JPH0570904A - Manufacture of aluminum alloy hard sheet for forming excellent in softening resistance - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to a method for producing an aluminum alloy sheet used for a can lid for a can of retort beverages such as coffee and oolong tea, particularly when coating and drying an anticorrosion coating at 250 to 300 ° C. This is a method for producing a hard plate that does not soften the material and is excellent in moldability. [Structure] Mg: 3.0 to 6.0%, Mn: 0.4 to
Al alloy ingot of 0.8% or more Cu: 0.05 to 0.4%, residual Al, and unavoidable impurities is homogenized and hot-rolled, and then cold-rolled at 20% or more. Then, after intermediate heat treatment at 200 to 250 ° C. for 1 hour or more, final cold rolling of 50% or more is performed to contain an Al—Mn-based precipitate. [Effect] A hard plate which is not softened when an Al alloy plate is coated with an anticorrosive paint or the like and dried and which is excellent in formability can be obtained by heat treatment at a low temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum alloy sheet material used for a can lid for a retort beverage can such as coffee and oolong tea, and particularly coating and drying an anticorrosion paint at 250 to 300 ° C. In this case, the present invention relates to a method for producing a hard plate which does not soften the material, maintains high strength and is excellent in moldability.

[0002]

2. Description of the Related Art When filling cans with coffee, oolong tea, etc., heating for sterilizing the cans, so-called retort heating is required. In addition, since the retort beverage can contains a component that easily corrodes the aluminum alloy, the inside of the can is coated with a polymer resin having a high anticorrosion effect. As the coating material of the polymer resin, there are vinyl type, vinyl organosol type, epoxy amino type, epoxy phenol type, epoxy acrylic type and the like.

Conventionally, a method for producing an aluminum alloy plate material used for a can lid for a retort beverage can such as coffee and oolong tea is a method of homogenizing an aluminum alloy ingot and then hot rolling it to a thickness of 3 to 5 mm. And (1) cold rolling → intermediate annealing (300 to 450 ° C.) → final cold rolling, or (2) hot rolling to a plate thickness of about 2 mm, and intermediate annealing at that plate thickness, Alternatively, a method has been proposed in which final cold rolling is performed as hot rolling to obtain a hard plate of 0.4 mm or less.

[0004]

The aluminum alloy plate material for the can lid of the retort beverage can is coated with a polymer resin coating material by a roll coater or the like, heated to 250 to 300 ° C. in a continuous heating furnace, and baked. ·dry. At this time, the above-mentioned conventional materials have the drawbacks that they are softened, the strength is lowered, and the material cannot be made thin. Therefore, an object of the present invention is to provide an aluminum alloy sheet material for a can lid that does not soften even when heated to 250 to 300 ° C. and does not cause strength reduction, and a method for producing the same.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention have conducted diligent research, and as a result, added a small amount of Mn or Cu to an Mg-based aluminum alloy and performed the intermediate annealing that has been conventionally performed. By performing at a low temperature (since it is performed at a temperature lower than the recrystallization temperature, it is called an intermediate heat treatment in the present invention)
The inventors have found that it is possible to improve the softening resistance during baking of a paint by finely precipitating an Al-Mn-based compound in crystal grain agglomerates, and completed the present invention.

That is, the gist of the present invention is Mg: 3.0.
After homogenizing and hot rolling an aluminum alloy ingot containing .about.6.0%, Mn 0.4 to 0.8%, or further containing Cu: 0.05 to 0.4%. After performing cold rolling with a rolling reduction of 20% or more, 200 to 250 ° C.
After performing an intermediate heat treatment for 1 hour or more at 50% or more, final cold rolling is performed, and an Al-Mn-based precipitate is contained in the crystal grains, which is excellent in softening resistance. It is a method for manufacturing an alloy hard plate.

[0007]

The function of the components and the processing conditions of the aluminum alloy of the present invention will be described. Mg: Mg is a basic additive element in the present invention and contributes to strength. M
If g is less than 3.0%, the required strength cannot be obtained. 6
If it exceeds%, cracking tends to occur during hot rolling.

Mn: Mn is an additional element indispensable for improving the softening resistance. If the addition amount is less than 0.4%, a sufficient effect cannot be obtained. If it exceeds 0.8%, the hot workability is deteriorated, and further, an Al—Fe—Mn-based coarse intermetallic compound is likely to be formed, and the formability of the hard plate is deteriorated.

