WO2017065137A1

WO2017065137A1 - Aluminum alloy plate for can end

Info

Publication number: WO2017065137A1
Application number: PCT/JP2016/080120
Authority: WO
Inventors: 康博有賀; 友己田中
Original assignee: 株式会社神戸製鋼所
Priority date: 2015-10-14
Filing date: 2016-10-11
Publication date: 2017-04-20
Also published as: CN108138271A; TWI607095B; JP2017075354A; TW201726937A

Abstract

A 5000-series aluminum alloy plate having a specific composition is produced by cold rolling without intermediate annealing so that the 5000-series aluminum alloy plate has a ratio of the minor axis to the major axis of crystal grains and an area ratio of Brass orientation crystal grains within specific ranges, has sufficient pressure-resistance strength after filling with a beverage and is excellent in rivet moldability as well as can openability and reduced in thickness to about 0.2 mm.

Description

Aluminum alloy plate for can lid

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 JIS 3000 (Al-Mn) aluminum alloy plate, and the can lid is made of AA to JIS 5000. (Al—Mg-based) aluminum alloy plates are widely used and widely 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.

Recently, 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.

Among these, as the texture of a 5000 series aluminum alloy plate for can lids having a 0.2% proof stress of less than about 300 MPa, the Cu orientation belonging to the rolling texture in the plate thickness surface or a quarter portion of the plate thickness direction, etc. It is known to control the ratio of the S direction and the Brass direction to the random direction.
For example, Patent Document 1 discloses that rivet formability and score processing are controlled by controlling any orientation component of the Cu orientation, S orientation, and Brass orientation belonging to the rolling texture on the surface of the plate thickness to 6 times or more of the random orientation. It has been proposed to improve performance.

In

Patent Documents

2 and 3, etc., the azimuth component of any one of the Cu azimuth, S azimuth, and Brass azimuth is controlled to be 50 times or less of the random azimuth to reduce the ear rate, It has been proposed to improve the tightening property when winding on the can body.

Furthermore, in Patent Document 4, a 5000 series aluminum alloy sheet for can lids is rolled to a final sheet thickness of 0.190 to 0.230 mm without intermediate annealing during hot rolling or cold rolling. It has been proposed to provide the required can lid strength with a 0.2% proof stress of 320 to 355 MPa by setting the ratio of crystal grain length to width and length / width to 20 or more (paragraph 0021, etc.).

Japanese Patent No. 3904868 Japanese Patent No. 3694859 Japanese Laid-Open Patent Publication No. 2001-348638 Japanese Unexamined Patent Publication No. 2012-112007

The above-described conventional 5000-series aluminum alloy plate for can lids with structure control still has a problem in improving the rivet formability when it is formed into a can lid. In order to obtain excellent rivet formability, it is necessary to reduce the material strength.

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 having a controlled structure as in Patent Documents 1 to 3, if the strength is increased, the rivet formability decreases, and in order to obtain excellent rivet formability, the material strength Needed to be reduced. That is, there is still a limit in achieving both excellent rivet formability and high strength.

Moreover, it is still a problem to realize both the rivet formability and the high strength by a low-cost manufacturing method by high-efficiency cold rolling without performing the intermediate annealing described in Patent Document 4 or the like. It had been.

In response to such a problem, the present invention has a high material strength and sufficient rivet formability, and even when it is thinned, there is no shortage of pressure strength after beverage filling, and rivet formability and An object of the present invention is to provide an aluminum alloy plate for can lids which is also excellent in can openability. And it aims at manufacturing the aluminum alloy plate for can lids which has such a high characteristic also by the cold rolling which does not perform intermediate annealing.

The gist of the aluminum alloy plate for can lids of the present invention for solving the above problems is as follows: Mg: 4.0 to 6.0 mass%, Fe: 0.10 to 0.50 mass%, Si: 0.05 to 0 .40% by mass, Mn: 0.01 to 0.50% by mass, Cu: 0.01 to 0.30% by mass, the balance being an aluminum alloy plate made of Al and inevitable impurities, SEM- As the structure of the plane parallel to the rolling surface at the sheet thickness center measured by the EBSD method, the average value of the ratio of the minor axis to the major axis in crystal grains having an orientation difference of 15 ° or more is 0.40 or more, 0.60. In addition, the average area ratio of the crystal grains having the Brass orientation to the measured total area is 15 to 30%.

