JP2008063623A - Method for producing aluminum alloy sheet for forming - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an Al alloy sheet for forming, which is excellent in strength and formability, particularly, deep drawability. <P>SOLUTION: An Al-Mg based or Al-Mg-Si based Al alloy is subjected to rolling, is thereafter subjected to warm difference peripheral speed rolling at 150 to 450°C and at a draft of 15 to <50%, and is subsequently subjected to softening heat treatment, so as to obtain an Al alloy sheet in which the average r value is ≥0.9, and the orientation density in the ä111} face by X-ray diffraction is ≥1. Further, as the rolling, warm rolling at 250 to 450°C is performed. Further, the peripheral speed ratio between the upper and lower rolls in the warm difference peripheral speed rolling is controlled to ≥1:1.2, preferably, to ≥1:1.5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an aluminum alloy plate for forming used for body parts of automobiles, various other vehicle parts, various electronic / electric equipment parts such as chassis and panels of electronic / electric equipment, etc. The present invention relates to a method for producing an aluminum alloy plate for forming made of an Al—Mg alloy or Al—Mg—Si alloy excellent in strength and formability.

  In the past, cold rolled steel sheets were often used for automobile body sheets, but recently there has been a growing demand for lighter cars and improved fuel economy in order to reduce global warming and reduce energy costs. Therefore, instead of the conventional cold-rolled steel plate, there is an increasing tendency to use an aluminum alloy plate having substantially the same strength as the cold-rolled steel plate and a specific gravity of about 1/3 for the body sheet of an automobile. Recently, aluminum alloy plates are often used for molded parts such as panels and chassis of electronic and electric devices other than automobiles.

  By the way, as such an aluminum alloy plate as a material for forming, conventionally, an Al-Mg-Si type AA6016 alloy, an AA6022 alloy, an AA6111 alloy or the like No. 6000 series alloy, an Al-Mg series JIS 5052 alloy, No. 5000 series alloys such as JIS 5182 alloy are widely used. As a method for producing such an aluminum alloy plate for forming, conventionally, it is generally cast by a DC casting method and subjected to a homogenization treatment, followed by hot rolling, further cold rolling, and then soft heating treatment. Or the method of performing solution treatment is applied. However, the aluminum alloy sheet for forming manufactured by the conventional general method is inferior to the cold-rolled steel sheet in terms of forming workability, especially deep drawing, although the strength is almost the same as that of the cold-rolled steel sheet. Is the actual situation.

By the way, in cold-rolled steel sheets, the Rankford value (r value) has been widely used as an index of formability, particularly deep drawability. And the higher the rankford value, especially the average rankford value (average r value), the better the deep drawability. Here, the average r value is an average value of r values (r ₀ , r ₄₅ , r ₉₀ ) measured in directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, and the average r value = ( r ₀ + 2 × r ₄₅ + r ₉₀ ) / 4.

  On the other hand, in general, it is well known that deep drawability is greatly influenced by the texture in a forming material. And in the cold-rolled steel sheet having a body-centered cubic lattice structure, the main orientation plane parallel to the plane of the rolled texture becomes the {111} plane, and the average r value is increased by increasing the orientation density of the {111} plane. It is known that the deep drawability is improved. And in cold-rolled steel sheets, the crystal orientation obtained by cold rolling / recrystallization heat treatment is the {111} plane as described above, so the orientation density of the {111} plane is increased to improve the deep drawability. The method for this is already well established.

  On the other hand, in the case of an aluminum alloy having a face-centered cubic lattice structure, if the heat treatment is performed by a conventional general method, not only the {111} plane effective for improving the formability is formed, but also the formability. The {100} <001> orientation, which is the cube orientation that hinders the above, becomes the main orientation, the average r value cannot be sufficiently increased, and the moldability, particularly deep drawability, can be improved. It was difficult. Therefore, various studies have been made on measures for reducing the cube orientation density in order to improve the formability of the aluminum alloy plate, but the actual situation is that sufficient results have not yet been obtained.

