JP5356359B2 - Aluminum alloy coated plate for positive pressure can lid and manufacturing method thereof - Google Patents

Abstract

Provided is a coated aluminum alloy sheet for pressurized-can lids which, even when produced in a reduced thickness without through a process annealing step, suffers no decrease in toughness, has satisfactory formability during lid forming, and has excellent resistance to cracking by buckling. The coated aluminum alloy sheet has a composition which contains, in terms of mass%, 0.04-0.20% Si, 0.35-0.70% Mn, 0.12-0.30% Fe, 0.01-0.10% Cu, and 4.0-5.5% Mg, the remainder comprising Al and incidental impurities, and has a thickness of 0.190-0.230 mm. The sheet is characterized by having a tensile strength of 360-400 MPa and a proof strength of 320-355 MPa. The sheet is further characterized in that when a test piece cut out of the sheet along the direction perpendicular to the rolling direction is subjected to a 90º reversed cyclic bending test at an inner bending radius of 1.0 mm while applying a constant load of 100 N to the test piece, then the number of cycles to rupture is 7 or more.

Description

  The present invention relates to an aluminum alloy coated plate for a can lid, and more particularly to an aluminum alloy coated plate for a positive pressure can lid that is suitably used as a lid for a positive pressure can and a method for producing the same.

  Easy open can lid materials used for beverage cans and the like are required to have excellent drawing processability, curl formability, rivet processability, score processability, can openability, and the like. In particular, in positive pressure cans such as beer cans and carbonated beverage cans, where high internal pressure is applied after filling the contents, high pressure resistance is necessary, and the can lid material, that is, the aluminum alloy coated plate for can lids, has high strength. Required.

  In recent years, the thickness of can lid materials has been reduced in order to reduce costs. On the other hand, in order to reduce environmental burden, in the production of can lid materials, the intermediate annealing process is omitted immediately after the hot rolling process or in the middle of the cold rolling process. Is strongly desired. However, the omission of the simple intermediate annealing step significantly reduces the toughness of the material, and therefore the buckling crack resistance is lowered particularly in a thinned can lid. Buckling resistance refers to buckling that not only causes the pressure inside the can to rise and the lid swells when the temperature rises in the car during the summer, but also causes the concave countersink part to deform into a convex shape. It means that the material does not easily crack when it is woken up.

  Therefore, even when the intermediate annealing step is omitted and the thickness is reduced at the same time, an aluminum alloy can lid material excellent in buckling crack resistance is required, and the resistance to buckling crack resistance is improved. Various methods have been proposed. For example, it has been proposed to improve the characteristics of can lid materials by controlling the size and number of intermetallic compounds and adjusting the amount of alloy components such as Si, Mn, Fe, Cu, Mg, and transition metal elements. However, it does not necessarily meet the strength required for a positive pressure can lid material, and when thinning progresses, it is not enough to maintain the pressure resistance after lid making and to maintain buckling crack resistance. Absent.

JP 2001-11558 A JP 2001-164347 A JP 2007-23340 A JP 2009-221567 A

  In order to obtain a can lid material for a positive pressure can that eliminates the above-mentioned conventional problems, the present invention provides production conditions for an aluminum alloy coated plate for a positive pressure can lid, that is, homogenization treatment of an ingot, hot rolling It was made as a result of repeated testing and examination of the relationship between conditions such as cold rolling and paint baking treatment and properties as a can lid material. Its purpose is to eliminate the intermediate annealing process and to reduce the thickness An object of the present invention is to provide an aluminum alloy coated plate for a positive pressure can lid, which has good formability at the time of lid forming without deterioration in toughness and is excellent in buckling crack resistance, and a method for producing the same.

