Aluminum alloy coated sheet for can lid

Abstract

To provide an aluminum alloy coated sheet for a can lid having high rivet moldability even when thinned.SOLUTION: An aluminum alloy coated sheet for a can lid includes an aluminum alloy sheet which contains 0.05 mass% or more and 0.40 mass% or less Si, 0.05 mass% or more and 0.50 mass% or less Fe, 0.01 mass% or more and 0.30 mass% or less Cu, 0.10 mass% or more and 0.60 mass% or less Mn, 4.0 mass% or more and 6.0 mass% or less Mg, and the balance Al with inevitable impurities, and a resin layer. In the aluminum alloy coated sheet for the can lid, a tissue in a region of 50 nm thickness in both thickness directions from a sheet thickness center on a surface parallel to a rolled surface has 45 pieces or more of sub-grains in total in a region of 205×10-12 m2 observed by a transmission type electron microscope of 50,000 magnifications.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aluminum alloy coated sheet for can lids.

Background Art

[0002] As a packaging container for beverages, a two-piece type aluminum can composed of a bottomed cylindrical body and a lid is widely used. In the forming of the can lid of the two-piece type aluminum can, the most severe forming is carried out in the rivet forming process. If fine cracks or cracks occur in this process, the risk of leakage of the contents increases. Therefore, conventionally, an intermediate annealing material that performs intermediate annealing during the cold rolling process with excellent formability has been used. However, in recent years, from the viewpoint of improving productivity, it has been required to manufacture a cold rolled material with improved formability in a process that does not perform intermediate annealing (hereinafter also referred to as a direct-through process).

[0003] Regarding the aluminum alloy plate for can lids, technologies have been developed to ensure formability even in the direct-through process. For example, Patent Document 1 describes an aluminum alloy plate for can lids having a grain structure in which the Cube orientation density on the plate surface is 1.5 times or more that of a random orientation sample and having excellent bend formability. Patent Document 2 also describes an aluminum alloy plate for can lids having excellent strength and formability with a solid solution Mg ratio of 80% or more and a subgrain area ratio of 10% or more and 90% or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in recent years, with the progress of thinning of the can lid material (for example, a plate thickness of about 0.2 mm), cracks may occur during rivet forming with conventional directly rolled aluminum alloy sheets for can lids. An object of the present invention is to provide an aluminum alloy coated sheet for can lids that has high rivet formability even when thinned.

Means for Solving the Problems

[0006] The aluminum alloy coated sheet for can lids according to the present invention comprises an aluminum alloy sheet containing Si: 0.05% by mass or more and 0.40% by mass or less, Fe: 0.05% by mass or more and 0.50% by mass or less, Cu: 0.01% by mass or more and 0.30% by mass or less, Mn: 0.10% by mass or more and 0.60% by mass or less, Mg: 4.0% by mass or more and 6.0% by mass or less, with the balance being Al and unavoidable impurities, and a resin layer. In the aluminum alloy coated sheet for can lids, in a plane parallel to the rolling plane, the structure in a region 50 nm thick from the center of the plate thickness in both thickness directions respectively has a total of 45 or more sub-grains in a region of 205×10 -12 m 2 observed by a transmission electron microscope with a magnification of 50,000.

Effects of the Invention

[0007] According to the present invention, it is possible to provide an aluminum alloy coated sheet for can lids that has high rivet formability even when thinned.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an aluminum alloy coated sheet for a can lid according to an embodiment of the present invention will be described. However, the following embodiments are examples for embodying the technical idea of the present invention, and the present invention is not limited to the following embodiments. Note that the sizes and positional relationships of the members shown in each drawing may be exaggerated for clarity of explanation. In this specification, the term "process" includes not only an independent process but also a process in which, even if it cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Also, the content of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified.

[0010] Aluminum alloy coated sheet for can lid The aluminum alloy coated sheet for a can lid according to an embodiment of the present invention includes an aluminum alloy sheet and a resin layer provided on one or both sides of the aluminum alloy sheet. The aluminum alloy coated sheet for a can lid, in a state where baking coating treatment is performed, in a plane parallel to the rolling plane, the structure of a region 50 nm thick from the center of the plate thickness in each of the two thickness directions (hereinafter sometimes referred to as the center of the plate thickness) is observed by a transmission electron microscope at 50,000 times magnification, and has a total of 45 or more sub-grains in the region of 205×10 -12 m 2 There are 45 or more sub-grains in total in the region.