  By the way, it is known that Bs orientation, S orientation, and Cu orientation (collectively β fiber), which are one of the rolling textures of face-centered cubic metals, are orientations that increase the average r value. Although the average r value is high, the ductility is poor and cracking occurs in the press molding process, making it difficult to obtain a molded product. On the other hand, if a softening treatment or a solution treatment is performed after rolling, recrystallized grains having a cube orientation that impairs the formability by recrystallization are generated, and therefore the formability is inferior. Therefore, for example, attempts have been made to suppress recrystallization in softening heat treatment or solution treatment by adjusting the composition of alloy components by adding transition elements or optimizing rolling conditions. In this case, however, the average r value becomes high. However, the in-plane anisotropy of the r value is increased, which is inappropriate for press molding.

  On the other hand, in Non-Patent Document 1, if a cut surface is cut from a hot-rolled material having a β-fiber rolled texture so that it becomes a {111} plane and subjected to softening heat treatment, deep drawability is improved. Has been reported.

  Furthermore, as a proposal for increasing the average r value, by applying different peripheral speed rolling in which the peripheral speeds of the upper and lower rolls are made different in Patent Document 1, and by using warm different peripheral speed rolling in Patent Document 2. An orientation that significantly changes the texture itself by applying shear deformation to the material has been proposed.

JP 2003-305503 A JP-A-2005-139494 H. Inoue, T. Takasugi: Proceedings of IBEC 2003, (2003), 471

  In order to sufficiently improve the formability, particularly deep drawability of the aluminum alloy sheet for forming work represented by Al-Mg alloy and Al-Mg-Si alloy as described above while maintaining high strength. This policy has not been well established.

  Here, what is shown in the Non-Patent Document 1 is a laboratory research report until it gets tired, and when drawing aluminum alloy for forming by an industrial mass production process, if any conditions are applied, deep drawing There is no disclosure up to the point of sufficiently improving the properties.

  In addition, in the method of applying the different speed rolling shown in Patent Documents 1 and 2, although a certain degree of effect is expected to improve the average r value, the manufacturing method on an actual industrial mass production scale The situation is not well established.

  The present invention has been made against the background of the above circumstances, and as a method for producing aluminum alloys for forming used in various vehicle parts including automobile body sheets or various electronic / electric equipment parts, etc. It is an object of the present invention to provide a method in which an aluminum alloy plate having excellent processability, particularly deep drawability, can be obtained industrially by mass production.

  In the present invention, the β fiber orientation is such that the accumulation of β fiber orientation groups contributing to increase the average r value is centered on the {111} pole figure, that is, the {111} plane is parallel to the plate surface. It has been found that rotating the group around the rolling perpendicular direction TD is effective for improving the deep drawability and reducing the in-plane anisotropy of the r value. Specifically, for a rolled material having a β-fiber rolling texture developed by performing hot rolling, warm rolling or cold rolling, a crystal around around TD is applied to the material by applying warm differential circumferential rolling. By inducing rotation, a texture in which the {111} plane is parallel to the plate surface can be obtained as shown in FIG. In order to maintain such a texture suitable for deep drawability even after the softening heat treatment or the solution heat treatment, the rolling conditions and the heat treatment conditions are optimized.

  Specifically, the manufacturing method of the aluminum alloy plate for forming according to the first aspect of the present invention is made by using an aluminum alloy made of Al-Mg or Al-Mg-Si as a raw material, and rolling to a predetermined plate thickness. After developing the β-fiber texture, by performing warm different peripheral speed rolling at a temperature in the range of 150 to 450 ° C. and a reduction rate of 15% or more and less than 50%, the {111} orientation is set as the main orientation. A rolled plate having a TD-rotated β-fiber texture is included, followed by softening heat treatment. The material after the softening heat treatment has a {111} plane orientation density by X-ray diffraction of 1 or more and an average Rankford value of 0. .9 or more aluminum alloy sheets are obtained.

