JP2014125677A - Aluminum alloy sheet for di can barrel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet improving the piercing resistance of a can barrel to be made into a can.SOLUTION: Upon production of a 3000 series aluminum alloy sheet for a DI can barrel having a specified composition, the soaking conditions and cold rolling conditions of an ingot are controlled, the density of the aggregate of specified atoms is regulated in the produced cold rolled sheet structure, and the making of the structure of the can barrel into subgrains when the same is subjected to coating baking treatment (heat treatment) after made into a can barrel is promoted, thus the piercing resistance of the can is made excellent even in a using environment where the internal pressure of the thinned can barrel is lower and severer.

Description

  The present invention relates to a packaging container used for beverages and food applications, and more particularly to an aluminum alloy plate for a DI can body that is DI molded into a body portion of a beverage can.

  Currently, as one of packaging containers used for beverages and foods, a bottomed cylindrical body (can body) whose bottom and side walls are integrated, and an upper surface sealed by an opening of the body A two-piece can comprising a disc-shaped lid (can lid) is known. As a material for such cans, aluminum alloy plates such as AA to JIS3000 are widely used in terms of formability, corrosion resistance, strength, and the like. Among the two-piece cans manufactured with this aluminum alloy plate, the cylindrical portion of the cylindrical can having a height particularly like a beverage can has a lot of drawing and ironing called DI (Drawing and wall Ironing) molding. Often formed by step processing. And it is painted and baked, the diameter of the opening is reduced by necking, and the edge of the opening is expanded outward by flanging to form a can body. Finally, the contents (beverage, food) are filled in the body, and the lid is wound around the opening and sealed. A can made by such a manufacturing method is called a DI can (hereinafter referred to as “can” as appropriate) and is widely distributed.

  Conventionally, in order to reduce the cost of beverages packaged with such aluminum alloy cans, cans that are packaging containers have been reduced in thickness as measures for reducing weight and reducing raw materials (aluminum alloys). As a result, the thickness of the side wall (thinnest part) of the current aluminum alloy can is about 0.105 to 0.110 mm excluding the coating film. However, in such a thinned can, when a protrusion is brought into contact with and pressed against a thin side wall (circumferential surface), the tip penetrates the side wall and a hole (pin (Hall) may open and the contents may leak. Protrusion contact may include contact of hard foreign matter from the outside during manufacturing (filling contents, tightening the lid, passing through the transport system in the manufacturing process), distribution, and even when handled by consumers. Can be mentioned. Also, in the flanging process, when the edge of the opening is expanded, a crack (flange crack) may occur at the end of the opening.

  Therefore, the material of the thinned can can prevent the occurrence of pinholes on the side walls and cracks in the flanges of the openings, that is, improve the piercing resistance and flanging workability (can expandability) of the side walls. Improvement of the aluminum alloy plate on the side is underway.

  For example, Patent Document 1 discloses a method for designing a can body formed by DI molding or drawing from an aluminum alloy cold-rolled sheet having a 3000 series composition. That is, the thickness of the can body subjected to heat treatment equivalent to paint baking is in the range of 0.07 mm to 0.14 mm, the tensile strength in the can axis direction of this wall portion is 300 MPa to 500 MPa, and the elongation is 3% to 8%. In this case, the puncture strength with respect to the wall thickness (t) after removing the surface film such as a coating film can be converted to the puncture strength of a can having a wall thickness of 0.105 mm to obtain a puncture resistance of 35 N or more. I am doing so. For this reason, the thickness of the wall portion for obtaining the piercing strength is determined from the Mg content, or the Mg content with respect to the predetermined wall portion thickness is determined from the desired piercing strength.

  Various techniques for improving the puncture resistance by controlling the intermetallic compound of the aluminum alloy cold rolled sheet having a 3000 series composition have also been proposed. For example, Patent Document 2 discloses a technique for distributing an intermetallic compound at a specific density and a specific area ratio on the surface of an aluminum alloy cold rolled sheet having a 3000 series composition. Then, when the side wall thickness including the outer surface and inner surface coating of the DI molded can body is 0.110 to 0.130 mm, the elongation of the side wall in the can axis direction is 3% or more and less than 6%. The strength exceeds 290 MPa and is equal to or less than 330 MPa to improve puncture resistance.

  In Patent Documents 3 and 4, a technique for improving strength (piercing resistance) and toughness by controlling the distribution density and area ratio of an intermetallic compound of a predetermined size in an aluminum alloy cold-rolled sheet having the same 3000 series composition. Is disclosed. Furthermore, in Patent Document 5, an aluminum alloy cold-rolled plate having the same 3000 series composition is DI molded at a predetermined processing rate and heat-treated at 210 to 250 ° C., thereby controlling work hardening and tensile strength by DI molding. And the technique which improves puncture resistance is disclosed.

  In addition, the technology for improving the properties such as DI formability and strength when thinned by specifying the solid solution amount of Si, Cu, Mn, Fe, etc. is also an aluminum alloy having a 3000 series composition for cans. Various proposals have been made in the field of sheeting.

Japanese Patent No. 4667722 JP 2004-68061 A JP 2007-197815 A JP 2009-270192 A JP 2007-169767 A

  In recent years, the handling and use conditions of DI cans have become more severe conditions such as the pressure difference between the inside and outside of the can becoming larger and the can body can be easily deformed. Accordingly, the puncture resistance (puncture strength) required for a thinned can body is also stricter. On the other hand, the above-described conventional technology still has room for improvement in order to obtain this strict puncture resistance.

  For example, only by controlling the Mg content as in Patent Document 1, there is a limit to setting the puncture strength that is greatly influenced by the presence of a compound in the tissue to the required level. Moreover, the technique disclosed in Patent Document 3 improves the puncture resistance by increasing the thickness of the side wall of the can to more than 0.110 mm, and cannot cope with the tendency of the can to reduce the thickness of the side wall of the can. . Furthermore, since the technique disclosed in Patent Document 5 is limited to a high baking temperature range when painting cans, it is unsuitable for requirements on the can-making side when heat treatment is desired at lower temperatures. Moreover, although the control of the intermetallic compounds disclosed in Patent Documents 3 to 5 is certainly effective for improving the puncture resistance, there is still room for improvement in order to obtain the strict puncture resistance. is there.

