JP4019084B2 - Aluminum alloy cold rolled sheet for bottle cans with excellent high temperature characteristics - Google Patents

Description

  The present invention is thinned to a plate thickness of 0.2 mm or less (about 120 to 130 μm where the thickness of the central portion of the can body is small) as a can body material for bottle cans (beverage cans) and heat-treated at a high temperature. In addition, the present invention relates to an aluminum alloy cold-rolled plate for bottle cans (a material plate for bottle cans) having excellent high-temperature characteristics such as low strength reduction, ensuring high strength and being difficult to deform. The aluminum cold-rolled alloy sheet referred to in the present invention is a rolled sheet (cold rolled sheet) rolled through hot rolling-cold rolling. Hereinafter, the aluminum alloy is also referred to as an Al alloy.

  As an aluminum-based beverage can, a two-piece aluminum can obtained by seaming a can body and a can lid (can end) is frequently used. The can body is DI-processed (deep drawing and ironing) an aluminum cold-rolled plate, trimmed to a predetermined size, degreased and washed, and then painted and printed for baking ( The can body edge is necked and flanged.

  Conventionally, hard plates such as JIS3004 alloy and 3104 alloy, which are Al-Mg-Mn alloys, have been widely used as cold rolled plates for the can body. This JIS3004 alloy and 3104 alloy are excellent in ironing workability, and show relatively good formability even when subjected to cold rolling at a high rolling rate in order to increase strength. It is said that.

  On the other hand, in the bottle can, a thermoplastic resin coating layer is formed on both surfaces of the aluminum alloy plate, a blank is obtained by punching out the one coated with a lubricant, the blank is drawn into a cup shape, The cup-shaped molded product is subjected to redrawing and stretching or ironing (DI processing) to form a bottomed cylindrical can with a barrel having a reduced diameter and a reduced thickness. Then, the bottom side of the can is drawn multiple times to form a shoulder and an unopened mouth, and after washing and trimming, a printing / painting process is performed on the can body, and the mouth is opened. Then, the curled part and the threaded part are formed (screw / curl molding), the neck part and the flange process are applied to the part on the opposite side of the threaded part, and the bottle is formed by tightening the separately formed bottom lid with a seamer. A can is obtained (see Patent Document 1).

  In this way, in the two-piece can, after performing the base treatment (chromate, etc.) on the aluminum alloy plate, the resin coating (resin coating or film lamination) is performed, and then punched into a circular blank and cup-shaped, Drawing and ironing is performed, and printing, painting, necking, trimming, etc. are performed.

  For bottle cans with threaded mouths, the aluminum alloy plate is grounded (chromate, etc.), then coated with resin (resin coating or film lamination), then punched into a circular blank, After molding, drawing and ironing is performed, trimming, printing and painting are performed, and after screw / curl molding, neck flange molding is performed.

  The can body of a bottle can usually has a substantially circular cross section in the horizontal direction immediately after DI processing. However, the can body is heated to a temperature of 200 ° C. or higher during printing and heat treatment for improving the adhesion of the laminate film.

  At this time, the can body itself is thinned from a cold-rolled sheet having a thickness of about 0.3 to 0.4 mm to a thickness of 0.2 mm or less. Therefore, when subjected to heat treatment at such a high temperature exceeding 200 ° C., the can body is freed from processing strain and residual stress during DI processing, and thermal softening occurs.

  In this case, a material that is easily softened has a problem that the degree of softening is significant, the strength and hardness of the can are significantly reduced, and sufficient can strength cannot be secured.

  Also, since the degree of softening becomes uneven in the circumferential direction of the can, the cross section of the can body is deformed as an ellipse, not a formed perfect circle, and the shape of the can body is uneven. There is a problem of becoming.

  In recent years, due to the demand for lighter cans, the thickness of aluminum cans has become thinner and thinner at a level of 0.2 mm or less. Phenomena such as non-uniformity are becoming prominent.

  Furthermore, in recent years, from the viewpoint of improving the productivity of cans, the heat treatment for improving the adhesion of the print coating and the laminate film has been performed at a higher temperature and a shorter time, for example, 290 ° C. × 20 seconds. Is progressing. Such a tendency further promotes a decrease in strength and hardness of the can body and non-uniform shape of the can body due to the thermal softening.

  On the other hand, if the plate thickness of the can body is increased in order to prevent the strength reduction and deformation of the can body due to this thermal softening, the weight of the can increases, and the strength of the aluminum material itself without increasing the plate thickness. When the value is increased, there is a disadvantage that breakage occurs during the ironing. Therefore, it is impossible to deal with such a problem only by the conventional can material and method.

  Conventionally, an aluminum alloy plate for DI cans has been proposed that can prevent the thermal deformation during the coating heat treatment and obtain a DI can with high roundness against the uneven shape of the can body due to the heat softening. (Patent Document 2). Specifically, as an aluminum alloy plate for a DI can, Mn: 0.5 to 1.3% by mass, Mg: 0.5 to 1.3% by mass, Cu: 0.1 to 0.3% by mass, Fe When heat-treated for 20 minutes at a baking temperature T (° C.) of 230 to 270 ° C. with an aluminum alloy composition containing 0.2 to 0.6 mass% and Si: 0.1 to 0.5 mass% The change in tensile strength ΔTS before and after heat treatment is to be reduced.

In addition, many proposals have been made to control the structure in order to improve the moldability of cans. For example, the Mn solid solution amount and the crystal grain size of the hot-rolled sheet are controlled within a predetermined range, and the ear ratio of the hot-rolled sheet is stabilized to −3 to −6%, which is then subjected to intermediate annealing. It has been proposed that the cold-rolled sheet to be obtained is stably rolled to 0 to 2% by cold rolling (Patent Document 3).
JP 2001-162344 A (full text) JP 2003-277865 A (Claims) JP 2003-342657 A (full text)

  However, only by controlling the metallurgical factors of the structure of the aluminum alloy plate for stabilizing the ear ratio such as the Mn solid solution amount and the crystal grain size, it is possible to prevent thermal deformation during the coating heat treatment. Can not.

  Further, as in Patent Document 2, depending on only the aluminum alloy composition such as Mn, Mg, Cu, Fe, Si, etc., there is a great limit to suppressing the strength reduction and deformation of the can body due to the thermal softening described above. .

  That is, Patent Document 2 may be effective for heat treatment at 230 to 270 ° C. × 20 minutes, as defined or assumed. However, as described above, especially for the high-speed heat treatment at 290 ° C. × 20 seconds, which is a higher temperature and shorter time, the heat treatment temperature is particularly high, and the can body is thinner. Therefore, it is impossible to prevent the strength reduction and deformation of the can body due to thermal softening.