  To achieve the above object, the aluminum alloy coated plate for a positive pressure can lid according to claim 1 is in mass%, Si: 0.04 to 0.20%, Mn: 0.35 to 0.70%, Fe : 0.12 to 0.30%, Cu: 0.01 to 0.10%, Mg: 4.0 to 5.5%, with the balance being composed of Al and inevitable impurities, Is an aluminum alloy coated plate having a thickness of 0.190 mm or more and 0.230 mm or less, a tensile strength of 360 to 400 MPa, a proof stress of 320 to 355 MPa, a test piece taken in a 90 ° direction with respect to the rolling direction, When a constant load of 100 N is applied to the test piece and a 90 ° double swing repeated bending test is performed with an inner bending radius of 1.0 mm, the fracture limit number is 7 or more. In the following description, all alloy component values are indicated by mass%.

  A method for producing an aluminum alloy coated plate for a positive pressure can lid according to claim 2 is a method for producing an aluminum alloy coated plate for a positive pressure can lid according to claim 1, wherein the aluminum alloy having the above composition is melted and cast. The ingot thus obtained is subjected to homogenization heat treatment, and then hot-rolled, cold-rolled to a thickness of 0.190 mm to 0.230 mm, and the resulting cold-rolled plate is coated, 260 When the Mn content% in the composition is [Mn], the coating baking process is performed at a temperature (° C) of not less than 33 × [Mn] +247 and not more than 300 ° C.

  A method for producing an aluminum alloy coated plate for a positive pressure can lid according to claim 3 is a method for producing an aluminum alloy coated plate for a positive pressure can lid according to claim 1, wherein the aluminum alloy having the above composition is melted and cast. The ingot thus obtained was subjected to homogenization heat treatment, followed by hot rolling and cold rolling to a thickness of 0.190 mm or more and 0.230 mm or less. Heating to a temperature of not less than 260 ° C. and a Mn content% in the composition of [Mn] at a temperature rise rate of 2 sec. Then, heat treatment is performed for 0 to 20 seconds, coating is performed, and coating baking is performed at a temperature of 220 ° C. or higher and lower than 260 ° C.

  Even if the intermediate annealing process is omitted and the thickness is reduced, the toughness does not decrease, the moldability at the time of lid molding is good, and the aluminum alloy coated plate for positive pressure can lids with excellent buckling crack resistance and its A manufacturing method is provided.

The significance and reasons for limitation of the alloy components in the aluminum alloy coated plate for a positive pressure can lid of the present invention will be described.
Si: 0.04 to 0.20%
Si is an element that cannot be avoided in order to use inexpensive bullion and recycled raw materials in order to reduce manufacturing costs, and the preferred content is in the range of 0.04 to 0.20%. If it exceeds 0.20%, it causes the formation and coarsening of intermetallic compounds Mg ₂ Si and Al—Mn—Si and Al—Fe—Mn—Si based intermetallic compounds that crystallize during the casting solidification process. Thus, the crack generation position and propagation path at the time of can lid molding and buckling become a phenomenon, and the buckling crack resistance and moldability are likely to deteriorate. If the Si content is less than 0.04%, a high-purity raw metal raw material is required, and the cost of the raw metal increases, and regulations at the time of casting become stricter and productivity is lowered. A more preferable content range of Si is 0.04 to 0.15% at which the amount of intermetallic compound is remarkably reduced.

Mn: 0.35 to 0.70%
Mn functions to increase the strength and refines the crystal grains. The preferred content is in the range of 0.35 to 0.70%, and when it exceeds 0.70%, Al—Mn system, Al—Fe—Mn system, Al—Mn—Si system that crystallizes in the solidification process, The generation of Al-Fe-Mn-Si-based intermetallic compounds and coarsening are caused, and the same problem as when excessive Si is added occurs. If the Mn content is less than 0.35%, sufficient strength cannot be obtained.

Fe: 0.12-0.30%
Fe functions to increase the strength and refines the crystal grains. The preferred content is in the range of 0.12 to 0.30%, and when it exceeds 0.30%, Al—Fe, Al—Fe—Mn, and Al—Fe—Si that crystallize during the casting solidification process. The generation of Al-Fe-Mn-Si-based intermetallic compounds and coarsening are caused, and the same problem as when Si is added excessively occurs. Therefore, it is necessary to suppress the addition amount. On the other hand, if the Fe content is less than 0.12%, a high-purity bare metal raw material is required, the cost of the bare metal raw material is increased, and regulations at the time of casting become strict and productivity is lowered. A more preferable content range of Fe is 0.12 to 0.26% which does not significantly reduce the solid solution amount of Mn.

