JP4495623B2 - Aluminum alloy plate excellent in stretch flangeability and bending workability and method for producing the same - Google Patents

Description

  The present invention relates to an Al alloy plate having high strength and excellent formability, and a method for producing the same, and an Al alloy plate having excellent stretch flangeability without deteriorating bending workability, and the Al alloy plate can be reliably obtained. It is related with the manufacturing method which can be performed. The aluminum alloy plate referred to in the present invention refers to a solution obtained by solution-treating a cold-rolled plate. Hereinafter, aluminum is also simply referred to as Al.

  In recent years, with respect to global environmental problems caused by exhaust gas and the like, improvement in fuel efficiency has been pursued by reducing the weight of the body of a transport aircraft such as an automobile. For this reason, the application of lighter Al alloy materials such as rolled plates, extruded shapes, or forged materials, in place of steel materials that have been used in the past, is increasing especially for automobile bodies.

  Of these, panels such as outer panels (outer panels) and inner panels (inner panels) of panel structures such as automobile hoods, fenders, doors, roofs, and trunk lids are made of high-strength Al-Mg-Si. The use of Al alloy plates of AA to JIS 6000 series (hereinafter simply referred to as 6000 series) is being studied.

  The 6000 series Al alloy sheet basically contains Si and Mg as essential and has excellent age-hardening ability. BH properties (bake hardness, artificial age hardening ability) that can ensure the required strength by age hardening by heating at the time of processing, such as paint baking treatment of the subsequent panel, and heat resistance during treatment. Paint bake hardenability).

  Further, the 6000 series Al alloy plate has a relatively small amount of alloy elements as compared with other 5000 series Al alloys having a large amount of alloy such as Mg. For this reason, when the scraps of these 6000 series Al alloy sheets are reused as an Al alloy melting material (melting raw material), the original 6000 series Al alloy ingot is easily obtained and the recyclability is also excellent.

  However, the 6000 series Al alloy sheet is not as good as the press formability compared to the 5000 series Al alloy sheet. Therefore, the third and fourth elements other than Mg and Si are added as an improvement measure. Attempts have been made to control the crystal grain size and the dispersion state of crystal precipitates.

  However, even these methods have not yet met the demands of consumers, which have become increasingly severe in recent years, and further improvements in press formability are required.

In order to improve press formability, it has been conventionally proposed to improve stretch flangeability of a 6000 series Al alloy plate. For example, in order to ensure a hole expansion rate of λ60% or more, it has been proposed to define the r-value anisotropy of the plate under the following conditions (see Patent Document 1). r ≦ −0.722 × Δr + 0.5739 [where r = 1/4 × (r ₀ + 2r ₄₅ + r ₉₀ ), Δr = 1/2 × (r ₀ + r ₉₀ −2r ₄₅ )]. In order to obtain such a structure, Patent Document 1 discloses that annealing is performed at a temperature rising rate of 100 ° C./min or higher and a temperature of 450 ° C. or higher after hot rolling and before cold rolling, and a cooling rate of 600 ° C./min after this annealing. It is cooling above. And it cold-rolls by making the cold rolling rate before final annealing 65% or more. However, λ according to Patent Document 1 is about 60 to 70%.

  In addition, as an aluminum alloy plate for hole expansion processing, it has been proposed that a hardening rate described later is 20% or less within a range of 1 mm from the inner surface of the punched hole (see Patent Document 2). Curing rate (%) = (Hardness of punched hole processed portion−Hardness of base material portion) × 100 / Hardness of base material. In order to obtain such a structure, in Patent Document 2, the punched hole is heated at 200 to 600 ° C. for 2 hours or less by a heating furnace, induction heating, high temperature body contact, burner heating, or the like.

  Furthermore, as an aluminum alloy rolled plate for hole expansion processing and a method for producing the same, Mg content of 5.5 to 9.5 wt.%, Cu content of 0.3 to 1.5 wt.% Are contained, respectively, and the crystal grain size in the direction parallel to the rolling direction is 100 μm or less. It has been proposed that the average crystal grain size in the direction parallel to the rolling direction / the average crystal grain size in the plate pressure direction be 2 or less (see Patent Document 3). In order to obtain such a structure, in Patent Document 3, hot rolling is performed at a temperature defined by the following formula, and then cold rolling is performed once or twice with intermediate annealing, and then the final cold rolling is performed. The cold rolling rate is over 20%. Hot rolling temperature (° C.) = Solidification start temperature (° C.)-25 × Mg amount (wt.%) + 15 × Cu amount (wt.%) + 10 × Zn amount (wt.%). However, the maximum value of λ according to Patent Document 3 is about 67%.

On the other hand, it has been conventionally proposed to improve the bending workability of the 6000 series Al alloy plate. For example, it has been proposed that the maximum diameter of the Mg-Si compound is 10 μm or more, the number of compounds having a diameter of ² to 10 μm is 1000 / mm ² or less, and the inner limit bending radius is 0.5 mm or less (Patent Document 4). reference). In order to obtain such a structure, in Patent Document 4, soaking conditions are performed in two stages or twice soaking at 450 ° C. for the first time.