  The invention of claim 2 is the method for producing an aluminum alloy sheet for forming according to claim 1, wherein the rolling process before the warm different peripheral speed rolling is warm at a temperature in the range of 250 to 450 ° C. It is characterized by rolling.

  Furthermore, the invention of claim 3 is the method of manufacturing an aluminum alloy sheet for forming according to claim 1 or claim 2, wherein the ratio of the upper and lower roll rotational peripheral speeds in the warm different peripheral speed rolling is 1: 1.2. It is characterized by the above.

  The invention of claim 4 is the method for producing an aluminum alloy sheet for forming according to claim 3, wherein the upper and lower roll rotation peripheral speed ratio in the warm different peripheral speed rolling is 1: 1.5 or more. It is characterized by this.

  According to the method for producing an aluminum alloy plate for forming according to the present invention, the forming material made of Al-Mg or Al-Mg-Si aluminum alloy has high strength required for an automobile body and the like. In addition, it is possible to obtain a mold having a remarkably superior moldability, particularly deep drawability.

  The aluminum alloy sheet for forming according to the present invention is optimal for various vehicle parts such as an automobile body, and can be used for various types of parts such as chassis and panels of various electric devices and other parts for forming. .

  The aluminum alloy applied in the production method of the present invention may be any Al—Mg alloy (so-called 5000 series alloy) or Al—Mg—Si alloy (so-called 6000 series alloy). The component composition is not limited, but as the Al-Mg alloy, for example, Mg 2.0 to 6.5% (mass%, the same shall apply hereinafter), with the balance being Al and inevitable impurities, or the above Mg In addition to the above, an alloy containing 0.05 to 1.8% of Cu can be preferably used. In addition to the above Mg, or Mg and Cu, Mn 0.03 to 0.8%, Cr 0.03 to 0 It is also possible to use one containing at least one of 0.3%, Zr 0.03-0.3% and V0.03-0.3%. On the other hand, as the Al—Mg—Si based alloy, for example, an alloy containing 0.3 to 2.0% Mg and 0.3 to 2.5% Si, with the balance being Al and inevitable impurities is preferably used. In addition to the above Mg and Si, Cu 0.05 to 1.5%, Mn 0.01 to 0.8%, Cr 0.01 to 0.3%, Zr 0.01 to 0.3%, and V0 What contains 1 type or 2 types or more in 0.01 to 0.2% can be used.

  In the method for producing an aluminum alloy sheet for forming according to the present invention, basically, the rolled texture obtained by rolling using the Al-Mg-based alloy or Al-Mg-Si-based alloy as described above is used. It is possible to improve the press formability of the material by changing to a more preferable texture by warm different circumferential speed rolling and increasing the orientation density of {111} planes after the softening heat treatment.

  Hereinafter, the method for producing the aluminum alloy sheet for forming according to the present invention will be described in detail.

  First, a molten aluminum alloy made of an Al—Mg alloy or an Al—Mg—Si alloy is melted according to a conventional method, and cast by a normal casting method such as a DC casting method (semi-continuous casting method). The resulting ingot is subjected to a homogenization process. This homogenization treatment is effective for homogenizing the ingot structure, improving the formability of the final plate, and stabilizing the recrystallized grains during the solution treatment. The conditions for the homogenization treatment are not particularly limited. However, if the treatment temperature is less than 450 ° C., a sufficient effect cannot be obtained. On the other hand, if the treatment temperature exceeds 570 ° C., eutectic melting may occur, and if the treatment time is less than 0.5 hours. A sufficient effect cannot be obtained, and if it exceeds 24 hours, the effect is saturated and the economic efficiency is only impaired. Therefore, it is desirable to set the condition at 450 to 570 ° C. for 0.5 to 24 hours.

