Aluminum alloy-made can lid and aluminum alloy sheet for can lid

Abstract

Provided are a can lid and an aluminum alloy sheet for a can lid, in which the amount of an Al-Fe-Mn-based compound or the like is reduced even if a recycled aluminum alloy using aluminum UBCs as a raw material is included and which have the performance required for a can lid in terms of pressure resistance strength, score strength, and the like.　The can lid comprises an aluminum alloy containing 0.17-0.40 mass% of Si, 0.23-0.50 mass% of Fe, 0.11-0.24 mass% of Cu, 0.5-1.0 mass% of Mn, and 0.6-2.7 mass% of Mg and is characterized in that: in a rolling direction / plate thickness direction plane of a panel part, the total of the area ratios of an Al-Fe-Mn-based compound and an Mg2Si compound is no more than 2.5%; and, in a plate thickness center part of a plane orthogonal to the rolling direction of the panel part, the area ratio occupied by crystal grains having an equivalent circle diameter of at least 2 μm is at least 70%.

Description

Aluminum alloy can lids and aluminum alloy plates for can lids

[0001] The present invention relates to aluminum alloy can lids and aluminum alloy sheets for can lids, and more specifically to can lids that have the performance required of can lids while using recycled materials made from aluminum cans after their contents have been consumed, and aluminum alloy sheets from which such can lids can be manufactured.

[0002] Food and beverage cans, consisting of a can body made of a metal such as aluminum or steel and an aluminum can lid attached thereto, are widely used as cans for filling beverages and foods, such as beer and soft drinks. Such aluminum can lids generally have a tab attached to them, which is used to tear a score formed in the panel to form an opening defined by the score. Materials used for can lids are required to have strength, formability, corrosion resistance, and other properties. Specifically, can lids must have excellent pressure resistance to prevent deformation, even in the case of positively pressurized cans containing carbonated beverages and the like, or in the case of negatively pressurized cans, which are decompressed due to a temperature drop caused by filling the contents at high temperature, and must also have sufficient toughness to prevent unintentional rupture of the score. Meanwhile, tabs must have sufficient breaking strength and toughness to prevent breakage, tearing, or the like when forming an opening.

[0003] As an aluminum alloy used for can lids, for example, Patent Document 1 listed below proposes a beryllium-free aluminum-magnesium alloy that is inhibited from being oxidized by melting, which contains 0.8 to 15 mass % of Mg and 0.2 to 0.6 mass % of Fe, with the total content of Al and Mg being 90 mass % or more, and the content of P as an impurity being 0.001 mass % or less. Furthermore, Patent Document 2 listed below discloses a cold-rolled sheet material having a thickness of 0.22 to 0.25 mm, which is made of an aluminum alloy containing, on a mass basis, 0.80 to 1.50% Mg, 0.80 to 1.20% Mn, 0.40 to 0.60% Fe, 0.20 to 0.40% Si, and 0.15 to 0.25% Cu, and which satisfies the content relations of Mn / Fe=1.5 to 2.5 and Mg / Mn≧1.0, with the remainder being aluminum and unavoidable impurities; The proposed aluminum alloy sheet for negative pressure can ends is characterized in that one or both sides thereof are coated with an organic resin film, and that after paint baking, the 45° earing is 1.5 to 3.0%, the 0-180° earing is 1.0 to 2.5%, and the formula: -0.6%≦(45° earing)−(0-180° earing)≦1.5% is satisfied, and further the tensile strength in the direction at 0° to the rolling direction is 270 to 300 MPa and the proof stress is 240 to 270 MPa.

[0004] Patent No. 5920705 Patent No. 5898426

[0005] Nearly 100% of used beverage cans (UBCs) are recovered after their contents have been consumed. In the case of aluminum beverage cans, they are recycled into aluminum ingots for recycling. While can bodies are generally made of 3000-series aluminum alloys, such as 3104 aluminum alloys, which have a high manganese content, can ends are made of 5000-series aluminum alloys, such as 5182 aluminum alloys, which have a high magnesium content and are superior in strength to 3000-series aluminum alloys in terms of strength, formability, corrosion resistance, and the like. Therefore, recycled aluminum alloys made of UBCs have a composition similar to that of 3104 aluminum alloy, which accounts for a large proportion of the weight of aluminum beverage cans. Compared to 5182 aluminum alloys, these alloys contain higher amounts of silicon, iron, copper, and manganese, but less magnesium. Therefore, it has been necessary to use virgin aluminum ingots for can ends. However, the production of virgin aluminum requires a large amount of electricity and the associated carbon dioxide emissions are significant, which places a burden on the environment. From this perspective, it is desirable to be able to use recycled materials for can lids as well.

[0006] In addition, aluminum alloys made from recycled aluminum alloys made from UBC contain a large amount of Si, Fe, and Mn, and are not suitable for use in Al-Fe-Mn compounds (including Al-Fe-Mn-Si compounds) or Mg ２ The increase in crystallized substances such as Si compounds reduces the strength of the score formed in the can lid panel, which may cause the score to break unintentionally when subjected to a drop impact, resulting in leakage of the contents. It has also been found that microcracks may occur in the organic coating on the inner surface of the score processing area (the inner surface of the can lid panel) and on the rivet forming area for attaching the tab, which may result in metal exposure or corrosion of the can lid over time during storage. Furthermore, aluminum alloys with an increase in crystallized substances such as Al-Fe-Mn compounds have reduced toughness, making them prone to cracking, which may cause the can lid to deviate from the score and break when breaking the score to form an opening.

[0007] Therefore, an object of the present invention is to provide a can lid that has the performance required for can lids, such as pressure resistance and score strength, even when it contains a recycled aluminum alloy made from UBC. Another object of the present invention is to provide an aluminum alloy sheet for can lids that has strength and toughness that enable the properties required for can lids, such as pressure resistance, to be favorably exhibited.

[0008] According to the present invention, the aluminum alloy contains 0.17 to 0.40 mass% of Si, 0.23 to 0.50 mass% of Fe, 0.11 to 0.24 mass% of Cu, 0.5 to 1.0 mass% of Mn, and 0.6 to 2.7 mass% of Mg, and the aluminum alloy contains Al-Fe-Mn compounds and Mg in the rolling direction-thickness direction surface of the panel portion. ２ The can lid is characterized in that the total area ratio of Si compounds is 2.5% or less, and the area ratio of crystal grains having a circle-equivalent diameter of 2 μm or more is 70% or more in the center of the plate thickness on the surface perpendicular to the rolling direction of the panel portion.

[0009] According to the present invention, there is also provided a panel assembly comprising an aluminum alloy containing 0.26 to 0.36 mass% of Si, 0.36 to 0.50 mass% of Fe, 0.18 to 0.23 mass% of Cu, 0.8 to 1.0 mass% of Mn, and 2.3 to 2.7 mass% of Mg, wherein the aluminum alloy contains Al-Fe-Mn compounds and Mg in the rolling direction-thickness direction surface of the panel portion. ２ The can lid is characterized in that the total area ratio of Si compounds is 2.5% or less, and the area ratio of crystal grains having a circle-equivalent diameter of 2 μm or more is 70% or more in the center of the plate thickness on the surface perpendicular to the rolling direction of the panel portion.

