JP2007169740A - Aluminum alloy sheet having excellent formability and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a 6000 series aluminum alloy sheet whose press formability and bending workability are improved even if the sheet thickness is improved or impurity elements are increased, and further, even in the case annealing is not performed after hot rolling and also before cold rolling, and to provide a production method therefor. <P>SOLUTION: Regarding the production method where scrap is used as a melting raw material, and cold rolling is performed without previously subjecting a hot rolled sheet to annealing, so as to produce a cold rolled sheet, in the 6000 series aluminum alloy sheet in which the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb and W is high in addition to the main element, the dispersed grains including the above other elements are controlled, and the average piece density and size distribution of the dispersed grains measured using EPMA (electron probe micro analyzer) under specified conditions are controlled as specified ranges, so as to improve the press formability and bending workability of the sheet. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an aluminum alloy plate having high strength and excellent formability and a method for producing the same, and without deteriorating strength / proof strength, strength / proof strength after baking (hereinafter also referred to as AB strength), bending workability, An aluminum alloy plate with excellent surface properties after molding (riding marks or surface irregularities that occur during molding called roping), and this aluminum alloy plate with raw materials with an increased scrap reuse rate (excellent recyclability) ), Which relates to a production method capable of reliably obtaining various characteristics.
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.

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 1). reference). In order to obtain such a structure, in Patent Document 1, the first soaking condition is that after soaking at 450 ° C. or more in the first time, cooling to 350 ° C. at a cooling rate of 100 ° C./h or more is performed in two stages, or 2 The soaking is performed once.

  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 to define the texture of a plate by the difference in crystal grain orientation (see Patent Documents 2 and 5). In addition, it has been proposed to specify the intensity ratio, density, and the like of the Cube orientation and the anisotropy of the r value (see Patent Documents 3, 4, 6, 7, 8, and 9).

  Among these, Patent Document 2 proposes that the ratio of crystal grain boundaries whose adjacent crystal orientation difference is 15 ° or less is 20% or more. For this reason, in Patent Document 2, the first soaking condition is soaking at 480 ° C or higher in the first time, then cooling to 300 ° C at a cooling rate of 150 ° C / h or more, and performing soaking in two stages or twice. ing. In Patent Documents 3 and 4, the soaking condition is that after the first soaking of 450 ° C or higher, cooling to 350 ° C is performed at a cooling rate of 100 ° C / h or more, and soaking in two stages or two times. Is doing. And also in the said patent document 5, after homogenizing the Al alloy ingot at the temperature of 500 degreeC or more and less than melting | fusing point, it cools from the temperature of 500 degreeC or more to the temperature range of 350-450 degreeC, and starts hot rolling (2 step soaking) or once cooled to a temperature from 500 ° C or higher to room temperature, reheated to a temperature range of 350-450 ° C and start hot rolling (2 soaking), stepwise homogeneous A processing method has been proposed.

  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 10).

  On the other hand, in order to further improve press formability, various methods have been proposed from the viewpoint of improving the ridging mark. For example, in an Al-Mg-Si-based aluminum alloy plate with a specific composition, the average particle size of the compound is regulated, the amount of Mn element present as the Mn compound, the amount of Mg element present as the Mg compound, It has been proposed to improve the ridging mark characteristics (Patent Document 11). In this patent document 11 as well, the temperature is maintained in a temperature range of 450 to 500 ° C. in the first stage and the temperature range of 500 to 550 ° C. is maintained in the second stage under the two-stage temperature rise condition (Example). A uniform homogenization method is used.

  In relation to this, the ridging mark problem has conventionally been solved by cooling the 6000 series Al alloy ingot after the homogenization heat treatment at a temperature of 500 ° C. or higher and at a relatively low temperature of 350 to 450 ° C. It is known to prevent the formation of coarse precipitates and prevent ridging marks by starting hot rolling (two-stage soaking) (see, for example, Patent Documents 12 and 13).

  Further, focusing on the crystal orientation component of the {110} plane of the 6000 series Al alloy plate, various methods for improving the ridging mark from the viewpoint of texture control and the like have been proposed. For example, it has been proposed to refine the degree of Cube orientation accumulation in the surface layer portion of the plate to 2 to 5 and the crystal grain size of the plate surface portion to 45 μm or less (see Patent Document 14). Further, it has been proposed that Goss orientation distribution density: 3 or less, PP orientation distribution density: 3 or less, and Brass orientation distribution density: 3 or less in a plate (see Patent Document 15).

It has also been proposed to improve the ridging mark by setting the ear rate in the 6000 series Al alloy plate to 4% or more and the crystal grain size to 45 μm or less (see Patent Document 16). Also, in Patent Document 17, etc., in order to improve formability, a two-stage soaking is performed in which a second soaking of 450 ° C. to 480 ° C. is performed on the 6000 series Al alloy ingot after the first homogenizing heat treatment at 560 ° C. or higher. Is done on condition.
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) JP 2005-240113 JP (Claims) Japanese Patent No. 2823797 (Claims) Japanese Patent No. 3590685 (Claims) JP-A-11-189836 (Claims) Japanese Patent Laid-Open No. 11-236639 (Claims) JP 2000-96175 A (Claims) JP 2003-518192 A (Claims)

  In a series of prior arts (Patent Documents 1 to 10) in which the texture described above has anisotropy, the Cube orientations of 6000 series Al alloy plates are accumulated to form a small-angle grain boundary compared to a large-angle 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 a starting point of cracking, and the bending workability and hem workability of the plate can be improved.