  Even if the Fe content is 0.30% or less, in the range of more than 0.26% and 0.30% or less, the solid solution amount of Mn is reduced, and even if the amount of Mn is the same, Al-Fe-Mn , Al-Fe-Mn-Si-based intermetallic compounds are used to increase the amount of intermetallic compounds, so that particularly severe buckling crack resistance is required. It can be a problem in the following cases: Therefore, when the content is a high-alcohol or non-alcoholic carbonated beverage or when the plate thickness is 0.220 mm or less, the Fe content is preferably limited to 0.26% or less.

Cu: 0.01 to 0.10%
Cu functions to increase strength and improve formability. The preferred content is in the range of 0.01 to 0.10%, and if it exceeds 0.10%, it tends to cause ingot cracking during casting and cracking during hot rolling, making it difficult to produce a plate material. . On the other hand, if it is less than 0.01%, a high-purity bare metal raw material is required, the cost of the bare metal raw material increases, and regulations at the time of casting become strict and productivity is lowered. A more preferable content range of Cu is 0.02 to 0.05% in which recycled raw materials can be used and productivity during hot rolling is not reduced.

Mg: 4.0 to 5.5%
Mg increases strength by solid solution of Mg itself, and imparts paint bake hardenability. In addition, Mg content is an indispensable element for increasing the amount of work hardening due to interaction with dislocations and obtaining the required strength for aluminum alloy can lid materials to which internal pressure is applied. Is in the range of 4.0-5.5%. If the Mg content is less than 4.0%, sufficient strength cannot be obtained as a lid for a positive pressure can, and if it exceeds 5.5%, cracking during hot rolling is likely to occur. Is difficult to manufacture.

  The manufacturing process of the aluminum alloy coated plate for a positive pressure can lid of the present invention includes a melting process, a casting process, a homogenizing heat treatment process, a hot rolling process, a cold rolling process, and a paint baking process as essential processes. Immediately after the hot rolling step, the intermediate annealing step during the cold rolling is omitted.

  The aluminum alloy having the above composition is melted and ingoted by a semi-continuous casting method (DC casting method), and the resulting ingot is subjected to a homogenization heat treatment. The homogenization heat treatment step is preferably performed under the condition that the ingot is heated to a temperature of 440 to 530 ° C. and held for 1 to 20 hours. When the homogenization heat treatment temperature is less than 440 ° C., the homogenization heat treatment time is required for a long time, resulting in a decrease in productivity. On the other hand, when the homogenization heat treatment temperature exceeds 530 ° C., the intermetallic compound is likely to be coarsened, and it becomes a crack generation position and propagation path at the time of can lid molding and buckling. Reduce. In addition, when the holding time at the homogenization heat treatment temperature is less than 1 hour, the homogenization of the structure is not obtained, and when it exceeds 20 hours, the intermetallic compound is easily coarsened, and the homogenization heat treatment temperature exceeds 530 ° C. The same problem occurs.

  After the homogenization heat treatment, hot rolling is performed. In the hot rolling step, the end temperature at the completion of hot rolling is preferably 300 ° C. or higher, and the recrystallization structure is obtained by setting the hot rolling end temperature to 300 ° C. or higher. When the hot rolling finish temperature is less than 300 ° C., a sufficiently homogeneous recrystallized structure cannot be obtained, resulting in a substantial increase in the work hardening amount including the cold rolling process for the product, formability and buckling resistance. In addition to inferior cracking properties, the product strength varies greatly, and the quality as a can lid material decreases.

  After hot rolling, cold rolling is performed to a final thickness of 0.190 mm or more and 0.230 mm or less. The rolling rate of cold rolling is preferably 85 to 93%. If the cold rolling rate is less than 85%, the sheet thickness at the end of hot rolling becomes thin and there is a risk that the lower limit of the sheet thickness that can be stably produced by hot rolling may be exceeded. The work hardening amount becomes small, and the strength required for the aluminum alloy can lid material to which the internal pressure is applied cannot be obtained. Further, if the cold rolling rate exceeds 93%, work hardening becomes excessively large and not only the formability is inferior, but also the edge cracks of the cold rolled plate end easily occur, and the productivity is inferior. .

