JP2004124151A - Heat treatment method for aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a formed article free from working defect and having excellent shape accuracy by softening the areas to be subjected to large working deformation in advance prior to press forming. <P>SOLUTION: High-temperature metal blocks 2u and 2d are pushed against the areas to be worked of a blank 1 cut out from an aluminum alloy sheet and the blank 1 in contact with the metal blocks 2u and 2d are subjected to local rapid heating to locally soften the contact areas. As a material, an aluminum alloy, such as age-hardening aluminum alloy, precipitation-hardening aluminum alloy and work-hardening aluminum alloy, in which strength can be improved by the precipitation of intermetallic compounds or second phases, is preferred. As the metal blocks 2u and 2d used to locally and rapidly heat the blank 1, blocks made of copper which are heated preferably to a high temperature not lower than 350°C are used and pushed against the areas to be worked of the blank 1 at ≥1 MPa pressurizing force. <P>COPYRIGHT: (C)2004,JPO

Description

【００１８】
５００℃に加熱したリング状の銅製ブロック２ｕ，２ｄを加圧力Ｐ：３ＭＰａで各ブランク１に押し当て、ブランク１と接触している部分でブランク１の昇温速度を測定した。熱伝導性の良好な銅製ブロック２ｕ，２ｄを押し当てたとき、金属間化合物の固溶，歪，応力の解放に有効な３５０℃以上の温度域にブランク１が極短時間で昇温した。他方、熱伝導性が低い鉄製ブロックを押し当てた場合、昇温速度が若干小さいものの、５秒以内の短時間で３５０℃以上の温度域に達した。（図４）
【００１９】
内径が４６ｍｍ（例１），５３ｍｍ（例２），６０ｍｍ（例３）と異なる３種類の銅製ブロック２ｕ，２ｄを用意した。各銅製ブロック２ｕ，２ｄを５００℃に加熱し、合金Ｎｏ．１のブランク１に０．６秒押し当てた後、ブランク１を水冷した。冷却後にブランク１の硬さを半径方向に測定し、銅製ブロック２ｕ，２ｄによる局部加熱がブランク１の軟化に及ぼす影響を調査した。何れの場合も銅製ブロック２ｕ，２ｄに接触した部位（軟化領域１ｓ）は、非接触部位（硬質領域１ｈ）のビッカース硬さに比較して大幅に軟化していた。軟化領域１ｓと硬質領域１ｈとの間の強度遷移幅も２０ｍｍ以下に抑えられていた。（図５）
急速加熱による軟化領域１ｓの形成は、合金Ｎｏ．２，３のアルミニウム合金板でも同様な傾向を示した。
【００２０】
局部加熱で軟化領域１ｓを形成した合金Ｎｏ．１のブランク１を直径６０〜８０ｍｍの円板状に切断し、内径３３ｍｍのカップ形状にプレス成形した。プレス成形では、開口直径３６．２ｍｍのダイ３にブランク１をセットし、ブランク１の周縁部をしわ抑え４で抑え、クリアランスを０．６ｍｍに設定してしわ抑え力２ｋＮで直径３３ｍｍ，肩アール５ｍｍのポンチ５をダイ３に押し込んだ。
プレス成形品の加工部位を観察し、破断，割れ等の有無を調査した。ＳＴ材，Ｔ６材，Ｏ材等では限界絞り比が２．０に留まり、２．０を超える絞り比でプレス成形するとポンチ５の肩部に当った個所に破断が生じていた。
【００２１】
他方、銅製ブロック２ｕ，２ｄを用いた急速加熱で軟化領域１ｓを形成したブランク１では、絞り比２．３でも破断，亀裂等の加工欠陥を生じることなくプレス成形できた。なかでも、内径４７ｍｍの銅製ブロック２ｕ，２ｄを用いて適正面積の軟化領域１ｓを形成したブランク１では、絞り比２．４の深絞りによっても加工欠陥が発生しなかった。
この対比から明らかなように、プレス成形時に大きく塑性変形する個所を予め軟化領域１ｓとしておくことにより、絞り比を高く設定した深絞り加工によっても破断，割れ等の加工欠陥を生じることなく、形状精度の良好なプレス成形品が得られることが確認された。局部加熱による軟化領域１ｓの形成が深絞り性の向上に及ぼす影響は、Ｎｏ．２，３のアルミニウム合金板でも同様であった。
【００２２】
【発明の効果】
以上に説明したように、大きな加工変形を受ける部位を予め軟化しておくことにより、高い絞り比でプレス成形した場合でも破断，割れ等の加工欠陥がなく、形状精度の良好な成形品が得られる。高温加熱された金属ブロックをブランクの加工予定部位に極短時間押し付けるだけで深絞り性向上に有効な軟化領域が形成されるため、時効処理による軟質化に比較して処理時間が大幅に短縮され、設備負担も軽減される。このように、簡単な操作でアルミニウム合金の加工性が改善されるので、従来法では困難であった複雑形状の製品も容易に且つ工数の少ないプレス成形で製造できる。
【図面の簡単な説明】
【図１】ブランクの加工予定部位に軟化領域を形成する説明図
【図２】局部的に軟質化したブランクをプレス成形金型のダイとポンチとの間にセットした状態を示す図
【図３】ブランクがプレス成形品になるまでの材質，形状変化を示す図
【図４】高温加熱された金属ブロックが押し当てられたブランクの昇温特性を示すグラフ
【図５】金属ブロックを用いて局部加熱されたブランクの半径方向に沿った硬さ分布を示すグラフ
【図６】軟化領域の形成が深絞り性の向上に及ぼす影響を従来材と対比したグラフ
【符号の説明】
１：ブランク　　１ｓ：軟化領域　　１ｈ：硬質領域　　１ｄ：変形領域　　１ｃ：被挟持部　　１ｐ：ポンチ当接部　　２ｕ，２ｄ：加圧加熱体（金属ブロック，銅製ブロック）　　３：ダイ　　４：しわ抑え　　５：ポンチ[0001]
[Industrial applications]
The present invention relates to a heat treatment method for improving the press formability of aluminum alloys used in a wide range of fields such as automobile parts, casings of electronic devices, housings of electric devices, etc. by utilizing lightness.
[0002]
[Prior art]