  After the homogenization treatment, a rolling process is performed to obtain a predetermined thickness. By this rolling process, the processed structure β fiber can be developed in the material. However, in order to sufficiently develop the processed structure, it is desirable to perform rolling at a rolling rate of 90% or more in total. The type of rolling process at this stage is not particularly limited, and any one of hot rolling, cold rolling, and warm rolling can be applied, or two or more can be used in combination. That is, in a general method for producing an aluminum plate, it is usual to first perform hot rolling after homogenization treatment, but also in the case of the method of the present invention, hot rolling is applied as the aforementioned rolling process. In this case, cold rolling may be performed after hot rolling in order to further develop a working texture. Moreover, you may perform warm rolling with the temperature of 250 to 450 degreeC with these hot rolling and cold rolling independently.

  In the case of the production method of the present invention, warm rolling is particularly effective as the rolling process performed after the homogenization treatment. In other words, warm rolling has the advantage that sufficient thermal stability can be imparted to the texture. Here, if the warm rolling temperature is less than 250 ° C., the thermal stability of the texture is inferior. On the other hand, if it exceeds 450 ° C., recrystallization occurs during rolling, so that a stable texture can be obtained. It becomes difficult. Therefore, when performing warm rolling, it is desirable to perform at the temperature within the range of 250 degreeC-450 degreeC. Of course, as described above, the hot rolling may be performed before the warm rolling, or the cold rolling may be performed after the warm rolling.

  In order to change the rolling texture obtained by the rolling process into a more preferable texture after performing the rolling process (one or more types of hot, warm, cold) as described above, Different circumferential speed rolling is applied. Here, the different peripheral speed rolling is a method of rolling the aluminum alloy sheet to be rolled by making the peripheral speed of the upper roll different from the peripheral speed of the lower roll. For example, the upper and lower rolls are individually motorized. There are various methods, such as changing the speed with a motor, changing the rotational speed of the upper and lower rolls via gears with different ratios of power from one motor, and changing the peripheral speed by changing the diameter of the upper and lower rolls, In the manufacturing method of this invention, the specific mechanism of the rolling mill for different peripheral speed rolling is arbitrary.

  Here, the different speed rolling must be performed at a temperature in the range of 150 to 450 ° C., that is, so-called warm, and the rolling reduction by the different speed rolling needs to be 15% or more and less than 50%. is there. When the rolling temperature in different circumferential speed rolling is less than 150 ° C, the rotation around the TD axis is not sufficiently applied to the inside of the material. On the other hand, when it exceeds 450 ° C, recrystallization occurs during rolling and the β fiber rolling texture disappears. Resulting in. In addition, when the rolling reduction ratio of the warm different peripheral speed rolling is 15% or less, the texture change is insufficient, and the orientation density of the TD-rotated β fiber including the {111} orientation as the main orientation does not increase after rolling. If it is 50% or more, the β-fiber rolled texture rotated around TD relatively decreases due to the development of the shear texture. Therefore, the rolling temperature and rolling reduction of the warm different peripheral speed rolling were determined as described above. In the warm different peripheral speed rolling, the higher the peripheral speed ratio of the upper and lower rolls, that is, the higher the different peripheral speed ratio, the more efficiently the rotation around the TD axis can be imparted. If the roll peripheral speed ratio is less than 1: 1.2, it is difficult to provide sufficient rotation about the TD axis. Therefore, the roll peripheral speed ratio is desirably 1: 1.2 or more, and particularly 1: 1. A peripheral speed ratio of 5 or more is more desirable. In addition, it is arbitrary which one of the upper and lower rolls is set to be high speed.

