JP4277157B2

JP4277157B2 - Method for producing extruded profile for plastic working with controlled surface coarse layer

Info

Publication number: JP4277157B2
Application number: JP2000104425A
Authority: JP
Inventors: 健小松; 秀樹石井; 茂岡庭
Original assignee: Nippon Light Metal Co Ltd
Current assignee: Nippon Light Metal Co Ltd
Priority date: 2000-04-06
Filing date: 2000-04-06
Publication date: 2009-06-10
Anticipated expiration: 2020-04-06
Also published as: JP2001286929A

Description

【０００１】
【産業上の利用分野】
本発明は、表面粗粒層の厚みが一定化され、曲げ加工，バルジ加工等に好適に使用される押出形材を製造する方法に関する。
【０００２】
【従来の技術】
アルミニウム合金の押出成形では、コンテナに装填された高温のビレットに押出圧を加え、ダイスから押し出すことによって所定の断面形状をもつ押出形材を押出成形している。６０６１，６Ｎ０１，７Ｎ０１等の再結晶を抑制する作用のある遷移元素を含むアルミニウム合金の押出成形で得られた押出形材の表面を観察すると、中心部に繊維状組織，外周部に再結晶粒からなる粗粒層が形成される。
表面粗粒層の厚みは押出形材の押出方向に関してばらついているため、押出形材を所定長さに切り出して製品とすると、製品ごとに表面粗粒層の厚みが異なる。表面粗粒層が不均一な押出製品に塑性変形を伴う曲げ加工，バルジ加工等の塑性加工を施すと、表面粗粒層に応じてスプリングバック量が異なることから、加工後の形状が一定化しない。また、色調，光沢等の表面性状も不安定化する。
【０００３】
【発明が解決しようとする課題】
表面粗粒層に起因する欠陥を抑制するため、ダイスの出口直後で押出形材に液体窒素等の低温冷媒を吹き付け、表面粗粒層の生成を抑制する方法が知られている（特開平２−１２７９１６号公報，特開平５−７９２７号公報）。しかし、ダイス出口直後の押出形材に低温冷媒を吹き付けることは、押出形材を急冷することであり、熱応力に起因する形状劣化が避けられない。また、吹き付けられた低温冷媒がダイスに接触すると、熱衝撃でダイスが破損する虞もある。ダイスの破損に至らないまでも、ダイスが部分的に急冷されるため、押出条件が不安定化し、押出形材の形状劣化やダイスの短命化等を引き起こす。
【０００４】
【課題を解決するための手段】
本発明は、このような問題を解消すべく案出されたものであり、コンテナ内のビレット残存量に応じてステム速度を制御することにより、押出形材の全長にわたって表面粗粒層の厚みを均一化し、塑性加工時のスプリングバック量の一定化を図り、形状精度の良好な加工品の製造に適した押出形材を提供することを目的とする。
【０００５】
本発明の製造方法は、その目的を達成するため、コンテナに装填した遷移元素を含むアルミニウム合金のビレットの後端にステムを押し当て、ステムの押出圧をビレットに加えてコンテナの前端に設けられているダイスから押出形材を押し出す際、コンテナに収容しているビレットの残存長さが短くなるに従ってステムの前進速度を小さくすることを特徴とする。
ステムの前進速度Ｖは、コンテナ内ビレットの残存長さをＬ（ｍ），押出比をＥとするとき、式ε＝（Ｖ／Ｌ）×Ｅで定義される歪速度ε（／秒）が一定になるようにコンテナ内ビレットの残存長さに応じて低下させる。
本発明で対象とするアルミニウム合金は、強度，耐食性等の特性を改善するため再結晶抑制作用のある遷移元素を含んだ２０１４，２０２４，６０６１，６Ｎ０１，６０８２，７００３，７Ｎ０１，７０７５等のアルミニウム合金が挙げられる。遷移元素としては、特にＣｒ，Ｍｎ，Ｚｒが有効な成分であり、それぞれ単独に添加した場合にはＣｒ：０．０４質量％以上，Ｍｎ：０．０８質量％以上，Ｚｒ：０．０５質量％以上で再結晶抑制効果が顕著となる。
【０００６】
【作用】
押出成形では、高温に加熱されたアルミニウム合金のビレットＢをコンテナ１に装填し、後方からステム２で押出圧ＦをビレットＢに加える。押出圧Ｆが加えられたビレットＢは、コンテナ１内を塑性流動し、コンテナ１の前端に設けられているダイス３の賦形空間から押し出され、所定断面形状をもつ押出形材Ｐになる（図１）。製造された押出形材Ｐには、押出成形時及び押出直後の冷却過程で再結晶が進行し、再結晶粒からなる表面粗粒層が生成する。
