JP5789150B2 - Method for manufacturing press-molded aluminum alloy blank, and method for manufacturing aluminum alloy press-formed body using the blank - Google Patents

Description

  The present invention relates to a method for producing an Al-Mg-Si-based aluminum alloy blank used for press molding, and a method for producing a press-molded body using the same, and more particularly to Al-Mg used for automobile body panels. -It is related with the manufacturing method of the blank made from Si type aluminum alloy, and the manufacturing method of a press-molding body using the same. Specifically, paint bake hardenability, which is an excellent feature of Al-Mg-Si based aluminum alloys, formability to improve design freedom, high surface quality, and hem for fastening to the inner panel The present invention relates to a method for producing a press-molding aluminum alloy blank having bendability, and a method for producing a press-formed body using the same.

Conventionally, cold-rolled steel sheets have often been mainly used as automobile body panel materials. 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 rolled aluminum alloy sheets having a low specific gravity is increasing.

  Of aluminum alloy rolled sheets, Al—Mg—Si aluminum alloys are often used for body panels such as automobile hoods, fenders, and doors. First, press formability is ensured by finishing the rolled sheet in a low proof stress state by taking advantage of the heat-treated alloy. Then, by age-hardening (called “paint bake hardening” or “bake hard (BH)”) by a paint baking process (about 20 minutes at about 170 ° C.) in the subsequent automobile manufacturing process, the proof stress is increased and the panel is increased. It is possible to impart high proof stress to the material. 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.

  By the way, since the formability of an aluminum alloy rolled sheet is generally inferior to that of a cold-rolled steel sheet, it is an obstacle to expanding its application. In order to improve the formability of the aluminum alloy rolled sheet, improvement of the formability of the material itself and the device of the forming method are strongly demanded.

  Press molding is usually a processing method in which a blank is formed into a predetermined shape by sandwiching the periphery of the blank with a die and a holder and relatively pressing a punch into the die. Here, by contacting the punch and the die, the blank is elastically deformed and accompanied by plastic deformation, and its shape is changed every moment to reach a predetermined shape. In the process of deforming the blank, the angle and direction of stretching at each portion of the blank change every moment. Furthermore, the distribution of tension (or stress distribution) applied to the blank becomes non-uniform due to the action of frictional force generated by contact with the punch or die. As a result, the strain distribution accumulated in the blank is also non-uniform.

  When the strain distribution becomes non-uniform in this way, the strain concentrates on a specific part depending on the shape of the panel (mold shape). The success or failure of the molding in such a case is determined by the molding limit of the material of the strain concentration portion (the occurrence of constriction and the limit of ductility) without utilizing the elongation of the entire blank. Generally, it is known that strain concentrates and breaks at a position corresponding to a punch shoulder which is a boundary between a punch head of a molded product and a vertical wall portion connected to the punch head.

  For improving the formability of the material itself, improvement of ductility, improvement of work hardening from the viewpoint of uniform strain distribution, improvement of Rankford value from the viewpoint of reduction of shrinkage flange deformation resistance in drawing, can be considered. These improvements have been attempted through organizational control. However, an example of industrially mass-producing aluminum alloy rolled sheets in which these have been dramatically improved has not yet been reported.

  In addition, the non-uniform tension distribution generated in the blank during the press molding described above is partly due to friction generated between the blank and the mold. Conventionally, in order to solve this problem, studies have been made on lubricating oils and lubricating films. However, negative effects such as the adverse effects on welding and joining caused by lubricating oil and lubricating coatings, and the fact that these cannot be completely removed by the existing degreasing process, leading to increased costs cannot be avoided, and the friction coefficient The problem that it was difficult to zero out was also left.

  It is known that when an aluminum alloy rolled plate is subjected to a large amount of strain due to forming, surface defects such as rough skin and ridging marks appear on the surface of the material. In particular, in the outer panel of an automobile, the commercial value is significantly reduced due to these surface defects. Therefore, when a surface defect occurs unintentionally, it is necessary to make a correction such as polishing the panel surface, which causes an increase in cost. For this reason, the design of the panel may be limited in advance so that the amount of strain accumulated in the blank by press molding is smaller than the amount of strain that causes surface defects. Thus, surface defects limit not only the formability but also the design and design freedom of aluminum parts.

  Studies are also underway to suppress such surface defects by controlling the metallographic structure. However, it is difficult to completely overcome surface defects, and it is necessary to make the strain distribution uniform by devising the processing method.

  In addition, the Al—Mg—Si based alloy is subjected to solution treatment and rapid cooling treatment in order to solidify Mg and Si, which are the main elements, in order to ensure paint bake hardenability. It is considered as a quality condition. The mechanical properties of T4 tempered Al-Mg-Si alloys are not stable at normal temperature, and fine precipitates gradually precipitate due to normal temperature aging, resulting in an increase in material strength (yield strength, tensile strength). There is. The normal temperature here is a temperature at which the material is transported and stored in the state where there is no air conditioning equipment, and means a temperature of 0 to 50 ° C.

  By the way, a body panel of an automobile is usually composed of an outer panel positioned outside the vehicle body and an inner panel positioned inside the vehicle body. When the outer panel is assembled with an inner panel that is separately press-molded after press molding, a bending process of about 180 ° called a hem bending process is performed on the peripheral part of the panel. This hem bending process is a very severe process in which cracks often occur during the process. Due to the increase in material strength due to the above-described normal temperature aging, there is also a problem that cracking is likely to occur in the hem bending process of the outer panel (that is, the hem bendability of the material is reduced).

  Various proposals have been made for the problems and problems described above. For example, as a method for improving the formability of an Al—Mg—Si-based aluminum alloy plate, Patent Document 1 describes a method in which a local heat treatment is performed on a blank to give a strength difference in the blank.

  According to this method, by heating the aluminum alloy plate to a melting temperature or lower, complex precipitates in the metal are completely or partially dissolved in the solid solution, and this is rapidly increased to room temperature. By cooling, the dissolved material temporarily maintains a supersaturated state in the solid solution, and the strength is reduced as compared with that before the treatment. By utilizing this phenomenon, the area engaged by the punch surface is heated and softened with respect to the blank before press molding, while the part extended around the corner of the punch is excluded from the heating area. The deformation pattern becomes uniform and the moldability is improved.

  However, the method disclosed in Patent Document 1 is divided into only two regions inside and outside the punch surface. On the other hand, in many press parts (metal molds), the punch itself has a complicated shape having a plurality of concave and convex shapes. To solve the uneven strain distribution of the blank in the punch surface, Patent Document 1 This method is not sufficient.

  The heating temperature is in the range of about 250 ° C. to about 530 ° C., which is the melting temperature or lower. However, when the heating temperature exceeds 300 ° C., Mg and Si in the matrix are precipitated as a β ′ phase which is a coarse precipitation phase in a short time. As a result, since the solid solution amount of Mg and Si is reduced, the strength increase in the subsequent artificial age hardening treatment is significantly reduced. That is, the inventors have found that the paint bake hardenability, which is an excellent feature of the Al—Mg—Si based aluminum alloy, is significantly reduced.

  In addition, there are some problems in locally heating the aluminum alloy plate. One of them is a difference in thermal expansion caused by the temperature difference between the heated part and the non-heated part, and the blank is deformed by thermal strain. There is a problem of so-called thermal deformation. In this Patent Document 1, a heating region and a region excluded from the heating region are defined. However, since the heating temperature is 250 ° C. to 530 ° C., assuming that the non-heating region is about 20 ° C., the temperature difference is about From 230 ° C to about 510 ° C. Since this thermal deformation increases as the temperature difference increases, it is considered that considerable heat deformation occurs when heat treatment is performed at this temperature difference. In particular, heating the central part of the blank that is engaged with the punch constrains thermal expansion by the surrounding non-heated part, resulting in large thermal strain and complicated distribution. It is conceivable that a wave outbreak occurs. When the degree of thermal deformation of these blanks is large, there is a possibility that they will remain in the molded product after press molding, so it is necessary to suppress them.

  Further, when an outer panel for an automobile body is targeted, a hem bending process is usually performed at the periphery of the molded product after press molding. Here, when there is a hem bent portion outside the punch surface, it remains in an aging-precipitated state due to normal temperature aging, and the problem that cracking occurs in the hem bent portion cannot be solved.

  A method of improving formability by applying a local heat treatment to an aluminum alloy blank to give a strength difference in the blank is also described in Patent Document 2. In this method, for the Al—Mg—Si-based aluminum alloy plate, in a blank state before press forming, a part of the blank outside the region where the punch shoulder is in contact is partially restored. The drawability is improved by softening and reducing the deformation resistance of shrinkage flange deformation. About improving the hem bendability after press molding by including the part that will be hem bent after press molding in the part outside the area where the punch shoulder will contact, Is also described.

  However, this method is premised on draw forming in which a material is allowed to flow from a wrinkle holding portion into a space constituted by a die and a punch. Therefore, in the case where the periphery of the blank is fixed with a bead and stretched, the outer region of the punch shoulder is restored and softened, so that there is a possibility of breakage with the bead. In addition, when the punch has a complicated shape as described above, the uneven strain distribution of the blank in the punch surface cannot be solved. In addition, the problem of so-called thermal deformation, in which the blank is deformed by the thermal strain caused by the temperature difference between the heating unit and the non-heating unit, cannot be solved.

Japanese Patent No. 3393185 JP 2009-161851 A

As described above, the conventionally proposed technique can achieve a certain effect of improving the formability of the Al—Mg—Si-based aluminum alloy plate, but can improve the press formability and the surface quality without excessive deformation of the blank. It is difficult to achieve a uniform strain distribution of the molded product after press molding, which is a means for improvement, and to recover hem bending workability, which is a process of bending the periphery of the molded product to 180 ° after press molding. Met.
In addition to the above problems, in the press forming process of an automobile body panel, when a blank is put into a press machine, air is usually emitted from a plurality of nozzles directed to the upper side of the blank pile where the blanks are stacked. Is used, and the method of peeling off the top blank with this air pressure is used, but the blank is often coated with oil for the purpose of rust prevention and lubricity, and this oil is placed between the blanks. There existed the problem of the separation failure that adsorption force acted by existence and it cannot be separated well.
This invention provides the manufacturing method of the aluminum alloy blanks for press molding for solving these subjects, and the manufacturing method of a press-molding body using the same.