Aluminum alloys are lightweight and excellent in corrosion resistance, so they are used for materials such as automobile parts, casings of electronic devices, housings of electric devices, etc., and are processed into product shapes by press molding. Some products are processed with an extremely large drawing ratio.
The material to be press-formed undergoes non-uniform deformation during processing. Therefore, if an appropriate strength difference or ductility difference corresponding to the deformation mode is given in the material in advance, processing at a high forming limit becomes possible. For example, in Japanese Patent Application Laid-Open No. 2000-80418, a heat-treated portion is locally softened by heat treatment to improve the formability of a steel sheet. Even in the case of aluminum alloy, it is possible to harden the central part receiving the punch load and harden it by shrinking and deforming the peripheral part that deforms by local aging treatment. It is introduced on pages 1363-1368.
[0003]
[Problems to be solved by the invention]
The conventional method of providing a difference in strength inside an aluminum alloy takes a long time to obtain a necessary difference in strength, and the productivity is low. In addition, it may not be applicable depending on the product shape, and equipment with a large burden is required.
The present invention has been devised to solve such a problem, and provides a necessary strength difference to the aluminum alloy by a short heat treatment, and does not require a large capital investment. The purpose is to improve the workability of the steel.
[0004]
[Means for Solving the Problems]
In order to attain the object, the heat treatment method of the present invention presses a high-temperature metal block against a portion to be processed of the blank, and locally rapidly heats the blank in contact with the metal block by heat transfer from the metal block. , Characterized in that the contact portion is locally softened.
As the material, an aluminum alloy whose strength is improved by precipitation of an intermetallic compound or a second phase, such as an age hardening type, a precipitation hardening type, and a work hardening type, is preferable. The part to be machined can be locally softened by pressing the metal block against the aluminum alloy plate before cutting the blank and rapidly heating the metal block, or pressing the metal block against the blank cut from the aluminum alloy plate and rapidly heating the metal block. .
[0005]
A metal block heated to a high temperature of 350 ° C. or higher is used as a pressurized heating element for locally rapidly heating the blank, and is pressed against a blank to be processed with a pressing force of 1 MPa or more. The temperature rise characteristics of the portion in contact with the metal block are affected by the heating temperature and pressure of the metal block. When regulating the strength of the softened region softened by contact with the metal block to 90% or less of the strength of the non-contact portion (hard region), and the strength transition width between the softened region and the hard region of the non-contact portion to 20 mm or less. Even if the drawing ratio is set to a large value, the blank can be press-formed into a product shape having no processing defects such as cracks, breakage, and buckling.
