JP2023054623A - Aluminum alloy sheet for can bodies - Google Patents

Abstract

To provide an aluminum alloy sheet for can bodies that has reduced circumferential anisotropy in the wall thickness of the opening of a drawing cup to be molded.SOLUTION: An aluminum alloy sheet for can bodies contains Si: 0.16 mass% or more and 0.60 mass% or less, Fe: 0.3 mass% or more and 0.6 mass% or less, Cu: 0.10 mass% or more and 0.35 mass% or less, Mn: 0.5 mass% or more and 1.2 mass% or less, Mg: 0.7 mass% or more and 2.0 mass% or less, with the balance being Al and inevitable impurities. When the aluminum alloy sheet for can bodies is subjected to a structural observation, the number density of intermetallic compounds with a circle equivalent diameter of 0.10 μm or more and less than 1.00 μm is 1.7×105/mm2 or more to 4.0×105/mm2, and the number density of intermetallic compounds equal to or greater than a critical circle equivalent diameter to be the core of recrystallization is 1.0×103/mm2 or more to 3.5×103/mm2 or less.SELECTED DRAWING: None

Description

The present invention relates to an aluminum alloy sheet for can bodies.

The body of an aluminum beverage can is manufactured through processes such as drawing, redrawing, ironing, washing/drying, printing/baking on the outside surface, coating/baking on the inside surface, and necking. The side wall of the cup after drawing and redrawing (drawn cup) becomes thicker from the bottom toward the opening than before the drawing. At this time, the degree of thickening varies in the circumferential direction due to the plastic anisotropy of the raw material, and as a result, the cup may have different thicknesses in the circumferential direction at the same height. If the wall thickness of the cup after drawing and redrawing is uneven in the circumferential direction, the processing rate will differ in the circumferential direction when processing to a uniform wall thickness in the circumferential direction in the subsequent ironing process, so the side wall The resulting tensile stress becomes non-uniform in the circumferential direction, making breakage more likely to occur during processing. In recent years, there has been an increasing trend in the number of can bodies with smaller diameters, in other words, with larger drawing ratios than in the past. Since the thickness difference in the circumferential direction of the cup tends to increase as the drawing ratio increases, there is a possibility that the problem of ironing workability will become more apparent.

In relation to the above, an aluminum alloy for cambodies with good roundness of the drawing cup, which defines the chemical composition, ear ratio, soaking conditions, rough hot rolling conditions, hot finish rolling conditions and cold rolling conditions A method for manufacturing a plate has been proposed (see Patent Document 1, for example). In addition, the chemical composition, soaking conditions, hot rough rolling conditions, hot finish rolling conditions, cold rolling conditions, finish annealing conditions, and the average grain size of hot rolled sheets are defined, and aluminum that can improve ironing formability A method for manufacturing an alloy plate has been proposed (see, for example, Patent Document 2). In addition, high-speed steels, which define the chemical composition, amount of dissolved Si, tensile strength, ear ratio, soaking conditions, hot rough rolling conditions, hot finish rolling conditions, intermediate annealing conditions, cold rolling conditions and finish annealing conditions, A method for producing an aluminum alloy sheet for DI can bodies having excellent ironing formability has been proposed (see, for example, Patent Document 3).

JP 2009-235475 A Japanese Patent Application Laid-Open No. 2006-207006 JP-A-10-121177

However, there is no known prior art that pays attention to the side wall thickness of the drawing cup and further to the thickness difference (anisotropy) in the circumferential direction. In addition, it is demanded to ensure ironing workability in can bodies with a large drawing ratio, which has been on the rise in recent years.

SUMMARY OF THE INVENTION An object of the present invention is to provide an aluminum alloy sheet for a can body in which the thickness anisotropy in the circumferential direction at the opening of a drawn cup is reduced.

The aluminum alloy plate for a can body according to the present invention has Si: 0.16% by mass or more and 0.60% by mass or less, Fe: 0.3% by mass or more and 0.6% by mass or less, and Cu: 0.10% by mass or more. 0.35% by mass or less, Mn: 0.5% by mass or more and 1.2% by mass or less, Mg: 0.7% by mass or more and 2.0% by mass or less, and the balance being Al and unavoidable impurities. In the observation of the structure of the aluminum alloy sheet for can bodies, the number density of intermetallic compounds having an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm is 1.7×10 ⁵ /mm ² or more and 4.0×10. ⁵ /mm ² or less, and the number density of intermetallic compounds having a critical circle equivalent diameter or more that serves as recrystallization nuclei is 1.0 × 10 ³ /mm ² or more and 3.5 × 10 ³ /mm ² or less. is.

According to the present invention, it is possible to provide an aluminum alloy sheet for a can body in which the thickness anisotropy in the circumferential direction at the opening of the formed drawn cup is reduced.

