JP4515363B2 - Aluminum alloy plate excellent in formability and method for producing the same - Google Patents

Description

The present invention relates to an aluminum alloy plate having high strength and excellent formability and a method for producing the same, and an aluminum alloy plate having excellent stretch flangeability without deteriorating bending workability, and the aluminum alloy plate The present invention relates to a manufacturing method that can be obtained. The aluminum alloy sheet of the present invention is particularly suitable for a molded panel having a flange portion that requires stretch flangeability.
The aluminum alloy plate referred to in the present invention refers to an aluminum alloy plate after the cold-rolled plate is subjected to a solution treatment. 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 automobile hoods, fenders, doors, roofs, and trunk lids, such as outer panels (outer plates) and inner panels (inner plates), 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. On the other hand, among the above-described automobile panels, molded panels having flange portions such as roofs and sunroofs are required to have particularly excellent stretch flangeability in order to prevent cracking at the flange portions during press molding. The

  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.

The gist of an aluminum alloy plate excellent in formability to achieve this purpose is an aluminum alloy plate containing, by mass%, Si: 0.1 to 2.5%, Mg: 0.1 to 3.0%, the balance being Al and impurities. In addition, the following shear surface ratio of the circular hole wall provided by the following punching test of this aluminum alloy plate is 50% or more, and the area ratio of Mg-Si based compound of 1 μm or more is 0.15% or less, The proof stress of this aluminum alloy plate is 135 MPa or more.
In the punching test, a circular hole is punched in a 1 mm thick aluminum alloy sheet using a punch with a diameter of 10.0 mmφ-shoulder R8 mm and a die with a diameter of 10.2 mmφ-shoulder R8 mm.
The shear surface ratio was measured by taking a photo of the wall surface at 45 ° in the rolling direction of the circular hole wall surface with a 100x optical microscope, and parallel to the plate thickness direction of any of the five points on this photograph. Each of the shear surface lengths l is measured, and the respective shear surface ratios calculated by the shear surface ratio = (shear surface length 1 / sheet thickness t) × 100 (%) are averaged.

Further, the gist of a method for producing an aluminum alloy plate excellent in formability for achieving the above object is a method for obtaining an aluminum alloy plate of the above gist or a preferred embodiment described later, and in mass%, Si: 0.1 to An aluminum alloy ingot containing 2.5% and Mg: 0.1-3.0%, the balance being Al and impurities, is subjected to homogenization heat treatment at a temperature of 500 ° C. or higher and lower than the melting point, and then cooled to a temperature of 200 ° C. or lower once. Reheat to a temperature of ~ 480 ° C or cool to a temperature of 390 ~ 480 ° C, both start hot rolling after holding in this temperature range, and set the end temperature of hot rolling to 170 ~ 300 ° C After producing a hot-rolled sheet and further annealing the hot-rolled sheet at a temperature of 470 ° C. or higher and then cooling at a rate of 100 ° C./s or higher, cold rolling is performed to perform cold rolling. A sheet is manufactured, and this cold-rolled sheet is solution treated at a temperature of 560 ° C or higher. In addition, the following shear surface ratio of the circular hole wall provided by the following punching test of the aluminum alloy plate after this treatment is set to 50% or more, and the area ratio of Mg-Si based compound of 1 μm or more is 0.15% or less Furthermore, the proof stress of this aluminum alloy plate is set to 135 MPa or more.
In the punching test, a circular hole is punched in a 1 mm thick aluminum alloy sheet using a punch with a diameter of 10.0 mmφ-shoulder R8 mm and a die with a diameter of 10.2 mmφ-shoulder R8 mm.
The shear surface ratio was measured by taking a photo of the wall surface at 45 ° in the rolling direction of the circular hole wall surface with a 100x optical microscope, and parallel to the plate thickness direction of any of the five points on this photograph. Each of the shear surface lengths l is measured, and the respective shear surface ratios calculated by the shear surface ratio = (shear surface length 1 / sheet thickness t) × 100 (%) are averaged.

  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, high stretch flangeability can be obtained by increasing the uniform elongation in the 45 ° direction with respect to the rolling direction of the plate, which is the direction in which the cracks are generated.

  In the present invention, in order to improve the uniform elongation in the direction of 45 ° with respect to the rolling direction, first, the area ratio of the coarse Mg—Si compound of the 6000 series aluminum alloy plate is regulated. According to this method, the stretch flangeability of the 6000 series aluminum alloy plate is improved and the bending workability is not lowered.

