JP2004002947A

JP2004002947A - Wrought aluminum alloy with excellent hot forgeability and machinability

Info

Publication number: JP2004002947A
Application number: JP2002221993A
Authority: JP
Inventors: Shinji Yoshihara; 吉原　伸二; Sunao Aiura; 相浦　直
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2002-04-15
Filing date: 2002-07-30
Publication date: 2004-01-08
Anticipated expiration: 2022-07-30
Also published as: JP3969672B2

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an Al-Cu type wrought aluminum alloy, e.g., extruded material, having excellent hot forgeability and machinability. <P>SOLUTION: The Al-Cu type wrought aluminum alloy, which has a composition consisting of, by mass, 4.5 to 6.0% Cu, 0.06 to 0.55% Sn, 0.08 to 0.55% Bi, 0.005 to 0.2% Ti and the balance Al with impurities and containing, if necessary, one or more kinds among 0.05 to 0.5% Mn, 0.05 to 0.5% Cr and 0.05 to 0.5% Zr, is provided. Moreover, the average grain size and distribution density of Sn-Bi compounds are made to 1 to 10μm and (100 to 5,000)pieces/mm<SP>2</SP>, respectively. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、熱間鍛造性及び切削性に優れたＡｌ−Ｃｕ系アルミニウム合金展伸材に関するものである。
【０００２】
【従来の技術】
アルミニウム合金のうち特に２０００系のＡｌ−Ｃｕ系合金を中心とした熱処理型合金は高い機械的性質をもち、航空機等の各種構造材としての使用実績が多い。この系の合金の一般的な加工法として、押出後、切削加工や穴あけ加工を施される場合が多いが、例えば２０１４合金や２０２４合金等は切削時に発生する切り屑が分断されにくいため切削性が劣り、複雑な切削や穴あけ加工する機械部品への採用が困難であった。
【０００３】
一方、この系のアルミニウム合金押出材の切削性を向上させるためには、従来は例えばＡＡ２０１１合金（Ｃｕ：５．０〜６．０％、Ｐｂ：０．２〜０．６％、Ｂｉ：０．２〜０．６％、残部Ａｌ）のように、Ｐｂ、Ｂｉ等の低融点金属が添加された。これら低融点金属はアルミニウム中にほとんど固溶せず、アルミニウム合金中に粒状に存在し、その低融点金属粒子が切削加工時の加工発熱により溶融して切り屑を分断し（溶融脆化）、アルミニウム合金押出材の切削性を向上させる。
【０００４】
ところが、近年の地球環境保護要求の高まりを受け、Ｐｂなどの有害成分の使用を規制する動きが大きくなってきた。Ｐｂは人体に摂取されると蓄積し、神経障害、貧血などのＰｂ中毒症を引き起こす。
国内では１９９７年に通産省が「品目別廃棄物処理・再資源化ガイドライン」を設定し、自動車とオートバイに対してＰｂ使用量削減に関する数値目標を設定した。これを受けて自動車メーカー各社は自主行動計画を策定した。一方、欧州連合ＥＵでは、「包装および包装廃棄物に関する指令」や「使用済み自動車に関するＥＵ指令案」があり、有害物質であるＰｂやＣｄ、Ｈｇ、６価Ｃｒの使用量を削減することを規定している。
【０００５】
このような情勢のなか、Ｐｂを実質的に含まず、かつ切削性に優れるアルミニウム合金が開発され、例えば特開２０００−３２８１６８、特開２００１−２４０９３１、ヨーロッパ公開特許第９８２４１０等に開示されている。これらの公報に記載されたＡｌ−Ｃｕ系アルミニウム合金はＳｎとＢｉを所定量含み、低融点のＳｎ−Ｂｉ化合物が晶出することで、切削性が向上する。