In this specification, the term "process" is not only an independent process, but even if it cannot be clearly distinguished from other processes, it is included in this term as long as the intended purpose of the process is achieved. . In addition, the content of each component in the composition means the total amount of the plurality of substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. Furthermore, the upper and lower limits of the numerical ranges described herein can be combined by arbitrarily selecting the numerical values exemplified as the numerical ranges. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiment shown below exemplifies the aluminum alloy plate for can body for embodying the technical idea of the present invention, and the present invention is limited to the aluminum alloy plate for can body shown below. not.

Aluminum Alloy Plate for Can Body The aluminum alloy plate for can body according to one embodiment of the present invention is made of, for example, an Al--Mn--Mg alloy, an Al--Mg--Mn alloy, or the like. Examples of Al--Mn--Mg alloys and Al--Mg--Mn alloys include general JIS alloys such as 3004 and 3104.

Specifically, the aluminum alloy plate for the can body contains Si: 0.16% by mass or more and 0.60% by mass or less, Fe: 0.3% by mass or more and 0.6% by mass or less, and Cu: 0.10% by mass. 0.35% by mass or less, Mn: 0.5% by mass or more and 1.2% by mass or less, Mg: 0.7% by mass or more and 2.0% by mass or less, and the balance being Al and unavoidable impurities . In the observation of the structure of the aluminum alloy sheet for can bodies, the number density of intermetallic compounds having an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm is 1.7×10 ⁵ /mm ² or more and 4.0×10. ⁵ /mm ² or less, and the number density of intermetallic compounds having a critical circle equivalent diameter or more that serves as recrystallization nuclei is 1.0 × 10 ³ /mm ² or more and 3.5 × 10 ³ /mm ² or less. is.

The aluminum alloy plate for can bodies contains Si, Fe, Cu, Mn and Mg in predetermined ranges, and the number density of intermetallic compounds having equivalent circle diameters in the predetermined range in structural observation and recrystallization. By setting the number density of the core intermetallic compound within a predetermined range, the anisotropy in the circumferential direction of the wall thickness at the opening of the drawn cup to be formed is reduced. For example, it is considered that the thickness difference in the circumferential direction of the drawn cup is reduced because the Cube orientation density, which affects the thickness difference in the circumferential direction of the drawn cup, is appropriately controlled. Specifically, for example, the Cube orientation density greatly affects the circumferential thickness distribution of the side wall thickness of the drawn cup. For example, when the Cube orientation density is low, the side wall of the drawn cup is thin in the direction of 45° to the rolling direction and thick in the direction of 90°, resulting in a large thickness difference in the circumferential direction. Moreover, it is thought that when the Cube orientation density is high, the side wall of the drawn cup becomes thin in the 0° direction with respect to the rolling direction, and the thickness difference in the circumferential direction increases. Furthermore, by adjusting the Si content to a predetermined range, the number density of the intermetallic compounds having an equivalent circle diameter within a predetermined range and the number density of the intermetallic compounds having an equivalent circle diameter serving as recrystallization nuclei are set to a predetermined number. It is believed that this allows the proper Cube orientation density to be achieved and the thickness difference in the circumferential direction in the side wall thickness of the drawing cup to be reduced.

The content of each component contained in the aluminum alloy sheet for can bodies and the reason for limiting the content will be described below.

Si: 0.16% by mass or more and 0.60% by mass or less When the Si content is less than 0.16% by mass, the number density of intermetallic compounds having an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm is small. The azimuth density becomes smaller, the side wall thickness in the 45° direction and the side wall thickness in the 90° direction of the produced drawn cup become thinner, and the thickness difference in the circumferential direction of the drawn cup increases. In addition, when it exceeds 0.60% by mass, the number density of intermetallic compounds having an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm increases, so the Cube orientation density increases. , the side wall thickness in the 0° direction becomes thin, and the thickness difference in the circumferential direction of the cup increases. The lower limit of the Si content is preferably 0.18% by mass or more, more preferably 0.20% by mass or more, still more preferably 0.24% by mass or more, and particularly preferably 0.3% by mass or more. It's okay. The upper limit of the Si content is preferably 0.56% by mass or less, more preferably 0.54% by mass or less, and even more preferably 0.50% by mass or less.

Fe: 0.3% by mass or more and 0.6% by mass or less When the Fe content is less than 0.3% by mass, the intermetallic compound (for example, Al-Fe-Mn intermetallic compound) is insufficient, and the side wall is deformed during ironing. surface defects (seizure) may occur. On the other hand, if it exceeds 0.6% by mass, the amount of large-sized intermetallic compounds increases, which may cause breakage during ironing. The lower limit of the Fe content is preferably 0.34% by mass or more, more preferably 0.36% by mass or more, and still more preferably 0.38% by mass or more. Also, the upper limit of the Fe content is preferably 0.55% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.46% by mass or less.

