JPH07316711A - Aluminum alloy sheet for forming, excellent in bendability, and its production - Google Patents

Abstract

PURPOSE:To improve strength and bendability by distributing specific amounts of secondary compounds of specific size in the surface of an Al alloy sheet containing specific amounts of Mg, Mn, Fe, and Al and providing specific proof stress to this Al alloy sheet after coating and baking. CONSTITUTION:This alloy is an Al alloy consisting of, by weight, 3-4% Mg, 0.4-0.7% Mn, 0.2-0.5% Fe, one or more kinds among 0.05-0.2% Cu, 0.1-0.4% Si, and 0.01-0.1% Ti, and the balance essentially Al. This Al alloy is held at 450-550 deg.C for 1-20hr to undergo homogenizing treatment. After hot rolling, cold rolling is carried out at >=60% draft, and the resultant rolled sheet is subjected to undercoating treatment. Thereafter, bake coating is carried out within 2min at 200-250 deg.C. Secondary phase compounds of <=2mum size and secondary phase compounds of 6-15mum are distributed in the sheet surface by <=1000 pieces/mm<2> and >=250pieces/mm<2>, respectively. Further, the proof stress of the sheet after baking coating is regulated to >=280MPa.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy sheet for forming which is excellent in bending workability, and a method for producing the same, and more particularly, an aluminum alloy sheet for a steion tab attached to the easy open end of a beverage can or a food can and its production. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Recently, as an easy open end for beverage cans and food cans, a Stein tub in which the tabs are not separated from the can ends has become popular due to environmental problems caused by scattering of the tabs after opening. Compared with the pull tab type tab material that has been used conventionally, due to the difference in the can opening method, a material with higher strength, higher rigidity, and excellent bendability is required as the material for the Steion tab. , Al-Mg type 5082 alloy,
5182 alloy is used as the material for the Steiontab.

On the other hand, a protective coating film is formed on the surface of the tab material in order to impart corrosion resistance. The coating film is usually formed using a solvent-based paint, and prior to coating, it consists of chemical conversion treatment such as alkali etching and phosphoric acid chromate treatment in order to improve the adhesion between the coating film and the aluminum alloy surface. A coating base treatment is applied. Industrially, from the viewpoint of production efficiency, a continuous line using a coil is used from alkali etching to coating baking.

Epoxy urea-based polymer resin is used as a solvent-based coating material for the tab material, but relatively high temperature is required for continuous coating in the above continuous line, and energy cost is high. Will be disadvantageous. When the coating temperature is set low, the adhesion of the coating film is lowered and the coating film is liable to peel off. Further, the solvent-based paint is not preferable in the working environment, and fumes are accumulated in the paint baking furnace, so that it is necessary to periodically remove the paint.

In order to solve the above-mentioned problems, a method of forming a coating film by using an epoxy acrylic water-based coating material has also been studied. The advantages of the water-based paint are that it improves the environment of painting work, ensures adhesion even when the painting temperature is low, and prevents the generation of fumes during the baking process.

When a water-based paint is applied to the conventional 5082 alloy for tabs and 5182 alloy, it does not cause any problem if it is baked at the same temperature as the solvent-based paint, but if the baking temperature is lowered in order to take advantage of the water-based paint. In conventional alloys, work hardening during cold rolling is large and strength is high, so softening is low and bending workability is inferior in low temperature baking, and cracking occurs in the bending part of the material and coating peeling is induced. There is a problem.

It is necessary to utilize work hardening to obtain the strength required for aluminum alloy plate materials for Stain tabs. However, if the work hardening is large like conventional alloys, water-based paint is used. In this case, the degree of softening at the time of low-temperature coating baking processing becomes small, and bending workability deteriorates. On the other hand, if the amount of cold rolling is reduced, the bending workability is improved, but for that purpose, the number of steps such as intermediate annealing during the cold rolling increases and the manufacturing cost increases. Also, it becomes difficult to obtain necessary strength and rigidity.

