Aluminum alloy sheet for can body and method for producing the same

Abstract

To provide an aluminum alloy sheet for a can body.SOLUTION: An aluminum alloy sheet for a can body according to the present disclosure includes an aluminum alloy having a composition containing, by mass%, Si: 0.20% to 0.4%, Fe: 0.32% to 0.6%, Cu: 0.15% to 0.52%, Mn: 0.80% to 1.25%, and Mg: 0.60% to 1.80%, with the balance being Al and inevitable impurities, An area ratio (α - phase conversion ratio) of an AlMnFeSi-based intermetallic compound (α - phase) is 75% or more, and a number-density of precipitates having circle-equivalent diameters of 0.2 μm or less in the AlMnFeSi-based intermetallic compound is in a range of 1.2 * 106 to 4.0 * 106 / mm2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy sheet for can bodies and a method for producing the same. [Background technology]

[0002] It is necessary to suppress the ears that form during the DI (Drawing and Ironing) process of can stock. Until now, this has been achieved by optimizing the hot and cold rolling conditions. On the other hand, can stock is becoming thinner due to carbon neutrality measures, etc., and requirements for suppressing ears are becoming stricter. Therefore, methods for suppressing ears other than the conventional optimization of hot rolling and cold rolling conditions are required.

[0003] Patent Document 1 below discloses an aluminum alloy sheet for can bodies in which the area ratio of the α-AlMnFeSi intermetallic compound phase having a circle equivalent diameter of 1 μm or less is limited. By limiting the area ratio of the α-AlMnFeSi intermetallic compound phase, excessive strength improvement after can making is suppressed. However, Patent Document 1 does not disclose details of the α-AlMnFeSi, such as its composition ratio. Patent Document 2 discloses an aluminum alloy sheet for bottle cans in which the mass composition ratio (Fe / Mn) is limited. By limiting the Fe / Mn ratio, dispersed precipitates of α phase with a diameter of less than 1 μm are formed at a rate of 3 particles / mm 2 By satisfying the following conditions, the recrystallization rate of the aluminum alloy hot-rolled sheet for bottle cans is improved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6054658 [Patent Document 2] International Publication No. 2012 / 043582 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have conducted extensive research into aluminum alloy sheets for can bodies and have found that when an aluminum alloy sheet for can bodies having a desired thickness is obtained from an aluminum alloy slab by homogenizing treatment, soaking treatment, hot rolling, and cold rolling, it is important to adjust the alloy components and control the metal structure. Aluminum alloy sheet for can bodies is formed into can bodies through DI forming, which involves drawing and ironing. However, 0°, 90°, and 45° ears can occur around the can body. If these ears are too high, the tips of the ears can tear off during DI forming and get caught in the process, causing the body to break or the bottom to break. They can also cause clogging during transportation after DI forming, resulting in reduced productivity. The formation of a recrystallization texture, Cube orientation, in aluminum alloy sheet texture affects the 0° and 90° ears, while the formation of Goss orientation affects the 0° ears. Furthermore, the formation of rolling textures, Brass orientation, S orientation, and Cu orientation, affects the 45° ears. In order to cope with the trend toward thinner can stock, it is preferable to obtain an aluminum alloy sheet in which the 0°, 90°, and 45° ears are well-balanced in order to suppress the formation of ears during DI forming. To achieve this, in addition to controlling the alloy composition, the structure is controlled by a homogenization treatment applied to the slab, and the material after the structure control is subjected to hot rolling and cold rolling. As a result of research into whether the desired structure control can be achieved, the present invention was arrived at.

[0006] In order to solve the above-mentioned problems, the present invention relates to a technology for providing an aluminum alloy sheet for can bodies that has excellent DI formability, and a manufacturing method thereof, by adjusting the transformation from the AlMnFe metastable phase to the stable α phase, adjusting the recrystallization rate due to the precipitation effect of fine precipitates, controlling the growth of Cube-oriented grains, and balancing the ears. [Means for solving the problem]

[0007] (1) An aluminum alloy sheet for can bodies according to the present embodiment is an aluminum alloy sheet for can bodies made of an aluminum alloy having a composition containing, by mass%, Si: 0.20 to 0.4%, Fe: 0.32 to 0.6%, Cu: 0.15 to 0.52%, Mn: 0.80 to 1.25%, Mg: 0.60 to 1.80%, and the balance being Al and unavoidable impurities, wherein the area ratio (alpha conversion rate) of an AlMnFeSi-based intermetallic compound phase (α phase) is 75% or more, and the number density of precipitates having a circle equivalent diameter of 0.2 μm or less in the AlMnFeSi-based intermetallic compound is 1.2 × 10 6 ~4.0×10 6 pieces / mm 2 The range is characterized by the following.

