JP2017095765A - Aluminum alloy sheet for can top - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for a can top, simultaneously realizing high strength, flexure processability and can-opening properties.SOLUTION: A 5000-series aluminum alloy sheet of a specific composition suppresses a variation of intervals of neighboring shear deformed organizations, from among shear deformed organizations that can be observed as a belt-like organization extending in parallel with intervals in a rolling direction and in a substantially parallel direction as in figure 1, as a difference between a maximum value and a minimum value of an average interval between the shear deformed organizations in each observation visual field, so as to simultaneously realize high strength, flexure processability and can-opening properties.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aluminum alloy plate for can lids, and relates to an aluminum alloy plate for easy open can lids having high strength, bending workability, and 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.

  For this reason, as a technique for improving formability while maintaining material strength even if the thickness of the 5000 series aluminum alloy plate for can lids is reduced, conventionally, the solid solution amount of alloy elements, intermetallic compounds, crystal grain size, Various control of textures such as grains or textures, precipitates, shear bands (shear bands) has been performed.

  For example, in Patent Document 1, as a structure of a 5000 series aluminum alloy plate having a specific composition made of Mg, Mn, Si, Cu, Fe, Ti, for can lids for carbonated drinks, beer, etc., While controlling the amount of solid solution Mn and the number of intermetallic compounds with a maximum length of 3 μm or more, the area ratio of the shear band (shear band) penetrating the cross-section parallel to the rolling direction of the product plate can be suppressed to 1% or less. Proposed.

  The shear band referred to in Patent Document 1 refers to an angle of 35 ° to 45 ° with respect to the rolling direction when a surface perpendicular to the plate width direction is observed with an optical microscope, SEM, or TEM when rolling the plate. In the patent document 1, the number of deformations concentrated in a partial area of the plate that can be observed (those whose deformation has been localized) is counted.

In Patent Document 1, the shear band is generated by cold rolling and has a geometrical arrangement inside the material, and the dislocation density inside the shear band is much higher than the dislocation density of the matrix (uniform deformation region). Depending on the deformation direction, the shear band inhibits the slip deformation, or the density of dislocation density is generated inside the material, and the strength anisotropy becomes remarkable.
For this reason, in Patent Document 1, the area ratio of the shear band is regulated to 1% or less so that the shear band does not interfere with the slip deformation even if the maximum shear stress works and the slip deformation starts. The strength anisotropy is suppressed. As a result, local stress concentration does not occur even when the lid swells due to internal pressure, and even when the cover is thinned, cracks during deformation are unlikely to occur.

Incidentally, the method for observing the shear band of Patent Document 1 is to heat-treat at 120 ° C. for one week, preferentially precipitate a beta phase (Al ₃ Mg ₂ ) on the shear band, and etch the deposited beta phase. Indirect observation of shear bands. Moreover, the area ratio measurement of the shear band is calculating | requiring the area ratio in 0.2 mm < ² > by observing with an optical microscope by the magnification of 400 times in the cross section parallel to the rolling direction of a product board.

JP 2001-303164 A

  As described above, the requirements for formability and pressure resistance of the 5000 series aluminum alloy plate for can lids are becoming higher as the thickness is reduced.

As an index for comprehensively evaluating severe formability and pressure resistance during such thinning, there is evaluation of bending workability by a push bending method (roller bending method) described later with reference to FIG.
This push-bending method is stricter than other winding methods such as the winding method and the V-block method. If the bending workability evaluated by this push-bending method is improved, the 5000 series aluminum alloy plate for can lids is formed. Even if the thickness is improved and the thickness is reduced, it is resistant to cracking due to the lid processing, and coating film defects such as peeling of the coating film due to the lid processing are less likely to occur. In addition, cracks are less likely to occur during deformation due to changes in internal pressure after beverage filling, and pressure resistance increases as a lid after being attached to a can.

