JP3784858B2

JP3784858B2 - Method for producing aluminum wear-resistant sintered alloy

Info

Publication number: JP3784858B2
Application number: JP17957495A
Authority: JP
Inventors: 善三石島; 淳一市川; 秀二佐々木; 英雄四方; 秀夫浦田; 祥司川瀬; 順一上田
Original assignee: Honda Motor Co Ltd; Hitachi Powdered Metals Co Ltd
Current assignee: Honda Motor Co Ltd; Resonac Corp
Priority date: 1995-06-22
Filing date: 1995-06-22
Publication date: 2006-06-14
Anticipated expiration: 2021-06-14
Also published as: JPH093563A

Description

【０００１】
【産業上の利用分野】
本発明は、軽量で、かつ強度および耐摩耗性が要求される歯車、プーリー、コンプレッサー用ベーン、コンロッド、ピストン等に好適なアルミニウム系焼結合金部材の製造方法に関するものである。
【０００２】
【従来の技術】
アルミニウム系焼結合金は、鋳造合金に比べて、初晶Ｓｉを微細化し、Ｓｉ含有量を多くすることができることから、比強度と耐摩耗性に優れた材料として期待されている。
【０００３】
従来のアルミニウム系焼結合金としては、特開昭５３−１２８５１２号公報に開示されているように、組成が重量比でＣｕ：０.２〜４％、Ｍｇ：０.２〜２％、Ｓｉ：１０〜３５％、および残部がＡｌとなるように、Ａｌ−１０〜３５％Ｓｉ粉、銅粉、Ｍｇ粉、Ａｌ−Ｃｕ粉、Ｃｕ−Ｍｇ粉、Ａｌ−Ｃｕ−Ｍｇ粉、Ｃｕ−Ｍｇ−Ｓｉ粉およびＡｌ−Ｃｕ−Ｍｇ−Ｓｉ粉のうちから選ばれた粉末に、必要に応じてＡｌ粉を混合し、圧粉成形した後、焼結して所望の製品を製造する方法がある。焼結合金には、通常の鋳造合金と同様に、溶体化処理および人工時効硬化処理（Ｔ６処理）が施される。この方法は各種の粉末を混ぜ合わせるいわゆる混合法である。このような混合法によれば、軟質金属粉末を混合することができるので、粉末成形性がよいという特徴があり、通常の圧粉成形−焼結の工程のみでも液相焼結によればある程度の強度のものが得られる。
【０００４】
また、特開昭６２−１０２３７号公報に記載されているように、組成が重量比でＳｉ：８〜３０％、必要に応じてＣｕ、Ｍｇ、Ｎｉ、Ｆｅ、Ｍｎのうち少なくとも１種の成分０.１〜１０％、および残部のＡｌからなる急冷凝固アルミニウム合金粉の圧粉体を熱間鍛造して作られ、Ａｌ−Ｓｉ系合金素地中に初晶Ｓｉが均一に分散した組織の合金がある。合金法によれば、混合法に比べて高い強度のものが得られる。しかし急冷凝固粉末は硬く、金型成形によるニアネットシェープ化が困難であること、粉末に強固な酸化皮膜があること、および焼結時に液相を発生しないこと等のために、焼結のみでは粉末粒子間を十分に結合させることができず、ビレット形状からの押出しや鍛造など数回の圧縮工程を必要とする。
【０００５】
さらに、混合法と合金法の組合せとして、特開平５−１５６３３９号公報に記載されているように、急冷凝固Ａｌ−Ｓｉ系合金粉に所定量の純Ａｌ粉を混合した粉を熱間鍛造して製造され、組成が重量比でＳｉ：２〜３０％、ＦｅおよびＮｉのうち１種または２種の成分１〜１０％、必要に応じＣｕ：１〜５％およびＭｇ：０.３〜２％のうち１種または２種の成分、および残部のＡｌからなり、微細な初晶Ｓｉが分散した共晶Ａｌ−Ｓｉ素地中に、熱間鍛造で変形したＡｌ固溶体粒が５〜２０容量％分散した組織の合金がある。この合金は、Ａｌ固溶体を接着剤として硬質な粒界相互の密着性を向上させ、耐摩耗性と強度を向上させたものである。
【０００６】
【発明が解決しようとする課題】
アルミニウム焼結合金としては、粉末の圧粉成形性が良好であり、材料の強度、伸びおよび靱性が高く、摩擦摺動耐摩耗性にも優れたものが要求されている。
【０００７】
そこで、本出願人は、特願平６−３７６０６号、特願平６−３３５７１２号および特願平７−７２２５９号において、粉末混合法によって作られ、最大粒径が特定された初晶Ｓｉが分散するＡｌ−Ｓｉ系合金相とＡｌ固溶体相との斑状組織を有し、両相の面積割合が限定されている合金を提案した。
これらの合金は、斑組織とＡｌ−Ｓｉ合金相中の初晶Ｓｉの最大粒径を特定したことにより、引張り強さおよび伸びが大きく、また、摩擦摺動中に脱落した初晶Ｓｉ粒子をＡｌ固溶体相が埋め込む効果を有しているので、特に耐摩耗性に優れた合金であり、製造方法においては成形性にも優れているものである。
【０００８】
上記合金の製造方法は、Ｓｉ含有量が１３〜３０重量％のＡｌ−Ｓｉ合金粉２０〜８０重量部に対して２０〜８０重量部のＡｌ粉を配合した粉末に、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、ＺｒおよびＮｂから選ばれる１種もしくは２種以上の遷移金属の含有量が０.２〜３０重量％のＣｕ−遷移金属合金粉、ならびにＭｇ含有量が３５重量％以上のＡｌ−Ｍｇ合金粉もしくはＭｇ粉を添加した混合粉、またはこの混合粉に更に、黒鉛、ＭｏＳ₂、ＢＮおよびＷＳ₂から選ばれる１種もしくは２種以上の固体潤滑材を添加した混合粉を用い、圧粉体を所定の条件で焼結し、最大粒径が５〜６０μｍの初晶Ｓｉが分散するＡｌ−Ｓｉ系合金相とＡｌ固溶体相との斑組織を呈する焼結体を得た後、必要に応じて熱間鍛造または冷間鍛造等の塑性加工を施し、通常の溶体化処理および人工時効処理を施すことからなる。上記熱処理としては、例えば、温度４９０℃から急冷して溶体化処理を行い、温度２４０℃で加熱して人工時効処理を行う。
【０００９】
また、前記の方法で得られる特徴を有する合金組織を表面部に形成し、内部は材料強度を向上させた合金からなる製品を提供するために、まず、焼結体の組織を、最大粒径５μｍ以下の初晶Ｓｉが分散するＡｌ−Ｓｉ系合金相とＡｌ固溶体相との斑組織になるように焼結し、次いでこの焼結体の表面を加熱して、合金表面部に存在するＡｌ−Ｓｉ系合金相中の初晶Ｓｉの最大粒径を５〜６０μｍに成長させる工程を加え、同様に溶体化処理および人工時効処理を施したものも提案されている。
【００１０】
なお、前記焼結合金の全体組成は、前者の合金は、重量比でＳｉ：２.４〜２３.５％、Ｃｕ：２〜５％、Ｍｇ：０.２〜１.５％、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、ＺｒおよびＮｂから選ばれる１種もしくは２種以上の遷移金属：０.０１〜１％、ならびに残部のＡｌおよび不可避不純物であり、後者の合金は、前者の合金組成に固体潤滑材を１〜４５重量％加えたものである。
【００１１】
これらの合金は、引張り強さ、伸びおよび耐摩耗性などに優れているが、これらの特性値が最も高くなるような熱処理条件については、未だ検討の余地が残されている。
【００１２】
