EP4610388A1

EP4610388A1 - Method for manufacturing aluminum alloy sheet for can lid

Info

Publication number: EP4610388A1
Application number: EP24792659.5A
Authority: EP
Inventors: Tomoyuki Kudo; Tomotaro EZAKI; Yusuke Sato; Daichi TAKAI
Original assignee: UACJ Corp
Current assignee: UACJ Corp
Priority date: 2023-04-17
Filing date: 2024-04-16
Publication date: 2025-09-03
Also published as: WO2024219385A1; US20260002243A1; EP4610388A4; JP7420994B1; JP2024153332A; CN119895070A

Abstract

One aspect of the present disclosure is a method of manufacturing an aluminum alloy sheet for a can lid. The method includes a process of casting an ingot that includes an Si content of 0.20 mass% or more and 0.47 mass% or less, an Fe content of 0.30 mass% or more and 0.59 mass% or less, a Cu content of 0.11 mass% or more and 0.40 mass% or less, an Mn content of 0.70 mass% or more and 0.98 mass% or less, and an Mg content of 1.3 mass% or more and 3.7 mass% or less; a process of homogenizing treatment on the ingot; and a process of rolling the ingot. In the process of rolling, cold rolling is completed without performing heat treatment after performing hot rolling on the ingot.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This international application claims the benefit of Japanese Patent Application No. 2023-067151 filed on April 17, 2023 with the Japan Patent Office, the entire disclosure of Japanese Patent Application No. 2023-067151 is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method of manufacturing an aluminum alloy sheet for a can lid.

BACKGROUND ART

In recent years, increasing environmental awareness calls for an aluminum alloy sheet that produces low CO₂ emissions in its manufacturing process. In the manufacturing process of aluminum, a major and indirect cause of CO₂ emissions is to blend primary aluminum in casting process.
Manufacturing the primary aluminum consumes a large amount of electricity in refining process, which leads to a large amount of CO₂ emissions. Thus, a reduction of a blending amount of the primary aluminum and an increase in closed recycling rate will lead to a reduction of CO₂ emissions in manufacturing the aluminum alloy sheet.
In general, it is said that CO₂ emissions can be reduced to about one-thirtieth in a case where aluminum scraps are re-melted for casting compared with a case where the primary aluminum is manufactured. In particular, since the amount of production of aluminum alloy sheets for beverage cans used around the world is very large, a further improvement in its closed recycling rate is significantly meaningful in the reduction of environmental impact.
Among those beverage cans, a can lid made of 5182 aluminum alloy (AA5182 alloy) has low upper limits on compositional standard of Si, Fe, Cu, Mn, and the like compared with a can body made of 3104 aluminum alloy (AA3104 alloy). Thus, it is difficult to blend scraps of can materials containing 3104 aluminum alloy with such a can lid.
For example, if can scraps (UBC: Used Beverage Can) gathered in a city are blended as they are, the resultant contains more compositions of the 3104 aluminum alloy than compositions of the 5182 aluminum alloy due to the weight ratio between can bodies and can lids, and thus the compositional upper limits of the 5182 aluminum alloy are easily exceeded. As a result, it becomes necessary to dilute the resultant composition with primary metal.
Thus, compared with an aluminum alloy sheet for a can body, an aluminum alloy sheet for a can lid is prepared by using a large amount of primary metal to adjust to the compositions of the 5182 aluminum alloy, which makes its recycling rate low. Accordingly, a usage rate of the primary metal for can lids can be significantly reduced by changing the alloy for can lids to an alloy including compositions that can be easily blended with the 3104 aluminum alloy.
Patent Documents 1 to 5 disclose aluminum alloy sheets for a can lid that include compositions relatively close to that of the 3104 aluminum alloy, which is excellent in recyclability.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-73106
Patent Document 2: Japanese Unexamined Patent Application Publication No. H9-070925
Patent Document 3: Japanese Unexamined Patent Application Publication No. H11-269594
Patent Document 4: Japanese Unexamined Patent Application Publication No. 2000-160273
Patent Document 5: Japanese Unexamined Patent Application Publication No. 2016-160511

