JP3843363B2

JP3843363B2 - Heat treatment type 7000 series aluminum alloy having high strength and excellent corrosion resistance and method for producing the same

Info

Publication number: JP3843363B2
Application number: JP12229796A
Authority: JP
Inventors: 学中井; 武比古江藤
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1996-04-19
Filing date: 1996-04-19
Publication date: 2006-11-08
Anticipated expiration: 2016-04-19
Also published as: JPH09287046A

Description

【０００１】
【発明の属する技術分野】
本発明は、航空機、鉄道車両、自動車等の輸送機器及び一般機械部品等の使用に適する熱処理型７０００系アルミニウム合金に関するものであり、特に本発明は高強度で耐食性に優れる熱処理型７０００系アルミニウム合金に関するものである。
【０００２】
【従来の技術】
熱処理型７０００系アルミニウム合金は溶体化焼入れ後の人工時効により高い強度が得られる析出型合金であり、大別してＡｌ−Ｚｎ−Ｍｇ−Ｃｕ系合金とＡｌ−Ｚｎ−Ｍｇ系合金とに分けられる。代表的な合金として、Ａｌ−Ｚｎ−Ｍｇ−Ｃｕ系合金では７０７５（Ａｌ−５．９Ｚｎ−２．２Ｍｇ−１．４Ｃｕ−０．２Ｃｒ）、７０５０（Ａｌ−５．９Ｚｎ−２．２Ｍｇ−２．２Ｃｕ−０．１２Ｚｒ）、７０５５（Ａｌ−８．０Ｚｎ−２．２Ｍｇ−２．２Ｃｕ−０．１５Ｚｒ）が、またＡｌ−Ｚｎ−Ｍｇ系合金では７００３（Ａｌ−５．８Ｚｎ−０．８Ｍｇ−０．１５Ｚｒ）等がある。
【０００３】
代表的な製造方法は、押出形材製品では例えば溶解鋳造にてビレット等の鋳塊にした後、均質化処理し、熱間押出を行い、溶体化処理水焼入れを行った後、必要に応じてストレッチ等で引張加工し、目的に応じた熱処理を行った後出荷され、加工メーカーで最終製品に成形加工されている。また、板製品でも同様に、溶解鋳造にて鋳塊にした後、均質化熱処理し、熱間圧延、さらには必要に応じて冷間圧延を行った後、溶体化処理水焼入れを行った後必要に応じて冷間圧延や引張加工し、目的に応じた熱処理を行った後出荷され、加工メーカーで最終製品に成形加工されている。
【０００４】
熱処理型７０００系アルミニウム合金において最高強度はＴ６調質で得られる。ＪＩＳ−Ｗ１１０３及びＭＩＬ−６０８８Ｆが定める代表的な調質条件は、７０７５では、溶体化処理及び焼入れを行った後に１２０℃で２４ｈｒの熱処理を行うものである。ところが、耐食性は極端に低下する。例えば、ＡＳＴＭ−Ｇ４７に従った耐ＳＣＣ試験において、耐ＳＣＣ応力（ＳＴ方向）は、４８Ｎ／ｍｍ²以下と極めて低い。また、ＡＳＴＭ−Ｇ３４に従った剥離試験において、耐層状腐食特性はランクＥＣ〜ＥＤと極めて低い。
【０００５】
耐食性を高くするため、Ｔ７調質で総称される過時効処理が一般に用いられている。耐ＳＣＣ応力は、例えばＴ７６調質、Ｔ７４調質及びＴ７３調質でそれぞれ１１７〜１７２、２４２及び２８９Ｎ／ｍｍ²と高くなり、また耐層状腐食特性もそれぞれ、ランクＥＢ及びランクＥＡ〜Ｐと高くなる。しかしながら、強度低下が著しく、Ｔ６調質での強度に対して１５〜３０％低くなる。つまり、耐食性を高くするために強度をわざわざ低くして使用されるのが実状であった。
【０００６】
高強度で且つ高耐食性を狙った熱処理方法としては、ＵＳＰ３８５６５８４が提案されている。これは、溶体化処理焼入れ後に、３段階の熱処理を行うものであり、第１段階で時効処理を、第２段階で復元処理を、第３段階で再時効処理を行う。具体的な熱処理条件は、時効処理：１２０℃で２４ｈｒ（Ｔ６調質）、復元処理：２００℃〜２６０℃で７〜１２０秒、再時効処理：１１５〜１２５℃（時間は任意）である。しかしながら、復元時間は上述したように７〜１２０秒と極めて短く、このため厚肉材への適用は極めて困難なものである。また、復元時の熱処理方法もオイルバス等の浴槽型の熱処理炉に限定されてしまう。
【０００７】
また、同様な手法は、ＵＳＰ５２２１３７７でも提案されている。これは、遷移元素としてＺｒを含有するＡｌ−Ｚｎ−Ｍｇ−Ｃｕ系合金において、時効処理及び再時効処理を１２０℃で２４ｈｒ、復元処理を１８２〜２４６℃の温度範囲内で５分以上保持するものである。これより、強度は７Ｘ５０−Ｔ６より１０％高くなり５７９Ｎ／ｍｍ²となる。また、耐層状腐食特性はランクＥＣ〜ＥＢとなり７Ｘ５０−Ｔ７６に匹敵するものになるとしている。しかしながら、耐ＳＣＣ特性については具体的にどのようなミクロ組織にすればこのような特性が得られるかは全く不明である。
【０００８】
以上のように、熱処理型７０００系アルミニウム合金において、耐食性を高くする熱処理方法としてＴ７６、Ｔ７４、Ｔ７３等の過時効処理があるが、強度の低下が著しい。そこで、高強度と高耐食性を同時に実現する熱処理方法として、溶体化処理及び焼入れ後の時効、復元及び再時効からなる３段階熱処理が提案されているが、復元時間が数十秒と極めて短く、工業的には実用的でない。また、復元条件を調整することで、熱処理時間の長時間化が図られているが、耐層状腐食性はＴ７６調質程度とまだまだ低く、耐ＳＣＣ性にいたっては全く不明である。さらに、どのようなミクロ組織にすれば高強度で高耐食性が得られるかは全く分からない。
【０００９】
【発明が解決しようとする課題】
本発明は上記従来の問題点に鑑みてなされたもので、航空機、鉄道車両、自動車等の輸送機器及び一般機械部品等の用途において、高強度でかつ高い耐食性（耐ＳＣＣ応力、耐層状腐食特性）が要求されてきた熱処理型７０００系アルミニウム合金において、強度及び耐食性をさらに高くし、且つこれらの特性が工業的にも容易に製造可能な熱処理型７０００系アルミニウム合金を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明に関わる高強度で耐食性に優れるアルミニウム合金は、熱処理型７０００系アルミニウム合金において、導電率を３８〜４０ＩＡＣＳ％とし、結晶粒界上のη相の最小間隔が２０ｎｍ以上で且つ結晶粒内のη’相の最大サイズが２０ｎｍ以下であるミクロ組織を有することを特徴とする。
【００１１】
