JPH09137243A - Aluminum alloy sheet excellent in bendability after press forming and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an Al alloy sheet for press forming excellent in proof stress after coating/baking, cold delayed aging properties and corrosion resistance by subjecting an Al alloy ingot contg. specified small amounts of Ti and B to hot and cold rolling and thereafter executing heat treatment under specified conditions. SOLUTION: The ingot of an Al alloy contg., by weight 2.0 to 3.0% Mg, 0.30 to 0.60% Cu, 0.08 to 0.15% Si, 0.005 to 0.15 Ti and 0.0002 to 0.05% B or furthermore contg. one or >=two kinds among 0.05 to 0.30% Mn, 0.05 to 0.10% Cr and 0.05 to 0.10% Zr with <=0.3% Fe as an impurity is subjected to homogenizing heating of single or multi-stage at 400 to 580 deg.C. Next, it is worked into a sheet material having prescribed thickness by hot rolling and cold rolling, is thereafter heated at 500 to 580 deg.C at a heating rate >=3 deg.C/sec and is held to the above temp. for 0 to 60sec. Successively, a heat treatment for executing cooling to 100 deg.C at a cooling rate of >=2 deg.C/sec is repeated for one to two times. After that, it is held at 60 to 150 deg.C for 1 to 48hr.

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 press forming which is excellent in proof stress after coating baking, late aging at room temperature, corrosion resistance and the like, and is particularly suitable for automobile bodies and the like having excellent bendability after press forming. Aluminum alloy plate and its manufacturing method.

[0002]

2. Description of the Related Art Surface-treated cold-rolled steel sheets have been frequently used as a plate material for forming an automobile body-sheet or the like. In recent years, there has been an increasing demand for weight reduction for improving fuel efficiency of automobiles. In order to satisfy such demands,
Aluminum alloy plates have begun to be used in products such as steel plates.

Currently, as an aluminum alloy for automobile bodies, M is mainly used in Japan from the viewpoint of formability.
g: 4 to 5% of 5000 series alloy is mainly used. However, it is difficult for this type of alloy to prevent the occurrence of stretcher strain marks (hereinafter abbreviated as SSM) due to dynamic strain aging due to solid solution Mg atoms. The productivity is reduced because it is necessary to adjust the surface by polishing. Further, when the Mg concentration is 3% or more, edge cracking and crocodile bleeding are likely to occur during hot rolling, leading to a decrease in yield.

On the other hand, the 6000 series alloy has a low Mg concentration and S
SM is unlikely to occur and hot rolling property is also good,
The press formability is significantly inferior to that of the 5000 series. In Japanese Patent Laid-Open No. 62-177143, after the solution treatment of a 6000-series alloy, a low temperature heat treatment at a temperature of 40 to 120 ° C. for 8 to 36 hours is performed within 72 hours to improve formability and bake hardenability. Although it is said that an excellent aluminum alloy sheet can be obtained, this alloy is originally not good in press formability, and particularly inferior in bendability.

On the other hand, the present inventors have previously located an intermediate composition between the 5000 series and the 6000 series, which suppresses the generation of SSM, has good hot rollability and excellent press formability. A 3% Mg-based aluminum alloy plate has been developed (see JP-A-4-304339, JP-A-4-365834, and JP-A-6-33179). Further, in addition to these various characteristics, an aluminum alloy plate having a room temperature delayed aging property has also been developed (JP-A-6-25617 and JP-A-7-97667).

Further, Japanese Patent Laid-Open No. 62-27544,
Japanese Patent Application Laid-Open No. 2-118049 discloses a technique in which strength, molding workability (bending property and bulging property) in T4 heat treatment, SSM characteristics, room temperature aging characteristics, and SCC resistance are considered in the similar components as described above. Has been done.

