JP3190957B2 - Manufacturing method of aluminum alloy sheet for packaging with excellent pitting corrosion resistance - Google Patents

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 sheets, and is suitable as a packaging material for severely corrosive contents such as food containers, especially marine products, and is used by baking. And a method for producing the same.

[0002]

2. Description of the Related Art Generally, aluminum alloys such as AA standards 3004, 5052 and 5182 are used as packaging materials for beverage cans, food cans and the like.

Generally, packaging materials are required to have quality characteristics such as (a) good moldability, (b) high strength, and (c) good corrosion resistance. system,
An Al-Mg-Mn-based aluminum alloy sheet is used by baking.

[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 rate of cold working, but a decrease in 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 a high concentration of chloride ions, pitting corrosion occurs and the reliability is insufficient. is there.

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

[0006]

Means for Solving the Problems To solve the above problems, the present inventors have conducted intensive studies on measures that have the strength and moldability necessary for various container materials and also have excellent corrosion resistance. Was. As a result, they have found that Cu, Mn, and Mg are essential components, and that the production conditions can be controlled by regulating the hot rolling conditions and the intermediate annealing conditions, and have made the present invention.

That is, the present invention provides 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%. After dissolving and casting an aluminum alloy consisting of Al and unavoidable impurities, a soaking treatment is performed at a temperature of 500 to 600 ° C., and after hot rolling is performed so that the end temperature of the hot rolling becomes 300 ° C. or less, the intermediate When performing cold rolling including annealing, as intermediate annealing, heating at a temperature of 400 to 600 ° C. at a heating rate of 100 ° C./min or more, and immediately after heating or holding within 10 minutes, and heating at 100 ° C./hour or more It is characterized by cooling to a temperature of 200 ° C. or less at a cooling rate, keeping the average crystal grain size to 80 μm or less, keeping the components contributing to bake hardening in a solid solution state, and performing cold rolling at a working ratio of 30% or more. Of manufacturing method of aluminum alloy sheet for packaging with excellent pitting corrosion resistance It is assumed that.

Hereinafter, the present invention will be described in more detail.

[0009]

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

Mg: Mg is an element effective for improving the strength. After baking, the required strength (about 30 kgf / mm ^{2) is obtained.}
2.9% or more is required in order to obtain the proof stress. However, if it exceeds 4.0%, the corrosion resistance is undesirably reduced. Therefore, the Mg content is set in the range of 2.9 to 4.0%.

Mn: Like Mg, Mn is an element necessary for improving the strength, and also has the effect of improving the potential. When used in combination with steel or the like having a higher potential than aluminum as a container material, It is necessary to suppress corrosion due to concerns about electrolytic corrosion. Further, since Fe which is inevitably present as an impurity is fixed as an Al-Mn-Fe-based intermetallic compound, there is an effect of improving corrosion resistance. However, when the amount of Mn is less than 0.3%, the above-mentioned action is small, and when the amount exceeds 1.5%, a huge intermetallic compound may be formed, and the moldability is lowered, which is not preferable. . Therefore, the amount of Mn is 0.3 to
The range is 1.5%.

Cu: Cu, like Mn, has the effect of increasing the potential and intensity. 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 Cu amount is 0.1.
The range is from 0.05 to 1.0%.

Ti: Ti has the effect of making the form of corrosion laterally wide and suppressing the progress of corrosion in the thickness direction. Therefore, an aluminum alloy sheet having further excellent pitting corrosion resistance can be obtained by adding it as necessary and combining it with the production method of the present invention. When adding Ti, the Ti amount is set to 0.
If it is less than 01%, the desired effect cannot be expected, and 0.20
%, It is useless because the effect is saturated. Therefore, the Ti amount is set in the range of 0.01 to 0.20%.

The elements that can be contained in addition to the above elements are not particularly limited as long as they are in the order of impurities contained in commercially available pure aluminum, but the smaller the content of Si and Fe, the more desirable. In particular, Fe is an element that inhibits corrosion resistance, and is preferably suppressed to 0.3% or less in order to secure sufficient corrosion resistance.

Next, a method for producing an aluminum alloy sheet for packaging according to the present invention will be described.

The aluminum alloy of the above chemical composition is melt-cast by a usual method to form an ingot, and
A soaking treatment is performed at a temperature of ６００600 ° C. This soaking treatment is for obtaining appropriate hot rolling and pitting corrosion resistance. At a soaking temperature of less than 500 ° C., ear cracks are likely to occur during hot rolling, and many fine precipitates are formed. However, pitting corrosion resistance is reduced, and burning and blistering occur at a soaking temperature exceeding 600 ° C., leading to deterioration in workability of product characteristics and surface quality. Therefore, the soaking temperature is 500 ~
Set to 600 ° C. The soaking time is appropriately determined according to the above-mentioned purpose.

Next, hot rolling is performed. It is necessary to regulate the end temperature of hot rolling to 300 ° C. or less. This condition is for obtaining pitting corrosion resistance. At an end temperature exceeding 300 ° C., many fine precipitates are formed, and the pitting corrosion resistance is reduced. Therefore, the end temperature of the hot rolling is set to 300 ° C. or less.

