JP2018154869A - Aluminum alloy sheet excellent in press moldability, ridging mark property and bh property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet excellent in press moldability, ridging mark property and BH property, high in r value in a 45° direction, low in anisotropy of r value Δr and capable of achieving ridging mark property while maintaining strength level high.SOLUTION: A r value in a 45° direction is high, anisotropy of r value Δr is low, ridging mark property is suppressed to make press moldability, ridging mark property and BH property excellent while maintaining high strength level by controlling solid solution amount of Si and Mg of an Al-Mg-Si-based aluminum alloy sheet with a specific composition, total peak strength in a Cupper orientation, a Brass orientation, an S orientation, a P orientation and a Q orientation as an aggregate structure over whole range of a sheet thickness direction of a cross section and standard deviation of a Cube orientation area rate W as the aggregate structure of a sheet surface.SELECTED DRAWING: None

Description

  The present invention relates to a 6000 series aluminum alloy plate excellent in press formability, ridging mark property, and BH property.

  In response to global environmental problems caused by exhaust gas from automobiles, improvement in fuel consumption by transportation equipment such as automobiles is required. In particular, a lighter aluminum alloy material is applied to the body of an automobile in place of a conventionally used steel material. Of these, demand for Al-Mg-Si 6000 series aluminum alloys with excellent age-hardening and corrosion resistance is increasing as materials for exterior materials (exterior plate materials, outer panel materials) such as automobile hoods, fenders, doors, and roofs. ing.

  Since an automotive exterior member is generally press-molded, an aluminum alloy plate to be applied is required to have excellent formability. In recent years, with the diversification, sharpening, and complexity of vehicle body design and character lines, the number of cases where press forming is complicated and the processing conditions are becoming stricter is increasing, and the fracture limit of plate materials in press forming is further improved. It is necessary to make it.

On the other hand, conventionally, in the material 6000 series aluminum alloy plate for the automobile panel material, the alloy composition for improving the formability and BH property (bake hard property, artificial age hardenability), and the structure control As is well known, a number of means have been proposed from control of the crystal grain size to control of an atomic aggregate (cluster) including control of the texture.
Of these means for controlling the structure, various techniques have been proposed to control the texture in order to improve the press formability of an automobile outer panel or the like by controlling the r value.

  For example, in Patent Document 1, an average total area ratio of Cube orientation, Brass orientation, S orientation, and Cu orientation of a 6000 series aluminum alloy plate is set to a texture of 20 to 65%, and the average area of the Cube orientation in this texture The r value when the rate is 5 to 15% and the r value in the 0 ° direction is r0, the r value in the 45 ° direction is r45, and the r value in the 90 ° direction is r90, respectively. As an average value of rbar, an rbar defined as rbar = 1/4 × (r0 + 2 × r45 + r90) is 1.5 or more, and an absolute value of Δr, which is an index indicating the anisotropy of the r value, is 1/4 × ( It has been proposed that Δr defined as r0−2 × r45 + r90) be 0.75 or less.

  In Patent Document 2, random orientation (%) = 100−Cube orientation (%) − Goss orientation (%) − by a crystal orientation distribution function analysis in a ¼ depth portion from the surface of a 6000 series aluminum alloy plate. The area ratio of random orientation, which is defined as Brass orientation (%)-Cu orientation (%)-S orientation (%)-PP orientation (%)-RW orientation (%), is set to 55 to 75%, and the Δr is set to 0.00. It has been proposed to make the plate excellent in stretch flangeability and bending workability by setting the average value of the r value to 0.5 or more, while setting it to 2 to 0.6.

  In patent document 3, the cube orientation distribution density by the crystal orientation distribution function analysis in the 1/4 depth part of the plate thickness from the surface of a 6000 series aluminum alloy plate is the range of 10-25, and rbar is 0.50 or more. , Δr is 0.30 or less, and it is proposed that the plate is excellent in bending workability and press formability.

  In addition, the 6000 series aluminum alloy plate subjected to press molding also has a problem that surface rough defects such as ridging marks are likely to occur. The ridging mark is a phenomenon in which streaky irregularities occur on the surface of the plate, and is caused by the texture formed inside the plate. This ridging mark is likely to occur when the press molding conditions become severe due to an increase in the size and complexity of the panel structure or a reduction in thickness. In addition, it is relatively inconspicuous immediately after press molding, and is easily noticeable after proceeding to the painting process (after painting), and the surface quality of the product plate (panel) is deteriorated.

  In order to solve the problem of this ridging mark, for example, in Patent Document 4, the standard deviation of each texture is expressed as ([Cube] + [CR] + [RW] + [Goss] + [Brass] + [S] + As [Cu] + [PP]) / 8 ≦ 1.0, a method for suppressing ridging marks by suppressing local accumulation of crystal orientation has been proposed.

  In Patent Document 5, the orientation density of the Cube orientation and the NDCube orientation is C <15, N <15, 1/20 <N / C <1, the ear ratio is 7% or less, and the crystal grain size is 5 or more. Thus, a method for suppressing the ridging mark has been proposed.

Japanese Patent No. 5432439 Japanese Patent No. 4495623 Japanese Patent Laying-Open No. 2015-67857 Japanese Patent No. 4499369 JP 2009-256722 A

  However, these conventional methods are patents in which only the control of the r value or only the control of the ridging mark is controlled, respectively. It is difficult to achieve both characteristics.

  For example, among the prior arts, Patent Documents 2 and 3 control the ratio of the texture by carrying out soaking at a relatively low temperature in the homogenizing heat treatment (soaking) step. A method for lowering the anisotropy has been proposed, but there is a concern that the strength is relatively lowered in this method.