  The present invention has been made in view of such problems, and on the premise of ensuring moldability such as DI processing, thermal deformation at the time of coating heat treatment is also applied to high-speed heat treatment with higher temperature and shorter time. An object of the present invention is to provide an aluminum alloy cold-rolled sheet for a bottle can excellent in high-temperature characteristics, which can prevent the above-described problem, ensure the strength of the can after heat treatment, and obtain a bottle can with high roundness.

  In order to achieve this object, the gist of the aluminum alloy cold-rolled sheet for bottle cans excellent in high temperature characteristics of the present invention is as follows: Mn: 0.7 to 1.5% (mass%, the same applies hereinafter), Mg: 0.00. 8 to 1.7%, Fe: 0.1 to 0.7%, Si: 0.05 to 0.5%, Cu: 0.1 to 0.6%, the balance being Al and inevitable impurities And having a crystal grain structure elongated in the rolling direction in which the average aspect ratio of the crystal grains is 3 or more by observing the upper surface of the central portion in the plate thickness direction, and 0.5 μm or more of this structure The average particle size of the dispersed particles in the observation of the dispersed particles is 5 μm or less, and ΔT indicating the solid-liquid coexistence temperature range of the liquid phase and the solid phase of aluminum is 40 ° C. or less.

  As described above, the DI can body of the bottle can is required to be further thinned mainly for the purpose of reducing the manufacturing cost and reducing the weight. In order to achieve this reduction in thickness, it is necessary to increase the strength of the aluminum alloy cold-rolled sheet as a material so that the buckling strength does not decrease. Moreover, in order to achieve thinning, it is further strongly required that the ear rate during DI molding is low. If the ear rate at the time of DI molding is lowered, the yield at the time of DI molding can be increased, and furthermore, the can body can be prevented from being broken due to the cutting out of the can body.

For this reason, conventionally, in order to highly stabilize the ear rate, it is known to control metallurgical factors of the structure of the aluminum alloy cold-rolled sheet, which is the DI can body material of the bottle can. Typically, control of crystal grain refinement, control of the number and size of compounds such as Mg ₂ Si, suppression of microsegregation of additive elements, control of solid solution amounts of alloy elements such as Mn, control of cube orientation , Etc.

  However, a technique for controlling metallurgical factors of the structure of an aluminum alloy cold-rolled sheet, which is a subject of the present invention, to prevent thermal deformation during coating heat treatment has not been substantially proposed yet. This is because the knowledge of the metallurgical factor of the structure correlating with the thermal deformation during the coating heat treatment has not yet been made. Moreover, thermal deformation during the coating heat treatment cannot be prevented only by controlling various metallurgical factors of the known structure for stabilizing the ear rate.

  On the other hand, in the present invention, among the metallurgical factors of a number of structures, the form of crystal grains and the existence form such as the average particle size of dispersed particles are the strength of the can after heat treatment and the heat treatment during coating heat treatment. It was found to correlate with thermal deformation.

  In addition, these metallurgical factors do not inhibit the stabilization of the ear rate, but on the contrary, it also has the effect of stabilizing the ear rate, thus ensuring the strength of the can after heat treatment and suppressing thermal deformation during the heat treatment of the coating. Above, moldability, such as DI processing, can be secured. In other words, the aluminum alloy cold-rolled sheet can ensure the formability such as DI processing, which is a basic required characteristic, while ensuring the strength of the can after heat treatment and suppressing thermal deformation at the time of coating heat treatment. .

  By controlling the crystal grain of the aluminum alloy cold-rolled sheet not to be equiaxed grains but to a structure with an average aspect ratio of 3 or more and stretched in the rolling direction, the heat treatment can be performed at a higher temperature and a shorter time. The thermal deformation during the coating heat treatment is suppressed, and the can strength after the heat treatment can be secured.

  In order to secure this effect, the present invention further controls the dispersed particles in this structure. That is, the average particle size of the dispersed particles is refined to 5 μm or less, and ΔT indicating the solid-liquid coexistence temperature range of the aluminum liquid phase and the solid phase is set to 40 ° C. or less.

  The larger this solid-liquid coexistence temperature range ΔT, the larger the solid-liquid coexistence temperature range of the dispersed particles such as Al (Fe, Mn) intermetallic compound and the liquid phase of aluminum. That is, it is a component system that is susceptible to fluctuations in the crystallized phase due to casting conditions, and whose form is likely to vary, resulting in a structure in which coarse compound particles are easily generated.

  Conversely, the smaller the solid-liquid coexistence temperature range ΔT, the smaller the solid-liquid coexistence temperature range of the dispersed particles and the aluminum liquid phase, and the generation of the intermetallic compound stable phase and metastable phase. It can be said that the variation is small and the compound particles have a fine structure.

(Al alloy cold-rolled sheet composition)
First, the preferable chemical component composition (unit: mass%) of the Al alloy cold-rolled sheet of the present invention will be described below including the reasons for limiting each element.

  The composition of the aluminum alloy cold-rolled sheet for bottle cans excellent in high temperature characteristics of the present invention is as follows: Mn: 0.7 to 1.5%, Mg: 0.8 to 1.7%, Fe: 0.1 to 0.00. 7%, Si: 0.05 to 0.5%, Cu: 0.1 to 0.6%, with the balance being Al and inevitable impurities.

  However, in the present invention, the component balance of the main constituent elements (Mn, Mg, Fe, Cu, Si) must be designed so that the solid-liquid coexistence temperature range ΔT of aluminum is 40 ° C. or less, as will be described later. There is.

Mn: 0.7 to 1.5%.
Mn is an effective element that contributes to improvement in strength and further contributes to improvement in formability. In particular, in the can body material (cold rolled plate) of the present invention, Mn is extremely important because ironing is performed during DI molding.

  More specifically, Mn forms various Mn-based intermetallic compounds such as an Al—Fe—Mn—Si-based intermetallic compound (α phase). And iron workability can be improved, so that the alpha phase is distributed appropriately. In other words, emulsion type lubricants are usually used in ironing of aluminum plates. However, if the amount of the α phase is small, lubricity is insufficient even when emulsion type lubricants are used. There is a risk of appearance defects such as scuffing and seizure. Accordingly, Mn is an indispensable element for generating an α phase and preventing surface flaws during ironing.

  If the Mn content is too small, the above effect cannot be exhibited. For this reason, the Mn content is 0.7% or more, preferably 0.8% or more, preferably 0.85% or more, and more preferably 0.9% or more.

  On the other hand, when Mn is excessive, the primary crystal giant metal compound of MnAl6 is crystallized and the formability is lowered. Therefore, the upper limit of the Mn content is 1.5%, preferably 1.3%, more preferably 1.1%, and still more preferably 1.0%.

Mg: 0.8-1.7%.
Mg is effective in that the strength can be improved. Furthermore, by including together with Cu described later, the can body material (cold rolled sheet) of the present invention is also called final annealing (also called finish annealing. For example, temperature: about 100 to 150 ° C., time: about 1 to 2 hours. Softening can be suppressed when baking (baking printing) is performed after annealing. That is, when both Mg and Cu are contained, Al—Cu—Mg is precipitated during baking (baking printing), so that softening during baking can be suppressed.

