JPH0633179A - Aluminum alloy sheet for press forming excellent in hardenability by high-temperature short-time baking and its production - Google Patents

Abstract

PURPOSE:To obtain the Al alloy sheet by adding Si to Al-Mg-Cu and allowing streaks to appear in an electron beam diffraction grating image after baking treatment under specific conditions. CONSTITUTION:An ingot of an Al alloy having a composition which consists of, by weight, 1.5-3.5% Mg, 0.3-1.0% Cu, 0.05-0.6% Si, and the balance Al and in which Mg/Cu is regulated to 2-7 is subjected to homogenizing treatment at 400-580 deg.C, hot-rolled, and cold-rolled to the desired sheet thickness. This sheet material is heated up to 500-580 deg.C at a rate of >=3 deg.C/sec, held at this temp. for 0-60sec, and cooled down to 100 deg.C at a rate of >=2 deg.C/sec. By this method, the Al alloy sheet where, in the electron beam diffraction grating image after baking treatment at 120-180 deg.C baking temp. for 5-40min baking time, a streaky modulation structure is allowed to appear in the position of the diffraction grating point of an Al-Mg-Cu compound can be obtained. Because this alloy sheet is reduced in strength before forming and excellent in delayed aging characteristic at ordinary temp., changes with the lapse of time before press forming can be prevented.

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 and a method for producing the same, and in particular, it has excellent bake hardenability even at a low temperature for a short time of 120 to 180 ° C. and a baking time of 5 to 40 minutes. The present invention relates to an aluminum alloy plate suitable for automobile bodies and the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, surface-treated cold-rolled steel sheets have been widely used as sheet materials for automobile body panels.
There is an increasing demand for weight reduction in order to improve the fuel efficiency of automobiles, and aluminum alloy sheets have begun to be used as sheet materials for automobile body panels to meet the demand.

In recent years, the demands of press working manufacturers have become strict, and the yield strength before pressing is low from the viewpoint of shape fixability (Automotive Technology Vol.45, No.6 (1991), 45), and yet deep. From the viewpoint of moldability such as drawing and overhanging and dent resistance, a material whose strength is improved by baking is demanded.

Therefore, among aluminum alloys, in particular, a non-heat treatment type Al—Mg alloy having excellent formability is added with Cu or Zn, and the strength is strengthened by age hardening. For example, an Al-Mg-Cu alloy (Japanese Patent Publication No. 62-42985, JP-A 1-22573).
8), Al-Mg-Cu-Zn based alloy (Japanese Patent Publication No. 56-3
1860) and so on. However, these are Al-Mg-S
Although it is superior in formability to the i-based alloy, it is inferior to the conventional surface-treated cold-rolled steel sheet and is also inferior in shape fixability because of its high strength before press forming. Furthermore, the hardening by the paint baking process is small, and it is only to the extent that the work hardening during pressing is not reduced. In particular, in Japanese Examined Patent Publication No. 62-42985, precipitation of an Al-Cu-Mg-based compound is attempted for the purpose of increasing the strength during coating baking, but it is still insufficient. In addition,
Conventionally, the effect of Si on bake hardening has not been recognized, so Si is regulated to a very small amount.

Further, the 5052-0 material which has been conventionally used as a material for body panels has low yield strength before press molding and is excellent in shape fixability, but has low strength due to lack of paint bake hardenability and dent resistance. There was a problem that it was inferior to.

Cu or Cu in the above Al-Mg system
Bake-hardening type alloys containing Zn and Zn are common,
After the final heat treatment, there is a problem of the change in strength before pressing due to room temperature aging (Sumilight Technical Report, 32, 1 (1991), 20, Japan Institute of Light Metals, 31st Symposium, page 31).
It is necessary to control the heat treatment period and the period until the actual press working.

One of the techniques for improving this problem is Al-
There is a Mg-Cu-Zn system in which aging is suppressed by lowering the amount of Zn, which largely controls room temperature aging (Japanese Patent Publication No. 4-69220).

However, although each alloy has a formability relatively close to that of a steel plate, it does not satisfy the bake hardenability or shape fixability, or undergoes room temperature aging.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is, firstly, an aluminum alloy for press forming which has good bake hardenability even at low temperature and in a short time. Secondly, it is to provide a plate and a method for producing the same, and secondly, an aluminum alloy plate for press forming which does not change with time before press forming because it further maintains the strength before press forming low and is excellent in room temperature delayed aging, and the same. It is to provide a manufacturing method.

