JP2017203201A - Can-top aluminum alloy sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a can-top aluminum alloy sheet providing excellent rivet moldability and can openability without causing insufficient pressure resistance even after charging a drink even when a thickness is thinned to approximately 0.2 mm.SOLUTION: Even when a sheet thickness is thinned to approximately 0.2 mm by making a crystal orientation difference in the same crystal grain having a large tilt angle grain boundary of a tilt angle of 15° or larger measured by a SEM-TKD method shown in FIG. 1 as a texture of a thickness center part of a 5000 series aluminum alloy having a specific composition, a can-top aluminum alloy sheet has excellent rivet moldability and can openability without causing insufficient pressure-resistance after charge of a drink.SELECTED DRAWING: Figure 1

Description

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

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

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

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

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

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

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

  Further, as a development of analytical analysis technology, in Non-Patent Document 1, although it is not a 5000 series aluminum alloy plate for can lids, the crystal orientation analysis of the Mg-2Gd-1Zn (at%) alloy structure is performed by the SEM-TKD method (Transmission Kikuchi Diffraction) describes that crystal orientation analysis has become possible. In Non-Patent Document 1, a clear crystal orientation map of crystal grains of the alloy is published.

As introduced in Non-Patent Document 2, the SEM-TKD method is an improved version of the electron backscatter diffraction (EBSD method) widely used for microstructural observation of materials. It is also expressed as an electron backscatter diffraction method, a transmission EBSD method, and t-EBSD.
Here, “transmission EBSD” or “t-EBSD” is an abbreviation for Transmission Electron BackScattered Diffraction Pattern.
The conventional SEM-EBSD method analyzes a Kikuchi pattern formed by diffraction of electrons reflected from a sample, and the Kikuchi pattern is relatively unclear in a strongly processed material, and crystal orientation analysis cannot be sufficiently performed. .
On the other hand, this SEM-TKD method analyzes the Kikuchi pattern formed by diffraction of the transmitted electron, not the sample, and has higher resolution than the conventional SEM-EBSD method, Since even a small misorientation can be detected, the crystal orientation analysis that could not be sufficiently analyzed until now can be made in detail. For this reason, including the present invention, this SEM-TKD method can be used to control the orientation difference in the crystal grains that could not be controlled until now. As described above, since 2012, it has begun to spread to crystal orientation analysis of metal materials in Japan.

Japanese Patent Laid-Open No. 11-229066

The Japan Institute of Metals 2015 (157th) Lecture Meeting “SEM-TKD Measurement Conditions and Application to Metal Materials” Toshika Yoda, Tomomi Moronaga, Kazuyoshi Ooi, Yasuhiro Ariga Journal of the Japan Institute of Metals, Vol. 77, No. 7 (2013), pp. 268-275 “Evaluation of Transmission EBSD Method and Application to Observation of Material Microstructure” Seiichi Suzuki

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

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 molding, a die having a V-shaped cutting edge is pressed to form the score 3 in FIGS. 3 and 4 which is the groove of the drinking mouth, and the formation of irregularities and letters 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, in the conventional structure control described above, when the strength is increased, the rivet formability is lowered, and in order to obtain excellent rivet formability, it is necessary to reduce the material strength. That is, in the conventional structure control, there is still a limit in achieving both rivet formability and high strength.

  Further, the SEM-TKD method has not yet been applied to the crystal orientation analysis of the aluminum alloy plate for can lids, and has been analyzed by the SEM-TKD method with the problem of compatibility between rivet formability and high strength. The relationship with the crystal orientation remained unknown.

