JPH08170138A - Aluminum alloy sheet for forming, excellent in chemical conversion treating property and corrosion resistance and reduced in deterioration in strength even after baking finish - Google Patents

Abstract

PURPOSE: To produce an Al alloy sheet excellent in chemical conversion treating property and corrosion resistance and reduced in deterioration in strength after baking finish by specifying a composition consisting of Mg, Cu, Mn, Fe, Si, and Al and also specifying the quantitative balance between Cu and Mn. CONSTITUTION: This sheet 15 an Al alloy sheet of Al-Mg type for forming, having a composition which consists of, by weight, 2.5-6.0% Mg, 0.05-0.25% Cu, 0.07-0.50% Mn, 0.05-0.30% Fe, 0.05-0.40% Si, and the balance Al with inevitable impurities and in which the relation between Cu and Mn satisfies 0.3<=2Cu+Mn<=0.7%. This Al alloy sheet can be obtained by casting an alloy of above composition, applying homogenizing treatment to the resultant cast slab at about 450-580 deg.C, hot-rolling and cold-rolling this cast slab, and then applying solution heat recrystallization treatment at about 470-570 deg.C to the resultant sheet.

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 chemical conversion treatment property and corrosion resistance and has little strength reduction even after baking.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been widely used as a forming material for automobile body sheets and the like. However, in recent years, in order to improve the fuel efficiency of automobiles, there has been an increasing demand for weight reduction of vehicle bodies, and aluminum alloy sheets have begun to be used for automobile body seats and the like as one of the means for weight reduction. The aluminum alloy used for such an application is a non-heat treatment type Al-Mg alloy 5052.
Alloy O material, 5182 alloy O material, etc., and heat treatment type Al-M
Examples thereof include g-Si-based 6009 alloy T4 material and 6010 alloy T4 material.

[0003]

However, the above-mentioned 5052 alloy O material and 5182 alloy O material have insufficient strength after being molded and subjected to paint baking. Therefore, it is possible to add Cu having an age hardening property to improve the strength after baking for coating.
It is proposed in Japanese Patent No. However, this proposal has a problem of reducing the corrosion resistance of the material.

On the other hand, the Al-Mg-Si-based 6009 alloy T4 material has insufficient strength after coating baking.
Although the 0 alloy T4 material satisfies the strength after baking, it has a problem that the formability is poor. Further, the heat treatment type Al-Mg-Si alloy has a drawback that the formability is deteriorated because the material properties largely change with time when a rolled plate has been manufactured for a certain period of time. Therefore, inventory management from manufacturing to molding and lot management become complicated.

Further, recently, it has been considered that the chemical conversion treatment as a base treatment for coating is performed on the same line as the steel sheet, and it is necessary that the chemical conversion film is easily formed under the same conditions as the chemical conversion treatment of the steel sheet. There is. However, the alloys listed for use as the above-mentioned automobile body sheet have a problem in chemical conversion treatment. The present invention solves the problems that the conventional aluminum alloy sheet for forming as described above has, and has excellent chemical conversion processability and corrosion resistance, and an aluminum alloy sheet for forming with less strength reduction even after coating baking. The purpose is to provide.

[0006]

The inventors of the present invention have conducted various experiments to achieve the above object, and as a result, Cu
It has been found that an aluminum alloy sheet having excellent chemical conversion treatability and corrosion resistance and having little decrease in strength after paint baking can be obtained by containing the added amount and the added amount of Mn in an appropriate balance. In the present invention, the weight% is: Mg: 2.5 to 6.0% Cu: 0.05 to 0.25% Mn: 0.07 to 0.50% Fe: 0.05 to 0.30% Si: 0.05 to 0.40%, and the relationship between Cu and Mn is 0.3 ≦ 2Cu + M
It is characterized by satisfying n ≦ 0.7 and the balance consisting of Al and unavoidable impurities.