However, it is difficult to suppress the generation of SSM even in the aluminum alloy sheets having the composition ranges of these prior arts when the Mg concentration exceeds 3%. On the other hand, when the Mg concentration is lowered, there is a problem that the proof stress after the paint baking treatment following the press working is inferior to that of the steel plate or the conventional 5000 series alloy. The proof stress after paint baking is correlated with the dent resistance of pressed parts and is an indispensable property as a material for automobile outer panels, but aluminum alloys with low Mg concentration have insufficient proof stress after paint baking. Is.

[0008] Therefore, the present inventors have taken into consideration the heat treatment of the above 3% Mg-based aluminum alloy, so that the press formability, the proof stress after baking, the room temperature delayed aging, the post-coating corrosion resistance, and the hot rolling property are excellent, We have developed an aluminum alloy plate that does not generate SSM.

However, although this alloy sheet satisfies all the properties which have been required as aluminum alloy sheets for automobiles up until now, a new problem arises that the bendability after press forming is poor.

[0010]

The present invention has been made in view of the above circumstances and is excellent in press formability, proof stress after baking, aging at room temperature, corrosion resistance after coating, hot rolling property, and SSM. It is an object of the present invention to provide an aluminum alloy sheet having satisfactory bendability after press forming while satisfying the characteristics required for an automobile body that does not occur, and a method for producing the same.

[0011]

[Means for Solving the Problems] For various characteristics required for automobile body sheets, 5% Mg-based 5
Although the 000 series alloy has good strength and press formability, it has a problem that SSM is generated, and the 1% Mg series 600
The 0-based alloy had good SSM and strength, but had a problem in press formability. That is, 5000 which has been conventionally considered as an aluminum alloy for automobile body sheets.
Each of the series alloys and the 6000 series alloy has advantages and disadvantages.

Therefore, the present inventors have examined an Al--Mg--Cu--Si alloy having Mg in the range of 2 to 3% Mg, and as a result, this alloy has SSM characteristics and press formability. It was found that the strength was good, but the strength was slightly lower than those of the 5000 series and 6000 series. Therefore, the strength was improved by performing an aging heat treatment after solution hardening, which was omitted in the 3% Mg-based alloy.

However, although the strength could be improved by this, the bendability after press molding was extremely poor, and there was a new problem that cracking occurred when hemming was performed after press molding.

Conventionally, in this type of alloy sheet, the bendability after press forming has never been a problem and has never been considered. Of course, bendability was taken into consideration as part of press formability, but since the bending process in the actual manufacturing of automobile outer panels is performed after press forming, it is possible to perform close contact bending in the bending test of the as-manufactured alloy sheet. Even then, there were cases where cracks occurred during manufacturing. That is, the bendability in a simple bending test and the bending workability after press forming do not always match, and the formability could not be sufficiently evaluated by the conventional bending test. It is considered that this is because the interaction between the deformation mode of press molding and the deformation mode of bending after molding changes depending on the material characteristics.

Based on such knowledge, the present inventors have
It has been conventionally required for automobile body seats on the premise that an Al-Mg-Cu-Si alloy having an amount of Mg between the 5000 alloy and the 6000 alloy is subjected to aging heat treatment after solution hardening. As a result of further studies in order to improve bendability after press molding without sacrificing various properties, as a result, the amount of Mg-Si was specified in a specific narrow range, and the amount of Cu was adjusted and added. It has been found that Ti and B may be added in small amounts in order to obtain a good balance of all properties.

The present invention has been made on the basis of such findings of the present inventors. That is, in the present invention, in terms of weight%, Mg: 2.0 to 3.0%, Cu: 0.3 to 0.
6%, Si: 0.08 to 0.15%, Ti: 0.005
0.15%, B: 0.0002 to 0.05%, Fe as an unavoidable impurity of 0.3% or less, and the balance substantially consisting of Al. An aluminum alloy sheet having excellent bendability after forming is provided.