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

Declines in a buckling pressure resistance of a can lid and in toughness of its material are raised as problems when making the alloy for can lids include compositions close to the compositions of a 3104 aluminum alloy. The buckling pressure resistance of the can lid is an internal pressure value when the can lid is reversely deformed against a pressure inside the can, and also is a resistance value when the internal pressure of the can accidentally increases due to a change in the external environment.
Particularly, positive pressure cans used for beer and carbonated beverages require a high buckling pressure resistance. In general, the buckling pressure resistance increases as the strength of the material increases and as a sheet thickness increases. Thus, a high-strength 5182 aluminum alloy containing a large amount of Mg is used for lids of the positive pressure cans.
In contrast, if the conventional 3104 aluminum alloy is used for the can lid, the buckling pressure resistance is largely reduced, which increases a risk of the lid being reversely deformed to cause the content to leak when the internal pressure of the can is unexpectedly increased. Also, if the sheet thickness is increased to increase the buckling pressure resistance, the weight of the lid and the cost of the lid are increased.
Furthermore, toughness of the material affects formability and openability of the lid. If the toughness of the material is low, a crack may occur particularly in a countersink part or a rivet part of the lid in forming them. In addition, a crack may occur in a score part when the internal pressure of the can is unexpectedly increased, which may increase a risk of a leakage of the content in the can. These cracks occur particularly in a rolling direction. Thus, toughness against a tensile stress and a bending stress in a direction perpendicular to the rolling direction is required.
However, the aluminum alloy sheets for a can lid that include compositions relatively close to that of the conventional 3104 aluminum alloy do not solve either one or both of the aforementioned two problems. In other words, they do not satisfy either one or both of the strength of the material (that is, the buckling pressure resistance of the lid) and the toughness of the material (that is, formability and openability).
To solve these problems, there is a possibility of achieving both high strength and high toughness by, for example, performing a solution heat treatment by using a continuous annealing furnace or the like after hot rolling or in the middle of cold rolling. However, materials for can lids are required to be produced in large quantities and at low cost, and at the same time, it is required to reduce energy consumption for manufacturing as much as possible in light of the environmental impact. Thus, it is preferable that intermediate heat treatment is omitted from the manufacturing process.
In one aspect of the present disclosure, it is desirable to provide a method of manufacturing an aluminum alloy sheet for a can lid that can achieve both high strength and high toughness while containing scrap materials derived from can materials without performing an intermediate heat treatment after hot rolling.

MEANS FOR SOLVING THE PROBLEMS

One mode of the present disclosure is a method of manufacturing an aluminum alloy sheet for a can lid. The method includes a process of casting an ingot. The ingot includes a silicon content of 0.20 mass% or more and 0.47 mass% or less; an iron content of 0.30 mass% or more and 0.59 mass% or less; a copper content of 0.11 mass% or more and 0.40 mass% or less; a manganese content of 0.70 mass% or more and 0.98 mass% or less; a magnesium content of 1.3 mass% or more and 3.7 mass% or less; and a balance consisting of or including aluminum and inevitable impurities. The method also includes a process of homogenizing treatment on the ingot, and a process of rolling the homogenized ingot. In the process of rolling, cold rolling is completed without performing heat treatment after performing hot rolling on the ingot.
According to such a configuration, the aluminum alloy sheet can achieve both high strength and high toughness while containing scrap materials derived from can materials without undergoing heat treatment after the hot rolling. In other words, it is possible to blend a certain amount of scraps of the 3104 aluminum alloy for a can body into the aluminum alloy sheet and to reduce a usage rate of primary metal and CO₂ emissions. Moreover, it is also possible to obtain an aluminum alloy sheet for a can lid that can be used for a can lid of a positive pressure can that requires a high buckling pressure resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a cyclic bending test.
FIG. 2 is a flowchart of a method of manufacturing an aluminum alloy sheet of the present embodiment.
FIG. 3 is a graph showing a relationship between S_min and standardized number of cyclic bendings in examples.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment to which the present disclosure is applied will be described with reference to the drawings.

[1. First Embodiment]

[1-1. Configuration]