  In the present invention, it is desirable not to perform intermediate annealing after hot rolling and during cold rolling. Therefore, after hot rolling, cold rolling is performed to a final thickness of 0.190 mm or more and 0.230 mm or less without performing intermediate annealing. In can lid materials manufactured without intermediate annealing, the ratio of crystal grain length to width (crystal grain length / crystal grain width) is 20 or more, giving the strength required for can lid materials. Is done. If (the length of crystal grains / the width of crystal grains) is less than 20, it is difficult to obtain the strength required for the can lid material.

  The ratio of crystal grain length to width, (crystal grain length / crystal grain width), was observed with an optical microscope using a polarizer at 200 times the cross section parallel to the rolling direction and perpendicular to the rolling surface, This is a value obtained by measuring the length and width of 20 or more crystal grains and averaging the values of (crystal grain length / crystal grain width). The length of the crystal grains is measured in the rolling direction, and the width of the crystal grains is measured in a direction perpendicular to the rolling direction. The value of (crystal grain length / crystal grain width) is geometrically determined from the shape of the recrystallized grains of the hot-rolled sheet and the cold rolling rate, and can be easily estimated. It is. When the hot rolling is completed, a recrystallized structure is obtained, and a substantially spherical recrystallized grain is obtained. When cold rolling is performed at a maximum cold rolling rate of 93%, the value of (crystal grain length / crystal grain width) is No more than 500.

  The resulting cold-rolled plate is coated with an organic resin and subjected to a paint baking process. This paint baking process not only coats and bakes organic resin on the surface of the can lid material plate, but also serves as temper annealing. In the paint baking process, the material arrival temperature (Peak Metal Temperature (PMT), hereinafter referred to as the paint baking temperature refers to the material arrival temperature in the paint baking process) at 260 ° C. or higher, and the present invention. When the Mn content% in the aluminum alloy composition is [Mn], the temperature (° C.) to 300 ° C. is obtained by 33 × [Mn] +247, and the holding time is longer than 0 seconds and not longer than 20 seconds. It is desirable to do it. If the coating baking temperature is less than 260 ° C., the dislocation structure introduced in the cold rolling process is not sufficiently recovered, and the buckling crack resistance of the can lid is poor. Further, as described above, as the Mn content increases, the resistance to buckling cracking is further reduced. Therefore, even when the coating baking temperature is 260 ° C. or higher, the temperature (° C.) required by 33 × [Mn] +247. If it is less than this, it is inferior to the buckling crack resistance of a can lid. If the coating baking temperature exceeds 300 ° C, the strength change in the PMT will increase, and it will be difficult to adjust the strength to meet the product specifications during mass production. Cannot be obtained.

  Also, in the case where the coating baking temperature cannot be 260 ° C. or more from the viewpoint of maintaining the coating film performance, it is preferable to use a continuous annealing furnace before the coating baking process, preferably at a heating rate of 4 to 25 ° C./second, 220 ° C. or higher and a temperature in the range of 33 ° C. (Mn) +247 (300 ° C.) to 300 ° C., preheating for a holding time exceeding 0 seconds and 20 seconds or less, coating, 220 The above-mentioned effect can be obtained by performing a coating baking process at a temperature of not lower than 260 ° C. and lower than 260 ° C. If the temperature increase rate of the preheating is less than 4 ° C / second, the time during which the material is kept at a high temperature becomes long, and it becomes difficult to adjust the strength to meet the product specifications at the time of mass production. The strength required for the lid cannot be obtained. When it exceeds 25 ° C./second, the dislocation structure introduced in the cold rolling step is not sufficiently recovered, and the can lid is inferior in buckling crack resistance.

