JP5495538B2 - Warm press forming method of bake hardening type aluminum alloy plate - Google Patents

Description

  The present invention relates to a warm press-molding method in which a 6000 series aluminum alloy containing Mg and Si as main additive elements is warm-formed using a heated mold.

  In recent years, conversion of materials from steel plates to aluminum alloy plates has been promoted as means for reducing the weight of automobile bodies. However, since the aluminum alloy plate is inferior to the steel plate in press formability, it is difficult to apply it to a component having a complicated shape. In addition, since the formability and strength of an aluminum alloy improve as the Mg content increases, a 5000 series aluminum alloy containing Mg as a main element is initially applied to members such as automobile panels. It was.

  On the other hand, a 6000 series aluminum alloy containing Mg and Si as main elements is inferior in press formability compared to a 5000 series aluminum alloy. However, the 6000 series aluminum alloy is characterized by exhibiting bake hardenability (called BH property) due to the formation of fine precipitates of Mg and Si.

  In the baking coating process, which is an automobile manufacturing process, a heat treatment is performed on a vehicle body at about 170 ° C. for about 20 minutes. Therefore, the 6000 series aluminum alloy whose strength is increased by precipitation strengthening compared with that before the treatment is a material suitable for the body of an automobile. Therefore, a 6000 series aluminum alloy and a method for producing the same have been proposed that have both press formability at room temperature and BH properties (for example, Patent Documents 1 and 2).

  In parallel with the development of such materials, development of molding technology for utilizing an aluminum alloy plate having inferior formability is also underway. In particular, when a 5000 series aluminum alloy having excellent formability is molded with a heated mold, deep drawability is improved as compared with molding at room temperature, and molding into a complicated shape becomes possible. Some of the present inventors have also proposed a method of warm forming a 5000 series aluminum alloy plate (for example, Patent Document 3).

  A warm forming method of an aluminum alloy having bake hardenability (referred to as bake hardening type aluminum alloy) has also been proposed (for example, Patent Documents 4 to 6). Among these, Patent Document 4 proposes a technique for generating and growing precipitates in order to reduce strength and improve moldability. Patent Document 5 proposes a technique for limiting the solid solution amount of Fe and Mn and improving ductility at a temperature of 200 to 300 ° C. However, these are intended to improve the warm formability of the 6000 series aluminum alloy and do not utilize the BH property.

  On the other hand, Patent Document 6 proposes a method of warm forming a 6000 series aluminum alloy that exhibits BH properties. This is aged at room temperature after the solution treatment, but better formability and BH properties are required to be applied to the body of an automobile.

JP 09-249950 A Japanese Patent Laid-Open No. 10-219382 JP 2007-125601 A Japanese Patent Laid-Open No. 02-190456 JP 2002-348625 A JP 2006-205244 A

  The present invention improves the formability and BH properties of a 6000 series aluminum alloy plate, particularly when applied to the body of an automobile, to a level that can greatly contribute to weight reduction. It proposes hot press forming.

