JP2016079503A - Aluminum alloy sheet for can-top - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for can-top having enough pressure resistance after filling beverage and excellent in rivet moldability and can opening property even with a thin wall with a thickness of about 0.2 mm.SOLUTION: There are provided a 5000 series aluminum alloy sheet containing Mg:3.8 to 5.5 mass%, Fe:0.10 to 0.50 mass%, Si:0.05 to 0.30 mass%, Mn:0.01 to 0.60 mass%, Cu:0.01 to 0.30 mass% and the balance Al with inevitable impurities and galling coating treated after cold rolling with intermediate annealing, which is an aluminum alloy sheet for can-top having enough pressure resistance after filling beverage and excellent in rivet moldability and can opening property even with a thin wall with a thickness of about 0.2 mm having a solid solution amount of Mg measured by a residual extraction method by a heated phenol of 80% or more of the Mg content and subgrain area percentage in a range of 10 to 90% as average as shown in Figure 1 as a structure of a sheet thickness center part.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aluminum alloy plate for a can lid, and relates to an aluminum alloy plate for an easy open can lid that combines high strength, excellent formability, and excellent can openability.

  At present, as one of the packaging containers widely used for beverages and foods, the bottom and side walls are sealed at the bottomed cylindrical body (can body, can body) and the opening of this body part. A two-piece all-aluminum can having a disk-shaped lid (can lid, can end) on the upper surface is well known.

  As materials for such aluminum cans, due to differences in strength and formability required for each, the can body is made of AA to JIS3000 (Al-Mn) aluminum alloy plate, and the can lid is made of AA to JIS5000. (Al—Mg-based) aluminum alloy plates and the like are properly used.

  Among these, the important characteristics required for a 5000 series aluminum alloy plate for can lids are: moldability that can withstand lid processing, pressure resistance that can withstand the internal pressure of a can after filling, and a tab that is normally and easily opened. Can be opened.

  In recent years, from the viewpoint of cost reduction of cans, these can lids, that is, 5000 series aluminum alloy plates for can lids, are also required to have a thickness of about 0.2 mm. Examples of problems with such thinning include a decrease in pressure strength and a decrease in moldability. Among these, the decrease in the pressure strength can be compensated by increasing the material strength of the aluminum alloy plate. However, with such an increase in strength, there arises a problem that the formability decreases. For this reason, in order to reduce the thickness of the aluminum alloy plate for can lids, it is necessary to improve both strength and formability.

  As a technology to improve formability while maintaining material strength even if the thickness of a 5000 series aluminum alloy plate for can lids is reduced, conventionally, intermetallic compounds (can openability, formability), crystal grain size (formability) Various control of the organization such as subgrain or texture has been performed.

  For example, in Patent Document 1, in the structure control of a 5000 series aluminum alloy plate for can lids, the area occupancy ratio of subgrains in the internal structure of the plate is controlled to 3 to 30%, and the can lid is attached to the can body. It has been proposed to improve curling and tightening properties when tightening.

Japanese Patent Laid-Open No. 11-229066

  However, the conventional 5000 series aluminum alloy plate for can lids still has a problem in improving the rivet formability when it is formed into a can lid, and the rivet formability decreases when the strength is increased when the thickness is reduced. In order to obtain excellent rivet formability, there is a problem that the material strength needs to be reduced.

Here, the can lid forming step will be described. First, after punching the material into a disk shape, a shell is formed by drawing, and then by conversion forming, rivet forming is performed by a press to form a convex portion for attaching a tab to the center of the shell.
This rivet molding is composed of a bubble molding process for projecting the central portion of the can lid and a button molding process for reducing the diameter of the projecting section (bubble) in 1 to 3 steps and making a sharp projection.
After this rivet forming, a die having a V-shaped cutting edge is pressed to form the score 3 in FIGS. 2 and 3 which is the groove of the drinking mouth, and the formation of irregularities and characters to increase the rigidity of the panel I do. After that, as a stake process, a tab formed separately is integrated with a convex portion processed at the center of the shell.

  At this time, in order to properly fix the tab, it is necessary to ensure the size of the rivet diameter after the stake. Therefore, the rivet molding that can form the protrusion (button) height sufficiently high after the button molding process is completed. Sex is required for the material.

  On the other hand, even in the case of a material plate in which the area occupancy ratio of the subgrains is controlled to 3 to 30% as in Patent Document 1, the rivet formability decreases and the rivet formability is excellent when the strength is increased. In order to obtain the properties, it was necessary to reduce the material strength. That is, there is still a limit in achieving both rivet formability and high strength.

  For such problems, the present invention can have sufficient rivet formability despite having high material strength, and even when it is thinned, there is no shortage in pressure strength after beverage filling, An object of the present invention is to provide an aluminum alloy plate for can lids which is excellent in rivet formability and can openability.