  After warm different peripheral speed rolling, softening heat treatment is performed to adjust the strength and ductility suitable for press forming. As the softening heat treatment, in the case of an Al—Mg alloy, it is common to perform box annealing at 250 to 400 ° C. for 0.5 to 10 hours, or continuous annealing at 350 to 580 ° C. for less than 2 minutes. is there. When softening heat treatment is applied to an Al-Mg alloy by applying box annealing, softening is insufficient at temperatures lower than 250 ° C, and ductility suitable for press forming cannot be obtained. The coarsening of crystal grains occurs and the surface oxide film becomes thick, which adversely affects the appearance after pressing. When softening heat treatment is performed on an Al—Mg-based alloy by continuous annealing, the softening is insufficient at 350 ° C. and ductility suitable for press molding cannot be obtained. The coarsening occurs and the surface oxide film becomes thick, which adversely affects the appearance after pressing.

  Further, the softening heat treatment for the Al—Mg—Si based alloy is generally performed by continuous annealing at 450 to 580 ° C. for less than 2 minutes as a solution treatment. In this case, if the temperature is lower than 450 ° C., the strength of the press-formed product is low due to insufficient solution, while if it exceeds 580 ° C., the recrystallized grains become coarse and the surface oxide film becomes thick, which adversely affects the appearance after pressing. Effect. In some cases, before the softening heat treatment at 450 to 580 ° C., the texture developed by the warm different speed rolling is stabilized by recovery / recrystallization, so that a thermally stable subgrain structure or Even if pre-annealing is performed for 0.5 to 50 hours at a low temperature of 230 to 300 ° C. for the purpose of pre-forming a fine recrystallized grain structure and maintaining it as a suitable recrystallized texture after the softening heat treatment. good.

  By performing the softening heat treatment in this way, a material having an average r value of 0.9 or more and an orientation density of {111} plane by X-ray diffraction of 1 or more can be obtained. Here, when the average r value is less than 0.9, the press formability of the material, particularly the deep drawability, is poor. Regarding the orientation density, the {111} plane is an advantageous surface for deep drawability as described above, and if the orientation density of the {111} plane is less than 1, good press formability cannot be obtained.

Here, the orientation density by X-ray diffraction is defined as follows. That is, a three-dimensional crystal orientation distribution function (ODF) is calculated from the positive point diagrams of {111}, {200}, and {220} planes, and φ ₂ = 45 ° cross section φ = 55 ° and φ ₁ = 0 in the Bunge method. The maximum azimuth density in the range from 0 to 90 ° is defined as the {111} plane orientation density.

  Each alloy having the component composition shown in alloy codes A to F in Table 1 was melted in accordance with a conventional method, and cast into an ingot having a thickness of 80 mm, a width of 200 mm, and a length of 1500 mm by laboratory DC casting.

  The obtained ingot was chamfered to a thickness of 75 mm, homogenized at 500 ° C. for 2 hours, and then subjected to only hot rolling (process 1) according to the processes shown in production process codes 1 to 11 in Table 2. Combination of hot rolling and cold rolling (process 2, 7 to 10), combination of hot rolling and warm rolling (process 3), combination of hot rolling and warm rolling, cold rolling (process 4), warm Rolling to a predetermined intermediate sheet thickness was performed by a combination of cold rolling and cold rolling (process 5), and only warm rolling (process 6), and then subjected to warm differential speed rolling to a sheet thickness of 1 mm. In the intermediate plate thickness before warm different peripheral speed rolling, the β fiber texture was strongly developed in all the plates. In Process 11, as a conventional method, only cold rolling was performed after hot rolling. Here, as the warm different peripheral speed rolling, using a warm different peripheral speed rolling machine in which the upper and lower rolls are driven by independent motors, the low speed roll speed is constant at 10 m / min, and the high speed roll speed is set in advance. It was changed according to the set different peripheral speed ratio.

  Here, in Table 2, production process numbers 1 to 6 are all subjected to appropriate warm differential rolling after rolling by one or a combination of hot rolling, warm rolling and cold rolling. The manufacturing process numbers 7 to 10 are comparative examples in which all the manufacturing process numbers 7 to 10 were subjected to the warm different peripheral speed rolling out of the range of the warm different peripheral speed rolling conditions defined in the present invention. This is a conventional example in which only hot rolling and cold rolling are performed without performing warm different peripheral speed rolling. In particular, those subjected to the warm different peripheral speed rolling in production process numbers 7, 9, and 11 did not have a TD-rotated β fiber texture including {111} orientation as the main orientation in any alloy of any composition. .