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

  The gist of the aluminum alloy plate for can lids of the present invention for solving the above problems is as follows: Mg: 3.8 to 5.5% by mass, Fe: 0.10 to 0.50% by mass, Si: 0.05 to 0 30% by mass, Mn: 0.01 to 0.60% by mass, Cu: 0.01 to 0.30% by mass, the balance being an aluminum alloy plate made of Al and inevitable impurities, In a crystal grain having a large-angle grain boundary having an inclination angle of 15 ° or more when measured by a SEM-TKD method with a step number of 0.025 μm using a cross section including the rolling direction and the thickness direction at the center of the plate thickness as an observation surface The average crystal orientation difference between adjacent measurement points, defined as “misorientation” on a line parallel to the rolling direction, is 1.5 ° or less (excluding 0 °), and the crystal Spacing of measurement points where the azimuth difference is 1.5 ° or more Is 400 nm or more on average.

  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 controls the crystal orientation difference in a crystal grain having a large tilt boundary as analyzed by the SEM-TKD method as a structure of an aluminum alloy plate for a 5000 series can lid, and maintains strength. Improve formability.
That is, adjacent to each other when a crystal orientation difference in a crystal grain having a large-angle grain boundary with an inclination angle of 15 ° or more is measured by the SEM-TKD method shown in FIG. Even when the average of the crystal orientation difference between the measurement points is reduced and the average distance (interval) of the measurement points having a large crystal orientation difference is increased to reduce the plate thickness to about 0.2 mm, There is no shortage of pressure strength after filling, and rivet formability and can openability are also improved.

As a result, the present invention can achieve both excellent rivet formability and high strength of the aluminum alloy plate for a 5000 series can lid, which has been difficult to combine in the past.
In the present invention, in order to obtain rivet formability as in the prior art, it is not necessary to reduce the material strength, and high rivet formability can be achieved despite having sufficient material strength. For this reason, even when the plate thickness is reduced to about 0.2 mm, there can be provided an aluminum alloy plate for can lids which is not deficient in pressure-resistant strength after beverage filling and is excellent in rivet formability and can openability.

It is the schematic which shows the SEM-TKD method used by this invention. It is a schematic diagram of the crystal orientation map measured by SEM-TKD method. It is a top view of the can lid formed by shape | molding an aluminum alloy plate. It is sectional drawing of the score of the can lid used at the time of evaluation of can opening property. It is a schematic diagram of the can open load measuring machine used at the time of evaluation of can openability. FIG. 5A is a perspective view of an open load measuring machine. FIG.5 (b) is a cross-sectional schematic diagram of the can lid vicinity at the time of the measurement of an open can load measuring machine. FIG.5 (c) 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.

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

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

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

Mg: 3.8 to 5.5% by mass
Mg has the effect of improving the strength of the aluminum alloy plate. When the content of Mg is less than 3.8% by mass, the strength of the aluminum alloy plate is insufficient, and the pressure strength when formed into a can lid is insufficient. On the other hand, when the Mg content exceeds 5.5% by mass, the strength of the aluminum alloy plate becomes excessive, and the formability, particularly the rivet formability, is lowered. Therefore, the Mg content is 3.8 to 5.5% by mass, preferably 3.8 to 5.0% by mass.

Here, when Mg forms a solid solution in the matrix phase, a large lattice strain is generated, so that work hardening characteristics are improved. When the solid solution amount of Mg is reduced, undissolved Mg exists as a compound of Mg ₂ Si or Mg ₂ Al ₃ , and this compound causes cracking and constriction at the time of rivet molding. Reduce sex.
Accordingly, in order to increase the strength of the Mg contained in the above range while maintaining the rivet formability, the higher the solid solution amount (solid solution ratio) of Mg, the better, and 80% or more of the Mg content, preferably Is preferably 88% or more. Although the upper limit of the solid solution amount (solid solution ratio) of Mg is not particularly defined, it is about 99%.