As described above, the structure and properties of the plate defined in the present invention are as follows: as an aluminum alloy plate for can lids, as a pre-coated aluminum alloy plate after coating and baking treatment on a cold-rolled plate, or molding this plate Stipulated as the structure and characteristics of the can 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.

In the present invention, even in the case of an aluminum alloy plate for can lids that has been baked and coated after cold rolling without intermediate annealing, in order to combine strength and rivet formability, the aspect ratio of the crystal grains (short Along with the ratio of the axis to the major axis), the area ratio of crystal grains having a Brass orientation is selected and controlled as a texture.

As a result, the present invention does not need to lower the material strength in order to obtain rivet formability as in the prior art, not only in cold rolling in which intermediate annealing is performed, but also in cold rolling in which intermediate annealing is not performed. Despite having material strength, it can have sufficient rivet formability. 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 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 opening load measuring machine used at the time of evaluation of can opening property, and is the perspective view. It is a cross-sectional schematic diagram of the can lid vicinity at the time of the measurement of an open can load measuring machine. It is a front schematic diagram which shows the direction of a can lid when installing a can lid in a can opening load measuring machine.

Embodiments for carrying out the aluminum alloy plate for can lids according to the present invention will be described below.

(Composition of aluminum alloy plate)
As described above, the aluminum alloy plate for can lids, after being baked and coated, has the characteristics required for can lids, such as formability to withstand lid processing, pressure strength to withstand internal pressure after beverage filling, and normal and easy opening. It is necessary to satisfy the ability to open.

Therefore, the alloy composition of the aluminum alloy plate for can lids according to the present invention is also Mg: 4.0 to 6.0% by mass, Fe: 0.10 to 0.50 in order to satisfy this required characteristic from the viewpoint of the alloy composition. Containing 0.5% by mass, Si: 0.05-0.40% by mass, Mn: 0.01-0.50% by mass, Cu: 0.01-0.30% by mass, the balance being Al and inevitable impurities Shall be. Hereinafter, the significance of each element contained will be described in order.

Mg: 4.0 to 6.0% by mass
Mg has the effect of improving the strength of the aluminum alloy plate. When the content of Mg is less than 4.0% by mass, the strength of the aluminum alloy plate is insufficient, and the pressure resistance when formed into a can lid is insufficient. On the other hand, when the Mg content exceeds 6.0% by mass, the strength of the aluminum alloy plate becomes excessive, and the formability, particularly the rivet formability, is lowered. Accordingly, the Mg content is set to 4.0 to 6.0% by mass. Furthermore, the lower limit is preferably 4.4% by mass or more, and the upper limit is preferably 5.0% by mass or less.

Fe: 0.10 to 0.50 mass%
Fe forms Al—Fe (—Mn) -based and Al—Fe (—Mn) -Si-based intermetallic compounds in an aluminum alloy plate to improve the tearability of the score part when it is molded into a can lid, and it can be opened. There is an effect of improving canability. When the Fe content is less than 0.1% 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%. Furthermore, the lower limit is preferably 0.15% by mass or more, and the upper limit is preferably 0.40% by mass or less.

Si: 0.05-0.40 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 0.40% 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 0.40 mass%. Furthermore, the lower limit is preferably 0.20% by mass or more, and the upper limit is preferably 0.30% by mass or less.

Mn: 0.01 to 0.50 mass%
Mn has the effect of improving the strength of the aluminum alloy sheet, and when the 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 0.50% by mass, an intermetallic compound generated during casting or hot rolling in the aluminum alloy plate increases, and the rivet formability decreases. Therefore, the Mn content is set to 0.01 to 0.50 mass%. Furthermore, the lower limit is preferably 0.30% by mass or more, and the upper limit is preferably 0.40% by mass or less.

Cu: 0.01 to 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, the balance between strength and formability is lowered, and rivet formability is not improved. 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%. Furthermore, the lower limit is preferably 0.05% by mass or more, and the upper limit is preferably 0.30% by mass or less.