また、高強度で耐食性に優れるアルミニウム合金の製造方法は、熱処理型７０００系アルミニウム合金を均熱処理及び熱間加工後必要により冷間加工を行い所定の製品サイズに調整後、溶体化熱処理及び焼入れ後必要に応じて冷間加工を行った後、時効処理を１００〜１４５℃で５〜５０ｈｒ、復元処理を１４０〜１９５℃で０．５〜３０ｈｒ、再時効処理を１００〜１４５℃で５〜５０ｈｒ行うことで、導電率を３８〜４０ＩＡＣＳ％とし、結晶粒界上のη相の最小間隔が２０ｎｍ以上で且つ結晶粒内のη’相の最大サイズが２０ｎｍ以下であるミクロ組織を有する熱処理型７０００系アルミニウム合金を得ることを特徴とする。ここで、時効処理と再時効処理の望ましい条件は１３０〜１４５℃で５〜２０ｈｒの処理である。
【００１２】
【発明の実施の形態】
さて、熱処理型７０００系アルミニウム合金は析出硬化型の合金であり、溶体化処理及び焼入れ後、例えば１２０℃で２４ｈｒ人工時効すると、粒内にＧＰゾーンが微細に析出するため強度は高くなる。また、粒界上には、η相が連続析出する。η相はアノディックであり溶出しやすい。このため、耐ＳＣＣ応力及び耐層状腐食特性は低い。一方、熱処理型７０００系アルミニウム合金を溶体化処理及び焼入れ後、過時効処理すると粒内のＧＰゾーンはη’相へと析出が進行し、強度は低下する。この際、η’相のサイズ分布は粗大化側にシフトする。しかしながら、粒界上のη相は粗大化し、不連続化するため、耐ＳＣＣ応力及び耐層状腐食特性等の耐食性は高くなる。
【００１３】
高強度及び高耐食性を同時に実現することを目的とした溶体化焼入れ後の時効処理、復元処理及び再時効処理からなる３段階の熱処理法では、粒内のＧＰゾーンの割合をできるだけ増やすことで高い強度を、また、粒界上では、η相の間隔を広げることで高耐食性を実現しようとするものである。３段階の熱処理中のミクロ組織の変化は、以下の通りとされている。すなわち、溶体化処理焼入れ後の時効処理で生じた粒内のＧＰゾーンは、復元処理で再固溶するが、その後の再時効処理で再びＧＰゾーンは析出する。一方、粒界上では、時効処理で生じたη相は復元処理で粗大化し、間隔が広がるために不連続化する。その後の再時効処理ではほとんど変化しない。
【００１４】
ＵＳＰ３８５６５８４では、復元温度の高温化で、処理時間を数十秒と短時間化されているが、熱処理時間が短すぎ、逆に工業化を困難としている。また、たとえ製品サイズに見合ったオイルバスを用意できた場合でも、厚肉材では加熱速度が遅く、このような短時間で復元処理を完全に行うことは不可能である。
一方、ＵＳＰ５２２１３７７では、復元処理温度を１８２〜２４６℃と、上記ＵＳＰ３８５６５８４の温度範囲２００〜２６０℃に比べ低温化することで、処理時間の長時間化を図っている。しかしながら、復元処理前後での時効処理及び再時効処理はそれぞれ１２０℃で２４ｈｒであり、このため３段階熱処理に必要な全熱処理時間は約５０ｈｒときわめて長い。また、得られる材料特性は、強度は高々５７９Ｎ／ｍｍ²であり、耐食性も耐層状腐食特性がランクＥＣ〜ＥＢとなる程度であり、耐ＳＣＣ応力に至っては具体的な記述すらない。また、適用される７０００系合金は遷移元素としてＺｒを含有するものと限定されている。しかも、どのようなミクロ組織にすればこのような特性が得られるかは、具体的な記述はなく皆目わからない。
【００１５】
本発明による溶体化焼入れ後の時効処理、復元処理及び再時効処理からなる３段階熱処理においては、復元処理温度を低温化し、望ましくは時効及び再時効処理温度を高温化することで、高強度と高耐食性を同時に実現するものである。
なお、７０００系アルミニウム合金の組成範囲を例示すれば、概略として、Ｚｎ：０．１〜１０ｗｔ％、Ｍｇ：０．１〜５ｗｔ％を含むとともに、Ｍｎ：０．４〜０．８ｗｔ％、Ｃｒ：０．１５〜０．３ｗｔ％、Ｚｒ：０．０５〜０．１５ｗｔ％、Ｓｃ：０．０１〜０．５ｗｔ％、及びＣｕ０．１〜３ｗｔ％よりなる群から選ばれる１種以上を含み、残部がＡｌ及び他の不純物からなるものである。また、その他必要に応じて、Ｔｉ、Ｖ、Ｈｆ等の元素を含むこともある。これらの元素は、鋳塊組織の微細化という作用を発揮するものであるが、成形性の劣化という観点から０．３ｗｔ％以下に規制される。Ｚｎ、Ｍｇ、Ｃｕは、高い強度を得るために添加される元素であり、０．１ｗｔ％未満では効果はない。また、Ｚｎ及びＭｇにおいては、添加量がそれぞれ１０ｗｔ％及び５ｗｔ％を越えると、きわめて加工性が劣化する。Ｃｕにおいては、添加量が３ｗｔ％を越えると耐食性は低下する。Ｍｎ、Ｃｒ、Ｚｒ及びＳｃは、主に均熱処理時に分散粒子として析出する。これら分散粒子のサイズ分布は、添加量と均熱条件とを組み合わせることで種々変化させることができ、これでミクロ組織を亜結晶組織、ファイバー組織、等軸組織等と製品目的に応じて変化させることができる。但し、添加量がそれぞれ０．８ｗｔ％、０．３ｗｔ％、０．１５ｗｔ％、０．５ｗｔ％を越えると成形性は大幅に低下する。また、それぞれ０．４ｗｔ％、０．１５ｗｔ％、０．０５ｗｔ％、０．０１ｗｔ％未満の添加では、上記の目的で組織制御することは困難となる。また、靱性及び疲労特性を高くするには、本出願人の出願に係る「破壊靱性、疲労特性および成形性に優れるアルミニウム合金」（特願平７−８９４０９号）のごとく、晶出物間距離及び分散粒子間距離を規制することで得られることは当然である。
【００１６】
本発明者らは特にミクロ組織と強度及び耐食性との関係を鋭意研究した結果、熱処理型７０００系合金において、導電率が３８〜４０ＩＡＣＳ％の範囲において、結晶粒界上のη相の最小間隔が２０ｎｍ以上であり且つ結晶粒内のη’相の最大サイズが２０ｎｍ以下にミクロ組織を制御すれば、高強度と高耐食性（高耐ＳＣＣ応力、高耐層状腐食特性）とを同時に実現できることが分かった。
粒界上のη相の最小間隔が２０ｎｍ未満であると、各η相が腐食環境下において連続的に溶出するため、耐ＳＣＣ応力及び耐層状腐食特性は劣る。強度にはＧＰゾーンが寄与するわけであるが、これは導電率３８〜４０ＩＡＣＳ％の範囲内において、粒内のη’相の最大サイズを２０ｎｍ以下にすることで高い強度が得られる。たとえ導電率３８〜４０ＩＡＣＳ％の範囲内においても粒内のη’相の最大サイズが２０ｎｍを越えるような時効状態では、強度に寄与すべきＧＰゾーンはη’相へと析出が進行している。このため、ＧＰゾーンの析出量が減少し、高い強度は得られない。また、このような時効状態では、一部のη’相がη相へと析出が進行しているため、ますますＧＰゾーンの析出量は減少する。一方、導電率が４０ＩＡＣＳ％を越える領域では、粒内中のη相の割合が顕著に増加する時効段階にあり、高い強度は得られない。また、導電率が３８ＩＡＣＳ％以下では、粒界上のη相は粗大化しないため、η相の間隔を大きくすることができず、このため耐食性は低下する。
