JP2013010998A - Method for manufacturing aluminum alloy blank for press forming, and method for manufacturing aluminum alloy press formed product using the blank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an aluminum alloy blank for press forming having formability, high surface quality, and high hem bendability, for improving the age hardenability by coating/baking and the degree of freedom in design, and also to provide a method for manufacturing a press formed product using the same.SOLUTION: The method for manufacturing an aluminum alloy blank for press forming made of an age-hardened Al-Mg-Si-based aluminum alloy includes a heating process at a heating temperature of 200°C or higher and 300°C or lower, and a subsequent cooling process to a temperature of 100°C or lower, in which there is formed a partial restoration treatment part of an arbitrary region X of a blank region A obtained by projecting an inner region than a punch shoulder part present as a bending part between a punch top part and a vertical wall part of the punch to a plane vertical to a press direction. In the heating process, the temperature rise rate from 100°C to an end-point temperature is set to 5°C/s or more, and a holding time at the end-point temperature is 20 s or less, and in the cooling process, the cooling rate to 100°C or lower is set to 5°C/s or more.

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. For example, the plate may be deformed due to thermal strain caused by the temperature difference between the heating part and the non-heating part. In addition, since the aluminum alloy plate has high thermal conductivity, the peripheral portion of the heating region is also heated by the heat conduction of the plate itself. Since the degree of these becomes severer as the heating temperature becomes higher, there is a practical impediment to heating in the temperature range from 250 ° C. to 530 ° C.

  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.

Japanese Patent No. 3393185 JP 2009-161851 A

  As described above, the conventionally proposed technique is a means for improving the press formability and the surface quality while having the paint bake hardenability which is an excellent feature of the Al—Mg—Si based aluminum alloy. It has been difficult to achieve uniform strain distribution of the molded product after press molding and recovery of hem bending workability, which is a process of bending the periphery of the molded product to 180 ° after press molding. 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 about the arbitrary area | region X of the area | region A, it decided to perform the restoration process which consists of heating and quenching partially before press molding. This reduces the proof stress value of the region and enables plastic deformation with a lower tension than before, so that the region can be actively stretched, while strain is concentrated and there is a high risk of breakage. It was found that the increase in the strain of the blank was alleviated, and as a result, the strain distribution of the entire blank could be made uniform.

  In addition, by appropriately selecting conditions such as the temperature reached by heating, the rate of temperature rise, the holding time, and the cooling rate after completion of heating, the selected portion can be softened efficiently in a very short time. It was found that heme bendability can be recovered and high paint bake hardenability can be obtained.

  Low-temperature clusters that are fine precipitates of Mg and Si in the matrix when rapidly cooled after solution treatment and alloy elements are supersaturated at room temperature and kept at room temperature or slightly higher than this. A so-called age-hardened rolled aluminum alloy sheet is obtained in which the strength increases due to the gradual formation of. Restoration means reducing the strength of the material by heating it to a temperature higher than the above-mentioned holding temperature for a short time to re-dissolve the low-temperature cluster generated at room temperature and then immediately quenching to bring it into a supersaturated state. Means the phenomenon 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. Arbitrary area X of blank area A projected on the plane perpendicular to the press direction from the area inside the shoulder as a partial restoration processing section,
The partial restoration processing part is formed by a heating step at an ultimate temperature of 200 ° C. or more and 300 ° C. or less and a subsequent cooling step to 100 ° C. or less. In the heating step, the rate of temperature increase from 100 ° C. to the ultimate temperature is 5 ° C. Of the aluminum alloy blank for press forming, characterized in that the holding time at the ultimate temperature is 20 seconds or less and the cooling rate to 100 ° C. or less is 5 ° C./second or more in the cooling step. It was set as the manufacturing method.

  According to claim 2 of the present invention, the Al—Mg—Si based aluminum alloy according to claim 1 is subjected to a solution treatment, and the Al—Mg—Si based aluminum alloy after the solution treatment is partially restored. Aged and hardened Al—Mg—Si based aluminum alloy is obtained by performing aging treatment at room temperature, artificial aging at 100 ° C. or lower, or a combination thereof.

In claim 3 of the present invention, in claim 1 or 2, 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.

