JPH0987790A - Aluminum alloy sheet for can lid and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for can lid, capable of maintaining and improving pressure-resisting strength while inhibiting buckling loss and having superior workability, and a method for producing it. SOLUTION: This sheet is an aluminum alloy sheet having a composition which consists of, by weight, 2.6-3.5% Mg, 0.4-1.0% Mn, 0.1-0.5% Cu, and the balance Al with inevitable impurities and in which the total content of Mg and Mn is regulated to 3.4-4.0%. This aluminum alloy sheet can be produced by subjecting an alloy ingot of the composition to homogenizing treatment at 450-550 deg.C, to hot rolling, to cold rolling, to process annealing, and further to finish cold rolling at 60-80% draft. By this method, the aluminum alloy sheet for can lid, excellent, e.g. in the workability of a rivet 3 of a lid material 1, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy plate used as a can lid of a beverage can and a method for manufacturing the same.
In particular, the present invention relates to an aluminum alloy plate for a can lid capable of suppressing so-called buckle loss in which pressure resistance decreases with time after processing, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, in the production of beverage cans, the lid material has been made thinner in order to reduce costs. The properties required for the lid material of beverage cans are that they have excellent drawability (shell processing), excellent rivet formation (multi-stage overhang), excellent pressure resistance, and can openability. It is excellent and has excellent corrosion resistance. Of these required characteristics, rivet formability and pressure resistance are problems when making the lid material thinner.

Here, the rivet of the lid material refers to a portion for fixing the tab (grasping portion) by molding in the central portion of the lid material by multi-step overhang. FIG. 1 is a top view showing a lid member to which a tab is attached, and FIG. 2 is a sectional view showing a method of forming a rivet for the lid member in the order of steps. This FIG. 2 (a) and (b)
As shown in FIG. 3, a protrusion 1a is formed in the central portion of the lid member 1 by multi-step overhanging, and a through hole 4 formed in the tab 2 and serving as a fulcrum when the can is opened is fitted into the protrusion 1a. Then, as shown in FIG. 2C, the tip of the protrusion 1a is crushed to form the rivet 3. With this rivet 3, the tab 2 can be caulked and fixed to the lid member 1.

The above-mentioned rivet formability can be improved by adjusting the rivet diameter (rivet outer shape in a crimped state) and adjusting coining, and with respect to pressure resistance, shell forming is reformed. Can be secured by forming the counter sink portion deeply by adding two steps. Since the rivet diameter is determined by the overhang height of the protrusion 1a, adjusting the rivet diameter is synonymous with adjusting the overhang height.

Generally, aluminum alloys used for can ends (lids) include Al--Mg type 5052 alloys, 5082 alloys and 5182 alloys. These have different strengths, and the non-carbonated beverages such as fruit juice and coffee use the relatively low strength 5052 alloy, and the carbonated beverages such as beer have high strength 5082 alloy. And 5182 alloy are used. Particularly, since the 5182 alloy has extremely high strength, it can be said that it is an extremely effective alloy when it is thinned.

In Japanese Patent Laid-Open No. 57-169071, Mn: 0.4 to 1.0% by weight, Mg: 1.3 to 2.
A method for producing an aluminum material for cans containing 5% by weight (claim 2) and Mn: 0.4-1.0% by weight, Mg: 1.3-2.5% by weight, 1.4 ≦ M
A method of manufacturing an aluminum material for cans in which g / Mn ≦ 4.4 and 2.0 ≦ Mg + Mn ≦ 3.3 wt% (claim 16) is disclosed.

[0007]

However, 518
Although the alloy No. 2 has extremely high strength, it has a large buckle loss. Therefore, if it is stored for a long period of time, the pressure resistance will decrease, and it will fall below the strength required for beverage cans. This buckle loss is a phenomenon in which the pressure resistance of the lid decreases with time after shell forming. The improvement of this buckle loss is
It is indispensable for thinning the can end portion, especially for reforming.

In particular, when the buckle loss of the aluminum material is significant, the reduction of the compressive strength starts from the molding of the can end, and the compressive strength continues to decrease even after being formed as a product, so that the compressive strength can be maintained. Have difficulty.
This phenomenon becomes noticeable when the aluminum material is thinned or when the counter sink portion is subjected to strong working, that is, in the case of reforming. The main cause of the decrease in pressure resistance of aluminum materials is the decrease in material strength of the counter sink, so it is desirable to develop an aluminum alloy material for can lids that can prevent buckle loss and ensure sufficient pressure resistance. ing.

