Aluminum alloy plate for ring-pull type cap and its manufacturing method

Abstract

To provide an aluminum alloy sheet for ring pull caps that has excellent blow-off resistance, easy openability, recyclability and long-term creep resistance even when the sheet is reduced in thickness, and a method for producing such an aluminum alloy sheet.SOLUTION: This aluminum alloy sheet is a rolled sheet having an alloy composition that contains, on a mass basis, Mn: 0.50% or more and 1.10% or less, Mg: 2.85% or more and less than 3.48%, Fe: 0.20% or more and 0.40% or less, Si: 0.05% or more and 0.20% or less, Cu: 0.01% or more and 0.15% or less, while optionally containing up to 0.10% of Ti on a mass basis, with the balance being aluminum and unavoidable impurities. For this aluminum alloy sheet, the tensile strength in the rolled direction after a heat treatment at 190°C for 10 minutes is 280 MPa or more to 320 MPa or less; the difference between the tensile strength and the proof stress is 35 MPa or more; the conductivity is 25% IACS or more to 34% IACS or less; and the creep strain rate after 60 to 80 hours, inclusive, from the start of a creep test at a material temperature of 80°C with a load to a test piece of 100 MPa is 3.0×10-4%h-1 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aluminum alloy plate suitable for use in the manufacture of a ring-pull type cap, particularly a maxi cap, and a method for manufacturing the same. TECHNICAL FIELD The present invention relates to an aluminum alloy plate suitable for use in the manufacture of a ring-pull type cap, particularly a maxi cap, and a method for manufacturing the same. [Background technology]

[0002] Ring-pull caps (especially Maxim Caps) are opened by pulling the ring tab and tearing the cap along the score (score, groove) on the top surface from the bottom (side) of the cap. Ring-pull caps are easy to open, and have high airtightness and TE properties (tamper resistance), so they are widely used for beverage applications.

[0003] In recent years, there has been a demand for ring-pull caps to be thinner and lighter. Currently, the mainstream plate thickness is 0.2 mm to 0.3 mm, and there is a demand for it to be less than 0.2 mm. However, it is not possible to simply make the cap thinner. For example, if the thickness of the score portion (the thickness of the aluminum alloy plate directly below the score) is too small, there is a risk of the sealing performance being reduced. In addition, it may become difficult to tear the cap along the score, and the ease of opening may be reduced.

[0004] Ring-pull caps are also required to be resistant to blow-off. The phenomenon known as "blow-off" occurs when the cap comes off (flies off) with great force from the mouth of a container, before the bottom of the cap is torn off and the pressure inside the container is released when the cap is first opened. This occurs because the bottom of the cap does not have sufficient force to hold the mouth of the container. There is also concern that making the cap thinner will reduce blow-off resistance.

[0005] In addition, recyclability is also required to reduce the environmental burden. From the viewpoint of efficient recycling processes, it is desirable to be able to recycle caps together with aluminum bottles, beverage cans, etc. However, alloys with different compositions are used depending on the application, which is an obstacle to efficient recycling.

[0006] According to Patent Document 1, by limiting the content of Mg, Mn, Fe, Si, and Cu, the range of earing ratio, and the grain size in the composition of the aluminum alloy, and further limiting the tensile strength after a predetermined heat treatment, an aluminum alloy sheet for a ring-pull type cap that is excellent in blow-off resistance, easy opening, and recyclability even when thinned can be provided. The composition of the aluminum alloy contains, by mass, 2.2 to 2.8% Mg, 0.20 to 0.50% Mn, 0.20 to 0.40% Fe, 0.05 to 0.20% Si, and 0.01 to 0.15% Cu, with the balance being aluminum and unavoidable impurities. The composition of the aluminum alloy may further contain, by mass, 0.01% to 0.10% Ti. The entire disclosure of Patent Document 1 is incorporated herein by reference. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2011-132592 A (Patent No. 5596337 A) Summary of the Invention [Problem to be solved by the invention]

[0008] According to the study by the inventors, the aluminum alloy described in Patent Document 1 has high blow-off resistance, but further improvement is required. For example, when used in a container for carbonated drinks, the internal pressure of the container is high, so the cap is required to have high blow-off resistance. If a container for carbonated drinks is stored for a long period of time at a high temperature, for example, above 40°C, the cap is subjected to high internal pressure for a long period of time, and the shape of the cap may change over time. In other words, if stored for a long period of time at high temperatures, the blow-off resistance may decrease. In order to suppress this decrease in blow-off resistance, it is required to improve the property of not deforming even when stress is applied for a long period of time at high temperatures (long-term creep resistance).