  In Claim 4 of this invention, in any one of Claims 1-3, in the said blank, the area | region outside the punch shoulder part nearest from the wrinkle pressing part pinched | interposed with die | dye and a holder is made into a surface perpendicular | vertical with respect to a press direction. Of the projected blank area C, the area Y, which is a shrinking flange deformed part, was also used as a partial restoration processing part.

  According to claim 5 of the present invention, in any one of claims 1 to 4, the hem bending portion which is a region subjected to hem bending after press molding is also a partial restoration processing portion.

  In Claim 6 of this invention, in any one of Claims 1-5, 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%, Zr: 0 .01-0.4 mass%, Cr: 0.01-0.4 mass%, Ti: 0.005-0.3 mass% and V: 0.01-0.4 mass% Further, an aluminum alloy containing the balance Al and inevitable impurities was obtained.

  According to a seventh 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 sixth aspects is subjected to press molding to produce a wrinkle. It was set as the manufacturing method of the press molding body made from an aluminum alloy characterized by the 2% or more distortion being introduce | transduced into the part used as the product inside a holding | suppressing part.

  In claim 8 of the present invention, in claim 7, the aging value of the partially restored portion is set to 190 MPa or more by performing artificial age hardening treatment at 170 to 185 ° C. for 20 to 30 minutes.

  By the above means of the present invention, the press formability of the Al—Mg—Si based aluminum alloy rolled sheet, which is inferior to that of the cold rolled steel sheet, is remarkably improved. In addition, 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 in design are significantly improved. Furthermore, it is an excellent feature of the Al-Mg-Si alloy by appropriately selecting conditions such as the temperature reached by heating and the rate of temperature rise, the holding time, and the cooling rate after completion of heating in the partial restoration process. Paint bake curability 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 due to the small tension applied in press molding 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 addition, since the rolled aluminum alloy plate used in the present invention has a smaller longitudinal elastic modulus than that of the steel plate, the amount of elastic recovery (spring back) of the residual stress in the plate after press forming is large, and it is difficult to ensure the shape freezing property. there were. 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. Furthermore, 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 conventional production efficiency is not reduced.

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 (T _W ) applied to the vertical wall portion of the molded product and the tension (T _P ) applied to the head portion of the molded product is the angle between the head of the molded product and the vertical wall portion of the molded product, and the punch angle It is a graph which shows changing with the friction coefficient (micro) which generate | occur | produces between a shoulder part and a molded article shoulder part. 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. It is a front view of the heating apparatus used for the restoration | recovery heat processing of the blank in the example 1, 2 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 based alloy, and its specific component composition is not particularly limited, but the component as defined in claim 6. 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 to dissolve Mg ₂ Si, elemental Si, etc. in the matrix, thereby imparting paint bake hardenability, and to improve the strength after the paint bake treatment performed after press molding. It is an important process. This process also contributes to lowering the distribution density of the second phase particles by solid solution of Mg ₂ Si, simple substance Si particles, etc., and improving ductility and bendability, and also good molding by recrystallization. This is also an important process for obtaining good performance. 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 difference in strength between the heated part and non-heated part of the blank by partial restoration processing, a certain amount of low-temperature clusters are generated by room temperature aging (natural aging) during the room temperature standing period after solution treatment. It is necessary to be. If such a low-temperature cluster is not generated, the restoration phenomenon does not occur even in the heating part in the subsequent partial restoration process, and the strength reduction of the heating part due to the partial restoration process is not realized.

  Therefore, after the solution treatment, it is necessary to leave at room temperature for one day or more before performing the partial restoration treatment. 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 within 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 combination of room temperature aging and artificial aging, by subsequent partial restoration processing An intensity difference can be imparted to the blank.

  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 before performing the next partial restoration process after aging as described above. When the proof stress value is less than 110 MPa, a sufficient strength difference cannot be imparted because the strength reduction at the portion restored by heating in the subsequent partial restoration process is insufficient.

<Partial restoration process>
Next, the partial restoration process that is the main point of the present invention will be described. The partial restoration process is a process in which an arbitrarily selected region of an age-hardened Al—Mg—Si-based aluminum alloy rolled sheet is heated to a predetermined temperature and then cooled to room temperature. The mechanism is 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.

<Heat treatment condition and cooling treatment condition of partial restoration process>
In the present invention, the heat treatment conditions for the partial restoration treatment are defined as follows. That is, the temperature reached by heating in the restoration process 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. In addition, when the plate is partially heated, there is a problem that the plate is deformed due to thermal strain caused by the temperature difference between the heated part and the non-heated part, but this becomes more noticeable as the heating temperature becomes higher. Is desirable.