[0010]

Means and Actions for Solving the Problems As a result of various studies conducted by the inventors of the present application to achieve the above object,
In the Al-Mg-Cu based alloy, the modulation structure G of the S'phase which is the precipitation phase of the Al-Cu-Mg based compound before the precipitation
It has been found that sufficient bake hardenability can be obtained when PB generation is promoted and streaks appear in an electron beam diffraction grating image. That is, the baking temperature 120 to 180
If a streak-like modulation structure is shown at the diffraction grating point position of the Al—Cu—Mg-based compound in the electron diffraction grating image after the baking treatment at a low temperature for a baking time of 5 to 40 minutes at ℃,
In this range, the bake hardenability in the low temperature and short time bake treatment becomes excellent. The present invention has been made based on such findings of the inventors of the present application. Al-Mg-C
It has a composition in which Si is added to the u system and has a baking temperature of 120 to 1
An electron beam diffraction grating image after baking treatment at 80 ° C. for 5 to 40 minutes shows a streaky modulation structure at a diffraction grating point position of an Al—Cu—Mg-based compound, and low temperature short time baking. The present invention provides an aluminum alloy plate for press molding having excellent curability.

The streak as described above is caused by Al--Mg--
It can be made to appear by adjusting the amount of Cu and Mg of the Cu-based alloy to a specific range and adding a specific amount of Si. Specifically, Mg is 1.5 to 3.5% by weight,
A composition containing Cu in an amount of 0.3 to 1.0%, Si in an amount of 0.05 to 0.6%, a Mg / Cu value of 2 to 7, and the balance being Al and inevitable impurities. In this case, the above configuration can be realized most effectively.

FIG. 1 shows an example of an electron diffraction grating image of the modulation structure of the S'phase, which is the precipitation phase of the Al-Cu-Mg compound, before the precipitation. FIG. 1 shows an Al (100) diffraction pattern, and streaks are observed at the diffraction grating point positions of the Al—Cu—Mg-based compound as indicated by the arrow. 2 is an electron beam transmission image, the modulation structure as shown in FIG. 1 is not recognized in FIG. That is, the above-mentioned modulation structure is so fine that it cannot be observed in an electron beam transmission image, and is different from a so-called precipitate. Since it is extremely fine as described above, it has a very strong reinforcing effect,
Therefore, it shows bake hardening.

From the viewpoint of delaying the room temperature aging of the Al-Mg-Cu alloy, 0.01 to 0.50% by weight of Sn is added to the above Al-Mg-Cu-based composition containing Si. , 0.01 to 0.50% Cd, 0.01 to 0.5
It is preferable that the composition further contains one or more selected from 0% In. That is, the bake hardening type aluminum alloy plate has a problem of room temperature aging in which the strength increases when left at room temperature, but the effect of room temperature aging is substantially caused by containing one or more of these. The normal temperature aging can be delayed to such an extent that it no longer exists.

In addition, 0.03 to 0.50% by weight relative to the composition in which Si is added to the Al-Mg-Cu system or the composition in which the above-mentioned room temperature aging retarding component is added.
Fe, 0.005-0.15% Ti, 0.0002
.About.0.05% B, 0.01 to 0.50% Mn, 0.
01-0.15% Cr, 0.01-0.12% Z
r, 0.01 to 0.18% V, and 0.5% or less Z
Even if one or more of n is further contained, the effect of the present invention is not impaired.

Furthermore, from the viewpoint of delaying the room temperature aging of the Al--Mg--Cu alloy, the Mg content is 1.5 to 3.5.
%, Cu 0.3 to 0.7%, Si 0.05 to 0.3
It is preferable that the range is 5% and the value of Mg / Cu is 2 to 7.

Next, the reasons for limiting the composition will be described.
In addition, all percentages indicate% by weight.

Mg: Mg is Al-Cu in the present invention.
-Mg-based modulation structure constituent element. However, if the content is less than 1.5%, the formation of the modulation structure is delayed, and the modulation structure does not form under the baking conditions of a baking temperature of 120 to 180 ° C. and a baking time of 5 to 40 minutes. Also, 1.5
If it is less than%, the ductility decreases. On the other hand, its content is 3.5
If it exceeds%, the formation of the modulation structure is also delayed, and the modulation structure is not formed under the baking conditions of a baking temperature of 120 to 180 ° C. and a baking time of 5 to 40 minutes. Therefore, the Mg content is preferably in the range of 1.5 to 3.5%.

Cu: Cu is Al-Cu in the present invention
-Mg-based modulation structure constituent element. However, if the content is less than 0.3%, no modulation structure is generated, while 1.0%
If it exceeds%, the corrosion resistance is significantly deteriorated. Therefore, the Cu content is preferably 0.3 to 1.0%. Further, when the Cu content exceeds 0.7%, an Al—Cu—Mg-based modulation structure is generated even at room temperature to increase the strength,
Change over time. In addition, the corrosion resistance is somewhat deteriorated. Therefore, from the viewpoint of room temperature delayed aging and corrosion resistance, 0.3 to 0.
7% is particularly desirable.