[0008]

DISCLOSURE OF THE INVENTION In order to solve the above problems in forming a coating film on an aluminum alloy sheet material with an aqueous paint, the present invention aims to solve the problems of strength, forming characteristics, work hardening characteristics and alloy composition of an aluminum alloy, and internal composition. This was done as a result of a multifaceted study on the relationship between the texture, especially the distribution of crystallized substances and precipitates.
The degree of work hardening is small, and it is softened moderately by low temperature baking to improve bending workability, and also has the strength and rigidity required as a Steion tab material, and is suitable for forming a coating film with an aqueous paint. An object of the present invention is to provide an aluminum alloy sheet material suitable for forming and processing, in particular, for a stay ion tab at the end of an easy open can, and a manufacturing method thereof.

[0009]

Means for Solving the Problems The aluminum alloy sheet for forming according to the present invention, which is excellent in bending workability in order to achieve the above object, has Mg: 3.0 to 4.0% and Mn: 0.4 to 0.7%.
%, Fe: 0.20 to 0.50%, the balance consisting of Al and unavoidable impurities, and an aluminum alloy plate having a surface protective coating formed thereon. The distribution of the second phase compound of 6 to 15 μm is 1000 / mm ² or less and 250 / mm ² respectively
² or more, and the proof stress after coating baking is 280 MPa or more, which is a basic structural feature.
u: 0.05-0.2%, Si: 0.1-0.4% and Ti: 0.01
The second and third characteristics of the constitution are that it contains at least one of 0.1 to 0.1%, and that the surface protective coating film is a coating film of a polymer resin having a thickness of 0.5 to 5 μm.

Further, according to the present invention, a method for producing an aluminum alloy sheet material for forming which is excellent in bending workability is as follows.
It is homogenized by holding it for 20 hours, then hot-rolled, cold-rolled with a workability of 60% or more, and then subjected to a coating base treatment consisting of alkali etching and chemical conversion treatment.
Another feature is that the coating is baked at a temperature of ~ 250 ° C within 2 minutes, and the coating is performed with an aqueous coating of polymer resin.

The aluminum alloy sheet for forming according to the present invention was subjected to coating baking treatment at a low temperature by limiting the component composition and the distribution state of the second phase compound crystallized and precipitated in the structure. In this case, a combination of predetermined strength and excellent bending workability can be obtained. Explaining the significance of each alloy component and the reason for limitation, Mg is an alloy material that increases work hardening and softens. It is an element that makes it difficult to do, and contributes to maintaining the strength after baking. The preferred content range is 3.0-4.0%, 3.0%
If it is less than 2,000 MPa, the proof stress after coating will be less than 280 MPa, and in particular, the strength required as a Steion tab material cannot be secured, and bending workability will also deteriorate. If the amount of Mg increases, the amount of second phase compounds with a size (average particle size) of 2 μm or less increases, and the bendability after low temperature baking tends to deteriorate. If it exceeds 4.0%, the workability during cold rolling increases. The hardening becomes large, and the softening of the material after the baking treatment at a low temperature becomes small, so that the bending workability is deteriorated.

Mn is an element that contributes to the improvement of strength,
By forming an Al-Fe-Mn-based crystallized substance with Fe during casting and controlling this to a size of 6 to 15 μm,
It also improves bending workability. The preferred content range is 0.4 to 0.
7%, and if the content is less than 0.4%, the size is 6-15μ.
The distribution of m-based Al-Fe-Mn-based crystallized substances is reduced, bending workability becomes insufficient, and the yield strength after coating also decreases. 0.
If the content exceeds 7%, coarse Al-F of 50 μm or more
Bending workability is inferior because the e-Mn-based crystallized product is formed and the bending workability is significantly deteriorated, and further the softening of the material after the baking treatment at a low temperature is small. Further, as a general feature of the Al-Mg alloy plate, during drawing, ears are apt to occur in two directions of 0 to 180 ° with respect to the rolling direction. In this case, the samples were taken at 90 ° to the rolling direction. The bending workability of the material is significantly deteriorated. The addition of Mn in the above range is 0 to 180 °
It has the effect of suppressing the occurrence of ears in the direction and effectively acts to improve bending workability.