Moreover, in the said patent document 4, it is an Al-Mg-Si type alloy plate, Comprising: 0.1-3.0 mass% of Mg, 0.1-2.5 mass% of Si, and Cube direction, Proposed is an Al—Mg—Si based alloy sheet characterized in that each texture of CR orientation, RW orientation, Goss orientation, Brass orientation, S orientation, Cu orientation, and PP orientation satisfies the following formula (1). Has been.
([Cube] + [CR] + [RW] + [Goss] + [Brass] + [S] + [Cu] + [PP]) / 8 ≦ 1.0 (%) (1)
(In the formula, [x] represents the standard deviation (%) of the area ratio of the orientation x in the plate cross section for every 500 μm in the plate width direction.)
Patent Document 4 proposes a method of obtaining such a texture and suppressing ridging marks by performing annealing before cold rolling and intermediate annealing at a relatively low temperature.
However, with this method, there is a concern that the area ratio of the Cube orientation itself is relatively high, the anisotropy of the r value is high, the r45 is low, and the press formability is lowered.

  The present invention has been made by paying attention to the limitations of such a conventional method. While maintaining the high strength level, the r value in the 45 ° direction is high, the r value anisotropy Δr is low, and It is an object of the present invention to provide an aluminum alloy plate that is excellent in press formability, ridging mark property, and BH property and that can achieve both ridging mark suppression.

Means for Solving the Invention

  In order to achieve the above object, the gist of the aluminum alloy plate excellent in press formability, ridging mark property and BH property of the present invention is mass%, Si: 0.4 to 1.5%, Mg: 0.3 -1.5%, Mn: 0.01-0.5%, Cu: 0.001-1.0%, the balance consisting of Al and irreversible impurities, and an Al-Mg-Si-based aluminum alloy plate As a texture in a cross section in a direction parallel to the rolling direction of the plate, a Cupper orientation determined by a crystal orientation distribution function measured by the SEM-EBSD method over the entire plate thickness direction of the cross section of the plate, The total peak intensity of the Brass orientation, S orientation, P orientation, and Q orientation satisfies 7.0 ≦ [Cupper] + [Brass] + [S] + [P] + [Q] ≦ 15.0, As a texture on the surface, When the rectangular area of 300 μm in the direction perpendicular to the rolling direction of the plate surface × 2000 μm in the direction parallel to the rolling direction is measured by the SEM-EBSD method, the rectangular area is defined as W in the rolling direction of the plate. The standard deviation of the Cube orientation area ratio W in a region where 10 pieces are arranged in parallel in a direction perpendicular to the direction is 3.0% or less, and further, at 20 to 30 ° C. after the final tempering of the aluminum alloy plate. It is assumed that the conductivity after leaving for 90 days is 47 IACS% or less.

If the standard deviation of the Cube orientation area ratio W is reduced as in Patent Document 4, the ridging mark property is improved, but since the Cube orientation area ratio is high, the r value anisotropy is high and the r45 is low. , Press formability tends to be reduced.
For this reason, in the present invention, the main texture of the plate is controlled, and the anisotropy of the r value is controlled to improve the press formability. On the other hand, for the Cube orientation, the crystal orientation texture on the plate surface is appropriately controlled to lower the standard deviation of the Cube orientation area ratio and improve the ridging mark property.
As a result, according to the present invention, while maintaining the strength level high, the r value in the 45 ° direction, which tends to be relatively low, is set to 0.45 or more and the anisotropy Δr of the r value is set to 0.20 or less. Formability can be improved. In addition, it can be controlled to have excellent surface properties in which generation of ridging marks is suppressed, and a 6000 series aluminum alloy plate excellent in press formability, ridging mark properties, and BH properties can be obtained.

  Below, the aluminum alloy plate for press molding of this invention is demonstrated concretely for every 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, required properties such as press formability, ridging mark property, BH property, and preferably weldability and corrosion resistance, which are necessary as a material plate for the automobile exterior material (outer panel material), are preferably 6000 series aluminum. It should be satisfied from the aspect of the composition of the alloy plate. However, even in this case, it is assumed that the conventional composition and manufacturing conditions are not greatly changed.
Here, the press formability of the aluminum alloy plate specifically refers to the r value in the 0 ° direction as r0 and the r value in the 45 ° direction as r45 and 90 °, respectively, with respect to the rolling direction of the plate. When the r value of r is r90, r45 is 0.45 or more, and Δr defined as 1/4 × (r0−2 × r45 + r90), which is an index indicating the anisotropy of the r value, It is preferable that it is 0.20 or less.
In addition, the ridging mark property of the aluminum alloy plate is preferably an excellent surface property in which generation of ridging marks is suppressed.
Further, the BH property of the aluminum alloy plate is specifically that the 0.2% proof stress is 210 MPa or more and the proof stress increase amount is 100 MPa or more when the plate is artificially age-hardened at 185 ° C. for 20 minutes. It is preferable that

In order to satisfy such problems and characteristics from the viewpoint of composition, the composition of the 6000 series aluminum alloy plate is mass%, Si: 0.4 to 1.5%, Mg: 0.3 to 1.5. %, Mn: 0.01 to 0.5%, Cu: 0.001 to 1.0%, and the balance is made of Al and inevitable impurities.
In addition to this composition, the aluminum alloy plate further comprises, in mass%, Fe: 0.05 to 0.5%, Zr: 0.04 to 0.1%, Cr: 0.04 to 0.3%. V: 0.02-0.1%, Ag: 0.01-0.1%, Sn: 0.001-0.1%, Zn: 0.01-0.3% It is good also as a composition which included the seed | species more selectively.

