JP2856936B2 - Aluminum alloy sheet for press forming excellent in strength-ductility balance and bake hardenability, and method for producing the same - Google Patents

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 having excellent balance between strength and ductility and bake hardenability, and a method for producing the same. In addition, the present invention relates to an aluminum alloy sheet for press forming suitable for an automobile body and the like having a high hardening ability even at a low temperature of about 170 ° C., and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, 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. Aluminum alloy sheets are beginning to be used for automobile body sheets and the like to satisfy the requirements.

As an aluminum alloy for an automobile body sheet, a non-heat-treated Al-M represented by 5182 is used.
g-based alloy, heat-treated Al-Cu-based, Al-Mg-S
It is divided into i-series. As a non-heat treatment type Al-Mg based alloy, an alloy premised on the premise that a small amount of Cu or Zn is added, and heat treatment is used has been developed (JP-A-57-12).
0648, JP-A-53-103914, etc.).

[0004] However, although these are slightly better in formability than heat-treated Al alloys, they are inferior to conventional surface-treated cold-rolled steel sheets, and furthermore, no increase in strength can be obtained by the paint baking step. Also, a heat treatment type Al-Cu
System 2036, Al-Mg-Si system 6009, 601
0, 6011, the moldability is inferior, and furthermore, the baking at 200 ° C. in Europe and the United States has been advanced from the viewpoint of energy saving. There was also a problem that the strength was not increased by baking, and conversely decreased in the 2000 series.

[0005] As described above, at present, conventional aluminum alloys do not sufficiently satisfy the characteristics required for an automobile body sheet, particularly, moldability and bake hardenability.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has a good balance between strength and ductility, and has sufficient press formability for use in automobile bodies and the like.
An object of the present invention is to provide an aluminum alloy sheet having good bake hardenability even at low temperature and short time baking, and a method for producing the same.

[0007]

The inventors of the present invention have made various studies to achieve the above object, and as a result,
By appropriately adjusting the chemical composition and optimizing the production conditions, the elongation after heat treatment is 30% or more, and the elongation after heat treatment is 170%.
It has been found that even after baking at a low temperature for a short period of time at 30 ° C. for 30 minutes, the yield strength after baking hardens by 3 to 5 kgf / mm ² or more than before baking, and the present invention has been completed.
That is, the present invention is intended to improve the strength-ductility balance, improve the formability, and improve the dent resistance after baking, and to elongate the material as a breaking elongation, yield strength after low-temperature and short-time baking. Are both improved.

In particular, regarding the chemical composition, Cu, M
g and Si are specified in a specific range,
Control the amount of Fe, Ti, B, Zn
To make the crystal grains equiaxed to improve formability
To balance strength and ductility, and
For low temperature and short time baking at 70 ° C for 30 minutes
Is also capable of obtaining excellent bake hardenability.
You.

More specifically, the aluminum alloy sheet for press forming according to the present invention, which has excellent strength-ductility balance and bake hardenability, contains 1.5 to 3.9 % of Mg and 0.25 to 3% of Cu by weight%. 0.0%, Si 0.02 to 0.15%, F
e is 0.03 to 0.25%, and Ti is 0.005 to 0.1%.
5%, B 0.0002-0.05%, Zn 0.02
０．１0.10% and Mg and Cu are M
In the coordinate of g-Cu, the coordinate point is defined as (Mg%, Cu
%), Shown in FIG. 1 (4.0, 0.2
5), (1.5, 0.8), (1.5, 3.0),
(4.0, 2.23), the remainder being made up of Al and 0.1% or less inevitable impurities,
Assuming that the axis length of the crystal grains in the rolling direction is L and the axis length in the thickness direction perpendicular to L is H, the average aspect ratio L / H is 1.3 or less, and 170 ° C. for 30 minutes 3kg / mm increase in yield strength when baking
It is characterized by being ² or more. Further, based on this composition, Mn of 0.01 to 0.15%, 0.01 to 0.15%
% Cr, 0.01-0.12% Zr, and 0.01%
One or more of V of 0.18% may be further contained. Since these are recrystallization suppressing elements,
It may be added for the purpose of suppressing abnormal grain growth, but its amount is limited to the above-mentioned range lower than the conventional range from the viewpoint of improving formability.