Cu: Cu is an element which improves the softening resistance when coexisted with Mn, but it is necessary to add a large amount by itself. However, in this alloy system, if it exceeds 0.4%, cracking occurs during hot rolling, which is not preferable. Also, 0.0
If it is less than 5%, the effect cannot be obtained.

Al-Mn-based precipitate: Al-M in crystal grains
When n-type precipitates are finely (0.05 μm or less) deposited,
When the material is deformed, the movement of dislocations is suppressed and the softening resistance is improved. However, if the size is 0.05 μm or more, the number of precipitates is reduced, dislocations are easily moved, and the softening resistance is deteriorated.

Cold rolling before intermediate heat treatment: Cold rolling performed before intermediate heat treatment has an effect of uniformly and finely precipitating Al-Mn-based compounds in crystal grains. However, the amount of reduction is 2
If it is less than 0%, there is no effect of the precipitation site of the Al-Mn-based compound, and a fine compound is not precipitated.

Intermediate heat treatment: Heat treatment at a low temperature (200 to 2) in order to finely precipitate Al-Mn compound in crystal grains.
At 50 ° C. for 1 hour or more). If the treatment temperature is less than 200 ° C., a holding time is required for a long time, which is industrially disadvantageous. On the other hand, when the temperature is higher than 250 ° C., the recovery of the work structure formed by cold rolling is quicker than the precipitation of the Al—Mn-based compound, and therefore the precipitation site of the Al—Mn-based compound disappears, resulting in uniform fineness. It is not possible to obtain a sufficient precipitation state and a sufficient effect cannot be expected.

When the holding temperature is in the range of 200 to 250 ° C., the holding time is 1 hour, and uniform and fine precipitation of the Al--Mn compound is obtained. However, this effect does not change even after 24 hours or more, which is industrially disadvantageous.

Final cold rolling: Strength required as a can lid material (proof strength after painting of 260 MPa or more, elongation of 10% or more)
Has the effect of increasing If the reduction amount is 50% or less, this effect does not occur, and if it exceeds 95%, the moldability is deteriorated, which is not preferable.

After the aluminum alloy is ingoted by a conventional method, it is desirable to homogenize it before hot rolling in order to remove segregation of solute atoms. This homogenization treatment is usually performed at 480 to 530 ° C. for 3 to 10 hours. Hot rolling usually heats the ingot at around 500 ° C and raises the recrystallization temperature or higher (>
280 ° C.).

[0016]

Example 1 An aluminum alloy having the composition shown in Table 1 was cast by a normal DC casting method, homogenized at 500 ° C. for 6 hours, and then 48
Start hot rolling at 0 ° C and finish at 300 ° C,
A plate having a plate thickness of 3.0 mm was obtained. After that, cold rolling was performed up to a plate thickness of 1 mm (rolling down amount: 66.7%), and then 1 hour at 250 ° C.
After performing intermediate heat treatment for a time, final cold rolling was performed to a plate thickness of 0.3 mm (rolling down amount: 70%). The obtained cold-rolled material is heated as it is and at 300 ° C. for 20 seconds (the maximum temperature of the coating baking temperature) and at 450 ° C. for 30 seconds (heating to the complete recrystallization temperature, so-called O material). , Was subjected to the test. The shape of the precipitate was investigated and the mechanical properties were tested. The proof stress of mechanical properties was used to calculate the degree of softening by the following formula. Softening degree = 100 {(cold rolled material-300 ° C. heated material) /
(Cold rolled material-heated material at 450 ° C)} (%) That is, the softening degree serves as an index for determining whether or not the material is softened during baking of the anticorrosion coating, and the heating temperature is set to 300.
The maximum temperature of the baking temperature of the anticorrosion paint was adopted as the temperature of 450 ° C., and the complete recrystallization temperature of this kind of material was adopted as the temperature of 450 ° C. Therefore, in the case of the present invention, the softening degree is high (10
0%), and the lower the softening degree, the better the softening resistance. The results of these tests are shown in Table 1.