【０００６】
【発明が解決しようとする課題】
一方、例えば自動車のＡＢＳ（アンチスキッド・ブレーキ・システム）のハウジングのような機械構造部品の小型、軽量化が進み、それに伴い小型の切削ドリル、例えば直径２ｍｍ程度のものも使用されるようになり、さらに高いレベルの切削性（切粉分断性）が要求されるようになった。
また、Ａｌ−Ｃｕ系アルミニウム合金には高強度鍛造材としての用途もあるが、Ｓｎ−Ｂｉ化合物等の低融点金属により切削性を向上させたＡｌ−Ｃｕ系アルミニウム合金は、熱間鍛造に供した場合に割れが発生しやすいという問題があった。
【０００７】
従って、本発明は、Ｐｂを実質的に含まず、ＳｎとＢｉにより切削性を向上させたＡｌ−Ｃｕ系アルミニウム合金展伸材において、さらに切削性の向上を図り、同時に熱間鍛造性を向上させることを目的とする。
【０００８】
【課題を解決するための手段】
本発明者らは前記課題を解決するために鋭意研究を重ねた結果、Ｓｎ−Ｂｉ化合物を、母相中に適当な粒径及び密度で分布させることにより、上記目的を達成できることを見い出し、その知見を基に本発明を完成するに至った。
すなわち、本発明に関わる熱間鍛造性及び切削性に優れたアルミニウム合金展伸材は、Ｃｕ：４．５〜６．０％、Ｓｎ：０．０６〜０．５５％、Ｂｉ：０．０８〜０．５５％、Ｔｉ：０．００５〜０．２％を含有し、残部がＡｌ及び不純物からなり、Ｓｎ−Ｂｉ化合物の平均粒径が１〜１０μｍ、分布密度が１００〜５０００個／ｍｍ^２であることを特徴とする。また、本発明に係る上記アルミニウム合金は、必要に応じて、さらにＭｎ：０．０５〜０．５％、Ｃｒ：０．０５〜０．５％、Ｚｒ：０．０５〜０．５％のうち１種以上を含有する。
【０００９】
【発明の実施の形態】
次に、上記アルミニウム合金展伸材における各元素の添加理由及び添加量の限定理由を説明する。
Ｃｕ：４．５〜６．０％
Ｃｕは熱処理により強度を高めるとともに、歪み硬化能を向上させるため切り屑分断を助長する。Ｃｕ含有量が４．５％未満ではその効果に乏しく、一方６．０％を越えて添加すると耐食性が低下し、また熱間加工性（押出性等）も低下する。望ましくは５．５％以下、特に強度と良好な耐食性及び熱間加工性を確保するとの観点から、５％を越え、５．４％以下が望まれる。
【００１０】
Ｂｉ：０．０８〜０．５５％
Ｓｎ：０．０６〜０．５５％
Ｂｉ及びＳｎを同時に添加することにより、低融点のＢｉ−Ｓｎ化合物の微粒子がアルミニウム合金中に分散され、切削加工熱による切り屑の溶融脆化が起こり、優れた切り屑分断性が得られる。ＢｉとＳｎの含有量が共晶組成（Ｂｉ：Ｓｎ＝５７：４３）に近いほど分散粒子の融点を低下させることができ、切り屑の溶融脆化の効率が上がる。一方、Ｂｉ単独又はＳｎ単独、あるいは同時添加されていてもＢｉとＳｎの含有量が共晶組成から外れるほど分散粒子の融点が高くなり、切削加工熱による切り屑の溶融脆化の効率が低く、切り屑分断性に劣るようになる。しかも、Ｂｉ及びＳｎは単独添加であると結晶粒界に偏析し、伸びが低下する。さらに、ＢｉとＳｎの含有量が少ないとＢｉ−Ｓｎ化合物粒子の平均粒径が小さくかつ分布密度が小さくなり、切削性改善の効果が少なく、含有量が多くなると平均粒径が大きくかつ分布密度が大きくなり、伸び及び熱間鍛造性を低下させる。以上の点から、ＢｉとＳｎは同時に添加することとし、その含有量はＳｎが０．０６〜０．５５％、Ｂｉが０．０８〜０．５５％とする。熱間鍛造性の面からいえば、Ｓｎは０．０６〜０．２５％、さらに０．０６〜０．１％が望ましい。切削性の面からは、Ｓｎは０．０８％以上が望ましい。なお、望ましい含有比率（質量比）は、切り屑分断性の面からいえばＢｉ／Ｓｎで１．０〜６．０、合計含有量は望ましくは０．５〜１．０％である。
【００１１】
Ｔｉ：０．００５〜０．２％
Ｔｉの添加により、鋳造組織が微細化し押出材等の組織の均一性が向上し、熱間鍛造性が向上する。しかし、Ｔｉ含有量が０．００５％未満ではその効果が得られず、一方０．２％を越えて添加してもその効果は飽和する。
Ｍｎ：０．０５〜０．５％
Ｃｒ：０．０５〜０．５％
Ｚｒ：０．０５〜０．５％
Ｍｎ、Ｃｒ、ＺｒはそれぞれＡｌとの金属間化合物を形成し、切り屑分断の起点となって切削性を向上させるため、適宜１種以上を添加する。添加量がそれぞれ０．０５％未満ではその効果が十分でなく、一方、０．５％を越えると粗大な金属間化合物を生成し熱間加工性（押出性等）が低下する。
【００１２】
不純物等