The present inventors examined a method for simultaneously improving the hot press formability and BH property of a 6000 series aluminum alloy plate. As a result, it was found that by performing a heat treatment at 70 ° C. or higher and lower than 150 ° C. after the solution treatment, the moldability and BH properties were improved more than expected. This invention is made | formed based on such knowledge, The summary is as follows.
(1) By mass%, Mg: 0.30 to 2.00%, Si: 0.20 to 2.10%, further satisfying Si-Mg / 2 ≧ 0.64 in atomic%, the balance After a solution treatment of a 6000 series aluminum alloy plate made of Al and unavoidable impurities, heat treatment is further performed at 70 ° C. or more and less than 150 ° C., and then the temperature of the flange portion is 170 ° C. or more. A method for warm press forming of a bake-hardening type aluminum alloy plate, characterized in that the die is formed using a die and a punch that is at a lower temperature than the flange portion of the die.
(2) The 6000 series aluminum alloy sheet contains Mg: 0.30 to 2.00% and Si: 0.30 to 2.00% in mass%, and the balance is made of Al and inevitable impurities. The method for warm press-molding a bake-hardening type aluminum alloy plate according to the above (1).
(3) The temperature of the bake-hardening type aluminum alloy plate according to (2), wherein the 6000 series aluminum alloy plate further contains Cu: 0.10 to 0.90% by mass%. Inter-press forming method.
(4) The 6000 series aluminum alloy plate is further in mass%, Ti: 0.005 to 0.150%, B: 0.0001 to 0.0500%, Mn: 0.03 to 0.40%, The bake curable mold according to (2) or (3) above, which contains one or more of Cr: 0.02 to 0.15% and Fe: 0.02 to 0.50% Warm press forming method of aluminum alloy plate.
(5) The baking according to any one of (2) to (4), wherein the 6000 series aluminum alloy plate further contains Zn: 0.03 to 1.00% by mass. A warm press forming method of a curable aluminum alloy plate.
(6) The above (1) to (1), wherein the solution treatment is performed at 500 to 590 ° C., cooled to less than 70 ° C., and then subjected to heat treatment at 70 ° C. or more and less than 150 ° C. for 30 minutes to 30 hours. (5) The warm press-molding method of the bake hardening type aluminum alloy plate according to any one of (5).
(7) The method for warm press forming of a bake-hardening type aluminum alloy plate according to (6) above, wherein after the solution treatment and before the heat treatment, it is kept at room temperature for 2 hours or more.
(8) The above (1), wherein the solution treatment is performed at 500 to 590 ° C., and heat treatment is performed for 30 minutes to 30 hours at 70 ° C. or more and less than 150 ° C. without cooling to less than 70 ° C. The warm press forming method of the bake hardening type aluminum alloy plate in any one of-(5).
(9) The press of the bake-hardening type aluminum alloy plate according to any one of the above (1) to (8), wherein the temperature of the punch is 170 ° C. or more lower than the temperature of the flange portion of the die. Molding method.
(10) The bake hardening mold according to any one of the above (1) to (9), wherein the 6000 series aluminum alloy plate is manufactured by cold rolling with a rolling reduction of more than 70%. Warm press forming method of aluminum alloy plate.
(11) The above-mentioned (1) to (1), wherein the 6000 series aluminum alloy sheet is manufactured by performing intermediate annealing after cold rolling and further performing final cold rolling. 9) The warm press forming method of the bake hardening type aluminum alloy plate according to any one of 9).
(12) The method of warm press forming of a bake-hardening type aluminum alloy plate according to (11) above, wherein the rolling reduction of the final cold rolling is more than 70%.

  According to the present invention, it is possible to provide a warm press forming method for a 6000 series aluminum alloy plate having a markedly improved press formability and an extremely good BH property, and particularly when applied to the body of an automobile. The improvement in moldability increases the flexibility of applicable members and designs, and the increase in strength may improve the dentability and contribute to the reduction of the plate thickness. Increasing the temperature increases the ductility and improves the hole expandability, making industrial contributions extremely remarkable.

  In the method of warm press forming of the bake hardened aluminum alloy plate of the present invention, the target of press formability is set to be equal to or higher than that of a conventional steel plate, and the target of BH property is set to a level when applied to an outer plate of an automobile. The press formability is evaluated by the limit drawing ratio (LDR), and the target value is set to 2.5 or more. In addition, the BH property is evaluated by the difference between the yield strength after 20% baking heat treatment at 170 ° C. after applying 2% tensile pre-strain, and the yield strength before baking heat treatment. 50 MPa or more.

  Conventionally, in the warm press forming of a bake-hardening type aluminum alloy, it has been considered preferable to reduce the strength before forming a steel sheet having BH properties at the room temperature. For this reason, a method has been proposed in which a 6000 series alloy is subjected to solution treatment and then naturally aged so as not to impair the formability, and the BH property is imparted using heating by a mold during warm forming. That is, it was thought that the increase in strength accompanying the heat treatment for imparting BH properties would reduce the press formability in the warm.

  However, the present inventors considered the following and directed a method of warm press-molding a bake-hardening type aluminum alloy subjected to heat treatment for imparting BH properties. First, in warm press molding, the flange portion of the die is heated to soften the material in contact therewith. Next, the temperature of the punch is made lower than the temperature of the flange portion of the die, and the strength of the material in contact with the punch is made higher than the strength of the material in contact with the flange portion of the die. When the drawing is performed in such a state, the strength of the material in contact with the flange portion is lowered, and in particular, the strength of the material in contact with the punch shoulder portion is higher than that of the flange portion.