  When the preheating temperature (material arrival temperature, the same applies hereinafter) is 260 ° C or higher and is out of the temperature range of 300 ° C from the temperature (° C) obtained by 33 × [Mn] +247, preheating is performed as described above. In the embodiment in which only the coating baking process is performed, the same problem as when the coating baking temperature is out of the condition occurs. When the coating baking temperature is less than 220 ° C., it is difficult to obtain necessary coating film performance such as coating film strength and adhesive strength with a base material. Above 260 ° C, it is difficult to adjust the strength to meet the product specifications during mass production due to the effect of preheating before the baking treatment, and the strength required for the can lid material is increased due to excessive recovery. I can't get it.

  In the aluminum alloy coated plate of the present invention, it is important that the tensile strength after baking is 360 to 400 MPa. The tensile strength after paint baking is closely related to the paint baking temperature and the repeated bending described later. When the coating baking temperature is high, the tensile strength after baking is small and the number of repeated bendings is large. If the tensile strength is less than 360 MPa, the strength of the can lid material is not sufficient, and buckling is likely to occur at a low internal pressure. If it exceeds 400 MPa, the number of repeated bendings will decrease, and cracks in the buckling will easily occur.

  It is important that the proof stress is 320 to 355 MPa. Yield after paint baking is closely related to paint baking temperature and repeated bending as well as tensile strength. When the paint baking temperature is high, the proof stress after paint baking is small, and the number of repeated bending increases. If the yield strength is less than 320 MPa, the strength of the can lid material is not sufficient, and buckling is likely to occur at a low internal pressure. When it exceeds 355 MPa, the number of times of repeated bending decreases, and cracks at the buckling tend to occur.

  In the aluminum alloy coated plate of the present invention, a test piece is taken in a direction of 90 ° with respect to the rolling direction, a constant load of 100 N is applied to the test piece, and 90 ° double swing bending is performed with an inner bending radius of 1.0 mm. It is also an important constituent requirement that the number of times of fracture limit when the test is performed is 7 times or more. The ease of cracking during buckling can be evaluated by the number of repeated bendings. The repeated bending test conditions are as follows. A test piece having a length of 200 mm and a width of 12.5 mm was taken in the direction of 90 ° with respect to the rolling direction, and a constant load of 100 N was applied to the test piece, and the inner bending R was set to 1.0 mm, and left and right Perform a swing test by bending at 90 °. Counting once every 90 ° bend, one cycle ends with 4 times. If it is less than 7 times, cracks are likely to occur during buckling, so it is rejected, and 7 times or more is evaluated as acceptable.

  In the aluminum alloy coated plate of the present invention, the plate thickness is preferably 0.190 to 0.230 mm. Thinning has a cost reduction effect by reducing the mass per lid, but if the plate thickness exceeds 0.230 mm, the cost reduction effect is small compared to the current lid material, while the plate thickness is 0 If it is less than 190 mm, it is difficult to obtain the strength and toughness of the positive pressure can lid material at the same time, resulting in insufficient pressure resistance after lid formation or cracking during buckling.

  The aluminum alloy coated plate for a positive pressure can lid of the present invention is particularly effective when the contents of the positive pressure can are used as a can lid of a positive pressure can which is a high alcohol or non-alcohol carbonated beverage. For example, compared to the case where the contents of the positive pressure can are beer, the contents of the high-capacity or carbonated drink cans have a higher required internal pressure because the initial internal pressure and the increase in the internal pressure due to the temperature increase are large. If the material strength is increased to ensure, buckling cracks are likely to occur. On the other hand, the aluminum alloy coated plate of the present invention is excellent in buckling resistance even if the material strength is increased, so it is very effective when the content is high-alcohol or non-alcoholic carbonated beverages. is there. The cocoon high means a drink obtained by dividing shochu with carbonated water, and the non-alcoholic carbonated drink means a carbonated drink substantially containing no alcohol.

  In the present invention, an intermediate annealing step immediately after hot rolling, which has been conventionally performed by the above-described manufacturing method, particularly a combination of the specified baking process, and the preheating process and the baking process, and cold Even if the intermediate annealing step during rolling is omitted, an aluminum alloy coated plate for a positive pressure can lid having excellent strength, formability and buckling crack resistance can be produced. By omitting the intermediate annealing step, the production energy can be reduced, the emission of CO2 gas due to the combustion of fossil fuel can be suppressed, and the environmental load can be reduced.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects of the present invention. In addition, these Examples show one embodiment of this invention, and this invention is not limited to these.