  Furthermore, as a method for improving the bending workability and hemming workability of the plate, various methods for giving anisotropy to the texture of the 6000 series Al alloy plate have been proposed. For example, it has been proposed that the texture of a plate is defined by the difference in crystal grain orientation (see Patent Documents 5 and 8). Further, it has been proposed to define the intensity ratio, density, and the like of the Cube orientation and the anisotropy of the r value (see Patent Documents 6, 7, 9, 10, 11, and 12).

  As for the manufacturing method for giving anisotropy to the texture of the 6000 series Al alloy plate, in the above Patent Documents 5 and 8, etc., the Al alloy ingot is homogenized at a temperature of 500 ° C. or higher and lower than the melting point. After that, cool it down from a temperature of 500 ° C or higher to a temperature range of 350 to 450 ° C and start hot rolling (two-stage soaking), or cool it from a temperature of 500 ° C or higher to room temperature and then 350 to 450 ° C. A stepwise homogenization method has been proposed in which hot rolling is started after reheating to a temperature range (two soaking).

On the other hand, hot-rolled Al-Mg-Si-based Al alloy sheets are cold-rolled at a rolling reduction of 10 to 50%, and then subjected to intermediate annealing at a temperature of 210 to 440 ° C, and an additional 70% It has also been proposed to provide anisotropy to the texture of the Al alloy sheet by performing cold rolling at the above rolling reduction, followed by solution treatment and quenching (see Patent Document 13).
JP 2003-129156 A (Claims) JP 2004-197184 A (Claims) Japanese Patent No. 3060991 (Claims) JP 2002-356730 A (Claims) JP 2003-171726 A (Claims) JP 2003-277869 A (Claims) JP 2003-277870 A (Claims) JP 2003-166029 A (Claims) JP 2003-226926 A (Claims) JP 2003-226927 A (Claims) JP 2003-321723 A (Claims) JP 2003-268475 A (Claims) JP 2003-321754 A (Claims)

  In the series of conventional techniques for improving the stretch flangeability (Patent Documents 1 to 3), the stretch flangeability is improved, but the bending workability is not sufficiently improved. Moreover, in patent document 2, a manufacturing cost increases for the heating of a punching hole part, or an accompanying facility is needed. Further, Patent Document 3 is substantially a 5000 series alloy plate, and there is no disclosure about a 6000 series Al alloy plate.

  In addition, in a series of conventional techniques (Patent Documents 4 to 13) in which the texture is made anisotropic, the Cube orientations of the 6000 series Al alloy plates are accumulated, and the small tilt grain boundary is larger than the large tilt grain boundary. To reduce or eliminate the grain boundary step. As a result, at the time of bending, the grain boundary step does not become the starting point of cracking, and the bending workability and hem workability of the plate can be improved.

  However, Patent Documents 4 to 13 have no disclosure of stretch flangeability in common and improvement of stretch flangeability is not sufficient.

  The present invention has been made paying attention to such circumstances, and its purpose is to ensure that the Al alloy plate having excellent stretch flangeability without degrading the bending workability and the Al alloy plate. An object of the present invention is to provide a production method that can be obtained.

In order to achieve this purpose, the outline of the aluminum alloy plate excellent in stretch flangeability and bending workability is mass%, Si: 0.1-2.5%, Mg: 0.1-3.0%, the balance being Al and inevitable Alloy plate made of mechanical impurities, of which r value in the 0 ° direction is r ₀ , and the r value in the 45 ° direction is r ₄₅ and 90 °, respectively, with respect to the rolling direction. When the r value in the direction is r ₉₀ , Δr = (r ₀ −2 × r ₄₅ + r ₉₀ ) / 2 is expressed, and Δr which is an index indicating the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ is 0.2. The average value of r values represented by (r ₀ + 2 × r ₄₅ + r ₉₀ ) / 4 is 0.5 or more, and is uniform in the 45 ° direction with respect to the rolling direction of the aluminum alloy sheet. The elongation is 24% or more and the hole expansion ratio λ is 61% or more .

Further, the summary of the method for producing an aluminum alloy plate excellent in stretch flangeability and bending workability for achieving the above object is a method for obtaining the aluminum alloy plate of the above summary, wherein Si: 0.1 An aluminum alloy ingot containing ~ 2.5%, Mg: 0.1-3.0%, the balance being Al and impurities, is cooled to a temperature of 200 ° C or lower after homogenization heat treatment at a temperature of 500 ° C or higher and lower than the melting point. Reheat to a temperature of 390 to 480 ° C or cool to a temperature of 390 to 480 ° C, both start hot rolling after holding in this temperature range, and set the end temperature of hot rolling to 170 to 300 ° C In addition, after the hot-rolled sheet was annealed at a temperature of 470 ° C or higher, the steel sheet was cooled at a rate of 100 ° C / s or higher, and then cold-rolled. A cold-rolled sheet is manufactured, and this cold-rolled sheet is solution-treated aluminum Of the r values of the nickel alloy sheet, when the r value in the 0 ° direction is r ₀ , the r value in the 45 ° direction is r ₄₅ , and the r value in the 90 ° direction is r ₉₀ , Δr = (R ₀ -2 × r ₄₅ + r ₉₀ ) / 2, and Δr which is an index indicating the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ is set to 0.2 to 0.6, and (r ₀ + 2 × r The average value of r values represented by ₄₅ + r ₉₀ ) / 4 is 0.5 or more, and the uniform elongation in the 45 ° direction with respect to the rolling direction of the cold-rolled sheet is 24% or more.

