JP7420996B1 - Aluminum alloy plate for can lids - Google Patents

Abstract

An object of the present invention is to provide an aluminum alloy plate for can lids that can achieve both high strength and high toughness while blending scrap raw materials derived from can stock. One aspect of the present disclosure is that Si is 0.27% by mass or more and 0.39% by mass or less, Fe is 0.35% by mass or more and 0.55% by mass or less, and Cu is 0.17% by mass or more and 0. .25 mass% or less, Mn is 0.75 mass% or more and 0.95 mass% or less, Mg is 2.2 mass% or more and 2.8 mass% or less, 0° direction, 45° direction with respect to the rolling direction, and 90° direction, the evaluation value S calculated by formula (1) using 0.2% proof stress σ0.2, tensile strength σB, and average value σfm of 0.2% proof stress and tensile strength. Among these, the aluminum alloy plate for can lids has a minimum evaluation value Smin of 330 MPa or more and 390 MPa or less. S=σfm/(σ0.2/σB) ...(1) [Selection diagram] None

Description

The present disclosure relates to an aluminum alloy plate for can lids.

In recent years, as environmental awareness has increased, there has been a demand for aluminum alloy plates that emit less _CO2 during the manufacturing process. In the aluminum manufacturing process, the composition of new aluminum ingots in the casting process indirectly contributes significantly to CO ₂ emissions.

The production of new aluminum ingots uses a large amount of electricity in the refining process, leading to large amounts of _CO2 emissions. Therefore, reducing the amount of new aluminum ingot mixed and increasing the horizontal recycling rate will lead to a reduction in CO ₂ emissions in the production of aluminum alloy sheets.

Generally, it is said that the amount of CO ₂ emitted when aluminum scrap is remelted and cast is reduced to about one-thirtieth of that when producing new aluminum ingots. In particular, the production volume of aluminum alloy sheets for beverage cans used around the world is extremely large, and further improving the horizontal recycling rate will have great significance in reducing environmental impact.

Among them, can lids made of 5182 aluminum alloy (AA5182 alloy) have lower upper limits of component specifications for Si, Fe, Cu, Mn, etc. than can bodies made of 3104 aluminum alloy (AA3104 alloy). It is difficult to mix scraps derived from can stock mixed with 3104 aluminum alloy.

For example, if used Beverage Can (UBC) generated from the market is blended as is, it will contain more of the 3104 aluminum alloy component due to the weight ratio of the can body to the can lid, which will exceed the upper limit of the 5182 aluminum alloy component. It becomes easier to use, and it becomes necessary to dilute the ingredients with new metal.

Therefore, aluminum alloy plates for can lids use more new metal to adjust the composition to 5182 aluminum alloy than aluminum alloy plates for can bodies, and the recycling rate is low. Therefore, by changing the can lid to an alloy whose components are easily blended with 3104 aluminum alloy, the usage rate of new metal in the can lid can be greatly reduced.

Patent Documents 1 to 5 disclose aluminum alloy plates for can lids whose components are relatively close to those of 3104 aluminum alloy, which has excellent recyclability.

Japanese Patent Application Publication No. 2001-73106 Japanese Patent Application Publication No. 9-070925 Japanese Patent Application Publication No. 11-269594 Japanese Patent Application Publication No. 2000-160273 Japanese Patent Application Publication No. 2016-160511

When using an alloy for can lids with a composition similar to that of 3104 aluminum alloy, problems include a decrease in the pressure resistance of the can lid and the toughness of the material. The withstand pressure of a can lid is the internal pressure value when the can lid is inverted with respect to the pressure inside the can, and is the resistance value when the internal pressure of the can unexpectedly increases due to a change in the external environment.

In particular, positive pressure cans for beer and carbonated beverages are required to withstand high pressure. Generally, the higher the strength of the material and the thicker the plate, the higher the withstand pressure. Therefore, a high-strength 5182 aluminum alloy containing a large amount of Mg, which is a component that contributes to increasing strength, is used for the lid of a positive pressure can.

On the other hand, when the conventional 3104 aluminum alloy is used for the can lid, the withstand pressure is greatly reduced, and when the internal pressure of the can suddenly increases, there is a high possibility that the lid will turn over and the contents will leak. Furthermore, increasing the plate thickness in order to increase the withstand pressure causes an increase in the weight of the lid and an increase in the cost of the lid.