The ratio Mg / Cu of the content of Mg and the content of Cu is preferably in the range of 2 to 7. Within this range, an Al-Cu-Mg based modulation structure can be effectively generated.

FIG. 3 is a diagram showing the relationship between the Mg and Cu contents and the presence or absence of streaks due to electron beam diffraction. From this figure, if the contents of Mg and Cu are in the above range,
It is understood that streaks occur.

Si: Si is an element that promotes the formation of an Al--Cu--Mg type modulation structure to enhance the hardening ability and suppresses room temperature aging, and its content is 0.05 in order to exert its function. % Or more is desirable. On the other hand, when the content exceeds 0.6%, the above-mentioned modulation structure is generated, but on the other hand, a GP (1) modulation structure of Mg ₂ Si is generated, which promotes normal temperature aging and before baking. Since the strength of No. 2 increases remarkably with aging, the amount of bake hardening decreases rather. Therefore, the Si content is preferably 0.6% or less.

FIG. 4 shows the effect of the Si content on the bake hardening amount. This figure shows the case where the intermediate annealing was not performed in the production of the alloy sheet. The bake hardening amount is a value obtained by subtracting the yield strength before the treatment from the yield strength after the bake treatment. As shown in this figure, a high bake hardening amount is exhibited in the above range.

From the viewpoint of delaying the room temperature aging without generating the GP (1) modulation structure of Mg ₂ Si, the Si content is particularly preferably 0.35% or less.

FIG. 5 shows the effect of Si on room temperature aging and bake hardenability.
The effect of quantity is shown. From this figure, the Si amount is 0.05-0.
It can be seen that in the range of 35%, the room temperature aging is suppressed while maintaining the bake hardenability of about 5 kgf / mm ² or more.

The reasons for limiting the other components of these basic components are as follows.

Sn, In, Cd: These alloy components are elements that strongly bond with frozen atomic vacancies generated by quenching after solution treatment. Therefore, the number of atomic vacancies, which are the formation sites of the GPB zone of the Al-Cu-Mg-based compound, is reduced, and the aging at room temperature can be delayed. However, if the content of each of these is less than 0.01%, the effect cannot be exerted, and 0.50%
If it exceeds, the effect is saturated, the effect corresponding to the added amount cannot be obtained, and the cost becomes high.

FIG. 6 shows the effect of Sn on room temperature aging. From this figure, it can be seen that the addition of 0.05% or more of Sn delays the room temperature aging.

Fe: When the Fe content exceeds 0.50%, coarse crystallized substances which adversely affect the formability are likely to be produced due to the coexistence with Al, and are useful for producing a modulation structure in association with Si. And reduce the amount of Si. Therefore, F
The content of e is preferably 0.5% or less. However, adding a small amount contributes to the improvement of moldability,
If less than 0.03%, the effect cannot be obtained,
It is preferably 0.03% or more.

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 and improving the hot workability and the like. Therefore, it is important to add them together. However, if these are added excessively, coarse crystallized substances are generated and the formability is deteriorated.
Therefore, the content of Ti and B is in the range where the above effects can be effectively obtained, that is, 0.005 to 0.15%, respectively.
And 0.0002 to 0.05% is preferable.

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 are
Since they have a negative effect on the equiaxing of recrystallized grains and reduce the formability, their contents must be specified in a range smaller than that of conventional aluminum alloys. Therefore, when these are added, the contents of Mn, Cr, Zr, and V are 0.01 to 0.50% and 0.01 to 0.15, respectively.
%, 0.01 to 0.12%, and 0.01 to 0.18%
Stipulated in.

Zn: Zn is an element that contributes to the improvement of strength, but if it exceeds 0.5%, the bake hardening amount decreases. That is, if it exceeds 0.5%, a modulation structure in the pre-precipitation stage of the Al-Zn compound is generated, but this modulation structure is also generated at room temperature, and the strength before baking remarkably increases with aging. However, the amount of baking and hardening rather decreases. Therefore, even if Zn is added, 0.5
It is essential not to exceed%.

Further, Be is 0.0 as another element.
You may add up to 1%. Be is an element that prevents oxidation during casting, improves castability and hot workability, and improves the formability of the alloy sheet. However, if it exceeds 0.01%, not only is the effect saturated, but since it is a highly toxic element, it may harm the casting work environment, which is not preferable. Therefore, even when Be is added, the amount is specified up to 0.01%.