[0010] The can lid of the present invention preferably has the following features: (1) the panel portion is formed with a breakable score that defines the intended opening portion, and a tab is attached to it; (2) the pressure resistance is 580 kPa or more; (3) the breakable score, in a vertical cross section in the width direction of the score, has opposing inclined surfaces and a bottom surface, the score width of which decreases downward, and a flat portion is formed in the center of the bottom surface, and the width of the flat portion has at least a portion that is 70% or less of the width of an imaginary bottom surface defined by an imaginary extension line of the inclined surface and an imaginary extension line passing through the center of the bottom surface; (4) the panel portion is formed with a rivet forming portion for attaching the tab, and the rivet forming portion is formed by a rivet forming tool whose working corner portion has a radius of curvature of more than 0.20 mm.

[0011] According to the present invention, the aluminum alloy plate further contains 0.17 to 0.40 mass% of Si, 0.23 to 0.50 mass% of Fe, 0.11 to 0.24 mass% of Cu, 0.5 to 1.0 mass% of Mn, and 0.6 to 2.7 mass% of Mg, and the aluminum alloy plate contains Al-Fe-Mn compounds and Mg in the rolling direction-thickness direction (RD-ND) plane in the width direction central portion. ２ There is provided an aluminum alloy sheet for can lids, characterized in that the total area ratio of Si compounds is 2.5% or less.

[0012] The aluminum alloy sheet for can lids preferably comprises an aluminum alloy containing 0.26 to 0.36% by mass of Si, 0.36 to 0.50% by mass of Fe, 0.18 to 0.23% by mass of Cu, 0.8 to 1.0% by mass of Mn, and 2.3 to 2.7% by mass of Mg, and the area ratio of crystal grains having a circle-equivalent diameter of 2 μm or more in a plane (TD-ND) perpendicular to the rolling direction in the width direction central part of the aluminum alloy sheet at the sheet thickness central part is 70% or more, and the average value of tensile strength (TS) and 0.2% proof stress (YS) [(TS+YS) / 2] is 330 to 360 MPa.

[0013] According to the aluminum alloy can lid of the present invention, even when recycled aluminum UBC, scrap from the production of aluminum plates, scrap from the production of can bodies and can lids, etc., are used, the main components of the alloy elements are within the above ranges, so that the can lid has an excellent pressure resistance of 580 kPa or more. ２ The total area ratio of Si compounds is reduced to 2.5% or less, which provides high toughness and high score strength, and coupled with the score shape described above, this effectively prevents cracks from occurring when the internal pressure of the can increases or when buckling occurs, and also effectively prevents problems such as unintended breakage or derailment of the score. Furthermore, the rivet is formed using a rivet forming tool with an active corner having a radius of curvature of more than 0.20 mm, making it possible to provide a rivet that is effectively prevented from cracking near its base (root).

[0014] Furthermore, the aluminum alloy sheet for can ends of the present invention makes it possible to reduce the amount of virgin aluminum used, which emits a large amount of carbon dioxide, and has high strength and high toughness that enable the formation of can ends having the above-mentioned excellent pressure resistance and score strength.

[0015] 1 is a diagram showing an example of a can lid of the present invention, where (A) is a plan view and (B) is a cross-sectional view. FIG. 2 is a diagram for explaining a score processing portion, and is a partially enlarged cross-sectional view in an axial cross section in the width direction of the score. FIG. 3 is a diagram showing an enlarged cross-sectional view for explaining the formation of a rivet forming portion. FIG. 4 is a diagram for explaining a score forming blade, and is an enlarged cross-sectional view in an axial cross section of the score forming blade. FIG. 5 is an enlarged cross-sectional view of a rivet forming portion. FIG. 6 is an enlarged cross-sectional view of a tab attachment portion. FIG. 7 is an explanatory diagram of a cross section for measuring intermetallic compounds and crystal grain size of an aluminum alloy plate.

[0016] (Aluminum Alloy Can Lid) A first important feature of the can lid of the present invention is that it is made of an aluminum alloy containing 0.17 to 0.40 mass% of Si, 0.23 to 0.50 mass% of Fe, 0.11 to 0.24 mass% of Cu, 0.5 to 1.0 mass% of Mn, and 0.6 to 2.7 mass% of Mg. The aluminum alloy contains Al-Fe-Mn compounds and Mg in the rolling direction-thickness direction surface of the panel portion. ２ A second important feature is that the total area ratio of Si compounds is 2.5% or less. As mentioned above, recycled materials made from UBCs are mostly made up of can bodies made from 3104 aluminum alloy, which has a low Mg content and high Si, Fe, Cu, and Mn content, and therefore have an alloy composition similar to that of 3104 aluminum alloy. Table 1 below shows the minimum content of each component required when blending 3104 aluminum alloy at various ratios. The second line in Table 1 lists the content (by mass%) of the components in the 3104 aluminum alloy. For example, if the blending ratio of 3104 aluminum alloy is 50% by mass or more, it must contain at least 0.17% by mass of Si, 0.23% by mass of Fe, 0.11% by mass of Cu, 0.5% by mass of Mn, and 0.6% by mass of Mg. If the target values ​​of the components are equal to or greater than these, blending with virgin aluminum ingot for dilution is unnecessary. Similarly, for example, when the blending ratio of 3104 aluminum alloy is 80 mass% or more, the can lid of the present invention must contain at least 0.26 mass% Si, 0.36 mass% Fe, 0.18 mass% Cu, 0.8 mass% Mn, and 1.0 mass% Mg. The can lid of the present invention has an alloy composition that allows the blending ratio of 3104 aluminum alloy to exceed 50 mass%, more preferably 80 mass%, thereby achieving a high recyclability, achieving both high strength and high toughness, and providing a can lid that has excellent pressure resistance and effectively prevents unintended breakage of the score.

[0017]

[0018] The aluminum alloy constituting the can lid of the present invention has the main components of the alloy elements in the above ranges, and also has Al-Fe-Mn compounds and Mg ２By keeping the total area ratio of Si compounds at 2.5% or less, the pressure resistance is excellent at 580 kPa or more, and cracks are effectively prevented from occurring even when the internal pressure of the can increases or buckling occurs. The method for measuring the pressure resistance will be described later.

[0019] The Si content is preferably in the range of 0.17 to 0.40 mass%, more preferably 0.26 to 0.36 mass%. If the Si content is less than the above range, the amount of 3104 aluminum alloy scrap to be added is limited. In addition, the amount of precipitation during the processing heat of cold rolling after hot rolling and annealing may decrease, which may result in insufficient strength of the alloy sheet. On the other hand, Si has the above-mentioned Mg ２ Since Si compounds are formed, when the Si content is higher than the above range, Mg ２ The amount of crystallized Si compounds increases, which may result in a decrease in toughness and a decrease in score strength.

[0020] The Fe content is preferably in the range of 0.23 to 0.50 mass%, particularly 0.36 to 0.50 mass%. If the Fe content is less than the above range, the amount of 3104 aluminum alloy scrap to be added is limited. On the other hand, if the Fe content is more than the above range, the increase in Al-Fe-Mn compounds may reduce toughness and score strength.