[0006]
[Action]
When the blank 1 made of an aluminum alloy plate is sandwiched between ring-shaped pressurizing and heating bodies 2u and 2d (FIG. 1) and the blank 1 is rapidly heated in a state where a predetermined pressure P is applied, the blank 1 comes into contact with the pressurizing and heating bodies 2u and 2d. The temperature of the heated portion rapidly rises, and intermetallic compounds such as Mg ₂ Si, Si, and Cu and the second phase (hereinafter collectively referred to as “intermetallic compounds”) deposited on the blank 1 solidify in the matrix. Dissolve. The pressurizing and heating elements 2u and 2d are not limited to the ring shape, and it is needless to say that blocks shaped into appropriate shapes in consideration of the processing shape can be used.
[0007]
The heated portion becomes the softened region 1s (FIG. 3) due to the solid solution of the intermetallic compound, and the remaining portion (hard region 1h) not heated by the pressurized heating bodies 2u and 2d maintains the original strength. In addition to the solid solution of the intermetallic compound, the blank 1 is locally softened by the strain and residual stress introduced during the manufacturing process of the aluminum alloy plate being released by rapid heating.
[0008]
The usable aluminum alloy is not particularly limited in material, but is preferably a composition containing Mg, Si, Cu, Fe, etc., which easily precipitates as an intermetallic compound in order to utilize local softening due to rapid heating. There are a hardening type, a precipitation hardening type, a work hardening type and the like. Specifically, aging containing one or more of Mg: 0.4 to 4.0% by mass, Si: 0.2 to 2.0% by mass, and Cu: 0.2 to 6.0% by mass. A hardening type or a work hardening type aluminum alloy is mentioned.
Although the temperature attained by heating depends on the type of the aluminum alloy, by setting the temperature to 350 ° C. or higher, most of the intermetallic compounds precipitated are dissolved in the matrix and the strain and stress are released.
[0009]
As the pressurizing and heating elements 2u and 2d, for example, a metal block heated at a high temperature is used. When the high-temperature metal blocks 2u and 2d are pressed against the blank 1, the temperature of the blank 1 is locally increased to a temperature range in which the intermetallic compound is dissolved in the matrix in a very short time. By maintaining the temperature rising state for a predetermined time, the intermetallic compound is solid-dissolved and reformed into the softened region 1s in which strain and stress are released. When the above-mentioned age hardening type aluminum alloy plate is observed after local softening, the average grain gap of the precipitate is 1 μm or less in the hard region 1h, whereas the total amount of Mg, Si and Cu is 0.1 μm in the softened region 1s. 5% by mass or more is dissolved in the matrix. As a result, a strength difference occurs between the metal block 2u and the hard region 1h that is not heated by the metal blocks 2u and 2d. A difference in strength effective for improving workability can be achieved by heating and holding within 5 seconds.
[0010]
The blank 1 having a strength difference between the softened region 1s and the hard region 1h is placed on, for example, a die 3 and its peripheral portion is fixed with a wrinkle suppressor 4 (FIG. 2). When the punch 5 is pushed into the die opening in this state, the blank 1 is plastically deformed according to the shape of the die 3 and the punch 5. Since the clamped portion 1c sandwiched between the die 3 and the wrinkle suppressor 4 undergoes the greatest plastic deformation, the blank 1 locally softened by the pressurizing and heating elements 2u and 2d is used so that the softened region 1s is located in this portion. Although the amount of plastic deformation is large also in the vicinity of the shoulder of the die 3, cracks are likely to occur at the time of molding if the strength of this portion is reduced. Therefore, it is preferable to set the softened region 1 s avoiding the shoulder of the die 3. .
[0011]
The softened region 1 s is plastically deformed to a target shape with high accuracy following the pressing of the punch 5, and becomes a deformed region 1 d after molding. The deformation region 1d is hardened by work hardening, but the flange formed from the softened region 1s remains soft.
The portion where the tip of the punch 5 comes into contact (punch contact portion 1p) has a small amount of plastic deformation, so that even if the initial strength is maintained, processing defects such as cracks and breakage do not occur. Although the press formability is improved as the softening region 1s is larger, it is not necessary to soften the entire area of the clamped portion 1c, and the press formability is improved only by softening the area ratio of the clamped portion 1c by 20% or more. Can be expected.
[0012]
The present inventors further investigated and examined the effect of local softening on press formability. As a result, when a metal block (pressurized heating body 2u, 2d) heated to 350 ° C. or higher is pressed against blank 1 and heated, heat transfer from pressurized heating body 2u, 2d to blank 1 by metal-metal contact. Was promoted, and the softened region 1s was formed in an extremely short time within 5 seconds. As the metal block, copper, a copper alloy, or the like having a large heat capacity and good thermal conductivity as compared with the blank 1, which is the object to be heated, is preferable.