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

Specifically, first, the intermediate annealing temperature is 400
If the temperature is lower than ℃, the solid solution of Cu is not sufficiently performed, and if the temperature is higher than 600 ° C, there is a possibility that burning may occur and the properties may be deteriorated. Therefore, the intermediate annealing temperature is in the range of 400 to 600 ° C. At that time, the heating rate is set to 100 ° C./min or more. Immediately after the heating or after holding within 10 minutes, the mixture is cooled to a temperature of 200 ° C. or less at a cooling rate of 100 ° C./hour or more. Thereby, the average crystal grain size becomes 80 μm or less, and desired moldability is obtained. Under the conditions outside these ranges, the above-described intermediate annealing effect cannot be obtained, and energy is wasted even if the heating and holding are performed for more than 10 minutes. Further, the cooling at a cooling rate of 100 ° C./hour or more to a temperature of 200 ° C. or less is for restricting the generation of fine precipitates that reduce pitting corrosion resistance. The heating / cooling rate is 200 ° C./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 perform rolling at a high working ratio in order to obtain finer crystal grains, and it is preferable that the rolling rate is 30% or more. Although cold rolling is performed after the intermediate annealing, it is important that the working ratio is 30% or more, whereby desired strength and formability can be obtained.

The aluminum alloy sheet thus obtained is subjected to a surface treatment by a conventional method and used for various purposes. In general, after a chemical conversion treatment such as phosphoric acid chromate is applied, an epoxy or vinyl chloride organosol paint is applied and baked at about 200 to 300 ° C. for several seconds to 10 minutes.

Next, an embodiment of the present invention will be described.

[0023]

【Example】

[Table 1] 520 in the aluminum alloy ingot having the chemical composition shown in
After 4% soaking at 4 ℃, 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 same table, and then cold-rolled to a thickness of 0.3 mm. The hot rolling end temperature is also shown in Table 1.

With respect to the obtained aluminum alloy thin plate,
The mechanical properties, moldability, 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

The formability was measured using a crank press, and 6.0 mmφ (1 elongation) → 4.0 mmφ (2 elongation) → 3.2 mmφ (3 mm).
The critical overhang height was determined and evaluated using the punch diameter of (elongation).

In the corrosion resistance test, as shown in FIG. 1, a test material 1 having the same area (1 cm ² ) and a tin plate 5 are connected by a copper wire 7 to form a couple, and the exposed portion 4 of the test material 1 is The exposed portions of the tin plate 5 are opposed to each other via the vinyl chloride pipe 2, and the pipe is subjected to a corrosive model solution of Cl 800 ppm, p
Fill H3 (salt, citric acid, sodium citrate)
After leaving this solution at 38 ° C. for 10 days, the pit depth was measured to evaluate (n = 5).

As shown in Table 2, each of the materials of the present invention has high strength, maintains excellent moldability, and shows good pitting resistance. It turns out that it is suitable as a packaging material used. On the other hand, the comparative material and the conventional material are all inferior in pitting corrosion resistance even if the moldability is obtained, and there is also a case where the strength cannot be obtained.

[0028]

As described in detail above, according to the present invention,
By controlling the soaking temperature, the end temperature of hot rolling and the conditions of intermediate annealing, etc. in conjunction with the adjustment of the components of the aluminum alloy, the generation of fine precipitates containing Cu and Mg, which lower the pitting corrosion resistance, is suppressed. Since the crystal grain size is 80 μm or less, high strength, good moldability and pitting corrosion resistance are obtained, and it is suitable for food containers used by baking coating, especially for packaging materials for severe contents such as marine products. I have.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a point of a corrosion test.

[Explanation of Signs] 1 Test material (aluminum alloy) 2 Vinyl chloride pipe 3 Contents (corrosion liquid) 4 Test material exposed portion 5 Tin 6 Tin exposed portion 7 Copper wire

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22F 1/04-1/057 C22C 21/00-21/18

Claims (2)

(57) [Claims] 1. Cu: 0.05 to 5% by weight (hereinafter the same).
1.00%, Mn: 0.3-1.5% and Mg: 2.9-4.0
%, With the balance being Al and unavoidable impurities, after dissolving and casting, performing soaking at a temperature of 500 to 600 ° C. so that the hot rolling end temperature is 300 ° C. or less. After performing the rolling, when performing the cold rolling including the intermediate annealing, as the intermediate annealing, 400 to 600
At a heating rate of 100 ° C./min or more, and immediately after heating or after holding within 10 minutes, cooled to a temperature of 200 ° C. or less at a cooling rate of 100 ° C./hour or more, and the average crystal grain size is 80 μm. A method for producing a thin aluminum alloy sheet having excellent pitting corrosion resistance, comprising: maintaining a component contributing to bake hardening in a solid solution state; and performing cold rolling at a working ratio of 30% or more. 2. The method according to claim 1, wherein the aluminum alloy further comprises Ti: 0.1.
2. The method according to claim 1, containing from 0.01 to 0.20%.