  As a result of repeated various experiments and studies to solve the above-mentioned problems, the inventors have made a blank made of an age-hardened Al-Mg-Si-based aluminum alloy rolled plate, that is, aging at room temperature after solution treatment, or Attention was paid to a blank made of an Al—Mg—Si-based aluminum alloy in a sub-aged state by artificial aging or a combination of normal aging and artificial aging after solution treatment. As a result, the tension applied by conventional press molding is small, and it is bent between the punch head, which is a portion that is hardly stretched, and the punch vertical wall, which is a continuous surface surrounding the outer periphery of this surface. Attention was paid to a blank area A in which the area inside the punch shoulder part existing as a part was projected onto a plane perpendicular to the pressing direction. And while setting arbitrary area | region X of the area | region A as a restored | restoration area | region, whole blanks other than a restored | restoration area | region are defined as a non-restoration area | region, and the finely produced | generated gradually by normal temperature aging with respect to this restored area | region before press molding In addition to heating at a temperature equal to or higher than the melting temperature of the precipitate, the non-restored region is heated at a temperature lower than the melting temperature, and then the entire blank is cooled to room temperature, thereby reducing the proof stress value only in the region X. However, by making plastic deformation with a small tension, the part is actively stretched, while the increase in strain at the part where the risk of fracture due to concentration of strain is high is alleviated. It has been found that the distribution can be made uniform.

  It has been found that deep drawability and hem bendability are improved by appropriately adding a shrinkage flange deformation region and a hem bending portion of the wrinkle holding portion to the restoration region depending on the part shape and application. In addition, by appropriately selecting conditions such as the temperature to reach heating, the temperature rise rate, the holding time, and the cooling rate after completion of heating in the restoration process, the restoration area can be efficiently softened in a very short time and the non-restoration area Was found to be not softened and high bake hardenability can be obtained. Furthermore, by selecting the difference between the heating ultimate temperatures of the restoration area and the non-restoration area within an appropriate range, while suppressing excessive thermal deformation, and applying slight thermal deformation to the blank, when the blanks are stacked, It has been found that material separation is improved by forming a slight gap between them.

  Here, the term “restoration” means that after the solution treatment, the alloy element is supersaturated at room temperature and then kept at room temperature or slightly higher, and then the matrix is finely composed of Mg and Si. A so-called age-hardened aluminum alloy rolled sheet whose strength increases due to the gradual formation of low-temperature clusters, which are precipitates, is heated at a temperature higher than the above-mentioned holding temperature for a short time. It means a phenomenon in which the strength of a material is reduced by re-solidifying and then rapidly cooling immediately thereafter to bring it into a supersaturated state. A series of processes of rapid heating and subsequent rapid cooling for causing such a phenomenon is referred to as restoration process.

The present invention is the press molding according to claim 1, which is made of an age-hardened Al-Mg-Si-based aluminum alloy and is molded into a predetermined shape by sandwiching the periphery between the die and the holder and relatively pushing the punch into the die. A method of manufacturing an aluminum alloy blank,
A punch that exists as a bent portion between a punch head surface, which is a surface substantially perpendicular to the press direction, and a punch vertical wall portion, which is a surface continuous so as to surround the outer periphery of this surface. An area including an arbitrary area X among blank areas A projected on a plane perpendicular to the press direction from an area inside the shoulder is defined as a restoration area, and the entire blank other than the restoration area is a non-restoration area As
A restoration process including a heating process for heating the entire blank before press molding and a cooling process for cooling the entire blank to 100 ° C. or less is performed thereafter. In the heating process, a heating temperature is 200 ° C. in the restoration region. In the non-restoration region, the temperature is set to 100 ° C. or more and less than 200 ° C., and in the restoration region, the heating rate from 100 ° C. to the heating attainment temperature is set to 5 ° C./second or more in the heating step. the retention time was 20 seconds or less, the cooling rate to 100 ° C. and 5 ° C. / sec or more in the cooling process, the time the blank throughout the restoration process stays above 100 ° C. with 2 minutes, the area X reduce the proof stress of, and, it said without increasing the yield strength values of the non-restored area, provide strength difference in the blank,
The Al—Mg—Si-based aluminum alloy has been subjected to a solution treatment, and the Al—Mg—Si-based aluminum alloy after the solution treatment is subjected to normal temperature aging or 100 ° C. or less before the restoration treatment is performed. It was set as the manufacturing method of the aluminum alloy blank for press molding characterized by making it an age-hardened Al-Mg-Si type aluminum alloy by performing the aging treatment by artificial aging or these combination .

  According to claim 2 of the present invention, in claim 1, the difference in the heating arrival temperature between the restored region and the non-restored region is set to 50 ° C. or more and 200 ° C. or less.

  In claim 3 of the present invention, in claim 1 or 2, the pre-heating step at an ultimate temperature of 100 ° C. or higher and lower than 200 ° C. is performed on the entire blank in advance, and then the heating ultimate temperature of 200 ° C. or higher and 300 ° C. or lower is applied only to the restoration region. The heating process was performed.

  In claim 4 of the present invention, in claim 1 or 2, both regions are heated simultaneously by bringing the heating body into contact with the blank while controlling the temperature of the heating body that heats the restoration region and the non-restoration region. It was supposed to be.

In Claim 5 of this invention, in any one of Claims 1-4, the area ratio of the area (S _X ) of the region X to the area (S _A ) of the blank region A is 25% or more and 100% or less. did.

  According to claim 6 of the present invention, in any one of claims 1 to 5, the restoration area of the blank is perpendicular to the press direction in the area outside the punch shoulder closest to the wrinkle pressing part sandwiched between the die and the holder. Of the blank area C projected onto the flat surface, the area Y that is a contracted flange deformed portion is also included.

  According to claim 7 of the present invention, in any one of claims 1 to 6, the restoration region of the blank includes a hem bending portion which is a region subjected to hem bending after press molding.

In Claim 8 of this invention, in any one of Claims 1-7, the said Al-Mg-Si type aluminum alloy is after solution treatment, Comprising: Room temperature aging or artificial aging of 100 degrees C or less, or these It was assumed that the preliminary aging treatment was performed before the combination aging treatment .

  In Claim 9 of this invention, in any one of Claims 1-8, said Al-Mg-Si type aluminum alloy is made into Mg: 0.2-1.5mass%, Si: 0.3-2.0mass%. 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 -0.4mass%, Cr0.01-0.4mass%, Ti0.005-0.3mass%, and V: 0.01-0.4mass% further 1 type or 2 types or more are further contained, and the remainder An aluminum alloy composed of Al and inevitable impurities was used.

  According to a tenth aspect of the present invention, the aluminum alloy blank for press molding produced by the method for producing a blank for aluminum alloy for press molding according to any one of the first to ninth aspects is subjected to press molding, thereby causing wrinkles. The aluminum alloy press-molded body is characterized in that a strain of 2% or more is introduced into a portion to be a product inside the holding portion.

  According to an eleventh aspect of the present invention, in the tenth aspect, an artificial age hardening treatment is performed at 170 to 185 ° C. for 20 to 30 minutes, whereby the yield strength value of the molded body is set to 190 MPa or more.

  According to the present invention, it is possible to obtain a press-molding aluminum alloy blank having a small thermal deformation and a strength difference. By using this blank, the strain introduced by press forming becomes uniform, and the press formability of the Al—Mg—Si based aluminum alloy rolled plate, which is inferior to that of the cold-rolled steel plate, is significantly improved. Further, surface defects such as rough skin and ridging marks generated on the material surface of the strain concentration portion can be suppressed, and the design of the panel and the degree of freedom of design are remarkably improved. Furthermore, high paint bake hardenability, which is an excellent feature of the Al-Mg-Si alloy, by appropriately selecting conditions such as the heating temperature, the heating rate, the holding time, and the cooling rate after completion of heating in the restoration process Can be achieved. As a result, a high strength of 190 MPa or more is obtained in terms of the proof stress value of the panel, and it is possible to reduce the weight and reduce the cost by thinning the material.

  In the present invention, it is possible to remarkably recover the hem bendability reduced by age hardening by applying a restoring process to the hem bent portion that is to undergo hem bending after press molding.

  In the present invention, the material of the punch head that has heretofore been hardly stretched because the tension applied by press molding is small is stretched and flows out to the surroundings. The amount of inflow from the blank wrinkle holding surface can be reduced by this outflow. As a result, the blank size can be reduced, and the material cost can be reduced.

  In the press-molding aluminum alloy blank of the present invention, a slight thermal deformation causes a gap when stacked and material separation is improved. Further, since the aluminum alloy rolled sheet has a smaller longitudinal elastic modulus than that of the steel sheet, the amount of elastic recovery (spring back) of the residual stress in the sheet after press forming is large, and it is difficult to ensure the shape freezing property. However, since the residual stress is reduced by reducing the material strength by the restoration process, it can be expected that the shape freezing property is also improved. And above all, since this restoration process can be performed in a pre-process before press molding or in a separate process, press molding itself can be performed by a conventional cold press facility, and the conventional production efficiency is not lowered.

It is the graph which showed the relationship between the temperature difference (DELTA) T of the decompression | restoration area | region in a linear expansion and a non-restoration area | region, and the thermal stress (sigma), and the proportional limit (sigma) _P. It is a front view of the heating apparatus used for the heat treatment of the preheating method in the restoration treatment. It is a front view of the heating apparatus used for the heating process of the simultaneous heating system in the restoration process. It is the schematic diagram of the vertical cross section shown in order to demonstrate the balance of the force in cylindrical overhang forming or hat bending forming. The ratio of the tension on the molded article the vertical wall portion (T _W) and tension on the molded article the head (T _P) is a Natsuki angle and the punch shoulder is the angle moldings vertical wall portion and the molded article head eggplant It is a graph which shows changing with the friction coefficient which generate | occur | produces between molded product shoulder parts. It is a schematic diagram for demonstrating the cylindrical overhang forming test in the example 1 of this invention. It is a schematic diagram for demonstrating the two-stage metal mold | die press-molding test in the example 2 of this invention. It is the top view and front view of a heating jig which were used for restoration heat treatment of a blank in example 1 of the present invention. In Example 1 of this invention, it is a top view which shows the position which extract | collects a small tension | tensile_strength test piece from the restoration | reconstruction area | region and non-restoration area | region of the blank which performed the restoration process. It is a top view which shows the shape and dimension of the small tension test piece extract | collected in the example 1 of this invention. In Example 1 of this invention, it is a schematic diagram for demonstrating the method to measure the curvature amount of the blank which performed the decompression | restoration process. In Example 1 of this invention, it is a graph which shows an example of the measurement result of the curvature amount of the blank which performed the restoration process. It is the top view and front view for demonstrating the method of the material separation test in the example 1 of this invention.