[0013]
The aluminum alloy blank 1 on which the metal blocks 2u and 2d are pressed reaches a high temperature of 350 ° C. or more at a temperature increase rate of 100 ° C./second or more, and is held in the high temperature region within 5 seconds. Remove 2d and immediately cool to below 200 ° C. The pressure P of the metal blocks 2u and 2d is preferably set to 1 MPa or more in order to promote heat transfer to the blank 1.
[0014]
By pressing the metal blocks 2u and 2d heated to 350 ° C. or more against the blank 1 with a pressing force P of 1 MPa or more, the blank 1 is locally heated in a very short time, and heat is applied to the heated portion (hard region 1h). The effect is also suppressed. In addition, the strength transition width generated between the softened region 1s and the hard region 1h can be suppressed to 20 mm or less, and the softened region 1s whose strength is reduced by 90% or less as compared with the strength of the hard region 1h is formed.
On the other hand, if the pressing force P is insufficient, a gap is likely to be formed at the interface between the metal blocks 2u and 2d / blank 1 and it takes time to reach a high temperature of 350 ° C. or more. Softens under the influence of heat. In this case, the intensity transition width between the softened region 1s and the hard region 1h is widened, and it is difficult to obtain a large difference in intensity.
When press-forming the locally softened blank 1 by pressing the high-temperature metal blocks 2u and 2d, the softened region 1s is plastically deformed preferentially and is processed into a product shape with high accuracy. When the processed product is observed, processing defects such as breakage, cracks, and buckling are not detected, and a deformed region 1d having no thickness variation is formed.
[0015]
The preferential plastic deformation of the softened region 1s is more likely to occur as the difference in strength between the hard region 1h and the softened region 1s increases, and it is preferable to reduce the strength of the softened region 1s by 90% or more based on the strength of the hard region 1h. . The strength transition width is preferably reduced to 20 mm or less so that the strength of the portion to be machined is selectively reduced and the strength of the portion other than the portion to be machined is not reduced. If the strength transition width is too large to soften even the portion in contact with the shoulder of the punch 5, the press-formability tends to decrease.
When a heat treatment such as an aging treatment is performed on a press-formed product obtained from a blank partially softened by the solution treatment, the strength reduced by the formation of the softened region 1s remaining after the press forming can be recovered. For example, the strength of the softened region 1s is restored to the same level as that of the hard region 1h by the aging treatment of heating to a temperature of 200 ° C. or less for 10 minutes or more.
[0016]
【Example】
A disc-shaped blank with a radius of 45 mm cut from a 1 mm-thick aluminum alloy cold-rolled sheet having the composition shown in Table 1 was used as a test piece. Alloy No. Nos. 1 and 2 are age hardening type aluminum alloys which have been subjected to a solution treatment at 500 ° C. and then subjected to aging treatment at 160 ° C. for 18 hours to precipitate Mg, Si, Cu, etc. as intermetallic compounds to thereby increase the strength, thereby increasing the strength. Alloy No. Reference numeral 3 denotes a work hardening type aluminum alloy obtained by performing 50% cold working on a solid solution strengthened aluminum alloy by adding Mg to increase strength.
[0017]

[0018]
Ring-shaped copper blocks 2u and 2d heated to 500 ° C. were pressed against each blank 1 at a pressure P of 3 MPa, and the rate of temperature rise of the blank 1 was measured at the portion in contact with the blank 1. When the copper blocks 2u and 2d having good thermal conductivity were pressed, the blank 1 was heated in a very short time to a temperature range of 350 ° C. or more effective for releasing solid solution of the intermetallic compound, strain, and stress. On the other hand, when the iron block having low thermal conductivity was pressed, the temperature range reached 350 ° C. or higher in a short time within 5 seconds, although the heating rate was slightly lower. (FIG. 4)
[0019]
Three types of copper blocks 2u and 2d having different inner diameters of 46 mm (Example 1), 53 mm (Example 2), and 60 mm (Example 3) were prepared. Each of the copper blocks 2u and 2d was heated to 500 ° C. After pressing the blank 1 for 1 second for 0.6 seconds, the blank 1 was water-cooled. After cooling, the hardness of the blank 1 was measured in the radial direction, and the effect of local heating by the copper blocks 2u and 2d on the softening of the blank 1 was investigated. In any case, the portion (softened region 1s) in contact with the copper blocks 2u and 2d was significantly softened as compared with the Vickers hardness of the non-contact portion (hard region 1h). The strength transition width between the softened region 1s and the hard region 1h was also suppressed to 20 mm or less. (FIG. 5)
The formation of the softened region 1s by rapid heating is performed according to alloy No. The same tendency was shown for a few aluminum alloy plates.