However, the conventional 5000 series aluminum alloy plate for can lids has a good evaluation of individual or individual formability, such as rivet formability, as well as formability such as the push bending method. There is still a problem that bending workability for comprehensively evaluating characteristics such as pressure resistance is not always good.
That is, this means the reality that conventional 5000 series aluminum alloy plates for can lids do not necessarily have comprehensive properties such as formability and pressure resistance on the premise that they have high material strength. To do.

  For such problems, the present invention is excellent in moldability and pressure resistance represented by the bending workability by the push bending method, and excellent in can openability, despite having high material strength. An object of the present invention is to provide an aluminum alloy plate for can lids (having high strength, bending workability, and can openability).

  The gist of the aluminum alloy plate for can lids having high strength, bending workability, and can openability of the present invention for solving the above problems is as follows: Mg: 3.8 to 5.5 mass%, Fe: 0.00. 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%, the balance being Al And an aluminum alloy plate made of unavoidable impurities, and when observing a plane parallel to the rolling surface at the center of the thickness of the plate, the rolling is performed while being arranged at a distance from each other in a direction substantially parallel to the rolling direction. In a shear deformation structure observed as a strip structure extending in a direction substantially perpendicular to the direction, four planes of a plane parallel to the rolling surface at the center of the plate thickness of this plate are observed with a SEM of 5000 times. The shear deformation structures adjacent to each other can be observed with When the average interval per field of view was calculated by averaging all the intervals, the difference between the maximum value and the minimum value among the average intervals in the four fields of view was 300 nm or less (excluding 0 nm) In other words, the variation in the spacing between the adjacent shear deformation tissues is suppressed.

  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 provides a structure of an aluminum alloy plate for a can lid, and a plurality of crystal grains arranged in a plane parallel to the rolling direction in a plane parallel to the rolling surface at the thickness center of the plate, spaced apart from each other. A shear band (shear band) structure extending in a band shape substantially perpendicular to the rolling direction across the grain boundary, and a band formed by local shear deformation in one crystal grain The bending processability (formability and pressure resistance) is improved by suppressing the variation in the interval between the shear deformation structures (shear deformation structures).

  Therefore, the present invention does not require the material strength to be reduced in order to obtain excellent moldability as in the prior art, and even when the plate thickness is reduced to about 0.2 mm, the pressure strength is not insufficient, and the high strength In addition, an aluminum alloy plate for can lids that has both bending workability and can openability can be provided.

It is a top view which shows typically the structure | tissue of this invention aluminum alloy plate. FIG. 2 is a partially enlarged view of FIG. FIG. 2 is a perspective view showing that the surface showing the structure of FIG. 1 is a surface extending in parallel with the rolling surface at the center of the plate thickness. It is a front view which shows the outline | summary of the testing apparatus of bending workability. It is a top view of the can lid used for the can open test. It is sectional drawing of the score 3 of the can lid used for the can open test. It is a schematic diagram of the can opening load measuring machine which measures the load at the time of can opening.

  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 has the characteristics required for can lids, such as formability to withstand lid processing, pressure resistance to withstand internal pressure after beverage filling, and can opening for normal and easy opening It is necessary to satisfy sex.

Therefore, the alloy composition of the aluminum alloy plate for can lids according to the present invention also satisfies these required characteristics from the aspect of the alloy composition, Mg: 3.8 to 5.5% by mass, Fe: 0.10 to 0.00. 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 It shall consist of
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 bending workability is lowered. Therefore, the Mg content is set to 3.8 to 5.5% by mass.

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 bending workability 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 bending workability 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 at the time of casting or hot rolling in the aluminum alloy plate increases, and bending workability 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 bending workability 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 Cr 0.3 mass% or less, Zn 0.3 mass% or less, Ti 0.1 mass% or less, Zr 0.1 mass% or less, B 0.1 mass% or less, Other elements are allowed within a range of 0.05% by mass or less. If the content of inevitable impurities is within this range, the characteristics of the aluminum alloy plate according to the present invention are not affected.

