JPH07166285A - Hardened al alloy sheet by baking and production thereof - Google Patents

Abstract

PURPOSE:To obtain a material excellent in strength, formability, and low temp. baking hardenability by specifying a composition and a structure, respectively. CONSTITUTION:This alloy has a composition containing, by weight ratio, 0.2-1.0% Mg and 0.5-2.0% Si, having Si content in excess of the content of Mg constituting Mg2Si and containing 0.35-1.5% Mg2Si and 0.35-1.2% residual Si, further containing 0.5-2.0% Cu and 0.05-0.50% Mn, and having the balance Al. Moreover, this sheet has a structure consisting of equiaxed particles of <=35mum crystalline grain size. This alloy sheet can be produced by subjecting an ingot to homogenizing treatment and to hot rolling, subjecting the resultant hot rolled plate to annealing consisting of heating up to 450-520 deg.C at a rate of 300 deg.C/min, holding for 0-10sec, and cooling at a rate of >=300 deg.C/min, applying cold rolling, and then subjecting the resultant cold rolled sheet to solution heat treatment, hardening down to 50-120 deg.C at >=300 deg.C/min cooling rate, and holding for 1-48hr. Baking finish of this alloy sheet is done by applying holding at 150-200 deg.C for 5-120min, and beta'-Mg2Si is age-precipitated by 10-45% by volume percentage of matrix.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a bake-hardenable Al alloy sheet which is excellent in moldability or moldability and has reduced room temperature aging, and a method for producing the same. , Al alloy plate materials used for panel materials for automobiles, home appliances, machine parts, etc., with excellent formability during processing such as pressing or bending, and for a short time such as baking coating (baking) in these manufacturing processes The present invention relates to a bake hardenable Al alloy plate having improved strength in heat treatment and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, Al alloy sheets, which have been mainly used for the purpose of reducing the weight of automobiles, home appliances, machine parts, etc., are subjected to molding such as pressing or bending, and in the coating process after processing. Heat treatment (baking coating, baking) is performed to give strength to the coating film. A method of improving the strength of the Al alloy plate by utilizing the heating temperature at that time is performed.

Such an Al alloy plate has low strength during forming such as pressing and is easy to form. On the other hand,
After molding, it is ideal that the strength of the material is remarkably improved by the heat treatment of baking coating.
A g-Si based aluminum alloy is used. As described above, regarding the Al alloy, JP-A-11-11851 has been proposed.

However, in the Al--Mg--Si type aluminum alloy and the manufacturing method thereof which have been conventionally used for this type of application, T4 is emphasized due to the importance of formability or shape fixability.
The strength in the state is extremely low, and further, even if the strength is improved after bake hardening, sufficient strength cannot be obtained, and there is a problem that it is deformed only by applying a slight external force.

On the other hand, the weight of automobile parts tends to be further reduced due to the regulation of low fuel consumption of automobiles.
As a result, it is required to reduce the thickness of the Al alloy plate. However, in the conventional Al alloy plate and the manufacturing method thereof, if the material strength in the T4 state is lowered and the formability is improved, the above problem occurs, or Therefore, when the material strength is increased, there is a problem that the formability is remarkably deteriorated.

Further, the recent baking conditions for baking coating are diversification of parts such as increase in parts that cannot be processed at high temperature such as resin in order to save energy and improve productivity.
The temperature has been decreasing due to the progress of paints. For example, the baking temperature of an Al alloy used for automobile parts is
Conventionally, it was about 200 ° C, but in recent years, it is 150-170 ° C.
It is designed to be processed at low temperatures. But conventionally,
In the Al-Mg-Si based aluminum alloy plate and the manufacturing method thereof, a manufacturing method for improving the bake hardenability by such low temperature and short time treatment has been proposed. The alloy has a drawback that the formability is remarkably reduced. Therefore, in order to cope with this low temperature baking coating treatment, JP-A-62-8985.
No. 2 is proposed.

[0007] However, in these proposals, when left at room temperature, the strength is increased, the springback amount after the processing is increased, and the formability is significantly deteriorated. For this reason, if left for several months after manufacturing, pressing becomes difficult, and under the pressing conditions immediately after manufacturing, a processed shape cannot be obtained or molding becomes impossible.

The present invention has been made in view of the above problems, and has a high material strength corresponding to a reduction in thickness accompanying a reduction in weight and a sufficient baking under the baking conditions of low temperature / short time baking coating. Provided are a bake-hardenable Al-Mg-Si-Cu-Mn-based Al alloy plate which has excellent moldability as well as hardenability and which has excellent moldability with suppressed aging at room temperature, and a method for producing the same. The purpose is to

[0009]

The bake hardenable Al alloy sheet according to the present invention has Mg: 0.2 to 1.0% and Si: 0.5.
In the range of up to 2.0%, Mg constituting Mg ₂ Si
On the other hand, the composition is excessive in Si, and Mg and Si are Mg ₂ S.
The i content is 0.35 to 1.5%, the remaining Si content is 0.35 to 1.2%, and Cu: 0.
5 to 2.0% and Mn: 0.05 to 0.50%, the balance consisting of Al and inevitable impurities, the structure of the plate material having a crystal grain size of 35 μm or less, and the surface and cross section of the plate. The tissue is characterized by equiaxed grains.