  The warm press molding of the present invention is a method for improving the drawability by utilizing such a difference in strength depending on the part. Therefore, softening of the heated material at a high temperature is more important than reducing the strength before molding. In this way, a material having a high strength at room temperature and a temperature range suitable for warm forming, for example, a material whose strength is easily reduced at a temperature of 150 to 300 ° C., is a material suitable for warm press forming. It can be said.

  Based on such a concept, the present inventors further studied heat treatment conditions for imparting BH properties and warm press molding conditions. As a result, the heat treatment temperature after solution treatment of the 6000 series aluminum alloy plate is preferably 70 ° C. or higher and lower than 150 ° C., and the heating temperature of the flange portion of the die is preferably 170 ° C. or higher. It was found that the press formability and BH property can be secured. In the present invention, a portion of the die that faces the wrinkle pressing mold is referred to as a flange portion of the die.

  Furthermore, the deep drawability is improved as the difference between the strength of the material in contact with the heated die and the strength of the material in contact with the punch increases. Without cooling, it is preferable to cool. In order to improve the deep drawability, it is also effective to reduce the inflow resistance of the material of the flange portion. Therefore, in warm forming, it is necessary to increase the temperature of the flange portion of the die, and in the present invention, the temperature is set to 170 ° C. or higher. On the other hand, it is difficult for the upper limit of the temperature of the flange portion of the die to be 300 ° C. or higher due to the limitation of the use temperature of the lubricant, and it is preferable to set it to 270 ° C. or lower.

  Further, the BH property and formability of the 6000 series aluminum alloy vary depending on the formation of Mg and Si clusters. A cluster is defined as an atomic group of one or both of Mg and Si as solute atoms, and is a precursor state of precipitates. Further, in the present invention, a cluster formed at less than 70 ° C. is defined as a low temperature cluster, and a cluster formed at 70 ° C. or more and less than 150 ° C. is defined as a high temperature cluster. In addition, the high temperature cluster grows and becomes beta double prime (β ″) when the holding temperature is high and the holding time is long.

  For example, when the temperature is maintained at 170 ° C. for 20 minutes, the high-temperature cluster is newly nucleated, or the generated high-temperature cluster grows or becomes β ″, so that the BH property is expressed. In order to achieve this, after the solution treatment, it is necessary to hold at a temperature of 70 ° C. or higher and lower than 150 ° C. to form a high-temperature cluster.

  On the other hand, a low temperature cluster formed at a temperature of less than 70 ° C. does not contribute to the improvement of the BH property, but is effective in improving the moldability near room temperature. Depending on the shape of the member, the material that contacts the bottom of the punch may be required to have stretchability. Therefore, when performing the warm press molding, it is preferable to form a low-temperature cluster to enhance the moldability at room temperature when it is stretch-molded in the shape of the bottom of the punch.

  In warm forming, if the material strength of the portion in contact with the punch is increased, the material flow input at the time of deep drawing increases, so that high formability can be obtained. This is achieved by improving the material strength at room temperature without changing the molding temperature of the part in contact with the punch. As a method for increasing the material strength of the portion in contact with the punch, refining the crystal grains of the aluminum alloy plate is an effective method. For that purpose, it is preferable to perform the solution treatment by increasing the reduction ratio of the cold rolling.

  Further, the reduction of the plastic anisotropy of the material is effective in improving the formability even in the warm forming due to the decrease in the material inflow resistance at the portion in contact with the die. The reduction in plastic anisotropy is specifically to reduce the r value anisotropy of the aluminum alloy sheet. For this purpose, it is preferable to increase the number of recrystallizations by performing intermediate annealing in the middle of cold rolling so as not to accumulate specific crystal orientations.

  Hereinafter, the present invention will be described in detail.

  First, the component composition of the bake hardening type aluminum alloy of this invention is demonstrated. In the warm press molding method of the present invention, it is necessary to employ a 6000 series aluminum alloy containing Mg and Si as essential components, which is suitable for automobile materials. This is to obtain excellent BH properties. In addition, the composition of the high temperature cluster and the low temperature cluster composed of Mg atoms and Si atoms formed by the heat treatment after the solution treatment has a structure in which Si atoms are nuclei. Therefore, it is preferable to contain more Si than Mg. Hereinafter, “%” means mass%.