  As described above, stretch flangeability and bending workability are usually in a contradictory relationship, and the series of conventional techniques for improving stretch flangeability deteriorates bending workability, and improves bending workability. The series of prior arts has a problem that stretch flangeability deteriorates.

  On the other hand, according to the method of controlling the coarse Mg-Si compound of the 6000 series aluminum alloy sheet and improving the uniform elongation in the 45 ° direction relative to the rolling direction as in the present invention, Flangeability can be improved and bending workability is not reduced.

  However, the high-strength 6000 series with a proof stress of 135 MPa or more can be achieved only by regulating the coarse Mg-Si series compounds in the 6000 series aluminum alloy sheet and improving the uniform elongation in the 45 ° direction relative to the rolling direction. The stretch flangeability of the aluminum alloy plate cannot be improved to a sufficiently high level of 60% or more. The same applies to the suppression of the anisotropy of the r value of the plate and the improvement of the average value of the r value of the plate in the prior art described above.

  The reason is due to the mechanism of stretch flange deformation. When the elongated flange is deformed, the initial hole is punched out by a punch and a die, and then the hole is expanded and deformed. Improvement of uniform elongation in the direction of 45 ° with respect to the rolling direction, suppression of the r-value anisotropy of the plate, or improvement of the average value of the r-value of the plate is due to hole expansion deformation at the time of deformation of the stretch flange. Is effective.

  However, according to the findings of the present inventors, the shear surface when the initial hole is punched out becomes small, and in the case where the fracture surface that is a crack becomes large, 45 ° with respect to the rolling direction. Even if the uniform elongation in the direction is improved, the stretch flangeability in a high-strength 6000 series aluminum alloy sheet having a proof stress of 135 MPa or more cannot be improved to a sufficiently high level of 60% or more. Further, even if the coarse Mg—Si compound is suppressed and the uniform elongation in the 45 ° direction with respect to the rolling direction is improved, the shear surface ratio is reduced to less than 50%, and the fracture surface which is a crack is 50%. It can happen inevitably when it becomes larger than%.

  For this reason, as a means for improving stretch flangeability in the high-strength 6000 series aluminum alloy sheet, in addition to the coarse Mg-Si compound suppression, the shear surface when the initial hole is punched becomes large, Material characteristics are required to reduce the fracture surface, which is a crack.

  However, the reason why the fracture surface, which is a crack when the initial hole is punched, increases, is because of the increase in hardness accompanying the increase in strength of 6000 series aluminum alloy sheets, Mg-Si series compounds or Al-Fe-Si series. There are many factors such as an increase in the number of compounds. Among these factors, there are many factors whose specific correlation with shear plane formation is unknown. For this reason, it is very difficult at the present time to specify all these related factors and to control the shear plane when the initial hole is punched out.

  On the other hand, it is possible to largely control the shear plane when the initial hole is punched by the manufacturing method of the present invention.

  Therefore, in the present invention, as a requirement for improving stretch flangeability in a high-strength 6000 series aluminum alloy plate, the above-mentioned hole expansion test, in other words, a circle provided by punching in the hole expansion test, which can be said to be an evaluation standard for stretch flangeability Defines the shearing area ratio on the hole wall surface and guarantees stretch flangeability.

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

(Al alloy plate 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.

In Examples other elements (Fe, Mn, Cr, Zr , V, Ti, Zn, Cu) is the content of each impurity levels along like AA or JIS standards (tolerance), which will be described later Are allowed up to the maximum value of each element, for example Fe: 0.10%, Mn: 0.10%, Cr: 0.05%, Zn: 0.10%, Cu: 0.15% 1 type or 2 types or more may be included.

  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: 1.5% or less, Mn: 1.0% or less, Cr: 0.5% or less, Zr: 0.5% or less, V: 0.3% or less, Ti: 0.2% or less, Zn = 1.5% or less.
These elements are easily mixed from melting raw materials 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: 1.0% or less.
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. Cu dissolved in the state also has the effect of improving the formability, while if it exceeds 1.0%, coarse compounds increase and become the starting point of fracture, and the stretch flangeability and bendability are reduced. Stress corrosion cracking resistance, post-coating corrosion resistance, thread rust resistance, and weldability are significantly deteriorated, so inclusion in the range of 1.0% or less is allowed.

(Al alloy plate structure)
Next, the requirements for the structure of the 6000 series Al alloy sheet of the present invention will be described.

