JP2013112858A - Aluminum alloy sheet for cap and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for a cap which controls variation among lots and in a lot and has small difference between tensile strength and yield strength and high rigidity.SOLUTION: The aluminum alloy sheet for a cap has a composition containing, in mass%, 1.5-1.8% of Mg, 0. 20% or less of Mn, 0.20% or less of Si, 0.30% or less of Fe, 0.02% or less of Cu, 0.02% or less of Zn, 0.02% or less of Cr, and 0.02% or less of Ti, with the balance comprising Al and unavoidable impurities, and has a sheet thickness of 0.200-0.260 mm, tensile strength of 205-225 MPa, yield strength of 170-200 MPa, and elongation of 6-12% in terms of mechanical properties. The standard deviation σ of the tensile strength in a lot is small, such as 3 MPa or less, and a ratio of the tensile strength to the yield strength in the mechanical properties is 0.8 or more, thereby providing the aluminum alloy sheet for a cap with small variation.

Description

  The present invention relates to an aluminum alloy plate for a cap and a method for producing the same.

In recent years, a beverage container including a bottle can having a trunk and a mouth and a screw-type cap attached to the mouth has been used. In addition, with the aluminumization of bottle cans, aluminum materials suitable for bottle cans are also used for caps.
In general, Al-Mn Al alloy (3000 series) such as JIS3004 (AA3004) or JIS3104 (AA3014) is used as the material of the bottle can, and AA5151 is used as the material of the cap. Al-Mg type Al alloy (5000 type) is used.

As an aluminum alloy plate used for such a cap, Mg: 1.61 to 1.9% by mass, Cu: 0.05% or less, Mn: 0.1% or less, Cr: 0.05% or less, An aluminum alloy sheet containing Zn: 0.2% or less, Si: 0.3% or less, Fe: 0.05 to 0.4%, Ti: 0.2% or less, and the balance containing inevitable impurities is known. ing. In this aluminum alloy plate, the base plate has a tensile strength of 202 to 235 MPa and a proof stress of 171 to 200 MPa, the shape of the ear generated at the opening of the cup is a hexagonal ear or an octagonal ear. It is provided as an alloy plate of 5% or less, a tensile strength after baking of 202 to 235 MPa, a proof stress of 160 to 195 MPa, and an elongation of 7 to 12% (see Patent Document 1).
Further, as an aluminum alloy plate for high strength cap, Mg: 0.8% to 2.0% is contained, the balance is composed of Al and inevitable impurities, the tensile strength is 170 to 214 MPa, and the elongation is 5 %, The ear ratio is 3% or less, and the limit drawing ratio is 1.9 or more, which is a method for producing an aluminum alloy plate for a high-strength cap, which is hot-rolled and cold-rolled to a slab There is provided a method for producing an aluminum alloy plate for a high-strength cap, characterized in that the final cold rolling rate is more than 50 to 80% and the final temper annealing is performed at 190 ° C. to 260 ° C. after the final cold rolling. (See Patent Document 2).
Furthermore, as an aluminum alloy plate for a cap, Mg: 1.6 to 2.1%, Fe: 0.05 to 0.35%, Cu: 0.03% or less, Mn: 0.01 to 0.10%, Cr: 0.06% or less, Si: 0.2% or less, Zn: 0.15% or less, Ti: 0.10% or less, with the balance consisting of Al and inevitable impurities, tensile strength There is provided an aluminum alloy plate for a bottle can screw cap, characterized by having a length of 215 to 270 MPa, an elongation of 6.1% or more and an ear rate of 3.5% or less. (See Patent Document 3)

JP 2008-144217 A Japanese Patent No. 4294448 Japanese Patent No. 4393943

When the bottle can is used as a hot beverage such as green tea, black tea, coffee, etc., when the bottle can is filled with a beverage and heated and the internal pressure rises, the cap may come off and jump out.
In order to suppress this protrusion, in order to reinforce the fitting maintenance force by screwing the screw portion of the bottle can and the screw portion of the cap, the technology described in the above-mentioned Patent Document 1 is Mg, Cu, Mn, Cr, Zn, Provide an aluminum alloy plate for caps with excellent heat resistance and high-temperature strength by containing component elements such as Si and Fe in an appropriate range and by optimizing the mechanical properties of the base plate and the mechanical properties after baking. I was able to.

