JPH05112854A - Manufacture of aluminum alloy thin sheet for packing excellent in pitting corrosion resistance - Google Patents

Abstract

PURPOSE:To provide the method for manufacturing an aluminum alloy thin sheet for packing excellent in pitting corrosion resistance. CONSTITUTION:An aluminum alloy contg. 0.05 to 1.00% Cu, 0.3 to 1.5% Mn and 2.9 to 4.0% Mg, contg., at need, 0.01 to 0.20% Ti and the balance Al with inevitable impurities is melted, is cast, is thereafter subjected to soaking treatment at 500 to 600 deg.C and is subjected to hot rolling in such a manner that the finishing temp. of the hot rolling is regulated to <=300 deg.C. After that, at the time of executing cold rolling including process annealing, as for the process annealing, the alloy is heated to 400 to 600 deg.C at >=100 deg.C/min heating rate; immediately after the heating or after held for <=10min, it is cooled to <=200 deg.C at >=100 deg.C/hr cooling rate to regulate the average grain size to <=80mum and to hold the state of the components contributing to its baking hardening into a solid soln. one and is furthermore subjected to cold rolling at >=30% draft. This alloy is suitable as a food container, particularly as the packing material for contents having severe corrosiveness such as aquatic products.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of aluminum alloy thin plates, and is suitable as a packaging material for food containers, particularly marine products, and other contents that are highly corrosive. The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art Generally, an aluminum alloy such as AA standard 3004, 5052 or 5182 is used as a packaging material for beverage cans, food cans and the like.

In general, packaging materials are required to have quality characteristics such as (a) good moldability, (b) high strength, (c) good corrosion resistance, and the above-mentioned Al-Mg. system,
An Al-Mg-Mn type aluminum alloy thin plate is baked and used.

[0004]

However, in order to increase the strength of these aluminum alloys, there is a method of increasing the amount of Mg or simply increasing the cold working rate, but the deterioration of the formability is inevitable. By the way. In addition, when used as a container material for highly corrosive contents such as marine products that have a high salt content and contain chlorine ions at a high concentration, pitting corrosion may occur, resulting in insufficient reliability. is there.

The present invention has been made to solve the above-mentioned problems of the prior art, and its object is to have a high strength as an aluminum alloy thin plate to be used by baking coating, It is an object of the present invention to provide a method for producing an aluminum alloy thin plate suitable as a packaging material for various packaging materials, especially for highly corrosive contents such as marine products.

[0006]

In order to solve the above-mentioned problems, the present inventor has conducted earnest research on a method which has strength and formability required for various container materials and can also have excellent corrosion resistance. It was As a result, they have found that Cu, Mn, and Mg are essential components, and that the manufacturing conditions can be controlled especially by regulating the hot rolling conditions and the intermediate annealing conditions, and the present invention has been made.

That is, according to the present invention, Cu: 0.05 to 1.0
0%, Mn: 0.3 to 1.5% and Mg: 2.9 to 4.0%, and if necessary, Ti: 0.01 to 0.20%, the balance being After melting and casting an aluminum alloy consisting of Al and unavoidable impurities, soaking is performed at a temperature of 500 to 600 ° C., and hot rolling is performed so that the end temperature of hot rolling becomes 300 ° C. or less, then the intermediate When performing cold rolling including annealing, as intermediate annealing, the temperature of 400 to 600 ° C. is heated at a heating rate of 100 ° C./minute or more, and immediately after heating or after holding for 10 minutes or more, 100 ° C./hour or more. It is characterized in that it is cooled to a temperature of 200 ° C. or less at a cooling rate to keep an average crystal grain size of 80 μm or less, components that contribute to bake hardening are in a solid solution state, and further cold rolled at a working rate of 30% or more. Of manufacturing method of aluminum alloy sheet for packaging with excellent pitting corrosion resistance It is what

The present invention will be described in more detail below.

[0009]

First, the reasons for limiting the chemical components in the present invention will be explained.

Mg: Mg is an element effective for improving the strength, and it has a required strength (about 30 kgf / mm ² after coating and baking).
Proof strength) is required to be 2.9% or more. However, if it exceeds 4.0%, the corrosion resistance decreases, which is not preferable. Therefore, the amount of Mg is set in the range of 2.9 to 4.0%.