  The gist of the aluminum alloy plate for can lids of the present invention for solving the above problems is as follows: Mg: 3.8 to 5.5% by mass, Fe: 0.10 to 0.50% by mass, Si: 0.05 to 0 .30% by mass, Mn: 0.01 to 0.60% by mass, Cu: 0.01 to 0.30% by mass, the balance being Al and inevitable impurities, baking after cold rolling with intermediate annealing A coated aluminum alloy plate, the Mg solid solution amount measured by a residue extraction method using hot phenol is 80% or more of the Mg content, and the plate thickness center in a plane parallel to the rolling surface The subgrain area ratio measured by a transmission electron microscope at a magnification of 50,000 times as an organization of 0.05 mm (thickness 0.1 mm) regions in both thickness directions from 10% to 90% on average Suppose that

  As described above, the structure and characteristics of the plate defined in the present invention are as follows: an aluminum alloy plate for a can lid, an aluminum alloy plate after a cold-rolled plate is subjected to painting and baking treatment, or a can formed from this plate It is defined as the tissue and characteristics of the lid. Moreover, the structure and the characteristic of the board after performing the heat processing on the specific conditions mentioned later which simulated the coating baking process to the said cold-rolled board may be sufficient.

  The present invention increases the strength of the structure of the aluminum alloy plate for can lids while increasing the subgrain area ratio and increasing the solid solution amount of Mg while maintaining the formability. As a result, the present invention can achieve both excellent rivet formability and high strength, which have been difficult to combine in the past.

  Therefore, according to the present invention, in order to obtain rivet formability as in the prior art, it is not necessary to reduce the material strength, and it is possible to have sufficient rivet formability despite having high material strength. For this reason, even when the plate thickness is reduced to about 0.2 mm, there can be provided an aluminum alloy plate for can lids which is not deficient in pressure-resistant strength after beverage filling and is excellent in rivet formability and can openability.

It is a drawing substitute photograph which shows the structure | tissue of this invention aluminum alloy plate. It is a top view of the can lid formed by shape | molding an aluminum alloy plate. It is sectional drawing of the score of the can lid used at the time of evaluation of can opening property. It is a schematic diagram of the can open load measuring machine used at the time of evaluation of can openability. FIG. 4A is a perspective view of an open load measuring machine. FIG. 4B is a schematic cross-sectional view of the vicinity of the can lid at the time of measurement by the can opening load measuring machine. FIG.4 (c) is a front schematic diagram which shows the direction of a can lid when installing a can lid in an open load measuring machine.

 The form for implementing the aluminum alloy plate for can lids which concerns on this invention is demonstrated below.

(Aluminum alloy composition)
As described above, the aluminum alloy plate for can lids satisfies the characteristics required for can lids, such as formability to withstand lid processing, pressure resistance to withstand internal pressure after beverage filling, and can openability for normal and easy opening. There is a need.

  Therefore, the alloy composition of the aluminum alloy plate for can lids according to the present invention is also Mg: 3.8 to 5.5% by mass, Fe: 0.10 to 0.50 in order to satisfy this required characteristic from the surface of the alloy composition. Contains mass%, Si: 0.05 to 0.30 mass%, Mn: 0.01 to 0.60 mass%, Cu: 0.01 to 0.30 mass%, with the balance consisting of Al and inevitable impurities Shall. In addition,% display of content of each element means the mass% altogether. Hereinafter, the significance of each element contained will be described in order.

Mg: 3.8 to 5.5% by mass
Mg has the effect of improving the strength of the aluminum alloy plate. When the content of Mg is less than 3.8% by mass, the strength of the aluminum alloy plate is insufficient, and the pressure strength when formed into a can lid is insufficient. On the other hand, when the Mg content exceeds 5.5% by mass, the strength of the aluminum alloy plate becomes excessive, and the formability, particularly the rivet formability, is lowered. Therefore, the Mg content is set to 3.8 to 5.5% by mass.

Mg solid solution (solid solution concentration)
Furthermore, when Mg forms a solid solution in the matrix phase, a large lattice strain is generated, so that work hardening characteristics are improved. On the other hand, when the solid solution amount of Mg decreases, Mg that is not solid solution exists as a compound of Mg ₂ Si or Mg ₂ Al ₃ , which causes cracking and constriction during rivet molding, Reduces rivet formability.

In the present invention, the Mg content in the above range is increased with the solid solution ratio as a reference (index) to increase the strength while maintaining the rivet formability. When the Mg solid solution amount (Mg solid solution ratio) is less than 80% of the Mg content of the plate, the amount of Mg compounds (Mg precipitates) increases and the rivet formability decreases.
Therefore, the higher the solid solution amount (solid solution ratio) of Mg, the better. The Mg content is 80% or more, preferably 88% or more. Although the upper limit of the solid solution amount (solid solution ratio) of Mg is not particularly defined, it is about 99%.

Fe: 0.10 to 0.50 mass%
Fe forms Al-Fe (-Mn) -based and Al-Fe (-Mn) -Si-based intermetallic compounds in the aluminum alloy plate, and improves the tearability of the score part when it is molded into a can lid. There is an effect of improving canability. If the Fe content is less than 0.10% by mass, the tearability of the score part does not improve, and score derailment occurs when the can is opened (the crack propagates to other than the score part when the can is opened) and the opening force increases. Opening defects such as tab breakage are likely to occur. On the other hand, when the Fe content exceeds 0.50% by mass, the number density and volume ratio of the intermetallic compound produced during casting or hot rolling in the aluminum alloy plate increase, and the rivet formability decreases. Therefore, the Fe content is set to 0.10 to 0.50 mass%.