  Recently, however, the above-mentioned outer panel and inner panel have been thinned to a thickness of about 1 mm in order to reduce the weight of the pedestrian and occupant. On the other hand, the thickness tends to be increased to a thickness of 1.1 to 1.2 mm. Thus, when the plate thickness is increased, the bending workability and hem workability of the plate are lowered.

  In recent years, the amount of scrap material used has increased as a raw material for melting 6000 series aluminum alloys in place of expensive aluminum bullion. For this reason, the contents of Fe, Mn, Cr, Zr, V, Ti, Zn, Cu and the like, which are conventionally included as impurities, are increasing. Furthermore, in addition to these impurity elements, the contents of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, W, etc., which have been rarely included as impurities in the past, tend to increase. is there. Although depending on the mixing ratio of the scrap material, the total content of Bi to W and the like is inevitably mixed up to 0.015% or more and about 0.1% with respect to the conventional 0.01% or less.

  The elements such as Fe to Cu and Bi to W tend to form dispersed particles in a 6000 series aluminum alloy structure. For this reason, the increase in content of these Fe-Cu and Bi-W2 means that the dispersion | distribution particle | grains of these elements increase in a 6000 series aluminum alloy structure | tissue. These increased dispersed particles greatly affect the press formability and bending workability of the plate.

  Therefore, in order to improve the press formability and bending workability of 6000 series aluminum alloy plates, as the plate thickness increases and the number of impurity elements increases, the dispersed particles of Si and Mg as the main elements that have been considered in the past In addition, the dispersed particles of these impurity elements must be considered.

  Furthermore, in the production line for 6000 series aluminum alloy sheets, in order to improve production efficiency and reduce production costs, it is important to perform a cold rolling process without pre-annealing the hot-rolled sheet. Yes. Conventionally, strength and surface properties can be satisfied in a step (batch type or continuous type) in which intermediate annealing is performed after hot rolling or during cold rolling. However, this process is expensive in terms of both the amount of intermediate annealing, heat treatment time and energy consumption. However, when annealing after this hot rolling and before cold rolling is not performed, the increase of the dispersed particles has a greater adverse effect on the press formability and bending workability of the plate.

  The present invention has been made paying attention to such circumstances, and its purpose is to perform annealing after hot rolling and before cold rolling even with an increase in sheet thickness or an increase in impurity elements. Even if it is not rubbed, the present invention intends to provide a 6000 series aluminum alloy plate with improved press formability and bending workability and a method for producing the same.

The gist of the aluminum alloy plate with excellent formability to achieve this purpose is mass%, Si: 0.5-1.5%, Mg: 0.2-2.0%, 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, Cu: 1.0% or less, and Bi, Sn, Ga, Co, Ni, An aluminum alloy plate in which the total content of Ca, Mo, Be, Pb, and W is 0.015% or more and 0.5% or less, and the balance is made of Al and impurities. The average number density of all dispersed particles with a size of 0.5 μm or more is 3000-20000 particles / mm ² , the size X μm of these measured dispersed particles is on the horizontal axis, and the number density Y particles / mm ² is on the vertical axis. In the dispersed particle size distribution formula represented by Y = Aexp (-BX), A / B is in the range of 1000 to 40000, and B is in the range of 0.5 to Be in range 2 To.
However, each measurement of the above dispersed particles was carried out by measuring an area of 0.2 mm ^{2 in} the rolling direction at a depth of 1/4 t from the surface of the aluminum alloy plate having a thickness t at 10 arbitrary measurement points with an electron beam probe microanalyzer. This is performed by scanning, and these are averaged.

  Further, the gist of the 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, wherein the mass% is Si: 0.5 to 1.5%, including Mg: 0.2-2.0%, 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, Cu: 1.0% or less, and further the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, W is 0.015% or more and 0.5% or less, and the balance An aluminum alloy ingot composed of Al and impurities is subjected to homogenization heat treatment at a temperature of 500 ° C or higher and lower than the melting point, and the average cooling rate from 500 ° C to 350 ° C is set to 40 ° C / h or higher and lower than 100 ° C / h. After cooling to a temperature below 300 ° C, re-heating to a temperature of 300-450 ° C and then starting hot rolling, producing a hot rolled sheet with an end temperature of this hot rolling of 170-300 ° C, This hot rolled sheet, without straining facilities previously annealed, and subjected to cold rolling to prepare a cold-rolled sheet is to solution treatment and quenching treatment to the cold-rolled sheet at 560 ° C. or higher.

  In the present invention, even with the increase in the plate thickness and impurity elements, and even when not subjected to annealing after hot rolling and before cold rolling, press formability and bending workability of 6000 series aluminum alloy plates In order to improve this, we focused on using these impurity elements, which are inevitably contained in the structure, as well as dispersed particles of the main elements Si and Mg .

  Specifically, the average number density and size distribution of all dispersed particles of a specific size or more, including the dispersed particles of Si and Mg as the main elements and the dispersed particles of these impurity elements are within a certain range. It is prescribed to enter. In other words, if the average number density and size distribution of all dispersed particles of a specific size or larger are within the specified range as described in the above summary, the increase in plate thickness, the number of impurity elements, and the increase in dispersed particles Even with this, it becomes possible to improve the press formability and bending workability of the 6000 series aluminum alloy plate. In addition, the presence of the identified dispersed particles contributes to the improvement of surface properties (residual mark suppression) during press forming of a 6000 series aluminum alloy plate even if the plate is manufactured in the process in which the intermediate annealing is omitted.