  However, when manufacturing the above-mentioned aluminum alloy sheet, it is manufactured as an aluminum alloy sheet of the required thickness by hot rolling and cold rolling from an aluminum alloy slab, but it is rarely strength between production lots or within lots. It was found that this variation occurred. If this variation is large, there is a possibility that an appropriate strength as an aluminum alloy plate for a cap cannot be obtained.

The present invention has been made in order to solve the above-described problems, has little variation in strength between production lots and within lots, can be molded as a cap having a threaded portion, has excellent pressure resistance, and is excellent. An object of the present invention is to provide an aluminum alloy plate for a cap with an ear ratio and a method for producing the same.
In addition, between the production lots in the specification of the present application refers to a lot (coil) in the final temper annealing furnace processed at one time. The number of lots varies depending on the size (kind) of the furnace, but is in the range of 2 to 10 lots. In addition, “within a lot” indicates variations in the front and rear ends of the lot (coil) and the plate end portion and the center portion in the plate width direction. Normally, the strength (tensile strength) of material products (aluminum plates) during mass production is small within a lot, but due to the variation in alloy composition between slabs and the effect of variation during production, there is a large variation between lots. A tendency to become prone is recognized.

  The aluminum alloy material for bottle can caps of the present invention is in mass%, Mg: 1.5-1.8%, Mn: 0.20% or less, Si: 0.20% or less, Fe: 0.30% or less Cu: 0.02% or less, Zn: 0.02% or less, Cr: 0.02% or less, Ti: 0.02% or less, with the balance being Al and inevitable impurities, Mechanical properties of tensile strength of 205 to 225 MPa, proof stress of 170 to 200 MPa, elongation of 6 to 12%, standard deviation σ of tensile strength between lots and within lots is within 3 MPa, and variation is small. The property is characterized in that the ratio of tensile strength to proof stress is 0.8 or more.

  The aluminum alloy material for bottle can caps of the present invention is a method for producing the aluminum alloy plate for caps described above, and the finished plate thickness of hot rough rolling is 10 to 30 mm, and then hot finish rolling is performed. When finished, the finished sheet thickness is 2.0 to 4.0 mm, the rolling speed is 100 to 500 m / min, and the finished temperature is 310 to 360 ° C.

  According to the present invention, it is possible to carry out in a similar alloy composition range without greatly changing the alloy composition previously proposed by the present applicant, variation in tensile strength between lots and within lots is small, and proof stress is reduced. By improving the rigidity close to the tensile strength, the cap pressure resistance can be improved and the wall thickness can be reduced, and it can be applied to the manufacturing method that performs hot rough rolling and hot finish rolling. And its manufacturing method.

Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below.
The target aluminum thickness of the cap aluminum alloy plate of this embodiment is 0.20 mm or more and 0.26 mm or less, and in mass%, Mg: 1.5 to 1.8%, Mn: 0.20% or less, Si: 0.20% or less, Fe: 0.30% or less, Cu: 0.02% or less, Zn: 0.02% or less, Cr: 0.02% or less, Ti: 0.02% or less The balance is made of an aluminum alloy having a composition comprising Al and inevitable impurities.

"Ingredient composition"
Hereinafter, the component composition limited in the aluminum alloy plate for caps of the present invention will be described. In addition, content of each element described in this specification is mass% unless otherwise specified, and includes an upper limit and a lower limit unless otherwise specified. Therefore, for example, the notation of 1.5 to 1.8% means 1.5% or more and 1.8% or less.
“Mg” 1.5-1.8%
In the aluminum alloy plate for caps of the present invention, Mg has a precipitation hardening action, enhances work hardening at the time of rolling, and exhibits dispersion hardening and precipitation hardening action by coexisting with Si and Cu, thereby increasing the strength. Improve.
If the Mg content is less than 1.5%, sufficient strength cannot be obtained. If the Mg content exceeds 1.8%, the strength is too high and the workability is lowered, and it is difficult to open the cap when used as a cap of a bottle can. Therefore, the Mg content needs to be in the range of 1.5 to 1.8%.