[0009] Therefore, an object of the present invention is to provide an aluminum alloy plate for a ring-pull type cap, which has excellent blow-off resistance, easy opening property, recyclability and long-term creep resistance even when made thin, and a manufacturing method for such an aluminum alloy plate. [Means for solving the problem]

[0010] According to an embodiment of the present invention, there are provided solutions as described in the following items. [Item 1] A rolled sheet having an alloy composition containing, by mass, Mn: 0.50% or more and 1.10% or less, Mg: 2.85% or more and less than 3.48%, Fe: 0.20% or more and 0.40% or less, Si: 0.05% or more and 0.20% or less, Cu: 0.01% or more and 0.15% or less, Ti as an optional element with an upper limit of 0.10% by mass, and the balance being aluminum and unavoidable impurities, Tensile strength in the rolling direction after heat treatment at 190℃ for 10 minutes is 280MP a The creep strain rate is 3.0×10 or more for 60 hours or more and 80 hours or less from the start of the test in a creep test under the following conditions: the difference between the tensile strength and the yield strength is 35 MPa or more, the electrical conductivity is 25% IACS or more and 34% IACS or less, and the material temperature is 80°C and the load on the test piece is 100 MPa. -4 %h -1 The aluminum alloy plate for the ring-pull type cap is shown below.

[0011] The alloy composition may contain, on a mass basis, Mn: more than 0.50% and 1.06% or less, and Mg: 2.90% or more and 3.09% or less.

[0012] The creep strain rate is 2.6×10 -4 %h -1 It may be the following.

[0013] [Item 2] 2. The aluminum alloy sheet according to item 1, wherein the alloy composition contains, on a mass basis, 0.01% or more of Ti.

[0014] [Item 3] 3. The aluminum alloy sheet according to item 1 or 2, wherein the Cr content of the inevitable impurities is less than 0.01% by mass.

[0015] [Item 4] A method for producing an aluminum alloy plate according to any one of items 1 to 3, A step A of heating an ingot made of an aluminum alloy having the alloy composition at a temperature rise rate of 30°C / hour or more in a temperature range of at least 400°C to 460°C; After the step A, a step B of subjecting the ingot to a homogenization treatment by holding the ingot at a first temperature of 460° C. or more and 540° C. or less for 2 hours or more and 24 hours or less; After the step B, a step C of performing rough hot rolling at a rolling rate of 5% to 35% per pass at a rolling temperature of 460° C. to 540° C. inclusive, and completing the rolling within 15 minutes; After the step C, a step D of performing hot finish rolling so that the end temperature is a third temperature of 300 ° C. or more and 350 ° C. or less to obtain a hot rolled sheet; A step E of cooling the hot-rolled plate obtained in the step D at a cooling rate of 20 ° C. / hour or less; After the step E, a step F of cold rolling the hot-rolled sheet at a rolling reduction of 70% or more and 93% or less without intermediate annealing; A step G of performing a stabilization heat treatment at a fourth temperature of 180° C. or more and 240° C. or less for 1 hour or more and 5 hours or less after the step F; The manufacturing method includes the steps of:

[0016] [Item 5] 5. The method according to item 4, further comprising, before step E, holding the hot-rolled sheet obtained in step D at a temperature of 300° C. or higher for 1 hour or more. Effect of the Invention

[0017] According to an embodiment of the present invention, there is provided an aluminum alloy sheet for a ring-pull type cap, which has excellent blow-off resistance, easy opening property, recyclability, and long-term creep resistance even when thinned, and a method for manufacturing such an aluminum alloy sheet. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is an explanatory diagram of a test specimen used in a creep test, showing a planar shape of the test specimen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an aluminum alloy plate for a ring-pull type cap and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. The aluminum alloy plate for a ring-pull type cap and a manufacturing method thereof according to an embodiment of the present invention are not limited to the following examples.

[0020] The present inventors have investigated alloy compositions capable of improving long-term creep resistance without impairing the blow-off resistance, easy opening property, and recyclability of the aluminum alloy plate described in Patent Document 1. As a result, as will be shown in some of the experimental examples (Examples and Comparative Examples) later, it has been found that by adjusting the contents of Mn (manganese) and Mg (magnesium), it is possible to improve long-term creep resistance without impairing other properties.