  If the Mg content is too small, the above effects cannot be exhibited. For this reason, the Mg content is 0.8% or more, preferably 0.9% or more, and more preferably 1.0% or more.

  On the other hand, if Mg is excessive, work hardening is likely to occur, and formability is reduced. For this reason, the upper limit of the Mg content is 1.7%, preferably 1.6%, and more preferably 1.35%.

  Mg also affects the amount of precipitated Mn and the amount of solid solution. That is, since the precipitation amount of the Al—Fe—Mn—Si intermetallic compound (α phase) is suppressed as the amount of Mg increases, the Mn solid solution amount tends to increase. For this reason, it is preferable to determine the Mg content in relation to the Mn solid solution amount.

Fe: 0.1 to 0.7%.
Fe has an effect of refining crystal grains, and further generates the above-described Al—Fe—Mn—Si intermetallic compound (α phase), which contributes to improvement of moldability. Fe is also useful in that it promotes Mn crystallization and precipitation, and controls the amount of Mn solid solution in the aluminum matrix and the dispersion state of Mn-based intermetallic compounds (such as the α phase). On the other hand, if Fe is excessive in the presence of Mn, a large primary intermetallic compound is likely to be generated, which may impair the moldability.

  Therefore, the content of Fe can be set according to the content of Mn, and the preferred mass ratio (Fe / Mn) between Fe and Mn is, for example, in the range of 0.1 to 0.7, preferably 0.2. It is the range of -0.6, More preferably, it is the range of 0.3-0.5.

  When the Mn content is in the above range, the lower limit content of Fe is 0.1% or more, preferably 0.2% or more, and more preferably 0.3% or more. Further, the upper limit content of Fe is 0.7% or less, preferably 0.6% or less, and more preferably 0.5% or less.

Si: 0.05 to 0.5%.
Si is an element useful for generating an Al—Fe—Mn—Si intermetallic compound (α phase) and controlling the dispersion state of the Mn intermetallic compound. As the α phase is appropriately distributed, the moldability can be improved.

  Therefore, the Si content is 0.05% or more, preferably 0.1% or more, and more preferably 0.2% or more. On the other hand, when Si is excessive, the material becomes too hard due to age hardening, and the formability deteriorates. For this reason, the upper limit of the Si content is 0.5%, preferably 0.45%, and more preferably 0.4%.

Cu: 0.1 to 0.6%.
When Cu is baked (baked printing) at the time of making a cold-rolled sheet, Al—Cu—Mg is precipitated, and by containing it together with Mg, softening can be suppressed. For this reason, the lower limit of Cu content is 0.1% or more, preferably 0.15% or more, and more preferably 0.2% or more. On the other hand, if Cu is excessive, age hardening can be easily obtained, but it becomes too hard, so that formability is lowered and corrosion resistance is also deteriorated. For this reason, the upper limit of Cu content is 0.6%, preferably 0.5%, and more preferably 0.35%.

  In addition to Cu, examples of the strength improving element having the same effect include Cr and Zn. In this respect, in addition to Cu, one or two of Cr and Zn can be selectively contained.

Cr: 0.001 to 0.3%.
At this time, the content of Cr is set to 0.001% or more, preferably 0.002% or more for exhibiting the effect of improving the strength. On the other hand, when Cr becomes excessive, a giant crystallized substance is generated and formability is lowered. For this reason, the upper limit of the Cr content is 0.3%, preferably 0.25%.

Zn: 0.05-1.0%.
Further, when Zn is contained, the strength can be improved by aging precipitation of Al—Mg—Zn-based particles. In order to exhibit this effect, the Zn content is 0.05% or more, preferably 0.06% or more. On the other hand, when Zn becomes excessive, corrosion resistance will fall. For this reason, the upper limit of Zn content is 0.5%, preferably 0.45%.

Ti: 0.005 to 0.2%.
Ti is a grain refinement element. When it is desired to exert this effect, it is selectively contained. In this case, the Ti content is 0.005% or more, preferably 0.01% or more, and more preferably 0.015% or more. In addition, when Ti becomes excess, a huge Al-Ti type intermetallic compound will crystallize and will inhibit a moldability. Therefore, the upper limit of the Ti content is 0.2%, preferably 0.1%, more preferably 0.05%.

  Ti may be contained alone, but may be contained together with a small amount of B. When used in combination with B, the effect of crystal grain refinement is further improved. For this reason, the B content when selectively contained is 0.0001% or more, preferably 0.0005% or more, and more preferably 0.0008% or more. On the other hand, when B is excessive, Ti-B-based coarse particles are generated and formability is lowered. Therefore, the upper limit of the B content is 0.05%, preferably 0.01%, and more preferably 0.005%.

  Other than the elements described above are unavoidable impurities, and in order not to inhibit the plate properties, the content should be basically low, but as long as the plate properties are not inhibited, it was described in JIS standards, Inclusion of up to about the upper limit of each element of 3000 series aluminum alloy is allowed.

(Al alloy cold rolled sheet structure)
Next, the Al alloy cold-rolled sheet structure of the present invention will be described below.

(Average aspect ratio of crystal grains)
As described above, the temperature of the aluminum alloy cold-rolled sheet was shortened by increasing the average aspect ratio to 3 or more in the rolling direction, instead of normal equiaxed grains. Thermal deformation at the time of coating heat treatment against high-speed heat treatment is suppressed, and can strength after heat treatment can be secured.

  That is, by making the crystal grains of the aluminum alloy cold-rolled sheet into elongated grains in the rolling direction, ironing workability is provided, and formability such as DI processing is secured, and then the above-mentioned components defined in the present invention The strength of the can after heat treatment can be secured under the composition and the solid solution and precipitation state structure described later. As a result, thermal deformation during the coating heat treatment is also suppressed.

  When the average aspect ratio of the crystal grains is less than 3, the difference from the normal equiaxed grains is not so large and the above effect is insufficient, so that it is impossible to achieve thermal deformation suppression during coating heat treatment and securing of can strength after heat treatment. In this respect, the elongation of the crystal grains in the rolling direction is better, and more preferably, the average aspect ratio of the crystal grains is 3.1 or more.

  The aspect ratio of the crystal grains is determined by the crystal grain structure of the hot-rolled sheet, the cold rolling rate, and the cold rolling temperature in the process without intermediate annealing. In this respect, the upper limit of the average aspect ratio of the crystal grains is determined from the capability limit of the manufacturing process for forming elongated grains such as hot rolling and cold rolling, but the level is about 6.

(Average aspect ratio measurement method)
The average aspect ratio of the crystal grains is measured by observing the upper surface (polarized light observation) at the center in the thickness direction. The central part in the plate thickness direction of the plate after the tempering treatment (before bottle can molding) and the upper surface of the rolled surface are subjected to polarization observation after mechanical polishing, electrolytic polishing, and anodizing treatment with Barker liquid.