“Mn” 0.2% or less In the aluminum alloy plate for caps of the present invention, Mn forms an Al—Mn—Fe-based intermetallic compound and exhibits a dispersion hardening action as a crystallization phase and a dispersed phase. If the Mn content exceeds 0.2%, workability deteriorates due to a decrease in toughness. The Mn content needs to be 0.2% or less.
“Si” 0.2% or less Si forms a compound with Mg or the like contained at the same time in the aluminum alloy plate for a cap of the present invention, and improves the strength by precipitation hardening and dispersion hardening.
If the Si content exceeds 0.2%, the strength becomes too high, and it may be difficult to open the cap when used as a bottle can cap. Therefore, the Si content needs to be 0.2% or less.
“Fe” 0.3% or less Fe increases the amount of Al—Mn—Fe intermetallic compound in the cap aluminum alloy plate of the present invention, and contributes to the refinement of crystals and the effect of improving toughness.
If the Fe content exceeds 0.3%, the amount of the Al—Mn—Fe intermetallic compound is excessively increased, and the workability is reduced due to a decrease in toughness. Therefore, the Fe content needs to be 0.3% or less.

“Cu” 0.02% or less Cu has an effect of increasing strength mainly by solid solution hardening, precipitation hardening and dispersion hardening in the aluminum alloy plate for a cap of the present invention.
If the Cu content exceeds 0.02%, variations between production lots are likely to occur. Therefore, the Cu content needs to be 0.02% or less.

“Zn, Cr, Ti” Zn: 0.02% or less, Cr: 0.02% or less, Ti: 0.02% or less The aluminum alloy plate for a cap of the present invention has Zn: 0.02% or less, Cr: It can be set as the component composition containing 0.02% or less and Ti: 0.02% or less.
Zn has an effect on workability and corrosion resistance, and when it exceeds 0.02%, workability and corrosion resistance tend to deteriorate. Therefore, the Zn content needs to be 0.02% or less.
In the aluminum alloy plate for a cap of the present invention, Cr contributes to improving the strength. However, when it exceeds 0.02%, the strength becomes too high, and when it is used as a bottle can cap, it is difficult to open the cap. Therefore, the Cr content needs to be 0.02% or less.
Ti contributes to improving the strength in the aluminum alloy plate for a cap of the present invention, but when it exceeds 0.02%, the strength becomes too high, and when it is used as a cap of a bottle can, it is difficult to open the cap. Therefore, the Ti content needs to be 0.02% or less.

In the method for producing an aluminum alloy plate for a cap according to the present embodiment, for example, an aluminum alloy slab having the above composition is melted, and the slab is heated to a plate thickness of about 10 to 30 mm using a hot rough rolling machine. After rough rolling, hot rolling to a sheet thickness of about 2.0 to 4.0 mm using a hot finish rolling mill, then cold rolling to about 0.7 mm in a cold rolling apparatus, and then continuous The target aluminum alloy sheet for a cap can be obtained by performing intermediate annealing in an annealing furnace, cold rolling to a final target plate thickness in a cold rolling apparatus, and final temper annealing.
The hot roughing mill includes, for example, upper and lower work rolls and backup rolls, and a conveyance path in which a plurality of conveyance rollers are arranged, and the aluminum alloy plate that has been conveyed passes between the work rolls to have a desired thickness. It is an apparatus that rolls into

  The hot finish rolling mill includes, for example, upper and lower work rolls and a backup roll, and winding devices installed on the entry side and the exit side of these rolls. This hot finish rolling mill reverses the hot-rolled plate material and the operation of winding the hot-rolled plate material from the inlet-side winding device and passing between the work rolls with the outlet-side winding device. This is a device that hot rolls aluminum alloy sheets to the desired plate thickness by repeatedly performing the rolling operation with the work rolls as many times as necessary, and gradually adjusting the interval between the work rolls for each rolling operation. .