Another bake-hardenable Al alloy plate according to the present invention is Mg: 0.3-1.0%, Si: 0.5-1.
In the range of 4%, the content of Si is excessive with respect to Mg constituting Mg ₂ Si, Mg and Si are contained in an amount of 0.9 to 1.1% as the amount of Mg ₂ Si, and the residual amount of Si is 0.6-1.2%, Cu: 0.5-1.0
% And Mn: 0.05 to 0.50%, the balance A
1 and unavoidable impurities, and the structure of the plate material has a crystal grain size of 35 μm or less, and the structure of the surface and cross section of the plate is equiaxed grains.

These bake hardenable Al alloy plates are further
Zr: 0.3% or less, Cr: 0.3% or less, Ti: 0.
You may contain 1 type or 2 types or more selected from the group which consists of 1% or less and Fe: 0.3% or less.

The method for producing a bake-hardenable Al alloy sheet according to the present invention is an Al-containing alloy having any of the above chemical components.
A step of homogenizing the alloy ingot at a temperature not higher than the burning temperature, a step of hot rolling, a heating rate of 300 ° C./min or more, a temperature of 450 to 520 ° C. maintained for 0 to 10 seconds, and a cooling rate. A step of annealing treatment for cooling at 300 ° C./min or more, a step of cold rolling to a desired plate thickness, a step of solution treatment, and a cooling rate of 300 ° C./min or more for 50 to 12
Quenching to a temperature of 0 ° C. and holding at a temperature of 50 to 120 ° C. for 1 to 48 hours within 5 minutes.

The temperature of 50 to 120 ° C. is 1 to 4
As a post-step of the step of holding for 8 hours, baking coating (baking treatment) is performed under the condition of holding at a temperature of 150 to 200 ° C. for 5 to 120 minutes, and the aged precipitate β′-Mg ₂ Si is contained in the matrix in a total volume content. A step of precipitating in the range of 10 to 45% may be provided.

[0014]

The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, have found that the strengthening mechanism of the conventional Al-Mg-Si alloy is based on the following age hardening mechanism. . S. S. (Solid solution) → G. P. Zone (T
4 state) → β'-Mg ₂ Si (after baking coating).

That is, the mechanism for increasing the strength of the material is due to this aging precipitate, and in the manufacturing method for increasing the bake hardenability in the low temperature and short time bake coating treatment, the strength of the material in the T4 state is Therefore, the moldability is significantly reduced. Therefore, if the amounts of Mg and Si are not appropriate, it is difficult for both the relationship between strength and formability to take good values. Therefore, the main mechanism of strengthening is the aging precipitate β'-
It has been found that a mechanism dependent on Mg ₂ Si is not desirable.

On the other hand, A known as 6009 and 6010
The 1-Mg-Si based alloy is an alloy to which Cu is added,
The aging precipitate θ′-CuAl ₂ is precipitated to increase the strength. Further, Cu has the effect of increasing the density and densification of the aging precipitate β′-Mg ₂ Si of the Al—Mg—Si alloy, improving the bake hardness, and further uniformly deforming the deformation mechanism. Therefore, it was found that it is desirable to make the main mechanism for strengthening the mechanism dependent on the aging precipitate β′-Mg ₂ Si.

Further, it has been found that by using Mn as a main additive element, recrystallization is suppressed and the crystal grain size is 35 μm or less, whereby high formability can be obtained.

Regarding the room temperature aging property, as described above, when the conventional Al--Mg--Si alloy is manufactured by a method for obtaining a high bake hardness at a low temperature, the change with time at room temperature is remarkable, and If left for several months, the strength increases, the springback amount increases, and the moldability remarkably deteriorates. This is a quenching treatment after solution heat treatment in order to bake harden at a low temperature, and a precipitation nucleus is generated in the matrix, and this precipitation nucleus grows in the low temperature and short time treatment, and becomes an aged precipitate. , Utilizes a mechanism to increase strength. As a result, it was found that this precipitate reacts sensitively to temperature and grows even at room temperature, resulting in an increase in strength, an accompanying increase in the amount of springback, and a decrease in formability.

To solve this problem, addition of Cu and Mg
It was found that normal temperature aging in the T4 state can be suppressed by controlling the amount of ₂ Si within a certain range.

The present invention has been completed as a result of further detailed research on the components and manufacturing conditions thereof based on the above findings.

The present invention will be described in more detail below. First, the reason for adding the components and the reason for limiting the composition in the present invention will be described. Mg Mg is an element that imparts strength to the solid solution strengthening itself and cooperates with Si, and precipitates an aging precipitate β′-Mg ₂ Si, and this amount depends on the added amount of Mg. But 0.2
If it is less than%, sufficient strength (hereinafter, strength means material and 17
Yield strength after baking at 0 ° C) is not obtained, and
If more than 1.0% is added, the equilibrium phase Mg ₂ Si
Grows as a crystallized product, and a decrease in elongation is observed, resulting in a marked decrease in formability. Therefore, the Mg content is 0.
The range is 2 to 1.0%.

Si Si mainly cooperates with Mg, and is mainly aged precipitate β′-Mg ₂ S.
It is an element strongly imparted by precipitation hardening due to precipitation of i, and this amount depends on the addition amount. However, if it is less than 0.5%, sufficient strength cannot be obtained, and if it exceeds 2.0%, the equilibrium phase M
g ₂ Si is crystallized and elongation is greatly reduced, resulting in deterioration of formability. Therefore, the Si content is set to the range of 0.5 to 2.0%.

However, regarding the relationship between Mg and Si, M
When the content of Si is excessive with respect to g, Mg and Si are Mg
_{2 The} amount of Si must be 0.35 to 1.5, and the amount of residual Si must be 0.35 to 1.2%.

That is, the strength and formability depend on the added amounts of Mg and Si, and it is the β'-Mg ₂ Si produced by these that contributes to the strength and strength increase in baking coating. However, if the amount of Mg ₂ Si is less than 0.35%, the strength is very low, and there is almost no bake hardenability.
If it exceeds 1.5%, the elongation is lowered and the formability is remarkably lowered. Therefore, the amount of Mg and Si is 0.3 as Mg ₂ Si.
The range is 5 to 1.5%. Furthermore, if Si is added excessively with respect to Mg, S that remains without being formed as Mg ₂ Si
i is present as residual Si, which has the effect of increasing the formability. Moreover, if this residual Si is in solid solution in the T4 state, the strength increases due to solid solution hardening. However, the remaining Si
Is less than 0.35%, sufficient strength cannot be obtained.
If it exceeds 2%, the strength increases and the formability deteriorates. Therefore, the residual Si amount is set to a range of 0.35 to 1.2%. Considering the amount of Mg ₂ Si and the amount of residual Si, the amounts of Mg and Si are properly mixed.

Mn Mn is similar to Cu in that MnAl ₆ precipitates as a second phase precipitate and can be sufficiently solution-treated to form a solid solution to increase the strength and suppress recrystallization of the alloy structure. This has the effect of refining the crystal grains. Therefore, it is an element imparted to the improvement of molding. However, if it is less than 0.05%, the grain refining effect does not appear, and the second phase precipitate MnAl
_Since the precipitation of ₆ is not remarkable, no improvement in molding processability is observed. Further, if the content exceeds 0.50%, coarse crystallized substances are formed, and the formability is lowered. Therefore, the Mn content is set to a range of 0.05 to 0.50%. By adding Mn in this range, the crystal grain becomes 35 μm or less even if the solution treatment is sufficiently performed and the material strength is increased.
No deterioration in moldability is observed.

Cu Cu is an element that imparts strength by the aging precipitate θ′-CuAl ₂ . In the present invention, the increase in strength is β′-Mg ₂
Not only due to Si (after baking coating), but also due to addition of Cu, this aging precipitate β ′ becomes dense and fine, thereby improving strength and bake hardenability at low temperature baking. However, if Cu is less than 0.5%, sufficient strength cannot be obtained during low temperature baking, and if it exceeds 2.0%, θ ′
-CuAl ₂ precipitation increases, and this θ'-CuA
Since the precipitate of l ₂ grows at room temperature, the strength increases with the lapse of time, and the elongation and the formability decrease accordingly. Therefore, the Cu content is in the range of 0.5 to 2.0%. When Cu is added within this range, β′-Mg ₂ is added as described above.
Si (after baking coating) is made dense and fine, and has the effect of improving strength, and also has the effect of improving the formability because the deformation mechanism of the Al-Mg-Si alloy is uniformly deformed.

In the present invention, by adjusting the above-mentioned components, it is possible to obtain a high material strength corresponding to the thinning, a sufficient bake hardenability in a low temperature and a short time bake coating, and an excellent moldability. In order to suppress the normal temperature aging property, the following component composition is preferable.

That is, Mg: 0.3 to 1.0%, Si:
In a range of 0.5 to 1.4%, the composition of Mg ₂ Si is excessive with respect to Mg constituting Mg ₂ Si, and Mg and Si are M.
The content of g ₂ Si is 0.9 to 1.1%, and the residual Si content is 0.6 to 1.2%.
5 to 1.0% and Mn: 0.05 to 0.50%, and if necessary, further Zr: 0.3% or less, Cr:
The composition contains one or more of 0.3% or less, Ti: 0.1% or less, and Fe: 0.3% or less, with the balance being Al and impurities. The reason is as follows.