  The present invention has been made in view of the above problems, and provides an aluminum alloy plate for a DI can body that can satisfy the stricter piercing resistance (piercing strength) required for a thinned can body. With the goal.

The gist of the aluminum alloy plate for DI can barrel of the present invention for solving the above problems is mass%, Mn: 0.3 to 1.3%, Mg: 0.7 to 3.0%, Si: 0.00. An aluminum alloy plate containing 1 to 0.5%, Fe: 0.1 to 0.8%, Cu: 0.01 to 0.4%, with the balance being composed of Al and inevitable impurities. In addition, as an aggregate of atoms measured by a three-dimensional atom probe field ion microscope, the aggregate of atoms includes a total of five or more of either or both of Mg atoms and Cu atoms, and Mg contained therein Atoms that satisfy these conditions, regardless of whether the atom is an atom or a Cu atom, the distance between the reference atom and any one of the other adjacent atoms is 0.80 nm or less. 1 × 10 ²⁴ pieces of average density of the aggregate of and it is restricted to m ³ or less.

Here, the aluminum alloy plate may further contain one or two of Cr: 0.001 to 0.1% and Zn: 0.05 to 0.5%. The aluminum alloy plate is DI-molded into a can body having a thinnest side wall thickness in the range of 0.085 to 0.110 mm, and this can body is heat-treated at 200 ° C. for 20 minutes. It is preferable that the 0.2% yield strength of the side wall in the can axis direction has a strength characteristic of 280 MPa or more and 350 MPa or less. The aluminum alloy plate is DI-molded into a can body having a thinnest side wall thickness of 0.085 to 0.110 mm, and the can body is heat-treated at 200 ° C. for 20 minutes. It is preferable that the 0.2% yield strength of the side wall in the can axis direction has a strength characteristic of 280 MPa or more and 350 MPa or less. Further, the puncture resistance of the aluminum alloy plate is such that an internal pressure of 1.7 kgf / cm ² (= 166.6 kPa) is applied to the can body, and a distance L in the can axis direction from the can bottom of the can body side wall L = 60 mm. Of the load measurement until the piercing needle penetrates the can barrel side wall at a speed of 50 mm / min. The maximum value is preferably 35 N or more.

  When the aluminum alloy plate of 3000 series composition, which is a material for the DI can body, is made into a can body (DI molding) and then subjected to a paint baking process (heat treatment), it promotes subgraining of the can body structure When it is done, the puncture resistance is improved. However, it is difficult to quantitatively define the degree of subgraining in this can body structure by structural factors such as dislocation density and crystal grain shape.

  On the other hand, in the present invention, the superiority or inferiority of the puncture resistance between 3000-based aluminum alloy plates containing Cu varies greatly depending on the existence state of a specific atomic aggregate that can be analyzed by a three-dimensional atom probe field ion microscope. I found out. That is, as the number of specific atom aggregates defined in the present invention is smaller, the subgraining of the above-described structure proceeds and the puncture resistance is improved, and conversely, the larger the number of specific atom aggregates is, It has been found that the sub-graining of the can body structure does not progress and the puncture resistance is inferior.

  Therefore, the existence state (average density) of the atomic aggregate defined in the present invention can be an index representing the relationship with the puncture resistance when a 3000 series aluminum alloy plate containing Cu is formed into a can body. By using this, in the present invention, the presence state (average density) of the specific atomic aggregate (cluster) of the 3000 series aluminum alloy plate containing Cu is controlled to be required for a thinned can body. The puncture resistance can be improved to a level that can satisfy more severe puncture resistance (puncture strength).

It is sectional drawing which illustrates typically the measuring method of the piercing strength of a can body.

  Hereinafter, the form for implement | achieving the aluminum alloy plate for can bodies which concerns on this invention (henceforth an aluminum alloy plate) is demonstrated.

(Aluminum alloy composition)
The composition of the aluminum alloy plate for DI can body according to the present invention is mass%, Mn: 0.3 to 1.3%, Mg: 0.7 to 3.0%, Si: 0.1 to 0.5. %, Fe: 0.1-0.8%, Cu: 0.01-0.4%, respectively, and the balance consists of Al and inevitable impurities. The aluminum alloy composition may further include one or two of Cr: 0.001 to 0.1% and Zn: 0.05 to 0.5%. In addition, all the% display regarding a composition (each element content) means the mass%.

(Mn: 0.3 to 1.3%)
Mn has an effect of improving the strength of the aluminum alloy, and when the aluminum alloy plate is formed on the can body, the side wall strength is increased to ensure buckling strength and puncture resistance. Further, Mn forms an Al—Mn—Fe-based intermetallic compound in the aluminum alloy and is appropriately dispersed, whereby recrystallization after hot rolling is promoted and the workability of the aluminum alloy sheet is improved. If the Mn content is less than 0.3%, these effects are insufficient. Therefore, the Mn content is 0.3% or more, preferably 0.4% or more. On the other hand, if the Mn content exceeds 1.2%, the amount of coarse Al—Mn—Fe intermetallic compound produced increases, and the puncture resistance decreases. Therefore, the upper limit of Mn is 1.3%, preferably 1.1%, and more preferably 1.0%.

(Mg: 0.7-3.0%)
Mg has the effect of improving the strength of the aluminum alloy. When the content of Mg is less than 0.7%, when the aluminum alloy plate is formed on the can body, the side wall strength is lowered and the puncture resistance is insufficient. On the other hand, if the Mg content exceeds 3.0%, the work hardening of the aluminum alloy plate becomes excessive, and cracks such as tear-off (fuselage cracks) during ironing, wrinkles and streaks during necking, etc. Is likely to occur. Therefore, the Mg content is in the range of 0.7 to 3.0%, preferably 1.0 to 2.6%, more preferably 1.2 to 2.2%.