[0008] (2) In the aluminum alloy sheet for can bodies according to this embodiment, the sum of the degrees of integration of Cu orientation, S orientation, and Bs orientation is preferably 34.0 or less. (3) In the aluminum alloy sheet for can bodies according to this embodiment, it is preferable that the 0.2% yield strength after heat treatment at 210°C for 10 minutes is 245 MPa or more and 305 MPa or less.

[0009] (4) A method for producing an aluminum alloy sheet for can bodies according to the present embodiment includes the steps of: subjecting a slab of an aluminum alloy having a composition, in mass%, of Si: 0.20 to 0.4%, Fe: 0.32 to 0.6%, Cu: 0.15 to 0.52%, Mn: 0.80 to 1.25%, Mg: 0.60 to 1.80%, with the balance being Al and unavoidable impurities to a homogenization treatment and a soaking treatment, followed by hot rolling and cold rolling to produce an aluminum alloy sheet for can bodies. In producing the above, a homogenization treatment is performed by holding the temperature at 500°C or more and 600°C or less for 3 hours or more, a soaking treatment is performed by holding the temperature at 500°C or more and 580°C or less for 1 hour or more, a strain rate of the final pass of hot rolling is set to 70 / s or more and 160 / s or less and an outlet temperature is set to 290°C or more and 380°C or less to obtain a hot-rolled sheet, and then this hot-rolled sheet is cold-rolled to a sheet thickness of 0.2 mm or more and 0.5 mm or less.

[0010] (5) In the method for producing an aluminum alloy sheet for can bodies according to this embodiment, it is preferable to obtain an aluminum alloy sheet for can bodies in which the sum of the degrees of integration of Cu orientation, S orientation, and Bs orientation is 34.0 or less. (6) In the method for producing an aluminum alloy sheet for can bodies according to this embodiment, it is preferable to obtain an aluminum alloy sheet for can bodies having a 0.2% yield strength of 245 MPa or more and 305 MPa or less after heat treatment at 210°C for 10 minutes. [Effects of the Invention]

[0011] The present invention has the above-mentioned composition, and the area ratio of the AlMnFeSi-based intermetallic compound phase is 75% or more, and the number density of the AlMnFeSi-based intermetallic compound with a circle equivalent diameter of 0.2 μm or less is 1.2 × 10 6 ~4.0×10 6 pieces / mm 2 By setting the thickness within this range, it is possible to provide an aluminum alloy sheet for can bodies that has good edge balance even when subjected to DI forming. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is an explanatory diagram showing the 0°, 90°, and 45° ears on a can body during can-making. [Figure 2] FIG. 2 is an explanatory diagram showing a cupping step when forming a can body from an aluminum alloy plate. [Figure 3] A conceptual diagram showing the correlation between second-phase particles precipitated in an aluminum alloy structure and grain boundary migration within the crystal. [Figure 4] FIG. 2 is an explanatory diagram showing an example of homogenization treatment conditions, soaking treatment conditions, and one process of hot rolling and cold rolling. [Figure 5] A conceptual diagram showing the transformation from a metastable phase with a composition represented by Al6(Fe,Mn) to the α-phase (stable phase) with a composition represented by Al12(Fe,Mn)3Si. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an example of an embodiment will be described in detail with reference to the accompanying drawings. Note that the drawings used in the following description may show characteristic portions in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand.

[0014] The aluminum alloy sheet for can bodies according to the present invention is made of an aluminum alloy having a composition containing, by mass%, Si: 0.20 to 0.4%, Fe: 0.32 to 0.6%, Cu: 0.15 to 0.52%, Mn: 0.80 to 1.25%, Mg: 0.60 to 1.80%, and the remainder being Al and unavoidable impurities. In this specification, when a specific range is expressed using "to," the range includes the lower and upper limits unless otherwise noted. Therefore, 0.2 to 0.4% means a range of 0.2% or more and 0.4% or less. Si: 0.2 to 0.4% In aluminum alloy sheets for can bodies, Si contributes to improving yield strength through the precipitation of Mg2Si, and also contributes to preventing seizure on the mold through the die cleaning effect during ironing in DI processing. If the Si content is less than 0.2%, the amount of Mg2Si precipitated is small, resulting in insufficient yield strength. If the Si content is extremely low, the alpha phase rate decreases, causing seizure on the DI mold. If the Si content exceeds 0.4%, the excessive increase in yield strength results in poor formability.