[0021] The aluminum alloy plate according to the embodiment of the present invention has an alloy composition including, by mass, Mn: 0.50% or more and 1.10% or less, Mg: 2.85% or more and less than 3.48%, Fe: 0.20% or more and 0.40% or less, Si: 0.05% or more and 0.20% or less, Cu: 0.01% or more and 0.15% or less, Ti as an optional element with an upper limit of 0.10% by mass, and the balance being aluminum and inevitable impurities. The alloy composition may include, by mass, Mn: more than 0.50% and 1.06% or less, and Mg: 2.90% or more and 3.09% or less. The alloy composition may also include, by mass, Ti: 0.01% or more. The Cr contained in the inevitable impurities is preferably less than 0.01% by mass.

[0022] The aluminum alloy sheet according to an embodiment of the present invention is a rolled sheet having the above-mentioned alloy composition, and has a tensile strength of 280 MP in the rolling direction after heat treatment at 190° C. for 10 minutes. a The creep strain rate is 3.0×10 or more for 60 hours or more and 80 hours or less from the start of the test in a creep test under the following conditions: the difference between the tensile strength and the yield strength is 35 MPa or more, the electrical conductivity is 25% IACS or more and 34% IACS or less, and the material temperature is 80°C and the load on the test piece is 100 MPa. -4 %h -1 The following is the result.

[0023] Although it is difficult to specify the relationship between the excellent long-term creep resistance of the aluminum alloy plate according to the embodiment of the present invention and the structure of the alloy microstructure, the aluminum alloy plate according to the embodiment of the present invention can be manufactured at least by the following method.

[0024] The manufacturing method according to an embodiment of the present invention includes a step A of heating an ingot made of an aluminum alloy having the above alloy composition at a temperature rise rate of 30°C / hour or more in a temperature range of at least 400°C to 460°C; a step B of homogenizing the ingot by holding the ingot at a first temperature of 460°C to 540°C for 2 hours to 24 hours after the step A; and a step B of rolling the ingot at a second temperature of 460°C to 540°C with a rolling reduction ratio of 5% to 35% per pass, and completing the rolling within 15 minutes. The method includes a step C of performing rough hot rolling so that the hot rolled sheet is heated to a temperature of 300° C. or more and 350° C. or less after the step C, a step D of performing hot finish rolling so that the end temperature is a third temperature of 300° C. or more and 350° C. or less to obtain a hot rolled sheet, a step E of cooling the hot rolled sheet obtained in the step D at a cooling rate of 20° C. / hour or less, a step F of cold rolling the hot rolled sheet at a rolling reduction rate of 70% or more and 93% or less after the step E without intermediate annealing, and a step G of performing stabilization heat treatment at a fourth temperature of 180° C. or more and 240° C. or less for 1 hour to 5 hours after the step F. Before the step E, the method may further include a step of holding the hot rolled sheet obtained in the step D at a temperature of 300° C. or more for 1 hour or more.

[0025] The alloy composition of the aluminum alloy plate according to the embodiment of the present invention will be described.

[0026] Mn exerts an effect of improving creep resistance, and the inventors have found that an aluminum alloy sheet containing 0.50 mass% or more of Mn has excellent long-term creep resistance. In this case, the Mn content is preferably 1.10 mass% or less. If the Mn content exceeds 1.10 mass%, it forms a huge intermetallic compound with elements such as Fe (iron) during casting, which may become the starting point of cracks during molding. The Mn content is more preferably more than 0.50 mass% and 1.06% or less, and from the viewpoint of strength, it is more preferably 0.70 mass% or more.

[0027] Mg exerts the effect of improving strength (pressure resistance, blow-off resistance) and ease of opening while maintaining formability. In the aluminum alloy plate containing Mn at the above content, the Mg content is preferably 2.85 mass% or more and less than 3.48 mass%. If the Mg content is 3.48 mass% or more, aging softening at room temperature increases, and there is a risk of the blow-off resistance at the time of opening after long-term storage decreasing. From the viewpoint of increasing strength and suppressing aging softening, the Mg content is preferably 2.90 mass% or more and 3.09 mass% or less.

