JP2014025101A - Method for producing blank made of aluminum alloy and method for producing press-formed body made of aluminum alloy - Google Patents

Abstract

An aluminum alloy blank manufacturing method and an aluminum alloy press molded body manufacturing method capable of suppressing generation of wrinkles in a blank due to press forming are provided.
An Al—Mg—Si aluminum alloy plate age-hardened by normal temperature aging or artificial aging is prepared, and a part of the aluminum alloy plate is predetermined as a softening region for reducing strength. Then, the softened region was heated to a heating attainment temperature of 200 ° C. or higher and 580 ° C. or lower, and then cooled to 100 ° C. or lower, thereby reducing the proof stress value of only the softened region and giving a strength difference in the blank. A blank for press molding is manufactured.
[Selection] Figure 2

Description

  The present invention relates to a method for producing an aluminum alloy blank for press forming and a method for producing an aluminum alloy press formed body.

Conventionally, a cold-rolled steel sheet has often been used as a body panel material for automobiles. However, recently, reduction of CO ₂ emissions has been demanded from the viewpoint of suppressing global warming, and the importance of weight reduction of the vehicle body has been widely recognized. As a result, the use of aluminum alloy plates having a low specific gravity is increasing.

  Of aluminum alloy plates, Al—Mg—Si based aluminum alloys are often used for body panels such as automobile hoods, fenders, and doors. In the Al—Mg—Si based aluminum alloy, press formability can be ensured by finishing the plate in a low proof stress state by taking advantage of the heat treatment alloy. And the yield strength is increased by age-hardening (called “paint bake hardening” or “bake hard (BH)”) by a paint baking process (for example, about 170 ° C. for about 20 minutes) in the subsequent automobile manufacturing process. High yield strength can be imparted to the panel. Ultimately, the panel is in a high yield strength state, so that the panel thickness can be reduced, and the light weight effect is improved.

  However, in general, aluminum alloy sheets are more likely to break and wrinkle than cold-rolled steel sheets, and formability is inferior. Recently, improvement in the design of automobile body panels has been strongly demanded, because the occurrence of wrinkles cannot be suppressed even if fracture does not occur, which is the most important viewpoint for determining whether or not the panel shape can be molded. In some cases, the use of aluminum alloy plates is postponed. Therefore, suppression of wrinkles in press forming is one key to expanding the application of aluminum alloy plates, and improvements in the aluminum alloy plates themselves and ingenuity in forming methods are strongly demanded.

  In press molding, usually, a blank is formed between a die and a holder, the die and the punch are relatively brought close together, and the punch is pushed into the die to form the blank into a predetermined shape. Here, the blank is pressed in contact with the punch and the die, so that the shape of the blank is changed while being accompanied by plastic deformation through elastic deformation and reaches a predetermined shape.

  Such press molding includes drawing forming mainly used for forming the inner panel and overhang forming mainly used for forming the outer panel. In draw forming, a blank sandwiched between a die and a holder is drawn from the periphery into a die hole and formed. At this time, a tensile force acts on the blank being molded from the periphery of the mold toward the center, and a compressive force acts on the circumferential direction perpendicular to the tensile force. In drawing, the plate thickness dimension is significantly smaller than the plane dimension of the plate, so that a material subjected to a compressive force easily causes buckling deformation. In the overhang forming, the material is formed by stretching deformation of the material in the die hole. Even in this overhang molding, a complicated panel shape such as an automobile body panel generally has a height difference in the punch molding surface, and when viewed in a vertical cross section parallel to the press direction, the punch head from the wrinkle holding surface is There is always a difference in line length when the line length to the opposite side wrinkle holding surface is compared in each cross section. In the region where the wire length is short, the material is left with a surplus, and a non-uniform tensile force acts to induce a compressive force or a shearing force, which may cause buckling deformation. In addition, the wrinkle pressing surface is not on the same plane, and the blank may buckle when the blank is held between the die and the holder. These buckling deformations are referred to as wrinkles, which are distortions of the surface that remain without being erased to the bottom dead center of press molding. Here, the term “wrinkle” is used as a general term for surface shape defects due to surface distortion. However, surface distortion that is a slight distortion of several tens to several hundreds of μm is also included in the wrinkles.

  As a method of suppressing wrinkles, from the viewpoint of mold shape and die face design, avoid sudden changes in shape, control excess tension with bead and bead, adjust punch and die clearance, absorb excess There is a method of providing a shape for the purpose. However, these degrees of freedom are limited, and even with these methods, there are cases where they cannot be suppressed.

  From the viewpoint of material characteristics, it is effective to use a high n value (work hardening index) material, a high r value (Lanckford value) material, and a low strength material. However, although various studies have been conducted on high n-value and high r-value materials, there has not yet been reported an example of industrial mass production of aluminum alloy sheets in which these have been dramatically improved.

  On the other hand, it is possible to manufacture a low strength material. However, there are some problems when using a low strength material, that is, when making the entire blank low strength. From the viewpoint of material properties, it is possible to reduce the yield strength by reducing the content of Mg and Si, but the tensile strength is also lowered, so that the formability is lowered. In addition, since Al—Mg—Si-based alloys have age-hardening properties, the proof stress value gradually increases during normal temperature holding, and it is difficult to maintain a low proof stress.

  Also, from the viewpoint of the forming method, in the case of draw forming, the blank sandwiched between the die and the holder is drawn from the periphery into the die hole, and the portion sandwiched by the die and the holder, that is, the blank wrinkle holding portion Receives frictional resistance by sliding with the mold. Considering the balance of forces acting on the blank during drawing, the molding force applied to the punch is balanced between the blank deformation resistance and the frictional resistance. If a low-strength material is used, the deformation resistance will decrease, but the tensile strength of the material will also decrease. The ratio of becomes large and breaks easily.

  Various proposals have been made for the problems and problems described above. For example, in Patent Document 1, prior to press forming a material, the material is wrinkled during press molding by compressing a planned compression site that is locally set on the material and processing and hardening the planned compression site. A method of suppressing this is described.

  According to this method, a plurality of dimples are formed at a pair of parts separated from each other on the line of action of the tensile force that causes wrinkles at or near a wrinkle-prone part where wrinkles are likely to occur in the material during press molding. Thus, it is said that wrinkle generation at the time of press molding is effectively suppressed if compression processing is performed and work hardening is performed.

  Patent Document 2 describes a method of suppressing the generation of wrinkles by heating a press mold and heating a wrinkle generating portion.

  According to this method, it is said that low strength and high ductility can be obtained by heating the wrinkle generating portion of the aluminum plate material to 200 to 300 ° C. with a press die, and the generation of wrinkles is suppressed.

JP-A-11-319964 JP 2008-254001 A

  The method disclosed in Patent Literature 1 cannot be applied to an outer panel that requires high surface quality because dimples are formed on the plate surface. In addition, it is difficult to obtain a sufficient strength difference in an aluminum alloy plate having low work hardenability, and the formation of dimples conversely causes stress concentration, which may cause breakage. Furthermore, aluminum powder is generated during dimple processing and adheres to the surface of the plate. When the aluminum powder is sandwiched between the mold and the plate during press molding, the surface of the plate may be damaged.

  Further, in the method disclosed in Patent Document 2, it is necessary to add a heating function such as a heater and a cooling function to the press die, and it takes time and cost to add this function to each press die. . Moreover, since it takes time to heat the aluminum plate material, the molding time becomes longer, and the productivity of press molding decreases. Moreover, since only the part which contacted the press metal mold | die is heated, it cannot apply when a wrinkle generate | occur | produces in the part which does not contact the metal mold | die of a board | plate material.

  As described above, the conventionally proposed technology does not impair the surface quality and formability of the aluminum alloy plate and the high productivity of press forming, and does not cause excessive cost increase, It was difficult to suppress the occurrence.

  The present invention has been made in view of the above circumstances, and it is possible to shorten the time required for press molding and to suppress generation of wrinkles in the blank by press molding, and to provide a method for manufacturing an aluminum alloy blank and an aluminum alloy press molded body. An object is to provide a manufacturing method.

In order to solve the above problems, a method for manufacturing an aluminum alloy blank according to the first aspect of the present invention includes:
A method for producing a blank made of an aluminum alloy for producing a press-formed body by performing press molding,
Preparing an age-hardened Al-Mg-Si-based aluminum alloy plate;
A heating step of pre-determining a partial region of the aluminum alloy plate as a softening region for reducing the strength, and heating the softening region to a heating attainment temperature of 200 ° C. or higher and 580 ° C. or lower;
A cooling step for cooling the heated softened region to 100 ° C. or less;
It is characterized by including.

  Moreover, it is preferable that the softened region includes a region where a main stress of a compression component that causes wrinkles is generated in the plate surface of the aluminum alloy plate in the press forming process.

  Moreover, it is preferable that the softened region is a region wider than the region where the tensile force acts in a direction orthogonal to the direction of the tensile force acting that generates the main stress of the compression component.

  The softened region is preferably a region narrower than the region between the fulcrums on which the tensile force acts with respect to the direction of the tensile force that generates the main stress of the compression component.

Further, in the heating step, the ultimate temperature is 200 ° C. or more and 300 ° C. or less, and the rate of temperature rise of the aluminum alloy plate from 100 ° C. to the ultimate temperature is 5 ° C./second or more
In the cooling step, the cooling rate of the aluminum alloy plate up to 100 ° C. or less is 5 ° C./second or more,
It is preferable that the holding time of the aluminum alloy plate at the heating ultimate temperature in the heating step is 20 seconds or less.

In the heating step, a region that is not the softened region of the aluminum alloy plate is defined as a non-softened region, the non-softened region is heated to a heating attainment temperature of 100 ° C. or higher and lower than 200 ° C., and the softened region is 200 ° C. Heat up to a temperature reaching 300 ° C or lower,
It is preferable that the time during which the aluminum alloy plate stays at 100 ° C. or higher through the heating step and the cooling step is within 2 minutes.

  Further, in this case, in the heating step, it is preferable that a difference between the heating arrival temperature of the softened region and the heating arrival temperature of the non-softening region is 50 ° C. or more and 200 ° C. or less.

  In the heating step, the entire aluminum alloy plate may be preheated to a temperature not lower than 100 ° C. and lower than 200 ° C. and then heated only to the softened region to a temperature not lower than 200 ° C. and not higher than 300 ° C. Good.