[0021] The Cu content is preferably in the range of 0.11 to 0.24 mass%, particularly 0.18 to 0.23 mass%. If the Cu content is lower than the above range, the amount of 3104 aluminum alloy scrap to be added is limited. If the Cu content is lower than the above range, the strength of the aluminum alloy may be insufficient compared to when the Cu content is within the above range. On the other hand, if the Cu content is higher than the above range, cracks may occur during hot rolling.

[0022] The Mn content is preferably in the range of 0.5 to 1.0 mass%, particularly 0.8 to 1.0 mass%. If the Mn content is less than the above range, the strength of the aluminum alloy decreases and the amount of scrap 3104 aluminum alloy that can be incorporated decreases. On the other hand, if the Mn content is more than the above range, the toughness decreases due to an increase in Al-Fe-Mn-based crystals, which may result in a decrease in score strength.

[0023] The Mg content is preferably in the range of 0.6 to 2.7% by mass, particularly 2.3 to 2.7% by mass. If the Mg content is less than the above range, the can lid may not have the strength required, and may be deformed when subjected to a positive pressure can or sterilization treatment. On the other hand, if the Mg content is more than the above range, coarse Mg particles may be formed. ２ The formation of Si not only significantly reduces formability but also may cause cracks in the ingot and during hot rolling and can lid formation.

[0024] The alloy plate may contain titanium (Ti). The upper limit of the Ti content is preferably 0.10 mass%. By including Ti, the ingot structure of the alloy plate is refined. The alloy plate may also contain zinc (Zn). The upper limit of the Zn content is preferably 0.25 mass%. Furthermore, the alloy plate may also contain chromium (Cr). The upper limit of the Cr content is preferably 0.10 mass%.

[0025] The alloy sheet may contain unavoidable impurities to the extent that the performance of the alloy sheet is not significantly impaired. That is, the alloy sheet contains Si, Fe, Cu, Mn, Mg, Ti, Zn, and Cr in the above-mentioned ranges, with the balance consisting of aluminum and unavoidable impurities. The upper limit of the total amount of unavoidable impurities is preferably 0.15% by mass.

[0026] As mentioned above, when the content of Fe, Mn, Si, and Mg increases, Al-Fe-Mn compounds and Mg ２The crystallization of Si compounds increases, and these particles become the starting point and propagation path of cracks, which reduces the toughness of the aluminum alloy and leads to a decrease in score strength. ２ Since the total area ratio of Si compounds is 2.5% or less, the toughness of the aluminum alloy is not reduced, the score strength is high, and there is no risk of unintended fracture or derailment of the score (fracture in areas other than the score).

[0027] Al-Fe-Mn compounds and Mg in can lids ２ The area ratio of Si compounds can be measured by the following method. Regarding a sample cut out from the panel portion of a can lid, the direction parallel to the rolling streaks (when visual confirmation is difficult, for example, the surface of the panel portion is polished, anodized using Barker's solution, and observed under an optical microscope using a polarizing filter to determine the direction in which the crystal grains extend) is considered to be the rolling direction (RD), the direction perpendicular to the panel surface is considered to be the thickness direction (ND), and the normal direction to the RD-ND plane is considered to be the width direction (TD). The RD-ND plane (RD: rolling direction, ND: thickness direction, TD: width direction) shown by the diagonal lines in Figure 7 is mechanically polished to a mirror finish. Next, the polished surface is observed using a Carl Zeiss Ultra Plus scanning electron microscope (SEM), and 10 fields of view are obtained in the central region of the plate thickness. The SEM acceleration voltage is 15 kV, the magnification is 1000x, and the range of one field of view is 0.012 mm. ２ The image is photographed as above, and a COMPO (backscattered electron composition image) is obtained. The photographed COMPO is analyzed using the image analysis software ImageJ. Specifically, the most frequent value of the brightness of the image in 256 gradations is taken as the brightness of the background, and particles with a brightness higher than the brightness of the most frequent value plus 20 are determined to be particles of an Al-Fe-Mn compound. Also, particles with a brightness lower than the brightness of the most frequent value minus 30 are determined to be particles of an Mg ２ The particles are judged to be Si compounds. The Al-Fe-Mn compounds and Mg ２ The total area of ​​the Si compound particles was calculated and divided by the photographed area to determine the area of ​​the Al-Fe-Mn compound and Mg ２ The area ratio of the Si compound particles is calculated.

[0028] In addition, excessively high anisotropy of the material structure reduces the toughness of the aluminum alloy, making it more susceptible to thickness reduction and cracking along the rolling direction during material forming. This material anisotropy increases during the cold rolling process. Cold rolling deforms the material under compressive stress, compressing the crystal grains in the ND direction. As a result, the proportion of relatively large crystal grains in the TD-ND plane (RD: rolling direction, ND: thickness direction, TD: width direction), which is a plane perpendicular to the rolling direction (RD), decreases. As can be seen from the examples, the can lid of the present invention is an aluminum alloy sheet with low anisotropy, in which the area ratio of crystal grains with a circle equivalent diameter of 2 μm or more in the TD-ND plane is 70% or more, so there is no reduction in toughness and cracking during forming.

[0029] The grain size of a can lid can be measured by the following method. A sample cut from a panel portion of a can lid was polished by ion milling on the TD-ND plane, which is a plane perpendicular to the rolling direction (RD). The central region of the plate thickness was observed with a Carl Zeiss Ultra Plus SEM (scanning electron microscope), and the texture was analyzed using SEM-EBSD. The SEM acceleration voltage was 15 kV and the magnification was 2000x. An IPF image (inverse pole figure) was acquired in one field of view, analyzing a rectangular region 70 μm in the ND direction and 38 μm in the TD direction every 0.1 μm. The measurement results were analyzed using the data analysis software TSL-OIM analysis. For each adjacent analysis point, particles with a crystal orientation difference of 15° or more are identified as different crystal grains, and the circle-equivalent diameter and area of ​​each crystal grain are calculated, thereby allowing the area ratio occupied by crystal grains with a circle-equivalent diameter of 2 μm or more in the observation region of the TD-ND plane to be calculated.

[0030] [Can Lid Shape] In the present invention, the shape of the can lid is not particularly limited and various shapes can be adopted. Fig. 1 shows an example of a can lid of the present invention, with (A) being a plan view and (B) being a cross-sectional view. The can lid shown in Fig. 1 is a stay-on-tab can lid (the entire can lid with the tab is indicated by 1) having a tab 4 fixed with a rivet 3 to a panel portion (center panel 21) of a shell 2. The shell 2 has a circular center panel 21, a chuck wall radius 22 protruding downward from the periphery of the center panel 21, a chuck wall 23 rising from the outer wall of the chuck wall radius 22, and a seaming panel 24 formed continuously with the chuck wall 23. The center panel 21 has a breakable score 25 that defines a planned opening portion. On the other hand, the tab 4 comprises a tab main body 41, an arc-shaped tab nose 42 formed at a position on the pouring direction side of the contents, a finger hook (grip) 43 formed on the opposite side of the tab nose 42, and a fixing part 44 to which the tab main body 41 is fixed with a rivet 3. The tab main body 41 is also bent at an outer peripheral edge 45 of the grip part 43, and a curled part 46 folded downward is formed around the entire periphery of the outer peripheral edge other than the grip part 43.