【００１７】
また、これらのミクロ組織は、熱処理型７０００系アルミニウム合金において、常法に則り均熱処理及び熱間加工後必要により冷間加工を行い所定の製品サイズに調整後、常法に則り溶体化熱処理及び焼入れ後、必要に応じて冷間加工を行った後、時効処理を１００〜１４５℃で５〜５０ｈｒ望ましくは１３０〜１４５℃で５〜２０ｈｒ、復元処理を１４０〜１９５℃で０．５〜３０ｈｒ、再時効処理を１００〜１４５℃で５〜５０ｈｒ望ましくは１３０〜１４５℃で５〜２０ｈｒ行うことで容易に得られる。
【００１８】
特に、復元処理においては温度が高すぎたり、あるいは低温でも処理時間が長すぎるとＧＰゾーンの復元が進行するとともに、η相及び粗大なη’相が析出してしまい、その後の再時効処理を行っても高い強度を得ることは困難である。復元処理でη相及び粗大なη’相の析出を防止するには、１９５℃を越えると処理時間が０．５ｈｒ未満とする必要がある。また、１４０℃未満では、処理時間が３０ｈｒを越えてしまう。それぞれ工業的に実用的条件ではない。従って、復元処理条件は１４０〜１９５℃で０．５〜３０ｈｒとする。
【００１９】
時効処理においては、粒内にη相及び粗大なη’相が析出する状態にまで時効析出を進行させてはならず、そのような状態まで時効析出が進行すると、復元処理時に復元するＧＰゾーンの量が減るため、再時効処理時に最終的に析出するＧＰゾーンの量が減る。このため、十分な強度は得られない。また、逆に時効処理が不十分でＧＰゾーンが僅かに析出する場合、この状態で次の復元処理を行っても、上述したように復元処理時に復元するＧＰゾーンの量が減るため、再時効処理時に最終的に析出するＧＰゾーンが減る。このため、十分な強度は得られない。このように時効処理時には、復元処理時に復元するＧＰゾーンを十分に析出させる必要がある。
【００２０】
時効処理温度が１４５℃を越えると短時間でη相及び粗大なη’相が析出しやすくなり、その分ＧＰゾーンの量が減る。また、１００℃未満では、十分なＧＰゾーンを析出させるには５０ｈｒを越える処理時間を必要とする。従って、時効処理条件は１００〜１４５℃で５〜５０ｈｒとする。なお、時効処理を１３０〜１４５℃で高温化すると十分なＧＰゾーンが析出し易く、また、時効処理時間を短縮化できるため、工業的にも有利である。さらに、粒界上では、η相が１３０℃未満で時効処理した場合に比べ間隔を広げて析出する。時効処理後の復元処理時には、これらのη相が粗大化するわけであり、時効処理時に既にη相の間隔を広げておくことで、復元処理が終わった時点でもη相の間隔を広げる事ができる。η相の間隔を広げる事で耐食性も高くすることができる。
【００２１】
再時効処理においても、粒内にη相及び粗大なη’相が析出する状態にまで時効析出を進行させてはならず、そのような状態にまで時効析出が進行すると、当然のことながら高い強度は得られない。また、逆に時効処理が不十分でＧＰゾーンが僅かに析出する場合でも、当然のことながら、十分な強度は得られない。このため、再時効条件は、時効条件と同様に１００〜１４５℃で５〜５０ｈｒとする。なお、時効処理は溶体化処理及び焼入れ後に行うため、空孔濃度が高くＺｎ、Ｍｇ等の溶質原子が拡散し易い。一方、再時効処理は時効処理及び復元処理を行った後に行うため空孔濃度は低下しており、高い強度が得られる程にＺｎ、Ｍｇを拡散させるには、時効処理に比べて時間を要する。従って、再時効処理は、１００〜１４５℃で５〜５０ｈｒの条件中でも１３０〜１４５℃で５〜２０ｈｒで行うことがなお望ましい。
【００２２】
なお、時効処理、復元処理及び再時効処理の各条件は、製品サイズによって熱処理時間が前後することは当然であるが、要するに導電率が３８〜４０ＩＡＣＳ％の範囲において、結晶粒界上のη相の最小間隔を２０ｎｍ以上で且つ結晶粒内のη’相の最大サイズを２０ｎｍ以下に制御することが重要である。
【００２３】
本発明の高強度で耐食性に優れる熱処理型７０００系アルミニウム合金は、押出形材製品では例えば溶解鋳造にて鋳塊にした後、均質化熱処理及び熱間押出後、溶体化処理及び焼入れが行われ、その後必要に応じて行われる冷間加工（例えば、ストレッチ加工）後、時効処理を１００〜１４５℃で５〜５０ｈｒ望ましくは１３０〜１４５℃で５〜２０ｈｒ、復元処理を１４０〜１９５℃で０．５〜３０ｈｒ、再時効処理を１００〜１４５℃で５〜５０ｈｒ望ましくは１３０〜１４５℃で５〜２０ｈｒ行うことにより製造される。溶解鋳造、均質化熱処理、熱間押出、溶体化処理及び焼入れ、ストレッチ等の各製造工程での条件は常法に則り行われればよく、溶解鋳造は半連続鋳造法、連続鋳造圧延法であってもよい。
【００２４】
溶体化処理及び焼入れ条件は金属間化合物を再固溶し且つ冷却中の再析出を十分に抑制するため、特に本発明材を航空機材に適用する場合はＪＩＳ−Ｗ−１１０３、ＭＩＬ−Ｈ−６０８８Ｆに規定された条件内にて行うことが望ましい。溶体化処理及び焼入れ後の結晶粒径は熱間押出あるいは熱間圧延時の温度、加工率等の条件とその後必要に応じて行われる冷間加工での圧下率さらには溶体化処理中の昇温速度との組合せにより任意に調整できる。溶体化処理に使用される熱処理炉はバッチ炉、連続焼鈍炉、溶融塩浴炉のいずれを用いてもよいが、結晶粒径を微細にするには５℃／分以上の昇温速度で加熱することがなお望ましい。また焼入れは水浸漬、水噴射、空気噴射のいずれを用いてもよい。
溶体化処理及び焼入れ後に行われる時効処理、復元処理及び再時効処理はバッチ炉、連続焼鈍炉、熱風ファン、オイルバス、温湯浴槽等のいずれを用いてもよい。
【００２５】
なお、本発明は熱処理型７０００系アルミニウム合金展伸材に適用できるものであり板材、形材及び鍛造材を問わないことは当然のことである。
【００２６】
【実施例】
以下、実施例により本発明をさらに詳述する。
（実施例１）
Ｚｎ５．９ｗｔ％、Ｍｇ２．３ｗｔ％、Ｃｕ１．４ｗｔ％、Ｃｒ０．１９ｗｔ％、Ｆｅ０．２３ｗｔ％、Ｓｉ０．０８ｗｔ％を含み残部不純物とアルミニウムとからなるアルミニウム合金を、溶湯中水素濃度０．０２ｃｃ／１００ｍｌＡｌまで脱ガス後溶解鋳造し、φ４００ｍｍの鋳塊とした。次に４５０℃で２４ｈｒの均熱処理を施した後、φ３８０ｍｍまで面削し、４５０℃に再加熱し、ｔ２５×ｗ１２０ｍｍサイズに押し出した。これを４７５℃に加熱した塩浴炉中で４０分間溶体化処理した後水焼入れし、０．５％のストレッチ引張を行った後に、下記表１に示す時効処理、復元処理及び再時効処理からなる３段階の熱処理を行い、それぞれ供試材とした。
【００２７】
【表１】