Si: 0.05-0.30 mass%
Si forms Mg-Si-based and Al-Fe (-Mn) -Si-based intermetallic compounds in an aluminum alloy plate, improves the tearability of the score part when molded into a can lid, and improves can openability There is an effect to make. When the Si content is less than 0.05% by mass, the can opening property is not improved as in the case of Fe. Moreover, since the required purity of the aluminum ingot used for the raw material of an aluminum alloy plate becomes high, cost increases. On the other hand, when the Si content exceeds 0.30% by mass, an intermetallic compound generated during casting or hot rolling in the aluminum alloy plate increases, and rivet formability decreases. Therefore, the Si content is 0.05 to 0.30 mass%.

Mn: 0.01-0.60 mass%
Mn has the effect of improving the strength of the aluminum alloy sheet, and when Al-Fe-Mn and Al-Fe-Mn-Si intermetallic compounds are formed in the aluminum alloy sheet and formed into a can lid. There is an effect of improving the tearability of the score part and improving the can openability. When the content of Mn is less than 0.01% by mass, the effect of improving the strength of the aluminum alloy plate or the effect of improving the openability when formed into a can lid cannot be obtained. On the other hand, when the content of Mn exceeds 0.60% by mass, an intermetallic compound generated during casting or hot rolling in the aluminum alloy plate increases, and rivet formability decreases. Therefore, the Mn content is set to 0.01 to 0.60 mass%.

Cu: 0.01-0.30 mass%
Cu has the effect of improving the strength of the aluminum alloy plate. Moreover, work hardening characteristics improve by making it dissolve. When the Cu content is less than 0.01% by mass, the solid solution amount is small and the strength is lowered. On the other hand, when the Cu content exceeds 0.30% by mass, the strength of the aluminum alloy plate becomes excessive, and the rivet formability decreases. Therefore, the Cu content is set to 0.01 to 0.30 mass%.

Inevitable Impurities The aluminum alloy according to the present invention comprises the balance Al and inevitable impurities in addition to the essential components. Inevitable impurities are 0.3 mass% or less for Cr, 0.3 mass% or less for Zn, 0.1 mass% or less for Ti, 0.1 mass% or less for Zr, 0.1 mass% or less for B, etc. Are permitted within a range of 0.05% by mass or less. If the content of inevitable impurities is within this range, it does not affect the characteristics of the aluminum alloy sheet according to the present invention.

(Aluminum alloy plate structure)
In the present invention, the alloy composition described above is used, and as the structure of the aluminum alloy plate for can lids, the subgrain area ratio is increased, and the strength is increased while maintaining the formability.

  For this purpose, a thickness of 0.05 mm (thickness 0.1 mm) in both thickness directions from the center of the thickness of the aluminum alloy plate for can lid after the baking coating treatment in a plane parallel to the rolling surface. The subgrain area ratio measured by a transmission electron microscope with a magnification of 50,000 times as the structure of the central region (hereinafter simply referred to as the center portion of the plate thickness) is 10% or more and 90% or less on average. I will do it.

  As a result, the present invention can achieve both rivet formability and high strength, which were difficult to combine in the past. That is, as the characteristics of the aluminum alloy plate for can lids, the 0.2% proof stress of the aluminum alloy plate for can lids after being baked and coated after cold rolling and the rivet formability of this plate are both high. can do.

  More specifically, as in the examples described later, even if the 0.2% proof stress is 300 MPa or more, it is possible to achieve high strength and high formability with a limit overhang height of 1.45 mm or more. If the limit overhang height of the plate is 1.45 mm or more, the above-described protrusion (button) having a sufficient height can be formed even when the can lid is actually formed, and has sufficient rivet formability. Yes.

  In addition, this data is a characteristic of the aluminum alloy plate for can lids after being baked and coated after cold rolling. This is the relationship between the strength and the formability when the 0.2% proof stress and the evaluation of the rivet formability of this plate are the limit overhang height when a φ6 mm minute overhang test is conducted.

Subgrains The details of the subgrain rules are described below.
Subgrains, also called sub-crystals, are small, irregularly shaped grains. A material (structure) introduced with dislocations by processing strain due to cold rolling, etc., is subjected to a given temperature, time, and stress. It is caused by progressing recovery to become a low energy structure.

  In other words, in the case of aluminum alloy plates for can lids, subgrains have a high density of dislocations such as dislocation cell walls and deformation bands by rearranging dislocations introduced by cold rolling and coalescence annihilation by heating such as baking coating. This occurs when the dislocation density in the region decreases and becomes a sharp boundary. The dislocation dense region has a high probability of coalescence and annihilation with newly moved dislocations, and the work hardening characteristics are deteriorated. However, the subgrain boundary is considered to prevent the movement of dislocations and improve the work hardening characteristics. It is considered that the rivet formability, which is biaxial overhang deformation, is improved because the uniform deformation ability is improved when the work hardening characteristics are improved. In addition to the effect of improving rivet formability, subgrains also have an effect of improving strength.

  As shown in FIG. 1, this subgrain has a sharp outer edge shape (clear and clear) as a boundary by a transmission electron microscope at a magnification of 50,000 times. It can be identified as a single irregular grain. Therefore, the subgrain area ratio to be defined can be calculated as a ratio of the total measurement area of each subgrain to the observation visual field area of the transmission electron microscope.