【０００７】
押出形材Ｐの断面観察で表面粗粒層の生成状況を調査したところ、表面粗粒層は押出形材Ｐの押出方向前方で薄く、後方になるほど厚くなっていた。表面粗粒層は再結晶組織であることから、押出形材Ｐの温度が表面粗粒層の生成・成長に影響を及ぼしているものと考えられるが、押出形材Ｐのダイス出口温度が一定になるように温度管理した定温押出でも依然として表面粗粒層の厚みが押出形材Ｐの押出方向前方と後方とで異なることが避けられない。
【０００８】
そこで、本発明者等は、コンテナ１内にある押出形材Ｐに蓄えられる歪速度が表面粗粒層の生成・成長に大きな影響を及ぼしているものと推定し、歪速度が一定となるようにステム２の前進速度Ｖを漸次低下させたところ、表面粗粒層の厚み変動が小さくなることを見出した。歪速度の管理により表面粗粒層の押出方向に関する厚み変動が抑制されることは、次のように推察される。
【０００９】
コンテナ１内のビレットＢは、塑性流動しながらダイス３から押し出されるが、ダイス３のベアリングを通過する際にベアリング接触面と内部との間でメタルの流速が異なり、流速差に起因する剪断歪が発生する。歪速度は、ビレットＢの後端部が押し出しされるに従って大きくなり、ダイス３から押し出された押出形材Ｐに持ち越される。歪は押出形材Ｐの再結晶を促進させる要因であり、同じステム２の前進速度ＶでビレットＢを押し出すと、歪速度が小さい押出形材Ｐの押出方向前方部に比較して歪速度が大きい後方部ほど再結晶が進行する。その結果、表面粗粒層は、押出形材Ｐの押出方向前方部で薄く、後方部で厚くなる。
【００１０】
歪速度が押出形材Ｐの表面粗粒層に影響を及ぼすことを前提とし、従来の等速押出では歪速度が大きな後端部になるほどステム２の前進速度Ｖを遅くした。ステム２の前進速度Ｖに前述の変化をつけるとき、実施例にもみられるように、押出方向に関する再結晶の進行状態が均一化され、表面粗粒層の厚み変動が抑制された押出形材Ｐが得られる。このようにして得られた押出形材Ｐは、表面粗粒層の厚みに起因するスプリングバック量が押出形材Ｐの押出方向に均一化されているので、曲げ加工，バルジ加工等の塑性変形を伴う加工を施しても各部が所定の形状に成形され、形状精度の良好な加工品となる。
【００１１】
歪速度は、本来、ベアリングを通過する材料のベアリング接触面と内部との流速差に起因する剪断歪速度で表わされる。しかし、流速差の検出は、現実的には困難である。そこで、ベアリング出口を塞いだ状態でコンテナ１内にあるビレットＢに加わる押出方向の圧縮歪速度がベアリング開放状態では剪断歪速度に対応するものと考え、式ε＝（Ｖ／Ｌ）×Ｅ〔ただし、Ｌ：コンテナ１内に残存しているビレットＢの長さ（ｍ），Ｖ＝ステム２の前進速度をＶ（ｍ／秒），Ｅ：押出比（＝コンテナ内断面積／ベアリング開口面積）〕で歪速度εを定義した。この歪速度εが一定になるように、コンテナ内ビレットの残存長さをＬに応じてステム２の前進速度Ｖを減少するとき、後述の実施例にみられるように表面粗粒層の生成・成長が精度良く制御された押出形材Ｐが得られることを見出した。
【００１２】
【実施例】
本発明者等は、先ずダイス３を出た直後の押出形材Ｐにベアリング部から突出させた熱電対の先端を押出形材の表面に接触させて押出形材のダイス出口温度Ｔ（℃）を測定しながら、押出形材Ｐを押出成形し、ダイス出口温度Ｔが表面粗粒層の生成・成長に及ぼす影響を調査した。この場合、５００℃に予熱した径１９６ｍｍ，長さ４７０ｍｍの６Ｎ０１アルミニウム合金ビレットＢを内径２０３ｍｍのコンテナ１に装填し、６０ｍｍ×５ｍｍのフラットバーを押し出した。
【００１３】

【００１４】
製造された押出形材が室温まで冷却した後、押出方向各位置における押出形材の断面を観察し、表面粗粒層の厚さを測定した。測定値から、押出形材の断面に占める表面粗粒層の割合（％）を面積率として算出した。求められた面積率とダイス出口温度Ｔとの関係を調査したところ、図２に示すように両者の間に明確な相関性がみられなかった。なお、図２中の凡例では、温度はビレット初期加熱温度，数値は押出速度（ｍ／分）を示す。
【００１５】
図２から、ダイス出口温度Ｔが高くなると表面粗粒層面積率が高くなる傾向がみられる。ただし、各ダイス出口温度Ｔにおける表面粗粒層面積率の幅が広く、たとえば押出速度３０ｍ／分の結果に表されているように表面粗粒層面積率が広幅になる傾向は高温域になるほど顕著となる。このように、ダイス出口温度Ｔが同じであっても表面粗粒層面積率が幅広の範囲をもつことから、表面粗粒層の生成・成長は単にダイス出口温度Ｔで一義的に定まらないことが判る。
【００１６】