この発明は、前記焼結合金の延性が改善され、かつ強度および耐摩耗性を兼ね備えた機械要素の製造に適するＡｌ−Ｓｉ系焼結合金の製造方法を提供することを目的とする。
【００１３】
【課題を解決するための手段】
上記の目的を達成するため、本発明の製造方法は、Ｓｉ含有量が１３〜３０重量％のＡｌ−Ｓｉ合金粉２０〜８０重量部に対して、２０〜８０重量部のＡｌ粉を配合した粉末に、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、ＺｒおよびＮｂから選ばれる１種もしくは２種以上の遷移金属の含有量が０.２〜３０重量％のＣｕ−遷移金属合金粉、ならびにＭｇ含有量が３５重量％以上のＡｌ−Ｍｇ合金粉またはＭｇ粉を添加して、全体組成が、重量比で、Ｓｉ：２.４〜２３.５％、Ｃｕ：２〜５％、Ｍｇ：０.２〜１.５％、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、ＺｒおよびＮｂから選ばれる１種もしくは２種以上の遷移金属：０.０１〜１％、ならびに残部のＡｌおよび不可避不純物からなる混合粉、または、前記混合粉に固体潤滑材を添加して全体組成が重量比でＳｉ：１.３〜２３.３％、Ｃｕ：１.１〜５％、Ｍｇ：０.１〜１.５％、Ｎｉ：０.００５〜１％、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、ＺｒおよびＮｂから選ばれる１種もしくは２種以上の遷移金属：０.０１〜１％、黒鉛、ＭｏＳ₂、ＢＮおよびＷＳ₂から選ばれる１種もしくは２種以上の固体潤滑材：１〜４５％、ならびに残部のＡｌおよび不可避不純物からなる混合粉、のいずれかの混合粉を圧粉成形した後、焼結して最大粒径が５〜６０μｍの初晶Ｓｉが分散するＡｌ−Ｓｉ系合金相とＡｌ固溶体相との斑組織を呈する焼結体を得る工程( １ )と、この焼結体または塑性加工体を加熱後急冷して溶体化処理する工程( ３ )と、さらに人工時効処理を行う工程( ４ )とからなり、前記時効処理を、過時効領域において、時効処理後の引張り強さが、前記焼結体の引張り強さよりも高い値を示すような温度および時間の範囲内の加熱処理により行なうことを特徴とするものである。
【００１４】
また、本発明は、最大粒径５μｍ以下の初晶Ｓｉが分散したＡｌ−Ｓｉ系合金相とＡｌ固溶体相との斑組織を呈する焼結体を得る前記工程( １ )に、焼結体の表面を加熱することによって、合金の表面部に存在するＡｌ−Ｓｉ系合金相中の初晶Ｓｉの最大粒径を５〜６０μｍに成長させて冷却する工程( ２ )を付加する場合も包含する。
【００１５】
すなわち、先に本出願人が提案した前記斑組織の焼結合金における焼結体またはその塑性加工体を溶体化処理し、かつ人工時効処理を、過時効領域において、しかも引張り強さが焼結体（溶体化処理する前の焼結合金、以下同じ）の引張り強さより高い値を示すような温度と時間の範囲内の加熱処理により行なうことを骨子とするものである。
【００１６】
【作用】
次に、本発明の合金組成、合金組織、粉末の選定、熱処理条件等の各構成要件について説明する。
（１）合金中のＳｉおよび粉末の選定
全体組成としてのＳｉの量は、後述の初晶Ｓｉが分散したＡｌ−Ｓｉ系合金相とＡｌ固溶体相とが斑状組織を呈するような範囲を選択し、２.４〜２３.５重量％である。全体組成のＳｉ量が少な過ぎると、初晶Ｓｉが分散したＡｌ−Ｓｉ系合金相中のＳｉ量が少ないか、あるいはＡｌ固溶体相の占める割合が多くなり、耐摩耗性に寄与する初晶Ｓｉの量が少ないために耐摩耗性が不十分となる。一方、Ｓｉ量が多過ぎると前記と反対の現象が生じ、同様に耐摩耗性が悪くなる。
ＳｉはＡｌ−Ｓｉ合金粉の形態で添加する。粉末混合法による製造の際に初晶Ｓｉが析出するためには、Ａｌ−Ｓｉ合金粉のＳｉ含有量を１３重量％以上にすることが必要である。また、Ｓｉ含有量が３０重量％を越えると粉末製造時の溶湯温度が高くなるため、Ｓｉ含有量は１３〜３０重量％が適当である。
焼結した後のＡｌ−Ｓｉ合金粉の部分には、後述のＭｇ、Ｃｕおよび遷移金属の一部が固溶しており、初晶Ｓｉが分散したＡｌ−Ｓｉ系合金となって焼結合金斑組織の一方の合金相を構成する。この相は比較的硬質であり、主に材料強度および耐摩耗性に寄与する。
【００１７】
（２）合金中のＭｇおよび粉末の選定
Ｍｇは焼結中に液相を生じて素地中に固溶し、焼結の促進と、時効析出するＭｇ₂Ｓｉによる素地強化および耐摩耗性向上の効果がある。
Ｍｇの量は、全体組成で０.２重量％未満では効果が不十分であり、１.５重量％を越えて添加してもそれ以上効果が増大しないため、０.２〜１.５重量％とするが、更に好ましい範囲は０.３〜０.７重量％である。
Ｍｇの添加手段としては、Ｍｇ含有量が３５重量％以上のＡｌ−Ｍｇ合金粉またはＭｇ粉の形態が適している。これは、Ａｌ−Ｍｇ二元系合金の融点がＭｇ含有量３３〜７０重量％の範囲で４６０℃程度の低い値を示すために、Ｍｇ含有量３５重量％以上のＡｌ−Ｍｇ合金を用いると、焼結過程でＡｌ−Ｍｇ合金とＡｌ素地との間に固相拡散が生じて、Ａｌ−Ｍｇ合金中のＭｇ濃度が低下することにより、液相が発生することによる。
【００１８】
（３）Ｃｕおよび遷移金属とその粉末の選定
ＣｕはＡｌ合金素地を強化する元素であり、時効処理により一層大きな効果が得られる。Ｃｕの量は、全体組成で２〜５重量％である。２重量％未満では所望の強度向上が認められず、５重量％を越えると粉末粒界近傍においてＣｕを主成分とする金属間化合物が多量に析出して靱性が低下する。Ｃｕの更に好ましい量は３.５〜４.５重量％である。
ＣｕをＣｕ粉またはＣｕ合金粉の形態で添加した場合に、Ｃｕを素地に固溶させるために必要な加熱を行った焼結体は、初晶Ｓｉが溶製材料のように粗大化し、反対に加熱の温度を下げ時間を短縮して焼結した場合は、粉末の粒界にＣｕの金属間化合物、例えばＡｌ₂ＣｕＭｇ、Ａｌ₆ＣｕＭｇ₄等が残存して、強度や伸びの低下を招く。溶体化処理および時効処理を施しても、このような粒界の金属間化合物を消滅させることは困難である。
【００１９】
そこで、適量の遷移金属（Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｚｒ、Ｎｂ）を共存させると、溶体化および過時効領域における時効処理を行うことにより、粒界の金属間化合物を消滅させることができる。遷移金属は、時効処理の際に、粒界部に析出したＣｕが素地中へ拡散することを促進する作用がある。理由は明らかではないが、溶体化処理によって形成される原子空孔の消滅挙動が変化することや、析出過程が変化することなどによって、時効処理中のＣｕの拡散を速めているものと考えられる。
全体組成中の遷移金属の量は、前記のＣｕ含有量（２〜５重量％）において、０.０１重量％未満ではその効果がなく、一方、１重量％を越えると遷移金属を主成分とする金属間化合物が析出して靱性が低下するため、０.０１から１重量％とする。
遷移金属は単体として添加すると拡散し難いため、Ｃｕ−遷移金属合金粉の形態で添加することが好ましいが、合金粉中の遷移金属量は、全体組成として必要なＣｕ量および遷移金属量を考慮して、０.２重量％以上が必要である。しかし、３０重量％を越えると合金粉末の融点が高くなり、固相拡散によって融点が低下しても液相を発生しなくなるので０.２〜３０重量％でなければならない。また、好ましくは０.２〜１０重量％である。