アルミニウム合金中には不純物として又は添加元素として、Ｆｅ、Ｓｉ、Ｚｎ、Ｖ等が含まれる。このうちＦｅ及びＳｉはアルミニウム合金に特に多く含まれる不純物であり、Ｓｉは切削性を改善する作用もあるが、いずれも含有量が多いと粗大な金属間化合物を晶出して合金の機械的性質を損なうため、本発明においてＦｅ、Ｓｉの含有量はそれぞれ１．０％、１．５％以下に規制する。Ｆｅについては望ましくは０．７％以下であり、Ｓｉについては、熱間鍛造性の観点から望ましくは０．７％以下、さらに０．２％以下、さらに０．１％未満に規制することが望ましい。Ｚｎ、Ｖについては、それぞれ１．０％以下、０．２％以下であれば、本発明のアルミニウム合金に含まれていても、特に悪影響は及ぼさない。また、アルミニウム合金を鋳造する際には地金、添加元素の中間合金等様々な経路より不純物が混入する。混入する元素は様々であるが、その他の不純物は単体で０．０５％以下、総量で０．１５％以下に規制する。なお、不純物のうちＢについては、Ｔｉの添加に伴い合金中にＴｉ含有量の１／５程度の量で混入するが、より望ましい範囲は０．０２％以下、さらに０．０１％以下が望ましい。
【００１３】
本発明のアルミニウム合金展伸材は、平均粒径が１〜１０μｍ、分布密度が１００〜５０００個／ｍｍ^２のＳｎ−Ｂｉ化合物が母相中に分散しているため、この低融点金属粒子が切削加工時の加工発熱により溶融して切り屑を分断し（溶融脆化）アルミニウム合金の切削性が向上する。しかし、平均粒径が１μｍより小さく、又は／及び分布密度が１００個／ｍｍ^２より少ない場合、粒子が分断の起点となりにくいか分断の起点になる箇所が減って切削性が不十分となる。一方、平均粒径が１０μｍより大きく、又は／及び分布密度が５０００個／ｍｍ^２より多い場合、溶融した粒子により熱間鍛造性が阻害される。本発明において平均粒径の望ましい範囲は３．５〜４．５μｍ、分布密度の望ましい範囲は２１０〜２８００個／ｍｍ^２である。
【００１４】
上記アルミニウム合金展伸材は、常法に従い溶解、鋳造、均質化処理を施した後、例えば押出加工又は圧延加工などの熱間加工を行い、得られた押出材あるいは圧延材（棒材等）に対し、必要に応じて熱間鍛造を施し、次いで溶体化・焼入れ処理及び時効処理（Ｔ６処理）を施して所定の強度を与え、切削加工に供する。熱間加工における押出比又は圧延比（棒材等）は、ＳｎとＢｉの含有量と共にＳｎ−Ｂｉ化合物粒子の平均粒径及び分布密度に支配的に影響し、これが小さいと平均粒径は大きくかつ分布密度が小さくなり、大きいと平均粒径は小さくかつ分布密度は大きくなる傾向にある。前記Ｓｎ及びＢｉの含有量範囲において、この押出比又は圧延比を概ね２０〜４０の範囲に設定することで、Ｓｎ−Ｂｉ化合物粒子について前記平均粒径及び分布密度を得ることができる。なお、通常の熱間鍛造やＴ６処理によってＳｎ−Ｂｉ化合物粒子の平均粒径及び分布密度が大きく変化することはなく、熱間鍛造時と切削時においてほぼ同じとみなすことができる。
【００１５】
【実施例】
以下、本発明の実施例について、比較例と比較して具体的に説明する。
表１に示した化学組成の合金を溶解し半連続鋳造により２００ｍｍ径の押出ビレットを作成し、４７０℃で４時間均質化熱処理を施した後、４００℃の押出温度で２５〜５８ｍｍ径（押出比１２〜６４）の各サイズの丸棒に押し出した。この押出材を供試材とし、下記要領で熱間鍛造性を測定した。
また、この押出材を５２０℃で１時間溶体化処理して水中に焼入れた後、１７０℃で６ｈｒの人工時効処理を行った。これを供試材とし、Ｓｎ−Ｂｉ化合物の平均粒径及び分布密度、さらに機械的性質及び切削性を下記の要領で測定した。
【００１６】
【表１】

【００１７】
熱間鍛造性；図１に示すように、押出棒中心部より径１５ｍｍ、高さ１５ｍｍの円柱状試験片を採取し、電気炉にて４７０℃に加熱し、２０分保持した後、図２に示すように、質量７４．５ｋｇの重りを試験片の上、ｈｍｍの高さより自由落下させ（落槌試験）、試験片を熱間鍛造した。なお、落槌試験の重り高さｈは、従来のｈ＝４００ｍｍと、近年鍛造製品が軽量化のため薄肉化する傾向があるのに対応して、より厳しいｈ＝６００ｍｍに設定した。熱間鍛造後の試験片を目視観察し、０．５ｍｍ以上の大きな割れが発生したものを×、０．５ｍｍ未満の微小割れが発生したものを○、割れのないものを◎と判定した。
Ｓｎ−Ｂｉ化合物粒子の平均粒径及び分布密度；押出材の中心部位の押出方向に垂直な面を撮影した４００倍の光学顕微鏡写真をもとに、画像解析装置（株式会社ニレコ製、商品名ルーゼックス）により、粒径は断面に現れた粒子の断面積と同一面積の円の直径に換算してその平均値を求め、分布密度はその粒子の個数を求めて単位面積（１ｍｍ^２）あたりの個数に換算した。ただし、０．０５μｍ未満の粒子は観測上のノイズを含むため、これらを削除したデータを用いて平均粒径及び分布密度を測定した。
【００１８】
機械的性質；押出方向に採取したＪＩＳ４号試験片を用い、ＪＩＳＺ２２４１に規定する金属材料試験方法に準じ、引張強さ、耐力、及び伸びを測定した。