  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 temperature reached by heating in the partial restoration process can be further divided into two temperature ranges according to the rate of change with time in the strength of the heated 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. These atomic vacancies promote the diffusion of Mg and Si while maintaining the room temperature in the part subjected to the partial restoration process, and accelerate the formation of low temperature clusters at room temperature. If left unchecked for a day, 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 partial restoration process. Specifically, 3 days or less is desirable.

  On the other hand, when the restoration heat treatment is performed in the 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 is partially The increase in the proof stress over time during the normal temperature holding period after the restoration process is sufficiently small. Therefore, when a partial 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 the flexibility of the production process schedule is important, the partial recovery process reaches the heating level so that it is possible to perform press forming even if the blank is held at room temperature for several days after the partial recovery process. The temperature is preferably 200 ° C. or higher and lower than 250 ° C. In addition, the normal temperature holding period from the partial restoration process to press molding is preferably within 10 days.

  The rate of temperature increase from 100 ° C. to the temperature reached to heating and the rate of cooling from the temperature reached to 100 ° C. are preferably as fast as possible, and each is defined as 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 temperature is preferably as short as possible, and is defined as 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). In the heat treatment, the non-heated part is also heated by the heat conduction of the aluminum alloy rolled sheet itself, but there is no problem if the holding time is 20 seconds or less. The reason why the temperature rising rate and the cooling rate are defined as those from 100 ° C. to 100 ° C. is that the transition to the β ″ phase does not occur at 100 ° C. or less, and the progress of age hardening is extremely slow. Thereafter, even if it is gradually cooled, the mechanical properties are not affected.

<Blank heating method for partial restoration>
As a method of partially heating a part of the blank, a metal plate (aluminum alloy, copper alloy, etc.) processed according to the shape of the part to be heated is heated with a heater, etc., and contacted with the blank to pressurize it. The method of transferring heat is the simplest. This may be processed one by one in the state of a plate, or a coiled aluminum alloy plate material may be continuously restored and cut with a blanking press. In addition, other known heating means such as induction heating, laser heating, infrared heating, and electric heating may be used as appropriate.

<Blank cooling method for partial restoration processing>
As a method of cooling after partially heating a part of the blank to a predetermined temperature, contact such as die quench that has a larger heat capacity than the blank and further cools by heat transfer with the blank sandwiched between metal blocks with built-in water-cooled piping The formula is most effective in terms of cooling rate and productivity. 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.

<Area where partial restoration processing is performed>
As one of means for solving the problems in the press forming described above, it is conceivable to make the strain distribution of the forming panel uniform, but in order to achieve this, the present inventors have the relationship between the tension applied to the blank and the proof stress value of the material. We examined using partial restoration for this.

FIG. 1 is a schematic view showing the left side from the center line (13) of a vertical section in cylindrical overhang forming or 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). The balance of the tension during molding in the molded product shoulder (11) in contact with the punch shoulder (6) will be described. 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 molded article vertical wall (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 magnitude changes depending on the value of TP. The larger the values of μ and θ, the smaller T _P becomes. 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, the region where the proof stress value is greatly reduced by the partial restoration process exceeds the region A which is the molded product head (10), and the punch shoulder (6) is projected onto a plane perpendicular to the press direction. When it exists to the area | region B which is an area | region, distortion concentrates on a molded article shoulder part (11), and will become easy to fracture | rupture conventionally. Therefore, the region where the proof stress value is lowered by the partial restoration process surrounds the punch head (5) which is a surface substantially perpendicular to the pressing direction in the punch forming surface (8) and the outer periphery of this surface. A blank (4) in which a region inside the punch shoulder (6) existing as a bent portion between the vertical wall portion (7) which is a continuous surface is projected on a plane perpendicular to the press direction An arbitrary region X is defined as the region A.

Next, the area ratio (S _X / S _A ), which is the ratio of the area (S _X ) of the region X to be subjected to the partial restoration process to the area (S _A ) of the region A onto which the punch head (5) is projected. Is preferably 25% or more and 100% or less. 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 processing 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 achieved. 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 region X subjected to the partial restoration process 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. 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 X may be excluded from the restoration processing unit, and the region X to be subjected to the partial restoration processing may be divided into a plurality of parts. However, the total area of the region X is preferably 25% or more and 100% or less. A more preferable range of the area ratio is 50% or more and 100% or less.