The method for producing an aluminum alloy sheet for press forming according to the present invention, which is excellent in strength-ductility balance and bake hardenability, comprises Mg in an amount of 1.5 to 3.9 % by weight,
Cu is 0.25 to 3.0%, Si is 0.02 to 0.15
%, Fe 0.03-0.25%, Ti 0.005-
0.15%, B in the range of 0.0002 to 0.05%, Zn in the range of 0.02 to 0.10%, and Mg and C
u sets the coordinate point of the Mg—Cu coordinates to (Mg
%, Cu%), as shown in FIG.
0.25), (1.5, 0.8), (1.5, 3..
0) and (4.0, 2.23). The range surrounded by the four points is 450 to 580 ° C. with respect to an aluminum alloy ingot consisting of Al and 0.1% or less inevitable impurities.
After performing one or more stages of homogenization at a temperature within the range, the ingot is hot-rolled and cold-rolled to a desired thickness, and then to a temperature within the range of 440 to 580 ° C. Heat at a heating rate of 3 ° C / sec or more,
Held for 120 seconds, the aluminum alloy plate an increase in yield strength when subjected to baking for 30 minutes at then cooled to 170 ° C. at a cooling rate of more than 2 ° C. / sec to 100 ° C. is 3 kg / mm ² or more It is characterized by obtaining.

In this case, between hot rolling and cold rolling,
Or between cold rolling and cold rolling, or both,
The intermediate annealing treatment at a temperature within the range of 0 to 580 ° C.
It is preferable to carry out once or twice or more.

Hereinafter, the present invention will be described in detail.
In addition, in the following description,% display represents weight%.

First, the reasons for limiting the component composition of the aluminum alloy according to the present invention will be described.

Mg is an essential basic component in the alloy according to the present invention, and when it is alloyed in an appropriate amount, it greatly contributes to improving the strength and ductility of the alloy. However, when Mg is 1.5
%, Sufficient strength and bake hardenability cannot be obtained. Conversely, if it exceeds 4.0%, cracks during hot rolling become remarkable,
Hot workability deteriorates and bake hardenability decreases. Hot
A particularly effective range in consideration of workability and bake hardenability is 1.
5 to 3.9%. Therefore, in the present invention, the content of Mg is defined in the range of 1.5 to 3.9%.

Cu: Cu is a component that mainly binds to Al—Mg to form an Al ₂ CuMg-based precipitate and contributes to hardening by baking. However, if the Cu content is less than 0.25%, the effect cannot be sufficiently obtained, and if it exceeds 3.0%, the moldability and the corrosion resistance deteriorate. Therefore, the content of Cu is specified in the range of 0.25 to 3.0%.

Further, the amounts of Mg and Cu are further limited to the range surrounded by the line connecting the coordinate points in FIG. 1 described above. If the range is out of this range, the strength, ductility, and post-baking strength of the material are reduced. Insufficient or insufficient bake hardenability
Because it is a minute . That is, in the coordinates of FIG.
If the amount of Mg or Cu is smaller than the line connecting B (4.0, 0.25) and C (1.5, 0.8), sufficient strength cannot be obtained. Also, E (8.0,1.0) and D
When the amount of Mg or Cu is larger than the line connecting (1.5, 3.0), ductility, that is, moldability is reduced. Further, when the amount of Mg or Cu is smaller than the range defined by C (1.5, 0.8) and D (1.5, 3.0), ductility (ie, formability) and after baking Is not strong enough. Furthermore, the range in which Mg exceeds 4.0, that is,
B (4.0, 0.25) and F (4.0, 2.23)
Baking hardenability is insufficient when the amount of Mg is larger than the connecting wire
Tends to be.