  Moreover, at the said heating process, the temperature of the heating body which heats the softening area | region and the non-softening area | region in the said aluminum alloy plate may be controlled, respectively, and the said aluminum alloy plate may be heated by making the said heating body contact.

  Further, in the step of preparing the aluminum alloy plate, the Al—Mg—Si based aluminum alloy plate is solution treated, and the room temperature aging and 100 ° C. or less are applied to the solution treated Al—Mg—Si based aluminum alloy plate. The aluminum alloy plate may be prepared by performing at least one of artificial aging.

  The aluminum alloy plate contains Mg: 0.2-1.5 mass%, Si: 0.3-2.0 mass%, Fe: 0.03-1.0 mass%, Zn: 0.03-2. 5 mass%, Cu: 0.01-1.5 mass%, Mn: 0.03-0.6 mass%, Zr0.01-0.4 mass%, Cr0.01-0.4 mass%, Ti0.005-0.3 mass % And V: 0.01-0.4 mass% of one or more may further be contained, and the balance may be composed of Al and inevitable impurities.

The method for producing an aluminum alloy press-formed body according to the second aspect of the present invention,
A step of preparing an aluminum alloy blank using the aluminum alloy blank manufacturing method according to the first aspect of the present invention;
A pressing process for press-forming the prepared aluminum alloy blank;
Including
In the pressing step, strain of 2% or more is introduced into a portion of the aluminum alloy blank that becomes a product after completion of the pressing step.
It is characterized by that.

A post-molding aging step of subjecting the press-formed aluminum alloy blank to an artificial age hardening treatment at 170 to 185 ° C. for 20 to 30 minutes,
Further, it may be included.

  According to the present invention, it is possible to easily manufacture a press-molding aluminum alloy blank partially imparted with a strength difference. By using this blank, generation of wrinkles in press molding is effectively suppressed. be able to. Moreover, since the softening treatment can be performed in a pre-process before press molding or in a separate process, the time required for press molding itself can be shortened. Therefore, according to the present invention, it is possible to provide a method for manufacturing an aluminum alloy blank and a method for manufacturing an aluminum alloy press-molded body that can reduce the time required for press molding and suppress the occurrence of wrinkles in the blank by press molding. it can.

It is the graph which showed the relationship between the temperature difference (DELTA) T of the softening area | region in a linear expansion, and the non-softening area | region, the thermal stress (sigma), and the proportional limit (sigma) _P. It is a front view of the heating apparatus used for the heat processing of the preheating system in a softening process, (A) is a figure for demonstrating the preheating of the whole blank, (B) demonstrates the heating of a softening area | region. It is a figure for doing. It is a front view of the heating apparatus used for the heat processing of the simultaneous heating system in softening processing. It is a perspective view which shows an example of the punch of a press die. (A) is a figure which shows the wrinkles which generate | occur | produce in the area | region A of the press die of FIG. 4, (B) is the schematic diagram which showed the position of the generated wrinkles. (A) is the figure which displayed the principal stress of the tensile component obtained from the numerical analysis at the time of using the press die shown in FIG. 4 with the vector, (B) displayed the principal stress of the compression component with the vector. FIG. It is a schematic diagram which shows the vertical cross section parallel to the axial direction of the wrinkle of the area | region A in the time of a shaping | molding stroke 30mm (10 mmUP from a bottom dead center) using the press metal mold | die shown in FIG. FIG. 4 is a diagram showing the shape and dimensions of a test piece used in Example 2. It is the schematic diagram which showed the convex part of a wrinkle part which grasps the test piece of Example 2, the gauge distance L, and wrinkles. In Example 2, it is the schematic diagram which showed the method of measuring the wrinkle height hb of the convex part of a test piece using a 3-point dial gauge. It is the figure obtained from the numerical analysis which simulated the test of Example 2, (A) is the figure which displayed the principal stress of the tensile component by the vector, (B) is the figure which displayed the principal stress of the compression component by the vector. It is. FIG. 6 is a schematic diagram showing the position of a softening process area pattern of Example 2. (A) is the top view and front view which show the heating jig used in Example 2, (B) is the top view and front view which show the soft heat insulating material used in Example 2. FIG. In Example 2, it is the graph which showed the relationship of elongation (lambda) in the test mark distance L of the test piece after a test, and wrinkle height hb. In Example 3, it is the top view which showed the positional relationship with respect to the punch shape of three types of softening area | region patterns given to the blank. In Example 3, in order to evaluate the wrinkle which generate | occur | produced in the press molding, it is the schematic diagram which showed the position which measured the outline shape. (A) is a graph which shows the outline shape of the wrinkle generation | occurrence | production part measured about the press molding in Example 3, (B) is a graph which shows angle distribution. 6 is a schematic diagram showing a method for measuring a blank warpage amount in Example 3. FIG. It is the schematic diagram which showed the example of the metal mold | die shape which concerns on embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  As a result of repeating various experiments and studies to solve the above-mentioned problems, the present inventors have obtained an age-hardened Al—Mg—Si-based aluminum alloy plate, that is, room temperature aging after solution treatment, or solution treatment. A temperature higher than the melting temperature of fine precipitates that are gradually generated by room temperature aging on an Al-Mg-Si aluminum alloy sheet that is in the sub-aged state by artificial aging or an aging treatment that combines room temperature aging and artificial aging. We focused on the restoration phenomenon in which the material strength is lowered by cooling to 100 ° C. or lower after heating.

  As a result, when a wrinkle occurs in a press-molded body obtained by press-molding a blank made of an Al-Mg-Si-based aluminum alloy plate, or when the possibility is high, it corresponds to a site where this wrinkle occurs. A region including the region is previously defined as a softened region before press molding, and the softened region is heated at a temperature equal to or higher than the melting temperature of fine precipitates that are gradually generated by normal temperature aging, and then 100 ° C or lower. It has been found that wrinkle generation can be suppressed by using a blank in which the proof stress value of only the softened region is reduced by performing a softening process including a cooling step of cooling to a low temperature.

  Here, the restoration phenomenon, which is a softening means, will be described in more detail. In an Al-Mg-Si-based aluminum alloy plate, the alloy element is rapidly cooled after solution treatment and the alloy element is dissolved in supersaturation at room temperature, or at room temperature or slightly higher than this. If kept at a high temperature, the strength is increased by gradually forming low-temperature clusters, which are fine precipitates made of Mg and Si, in the matrix. This is a so-called “age hardening” state. The age-hardened plate is heated to a temperature higher than the above-mentioned holding temperature for a short time, so that the low-temperature cluster generated at room temperature is re-dissolved, and immediately after that, it is supersaturated by rapid cooling. A phenomenon that reduces the strength is restoration. A series of processes of rapid heating and subsequent cooling for causing such a phenomenon is referred to as “softening process”.

  The aluminum alloy blank for press forming according to the present embodiment is an Al-Mg-Si aluminum alloy plate, which has been subjected to solution treatment at a high temperature and is in an aging-precipitated state due to normal temperature aging, or a high temperature. After being solution-treated in step (1), an artificial aging or an aging treatment combining room temperature aging and artificial aging is applied and the material is in a sub-aging state. Below, it explains in detail according to main items.

<Component composition of aluminum alloy plate>
The aluminum alloy plate used for the production of the aluminum alloy blank may be basically an Al—Mg—Si alloy, and its specific component composition is not particularly limited. Is described. That is, Mg: 0.2 to 1.5 mass% (hereinafter simply referred to as “%”) and Si: 0.3 to 2.0% are contained as basic alloy elements, Fe: 0.03 to 1.0%, Zn: 0.03-2.5%, Cu: 0.01-1.5%, Mn: 0.03-0.6%, Zr: 0.01-0.4%, Cr : 0.01 to 0.4%, Ti: 0.005 to 0.3%, and V: 0.01 to 0.4%, further containing one or more, the balance Al and inevitable It is preferable to use an aluminum alloy made of mechanical impurities. Each component element will be described below.

Mg:
Mg is an alloy element that is the basis of the aluminum alloy in the present embodiment, and contributes to strength improvement in cooperation with Si. If the Mg content is less than 0.2%, the amount of β ″ phase that contributes to strength improvement by precipitation hardening during baking is reduced, so that sufficient strength improvement cannot be obtained. As a result, a coarse Mg—Si-based intermetallic compound is produced, and the formability, particularly the bending workability, is lowered, so that the Mg content is within the range of 0.2 to 1.5%. In order to improve the properties, in particular the bending workability, the Mg content is preferably in the range of 0.3 to 0.9%.

Si:
Si is an alloy element which is the basis of the aluminum alloy in the present embodiment, and contributes to strength improvement in cooperation with Mg. In addition, Si is produced as a crystallized product of metal Si during casting, and the periphery of the metal Si particles is deformed by processing and becomes a recrystallization nucleus generation site during solution treatment. It also contributes to If the Si content is less than 0.3%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 2.0%, coarse Si particles and coarse Mg—Si-based intermetallic compounds are produced, which leads to deterioration of moldability, particularly bending workability. Therefore, the Si content is within the range of 0.3 to 2.0%. In order to obtain a better balance between press formability and bending workability, the Si content is preferably in the range of 0.5 to 1.4%.

  Mg and Si are basic alloy elements as an Al—Mg—Si based aluminum alloy, but Fe: 0.03 to 1.0%, Zn: 0.03 to 2.5%, Cu: 0.01-1.5%, Mn: 0.03-0.6%, Zr: 0.01-0.4%, Cr: 0.01-0.4%, Ti: 0.005-0. It is preferable to contain 1 type (s) or 2 or more types selected from 3% and V: 0.01-0.4%. The reason for addition and the amount of addition will be described below.

Fe:
Fe is usually contained as an inevitable impurity of less than 0.03% in a general aluminum alloy. On the other hand, Fe is an element effective for strength improvement and crystal grain refinement, and in order to exert these effects, Fe may be positively added by 0.03% or more. However, if the content is less than 0.03%, the above effect cannot be obtained sufficiently. On the other hand, if the content exceeds 1.0%, moldability, particularly bending workability, may be deteriorated. Therefore, the amount of Fe in the case where Fe is positively added is preferably within a range of 0.03 to 1.0%.