Furthermore, the toughness of the material affects the formability and opening properties of the lid. If the toughness of the material is low, molding cracks may occur, especially at the rivet and countersink areas of the lid. Moreover, when the internal pressure of the can suddenly increases, cracks occur in the score portion, increasing the possibility that the contents of the can will leak. In particular, these cracks occur along the rolling direction. Therefore, toughness against tensile stress and bending stress in the direction perpendicular to the rolling direction is required.

However, an aluminum alloy plate for can lids whose composition is relatively close to that of conventional 3104 aluminum alloy has problems with the above two issues: material strength (i.e., pressure resistance of the lid) and toughness (i.e., formability and opening properties). Or, it does not satisfy both.

One aspect of the present disclosure is to provide an aluminum alloy plate for can lids that can have both high strength and high toughness while incorporating scrap raw materials derived from can stock.

In one embodiment of the present disclosure, the content of silicon (Si) is 0.27% by mass or more and 0.39% by mass or less, and the content of iron (Fe) is 0.35% by mass or more and 0.55% by mass or less. , the copper (Cu) content is 0.17% by mass or more and 0.25% by mass or less, the manganese (Mn) content is 0.75% by mass or more and 0.95% by mass or less, and the magnesium (Mg) content is 2.2% by mass or more and 2.8% by mass or less, the remainder consists of aluminum (Al) and inevitable impurities, and the rolling direction is 0°, 45°, and 90° with respect to the rolling direction. In each direction, the evaluation value S is calculated by the following formula (1) using 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. Among these, the aluminum alloy plate for can lids has a minimum evaluation value S _min of 330 MPa or more and 390 MPa or less.
S=σ _fm /(σ _0.2 /σ _B )...(1)

According to such a configuration, high strength and high toughness can be achieved in the aluminum alloy plate while blending scrap raw materials derived from can stock. That is, a certain amount of 3104 aluminum alloy scrap for can bodies can be mixed in, reducing the usage rate of new metal and reducing CO ₂ emissions. Furthermore, an aluminum alloy plate for can lids with high formability that can be used for positive pressure can lid applications requiring high pressure resistance can be obtained.

FIG. 1 is an explanatory diagram of the L-ST cross section. FIG. 2 is a graph showing an example of the relationship between cold rolling reduction and strength anisotropy.

Embodiments to which the present disclosure is applied will be described below with reference to the drawings.
[1. First embodiment]
[1-1. composition]
<Composition>
The aluminum alloy plate for can lids of the present disclosure (hereinafter also simply referred to as "alloy plate") includes aluminum (Al), silicon (Si), iron (Fe), copper (Cu), manganese (Mn), and magnesium ( Mg).

The lower limit of the Si content is 0.27% by mass, preferably 0.30% by mass. If the Si content is less than 0.27% by mass, the amount of Si precipitated in the processing heat of hot rolling and cold rolling after solution treatment decreases, and the strength of the alloy plate may be insufficient.

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

The upper limit of the Si content is 0.39% by mass, preferably 0.35% by mass. When the Si content exceeds 0.39% by mass, Mg ₂ Si particles increase and the toughness of the alloy plate decreases.

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

The upper limit of the Fe content is 0.55% by mass. If the Fe content exceeds 0.55% by mass, the amount of Al-Fe-Mn-based or Al-Fe-Mn-Si-based intermetallic compounds (ie, second phase particles) increases. As a result, a crack propagation path is created and the toughness of the alloy plate is reduced.

The lower limit of the Cu content is 0.17% by mass, preferably 0.20% by mass. If the Cu content is less than 0.17% by mass, Cu, which increases strength through solid solution or precipitation, is insufficient, and the strength of the alloy plate decreases. Note that the strength of the alloy plate is significantly increased by precipitating Cu during hot rolling and cold rolling after solution treatment.

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

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

The lower limit of the Mn content is 0.75% by mass, preferably 0.80% by mass. When the Mn content is less than 0.75% by mass, Mn, which increases strength through solid solution or precipitation, is insufficient, and the average strength of the alloy plate decreases.