An aluminum alloy sheet for a can lid according to the present disclosure (hereinafter also simply referred to as "alloy sheet") includes aluminum (Al), silicon (Si), iron (Fe), copper (Cu), manganese (Mn), and magnesium (Mg).
The lower limit of the Si content is 0.20 mass%. The average value of compositional standard of Si in a 3104 aluminum alloy specified in JIS-H-4000:2014 is 0.30 mass%. The average value of compositional standard of Si in a 5182 aluminum alloy specified in JIS-H-4000:2014 is 0.10 mass%. Thus, by arranging the Si content to be 0.20 mass% or more, a large amount of scraps of the 3104 aluminum alloy can be blended.
The upper limit of the Si content is 0.47 mass%, and preferably 0.30 mass%. If the Si content exceeds 0.47 mass%, the difference between a solid solutionizing temperature of Mg₂Si and a solidus temperature of an aluminum matrix becomes small, which makes it difficult to have a great deal of Mg₂Si existing in an ingot of the aluminum alloy formed into a solid solution in a homogenizing treatment process. Also, a coarse Mg₂Si newly precipitates in a hot rolling. As a result, strength and toughness are decreased.
Meanwhile, by arranging the Si content to be 0.30 mass% or less, Mg₂Si can be relatively easily formed into a solid solution in the homogenizing treatment process. Furthermore, precipitation of a coarse Mg₂Si in the hot rolling is inhibited, and thus more excellent strength and toughness can be obtained without performing heat treatment after the hot rolling.
The lower limit of the Fe content is 0.30 mass%. The average value of compositional standard of Fe in the 3104 aluminum alloy is 0.40 mass%. The average value of compositional standard of Fe in the 5182 aluminum alloy is 0.18 mass%. Thus, by arranging the Fe content to be 0.30 mass% or more, a large amount of the scraps of the 3104 aluminum alloy can be blended.
The upper limit of the Fe content is 0.59 mass%, and preferably 0.55 mass%. If the Fe content exceeds 0.59 mass%, unusually coarse Al-Fe-Mn-based or Al-Fe-Mn-Si-based intermetallic compound (in other words, giant compound) increases. As a result, a crack propagation path is generated and the toughness of the alloy sheet is decreased. Meanwhile, by arranging the Fe content to be 0.55 mass% or less, crystallization of the aforementioned coarse intermetallic compound can be reduced when the amount of Mg addition to supplement the strength and toughness is increased.
The lower limit of the Cu content is 0.11 mass%, preferably 0.17 mass%, and more preferably 0.20 mass%. If the Cu content is less than 0.11 mass%, due to a lack of Cu, which increases the strength of the alloy sheet by forming a solid solution or precipitation, the strength of the alloy sheet decreases. The average value of compositional standard of Cu in the 3104 aluminum alloy is 0.15 mass%. The average value of compositional standard of Cu in the 5182 aluminum alloy is 0.075 mass%. Thus, by arranging the Cu content to be 0.11 mass% or more, a large amount of scraps of the 3104 aluminum alloy can be blended.
The upper limit of the Cu content is 0.40 mass%, and preferably 0.25 mass%. If the Cu content exceeds 0.40 mass%, coarse precipitates increase which decreases the toughness of the alloy sheet. By arranging the Cu content to be 0.25 mass% or less, the strength of the alloy sheet can be increased without having its toughness largely impaired.
The lower limit of the Mn content is 0.7 mass%. If the Mn content is less than 0.7 mass%, due to a lack of Mn, which increases the strength of the alloy sheet by forming a solid solution or precipitation, the average strength of the alloy sheet decreases. The average value of compositional standard of Mn in the 3104 aluminum alloy is 1.1 mass%. The average value of compositional standard of Mn in the 5182 aluminum alloy is 0.35 mass%. Thus, by arranging the Mn content to be 0.7 mass% or more, a large amount of the scraps of the 3104 aluminum alloy can be blended.
The upper limit of the Mn content is 0.98 mass%. If the Mn content exceeds 0.98 mass%, unusually coarse Al-Fe-Mn-based or Al-Fe-Mn-Si-based intermetallic compound increases. As a result, a crack propagation path is generated and the toughness of the alloy sheet is decreased.
The lower limit of the Mg content is 1.3 mass%, and preferably 2.6 mass%. If the Mg content is less than 1.3 mass%, due to a lack of Mg, which increases the strength of the alloy sheet by forming a solid solution, the average strength of the alloy sheet decreases. By arranging the Mg content to be 2.6 mass% or more, more excellent strength and toughness can be obtained without performing heat treatment after the hot rolling.
The upper limit of the Mg content is 3.7 mass%. If the Mg content exceeds 3.7 mass%, the solidus temperature of the aluminum matrix decreases and the solid solutionizing temperature of Mg₂Si increases. Thus, it becomes difficult to have Mg₂Si existing in the ingot formed into a solid solution in the homogenizing treatment process. Furthermore, due to a decrease in the solidus temperature of the aluminum matrix, coarse Al-Fe-Mn-based or Al-Fe-Mn-Si-based intermetallic compounds increase. Accordingly, the strength and toughness are impaired.
The alloy sheet may contain titanium (Ti). The upper limit of the Ti content is preferably 0.10 mass%. An ingot structure of the alloy sheet is micronized by containing Ti. The alloy sheet may also contain zinc (Zn). The upper limit of the Zn content is preferably 0.25 mass%. The alloy sheet may also contain chromium (Cr). The upper limit of the Cr content is preferably 0.10 mass%.
The alloy sheet may contain inevitable impurities to the extent that the performance of the alloy sheet is not significantly impaired. In other words, the alloy sheet contains Si, Fe, Cu, Mn, and Mg to the extent described above, and the balance consists of or includes aluminum and inevitable impurities. The upper limit of the total amount of the inevitable impurities is preferably 0.15 mass%. The balance may contain a substance other than aluminum and the inevitable impurities.

It is known by experience that a buckling pressure resistance value of a lid made of the aluminum alloy sheet has a strong positive correlation with a value V of the following formula (1) obtained from a 0.2% yield strength σ_0.2 and a tensile strength σ_B, which are material strength of the aluminum alloy sheet, an average value σ_fm of the 0.2% yield strength and the tensile strength, and a sheet thickness t (see p 185 to 195 of Sumitomo Light Metal Industries technical report Vol. 54, First Issue, 2013). $V = t^{2.27} \times σ_{fm} / (σ_{0.2} / σ_{B})$
Thus, buckling pressure resistance of a lid made of the aluminum alloy sheet improves as the sheet thickness increases. Since the aluminum alloy sheet of the present disclosure has a high material strength, it is possible to inhibit an increase in the sheet thickness to improve the buckling pressure resistance.
The larger the S calculated through the following formula (2) is, the more the buckling pressure resistance of the lid increases. Particularly, considering anisotropy of the material, among three Ss obtained from the results of tensile tests in 0° direction, 45° direction, and 90° direction with respect to a rolling direction, it is preferable that S_min, which is the minimum value, is large. $S = σ_{fm} / (σ_{0.2} / σ_{B})$
S_min is preferably 330 MPa or more, and more preferably 350 MPa or more. By having S_min be such values, it is possible to form a lid having a sufficient buckling pressure resistance value without largely increasing the sheet thickness.
The 0.2% yield strength σ_0.2 and the tensile strength σ_B in the formulas (1) and (2) are measured through a method specified in JIS-Z-2241:2011. The sheet thickness t is measured by using a microgauge, for example.