[0031] As described above, the can lid of the present invention is formed from an aluminum alloy plate that has a predetermined alloy composition and a reduced amount of specific compounds in order to achieve the pressure resistance strength and other characteristics required of the can lid. This improves the strength and toughness of the can lid, and therefore improves the score strength as well. Furthermore, by adjusting the shape of the score formed on the can lid, unintended score fracture can be more effectively suppressed.

[0032] [Score] In the can lid of the present invention, as is clear from Fig. 2 , which shows an axial cross section in the width direction of the score, it is preferable that at least a portion of the breakable score 25 defining the intended opening portion has opposing inclined surfaces 26a, 26b whose score width W decreases downward, and a bottom surface 27 having a central flat surface 27a, the inclined surfaces 26a, 26b and the bottom surface 27 being continuous with each other via a curved surface R, and that at least a portion of the flat surface 27a of the bottom surface has a width W1 that is 70% or less of the width W0 of an imaginary bottom surface 27 defined by imaginary extension lines La, Lb of the inclined surfaces 26a, 26b and an imaginary extension line Lc passing through the center of the bottom surface 27. In this way, the breakable score is formed so that the inclined surfaces and the bottom surface are continuous with each other via a curved surface, and the width of the bottom surface (the width of the flat surface 27a in the specific example shown in Fig. 2) is 70% or less of the imaginary bottom surface, thereby improving the strength of the score and effectively preventing breakage of the score even when the can is dropped or subjected to vibrations during transportation while filled with contents.

[0033] In other words, if the width W1 of the flat surface is greater than the above range, the score may break when subjected to a drop impact or vibration during transportation, resulting in leakage of the contents. The width of the bottom surface is the distance at the center of the bottom surface, excluding the curved surface connecting the inclined surface and the bottom surface. As shown in Figure 2 , if there is a flat surface at the center, this width is the width of the flat surface. However, this width may be as close to zero as possible. In such cases, the bottom surface has a generally arc-shaped shape that is continuous with the curved surface. In the preferred embodiment of the present invention shown in the figures, the inclined surface of the score and the bottom surface are connected via a curved surface. However, even if the inclined surface and the bottom surface are not connected via a curved surface, the same effect as when a curved surface is connected may be obtained, depending on the remaining thickness of the score, if the remaining thickness of the score is thick, or depending on the angle formed by the inclined surface and the bottom surface. In the can lid of the present invention, the score is preferably formed throughout the entire area of ​​the score when the flat surface of the bottom surface falls within the above numerical range from the viewpoint of improving the strength of the score. However, the score may be formed partially in a thin-walled portion where the remaining thickness of the score is small, such as the latter half of the opening.

[0034] The width W0 of the imaginary bottom of the score bottom is preferably in the range of 15 to 40 μm. This prevents microcracks from occurring in the organic coating (thermoplastic resin coating or paint film) on the inside surface of the score (the back side of the can lid), effectively prevents metal exposure on the inside surface of the can lid, and makes it possible to provide a can lid with excellent corrosion resistance. If the width W0 of the imaginary bottom is smaller than the above range, stress corrosion cracking may occur, although this depends on the material used and the remaining thickness of the score. On the other hand, if the width W0 is larger than the above range, microcracks may occur on the inside surface of the score compared to when it is within the above range.

[0035] As shown in FIG. 2, the unprocessed portion (original thickness) t ０ The remaining score thickness (thickness of the score processed part) t in the initial opening part of the score processed part where the score 25 is formed １ The proportion of {(t １ / t ０ ) × 100(%)} is preferably 71% or less. ０ Score remaining thickness t １ The ratio of varies depending on the original plate thickness, and decreases as the original plate thickness increases. Specifically, within the range of the original plate thickness of the can lid of 0.19 mm to 0.30 mm, when the original plate thickness is greater than 0.190 mm and less than 0.200 mm, it is 71% or less, when the original plate thickness is greater than 0.200 mm and less than 0.210 mm, it is 68% or less, when the original plate thickness is greater than 0.210 mm and less than 0.220 mm, it is 64% or less, when the original plate thickness is greater than 0.220 mm and less than 0.230 mm, it is 61% or less, when the original plate thickness is greater than 0.230 mm, it is 62% or less, when the original plate thickness is greater than 0.230 mm, it is 64% or less, when the original plate thickness is greater than 0.230 mm, it is 65% or less, when the original plate thickness is greater than 0.230 mm, it is 66% or less, when the original plate thickness is greater than 0.230 mm, it is 67% or less, when the original plate thickness is greater than 0.230 mm, it is 68% or less, when the original plate thickness is greater than 0.230 mm, it is 68% or less, when the original plate thickness is greater than 0.230 mm, it is 68% or less, when the original plate thickness is greater than 0.230 mm, it is 64% or less, when the original plate thickness is greater than 0.230 mm, it is 65% or less, when the original plate thickness is greater than 0.230 mm, it is 65% or less, when the original plate thickness is greater than 0.230 mm, it is 66% or less, when the original plate thickness is greater than 0.230 mm, it is 67 It is preferable that the thickness is 59% or less when the thickness is less than 0.240 mm, 56% or less when the thickness is greater than 0.240 mm and less than 0.250 mm, 54% or less when the thickness is greater than 0.250 mm and less than 0.260 mm, 52% or less when the thickness is greater than 0.260 mm and less than 0.270 mm, 50% or less when the thickness is greater than 0.270 mm and less than 0.280 mm, 48% or less when the thickness is greater than 0.280 mm and less than 0.290 mm, and 47% or less when the thickness is greater than 0.290 mm and less than 0.300 mm.

[0036] In the can lid of the present invention, as described above, the Al-Fe-Mn compound and Mg of the aluminum alloy used ２ The reduced content of Si compounds provides high toughness and improves score strength, but by adjusting the score shape and remaining score thickness, it is possible to further improve score strength, which, as will be described later, makes it possible to effectively prevent the occurrence of microcracks in the organic coating on the back surface of the scored area (the inner surface of the can lid), derailment when the score breaks, and the so-called pop missile phenomenon when the can is initially opened.

[0037] [Rivet] As described below, the can lid used in the present invention has a rivet-forming section formed in a shell formed by press-forming an aluminum alloy sheet by rivet forming. In this case, it is preferable that the rivet-forming section is formed using a rivet-forming tool having a curvature radius of the working corner R of the rivet-forming tool greater than 0.20 mm, particularly in the range of 0.24 to 0.30 mm. That is, as shown in FIG. 3 , the rivet-forming section is formed by sandwiching and pressing the shell 2 between a male mold 60 and a rivet-forming tool 61, thereby forming an upwardly protruding rivet-forming section 30. Since the curvature radius of the working corner R of the rivet-forming tool 61 is within the above range, excessive processing is not applied to the base portion 31 of the rivet-forming section 30. Therefore, in the can lid of the present invention, even when the rivet-forming section is crimped during tab attachment, the occurrence of microcracks and the like in the organic coating is effectively prevented. In the can lid of the present invention, the tab can be formed from 5182 aluminum alloy, which has been conventionally used for tabs, or the same aluminum alloy as the can lid.