  On the other hand, a grain that is in contact with or intersects with the dislocation dense region and has a wide boundary and is difficult to identify as an independent small grain is not regarded as a subgrain and is not counted. Specifically, as shown in FIG. 1, a part or many of such grains are in contact with or intersect with the dislocation dense region, or the boundary (outer edge shape) as a whole is not sharp. A grain with a width. Since such grains are difficult to identify as individual grains that are independent or isolated, they are not regarded as subgrains and are not counted. In the present invention, a series of these determination methods is collectively referred to as “subgrain area ratio measured by a transmission electron microscope with a magnification of 50,000 times”.

  In the present invention, such a subgrain area ratio in the central portion of the thickness of the aluminum alloy plate for can lids is 10% or more and 90% or less on average.

  If this subgrain area ratio is as small as less than 10% on average, the higher the strength of the plate, the lower the rivet formability, making it impossible to achieve both excellent rivet formability and high strength. That is, even if the alloy composition is satisfied and the solid solution amount of the Mg is satisfied, the strength cannot be increased while maintaining the formability of the aluminum alloy plate for can lids.

The larger the subgrain area ratio, the better the rivet formability. However, from the actual production limit, the upper limit of the area ratio is 90% on average.
Therefore, in the present invention, such a subgrain area ratio in the central portion of the thickness of the aluminum alloy plate for can lids is 10% or more and 90% or less on average.

  Incidentally, although the said patent document 1 overlaps with the aluminum alloy plate for can lids of this invention, and an alloy composition and the area rate (area occupancy rate) of a subgrain, from the difference in the manufacturing conditions, the amount of solid solution of Mg is Lower. Patent Document 1 uses a tandem rolling mill in which rolling stands are arranged in series instead of a single rolling mill for cold rolling of a plate, and the temperature inevitably rises unless it is forcibly cooled, The temperature at the time of rolling becomes comparatively high, Mg precipitation proceeds, and the solid solution amount of Mg decreases. That is, the strength of the can lid aluminum alloy sheet cannot be increased while maintaining the formability, and the rivet formability when compared with the present invention at the same strength level is lowered.

  As described above, the structure and characteristics of the plate defined in the present invention described above are as follows. The aluminum after the cold-rolled plate (the plate after cold-rolling) is coated and baked as an aluminum alloy plate for a can lid It is the structure and characteristics of an alloy plate (pre-coated plate) or the structure and characteristics of a can lid formed with this plate. In addition, the plate after the heat treatment under the specific conditions described later was performed on the cold-rolled plate, which was not subjected to such painting or paint baking treatment, or formed into a can lid, simulating the paint baking treatment. The organization and characteristics of These structures and characteristics are the same or the structures and characteristics that can be considered to be the same or slightly the same if the conditions of the paint baking process and the heat treatment are the same.

(Production method)
Next, the manufacturing method of the aluminum alloy plate for can lids in this invention is demonstrated.
The production process itself of the aluminum alloy plate of the present invention includes, as usual, a casting process in which an aluminum alloy having the above composition is melted and cast to form an ingot, and a soaking process that homogenizes the ingot by heat treatment, It is manufactured by a hot rolling process in which a homogenized ingot is hot-rolled to form a hot-rolled sheet, and a cold rolling process in which the hot-rolled sheet is cold-rolled.

  However, subgrains are produced by a decrease in dislocations (dislocation density) introduced into the aluminum alloy plate for can lids by cold rolling. Further, Mg once dissolved by soaking is likely to precipitate by subsequent hot rolling or the like. For this reason, both the solid solution Mg and the subgrain cannot be increased only by the conventional method described above. For this reason, in the present invention, the hot rolling condition, the cold rolling condition, and the like are particularly controlled as will be described later in this known process. As a result, by increasing both the subgrain area ratio and the dislocation density, the structure defined by the aluminum alloy sheet of the present invention is increased in strength while maintaining formability. Hereinafter, it demonstrates in order of a process.

  First, an aluminum alloy is melted, and an aluminum alloy having the above composition is cast by a known semi-continuous casting method such as a DC casting method.

  Next, after removing the area | region used as an inhomogeneous structure | tissue of an ingot surface layer by chamfering, homogenization heat processing is performed. As a result, internal stress is removed, solute elements segregated during casting are homogenized, and intermetallic compounds crystallized during casting are diffused and solidified to homogenize the structure. For this purpose, the homogenization heat treatment is held at a temperature of 450 ° C. or higher for 1 hour or longer.

  When the homogenization heat treatment temperature is less than 450 ° C or the holding time is less than 1 hour, the amount of Mg solid solution decreases, and the subgrain area is also reduced by intermediate annealing during cold rolling of the plate and baking during can coating. It becomes impossible to make 10% or more on the average which prescribes | regulates a rate. Moreover, the said homogenization effect falls and a mechanical characteristic and can openability fall. The upper limit of the holding time is 20 hours, and even if the upper limit is exceeded, the homogenization effect is not significantly different and the productivity is lowered.

Hot rolling:
After this homogenization heat treatment, the ingot is continuously cooled or cooled to a predetermined starting temperature, first hot rough rolled, and further hot finish rolled to hot-roll aluminum alloy having a predetermined thickness. A board. At this time, hot rolling is performed while suppressing the precipitation of Mg so as not to reduce the solid solution amount of Mg secured by soaking.