  The blank made of aluminum alloy for press forming used in the present invention is basically an Al-Mg-Si aluminum alloy rolled plate, which is in a state of aging precipitation by normal temperature aging after solution treatment at high temperature, Alternatively, after being solution-treated at a high temperature, artificial aging or an aging treatment combining room temperature aging and artificial aging is applied to be in a sub-aging state. Hereinafter, the present invention will be described in detail for each main item.

<Component composition of aluminum alloy plate>
The aluminum alloy plate used in the present invention may basically be an Al-Mg-Si alloy, and its specific composition is not particularly limited. An alloy having a composition is preferable. That is, Mg: 0.2 to 1.5 mass% (hereinafter simply referred to as “%”), Si: 0.3 to 2.0%, 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- Aluminum further containing one or more selected from 0.4%, Ti: 0.005 to 0.3% and V: 0.01 to 0.4%, the balance being Al and inevitable impurities An alloy is preferably used as a material.

  The reason for limiting such component composition will be described below.

Mg:
Mg is an alloy element which is a basic alloy of the system targeted by the present invention, 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 also an alloy element that is a basic alloy of the system of the present invention, 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. 3% and V: One or more selected from 0.01 to 0.4% are included. The reason for these additions and the reason for limiting the addition amount are as follows.

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 when Fe is positively added is in the 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 set in the range of 0.03 to 2.5%.

Cu:
Cu is an element added for improving formability and strength, and 0.01% or more is added 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 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 possibility that the moldability, particularly the hem bendability, may be adversely affected. Therefore, 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. 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 due to the addition of 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 moldability and hemmability. Therefore, the Ti content is within the range of 0.005 to 0.3%, and the V content is within 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. In the present invention, it is allowed to add 500 ppm or less of B together with Ti.

<Method for producing Al-Mg-Si-based aluminum alloy rolled sheet>
The Al—Mg—Si-based aluminum alloy rolled sheet can be produced by a usual method.
Specifically, an aluminum alloy melt adjusted to a predetermined component is cast by appropriately selecting a normal melting casting method. Here, as a normal melt casting method, for example, a semi-continuous casting method (DC casting method), a thin plate continuous casting method (roll casting 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 usually 1 hour or more, and is usually 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, chamfering is performed as appropriate, then hot rolling is started in a temperature range of 300 to 590 ° C., and then cold rolling is performed to obtain a rolled aluminum alloy sheet having a predetermined thickness. To manufacture. 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 rolled aluminum alloy sheet after the cold rolling. This solution treatment is important for improving the strength after the paint baking process performed after press molding, by dissolving Mg ₂ Si, elemental Si, etc. in the matrix, thereby imparting paint bake hardenability. It is a difficult 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 hem bendability. This is an important process for obtaining moldability. In order to exhibit these effects, treatment at 480 ° C. or higher is necessary. If the solution treatment temperature exceeds 590 ° C., eutectic melting may occur, so the temperature is set to 590 ° C. or less.

  Here, the solution treatment can be efficiently performed by continuously passing the cold rolled sheet wound in a coil shape through a continuous annealing furnace having a heating zone and a cooling zone. In such a continuous annealing furnace, the aluminum alloy rolled sheet 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 alloying elements of the alloy targeted by the present invention, are once dissolved in the matrix at a high temperature and then rapidly cooled to form a supersaturated solution at room temperature. It becomes.

  In the case of imparting high paint bake hardenability to the Al—Mg—Si-based aluminum alloy rolled sheet, a pre-aging treatment is performed in which a solution treatment is performed and the mixture is rapidly cooled and maintained at a temperature of about 60 to 100 ° C. for about 1 to 24 hours. Accordingly, it is possible to generate and grow a high-temperature cluster that is a fine precipitate made of Mg and Si that is generated at a temperature slightly higher than normal temperature, which is different from the low-temperature cluster generated at normal temperature described above. This high-temperature cluster is age-hardened by transition to the β ″ phase, which is a precipitation strengthening phase, by a subsequent coating baking process (for example, heating performed at about 170 ° C. for about 20 minutes), and the proof stress value is It improves to 190 MPa or more.

<Aging from solution treatment to restoration treatment>
In order to give a strength difference between the blank restoration area and the non-restoration area by the restoration process, a certain amount of low-temperature clusters are generated by room temperature aging (natural aging) during the room temperature standing period after the solution treatment. It is necessary. If such a low-temperature cluster is not generated, the restoration phenomenon does not occur in the subsequent restoration process, and the proof stress value is not reduced.

  Therefore, after the solution treatment, it is necessary to leave at room temperature for one day or more before the restoration treatment is performed. In addition, the normal temperature standing period from solution treatment to press molding is generally 10 days or more. In addition, this room temperature aging proceeds rapidly in the initial stage, but after about half a year, it becomes difficult to proceed further, so there is no particular upper limit for the room temperature standing period before the restoration heat 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, in the present invention, for the purpose of generating low-temperature clusters at an early stage, even when artificially aging after solution treatment, or when performing a combination of room temperature aging and artificial aging, it is made into a blank by subsequent restoration processing. An intensity difference can be imparted.

  However, the temperature of artificial aging must be 100 ° C. or less, and the Al—Mg—Si-based aluminum alloy rolled 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. Since coarse precipitates are deposited, 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 series aluminum alloy rolled sheet, 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 sufficient 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 a low temperature cluster is generated by holding.

  In the present invention, it is desirable that the proof stress is 110 MPa or more as the material strength immediately after performing the aging as described above and performing the next restoration process. When the proof stress value is less than 110 MPa, a sufficient strength difference cannot be imparted because the strength reduction at the portion to be restored in the subsequent restoration process becomes insufficient.

<Restore process>
Next, the restoration process that is the main point of the present invention will be described. Restoration treatment refers to a treatment in which an arbitrarily selected region of an age-hardened Al—Mg—Si-based aluminum alloy rolled plate is heated to a predetermined temperature and then cooled to room temperature. This will be explained as follows.

  That is, during standing at room temperature after solution treatment, low-temperature clusters, which are fine precipitates made of Mg and Si, are generated and grown in the matrix, thereby increasing the material strength. When the material in such a state is heated to a predetermined temperature for a short time, the thermally unstable low-temperature cluster is easily re-dissolved and disappears. Thereby, the material strength after cooling to normal temperature falls compared with before heating. In addition, since the hem bendability of the material decreases as the material strength increases due to age hardening, the hem bendability is also restored by restoration.

<Recovery area heat treatment conditions>
In the present invention, the heat treatment conditions for the restoration treatment are defined as follows. That is, the heating arrival temperature in the restoration region was in the range of 200 ° C. or higher and 300 ° C. or lower. When the temperature reached by heating is lower than 200 ° C., the amount of low-temperature clusters dissolved in a short time is small, so the strength reduction due to restoration is small, and the hem bendability is hardly recovered. On the other hand, when the heating attainment temperature 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, and the solid solution amount of Mg and Si decreases. The strength increase in the subsequent artificial age hardening treatment is significantly reduced. That is, the paint bake hardenability, which is an excellent feature of the Al—Mg—Si based aluminum alloy, is significantly reduced.

  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 the ductility of the material is also reduced, it is necessary to optimally select the heating temperature for each panel shape in consideration of the balance between imparting strength difference and reducing ductility.

  Here, the ultimate heating temperature of the restoration region can be further divided into two temperature ranges according to the rate of change with time in the strength of the heating portion. When the temperature reached by heating is 250 ° C. or more and 300 ° C. or less, immediately after the low temperature cluster composed of Mg and Si is sufficiently solid-solved in a short time of several seconds and the restoration is completed, and cooling to room temperature at a predetermined cooling rate In, a big strength difference can be provided between a heating part and a non-heating part. However, when restoration heating is performed in this temperature range, many atomic vacancies remain at room temperature after cooling. This atomic vacancy promotes the diffusion of Mg and Si while maintaining the room temperature in the restored part, and accelerates 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 restoration process. 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 causes incompatibility with the press molding conditions optimized in advance and increases the possibility of forming defects. Therefore, to stably produce good molded products Is preferably subjected to press molding and hem bending as short as possible after the restoration treatment. Specifically, 3 days or less is desirable.

  On the other hand, when the restoration heat treatment is performed in a temperature range of 200 ° C. or more and less than 250 ° C., the amount of decrease in the proof stress value is reduced, but the atomic vacancy density at room temperature after cooling is sufficiently low, and the restoration treatment is performed. The increase in the proof stress over time in the subsequent normal temperature holding period is sufficiently small. Therefore, when the restoration process is performed within such a temperature range, it is possible to stably produce a good molded product even when kept at room temperature for several days. Therefore, when importance is attached to the flexibility of the schedule of the production process, the heating temperature of the restoration 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 restoration process. It is preferable that the temperature is lower than 250 ° C. The normal temperature holding period from the restoration process to press molding is preferably within 10 days.

  In addition, the rate of temperature increase from 100 ° C. to the ultimate temperature is preferably as fast as possible, and is 5 ° C./second or more. When the temperature is less than 5 ° C./second, high-temperature clusters are generated and grown, and this transitions to a β ″ phase that is a precipitation strengthening phase, which increases the strength contrary to the original purpose. Moreover, ductility will fall and hem bendability will also deteriorate. Further, from the viewpoint of productivity, it is preferably as fast as possible, and preferably 10 ° C./second or more. For the same reason, the holding time after reaching the heating attainment temperature is preferably as short as possible, and is 20 seconds or less. If the heating region can be heated uniformly, the holding time may be 0 seconds (cooling immediately after reaching a predetermined temperature without staying).