[0038] The tab is attached to the rivet forming portion by fitting the tab into the rivet forming portion and then crimping the rivet forming portion while pressing the top surface of the rivet forming portion. In the can lid of the present invention, as shown in FIG. 6, the thickness at the center of the rivet forming portion 30 (i.e., the thickness t ３ ) is the original plate thickness t ０It is preferable that the diameter be 30% or more of the inner diameter D1 of the rivet. This effectively prevents the occurrence of microcracks in the organic coating at the center of the rivet top surface. In addition, in the rivet forming portion 30 of a can lid to which a tab is attached by crimping the rivet forming portion, as shown in Figure 5, the central region of the top surface 31 that has been coined (the region indicated by diameter D1 in Figure 5) is thinner than its surroundings. It is preferable that the ratio of the diameter D1 of this central region to the inner diameter D2 of the side wall portion 32 of the rivet forming portion [(D1 / D2) x 100] be 40 to 95%. This effectively prevents the occurrence of microcracks in the organic coating at the rivet forming portion.

[0039] (Can End Manufacturing Method) The can end manufacturing method of the present invention is similar to the conventional can end manufacturing method, except that a specific score-forming blade described below is used. That is, although not limited to this, a metal plate such as an aluminum alloy plate is punched into a circle in a press-forming process and formed into a shell shape having the aforementioned seaming panel portion and chuck wall radius portion, and a compound is applied to the groove of the seam panel portion in a lining process. Next, a cylindrical rivet projection is formed, and a score is engraved from the outer surface of the can end in a score-forming process. Finally, a tab is fitted into the rivet projection, and the head of the rivet projection is crimped to attach the tab, thereby producing a can end that can be attached to a can body.

[0040] In the present invention, it is preferable that the score-forming blade used in the score-forming step in the above-described manufacturing method has a shape for forming scores as shown in Fig. 2. That is, as shown in Fig. 4, in a vertical cross section in the width direction of the score-forming blade 50, the blade width decreases toward the tip, and the blade is composed of opposing inclined side surfaces 51a, 51b and a tip portion 52 located at the lower end of the inclined side surfaces 51a, 51b, and the width w1 of the tip portion 52 is preferably 70% or less of the width W0 of an imaginary tip surface defined by imaginary extension lines La, Lb of the inclined side surfaces 51a, 51b and an imaginary extension line Lc passing through the center of the tip portion 52. Note that the width of the tip portion is the distance at the center of the tip portion excluding the curved surface connecting the inclined side surfaces and the tip portion. When a flat surface 52a is present at the center as shown in Fig. 4, this width is the width of the flat surface, but it also includes cases where the width is as close to zero as possible, in which the tip surface is substantially arc-shaped and continuous with the curved surface.

[0041] In the preferred embodiment shown in Figure 4, both sides of the leading edge 52 are continuous with the inclined side surfaces 51a, 51b via curved surfaces R. However, even if both sides of the leading edge are not connected to the inclined side surfaces, the remaining score thickness may be increased, or the same effect as when a curved surface is connected may be obtained depending on the angle formed by the inclined side surfaces and the leading edge. By using a score-forming blade having the above-mentioned characteristics when scoring a can lid, a score that reflects the characteristics of the score-forming blade as described above can be formed. This makes it possible to form a score with improved score strength as described above and to prevent microcracks from occurring on the inner surface of the score-forming area.

[0042] Furthermore, the imaginary edge width W0, defined by the imaginary extension lines La and Lb of the inclined side surfaces 51a and 51b of the score blade and the imaginary extension line Lc passing through the center of the tip 52 of the score blade, shown in Figure 4, is preferably in the range of 15 to 40 µm. This prevents microcracks from occurring in the organic coating (thermoplastic resin coating or paint film) on the inside surface of the score (the back side of the can lid), effectively prevents metal exposure on the inside surface of the can lid, and enables the formation of can lids with excellent corrosion resistance. If the imaginary edge width W0 is smaller than this range, stress corrosion cracking may occur in the can lid, although this depends on the material used. On the other hand, if the imaginary edge width W0 is larger than this range, microcracks may occur on the inside surface of the score compared to when it is within the above range.

[0043] (Aluminum Alloy Sheet) The aluminum alloy sheet for can ends of the present invention contains Si: 0.17 to 0.40 mass%, Fe: 0.23 to 0.50 mass%, Cu: 0.11 to 0.24 mass%, Mn: 0.5 to 1.0 mass%, and Mg: 0.6 to 2.7 mass%, and the aluminum alloy sheet has Al—Fe—Mn-based compounds and Mg on the RD-ND plane in the width direction central portion. ２ By reducing the total area ratio of Si compounds to 2.5% or less, it is possible to provide an alloy sheet having high strength and high toughness, as described above, and it is possible to form a can end having excellent pressure resistance and score strength. ２ The area ratio of the Si compound was measured in the same manner as in the case of the Al-Fe-Mn compound and the Mg compound in the can lid described above, except that the measurement point in the alloy plate was the RD-ND surface in the width direction center part of the alloy plate as shown by the diagonal lines in Figure 7. ２ Similarly, the area ratio of crystal grains having a circle-equivalent diameter of 2 μm or more in an aluminum alloy plate can be measured in the same manner as the measurement method for can lids described above, except that the measurement location in the alloy plate is the TD-ND plane, which is a plane perpendicular to the rolling direction (RD) in the central part in the width direction of the alloy plate.

[0044] In the aluminum alloy sheet for can ends of the present invention, it is preferable that the average value [(TS + YS) / 2] of the tensile strength (TS) and 0.2% proof stress (YS) is in the range of 330 to 360 MPa. This makes it possible to form ends having a sufficient pressure resistance value without significantly increasing the sheet thickness, and the sheet can also be used as a can end for a positively pressure can. The tensile strength (TS) and 0.2% proof stress (YS) are measured by the method specified in JIS Z 2241:2011.

[0045] (Method for manufacturing aluminum alloy sheet) The aluminum alloy constituting the can end is adjusted to have the above alloy composition by adding Mg to a recycled material made of UBC, and, if necessary, by adding primary aluminum metal, scrap material discharged in the aluminum alloy sheet manufacturing process and the aluminum can manufacturing process, and additive metals.