[0028] Fe (iron) forms intermetallic compounds with Mn and the like, and has the effect of making recrystallized grains fine after hot rolling, thereby improving the ease of opening. The Fe content is preferably 0.20% by mass or more and 0.40% by mass or less. If the Fe content is less than 0.20% by mass, it becomes difficult to obtain the above-mentioned effects. In addition, it is necessary to increase the purity of the ingot, and recycled materials cannot be used as they are. If the Fe content exceeds 0.40% by mass, giant intermetallic compounds are generated, which may become the starting point of cracks during molding. The Fe content is preferably 0.20% by mass or more and 0.35% by mass or less.

[0029] Si (silicon) is one of the impurity elements. In order to promote the use of recycled materials, the Si content is preferably 0.10 mass% or more. On the other hand, if the Si content exceeds 0.20 mass%, it may form an intermetallic compound with Mg or Mn and Fe, reducing the amount of solid solution of Mg or Mn and reducing the above-mentioned effects of Mg or Mn. Therefore, the Si content is preferably 0.20 mass% or less.

[0030] Cu (copper) contributes to improving the strength of the cap. The Cu content is preferably 0.01% by mass or more and 0.15% by mass or less. If the Cu content is less than 0.01% by mass, the effect of Cu may not be exerted, and if the Cu content exceeds 0.15% by mass, the strength may become too high, resulting in a decrease in formability.

[0031] Furthermore, Ti (titanium) may be contained. Ti is an optional element and may not be contained, but may be contained up to an upper limit of 0.10 mass%. Ti has the effect of reducing microsegregation of aluminum alloy ingots during production and finely dispersing intermetallic compounds, thereby making crystal grains finer and making the structure uniform. In order to obtain the effect of Ti, the Ti content is preferably 0.01 mass% or more. However, if the Ti content exceeds 0.10 mass%, it may generate a giant intermetallic compound (Al-Ti compound) with Al (aluminum), so the Ti content is preferably 0.10 mass% or less.

[0032] The alloy composition of the aluminum alloy according to the embodiment of the present invention is composed of Al and inevitable impurities other than the above elements. The inevitable impurities are inevitably mixed in when preparing the target aluminum alloy, and their content is controlled so that they are present at a known impurity content. For example, Zn (zinc) and Cr (chromium) may be contained as inevitable impurities, and as long as each is 0.10 mass% or less, the above-mentioned characteristics are not impaired and the inclusion of these components is permitted, and within that range, recyclability is not impaired. The contents of Zn and Cr are preferably less than 0.01 mass% each. In addition, the total content of inevitable impurities (elements other than Al, Mn, Mg, Fe, Si, Cu, and Ti) is preferably 0.10 mass% or less.

[0033] The aluminum alloy sheet according to the embodiment of the present invention has a tensile strength in the rolling direction of 280 MP after heat treatment at 190°C for 10 minutes. a The tensile strength is 320 MPa or more, and the difference between the tensile strength and the yield strength is 35 MPa or more. If the tensile strength is less than 280 MPa, the pressure resistance may be insufficient. If the tensile strength is more than 320 MPa, wrinkles may occur during drawing, and sufficient sealing may not be obtained, and the ease of opening may decrease.

[0034] Furthermore, in a creep test under the conditions of a material temperature of 80° C. and a load of 100 MPa on a test piece, the aluminum alloy plate according to the embodiment of the present invention has a creep strain rate of 3.0×10-4 for 60 hours or more and 80 hours or less from the start of the test. -4 %h -1 According to the inventor's experiments, in the creep test under the above conditions, the creep strain rate is 3.0×10 -4 %h -1 If the creep strain rate is less than 0.3%, the test time will exceed 1000 days before the creep strain reaches 0.3%. Since the creep strain rate slows down with the passage of test time, in the creep test under the above conditions, the creep rate is 3.0×10 -4 %h -1 If the creep strain is less than 0.3%, the test time until the creep strain reaches 0.3% will definitely exceed 1000 days. Blow-off may occur, for example, when the creep strain reaches 0.3%. Thus, an aluminum alloy plate satisfying the above conditions can provide a cap having excellent long-term creep resistance and suppressing the deterioration of blow-off resistance due to long-term storage compared to conventional caps.

