JP2003321754A - Method for manufacturing aluminum alloy sheet with excellent bendability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a 6,000 series Al alloy sheet which has excellent bendability such as hemming even if subjected to room- temperature aging and further has excellent press formability by the suppression of ridging marks and rough surface. <P>SOLUTION: A hot rolled Al-Mg-Si based aluminum alloy sheet is cold rolled at 10 to 50% draft, annealed at 210 to 440°C, further cold rolled at ≥70% draft and then subjected to solution heat treatment and hardening treatment. In this way, the texture of the resultant aluminum alloy sheet can be provided with anisotropy, and also the average grain size is made to ≤50 μm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is excellent in bending workability such as hemming even when room temperature aging is advanced after plate production, and is required for panelization such as press formability and low temperature age hardening ability. The present invention relates to an Al-Mg-Si-based aluminum alloy plate (hereinafter, aluminum is simply referred to as Al) excellent in other various properties.

[0002]

2. Description of the Related Art Conventionally, it has been excellent in moldability (hereinafter simply referred to as "formability") for transportation vehicles such as automobiles, ships or vehicles, home electric appliances, construction and structural members.
Al-Mg-based AA to 5000 system specified or equivalent to JIS standard, and Al-Mg-Si-based AA to JI excellent in moldability and bake hardenability
S 6000 series (hereinafter simply referred to as 5000 series to 6000 series) Al alloy materials (rolled sheet materials, extruded shape materials, forged materials and other aluminum alloy wrought materials are collectively referred to) are used.

In recent years, in response to global environmental problems caused by exhaust gas and the like, improvement in fuel consumption has been pursued by reducing the weight of vehicle bodies of transportation machines such as automobiles. For this reason, in particular, the application of lighter Al alloy materials to the body of automobiles is increasing in place of the steel materials that have been conventionally used.

Among these Al alloy materials, automobile hoods,
For panels such as outer panels (outer plates) and inner panels (inner plates) of panel structures such as fenders, doors, roofs, and trunk lids, a thin, high-strength Al alloy plate is used as an excess Si type 6000 series. The use of Al alloy plates is being considered.

This excess Si type 6000 series Al alloy is basically an Al-Mg-Si series aluminum alloy which essentially contains Si and Mg and has Si / Mg of 1 or more. And since this excess Si type 6000 series Al alloy has excellent age hardening ability, it secures formability by low yield strength at the time of press forming and bending, and at the same time, such as paint baking treatment of the panel after forming. The material has an age hardening ability capable of ensuring the required strength by age hardening by heating at the time of artificial aging treatment at a relatively low temperature to improve the yield strength.

Further, these excess Si type 6000 series Al alloy materials are
Compared to other 5000 series Al alloys, which have a large amount of alloys such as Mg, the amount of alloying elements is relatively small. Because of this, these 60
When the scrap of 00 series Al alloy material is reused as the Al alloy melting material (melting raw material), the original 6000 series Al alloy ingot is easily obtained and the recyclability is excellent.

However, because of their excellent age hardening ability, these excess Si type 6000 series Al alloy materials have a large room temperature after the Al alloy materials themselves are manufactured and before they are used for each of the above-mentioned applications.
(At room temperature) There is a problem that aging occurs.

[0008] For example, due to this room temperature aging, excess Si type
Even after 2 weeks from the production of the 6000 series Al alloy material itself, the phenomenon that the yield strength increases by about 10% or more occurs.

When such room temperature aging occurs, immediately after manufacturing, even if the excess Si type 6000 series Al alloy plate satisfies the required characteristics for each of the above-mentioned applications, after a certain period of time, it is actually used. When it is used for, the above-mentioned required characteristics cannot be satisfied. That is, in particular, the bending workability such as hemming workability is remarkably lowered, and other various properties such as the press formability and the age hardening at a relatively low temperature are also lowered, and the required shape accuracy as a panel and The strength cannot be obtained.

On the other hand, the present applicant has filed Japanese Patent Application No. 2001-36670.
No. 0, Japanese Patent Application No. 2001-366701, etc.
In the texture of 00 series Al alloy material, the ratio of the integrated strength of {200} plane on the surface of the aluminum alloy plate is 70% or more and the ratio of the total integrated strength of {200} plane and {400} plane is 80%. % Or more, anisotropic texture
(Structure with many crystal grains having a cube orientation), even if it is aged at room temperature, it is particularly excellent in bending workability such as hemming, and it is required for panelization such as press formability and low temperature age hardening ability. 6000 series with excellent characteristics
An Al alloy plate was proposed.

[0011] With these textures having anisotropy, Mg-S, which has been conventionally used for suppressing room temperature aging,
Even without complicated control of i clusters (formed during room temperature after solution heat treatment and quenching), it is particularly excellent in bending workability such as hemming and has excellent properties such as low temperature age hardening ability. We can provide 6000 series Al alloy plates.

[0012]

In order to obtain a texture having the above-mentioned anisotropy, unlike the conventional method for producing a plate, cold rolling with a high reduction ratio is performed, and during cold rolling, It is preferable to add intermediate annealing.

However, when manufactured by the above manufacturing method, an anisotropic texture is obtained, but depending on the manufacturing conditions, 6000 after the final solution heat treatment and quenching treatment.
The grain size of the Al-based alloy plate may become coarse. When the crystal grain size becomes coarse in this way, a new problem arises in that the panel structure after molding is apt to suffer from rough surface defects such as ridging marks due to press molding. Also, if the crystal grain size becomes too large,
It also reduces the processability of hem such as flat hem.

