JPS61264149A - Aluminum alloy sheet for can superior in formability - Google Patents

Abstract

PURPOSE:To improve ironing and bulging workabilities, by specifying average grain width, area ratio of intermetallic compd., shape and the number thereof, in Al-Mg-Mn alloy sheet having a specified compsn. after intermediate annealing. CONSTITUTION:In Al alloy sheet having a compsn. composed of, by weight 0.5-0.8% Mn, 0.5-2.0% Mg and the balance Al and impurities, average grain width after intermediate annealing is regulated to <=45mum, to prevent deterioration of bulging property. Area ratio of intermetallic compds. formed during ingot making is regulated to 1-3%, max. length of the compd. is to <=25mum, further the number of the compd. per 0.25mm<2> is to <=1,000 pieces. Al sheet for can having the constitution is superior in formabilities such as ironing and bulging workabilities, further superior in mechanical property, and suitable for can material requiring pressure resistant strength.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention relates to an aluminum alloy for packaging with excellent formability, and more specifically to a can body material for beer and soft drinks. This invention relates to an aluminum alloy for packaging which has excellent formability and good extensibility of the can wall afterwards.

In general, aluminum beverage can bodies are manufactured by drawing an aluminum plate material, ironing, painting and printing, and 7-run processing.However, since the can body does not undergo any special processing, it has traditionally been drawn, 3004-H, 9 material, which has particularly excellent ironing workability, is used.

However, in recent years, there has been a phenomenon of diversification along with energy saving and resource saving, and beverage cans of various capacities and irregular shapes have been developed. Due to this diversification, conventional materials cannot adequately handle the irregularly shaped cans. That is, in the side wall bulging process (bulge process) after ironing process (DI process), conventional materials tend to crack due to their low ductility. As a countermeasure against this problem, heating at a high temperature after ironing is effective in improving the ductility to a certain extent and preventing the occurrence of cracks.

However, the heat treatment temperature in this case is 240°C or higher, and
The temperature can reach over 270℃. At this temperature, some aluminum may undergo crystallization, leading to a significant decrease in strength.

However, since aluminum cans are used as containers for beer, soft drinks, etc., a pressure of 5 kg/cm2 or more is generated within the can, so aluminum cans need to be pressure resistant, which can reduce the strength of the can. is problematic.

Furthermore, heat treatment at high temperatures shortens the life of the furnace and wastes energy.

Therefore, for molding applications such as irregularly shaped cans, a material is required that exhibits low work hardening during processing and has high ductility at a relatively low heat treatment temperature, as well as a material with low crack initiation and crack propagation. is required.

[Problem to be Solved by the Invention 1] As explained above, the present invention solves various problems that occur in the conventional manufacturing of cans for beer, drinking water, etc., and in particular,
Heat treatment at low temperatures (below 270°C) does not provide high ductility, and heat treatment at high temperatures (above 270°C) causes constriction and is prone to cracking during bulge processing. conducted research on these issues and found that high ductility cannot be obtained with low-temperature heat treatment because fine precipitates in the material strongly fix dislocations and prevent subgrain formation. Heat treatment is required, and at high temperatures, subgrains immediately turn into recrystallized grains, reducing strength, and these fine precipitates become Al-Mn-
The fact that it is an Fe-based material, and that even high-temperature heat treatment causes constrictions and cracks during bulge processing is likely because cracks originate from relatively large intermetallic compounds (25
We discovered that these cracks propagate in large numbers (if they exist, cracks propagate), and that conventional materials that focused only on ironing properties could not deal with this issue. He developed the board.

[Means for Solving the Problems 1] The aluminum alloy plate for packaging with excellent formability according to the present invention is characterized by: Mn 0.5-0.8 ut%, Mg 0.5-2
．． It is an aluminum alloy containing Ou + t%, the balance consisting of Al and impurities, the average grain width after intermediate annealing is 45 μm or less, the area ratio of intermetallic compounds generated during agglomeration is 1 to 3%, and this intermetallic compound The maximum length is 25 μm or less, and the number of intermetallic compounds per 0.25 mm2 is 1
000 or less.

The aluminum alloy plate for packaging with excellent formability according to the present invention will be described in detail below.

In general, the lack of ductility of aluminum alloys is due to fine precipitates of Mn, and in order to suppress these, the content must be kept low. It is an element necessary for formation, and if the content is less than 0.5 wt%, the amount of precipitates formed will decrease and high ductility at low temperatures can be obtained, but this will also be accompanied by a decrease in intermetallic compounds, so ironing The lubricating effect of
．． If the content exceeds 8u+t%, a large number of fine precipitates will increase, suppressing subgrain formation (high ductility) at low temperatures. Mg is an effective element for improving strength without affecting fine precipitates. If the content is less than 0.5 u+t%, the effect of improving strength will be small, and if the content exceeds 2.0 wt%, the strength will become too high and it will be impossible to process. Therefore, the Mg content is set to 0.5 to 2.0 wt%.