The present invention also provides Mg: 2.0 by weight.
~ 3.0%, Cu: 0.3-0.6%, Si: 0.08
~ 0.15%, Ti: 0.005-0.15%, B:
0.0002 to 0.05%, and Mn: 0.
05-0.30%, Cr: 0.05-0.10%, Z
r: 0.05 to 0.10%, containing 1 or 2 or more kinds, Fe as an unavoidable impurity of 0.3% or less, and the balance substantially consisting of Al. ,
An aluminum alloy sheet having excellent bendability after press forming is provided.

Further, according to the present invention, the ingot having any of the above alloy compositions is subjected to a one-step or multi-step homogenization treatment at a temperature in the range of 400 to 580 ° C., and then the ingot is heated. The desired plate thickness is obtained by hot rolling and cold rolling, and then 3 ° C / ° C up to a temperature in the range of 500 to 580 ° C.
The heat treatment of heating at a heating rate of 2 seconds or more and holding at that temperature for 0 to 60 seconds, and subsequently cooling to 100 ° C. at a cooling rate of 2 ° C./second or more is repeated once or twice or more, and then 60 to 150 ° C. The present invention provides a method for producing an aluminum alloy sheet having excellent bendability after press forming, which is characterized by holding at a temperature for 1 to 48 hours.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The aluminum alloy plate according to the present invention has a weight%
Then, Mg: 2.0 to 3.0%, Cu: 0.30 to 0.6
0%, Si: 0.08 to 0.15%, Ti: 0.005
.About.0.15%, B: 0.0002 to 0.05%, Fe as an unavoidable impurity is 0.3% or less, and the balance substantially consists of Al. In addition, Mn:
0.05-0.30%, Cr: 0.05-0.10%,
Zr: 0.05 to 0.10%, Ti: 0.005 to 0.
You may contain 1 type (s) or 2 or more types among 15%.

The alloy composition in the present invention is Al-Mg-C.
Based on u-Si system, by forming a modulation structure (GPB zone) in the pre-deposition stage of Al-Cu-Mg-based compound precipitation, the coating film bake hardenability is made excellent, and in the production thereof, solution heat treatment is performed. After that, it is rapidly cooled and then heat-treated at a low temperature to obtain press formability, proof stress after baking of the coating film, and room temperature delayed aging. Furthermore, by optimizing the alloy components, excellent bend formability after press forming is obtained. ing.

Next, the reason for defining the above composition range will be explained for each component. Mg: As a solid solution element, Mg contributes to an increase in the work hardening coefficient, and consequently to an improvement in uniform elongation, and is also a constituent element of the Al—Cu—Mg-based modulation structure that contributes to bake hardenability. However, if the content is less than 2.0%, not only does ductility and press formability deteriorate, but Al-Cu
The formation of the Mg-based modulation structure is delayed, and if it exceeds 3.0%, hot rolling cracks are likely to occur, and the spot weldability is further deteriorated. Therefore, the Mg content is 2.0 to 3.
It is specified in the range of 0%. 2.5% from the viewpoint of press formability (especially overhanging property) and bendability after press forming.
It is desirable that this is the case.

Cu: Cu contributes to the strength increase of the material as a solid solution element and is a constituent element of the above Al—Cu—Mg type modulation structure. However, when its content is 0.1.
If it is less than 30%, no modulation structure is generated, and the strength and the bake hardenability of the coating film are insufficient. Further, from the viewpoint of zinc phosphate treatment during coating, it is essential that the content be 0.30% or more. On the other hand, if it exceeds 0.60%, cracks are likely to occur during hot rolling, and the corrosion resistance after coating deteriorates. Therefore, the Cu content is specified in the range of 0.30 to 0.60%. Note that Cu is 0.40% from the viewpoint of further strengthening.
It is desirable that this is the case. From the viewpoint of corrosion resistance, it is preferably 0.55% or less.