Example 1
Aluminum alloys (alloys A to J) having the compositions shown in Table 1 were melted and cast by DC casting. The resulting ingot was homogenized at 500 ° C. for 4 hours, and then heated to a thickness of 2.1 mm. Rolled for a while. The end temperature of hot rolling was 310 to 350 ° C., and a recrystallized structure was obtained. Then, cold rolling was performed without intermediate annealing so that the cold rolling rate was 90%, and a cold rolled sheet (test material) having a sheet thickness of 0.210 mm was obtained.

  The test material was subjected to paint baking under the conditions shown in Table 2, and then subjected to a tensile test and a repeated bending test by the following methods to evaluate the pressure resistance and buckling crack resistance, and the ratio of crystal grain length to width. . The results are shown in Table 2. In addition, about the test materials 7-9, the preheating was performed on the conditions shown in Table 2 before the coating baking process. Moreover, in Table 1, the thing outside the conditions of this invention was underlined.

Tensile test: No. 5 test piece was taken with the rolling direction as the longitudinal direction, a tensile test was performed in accordance with JIS Z 2201, and tensile strength and yield strength were measured.
Repeated bending test: The above method was used, and the number of bendings of 7 times or more was evaluated as acceptable, and less than 7 were evaluated as unacceptable.
Pressure resistance and buckling resistance: 20 cold-rolled plates (test materials), each having 204 diameters (outer diameter: 2 inches + 4/16 inches), 20 pieces of lids are taken and wound around a can body. I made it buckle over. With regard to pressure resistance, the minimum value of the pressure when buckling was evaluated was 540 kPa or more as acceptable (◯), and less than 540 kPa as unacceptable (x). The buckling crack resistance was determined to be acceptable (◯) when no cracks occurred on all 20 sheets and rejected (×) when even one crack was observed.
(Crystal grain length / Crystal grain width): The ratio of the crystal grain length to the width, (Crystal grain length / Crystal grain width) was measured by the method described above.

  As shown in Table 2, each of the test materials 1 to 10 according to the present invention has excellent tensile strength of 360 to 400 MPa, proof strength of 320 to 355 MPa, good pressure resistance, and the number of repeated bendings is 7 times or more. Thus, it had good buckling crack resistance, and the ratio between the length and the width of the crystal grains exceeded 20.

Comparative Example 1
The aluminum alloy (alloys A to J) ingot obtained in Example 1 was homogenized at 500 ° C. for 4 hours, and then hot-rolled to a thickness of 2.1 mm. The end temperature of hot rolling was 310 to 350 ° C., and a recrystallized structure was obtained. Then, cold rolling was performed without intermediate annealing so that the cold rolling rate was 90%, and a cold rolled sheet (test material) having a sheet thickness of 0.210 mm was obtained. However, the test materials 15 and 20 were cold-rolled to a plate thickness of 0.185 mm (rolling rate: 91.2%). After the hot rolling, the test material 32 is cold-rolled to a sheet thickness of 0.6 mm, then subjected to intermediate annealing that is held at 450 ° C. for 5 seconds, and cold-rolled to a sheet thickness of 0.210 mm.

  About the test material, after performing the paint baking treatment under the conditions shown in Table 3, the tensile test and the repeated bending test were performed in the same manner as in the examples, the pressure resistance and the buckling crack resistance, the ratio of the length and width of the crystal grains. Evaluated. The results are shown in Table 3. In addition, about the test materials 29-31, the preheating was performed on the conditions shown in Table 3 before the coating baking process. Further, in Table 3, those that deviated from the conditions of the present invention in the preheating, paint baking treatment, tensile strength, proof stress, and number of repeated bendings were underlined.