[0015] Fe: 0.32 to 0.6% In aluminum alloy sheets for can bodies, Fe contributes to improving yield strength by forming Al-Mn-Fe intermetallic compounds, and also contributes to preventing seizure on the mold by its die cleaning effect during ironing. If the Fe content is less than 0.32%, the aluminum alloy sheet for can bodies will have insufficient yield strength due to the small amount of Al-Mn-Fe intermetallic compound phase. Furthermore, there is a risk of seizure on the mold during ironing. If the Fe content exceeds 0.6%, the formability will deteriorate due to excessive improvement in yield strength and decrease in elongation. Furthermore, this will lead to a decrease in corrosion resistance.

[0016] Cu: 0.15 to 0.52% In aluminum alloy sheets for can bodies, Cu contributes to improving yield strength through solid solution strengthening. If the Cu content is less than 0.15%, the yield strength is insufficient, and if the Cu content exceeds 0.52%, the yield strength is excessively improved, which leads to a decrease in formability and a decrease in corrosion resistance. Mn: 0.80 to 1.25% In aluminum alloy sheets for can bodies, Mn contributes to the formation of Al-Mn-Fe intermetallic compounds and Al-Mn-Fe-Si intermetallic compounds, and by dispersing it in the matrix, it contributes to dispersion strengthening without reducing corrosion resistance and contributes to improving yield strength. If the Mn content is less than 0.80%, the amount of intermetallic compounds formed and the dispersion state thereof will be insufficient, resulting in a decrease in yield strength.If the Mn content exceeds 1.25%, the excessive increase in yield strength will lead to a deterioration in formability.

[0017] Mg: 0.60-1.80% In aluminum alloy sheets for can bodies, Mg contributes to improving yield strength and work hardening through solid solution strengthening or the precipitation of Mg2Si. If the Mg content is less than 0.60%, the amount of solid solution and Mg2Si is low, resulting in insufficient yield strength. Furthermore, work hardening is insufficient, resulting in insufficient can body strength after can forming. If the Mg content exceeds 1.80%, excessive yield strength is increased and elongation is reduced, resulting in poor formability, and excessive work hardening can cause body breakage during ironing.

[0018] "Method of manufacturing aluminum alloy plate" To produce an aluminum alloy sheet having the above-described composition, a slab is obtained from a molten aluminum alloy having the desired composition by using a semi-continuous casting method or the like, and the slab is subjected to a homogenization treatment and a soaking treatment, and then to hot rolling and cold rolling. The homogenization temperature and treatment time are preferably 500 to 600°C x 3 hours or more, and the soaking temperature and treatment time are preferably 500 to 580°C x 1 hour or more. In hot rolling, the strain rate in the final pass is preferably set to 70 to 160 / s, and the delivery temperature is preferably set to 290 to 380° C. As for the hot rolling conditions, the effects of the present invention are not hindered if the error in the strain rate is about ±10 / s from the target value, and if the error in the delivery temperature is about ±5° C. from the target value. It is preferable to cold roll the steel sheet to a final thickness of 0.2 to 0.5 mm for can bodies.

[0019] Homogenization conditions: 500-600°C x 3 hours or more Improved slab homogeneity, controllability of hot-rolled sheet structure and α phase (Al 12 To transform the material into (Fe, Mn)3Si) and control the size of the precipitates, the material is homogenized at 500-600°C for at least 3 hours (500-600°C x 3 hours or more). If the homogenization temperature is lower than 500°C or if the homogenization time is less than 3 hours, the homogenization is insufficient, and the metastable phase represented by Al6(Fe,Mn) changes to the α phase (Al 12 Insufficient phase transformation to (Fe,Mn)3Si) can cause material to seize onto the DI mold. Furthermore, an increase in precipitates with a circle-equivalent diameter of 0.2 μm or less leads to insufficient recrystallization, resulting in the formation of excessive 45°-direction ears due to an increased concentration of Cu+S+Bs orientation. For this reason, it is preferable to set the lower limit of the homogenization temperature at 500°C. At a high homogenization temperature, the precipitates become coarse, and at a low temperature, the precipitates become fine. At a long homogenization time, the gelatinization rate increases, and at a short time, the gelatinization rate decreases. The area ratio of the α phase (α phase ratio) is determined by the homogenization treatment conditions (temperature, time). The α phase ratio increases as the homogenization treatment time increases. There is an optimum homogenization treatment temperature at which the α phase easily progresses, and this temperature varies depending on the alloy components. Hereinafter, in this specification, the area ratio of the α phase will be referred to as the α phase ratio and explained. The α phase ratio will be explained again later.

[0020] If the homogenization temperature exceeds 600°C, there is a risk of remelting, and the α phase (Al 12This may result in the material sticking to the DI mold due to insufficient phase transformation to (Fe, Mn)3Si. Furthermore, the number of precipitates of AlMnFeSi-based intermetallic compounds with a circle-equivalent diameter of 0.2 μm or less decreases. Therefore, it is preferable to set the upper limit of the homogenization temperature to 600°C. In order to obtain homogeneity of the slab and from the viewpoint of productivity, the homogenization treatment time is set to 3 hours or more. The homogenization treatment time is determined based on the heterogeneity of the metal structure, the α phase (Al 12 The lower limit is set at 3 hours to prevent the material from seizing onto the DI mold due to insufficient phase transformation to (Fe,Mn)3Si). Even within the above-mentioned range, the homogenization temperature is more preferably 520° C. or higher and 595° C. or lower for 3 hours or longer.