そこで、式ε＝（Ｖ／Ｌ）×Ｅで定義される歪速度εを用い、ダイス出口温度Ｔ４７０℃以上で押出された押出形材Ｐに生成した表面粗粒層の面積率と歪速度εとの関係を調査した。図３の調査結果にみられるように、歪速度εが大きくなるに従って表面粗粒層の面積率Ａｒ（％）が増加した。このとき、歪速度εと面積率Ａｒとの関係はＡｒ＝１７×ε^1/2で表わされ、相関係数０．８８０と極めて高い相関関係にあった。したがって、図３の関係を利用して歪速度εから表面粗粒層の面積率Ａｒを推定できることが判る。
【００１７】
次いで、表面粗粒層の面積率Ａｒを一定にした操業例を説明する。径１９６ｍｍ，長さ４７０ｍｍの６Ｎ０１アルミニウム合金ビレットＢを４６０℃に加熱した後、内径２０３ｍｍのコンテナ１に装填し、幅６０ｍｍ，厚み５ｍｍのフラットバーを押出成形した。ディスカード厚を３０ｍｍに設定すると、押出長さは（１９６／２）²×π×６０^-1×５^-1×（４７０−３０）＝４４．２ｍと算出される。
【００１８】
このとき、コンテナ内ビレットの残存長さをＬに応じて押出速度（ステム２の前進速度Ｖ）を図４に示すように減少させた。すなわち、コンテナ内ビレットの残存長さをＬが４７０ｍｍから７８ｍｍになるまでの間は歪速度εを一次関数的に減少させ、残存長さをＬが７８ｍｍとなった時点で押出速度を一定値５ｍ／分に維持した。Ｌ＝７８ｍｍは押出時間が長くなることを避けるために設定した下限値であり、押出時間に制約がない場合には図４に点線で示すように押出速度を更に遅くすることも可能である。
【００１９】
得られた押出形材Ｐの表面を観察したところ、図５に示すように、押出形材Ｐの先端から押出方向に沿って４０ｍの範囲にわたって表面粗粒層の面積率は約４０％の一定範囲に収まっていた。そして、押出速度を５ｍ／分の一定値に維持した押出後期で成形された押出形材Ｐの先端から４０ｍ以上の部分では表面粗粒層の面積率が上昇していた。表面粗粒層の面積率に上昇傾向がみられる部分は、押出形材Ｐを整直した後で切り落とされた。整直された押出形材Ｐは、所定長さに切断されて押出製品となるが、押出形材Ｐの押出方向に沿った表面粗粒層面積率の変動が抑制されているため、切断後に得られた押出製品相互の間で表面粗粒層面積率にバラツキがない。したがって、各押出製品を同一条件下で目的形状に曲げ加工でき、形状精度の良好な曲げ加工品が得られた。
【００２０】
比較のため、全押出工程を通して３０ｍ／分の一定した押出速度でビレットＢから押出形材Ｐを押出成形した。この場合に得られた押出形材Ｐの表面を観察すると、図６に示すように押出形材Ｐの押出方向に関して表面粗粒層の面積率が次第に大きくなっていた。そのため、押出形材Ｐから長さ１０ｍの押出製品を４本切り出すと、押出形材Ｐの先端から切り出された押出製品と後端から切り出された押出製品の間で表面粗粒層の面積率が５０％以上も異なっていた。したがって、同一条件下で各押出製品を曲げ加工すると、スプリングバック量が異なることから曲げ加工品の形状が不安定であった。
【００２１】
【発明の効果】
以上に説明したように、本発明においては、コンテナに装填されているビレットの残存長さが短くなるに従ってステムの前進速度を低下させ、歪速度を実質的に一定化しているので、押出形材表面に生成する粗粒層が押出方向に関してほぼ均一な厚みとなる。表面粗粒層の厚みが均一化された押出形材は、曲げ加工，バルジ加工等の際に表面粗粒層の肉厚変動に起因したスプリングバック量の相違が抑えられているため、形状精度の良好な加工品に成形される。
【図面の簡単な説明】
【図１】コンテナに装填したビレットを押し出している説明図
【図２】押出形材のダイス出口温度と表面粗粒層の面積率との間の相関性が低いことを示すグラフ
【図３】歪速度と表面粗粒層の面積率との間に密接な相関関係が成立していることを示すグラフ
【図４】コンテナ内ビレットの残存長さに応じて押出速度を低下させた実施例の押出成形を説明するグラフ
【図５】本発明に従って製造された押出形材の押出方向に沿った表面粗粒層の面積率の分布を示すグラフ
【図６】一定の押出速度で製造された押出形材の押出方向に沿った表面粗粒層の面積率の分布を示すグラフ
【符号の説明】
１：コンテナ２：ステム３：ダイスＢ：ビレットＰ：押出形材[0001]
[Industrial application fields]
The present invention relates to a method for producing an extruded profile in which the thickness of a surface coarse-grained layer is constant and is suitably used for bending, bulging, and the like.
[0002]
[Prior art]