It is known that the toughness of the aluminum alloy sheet affects the formability of the lid and a force (that is, an opening force) required to open a score part.

(Number of Cyclic Bendings)

A cyclic bending test is one of evaluation indicators of the toughness of the aluminum alloy sheet. If the sheet thickness is the same, the more the cyclic bendings are performed, the more excellent in toughness the aluminum alloy sheet is. Particularly, a crack in the rolling direction becomes a problem in the aluminum alloy sheet. Thus, the number of the cyclic bendings in a case where the rolling direction is parallel to a direction of a bending ridge line is important. The aluminum alloy sheet of the present disclosure can achieve the number of the cyclic bendings that is satisfactory.
The cyclic bending test is performed according to the following procedure. For example, as shown in FIG. 1, a strip-shaped test piece having a width of 12.5 mm and a length of 200 mm is disposed such that its bending ridge line R is parallel to a rolling direction D of the alloy sheet. Both ends of this test piece are fixed with chucks, and the test piece is tensioned with a load of 200 N.
In this state, by using a jig having a bending radius of 2.0 mm and disposed at a position of 150 mm from one end of the test piece fixed with a stationary chuck in the longitudinal direction of the test piece serving as a fulcrum, the cyclic bending is performed by rotating the other chuck at 90° to the right and left. The number of bendings is measured until the test piece breaks.
The bending is counted as one when an operation to bend the test piece at 90° to the right or left, or another operation to bend back the test piece to the original position is performed. In a case where the test piece breaks during the test, the angle θ thereof (0° to 90°) is read, and the number of cyclic bendings N is calculated through the following formula (3). In the formula (3), N₀ is the total number of the operations to bend the test piece 90° to the right or left and to bend the 90°-bent test piece back to the original position at 0°, which are performed until the test piece breaks. $N = N_{0} + θ / 90$
Since an evaluation of the cyclic bendings is unfavorable as the sheet thickness increases, it is necessary to correct the number of cyclic bendings N using a reference sheet thickness. Thus, the standardized number of cyclic bendings N_s is obtained by the following formula (4) using a sheet thickness of 0.235 mm as the standard. Here, "t" (mm) is a sheet thickness of the test piece. $N_{s} = N \times t / 0.235$
The standardized number of cyclic bendings of the aluminum alloy sheet of the present disclosure is preferably 17 counts or more, and more preferably 18 counts or more. By allowing the standardized number of cyclic bendings to be such counts, the toughness of the aluminum alloy sheet is increased so that the lid can have sufficient formability.

(Second Phase Particles)

The toughness is affected by strength and distribution of second phase particles. In other words, the higher the strength is, and the higher the density of the second phase particles is, the lower the toughness becomes. Particularly, if the Mg content and the Si content are increased, Mg₂Si particles are more likely to be formed. As a result, the Mg₂Si particles become a starting point and a propagation path of a crack, which affects the decrease in toughness.
In the aluminum alloy sheet of the present disclosure, a ratio of a total area of the Mg₂Si particles having an area of 0.3 µm² or more is preferably 0.2% or less, and more preferably 0.1% or less in a center region in a sheet thickness direction of a cross section perpendicular to a sheet surface and parallel to the rolling direction.
The ratio of the area of the Mg₂Si particles can be measured by the following method, for example. Among surfaces of a measurement sample, a surface to be measured (in other words, a cross section perpendicular to a rolling surface, which is the sheet surface of the alloy sheet, and parallel to the rolling direction) is mechanically polished to a mirror finish.
The polished surface (in other words, the cross section perpendicular to the rolling surface, which is the sheet surface of the alloy sheet, and parallel to the rolling direction) is observed using a scanning electron microscope (SEM), and 10 fields of view are obtained. Imaging is performed with the accelerating voltage of the SEM being set to 15 kV, the magnification of the SEM being set to 1000 times, and a range of one field of view being set to 0.012 mm². Then, a backscattered electron composition image (COMPO) is obtained.
The obtained COMPO is analyzed by ImageJ, an image analysis software. Specifically, the most frequent brightness value of the image in 256 shades is used as a background brightness, and particles with brightness of less than a value obtained by subtracting 30 from the most frequent brightness value is determined to be the Mg₂Si particles.
Among thus determined Mg₂Si particles, a total area of particles each having an area of 0.3 µm² or more is calculated. By dividing thus obtained total area by an imaged area of the 10 fields of view, the ratio of the total area of the Mg₂Si particles having an area of 0.3 µm² or more in the cross section is calculated.