切削性；市販の高速度鋼製の２ｍｍ径ドリルを用い、回転数３０００ｒｐｍ、送り速度６００ｍｍ／分の条件にて切削し、ドリルへの巻き付き発生の有無を観察するとともに、切り屑分断性を調べるために切り屑１００ｇ当りの切り屑個数を測定した。４５０００個以上を合格とした。
【００１９】
これらの試験結果を表２に示す。
本発明の実施例に相当する合金１〜８は、いずれも優れた熱間鍛造性、機械的性質及び切削性を示す。また、押出材にはむしれや焼き付き痕はなく表面性状は良好で、押出性も優れている。特に合金２は、ｈ＝６００ｍｍの条件でも熱間鍛造性が優れている。
これに対し、比較例の合金９〜１４はＳｎとＢｉの含有量、Ｓｎ−Ｂｉ化合物の粒径又は分布密度のいずれかが本発明の範囲外の合金であり、切削性又は熱間鍛造性が実施例合金１〜８に比べ劣っている。すなわち、合金９はＳｎとＢｉの含有量が不足するためＳｎ−Ｂｉ化合物の平均粒径が小さく、切削性が劣る。合金１０は押出比が小さいためＳｎ−Ｂｉ化合物の分布密度が小さく、切削性が劣る。合金１１はＳｎ及びＢｉの含有量が過剰のためＳｎ−Ｂｉ化合物の平均粒径が大きく、熱間鍛造性が劣る。合金１２は押出比が小さいためＳｎ−Ｂｉ化合物の平均粒径が大きく、熱間鍛造性が劣る。合金１３は押出比が大きいためＳｎ−Ｂｉ化合物の平均粒径が小さくかつ分布密度が大きく、切削性と熱間鍛造性が劣り、合金１２は押出比が大きいためＳｎ−Ｂｉ化合物の分布密度が大きく、熱間鍛造性に劣る。
【００２０】
【表２】

【００２１】
【発明の効果】
このように、本発明では、所定量のＣｕを含有し、かつ所定量のＳｎとＢｉを同時添加したＡｌ−Ｃｕ系アルミニウム合金展伸材において、Ｓｎ−Ｂｉ化合物の平均粒径を１〜１０μｍ、分布密度を１００〜５０００個／ｍｍ^２と規定することにより、熱間鍛造性を改善し、かつ切削性をさらに向上させることができ、切削用アルミニウム合金材として、あるいは熱間鍛造及び切削用アルミニウム合金材として好適に利用できる。
【図面の簡単な説明】
【図１】実施例の熱間鍛造試験における試験片採取方法の説明図である。
【図２】同じく落追試験法を説明する図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an Al-Cu-based aluminum alloy wrought material excellent in hot forgeability and machinability.
[0002]
[Prior art]
Among the aluminum alloys, heat-treatable alloys, especially aluminum-based Al-Cu alloys, have high mechanical properties and are often used as various structural materials for aircraft and the like. As a general processing method for this type of alloy, cutting or drilling is often performed after extrusion. For example, in 2014 alloy and 2024 alloy, etc., cutting chips generated during cutting are hard to be divided, so that cutting performance is high. And it is difficult to adopt it for machine parts that perform complicated cutting and drilling.
[0003]
On the other hand, in order to improve the machinability of the aluminum alloy extruded material of this type, conventionally, for example, AA2011 alloy (Cu: 5.0 to 6.0%, Pb: 0.2 to 0.6%, Bi: 0) Low melting point metals such as Pb, Bi, etc. were added. These low-melting-point metals hardly form a solid solution in aluminum, but exist in a granular form in an aluminum alloy, and the low-melting-point metal particles are melted by the heat generated during cutting to separate chips (melt embrittlement), Improves machinability of extruded aluminum alloy.
