JP7426243B2 - Aluminum alloy plate for bottle body - Google Patents

Description

The present invention relates to an aluminum alloy plate for bottle bodies.

Two-piece cans consisting of a bottomed cylindrical body and a lid have been widely used as packaging containers for beverages. In recent years, resealable bottle cans have been developed. Aluminum alloys such as AA or JIS 3000 series (Al--Mn series) are commonly used as materials for bottle body materials. The can bodies of bottle cans are generally manufactured through the following process. First, an aluminum alloy plate as a raw material is blanked into a disk shape, and the resulting blank material is cup-formed. The molded cup is then redrawn and ironed to form a can body shape. The sample after this ironing process is called a DI can. Thereafter, the diameter of the opening of the DI can is reduced by necking to form a mouth, and the mouth is threaded and then curled to produce a bottle can.

For bottle cans, it is necessary to suppress wrinkles and cracks even when processing is more severe than for two-piece cans, such as necking, subsequent screw processing, and curling. Technologies focused on improvement are being developed. For example, Patent Document 1 describes an aluminum alloy plate for bottle can bodies with specified strength and work hardening index, and is said to be able to prevent wrinkles and cracks during neck forming. On the other hand, aluminum alloy plates for bottle bodies are becoming thinner in order to reduce costs and reduce environmental impact, and in addition to technology to improve neck formability, there is a need for materials with higher strength. In addition, due to the increase in deformation resistance associated with higher strength materials, a new issue is the occurrence of uneven thickness due to uneven side wall thickness and fluctuations during ironing. For example, Patent Document 2 describes an aluminum alloy plate for bottle can bodies in which the crystal grain size and in-plane anisotropy of the r value of the material are specified, and it is said to have excellent strength, ironing workability, necking workability, etc. has been done.

JP2003-82429A JP2006-89828A

In the technique described in Patent Document 2, the target plate thickness is as thick as 0.4 mm, and it is difficult to cope with the thinning of the plate thickness from 0.30 mm to 0.38 mm, which will be required in the future. Therefore, there is a need for a technology that can further increase strength and improve ironing workability. In order to increase the strength, it is effective to increase the content of Mg, which is a solid solution strengthening element, but as the Mg content increases, the amount of work hardening during ironing increases, resulting in deformation during ironing. The resistance may increase and the uneven thickness of the DI can may become large. On the other hand, if higher strength is achieved by increasing the content of Cu, which is also a solid solution strengthening element, instead of Mg, intermetallic compounds containing solid solution strengthening elements will precipitate when the coil is cooled after hot rolling, resulting in increased strength. A decrease may occur.

In view of the above, an object of the present invention is to provide an aluminum alloy plate for bottle can bodies that has high strength and suppresses the occurrence of uneven thickness during ironing.

The aluminum alloy plate for bottle can bodies according to the present invention includes Si: 0.1% by mass or more and 0.5% by mass or less, Fe: 0.3% by mass or more and 0.6% by mass or less, Cu: 0.1% by mass. 0.35% by mass or less, Mn: 0.5% by mass or more and 1.2% by mass or less, Mg: 1.0% by mass or more and 2.5% by mass or less, and the remainder consists of Al and inevitable impurities. . The aluminum alloy plate for bottle can bodies has a ratio of Mg content to Cu content (Mg mass %/Cu mass %) of 4.2 or less, and cans obtained by a can wall tensile test of DI cans after can body forming. The value obtained by subtracting the plate strength obtained in a tensile test of the plate before forming the can body from the wall strength (can wall strength - plate strength) is 97 MPa or less.

According to the present invention, it is possible to provide an aluminum alloy plate for bottle can bodies that has high strength and suppresses the occurrence of uneven thickness during ironing.

FIG. 2 is a graph showing an example of a change in thickness unevenness after forming a can body. FIG.