<Heat treatment conditions of non-restoration area>
The main purpose of heating the non-restoration region is to minimize the difference in the temperature reached by heating between the restoration region and the non-restoration region as much as possible to suppress excessive thermal deformation. However, in order to give a strength difference to the blank, which is the original purpose of the restoration process, the non-restored region is required to have no strength reduction or a strength reduction as small as possible. Therefore, the heating ultimate temperature in the non-restoration region is defined as 100 ° C. or more and less 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 a decompression | restoration area | region does not become excessive. However, even within the above temperature range, if kept at that temperature for a long time, melting of the low temperature cluster occurs and softens, or age hardening occurs beyond that and the strength increases and the elongation decreases, The time during which the blank stays at 100 ° C. or higher throughout the entire restoration process is set to be 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. Therefore, even if it is gradually cooled thereafter, the mechanical properties are not affected.

<Difference in heating temperature between the restored area and the non-restored area>
In the present invention, it is preferable that the difference in the heating arrival temperature between the restored region and the non-restored region in the restoration process is 50 ° C. or more and 200 ° C. or less. The purpose of heating the non-restoration area is to suppress the excessive heat deformation and to give a slight heat deformation to the blank by selecting the difference in the heating arrival temperature between the restoration area and the non-restoration area within an appropriate range. The material separation property is improved by forming a slight gap between the blanks when the blanks are stacked. The thermal deformation referred to here is a deformation such as warping or twisting that occurs in the blank due to thermal distortion at the boundary between the restored area and the non-restored area due to the difference in thermal expansion between the restored area and the non-restored 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 σ _P in the stress-strain diagram, plastic deformation occurs, so-called thermal deformation remains.

  In the present invention, the restoration area is thermally expanded by heating the vicinity of the center of the blank that is the restoration area to a temperature higher than the surrounding area that is the non-restoration area, and thermal stress is generated at the boundary between the restoration area and the non-restoration area. . Actually, the circumference of the restoration area is surrounded by the non-restoration area, and the thermal stress generated at the boundary between the restoration area and the non-restoration area is increased by the thermal expansion of the restoration area. It is smaller than the value of the example of the bar constrained by the rigid wall.

Therefore, 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 restored region and the non-restored region, which is the condition for the greatest thermal stress, was determined as follows. It is known that when the temperature of the material increases, the strength and the longitudinal elastic modulus E decrease, and 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 restoration 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. It was about 73 MPa at 300 ° C. and about 70 MPa at 300 ° C., which is the maximum temperature in the restoration region.

FIG. 1 shows the result of obtaining the relationship between the temperature difference ΔT between the restored region and the non-restored region, the thermal stress σ, and the proportional limit σ _P using these values. The thermal stress applied to the restoration region heated to 200 ° C., which is the lowest temperature of the restoration region, reaches a proportional limit when the temperature difference is about 50 ° C. (the non-restoration region is about 150 ° C.). On the other hand, the thermal stress received by the restoration region heated to 300 ° C., which is the highest temperature of the restoration region, reaches a proportional limit when the temperature difference is about 58 ° C., but the temperature reached in the non-restoration region is 100 ° C. or more and less than 200 ° C. Therefore, at least the temperature difference is greater than 100 ° C. Therefore, since the minimum temperature difference required to impart a slight thermal deformation to the blank is 50 ° C. or higher, the difference in the heating arrival temperature between the restored region and the non-restored region in the restoration process should be 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 restored region and the minimum temperature of 100 ° C. in the non-restored region.

<Cooling conditions>
The cooling rate to 100 ° C. in the cooling after the heat treatment is preferably as fast as possible, and is 5 ° C./second or more. When the temperature is less than 5 ° C./second, high-temperature clusters are generated and grown, and this transitions to the β ″ phase that is a precipitation strengthening phase, which increases the strength contrary to the original purpose. Moreover, ductility will fall and hem bendability will also deteriorate. Further, from the viewpoint of productivity, it is preferably as fast as possible, and preferably 10 ° C./second or more. In addition, although the upper limit of a cooling rate is not prescribed | regulated in particular, if it is the method immersed in a water tank, the cooling rate of about 1000 degree-C / sec is obtained.

<Heating method for restoration processing>
The restoration process of the present invention can be roughly divided into two methods. One is a preheating method in which only the restoration 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 elements corresponding to the restoration area and the non-restoration area are individually controlled, and both areas are heated simultaneously by pressing the heating element 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. Therefore, 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 such as induction heating, infrared heating, or electric heating. 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 restoration region to an ultimate temperature of 200 ° C. or more and 300 ° C. or less, a metal plate or metal block (aluminum alloy, copper alloy, etc.) processed according to the shape of the part to be heated is heated with a heater or the like. The simplest method is to heat and contact and pressurize the part to be heated for heat transfer. In addition to this, by processing the black body such as carbon, which has a higher thermal emissivity (heat absorption rate) than the aluminum plate, according to the shape of the part to be heated, pasting it on the part to be heated, and heating with infrared rays, Only the region where the black body is pasted can be heated to a high temperature instantly.

  Here, a specific example of the preheating method will be described. As shown in FIG. 2, as a heating device, a pressing lower die (25) having a heater built in on a bolster (22), and a pressing upper die (24) having a heater also built in the slide plate (21). Use a hydraulic press machine equipped with. The pressing lower die (25) is supported by a cushion pin (23), and when pressing, a predetermined pressing pressure can be maintained by a cushion mechanism of a press machine. On the other hand, the pressing upper die (24) is attached via a hard heat insulating material (27), and the lower surface of the pressing upper die (24) is processed so that only the restoration region is convex and the non-restoration region is concave. A heating jig (28) made of a metal plate is attached, and a soft heat insulating material (33) slightly thicker than the convex part (31) of the heating jig is attached to the non-restoring region. The heater (26) is controlled by a temperature control device (not shown) so as to maintain each set temperature, and the pressing lower mold (25) and the pressing upper mold (24) are brought to a predetermined temperature by the heater (26). Heated. The heating jig (28) attached to the lower surface of the pressing upper die (24) is also heated by heat transfer.

  As a method of heating using this heating apparatus, as shown in FIG. 2A, first, the blank (4) is placed on the pressing lower mold (25), and the blank (4) is blanked. A hard heat insulating material (27) having a thickness larger than that of (4) in the press direction and having a thickness that does not cause cracking or the like due to pressurization of the press is placed. The slide plate (21) is lowered by the press mechanism of the press machine, and the soft heat insulating material (33) attached to the lower surface other than the convex portion (31) of the heating jig (28) and the convex portion (31) of the heating jig (28). Contacts the hard heat insulating material (27) on the blank (4) and presses the blank (4) for a certain time with a constant load by the cushion mechanism of the press machine, so that the heat of the lower mold (25) for pressing is pressed. Is transmitted to the blank (4), and the blank (4) is heated to a predetermined temperature of 100 ° C. or higher and lower than 200 ° C. On the other hand, the heat of the pressing upper die (24) is not transmitted to the blank (4) by the hard heat insulating material (27). This completes the preheating.

  Next, as shown in FIG. 2A, after removing the hard heat insulating material (27) placed on the blank (4), the slide plate (21) is lowered by the press mechanism of the press machine, and the heating jig The soft insulating material (33) attached to the lower surface other than the convex portion (31) of (28) and the convex portion (31) of the heating jig (28) contacts the blank (4), and a constant load is applied by the cushion mechanism of the press machine. And pressurizing the blank (4) for a certain period of time, the heat of the pressing upper mold (24) is transmitted to the blank (4) via the convex portion (31) of the heating jig (28), and the restoration region ( Only 29) is heated to a predetermined temperature of 200 ° C. or more and 300 ° C. or less. In the region other than the restoration region (non-restoration region), the heat of the pressing upper die (24) is not transmitted because the soft heat insulating material (33) is in contact. This completes the heating of the restoration 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 (31). When this soft heat insulating material (33) is not present or is thinner than the convex portion (31) of the heating jig (28), the hard heat insulating material (27) placed on the blank (4) is pressurized by preheating. A range becomes only the convex part (31) of a heating jig (28), and the whole blank (4) is not heated uniformly. Further, when the restoration region is heated, the blank (4) is likely to have a pressing mark at the edge of the convex portion (31) of the heating jig (28). Further, in the case of a hard heat insulating material instead of the soft heat insulating material (33), it is difficult to strictly control the thickness of the heat insulating material. Therefore, if the thickness of the heat insulating material is thicker than the convex portion (31) of the heating jig (28). The convex part (31) of the heating jig (28) cannot contact the blank, and there is a possibility that the restored region cannot be heated. Therefore, by using the soft heat insulating material (33) that is slightly thicker than the convex portion (31) of the heating jig (28), the thickness is compressed during pressurization, so that the thickness of the convex portion (31) of the heating jig (28) is reduced. ) And uniform pressurization and heat insulation effects can be obtained.

  As a specific example of the simultaneous heating method, as shown in FIG. 3, a lower die (25) for pressing on the bolster (22) and a heater (30A, A hydraulic press machine equipped with a pressing upper die (24) to which a plurality of 30B) can be attached is used. The pressing lower die (25) is supported by a cushion pin (23). When pressing, a predetermined pressing pressure can be maintained by a cushion mechanism of a press machine, and a hard heat insulating material (27) is provided on the upper surface. It is attached. On the other hand, the pressing upper die (24) is attached through a hard heat insulating material (27), and the lower surface of the pressing upper die (24) is made of a metal block processed according to the heating region, and the heater (26) is provided. Built-in heating elements (30A, 30B) are attached. The heater is controlled by a temperature control device (not shown) so as to maintain the set temperature of each heating element (30A, 30B).

  As a method of heating using this heating apparatus, first, the blank (4) is placed on the hard heat insulating material (27) on the pressing lower mold (25). The slide plate (21) is lowered by the press mechanism of the press machine, the heating elements (30A, 30B) come into contact with the blank (4), and the blank (4) is added by pressing with a constant load for a certain time by the cushion mechanism of the press machine. By pressing, the heat of the heating elements (30A, 30B) is transmitted to the blank (4), and the blank (4) is heated to a predetermined temperature.