In a 6000 series aluminum alloy plate (a plate obtained by solution-treating a cold-rolled plate), the stretch flangeability and the r value of the plate, and the anisotropy of the stretch flangeability and the r value (Rankford value) of the plate are correlated. If the r value of the plate is increased or the anisotropy of the r value (rankford value anisotropy) is suppressed, the hole expansion ratio λ required by the burring test is increased in Patent Document 1 and the like. Ru known der.

On the other hand, when the stretch flangeability of the 600 00 series aluminum alloy plate is improved, there is a new problem that bending workability is lowered.

  On the other hand, in the present invention, in addition to suppressing the anisotropy of the r value (anisotropy of the Rankford value) and increasing the average value of the r value of the plate, Improves uniform elongation in the 45 ° direction with respect to the rolling direction.

According to the knowledge of the present inventors, in the hole expansion test for evaluating the stretch flangeability (λ) of the 6000 series aluminum alloy plate, the direction of occurrence of cracks in the hole expanded portion is approximately 45 ° with respect to the rolling direction. Become. Therefore, to improve the generating direction of the crack, i.e., by increasing the uniform elongation of 45 ° direction of the plate, it is possible to obtain stretch flangeability has high.

  This improvement in uniform elongation in the 45 ° direction is due to the formation of coarse recrystallized grains and the intermetallic compound precipitation phase (mainly Mg-Si in the grain boundary in the process of homogenization heat treatment and hot rolling before the roughening. This is realized by suppressing the formation of the system.

  When a large amount of coarse recrystallized grains and intermetallic compound precipitation phases at grain boundaries are formed, the uniform elongation of the 6000 series aluminum alloy sheet, particularly in the 45 ° direction with respect to the rolling direction, is significantly reduced.

  Therefore, the definition of uniform elongation in the direction of 45 ° with respect to the rolling direction in the present invention is not merely a specification of the characteristics of the plate, but also an indicator of the formation state of coarse recrystallized grains and precipitate phases at grain boundaries. That is, it is possible to analogize the formation state by grasping the uniform elongation in the 45 ° direction without directly grasping the formation state of these coarse recrystallized grains and the precipitation phase at the grain boundary by the complicated structure analysis of the plate. can do.

Thus, by improving the uniform elongation of the 6000 series aluminum alloy plate in the 45 ° direction relative to the rolling direction, suppressing the anisotropy of the r value of the plate, and improving the average value of the r value of the plate, in the present invention, it is possible to the upper direction stretch flangeability of 6000 series aluminum alloy sheet, thereby it is not to reduce the bending workability.

  Hereinafter, embodiments of the present invention will be described in detail.

(Chemical composition)
First, the chemical component composition of the 6000 series Al alloy plate targeted by the present invention will be described. The 6000 series Al alloy plate targeted by the present invention is required to have various properties such as excellent formability, BH property, strength, weldability, and corrosion resistance as the above-mentioned automobile material. In order to satisfy such requirements, the basic composition of the Al alloy plate is, in mass%, Si: 0.1-2.5%, Mg: 0.1-3.0%, and the balance is made of Al and impurities.

Other elements include Fe, Mn, Cr, Zr, V, Ti, Zn, and Cu. These elements are the contents of each impurity level of 6000 series aluminum alloys in accordance with AA or JIS standards. (Tolerance) is allowed. Further, as shown in the examples described later, Fe: 0.15% by mass, Zr: 0.10% by mass, Cu: 0.60% by mass, Zn: up to 0.10% by mass are allowed, and these elements (Fe, Mn, Cr, Zr, V, Ti, Zn, Cu) may be used alone or in combination of two or more.

  Other alloy elements and gas components other than the above alloy elements are also impurities. However, from the viewpoint of recycling, not only high-purity Al ingots but also 6000 series alloys and other Al alloy scrap materials, low-purity Al ingots, etc. are used as melting raw materials as melting materials. In the case of melting, these other alloy elements are necessarily included. Therefore, in the present invention, these impurity elements are allowed to be contained within a range that does not hinder the intended effect of the present invention.

The preferable content range and significance of each element in the 6000 series Al alloy, or the allowable amount will be described below.
Si: 0.1-2.5%.
Si, together with Mg, forms a compound phase such as GP zone at the time of artificial aging treatment at low temperatures such as solid solution strengthening and paint baking treatment, exhibits age-hardening ability, and is necessary as an automotive panel, for example, 170 MPa It is an essential element for obtaining the above required strength. Furthermore, in the 6000 series Al alloy plate of the present invention, it is the most important element for combining various properties such as stretch flangeability and bendability.

  In order to demonstrate the excellent low-temperature age-hardening ability to increase the yield strength after low-temperature paint baking after molding on the panel (at the time of low-temperature aging treatment at 170 ° C for 20 minutes after applying 2% stretch), Si It is preferable to have an excess Si type 6000 series Al alloy composition in which / Mg is 1.0 or more by mass and Si is excessively contained with respect to Mg.