In the extrusion molding of an aluminum alloy, an extrusion shape having a predetermined cross-sectional shape is extruded by applying an extrusion pressure to a high-temperature billet charged in a container and extruding it from a die. When the surface of an extruded shape obtained by extrusion molding of an aluminum alloy containing a transition element having an action of suppressing recrystallization such as 6061, 6N01, and 7N01 is observed, a fibrous structure is observed at the center, and recrystallized grains are present at the outer periphery. A coarse layer consisting of is formed.
Since the thickness of the surface coarse-grained layer varies with respect to the extrusion direction of the extruded profile, the thickness of the surface coarse-grained layer varies from product to product when the extruded profile is cut into a predetermined length. If the extruded product with non-uniform surface coarse layer is subjected to plastic processing such as bending or bulge processing with plastic deformation, the amount of springback differs depending on the surface coarse layer, so the shape after processing becomes constant. do not do. In addition, surface properties such as color tone and gloss become unstable.
[0003]
[Problems to be solved by the invention]
In order to suppress defects caused by the surface coarse particle layer, a method of suppressing the generation of the surface coarse particle layer by spraying a low-temperature refrigerant such as liquid nitrogen on the extruded shape immediately after the exit of the die is known (Japanese Patent Laid-Open No. 2). -127916, JP-A-5-7927). However, spraying a low-temperature refrigerant onto the extruded shape immediately after the die exit is to rapidly cool the extruded shape, and shape deterioration due to thermal stress is inevitable. In addition, when the sprayed low-temperature refrigerant contacts the die, the die may be damaged by thermal shock. Even if the die is not damaged, the die is partially quenched, so that the extrusion conditions become unstable, resulting in deterioration of the shape of the extruded shape, shortening of the die, and the like.