[0011] The aluminum alloy plate alloy coated sheet for a can lid, in a state where baking coating treatment is performed, needs to satisfy the properties required for a can lid, such as formability to withstand lid processing, pressure resistance to withstand the internal pressure after beverage filling, and openability for normal and easy opening. In the aluminum alloy coated sheet for a can lid according to an embodiment of the present invention, by increasing the number of sub-grains contained in the structure of the center of the plate thickness in a state where baking coating treatment is performed after cold rolling to a predetermined value or more, it is possible to improve formability, particularly rivet formability, while maintaining strength.

[0012] Aluminum alloy composition The aluminum alloy plate that constitutes the aluminum alloy coated plate for can lids is made of, for example, an Al-Mg alloy. Examples of the Al-Mg alloy include general JIS alloys such as 5182 and the like.

[0013] Specifically, the aluminum alloy plate contains Si: 0.05% by mass or more and 0.40% by mass or less, Fe: 0.05% by mass or more and 0.50% by mass or less, Cu: 0.01% by mass or more and 0.30% by mass or less, Mn: 0.10% by mass or more and 0.60% by mass or less, Mg: 4.0% by mass or more and 6.0% by mass or less, and the balance consists of Al and unavoidable impurities. Hereinafter, the content of each component contained in the aluminum alloy plate and the reasons for limiting the content will be described.

[0014] (Si: 0.05% by mass or more and 0.40% by mass or less) When the Si content is less than 0.05% by mass, high-purity aluminum ingots are required during casting, increasing the cost. Also, when the Si content exceeds 0.40% by mass, a large number of intermetallic compounds are formed during casting or hot rolling, promoting the generation and propagation of cracks, resulting in a decrease in the opening force of the can and making unintended can opening likely to occur. The Si content is preferably 0.30% by mass or less, more preferably 0.20% by mass or less. Also, the Si content is preferably 0.06% by mass or more.

[0015] (Fe: 0.05% by mass or more and 0.50% by mass or less) When the Fe content is less than 0.05% by mass, high-purity aluminum ingots are required during casting, increasing the cost. On the other hand, when the Fe content exceeds 0.50% by mass, the amount of Al-Fe-Mn-based intermetallic compounds increases, and a large number of intermetallic compounds are formed during casting or hot rolling, promoting the generation and propagation of cracks, resulting in a decrease in the opening force of the can and making unintended can opening likely to occur. The Fe content is preferably 0.10% by mass or more, more preferably 0.15% by mass or more. Also, the Fe content is preferably 0.40% by mass or less, more preferably 0.35% by mass or less, and even more preferably 0.30% by mass or less.

[0016] (Cu: 0.01 mass% or more and 0.30 mass% or less) If the Cu content is less than 0.01 mass%, the strength is insufficient and the pressure resistance of the lid is insufficient. On the other hand, if the Cu content exceeds 0.30 mass%, the strength becomes excessive and the rivet formability decreases. The Cu content is preferably 0.02 mass% or more, more preferably 0.03 mass% or more. Also, the Cu content is preferably 0.25 mass% or less, more preferably 0.20 mass% or less, and even more preferably 0.15 mass% or less.

[0017] (Mn: 0.10 mass% or more and 0.60 mass% or less) If the Mn content is less than 0.10 mass%, the strength is insufficient and the pressure resistance of the lid is insufficient. On the other hand, if the Mn content exceeds 0.60 mass%, the strength becomes excessive and the amount of Al-Fe-Mn based intermetallic compound increases, resulting in a decrease in rivet formability. The Mn content is preferably 0.20 mass% or more. Also, the Mn content is preferably 0.55 mass% or less, more preferably 0.50 mass% or less.