[0046] The aluminum alloy sheet of the present disclosure can be produced, for example, as follows. First, an aluminum alloy having the composition of the aluminum alloy sheet of the present disclosure is subjected to a semi-continuous casting method (i.e., DC casting) according to a conventional method to produce an ingot. Next, the four sides of the ingot, excluding the front and rear ends, are chamfered. Thereafter, the ingot is placed in a soaking furnace and subjected to a homogenization treatment. The temperature in the homogenization treatment is preferably, for example, 400°C or higher and 620°C or lower. The time period for the homogenization treatment is preferably, for example, 1 hour or higher and 20 hours or lower. When the temperature in the homogenization treatment is 400°C or higher, segregation of the ingot structure is easily eliminated. Furthermore, when the temperature in the homogenization treatment is 470°C or higher, Mg ２ The Si compound is redissolved in the solid solution, and the strength and toughness of the alloy plate can be improved. ２ When the temperature is higher than the solid solution temperature of Si, Mg ２ The re-solidification of the Si compound is promoted, and the strength and toughness of the alloy sheet can be further improved. On the other hand, when the temperature in the homogenization treatment is 620°C or less, more preferably the solidus temperature or less, local melting of the aluminum alloy is unlikely to occur. ２The solid solution temperature and solidus temperature of Si can be determined by calculating the equilibrium phase diagram of the aluminum alloy using "JMatPro". When the homogenization treatment time is 1 hour or more, the temperature of the entire slab becomes uniform, and the segregation of the ingot structure is easily eliminated. ２ The longer the homogenization time, the easier it is to redissolve the Si compound. ２ The Si compound can be redissolved. However, if the homogenization treatment time exceeds 20 hours, the effect of the homogenization treatment becomes saturated.

[0047] After the homogenization treatment, the ingot is subjected to hot rolling. The hot rolling process includes a rough rolling process and a finish rolling process. In the rough rolling process, the ingot is processed into a plate material with a thickness of about several tens of mm by reverse rolling. In the finish rolling process, the thickness of the plate material is reduced to about several mm by, for example, tandem rolling, and the plate material is wound into a coil to form a hot rolled coil. If the total reduction rate of the finish rolling is high, a recrystallized structure is formed after coiling, which can increase the concentration of isotropic Cube orientation. If the coiling temperature of the finish rolling is high, a recrystallized structure is formed after coiling, which can increase the concentration of Cube orientation.

[0048] Following hot rolling, the plate material is cold-rolled. In cold rolling, the hot-rolled coil is rolled to the product thickness. Cold rolling may be either single rolling or tandem rolling. Cold rolling by single rolling is preferably performed in two or more passes. Furthermore, intermediate heat treatment of the coil during cold rolling is performed to re-dissolve Mg and other elements, thereby increasing the strength of the material and recrystallizing it, thereby reducing the final cold reduction rate and obtaining an alloy plate with reduced anisotropy of the material. This suppresses cracking along the rolling direction during forming. For example, intermediate heat treatment (i.e., annealing) at a target solid temperature of 440°C or higher is performed using a continuous annealing furnace (CAL), followed by forced cooling by air cooling or the like, which can effectively increase the strength of the alloy plate. Furthermore, by setting the final cold rolling temperature in passes other than the final pass to 90°C or higher, Si, Cu, and Mg precipitate finely and age harden, thereby increasing the strength of the alloy plate. Furthermore, by setting the rising temperature to 130°C or higher, the strength of the alloy plate can be further increased.

[0049] If no intermediate heat treatment is performed during cold rolling, the cold rolling rate is preferably 80% or more. When the cold rolling rate is 80% or more, the strength of the alloy sheet can be increased. Furthermore, the lower the cold rolling rate, the smaller the anisotropy of the material, so the cold rolling rate is preferably 92% or less. If intermediate heat treatment is performed during cold rolling, the cold rolling rate after intermediate heat treatment is preferably 50% or more. By resolving Mg and the like through intermediate heat treatment, the strength of the alloy sheet can be increased even with a low cold rolling rate. Furthermore, the lower the cold rolling rate, the smaller the anisotropy of the material, so that thickness reduction and cracking along the rolling direction can be suppressed during material forming, so the cold rolling rate is preferably 80% or less. The cold rolling rate R (%) is the thickness t after hot rolling or after intermediate heat treatment. ａ (mm), product thickness after cold rolling t ０ (mm), it can be calculated by the following formula (1): R = (t ａ -t ０ ) / t ａ ×100...(1) Product board thickness t ０ The thickness of the can lid material is preferably in the range of 0.19 to 0.30 mm, and the thickness of the tab material is preferably in the range of 0.24 to 0.35 mm.

[0050] Coils that have been cold-rolled to the product thickness are pre-coated on a coating line, etc. The surface of the cold-rolled coil is degreased, cleaned, and chemically treated, and then painted, and then painted and baked to form a thermoplastic resin coating or an organic coating such as a paint film.

[0051] Chemical solutions such as chromate-based and zirconium-based solutions are used for chemical conversion treatment, but are not limited to these. Epoxy-based and polyester-based paints are used for coatings. These can be selected according to the application. The coating baking process involves heating the coil to a peak metal temperature (PMT) of 220°C or higher for approximately 30 seconds.

[0052] Examples of thermoplastic resin coatings include olefin-based resin films such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, and ionomer; polyester films such as polyethylene terephthalate; polyamide films such as nylon 6, nylon 6,6, nylon 11, and nylon 12; polyvinyl chloride films; and polyvinylidene chloride films. These thermoplastic resin films may be unstretched or biaxially stretched. Examples of film-forming coating materials include modified epoxy coating materials such as phenol-epoxy and amino-epoxy; vinyl chloride-vinyl acetate copolymers; saponified vinyl chloride-vinyl acetate copolymers; vinyl chloride-vinyl acetate-maleic anhydride copolymers; epoxy-modified, epoxyamino-modified, and epoxyphenol-modified vinyl coating materials or modified vinyl coating materials; acrylic coating materials; and synthetic rubber-based coating materials such as styrene-butadiene copolymers.

[0053] In this case, the lower the PMT, the more the recovery of the material is suppressed, and the higher the strength of the alloy plate can be maintained. Therefore, the baking temperature of the paint (i.e., PMT) is preferably 270°C or less. In addition, the cold rolling rate can be reduced to improve toughness, and the resulting decrease in strength can be compensated for by lowering the PMT.

[0054] The following describes the details of tests conducted to verify the effects of the present disclosure and their evaluation. (Experimental Examples S1 to S22) <Forming of Aluminum Ends> Using aluminum alloy sheets Nos. 1 to 8 with the compositions shown in Table 2, the metal sheets were punched into a circular shape in a press-forming process, similar to conventional can ends, and formed into 204-diameter shells with seaming panels and chuck wall radii. Compound was then applied to the grooves in the seaming panels in a lining process. The resulting 204-diameter shells were then subjected to rivet forming and score forming. For rivet forming, the shell was sandwiched between a male mold 60 and a rivet-forming tool 61 (see Figure 3) and pressed to form an upwardly protruding rivet-forming portion 30. The rivet-forming tool 61 had a curvature radius (R in Figure 3) of 0.20 mm or 0.28 mm at the active corner. For score forming, scores were engraved on the outer surface of the shell. As shown in Figure 4, in a vertical cross section in the width direction of the score forming blade 50, the blade width decreases toward the tip. The blade comprises opposing inclined side surfaces 51a, 51b and a tip portion 52 located at the lower end of the inclined side surfaces 51a, 51b. The width w1 of the tip portion 52 is determined by the width W0 of the imaginary tip surface defined by imaginary extension lines La, Lb of the inclined side surfaces 51a, 51b and an imaginary extension line Lc passing through the center of the tip portion 52. The ratios of w1 / W0 to the width W0 are 40%, 65%, and 80%. The tab is fitted to the rivet projection, and then attached to the can body by crimping the head of the rivet projection. The tab was made of 5182 alloy, the same as for conventional can lids. As is clear from Table 3, Alloy Plate No. 1 is a conventional material with a low scrap content of 3104 aluminum alloy (30% by mass), i.e., a low recycled material usage rate, and corresponds to a reference example.