[0035] Furthermore, the electrical conductivity of the rolled plate after the stabilization treatment is preferably 25% IACS or more and 34% IACS or less. If the electrical conductivity is less than 25% IACS or more than 34% IACS, the bottom of the cap may not be able to maintain a sufficient binding force. If the aluminum alloy has a large amount of solute elements (especially Mn and Mg) in solid solution, the electrical conductivity may decrease, the alloy may be easily work-hardened, and the formability of the cap may decrease. On the other hand, if the amount of solute elements (especially Mn and Mg) in solid solution is small, the electrical conductivity may increase, the strength may decrease, and the binding force may decrease.

[0036] The aluminum alloy plate according to the embodiment of the present invention can be manufactured by a manufacturing method including the above-mentioned steps A to G. First, casting is performed according to a conventional method to obtain an ingot made of an aluminum alloy having the above-mentioned alloy composition. The obtained ingot of the aluminum alloy is heated under predetermined conditions (step A), and then subjected to a predetermined homogenization treatment (step B), hot rough rolling (step C), hot finish rolling (step D), cooling (step E), cold rolling (step F), and stabilization heat treatment (step G). Here, after cooling (step E), cold rolling (step F) is performed without intermediate annealing. Note that intermediate annealing refers to a heat treatment performed before cold rolling or between passes of cold rolling.

[0037] Here, in the heating (step A) and homogenization treatment (step B), an aluminum alloy ingot with a slab thickness of about 450 mm to 600 mm obtained by casting using a known casting method such as semi-continuous casting (DC casting) is used. In the heating step, the temperature is increased at a rate of 30°C / hour or more in a temperature range of at least 400°C to 460°C. Thereafter, the ingot is subjected to homogenization treatment by holding it at a first temperature of 460°C to 540°C for 2 hours to 24 hours. Here, the first temperature does not need to be constant for 2 hours to 24 hours, and may vary in the range of 460°C to 540°C. Such homogenization treatment can make the size and distribution of precipitates effective for suppressing the growth of Cube orientation, which is a recrystallization texture formed during recrystallization of a hot-rolled sheet. Here, such precipitates are Al-Mn-based compounds and Al-Mn-Si-based compounds, and are most abundant at around 480°C. Such compounds have a higher interfacial energy with the parent phase than other intermetallic compounds, and since they precipitate in fine spheres, they have the effect of suppressing the growth of the Cube orientation. In addition, if many crystal grains that have grown in the Cube orientation accumulate in a recrystallized hot-rolled sheet, the earing of the four peaks in the 0° and 90° directions (four peaks) becomes large, and it may be difficult to obtain an appropriate earing even after cold rolling.

[0038] The heating rate in the temperature range of 400°C to 460°C in the heating process has a particularly large effect on the precipitation behavior of the intermetallic compounds described above. If the heating rate is lower than 30°C / hour, the holding time in that temperature range becomes long, and the size of the precipitates remains fine, at 0.5 μm or less. As a result, sufficient recrystallization structure may not be obtained at the end of hot rolling. This may result in the strength of the cap material being excessively high and / or the earing ratio being excessively large. The upper limit of this heating rate is, for example, 200°C / hour.

[0039] The homogenization treatment is performed by holding the temperature range of 460°C to 540°C after the heating step. If the holding temperature is less than 460°C, the diffusion speed is slow, so the size of the compounds becomes too fine, 0.5 μm or less, and sufficient recrystallization structure may not be obtained at the end of hot rolling. If the holding temperature exceeds 540°C, the amount of compounds present in the equilibrium state decreases, so the amount of precipitation may be insufficient. Furthermore, the interface energy with the parent phase is relatively low, so the precipitate size is likely to become large, and the effect of suppressing the growth of the Cube orientation after hot rolling may decrease. If the holding time in the temperature range of 460°C to 540°C is less than 2 hours, the amount of precipitation described above becomes insufficient, while if the holding time exceeds 24 hours, the precipitates may become coarse, and the effect of suppressing the growth of the Cube orientation after hot rolling may decrease. In addition, a long holding time is not preferable from the viewpoint of environmental load.

[0040] The hot rough rolling carried out after the homogenization treatment is carried out with a rolling ratio of 5% to 35% per pass, at a rolling temperature of a second temperature of 460°C to 540°C, and completed within 15 minutes. The second temperature does not need to be constant and may vary within a range of 460°C to 540°C. The second temperature is set independently of the first temperature. The hot rough rolling can be carried out using a known rolling mill, but it is preferable to use, for example, a reverse-type rough rolling mill.