As described above, Cu is an aging precipitate θ'-C.
It is an element that gives strength by uAl ₂ . However, in the present invention, the increase in strength is almost due to β'-Mg ₂ Si, and the effect of Cu addition is that the aging precipitates are made dense and fine to improve the strength and bake hardenability by low temperature baking. Is to improve. Furthermore, the addition of Cu has the effect of suppressing the room temperature aging. As shown in Examples described later, the addition range of Cu is 0.5 to 1 for both strength and formability.
It was found that at 0%, the room temperature aging property was drastically suppressed. However, if it is less than 0.5%, the effect of increasing the strength and suppressing the room temperature aging is not recognized, and if it exceeds 1.0%, the precipitation of θ′-CuAl ₂ increases, and this θ ′
Precipitate -CuAl ₂ lowers the elongation and formability, further corrosion resistance is degraded. Therefore, the Cu content is 0.5 to 1.
The range is 0%.

Further, in order to suppress the increase in strength due to normal temperature aging and the deterioration of formability accompanying it, the lower limit of Mg is set to 0.
3%, the upper limit of Si is 1.4%, and Mg ₂ Si
Content of 0.9 to 1.1% and residual Si content of 0.6 to 1.
2%

In the present invention, Al-Mg-Si-
The Cu-Mn alloy is the above-mentioned Mg, Si, Cu and Mn.
If is an essential component, the effect can be sufficiently obtained, but other elements can be added as necessary or acceptable as impurities so long as the effect of the present invention is not impaired. In particular, Zr: 0.
3% or less, Cr: 0.3% or less, Ti: 0.1% or less,
Fe: If one or more of 0.3% or less is contained, the moldability is improved.

Here, Cr forms an intermetallic compound, and the finely divided compound suppresses recrystallization and makes the crystal grains finer and has the effect of improving the formability, but is added in excess of 0.3%. Then, it grows as a coarse intermetallic compound, which causes a remarkable decrease in elongation and a sharp deterioration in formability. Therefore,
The Cr addition amount is preferably 0.3% or less.

Zr forms an intermetallic compound similar to Cr, and the finely divided compound suppresses recrystallization and makes the crystal grains finer, which is effective for improving the formability, but exceeds 0.3%. If it is added as a compound, it grows as a coarse intermetallic compound, which causes a remarkable decrease in elongation and a sharp deterioration in formability. Therefore, the amount of Cr added is preferably 0.3% or less.

Ti is an element which makes the crystal grains of the ingot finer and improves the formability, but when it is contained in excess of 0.1%, coarse crystallized substances are formed and the formability is lowered. Therefore, the Ti content is preferably 0.1% or less.

Fe has a small effect of improving strength, but 0.3%
If it exceeds, crystallized substances are remarkably generated, which causes coarsening and further coarsens the crystal grains. These significantly reduce the moldability. Therefore, the Fe content is 0.
3% or less is desirable.

Next, the manufacturing conditions of the present invention will be described.

The above Al-Mg-Si-Cu-Mn-based aluminum alloy is melted, cast, homogenized, heat-rolled and hot-rolled by a conventional method, and after hot-rolling, an annealing treatment is performed to control the structure.

However, in the present invention, by performing this annealing, the precipitates in the alloy are finely and uniformly dispersed,
By suppressing recrystallization, there is an effect of refining the crystal grain structure after cold rolling → solution treatment, and is a treatment for obtaining an increase in formability by refining the crystal grains. However, if the heating and cooling rate is less than 300 ° C./min, Mg ₂ Si, which is an aging precipitate, is coarsely precipitated during annealing, and the precipitate does not melt even after T4 treatment after cold rolling. Bake hardness in time baking is reduced.
Therefore, the heating / cooling rate during this annealing is set to 300 ° C./min or more. If the heating temperature at that time is less than 450 ° C., there is no effect of refining the crystal grains, and the formability is not improved. Further, when the temperature exceeds 520 ° C., the solid solution strengthens due to approaching the solution treatment temperature, and the strength increases, which causes ear cracks and the like in the subsequent cold rolling. Therefore, the annealing temperature after hot rolling is in the range of 450 to 520 ° C. A holding time of 10 seconds or less is sufficient.

After that, cold rolling is performed to obtain a desired plate thickness, and then solution treatment is performed. The conditions of the step of cold rolling → solution treatment are not particularly limited.

After the solution treatment, quenching was conventionally performed by water cooling or air cooling to room temperature, but in the present invention, a new process of quenching → holding is adopted, and as shown below,
It controls the quenching temperature, the cooling rate during quenching, and the holding time at the quenching temperature.

Quenching temperature (that is, quenching end temperature) is 50 ° C.
When it is less than 1, there is almost no bake hardenability by baking coating at a very low temperature of about 150 ° C., and it disappears with the passage of time when left at room temperature. On the other hand, if the quenching temperature exceeds 120 ° C., the strength in T4 treatment increases too much due to the precipitation of Mg ₂ Si, the moldability deteriorates, and the bake hardenability is not recognized. Therefore, the quenching temperature range is 50 to 120 ° C.

If the cooling rate when quenching to this quenching temperature (50 to 120 ° C.) is less than 300 ° C./min, the strength after quenching will be low and the bake hardenability at low temperature (150 ° C.) will be low. Will not be recognized. Therefore, the cooling rate is 300 ° C./minute or more.