Si: Si is an element that promotes the formation of an Al—Cu—Mg-based modulation structure and enhances the hardening ability. In order to exert its function, it is essential to contain 0.08% or more. On the other hand, if the content exceeds 0.15%, coarse Mg ₂ Si-based crystallized substances increase, and as a result, bending workability particularly after pressing is significantly deteriorated, causing defects such as cracks during hemming. Becomes Therefore, the Si content is specified in the range of 0.08 to 0.15%.

Fe: Fe is usually contained in an aluminum alloy as an unavoidable impurity, and when the content exceeds 0.3%, the formation of coarse Al—Fe-based crystallized substances becomes remarkable, which is especially caused by pressing. It promotes the propagation of cracks in bending after forming. Therefore, the Fe content is restricted to 0.3% or less.

Ti, B: Ti, B forms TiB ₂ and has the effect of making the crystal grains of the ingot uniform. But,
When Ti and B are less than 0.005% and less than 0.0002%, respectively, the cast structure becomes coarse, resulting in Mg ₂ Si and Al.
The —Fe-based crystallized product is coarsened, so that cracks are likely to occur during hot rolling, and the coarse precipitate deteriorates the bending property after press forming. On the other hand, if these are added excessively, Ti and B form coarse crystallized substances and deteriorate the formability. Therefore, the contents of Ti and B are 0.005-0.15% and 0.0002-, respectively.
It is specified in the range of 0.05%.

Mn, Cr, Zr: These elements are generally added for the purpose of suppressing recrystallized grain growth. By making the crystal grains fine, roughness of the skin, especially after press molding, is suppressed. Rough skin not only impairs the appearance of the product, but also acts as a starting point of cracks during hemming after press molding. Therefore, by appropriately refining the crystal grains, bendability after press molding is improved. Such action is M
It can be effectively exhibited by adding 0.05% or more of each of n, Cr and Zr. However,
Mn 0.30%, Cr 0.10%, Zr 0.10
%, The crystal grain size becomes too fine and S
SM occurs and the ductility decreases. Therefore, M
n: 0.05 to 0.30%, Cr: 0.05 to 0.10.
%, Zr: 0.05 to 0.10%, and it is preferable to add one or more of them as necessary.

Be is 0.01 as the other element.
% May be added. Be prevents oxidation during casting,
It is an element that improves the castability and hot rolling property and improves the formability of the alloy plate. However, if the content exceeds 0.01%, not only the effect is saturated, but also since it is a highly toxic element, it may harm the casting work environment, which is not preferable. Therefore, even if the Be is added, the addition amount is limited to 0.01%.

In addition to these elements, inevitable impurities are contained as in the case of ordinary aluminum alloys, but the amount thereof is acceptable as long as the effects of the present invention are not impaired. Next, the manufacturing conditions of the alloy plate having the above composition will be described.

An aluminum alloy having the components and compositions defined in the above range is melted and cast by a conventional method, and the ingot is subjected to one-step or multi-step homogenization heat treatment at a temperature in the range of 400 to 580 ° C. . By performing such a homogenization treatment, diffusion and solid solution of the eutectic compound crystallized during casting are promoted, and local microsegregation is reduced. Further, by this treatment, it is possible to finely precipitate the compounds of Mn, Cr, and Zr, which play an important role in suppressing the abnormal grain growth of the crystal grains of the final product and achieving uniformity. However, if the temperature of this treatment is lower than 400 ° C., the above-mentioned effects are insufficient, while if it exceeds 580 ° C., eutectic melting occurs. Therefore, the temperature of the homogenization treatment is set in the range of 400 to 580 ° C. If the holding time within this temperature range is less than 1 hour, the above-mentioned effect cannot be sufficiently obtained, and heating for a long time exceeding 72 hours will saturate the effect. Is preferably 1 to 72 hours.

Then, the ingot subjected to such homogenization treatment is subjected to hot rolling and cold rolling in order to obtain a predetermined plate thickness according to a conventional method. Further, in order to correct the strain or adjust the surface roughness, 5% or less of leveling, stretching, or skin pass rolling may be performed before or after the heat treatment described below, or either one of them.