(Si: 0.1-0.5%)
Si forms an Al—Fe—Mn—Si intermetallic compound, and the more appropriately it is distributed, the better the moldability. Therefore, the Si content is 0.1% or more, preferably 0.2% or more. On the other hand, when Si becomes excessive, a large number of Al—Mn—Fe—Si intermetallic compounds and Mg—Si intermetallic compounds are formed, and the puncture resistance is lowered. For this reason, the upper limit of Si content is 0.5%, preferably 0.4%.

(Fe: 0.1-0.8%)
Fe is mixed into the aluminum alloy as a metal alloy impurity, but forms an Al-Mn-Fe intermetallic compound in the aluminum alloy and is appropriately dispersed to promote recrystallization after hot rolling. As a result, the workability of the aluminum alloy plate is improved. Fe is also useful in that it promotes crystallization and precipitation of Mn, and controls the Mn average solid solution amount in the aluminum matrix and the dispersion state of the Mn-based intermetallic compound. Therefore, the Fe content is 0.1% or more, preferably 0.3% or more. On the other hand, when the Fe content is excessive, a huge primary intermetallic compound is likely to be generated, and DI moldability and puncture resistance are also lowered. Therefore, the upper limit of the Fe content is 0.8%, preferably 0.7%.

(Cu: 0.01-0.4%)
Cu increases the strength by solid solution strengthening. For this reason, Cu is contained essential. The lower limit of the Cu content is 0.01% or more, preferably 0.05% or more. On the other hand, if Cu is excessive, high strength can be easily obtained, but it becomes too hard, so that formability is lowered and corrosion resistance is also deteriorated. For this reason, the upper limit of Cu content is 0.4%, preferably 0.3%.

(Cr: 0.001 to 0.1%, Zn: 0.05 to 0.5%)
Examples of strength improving elements having the same effect as Cu include Cr and Zn. One or two of Cr: 0.001 to 0.1% and Zn: 0.05 to 0.5% are selected in addition to Cu. Can be included. When selectively contained, the Cr content is 0.001% or more, preferably 0.002% or more. On the other hand, when Cr is excessive, giant crystals are generated and the formability is lowered. Therefore, the upper limit of Cr content is set to 0.1%, preferably about 0.05%. Further, when Zn is selectively contained, the Zn content is 0.05% or more, preferably 0.06% or more. On the other hand, since corrosion resistance falls when Zn becomes excessive, the upper limit of Zn content is made into 0.5%, Preferably it is about 0.45%.

  In addition to these elements, there are inevitable impurities. Examples of the inevitable impurities include Zr: 0.10% or less, Ti: 0.2% or less, preferably 0.1% or less, and B: 0.05%. Hereinafter, if it is preferably 0.01%, the content of the aluminum alloy plate according to the present invention is not affected and the inclusion is allowed. Of these, Ti also has an effect of refining crystal grains, and when contained together with a small amount of B, the effect of refining the crystal grains is further improved. Intermetallic compounds and Ti-B-based coarse particles crystallize and hinder formability.

(Structure of aluminum can plate for DI can body)
Aggregation of atoms and puncture resistance:
Based on the above aluminum alloy composition, in order to improve the puncture resistance (puncture strength), in the present invention, the control of very fine atomic aggregates present in the structure of the aluminum alloy plate for DI can barrels is performed. I do.

  The piercing resistance of a can body made of an aluminum alloy plate of 3000 series composition is a sub-structure of the can body structure when this material plate is subjected to paint baking after being made into a can body (DI molding). Improve by graining. This subgrain is also called a substructure or subcrystal, and is a small structure formed in a crystal grain. The inside of this subgrain becomes a partial dislocation-free region, and when the deformation is applied, the activity of the slip surface becomes possible. For this reason, even when a so-called piercing is applied to the can body during pin use or handling, so-called piercing occurs, the work hardening due to the accumulation of new dislocations appears in the piercing portion. The piercing property is improved.

  In comparison of structures (photographs) by TEM between can bodies that have a large difference in the effect of piercing resistance, the qualitative distinction between sub-grains of each can body structure differs in the number of dislocations. Easy. The structure of the can body having poor puncture resistance has many streak or linear dislocations, and can easily be distinguished from the structure of a can body having few punctures and excellent puncture resistance. However, it is currently difficult to quantitatively distinguish these tissues from each other based on the structure elements that can be observed by SEM or TEM, such as the degree of dislocation or the degree of subflaring.

  On the other hand, the degree of subgraining of the can body tissue differs depending on the analysis of the existence state of the atomic aggregate using a three-dimensional atom probe field ion microscope, and the atomic aggregate (density of the aggregate) defined by the present invention It has been found that the smaller the), the more the tissue becomes subgrained and the better the puncture resistance.

  On the other hand, it was found that the more the specific aggregate of atoms is, the more the can body tissue is not subgrained and the puncture resistance is inferior.

  In a 3000 series aluminum alloy plate containing Cu, this is controlled by controlling the average density, which is an existence state of an aggregate of atoms containing at least Mg atoms or Cu atoms, as measured by a three-dimensional atom probe field ion microscope. The degree of subgraining of the can body structure and the puncture resistance of the plate can be controlled. Thereby, the puncture resistance of the 3000 series aluminum alloy plate containing Cu can be improved to a stricter level required for the thinned can body.

Definition of a set of atoms:
In the present invention, sub-graining and puncture resistance of the can body structure out of the aggregate of atoms measured by a three-dimensional atom probe field ion microscope per structure of 3000 series aluminum alloy plate containing Cu for DI can body. Defines a particular set of atoms that can be controlled.

  The specific aggregate of atoms includes a total of 5 or more of either or both of Mg atoms and Cu atoms, and any of these atoms of Mg or Cu atoms can be used as a reference. Is an aggregate of atoms satisfying the condition that the distance between each atom and any one of the other adjacent atoms is 0.80 nm or less.