In addition to the above-mentioned 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. For example, even if each of Na and K is contained in an amount of 0.001% or less, there is no problem in characteristics.

Next, the manufacturing conditions for obtaining the alloy sheet of the present invention 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 homogenization treatment, diffusion solid solution of the eutectic compound crystallized during casting is promoted and local microsegregation is reduced. Further, by this treatment, it is possible to finely precipitate the compounds of Mn, Cr, Zr, and V that 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 400-580 ° C
And the range. Note that the holding time within this temperature range is 1
If the time is less than the above, the above-mentioned effect cannot be sufficiently obtained, and if the heating for a long time exceeding 72 hours is saturated, the effect is saturated.
The holding time of this homogenization treatment is preferably 1 to 72 hours.

Next, the ingot subjected to the homogenizing 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 subsequent heat treatment, or either 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 60
After being held for a period of not more than 2 seconds, heat treatment is performed under the condition of being rapidly cooled to 100 ° C. at a cooling rate of 2 ° C./second or more. This heat treatment is carried out in order to achieve solution hardening of Cu and Mg forming the modulation structure of the Al-Cu-Mg-based compound and to obtain sufficient bake hardening. In this case, if the heating temperature is less than 500 ° C., the above effect cannot be sufficiently obtained. Also, the heating temperature exceeds 580 ° C, the heating rate is less than 3 ° C / sec, and the holding time is 6
If it exceeds 0 seconds, some of the crystal grains are likely to cause abnormal grain growth. Further, if the cooling rate up to 100 ° C. is less than 2 ° C./sec, a coarse Al—Cu—Mg compound precipitates during cooling, which is not preferable because the bake hardenability is improved.

In addition to the above steps, after rolling to an intermediate plate thickness, the temperature in the range of 500 to 580 ° C. is 3 ° C. /
It is heated at a heating rate of 2 seconds or more, held at that temperature for 0 to 60 seconds, and then subjected to intermediate annealing in which it is cooled to 100 ° C. at a cooling rate of 2 ° C./second or more, and then within a range of rolling rate of 5 to 45%. It is preferable to apply cold rolling to obtain a desired plate thickness. By adding such a step, Al--Cu
-The generation of the modulation structure of the Mg-based compound is promoted, and the bake hardenability is increased.

FIG. 7 is a diagram showing the relationship between the intermediate plate thickness and the amount of bake hardening during intermediate annealing. The final plate thickness is 1.0 mm.
It shows the case where it is made constant. In addition to the intermediate plate thickness, the horizontal axis also shows the rolling ratio of cold rolling after intermediate annealing. Also in this figure, the bake hardening amount is a value obtained by subtracting the yield strength before the treatment from the yield strength after the bake treatment. As is clear from this figure, the final rolling rate is 5 to
By performing intermediate annealing with an intermediate plate thickness of 45%, the bake hardening amount becomes an extremely high value of about 7 kg / mm ² . If the final rolling rate is 5% or less, the formation of the modulation structure of the Al-Cu-Mg-based compound is not promoted, the bake hardenability is low, and abnormal grain growth may occur, impairing the formability. The conditions of this intermediate annealing are the same as the heat treatment conditions after rolling. When the heating rate and the cooling rate at this time are less than the lower limit values, coarse Al—Cu—Mg compounds are precipitated and the bake hardenability is reduced.

The aluminum alloy sheet thus obtained is excellent in curability by baking at low temperature for a short time, and is suitable for automobile body sheet.

[0041]

Embodiments of the present invention will be described below. Example 1 Alloys having the components and compositions shown in Tables 1 and 2 were melt-continuously cast, the obtained ingots were chamfered, and then 440 ° C. for 4 hours and 510 ° C. for 10 hours. Perform a two-stage homogenization treatment, then heat the slab to 460 ° C,
After hot rolling to a plate thickness of 4 mm and cooling to room temperature, cold rolling was performed to a plate thickness of 1.4 mm. After that, heating temperature 3 ℃
The intermediate annealing was carried out by heating to 550 ° C./sec, holding at that temperature for 10 seconds, and then forced air cooling to 100 ° C. at a cooling rate of 20 ° C./sec. Then, after cooling to room temperature, cold rolling was performed to a final plate thickness to obtain a plate 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.

The plate material thus produced was left at room temperature for one week, cut into a predetermined shape, and subjected to a tensile test (JIS No. 5,
Tensile direction: rolling direction) and conical cup test (JIS
Z2249: test tool type 17) was carried out. The conical cup test was carried out as a simulation of press molding, and the composite formability of overhanging and deep drawing was evaluated by CCV (mm) (the smaller the CCV, the better the formability). Also, in order to simulate baking coating after press molding, heat treatment at 170 ° C for 20 minutes (corresponding to baking)
After that, the tensile test was performed again under the same conditions as the above-mentioned test. Further, an electron microscope observation was performed.