  If the Si amount is less than 0.1%, the age-hardening ability, and further, various properties such as stretch flangeability and bendability, or press formability, which are required for automobile panel applications, etc. cannot be provided. On the other hand, if Si is contained in excess of 2.5%, coarse compounds increase and become the starting point of fracture, and stretch flangeability and bendability are deteriorated. Furthermore, the weldability is significantly impaired. Therefore, Si is in the range of 0.1 to 2.5%. In addition, in the outer panel of automobiles, hem workability is particularly important. Therefore, in order to further improve the bendability such as flat hem workability, the Si content is set to a lower range of 0.6 to 2.0%. It is preferable.

Mg: 0.1-3.0%.
Mg forms a compound phase such as GP zone together with Si during the above-mentioned artificial aging treatment such as solid solution strengthening and paint baking treatment, and exhibits age hardening ability, and as a panel, for example, the required strength of 170 MPa or more is obtained. Furthermore, it is an essential element for obtaining stretch flangeability and bendability.

  If the Mg content is less than 0.1%, the absolute amount is insufficient, so that the compound phase cannot be formed during the artificial aging treatment, and the age hardening ability cannot be exhibited. For this reason, the required strength of 170 MPa or more necessary for a panel cannot be obtained.

  On the other hand, if the Mg content exceeds 3.0%, on the contrary, coarse compounds increase to become a starting point of fracture, and stretch flangeability and bendability are deteriorated. Therefore, the Mg content is in the range of 0.1 to 3.0%. Also, in order to further improve the hem workability such as flat hem, which is important in automobile outer panels, etc., when the Si content is set to a lower range of 0.6 to 2.0%, in response to this, The Mg content is also preferably in the lower range of 0.4 to 2.5%.

Fe, Mn, Cr, Zr, V, Ti, and Zn are elements that are easily mixed from a melting raw material such as scrap, but have an effect of refining crystal grains and an effect of improving workability. However, if the content is too large, a coarse compound is formed, which acts as a starting point of destruction, and the workability deteriorates on the contrary. Therefore, the content up to the upper limit is allowed.

Cu is also an element easily mixed from melting raw materials such as scrap, but under the conditions of artificial aging treatment, it also has the effect of promoting GPII and β "phase precipitation in the crystal grains of the Al alloy material structure. the Cu was dissolved in the state also has an effect of improving formability. on the other hand, crude large compounds is increased it becomes a starting point of fracture, lowering stretch flangeability and bendability. Moreover, Ya stress corrosion cracking resistance , filiform rust resistance of the corrosion resistance after painting, also significantly degrade the weldability. Therefore, the content of the above upper limit or permits.

(Organizational characteristics)
Next, the structure characteristics of the 6000 series Al alloy sheet targeted by the present invention will be described.
(Anisotropy of r value)
In the present invention, in order to improve stretch flangeability in a 6000 series aluminum alloy plate, the anisotropy of the r value (Rankford value) of the plate is suppressed. However, if the r-value anisotropy of the plate (rankford-value anisotropy) becomes too small, the bendability deteriorates.

Therefore, in the present invention, Δr, which is an index indicating the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ , is defined as a range of 0.2 to 0.6.
Here, r ₀ is the r value in the 0 ° direction relative to the rolling direction, r ₄₅ is the r value in the 45 ° direction relative to the rolling direction, and r ₉₀ is the r value in the 90 ° direction relative to the rolling direction. . Δr is expressed as Δr = (r ₀ −2 × r ₄₅ + r ₉₀ ) / 2 as an index indicating the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ .

If Δr is less than 0.2, good bendability cannot be obtained. Conversely, if Δr exceeds 0.6, the local thickness reduction during hole expansion is significantly generated in the constriction promotion, stretch flangeability is degraded. Therefore, Δr is in the range of 0.2 to 0.6, preferably 0.3 to 0.5.

(Average r value)
In order to guarantee bending workability, the average value of r values represented by (r ₀ + 2 × r ₄₅ + r ₉₀ ) / 4 is set to 0.5 or more for each r value. If the average r value is less than 0.50, the r value becomes too small, and bending workability cannot be guaranteed. In other words, stretch flangeability and bending workability cannot be combined. Therefore, the average value of r values is 0.50 or more, preferably 0.55 or more.

These r-values were measured by collecting tensile test pieces whose longitudinal directions were 0, 45, and 90 ° with respect to the rolling direction of the plate. Measure the width and thickness, then measure the plate width and thickness at the stage where 15% strain was given by the JIS No. 5 tensile test, and substitute them into the following equations to obtain r ₀ , r ₄₅ , Obtain r values of r ₉₀ respectively. In addition, about each r value, it was set as the average value which performed the test 3 times.
r = ln (W ₀ / W) / ln (t ₀ / t). Here, W0, t0: width and thickness before tensile test, W, t: width and thickness after 15% tension.

  Further, the average value of Δr and r values can be obtained by substituting each of these r values into the above equation.

(Uniform elongation in 45 ° direction)
Conventionally, in a 6000 series aluminum alloy plate, it is known that stretch flangeability improves as the stretch property increases. However, during the hole expansion test to evaluate the stretch flangeability (λ) of 6000 series aluminum alloy sheets, it is not known that the direction of crack generation at the hole expansion part is approximately 45 ° to the rolling direction. . Accordingly, this improves the generating direction of the plate characteristics of cracks by increasing the 45 ° direction of uniform elongation of the plate, is not known to be able to obtain stretch flangeability has high.