  In the present invention, the measurement of the average number density and size distribution of all the dispersed particles of a specific size or more, including the dispersed particles of Si and Mg as the main elements and the dispersed particles of these impurity elements, This is possible only by using an electron probe microanalyzer (hereinafter also referred to as EPMA for short). According to this EPMA, it becomes possible to analyze the area of dispersed particles having a certain size on a plate.

On the other hand, the conventional analysis of dispersed particles is carried out on an ultra-micro area of μm ² unit even if the number of observation points on the plate is increased using TEM or SEM. For this reason, the correlation between such ultra-micro analysis results and the press formability and bending workability, which are macro properties of the 6000 series aluminum alloy sheet, is always a problem or a question.

On the other hand, according to the EPMA of the present invention, an area of 0.2 mm ^{2 in} the rolling direction is analyzed relatively macroscopically even at only one measurement point on the plate. Therefore, the present invention can be said to be a so-called macro dispersed particle analysis. As the number of measurement points is increased, the present invention better corresponds to the press formability and bending workability which are macro properties of the 6000 series aluminum alloy plate. For this reason, the press formability and bending workability of the 6000 series aluminum alloy plate can be improved even when the plate thickness increases and the impurity elements increase, and even if annealing is not performed after hot rolling and before cold rolling. It becomes possible to improve.

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 a requirement, the composition of the Al alloy plate first includes Si and Mg main elements including Si: 0.5 to 1.5% and Mg: 0.2 to 2.0%. In addition, description of% which is element content all means the mass%.

  In the composition of the present invention, among the elements other than Si and Mg, the following elements are elements that are easily mixed from melting raw materials such as scrap, and are described in AA to JIS standards. Each allowable amount. Specifically, these elements are a group of Fe, Mn, Cr, Zr, V, Ti, Zn, and Cu. When the content of each of these elements exceeds the respective upper limit prescribed amount, even if the average number density and size distribution of the dispersed particles in the present invention are prescribed, the press formability and bending workability of the 6000 series aluminum alloy plate are improved. Reduce. Therefore, these elements have upper limits of 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% Hereinafter, Cu: 1.0% or less.

  In the composition of the present invention, among other elements other than Si and Mg, the element amounts of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, and W, which are not described in the AA to JIS standards Also stipulate. In the present invention, as described above, the scrap material is allowed to be used instead of or in addition to the aluminum metal as the melting material of the aluminum alloy. For this reason, the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, W and the like increases from the conventional level, and is inevitably mixed by 0.015% or more.

  However, in the present invention, as described above, these impurity elements are used in reverse. That is, the presence of these impurity elements delays the precipitation behavior of Al-Fe-Si, Al-Mn-Fe-Si, Mg-Si (Mg2Si), Si, etc. present in the alloy of the present invention, The precipitate is not coarsened during soaking. In order to exert this effect, the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, W and the like needs to be 0.015% or more. On the other hand, when the total content of these elements exceeds 0.5%, even if the average number density and size distribution of the dispersed particles in the present invention are defined, coarse precipitates are formed (the formation of coarse precipitates can be suppressed). 1) This reduces the press formability and bending workability of the 6000 series aluminum alloy sheet. Therefore, in the present invention, the upper limit of the total content of these elements is 0.5%.

  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 preferred range and significance of Si and Mg, which are the main alloy elements, in the 6000 series Al alloy of the present invention will be described below.

Si: 0.5-1.5%
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 formability, draw formability, 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 content is less than 0.5%, the above-mentioned age-hardening ability, and further, various properties such as stretch flangeability and bendability, or press formability, which are required for automobile panel use, etc. cannot be provided. On the other hand, if Si is contained in excess of 1.5%, 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 0.5 to 1.5%. In addition, in an outer panel of an automobile or the like, hem workability is particularly important. Therefore, in order to further improve bendability such as flat hem workability, the Si content is preferably set in the range of 0.6 to 1.3%.

Mg: 0.2-2.0%
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 formability, draw formability, 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 2.0%, on the other hand, coarse compounds increase to become the starting point of fracture, and stretch flangeability and bendability are lowered. Therefore, the Mg content is in the range of 0.2 to 2.0%. 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 1.3%, correspondingly, The Mg content is also preferably in the range of 0.4 to 1.0.

(Al alloy plate structure)
Next, the requirements for the structure of the 6000 series Al alloy sheet of the present invention will be described.
(Dispersed particles)
In the present invention, the total dispersed particles mean all dispersed particles having a size of 0.5 μm or more counted by EPMA regardless of the type of the dispersed particles.

  The dispersion particle size of 0.5 μm or more is the detection limit by EPMA that it is difficult to detect smaller dispersed particles, and smaller dispersed particles have little effect on the plate press formability and bending workability. With recognition.

  Incidentally, these dispersed particles are formed by the dispersed particles composed of Si and Mg as the main elements contained in the 6000 series Al alloy, and the Fe to Cu and Bi to W which are increasing in content as impurities. Dispersed particles.

(Dispersed particle number density)
In the present invention, in order to improve press formability and bending workability even with an increase in plate thickness and impurity elements, first of all dispersed particles having a size of 0.5 μm or more measured using EPMA. The average number density is 3000-20000 pieces / mm ² . If the average number density of the dispersed particles is less than 3000 particles / mm ² , the strength, BH (bake hard) property, and ridging mark generation suppressing effect in press molding are reduced. On the other hand, when the average number density of the dispersed particles exceeds 20000 particles / mm ² , press formability and bendability deteriorate.