(Mg-Si compound)
In the present invention, the area ratio of the Mg-Si based compound of 1 μm or more in the structure of the 6000 series Al alloy plate is set to 0.15% or less. By suppressing the coarse Mg-Si based compound of 1 μm or more to an area ratio of 0.15% or less, the uniform elongation in the 45 ° direction with respect to the rolling direction is improved. This makes it possible to improve the stretch flangeability of a high-strength 6000 series aluminum alloy plate having a proof stress of 135 MPa or more to a sufficiently high level of 60% or more by a synergistic effect with the regulation of the shearing area ratio described later.

  When the area ratio of these coarse Mg-Si compounds of 1 μm or more exceeds 0.15%, the uniform elongation in the 45 ° direction with respect to the rolling direction is lowered, and the stretch flangeability is significantly lowered.

(Measurement of area ratio of Mg-Si compounds)
In the present invention, the area of the Mg—Si compound is measured at a right-angle cross section in the plate thickness direction, and is measured at an arbitrary point of 1/4 part in the plate thickness direction from the surface of the aluminum 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 final annealing is measured using a 500 times SEM (Scanning Electron Microscope).

  More specifically, a plurality of sampled plate cross-section sample surfaces from the above part are mechanically polished, about 0.25 mm from the plate surface is scraped off by mechanical polishing, and further, a sample whose surface is adjusted by buffing is prepared. . Next, a backscattered electron image is taken, and the area ratio of the Mg-Si compound is measured with an automatic analyzer. The measurement site is the sample polishing surface, and the measurement area is an area of 1000 μm × 1000 μm. The resolution of the analysis image is 1 pixel = 0.65 μm. Differentiation from other compounds than Mg-Si compounds, such as Al-Fe compounds, is done by the brightness of the compound, and the compound particles are confirmed in advance by point analysis, and the detection conditions are set so that only the Mg-Si compound can be detected. After selection, the area ratio of the Mg-Si compound is measured by automatic analysis.

(Shear area ratio during hole expansion test)
In the present invention, the coarse Mg-Si compound is suppressed, and the shear surface ratio of the wall surface of the circular hole provided by punching during the hole expansion test is set to 50% or more, whereby the proof stress is 135 MPa or more. The stretch flangeability of high-strength 6000 series aluminum alloy sheets is improved to a sufficiently high level of 60% or more.

  Even if the coarse Mg-Si compound is suppressed and the uniform elongation in the 45 ° direction with respect to the rolling direction is improved, the shear surface ratio is reduced to less than 50%, and the fracture surface that is a crack is reduced to 50%. In some cases, it becomes larger than that. In such a case, even if the coarse Mg-Si based compound is suppressed and the uniform elongation in the 45 ° direction with respect to the rolling direction is improved, the high strength 6000 series aluminum alloy sheet having a proof stress of 135 MPa or more is particularly good. The stretch flangeability cannot be improved to a sufficiently high level of 60% or more.

  FIG. 1 shows the state of the hole expansion (punching) test for obtaining the shear surface ratio. The punching in this hole expansion test specifically defines test conditions that can guarantee reproducibility in order to provide reproducibility in measuring the shear surface ratio.

  In other words, punching is performed by making a circular hole with a diameter of 10 mm in an aluminum alloy plate with a side of 70 mm and a thickness of 1 mm. The press used for this is a punch with a diameter of 10.0mmφ-shoulder R8mm and a die with a diameter of 10.2mmφ-shoulder R8mm, and the punch (upper die) and die (die: lower die) are moved relatively. Drill the circular hole. At this time, the clearance between the punch and the die is 0.2 mm.

  The measurement of the shear surface ratio of the circular hole wall surface also specifically defines the measurement conditions in order to make the measurement reproducible. That is, as shown in a partially enlarged view in FIG. 1, the shear surface ratio is determined by measuring the wall surface (microstructure) in the 45 ° direction portion of the circular hole wall surface with a 100 × optical microscope. Take a photograph and measure the length l of the shear plane parallel to the plate thickness direction at any five points on this photo. Shear surface ratio = (Shear plane length l / plate thickness t) x 100 (% ) Average the shear surface ratios calculated by

  As shown in FIG. 2, the punching state of the plate over time, the punch (punch) descends to contact the aluminum alloy plate, and when further lowered, Sagging occurs. When the punch is further lowered, a crack is generated in the aluminum alloy plate from the punch and the cutting edge of the die. At this time, the blade side surface side of the punch and die becomes a shear surface, and the crack becomes a fracture surface. And a punch side crack and a die side crack are connected, and punching is completed.