Fe: 0.10 to 0.50 mass%
Fe forms Al-Fe (-Mn) -based and Al-Fe (-Mn) -Si-based intermetallic compounds in the aluminum alloy plate, and improves the tearability of the score part when it is molded into a can lid. There is an effect of improving canability. 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 0.10 to 0.50 mass%, preferably 0.10 to 0.30 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, the number density and volume ratio of the intermetallic compound produced during casting and hot rolling in the aluminum alloy plate increase, and the rivet formability decreases. Accordingly, the Si content is 0.05 to 0.30 mass%, preferably 0.05 to 0.20 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, the number density and volume ratio of the intermetallic compound generated during casting or hot rolling in the aluminum alloy plate increase, and the rivet formability decreases. Therefore, the Mn content is 0.01 to 0.60 mass%, preferably 0.30 to 0.50 mass%.

Cu: 0.01-0.30 mass%
Cu has the effect of improving the strength of the aluminum alloy plate. Moreover, work hardening characteristics improve by making it dissolve. When the Cu content is less than 0.01% by mass, the solid solution amount is small and the strength is lowered.
On the other hand, when the Cu content exceeds 0.30% by mass, the strength of the aluminum alloy plate becomes excessive, and the rivet formability decreases. Therefore, the Cu content is 0.01 to 0.30 mass%, preferably 0.05 to 0.20 mass%.

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

(Aluminum alloy plate structure)
In the present invention, the above-mentioned alloy composition is used, and the crystal orientation difference in the crystal grains having a large tilt boundary is determined based on the crystal orientation analysis by the SEM-TKD method in the structure of the aluminum alloy plate for can lids. Control to improve moldability while maintaining strength.
For this purpose, as a structure of the thickness center portion (plate thickness center position) of the aluminum alloy plate for can lids, on a line parallel to the rolling direction in a crystal grain having a large tilt grain boundary with a tilt angle of 15 ° or more, Defines the crystal orientation difference between adjacent measurement points, defined as “misorientation”.
A crystal orientation map as schematically shown in FIG. 2 is obtained by crystal orientation analysis by the SEM-TKD method. In the crystal orientation map of FIG. 2, the vertical direction is the rolling direction of the plate, the horizontal direction is the plate thickness direction, and the cross section of the plate including the rolling direction and the plate thickness direction at the plate thickness center is observed. It is a surface.
In the visual field shown in FIG. 2, each drawn solid line is a large-angle grain boundary having an inclination angle of 15 ° or more, and crystal grains having the large-angle grain boundary extend in the rolling direction (vertical direction in the figure). In addition, they are arranged adjacent to each other in the plate thickness direction (left-right direction in FIG. 2).
And even if it is one crystal grain, for example, as shown in each crystal orientation shown by a leader line on a one-dot chain line parallel to the rolling direction in the central crystal grain shown in FIG. There are various crystal orientations depending on the position, and there are crystal orientation differences.
As shown in FIG. 2, the difference in crystal orientation depending on the position in one crystal grain has a great influence on characteristics such as rivet formability even if it is very small (not large). They found out.

For this reason, in the present invention, the average (°) of crystal orientation difference between the adjacent measurement points on the line parallel to the rolling direction in the crystal grain having a large tilt grain boundary with a tilt angle of 15 ° or more, That is, an average angle and an average (nm) of intervals between measurement points at which the crystal orientation difference is 1.5 ° or more are defined.
Specifically, as in the crystal orientation map shown in FIG. 2, a step including the rolling direction and the plate thickness direction at the plate thickness center of the plate is used as an observation plane, and the step is performed by the SEM-TKD method shown in FIG. The measurement is performed at several 0.025 μm, and analysis is performed by paying attention to the slight difference in crystal orientation or crystal orientation due to the position in the grain.
And in the crystal grain having a large inclination grain boundary with an inclination of 15 ° or more obtained by this measurement, the average (misorientation) of the crystal orientation difference between the adjacent measurement points on the line parallel to the rolling direction is calculated. 1.5 ° or less (excluding 0 °), preferably 1.0 ° or less (excluding 0 °), more preferably 0.7 ° or less (excluding 0 °). . Here, “1.5 ° or less (excluding 0 °)” has the same meaning as “range of more than 0 ° and 1.5 ° or less”.
In the present invention, at the same time, the interval between the measurement points obtained by the measurement and having the crystal orientation difference of 1.5 ° or more is increased to an average of 400 nm or more, preferably 600 nm or more.