(Dispersed particle size distribution)
The concept of the dispersed particle size distribution regulation in the present invention will be described with reference to FIG. Figure 1 shows a conceptual diagram of the size distribution of all dispersed particles with a size of 0.5 μm or more, measured using an electron probe microanalyzer (hereinafter also referred to as EPMA). In the coordinates of FIG. 1, the horizontal axis represents the measured size X μm of the dispersed particles, and the vertical axis represents the number density Y 1 / mm ² .

  In Fig. 1, the curve shown by the solid line that rises to the left is the dispersed particle size distribution formula expressed by Y = Aexp (-BX) for the dispersed particles with a size of X 10 μm or less. The right end of the curve shows the region where X exceeds 10μm). When obtaining this distribution formula, the size of the dispersed particles is set to 10 μm or less. When there are many coarse dispersed particles larger than this, the size distribution of the dispersed particles having a size of 10 μm or less in the present invention is used. This is because the upper limit of the formula definition is not necessarily satisfied, and the properties of the press formability and the bending workability are deteriorated regardless of the size distribution formula definition of the dispersed particles.

Therefore, in the present invention, regarding the number density of coarse dispersed particles of 10 μm or more, the average number density of dispersed particles of 10 μm or more is preferably 100 particles / mm ² or less. That is, the average number density of dispersed particles having a size of 10 μm or more among all the dispersed particles having a size of 0.5 μm or more is preferably 100 particles / mm ² or less. Incidentally, in FIG. 1, the average number density of dispersed particles of 10 μm or more is about 60 / mm ² .

  In the dispersion particle size distribution equation represented by Y = Aexp (−BX), A / B is the width in the vertical direction in the coordinates of the dispersion particles having a size of X 1 of 10 μm or less. As shown in the direction of the upward arrow in FIG. 1, the larger the A / B, the higher the curve indicated by the solid line goes up, and the number density of dispersed particles increases. For this reason, while bending property falls, generation | occurrence | production of the ridging mark in press molding is suppressed.

  On the other hand, the smaller the A / B, the lower the curve indicated by the solid line, and the smaller the number density of the dispersed particles. For this reason, while the bendability is improved, the generation of ridging marks in press forming is not suppressed in the plate manufacturing process in which the intermediate annealing as a precondition in the present invention is omitted. In the manufacturing process of a plate having a normal intermediate annealing, ridging marks at the time of press forming are suppressed even if the number density of dispersed particles is reduced.

  Therefore, in order to satisfy both the contradictory improvement in bendability and the suppression of ridging marks, this A / B is set within a certain range. This is a range of A / B defined by the present invention in the range of 1000 to 40000. In FIG. 1, the fine dotted line indicated by [I] is the lower limit line where A / B is 1000. Also, the rough dotted line indicated by [A] is the upper limit line where the above A / B is 40000.

   When the fine dotted line indicated by [I], that is, the above A / B becomes smaller than the lower limit of 1000, the possibility of ridging marks in press forming increases. On the other hand, when the rough dotted line indicated by [A], that is, the above A / B increases beyond the upper limit line of 40,000, the possibility that the bendability deteriorates increases.

  Furthermore, in the dispersed particle size distribution equation represented by Y = Aexp (-BX), B represents the slope of this distribution equation. The straight line that rises to the left and overlaps the curve of the dispersion particle size distribution equation shown in Fig. 1 indicates the slope B of the distribution equation. As shown by the slanting arrow that rises to the right in Fig. 1, the smaller the slope B, the lower the left shoulder of the curve shown by the solid line. The number density of particles increases. For this reason, bendability is improved, but generation of ridging marks in press molding is not suppressed.

  On the other hand, as B 1 is larger, the left shoulder of the curve indicated by the solid line is increased, the number density of dispersed particles having a small size is increased, and the number density of coarse dispersed particles is decreased. For this reason, while bending property falls, generation | occurrence | production of the ridging mark in press molding is suppressed.

  For this reason, in order to satisfy both the contradictory improvement in bendability and the suppression of ridging marks, B is set within a certain range. This is the range of B defined in the present invention in the range of 0.5-2. When B is smaller than 0.5, the lower limit of the line a indicated by the fine dotted line is exceeded, and the possibility of ridging marks in press forming increases. On the other hand, when B is larger than 2, it exceeds the line b shown by a rough dotted line, and the possibility that the bendability is lowered increases.

(Measurement of dispersed particles)
The average number density of all dispersed particles having a size of 0.5 μm or more and the size distribution (formula) of dispersed particles having a size of X 10 μm or less are measured by EPMA. However, in order to give reproducibility to the measurement, each measurement condition of the dispersed particles is as follows.The surface of the aluminum alloy plate having a thickness t is an area of 0.2 mm ^{2 in} the rolling direction at a depth of 1/4 t. It is assumed that 10 measurement points are scanned with an electron beam probe microanalyzer, and these are averaged.

  As described above, according to the macroscopic dispersed particle analysis and regulation of the present invention, even with the increase of the plate thickness and the impurity element, and even when not subjected to annealing before cold rolling after hot rolling, 6000 It becomes possible to improve the press formability and bending workability of the aluminum alloy plate.

(Mg-Si compound)
In the present invention, the sum of the number of Mg-Si based compound particles and single Si particles among the total dispersed particles having a size of 0.5 μm or more in the structure of a 6000 series Al alloy plate is 1500 to 5000 / mm ² . Preferably there is.