In the present invention, in order to obtain high stretch flangeability of 70% or more, the uniform elongation in the 45 ° direction with respect to the rolling direction of the 6000 series aluminum alloy sheet is defined as 24% or more, preferably 26% or more. When the uniform elongation is less than 24%, and more strictly less than 26% is not obtained stretch flangeability has high.

(Random orientation)
In the present invention, as described above, the anisotropy of the r value (Rankford value) of the plate is suppressed in order to improve the stretch flangeability of the 6000 series aluminum alloy plate. However, in order to guarantee this characteristic from the point of texture, it is preferable to set the random orientation by the crystal orientation distribution function analysis to a certain ratio or more.

  It is known that the following texture is formed in a normal aluminum alloy. (For example, Shinichi Nagashima edited by “texture” (published by Maruzen Co., Ltd.) and Light Metal Society of Japan “Light Metal” commentary Vol.43 (1993) P 285 -293) In the case of a plate material by rolling, it is necessary to represent the rolling surface and the rolling direction. The rolling surface is represented by [XX] and the rolling direction is represented by <ΔΔΔ> (◯ and Δ are integers).

Based on such an expression method, each direction is represented as follows.
Cube orientation: {001} <100>
Goss orientation: {011} <100>
Brass orientation: {011} <211>
Cu orientation: {112} <111>
(Or D direction: {4 4 11} <11 11 8>)
S direction: {123} <634>
PP orientation: {011} <1-22>
RW orientation: {001} <110> (Cube orientation is the orientation in which the plate is rotated)
There are many types of crystal orientations.

  In the present invention, the random orientation is defined as random orientation (%) = 100-Cube orientation (%)-Goss orientation (%)-Brass orientation (%)-Cu orientation (%)-S orientation (%)-PP orientation (% ) -RW orientation (%).

  And as described above, for the purpose of improving the stretch flangeability of the 6000 series aluminum alloy plate, the random orientation is preferably set to a certain ratio or more. That is, among the textures of the plate, the area ratio of the random orientation is increased, and the anisotropic Cube orientation, Goss orientation, Brass orientation, Cu orientation, S orientation, PP orientation, RW orientation, etc., selected from the above orientations, etc. The sum of the average area ratios of the orientation components of each texture is reduced.

  More specifically, the area ratio of the random orientation by the crystal orientation distribution function analysis in the 1/4 depth portion from the surface of the aluminum alloy plate is specified to be 55 to 75%.

  When the area ratio of the random orientation is less than 55%, the anisotropy of the r value (Rankford value) of the plate increases. On the other hand, it is difficult for the rolled material to increase the area ratio of the random orientation beyond 75%.

  The measurement site of the texture distribution in the present invention is a right-angle cross section in the plate thickness direction, and is measured at an arbitrary point of ¼ part in the plate thickness direction from the surface of the alloy plate. That is, a surface parallel to the plate surface passing through an arbitrary point of 1/4 part of the plate thickness cross section after the final annealing is measured using SEM-EBSP (Electron Back Scattering (Scattered) Pattern). However, the area ratio of each texture is the area ratio of the azimuth region whose deviation from each ideal azimuth is within ± 15 °.

  More specifically, a sample whose surface was adjusted by mechanical polishing on the surface of a sample of a cross-section of a plate sampled from a plurality of the above parts, scraping about 0.25 mm from the surface of the plate by mechanical polishing, and further performing buffing and electrolytic polishing. Prepare. Next, the measurement site is the sample polished surface, the measurement area is 1500 μm × 1500 μm, the measurement step interval is 5 μm, the texture composition is measured at a plurality of locations, and the average area ratio in each direction is calculated.

  As the SEM-EBSP, for example, SEM (scanning electron microscope: JEOL JSM 5410) manufactured by JEOL Ltd. is used, and for the EBSP measurement / analysis system, for example, TSL (OIM) is used.

(Average crystal grain size)
The average crystal grain size of the Al alloy plate thus obtained is preferably refined to 50 μm or less. By making the crystal grain size fine or small within this range, stretch flangeability and bendability, or press formability can be ensured or improved. When the crystal grain size becomes larger than 50 μm, the stretch flangeability and bendability, or press formability are likely to deteriorate significantly.

  The crystal grain size referred to here is the maximum diameter of crystal grains in the longitudinal (L) direction of the plate. The crystal grain size is measured by a line intercept method in the L direction by observing the surface of the Al alloy plate that has been mechanically polished by 0.05 to 0.1 mm and then electrolytically etched using an optical microscope. 1 The measurement line length is 0.95mm, and the total measurement line length is 0.95 x 15mm by observing a total of 5 fields with 3 lines per field.

(Production method)
Next, production conditions for the Al alloy sheet of the present invention will be described below. A normal Al alloy sheet is manufactured through each process of casting → homogenization heat treatment → hot rolling → intermediate annealing → cold rolling → final annealing. However, since the formation of coarse recrystallized grains and the precipitation phase at grain boundaries and the state of anisotropy of the plate change depending on the chemical composition of the Al alloy plate and the setting conditions of each process, a series of production The conditions should be selected and determined comprehensively as a process. Hereinafter, preferable conditions for reliably obtaining an Al alloy having excellent stretch flangeability and bendability intended in the present invention will be described.