[0007]

The present invention will be described in detail below. First,
The reasons for limiting the component composition in the present invention will be described. Mg: Mg is an essential alloying element mainly for increasing strength and ductility, and its content is 2.5 to 6.0%.
And If Mg is less than 2.5%, the strength and ductility are insufficient, and if it is more than 6.0%, the hot workability is deteriorated. The preferred range of components is 4.0 to 5.5.
%.

Cu: Cu is effective mainly for improving the strength by precipitation hardening, and particularly, the strength is improved by precipitation hardening during baking of the coating, so that the softening amount during baking can be slightly suppressed. Further, although Cu improves the chemical conversion treatment property, it adversely affects the corrosion resistance. Therefore, the content of Cu is 0.05 to 0.25 from the viewpoint of securing strength during coating baking, chemical conversion treatability and corrosion resistance.
%. When the amount of Cu is less than 0.05%, the strength after coating baking is large, and the chemical conversion treatability also deteriorates. However, if the Cu content exceeds 0.25%, there is no problem in chemical conversion treatability, but good corrosion resistance cannot be obtained. The preferred component range is 0.1-0.2
%.

Mn: Mn contributes to miniaturization of recrystallized grains and suppresses recovery and recrystallization during coating baking,
It has the effect of reducing the amount of softening during baking. The content of Mn was 0.07 to 0.50%. If the Mn content is less than 0.07%, the above effect cannot be sufficiently obtained. Further, if the content exceeds 0.50%, the ductility decreases. As a preferable component range, 0.15 to 0.35%
Is.

2Cu + Mn: Cu and M in the present invention
Not only is n limited to the above, but Cu and M
It also defines the mutual quantitative relationship of n. The quantitative relationship is
0.3 ≦ 2Cu + Mn ≦ 0.7. If Cu and Mn do not satisfy this quantitative relationship, good chemical conversion treatability, corrosion resistance, and strength after coating baking cannot all be sufficiently secured.

Fe: Fe is an element that deteriorates moldability, and the content thereof is preferably as small as possible. The content was 0.05 to 0.30%. Good characteristics can be obtained even when the Fe content is less than 0.05%, but this is not preferable because the manufacturing cost increases. Further, if Fe is contained in an amount of more than 0.30%, a large number of coarse crystallized substances such as Al-Fe system are formed, resulting in deterioration of moldability.

Si: Si is also an element which, like Fe, forms crystallized substances and deteriorates moldability, and the content thereof is preferably as small as possible. As content: 0.05-0.4
It was set to 0%. Good characteristics can be obtained even if the Si content is less than 0.05%, but this is not preferable because the manufacturing cost increases.
Further, if Si is contained in an amount of more than 0.40%, a large number of coarse crystallized substances are formed and the moldability is deteriorated.

The above is the basic composition that characterizes the aluminum alloy sheet of the present invention.
Addition of i, B and Be does not impair the effects of the present invention. Ti or Ti and B may be added for refining the crystal grains in the ingot. However, primary crystal Al
_{3 In} order to prevent the crystallization of Ti particles, the Ti amount should be 0.1
It is desirable that the amount be 5% or less, and that the amount of B be 500 ppm or less in order to prevent the formation of TiB ₂ particles. Furthermore, Mg containing 1.5% or more of A
In the molten alloy of 1 alloy, Be has been conventionally added to prevent oxidation of the molten alloy. In the present invention, Be may be added at 50 ppm or less to prevent oxidation of the molten alloy. Impurities other than Fe and Si, such as Cr,
Since Zn and the like have an adverse effect on moldability and corrosion resistance, it is preferable that the content be as small as possible, and it is desirable that the total content be 0.1% or less.

Next, a method for manufacturing the aluminum alloy sheet of the present invention will be described. The alloy composition of the present invention is cast by a DC casting method or another ordinary casting method. The obtained slab is subjected to homogenization treatment within the range of 450 to 580 ° C. and hot rolling. Next, after cold rolling, 470 to 57
A solution recrystallization treatment is performed at 0 ° C. Since the alloy of the present invention contains Mn that stabilizes the recrystallized grains, it is not necessary to strictly define the solution treatment recrystallization treatment conditions, but it is possible to prevent the generation of Luders marks and rough skin during molding. In order to achieve this, the average grain size of the alloy plate should be set to an appropriate size
m to 150 μm) is applied. The treatment conditions are preferably a temperature rising rate of 40 ° C./min or more, a heating temperature of 470 to 570 ° C., a holding time of 30 minutes or less, and a cooling rate of 50 ° C./min or more. Regarding the relationship between the heating temperature and the holding time, it is preferable that the higher the heating temperature, the shorter the holding time.