Further, the average value of the Mn component specifications for the 3104 aluminum alloy is 1.1% by mass, and the average value of the Mn component specifications for the 5182 aluminum alloy is 0.35% by mass. Therefore, by setting the Mn content to 0.75% by mass or more, more scrap of 3104 aluminum alloy can be blended than the conventional 5182 aluminum alloy.

The upper limit of the Mn content is 0.95% by mass, preferably 0.90% by mass. When the Mn content is more than 0.95% by mass, Al-Fe-Mn-based or Al-Fe-Mn-Si-based intermetallic compounds (ie, second phase particles) increase. As a result, a crack propagation path is created and the toughness of the alloy plate is reduced.

The lower limit of the Mg content is 2.2% by mass. When the Mg content is less than 2.2% by mass, Mg, which increases strength through solid solution, is insufficient, and the average strength of the alloy plate decreases. Note that the strength of the alloy plate is significantly increased by precipitating Mg during hot rolling and cold rolling after solution treatment.

The upper limit of the Mg content is 2.8% by mass. The average value of the Mg component specifications for 3104 aluminum alloy is 1.05% by mass, and the average value of the Mg component specifications for 5182 aluminum alloy is 4.5% by mass. Therefore, by setting the Mg content to 2.8% by mass or less, it is possible to mix in a large amount of 3104 aluminum alloy scrap and reduce the additional blending amount of the Mg-containing raw material.

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

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, Mg, Ti, Zn, and Cr in the above-mentioned ranges, and the remainder consists of aluminum and inevitable impurities. The upper limit of the total amount of unavoidable impurities is preferably 0.15% by mass.

<Material strength and pressure resistance>
A rolled aluminum alloy plate has material anisotropy, and its strength shows different values in the 0° direction, 45° direction, and 90° direction with respect to the rolling direction. As the pressure inside the can increases, deformation begins in the direction of lowest strength.

Therefore, the alloy plate of the present disclosure has 0.2% yield strength σ _0.2 , tensile strength σ _B , and 0.2% yield strength in the 0° direction, 45° direction, and 90° direction with respect to the rolling direction. Among the evaluation values S (S _0° , S _45° , and S _90° ) calculated by the following formula (1) using the average value σ _fm of and the tensile strength, the minimum evaluation value S _min is the minimum value. (=min(S _0° , S _45° , S _90° )) is 330 MPa or more and 390 MPa or less.
S=σ _fm /(σ _0.2 /σ _B )...(1)

The pressure resistance value of the lid made of an aluminum alloy plate has a strong positive correlation with the value V of the following formula (2), which is empirically expressed by the minimum evaluation value S _min and the plate thickness t.
V= ^t2.27 ×S _min ...(2)

Therefore, by setting the minimum evaluation value S _min of the alloy plate to 330 MPa or more, a lid having sufficient pressure resistance can be formed without increasing the plate thickness. Furthermore, the minimum evaluation value S _min is preferably 360 MPa or more. By setting the minimum evaluation value S _min to 360 MPa or more, the pressure resistance of the lid can be further improved.

Moreover, when the minimum evaluation value S _min exceeds 390 MPa, the material strength becomes excessively high and the toughness of the material decreases. That is, shear bands are likely to occur due to tensile stress and bending stress generated in the material during molding, and mold cracks are likely to occur. By setting the minimum evaluation value S _min to 390 MPa or less, it is possible to achieve both the strength of the material (that is, the pressure resistance of the lid) and the toughness (that is, formability and openability).

The 0.2% yield strength σ _0.2 and the tensile strength σ _B in formula (1) are measured by the method specified in JIS-Z-2241:2011. The plate thickness t is measured using a micro gauge, for example.

<Toughness>
It is known that the toughness of the aluminum alloy plate affects the formability of the lid and the force required to open the score portion (that is, the opening force).

(Number of repeated bending)
A repeated bending test is one of the evaluation indicators of the toughness of aluminum alloy plates. If the plate thickness is the same, the greater the number of repeated bending, the better the toughness of the aluminum alloy plate.

The cyclic bending test is performed using the following procedure. For example, a test piece cut into a rectangular shape with a width of 12.5 mm and a length of 200 mm is placed in such a direction that 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 tension is applied with a load of 200N.