  The aggregate (cluster) of atoms defined in the present invention is not necessarily composed of only two atoms, Mg atoms and Cu atoms, and in many cases includes Al atoms of the parent phase. Moreover, it may contain atoms, such as Mn, Si, and Fe, which are other alloy elements. Depending on the component composition of the 3000 series aluminum alloy, atoms such as Cr, Zn, V, Ti, etc. contained as selective elements and impurities may be included in the aggregate of atoms, and these other atoms may be counted by 3DAP analysis. Inevitable.

  However, even if these other atoms (from alloy elements and impurities) are included in the aggregate (cluster) of the atoms defined in the present invention, the level is smaller than the total number of Mg atoms and Cu atoms. Therefore, even when such other atoms are included in the aggregate, those satisfying the conditions of the prescribed distance between Mg atoms and Cu atoms and the prescribed total number are Mg atoms as the aggregate of atoms of the present invention. And functions in the same manner as an aggregate of atoms consisting only of Cu atoms. Therefore, when the number of atoms within the adjacent distance is satisfied, even when other atoms are included in the aggregate, it is counted as the aggregate of atoms of the present invention and does not satisfy the condition for the number of atoms within the adjacent distance. In the case, it is not counted as an aggregate of atoms according to the present invention.

  In this respect, the atoms adjacent to each other in the aggregate of atoms of the present invention may be not only atoms different from Mg atoms and Cu atoms, but also Mg atoms and Cu atoms. For example, in an aggregate of atoms, either Mg atom or Cu atom is not detected and is zero (even if only Mg atom or Cu atom), or between Mg atoms or Cu atoms If any one of the atoms satisfies the adjacent distance (0.80 nm or less) and the number (5 or more), it is an aggregate of atoms defined in the present invention, and an aggregate of atoms defined in the present invention. As an average number density. Therefore, when measuring by 3DAP analysis, even if the number of atoms within adjacent distances satisfies the prescribed number, this aggregate of atoms does not contain any Mg atom or Cu atom If so, it is not an aggregate of atoms defined by the present invention, and does not count. That is, the aggregate of atoms defined in the present invention necessarily includes both Mg atoms and Cu atoms, or atoms of either Mg atoms or Cu atoms.

  Here, the definition of the distance of atoms in the aggregate of atoms is that any atom of Mg atom and Cu atom included in the aggregate of atoms is adjacent to the atom (reference Mg atom or Cu atom). It is only necessary that the distance between each other atom (Mg atom, Cu atom or other atom) is 0.80 nm or less. That is, all the distances between the reference atom and all other atoms adjacent to the reference Mg atom or Cu atom may be 0.80 nm or less. Also, there may be adjacent atoms at a distance away from this, as long as there is at least one other atom that satisfies this distance. The Mg atoms and Cu atoms included in the aggregate of atoms in a total of 5 or more satisfy the distance relationship with other adjacent atoms.

Average density of atomic aggregate:
In the present invention, the aggregate of atoms in the DI can body material aluminum alloy sheet structure, which is defined as described above and measured by 3DAP analysis, is 1 × 10 ²⁴ atoms / average density of the aggregate of atoms. Restrict to m ³ or less. This promotes the subgraining of the can body structure when the material aluminum alloy plate is subjected to a paint baking process after being made on the can body, and improves the piercing resistance of the can body.

  In this way, by regulating this specific atomic aggregate, a 3000 series aluminum alloy plate containing Cu can be made into a can body, and then subgraining is promoted when subjected to a paint baking process. Slip surface activity in a dislocation-free area. For this reason, even when a so-called piercing is applied to the can body during pin use or handling, so-called piercing occurs, the work hardening due to the accumulation of new dislocations appears in the piercing portion. The piercing property is improved.

On the other hand, when the average density of this specific atomic aggregate exceeds the upper limit of 1 × 10 ²⁴ / m ³ , there are too many atomic aggregates, and the material aluminum alloy plate becomes a can body. Sub-graining of the can body structure does not progress even if it is subjected to paint baking after it is made. For this reason, when an external force is applied and a puncture occurs during use or handling of the can, work hardening due to the accumulation of new dislocations hardly occurs in the pierced portion, and the puncture resistance is not improved.

In the present invention, the upper limit of the average density of the specific atomic aggregate includes zero atoms that cannot be detected or measured and are regarded as nonexistent. However, it is not necessary to deliberately reduce the number of atomic aggregates to zero, and it is only necessary to regulate the average density to 1 × 10 ²⁴ / m ³ or less, which is preferable from the viewpoint of not reducing the production efficiency of the material plate. As a guideline for the lower limit, the presence of 1 × 10 ²² pieces / m ³ or more is allowed.

3D atom probe field ion microscope:
In the field of aluminum alloy materials, a method for measuring the average density of an atomic aggregate with a three-dimensional atom probe field ion microscope is exemplified in Japanese Patent Application Laid-Open No. 2011-184895. In this publication, an atomic assembly contributing to improvement of press formability of a 5000 series aluminum alloy plate containing Zn is measured by a three-dimensional atom probe field ion microscope. And as an aggregate of these atoms, a total of 20 or more of either or both of Mg atoms and Cu atoms is included, and any of these atoms of Mg or Cu atoms is used as a reference. The distance between each atom and any one of the other adjacent atoms is defined as 0.80 nm or less. And the aluminum alloy plate which suppressed generation | occurrence | production of the stretcher strain mark by including the aggregate | assembly of the atom which satisfy | fills such conditions with the average density of 1 * 10 < ⁴ > piece / micrometer < ³ > or more is proposed.

  This analysis by a three-dimensional atom probe field ion microscope is widely used for analysis of structures and atomic aggregates in the fields of high-density magnetic recording films and electronic devices, aluminum alloy materials, steel materials, and copper alloy materials. Yes.

  The three-dimensional atom probe field ion microscope (3DAP: 3D Atom Probe Field Ion Microscope, hereinafter also abbreviated as 3DAP) is obtained by attaching a time-of-flight mass analyzer to a field ion microscope (FIM). With such a configuration, the local analyzer is capable of observing individual atoms on a metal surface with a field ion microscope and identifying these atoms by time-of-flight mass spectrometry. In addition, 3DAP is a very effective means for structural analysis of atomic aggregates because it can simultaneously analyze the type and position of atoms emitted from a sample.