[0041] In the hot rough rolling process, if the rolling temperature exceeds 540 ° C, the material may adhere to the rolling roll, which may cause a deterioration in the surface quality of the material. During hot rolling, precipitation sites of intermetallic compounds are introduced successively, so that dense precipitation can be achieved even in a short time. However, if the rolling temperature is less than 460 ° C, the compounds may precipitate finely, as in the case where the homogenization treatment temperature is less than 460 ° C, and a sufficient recrystallized structure may not be obtained after the hot rolling is completed. In addition, if the rolling reduction is less than 5%, the amount of processing heat is reduced, so that the rolling temperature may fall below 460 ° C., while if the rolling reduction exceeds 35%, the amount of processing heat is excessive, and the rolling temperature may exceed 540 ° C. It is preferable to complete the hot rough rolling within 15 minutes. If it exceeds 15 minutes, the time for the precipitates to precipitate finely increases as described above, so that a sufficient recrystallized structure may not be obtained after the hot rolling. By such rough hot rolling, for example, a rough hot rolled sheet having a thickness of about 22 mm to 32 mm is obtained.

[0042] Next, hot finish rolling is performed so that the end temperature is a third temperature of 300° C. or more and 350° C. or less to obtain a hot rolled sheet. The hot finish rolling can be performed using various known hot rolling mills, but it is preferable to use, for example, a tandem hot rolling mill having three or more stands.

[0043] In hot finish rolling, if the end temperature is lower than 300°C, sufficient recrystallization structure cannot be obtained, and the 45° edge of the product sheet becomes too large, which causes transportation trouble during cap manufacturing, and the undulation of the mouth end becomes large, and sufficient sealing may not be obtained. On the other hand, if the end temperature exceeds 350°C, a part of the rolled material may adhere to the rolling roll, which may cause a deterioration in the surface quality of the hot rolled sheet. In this hot finish rolling, a rolling reduction of about 88% to 94% is generally adopted. If the rolling reduction is too low, the amount of strain accumulated during hot finish rolling is small, and recrystallization after the end of rolling may be insufficient. Also, if the rolling reduction is too high, the amount of rolling per stand increases, which may cause a part of the rolled material to adhere to the rolling roll, which may cause a deterioration in the surface quality of the hot rolled sheet. By such hot finish rolling, for example, a hot rolled sheet having a thickness of about 1.8 mm to 2.8 mm can be obtained.

[0044] The hot-rolled sheet immediately after hot finish rolling is cooled from the hot rolling end temperature to about room temperature of 50°C or less at a cooling rate of 20°C / hour or less. This allows sufficient recrystallization in the hot-rolled sheet to obtain a suitable earing ratio. Prior to the cooling step, the sheet immediately after hot finish rolling may be held at a temperature of 300°C or more for 1 hour or more (holding step). If the hot-rolled sheet after this holding step is cooled under the above-mentioned conditions, the recrystallization of the hot-rolled sheet can be further promoted and the earing ratio characteristics can be further improved. The upper limits of the holding temperature and holding time in the holding step can be appropriately selected in consideration of the action and effect, but for example, the upper limit of the holding temperature is about 350°C and the upper limit of the holding time is about 5 hours.

[0045] Next, the cooled hot-rolled sheet is further cold-rolled to obtain an aluminum alloy sheet having a desired thickness. The cold rolling is preferably performed at a rolling reduction of 70% or more and 93% or less. By cold rolling, a rolled sheet having a thickness of, for example, about 0.2 mm to 0.7 mm is obtained. The alloy composition of the aluminum alloy sheet according to the embodiment of the present invention has a higher Mg (and Mn) content than the alloy composition described in Patent Document 1, and therefore has high work hardenability. Therefore, the lower limit of the rolling reduction of the cold rolling can be set lower (70% or more) than that of Patent Document 1 (83% or more).

[0046] In cold rolling, if the reduction is less than 70%, sufficient strength may not be obtained. Also, the ears in the 0° and 180° directions relative to the rolling direction may not be made sufficiently small, and the ears in the 45° direction may become small, which may result in instability during transportation after cap formation and reduced productivity. Furthermore, the undulation of the cap mouth end may become large after plugging, and sufficient sealing may not be obtained. On the other hand, if the reduction exceeds 93%, the work hardening of the obtained rolled plate may become significant, and the formability and blow-off resistance may decrease. Also, the desired ear ratio may not be obtained, and productivity may decrease.