Fe is an Al having a preferable distribution state during casting.
It is an element that forms a —Fe—Mn-based compound and contributes to the improvement of bending workability, and the preferable Fe content range is 0.2 to
0.5%. When Fe content is less than 0.2%, Al-Fe-M
Since the preferable distribution of n-type crystallized substances is not sufficiently obtained, the effect of improving bending workability is small.
A coarse Al-Fe-Mn-based crystallized product of m or more is formed, and bending workability is significantly deteriorated.

Cu, which is added as a selective component, has the effect of improving the strength, and is added in an appropriate amount within the range of 0.05 to 0.2% depending on the strength required for the material. Cu amount is 0.05
If it is less than 0.1%, the effect of improving the strength is small, and if it exceeds 0.2%, the bending workability is deteriorated. Si is an element that is unavoidably contained in the aluminum alloy, but since it acts to suppress the softening of the material by forming the Mg ₂ Si phase during the coating and baking treatment, it should be controlled within the range of 0.1 to 0.4%. preferable. If it is less than 0.1%, its effect is small, and it is 0.
If it exceeds 4%, the bending workability deteriorates. Ti is an element that improves bending workability, and is preferably 0.01 to 0.1%.
Add in the range of. If it is less than 0.01%, its effect is small,
If it exceeds 0.1%, a coarse Al-Ti compound is formed at the time of ingot formation, and bending workability deteriorates.

In the present invention, it is necessary to strictly control the distribution state of the second phase compound in the alloy structure in order to obtain good bending workability in the low temperature paint baking treatment. The compound having a size of 2 μm or less on the surface of the plate material of the present invention acts to enhance work hardening during cold rolling and suppress softening during coating baking treatment. A preferable distribution condition is 1000 pieces / mm ² or less on the surface of the plate material, and when it exceeds 1000 pieces / mm ² , bending workability is poor when baking is performed at a low temperature after coating with an aqueous paint.

The bending workability of the plate material after paint baking is
In particular, in order to make it practically sufficient as a material for the Stein tab, the size of the plate surface should be 6 to 15 μm.
Distribution density of the compound of 250 on the surface of the plate material / mm ²
The above is an essential requirement. If the density is less than 250 pieces / mm ² , sufficient bendability cannot be obtained. In addition, since bending workability is impaired when the number of compounds having a size of more than 15 μm on the surface of the plate material is impaired, it is preferable to limit the number of compounds having a size of more than 15 μm to less than 5 pieces / mm ^{2 on the} surface of the plate material.

In the present invention, it is necessary to set the proof stress after the coating baking treatment to 280 MPa or more in order to obtain sufficient strength as a Stein tub. Further, the surface protective coating film formed on the plate material of the present invention is preferably a coating film of an aqueous paint of a polymer resin such as epoxy acrylic,
The coating thickness is preferably in the range of 0.5 to 5 μm. Coating thickness
If it is less than 0.5 μm, coating film cracking may occur during bending, and if it exceeds 5 μm, there is no practical problem, but it is not preferable because the manufacturing cost increases. An inner wax may be added to the water-based paint in order to improve workability.

A preferred method for producing the aluminum alloy sheet for forming according to the present invention will be described. Mg: 3.0-4.
0%, Mn: 0.4 to 0.7%, Fe: 0.20 to 0.50%,
Aluminum alloy consisting of balance Al and unavoidable impurities,
Alternatively, an ingot of an aluminum alloy obtained by adding at least one of Cu: 0.05 to 0.2%, Si: 0.1 to 0.4% and Ti: 0.01 to 0.1% at a temperature of 450 to 550 ° C.
Hold for ~ 20 hours to homogenize and hot roll.

The homogenizing treatment is carried out in order to control the distribution state of the second phase compound and improve the bending workability. In the state where the aluminum alloy of the present invention is ingot, the Al-Fe-Mn-based crystallized product formed during casting has many needle-shaped portions,
During bending, the tips of needle-shaped crystallized substances cause a notch effect, which causes the material to crack or fracture. By maintaining the ingot at a high temperature, the shape of the crystallized substance changes from needle-like to granular,
Bendability is improved. In addition, the compound segregated at the grain boundary portion forms a solid solution in the matrix, improving bending workability.