The aluminum alloy sheet of the present disclosure can be obtained through a method of manufacturing an aluminum alloy sheet of the present disclosure. As shown in FIG. 2, the method of manufacturing an aluminum alloy sheet of the present disclosure includes a casting process at S110, a homogenizing treatment process at S120, a rolling process at S130, and a coating process at S140.

(Casting Process)

In this process, an aluminum alloy having a composition of the aluminum alloy sheet of the present disclosure is subjected to a semi-continuous casting method (in other words, DC casting) in accordance with a normal manner to manufacture an ingot. In this process, an Al-Ti-B-based micronizing material may be blended into a base material. This inhibits coarsening of crystal grains and the second phase particles in the ingot.

(Homogenizing Treatment Process)

In this process, the ingot is placed in a soaking furnace after the surfaces of the ingot are grinded to perform the homogenizing treatment. The temperature of the homogenizing treatment is preferably higher than or equal to the solid solutionizing temperature of Mg₂Si and lower than or equal to the solidus temperature of the aluminum matrix.
If the temperature of the homogenizing treatment is higher than or equal to the solid solutionizing temperature of Mg₂Si, the amount of presence of Mg₂Si, which is the second phase particle crystallized and precipitated in the ingot, can be reduced. As a result, both the strength and the toughness of the aluminum alloy sheet are improved. Moreover, it is preferable that the homogenizing treatment temperature is set higher than the solid solutionizing temperature of Mg₂Si by 40 °C or more. This can results in extremely reducing the amount of presence of Mg₂Si.
Also, by setting the homogenizing treatment temperature lower than or equal to the solidus temperature of the aluminum matrix, it is possible to manufacture the aluminum alloy sheet without an occurrence of local fusion. Moreover, it is preferable that the homogenizing treatment temperature is set lower than the solidus temperature of the aluminum matrix by 10 °C or more. This can result in stably producing the aluminum alloy sheet without an occurrence of the local fusion.
The solid solutionizing temperature of Mg₂Si and the solidus temperature of the aluminum matrix are uniquely determined depending on the composition of the aluminum alloy. The solid solutionizing temperature of Mg₂Si and the solidus temperature of the aluminum matrix can be obtained by inputting the composition of the aluminum alloy into, for example, "JMatPro", a thermodynamic calculation software developed by Sente Software, to calculate an equilibrium diagram. CALPHAD method is used as a thermodynamic model for calculating the equilibrium diagram.
The duration of time for the homogenizing treatment is preferably one hour or more and 20 hours or less, for example. When the duration of time for the homogenizing treatment is one hour or more, the temperature of the entire slab becomes uniform, segregation of the ingot structure is easily reduced, and the Mg₂Si particles are easily re-solid solutionized. The longer the duration of time for the homogenizing treatment is, the more the Mg₂Si particles can be re-solid solutionized. However, if the duration of time for the homogenizing treatment exceeds 20 hours, the effect of the homogenizing treatment is saturated.

(Rolling Process)

In this process, the ingot that underwent the homogenizing treatment is subjected to the rolling. This process includes a hot rolling process at S131 and a cold rolling process at S132.
The hot rolling process at S131 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 tens of millimeters by reverse rolling. In the finish rolling process, the thickness of the plate material is reduced to about a few millimeters by tandem rolling, for example, and a hot-rolled coil is formed by winding the plate material into a form of coil.
If the total reduction is high in the finish rolling, then the aluminum alloy sheet becomes a recrystallization structure after winding, which can increase a degree of integration of cube orientation. If the temperature is high during winding in the finish rolling, then the aluminum alloy sheet becomes a recrystallization structure after winding, which can increase the degree of integration of the cube orientation. The number of cyclic bendings is improved by increasing the degree of integration of the cube orientation of the aluminum alloy sheet.
The hot rolling process at S131 is followed by the cold rolling process at S132. In the cold rolling, the hot-rolled coil is rolled until its thickness reaches a product sheet thickness. The cold rolling may be either single rolling or tandem rolling. In the cold rolling in a case of the single rolling, it is preferable that the rolling is performed in two or more divided passes.
A cold rolling ratio (that is, target total reduction) is preferably 70% or more, and more preferably 80% or more. By setting the lower limit of the cold rolling ratio as mentioned above, the strength of the aluminum alloy sheet can be increased. Meanwhile, the cold rolling ratio is preferably 90% or less. By setting the upper limit of the cold rolling ratio as mentioned above, anisotropy of a crystal grain structure is reduced, and the toughness of the alloy sheet against a tensile stress and a bending stress in a direction perpendicular to the rolling direction is improved.
The cold rolling ratio R(%) is obtained through the following formula (5) by using a sheet thickness t₀ (mm) of the hot rolled sheet, and the product sheet thickness t₁ (mm) after the cold rolling. $R = (t_{0} - t_{1}) / t_{0} \times 100$
In the rolling process at S130, after hot rolling the ingot, the cold rolling is completed without performing a heat treatment (that is, annealing). In other words, in the method of manufacturing the aluminum alloy sheet in the present disclosure, the cold rolling is performed until the final product sheet thickness is achieved without performing the heat treatment on the plate material (that is, the coil) between the hot rolling and the cold rolling or in the middle of the cold rolling. This enables a significant reduction of the number of processes, an improvement in production efficiency, and a reduction of energy consumption.