  FIG. 4 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 partially restored in the area A of the blank (4) on 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 split wrinkle pressing surface and a split 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. It is preferable to perform the partial restoration process of the present invention on the region Y which is the contracted flange deformed portion in the region C. Thereby, since the proof stress value can be partially reduced, the deformation resistance of the material is reduced, and the blank can easily flow in only the region Y that has been partially restored. By such partial restoration processing, it is possible to mitigate the increase in strain at the molded product shoulder (11B) in contact with the second-stage punch shoulder (6B). In addition, since the processing force required for molding can be reduced as the softened region increases, the tension applied to the periphery of the first-stage molded product shoulder (11A) is reduced, 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 lowered by aging. Therefore, in the molding of an automobile body outer panel or the like, the area where the partial restoration process is performed and the area where the hem bending process is performed after the press molding. It is preferable to include a hem bend.

  As described above, the region to be subjected to the partial restoration process is determined. However, since the aluminum alloy plate has a relatively high thermal conductivity, the peripheral portion of the heating region is also heated by the heat transfer of the plate itself. It is necessary to adjust the heating rate, the holding time, and the cooling rate so that the temperature reached in the region B where the punch shoulder is projected is less than 200 ° C. with respect to the predetermined heating temperature and heating region.

<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 partial 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 partial restoration process as described above. This is because after the partial restoration process, the material strength remains low 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 partial restoration treatment, and accordingly, the hem bendability also decreases. Therefore, it is desirable to perform the hem bending process within 10 days after the partial restoration process. More preferably, the hem bending process is performed within 3 days after the partial 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 process of the said restoration process part of the press molding obtained by performing press molding to the blank which performed the partial restoration process of this invention 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 proof stress value of the restoration processing portion whose proof stress value has decreased even in such a short time heat treatment is improved to 190 MPa or more. It rises further.

  In the partial restoration processing section, 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 grow 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 partial restoration processing part can obtain higher paint bake hardenability with respect to the untreated area, even after the proof stress value is lowered by the partial restoration treatment, the proof stress value is higher than 190 MPa. Strength is obtained.

  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.

  After the aluminum alloy was dissolved and the components were adjusted, the aluminum alloy ingot having five types (I to V) of alloy compositions shown in Table 1 was produced by casting by a DC casting method. 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.

[Invention 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. 3, 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. 3, a blank (4) of 180 mm × 180 mm was produced from the above-mentioned aging-treated plate as a test material, and a partial restoration process was performed under the conditions shown in Table 3. Here, of the punch forming surface (8), the punch head (5) that is a surface substantially perpendicular to the pressing direction and the punch vertical wall portion (the surface that is continuous so as to surround the outer periphery of this surface) 7), the blank area A, which is a projection of the area inside the punch shoulder (6) existing between the punch shoulders (6) and the plane perpendicular to the press direction, is flat with φ80 mm of the punch head (5). This is the area where the surface is projected. The area of the 80 mm _{S A,} the area of the region X performing partial reversion treatment tests were carried out with shaking several levels the area ratio _(S X / S _A) in the case of the _{S X.} In FIG. 3, (9) represents a die shoulder, (11) represents a molded product shoulder, and (12) represents a molded product vertical wall.

  As shown in FIG. 5, the aluminum alloy plate having a thickness of 200 mm × 200 mm and a plate thickness of 10 mm (thickness is not shown) is projected 5 mm (not shown in the drawing) at the center. Several kinds of heating jigs (21) obtained by cutting out a round circle (22) were produced by changing the size of the convex circle.

  As shown in FIG. 6, the blank restoration heating device is configured so that the upper die (18) of the pressing die in which the heater is built in the slide plate (16) of the hydraulic press having a press capacity of 50 TON is not transmitted to the press machine. A heating jig (21) provided with the convex circle (22) is attached to the pressing surface of the upper mold (18) through a heat insulating material (20). The heating jig is heated to a predetermined temperature by heat transfer from the heater through a mold, and the heater is controlled to maintain a set temperature by a temperature control panel (not shown). On the other hand, on the bolster (17) of the press machine, a lower mold (19) is installed by a lower mold mounting plate (24), and a blank ( 4) is set. The lower mold is supported by a cushion pin (25) of the press machine.