The contents of Mg and Si are 0.30 to 2.00% and 0.20 to 2.10%, respectively. Thereby, the nucleation of the high temperature cluster and the low temperature cluster is promoted, and the improvement of BH property and moldability becomes remarkable. Further, in order to promote the formation of high temperature clusters and low temperature clusters, it is preferable to add more Si than Mg in this range, which is effective in improving BH properties and formability.
As the amount of Si contained, the amount consumed by forming Mg and Mg ₂ Si contained therein is subtracted, and further, 0.64 at% or more (see Example No. 4 in Table 1) exists in the structure. It only has to be.
On the other hand, when the addition amount of Mg and Si is less than 0.3% and 0.20%, respectively, the BH property becomes insufficient when the temperature of the coating baking process is low or when the time is short. Sometimes. Moreover, in order to improve BH property, it is more preferable that the lower limit value of the Si amount is 0.30% or more. On the other hand, when the addition amounts of Mg and Si exceed 2.00% and 2.10%, respectively, when the solution treatment temperature is low, Mg ₂ Si as an equilibrium phase remains. There is a possibility that the moldability at room temperature is slightly lowered. In order to improve the warm formability, it is more preferable that the amount of Si added is 2.00% or less. Further preferable upper limits of the addition amounts of Mg and Si are 1.00% and 1.60%, respectively.

  In particular, Cu is an element that greatly contributes to formability at room temperature, and since an effect of promoting the formation of high-temperature clusters can be expected, it is preferable to add 0.10 to 0.90%. When Cu is added in an amount of 0.10% or more, the formability is significantly improved. On the other hand, if the amount of Cu exceeds 0.90%, the corrosion resistance may deteriorate.

  Furthermore, in order to refine the crystal grain size, one or more of Ti, B, Mn, Cr, and Fe may be included as necessary.

  Ti and B are effective elements for improving the formability and the like by refining the crystal grains of the ingot by adding a small amount. In order to obtain this effect, it is preferable that the Ti content is 0.005% or more and the B content is 0.0001% or more. On the other hand, if the Ti content exceeds 0.150% and the B content exceeds 0.0500%, the formability may deteriorate due to the formation of crystallized substances. Therefore, the preferable range of the Ti content is 0.005 to 0.150%, and the preferable range of the B content is 0.0001 to 0.0500%.

  Mn, Cr, and Fe are elements that improve formability by refining crystal grains, and also contribute to improvement in strength. In order to obtain this effect, it is preferable that Mn is 0.03% or more, Cr is 0.02% or more, and Fe is 0.02% or more. On the other hand, if Mn exceeds 0.40%, Cr exceeds 0.15%, and Fe exceeds 0.50%, formability may be impaired due to generation of crystallized substances. Therefore, it is preferable that Mn is 0.03 to 0.40%, Cr is 0.02 to 0.15%, and Fe is 0.02 to 0.50%.

  Furthermore, in order to improve the strength, Zn may be contained as necessary.

  Zn is an element that improves the strength. In order to obtain the effect, the content is preferably set to 0.03% or more. On the other hand, if the Zn content exceeds 1.00%, the moldability may be impaired due to an increase in strength. Therefore, the addition amount of Zn is preferably 0.03 to 1.00%.

  Moreover, you may contain Sc which is effective for refinement | miniaturization of an ingot structure | tissue. Sc is preferably in the range of 0.01 to 0.20%.

  The aluminum alloy of the present invention is a 6000 series aluminum alloy containing Mg and Si as main elements, preferably a 6000 series aluminum alloy cold-rolled plate composed of the above-mentioned components, and further subjected to a solution treatment, and further 70 ° C. or higher. Manufactured by heat treatment at less than 150 ° C. The aluminum alloy cold-rolled sheet of the present invention is manufactured by melting, casting, hot rolling, and cold rolling in a conventional manner. Intermediate annealing may be performed during the cold rolling. In addition, when performing intermediate annealing, the cold rolling before intermediate annealing is called primary cold rolling, and the cold rolling after intermediate annealing and before solution treatment is called final cold rolling.

