JP3867908B2 - Heat-resistant fatigued aluminum alloy casting and manufacturing method thereof - Google Patents
Heat-resistant fatigued aluminum alloy casting and manufacturing method thereof Download PDFInfo
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- JP3867908B2 JP3867908B2 JP2002198561A JP2002198561A JP3867908B2 JP 3867908 B2 JP3867908 B2 JP 3867908B2 JP 2002198561 A JP2002198561 A JP 2002198561A JP 2002198561 A JP2002198561 A JP 2002198561A JP 3867908 B2 JP3867908 B2 JP 3867908B2
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- 229910000838 Al alloy Inorganic materials 0.000 title claims description 87
- 238000005266 casting Methods 0.000 title claims description 34
- 238000004519 manufacturing process Methods 0.000 title claims description 20
- 239000010949 copper Substances 0.000 claims description 56
- 229910052802 copper Inorganic materials 0.000 claims description 38
- 229910052782 aluminium Inorganic materials 0.000 claims description 26
- 229910045601 alloy Inorganic materials 0.000 claims description 24
- 239000000956 alloy Substances 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 24
- 238000011282 treatment Methods 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 21
- 208000025599 Heat Stress disease Diseases 0.000 claims description 20
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 20
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 19
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 18
- 239000010419 fine particle Substances 0.000 claims description 15
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- 239000010703 silicon Substances 0.000 claims description 14
- 239000011572 manganese Substances 0.000 claims description 12
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- 238000007711 solidification Methods 0.000 claims description 11
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- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 5
- 238000002844 melting Methods 0.000 claims description 4
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- KLZUFWVZNOTSEM-UHFFFAOYSA-K Aluminium flouride Chemical compound F[Al](F)F KLZUFWVZNOTSEM-UHFFFAOYSA-K 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
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Description
【０００１】
【発明の属する技術分野】
本発明は、耐熱疲労性に優れたアルミニウム合金鋳物およびその製造方法に関するものである。
【０００２】
【従来の技術】
従来、シリンダヘッド用アルミニウム合金としては、優れた強度や耐熱性が要求されるので、２〜４％のＣｕを含む合金が最適とされていた（例えば、特開昭57−126944号公報）。しかしながら、耐熱疲労性に優れたアルミニウム合金については、ほとんど研究がされていないのが現状であり、従来より好適とされていた上記２〜４％Ｃｕ含有のアルミニウム合金が耐熱疲労性に優れているかどうかは不明であった。
【０００３】
また、シリンダヘッド鋳物の耐熱疲労亀裂性を改良する技術として、ＴＩＧ再溶融処理（M. Koyama, J. Miyake and K. Sakaguchi; SAE paper, No.891989, 1989.) がある。この技術は、危険部を局部加熱により溶融させた後、急冷凝固させることにより組織を微細にするとともに、鋳造欠陥であるポロシティを減少させて熱疲労による亀裂を生じにくくするものである。
【０００４】
【発明が解決しようとする課題】
しかしながら、前記SAE paper,No.891989 に記載されたアルミニウム合金を製造するには、熱電導率が高くて局部的に加熱されにくいアルミニウム合金鋳物を再溶融するまで加熱する設備と工程が必要になるという問題点を有している。
【０００５】
また、アルミニウム合金は、２００℃以上ではその変形挙動や強度が著しく変化するとともに、材料の組織も変化する。熱疲労では、それらに加えて熱応力や熱歪みも負荷されるため、現象が非常に複雑となる。従って、どのような材料が耐熱疲労性に優れるかを予測することは非常に難しく、実際に熱疲労試験を行ってみないと分からないという問題を有している。しかも、通常、熱疲労試験には大がかりな装置と高度な試験技術が必要であり、評価に時間がかかる。この評価の困難さが研究開発の妨げとなっていた。
【０００６】
そこで、本発明者らは、上述の如き従来技術の問題点を解決すべく鋭意研究し、各種の系統的実験を重ねた結果、本発明を成すに至ったものである。
【０００７】
（発明の目的）本発明の目的は、耐熱疲労性に優れたアルミニウム合金鋳物を提供するにある。本発明の他の目的は、耐熱疲労性に優れたアルミニウム合金鋳物の製造方法を提供するにある。
【０００８】
（着眼点）本発明者らは、上述の従来技術の問題に対して、以下のことに着眼した。すなわち、アルミニウム合金鋳物の熱疲労とは、どのような現象であり、材料の組織および組織変化とどのように関連しているかを明かにし、その知見に基づいて耐熱疲労特性の向上策を見いだそうとした。具体的には、(1) 基地Ａｌ中に分散する強化相であるが，加熱によって粗大化するＡｌとＣｕを主成分とする析出物と、(2) 晶出物の大きさや間隔を決定する凝固時間、(3) 通常は不純物として低いほうが良いとされるが耐熱性の点では多いほうが良いとも考えられるＦｅ，Ｍｎ量、および、(4) 重大な鋳物欠陥であるポロシティ、に着目した。
【０００９】
【課題を解決するための手段】
（第１発明）本発明の耐熱疲労アルミニウム合金鋳物は、珪素：３〜２４重量％、銅：０．２〜２重量％、残部がアルミニウムとからなる耐熱疲労性に優れたアルミニウム合金鋳物であって、該アルミニウム合金の基地中に、晶出物のネットワーク組織と、アルミニウムと銅とを主成分とする０．２μｍ以下の微粒子が０．４〜４重量％分散してなることを特徴とする。
【００１０】
（第２発明）本発明の耐熱疲労アルミニウム合金は、前記第１発明合金の合金組成に加えて、さらに鉄を０．２５重量％以下、およびマンガンを０．２５重量％以下含有する合金からなる鋳物であることを特徴とする。
【００１１】
（第３発明）本発明の耐熱疲労アルミニウム合金鋳物の製造方法は、合金組成が珪素：３〜２４重量％、銅：０．２〜２重量％、残部がアルミニウムとなるように原料物質を準備する工程と、該準備した原料物質を溶解し、凝固時間を５０ｓｅｃ以上として凝固させる工程と、該凝固した鋳物に溶体化処理と時効処理とを施す熱処理工程とを含んでなり、アルミニウム合金の基地中に、晶出物のネットワーク組織と、アルミニウムと銅とを主成分とする０．２μｍ以下の微細粒子を０．４〜４重量％分散させてなることを特徴とする。