[0047] Generally, intermediate annealing is performed during cold rolling to control formability, but in the manufacturing method according to the embodiment of the present invention, cold rolling is performed without intermediate annealing after the cooling step. If intermediate annealing is performed, the amount of Mn in solid solution decreases, and long-term creep resistance may decrease. In addition, omitting intermediate annealing can contribute to reducing environmental load.

[0048] Thereafter, the cold-rolled aluminum alloy sheet is subjected to a stabilization heat treatment at a fourth temperature of 180°C or more and 240°C or less for 1 hour or more and 5 hours or less. Here, the fourth temperature does not need to be constant for 1 hour or more and 5 hours or less, and may vary within a range of 180°C or more and 240°C or less. In the stabilization heat treatment, the strain accumulated by the cold rolling is alleviated, the strain distribution on the surface of the rolled sheet is uniformed, and, for example, the occurrence of wicket marks during painting baking can be prevented. The higher the stabilization heat treatment temperature, the higher the effect, but if it exceeds 240°C, the material strength may decrease. On the other hand, if the temperature is less than 180°C, the strain may not be sufficiently alleviated. In addition, if the treatment time is less than 1 hour, a sufficient effect cannot be obtained, and if it exceeds 5 hours, the strength may decrease. In addition, prolonging the treatment time is not preferable from the viewpoint of environmental load.

[0049] As described above, according to the embodiments of the present invention, an aluminum alloy plate for a ring-pull type cap, which has excellent blow-off resistance, easy opening property, recyclability, and long-term creep resistance even when thinned, and a manufacturing method thereof can be obtained.

[0050] The aluminum alloy sheet and the manufacturing method thereof according to the embodiment of the present invention will be described below by way of experimental examples (Examples 1 to 4 and Comparative Examples 1 to 4).

[0051] Example 1 Aluminum alloys (Examples 1 to 4 and Comparative Examples 1 to 4) having various alloy compositions shown in Table 1 below were produced according to the above-mentioned manufacturing method. After soaking at 490°C for 2 hours, the alloys were hot-rolled, cold-rolled at room temperature, and then subjected to stabilization heat treatment for 2 hours in a temperature range of 215°C to 233°C. The alloy compositions were analyzed using a Quantometer (Thermo Fisher Scientific ARL4460). In addition, an A5052 alloy material was used as a comparative material. In Comparative Example 1, intermediate annealing was performed. The intermediate annealing conditions were a heating rate of 100°C / min or more, and the temperature of the rolled plate was held in the range of 400°C to 500°C for 10 minutes or less.

[0052] [Table 1] The aluminum alloy sheets thus obtained were used as samples, and were subjected to heat treatment at 190°C for 10 minutes in an air furnace, and then allowed to cool. The tensile strength and yield strength, creep strain, and electrical conductivity of the samples thus obtained were measured. The results are shown in Table 2 below.

[0053] -Measurement of tensile strength- From each sample, a JIS Z 2201 No. 5 test piece was taken in a direction at an angle of 0° to the rolling direction, and a tensile test was conducted in accordance with JIS Z 2241 to measure the tensile strength. Those with a tensile strength in the range of 280 MPa to 320 MPa and a difference between the tensile strength and the yield strength of 35 MPa or more were deemed to have passed, and those with other values ​​were deemed to have failed. If the tensile strength is too low, there is a risk that sufficient rigidity cannot be obtained, and if the tensile strength is too high, there is a risk that the formability of the cap may be impaired.

[0054] -Creep strain measurement- A strain gauge 12 was attached to a test piece 10 shown in FIG. 1, and the creep strain was measured. The numerical values ​​in FIG. 1 indicate dimensions in mm. A test piece shown in FIG. 1 was taken from each sample in a direction forming an angle of 0° with respect to the rolling direction, and the creep strain was measured under conditions of an ambient temperature of 80°C and a load of 100 MPa. The creep strain rate from 60 to 80 hours after the start of the test was 3.0×10 -4 %h -1 The following were rated as pass, and anything else was rated as fail. The creep strain rate was calculated by using the least squares method to find the slope of a graph of creep strain versus time in the range of 60 to 80 hours after the start of the test.

[0055] - Conductivity measurement - The samples were stacked so that the total thickness was 1 mm or more, and the electrical conductivity of the rolled surface was measured. Those that were 25% IACS or more and 34% IACS or less were deemed to have passed the test, and those that were not were deemed to have failed the test.