  The blank reheating method is such that the slide jig (16) of the press machine descends in the direction of the arrow in the figure, so that the heating jig (21) contacts the blank (4), and a constant load is applied for a certain time by the cushion mechanism of the press machine. After pressing, the slide rises and heating ends. At this time, the time from when the heating jig (21) contacts the blank (4) until it leaves is adjusted by the press stroke, the pressing pressure is adjusted by the cushion pressure, and the heating rate is the heating temperature of the heater and the pressing pressure. Adjusted. On the other hand, cooling after heating was mainly performed by a method of immersing the blank (4) in a water tank and a method of sandwiching the blank (4) with a metal block at room temperature.

  Subsequently, the cylindrical overhang forming test will be described with reference to FIG. The punch (1), die (2), and holder (3) are attached to the hydraulic press with the press capacity of 12 TON, and an appropriate amount of cleaning rust preventive oil is applied to the blank (4) subjected to the partial restoration process with a sponge. 3) Set up. Note that FIG. 3 does not show the hydraulic press. As shown in FIG. 3A, 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 speed is lowered at a molding speed of 1 mm / second, and as shown in FIG. 3 (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 confirmed by polishing the molded product vertical wall portion (12) of a molded product having a molding height of 14 mm with # 800 abrasive paper at a right angle to the rolling direction.

  A tensile test was performed on a JIS No. 5 tensile test piece prepared from an aged plate, and the mechanical properties (yield strength and elongation) of the blank before the restoration treatment were investigated. In addition, a JIS No. 5 tensile test piece prepared from an aging-treated plate was subjected to a restoration treatment by the above method, and the following evaluation was performed. First, a tensile test was performed to determine the amount of change in yield strength and the amount of change in elongation due to the restoration process. In addition, a bending test was performed by simulating the hem bending process performed in the automobile manufacturing process. After applying a tensile prestrain of 5% to the restored test piece, a bend radius of 0.degree. Is obtained until an angle of 90.degree. Is obtained with a line perpendicular to the tensile direction located at the center of the parallel part of the test piece as a fold line. Bend at 8 mm, and further bend to an angle of 135 °, then insert a plate with a thickness of 0.8 mm assuming that the inner panel is inserted inside, and then bend to an angle of 180 ° so as to sandwich this plate Adhered. The outside of the bent portion was confirmed with a magnifying glass, and it was determined that the bending workability was good when no crack was generated, and the bending workability was determined to be poor when the crack was generated. Further, after applying 2% tensile pre-strain to the restored test piece, an artificial age hardening treatment at 170 ° C. for 20 minutes was performed, and the yield strength after the paint baking treatment in the automobile manufacturing process was measured. In addition to this, a tensile test was performed in which the pre-strain amount and artificial age hardening treatment conditions were changed.

  The above test was performed three times under the same conditions, and an average value of three times was adopted. Tables 3 and 4 show the partial restoration processing conditions and the evaluation results. Test Nos. 1 to 10 are the results of Alloy Nos. I and II, which are Al—Mg—Si based Cu-free alloys. Test numbers 11 to 18 are the results of alloy numbers III, IV, and V, which are Al—Mg—Si based Cu-added alloys. Moreover, the test numbers 19-22 are the result of having implemented only the tension test which changed the amount of pre-strain and artificial age hardening processing conditions.

  Among the test numbers 1 to 10, the test number 7 is a condition of normal press molding that is not subjected to the partial restoration process. Since deformation tends to concentrate on the shoulder portion of the molded product corresponding to the punch shoulder portion, the fracture occurred at the shoulder portion of the molded product, 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.

  On the other hand, test numbers 1 to 6, which are examples of the present invention, can give a difference in proof stress with the non-restoration processing part by reducing the proof stress of the restoration processing part, compared with the comparative example. The limit overhang height is high and the moldability is improved. Moreover, it can be seen that the plate thickness reduction rate range is small and the strain is made uniform. As this effect, generation of ridging is suppressed by suppressing an increase in distortion of the vertical wall portion of the molded product. In addition to this, bendability has also recovered. Moreover, the proof stress value after the artificial age hardening treatment is significantly higher than 190 MPa.