Next, regarding the holding time at the quenching temperature,
In the case of quenching at a low temperature of 50 ° C, improvement in bake hardenability at the target low temperature is not recognized by holding for a short time, and 1
Equilibrium phase Mg ₂ Si precipitates when kept at 20 ° C for a long time,
The strength of T4 treatment is too high, and bake hardenability is not observed. Also, when the baking temperature is below 50 ° C., 48 when a long time to hold more than hours, low temperature bake hardenability disappeared, also 120 exceeds ° C. Mg ₂ be subjected to short-time retention of less than 1 hour at a temperature Si Bake-hardenability is not recognized because it has already been deposited. Therefore, as the quenching conditions, the quenching temperature is 50 to 120 ° C. and the holding time is 1 to 48 hours. Further, if this holding step at the quenching temperature is performed after 5 minutes or more have passed after quenching, the bake hardenability at a low temperature is remarkably deteriorated, so the holding step is performed within 5 minutes.

Further, the structure of the Al alloy plate material of the present invention will be described.

The crystal grain size is an important factor that affects the formability, SS mark, surface roughness, bending workability and the like.
Formability, especially bulging property, is improved when the crystal grain size is small, and skin roughness and bending workability are also better as the crystal grain size is smaller. Regarding the SS mark, deterioration due to fine crystal grains as seen in Al-Mg alloys and the like is hardly recognized in the Al-Mg-Si alloy of the present invention.
Even if the crystal grain size is reduced, SS marks do not occur. Therefore, if the crystal grain size is larger than 35 μm, the moldability and the surface roughness are remarkably reduced, and therefore the crystal grain size is set to 35 μm or less.

Further, since the surface and cross-sectional structure of the plate are equiaxed grains, there is almost no directivity for molding, there is no local deformation, and deformation occurs with a uniform deformation mechanism.
It has an effect of improving molding such as overhang and drawing. Among the manufacturing conditions, especially annealing treatment after hot rolling (heating rate 300 ° C
/ Minute or more and hold at a temperature of 450 to 520 ° C for 0 to 10 seconds)
This equiaxed grain is obtained by carrying out, and it is difficult to obtain the equiaxed grain if this treatment is outside the scope of the present invention.

The internal structure of the alloy is 150 to 20 depending on the effect of Cu addition and the effect of high temperature quenching treatment.
After the baking treatment at 0 ° C. for 5 to 120 minutes, the precipitation of the aged precipitate β′-Mg ₂ Si is 10 to 45% in terms of the volume content of the entire matrix. If the volume content of the aging precipitate after the baking treatment is less than 10%, sufficient strength cannot be obtained, and if it exceeds 45%, overaging occurs and the strength decreases.

The deformation mechanism of the material is 6000.
The type alloy is a local deformation type, and since the total deformation is smaller than that of the 5000 type alloy, the formability is poor. However, since the 5000 series alloy is a uniform deformation type, the forming is relatively good among the types of Al alloys. In this respect,
The alloy of the present invention has a basic composition of 6000 series Al-Mg-
By adding Cu to Si, the defects of the 6000 series alloy are eliminated and the advantages of the 5000 series alloy are utilized, and the deformation mechanism becomes uniform deformation.

[0049]

EXAMPLES Next, examples of the present invention will be described. First Example An aluminum alloy having the chemical composition shown in Table 1 below was melted and cast into a 50 mm thick ingot obtained by a conventional method to obtain 510
After subjecting to a homogenizing treatment at 4 ° C for 4 hours, hot rolling was performed at a temperature of 480 ° C or less to a plate thickness of 5 mm. After leaving the hot-rolled material to room temperature, the temperature rise rate is 40 ° C / hour and 450 ° C ×
Annealing treatment was performed under the condition of 5 seconds, and then cold rolling was performed at room temperature to a plate thickness of 1 mm, which was then subjected to an experiment.

This cold-rolled material was heated to a solution heat treatment temperature of 530 ° C. and held for 20 seconds, and then, in Table 2, quenching conditions, that is, the average cooling rate when cooling from 530 ° C. to room temperature was 50 to 800. After quenching to the quenching temperature by changing in the range of ° C / min, the quenching temperature was maintained for 0.3 to 72 hours and then cooled to room temperature.

The obtained material was examined for mechanical properties after being left to stand at room temperature for 5 days after quenching and at 170 ° C.
The mechanical properties (bake hardenability) when baked for 20 minutes were examined. The results are shown in Table 3.

As is clear from Table 3, in the examples of the present invention, by performing the quenching under the quenching conditions shown in Table 2, the bake hardenability is extremely excellent in the baking treatment at a low temperature (170 ° C.). I understand. Furthermore, it can be seen that the examples of the present invention have excellent formability even when treated under the quenching conditions shown in Table 2. On the other hand, with an Al alloy having a chemical composition outside the scope of the present invention, bake hardenability is not observed at all even when the quenching conditions within the scope of the present invention are adopted.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

Second Embodiment Al alloy No. 3 shown in Table 1 of the first embodiment (chemical composition within the scope of the present invention) and No. 10 Al alloy (chemical composition outside the scope of the present invention) Was melted and cast by a conventional method, and the obtained ingot was heated at a heating rate of 40 ° C./hour to a temperature of 510 ° C.
After performing a homogenizing heat treatment for holding for a time, hot rolling was performed to obtain a plate having a thickness of 5 mm. The obtained hot rolled material is shown in Table 4.
Annealing treatment was performed under the conditions shown in (1) and then cold rolling was performed to obtain a plate having a thickness of 1.0 mm.