The temperature of the solution treatment is preferably 500 ° C. or higher in order to dissolve precipitates generated in the cold-rolled sheet, in particular Mg ₂ Si as an equilibrium phase, so that Mg and Si are dissolved. On the other hand, depending on the contents of Mg and Si, if the solution treatment temperature is too high, the crystal grain boundaries may melt, so the upper limit is preferably made 590 ° C. or lower.

In the solution treatment, after reaching the maximum temperature, the solution may be cooled without being held, but it is preferable to hold for 0.1 to 5 minutes. When the lower limit of the holding time is 0.1 minutes or more, the dissolution of Mg ₂ Si is promoted, and the solid solution amount of Mg and Si increases. In order to increase productivity, it is preferable to use a continuous heat treatment facility for passing through the heating furnace. However, in order to lengthen the holding time of the solution treatment, it is necessary to lengthen the heating furnace or slow the sheet passing speed, and it is preferable to set it to 5 minutes or less in order to impair productivity.

  The cooling after the solution treatment may be air cooling, but when hemming is performed, it is preferable to forcibly cool using a blowing means in order to improve bendability. In particular, after solution treatment, it is preferable to cool to 250 ° C. at 10 ° C./s or more. As a result, the formation of precipitates at 250 ° C. or higher can be prevented, the increase in strength can be suppressed, and solid solution Mg and solid solution Si contributing to improvement in BH properties and press formability can be secured. can do. In order to control the cooling rate, mist cooling or water cooling may be performed.

  The reason why the heat treatment after the solution treatment is performed at 70 ° C. or higher and lower than 150 ° C. is to promote the formation of high temperature clusters as described above. The heat treatment at 70 ° C. or higher and lower than 150 ° C. after the solution treatment is also referred to as a stabilization treatment in the present invention. If the temperature of the stabilization treatment is less than 70 ° C., low temperature clusters are preferentially generated over high temperature clusters, and the BH property becomes insufficient. On the other hand, when the temperature of the stabilization treatment is 150 ° C. or higher, the strength is increased due to the formation of β ″, and the warm press formability is slightly lowered. This makes it difficult to apply to parts having complicated shapes.

  Further, in the warm press molding method of the present invention, since the improvement of BH property is emphasized, the holding time of the stabilization treatment is preferably set to 30 minutes or more. On the other hand, if the holding time of the stabilization treatment exceeds 30 hours, the strength increases and the warm press formability slightly decreases.

  In addition to the BH property, in order to improve the formability at room temperature, it is preferable to perform the stabilization treatment after cooling to less than 70 ° C. after the solution treatment. This is because cooling to below 70 ° C. generates low temperature clusters that contribute to press formability at room temperature.

  Furthermore, when improvement in press formability at room temperature is required, it is preferable to hold for at least 2 hours after solution treatment, before cooling to room temperature and performing stabilization treatment. Furthermore, when emphasizing press formability at room temperature, it may be held at room temperature for two days or more. On the other hand, in order to obtain the effect of improving the BH property, the retention at room temperature is preferably 7 days or less. In addition, although the room temperature in this invention changes with seasons, possibility that it will be less than -40 degreeC or more than 50 degreeC is low.

  On the other hand, when the BH property is more important than the moldability at room temperature, it is preferable to perform the stabilization treatment without cooling to less than 70 ° C. after the solution treatment. For this purpose, it is sufficient to use the fact that the cooling rate of the coil after winding is remarkably lowered, and it is preferable that the winding temperature after the solution treatment is 70 ° C. or more and less than 150 ° C. When the time from the solution treatment to the stabilization treatment is long, the lower limit of the coiling temperature may be increased as necessary, and is preferably 80 ° C. or higher.

  When intermediate annealing is performed in the middle of cold rolling, recrystallization can be performed before the solution treatment. Therefore, the texture becomes isotropic and the plastic anisotropy is reduced as compared with the case where intermediate annealing is not performed. Therefore, the intermediate annealing reduces the direction difference of the r value in the material plate surface, lowers the material inflow resistance in deep drawing, and improves warm formability.