On the other hand, test numbers 8 and 9 are conditions under which the restoration processing temperature deviates from the scope of the present invention. In Test No. 8, since the treatment temperature was as low as 180 ° C., the low temperature clusters could not be melted in a short time, and the yield strength was not reduced. Therefore, there was no improvement in moldability and no suppression of ridging. Moreover, there was no recovery of hem bendability.
In Test No. 9, since the processing temperature is as high as 330 ° C., age hardening occurs simultaneously with softening due to dissolution of the low temperature cluster, and the elongation of the restoration region is greatly reduced, so that the restoration region is extended but the elongation is insufficient. Fracture 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 which is a coarse precipitation phase within a short time, and the solid solution amount of Mg and Si is reduced. Decreased and below 190 MPa.

  In Test No. 10, the heating rate was slow and the holding time after reaching the heating temperature was long, so that age hardening occurred contrary to the original intention and the moldability deteriorated. Moreover, there was no suppression of ridging and recovery of bendability.

  Next, among the test numbers 11 to 18 using the Cu-added alloy, the test number 15 is a condition of normal press forming that is not subjected to the partial restoration process. 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 16.0 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.

  On the other hand, Test Nos. 11 to 14, which are examples of the present invention, can give a difference in proof stress from the non-restored portion due to a decrease in the proof strength of the restored portion, similarly to the Cu-free alloy. The limit overhang height is high and the moldability is improved as compared with the comparative example. Moreover, it can be seen that the plate thickness reduction rate range is small and the strain is made uniform. As this effect, generation of ridging is suppressed by suppressing an increase in distortion of the vertical wall portion of the molded product. In addition to this, bendability has also recovered. Moreover, the proof stress value after the artificial age hardening treatment is significantly higher than 190 MPa.

  On the other hand, test No. 16 has a high processing temperature of 430 ° C., so that a fracture line entered the boundary between the heated part and the non-heated part of the blank due to the thermal strain caused by the temperature difference between the heated part and the non-heated part. However, the limit overhang height was significantly reduced. Moreover, the yield strength value after the artificial age hardening treatment was significantly reduced.

  Test number 17 is a condition in which the sample was allowed to cool without performing a cooling process after the heat treatment, and the cooling rate was slow. For this reason, since the yield strength decreased by the heat treatment increased during cooling and the elongation decreased, the moldability deteriorated. There was also no improvement in ridging and no recovery in bendability.

  In Test No. 18, the restoration area ratio is 127%, and the restoration process extends to the region B where the punch shoulder is projected. Deformation concentrates on the shoulder of the molded product, and the limit overhang height is significantly reduced. It was. As a result, moldability deteriorated.

  On the other hand, test numbers 19 to 22 are the results of a tensile test in which the pre-strain amount after the restoration process and the artificial age hardening treatment conditions are changed. Test numbers 19 to 21 are conditions obtained by changing the pre-strain amount or artificial age hardening treatment conditions with respect to test number 5. In Test No. 19, the pre-strain amount was increased to 4%, so that the yield strength after the artificial age hardening treatment was increased. On the other hand, since the test number 20 did not add pre-strain, the yield strength after the artificial age hardening treatment was low, and it was less than 190 MPa. In Test No. 21, the artificial age-hardening treatment conditions were as high as 185 ° C. × 30 minutes and the time was prolonged, so that the proof stress after the artificial age-hardening treatment was increased.

  Test No. 22 is the case where the heat reaching temperature of the restoration process is higher than the temperature range of the present invention, and the artificial ageing treatment condition is 185 ° C. × 30 minutes. The yield strength after the curing treatment was less than 190 MPa.

[Invention 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. 4, 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.

  As a test material, a blank of 360 × 440 mm was prepared from a plate of alloy number I in Table 1 and aging treatment number A in Table 2, and the region X for the blank region A and the region Y for the region C shown in FIG. A partial restoration process was applied.

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.

  In addition, a JIS No. 5 tensile test piece prepared from an aging-treated plate was subjected to a restoration treatment by the above method, and a tensile test was performed to measure a proof stress value after the restoration treatment, thereby obtaining a change in the proof stress value due to the restoration treatment. It was.

  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. 4C, 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.

