (σ 0.2 / σ B ) being 380 MPa or more can further increase the pressure resistance value of the lid.

[0043] The 0.2% proof stress σ 0.2 and the tensile strength σ B in formula (1-1), formula (1-2) and formula (3) are measured by the method specified in JIS-Z-2241:2011. The plate thickness t is measured with, for example, a micro gauge.

[0044] The pressure resistance of the aluminum alloy plate is measured, for example, by the following procedure. A shell formed from the aluminum alloy plate after painting and baking is fixed to a jig, and an internal pressure is applied. The internal pressure is gradually increased, and the internal pressure value when the shell is inverted (i.e., buckled) is taken as the pressure resistance value.

[0045] Specifically, a φ204 Fullform (B64) shape shell mold is used for forming the shell. For measuring the internal pressure value, a buckling & missile measuring machine DV036E from VERSATILE TECHNOLOGY is used. Specifically, after fixing a shell formed with a dedicated jig, the internal pressure is increased by a program, and the internal pressure value when the shell is inverted is read. For example, the internal pressure is increased at a speed of approximately 175 kPa / s, and when it reaches approximately 350 kPa to 400 kPa, the internal pressure is increased at a speed of 10 kPa / s.

[0046] <Toughness> It is known that the toughness of the aluminum alloy plate after painting and baking affects the formability of the lid and the force required for opening the score part (i.e., the opening force).

[0047] (Number of repeated bending times) As one of the evaluation indices for the toughness of an aluminum alloy plate, there is a repeated bending test. If the plate thickness is the same, the more the number of repeated bends, the better the toughness of the aluminum alloy plate. The aluminum alloy plate of the present disclosure can achieve good numbers of repeated bends after painting and baking.

[0048] The repeated bending test is carried out according to the following procedure. For example, a test piece cut into a strip shape with a width of 12.5 mm and a length of 200 mm, which has been heat-treated at 250 °C for 30 seconds assuming painting and baking, is arranged in a direction where the bending ridge line is parallel to the rolling direction of the alloy plate. Both ends of this test piece are fixed with chucks, and a tension is applied with a load of 200 N.

[0049] In this state, starting from the end of the test piece fixed to one immovable chuck, using a bending jig with a bend R of 2.0 mm arranged at a position 150 mm in the longitudinal direction of the test piece as a fulcrum, the other chuck is rotated 90° to the left and right to perform repeated bending, and the number of bends until the test piece breaks is measured.

[0050] The number of bends is counted as one each for the operation of bending 90° to either the left or right and the operation of returning to the original position. If it breaks halfway, the angle Θ (0° - 90°) is read, and the number of repeated bends N is calculated by the following formula (3). In formula (4), N0 is the total number of times the operation of bending 90° to either the left or right and the operation of returning from the 90° bent position to the original 0° position are performed until the test piece breaks. N = N0 + Θ / 90 ···(4)

[0051] Since the repeated bending evaluation is more disadvantageous as the plate thickness increases, it is necessary to correct and consider it with a reference plate thickness. Therefore, the number of repeated bends N standardized by the following formula (5) is obtained with a reference plate thickness of 0.245 mm. s t (mm) is the plate thickness of the test piece. N s = N × t / 0.245 ···(5)

[0052] (Second-phase particles) Toughness is affected by the distribution of second-phase particles. That is, the higher the density of second-phase particles, the lower the toughness. In particular, when the contents of Mg and Si are high, Mg2Si particles are likely to be formed. As a result, the Mg2Si particles serve as crack initiation points and propagation paths, affecting the reduction of toughness.

[0053] The uncoated aluminum alloy plate of the present disclosure has a total area ratio of Mg2Si particles with an area of 0.3 μm or more of 1.0% or less on the plate surface (L-LT surface) after heat treatment at 270 °C for 30 seconds. 2 It is preferably 1.0% or less.

[0054] The area ratio of Mg2Si particles can be measured by the following method. Of the surface of the measurement sample, the surface to be measured (that is, the L-LT surface) is mechanically polished to a mirror finish. The depth of polishing is about 1% of the plate thickness of the measurement sample.