  Thereby, even when the plate thickness is reduced to about 0.2 mm, there is no shortage of pressure strength after filling the beverage, and the rivet moldability and can openability are improved.

The rivet formability can improve the formability by suppressing cracks and constriction at the time of molding by suppressing the shear band generated at the time of overhanging.
In the present invention, the smaller the crystal orientation difference in the same crystal grains of the plate and the smaller the number of locations where the orientation difference is, the more the shear band that occurs when the rivet formability is extended is suppressed, and cracks and constriction during molding occur. It was found that the rivet formability was improved.

  Therefore, when the average crystal orientation difference between adjacent measurement points exceeds 1.5 °, or the interval between the measurement points at which the crystal orientation difference is 1.5 ° or more is less than 400 nm on average In this case, the shear band generated when the rivet formability is extended is not suppressed, and cracking and constriction during forming cannot be suppressed, and the rivet formability is not improved.

Thus, the present invention can achieve both rivet formability and high strength, which have been difficult to achieve in the past. That is, as the characteristics of the aluminum alloy plate for can lids, the 0.2% proof stress of the aluminum alloy plate for can lids after being baked and coated after cold rolling and the rivet formability of this plate are both high. can do.
Specifically, as in the examples described later, even if the 0.2% proof stress is 300 MPa or more, it is possible to achieve high strength and high formability with a limit overhang height of 1.50 mm or more. If the limit overhang height of the plate is 1.50 mm or more, the above-described protrusion (button) having a sufficient height can be formed even when the can lid is actually formed, and has sufficient rivet formability. Yes.

  In addition, this data is a characteristic of the aluminum alloy plate for can lids after being baked and coated after the cold rolling, as simulated in the examples described later, after the heat treatment of 260 ° C. × 20 seconds, simulating the coating and baking process. This is the relationship between the strength and the formability when the 0.2% proof stress and the evaluation of the rivet formability of this plate are the limit overhang height when a φ6 mm minute overhang test is conducted.

(Crystal orientation analysis method by SEM-TKD method)
Below, the crystal orientation analysis method by SEM-TKD method is demonstrated.
In the present invention, the SEM-TKD method (Transmission Kikuchi Diffraction) of the structure at the thickness center (plate thickness center position) of the 5000 series aluminum alloy plate for can lids under the same conditions as the method disclosed in Non-Patent Document 1 above. Perform crystal orientation analysis.
The measurement principle of the SEM-TKD method is shown in the schematic diagram of FIG.
As shown in FIG. 1, an electron beam (Primary Electron Beam) is incident on a thin film sample (TEM Specimen) collected from the center of the thickness of a 5000 series aluminum alloy plate for can lids.
The Kikuchi pattern formed by diffraction of electrons transmitted through the thin film sample is captured by a detector of a SEM-EBSD system (scanning electron microscope-backscattered electron diffraction [EBSD "Electron Back Scattering Diffraction"]). .
Further, the Kikuchi pattern is subjected to crystal orientation analysis by creating a crystal orientation map as shown in FIG. 2 by the electronic channeling pattern method (ECP method) in the same manner as the SEM-EBSD method.
Details of this crystal orientation analysis method are described in Kobe Steel Technical Report / Vol. 52 no. 2 (Sep. 2002) P66-70 and the like.

According to the SEM-TKD method, as shown in the crystal orientation map of FIG. 2, it extends over the rolling direction (vertical direction in the figure) and is adjacent to each other in the plate thickness direction (horizontal direction in FIG. 2). It is possible to clearly recognize and identify crystal grains themselves having a plurality of aligned grain boundaries having a large tilt angle of 15 ° or more, and crystal orientations that are different from each other within each grain.
For this reason, the crystal orientation on a line parallel to the rolling direction in crystal grains having a large tilt grain boundary with an tilt angle of 15 ° or more can be continuously measured at a constant measurement interval.
Thereby, the crystal misorientation at each measurement point on the line parallel to the rolling direction in the crystal grain can be measured, and the crystal grain having the large tilt grain boundary is parallel to the rolling direction. The crystal orientation difference (°) between adjacent measurement points (adjacent measurement points) on the line and the interval (nm) between the measurement points where the crystal orientation difference is 1.5 ° or more can be analyzed.