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

(Si: 0.4-1.5%)
Si, together with Mg, forms Mg-Si-based precipitated particles that contribute to strength increase in low temperature artificial aging treatment such as solid solution strengthening and paint baking, and exhibits artificial age hardening ability (BH property). It is an indispensable element for obtaining the necessary strength (proof strength) as an automotive panel material such as an outer panel.

  If the Si content is too small, the amount of Mg-Si-based precipitates produced is insufficient during the artificial aging treatment, so that the BH property is lowered and the strength after the baking coating treatment 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 0.4 to 1.5%.

(Mg: 0.3-1.5%)
Mg, together with Si, forms Mg-Si-based precipitated particles that contribute to strength increase during artificial aging treatment such as solid solution strengthening and paint baking, and exhibits artificial aging hardening ability (BH property). It is an essential element for obtaining the necessary proof stress as a material.
If the Mg content is too small, the amount of Mg-Si-based precipitates is insufficient, so that the BH property is lowered and the strength after 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 0.3 to 1.5%.

(Solution amount of Si and Mg)
Here, as the existence form of Si and Mg contained in the plate, the added Si and Mg are largely dispersed and precipitated as coarse second phase particles depending on the production method and production conditions, and the solid solution after the solution treatment of the plate is performed. When the amount of dissolved Si and the amount of dissolved Mg are reduced, the amount of increase in 0.2% proof stress in the age-hardening treatment (paint baking hardening treatment, etc.) after the final tempering treatment is small, and the BH property is reduced. There is a possibility that the strength will be insufficient.
Therefore, in order to secure the BH property of the aluminum alloy plate, it is necessary to secure the solid solution Mg amount and the solid solution Si amount after the solution treatment or the final tempering treatment of the aluminum alloy plate. Specifically, as a measure of the solid solution Mg amount and the solid solution Si amount, the aluminum alloy plate after the final tempering treatment is left at 20 to 30 ° C. for 90 days, and the conductivity is 47 IACS% or less. It is necessary to be.
Here, the timing of measuring the electrical conductivity of the aluminum alloy sheet was deliberately defined as being left for 90 days at 20 to 30 ° C. after the final tempering process in the production of the rolled sheet, after the final tempering process. This is for reproducibility of the conductivity measurement of the aluminum alloy plate, which changes with the elapsed time of room temperature aging.
In addition, the final tempering treatment here refers to a heat treatment at a low temperature when the final heat treatment at a low temperature such as a preliminary aging treatment is performed after the solution heat treatment and quenching treatment of the rolled plate. Is the final tempering treatment, and when the solution treatment and the quenching treatment are final heat treatment, this solution treatment and quenching treatment is the final tempering treatment.

(Mn: 0.01 to 0.5%)
Mn forms second phase particles during casting or during homogenization heat treatment, and these have the effect of acting as an obstacle to grain boundary movement after recrystallization. Therefore, the effect of obtaining fine crystal grains can be obtained. is there. If the Mn content is more than 0.5%, coarse second-phase particles are formed, and press formability and weldability deteriorate. Therefore, the Mn content is 0.01 to 0.5%, preferably 0.1 to 0.3%.

(Cu: 0.001 to 1.0%)
Cu has an effect of promoting the formation of aging precipitation particles under relatively low temperature and short-time artificial aging treatment conditions, and solid solution Cu is an element that can improve formability. If the Cu content is more than 1.0%, the stress corrosion cracking resistance, yarn rust resistance and weldability deteriorate. Therefore, the Cu content is 0.001 to 1.0%, preferably 0.1 to 0.8%.

(One or more of Fe, Zr, Cr, V, Ag, Sn, Zn)
Since these elements have the effect of increasing the strength of the plate in common, they can be regarded as equivalent elements in the present invention, and are selectively contained as necessary, but the specific mechanism also includes common parts. Of course, there are also different parts.

  Fe forms a crystallized product, serves as a nucleus of recrystallized grains, plays a role of preventing coarsening of crystal grains and improving strength. If the content is too small, the effect is small. If the content is too large, a coarse compound is formed, which becomes a starting point of destruction, and the strength and formability are lowered.

  Zr, Cr, and V contribute to strength improvement by refining the crystal grains of the ingot and the final plate product. Further, these elements exist as dispersed particles, contribute to crystal grain refinement, and improve moldability. When each content is too small, the effect of improving strength and formability due to the refinement of crystal grains is insufficient. On the other hand, when there are too many of these elements, a coarse compound will be formed and ductility will deteriorate.

  Ag has the effect of precipitating finely aging precipitates that contribute to strength improvement by artificial aging heat treatment after molding to automobile members, thereby promoting high strength. If the content is too small, the effect of improving the strength is small, and if the content is too large, various properties such as rollability and weldability are reduced, and the effect of improving the strength is saturated and expensive.

  Sn has the effect of suppressing the cluster formation at room temperature and maintaining the excellent formability of the plate after solution treatment and quenching treatment for a long time, and then artificial aging heat treatment such as baking coating treatment. If you improve the strength. If the content is too small, the effect is small. If the content is too large, hot brittleness is caused and hot workability (hot ductility) is remarkably deteriorated.

  Zn is useful for improving artificial age-hardening ability (BH property), and has the effect of increasing the strength by promoting the precipitation of a compound phase such as a GP zone in the crystal grains of the plate structure in the baking coating process. is there.

  Therefore, when these Fe, Zr, Cr, V, Ag, Sn, Zn are contained, as described above, Fe: 0.05 to 0.5%, Zr: 0.04 to 0.1%, Cr: 0.04-0.3%, V: 0.02-0.1%, Ag: 0.01-0.1%, Sn: 0.001-0.1%, Zn: 0.01- In the range of 0.3%, one kind or two or more kinds are contained.