[0055] Next, the polished surface (that is, the L-ST cross section) is observed using an 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 (a total of 0.49 mm for 10 fields of view 2 ) and photographed to obtain a COMPO (backscattered electron composition) image. When the magnification of the SEM is 1000 times, the range of one field of view is 0.012 mm 2 (a total of 0.12 mm for 10 fields of view 2 ) and photographed to obtain a COMPO (backscattered electron composition) image.

[0056] The photographed COMPO image is analyzed using image analysis software ImageJ. Specifically, the most frequent value of the brightness of the image in 256 gradations is used as the background brightness, and particles with a brightness lower than the value obtained by subtracting 30 from the brightness of the most frequent value are determined as Mg2Si particles.

[0057] Of the determined Mg2Si particles, the total area of particles having an area of 0.3 μm 2 or more is calculated and divided by the photographed area for 10 fields of view (that is, the total photographed area), whereby the area ratio of Mg2Si particles with an area of 0.3 μm 2The ratio of the total area on the L-LT plane of the above Mg2Si particles is calculated.

[0058] (Earing Ratio) The repeating bending times also affect the texture, and the higher the degree of aggregation of the cube orientation, the better. The degree of aggregation of the cube orientation is represented by the ear shape of the Erichsen cup 1 formed from an aluminum alloy sheet by the Erichsen test shown in FIGS. 1A and 1B.

[0059] Specifically, the higher the relative side wall height H in the 0° / 180° direction with respect to the side wall height H in the 45° direction (i.e., the ear height) of the aluminum alloy sheet of the Erichsen cup 1, the higher the degree of aggregation of the cube orientation is suggested. That is, the aluminum alloy sheet of the present disclosure includes those having a relatively large degree of aggregation of the cube orientation and a high side wall height H in the 0° / 180° direction.

[0060] The relative side wall height in the 0° / 180° direction with respect to the side wall height in the 45° direction can be evaluated by an index called the earing ratio (Earing Balance). Hereinafter, the measurement procedure of the earing ratio will be described.

[0061] The earing ratio is represented by the left side of the following formula (2). (h 0p -h 45p ) / h v ×100≧-7.0 ···(2)

[0062] In formula (2), h 0p is the average value of the maximum values of the side wall 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.

[0063] h 45pis the average value of the maximum values of the side wall heights in the third region A3 around 45° with respect to the rolling direction, the fourth region A4 around 135°, the fifth region A5 around 225°, and the sixth region A6 around 315° respectively.

[0064] 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.

[0065] h v is the average value of the minimum values of the side wall heights in the seventh region A7 from 0° to 45° with respect to the rolling direction, 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° respectively.

[0066] Figure 2 is a graph showing an example of the measurement results of the side wall height of the Erichsen cup. The angles shown in Figure 2 are angles with respect to the rolling direction. Also, the distance from the center of the graph indicates the side wall height.

[0067] a - d in the figure are the maximum values in the third region A3 to the sixth region A6 respectively. e, f are the maximum values in the first region A1 and the second region A2 respectively. g - l are the minimum values in the seventh region A7 to the twelfth region A12 respectively.

[0068] 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 side wall height of the Erichsen cup is measured, for example, using Roncorder EC1550 - H manufactured by Kosaka Laboratory Ltd.

[0069] Specifically, with the rolling direction as the reference (0° / 180°), measurement terminals are placed at the opening of the Erichsen cup, the table on which the Erichsen cup is placed is rotated one full circle, and the opening height in the circumferential direction of 360° is measured.

[0070] In an Erichsen cup formed by Erichsen test after heat treatment at 250°C for 30 seconds, when formula (2) is satisfied, that is, when the ear ratio is -7.0% or more, the degree of aggregation in the cube orientation becomes high. As a result, the number of repeated bending times of the alloy plate can be increased.

[0071] Regarding the properties such as the strength, pressure resistance, number of repeated bending times, area ratio of the second-phase particles, and ear ratio described above, the values of the aluminum alloy plate after painting and baking are important. Therefore, when measuring these, a heat treatment simulating painting and baking at, for example, 230°C to 280°C within 30 seconds is performed on the aluminum alloy plate of the present disclosure, and then the measurement is performed by the method described above. Here, the heat treatment of "270°C - 30 seconds" means heat treatment with a heating curve in which the actual temperature reaches 220°C or more at the 15-second point from the start of heat treatment and reaches 270 ± 5°C at the 30-second point. Also, the heat treatment of "250°C - 30 seconds" means heat treatment with a heating curve in which the actual temperature reaches 200°C or more at the 15-second point from the start of heat treatment and reaches 250 ± 5°C at the 30-second point. As the device to be used, for example, a large drawer-type dryer manufactured by Tokojyo Netsugaku Co., Ltd. is used.