Si: Si is an element usually contained as an unavoidable impurity, but if added in a small amount, it is an important element contributing to the improvement of formability. Also, Cu, Mg and
Baking in low temperature and short time by adding appropriate amount
It is an element that improves curability . However, if the Si content is less than 0.02%, the effect is not sufficient, and if the Si content is more than 0.15%, coarse Mg ₂ Si-based precipitates deposited by hot rolling or the like even in solution treatment. Things do not dissolve,
Decreases moldability. Therefore, the content of Si is set to 0.02
It is specified in the range of 0.15%. Desirably 0.02-
0.1%.

Fe: Fe is usually contained as an inevitable impurity in aluminum alloys. When the content exceeds 0.25%, coarse crystals are easily formed due to the coexistence with Al, and the press formability is reduced. Adversely affect. However, the addition of a small amount contributes to the improvement of the moldability, and if their content is too small, less than 0.02%, the moldability deteriorates. Therefore, the content of Fe is defined in the range of 0.02 to 0.25%.

Ti, B: Ti and B are present as TiB _{2 and the} like, and have the effect of refining the crystal grains of the ingot to improve the workability during hot work and the like. is important. However, if these are added excessively, coarse crystals are formed and the formability is degraded. Therefore, the contents of Ti and B are reduced to 0.005 to 0.15, respectively.
% And a range of 0.0002 to 0.05%.

Zn: Zn is an element contributing to the improvement of the strength. For this reason, Zn is added in an amount of 0.02% or more. If the content exceeds 0.1%, the ductility and the curability after baking are reduced. , Its content is specified to be 0.02 to 0.1% or less. The alloy numbers 1 to 10 in Table 1 (3, 5, 6,
9 are missing numbers) are examples within the composition range of the present invention.
Are comparative examples out of the range. The alloy numbers 31 to 33 are alloys conventionally used for body sheets.
82,6010.

In the present invention, one or more of Mn, Cr, Zr and V may be added in an appropriate amount, if necessary, in addition to the above elements.

Mn, Cr, Zr, V: Since these elements are recrystallization suppressing elements, they may be added in appropriate amounts for the purpose of suppressing abnormal grain growth. However, these alloy components
Since these materials have a negative effect on equiaxing recrystallized grains and lower the formability, their contents need to be specified in a range smaller than that of conventional aluminum alloys. Therefore, Mn,
The contents of Cr, Zr, and V are each 0.01 to 0.15%,
0.01-0.15%, 0.01-0.12%, 0.0
It is defined as 1 to 0.18%.

In addition to the above-mentioned elements, unavoidable impurities are contained as in the case of ordinary aluminum alloys, but the amount is acceptable as long as the effects of the present invention are not impaired. For example, Be, Na, K, and the like each have a content of about 0.001% or less, and a total of 0.1% or less.

Next, the organization will be described.

The formability of an aluminum alloy largely depends on the crystal grain shape. Equiaxial average aspect ratio L / H
If (L: grain axis length in the rolling direction, H: axis length in the thickness direction perpendicular to L) exceeds 1.3, a distorted pattern appears at the time of press working, and the formability also decreases. The aspect ratio needs to be 1.3 or less. In the present invention,
With the above chemical composition and organization, 17
In the case of baking at low temperature and short time of 30 minutes at 0 ° C
Also have bake hardenability of 3 kg / mm ² or more
It is.

Next, the conditions for producing the alloy of the present invention will be described.

An aluminum alloy having a specified composition and composition in the above range is melted and cast by a conventional method, and the ingot is subjected to one or more stages of homogenizing heat treatment at a temperature in the range of 450 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 suppress abnormal grain growth of crystal grains of the final product and to precipitate finely the compounds of Mn, Cr, Zr, and V which play an important role in achieving uniformity. However, if the temperature of this treatment is lower than 450 ° 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 to 450 to 580 ° C.
Range. The holding time within this temperature range is 1
If the time is less than the time, the above-mentioned effect cannot be sufficiently obtained, and the long-time heating exceeding 72 hours saturates the effect.
The holding time of this homogenization treatment is desirably 1 to 72 hours.