The average grain width after intermediate annealing is set to 45 μm or less because
Crystal grains have a great influence on the bulge properties of the can wall, and the finer they are, the better. This is because if the average grain width after annealing exceeds 45 μm, the bulge property will be greatly reduced. Therefore, the average grain width after intermediate annealing is 45 μm or less. In addition, since the product is cold rolled, the grains are elongated, i.e.
The grain width in the product becomes the average grain width after intermediate annealing.

Next, I will explain about intermetallic compounds.
-A aln l+: Hair Hiroshi n Left T - Le Old Tens, so the distribution of this 04 mo is influenced by the components (Fe, Mn) and agglomeration conditions such as solidification rate. In addition, intermetallic compounds are the starting point for cracking during bulge processing, but on the other hand, they are necessary as a feedstock to improve ironing workability, so there is an optimal range for the distribution of intermetallic compounds. .

First, if the area ratio of intermetallic compounds is less than 1%, ironing workability will be reduced and cause cracking of the can body.
If it exceeds this value, the crack propagation speed during bulge processing will increase and breakage will occur easily.

In addition, if the number of intermetallic compounds is too large, crack propagation will increase, so the maximum length of the intermetallic compounds should be 25 μm or less, and the number of intermetallic compounds per 0.25 mm2 should be 1
Must be less than 000. Note that the intermetallic compound distribution was measured by image processing using a scanning electron microscope (SEM).

In addition, components other than Mn and Mg explained above are F
e0.7mt% or less, Si 0.5wt% or less, Cu0
．． It is desirable that the content be 5u+t%, Or 0.3wt% or less, and other elements are also allowed as long as they are at the level of impurities.

There are no particular restrictions on the method of manufacturing the aluminum alloy sheet for packaging with excellent formability according to the present invention, but in order to suppress fine precipitates, the homogenization heat treatment is preferably performed at a temperature of 500°C or higher for 2 hours or more, and , the hot rolling conditions are the final plate thickness (Hot
Co11) It is preferable that the thickness is 1.8 mm or more and the temperature is about 300°C, and further, the intermediate annealing is performed under the conditions of hot rolling and recrystallization after cold rolling if necessary, for example, 350'CX.
In the case of CAL, it is preferable to carry out the rolling for 2 hours or more at a temperature of about 500°C, and the product needs to be finished cold rolled by at least 30% in terms of compressive strength.

[Example 1] An example of an aluminum alloy plate for packaging with excellent formability according to the present invention will be described.

Example A small ingot (50t x 200w x 1451) of an aluminum alloy having the ingredients and proportions shown in Table 1 was formed into an ingot, solidified, soaked (540°C x 6 hours) and hot rolled to a thickness of 6mmt ( The final temperature was 300°C.

After that, it was cold rolled to 1 mmt and intermediate annealed (36 mm).
0℃ x 2 hours) and finish cold rolling to 0.4mm
I made a thick board.

Table 2 shows the mechanical properties and metallographic structure of the original plate.

The materials shown in Table 2 were ironed, baked (200
Bulge processing and pressure resistance test were carried out after 'CX 20 minutes).

The results are shown in Table 3.

As for ironing workability, it is desired that the ironing rate is at least 56% and that there is no burning on the can surface.

Further, the bulge property of the can wall is required to be 5IIIH or more, and the pressure resistance is required to be 6.5 kg/am2 or more.

*2)...Erichsen test (method A).

From Tables 2 and 3, it can be seen that the aluminum alloy plate for packaging with excellent formability according to the present invention has an area ratio of intermetallic compounds of 1
~3%, the maximum length is 25 μm or less, the number of grains per 0.25 mm is 1000 or less, and the grain width is 45 μm.
m or less, and is fully satisfactory in terms of ironing workability, bulge property, and compressive strength,
It can be seen that one of the comparative materials is insufficient and unsatisfactory.

Note that the heat treatment after ironing was set at 200℃ for 20 minutes, but in reality, it is necessary to use a slightly higher temperature of 230 to 250℃ for stability reasons. It is possible to improve the life of the furnace along with excellent bulge property.

[Effects of the invention 1

Claims (1)

[Claims] Mn0.5-0.8wt%, Mg0.5-2.0wt%
It is an aluminum alloy containing aluminum with the remainder being Al and impurities, the average grain width after intermediate annealing is 45 μm or less, the area ratio of intermetallic compounds generated during agglomeration is 1 to 3%,
The maximum length of this intermetallic compound is 25 μm or less and 0
．． An aluminum alloy for packaging with excellent formability, characterized in that the number of intermetallic compounds per 25 mm^2 is 1000 or less.