[0004]
However, in response to recent demands for global environmental protection, there has been an increasing movement to regulate the use of harmful components such as Pb. Pb accumulates when ingested by the human body and causes Pb poisoning such as neuropathy and anemia.
In Japan, the Ministry of International Trade and Industry set the "Guidelines for Waste Management and Recycling by Item" in 1997, and set numerical targets for reducing Pb usage for cars and motorcycles. In response, automakers have formulated voluntary action plans. On the other hand, in the EU, there are “Directive on packaging and packaging waste” and “European directive on end-of-life vehicles” to reduce the use of harmful substances such as Pb, Cd, Hg and hexavalent Cr. Stipulates.
[0005]
Under such circumstances, an aluminum alloy that does not substantially contain Pb and has excellent machinability has been developed, and is disclosed in, for example, JP-A-2000-328168, JP-A-2001-249931, and European Patent Publication No. 982410. . The Al-Cu-based aluminum alloys described in these publications contain predetermined amounts of Sn and Bi, and a low melting point Sn-Bi compound is crystallized, thereby improving the machinability.
[0006]
[Problems to be solved by the invention]
On the other hand, the size and weight of mechanical structural parts such as housings of anti-skid brake systems (ABS) of automobiles have been reduced, and accordingly, small cutting drills, for example, having a diameter of about 2 mm have been used. Therefore, a higher level of cutting property (cutting chip breaking property) has been required.
Al-Cu-based aluminum alloys also have applications as high-strength forgings. However, Al-Cu-based aluminum alloys whose cutting properties have been improved by low-melting metals such as Sn-Bi compounds are used for hot forging. In this case, there is a problem that cracks are easily generated.
