JP2017078211A - Aluminum alloy sheet having high moldability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 6000 series aluminum alloy sheet having high moldability capable of being manufactured as for an automotive panel material without largely changing a conventional composition or manufacturing condition.SOLUTION: High work hardening property is achieved by increasing a solid solution Si amount and a solid solution Cu amount of an Al-Mg-Si-based aluminum alloy sheet at good balance, suppressing localization of transition introduced into a material by tensile deformation during press molding to an automotive panel material with transition density in a specific range when tensile deformation in low strain region to the sheet, increasing transition uniformly from low strain range to high strain range and suppressing nonuniform deformation in molding to the automotive panel material.SELECTED DRAWING: None

Description

  The present invention relates to an Al—Mg—Si-based aluminum alloy plate excellent in formability. The aluminum alloy plate referred to in the present invention is a rolled plate such as a hot-rolled plate or a cold-rolled plate, and after being subjected to tempering such as solution treatment and quenching treatment, the member to be used This refers to an aluminum alloy plate before being bent or painted and hardened. In the following description, aluminum is also referred to as aluminum or Al.

  In recent years, due to consideration for the global environment and the like, social demands for weight reduction of vehicles such as automobiles are increasing. In order to respond to such demands, instead of steel materials such as steel plates, the application of lighter aluminum alloy materials with excellent formability and paint bake hardenability (bake hard property, hereinafter also referred to as BH property) as automobile materials Is increasing.

  Examples of aluminum alloy plates for large automobile panel materials such as automobile outer panels and inner panels are typically Al-Mg-Si AA to JIS 6000 series (hereinafter also simply referred to as 6000 series) aluminum alloy sheets. Is done. This 6000 series aluminum alloy sheet has a composition containing Si and Mg as essential components, and has a low yield strength (low strength) during molding and ensures formability. Artificial aging (hardening) such as paint baking treatment of panels after molding. Yield (strength) is improved by heating at the time of processing, and the necessary baking strength can be secured.

From the viewpoint of design, the outer panel of an automobile needs to realize a beautiful curved surface configuration and a character line that are free from distortion and wrinkles even if the shape of a corner portion or character line is sharpened or complicated. Further, even in an inner panel of an automobile, it is necessary to realize a curved surface configuration free from distortion and wrinkles even if the uneven shape to be designed becomes deeper (higher) and complicated due to the relationship with the outer panel.
And the request | requirement of such high moldability has become severe every year with the adoption expansion of the aluminum alloy plate which is a raw material.

  However, the high formability required for such automotive panel material applications, the normal (conventional) alloy composition range of 6000 series aluminum alloy plates, which are harder to process than steel plate materials, and normal manufacturing Achieving this without significantly changing the process and conditions is a rather difficult task.

On the other hand, as is well known, conventionally, the composition and structure control means for improving the formability and strength properties of the material 6000 series aluminum alloy plate as the panel material are from the control of the crystal grain size, Many proposals have been made up to the control of atomic clusters (clusters), including control of textures.
Among these means for controlling the structure, various proposals have been made to control the amount of solid solution Mg, the amount of solid solution Si, or the amount of solid solution Cu, and the control of the dislocation density.

  For example, in Patent Document 1, for the purpose of obtaining a 6000 series aluminum alloy plate that is excellent in room temperature stability and hardly deteriorates in material such as bake hardness (BH property) due to room temperature aging as the panel material. The amount of Si may be 0.55 to 0.80 mass%, the amount of solid solution Mg may be 0.35 to 0.60 mass%, and the amount of solid solution Si / solid solution Mg may be 1.1 to 2. Proposed.

  Moreover, in patent document 2, 6000 type | system | group for warm forming excellent in BH property which made Cu solid solution amount measured by the residue extraction method 0.01-0.7%, and made the average crystal grain diameter 10-50 micrometers. Aluminum alloy plates have been proposed.

Furthermore, in Non-Patent Document 1, in order to further increase the strength of a 6000 series aluminum alloy sheet, a microstructural parameter (dislocation density) that optimally combines dislocation strengthening or grain refinement strengthening and precipitation strengthening. , Crystal grain size) has been proposed.
And about the sample which gave cold rolling or HPT processing which is one of the giant strain processing methods to a 6000 series aluminum alloy plate, a dislocation density is investigated and the dislocation density of a non-processed material is about 10 ^{< 11 >} m ^<-2 >. It is described that the dislocation density of the cold-rolled material subjected to a rolling rate of 30% (equivalent strain 0.36) is about 10 ¹⁴ m ⁻² .
The dislocation density is measured by the cross-cut analysis method using the TEM photograph 5 fields of view with a magnification of 100,000 times by the equal thickness interference fringe method.

JP 2008-174797 A JP 2008-266684 A

Journal of the Japan Institute of Metals, Vol. 75, No. 5 (2011), pp. 283-290, "Experimental and computational science of competitive precipitation observed in Al-Mg-Si alloys with high dislocation density and ultrafine grain structure Research ”Tetsuya Masuda, Shinichi Serizawa, Zenji Hotta, Kenji Matsuda

  However, in these conventional techniques, the control of the amount of solid solution elements and the control of the dislocation density are performed for the purpose of improving particularly the strength characteristics of the 6000 series aluminum alloy plate. For this reason, although the combination of formability is taken into consideration, the level does not fall within the range of normal hem workability and press formability, and is as severe as required for the above-mentioned recent automobile panel materials. It is not the purpose of achieving high formability.

  Therefore, in order to achieve the strict high formability required for such automotive panel material applications, the panel design can be changed or the molding conditions can be changed to reduce the load during molding, or the 6000 series aluminum alloy plate Actually, there has been only a conventionally known measure such as lowering the strength at the time of molding.