[0021] Soaking conditions: 500-580℃ x 1 hour or more From the viewpoint of temperature controllability during hot rolling and productivity, the soaking treatment is preferably performed at 500 to 580°C for 1 hour or more. The soaking treatment is performed to prevent uneven temperature, insufficient temperature, or excessive temperature of the slab before hot rolling. For this reason, it is desirable to perform the soaking treatment for 1 hour or more, but productivity decreases if the time is too long. Even within the above range, it is more preferable that the soaking temperature is 500° C. or higher and 575° C. or lower for 1 hour or longer.

[0022] Average strain rate of the final pass during hot rolling: 70 / s to 160 / s The average strain rate of the final pass during hot rolling affects the recrystallization rate of the hot-rolled sheet. To prevent excessive 45° ear formation due to a decrease in the recrystallization rate, the lower limit is set to 70 / s. To eliminate the risk of reduced productivity due to roll heat and to prevent the risk of deterioration of sheet profile controllability, the upper limit is set to 160 / s. Exit temperature of the final hot rolling pass: 290℃~380℃ The exit temperature of the final pass of hot rolling affects the recrystallization rate of the hot-rolled sheet. To prevent excessive 45° direction selvage formation due to an increase in the concentration of Cu+S+Bs orientation, the lower limit is preferably set to 290°C. Furthermore, to eliminate the risk of reduced productivity due to roll heat, the upper limit is preferably set to 380°C.

[0023] "Structure and characteristics of aluminum alloy sheets" The aluminum alloy sheet for can bodies of this embodiment obtained by the manufacturing method described above has an area ratio (alpha ratio) of AlMnFeSi-based intermetallic compound phase (α phase) of 75% or more, and the number density of precipitates with a circle-equivalent diameter of 0.2 μm or less in the AlMnFeSi-based intermetallic compound is 1.2 × 10 6 ~4.0×10 6 pieces / mm 2 It is preferable that the range is: In the aluminum alloy sheet for can bodies of this embodiment, the total of the integration degrees of Cu orientation, S orientation, and Bs orientation is preferably 34.0 or less. The aluminum alloy sheet for can bodies of this embodiment preferably has a 0.2% yield strength of 245 MPa or more and 305 MPa or less after heat treatment at 210°C for 10 minutes.

[0024] The sum of the concentrations of Cu, S, and Bs orientations affects the ear shape after DI forming. If the sum of the concentrations of Cu, S, and Bs orientations exceeds 34.0, it will lead to the formation of excessive 45° ears. After DI processing, the height of the peaks at 45° to the rolling direction will increase, and the earing ratio will not be within the appropriate range. The lower limit of the total accumulation degree of Cu orientation + S orientation + Bs orientation is not particularly limited, but may be 15.0 or more.

[0025] "How to check the total density of Cu orientation + S orientation + Bs orientation" To confirm the total degree of integration of Cu orientation + S orientation + Bs orientation, an incomplete pole figure is obtained and then the value can be determined from the incomplete pole figure using crystal orientation function analysis software. As an example, a circular sample with a diameter of 40 mm is taken from an aluminum alloy plate so that the plate surface serves as the measurement surface. Next, an X-ray diffraction system (Rigaku Corporation SmartLab) is used to measure the measurement surface using the Schulz reflection method (α = 20° to 90°, β = 0° to 360°, measurement interval 5.0°) with a Cu tube voltage of 40 kV and a tube current of 50 mA, and (220), (200), and (111) incomplete pole figures are obtained. From this incomplete pole figure, the crystal orientation distribution function f(ψ1, φ, ψ2) is determined using crystal orientation distribution function analysis software (StandardODF, manufactured by Norm Engineering Co., Ltd.) with a 22nd-order series expansion method. The values ​​for ψ1=90°, φ=30°, ψ2=45° are taken as the concentration of Cu orientation. The values ​​for ψ1=60°, φ=35°, ψ2=65° are taken as the concentration of S orientation. The values ​​for ψ1=35°, φ=45°, ψ2=0° are taken as the concentration of Bs orientation.