Shear Deformation Structure As for the shear deformation structure defined in the present invention, an actual SEM structure photograph is a complicated pattern that is difficult to understand by visual observation, and is schematically shown in FIG.
FIG. 1 shows a structure on a hatched surface parallel to the rolling surface at the thickness center of the plate in plan view, that is, a SEM observation surface, shown in a perspective view in FIG.
In the SEM observation surface in the plane parallel to the rolling surface at the thickness center of the plate in FIG. 1, the shear deformation structure is arranged substantially at right angles to the rolling direction while being arranged at intervals from each other in the direction substantially parallel to the rolling direction. Observed as a strip or streak pattern extending across the direction.
This shear deformation structure is a locally deformed portion formed by concentrating deformation in a partial region of the plate when the plate is cold-rolled (deformation is localized), and when the cold rolling rate increases The number increases and the spacing decreases.

The shear deformation structure defined in the present invention means a structure generated by shear deformation, and includes both a structure extending over a plurality of crystal grains and a structure generated within one crystal grain.
That is, as described in paragraph 0018, the shear deformation structure defined in the present invention is arranged in a plane parallel to the rolling surface at the center of the plate thickness of the plate, spaced apart from each other in a direction substantially parallel to the rolling direction, It was generated by a shear band (shear band) structure extending in a band shape over a direction substantially perpendicular to the rolling direction across a plurality of crystal grains (grain boundaries) and local shear deformation within one crystal grain. It consists of a tissue extending in a band shape.

These shear deformation structures greatly influence the bending workability of the aluminum alloy plate for can lids. In particular, the variation in the spacing between the shear deformation structures greatly affects the bending workability of the aluminum alloy plate for can lids.
Here, the interval between the shear deformation structures also has a great influence on the bending workability of the aluminum alloy plate for can lid.
However, the aluminum alloy plate for can lids falls within a certain range as long as it is within the range of normal production conditions including the alloy composition and normal rolling conditions. And, when it falls within this certain range, the influence on bending workability is small, and in the present invention, it is not particularly controlled or specified.

On the other hand, the variation in the spacing between the shear deformation structures varies greatly in the range of the normal components and production conditions or normal rolling conditions of the aluminum alloy plate for can lids, Moreover, it causes cracks and wrinkles during bending deformation, and greatly affects the bending workability of the aluminum alloy plate for can lids.
Therefore, in the present invention, as an effective control means for improving the bending workability, the variation in the interval between the shear deformation structures adjacent to each other in the direction substantially parallel to the rolling direction is selected.
That is, in order to improve the bending workability with the above-described alloy composition, as the structure of the aluminum alloy plate for can lids, the variation in the interval between the shear deformation structures is suppressed.

When the variation in the interval of the shear deformation structure of the plate is large, the deformation concentrates in a portion where the interval is narrow, and cracks and wrinkles occur during bending deformation. Therefore, the present invention improves the bending workability by reducing the variation in the interval between the shear deformation structures.
Specifically, in plane view, a plane parallel to the rolling surface at the thickness center of this plate can be observed in each field of view (within 1 field) when observing 4 fields (4 locations) with a 5000 times SEM. The total interval between the shear deformation structures adjacent to each other is averaged to obtain an average interval per field of view.
In addition, the variation in the spacing between the shear deformation structures adjacent to each other in the direction substantially parallel to the rolling direction of the plate is defined as the difference between the maximum value and the minimum value of the average intervals in the four fields of view as 300 nm. Suppressed below (however, not including 0 nm).

The variation in the spacing between the adjacent shear deformation structures in the direction substantially parallel to the rolling direction of the plate does not actually become 0 nm from the manufacturing limit, but the smaller the smaller, the higher the bending workability improvement effect. 200 nm or less, more preferably 100 nm or less.
When the difference between the maximum value and the minimum value of the average interval exceeds 300 nm, the variation in the interval of the shear deformation structure of the plate is too large, and the deformation concentrates in the narrow interval, and cracking occurs during bending deformation. My self is generated. For this reason, bending workability falls remarkably.