  When the central portion in the plate thickness direction of the plate is observed from the upper surface and the crystal grain structure is observed with polarized light using an optical microscope, the difference in black and white appears due to the difference in crystal orientation. In this observation, the maximum length in the rolling direction and the maximum length in the plate width direction of each crystal grain are measured for crystal grains in the field of view where the outline can be clearly observed. Then, the (maximum length in the rolling direction) / (maximum length in the sheet width direction) of each individual crystal grain is calculated as the aspect ratio. The average aspect ratio of the crystal grains is obtained from the average value of the aspect ratios of the crystal grains with 100 crystal grains to be measured by observation with an optical microscope of × 100 magnification.

  Furthermore, in the present invention, the point of controlling dispersed particles in the aluminum alloy cold-rolled sheet structure will be described. As described above, in order to ensure the effect of the elongated crystal grains, the present invention further controls the average particle size of the dispersed particles in this structure. That is, in observation of particles of 0.5 μm or more, the average particle size of the dispersed particles is refined to 5 μm or less, and ΔT indicating the solid-liquid coexistence temperature range of the aluminum liquid phase and the solid phase is set to 40 ° C. or less.

(Average particle size of dispersed particles)
The dispersed particles in the aluminum alloy cold-rolled sheet structure are various intermetallic compounds such as the Al—Fe—Mn—Si intermetallic compound (α phase), and the average particle size of the dispersed particles is preferably as fine as possible.

  When the average particle size of the dispersed particles exceeds 5 μm and the proportion of coarse dispersed particles (precipitated compounds) increases, it tends to become the core of recovery and recrystallization, and the softening at high temperature increases, and elliptical deformation or It tends to cause a decrease in strength. For this reason, the effect of the elongated crystal grains is offset.

  Therefore, in the present invention, the average particle size of the dispersed particles when observing particles of 0.5 μm or more is set to 5 μm or less, preferably 4.5 μm or less.

  Here, the dispersed particles to be analyzed and measured have a size (center of gravity diameter) of 0.5 μm or more. This is because the presence of particles of 0.5 μm or more greatly affects the softening resistance as described above, and particles of less than 0.5 μm have a small influence. In addition, small dispersed particles of less than 0.5 μm are difficult to observe and the measurement variation due to the main measurement increases, so they are excluded from the provisions of the present invention and the measurement target.

(Measurement of average particle size)
The average particle size of the dispersed particles in the observation of particles of 0.5 μm or more is measured with a scanning electron microscope (SEM) of a plate structure. More specifically, the test material at the center of the plate thickness and the upper surface of the rolling surface is mirror-polished, and the structure of the polished surface is changed to 500 times or 1000 times SEM (for example, Hitachi, Ltd .: S4500 type field emission scanning electron microscope FE). -The tissue of each 10 visual fields of about 200 micrometers x about 150 micrometers size is observed by SEM: Field Emissionn Scanning Electron Microscopy.

  At this time, in order to clearly observe the dispersed particle phase (intermetallic compound phase), observation is performed by observing a reflected electron image. The black image is Al, and the dispersed particle phase becomes clear with different contrasts. These dispersed particles are traced, and the average size (average value of the center of gravity diameter) of each dispersed particle is obtained by image analysis using Image-ProPlus manufactured by MEDIACYBERNETICS as image analysis software. The number of dispersed particles measured was 200 or more in total in the above-mentioned 10-field structure observation, and the average value was calculated.

(Solid-liquid coexistence temperature range △ T)
FIG. 1 schematically shows a phase diagram of an Al—Mg—Mn alloy, which is a liquid phase line, a solidus line of aluminum, and crystals of AlMn-based and Al (Fe, Mn) -based compounds that are main crystallization products. The relationship between the output temperatures is schematically shown. In FIG. 1, the temperature range (temperature difference) between the Al liquidus and the solidus is the solid-liquid coexistence temperature range ΔT referred to in the present invention.

  A component system having a wider (longer) ΔT tends to have a larger variation in the generation of a stable phase and a metastable phase of an intermetallic compound depending on conditions in the solidification / cooling process during casting. In this case, the crystallized product is in a structure state in which elements other than the constituent elements of the intermetallic compound are forcibly dissolved. For this reason, softening at a high temperature increases in the state of the bottle can body, and the high-temperature heat treatment tends to cause elliptical deformation and strength reduction. Therefore, similarly to the increase in the average particle size of the dispersed particles, the effect of the elongated crystal grains is offset.

  In addition, a component system having a wider (large) ΔT is likely to have a coarse distribution of compound particles because an intermetallic compound grows more rapidly in the liquid phase. As a result, it becomes impossible to reduce the average particle size of the prescribed dispersed particles. For this reason, as explained in the part of the dispersed particles, coarse particles serve as nuclei for recovery and recrystallization, and the softening of the bottle can body is increased by the heat treatment, which tends to cause elliptical deformation. In addition, the presence of coarse compounds tends to cause defects on the can surface and pinholes.

  As described above, strictly speaking, there is a method of defining the range of the crystallization temperature of the Al—Mn intermetallic compound and the solid phase temperature of Al as ΔT, but in the Al alloy system of the present invention, Al Since the melting point of the alloy system and the crystallization temperature of the Al—Mn compound only change by about 4 to 7 ° C., there is a situation that cannot be an accurate index. For this reason, in the measurement evaluation, there was a sufficient difference (margin) in ΔT, and the range (temperature difference) between the Al liquid phase temperature and the solid phase temperature, which can be an accurate index, was specified.

  The narrower (smaller) this ΔT (solid-liquid coexisting temperature range) is, the smaller the solid-liquid coexisting temperature range of the dispersed particles and the aluminum liquid phase, and the generation of the stable phase and metastable phase of the intermetallic compound. The variation in the particle size is small, and the compound particles have a fine structure. For this reason, the softening resistance at high temperature is increased in the state of the bottle can body, and elliptical deformation and strength reduction can be suppressed by high-temperature heat treatment.

  As will be described later, as ΔT increases, the average particle size of the dispersed particles also increases. In particular, when ΔT exceeds 40 ° C., the tendency of the average particle size of the dispersed particles to become large increases. Therefore, ΔT is preferably as small as 40 ° C. or less, more preferably 38 ° C. or less, still more preferably 36 ° C. or less, and still more preferably 34 ° C. or less.

(Calculation of solid-liquid coexistence temperature range ΔT)
ΔT is calculated by measuring the melting point and the solid phase temperature of the target aluminum alloy cold-rolled sheet (test piece) by differential thermal analysis, thereby calculating the temperature range ΔT in which the liquid phase of aluminum coexists. calculate. Within the range of the aluminum alloy system of the present invention, the melting point is around 645 ° C. to 660 ° C., and the change detected around 600 ° C. to 630 ° C. is the solid phase temperature.