【００２０】
（４）Ａｌ固溶体相と粉末の選定
Ａｌ固溶体相は、純アルミニウム粉の形態で添加されたＡｌ中に、Ｓｉ、Ｍｇ、Ｃｕおよび遷移金属が拡散した固溶体であって、比較的軟質であり、合金の靱性に寄与すると共に、初期摩耗を受けてＡｌ−Ｓｉ系合金相間に油だまりを形成し、潤滑性および摩擦中の相手材とのなじみ性に寄与する。また、塑性変形し易いので、摺動面近傍の硬質な初晶Ｓｉ粒子が摩耗粉として脱落しそうになったり、脱落した場合に、それらを埋没させ、Ｓｉ粒子が研磨粒子として作用することを防ぐ効果がある。
【００２１】
（５）斑状組織
前述の初晶Ｓｉ粒子が分散したＡｌ−Ｓｉ系合金相と軟質なＡｌ固溶体相の２相において、Ａｌ−Ｓｉ系合金相が合金断面の面積比で２０％未満のときは初晶Ｓｉの量が少ないため、また、８０％を越える場合は、摩擦摺動により脱落したＳｉ粒子を埋没させるＡｌ固溶体相の量が少ないために、耐摩耗性は著しく悪化する。したがって、２相が合金断面の面積比で２０〜８０：８０〜２０の割合で斑状に混在した複合組織であるときに、相互の作用で強度および耐摩耗性が良好になる。
【００２２】
（６）Ａｌ−Ｓｉ系合金相中の初晶Ｓｉの粒径
初晶Ｓｉの断面形状は、粒径が小さいものは縦横の寸法がほぼ同じで円形に近いが、大きい粒子は小さい粒子が集合して凝集したり、粒成長したものと考えられ、不規則な形状を呈する。最大粒径とは、このような不規則な形状の粒子の両端距離のうち最も長い寸法を表したものである。
初晶Ｓｉの粒径が大きくなると、硬質な初晶Ｓｉ粒子が突起物の状態で相手材を引っかき、摩耗させる。一方、初晶Ｓｉの量が少ないか、または初晶Ｓｉの粒径が小さいと、摩擦摺動時に素地から脱落し、脱落した初晶Ｓｉ粒子が研磨粒子として作用するため摩耗が進行する。したがって耐摩耗性の観点から、初晶Ｓｉの粒径は適度の大きさであることが必要であり、最大粒径が５〜６０μｍのものが適当である。
【００２３】
一方、強度の点から考察する、初晶Ｓｉの粒径が大きいほど強度や延性が低く、逆に初晶Ｓｉの粒径が小さいほどこれらの値は高くなるので好ましく、５μｍ以下が好適である。
そこで、摩擦部材の表面部分もしくは少なくとも摺動する部位の表面部分の初晶Ｓｉは、耐摩耗性を維持するために最大粒径を５〜６０μｍにすると共に、内部の初晶Ｓｉは強度および延性を維持するために粒径を５μｍ以下になるように構成することにより、耐摩耗性と強度および延性とを共に向上させることが可能となる。
このように合金の内部と表面部の初晶Ｓｉの粒径を変える方法としては、予め初晶Ｓｉの粒径が５μｍ以下になるように焼結した焼結合金を製作し、その合金の少なくとも摺動する部位の表面を、高周波加熱、プラズマ加熱あるいはレーザー加熱等の加熱手段によって加熱して、初晶Ｓｉの最大粒径を５〜６０μｍになるように成長させる。このような表面改質を行う部分の深さは０.５〜１ｍｍ程度が好適である。
【００２４】
（７）時効処理
溶体化されたアルミニウム合金を所定の温度で人工時効処理を行うと、溶質原子は集合して析出する。この変化は温度と時間によって支配され、物理的および機械的性質が変化する。溶製アルミニウム合金の場合、一般的には加熱時間の経過と共に引張り強さは、先ず上昇しその後低下する放物線状の変化を示す。伸びは引張り強さが最大のときに最低値を示した後、僅かずつ上昇することが知られている。一般的には引張り強さおよび硬さが最も高くなる領域で処理を行う。
【００２５】
一方、混合法で製作されたＣｕを含むＡｌ−Ｓｉ系焼結合金の場合は、焼結中に素地中へ拡散し得なかったＣｕまたはその金属間化合物が粉末粒界部に偏析する。溶製材の場合とは異なり、過時効領域の引張り強さの低下は緩やかになる。合金の伸びは、遷移金属を含有しない材料では、溶製材の場合と同様であるが、遷移金属を含有する場合は、過時効領域で加熱時間と共に著しく上昇する。
すなわち、本発明の方法により製作された合金の場合は、焼結中に素地中へ拡散し得ずに残ったＣｕの金属間化合物が粉末粒界に存在しており、それは耐摩耗性には影響を及ぼさないが、靱性の点で不十分な状態である。未拡散Ｃｕの金属間化合物の存在および適量の遷移金属の共存により、過時効領域で素地中へＣｕの拡散が進行する結果、合金の強度低下が少なくなり、伸びが著しく改善される。このような時効処理条件としては、温度が２４０℃の場合、処理時間を約２〜５時間とすることが適当である。
【００２６】
【実施例】
以下に本発明を実施例により説明する。
＜実施例１＞Ａｌ固溶体相の量と摩耗特性
原料粉として、Ｓｉ含有量が１５％、１７％、２０％、２５％および３０％の５種類のＡｌ−Ｓｉ合金粉、純Ａｌ粉、Ｃｕ−４％Ｎｉ合金粉およびＡｌ−５０％Ｍｇ合金粉を用い、Ｃｕ−４％Ｎｉ合金粉を４.１７重量％およびＡｌ−５０％Ｍｇ合金粉を１重量％の一定量とし、Ａｌ−Ｓｉ合金粉の種類と配合量、および純Ａｌ粉の配合量を変えて各種の混合粉を作製し、それぞれ所定形状に成形した。成形体は４００℃で脱ろうを行い、５４０℃で６０分間の焼結を行った後、熱間鍛造で密度比１００％とし、４９０℃で加熱して溶体化および焼入れを行った。さらに２４０℃で３時間加熱することによって時効処理を行ない試料１〜１８を作製した。表１に、Ａｌ−Ｓｉ合金粉の種類、全体組成におけるＳｉ含有量および斑組織中に占める軟質のＡｌ固溶体相の面積比を示す。
各試料の組織は、Ａｌ−Ｓｉ系合金相とＡｌ固溶体相の面積比がＡｌ−Ｓｉ合金粉と純Ａｌ粉の配合割合と同一であり、Ａｌ−Ｓｉ系合金相中の初晶Ｓｉの最大粒径は２０〜２５μｍであった。
各試料についてピンオンディスク摩擦摩耗試験による試料の摩耗量を測定し比較した。ピンオンディスク摩擦摩耗試験は、試料をピンとし、回転する相手のディスクとしてＳ４８Ｃ材（機械構造用炭素鋼）の熱処理品を用い、鉱油潤滑下、面圧４９ＭＰａ、摩擦速度５ｍ／秒の条件で行った。
表１に摩耗量を示す。Ａｌ−Ｓｉ合金粉中のＳｉ含有量が所定の範囲であり、合金断面に占めるＡｌ固溶体の面積比が２０〜８０％の間であると、摩耗量が少ないことが判る。
【００２７】
【表１】

【００２８】
＜実施例２＞初晶Ｓｉの最大粒径と引張り強さおよび摩耗量の関係
Ａｌ−２０％Ｓｉ合金粉と純Ａｌ粉を重量比で７５：２５で混ぜ合わせた粉末に、Ｃｕ−４％Ｎｉ合金粉とＡｌ−５０％Ｍｇ合金粉を混合し、全体組成を重量比でＳｉ１５％、Ｃｕ４％、Ｍｇ０.５％、Ｎｉ０.１７％および残部をＡｌとし、この混合粉を用いた圧粉体を４００℃で脱ろうし、温度５４０℃で５〜１８０分間、各種温度で焼結した試料を作製し、前記実施例の場合と同様に熱間鍛造、溶体化処理および時効処理を行って、表２に示す試料１９〜２３を作製した。
焼結時間が短い試料は、初晶Ｓｉの粒径が小さく、焼結時間の長い試料は大きくなっている。これらの試料の引張り強さおよび前記実施例と同様に測定した摩耗量の測定結果をやはり表２に示す。初晶Ｓｉの最大粒径が小さいほど強度は高く、かつ初晶Ｓｉの最大粒径が５μｍ〜６０μｍの範囲では摩耗試験の結果は良好であるが、この範囲を外れると焼付きが起こりあるいは摩耗量が増大することが判る。
【００２９】