[0072] <Manufacturing method of aluminum alloy plate> The unpainted aluminum alloy plate of the present disclosure can be manufactured, for example, as follows. First, an aluminum alloy having the composition of the unpainted aluminum alloy plate of the present disclosure is used to produce an ingot by using a semi-continuous casting method (that is, DC casting) according to a conventional method.

[0073] Next, the surface of the ingot is faced. After that, the ingot is put into a soaking furnace and homogenization treatment is performed. The temperature in the homogenization treatment is preferably, for example, 470°C or more and 620°C or less. The time of the homogenization treatment is preferably, for example, 1 hour or more and 20 hours or less.

[0074] When the temperature in the homogenization treatment is 400 °C or higher, it is easy to eliminate the segregation of the ingot structure. Furthermore, when the temperature in the homogenization treatment is 450 °C or higher, Mg2Si particles can be redissolved, and the strength and toughness of the alloy plate can be improved. Furthermore, when the temperature in the homogenization treatment is 490 °C or higher, more preferably 550 °C or higher, the redissolution of Mg2Si particles is promoted, and the strength and toughness of the alloy plate can be further improved. On the other hand, when the temperature in the homogenization treatment is 620 °C or lower, local melting of the aluminum alloy hardly occurs.

[0075] When the homogenization treatment time is 1 hour or longer, the temperature of the entire slab becomes uniform, the segregation of the ingot structure is also easily eliminated, and the Mg2Si particles are easily redissolved. The longer the homogenization treatment time, the more the Mg2Si particles can be redissolved. However, when the homogenization treatment time exceeds 20 hours, the effect of the homogenization treatment saturates.

[0076] After the homogenization treatment, the ingot is subjected to hot rolling. The hot rolling process has a rough rolling process and a finish rolling process. In the rough rolling process, the ingot is processed into a plate material with a thickness of about several tens of mm by reverse rolling. In the finish rolling process, for example, by tandem rolling or the like, the thickness of the plate material is reduced to about several mm, and a hot-rolled coil in which the plate material is wound into a coil shape is formed.

[0077] When the total reduction ratio of the finish rolling is high, a recrystallized structure is formed after winding, and the degree of aggregation of the cube orientation can be increased. When the winding temperature of the finish rolling is high, a recrystallized structure is formed after winding, and the degree of aggregation of the cube orientation can be increased.

[0078] In addition, a high-strength alloy plate can be obtained by solution treatment of the hot-rolled coil and redissolving Mg and the like. For example, by using a continuous annealing furnace to perform heat treatment (i.e., annealing) at a target solid temperature of 440 °C or higher for 30 seconds or longer, and then performing forced cooling by air cooling or the like, it is possible to effectively increase the strength of the alloy plate.

[0079] Subsequent to hot rolling, cold rolling of the sheet material is performed. In cold rolling, the hot-rolled coil is rolled until the product sheet thickness is reached. Cold rolling may be either single rolling or tandem rolling. In cold rolling by single rolling, it is preferable to perform rolling in a plurality of passes of two or more passes.

[0080] By setting the outgoing temperature of cold rolling in the intermediate passes other than the final pass to 120°C or higher, Si, Cu, and Mg are finely precipitated and age-hardened, so that the strength of the alloy sheet can be increased. Furthermore, by setting the outgoing temperature to 130°C or higher, the strength of the alloy sheet can be further increased.

[0081] The cold rolling reduction rate (i.e., the total reduction rate aimed for) is preferably 80% or more. When the cold rolling reduction rate is 80% or more, the strength of the alloy sheet can be increased. The lower the cold rolling reduction rate, the more the cube orientation remains. The cold rolling reduction rate is preferably 92% or less.