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.

(Aluminum alloy plate structure)
In the present invention, the area ratio of the crystal grains having the Brass orientation in a specific range as the structure of the aluminum alloy plate for can lids in the state of being baked and coated after cold rolling as a structure of the aluminum alloy plate for can lids. In addition, the aspect ratio of the crystal grains (ratio of minor axis to major axis) is controlled to increase the strength while maintaining the formability.

For this purpose, the average area ratio with respect to the total measured area of crystal grains having a Brass orientation as the structure of the center part of the thickness measured by the SEM-EBSD method of the aluminum alloy plate for can lid after the baking coating treatment Is 15 to 30%.
The structure of the center portion of the plate thickness is a plane parallel to the rolling surface at the center of the plate thickness (or the center of the plate thickness in a plane parallel to the rolling surface), that is, the rolling surface (rolling at the center of the plate thickness in a plan view of the plate). The surface is a structure extending in parallel with the surface), and this surface is an observation surface by the SEM-EBSD method.
Moreover, as the structure of the plate thickness center part, the average value of the ratio of the short axis to the long axis in the crystal grains having the orientation difference of 15 ° or more is set to 0.40 or more and 0.60 or less.

Thus, 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 heat treatment simulating the paint baking process and the rivet formability of this plate are as in the examples described later. Both can be at a high level.

Here, 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 sufficient rivet formability can be obtained. It can be said that it has.

As shown in the examples described later, this data is a 0.2% proof stress after heat treatment of 255 ° C. × 20 seconds simulating a paint baking process, and an evaluation of the rivet formability of this plate is a micro-extrusion test of φ6 mm. This is the relationship between the strength and the formability when the limit overhang height is set.

Crystal grains having a Brass orientation:
In the present invention, in an aluminum alloy plate for can lids that has been baked and coated after cold rolling without intermediate annealing, in order to combine strength and rivet formability, a crystal having a Brass orientation in the texture. Control the grain area ratio.
Specifically, the average area ratio of crystal grains having a Brass orientation as a structure in the central portion of the plate thickness measured by the SEM-EBSD method of the aluminum alloy plate for can lids is 15 to 30% with respect to the total measured area. And

If the average area ratio of the crystal grains having the Brass orientation is less than 15%, a 0.2% proof stress of 320 MPa or more cannot be ensured particularly in cold rolling in which intermediate annealing is not performed.
On the other hand, when the average area ratio of the crystal grains having the Brass orientation exceeds 30%, particularly in cold rolling without intermediate annealing, a 0.2% proof stress of 320 MPa or more can be secured, but the limit overhanging is achieved. It is not possible to achieve high formability with a high level.

Incidentally, the rivet formability of a high-strength plate having a 0.2% proof stress of 320 MPa or more is particularly affected by crystal grains having the Brass orientation, among Cu orientation, S orientation, and Brass orientation belonging to the rolling texture. . Therefore, in the vague method of controlling the crystal grain of any one of Cu orientation, S orientation, and Brass orientation as in the prior art, the 0.2% proof stress is 320 MPa or more particularly in cold rolling without intermediate annealing. There is no guarantee that the rivet formability of a plate with a high strength can be improved.

Grain aspect ratio:
In the present invention, in the aluminum alloy plate for can lids that has been baked and coated particularly after cold rolling without intermediate annealing, in order to combine strength and rivet formability, the area of the crystal grains having the Brass orientation Along with the rate, the aspect ratio of the crystal grains is also controlled.
Specifically, the ratio of the minor axis to the major axis (aspect ratio) of the crystal grains having an orientation difference of 15 ° or more as the structure of the aluminum alloy plate for can lids at the center of the plate thickness measured by the SEM-EBSD method. Ratio) is 0.40 or more and 0.60 or less.

Here, the short axis and the long axis in the crystal grains are the longest linear axes in the individual crystal grains (or regardless of the rolling direction (longitudinal direction of the plate) or the plate thickness direction in the crystal grains) Side) is defined as the major axis, and the shortest straight axis (or side) is defined as the minor axis. The ratio of the length of the short axis to the length of the long axis is defined as the ratio of the short axis to the long axis (short axis / long axis, aspect ratio).