[0026] "Number density of precipitates with a circular equivalent diameter of 0.2 μm or less" Among AlMnFeSi intermetallic compounds, the number density of precipitates with a circle equivalent diameter of 0.2 μm or less affects the prevention of seizure on the mold during DI molding and the strength of the can body. 6 pieces / mm 2 If the number density is less than 4.0×10, the material will stick to the DI mold and the body will be easily torn. 6 pieces / mm 2 If the angle exceeds this value, the height of the peaks at 45° to the rolling direction after DI processing will be too high, making ears more likely to form. In addition, excessive strength improvement in the can body neck will result in a decrease in neck formability.

[0027] "Method for determining the number density of precipitates with a circle equivalent diameter of 0.2 μm or less" The surface of the aluminum alloy plate was mechanically polished to expose the central plane of the plate thickness, and the observation range was measured using a field emission scanning electron microscope (FE-SEM) at a magnification of 10,000 times, with a total observation area of ​​1,000 μm 2 Images are taken from multiple fields of view so that the above is achieved. The observation position is at least 5 μm away from the edge of coarse particles with an equivalent circle diameter of 5 μm or more. The obtained images are binarized using ImageJ so that the Al matrix and particles can be distinguished. The equivalent circle diameter is calculated from the area of ​​each particle, and particles with an equivalent circle diameter of 0.2 μm or less are counted. This is done for all images, and the total count of particles with an equivalent circle diameter of 0.2 μm or less is divided by the observation range to obtain the number density of precipitates with an equivalent circle diameter of 0.2 μm or less.

[0028] The precipitation state of precipitates with an equivalent circle diameter of 0.2 μm or less can be determined by setting the Si, Fe, and Mn element values ​​and the homogenization treatment temperature conditions. The higher the homogenization treatment temperature, the lower the number density of precipitates with an equivalent circle diameter of 0.2 μm or less. The higher the Si element value, the lower the number density of precipitates, and the higher the Fe and Mn element values, the higher the number density of precipitates. The number density of precipitates for suppressing ear formation and the delivery temperature of the final pass of hot rolling have the following relationship. Exit temperature of the final pass of hot rolling (K) / Number density of precipitates (pieces / mm 2 )>0.14×10 -3

[0029] "Area ratio of AlMnFeSi intermetallic compound phase (α phase) (α phase ratio)" The area ratio (alpha ratio) of the AlMnFeSi-based intermetallic compound phase (α phase) affects the prevention of seizure on the die during DI molding, and if the area ratio is less than 75%, seizure on the DI die is more likely to occur. Alphaling rate: 75% or more The area ratio of the α phase (α-phase ratio) is determined by the homogenization conditions (temperature, time). The α-phase ratio increases as the homogenization time increases. There is an optimum homogenization temperature at which α-phase easily progresses, and this varies depending on the component values. To prevent seizure on the mold during DI molding, the α-phase ratio must be 75% or more, preferably 80% or more. There is no particular upper limit to the α-phase ratio, but it may be 95% or less.

[0030] "How to check the alpha conversion rate" The surface of the aluminum alloy plate was mechanically polished and exposed at the center of the plate thickness. The analysis range was 12.0 mm using FE-EPMA. 2 Elemental surface analysis is performed for Fe, Mn, and Si as described above. The distribution maps of Fe and Mn are superimposed to calculate the area A containing Fe, Mn, or both. Next, the distribution maps of Fe, Mn, and Si are superimposed to calculate the area B containing Fe and Si, or Mn and Si, or Fe, Mn, and Si. B / A x 100% is the alpha conversion rate.

[0031] "How to check 0.2% yield strength after heat treatment at 210℃ for 10 minutes" JIS No. 5 test pieces are cut out from the aluminum alloy plate so that the rolling direction and the tensile direction are the same. The JIS No. 5 test pieces are heat treated in a heat treatment furnace at 210°C for 10 min. Then, the initial strain rate is 6.67 x 10 -4 A tensile test is carried out at 1000 kJ / s, and the 0.2% yield strength is measured. This test is repeated three times, and the average value is the 0.2% yield strength of the aluminum alloy plate after heat treatment at 210°C for 10 minutes.

[0032] 0.2% yield strength after heat treatment at 210°C for 10 minutes: 245-305 MPa If the 0.2% yield strength after heat treatment at 210°C for 10 minutes is less than 245 MPa, the strength of the can body will be low, and there is a risk that the can body will buckle due to the indentation load during the can lid seaming process. If the 0.2% yield strength after heat treatment at 210°C for 10 minutes exceeds 305 MPa, the strength of the can body will be excessively high, and there is a risk of flange cracking occurring during flanging.