Cu: 0.10% by mass or more and 0.35% by mass or less If the Cu content is less than 0.10% by mass, the strength (yield strength after baking) is insufficient, and the pressure resistance strength of the can is insufficient. On the other hand, if it exceeds 0.35% by mass, the strength may become excessively high, resulting in deterioration of formability. The lower limit of the Cu content is preferably 0.14% by mass or more, more preferably 0.16% by mass or more, and even more preferably 0.18% by mass or more. The upper limit of the Cu content is preferably 0.33% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.26% by mass or less.

Mn: 0.5% by mass or more and 1.2% by mass or less If the Mn content is less than 0.5% by mass, the strength (yield strength after baking) is insufficient, and the compressive strength of the can is insufficient. If it exceeds 1.2% by mass, the amount of large-sized intermetallic compounds increases, and breakage may occur during ironing. The lower limit of the Mn content is preferably 0.6% by mass or more, more preferably 0.8% by mass or more, and even more preferably 0.9% by mass or more. The upper limit of the Mn content is preferably 1.15% by mass or less, more preferably 1.10% by mass or less, still more preferably 1.08% by mass or less, and particularly preferably 1.06% by mass. % by mass or less.

Mg: 0.7% by mass or more and 2.0% by mass or less If the Mg content is less than 0.7% by mass, the strength (yield strength after baking) is insufficient, and the pressure resistance strength of the can is insufficient. If it exceeds 2.0% by mass, the strength may become excessively high and the formability may deteriorate. The lower limit of the Mg content is preferably 0.8% by mass or more, more preferably 0.9% by mass or more, and still more preferably 0.94% by mass or more. Also, the upper limit of the Mg content is preferably 1.6% by mass or less, more preferably 1.4% by mass or less, and even more preferably 1.35% by mass or less.

Cr: 0.01 mass % or more and 0.10 mass % or less As generally known, the aluminum alloy plate may contain Cr. A Cr content of 0.01% by mass or more contributes to an improvement in the strength of the material. Also, if the Cr content is 0.10% by mass or less, it does not affect the material properties of the aluminum alloy plate and the can properties after ironing. When the Cr content is 0.10% by mass or less, generation of coarse intermetallic compounds is suppressed, and deterioration of formability during ironing is suppressed. The upper limit of the Cr content may preferably be 0.05% by mass or less, or 0.03% by mass or less.

Zn: 0.01 mass % or more and 0.40 mass % or less As generally known, the aluminum alloy plate may contain Zn. If the content of Zn is 0.40% by mass or less, it does not significantly affect the material properties of the aluminum alloy sheet and the can properties after ironing. Zn is an unavoidable impurity, but Zn can be positively added within the above range. The upper limit of the Zn content is preferably 0.30% by mass or less, more preferably 0.26% by mass or less, more preferably 0.24% by mass or less, and still more preferably 0.20% by mass. may be: Also, the lower limit of the Zn content may be, for example, 0.01% by mass or more, preferably 0.10% by mass or more, and more preferably 0.16% by mass or more.

Ti: 0.005 mass % or more and 0.100 mass % or less As generally known, the aluminum alloy plate may contain Ti. Ti is added as necessary for the purpose of refining ingot crystal grains. Refining the ingot structure during casting improves the castability and enables high-speed casting. The effect is obtained by adding 0.005% by mass or more. On the other hand, when the Ti content is 0.100% by mass or less, generation of coarse intermetallic compounds can be suppressed. When adding Ti, for example, an ingot refiner (Al--Ti--B) may be added to the molten metal before casting. In this case, for example, if the mass ratio of Ti and B is 5:1, B is inevitably added according to the content ratio, but this does not affect the properties. The upper limit of the Ti content is preferably 0.080% by mass or less, more preferably 0.060% by mass or less, and even more preferably 0.040% by mass or less. Also, the lower limit of the Ti content may be, for example, 0.005% by mass or more.

The total content of Cr and Ti is 0.01% by mass or more and 0.150% by mass or less When the total content of Cr and Ti elements is 0.150% by mass or less, generation of coarse intermetallic compounds is suppressed. , the deterioration of moldability is suppressed. If the content of the elements Cr and Ti does not exceed the upper limit value described above, the aluminum alloy contains not only one type or more, that is, only one type, but also two or more types. Impairment of the effects of the invention is suppressed.

(Remainder: Al and unavoidable impurities)
The aluminum alloy sheet for can bodies may contain unavoidable impurities in addition to Al and the above alloy components. Examples of unavoidable impurities include V, Na, Zr, Ni, Ca, In, Sn, and Ga. The upper limit of the allowable content of inevitable impurities for Zr may be, for example, 0.3% by mass or less, preferably 0.1% by mass or less, and more preferably 0.05% by mass or less. Elements other than Zr may be, for example, 0.05% by mass or less and 0.15% by mass or less in total. Within the above range, the effect of the present invention is suppressed not only when it is contained as an unavoidable impurity, but also when the element is added.