[0007]
Therefore, the present invention further improves the machinability of Al-Cu-based aluminum alloy wrought material that is substantially free of Pb and has improved machinability by Sn and Bi, and at the same time, improves hot forgeability. The purpose is to let them.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above-described problems, and as a result, have found that the above object can be achieved by distributing the Sn-Bi compound at an appropriate particle size and density in the mother phase. The present invention has been completed based on the findings.
That is, the wrought aluminum alloy excellent in hot forgeability and machinability according to the present invention is Cu: 4.5 to 6.0%, Sn: 0.06 to 0.55%, Bi: 0.08. ０．５0.55%, Ti: 0.005 to 0.2%, the balance being Al and impurities, the average particle size of the Sn—Bi compound is 1 to 10 μm, and the distribution density is 100 to 5000 particles / mm. ² . Further, the aluminum alloy according to the present invention may further contain, if necessary, Mn: 0.05 to 0.5%, Cr: 0.05 to 0.5%, and Zr: 0.05 to 0.5%. Contains at least one of them.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the reason for adding each element in the wrought aluminum alloy and the reason for limiting the amount of addition will be described.
Cu: 4.5-6.0%
Cu enhances the strength by heat treatment, and promotes chip breaking to improve strain hardening ability. When the Cu content is less than 4.5%, the effect is poor. On the other hand, when the Cu content exceeds 6.0%, the corrosion resistance decreases and the hot workability (extrudability, etc.) also decreases. It is desirably 5.5% or less, particularly from 5% or more and 5.4% or less, from the viewpoint of securing strength and good corrosion resistance and hot workability.
[0010]
Bi: 0.08 to 0.55%
Sn: 0.06 to 0.55%
By adding Bi and Sn at the same time, the fine particles of the Bi-Sn compound having a low melting point are dispersed in the aluminum alloy, and the melt is embrittled by the heat of the cutting process, whereby excellent chip breaking properties are obtained. As the content of Bi and Sn is closer to the eutectic composition (Bi: Sn = 57: 43), the melting point of the dispersed particles can be reduced, and the efficiency of melt embrittlement of chips increases. On the other hand, the melting point of the dispersed particles increases as the Bi and Sn contents deviate from the eutectic composition even if Bi alone or Sn alone, or even when they are added simultaneously, the melting embrittlement efficiency of the chips due to the cutting heat is low. , Resulting in poor chip breaking performance. Moreover, if Bi and Sn are added alone, they segregate at the crystal grain boundaries, and the elongation is reduced. Further, when the content of Bi and Sn is small, the average particle size of the Bi-Sn compound particles is small and the distribution density is small, and the effect of improving the machinability is small. When the content is large, the average particle size is large and the distribution density is small. And elongation and hot forgeability decrease. From the above points, Bi and Sn are added at the same time, and the contents of Sn are 0.06 to 0.55% and Bi is 0.08 to 0.55%. In terms of hot forgeability, Sn is desirably 0.06 to 0.25%, and more desirably 0.06 to 0.1%. From the viewpoint of machinability, Sn is desirably 0.08% or more. In addition, a desirable content ratio (mass ratio) is 1.0 to 6.0 by Bi / Sn in terms of chip breaking property, and a total content is desirably 0.5 to 1.0%.
[0011]
Ti: 0.005 to 0.2%
The addition of Ti makes the cast structure finer, improves the uniformity of the structure of the extruded material and the like, and improves the hot forgeability. However, if the Ti content is less than 0.005%, the effect cannot be obtained, and if the content exceeds 0.2%, the effect is saturated.
Mn: 0.05-0.5%
Cr: 0.05-0.5%
Zr: 0.05-0.5%
Mn, Cr, and Zr each form an intermetallic compound with Al and serve as a starting point of chip breaking to improve machinability, so that one or more of them are appropriately added. If the added amount is less than 0.05%, the effect is not sufficient. On the other hand, if it exceeds 0.5%, a coarse intermetallic compound is formed and the hot workability (extrudability, etc.) is reduced.