  Here, as shown in the figure, the sag portion has a smooth R shape, the shearing surface portion has a vertical vertical line with gloss, and the fractured surface portion has a state where the material is peeled off. And can be clearly distinguished from each other.

(Uniform elongation in 45 ° direction)
In the present invention, the uniform elongation in the 45 ° direction with respect to the rolling direction is improved by suppressing the coarse Mg—Si based compound of 1 μm or more in the structure of the 6000 series Al alloy sheet to an area ratio of 0.15% or less.

  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. . Therefore, it has not been known that high stretch flangeability can be obtained by improving the plate characteristics in the crack generation direction and increasing the uniform elongation in the 45 ° direction of the plate.

  Rolling direction of 6000 series aluminum alloy sheet as a standard for improving uniform elongation in the direction of 45 ° to the rolling direction by suppressing this coarse Mg-Si compound, that is, as a standard for obtaining high stretch flangeability of 60% or more. The uniform elongation in the 45 ° direction is preferably 24% or more, and preferably 26% or more. If this uniform elongation is low, there is a high possibility that high stretch flangeability of 60% or more cannot be obtained.

(Anisotropy of r value)
In the present invention, in order to improve stretch flangeability in a 6000 series aluminum alloy plate, it is preferable to further suppress the anisotropy of the r value (Rankford value) of the plate. However, if the anisotropy of the r-value of the plate (anisotropy of the Rankford value) becomes too small, the bendability decreases on the contrary, and this is an index showing the anisotropy of r ₄₅ with respect to r ₀ and r ₉₀ Δr is preferably in the 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 may not be obtained. On the other hand, when Δr exceeds 0.6, the local thickness reduction during hole expansion becomes significant, the occurrence of constriction is promoted, and stretch flangeability may be reduced.

(Average r value)
In order to guarantee bending workability, it is preferable that the average value of r values represented by (r ₀ + 2 × r ₄₅ + r ₉₀ ) / 4 is 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 may not be guaranteed. In other words, stretch flangeability and bending workability may not be combined. Therefore, preferably, the average value of r values is 0.50 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. The average value of Δr and r values is obtained by substituting each of these r values into the above equation.
r = ln (W ₀ / W) / ln (t ₀ / t). Here, W0, t0: width and thickness before tensile test, W, t: 15% width and thickness after tensile test.

(Average crystal grain size)
The average crystal grain size of the Al alloy plate 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.

(Homogenization heat treatment)
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.

(Hot rolling)
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.

(Hot rolled sheet annealing)
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.

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

(Solution and quenching)
The plate after cold rolling is essentially subjected to solution treatment and quenching treatment as a tempering treatment to obtain an Al alloy plate. In this solution treatment and quenching treatment, the area ratio of Mg-Si compound of 1 μm or more in the structure of 6000 series Al alloy sheet is set to 0.15% or less, and the shearing area ratio in the hole expansion test is set to 50% or more. This is an important process. It is also an important process for sufficiently depositing a compound phase such as a GP zone in a grain by an artificial age hardening treatment such as a paint baking hardening treatment.

  In order to exert this effect, in the present invention, it is necessary to increase the amount of the compound in the solution treatment. In order to increase the solid solution amount of this compound, in the present invention, the cold-rolled sheet is subjected to a solution treatment at a relatively high temperature of 560 ° C. or higher.

  The normal solution treatment temperature is lower than 560 ° C. Thus, when the solution treatment temperature is less than 560 ° C., in the quenching treatment immediately after the solution treatment, the compound phase such as the GP zone can be sufficiently precipitated in the grains by an artificial age hardening treatment such as a paint baking hardening treatment. . However, as in the present invention, it is difficult to make the area ratio of a coarse Mg—Si compound having a size of 1 μm or more 0.15% or less and further to make the shearing area ratio in a hole expansion test 50% or more.

  This is because there is a large difference in the solid solution amount between the solution treatment temperature of less than 560 ° C. and 560 ° C. or more. If the solution treatment temperature is less than 560 ° C, it is not possible to secure a sufficient amount of solid solution to make the area ratio of coarse Mg-Si compounds of 1 µm or more 0.15% or less. In addition, not only Mg—Si based compounds but also other Al—Fe—Si based compounds are insufficient. For this reason, Mg-Si based compounds and Al-Fe-Si based compounds that precipitate in the quenching treatment immediately after the solution treatment are coarsened. As a result, there is a high possibility that the area ratio of a coarse Mg-Si compound having a size of 1 μm or more is set to 0.15% or less, and the shearing area ratio during the hole expansion test cannot be set to 50% or more.