On the other hand, the method of manufacturing an aluminum material for cans disclosed in Japanese Patent Laid-Open No. 57-169071 uses UBC.
This is a method for manufacturing an aluminum material for the purpose of effectively utilizing (used beverage cans), and does not take into consideration the pressure resistance and buckle loss required as can properties. When the inventors of the present application conducted a follow-up test on an aluminum alloy material having the above-described composition, the aluminum material for a can having the above-described composition has a Mg content of 1.3 to 2.
It is as low as 5% by weight, and the total amount of Mg and Mn is 2.0 to
Since it was as low as 3.3% by weight, although it had some effect of suppressing buckle loss, it was found that the pressure resistance required as a lid material for a positive pressure can cannot be obtained.

The present invention has been made in view of the above problems, and can suppress the buckle loss, maintain and improve the pressure resistance, and have good workability as a lid material. The purpose is to provide an alloy plate.

[0011]

The aluminum alloy plate for a can lid according to the present invention is Mg: 2.6 to 3.5% by weight, M
n: 0.4 to 1.0% by weight, Cu: 0.1 to 0.5
% By weight, and the total amount of Mg and Mn is 3.4 to 4.
It is 0% by weight, and the balance is characterized by comprising Al and inevitable impurities.

The method for producing an aluminum alloy plate for a can lid according to the present invention is Mg: 2.6 to 3.5% by weight, Mn:
0.4 to 1.0% by weight, Cu: 0.1 to 0.5% by weight, the total amount of Mg and Mn is 3.4 to 4.0% by weight, and the balance is Al and inevitable impurities. The aluminum alloy ingot consisting of is subjected to homogenizing treatment at a temperature of 450 to 550 ° C., then hot-rolled and cold-rolled, then annealed, and further finished at a working rate of 60 to 80%. It is characterized by performing hot rolling. Further, finish annealing may be performed after the finish cold rolling.

[0013]

The present inventors suppress the buckle loss and
Various experimental studies were conducted to develop an aluminum alloy plate for a can lid that can maintain and improve pressure resistance and ensure workability. As a result, it was found that the buckle loss is greatly influenced by the amount of Mg added in the material, and the buckle loss becomes more remarkable as the Mg amount increases, and the buckle loss is suppressed as the Mg amount decreases.

By the way, the can end is coated and printed (base printing).
King) is processed later. Since baking is performed before processing, the strength does not change with time, but when subjected to strong processing such as reform shell processing, a relatively large processing strain occurs in the counter sink portion. For this reason,
The Mg element, which had been in the form of a solid solution until then and had a role of maintaining the strength of the aluminum alloy plate, diffuses and precipitates, causing a recovery phenomenon (strength reduction). Since this recovery phenomenon requires time to reach an equilibrium state, the pressure resistance strength decreases (buckle loss) with time. Therefore, in order to suppress the buckle loss, it is effective to reduce the added amount of Mg that causes the recovery phenomenon.

However, normally, when the amount of Mg added is reduced,
Its pressure resistance is reduced. Therefore, in the present invention, Mn and Cu capable of improving the pressure resistance strength
By adjusting the addition amount of other components such as the above and adjusting the working rate of finish cold rolling, it was possible to suppress the reduction of the compressive strength or improve the compressive strength without impairing the workability. Also,
In order to suppress buckle loss, conventional Mg: 1.3-
Even if Mg is not extremely lowered like 2.5% by weight,
It has been found that a reduction to 3.5% by weight or less is sufficient.

The present invention has been made from this point of view. Hereinafter, the reason for adding the components and the reason for limiting the composition of the aluminum alloy plate for a can lid according to the present invention will be described.

Mg (magnesium): 2.6 to 3.5
Weight% Mg improves the strength of the aluminum alloy plate,
Although it is an element added to ensure corrosion resistance, the amount of Mg added has a great influence on buckle loss. That is, when Mg is added in excess of 3.5% by weight, buckle loss becomes large and the pressure resistance strength decreases with time. On the other hand, if the amount of addition of Mg is less than 2.6%, the aluminum alloy plate will have insufficient compressive strength. Therefore, the amount of added Mg is 2.6 to 3.5% by weight.