  These test results are shown in Table 5. Test number 23 is an age-hardened condition, and no partial restoration treatment has been performed. Under this condition, since the shoulder (11A) of the first-stage molded product was broken at a DC load of 175 kN, the front 150 kN was set as the breaking limit DC load, and this was set 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 25 to 28 are examples in which the region X of the present invention is restored. In all cases, the moldability was improved with respect to the standard. Particularly, in the test number 25 with a restoration area ratio of 100%, the breaking limit DC load was improved by 250 kN, which is + 67%. Moreover, the fracture | rupture position of the test numbers 25-28 moved to the molded article shoulder part (11B) corresponded to the punch shoulder part of the 2nd step | stage by the effect of restoring and softening the area | region X.

  On the other hand, the test number 24 is a case where the restoration area ratio is 127%, which is larger than the range of the present invention, and since the region softened by the restoration hits the first-stage molded product shoulder (11A), strain is concentrated at that part. However, there was no improvement in the breaking limit DC load.

  And test numbers 29-31 are conditions which added the area | region Y which is a shrinkage | contraction flange deformation | transformation part to a decompression | restoration area | 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 fracture 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 + 133% with respect to the reference.

  Aluminum blank for press molding according to the present invention and a press-molded body using the same, and the production method thereof, formability for improving paint bake hardenability and design freedom, high surface quality, and Good hem bendability for fastening with the inner panel is achieved.

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 16 …… Slide plate 17 …… Bolster 18 …… Upper mold 19 …… Lower mold 20 …… Heat insulation 21 …… Heating jig 22 …… Convex circle 23 …… Upper mold mounting plate 24 …… Lower mold Mounting plate 25 …… Cushion pin B …… Area projected from the punch shoulder C …… Area projected from the punch shoulder closest to the wrinkle holding part S _A …… Area A area S _X …… Area Area of X X …… Any area of A T _P ...... region is flange deformation part shrinkage of the tension Y ...... C applied to the molded article the vertical wall portion direction at a tension T _W ...... moldings shoulder exerted on the molded article the head direction in the molded article shoulder θ ...... Nagging angle μ …… Friction coefficient

Claims (8)

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. Arbitrary area X of blank area A projected on the plane perpendicular to the press direction from the area inside the shoulder as a partial restoration processing section,
The partial restoration processing part is formed by a heating step at an ultimate temperature of 200 ° C. or more and 300 ° C. or less and a subsequent cooling step to 100 ° C. or less. In the heating step, the rate of temperature increase from 100 ° C. to the ultimate temperature is 5 ° C. Of the aluminum alloy blank for press forming, characterized in that the holding time at the ultimate temperature is 20 seconds or less and the cooling rate to 100 ° C. or less is 5 ° C./second or more in the cooling step. Production method.   The Al—Mg—Si-based aluminum alloy has been solution-treated, and the Al—Mg—Si-based aluminum alloy after the solution treatment has been subjected to normal temperature aging or an artificial temperature of 100 ° C. or less before being partially restored. The manufacturing method of the aluminum alloy blank for press molding of Claim 1 which makes it an age-hardened Al-Mg-Si-type aluminum alloy by performing an aging treatment by aging or these combinations. The aluminum alloy blank for press forming according to claim 1 or 2, 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. Manufacturing method.   In the blank, a region Y which is a contracted flange deformed portion of a blank region C projected on a plane perpendicular to the pressing direction from a region outside the punch shoulder closest to the wrinkle holding portion sandwiched between the die and the holder. The manufacturing method of the aluminum alloy blank for press forming as described in any one of Claims 1-3 whose is a partial restoration process part.   The manufacturing method of the aluminum alloy blank for press forming as described in any one of Claims 1-4 whose hem bending part which is an area | region which receives a hem bending process after press molding is a partial restoration process part.   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%, Zr: 0.01-0.4 mass%, Cr: 0.01-0.4 mass %, Ti: 0.005 to 0.3 mass%, and V: 0.01 to 0.4 mass%, further containing one or more selected from the group consisting of Al and inevitable impurities. The manufacturing method of the aluminum alloy blank for press molding as described in any one of Claims 1-5.   By applying press forming to the aluminum alloy blank for press forming manufactured by the method for manufacturing the aluminum alloy blank for press forming according to any one of claims 1 to 6, A manufacturing method of an aluminum alloy press-molded body, wherein a strain of 2% or more is introduced into the portion.   The manufacture of an aluminum alloy press-molded body according to claim 7, wherein the yield strength value of the partial restoration processing part is set to 190 MPa or more by performing an artificial age hardening treatment at 170 to 185 ° C for 20 to 30 minutes. Method.

Images