Zn:
Zn is an element that contributes to improving the strength by improving the bake hardenability of coating and is effective for improving the surface treatment property. If the added amount of Zn is less than 0.03%, the above effects cannot be obtained sufficiently. On the other hand, if it exceeds 2.5%, moldability and corrosion resistance are lowered. Therefore, the Zn content is preferably within the range of 0.03 to 2.5%.

Cu:
Cu is an element added for improving formability and strength, and is preferably added in an amount of 0.01% or more for the purpose of improving formability and strength. However, if the Cu content exceeds 1.5%, the corrosion resistance (intergranular corrosion resistance, yarn rust resistance) deteriorates, so the Cu content is preferably regulated to 1.5% or less. When emphasizing strength improvement, the Cu content is preferably 0.4% or more, and when further improving corrosion resistance, the Cu content is preferably 1.0% or less. . Furthermore, when importance is attached to corrosion resistance, it is preferable not to add Cu positively and to regulate Cu content to 0.01% or less.

Mn, Zr, Cr:
These elements are effective for improving the strength, refining crystal grains, or improving the bake hardenability. If the Mn content is less than 0.03%, or the Zr and Cr contents are each less than 0.01%, the above effects cannot be obtained sufficiently. On the other hand, if the Mn content exceeds 0.6% or the Zr and Cr contents exceed 0.4%, not only the above effects are saturated but also a large number of intermetallic compounds are produced. There is a risk of adversely affecting moldability, particularly bending workability. Therefore, it is preferable that the Mn content is in the range of 0.03 to 0.6% and the Cr and Zr contents are in the range of 0.01 to 0.4%, respectively.

Ti, V:
Ti is an element effective for improving the strength and preventing corrosion by refining the ingot structure, and V is an element effective for improving the strength and preventing corrosion. If the Ti content is less than 0.005%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.3%, the ingot structure refinement and the anticorrosion effect due to the addition of Ti are saturated. On the other hand, if the V content is less than 0.01%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.4%, the anticorrosion effect by adding V is saturated. When the upper limit of Ti or V is exceeded, coarse Ti-based or V-based intermetallic compounds increase, resulting in deterioration of formability and bending workability. Therefore, it is preferable that the Ti content is in the range of 0.005 to 0.3% and the V content is in the range of 0.01 to 0.4%.

  In general aluminum alloys, B may be added at the same time as Ti to refine the ingot structure, and by adding B together with Ti, the ingot structure can be refined and stabilized. The effect becomes more remarkable. For this reason, you may add 500 ppm or less B with Ti.

<Method for producing Al-Mg-Si aluminum alloy plate>
The Al—Mg—Si-based aluminum alloy plate can be manufactured using a conventionally known method. Specifically, an Al—Mg—Si-based aluminum alloy ingot can be prepared by casting an aluminum alloy melt adjusted to a predetermined component by appropriately selecting a known melting casting method. Here, as the melt casting method, for example, a semi-continuous casting method (DC casting method), a thin plate continuous casting method (roll cast method or the like), or the like can be used.

  Next, the aluminum alloy ingot is homogenized at a temperature of 480 ° C. or higher. Homogenization treatment mitigates the microsegregation of alloy elements during solidification of the molten metal, and when various transition elements such as Mn and Cr are included, dispersed particles of intermetallic compounds containing these as the main components are matrixed. It is a process necessary for depositing uniformly and densely therein. The heating time for the homogenization treatment is generally 1 hour or more, and is terminated within 48 hours for economic reasons. However, since the heating temperature in this homogenization treatment is close to the heat treatment temperature for heating to the hot rolling start temperature before hot rolling, it is possible to perform the homogenization processing also as the pre-hot rolling heat treatment. Before or after this homogenization treatment process, after appropriate chamfering, hot rolling is started in a temperature range of 300 to 590 ° C., and then cold rolling is performed to produce an aluminum alloy plate having a predetermined thickness. To do. In the middle of hot rolling, in the middle of hot rolling and cold rolling, or in the middle of cold rolling, intermediate annealing may be performed as necessary.

Next, a solution treatment is performed on the aluminum alloy sheet after the cold rolling. This solution treatment is to dissolve Mg ₂ Si, elemental Si, etc. in the matrix, thereby imparting paint bake hardenability, and to improve the strength after the paint bake treatment performed after press molding. It is an important process. This process also contributes to lowering the distribution density of the second phase particles by solid solution of Mg ₂ Si, simple substance Si particles, etc., and improving ductility and bending workability. This is an important process for obtaining moldability. In order to exert these effects, the solution treatment temperature needs to be 480 ° C. or higher. In addition, since there exists a possibility that eutectic melting may arise when solution treatment temperature exceeds 590 degreeC, it is preferable to set it as 590 degrees C or less.

  The solution treatment can be efficiently performed, for example, by continuously passing a cold rolled sheet wound in a coil shape through a continuous annealing furnace having a heating zone and a cooling zone. In the treatment by the continuous annealing furnace, the aluminum alloy plate is heated to a high temperature of 480 ° C. or more and 590 ° C. or less when passing through the heating zone, and then rapidly cooled when passing through the cooling zone. Through such a series of treatments, Mg and Si, which are the main alloy elements of the aluminum alloy plate, are dissolved in the matrix by the temperature rise, and then rapidly cooled to be in a state of being supersaturated at room temperature.

  In order to impart high paint bake hardenability to the Al-Mg-Si-based aluminum alloy plate, after pre-cooling in the solution treatment, a preliminary aging treatment may be performed at a temperature of about 60 to 100 ° C for about 1 to 24 hours. Good. As a result, a high-temperature cluster different from the low-temperature cluster generated at room temperature described above can be generated and grown. High-temperature clusters are fine precipitates composed of Mg and Si, and are generated at a temperature slightly higher than room temperature. This high-temperature cluster undergoes age hardening by transition to the β ″ phase, which is a precipitation strengthening phase, by a subsequent paint baking process (for example, heating performed at about 170 ° C. for about 20 minutes), and the proof stress is 190 MPa or more. To improve.

<Aging between solution treatment and softening treatment>
In order to give a strength difference between the softened region and the non-softened region of the aluminum alloy blank by softening treatment, a certain amount of low-temperature clusters are generated by room temperature aging (natural aging) during the room temperature standing period after solution treatment. Need to be. If the low-temperature cluster is not sufficiently generated, the restoration phenomenon does not occur in the subsequent softening process, and the yield strength is not lowered.

  Therefore, after the solution treatment, it is necessary to leave at room temperature for one day or more before performing the softening treatment. In addition, the normal temperature standing period from solution treatment to press molding is generally 10 days or more. In addition, although this room temperature aging rapidly proceeds in the initial stage after the solution treatment, it does not progress further after about half a year, so there is no particular upper limit for the room temperature standing period before the softening treatment. Here, room temperature specifically means a temperature in the range of 0 to 50 ° C.

  In the above description, normal temperature aging has been described as aging after solution treatment. However, the aging after the solution treatment is not limited to the one that performs only normal temperature aging, and artificial aging may be performed, or room temperature aging and artificial aging may be combined. By using artificial aging, a low temperature cluster can be generated at an early stage, and also in this case, a strength difference can be imparted to the blank by subsequent softening treatment.

  However, the temperature of artificial aging is preferably 100 ° C. or less, and the Al—Mg—Si aluminum alloy sheet must be in a sub-aging state after the artificial aging treatment. When the temperature of artificial aging exceeds 100 ° C., or when artificial aging is performed for a long time even under conditions of 100 ° C. or less and peak aging or an overaging state exceeding this is reached, it is composed of Mg and Si. Precipitates are deposited excessively. For this reason, the solid solution amount of Mg and Si is reduced, and the paint bake hardenability is significantly lowered. Here, when giving high paint bake hardenability to an Al-Mg-Si type aluminum alloy plate, it is necessary to give artificial aging after the above-mentioned preliminary aging treatment. High-temperature clusters can be generated in a state where there are enough atomic vacancies formed by solid solution of Mg and Si in the matrix by solution treatment, that is, in a state where the atomic vacancy density is high. This is because a high-temperature cluster cannot be generated after the cluster is generated.

  When performing the next softening treatment by performing the aging as described above, it is desirable that the proof stress value is 110 MPa or more as the material strength of the aluminum alloy plate immediately before the softening treatment. When the proof stress value is less than 110 MPa, the strength of the portion to be restored in the subsequent softening treatment is insufficiently lowered, and there is a possibility that a sufficient strength difference cannot be imparted.

<Softening treatment>
The softening treatment is a treatment in which an arbitrarily selected region in the age-hardened Al—Mg—Si based aluminum alloy plate as described above is heated to a predetermined temperature and then cooled to 100 ° C. or lower. In the softening treatment, the strength of the aluminum alloy plate can be reduced by the following mechanism. That is, low temperature clusters composed of Mg and Si are generated and grown in the matrix during standing at room temperature after the solution treatment, thereby increasing the material strength. Since the low temperature clusters are thermally unstable, when the aluminum alloy plate in this state is heated to a predetermined temperature for a short time, the low temperature clusters easily re-dissolve and disappear (restore). For this reason, the material strength after cooling to 100 ° C. or less by the softening treatment is lower than before the softening treatment.

<Heating conditions for softening region>
The heating conditions in the softening treatment were such that the temperature reached by heating was in the range of 200 ° C. to 580 ° C. This is because, when the heating attainment temperature is lower than 200 ° C., the amount of low temperature clusters dissolved in a short time is small, so that the strength reduction due to restoration is small, and when the heating attainment temperature exceeds 580 ° C., local melting occurs.

  In particular, by setting the heating ultimate temperature in the softened region to be in the range of 200 ° C. or higher and 300 ° C. or lower, the blank after the softening treatment can have high paint bake hardenability. When the heating attainment temperature is lower than 200 ° C., the amount of low-temperature clusters dissolved in a short time is small, so that the strength reduction due to restoration is small. On the other hand, when the temperature reached by heating exceeds 300 ° C., Mg and Si in the matrix are precipitated as a β ′ phase that is a coarse precipitation phase in a short time. Thereby, the solid solution amount of Mg and Si in the aluminum alloy plate is reduced, and the strength increase in the subsequent artificial age hardening treatment is reduced. That is, the paint bake hardenability which is an excellent feature of the Al—Mg—Si based aluminum alloy is lowered.

