JP5260883B2 - Aluminum alloy plate for warm forming and warm forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide 6000 series Al alloy sheet improving a warm-formability, and warm-forming method therefor. <P>SOLUTION: A composition balance of Si and Mg in the 6000 series Al alloy sheet having special composition containing Cu is controlled as the followings. In the figure 1, condition A; in the case of 0.57-3.8% Mg content; (0.578&times;Mg content)&le;Si content&le;[(0.578&times;Mg content)+0.3]. Condition B; in the case of 0.57-4.5% Mg content and 0.33-2.2% Si content, [(0.578&times;Mg content)-0.4]&le;Si content&le;[(0.578&times;Mg content)]. The either one of the above two conditions is satisfied and further, Cu solid solution and average crystal granular diameter are in the specific ranges to improve a bake-hardening property and the warm-formability. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an Al—Mg—Si alloy plate for warm forming in which a forming process such as press forming is performed warm, and a warm forming method for the Al—Mg—Si alloy plate. The aluminum alloy plate referred to in the present invention refers to an aluminum alloy produced in a plate shape by rolling, extrusion, forging, casting or the like. Hereinafter, aluminum is also referred to as Al, and an Al—Mg—Si alloy plate is also referred to as a 6000 Al alloy plate.

  As is well known, various aluminum alloy plates have conventionally been used for each alloy for transporting machines such as automobiles, ships, airplanes or vehicles, machines, electrical products, architecture, structures, optical instruments, and components and parts of equipment. It is widely used depending on the characteristics.

  In many cases, these aluminum alloy plates are formed by press molding or the like, and are used as members and parts for the above-described applications. For this reason, conventionally, Al-Mg alloy (5000 series Al alloy) plates having relatively good formability have been used.

  On the other hand, the 6000 series Al alloy plate has a relatively small amount of alloy elements as compared with 5000 series Al alloy having a large amount of alloy such as Mg. For this reason, when the scraps of these 6000 series Al alloy plates 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 excellent. In addition, since the 6000 series Al alloy plate basically includes Si and Mg and has excellent age-hardening ability, it ensures formability by reducing the yield strength during press molding and bending. BH properties (bake hardness, artificial aging) that can improve the proof stress by heating at the time of relatively low-temperature artificial aging (curing) treatment, such as paint baking treatment of molded panels, and improve the yield strength. Curability and paint bake hardenability).

  However, the 6000 series Al alloy plate has poor press formability compared with the 5000 series Al alloy plate. For this reason, until now, in order to improve the properties on the material plate side, the third and fourth elements other than Mg and Si are added, or in addition to the addition of alloy elements, the crystal grain size, the dispersion state of crystal precipitates Various methods have been tried for metallurgical improvements to control the microstructure such as grain boundary precipitates.

  On the other hand, a method for improving the formability of an Al alloy plate has also been proposed from the processing side of press forming. One example is warm forming. This warm forming is, for example, a method of forming a plate by setting the punch portion at room temperature and the die portion warm. This warm forming is at a relatively low temperature as compared with hot forming, blow molding, etc., and there is no fear that the properties of the plate will change at high temperatures, and the formability of the Al alloy plate is greatly improved.

  Various methods for forming an aluminum alloy plate by this warm forming have been proposed. For example, a 5000 series aluminum alloy plate excellent in warm formability has been proposed (see Patent Documents 1 and 2).

  Further, Fe: 0.5 to 2.0 wt%, Mn: 0.01 to 0.6 wt%, and a cast structure refining agent of 0.10 wt% or less, respectively, with a specific composition comprising the balance Al and inevitable impurities Proposed aluminum alloy plate with excellent warm formability, with a high tensile elongation of 65% or more in the warm working temperature range of 200-300 ° C, with the Fe and Mn solid solution amounts in the aluminum alloy plate specified below the specified value (See Patent Document 3).

  Furthermore, the two Al plates sandwiching the resin are fixed in advance with a solder material containing Al, and the warming of the vibration-damping Al plate that prevents the resin from being displaced by suppressing the resin peeling due to heating at the time of warm forming as much as possible. Molding has also been proposed (see Patent Documents 4 and 5).

  On the other hand, the means for improving the warm formability of the 6000 series Al alloy plate has not been proposed so far, but many proposals have been made regarding the improvement of forming at room temperature. For example, according to Patent Documents 6 to 8, the maximum diameter of Si and Mg-Si compounds is 10 μm or less, and the number of 2 to 10 μm Si and Mg-Si compounds is 1000 / mm 2 or less. , Paint bake hardenability and bending workability are improved.

  According to Patent Document 9, the average number density of all dispersed particles having a size of 0.5 μm or more is 3000 to 20000 particles / mm 2, the measured dispersed particle size X μm is the vertical axis, and the number density Y particles / mm 2 is horizontal. In the dispersed particle size distribution formula in which the dispersed particles having a size of X of 10 μm or less are represented by Y = Aexp (−BX) in the coordinates as axes, A / B is in the range of 1000 to 40000, and B is in the range of 0.5 to By making it in the range of 2, the strength, BH property, and moldability are improved.

  According to Patent Document 10, the number of crystallized substances having a maximum diameter of 10 μm or more seen in a cross section in the rolling direction is 300 pieces / mm 2 or less, and the ratio of the maximum diameter to the minimum diameter (maximum diameter / minimum diameter) is By controlling the number of crystallized substances of 3.5 or more to 100 pieces / mm2 or less, press formability, corrosion resistance, and strength after baking are improved.

In addition, as a measure for improving formability from the forming side, attempts have been made to improve formability by optimizing forming conditions represented by a local heating blank method, a warm forming method, and a high temperature blow forming method. For example, according to Patent Document 11, a part that undergoes a large deformation prior to press forming is softened in advance to improve formability.
Japanese Patent Laid-Open No. 4-72030 JP 7-310137 A JP 2002-348625 A JP-A-11-221876 JP 2000-317534 A JP 2003-105471 A JP 2003-105472 A JP 2002-356730 A JP 2005-370484 A JP-A-11-71623 JP 2004-124151 A

  Even if the means for improving the warm formability of an Al alloy other than the 6000 series Al alloy plate, such as Patent Documents 1 to 5, are adopted, the warm formability of the 6000 series Al alloy plate is not necessarily improved. This is because different alloy systems have different mechanisms for improving the warm formability, and naturally the presence or absence of the effect of improving the warm formability also differs.

  On the other hand, even if the room temperature formability improving means of the 6000 series Al alloy plate such as Patent Documents 6 to 10 is adopted, the warm formability of the 6000 series Al alloy plate is not always improved. This is because if the molding temperature is different, the mechanism for improving the moldability is different, and naturally the presence or absence of the effect of improving the warm moldability is also different.

  For this reason, even if the 6000 series Al alloy plate is warm-formed, its formability is not always sufficiently improved. In other words, the improvement of the warm formability of the 6000 series Al alloy plate has not been sufficient until now.

  Further, when the 6000 series Al alloy plate is warm-formed, precipitation of compounds such as Mg-Si series or Si series is promoted, and the baking hardness in the subsequent artificial age hardening treatment process or paint bake hardening process is promoted. There is also a new problem of reducing the properties (artificial age hardening ability, paint bake hardening). For this reason, when a 6000 series Al alloy board was warm-formed, there also existed a problem that the required intensity | strength of a 6000 series Al alloy board could not be ensured.

  Therefore, until now, the means for improving the warm formability without reducing the bake hardness of the 6000 series Al alloy sheet has not always been clear. For this reason, the problem of improving the warm formability, which has been increasingly severe in recent years, has not been met, and further improvement of the warm formability of the 6000 series Al alloy sheet is required.

  The present invention has been made in order to solve such problems, and its purpose is to improve the warm formability of the 6000 series Al alloy plate without reducing the bake hardness, and the warm form thereof. Is to provide a method.

In order to achieve this object, the gist of the aluminum alloy sheet for warm forming according to the present invention is, by mass, Mg: 0.62 to 3.60%, Si: 0.35 to 2.30%, Cu: 0 comprises .05～1.5%, the Al alloy ingot balance ing of Al and unavoidable impurities, 200 to 450 ° C. the heating temperatures at the homogenization heat treatment for the first time, the heating time and 0.5~40hr In the second homogenization heat treatment, after performing a two-step homogenization heat treatment at a heating rate of 5 ° C./hr or more, a heating temperature of 450 ° C. or more, less than the melting point, and a heating time of 2 to 30 hr, Al-Mg produced by cold rolling and quenching the cold-rolled sheet at a temperature of 470 ° C or higher and lower than the melting point followed by cooling at a cooling rate of 50 ° C / min or higher and 2500 ° C / s or lower. -In the Si-based aluminum alloy plate, g and Si satisfy (0.578 × Mg content) ≦ Si content ≦ [(0.578 × Mg content) +0.3], and in the structure of the aluminum alloy sheet, a residue extraction method is used. The measured Cu solid solution amount is set to 0.01 to 0.7%, the average crystal grain size is set to 10 to 50 μm, and the average value of the center of gravity diameter analyzed by the electron beam probe microanalyzer is 0.5 μm or more. While the average total area ratio a of a certain Mg—Si (—Cu) compound and Si (—Cu) compound is 1 to 7%, the average area ratio b of this Si (—Cu) compound is The average number density of the Mg—Si (—Cu) compound having a ratio b / a to the average total area ratio a of 1.0 or less and an average value of the center of gravity diameter of 0.5 μm or more is 2000 counts / a mm ² or more, the average value of the centroid diameters The average number density of Si (-Cu) based compound is .5μm above is that it is 2000 counts / mm ² or less.

Here, in the structure of the aluminum alloy plate, an Mg—Si (—Cu) compound and an Si (—Cu) compound having an average value of the center-of-gravity diameter of 0.5 μm or more, analyzed by an electron beam probe microanalyzer. The average total area ratio a is 1 to 7%, while the ratio b / a of the average area ratio b of the Si (—Cu) -based compound to the average total area ratio a is 1.0 or less. Oh Ru. Furthermore, the average number density of the Mg—Si (—Cu) -based compound having an average value of the centroid diameter of 0.5 μm or more is 2000 counts / mm ² or more, and the average value of the centroid diameter is 0.5 μm or more. the average number density of Si (-Cu) compound is the Ru der 2000 counts / mm ² or less.

Further, in the aluminum alloy plate, in mass%, Fe: 0.3% or less, Mn: 0.1% or less, Cr: 0.5% or less, Zr: 0.5% or less, V: 0.3% hereinafter, Ti: 0.2% or less under allowed to contain a.

  In order to achieve this object, the gist of the method for warm forming an aluminum alloy plate of the present invention is as follows. While the temperature is set to a relatively high temperature of 400 ° C., the punched portion of the aluminum alloy plate is press-formed at a relatively low temperature of 100 ° C. or less.

  In the present invention, by controlling the composition balance between Si and Mg, the precipitation of the Mg—Si (—Cu) -based compound is promoted and the deposition is controlled to be suppressed. Here, the Mg-Si (-Cu) -based compound referred to in the present invention is a general term for Mg-Si-based compounds and Mg-Si-Cu-based compounds, and Si (-Cu) -based compounds are Si-based compounds. And a general term for Si-Cu compounds.

  The formation of the Mg—Si (—Cu) -based compound promotes the accumulation of strain around the compound during warm forming and facilitates dynamic recovery, thereby increasing the local elongation of the plate in the warm condition. Interformability is improved. On the other hand, since Si (—Cu) -based compounds are hard and tend to act as a starting point of fracture during warm forming, if there are too many Si (—Cu) -based compounds, warm formability is obtained. descend.

  The coexistence of these Mg—Si (—Cu) -based compounds and Si (—Cu) -based compounds, and the great influence of the mutual coexistence state on the warm formability are Al—Mg—Si-based aluminum alloy plates. It is a problem peculiar to (the organization).

  In addition to these structure controls, the present invention reduces the average crystal grain size, increases the local elongation of the plate in the warm state, and improves the warm formability.

  Furthermore, in addition to the structure control for improving the formability, in the present invention, the Al-Mg-Si-based aluminum alloy sheet contains Cu, and the amount of solid solution Cu is secured to a certain level or more, thereby baking the coating. The precipitates that are sometimes generated are finely and densely dispersed to improve the bake hardness (BH property). By these combined effects or synergistic effects, it is possible to improve the warm formability of the 6000 series Al alloy plate without reducing the bake hardness.

  Furthermore, in the present invention, the warm forming conditions of such an aluminum alloy plate are defined to further improve the warm formability and guarantee the warm formability. For this reason, in the warm forming method of the present invention, when the aluminum alloy plate of the above-described summary or a preferred embodiment described later is warm formed, the flange portion of the aluminum alloy plate is set to a relatively high temperature of 150 to 400 ° C., The punched portion of the aluminum alloy plate is press-molded at a relatively low temperature of 100 ° C. or lower.

  In warm forming, the punch (bottom) portion is formed at a relatively low temperature and the die portion is formed at a relatively high temperature. In terms of the material of the aluminum alloy plate, the flange portion of the plate (the plate portion sandwiched between the peripheral edge portion of the die and the plate pressing portion) is relatively hot, while the punched portion of the plate is relatively cold. Become.

  In warm forming, the reason for making the punched portion of the plate relatively low is that the punched portion of the plate is a load-bearing portion (particularly the abutting portion with the punch bottom) of the punch and has a high breaking strength. This is because it is better.

  On the other hand, the reason why the flange portion (die portion) of the plate is set to a relatively high temperature is because the plate deforms and the material flows into the die at the flange portion of the plate. This is because it is necessary to lower the deformation resistance and the maximum value of the material flow resistance.

  Therefore, the punched portion of the aluminum alloy plate is first heated as a flange portion of the plate to lower the deformation resistance, and after the maximum value of the material flow resistance is lowered, the punched portion of the plate is punched. As a contact portion with the bottom portion, it is cooled and the breaking strength is increased.

  Therefore, in terms of material, the punched portion of the aluminum alloy plate has a low flow stress when heated as a flange portion of the plate, and has a breaking strength when cooled as a contact portion with the punch bottom. Higher is better. That is, the moldability is better when the difference between the breaking strength when cooled and the flow stress when heated is larger.

  In the present invention, this characteristic promotes the precipitation of the Mg—Si (—Cu) compound and suppresses the precipitation of the Si (—Cu) compound in the structure of the Al—Mg—Si aluminum alloy plate. Achieve in the direction. As a result, the local elongation at 200 to 300 ° C. is high as a characteristic of the plate, and the ratio of the local elongation to the total elongation is high, and the warm formability is improved.

  Hereinafter, embodiments of the present invention will be specifically described for each requirement.

(Al alloy composition)
The aluminum alloy sheet of the present invention must have a certain degree of elongation and ductility as a premise in order to improve warm formability. This is because in actual warm forming, it becomes difficult for the material to flow in due to frictional resistance or the like, and a deformed portion that requires an overhanging element occurs. For this reason, in order to have good warm formability, “a certain degree” of elongation, ductility, and strength are required.

  In order to satisfy this and to achieve a composition balance and structure of Si and Mg for improving the warm formability described later, the aluminum alloy sheet composition of the present invention is based on the assumption that the composition of Mg: Al—Mg—Si based aluminum alloy composition containing 0.57 to 4.5%, Si: 0.33 to 2.5%, Cu: 0.05 to 1.5%, and the balance consisting of Al and impurities To do. In addition,% display of content of each element is all the mass%.

(Remainder composition)
In order to guarantee the improvement of warm formability due to the composition balance between Si and Mg contained, in the Al-Mg-Si alloy plate of the present invention, the balance composition is basically composed of aluminum and inevitable impurities. To do. However, this unavoidable impurity contains Fe, Ti, Mn, Cr, Cr, V, Zn, or other elements as long as they do not impair various properties required for warm formability and automotive material panels. Allow that. More specifically, Fe: 1.5% or less, Ti: 0.2% or less, Mn: 1.0% or less, Cr: 0.5% or less, Zr: 0.5% or less, V: 0.0. Inclusion of 3% or less and Zn: 1.5% or less is allowed.

  For example, from the viewpoint of recycling, not only high-purity Al ingots but also 6000 series alloys, other Al alloy scrap materials, low-purity Al ingots, etc. are used as melting raw materials as melting materials. These elements are inevitably contained in the case of melting. For this reason, in the present invention, as described above, these impurity elements are allowed to be contained in an amount that does not inhibit the intended effect of the present invention.

(Mg: 0.57 to 4.5%)
This Mg content controls the composition balance of Si and Mg, which will be described later, and promotes the precipitation of the Mg—Si (—Cu) compound in the structure of the Al—Mg—Si aluminum alloy plate, and It is a content range which is a precondition for controlling in a direction to suppress the precipitation of the Si (—Cu) -based compound.

  In addition, Mg is used for automobile panel materials, etc., during solid solution strengthening and artificial aging treatment such as paint baking treatment, forms an aging precipitate that contributes to strength improvement together with Si, and exhibits age hardening ability. Yield strength required for the automobile panel is obtained. If the Mg content is less than 0.57%, the composition balance between Si and Mg cannot be controlled. Moreover, since the absolute amount of Mg is insufficient, the compound phase cannot be formed during the artificial aging treatment, and the age hardening ability cannot be exhibited. For this reason, the said proof stress required as a motor vehicle panel cannot be obtained. On the other hand, if the Mg content exceeds 4.5%, the composition balance between Si and Mg cannot be controlled. On the other hand, hem bending workability and press formability are reduced.

(Si: 0.33-2.5%)
This Si content controls the composition balance between Si and Mg, which will be described later, and promotes the precipitation of the Mg—Si (—Cu) compound in the structure of the Al—Mg—Si aluminum alloy plate, and It is a content range which is a precondition for controlling in a direction to suppress the precipitation of the Si (—Cu) -based compound.

  Also, Si, together with Mg, forms aging precipitates that contribute to strength improvement during the above-mentioned low-temperature and short-time artificial aging treatments such as for automotive panel materials and for solid-solution strengthening and paint baking treatments. Demonstrate. Thus, for example, the strength (proof strength) required for an automobile panel can be obtained, and various characteristics such as press formability and hem (bending) workability can be provided. If the Si content is less than 0.33%, the composition balance between Si and Mg cannot be controlled. In addition, the age-hardening ability, press formability and the like are lowered. On the other hand, if Si exceeds 2.5%, the composition balance between Si and Mg cannot be controlled. On the other hand, hemmability and press formability are reduced. Furthermore, weldability is significantly impaired.

(Composition balance of Si and Mg)
In order to improve the warm formability of the plate, the local elongation at 200 to 300 ° C. is high, and the ratio of the local elongation to the total elongation is increased. For this reason, in the Al—Mg—Si based alloy plate composition of the present invention, the composition balance between Si and Mg contained is important.

By controlling the composition balance between Si and Mg, in the present invention, in the structure of the Al—Mg—Si based aluminum alloy plate, precipitation of the Mg—Si (—Cu) based compound is promoted, and Si (—Cu) is promoted. It controls to the direction which suppresses precipitation of a system compound. For this reason, in this invention, Si and Mg which an Al-Mg-Si type alloy plate contains satisfy | fills either of the following conditions A and condition B.
Condition A: When the Mg content is 0.57 to 3.8%, (0.578 × Mg content) ≦ Si content ≦ [(0.578 × Mg content) +0.3].
Condition B: [(0.578 × Mg content) −0.4] ≦ Si when the Mg content is 0.57 to 4.5% and the Si content is 0.33 to 2.2% Content ≦ [(0.578 × Mg content)].

  FIG. 1 shows regions A and B that are the conditions A and B, respectively. In FIG. 1, the horizontal axis represents the Mg content and the vertical axis represents the Si content. In FIG. 1, the hatched line at the center indicated by a dotted line is a line equivalent to Mg having an Si content of (0.578 × Mg content). An oblique solid line above the oblique line (dotted line) and parallel to the oblique line (dotted line) is a line having an Si content of [(0.578 × Mg content) +0.3]. In addition, an oblique solid line parallel to the oblique line (dotted line) below the oblique line (dotted line) is a line having an Si content of [(0.578 × Mg content) −0.4].

  The range surrounded by these two oblique solid lines is a range that satisfies the above conditions A and B, and the range above the central oblique line indicated by the dotted line is the range that satisfies the above condition A, from the central oblique line indicated by the dotted line The lower side is a range that satisfies the condition B.

  In the above condition A, when the Si content exceeds [(0.578 × Mg content) +0.3] (when it exceeds the oblique solid line above the central oblique line shown by the dotted line in FIG. 1), Mg—Si The ratio of the area ratio occupied by the Si (-Cu) -based compound consisting only of Si in the area ratio occupied by the (-Cu) -based compound becomes too large. As a result, since the starting point of destruction increases too much, warm formability falls. More preferably, the Si content ≦ [(0.578 × Mg content) +0.2], and more preferably the Si content ≦ [(0.578 × Mg content) +0.1.

  In the above-mentioned condition B, when the Si content is less than [(0.578 × Mg content) −0.4] (below the oblique solid line below the central oblique line shown by the dotted line in FIG. 1), The total area ratio obtained by summing the area ratio occupied by the Mg—Si (—Cu) -based compound and the area ratio occupied by the Si (—Cu) -based compound consisting only of Si becomes too large. Therefore, a coarse compound is formed, and the warm moldability is lowered.

  Further, in the above condition A, when the Mg content exceeds 3.8% (when the Mg content in FIG. 1 exceeds 3.8%) and under the above condition B, the Si content is 2. When it exceeds 2% (when the Si content in FIG. 1 exceeds 2.2%), the area ratio occupied by the Mg—Si (—Cu) -based compound and the Si (− The total area ratio of the total area ratio occupied by the Cu) -based compound is too large. Therefore, a coarse compound is formed, and the warm moldability is lowered.

  In addition, the upper limit of Mg content in the said condition A becomes like this. Preferably it is 2.85% or less, More preferably, it is 2.21% or less. Moreover, the upper limit of Si content in the said condition B becomes like this. Preferably it is 1.65% or less, More preferably, it is 1.28% or less.

(Cu: 0.05-1.5%)
This Cu content is a content range which is a premise for securing the Cu solid solution amount described later. Further, Cu has the effect of facilitating the formation of aging precipitates that contribute to improving the strength of the Al alloy material structure in the crystal grains under the conditions of the artificial aging treatment at a low temperature for a short time, and easily obtaining high yield strength. Moreover, solid solution Cu also has the effect of improving moldability. When there is too little Cu content, the Cu solid solution amount mentioned later cannot be secured. However, corrosion resistance falls when there is too much Cu content. Therefore, Cu is contained in the range of 0.05 to 1.5%.

(Solubility of Cu)
In addition to the structure control for improving the warm formability, in the present invention, the Al—Mg—Si-based aluminum alloy plate contains Cu, and the Cu solid solution amount (solid solution Cu measured by the residue extraction method). The amount is set to 0.01 to 0.7%, and a certain level or more is secured. As a result, precipitates generated during coating baking are finely and densely dispersed, and the bake hardness (BH property) is improved.

  If the Cu solid solution amount is less than 0.01%, the BH property cannot be secured. On the other hand, if the Cu solid solution amount exceeds 0.7%, the strength becomes too large, and the local elongation in the warm is lowered, so that the high temperature formability is lowered. The lower limit value of the Cu solid solution amount is preferably 0.03% or more, more preferably 0.05% or more, and the upper limit value of the Cu solid solution amount is preferably 0.5% or less, more preferably 0. .3% or less.

  The amount of Cu solid solution is measured by a residue extraction method using hot phenol. That is, the Al—Mg—Si-based aluminum alloy plate is dissolved with hot phenol, and the solution is filtered with a filter having a mesh size of 0.1 μm. And as a residue on a filter, it isolate | separates into the oxide, the crystallization thing, precipitate, etc. in the aluminum alloy in which particle size exceeds 0.1 micrometer, and the filtered filtrate. Then, the amount of Cu in the separated filtrate (in the precipitate and the residue) is analyzed as an amount of Cu solid solution by ICP emission spectroscopic analysis (the amount of Cu in the residue on the filter is not solid solution). Considered as Cu-based precipitates).

(Average crystal grain size)
In the present invention, in addition to the above-described structure control, in the present invention, the average crystal grain size is decreased, the local elongation of the plate in the warm state is increased, and the warm formability is improved. In order to increase the local elongation at 200 to 300 ° C. and improve the warm formability of the plate, the average crystal grain size is set to 10 to 50 μm. Although it is better that the average crystal grain size is small, it is difficult to produce an alloy of 10 μm or less by the current mass production process. On the other hand, when the average crystal grain size exceeds 50 μm, the local elongation in the warm state is lowered, so that the warm formability is lowered. The upper limit value of the average crystal grain size is preferably 45 μm or less, more preferably 40 μm or less.

(Organization)
In the present invention, as described above, in order to improve the warm formability, the composition balance between Si and Mg in the structure of the Al—Mg—Si based aluminum alloy plate is controlled. And while promoting precipitation of Mg-Si (-Cu) type compound (Mg-Si type compound and Mg-Si-Cu type compound), Si (-Cu) type compound (Si type compound and Si-Cu type) The precipitation of the compound). If such a tissue state can be defined quantitatively, it is more preferable in terms of reproducibility. In this regard, in the present invention, the average total area ratio and the average total area ratio of these compounds are defined as being relatively correlated with the warm formability.

  That is, in the structure of an Al—Mg—Si-based aluminum alloy plate, an Mg—Si (—Cu) -based compound having an average value of the center-of-gravity diameter of 0.5 μm or more and Si (−) analyzed by an electron beam probe microanalyzer. It can be defined by the ratio B / A of the average total area ratio A of the Cu) -based compound and the average total area ratio A of the average area ratio B of the Si (—Cu) -based compound. Moreover, it can prescribe | regulate also with the average number density of a Mg-Si (-Cu) type compound and a Si (-Cu) type compound.

  In the present invention, by quantification of the total area ratio and number density of these compounds, the precipitation of Mg—Si (—Cu) compounds is promoted by controlling the composition balance between Si and Mg, which is the technical idea of the present invention. , Si (—Cu) -based compound precipitation suppression is supported in a reproducible and complex manner.

(Compound area ratio)
The average total area ratio a of the Mg—Si (—Cu) compound and the Si (—Cu) compound having an average value of the center of gravity diameter of 0.5 μm or more is 1 to 7%, preferably 2 to 6%. It is preferable to do. On the other hand, the ratio b / a of the average area ratio b of the Si (—Cu) -based compound to the average total area ratio a is preferably 1.0 or less.

  As the average total area ratio a of the Mg-Si (-Cu) -based compound and Si (-Cu) -based compound increases, the warm forming is performed. Improves. When the average total area ratio a is small, the total compound having a certain size or more is too small, dynamic recovery is difficult to occur, the local elongation in the warm is lowered, and the warm formability is lowered. To do. On the other hand, if this a is too much, there are too many all these compounds having the above-mentioned size, and conversely, the warm moldability is lowered. Moreover, these compounds form a coarse compound, which also decreases the warm moldability.

  As the average area ratio b of the Si (—Cu) compound decreases, the warm formability improves. That is, as the ratio of the Si (—Cu) -based compound to the total compound is smaller, the warm formability is improved. In this respect, the ratio b / a of the average area ratio b of the Si (—Cu) -based compound to the average total area ratio a with respect to the average total area ratio a is 1.0 or less, preferably 0.5. Below, it is more preferable that it is 0.2 or less.

(Compound number density)
In the present invention described above, Mg—Si (—Cu) -based compound precipitation acceleration and Si (—Cu) -based compound precipitation suppression are achieved through composition balance control of Si and Mg for improving warm formability. Is preferably also expressed as the average number density of the Mg—Si (—Cu) -based compound and the Si (—Cu) -based compound.

That is, preferably, the average number density of Mg—Si (—Cu) compounds having an average value of the center-of-gravity diameter of 0.5 μm or more is 2000 (count number) / mm ² or more. Here, a preferable upper limit is 20000 pieces (count number) / mm ² or less, more preferably 2000 pieces (count number) / mm ² or more and 15000 pieces (count number) / mm ² or less. On the other hand, the average number density of Si (—Cu) compounds having an average value of the center of gravity diameter of 0.5 μm or more is preferably 2000 (count number) / mm ² or less. Here, a preferable lower limit is 200 pieces (count number) / mm ² or more, and more preferably 200 pieces (count number) / mm ² or more and 1500 (count number) / mm ² or less.

  When the average number density of the Mg—Si (—Cu) compound is too small, dynamic recovery is difficult to occur, the local elongation in the warm is lowered, and the warm formability is lowered. This is the same even if the average number density of the Si (—Cu) compound is too small. On the other hand, if the average number density of the Si (—Cu) -based compound is too large, the starting point of fracture becomes too large, and the warm formability is lowered. This is the same even if the average number density of the Mg—Si (—Cu) compound is too large.

(Measurement of compound average area ratio and average number density)
The average area ratio and average number density of compounds having an average value of the center of gravity diameter of 0.5 μm or more can be analyzed and measured by an electron probe microanalyzer (EPMA). However, in order to give reproducibility to the measurement, the measurement conditions are as follows: 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 any 10 measurement points. Scanning with EPMA is performed, and these are averaged.

(Production method)
Next, a method for producing the Al alloy plate of the present invention will be described below. The aluminum alloy plate referred to in the present invention may be a plate-like aluminum alloy produced by rolling, extrusion, forging, casting, or the like, or an aluminum alloy that has been subjected to tempering treatment such as solution treatment and quenching treatment. Among these, a representative method for producing a rolled sheet will be described below.

  In the method for producing a rolled plate, the Al alloy ingot having the above-described composition is hot-rolled after homogenizing heat treatment, further subjected to selective annealing, and then cold-rolled, and then solutionized and quenched. The process is the same as the conventional method. However, in order to combine hem bendability and bake hardness, there are preferable manufacturing process conditions such as particularly controlling the homogenization heat treatment conditions and the pre-aging treatment conditions after solution treatment and quenching treatment.

  Since the physical properties and structure obtained by the alloy composition of the plate to be manufactured and the setting conditions of each process change, the conditions should be determined and selected comprehensively as a series of manufacturing processes. It is not appropriate to set it strictly. However, in particular, if the homogenization heat treatment and the solution treatment are performed under the following conditions, an Al alloy plate having excellent warm formability intended in the present invention can be obtained with certainty.

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

(Homogenization heat treatment)
Next, the cast Al alloy ingot is subjected to homogenization heat treatment. At this time, it is preferable to perform the homogenization heat treatment in two stages. The heating temperature in the first homogenization heat treatment is set to 200 to 450 ° C., and in the first homogenization heating, fine precipitates that contribute to the refinement of crystal grains are formed. When the first homogeneous heating temperature is lower than 200 ° C, fine precipitates are not sufficiently obtained, crystal grains are coarsened, and warm formability is lowered. On the other hand, when the homogeneous heating temperature exceeds 450 ° C., the precipitates become coarse and the warm formability decreases. The first homogeneous heating time is 0.5 to 40 hr. If the homogeneous heating time is short, fine precipitates cannot be obtained sufficiently, the crystal grains become coarse, and the warm formability is lowered. On the other hand, if the homogeneous heating time is long, the precipitates are coarsened, the crystal grains are coarsened, and the warm formability is lowered.

  After the completion of the first homogeneous heat treatment, a second homogeneous heat treatment is performed. As the temperature of the homogenization heat treatment, a temperature of 450 ° C. or higher and lower than the melting point is appropriately selected. 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. If the annealing temperature is too low, intragranular segregation of the ingot cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that the warm formability is lowered.

  At the time of the second homogeneous heat treatment, after the first homogeneous heat treatment is completed, the ingot is continuously heated (without cooling the ingot) and the second homogeneous heat treatment is performed, or The ingot may be once cooled to near room temperature, heated again, and the second homogeneous heat treatment may be started.

Heating rate up to the second homogeneous heating temperature, even when heating it after the first homogenization heat treatment ended, once even when cooled ingot to near room temperature, and 1 ° C. / hr greater. If the rate of temperature rise is 1 ° C./hr or less, the precipitates become coarse and the warm formability decreases. The second homogeneous heating time is 2 to 30 hr. If the homogeneous heating time is short, the intragranular segregation of the ingot cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that the warm formability is lowered. Further, even if the homogeneous heating time is long, the effect of homogenization is saturated. Therefore , even if annealing is performed for a longer time, there is no effect.

(Hot rolling)
In the present invention, there are no particular restrictions on the hot rolling conditions, but preferably a lower hot rolling start temperature suppresses precipitation promotion and precipitate coarsening during hot rolling, and formation of coarse recrystallized grains. Is suppressed and strength and formability are not deteriorated. Preferably it is 400 degrees C or less, and a minimum is preferably 250 degrees C or more.

(Hot rolled sheet annealing)
The hot rolled sheet is annealed (roughened) before cold rolling as necessary. It may be omitted for the sake of manufacturing efficiency and reduction of manufacturing cost, and cold rolling may be performed without pre-annealing the hot-rolled sheet.

(Cold rolling)
Cold rolling after hot rolling is performed to produce cold rolled sheets (including coils) with a desired thickness.

(Solution and quenching)
In the solution treatment, the Si (—Cu) compound is re-dissolved, and the precipitation of the Mg—Si (—Cu) compound in the subsequent cooling (quenching) step and the subsequent artificial age hardening treatment is promoted. . Therefore, the solution temperature is 470 ° C. or higher and lower than the melting point, and the cooling (quenching) rate after solution is 50 ° C./min or more and 2500 ° C./s or less. In order to ensure this cooling rate, it is preferable that the quenching process is rapid cooling by selecting and using water cooling means and conditions such as forced air cooling by a fan, mist, spray, and immersion.

  If the solution temperature is too low, the re-solution of the Si (-Cu) compound in the solution treatment becomes incomplete, the Si (-Cu) compound increases too much, and the warm formability is improved. , Mg-Si (-Cu) -based compound precipitation acceleration and Si (-Cu) -based compound precipitation suppression cannot be performed. For this reason, warm moldability falls and it is highly likely that the conditions of the area ratio B / A and the compound number density cannot be satisfied.

  On the other hand, when the solution temperature exceeds the melting point, the crystal grains are coarsened and the warm formability is lowered. In addition, if the cooling rate is too slow, the crystal grains become coarse during the cooling process, and the Si (-Cu) -based compound is precipitated, so that the Si (-Cu) -based compound is excessively increased, which improves the warm formability. Therefore, the Mg—Si (—Cu) -based compound precipitation acceleration and the Si (—Cu) -based compound precipitation suppression cannot be performed. For this reason, warm moldability falls and it is highly likely that the conditions of the area ratio B / A and the compound number density cannot be satisfied. However, since the upper limit of the cooling rate on the equipment in the mass production process is about 2500 ° C./s, this is the upper limit.

  In the present invention, in order to enhance age-hardening in an artificial age-hardening treatment such as a paint baking process of a molded panel, in order to suppress the formation of clusters after solution hardening and to promote the precipitation of GP zone, pre-aging It may be processed. This preliminary aging treatment is preferably held in a temperature range of 50 to 140 ° C. for a required time of 1 to 24 hours.

  As the preliminary aging treatment, the quenching end temperature after the solution treatment is increased to 50 to 140 ° C. and then immediately reheated or held as it is. Alternatively, after the solution treatment, after the quenching treatment to room temperature, it is immediately reheated to 50 to 140 ° C. 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.

(Warm forming method)
Next, a preferred warm forming method to which the 6000 series Al alloy plate of the present invention is applied will be described below. The 6000 series Al alloy plate of the present invention can be applied to various hot press forming such as deep drawing and overhanging. In other words, as the warm forming method itself, normal press forming such as deep drawing and overhanging can be applied. Moreover, the press apparatus used with these warm forming methods can also apply a normal warm forming press.

  Press forming intended for deep drawing will be described with reference to a cross-sectional view of the press forming machine in FIG. In FIG. 2, 1 is a 6000 series aluminum alloy plate to be formed, 5 is a punch, 6 is a die (die), and 7 is a plate retainer. Reference numeral 2 denotes a flange portion around the plate 1 sandwiched between the plate presser 7 and a die (die) 6, 3 denotes a cylindrical wall portion of the cylindrical molded product that flows into the die 6 of the plate 1, and 4 denotes a punch 5. It is the cylinder bottom part of the cylindrical molded product shape | molded by contact | abutting to the bottom part of this (load load).

  Here, as a preferable warm forming method, the flange portion 2 of the plate 1 is set to a relatively high temperature of 150 to 400 ° C. so that the flange portion 2 of the plate 1 can easily flow into the die 6. For this purpose, the flange part 2 of the plate 1 is heated. In this heating method, the entire plate or only the flange portion 2 of the plate 1 is heated in advance using a heater, a furnace or the like before being introduced into the press, or the die 6 and / or the plate presser 7 shown in the figure is used. It heats with the heater 8 etc., and the flange part 2 around the board 1 is partially heated after introducing into a press.

  In the present invention, as described above, due to the compositional balance between Si and Mg contained in the 6000 series Al alloy plate that is warm-formed, the punched portion of the Al alloy plate is heated as a flange portion of the plate. The flow stress is low, and the breaking strength when cooled as a contact portion with the punch bottom is increased. That is, the difference between the breaking strength when cooled and the flow stress when heated is large, and the warm formability is improved.

  However, the heating temperature is preferably 150 ° C. or higher. If the heating temperature is less than 150 ° C., the heating temperature is too low, which is no different from normal room temperature forming, and even the 6000 series Al alloy plate of the present invention loses the advantages of warm forming itself.

  On the other hand, when the heating temperature exceeds 400 ° C., the temperature is too high, and even the 6000 series Al alloy plate of the present invention may cause the amount of material flowing into the die 6 to be too large. I am prone to wrinkles.

  On the other hand, as the portion to be punched of the plate 1, the corner portion of the plate 3 that contacts the corner portion of the punch 5 and the portion of the plate 4 that contacts the bottom portion of the punch 5, Use a relatively low temperature of ℃ or less.

  For this purpose, it is necessary to cool the heated plate, and the bottom of the punch 5 is cooled to a relatively low temperature of 100 ° C. or less by circulating water or the like. The lower limit temperature of 100 ° C. or less is about room temperature although it depends on the cooling ability of the plate 4 by the punch 5.

  However, when this temperature exceeds 100 ° C., even in the 6000 series Al alloy plate of the present invention, the corner portion of the plate 3 that contacts the corner portion of the punch 5 or the portion of the plate 4 that contacts the bottom portion of the punch 5 The breaking strength of the sheet becomes low, and the possibility of cracking during the molding increases.

  Warm formability is further improved by such warm forming conditions and the composition balance of Si and Mg contained in the 6000 series Al alloy plate of the present invention.

  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. 6000 series Al alloy plates having each composition of 1 to 9 (invention example) and 10 to 15 (comparative example) shown in Table 1 and a composition balance of Si and Mg are manufactured under the conditions shown in Table 2, respectively. The structure and warm formability were measured and evaluated. These results are shown in Table 3, respectively.

  More specific common manufacturing conditions for each test material Al alloy plate are as follows. An ingot of 500 mm thickness, 2000 mm width, and 7 m length of each composition shown in Table 1 was melted by a DC casting method, and then subjected to two-stage homogenization heat treatment under each condition shown in Table 2. After this homogenization heat treatment, hot rolling was performed at a start temperature of 390 ° C. and an end temperature of 280 ° C. to a plate thickness of 2.5 mm. The hot-rolled sheet was subjected to direct cold rolling after omitting the roughening to obtain a cold-rolled sheet coil having a sheet thickness of 1.0 mm. This plate coil was subjected to a solution treatment in which the holding time at the solution temperature was several seconds and water quenching to cool to room temperature under the conditions shown in Table 2 in a continuous furnace. Immediately after that, a series of tempering treatments were carried out, such as reheating to a temperature of 70 ° C. and maintaining in this temperature range for 2 hours.

(Warm local growth)
A tensile test piece having a longitudinal direction of 90 ° from the tempered plate is taken from the tempered plate, and a stress-strain curve is obtained by a JIS No. 5 tensile test. %). The atmospheric temperature at the time of the tensile test was 250 ° C. The tensile test piece was attached after reaching the atmospheric temperature in advance, and held for about 10 minutes after the attachment, and then the tensile test was performed. Furthermore, the test was performed 3 times for each sample, and the average value was adopted.

(BH property)
The BH property (bake hard property) is the plate after each tempering treatment and the plate after heat treatment (artificial age hardening treatment) at 170 ° C. for 20 minutes. Tensile test pieces were collected and a stress-strain curve was obtained by a JIS No. 5 tensile test, and then 0.2% yield strength (AB yield strength: MPa) was obtained. Furthermore, the difference with the proof stress of the board after the said tempering process was computed by the following formula, and BH property was evaluated by the magnitude | size of the difference. BH property = yield strength after artificial age hardening (AB proof strength) −yield strength after tempering treatment (AS proof strength). The ambient temperature during the tensile test was room temperature, and the tensile test was performed. Furthermore, the test was performed 3 times for each sample, and the average value was adopted.

(Compound area ratio)
The compound area ratio of the Mg—Si (—Cu) -based compound and the Si (—Cu) -based compound is measured by mechanical polishing from the rolled surface to a depth of 0.25 mm with respect to the plate after each tempering treatment. The polished surface was subjected to EPMA (JXA-8000 series, manufactured by JEOL Ltd., measurement conditions were acceleration voltage 20 kV). The measurement area was about 0.1 to 0.2 mm ² and the magnification at the time of measurement was × 600. The measurement object measured the particle | grains whose gravity center diameter is 0.5 micrometer or more. The reason why the measurement object has a diameter of the center of gravity of 0.5 μm or more is that it is difficult to detect particles smaller than that due to the resolution of the apparatus.

  Of all the compound particles detected by these measurements, Mg-Si (-Cu) -based compounds and Si (-Cu) -based compounds were extracted as follows. First, the elemental element analysis Fe, Mn, Mg, Si, and Cu contained in each particle is analyzed by the EPMA apparatus (at%). Since the quantitative value obtained here has a problem in analysis accuracy depending on the size of each compound particle and the beam diameter of EPMA, in this patent, depending on the ratio of the main contained elements, the Mg—Si (—Cu) -based compound and Discrimination from Si (-Cu) -based compounds was performed. A specific analysis method is shown below.

  With the above EPMA apparatus, the total amount of Fe, Mn, Mg, Si, Cu and the total amount of Fe (at%) + Mn (at%) + Mg (at%) + Si (at%) + Cu (at%) (total amount) ) Next, for each compound particle, Fe amount / total amount, Mn amount / total amount, Mg amount / total amount, Si amount / total amount, Cu amount / total amount, and Fe with respect to the total amount of five elements contained , Each content ratio of Mn, Mg, Si, and Cu is obtained. Among these, even if the Fe amount / total amount is 0.05 or less and the Mn amount / total amount is 0.3 or less, or the Fe amount / total amount exceeds 0.05, the Mg amount / total amount is A material corresponding to any of 0.3 or more was determined to be a Mg—Si (—Cu) -based compound or a Si (—Cu) -based compound.

  Further, for each compound particle determined to be an Mg-Si (-Cu) compound or an Si (-Cu) compound, an Mg / (Mg + Si) of 0.05 or less was obtained for each compound particle. It was determined that it was a (—Cu) -based compound. Therefore, those having Mg / (Mg + Si) exceeding 0.05 were determined to be Mg—Si (—Cu) based compounds.

  Thus, the area of each compound particle is obtained from the sum of the number of pixels on the image of the Mg—Si (—Cu) compound and the Si (—Cu) compound analyzed and discriminated, and the total area is measured. To obtain the average total area ratio a of the Mg—Si (—Cu) -based compound and the Si (—Cu) -based compound.

  In addition, by calculating the area of each Si (-Cu) compound particle with the sum of the number of pixels on the image of the analyzed and discriminated Si (-Cu) compound, and dividing the sum by the measurement area, The average area ratio b of the Si (—Cu) -based compound was used. The area ratio of the average area ratio b of the Si (—Cu) -based compound to the average total area ratio a was b / a. The area ratios a and b were averaged by measuring the area ratios a and b at any five different measurement locations on the same sample and averaging the results.

(Compound number density)
The total number (total count number) of each of the Mg—Si (—Cu) compound and Si (—Cu) compound obtained in the process of area ratio analysis (measurement) of these compound particles was measured. By dividing by the area, the number density (pieces / mm ² ) of each of the Mg—Si (—Cu) -based compound and the Si (—Cu) -based compound was obtained.

(Cu solid solution amount)
The amount of Cu solid solution is measured by the residual extraction method using hot phenol as described above. That is, only the aluminum alloy matrix of the plate after each tempering treatment is dissolved with hot phenol, and the solution is filtered with a filter having a mesh size of 0.1 μm. Then, the residue on the filter is separated into a residue such as an oxide, a crystallized substance, and a precipitate in an aluminum alloy having a particle size exceeding 0.1 μm and a filtered solution. Then, the amount of Cu (such as precipitates and residues in the filtrate) in the separated filtrate was determined by ICP emission spectroscopy.

(Average crystal grain size)
The average crystal grain size of the plate after each tempering treatment is measured by measuring the texture of the rolled surface at a depth of 1/4 t from the surface. Specifically, 0.25 mm was scraped by mechanical polishing in the vertical direction (plate thickness direction) in the rolling direction of the plate after each tempering treatment, and the surface was adjusted by electrolytic polishing following buff polishing. A sample was prepared. Thereafter, crystal orientation measurement and crystal grain size measurement by EBSP (Electron Back Scattering (Scattered) Pattern) were performed using SEM (JEOL JSM 5410) manufactured by JEOL Ltd. The measurement area was an area of 1500 μm × 1500 μm, and the measurement step interval was 2 μm. As the EBSP measurement / analysis system, EBSP: manufactured by TSL (OIM) was used. Here, the deviation of the orientation within ± 15 ° belongs to the same crystal grain.

(Warm formability)
In addition, a test plate (blank) is cut out from the tempered plate and subjected to a warm forming test using the press shown in FIG. 2 to determine the forming height (maximum punch depth until breakage). / Mm) was measured and evaluated.

  At this time, as a temperature condition of warm forming by the press shown in FIG. 2, heating was performed using the heater 8 so that the flange portion 2 of the plate 1 became 260 ° C. Moreover, the bottom part of the punch 5 is cooled with circulating water, and the corner part of the plate 3 in contact with the corner part of the punch 5 and the part of the plate 4 in contact with the bottom part of the punch 5 are set to a relatively low temperature of 100 ° C. or less. . These temperatures were measured with a contact-type thermometer and used as an average temperature in a plurality of measurements within a predetermined measurement time.

  The temperature condition of this warm forming is a condition of the warm forming method of the aluminum alloy plate of the present invention, while the flange portion of the aluminum alloy plate is set to a relatively high temperature of 150 to 400 ° C., while the aluminum alloy plate is punched. Satisfying the press molding at a relatively low temperature of 100 ° C. or lower.

The size of the test plate is 120 x 120mm, punch: 50mmφ-shoulder R4.5mm, die: 54.5-56.0mmφ-shoulder R8-10mm, using a lubricant CF853 made by Nippon Yasushi Osamu, wrinkle holding load A deep drawing test was performed under the conditions of 1.2 kg / cm ² and a punch speed of 80 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 drawing formability. For example, in order to satisfy the deep drawing formability required for forming into an automotive panel, the forming height is about 25 mm or more. I just need it.

  As shown in Tables 1 to 3, the invention examples are manufactured under preferable production conditions as shown in Table 2 using alloys having respective compositions within the scope of the invention shown in Table 1. For this reason, as shown in Table 3, when Mg and Si are in Condition A: Mg content is 0.57 to 3.8% (0.578 × Mg content) ≦ Si content ≦ [(0 .578 × Mg content) +0.3], Condition B: When Mg content is 0.57 to 4.5% and Si content is 0.33 to 2.2%, [(0.578 × Any of Mg content) −0.4] ≦ Si content ≦ [(0.578 × Mg content)] is satisfied. Further, the Cu solid solution amount and the average crystal grain size measured by the residue extraction method are within the scope of the invention.

By controlling the composition balance between Si and Mg, the invention example promotes the precipitation of Mg—Si (—Cu) compound in the structure of an Al—Mg—Si aluminum alloy plate, and Si (—Cu). It is controlled to suppress the precipitation of the system compound. Therefore, as shown in Table 3, the average total area ratio a of the Mg—Si (—Cu) compound and the Si (—Cu) compound having an average value of the center of gravity diameter of 0.5 μm or more is 1 to 7%. Satisfy certain favorable conditions. Further, the preferable condition that the ratio b / a of the average area ratio b of the Si (—Cu) -based compound to the average total area ratio a is 1.0 or less is also satisfied. Furthermore, the average number density of the Mg—Si (—Cu) -based compound is preferably 2000 count / mm ² or more, and the average number density of the Si (—Cu) -based compound is preferably 2000 count / mm ² or less. The conditions are also met.

  As a result, as shown in Table 3, the invention examples have high local elongation at 250 ° C. as the characteristics of the plate, the molding height in the warm molding is 25 mm or more, and is excellent in BH property (bake hard property). And, it has both warm formability and BH property.

  On the other hand, as shown in Table 2, although Comparative Examples 26 to 32 use an alloy having a composition within the invention range of Table 1, the manufacturing conditions deviate from the preferred range as shown in Table 2. For this reason, Comparative Examples 26 to 32 promote the precipitation of the Mg—Si (—Cu) compound and the precipitation of the Si (—Cu) compound in the structure of the Al—Mg—Si aluminum alloy plate. It is not controlled in the direction to suppress. Therefore, as shown in Table 3, the Mg—Si (—Cu) -based compound and the Si (—Cu) -based compound do not satisfy any of the conditions such as area ratio and number density. As a result, as shown in Table 3, in Comparative Examples 26 to 32, as the characteristics of the plate, any of local elongation at 250 ° C., molding height in warm molding, and BH property is remarkably compared with the invention examples. Inferior.

  In Comparative Examples 19 to 22, as shown in Table 1, Mg and Si are alloys having a composition outside the scope of the invention in which either the condition A or the condition B is outside the scope of the invention. Therefore, in Comparative Examples 19 to 22, although the manufacturing conditions are within the preferable range as shown in Table 2, the area of the Mg—Si (—Cu) compound or Si (—Cu) compound as shown in Table 3 is shown. The conditions such as rate and number density are not satisfied. Therefore, as shown in Table 3, Comparative Examples 19 to 22 are, in terms of properties, either warm formability or BH property, or both are significantly inferior to the inventive examples, and these cannot be combined.

  Further, Comparative Examples 23 to 25, which are compositions outside the scope of the invention in terms of too little or too much Cu or too much Cr, are within the preferable production conditions as shown in Table 2, and as shown in Table 3. Although Mg-Si (-Cu) -based compounds and Si (-Cu) -based compounds satisfy the conditions such as area ratio and number density, as shown in Table 3, either warm formability or BH properties are characteristically used. Kaga is inferior to the invention examples, and these are not combined.

  The above examples support the critical significance of combining the warm formability and the BH property of each requirement or preferred condition of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the 6000 series Al alloy plate which improved warm formability, without reducing bake hard property, and its warm forming method can be provided. As a result, the application of the 6000 series aluminum alloy plate can be expanded for press forming applications such as automobile panels.

The Mg ₂ Si composition range of the balance to which the present invention is defined is an explanatory diagram showing. It is sectional drawing which shows warm forming of an aluminum alloy plate.

Explanation of symbols

1: plate, 2: plate flange, 3: plate wall, 4: plate bottom (contact portion with punch),
5: Punch, 6: Die (mold), 7: Plate holder

Claims (3)

By mass%, Mg: 0.62~3.60%, Si : 0.35~2.30%, Cu: includes 0.05 to 1.5%, Al balance ing of Al and unavoidable impurities The heating temperature of the alloy ingot in the first homogenization heat treatment is 200 to 450 ° C., the heating time is 0.5 to 40 hr, the heating rate in the second homogenization heat treatment is 5 ° C./hr or more, and the heating temperature is 450 ° C or higher, less than melting point, and two-stage homogenization heat treatment with heating time of 2 to 30 hr, followed by hot rolling and cold rolling, and this cold-rolled sheet is formed into a solution at a temperature of 470 ° C or more and less than the melting point In an Al—Mg—Si-based aluminum alloy plate manufactured by performing a quenching process of cooling at a cooling rate of 50 ° C./min or more and 2500 ° C./s or less after the treatment , Mg and Si are (0.578 × Mg content) ) ≦ Si content ≦ [(0.578 × M g content) +0.3], and in the structure of the aluminum alloy plate, the Cu solid solution amount measured by the residue extraction method is 0.01 to 0.7%, and the average crystal grain size is 10%. The average total area ratio a of Mg—Si (—Cu) -based compounds and Si (—Cu) -based compounds having an average value of the center of gravity diameter of 0.5 μm or more, analyzed by an electron beam probe microanalyzer. Is 1 to 7%, the ratio b / a of the average area ratio b of the Si (—Cu) -based compound to the average total area ratio a is 1.0 or less, and the average of the center-of-gravity diameters The average number density of Mg—Si (—Cu) compounds having a value of 0.5 μm or more is 2000 counts / mm ² or more, and the average value of the center-of-gravity diameter is 0.5 μm or more. The average number density of chemical compounds is 2000 counts An aluminum alloy plate for warm forming excellent in bake hardness, characterized by being / mm ² or less.   In the aluminum alloy plate, the impurities are, by mass, Fe: 0.3% or less, Ti: 0.2% or less, Mn: 0.1% or less, Cr: 0.5% or less, Zr: 0.00%. The aluminum alloy plate for warm forming according to claim 1, wherein a content of 5% or less and V: 0.3% or less is allowed.   When the aluminum alloy plate according to claim 1 or 2 is warm-formed, the flange portion of the aluminum alloy plate is set to a relatively high temperature of 150 to 400 ° C, while the punched portion of the aluminum alloy plate is set to 100 ° C. A warm forming method characterized by press forming at a relatively low temperature as follows.

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