(Coating Process)

In this process, a coating is baked on the plate material obtained through the cold rolling of the ingot. Specifically, a pre-coating is performed firstly on a coating line or the like on the coil that had undergone the cold rolling until the product sheet thickness was achieved. The coil that had undergone the cold rolling is subjected to degreasing, cleaning, and chemical conversion coating, on its surface, and baking treatment for coating after being coated with a coating material.
In the chemical conversion coating, chemicals such as a chromate-based chemical and a zirconium-based chemical are used. As the coating material, materials such as an epoxy-based material and a polyester-based material are used. These chemicals and coating materials can be selected in accordance with applications. In the baking treatment for coating, the coil is heated within about 30 seconds at 220 °C or higher in an actual temperature of the coil (PMT: Peak Metal Temperature).
In this stage, the lower the PMT is, the more the recovery of the material is inhibited, which makes it possible to keep the strength of the alloy sheet high. Thus, it is preferable that the baking temperature of the coating (that is, PMT) is 270 °C or lower. In addition, it is possible to reduce the cold rolling ratio to improve the toughness and cover the resulting shortfall of the strength by lowering the PMT.

[1-2. Effect]

According to the embodiment explained in detail above, the following effect can be obtained.
(1a) The manufactured aluminum alloy sheet can achieve both high strength and high toughness while containing scrap materials derived from can materials. In other words, since it is possible to blend a certain amount of scraps of the 3104 aluminum alloy for a can body into raw materials, a usage rate of primary metal and CO₂ emissions can be reduced. Moreover, it is possible to obtain the aluminum alloy sheet for a can lid that can be used for a can lid of a positive pressure can that requires a high buckling pressure resistance.

[2. Other Embodiments]

The embodiment of the present disclosure has been explained above; however, it is needless to say that the present disclosure is not limited to the aforementioned embodiment and can be implemented in various forms.
(2a) In addition to the method of manufacturing an aluminum alloy sheet of the aforementioned embodiment, the present disclosure also includes various other forms, such as an aluminum alloy sheet obtained through this method, and a member including this aluminum alloy sheet.
(2b) Functions of one element in the aforementioned embodiments may be distributed to two or more elements, and functions of two or more elements may be integrated into one element. A part of the configuration of the aforementioned embodiment may be omitted. In addition, at least a part of the configuration of the aforementioned embodiment may be added to or replaced with another configuration of the aforementioned embodiment. Any and all modes included in the technical idea specified by the languages used in the claims are embodiments of the present disclosure.

[3. Examples]

Hereinafter, details of tests conducted to confirm the effects of the present disclosure and evaluation thereof will be explained.

As examples and comparative examples, aluminum alloy sheets S1 to S12 as shown in Table 1 and Table 2 were manufactured. Specific processes of manufacture will be explained hereinafter.
Firstly, ingots containing components (mass%) of alloys No. 1 to 7 shown in Table 3 and a balance consisting of aluminum and inevitable impurities were manufactured through a semi-continuous casting method. The ingots include a Ti content of 0.10 mass% or less, a Zn content of 0.25 mass% or less, a Cr content of 0.10 mass% or less, and the inevitable impurities of 0.15 mass% or less.
Secondly, six surfaces of each ingot were ground. Then, each ingot was placed in a furnace and subjected to the homogenizing treatment. The temperature of the homogenizing treatment is as shown in Table 1. With respect to the ingots S1 to S11, the temperature of the homogenizing treatment was set at or higher than the solid solutionizing temperature of Mg₂Si and at or lower than the solidus temperature of the aluminum matrix shown in Table 3. The temperature of the homogenizing treatment of the ingot of S12 was set lower than the solid solutionizing temperature of Mg₂Si shown in Table 3. After performing the homogenizing treatment for four hours or longer, the ingots were taken out from the furnace and immediately subjected to the hot rolling and made into rolled sheets.
The cold rolling was performed on the rolled sheets after the hot rolling. The target total reduction in the cold rolling was as shown in Table 1. The product sheet thickness after the cold rolling (that is, t₁ in the formula (5)) was set in a range of about 0.235 ± 0.01 mm.

After the cold rolling, the baking treatment for coating was performed for 30 seconds. The actual temperatures (PMT) at the time of baking the coating were shown in Table 1. The aluminum alloy sheets of S1 to S12 were obtained through the aforementioned processes. The sheet thicknesses (that is, product sheet thicknesses) of the aluminum alloy sheets of S1 to S12 measured by using a microgauge were shown in Table 1.