【００１２】
（第４発明）本発明の耐熱疲労アルミニウム合金鋳物の製造方法は、第２発明の耐熱疲労アルミニウム合金鋳物を製造する方法であって、合金組成が珪素：３〜２４重量％、銅：０．２〜２重量％、鉄：０．２５重量％以下、マンガン：０．２５重量％以下、残部がアルミニウムとからなるように原料物質を準備する工程と、該準備した原料物質を溶解し、凝固時間を５０ｓｅｃ以上として凝固させる工程と、該凝固した鋳物に溶体化処理と時効処理とを施す熱処理工程と、を含んでなることを特徴とする。
【００１３】
前記熱処理工程は、４５０℃〜５５０℃で１〜１０時間加熱保持後急冷する溶体化処理と、しかる後に１５０℃〜３００℃で１〜２０時間加熱保持する時効処理とからなる工程であることが望ましい。
【００１４】
【発明の効果】
（第１発明の効果）本発明のアルミニウム合金は、耐熱疲労性に優れている。また、このアルミニウム合金は、熱疲労寿命が長いだけでなく、変形も生じにくい。さらに、これにより、部品の設計自由度が広がり、これを用いた製品の性能向上に寄与するとともに、地球環境に優しい自動車用エンジンの実現に貢献することができる。
【００１５】
（第２発明の効果）本発明のアルミニウム合金は、耐熱疲労性に優れている。また、このアルミニウム合金は、熱疲労寿命により優れているとともに、変形も生じにくい。さらに、これにより、部品の設計自由度が広がり、これを用いた製品の性能向上に寄与するとともに、地球環境に優しい自動車用エンジンの実現に貢献することができる。
【００１６】
（第３発明の効果）本発明の製造方法により、耐熱疲労性に優れたアルミニウム合金を容易に得ることができる。また、この方法は簡便であるので、有用である。
【００１７】
（第４発明の効果）本発明の製造方法により、耐熱疲労性により優れたアルミニウム合金を容易に得ることができる。また、この方法は簡便であるので、有用である。
【００１８】
【発明の実施の形態】
以下に、前記発明をさらに具体的にした発明やこれら発明の実施の形態について説明する。
【００１９】
（第１発明の実施の形態）
【００２０】
本発明の耐熱疲労アルミニウム合金が優れた効果を発揮するメカニズムについては、未だ必ずしも明らかではないが、次のように考えられる。すなわち、本発明の耐熱疲労アルミニウム合金を、高温で圧縮、低温で引張の応力が繰り返し作用する熱疲労の条件下で使用すると、析出物が粗大化してもその数が少ないので、粗大化に伴い発生する内部応力が低く、割れが生じにくい。さらに、適度な析出強化相と、晶出物のネットワーク組織により、局部的な変形が抑制できる。
【００２１】
ここで、本発明の耐熱疲労アルミニウム合金は、珪素（Ｓｉ）の含有量が３〜２４重量％である。このＳｉは、Ａｌ合金の鋳造性を改善するのに不可欠な元素である。Ｓｉ含有量が３重量％未満の場合、鋳造性が悪く、鋳造欠陥が生じ易い、また、熱膨張係数が大きいという問題を有する。Ｓｉ含有量が２４重量％を超える場合、強度と靱性が著しく小さくなるという問題を有する。なお、珪素（Ｓｉ）含有量の好適範囲は、４〜８重量％である。該範囲内の場合、鋳造性、強度、靱性がさらに向上する。また、珪素（Ｓｉ）含有量の最適範囲は、５〜７重量％である。
【００２２】
また、銅（Ｃｕ）の含有量が、０．２〜２重量％である。このＣｕは、熱処理によって、強度・靱性を改善し、均一な変形をもたらす不可欠の元素である。Ｃｕ含有量が０．２重量％未満の場合、熱疲労によりバルジ変形が発生するという問題を有する。Ｃｕ含有量が２重量％を超える場合、熱疲労寿命が短いという問題を有する。なお、銅（Ｃｕ）含有量の好適範囲は、０．５〜１．５重量％である。該範囲内の場合、寿命がより向上する。また、銅（Ｃｕ）含有量の最適範囲は、０．５〜１．０重量％である。
【００２３】
また、アルミニウム合金中の基地α−Ａｌ中に分散する微細粒子は、アルミニウムと銅とを主成分とする微細粒子であり、大きさが１μｍ以下である。粒子の大きさが１μｍ以下の場合、分散粒子が基地Ａｌの強化に寄与し、鋳物の強度を高めるとともに熱疲労による変形防止に効果がある。該微粒子の大きさが１μｍを超える場合は、鋳物の強度が低くなるという問題を有する。なお、該微細粒子の好適な大きさは、０．５μｍ以下である。これにより、適度な強度が得られる。
【００２４】
また、アルミニウム合金中の基地中に分散する微細粒子は、含有量が、アルミニウム合金の０．４〜４重量％である。これにより、強度と靱性および耐熱疲労性が改善される。該微粒子の含有量が０．４重量％未満の場合は、熱疲労により変形が生じるという問題を有する。また、該微粒子の含有量が４重量％を超える場合は、熱疲労により割れが生じやすいという問題を有する。なお、該微細粒子の含有量の好適な範囲は、１．０〜３．０重量％である。これにより、強度と靱性および耐熱疲労性がより改善される。また、該微細粒子の含有量の最適な範囲は、１．０〜２．０重量％である。
【００２５】
すなわち、本発明の耐熱疲労アルミニウム合金は、基地Ａｌ部にＡｌとＣｕを主成分とする微細析出粒子が少量分散した合金である。拘束下で、加熱・冷却される熱疲労を受けると、このような析出物が粗大化し、図２に示すように粗大化した析出粒子の周囲に内部応力が発生する。この内部応力は、図３のような基地Ａｌ中の亀裂発生を助長する。従って、熱疲労による亀裂発生を防止するためには、このような析出粒子はある程度少ないほうがよい。しかし、析出粒子は、析出強化の効果があり、全くないと基地Ａｌ中が柔らかくなりすぎて図４に示すような局部変形が生じてしまい、バルジ変形を引き起こす。
【００２６】
本第１発明の好適な耐熱疲労アルミニウム合金は、珪素：３〜２４重量％、銅：０．２〜２重量％、残部がアルミニウムと１．０重量％以下の不純物とからなる耐熱疲労性に優れたアルミニウム合金であって、該アルミニウム合金中の基地中に、アルミニウムと銅とを主成分とする１μｍ以下の微細粒子が０．４〜４重量％分散してなることを特徴とする。すなわち、本発明の耐熱疲労アルミニウム合金は、不純物が１．０重量％以下であることが好ましい。これより、強度と靱性が改善される。不純物の含有量が１．０重量％を超えると、脆弱な化合物が生じて鋳物の強度や靱性が低下したり、ポロシティが発生し易くなる虞がある。なお、耐熱疲労アルミニウム合金の不純物が、０．５重量％以下であることがより好ましい。
【００２７】
以上のように、本発明のアルミニウム合金は、耐熱疲労性に優れている。例えば、５０℃〜２５０℃で、全ひずみ範囲０．４５％の Out-of-phase 熱疲労試験における寿命が２０００サイクル以上と耐熱疲労性に優れたアルミニウム合金である。また、このアルミニウム合金は、熱疲労寿命が長いだけでなく、変形も生じにくい。さらに、この合金により、部品の設計自由度が広がり、これを用いた製品の性能向上に寄与するとともに、地球環境に優しい自動車用エンジンの実現に貢献することができる。
【００２８】
（第２発明の実施の形態）
【００２９】
本発明の耐熱疲労アルミニウム合金が優れた効果を発揮するメカニズムについては、未だ必ずしも明らかではないが、次のように考えられる。
【００３０】
本発明の耐熱疲労アルミニウム合金を、高温で圧縮、低温で引張りの応力が繰り返し作用する熱疲労（out-of-phase）の条件下で使用すると、析出物が粗大化しても発生する内部応力が低く、割れが生じにくい。さらに、適度な析出強化相とネットワーク状に存在する晶出物により、局部的な変形が抑制できる。しかも、ポロシティによる寿命低下も抑制できる。
【００３１】
本発明の耐熱疲労アルミニウム合金は、第１発明と同様のＳｉおよびＣｕを含有し、上記と同様の作用・効果を奏する上に、さらにＦｅおよびＭｎを含有してなる。このＦｅ，Ｍｎは、高温強度を高める作用がある。特に、Ｍｎは、Ｆｅ化合物の形状を変え靱性を改善させるとともに、基地Ａｌ中に固溶して高温強度を改善させる作用があるが、両者とも多すぎると強度，靱性に悪影響を及ぼす。Ｆｅ，Ｍｎの含有量は、共に０．２５重量％以下である。Ｆｅ，Ｍｎの含有量は、何れかが０．２５重量％を超えると、熱疲労寿命が短い。
【００３２】
また、本発明の耐熱疲労アルミニウム合金は、ポロシティ量が0.２cc／100g以下である。このポロシティ量が0.２cc／100gを超えると、熱疲労寿命が短い。すなわち、ポロシティを多く含む合金は、ポロシティの周辺で局部変形が生じ、それが寿命の低下をもたらすものと考えられる。なお、該ポロシティの好適な量は、0.１cc／100g以下である。これにより、熱疲労寿命がより改善される。また、該ポロシティの最適な量は、0.０５cc／100g以下である。
【００３３】
本第２発明の好適な耐熱疲労アルミニウム合金は、珪素：３〜２４重量％、銅：０．２〜２重量％、鉄：０．２５重量％以下、マンガン：０．２５重量％以下、残部がアルミニウムと１．０重量％以下の不純物とからなり、ポロシティ量が0.２cc／100g以下であることを特徴とする。
【００３４】
以上のように、本発明のアルミニウム合金は、耐熱疲労性に優れている。例えば、５０℃〜２５０℃で、全ひずみ範囲０．４５％の Out-of-phase 熱疲労試験における寿命が２０００サイクル以上と耐熱疲労性に優れたアルミニウム合金である。また、このアルミニウム合金は、熱疲労寿命により優れているとともに、変形も生じにくい。さらに、この合金により、部品の設計自由度が広がり、これを用いた製品の性能向上に寄与するとともに、地球環境に優しい自動車用エンジンの実現に貢献することができる。