For example, the test apparatus uses TG / DTA (TGD7000) manufactured by ULVAC-RIKO, and the test conditions are as follows.
Heat pattern: RT to 700 ° C. to RT: 10 ° C./min Atmosphere: Ar (100 ml / min)
Sample weight: about 500mg
Reference: Alumina powder Sample container: Alumina (macro type 8 × 10mm)

  In addition to the differential thermal analysis, ΔT may be obtained from the calculated state diagram, but the differential thermal analysis is more accurate. However, ΔT based on thermodynamic equilibrium diagram calculation is useful when an alloy is designed so that ΔT is 40 ° C. or less in advance. FIG. 2 illustrates ΔT in the calculation state diagram of Invention Example C alloy in Example Table 1 described later.

(Control of ΔT)
The control of ΔT depends on the manufacturing conditions described later, but basically the main constituent elements (Mn, Mg, Fe, etc.) in the present invention so that the solid-liquid coexistence temperature range ΔT of aluminum is 40 ° C. or less. This is done by designing each component balance of Cu and Si).
In addition, as a general tendency of each alloy element (component), Mn, Fe, etc. have a large ΔT as the content increases or decreases from the median of the specified range of content. Become. In addition, Mg, Cu, Si, etc. tend to have a large ΔT due to an increase in content, and generally within a content rule of the present invention, ΔT becomes smaller when these alloy elements are smaller.

  However, as an aluminum alloy cold-rolled sheet for bottle cans, in order to satisfy the required strength, formability, etc., it is difficult to simply reduce the content of each of the above-mentioned main constituent elements.

  Furthermore, the crystallization temperature of the Al (Fe, Mn) -based intermetallic compound varies depending on the multicomponent component balance including the other selective additive elements and impurity elements. Therefore, ΔT also varies greatly depending on the other selective additive elements and impurity elements.

  In particular, as in recent years, the ratio of scrap cans, etc. to the melting raw materials used in cans has been increasing year by year compared to bare metal, which is unavoidably mixed in other than the basic component elements. Impurity elements are increasing. These inevitable impurity elements are Zr, Bi, Sn, Ga, V, Co, Ni, Ca, Mo, Be, Pb, W, and the like. The total content (total amount) of these elements has been 0.01% or less in the past, but as the scrap content increases in recent years, 0.015% or more, 0.02% or more, and in some cases 0.05% or 0.1% or more is inevitably mixed.

  Therefore, even if the amount of each of the main constituent elements and the amount of selective additive elements are the same, ΔT also changes greatly due to this influence when the amount of these impurity elements exceeds 0.01%. To do. In addition, the degree of influence varies depending on the type of alloying element, and in the case of a multi-component system, the solid-liquid coexistence temperature range varies depending on the interaction of each component. For this reason, when the amount of these inevitable impurity elements becomes high, due to the complexity of the component system, solid-liquid coexistence can be achieved only with a simple content range and basic component balance (Mg / Mn ratio, etc.). It is extremely difficult to design a component for making the temperature range ΔT an optimum range.

  Therefore, when controlling ΔT, first, an aluminum alloy for bottle cans is designed by designing each component balance of main constituent elements (Mn, Mg, Fe, Cu, Si) and selective additive elements in the present invention. As a cold-rolled sheet, an alloy design that satisfies the required strength, formability, etc. is performed.

  Then, as a calculation method for the liquid phase temperature and the solid phase temperature, etc., the thermodynamic equilibrium state diagram calculation as shown in FIG. 1 is performed so that the solid-liquid coexistence temperature range ΔT of aluminum is 40 ° C. or less. After actually modifying the alloy design, if it is actually manufactured on a trial basis, the solid-liquid coexistence temperature range ΔT of aluminum will be 40 ° C. or less under the mass production conditions described later. It is necessary to verify in advance.

(Production method)
The Al alloy cold-rolled sheet of the present invention can be manufactured without greatly changing the conventional steps of soaking, hot rolling and cold rolling. However, in order to secure the structure defined in the present invention and not impair the basic material characteristics (ear ratio, strength), moldability, and ironing processability for bottle can molding, the above individual steps Must be limited to the optimum condition range, and these steps must be combined.

(Soaking conditions)
The soaking temperature is 550 to 650 ° C. If the soaking temperature is too low, it takes too much time to homogenize and the productivity is lowered. If the soaking temperature is too high, the ingot surface is swollen, so the soaking temperature is set in the above range. Preferable soaking temperatures are 580 ° C. or higher (particularly 590 ° C. or higher) and 615 ° C. or lower (particularly 610 ° C. or lower).

  The soaking time (homogenization time) is preferably as short as possible so that the ingot can be homogenized, for example, 12 hours or less, preferably 6 hours or less, but when the soaking temperature is 550 ° C. or more. Soaking time needs 6 hours or more, soaking temperature is 580 ° C or more, soaking time is 5 hours or more, soaking temperature is 590 ° C or more, soaking time Requires more than 4 hours.

  The soaking process may be performed in a plurality of stages. In that case, the temperature increase rate of the soaking process, the temperature of the soaking process (homogenization temperature), and the cooling rate may be controlled in any stage, and may be performed in all stages. It is desirable to do this at the second stage.

  When the temperature of the first soaking is set in the above range, the temperature of the soaking after the second is often lower than the soaking temperature of the first. The temperature of the soaking process after the second time is, for example, about 10 to 100 ° C., preferably about 50 to 100 ° C. lower than the soaking temperature of the first time.

(Hot rolling start condition)
The ingot after the soaking process is handled may be cooled and reheated before hot rough rolling, or may be hot rough rolled as it is without being excessively cooled. In the case of hot rough rolling as it is without excessive cooling, the average particle size of the dispersed particles in the observation of the dispersed particles of 0.5 μm or more in the final plate structure is 5 μm or less, and further the dispersed particle solid phase and aluminum in the structure ΔT, which indicates the solid-liquid coexistence temperature range with the liquid phase, is easily set to 40 ° C. or less. In addition, the self-heating of the ingot after soaking can be used, and not only can the production time and heat energy be saved, but also the number density of precipitates of alloy elements can be reduced, and the ear rate can be reduced.

  In addition, when the ingot is once cooled and reheated, it is desirable to rapidly heat at a rate of 30 ° C./hour or more. By this rapid heating, the average particle size of the dispersed particles in observing dispersed particles of 0.5 μm or more in the final plate structure is set to 5 μm or less, and the solid-liquid coexistence temperature range between the dispersed particle solid phase and the aluminum liquid phase in the structure It is easy to make ΔT indicating 40 ° C. or less. Moreover, it can prevent that the number density of the precipitate of an alloy element becomes high too much, and can reduce an ear rate.