  The present invention has been made to solve such problems, and has a high formability of 6000 that can be manufactured for automobile panel materials without greatly changing the composition and manufacturing conditions of a conventional 6000 series aluminum alloy plate. An object of the present invention is to provide an aluminum alloy plate.

In order to achieve this object, the gist of the high formability aluminum alloy plate of the present invention is mass%, Si: 0.30 to 2.0%, Mg: 0.20 to 1.5%, Cu: 0. 0.05 to 1.0%, Mn: 1.0% or less (excluding 0%), Fe: 1.0% or less (excluding 0%), the balance being Al and inevitable An Al—Mg—Si-based aluminum alloy plate made of impurities having a solid solution Si amount of 0.30 to 2.0% and a solid solution Cu amount in the solution separated by the hot phenol residue extraction method of this plate 0.05 to 1.0%, and the average dislocation density of the rolled surface of the plate measured by X-ray diffraction was 6 when a tensile deformation of 5% strain was applied in the rolling direction of the plate. and that it is ^{.0 × 10 14 ~12 × 10 14} m -2.

In the present invention, the amount of solute Si and the amount of solute Cu of the 6000 series aluminum alloy plate is increased, and at the time of molding into an automobile panel material, the localization of dislocations introduced into the material by tensile deformation is suppressed, It is intended to propagate dislocations uniformly (relatively higher) from the low strain region to the high strain region of the tensile deformation.
As a result, it is possible to suppress non-uniform deformation from high strain range to breakage in press molding of automobile panel material, and to exhibit high work hardening characteristics.

However, in order to ensure that such a solid solution Si or solid solution Cu mechanism is exhibited and to achieve high formability for automobile panel materials, it is assumed that molding to actual automobile panel materials is performed. The amount of dislocation density of the plate in the low strain region of the tensile deformation is an important index.
In other words, the increase in solute Si and solute Cu is not sufficient, and the amount of dislocation density of the plate in the low strain region of the tensile deformation is satisfied, thereby achieving high formability for automobile panel materials. I found out that I can do it.
In addition, the amount of dislocation density in the low strain region at the time of forming into an actual automobile panel material (at the time of tensile deformation) is simulated by the dislocation density when a tensile deformation of 5% strain is applied in the rolling direction of the base plate. It was also found that they can be correlated with each other.

That is, it is necessary to increase the amount of solute Si and solute Cu in the material plate in a well-balanced manner, and when a tensile deformation of 5% strain is applied in the rolling direction of the material plate, it has a predetermined dislocation density. This is a sufficient condition, and by satisfying both of these conditions, high formability for automobile panel materials can be achieved.
In addition, high formability by these controls has the advantage that it can be achieved without greatly changing the conventional aluminum alloy composition and manufacturing conditions.

  Hereinafter, embodiments of the present invention will be specifically described for each requirement.

(Chemical composition)
First, the chemical component composition of the Al—Mg—Si (hereinafter also referred to as 6000) aluminum alloy sheet of the present invention will be described below. In the present invention, various requirements such as high formability, BH property, strength, weldability, and corrosion resistance necessary for the panel material are satisfied from the viewpoint of composition. However, even in this case, it is assumed that the conventional composition and manufacturing conditions are not greatly changed.

  In order to satisfy such a problem from the viewpoint of composition, the composition of the 6000 series aluminum alloy plate is mass%, Si: 0.30 to 2.0%, Mg: 0.20 to 1.5%, Cu: 0.05-1.0%, Mn: 1.0% or less (excluding 0%), Fe: 1.0% or less (excluding 0%), respectively, the balance being It shall consist of Al and inevitable impurities.

  In addition to this, Cr: 0.3% or less (excluding 0%), Zr: 0.3% or less (excluding 0%), V: 0.3% or less (providing that , 0% not included), Ti: 0.1% or less (excluding 0%), Zn: 1.0% or less (excluding 0%), Ag: 0.2% or less ( However, it is allowed to contain one or more of Sn: 0.15% or less (however, not including 0%).

  The content range and significance of each element in the 6000 series aluminum alloy sheet, or the allowable amount will be described below. In addition,% display of content of each element means the mass% altogether.

Si: 0.30 to 2.0%
Si, together with Mg, forms Mg-Si based precipitates that contribute to strength improvement during solid solution strengthening and artificial aging treatment such as baking coating treatment, and exhibits artificial age hardening ability (BH property). It is an indispensable element for obtaining the strength (proof strength) required for the outer panel.
Further, solute Si suppresses the localization of dislocations introduced into the material in press molding to automobile panel materials, and has the effect of uniformly growing dislocations from a low strain region to a high strain region of tensile deformation. As a result, non-uniform deformation from high strain range to breakage during press molding can be suppressed, and high elongation and work hardening characteristics can be exhibited.

If the Si content is too small, the amount of dissolved Si decreases, the elongation during press molding and work hardening characteristics decrease, and the amount of dislocation growth after imparting 5% strain tensile deformation decreases. In addition, since the amount of Mg—Si-based precipitates is insufficient, the BH property is lowered, and the strength after the baking coating process is significantly lowered.
On the other hand, when there is too much Si content, a coarse crystallization thing and a precipitate will be formed and a big board crack will arise during hot rolling.
Therefore, Si is set to a range of 0.30 to 2.0%. The preferable lower limit value of Si is 0.50%, and the preferable upper limit value is 1.5%.

Mg: 0.20 to 1.5%
Mg, together with Si, forms a Mg-Si-based precipitate that contributes to strength improvement during solid solution strengthening and artificial aging treatment such as baking coating, and exhibits artificial aging hardening ability (BH property) as a panel It is an essential element for obtaining the required proof stress.
In addition, solid solution Mg, like solid solution Si, suppresses the localization of dislocations introduced into the material during press molding of automotive panel materials, and dislocations uniformly from the low strain region to the high strain region of tensile deformation. Has the effect of proliferating. As a result, non-uniform deformation from high strain range to breakage during press molding can be suppressed, and high elongation and work hardening characteristics can be exhibited.