Hereinafter, an aluminum alloy plate for a bottle can body according to an embodiment of the present invention will be described. However, the embodiment shown below is an example for embodying the technical idea of the present invention, and the present invention is not limited to the following embodiment. In addition, in this specification, the term "process" does not only refer to an independent process, but also refers to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. included.

The aluminum alloy plate for a bottle body according to an embodiment of the present invention is made of, for example, an Al-Mn-Mg alloy, an Al-Mg-Mn alloy, or the like. Examples of the Al-Mn-Mg alloy, Al-Mg-Mn alloy, etc. include general JIS alloys such as 3004 and 3104.

Specifically, the aluminum alloy plate for bottle can body contains Si: 0.1% by mass or more and 0.5% by mass or less, Fe: 0.3% by mass or more and 0.6% by mass or less, Cu: 0.1% by mass. % or more and 0.35% by mass or less, Mn: 0.5% by mass or more and 1.2% by mass or less, Mg: 1.0% by mass or more and 2.5% by mass or less, with the remainder being Al and unavoidable impurities. Become. The aluminum alloy plate for bottle can bodies has a ratio of Mg content to Cu content (Mg mass %/Cu mass %) of 4.2 or less, and cans obtained by a can wall tensile test of DI cans after can body forming. The value obtained by subtracting the plate strength obtained in a tensile test of the plate before forming the can body from the wall strength (can wall strength - plate strength) is 97 MPa or less.

The aluminum alloy plate for bottle can bodies contains Si, Fe, Cu, Mn, and Mg within a predetermined range, and the value of (can wall strength - plate strength) determined by a tensile test is within a predetermined range. It has become. This reduces the deformation resistance during ironing and suppresses the occurrence of uneven thickness of the DI can. This is thought to be because, for example, by increasing the Cu content instead of the Mg content and controlling the cooling rate of the wound coil after hot rolling, precipitation of intermetallic compounds can be suppressed. I can do it.

Hereinafter, the content of each component contained in the aluminum alloy plate for bottle can body and the reason for limiting the content will be explained.

(Si: 0.1% by mass or more and 0.5% by mass or less)
If the Si content is less than 0.1% by mass, the required purity of the base metal used as a raw material increases, which may result in an increase in cost. On the other hand, when the Si content exceeds 0.5% by mass, formability deteriorates due to unrecrystallized remains in the hot coil. The Si content is preferably 0.2% by mass or more, more preferably 0.25% by mass or more, and even more preferably more than 0.28% by mass. Further, the Si content is preferably 0.45% by mass or less, and more preferably 0.4% by mass or less.

(Fe: 0.3% by mass or more and 0.6% by mass or less)
If the Fe content is less than 0.3% by mass, unrecrystallized remains in the hot coil, resulting in a 45° edge becoming high during DI molding, which tends to cause edge breakage and tear-off due to this during ironing. On the other hand, when the Fe content exceeds 0.6% by mass, the amount of Al-Fe-Mn intermetallic compounds increases, which tends to cause molding defects during ironing. The Fe content is preferably 0.35% by mass or more, more preferably 0.40% by mass or more, and even more preferably more than 0.42% by mass. Further, the Fe content is preferably 0.55% by mass or less, more preferably 0.5% by mass or less.

(Cu: 0.1% by mass or more and 0.35% by mass or less)
If the Cu content is less than 0.1% by mass, the strength will be insufficient and the pressure resistance of the can will be insufficient. On the other hand, if the Cu content exceeds 0.35% by mass, the strength will be too high and molding defects will likely occur during ironing. The Cu content is preferably 0.15% by mass or more, more preferably 0.18% by mass or more, and even more preferably more than 0.24% by mass. Further, the Cu content is preferably 0.33% by mass or less, and more preferably 0.30% by mass or less.