In this state, the other chuck is rotated 90 degrees left and right using a jig with a bending radius of 2.0 mm placed at a position 150 mm in the longitudinal direction of the test piece from the end of the test piece fixed on one immovable chuck. The test piece is repeatedly bent and the number of bends until it breaks is measured.

As for the number of times of bending, each operation of bending 90 degrees to the left or right and returning to the original position is counted as one time. If it breaks midway, the angle Θ (0°-90°) is read and the number of repeated bends N is calculated using the following equation (3). In formula (3), _N0 is the total number of times the test specimen is bent 90° to the left or right and returned to its original 0° position from the 90° bent position until it breaks. .
N= _N0 +Θ/90...(3)

In repeated bending evaluation, the larger the plate thickness, the more disadvantageous it becomes, so it is necessary to correct it using the standard plate thickness. Therefore, the standardized number of repeated bending cycles N _s is determined using the following formula (4) based on the plate thickness of 0.235 mm. Note that t (mm) is the thickness of the test piece.
_Ns = N×t/0.235 (4)

The standardized number of times _Ns of repeated bending of the aluminum alloy plate of the present disclosure is preferably 17 times or more.

(Second phase particles)
Toughness is influenced by strength and second phase particle distribution. In other words, the higher the strength and the higher the density of the second phase particles, the lower the toughness. In particular, when the contents of Mg and Si are high, Mg ₂ Si particles are likely to be formed. As a result, the Mg ₂ Si particles become the starting point and propagation path of cracks, which affects the reduction in toughness.

The aluminum alloy plate of the present disclosure has an area of 0.3 _μm ² or more in the L-ST cross section of the center portion in the width direction, which is indicated by diagonal lines in FIG. .2% or less is preferable. In addition, in FIG. 1, L indicates the longitudinal direction, ST indicates the plate thickness direction, and LT indicates the width direction.

The area ratio of Mg ₂ Si particles can be measured, for example, by the following method. First, a measurement sample is cut, and the surface to be measured (that is, the L-ST cross section) is mechanically polished to a mirror finish. Next, the polished surface (that is, the L-ST cross section) is observed using a SEM (scanning electron microscope) to obtain 10 fields of view in the central region of the plate thickness. The acceleration voltage of the SEM is 15 kV, the magnification is 1000 times, and the range of one field of view is 0.012 mm ² . Photographing is performed to obtain a COMPO (backscattered electron composition) image.

The photographed COMPO image is analyzed using image analysis software "ImageJ". Specifically, the mode of brightness of the image at 256 gradations is set as the background brightness, and particles with a brightness lower than the value obtained by subtracting 30 from the brightness of the mode are determined to be Mg ₂ Si particles.

Among the determined Mg ₂ Si particles, the total area of particles with an area of 0.3 μm ² or more is calculated and divided by the photographed area of 10 fields of view (that is, the total photographed area), so that the area is 0. The ratio of the total area of Mg ₂ Si particles of 3 μm ² or more in the L-ST cross section is calculated.

<Strength anisotropy>
It is known that materials with a low cold rolling rate (hereinafter abbreviated as cold rolling rate) have high toughness. Further, the higher the cold rolling rate, the larger the 0.2% proof stress σ _{0.2_90°} in the 90° direction with respect to the rolling direction compared to the 0.2% proof stress σ _{0.2_0°} in the 0° direction. Therefore, the difference in 0.2% proof stress between the 0° direction and the 90° direction with respect to the rolling direction, that is, the strength anisotropy, can be correlated with the cold rolling rate of the material.

The alloy plate of the present disclosure has a 0.2% proof stress σ _{0.2_0°} in a 0° direction with respect to the rolling direction, which is determined by formula (5), and a 0.2% proof stress σ ₀ in a 90° direction with respect to the rolling direction. It is preferable that the value D obtained by subtracting _{.2_90°} is -12 MPa or more and 12 MPa or less.
D=σ _{0.2_0°} -σ _{0.2_90°} ...(5)

Material structure of strength anisotropy, which is obtained by subtracting 0.2% proof stress σ _{0.2_90°} in the 90° direction to the rolling direction from 0.2% proof stress σ _{0.2_0°} in the 0° direction with respect to the rolling direction. The meaning can be explained as follows.