  In addition, as the pressing pressure of the heating jig or the heating body to the blank in the case of heat transfer heating, 0.1 MPa or more is preferable for efficient heat transfer, and heat transfer efficiency is almost constant at 0.5 MPa or more. 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.

<Cooling method for restoration processing>
As a method of cooling the blank after heating it to a predetermined temperature, the contact type 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 and cools by heat transfer, is used for cooling speed and production. It is most effective from the viewpoint of sex. 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.

<Restore area>
As one of the means for solving the above-mentioned problems in press forming, it is conceivable to make the strain distribution of the forming panel uniform, but in order to achieve this, the present inventor is in a relationship between the tension applied to the blank and the proof stress value of the material. Attention was paid to the use of restoration processing.

FIG. 4 is a schematic diagram showing the left side from the center line (13) of the vertical cross section in the cylinder overhang forming or the hat bending forming. The blank (4) is sandwiched between the die (2) and the holder (3), and the punch (1) is relatively pushed into the die (2) side to form a hat cross-sectional shape. A tension is generated in the blank. Here, a molded product head (10) that is deformed in contact with the punch head (5), and a molded product vertical wall (12) deformed by the punch shoulder (6) and the die shoulder (9). Consider the balance of tension during molding at the molded product shoulder (11) in contact with the punch shoulder (6). When the tension applied in the direction of the molded article head (10) is T _P and the tension applied in the direction of the vertical section of the molded article (12) is T _W , the relationship between them is expressed as T _P = T _W exp (−μθ). be able to. _TP is the friction coefficient μ between the punch shoulder (6) and the molded product shoulder (11), the angle formed by the molded product head (10) and the molded product vertical wall (12), the so-called slack angle θ. the size varies with, T _P as the value of μ and θ is large becomes small. Further, T _P ≦ T _W is always satisfied. Generally, as the molding progresses, the incident angle θ increases, so that T _P / T _W decreases as the molding proceeds as shown in FIG. Therefore, since the tension applied in the direction of the molded product head (10) is always smaller than the tension applied in the direction of the molded product vertical wall (12), the amount by which the molded product head (10) is stretched is Compared to (12).

  Here, the case where the proof stress value of the area | region A which is a molded article head (10) is partially made low like this invention is considered. The molded product head (10) starts plastic deformation with a lower stress than that of the molded product vertical wall (12). Therefore, when the same tension is applied to the molded product head (10), the amount to be stretched increases. That is, in the deformation given to the blank by relatively pushing the punch into the die, the difference in the ratio of the amount by which the molded product head (10) and the molded product vertical wall (12) are stretched is compared with the conventional case. The strain distribution in the entire molded product becomes uniform. Therefore, the distortion of the molded product vertical wall portion (12) is relieved and the distortion of the molded product shoulder portion (11), which is a fracture risk portion, is relieved.

  Here, a region where the proof stress value is greatly reduced by the restoration process exceeds the region A which is the molded product head (10), and the punch shoulder (6) is a region projected on a plane perpendicular to the press direction. When it exists to a certain area | region B, distortion will concentrate on a molded article shoulder part (11), and will become easy to fracture | rupture conventionally. Therefore, the restoration region where the proof stress value is reduced by the restoration process surrounds the punch head (5), which is a surface substantially perpendicular to the pressing direction, of the punch forming surface (8) and the outer periphery of this surface. Of the blank (4) in which a region inside the punch shoulder (6) existing as a bent portion between the punch vertical wall portion (7) and the surface continuous with the projection is projected onto a plane perpendicular to the press direction. Of the area A, an arbitrary area X was designated.

Next, the area ratio (S _X / S _A ), which is the ratio of the area (S _X ) of the restoration region X to the area (S _A ) of the region A onto which the punch head (5) is projected, is 25% or more and 100 % Or less is preferable. An area ratio of 25% corresponds to approximately 50% when expressed by a scale ratio of the shape of the punch head (5). If the restoration region X is smaller than this area ratio (25%), the amount of stretch of the punch head is small, so the amount of strain relaxation in the fracture risk portion (strain concentration portion) is small, and the effect of uniform strain distribution is small. . In addition, when the amount of decrease in the proof stress value is large, the deformation tends to concentrate on the restoration region, so that there is a possibility of breaking at the boundary of the restoration region. On the other hand, exceeding the area ratio of 100% means that the yield strength value is reduced by the restoration process up to the region B where the punch shoulder (6) is projected. In this case, the molded product shoulder (11) is strained. Concentrate and break more easily than in the past. Therefore, the area ratio (S _X / S _A ), which is the ratio of the area (S _X ) of the restoration region X to the area (S _A ) of the region A onto which the punch head (5) is projected, is 25% or more and 100%. The following is preferable. Also, when there are complex irregularities on the punch head and there are parts that are difficult to form, or there are parts that need to be stretched in secondary forming (restriction etc.) after drawing or stretch forming The region may be excluded from the restoration region, and the region X may be divided into a plurality. However, the total area of the region X is preferably 25% to 100%. A more preferable range of the area ratio is 50% or more and 100% or less.

  FIG. 7 shows a case where the punch forming surface (8) has a complicated shape having a plurality of steps. The vertical cross section from the center to the corner indicated by AA in the plan view of the punch forming surface (left side from the center line (13)) is shown as (a), (b), and (c) in the molding order. From the so-called blank hold state (A) to the state (B) in the middle of molding, where the periphery of the blank (4) is sandwiched between the die (2) and the holder (3), the first punch shoulder ( This is done by deforming the blank between 6A) and the second die shoulder (9B). At this time, friction occurs between the first-stage punch shoulder (6A) and the molded product shoulder (11A), and the blank slack angle increases, so the first-stage punch shoulder (6A) The tension generated in the molded product head (10) on which the punch head (5) that is the inner region of the molded product is projected is smaller than that of the molded product vertical wall (12). Therefore, the distortion of the molded product vertical wall (12) increases and the distortion of the molded product shoulder (11A) increases.

  Here, an arbitrary area X is restored from the area A of the blank (4) in which the area inside the punch shoulder (6A) at the first stage is projected. Thereby, by lowering the proof stress value, the distortion of the molded product vertical wall portion (12) and the molded product shoulder portion (11A) is relieved by the above-described action. As described above, since the distortion of the vertical wall portion (12) of the molded product and the shoulder portion (11A) of the molded product is alleviated during the molding (b), even if the molding further proceeds and the strain is introduced. It becomes difficult to break compared to the conventional case.

  Next, when the molding proceeds from the state (a), the blank (4) comes into contact with the punch shoulder (6B) at the second stage, and a frictional force is generated here. Accordingly, since the movement of the blank (4) is suppressed, the molded product shoulder in contact with the second punch shoulder (6B) is the same as the molded product shoulder (11A) in contact with the first punch shoulder (6A). In the portion (11B), the strain increases and becomes a fracture risk portion. In this case, the increase in strain can be mitigated by increasing the blank inflow from the wrinkle holding surface (14). As means for increasing such a blank inflow amount, it is usually possible to reduce the wrinkle pressing force or reduce the tension of the bead (15).

  However, the wrinkle pressing force cannot be adjusted for each part unless a press machine having a mold having a divided wrinkle pressing force and a divided cushion mechanism is used. Therefore, when using a normal press machine, the method to increase / decrease the wrinkle pressing force with respect to the whole wrinkle pressing surface (14) must be adopted. If the wrinkle holding force is reduced as a whole, there is a possibility that a defect such as wrinkles may occur in a molded product depending on the shape. Therefore, it is difficult to adjust the inflow amount balance by increasing or decreasing the wrinkle pressing force with respect to the entire wrinkle pressing surface (14).

  It is also possible to adjust the inflow amount balance of the blank by changing the shape of the bead (15) for each part. However, since the bead (15) is connected in a ring shape on the wrinkle holding surface (14), if the bead shape is extremely changed locally, there is a possibility that the blank breaks at that portion. There is. Thus, in the system in which the bead shape is changed for each part, the degree of freedom of shape change is limited.

  Therefore, the area outside the punch shoulder (6B) closest to the wrinkle holding part sandwiched between the die (2) and the holder (3) (excluding the punch shoulder 6B) is projected onto a plane perpendicular to the press direction. Of the region C, the region Y which is the contracted flange deformed portion is also preferably set as the restoration region. As a result, the deformation resistance of the material is reduced, and the blank can easily flow in only the restoration region Y. Such a restoration region Y can mitigate the increase in strain at the molded product shoulder (11B) in contact with the second-stage punch shoulder (6B). Further, since the processing force required for molding can be reduced as the restoration softening region increases, the tension applied to the periphery of the first-stage molded product shoulder (11A) decreases, and the increase in strain can be mitigated also in this portion.

  Here, the reason why the region Y is contracted and limited to the flange deformed portion will be described. The shrinkage flange deformation is a deformation in which the thickness of the blank increases by being compressed toward the center of the punch while being compressed in the circumferential direction. When this part passes through the bead (15), even if the wrinkle pressing force during molding is constant, the inflow resistance of the blank at this part increases with the progress of molding because the plate thickness increases. For this reason, a greater pulling force (punch load) is applied to the punch shoulder portions (6A, 6B) at this portion than at the portion where the flange does not shrink and deform. As a result, the concentration of strain becomes more prominent in the molded product shoulders (11A, 11B) corresponding to these punch shoulders (6A, 6B).

  Further, as described above, the restoration process can recover the hem bendability reduced by aging, so in the molding of automobile body outer panels, etc., the hem bending, which is the area that undergoes hem bending after the press molding in the restoration area. Parts are preferably included.

<Blank oil>
In general, the aluminum alloy plate is coated with a rust preventive oil or the like in order to prevent scratches and corrosion during transportation. When the plate is heated in the state of being coated in this manner, oil seizure and smoke generation may occur, which may cause poor appearance of the press-formed product and deterioration of the working environment. Therefore, the plate to be subjected to the restoration process is pre-greased oil removed by a degreasing process or the like before the restoration process, or the state of uncoated oil packed so as not to be damaged during transportation. Use one. In addition, the restoration process is performed in the state of no oil coating, but the press molding performed after the restoration process requires press lubricant, so the plate that has been subjected to the restoration process has the lubricant for press molding on the surface as usual. Press molding after applying appropriate amount of oil.