Measurement of Spacing Between Shear Deformed Tissues The spacing between the shear deformable tissues is partially enlarged and shown in FIG. 2, which is the same schematic diagram as FIG.
As shown in FIG. 2, the interval between the shear-deformed tissues can be measured as an interval between adjacent boundaries (contrasts) having different colors and brightness indicated by square marks.
In the present invention, at the center of the thickness of the plate in plan view shown in FIG. 3, a hatched surface parallel to the rolling surface (rolling surface) is used as a structure observation surface (measurement surface) with a 5000 times SEM. When observed, all the intervals between adjacent shearing tissue bands that can be observed within the field of view of this SEM are measured and averaged to obtain the average interval between shearing deformed tissues per field of view.
And among the four average fields (average distance per field) when observing the four central portions in the plate width direction of the plate having arbitrary distances as the four fields by the SEM, The difference between the average interval that is the maximum value and the average interval that is the minimum value is the variation in the interval between the shear deformation structures.

As a result, the present invention can achieve both bending workability and high strength, which has been difficult to achieve in the past. That is, as a characteristic 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 bending workability of this plate are both high. can do.
More specifically, as in the examples described later, even when the 0.2% proof stress is 300 MPa or more, it has high bending workability and can have high strength and high formability.

Bending test As an evaluation index for bending workability of aluminum alloy plates for can lids, and as an evaluation index for comprehensive evaluation of severe formability and pressure resistance during thinning, push bending described later in FIG. Method (roller bending method). In this push-bending method, a plate-shaped test piece is placed on two supporting rotating rolls spaced apart, and a load is applied from above to the center of the plate with a pressing metal, and the plate is bent downward. Bend into a letter shape.

This push-bending method is a severe test method among bending work tests. If the bending workability evaluated by this push-bending process is improved, the formability of a 5000 series aluminum alloy plate for can lids is improved and the wall thickness is reduced. Even if it is done, it resists lid processing and is difficult to break, and coating film defects such as coating film peeling due to lid processing are less likely to occur.
In addition, cracks are less likely to occur during deformation due to changes in internal pressure after beverage filling, and pressure resistance increases as a lid after being attached to a can.
That is, according to this push-bending method, whether the conventional 5000 series aluminum alloy plate for can lids has comprehensive properties such as formability and pressure resistance on the premise of having high material strength. Can be evaluated.
In other words, even if individual or individual evaluation of specialized formability such as rivet formability is good, if the bending workability by this push bending method is not excellent, as a 5000 series aluminum alloy plate for can lids, This means that it does not always have characteristics such as moldability and pressure resistance.

  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.

Manufacturing method Next, the manufacturing method of the aluminum alloy plate for can lids in this invention is demonstrated.
The production process of the aluminum alloy sheet of the present invention itself 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 homogenization heat treatment process in which the ingot is homogenized by heat treatment. A hot rolling process in which a homogenized ingot is hot-rolled to form a hot-rolled sheet, a primary cold-rolling process in which the hot-rolled sheet is cold-rolled, and an intermediate annealing of the primary cold-rolled sheet The intermediate annealing process is performed, and the secondary cold rolling process is performed to cold-roll the intermediate annealed plate. 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. Incidentally, in continuous (CC) casting, the size of the intermetallic compound is small and the volume ratio is also small, so there is a possibility that the openability of the can deteriorates (the open load increases), and it is better to use the DC casting method. preferable.

Homogenization heat treatment Next, after removing a region that becomes a non-uniform structure of the ingot surface layer by chamfering, a homogenization heat treatment 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. Therefore, the homogenization heat treatment is preferably maintained 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 homogenization effect may be reduced, and the mechanical properties and can openability may be reduced. The upper limit of the holding time is 20 hours, and even if it exceeds this, there is no great difference in the homogenizing effect, and the productivity may decrease.

Hot rolling After this homogenization heat treatment, the ingot is continuously cooled or cooled to a predetermined starting temperature, first hot rough rolled, and then hot finish rolled to obtain an aluminum alloy having a predetermined thickness. A hot rolled sheet is used. At this time, it is preferable to finish the finish hot rolling at 300 ° C. or higher.