[0033] "About ear rate" When aluminum alloy sheets are used in can manufacturing, ears are generated. Figure 1 shows examples of 0°, 90°, and 45° ears that occur during can manufacturing. As shown in Figure 2, an aluminum alloy sheet can be formed into a cylindrical shape by deep drawing an aluminum alloy sheet 2 with a punch 1 while sandwiching it between a drawing die 3 and blank holder 4. In the processed cylindrical tube 5 with a bottom shown in Figure 1, if the rolling direction is the direction indicated by the arrow, the ears occurring at the 0° and 90° positions around the circumferential direction of the opening of the tube 5, starting from the position of the arrow, are the 0° ear and the 90° ear, and the ears occurring at positions 45° offset from these positions around the circumferential direction of the tube 5 are the 45° ear. The earing ratio can be determined by measuring the height of the peaks (the height from the bottom of the tube to the top of the peaks) and the height of the valleys (the height from the bottom of the tube to the bottom of the valleys) at the opening of the tube 5 at each of these positions. The earing ratio can be calculated from the side wall height of a cup obtained by deep drawing an aluminum alloy sheet using an Erichsen tester. (average peak height - average valley height) ÷ average valley height × 100 = earing rate (%) The detailed measurement of the ear ratio will be explained in the examples given later.

[0034] The alloy has the above-mentioned alloy composition, the area ratio (alpha ratio) of the AlMnFeSi intermetallic compound phase (α phase) is 75% or more, and the number density of precipitates with a circle equivalent diameter of 0.2 μm or less in the AlMnFeSi intermetallic compound is 1.2 × 10 6 ~4.0×10 6 pieces / mm 2 This aluminum alloy sheet has a low earing ratio when made into a can by DI processing, and can be used as a thin-walled can material with little waste, making it carbon-neutral. Furthermore, this aluminum alloy sheet exhibits a 0.2% yield strength in the range of 245 to 305 MPa, which is appropriate for can manufacturing.

[0035] The aforementioned alpha conversion rate is 75% or more, and the number density of precipitates with a circle equivalent diameter of 0.2 μm or less is 1.2 × 10 6 ~4.0×10 6 pieces / mm 2 The following phenomena are thought to be the effects that the metal structure may experience due to the range. Al6(Mn,Fe) metastable phase to stable phase (α phase: Al 12 The transformation into (Fe,Mn)3Si) can be called α-phase. The α-phase is thought to prevent adhesion to the mold used in DI molding. However, the number density of fine precipitates of 0.2 μm or less can be understood as the density of second-phase particles in the aluminum alloy structure mentioned above. When precipitates are coarse particles with a size of approximately 1 μm or more, a strain field is generated around them, which is thought to make them more likely to become nuclei for randomly oriented recrystallized grains. In the metal structure where multiple second-phase particles are precipitated as shown in Figure 3, the influence on grain growth is thought to be that the second-phase particles exert a pinning effect, suppressing grain boundary migration in the crystal grain structure. Differences in the growth rate of the crystal grain boundaries are thought to affect the generation of texture in the metal structure through influences such as preferential growth of the Cube orientation, which is a recrystallization texture. Therefore, it is considered that the balance between the Cube orientation and the rolling texture such as Cu orientation is important for aluminum alloy sheets manufactured through rolling.

[0036] In Fig. 5, the composition shown as Al6(Mn,Fe) changes from the metastable phase to the stable phase (α phase: Al 12 A model of the transformation process from (Fe,Mn)3Si to (Fe,Mn)3Si is shown. Assuming that the Al6(Mn,Fe) metastable phase6 is formed in the metal structure before the homogenization treatment, by performing the homogenization treatment under the above conditions, the elemental Si in the Al matrix diffuses, or Mg2Si decomposes, and Si diffuses, forming the α phase (Al 12 (Fe,Mn)3Si).

[0037] The aluminum alloy slab having the above-mentioned composition is subjected to the homogenization treatment and soaking treatment conditions described above to adjust the metal structure, and then subjected to the hot rolling and cold rolling conditions described above to obtain a thickness suitable for can manufacturing, thereby obtaining a target aluminum alloy sheet. This aluminum alloy sheet has the characteristic that, when it is made into a can by DI processing, it can be made into a can with good ear balance and a low ear ratio. [Example]

[0038] Aluminum alloy slabs having the compositions shown in Table 1 below (balance: Al and unavoidable impurities) were produced by semi-continuous casting, and these aluminum alloy slabs were subjected to a homogenization treatment under the conditions (temperature, time) shown in Table 2 below, and then to a soaking treatment under the conditions (temperature, time) shown in Table 2. After these treatments, the slabs were hot-rolled under the conditions (strain rate in the final pass, delivery temperature) shown in Table 2, and subsequently cold-rolled to obtain aluminum alloy plates (Samples Nos. 1 to 29) having thicknesses of 0.2 to 0.5 mm. An overview of the thermal history for the homogenization and soaking conditions, as well as an overview of the hot rolling and cold rolling processes, is shown in Figure 4. The temperature and time of the homogenization and the temperature and time of the soaking are as shown in Table 2, and the thickness of the sheet after cold rolling is as shown in Figure 4.