[0004]
[Means for Solving the Problems]
The present invention has been devised to solve such problems, and by controlling the stem speed in accordance with the remaining billet in the container, the thickness of the surface coarse particle layer can be reduced over the entire length of the extruded profile. An object is to provide an extruded profile that is uniform and makes the amount of spring back constant during plastic processing, and is suitable for manufacturing a processed product with good shape accuracy.
[0005]
In order to achieve the object, the manufacturing method of the present invention is provided at the front end of the container by pressing the stem against the rear end of the aluminum alloy billet containing the transition element loaded in the container and applying the extrusion pressure of the stem to the billet. When extruding the extruded shape from the die, the advance speed of the stem is reduced as the remaining length of the billet accommodated in the container becomes shorter.
The stem advance speed V is expressed by the equation ε = (V / L) × E, where L (m) is the remaining length of the billet in the container and E is the extrusion ratio. It is lowered according to the remaining length of the billet in the container so as to be constant.
The aluminum alloy targeted by the present invention is an aluminum alloy such as 2014, 2024, 6061, 6N01, 6082, 7003, 7N01, 7075 and the like containing a transition element having an action of suppressing recrystallization in order to improve properties such as strength and corrosion resistance. Is mentioned. As transition elements, particularly Cr, Mn, and Zr are effective components. When added individually, Cr: 0.04 mass% or more, Mn: 0.08 mass% or more, Zr: 0.05 mass Recrystallization suppression effect becomes remarkable at more than%.
[0006]
[Action]
In the extrusion molding, a billet B made of an aluminum alloy heated to a high temperature is loaded into the container 1, and an extrusion pressure F is applied to the billet B from the rear with a stem 2. The billet B to which the extrusion pressure F has been applied plastically flows in the container 1 and is extruded from the shaping space of the die 3 provided at the front end of the container 1 to become an extruded shape P having a predetermined cross-sectional shape ( FIG. 1). In the manufactured extruded shape member P, recrystallization proceeds in the cooling process at the time of extrusion molding and immediately after extrusion, and a surface coarse particle layer made of recrystallized grains is generated.
[0007]
When the state of formation of the surface coarse particle layer was investigated by observing the cross section of the extruded profile P, the surface coarse particle layer was thin in the forward direction of the extruded profile P in the extrusion direction and thicker toward the rear. Since the surface coarse grain layer has a recrystallized structure, it is considered that the temperature of the extruded profile P affects the generation and growth of the surface coarse grain layer, but the die outlet temperature of the extruded profile P is constant. Even in the constant temperature extrusion in which the temperature is controlled, it is inevitable that the thickness of the coarse-grained layer is still different between the front side and the rear side of the extruded shape member P in the extrusion direction.
[0008]
Therefore, the present inventors estimate that the strain rate stored in the extruded profile P in the container 1 has a great influence on the generation and growth of the surface coarse particle layer, so that the strain rate becomes constant. In addition, when the forward speed V of the stem 2 was gradually decreased, it was found that the variation in the thickness of the surface coarse particle layer was reduced. It is inferred that the thickness variation in the extrusion direction of the surface coarse particle layer is suppressed by controlling the strain rate as follows.
[0009]
The billet B in the container 1 is pushed out of the die 3 while being plastically flowed. However, when passing through the bearing of the die 3, the flow velocity of the metal differs between the bearing contact surface and the inside, and the shear strain caused by the flow velocity difference. Will occur. The strain rate increases as the rear end portion of the billet B is pushed out, and is carried over to the extruded shape member P pushed out from the die 3. Strain is a factor that promotes recrystallization of the extruded profile P. When the billet B is extruded at the same advance speed V of the stem 2, the strain rate is lower than that of the forward portion of the extruded profile P with a smaller strain rate. The larger the rear part, the more recrystallization proceeds. As a result, the surface coarse particle layer is thin at the front portion in the extrusion direction of the extruded shape member P and thick at the rear portion.
[0010]
Assuming that the strain rate affects the surface coarse-grained layer of the extruded profile P, in the conventional constant speed extrusion, the forward speed V of the stem 2 is decreased toward the rear end portion where the strain rate becomes larger. When the above-described change is made to the advance speed V of the stem 2, as shown in the examples, the progress of recrystallization in the extrusion direction is made uniform, and the extruded profile P in which the thickness variation of the surface coarse grain layer is suppressed. Is obtained. The extruded profile P thus obtained has a uniform amount of springback due to the thickness of the coarse-grained layer in the extrusion direction of the extruded profile P. Therefore, plastic deformation such as bending and bulging is performed. Even if processing is performed, each part is formed into a predetermined shape, resulting in a processed product with good shape accuracy.