The results of these tests are shown in Tables 3 and 4. The column of "bake hardening" shows a value obtained by subtracting the yield strength after the final heat treatment from the yield strength after the baking simulation. The presence / absence of streaks corresponding to the modulation structure of the Al-Cu-Mg-based compound is also shown.

The numbers 1 to 15 in Table 1 are within the composition range of claims 2 and 3 of the present invention, and the number 16 in Table 2 is
-30 is out of the range.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4] As is clear from Table 3, the numbers 1 to 15 have an elongation of 30.
%, The CCV was good, and it was confirmed that excellent moldability was obtained. In addition, by baking treatment, Al-Cu
It was confirmed that streaks corresponding to the modulation structure of the Mg-based compound were generated and the bake hardening had a high yield strength of 6.5 kgf / mm ² or more.

On the other hand, the numbers 16 to 30 shown in Table 2 are shown in Table 4.
As is clear from the above, either the moldability or the bake hardenability was insufficient. For example, the number 1 which has a low content of Mg, Si, or Cu, which is a component contributing to bake hardening,
6,18,20 or higher numbers 17,1
Nos. 9 and 21 did not show streaks in the electron beam diffraction after the baking treatment, and the bake hardenability was at most about 4 kgf / mm ² . Further, No. 25 having a high Zn has a bake hardenability of 2.4.
The value was as low as kgf / mm ² . Fe, Ti-B, Mn,
The numbers 22, 23, 24, 26, 27, 28, and 29 in which the amounts of Cr, Zr, and V were out of the preferable ranges had low moldability. Further, No. 30 in which Mg / Cu was out of the range of 2 to 7 had bake hardening of 3.6 kgf / mm ² . (Example 2) Here, using the same composition as the numbers 1 to 30 shown in Tables 1 and 2, except that the intermediate annealing is not performed,
The same test as in Example 1 was performed on the alloy plate manufactured under the same conditions as in Example 1. The results are shown in Tables 5 and 6. In Tables 5 and 6, the numbers 1'to 30 'are shown corresponding to the compositions similar to the numbers 1 to 30.

[0050]

[Table 5]

[0051]

[Table 6] As shown in Table 5, it was confirmed that Nos. 1 ′ to 15 ′ had a high elongation of 30% or more like Nos. 1 to 15. In addition, the streak corresponding to the modulation structure of the Al-Cu-Mg-based compound is generated by the baking treatment, and the bake hardening is lower than that with the intermediate annealing, but the yield strength is as high as 5.2 kgf / mm ² or more. It was confirmed to have.

Also, as shown in Table 6, it was confirmed that the bake hardenability of Nos. 16 'to 30' was slightly lower than that of Nos. 16 to 30. (Example 3) Next, among the alloys shown in Table 1, an ingot having a composition corresponding to No. 1 was used to produce an alloy plate material under the production conditions shown in Table 7. The conditions of Example 1 were adopted for the treatments not particularly described in Table 7 (rolling conditions, etc.). The results of the same evaluation test as in Example 1 are also shown in Table 7. In Table 7, symbols A to E are within the range of the manufacturing method according to the present invention, and symbols F to L are out of the range.

The same evaluation test as in Example 1 was conducted on the plate material thus manufactured. The results are also shown in Table 7.

[0054]

[Table 7] As is apparent from Table 7, it was confirmed that symbols F to L that do not satisfy the conditions of the present invention have insufficient elongation and moldability, or bake hardenability.

For example, when the homogenization temperature and the heat treatment temperature are high as in Comparative Examples F, G, I, and J, or the cold rolling rate after the intermediate annealing is low, and the heating rate of the heat treatment is small, it is abnormal. Grain growth occurs, resulting in poor elongation and moldability. In addition, as in H, the cold rolling rate after intermediate annealing is high,
When the cooling rate under the solution hardening condition is low as in L, the electron diffraction pattern shows Al-Cu-Mg.
The streak corresponding to the modulation structure of the compound does not appear,
Inferior to bake hardenability. Further, when the heating and holding temperature of the solution quenching condition is low as in the case of K, the elongation is low and the formability is poor, and sufficient bake hardening cannot be obtained. (Example 4) In this example, ingots having a composition corresponding to No. 1 were used, and no intermediate annealing was performed.
An alloy plate was manufactured under the same conditions as for L, and the same test as in Example 3 was performed. The results are shown in Table 8. In Table 8, the symbols A to L are indicated by A'to L '.