Mn (manganese): 0.4 to 1.0 weight
% Mn is also an element that improves the compressive strength of the aluminum alloy plate, but when Mn is added in an amount of more than 1.0% by weight,
Coarse crystallized substances are generated, and the workability of the aluminum alloy plate is deteriorated. The addition amount of Mn is 0.4% by weight.
If it is less than the above range, the aluminum alloy plate will have insufficient pressure resistance and the tearability required as a lid material will be reduced. Therefore, the added amount of Mn is 0.4 to 1.0% by weight.

3.4 wt% ≦ Mn + Mg ≦ 4.0 wt% The addition amounts of Mg and Mn are within the above ranges, respectively, and the total amount thereof is 3.4 wt% or more and 4.0 wt% or less. It is necessary. This is Mg + Mn 3.4% by weight
If it is less than the above range, sufficient strength cannot be obtained, and if it is added in excess of 4.0% by weight, the strength is too high and the workability of the aluminum alloy sheet is deteriorated.
Therefore, by setting the total amount of Mn and Mg within the above range, the aluminum alloy plate can obtain a sufficient pressure resistance as a lid material for carbonated beverages such as beer.

Cu (copper): 0.1 to 0.5% by weight Cu is also an element that improves the strength of the aluminum alloy plate, but if the addition amount of Cu is less than 0.1% by weight, the aluminum alloy plate Cannot obtain sufficient strength, and 0.
If Cu is added in excess of 5% by weight, the corrosion resistance will be reduced. Therefore, the addition amount of Cu is set to 0.1 to 0.5% by weight.

Other elements such as Si, Fe,
Regarding Cr, Ti, Zn, etc., Si <0.3 wt%, Fe <0.5 wt%, Cr <0.5 wt%, Ti
If it is <0.2% by weight and Zn <1.0% by weight, the characteristics of the aluminum alloy plate are not adversely affected.

Next, the reasons for limiting the manufacturing conditions of the aluminum alloy plate for a can lid according to the present invention will be described.

Homogenization treatment temperature: 450 to 550 ° C. The soaking temperature of the aluminum alloy ingot has a great influence on the hot rolling property. That is, when the soaking temperature is less than 450 ° C., homogenization becomes insufficient and ear cracks may occur during hot rolling. On the other hand, if the homogenization treatment is performed at a temperature higher than 550 ° C, burning or the like will occur and the surface quality will deteriorate. Therefore, the homogenization treatment temperature is set to 450 to 550 ° C.

Then, the aluminum alloy ingot subjected to the homogenization treatment is subjected to hot rolling and cold rolling, and then subjected to intermediate annealing. The conditions for this intermediate annealing are not particularly specified, but it is essential that they are in a completely recrystallized state, and from the viewpoint of crystal grains, continuous annealing is preferable. The conditions for continuous annealing include, for example, heating / cooling rate of 10
It is preferable that the temperature is 0 ° C./minute or more, the holding temperature is 380 ° C. to 600 ° C., and the holding time is 1 minute or less.

Work ratio of finish cold rolling: 60 to 80% The work ratio of finish cold rolling after intermediate annealing has an effect on strength and earring. In order to improve the strength and ear ratio of the aluminum alloy plate, it is necessary to set the processing rate to 60% or more. On the other hand, when the processing rate exceeds 80%, the workability of the aluminum alloy plate is extremely deteriorated, and the ear rate becomes high during the drawing process. Therefore, the working ratio of finish cold rolling is set to 60 to 80%.

After the finish cold rolling, if it is necessary to adjust the strength of the material, it is preferable to perform finish annealing. For example, finish annealing is performed when the workability is high and it is necessary to improve the workability of the material.

[0027]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples that depart from the claims of the present invention.

First Example An aluminum alloy ingot having the composition shown in Table 1 below was homogenized at a temperature of 510 ° C., and then hot-rolled and cold-rolled to produce a rolled plate. . Then, the rolled sheet was continuously annealed as follows. First, 70
It was heated at a rate of 0 ° C./minute, kept at a temperature of 420 ° C. for 2 seconds, and then cooled at a rate of 700 ° C./minute. And 70
A product plate having a predetermined thickness was manufactured at a processing rate of%, and a can end was produced from the product plate by a reforming process including two steps.