【００３５】
（第３発明および第４発明の実施の形態）
【００３６】
本第３発明および第４発明の耐熱疲労アルミニウム合金の製造方法が優れた効果を発揮するメカニズムについては、未だ必ずしも明らかではないが、次のように考えられる。すなわち、本発明の耐熱疲労アルミニウム合金の製造方法において、目的組成の原料物質を準備した後、該原料物質を溶解し、凝固時間を５０sec 以上として凝固させてなる。これにより、晶出物がネットワーク状の骨格を形成した組織が得られ、熱疲労による局部への変形集中が防止できる。
【００３７】
ここで、凝固工程における凝固時間は、５０sec 以上である。これにより、熱疲労に伴う局部変形が防止できる。凝固時間が５０sec 未満では、晶出物粒子が小さく、ネットワーク組織ができなくなるため、局部変形が生じやすい。
【００３８】
本第３発明の好適な耐熱疲労アルミニウム合金は、請求項１に記載の耐熱疲労アルミニウム合金を製造する方法であって、合金組成が珪素：３〜２４重量％，銅：０．２〜２重量％，残部がアルミニウムと１．０重量％以下の不純物とからなるように原料物質を準備する工程と、該準備した原料物質を溶解し，凝固時間を５０sec 以上として凝固させる工程とを含んでなり、アルミニウム合金の基地中に，アルミニウムと銅とを主成分とする１μｍ以下の微細粒子を０．４〜４重量％分散させてなることを特徴とする耐熱疲労アルミニウム合金の製造方法である。
【００３９】
本第４発明の好適な耐熱疲労アルミニウム合金は、請求項２に記載の耐熱疲労アルミニウム合金を製造する方法であって、合金組成が珪素：３〜２４重量％，銅：０．２〜２重量％，鉄：０．２５重量％以下，マンガン：０．２５重量％以下，残部がアルミニウムと１．０重量％以下の不純物とからなるように原料物質を準備する工程と、該準備した原料物質を溶解し，凝固時間を５０sec 以上として凝固させる工程と、を含んでなることを特徴とする。
【００４０】
次に、本発明のより好適な耐熱疲労アルミニウム合金の製造方法は、前記第１発明または前記第２発明の組成、さらにはこれら発明の好適な発明や実施の形態に記載された組成となるように準備された合金を溶解して、凝固時間５０sec 以上で凝固させた鋳物に、４５０℃〜５５０℃で１〜１０時間加熱保持後急冷し、１５０℃〜３００℃で１〜２０時間加熱保持する熱処理を施すことを特徴とする。
【００４１】
これにより、基地のα−Ａｌ中に、ＡｌとＣｕを主成分とする１μｍ以下の微細析出粒子が０．４〜４重量％分散し、晶出物がネットワーク状の骨格を形成した合金を得ることができる。
【００４２】
溶体化処理温度が５５０℃を超える場合は、液相が出て冷却時にポロシティが発生するために強度と靱性が低下し、４５０℃未満の場合には、時効処理により析出する粒子が少ない場合がある。この溶体化処理の時間は、１０時間を超える処理は必要なく、１時間では十分な効果が得られないことや、晶出物の角が丸くならないことがあり、強度と靱性が低い。時効温度は、３００℃を超える場合、析出物が大きくなりすぎて強度が低く、１５０℃未満では、析出速度が遅く、１０時間加熱しても十分な強度が得られない。また、この場合には、寸法安定性が悪い。時効時間が１時間未満では、析出が十分に生じず、強度が低い。１０時間超える場合は、析出物が粗大化して強度が低下する。
【００４３】
なお、本発明の耐熱疲労性アルミニウム合金、および本発明の製造方法によって得られた耐熱疲労性アルミニウム合金は、例えば、この合金をシリンダヘッドなどの部品として適用する場合には、使用時に高温となる部分は使用時間とともに強度が低下するが、それ以外の部分の強度は、使用開始時のままであるから、熱処理によりある程度の強度をもたせることが好ましい。また、使用時の寸法変化を低減するためには、やや過時効状態にしておくことが好ましい。
【００４４】
【実施例】
【００４５】
（第１実施例）目的組成になるように、９９．９９重量％純アルミ地金と各種母合金を配合して溶解し、０．３重量％のフラックス（ＮａＣｌ＋２５重量％ＡｌＦ3 ）を添加する除さい処理を施し、約１０Ｐａ・２０min 加熱の条件で真空脱ガス処理を施した後、高さ６０mmの押湯付きジルコン砂シェル型に鋳込んで本発明にかかる本実施例のアルミニウム合金試料素材を作製した（試料番号：１、２）。このとき、溶解および各種溶湯処理は７５０℃、注湯は７００℃で行った。試料採取位置における凝固時間は約３００sec であり、２次デンドライトアーム間隔は、約５５μｍであった。
【００４６】
アルミニウム合金試料の配合組成とポロシティ量を、表１に示す。なお、これらの配合組成値は、鋳物の組成とほぼ等しいことをＩＰＣ発光分析等で確認した。また、ポロシティ量は、アルキメデス法で測定した密度と推定式（特願平６−３３９５７６号に示す推定式）からもとめた真密度値から算出した。
【００４７】
【表１】
また、得られたアルミニウム合金試料の基地Ａｌ部の金属組織を、透過型電子顕微鏡で観察し、さらに、制限視野回折法により、分散粒子の組織と大きさを調べた。その結果、試料番号１では、大きさが0.２μｍ以下（≦0.２μｍ）のＡｌとＣｕを主成分とする微細組織（原子比で、Ａｌ：Ｃｕがほぼ２：１）が１.9重量％含有していることが分かった。また、試料番号２では、大きさが0.２μｍ以下のＡｌとＣｕを主成分とする微細組織が３.8重量％含有していることが分かった。
【００４９】
比較のために、本発明の組成外の配合組成や条件で、比較用Ａｌ合金試料素材を得た。
比較例１Ｃｕの配合割合を０．０重量％とした以外は、上記第１実施例と同様にして比較用Ａｌ合金試料素材を得た（試料番号：Ｃ１）。
【００５０】
比較例２Ｃｕの配合割合を３．５重量％とした以外は、上記第１実施例と同様にして比較用Ａｌ合金試料素材を得た（試料番号：Ｃ２）。これら、比較用試料の配合組成とポロシティ量を、表１に併せて示す。なお、配合組成の確認、およびポロシティ量の算出は、上記第１実施例と同様にして行った。
【００５１】
次に、得られたアルミニウム合金試料、および比較用Ａｌ合金試料に対して、Ｔ６処理（溶体化処理： 500℃×５時間→水冷、時効処理： 160℃×５時間）を施した後、試験片に加工して熱疲労試験を行った。
【００５２】
性能評価試験熱疲労試験は、低熱膨張の拘束ホルダと試験片を一体化して加熱・冷却を繰返す方式で実施した（例えば、特開平５−１８８８１８号公報に示される熱疲労試験方法）。試験温度範囲は、５０〜２５０℃で、繰り返し速度は５min/サイクルとした。その結果、高温ひずみゲージで実測した試験初期の全ひずみ範囲はいずれも約０.45 ％であり、平均ひずみは約−０.65 ％であった。これらのひずみ条件は、バルジ変形が生じた試料番号Ｃ１の試験では、やや変化したが、その他の試験片では、破断するまでほぼ一定であった。
【００５３】
熱疲労寿命は、各サイクルの最低温度（５０℃）において発生する最大の引張応力の値が、サイクル数とともに急激に零まで低下しはじめるサイクル数と定義した。この値は、試験片表面の亀裂が急激に進展しはじめるサイクル数とほぼ一致する。
【００５４】
ポロシティが０．１cc／100g以下の試料におけるＣｕ量と熱疲労寿命の関係、および熱疲労によるバルジ変形の有無を、図１に示す。なお、図中、「１」は試料番号１を、「２」は試料番号２を、「Ｃ１」は試料番号Ｃ１を、「Ｃ２」は試料番号Ｃ２を、それぞれ示す。本実験結果から、２重量％Ｃｕ材は、３.5重量％Ｃｕ材よりも約２倍寿命が長くてバルジ変形も生じないことが分かる。１重量％Ｃｕ材は、さらに寿命が長く３.5重量％Ｃｕ材の約３倍の寿命を示しており、バルジ変形も生じていない。しかし０重量％Ｃｕ材では、１００００サイクルでも破断しないが、バルジ変形が生じてしまうことが分かる。
【００５５】
５００サイクルの熱疲労試験に供した後、平行部から薄膜試料を採取し、基地Ａｌの組織を透過型電子顕微鏡（倍率：５００００倍）で観察した。試料番号Ｃ２（３.5重量％Ｃｕ材）の基地Ａｌ部の金属組織写真（微細組織写真）を、図２に示す。同図より、多くの平板状粒子が認められ、これらはほとんどがＡｌ−Ｃｕ系の析出物であることが確認された。このような析出物の周囲には黒白のコントラストがあり、このコントラストは格子のゆがみ、すなわち弾性的なひずみの存在を意味する。また、析出物は、試験前に比べて大きくなっている。この観察結果から、析出物は、熱疲労試験の加熱過程に成長するが、成長がひずみの拘束下で起こるため析出粒子の周囲に局部的に内部応力が発生したと考えられる。このような内部応力は、基地Ａｌ部の破壊を助長する可能性がある。
【００５６】
また、熱疲労試験で破断した３．５重量％Ｃｕ材（試料番号：Ｃ２）試験片の断面の金属組織を光学顕微鏡（倍率：４００倍）で観察した。その結果を、図３に示す。図３から明らかなように、熱疲労試験で破断した試験片においても、基地Ａｌ中を進む亀裂が観察されている。従って、Ｃｕ量を少なくするほど内部応力の原因となる析出物が少なくなるため、熱疲労寿命が向上すると考えられる。
【００５７】
また、熱疲労試験によりバルジ変形が生じた０重量％Ｃｕ材（試料番号：Ｃ１）の表面状態を走査型電子顕微鏡（倍率：１００倍）で観察した結果を、図４に示す。同図より明らかなように、バルジ変形部には、局部的に変形した凹凸の激しい部分とあまり変形していない表面が滑らかな部分が混在している。０重量％Ｃｕ材は、Ａｌ−Ｓｉ−Ｃｕ系の合金の主要な析出強化相であるＡｌ−Ｃｕ系の析出物が全くないため、基地Ａｌ部が非常に軟らかくて局部変形が生じ易い。従って、熱疲労の場合にも、局部的に変形してバルジ変形が生じたと考えられる。このことから、逆に、Ｃｕを少しでも添加すれば、Ａｌ−Ｃｕ系の析出物による析出強化が期待できるため、このような局部変形が防止でき、熱疲労によるバルジ変形も生じにくいと考えられる。
【００５８】
実用鋳物における耐熱疲労性としては、寿命が長いだけでなく変形が生じないことが要求される。以上より、Ｃｕ量の好適量は０.5重量％〜２重量％であり、Ｃｕ量がこの範囲の場合、変形が生じないで、熱疲労寿命も長いことが期待でき、耐熱疲労性により優れていることが分かる。
【００５９】
（第２実施例）
【００６０】
前記第１実施例と同様の方法で、目的組成になるように、９９．９９重量％純アルミ地金と各種母合金を表１に示す量配合して溶解し、０．３重量％のフラックス（ＮａＣｌ＋２５重量％ＡｌＦ3 ）を添加する除さい処理を施し、約１０Ｐａ・２０min 加熱の条件で真空脱ガス処理を施した後、高さ６０mmの押湯付きジルコン砂シェル型に鋳込んで本発明にかかる本実施例のアルミニウム合金試料素材を作製した（試料番号：３）。このとき、溶解および各種溶湯処理は７５０℃、注湯は７００℃で行った。試料採取位置における凝固時間は約３００sec であり、２次デンドライトアーム間隔は、約５５μｍであった。
【００６１】
得られたアルミニウム合金試料の、基地Ａｌ部の金属組織を、透過型電子顕微鏡で観察し、さらに、制限視野回折法により、分散粒子の組織と大きさを調べた。その結果、大きさが0.２μｍ以下（≦0.２μｍ）のＡｌとＣｕを主成分とする微細組織が１.9重量％含有していることが分かった。
【００６２】
比較のために、本発明の組成外の配合組成や条件で、比較用Ａｌ合金試料素材を得た。
比較例３配合割合を表１の試料番号Ｃ３、Ｃ４とし、上記第２実施例の真空脱ガス処理を省略した他は、前記第２実施例と同様にして比較用Ａｌ合金試料素材を得た（試料番号：Ｃ３、Ｃ４）。
【００６３】
比較例４配合割合を表１の試料番号Ｃ５、Ｃ６とし、上記第２実施例の真空脱ガス処理および除さい処理を省略し、それに変えて、水と油に浸した黒鉛棒を７５０℃の溶湯中に投入して溶湯に水素ガスを含浸させるガス含有処理を追加した他は、前記第２実施例と同様にして比較用Ａｌ合金試料素材（ガス含有処理処理材）を得た（試料番号：Ｃ５、Ｃ６）。
【００６４】
性能評価試験上記試料番号３、および試料番号Ｃ３〜Ｃ６の配合組成とポロシティ量を、表１に併せて示す。なお、ポロシティ量は、前記第１実施例と同様にして算出した。次いで、得られたアルミニウム合金試料、および比較用Ａｌ合金試料に、前記第１実施例と同様に熱処理（Ｔ６処理）を施し、試験片を作製した。
【００６５】
次に、得られた試験片の熱疲労試験を実施した。熱疲労試験方法および試験条件は、前記第１実施例と同様で、試験温度範囲は５０〜２５０℃、繰り返し速度は５min/サイクル、全ひずみ範囲は約０.45 ％、平均ひずみは約−０.65 ％であった。ひずみ条件は、破断するまでほぼ一定であり、バルジ変形はいずれの試験でも生じなかった。
【００６６】
試験試料の熱疲労寿命を、表１に示す。表１より、Ｃｕが１重量％と少ない試料は、ポロシティが0.１cc/100g 以下と少ない場合（試料番号：３）には、前記比較例２のＣｕが３．５重量％の試料の場合（試料番号：Ｃ２）に比べて寿命が約３倍長いが、ポロシティが0.５cc/100g 以上の場合（試料番号：Ｃ３およびＣ５）には、著しく寿命が短いことが分かる。ポロシティを多く含む試料では、ポロシティの周辺で局部変形が生じ、それが寿命の低下をもたらすものと考えられる。一方、Ｃｕが少ないと、析出強化粒子が少なく、やや局部的な変形も生じやすいが、ポロシティの周辺ではさらに局部変形が助長されて寿命低下を招いているものと推察される。
【００６７】
以上より、耐熱疲労性に優れたアルミニウム合金の好適なポロシティの量は、0.２cc/100g 以下と考えられる。
【図面の簡単な説明】
【図１】本発明の第１実施例、および比較例１〜比較例２において得られた性能評価試験結果を示す図で、ポロシティが０．１cc／100g以下の試料におけるＣｕ量と熱疲労寿命の関係、および熱疲労によるバルジ変形の有無を示す線図である。
【図２】比較例２において得られた、５００サイクルの熱疲労試験後の基地Ａｌ部の金属組織を示す透過型電子顕微鏡写真図（倍率：５００００倍）である。
【図３】比較例２において得られた、熱疲労試験後の試験片の断面の金属組織を示す光学顕微鏡写真図（倍率：４００倍）である。
【図４】比較例１において得られた、熱疲労試験後の試験片の表面の金属組織を示す走査型電子顕微鏡写真図（倍率：１００倍）である。
【符号の説明】
１・・・試料番号１
２・・・試料番号２
Ｃ１・・・試料番号Ｃ１
Ｃ２・・・試料番号Ｃ２[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aluminum alloy casting excellent in heat fatigue resistance and a method for producing the same.
[0002]
[Prior art]
Conventionally, as an aluminum alloy for a cylinder head, since excellent strength and heat resistance are required, an alloy containing 2 to 4% of Cu has been optimum (for example, JP-A-57-126944). However, there is almost no research on aluminum alloys with excellent heat fatigue resistance, and is the above-described aluminum alloy containing 2 to 4% Cu, which has been considered suitable, excellent in heat fatigue resistance? It was unknown.
[0003]
Further, as a technique for improving the heat fatigue crack resistance of the cylinder head casting, there is a TIG remelting treatment (M. Koyama, J. Miyake and K. Sakaguchi; SAE paper, No. 891989, 1989.). In this technique, the critical part is melted by local heating and then rapidly solidified to make the structure finer, and the porosity, which is a casting defect, is reduced to make it difficult to cause cracks due to thermal fatigue.
[0004]
[Problems to be solved by the invention]
However, in order to manufacture the aluminum alloy described in the SAE paper, No. 891989, equipment and a process for heating the aluminum alloy casting, which has a high thermal conductivity and is difficult to be locally heated, until remelting are required. Has the problem.
[0005]
In addition, the deformation behavior and strength of an aluminum alloy change remarkably at 200 ° C. or higher, and the material structure also changes. In thermal fatigue, in addition to these, thermal stress and thermal strain are also applied, so the phenomenon becomes very complicated. Therefore, it is very difficult to predict what kind of material is excellent in heat fatigue resistance, and there is a problem that it is not known unless a thermal fatigue test is actually performed. In addition, the thermal fatigue test usually requires a large-scale apparatus and advanced test technology, and takes time to evaluate. This difficulty of evaluation hindered research and development.
[0006]
Therefore, the present inventors have intensively studied to solve the problems of the prior art as described above, and as a result of repeating various systematic experiments, the present invention has been achieved.
[0007]
(Object of the invention) An object of the present invention is to provide an aluminum alloy casting excellent in heat fatigue resistance. Another object of the present invention is to provide a method for producing an aluminum alloy casting excellent in heat fatigue resistance.
[0008]
(Focus Points) The present inventors have focused on the following with respect to the above-described problems of the prior art. In other words, it was clarified what kind of phenomenon is thermal fatigue of aluminum alloy castings, and how it is related to the structure and change of the material. did. Specifically, (1) the strengthening phase dispersed in the base Al, the precipitates mainly composed of Al and Cu that are coarsened by heating, and (2) the size and spacing of the crystallized matter are determined. We focused on solidification time, (3) Fe and Mn amounts, which are usually considered to be low as impurities, but considered to be better in terms of heat resistance, and (4) porosity, which is a serious casting defect.
[0009]
[Means for Solving the Problems]
(First invention) The heat-resistant fatigued aluminum alloy casting of the present invention is an aluminum alloy casting excellent in heat-resistant fatigue comprising silicon: 3 to 24% by weight, copper: 0.2 to 2% by weight, and the balance being aluminum. In the base of the aluminum alloy,Network structure of crystallized materials,Mainly composed of aluminum and copper0.2It is characterized in that fine particles of μm or less are dispersed by 0.4 to 4% by weight.
[0010]
(Second invention) The heat-resistant fatigued aluminum alloy of the present invention isIn addition to the alloy composition of the first invention alloy,ironThe0.25% by weight or less,andmanganeseThe0.25 wt% or lessIncludingIt is the casting which consists of an alloy which has.
[0011]
(Third Invention) A method for producing a heat-resistant fatigued aluminum alloy casting of the present invention is prepared by preparing a raw material so that the alloy composition is silicon: 3-24% by weight, copper: 0.2-2% by weight, and the balance is aluminum. A step of dissolving the prepared raw material and solidifying with a solidification time of 50 sec or more; andHeat treatment with solution treatment and aging treatmentAnd comprising the steps of, during the base of the aluminum alloy,Network structure of crystallized materials,Mainly composed of aluminum and copper0.2It is characterized in that 0.4 to 4% by weight of fine particles of μm or less are dispersed.The
[0012]
(Fourth invention) The method for producing the heat-resistant fatigued aluminum alloy casting of the present invention comprises:Second inventionHeat resistant fatigue aluminum alloycastingThe alloy composition is silicon: 3-24% by weight, copper: 0.2-2% by weight, iron: 0.25% by weight or less, manganese: 0.25% by weight or less, and the balance is aluminum A step of preparing a raw material so as to consist of: a step of dissolving the prepared raw material and solidifying with a solidification time of 50 sec or more; andHeat treatment with solution treatment and aging treatmentAnd a process.
[0013]
The heat treatment step is performed after heating and holding at 450 ° C. to 550 ° C. for 1 to 10 hours.Rapid solution treatmentThen, heat and hold at 150 to 300 ° C. for 1 to 20 hoursWith aging treatmentIt is desirable to be a process.
[0014]
【The invention's effect】
(Effect of the first invention) The aluminum alloy of the present invention is excellent in heat fatigue resistance. In addition, this aluminum alloy not only has a long thermal fatigue life, but also hardly deforms. In addition, this increases the degree of freedom in designing parts, contributing to improving the performance of products using the parts, and contributing to the realization of an automobile engine that is friendly to the global environment.
[0015]
(Effect of the second invention) The aluminum alloy of the present invention is excellent in heat fatigue resistance. In addition, this aluminum alloy is superior in thermal fatigue life and hardly deforms. In addition, this increases the degree of freedom in designing parts, contributing to improving the performance of products using the parts, and contributing to the realization of an automobile engine that is friendly to the global environment.
[0016]
(Effect of the third invention) By the production method of the present invention, an aluminum alloy excellent in heat fatigue resistance can be easily obtained. This method is useful because it is simple.
[0017]
(Effect of the fourth invention) By the production method of the present invention, an aluminum alloy superior in heat fatigue resistance can be easily obtained. This method is useful because it is simple.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In the following, the inventions that further make the inventions more specific and the embodiments of these inventions will be described.
[0019]
(Embodiment of the first invention)
[0020]
The mechanism by which the heat-resistant fatigued aluminum alloy of the present invention exhibits an excellent effect is not necessarily clear yet, but is considered as follows. That is, when the heat-resistant fatigued aluminum alloy of the present invention is used under the conditions of thermal fatigue in which tensile stress is repeatedly applied at high temperatures and tensile stresses at low temperatures, the number of precipitates is small even if they are coarsened. The generated internal stress is low and cracking is difficult to occur. Furthermore, local deformation can be suppressed by an appropriate precipitation strengthening phase and a network structure of crystallized substances.
[0021]
Here, the heat-resistant fatigued aluminum alloy of the present invention has a silicon (Si) content of 3 to 24% by weight. This Si is an essential element for improving the castability of the Al alloy. When the Si content is less than 3% by weight, the castability is poor, casting defects are likely to occur, and the thermal expansion coefficient is large. When Si content exceeds 24 weight%, there exists a problem that intensity | strength and toughness become remarkably small. In addition, the suitable range of silicon (Si) content is 4 to 8 weight%. Within the range, the castability, strength and toughness are further improved. Moreover, the optimal range of silicon (Si) content is 5-7 weight%.
[0022]
Moreover, content of copper (Cu) is 0.2 to 2 weight%. This Cu is an indispensable element that improves strength and toughness by heat treatment and brings about uniform deformation. When the Cu content is less than 0.2% by weight, there is a problem that bulge deformation occurs due to thermal fatigue. If the Cu content exceeds 2% by weight, the thermal fatigue life is short. In addition, the suitable range of copper (Cu) content is 0.5 to 1.5 weight%. In the range, the life is further improved. Moreover, the optimal range of copper (Cu) content is 0.5 to 1.0% by weight.
[0023]
The fine particles dispersed in the matrix α-Al in the aluminum alloy are fine particles mainly composed of aluminum and copper and have a size of 1 μm or less. When the particle size is 1 μm or less, the dispersed particles contribute to strengthening of the base Al, and are effective in increasing the strength of the casting and preventing deformation due to thermal fatigue. When the size of the fine particles exceeds 1 μm, there is a problem that the strength of the casting is lowered. The preferred size of the fine particles is 0.5 μm or less. Thereby, moderate intensity | strength is obtained.
[0024]
The fine particles dispersed in the matrix in the aluminum alloy have a content of 0.4 to 4% by weight of the aluminum alloy. Thereby, strength, toughness and heat fatigue resistance are improved. When the content of the fine particles is less than 0.4% by weight, there is a problem that deformation occurs due to thermal fatigue. Further, when the content of the fine particles exceeds 4% by weight, there is a problem that cracking is likely to occur due to thermal fatigue. In addition, the suitable range of content of this fine particle is 1.0 to 3.0 weight%. Thereby, strength, toughness, and heat fatigue resistance are further improved. The optimum range of the content of the fine particles is 1.0 to 2.0% by weight.
[0025]
That is, the heat-resistant fatigued aluminum alloy of the present invention is an alloy in which a small amount of fine precipitated particles mainly containing Al and Cu are dispersed in the base Al portion. When subjected to thermal fatigue that is heated and cooled under restraint, such precipitates are coarsened, and internal stress is generated around the coarsened precipitated particles as shown in FIG. This internal stress promotes the generation of cracks in the matrix Al as shown in FIG. Therefore, in order to prevent the occurrence of cracks due to thermal fatigue, it is better that the number of such precipitated particles is small. However, the precipitation particles have the effect of precipitation strengthening, and if there is no precipitation at all, the base Al becomes too soft and local deformation as shown in FIG. 4 occurs, causing bulge deformation.
[0026]
The preferred heat-resistant fatigued aluminum alloy of the first invention has a heat-resistant fatigue resistance consisting of silicon: 3 to 24% by weight, copper: 0.2 to 2% by weight, the balance being aluminum and impurities of 1.0% by weight or less. It is an excellent aluminum alloy, characterized in that 0.4 to 4% by weight of fine particles of 1 μm or less mainly composed of aluminum and copper are dispersed in a matrix in the aluminum alloy. That is, the heat-resistant fatigued aluminum alloy of the present invention preferably contains 1.0% by weight or less of impurities. This improves strength and toughness. If the impurity content exceeds 1.0% by weight, a fragile compound is produced, and the strength and toughness of the casting may be reduced, or porosity may be easily generated. The impurity of the heat resistant fatigue aluminum alloy is more preferably 0.5% by weight or less.
[0027]
As described above, the aluminum alloy of the present invention is excellent in heat fatigue resistance. For example, it is an aluminum alloy that has excellent heat fatigue resistance with a life of 2000 cycles or more in an out-of-phase thermal fatigue test at 50 ° C. to 250 ° C. and a total strain range of 0.45%. In addition, this aluminum alloy not only has a long thermal fatigue life, but also hardly deforms. Furthermore, this alloy increases the degree of freedom in designing parts, contributing to improving the performance of products using the alloy, and contributing to the realization of an automobile engine that is friendly to the global environment.
[0028]
(Embodiment of the second invention)
[0029]
The mechanism by which the heat-resistant fatigued aluminum alloy of the present invention exhibits an excellent effect is not necessarily clear yet, but is considered as follows.
[0030]
When the heat-resistant fatigued aluminum alloy of the present invention is used under the condition of thermal fatigue (out-of-phase) in which tensile stress is repeatedly applied at high temperature and tensile stress is applied at low temperature, the internal stress generated even when the precipitate is coarsened. Low and not easily cracked. Furthermore, local deformation can be suppressed by a moderate precipitation strengthening phase and a crystallized substance existing in a network. In addition, a decrease in life due to porosity can be suppressed.
[0031]
The heat-resistant fatigued aluminum alloy of the present invention contains Si and Cu similar to those of the first invention, exhibits the same actions and effects as described above, and further contains Fe and Mn. These Fe and Mn have the effect of increasing the high temperature strength. In particular, Mn has the effect of improving the toughness by changing the shape of the Fe compound and improving the high temperature strength by dissolving in the matrix Al, but if both are too much, the strength and toughness are adversely affected. The contents of Fe and Mn are both 0.25% by weight or less. If either Fe or Mn content exceeds 0.25 wt%, the thermal fatigue life is short.
[0032]
The heat-resistant fatigued aluminum alloy of the present invention has a porosity amount of 0.2 cc / 100 g or less. When the porosity exceeds 0.2 cc / 100 g, the thermal fatigue life is short. That is, in an alloy containing a lot of porosity, it is considered that local deformation occurs around the porosity, which leads to a decrease in life. The preferred amount of porosity is 0.1 cc / 100 g or less. Thereby, the thermal fatigue life is further improved. The optimum amount of porosity is 0.05 cc / 100 g or less.