【００２８】
続いて、この供試材につき、導電率、粒内η’相最大サイズ、粒界η相の最小間隔、強度、耐ＳＣＣ応力、耐層状腐食特性を調べた。その結果を表２に示す。なお、導電率はＪＩＳ−Ｈ０５０５の導電率測定方法に従い、強度は押出方向に採取したＪＩＳ１４Ａ号試験片を用いてＪＩＳ−Ｚ２２４１の引張試験方法に従い、耐ＳＣＣ応力はＡＳＴＭ−Ｇ４７の耐ＳＣＣ試験に従い、耐層状腐食特性はＡＳＴＭ−Ｇ３４の剥離試験に従って求めた。粒内η’相最大サイズ及び粒界η相最小間隔はＴＥＭによるミクロ組織観察の結果である。粒内η’相最大サイズは５万倍の倍率で２０視野（視野：５ｃｍ×３．５ｃｍ）以上観察し、全視野中の最大サイズを示す。また、粒界η相間隔も５万倍の倍率で２０視野以上観察し、全視野中の最小間隔を示す。
【００２９】
【表２】

【００３０】
表２よりわかるように、導電率、粒内η’相最大サイズ及び粒界η相最小間隔が本発明の規定を満たすＮｏ．１〜４は、そのいずれをも満たさないＮｏ．５，６に比べ、強度及び耐食性が向上している。粒内η’相最大サイズがより小さく、粒界η相間隔がより大きくなっているＮｏ．１〜３、なかでもＮｏ．１の強度及び耐食性が向上している。
製造法の面からみると、Ｎｏ．４の製造法のようにＮｏ．５，６に比べ復元温度を低温化することで強度及び耐食性は向上している。時効処理及び再時効処理温度を高温化したＮｏ．１〜３では、強度及び耐食性はさらに向上する。特に、Ｎｏ．１では強度と耐食性が優れ、総熱処理時間は約２３ｈｒと、Ｎｏ．５，６に比べて半減している。
【００３１】
（実施例２）
Ｚｎ５．９ｗｔ％、Ｍｇ２．３ｗｔ％、Ｃｕ２．２ｗｔ％、Ｚｒ０．１２ｗｔ％、Ｆｅ０．０９ｗｔ％、Ｓｉ０．０８ｗｔ％を含み残部不純物とアルミニウムとからなるアルミニウム合金を、溶湯中水素濃度０．０１５ｃｃ／１００ｍｌＡｌまで脱ガス後溶解鋳造し、φ４００ｍｍの鋳塊とした。次に４５０℃で２４ｈｒの均熱処理を施した後、φ３８０ｍｍまで面削し、４５０℃に再加熱し、ｔ２５×ｗ１２０ｍｍサイズに押し出した。これを４７５℃に加熱した塩浴炉中で４０分間溶体化処理した後、水焼入れし、０．５％のストレッチ引張を行った後に、下記表３に示す時効処理、復元処理及び再時効処理からなる３段階の熱処理を行い、それぞれ供試材とし、この供試材につき、実施例１と同様に導電率、粒内η’相最大サイズ、粒界η相最小間隔、強度、耐ＳＣＣ応力、耐層状腐食特性を調べた。その結果を表４に示す。
【００３２】
【表３】

【００３３】
【表４】

【００３４】
表４よりわかるように、導電率、粒内η’相最大サイズ及び粒界η相最小間隔が本発明の規定を満たすＮｏ．７〜９は、そのいずれか又はいずれをも満たさないＮｏ．１０，１１に比べ、強度及び耐食性が向上している。なかでも、粒内η’相最大サイズがより小さく、粒界η相間隔がより大きくなっているＮｏ．７，８の強度及び耐食性が向上している。
製造法の面からみると、Ｎｏ．９の製造法のようにＮｏ．１０，１１に比べ復元温度を低温化することで強度及び耐食性は向上している。さらに、時効処理及び再時効処理温度を高温化したＮｏ．７，８では、強度及び耐食性はさらに向上し、総熱処理時間は約２３ｈｒと、Ｎｏ．１０，１１に比べて半減する。
【００３５】
【発明の効果】
本発明によれば、熱処理型７０００系アルミニウム合金の強度及び耐食性をさらに高くすることができ、且つこれを工業的にも容易に製造可能となる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat treatment type 7000 series aluminum alloy suitable for use in transportation equipment such as aircraft, railway vehicles and automobiles, and general machine parts. In particular, the present invention relates to a heat treatment type 7000 series aluminum alloy having high strength and excellent corrosion resistance. It is about.
[0002]
[Prior art]
The heat treatment type 7000 series aluminum alloy is a precipitation type alloy in which high strength is obtained by artificial aging after solution hardening and is roughly divided into an Al—Zn—Mg—Cu series alloy and an Al—Zn—Mg series alloy. As typical alloys, Al—Zn—Mg—Cu based alloys are 7075 (Al-5.9Zn-2.2Mg-1.4Cu-0.2Cr) and 7050 (Al-5.9Zn-2.2Mg-2). .2Cu-0.12Zr), 7055 (Al-8.0Zn-2.2Mg-2.2Cu-0.15Zr) and 7003 (Al-5.8Zn-0.8Mg) for Al-Zn-Mg alloys. -0.15Zr).
[0003]
A typical manufacturing method is, for example, an extruded shape product, for example, it is made into an ingot such as a billet by melt casting, then homogenized, hot extruded, solution-treated with water quenching, and if necessary They are stretched by stretching, etc., heat-treated according to the purpose, and shipped before being processed into a final product by a processing manufacturer. Similarly, in the case of plate products, after ingot by melt casting, homogenized heat treatment, hot rolling, and further cold rolling as necessary, after solution treatment water quenching Cold-rolled or tensioned as necessary, heat-treated according to the purpose, shipped before being processed into a final product by a processing manufacturer.
[0004]
The highest strength can be obtained by T6 tempering in the heat treatment type 7000 series aluminum alloy. The typical tempering conditions defined by JIS-W1103 and MIL-6088F are 7075, in which after the solution treatment and quenching, heat treatment is performed at 120 ° C. for 24 hours. However, the corrosion resistance is extremely lowered. For example, in the SCC resistance test according to ASTM-G47, the SCC stress resistance (ST direction) is extremely low at 48 N / mm ² or less. In the peel test according to ASTM-G34, the layered corrosion resistance is extremely low, rank EC to ED.
[0005]
In order to increase the corrosion resistance, an overaging treatment generally referred to as T7 tempering is generally used. For example, the SCC stress becomes high at 117 to 172, 242 and 289 N / mm ^{2 in the} T76 tempering, the T74 tempering and the T73 tempering, respectively, and the layered corrosion resistance is rank EB and rank EA to P, respectively. Get higher. However, the strength is remarkably reduced, and is 15 to 30% lower than the strength in the T6 tempering. In other words, the actual situation is that the strength is both lowered to increase the corrosion resistance.
[0006]
As a heat treatment method aiming at high strength and high corrosion resistance, USP 3856584 has been proposed. This is a three-stage heat treatment after solution treatment quenching, in which an aging treatment is performed in the first stage, a restoration process is performed in the second stage, and a re-aging process is performed in the third stage. Specific heat treatment conditions are aging treatment: 120 ° C. for 24 hours (T6 tempering), restoration treatment: 200 ° C. to 260 ° C. for 7 to 120 seconds, and reaging treatment: 115 to 125 ° C. (time is arbitrary). However, as described above, the restoration time is as short as 7 to 120 seconds, so that it is very difficult to apply to thick materials. In addition, the heat treatment method at the time of restoration is limited to a bathtub-type heat treatment furnace such as an oil bath.
[0007]
A similar method is also proposed in USP 5221377. In an Al—Zn—Mg—Cu-based alloy containing Zr as a transition element, aging treatment and reaging treatment are held at 120 ° C. for 24 hours, and restoration treatment is held within a temperature range of 182 to 246 ° C. for 5 minutes or more. Is. Accordingly, the strength is 10% higher than 7 × 50-T6 and becomes 579 N / mm ² . In addition, the layered corrosion resistance is ranked EC to EB and is comparable to 7X50-T76. However, regarding the SCC resistance, it is unclear exactly what kind of microstructure can be obtained.
[0008]
As described above, in the heat treatment type 7000 series aluminum alloy, there are overaging treatments such as T76, T74, T73, etc. as a heat treatment method for improving the corrosion resistance, but the strength is remarkably lowered. Therefore, as a heat treatment method that simultaneously realizes high strength and high corrosion resistance, a three-stage heat treatment consisting of solution treatment and aging after quenching, restoration and re-aging has been proposed, but the restoration time is as short as tens of seconds, Not industrially practical. Although the heat treatment time has been extended by adjusting the restoration conditions, the layered corrosion resistance is still as low as T76 refining, and the SCC resistance is completely unknown. Furthermore, it is not known at all what microstructure is used to obtain high strength and high corrosion resistance.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described conventional problems, and has high strength and high corrosion resistance (SCC stress resistance, layered corrosion resistance characteristics) in applications such as aircraft, railway vehicles, automobiles and other transportation equipment and general machine parts. The purpose of the present invention is to provide a heat-treatable 7000 series aluminum alloy that is further enhanced in strength and corrosion resistance and that can be easily manufactured industrially. .
[0010]
[Means for Solving the Problems]
An aluminum alloy having high strength and excellent corrosion resistance according to the present invention is a heat treatment type 7000 series aluminum alloy having an electrical conductivity of 38 to 40 IACS%, a minimum interval of η phase on the crystal grain boundary of 20 nm or more, and in the crystal grains. It has a microstructure in which the maximum size of η ′ phase is 20 nm or less.
[0011]
In addition, the manufacturing method of an aluminum alloy having high strength and excellent corrosion resistance is as follows. After heat treatment type 7000 series aluminum alloy is soaked and hot-worked, cold-worked if necessary, adjusted to a predetermined product size, after solution heat treatment and quenching After performing cold working as needed, aging treatment is 5 to 50 hr at 100 to 145 ° C., restoration treatment is 0.5 to 30 hr at 140 to 195 ° C., and reaging treatment is 5 to 50 hr at 100 to 145 ° C. The heat treatment type 7000 has a microstructure in which the electrical conductivity is 38 to 40 IACS%, the minimum interval of the η phase on the crystal grain boundary is 20 nm or more, and the maximum size of the η ′ phase in the crystal grain is 20 nm or less. It is characterized by obtaining an aluminum alloy. Here, desirable conditions for the aging treatment and the re-aging treatment are treatments at 130 to 145 ° C. for 5 to 20 hours.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The heat treatment type 7000 series aluminum alloy is a precipitation hardening type alloy, and after solution treatment and quenching, for example, when artificial aging is performed at 120 ° C. for 24 hours, the GP zone is finely precipitated in the grains, so that the strength is increased. In addition, the η phase continuously precipitates on the grain boundaries. The η phase is anodic and easily eluted. For this reason, the SCC stress resistance and the layered corrosion resistance are low. On the other hand, when the heat treatment type 7000 series aluminum alloy is subjected to an overaging treatment after solution treatment and quenching, precipitation in the intra-granular GP zone progresses to the η ′ phase, and the strength decreases. At this time, the size distribution of the η ′ phase shifts to the coarse side. However, since the η phase on the grain boundary becomes coarse and discontinuous, corrosion resistance such as SCC stress resistance and layered corrosion resistance is increased.