  The intermediate annealing may be performed at a temperature of 400 ° C. or higher in order to recrystallize the processed structure after cold rolling, but if the temperature is lower than 500 ° C., the time required for recrystallization becomes longer. On the other hand, when the temperature of the intermediate annealing exceeds 590 ° C., the crystal grain boundary may melt depending on the component. Therefore, in consideration of productivity and manufacturability, the intermediate annealing is preferably performed at 500 to 590 ° C. In the case of continuous annealing, after reaching the maximum temperature, cooling may be performed without holding. On the other hand, if the holding time exceeds 300 s, productivity is impaired, and thus the holding time is preferably 300 s or less. In order to promote recrystallization, the holding time is preferably 60 s or longer.

  Moreover, in order to improve warm formability, it is preferable to raise the reduction rate of cold rolling. If the rolling reduction of the cold rolling is set to 70% or more, the crystal grains after the solution treatment are refined, and the material strength of the portion in contact with the punch is increased, so that the warm formability is improved. In order to refine the crystal grains, it is necessary to increase the amount of strain accumulated in the processed structure before the solution treatment. Therefore, when intermediate annealing is performed, the final cold rolling before the solution treatment is performed. It is preferable to set the rolling reduction of 70% or more. However, after the intermediate annealing, when the rolling reduction of the final cold rolling is set to 70% or more, the effect of reducing the plastic anisotropy is slightly smaller than when the rolling reduction is less than 70%. Sometimes.

  After producing the 6000 series aluminum alloy, warm press forming is performed. In addition, since a low temperature cluster may produce | generate by holding | maintenance at room temperature after manufacture, it is preferable to give warm press molding within three months from manufacture.

  Further, in the method for warm press forming of an aluminum alloy of the present invention, the temperature of the flange portion of the die and the temperature of the punch are extremely important. As described above, the warm press formability is improved by softening the material in contact with the flange portion of the die and particularly ensuring the strength of the material in contact with the punch shoulder. Therefore, the punch temperature, particularly the punch shoulder temperature, needs to be lower than the temperature of the flange portion of the die.

  In order to reduce the inflow resistance of the material in contact with the flange portion of the die, the temperature of the flange portion of the die needs to be 170 ° C. or higher. This is because when the 6000 series aluminum alloy is 170 ° C. or higher, the inflow resistance is significantly decreased due to the decrease in strength. In order to improve deep drawability, the temperature of the flange portion of the die is preferably set to 200 ° C. or higher. Thereby, it becomes possible to prevent the shape defect of the molded product due to the spring back. Further, the hole expanding process may be performed in a state where the temperature of the material is high. Since the ductility of an aluminum alloy is improved by increasing the temperature, warm forming is also effective for improving hole expansibility.

  As a specific means for heating the dice, a heater may be embedded in the dice, in particular, the flange portion of the dice and heated. A heater may be embedded in the wrinkle holding mold and heated. Even if the temperature of the flange portion of the die is higher than the temperature of the punch, if the aluminum alloy plate is in contact with only the die, the temperature of the punch shoulder due to heat conduction will be the same as the temperature of the flange portion of the die. It may rise equally and soften. Therefore, when performing press molding, it is preferable that the punch is brought into contact with the material at the same time as the material is sandwiched between the dies.

  Further, in order to improve the deep drawability, it is preferable that the difference between the temperature of the flange portion of the die and the temperature of the punch is 170 ° C. or more. In order to give such a temperature difference, it is preferable to circulate the coolant inside the punch, particularly the inside of the punch shoulder. The coolant may be water, but when cooling to 0 ° C. or lower, it is preferable to use alcohol, glycerin, or the like.

  A 6000 series aluminum alloy having the components shown in Table 1 was melted and cast in a laboratory, subjected to hot rolling and cold rolling to obtain a cold rolled sheet having a thickness of 1 mm. From these cold-rolled sheets, test pieces used for a warm press forming test and a tensile test described below and a BH property evaluation test were collected. The test piece used for warm press molding is a disk shape, and the tensile test piece is a No. 5 test piece of JIS Z 2201 whose longitudinal direction is the rolling direction. In addition, the blank of Table 1 means that the component is not added intentionally.