Other elements Other elements such as Ti and B other than those described above are unavoidable impurities. Ti, together with B, forms a coarse compound and degrades mechanical properties. However, since the inclusion of a small amount also has the effect of refining the crystal grains of the aluminum alloy ingot, each content in the range specified by the JIS standard is allowed as a 6000 series alloy. As an example of this allowable amount, Ti is 0.1% or less, preferably 0.05% or less. Further, B is set to 0.03% or less.

(Group organization)
In the present invention, while maintaining the strength level high, the r value in the 45 ° direction, which tends to be relatively low, is set to 0.45 or more, and the anisotropy Δr of the r value is controlled to 0.20 or less to control the r value. In order to improve press formability and achieve both control of r value and suppression of ridging marks, each crystal orientation texture component in the plate was reviewed.
As a result, in order to control the r value as described above, in the texture in the longitudinal section in the direction parallel to the rolling direction, evaluated by the SEM-EBSD method, the 45 ° direction tends to be relatively low. It has been found that it is important to positively control the degree of crystal orientation accumulation, which increases the r value (r45).
On the other hand, in order to suppress the ridging marks on the panel surface after press-molding the plate and to have excellent surface properties as exterior materials (coating appearance without ridging marks, sharpness, gloss) In the texture evaluated by EBSD measurement of the plate surface, it was found that it is important to control the distribution of the Cube orientation.

That is, in order to control the r value, as a texture in a cross section in a direction parallel to the rolling direction of the plate, a crystal orientation distribution measured by the SEM-EBSD method over the entire plate thickness direction of the vertical cross section of the plate. The total peak intensity of the Cupper orientation, the Brass orientation, the S orientation, the P orientation, and the Q orientation determined by the function is 7.0 ≦ [Cupper] + [Brass] + [S] + [P] + [Q] ≦ 15 0 (hereinafter also referred to as Equation 1).
Here, the cross section in the direction parallel to the rolling direction of the plate is a direction perpendicular to the plane direction (horizontal direction) of the plate in a direction parallel to the rolling direction in any part of the plate (longitudinal direction). ) Refers to the section (longitudinal section) cut.
Thereby, as the press formability of the aluminum alloy plate, r45 of the plate can be set to 0.45 or more, and Δr, which is an index indicating the anisotropy of the r value of the plate, can be set to 0.20 or less. it can.

  In contrast, when Equation 1 is smaller than 7.0, the degree of integration of the Cupper, Brass, S, P, and Q orientations, which are crystal orientations that increase the r value (r45), is too small. R45 tends to be low, and Δr is unlikely to be 0.20 or less. For this reason, [Cupper] + [Brass] + [S] + [P] + [Q] is preferably 7.0 or more, and more preferably 7.5 or more.

  On the other hand, when Equation 1 is higher than 15.0, the degree of integration of the Copper, Brass, S, P, and Q orientations, which are crystal orientations that increase the r value (r45), increases. Therefore, r45 is too high as compared with r0 and r90, and Δr is not easily reduced to 0.20 or less. For this reason, [Cupper] + [Brass] + [S] + [P] + [Q] is preferably 15.0 or less, more preferably 12.0.

Furthermore, in order to suppress ridging marks, a rectangular region of 300 μm in the direction perpendicular to the rolling direction of the plate surface and 2000 μm in the direction parallel to the rolling direction is used as a texture on the surface of an arbitrary part of the plate by the SEM-EBSD method. When the Cube azimuth area ratio measured by the above is W, the standard deviation of the Cube azimuth area ratio W in a region where ten rectangular regions are arranged in parallel in a direction perpendicular to the rolling direction of the plate is 3. 0% or less.
Here, the rectangular region is a rectangular region having a length of 300 μm in a direction perpendicular to the rolling direction of the plate surface (width direction of the plate) × 2000 μm in a direction parallel to the rolling direction (longitudinal direction of the plate). Yes, the Cube orientation area ratio measured in this rectangular region is W. Then, 10 rectangular regions are arranged in parallel in a direction perpendicular to the rolling direction of the plate (width direction of the plate), and the Cube orientation area ratio W in each rectangular region is the 10 regions. Find the standard deviation.

By controlling the standard deviation of the Cube orientation area ratio W on the surface of the plate as described above, ridging marks on the surface of the panel after press-molding the plate are suppressed, and excellent surface properties as exterior materials (sharpness of the coating film, Gloss).
When the standard deviation of the Cube azimuth area ratio is larger than 3.0%, the Cube azimuth is likely to be distributed in a streak shape, and ridging marks are likely to occur. For this reason, the standard deviation of the Cube orientation area ratio needs to be 3.0% or less, and more preferably 2.5% or less.

(Definition of texture)
In ordinary aluminum alloys, the existence of the following crystal orientation texture is known, and depending on the volume fraction of these crystal orientations, even when tensile deformation is equally applied, the deformation state differs depending on the crystal orientation. .

Cube orientation: {001} <100>
Goss orientation: {011} <100>
Cupper orientation: {112} <111>
Brass orientation: {011} <211>
S orientation: {123} <634>
P direction: {011} <211>
Q direction: {130} <312>

  Here, the expression method of the crystal orientation texture is expressed by a rolling surface and a rolling direction in the case of a rolled sheet. In other words, the rolling surface is represented by {xxx} and the rolling direction is represented by <xxx>. ○ and X represent integers. In addition, these are described in (Shinichi Nagashima "texture" (Maruzen Co., Ltd.), light metal society "light metal" commentary Vol. 43, (1993) 285-293).

(Measuring method of texture)
Each crystal orientation texture defined in the present invention is obtained by using a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), and SEM-EBSD. Evaluate by law. The sample to be used for the measurement is the surface of the cold-rolled plate that has undergone the final tempering treatment, such as mechanically polishing and buffing the surface of the cold-rolled plate, followed by electrolytic polishing to remove the oxide film on the surface. To prepare.