After completion of rolling, the rolled plate material
Heating to a temperature in the range of 500 to 580 ° C. at a heating rate of 3 ° C./sec or more and immediately after reaching that temperature, or 6
After holding for a period of 0 second or less, heat treatment is performed under conditions such as rapid cooling to 100 ° C. at a cooling rate of 2 ° C./second or more. This heat treatment is performed in order to achieve solution treatment of Cu and Mg forming the modulation structure of the Al-Cu-Mg-based compound, and to obtain sufficient bake hardening in the age hardening process by heating during subsequent baking of the coating film. is there. In this case, if the heating temperature is lower than 500 ° C., solution treatment becomes insufficient,
The bake-hardening amount becomes insufficient. Also, the heating temperature is 580 ℃
, The heating rate is less than 3 ° C / sec, and the holding time exceeds 60 seconds, eutectic melting occurs, and some of the crystal grains grow abnormally. Therefore, the moldability is lowered. Furthermore, 100 ℃
If the cooling rate up to 2 ° C / sec is less than Al-C during cooling
The u-Mg-based compound precipitates and impairs the baking hardening property, which is not preferable. By repeating this heat treatment twice or more, productivity is impaired, but bake hardenability is improved. Therefore, it may be performed twice or more as necessary.

After such solution treatment, heat treatment (low temperature aging treatment) is performed at a temperature of 60 to 150 ° C. for 1 to 48 hours after being kept at room temperature or directly. By this heat treatment, the Al-Cu-Mg-based modulation structure is formed to some extent in advance to improve the stability of characteristics at room temperature.
Further, the modulation structure formed here is, together with the Al-Cu-Mg type modulation structure formed during the coating baking process, in order to suppress the recovery of the processing strain introduced by press molding during the baking of the coating film, Contributes to an increase in strength after baking the coating film. In addition, since Mg atoms forming the modulation structure do not contribute to dynamic strain aging, generation of SSM is suppressed by this heat treatment. However, when the heat treatment temperature is lower than 60 ° C. or when the holding time is less than 1 hour, the above curing cannot be sufficiently obtained, and when the heating temperature exceeds 150 ° C. or the holding time is 48 hours. If the time is exceeded, the modulation structure will be excessively formed, and the bake hardening ability will be insufficient, and the coarse Al-Cu will contribute little to the strength.
-Mg-based compound precipitates, which is not preferable.

As described above, by subjecting the aluminum alloy having the above-mentioned composition to such a step, the bake hardenability which has been conventionally required for automobile bodies,
In addition to late aging at room temperature, bending workability after press molding is excellent, and an aluminum alloy sheet suitable for automobile bodies can be obtained.

[0034]

Embodiments of the present invention will be described below. (Example 1) An alloy having the components and compositions shown in Table 1 was melted, DC cast, and the obtained ingot was subjected to a two-stage homogenization heat treatment at 440 ° C for 4 hours and then at 510 ° C for 10 hours. Then, the slab was heated to 460 ° C. and hot rolled to a plate thickness of 4 mm. Next, after cooling to room temperature, cold rolling was performed to the final sheet thickness to obtain a sheet material having a thickness of 1 mm. The finishing temperature of hot rolling was 280 ° C. The plate material having a thickness of 1 mm was heated to 550 ° C. at a rate of 10 ° C./second, held for 10 seconds, and then forcedly cooled to 100 ° C. at a cooling rate of 20 ° C./second. After this heat treatment, it was left to stand at room temperature for 2 days, and then heat treated at 100 ° C. for 24 hours.

The plate material which has been subjected to the above-mentioned treatment is kept at room temperature for 1 hour.
After holding for a week, it was cut into a predetermined shape and subjected to a tensile test (JIS5
No., tensile direction: rolling direction), deep drawing test, and stretch forming test.

In order to evaluate the amount of normal temperature aging, the sampled tensile test pieces were subjected to accelerated aging treatment at 40 ° C. for 90 days and then subjected to a tensile test to compare the yield strength immediately after production. In addition, 2% and 5% tensile deformation (corresponding to press working) to simulate coating baking after press molding
Then, heat treatment (corresponding to coating baking, abbreviated as BH treatment hereinafter) was performed at 170 ° C. for 20 minutes, and a tensile test was performed.

The bulge test is carried out by completely locking the disc-shaped test piece with a beaded crease holder and molding it with a ball head punch, and measuring the minimum height at which cracks occur, and then bulging molding The sex was evaluated. The deep drawing test is performed by applying a constant wrinkle holding force to the disc-shaped test piece and forming it with a cylindrical punch, and measuring the height in the same manner as the overhang,
Thereby, the deep drawing formability was evaluated.

The bending workability after press molding is 20 × 20.
What was pre-processed by a tensile tester using a strip test of 0 mm was further subjected to 180 ° contact bending, and evaluated by the minimum pre-strain amount at which cracking occurred. The larger the value, the better the bending workability after press forming.

The evaluation of SSM was carried out by using a 40 × 200 mm strip test piece to simulate the generation of SSM during press molding, and pulling 10% at a strain rate of 10 ⁻² on a test piece surface by a tensile tester. The presence or absence of the generated parallel band was visually evaluated.

In the post-painting corrosion resistance test, a 70 × 150 mm test piece was cut out from the coil after treatment, degreased and pickled, then subjected to chemical conversion treatment with a commercially available zinc phosphate treatment solution, washed with water and dried, and then subjected to cationic electrolysis. A sample was prepared by applying an undercoat by coating, a middle coat by spraying, and a topcoat, and this sample was used. At this time, the total coating film thickness was about 100 μm. A cross cut reaching the aluminum base is put on the surface of this sample.
The salt spray test according to Z2371 was conducted for 24 hours, and then left in a humid atmosphere of 50 ° C. and 95% RH for 2000 hours, after which the maximum length of the thread rust generated from the cross-cut portion was measured, whereby the corrosion resistance after painting was evaluated. evaluated. Table 2 shows the test results.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from Table 2, Alloy Nos. 1 to 14, which are within the composition range of the present invention, have high yield strength after BH treatment after 2% and 5% tension, and accelerated aging treatment at 40 ° C. for 90 days. It was confirmed that there was almost no change in yield strength. Further, it had good overhanging and deep drawing formability, and had good post-forming bending workability in which cracking did not occur even when performing contact bending after pre-strain of 14%. Furthermore, SSM does not occur,
The corrosion resistance after painting was also excellent. It has been confirmed that the alloy having a Cu content of 0.5% or less is particularly excellent in corrosion resistance.

On the other hand, Alloy Nos. 15 to 26, which are out of the composition range of the present invention, were inferior in any of the above characteristics. For example, Mg, Si, or Cu is low,
Alloy Nos. 16, 18, and 20 had low curability (coating bake curability) after BH treatment. Alloy No. 15 to which Ti and B were not added exhibited abnormal crystal grain growth and was inferior in elongation, formability, and bending workability after forming. Alloy No. 17 with a large amount of Mg generated SSM. Alloy number 1 with high Si content
Nos. 9 and 22 had a large amount of aging at room temperature, and bending workability after molding was extremely low. Alloy No. 21, which had a large amount of Cu, had a large amount of aging at room temperature and was significantly inferior in corrosion resistance. Mn, C
In Alloy Nos. 23, 24 and 25 to which r and Zr were added excessively, crystal grains became too fine and SSM was generated, and bending workability after forming was deteriorated. Alloy No. 26 with high Fe content
Had many Al-Fe-based crystallized substances, and was inferior in moldability and bendability after molding. (Example 2) Of the alloys shown in Table 1, an alloy having a composition of alloy No. 11 was used, melting and DC casting were performed, and the obtained ingot was heated at 440 ° C for 4 hours and then at 510 ° C for 10 hours.
A step homogenization heat treatment was carried out, the slab was then heated to 460 ° C., and hot rolled to a plate thickness of 4 mm. Then, after cooling to room temperature, cold rolling is performed to the final plate thickness to obtain a thickness of 1
mm plate material. The finish temperature of hot rolling is 2
80 ° C. The plate material having a thickness of 1 mm is heated to 550 ° C. at a rate of 10 ° C./sec, and after holding for 10 seconds, 100 ° C.
Up to 20 ° C / sec for forced air cooling. After this heat treatment, it was left at room temperature for 2 days, and then heat treatment as shown in Table 3 was performed. The same evaluation test as in Example 1 was performed on the alloy plate thus manufactured. The results are also shown in Table 3.