Then, the obtained plate was heated at a heating rate of 400 ° C. /
It was kept at a temperature of 530 ° C. for 20 seconds, quenched at a temperature of 50 ° C. at a cooling rate of 800 ° C./minute, kept at a temperature of 50 ° C. for 24 hours, and then subjected to an experiment. The strength, moldability and crystal grains of the obtained material were measured. For crystal grains, use a 1.0 mm thick material plate on emery paper (320-1
After polishing with # 200, buff (alumina particle size 50
(μm) and mirror-polished, and electrolytically corroded with hydrofluoric acid. After that, the structure was observed with an optical microscope, and the size was measured by a section method. Table 5 shows the characteristics of the obtained material, the crystal grain size, and the bake hardenability after baking (170 ° C. × 20 minutes). In addition, each crystal structure photograph of the material annealed under the annealing conditions (iii) in Table 4 for the Al alloy No. 3 and the material under the annealing conditions (iv) in Table 4 for the alloy No. 10 is shown. This is shown in FIGS. 1 and 2.

As is clear from Table 5 and FIGS. 1 and 2,
The present invention example was performed under the present invention conditions after hot rolling, and by cold rolling, crystal grains of 20 μm or less were obtained, and compared with the comparative example alloys annealed under conditions outside the present invention range. It can be seen that they are becoming finer. Furthermore, the inventive examples have excellent moldability and improved bake hardenability.

[0059]

[Table 4]

[0060]

[Table 5]

Third Example Al alloy No. 3 shown in Table 1 of the first example (chemical composition within the range of the present invention) and Al No. 10 alloy (chemical composition outside the range of the present invention) ) Is melted and cast by a conventional method, and the obtained ingot is subjected to homogenizing heat treatment in which the temperature is kept at 510 ° C. for 4 hours at a heating rate of 40 ° C./hour, followed by hot rolling to obtain a thickness of It was a 5 mm plate. After leaving the obtained hot-rolled material to room temperature, it is heated to 500 ° C at a temperature rising rate of 300 ° C / min.
Annealing treatment under the condition of × 5 seconds and then a cooling rate of 300 ° C./min, followed by cold rolling to a thickness of 1.0 m
m plate.

Then, the obtained plate was heated at a heating rate of 400 ° C. /
It was kept at a temperature of 530 ° C. for 20 seconds, quenched at a temperature of 50 ° C. at a cooling rate of 800 ° C./minute, kept at a temperature of 50 ° C. for 24 hours, and then subjected to an experiment. The heat-treated material was processed into JIS No. 5 tensile test pieces, and in the parallel portion, as shown in FIG. 3, a gauge length (GL) was scribed at 11 points up to 50 mm.
It was subjected to an experiment. In the experiment, the initial state of the gauge length and the state after the tensile test were measured, the difference between them was taken, and the change was taken. The result is shown in FIG. It can be seen that the inventive examples have a uniform deformation mechanism and increase the total elongation as compared with the comparative examples. Therefore, the alloys of the examples of the present invention have good formability.

Fourth Example The alloy No. 3 Al alloy (chemical components within the scope of the present invention) and No. 10 Al alloy (comparative alloy) shown in Table 1 of the first example were melted by a conventional method, After casting, the obtained ingot was subjected to a homogenizing heat treatment of holding it at a temperature of 510 ° C. for 4 hours at a heating rate of 40 ° C./hour, followed by hot rolling to obtain a plate having a thickness of 5 mm. After leaving the obtained hot rolled material to room temperature,
An annealing treatment was performed at a temperature rising rate of 300 ° C./min at 500 ° C. for 5 seconds and then at a cooling rate of 300 ° C./min, and then cold rolling was performed at room temperature to a plate thickness of 1 mm. The plate was kept at a temperature of 530 ° C. for 20 seconds at a heating rate of 400 ° C./min, quenched at a temperature of 50 ° C. at a cooling rate of 800 ° C./min, and kept at a temperature of 50 ° C. for 24 hours to be subjected to an experiment. . A baking treatment was performed on the heat-treated material. Table 6 shows the baking treatment conditions and the volume content and strength of the aged precipitate at that time. Furthermore, the result of observing the precipitation state of the aging precipitate after the baking treatment with a transmission electron microscope is shown in FIG.

From these results, the volume content of aging precipitates was 26 by performing the baking treatment within the range of the present invention.
It can be seen that the strength is as high as 170 to 230 N / mm ^{2 at} ˜42%.