Mg-Si compound particles and simple Si particles are the main dispersed particles that greatly affect the properties of the plate even if the number of dispersed particles formed by other Fe-Cu and Bi-W increases. There is no change. For this reason, in order to improve press formability and bending workability even with an increase in plate thickness and impurity elements, the sum of the Mg-Si compound particles and single Si particles is 1500 to 5000 / it is preferable that the mm ^2.

If the sum of the Mg—Si compound particles and the simple Si particles is less than 1500 particles / mm ² , the strength, BH (bake hard) property, and the effect of suppressing ridging mark generation in press molding are likely to decrease. On the other hand, when the sum of the Mg-Si compound particles and the single Si particles exceeds 5000 particles / mm ² , there is a high possibility that the press formability and bendability are lowered.

The measurement of the number of the Mg—Si compound particles and the simple Si particles is the same as the measurement conditions by EPMA for the size distribution of the dispersed particles. The number of dispersed particles and the constituent elements of each particle were measured using EPMA (JXA-8000 series, manufactured by JEOL Ltd., measurement conditions were acceleration voltage 20 kV). Note that the measurement measures about 0.1 to 0.2 mm ² degree measurement target is measured 0.5μm or more particles, in Table 1 described the converted value per 1 mm ^2. Moreover, the dispersed particles classified Mg-Si type and Si type among all particles according to the constituent elements.

  The dispersed particles existing in the alloy of the present invention are classified into almost four types of Al-Fe-Si, Al-Fe-Mn-Si, Mg-Si, and Si. A method for determining and analyzing Mg-Si compound particles and simple Si particles will be described.

  First, the constituent element analysis contained in each particle is analyzed by the EPMA apparatus. The four elements of Fe, Mn, Mg, and Si are analyzed (at%). Since the quantitative value obtained here causes a problem in analysis accuracy depending on the size and beam diameter of each particle, in this patent, Mg-Si and Si particles were discriminated based on the ratio of the main contained elements. A specific analysis method is shown below.

  The total amount (TOTAL amount) of Fe (at%) + Mn (at%) + Mg (at%) + Si (at%) is obtained by the above EPMA apparatus. Next, Fe, Mn, Mg, Si contained in the four contained elements by Fe / TOTAL, Mn / TOTAL, Mg / TOTAL, Si / TOTAL (relative to the total amount of the four contained elements) per particle. Each content ratio of is calculated | required.

  Of these, those with Fe / TOTAL of 0.05 or less and Mn / TOTAL of 0.3 or less, those with Fe / TOTAL exceeding 0.05, or those with Mg / TOTAL of 0.3 or more belong to the Mg-Si series. Or it confirmed that it belonged to Si particle | grains, and evaluated it as the sum of the said Mg-Si type compound particle | grains and single-piece | unit Si particle | grains with "the sum of the number of +" by the said criterion.

(Average crystal grain size)
Regarding the crystal grain size, it is preferable to refine the average crystal grain size of the Al alloy plate to 60 μm or less. By making the crystal grain size fine or small within this range, the stretch formability, drawability, stretch flangeability and bendability, or press formability can be ensured or improved. When the crystal grain size becomes larger than 60 μm, it is highly possible that stretch flangeability and bendability or press formability will be significantly reduced. Moreover, when it is a coarse grain, problems, such as rough skin, arise and are unpreferable.

  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.
In the present invention, since it is assumed that intermediate annealing is omitted, an aluminum alloy having the above-described composition is subjected to normal DC casting → homogenization heat treatment → hot rolling → (intermediate annealing omitted) → cold rolling → final annealing. It is manufactured through.

  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 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)
In the present invention, the homogenization heat treatment is performed under a soaking condition that is preferable for suppressing ridging marks and omitting intermediate annealing.
(First soaking condition)
In the first soaking condition, the Al alloy ingot having the above composition 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.

  Cooling is performed after the first homogenization heat treatment. At this time, the average cooling rate in the temperature range between 500 ° C and 350 ° C is 40 ° C / h or more and less than 100 ° C / h as the cooling rate in order to make the dispersed particles fine and suppress the formation of coarse precipitates. Then, cool down.

  Usually, the cooling rate in the soaking process at the actual slab size is large (about 400 to 600mm thickness, width 1000 to 2500mm, length 5 to 10m) because of the large slab size. Is less than 20 ° C / h, and the cooling rate is about 30-40 ° C / h even if the slab is opened outside the furnace. If cooling is performed under such normal batch soaking furnace conditions, the precipitates become coarse in this cooling process, and in the second soaking process, the strength is reduced, the post-baking proof stress is lowered, the bending cracks, etc. Occurs.

  For this reason, in Patent Documents 1 to 3 of the above-mentioned 2-time soaking, the cooling rate after the first soaking in the 2-time soaking step is specified to be larger, 100 ° C / h or more, 150 ° C / h or more, etc. Has been. However, a high cooling rate of 100 ° C / h or more from holding at a high temperature may be feasible with a small slab, but forced cooling is necessary to realize the entire large slab and the center of the slab, It becomes an obstacle to productivity. In addition, when forced cooling is performed, new problems such as deformation and warpage due to thermal contraction of the slab occur.

  Therefore, the upper limit cooling rate range specified in the present invention does not cause the above-mentioned productivity and slab shape problems associated with forced cooling, and the dispersed particles can be controlled within the specified range, 40 ° C./h or more, 100 ° C. The cooling rate is less than / h. More preferably, it is 45 ° C./h or more. In this specified range, the faster the cooling rate, the finer the dispersed particles, which is advantageous for improving strength, post-baking proof stress, bendability and the like. In the present invention, as described above, the amount of impurity elements is also defined as a point for suppressing the formation of coarse precipitates, and the formation of coarse precipitates is suppressed even at a cooling rate of less than 100 ° C / h. it can.