[0020]
The alloy No. which formed the softened region 1s by local heating One blank 1 was cut into a disk shape having a diameter of 60 to 80 mm and press-formed into a cup shape having an inner diameter of 33 mm. In the press molding, the blank 1 is set on a die 3 having an opening diameter of 36.2 mm, the peripheral edge of the blank 1 is suppressed with a wrinkle suppressor 4, the clearance is set at 0.6 mm, the diameter is 33 mm with a wrinkle suppressing force of 2 kN, and the shoulder radius is set. A 5 mm punch 5 was pushed into the die 3.
The processed part of the press-formed product was observed, and the presence or absence of breakage, cracking, etc. was investigated. In the case of the ST material, the T6 material, the O material and the like, the limit drawing ratio remained at 2.0, and when press forming was performed at a drawing ratio exceeding 2.0, breakage occurred at a position where the punch 5 hit the shoulder.
[0021]
On the other hand, in the blank 1 in which the softened region 1s was formed by rapid heating using the copper blocks 2u and 2d, press forming could be performed without generating processing defects such as breakage and cracking even at a draw ratio of 2.3. Above all, in the blank 1 in which the softened region 1 s having an appropriate area was formed using the copper blocks 2 u and 2 d having an inner diameter of 47 mm, no processing defects were generated even by deep drawing with a drawing ratio of 2.4.
As is clear from this comparison, by setting a portion where plastic deformation is large during press forming in advance as the softened region 1 s, the shape can be formed without generating a processing defect such as breakage or cracking even in deep drawing with a high drawing ratio set. It was confirmed that a press-formed product with good precision was obtained. The effect of the formation of the softened region 1s due to local heating on the improvement of the deep drawability is described in The same applies to a few aluminum alloy plates.
[0022]
【The invention's effect】
As described above, by softening in advance the part that undergoes large deformation, a molded product having good shape accuracy without processing defects such as breakage and cracking even when pressed at a high drawing ratio can be obtained. Can be By pressing the metal block heated at high temperature against the blank to be processed for a very short time, a softened area effective for improving deep drawability is formed, so the processing time is significantly reduced compared to softening by aging treatment. Also, the equipment burden is reduced. As described above, since the workability of the aluminum alloy is improved by a simple operation, a product having a complicated shape, which has been difficult with the conventional method, can be easily manufactured by press molding with a small number of steps.
[Brief description of the drawings]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of forming a softened region at a portion to be processed of a blank. FIG. 2 is a view showing a state where a locally softened blank is set between a die of a press forming die and a punch. FIG. 4 is a diagram showing a change in material and shape until the blank becomes a press-formed product. FIG. 4 is a graph showing a temperature rise characteristic of the blank pressed against a metal block heated at a high temperature. FIG. 6 is a graph showing the hardness distribution of a heated blank along the radial direction. FIG. 6 is a graph comparing the effect of the formation of a softened region on the improvement of deep drawability with a conventional material.
1: blank 1s: softened area 1h: hardened area 1d: deformed area 1c: pinched part 1p: punch contact part 2u, 2d: pressurized and heated body (metal block, copper block) 3: die 4: wrinkle suppression 5: Punch

Claims (7)

An aluminum alloy characterized in that a high-temperature metal block is pressed against a portion to be processed of a blank, and the blank that is in contact with the metal block is rapidly heated locally by heat transfer from the metal block, and the contact portion is locally softened. Heat treatment method. The heat treatment method according to claim 1, wherein a metal block is pressed against an aluminum alloy plate before blank cutting or a blank cut from the aluminum alloy plate to rapidly heat a portion to be processed. The heat treatment method according to claim 1, wherein the metal block heated to a high temperature of 350 ° C. or more is pressed against an aluminum alloy blank with a pressing force of 1 MPa or more. 3. The heat treatment method according to claim 1, wherein the strength transition width between the softened region locally softened by contact with the metal block and the hard region of the non-contact portion is restricted to 20 mm or less. 3. The heat treatment method according to claim 1, wherein the strength of the softened region is reduced by 10% or more based on the strength of the hard region. The heat treatment method according to any one of claims 1 to 5, wherein an age hardening type or a work hardening type aluminum alloy is used as a material. The strength of the softened region softened by the pressing of the metal block heated at a high temperature is 90% or less of the strength of the hard region not in contact with the metal block, and the strength transition width between the softened region and the hard region is 20 mm or less. Aluminum alloy plate for press working adjusted to

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