  First, in the melting and casting process, a normal melt casting method such as a continuous casting rolling method and a semi-continuous casting method (DC casting method) is appropriately selected for the molten Al alloy melt adjusted within the above-mentioned 6000 component standard range. And cast.

  The Al alloy ingot is subjected to a homogenization heat treatment at a temperature of 500 ° C. or higher and lower than the melting point. The purpose of this homogenization heat treatment is to homogenize the structure, that is, to eliminate segregation in the crystal grains in the ingot structure. When the heat treatment temperature is lower than 500 ° C., intragranular segregation of the ingot cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that stretch flangeability and bendability deteriorate. Further, the heat treatment time is preferably 2 hours or more, although it depends on the thickness of the ingot. If it is lower than 2 hours, intragranular segregation in the ingot cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that stretch flangeability and bendability may be deteriorated.

  After this homogenization heat treatment (first homogenization heat treatment), a homogenization heat treatment (twice soaking) is performed in which the mixture is once cooled to a temperature of 200 ° C or lower and reheated to a temperature of 390 to 480 ° C. After the homogenization heat treatment, it is cooled to a temperature of 390 to 480 ° C., and after performing the homogenization heat treatment (two-stage soaking) in which all of these temperatures are maintained, hot rolling is started. As a result, stretch flangeability and bendability are further improved as compared with a single homogenization heat treatment.

  In either case of the two-stage soaking or the two-stage soaking, the structure before the hot rolling is maintained by holding in each temperature range in the first and second or second homogenization heat treatment. Is optimized. When this holding temperature is low, formation of a precipitated phase at the grain boundary is promoted, and stretch flangeability and bendability deteriorate. On the other hand, if the holding temperature is too high, the strength becomes too high, and the stretch characteristics deteriorate, so the stretch flangeability also decreases.

  The retention time in the first and second or second homogenization heat treatment is 2 to 15 hours as a guide. If the holding time is shorter than 2 hours, the strength becomes too high, and the elongation characteristics deteriorate, so the stretch flangeability may also deteriorate. On the other hand, if the holding time is longer than 15 hours, the formation of a precipitated phase at the grain boundary is promoted, and the stretch flangeability and bendability may be deteriorated.

  After these homogenization heat treatments, hot rolling is started at a temperature of 390 to 480 ° C. When the hot rolling start temperature exceeds 480 ° C., recrystallization occurs and coarse recrystallized grains are generated during hot rolling, and stretch flangeability and bendability deteriorate. In addition, when the hot rolling start temperature is less than 390 ° C., the hot rolling itself becomes difficult.

  Further, the hot rolling finished temperature is set to 170 to 300 ° C. to produce a hot rolled sheet such as a coil or plate. When the hot rolling finish temperature exceeds 300 ° C, the excess Si type 6000 series Al alloy sheet with a Si / Mg mass ratio of Si / Mg of 1 or more tends to recrystallize, stretch flangeability and bending Deteriorates. If the end temperature of hot rolling is less than 170 ° C., hot rolling itself becomes difficult.

  The hot-rolled sheet is annealed (roughened) at a temperature of 470 ° C. or higher before cold rolling, and then cooled at a rate of 100 ° C./s or higher. When the rough temperature is lower than 470 ° C., formation of a precipitated phase at the grain boundary is promoted, and stretch flangeability and bendability deteriorate. On the other hand, if the cooling rate is less than 100 ° C./s, the formation of a precipitated phase at the grain boundary is promoted in the cooling process, and the stretch flangeability and bendability deteriorate.

  In order to have both stretch flangeability and bendability, a roughening process under these conditions is indispensable in addition to the two-step soaking or the two-step soaking. The conventional technology intended to improve stretch flangeability does not have bendability because the soaking condition is not the above-described two-step soaking or two-stage soaking. In addition, the conventional technology intended to improve bendability did not have stretch flangeability even because of the absence of this roughening process (the cold rolling was performed without the roughening process). is there.

  After the roughening, cold rolling is subsequently performed to produce a cold-rolled sheet (including a coil) having a desired thickness.

  The plate after cold rolling is essentially subjected to solution treatment and quenching treatment as a tempering treatment to obtain an Al alloy plate. The solution treatment and quenching treatment are important steps for sufficiently depositing the compound phase such as the GP zone in the grains by an artificial age hardening treatment such as a subsequent paint bake hardening treatment. The solution treatment conditions for producing this effect are preferably performed in a temperature range of 500 to 560 ° C. Thus, a high-strength plate having the stretch flangeability and bendability of the Al alloy plate is obtained.

  In quenching after the solution treatment, the cooling rate is preferably 50 ° C./min or higher. When the cooling rate is slow at less than 50 ° C./min, the strength after quenching is low, the age hardening ability is insufficient, and the high proof stress of 170 MPa or more cannot be ensured by the artificial aging treatment at a low temperature for a short time.

In addition, Si, Mg ₂ Si and the like are likely to be precipitated on the grain boundary, which is likely to be a starting point of cracking during press forming and bending, and the stretch flangeability and bendability of the Al alloy plate are deteriorated. In order to ensure this cooling rate, the quenching process may be air cooling such as a fan, but there is a high possibility that the cooling rate will be slow, and it is preferable to perform the quenching process by selecting from water cooling means such as mist, spray, and immersion.