[0017]

[Table 1]

The material of the present invention No. 1-4, the size of most of the precipitates in the crystal grains is 0.05 μm or less, the tensile strength (proof stress after heating at 300 ° C. × 20 seconds, the same applies below) is 270 MPa or more, and the softening degree is 54.9%. The following was obtained, and the softening resistance was excellent. However, No. 5 is Mn
Since the content is as low as 0.35%, the softening degree is as high as 61.3% and the softening resistance is poor. No. 6 has a Mg content of 2.7 and a Mn content of 0.3.
%, The tensile strength is as low as 201 MPa, and
The softening degree is as high as 64.1% and the softening resistance is poor. No. 7 has a high Cu content of 0.60% and N
o. 8 has Mg and Mn contents of 6.3% and 0.8
Since it was as high as 2%, cracking occurred during hot rolling, so the subsequent tests were stopped.

Example 2 No. 1 shown in Table 1 Ingots 1 and 3 were cast by a normal DC casting method, homogenized at 500 ° C for 6 hours, and then 480 ° C.
Then, hot rolling was started at a plate thickness of 4.0 mm. Then, cold rolling, intermediate heat treatment and final cold rolling were carried out under the conditions shown in Table 2 for the invention material and under the conditions shown in Table 3 for the comparative material, and the same as in Example 1. Tests and Erichsen tests were conducted. The results are shown in Table 2 and Table 3.
It was shown to. In addition, No. in Table 2 Nos. 9 to 13 and No. 3 in Table 3. Nos. 16 to 20 are Nos. In Table 1. 1 material,
No. in Table 2 Nos. 14, 15 and 21, 22 in Table 3 are No. It uses three materials.

[0020]

[Table 2]

[0021]

[0022]

[Table 3]

[0023]

Inventive material No. 9 to 15 are tensile strength (3
The yield strength after heating at 00 ° C for 20 seconds, the same applies below) is 260MP.
The softening degree of a or more and the softening degree of 55.8% or less are obtained, and the softening resistance is excellent.

On the other hand, the comparison material No. 16 and 1
No. 7 had a cold rolling reduction of 10% and 1 before the intermediate heat treatment.
Softness of 62.8% and 60.1% due to low 5%
It is high and inferior in softening resistance. No. No. 18 has a high intermediate heat treatment temperature of 300 ° C. and a high softening degree of 61.4%, which is inferior in softening resistance. No. No. 19 has a low intermediate heat treatment temperature of 180 ° C. and a high softening degree of 61.3%, and is inferior in softening resistance. No. In No. 20, the final cold rolling reduction is as low as 40% and the softening degree is as high as 62.6%, which is inferior in softening resistance. No. No. 21 was No. 21 when the cold rolling reduction before the intermediate heat treatment was reduced to 10%. 22 is the intermediate heat treatment temperature 400 ℃
In all cases, the materials are different from those mentioned above, but the softening degree is high and the softening resistance is poor.

[0026]

[Effects of the Invention] That is, according to the present invention, when an anticorrosion paint of an aluminum alloy plate material used for a can lid for a retort beverage can such as coffee and oolong tea is applied and dried, the material does not soften and the moldability is improved. An excellent hard plate
It is an industrially useful invention, obtained by carrying out a low temperature heat treatment at an intermediate annealing temperature that has been conventionally used.

Claims (2)

[Claims] 1. Mg: 3.0-6.0%, Mn: 0.4
After homogenizing and hot rolling an aluminum alloy ingot containing the balance of Al and unavoidable impurities, the cold rolling with a reduction amount of 20% or more is performed. After performing an intermediate heat treatment at 200 to 250 ° C. for 1 hour or more, 50% or more final cold rolling is performed to form A in the crystal grains.
A method for producing an aluminum alloy hard plate for forming which is excellent in softening resistance, characterized by containing an l-Mn-based precipitate. 2. Mg: 3.0-6.0%, Mn: 0.4
~ 0.8%, Cu: 0.05-0.4%, aluminum alloy ingot consisting of balance Al and unavoidable impurities is homogenized and hot-rolled, and then the reduction amount is 20%.
After performing the above cold rolling, after performing an intermediate heat treatment at 200 to 250 ° C. for 1 hour or more, 50% or more final cold rolling is performed to contain Al-Mn-based precipitates in the crystal grains. A method of manufacturing an aluminum alloy hard plate for molding having excellent softening resistance, which is characterized by the following.