[0033]
The preferred heat-resistant fatigued aluminum alloy of the second invention is silicon: 3-24% by weight, copper: 0.2-2% by weight, iron: 0.25% by weight or less, manganese: 0.25% by weight or less, the balance Is composed of aluminum and impurities of 1.0 wt% or less, and has a porosity of 0.2 cc / 100 g or less.
[0034]
As described above, the aluminum alloy of the present invention is excellent in heat fatigue resistance. For example, it is an aluminum alloy that has excellent heat fatigue resistance with a life of 2000 cycles or more in an out-of-phase thermal fatigue test at 50 ° C. to 250 ° C. and a total strain range of 0.45%. In addition, this aluminum alloy is superior in thermal fatigue life and hardly deforms. Furthermore, this alloy increases the degree of freedom in designing parts, contributing to improving the performance of products using the alloy, and contributing to the realization of an automobile engine that is friendly to the global environment.
[0035]
(Embodiments of the third and fourth inventions)
[0036]
The mechanism by which the method for producing the heat-resistant fatigued aluminum alloy of the third and fourth inventions exerts an excellent effect is not yet clear, but is considered as follows. That is, in the method for producing a heat-resistant fatigued aluminum alloy of the present invention, after preparing a raw material having a target composition, the raw material is dissolved and solidified with a solidification time of 50 seconds or more. Thereby, the structure | tissue in which the crystallization thing formed the network-like frame | skeleton is obtained, and the deformation | transformation concentration to the local part by thermal fatigue can be prevented.
[0037]
Here, the solidification time in the solidification step is 50 seconds or more. Thereby, local deformation accompanying thermal fatigue can be prevented. If the solidification time is less than 50 seconds, the crystallized particles are small and a network structure cannot be formed, so local deformation is likely to occur.
[0038]
A preferred heat-resistant fatigued aluminum alloy of the third invention is a method for producing the heat-resistant fatigued aluminum alloy according to
[0039]
A preferred heat-resistant fatigued aluminum alloy of the fourth invention is a method for producing a heat-resistant fatigued aluminum alloy according to
[0040]
Next, a more preferable method for producing a heat-resistant fatigued aluminum alloy of the present invention is the composition described in the first invention or the second invention, and further the composition described in the preferred invention or embodiment of the present invention. The alloy prepared in 1) is melted and solidified in a solidification time of 50 seconds or more, then heated and held at 450 ° C. to 550 ° C. for 1 to 10 hours, then rapidly cooled, and then heated and held at 150 ° C. to 300 ° C. for 1 to 20 hours It is characterized by performing a heat treatment.
[0041]
As a result, an alloy in which 0.4 to 4% by weight of finely precipitated particles of 1 μm or less mainly composed of Al and Cu are dispersed in the base α-Al, and a crystallized substance forms a network-like skeleton is obtained. be able to.
[0042]
When the solution treatment temperature exceeds 550 ° C., the liquid phase comes out and porosity is generated at the time of cooling, so the strength and toughness decrease. When it is less than 450 ° C., there may be few particles precipitated by the aging treatment. is there. The solution treatment time does not need to exceed 10 hours, and a sufficient effect may not be obtained in 1 hour, and the corners of the crystallized product may not be rounded, resulting in low strength and toughness. When the aging temperature exceeds 300 ° C., the precipitate becomes too large and the strength is low, and when it is less than 150 ° C., the precipitation rate is slow and sufficient strength cannot be obtained even after heating for 10 hours. In this case, the dimensional stability is poor. When the aging time is less than 1 hour, precipitation does not occur sufficiently and the strength is low. When it exceeds 10 hours, a precipitate coarsens and intensity | strength falls.
[0043]
In addition, the heat-resistant fatigue-resistant aluminum alloy of this invention and the heat-resistant fatigue-resistant aluminum alloy obtained by the manufacturing method of this invention become high temperature at the time of use, for example, when applying this alloy as components, such as a cylinder head. The strength of the portion decreases with the use time, but the strength of the other portions remains at the start of use, so it is preferable to give a certain strength by heat treatment. Moreover, in order to reduce the dimensional change at the time of use, it is preferable to be in a slightly overaged state.
[0044]
【Example】
[0045]
(First Example) 99.99% by weight pure aluminum ingot and various master alloys were mixed and dissolved so as to obtain the target composition, and 0.3% by weight flux (NaCl + 25% by weight AlF3) was added. After performing a vacuum treatment under a heating condition of about 10 Pa · 20 min, cast into a zircon sand shell mold with a feeder with a height of 60 mm to obtain the aluminum alloy sample material of this example according to the present invention. It produced (sample number: 1, 2). At this time, melting and various molten metal treatments were performed at 750 ° C., and pouring was performed at 700 ° C. The coagulation time at the sampling position was about 300 sec, and the secondary dendrite arm spacing was about 55 μm.
[0046]
Table 1 shows the composition of the aluminum alloy sample and the amount of porosity. In addition, it confirmed that these compounding composition values were substantially equal to the composition of a casting by IPC emission analysis. The porosity amount was calculated from the density measured by the Archimedes method and the true density value obtained from the estimation formula (estimation formula shown in Japanese Patent Application No. 6-339576).
[0047]
[Table 1]
Further, the metal structure of the base Al portion of the obtained aluminum alloy sample was observed with a transmission electron microscope, and the structure and size of the dispersed particles were examined by a limited field diffraction method. As a result, Sample No. 1 has a fine structure (atomic ratio, Al: Cu is approximately 2: 1) of Al and Cu having a size of 0.2 μm or less (≦ 0.2 μm) as the main component. It was found that it contained by weight. Sample No. 2 was found to contain 3.8% by weight of a fine structure mainly composed of Al and Cu having a size of 0.2 μm or less.
[0049]
For comparison, a comparative Al alloy sample material was obtained with a composition and conditions outside the composition of the present invention.
Comparative Example 1 A comparative Al alloy sample material was obtained in the same manner as in the first example except that the Cu content was 0.0 wt% (sample number: C1).
[0050]
Comparative Example 2 A comparative Al alloy sample material was obtained in the same manner as in the first example except that the compounding ratio of Cu was 3.5 wt% (sample number: C2). Table 1 shows the composition of these comparative samples and the amount of porosity. The confirmation of the composition and the calculation of the amount of porosity were performed in the same manner as in the first example.
[0051]
Next, T6 treatment (solution treatment: 500 ° C. × 5 hours → water cooling, aging treatment: 160 ° C. × 5 hours) was performed on the obtained aluminum alloy sample and the comparative Al alloy sample, and then tested. The piece was processed into a thermal fatigue test.
[0052]
The performance evaluation test thermal fatigue test was carried out by a system in which a low thermal expansion restraint holder and a test piece were integrated and heating and cooling were repeated (for example, a thermal fatigue test method disclosed in Japanese Patent Laid-Open No. 5-188818). The test temperature range was 50 to 250 ° C., and the repetition rate was 5 min / cycle. As a result, the total strain range at the initial stage of the test measured with a high-temperature strain gauge was about 0.45%, and the average strain was about -0.65%. These strain conditions changed somewhat in the test of sample number C1 in which bulge deformation occurred, but remained almost constant until the other test pieces broke.
[0053]
The thermal fatigue life was defined as the number of cycles at which the value of the maximum tensile stress generated at the minimum temperature (50 ° C.) of each cycle began to decrease rapidly to zero with the number of cycles. This value almost coincides with the number of cycles at which cracks on the surface of the test piece begin to develop rapidly.