[0013]
In the three-stage heat treatment method consisting of aging treatment, solution treatment and re-aging treatment after solution hardening for the purpose of realizing high strength and high corrosion resistance at the same time, it is high by increasing the proportion of GP zone in the grain as much as possible. It is intended to achieve high corrosion resistance by increasing the strength and on the grain boundaries by increasing the interval of the η phase. The changes in the microstructure during the three-stage heat treatment are as follows. That is, the intra-granular GP zone produced by the aging treatment after the solution hardening and quenching is re-solidified by the restoration treatment, but the GP zone is precipitated again by the subsequent re-aging treatment. On the other hand, on the grain boundary, the η phase generated by the aging treatment is coarsened by the restoration treatment and becomes discontinuous because the interval is widened. Subsequent reaging treatment hardly changes.
[0014]
In US Pat. No. 3,856,584, the processing time is shortened to several tens of seconds by increasing the restoration temperature, but the heat treatment time is too short, making it difficult to industrialize. Moreover, even when an oil bath suitable for the product size can be prepared, the heating rate is slow with a thick material, and it is impossible to complete the restoration process in such a short time.
On the other hand, in USP 5221377, the restoration processing temperature is 182 to 246 ° C., which is lower than the temperature range of 200 to 260 ° C. in US Pat. No. 3,856,584, thereby increasing the processing time. However, the aging treatment and the re-aging treatment before and after the restoration treatment are each 24 hours at 120 ° C. Therefore, the total heat treatment time required for the three-step heat treatment is as long as about 50 hours. Further, the material properties obtained are as strong as 579 N / mm ² and the corrosion resistance is such that the layered corrosion resistance is rank EC to EB, and the SCC stress resistance is not specifically described. The applied 7000 series alloy is limited to contain Zr as a transition element. Moreover, there is no specific description of what kind of microstructure can be used to obtain such characteristics, and it is difficult to see.
[0015]
In the three-stage heat treatment consisting of aging treatment, solution treatment and reaging treatment after solution hardening according to the present invention, it is possible to reduce the restoration treatment temperature, preferably by raising the aging treatment temperature and the reaging treatment temperature, thereby increasing the strength. High corrosion resistance is realized at the same time.
As an example, the composition range of the 7000 series aluminum alloy includes Zn: 0.1 to 10 wt%, Mg: 0.1 to 5 wt%, Mn: 0.4 to 0.8 wt%, Cr : One or more selected from the group consisting of 0.15 to 0.3 wt%, Zr: 0.05 to 0.15 wt%, Sc: 0.01 to 0.5 wt%, and Cu 0.1 to 3 wt% The balance is made of Al and other impurities. In addition, elements such as Ti, V, and Hf may be included as necessary. These elements exhibit the effect of refining the ingot structure, but are restricted to 0.3 wt% or less from the viewpoint of deterioration of formability. Zn, Mg, and Cu are elements added to obtain high strength, and there is no effect at less than 0.1 wt%. In addition, when Zn and Mg are added in amounts exceeding 10 wt% and 5 wt%, respectively, the workability is extremely deteriorated. In Cu, when the addition amount exceeds 3 wt%, the corrosion resistance decreases. Mn, Cr, Zr and Sc are precipitated as dispersed particles mainly during soaking. The size distribution of these dispersed particles can be changed in various ways by combining the addition amount and the soaking condition, and this changes the microstructure according to the purpose of the product, such as subcrystalline structure, fiber structure, equiaxed structure, etc. be able to. However, if the added amount exceeds 0.8 wt%, 0.3 wt%, 0.15 wt%, and 0.5 wt%, respectively, the moldability is significantly reduced. In addition, when the addition is less than 0.4 wt%, 0.15 wt%, 0.05 wt%, and 0.01 wt%, respectively, it is difficult to control the structure for the above purpose. Further, in order to increase the toughness and fatigue characteristics, the distance between crystallized substances as described in “aluminum alloy excellent in fracture toughness, fatigue characteristics and formability” (Japanese Patent Application No. 7-89409) according to the applicant's application. Naturally, it can be obtained by regulating the distance between dispersed particles.
[0016]
As a result of intensive studies on the relationship between the microstructure and the strength and corrosion resistance, the present inventors have found that the minimum spacing of the η phase on the grain boundary is within the range of 38 to 40 IACS% in the heat treatment type 7000 series alloy. It is understood that high strength and high corrosion resistance (high SCC stress, high layered corrosion resistance) can be realized at the same time if the microstructure is controlled to 20 nm or more and the maximum size of the η ′ phase in the crystal grains is 20 nm or less. It was.
When the minimum interval of the η phase on the grain boundary is less than 20 nm, each η phase elutes continuously in a corrosive environment, so that the SCC stress resistance and the layered corrosion resistance are inferior. The GP zone contributes to the strength. This can be achieved by setting the maximum size of the η ′ phase in the grains to 20 nm or less within the range of the conductivity of 38 to 40 IACS%. Even in the range of electrical conductivity of 38 to 40 IACS%, in the aging state where the maximum size of the η ′ phase in the grains exceeds 20 nm, the GP zone that should contribute to the strength has progressed to the η ′ phase. . For this reason, the precipitation amount of the GP zone decreases, and high strength cannot be obtained. Further, in such an aging state, the precipitation of the GP zone is further reduced because some of the η ′ phase has progressed to the η phase. On the other hand, in the region where the conductivity exceeds 40 IACS%, the ratio of the η phase in the grains is in an aging stage where the strength is remarkably increased, and high strength cannot be obtained. On the other hand, when the conductivity is 38 IACS% or less, the η phase on the grain boundary is not coarsened, so that the interval between the η phases cannot be increased, and the corrosion resistance is lowered.
[0017]
In addition, these microstructures are heat treated 7000 series aluminum alloy, soaking heat treatment and hot working according to conventional methods, cold processing if necessary and adjusting to a predetermined product size, solution heat treatment and After quenching, after cold working as necessary, the aging treatment is 100 to 145 ° C. for 5 to 50 hours, preferably 130 to 145 ° C. for 5 to 20 hours, and the restoration treatment is 140 to 195 ° C. for 0.5 to 30 hours. It can be easily obtained by performing the re-aging treatment at 100 to 145 ° C. for 5 to 50 hours, desirably 130 to 145 ° C. for 5 to 20 hours.