  After that, homogenization heat treatment (twice soaking) is performed by cooling to a temperature of 200 ° C or lower and reheating to a temperature of less than 300 to 450 ° C. After the homogenization heat treatment, heating to a temperature of 300 to 450 ° C is performed. Start hot rolling. Also in this two-time soaking, the structure before hot rolling is optimized by maintaining the temperature ranges in the first and second homogenization heat treatments. When this holding temperature is low, the formation of a precipitated phase at the grain boundary is promoted, and the strength, 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 homogenization heat treatment is 2 to 15 hours as a guide. If the holding time is shorter than 2 hours, the ingot crystallized product remains undissolved and element segregation also remains at the grain boundary, thereby degrading the formability. On the other hand, if the holding time is longer than 15 hours, on the contrary, the precipitation phase of Al-Fe-Mn-based precipitates and impurity elements becomes coarse, and on the contrary, the formability, stretch flangeability and bendability may be deteriorated. .

(Hot rolling)
After these homogenization heat treatments, hot rolling is started at a temperature of 300 to less than 450 ° C. When the hot rolling start temperature is 450 ° C. or higher, recrystallization occurs and coarse recrystallized grains are generated during hot rolling, and stretch flangeability and bendability deteriorate. Further, when the hot rolling start temperature is less than 300 ° 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)
Annealing (roughening) of the hot-rolled sheet before cold rolling is omitted in order to improve manufacturing efficiency and reduce manufacturing costs, and the hot-rolled sheet is cold-rolled without pre-annealing. (Premise of this patent). Moreover, according to this invention, even if it cold-rolls, without giving a hot-rolled sheet beforehand, the press moldability and bending workability of a board can be improved.

(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)
Utilizing dispersed particles controlled to a size distribution and amount within the range of the present invention by soaking of the ingot, random orientation as a recrystallization nucleus for suppressing ridging marks in the final solution treatment and quenching treatment In order to obtain a recrystallization orientation having the above, it is preferable that the temperature raising rate of the final solution treatment is 100 ° C./min or more. In the temperature rising process of 100 ° C./min or more in the final solution treatment, the dispersed particles serve as nuclei for forming random recrystallized crystal orientations. The rate of temperature rise is more preferably 200 ° C./min or more, and more preferably 300 ° C./min or more.

  The solution treatment conditions are preferably 500 ° C. or higher, in order to sufficiently precipitate Mg / Si clusters and β ”phases in the grains by artificial aging treatment such as paint baking hardening after press molding of the plate. It is carried out in the temperature range up to the following, more preferably from 510 ° C. to 570 ° C., still more preferably from 520 ° C. to 560 ° C.

  Next, in the quenching treatment from the solution treatment temperature, if the cooling rate is slow, Si, MgSi, etc. are likely to precipitate on the grain boundary, which tends to be the starting point of cracks during press molding and bending, and these formability decreases. To do. In order to ensure this cooling rate, the quenching treatment should be performed by selecting and using water cooling means and conditions such as air cooling such as fans, mist, spraying, immersion, etc., and quenching at a cooling rate of 300 ° C / min or more. preferable. More preferably, it is 600 ° C./min or more, more preferably 700 ° C./min or more, and still more preferably 800 ° C./min or more.

  In the present invention, in order to further improve the age-hardening property in the artificial age-hardening treatment such as the paint baking process of the molded panel, after the quenching treatment, to suppress the formation of clusters and promote the precipitation of the GP zone, the pre-aging treatment You may do it. This preliminary aging treatment is preferably held at a temperature range of 60 to 150 ° C., preferably 70 to 120 ° 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 this preliminary aging treatment, after the cooling end temperature of the quenching treatment is increased to 60 to 150 ° C., it is immediately reheated or kept as it is. Alternatively, it is immediately reheated to 60-150 ° C. within 5 minutes after solution treatment and quenching to room temperature.

  Furthermore, in order to suppress aging at room temperature, a GP zone may be further generated by performing a heat treatment (artificial aging treatment) at a relatively low temperature without time delay after the preliminary aging treatment. When the time delay is present, room temperature aging (natural aging) occurs with time even after the preliminary aging treatment, and after the room temperature aging occurs, the effect of the heat treatment at the relatively low temperature is exhibited. It becomes difficult.

  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. As shown in Table 1, a 6000 series Al alloy with a relatively high total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, and W as impurities has a high scrap melting raw material ratio. Then, a 400 mm thick ingot cast by DC casting is subjected to homogenization heat treatment (also abbreviated as soaking) and hot rolling under various conditions shown in Table 2. Each of the obtained hot-rolled sheets was subjected to cold rolling, solution treatment and quenching treatment under various conditions shown in Table 2 and then subjected to cold rolling, solution treatment, and quenching treatment 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. Soaking was performed twice.

  After this soaking, hot rolling was performed to a thickness of 2.5 mmt at each start temperature and each end temperature of rough rolling shown in Table 2 and each end temperature of finish rolling. The hot-rolled sheet was subjected to direct cold rolling after omitting the roughening to obtain a cold-rolled sheet having a thickness of 1 mm.