The pressure resistance of the can ends thus produced was measured immediately after processing (within 30 minutes after processing) and after being stored at room temperature for 3 months.

Regarding the comparative examples shown in Table 1 below, the values of the compositions outside the scope of the claims are underlined and the mechanical properties of each alloy are shown in Table 2 below.

[0031]

[Table 1]

[0032]

[Table 2]

Table 3 below shows the measurement results of the compressive strength of the can ends made of the alloys shown in Table 1 above immediately after processing and after storage at room temperature for 3 months.

[0034]

[Table 3]

As shown in Table 3 above, Examples No. 1 to No. 6
Regarding, the pressure resistance of the can end immediately after processing was 6.00 kg / cm ² or more, and the buckle loss after 3 months was a value near 0.10.
It was halved compared to the conventional example consisting of two alloys, and buckle loss could be suppressed.

On the other hand, in Comparative Examples Nos. 1, 3, 5 and 8, the amount of the element to be added was small, so
The compressive strength immediately after processing became less than 6.00 kg / cm ² , and sufficient strength could not be obtained. In addition, in Comparative Example No. 2, the amount of Cu added was larger than the predetermined amount, so that the corrosion resistance was extremely reduced. Furthermore, for Comparative Examples Nos. 4 and 7, Mn and Mn + Mg, respectively.
Since the addition amount of was larger than the predetermined amount, molding defects occurred due to formation of coarse crystallized substances.

Second Example After an alloy ingot having the same composition as that of Example No. 1 shown in Table 1 above was subjected to homogenizing treatment, rolling treatment and intermediate annealing under the same conditions as in the above-mentioned first example. Then, finish cold rolling was performed at a processing rate shown in Table 4 below to manufacture a product plate having a predetermined thickness, and then a can end was prepared in the same manner as in the above-mentioned first embodiment.

The pressure resistance of the produced can ends was measured immediately after processing (within 30 minutes after processing). The results are shown in Table 4 below together with the mechanical properties.

[0039]

[Table 4]

As shown in Table 4 above, Example Nos. 7-9
In each case, the compressive strength was 6.00 kgf / cm ² or more, and good compressive strength could be obtained.

On the other hand, in Comparative Example No. 9, the working ratio of finish cold rolling was lower than the predetermined range, so that sufficient strength could not be obtained, and in Comparative Example No. 10, the working ratio was lower than the predetermined range. Since it is large, the aluminum alloy plate was cracked when it was processed into a can end, resulting in defective molding.

[0042]

As described above, according to the present invention,
Since the composition of Mg, Mn, and Cu and the total amount of Mg + Mn are properly defined, buckle loss is suppressed, pressure resistance itself is high, and workability is excellent. Further, according to the method of the present invention, an aluminum alloy sheet having excellent properties as described above can be produced with high efficiency, and an aluminum alloy sheet for a can lid suitable for a can lid material of a carbonated beverage container such as beer is produced. can do.

[Brief description of drawings]

FIG. 1 is a top view showing a lid member to which a tab is attached.

FIG. 2 is a cross-sectional view showing a step of forming a rivet for a lid material.

[Explanation of symbols]

 1; lid material 2; tab 3; rivet 4; through hole

Claims (3)

[Claims] 1. Mg: 2.6 to 3.5% by weight, Mn:
0.4 to 1.0% by weight, Cu: 0.1 to 0.5% by weight, the total amount of Mg and Mn is 3.4 to 4.0% by weight, and the balance is Al and inevitable impurities. An aluminum alloy plate for a can lid, which is made of 2. Mg: 2.6 to 3.5% by weight, Mn:
0.4 to 1.0% by weight, Cu: 0.1 to 0.5% by weight, the total amount of Mg and Mn is 3.4 to 4.0% by weight, and the balance is Al and inevitable impurities. The aluminum alloy ingot consisting of is subjected to homogenization treatment at a temperature of 450 to 550 ° C., then hot-rolled and cold-rolled, then subjected to intermediate annealing, and further finish-cooled at a working rate of 60 to 80%. A method for manufacturing an aluminum alloy plate for a can lid, which comprises performing hot rolling. 3. The method for producing an aluminum alloy sheet for a can lid according to claim 2, wherein after the finish cold rolling is performed, finish annealing is performed.