Here, the said observation surface (analysis surface) by SEM-TKD method makes the plate | board thickness center in the 5000 series aluminum alloy plate for can lids an observation surface.
From the reproducibility of measurement, the plate thickness center observation surface is preferably the plate thickness in the cross section (cross section perpendicular to the plate width direction) including the rolling direction and the plate thickness direction at the plate thickness center shown in FIG. An observation surface having a width of 10 to 15 μm in the thickness direction (left and right direction in FIG. 2) with the center at the center is assumed.
A crystal grain having a large tilt grain boundary for measuring a crystal orientation difference in a crystal grain is a plurality of crystal grains arranged in the plate thickness direction from the reproducibility of the measurement, and the number of crystal grains is 6 or more. And And each average (value) prescribed | regulated in Claim 1 by averaging the crystal orientation difference between adjacent measurement points, and the space | interval of the measurement points from which the said crystal orientation difference becomes 1.5 degrees or more, respectively. To do.

  In addition, the measurement length (distance) is set to 0 (measurement interval (step size)) over a length of 10 μm or more in the rolling direction (vertical direction in FIG. 2) of the plate in the crystal grains from the reproducibility of the measurement. As 0.25 μm, for example, the measurement is continuously performed on the straight line shown in FIG.

The measuring device of the SEM-TKD method can use, for example, Ultra55 made by FESEM Carl Zeiss, which is the same as Non-Patent Document 1, and the EBSD system / detector can also use Channel 5 made by Oxford.
Furthermore, the preparation of the sample collected from the center of the thickness of the 5000 series aluminum alloy plate for can lids as a thin film sample is FIB processing (focused ion beam processing: Focused) known as a method for preparing a thin film sample used in TEM or the like. Ion Beam method is used.

  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 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.

Next, after removing the area | region used as an inhomogeneous structure | tissue of an ingot surface layer by chamfering, homogenization heat processing is performed. As a result, internal stress is removed, solute elements segregated during casting are homogenized, and intermetallic compounds crystallized during casting are diffused and solidified to homogenize the structure. Therefore, the homogenization heat treatment is preferably maintained at a temperature of 450 ° C. or higher for 1 hour or longer.
If the homogenization heat treatment temperature is less than 450 ° C. or the holding time is less than 1 hour, the solid solution amount of Mg decreases, the homogenization effect also decreases, and mechanical properties and can openability may decrease. . The upper limit of the holding time is 20 hours, and even if the upper limit is exceeded, the homogenization effect is not significantly different and the productivity is lowered.

Hot rolling:
After this homogenization heat treatment, the ingot is continuously cooled or cooled to a predetermined starting temperature, first hot rough rolled, and further hot finish rolled to hot-roll aluminum alloy having a predetermined thickness. A board. At this time, it is preferable to perform hot rolling while suppressing precipitation of Mg so as not to reduce the solid solution amount of Mg secured by soaking. For this reason, in the hot rough rolling, the temperature at which the rough rolled sheet is minimum between passes is preferably 450 ° C. or higher.

  Following this hot rough rolling, hot finish rolling at an end temperature of preferably 300 to 360 ° C. 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., the rolling load increases and the productivity decreases. On the other hand, in order to obtain a recrystallized structure without leaving a large amount of processed structure, when the finish temperature of hot finish rolling is increased, if this temperature exceeds 360 ° C., an Mg—Si compound tends to precipitate and become solid. There is a possibility that the amount of dissolved Mg decreases.