Primary cold rolling, intermediate annealing, secondary cold rolling Next, this hot rolled sheet is subjected to primary cold rolling (primary cold rolling), intermediate annealing, secondary cold rolling (secondary cold rolling). Cold-rolled sheet (cold rolled sheet). In this cold rolling, both the primary cold rolling and the secondary cold rolling are performed as many times as necessary.

  Here, the number of rolling is the number of times the plate is rolled.

Primary cold rolling The total rolling reduction (total rolling reduction) of the primary cold rolling is preferably 60% or more and 90% or less, more preferably 70% or more and 85% or less.
When the total rolling rate is less than 60%, the accumulated strain due to rolling is insufficient, the recrystallized grain size becomes large in the intermediate annealing in the next process, and the bending workability may be deteriorated.
On the other hand, if the total rolling rate exceeds 90%, the number of rolling increases and productivity deteriorates.

  In the primary cold rolling, the winding temperature of the final pass is preferably 120 ° C. or higher, more preferably 150 ° C. or higher. When the coiling temperature is low, the variation in the dislocation density that remains is increased, and the bending workability is deteriorated.

Intermediate annealing It is preferable to increase the solid solution amount of the alloy element while performing the intermediate annealing and recrystallizing the cold-rolled sheet that has been subjected to the primary cold rolling.
This intermediate annealing is performed in a continuous annealing process (equipment), and is preferably performed in the shortest possible time of the maximum attainable temperature of 400 ° C to 550 ° C and the holding time at the maximum attainable temperature of 60s or less. It is preferable that both the heating rate up to and the cooling rate from the maximum temperature reached 100 ° C./min or more.
When the heating rate is less than 100 ° C./min, when the highest temperature exceeds 550 ° C., when the holding time exceeds 60 s, and when the cooling rate is less than 100 ° C./min, recrystallization after the annealing step is completed, respectively. Grain tends to be large. For this reason, bending workability may fall. Moreover, when the highest temperature of intermediate annealing is less than 400 degreeC, while a process structure | tissue will remain in the aluminum alloy plate after completion | finish of an annealing process, the solid solution amount of an alloy element may reduce.

Secondary cold rolling Subsequently, the cold-rolled sheet subjected to the intermediate annealing is subjected to secondary cold rolling again at a rolling frequency of 2 times or more.
At this time, in all rolling, the rolling rate (rolling rate) per rolling is preferably 30% or more, more preferably 40% or more, and further preferably 45% or more.
When the rolling rate per rolling is small, the strain penetration depth becomes shallow, and the strain at the center of the plate thickness becomes small. For this reason, the strain amount to be introduced differs depending on the crystal grains, and there is a possibility that the variation in the average interval of the shear deformation structure becomes large.

  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: After the metal baking temperature is 200 to 280 ° C. and a pre-coating plate is formed, it is formed into a can lid. In the present invention, the heat treatment simulating a paint baking process for evaluation of strength, bending workability, and can openability is 260 ° C. × 20 seconds in order to provide reproducibility from this paint baking process condition range. Is selected as one point.

(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 (blanking) a blank aluminum alloy plate (pre-coated plate), which has been pre-painted and baked, is drawn with a press to curl the outer periphery. After that, 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. 5 and 6 that is a groove of the drinking mouth, and to form irregularities and characters 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 wound and sealed from the opening to the opening of the can body filled with the 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 27 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 predetermined thickness.

In each example, as shown in Table 1, the hot-rolled sheet was subjected to primary cold-rolling by variously changing the rolling rate of the primary cold rolling and the winding temperature of the final pass, and the sheet thickness was set to 0. An 85 mm primary cold rolled sheet was used.
After this primary cold rolling, in each example, intermediate annealing was performed in a continuous annealing facility under the conditions that the maximum temperature of the plate was 400 ° C. and the holding time was less than 30 s. The heating rate up to the highest temperature and the cooling rate from the highest temperature during the intermediate annealing were set to 100 ° C./min or more in common with each example.
After this intermediate annealing, secondary cold rolling is performed by changing the rolling rate of each rolling in various ways as shown in Table 1 for each example in 2 to 4 rolling cycles. An aluminum alloy plate for can lid having a plate thickness of 0.215 mm was produced.