<Press molding>
The press molding performed on the blank subjected to the above restoration treatment can be performed cold as in the case of normal press molding. However, it is desirable to perform press molding within 3 days after performing the restoration process as described above. This is because, after the restoration process, the material strength remains lowered for a while, but the strength increases again due to normal temperature aging, and the strength difference imparted to the blank is lost.

  Moreover, in this invention, it prescribed | regulated that 2% or more of distortion was introduce | transduced into the part used as the product inside the wrinkle pressing part of the press-molding body obtained by press-molding the said blank. 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.

<Hem bending process>
When the press-molded body is an outer panel, after trimming an excess portion, a hem bending process is performed on a predetermined portion of the peripheral portion of the panel and assembled with an separately manufactured inner panel. As described above, the strength gradually increases due to normal temperature aging after the restoration treatment, and accordingly, the hem bendability also decreases. Therefore, it is desirable to perform the hem bending process within 10 days after the restoration process. More preferably, the hem bending process is preferably performed within 3 days after the restoration process.

<Artificial age hardening treatment>
In the automobile manufacturing process, the paint baking process is performed on the car body manufactured by joining the press-formed panels. Such heat treatment is applied to the Al-Mg-Si aluminum alloy plate after the solution treatment. Thus, the strength can be increased. 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.

  It is preferable that the proof stress value after the artificial age hardening treatment of the restoration processing portion of the press-molded body obtained by subjecting the blank subjected to the restoration treatment of the present invention to press molding is 190 MPa or more. When the proof stress 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 weight and material cost.

  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. It is a feature of the present invention that the yield strength of the molded body including the restored region where the yield strength has decreased even in such a short-time heat treatment, is a feature of the present invention. The yield strength further increases.

  In the restoration region, the low temperature clusters are dissolved and the atomic vacancy density is increased again during the heat treatment, so that high temperature clusters are generated and grown instead of the low temperature clusters. This high-temperature cluster transitions to β ″ that is a precipitation strengthening phase by heating in the artificial age hardening treatment, so that a high yield strength can be imparted to the panel. Therefore, since the said restoration | restoration area | region can obtain higher paint bake hardenability with respect to a non-restoration area | region, even after a proof stress value falls by a restoration process, the high intensity | strength of 190 MPa or more is obtained with a proof stress value.

  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 a rolled aluminum alloy sheet having a thickness of 0.9 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 example of the present invention, a cylindrical overhang test was conducted using these aging-treated plates as test materials. As shown in FIG. 6, a punch (1) having a cylindrical shape of φ100 mm, a flat head (φ80 mm), and an R shape (not shown in the figure but a radius of 10 mm) on the shoulder, and a punch (1 ) And a die (2) in which a convex bead (15) is provided on the wrinkle holding surface (14) It has a ring shape with a hole for inserting the punch (1), and the wrinkle holding surface (14) is provided with a convex bead (15) of the die (2) and a concave bead (15) for sandwiching the blank. The holder (3) is attached to a hydraulic press with a press capacity of 12 TON. The material of these molds is SKD11, and the surface is plated with hard chrome.

As shown in FIG. 6, as a test material, a blank (4) of 180 mm × 180 mm was produced from the above-mentioned aging-treated plate and subjected to a restoration treatment under the following treatment method and treatment conditions shown in Table 3. Here, the punch forming surface (8) was in contact with the blank in the initial stage of molding, and was continuous so as to surround the punch head (5) which is a surface substantially perpendicular to the pressing direction and the outer periphery of this surface. A blank area A obtained by projecting an area inside the punch shoulder part (6) existing as a bent part between the punch vertical wall part (7) and the surface onto a plane perpendicular to the press direction is a punch head. This is a region where a flat surface of φ80 mm of part (5) is projected. The test was conducted by varying the area ratio (S _X / S _A ) when the area of φ80 mm was S _A and the area of the restoration region X was S _X. In FIG. 6, (9) represents a die shoulder, (11) represents a molded product shoulder, and (12) represents a molded product vertical wall.

  In order to heat the restoration area, as shown in FIG. 8 (a), the restoration area at the center is projected by 5 mm from an aluminum alloy plate having a thickness of 200 mm × 200 mm and a thickness of 10 mm (thickness is not shown). Several types of heating jigs (28) in which convex circles (31) having a convex height (not shown in the figure) were cut out were produced by changing the size of the convex circles (31). Further, as shown in FIG. 8 (a), the central portion of the soft heat insulating material (33) of 200 mm × 200 mm and a thickness of about 5 mm is cut out according to the convex circle (31) of the heating jig (28), and the heating jig ( By aligning with the convex circle (31) side of 28), the surface that comes into contact with the blank when pressed is 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 described later with screws.

  As shown in FIG. 2, the blank restoration heating apparatus is provided with a pressing lower die (25) having a heater (26) mounted on a bolster (22) of a hydraulic press having a pressing capacity of 50 TON, and this pressing lower die (25 ) Is supported by cushion pins (23). When pressing, a predetermined pressing pressure can be maintained by a cushion mechanism of a press. On the other hand, a pressing upper die (24) having a built-in heater (26) is attached to the slide plate (21) via a hard heat insulating material (27) so that heat is not transmitted to the press machine. A heating jig (28) was attached to the lower surface of (24). The heaters were controlled by a temperature control device (not shown) so as to maintain the respective set temperatures, and the lower pressing mold (25) and the upper pressing mold (24) were heated to a predetermined temperature by the heater (26). The heating jig (28) attached to the lower surface of the pressing upper die (24) was also heated by heat transfer.

  Next, the heating apparatus was used and the blank was heat-processed. First, as shown in FIG. 2A, a blank (4) is placed on the pressing lower mold (25), and a hard heat insulating material (27) having a thickness of about 25 mm is placed on the blank (4). It was. The slide plate (21) is lowered by the press mechanism of the press machine, the heating jig (28) contacts the hard heat insulating material (27) on the blank (4), and the blank (4) is predetermined by the cushion mechanism of the press machine. The preheating was completed by pressurizing for a predetermined time with the pressing pressure of.

  Next, as shown in FIG. 2A, after removing the hard heat insulating material (27) placed on the blank (4), the slide plate (21) is lowered by the press mechanism of the press machine, and the heating jig (28) was in contact with the blank (4), and the heating of the restoration region was completed by pressing the blank (4) with a predetermined pressing pressure for a predetermined time by the cushion mechanism of the press. In this heat treatment, the time from when the heating jig (28) contacts the blank (4) until it leaves is adjusted by the sliding 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 cooling treatment of the blank after the heat treatment was performed by a method of immersing the blank in a water tank, a method of sandwiching the blank with a metal block at room temperature, and a method of air cooling with a fan.

  In this way, a plurality of blanks that were subjected to the restoration process under the conditions of specimen numbers 1 to 15 in Table 3 were produced for each condition. These blanks were subjected to a cylindrical stretch forming test described below, and the following tests were performed.

<Blank mechanical properties>
The mechanical properties (strength and elongation) of the restored area and the non-restored area, and the difference in yield strength between the restored area and the non-restored area were measured. Specifically, as shown in FIG. 9, a small tensile test piece (41) was collected from both the restoration region X and the non-restoration region of each blank (4). The longitudinal direction of the small tensile test piece (41) coincides with the rolling direction of the aluminum alloy rolled sheet of each blank (4). FIG. 10 shows the dimensions of the small tensile test piece (41). The unit of the numerical value in the figure is mm, and the thickness of the test piece is 0.9 mm. Table 4 shows the measurement results.

<Yield strength after artificial age hardening treatment>
In addition, in order to measure the proof stress after paint baking in the automobile manufacturing process, 2% tensile strain was applied to the small tensile test piece taken from the restored region and the non-restored region, and then an artificial temperature of 170 ° C. × 20 minutes was applied. Age hardening treatment was performed, and the yield strength value was measured by a tensile test. In addition, a tensile test was performed in which the pre-strain amount and artificial age hardening treatment conditions were changed. The results are shown in Table 4.

<Bendability>
Furthermore, a bending test simulating the hem bending process performed in the automobile manufacturing process was performed. First, 5% tensile strain was applied to the small tensile test piece taken from the restoration region. Next, along the bend line perpendicular to the tensile direction at the center of the test piece, bend at a bend radius of 0.8 mm until an angle of 90 °, and further bend to an angle of 135 °. A plate having a thickness of 1.0 mm was inserted on the assumption that the plate would be inserted, and the plate was bent to an angle of 180 ° so that the plate was sandwiched between the plates. The outside of the bent portion was observed with a loupe, and it was judged that the bending workability was good when no crack was generated, and the bending workability was judged to be poor when the crack was generated. For specimen No. 14, a small tensile test piece could not be collected because the area ratio of the restored region was small. The results are shown in Table 4.

<Influence of thermal deformation>
Further, in order to evaluate the degree of thermal deformation of the blank, the amount of warpage of the blank was measured. The blank subjected to the restoration process was placed on the surface plate with the surface opposite to the side on which the heating jig contacted when the restoration region was heated. As shown in FIGS. 11 (a) and 11 (a), the stylus (42) of the stylus type CNC contour measuring machine is placed on the center line of the blank (4) along the direction coinciding with the rolling direction of the aluminum alloy sheet. Were scanned and the outline of the blank was measured as XY coordinate data. About this XY coordinate data, as shown in FIG. 12, the blank rolling direction position is taken as the X axis, the displacement in the direction perpendicular to the blank plane is taken as the Y coordinate, both ends of the blank are taken as the Y coordinate 0, The maximum value of displacement was evaluated as the amount of warpage. The results are shown in Table 4.

Moreover, in order to evaluate the material-separability of the blank which performed the decompression | restoration process, the material-separation test was done. Wash and rust preventive oil (viscosity: 4.0 mm ² / s, 40 ° C.) is applied to both the front and back sides of each blank so that the amount of oil on one side is about 2 g / m ^2. A blank pile (43) was formed by overlapping 10 blanks. A weight of 20 kg was placed on these blanks (43) and allowed to elapse for 24 hours. Then, as shown in Fig. 13 (a) Plan view and (b) Front view, each blank pile (43) is fixed with both sides sandwiched by vise (44) except for the top blank. Then, 0.5 MPa of compressed air was injected from both side surfaces from the multi-hole air nozzle (45) having a width of 50 mm toward the uppermost blank and the lower blank. At this time, when the uppermost blank was lifted and could be separated from the lower blank pile (43), it was evaluated that the material was separable, and when it could not be separated, it was evaluated as unacceptable. The results are shown in Table 4.