Cold rolling and intermediate annealing:
Subsequently, this hot-rolled sheet is subjected to primary cold rolling (primary cold rolling), intermediate annealing, secondary cold rolling (secondary cold rolling) to obtain a cold rolled sheet (cold rolled sheet). The primary cold rolling and the secondary cold rolling are divided into a plurality of times of rolling and rolled to a predetermined rolling rate. Under the present circumstances, the said crystal orientation difference in the crystal grain which has a large inclination grain boundary of a cold rolled sheet is controlled to the range prescribed | regulated by this invention with the roll diameter and roll temperature in the case of the final rolling of the said secondary cold rolling.

First, the total rolling rate of the primary cold rolling is preferably 50% or more. When the total rolling rate is less than 50%, the accumulated strain due to rolling becomes insufficient, the recrystallized grain size becomes large by the intermediate annealing in the next step, and the formability including the rivet formability may be deteriorated.
The primary cold-rolled cold-rolled sheet is subjected to intermediate annealing and recrystallization, and the solid solution amount of Mg is increased. This intermediate annealing is performed in a continuous annealing step (equipment), preferably in a material holding temperature range of 450 ° C. to 550 ° C. and a holding time of 10 minutes or less, from the heating rate up to the holding temperature and the holding temperature. The cooling rate is preferably 100 ° C./min or more. When the heating rate is less than 100 ° C./min, when the holding temperature exceeds 550 ° C., when the holding time exceeds 10 minutes, and when the cooling rate is less than 100 ° C./min, recrystallized grains after completion of the annealing step, respectively Becomes larger. For this reason, rivet formability may be reduced. Moreover, when the holding temperature of intermediate annealing is less than 450 ° C., the solid solution amount of Mg decreases, and the rivet formability may also decrease.

The total rolling rate of the secondary cold rolling is set to 60% or more, and the roll diameter in the final rolling of the secondary cold rolling is preferably a small diameter roll of 800 mm or less, more preferably 400 mm or less. Together with this, it is preferable that the roll temperature in the final rolling of the secondary cold rolling is 80 ° C. or higher.
Thereby, dynamic recovery is promoted. Specifically, as the structure of the plate thickness center portion of the plate, the measurement points adjacent to each other in the crystal grains having a large tilt grain boundary having a tilt angle of 15 ° or more. The average of crystal orientation differences can be reduced, and the average interval between measurement points having a large crystal orientation difference can be increased.
When the temperature is lower than 80 ° C., the amount of dynamic recovery decreases, the average of crystal orientation difference becomes too large, and the average of the interval between measurement points where the crystal orientation difference becomes 1.5 ° or more becomes too small. The upper limit of the temperature is not particularly set, but is set to about 150 ° C. due to rolling mill restrictions.
Such roll temperature control is performed by using a coolant or a lubricant that is usually used for cold rolling.

By the secondary cold rolling under these conditions, the crystal orientation difference in the crystal grains having a large tilt grain boundary can be controlled within the range defined in the present invention.
On the other hand, when the roll diameter and the roll temperature at the time of the secondary cold rolling are out of the above preferable ranges, the crystal orientation in the crystal grains having a large tilt grain boundary, depending on the alloy composition. There is a high possibility that the difference cannot be controlled within the specified range.

The aluminum alloy plate for can lids manufactured in the above process is subjected to surface treatment such as chromate and zircon, and applied with organic paint such as epoxy resin, vinyl chloride sol, and polyester, and PMT (Peak Metal Temperature: metal arrival) After a coating baking process is performed at a temperature of 230 to 280 ° C. to form a pre-coated plate, it is formed into a can lid.
In the present invention, the heat treatment simulating a paint baking process for evaluating strength and rivet formability is performed at 260 ° C. × 20 seconds in order to provide reproducibility from the range of the paint baking process. Selected as a 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 a blank aluminum alloy plate (pre-coated plate) that has been pre-painted and baked into a disk shape (blanking) is drawn with a press machine to curl the outer periphery. After application, a sealing compound is applied to the curled portion to make a shell.
Thereafter, the following molding is performed as conversion molding. Using a press machine, rivet forming is performed to form a protrusion for attaching a tab to the center of the shell. This rivet molding is composed of a bubble molding process for projecting the central portion of the can lid and a button molding process for reducing the diameter of the projecting section (bubble) in 1 to 3 steps and making a sharp projection.