  The cold-rolled sheet was heated in a continuous heat treatment facility at a rate of temperature increase of about 300 ° C./min in common with each example, and when the solution treatment temperature of 550 ° C. was reached (holding time 10 Immediately after quenching to room temperature, quenching was performed at a cooling rate of approximately 600 ° C./min. Immediately after this quenching, a preliminary aging treatment was carried out at a temperature of 100 ° C. for 2 hours (after the holding, 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 tempering, and 0.5 μm is required as the dispersed particle requirement for each test plate structure after aging for 3 months (90 days) at room temperature. Average number density of all dispersed particles of the above size, A / B and B in the dispersed particle size distribution equation represented by Y = Aexp (-BX), 10 μm or more of all dispersed particles of 0.5 μm or larger size The average number density of dispersed particles having a size and the sum of the number of Mg-Si compound particles and single Si particles among all dispersed particles having a size of 0.5 μm or more were respectively measured by the measurement methods described above.

  Similarly, the characteristics of each test plate after room temperature aging for 3 months after the tempering treatment were as follows: average grain size (μm), 0.2% proof stress (MPa) in the direction of 45 ° to the rolling direction. Elongation (%) and bendability in the direction of 45 ° with respect to the rolling direction were measured and evaluated. These results are shown in Table 3. The average crystal grain size (μm) was determined by the method described above.

(Riding mark)
The ridging mark was evaluated by observing the occurrence of surface irregularities by a tensile test and the surface roughness of the molded product after drawing.
Specifically, No. 5 test piece (25 mm × 50 mmGL × plate thickness) of JISZ2201 was sampled from the Al alloy plate obtained as described above, and a room temperature tensile test was performed. The room temperature tensile test was performed at room temperature of 20 ° C. based on JISZ2241 (1980) (metal material tensile test method). At this time, the specimens were sampled in a direction perpendicular to the rolling direction and a direction perpendicular to the rolling direction. The tensile speed was 5 mm / min up to 0.2% proof stress, and 20 mm / min after proof stress.

  By this tensile test, 20% tensile deformation was given to the plate, and the unevenness on the surface of the plate was measured with a roughness meter. As shown in Fig. 3, the profile of the unevenness on the surface of the plate with a length of about 20 mm was measured. The difference h between the peak portion a of the height and the valley portion b of the maximum depth was measured, and the average value of the three measurement points of the Al alloy plate was obtained. Note that the actual measured value is a fine fluctuation profile as shown by the dotted line in Fig. 3, and as shown in Fig. 3, the profile of the plate surface averaged at each surface position (solid line) is used. The height h (μm) of the unevenness obtained with this profile was evaluated.

(As proof stress)
A JISZ2201 No. 5 test piece (25 mm × 50 mmGL × plate thickness) was collected from the original Al alloy plate of the test plate immediately after the tempering treatment, and a room temperature tensile test was performed. The room temperature tensile test was performed at room temperature of 20 ° C. based on JISZ2241 (1980) (metal material tensile test method). At this time, the specimen was collected in the direction parallel 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. By this method, 0.2% proof stress was evaluated, and AS proof strength was set (N number = average value of 5).

(Yield strength after BH)
In order to investigate the artificial aging treatment ability, after simulating that these Al alloy plates were press-molded as panels, the JIS No. 5 test piece was preliminarily given a strain of 2%, and then 170 ° C. for 20 minutes. Artificial age hardening treatment was performed, and the yield strength (MPa) of each test plate after treatment was measured as the post-BH yield strength (MPa) under the tensile test conditions described above.

(Test plate characteristics)
As the formability of the test plate, the crack limit height (LDH ₅₀ ), limit drawing ratio (LDR), and bendability for the evaluation of the stretch formability were each tested. These results are shown in Table 3, respectively.

For the crack limit height (LDH ₅₀ ) 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 part 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.
Of the above ranks, 0 to 2 stages are acceptable and 3 to 5 are unacceptable.

  As representative examples of the size distribution of the dispersed particles in Tables 2 and 3, FIG. 2 shows the size distribution of all dispersed particles having a size of 0.5 μm or more in Invention Examples 1, 3, 4 and Comparative Examples 10 and 11, respectively. In FIG. 2, the black circle mark is Invention Example 1, the black square mark is Invention Example 3, the black triangle mark is Invention Example 4, the X mark is Comparative Example 10, and the white diamond mark is Comparative Example 11.

In FIG. 2, the dispersion particle size distribution formulas represented by Y = Aexp (−BX) in these inventive examples and comparative examples are also shown as follows.
The thick solid line that approximates the size distribution of the black circles is the size distribution formula of Invention Example 1.
A thick hatch line that approximates the size distribution of the black square marks is the size distribution formula of Invention Example 3.
The thin hatch line that approximates the size distribution of the black triangle mark is the size distribution formula of Invention Example 4.
A fine dotted line approximating the size distribution of the x mark is the size distribution formula of Comparative Example 10.
The long dotted line that approximates the size distribution of the white diamond marks is the size distribution formula of Comparative Example 11.

  As is clear from Tables 1 to 3, the plates of Invention Examples 1 to 9 have a component composition within the range of the invention, and are manufactured within the range of preferable production conditions. Therefore, the average number density of all dispersed particles having a size of 0.5 μm or more, A / B and B in the dispersed particle size distribution formula represented by Y = Aexp (−BX) are within the scope of the invention. In addition, the average number density of dispersed particles of 10 μm or more among all dispersed particles of 0.5 μm or more, and the Mg—Si compound particles and single Si particles of all dispersed particles of 0.5 μm or more in size. The sum of the numbers is also within a preferable range. As a result, even if the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, and W is high, the press formability and bending workability are excellent.

  On the other hand, Comparative Examples 10, 11, and 12 have the component composition (A) within the range of the invention, but the production conditions of the plate are out of the preferred range.

  The comparative example 10 is manufactured not by twice soaking but by soaking only once. For this reason, the average number density of all the dispersed particles is too small, and A / B in the dispersed particle size distribution equation is also slightly lower. As a result, when the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, and W is high, the ridging mark property is low (the height of the unevenness is high).

  Although the comparative example 11 is soaking twice, the cooling rate is too small. For this reason, the average number density of all the dispersed particles is too large, A / B in the dispersed particle size distribution equation is increased, and B is also deviated slightly. In addition, the sum of the number of Mg-Si based compound particles and single Si particles among all the dispersed particles is too large. As a result, when the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, and W is high, the yield strength is low and the bending workability is poor.

  Although the comparative example 12 is soaking twice, the cooling rate is too large due to forced cooling after soaking. For this reason, the average number density of all the dispersed particles and A / B 1 and B 2 in the dispersed particle size distribution formula are within the scope of the invention. In addition, the average number density of dispersed particles having a size of 10 μm or more among all the dispersed particles and the sum of the number of Mg—Si based compound particles and single Si particles in the all dispersed particles are also within a preferable range. Therefore, although characteristics such as formability are good, abnormalities in the shape such as deformation and warping due to heat shrinkage of the slab have occurred, resulting in a large increase in the amount of chamfering, a significant decrease in yield, and efficient or practical production. It was difficult.

  Comparative Examples 13 to 22 have component compositions (I to R) outside the scope of the invention. That is, in Comparative Examples 13 to 22, each content of Fe, Mn, Cr, Zr, V, and Cu exceeds the upper limit specified amount. Therefore, although the production conditions of the plate are within a preferable range, the average number density of dispersed particles having a size of 10 μm or more among all the dispersed particles, or A / B, B in the dispersed particle size distribution formula is It is out of the scope of the invention. As a result, when the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, W is high, bending workability is commonly poor, and this has low yield strength and ridging marks. Low properties (high concavo-convex height), low formability, and the like are selectively added.

  According to the present invention, the press formability and the bending workability are improved even when the plate thickness is increased and the impurity elements are increased, and even when annealing is not performed after hot rolling and before cold rolling. A 6000 series aluminum alloy plate and its manufacturing method can be provided. As a result, it is possible to expand the application of 6000 series Al alloy materials for automobiles, ships, vehicles and other transport equipment, home appliances, buildings, structural members and parts, and especially for automobile molded panels.

It is a conceptual diagram which shows the meaning of the size distribution of the dispersion | distribution particle | grains prescribed | regulated to this invention. It is explanatory drawing which shows the size distribution condition of the dispersed particle of each Example. It is explanatory drawing which shows the profile of the board surface unevenness for ridging mark property evaluation.

Claims (5)

In mass%, Si: 0.5-1.5%, Mg: 0.2-2.0%, 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, Cu: 1.0% or less, and further, the total content of Bi, Sn, Ga, Co, Ni, Ca, Mo, Be, Pb, W is 0.015% or more, And 0.5% or less, the balance being an aluminum alloy plate made of Al and impurities, the average number density of all dispersed particles having a size of 0.5 μm or more measured under the following conditions of the aluminum alloy plate is 3000 to 20000 a number / mm ^2, the horizontal axis size X [mu] m of measured dispersion particles, the number density Y pieces / mm ² the vertical axis coordinates, X is the dispersed particles of a size less than 10 [mu] m, Y = Aexp An aluminum alloy sheet having excellent formability, wherein A / B is in the range of 1000 to 40000 and B is in the range of 0.5 to 2 in the dispersed particle size distribution formula represented by (-BX) .
However, each measurement of the above dispersed particles was carried out by measuring an area of 0.2 mm ^{2 in} the rolling direction at a depth of 1/4 t from the surface of the aluminum alloy plate having a thickness t at 10 arbitrary measurement points with an electron beam probe microanalyzer. This is performed by scanning, and these are averaged. ^{2. The} aluminum alloy sheet having excellent formability according to claim 1, wherein among all the dispersed particles having a size of 0.5 μm or more, an average number density of dispersed particles having a size of 10 μm or more is 100 particles / mm ² or less. The formability according to claim 1 or 2, wherein the sum of the number of Mg-Si compound particles and single Si particles among all the dispersed particles having a size of 0.5 µm or more is 1500 to 5000 particles / mm ² . Excellent aluminum alloy plate.   The aluminum alloy plate having excellent formability according to claim 1, 2 or 3, wherein the aluminum alloy plate is for a molded panel having a flange portion.   It is a method of obtaining the aluminum alloy plate in any one of Claims 1 thru | or 3, Comprising: By mass%, Si: 0.5-1.5%, Mg: 0.2-2.0%, 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, Cu: 1.0% or less, and Bi, Sn, Ga, Co, Ni, An aluminum alloy ingot with a total content of Ca, Mo, Be, Pb, and W of 0.015% or more and 0.5% or less, with the balance being Al and impurities, is homogenized heat treatment at a temperature of 500 ° C or higher and lower than the melting point. Later, the average cooling rate from 500 ° C to 350 ° C was set to 40 ° C / h or more and less than 100 ° C / h, and after cooling to 200 ° C or less, it was hot-rolled after reheating to a temperature of 300 to 450 ° C. The hot rolled sheet was manufactured at a temperature of 170 to 300 ° C., and the hot rolled sheet was further subjected to cold rolling without annealing in advance. Produce this cold rolled sheet at 560 ℃ Characterized by solution heat treatment and quenching treatment at a temperature above manufacturing method of an aluminum alloy sheet with excellent formability.

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