  Further, in the range of the heating attainment temperature of 200 ° C. or more and 300 ° C. or less, the higher the heating attainment temperature, the more efficiently the low-temperature cluster is re-dissolved, so that the amount of decrease in strength also increases. However, since age hardening also occurs at the same time, the ductility of the material is reduced.Therefore, considering the balance between imparting a difference in strength and lowering the ductility, depending on the shape of the molding, that is, depending on the state and degree of occurrence of wrinkles, Choose the best.

  Here, in the case where the heating attainment temperature is in the range of 200 ° C. or more and 300 ° C. or less, when the heating attainment temperature is in the range of 250 ° C. or more and 300 ° C. or less, the low temperature composed of Mg and Si within a short time of several seconds. Immediately after the cluster is sufficiently solid-solved and the restoration is completed and the cluster is cooled to 100 ° C. or less at a predetermined cooling rate, a large strength difference can be imparted between the heated part and the non-heated part. However, when heating is performed in this temperature range, many atomic vacancies remain at room temperature after cooling. These atomic vacancies promote the diffusion of Mg and Si while maintaining the room temperature in the softened part and accelerate the generation of low temperature clusters at room temperature. The proof value once lowered in this part is a few days at room temperature. If left unattended, it quickly returns to the state before the softening treatment. This atomic vacancy density increases as the heating temperature increases, and as the atomic vacancy density increases, the proof stress increases at room temperature. Such rapid recovery of the proof stress value means an early decrease in the wrinkle suppression effect. Therefore, in order to obtain a stable effect, it is preferable to perform press molding as short as possible after the softening treatment. Specifically, 3 days or less is desirable.

  On the other hand, when heat treatment is performed at a heating attainment temperature of 200 ° C. or more and less than 250 ° C., the amount of decrease in the proof stress value is less than when the heating attainment temperature is 250 ° C. or more and 300 ° C. or less. However, the density of atomic vacancies at room temperature after cooling is sufficiently low, and the increase in the proof stress over time during the room temperature holding period after the softening treatment is sufficiently small. Therefore, when the softening treatment is performed with the heating temperature within a temperature range of 200 ° C. or higher and lower than 250 ° C., a stable wrinkle suppressing effect can be exhibited even when held at room temperature for several days. Therefore, when importance is attached to the flexibility of the schedule of the production process, the heating reached temperature of the softening process is set to 200 ° C. so that press forming can be performed even if the blank is held at room temperature for several days after the softening process. It is preferable that the temperature is lower than 250 ° C. In this case, the normal temperature holding period from the softening treatment to press molding is preferably within 10 days.

  Moreover, when making the blank after a softening process high coating bake hardenability, the one where the temperature increase rate from 100 degreeC to a heating attainment temperature is as fast as possible is preferable, specifically 5 degreeC / second or more is preferable. When the rate of temperature rise is less than 5 ° C / sec, the high temperature cluster is generated and grown, and then the high temperature cluster transitions to the β "phase, which is a precipitation strengthening phase, which increases the strength contrary to the original purpose. In addition, ductility may be reduced, and from the viewpoint of productivity, it is preferably as fast as possible, more preferably 10 ° C./second or more. The holding time after reaching the temperature is preferably as short as possible, specifically 20 seconds or less If the heating region can be heated uniformly, the holding time is 0 seconds (cooling immediately after reaching the predetermined temperature without staying) Yes).

<Heating conditions for non-softening region>
The main purpose of positively heating the non-softening region is to minimize the difference in the heating temperature between the softening region and the non-softening region as much as possible, and to suppress excessive thermal deformation of the blank. However, in order to give a strength difference to the blank, which is the original purpose of the softening treatment, the non-softened region is required to have no strength reduction or to have a strength reduction as small as possible. Therefore, the heating ultimate temperature in the non-softening region is preferably 100 ° C. or higher and lower than 200 ° C. If it is less than 200 degreeC, since a low temperature cluster hardly melt | dissolves in a short time, intensity | strength fall will hardly arise. Moreover, if it is 100 degreeC or more, it is because the difference with the heating reached temperature of the area | region which performs a softening process does not become excessive. However, even within the above temperature range, if kept at that temperature for a long time, the low temperature cluster may melt and soften, or age hardening may occur and the strength may increase and the elongation may decrease. Therefore, the time during which the blank stays at 100 ° C. or higher throughout the entire softening treatment is preferably within 2 minutes. If the temperature is lower than 100 ° C., the transition to the β ″ phase does not occur, and the progress of age hardening is extremely slow. Even if it is gradually cooled thereafter, the mechanical properties are not affected.

<Difference in heating temperature between softened region and non-softened region>
It is preferable that the difference in the heating temperature between the softened region and the non-softened region in the softening treatment is 50 ° C. or higher and 200 ° C. or lower. The purpose of heating the non-softened region is to suppress excessive thermal deformation of the blank by selecting a difference between the heating arrival temperatures of the softened region and the non-softened region within an appropriate range. Moreover, a slight gap is formed between the blanks when the blanks are stacked by positively applying a slight thermal deformation to the blanks. Thereby, it is also possible to improve the separation between the blanks loaded during press molding. The thermal deformation mentioned here is the deformation such as warp and twist generated in the blank due to the thermal strain at the boundary between the softened area and the non-softened area due to the difference in thermal expansion between the softened area and the non-softened area during heating. Point to. Since the shape and size of the molded product and the blank that are actually press-molded are various, here, a concept that is simplified and treated as one-dimensional linear expansion will be described below.

When a rod of length L is heated and the temperature rise is ΔT ° C., if the linear expansion coefficient of the material is α, the increase in length of the rod can be expressed as ΔL = αLΔT. For example, when both ends of the rod are constrained by a rigid wall, the rod cannot be stretched, so that it is subjected to a compressive strain ε = αΔT in the axial direction. This compressive strain is thermal strain. In the elastic deformation region, the thermal stress σ = αEΔT after heating can be obtained from the thermal strain ε and the longitudinal elastic modulus E by the Hooke's law σ = Eε. When the thermal stress σ exceeds the limit of elastic deformation, that is, the proportional limit (yield stress) σ _P in the stress-strain diagram, plastic deformation occurs, so-called thermal deformation remains.

  In this embodiment, since the softened region is an arbitrary part of the blank, the periphery of the softened region may be surrounded by the non-softened region in some cases. By heating the softened region to a temperature higher than that of the non-softened region, the softened region is thermally expanded, and thermal stress is generated at the boundary between the softened region and the non-softened region. The thermal stress generated at the boundary between the softened region and the non-softened region due to the expansion of the non-softened region to the surroundings due to the thermal expansion of the softened region is smaller than the value of the above example of the rod constrained by the rigid wall. Become.

Accordingly, the temperature difference ΔT at which plastic deformation starts due to the thermal stress σ in the state where there is no displacement between the softened region and the non-softened region, which is the condition for the greatest thermal stress, was determined as follows. It is known that the strength and the longitudinal elastic modulus E decrease as the temperature of the material increases. The longitudinal elastic modulus E of the Al—Mg—Si based aluminum alloy having the above component composition range is about 66.4 GPa at room temperature. It is about 56.8 GPa at 200 ° C. which is the lowest temperature of the region, and about 47.5 GPa at 300 ° C. which is the highest temperature of the softened region. On the other hand, the proportional limit σ _P was subjected to a tensile test using a JIS No. 5 test piece at each temperature, and obtained from the obtained stress-strain diagram. As a result, it was about 90 MPa at normal temperature and the lowest temperature in the softening region was 200. It was about 73 MPa at 300 ° C. and about 70 MPa at 300 ° C., which is the maximum temperature in the softened region.

The relationship between the temperature difference ΔT and the thermal stress sigma softening region and the non-softened area by using these values, the result of obtaining a relation between the proportional limit sigma _P shown in FIG. As shown in the figure, the thermal stress applied to the softened region heated to 200 ° C. reaches a proportional limit when the temperature difference is about 50 ° C. (the non-softened region is about 150 ° C.). On the other hand, the thermal stress applied to the softened region heated to 300 ° C. reaches a proportional limit when the temperature difference is about 58 ° C. (the non-softened region is about 242 ° C.). However, as described above, the heating ultimate temperature in the non-softening region is 100 ° C. or higher and lower than 200 ° C., so that at least the temperature difference is larger than 100 ° C. Therefore, since the minimum temperature difference necessary to impart a slight thermal deformation to the blank is 50 ° C. or more, the difference in the ultimate temperature in the softening treatment and the non-softening region is 50 ° C. or more. preferable. Further, the upper limit of the difference in the heating temperature is preferably 200 ° C. or less, which is the difference between the maximum temperature of 300 ° C. in the softened region and the minimum temperature of 100 ° C. in the non-softened region.

<Cooling conditions>
In the case where the blank after softening treatment is provided with high paint bake hardenability, the cooling rate to 100 ° C. in cooling after heating is preferably as fast as possible, specifically 5 ° C./second or more. When the cooling temperature is less than 5 ° C./second, the high temperature cluster is generated and grown, and then the high temperature cluster transitions to the β ″ phase, which is a precipitation strengthening phase, which increases the strength contrary to the original purpose. In addition, ductility may also be reduced, and from the viewpoint of productivity, it is preferably as fast as possible, and more preferably 10 ° C./second or more. Although the upper limit is not particularly defined, a cooling rate of about 1000 ° C./second can be obtained if the method is immersed in a water bath.

<Heating method for softening treatment>
The heat treatment of the present invention can be roughly divided into two methods. One is a preheating method in which only the softened region is further heated at the restoration temperature in a state where the entire blank is preheated below the restoration temperature in advance. The other is a simultaneous heating method in which the temperatures of the heating bodies corresponding to the softened region and the non-softened region are individually controlled and both regions are heated simultaneously by pressing the heated body against the blank.

  As the preheating heating method, first, the entire blank is heated to an ultimate temperature of 100 ° C. or higher and lower than 200 ° C. Since this is a heating at a temperature that does not recover in a short time, it is acceptable even if the heating rate is somewhat slow, but from the viewpoint of productivity, it is desirable to select a method with the fastest heating rate as much as possible. Accordingly, it is preferable to use a method of transferring heat by contacting / pressing a metal plate or metal block heated by a heater or the like, or a method of induction heating, infrared heating, current heating or the like. In addition, as long as the time from when the temperature is raised to 100 ° C. or higher to the start of cooling can be made 2 minutes or less, known heating means such as furnace heating or hot air heating may be used as appropriate.