Next, a die having a V-shaped cutting edge is pressed to form a score 3 in FIGS. 3 and 4 which 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 wrapped around and sealed in the opening of the can body 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)
Each aluminum alloy having the composition shown in Table 1 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 is subjected to a homogenization heat treatment at 500 ° C. for 4 hours in common with each example, and then hot rough rolling is started at the temperature of 500 ° C., and the temperature at which the rough rolled plate is minimum between passes. The hot rough rolling was performed at a temperature of 450 ° C. or higher, the end temperature of the subsequent hot finish rolling was 330 ° C., and a hot rolled plate having a thickness of 3 mm was obtained.

The hot rolled sheet was subjected to primary cold rolling. However, in order to obtain the same final sheet thickness in each example while changing the secondary cold rolling rate, the rolling rate was performed at various rolling rates of 50% or more.
Thereafter, in each example, intermediate annealing was performed in a continuous annealing facility at a maximum material temperature of 450 ° C. and a holding time of less than 1 minute. The heating rate up to the holding temperature and the cooling rate from the holding temperature during the intermediate annealing were both set to 100 ° C./min or more in common.

  Thereafter, the secondary cold rolling is performed at the rolling rate (%) and the roll diameter (mm) shown in Table 1, the number of rolling is set to 2 times, and the roll temperature shown in Table 2 in the second final rolling. Rolling was performed so as to be (° C.). By this secondary cold rolling, an aluminum alloy plate for can lids having a plate thickness of 0.22 mm was produced in common with each example.

  The aluminum alloy plate produced in this way was simulated by a paint baking process, and in common, without being painted, only subjected to heat treatment at 260 ° C. for 20 seconds in an oil bath, with the following structure and characteristics: Samples for measurement and evaluation were used. These results are shown in Table 1.

(Mg solid solution amount)
The Mg solid solution amount (solid solution ratio) of the test material was measured as follows.
That is, first, after putting phenol into a decomposition flask and heating, the sample taken from each test plate (plate thickness center part) to be measured is transferred to this decomposition flask and heated and decomposed with hot phenol. To do. Next, it is filtered using a membrane filter with a mesh (collected particle diameter) of 0.1 μm, and the filtrate is introduced into an ICP (Inductively Coupled Plasma) emission spectroscopic analyzer, which is atomized with a nebulizer and made into a small mist. Only Mg was blown into the plasma, and the solid solution amount of Mg was measured. Even if the filtrate contains a precipitate of less than 0.1 μm, it is discharged without being analyzed as a large mist when the mist is formed. Is not included. And the ratio (%) with respect to Mg content of this board | plate of the solid solution amount of this Mg was calculated. As a result, in each example, the ratio (%) to the Mg content of the plate was 88% or more.

(Crystal orientation analysis by SEM-TKD method)
The structure at the center of the thickness of the specimen was measured by the SEM-TKD method with the number of steps of 0.025 μm using the cross section including the rolling direction and the thickness direction at the thickness center of the plate as the observation surface.
Then, in a crystal grain having a large tilt grain boundary with a tilt angle of 15 ° or more, the average (°) of crystal orientation difference between adjacent measurement points defined as “misorientation” on a line parallel to the rolling direction. The average (nm) of intervals between measurement points at which the crystal orientation difference was 1.5 ° or more was measured. Here, OIM Analysis ver.7.1.0 manufactured by EDAX was used as the analysis software.