[0012]
Aluminum alloys such as impurities include Fe, Si, Zn, V, and the like as impurities or as additional elements. Of these, Fe and Si are impurities particularly contained in aluminum alloys, and Si also has an effect of improving machinability. However, if both contents are large, a coarse intermetallic compound is crystallized and the mechanical properties of the alloy are increased. In the present invention, the contents of Fe and Si are restricted to 1.0% and 1.5% or less, respectively. Fe is desirably 0.7% or less, and Si is desirably regulated to 0.7% or less, further 0.2% or less, and further less than 0.1% from the viewpoint of hot forgeability. desirable. If Zn and V are 1.0% or less and 0.2% or less, respectively, there is no particular adverse effect even if they are contained in the aluminum alloy of the present invention. Further, when casting an aluminum alloy, impurities are mixed from various routes such as a base metal, an intermediate alloy of an additive element, and the like. The elements to be mixed are various, but other impurities are regulated to 0.05% or less in a simple substance and 0.15% or less in total amount. In addition, B among impurities is mixed into the alloy in an amount of about 1/5 of the Ti content with the addition of Ti, but a more preferable range is 0.02% or less, and further preferably 0.01% or less. .
[0013]
In the wrought aluminum alloy of the present invention, the Sn-Bi compound having an average particle size of 1 to 10 μm and a distribution density of 100 to 5000 particles / mm ² is dispersed in the matrix. The cutting heat is melted by the heat generated during the cutting to separate the chips (melt embrittlement), thereby improving the machinability of the aluminum alloy. However, when the average particle size is smaller than 1 μm and / or the distribution density is smaller than 100 particles / mm ² , the particles are less likely to be the starting points of the division or the number of the starting points of the division is reduced, resulting in insufficient cutability. On the other hand, when the average particle size is larger than 10 μm or / and the distribution density is larger than 5000 particles / mm ² , hot forgeability is impaired by the molten particles. In the present invention, a desirable range of the average particle size is 3.5 to 4.5 μm, and a desirable range of the distribution density is 210 to 2800 particles / mm ² .
[0014]
The above-mentioned wrought aluminum alloy is subjected to melting, casting, and homogenization according to a conventional method, and then subjected to hot working such as extrusion or rolling to obtain an extruded or rolled material (a bar material, etc.). Is subjected to hot forging, if necessary, then subjected to a solution heat treatment, a quenching treatment and an aging treatment (T6 treatment) to give a predetermined strength, and then subjected to cutting. The extrusion ratio or the rolling ratio (bar, etc.) in hot working has a dominant effect on the average particle size and distribution density of Sn—Bi compound particles together with the contents of Sn and Bi. In addition, when the distribution density is small, and when the distribution density is large, the average particle size tends to be small and the distribution density tends to be large. By setting the extrusion ratio or the rolling ratio within the range of Sn and Bi in the range of approximately 20 to 40, the average particle size and the distribution density of the Sn-Bi compound particles can be obtained. The average particle size and distribution density of the Sn—Bi compound particles do not change significantly by ordinary hot forging or T6 treatment, and can be regarded as substantially the same during hot forging and during cutting.
[0015]
【Example】
Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples.
An alloy having a chemical composition shown in Table 1 was melted, an extruded billet having a diameter of 200 mm was prepared by semi-continuous casting, and subjected to a homogenizing heat treatment at 470 ° C. for 4 hours. (Ratio of 12 to 64). The extruded material was used as a test material, and hot forgeability was measured in the following manner.
Further, the extruded material was subjected to a solution treatment at 520 ° C. for 1 hour, quenched in water, and then subjected to an artificial aging treatment at 170 ° C. for 6 hours. Using this as a test material, the average particle size and distribution density of the Sn—Bi compound, and further, mechanical properties and machinability were measured in the following manner.