  Next, as a method of heating only the softened region, heat a metal plate or metal block (aluminum alloy, copper alloy, etc.) processed according to the shape of the part to be heated with a heater to contact the part to be heated.・ The method of transferring heat by applying pressure is the simplest. In addition to this, a black body such as carbon having a higher heat emissivity (heat absorption rate) than that of an aluminum alloy plate is processed according to the shape of the portion to be heated, and this is applied to the portion to be heated and heated by infrared rays. In addition, the region where the black body is pasted can be heated to a high temperature instantaneously.

  Here, a specific example of the preheating method will be described. As shown in FIG. 2, as a heating device, a hydraulic lower press 25 in which a pressing lower die 25 incorporating a heater 26 is mounted on a bolster 22, and a pressing upper die 24 also including a heater 26 is mounted on a slide plate 21. Use the machine. The pressing lower mold 25 is supported by a cushion pin 23, and a predetermined pressing pressure can be maintained by a cushion mechanism (not shown) during pressing. On the other hand, the pressing upper die 24 is attached to the slide plate 21 via a hard heat insulating material 27. A heating jig 28 made of a metal plate processed to be convex (convex portion 28a) in the softened region and concave in the non-softened region is attached to the lower surface of the pressing upper die 24. Further, a soft heat insulating material 33 (thick) slightly protruding from the top surface of the convex portion 28 a of the heating jig 28 is attached to a portion corresponding to the non-softening region of the heating jig 28. The heater 26 is controlled by a temperature control device (not shown) so as to maintain each set temperature, and heats the lower pressing mold 25 and the upper pressing mold 24 to respective predetermined temperatures. The heating jig 28 attached to the lower surface of the pressing upper mold 24 is heated by heat transfer as the pressing upper mold 24 is heated.

  As a method of heating using this heating device, as shown in FIG. 2 (A), first, a blank 1 is placed on the pressing lower mold 25, and the blank 1 is pressed more than the blank 1. A hard heat insulating material 27 having a large projected area in the direction and having a thickness that does not cause cracks or the like due to pressurization by a press is placed. Subsequently, the slide plate 21 is lowered by the press mechanism of the press machine, whereby the convex portion 28a of the heating jig 28 and the soft heat insulating material 33 attached to the lower surface other than the convex portion 28a are placed on the blank 1. It contacts the heat insulating material 27. Pressurization by the press machine is held at a constant load by a cushion mechanism, and pressurizing the blank 1 for a certain period of time, the heat of the pressing lower mold 25 is transferred to the blank 1, and the blank 1 is a predetermined temperature of 100 ° C. or higher and lower than 200 ° C. Heated to a temperature of On the other hand, the heat of the pressing upper mold 24 is not transmitted to the blank 1 by the hard heat insulating material 27. This completes the preheating.

  Next, as shown in FIG. 2 (B), the hard heat insulating material 27 placed on the blank 1 is removed. Subsequently, the slide plate 21 is lowered by the press mechanism of the press machine, whereby the convex portion 28 a of the heating jig 28 and the soft heat insulating material 33 attached to the lower surface other than the convex portion 28 a come into contact with the blank 1. Pressurization by the press machine is held at a constant load by the cushion mechanism, and by pressurizing the blank 1 for a certain period of time, the heat of the pressing upper die 24 is transmitted to the blank 1 through the convex portion 28a of the heating jig 28, Only the softened region 29 is heated to a predetermined temperature (see the shaded portion in FIG. 2B). At this time, the heat of the pressing upper die 24 is not transmitted to the region other than the softened region (non-softened region) because the soft heat insulating material 33 is in contact (see the hatched portion in FIG. 2B). This completes the heating of the softened region.

  As described above, it is preferable to attach the soft heat insulating material 33 to the lower surface of the heating jig 28 other than the convex portion 28a. When the soft heat insulating material 33 is not provided or when the soft heat insulating material 33 is thinner than the height of the convex portion 28a of the heating jig 28, the range in which the hard heat insulating material 27 placed on the blank 1 is pressurized by preheating is heated. Only the convex portion 28a of the jig 28 is provided, and the entire blank 1 is not heated uniformly. Further, when the softened region is heated, the blank 1 is likely to have a pressing mark at the edge of the convex portion 28 a of the heating jig 28. Further, when a hard heat insulating material is used instead of the soft heat insulating material 33, it is necessary to strictly control the thickness of the heat insulating material. If the thickness of the hard heat insulating material is thicker than the height of the convex portion 28a of the heating jig 28, There is a possibility that the convex portion 28a of the jig 28 cannot contact the blank and the softened region cannot be heated. By using the soft heat insulating material 33 that is slightly thicker than the height of the convex portion 28a of the heating jig 28, the soft heat insulating material 33 is compressed during pressing and becomes flush with the top surface of the convex portion 28a of the heating jig 28. Uniform pressure and heat insulation effects can be obtained.

  As a specific example of the simultaneous heating method, as shown in FIG. 3, a hydraulic press machine in which a plurality of heating bodies 30 </ b> A and 30 </ b> B incorporating a heater 26 are attached to a pressing upper die 24 is used as a heating device. . In this heating apparatus, as in the hydraulic press shown in FIG. 2, the lower pressing mold 25 is mounted on the bolster 22, and the pressing upper mold 24 is mounted on the slide plate 21. The pressing lower die 25 is supported by a cushion pin 23, and can hold a predetermined pressing pressure by a cushion mechanism (not shown) during pressing, and a hard heat insulating material 27 is attached to the upper surface thereof. On the other hand, the pressing upper die 24 is attached via a hard heat insulating material 27, and heating bodies 30A and 30B made of metal blocks processed according to the heating region are attached to the lower surface of the pressing upper die 24. The heaters 30A and 30B have a built-in heater 26, and the heater 26 is controlled by a temperature control device (not shown) so as to maintain the set temperatures of the respective heaters 30A and 30B.

  As a method of heating using this heating device, first, the blank 1 is placed on the hard heat insulating material 27 on the pressing lower mold 25. Subsequently, the heating plates 30 </ b> A and 30 </ b> B come into contact with the blank 1 by lowering the slide plate 21 by the press mechanism of the press machine. Pressurization by the press is held at a constant load by the cushion mechanism, and pressurizing the blank 1 for a certain period of time causes the heat of the heating bodies 30A and 30B to be transferred to the blank 1 so that the blank 1 is heated to a predetermined temperature.

  In addition, as the pressing pressure of the heating jig 28 or the heating bodies 30A and 30B to the blank 1 in the case of heat transfer heating, 0.1 MPa or more is preferable for efficient heat transfer, and at 0.5 MPa or more, the heat transfer efficiency is Since it is almost constant, there is no particular upper limit. These heating may be performed one by one in the state of a plate, or the coiled aluminum alloy plate material may be continuously heat-treated and cut by a blanking press.

  In the above description, it is assumed that the non-softened region is heated. However, when thermal deformation of the blank does not matter, only the softened region may be heated without heating the non-softened region.

<Cooling method for softening treatment>
As a method of cooling the blank after heating it to a predetermined temperature, a contact type method such as die quenching, which has a larger heat capacity than the blank and further sandwiches the blank with a metal block with built-in water-cooled piping, is used for cooling rate and productivity. It is effective from the viewpoint. In addition, known cooling means such as a water cooling method such as immersion or shower, an air cooling method such as a fan, and the like may be used and combined as appropriate.

<Softening area>
The object of the present invention is to suppress the generation of wrinkles in the blank due to press forming. As described at the beginning, wrinkles in press forming are caused by the buckling deformation generated in the blank by press forming up to the bottom dead center. It is the distortion of the surface that remains without being erased. The cause of this buckling deformation is the principal stress of the compression component generated by the non-uniform tensile force acting on the blank plate surface during molding.

  Therefore, consider reducing the principal stress of the compression component around the area where wrinkles occur. The method is softening, that is, lowering the yield strength, and by reducing the yield strength in the region including the wrinkle generating portion, the punching force, that is, the processing force required for molding, is reduced, and the principal stress of the compression component that causes buckling deformation Becomes smaller. In addition, the region where wrinkles are generated generally has a smaller amount of plastic deformation than the periphery thereof and often has a non-uniform stress distribution. Therefore, by limiting the softened region to this region, the amount of plastic deformation in this region increases, and by uniforming the amount of plastic deformation in the surrounding area including this region, the non-uniform stress distribution is also eliminated and compression is performed. Generation of main stress of the component is also suppressed. Further, by limiting the softening region to this region, the strength around the punch shoulder, which is mainly important in drawing, can be kept high, so that the formability against breakage is not impaired. Therefore, in this embodiment, the region where the wrinkle of the press-formed body is likely to be generated is set as the softened region.

  The softened region preferably includes a region where the main stress of the compression component is generated on the inner side and is slightly larger than that. Since the area where the principal stress of the compression component obtained from numerical analysis etc. occurs and the area where wrinkles actually occur may differ, observing only the wrinkle occurrence state and determining the softening area may have little effect. Because there is.

  Here, a method for obtaining a region where the main stress of the compression component is generated will be described. One is numerical analysis such as a finite element method using a computer. Due to the dramatic improvement in computer processing speed in recent years, it has become common to perform a press molding simulation by numerical analysis before manufacturing a press mold. If this is used, it is possible to easily know the state of stress and strain generated in the blank during press molding. By inputting boundary conditions such as mold shape data, material characteristic values, and friction coefficient, the area where the principal stress of the compression component around the area where wrinkles actually occurred is obtained, or the compression component is pre-pressed before press molding. It is possible to identify a dangerous area where wrinkles are likely to occur by obtaining a region where the main stress is generated.

  Moreover, as a method other than the numerical analysis, there is a method of obtaining a region where the main stress of the compression component is indirectly generated by measuring the compressive strain generated in the aluminum alloy blank by press forming. For example, there is a method known under the name of the scribed circle test. That is, a pattern in which circles of a certain diameter (for example, 10 mm) are regularly arranged is drawn on the surface of a blank before press molding by ink or etching, and the change of the circle diameter after molding is expressed as a major axis and a minor axis. This is a method of measuring the strain in two directions on the plate surface by reading with. Here, when the circle diameter after press molding becomes smaller than the original diameter, it can be considered that compressive strain has occurred, and it can be considered that the main stress of the compression component has occurred there.