(Hot rough rolling conditions)
When hot rolling is divided into rough rolling and finish rolling and continuously carried out, if the end temperature of hot rough rolling becomes too low, the rolling temperature becomes lower in the next hot finishing rolling and the edge Cracks are likely to occur. In addition, if the end temperature of hot rough rolling is too low, the self-heating necessary for recrystallization after finish rolling tends to be insufficient, so that the crystal grain size becomes too small. For this reason, it is preferable that the completion | finish temperature of hot rough rolling shall be 420 degreeC or more. Further preferable end temperatures are 430 ° C. or higher (particularly 440 ° C. or higher) and 470 ° C. or lower (particularly 460 ° C. or lower).

  In order to keep the end temperature of this hot rough rolling at about 420 to 480 ° C., the start temperature of hot rough rolling is, for example, about 490 to 550 ° C., preferably about 495 to 540 ° C., more preferably 500. It is desirable to keep it at about ˜530 ° C. If the starting temperature is set to 550 ° C. or lower, surface oxidation of the hot rolled sheet can be prevented. Furthermore, since the coarsening of recrystallized grains can be prevented, the moldability can be further improved.

  It is desirable that the aluminum alloy sheet that has been subjected to hot rough rolling is subjected to hot finish rolling quickly, such as continuously. By rapidly performing hot finish rolling, it is possible to prevent the distortion accumulated in the hot rough rolling from recovering, and it is possible to increase the strength of the cold rolled sheet obtained thereafter. The aluminum alloy sheet that has been subjected to the hot rough rolling is preferably hot finish rolled, for example, within 5 minutes, preferably within 3 minutes.

(Hot finish rolling conditions)
The finishing temperature of hot finish rolling is preferably 310 to 350 ° C. The hot finish rolling step is a step of finishing the plate to a predetermined size. Since the structure after the end of rolling becomes a recrystallized structure due to self-heating, the end temperature affects the recrystallized structure. By setting the finish temperature of hot finish rolling to 310 ° C. or higher, the final plate structure can be easily made into a structure extended in the extending direction with an average aspect ratio of 3 or more, along with the subsequent cold rolling conditions. When the finish temperature of hot finish rolling is less than 310 ° C., even if the cold rolling rate of the subsequent cold rolling is increased, the above-described structure of the present invention is hardly obtained.

  On the other hand, when the temperature exceeds 350 ° C., the final plate structure becomes a structure elongated in the rolling direction with an average aspect ratio of 3 or more, and coarse Mg 2 Si or the like is precipitated, and the dispersed particles in the observation of dispersed particles of 0.5 μm or more are observed. The average particle size is less than 5 μm. Therefore, the lower limit of the finish temperature of hot finish rolling is 310 ° C or higher, preferably 320 ° C or higher. The upper limit is 350 ° C. or lower, preferably 340 ° C. or lower.

(Hot finish rolling mill type)
As the hot finish rolling mill, a tandem hot rolling mill having three or more stands is used. By setting the number of stands to 3 or more, the rolling rate per stand can be reduced, and strain can be accumulated while maintaining the surface properties of the hot-rolled plate. Therefore, the strength of the cold-rolled plate and its DI molded body can be reduced. It can be further increased.

(Total rolling ratio of hot finish rolling)
The total rolling rate of hot finish rolling is preferably 80% or more. By making the total rolling rate 80% or more, in combination with the cold rolling described later, the final plate structure is a structure in which the average aspect ratio is elongated in the rolling direction of 3 or more, and the dispersion is 0.5 μm or more. The average particle size of dispersed particles in particle observation is easily set to 5 μm or less. Moreover, the intensity | strength of a cold-rolled board and its DI molded object can be raised.

(Hot rolled sheet thickness)
Hot (Finish) The thickness of the alloy plate after rolling is preferably about 1.8 to 3 mm. By setting the plate thickness to 1.8 mm or more, it is possible to prevent the surface properties (seizure, rough skin, etc.) and the plate thickness profile of the hot rolled plate from deteriorating. On the other hand, by setting the plate thickness to 3 mm or less, it is possible to prevent the rolling rate from becoming too high when manufacturing a cold rolled plate (usually, plate thickness: about 0.28 to 0.35 mm). Can reduce the ear rate.

(Cold rolling)
In the cold rolling step, it is desirable to perform so-called direct through with a plurality of passes without intermediate annealing, so that the total rolling ratio is 77 to 90%. By making the total rolling rate 77% or more without intermediate annealing, the final plate structure is a structure in which the average aspect ratio of the crystal grains is elongated in the rolling direction of 3 or more, and 0.5 μm or more. The average particle size of the dispersed particles in the dispersed particle observation can be 5 μm or less. In addition, the pressure resistance of the can can be further increased. When intermediate annealing is performed or when the total rolling reduction is low, it tends to become equiaxed grains and hardly becomes elongated grains.

  On the other hand, if the rolling rate exceeds 90%, the average aspect ratio of the crystal grains can be increased, but the positive ears during DI molding become too large, and the strength becomes too strong. There is a high possibility of cracking.

  The plate thickness after cold rolling is about 0.28 to 0.35 mm in terms of forming into a bottle can.

  In the cold rolling process, it is desirable to use a tandem rolling mill in which two or more rolling stands are arranged in series. By using such a tandem rolling mill, even with the same total cold rolling rate as compared with a single rolling mill that has a single rolling stand and repeatedly performs passes (passing plates) to cold roll to a predetermined plate thickness. The number of passes (passing plates) can be reduced, and the rolling rate in one pass can be increased.

  Therefore, it becomes easy to obtain a structure obtained by extending the final plate structure in the rolling direction in which the average aspect ratio of crystal grains is 3 or more.

  Further, as in the conventional case, after cold rolling using a single rolling mill, it is possible to generate subgrains by causing recovery at a lower temperature and continuously compared to the case where finish annealing is performed. . However, the rolling mill is not limited to a tandem rolling mill as long as it can recover sufficiently by cold rolling and sufficiently generate subgrains.

  However, in cold rolling with a tandem rolling mill, the rolling rate in one pass plate increases, so the amount of heat generated in one pass plate increases. When this calorific value becomes too high, there is a possibility that the average particle size of the dispersed particles in observing dispersed particles of 0.5 μm or more becomes coarse.

  For this reason, in cold rolling with a tandem rolling mill, when the temperature of the aluminum plate immediately after the cold rolling in the cold rolling process rises most, the aluminum plate is forcibly cooled, and the temperature of the aluminum plate after cold rolling It is preferable to prevent the temperature from rising to a temperature exceeding 200 ° C.

  As a means for forcibly cooling the aluminum plate during such cold rolling, the usual aqueous rolling-free rolling oil is changed to an emulsion type such as a water-soluble oil or a water-soluble lubricant, and this emulsion aqueous solution is used. It is preferable to enhance the cooling performance without reducing the lubrication performance.