When this ridging mark or rough skin occurs, a panel structure for an outer panel or the like, which requires a particularly beautiful surface, has a poor appearance and cannot be used. Further, there is also a troublesome problem that the ridging marks and the rough surface are relatively inconspicuous immediately after the press molding, and become prominent after the coating when the panel structure is directly subjected to the coating process.

The present invention has been made in view of such circumstances, and its purpose is to have excellent bending workability such as hemming even when aged at room temperature, and to suppress ridging marks and rough skin. An object of the present invention is to provide a method for producing a 6000 series Al alloy sheet which is also excellent in press formability.

[0016]

In order to achieve this object, the subject matter of claim 1 of the present invention is that hot-rolled Al-Mg-
A Si-based aluminum alloy sheet is cold-rolled at a reduction rate of 10 to 50%, annealed at a temperature of 210 to 440 ° C, cold-rolled at a reduction rate of 70% or more, and then solution-treated and quenched. The texture of the aluminum alloy plate should be anisotropic, and the average grain size should be 50 μm or less.

The Al alloy sheet referred to in the present invention is a sheet which has been subjected to tempering treatment after cold rolling and then aged at room temperature (rolled sheet).
Say Therefore, each of the above requirements is not just after the tempering treatment (immediately after the plate production), but after the tempering treatment (after the plate production) until the press forming or bending process (for example, one month or more after the plate production. (After lapse of time) refers to the state of the Al alloy plate aged sufficiently at room temperature. Further, the tempering treatment here mainly refers to solution heat treatment and quenching treatment, but any heat treatment thereafter, for example, various tempering treatments such as a preliminary aging treatment described later and an aging treatment to be performed if necessary. Including.

The following description will be made especially for the excess Si type 6000 series.
Mainly on the Al alloy plate. The present invention is Al-Mg- other than excess Si type
The Si-based or 6000-based Al alloy plate also has the effect, though not as severe as the excessive Si type, but can be included in the scope of the present invention because it has an effect. Similarly, the following description of bending workability is
Especially, hem processing such as flat hem is mainly performed, but if the hem processing is good, other hat-shaped bending processing and 90-degree bending processing that have the same processing (deformation) mechanism are also good. Becomes Therefore, the present invention can be applied to bending work other than hemming and can be included in the scope of the present invention.

As a result of the study conducted by the present inventors, in the method for obtaining the above-mentioned texture having anisotropy, in other words, the texture having a large number of crystal grains having the cube orientation, after solution treatment and quenching treatment, The average grain size of the Al alloy plate, the reduction ratio of the cold rolling in the first half before the annealing process (during cold rolling) and the reduction ratio of the cold rolling in the latter half before the solution treatment and quenching treatment after the annealing process. It was found to be correlated with.

The cold rolling itself is an important step for accumulating sufficient strain energy in the cold rolled sheet, and a tempering treatment including annealing and solution treatment to obtain an anisotropic texture.
Therefore, in order to accumulate sufficient strain energy in the cold-rolled sheet, it is preferable that the cold rolling reduction ratio be as high as possible. However, when the reduction rate of the cold rolling in the first half before the annealing step is increased, the tempering treatment including annealing and solution treatment facilitates the growth of the crystal grains of the Al alloy plate, and the crystal grains tend to become coarse. Can be seen.

In the present invention, in order to prevent the coarsening of the crystal grain size, the crystal grain size of the Al alloy plate to be 50 μm or less, and to suppress ridging marks and rough skin on the surface of the panel structure after press molding, The reduction ratio of the cold rolling in the first half before the annealing step is lowered. On the other hand, the reduction ratio of the cold rolling in the latter half after the annealing process and before the solution treatment and quenching treatment is increased to obtain an anisotropic texture.

In the present invention, in order to exhibit the above characteristics, Al
From the viewpoint of the composition of the alloy plate, as in claim 2, the Al alloy plate contains Si: 0.4 to 1.3%, Mg: 0.2 to 1.2%, Mn: 0.01 to 0.65.
%, Cu: 0.001 to 1.0%, Si / Mg in a mass ratio of 1 or more, and the balance being Al and inevitable impurities.

In the present invention, as the texture having anisotropy, preferably, as described in claim 3, the aluminum alloy plate has a ratio of integrated intensity of {200} planes on the surface thereof.
The structure is 70% or more and the ratio of the total integrated intensity of the {200} plane and the {400} plane is 80% or more.

According to the present invention, even if the 0.2% proof stress in the direction parallel to the rolling direction of the Al alloy plate is not made as low as 140 MPa or less as in the conventional case, heme workability such as flat hem and stretch formability can be achieved. Is excellent. As a result, the Al alloy plate after aging at room temperature
The 0.2% proof stress can be increased to a high strength exceeding the above 140MPa, and 160 ℃ × 20
Even with a low temperature artificial age hardening treatment for a minute, a high-strength panel exceeding 170 MPa can be obtained.

Further, the Al alloy sheet of the present invention is particularly excellent in bending workability such as hemming and is excellent in other various properties required for forming a panel, such as press formability and low temperature age hardening ability. As described in item 4, it is preferably applied when the Al alloy plate is hemmed after the stretch forming.