Under the industrial manufacturing conditions, the heating rate during homogenization is gradual heating of about 50 ° C./h, so that A
Precipitates such as 1-Mn-based compounds and Mg ₂ Si are formed. When kept at high temperature, these precipitates become larger than 2 μm in size and work hardening is suppressed. The preferred temperature range for the homogenization treatment is 450 to 550 ° C., and if it is less than 450 ° C., it is necessary to hold for a long time to obtain a predetermined bending workability, which is industrially disadvantageous. If it exceeds 550 ° C, eutectic melting may occur, causing cracking during hot rolling and deterioration of bending workability. Further, since the compound also grows large and the number of particles decreases, the effect of improving the coating adhesion becomes small. The retention time of homogenization treatment is preferably 1 to 20 hours.If it is less than 1 hour, the distribution of compounds with a size of 2 μm or less is large and the bending workability is poor, and if it exceeds 20 hours, the size of compounds with a size of 6 to 15 μm decreases and bending Workability becomes insufficient.

The homogenizing treatment and the cold rolling performed after the hot rolling impart work hardening to the material to enhance the strength. The preferable working ratio is 60% or more. When the working ratio is less than 60%, the yield strength after baking treatment does not reach 280 MPa, and the strength as a Steion tub is particularly insufficient. If the cold rolling reduction is too high, the bending workability will deteriorate.
% Or less is desirable.

After cold rolling, a coating undercoating treatment consisting of alkali etching and chemical conversion treatment is carried out for coating. The coating base treatment is a treatment performed to improve the adhesion between the coating film and the material to be coated.First, in order to remove oxides on the surface of the aluminum alloy, alkali etching using caustic soda is performed, Then, the film is formed by immersing it in a chemical conversion treatment tank such as a phosphoric acid chromate solution to improve the adhesion to the coating film.

After the coating base treatment, coating is preferably performed with the above-mentioned polymer resin water-based coating material, and coating baking treatment is performed to form a surface protective coating film. The baking is preferably carried out within a temperature range of 200 to 250 ° C. for a period of less than 2 minutes. If the baking temperature is less than 200 ° C, it will be necessary to maintain for a long time in order to obtain sufficient coating performance, so productivity will decrease, and if it exceeds 250 ° C, the energy cost advantage over solvent-based paints will be improved. Will not be obtained. The baking time is also limited from the viewpoint of industrial productivity.

The preferred embodiments of the present invention are listed below. 1.Mg:3.0-4.0%, Mn: 0.4-0.7%, Fe: 0.20-
Aluminum alloy plate containing 0.50% and balance Al and unavoidable impurities, or Cu: 0.005-0.2%, S
An aluminum alloy plate to which at least one of i: 0.1 to 0.4% and Ti: 0.01 to 0.1% is added, a protective coating film is formed on the surface, and the second phase having a size of 2 μm or less on the plate surface. The distribution of the compound and the second phase compound with a size of 6 to 15 μm is 1000 / mm ² or less and 250 / mm ² respectively.
² or more, stay-on tab for the aluminum alloy sheet excellent in bending workability, wherein the yield strength after paint baking is not less than 280 MPa.

2. The above ingot of aluminum alloy is put in the range of 450-55.
It is kept at 0 ° C for 1 to 20 hours to homogenize it, and after hot rolling it is cold-rolled with a workability of 60% or more. A method for producing an aluminum alloy sheet material for a stain ion tab, which is excellent in bending workability, which comprises coating baking treatment at a temperature of 250 ° C for a time within 2 minutes.

[0026]

In the present invention, the component composition of the Al-Mg alloy is limited and the distribution state of the second phase compound in the alloy structure is defined, and by combining these, sufficient strength,
Aluminum that has rigidity and low work hardening degree, and has excellent bending workability even when paint baking is performed at low temperature using water-based paint, especially suitable for Stein tab An alloy plate material is obtained.