<Cylindrical overhanging test>
Next, a cylindrical overhang forming test will be described based on FIG. Washing rust preventive oil for blanks (4) of specimen numbers 1 to 15 with the punch (1), die (2) and holder (3) attached to the hydraulic press with the press capacity of 12 TON and subjected to restoration treatment Was applied with a sponge and set on the holder (3). Note that FIG. 6 does not show the hydraulic press. As shown in FIG. 6A, the periphery of the blank (4) is sandwiched between the die (2) and the holder (3), and a bead (15) is formed around the blank (4). At this time, the holder is supported by a cushion pin of the press machine, and a set wrinkle pressing load of 15 TON is applied to the wrinkle pressing surface (14). Next, when the die (2) is lowered from such a set state, the die (2) and the holder (3) are put on the punch (1) while the periphery of the blank (4) is held by the beads (15). The molding proceeds downward at a molding speed of 1 mm / second, and as shown in FIG. 6 (a), molding proceeds while the blank (4) contacts the punch (1) and undergoes deformation. By this method, a molded product that had been molded at a molding height of 14 mm and a molded product that was molded until it broke were produced.

  For each blank, the limit overhang height which is the height at which the blank broke, the plate thickness reduction rate range of the molded product having a molding height of 14 mm, and the occurrence of ridging of the molded product were evaluated. The limit overhang height was the stroke at the maximum load point in the punch load-stroke diagram, and was evaluated for formability. Also, the difference in thickness reduction rate between the center of the molded product head and the shoulder of the molded product (punch shoulder) in the rolling direction of the molded product with a molded height of 14 mm is defined as the thickness reduction rate range, It was evaluated. Further, the presence or absence of ridging was visually observed by polishing the vertical wall portion (12) of the molded product having a molding height of 14 mm with # 800 abrasive paper at a right angle to the rolling direction. Evaluation was made as if there were some that showed streaks and none that showed no streaks.

  The above test was performed three times under the same conditions, and an average value of three times was adopted. The evaluation results are shown in Table 4. Test material numbers 1 to 7 are examples of the present invention, and test material numbers 8 to 15 are comparative examples.

  First, test material number 8 as a comparative example is a condition of normal press molding in which a restoration process is not performed. Since deformation tends to concentrate on the shoulder portion of the molded product corresponding to the punch shoulder portion, the fracture occurred at this molded product shoulder portion, and the limit overhang height was 15.6 mm. For molded products stopped at 14 mm before breaking the molding height, the plate thickness is greatly reduced at the shoulder of the molded product, so the thickness reduction rate range is large and more distortion is introduced compared to the molded product head. Ridging occurred on the vertical wall of the molded product. Moreover, since the material remained aged, cracks occurred in the bending test. Furthermore, since the blanks remain flat, in the material separation test, since the blanks are in close contact with each other by the cleaning rust preventive oil, the air injected from the air nozzle cannot enter the interface and can be separated. There wasn't.

  On the other hand, in the test material numbers 1 to 7 which are the examples of the present invention, all of the restoration regions were softened, thereby giving a proof stress difference with the non-restoration regions, compared with the comparative examples. The limit overhang height is high and the moldability is improved. Moreover, the plate thickness reduction rate range is small, the strain is made uniform, and the rise in strain at the vertical wall portion of the molded product is suppressed, so that the generation of ridging is suppressed. In addition to this, the bendability of the restored region was recovered, and no cracks were observed. Moreover, since the clearance gap generate | occur | produced between blanks because the slight curvature generate | occur | produced in the blank, material-separability improved. Furthermore, the strength value after the artificial age hardening treatment increased the strength increase by applying the restoration treatment, and greatly exceeded 190 MPa.

  On the other hand, the test material numbers 9 and 10 which are comparative examples are conditions in which the temperature reached by heating in the restoration region is out of the scope of the present invention. In specimen No. 9, since the temperature reached by heating was low, the restored region was not softened, and the moldability and bendability were not improved. However, since the blank was slightly warped by the restoration process, only the material separability was improved. Further, in the test material No. 10, since the temperature reached by heating was high, age hardening occurred simultaneously with softening due to dissolution of the low temperature cluster, and the elongation of the restoration region was greatly reduced. The fracture occurred at the boundary between the restored area and the non-restored area. Therefore, there was no improvement in moldability. In addition, Mg and Si in the matrix are precipitated as a β ′ phase that is a coarse precipitation phase within a short period of time, and the solid solution amount of Mg and Si is reduced. The rise was significantly reduced and was below 190 MPa.

  In the test material No. 11, which is a comparative example, since the temperature reached by heating in the non-restoration region is high, dissolution of low temperature clusters and age hardening occurred in the non-restoration region, resulting in a decrease in yield strength and elongation. Since the restored region was further heated, age hardening further occurred, resulting in an increase in yield strength and a decrease in elongation. As a result, the proof stress was higher in the restored region than in the non-restored region, which was contrary to the originally intended strength difference, so that deformation was concentrated on the shoulder portion of the molded product and the moldability deteriorated. Further, since the temperature difference between the restored region and the non-restored region is small, the blank did not warp and the material separability was not improved. In test material No. 12, which is a comparative example, the non-restoration region was not heated, so the temperature difference between the restoration region and the non-restoration region was large, excessive thermal deformation occurred in the blank, and the amount of warpage was very large. In addition, streak marks due to thermal deformation occurred at the boundary between the restored area and the non-restored area, and this trace remained in the molded product even after press molding.

  Moreover, the test material number 13 which is a comparative example is the conditions from which the temperature rising rate in heating of a decompression | restoration area | region and the heat holding | maintenance time, and the time for which a blank stays at 100 degreeC or more through the whole restoration | recovery process remove | deviated from the range of this invention It is. Since the rate of temperature rise is slow, the heating and holding time is long, and the time to stay above 100 ° C is also long, both the non-restoration region and the restoration region are age-hardened, and the total heating time is long and the restoration region is high in temperature. Since this was hardened more, it was contrary to the original strength difference, and deformation was concentrated on the shoulder portion of the molded product, resulting in deterioration of moldability. Moreover, there was no suppression of ridging and recovery of bendability. Sample No. 14, which is a comparative example, is a condition in which the sample is allowed to cool without being actively cooled after heating. Since the time during which the blank stays at 100 ° C. or more throughout the cooling rate and the entire restoration process is out of the scope of the present invention, the yield strength decreased by the heat treatment increases during cooling, and the elongation decreases. It got worse. There was also no improvement in ridging and no recovery in bendability.

The specimen number 15 defines the restoration region X beyond the range of the region A where the punch head is projected. Since the area ratio of the restoration area is large and the restoration area extends to the shoulder of the molded product, deformation concentrates on the shoulder of the molded product, and the limit overhang height is 10.5 mm, which is significantly lower than usual.
On the other hand, specimen numbers 16 to 19 are the results of a tensile test in which the pre-strain amount after the restoration treatment and the artificial age hardening treatment conditions were changed. Specimen Nos. 16 to 18 are conditions obtained by changing the pre-strain amount or artificial age hardening treatment conditions with respect to Specimen No. 2. Since the test material number 16 increased the pre-strain amount to 4%, the yield strength after the artificial age hardening treatment increased. On the other hand, since the test material number 17 did not add prestrain, the yield strength after the artificial age hardening treatment was low, and it was less than 190 MPa. Moreover, since the test material number 18 made the artificial age-hardening treatment conditions high at 185 ° C. × 30 minutes and lengthened the time, the yield strength after the artificial age-hardening treatment was increased.
Specimen No. 19 is the case where the heat reaching temperature of the restoration process is higher than the temperature range of the present invention, and even if the artificial age hardening condition is 185 ° C. × 30 minutes and the temperature is increased and the time is prolonged, the restoration is performed. The yield strength of the region after the artificial age hardening treatment was less than 190 MPa.

[Example 2]
As a second example of the present invention, a two-stage press molding test was conducted using an aging-treated plate as a test material. As shown in FIG. 7, the mold has a two-stage shape in which the vertical wall portion of the punch forming surface is a first-stage punch vertical wall portion (7A) and a second-stage punch vertical wall portion (7B). The punch shoulder of the eye (6A) is R16mm, the punch shoulder of the second step (6B) is R8mm, and the rough dimension of the punch forming surface in plan view is about 170mm x about 270mm for the first step and about 200mm for the second step. X About 300 mm. The die (2) also has two shoulders (9A, 9B), and the molded product also has two shoulders (11A, 11B) and two vertical walls (12A, 12B). The molding height is 40 mm. The material of these molds is FCD550, and the surface is hard chrome plated. This mold was set in a mechanical press machine with a press capacity of 300 TON and tested.

In addition to the area X for the blank area A shown in FIG. 7, the restored area is also determined as the restored area for some blank areas Y. Here, between the punch head (5) which is a surface substantially perpendicular to the pressing direction among the punch forming surfaces, and the punch vertical wall portion which is a continuous surface surrounding the outer periphery of the surface. A blank area A obtained by projecting an area inside an R-shaped punch shoulder existing as a bent part onto a plane perpendicular to the press direction is a flat surface inside the first-stage punch shoulder (6A). It is the area | region which projected the punch head (5) which is. The area of this region A S _A, the area ratio when the area of the region X performing partial reversion treatment was _{S X (S X / S A} ) Several prepared by restoration process heating jig shaken several levels of the gave.
Further, in the blank (4), the shrinkage flange deformed portion of the blank region C projected from the region outside the punch shoulder closest to the wrinkle holding portion sandwiched between the die and the holder onto the plane perpendicular to the press direction. The region Y is a region in contact with the R shape at the four corners excluding the immediate side portion of the punch forming surface in a plan view of the blank among the regions projected from the outside of the punch shoulder portion (6B) of the second stage. . Also for this region Y, a corresponding heating jig was prepared and subjected to a restoration process.