[0026]

(Manufacturing Method) The manufacturing method of the present invention will be described below. In order to suppress ridging marks and skin roughness on the surface of the panel structure after press molding and to have an anisotropic texture (a structure in which many crystal grains having a cube orientation are present), it is usually used in the production of Al alloy plates. Unlike the method, a special process such as weak rolling by cold rolling, annealing at a specific temperature, strong rolling by cold rolling, and subsequent heat treatment is required. In this respect, a normal Al alloy plate obtained by a conventional method has a small proportion of crystal grains having a cube orientation, has an isotropic structure, has anisotropy as in the present invention, or has a strong anisotropy. It does not become a collective organization.

More specifically, in the present invention, coarsening of the crystal grain size is prevented, the average crystal grain size of the Al alloy plate is set to 50 μm or less, and ridging marks and skin roughness on the surface of the panel structure after press molding are prevented. In order to suppress, first, the reduction ratio of the cold rolling in the first half before the annealing step is 10 to 50%, preferably 10 to 40%.
A relatively low rolling reduction in the range of%.

When the rolling reduction is less than 10%, even if the rolling reduction in the latter half of the cold rolling after the annealing step and before the solution heat treatment and quenching is increased, the crystal grains having the cube orientation have a preferable ratio described below. It is difficult to obtain a highly anisotropic texture.

On the other hand, if the reduction ratio exceeds 50%, or more strictly exceeds 40%, the reduction ratio of the cold rolling in the latter half after the annealing step and before the solution treatment and quenching treatment is increased. However, there is a high possibility that the crystal grain size of the 6000 series Al alloy plate after the final solution heat treatment and quenching will exceed 50 μm and become coarse. As a result, ridging marks and rough skin are likely to occur on the panel structure by press molding. In addition, the processability of hem such as flat hem is also reduced.

Next, the reduction ratio of the cold rolling in the latter half after the annealing process and before the solution treatment and quenching treatment is increased to 70% or more to obtain an anisotropic texture. By increasing the reduction ratio in the latter half cold rolling in this way, sufficient strain energy can be accumulated in the cold rolled sheet. As a result, in the subsequent heat treatment including solution treatment, many crystal grains having a cube orientation can be grown and a highly anisotropic texture can be obtained.

If the rolling reduction is less than 70%, sufficient strain energy cannot be accumulated for growing crystal grains having a cube orientation, and it is difficult to obtain an anisotropic texture. And, preferably, the ratio of the crystal grains having the cube orientation on the Al alloy panel surface is 50% or more of the integrated strength ratio of the {200} plane on the Al alloy plate surface, and the {200} plane and the {400} plane. The ratio of the total integrated intensity with the surface
It cannot be more than 60%. That is, when this reduction rate is low, it does not differ from the ordinary method material, and in the tempering process described later,
A structure having anisotropy of elongation cannot be formed. On the other hand, the higher the reduction ratio in cold rolling, the more difficult the process itself such as the occurrence of edge cracks, so the upper limit of the reduction ratio is 95%.
It is preferably about the same.

Annealing during the cold rolling (intermediate annealing) is
It is an essential step to grow a specific amount of fine recrystallized grains or sub-crystalline grains having a cube orientation and to make the cubic orientation easy to develop in the final solution treatment and to obtain an anisotropic texture. . 210-440 ° C to produce this effect
It is necessary to anneal at the temperature. The annealing time is 1 to 5
It is preferably 0 hours.

When the annealing temperature is less than 210 ° C., the grain growth having the cube orientation is not effective due to the relationship with the low pressure reduction ratio of the cold rolling in the first half, and the anisotropic texture cannot be obtained. . And, preferably, the ratio of the crystal grains having the cube orientation on the surface of the Al alloy panel is such that the ratio of the integrated strength of the {200} plane on the surface of the Al alloy plate is 70% or more, and the {200} plane and the {400} plane are The ratio of the total integrated intensity with the plane cannot be 80% or more. As a result, there is not much difference from the texture of the conventional Al alloy plate, and there is no effect of improving the hem workability such as flat hem.

On the other hand, when the annealing temperature exceeds 440 ° C., the average crystal grain size exceeds 50 μm and the particles tend to be coarsened, and press molding tends to cause ridging marks and rough skin on the surface of the panel structure. Note that this annealing can be performed by appropriately using various furnaces such as a batch furnace and a continuous annealing furnace.

The average crystal grain size referred to in the present invention is the average grain size of the crystal grains in the rolling direction (L direction) of the plate. The measuring method was to observe the surface electrolytically etched after mechanically polishing the surface including the rolling direction (L direction) and the plate thickness direction (ST direction) of the Al alloy plate using an optical microscope, 1/8 part, 2/8 part of thickness, 3/8 part of thickness, 4 / of thickness
At each part of section 8, measure in the L direction by the line intercept method. The length of one measurement line is 0.95 mm, and a total of 5 fields of view are observed for each 5 fields, and the crystal grain sizes are measured and averaged to obtain the average crystal grain size.

Further, as an anisotropic texture, particularly in order to improve the processability of hem such as flat hem, the cube orientation of the Al alloy plate crystal grains is, as described above, {200} on the surface of the Al alloy plate. The ratio of the integrated intensity by X-ray diffraction of the plane is set to 70% or more, and the {200} plane and the {400} plane
The ratio of the total integrated intensity by X-ray diffraction is preferably 80% or more.