[Table 1]

Examples	Alloy No.	Homogenizing Treatment Temperature	Cold Rolling Reduction	PMT	Sheet Thickness	Rolling in 0° direction			Rolling in 45° direction
		Homogenizing Treatment Temperature	Cold Rolling Reduction	PMT	Sheet Thickness	σ_0.2	σ_B	σ_fm	σ_0.2	σ_B	σ_fm
		°C	%	°C	mm	MPa	MPa	MPa	MPa	MPa	MPa
S1	1	600	87	260	0.236	250	279	264	262	285	274
S2	2	580	88	250	0.239	296	332	314	295	331	313
S3	2	580	88	270	0.230	283	323	303	286	318	302
S4	3	580	88	250	0.237	295	332	314	300	332	316
S5	3	580	88	270	0.234	286	327	306	289	322	306
S6	4	580	88	250	0.235	296	332	314	300	334	317
S7	4	580	88	270	0.233	284	323	303	288	323	305
S8	5	580	88	250	0.236	310	349	330	309	345	327
S9	5	580	88	270	0.231	294	337	316	300	335	317
S10	6	580	88	250	0.238	308	348	328	310	348	329
S11	6	580	88	270	0.232	296	339	317	298	335	316
S12	7	520	88	260	0.234	284	316	300	291	319	305

[Table 2]

Examples	Alloy No.	Rolling in direction			Smin	Area Ratio of Mg₂Si	Number of Cyclic Bendings	Standardized Number of Cyclic Bendings
		σ_0.2	σ_B	σ_fm	σ_fm/(σ_0.2/σ_B)	Area Ratio of Mg₂Si	Number of Cyclic Bendings	Standardized Number of Cyclic Bendings
		MPa	MPa	MPa	MPa	%	counts	counts
S1	1	270	296	283	295	0.000	21.2	21.3
S2	2	315	348	331	351	0.011	19.0	19.3
S3	2	306	338	322	336	0.011	22.1	21.6
S4	3	318	352	335	349	0.007	20.0	20.2
S5	3	306	340	323	340	0.007	21.0	20.9
S6	4	317	351	334	352	0.007	18.3	18.3
S7	4	306	339	323	342	0.007	22.3	22.2
S8	5	330	365	347	365	0.133	17.6	17.7
S9	5	316	351	333	354	0.133	21.3	20.9
S10	6	328	368	348	369	0.031	18.7	19.0
S11	6	318	356	337	355	0.031	21.8	21.6
S12	7	292	322	307	335	0.722	17.7	17.6

[Table 3]

Alloy No.	Si	Fe	Cu	Mn	Mg	Solid Solutionizing Temperature of Mg₂Si	Solidus Temperature of Al
Alloy No.	mass%					°C
1	0.33	0.45	0.22	1.00	1.2	419	623
2	0.33	0.44	0.21	0.82	2.4	537	602
3	0.27	0.45	0.21	0.83	2.4	489	604
4	0.21	0.46	0.21	0.82	2.5	490	602
5	0.33	0.45	0.21	0.82	2.8	552	595
6	0.27	0.45	0.21	0.81	2.8	511	597
7	0.32	0.43	0.22	0.80	2.6	544	598

(Tensile Property)

Three No. 5 test pieces, specified in JIS-Z-2241:2011, were prepared from each of the aluminum alloy sheets S1 to S12. The longitudinal directions of these three test pieces respectively extend in directions forming 0°, 45°, and 90° with respect to the rolling direction.
A tensile test was conducted on these test pieces in accordance with JIS-Z-2241:2011, and 0.2% yield strengths and tensile strengths were measured. Table 1 and Table 2 show results of the measurement of the 0.2% yield strength σ_0.2 and the tensile strength σ_B, as well as an average value σ_fm of the 0.2% yield strength and the tensile strength. In addition, three Ss were calculated from the results of the tensile tests in each of the directions forming 0°, 45°, and 90° with respect to the rolling direction and the formula (2). The minimum value S_min of these Ss is shown in Table 2.

(Toughness)

In each of the aluminum alloy sheets of S1 to S12, the ratio of the total area (area ratio) of the Mg₂Si particles each having an area of 0.3 µm² or more in a cross section was calculated through the method of measurement explained in the embodiment. The results of the measurement are shown in Table 2.
In each of the aluminum alloy sheets of S1 to S12, the number of cyclic bendings and the standardized number of cyclic bendings were calculated through the method of measurement explained in the embodiment and formulas (3) and (4). The results are shown in Table 2.

(Scrap Blending Ratio)

With respect to the composition of each of the aluminum alloy sheets of S1 to S12, it was determined whether a possible blending ratio of scraps of the 3104 aluminum alloy was 50 mass% or more. The possible blending ratio of scraps of the 3104 aluminum alloy is determined based on Table 4.
Table 4 shows blending ratios of the 3104 aluminum alloy and the 5182 aluminum alloy in correspondence with their average values of the compositional standard. The first line of Table 4 shows the average values of the compositional standard of the components of the 3104 aluminum alloy, and the second line shows the average values of the compositional standard of the components of the 5182 aluminum alloy.
For example, when the blending ratio of the 3104 aluminum alloy is 50 mass%, the average value of the Si content is 0.20 mass%, the average value of the Fe content is 0.29 mass%, the average value of the Cu content is 0.11 mass%, the average value of the Mn content is 0.7 mass%, and the average value of the Mg content is 2.8 mass%.

Accordingly, if the ratio of each of the components Si, Fe, Cu, Mn, and Mg of the aluminum alloy sheet is more than or equal to the aforementioned value, the possible blending ratio of scraps of the 3104 aluminum alloy sheet is 50 mass% or more. The more the blending ratio of the 3104 aluminum alloy increases, the more the contents of Si, Fe, Cu, and Mn increase, but the more the content of Mg decreases. The aluminum alloy sheets of S2 to S12 can include 50 mass% or more of scraps of the 3104 aluminum alloy.

[Table 4]

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

Blending Ratio of 3104	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

(Evaluation)

FIG. 3 shows the relationship between S_min of each of the aluminum alloy sheets of S1 to S12 and the standardized number of cyclic bendings. The graph in FIG. 3 shows that the larger the values of both S_min and the standardized number of cyclic bendings are (that is, the more the graph is plotted in the upper right area), the more favorable the property of the alloy is.
Since the Mg content was small in the aluminum alloy sheet of S1, not enough strength (that is, S_min) was obtained. Meanwhile, in all of the aluminum alloy sheets of S2 to S12 obtained through the manufacturing method of the present disclosure, S_min was 330 MPa or more and the standardized number of cyclic bendings was 17 counts or more.
Moreover, in all of the aluminum alloy sheets of S8 to S11, each of which contains a large amount of Mg, S_min is 350 MPa or more. In particular, the aluminum alloy sheets of S10 and S11 are both notably excellent in strength and toughness since the area ratio of the Mg₂Si particles is 0.1% or less despite the fact that their Mg contents are large due to their Si contents being small compared with S8 and S9. Meanwhile, in S12, the area ratio of the Mg₂Si particles became large due to the homogenizing treatment temperature being lower than the solid solutionizing temperature of Mg₂Si; and accordingly, S_min and the standardized number of cyclic bendings became relatively small despite the fact that its Mg content was large.
In all of the aluminum alloys, the lower the baking temperature for coating (PMT) was, the more the strength (that is, S_min) was increased. For example, if comparisons were made between the aluminum alloy sheets of S2 and S3, S4 and S5, S6 and S7, S8 and S9, and S10 and S11, high S_min was obtained in examples that had lower baking temperatures for coating. Meanwhile, the standardized number of cyclic bendings was large in the examples that had higher baking temperatures for coating.

Claims

A method of manufacturing an aluminum alloy sheet for a can lid, the method comprising:
a process of casting an ingot, the ingot including:
a silicon (Si) content of 0.20 mass% or more and 0.47 mass% or less;

an iron (Fe) content of 0.30 mass% or more and 0.59 mass% or less;

a copper (Cu) content of 0.11 mass% or more and 0.40 mass% or less;

a manganese (Mn) content of 0.70 mass% or more and 0.98 mass% or less;

a magnesium (Mg) content of 1.3 mass% or more and 3.7 mass% or less; and

a balance consisting of or including aluminum (Al) and inevitable impurities;

a process of homogenizing treatment on the ingot; and

a process of rolling the ingot that underwent the homogenizing treatment,

wherein, in the process of rolling, cold rolling is completed without performing heat treatment after performing hot rolling on the ingot.
The method of manufacturing an aluminum alloy sheet for a can lid according to claim 1,
wherein, in the process of homogenizing treatment, homogenizing treatment is performed on the ingot at a temperature higher than or equal to a solid solutionizing temperature of Mg₂Si and lower than or equal to a solidus temperature of an aluminum matrix.
The method of manufacturing an aluminum alloy sheet for a can lid according to claim 2,
wherein, in the process of casting, the casting is performed on the ingot that includes:
a silicon (Si) content of 0.20 mass% or more and 0.47 mass% or less;

an iron (Fe) content of 0.30 mass% or more and 0.55 mass% or less;

a copper (Cu) content of 0.17 mass% or more and 0.25 mass% or less;

a manganese (Mn) content of 0.70 mass% or more and 0.98 mass% or less;

a magnesium (Mg) content of 2.6 mass% or more and 3.7 mass% or less; and

a balance consisting of or including aluminum (Al) and inevitable impurities.
The method of manufacturing an aluminum alloy sheet for a can lid according to claim 3,
wherein, in the process of casting, the casting is performed on the ingot that includes:
a silicon (Si) content of 0.20 mass% or more and 0.30 mass% or less;

an iron (Fe) content of 0.30 mass% or more and 0.55 mass% or less;

a copper (Cu) content of 0.17 mass% or more and 0.25 mass% or less;

a manganese (Mn) content of 0.70 mass% or more and 0.98 mass% or less;

a magnesium (Mg) content of 2.6 mass% or more and 3.7 mass% or less; and

a balance consisting of or including aluminum (Al) and inevitable impurities.
The method of manufacturing an aluminum alloy sheet for a can lid according to claim 4, further comprising
a process of baking, at 270 °C or lower, a coating on a plate material obtained through the cold rolling of the ingot.
The method of manufacturing an aluminum alloy sheet for a can lid according to claim 5,
wherein, in the process of rolling, the cold rolling is performed at a reduction of 90% or less.