  After cold rolling, if necessary, finish annealing (final annealing) may be performed at a temperature lower than the recrystallization temperature. When finish annealing is performed, the processed structure is recovered, and DI moldability and can bottom moldability are improved. The finish annealing temperature is preferably about 100 to 150 ° C., and more preferably about 115 to 150 ° C., for example. By setting the temperature to 100 ° C. or higher, the processed structure can be sufficiently recovered. On the other hand, by setting the temperature to 150 ° C. or less, excessive precipitation of solid solution elements can be prevented, and DI moldability and flange moldability can be further improved.

  The finish annealing time is preferably 4 hours or less (particularly about 1 to 3 hours). By avoiding annealing too long, excessive precipitation of solid solution elements can be prevented, and DI moldability can be further enhanced.

  However, in the cold rolling by the tandem rolling mill described above, finish annealing is basically unnecessary because it is possible to generate recovery continuously and generate subgrains at a lower temperature.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and both are included in the technical scope of the present invention.

  In addition to aluminum ingots, can scraps and other materials are used as melting raw materials, and molten aluminum alloys having the composition of components A to N shown in Table 1 below are melted and cast with a plate thickness of 600 mm and a width of 2100 mm by the DC casting method. A lump was produced. In Table 1, the element content indicated by “−” is below the detection limit.

  In this ingot, as shown in Table 1, inventive and comparative examples, the total amount of other elements is inevitable impurity elements, Zr, Bi, Sn, Ga, V, Co, Ni, Ca, Mo, Be. , Pb and W are contained in an amount of 0.03% or more in terms of the total content of these elements.

  For this reason, first, strength and formability required for aluminum alloy cold-rolled plates for bottle cans by designing each component balance of main constituent elements (Mn, Mg, Fe, Cu, Si) and selective additive elements An alloy design satisfying these requirements was conducted. Then, in order to control ΔT, the thermodynamic equilibrium diagram of each example was calculated, the solid-liquid coexisting temperature range ΔT of aluminum was calculated, and the alloy was designed or modified. And it was set as the actual aluminum alloy component composition of A-N shown in the said Table 1.

  Ingots having these component compositions were soaked according to the conditions shown in Table 2. The soaking process was two soaking processes in which after the first soaking process, after cooling to room temperature at the cooling rate shown in Table 2, reheating and performing the second soaking process.

Here, the rate of temperature increase under the first soaking condition substantially refers to the rate of temperature increase from 300 ° C. to the maximum temperature that affects the characteristics. The cooling rate under the first soaking condition substantially refers to the cooling rate from “maximum temperature to 300 ° C., which affects the characteristics.
After this soaking, hot reverse rolling is performed using a reverse hot roughing mill with one stand, and a hot finish rolling mill with a tandem hot rolling mill with four stands. Rolled. At that time, the time for starting hot finish rolling after completion of hot rough rolling was set to be within 3 minutes. Then, an aluminum alloy hot-rolled sheet having a thickness of 2.5 mm after hot finish rolling was manufactured in common.

  The obtained hot-rolled sheet is cold-rolled by a single pass through a two-stage tandem rolling mill without intermediate annealing, and in common a bottle can with a final sheet thickness of 0.3 mm A plate material for a trunk (cold rolled plate) was produced. At this time, in cold rolling with a tandem rolling mill, the aluminum plate was forcibly cooled using an aqueous emulsion solution so that the temperature of the aluminum plate immediately after cold rolling did not rise to a temperature exceeding 250 ° C. Finish annealing (final annealing) after this cold rolling was not performed.

  In addition, only the comparative example 10 has the same total cold rolling ratio, but for comparison, the roll stand is passed twice with a single rolling mill with one stage, and between the first and second passes, Intermediate annealing at 150 ° C. for 1 hour was performed.

  Test specimens were taken from the plate material (coil) for bottle cans after cold rolling, and the average aspect ratio of crystal grains and the average size of intermetallic compounds with a size of 0.5 μm or more were measured as described above as the specimen structure. (Plate thickness center part), solid-liquid coexistence temperature range (DELTA) T was investigated by the differential thermal analysis. These results are shown in Table 3.

  Further, as the high temperature characteristics of the test piece, the hardness and 0.2% proof stress of the surface of the test piece at room temperature, and the hardness and 0.2% proof stress of the surface when the test piece is heat treated at 290 ° C. for 20 seconds, respectively. Then, the hardness change (hardness reduction amount) ΔHv (Hv) of the test piece surface before and after the heat treatment was obtained. Furthermore, the amount of elliptic deformation after baking of the can body after molding was measured. These results are also shown in Table 3.

(0.2% proof stress measurement)
A tensile test for measuring 0.2% proof stress was performed according to JIS Z 2201, and the shape of the test piece was a JIS No. 5 test piece so that the longitudinal direction of the test piece coincided with the rolling direction. The crosshead speed was 5 mm / min, and the test piece was run at a constant speed until the test piece broke.

(Hardness measurement)
The hardness of the cold-rolled sheet sample was measured with a micro Vickers hardness tester by applying a load of 100 g at four locations, and the hardness was an average value thereof.

(Ellipse deformation evaluation)
As will be described later, the elliptical deformation was evaluated by baking the bottle can body formed by DI molding of the above-mentioned plate material for the bottle can body after being washed and baked under the condition that the body temperature of the can reaches 300 ° C. in 30 seconds. The degree of deformation was investigated. In the ellipse deformation degree investigation, the diameter of the mouth portion of the bottle can body is sequentially investigated in the circumferential direction, and the amount obtained by subtracting the minimum diameter from the maximum diameter is obtained as the amount of ellipse deformation (mm). The average value of 10 cans was evaluated. In addition, this ellipse deformation amount evaluated that the ellipse deformation property was 4 mm or less. When this elliptical deformation exceeds 4 mm, in the can manufacturing process, defects such as overturning and jamming occur in the transport process and necking process in the subsequent process, making continuous and efficient manufacture of the can difficult.

  Furthermore, as a formability that the bottle can body plate material should basically satisfy, the ear rate and DI (ironing) formability (number of cracks generated during forming) were measured and evaluated. These results are also shown in Table 3.

(Ear rate)
The ear rate was obtained by collecting a blank from the plate material for the bottle can body and lubricating oil [D. A. After applying Naruco 147] manufactured by Stuart, a 40% deep-drawing test was conducted by using an Erichsen tester, which was then formed into a cup shape and investigated. The test conditions were as follows: blank diameter = 66.7 mm, punch diameter = 40 mm, die side shoulder R = 2.0 mm, punch shoulder R = 3.0 mm, wrinkle holding pressure = 400 kgf.

  8 directions of the opening peripheral edge of the cup thus obtained (0 ° direction, 45 ° direction, 90 ° direction, 135 ° direction, 180 ° direction, 225 ° direction, 270 ° direction, assuming the rolling direction as 0 °, And 315 ° direction) were measured, and the average ear rate was calculated.