  These test pieces were kept in a salt bath at 560 ° C. for 1 minute, quenched in water and cooled. After cooling, it was immediately stored in liquid nitrogen to avoid holding at room temperature. The retention time at room temperature after the solution treatment is about 1 to 2 minutes, and the influence of the generation of low-temperature clusters after the solution treatment can be ignored.

  Thereafter, some test pieces were kept at room temperature. The room temperature is 25 ° C. Further, the test piece was subjected to heat treatment simulating stabilization using an oil bath at 60 to 200 ° C. Table 2 shows the holding time at room temperature, and the oil bath temperature and holding time are shown as the holding temperature and holding time of the stabilization treatment. The blank in the column after the solution treatment in Table 2 means that the stabilization treatment was performed without setting the temperature below 70 ° C. after the solution treatment.

  After the stabilization treatment, a warm press molding test, a tensile test, and a BH property evaluation test were performed. The warm press molding test was performed using a deep drawing test apparatus having a die with a heater embedded in the flange portion. The punch is cylindrical, the outer diameter is 78 mm, and the inner diameter of the die is 80 mm. Water was circulated inside the punch to adjust the temperature of the shoulder surface to 30 ° C.

  The warm press formability was evaluated by the limit drawing ratio (LDR). LDR is a value obtained by dividing the maximum diameter of a test piece that can be drawn without breaking by the outer diameter of the punch. In the warm press molding test, a lubricant obtained by adding water to molybdenum disulfide was used. The wrinkle pressing pressure was 1 ton or less.

  The tensile test was performed according to JIS Z 2241, and the yield strength after stabilization (YS before BH) was measured. In addition, by simulating the coating baking process, a test piece given 2% tensile pre-strain is held in an oil bath at 170 ° C. for 20 minutes, and a tensile test is performed in accordance with JIS Z 2241. The yield strength (YS after BH) was measured. Furthermore, the difference (ΔYS) between YS after BH and YS before BH was determined. The yield strength is 0.2% proof stress. In an actual member, the coating baking process is performed after the warm press forming, so that the BH property is considered to be improved from the result of this example.

The results are shown in Table 3. No. 2 to 8, 11 to 13 are examples of the present invention, and LDR is 2.5 or more and ΔYS is 50 MPa. In addition, No. Nos. 11 to 13 are examples of simulating a manufacturing method in which a stabilization treatment is performed after cooling to less than 70 ° C. after the solution treatment. In addition , no . In No. 8, since the Si amount is slightly larger, LDR and ΔYS are slightly lower than those of the other invention examples.

  On the other hand, no. 9, 10, and 14 are comparative examples. No. No. 9 has a low LDR because the temperature of the flange portion of the hot press-formed die is low. No. No. 10 is an example in which β ″ is precipitated and the strength is increased and LDR and ΔYS are decreased because the temperature of the stabilization treatment is high. No. 14 is a high BH property because the temperature of the stabilization treatment is low. This is an example in which

  In the same manner as in Example 1, a 6000 series aluminum alloy having the components shown in Table 4 was melted and cast in a laboratory and subjected to hot rolling. The obtained hot-rolled sheet was cold-rolled under the conditions shown in Table 5, and a part thereof was subjected to intermediate annealing to obtain a cold-rolled sheet having a thickness of 1 mm. From these cold-rolled sheets, specimens to be subjected to a warm press forming test, a tensile test, and a BH property evaluation test were collected in the same manner as in Example 1, and were subjected to a solution treatment under the conditions shown in Table 5. Was given.

  The solution treatment was performed by immersing in a salt bath, quenched in water and cooled. The holding time was controlled based on the heating curve obtained by measuring the temporal change of temperature under various conditions using a test piece equipped with a thermocouple in advance. In order to avoid holding at room temperature after cooling, the solution was stored in liquid nitrogen so that the holding time at room temperature after the solution treatment was about 1 to 2 minutes. Thereafter, some test pieces were kept at room temperature under the conditions shown in Table 5. The room temperature is 25 ° C.

  Further, as in Example 1, the test piece was subjected to a heat treatment that simulated the stabilization treatment under the conditions shown in Table 5 using an oil bath. The example in which the column after the solution treatment in Table 5 is blank is a case where the stabilization treatment is performed without setting the temperature below 70 ° C. after the solution treatment. These simulate the manufacturing method which performs a stabilization process, without cooling to less than 70 degreeC after a solution treatment.