(Mn: 0.5% by mass or more and 1.2% by mass or less)
If the Mn content is less than 0.5% by mass, the strength will be insufficient and the pressure resistance of the can will be insufficient. On the other hand, when the Mn content exceeds 1.2% by mass, the amount of Al-Fe-Mn based intermetallic compounds increases and pinholes are likely to occur on the side wall of the can. In addition, molding defects are likely to occur during ironing. The Mn content is preferably 0.6% by mass or more, more preferably 0.8% by mass or more, and even more preferably 0.85% by mass or more. Further, the Mn content is preferably 1.15% by mass or less, more preferably 1.10% by mass or less, even more preferably 1.0% by mass or less, particularly preferably 0.87% by mass. It may be the following.

(Mg: 1.0 mass% or more and 2.5 mass% or less)
If the Mg content is less than 1.0% by mass, the strength will be insufficient and the pressure resistance of the can will be insufficient. On the other hand, when the Mg content exceeds 2.5% by mass, the strength becomes excessive, the formability decreases, and forming defects are likely to occur during ironing. The Mg content is preferably 1.05% by mass or more, more preferably 1.08% by mass or more, and even more preferably 1.1% by mass or more. Further, the Mg content is preferably 2.0% by mass or less, more preferably 1.7% by mass or less, and even more preferably 1.6% by mass or less.

(Zn: 0.4% by mass or less)
As is generally known, the aluminum alloy plate may contain Zn. If the content of Zn is 0.4% by mass or less, it will not have a large effect on the material properties of the aluminum alloy plate and the can properties after ironing. Although Zn is an unavoidable impurity, Zn can also be actively added within the above range. The Zn content is preferably 0.3% by mass or less, more preferably 0.27% by mass or less, more preferably 0.25% by mass or less, still more preferably 0.2% by mass or less. It's good. Further, the lower limit of the Zn content may be, for example, 0.1% by mass or more.

(Ti: 0.1% by mass or less)
As is generally known, the aluminum alloy plate may contain Ti. Ti is added as necessary for the purpose of refining the ingot crystal grains. Refinement of the ingot structure during casting improves castability and enables high-speed casting. This effect can be obtained by adding 0.01% by mass or more. On the other hand, when the Ti content is 0.1% by mass or less, clogging of the filter can be suppressed, and it is suppressed that the molten metal gradually becomes difficult to pass through the filter during casting. Cancellation can be avoided. Therefore, the Ti content in the aluminum alloy may be limited within the above range. In addition, when adding Ti, for example, an ingot refining agent (Al-Ti-B) with a mass ratio of Ti and B of 5:1 is added. Since B is added to the molten metal before casting in the form of a waffle or rod, B is also necessarily added in proportion to the content. The Ti content is preferably 0.08% by mass or less, and more preferably 0.06% by mass or less.

(Cr: 0.1% by mass or less)
As is generally known, the aluminum alloy plate may contain Cr. If the content of Cr is 0.1% by mass or less, it does not affect the material properties of the aluminum alloy plate and the can properties after ironing. Although Cr is an unavoidable impurity, in order to reduce costs, Cr can be actively added within the above range, for example by increasing the proportion of scrap (such as scrap containing a large amount of Cr) in the raw material. When the Cr content is 0.1% by mass or less, unrecrystallized remains in the hot coil are suppressed, and formation defects during ironing are suppressed. The Cr content may preferably be 0.05% by mass or less.

The above-mentioned Zn, Ti, and Cr are of course true even if the aluminum alloy contains one or more types, that is, not only one type, but also two or more types, as long as the above-mentioned upper limit is not exceeded. This prevents interference with the effects of the invention.

(Remainder: Al and inevitable impurities)
The aluminum alloy plate for bottle bodies may contain inevitable impurities in addition to Al and the above alloy components. Examples of unavoidable impurities include Zr, B, V, Na, Ca, Ni, In, Sn, and Ga. The allowable content of unavoidable impurities may be, for example, 0.3% by mass or less, preferably 0.1% by mass or less, and more preferably 0.05% by mass or less for Zr. Regarding other elements other than Zr, the content of each element may be 0.05% by mass or less and the total content may be 0.15% by mass or less, for example. As long as the element is within the above range, the effect of the present invention will not be hindered not only when the element is contained as an unavoidable impurity but also when the element is added.