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

After the completion of rolling, such a rolled sheet material is
Heating to a temperature in the range of 440 to 580 ° C. at a heating rate of 3 ° C./sec or more, and immediately after reaching the temperature, or
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. By this treatment, the structure is made uniform, the average aspect ratio of the crystal grains is adjusted to 1.3 or less, and the processing strain is removed, and as a result, the press formability can be improved. In addition, this heat treatment aims to form a solution of an Al-Cu-Mg intermetallic compound that greatly contributes to bake hardening,
This achieves improvement in bake hardenability. In this case,
If the heating temperature is lower than 440 ° C., the above-mentioned effects cannot be sufficiently obtained. If the heating rate is less than 3 ° C./sec, the heating temperature exceeds 580 ° C., or the holding time is longer than 120 seconds, some of the crystal grains will undergo abnormal grain growth. Further, if the cooling rate to 100 ° C. is less than 2 ° C./sec, the above-mentioned compound is coarsely precipitated during cooling, which is not desirable in terms of press formability and bake hardenability. Therefore, the manufacturing conditions are defined as described above.

In addition to such steps, one or more intermediate annealings may be performed between the above-described hot rolling and cold rolling, or between cold rolling and cold rolling, or both. It is desirable to apply. By performing this intermediate annealing, it is possible to prevent edge cracking during cold rolling during strong rolling, and to precipitate a Mg compound functioning as a recrystallization nucleus to homogenize the structure, thereby improving formability. Can be done. However, if the temperature at this time is lower than 320 ° C., the effect is not sufficient, and if it exceeds 580 ° C., eutectic melting occurs. Therefore, the intermediate annealing is performed in the range of 320 to 580 ° C. Note that this intermediate annealing is not an essential process, and may be omitted from the viewpoint of saving the process.

The aluminum alloy sheet thus obtained is excellent in balance between strength and ductility, has an elongation at break of 30% or more, and also has excellent curability by low-temperature baking.
Therefore, such an aluminum alloy plate is suitable for use in an automobile body sheet.

[0032]

Embodiments of the present invention will be described below. (Example 1) An alloy having the components and compositions shown in Tables 1 and 2 was melt-continuously cast, and the obtained ingot was face-cut. ° C
And a two-hour homogenization treatment for 4 hours.
Heated to 00 ° C, hot-rolled to a thickness of 4 mm,
Intermediate annealing was performed at 1 ° C. for 1 hour. Thereafter, the plate was cooled to room temperature, and cold-rolled at a rolling reduction of 75% to obtain a sheet having a thickness of 1 mm. The finishing temperature of the hot rolling was 280 ° C. In addition, the intermediate annealing was performed by gradually heating and cooling at 50 ° C./hour for both heating and cooling. 530 pieces of this 1 mm thick plate
To 10 ° C. at a rate of 10 ° C./sec.
Forced air cooling was performed at a cooling rate of 20 ° C./sec to 00 ° C.

[0033] The plate material produced in this way is kept at room temperature for 30 minutes.
After standing for a few days, cut out into a predetermined shape and use a tensile test (JIS5
No., tensile direction: rolling direction) and conical cup test (J
ISZ2249: test tool type 17), and the average aspect ratio L / H of the crystal grains was measured. The conical cup test was performed as a simulation of press molding, and the composite formability of overhang and deep drawing was evaluated by CCV (mm) (the smaller the CCV, the better the formability). Also,
The crystal grain shape was obtained by a micro-processing, in which a microstructure was revealed by the Ga treatment, and the number of samples was 50, and the cutting method was used. Further, in order to simulate the baking of the paint after press molding, the temperature of 170 ° C.
For 30 minutes (corresponding to seizure), and then a tensile test was again performed under the same conditions as the above-mentioned test after the heat treatment.

Tables 3 and 4 show the test results. The surface properties after the conical cup test are also shown. The bake hardening was determined by subtracting the yield strength after the final heat treatment from the yield strength after the bake simulation.

The alloy numbers 1 to 10 in Table 1 are examples within the composition range of the present invention, and the alloy numbers 11 to 33 in Table 2
Are comparative examples out of the range. In addition, alloy number 3
Reference numerals 1 to 33 denote alloys conventionally used for body sheets, which correspond to 2036, 5182 and 6010, respectively.