As the cold rolling ratio increases, the crystal grains tend to become elongated grains (flat grains) having a shorter short axis and a longer long axis.
However, if the average value of the ratio of the minor axis to the major axis in this crystal grain is less than 0.40, the major axis is too long, or the minor axis is too short, and the crystal grains are excessively elongated (flattened) The rivet formability is reduced. For this reason, particularly in cold rolling without intermediate annealing, a 0.2% proof stress of 320 MPa or more can be secured, but the high formability at which the limit overhang height is at a high level is not achieved.

On the other hand, the fact that the average value of the ratio of the minor axis to the major axis in the crystal grains is higher than 0.60 indicates that the crystal grains are equiaxed grains or have a shape close to this, especially intermediate annealing. In cold rolling that does not perform, 0.2% proof stress of 320 MPa or more cannot be secured. Therefore, the upper limit of the average value of the ratio of the short axis to the long axis is preferably a small value for securing 0.2% proof stress, and is set to 0.60 or less, preferably 0.50 or less.

(Measurement by SEM-EBSD method)
In the above plate structure, the average area ratio of the crystal grains having the Brass orientation of the crystal grains having an orientation difference of 15 ° or more, and the average value of the ratio of the short axis to the long axis are measured with the rolling surface of the plate. The structure of the central part of the plate thickness on the parallel plane is measured by SEM-EBSD method.
Here, “a crystal grain having an orientation difference of 15 ° or more” measured by the SEM-EBSD method is “a crystal grain having a grain boundary (boundary) having an orientation difference of 15 ° or more”. Many crystal grains having an orientation difference of 15 ° or more, such as 20 °, are included in the category.

The specific measurement method is to use a measurement sample (three pieces) taken from an arbitrary position of the plate (approximately the center position in the width direction of the plate) as a plate thickness center portion of the sample in plan view of the plate. Polishing is performed so that an observation surface extending in parallel with the rolling surface (rolling surface) appears at the center. Then, using SEM-EBSD, 1.0 μm is measured with respect to a measurement range of a rectangular region in which the length of the side in the rolling direction of the plate is 1000 μm × the length of the side in the width direction of the plate is 320 μm. Irradiate an electron beam at a pitch.
Then, the average value of the ratio of the minor axis to the major axis of crystal grains having an orientation difference of 15 ° or more per sample, and the area of the measurement range that is the total measurement area of crystal grains having the Brass orientation (320,000 μm ² ) And the average area ratio (%) is measured and further averaged with three measured samples.

The SEM-EBSD (EBSP) method is a field emission scanning electron microscope (Field Emission Scanning Electron Microscope: FESEM) and a backscattered electron diffraction image [EBSD: Electron Back Scattering (Scattered) system equipped with a Scattered] system. This is a crystal orientation analysis method.

More specifically, the observation sample of SEM-EBSD is prepared by mirror-polishing the observation sample (cross-sectional structure) after further mechanical polishing. Then, it is set in a lens barrel of FESEM, and an electron beam is irradiated onto the mirror-finished surface of the sample to project EBSD (EBSP) on the screen. This is taken with a high-sensitivity camera and captured as an image on a computer.
In the computer, the orientation of the crystal is determined by analyzing this image and comparing it with a pattern obtained by simulation using a known crystal system. The calculated crystal orientation is recorded as a three-dimensional Euler angle together with position coordinates (x, y) and the like. Since this process is automatically performed for all measurement points, crystal orientation data of tens of thousands to hundreds of thousands of points in the cross section of the plate can be obtained at the end of measurement.

In the case of an aluminum alloy plate, usually, a texture composed of many orientation factors (crystal grains having these orientations) shown below is formed, and there are crystal planes corresponding to them. In general, a texture in a rolled sheet of an aluminum alloy mainly includes a Cube orientation, a Goss orientation, a Brass orientation, an S orientation, and a Copper orientation. How these textures are formed differs depending on the processing and heat treatment methods even in the case of the same crystal system. In the case of a texture of a plate material by rolling, the rolling surface is represented by the rolling surface and the rolling direction, and the rolling surface is represented by {hkl}. Expressed and the rolling direction is expressed as <uvw>. Based on this expression, each direction is expressed as follows.