[0045]

[Table 3]

As is clear from Table 3, all the symbols A to D satisfying the conditions of the present invention are B after 2% and 5% tension.
After the H treatment, the yield strength was high, the overhanging and deep drawing formability were good, and the post-formation bending workability was such that cracks did not occur even when contact bending after prestrain of 14% was performed.

On the other hand, symbols E to H which do not satisfy the conditions of the present invention were inferior in any of the characteristics. For example, the symbol E of the present invention in which the low temperature aging treatment is not performed and the symbol F of which the temperature of the low temperature aging treatment is low are 40 MPa and 30 MPa, respectively, in the proof stress change due to the accelerated aging treatment at 40 ° C. for 90 days.
And the yield strength after BH treatment was not sufficient. In addition, the symbol G for which the low temperature aging treatment time was too long and the symbol H for which the temperature was high were low in elongation and moldability, and remarkably low in workability after molding.

[0048]

EFFECTS OF THE INVENTION According to the present invention, it is excellent in press formability, proof stress after baking, aging at room temperature, corrosion resistance after coating and hot rolling property, and satisfies the properties required for automobile bodies that SSM does not occur. At the same time, it is possible to obtain an aluminum alloy plate which is excellent in bendability after press forming and which is most suitable for an automobile body and a manufacturing method thereof.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masakazu Niikura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan KK (72) Inventor Koichi Ohori 85 Hiramatsu, Susono-shi, Shizuoka Mitsubishi Aluminum Co., Ltd. Inside the Technology Development Center

Claims (3)

[Claims] 1. Mg: 2.0 to 3.0% by weight, C
u: 0.30 to 0.60%, Si: 0.08 to 0.15
%, Ti: 0.005 to 0.15%, B: 0.0002
An aluminum alloy sheet having an excellent bendability after press forming, characterized in that the content of Fe is 0.05% or less, Fe as an unavoidable impurity is 0.3% or less, and the balance is substantially Al. 2. Mg: 2.0 to 3.0% by weight, C
u: 0.30 to 0.60%, Si: 0.08 to 0.15
%, Ti: 0.005 to 0.15%, B: 0.0002
To 0.05%, and Mn: 0.05 to 0.3
0%, Cr: 0.05 to 0.10%, Zr: 0.05 to
Bending property after press molding, characterized by containing one or more of 0.10%, Fe as an unavoidable impurity of 0.3% or less, and the balance substantially consisting of Al. Excellent aluminum alloy plate. 3. The ingot having the alloy composition according to claim 1 or 2 at a temperature in the range of 400 to 580 ° C.
After performing a step or multi-step homogenization treatment, this ingot is hot-rolled and cold-rolled to a desired plate thickness, and then heated to a temperature in the range of 500 to 580 ° C at 3 ° C / sec or more. Heat at a speed and hold at that temperature for 0-60 seconds,
Subsequently, heat treatment for cooling to 100 ° C. at a cooling rate of 2 ° C./second or more is repeated once or twice or more, and then 60 to
A method for producing an aluminum alloy sheet having excellent bendability after press forming, which is characterized by holding at a temperature of 150 ° C for 1 to 48 hours.