  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 135 MPa or more cannot be ensured by the artificial aging treatment at 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 of the obtained hot rolled sheets was subjected to roughing, cold rolling, solution treatment and quenching treatment under various conditions shown in Table 2 to obtain a final product 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.

  More specifically, after the first soaking of the heating temperature and holding time shown in Table 2, the soaking is once cooled to room temperature, and then the second soaking of the heating temperature and holding time shown in Table 2. After the first soaking of the heating temperature and holding time shown in Table 2, it is further cooled to the temperature shown in Table 2 and held, and then the second soaking is performed. Two types of soaking were used.

  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. Then, this cold-rolled sheet is used in a continuous heat treatment facility, and in common with each example, when each solution treatment temperature is reached (holding time 0 second), it is immediately cooled rapidly to room temperature at 200 ° C / second. Quenching and immediately after this quenching, a pre-aging treatment was carried out at 70 ° C. for 1 hour (after cooling, slow cooling at a cooling rate of 0.6 ° C./hr).

(Test plate requirements)
A test plate (blank) is cut out from each final product plate after the tempering treatment, and the characteristic requirement of each test plate after room temperature aging for 3 months (90 days) after the tempering treatment is 1 μm or more. The area ratio (%) of the Mg—Si compound and the shear surface ratio (%) of the circular hole wall surface in the punching test were measured by the measurement methods described above.

  Similarly, as the characteristics of each test plate after aging at room temperature for 3 months after the tempering treatment, Δr, average value of r value, average grain size (μm), and 45 ° direction with respect to the rolling direction. 0.2% proof stress (MPa), uniform elongation (%), stretch flangeability (λ:%), bendability in the direction of 45 ° with respect to the rolling direction, and the like were measured and evaluated. These results are shown in Table 3. Δr, the average value of r and the average grain size (μm) were determined by the methods described above.

  The 0.2% proof stress (MPa) in the 45 ° direction was 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.

(Test plate characteristics)
As the formability of the test plate, hole expandability (λ) for stretch flangeability evaluation, crack limit height (LDH ₀ ) and limit draw ratio (LDR) for bendability evaluation, and bendability were tested. did. These results are shown in Table 3.

In the hole expansion test, a circular hole having a diameter of 10 mm was first punched in a square test plate having a side of 70 mm, as in the punching test in which the shear surface ratio was obtained. 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 crack limit height (LDH ₀ ) test, the test plate was cut into a test piece with a length of 180 mm and a width of 110 mm, a spherical overhanging punch with a diameter of 101.6 mm was used, and R-303P was used as the lubricant. Stretching was performed at a pressure of 200 kN and a punching speed of 4 mm / S, and the height (mm) at which the test piece cracked was determined. Each sample was tested 3 times and the average value was adopted. The larger the crack limit height, the better the stretch formability. For example, in order to satisfy the stretch formability required for a molded panel for automobiles, it may be 27.0 mm or more.

The limit drawing ratio (LDR) was obtained by punching test pieces of various diameters from the test plate, punching: 50mmφ-shoulder R8mm, die: 53mmφ-shoulder R8mm, and using the lubricant R-303P. A deep drawing test was performed under the conditions of a pressing pressure of 300 to 600 kgf and a test speed of 20 mm / min.
And the shaping | molding limit blank diameter which cannot be deep-drawn was determined, and the limit drawing ratio was computed by the following formula | equation. Limit drawing ratio = forming limit blank diameter / punch diameter. The larger the limit drawing ratio, the better the deep drawability. For example, in order to satisfy the deep drawability required for a molded panel for automobiles, it may be 1.8 or more.

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 are produced within the composition range of the present invention and within the preferred conditions of the present invention such as solution treatment. Therefore, as shown in Table 3, the shear rate of the obtained aluminum alloy plate is 50% or more, and the area ratio of Mg-Si compound of 1 μm or more is 0.15% or less. The proof stress of the aluminum alloy plate is 135 MPa or more.

  Furthermore, in Invention Examples 1 to 9, Δr, which is a preferable requirement, is in the range of 0.2 to 0.6, the average value of r values is 0.5 or more, and 45 ° with respect to the rolling direction of the aluminum alloy sheet. Uniform elongation in the direction is 24% or more.

  As a result, as shown in Table 3, Invention Examples 1 to 9 have a stretch flangeability λ of 60% or more and are excellent in bending workability.