【表２】

【００３０】
＜実施例３＞固体潤滑剤の効果
原料粉として、前記実施例２の場合と同じ混合粉を母材とし、この母材に固体潤滑剤として黒鉛粉を量を変えて添加して、表３に示す試料２４〜２９の混合粉を所定形状に圧粉成形した。圧粉体は４００℃で脱ろうを行い、５４０℃で６０分間の焼結を行った後、熱間鍛造で密度比１００％とし、４９０℃で溶体化処理および２４０℃で時効処理を行った。
各試料について、引張り強さおよびピンオンディスク摩擦摩耗試験による試料の摩耗量および摩擦係数を測定して比較した。表３に測定結果を示す。
固体潤滑材を含有するアルミニウム焼結合金試料は、摩擦係数および摩耗量が小さい。一方、固体潤滑材の含有量が多くなると引張り強さが低下している。強度をあまり要求されない部材用としては、固体潤滑剤の含有量が３０体積％のものも使用可能と考えられるが、２０体積％を越えると引張り強さの低下が大きくなるので、１〜２０体積％の範囲が望ましいと考えられる。
【００３１】
【表３】

【００３２】
＜実施例４＞表面加熱処理による改質
前記実施例２と同様にして、Ａｌ−２０％Ｓｉ合金粉と純Ａｌ粉を、重量比で７５：２５で混ぜ合わせた粉末にＣｕ−４％Ｎｉ合金粉とＡｌ−５０％Ｍｇ合金粉を混合し、全体組成を重量比でＳｉ１５％、Ｃｕ４％、Ｍｇ０.５％、Ｎｉ０.１７％および残部をＡｌとし、所定の形状に成形した。成形体は４００℃で脱ろうを行い、５４０℃で１０分間の焼結を行い、熱間鍛造で密度比１００％とした後、高周波誘導炉によって表面を加熱処理した。
次に、試料を４９０℃で加熱して溶体化および焼入れを行ない、２４０℃で３時間加熱し時効処理を行った。
この試料の内部の初晶Ｓｉ最大粒径は４μｍであり、表面部は約０.１ｍｍの深さにわたって初晶Ｓｉ最大粒径が２４μｍであり、また引張強さは４１６ＭＰａおよびピンオンディスク摩擦摩耗試験による試料の摩耗量は０.０３ｍｍであった。初晶Ｓｉの最大粒径が２５μｍの前記試料番号２１の場合は、引張強さが３８０ＭＰａ、摩耗量が０.０１ｍｍであるのと比較すると、内部初晶Ｓｉ粒径が小さいため、引張強さが大きく、表面部の初晶Ｓｉ粒径が同等であるため摩耗量は同様な結果を示した。
【００３３】
＜実施例５＞遷移金属の添加と人工時効処理の効果
遷移金属としてＮｉを添加した試料３０と、遷移金属を添加せずＳｎを添加した試料３１を作製した。
試料３０は、Ａｌ−２０％Ｓｉ合金粉６０重量％、純Ａｌ粉３４.８重量％、Ｃｕ−４％Ｎｉ粉４.２重量％およびＡｌ−５０％Ｍｇ粉１％を混合し、その成形体を４００℃で脱ろうし、５４０℃で６０分間の焼結を行った後、熱間鍛造で密度比１００％とし、４９０℃で加熱して溶体化および焼入れを行った。そして温度２４０℃で加熱時間を変えて時効処理を行った。
また、試料３１は、Ａｌ−２０％Ｓｉ合金粉６０重量％、純Ａｌ粉３５.７重量％、Ｃｕ−１０％Ｓｎ粉３.３重量％およびＡｌ−５０％Ｍｇ粉１％の混合粉を用い、以下同様にして作製した。
【００３４】
図１に試料３０および３１における時効処理時間と処理後の引張り強さおよび伸びとの関係をグラフで示す。引張り強さは、両試料共、加熱時間の経過と共に上昇して１時間で最大値を示した後、緩やかに低下する傾向を示し、約５時間で鍛造体とほぼ同じ値を示している。これらの合金においては、処理温度を２４０℃とした場合に、処理時間１時間までが亜時効領域であり、それ以上の処理時間では過時効領域になる。
一方、伸びは、加熱時間１時間において最低値を示した後、過時効領域では上昇する傾向を示すが、過時効領域における伸びの上昇は、遷移金属を含まない試料３１の場合には緩やかで僅かであるのに対して、遷移金属Ｎｉを添加した試料３０の場合には大きいことが判る。すなわち、遷移金属を添加した焼結合金を過時効領域で処理すると、延性の高い材料が得られる。
また、時効処理を必要以上に過剰に行うと引張り強さが低下するので、処理温度を２４０℃とした場合には、処理時間は５時間未満とすることが好ましいことが判る。
【００３５】
＜実施例６＞遷移金属の添加とＣｕの拡散
遷移金属を含まない試料３２と、遷移金属としてＮｉを添加した試料３３とを作製し、時効処理後の偏析したＣｕの分布を比較した。
試料３２は、Ａｌ粉、Ａｌ−２０％Ｓｉ合金粉、Ｃｕ粉およびＡｌ−５０％Ｍｇ合金粉とを混合して、全体組成を１５％Ｓｉ−４％Ｃｕ−０.５％Ｍｇ−残部Ａｌとした粉末を用いたものであり、試料３３は、Ａｌ粉、Ａｌ−２０％Ｓｉ合金粉、Ｃｕ−４％Ｎｉ合金粉およびＡｌ−５０％Ｍｇ合金粉とを混合して、全体組成が１５％Ｓｉ−４％Ｃｕ−０.５％Ｍｇ−０.１７％Ｎｉ−残部Ａｌの粉末を用いたものである。
各粉末を圧粉成形し、温度５４０℃で６０分間の焼結を行い、熱間鍛造を施した後、温度４９０℃で６０分間加熱した後、温水中で急冷して溶体化処理し、温度２４０℃で３時間の時効処理を行い試料とした。
各試料は組織観察の場合と同様に研磨した面をＨＦ−ＨＣｌ−ＨＮＯ₃−Ｈ₂Ｏ混合液で腐蝕し、ＳＥＭ（走査電子顕微鏡）写真およびＣｕ面分析写真を撮り、その結果を比較した。
図２にＳＥＭ写真およびＣｕ面分析写真を示す。各写真の横幅は１００μｍに相当する。ＳＥＭ写真の中央部分の相は、純Ａｌの形態で添加した部分のＡｌ固溶体相であり、その周囲はＡｌ−Ｓｉ合金粉として添加した部分のＡｌ−Ｓｉ系合金相である。Ａｌ−Ｓｉ系合金相には粒状に観察される初晶Ｓｉがあり、著しく白い部分がＣｕの金属間化合物である。Ｃｕ面分析写真から判るように、Ｎｉを含まない試料３２においては、Ａｌ固溶体相の周囲にＣｕ濃度の高い偏析部分が多く認められるが、Ｎｉを含む試料３３では、その量が少なくなっている。
【００３６】
【発明の効果】
以上説明したように、本発明のアルミニウム系焼結合金の製造方法は、混合法によるものであるから粉末成形性がよく、焼結合金の組織において、初晶Ｓｉが分散しているＡｌ−Ｓｉ系合金相とＡｌ固溶体相とが面積比２０〜８０％で斑状組織を示していると共に、合金の少なくとも表面部のＡｌ−Ｓｉ系合金相の初晶Ｓｉの最大粒径を５〜６０μｍとすることにより、材料強度が高く耐摩耗性のよい合金が得られるほか、時効処理を過時効領域で行うことにより、未拡散のＣｕが素地中に拡散して消失し、延性の優れた合金を製作することができるため、アルミニウム系焼結合金の各種の摺動を伴う機械要素への適用範囲を拡大することができる。
【図面の簡単な説明】
【図１】アルミニウム系焼結合金の時効処理時間との引張り強さおよび伸びとの関係を示すグラフである。
【図２】アルミニウム系焼結合金のＳＥＭ写真およびＣｕ面分析写真である。[0001]
[Industrial application fields]
The present invention relates to a method for producing an aluminum-based sintered alloy member that is suitable for gears, pulleys, compressor vanes, connecting rods, pistons, and the like that are lightweight and require strength and wear resistance.