When the ratio of the integrated intensity of the {200} plane by X-ray diffraction is less than 70% and the ratio of the total integrated intensity of the {200} plane and the {400} plane by X-ray diffraction is less than 80%, of
There is almost no difference from the crystal grain structure of the Al alloy plate, and there is a possibility that the effect of improving the hem processability such as flat hem may not occur.

On the other hand, the ratio of the integrated intensity of the {200} plane is 90%.
When the total integrated strength of the {200} plane and the {400} plane exceeds 95%, depending on the component composition of the Al alloy plate, press forming such as bulging or drawing may occur. Moldability may decrease. As a result, in press molding, there is a possibility that shape accuracy or shape fixability, which is important particularly as an outer panel, may be significantly reduced. Therefore, in order to prevent deterioration of other properties such as press formability other than hemmability, the ratio of the crystal grains having a cube orientation should be 70 to 70% of the integrated strength of the {200} plane on the Al alloy plate surface. It is more preferable that it is in the range of 90% and the ratio of the total integrated intensity of the {200} plane and the {400} plane is in the range of 80% to 95%.

An X-ray diffractometer (for example, Rigaku RAD-RC) was used to measure the degree of cube orientation development of the crystal grains of the Al alloy plate.
Is used to measure the surface of the Al alloy plate as it is without pretreatment. A non-oriented Al sample was used as the standard sample, and the {111} plane, {200} plane, and
{220} plane, {311} plane, {222} plane, {400} plane,
The sum A of the integrated intensities of the {331} plane, {420} plane, and {422} plane is obtained. And the {20
Ratio (%) of integrated intensity I ₁ of 0} plane, {200} plane and {400} plane
The ratio (%) of the total integrated intensity I _{2 to} the surface is defined as the ratio (%) of each integrated intensity.

In the present invention, other conditions of other manufacturing steps can be performed by a conventional method, but there are preferable conditions for improving the flat hem processability and other characteristics as an outer panel, which will be described below. .

First, in the melting and casting process, an ordinary molten casting method such as a continuous casting rolling method or a semi-continuous casting method (DC casting method) is appropriately used for an Al alloy molten metal whose melting is adjusted within the 6000 series component standard range. Select and cast. Next, this Al alloy ingot is subjected to homogenizing heat treatment, and then hot rolled to be processed into a plate shape such as a coil shape or a plate shape.

The Al alloy plate after the cold rolling is inevitably subjected to solution heat treatment and quenching as heat treatment. Solution treatment and quenching are important steps for precipitating a compound phase such as GP zone in the grains sufficiently by an artificial age hardening treatment such as a paint baking hardening treatment to be performed later. The solution treatment conditions for producing this effect are preferably in the temperature range of 500 to 560 ° C. As a result, the 0.2% proof stress of the Al alloy plate is made to have a high strength exceeding 140 MPa, and high strength exceeding 170 MPa even with the artificial aging hardening treatment at a low temperature for a short time in the coating process after bending such as press forming and hem. Panel.

Upon quenching after the solution treatment, the cooling rate is preferably a rapid cooling rate of 50 ° C./minute or more. When the cooling rate is slower than 50 ° C./min, the strength after quenching becomes low, the age hardening ability becomes insufficient, and the high yield strength of 170 MPa or more cannot be secured by the artificial aging treatment at a low temperature for a short time and at a low temperature.

Further, Si, MgSi, etc. are likely to be deposited on the grain boundaries, which easily becomes a starting point of cracks during press molding or flat hem processing, and these moldability are deteriorated. In order to secure this cooling rate, the quenching treatment may be performed by air cooling using a fan or the like, but the cooling rate is likely to be slow, and it is preferable to perform the quenching treatment by selecting from water cooling means such as mist, spraying and dipping.

In the present invention, in order to enhance the age hardenability in the artificial age hardening treatment such as the paint baking process of the molded panel, the formation of clusters after the solution hardening treatment is suppressed,
A pre-aging treatment may be performed to accelerate the precipitation in the GP zone. This pre-aging treatment is performed at 50 to 100 ° C, preferably
It is preferable to maintain the temperature range of 60 to 90 ° C. for the required time of 1 to 24 hours. The cooling rate after the preliminary aging treatment is
It is preferably 1 ° C./hr or less.

As the preliminary aging treatment, after the quenching completion temperature after the solution treatment is raised to 50 to 100 ° C., it is immediately reheated or kept as it is. Alternatively, after the solution treatment, quenching treatment up to room temperature and immediately reheating to 50 to 100 ° C. are performed.

In the case of continuous solution hardening treatment,
The quenching process is completed within the temperature range of the preliminary aging, and the coil is wound around the coil at the high temperature as it is. Note that the coil may be reheated before being wound on the coil, or may be kept warm after being wound. Further, after the quenching treatment up to room temperature, it may be reheated to the above temperature range and wound at a high temperature.

Further, in order to suppress room temperature aging, after the preliminary aging treatment, heat treatment at a relatively low temperature without any time delay.
(Artificial aging treatment) may be performed to further generate a GP zone. If there is a time delay, room temperature aging (natural aging) occurs over time even after pre-aging treatment, and after this room temperature aging occurs, the effect of the heat treatment at the relatively low temperature is exerted. It gets harder.

In order to obtain these effects, in the above composition range of the Al alloy material, the aging treatment temperature is in the range of 80 to 120 ° C., and the aging treatment time is the necessary time, preferably in the range of 1 to 24 hours, From this range, depending on the composition,
It is preferable to select the temperature and time at which the aging treatment effect is obtained. The cooling rate after this aging treatment is 1 ° C / hr.
The following is preferable. If the aging temperature is less than 80 ° C and the holding time is too short, GP zone cannot be generated. Therefore, the room temperature aging suppression effect and the low temperature age hardening ability cannot be obtained. On the other hand, at temperatures above 120 ° C, there is not much difference from normal aging treatment, β "phase also precipitates, aging proceeds too much, and strength becomes too high. This is the same even if the holding time of aging treatment is too long. The pre-aging treatment temperature may be set to be as high as the aging treatment described below, and heat treatment may be combined with or continuous with the aging treatment.

In addition, it is of course possible to further increase the strength by performing aging treatment or stabilization treatment at a higher temperature depending on the use and the required characteristics.

Next, an embodiment of the chemical composition of the Al alloy sheet of the present invention will be described below. The basic composition of the Al alloy sheet of the present invention is an Al-Mg-Si-based (6000-based) Al alloy in order to ensure the above-mentioned elongation, microstructure, and other characteristics and various properties. Al-M
Unless it is in the range of g-Si (6000 series) Al alloy, the above-mentioned elongation and structure defined in the present invention are not obtained, and various properties are not exhibited.

Further, in order to secure the above-mentioned regulation such as elongation and structure and various necessary characteristics as a plate, Si: 0.4 to 1.3%,
Excess Si-type Al-M containing Mg: 0.2 to 1.2%, Mn: 0.01 to 0.65%, Cu: 0.001 to 1.0%, and Si / Mg of 1 or more by mass ratio.
It is preferable to use a g-Si-based Al alloy. In order to ensure the regulation and various characteristics of the above-mentioned structure, more strictly, it is preferable that the balance other than the prescribed components is Al and inevitable impurities. Incidentally,% of the chemical composition of the present invention
All the indications mean the mass% including the% indication in the above claims.

Other than the above alloying elements, Cr, Zr, Ti, B, F
Other alloy elements such as e, Zn, Ni and V are basically impurity elements. However, from the viewpoint of recycling, as a melting material, not only high-purity Al ingots, but also 6000 series alloys and other Al alloy scrap materials, low-purity Al ingots, etc. are used as melting raw materials, In the case of smelting, these other alloying elements are inevitably included. Therefore, the present invention permits the inclusion of these other alloying elements within a range that does not impair the intended effect of the present invention.

The preferable range and meaning of each element, or the permissible amount will be described below. Si: 0.4 to 1.3%. Si is a solid solution strengthener and forms a compound phase such as GP zone with Mg during artificial aging treatment at a low temperature and a short time, such as paint baking treatment, and exhibits age hardening ability, and a panel with 170 MPa or more as a panel. It is an essential element for obtaining the required strength. Therefore, in the excess Si type 6000 series Al alloy plate of the present invention, it is the most important element to combine various characteristics such as press formability and hemmability.

Further, at the time of artificial aging treatment at a low temperature for a short time (coating baking treatment after molding on a panel, as an evaluation test,
In order to exert an excellent low temperature age hardening ability of 170 MPa or more at the time of low temperature aging treatment of 160 ° C × 20 minutes after applying 2% stretch, Si / Mg is set to 1.0 or more by mass ratio and Si is
It is preferable to use an excessive Si type 6000 series Al alloy composition that is contained in excess of Mg.

When the amount of Si is less than 0.4%, it is impossible to combine the above-mentioned age hardening ability and various characteristics required for each application such as press formability and hemmability. On the other hand, Si is 1.
If the content exceeds 3%, heme workability and bending workability are significantly impaired. Furthermore, the weldability is significantly impaired.
Therefore, Si is preferably in the range of 0.4 to 1.3%. In the outer panel, since heme workability is particularly important, in order to further improve flat heme workability without deteriorating other properties such as press formability, the Si content is 0.6 to 1.2%, A lower range is preferable.

Mg: 0.2-1.2%. In order to obtain the necessary strength of 170 MPa or more as a panel, Mg forms a compound phase such as GP zone together with Si during solid solution strengthening and artificial aging treatment such as paint baking treatment, and exhibits age hardening ability. Is an essential element of.

When the content of Mg is less than 0.2% (mass%, the same applies hereinafter), the absolute amount is insufficient, so that the compound phase cannot be formed during the artificial aging treatment and the age hardening ability cannot be exhibited. Therefore, the required strength required for the panel cannot be obtained.

On the other hand, when the content of Mg exceeds 1.2%, the formability such as press formability and bending workability (hem workability) is significantly impaired. Therefore, the content of Mg is 0.2-1.
The amount is within the range of 2% and the Si / Mg is 1.0 or more. Further, in order to further improve the flat heme workability, when the Si content is set to a lower range of 0.6 to 1.0%, in order to correspond to this, in order to obtain an excess Si type 6000 series Al alloy composition The Mg content is preferably in the lower range of 0.2 to 0.8%.

Cu: 0.001 to 1.0% Cu has the effect of promoting the precipitation of a compound phase such as GP zone in the crystal grains of the Al alloy material structure under the conditions of artificial aging treatment at a relatively low temperature and a short time according to the present invention. There is. Further, Cu solid-dissolved in the aging treatment state also has an effect of improving formability. This effect does not occur when the Cu content is less than 0.001%. On the other hand, if it exceeds 1.0%, the stress corrosion cracking resistance, the thread rust resistance of the corrosion resistance after coating, and the weldability are significantly deteriorated. Therefore, in the case of structural material applications where corrosion resistance is important, 0.8% or less,
In the case of panel applications such as automobile outer panels, the amount is preferably 0.1% or less at which the expression of yarn rust resistance becomes remarkable.

Mn: 0.01 to 0.65% Mn produces dispersed particles (dispersed phase) during the homogenizing heat treatment, and these dispersed particles have an effect of hindering the movement of grain boundaries after recrystallization. It has the effect of obtaining grains. As described above, the press formability and hemmability of the Al alloy sheet of the present invention are improved as the crystal grains of the Al alloy structure are finer. In this respect, if the Mn content is less than 0.01%, these effects are not obtained.

On the other hand, when the Mn content increases, dissolution,
Coarse Al-Fe-Si- (Mn, Cr, Zr) -based intermetallic compounds and crystalline precipitates are easily generated during casting, which easily causes the starting point of fracture. Become. In addition, especially in flat hem processing where the processing conditions became strict due to the complicated shape and thinning, or the presence of a gap between the inner panel edge and the inner surface of the curved edge of the outer panel, the Mn content was 0.25%. If it exceeds the limit, the processability of the hem decreases. Therefore, Mn is set in the range of 0.01 to 0.65%, and more preferably in the range of 0.01 to 0.25% in the flat hem processing in which the processing conditions are severe.

Cr, Zr. Similar to Mn, these transition elements of Cr and Zr have an effect that dispersed particles (dispersed phase) are generated during homogenization heat treatment, and fine crystal grains can be obtained. However, when Cr and Zr also exceed 0.15%, the hem workability is deteriorated in the flat hem processing in which the above-mentioned processing conditions are severe. Therefore Cr,
The Zr content is also preferably regulated to 0.20% or less.

Ti, B. If Ti and B are contained in amounts exceeding Ti: 0.1% and B: 300 ppm, respectively, coarse crystallized substances are formed and formability is deteriorated. However, if Ti and B are contained in a small amount, they also have the effect of refining the crystal grains of the ingot and improving the press formability. Therefore, Ti: 0.1% or less and B: 300ppm or less are allowed.

Fe. Fe contained as an impurity by mixing from the melting raw material is Al
Crystallized substances such as ₇ Cu ₂ Fe, Al ₁₂ (Fe, Mn) ₃ Cu ₂ and (Fe, Mn) Al ₆ are formed. These crystallized substances become nuclei of recrystallized grains and Fe
When it is contained in an amount of 0.08% or more, it serves to prevent coarsening of the crystal grains and make the crystal grains fine particles of 50 μm or less.
However, on the other hand, these crystallized substances significantly deteriorate the fracture toughness and fatigue properties, and further the flat heme processability and press formability under severer processing conditions. These deterioration characteristics become remarkable when the Fe content exceeds 0.50%. Therefore, the content of Fe when it is contained is 0.
It is preferably set to 08 to 0.50%.

Zn. If Zn is contained in excess of 0.5%, the corrosion resistance is significantly reduced. Therefore, the Zn content is preferably 0.5% or less.

(Molding) The hem processing targeted by the present invention is intended to be a flat hem processing. That is, the inner panel edge is stored in the bent part of the outer panel through a down-flange process that bends the outer panel edge to an angle close to 90 ° with a tool such as a punch, and a prehem process that bends the outer panel edge further inward to approximately 135 °. (Insert), and then the edge of the outer panel
The flat hem is formed by bending inward to an angle of 0 °. In this flat hem, the inner panel and the 180-degree bent portion of the outer panel are joined and adhered to each other to have a flat bent portion shape.

However, since the present invention is excellent in workability in flat hem, which is a severe condition, it is a condition looser than that, such as a rope hem having a rope-shaped cross section in which the bent portion bulges in an arc shape. Naturally also excellent in workability. In addition, bending workability such as hat-type bending work and 90-degree bending work other than the above, which has a common processing (deformation) mechanism, or generally, V bending, U bending, end bending, wave bending, tensile bending Also has excellent bending workability. Therefore, the present invention is also applicable to hem processing such as other rope hem, and also to bending processing other than hem processing.

The hem processing is not limited to the normal hem processing performed by the down-flange process, the pre-hem process, the flat hem or the rope hem process described above, and if the hem is finally formed, it is a roller hem process. Such,
Those having different processes and process conditions are also applicable and applicable as hemming.

It should be noted that the hem processing such as the flat hem is carried out on all four peripheries of the Al alloy sheet of the present invention, or only on the selected side (side edge portion), and the hem processing is carried out. Whether the end shape of the outer panel to be formed is a linear shape, an arc shape, or a complicated shape having a corner is appropriately selected according to the member design of the outer panel and the like.

The present invention is also directed to press forming such as the above-mentioned overhanging, as well as hemmability. Further, among the press forming, particularly, the bulging forming when the above-mentioned shape becomes large and complicated in the outer panel or the like is targeted. However, the excellent bulging formability means that the processability is relatively mild and the formability of other drawing is excellent. Therefore, the Al alloy sheet of the present invention is particularly intended for stretch forming, and other press forming represented by stretch forming.

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EXAMPLES Next, examples of the present invention will be described. Regarding the excess Si type 6000 series Al alloy plate (hot rolled plate) shown in Table 1, in order to obtain a texture with anisotropy, as shown in Table 2, the reduction ratio of the cold rolling in the first half, The Al alloy cold-rolled sheet with a thickness of 1.0 mm was variously changed by varying the annealing temperature of the intermediate annealing after the cold rolling (the annealing time was all 3 hours) and the reduction rate of the cold rolling in the latter half after the intermediate annealing. It was created.

The production of the Al alloy plate until hot rolling is
The same conditions were used except for the thickness of the hot rolled plate for changing the reduction ratio of the cold rolling. That is, a 400 mm thick ingot having the composition range shown in Table 1 was melted by the DC casting method,
540 ℃ × 4 hours homogenized heat treatment, finish temperature 300 ℃
Was hot-rolled with various thicknesses ranging from 2.3 to 8 mmt.

Further, the cold-rolled sheet was heat-treated under the following conditions. First, the cold-rolled sheet was placed in an air furnace maintained at 570 ° C, and when each test piece reached the solution treatment temperature of 550 ° C (holding time 0 seconds), it was quenched in hot water of 80 ° C. I went. The cooling rate at the time of the quenching treatment was 200 ° C / sec, the quenching end temperature (quenching temperature) was 80 ° C in common, and the pre-aging treatment was held at this temperature for 2 hours after quenching.
(After holding, it was gradually cooled at a cooling rate of 0.6 ° C / hr).

A plurality of test plates (blanks) each having a width of 500 mm and a length of 500 mm for testing were cut out from the Al alloy plate after the heat treatment, and the Al alloy plate sufficiently aged at room temperature after the heat treatment was press-formed and hem. Assuming that it is processed, the average grain size of each test plate, AS proof stress (σ _0.2 ) parallel to the rolling direction, and Al after 4 months (120 days) after tempering treatment at room temperature
The ratio of the integrated intensity of the {200} plane on the alloy plate surface,
The ratio of the total integrated intensity of the {200} plane and the {400} plane was measured by the above-mentioned X-ray diffraction measurement method. The results are shown in Table 2.

The tensile test for measuring the proof stress is JIS Z
According to 2201, the test piece shape was JIS 5 test piece. Also, the crosshead speed is 5 mm / min,
The test was performed at a constant speed until the test piece broke.

The test plate aged at room temperature was subjected to a forming test by simulating press forming and hemming as an automobile panel. More specifically, an extension molding test and a flat hem processing test after the extension molding were performed to evaluate the formability. The results are shown in Table 3.

The conditions for the bulging molding test were as follows: the test plate (blank) was a rectangular tubular bulging part with a side of 300 mm and a height of 30 mm in the central part, and four surrounding parts of the bulging part. A hat-shaped panel having a flat flange portion (width 30 mm) was stretch-molded by a mechanical press using a beaded mold.

In the bulging test, the wrinkle holding force was 49 kN, the lubricating oil was general rust preventive oil, and the molding speed was 3 mm under the same conditions of 20 mm / min.
Molding was carried out three times, and in all three cases, there were no cracks in the overhanging corners of the hat-shaped panel and normal molding was possible, and in all three cases, cracking occurred and molding could not be carried out.

The surface properties such as the ridging mark of the molded product were evaluated by washing the molded product of the above-mentioned bulging test and then applying the zinc phosphate treatment, coating and baking treatment under the same conditions to the appearance of the surface of the molded product. The evaluation was performed according to the occurrence status of ridging marks and rough skin. On all three surfaces (three pieces) of the surface of the molded article, all three pieces without ridging marks or rough skin were evaluated as ◯, and even one piece with ridging marks or rough surface was evaluated as x.

In this case, the zinc phosphate treatment is performed by a colloidal dispersion of titanium phosphate, and then immersed in a zinc phosphate bath containing fluorine at a low concentration of 50 ppm to form a zinc phosphate coating on the surface of the molding material. Formed. The subsequent coating treatment was carried out under the condition of performing cationic electrodeposition coating and then baking at 170 ° C. for 20 minutes.

Next, the flat hem processing test was conducted as follows. The bulging-formed Al alloy panel, simulating that it is hem processed as an outer panel, of the flat flange portion of the panel, the entire end portion of the flange portion parallel to the rolling direction (width 130 mm) Flat hem processing was performed under the following conditions.

More specifically, first, the flat hemming allowance of the Al alloy panel (distance from the end bent inside the panel after the hemming to the end of the bent part) is 12 mm.
As a result, the down flange process was simulated, and the edge of the Al alloy panel was bent to an angle of 90 degrees. At this time, the 90 ° bending radius of the Al alloy panel was 0.8. Next, by simulating the prehem process, the edge of the Al alloy panel was further bent inward to an angle of 135 °.

After that, simulating the severe flat hem processing conditions, without inserting the inner panel into the bent portion of the Al alloy panel, the bent portion is bent 180 degrees inward, and the flat bending processing is performed to bring it into close contact with the panel surface. went.
The hemming direction was made to coincide with the rolling direction of the original Al alloy plate.