[0011]
The strain rate is originally expressed as a shear strain rate caused by a difference in flow velocity between the bearing contact surface and the inside of the material passing through the bearing. However, it is actually difficult to detect the flow rate difference. Therefore, it is considered that the compressive strain rate in the extrusion direction applied to the billet B in the container 1 in a state where the bearing outlet is closed corresponds to the shear strain rate in the state where the bearing is open, and the equation ε = (V / L) × E [ Where, L: length of billet B remaining in container 1 (m), V = advance speed of stem 2 V (m / sec), E: extrusion ratio (= container cross-sectional area / bearing opening area) )] Defined the strain rate ε. When the advance speed V of the stem 2 is reduced according to the remaining length of the billet in the container in accordance with L so that the strain rate ε becomes constant, the formation of the surface coarse particle layer as shown in the examples described later is performed. It has been found that an extruded profile P whose growth is accurately controlled can be obtained.
[0012]
【Example】
The inventors first contact the surface of the extruded shape member with the tip of the thermocouple that is protruded from the bearing portion on the extruded shape member P immediately after exiting the die 3, and the die outlet temperature T (° C.) of the extruded shape member. The extrusion shape P was extruded while measuring the effect of the die outlet temperature T on the formation and growth of the surface coarse layer. In this case, a 6N01 aluminum alloy billet B having a diameter of 196 mm and a length of 470 mm preheated to 500 ° C. was loaded into the container 1 having an inner diameter of 203 mm, and a 60 mm × 5 mm flat bar was extruded.
[0013]

[0014]
After the manufactured extruded shape was cooled to room temperature, the cross section of the extruded shape at each position in the extrusion direction was observed, and the thickness of the surface coarse particle layer was measured. From the measured value, the ratio (%) of the surface coarse grain layer in the cross section of the extruded profile was calculated as an area ratio. When the relationship between the obtained area ratio and the die outlet temperature T was investigated, no clear correlation was found between the two as shown in FIG. In the legend in FIG. 2, the temperature indicates the billet initial heating temperature, and the numerical value indicates the extrusion rate (m / min).
[0015]
From FIG. 2, when the die outlet temperature T increases, the surface coarse particle layer area ratio tends to increase. However, the range of the surface coarse particle layer area ratio at each die outlet temperature T is wide. For example, as shown in the result of the extrusion speed of 30 m / min, the tendency for the surface coarse particle layer area ratio to become wider is higher in the higher temperature range. Become prominent. Thus, even if the die outlet temperature T is the same, the surface coarse particle layer area ratio has a wide range, and therefore the generation and growth of the surface coarse particle layer is not simply determined by the die outlet temperature T. I understand.
[0016]
Therefore, using the strain rate ε defined by the formula ε = (V / L) × E, the area ratio and strain rate ε of the surface coarse grain layer formed on the extruded profile P extruded at a die outlet temperature T470 ° C. or higher. And investigated the relationship. As can be seen from the investigation results in FIG. 3, the area ratio Ar (%) of the surface coarse-grained layer increased as the strain rate ε increased. At this time, the relationship between the strain rate ε and the area ratio Ar is expressed by Ar = 17 × ε ^1/2 , and has a very high correlation with a correlation coefficient of 0.880. Therefore, it can be seen that the area ratio Ar of the surface coarse-grained layer can be estimated from the strain rate ε using the relationship of FIG.
[0017]
Next, an operation example in which the area ratio Ar of the surface coarse particle layer is constant will be described. A 6N01 aluminum alloy billet B having a diameter of 196 mm and a length of 470 mm was heated to 460 ° C. and then loaded into a container 1 having an inner diameter of 203 mm, and a flat bar having a width of 60 mm and a thickness of 5 mm was extruded. When the discard thickness is set to 30 mm, the extrusion length is calculated as (196/2) ² × π × 60 ⁻¹ × 5 ⁻¹ × (470-30) = 44.2 m.