[0056]

[Table 8] As shown in Table 8, it was confirmed that all of the symbols A ′ to E ′ were still inferior in bake hardenability to A to E, but still showed high values. The symbols F ′ to L ′ also showed a slightly lower bake hardenability than F to L. (Example 5) In this example, an alloy plate having the same composition as No. 1 in Table 1 and manufactured under the condition of symbol A'in Table 8 was used.
Tests were performed on the characteristics after baking when the baking conditions were changed. The results are shown in Table 9 and FIG.

[0057]

[Table 9] As is clear from these, the baking temperature of 120 to 180
℃, baking time 5-40 minutes Al-
It was confirmed that streaks corresponding to the modulation structure of the Cu-Mg-based compound were generated, and high bake hardenability was exhibited. (Embodiment 6) In this embodiment, basically Sn, In, C
The test was conducted on the one to which d was added.

Alloys having the components and compositions shown in Tables 10 and 11 were made into a plate material having a thickness of 1 mm under the same conditions as in Example 1, and heat treatment was performed under the same conditions as in Example 1.

After this heat treatment, it was left at room temperature for 1 day and left for 60 days in order to investigate the influence of normal temperature aging, cut into a predetermined shape, and subjected to a tensile test and a conical cup test as in Example 1. Further, similarly to Example 1, the bake coating after press molding was simulated to grasp the bake hardenability. Further, an electron microscope observation was performed.

The results are shown in Tables 12 and 13.

The numbers 31 to 46 in Table 10 are within the composition range of claims 4 and 5 of the present invention, and the numbers 47 to 61 in Table 11 are out of the range.

[0062]

[Table 10]

[0063]

[Table 11]

[0064]

[Table 12]

[0065]

[Table 13] As is clear from Table 12, it was confirmed that Nos. 31 to 46 had an elongation of 30% or more, a good CCV, and excellent moldability. Also, due to the baking treatment, Al-
It was confirmed that streaks were generated corresponding to the modulation structure of the Cu-Mg-based compound, and the bake hardening had a high yield strength of 6.5 kgf / mm ² or more. Furthermore, the yield strength is 0.5 kgf at most even after it is kept at room temperature for 60 days.
It was confirmed that the aging was delayed only at about / mm ² and the room temperature aging was delayed.

On the other hand, as is clear from Table 13, the numbers 47 to 61 shown in Table 11 were insufficient in formability, bake hardenability, and room temperature delayed aging. For example, the numbers 47, 49, 51 having a low content of Mg, Si, or Cu, which are components contributing to bake hardening, or the numbers 48, 50 having a high content thereof show streaks in the electron beam diffraction after the baking treatment. However, the bake hardenability was at most about 4 kgf / mm ² . Moreover, Si, Cu, and Zn are high numbers 50,
It was confirmed that 52, 55 or No. 60, which has a low Sn, In, Cd content, increased the yield strength by 5 kgf / mm ² or more by holding it at room temperature for 60 days, and the aging at room temperature was remarkable.

As in the first embodiment, Fe, Ti-
The amounts of B, Mn, Cr, Zr, and V deviate from the preferable ranges. Numbers 53, 54, 56, 57, 58, and 59 have low moldability, and Mg / Cu deviates from the range of 2 to 7. The number 61 had bake hardening of 3.6 kgf / mm ² . (Example 7) Next, among the alloys shown in Table 10, No. 3
Using an ingot having a composition corresponding to No. 1, alloy plate materials were manufactured under the manufacturing conditions shown in Table 14. Note that the conditions of Example 6 were adopted for the treatments not particularly described in Table 14 (rolling conditions, etc.). The results of the same evaluation test as in Example 6 are also shown in Table 14. The symbols M to Q in Table 14 are within the range of the manufacturing method according to the present invention, and the symbols R to
X is outside the range.

The plate material thus manufactured was subjected to the same evaluation test as in Example 6. The results are also shown in Table 14.

[0069]

[Table 14] As is clear from Table 14, it was confirmed that symbols R to X that do not satisfy the conditions of the present invention have insufficient elongation and moldability, or bake hardenability.