  No. 1 of Table 1 produced in this way. 1 to 27 aluminum alloy sheets were simulated by painting and baking treatment, and the same structure and properties were measured after applying only heat treatment at 260 ° C for 20 seconds in an oil bath without painting. This was used as a test material for evaluation.

Variation in Average Interval Between Shear Deformed Structures Variation in average interval between shear deformed structures of this test material was measured as described above. That is, samples for measurement were collected from arbitrary four locations from the above-mentioned test materials, and cross-section processing was performed using a cross section polisher made by JEOL, and the hatched surface of FIG. The surface parallel to the rolled surface in FIG. 1 is exposed to the surface as an SEM observation surface, and the average distance between the shear deformation structures adjacent to each other in FIG. Observed and measured.
At this time, the area per one visual field (measurement area) was set to 450 μm ^{2 for the} four visual fields.
And the difference (nm) of the maximum value and the minimum value of each average space | interval in these 4 visual fields was calculated | required, and 300 nm or less (excluding 0 nm) was set as the pass.
These results are shown in Table 1.

0.2% Yield Strength A JIS-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.

Bending workability The bending workability is obtained by processing the sample material into a plate-like test piece having a length of 80 mm and a width of 25 mm, and then pressing the plate-like test piece by a press bending method (roller bending method) shown in FIG. Placed on two supporting rotating rolls spaced 0.95 mm apart, bent from the top to the center of the plate by applying a load with a pusher with a tip of R of 0.2 mm from the top. It was bent into an acute V shape with an angle of 15 ° (shown in the range of 10 ° to 20 ° in FIG. 4).
And by observing the surface of the tip part, it is evaluated as ◯ that there is no wrinkle or crack, or wrinkle but not cracked has good bending workability and can be used for can lids did.
In addition, those having wrinkles and cracks with a width of 150 μm or less were evaluated as Δ for being usable for can lids depending on conditions.
Furthermore, those having large cracks with a width of 150 μm or more were evaluated as x because the bending workability was inferior and they could not be used for can lids.

Can Opening Load The test material was subjected to shell molding, conversion molding, and tab stake using a 204-diameter full-form end mold, and then a can opening test was performed.
FIG. 5 is a plan view of the can lid used in the can open test.
FIG. 6 is a cross-sectional view of the score 3 of the can lid used in the can open test.
FIG. 7 is a schematic view of a can opening load measuring machine for measuring the load at the time of opening the can. Among these, FIG. 7A is a perspective view of the can opening load measuring device 5. FIG. 7B is a schematic cross-sectional view of the vicinity of the can lid 1 at the time of measurement by the open load measuring device 5. FIG. 7C 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.

  Specifically, the can lid 1 is placed on the can opening load measuring device 5 so that the tab 4 is located above the score 3 with respect to the score 3 (FIG. 7C). A latch 6 is hooked on the tab 4 of the can lid 1 to form a latch 7 (FIG. 7B). 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 22 N or less.

As shown in Table 1, No. 1 within the specified range of the present invention. In Examples 1 to 14, the component composition is within the range of the invention, and all of them are manufactured under preferable manufacturing conditions.
For this reason, the dispersion | variation in the average space | interval of the said shear deformation structures can be suppressed to 300 nm or less (0 nm is not included) as a difference of the maximum value and the minimum value among the said average space | intervals.
As a result, no. In Examples 1 to 14, as shown in Table 1, 0.2% proof stress and can open load are appropriate, and bending workability is excellent. That is, the strength is increased while maintaining the moldability, and both the moldability and the strength 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 smaller the variation in the average interval between the shear deformation structures, the better the bending workability, and the difference between the maximum value and the minimum value of the average interval is 100 nm or less. It can be seen that (1, 5, 7 to 9.13, 14) is superior in bending workability to Examples (2-4, 6, 10-12) exceeding 100 nm. This tendency is the same in the comparative examples described later.

  On the other hand, no. In Comparative Examples 15 to 27, either the component composition or the variation in the average interval between the shear deformation structures is not within the specified range of the present invention, and as described below, 0.2% proof stress, bending workability, One of the opening loads does not meet the appropriate value.