[0054]
FIG. 1 shows the relationship between the amount of Cu and thermal fatigue life in a sample having a porosity of 0.1 cc / 100 g or less, and the presence or absence of bulge deformation due to thermal fatigue. In the figure, “1” indicates
[0055]
After being subjected to a 500-cycle thermal fatigue test, a thin film sample was taken from the parallel portion, and the structure of the base Al was observed with a transmission electron microscope (magnification: 50000 times). The metal structure photograph (microstructure photograph) of the base Al part of sample number C2 (3.5 wt% Cu material) is shown in FIG. From the figure, many tabular grains were observed, and it was confirmed that most of these were Al-Cu-based precipitates. There is a black-and-white contrast around such precipitates, which means that the lattice is distorted, that is, the presence of elastic strain. Moreover, the deposit is larger than before the test. From this observation result, the precipitate grows in the heating process of the thermal fatigue test, but it is considered that internal stress was locally generated around the precipitated particles because the growth occurred under strain constraint. Such internal stress may promote the destruction of the base Al portion.
[0056]
Moreover, the metal structure of the cross section of the 3.5 wt% Cu material (sample number: C2) test piece fractured in the thermal fatigue test was observed with an optical microscope (magnification: 400 times). The result is shown in FIG. As is clear from FIG. 3, cracks traveling through the base Al are also observed in the test piece fractured in the thermal fatigue test. Therefore, it is considered that the thermal fatigue life is improved because the amount of precipitates causing internal stress decreases as the amount of Cu decreases.
[0057]
Moreover, the result of having observed the surface state of 0 weight% Cu material (sample number: C1) in which the bulge deformation | transformation produced by the thermal fatigue test was observed with the scanning electron microscope (magnification: 100 times) is shown in FIG. As is clear from the figure, the bulge deformed portion is a mixture of a locally deformed and uneven portion and a portion having a smooth surface that is not so deformed. The 0 wt% Cu material has no Al—Cu based precipitates which are the main precipitation strengthening phases of Al—Si—Cu based alloys, so the base Al portion is very soft and local deformation is likely to occur. Therefore, even in the case of thermal fatigue, it is considered that bulge deformation occurred due to local deformation. From this, conversely, if Cu is added even a little, precipitation strengthening by Al-Cu-based precipitates can be expected, so that such local deformation can be prevented and bulge deformation due to thermal fatigue is unlikely to occur. .
[0058]
Thermal fatigue resistance in practical castings is required not only to have a long life but also to prevent deformation. From the above, the preferred amount of Cu is 0.5 wt% to 2 wt%, and when the Cu amount is within this range, no deformation occurs and a long thermal fatigue life can be expected, and the heat fatigue resistance is excellent. I understand that
[0059]
(Second embodiment)
[0060]
In the same manner as in the first embodiment, 99.99 wt% pure aluminum ingot and various master alloys were mixed and dissolved in the amounts shown in Table 1 so that the target composition was obtained, and 0.3 wt% flux was obtained. (NaCl + 25% by weight AlF3) is added, and vacuum degassing is performed under heating conditions of about 10 Pa · 20 min. An aluminum alloy sample material of this example was produced (sample number: 3). At this time, melting and various molten metal treatments were performed at 750 ° C., and pouring was performed at 700 ° C. The coagulation time at the sampling position was about 300 sec, and the secondary dendrite arm spacing was about 55 μm.
[0061]
The metal structure of the base Al portion of the obtained aluminum alloy sample was observed with a transmission electron microscope, and the structure and size of the dispersed particles were examined by a limited field diffraction method. As a result, it was found that a fine structure mainly composed of Al and Cu having a size of 0.2 μm or less (≦ 0.2 μm) contained 1.9% by weight.
[0062]
For comparison, a comparative Al alloy sample material was obtained with a composition and conditions outside the composition of the present invention.
A comparative Al alloy sample material was obtained in the same manner as in the second example except that the mixing ratio of Comparative Example 3 was set to sample numbers C3 and C4 in Table 1 and the vacuum degassing process in the second example was omitted. (Sample numbers: C3, C4).
[0063]
Comparative Example 4 The blending ratio was set to sample numbers C5 and C6 in Table 1, and the vacuum degassing process and the removal process of the second example were omitted. Instead, a graphite rod immersed in water and oil was 750 ° C. A comparative Al alloy sample material (gas-containing treatment material) was obtained in the same manner as in the second example except that a gas-containing treatment for impregnating the molten metal with hydrogen gas was added (sample number). : C5, C6).
[0064]
Performance Evaluation Test Table 1 shows the composition and the amount of porosity of Sample No. 3 and Sample Nos. C3 to C6. The porosity amount was calculated in the same manner as in the first example. Next, the obtained aluminum alloy sample and the comparative Al alloy sample were subjected to heat treatment (T6 treatment) in the same manner as in the first example, to prepare test pieces.
[0065]
Next, the thermal fatigue test of the obtained test piece was implemented. The thermal fatigue test method and test conditions are the same as in the first example, the test temperature range is 50 to 250 ° C., the repetition rate is 5 min / cycle, the total strain range is about 0.45%, and the average strain is about −0. It was .65%. The strain conditions were almost constant until rupture and bulge deformation did not occur in any test.
[0066]
Table 1 shows the thermal fatigue life of the test samples. From Table 1, the sample with less Cu of 1% by weight has a porosity of less than 0.1 cc / 100g or less (sample number: 3). Although the life is about three times longer than (Sample No .: C2), it can be seen that when the porosity is 0.5 cc / 100 g or more (Sample No .: C3 and C5), the life is remarkably short. In the sample containing a lot of porosity, local deformation occurs around the porosity, which is considered to cause a decrease in the life. On the other hand, when Cu is small, precipitation strengthening particles are small and local deformation is likely to occur, but it is surmised that local deformation is further promoted around the porosity, leading to a decrease in life.
[0067]
From the above, it is considered that the suitable amount of porosity of the aluminum alloy having excellent heat fatigue resistance is 0.2 cc / 100 g or less.
[Brief description of the drawings]
FIG. 1 is a diagram showing the performance evaluation test results obtained in the first embodiment of the present invention and Comparative Examples 1 and 2, and the Cu amount and thermal fatigue life in a sample having a porosity of 0.1 cc / 100 g or less. It is a diagram which shows the relationship of this, and the presence or absence of the bulge deformation by thermal fatigue.
FIG. 2 is a transmission electron micrograph (magnification: 50000 times) showing the metal structure of the base Al part obtained after 500 cycles of thermal fatigue test, obtained in Comparative Example 2.
3 is an optical micrograph (magnification: 400 times) showing a metal structure of a cross section of a test piece after a thermal fatigue test obtained in Comparative Example 2. FIG.
4 is a scanning electron micrograph (magnification: 100 times) showing the metallographic structure of the surface of the test piece after the thermal fatigue test obtained in Comparative Example 1. FIG.
[Explanation of symbols]
1 ...
2 ...
C1 ... Sample number C1
C2 ... Sample number C2
Claims (6)
該準備した原料物質を溶解し、凝固時間を５０ｓｅｃ以上として凝固させる工程と、 該凝固した鋳物に溶体化処理と時効処理とを施す熱処理工程と、を含んでなることを特徴とする耐熱疲労アルミニウム合金鋳物の製造方法。 A method for producing a heat-resistant fatigued aluminum alloy casting according to claim 2, wherein the alloy composition is silicon: 3-24% by weight, copper: 0.2-2% by weight, iron: 0.25% by weight or less, manganese : 0.25% by weight or less, a step of preparing a raw material so that the balance is aluminum,
A heat-resistant fatigued aluminum comprising: a step of melting the prepared raw material and solidifying the solidification time to be 50 sec or longer; and a heat treatment step of subjecting the solidified casting to solution treatment and aging treatment. Manufacturing method of alloy castings.
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