Number density of intermetallic compounds with an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm: 1.7×10 ⁵ /mm ² or more and 4.0×10 ⁵ /mm ² or less Equivalent circle diameter of 0.10 μm or more The number density of intermetallic compounds of less than 1.00 μm is calculated by observing the structure of a cross section parallel to the rolling direction of the aluminum alloy plate as a backscattered electron composition (COMPO) image. Specifically, the area of each intermetallic compound (eg, Al-Fe-Mn system, Al-Fe-Mn-Si system, etc.) identified from the COMPO image is measured, and the equivalent circle diameter obtained from the area is The number density of intermetallic compounds is calculated as the number of intermetallic compounds having a size of 0.10 μm or more and less than 1.00 μm per unit area.

When the number density of the intermetallic compounds whose equivalent circle diameter is within the predetermined range is less than 1.7×10 ⁵ /mm ² , the Cube orientation density becomes small during recrystallization, and in the produced drawn cup, in the rolling direction On the other hand, the side wall thickness in the 45° direction becomes thin and the side wall thickness in the 90° direction becomes thick, resulting in a large difference in thickness of the draw cup in the circumferential direction. Moreover, when it exceeds 4.0×10 ⁵ pieces/mm ² , the Cube orientation density increases during recrystallization, and in the manufactured drawn cup, the side wall thickness in the direction of 0° to the rolling direction becomes thin, and the drawn cup has a thickness of 0°. The thickness difference in the circumferential direction increases. The lower limit of the number density of intermetallic compounds having equivalent circle diameters within a predetermined range is preferably 1.8×10 ⁵ /mm ² or more, more preferably 1.85×10 ⁵ /mm ² or more. you can The upper limit of the number density of the intermetallic compounds whose equivalent circle diameter is within the predetermined range is preferably 3.8×10 ⁵ /mm ² or less, more preferably 3.6×10 ⁵ /mm ² or less. Yes, more preferably 3.2×10 ⁵ pieces/mm ² or less.

Number density of intermetallic compounds having a diameter equal to or larger than the critical circle that serves as the nucleus for recrystallization: 1.0×10 ³ pieces/mm ² or more and 3.5×10 ³ pieces/mm ² or less Equivalent to the critical circle that serves as the nucleus for recrystallization The diameter η _PSN is calculated by the following formula (for example, HE Vatne, O Engler, E. Nes: Materials Science and Technology, February, 1997, Vol.13, pp.93-102.).
η _PSN =(4/3)/(10 ⁶ -(3f/2r))
It is said that when a compound having a diameter equal to or larger than the critical circle is recrystallized as nuclei, the crystal orientation of the recrystallized grains becomes random.

The critical circle-equivalent diameter of the intermetallic compound serving as recrystallization nuclei of the aluminum alloy sheet for can bodies may be, for example, greater than 1.48 μm and equal to or less than 1.80 μm. The lower limit of the critical circle equivalent diameter of the intermetallic compound may preferably be 1.49 μm or more. Also, the upper limit of the critical circle equivalent diameter of the intermetallic compound is preferably 1.70 μm or less, and more preferably 1.68 μm or less.

When the number density of intermetallic compounds having a critical circle equivalent diameter or more, which serve as recrystallization nuclei, is less than 1.0×10 ³ /mm ² , the Cube orientation density increases during recrystallization, and the produced drawing cup , the thickness of the side wall in the 0° direction with respect to the rolling direction becomes thin, and the thickness difference in the circumferential direction of the drawn cup becomes large. Moreover, when it exceeds 3.5 × 10 ³ /mm ² , the Cube orientation density becomes small during recrystallization, and in the produced drawn cup, the side wall thickness in the direction of 45° to the rolling direction becomes thin and the thickness in the direction of 90° As a result, the thickness of the side wall of the drawing cup increases, and the thickness difference in the circumferential direction of the cup increases. The lower limit of the number density of intermetallic compounds having a critical circle equivalent diameter or more is preferably 1.6×10 ³ /mm ² or more, and more preferably 2.0×10 ³ /mm ^{2 or} more. . Further, the upper limit of the number density of intermetallic compounds having a diameter equal to or larger than the critical circle may preferably be 3.2×10 ³ /mm ² or less.

In a draw cup formed from an aluminum alloy plate for a can body, variations in thickness in the circumferential direction are suppressed in the vicinity of the opening. Circumferential wall thickness variation is the circumferential anisotropy calculated as a percentage by dividing the value obtained by subtracting the minimum value from the maximum wall thickness measured in the circumferential direction by the average wall thickness in the circumferential direction. It can be evaluated by the nature (%). The upper limit of the circumferential anisotropy may be, for example, 10.8% or less, preferably 10.7% or less. The lower limit of circumferential anisotropy is 0%.

Manufacturing Method An example of a method for manufacturing an aluminum alloy sheet for a can body will be described. A method for manufacturing an aluminum alloy sheet for a can body comprises a first step of casting, a second step of homogenization heat treatment, a third step of hot rolling, and a fourth step of cold rolling. , and these steps are performed in this order.