No. No. 15, the Mg content is insufficient below the lower limit, is manufactured under preferable manufacturing conditions, satisfies the variation in the average distance between the shear deformation structures, and has good bending workability, but the 0.2% yield strength is too low. .
No. No. 16 is produced under preferable production conditions because the Mg content is excessive beyond the upper limit and satisfies the variation in the average interval between the shear deformation structures, but the strength is too high and bending workability is poor (bending A large crack occurred in the processing test), and the can open test was not performed.
No. No. 17 is produced under preferable production conditions because the Fe content is insufficient below the lower limit, satisfies the variation in the average distance between the shear deformation structures, and has good bending workability, but the can opening load is too large.
No. No. 18, since the Fe content exceeds the upper limit and is produced under preferable production conditions and satisfies the variation in the average interval between the shear deformation structures, a large crack (crack) occurs in the bending test, The can open test was not performed.

No. No. 19 is manufactured under preferable manufacturing conditions because the Si content is insufficient below the lower limit, satisfies the variation in the average distance between the shear deformation structures, and has good bending workability, but the opening load is too large.
No. No. 20, since the Si content exceeds the upper limit and is produced under preferable production conditions and satisfies the variation in the average interval between the shear deformation structures, a large crack (crack) occurs in the bending test, The can open test was not performed.
No. No. 21 has a Mn content of less than the lower limit, and is produced under preferable production conditions, satisfies the variation in the average distance between the shear deformation structures, and has good bending workability, but the 0.2% yield strength is too low.
No. No. 22, since the Mn content is excessive beyond the upper limit, it is manufactured under preferable manufacturing conditions and satisfies the variation in the average interval between the shear deformation structures, but a large crack (crack) occurs in the bending test, The can open test was not performed.

No. No. 23 has a Cu content of less than the lower limit, so that the 0.2% yield strength is too low.
No. 24, because the Cu content is excessive beyond the upper limit, it is manufactured under preferable manufacturing conditions and satisfies the variation in the average interval between the shear deformation structures, but a large crack (crack) occurs in the bending test, The can open test was not performed.

No. No. 25, although the alloy composition is within the scope of the present invention, the rolling ratio of the primary cold rolling is too high, the variation in the average interval between the shear deformation structures exceeds 300 nm, and the bending workability is poor.
No. No. 26, although the alloy composition is within the scope of the present invention, the winding temperature of the final pass of the primary cold rolling is too low, the variation in the average spacing between the shear deformation structures exceeds 300 nm, and the bending workability Is bad.
No. 27, although the alloy composition is within the scope of the present invention, the rolling ratios of the second and third passes in the secondary cold rolling are each too low, and the variation in the average interval between the shear deformation structures exceeds 300 nm, Bending workability is poor.

  The above results support the significance of each requirement and preferred production conditions of the present invention for combining high strength, bending workability, and can openability.

As described above, the present invention provides a can lid aluminum alloy plate that has high strength, bending workability, and can openability without the need to reduce material strength to obtain formability as in the prior art. it can.
For this reason, it is optimal for an aluminum alloy plate used for a can lid that is thinned and strengthened, and that requires high formability under more severe conditions and can openability.

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: It is an aluminum alloy plate containing 0.01 to 0.30% by mass with the balance being Al and inevitable impurities, and when a plane parallel to the rolling surface at the center of the plate thickness is observed, In a shear deformation structure observed as a band-like structure extending in a direction substantially perpendicular to the rolling direction while being arranged at a distance from each other in a substantially parallel direction, parallel to the rolling surface at the thickness center of the plate. When the average surface per field of view is calculated by observing four planes with a SEM of 5000 times, averaging the total intervals between the shear deformation structures adjacent to each other that can be observed in each field of view, Maximum of each average interval in the field of view 300nm or less difference between the minimum value (not inclusive of 0 nm) as, wherein the suppressed variation of the shear deformation tissue interval between the adjacent, aluminum alloy sheet for can lid.