[0055] [Presence or absence of shell molding cracks] For the can lids obtained as described above, the surface of the chuck wall radius portion was observed with a digital microscope (Keyence VHX-8000), and the shell molding defects were evaluated by marking those with cracks as "x" and those without cracks as "o". The results are shown in Table 2.

[0056] [Measurement of Pressure Resistance Strength] The can lid obtained as described above was attached to the opening of a seamless can, and the pressure resistance was measured using a water pressure buckling tester WBT-1600 (manufactured by Containers Laboratory). The pressure rise rate was about 0.33 kgf / cm per second. ２ The peak value when the lid was inverted was confirmed. 24 plates were measured, and an average value exceeding 580 kPa was marked with "O", and an average value below that or a value that cracked when the pressure was increased was marked with "X" to evaluate the pressure resistance. The results are shown in Table 2.

[0057] [Inverted Drop Test] The can lid obtained above was attached to the opening of a seamless can with a nominal diameter of 211 mm (outer diameter of the can body: 66 mm) for filling 350 ml of beer, and 350 ml of beer chilled to 5°C was filled. The can was dropped with the lid side facing downwards from a height of 120 cm at a can temperature of 37°C and an internal pressure of 370 kPa, and the beer leakage from the score was checked. 24 cans were dropped, and those that did not leak, i.e., 0%, were rated as "A," those that leaked 1% to 50% were rated as "B," and those that leaked 51% or more were rated as "C."

[0058] [Presence or absence of rivet forming cracks] For 100 can lids obtained as described above, the base of the rivet was observed from the inside surface of the lid using a digital microscope (VHX-8000 manufactured by Keyence Corporation). Can lids with 0% metal surface cracking were rated as "A", can lids with 1% to 50% metal surface cracking were rated as "B", and can lids with 51% or more metal surface cracking were rated as "C".

[0059]

[0060] <Production of Aluminum Alloy Sheets> As examples and comparative examples, aluminum alloy sheets 1-8 shown in Table 3 were produced. Specific production procedures are described below.

[0061] An ingot containing the components 1 to 8 (% by mass) shown in Table 3, with the remainder being aluminum and unavoidable impurities, was produced by semi-continuous casting. The ingot contained 0.10% by mass or less of Ti, 0.25% by mass or less of Zn, 0.10% by mass or less of Cr, and 0.15% by mass or less of unavoidable impurities.

[0062] Next, six faces of the ingot were chamfered, and the ingot was placed in a furnace and subjected to homogenization treatment. ２ After homogenization treatment for 4 hours or more at a temperature below the solid solution temperature and solidus temperature of Si, the ingot was taken out of the furnace and immediately hot-rolled to obtain a rolled sheet. ２ After homogenization treatment at a temperature above the solid solution temperature of Si and below the solidus temperature for 4 hours or more, the ingot was taken out of the furnace and immediately hot rolling was started to produce a rolled sheet.

[0063] For Nos. 1 and 6-8 shown in Table 3, the rolled sheet after hot rolling was subjected to cold rolling, and intermediate heat treatment (i.e., annealing) was performed using a continuous annealing furnace (CAL) during the cold rolling at a target substantial temperature of 440°C or higher. Thereafter, the rolled sheet after the intermediate heat treatment was subjected to cold rolling at a cold reduction ratio of 50% or more and 80% or less.

[0064] For 2 and 4 shown in Table 3, the rolled sheets after hot rolling were subjected to intermediate heat treatment (i.e., annealing) at a target substantial temperature of 440°C or more using a continuous annealing furnace (CAL). The rolled sheets after the intermediate heat treatment were subjected to cold rolling at a cold reduction ratio of 80% or more and 92% or less.

[0065] For Nos. 3 and 5 shown in Table 3, the rolled sheets after hot rolling were subjected to cold rolling so that the cold rolling ratio was 80% or more and 92% or less.

[0066] After cold rolling, a paint baking treatment was carried out for 30 seconds at a paint baking temperature (PMT) of 220°C or more and 270°C or less. By the above steps, aluminum alloy sheets 1-8 shown in Table 3 were obtained. For these aluminum alloy sheets, a tensile test was carried out in accordance with JIS-Z-2241:2011 to measure 0.2% proof stress (YS) and tensile strength (TS). The tensile strength (TS), 0.2% proof stress (YS), and the average value [(TS + YS) / 2] of the tensile strength (TS) and 0.2% proof stress (YS) are shown in Table 3.

[0067] In the aluminum alloy plate No. 1-8 shown in Table 3, the area was 0.3 μm by the measurement method described in the embodiment. ２ The above Al-Fe-Mn compounds and Mg ２The ratio (area ratio) of the total area of ​​the Si compound in the cross section was calculated. The measurement results are shown in Table 3.

[0068] In the aluminum alloy sheets 1-8 shown in Table 3, the area ratio of crystal grains with a circle equivalent diameter of 2 μm or more on the TD-ND plane was measured by the measurement method described in the embodiment.

[0069] (Scrap Blending Ratio) It was determined whether the possible blending ratio of 3104 aluminum alloy scrap was 50 mass% or more for the compositions of aluminum alloy plates 1-8 shown in Table 3. The possible blending ratio of 3104 aluminum alloy was determined based on Table 1.

[0070] For example, when the blending ratio of 3104 aluminum alloy is 50 mass%, it contains at least 0.17 mass% Si, 0.23 mass% Fe, 0.11 mass% Cu, 0.5 mass% Mn, and 0.6 mass% Mg. Therefore, when the ratio of each component of the aluminum alloy plate is equal to or greater than the above-mentioned values ​​of Si, Fe, Cu, Mn, and Mg, the possible blending ratio of 3104 aluminum alloy plate scrap is 50 mass% or more.

[0071] The aluminum alloy plate No. 1 shown in Table 3 has a low recyclability due to small amounts of Si, Fe, Cu, Mn, and Mg. In contrast, the aluminum alloy plates Nos. 2 to 8 shown in Table 3 obtained by the manufacturing method of the present disclosure all have a 3104 blendable ratio exceeding 50 mass%.

[0072] The aluminum alloy plate No. 2 shown in Table 3 contains Al-Fe-Mn compounds and Mg ２ In contrast, the aluminum alloy sheets 3-8 shown in Table 3 obtained by the manufacturing method of the present disclosure all have a high area ratio of Al—Fe—Mn compounds and Mg ２ The area ratio of the Si compound is less than 2.5% and the moldability is excellent, so that it can be molded into a shell shape.

[0073] The aluminum alloy plate No. 3 shown in Table 3 has a 3104 compounding ratio exceeding 50 mass % and contains Al-Fe-Mn compounds and Mg ２Although the area ratio of the Si compound is below 2.5%, which allows molding into a shell shape, the Mg content is low compared to Si: 0.26 to 0.36 mass%, Fe: 0.36 to 0.50 mass%, Cu: 0.18 to 0.23 mass%, Mn: 0.8 to 1.0 mass%, and Mg: 2.3 to 2.7 mass%, so the strength is insufficient and the pressure resistance required for the lid cannot be met. In contrast, the aluminum alloy plate 4-8 shown in Table 3 obtained by the manufacturing method of the present disclosure satisfies the above-mentioned component ranges and can meet the pressure resistance performance.