As is clear from Table 3, the alloy Nos. 1 to 10 of Examples have an average aspect ratio of 1.3 or less, a high elongation at break of 30% or more, a good CCV, and excellent moldability. Was done. In addition, bake hardening is 3.7 kgf in yield strength.
YSBH × El (yield strength × elongation), which has a high value of at least / mm ² and indicates the balance between strength after baking and elongation before baking.
And TSBH × El (tensile strength × elongation) were confirmed to be high.

On the other hand, as is apparent from Table 4, the alloy numbers 11 to 33 of the comparative examples shown in Table 2 have the formability and the bake hardenability even if the average aspect ratio is 1.3 or less. Both or one of them was inferior to the examples. For example, Alloy No. 11 having a low content of Mg and Cu as components contributing to bake hardening and Alloy No. 18 having a large content of Zn which is a component lowering bake hardenability have low bake hardenability and 2 kgf / mm ² . Also, Mg
The alloy numbers 26 to 30 exceeding 3.9 % also had slightly poor bake hardenability. Further, Si, Mn, Cr, Zr, V,
Alloy numbers 15, 17, 19, with large amounts of Ti-B and Fe
Since 20, 21, 22, and 24 have low elongation and an average aspect ratio of 1.3 or more, they are inferior in moldability and are likely to have a distorted pattern.

The conventional materials of Alloy Nos. 31 , 32 , and 33 had no bake hardenability and low elongation at break, and thus were inferior in strength-elongation balance.

As shown by the coordinates in FIG. 1, A (8.0,
0.25), B (4.0, 0.25), C (1.5,
0.8), D (1.5, 3.0), E (8.0, 1..
In the range surrounded by the five points (0), the strength and elongation balance
Is good, Mg than this range, the alloy number 12, 13 high amount of Cu has a low elongation, also, Mg than this range, Cu is low alloy number 11 is a strength conversely insufficient It was confirmed that the balance between strength and elongation was poor. one
On the other hand, as shown in FIG.
Good values are obtained in the range. Therefore, the strength and elongation
The reason that both the bounce and bake hardenability are good is that A
(4.0, 0.25), B (1.5, 0.8), C
(1.5, 3.0) and D (4.0, 2.23)
It was confirmed that the area was enclosed.

FIG. 2 shows the relationship between the amount of Si and CCV.
As shown in this figure, when the amount of Si was out of the range of the present invention (alloy Nos. 14 and 15 ), it was confirmed that the CCV characteristics were low and the formability was poor. (Example 2) Next, among the alloys shown in Table 1, an ingot having a composition of alloy number 3 was used, and an alloy sheet material was manufactured under the manufacturing conditions shown in Table 5. In addition, the conditions of Example 1 were adopted for the processing not particularly described in Table 5 (rolling conditions and the like). In addition,
Symbols A to E in Table 3 are examples within the range of the production method according to the present invention, and symbols F to M are comparative examples out of the range.

An evaluation test similar to that of Example 1 was performed on the plate material thus manufactured. The results are also shown in Table 5.

As is evident from Table 5, it was confirmed that Comparative Examples not satisfying the conditions of the present invention had insufficient elongation and moldability or bake hardenability.

For example, when the homogenizing treatment temperature, the intermediate annealing treatment temperature, or the solution quenching heating temperature is high as in Comparative Examples G, I, and L, the formability is inferior. When the cooling rate of solution quenching was low as in Comparative Example J or when the homogenization treatment temperature was low as in F, it was confirmed that the bake hardenability was poor. In Comparative Example M, in which the heating temperature for solution quenching was low, the average aspect ratio exceeded 1.3 and the elongation was low, so that the moldability was poor and a strain pattern was generated. In addition, since sufficient bake hardenability was not obtained, the balance between strength and elongation was low. In the case of Comparative Example K, in which the heating time of the solution quenching is long, and in the case of H, in which the heating rate in the solution quenching is small, abnormal grain growth occurs, the formability is poor, and a strain pattern is generated. confirmed.

[0044]

According to the present invention, the balance between strength and ductility, press formability, and bake hardening ability at the time of low-temperature and short-time coating baking are superior to those of conventional aluminum alloy sheets. Provided are an aluminum alloy sheet suitable for use in an automobile body sheet or the like which requires dent resistance after baking, and a method for producing the same.