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

(Rivet formability)
The rivet formability was evaluated by a test simulating the bubble process. That is, a φ6 mm minute overhang test was performed on the specimen, and the limit overhang height at which no necking or cracking occurred was obtained. The appropriate range of the limit overhang height was 1.50 mm or more. If the limit overhang height of the aluminum alloy plate is 1.50 mm or more, the protrusions (buttons) having a sufficient height can be formed even when the can lid is actually formed, and the rivet formability is sufficient. doing.

(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. 3 is a plan view of the can lid used in the can open test.
FIG. 4 is a cross-sectional view of the score 3 of the can lid used in the can open test.
FIG. 5 is a schematic view of a can opening load measuring machine that measures a load at the time of opening the can.
FIG. 5A is a perspective view of the can opening load measuring machine 5.
FIG. 5B is a schematic cross-sectional view of the vicinity of the can lid 1 at the time of measurement by the can opening load measuring device 5.
FIG. 5C is a schematic front view showing the direction of the can lid 1 when the can lid 1 is installed in the can opening load measuring device 5.

  The can lid 1 is placed on the can opening load measuring machine 5 so that the tab 4 is located above the score 3 with respect to the score 3 (FIG. 5C). A latch 6 is hooked on the tab 4 of the can lid 1 to form a latch 7 (FIG. 5B). 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 21 N or less.

As shown in Table 1, the inventive examples are produced under production conditions in which the component composition is within the scope of the invention and secondary cold rolling is preferred.
For this reason, as defined in the present invention, the average (average) of crystal orientation differences between adjacent measurement points on a line parallel to the rolling direction in a crystal grain having a large tilt grain boundary with a tilt angle of 15 ° or more. Angle) is 1.5 ° or less, and the interval between measurement points at which the crystal orientation difference is 1.5 ° or more is 400 nm or more on average.

  As a result, as shown in Table 1, the inventive examples have appropriate 0.2% proof stress and can open load, and excellent rivet formability. That is, the strength is increased while maintaining the moldability, and both the rivet moldability and the strength increase can be achieved. Specifically, high strength and high formability with a 0.2% proof stress of 300 MPa or more and a limit overhang height of 1.50 mm or more can be achieved. Therefore, the aluminum alloy plate of the embodiment has a thin plate thickness of 0.22 mm, but can be suitably used for an easy open can lid.

On the other hand, in the comparative example of Table 1, 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 as shown in Table 1, any of 0.2% proof stress, can open load and rivet formability Does not meet the appropriate value.
Comparative Example 17 has too little Mg.
Comparative Example 18 has too much Mg.
Comparative Example 19 has too little Fe.
Comparative Example 20 has too much Fe.
Comparative Example 21 has too little Si.
Comparative Example 22 has too much Si.
Comparative Example 23 has too little Mn.
Comparative Example 24 has too much Mn.
Comparative Example 25 has too little Cu.
Comparative Example 26 has too much Cu.
In Comparative Examples 27 and 28, the roll diameter of secondary cold rolling (final rolling) is too large.
In Comparative Examples 28 and 29, the roll temperature of secondary cold rolling (final rolling) is too low.

  From the above results, the significance of each requirement and preferred production conditions of the present invention for combining 0.2% proof stress, open load and rivet formability is supported.

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

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

Claims (1)

Mg: 3.8 to 5.5% by mass, Fe: 0.10 to 0.50% by mass, Si: 0.05 to 0.30% by mass, Mn: 0.01 to 0.60% by mass, Cu: An aluminum alloy plate containing 0.01 to 0.30% by mass with the balance being Al and inevitable impurities, and a cross section including the rolling direction and the plate thickness direction at the plate thickness center of this plate is used as an observation surface. -Adjacent, defined as "misorientation" on a line parallel to the rolling direction within a crystal grain having a large tilt grain boundary with a tilt angle of 15 ° or more when measured at a step number of 0.025 µm by the TKD method The average crystal orientation difference between the measurement points is 1.5 ° or less (excluding 0 °), and the interval between the measurement points at which the crystal orientation difference is 1.5 ° or more is 400 nm or more on average. Aluminum can for lids Gold plate.