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

  As the preliminary aging treatment, the quenching end temperature after the solution treatment is increased to 50 to 100 ° C., and then immediately reheated or kept as it is. Alternatively, it is immediately reheated to 50 to 100 ° C. after quenching to room temperature after solution treatment.

  Further, in the case of continuous solution quenching, the quenching process is completed within the temperature range of the preliminary aging, and the coil is wound around a coil at the same high temperature. In addition, you may reheat before winding up to a coil, and you may heat-retain after winding. Moreover, after the quenching process to room temperature, it may be reheated to the above temperature range and wound at a high temperature.

  In addition to this, it is of course possible to further increase the strength by performing aging treatment or stabilization treatment at a higher temperature according to the application or required characteristics.

  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. A 400mm-thick ingot obtained by DC casting of a 6000 series Al alloy with each composition of 1 to 27 shown in Table 1 is subjected to homogenization heat treatment (abbreviated as soaking) and hot rolling under various conditions shown in Table 2. I do. Each hot-rolled sheet obtained was subjected to roughening under various conditions shown in Table 2, followed by cold rolling, solution treatment, and quenching treatment to obtain a final sheet having a thickness of 1 mm. In addition, in the display of the content of each element in Table 1, “−” indicates that the content is below the detection limit.

  In the soaking process, after the first soaking of the heating temperature and holding time shown in Table 2, after cooling to room temperature, the second soaking of the heating temperature and holding time shown in Table 2 is performed twice. After the first soaking of the heating temperature and holding time shown in Table 2, the heat is further cooled to the temperature shown in Table 2 and held, and then the second soaking is performed. Kind.

  After this soaking, hot rolling was performed to a thickness of 5 mmt at each start temperature and each end temperature shown in Table 2. The hot-rolled sheet was roughened at the temperature and cooling rate shown in Table 2, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 1.0 mmt. This cold-rolled sheet is then rapidly cooled down to room temperature at a rate of 200 ° C / second immediately after reaching the solution treatment temperature of 510 ° C (holding time 0 seconds) in a continuous heat treatment facility. Immediately after this quenching, a preliminary aging treatment was carried out at 70 ° C. for 1 hour (after cooling, slow cooling at a cooling rate of 0.6 ° C./hr).

  A test plate (blank) was cut out from each of the Al alloy plates after the tempering treatment, and the anisotropy of each test plate after room temperature aging for 3 months (90 days) after the tempering treatment was expressed as Δr, r The average value and the random azimuth area ratio (%) were measured. Similarly, average grain size (μm), 0.2% proof stress (MPa) and uniform elongation (%) in the direction of 45 ° with respect to the rolling direction, stretch flangeability (λ:%), 0 with respect to the rolling direction The bendability in each direction at 45 ° and 90 ° was measured and evaluated. These results are shown in Table 3.

  Δr, average value of r values, random orientation area ratio (%), and average crystal grain size (μm) were determined by the methods described above.

  The 0.2% proof stress (MPa) and uniform elongation in the 45 ° direction were measured in accordance with JIS Z 2201 by collecting JIS No. 5 tensile test pieces whose longitudinal direction was 45 ° with respect to the rolling direction. The crosshead speed was 5 mm / min, and the test was performed at a constant speed until the test piece broke. Each sample was tested three times and the average value was adopted.

  The uniform elongation in the 45 ° direction was obtained by subtracting 0.2% from the strain amount (%) at the maximum stress point after obtaining the stress-strain curve by the tensile test.

In the hole expansion test for evaluating the stretch flangeability, first, a hole having a diameter of 10 mm was punched into a square plate having a side of 70 mm. Then, using a 60 ° conical punch with a diameter of 33 mm, with a burr on the upper surface (die surface) side, a hole expansion test was performed at a wrinkle holding force of 3 tons and a punch speed of 10 mm / min, and breakage occurred at the edge of the punched hole At this stage, the punch was stopped, and the hole expansion rate (λ) was obtained from the following formula from the hole inner diameter (d _s ) after fracture and the initial hole diameter (d ₀ ) before the molding test.
λ = (d _s -d ₀ ) / d ₀ × 100 (%)
About the hole internal diameter after a fracture | rupture, it measured in the rolling direction and the direction perpendicular | vertical to a rolling direction, respectively, calculated | required each hole expansion rate, and averaged it as the hole expansion rate of each sample. Further, three hole expansion tests were performed on each sample, and the average value was finally set as the hole expansion ratio (λ:%).

For the evaluation of bendability, a bend test specimen having a length of 150 mm and a width of 30 mm was taken from a test plate, and bendability assuming flat hemming was evaluated. That is, a 15% strain was preliminarily applied to the test piece, and then contact bending at an angle of 180 ° (inner bending radius R = about 0.25 mm) was performed. The evaluation of bendability was evaluated in five stages based on the following criteria by visually confirming the degree of cracking at the bent edge of the test piece after bending.
0: No rough skin or fine cracks.
1: Rough skin has occurred.
2: Although there is rough skin, there are no cracks including minute ones.
3: Small cracks occur.
4: Large cracks occur.
5: Multiple or many large cracks occurred.
Among the above ranks, 0 to 2 levels are acceptable and 3 to 5 are unacceptable.