[0045]

[0046]

[Table 2]

[0047]

[0048]

[Table 4]

[0049]

[Table 5]

[Brief description of the drawings]

FIG. 1 is a view showing ranges of contents of Mg and Cu.

FIG. 2 is a graph showing the relationship between Si content and CCV characteristics.

FIG. 3 is a graph showing the relationship between the Mg content and bake hardenability.

Continuation of the front page (72) Inventor Hiroshi Tsuchida 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Naotake Yoshiwara 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Shinji Mitao 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-2-118049 (JP, A) JP-A-2-118050 (JP, A JP-A-2-47234 (JP, A)

Claims (5)

(57) [Claims] 1. An amount of Mg of 1.5 to 3.9 % by weight,
u is 0.25 to 3.0%, Si is 0.02 to 0.15
%, Fe 0.03-0.25%, Ti 0.005-
0.15%, B in the range of 0.0002 to 0.05%, Zn in the range of 0.02 to 0.10%, and Mg and C
u sets the coordinate point of the Mg—Cu coordinates to (Mg
%, Cu%), as shown in FIG.
0.25), (1.5, 0.8), (1.5, 3..
0) and (4.0, 2.23), and the remainder is made up of Al and 0.1% or less inevitable impurities. The axial lengths of the crystal grains in the rolling direction are L and L. The average aspect ratio L / H is 1.3 or less when the axial length in the thickness direction perpendicular to the thickness is H, and the yield strength increases when a baking treatment is performed at 170 ° C. for 30 minutes. Is 3kg
/ Mm ² or more, an aluminum alloy sheet for press forming having excellent balance between strength and ductility and bake hardenability. 2. 0.01 to 0.15% of M by weight.
n, 0.01 to 0.15% Cr, 0.01 to 0.12
% Of Zr and 0.01 to 0.18% of V, further comprising one or two or more kinds of V. Excellent in balance between strength and ductility and bake hardenability according to claim 1. Aluminum alloy plate for press forming. 3. An amount of Mg of 1.5 to 3.9 % by weight,
u is 0.25 to 3.0%, Si is 0.02 to 0.15
%, Fe 0.03-0.25%, Ti 0.005-
0.15%, B in the range of 0.0002 to 0.05%, Zn in the range of 0.02 to 0.10%, and Mg and C
u sets the coordinate point of the Mg—Cu coordinates to (Mg
%, Cu%), as shown in FIG.
0.25), (1.5, 0.8), (1.5, 3..
0) and (4.0, 2.23). The range surrounded by the four points is 450 to 580 ° C. with respect to an aluminum alloy ingot consisting of Al and 0.1% or less inevitable impurities.
After performing one or more stages of homogenization at a temperature within the range described above, the ingot is subjected to hot rolling and cold rolling to a desired thickness, and then to a temperature within the range of 440 to 580 ° C. Heat at a heating rate of 3 ° C / sec or more,
Held for 120 seconds, the aluminum alloy plate an increase in yield strength when subjected to baking for 30 minutes at then cooled to 170 ° C. at a cooling rate of more than 2 ° C. / sec to 100 ° C. is 3 kg / mm ² or more A method for producing a press-formed aluminum alloy sheet having excellent strength-ductility balance and bake hardenability, characterized by being obtained. 4. The ingot of the aluminum alloy has a weight percentage of
, 0.01 to 0.15% Mn, 0.01 to 0.15%
% Cr, 0.01-0.12% Zr, and 0.01%
4. The aluminum alloy sheet for press forming according to claim 3, further comprising one or more of V of 0.18% to 0.18%, which is excellent in balance between strength and ductility and bake hardenability. Method. 5. 320 to 580 between hot rolling and cold rolling, or between cold rolling and cold rolling, or both.
5. The aluminum alloy sheet for press forming having excellent strength-ductility balance and bake hardenability according to claim 3 or 4, wherein the intermediate annealing treatment at a temperature in the range of ° C is performed once or twice or more. Production method.