[0002]
[Prior art]
The aluminum-based sintered alloy is expected as a material excellent in specific strength and wear resistance because it can refine the primary crystal Si and increase the Si content as compared with the cast alloy.
[0003]
As a conventional aluminum-based sintered alloy, as disclosed in JP-A-53-128512, the composition is Cu: 0.2-4% by weight, Mg: 0.2-2%, Si : Al-10 to 35% Si powder, copper powder, Mg powder, Al-Cu powder, Cu-Mg powder, Al-Cu-Mg powder, Cu-Mg so that 10 to 35% and the balance is Al There is a method of producing a desired product by mixing Al powder with powder selected from -Si powder and Al-Cu-Mg-Si powder as necessary, compacting and then sintering. . The sintered alloy is subjected to a solution treatment and an artificial age hardening treatment (T6 treatment) in the same manner as a normal casting alloy. This method is a so-called mixing method in which various powders are mixed. According to such a mixing method, since soft metal powder can be mixed, there is a feature that the powder moldability is good. Can be obtained.
[0004]
Moreover, as described in JP-A-62-1237, the composition is Si: 8 to 30% by weight, and at least one of Cu, Mg, Ni, Fe and Mn as required. An alloy having a structure in which primary Si is uniformly dispersed in an Al-Si based alloy base material, which is made by hot forging a compact of rapidly solidified aluminum alloy powder composed of 0.1 to 10% and the balance Al. There is. According to the alloy method, a material having higher strength than the mixing method can be obtained. However, the rapidly solidified powder is hard, and it is difficult to form a near net by molding, there is a strong oxide film on the powder, and no liquid phase is generated during sintering. The powder particles cannot be sufficiently bonded, and several compression steps such as extrusion from a billet shape and forging are required.
[0005]
Further, as described in JP-A-5-156339, as a combination of a mixing method and an alloy method, a hot-forged powder in which a predetermined amount of pure Al powder is mixed with rapidly solidified Al-Si alloy powder. The composition by weight is Si: 2 to 30%, one or two of Fe and Ni, 1 to 10%, Cu: 1 to 5% and Mg: 0.3 to 2 as necessary 5% to 20% by volume of Al solid solution particles deformed by hot forging in a eutectic Al-Si substrate composed of one or two components of Al and the balance Al and fine primary Si dispersed therein. There are alloys of dispersed structure. This alloy uses Al solid solution as an adhesive to improve adhesion between hard grain boundaries, and to improve wear resistance and strength.
[0006]
[Problems to be solved by the invention]
As an aluminum sintered alloy, a powder having good powder compactibility, high material strength, elongation and toughness, and excellent friction sliding wear resistance is required.
[0007]
In view of this, the present applicant, in Japanese Patent Application No. 6-37606, Japanese Patent Application No. 6-335712, and Japanese Patent Application No. 7-72259, has a primary crystal Si having a maximum particle size specified by a powder mixing method. An alloy having a mottled structure of dispersed Al—Si based alloy phase and Al solid solution phase and in which the area ratio of both phases is limited has been proposed.
These alloys have a high tensile strength and elongation due to the specification of the maximum grain size of the primary crystal in the plaque structure and the Al-Si alloy phase, and the primary crystal Si particles that fall off during friction sliding Since the Al solid solution phase has an effect of embedding, the alloy is particularly excellent in wear resistance, and in the manufacturing method, it is excellent in formability.
[0008]
The manufacturing method of the above alloy includes Ti, V, Cr, and a powder in which 20 to 80 parts by weight of Al powder is mixed with 20 to 80 parts by weight of Al-Si alloy powder having a Si content of 13 to 30% by weight. Cu-transition metal alloy powder having a content of one or more transition metals selected from Mn, Fe, Co, Ni, Zr and Nb of 0.2 to 30% by weight, and a Mg content of 35% by weight The above Al-Mg alloy powder or mixed powder to which Mg powder is added, or further mixed with graphite, MoS₂, BN and WS₂Al-Si in which primary powder Si having a maximum particle size of 5 to 60 μm is dispersed by sintering a green compact under predetermined conditions using a mixed powder to which one or more solid lubricants selected from After obtaining a sintered body exhibiting a mottled structure of an Al alloy phase and an Al solid solution phase, plastic working such as hot forging or cold forging is performed as necessary, and normal solution treatment and artificial aging treatment are performed. Consists of. As the heat treatment, for example, a solution treatment is performed by rapidly cooling from a temperature of 490 ° C., and an artificial aging treatment is performed by heating at a temperature of 240 ° C.
[0009]
In addition, in order to provide a product made of an alloy having the characteristics obtained by the above-described method on the surface portion and the inside having improved material strength, first, the structure of the sintered body is made to have a maximum grain size. Sintering is performed so as to form a patchy structure of an Al—Si based alloy phase in which primary crystal Si of 5 μm or less is dispersed and an Al solid solution phase, and then the surface of the sintered body is heated to obtain Al present on the alloy surface. There has also been proposed a solution in which a step of growing the maximum grain size of primary crystal Si in the Si-based alloy phase to 5 to 60 μm and a solution treatment and an artificial aging treatment are applied.
[0010]
The overall composition of the sintered alloy is that the former alloy has a weight ratio of Si: 2.4 to 23.5%, Cu: 2 to 5%, Mg: 0.2 to 1.5%, Ti, One or more transition metals selected from V, Cr, Mn, Fe, Co, Ni, Zr and Nb: 0.01 to 1%, and the balance Al and inevitable impurities, the latter alloy being 1 to 45% by weight of a solid lubricant is added to the former alloy composition.
[0011]
These alloys are excellent in tensile strength, elongation, wear resistance, and the like, but there is still room for examination regarding heat treatment conditions that maximize these characteristic values.