  This 3DAP uses an ionization phenomenon of sample atoms under a high electric field called field evaporation. When a high voltage necessary for the field evaporation of sample atoms is applied to the sample, the atoms are ionized from the sample surface and pass through the probe hole to reach the detector.

  This detector is a position-sensitive detector, and it is detected by measuring the time of flight to the individual ion detector along with mass analysis of individual ions (identification of elements that are atomic species). The determined position (atomic structure position) can be determined simultaneously. Therefore, 3DAP has the feature that the atomic structure at the tip of the sample can be reconstructed and observed three-dimensionally because the position and atomic species of the atom at the tip of the sample can be measured simultaneously. Further, since field evaporation occurs sequentially from the tip surface of the sample, the distribution of atoms in the depth direction from the sample tip can be examined with atomic level resolution.

  Since this 3DAP uses a high electric field, the sample to be analyzed must be highly conductive, such as metal, and the shape of the sample is generally very fine with a tip diameter of around 100 nmφ or less. Need to be needle-shaped. For this reason, a sample is taken from the central portion of the aluminum alloy plate, etc., and this sample is cut and electropolished with a precision cutting device to produce a sample having an ultra-fine needle tip for analysis. As a measuring method, for example, using “LEAP3000” manufactured by Imago Scientific Instruments, a high pulse voltage of 1 kV order is applied to an aluminum alloy plate sample whose tip is shaped like a needle, and several millions from the sample tip. This is done by ionizing atoms continuously. The ions are detected by a position sensitive detector, and a pulse voltage is applied. From the time of flight from when each ion jumps out of the sample tip until it reaches the detector, mass analysis of ions (atomic species) Element identification).

  Furthermore, using the property that field evaporation occurs regularly from the tip surface of the sample, coordinates in the depth direction are given to a two-dimensional map indicating the arrival location of ions as appropriate, and analysis software “IVAS” Is used to perform three-dimensional mapping (three-dimensional atomic structure: construction of an atom map). Thereby, a three-dimensional atom map of the sample tip is obtained.

  The three-dimensional atom map is further analyzed for an aggregate of atoms (cluster) using a maximum separation method which is a method of defining atoms belonging to precipitates and clusters. In this method, the maximum distance dmax between specified solute atoms and the minimum number of atoms Nmin constituting the cluster are given as parameters. In this analysis, the cluster is defined with the maximum interval dmax between adjacent Mg and Cu atoms being 0.80 nm and the total minimum number of atoms Nmin of Mg and Cu atoms being five. From this result, the cluster dispersion state is evaluated, and the number density of the clusters (the specified average density when the number of measurement samples is 3 or more) is quantified.

Detection efficiency of atoms by 3DAP:
However, the detection efficiency of these atoms by 3DAP is currently limited to about 50% of the ionized atoms, and the remaining atoms cannot be detected. If the detection efficiency of atoms by 3DAP is greatly changed, such as an improvement in the future, the measurement result by 3DAP of the average number density (atom / m ³ ) of the aggregate of atoms defined by the present invention may change. There is sex. Therefore, in order to give reproducibility to the measurement of the average number density of the aggregate of atoms, it is preferable that the detection efficiency of atoms by 3DAP is substantially constant at about 50%.

(Production method)
Next, the manufacturing method of the aluminum alloy plate for DI can bodies in this invention is demonstrated. The aluminum alloy sheet of the present invention includes a casting process in which an aluminum alloy having the above composition is melted and cast into an ingot, a soaking process in which the ingot is homogenized by heat treatment, and the homogenized ingot is hot-rolled. And a hot rolling process for producing a hot rolled sheet and a cold rolling process for performing cold rolling without annealing the hot rolled sheet. And in this manufacturing method, while performing soaking | uniform-heating treatment of an ingot twice on the conditions mentioned later, cold rolling is also performed on the specific conditions mentioned later, and the structure which prescribes | regulates the aluminum alloy sheet structure after cold rolling in this invention And

(Melting, casting)
First, an aluminum alloy is melted, cast by a known semi-continuous casting method such as a DC casting method, and cooled to below the solidus temperature of the aluminum alloy to form an ingot. When the casting rate is less than 40 mm / min or the cooling rate is less than 0.5 ° C./sec, a large amount of coarse intermetallic compounds are crystallized in the ingot. On the other hand, if the casting speed is 65 mm / min or the cooling speed is faster than 1.5 ° C./sec, ingot cracking or “shrinkage” or “shrinkage cavity” is likely to occur. The yield drops. Accordingly, in casting, the casting speed is 40 to 65 mm / min, and the cooling speed is 0.5 to 1.5 ° C./second. This cooling rate is for the temperature of the central part of the ingot, that is, the temperature of the central part of the surface perpendicular to the casting direction, and the cooling rate from the liquidus temperature to the solidus temperature of the aluminum alloy. And

(Soaking)
Before rolling the ingot, it is necessary to perform a homogenization heat treatment (soaking) at a predetermined temperature. By applying heat treatment, 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.

  However, in the present invention, the soaking process is soaking twice. This two-time soaking is distinguished from two-stage soaking. Two-stage soaking means cooling after the first soaking, but it is not cooled to 200 ° C. or lower, and after stopping the cooling at a higher temperature, after maintaining at that temperature, Hot rolling is started after reheating to a high temperature. In contrast, the second soaking of the present invention means that after the first soaking, once cooled to a temperature of 200 ° C. or less including room temperature, reheated, and maintained at that temperature for a certain period of time, Hot rolling is started.

  Specifically, first, the first soaking temperature is set to 580 ° C. or higher and lower than the melting point temperature. The reason for setting the soaking temperature to 580 ° C. or higher is to dissolve the coarse Al—Fe—Mn compound produced during casting. When the soaking temperature is less than 580 ° C., the coarse Al—Fe—Mn compound remains without being dissolved, and the formability of the cold-rolled sheet to the can body decreases.