The cold rolling apparatus includes, for example, upper and lower work rolls and a backup roll, a reel type winding device installed on the entry side of these rolls, and a reel type winding device installed on the exit side. . This cold rolling mill has an operation of winding the sheet material which has been fed out from the winding device on the inlet side and passed between the work rolls and cold rolled by the winding device on the outlet side, and again from the winding device on the outlet side. The aluminum alloy plate is obtained by repeatedly winding the plate cold-rolled by passing between the rolls with the winding device on the entry side as many times as necessary, and gradually adjusting the interval between the work rolls for each rolling operation. Is an apparatus that sequentially rolls up to the desired plate thickness.
By using each apparatus described above as a main body and sequentially carrying out the steps described in detail below, the target aluminum alloy plate for a cap can be manufactured.

When performing hot rolling from a slab, the number of hot rolling passes depends on the slab thickness, finish thickness, slab width, alloy composition, etc., but a range of ten to twenty dozen passes is common. is there.
In hot rolling, while a rolled material is thick, it can be rolled using a one-stand reversible rolling mill in which a conveyance table is installed before and after the normal rolling mill. However, when the plate is thinned, the necessary transport table length is increased, the slack due to the weight of the plate is increased, and the plate is likely to be cooled.
For this reason, until the aluminum alloy sheet is thinned to some extent, for example, hot roughing is performed with a hot roughing mill until it becomes 10 mm or more and 30 mm or less, and then hot rolling is performed with a hot rolling mill, It is preferable to perform hot finish rolling at about 2.0 to 4.0 mm.
If the hot rough rolled finished sheet thickness is less than 10 mm, the productivity of rough rolling is inferior, and if it exceeds 30 mm, the productivity of subsequent finish rolling is lowered.

As described above, the hot finish rolling finish plate thickness is preferably 2.0 to 4.0 mm. However, if the plate thickness is less than 2.0 mm, the productivity of finish rolling is inferior. The productivity of hot rolling is inferior.
The hot finish rolling speed is desirably 100 to 500 (m / min), and if it is less than 100 (m / min), the productivity is poor, and if it exceeds 500 (m / min), the shape defect and the surface property deteriorate.
The hot finish rolling finish temperature is preferably in the range of 310 ° C to 360 ° C. When the hot finish rolling finish temperature is less than 310 ° C., the 45 ° ear develops too much and the ear rate deteriorates, and when it exceeds 360 ° C., the 0-180 ° ear develops and the ear rate deteriorates.

The value of the crystal grain size at the center of the hot finish rolled sheet thickness is desirably less than 50 μm, and if it exceeds 50 μm, the crystal grains are coarsened in the subsequent steps, and surface defects such as rough skin are likely to occur.
By making hot rolling into two steps of rough rolling and finish rolling as described above, it is possible to perform low temperature annealing in final temper annealing described later, and as a result, the stability of mechanical properties is improved, The variation in the lot can be suppressed, the difference between the tensile strength and the yield strength of the mechanical properties can be reduced, and a highly rigid cap material can be obtained.

After hot rolling, cold rolling is performed a plurality of times at a required reduction rate. Intermediate annealing is performed during cold rolling.
As an example of intermediate annealing, continuous annealing can be performed, and heating is performed at an average heating rate of 10 to 50 ° C./s to a predetermined temperature of 400 ° C. or more and 600 ° C. or less, and then at an average cooling rate of 30 to 150 ° C./s. To a predetermined temperature of 100 ° C. or lower. For example, by performing a heat treatment corresponding to an actual temperature of 420 ° C. by continuous annealing and reducing the sheet thickness to 0.7 mm or less, the final cold rolling ratio is lowered, and the ear ratio of the raw material product at a drawing ratio of 1.97 is 1.5. % Or less. In this case, it is possible to obtain a 0-45-90 ° eight-way ear called an ideal ear shape.
The thickness of the intermediate annealing is preferably 0.7 mm or less. When the sheet thickness at the time of intermediate annealing exceeds 0.7 mm, the final cold rolling rate increases and the ear rate deteriorates.
After the intermediate annealing treatment, final cold rolling is performed to obtain a target plate thickness, for example, a range of 0.200 to 0.260 mm, for example, 0.23 mm.