[0012]
An object of the present invention is to provide a method for producing an Al—Si based sintered alloy suitable for producing a mechanical element having improved ductility of the sintered alloy and having both strength and wear resistance.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, in the production method of the present invention, 20 to 80 parts by weight of Al powder is blended with 20 to 80 parts by weight of Al-Si alloy powder having a Si content of 13 to 30% by weight. Cu-transition metal alloy powder in which the content of one or more transition metals selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zr and Nb is 0.2 to 30% by weight. As well as adding Al-Mg alloy powder or Mg powder having an Mg content of 35 wt% or more, the total composition is Si: 2.4 to 23.5%, Cu: 2 to 5% by weight, Mg: 0.2 to 1.5%, one or more transition metals selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zr and Nb: 0.01 to 1%, and the balance Mixed powder of Al and inevitable impurities, or solid lubricant added to the mixed powder The total composition by weight is Si: 1.3 to 23.3%, Cu: 1.1 to 5%, Mg: 0.1 to 1.5%, Ni: 0.005 to 1%, Ti, V One or more transition metals selected from Cr, Mn, Fe, Co, Ni, Zr and Nb: 0.01 to 1%, graphite, MoS₂, BN and WS₂1 type or 2 or more types of solid lubricants selected from 1 to 45%, and a powder mixture of any one of the mixed powder composed of Al and unavoidable impurities in the balance, and then sintered to obtain the largest particles The process of obtaining the sintered compact which exhibits the plaque structure of the Al-Si type-alloy phase in which primary Si with a diameter of 5-60 micrometers disperse | distributes, and an Al solid solution phase( 1 )And a step of solution cooling by heating and rapidly cooling the sintered body or plastic processed body( 3 )And the process of further artificial aging treatment( 4 )The aging treatment is performed by a heat treatment within a temperature and time range in which the tensile strength after the aging treatment is higher than the tensile strength of the sintered body in the overaging region. It is characterized by.
[0014]
Further, the present invention provides the above-mentioned step of obtaining a sintered body exhibiting a plaque structure of an Al—Si based alloy phase in which primary crystal Si having a maximum particle size of 5 μm or less is dispersed and an Al solid solution phase.( 1 )In addition, by heating the surface of the sintered body, the maximum grain size of primary crystal Si in the Al—Si based alloy phase existing on the surface portion of the alloy is grown to 5 to 60 μm and cooled.( 2 )It also includes the case where is added.
[0015]
That is, the sintered body or the plastic processed body in the sintered alloy of the plaque structure previously proposed by the present applicant is subjected to a solution treatment, and the artificial aging treatment is performed in the overaging region and the tensile strength is sintered. The main point is to carry out the heat treatment within a temperature and time range that shows a higher value than the tensile strength of the body (sintered alloy before solution treatment, the same applies hereinafter).
[0016]
[Action]
Next, each constituent requirement such as the alloy composition, alloy structure, powder selection, and heat treatment conditions of the present invention will be described.
(1) Selection of Si and powder in the alloy
The amount of Si as the overall composition is selected from a range in which an Al—Si based alloy phase in which primary crystal Si described later is dispersed and an Al solid solution phase exhibits a patchy structure, and is 2.4 to 23.5 wt%. is there. If the total amount of Si is too small, the amount of Si in the Al-Si alloy phase in which primary Si is dispersed is small, or the proportion of the Al solid solution phase increases, and primary Si that contributes to wear resistance. Due to the small amount, the wear resistance becomes insufficient. On the other hand, when the amount of Si is too large, a phenomenon opposite to the above occurs, and the wear resistance is similarly deteriorated.
Si is added in the form of Al-Si alloy powder. In order to precipitate primary crystal Si during the production by the powder mixing method, the Si content of the Al—Si alloy powder needs to be 13% by weight or more. On the other hand, if the Si content exceeds 30% by weight, the melt temperature at the time of powder production becomes high, and therefore the Si content is suitably 13-30% by weight.
In the Al-Si alloy powder part after sintering, a part of Mg, Cu and transition metal, which will be described later, are dissolved, and an Al-Si alloy in which primary Si is dispersed becomes a sintered alloy. It constitutes one alloy phase of the plaque tissue. This phase is relatively hard and contributes mainly to material strength and wear resistance.
[0017]
(2) Selection of Mg and powder in the alloy
Mg forms a liquid phase during sintering and dissolves in the substrate, accelerating sintering and aging precipitation.₂There is an effect of strengthening the substrate and improving wear resistance by Si.
If the total amount of Mg is less than 0.2% by weight, the effect is insufficient, and even if added over 1.5% by weight, the effect is not further increased. %, But a more preferable range is 0.3 to 0.7% by weight.
As a means for adding Mg, an Al—Mg alloy powder or Mg powder having an Mg content of 35% by weight or more is suitable. This is because when the melting point of the Al—Mg binary alloy shows a low value of about 460 ° C. in the Mg content range of 33 to 70% by weight, an Al—Mg alloy having an Mg content of 35% by weight or more is used. This is because solid phase diffusion occurs between the Al—Mg alloy and the Al base during the sintering process, and the Mg concentration in the Al—Mg alloy decreases, thereby generating a liquid phase.
[0018]
(3) Selection of Cu and transition metals and their powders
Cu is an element that reinforces the Al alloy substrate, and a greater effect can be obtained by aging treatment. The amount of Cu is 2 to 5% by weight in the total composition. If the amount is less than 2% by weight, the desired strength improvement is not observed. If the amount exceeds 5% by weight, a large amount of an intermetallic compound containing Cu as a main component is precipitated in the vicinity of the powder grain boundary and the toughness is lowered. A more preferred amount of Cu is 3.5 to 4.5% by weight.
When Cu is added in the form of Cu powder or Cu alloy powder, the sintered body that has been heated to dissolve Cu in the substrate is coarsened like primary material Si is melted. In the case of sintering by lowering the heating temperature to shorten the time, Cu intermetallic compounds such as Al₂CuMg, Al₆CuMg_FourEtc. remain, causing a decrease in strength and elongation. Even if solution treatment and aging treatment are performed, it is difficult to eliminate such intermetallic compounds at the grain boundaries.
[0019]
Therefore, when an appropriate amount of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb) coexist, an intermetallic compound at a grain boundary is formed by performing solution treatment and aging treatment in an overaging region. Can be extinguished. The transition metal has an effect of accelerating diffusion of Cu precipitated in the grain boundary portion into the base during the aging treatment. The reason is not clear, but it is thought that the diffusion of Cu during the aging treatment is accelerated by changing the disappearance behavior of atomic vacancies formed by the solution treatment or by changing the precipitation process. .
If the amount of transition metal in the total composition is less than 0.01% by weight in the Cu content (2 to 5% by weight), the effect is not obtained. Since the intermetallic compound which precipitates will precipitate and toughness will fall, it is set to 0.01 to 1 weight%.
Since transition metals are difficult to diffuse when added as a simple substance, it is preferable to add them in the form of Cu-transition metal alloy powder. However, the amount of transition metal in the alloy powder takes into account the amount of Cu and transition metal required as a whole composition. Therefore, 0.2% by weight or more is necessary. However, if it exceeds 30% by weight, the melting point of the alloy powder becomes high, and even if the melting point is lowered by solid phase diffusion, no liquid phase is generated, so it must be 0.2-30% by weight. Moreover, it is preferably 0.2 to 10% by weight.
[0020]
(4) Selection of Al solid solution phase and powder
The Al solid solution phase is a solid solution in which Si, Mg, Cu and transition metals are diffused in Al added in the form of pure aluminum powder, which is relatively soft and contributes to the toughness of the alloy, as well as initial wear. As a result, an oil pool is formed between the Al—Si based alloy phases, contributing to lubricity and compatibility with the mating material during friction. In addition, since it is easily plastically deformed, hard primary crystal Si particles near the sliding surface are likely to fall off as wear powder, and when they fall off, they are buried to prevent the Si particles from acting as abrasive particles. effective.
[0021]
(5) Plaque tissue
In the two phases of the Al—Si based alloy phase in which the primary Si particles are dispersed and the soft Al solid solution phase, when the Al—Si based alloy phase is less than 20% in the area ratio of the alloy cross section, the amount of primary Si In addition, when the amount exceeds 80%, the wear resistance is remarkably deteriorated because the amount of the Al solid solution phase in which the Si particles dropped by frictional sliding are buried is small. Therefore, when the two phases are a composite structure in which the area ratio of the alloy cross section is 20 to 80:80 to 20 in a patchy state, strength and wear resistance are improved by the mutual action.
[0022]
(6) Particle size of primary Si in Al-Si alloy phase
As for the cross-sectional shape of primary Si, small particles with the same vertical and horizontal dimensions are nearly circular, but large particles are considered to be aggregated or agglomerated small particles, which are irregular. Presents a shape. The maximum particle diameter represents the longest dimension among the distances between both ends of such irregularly shaped particles.