[0074] In order to manufacture a lid that can withstand higher internal pressure, it is necessary to reduce the anisotropy of the material by intermediate heat treatment, while increasing the strength of the material by resolving Mg, etc. In the aluminum alloy sheets 4 and 5 shown in Table 3, in the rolling direction-sheet thickness direction plane, the area ratio of crystal grains with a circle equivalent diameter of 2 μm or more is less than 70% at the center of the sheet thickness on the plane perpendicular to the rolling direction, i.e., the anisotropy of the material is large.

[0075] In Example 4 shown in Table 3, cracks occurred when the internal pressure increased, as shown in Experimental Examples S4-S6 in Table 2, and this was due to cracks occurring during forming or localized thickness reduction. In Example 5 shown in Table 3, intermediate heat treatment was not performed, so the strength was low. If the cold rolling rate is increased to obtain a material with higher strength, the anisotropy of the material increases, and cracks may occur when the internal pressure increases due to cracks occurring during forming or localized thickness reduction, as in Examples S4-S6 in Table 2, for example.

[0076] The anisotropy of the material also affects score molding. Efforts have been made to change the score shape to prevent breakage in the score during lid molding, and the effectiveness of this approach can be confirmed by comparing experimental examples S8-S10 with experimental examples S11-S16. However, in experimental examples S4 and S5, the material has a high anisotropy, so it is difficult to prevent breakage in the score simply by changing the score shape.

[0077] Similarly, the anisotropy of the material also affects rivet forming. The shape of the rivet forming die has been modified to prevent rivet breakage during cap forming, and this effect can be seen, for example, in a comparison of S11-S16 and S17-S22. However, in experimental examples S5 and S6, the material has a high anisotropy, making it difficult to prevent rivet breakage simply by modifying the shape of the rivet forming die.

[0078] In contrast, the aluminum alloy sheets 6-8 shown in Table 3 obtained by the manufacturing method of the present disclosure all have an area ratio of crystal grains with an equivalent circle diameter of 2 μm or more exceeding 70%, i.e., the anisotropy of the material is small. In addition, since the average value [(TS + YS) / 2] of the tensile strength (TS) and 0.2% proof stress (YS) is 330 to 360 MPa, it is possible to obtain a lid material that can withstand higher internal pressure while suppressing fracture of the score and rivet portions.

[0079]

[0080] Even when the can lid of the present invention uses a recycled aluminum UBC material, the amount of alloying elements is adjusted, and the amount of Al-Fe-Mn compounds and Mg ２ Since the content of Si compounds is reduced, the can closure of the present invention has high pressure resistance and high toughness, and cracks do not occur even when pressure is increased or buckling occurs. The high score strength effectively prevents unintended breakage or derailment of the score, as well as the occurrence of microcracks in the organic coating. Furthermore, the can closure of the present invention is suitable for use in positive pressure cans. Furthermore, despite using a smaller amount of virgin aluminum than conventional can closures, which use a larger amount, the can closure of the present invention is still able to fully satisfy the properties required for can closures for food and beverages. Therefore, it is possible to reduce carbon dioxide emissions during the manufacturing process, and the can closure of the present invention is suitable for applications requiring reduced carbon dioxide emissions.

[0081] REFERENCE SIGNS LIST 1 can lid, 2 shell, 3 rivet, 4 tab, 21 center panel, 22 chuck wall radius, 23 chuck wall, 24 seaming panel, 25 score, 26 score inclined surface, 27 score bottom surface, 30 rivet forming portion, 41 tab body, 42 tab nose portion, 43 grip portion, 44 fixing portion, 46 curl portion.

Claims

1. The aluminum alloy contains 0.17 to 0.40% by mass of Si, 0.23 to 0.50% by mass of Fe, 0.11 to 0.24% by mass of Cu, 0.5 to 1.0% by mass of Mn, and 0.6 to 2.7% by mass of Mg, and the aluminum alloy contains Al-Fe-Mn compounds and Mg on the rolling direction-thickness direction surface of the panel. ２ A can lid characterized in that the total area ratio of Si compounds is 2.5% or less, and the area ratio of crystal grains having a circle-equivalent diameter of 2 μm or more is 70% or more in the center of the plate thickness on a surface perpendicular to the rolling direction of the panel portion.

2. Made of an aluminum alloy containing Si: 0.26 to 0.36 mass%, Fe: 0.36 to 0.50 mass%, Cu: 0.18 to 0.23 mass%, Mn: 0.8 to 1.0 mass%, and Mg: 2.3 to 2.7 mass%, and the aluminum alloy contains Al-Fe-Mn compounds and Mg on the rolling direction-thickness direction surface of the panel part. ２ A can lid characterized in that the total area ratio of Si compounds is 2.5% or less, and the area ratio of crystal grains having a circle-equivalent diameter of 2 μm or more is 70% or more in the center of the plate thickness on a surface perpendicular to the rolling direction of the panel portion.

3. A can lid according to claim 1 or claim 2, wherein the panel portion is formed with a breakable score that defines the intended opening portion, and a tab is attached.

4. A can lid according to claim 3, which has a pressure resistance of 580 kPa or more.

5. A can lid as described in claim 3, wherein the breakable score has opposing inclined surfaces and a bottom surface in a vertical cross section in the width direction of the score, the score width decreasing downward, and a flat portion is formed in the center of the bottom surface, and the width of the flat portion has at least a portion that is 70% or less of the width of an imaginary bottom surface defined by an imaginary extension line of the inclined surfaces and an imaginary extension line passing through the center of the bottom surface.

6. A can lid according to claim 3, wherein the panel portion is formed with a rivet forming portion for attaching the tab, and the rivet forming portion is formed by a rivet forming tool having an operating corner portion with a curvature radius of more than 0.20 mm.

7. An aluminum alloy plate containing 0.17 to 0.40 mass% Si, 0.23 to 0.50 mass% Fe, 0.11 to 0.24 mass% Cu, 0.5 to 1.0 mass% Mn, and 0.6 to 2.7 mass% Mg, wherein the aluminum alloy plate has an Al-Fe-Mn compound and Mg in the rolling direction-thickness direction surface of the width direction central portion. ２ An aluminum alloy sheet for can lids, characterized in that the total area ratio of Si compounds is 2.5% or less.

8. The aluminum alloy sheet for can ends according to claim 7, which consists of an aluminum alloy containing 0.26 to 0.36 mass% Si, 0.36 to 0.50 mass% Fe, 0.18 to 0.23 mass% Cu, 0.8 to 1.0 mass% Mn, and 2.3 to 2.7 mass% Mg, wherein at the center of the sheet thickness of the plane perpendicular to the rolling direction in the center part of the width direction of the aluminum alloy sheet, crystal grains having an equivalent circle diameter of 2 μm or more account for 70% or more, and the average values of tensile strength and 0.2% proof stress are 330 to 360 MPa.

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