  As shown in Table 3, since the test materials 11 and 12 had a small amount of Mn, the proof stress was low and the pressure resistance was inferior. Since the test materials 13, 16, and 18 had a low coating baking temperature, the number of repeated bending was small, and the buckling crack resistance was inferior. Since the test material 14 had a high coating baking temperature, the tensile strength and proof stress were low, and the pressure resistance was inferior. Since the test materials 17 and 19 had a high coating baking temperature, the proof stress was low and the pressure resistance was inferior.

  Since the test materials 15 and 20 were thin, their pressure resistance was inferior. Since the test material 21 had a large amount of Mn and a low coating baking temperature, the tensile strength and proof strength were high, the number of repeated bending was small, and the buckling crack resistance was inferior. Since the test materials 22 and 23 have a large amount of Mn, the test material 24 has a large amount of Si, and the test material 25 has a large amount of Fe. Therefore, the number of repeated bendings was small, and the buckling crack resistance was inferior. . Since the test material 26 has a large amount of Cu, the test material 28 has a large amount of Mg. Therefore, in all cases, ear cracking occurred during hot rolling, making it difficult to produce a sound plate material, and the productivity was significantly reduced. .

  Since the test material 27 had a small amount of Mg, the tensile strength and proof stress were low, and the pressure resistance was inferior. The test material 29 had low proof stress and poor pressure resistance because of the slow heating rate of preheating. Since the test material 30 had a high rate of temperature increase during the preliminary heating, the yield strength was high, the number of repeated bendings was small, and the buckling crack resistance was inferior. Since the test material 31 had a high coating baking temperature when preheating was performed, the proof stress was low and the pressure resistance was poor. The test material 32 was hot-rolled and then cold-rolled by intermediate annealing. The ratio of the crystal grain length to the width was as small as 9.7, the proof stress was low, and the pressure resistance was poor. In addition, about the test materials 11-31, it cold-rolled to the final board thickness, without performing intermediate annealing after hot rolling, and the ratio of the length and width of a crystal grain exceeded 20 in all.

Claims (3)

In mass%, Si: 0.04 to 0.20%, Mn: 0.35 to 0.70%, Fe: 0.12 to 0.30%, Cu: 0.01 to 0.10%, Mg: It is an aluminum alloy coated plate containing 4.0 to 5.5%, the balance being Al and inevitable impurities, and having a thickness of 0.190 mm or more and 0.230 mm or less, and having a tensile strength of A test piece is taken in a direction of 90 ° with respect to the rolling direction at 360 to 400 MPa and a proof stress of 320 to 355 MPa. A constant load of 100 N is applied to the test piece, and 90 ° double swing is repeated with an inner bending radius of 1.0 mm. An aluminum alloy coated plate for a positive pressure can lid, wherein the number of times of fracture limit in a bending test is 7 or more. A method for producing an aluminum alloy coated plate for a positive pressure can lid according to claim 1, wherein the aluminum alloy having the above composition is melted and cast, the ingot obtained is subjected to homogenization heat treatment, and then hot rolled. And cold-rolled to a thickness of 0.190 mm or more and 0.230 mm or less, and the obtained cold-rolled plate was coated, and the Mn content% in the composition was set to [Mn] at 260 ° C. or more. A method of producing an aluminum alloy coated plate for a positive pressure can lid, characterized in that a coating baking process is performed at a temperature (° C.) or higher and 300 ° C. or lower calculated by 33 × [Mn] +247. A method for producing an aluminum alloy coated plate for a positive pressure can lid according to claim 1, wherein the aluminum alloy having the above composition is melted and cast, the ingot obtained is subjected to homogenization heat treatment, and then hot rolled. And cold-rolled to a thickness of 0.190 mm to 0.230 mm, and the obtained cold-rolled sheet has a temperature increase rate of 4 to 25 ° C./second and is 260 ° C. or more and contains Mn in the composition When the amount% is [Mn], a heat treatment is performed by heating to a temperature (° C.) of not less than 33 × [Mn] +247 and maintaining at a temperature of 300 ° C. or less and holding for 0 to 20 seconds, and coating is performed. A method for producing an aluminum alloy coated plate for a positive pressure can lid, wherein the coating baking treatment is performed at a temperature of 260 ° C. or lower.