When the particle size of the primary crystal Si becomes large, the hard primary crystal Si particles scratch and wear the counterpart material in the state of protrusions. On the other hand, if the amount of primary crystal Si is small or the particle size of primary crystal Si is small, the primary crystal Si particles fall off from the substrate during frictional sliding, and wear proceeds because the primary crystal Si particles that fall off act as abrasive particles. Therefore, from the viewpoint of wear resistance, the grain size of the primary crystal Si needs to be an appropriate size, and a maximum grain size of 5 to 60 μm is appropriate.
[0023]
On the other hand, considering the strength, the larger the primary Si particle size, the lower the strength and ductility. Conversely, the smaller the primary Si particle size, the higher these values, and preferably 5 μm or less. .
Therefore, the primary crystal Si of the surface portion of the friction member or at least the surface portion of the sliding portion has a maximum particle size of 5 to 60 μm in order to maintain wear resistance, and the internal primary crystal Si has strength and ductility. In order to maintain the above, it is possible to improve both the wear resistance, strength and ductility by configuring the particle size to be 5 μm or less.
Thus, as a method of changing the grain size of the primary crystal of the inside and the surface part of the alloy, a sintered alloy that has been sintered in advance so that the grain size of the primary crystal Si is 5 μm or less is manufactured, and at least The surface of the sliding part is heated by heating means such as high-frequency heating, plasma heating, or laser heating to grow the primary crystal Si to have a maximum particle size of 5 to 60 μm. The depth of such a surface modification is preferably about 0.5 to 1 mm.
[0024]
(7) Aging treatment
When the solution-treated aluminum alloy is subjected to artificial aging treatment at a predetermined temperature, solute atoms are collected and precipitated. This change is governed by temperature and time and changes in physical and mechanical properties. In the case of a molten aluminum alloy, the tensile strength generally shows a parabolic change that first increases and then decreases as the heating time elapses. It is known that the elongation gradually increases after showing a minimum value when the tensile strength is maximum. Generally, the treatment is performed in a region where the tensile strength and hardness are the highest.
[0025]
On the other hand, in the case of an Al—Si sintered alloy containing Cu manufactured by a mixing method, Cu or its intermetallic compound that could not diffuse into the substrate during sintering segregates at the powder grain boundary. Unlike the case of melted lumber, the decrease in tensile strength in the overaged region is moderate. The elongation of the alloy is the same as that of the smelting material in the case of the material not containing the transition metal, but in the case of containing the transition metal, the elongation of the alloy increases remarkably with the heating time in the overaging region.
That is, in the case of the alloy manufactured by the method of the present invention, the intermetallic compound of Cu that cannot be diffused into the substrate during sintering exists in the powder grain boundary, It has no effect but is inadequate in terms of toughness. The presence of undiffused Cu intermetallic compound and the coexistence of an appropriate amount of transition metal result in the diffusion of Cu into the substrate in the overaged region, resulting in a decrease in the strength of the alloy and a marked improvement in elongation. As such an aging treatment condition, when the temperature is 240 ° C., it is appropriate that the treatment time is about 2 to 5 hours.
[0026]
【Example】
Hereinafter, the present invention will be described by way of examples.
<Example 1> Amount of Al solid solution phase and wear characteristics
Five types of Al-Si alloy powders, pure Al powder, Cu-4% Ni alloy powder and Al-50% Mg alloy having Si content of 15%, 17%, 20%, 25% and 30% as raw material powder Powder, 4.17% by weight of Cu-4% Ni alloy powder and 1% by weight of Al-50% Mg alloy powder, the type and amount of Al-Si alloy powder, and pure Al powder Various mixed powders were prepared by changing the blending amounts, and each was formed into a predetermined shape. The molded body was dewaxed at 400 ° C., sintered for 60 minutes at 540 ° C., then hot forged to a density ratio of 100%, and heated at 490 ° C. for solution treatment and quenching. Furthermore, aging treatment was performed by heating at 240 ° C. for 3 hours to prepare Samples 1 to 18. Table 1 shows the type of Al—Si alloy powder, the Si content in the overall composition, and the area ratio of the soft Al solid solution phase in the plaque structure.
The structure of each sample is such that the area ratio of the Al—Si alloy phase to the Al solid solution phase is the same as the blending ratio of the Al—Si alloy powder and the pure Al powder, and the maximum primary crystal Si in the Al—Si alloy phase. The particle size was 20-25 μm.
For each sample, the amount of sample wear by a pin-on-disk friction and wear test was measured and compared. The pin-on-disk friction and wear test uses a sample as a pin, uses a heat-treated product of S48C material (carbon steel for mechanical structure) as a rotating partner disk, and is lubricated with mineral oil under a surface pressure of 49 MPa and a friction speed of 5 m / sec. went.
Table 1 shows the amount of wear. It can be seen that the amount of wear is small when the Si content in the Al-Si alloy powder is within a predetermined range and the area ratio of the Al solid solution in the alloy cross section is between 20 and 80%.
[0027]
[Table 1]

[0028]
<Example 2> Relationship between maximum grain size of primary crystal Si, tensile strength and wear amount
Cu-4% Ni alloy powder and Al-50% Mg alloy powder are mixed in a powder obtained by mixing Al-20% Si alloy powder and pure Al powder at a weight ratio of 75:25, and the overall composition is weight ratio. Si 15%, Cu 4%, Mg 0.5%, Ni 0.17% and the balance are Al, and the green compact using this mixed powder is dewaxed at 400 ° C., and baked at various temperatures for 5 to 180 minutes at a temperature of 540 ° C. Samples were prepared, and hot forging, solution treatment, and aging treatment were performed in the same manner as in the above Examples to prepare Samples 19 to 23 shown in Table 2.
A sample having a short sintering time has a small particle size of primary Si, and a sample having a long sintering time is large. Table 2 also shows the measurement results of the tensile strength of these samples and the amount of wear measured in the same manner as in the previous examples. The smaller the maximum primary particle size of the primary crystal Si, the higher the strength, and the results of the wear test are good when the maximum particle size of the primary crystal Si is in the range of 5 μm to 60 μm, but seizure occurs or wear occurs outside this range. It can be seen that the amount increases.
[0029]
[Table 2]

[0030]
<Example 3> Effect of solid lubricant
As raw material powder, the same mixed powder as in Example 2 was used as a base material, and graphite powder was added as a solid lubricant in varying amounts to this base material, and the mixed powders of Samples 24-29 shown in Table 3 were added. Compacted into a predetermined shape. The green compact was dewaxed at 400 ° C., sintered at 540 ° C. for 60 minutes, hot forged to a density ratio of 100%, solution treated at 490 ° C. and aging treated at 240 ° C. .
For each sample, the amount of wear and the coefficient of friction of the sample by the tensile strength and the pin-on-disk friction and wear test were measured and compared. Table 3 shows the measurement results.
A sintered aluminum alloy sample containing a solid lubricant has a small coefficient of friction and wear. On the other hand, when the content of the solid lubricant increases, the tensile strength decreases. For members that do not require much strength, it is considered that a solid lubricant content of 30% by volume can be used, but if it exceeds 20% by volume, the decrease in tensile strength increases, so 1-20 volumes. % Range is considered desirable.
[0031]
[Table 3]

[0032]
<Example 4> Modification by surface heat treatment
In the same manner as in Example 2, Cu-4% Ni alloy powder and Al-50% Mg alloy powder were mixed with Al-20% Si alloy powder and pure Al powder mixed at a weight ratio of 75:25. After mixing, the total composition was Si 15% by weight, Cu 4%, Mg 0.5%, Ni 0.17% and the balance Al, and molded into a predetermined shape. The molded body was dewaxed at 400 ° C., sintered at 540 ° C. for 10 minutes, hot forged to a density ratio of 100%, and then the surface was heat-treated with a high frequency induction furnace.