For example, when the homogenization temperature and the heat treatment temperature are high like R, G, U and V of the comparative example, or the cold rolling rate after the intermediate annealing is low, and the heating rate of the heat treatment is small, it is abnormal. Grain growth occurs, resulting in poor elongation and moldability. In addition, as in T, the cold rolling rate after the intermediate annealing is high,
When the cooling rate under the solution hardening condition is low like X, the electron diffraction pattern shows Al-Cu-Mg.
The streak corresponding to the modulation structure of the compound does not appear,
Inferior to bake hardenability. Further, when the heating and holding temperature of the solution quenching condition is low like W, the elongation is low and the formability is poor, and sufficient bake hardening cannot be obtained. (Example 8) In this example, Mg: 1.5 to 3.5.
%, Cu: 0.3 to 0.7%, Si: 0.05 to 0.3
The effect prescribed to 5% was grasped. Of the alloys already mentioned,
Alloy Nos. 1, 4, 6 included in this range and Alloy Nos. 5, 7 deviating from this range were made into a plate material having a thickness of 1 mm under the same conditions as in Example 1, and heat treated under the same conditions as in Example 1. I went.

After this heat treatment, it was left for 1 day at room temperature and left for 30 days and 90 days in order to investigate the influence of room temperature aging, and a tensile test and a conical cup test were carried out as in Example 1. Table 15 shows the results.

[0072]

[Table 15] As is clear from Table 15, the numbers 1, 4, and 6 included in the above composition range were retained at room temperature for 90 days,
There is almost no increase in yield strength, and CC
It was also confirmed that V was also excellent and that the room temperature aging was delayed.

On the other hand, the numbers 5 and 7 out of the above composition range
It was confirmed that the yield strength increased and the formability also decreased with the number of days kept at room temperature.

[0074]

According to the present invention, an aluminum alloy sheet for forming which has a good bake hardenability even at low temperature and for a short time, and a method for producing the same, and further, the strength before press forming is kept low and the temperature is slow at room temperature. Provided are an aluminum alloy sheet for press forming and a method for producing the same, which is excellent in aging property and does not change with time before press forming. This aluminum alloy plate is suitable for automobile bodies.

[Brief description of drawings]

FIG. 1 is a photograph showing a crystal structure of an aluminum alloy plate according to the present invention.

FIG. 2 is a photograph showing a metallographic structure of an aluminum alloy plate according to the present invention.

FIG. 3 is an electron diffraction grating image showing Al-Cu-Mg.
The figure which shows the influence of Mg and Cu on the generation | occurrence | production of the streak corresponding to the modulation | alteration structure of a system compound.

FIG. 4 is a diagram showing the effect of Si on the bake-hardening amount.

FIG. 5 is a diagram showing the influence of Si on the bake hardening amount and the room temperature aging amount.

FIG. 6 is a diagram showing the effect of Sn on room temperature aging.

FIG. 7 is a diagram showing the effect of the rolling ratio after intermediate annealing on the bake hardening amount.

FIG. 8 is a diagram showing a relationship between baking temperature and time and Vickers hardness after baking.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masataka Suga 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (15)