  However, in the case of a complicated shape such as an automobile body panel, the magnitude and direction of the stress generated in the blank during press molding changes every moment. The strain value measured as described above for the press molded body molded to the bottom dead center of the press is the integrated value of the strain that has been continuously deformed so far, so it is the compression that causes wrinkles. It is difficult to specify the region where the principal stress of the component has occurred. Therefore, it is preferable to measure the change in strain in the stroke before and after the wrinkle during the molding stroke (during press molding) occurs.

  FIG. 4 is a perspective view showing an example of a punch of a press molding die. A die or a blank holder having a shape corresponding to the punch 2 shown in FIG. 4 is used. In a press-molded body that is press-molded by using the punch 2 shown in FIG. 4, wrinkles as shown in FIG. 5 may occur in a region A (region surrounded by a broken line) in FIG.

  The inventor simulated press forming using the punch 2 shown in FIG. 4 by using a dynamic explicit method of numerical analysis software “LS-DYNA” based on the nonlinear finite element method. As conditions for the simulation, the blank is an AA6022 alloy plate with a thickness of 1 mm, physical property values (density, Young's modulus, Poisson's ratio), work hardening characteristics (stress-strain curve obtained from a tensile test), and anisotropic characteristics (rolling direction). The r value in three directions (0 °, 90 °, 45 °) was input, and Barlat'89 (index m = 8) was used as the yield function. As for the shape of the mold, CAD data of three parts of a punch, a die, and a blank holder was input, and the friction coefficient between the blank and the mold was set to 0.15. The molding stroke to the bottom dead center was 40 mm.

  According to this simulation, when press molding was performed with a die cushion load (DC load) of 100 kN, wrinkles occurred in the region A at a stroke of 30 mm (10 mm UP from bottom dead center). FIG. 6A shows a diagram in which the principal stress of the tensile component around the wrinkle generating portion at this time is displayed as a vector, and FIG. 6B shows a diagram in which the principal stress of the compression component is displayed as a vector. Here, the direction and magnitude of the arrow in the figure represent the direction and magnitude of the main stress.

  When the wrinkles generated in this region A are targeted, the region where the tensile force parallel to the wrinkle axial direction acts in the direction perpendicular to the wrinkle axial direction is approximately XX shown in FIG. It is a range. In other words, the range of XX in FIG. 6A is a region where a tensile force that generates a main stress of a compression component that causes wrinkles acts. This tensile force generates a main stress of a compressive component that causes wrinkles as shown in FIG. In this mold shape, the main stress of the compression component was generated within the range of XX and beyond the outside. As described above, generally, the principal stress of the compression component may be generated in a region where a tensile force parallel to the axial direction of the wrinkle acts and outside the region. Therefore, the softened region is preferably a region wider than the region where the tensile force acts in the direction perpendicular to the direction of the tensile force acting that generates the main stress of the compression component.

  Further, if the softened region is extremely narrow, there will be an abrupt strength difference in the narrow region, and stress concentration will occur there, making it easy to break. Therefore, by taking a softened region wider as described above, an effect of avoiding breakage is obtained and a wrinkle suppressing effect is increased. However, it is preferable not to include in the softened region the risk of fracture, such as punch shoulders, die shoulders, and vertical wall portions, where stress concentration tends to occur.

  Further, FIG. 7 shows a vertical sectional view parallel to the wrinkle axial direction of the region A in FIG. 4 at a molding stroke of 30 mm (10 mm UP from bottom dead center). The fulcrum on which the tensile force that generates the main stress of the compression component causing wrinkles acts is the upper punch shoulder 6A and the lower die shoulder 7B, and the region between these fulcrums corresponds to the YY region in the blank. That is, the region between the punch shoulder 6A and the die shoulder 7B that is pulling the region of the blank when the wrinkle is generated. The principal stress of the compression component that causes wrinkles is generated in this region. If the softening region is exceeded beyond this region, the strength of the material around the punch shoulder 6A and the die shoulder 7B, which is the portion pulling the blank, will be reduced, and this portion will easily break. End up. Therefore, the softened region is preferably a region narrower than the region between the fulcrums on which the tensile force acts with respect to the acting direction of the tensile force that generates the principal stress of the compression component that causes wrinkles in the plate surface.

<Blank oil>
Usually, the aluminum alloy plate is coated with rust preventive oil or the like in order to prevent scratches and corrosion during transportation. Heating the oil-coated plate in this way may cause oil seizure and smoke generation, which may cause poor appearance of the press-formed product and deterioration of the working environment. Therefore, the plate subjected to the softening treatment is pre-greased before removing the rust-preventing oil by a degreasing process or the like, or it is packed in an oil-free state so as not to be damaged during transportation. Are preferably used. However, this is not the case when the plate is coated with oil having a characteristic that does not cause smoke or ignition even at the heating temperature of the softening treatment.

  In addition, when the softening treatment is performed in an uncoated oil state, the press forming performed after the softening treatment requires a press lubricant, so the softened plate is subjected to the press forming lubricant as usual. It is preferable to perform press molding after applying an appropriate amount of oil.

<Press molding>
The press molding performed on the blank subjected to the above softening treatment can be performed cold as in the case of normal press molding. However, it is preferable to perform press molding within 10 days after the softening treatment as described above. More preferably, it is performed within 3 days. This is because, after the softening treatment, the softened state is maintained for a while, but the strength increases again due to normal temperature aging, and the strength difference imparted to the blank is lost.

  Moreover, it is preferable that a strain of 2% or more is introduced into the blank after the press process is completed. This is because if the strain to be introduced is less than 2%, the amount of increase in the yield strength due to work hardening is small, and a high strength of 190 MPa or more may not be obtained by the subsequent artificial age hardening treatment.

<Artificial age hardening treatment>
In the automobile manufacturing process, several press-formed bodies obtained by press-molding a blank are joined together to produce a car body, and this car body is subjected to paint baking treatment. The strength can be increased by applying to the Al—Mg—Si aluminum alloy plate after the crystallization treatment. This is called artificial age hardening treatment. The above-described paint baking process is mainly intended to bake the paint applied to the vehicle body, and is generally performed at 170 to 185 ° C. for 20 to 30 minutes in consideration of productivity.

  In the press-molded body obtained by subjecting the blank subjected to the softening treatment to press molding according to the present embodiment, the yield strength value after the artificial age hardening treatment of the softening treatment portion is preferably 190 MPa or more. When the proof stress value is less than 190 MPa, the dent resistance and the impact strength are insufficient, so that the plate thickness must be increased, resulting in an increase in the weight of the vehicle body and an increase in material costs.

  The conditions for the artificial age hardening treatment applied to the press-molded body are preferably 20 to 30 minutes at 170 to 185 ° C., which is a general paint baking treatment condition in the automobile manufacturing process. The blank made of an aluminum alloy manufactured by the manufacturing method according to the present embodiment can improve the proof stress value of the press-formed body including the softened region to 190 MPa or more even by such heat treatment at a relatively low temperature for a short time. In addition, when the temperature and temperature are longer than these processing conditions, the proof stress value further increases.

  In the softening region described above, the low temperature clusters dissolve in the heat treatment, and the atomic vacancy density increases again, so that high temperature clusters are generated and grow instead of the low temperature clusters. This high-temperature cluster transitions to β ″, which is a precipitation strengthening phase, by heating in the artificial age hardening treatment, so that it is possible to impart high yield strength to the press-molded body. Therefore, the above-mentioned softened region becomes a non-softened region. On the other hand, since higher paint bake hardenability can be obtained, even after the proof stress value is lowered by the softening treatment, a high strength of 190 MPa or more in proof stress value can be obtained by the heat treatment.

(Example)
Examples of the present invention are described below together with comparative examples. The following examples of the present invention are for explaining the effects of the present invention, and the processes and conditions described in the examples of the present invention do not limit the technical scope of the present invention.

  The aluminum alloy was melted and the components were adjusted, and then cast by the DC casting method to produce aluminum alloy ingots having five types (I to V) of alloy components shown in Table 1. These ingots were homogenized at 530 ° C. for 10 hours, then hot-rolled and cold-rolled according to conventional methods, solution treated at 530 ° C., rapidly cooled to room temperature, and 10% at 70 ° C. A time-preliminary aging treatment was applied to produce an aluminum alloy plate having a thickness of 1.0 mm.

  Thereafter, aging treatment was performed by normal temperature aging, artificial aging of 100 ° C. or less, or a combination thereof. Table 2 shows the aging treatment conditions.

[Example 1]
As a first test, in order to investigate the influence of the softening treatment conditions on the mechanical properties of the aluminum alloy plate, a JIS No. 5 tensile test piece was prepared from the above-aged aluminum alloy plate, and the softening treatment was performed by changing the conditions. Was carried out by the following procedure.

  As the heating device for heating the test piece, the above-described device shown in FIG. 2 was used. Note that a hydraulic press having a press capacity of 50 TON was used as the heating device. In this test, since partial heating is not performed, the heating jig 28 and the soft heat insulating material 33 in FIG. 2 are not used.

  The test piece was preheated using this heating apparatus. First, as shown in FIG. 2A, the test piece 1 was placed on the pressing lower mold 25, and a hard heat insulating material 27 having a thickness of about 25 mm was placed on the test piece 1. The upper die 24 for pressing comes into contact with the hard heat insulating material 27 on the test piece 1 by lowering the slide plate 21 by the press mechanism of the press machine. Then, the test piece was preheated by applying a predetermined pressing pressure to the test piece 1 over a predetermined time by the cushion mechanism of the press machine.

  Next, as shown in FIG. 2B, the hard heat insulating material 27 placed on the test piece 1 is removed. Subsequently, the upper die 24 for pressing comes into contact with the test piece 1 by lowering the slide plate 21 by the press mechanism of the press machine. Then, the softening region was restored and heated by applying a predetermined pressing pressure to the test piece 1 over a predetermined time by a cushion mechanism of the press machine. In this restoration heating process, the time from when the pressing upper mold 24 comes into contact with the test piece 1 until it is separated is adjusted by the slide speed and the press stroke, and the heating rate is determined by the heating temperature of the heater and the pressing pressure ( = Cushion pressure).