Next, the sample was heated at 490 ° C. for solution treatment and quenching, and heated at 240 ° C. for 3 hours to perform an aging treatment.
The maximum primary Si particle size inside this sample is 4 μm, the surface portion has a maximum primary Si maximum particle size of 24 μm over a depth of about 0.1 mm, and the tensile strength is 416 MPa and pin-on-disk friction wear. The amount of wear of the sample by the test was 0.03 mm. In the case of the sample number 21 where the maximum grain size of primary Si is 25 μm, the tensile strength is lower because the internal primary crystal Si grain size is smaller than the tensile strength is 380 MPa and the wear amount is 0.01 mm. Since the primary crystal grain size of the surface portion is the same, the amount of wear showed similar results.
[0033]
<Example 5> Effect of transition metal addition and artificial aging treatment
A sample 30 to which Ni was added as a transition metal and a sample 31 to which Sn was added without adding a transition metal were prepared.
Sample 30 was formed by mixing 60% by weight of Al-20% Si alloy powder, 34.8% by weight of pure Al powder, 4.2% by weight of Cu-4% Ni powder and 1% of Al-50% Mg powder, and forming the mixture. The body was dewaxed at 400 ° C., sintered at 540 ° C. for 60 minutes, hot forged to a density ratio of 100%, and heated at 490 ° C. for solution treatment and quenching. An aging treatment was performed at a temperature of 240 ° C. while changing the heating time.
Sample 31 is a mixed powder of 60% by weight of Al-20% Si alloy powder, 35.7% by weight of pure Al powder, 3.3% by weight of Cu-10% Sn powder and 1% of Al-50% Mg powder. It was used in the same manner.
[0034]
FIG. 1 is a graph showing the relationship between the aging treatment time and the tensile strength and elongation after treatment in samples 30 and 31. The tensile strength of both samples increased with the lapse of heating time, showed a maximum value in 1 hour, and then showed a tendency to gradually decrease, and showed almost the same value as the forged body in about 5 hours. In these alloys, when the processing temperature is 240 ° C., a processing time of up to 1 hour is a sub-aging region, and a processing time longer than that is an over-aging region.
On the other hand, the elongation shows a tendency to increase in the overaging region after showing the minimum value in the heating time of 1 hour, but the increase in the elongation in the overaging region is moderate in the case of the sample 31 that does not contain a transition metal. In contrast to the slight amount, the sample 30 to which the transition metal Ni was added is large. That is, when a sintered alloy to which a transition metal is added is treated in the overaging region, a material having high ductility can be obtained.
Further, if the aging treatment is performed excessively more than necessary, the tensile strength is lowered. Therefore, it can be seen that when the treatment temperature is 240 ° C., the treatment time is preferably less than 5 hours.
[0035]
<Example 6> Addition of transition metal and diffusion of Cu
Sample 32 containing no transition metal and sample 33 added with Ni as a transition metal were prepared, and the distribution of segregated Cu after aging treatment was compared.
Sample 32 is a mixture of Al powder, Al-20% Si alloy powder, Cu powder and Al-50% Mg alloy powder, and the total composition is 15% Si-4% Cu-0.5% Mg-balance Al. Sample 33 was mixed with Al powder, Al-20% Si alloy powder, Cu-4% Ni alloy powder and Al-50% Mg alloy powder, and the total composition was 15 % Si-4% Cu-0.5% Mg-0.17% Ni-balance Al powder is used.
Each powder is compacted, sintered at a temperature of 540 ° C. for 60 minutes, subjected to hot forging, heated at a temperature of 490 ° C. for 60 minutes, and then rapidly cooled in warm water to form a solution. A sample was subjected to aging treatment at 240 ° C. for 3 hours.
Each sample has a polished surface of HF-HCl-HNO in the same manner as in the structure observation._Three-H₂It corroded with O liquid mixture, the SEM (scanning electron microscope) photograph and the Cu surface analysis photograph were taken, and the result was compared.
FIG. 2 shows an SEM photograph and a Cu plane analysis photograph. The width of each photograph corresponds to 100 μm. The phase of the central part of the SEM photograph is the Al solid solution phase of the part added in the form of pure Al, and the surrounding area is the Al-Si based alloy phase of the part added as Al-Si alloy powder. The Al—Si based alloy phase has primary Si observed in a granular form, and the remarkably white portion is an intermetallic compound of Cu. As can be seen from the Cu surface analysis photograph, in the sample 32 that does not contain Ni, many segregation portions with high Cu concentration are observed around the Al solid solution phase, but in the sample 33 that contains Ni, the amount is small. .
[0036]
【The invention's effect】
As described above, the method for producing an aluminum-based sintered alloy according to the present invention is based on a mixing method, so that powder formability is good, and primary crystal Si is dispersed in the structure of the sintered alloy. The alloy-based alloy phase and the Al solid solution phase show a patchy structure with an area ratio of 20 to 80%, and the maximum grain size of primary crystal Si of the Al—Si-based alloy phase at least on the surface of the alloy is 5 to 60 μm. In addition to obtaining an alloy with high material strength and good wear resistance, non-diffused Cu diffuses into the substrate and disappears by performing aging treatment in the overaging region, producing an alloy with excellent ductility Therefore, the range of application to machine elements that accompany various types of sliding of aluminum-based sintered alloys can be expanded.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between aging treatment time and tensile strength and elongation of an aluminum-based sintered alloy.
FIG. 2 is an SEM photograph and a Cu plane analysis photograph of an aluminum-based sintered alloy.

Claims

Ti, V, Cr, Mn, Fe, Co, and Ni are mixed with 20-80 parts by weight of Al powder with respect to 20-80 parts by weight of Al-Si alloy powder having a Si content of 13-30% by weight. Cu-transition metal alloy powder having a content of one or more transition metals selected from Zr and Nb of 0.2 to 30% by weight, and Al-Mg alloy powder having a Mg content of 35% by weight or more Alternatively, by adding Mg powder, the total composition is in a weight ratio of Si: 2.4 to 23.5%, Cu: 2 to 5%, Mg: 0.2 to 1.5%, Ti, V, Cr One or more transition metals selected from Mn, Fe, Co, Ni, Zr and Nb: 0.01 to 1%, and a mixed powder comprising the balance Al and inevitable impurities,
Alternatively, a solid lubricant is added to the mixed powder, and the total composition is Si: 1.3 to 23.3%, Cu: 1.1 to 5%, Mg: 0.1 to 1.5% in weight ratio. Ni: 0.005 to 1%, one or more transition metals selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zr and Nb: 0.01 to 1%, graphite, MoS ₂ , one or more solid lubricants selected from BN and WS ₂ : 1 to 45%, and mixed powder comprising the balance Al and inevitable impurities,
After compacting any of the mixed powders, a sintered body exhibiting a plaque structure of an Al—Si alloy phase in which primary Si having a maximum particle size of 5 to 60 μm is dispersed and an Al solid solution phase is sintered. and step (1) to obtain, as in step (3) of solution treated and quenched after heating the sintered body, or a plastic worked body, further comprising a step (4) to perform the artificial aging, the aging processing subjected to a heat treatment in the overaging region, and wherein the tensile strength after the aging treatment, performs a process within the scope of the sintered body of the tensile strength higher value shows the temperature and time than A method for producing an aluminum-based wear-resistant sintered alloy.

In the step (1) of obtaining a sintered body exhibiting a plaque structure of an Al—Si based alloy phase in which primary Si having a maximum particle size of 5 μm or less and an Al solid solution phase are dispersed, the surface of the sintered body is heated. The method further comprises the step ( 2 ) of cooling by growing the maximum grain size of primary crystal Si in the Al—Si based alloy phase existing on the surface of the alloy to 5 to 60 μm. The manufacturing method of the aluminum type wear-resistant sintered alloy as described in 1 above.