[0018] (Mg: 4.0 mass% or more and 6.0 mass% or less) If the Mg content is less than 4.0 mass%, the strength is insufficient and the pressure resistance of the lid is insufficient. Also, the work hardening ability of the aluminum alloy coated plate is insufficient, and necking is likely to occur during rivet forming. On the other hand, if the Mg content exceeds 6.0 mass%, the strength becomes excessive and the rivet formability decreases. The Mg content is preferably 4.5 mass% or more. Also, the Mg content is preferably 5.5 mass% or less, more preferably 5.0 mass% or less.

[0019] (Ti: 0.1 mass% or less) The aluminum alloy plate may contain Ti. Ti is added as needed for the purpose of refining the ingot crystal grains. When the ingot structure is refined during casting, the castability is improved and high-speed casting becomes possible. The effect can be obtained by adding 0.01% by mass or more. On the other hand, when the Ti content exceeds 0.1% by mass, coarse compounds are formed, resulting in a decrease in rivet formability. Therefore, the Ti content in the aluminum alloy may be limited within the above range. When adding Ti, for example, an ingot refining agent (Al-Ti-B) with a mass ratio of Ti to B of 5:1 is added. Since it is added to the molten metal before casting in the form of a waffle or rod, B corresponding to the content ratio is inevitably added. The Ti content is preferably 0.08% by mass or less, and more preferably 0.06% by mass or less.

[0020] (Cr: 0.1% by mass or less) The aluminum alloy plate may contain Cr. If the Cr content is 0.1% by mass or less, it does not affect the material properties of the aluminum alloy plate. Although Cr is an unavoidable impurity, in order to reduce costs, for example, the mixing ratio of scrap (scrap containing a large amount of Cr, etc.) in the raw material can be increased, and Cr can be actively added within the above range. The Cr content is preferably 0.05% by mass or less.

[0021] The above-mentioned Ti and Cr, as long as they do not exceed the above-mentioned upper limit values, of course, the effects of the present invention are suppressed from being hindered not only when one or more kinds, that is, only one kind, are contained in the aluminum alloy, but also when two or more kinds are contained.

[0022] (Balance: Al and unavoidable impurities) The aluminum alloy plate may contain inevitable impurities in addition to Al and the above alloy components. Examples of the inevitable impurities include Zn, Zr, B, V, Na, Ca, Ni, In, Sn, Ga, etc. The allowable content of the inevitable impurities may be, for example, 0.3% by mass or less, preferably 0.1% by mass or less, more preferably 0.05% by mass or less for Zr. For other elements other than Zr, it may be, for example, 0.05% by mass or less for each and 0.15% by mass or less in total. Within the above range, whether contained as inevitable impurities or added as the above elements, the effects of the present invention are suppressed from being hindered.

[0023] The thickness of the aluminum alloy plate constituting the aluminum alloy coated plate for can lids may be, for example, 0.15 mm or more and 0.30 mm or less.

[0024] The structure of the aluminum alloy plate In one embodiment of the present invention, after cold rolling without intermediate annealing with the above alloy composition, the structure of the aluminum alloy plate in the state heat-treated by baking coating treatment has 45 or more sub-grains in a predetermined region at the center of the plate thickness. By making the structure of the aluminum alloy plate have a predetermined number or more of sub-grains, it is possible to solve the problem that was conventionally difficult to solve, that is, the rivet formability can be improved while maintaining the strength. The sub-grains of the aluminum alloy plate are counted by observing with a transmission electron microscope (TEM) with a magnification of 50,000 times in a plane parallel to the rolling plane and a thickness of 100 nm at the center of the plate thickness. -12 m 2 A sub-grain is also called a sub-grain and is a small amorphous grain. It is generated when a material (structure) into which dislocations are introduced by cold rolling or the like proceeds with recovery to form a structure with low energy under a given temperature, time, and strain.

[0025]

[0026] ​That is, in the case of an aluminum alloy coated sheet for a can lid, sub-grains with sharp boundaries are formed by the coalescence disappearance and rearrangement of dislocations in dislocation-dense regions such as dislocation cell walls and deformation bands introduced by cold rolling. When a large number of dislocation-dense regions are formed, the probability of coalescence disappearance with newly migrated dislocations increases, and the work hardening index (n value) decreases. However, the work hardening index (n value) improves by forming a sub-grain structure. When the work hardening index (n value) improves, the uniform deformation ability improves, so the rivet formability improves. Therefore, the more sub-grains there are, the better the rivet formability.