If the Mg content is too small, the solid solution Mg amount is decreased, the work hardening characteristics are lowered, and the dislocation growth amount after applying a tensile deformation of 5% strain is lowered. Furthermore, since the production amount of Mg—Si-based precipitates is insufficient, the BH property is lowered and the strength after the baking coating treatment is lowered.
On the other hand, when there is too much Mg content, a coarse crystallization thing and a precipitate will be formed and a big plate crack will arise during hot rolling.
Therefore, the Mg content is in the range of 0.20 to 1.5%. A preferable lower limit value of Mg is 0.30%, and a preferable upper limit value is 1.2%.

Cu: 0.05 to 1.0%
Cu contributes to improvement of strength and formability. And solid solution Cu improves work hardening characteristic like solid solution Si, and raises the balance of intensity and formability.
When the amount of Cu is less than 0.05%, the effect of Cu itself is reduced, and at the same time, the amount of solid solution Cu is insufficient, and the effect of solid solution Cu is also insufficient.
On the other hand, when the amount of Cu exceeds 1.0%, the yarn rust resistance and stress corrosion cracking resistance after coating are remarkably deteriorated. For this reason, it is preferable to set it as 0.80% or less in the use etc. where corrosion resistance is regarded as important.

Mn: 1.0% or less (excluding 0%)
Mn improves the strength of the aluminum alloy by solid solution strengthening and crystal grain refinement effects.
However, when it exceeds 1.0% and it contains excessively, the amount of Al-Mn type intermetallic compounds will increase, it will become a starting point of destruction, and elongation will fall easily. Moreover, when a low strain of about 5% is applied to the plate, dislocations are localized around the Al—Mn intermetallic compound, and work hardening characteristics also deteriorate.
Therefore, the Mn content is 1.0% or less (however, not including 0%), preferably 0.8% or less (however, not including 0%).

Fe: 1.0% or less (excluding 0%)
Since Fe forms an Al—Fe-based intermetallic compound in the aluminum alloy, when the content is increased, the amount of the compound is increased to become a starting point of fracture, and elongation is likely to decrease. Moreover, Si is often included in the Al—Fe-based intermetallic compound, and the amount of solute Si is reduced by the amount of Si taken into the intermetallic compound.
Fe is mixed into the aluminum alloy as a metal impurity, and the content increases as the amount of aluminum alloy scrap (ratio to the aluminum metal) increases as a melting raw material. Therefore, the smaller the content, the better. However, reducing Fe below the detection limit or the like increases the cost, so a certain amount of allowance is required.
Therefore, the Fe content is 1.0% or less (however, not including 0%), preferably 0.5% or less (however, not including 0%).

Other Elements In addition, in the present invention, Cr: 0.3% or less (excluding 0%), Zr: 0.3% or less (excluding 0%), V: 0.3 % Or less (excluding 0%), Ti: 0.1% or less (excluding 0%), Zn: 1.0% or less (excluding 0%), Ag: 0. It is allowed to contain one or more of 2% or less (excluding 0%) and Sn: 0.15% or less (excluding 0%).

Since these elements have the effect of increasing the strength of the plate in common, they can be regarded as synergistic elements for increasing the strength, but the specific mechanism includes not only common parts but also different parts. Of course there is.
Cr, Zr, and V, like Mn, produce dispersed particles (dispersed phase) during the homogenization heat treatment, and these dispersed particles have the effect of hindering grain boundary movement after recrystallization. To play a role.
Ti forms a crystallized substance together with B, serves as a nucleus of recrystallized grains, prevents coarsening of the crystal grains, and plays a role of refining the crystal grains.
Zn and Ag are useful for improving the artificial age hardening ability (BH property), and precipitate a compound phase such as a GP zone in the crystal grains of the plate structure under conditions of artificial aging treatment at a relatively low temperature for a short time. There is an effect to promote.
Sn captures atomic vacancies, suppresses diffusion of Mg and Si at room temperature, suppresses an increase in strength at room temperature (room temperature aging), releases vacancies captured during artificial aging treatment, It has the effect of promoting the diffusion of Mg and Si and increasing the BH property.

  However, if the content of each of these elements is too large, it becomes difficult to produce a plate by forming a coarse compound, and formability such as strength and bending workability and corrosion resistance are also lowered. Therefore, when these elements are contained, the content is not more than the above upper limit values.

(Organization)
Based on the above alloy composition, in the present invention, in order to improve formability, the structure of the plate also defines the amount of solute Si, the amount of solute Cu, and the dislocation density as follows.

The amount of solute Si and the amount of solute Cu In the conventional automotive panel material application, the control of the amount of solute Si and the amount of solute Cu of the 6000 series aluminum alloy plate is mainly based on strength characteristics as described in Patent Documents 1 and 2 above. The purpose was to improve.
On the other hand, in this invention, the moldability to a motor vehicle panel material is improved by increasing the amount of solute Si and the amount of solute Cu with good balance.
In the 6000 series aluminum alloy plate for automobile panel materials, the present inventors have not found an example in which the control of the solid solution Si amount and the solid solution Cu amount is performed for the purpose of improving formability.
In the following, the specified ranges of the solute Si amount and the solute Cu amount and their significance will be described.

Solid solution Si amount 0.30-2.0%
The higher the amount of solute Si, the lower the stacking fault energy of the aluminum alloy together with the solute Cu, which suppresses the localization of dislocations introduced into the material during tensile deformation, such as during press forming on automobile panel materials. Thus, dislocations are uniformly propagated from a low strain region to a high strain region of tensile deformation. As a result, work hardening characteristics are improved, yield ratio is reduced, and elongation is increased.
If the amount of solid solution Si is less than 0.30%, even if the amount of solid solution Cu is satisfied, the effect is insufficient.
The upper limit of the solute Si amount is substantially the same as the upper limit of the Si content described above.

Incidentally, solid solution Mg, like solid solution Si, improves work hardening characteristics, reduces the yield ratio, and increases elongation.
However, since Si precipitates together with Al—Fe and Al—Mn intermetallic compounds, control of the amount of dissolved Si is complicated and important, whereas Mg mainly precipitates together with Si. Control of the solid solution Mg amount is relatively easy.
Furthermore, since the increase or decrease in the amount of solid solution Mg shows the same behavior and tendency as the amount of solid solution Si, if the amount of solid solution Si is measured and controlled to satisfy the above regulations, the amount of solid solution Mg is necessarily increased. There is no need to measure and control the solid solution Mg amount.
Therefore, in the present invention, although the effect is expected, the solid solution Mg amount is not defined.

Solid solution Cu amount 0.05-1.0%
Along with the solid solution Si amount, the solid solution Cu amount is also important. As the amount of solid solution Cu increases, the work hardening characteristics can be improved, the yield ratio can be reduced, the elongation can be increased, and the balance between strength and formability can be increased, as in the case of solid solution Si.
If the amount of solid solution Cu is less than 0.05%, even if solid solution Si is satisfied, the effect is insufficient.
The upper limit of the amount of solid solution Cu is substantially the same as the upper limit of the addition amount.

Dislocation density Control of the amount of solute Si and the amount of solute Cu in order to reliably exhibit the above-described mechanism of solute Si and solute Cu and to reliably achieve high formability for automobile panel materials. In addition to this, it is necessary to control the amount of dislocation density of the plate in a low strain region during molding into an actual automobile panel material.
The amount of dislocation density in such a low strain region is reproducible due to the dislocation density when applying 5% strain tensile deformation in the rolling direction of the plate, simulating press forming on an actual automobile panel material. Can measure well.

Therefore, in the present invention, a tensile test simulating press forming on an actual automobile panel material is performed on a plate that satisfies the above composition and the amount of solute Si or solute Cu. Then, the dislocation density of the plate when the tensile deformation of 5% strain is applied (after application) is controlled in the range of 6.0 × 10 ^{14 to} 12 × 10 ¹⁴ m ^{−2 on} average.
This dislocation density is measured by measuring the structure of the rolled surface of the plate (rolled surface of the plate) by X-ray diffraction when a tensile deformation of 5% strain is applied in the rolling direction of the plate.

In the low strain region where the strain at the time of the tensile test is about 5%, the dislocations are propagated uniformly (relatively high) in the above range, so that non-uniform deformation from the subsequent high strain region to breakage can be achieved. Suppressed and high work hardening characteristics (reduction in yield ratio, increase in elongation) are exhibited.
This dislocation density lower than 6.0 × 10 ¹⁴ m ⁻² suggests that the dislocations are difficult to proliferate and have low work hardening properties, which causes early breakage in the high strain region. This results in a reduction in moldability.
On the other hand, if the dislocation density in the low strain region where the strain is 5% is higher than 12 × 10 ¹⁴ m ⁻² , dislocations that can be introduced and accumulated in the subsequent high strain region are reduced, so that the moldability is not improved. .
Therefore, the (after) dislocation density when 5% tensile deformation is applied in the rolling direction of the plate is in the range of 6.0 × 10 ^{14 to} 12 × 10 ¹⁴ m ^{−2 on} average, and preferably 7.0. in the range of ^{× 10 14 ~11 × 10 14 m} -2.

Incidentally, as described in Non-Patent Document 1, an ordinary 6000 series aluminum alloy plate that does not give a tensile deformation of 5% strain as in the present invention has a different measurement method (magnification of 100,000 times). However, it has a dislocation density of about 10 ¹¹ m ⁻² in an unprocessed state (solution treated material). Further, this plate has only a dislocation density of about 10 ¹⁴ m ^{−2 in} a state where cold rolling with a rolling rate of 30% (equivalent strain 0.36) is performed.

On the other hand, in the present invention, it is more than the cold rolling addition of Non-Patent Document 1 described above, only by applying a low strain tensile deformation of only 5% to the cold-rolled sheet that has undergone solution treatment. A dislocation density of × 10 ^{14 to} 12 × 10 ¹⁴ m ⁻² can be introduced.
This is due to an increase in the amount of solid solution Si and the amount of solid solution Cu in the present invention, and unless this is present, it means that the dislocation density specified in the present invention cannot be introduced. Also, it means that the strain deformation and dislocation density introduced into the material are completely different between the tensile deformation at the time of forming into an automotive panel material and the cold rolling of the plate as in Non-Patent Document 1. ing.

The technical idea of increasing the solute Si amount and the solute Cu amount of the present invention does not occur unless the formability to an automobile panel material and the relationship between the solute Si amount and the solute Cu amount are known. .
Also, the technical idea to control the amount of dislocation density of the plate does not pay attention to the dislocation density introduced into the material by tensile deformation, such as when forming into automobile panel materials, nor the dislocation density in the low strain region. It does not occur as much as possible.
Furthermore, it is recognized that dislocation density of 6.0 × 10 ^{14 to} 12 × 10 ¹⁴ m ⁻² can be introduced only by applying a low strain strain of only 5% to a solution-treated material (unprocessed material). It does not occur unless the technical idea is obtained and actually tested and confirmed.
Therefore, even if the above-mentioned non-patent document 1 and other known examples pay attention to the influence on the properties such as the strength of the dislocation density of the plate, it is also possible to increase the amount of solid solution Si and solid solution Cu. Even if there is a publicly known example that improves the strength, the configuration of the present invention cannot be easily obtained.

Measurement method of dislocation density Measurement of dislocation density with a transmission electron microscope or the like is also widely used as in Non-Patent Document 1, but in the present invention, measurement is simpler and more reproducible by X-ray diffraction. To do.
Of the dislocations, regions (cell walls and shear bands) in which linear and streak dislocations are dense are difficult to discriminate with a transmission electron microscope, and can cause measurement errors when determining the dislocation density ρ. On the other hand, in X-ray diffraction, as will be described later, since the dislocation density ρ is calculated from the half-value width of the diffraction peak from each surface in the texture, there is less error even with such a forest dislocation. There are advantages.

  In the structure of a plate in which dislocations are introduced by applying plastic deformation such as cold rolling or tensile test, lattice strain is generated around dislocations. In addition, small tilt grain boundaries, cell structures, and the like develop due to the dislocation arrangement. When such dislocations and the domain structure associated therewith are taken from the X-ray diffraction pattern, a characteristic spread corresponding to the diffraction index and a shape appear in the diffraction peak. By analyzing the shape (line profile) of this diffraction peak (line profile analysis), the dislocation density can be obtained.

  Specifically, first, a JISZ2201 No. 5 test piece (25 mm × 50 mmGL × plate thickness) was collected as a test plate from a tempered cold-rolled plate in the manner of a tensile test, and the test piece was collected at room temperature. Pulling is performed with the pulling direction as the rolling direction. This simulates the dislocation density of a plate in a low strain region during molding into an actual automobile panel material, and gives a tensile deformation of 5% strain as the low strain region.

  X-ray diffraction of the texture of the rolled surface (rolled surface) of the test piece imparted with the tensile deformation of 5% strain is the main orientation in the texture of the plate (test piece) surface part (111), The half width of the diffraction peak from each surface (each azimuth surface) of (200), (220), (311), (400), (331), (420), (422) is obtained. The higher the dislocation density ρ, the larger the half width of the diffraction peak on each of these surfaces. In addition, even if the rolled surface used as the measurement object of X-ray diffraction of the test piece which gave the tensile deformation of 5% distortion was the state of a test piece, even if the cleaning without etching was given good.

Next, after obtaining the lattice strain (crystal strain) ε by the Williamson-Hall method from the half-value width of the diffraction peak of each surface, the dislocation density ρ can be calculated by the following equation.
ρ = 16.1ε ² / b ²
Here, ρ is the dislocation density, ε is the lattice strain, and b is the size of the Burgers vector.
The size of Burgers vector was 2.8635 × 10 ^-10 m.

  The Williamson-Hall method is a well-known line profile analysis method that is widely used to determine the dislocation density and the crystal grain size from the relationship between the half width of a plurality of diffractions and the diffraction angle. In addition, a series of methods for obtaining the dislocation density by X-ray diffraction is also known, and the series of methods for obtaining the dislocation density by X-ray diffraction are collectively referred to as “dislocation density measured by X-ray diffraction” in the present invention. Dislocation density ".

Index of high work hardening characteristics (high formability) Yield ratio and elongation are examples of indices (standards) for achieving high work hardening characteristics (high formability) of a plate by controlling the composition and structure described above.
If the yield ratio is low and the elongation is high at the same time, high formability for automotive panel materials can be achieved without performing molding tests on small test pieces of the plate or molding tests on actual automotive panel materials. Is supported.
Specifically, the index (standard) for achieving high formability is the ratio between the 0.2% proof stress and the tensile strength (0.2% proof stress / tensile strength) of the aluminum alloy sheet, as will be explained in the examples described later. The yield ratio defined in (1) is 0.56 or less and the total elongation is 26% or more.
If this yield ratio exceeds 0.56 and is too high, or if the total elongation is too low as less than 26%, high work hardening characteristics and high formability cannot be achieved for automobile panel materials.

(Production method)
Next, a method for producing the aluminum alloy plate of the present invention will be described below.
The aluminum alloy sheet of the present invention is a conventional process or a known process, and the aluminum alloy ingot having the above-mentioned 6000 series component composition is subjected to homogenization heat treatment after casting, and then subjected to hot rolling and cold rolling to obtain a predetermined process. It is manufactured by being subjected to a tempering treatment such as solution hardening and quenching.

  However, in these manufacturing processes, in order to ensure that the structure (the amount of dissolved Si and the amount of dissolved Cu or the dislocation density) defined by the present invention is reproducibly ensured, as described later, soaking conditions, heat Conditions such as interfinish rolling conditions, solution treatment and quenching treatment are set in a preferred range.

Melting and casting cooling rate First, in the melting and casting process, an aluminum alloy melt adjusted to be dissolved within the above-mentioned 6000-based component composition range is converted into a normal melting and casting method such as a continuous casting method or a semi-continuous casting method (DC casting method). Is appropriately selected and cast. Here, in order to control the structure (the amount of solute Si and the amount of solute Cu, or dislocation density) within the specified range of the present invention, the average cooling rate during casting is from the liquidus temperature to the solidus temperature. Is preferably as large as possible (faster) at 30 ° C./min or more.

  When such temperature (cooling rate) control in the high temperature region during casting is not performed, the cooling rate in this high temperature region is inevitably slow. As described above, when the average cooling rate in the high temperature region becomes slow, the amount of crystallized material generated coarsely in the temperature range in this high temperature region increases, and the amount of solute Si and the amount of solute Cu in the ingot Less. As a result, there is a high possibility that the tissue cannot be controlled within the scope of the present invention.

Homogenization heat treatment Next, the cast aluminum alloy ingot is subjected to a homogenization heat treatment prior to hot rolling. This homogenization heat treatment (uniform heat treatment) is important for sufficiently dissolving Si and Mg in addition to the normal purpose of homogenizing the structure (eliminating segregation in crystal grains in the ingot structure). It is. The conditions are not particularly limited as long as the object is achieved, and normal one-stage or one-stage processing may be performed.

  The homogenization heat treatment temperature is 500 ° C. or more, 560 ° C. or less, and the homogenization (retention) time is appropriately selected from a range of 1 hour or more to sufficiently dissolve Si and Cu. If this homogenization temperature is low, the solid solution amount of Si or Cu cannot be secured, and the structure (solid solution Si) prescribed by the present invention is also obtained by preliminary aging treatment (reheating treatment) after solution treatment and quenching treatment described later. Amount and solute Cu amount). Further, segregation in the crystal grains cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that formability is lowered.

After this homogenization heat treatment, hot rolling is performed. Until the start of hot rough rolling after the homogenization heat treatment, the solution of Si or Cu is dissolved at 500 ° C. or lower without lowering the temperature of the ingot. It is necessary to secure the quantity.
When the temperature of the ingot is lowered to 500 ° C. or less by the start of rough rolling, Si and Cu are precipitated, and it is not possible to secure the solid solution amount of Si and Cu to obtain the above-defined structure of the present invention. Increases nature.

Hot rolling Hot rolling is composed of a rough rolling process of an ingot (slab) and a finish rolling process according to the sheet thickness to be rolled. In these rough rolling process and finish rolling process, a reverse or tandem rolling mill is appropriately used.

During rolling from the start to the end of hot rough rolling, it is necessary to ensure the solid solution amount of Si or Mg without lowering the temperature to 450 ° C. or lower.
If the minimum temperature of the rough rolled sheet between passes falls to 450 ° C. or lower due to an increase in rolling time or the like, Mg—Si based compounds are likely to precipitate, and the amount of solute Si and solute Cu decreases. For this reason, possibility that the solid solution amount of Si or Cu for setting it as the said structure | tissue which this invention prescribes | regulates becomes high.

After such hot rough rolling, hot finish rolling with an end temperature in the range of 300 to 360 ° C. is performed.
When the finishing temperature of this hot finish rolling is too low, such as less than 300 ° C., the rolling load becomes high and the productivity is lowered. On the other hand, in order to obtain a recrystallized structure without leaving a large amount of processed structure, when the finish temperature of hot finish rolling is increased, if this temperature exceeds 360 ° C., an Mg—Si compound tends to precipitate and become solid. The amount of dissolved Si and the amount of dissolved Cu decrease. For this reason, possibility that the solid solution amount of Si or Cu for setting it as the said structure | tissue which this invention prescribes | regulates becomes high.

Further, the average cooling rate from the material (plate) temperature immediately after the hot finish rolling to the material temperature of 150 ° C. is controlled to at least 5 ° C./hour or more.
When this average cooling rate is less than 5 ° C./hour, the amount of Mg—Si-based precipitates generated during the cooling increases, and the amount of solute Si in the product plate decreases.
Accordingly, the average cooling rate immediately after the end of hot finish rolling is preferably large, and at least 5 ° C./hour or more, preferably 8 ° C./hour or more.

Annealing of hot-rolled sheet Annealing (roughening) of the hot-rolled sheet before cold rolling is not necessary, but may be performed.

Cold Rolling In cold rolling, the hot rolled sheet is rolled to produce a cold rolled sheet (including a coil) having a desired final thickness. However, in order to further refine the crystal grains, the cold rolling rate is desirably 30% or more, and intermediate annealing may be performed between the cold rolling passes for the same purpose as the above roughening. .

Solution treatment and quenching treatment After cold rolling, solution treatment and subsequent quenching treatment to room temperature are performed. For this solution hardening treatment, a normal continuous heat treatment line may be used.
However, in order to obtain a sufficient solid solution amount of each element such as Mg, Si, etc., after holding at a solution treatment temperature not lower than 550 ° C. and not higher than the melting temperature for 10 seconds or more, an average from the holding temperature to 100 ° C. The cooling rate is preferably 20 ° C./second or more.
When the temperature is lower than 550 ° C. or the holding time is shorter than 10 seconds, the re-solution of the Al—Mn-based compound, the Al—Fe-based compound containing Cu, or the Mg—Si-based compound, which was generated before the solution treatment, is caused. It becomes insufficient and the amount of solute Si and the amount of solute Cu decrease.

  In addition, when the average cooling rate is less than 20 ° C./second, Mg-Si-based precipitates are mainly generated during cooling and the amount of solid solution Si is lowered, and the solid solution amount of Si may still not be ensured. Get higher. In order to ensure this cooling rate, the quenching treatment is performed by selecting water cooling means and conditions such as air cooling such as a fan, mist, spray, and immersion, respectively.

Pre-aging treatment: Reheating treatment After such solution treatment and quenching treatment, preliminary aging treatment is performed if necessary. Incidentally, the effect of this preliminary aging treatment on the amount of dissolved Si and Cu is small, and it is selectively performed if there is a need for improving the BH property.
In the case of performing a pre-aging treatment (reheating treatment), it is preferable to perform the quenching treatment within 1 hour after cooling to room temperature.
If the room temperature holding time from the completion of the quenching treatment to room temperature until the start of pre-aging treatment (heating start) is too long, Mg-Si clusters that do not contribute to BH properties are generated due to room temperature aging, which contributes to BH properties. It becomes difficult to increase the number of Mg-Si clusters having a good balance between Mg and Si. Accordingly, the shorter the room temperature holding time is better, the solution treatment and quenching treatment and the reheating treatment may be continued so that there is almost no time difference, and the lower limit time is not particularly set.

  In this preliminary aging treatment, the holding time at 60 to 120 ° C. is held for 10 hours or more and 40 hours or less. As a result, Mg—Si clusters having a good balance between Mg and Si are formed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  Next, examples of the present invention will be described. As shown in Table 1 and the structure shown in Table 2, the 6000 series aluminum alloy plates differ in composition and structure composed of dislocation density when imparted with 5% tensile deformation. Were manufactured with different manufacturing conditions.

  Then, after holding the plate at room temperature for 10 days (after aging at room temperature), the dislocation density, 0.2% proof stress, and tensile strength when applying a tensile deformation of 5% solute Si amount, solute Cu amount, and the like. , Yield ratio (0.2% yield strength / tensile strength) and total elongation were measured and evaluated. These results are also shown in Table 2. Here, Table 2 is a continuation of Table 1, and the alloy numbers in Table 1 are the same as the numbers in Table 2, respectively.

Specifically, the 6000 series aluminum alloy plate having the chemical composition shown in Table 1 is the lowest in the soaking temperature and the rough rolled plate between the hot rough rolling passes as shown in Table 2. Temperature (described as minimum temperature in Table 2), end temperature of hot finish rolling, average cooling rate from material (plate) temperature immediately after end of hot finish rolling to material temperature of 150 ° C, solution treatment The production conditions such as the holding temperature and the average cooling rate were varied.
Here, in the display of the content of each element in Table 1, the display in which the numerical value of each element is blank indicates that the content is below the detection limit.

The specific production conditions for the aluminum alloy plate were as follows. Aluminum alloy ingots having respective compositions shown in Table 1 were commonly melted by DC casting. At this time, in common with each example, the average cooling rate during casting was set to 50 ° C./min from the liquidus temperature to the solidus temperature. Subsequently, the ingot was subjected to a soaking treatment in common for 6 hours under the temperature conditions shown in Table 2 in each example, and hot rough rolling was started at that temperature. Table 2 also shows the minimum (pass) temperature of the hot rough rolling at this time.
Then, in common with each example, the subsequent hot finish rolling is hot rolled to a thickness of 2.5 mm at the end temperature shown in Table 2 and the average cooling rate (° C./hour) after the end, A rolled sheet was used.
This hot-rolled aluminum alloy sheet is subjected to rough annealing at 500 ° C. for 1 minute in common with each example, and then cold-rolled at a processing rate of 50% without intermediate annealing in the middle of the cold rolling pass. And a cold-rolled sheet having a thickness of 1.0 mm was obtained.

  Further, the cold-rolled sheets were tempered (T4) continuously while being rewound and wound up in a continuous heat treatment facility in common with each example. Specifically, the solution treatment is performed at an average heating rate of up to 500 ° C. at 50 ° C./second, and after reaching each target temperature (holding temperature) shown in Table 2 for each example, 20 seconds is commonly used for each example. Thereafter, each example was cooled to room temperature by performing water cooling at each average cooling rate (° C./second) shown in Table 2.

  After these tempering treatments, a test plate (blank) is cut out from each final product plate after being left at room temperature for 10 days, and a structure defined by the solid solution Si amount, solid solution Cu amount, and dislocation density of each test plate. In addition, the mechanical properties were measured and evaluated. These results are shown in Table 2.

Measurement of the amount of solid solution Si and the amount of solid solution Cu The measurement of the amount of solid solution Si and the amount of solid solution Cu of each test plate was performed by dissolving a sample to be measured by a residue extraction method using hot phenol, The solid and liquid were separated by filtration with a filter of 1 μm, and the contents of Si and Cu in the separated solution were measured as the amount of solid solution Si and the amount of solid solution Cu, respectively.

The residue extraction method using hot phenol was specifically performed as follows. First, after putting phenol into a decomposition flask and heating, each sample plate sample to be measured was transferred into this decomposition flask and thermally decomposed. Next, after adding benzyl alcohol, the solution was suction filtered through the filter, the solid-liquid was separated by filtration, and the contents of Si and Cu in the separated solution were each quantitatively analyzed.
For this quantitative analysis, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES) or the like was appropriately used.
As described above, a membrane filter having a mesh (collected particle diameter) of 0.1 μm and a diameter of 47 mm was used for the suction filtration.
This measurement and calculation are performed on three samples taken from a total of three locations, one central portion in the plate width direction of the test plate and two end portions in the plate width direction from the central portion. The solid solution amounts (mass%) of Si and Cu of the sample were averaged to obtain the solid solution Si amount and the solid solution Cu amount of the plate.

Measurement of dislocation density The dislocation density (× 10 ¹⁴ m ^-2 ) on the rolling surface when each sample plate (collected specimen) was given a tensile deformation of 5% strain in the rolling direction as described above. , And measured under the specific conditions described above by X-ray diffraction. The measurement was performed at any five locations on each test plate, and the average dislocation density at these five locations was defined as the average dislocation density (× 10 ¹⁴ m ⁻² ).

Tensile test For each of the test plates, a JISZ2201 No. 5 test piece (25 mm × 50 mmGL × plate thickness) was sampled from each of the test plates, and a tensile test was performed at room temperature. The tensile direction of the test piece at this time was the parallel direction of the rolling direction. The tensile speed was 5 mm / min until 0.2% proof stress, and 20 mm / min after proof stress. The N number of the mechanical property measurement was 3, and each was calculated as an average value.
In each example, 0.2% yield strength, tensile strength, yield ratio (0.2% yield strength / tensile strength), and total elongation were calculated.

As shown in Tables 1 and 2, Invention Examples 1 to 11 are manufactured within the component composition range of the present invention and in a preferable condition range.
Therefore, as shown in Table 2, each of these inventive examples has a solid solution Si content of 0.30 to 2.0% in a solution separated by a hot phenol residue extraction method as defined in the present invention. The amount of Cu is 0.05 to 1.0%, and the average dislocation density measured by X-ray diffraction on the rolled surface of the plate when a tensile deformation of 5% strain is applied in the rolling direction of the plate. in a ^{6.0 × 10 14 ~12 × 10 14} m -2.

  As a result, as shown in Table 2, the yield ratio defined by the ratio between the 0.2% proof stress and the tensile strength (0.2% proof stress / tensile strength) is shown in Table 2. Is 0.56 or less, and the total elongation is 26% or more.

On the other hand, although Comparative Examples 12-16 of Table 2 are manufactured in a preferable condition range, alloy numbers 12-16 of Table 1 are used, and the contents of Si, Mg, Cu, Mn, and Fe Are outside the scope of the present invention.
For this reason, as shown in Table 2, in these comparative examples, either the amount of solute Si, the amount of solute Cu, or the average dislocation density in the low strain region is out of the range defined by the present invention, and the yield ratio is It exceeds 0.56 or the total elongation is less than 26%, and the moldability is inferior to the inventive examples. Therefore, it is unacceptable for automobile panel materials.

The comparative example 12 is the alloy 12 of Table 1, and there is too little Mg.
The comparative example 13 is the alloy 13 of Table 1, and there is too little Si.
The comparative example 14 is the alloy 14 of Table 1, and there is too little Cu.
The comparative example 15 is the alloy 15 of Table 1, and there is too much Mn.
The comparative example 16 is the alloy 16 of Table 1, and there is too much Fe.

Moreover, Comparative Examples 17 to 21 in Table 2 use alloy examples within the scope of the present invention as shown in Table 1. However, as shown in Table 2, each of these comparative examples has a soaking temperature, a minimum temperature of hot rough rolling, an end temperature of hot finish rolling, an average cooling rate (° C./hour) after the end, and a solution treatment. The production conditions such as the holding temperature and the average cooling rate (° C./second) are out of the preferable conditions.
As a result, the amount of solid solution Si, the amount of solid solution Cu, the average dislocation density in the low strain region, etc. deviates from the range defined in the present invention, and the yield ratio exceeds 0.56 as compared with the invention example, Total elongation is inferior at less than 26%. Therefore, it is unacceptable for automobile panel materials.

Among these, in Comparative Example 17, the soaking temperature and the minimum temperature of hot rough rolling are too low. For this reason, both the amount of solute Si and the amount of solute Cu are too small beyond the lower limit, and the average dislocation density in the low strain region is too low. For this reason, the yield ratio exceeds 0.56, the total elongation is less than 26%, and the formability is inferior.
In Comparative Example 18, the minimum temperature of hot rough rolling and the end temperature of hot finish rolling are too low. For this reason, both the amount of solute Si and the amount of solute Cu are too small beyond the lower limit, and the average dislocation density in the low strain region is too low. For this reason, the yield ratio exceeds 0.56, the total elongation is less than 26%, and the formability is inferior.
In Comparative Example 19, the average cooling rate (° C./hour) after hot finish rolling is too slow. For this reason, the amount of solute Si is too small beyond the lower limit, and the average dislocation density in the low strain region is too low. For this reason, the yield ratio exceeds 0.56, the total elongation is less than 26%, and the formability is inferior.
In Comparative Example 20, the holding temperature of the solution treatment is too low. For this reason, the amount of solute Si and the amount of solute Cu are too small beyond the lower limit, and the average dislocation density in the low strain region is too low. For this reason, the yield ratio exceeds 0.56, the total elongation is less than 26%, and the formability is inferior.
In Comparative Example 21, the average cooling rate (° C./second) after the solution treatment is too slow. For this reason, the amount of solute Si is too small beyond the lower limit, and the average dislocation density in the low strain region is too low. For this reason, although the amount of solute Cu satisfies the regulation, the yield ratio exceeds 0.56, the total elongation is less than 26%, and the formability is inferior.

  Therefore, from the results of the above examples, the composition and structure prescribed in the present invention for obtaining a high formability 6000 series aluminum alloy plate for automobile panel materials without greatly changing the conventional composition and production conditions. The significance of meeting all requirements is supported.

  ADVANTAGE OF THE INVENTION According to this invention, the high moldability 6000 series aluminum alloy plate which can be manufactured for car panel materials, without changing a conventional composition and manufacturing conditions largely can be obtained. As a result, the application of the 6000 series aluminum alloy plate can be expanded for automobile panel materials.

Claims (3)

In mass%, Si: 0.30 to 2.0%, Mg: 0.20 to 1.5%, Cu: 0.05 to 1.0%, Mn: 1.0% or less (however, 0% Not including), Fe: 1.0% or less (however, not including 0%), each of which is an Al—Mg—Si aluminum alloy plate made of Al and inevitable impurities, The amount of solute Si in the solution separated by the residue extraction method is 0.30 to 2.0%, the amount of solute Cu is 0.05 to 1.0%, and a 5% strain is applied in the rolling direction of this plate. The dislocation density on the rolled surface of this plate, measured by X-ray diffraction at the time of imparting the tensile deformation, is 6.0 × 10 ^{14 to} 12 × 10 ¹⁴ m ⁻² on average. Formable aluminum alloy plate.   The aluminum alloy plate is Cr: 0.3% or less (excluding 0%), Zr: 0.3% or less (excluding 0%), V: 0.3% or less (provided that 0%), Ti: 0.1% or less (excluding 0%), Zn: 1.0% or less (excluding 0%), Ag: 0.2% or less (excluding The high formability aluminum alloy sheet according to claim 1, comprising one or more of Sn: 0.15% or less (excluding 0%).   The yield ratio defined by the ratio of 0.2% proof stress to tensile strength (0.2% proof stress / tensile strength) of the aluminum alloy sheet is 0.56 or less and the total elongation is 26% or more. Or the high formability aluminum alloy plate of 2.