Then, the surface condition such as rough skin, fine cracks, and large cracks was visually observed at the curved edge of the flat hem. The evaluation is 1; good with no rough skin or fine cracks, 2; no rough cracks, including small ones, 3; fine cracks, 4; large cracks, 5 ; Evaluation in 5 levels, with multiple or multiple major cracks
(Including the evaluation of each of the five stages). For this evaluation, it is judged that the hemmability is good (usable) from 1 to
It is judged that the hem processability is inferior (unusable) for 3 or more steps up to 2 steps.

Further, in order to investigate the artificial aging treatment ability, a sample plate was taken from the press-formed Al alloy panel and subjected to artificial aging hardening treatment at a low temperature for a short time of 160 ° C. × 20 minutes,
The proof stress (AB σ _0.2 ) parallel to the rolling direction (of the original Al alloy plate) (AB σ _0.2 ) of each test plate after the treatment was measured. The results are shown in Table 3.

As is clear from Tables 2 and 3, Invention Examples 1 to 6 satisfying the manufacturing conditions of the present invention, such as the first half cold rolling reduction, the intermediate annealing temperature, and the second half cold rolling reduction, were prepared. , The average grain size is as fine as 50 μm or less, and
After aging at room temperature for 0 days), neither ridging marks nor rough skin was observed after stretch molding, and the surface quality of the molded product was evaluated as ○.
Is remarkably excellent in. In addition, {20 on the surface of the Al alloy plate
The ratio of the integrated intensity of the 0} plane is 70% or more, and the {200} plane and the {40} plane
The ratio of the total integrated intensity with respect to the (0) plane is 80% or more, the ratio of the crystal grains having the cube orientation is a highly anisotropic texture, and the flat heme processability is excellent. Furthermore, it has excellent stretchability, AB proof stress of 200 MPa or more, and various properties such as age hardening.

The test conditions and evaluation of the flat hem processability lead to the evaluation of the flat hem processability under actual severe process conditions such as the outer panel of an automobile. Therefore, Invention Examples 1 to 6 show that even hemming such as an actual flat hem can be sufficiently processed.

The test conditions and evaluation of the above-mentioned bulge molding are as follows.
This leads to evaluation of stretch forming under actual severe processing conditions such as automobile outer panels. Therefore, Invention Examples 1 to 6 show that in actual press forming such as bulging and drawing, even if the bulging height and bulging area increase, the bulging formability is excellent and sufficient processing is possible. There is.

On the other hand, the rolling reduction in the first half cold rolling was too low, and the rolling reduction in the latter half cold rolling was too high. Comparative Example 7, the rolling reduction in the first half cold rolling was too high, and the rolling reduction in the second half cold rolling was too low. Comparative Example 8 too, intermediate annealing temperature is too high Comparative Example 9, intermediate annealing temperature is too low Comparative Example 10, the rolling reduction in the first half cold rolling is high, the rolling reduction in the latter half cold rolling is too low Comparative Example In Nos. 11 and 12, the average average crystal grain size exceeds 50 μm, and ridging marks and skin roughness are generated after the bulging and the surface properties of the molded product are remarkably inferior.

In Comparative Examples 7, 8, 9, and 11, although the stretch forming was good, the proportion of crystal grains having the cube orientation was low and the flat heme processability was also poor. Therefore,
From these results, the critical significance of each regulation in the production method of the present invention is understood. Moreover, these results (effects) are also applicable to Al-Mg-Si based Al alloy plates other than the excess Si type.

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[Table 1]

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[Table 2]

[0094]

[Table 3]

[0095]

According to the present invention, the 6000 series is excellent in bending workability such as hemming even when aged at room temperature, and is excellent in press formability by suppressing ridging marks and rough skin.
A method for manufacturing an Al alloy plate can be provided. Therefore, it has a great industrial value in that the 6000 series Al alloy plate can be expanded to panel applications.

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Claims (4)

[Claims] 1. A hot rolled Al-Mg-Si based aluminum alloy sheet is cold rolled at a rolling reduction of 10 to 50%, and then 210 to 440.
After annealing at a temperature of ℃ and cold rolling at a reduction of 70% or more, solution treatment and quenching are applied to make the texture of the aluminum alloy sheet anisotropic, and the average grain size is 50 μm or less. A method for producing an aluminum alloy sheet having excellent bending workability, comprising: 2. The aluminum alloy plate has a Si: 0.4-1.
3%, Mg: 0.2-1.2%, Mn: 0.01-0.65%, Cu: 0.001-1.0%
And the ratio of Si / Mg is 1 or more by mass and the balance is Al
The method for producing an aluminum alloy sheet having excellent bendability according to claim 1, wherein the aluminum alloy sheet has a composition of unavoidable impurities. 3. The anisotropy of the structure of the aluminum alloy plate is such that the ratio of the integrated strength of the {200} face on the surface of the aluminum alloy plate is 70% or more and the anisotropy of the {200} face and the {4} face is
The method for producing an aluminum alloy sheet having excellent bending workability according to claim 1 or 2, wherein a ratio of the total integrated strength with respect to the {00} plane is 80% or more. 4. The method for producing an aluminum alloy sheet having excellent bending workability according to claim 1, wherein the aluminum alloy sheet is hemmed after stretch forming.