[0065]

[Table 6]

Fifth Example An aluminum alloy having the chemical composition shown in Table 7 below was melted by a conventional method and cast into a 50 mm thick ingot obtained by casting 560
After subjecting to homogenizing treatment at 4 ° C. for 4 hours, hot rolling was performed immediately to obtain a plate thickness of 5 mm. Leave the hot rolled material to room temperature,
Annealing treatment was performed at a temperature rising rate of 200 ° C./hour under conditions of 500 ° C. for 5 seconds, and then cold rolling was performed at room temperature to obtain a sheet thickness of 1
mm. This cold rolled material was heated to a solution treatment temperature of 530 ° C. and held for 30 seconds, then quenched in hot water of 50 ° C. and held for 2 hours to produce a T4 material. afterwards,
A material that had been left to stand at room temperature for 7 days and a material that had been left at room temperature for 3 months were manufactured and subjected to experiments.

To measure the strength, a tensile test was carried out using an autograph manufactured by Shimadzu, and a change in the proof stress due to room temperature aging was determined. (3 months time σ _0.2 -7 date σ _0.2 ) was 15 N / mm ²
The following were accepted.

The moldability was measured by JI using an Erichsen tester.
It was evaluated according to the S-Z2247 Erichsen Test B method. A material that had been used for 3 months and had an Erichsen value of 9.8 mm or more at that time had the same formability as that of the Al-Mg alloy and was regarded as acceptable.

The results of the strength and molding test are shown in Table 8 below. As is clear from Table 8, the alloy strengths of Examples 21 to 24 of the present invention are (σ _{0.2 −7} date and time σ _0.2 at 3 months).
Is 15 N / mm ² or less and the Erichsen value, which is an index of moldability, is 9.8 mm or more, and it is clear that the moldability does not deteriorate even when left at room temperature and is excellent.

[0070]

[Table 7]

[0071]

[Table 8]

Sixth Embodiment Alloy No. shown in Table 7 of the fifth embodiment. 21 Al alloy (chemical composition within the scope of the present invention) and alloy No. 21. 25 Al alloys (chemical components outside the scope of the present invention) were melted and cast by a conventional method,
The obtained ingot was homogenized at 560 ° C. for 4 hours and then immediately hot-rolled to a plate thickness of 2.5 mm.
No. For alloy No. 21, the hot-rolled material was allowed to stand to room temperature, annealed at a temperature rising rate of 200 ° C./hour under conditions of 500 ° C. for 5 seconds, and then cold rolled at room temperature to obtain a plate thickness of 1 mm.
And No. For comparison, alloy 25 was not annealed, but was hot-rolled and then cold-rolled at room temperature to obtain a sheet thickness of 1
mm. These cold rolled materials were heated to a solution treatment temperature of 530 ° C. and held for 30 minutes, then quenched in hot water of 50 ° C. and held for 2 hours to produce T4 material.

Moldability and crystal grains of the obtained material were measured. Moldability is measured by JIS-
2247 Erichsen test B method evaluated. The crystal grain size is 1 mm thick and the material plate is emery paper (320-120
No. 0), mirror-polished with buff (alumina particle size 50 μm), electrolytic corrosion with hydrofluoric acid, then microscopic observation of the structure with an optical microscope, and measurement of crystal grain size by sectioning method did.

Table 9 below shows No. 21 material (example of the present invention) and No. 21 material. The Erichsen height and the crystal grain size of No. 25 material (comparative example) are shown in FIG. 6 and FIG. No. 21 material, No. The crystal structure photograph of 25 materials is shown. As is clear from Table 9 and FIGS. 21 material (Example of the present invention) has a crystal grain of 25 μm.
The following crystal grains were obtained, and the Erichsen value was 10.0.
mm, which is very high, From No. 25 (Comparative Example), it is found that the crystal grains are made finer and the formability is excellent.

[0075]

[Table 9]

[0076]

As described in detail above, according to the present invention,
By adjusting the content of Mg and Si of the Al-Mg-Si-Cu-Mn-based alloy plate to the optimum Mg ₂ Si content and the remaining Si content, Cu and Mn having the effect of further improving strength and formability are selected. And the crystal grain size is 35 μm or less,
The material strength is high, and sufficient bake hardenability can be obtained even in baking coating at low temperature, and molding processability can be made excellent. This is different from the conventional material in that the addition of Cu makes the aging precipitate β'-Mg ₂ Si (after baking coating) denser and finer to increase the strength and to obtain excellent bake hardenability in baking coating at low temperature. And further C
By uniformly deforming the deformation mechanism by adding u, the moldability is improved even in baking coating at low temperature. Therefore, the thickness of the Al alloy plate can be reduced, and since the moldability is good, the effect of contributing to the weight reduction of automobiles, home appliances, and mechanical parts and improving the frequency of use is extremely remarkable.

Further, by further limiting the component adjustment, the increase in strength due to room temperature aging and the accompanying deterioration in moldability are suppressed, and the performance which is almost the same as that at the time of manufacture is maintained even after 3 months have passed. As an Al alloy plate material, since it does not change the conditions at the time of press working over time, it contributes to the weight reduction of automobiles, home electric appliances, and mechanical parts, and it is possible to further improve the frequency of use industrially. Extremely high.

[Brief description of drawings]

FIG. 1 is a photograph showing the metallographic structure of the material obtained in the second example, which is the case of the example of the present invention.