First and Second Steps: Casting Step, Homogenization Heat Treatment Step The first step is a step of producing an ingot having a target composition by a semi-continuous casting method. The second step is a step of subjecting the aluminum alloy ingot produced in the first step to a homogenization heat treatment.

In the first step, an aluminum alloy is cast by a semi-continuous casting method (DC (direct chill) casting) to obtain an ingot. Next, a second step is performed in which the surface layer of the ingot has a non-uniform structure and is subjected to chamfering and homogenization heat treatment. In the homogenization heat treatment, it is preferable to maintain the temperature at about 480° C. or higher and 600° C. or lower for 2 hours or longer. After the homogenization heat treatment is completed, it may be cooled to the hot rolling start temperature and hot rolling, which is the third step, may be started, or once cooled to a temperature of 200 ° C. or less including room temperature, and then hot Hot rolling may be started after reheating to the rolling start temperature. Chamfering may be performed before the homogenization heat treatment, or may be performed after cooling to a temperature of 200° C. or less including room temperature after the homogenization heat treatment.

Third Step: Hot Rolling Step The third step is a step of hot rolling the aluminum alloy ingot subjected to the homogenizing heat treatment in the second step. The thickness of the hot-rolled sheet obtained by hot rolling is usually set by back-calculating the total rolling reduction by cold rolling from the thickness of the product sheet obtained by cold rolling.

The starting temperature of hot rolling may be, for example, 450° C. or higher, preferably 480° C. or higher. The lower limit of the coiling temperature, which is the end temperature of hot rolling, may be, for example, 300° C. or higher, preferably 330° C. or higher, and more preferably 340° C. or higher. The upper limit of the winding temperature may be, for example, 370° C. or lower, preferably 360° C. or lower. When the coiling temperature is 370° C. or lower, the occurrence of surface defects called seizure on the surface of the hot-rolled sheet is suppressed, and the properties of the sheet surface are improved.

Fourth Step: Cold Rolling Step The fourth step is a step of cold rolling the hot-rolled plate hot-rolled in the third step. The fourth step may include a primary cold rolling step, a primary intermediate annealing step, a secondary cold rolling step, a secondary intermediate annealing step, and a final cold rolling step.

In the primary cold rolling step, the hot-rolled sheet after hot rolling is cold-rolled to a predetermined thickness. The working ratio (rolling ratio) in the primary cold rolling step is preferably 40% or more. When the processing rate is 40% or more, the decrease in the Cube orientation density during recrystallization is suppressed. As a result, in the formed drawn cup, the side wall thickness in the direction of 45° to the rolling direction is suppressed from becoming thin, and the side wall thickness in the direction of 90° is suppressed from becoming thick, so that the side wall thickness in the circumferential direction of the drawn cup is suppressed. An increase in thickness difference is suppressed. The lower limit of the working ratio in the primary cold rolling step is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more.

In the primary intermediate annealing step, the primary cold-rolled sheet is subjected to intermediate annealing. The annealing temperature at this time is preferably in the range of 250°C or higher and 290°C or lower. Within this range, the decrease in Cube orientation density during recrystallization is suppressed. As a result, in the formed drawn cup, the side wall thickness in the direction of 45° to the rolling direction is suppressed from becoming thin, and the side wall thickness in the direction of 90° is suppressed from becoming thick, so that the side wall thickness in the circumferential direction of the drawn cup is suppressed. An increase in thickness difference is suppressed. The lower limit of the annealing temperature in the primary intermediate annealing step may preferably be 260°C or higher. Moreover, the upper limit of the annealing temperature in the primary intermediate annealing step may preferably be 280° C. or lower. By performing the primary intermediate annealing process at a predetermined annealing temperature, it is considered that the Cube orientation density is improved in the secondary intermediate annealing process described later.

In the primary intermediate annealing step, the primary cold-rolled sheet may preferably be heated to the annealing temperature at a temperature elevation rate of 30° C./hour or more and 50° C./hour or less. The lower limit of the heating rate may preferably be 35° C./hour or more. Moreover, the upper limit of the temperature increase rate may preferably be 45° C./hour or less. The time for holding the annealing temperature may be, for example, 2 hours or more and 6 hours or less. The lower limit of the time for holding the annealing temperature may preferably be 3 hours or longer. Moreover, the upper limit of the time for which the annealing temperature is maintained may preferably be 5 hours or less. After holding the annealing temperature, the material may be cooled to a predetermined cooling temperature at a temperature decreasing rate of, for example, 30° C./hour or more and 50° C./hour or less. The lower limit of the temperature drop rate may preferably be 35° C./hour or more. Moreover, the upper limit of the temperature drop rate may preferably be 45° C./hour or less. The cooling temperature may be, for example, 220° C. or lower, preferably 210° C. or lower.