This SEM-EBSD method is widely used as a method for measuring crystal orientation texture, and is applied to a field emission scanning electron microscope (for example, JSM-7000F manufactured by JEOL Ltd.) with a backscattered electron diffraction image (EBSD). Pattern: EBSD) A crystal orientation analysis method equipped with a system.
In the SEM-EBSD method, a sample of an Al alloy plate set in the lens barrel of the FE-SEM is irradiated with an electron beam, and the diffraction pattern of the backscattered electrons is measured by an EBSD apparatus (for example, EBSD measurement manufactured by TSL).・ Analysis system: OIM (Orientation Imaging Macrograph) Data & Analysis) scans the sample surface every 1 μm while analyzing the crystal orientation. As a result, EBSP (Electron Back Scatter Diffraction Pattern) at each point is obtained and indexed to obtain the crystal orientation of the electron beam irradiation site. The crystal orientation distribution function when the obtained crystal orientation measurement data is rotated 90 ° around the rolling direction axis and further rotated 90 ° in the normal direction of the rolling surface, and the crystal orientation is measured by EBSD in the entire measurement region. Calculate (ODF) and area ratio. Details of the crystal orientation analysis method in which the EBSD system is mounted on these FE-SEMs are described in detail in Kobe Steel Technical Report / Vol. 52 No. 2 (Sep. 2002) P66-70 and the like.

  In the present invention, in order to control the r value, the SEM-EBSD method is used to calculate from the crystal orientation distribution function (ODF) when measured over the entire region in the thickness direction of the longitudinal section parallel to the rolling direction of the plate. The peak intensity of each crystal orientation texture is defined. The evaluation method will be described below.

(Definition of the distribution of crystallographic texture in an arbitrary cross section parallel to the rolling direction of the plate)
The distribution state of the crystal orientation texture in the longitudinal section in the direction parallel to the rolling direction of the plate is the SEM-EBSD method, and the peak intensities of Copper orientation, Brass orientation, S orientation, P orientation, and Q orientation are used. Is obtained using a crystal orientation distribution function (ODF).
The sample is a cross-section in a direction parallel to the rolling direction of the plate whose surface is prepared, and an arbitrary part of the plate is parallel to the rolling direction, and is perpendicular to the plane direction (horizontal direction) of the plate (longitudinal). (Direction), and the cross section (longitudinal cross section) to be measured is taken out and adjusted. And the area | region enclosed in the plate | board thickness direction whole of the cross section of this sample and the range of 1000 micrometers of rolling directions is measured, a measurement visual field is made into 2 visual fields, and a measured value is made into the average.

Then, in the measurement range, the ODF is calculated up to the expansion series 22 in the range where the three Euler angles φ1, φ, φ2 are 0 to 90 °, and the obtained ODF value is obtained for each orientation as the degree of integration. . Then, the ODF value of each of these orientations is obtained as the degree of integration of each crystal orientation = peak intensity. The obtained numerical value (dimensionless) indicates the size of the random orientation relative to that, and the larger the value, the higher the degree of integration of the orientation.
At that time, the three Euler angles in each direction are as follows.
φ1: 0 ° and φ: 0 ° and φ2: 0 ° are Cube orientations.
φ1: 0 ° and φ: 45 ° and φ2: 0 ° are Goss orientations.
φ1: 35 °, Φ: 45 ° and φ2: 0 ° are Brass orientations.
φ1: 0 ° and φ: 30 ° and φ2: 45 ° are Cupper orientations.
φ1: 58 °, Φ: 29 ° and φ2: 63 ° are S orientations.
φ1: 70 °, Φ: 45 °, and φ2: 0 ° are P directions.
φ1: 45 °, Φ: 15 °, and φ2: 10 ° are Q directions.

  In the present invention, basically, an angle deviation within ± 2.5 ° from the Euler angle is defined as belonging to the same angle factor. This is because, within such a range, almost the same properties are exhibited.

  Moreover, in this invention, in order to suppress a ridging mark, the standard deviation of the area ratio of the Cube direction for ten rectangular regions on an arbitrary rolled surface is defined. The evaluation method will be described below.

(Definition of distribution state of Cube orientation on plate surface)
When measuring the texture of the plate surface (rolled surface excluding the oxide film on the plate), the distribution state of the crystal orientation texture on the surface of the plate from which the surface was prepared is first determined using the SEM-EBSD method. The area ratio W of the Cube orientation is measured in a rectangular region extending in a rolling width direction of 300 μm and a rolling length direction of 2000 μm.
Then, this measurement is performed for 10 rectangular areas having the same area adjacent to the rectangular area in the rolling width direction, and the standard deviation of the area ratio W of the Cube orientation in these 10 rectangular areas is obtained. ,evaluate.

  In the present invention, if the deviation of the measured crystal orientation is basically within ± 10 ° from the crystal plane of the Cube orientation, it is defined as belonging to the same orientation factor. This is because, within such a range, almost the same properties are exhibited.

(Production method)
Next, the manufacturing method of the aluminum alloy plate of this invention is demonstrated below. In the manufacturing method according to the present invention, the alloy ingot is subjected to homogenization heat treatment at a relatively high temperature, intermediate annealing is performed during cold rolling, and cold rolling from hot rolling to intermediate annealing to the final plate thickness is performed. By setting the total rolling rate (total plate thickness reduction rate) to 80% or more, it has a great feature in controlling the texture components in the plate material and reducing the streak Cube orientation on the plate surface.