  After the first soaking process, the temperature is once cooled to 200 ° C. or less including room temperature. Under the present circumstances, the average cooling rate of the ingot between 500-200 degreeC shall be 80 degreeC / hour or more. When the average cooling rate between these temperatures is less than 80 ° C./hour, not only the amount of Al—Fe—Mn compound generated during cooling increases but also the aggregation of Mg and Cu atoms regulated in the present invention increases. To do. Further, as in the case of the two-stage soaking, when the cooling is stopped in the middle high temperature state (above 200 ° C.) and the second soaking is performed continuously, the Al—Fe—Mn system already dispersed is obtained. Since the amount of the compound increases as a nucleus, it is necessary to cool it to 200 ° C. or lower once. If this condition is not satisfied, the structure of the portion extending in the plate width direction and plate thickness direction of the cold rolled sheet for DI can cannot be made excellent in the piercing resistance of the can body.

  The second soaking temperature is 450 ° C. or higher and 550 ° C. or lower. And the average heating rate of the ingot between 200-400 degreeC in this soaking | uniform-heating is made into the speed | rate which exceeds 30 degreeC / hour. This is because the Mg-Si-based compound is generated during the temperature increase in the second soaking, but by setting the average heating rate of the ingot between the temperatures of 200 to 400 ° C to more than 30 ° C / hour, The amount of Mg and Cu atom aggregates regulated in the present invention is suppressed. If the heating rate is low, the amount of Mg and Cu atom aggregates regulated in the present invention cannot be suppressed, and the upper limit may be exceeded.

  If the first and second soaking times are less than 2 hours, homogenization of the ingot may not be completed. On the other hand, even if soaking for more than 8 hours is performed, the effect is not improved and the productivity is lowered. Accordingly, the first and second soaking times are preferably 2 to 8 hours, but are not particularly limited.

(Hot rolling)
The ingot homogenized in the soaking process is hot-rolled, but this hot rolling condition may be in the range of ordinary methods or general conditions, first roughly rolling the ingot, and further by finish rolling, An aluminum alloy hot-rolled plate having a predetermined thickness is used.

(Cold rolling)
The hot-rolled sheet is cold-rolled without pre-annealing and without intermediate annealing between passes, and finished to an aluminum alloy sheet having a predetermined thickness. The total rolling rate (cold working rate) in cold rolling is preferably 77 to 90%, and the thickness of the cold rolled sheet after cold rolling is preferably 0.25 to 0.33 mm. The total rolling ratio in the cold rolling is, of course, determined by the relationship with the desired thickness of the cold-rolled sheet, but preferable winding for controlling the average density of Mg and Cu atoms within the scope of the present invention. In order to set the temperature range, the above range is preferable.

Here, the winding temperature around the coil after the cold rolling needs to be in the range of 120 to 160 ° C. If the coil is not wound in such a warm temperature range, the cold rolled sheet structure is not likely to be the range of the Mg and Cu atoms defined in the present invention. When the coiling temperature exceeds 160 ° C., the average density of the aggregate of Mg and Cu atoms defined in the present invention exceeds 1 × 10 ²⁴ / m ³ , and the can is made into a can body. Subgrain formation upon heat treatment at 20 ° C. for 20 minutes is suppressed, and puncture resistance is reduced. On the other hand, when this winding temperature is in a state such as a room temperature of less than 120 ° C. as in ordinary cold rolling, the strength immediately after winding becomes high and the elongation is low. Will fall.

  Under normal cold rolling conditions, the rolled-up plate (coil) is sufficient to cool the plate with the rolling rate and the amount of lubricating oil and coolant used from the viewpoint of controlling heat generation as well as lubrication. In order to obtain a quantity, the temperature is set to around room temperature. On the other hand, in the present invention, on the contrary, the processing heat generation is rather accelerated, and the coiling temperature after cold rolling is set to the high temperature side, and the temperature is 120 to 160 ° C., preferably 120 to 145 ° C. A zone.

(DI can manufacturing method)
An example of a can manufacturing method for producing a can body of a DI can from a material aluminum alloy plate (cold rolled plate) according to the present invention will be described below. First, an aluminum alloy plate according to the present invention is punched into a disc shape (blanking process), drawn into a shallow cup shape (capping process), and subjected to DI molding. These drawing and ironing processes are repeated a plurality of times to gradually increase the side wall to obtain a bottomed cylindrical shape having a predetermined bottom surface shape and side wall height. It is preferable that the plate | board thickness reduction | decrease rate (ironing process rate) of the side wall of a can body by these processes shall be 60 to 70%. Then, the edge of the side wall (opening) is trimmed and trimmed (trimming process). In this state, DI molding is performed on a thin can body in which the side wall thickness of the thinnest part is in the range of 0.085 to 0.110 mm.

  Next, the can body is degreased and cleaned, and the outer surface and the inner surface are respectively painted and baked (baked), and the 0.2% proof stress is 280 MPa to 350 MPa as the strength of the thinnest side wall in the can axis direction. The strength is high. By the way, this strength is equivalent to the baking of the coating film as the “can heat treatment equivalent to the baking of the coating film of the can body” as used in the present invention, without actually baking (baking) the coating film. The strength after heat treatment at 200 ° C. for 20 minutes at a temperature and time can be substituted. When this coating baking treatment (heat treatment) is applied, if the above-mentioned can body texture is promoted to be subgrained, the puncture resistance is improved.

  The can body after the coating film is baked has a diameter of the opening (necking process), and an edge of the opening is expanded outward (flanging process) to become a final can body. When used for beverages and foods, the contents (beverages and food) are filled into the can body from the opening, and a can lid produced in a separate process is wound around the opening and sealed.

  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)
An aluminum alloy having the composition shown in Table 1 was melted, and an ingot was produced using a semi-continuous casting method at a casting rate and a cooling rate within the preferable numerical ranges described above in common with each example.

  This ingot is soaked twice, and in each case, after the first soaking for 4 hours at a soaking temperature of 600 ° C., an average cooling rate (° C./hour) of 500 to 200 ° C. is once brought to room temperature. Various changes were made as shown in Table 2 for cooling. Then, as the second soaking, the ingot was heated again from room temperature, and the average heating rate (° C./hour) of 200 to 400 ° C. was changed variously as shown in Table 2. A second soaking process was performed for 4 hours at a hot temperature.