The final tempering treatment is desirably performed in a batch furnace, and it is desirable to perform low temperature annealing in the range of 195 ° C to 225 ° C. When the final temper annealing treatment is performed at a temperature lower than 195 ° C., it becomes difficult to obtain a predetermined strength, and there is a possibility that the physical properties may be changed by a heat treatment at the time of subsequent painting / printing, at a temperature exceeding 225 ° C. When it is carried out, the rigidity becomes inferior, and when the temperature is further raised, it softens rapidly, partly recrystallization starts, and physical properties tend to become unstable.
The cap aluminum alloy plate manufactured according to the above process desirably has an ear rate of 1.5% or less. When the ear rate exceeds 1.5%, the effect of anisotropy as a material becomes large, and when a cap for a bottle can is configured, there is a problem that characters at the time of painting and printing are distorted. is there. Moreover, the crystal grain diameter of the plate | board thickness center part of the aluminum alloy plate obtained by implementing each above-mentioned process can be refined | miniaturized with 50 micrometers or less.
According to the manufacturing method described above, the standard deviation can be reduced to 3 MPa or less in both the variation between the manufacturing lots and the variation in the strength within the manufacturing lot.

"Mechanical properties of aluminum alloy sheets for caps"
Below, the various mechanical characteristics prescribed | regulated with the aluminum alloy plate for caps which concerns on this invention are demonstrated.
In the aluminum alloy plate for caps according to the present invention, it is desirable that the tensile strength (TS) of mechanical properties is 205 MPa or more and 225 MPa or less, and the ratio of tensile strength to proof stress (YS) is 0.8 (proof strength YS / The tensile strength TS) or more is preferable.
If the tensile strength is less than 205 MPa, the desired cap performance cannot be obtained, and if the tensile strength exceeds 225 MPa, it may be difficult to open the cap.

When the yield strength is less than 170 MPa, a predetermined strength as a cap cannot be obtained, and when the yield strength exceeds 200 MPa, the moldability becomes inferior.
By setting the ratio of tensile strength to proof stress (YS / TS) to 0.8 or more, high rigidity according to the strength can be obtained, and cap performance such as pressure resistance is improved.
If the elongation (EL) is less than 6%, it is difficult to form a cap. If the elongation exceeds 12%, a predetermined strength cannot be obtained, and the performance as a cap is deteriorated.

Hereinafter, although an Example is shown and the manufacturing method of the aluminum alloy plate for caps which concerns on this invention is demonstrated in detail, this invention is not limited to a following example.
Aluminum alloys having various compositions shown in Table 1 were melted, degassed and filtered with a molten metal, and then cast into a slab having a thickness of 600 mm, a width of 1100 mm, and a length of 4.5 m by semi-continuous casting.
After chamfering the slab, hot rough rolling and hot finish rolling, the coil around which the rolled material was wound was cold-rolled, subjected to intermediate annealing under the conditions shown in Table 2, and cold-rolled to the target plate thickness. Then, final temper annealing was performed on the conditions of Table 2, and the aluminum alloy plate for caps was obtained.

About the obtained aluminum alloy plate for caps, the value of tensile strength (TS), yield strength (YS), and elongation (EL) was calculated | required. Further, the variation in the tensile strength (TS) between lots (standard deviation: σ) and the value of YS / TS were determined. Table 1 also shows the hot rough rolling finish plate thickness (mm), hot finish rolling finish plate thickness (mm), hot finish rolling speed (m / min), hot finish rolling finish temperature (° C), hot Finished rolled sheet thickness center part crystal grain size (μm), intermediate annealing sheet thickness (mm), final tempering annealing temperature (° C.), ear ratio (%) are shown.
For each of Examples 1 to 14 and Comparative Examples 1 to 6 shown in Table 1, 10 lots (coils) were manufactured, and a total of 6 in both ends of the front and rear ends and both ends in the plate width direction and the center in one coil. The variation in tensile strength (TS) between lots and within lots was calculated with the number of places and the total number of samples n = 60. The results are shown in Table 2.
In addition, the value of the cap performance (mechanical property) described in Table 1 is an average value of n = 60. In the case of non-standard, the data value of n = 1 that is the most out of the range is shown. For example, with respect to the TS standard of 215 ± 10 MPa, the non-standard comparative examples 1 to 5 describe not the average value but the most out-of-standard value (data farthest from 215).