(Mg mass%/Cu mass%≦4.2)
The ratio of the Mg content to the Cu content (Mg mass %/Cu mass %) determines the work hardening characteristics, and by appropriately controlling it, it has the effect of reducing the amount of uneven thickness during ironing. When the amount of Mg in solid solution is large, work hardening is likely to occur, and when Mg mass %/Cu mass % exceeds 4.2, the deformation resistance during ironing increases, and the thickness deviation during ironing increases. For the above reasons, Mg mass %/Cu mass %≦4.2. Mg mass %/Cu mass % may be preferably 4.15 or less, more preferably 4.1 or less. Moreover, Mg mass %/Cu mass % becomes like this. Preferably it is 3.6 or more, More preferably, it may be 3.8 or more.

(Plate strength)
The plate strength of an aluminum alloy plate for a bottle body before forming the can body can be evaluated, for example, as follows. Using a cold-rolled aluminum alloy plate for a bottle can body, a tensile test piece is taken so that the rolling direction and the tensile direction during the test are parallel. A tensile test was conducted on the sampled tensile test piece in a direction parallel to the rolling direction, and the 0.2% proof stress was measured, which was taken as the plate strength. The plate strength may be preferably 260 MPa or more, more preferably 270 MPa or more, in order to ensure the body strength of the DI can. Further, the plate strength is preferably 290 MPa or less, more preferably 280 MPa or less.

(Can wall strength)
The can wall strength of the aluminum alloy plate for bottle can bodies after forming the can body can be evaluated, for example, as follows. A tensile test piece is taken in the axial direction of the can wall of the DI can from a position where the rolling direction of the plate is parallel to the can axial direction of the DI can. A tensile test was conducted on the sampled tensile test piece, and the 0.2% proof stress was measured, which was taken as the can wall strength. From the viewpoint of ensuring can body strength, the can wall strength is preferably 350 MPa or more, more preferably 360 MPa or more. Further, the can wall strength is preferably 380 MPa or less, more preferably 370 MPa or less.

(Can wall strength - plate strength)
The smaller the value obtained by subtracting the plate strength before can body formation from the can wall strength after can body formation (can wall strength - plate strength), the harder it is to work harden. The value of (can wall strength - plate strength) may be 97 MPa or less, preferably 95 MPa or less. By keeping the value of (can wall strength - plate strength) below a predetermined value, the deformation resistance during ironing can be reduced and the occurrence of uneven thickness of the DI can can be suppressed. Further, the value of (can wall strength - plate strength) is preferably 85 MPa or more, and more preferably 90 MPa or more.

(Production method)
An example of a method for manufacturing an aluminum alloy plate for a bottle body will be described. The method for manufacturing aluminum alloy plates for bottle bodies includes a first step of casting, a second step of homogenization heat treatment, a third step of hot rolling, and a fourth step of cold rolling. and a rolling step, and these steps are performed in this order.

(1st process to 2nd process: casting process, homogenization heat treatment process)
The first step is a step of producing an ingot having a desired composition by a semi-continuous casting method. The second step is a step of subjecting the aluminum alloy ingot produced in the first step to homogenization heat treatment.

In the first step, an aluminum alloy is cast by a semi-continuous casting method (DC (direct chill) casting) to obtain an ingot. Next, after performing a step of removing by face milling a region of the ingot surface layer that has a non-uniform structure, a second step of performing homogenization heat treatment is performed. In the second step, a two-stage homogenization heat treatment or a two-time homogenization heat treatment may be employed. The two-stage homogenization heat treatment referred to here means that after the ingot is held at a predetermined homogenization temperature for a predetermined period of time and the first stage homogenization heat treatment is performed, the ingot is not cooled to room temperature, but heated to a temperature exceeding 200℃. This means that cooling is stopped at that temperature, and the temperature is maintained for a predetermined period of time to perform the second homogenization heat treatment. In addition, double homogenization heat treatment means that the ingot is held at a predetermined homogenization temperature for a predetermined period of time to carry out the first homogenization heat treatment, and then once cooled to a temperature of 200°C or less including room temperature. This means performing a second homogenization heat treatment by reheating and holding at a predetermined homogenization temperature for a predetermined time. Furthermore, in the case of double homogenization heat treatment, the facing step can be performed before the first homogenization heat treatment or between the first and second homogenization heat treatments. In the case of two-stage homogenization heat treatment, surface cutting is performed before homogenization heat treatment.