[0082] The cold rolling reduction rate R (%) is obtained by the following formula (6) using the plate thickness t0 (mm) of the hot-rolled sheet and the product sheet thickness t1 (mm) after cold rolling. R = (t0 - t1) / t0 × 100 ···(6)

[0083] The product sheet thickness can be appropriately selected so as to obtain a desired pressure resistance. As shown in the above formula (3), the pressure resistance improves as the plate thickness increases. The product sheet thickness is t after heat treatment at 270°C for 30 seconds. 2.27 ×σ fm / (σ 0.2 / σ B ) ≧ 14, and it is preferable to select within this range. As described above, according to the uncoated aluminum alloy sheet of the present disclosure, an increase in the plate thickness for maintaining high pressure resistance can be suppressed.

[0084] Also, as long as the uncoated aluminum alloy sheet of the present disclosure exhibits its effects, in the manufacturing method of the above-described aluminum alloy sheet, for example, annealing may be performed before and after cold rolling or between passes.

[0085] For the coil cold-rolled to the product plate thickness, degreasing, cleaning, and chemical conversion treatment on the surface may be performed on a painting line or the like. Through the above treatments, an unpainted aluminum alloy plate can be obtained. After the paint is further applied to the coil of the unpainted aluminum alloy plate, it is subjected to a paint baking treatment to obtain a painted aluminum alloy plate.

[0086] In the chemical conversion treatment, chemical solutions such as chromate-based and zirconium-based are used. For the paint, epoxy-based, polyester-based, etc. are used. These can be selected according to the application. In the paint baking treatment, it is heated at the peak metal temperature (PMT) of the coil at 220 °C or higher and 270 °C or lower for approximately 30 seconds or less. At this time, the lower the PMT, the more the recovery of the material is suppressed, and the strength of the alloy plate can be maintained high.

[0087] [1-2. Effect] According to the embodiments described in detail above, the following effects can be obtained. (1a) While blending scrap raw materials derived from can materials, it is possible to achieve both high strength and high toughness of the aluminum alloy plate after paint baking. That is, a certain amount of scrap of 3104 aluminum alloy for can bodies can be blended, reducing the new metal usage rate and CO2 emissions. Furthermore, an unpainted aluminum alloy plate for positive pressure can lids that can be used for applications requiring high pressure resistance can be obtained.

[0088] [2. Other Embodiments] As described above, the embodiments of the present disclosure have been explained, but it goes without saying that the present disclosure is not limited to the above embodiments and can take various forms.

[0089] (2a) The present disclosure includes, in addition to the unpainted aluminum alloy plate of the above embodiments, various forms such as members composed of this unpainted aluminum alloy plate and manufacturing methods of this unpainted aluminum alloy plate.

[0090] (2b) The functions of one component in the above embodiment may be distributed among a plurality of components, or the functions of a plurality of components may be integrated into one component. Also, a part of the configuration of the above embodiment may be omitted. Further, at least a part of the configuration of the above embodiment may be added to, replaced with, etc., the configuration of other above embodiments. Note that all aspects included in the technical idea specified from the language described in the claims are embodiments of the present disclosure.

[0091] [3. Examples] The content of the tests conducted to confirm the effects of the present disclosure and their evaluations will be described below.

[0092] <Manufacture of Unpainted Aluminum Alloy Sheets> As examples and comparative examples, unpainted aluminum alloy sheets of S1 - S10 shown in Tables 1 and 2 were manufactured. The specific manufacturing procedures will be described below.

[0093] First, ingots containing the components (mass %) of alloy numbers 1 - 9 shown in Table 3, with the balance being aluminum and inevitable impurities, were manufactured by the semi - continuous casting method. The ingots contain 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.

[0094] Next, the four sides of the ingot were face - planed. Then, the ingot was put into a furnace and homogenization treatment was performed. The temperature of the homogenization treatment is as shown in Table 1. After the homogenization treatment, the ingot was taken out of the furnace and hot rolling was immediately started to obtain a rolled plate.