FIG. 2 is a photograph showing a metallographic structure of the material obtained in the second example, which is a comparative example.

FIG. 3 is a view showing a shape of a test piece for measuring a deformation mechanism.

FIG. 4 is a diagram showing a deformation mechanism (a state of full extension).

FIG. 5 is a photograph showing the metallographic structure of the material after the baking treatment obtained in the fourth example, in which (a) is the example of the present invention (170 ° C.).
X 20 minutes baking), (b) is a comparative example (120 ° C x 1)
0 minute baking), (c) is a comparative example (200 ° C. × 120
Minute baking).

FIG. 6 is a photograph showing the metallographic structure of the T4 material obtained in the sixth example, which is the case of the example of the present invention.

FIG. 7 is a photograph showing the metal structure of the T4 material obtained in the sixth example, which is the case of the comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shojiro Oya 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Prefecture Kobe Steel Co., Ltd. Kobe Research Institute of Technology (72) Inventor Osamu Takezoe Kinuike, Moka City, Tochigi Prefecture Oka No. 15 Kado Steel Works Moka Works

Claims (6)

[Claims] 1. In weight% (hereinafter the same), Mg: 0.2
~ 1.0%, in the range of Si: 0.5-2.0%,
It is a mixture of Si in excess of Mg constituting Mg ₂ Si, and Mg and Si are 0.35 to 1.5 as the amount of Mg ₂ Si.
%, And the amount of residual Si is 0.35 to 1.2%
And Cu: 0.5 to 2.0% and Mn: 0.
It is characterized by containing 0.05 to 0.50%, the balance consisting of Al and inevitable impurities, the structure of the plate material having a crystal grain size of 35 μm or less, and the structure of the surface and cross section of the plate being equiaxed grains. Bake hardening type Al alloy plate. 2. Mg: 0.3 to 1.0%, Si: 0.5
Mg constituting Mg ₂ Si in the range of up to 1.4%
On the other hand, the composition is excessive in Si, and Mg and Si are Mg ₂ S.
i content of 0.9 to 1.1% and remaining S
The i content is 0.6 to 1.2%, and further Cu: 0.5 to
1.0% and Mn: 0.05 to 0.50%, the balance consisting of Al and unavoidable impurities, the structure of the plate material having a crystal grain size of 35 μm or less, and the structure of the surface and cross section of the plate. A bake hardening type Al alloy plate characterized by equiaxed grains. 3. Mg: 0.2-1.0%, Si: 0.5
In the range of up to 2.0%, the composition of Mg ₂ Si is excessive with respect to Mg constituting Mg ₂ Si, and Mg and Si are Mg ₂ Si.
S content of 0.35 to 1.5% and remaining S
The i content is 0.35 to 1.2% and further Cu: 0.5
-2.0% and Mn: 0.05-0.50%,
Furthermore, Zr: 0.3% or less, Cr: 0.3% or less, T
i: 0.1% or less and Fe: 0.3% or less, and one or more selected from the group, the balance consisting of Al and unavoidable impurities, and the structure of the plate material having a crystal grain size. Three
A bake hardening type Al alloy plate having a size of 5 μm or less and having a surface and cross-section structure of equiaxed grains. 4. Mg: 0.3 to 1.0%, Si: 0.5
Mg constituting Mg ₂ Si in the range of up to 1.4%
On the other hand, the composition is excessive in Si, and Mg and Si are Mg ₂ S.
i content of 0.9 to 1.1% and remaining S
The i content is 0.6 to 1.2%, and further Cu: 0.5 to
1.0% and Mn: 0.05 to 0.50%, and further Zr: 0.3% or less, Cr: 0.3% or less, Ti:
0.1% or less and Fe: 1% or more selected from the group consisting of 0.3% or less are contained, the balance is made of Al and inevitable impurities, and the structure of the plate material has a crystal grain size of 35 μm.
A bake-hardenable Al alloy plate having a grain size of m or less and the surface and cross-section of the plate having equiaxed grains. 5. A step of homogenizing the Al alloy ingot having the chemical composition according to claim 1 at a temperature not higher than the burning temperature, a step of hot rolling, and a heating rate 300. 0 to a temperature of 450 to 520 ℃ above ℃ / min
Annealing process of holding for 10 seconds and cooling at a cooling rate of 300 ° C./min or more, cold rolling to a desired plate thickness, solution treatment process, and cooling of 300 ° C./min or more Quenching to a temperature of 50 to 120 ° C. at a speed and holding at a temperature of 50 to 120 ° C. for 1 to 48 hours within 5 minutes, a method for producing a bake hardening type Al alloy plate. 6. As a post-step of the step of holding at the temperature of 50 to 120 ° C. for 1 to 48 hours, baking coating (baking treatment) is performed at a temperature of 150 to 200 ° C. for 5 to 120 minutes, and aged precipitation. The method for producing a bake-hardenable Al alloy sheet according to claim 5, further comprising a step of precipitating the material β'-Mg ₂ Si in a range of 10 to 45% in a total volume content of the matrix.