(Third process: hot rolling process)
The third step is a step of hot rolling the aluminum alloy ingot that has been subjected to the homogenization heat treatment in the second step. The thickness of a hot rolled sheet obtained by hot rolling is usually set by back calculating the total rolling reduction by cold rolling from the thickness of the product sheet obtained by cold rolling.

The winding temperature, which is the end temperature of hot rolling, is, for example, 300°C or more and 370°C or less, preferably 330°C or more and 370°C or less, and more preferably 340°C or more and 360°C or less. When the winding temperature is 330°C or higher, the residual processed structure is further suppressed, and when the cold-rolled aluminum alloy plate is formed into a cylindrical cup shape, the 45° edge becomes low and tear-off or edge breakage occurs. suppressed. On the other hand, when the winding temperature is 370° C. or lower, the occurrence of surface defects called seizure on the surface of the hot rolled sheet is suppressed, and the properties of the sheet surface are improved.

In the present invention, since relatively large amounts of Cu and Mg are contained in the aluminum alloy, when the coil is cooled after hot rolling, it remains at around 250°C, which is the precipitation peak of intermetallic compounds containing solid solution strengthening elements, for a long time. If held, a large amount of intermetallic compounds will precipitate, resulting in a decrease in the strength of the aluminum alloy plate for bottle can bodies. Therefore, it is preferable that the cooling rate from immediately after hot rolling until reaching about 250°C is 28°C/hr or more.

(4th process: cold rolling process)
The fourth step is a step of cold rolling the hot rolled plate hot rolled in the third step. In the fourth step, the hot rolled plate is cold rolled without annealing to finish it into an aluminum alloy plate with a predetermined thickness. Cold rolling is performed by setting a plurality of passes at a predetermined total rolling rate so that the hot rolled plate is rolled to the thickness of the product plate within an appropriate load range. Note that a pass means that the plate is rolled by passing it once between a pair of work rolls.

The total rolling ratio of cold rolling may be, for example, 80% or more and 95% or less. When the total rolling reduction of cold rolling is 80% or more, sufficient strength of the aluminum alloy plate for bottle can bodies can be obtained, and sufficient pressure resistance strength of the can bodies after DI forming and baking can be obtained. The total rolling reduction of cold rolling may preferably be 82% or more. On the other hand, when the total rolling reduction is 95% or less, the strength of the aluminum alloy plate is prevented from becoming excessive, and the deterioration of formability is suppressed.

In the method for manufacturing an aluminum alloy plate for a bottle can body, after cold rolling, finish annealing may be performed if necessary, but it is preferable not to perform finish annealing. In addition, in the above method for manufacturing an aluminum alloy plate for bottle can bodies, after the third step and before the end of the fourth step, intermediate annealing exceeding the temperature reached by the paint baking treatment of DI cans is performed. shall not be carried out.

The embodiments of the present invention have been described above, and below, examples in which the effects of the present invention were confirmed will be specifically described in comparison with comparative examples that do not meet the requirements of the present invention. Note that the present invention is not limited to these examples.