[0027] An example of the observed sub-grains is shown in Fig. 1. Fig. 1 is an example of a transmission electron microscope (TEM) image at a magnification of 50,000 times. Sub-grains 20 are formed from the dislocation-dense region 10, and the sub-grains 20 are identified in the crystal grains as small, irregular grains with sharp (distinct and clear) outer edge shapes at their boundaries and few dislocations inside.

[0028] In this way, the number of individual sub-grains can be counted in the observation field of the transmission electron microscope. Instead of the number of sub-grains present in a predetermined observation field, it is also conceivable to measure the area ratio of sub-grains. However, in that case, since the size of the sub-grains is not considered, a high sub-grain area ratio can be obtained even in the case of a coarse sub-grain structure. Since a coarse sub-grain structure has a lower dislocation density than a fine sub-grain structure, the strength decreases and the strength required for a can lid cannot be obtained.

[0029] Therefore, in one embodiment, the size of the sub-grains may be, for example, 1500 nm or less in terms of the equivalent circle diameter, preferably 1000 nm or less. The lower limit of the equivalent circle diameter of the sub-grains may be, for example, 50 nm or more. The equivalent circle diameter is calculated by measuring the boundary length of the sub-grain and taking it as the diameter of a circle having the same length as the boundary length.

[0030] In one embodiment, the number of sub-grains in a predetermined region at the center of the thickness of the aluminum alloy plate constituting the aluminum alloy coated plate for can lids may be 45 or more, preferably 60 or more, more preferably 100 or more. The upper limit of the number of sub-grains may be, for example, 600 or less.

[0031] When the number of sub-grains in a predetermined region at the center of the thickness of the aluminum alloy plate is less than 45, the aluminum alloy plate has high strength, but on the other hand, it may not be possible to achieve both excellent rivet formability and high strength. That is, it may not be possible to increase the strength while maintaining the formability of the aluminum alloy coated plate for can lids.

[0032] The aluminum alloy coated plate for can lids is excellent in strength and formability. The plate strength of the aluminum alloy coated plate for can lids may be, for example, 300 MPa or more, preferably 320 MPa or more, more preferably 330 MPa or more, still more preferably 340 MPa or more as the 0.2% proof stress. The upper limit of the plate strength of the aluminum alloy coated plate for can lids is 390 MPa or less as the 0.2% proof stress. Further, the formability of the aluminum alloy coated plate for can lids can be evaluated, for example, by the limiting bulge height in a micro bulge test with a diameter of φ6 mm. The limiting bulge height in the micro bulge test with a diameter of φ6 mm may be, for example, 1.65 mm or more, preferably 1.66 mm or more. Also, the upper limit of the limiting bulge height is about 2.0 mm or less, for example. When the 0.2% proof stress is 300 MPa or more and the limiting bulge height is 1.65 mm or more, it is possible to form the rivet part without causing cracks, cracks, etc. even during actual forming of the can lid while maintaining sufficient strength.

[0033] The structure and properties of the aluminum alloy sheet described above are those of an aluminum alloy coated sheet (pre-coated sheet) after coating and baking treatment are applied to a cold-rolled sheet (sheet after cold rolling). Note that such structure and properties may also be those of an aluminum alloy sheet after heat treatment under specific conditions simulating the baking treatment on the cold-rolled sheet, without applying the coating and baking treatment or forming it into a can lid. These structures and properties can be regarded as the same or approximately the same if the conditions of the coating baking treatment and the heat treatment are the same.

[0034] The aluminum alloy coated sheet for can lids may be a pre-coated sheet provided with a resin layer on one or both sides of the aluminum alloy sheet. The resin layer may be a baked resin layer formed by applying an organic paint such as an epoxy resin, a vinyl chloride resin, or a polyester resin and then performing heat treatment. The aluminum alloy sheet to which the organic paint is applied may be a surface-treated aluminum alloy sheet surface-treated or chemical-converted with a surface treatment agent such as a chromate-based or zirconium-based agent. The temperature of the heat treatment may be, for example, a temperature at which the peak metal temperature (PMT) is about 200°C or higher and 290°C or lower. The thickness of the resin layer may be, for example, about 0.5 μm or more and 15 μm or less.

[0035] The aluminum alloy coated sheet for can lids is formed into a can lid as follows, for example. The aluminum alloy coated sheet for can lids is blanked into a disc shape, and then the obtained blank material is shell formed. A winding portion for winding with the can body is formed on the formed shell. A compound lining for injecting rubber into the winding portion is performed on the can lid with the winding portion formed. Then, a rivet forming process including a bubble forming for protruding the central portion of the can lid and a button forming for making the protruding portion a steep protrusion, a score process for grooving the opening portion, a bead embossing process for performing processes such as unevenness and characters, and a stake forming process for tabbing are performed, and conversion forming is performed to form the can lid. The can lid thus formed is wound around a bottomed cylindrical can body filled with contents, and the aluminum can sealed with the can lid is washed and sterilized.

[0036] Manufacturing method An example of the manufacturing method of the aluminum alloy sheet constituting the aluminum alloy coated sheet for can lids will be described. The manufacturing method of the aluminum alloy sheet includes a casting process as the first process, a homogenization heat treatment process as the second process, a hot rolling process as the third process, and a cold rolling process as the fourth process, and these processes are performed in this order.

[0037] (From the first process to the third process: casting process, homogenization heat treatment process, hot rolling process) The first process is a process of producing an ingot having a target composition by a semi - continuous casting method. The second process is a process of performing a homogenization heat treatment on the ingot of the aluminum alloy produced in the first process.

[0038] In the first process, an aluminum alloy is cast by a semi - continuous casting method (DC (direct chill) casting) to obtain an ingot. Next, a process of removing the region with a non - uniform structure on the ingot surface by facing and the second process of performing a homogenization heat treatment are performed. This homogenization heat treatment is carried out, for example, in the range of 400°C or more and 600°C or less, and also serves as a preliminary heating for subsequent hot rolling.

[0039] The third step is a hot rolling step of an aluminum alloy ingot that has been subjected to homogenization heat treatment in the second step. The plate thickness of the hot-rolled plate obtained by hot rolling is usually set by inversely calculating the total rolling ratio by cold rolling from the plate thickness of the product plate obtained by cold rolling.

[0040] The coiling temperature, which is the finishing temperature of hot rolling, is, for example, 300°C or higher and 370°C or lower, preferably 320°C or higher and 370°C or lower. When the coiling temperature is 300°C or higher, the recrystallization rate of the hot-rolled plate improves, and the rivet formability of the aluminum alloy plate after painting baking is further improved. On the other hand, when the coiling temperature is 370°C or lower, the occurrence of surface defects called burning on the plate surface is suppressed, and the surface properties of the plate are improved.

[0041] The fourth step is a cold rolling step of the hot-rolled plate hot-rolled in the third step. In the fourth step, the hot-rolled plate is cold-rolled without intermediate annealing to finish into an aluminum alloy plate with a predetermined plate thickness. Cold rolling is performed by setting a plurality of passes with a predetermined total rolling ratio so that the hot-rolled plate is rolled to the plate thickness of the product plate within an appropriate load range. Note that a pass means that the plate passes between a pair of work rolls once and is rolled.

[0042] The total rolling ratio of cold rolling is preferably 85.0% or more, more preferably 90.0% or more. When the total rolling ratio of cold rolling is 85.0% or more, not only can the strength of the aluminum alloy plate be sufficiently obtained, but also the dislocation density increases, and sub-grain formation after baking painting treatment is promoted. As shown in FIG. 1, by introducing dislocations, linear dislocations are likely to tangle, and many dislocation-dense regions 10 such as forest dislocations, cell walls, and shear bands are formed. Then, by heat treatment such as subsequent baking painting, sub-grains 20 are formed from the dislocation-dense region 10, and the number of sub-grains within the range defined in the present invention can be obtained. As a result, the rivet formability tends to improve.

[0043] In addition to setting the total rolling reduction of cold rolling within a predetermined range, it is preferable that the threading interval between the final rolling pass of cold rolling and the rolling pass immediately before it is within 1.0 second, and the final coiling temperature after the final rolling pass is 135°C or higher. By setting the threading interval within 1.0 second, dynamic recovery in the final rolling pass is more promoted, formation of sub-grains in the dislocation dense region is more promoted, more sub-grains are formed during painting and baking in the next process than before, and the material temperature on the inlet side of the final pass is maintained high, so that the final coiling temperature after the final rolling pass can be 135°C or higher. Thereby, static recovery of dislocations after coiling is promoted, and improvement in rivet formability due to an improvement in the work hardening index (n value) is obtained. Furthermore, since the rolling speed is improved without increasing the number of rolling passes in cold rolling, productivity can be further improved. The range of the threading interval is preferably within 0.80 second, more preferably within 0.50 second, and the range of the final coiling temperature is preferably 140°C or higher, more preferably 150°C or higher.

[0044] The aluminum alloy sheet manufactured by the above process is subjected to chemical conversion treatment with a surface treatment agent such as a chromate-based or zirconium-based agent. Thereafter, an organic paint containing an epoxy-based resin, a PVC sol-based resin, a polyester-based resin, etc. is applied to form a coating film. The formed coating film is subjected to painting and baking treatment at a PMT (Peak Metal Temperature) of about 200°C or higher and 290°C or lower to manufacture an aluminum alloy coated sheet for a can lid as a pre-coated sheet.

Examples

[0045] The embodiments of the present invention have been described above. Hereinafter, examples in which the effects of the present invention were confirmed will be specifically described. Note that the present invention is not limited to these examples.

[0046] (Preparation of Test Specimens) An aluminum alloy having the composition shown in Table 1 was cast by the semi - continuous casting method, and surface machining and homogenization heat treatment were performed by the methods shown in the first and second steps, followed by hot rolling without cooling. The finish temperature of the hot rolling was set to be 300 °C or higher and 370 °C or lower as the coiling temperature. Then, the obtained hot - rolled sheet was cold - rolled under the conditions shown in Table 1 without intermediate annealing to obtain an aluminum alloy sheet as a cold - rolled sheet with a thickness of 0.25 mm. The balance of the composition shown in Table 1 is Al and inevitable impurities. Also, the cold rolling ratio is the total rolling ratio in cold rolling, and the sheet - passing interval is the required time between the final rolling pass and the rolling pass immediately before it in cold rolling.

[0047] Subsequently, the obtained aluminum alloy sheet was subjected to a strain - rectifying treatment and a chemical conversion treatment, and then an epoxy - based paint was applied and baked at a PMT of 200 °C or higher and 290 °C or lower in a continuous baking furnace. The baking temperature and baking time were made the same in all production examples from No.1 to No.12.

[0048]

Table 1

[0049] The manufactured aluminum alloy painted sheet was used as a test specimen, and the sub - grain number, 0.2% proof stress, and limit bulge height (rivet formability) were measured by the following methods. The results are shown in Table 1. Note that “ - ” in Table 1 indicates unmeasured.

[0050] Number of sub - grains Regarding the structure at the center of each plate thickness on the plane parallel to the rolling plane of each test specimen, sub - grains were counted by observation with a transmission electron microscope (TEM) at a magnification of 50,000 times to calculate the number of sub - grains.

[0051] Specifically, the test specimen was mechanically polished to a thickness of 0.05 mm (thickness 0.1 mm) in both thickness directions from the center of the plate thickness, then made into a thin film with a thickness of 100 nm by the twin - jet type electrolytic polishing method, and this thin film was observed with a transmission electron microscope at a magnification of 50,000 times at 205×10 -12 m2 The area was photographed. The total number of sub-grains measured within the photographed field of view was summed to calculate the number of sub-grains. Regarding the measurement of the number of sub-grains, considering the evaluation results of the rivet formability, a test material that clearly shows the effects of the present invention was extracted and measured. Although the upper limit of the number of sub-grains is not particularly defined, it is usually about 600 grains.

[0052] Measurement of 0.2% proof stress For each test material, a JIS No. 5 tensile test piece with the tensile direction parallel to the rolling direction was prepared, and a tensile test was conducted according to the provisions of JIS Z2241. The plate thickness excluding the coating thickness was calculated to obtain the 0.2% proof stress. The appropriate range of the 0.2% proof stress is 300 MPa or more. Within this range, even a thin-walled can lid can satisfy the pressure resistance of the lid. Although the upper limit of the 0.2% proof stress is not particularly defined, it is usually about 390 MPa.

[0053] Measurement of the limiting bulging height A 50 mm × 50 mm test piece was prepared from each test material, and a bulging test simulating the bubble process was carried out to obtain the limiting bulging height. As shown in Figure 2, in the bulging test, test piece 1 was clamped between the upper and lower dies 2 and 3 and fixed with a certain wrinkle suppressing force, and the punch 4 was pushed vertically into the center of test piece 1 to perform the bulging process. The inner diameter of the hole of dies 2 and 3 is 6.60 mm, the shoulder radius is 0.40 mm, the outer diameter of punch 4 is 6.00 mm, the diameter of the central flat part of the head is 1 mm, and the shoulder radius of the head is 2.50 mm. By this bulging test, the limiting value (limiting bulging height) of the bulging height at which the bulging process can be performed without cracking of test piece 1 was measured. The test was carried out 8 times with the same test material, and the value obtained by averaging the 6 results excluding the maximum and minimum measurement results of the 8 measurements was taken as the limiting bulging height. The appropriate range of the limiting bulging height was set to 1.65 mm or more. If the limiting bulging height is 1.65 mm or more, a button with a sufficient height can be formed during actual forming, the rivet formability is excellent, and the tab can be firmly fixed by the stake process. Although the upper limit of the limiting bulging height is not particularly defined, it is usually about 2.0 mm.

[0054] As shown in Table 1, Nos. 1 to 12, where the composition of the aluminum alloy coated plate is within the specified range of the present invention, correspond to the examples because the number of sub-grains is within the specified range of the present invention. For any of Nos. 1 to 12, the threading interval between the final pass and the pass immediately before it in cold rolling is within 1.0 second and the coiling temperature is 135°C or higher, and the limit bulge height (rivet formability) also reaches the passing value. Also, as shown in Figure 3, there is a proportional relationship between the limit bulge height and the final coiling temperature, and it is expected that the final coiling temperature at which the limit bulge height becomes 1.65 mm or more is about 135°C from the slope of the linear approximation line. Further, as shown in Figure 4, there is a proportional relationship between the limit bulge height and the number of sub-grains, and it is expected that the number of sub-grains at which the limit bulge height becomes 1.65 mm or more is about 45 or more from the slope of the linear approximation line.

Explanation of Signs

[0055] 1 Specimen 2 Die 3 Die 4 Punch 10 Dislocation Dense Region 20 Sub-grain

Claims

1. An aluminum alloy plate comprising: Si: 0.05% by mass or more and 0.40% by mass or less; Fe: 0.05% by mass or more and 0.50% by mass or less; Cu: 0.01% by mass or more and 0.30% by mass or less; Mn: 0.10% by mass or more and 0.60% by mass or less; Mg: 4.0% by mass or more and 6.0% by mass or less; and the balance being Al and inevitable impurities; and a resin layer; In a plane parallel to the rolled surface, the structure of a region 50 nm thick in both thickness directions from the center of the sheet thickness is observed by a transmission electron microscope at 50,000 magnifications. －１２ m ２ The coated aluminum alloy plate for can ends has a total of 45 or more subgrains in an area of ​​10 mm.

2. 2. The coated aluminum alloy sheet for can ends according to claim 1, wherein the aluminum alloy sheet contains Ti as an alloy component in an amount of 0.1 mass % or less.

3. 3. The coated aluminum alloy sheet for can ends according to claim 1, wherein the aluminum alloy sheet contains Cr as an alloy component in an amount of 0.1 mass % or less.

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