[0039] For each aluminum alloy plate sample, the alpha phase ratio, number density, and accumulation degree were determined based on the method for confirming the area ratio (alpha phase ratio) of the AlMnFeSi-based intermetallic compound phase (alpha phase), the method for confirming the number density of precipitates with a circle equivalent diameter of 0.2 μm or less, and the method for confirming the total accumulation degree of Cu orientation + S orientation + Bs orientation, all of which were described above. These results are shown in Table 2 below. Next, the 0.2% yield strength was determined based on the method for determining the 0.2% yield strength after heat treatment at 210°C for 10 minutes described above, and the results are shown in Table 2. In addition, the earing ratio was measured and evaluated, and the DI formability (evaluation of body breakage) and can body formability (evaluation of flange formability) were evaluated based on the methods described below, and the results are shown in Table 2.

[0040] How to evaluate your ears To evaluate the suppression of earing in aluminum alloy sheets, the earing rate during can manufacturing was measured. The earing ratio was calculated from the sidewall height of a cup obtained by deep drawing an aluminum alloy sheet using an Erichsen testing machine. The processing conditions were a punch diameter of 33 mm (flat-head punch), drawing ratio of 1.75, and blank holding force of 5 kN. The sidewall height of this cup was measured with a digital micrometer, and the earing ratio was calculated using the following formula. (average peak height - average valley height) ÷ average valley height × 100 = earing rate (%) The average of the maximum heights of the peaks in the 0±20° and 180±20° directions relative to the rolling direction, and the average of the maximum heights of the peaks in the 45±20°, 135±20°, 225±20°, and 315±20° directions relative to the rolling direction were calculated, and the average of the higher maximum heights was used as the average peak height in the above formula. The average of the minimum heights of the valleys in the 90±20° and 270±20° directions relative to the rolling direction was used as the average valley height in the above formula. If the ear rate was 7.0% or less, it was rated as "A", if it was over 7.0% but not more than 9.5%, it was rated as "B", and if it was over 9.5%, it was rated as "C". A rating of "A" or "B" was judged as passing, and a rating of "C" was judged as failing.

[0041] "Evaluation of DI moldability" For DI formability, a can with no body breakage during continuous can-making of 10,000 cans was rated as "A," a can with one body breakage was rated as "B," and a can with two or more body breakages was rated as "C." Cans with an "A" or "B" rating were judged as passing, and cans with a "C" rating were judged as failing.

[0042] "Evaluation of can body formability" Can body formability was evaluated as follows: no flange cracks occurred during continuous can-making of 10,000 cans, and the grade was "A." If one can had a flange crack, the grade was "B." If two or more cans had a flange crack, the grade was "C." Cans that received a grade of "A" or "B" were judged to be acceptable, and those that received a grade of "C" were judged to be unacceptable.

[0043] [Table 1]

[0044] [Table 2]

[0045] [Table 3]

[0046] As shown in the test results in Table 3, samples Nos. 1 to 22 are aluminum alloy sheets for can bodies, each containing, by mass%, 0.20 to 0.4% Si, 0.32 to 0.6% Fe, 0.15 to 0.52% Cu, 0.80 to 1.25% Mn, and 0.60 to 1.80% Mg, with the remainder being Al and unavoidable impurities. These samples have an area ratio (alpha phase ratio) of 75% or more of an AlMnFeSi-based intermetallic compound phase (α phase), and a number density of precipitates with a circle-equivalent diameter of 0.2 μm or less among the AlMnFeSi-based intermetallic compounds of 1.2 × 10 6 ~4.0×10 6 pieces / mm 2 Specifically, the alpha conversion rate was 75.3% to 91.9%, and the number density was 1.22 × 10 6 ~3.95×10 6 pieces / mm 2 It was. These samples had excellent earing ratios, little occurrence of trunk breakage, and were also evaluated as excellent in flange formability. Furthermore, the sum of the integration degrees of Cu orientation, S orientation, and Bs orientation for these samples was 34 or less. Specifically, it was 33.8 or less. The 0.2% proof stress of these samples was in the range of 245 to 305 MPa. Specifically, it was 247 to 304 MPa.

[0047] Comparative Example No. 23 shown in Table 3 had a low Si content and a high Mg content as shown in Table 1, and therefore had a low alpha conversion rate and suffered from body breakage during DI forming. As shown in Table 1, the No. 24 sample had too high an Fe content, Cu content, and Mn content, which resulted in an excessively high number density of precipitates, and the total value of the accumulation of Cu orientation, S orientation, and Bs orientation became too high, resulting in a high earing ratio. As shown in Table 1, the Fe, Cu, and Mg contents of sample No. 25 were too low, resulting in a low number density of precipitates, a decrease in yield strength, the occurrence of trunk breakage during DI forming, and a low evaluation of flange formability.