  In common with each example, hot rolling was started at a temperature of 500 ° C., an end temperature was set to 330 ° C., and a hot rolled plate having a thickness of 2.0 to 3.0 mm was obtained.

  Further, in common with each example, the hot-rolled sheet is cold-rolled without being roughened (annealed) and without being subjected to intermediate annealing in the middle, and the sheet thickness is 0.28 mm. Was a long aluminum alloy plate having a coil shape of 2000 mm. At this time, the total (total) rolling reduction (%) and the coiling temperature (° C.) of the cold rolling were changed as shown in Table 2.

  In addition, the indication of "-" in the chemical composition composition of the aluminum alloy plate in Table 1 indicates that it is below the detection limit and is substantially 0% not containing this element.

(Can body)
The coiled aluminum alloy plate thus obtained was cupped, DI-molded (ironing rate 65-70%), the opening was trimmed, the outer diameter was about 66 mm, and the height (length in the can axis direction) 124 mm, A bottomed cylindrical can body having a side wall thickness of 0.090 mm was used. Furthermore, after the can body was degreased and washed, heat treatment was performed under the conditions of the above-mentioned 200 ° C. for 20 minutes assuming (simulating) baking during coating, thereby obtaining a can body test material.

[Evaluation]
The average density of the aggregate of atoms defined in the present invention was measured for the microstructure of the aluminum alloy cold-rolled plate by the measurement method using a three-dimensional atom probe field ion microscope and analysis analysis software. Moreover, DI moldability to a can body and 0.2% yield strength were also measured. And the piercing resistance and 0.2% proof stress in the can body (after the heat treatment assumed for the paint baking) were also measured and evaluated. These results are shown in Table 2 following Table 1 (the numbers in Tables 1 and 2 are common to each other).

(Tissue measurement by 3DAP)
Measurement by the 3DAP method is performed by cutting three test pieces each having a length of 30 mm and a width of 1 mm from the cold-rolled plate by 1 mm in the width direction with a cutting device, and then thinning the test piece by electrolytic polishing. Then, a needle-like sample having a tip radius of about 50 nm was prepared. For this reason, the measurement location measures the vicinity of the center of the plate thickness. The sample with the tip shaped like a needle is subjected to 3DAP measurement using the “LEAP3000”, and the density of atoms (matter / m ³ ) defined in the present invention for each of the three test pieces is measured. And averaged (averaged density). Incidentally, the measurement volume by the 3DAP method is approximately 1.0 × 10 ⁻²⁴ to 10 ⁻²¹ m ³ .

(Formability)
In the DI molding described above, 1000 blanks were cut out from a total of three locations in the vicinity of the central portion in the plate width direction of the center portion in the longitudinal direction of the aluminum alloy cold rolled plate coil and in the vicinity of each of the two ends. Cans were made by continuous molding (cupping, DI molding) at an ironing rate of 65%. When no defects (tear-off, pinholes, etc.) occurred during molding, the moldability was evaluated as “◯”, and when defects occurred, the moldability was evaluated as “x”.

(Puncture resistance)
For each example, it was verified whether or not the piercing resistance of the can body produced, particularly the piercing resistance in the plate width direction and the plate thickness direction of the cold-rolled plate was improved. For this reason, in each example, all the ten pieces that can be formed so that the can bodies made from three places of the center portion in the plate width direction and both end portions of the aluminum alloy cold-rolled plate coil are evenly included. A piercing test was performed to evaluate piercing resistance.

As shown in FIG. 1, this piercing resistance test is performed by fixing the can body, applying an internal pressure of 1.7 kgf / cm ² (= 166.6 kPa), and rolling the aluminum alloy plate on the side wall of the can body. Is aligned with the can axis direction, and at the site where the distance L in the can axis direction from the can bottom is 60 mm, a piercing needle whose tip is a hemisphere with a radius of 0.5 mm is perpendicular to the side wall at a speed of 50 mm / Stabbed in minutes. And the load (N) until a piercing needle penetrates a side wall was measured, and the obtained maximum load was made into the piercing strength.

  In the puncture resistance test results, the average maximum load of all can bodies was 40 N or more. If the overall width direction of the aluminum alloy cold-rolled sheet is excellent in puncture resistance, In addition, it was also evaluated as “◯” that was 35 N or more. On the other hand, if the average maximum load of all can bodies was less than 35N, the puncture resistance of the aluminum alloy cold-rolled sheet was poor in the sheet width direction and the entire sheet thickness direction. evaluated.

In the present invention, as the handling or use conditions of the DI can, the pressure difference between the inside and outside of the can is larger, the deformation of the can body becomes larger, and the puncture resistance is more severe. 1.7 kgf / cm ² ( = 166.6 kPa). The actual rupture at the time of piercing of the can body is caused by collisions of various shapes, but it is not possible to evaluate all of them, and there is a demand for evaluation by a stricter evaluation method. Therefore, it was made difficult to increase the puncture strength by adopting the conditions where the internal pressure was lowered and the deformation was increased.

The evaluation of puncture resistance so far is usually performed by applying a higher internal pressure of 2.0 kgf / cm ² (= 196 kPa). For this reason, even with the same test material, the test method of the present invention has stricter test conditions and lower puncture strength. That is, the value of the piercing strength (N) in the test with the internal pressure of 2.0 kgf / cm ² and the value of the piercing strength (N) by the test method of the present invention are the same, for example, slightly lower values. Even so, it can be said that the material of the present invention is superior in puncture resistance. In other words, even if the penetration resistance of the internal pressure test of 2.0 kgf / cm ² was excellent, quite be said penetration resistance at lower internal pressure of 1.7 kgf / cm ² of the present invention is excellent Absent.