(Dissolution)
An ingot having a predetermined shape is produced from a molten metal in which an aluminum alloy having the above composition is melted. The method for melting and casting the aluminum alloy is not particularly limited, and a conventional method or a known method may be used.

(Homogenization heat treatment)
Next, the cast aluminum alloy ingot is subjected to homogenization heat treatment (soaking) prior to hot rolling. This homogenization heat treatment is performed in order to make a non-uniform structure during casting uniform. The homogenization heat treatment temperature is preferably 500 ° C. or higher and lower than the melting point. If it is less than 500 degreeC, dispersion | distribution of 2nd phase particle | grains will increase and the intensity | strength after artificial aging will fall easily. For this reason, the homogenization heat treatment temperature is preferably 500 ° C. or higher, more preferably 520 ° C. or higher.
The homogenization heat treatment may be performed only once under the above conditions. The heat treatment is once performed at 500 ° C. or higher, cooled to room temperature, and then heated to 500 ° C. or lower again. There is no need to perform a heat treatment or a two-stage homogenization heat treatment such as heating to a temperature of 500 ° C. or lower without cooling to room temperature. When these two or two-stage homogenization heat treatments are performed, the added Mg and Si are largely dispersed as coarse second-phase particles, and the amount of solid solution Mg and Si after the solution treatment is reduced. For this reason, there is a possibility that the 0.2% yield strength increase in the artificial age hardening treatment (paint baking treatment) after the final tempering treatment is small, the BH property is lowered, and the strength is insufficient.

(Hot rolling)
After the homogenization heat treatment, hot rolling is performed to obtain a predetermined thickness. Hot rolling is divided into a rough rolling process and a finish rolling process according to the sheet thickness to be rolled. In these rough rolling process and finish rolling process, a reverse type or tandem type rolling mill is appropriately used.

  The starting temperature of the hot rolling, particularly the rough rolling process, is desirably 400 to 550 ° C. If the starting temperature of rough rolling is low, deformation resistance during rolling increases, which is not preferable. If the starting temperature of rough rolling exceeds 550 ° C., recrystallized grains are formed during rolling, and strain accumulation is insufficient, so that the predetermined properties are not satisfied. When the starting temperature of rough rolling is lower than the homogenization heat treatment temperature, cooling is appropriately performed.

  The finishing temperature of the hot rolling finishing step is preferably 350 ° C. or lower, more preferably 300 ° C. or lower. When the end temperature of hot rolling exceeds 350 ° C, recrystallized grains are generated around the surface of the plate, and the amount of accumulated strain is insufficient, so that only a specific crystal orientation develops during solution heat treatment, resulting in deformation. Due to the difference, the aluminum alloy plate cannot be made isotropic.

(Cold rolling)
The sheet material obtained by the hot rolling preferably has a sheet thickness reduction rate of 60% or more, more preferably 65% or more, from hot rolling to intermediate annealing. Further, the total sheet thickness reduction rate from hot rolling to solution treatment is preferably 80% or more, more preferably 85% or more. If the plate thickness reduction rate in cold rolling from hot rolling to intermediate annealing is less than 60%, or the total plate thickness reduction rate from hot rolling to solution treatment is less than 80%, the amount of strain is insufficient, Since the amount of formation of the Brass azimuth, Cupper azimuth, S azimuth, P azimuth, and Q azimuth decreases, r45 tends to be low.

(Intermediate annealing)
Intermediate annealing is performed at a temperature increase rate of 5 ° C./s or higher at a temperature of 400 ° C. or higher. When the intermediate annealing temperature is less than 400 ° C., recrystallization is not promoted and the Cube orientation is easily formed in a streak shape. Therefore, the intermediate annealing temperature is preferably 400 ° C. or higher, more preferably 450 ° C. or higher. Further, when the rate of temperature increase in the intermediate annealing is less than 5 ° C./s, the Cube orientation is formed in a streak shape, the standard deviation is likely to be 4.0% or more, and ridging marks are likely to occur. Therefore, the temperature increase rate in the intermediate annealing is desirably 5 ° C./s or more, more preferably 10 ° C./s or more.

(Solution and quenching)
After cold rolling, a solution hardening treatment is performed. The solution treatment is preferably performed at a temperature of 500 ° C. to 570 ° C. and held for 0 to 20 s, and then a quenching treatment is preferably performed at a cooling rate of 10 ° C./s or more. When the cooling rate of the quenching process is slow, Si and Mg—Si based precipitates are likely to be formed on the crystal grain boundaries, which are likely to become starting points of cracks in press molding and bending, and formability is lowered. In order to ensure this cooling rate, the quenching process is performed by selecting various cooling means and conditions such as air cooling such as a fan, mist, spray, and immersion, and the cooling rate is 10 ° C./s or more.

  Further, in order to improve age-hardening in an artificial age-hardening treatment such as a paint baking process for a molded panel, a preliminary aging treatment is performed immediately after the solution treatment. In the preliminary aging treatment, it is desirable that the temperature range is 70 to 120 ° C., and the temperature is kept isothermal for 1 to 24 hours. The preliminary aging treatment is preferably performed within 10 minutes after the quenching or at a high cooling end temperature of 70 to 120 ° C. during quenching.

   Next, examples of the present invention will be described. An aluminum alloy plate having the composition shown in Table 1 was subjected to homogenization heat treatment, hot rolling, cold rolling and intermediate annealing under the conditions shown in Table 2, and then made into a product by solution heat treatment. In addition, in the display of the content of each element in Table 1, an element whose numerical value is blank indicates that the content is below the detection limit.