[0027]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 An aluminum alloy having the composition shown in Table 1 was cast by semi-continuous casting. The obtained ingot was homogenized, hot-rolled and then cold-rolled to obtain a plate material having a thickness of 0.35 mm. The finished sheet thickness of hot rolling was adjusted according to the workability of cold rolling. About the plate material after cold rolling,
After dipping in a solution containing 5% NaOH and pH 13 at 60 ℃ for 20 seconds to perform alkali etching, 50% CrPO ₄ , 20% AlPO ₄ , 15
% AlO (OH) in a solution at 65 ° C for 1 minute, chemical conversion treatment, washing with water, drying, and coating with an epoxy acrylic water-based paint (Canliner 100 manufactured by Nippon Paint Co., Ltd.). A film was formed.

In the coating baking process, the temperature rising rate was 5 ° C./s, the temperature was maintained for 5 seconds when the temperature reached a predetermined temperature,
Air cooling was performed at a cooling rate of 10 ° C / s. The coating thickness was 3 μm. Table 2 shows the homogenization treatment conditions, the cold rolling workability, the paint baking treatment temperature, and the distribution state of the second phase compound. The distribution state of the compound was determined by subjecting the coated plate material to a film removal treatment and measuring the surface with an image analyzer (manufactured by Nireco: Luzex III U).

[0029]

[Table 1]

[0030]

[Table 2]

The mechanical properties of the samples before coating and after baking were measured with JIS No. 5 test pieces, and the coating adhesion and bending workability were evaluated for each sample after baking. For coating film adhesion, bend the test piece (10 mm width) 180 ° using a jig with a radius of 1 mm, cover the end surface of the test piece with insulating paint, and then dip it in a 0.1 M NaCl solution together with a platinum electrode. Then, it was evaluated by measuring the value of the current flowing when a voltage of 6 V was applied between the test piece and the platinum electrode. When the coating film is peeled off, a current of tens of mA flows. For bending workability, a jig with R = 1 mm was used to cut a test piece (10 mm width) in the 90 ° direction with respect to the rolling direction and 180 °
It was evaluated by observing the surface properties (cracked state) of the bent part after bending. The evaluation results are shown in Table 3. As can be seen in Table 3, the samples according to the invention were all after paint baking.
It has a proof stress of 280 MPa or more, good coating adhesion, and 180 ° bending workability. In the measurement range of the present invention, 20μ
No coarse compound exceeding m 2 was observed.

[0032]

[Table 3]

Comparative Example 1 An aluminum alloy having the composition shown in Table 4 was cast, hot rolled and cold rolled in the same manner as in Example 1 to have a thickness of 0.35 mm.
As the plate material of No. 3, the coating base treatment, the coating and the coating baking treatment were performed under the same conditions as in Example 1, the mechanical properties were measured by the same method as in Example 1, and the coating film adhesion and bending workability were evaluated. Table 5 shows the homogenization conditions of the ingot, the cold working degree, the coating baking temperature and the distribution state of the second phase compound, and Table 6 shows the evaluation results of the performance. In Tables 4 and 5, those out of the conditions of the present invention are underlined.

[0034]

[Table 4] << Table Note >> Alloy No. K contains Cr: 0.10%.

[0035]

[Table 5]

[0036]

[Table 6] << Table Note >> Bendability: No cracks ○ Micro cracks × Cracks × ×

As shown in Table 6, since the coating temperature of sample No. 1 is less than 200 ° C., the adhesion of the coating film is poor. Sample No. 2 has a low cold rolling workability, so the prescribed yield strength cannot be obtained after paint baking. Since the sample No. 3 had a too long homogenization treatment time, the number of compounds having a size of 6 to 15 μm was small and the bending workability was poor. Sample No. 4 has a low temperature of homogenization treatment, so there are many compounds of 2 μm or less and bending workability deteriorates. The adhesion of the coating film is also poor. Sample No.5
However, the test material could not be obtained because the homogenization temperature was too high and eutectic melting occurred and cracking occurred during hot rolling. In sample No. 6, since the contents of Mn and Fe are large, a coarse Al—Fe—Mn-based compound is generated and bending workability is deteriorated. The adhesion of the coating film is also poor. In sample No. 7, the homogenization treatment time was short, so the distribution of compounds of 2 μm or less was large, and bending workability and coating adhesion were poor.