[0095] Annealing was performed on the obtained rolled plate. The annealing temperature was as shown in Table 1, and the time was 30 seconds. After annealing, the rolled plate was air-cooled to room temperature. After cooling, cold rolling was performed on the rolled plate. The target total reduction ratio in cold rolling was as shown in Table 1. Note that the product plate thickness after cold rolling (i.e., t1 in Equation (6)) was in the range of approximately 0.245 ± 0.01 mm. During cold rolling and after the final cold rolling, the temperature rises shown in Table 1 were applied. The uncoated aluminum alloy plates of S1 - S10 were obtained by the above-described treatment.

[0096]

Table 1

[0097]

Table 2

[0098]

Table 3

[0099] <Evaluation of Uncoated Aluminum Alloy Plate> (Tensile Properties) Regarding the uncoated aluminum alloy plates of S1 - S10, 5 - type test pieces defined in JIS - Z - 2241:2011 were prepared from the aluminum alloy plates after heat treatment at 270°C or 250°C for 30 seconds, which is the heat treatment assuming the paint baking described in the embodiment, and the aluminum alloy plates before this heat treatment. This test piece extends in the direction forming an angle of 0° with respect to the rolling direction. For this test piece, a tensile test was conducted in accordance with JIS - Z - 2241:2011, and the 0.2% proof stress and tensile strength were measured. The 0.2% proof stress σ 0.2 and the tensile strength σ B measurement results, and the average value σ fm of the 0.2% proof stress and tensile strength are shown in Table 1 and Table 2.

[0100] In the uncoated aluminum alloy plates of S1 - S10, the plate thickness was measured with a micro gauge, and the value V (= t 2.27 × σ fm / (σ 0.2 / σ B )) of the above formula (3) after heat treatment was calculated. The calculation results of the value V and the value of σ fm / (σ 0.2 / σ B ) are shown in Table 2.

[0101] (Toughness) In the uncoated aluminum alloy plates of S1 - S10, by the measurement method described in the embodiment, after heat treatment at 270 °C for 30 seconds as described in the embodiment, the ratio (area ratio) of the total area on the L - LT plane of Mg2Si particles with an area of 0.3 μm 2 or more was calculated. The measurement results are shown in Table 2.

[0102] In the uncoated aluminum alloy plates of S1 - S10, the ear rate after heat treatment at 250 °C for 30 seconds was calculated from the measurement method and the left side of formula (2) described in the embodiment. The results are shown in Table 2. Note that "-" in the table indicates unmeasured.

[0103] In the uncoated aluminum alloy plates of S1 - S10, the number of repeated bending times after heat treatment at 250 °C for 30 seconds was measured from the measurement method and formulas (4) and (5) described in the embodiment, and the normalized number of repeated bending times was calculated. The results are shown in Table 2. Note that "-" in the table indicates unmeasured.

[0104] (Scrap blending ratio) Regarding the composition of the uncoated aluminum alloy plates of S1 - S10, it was determined whether the possible blending ratio of 3104 aluminum alloy scrap is 50 mass% or more. The results are shown in Table 2.

[0105] In Table 2, the uncoated aluminum alloy plates marked as "≧ 50" can be blended with 3104 aluminum alloy at 50 mass% or more. The possible blending ratio of 3104 aluminum alloy scrap is determined based on Table 4.

[0106] Table 4 shows the correspondence between the blending ratio of 3104 aluminum alloy and 5182 aluminum alloy and the average value of the component specifications. The first row of Table 4 is the average value of the component specifications of 3104 aluminum alloy, and the second row is the average value of the component specifications of 5182 aluminum alloy.

[0107] For example, when the blending ratio of 3104 aluminum alloy is 50% by mass, the average value of Si is 0.20% by mass, the average value of Fe is 0.29% by mass, the average value of Cu is 0.11% by mass, the average value of Mn is 0.7% by mass, and the average value of Mg is 2.8% by mass.

[0108] Therefore, when the ratio of each component of the unpainted aluminum alloy sheet is equal to or greater than the above numerical values of Si, Fe, Cu, Mn, and Mg, the possible blending ratio of the 3104 aluminum alloy sheet is 50% by mass or more. The greater the blending ratio of the 3104 aluminum alloy, the higher the contents of Si, Fe, Cu, and Mn, and the lower the content of Mg. The unpainted aluminum alloy sheets of S1 and S9 - S10 can be blended with 50% by mass or more of the scrap of 3104 aluminum alloy.