[0015]

EXAMPLES The present invention will be described below with reference to examples. The alloys having the composition as shown in Table 1 were prepared by the DC casting method.
It was cast into a slab having a thickness of 0 mm, the ingot was subjected to homogenization treatment at 530 ° C., hot-rolled to a plate thickness of 4 mm, and further cold-rolled to a plate thickness of 1 mm. Then, the heating rate 12
Solution heat treatment was performed at 00 ° C./min, heating temperature of 540 ° C., holding time of 3 minutes, and cooling rate of 1200 ° C./min.

[0016]

[Table 1]

The aluminum alloy plate obtained by the above method was subjected to the following mechanical property investigation and surface property investigation. Mechanical properties: (a) Tensile properties: Tensile strength, proof stress, elongation,
(B) Formability: Erichsen value, (c) Softening behavior after paint baking: After 3% cold working, baking at 180 ° C x 30 minutes corresponding to paint baking treatment is performed, and during cold working The amount of change in yield strength after baking was investigated. Surface characteristics: (a) Chemical conversion treatment property: It was immersed in a commercially available zinc phosphate bath (bath temperature 40 ° C.) for 2 minutes under stirring conditions, and evaluated by the adhesion amount (g / mm ² ) of the chemical conversion treatment film. .
An adhesion amount of 1.7 g / mm ² or more was judged to be good. (B) Corrosion resistance: 35 ° C, salt spray (5% NaC
under 1) → 1 day → 40 ° C., 85% RH for 5 days → indoor standing for 1 day ”as one cycle, and the maximum thread rust length (mm) was evaluated after 8 cycles. Maximum thread rust length is 1.5 mm
The following were judged to be good.

The results of the above evaluations are shown in Tables 2 and 3, and the aluminum alloy plate No. 1 to No. Thirteen
Is a conventional example. No. 1 (6010 alloy), No. 2 (5
182 alloy), the decrease in strength after baking is 5
It has a low N / mm ^{2 or} less, and the chemical conversion coating amount is 1.7 g / mm ² or more, which has excellent chemical conversion treatment characteristics, and the maximum thread rust length is 1.5 mm or less, which combines excellent corrosion resistance. I know I have it. In contrast, Cu and Mn
Comparative Example No. whose quantitative balance is outside the scope of the present invention. 1 to N
o. In No. 7, strength reduction due to coating baking, chemical conversion treatability and corrosion resistance cannot all be satisfied at the same time.

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

As described above, in the Al-Mg type aluminum alloy plate, by specifying the quantitative balance between the Cu addition amount and the Mn addition amount as in the present invention,
It is possible to obtain an aluminum alloy plate which has a small decrease in strength due to coating baking, and has surface properties that are excellent in chemical conversion treatment and corrosion resistance. Therefore, the application for forming and processing of automobile body sheets and other automobile parts is expanded, which can contribute to weight reduction of the vehicle body.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshikazu Suzuki, 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd. (72) Mamoru Matsuo 4-3-1-18 Nihombashi Muromachi, Chuo-ku, Tokyo Within Sky Aluminum Co., Ltd.

Claims (1)

[Claims] 1. By weight%, Mg: 2.5 to 6.0% Cu: 0.05 to 0.25% Mn: 0.07 to 0.50% Fe: 0.05 to 0.30% Si : 0.05 to 0.40% and the relationship between Cu and Mn is 0.3 ≦ 2Cu + M
An aluminum alloy plate for forming, which has excellent chemical conversion treatability and corrosion resistance, and which has a small decrease in strength after coating baking, characterized by satisfying n ≦ 0.7 and the balance consisting of Al and unavoidable impurities.