In the secondary cold rolling step, the primary cold rolled sheet after the primary intermediate annealing is cold rolled to a predetermined thickness. The working rate (rolling rate) in the secondary cold rolling step is preferably 20% or less. If the processing ratio is 20% or less, the decrease in the Cube orientation density during recrystallization is suppressed. As a result, in the formed drawn cup, the side wall thickness in the direction of 45° to the rolling direction is suppressed from becoming thin, and the side wall thickness in the direction of 90° is suppressed from becoming thick, so that the side wall thickness in the circumferential direction of the drawn cup is suppressed. An increase in thickness difference is suppressed. The upper limit of the working ratio in the secondary cold rolling step is preferably 18% or less, more preferably 16% or less, and even more preferably 14% or less. The lower limit of the working ratio in the secondary cold rolling step may be, for example, 5% or more.

In the method of manufacturing an aluminum alloy sheet for can bodies, if the primary intermediate annealing step and the secondary cold rolling step are not performed, the Cube orientation density will not be sufficiently large in the subsequent secondary intermediate annealing step. As a result, the formed drawn cup has a thin side wall thickness in the direction of 45° to the rolling direction and a side wall thickness in the direction of 90° to the rolling direction.

In the secondary intermediate annealing step, the secondary cold rolled sheet is subjected to intermediate annealing. The annealing temperature at this time is preferably in the range of 300° C. or higher and 450° C. or lower. Within this range, the decrease in Cube orientation density during recrystallization is suppressed. As a result, in the formed drawn cup, the side wall thickness in the direction of 45° to the rolling direction is suppressed from becoming thin, and the side wall thickness in the direction of 90° is suppressed from becoming thick, so that the side wall thickness in the circumferential direction of the drawn cup is suppressed. An increase in thickness difference is suppressed. The lower limit of the annealing temperature in the secondary intermediate annealing step may be preferably 300°C or higher, more preferably 320°C or higher. The upper limit of the annealing temperature in the secondary intermediate annealing step is preferably 400°C or lower, more preferably 380°C or lower.

In the secondary intermediate annealing step, the secondary cold-rolled sheet may preferably be heated to the annealing temperature at a temperature elevation rate of 30° C./hour or more and 50° C./hour or less. The lower limit of the heating rate may preferably be 35° C./hour or more. Moreover, the upper limit of the temperature increase rate may preferably be 45° C./hour or less. The time for holding the annealing temperature may be, for example, 2 hours or more and 6 hours or less. The lower limit of the time for holding the annealing temperature may preferably be 3 hours or more. Moreover, the upper limit of the time for which the annealing temperature is maintained may preferably be 5 hours or less. After holding the annealing temperature, the material may be cooled to a predetermined cooling temperature at a temperature decreasing rate of, for example, 30° C./hour or more and 50° C./hour or less. The lower limit of the temperature drop rate may preferably be 35° C./hour or more. Also, the upper limit of the temperature drop rate may preferably be 45° C./hour or less. The cooling temperature may be, for example, 240° C. or lower, preferably 210° C. or lower.

In the final cold-rolling step, the secondary cold-rolled sheet after the secondary intermediate annealing is cold-rolled to a predetermined thickness. It is preferable that the working ratio of the final cold rolling step is 80% or more and 95% or less. When the processing ratio is 80% or more, the strength of the aluminum alloy sheet is sufficiently obtained, and the pressure resistance strength of the can after DI forming and baking is sufficiently obtained. In addition, the Cube orientation density after the final cold rolling process is suppressed from becoming too large, and the side wall thickness in the 0° direction with respect to the rolling direction is suppressed from becoming thin in the drawn cup to be formed. The thickness difference in the circumferential direction becomes smaller. In addition, when the working ratio is 95% or less, excessive strength of the aluminum alloy plate is suppressed, and deterioration of formability is suppressed. In addition, it is suppressed that the Cube orientation density after the final cold rolling process becomes too small, and in the formed drawn cup, the side wall thickness in the direction of 45 ° with respect to the rolling direction is suppressed from becoming thin, and the thickness of the side wall in the direction of 90 ° is suppressed. increase in the thickness of the side wall of the drawer cup is suppressed, and an increase in the thickness difference in the circumferential direction of the draw cup is suppressed. The lower limit of the working ratio in the final cold rolling step may preferably be 85% or more. Moreover, the upper limit of the working ratio in the final cold rolling step may preferably be 90% or less.

In the primary cold rolling process, the secondary cold rolling process and the final cold rolling process, multiple passes with a predetermined total rolling reduction are performed so that the plate is rolled to a desired thickness within an appropriate range of load. You can set it. In addition, a pass means that a plate is passed between a pair of work rolls once and rolled.

In the method for manufacturing an aluminum alloy sheet for can bodies, after cold rolling, a finish annealing step may be performed as necessary. In the finish annealing step, the cold-rolled sheet after the final cold rolling step is held at a given finish annealing temperature for a given time. The finish annealing temperature may be, for example, 100° C. or higher and 200° C. or lower. Moreover, the time for which the finish annealing temperature is maintained may be, for example, 2 hours or more and 4 hours or less.

The embodiments of the present invention have been described above. Hereinafter, examples in which the effects of the present invention have been confirmed will be described in detail in comparison with comparative examples that do not satisfy the requirements of the present invention. However, the present invention is not limited to these examples.

Production of Aluminum Alloy Plate for Can Body Molten aluminum alloys (No. 1 to No. 8) having the compositions shown in Table 1 were cast into metal molds to produce ingots having a thickness of 50 mm. The surface layer of the produced ingot was chamfered to a thickness of 45 mm. The ingot after facing is put into an atmospheric furnace, heated from room temperature to 600°C at a heating rate of 40°C/hour, held at 600°C for 10 hours, and then cooled to 500°C at a cooling rate of 10°C/hour. and then held at 500° C. for 10 hours. Hot rolling was started immediately after the holding was completed to obtain a hot rolled sheet having a thickness of 10 mm.

The obtained hot-rolled sheet was subjected to a primary cold-rolling step so as to have a sheet thickness of 2.7 mm (processing rate: 73%) to obtain a primary cold-rolled sheet. The obtained primary cold-rolled sheet was heated from room temperature to 270°C at a heating rate of 40°C/hour, held at 270°C for 4 hours, and then cooled to 200°C at a cooling rate of 40°C/hour. After that, it was air-cooled.

Next, a secondary cold-rolling step was carried out to obtain a secondary cold-rolled sheet so that the sheet thickness became 2.4 mm (reduction ratio: 11%). The obtained secondary cold-rolled sheet was heated from room temperature to 340°C at a heating rate of 40°C/hour, held at 340°C for 4 hours, and then cooled to 200°C at a cooling rate of 40°C/hour. After that, it was air-cooled. Then, a cold-rolled sheet was obtained by performing a final cold-rolling step so as to have a sheet thickness of 0.3 mm (processing rate: 87.5%). After that, the cold-rolled sheet was placed in an atmospheric furnace heated to 150° C., held at 150° C. for 3 hours, and subjected to a finish annealing step to produce an aluminum alloy sheet for can bodies having a thickness of 0.3 mm.

In addition, No. 1 to No. 5 corresponds to an example, and No. 6 to No. 8 corresponds to a comparative example.

Yield Strength after Baking Each aluminum alloy plate produced was subjected to heat treatment (baking treatment) at 200° C. for 20 minutes. From the plate after the heat treatment, a tensile test piece whose width and length were halved based on the JIS No. 5 test piece specified in JIS Z 2241 (2011) was taken. At this time, the rolling direction was taken as the longitudinal direction of the test piece. Using this test piece, a tensile test was performed to obtain a 0.2% yield strength, which was defined as a yield strength after baking. A sample with a yield strength after baking of 200 MPa or more and 300 MPa or less was rated as A (passed), and a sample with a yield strength of less than 200 MPa was rated as B (failed). Table 2 shows the results.

Number Density of Intermetallic Compounds with Circle Equivalent Diameter of 0.10 μm or More and Less than 1.00 μm A cross section parallel to the rolling direction of each aluminum alloy plate was embedded with resin and polished to prepare a sample for cross section observation. Using a scanning electron microscope "JSM-7001F" manufactured by JEOL Ltd., 10 COMPO images (composition images) were photographed under the conditions of an acceleration voltage of 15 kV and a magnification of 5000 times. Using the obtained COMPO image, the area of each Al--Fe--Mn system or Al--Fe--Mn--Si system intermetallic compound was measured. The equivalent circle diameter was calculated from the area of each intermetallic compound, and the number of intermetallic compounds having an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm per unit area was calculated as the number density. If the number density of intermetallic compounds with an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm is 1.7×10 ⁵ pieces/mm ² or more and 4.0×10 ⁵ pieces/mm ² or less, A (accepted). , less than 1.7×10 ⁵ pieces/mm ² or more than 4.0×10 ⁵ pieces/mm ² were rated as B (failed). Table 2 shows the results.

Number density of intermetallic compounds having a critical circle-equivalent diameter or more serving as recrystallization nuclei For the intermetallic compounds having an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm obtained by the above method, the area ratio f of the intermetallic compound and the average radius r were calculated. The area ratio f was calculated as a ratio of the total area of the intermetallic compound to the area of the observation field. Also, the average radius r was calculated as the arithmetic mean of the equivalent circle diameters of the intermetallic compounds. From the calculated area ratio f and average radius r of the intermetallic compound, the following formula (HE Vatne, O. Engler, E. Nes: Materials Science and Technology, February, 1997, Vol.13, pp.93-102. ), the critical circle-equivalent diameter η _PSN of the intermetallic compound serving as the nucleus for recrystallization was calculated for each sample.
η _PSN =(4/3)/(10 ⁶ -(3f/2r))