Cube orientation {001} <100>
Goss orientation {011} <100>
Brass orientation (B orientation) {011} <211>
Cu orientation (Copper orientation) {112} <111>
S orientation {123} <634>

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 without being annealed. In other words, the aluminum alloy plate for can lids in the present invention has an advantage that it can be manufactured without greatly changing the conventional method.

The aluminum alloy plate for can lids of the present invention can be manufactured by cold rolling with intermediate annealing, but the present invention has high material strength and excellent rivet formability and can openability. It aims at being able to manufacture the aluminum alloy plate for can lids by cold rolling which is more difficult to manufacture and does not perform intermediate annealing.
Therefore, when explaining the following manufacturing steps, although it is common to cold rolling in which intermediate annealing is performed, preferable conditions for manufacturing by cold rolling in which intermediate annealing is not performed and its significance will be described.

First, the step of melting and casting the aluminum alloy can be performed by a conventional method using a known semi-continuous casting method such as a DC casting method, thereby casting an aluminum alloy ingot having the above composition.

Soaking process:
Next, after removing the area | region used as a non-uniform structure | tissue of the said ingot surface layer by chamfering, a soaking | uniform-heating process (homogenization heat processing) is performed. By this soaking process, the alloy elements are dissolved. Also, internal stress is removed, solute elements segregated during casting are homogenized, and intermetallic compounds crystallized during casting are diffused and dissolved to homogenize the structure. For this purpose, the homogenization heat treatment is selected from a range of conditions in which the temperature is maintained at a temperature exceeding 500 ° C. and not exceeding 550 ° C. for 1 hour or more.

When the homogenization heat treatment temperature is 500 ° C. or lower or when the holding time is less than 1 hour, the solid solution amount of Mg or Mn may be reduced and the strength may be insufficient. New characteristics and can openability may be reduced. On the other hand, if the homogenization heat treatment temperature exceeds 550 ° C., burning may occur during hot rolling. Accordingly, the homogenization heat treatment temperature is preferably in the range of more than 500 ° C. and 550 ° C. or less.
Moreover, the preferable upper limit of the holding time of the homogenization heat treatment under this temperature condition is 20 hours, and if it exceeds this, 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.

The end temperature of hot rough rolling is preferably 450 ° C. or higher. When this end temperature is less than 450 ° C., Mg—Si compounds are likely to precipitate, and the amount of solid solution Mg may decrease. Moreover, the rolling temperature in the hot finish rolling in the next step is lowered, and there is a possibility that edge cracks are likely to occur.

Subsequent to 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. Let it be a sheet.
When the finish temperature of hot finish rolling is less than 300 ° C., not only the rolling load increases and the productivity decreases, but also the ratio of the processed structure after the hot rolling finishes increases, and the baking finish treatment is performed after the cold rolling. There is a possibility that the area ratio of the crystal grains having the Brass orientation in the product plate becomes too high. On the other hand, when the temperature is higher than 360 ° C., the ratio of the recrystallized structure after the hot rolling is finished is high, and the area ratio of the Brass orientation grains in the product plate may be too low.

In order to control the texture, the average cooling rate between the material (plate) temperature immediately after completion of hot finish rolling and the material temperature of 150 ° C. is preferably controlled to 5 to 30 ° C./hour.
When this average cooling rate increases beyond 30 ° C./hour, the ratio of the processed structure of the plate after the hot finish rolling is increased, and the crystal grains having the Brass orientation in the product plate that has been baked and coated after the cold rolling. The area ratio may be higher than 30%. In addition, the average value of the ratio of the minor axis to the major axis of the crystal grains may be less than 0.40.
On the other hand, when the average cooling rate is less than 5 ° C./hour, the ratio of the recrystallized structure after the hot finish rolling is increased, and the crystal grains having the Brass orientation in the product plate that has been baked and coated after the cold rolling. The area ratio may be lower than 15%. In addition, the average value of the ratio of the minor axis to the major axis of the crystal grains becomes larger than the upper limit of 0.60, which may be too close to the equiaxed grains.