Sample No. 8 has a small amount of Mn and Fe,
The number of compounds with a size of 6 to 15 μm decreases, resulting in poor bending workability and coating adhesion. Sample No. 9 has a large size due to the large amount of Cu
The number of compound distributions of 2 μm or less increases and bending workability and coating adhesion are poor. Sample No. 10 has a low Mg content and therefore cannot obtain a predetermined yield strength. Sample No. 11 had a small amount of Fe, so that an appropriate distribution of the second phase compound could not be obtained and bending workability was not sufficient. Sample No. 12 is a conventional 5182 alloy sheet, and Sample No. 13 is a conventional 5082 alloy sheet, both of which have a large amount of Mg and a small amount of Mn. When the temperature is out of the limited range, the bending workability is remarkably deteriorated by the low temperature baking treatment using the water-based paint.

Example 2 In the aluminum alloy plate material of sample No. 1 of Example 1,
The test material which changed the coating film thickness was produced. The coating film adhesion of these test materials was evaluated by the same method as in Example 1. The results are shown in Table 7. Those having a coating thickness according to the present invention are:
The current value was small and sufficient coating film adhesion was shown, but for the coating film thickness less than 0.5 μm, the current value was large and peeling of the coating film occurred.

[0040]

[Table 7]

[0041]

As described above, according to the present invention, there is provided an aluminum alloy sheet material for forming which has sufficient strength and excellent bending workability even when the temperature of the coating baking process is lowered. When this plate material is applied as an easy open-end Steion tab material for beverage cans and food cans in particular, it is possible to use water-based paints, and it is possible to improve the coating work environment and reduce energy costs.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location // C23C 22/00 Z (72) Inventor Tsutomu Moriyama 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd. (72) Inventor Shin Tsuchida 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd.

Claims (6)

[Claims] 1. Mg: 3.0 to 4.0% (mass%, the same applies hereinafter)
, Mn: 0.4 to 0.7%, Fe: 0.20 to 0.50%, the balance consisting of Al and unavoidable impurities, and an aluminum alloy plate having a surface protective coating, the size of the plate surface being 2 μm or less. Biphasic compounds and sizes between 6 and 1
The distribution of phase 2 compounds of 5 μm is 1000 / mm ² each
Aluminum alloy sheet material for forming with excellent bending workability, characterized by the following and 250 pieces / mm ² or more, and a proof stress after coating baking of 280 MPa or more. 2. The aluminum alloy contains Cu: 0.05 to 0.2.
%, Si: 0.1 to 0.4%, and Ti: 0.01 to 0.1%. One or more of the following: 1. The aluminum alloy sheet material for forming according to claim 1, which is excellent in bending workability. 3. The surface protective coating film is a polymer resin coating film having a thickness of 0.5 to 5 μm.
Alternatively, the aluminum alloy plate material for forming, which is excellent in bending workability according to 2. 4. Mg: 3.0-4.0%, Mn: 0.4-0.7%,
An ingot of an aluminum alloy containing Fe: 0.20 to 0.50% and the balance Al and unavoidable impurities was heated at 450 to 550 ° C.
Homogenize by holding at the temperature of 1-20 hours,
After hot rolling, cold rolling with a working rate of 60% or more is applied, a coating base treatment consisting of alkali etching and chemical conversion treatment is performed, and after coating, a coating baking treatment at a temperature of 200 to 250 ° C for 2 minutes or less is required. A method for producing an aluminum alloy sheet material for forming, which is excellent in bending workability. 5. The aluminum alloy contains Cu: 0.05 to 0.2.
%, Si: 0.1-0.4%, and Ti: 0.01-0.1%, and at least one of them is contained. 5. The method for producing an aluminum alloy sheet for forming according to claim 4, which is excellent in bending workability. 6. The method for producing an aluminum alloy sheet for forming, which is excellent in bending workability, according to claim 4, wherein the coating is performed with an aqueous paint of a polymer resin.