Next, a cross-section parallel to the rolling direction of each aluminum alloy plate thus produced was filled with resin and polished to prepare a sample for cross-sectional observation. Using a scanning electron microscope "JSM-7001F" manufactured by JEOL Ltd., COMPO images (composition images) were photographed in 20 fields of view under the conditions of an acceleration voltage of 15 kV and a magnification of 500 times. Using the obtained COMPO image, the area of each Al--Fe--Mn system or Al--Fe--Mn--Si system intermetallic compound was measured. The circle equivalent diameter was calculated from the area of each intermetallic compound, and the number per unit area of the intermetallic compounds having the critical circle equivalent diameter η _PSN or more obtained above was calculated as the number density. A sample whose number density was 1.0 × 10 ³ /mm ² or more and 3.5 × 10 ³ /mm ^{2 or} less was A (accepted), and less than 1.0 × 10 ³ /mm ² or 3 Samples exceeding 0.5×10 ³ pieces/mm ² were rated as B (rejected). Table 2 shows the results.

Circumferential anisotropy of the thickness of the opening of the drawing cup A blank with a diameter of 66.7 mm was punched from the prepared aluminum alloy plate with a thickness of 0.3 mm, and the blank was drawn under a wrinkle holding load of 3 kN. A drawn cup with a diameter of 40 mm (hereinafter also simply referred to as "cup") was produced (drawing ratio: 1.67). Using the prepared cup, the thickness in the vicinity of the cup opening (at a height of 17 mm from the bottom) was measured at intervals of 22.5° in the circumferential direction. That is, when the rolling direction is 0°, 0° direction, 22.5° direction, 45° direction, 67.5° direction, 90° direction, 112.5° direction, 135° direction, 157.5° direction, 180° direction The thickness was measured in the ° direction, 202.5 ° direction, 225 ° direction, 247.5 ° direction, 270 ° direction, 292.5 ° direction, 315 ° direction and 337.5 ° direction. From the data of a total of 16 points obtained, the 0° direction average value as the average value of the wall thickness in the 0° direction and 180° direction; 22.5° direction average value as average value of thickness in 5° direction; 45° direction average value as average value of thickness in 45° direction, 135° direction, 225° direction and 315° direction; 67.5° 67.5° directional average value as average value of wall thickness in 112.5° direction, 247.5° direction and 292.5° direction; 90° as average value of wall thickness in 90° direction and 270° direction A directional mean value was calculated for each. Furthermore, from these five numerical values, the maximum value (maximum thickness), minimum value (minimum thickness) and average value (average thickness) were calculated, and the circumferential anisotropy (%) was calculated from the following formula.
Circumferential anisotropy = (maximum thickness - minimum thickness) / average thickness x 100 [%]
Samples whose circumferential anisotropy calculated from the above formula was 10.8% or less were rated as A (acceptable), and samples exceeding 10.8% were rated as B (failed). Table 2 shows the results.

As shown in Tables 1 and 2, the number of intermetallic compounds having a Si content of 0.16% by mass or more and 0.60% by mass or less and an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm The density is 1.7×10 ⁵ pieces/mm ² or more and 4.0×10 ⁵ pieces/mm ² or less, and the number density of intermetallic compounds having a critical circle equivalent diameter or more is 1.0×10 ³ pieces/mm ² No. 3.5×10 ³ pieces/mm ² or less. 1 to 5 were small in circumferential anisotropy and excellent.

Claims (3)

Si: 0.16% by mass or more and 0.60% by mass or less Fe: 0.3% by mass or more and 0.6% by mass or less Cu: 0.10% by mass or more and 0.35% by mass or less Mn: 0.5 % by mass or more and 1.2% by mass or less, Mg: 0.7% by mass or more and 2.0% by mass or less, the balance being Al and unavoidable impurities,
In structural observation, the number density of the intermetallic compounds having an equivalent circle diameter of 0.10 μm or more and less than 1.00 μm is 1.7×10 ⁵ pieces/mm ² or more and 4.0×10 ⁵ pieces/mm ² or less,
An aluminum alloy sheet for can bodies, wherein the number density of intermetallic compounds having a critical circle equivalent diameter or more serving as recrystallization nuclei is 1.0×10 ³ pieces/mm ² or more and 3.5×10 ³ pieces/mm ² or less. further comprising at least one component selected from the group consisting of Cr, Zn and Ti;
The contents of Cr, Zn, and Ti are Cr: 0.01% by mass or more and 0.10% by mass or less, Zn: 0.01% by mass or more and 0.40% by mass or less, and Ti: 0.005% by mass or more. The aluminum alloy plate for can bodies according to claim 1, wherein the content is 0.100% by mass or less. further comprising at least one component selected from the group consisting of Cr and Ti;
The contents of Cr and Ti are respectively Cr: 0.01% by mass or more and 0.10% by mass or less, and Ti: 0.005% by mass or more and 0.100% by mass or less,
The aluminum alloy plate for can bodies according to claim 1, wherein the total content of Cr and Ti is 0.01% by mass or more and 0.150% by mass or less.