Cold rolling:
The hot-rolled sheet is cold-rolled without being subjected to intermediate annealing before cold rolling or in the middle of passes. In this cold rolling, the rolling stands are single (one stand) or two or more tandem rolling mills arranged in series to perform cold rolling for the required number of passes (number of sheets).

The cold rolling rate (total rolling rate) is preferably 85% or more and 92% or less.
The average value of the ratio of the minor axis to the major axis in the crystal grains having a cold rolling ratio of 92% or less and the orientation difference of 15 ° or more can be set to 0.40 or more. On the other hand, when the cold rolling rate exceeds 92%, the average value of the ratio of the minor axis to the major axis of the crystal grain becomes small, and the average value of the ratio of the minor axis to the major axis of the crystal grain becomes 0.40. Tends to be less than.
Further, the cold rolling rate is 85% or more, and the average value of the ratio of the minor axis to the major axis in the crystal grains can be less than 0.6. When the cold rolling ratio is less than 85%, the average value of the ratio of the minor axis to the major axis in the crystal grains becomes larger than the upper limit of 0.60, which may be too close to equiaxed grains.

In the final pass of this cold rolling, it is preferable that the tension on the unrolling side is 200 MPa to 600 MPa. When the tension on the plate exit side of this final pass is less than 200 MPa, there is a possibility that the area ratio of the crystal grains having the Brass orientation in the product plate that has been baked and coated after cold rolling is lower than 15%. Moreover, when the tension | tensile_strength of the plate | board exit side of the last pass exceeds 600 Mpa, not only the area ratio of the crystal grain which has a Brass orientation will become higher than 30%, but there exists a possibility that a plate may be cut | disconnected during rolling.

The aluminum alloy plate for can lids manufactured by the above process is subjected to a surface treatment such as chromate or zircon, applied with an organic paint such as epoxy resin, vinyl chloride sol or polyester, and PMT (Peak Metal Temperature: The metal reached temperature is about 230 to 280 ° C., and is baked to form a pre-coated plate, which is 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 the 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 25 was cast by a semi-continuous casting method (DC), and an ingot (slab) whose surface layer was faced was produced in common with each example. Then, as shown in Table 1, various conditions in the hot rolling and cold rolling of the ingot were changed, and the texture of the plate in the state of being baked and coated after the cold rolling was created.

The manufacturing conditions common to each example were as follows. That is, in each example, after performing a homogenization heat treatment of 520 ° C. × 4 hours, hot rough rolling is started at a temperature of 520 ° C., and the end temperature of the hot rough rolling is set to 450 ° C. or more. After the hot rough rolling, hot finish rolling was started immediately to obtain a hot rolled sheet having a sheet thickness of 1.4 to 3.6 mm. And this hot-rolled sheet is used for a can lid having a plate thickness of 0.215 mm by using tandem cold rolling with two rolling stands without performing any intermediate annealing after hot rolling or between cold rolling passes. A cold rolled sheet was created.

At this time, as shown in Table 1, among the manufacturing conditions of the plate, the finish temperature in the hot finish rolling and the average cooling rate from the material temperature immediately after the finish of the hot finish rolling to the material temperature of 150 ° C. are variously changed. At the same time, the texture of the plate was controlled by variously changing the total rolling rate in cold rolling and the tension on the plate exit side during the final pass.
And the No. of Table 1 manufactured in this way is shown. 1 to 25 aluminum alloy sheets that have been subjected to a heat treatment of 255 ° C. × 20 seconds in an oil bath, simulating the painting and baking process, are used for the following measurement and evaluation of the structure and properties. Samples were used. The measurement results of the following structures and characteristics are also shown in Table 1.

(Board texture)
The average area ratio of the crystal grains having the Brass orientation and the average value of the ratio of the minor axis to the major axis of the specimen were determined by the SEM-EBSD method using the above-described specific method. Measured by.

(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 320 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. As the 0.2% yield strength increases, the limit overhang height usually decreases. Therefore, when the 0.2% yield strength is in the range of 320 to 340 MPa, the limit overhang height exceeds 1.60 mm and the 0.2% yield strength is 340 MPa. Over the range of 360 MPa or less and the limit overhang height is 1. When the 0.2% proof stress exceeds 50 MPa at 50 mm or more, the limit overhang height is 1.45 mm or more as the appropriate range. If the limit overhang height of the aluminum alloy plate is more than 1.45 mm, 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. 1 is a plan view of a can lid used in a can open test.
FIG. 2 is a cross-sectional view of the score 3 of the can lid used in the can open test.
FIG. 3 is a schematic view of a can opening load measuring machine that measures the load at the time of opening the can.
FIG. 3A is a perspective view of the can opening load measuring machine 5.
FIG. 3B 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. 3C 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 device 5 so that the tab 4 is located above the score 3 with respect to the score 3 (FIG. 3C). A hook 6 is hooked on the tab 4 of the can lid 1 to form a hook 7 (FIG. 3B). 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. within the specified range of the present invention. In the inventive examples 1 to 9, the component composition is within the invention range, the finish temperature of hot finish rolling, the average cooling rate from the material temperature immediately after the finish of hot finish rolling to 150 ° C., the total rolling rate in cold rolling, The tension on the plate exit side at the final pass is all manufactured under preferable manufacturing conditions.

For this reason, the average value of the ratio of the minor axis to the major axis in crystal grains having a misorientation of 15 ° or more is 0.40 or more and 0.60 or less as the structure of the plate thickness center portion measured by the SEM-EBSD method. In addition, the average area ratio of the crystal grains having the Brass orientation to the measured total area is 15 to 30%. That is, in these invention examples, the ratio of the crystal grains having the Brass orientation and the average value of the ratio of the short axis to the long axis in the crystal grains are appropriately controlled as the structure of the aluminum alloy plate for the can lid.

As a result, No. Inventive examples 1 to 9, as shown in Table 1, the 0.2% proof stress and the can open load are appropriate, and the 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. Further, the can opening load is appropriate at 25 N or less.

Specifically, when the 0.2% yield strength is in the range of 320 to 340 MPa, the limit overhang height exceeds 1.60 mm, and when the 0.2% yield strength exceeds 340 MPa, the limit overhang height is increased. 1. When it is 50 mm or more and over 360 MPa, the limit overhanging height can be high strength and high formability at a level of 1.45 mm or more.
Therefore, no. The aluminum alloy plates 1 to 9 are as thin as 0.215 mm, but can be suitably used for easy open can lids.

On the other hand, no. In Comparative Examples 10 to 25, either the component composition or the structure at the center of the plate thickness is not within the specified range of the present invention, and any of 0.2% proof stress, can open load, and rivet formability is an appropriate value. Do not meet.

No. No. 10 has a Mg content of less than the lower limit and is produced under preferable production conditions, but the 0.2% yield strength is too low.
No. No. 11 was produced under preferable production conditions because the Mg content was excessive beyond the upper limit, but in the range where the 0.2% proof stress exceeded 360 MPa, the limit overhang height was the same as the above invention example. The rivet formability is inferior and the opening load is relatively large.

No. No. 12 is produced under preferable production conditions because the Fe content is insufficient below the lower limit, but the can opening load is too large and the can opening property is low.
No. No. 13 was produced under preferable production conditions because the Fe content exceeded the upper limit, but the 0.2% proof stress was in the range of 320 to 340 MPa. The rivet formability is inferior.

No. No. 14, since the Si content is insufficient below the lower limit, it is produced under preferable production conditions, but the can opening load is too large and the can opening property is low.
No. 15 is produced under preferable production conditions because the Si content exceeds the upper limit, but the 0.2% proof stress is as low as 315 MPa, but the above-mentioned limit overhang height is low, and rivet formability is low. Inferior.

No. No. 16 does not contain Mn and is manufactured under preferable manufacturing conditions, but the 0.2% proof stress is too low, the can opening load is too large, and the can opening property is low.
No. No. 17 is produced under preferable production conditions because the Mn content is excessive beyond the upper limit, but the limit overhang height at 0.2% proof stress is 358 MPa does not become 1.50 mm or more, and rivet molding Inferior.