The material after hot rolling or annealing is in a recrystallized state and has a high degree of accumulation of isotropic cube orientations. From this point on, due to plastic deformation due to cold rolling, the cube orientation deforms into a rolling texture with anisotropy in the rolling direction. Furthermore, the larger the cold rolling rate, the more elongated the crystal grains are in the rolling direction. The change in the crystal grain diameter is smaller than in the 0° direction.

The relationship between these structural changes caused by rolling and the 0.2% proof stress σ _0.2 is expressed by Equation (6) with reference to Hall-Petch's equation. In Equation (6), κ is the resistance to sliding of grain boundaries, and d is the grain size.
σ _0.2 ∝κ×d ^-1/2 ...(6)

The resistance κ has different values for tension in the 0° direction or 90° direction with respect to the rolling direction. This is because the degree of accumulation of the rolling texture, which has anisotropy in the rolling direction, increases as the cold rolling rate increases, so that the resistance to grain boundary slip changes depending on the tensile direction.

Furthermore, in the direction of 0° to the rolling direction, the grains elongate and the diameter increases as the cold rolling rate increases, while in the direction of 90° to the rolling direction, the change in grain size with respect to the cold rolling rate is relative. relatively small. By integrating these effects, strength anisotropy occurs as the cold rolling reduction increases.

<Method for manufacturing aluminum alloy plate>
The aluminum alloy plate of the present disclosure can be manufactured, for example, as follows. First, an aluminum alloy having the composition of the aluminum alloy plate of the present disclosure is subjected to a semi-continuous casting method (that is, DC casting) according to a conventional method to produce an ingot.

Next, the four sides of the ingot excluding the front and rear ends are milled. 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 more and 20 hours or less.

When the temperature in the homogenization treatment is 400° C. or higher, segregation of the ingot structure is easily eliminated. Furthermore, when the temperature in the homogenization treatment is 450° C. or higher, the Mg ₂ Si particles can be solid-dissolved again and the strength and toughness of the alloy plate can be improved. Furthermore, when the temperature in the homogenization treatment is 470° C. or higher, more preferably 550° C. or higher, re-solid solution of the Mg ₂ 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 lower, local melting of the aluminum alloy is unlikely to occur.

When the homogenization treatment time is 1 hour or more, the temperature of the entire slab becomes uniform, the segregation of the ingot structure is easily eliminated, and the Mg ₂ Si particles are easily dissolved again. The longer the homogenization treatment time, the more the Mg ₂ Si particles can be solid-dissolved again. However, if the homogenization treatment time exceeds 20 hours, the effect of the homogenization treatment will be saturated.

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 with 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.

When the total reduction ratio in finish rolling is high, a recrystallized structure is formed after winding, and the degree of accumulation of isotropic cube orientations can be increased. When the winding temperature in finish rolling is high, a recrystallized structure is formed after winding, and the degree of accumulation of cube orientation can be increased.

Following the hot rolling, the plate material is cold rolled. In cold rolling, a hot rolled coil is rolled until it reaches the product plate thickness. Cold rolling may be either single rolling or tandem rolling. In cold rolling by single rolling, rolling is preferably carried out in multiple passes of two or more passes.

In addition, the coil is subjected to solution treatment during cold rolling to increase the strength of the material by solid solutioning Mg, etc., while reducing the final cold rolling rate to suppress the anisotropy of the material. can be obtained. For example, by performing heat treatment (that is, annealing) at a target actual temperature of 440°C or higher using a continuous annealing furnace (CAL), and then performing forced cooling using air cooling, etc., it is possible to effectively increase the strength of the alloy plate. It is.

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

When solution treatment is not performed during cold rolling, the cold rolling rate is preferably 80% or more. When the cold rolling rate is 80% or more, the strength of the alloy plate can be increased. Furthermore, since the lower the cold rolling rate is, the more isotropic cube orientation remains, the cold rolling rate is preferably 92% or less.

When solution treatment is performed during cold rolling, the cold rolling rate after solution treatment (that is, annealing) is preferably 50% or more. By redissolving Mg and the like through solution treatment, the strength of the alloy sheet can be increased even if the cold rolling rate is low. Furthermore, since the lower the cold rolling rate is, the more isotropic cube orientation remains, the cold rolling rate is preferably 80% or less.