(0.2% yield strength)
Tensile tests for measuring 0.2% proof stress of the cold-rolled plate and the side wall of the can body were conducted by using test pieces taken from the cold-rolled plate and the side wall of the can body (after the heat treatment assumed for paint baking), respectively. While performing according to 2201, the shape of the test piece was a JIS No. 5 test piece, and the test piece was prepared so that the longitudinal direction of the test piece coincided with the rolling direction (can axis direction). The crosshead speed was 5 mm / min, and the test piece was run at a constant speed until the test piece broke.

  As shown in Tables 1 and 2, Inventive Examples 1 to 10 each have a composition of an aluminum alloy within the scope of the present invention, and are manufactured under preferable manufacturing conditions. For this reason, in each invention example, as shown in Table 2, the cold rolled sheet is within the range of the average density of the aggregate of atoms defined in the present invention.

As a result, each of the inventive examples is based on the premise that the DI moldability is good, and the aluminum alloy plate is DI molded into a thin can body having a side wall thickness of 0.090 mm at the thinnest portion, and the coating film is baked. The puncture resistance is excellent when the 0.2% proof stress in the can axis direction of the side wall after considerable heat treatment is high strength of 280 MPa to 350 MPa. Moreover, this piercing resistance is excellent at 35N or more or 40N or more despite the strict evaluation that applied an internal pressure of 1.7 kgf / cm ² (= 166.6 kPa) to the can body. That is, in a can body having a thin can wall thickness and high strength, good moldability and excellent puncture resistance under more severe conditions were obtained.

  On the other hand, in Comparative Examples 11 to 20 in Tables 1 and 2, although the composition of the aluminum alloy is within the scope of the present invention, any of the conditions in the soaking or cold rolling is the preferred condition of the present invention. It is off. For this reason, in each comparative example, the average density of the aggregate of atoms defined in the present invention of the cold-rolled sheet is out of the range and the puncture resistance is inferior, the DI moldability is inferior, or the strength is decreased. Yes.

  In Comparative Example 11, the average cooling rate of 500 to 200 ° C. at the time of cooling to room temperature after the first soaking process is too small as less than 70 ° C./hour. As a result, the aggregate of atoms defined in the present invention generated during cooling increases, the average density exceeds the upper limit, and the puncture resistance is inferior.

  In Comparative Example 12, the average heating rate of 200 to 400 ° C. at the second soaking temperature is too small as less than 30 ° C./hour. As a result, the aggregate of atoms defined in the present invention generated during heating increases, the average density exceeds the upper limit, and the puncture resistance is inferior.

  In Comparative Example 13, the total rolling rate in cold rolling is too low, the strength of the can body after cold rolling and BH is too low, and the puncture resistance is also inferior.

  In Comparative Example 14, the coiling temperature in cold rolling is too high, the number of atomic aggregates defined in the present invention of the cold rolled sheet is increased, the average density exceeds the upper limit, and the puncture resistance is inferior. ing.

  In Comparative Examples 15 to 20 in Tables 1 and 2, the content of any one of Cu, Mn, Mg, Si, and Fe is out of the scope of the present invention.

  In Comparative Example 15, the amount of Mg is too small, and the amount of solid solution Mg is too small. In Comparative Example 16, the amount of Mn is excessive. As a result, these comparative examples are inferior in puncture resistance in the plate width direction when the internal pressure conditions are severe.

  In Comparative Example 17, the amount of Mn is too small. In Comparative Example 18, the amount of Si is excessive. In Comparative Example 19, the amount of Fe is excessive. As a result, since these defectives occurred during DI molding, they could not be put into practical use for cans and were stopped because there was no point in carrying out a subsequent piercing test.

  Comparative Example 20 does not contain Cu. As a result, the strength of the can body is low, and the puncture resistance in the plate width direction when the internal pressure conditions are severe is also poor.

  As described above, the aluminum alloy plate (cold rolled plate) for DI can body according to the present invention improves the piercing resistance of the can body manufactured from the aluminum alloy cold rolled plate to a target level, and improves the piercing resistance of the can body. Can be ensured. For this reason, the can wall thickness is reduced in thickness and strength, and it is optimal for an aluminum alloy cold-rolled sheet used for a DI can body that requires puncture resistance under more severe use conditions.

Claims (4)

In mass%, Mn: 0.3 to 1.3%, Mg: 0.7 to 3.0%, Si: 0.1 to 0.5%, Fe: 0.1 to 0.8%, Cu: An aluminum alloy plate containing 0.01 to 0.4% each, the balance being composed of Al and inevitable impurities, and as an aggregate of atoms measured by a three-dimensional atom probe field ion microscope, The aggregate of atoms contains a total of 5 or more of either or both of Mg atoms and Cu atoms, and even if any of these Mg atoms or Cu atoms is used as a reference, it is adjacent to the reference atom. The distance from one of the other matching atoms is 0.80 nm or less, and the average density of the aggregate of atoms satisfying these conditions is restricted to 1 × 10 ²⁴ atoms / m ³ or less. Aluminum alloy plate for DI can body characterized by   The aluminum alloy plate for a DI can body according to claim 1, wherein the aluminum alloy plate further contains one or two of Cr: 0.001 to 0.1% and Zn: 0.05 to 0.5%.   The aluminum alloy plate is DI-molded into a can body having a thinnest side wall thickness of 0.085 to 0.110 mm, and when the can body is heat-treated at 200 ° C. for 20 minutes, The aluminum alloy plate for a DI can body according to claim 1 or 2, wherein the aluminum alloy plate has a strength characteristic that a 0.2% proof stress in a can axis direction is 280 MPa or more and 350 MPa or less. The puncture resistance of the aluminum alloy plate is such that an internal pressure of 1.7 kgf / cm ² (= 166.6 kPa) is applied to the can body, and the distance L in the can axis direction from the can bottom of the can body side wall is L = 60 mm. In addition, a piercing needle whose tip is a hemispherical surface with a radius of 0.5 mm is pierced at a speed of 50 mm / min perpendicularly to the side wall of the can body, and the maximum load measurement value until the piercing needle penetrates the side wall of the can body The aluminum alloy plate for a DI can body according to any one of claims 1 to 3, which has a value of 35N or more.

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