A method of calculating the average ear rate will be described with reference to FIG. FIG. 3 is a developed view of a cup obtained by DI molding a bottle can body plate. In this development view, the height of the ears (T1, T2, T3, T4; referred to as minus ears) measured in the directions of 0 °, 90 °, 180 °, and 270 °, where the rolling direction is 0 °, is measured. Measure the height of the ears (Y1, Y2, Y3, Y4; referred to as plus ears) occurring in the directions of °, 135 °, 225 °, and 315 °. Each of the heights Y1 to Y4 and T1 to T4 is a height from the bottom of the cup. Then, the average ear rate is calculated from each measured value based on the following equation.
Average Ear Ratio (%) = [{(Y1 + Y2 + Y3 + Y4) − (T1 + T2 + T3 + T4)} / {1/2 × (Y1 + Y2 + Y3 + Y4 + T1 + T2 + T3 + T4)}] × 100

  In the cold-rolled sheet of the present invention, when the average ear rate is close to 0, four plus ears (Y1 to Y4) and two minus ears in the 90 ° direction and the 270 ° direction (T2 in FIG. 3). , T4) is suppressed, but it is difficult to suppress the development of the two minus ears (T1, T3 in FIG. 3) in the 0 ° direction and the 180 ° direction. When the absolute value of the average ear rate is simply reduced, for example, when the average ear rate is -2 to 2% (2% or less in absolute value), the average ear rate is -2 to less than 0%. However, since the suppression of the minus ears (T1, T3 in FIG. 3) is insufficient, the wrinkle pressing pressure of the drawing molding is concentrated on these two minus ears (T1, T3 in FIG. 3), When the average ear rate is 0% to 2% (positive side), the remaining two negative ears (T1 and T3 in FIG. 3) are also sufficient. Therefore, it is possible to prevent the can body from being broken due to the cutting of the ears. In the present invention, the allowable range is + 0% to + 3.5%.

(DI moldability)
A blank with a diameter of 156 mm is punched from the plate material for the bottle can body (plate thickness is 0.3 mm), a cup with a cup diameter of 92 mm is formed, redrawing, ironing, and trimming, and a can-making speed of 300 cans / minute A DI can barrel (inner diameter 66 mmφ, height 170 mm, side wall plate thickness 103 μm, side wall tip plate thickness 165 μm, final third ironing rate 40%) was manufactured at a speed of The number of occurrences of body cracks per 50,000 cans was determined, and the DI moldability was evaluated. Those that did not exist at all ◎ (very good), those that were 1 can or less ○ (good), those that were 2 to 4 cans △ (generally good), those that exceeded 5 cans × ( Bad).

  As is apparent from Table 3, Invention Examples 1 to 6 have the composition of the present invention, and the average aspect ratio of crystal grains is 3 or more, and the average particle size of dispersed particles of 0.5 μm or more is 5 μm or less. It has a structure in which ΔT indicating a solid-liquid coexistence temperature range of an aluminum liquid phase and a solid phase is 40 ° C. or less.

  As a result, as is apparent from Table 3, Invention Examples 1 to 6 have a hardness change ΔHv of 30 Hv or less after heat treatment (after baking hard) at 290 ° C. × 20 seconds and 0.2% proof stress. It is 270 MPa or more, and there is little decrease in hardness and strength, and excellent high temperature characteristics.

  Further, Invention Examples 1 to 6 are excellent in the ear rate and DI moldability. Therefore, it turns out that the improvement of the high temperature characteristic in this invention has not inhibited the moldability which the board | plate material for bottle can bodies should satisfy | fill fundamentally.

In contrast, Comparative Example 10, although the present invention the component composition, for the rolling condition is out of the preferred conditions, the average aspect ratio of crystal grains is in the tissue outside the provisions of the present invention. As a result, the hardness and strength are greatly reduced and the high temperature characteristics are inferior to those of the above invention examples.

The ratio Comparative Examples 10 were subjected to intermediate annealing in the course of cold rolling.

  Comparative Examples 11 to 20 are manufactured under preferable manufacturing conditions. However, the alloy composition deviates from the composition of the present invention. For this reason, any one of the average aspect ratio of crystal grains, the average particle size of dispersed particles of 0.5 μm or more, and ΔT is a structure that does not fall within the scope of the present invention. As a result, the hardness and strength are greatly reduced and the high temperature characteristics are inferior to those of the above invention examples. Moreover, the moldability is also low.

  From the above results, the critical significance of each requirement of the present invention can be understood.

  As described above, the present invention prevents thermal deformation during coating heat treatment even after high-speed heat treatment with higher temperature and shorter time on the premise of ensuring moldability such as DI processing, and so on. It is possible to provide an aluminum alloy cold-rolled sheet for a bottle can excellent in high-temperature characteristics, which can secure a high strength of the can and obtain a bottle can having a high roundness. Therefore, even if it is heat-treated with a thin wall such as a bottle can, it is demanded that there is no strength reduction or deformation, and it is suitable for severe demand characteristic applications where the moldability needs to be maintained as it is.

FIG. 3 is a schematic state diagram showing ΔT defined in the present invention. It is a calculation state diagram for calculating | requiring (DELTA) T by calculation. It is an expanded view of the cup obtained by carrying out DI shaping | molding of a board | plate material.

Claims (4)

  Mn: 0.7 to 1.5% (mass%, the same applies hereinafter), Mg: 0.8 to 1.7%, Fe: 0.1 to 0.7%, Si: 0.05 to 0.5% Cu: 0.1 to 0.6%, with the balance being composed of Al and unavoidable impurities, and the average aspect ratio of the crystal grains by observing the crystal grain structure at the top surface in the central part in the plate thickness direction The structure is a structure elongated in the rolling direction with a ratio of 3 or more. The average particle size of the dispersed particles in the observation of dispersed particles of 0.5 μm or more in this structure is 5 μm or less. An aluminum alloy cold-rolled sheet for bottle cans having excellent high-temperature characteristics, wherein ΔT indicating the coexistence temperature range is 40 ° C. or less.   The high temperature characteristic according to claim 1, wherein the aluminum alloy cold rolled sheet further contains one or two selected from Cr: 0.001-0.3% and Zn: 0.05-1.0%. Excellent aluminum alloy cold rolled sheet for bottle cans.   The high temperature characteristic according to claim 1 or 2, wherein the aluminum alloy cold-rolled sheet further contains 0.005 to 0.2% Ti alone or in combination with 0.0001 to 0.05% B. Excellent aluminum alloy cold rolled sheet for bottle cans. When the aluminum alloy cold-rolled sheet was heat-treated at 290 ° C. for 20 seconds, the change in hardness ΔHv of the aluminum alloy cold-rolled sheet before and after the heat treatment was 30 Hv or less. The aluminum alloy cold-rolled sheet for bottle cans having excellent high-temperature characteristics according to any one of claims 1 to 3, wherein the 2% proof stress is 215 MPa or more .

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