(Production of aluminum alloy plate for bottle body)
Aluminum alloys (No. 1 to No. 3) having the compositions shown in Table 1 are cast using a semi-continuous casting method, subjected to surface milling and homogenization heat treatment using the methods shown as the first and second steps, and then cooled. Hot rolling was carried out without any process. The end temperature of hot rolling was set to 330° C. or higher as the coiling temperature. No. 1 and no. For No. 2, the cooling rate from the end of hot rolling to about 250° C. was set as shown in Table 1. The obtained hot-rolled plate was then cold-rolled to obtain a 0.37 mm cold-rolled plate without performing intermediate annealing. In addition, No. 1 corresponds to the example, and No. 1 corresponds to the example. 2 and no. 3 corresponds to a comparative example.

(Plate strength)
A JIS No. 5 test piece was taken from the cold-rolled plate in a direction parallel to the rolling direction, a tensile test was conducted, and the 0.2% proof stress was measured, and the plate strength was determined.

(Preparation of DI can)
A DI can was produced using a cold rolled plate. As a manufacturing method, first, a blank with a diameter of 140 mm was punched out from a cold-rolled plate, and this blank was drawn to form a cup with a diameter of 90 mm. The obtained cup was re-drawn using a general-purpose aluminum can body forming machine, and each can body was further ironed three times to give a final ironing rate of 39.9%, and the thinnest part A DI can with a thickness of 140 μm and a body diameter of 66 mm was produced.

(Can wall strength)
Tensile test with the gauge distance shortened to 25 mm based on the JIS No. 13 B test piece shape from the thinnest part of the can wall of the prepared DI can, from the position where the rolling direction of the cold rolled plate and the can axis direction are parallel. A piece was taken. A tensile test was conducted on the sampled tensile test piece, and the 0.2% proof stress was measured, which was taken as the can wall strength. The value of the difference between this can wall strength and the above-mentioned plate strength (can wall strength - plate strength) was calculated, and those with a value of (can wall strength - plate strength) of 97 MPa or less were accepted.

<Evaluation of uneven thickness during ironing process>
The side wall thickness distribution of the prepared DI can was measured at 1 mm pitch at 45° intervals in the circumferential direction of the can from the height of 14 mm from the bottom of the can to the height of the open end (125 mm in this case), and the amount of wall thickness deviation ( (maximum difference in side wall thickness at 180° symmetrical positions)/2) was calculated. The measurement results are shown in Figure 1. The average value of the thickness deviation amount calculated at each height position over all height positions (average thickness deviation amount) is 1.5 μm or less, A is 2.5 μm or less, B is over 2.5 μm. The item was designated as C. The results are shown in Table 1.

As shown in Table 1, even if the plate thickness is 0.30 mm or more and 0.38 mm or less, the composition and (can wall strength - plate strength) are within the range of the present invention. No. 1 was excellent in that the amount of uneven thickness was small.

Claims (4)

Si: 0.1% by mass or more and 0.5% by mass or less,
Fe: 0.3% by mass or more and 0.6% by mass or less,
Cu: 0.1% by mass or more and 0.35% by mass or less,
Mn: 0.5% by mass or more and 1.2% by mass or less,
Mg: Contains 1.0% by mass or more and 2.5% by mass or less,
The remainder consists of Al and inevitable impurities,
The ratio of Mg content to Cu content (Mg mass%/Cu mass%) is 3.6 or more and 4.2 or less,
The value obtained by subtracting the plate strength before forming the can body from the can wall strength after forming the can body is 97 MPa or less,
After forming, the can body is made by drawing a 0.37 mm thick, 140 mm diameter blank into a 90 mm diameter cup, then redrawing the resulting can body, which is then ironed three times. An aluminum alloy plate for a bottle body , which has a final ironing rate of 39.9%, a thickness at the thinnest part of 140 μm, and a body diameter of φ66 mm . The aluminum alloy plate for can bodies according to claim 1, wherein the Zn content is 0.4% by mass or less. The aluminum alloy plate for can bodies according to claim 1 or 2, wherein the Ti content is 0.1% by mass or less. The aluminum alloy plate for a can body according to any one of claims 1 to 3, wherein the Cr content is 0.1% by mass or less.