  On the other hand, Comparative Examples 10 to 30 are out of the invention conditions. For this reason, any of stretch flangeability, bending workability, and moldability is remarkably inferior to the inventive examples.

Although Comparative Examples 10 to 20 are within the composition range of the present invention, the production conditions deviate from the preferred range.
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.
Comparative Example 12 is a single soaking process, and 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, the temperature of the second soaking process is too high.
In Comparative Example 15, the time of the second soaking is too short.
In Comparative Example 16, the time for the second soaking process is too long.

In Comparative Example 17, the temperature of rough firing is too low.
In Comparative Example 18, the cooling rate after rough firing is too low.
In Comparative Example 19, the solution treatment temperature is too low.
In Comparative Example 20, the cooling rate after the solution treatment is too small.

In Comparative Examples 21 to 25, although the production conditions are within the preferred range, they are outside the composition range of the present invention.
In Comparative Example 21, the amount of Mg exceeds the upper limit and is too large.
In Comparative Example 22, the amount of Si exceeds the upper limit and is too large.
Comparative Example 23 has too much Fe.
Comparative Example 24 has too much Cr.
Comparative Example 25 has too much Cu.

Although Comparative Examples 26-30 are within the composition range of the present invention, the solution treatment temperature is too low.
In Comparative Examples 26 and 27, the soaking process is performed only once, and the hot rolling start temperature and the hot rolling end temperature are too high.
Comparative Examples 28 and 29 do not have a rough firing process itself.

  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 has excellent stretch flangeability because it has flange parts such as automobiles, ships or vehicles, etc., home appliances, construction, structural members and parts, especially roofs and sunroofs of automobile panels. The application of 6000 series Al alloy materials can be expanded for use in molded panels that require high pressure.

It is explanatory drawing which shows the state of the hole expansion test which calculates | requires a shearing area rate. It is explanatory drawing which shows the state of the punching of a board over time.

Claims (3)

% By mass of Si: 0.1 to 2.5%, Mg: 0.1 to 3.0%, the balance being an aluminum alloy plate made of Al and impurities, and the following wall surface of the circular hole provided by the following punching test of this aluminum alloy plate Formability, characterized in that the shear area ratio is 50% or more, the area ratio of Mg-Si compound of 1μm or more is 0.15% or less, and the proof stress of this aluminum alloy sheet is 135MPa or more Excellent aluminum alloy plate.
In the punching test, a circular hole is punched in a 1 mm thick aluminum alloy sheet using a punch with a diameter of 10.0 mmφ-shoulder R8 mm and a die with a diameter of 10.2 mmφ-shoulder R8 mm.
The shear surface ratio was measured by taking a photo of the wall surface at 45 ° in the rolling direction of the circular hole wall surface with a 100x optical microscope, and parallel to the plate thickness direction of any of the five points on this photograph. Each of the shear surface lengths l is measured, and the respective shear surface ratios calculated by the shear surface ratio = (shear surface length 1 / sheet thickness t) × 100 (%) are averaged. The aluminum alloy plate excellent in formability according to claim 1 , wherein the aluminum alloy plate is for a molded panel having a flange portion . A method for obtaining an aluminum alloy plate according to any one of claims 1 to 2, comprising , by mass%, Si: 0.1-2.5%, Mg: 0.1-3.0%, the balance comprising 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. After cooling at a rate of 100 ° C / s or higher, cold rolling is performed to produce a cold-rolled sheet, and the cold-rolled sheet is subjected to solution treatment and quenching at a temperature of 560 ° C or higher. Wall surface of circular hole provided by the following punching test of the aluminum alloy plate after this treatment The following shear surface ratio is 50% or more, the area ratio of Mg-Si based compounds of 1 μm or more is 0.15% or less, and the proof stress of this aluminum alloy sheet is 135 MPa or more. A method for producing an aluminum alloy sheet having excellent properties.
In the punching test, a circular hole is punched in a 1 mm thick aluminum alloy sheet using a punch with a diameter of 10.0 mmφ-shoulder R8 mm and a die with a diameter of 10.2 mmφ-shoulder R8 mm.
The shear surface ratio was measured by taking a photo of the wall surface at 45 ° in the rolling direction of the circular hole wall surface with a 100x optical microscope, and parallel to the plate thickness direction of any of the five points on this photograph. Each of the shear surface lengths l is measured, and the respective shear surface ratios calculated by the shear surface ratio = (shear surface length 1 / sheet thickness t) × 100 (%) are averaged.

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