Mn: Mn, like Mg, is an element necessary for improving the strength and also has the effect of improving the electric potential, and is used as a container material when used in combination with steel or the like having a higher electric potential than aluminum. It is necessary to suppress corrosion due to concern about electrolytic corrosion. Furthermore, Fe, which is inevitably present as an impurity, has a function of fixing as an Al-Mn-Fe-based intermetallic compound, so that it has an effect of improving corrosion resistance. However, if the amount of Mn is less than 0.3%, the above-mentioned effects are small, and if it exceeds 1.5%, a huge intermetallic compound may be formed, which deteriorates moldability, which is not preferable. .. Therefore, the amount of Mn is 0.3-
The range is 1.5%.

Cu: Cu has the action of increasing the potential and strength like Mn. However, if it is less than 0.05%, the desired effect cannot be expected, and if it exceeds 1.0%, the intergranular corrosion susceptibility increases, which is not preferable. Therefore, the amount of Cu is 0.
The range is from 05 to 1.0%.

Ti: Ti has the effect of laterally spreading the corrosion form and suppressing the progress of corrosion in the plate thickness direction. Therefore, an aluminum alloy thin plate further excellent in pitting corrosion resistance can be obtained by adding it as needed and combining it with the production method of the present invention. When added, the Ti content is 0.
If it is less than 01%, the desired effect cannot be expected, and it is 0.20.
If it is contained in excess of%, the effect is saturated and it is useless. Therefore, the Ti content is set in the range of 0.01 to 0.20%.

There are no particular restrictions on the elements that can be contained in addition to the above, as long as they are impurities contained in commercially available pure aluminum, but Si and Fe are preferably as small as possible. In particular, Fe is an element that inhibits corrosion resistance, and it is preferable to suppress Fe to 0.3% or less in order to secure sufficient corrosion resistance.

Next, a method for manufacturing the aluminum alloy thin plate for packaging according to the present invention will be described.

The aluminum alloy having the above chemical composition is melt cast by an ordinary method to form an ingot, and the ingot is made into
Soaking is performed at a temperature of up to 600 ° C. This soaking treatment is for obtaining appropriate hot rolling and pitting corrosion resistance, and at soaking temperature of less than 500 ° C, ear cracks are apt to occur during hot rolling and many fine precipitates are formed. However, pitting corrosion resistance decreases, and burning and blistering occur at a soaking temperature exceeding 600 ° C., which leads to deterioration in product property workability and surface quality. Therefore, the soaking temperature is 500-
The temperature is 600 ° C. The soaking time is appropriately determined according to the above purpose.

Next, hot rolling is performed, but it is necessary to regulate the end temperature of hot rolling to 300 ° C. or lower. This condition is for obtaining pitting corrosion resistance, and a large amount of fine precipitates are formed at the end temperature exceeding 300 ° C., and the pitting corrosion resistance is reduced. Therefore, the end temperature of hot rolling is set to 300 ° C or lower.

After the hot rolling, cold rolling including intermediate annealing is performed. In the intermediate annealing, Cu which is an essential component is solid-dissolved,
In order to increase the potential more effectively and to obtain fine crystal grains, it is important to control the conditions as follows.

Specifically, first, the intermediate annealing temperature is 400
If the temperature is lower than 0 ° C, solid solution of Cu is not sufficiently performed, and if the temperature exceeds 600 ° C, burning may occur and the characteristics may be deteriorated. Therefore, the intermediate annealing temperature is set to 400 to 600 ° C. At that time, the heating rate is set to 100 ° C./minute or more, and the heating is performed immediately after heating or within 10 minutes, and then cooled to a temperature of 200 ° C. or less at a cooling rate of 100 ° C./hour or more. As a result, the average crystal grain size becomes 80 μm or less, and desired moldability is obtained. Under conditions outside these ranges, the above-mentioned intermediate annealing effect cannot be obtained, and even if heating and holding are performed for more than 10 minutes, energy is wasted. Further, the reason for cooling to a temperature of 200 ° C. or lower at a cooling rate of 100 ° C./hour or more is to control the formation of fine precipitates that reduce the pitting corrosion resistance. Heating / cooling rate is 200 ℃ / min or more (eg 800
(° C / min) is desirable.