[0018]
At this time, the extrusion speed (the advance speed V of the stem 2) was decreased as shown in FIG. That is, the strain rate ε is decreased linearly until the remaining length of the billet in the container is changed from 470 mm to 78 mm, and when the remaining length L becomes 78 mm, the extrusion speed is set to a constant value of 5 m. / Min. L = 78 mm is a lower limit value set to avoid an increase in the extrusion time. When there is no restriction on the extrusion time, the extrusion speed can be further reduced as shown by a dotted line in FIG.
[0019]
When the surface of the obtained extruded profile P was observed, as shown in FIG. 5, the area ratio of the surface coarse-grained layer was constant at about 40% over the range of 40 m along the extrusion direction from the tip of the extruded profile P. It was in range. And the area ratio of the surface coarse-grained layer rose in the part 40 m or more from the front-end | tip of the extrusion shape material P shape | molded in the latter stage of extrusion which maintained the extrusion speed at the constant value of 5 m / min. The portion in which the area ratio of the surface coarse particle layer showed an upward trend was cut off after the extruded profile P was resized. The reshaped extruded profile P is cut into a predetermined length to become an extruded product, but since the fluctuation of the surface coarse layer area ratio along the extrusion direction of the extruded profile P is suppressed, There is no variation in the surface coarse particle layer area ratio between the obtained extruded products. Therefore, each extruded product could be bent into the target shape under the same conditions, and a bent product with good shape accuracy was obtained.
[0020]
For comparison, an extruded profile P was extruded from billet B at a constant extrusion speed of 30 m / min throughout the entire extrusion process. When the surface of the extruded profile P obtained in this case was observed, the area ratio of the surface coarse particle layer gradually increased in the extrusion direction of the extruded profile P as shown in FIG. Therefore, when four extruded products having a length of 10 m are cut out from the extruded profile P, the area ratio of the surface coarse-grained layer between the extruded product cut from the front end of the extruded profile P and the extruded product cut from the rear end. Was more than 50% different. Therefore, when each extruded product was bent under the same conditions, the amount of spring back was different, and the shape of the bent product was unstable.
[0021]
【The invention's effect】
As described above, in the present invention, as the remaining length of the billet loaded in the container becomes shorter, the advance speed of the stem is lowered and the strain speed is substantially constant. The coarse particle layer formed on the surface has a substantially uniform thickness in the extrusion direction. Extruded profile with uniform surface coarse layer thickness suppresses the difference in springback due to fluctuations in the surface coarse layer thickness during bending, bulging, etc. Is formed into a good processed product.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for extruding a billet loaded in a container. FIG. 2 is a graph showing a low correlation between the die outlet temperature of an extruded profile and the area ratio of a surface coarse particle layer. FIG. 4 is a graph showing that a close correlation is established between the strain rate and the area ratio of the surface coarse particle layer. FIG. 4 shows an example in which the extrusion rate was reduced according to the remaining length of the billet in the container. Graph illustrating extrusion molding FIG. 5 is a graph showing the distribution of the area ratio of the surface coarse particle layer along the extrusion direction of the extruded profile manufactured according to the present invention. FIG. 6 is an extrusion manufactured at a constant extrusion speed. Graph showing the distribution of the area ratio of the surface coarse layer along the extrusion direction of the profile [Explanation of symbols]
1: Container 2: Stem 3: Die B: Billet P: Extruded profile

Claims

When a stem is pressed against the rear end of an aluminum alloy billet containing transition elements loaded in the container and the extrusion pressure of the stem is applied to the billet to extrude the extruded shape from the die provided at the front end of the container, it is accommodated in the container. A method for producing an extruded profile for plastic working by controlling a coarse-grained surface layer, wherein the advance speed of the stem is reduced as the remaining length of the billet is reduced.

Strain rate ε defined by the equation ε = (V / L) × E, where L (m) is the remaining length of the billet in the container, V (m / sec) is the stem advance speed, and E is the extrusion ratio. The manufacturing method according to claim 1, wherein the advancing speed of the stem is reduced according to the remaining length of the billet in the container so that (/ second) is constant.

An extruded profile for plastic working produced by the method according to claim 1 or 2.