  Subsequently, the test piece after heating was cooled by a method of immersing the test piece in a water tank, a method of sandwiching the test piece with a metal block at room temperature, and a method of air cooling with a fan.

  For each condition in which the test material and softening treatment conditions were changed, a preheated product that was preheated only and a reheated product that was reheated after preheating were prepared. In addition, although the softening processing method in the case of preheating was described above, in the condition which does not preheat, the restoration | recovery heating goods which gave only restoration heating without performing preheating were prepared. Table 3 shows the respective softening treatment conditions.

<Tensile test>
As shown in Table 3, a tensile test was performed on the test pieces of test numbers 1 to 15, and the proof stress value σn of the untreated product or the preheated product and the proof stress value σr of the restored heated product were measured. A certain intensity difference (σn−σr) was calculated.

<Tensile test after artificial age hardening>
In order to measure the proof stress after paint baking in automobile manufacturing process, 2% tensile pre-strain is applied to untreated or preheated and reheated products, followed by artificial age hardening at 170 ° C for 20 minutes. And the yield strength value was measured by a tensile test. Test numbers 13 and 14 were measured with the pre-strain amount being changed to 4% and 0%, and test number 15 was measured with the artificial age hardening condition being 185 ° C. × 30 minutes. ing.

  In Table 3, the above two tensile tests are performed three times under the same conditions, and the average value of the three times is adopted.

  Test numbers 1 to 10 shown in Table 3 are examples of the present invention. In any case, the proof stress value of the restored heated product is reduced, and a difference in strength from the untreated product or the preheated product can be obtained. Further, in test numbers 4 to 10, the temperature reached in the heating for restoration heating is in the range of 200 to 300 ° C., the heating rate or cooling rate of 100 ° C. or higher is set to 5 ° C./second or higher, and Since the time taken to be 100 ° C. or higher is within 2 minutes (120 seconds), it has high paint bake hardenability, and has a high strength whose proof stress value after artificial age hardening treatment greatly exceeds 190 MPa. .

  On the other hand, specimen numbers 11 and 12 are comparative examples, and the proof stress is not sufficiently lowered because the heating reaching temperature of the restoration heating is lower than the range of the present invention.

  Test numbers 13 and 14 are the results of changing the pre-strain amount after the softening treatment. In Test No. 13, the pre-strain amount was increased to 4%, so that the yield strength after the artificial age hardening treatment was increased. On the other hand, since test number 14 did not add prestrain, the yield strength after the artificial age hardening treatment was low, and it was less than 190 MPa. Test No. 15 was the result of changing the artificial age hardening treatment conditions to 185 ° C. × 30 minutes at a high temperature for a long time, and the proof stress after the artificial age hardening treatment was increased. Test numbers 13 and 15 correspond to examples of the present invention, and the test piece 14 corresponds to a comparative example.

[Example 2]
As a second test, a wrinkle model test was conducted to investigate the relationship between the softened region and the wrinkle suppression effect during press molding.
First, the test piece used for this test is demonstrated. As shown in FIG. 8, the shape of the test piece is a shape in which a grip portion having a width of 40 mm is added to a pair of diagonals having a side length of 100 mm, and the total length in the direction along the grip portion is 200 mm. It is. As shown in FIG. 9, a pair of scribing lines with a rating distance L (= 40 mm) was applied to the surface of the test piece at intervals of 20 mm from the center to both sides in the longitudinal direction.

  Next, the content of the wrinkle model test using this test piece will be described. The grip portions on both sides of the test piece were gripped with a gripping device of a tensile tester and adjusted so that the distance between the grip portions was about 114 mm (so that the portion from the end of the grip portion to about 43 mm was gripped). When a uniaxial tensile load was applied in the longitudinal direction of the test piece, the test piece was buckled and deformed in the width direction and the longitudinal direction, and a convex portion was formed in a region surrounded by a broken line portion shown in FIG. This convex portion is regarded as a wrinkle, and a test piece removed from the testing machine is used for a test piece using a three-point dial gauge having legs with a fulcrum distance l (= 40 mm) as shown in FIG. The wrinkle height hb in the width direction WW cross section was measured. Further, the score distance L ′ after the test is measured with a contour shape measuring machine, the elongation λ (%) of the test piece is obtained from the formula λ = (L′−L) / L × 100, and the elongation λ of the test piece is obtained. The relationship between the wrinkle height hb was evaluated.

  Next, the softening area | region defined in this test piece is demonstrated. Prior to defining the softening region, the wrinkle model test was simulated by numerical analysis using a computer. FIG. 11A is a diagram showing a principal component of a tensile component when a tensile displacement of 3 mm is applied in the longitudinal direction to a test piece made of an Al—Mg—Si aluminum alloy plate having a thickness of 1 mm, and FIG. FIG. 11B shows a diagram in which the principal stress is displayed as a vector. From FIG. 11 (B), it was confirmed that the region where the main stress of the compression component is generated in the plane of the test piece is the central part of the test piece. As is clear from the relationship between the shape of the test piece and the position where the tensile force is applied, the region where the tensile force acts in the direction perpendicular to the direction of the tensile force acting that generates the principal stress of the compression component causing wrinkles is This is a region having a grip portion width of 40 mm. Similarly, the region between the fulcrums where the tensile force acts is 114 mm between the gripping portions with respect to the acting direction of the tensile force that generates the principal stress of the compressive component that causes wrinkles.

  The test was performed by changing the width direction dimension x of the softened region and the longitudinal direction dimension y of the softened region shown in FIG. Table 4 shows the dimensions x and y of the softened region and the dimension ratios (x / X) and (y / Y) where X is the grip width 40 mm and Y is the distance 114 mm between the grips. The softened area of the softened area pattern No. 9 is determined so that a part of the softened area protrudes from the test piece, and the softened area of the softened area pattern 10 is grasped by the gripping device of the tensile tester among the test pieces. Not all areas are defined.

  The softening treatment for restoring and softening the softened region of the test piece was basically performed by the method described in Example 1. However, here, in order to restore and heat the softened region, each of the aluminum alloy plates having a thickness of 200 mm × 200 mm and a thickness of 10 mm (thickness is not shown) as shown in FIG. Ten types of heating jigs 28 were produced in which the convex portions 28a were cut so that the region corresponding to the softened region had a convexity of 5 mm (the convex height is not shown in the drawing). Further, as shown in FIG. 13B, the central portion of the soft heat insulating material 33 having a size of 200 mm × 200 mm and a thickness of about 5 mm is cut out according to the convex portion 28 a of the heating jig 28, and the convex portion 28 a side of the heating jig 28. By combining them, the surface that comes into contact with the test piece when pressed was made to have no step. The heating jig 28 and the soft heat insulating material 33 are provided with mounting holes 32 so that they can be attached to the lower surface of the pressing upper mold 24 with screws. As described above, the heating jig 28 is heated by heat transfer from the pressing upper mold 24.

  Ten kinds of test pieces subjected to the softening treatment and untreated test pieces not subjected to the softening treatment were prepared according to the combination of the test material of Test No. 6 in Example 1 and the softening treatment conditions, and used for the wrinkle model test. did. In the test, a 5TON tensile tester was used, and the tensile amount was adjusted so that the elongation λ of each test piece was the same. The test results are shown in FIG. In Table 5, “◎”, “◯”, and “Δ” are given in the order in which the effect is particularly favorable.

  In FIG. 14, when the wrinkle height hb at the same elongation λ is compared, it is confirmed that the wrinkle height of all of the softened region patterns 1 to 10 is lower than that of the untreated, and wrinkles are suppressed. it can. Moreover, this tendency becomes more remarkable as the elongation increases.

  Table 5 shows the relationship between the softening region and the wrinkle suppression effect. The width direction dimension x of the softened region is larger than X of the grip portion width of 40 mm, which is the region where the tensile force acts, in the direction perpendicular to the direction of the tensile force that generates the principal stress of the compression component in the plate surface. In other words, that is, when the dimensional ratio x / X between them is 100% or more, the effect of suppressing wrinkles is great.

  In addition, with respect to the direction of the tensile force that generates the principal stress of the compression component in the plate surface, the longitudinal dimension y of the softened region is Y with respect to the distance between the gripping portions of 114 mm, which is the region between the fulcrums where the tensile force acts. In both cases, since the dimensional ratio y / Y of both was 100% or less, no breakage occurred. Moreover, the wrinkle suppression effect is large under the condition where the dimensional ratio y / Y is 30 to 50%.

[Example 3]
As a third test, the wrinkle suppressing effect of the present invention was verified by a press molding test using the punch-shaped mold shown in FIG.
In the third test, as shown in FIG. 4 and FIG. 7, the mold includes a punch 2 having a two-stage punch forming surface 5, a die 3 having a shape offset from this shape, and a punch 2. The holder 4 is arranged so as to surround the periphery, and sandwiches the periphery of the die 3 and the blank. The punch 2 has a rough dimension in plan view of the punch forming surface 5 of about 170 mm × about 270 mm on the upper stage, about 200 mm × about 300 mm on the lower stage, R16 mm for the upper punch shoulder 6A, and R8 mm for the lower punch shoulder 6B. Using. Moreover, the die | dye 3 used what the upper die shoulder part 7A is R10mm, and the lower die shoulder part 7B is R12mm. The molding height in the third test was 40 mm. A convex bead 9 is formed on the side of the holder 4 with a depth of 3 mm on the wrinkle pressing surface 8 of the die 3 and the holder 4. The material of these molds is FCD550, and the surface is hard chrome plated. The mold was set in a press machine having a press capacity of 300 TON and tested.

  Three types of softening regions are shown in FIG. The softened region pattern 1 is set so that the wrinkle axial direction (the direction of action of the tensile force that generates the principal stress of the compression component) is within the YY region shown in FIG. The direction of the tensile force that generates the main stress of the compressive component was set to be larger than the region XX shown in FIG. The softened region pattern 2 is a region narrower than the softened region pattern 1 in the wrinkle axial direction and width direction. Further, in the softened region pattern 3, the softened region is circular, the wrinkle axial dimension is larger than the YY region shown in FIG. 7, and the region includes a part of the upper punch head.