The cold rolling ratio R (%) is calculated by the following formula (7) using the plate thickness t ₀ (mm) after hot rolling or solution treatment and the product plate thickness t ₁ (mm) after cold rolling. Desired.
R=(t ₀ - t ₁ )/t ₀ ×100 (7)

The thickness of the product plate can be appropriately selected so as to obtain the desired pressure resistance. As shown in equation (2) above, as the plate thickness increases, the withstand pressure improves. The product board thickness can be selected according to the value V of formula (2), and the value V is preferably 13.0 or more, preferably 14.0 or more. As described above, according to the aluminum alloy plate of the present disclosure, it is possible to suppress an increase in the plate thickness in order to maintain high pressure resistance.

The coils are cold-rolled to the product thickness and then pre-coated on a painting line. The surface of the cold-rolled coil is subjected to degreasing, cleaning, and chemical conversion treatment, and then a paint is applied, followed by a paint baking treatment.

In the chemical conversion treatment, chromate-based, zirconium-based, and other chemical solutions are used. As the paint, epoxy type, polyester type, etc. are used. These can be selected depending on the purpose. In the paint baking process, the coil is heated at a peak metal temperature (PMT) of 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.

[1-2. effect]
According to the embodiment described in detail above, the following effects can be obtained.
(1a) High strength and high toughness of aluminum alloy plates can be achieved while blending scrap raw materials derived from can stock. That is, a certain amount of 3104 aluminum alloy scrap for can bodies can be mixed in, reducing the usage rate of new metal and reducing CO ₂ emissions. Furthermore, an aluminum alloy plate for can lids with high formability that can be used for positive pressure can lid applications requiring high pressure resistance can be obtained.

[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 embodiments and can take various forms.

(2a) In addition to the aluminum alloy plate of the above embodiments, the present disclosure also includes various forms such as members made of this aluminum alloy plate and methods of manufacturing this aluminum alloy plate.

(2b) The function of one component in the above embodiment may be distributed as multiple components, or the functions of multiple components may be integrated into one component. Further, 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. in the configuration of other embodiments. Note that all aspects included in the technical idea specified from the words in the claims are embodiments of the present disclosure.

[3. Example]
Below, the contents and evaluation results of tests conducted to confirm the effects of the present disclosure will be explained.

<Manufacture of aluminum alloy plate>
As Examples and Comparative Examples, aluminum alloy plates S1 to S11 shown in Tables 1 and 2 were manufactured. The specific manufacturing procedure will be explained below.

First, an ingot containing the components (mass%) of alloy numbers 1-5 shown in Table 3, with the remainder consisting of aluminum and unavoidable impurities was produced by a semi-continuous casting method. The ingot contains 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.

Next, the four sides of the ingot except for the front and rear ends were milled. Thereafter, the ingot was placed in a furnace and subjected to homogenization treatment. 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 form a rolled plate.

Furthermore, for S1, S2, S6-S9, and S11, the hot-rolled rolled plates were cold-rolled until they reached the CAL plate thickness shown in Table 1. Thereafter, the rolled plate having a CAL plate thickness was annealed in a continuous annealing furnace (CAL). The CAL temperature during annealing is as shown in Table 1. After annealing, the rolled plate was cooled to room temperature by air cooling. After cooling, the rolled plate was cold rolled again. The target cold rolling rate in cold rolling after annealing is as shown in Table 1.

For S3-S5 and S10, the hot-rolled rolled plates were cold-rolled without annealing. The target cold rolling rate in cold rolling is as shown in Table 1.

The product plate thickness after cold rolling in S1-S11 (that is, t ₁ in formula (7)) was set in the range of approximately 0.235±0.03 mm.

In S1-S11, after cold rolling, a paint was applied to the board surface, and a paint baking treatment was performed for about 30 seconds. The actual temperature (PMT) during paint baking is as shown in Table 1. By baking the paint, aluminum alloy plates S1-S11 were obtained. Table 1 also shows the plate thicknesses (ie, product plate thicknesses) of the aluminum alloy plates S1-S11 measured using a microgauge.

<Evaluation of aluminum alloy plate>
(Tensile properties)
Three No. 5 test pieces specified in JIS-Z-2241:2011 were prepared from aluminum alloy plates of S1-S11 by milling. The longitudinal directions of the three test pieces extend in directions making angles of 0°, 45°, and 90° with respect to the rolling direction, respectively.

A tensile test was conducted on these test pieces in accordance with JIS-Z-2241:2011, and the 0.2% proof stress and tensile strength were measured. The measurement results of 0.2% proof stress σ _0.2 and tensile strength σ _B and the average value σ _fm of 0.2% proof stress and tensile strength are shown in Tables 1 and 2.

In addition, three evaluation values S were calculated from the measurement results of the tensile test in the 0° direction, 45° direction, and 90° direction and equation (1) with respect to the rolling direction. The minimum evaluation value S _min , which is the minimum value of these evaluation values S, is shown in Table 2.

(toughness)
For the aluminum alloy plates S1-S11, the ratio of the total area (area ratio) in the L-ST cross section of Mg ₂ Si particles having an area of 0.3 μm ² or more was calculated using the measurement method described in the embodiment. The measurement results are shown in Table 2.

For the aluminum alloy plates S1 to S11, the number of repeated bending times and the normalized number of repeated bending times were calculated from the measurement method described in the embodiment and equations (3) and (4). The results are shown in Table 2.

(Strength anisotropy)
For the aluminum alloy plates S1-S11, the strength anisotropy (that is, the value D) was calculated from equation (5) described in the embodiment. The results are shown in Table 2.

(Scrap content ratio)
Regarding the composition of the aluminum alloy plates S1-S11, it was determined whether the possible blending ratio of scrap of 3104 aluminum alloy was 50% by mass or more. The results are shown in Table 2.

In Table 2, aluminum alloy plates with "≧50" can contain 50% by mass or more of 3104 aluminum alloy. Note that the possible scrap content ratio of 3104 aluminum alloy is determined based on Table 4.

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 for 3104 aluminum alloy, and the second row is the average value of the component specifications for 5182 aluminum alloy.

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, and the average value of Mn is 0.20% by mass. The average value is 0.7% by mass, and the average value of Mg is 2.8% by mass.

Therefore, when the proportion of each component in the aluminum alloy plate is equal to or greater than the above-mentioned values of Si, Fe, Cu, Mn, and Mg, the possible blending ratio of the 3104 aluminum alloy plate is 50% by mass or more. As the blending ratio of the 3104 aluminum alloy increases, the content of Si, Fe, Cu, and Mn increases, and the content of Mg decreases. The aluminum alloy plates S1 to S10 can contain 50% by mass or more of 3104 aluminum alloy scrap.

(evaluation)
The aluminum alloy plates S1-S9 have lower Mg content than the aluminum alloy plate S11, but have higher strength (that is, S _min ). In addition, the aluminum alloy plates S1 to S7, which were subjected to a higher homogenization temperature, exhibited high strength and a high number of repeated bending cycles. For example, when comparing S6-S7 and S8-S9, S6-S7 has a higher homogenization temperature, so it has higher strength than S8-S9 even if the process and paint baking temperature are the same.

Furthermore, the lower the paint baking temperature (PMT), the higher the strength of the alloy plate. For example, when comparing S3-S5, S6-S7, and S8-S9, the lower the paint baking temperature, the higher the strength.

The aluminum alloys S1 to S7 had a small area ratio of Mg ₂ Si particles, which was 0.2% or less. A comparison between S1-S7 and S8-S9 shows that the area ratio of Mg ₂ Si particles can be significantly reduced by increasing the homogenization temperature. Furthermore, when comparing S6-S7 and S8-S9, for example, S6-S7, which has a small area ratio of Mg ₂ Si particles, has a high strength and high It has toughness.

The number of repeated bending varies depending on the strength, and when comparing S3-S5 and S6-S7, which have a relatively small area ratio of Mg ₂ Si particles and the same cold rolling rate, S3 has a lower strength than S6-S7. - In S5, the number of repeated bending is much higher than in S6-S7.

Furthermore, the number of repeated bending changes also depends on the anisotropy of the material structure. For example, when comparing S1-S2, whose strength anisotropy is -12 MPa or more and 10 or less, and S6-S8, whose strength anisotropy is less than -12 MPa, the strength is comparable. Although the target is close, the number of repeated bendings of S1-S2 is much higher than that of S6-S8. Furthermore, when S1-S2 and S3-S5 are compared, the number of repeated bending times is the same, but S1-S2 has higher strength than S3-S5. S1-S2 is a material with a lower cold rolling rate and less anisotropy of material structure than S3-S8, and has high strength and high toughness.

As shown in FIG. 2, when S1, S2, and S3 are compared, the strength anisotropy has a negative correlation with the cold rolling rate. In a high-toughness material whose cold rolling ratio is suppressed to 50% or more and 80% or less by intermediate annealing or the like, the absolute value of strength anisotropy is considered to reach its maximum in the negative direction at a cold rolling ratio of 80%. Here, from the trend in FIG. 2, it is estimated that the strength anisotropy at a cold rolling reduction of 80% is -12 MPa, so it can be said that -12 MPa is the lower limit of the strength anisotropy.

Similarly, the absolute value of strength anisotropy is considered to be maximum in the positive direction at a cold rolling reduction of 50%, and from the trend in Figure 2, the strength anisotropy at a cold rolling reduction of 50% is estimated to be 15 MPa. Ru. On the other hand, the lower the cold rolling rate, the closer to the recrystallized state which is an isotropic material structure with less anisotropy, so it is difficult to think that the absolute value of strength anisotropy increases monotonically in the positive direction. Therefore, referring to S1, S2, and S11, it is considered appropriate that the strength anisotropy at a cold rolling reduction of 50% is about 12 MPa.

Claims (4)

The content of silicon (Si) is 0.27% by mass or more and 0.39% by mass or less,
The content of iron (Fe) is 0.35% by mass or more and 0.55% by mass or less,
The content of copper (Cu) is 0.17% by mass or more and 0.25% by mass or less,
The content of manganese (Mn) is 0.75% by mass or more and 0.95% by mass or less,
The content of magnesium (Mg) is 2.2% by mass or more and 2.8% by mass or less,
The remainder consists of aluminum (Al) and inevitable impurities,
0.2% proof stress σ _0.2 , tensile strength σ _B , and average value of 0.2% proof stress and tensile strength σ _fm in each of the 0° direction, 45° direction, and 90° direction with respect to the rolling direction. Among the evaluation values S calculated by the following formula (1) using, the minimum evaluation value S _min is 330 MPa or more and 390 MPa or less,
An aluminum alloy plate for a can lid, wherein the ratio of the total area of Mg ₂ Si particles having an area of 0.3 μm ² or more in the L-ST cross section at the center portion in the width direction is 0.2% or less .
S=σ _fm /(σ _0.2 /σ _B )...(1) The aluminum alloy plate for can lids according to claim 1 ,
The minimum evaluation value S _min is 360 MPa or more and 390 MPa or less,
The value obtained by subtracting the 0.2% proof stress σ _{0.2_0°} in the 90° direction to the rolling direction from the 0.2% proof stress σ _{0.2_0°} in the 0° direction with respect to the rolling direction is -12 MPa or more and 12 MPa or less. , aluminum alloy plate for can lids. The aluminum alloy plate for can lids according to claim 1 ,
When a test piece cut into a strip with a width of 12.5 mm and a length of 200 mm was repeatedly bent 90° and returned to the 0° position with the bending ridge line parallel to the rolling direction, The number of repeated bending times N, which is the number of times of the bending operation until the test piece breaks, is standardized by the plate thickness t of the test piece and the following formula (2), and the standardized number of repeated bending times _Ns is 17 times or more. , aluminum alloy plate for can lids.
_Ns = N×t/0.235 (2) The aluminum alloy plate for can lids according to claim 2 ,
When a test piece cut into a strip with a width of 12.5 mm and a length of 200 mm was repeatedly bent 90° and returned to the 0° position with the bending ridge line parallel to the rolling direction, The number of repeated bending times N, which is the number of times of the bending operation until the test piece breaks, is standardized by the plate thickness t of the test piece and the following formula (2), and the standardized number of repeated bending times _Ns is 17 times or more. , aluminum alloy plate for can lids.
_Ns = N×t/0.235 (2)

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