[0016]
[Table 1]

[0017]
Hot forgeability: As shown in FIG. 1, a cylindrical test piece having a diameter of 15 mm and a height of 15 mm was collected from the center of the extruded rod, heated to 470 ° C. in an electric furnace, and held for 20 minutes. As shown in Table 2, a weight having a mass of 74.5 kg was dropped freely from a height of hmm on the test piece (drop hammer test), and the test piece was hot forged. In addition, the weight height h of the hammer test was set to h = 400 mm, which is the conventional value, and stricter h = 600 mm in response to the recent tendency of forged products to become thinner due to weight reduction. The test piece after hot forging was visually observed, and a specimen having a large crack of 0.5 mm or more was judged as x, a specimen having a small crack of less than 0.5 mm as ○, and a specimen without cracks as ◎.
Average particle size and distribution density of Sn-Bi compound particles; an image analyzer (manufactured by Nireco Co., Ltd., trade name) the LUZEX), particle size and the average value calculated in terms of the diameter of the circle of the cross-sectional area and the same area of the particles appearing in the cross section, the distribution density per unit area to seek the number of the particles (1 mm ²⁾ It was converted to the number. However, since particles having a particle size of less than 0.05 μm include observational noise, the average particle size and distribution density were measured using data from which these were deleted.
[0018]
Mechanical properties: Tensile strength, proof stress, and elongation were measured using a JIS No. 4 test piece sampled in the extrusion direction according to the metal material test method specified in JISZ2241.
Machinability: Cutting is performed using a commercially available high-speed steel 2 mm diameter drill under the conditions of a rotation speed of 3000 rpm and a feed speed of 600 mm / min. For this purpose, the number of chips per 100 g of chips was measured. 45,000 or more pieces were accepted.
[0019]
Table 2 shows the test results.
All of the alloys 1 to 8 corresponding to the examples of the present invention show excellent hot forgeability, mechanical properties and machinability. In addition, the extruded material has no peeling or seizing marks, has good surface properties, and has excellent extrudability. Particularly, Alloy 2 has excellent hot forgeability even under the condition of h = 600 mm.
On the other hand, the alloys 9 to 14 of the comparative examples are alloys in which either the content of Sn and Bi, the particle size or the distribution density of the Sn—Bi compound is out of the range of the present invention, and the machinability or hot forgeability is high. Are inferior to the alloys of Examples 1 to 8. That is, since the content of Sn and Bi is insufficient in the alloy 9, the average particle size of the Sn—Bi compound is small and the machinability is poor. Since the extrusion ratio of the alloy 10 is small, the distribution density of the Sn—Bi compound is small and the machinability is poor. The alloy 11 has an excessive Sn and Bi content, so that the average particle size of the Sn—Bi compound is large and the hot forgeability is inferior. Since the alloy 12 has a small extrusion ratio, the average particle size of the Sn—Bi compound is large, and the hot forgeability is poor. Alloy 13 has a high extrusion ratio, so the average particle size of the Sn-Bi compound is small and the distribution density is large, and the machinability and hot forgeability are inferior. Alloy 12 has a high extrusion ratio, so the distribution density of the Sn-Bi compound is low. Large and poor in hot forgeability.
[0020]
[Table 2]

[0021]
【The invention's effect】
As described above, in the present invention, in the Al-Cu-based aluminum alloy wrought material containing a predetermined amount of Cu and simultaneously adding predetermined amounts of Sn and Bi, the average particle size of the Sn-Bi compound is 1 to 10 μm. By defining the distribution density to be 100 to 5,000 pieces / mm ² , the hot forgeability can be improved and the machinability can be further improved, and can be used as an aluminum alloy material for cutting or for hot forging and cutting. It can be suitably used as an aluminum alloy material.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a method for collecting a test piece in a hot forging test of an example.
FIG. 2 is a diagram illustrating the drop-out test method.

Claims

Cu: 4.5 to 6.0% (mass%, the same applies hereinafter), Sn: 0.06 to 0.55%, Bi: 0.08 to 0.55%, Ti: 0.005 to 0.2% And the balance consists of Al and impurities, the average particle size of the Sn—Bi compound is 1 to 10 μm, and the distribution density is 100 to 5000 / mm ^2. Excellent wrought aluminum alloy.

Further, at least one of Mn: 0.05 to 0.5%, Cr: 0.05 to 0.5%, and Zr: 0.05 to 0.5% is contained. Wrought aluminum alloy excellent in hot forgeability and machinability described in 1.