  From the results shown in Tables 1 and 2, regarding the Mg content, 1.4% of the sample of Comparative Example 1 that is less than 1.5% and 1.9% of the sample that is more than 1.8% have a high ear rate. I found out. It was also found that the sample of Comparative Example 3 having too much Mn content, Si content, Fe content, Zn content, Cr content, and Ti content had a large variation in TS. In the sample of Comparative Example 6 having a large Cu content, the variation in TS between lots within a lot increased.

The sample of Comparative Example 5 having a hot finish rolling speed of 90 (m / min) lower than 100 (m / min) has a large variation in TS and the sample of Comparative Example 1 having a low hot finish rolling finish temperature is the same. In the sample of Comparative Example 2 where the temperature was too high, the variation in TS increased.
The sample of Comparative Example 3 in which the final temper annealing temperature is too low has a large TS variation, and the sample of Comparative Example 4 in which the final temper annealing temperature is too high has a large TS variation. Further, regarding the sample of Comparative Example 6 in which the Cu content was 0.03% and Cu was contained more than 0.02%, the variation in TS within and between lots was large.

From the above test results, the alloy composition of the aluminum alloy plate for caps according to the present invention is, in mass%, Mg: 1.5 to 1.8%, Mn: 0.20% or less, Si: 0.20% or less. Fe: 0.30% or less, Cu: 0.02% or less, Zn: 0.02% or less, Cr: 0.02% or less, Ti: 0.02% or less, the balance being Al and inevitable impurities It has been found desirable to have a composition consisting of
Moreover, as an aluminum alloy plate for caps according to the present invention, the plate thickness is 0.200 to 0.260 mm, the tensile strength of mechanical properties is 205 to 225 MPa, the proof stress is 170 to 200 MPa, and the elongation is 6 to 12%. Thus, it has been found that an alloy plate having a small variation in the standard deviation σ of the tensile strength between lots and within lots can be produced within 3 MPa.
Moreover, in order to manufacture such an aluminum alloy plate for a cap, the hot rough rolled finish plate thickness is set to a range of 10 to 30 mm, and the finish plate thickness when hot finish rolling is performed is 2.0 to 4 mm. It was found that it was important to set the range to 0.0 mm, the hot finish rolling speed to 100 to 500 m / min, and the hot finish rolling finish temperature to 310 to 360 ° C.

Claims (2)

In mass%, Mg: 1.5 to 1.8%, Mn: 0.20% or less, Si: 0.20% or less, Fe: 0.30% or less, Cu: 0.02% or less, Zn: 0 0.02% or less, Cr: 0.02% or less, Ti: 0.02% or less, with the balance being composed of Al and inevitable impurities,
Mechanical properties of tensile strength of 205 to 225 MPa, proof stress of 170 to 200 MPa, elongation of 6 to 12%, standard deviation σ of tensile strength between lots and within lots is within 3 MPa, and variation is small. An aluminum alloy plate for caps, wherein the ratio of the tensile strength and proof stress of the mechanical properties is 0.8 or more.   It is a method of manufacturing the aluminum alloy plate for caps of Claim 1, Comprising: The finishing board thickness of hot rough rolling is 10-30 mm, and the finishing board thickness at the time of performing hot finish rolling after that is 2. A method for producing an aluminum alloy plate for a cap, characterized by being 0 to 4.0 mm, a rolling speed of 100 to 500 m / min, and a finishing temperature of 310 to 360 ° C.