[Claims] 1. A composition having a composition in which Si is added to an Al—Mg—Cu system, a baking temperature of 120 to 180 ° C., and a baking time of 5
In the electron beam diffraction grating image after the baking treatment for -40 minutes, the streak-like modulation structure was exhibited at the diffraction grating point position of the Al-Cu-Mg-based compound, which was excellent in the curability by the low temperature short time baking. Aluminum alloy plate for press forming. 2. Mg is 1.5 to 3.5% by weight, and C
u is included in the range of 0.3 to 1.0%, Si is included in the range of 0.05 to 0.6%, the value of Mg / Cu is 2 to 7, and the balance is Al and inevitable impurities. An aluminum alloy plate for press forming which is excellent in curability by low temperature short time baking according to claim 1. 3. 0.01 to 0.50% S by weight.
n, 0.01 to 0.50% Cd, 0.01 to 0.50
The aluminum alloy plate for press forming having excellent curability by low temperature short time baking according to claim 2, further containing one or two or more selected from In. 4. 0.03 to 0.50% by weight of F
e, 0.005 to 0.15% Ti, 0.0002 to
0.05% B, 0.01-0.50% Mn, 0.0
1 to 0.15% Cr, 0.01 to 0.12% Zr,
Curing by low temperature short-time baking according to claim 2 or 3, further comprising one or more of 0.01 to 0.18% V and 0.5% or less Zn. Aluminum alloy plate for press forming with excellent properties. 5. A Mg content of 1.5 to 3.5% and a C content of C.
u is included in the range of 0.3 to 0.7%, Si is included in the range of 0.05 to 0.35%, the value of Mg / Cu is 2 to 7, and the balance is Al and inevitable impurities. An aluminum alloy plate for press forming which is excellent in curability by low temperature short time baking according to claim 1. 6. 0.01 to 0.50% S by weight.
n, 0.01 to 0.50% Cd, 0.01 to 0.50
The aluminum alloy plate for press forming having excellent curability by low temperature short time baking according to claim 5, further containing one or more selected from In. 7. 0.03 to 0.50% by weight of F
e, 0.005 to 0.15% Ti, 0.0002 to
0.05% B, 0.01-0.50% Mn, 0.0
1 to 0.15% Cr, 0.01 to 0.12% Zr,
Hardening by low temperature short time baking according to claim 5 or 6, further comprising one or more of 0.01 to 0.18% V and 0.5% or less Zn. Aluminum alloy plate for press forming with excellent properties. 8. The weight percentage of Mg is 1.5 to 3.5%, and C
Aluminum containing u in an amount of 0.3 to 1.0%, Si in an amount of 0.05 to 0.6%, a Mg / Cu value of 2 to 7, and the balance Al and inevitable impurities. The alloy ingot is subjected to a one-stage or multi-stage homogenization treatment at a temperature in the range of 400 to 580 ° C., and then this ingot is hot-rolled and cold-rolled to a desired plate thickness, Then 50
It is heated to a temperature in the range of 0 to 580 ° C. at a heating rate of 3 ° C./sec or more and held at that temperature for 0 to 60 seconds, and then 1
A method for producing an aluminum alloy sheet for press forming which is excellent in hardenability by low temperature short time baking, which comprises cooling to 00 ° C at a cooling rate of 2 ° C / sec or more. 9. The aluminum alloy ingot has a weight% of
, 0.01 to 0.50% Sn, 0.01 to 0.50
% Cd and 0.01 to 0.50% In selected from the group of 1 or 2 or more, and the press excellent in curability by low temperature short time baking according to claim 8. Manufacturing method of aluminum alloy sheet for forming. 10. The ingot of the aluminum alloy is 0.03 to 0.50% Fe, and 0.005 to 0.
15% Ti, 0.0002-0.05% B, 0.0
1 to 0.50% Mn, 0.01 to 0.15% Cr,
One or two or more of 0.01 to 0.12% Zr, 0.01 to 0.18% V, and 0.5% or less Zn are further contained. 8. A method for producing an aluminum alloy plate for press forming, which is excellent in curability by low temperature short time baking according to 8 or 9. 11. After rolling to an intermediate plate thickness before being rolled to the desired plate thickness, it is heated to a temperature in the range of 500 to 580 ° C. at a heating rate of 3 ° C./sec or more and 0 at that temperature. ~
Hold for 60 seconds, then perform intermediate annealing of cooling to 100 ° C. at a cooling rate of 2 ° C./second or more, and then roll rate 5 to 5
Aluminum for press forming excellent in hardenability by low temperature short time baking according to any one of claims 8 to 10, wherein cold rolling is performed within a range of 45% to obtain a desired plate thickness. Method for manufacturing alloy plate. 12. Mg is 1.5 to 3.5% by weight,
Cu 0.3-0.7%, Si 0.05-0.35%
Contained in the range of and the value of Mg / Cu is 2 to 7,
1 at a temperature in the range of 400 to 580 ° C. with respect to an ingot of an aluminum alloy in which the balance is Al and unavoidable impurities
After the 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. Aluminum alloy for press forming, which is excellent in hardenability by low-temperature short-time baking, characterized by being heated at a rate, kept at that temperature for 0 to 60 seconds, and then cooled to 100 ° C at a cooling rate of 2 ° C / second or more. Method of manufacturing a plate. 13. The ingot of the aluminum alloy is 0.01 to 0.50% Sn, 0.01 to 0.5% by weight.
The curability according to the low temperature short time baking according to claim 12, further comprising one or more selected from 0% Cd and 0.01 to 0.50% In. A method for manufacturing an aluminum alloy sheet for press forming. 14. The aluminum alloy ingot has a weight percentage of 0.03 to 0.50% Fe and 0.005 to 0.
15% Ti, 0.0002-0.05% B, 0.0
1 to 0.50% Mn, 0.01 to 0.15% Cr,
One or two or more of 0.01 to 0.12% Zr, 0.01 to 0.18% V, and 0.5% or less Zn are further contained. 12 or 13
A method for producing an aluminum alloy sheet for press forming, which has excellent hardenability by baking at low temperature for a short time. 15. After rolling to an intermediate plate thickness before being rolled to the desired plate thickness, it is heated to a temperature in the range of 500 to 580 ° C. at a heating rate of 3 ° C./sec or more and 0 at that temperature. ~
Hold for 60 seconds, then perform intermediate annealing of cooling to 100 ° C. at a cooling rate of 2 ° C./second or more, and then roll rate 5 to 5
Aluminum for press forming excellent in hardenability by low temperature short time baking according to any one of claims 12 to 14, wherein cold rolling is performed within a range of 45% to obtain a desired plate thickness. Method for manufacturing alloy plate.