  After that, the final heat treatment as the softening heat treatment is performed at 530 ° C. for 30 seconds using a salt bath corresponding to the continuous annealing method for Al—Mg alloys (alloy codes A, B, C), or 350 ° C., 2 h. For the Al-Mg-Si based alloys (alloy codes D, E, F), after holding at 530 ° C for 30 seconds using a salt bath corresponding to the continuous annealing method for solution treatment. The test was performed under the condition of forced air cooling.

With respect to the plate after the final heat treatment obtained as described above, tensile test pieces were taken in the directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, and mechanical properties (TS, YS and EL), The r value was measured, and the average r value was determined from the above formula. In addition, the Erichsen value was measured as an index of stretch formability, and LDR (limit drawing ratio) was measured as an index of deep drawability. On the other hand, a pole figure of the rolled plate with respect to pure aluminum powder was measured by X-ray diffraction, and a three-dimensional crystal orientation distribution function (ODF) analysis was performed. The maximum orientation density at F = 55 ° and Φ ₁ = 0 ° to 90 ° of the φ ₂ = 45 ° section in the Bunge method was taken as the orientation density of the {111} plane. These results are shown in Tables 3-5.

  As apparent from Tables 3 to 5, in the present invention example in which the warm different peripheral speed rolling was performed under the conditions satisfying the temperature range, reduction ratio, and different peripheral speed ratio specified in the present invention, all {111} faces Has a recrystallization texture that is advantageous for formability, particularly deep drawability, and has an average r value of 0.9 or more, and is evaluated by Erichsen value and LDR. It is clear that the moldability is excellent.

  On the other hand, in the case of each comparative example and the conventional example in which the warm different peripheral speed rolling was not performed under the conditions satisfying the temperature range, rolling rate, and different peripheral speed ratio specified in the present invention, the orientation of the {111} plane Density is less than 1, recrystallized texture is formed which is disadvantageous for deep drawability, and the average r value is less than 0.9, and the improvement of formability evaluated by Erichsen value and LDR is seen. There wasn't.

It is a pole figure showing an example of a texture of material after warm different peripheral speed rolling by the method of the present invention, and is a {111} pole figure of a β fiber texture rotated about 20 ° around the TD axis.

Claims (4)

  An aluminum alloy composed of Al-Mg or Al-Mg-Si is used as a raw material, rolled to a predetermined plate thickness to develop a β-fiber texture, and then at a temperature in the range of 150 to 450 ° C and 15 % Rolling to a rolling plate having a TD-rotated β-fiber texture containing the {111} orientation as the main orientation, and then subjected to a softening heat treatment. An aluminum alloy plate for forming, characterized by obtaining an aluminum alloy plate having an orientation density of {111} plane by X-ray diffraction of 1 or more and an average Rankford value of 0.9 or more by X-ray diffraction Production method. In the manufacturing method of the aluminum alloy plate for shaping | molding of Claim 1;
A method for producing an aluminum alloy sheet for forming, characterized by performing warm rolling at a temperature within a range of 250 to 450 ° C as the rolling process before warm different peripheral speed rolling. In the manufacturing method of the aluminum alloy plate for shaping | molding processing of Claim 1 or Claim 2;
The manufacturing method of the aluminum alloy plate for shaping | molding characterized by making upper and lower roll rotational peripheral speed ratio in said warm different peripheral speed rolling 1: 1.2 or more. In the manufacturing method of the aluminum alloy plate for shaping | molding of Claim 3;
The manufacturing method of the aluminum alloy plate for shaping | molding characterized by making upper and lower roll rotation peripheral speed ratio in the said warm different peripheral speed rolling 1: 1.5 or more.

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