[0018]
In particular, in the restoration process, if the temperature is too high or the treatment time is too long even at a low temperature, the restoration of the GP zone proceeds, and the η phase and the coarse η ′ phase precipitate, and the subsequent re-aging treatment is performed. Even if it goes, it is difficult to obtain high strength. In order to prevent the precipitation of the η phase and the coarse η ′ phase by the restoration treatment, the treatment time needs to be less than 0.5 hr when the temperature exceeds 195 ° C. Moreover, if it is less than 140 degreeC, processing time will exceed 30 hr. These are not industrially practical conditions. Therefore, the restoration processing condition is 140 to 195 ° C. and 0.5 to 30 hours.
[0019]
In the aging treatment, the aging precipitation must not proceed to a state in which the η phase and the coarse η ′ phase are precipitated in the grains, and when the aging precipitation proceeds to such a state, the GP zone is restored during the restoration treatment. Therefore, the amount of GP zone that is finally precipitated during the re-aging treatment is reduced. For this reason, sufficient strength cannot be obtained. On the other hand, when the aging treatment is insufficient and the GP zone is slightly precipitated, even if the next restoration process is performed in this state, the amount of the GP zone restored during the restoration process is reduced as described above. The GP zone finally deposited during processing is reduced. For this reason, sufficient strength cannot be obtained. Thus, at the time of aging treatment, it is necessary to sufficiently precipitate the GP zone to be restored at the time of restoration processing.
[0020]
When the aging temperature exceeds 145 ° C., the η phase and the coarse η ′ phase are likely to precipitate in a short time, and the amount of the GP zone is reduced accordingly. If the temperature is less than 100 ° C., a treatment time exceeding 50 hr is required to deposit a sufficient GP zone. Accordingly, the aging treatment condition is 100 to 145 ° C. and 5 to 50 hours. When the aging treatment is performed at a temperature of 130 to 145 ° C., a sufficient GP zone is likely to precipitate, and the aging treatment time can be shortened, which is industrially advantageous. Furthermore, on the grain boundary, the η phase precipitates at a wider interval than when aging is performed at a temperature lower than 130 ° C. During the restoration process after the aging treatment, these η phases are coarsened. By increasing the interval between the η phases during the aging treatment, the interval between the η phases can be increased even after the restoration process is completed. it can. Corrosion resistance can be increased by increasing the interval of the η phase.
[0021]
Even in the re-aging treatment, aging precipitation must not proceed to a state where the η phase and coarse η ′ phase are precipitated in the grains, and naturally, when aging precipitation proceeds to such a state, it is naturally high. Strength cannot be obtained. On the contrary, even when the aging treatment is insufficient and the GP zone is slightly precipitated, it is a matter of course that sufficient strength cannot be obtained. For this reason, re-aging conditions shall be 5-50 hr at 100-145 degreeC similarly to aging conditions. Since the aging treatment is performed after the solution treatment and quenching, the vacancy concentration is high and solute atoms such as Zn and Mg are likely to diffuse. On the other hand, since the re-aging treatment is performed after the aging treatment and the restoration treatment, the vacancy concentration is lowered, and it takes more time to diffuse Zn and Mg to obtain a high strength compared to the aging treatment. . Therefore, it is more desirable that the re-aging treatment is performed at 130 to 145 ° C. for 5 to 20 hours even at 100 to 145 ° C. for 5 to 50 hours.
[0022]
In addition, as for each condition of an aging treatment, a restoration process, and a re-aging treatment, it is natural that the heat treatment time varies depending on the product size, but in short, the η phase on the grain boundary is in the range of conductivity of 38 to 40 IACS%. It is important to control the minimum spacing of 20 nm or more and the maximum size of the η ′ phase in the crystal grains to 20 nm or less.
[0023]
The heat treatment type 7000 series aluminum alloy of the present invention having high strength and excellent corrosion resistance is formed into an ingot by, for example, melt casting in an extruded shape product, and then subjected to solution treatment and quenching after homogenization heat treatment and hot extrusion. Then, after cold processing (for example, stretch processing) performed as necessary, aging treatment is performed at 100 to 145 ° C. for 5 to 50 hours, preferably 130 to 145 ° C. for 5 to 20 hours, and restoration treatment is performed at 140 to 195 ° C. 5 to 30 hours, and re-aging treatment is performed at 100 to 145 ° C. for 5 to 50 hours, preferably 130 to 145 ° C. for 5 to 20 hours. Conditions in each manufacturing process such as melt casting, homogenization heat treatment, hot extrusion, solution treatment and quenching, stretching, etc. may be performed in accordance with conventional methods, and melt casting is a semi-continuous casting method or a continuous casting rolling method. May be.
[0024]
The solution treatment and quenching conditions are to re-dissolve the intermetallic compound and sufficiently suppress reprecipitation during cooling. Therefore, particularly when the present invention material is applied to aircraft materials, JIS-W-1103, MIL-H- It is desirable to carry out within the conditions specified in 6088F. The crystal grain size after solution treatment and quenching depends on conditions such as the temperature during hot extrusion or hot rolling, the processing rate, and the reduction rate in the cold processing performed as necessary, and further the rise during the solution treatment. It can be arbitrarily adjusted by the combination with the temperature rate. The heat treatment furnace used for the solution treatment may be any of a batch furnace, a continuous annealing furnace, and a molten salt bath furnace. In order to make the crystal grain size fine, heating is performed at a heating rate of 5 ° C./min or more. It is still desirable to do. Moreover, quenching may use any of water immersion, water injection, and air injection.
Any of a batch furnace, a continuous annealing furnace, a hot air fan, an oil bath, a hot water bath, etc. may be used for the aging treatment, the restoration treatment, and the reaging treatment performed after the solution treatment and quenching.
[0025]
In addition, this invention is applicable to heat processing type | mold 7000 type | system | group aluminum alloy extended material, and naturally, it does not ask | require a board | plate material, a shape material, and a forging material.
[0026]
【Example】
Hereinafter, the present invention will be described in more detail by way of examples.
Example 1
An aluminum alloy containing Zn 5.9 wt%, Mg 2.3 wt%, Cu 1.4 wt%, Cr 0.19 wt%, Fe 0.23 wt%, Si 0.08 wt% and the remaining impurities and aluminum is used. After degassing to 100 ml Al, melt casting was performed to obtain an ingot of φ400 mm. Next, after soaking at 450 ° C. for 24 hours, it was chamfered to φ380 mm, reheated to 450 ° C., and extruded to a size of t25 × w120 mm. This was subjected to a solution treatment for 40 minutes in a salt bath furnace heated to 475 ° C., then quenched in water and stretched to 0.5%, and then from the aging treatment, restoration treatment and reaging treatment shown in Table 1 below. The following three stages of heat treatment were performed, and each was used as a test material.
[0027]
[ Table 1 ]