No. No. 18 does not contain Cu and is manufactured under preferable manufacturing conditions, but the 0.2% proof stress is too low as less than 320 MPa, and the rivet formability is low even though the strength is low.
No. No. 19, because the Cu content is excessive beyond the present, and is manufactured under preferable manufacturing conditions, the 0.2% proof stress is 377 MPa, the limit overhang height is not 1.45 mm or more, Riveting formability is inferior.

No. No. 20, although the alloy composition is within the scope of the present invention, the average cooling rate from the material temperature immediately after completion of hot finish rolling to 150 ° C. is too slow, and the average area ratio relative to the measured total area of crystal grains having the Brass orientation Is too small with a lower limit of less than 15%. As a result, the 0.2% yield strength is too low, less than 320 MPa.
No. No. 21, although the alloy composition is within the scope of the present invention, the average cooling rate from the material temperature immediately after completion of hot finish rolling to 150 ° C. is too high, and the average area ratio with respect to the measured total area of crystal grains having the Brass orientation Is 36%, too much exceeding the upper limit of 30%. Moreover, the average value of the ratio of the short axis to the long axis in crystal grains having an orientation difference of 15 ° or more is 0.38, which is too small with a lower limit of less than 0.40. As a result, the limit overhang height when the 0.2% proof stress exceeds 360 MPa is not 1.45 mm or more, and the rivet formability is low.

No. No. 22, although the alloy composition is within the range of the present invention, the finish rolling finish temperature is too high, and the average area ratio with respect to the measured total area of the crystal grains having the Brass orientation is 10%, which is too small with a lower limit of less than 15%. . As a result, the 0.2% yield strength is too low, less than 320 MPa.
No. No. 23, although the alloy composition is within the range of the present invention, the total rolling ratio in cold rolling is too high, and the average value of the ratio of the minor axis to the major axis in crystal grains having an orientation difference of 15 ° or more is 0.38. The lower limit is less than 0.40 and is too small. Moreover, the average area ratio of the crystal grains having the Brass orientation with respect to the measured total area is 32%, too much, exceeding the upper limit of 30%. As a result, the limit overhang height at 0.2% proof stress of 372 MPa does not exceed 1.45 mm, and the rivet formability is low.

No. No. 24, although the alloy composition is within the range of the present invention, the tension on the platen side during the final pass in cold rolling is too low, and the average area ratio with respect to the measured total area of the crystal grains having the Brass orientation is 13%. Less than 15% and too little. As a result, the 0.2% proof stress is too low, less than 320 MPa, and the rivet formability is low even though the strength is low.
No. No. 25, although the alloy composition is within the range of the present invention, the tension on the plate-out side at the final pass in cold rolling is too high, and the average area ratio with respect to the measured total area of crystal grains having the Brass orientation is also 33% Too much over 30%. As a result, the limit overhang height when the 0.2% proof stress is 342 MPa does not exceed 1.50 mm, and the rivet formability is low.

From the above results, even in cold rolling without intermediate annealing, high rivet formability, high strength, and the ability to open cans can be combined. It is done.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on October 14, 2015 (Japanese Patent Application No. 2015-202844), the contents of which are incorporated herein by reference.

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 is no shortage of pressure resistance after beverage filling, excellent rivet formability and openability, and manufactured by cold rolling without intermediate annealing An aluminum alloy plate for a can lid can be provided.
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

Mg: 4.0 to 6.0% by mass, Fe: 0.10 to 0.50% by mass, Si: 0.05 to 0.40% by mass, Mn: 0.01 to 0.50% by mass, Cu: An aluminum alloy plate containing 0.01 to 0.30% by mass with the balance being Al and inevitable impurities, and the structure of the plane parallel to the rolling surface at the center of the plate thickness measured by the SEM-EBSD method Average ratio of the ratio of minor axis to major axis in crystal grains having an orientation difference of 15 ° or more is 0.40 or more and 0.60 or less, and the average area ratio with respect to the measured total area of crystal grains having a Brass orientation An aluminum alloy plate for can lids, characterized in that is 15 to 30%.