After the stabilization treatment, a warm press molding test, a tensile test, and a BH property evaluation test were conducted in the same manner as in Example 1. Table 6 shows the punch temperature, the die temperature, and the mold temperature difference in the warm molding press test, and the tests were conducted under the same conditions. The plastic anisotropy was evaluated according to JIS Z 2254. rL, rc, and rx are r values evaluated using test pieces with the longitudinal direction being the rolling direction, the width direction, and the 45 ° direction, respectively. Δr is an index representing the anisotropy difference between the r values in these three directions.
Δr = (rL + rC) −2rX) / 2
Defined by

The results are shown in Table 7. No. 16 -1～20-4 are both an invention example, LDR is 2.5 or more, DerutaYS is 50 MPa. Further, as shown in Table 7, when the cold rolling rate is high, YS before BH becomes high, and when intermediate annealing is performed, Δr becomes small and LDR becomes large.

Claims (12)

% By mass
Mg: 0.30 to 2.00%,
Si: 0.20 to 2.10% is contained,
Furthermore, after satisfying Si—Mg / 2 ≧ 0.64 in atomic%, and a solution treatment of a 6000 series aluminum alloy plate with the balance being Al and inevitable impurities, heat treatment is further performed at 70 ° C. or more and less than 150 ° C., Thereafter, the 6000 series aluminum alloy plate is formed by using a die having a flange portion temperature of 170 ° C. or higher and a punch having a lower temperature than the flange portion of the die. Warm press molding method.   The 6000 series aluminum alloy plate contains, by mass%, Mg: 0.30 to 2.00%, Si: 0.30 to 2.00%, and the balance is made of Al and inevitable impurities. The warm press-forming method of the bake hardening type aluminum alloy plate according to claim 1.   The method for warm press forming a bake-hardening type aluminum alloy plate according to claim 2, wherein the 6000 series aluminum alloy plate further contains Cu: 0.10 to 0.90% by mass. .   The 6000 series aluminum alloy plate is further, in mass%, Ti: 0.005 to 0.150%, B: 0.0001 to 0.0500%, Mn: 0.03 to 0.40%, Cr: 0 The warm of the bake-hardening type aluminum alloy plate according to claim 2 or 3, characterized by containing one or more of 0.02 to 0.15% and Fe: 0.02 to 0.50%. Press molding method.   The bake-hardening type aluminum alloy according to any one of claims 2 to 4, wherein the 6000 series aluminum alloy plate further contains Zn: 0.03 to 1.00% by mass. Warm press forming method for plates.   The solution treatment is performed at 500 to 590 ° C., cooled to less than 70 ° C., and then subjected to heat treatment that is maintained at 70 ° C. or more and less than 150 ° C. for 30 minutes to 30 hours. A warm press-forming method of the bake hardening type aluminum alloy plate according to item 1.   The method for warm press forming of a bake-hardening type aluminum alloy plate according to claim 6, wherein after the solution treatment and before the heat treatment, it is kept at room temperature for 2 hours or more.   6. The solution treatment according to claim 1, wherein the solution treatment is performed at 500 to 590 ° C., and a heat treatment is performed for 30 minutes to 30 hours at 70 ° C. or more and less than 150 ° C. without cooling to less than 70 ° C. A warm press forming method of the bake hardening type aluminum alloy plate according to claim 1.   The method for warm press forming of a bake hardening type aluminum alloy plate according to any one of claims 1 to 8, wherein the temperature of the punch is 170 ° C or more lower than the temperature of the flange portion of the die.   The bake-hardening type aluminum alloy plate according to any one of claims 1 to 9, wherein the 6000 series aluminum alloy plate is manufactured by cold rolling with a reduction ratio of more than 70%. Warm press forming method.   The 6000 series aluminum alloy sheet is manufactured by performing intermediate annealing after cold rolling and further performing final cold rolling. A warm press-forming method of the bake-hardening type aluminum alloy plate according to the item.   The method of warm press forming of a bake hardening type aluminum alloy sheet according to claim 11, wherein the rolling reduction of the final cold rolling is more than 70%.