The restoration heating apparatus used in Example 1 was used for the blank restoration process. A heating jig having a shape corresponding to the region X and the region Y was manufactured and attached to a restoration heating apparatus, and a restoration process was performed. In addition, the heating jig of the region _X was prepared for six levels in which the area ratio (S _X / S _A ) was changed when the area of the region A was S _A and the area of the restoration region X was S _X.

  As a test material, a blank of 440 mm × 360 mm was cut out from a plate having an aging treatment number A in Table 2 with an alloy number I in Table 1, and a restoration treatment was performed under the restoration treatment conditions in Table 5. In addition, in order to measure the mechanical properties (strength and elongation) of the restored area and the non-restored area after restoration processing and the difference between the proof strength of the restored area and the non-restored area, as in Example 1, for each blank, FIG. A small tensile test piece having the shape shown in Fig. 2 was taken from both the restored region and the non-restored region along the rolling direction of the aluminum alloy sheet and subjected to a tensile test. The results are shown in Table 5.

  Next, a two-stage press molding test will be described. First, when the die is lowered from the state where the blank (4) is set on the holder (3), the periphery of the blank (4) is sandwiched between the die (2) and the holder (3) as shown in FIG. A bead (15) is formed around the blank (4). At this time, the holder (3) is supported by the cushion pin of the press machine, and a set DC (die cushion) load is applied to the wrinkle holding surface (14). Next, the die (2) and the holder (3) descend toward the punch (1) in a state where the periphery of the blank (4) is gripped by the bead (15). As a result, the blank contacts the punch (1) as shown in FIG. Then, as shown in FIG. 7C, when the press stroke is lowered by 40 mm from the state of FIG.

  In this molding, when the DC load is increased, the inflow amount of the blank from the wrinkle pressing surface (14) is decreased. Therefore, the amount of strain introduced into the blank inside the wrinkle holding surface (14) increases, and the molded product is easily broken. On the other hand, when the molding can be performed without breaking even with a DC load higher than the conventional one, it means that the moldability is improved by uniformizing the strain. Therefore, each blank was molded while increasing the DC load in increments of 25 kN, and the DC load before the fractured DC load was evaluated as the fracture limit DC load. The test was performed three times under the same conditions, and an average value of three times was adopted.

  These test results are shown in Table 6. Test number A is a condition of normal press molding that has not been restored. Under this condition, the molded product shoulder portion (11A) corresponding to the upper punch shoulder portion with a DC load of 175 kN broke, so the front 150 kN was set as the breaking limit DC load, which was used as the reference DC load for the DC load improvement rate. . That is, the DC load improvement rate was {(break limit DC load−reference DC load) / (reference DC load)} × 100.

  Test numbers C, D, E, and F are examples of the present invention obtained by restoring and softening the region X of the present invention. In all cases, the moldability was improved with respect to the standard. In particular, in the test number C with a restoration area ratio of 100%, the fracture limit DC load was improved by 250% and + 67%. In addition, due to the effect of restoring and softening the region X, the break position moved to the molded product shoulder (11B) corresponding to the punch shoulder of the second stage in test numbers C, D, E, and F.

  On the other hand, the test number A is a condition in which the area ratio of the restoration region X with respect to the area A is out of the scope of the present invention, and the restoration area ratio is larger than the scope of the present invention. Since the restoring region hits the upper shoulder of the molded product, strain was concentrated at that portion, and the breaking limit DC load was not improved. Further, the fracture position was the same as the reference, and was the molded product shoulder (11A) corresponding to the upper punch shoulder.

  The test numbers “K”, “K”, “K”, and “K” are conditions obtained by adding a region Y that is a shrinkage flange deformed portion to the restoration region. Since the inflow resistance of the blank of the said site | part decreased by softening of the area | region Y, the tension | tensile_strength applied to a molded article shoulder part (11A, 11B) decreased, and the raise of the distortion was relieved. As a result, the breaking limit DC load was greatly improved as compared with the case where the restoration process was performed only on the region X, and the maximum improvement was + 167% with respect to the reference.

  By the manufacturing method of the aluminum alloy blank for press forming according to the present invention, the formability for improving the paint bake hardenability and the design freedom, which are excellent features of the Al-Mg-Si based aluminum alloy, high surface quality, In addition, it is possible to provide a blank made of aluminum alloy for press forming that also has hem bendability for fastening to the inner panel, and it is also possible to provide a press formed body using the blank.

DESCRIPTION OF SYMBOLS 1 ... Punch 2 ... Die 3 ... Holder 4 ... Blank 5 ... Punch head 6, 6A, 6B ... Punch shoulder part 7, 7A, 7B ... Punch vertical wall part 8 ... Punch molding surface 9 , 9A, 9B ... Die shoulder 10 ... Molded product head 11, 11A, 11B ... Molded product shoulder 12, 12A, 12B ... Molded product vertical wall 13 ... Center line 14 ... Wrinkle holding surface 15 …… Bead 21 …… Slide plate 22 …… Bolster 23 …… Cushion pin 24 …… Pressing upper mold 25 …… Pressing lower mold 26 …… Heater 27 …… Hard insulation 28 …… Heating jig 29 …… Restoration area 30A, 30B ... Heating element 31 ... Convex part, Convex circle 32 ... Mounting hole 33 ... Soft heat insulating material 41 ... Small tensile test piece 42 ... Stylus 43 ... Blank mountain 44 ... Vise 45 …… Air nozzle B …… Pan Any region T _P ...... moldings head direction in the molded article shoulder of the nearest punched region obtained by projecting the region outside the shoulder X ...... A from the region C ...... wrinkle pressing portion obtained by projecting shoulders tension T _W ...... applied to moldings vertical wall direction in the molded article shoulder tension Y ...... a shrinkage flange deformation portion is a region θ ...... Natsuki angle μ ...... friction coefficient of C applied to

Claims (11)

It is made of age-hardened Al-Mg-Si-based aluminum alloy, and it is a manufacturing method of a press-molding aluminum alloy blank that is formed into a predetermined shape by sandwiching the periphery with a die and a holder and relatively pushing the punch into the die. There,
A punch that exists as a bent portion between a punch head surface, which is a surface substantially perpendicular to the press direction, and a punch vertical wall portion, which is a surface continuous so as to surround the outer periphery of this surface. An area including an arbitrary area X among blank areas A projected on a plane perpendicular to the press direction from an area inside the shoulder is defined as a restoration area, and the entire blank other than the restoration area is a non-restoration area As
A restoration process including a heating process for heating the entire blank before press molding and a cooling process for cooling the entire blank to 100 ° C. or less is performed thereafter. In the heating process, a heating temperature is 200 ° C. in the restoration region. In the non-restoration region, the temperature is set to 100 ° C. or more and less than 200 ° C., and in the restoration region, the heating rate from 100 ° C. to the heating attainment temperature is set to 5 ° C./second or more in the heating step. the retention time was 20 seconds or less, the cooling rate to 100 ° C. and 5 ° C. / sec or more in the cooling process, the time the blank throughout the restoration process stays above 100 ° C. with 2 minutes, the area X reduce the proof stress of, and, it said without increasing the yield strength values of the non-restored area, provide strength difference in the blank,
The Al—Mg—Si-based aluminum alloy has been subjected to a solution treatment, and the Al—Mg—Si-based aluminum alloy after the solution treatment is subjected to normal temperature aging or 100 ° C. or less before the restoration treatment is performed. A method for producing an aluminum alloy blank for press forming, characterized in that an age-hardened Al-Mg-Si-based aluminum alloy is obtained by performing an aging treatment by artificial aging or a combination thereof .   The manufacturing method of the aluminum alloy blank for press forming of Claim 1 which makes the difference of the heating attainment temperature in the said restoration | reconstruction area | region and a non-restoration area | region into 50 to 200 degreeC.   The press according to claim 1 or 2, wherein after the preheating step at an ultimate temperature of 100 ° C to less than 200 ° C is performed on the entire blank in advance, a heating step at a heating ultimate temperature of 200 ° C to 300 ° C is performed only on the restoration region. A method for producing a blank made of aluminum alloy for molding.   The aluminum alloy for press forming according to claim 1 or 2, wherein both regions are heated simultaneously by bringing the heating body into contact with a blank while controlling the temperature of the heating body that heats the restoration region and the non-restoration region, respectively. A manufacturing method for a blank. The press molding according to any one of claims 1 to 4, wherein an area ratio of the area (S _X ) of the region X to the area (S _A ) of the blank region A is 25% or more and 100% or less. For manufacturing aluminum alloy blanks.   The restoration area of the blank is a shrinking flange deformed portion of the blank area C projected from the area outside the punch shoulder closest to the wrinkle holding part sandwiched between the die and the holder onto a plane perpendicular to the pressing direction. The manufacturing method of the aluminum alloy blank for press molding as described in any one of Claims 1-5 also including the certain area | region Y.   The manufacturing method of the aluminum alloy blank for press forming as described in any one of Claims 1-6 in which the restoration | recovery area | region of the said blank also includes the hem bending part which is an area | region which receives hem bending after press molding. The Al-Mg-Si-based aluminum alloy is subjected to preliminary aging treatment after solution treatment and before performing aging treatment at room temperature or artificial aging at 100 ° C. or lower, or aging treatment by a combination thereof. The manufacturing method of the aluminum alloy blank for press forming as described in any one of claim | item 1 -7.   The Al—Mg—Si based aluminum alloy contains Mg: 0.2 to 1.5 mass%, Si: 0.3 to 2.0 mass%, Fe: 0.03 to 1.0 mass%, Zn: 0 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. It is an aluminum alloy which further contains 1 type or 2 types or more selected from 005-0.3 mass% and V: 0.01-0.4 mass%, and consists of remainder Al and an unavoidable impurity. The manufacturing method of the aluminum alloy blank for press molding as described in any one of these.   By applying press forming to the aluminum alloy blank for press forming manufactured by the method for manufacturing an aluminum alloy blank for press forming according to any one of claims 1 to 9, a product inside the wrinkle holding portion and A manufacturing method of an aluminum alloy press-molded body, wherein a strain of 2% or more is introduced into the portion.   The manufacturing method of the aluminum alloy press-molded body according to claim 10, wherein the yield strength of the molded body is set to 190 MPa or more by performing an artificial age hardening treatment at 170 to 185 ° C for 20 to 30 minutes.

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