  Below, the more concrete manufacturing conditions of an aluminum alloy plate are demonstrated. Ingots having respective compositions shown in Table 1 were melted by a DC casting method. Subsequent homogenization heat treatment was performed at the temperatures shown in Table 2 for 4 hours in common with each example. After the homogenization heat treatment was completed, the hot rolling rough rolling was performed after cooling to the hot rolling start temperature shown in Table 2 without cooling to room temperature. And finish rolling was completed at 300 degrees C or less. The final thickness of each hot rolled plate was 3.5 to 10 mm.

  For the aluminum alloy plate after hot rolling, except for the examples of Comparative Examples 1 and 2 in Tables 1 to 3, after performing cold rolling, intermediate annealing is performed in a continuous annealing furnace or a batch type atmospheric furnace. Carried out. In Comparative Example 1 of Tables 1 to 3, intermediate annealing was not performed, and in Comparative Example 2, intermediate annealing was performed at 500 ° C. after the hot rolling was completed. After the intermediate annealing was completed, cold rolling was performed again, and the final thickness was 1 mm in common with each example. In a continuous heat treatment facility, a solution quenching process was performed in which the solution was heated to 550 ° C. and immediately cooled to room temperature at a cooling rate of 10 ° C./s or more. Also. In common with each example, after cooling to room temperature, it heated immediately to 100 degreeC, and the preliminary aging process which hold | maintains at the temperature for 2 hours was implemented as a final tempering process.

  Sample plates were collected from the aluminum alloy plates after the final tempering treatment, and the mechanical properties and the microstructure (texture structure) of each test plate were examined for room temperature aging 30 days after the final tempering treatment. Moreover, the electrical conductivity of each test plate which was aged at room temperature for 90 days in the temperature range of 20-30 ° C. after the final tempering treatment was examined.

(mechanical nature)
The tensile test piece used for measuring the mechanical properties is a JIS2201 No. 13A test piece (20 mm × 80 mmGL × plate thickness 1 mm) so that the tensile direction from the test plate is parallel to the rolling direction, 45 ° direction and perpendicular. Were collected and prepared, and a tensile test was performed at room temperature. The tensile test is 5 mm / min until 0.2% proof stress measurement, 30 mm / min after proof stress, and r value r0 parallel to the rolling direction when 0.2% proof stress and 10% plastic strain are added. The r value r45 in the 45 ° direction and the r value r90 in the vertical direction were measured. Δr was calculated from ¼ × (r0−2 × r45 + r90). These results are shown in Table 3. The number of measurements in the tensile test was two, and various characteristics were obtained as average values.
Here, as an automotive exterior material, the press formability of an aluminum alloy plate was acceptable when r45 was 0.45 or more and Δr was 0.20 or less.

(BH property)
The BH property (bake hard property) is obtained by simulating the formation of the large panel, and applying a tensile deformation of 2% strain to the test plate in the rolling direction of the plate in advance. Simulating age hardening treatment (paint baking treatment), from the plate after artificial age hardening treatment (BH) at 185 ° C. for 20 minutes, the tensile test piece that is perpendicular to the rolling direction is collected, A tensile test was performed as described above, and 0.2% yield strength was measured. Then, by subtracting the 0.2% yield strength value before the age hardening treatment, the amount of increase in yield strength by the age hardening treatment was calculated.
Here, as the automobile exterior material, the BH property of the aluminum alloy plate is acceptable when the 0.2% yield strength after BH is 210 MPa or more and the yield increase by BH is 100 MPa or more.

(Riding mark)
Each test piece cut out from the test plate was subjected to 15% plastic strain in the direction perpendicular to the rolling direction, and then subjected to ED coating to visually evaluate the presence or absence of ridging marks. The evaluation of the ridging mark as an automobile exterior material was evaluated as ◯ when no ridging mark was generated, and x when a clear ridging mark was generated.

(Gathering organization)
The texture of the test plate was measured by TSL Solution Co., Ltd. using the FE-SEM (JSM-7100F) manufactured by JEOL Ltd. under the condition of an acceleration voltage of 20 kV by the SEM-EBSD method described above. With the software (TSL-OIM Data Collection Ver. 5), the crystal orientations on the predetermined observation surface and the predetermined measurement rectangular region were measured. Subsequently, each crystal orientation texture was analyzed with measurement software (TSL-OIM Data Collection Ver. 6.2) manufactured by TSL Solution Co., Ltd., and the degree of integration and standard deviation were obtained. The interval (step) between electron beams in this analysis was 2 μm. The results are also shown in Table 3.

(conductivity)
The conductivity of the test plate was measured at 5 points with a conductivity meter (SIGMATEST D 2.068) manufactured by Nippon Ferster Co., Ltd. while maintaining the plate surface at 20 ° C., and the average value thereof was calculated. The conductivity of the sample was used.

As shown in Tables 1 to 3, each example is within the composition range of the present invention, and the thickness reduction rate of cold rolling before intermediate annealing, the heat treatment temperature and the heating rate of intermediate annealing, and hot The total sheet thickness reduction rate from rolling to solution heat treatment is produced in a preferable condition range.
Therefore, as shown in Table 3, each example has a solid solution amount of Si and Mg and a crystal orientation texture defined in the present invention. That is, in order to achieve both r value control and ridging mark suppression, the crystal orientation distribution in a relatively wide area of the plate can be controlled within the specified range of the present invention. Further, a sufficient amount of Si and Mg is ensured to ensure the BH property.
As a result, in each invention example, r value control (press formability), ridging mark suppression, and BH properties are compatible with each other.
That is, in each example, the press formability of the aluminum alloy plate was such that the r45 was 0.45 or more, the Δr was 0.20 or less, and the surface properties were free of ridging marks. It is. Further, the 0.2% yield strength after BH of the aluminum alloy plate is 210 MPa or more, and the increase in yield strength is 100 MPa or more. Accordingly, each example satisfies the required characteristics of the automobile exterior material.