[0056] [Table 2] Table 2 shows the evaluation results of tensile strength, yield strength, difference between tensile strength and yield strength, creep strain rate, and electrical conductivity. If any of these evaluation results pass, the overall judgment is given a ○ (Good). On the other hand, if at least one of these evaluation results fails, the overall judgment is given a × (NG). Note that the "cold rolling ratio" in Table 2 indicates the reduction ratio during cold rolling. The reduction ratios in other rolling processes do not affect the properties.

[0057] The aluminum alloy sheets of Examples 1 to 4 were all evaluated as ◯, and thus were suitable for use as aluminum alloy sheets for ring-pull caps. On the other hand, the aluminum alloy sheets of Comparative Examples 1 to 4 all failed at least one evaluation, and thus were not suitable for use as aluminum alloy sheets for ring-pull caps.

[0058] Comparative Example 1 has the same alloy composition as Example 2, but does not have sufficient long-term creep resistance. This is believed to be due to the reduction in the amount of Mn dissolved in solid solution caused by intermediate annealing. Comparative Example 2 does not have sufficient long-term creep resistance because the Mg content is high. This is believed to be due to the occurrence of aging softening due to the high diffusion rate of Mg. Comparative Examples 3 and 4 do not have sufficient long-term creep resistance because the Mn content is low. This is believed to be due to the fact that the effect of reducing the dislocation motion velocity due to the dissolved Mn cannot be obtained when the Mn content is low. [Industrial Applicability]

[0059] The aluminum alloy plate according to the embodiment of the present invention is preferably used for ring-pull type caps used in carbonated drink containers, for example, and can provide better blow-off resistance during long-term storage than conventional ones. [Explanation of symbols]

[0060] 10 Test Pieces 20 Strain Gauge

Claims

1. A rolled sheet having an alloy composition containing, by mass, Mn: 0.50% or more and 1.10% or less, Mg: 2.85% or more and less than 3.48%, Fe: 0.20% or more and 0.40% or less, Si: 0.05% or more and 0.20% or less, Cu: 0.01% or more and 0.15% or less, Ti as an optional element with an upper limit of 0.10% by mass, and the balance being aluminum and unavoidable impurities, The tensile strength in the rolling direction after heat treatment at 190°C for 10 minutes is 280 MPa or more and 320 MPa or less, the difference between the tensile strength and the yield strength is 35 MPa or more, the electrical conductivity is 25% IACS or more and 34% IACS or less, and in a creep test under the conditions of a material temperature of 80°C and a load on the test piece of 100 MPa, the creep strain rate from 60 hours to 80 hours from the start of the test is 3.0 x 10 －４ %h －１ The aluminum alloy plate for the ring-pull type cap is shown below.

2. The aluminum alloy plate according to claim 1, wherein the alloy composition contains, on a mass basis, Ti: 0.01% or more.

3. The aluminum alloy sheet according to claim 1 or 2, wherein the Cr content of the inevitable impurities is less than 0.01% by mass.

4. A method for producing the aluminum alloy plate according to any one of claims 1 to 3, A step A of heating an ingot made of an aluminum alloy having the alloy composition at a temperature rise rate of 30° C. / hour or more in a temperature range of at least 400° C. to 460° C.; After the step A, a step B of subjecting the ingot to a homogenization treatment by holding the ingot at a first temperature of 460° C. or more and 540° C. or less for 2 hours or more and 24 hours or less; After the step B, a step C of performing rough hot rolling at a rolling rate of 5% to 35% per pass at a rolling temperature of 460° C. to 540° C. inclusive, and completing the rolling within 15 minutes; After the step C, a step D of performing hot finish rolling so that the end temperature is a third temperature of 300 ° C. or more and 350 ° C. or less to obtain a hot rolled plate; A step E of cooling the hot-rolled plate obtained in the step D at a cooling rate of 20 ° C. / hour or less; After the step E, a step F of cold rolling the hot-rolled sheet at a rolling reduction of 70% or more and 93% or less without intermediate annealing; A step G of performing a stabilization heat treatment at a fourth temperature of 180° C. or more and 240° C. or less for 1 hour or more and 5 hours or less after the step F; The manufacturing method includes the steps of:

5. The manufacturing method according to claim 4, further comprising, before the step E, a step of holding the hot-rolled sheet obtained in the step D at a temperature of 300° C. or more for one hour or more.

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