[0109]

Table 4

[0110] (Pressure resistance) In the unpainted aluminum alloy sheets of S1 - S10, the pressure resistance after heat treatment at 270°C for 30 seconds was measured by the measurement method described in the embodiment. The results are shown in Table 2. The unpainted aluminum alloy sheets of S1 and S9 - S10 showed a high pressure resistance of 550 kPa or more after heat treatment.

[0111] The value V of formula (3) (= t 2.27 × σ fm / (σ 0.2 / σ B) and the pressure resistance of the alloy plate is shown in Fig. 3. From Fig. 3, it was confirmed that there is a high correlation between the value V and the pressure resistance. Therefore, if the value of σ on the left side of Equation (1-1) fm / (σ 0.2 / σ B ) is 350 MPa or more, it is possible to have a high pressure resistance of 550 kPa or more without accompanying a large increase in plate thickness.

[0112] The unpainted aluminum alloy plate of S1 with a high homogenization treatment temperature showed extremely high pressure resistance. In addition, since the annealing temperature after hot rolling of the unpainted aluminum alloy plate of S1 was also high, high strength and pressure resistance were obtained even with a small Mg content.

[0113] For the unpainted aluminum alloys of S1 and S10, the area ratio of Mg2Si particles after heat treatment was small, 1.0% or less. The unpainted aluminum alloy plate of S10 with a high homogenization treatment temperature had a smaller area ratio of Mg2Si particles after heat treatment than the unpainted aluminum alloy plate of S9.

[0114] Therefore, when comparing the unpainted aluminum alloy plate of S9 and the unpainted aluminum alloy plate of S10, although the pressure resistance of the aluminum alloy of S10 was nearly 25 kPa higher than that of the aluminum alloy plate of S9, the number of repeated bending times was the same.

Explanation of symbols

[0115] 1… Erichsen cup.

Claims

1. The aluminum alloy sheet for an uncoated can lid has a silicon (Si) content of 0.10 mass% or more and 0.60 mass% or less, an iron (Fe) content of 0.20 mass% or more and 0.70 mass% or less, a copper (Cu) content of 0.10 mass% or more and 0.40 mass% or less, a manganese (Mn) content of 0.5 mass% or more and 1.2 mass% or less, and a magnesium (Mg) content of 1.1 mass% or more and 4.0 mass% or less. 0.2% proof stress σ ０．２ , 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. An aluminum alloy sheet for an uncoated can lid according to Claim 1, 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 An aluminum alloy sheet for an unpainted can lid, wherein the following formula (1-2) is satisfied. 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, On the plate surface after heat treatment at 270°C for 30 seconds, the ratio of the total area of Mg ２ Si particles with an area of 0.3 μm ２ or more is 1.0% or less, an aluminum alloy sheet for an unpainted can lid.

4. An aluminum alloy sheet for an uncoated can lid according to Claim 1 or Claim 2, After heat treatment at 250°C for 30 seconds, the average value h of the maximum value of the side wall height in the circumferential direction of an Erichsen cup formed by an Erichsen test, in the regions around 0° and 180° with respect to the rolling direction respectively ０ｐ and the average value h of the maximum value of the side wall height in the regions around 45°, 135°, 225°, and 315° with respect to the rolling direction respectively ４５ｐ and the average value h of the minimum value of the side wall height in the regions from 0° to 45°, 45° to 135°, 135° to 180°, 180° to 225°, 225° to 315°, and 315° to 360° with respect to the rolling direction respectively ｖ satisfy the following formula (2), an aluminum alloy sheet for an unpainted can lid. (h ０ｐ -h ４５ｐ ) / h ｖ × 100 ≥ -7.0...(2)

5. An aluminum alloy sheet for an uncoated can lid according to Claim 1 or Claim 2, wherein the Si content is 0.20 mass% or more and 0.60 mass% or less, the Fe content is 0.30 mass% or more and 0.70 mass% or less, the Cu content is 0.11 mass% or more and 0.40 mass% or less, the Mn content is 0.7 mass% or more and 1.2 mass% or less, and the Mg content is 1.1 mass% or more and 3.0 mass% or less: an aluminum alloy sheet for an uncoated can lid.

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