  On the other hand, as shown in Tables 1 to 3, in Comparative Examples 1 to 8, the component composition range of the present invention or the production conditions are out of the preferred range. For this reason, these comparative examples are out of the range defined by the texture of the present invention, and the r value and the ridging mark property are inferior to the examples.

  In Comparative Example 1, the thickness reduction rate of the cold rolling is increased to 83%, but the intermediate annealing is not performed. For this reason, the Cube orientation is formed in a streak shape on the rolling surface, the standard deviation of the Cube orientation exceeds 3.0%, and the ridging mark is not suppressed.

  In Comparative Example 2, intermediate annealing is performed immediately after hot rolling, and cold rolling from hot rolling to intermediate annealing is not performed. For this reason, the ridging mark is suppressed, but the formation amount of the Brass orientation, Cupper orientation, S orientation, P orientation, and Q orientation is small, r45 is less than 0.45, and Δr exceeds 0.20.

  In Comparative Example 3, the sheet thickness reduction rate of the cold rolling before the intermediate annealing is within the range of the present invention, but the temperature increase rate of the intermediate annealing is as low as 5 ° C./s or less. For this reason, the amount of formation of the Brass orientation, Cupper orientation, S orientation, P orientation, and Q orientation is small, r45 is less than 0.45, and Δr exceeds 0.20.

  Since Comparative Example 4 is a step in which heat treatment is once performed at 500 ° C. or higher in the homogenization heat treatment, and then cooled to room temperature, and then heated again to a temperature of 500 ° C. or lower, second phase particles in which the added Si and Mg are coarse The electrical conductivity after leaving the aluminum alloy sheet for 90 days at 20-30 ° C. after final tempering exceeds 47 IACS%, and the amount of solute Si and the amount of solute Mg are too small. For this reason, the 0.2% yield strength after BH and the increase amount of 0.2% yield strength are small.

  In Comparative Example 5, the sheet thickness reduction rate of the cold rolling before the intermediate annealing is less than 60%, so the formation of the Brass orientation, Cupper orientation, S orientation, P orientation, and Q orientation does not proceed, and r45 is 0.45. And Δr exceeds 0.20.

  In Comparative Example 6, the thickness reduction rate of cold rolling before intermediate annealing is less than 60%, and the total thickness reduction rate from hot rolling to solution heat treatment is less than 80%. Formation of Cupper orientation, S orientation, P orientation, and Q orientation does not proceed, r45 is less than 0.45, and Δr is more than 0.20.

  In Comparative Example 7, as shown in Table 1, the added amount of Mg does not satisfy the component composition range in the present invention in Comparative Example 8, and 0 in the age hardening treatment after the final tempering treatment. .2% yield strength increase is less than 100 MPa.

  Therefore, from the results of the above examples, all the requirements of the composition and structure defined in the present invention for obtaining an Al—Mg—Si based aluminum alloy excellent in surface properties and r value after forming are satisfied. The significance of is supported.

  According to the present invention, while maintaining a high strength level, the r value in the 45 ° direction is high, the anisotropy Δr of the r value is low, and ridging mark suppression can be achieved at the same time. An aluminum alloy plate excellent in properties can be provided. As a result, the application of a 6000 series aluminum alloy plate can be expanded as an automobile exterior material including a panel material.

Claims (3)

  In mass%, Si: 0.4-1.5%, Mg: 0.3-1.5%, Mn: 0.01-0.5%, Cu: 0.001-1.0%, The balance is made of Al and irreversible impurities, and is an Al-Mg-Si-based aluminum alloy plate, and as a texture in a cross section in a direction parallel to the rolling direction of the plate, Thus, the total peak intensity of the Cupper orientation, the Brass orientation, the S orientation, the P orientation, and the Q orientation determined by the crystal orientation distribution function measured by the SEM-EBSD method is 7.0 ≦ [Cupper] + [Brass] + [ SEM + [P] + [Q] ≦ 15.0 is satisfied, and as a texture on the surface of the plate, a rectangular region of 300 μm in the direction perpendicular to the rolling direction on the surface of the plate × 2000 μm in the direction parallel to the rolling direction is SEM. -By EBSD method When the Cube azimuth area ratio at the time of measurement is W, the standard deviation of the Cube azimuth area ratio W in a region where ten rectangular regions are arranged in parallel in a direction perpendicular to the rolling direction of the plate is 3.0. Press formability and ridging mark property, wherein the aluminum alloy plate has a conductivity of 47 IACS% or less after being left at 20-30 ° C. for 90 days after final tempering. Aluminum alloy plate with excellent BH properties.   The aluminum alloy plate is further mass%, Fe: 0.05-0.5%, Zr: 0.04-0.1%, Cr: 0.04-0.3%, V: 0.02. ~ 0.1%, Ag: 0.01-0.1%, Sn: 0.001-0.1%, Zn: 0.01-0.3%, containing one or more kinds The aluminum alloy plate excellent in press formability, ridging mark property, and BH property according to claim 1.   The press formability of the aluminum alloy plate is determined when the r value in the 0 ° direction is r0, the r value in the 45 ° direction is r45, and the r value in the 90 ° direction is r90 with respect to the rolling direction of the plate. And r45 is 0.45 or more, and Δr defined as 1/4 × (r0−2 × r45 + r90) as an index indicating the anisotropy of the r value is 0.20 or less, and the aluminum alloy 3. The BH property of the plate according to claim 1, wherein the 0.2% yield strength when the plate is subjected to artificial age hardening treatment at 185 ° C. × 20 minutes is 210 MPa or more, and the increase in yield strength is 100 MPa or more. Aluminum alloy plate with excellent press formability, ridging mark properties, and BH properties.