The cold rolling conditions before the intermediate annealing are not particularly limited, but it is preferable to roll at a high working rate to obtain finer crystal grains, and 30% or more is preferable. Further, cold rolling is performed after the intermediate annealing, but it is important that the working rate is 30% or more, and thereby desired strength and formability can be obtained.

The thus obtained aluminum alloy thin plate is subjected to surface treatment by a conventional method and used for various purposes. Generally, after a chemical conversion treatment such as chromate phosphate is applied, an epoxy or vinyl organosol-based coating material is applied and baking is performed at about 200 to 300 ° C. for several seconds to 10 minutes.

Next, examples of the present invention will be described.

[0023]

【Example】

[Table 1] 520 to the aluminum alloy ingot having the chemical composition shown in
After soaking for 4 hours at ℃, 4mm by hot rolling
A thick hot-rolled sheet was formed, then cold-rolled to a thickness of 1 mm, subjected to intermediate annealing under the conditions shown in the table, and then cold-rolled to a thickness of 0.3 mm. The hot rolling finish temperature is also shown in Table 1.

Regarding the obtained aluminum alloy thin plate,
The mechanical properties, formability, crystal grain size and corrosion resistance after heating at 200 ° C. for 20 minutes assuming baking coating were investigated. The result

[Table 2] Shown in.

As for the formability, using a crank press, 6.0 mmφ (1 extension) → 4.0 mmφ (2 extension) → 3.2 mmφ (3
The limit overhang height was obtained by the punch diameter of (elongation) and evaluated.

In the corrosion resistance test, as shown in FIG. 1, the specimen 1 and the tin plate 5 having the same area (1 cm ² ) are connected by the copper wire 7 to form a couple, and the exposed portion 4 of the specimen 1 is connected. The exposed parts of the tin plate 5 are made to face each other via the vinyl chloride pipe 2, and the pipe has a Cl of 800 ppm, p as a model liquid with severe corrosiveness.
Fill with H3 (salt, citric acid, sodium citrate),
After standing in this solution at 38 ° C. for 10 days, the pitting depth was measured for evaluation (n = 5).

As shown in Table 2, all of the materials of the present invention have high strength, maintain excellent formability, and exhibit good pitting corrosion resistance. Therefore, they can be baked on food containers and the like. It turns out that it is suitable as a packaging material to be used. On the other hand, the comparative materials and the conventional materials have poor pitting corrosion resistance even if the moldability is obtained, and some of them cannot obtain further strength.

[0028]

As described in detail above, according to the present invention,
By controlling the soaking temperature, the end temperature of hot rolling, and the intermediate annealing conditions together with the adjustment of the composition of the aluminum alloy, the formation of fine precipitates containing Cu and Mg that reduce the pitting corrosion resistance is suppressed, With a crystal grain size of 80 μm or less, it has high strength, good moldability and pitting corrosion resistance, and is suitable for food containers used by baking coating, especially packaging materials for severe contents such as marine products. There is.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a procedure of a corrosion test.

[Explanation of symbols] 1 test material (aluminum alloy) 2 vinyl chloride pipe 3 contents (corrosion liquid) 4 test material exposed part 5 tin plate 6 tin plate exposed part 7 copper wire

Claims (2)

[Claims] 1. In weight% (hereinafter, the same), Cu: 0.05
1.00%, Mn: 0.3-1.5% and Mg: 2.9-4.0
% Of aluminum alloy, the balance of which is Al and unavoidable impurities, and after casting, soaking is performed at a temperature of 500 to 600 ° C. so that the end temperature of hot rolling becomes 300 ° C. or less. After performing rolling, when performing cold rolling including intermediate annealing, 400 to 600 as intermediate annealing.
After heating to a temperature of 100 ° C at a heating rate of 100 ° C / min or more and holding immediately or after heating for 10 minutes or less, it is cooled to a temperature of 200 ° C or less at a cooling rate of 100 ° C / hour or more, and an average crystal grain size of 80 µm. A method for producing an aluminum alloy thin sheet for packaging having excellent pitting corrosion resistance, characterized in that the following components are maintained and the components contributing to bake hardening are kept in a solid solution state, and further cold rolling is performed at a working rate of 30% or more. 2. The aluminum alloy further has a Ti: 0.0.
The method according to claim 1, which contains 01 to 0.20%.