[0048] In sample No. 26, the Si content was too high and the Mn content was too low, as shown in Table 1, and manufacturing method F was used, as shown in Table 2. As a result, the alpha conversion rate was low and trunk breakage occurred during DI forming.

[0049] As shown in Table 1, the Cu content and Mg content of sample No. 27 were too high, resulting in an excessively high yield strength and a poor evaluation of flange formability. The alloy composition of sample No. 28 was within the desired range, but because manufacturing method G shown in Table 2 was used, the alpha conversion rate was low and cuts occurred during DI forming. The alloy composition of sample No. 29 was within the desired range, but because manufacturing method H shown in Table 2 was used, the alpha conversion rate was low and cuts occurred during DI forming.

[0050] Furthermore, it is thought that the effect of core breakage due to die seizure during DI molding can be understood to some extent by focusing on intermetallic compound phases in a wide range, such as a circle equivalent diameter of 1 μm or less. However, even if we focus only on mold seizure during DI molding and solve this problem, the problem of high earing ratio that occurs during DI molding cannot be solved. The present invention has been made to solve two problems: to understand the influence on body breakage during DI molding, and to reduce the earing rate that occurs during DI molding. In order to solve the two problems simultaneously, the number density of precipitates having a circle equivalent diameter of 0.2 μm or less is optimized, and the homogenization conditions are adjusted so that the alpha phase ratio is a certain value or more to prevent the occurrence of trunk breaks. That is, in the above examples, an aluminum alloy sheet having a composition shown in Table 1 was used, and it was demonstrated that an aluminum alloy sheet capable of solving the two problems simultaneously can be provided by adjusting the conditions shown in Table 2 and the alpha phase ratio and precipitate number density shown in Table 3 to be within suitable ranges. [Explanation of symbols]

[0051] 1...punch, 2...aluminum alloy plate, 3...drawing die, 4...wrinkle holder, 5...cylinder.

Claims

1. an aluminum alloy sheet for can bodies, the aluminum alloy sheet comprising an aluminum alloy having a composition containing, in mass %, 0.20 to 0.4% Si, 0.32 to 0.6% Fe, 0.15 to 0.52% Cu, 0.80 to 1.25% Mn, 0.60 to 1.80% Mg, and the balance being Al and unavoidable impurities; The area ratio (alpha ratio) of the AlMnFeSi intermetallic compound phase (α phase) is 75% or more, and the number density of precipitates with a circle equivalent diameter of 0.2 μm or less in the AlMnFeSi intermetallic compound is 1.2 × 10 ６ ~4.0 x 10 ６ pieces / mm ２ is in the range of 1. An aluminum alloy sheet for can bodies, comprising:

2. 2. The aluminum alloy sheet for can bodies according to claim 1, wherein the sum of the degrees of integration of Cu orientation, S orientation and Bs orientation is 34.0 or less.

3. 3. The aluminum alloy sheet for can bodies according to claim 1, wherein the 0.2% yield strength after heat treatment at 210° C. for 10 minutes is 245 MPa or more and 305 MPa or less.

4. An aluminum alloy slab having a composition comprising, in mass%, Si: 0.20 to 0.4%, Fe: 0.32 to 0.6%, Cu: 0.15 to 0.52%, Mn: 0.80 to 1.25%, Mg: 0.60 to 1.80%, with the balance being Al and inevitable impurities, is subjected to a homogenization treatment and a soaking treatment, and then subjected to hot rolling and cold rolling to produce an aluminum alloy sheet for a can body, A homogenization treatment is performed by holding the temperature at 500°C or higher and 600°C or lower for 3 hours or more. A soaking treatment is performed by holding the temperature at 500°C or higher and 580°C or lower for 1 hour or more, A hot-rolled sheet is obtained by setting the strain rate of the final pass of hot rolling to 70 / s or more and 160 / s or less and the delivery temperature to 290°C or more and 380°C or less, The method for producing an aluminum alloy sheet for can bodies is characterized in that the hot-rolled sheet is cold-rolled to a thickness of 0.2 mm to 0.5 mm.

5. 5. The method for producing an aluminum alloy sheet for can bodies according to claim 4, wherein the aluminum alloy sheet for can bodies has a total of the degrees of integration of Cu orientation, S orientation and Bs orientation of 34.0 or less.

6. 6. The method for producing an aluminum alloy sheet for can bodies according to claim 4 or 5, wherein the aluminum alloy sheet for can bodies has a 0.2% yield strength of 245 MPa or more and 305 MPa or less after heat treatment at 210°C for 10 minutes.

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