For this reason, it is preferable to perform hot rough rolling within 10 minutes. For this reason, the temperature at which the steady speed of all passes is at least 25 m / min and at least the rough rolled plate between passes is the lowest. 450 ° C. or higher, preferably 460 ° C. or higher.
Regarding the steady speeds of all passes, even at one of these passes, if the speed is less than 25 m / min, the rolling time becomes longer, the Mg-Si based compound tends to precipitate, and the amount of solid solution Mg decreases. Therefore, it is impossible to make the average of the subgrain area ratio 10% or more.
Further, even when the minimum temperature of the rough rolled sheet between passes is less than 450 ° C., Mg—Si based compounds are likely to be precipitated, the amount of solid solution Mg is reduced, and the average of defining the subgrain area ratio is 10 % Or more cannot be achieved.
Further, the compound deposited during hot rolling, such as during hot rough rolling, is large in size, and is difficult to dissolve even under intermediate annealing conditions during cold rolling to be described later for dissolving Mg.

  Following this hot rough rolling, hot finish rolling with an end temperature of preferably 300 to 360 ° C. or more is performed without delay or continuously in order to prevent precipitation of Mg—Si based compounds, Use hot-rolled sheet. When the finish temperature of hot finish rolling is less than 300 ° C., the rolling load increases and the productivity decreases. On the other hand, in order to obtain a recrystallized structure without leaving a large amount of processed structure, when the finish temperature of hot finish rolling is increased, if this temperature exceeds 360 ° C., an Mg—Si compound tends to precipitate and become solid. The amount of dissolved Mg decreases.

Cold rolling:
Subsequently, this hot-rolled sheet is subjected to primary cold rolling (primary cold rolling), intermediate annealing, secondary cold rolling (secondary cold rolling) to obtain a cold rolled sheet (cold rolled sheet). This cold rolling is performed by a required number of passes (the number of plates) in a tandem rolling mill in which the rolling stands are single (one stand) or two or more rolling stands are arranged in series.
This cold rolling consists of a primary cold rolling (primary cold rolling) process in which a single rolling mill or a tandem rolling mill is passed once or twice (pass), and an intermediate in which the primary cold rolled sheet is annealed. The secondary cold rolling (secondary rolling) in which the single rolling mill is passed twice (pass) or the tandem rolling mill is passed once or twice (pass) through the annealing step and this intermediate annealing material again. Cold-rolled).
Here, the number of passing plates (passes) is the number of passes through a single rolling mill or a tandem rolling mill. The number of rolling is the number of times the plate passes through the stand. For example, in the case of a tandem rolling mill in which two rolling mills are arranged in series, if the plate is passed once, the number of rolling (the number of times the plate passes through the stand) is 2 times.

The total rolling ratio of the primary cold rolling is preferably 50% or more. When the total rolling rate is less than 50%, the accumulated strain due to rolling becomes insufficient, the recrystallized grain size becomes large in the subsequent intermediate annealing, and the formability including the rivet formability is deteriorated.
The primary cold-rolled cold-rolled sheet is subjected to intermediate annealing and recrystallization, and the solid solution amount of Mg is increased. This intermediate annealing is performed in a continuous annealing step (equipment), preferably in a material holding temperature range of 450 ° C. to 550 ° C. and a holding time of 10 minutes or less, from the heating rate up to the holding temperature and the holding temperature. The cooling rate is preferably 100 ° C./min or more. When the heating rate is less than 100 ° C./min, when the holding temperature exceeds 550 ° C., when the holding time exceeds 10 minutes, and when the cooling rate is less than 100 ° C./min, recrystallized grains after completion of the annealing step, respectively Becomes larger. For this reason, rivet formability falls. Further, when the holding temperature of the intermediate annealing is less than 450 ° C., the processed structure remains on the aluminum alloy plate after the annealing process is finished, and the solid solution amount of Mg is reduced, so that the rivet formability is also lowered. That is, if there is no such intermediate annealing, it becomes difficult to obtain the structure defined in the present invention.

  Subsequently, the intermediate-annealed cold-rolled sheet is secondarily cold-rolled again with the number of rolling times (the number of times the plate passes through the stand) being two times or more. In order to increase it, it is increased to 60% or more, preferably higher than 80%. If the total rolling ratio of this secondary cold rolling is low, the dislocation density is low. Subgrains are formed from dislocation dense regions. If the total rolling rate is as low as less than 60%, the dislocation dense regions are reduced (deficient), and the subgrain area ratio after baking is reduced.

In the secondary cold rolling, in order to increase the dislocation density, not only the total rolling rate but also the number of rolling (the number of times the plate passes through the stand) is performed twice or more, and the previous stand other than the final rolling The material temperature after rolling at (outside of the stand) is 100 ° C. or less. More specifically, in the case of a single rolling mill, the material temperature after pre-rolling is set to 100 ° C. or less except for the last rolling (final feeding plate or final pass). In the case of a tandem rolling mill, the material temperature on the exit side of each stand serving as the front stand other than the last stand is set to 100 ° C. or less. For example, in the case of a rolling mill having two stands, the number of rolling operations is twice with one sheet passing, and the material temperature on the exit side of the first stand is 100 ° C. or less.
By introducing dislocations before final rolling due to these secondary cold rolling conditions, dislocations tend to tangle (entangle and entangle) in the final rolling, and dislocation dense regions such as cell walls and shear bands are formed. Many are formed. Subgrains are then formed from the dislocation dense region by subsequent heat treatment such as baking.

  On the other hand, when the material temperature after rolling other than the final rolling in the secondary cold rolling (before the final rolling) exceeds 100 ° C., the recovery of dislocation proceeds and the dislocation density before the final rolling becomes low. Grain area ratio decreases. By the way, the higher the rolling ratio in the secondary cold rolling, the more the processing heat is generated, and the material temperature after rolling exceeds 100 ° C and tends to be relatively high at 150 to 160 ° C. For this reason, in order to keep the material temperature after rolling (on the stand exit side) at 100 ° C. or less during rolling before final rolling, the amount of lubricating oil or coolant is set to an amount sufficient to cool the plate The processing heat generation of the rolled plate is suppressed, and the material temperature after rolling at the time of passing before final rolling is controlled to 100 ° C. or lower.

  The aluminum alloy plate for can lids manufactured by the above process is subjected to a surface treatment such as a chromate type or a zircon type, and an organic paint such as an epoxy resin, a vinyl chloride sol type, or a polyertel type is applied, and PMT (Peak Metal Temperature: A metal baking temperature is 230 to 280 ° C., and a pre-coating plate is formed, and then formed into a can lid. In the present invention, the heat treatment simulating a paint baking process for evaluation of strength and rivet formability is one point of 255 ° C. × 20 seconds in order to have reproducibility from the range of the paint baking process. Selected.

(Production method of can lid)
An example of a known method for producing a can lid from a material aluminum alloy plate (cold rolled plate) will be described below.

As described above, a blank material obtained by punching a blank aluminum alloy plate (pre-coated plate) that has been pre-painted and baked into a disk shape (blanking) is drawn with a press machine to curl the outer periphery. After application, a sealing compound is applied to the curled portion to make a shell.
Thereafter, the following molding is performed as conversion molding. Using a press machine, rivet forming is performed to form a protrusion for attaching a tab to the center of the shell. This rivet molding is composed of a bubble molding process for projecting the central portion of the can lid and a button molding process for reducing the diameter of the projecting section (bubble) in 1 to 3 steps and making a sharp projection.

Next, a die having a V-shaped cutting edge is pressed to form a score 3 in FIGS. 2 and 3 which is a groove of the drinking mouth, and to form irregularities and letters for increasing the rigidity of the panel.
Further, a tab formed separately is caulked and integrated with the convex portion processed at the center of the shell (this is called a stake process). A plan view of this integrated can lid is shown in FIG.
Then, the can lid is wrapped and sealed in the opening of an aluminum alloy can body that is separately DI-molded and filled with contents (beverage, food) from the opening.

  As mentioned above, although the form for implementing this invention was described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. In addition, this invention is not limited to this Example.

(Sample aluminum alloy plate)
No. 1 shown in Table 1. Each aluminum alloy having a composition of 1 to 30 was cast by a semi-continuous casting method (DC), and in common with each example, the ingot surface layer was chamfered to produce a slab. The slab was subjected to a homogenization heat treatment of 500 ° C. × 4 hours in common with each example, and then hot rough rolling was started at the temperature of 500 ° C., and the end temperature of the subsequent hot finish rolling was set to 330 ° C. As a hot rolled plate having a plate thickness of 1.3 to 5.1 mm.

  For this hot-rolled sheet, in common with each example, after the first cold rolling (rolling rate of 65%), the maximum material reaching temperature of 450 ° C. and the holding time of less than 1 minute are used for continuous annealing equipment. Intermediate annealing was performed. The heating rate up to the holding temperature and the cooling rate from the holding temperature during the intermediate annealing were both set to 100 ° C./min or more in common. Thereafter, secondary cold rolling was performed sequentially at the number of rollings of 2 times in common with each example.

  At this time, as shown in Table 1, the steady speed in the hot rough rolling, the minimum temperature of the rough rolled plate between passes, the total rolling rate in the secondary cold rolling, and 1 before the final rolling (second rolling) After changing the material temperature after the second rolling (stand exit side), an aluminum alloy plate for can lid having a plate thickness of 0.215 mm was prepared in common with each example.

  No. 1 of Table 1 produced in this way. 1-30 aluminum alloy plates were simulated by painting and baking treatment, and in common, without being painted, only subjected to heat treatment at 255 ° C. for 20 seconds in an oil bath, measurement of the following structure and characteristics This was used as a test material for evaluation.

(Mg solid solution amount)
The Mg solid solution amount (solid solution ratio) of the test material was measured as follows.
That is, first, after putting phenol into a decomposition flask and heating, the sample taken from each test plate (plate thickness center part) to be measured is transferred to this decomposition flask and heated and decomposed with hot phenol. To do. Next, it is filtered using a membrane filter with a mesh (collected particle diameter) of 0.1 μm, and the filtrate is introduced into an ICP (Inductively Coupled Plasma) emission spectroscopic analyzer, which is atomized with a nebulizer and made into a small mist. Only Mg was blown into the plasma, and the solid solution amount of Mg was measured. Even if the filtrate contains a precipitate of less than 0.1 μm, it is discharged without being analyzed as a large mist when the mist is formed. Is not included. And the ratio (%) with respect to Mg content of this board | plate of the solid solution amount of this Mg was calculated. The results are shown in Table 1.

(Subgrain area ratio)
The subgrain area ratio was measured with a transmission electron microscope at a magnification of 50,000 times for the structure at the center of each plate thickness in the plane parallel to the rolling surface of the test material, and the average value corresponding to the number of measurement fields It calculated in.

  Specifically, the specimen is mechanically polished to 0.05 mm (thickness 0.1 mm) in both thickness directions from the center of the plate thickness, and then from the center of the plate thickness by a twin jet electrolytic polishing method. A thin film having a thickness of 100 nm was formed, and this thin film was photographed with a transmission electron microscope (TEM) at four magnifications at a magnification of 50,000 times. Only the subgrains are transferred from the photographed image to a transparent film, and the total area of the subgrains within the photographing range is measured using the image analysis software Image-Pro Plus, and the area ratio relative to the visual field area (photographing area) Calculation was performed using an average of 4 fields of view.

  Here, as described above, the subgrain is a grain surrounded by a sharp boundary having no width, and the boundary (outer edge shape) as a whole has a width rather than a sharp, independent or isolated small Grains that were difficult to identify as individual grains were not considered subgrains and were not counted.

(0.2% yield strength)
A JIS No. 5 tensile test piece was prepared from the specimen so that the tensile direction was parallel to the rolling direction. Using this test piece, a tensile test was performed according to JIS-Z2241, and a 0.2% yield strength was obtained. An appropriate range of 0.2% proof stress is 300 MPa or more, and within this range, even a thin can lid satisfies the compressive strength.

(Rivet formability)
The rivet formability was evaluated by a test simulating the bubble process. That is, a φ6 mm minute overhang test was performed on the specimen, and the limit overhang height at which no necking or cracking occurred was obtained. The appropriate range of the limit overhang height was 1.45 mm or more. If the limit overhang height of the aluminum alloy plate is 1.45 mm or more, a button having a sufficient height can be formed during actual forming.

(Opening load)
The specimen was subjected to shell molding, conversion molding, and tab stake using a 204-diameter full-form end mold, and then a can open test was performed.
FIG. 2 is a plan view of the can lid used in the can open test.
FIG. 3 is a cross-sectional view of the score 3 of the can lid used in the can open test.
FIG. 4 is a schematic view of a can opening load measuring machine for measuring the load at the time of opening the can.
FIG. 4A is a perspective view of the opening load measuring machine 5.
FIG. 4B is a schematic cross-sectional view of the vicinity of the can lid 1 when measured by the can opening load measuring device 5.
FIG. 4C is a schematic front view showing the direction of the can lid 1 when the can lid 1 is installed in the can opening load measuring device 5.

  The can lid 1 is placed on the can opening load measuring machine 5 so that the tab 4 is positioned above the score 3 with respect to the score 3 (FIG. 4C). A latch 6 is hooked on the tab 4 of the can lid 1 to form a latch 7 (FIG. 4B). The latch 6 was pulled in the horizontal direction to apply a 3N tensile load, and the latch 6 was stationary in that state, and then the can lid 1 was rotated in the X direction. The load was measured with a load cell, and the highest load was taken as the can open load. The appropriate range of the can opening load was 25 N or less.

  As shown in Table 1, No. 1 within the specified range of the present invention. In Examples 1 to 16, the composition of the components is within the scope of the invention, the hot rough rolling is finished within 10 minutes as a preferable steady speed, and the minimum temperature of the rough rolled plate between passes is also set. They are all manufactured under favorable manufacturing conditions such as the total rolling rate in the secondary cold rolling and the material temperature after the first rolling (on the stand exit side).

  For this reason, the solid solution amount ratio of Mg is 80% or more, and the center part of the plate thickness has the structure shown in FIG. 1 and the subgrain area ratio measured by a transmission electron microscope with a magnification of 50,000 times is obtained. The average is 10% or more and 90% or less. That is, in these examples, the structure of the aluminum alloy plate for can lids is a structure with an increased subgrain area ratio. Incidentally, FIG. 1 is an example of the first embodiment.

As a result, no. In Examples 1 to 16, as shown in Table 1, 0.2% proof stress and can open load are appropriate, and rivet formability is excellent. That is, the strength is increased while maintaining the moldability, and both the rivet moldability and the strength increase can be achieved. Specifically, high strength and high formability with a 0.2% proof stress of 300 MPa or more and a limit overhang height of 1.45 mm or more can be achieved. Therefore, although the aluminum alloy plate of an Example is as thin as 0.215 mm, it can be used conveniently for an easy open can lid.
Among the examples, the example in which the solid solution Mg amount ratio is 88% or more has the same strength level than the example in which the solid solution Mg amount ratio is 80% or more and less than 88%. The rivet formability is generally high.

  On the other hand, no. In Comparative Examples 17 to 30, any one of the component composition, the Mg solid solution amount ratio, and the subgrain area ratio as the structure at the center of the plate thickness is not within the specified range of the present invention. Any of 2% yield strength, can open load, and rivet formability does not satisfy the appropriate values.

No. No. 17 is insufficient because the Mg content is less than the lower limit and is produced under preferable production conditions, and satisfies the Mg solid solution ratio and the subgrain area ratio of the structure at the center of the plate thickness. % Proof stress is too low.
No. No. 18 is produced under preferable production conditions because the Mg content is excessive beyond the upper limit and satisfies the solid solution amount ratio of Mg, but the limit overhang height is necessary for the rivet formability of the can lid 1 .45 mm is not satisfied and rivet formability is poor.
No. 19 is produced under preferable production conditions because the Fe content is insufficient below the lower limit, and satisfies the solid solution amount ratio of Mg and the subgrain area ratio of the structure at the center of the plate thickness, but the can opening load is large.
No. No. 20 is produced under preferable production conditions because the Fe content is excessive beyond the upper limit, and although it satisfies the solid solution amount ratio of Mg and the subgrain area ratio of the structure at the center of the plate thickness, The height does not satisfy the 1.45 mm required for the rivet formability of the can lid, and the rivet formability is poor.
No. No. 21 is produced under preferable production conditions because the Si content is insufficient below the lower limit, and satisfies the solid solution amount ratio of Mg and the subgrain area ratio of the structure at the center of the plate thickness. large.
No. No. 22 is produced under preferable production conditions because the Si content is excessive beyond the upper limit, and although it satisfies the solid solution amount ratio of Mg and the subgrain area ratio of the structure at the center of the plate thickness, The height does not satisfy the 1.45 mm required for the rivet formability of the can lid, and the rivet formability is poor.
No. No. 23 is produced under preferable production conditions because the Mn content is insufficient below the lower limit, and satisfies the solid solution amount ratio of Mg and the subgrain area ratio of the structure at the center of the plate thickness, but 0.2% The proof stress is too low and the opening load is large.
No. No. 24 is manufactured under preferable manufacturing conditions because the Mn content is excessive beyond the upper limit and satisfies the solid solution amount ratio of Mg and the subgrain area ratio of the structure at the center of the plate thickness. The height does not satisfy the 1.45 mm required for the rivet formability of the can lid, and the rivet formability is poor.
No. No. 25 has a Cu content of less than the lower limit, so that the 0.2% yield strength is too low.
No. No. 26 is produced under preferable production conditions because the Cu content is excessive and exceeds the upper limit, and although the Mg solid solution ratio and the subgrain area ratio of the structure at the center of the plate thickness are satisfied, The height does not satisfy the 1.45 mm required for the rivet formability of the can lid, and the rivet formability is poor.

No. No. 27, although the alloy composition is within the range of the present invention, the minimum steady-state speed of hot rough rolling is too slow, hot rough rolling does not finish within 10 minutes, and Mg precipitation cannot be suppressed. The solid solution ratio is too small, and the subgrain area ratio is too small. As a result, the limit overhang height does not satisfy the 1.45 mm necessary for the rivet formability of the can lid, and the rivet formability is poor.
No. No. 28, although the alloy composition is within the scope of the present invention, the minimum temperature of the rough rolled plate between passes is less than 450 ° C., Mg-Si based compounds are likely to precipitate, and Mg precipitation can be suppressed. However, the solid solution amount ratio of Mg is too small, and the subgrain area ratio is too small. As a result, the limit overhang height does not satisfy the 1.45 mm necessary for the rivet formability of the can lid, and the rivet formability is poor.
No. No. 29, although the alloy composition is within the range of the present invention, the total rolling ratio in secondary cold rolling is too low as less than 60%, and the subgrain area ratio is too small beyond the lower limit. As a result, the strength cannot be increased while the moldability is maintained.
No. No. 30, although the alloy composition is within the scope of the present invention, the material temperature after the first rolling in the secondary cold rolling is too high exceeding 100 ° C., and the solid solution amount ratio and the subgrain area ratio of Mg have lower limits. Too little to come off. As a result, the rivet formability is too low, and high rivet formability and high strength cannot be combined. Incidentally, the comparative example 30 corresponds to the above-mentioned Patent Document 1.

  From the above results, the significance of each requirement and preferred production conditions of the present invention for combining high rivet formability and high strength is supported.

As described above, according to the present invention, in order to obtain rivet formability as in the prior art, it is not necessary to reduce the material strength, and it is possible to have sufficient rivet formability despite having high material strength. For this reason, even when the plate thickness is reduced to about 0.2 mm, there can be provided an aluminum alloy plate for can lids which is not deficient in pressure resistance after beverage filling and is excellent in rivet formability and can openability.
For this reason, the can lid thickness is reduced in thickness and strength, and it is optimal for an aluminum alloy plate used for a can lid that requires high rivet formability and high strength under more severe use conditions.

1 Can Lid 2 Rivet 3 Score 4 Tab 5 Opening Load Measuring Machine 6 Hook 7 Hook

Claims (1)

Mg: 3.8 to 5.5% by mass, Fe: 0.10 to 0.50% by mass, Si: 0.05 to 0.30% by mass, Mn: 0.01 to 0.60% by mass, Cu: An aluminum alloy plate containing 0.01 to 0.30% by mass, the balance being Al and inevitable impurities, and subjected to baking coating after cold rolling with intermediate annealing, measured by a residue extraction method using hot phenol The solid solution amount of Mg is 80% or more of the Mg content, and in a plane parallel to the rolling surface, the thickness is 0.05 mm (thickness 0.1 mm) in both thickness directions from the thickness center. An aluminum alloy plate for can lids, characterized in that, as a structure, the subgrain area ratio measured by a transmission electron microscope at a magnification of 50,000 times is 10% or more and 90% or less on average.