[0028]
Subsequently, the electrical conductivity, the maximum size of intragranular η ′ phase, the minimum interval of grain boundary η phase, the strength, the SCC stress resistance, and the layered corrosion resistance were examined for this test material. The results are shown in Table 2. The electrical conductivity is in accordance with the electrical conductivity measurement method of JIS-H0505, the strength is in accordance with the tensile test method in JIS-Z2241 using a JIS14A test piece taken in the extrusion direction, and the SCC stress resistance is in accordance with the SCC resistance test in ASTM-G47. The layered corrosion resistance was determined according to the peel test of ASTM-G34. The maximum size of the intragranular η ′ phase and the minimum interval of the grain boundary η phase are the results of microstructure observation by TEM. The maximum size of the intragranular η ′ phase is observed over 20 fields of view (field of view: 5 cm × 3.5 cm) at a magnification of 50,000 times, and indicates the maximum size in the entire field of view. In addition, the grain boundary η phase interval is also observed at 20 times or more at a magnification of 50,000 times, and indicates the minimum interval in the entire visual field.
[0029]
[ Table 2 ]

[0030]
As can be seen from Table 2, the electrical conductivity, the maximum size of the intragranular η ′ phase and the minimum interval of the grain boundary η phase satisfy No. 1 of the present invention . Nos. 1 to 4 satisfy No. 1 . Compared with 5 and 6 , strength and corrosion resistance are improved. No. 1 in which the maximum size of intragranular η ′ phase is smaller and the intergranular η phase interval is larger . 1 to 3 , especially No. 1 has improved strength and corrosion resistance.
From the viewpoint of manufacturing method, no . No. 4 like the manufacturing method No. 4 The strength and corrosion resistance are improved by lowering the restoration temperature compared to 5 and 6 . No. with increased aging treatment and re-aging treatment temperature . In 1-3 , intensity | strength and corrosion resistance further improve. In particular, no . No. 1 is excellent in strength and corrosion resistance, and the total heat treatment time is about 23 hr . Compared to 5 and 6 , it is halved.
[0031]
(Example 2)
An aluminum alloy containing Zn 5.9 wt%, Mg 2.3 wt%, Cu 2.2 wt%, Zr 0.12 wt%, Fe 0.09 wt%, Si 0.08 wt% and the balance of impurities and aluminum is used. After degassing to 100 ml Al, melt casting was performed to obtain an ingot of φ400 mm. Next, after soaking at 450 ° C. for 24 hours, it was chamfered to φ380 mm, reheated to 450 ° C., and extruded to a size of t25 × w120 mm. This was subjected to a solution treatment for 40 minutes in a salt bath furnace heated to 475 ° C., then water-quenched and 0.5% stretch tensioned, followed by aging treatment, restoration treatment and reaging treatment shown in Table 3 below. As in Example 1, the conductivity, the intra-granular η ′ phase maximum size, the grain boundary η phase minimum spacing, the strength, and the SCC stress resistance were obtained. The layered corrosion resistance was investigated. The results are shown in Table 4.
[0032]
[ Table 3 ]

[0033]
[ Table 4 ]

[0034]
As can be seen from Table 4, the electrical conductivity, the maximum size of intragranular η ′ phase and the minimum interval of grain boundary η phase satisfy the provisions of the present invention . Nos. 7 to 9 satisfy No. 1 or No. Compared with 10 and 11 , the strength and corrosion resistance are improved. Among them, No. 1 in which the maximum size of the intragranular η ′ phase is smaller and the intergranular η phase interval is larger . The strength and corrosion resistance of 7 , 8 are improved.
From the viewpoint of manufacturing method, no . No. 9 like the production method No. 9 Compared to 10 and 11 , the strength and corrosion resistance are improved by lowering the restoration temperature. Furthermore, No. 1 in which the aging treatment and the reaging treatment temperature were increased . 7 and 8 , the strength and corrosion resistance were further improved, and the total heat treatment time was about 23 hr . Compared to 10 and 11 , it is halved.
[0035]
【The invention's effect】
According to the present invention, the strength and corrosion resistance of the heat treatment type 7000 series aluminum alloy can be further increased, and this can be easily manufactured industrially.

Claims

Heat treatment type 7000 series aluminum alloy having a conductivity of 39 to 40 IACS%, a minimum interval of η phase on grain boundaries of 20 nm or more, and a maximum size of η ′ phase in crystal grains of 20 nm or less An aluminum alloy having high strength and excellent corrosion resistance.

After heat treatment type 7000 series aluminum alloy is soaked and hot-worked, cold-worked if necessary, adjusted to the prescribed product size, after solution heat treatment and quenching, cold-worked as needed, and then subjected to aging treatment Conductivity is set to 38 to 40 IACS% by performing 5 to 20 hr at 130 to 145 ° C., 0.5 to 30 hr at 140 to 195 ° C. and 5 to 20 hr at re-aging treatment at 130 to 145 ° C. A high-strength and corrosion-resistant aluminum alloy having a microstructure in which the minimum interval of η phase on the boundary is 20 nm or more and the maximum size of η ′ phase in crystal grains is 20 nm or less is obtained. An excellent method for producing an aluminum alloy.