  As shown in Tables 1 and 2, Invention Examples 1 to 9 were subjected to homogenization heat treatment and hot rolling within the composition range of the present invention and within the preferred conditions of the present invention, and further subjected to roughening. Yes. Therefore, as shown in Table 3, Δr of the obtained Al alloy sheet is in the range of 0.2 to 0.6, the average value of r value is 0.5 or more, and further, with respect to the rolling direction of the aluminum alloy sheet. The uniform elongation in the 45 ° direction is 24% or more. The structure of the aluminum alloy plate also has a random orientation area ratio in the range of 55 to 75%. As a result, Invention Examples 1 to 9 are excellent in stretch flangeability and bending workability.

On the other hand, Comparative Examples 10 to 27 are out of the invention conditions. For this reason, stretch flangeability and / or bending workability are remarkably inferior to those of the inventive examples.
In Comparative Example 10, the temperature of the first soaking is too low.
In Comparative Example 11, the time for the first soaking is too short.
In Comparative Example 12, in addition to the one-time soaking process, the hot rolling start temperature is too high. In Comparative Example 13, in addition to the temperature of the second soaking process being too low, the hot rolling start temperature is too low.
In Comparative Example 14, in addition to the temperature of the second soaking process being too high, the hot rolling end temperature is too high.
In Comparative Example 15, the time for the first soaking is too short.
In Comparative Example 16, the time for the second soaking process is too long.
In Comparative Examples 24 and 25, the hot rolling start temperature and the hot rolling end temperature are too high, in addition to the single soaking.

In Comparative Examples 17 and 26, the temperature of rough firing is too low.
In Comparative Example 18, the cooling rate after rough firing is too low.
Comparative Example 27 does not have a rough baking process itself.

In Comparative Example 19, the amount of Mg exceeds the upper limit and is too large.
In Comparative Example 20, the amount of Si exceeds the upper limit and is too large.
In Comparative Example 21, in addition to the excessive amount of Fe, the hot rolling start temperature is too low.
Comparative Example 22 has too much Ti.
Comparative Example 23 has too much Cu.

Therefore, the results of the above examples support the critical significance or effect of each requirement of the present invention.

According to the present invention, it is possible to provide an Al alloy plate having excellent stretch flangeability without deteriorating bending workability, and a production method capable of reliably obtaining this Al alloy plate. As a result, it is possible to expand the application of 6000 series Al alloy materials for transportation equipment such as automobiles, ships or vehicles, household appliances, construction, structural members and parts, and especially for transportation equipment such as automobiles. .

Claims (3)

An aluminum alloy plate containing Si: 0.1 to 2.5% and Mg: 0.1 to 3.0% in mass%, with the balance being Al and inevitable impurities. Of the r value of the aluminum alloy plate, When r value in the 0 ° direction is r ₀ , r value in the 45 ° direction is r ₄₅ , and r value in the 90 ° direction is r ₉₀ , Δr = (r ₀ −2 × r ₄₅ + r ₉₀ ) / 2 and Δr, which is an index indicating the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ , is 0.2 to 0.6, and the r value represented by (r ₀ + 2 × r ₄₅ + r ₉₀ ) / 4 The average value is 0.5 or more, and further, the uniform elongation in the 45 ° direction with respect to the rolling direction of this aluminum alloy sheet is 24% or more , and the hole expansion ratio λ is 61% or more. Aluminum alloy plate with excellent flangeability and bending workability.   2. The stretch flangeability and bending workability of claim 1, wherein the area ratio of the random orientation is 55 to 75% by crystal orientation distribution function analysis at a quarter depth from the surface of the aluminum alloy plate. Aluminum alloy plate. A method for obtaining an aluminum alloy sheet according to claim 1 or 2, comprising, by mass%, Si: 0.1-2.5%, Mg: 0.1-3.0%, the balance being Al and impurities. After the homogenization heat treatment at a temperature of 500 ° C. or higher and lower than the melting point, it is once cooled to a temperature of 200 ° C. or lower and reheated to a temperature of 390 to 480 ° C., or cooled to a temperature of 390 to 480 ° C. In addition, hot rolling is started after holding in this temperature range, a hot rolled sheet is manufactured at a hot rolling end temperature of 170 to 300 ° C, and the hot rolled sheet is annealed at a temperature of 470 ° C or higher. Then, after performing the process of cooling at a rate of 100 ° C./s or higher, cold rolling is subsequently performed to produce a cold-rolled sheet, and the r-value of the aluminum alloy sheet obtained by solution-treating the cold-rolled sheet each to the rolling direction, 0 ° direction of the r value r _0, 45 ° direction of the r value r _45, 90 When the direction of the r value was r _90, [Delta] r = is represented by _{(r 0 -2 × r 45 +} r 90) / 2, the [Delta] r is an index showing the anisotropy of the r ₄₅ for r ₀ and r ₉₀ 0.2 To 0.6, and the average value of r values represented by (r ₀ + 2 × r ₄₅ + r ₉₀ ) / 4 is 0.5 or more, and the uniform elongation in the 45 ° direction with respect to the rolling direction of the cold-rolled sheet A method for producing an aluminum alloy plate excellent in stretch flangeability and bending workability, characterized in that the content is 24% or more.