  Subsequently, the softening treatment applied to the blank to be subjected to the press molding test was basically performed by the method described in Example 1. However, here, as in Example 2, in order to restore and heat the softened region, a heating jig in which the region corresponding to each softened region became a convex portion was produced and screwed to the lower surface of the pressing upper mold described above. .

  The blank used for the press molding test has a plane size of 440 mm × 360 mm, and three types of blanks subjected to softening treatment and a softening treatment according to the combination of the test material of test number 6 in Example 1 and the softening treatment conditions are applied. An untreated blank was made.

  Subsequently, the procedure of the press molding test will be described. By lowering the die from a state where a blank coated with an appropriate amount of rust preventive oil is set on the holder, the periphery of the blank is sandwiched between the die and the holder, and a bead is formed around the blank. At this time, the holder is supported by the cushion pin of the press machine, and the set die cushion load (DC load) is applied to the holder. Next, the die, the holder, and the blank descend toward the punch while a DC load is applied around the blank. As a result, the blank contacts the punch and undergoes deformation. Then, the molding ends when the press stroke drops by 40 mm.

  The DC load was 130 kN where wrinkles occurred in the region A in the untreated blank, and press molding was performed to the bottom dead center. All blanks could be formed without breaking, but in Pattern 3, the upper vertical wall was constricted.

  In order to quantitatively compare the state of wrinkles of the press-molded bodies thus obtained, the contour shape of region A in FIG. 4 which is a wrinkle generating portion of the molded body was measured. Specifically, the stylus was scanned along the wrinkle measurement line shown in FIG. 16 using a stylus type CNC contour shape measuring machine, and the contour shape was measured as XY coordinate data. And this XY coordinate data was converted into the angle distribution with respect to a horizontal surface. FIG. 17A shows the contour shape of each molded body molded with a DC load of 130 kN, and FIG. 17B shows the angular distribution. Further, in the angular distribution, the wrinkle angle range R which is the difference between the maximum value (θmax) and the minimum value (θmin) of the angle in the evaluation section shown in FIG. 17B is expressed as R = | θmax | + | θmin | The degree of wrinkle was evaluated by calculating from the above. The results are shown in Table 6.

  An untreated press-molded body that has not been subjected to softening treatment has a wavy shape in which the vicinity of the corners on both sides is convex and the center is concave, and the angle change is also large. On the other hand, the swells are suppressed in the press-formed bodies of the patterns 1 to 3 subjected to the softening process, and the change in angle is also small. When compared in the wrinkle angle range R, the values of all of the patterns 1 to 3 are small, and the effect of the pattern 1 is particularly great.

  Moreover, in order to confirm the suppression effect of the thermal deformation of the blank by heating a non-softening process area | region, the curvature amount of the blank which pre-heated the whole before the restoration | restoration heating in a softening process, and the blank which was not performed was measured. Specifically, as shown in FIG. 18, a weight was placed on one end of the blank in the longitudinal direction and fixed, and the amount of warpage at the other end was measured with a height gauge. The results are shown in Table 7. As shown in Table 7, since the shape and size of the softened region differ depending on the softened region pattern, the amount of warpage varies depending on each pattern, but by preheating all, that is, by heating the non-softened region as well. The amount of warping is greatly reduced.

  The production method of the aluminum alloy blank according to the present embodiment and examples described above can effectively suppress generation of wrinkles in press forming without impairing formability against breakage. As a result, the formability of the Al-Mg-Si-based aluminum alloy plate, which was inferior to that of cold-rolled steel plates, is improved, and the design flexibility of the automobile body panel is improved. Easy to apply.

  In addition, by appropriate selection of conditions such as the ultimate heating temperature, heating rate, holding time, and cooling rate after completion of heating in softening treatment, high paint bake hardenability, which is an excellent feature of Al-Mg-Si alloys Can be provided. As a result, the press-molded body obtained by press-molding the blank has a high strength of 190 MPa or more after the paint baking process in the automobile manufacturing process, and can be reduced in weight and cost by making the material thinner. Become. Further, in the softening treatment, the non-softened region other than the softened region is heated to a temperature lower than the restoration temperature, whereby the thermal deformation of the blank can be suppressed, and the value as a press molding blank is not impaired.

  The present invention is not limited to the above-described embodiments and examples, and various modifications and applications are possible. For example, in the above-described embodiments and examples, a mold having a punch shape having two steps has been described. However, the present invention is not limited to such a form, and can be applied to molds having various shapes. For example, when the punch shape as shown in FIG. 19A is one step and the vertical wall is curved in an arc shape, wrinkles may occur in the vertical wall. In addition, when the punch shape as shown in FIG. 19B has a sudden unevenness, wrinkles may occur on the punch surface and the vertical wall of the shape suddenly changing portion. In addition, when there is a recess on the top surface of the punch head as shown in FIG. 19C, wrinkles may occur on the top surface of the punch head at the corner of the recess. The wrinkle generation part can also suppress the generation of wrinkles by partially reducing the proof stress by the softening treatment described in the present invention.

1 ... Blank 2 ... Punch 3 ... Die 4 ... Holder 5 ... Punch molding surface 6, 6A, 6B ... Punch shoulder 7, 7, A, 7B ... Die shoulder 8 ... Wrinkle holding surface 9 ... ... Bead 10 ... 3-point dial gauge 11 ... Press molded body 21 ... Slide plate 22 ... Bolster 23 ... Cushion pin 24 ... Pressing upper die 25 ... Pressing lower die 26 ... Heater 27 ... ... Hard heat insulating material 28 ... Heating jig 28a ... Convex part 29 ... Softening region 30A, 30B ... Heating body 32 ... Mounting hole 33 ... Soft heat insulating material

Claims (13)

A method for producing a blank made of an aluminum alloy for producing a press-formed body by performing press molding,
Preparing an age-hardened Al-Mg-Si-based aluminum alloy plate;
A heating step of pre-determining a partial region of the aluminum alloy plate as a softening region for reducing the strength, and heating the softening region to a heating attainment temperature of 200 ° C. or higher and 580 ° C. or lower;
A cooling step for cooling the heated softened region to 100 ° C. or less;
The manufacturing method of the aluminum alloy blank characterized by including. The softened region includes a region where a main stress of a compression component that causes wrinkles is generated in the plate surface of the aluminum alloy plate in the forming process of the press molding.
The manufacturing method of the blank made from aluminum alloy of Claim 1 characterized by the above-mentioned. The softened region is a region wider than a region where the tensile force acts in a direction perpendicular to the acting direction of the tensile force that generates the main stress of the compression component.
The manufacturing method of the aluminum alloy blank of Claim 2 characterized by the above-mentioned. The softened region is a region narrower than the region between fulcrums on which the tensile force acts with respect to the acting direction of the tensile force that generates the principal stress of the compression component.
The manufacturing method of the blank made from aluminum alloy of Claim 2 or 3 characterized by the above-mentioned. In the heating step, the ultimate temperature is 200 ° C. or more and 300 ° C. or less, and the rate of temperature rise of the aluminum alloy plate from 100 ° C. to the ultimate temperature is 5 ° C./second or more.
In the cooling step, the cooling rate of the aluminum alloy plate up to 100 ° C. or less is 5 ° C./second or more,
The holding time at the temperature reached by heating in the heating step of the aluminum alloy plate is 20 seconds or less,
The manufacturing method of the aluminum alloy blank of any one of Claims 1 thru | or 4 characterized by the above-mentioned. In the heating step, a region that is not the softened region of the aluminum alloy plate is defined as a non-softened region, the non-softened region is heated to a heating attainment temperature of 100 ° C. or higher and lower than 200 ° C., and the softened region is 200 ° C. or higher and 300 ° C. or higher. It is heated to a temperature that reaches a heating temperature of ℃ or less, and the time that the aluminum alloy plate stays at 100 ℃ or more through the heating step and the cooling step is within 2 minutes,
The manufacturing method of the aluminum alloy plate blank of Claim 5 characterized by the above-mentioned. In the heating step, the difference between the heating arrival temperature of the softening region and the heating arrival temperature of the non-softening region is 50 ° C. or more and 200 ° C. or less.
The manufacturing method of the blank made from aluminum alloy of Claim 6 characterized by the above-mentioned. In the heating step, after preheating the entire aluminum alloy plate to a temperature not lower than 100 ° C. and lower than 200 ° C., only the softening region is heated to a temperature reaching not lower than 200 ° C. and not higher than 300 ° C.,
The manufacturing method of the blank made from aluminum alloy of Claim 6 or 7 characterized by the above-mentioned. In the heating step, the temperature of the heating body for heating the softened region and the non-softened region in the aluminum alloy plate is controlled, and the entire aluminum alloy plate is heated by bringing the heating body into contact with each other.
The manufacturing method of the blank made from aluminum alloy of Claim 6 or 7 characterized by the above-mentioned. In the step of preparing the aluminum alloy plate, the Al—Mg—Si-based aluminum alloy plate is subjected to solution treatment, and the solution-treated Al—Mg—Si-based aluminum alloy plate is subjected to normal temperature aging and 100 ° C. or less. Preparing the aluminum alloy plate by performing at least one of artificial aging,
A method for producing an aluminum alloy blank according to any one of claims 1 to 9. The aluminum alloy plate contains Mg: 0.2-1.5 mass%, Si: 0.3-2.0 mass%, Fe: 0.03-1.0 mass%, Zn: 0.03-2. 5 mass%, Cu: 0.01-1.5 mass%, Mn: 0.03-0.6 mass%, Zr0.01-0.4 mass%, Cr0.01-0.4 mass%, Ti0.005-0.3 mass % And V: 0.01-0.4 mass% further containing one or more kinds, the balance consisting of Al and inevitable impurities,
The method for producing an aluminum alloy blank according to any one of claims 1 to 10, wherein: A step of preparing an aluminum alloy blank using the aluminum alloy blank manufacturing method according to any one of claims 1 to 11,
A pressing process for press-forming the prepared aluminum alloy blank;
Including
In the pressing step, strain of 2% or more is introduced into a portion of the aluminum alloy blank that becomes a product after completion of the pressing step.
A method for producing an aluminum alloy press-molded body. A post-molding aging step of subjecting the press-formed aluminum alloy blank to an artificial age hardening treatment at 170 to 185 ° C. for 20 to 30 minutes,
The method for producing a press-formed body made of an aluminum alloy according to claim 12, further comprising: