JP3681822B2 - Al-Zn-Mg alloy extruded material and method for producing the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、焼鈍材（０材）で加工性に優れ、溶体化時効硬化処理材（Ｔ６材）で靱性と耐応力腐食割れ性に優れたＡｌ−Ｚｎ−Ｍｇ系合金押出材とその製造方法に関するものであり、さらに詳しくは自動車用の成形部材例えばバンパー、二輪用のメインフレーム、スイングアーム等、切削及び鍛造等による電気、機械部品に使用されるＡｌ−Ｚｎ−Ｍｇ系合金押出材（押出形材、押出棒材）とその製造方法に関するものである。
【０００２】
【従来の技術】
近年押出形材は、産業界のニーズから複雑な断面形状で中空を有し、曲げ、スウェ−ジング、拡管、バルジ加工等の成形加工（塑性加工）を施すのが主流となっている。
押出棒についても切削、冷間鍛造加工等の２次加工を行って所定の形状とした後、熱処理即ち溶体化処理後時効硬化処理（このように処理した材料を以下Ｔ６材という）を施す。
よって、Ａｌ合金素材に要求される特性は、押出材が種々の加工性に優れることであり、このため押出後焼鈍処理をして軟化した材料（以下０材という）とする必要がある。しかし、熱処理型合金であるＡｌ−Ｚｎ−Ｍｇ系の従来合金では、軟化させた押出材に塑性加工を施した後にＴ６処理を行うと、その断面の全面もしくは大部分に再結晶を生じ、押出材表層部にオレンジピール等の欠陥を生じると共に、応力腐食割れを生じるため、塑性加工後のＴ６処理は行わないのが一般的であり、成形加工後にＴ６処理して強度と靱性に優れ、かつ応力腐食割れ性に優れた材料を得ることができなかった。
【０００３】
【発明が解決しようとする課題】
本発明の課題は、前記の問題を解決することであり、具体的にはＡｌ−Ｚｎ−Ｍｇ系合金押出材の０材での各種の塑性加工（曲げ、スウェ−ジング、バルジ、据込加工等）性を改善し、又このような加工材のＴ６処理材の強度と靱性、金属組織及び耐応力腐食割れ性を改善したＡｌ−Ｚｎ−Ｍｇ系合金押出材とその製造方法を見出すことである。
【０００４】
【課題を解決するための手段】
本発明は、前記の状況に鑑み鋭意検討の結果、合金成分と押出後の０材焼鈍処理条件の検討により加工性を改善し、さらに加工後のＴ６処理条件の検討によりＴ６処理後の押出材の強度と靱性、組織、耐応力腐食割れ性を改善したものである。
即ち、前記課題を解決するための請求項１の発明は、Ｚｎ４．００〜６．５０ｗｔ％、Ｍｇ０．５０〜１．５０ｗｔ％、Ｃｕ０．１０〜０．５０ｗｔ％、Ｚｒ０．１０〜０．５０ｗｔ％、Ｍｎ０．０５〜０．２０ｗｔ％、Ｃｒ０．０５〜０．２０ｗｔ％を含み、残部がＡｌと不可避的不純物とからなるＡｌ合金押出材の成形加工材であって、Ｔ６処理されており、材料の伸び／引張強さの比が０．０３０以上で、かつ断面組織がすべて繊維状組織か又は再結晶組織が表層部深さ３００μｍ以下とした靱性と耐応力腐食割れ性に優れることを特徴とするＡｌ−Ｚｎ−Ｍｇ系合金押出材である。
【０００５】
請求項２の発明は、Ｚｎ４．００〜６．５０ｗｔ％、Ｍｇ０．５０〜１．５０ｗｔ％、Ｃｕ０．１０〜０．５０ｗｔ％、Ｚｒ０．１０〜０．５０ｗｔ％、Ｍｎ０．０５〜０．２０ｗｔ％、Ｃｒ０．０５〜０．２０ｗｔ％を含み、残部がＡｌと不可避的不純物とからなるＡｌ合金鋳塊を、４２０〜５２０℃の温度で２〜２４時間の均質化熱処理をした後、４３０〜５２０℃の温度で押出加工を行い、次にこれを３６０〜４２０℃の温度で焼鈍処理を行い、これを３０℃／hr以下の冷却速度で室温まで冷却して成形加工性に優れた材料とすることを特徴とするＡｌ−Ｚｎ−Ｍｇ系合金押出材の製造方法である。
【０００６】
請求項３の発明は、Ｚｎ４．００〜６．５０ｗｔ％、Ｍｇ０．５０〜１．５０ｗｔ％、Ｃｕ０．１０〜０．５０ｗｔ％、Ｚｒ０．１０〜０．５０ｗｔ％、Ｍｎ０．０５〜０．２０ｗｔ％、Ｃｒ０．０５〜０．２０ｗｔ％を含み、残部がＡｌと不可避的不純物とからなるＡｌ合金鋳塊を、４２０〜５２０℃の温度で２〜２４時間の均質化熱処理をした後、４３０〜５２０℃の温度で押出加工を行い、次にこれを３６０〜４２０℃の温度で焼鈍処理を行い、これを３０℃／hr以下の冷却速度で室温まで冷却した後、これに成形加工を施こし、続いてこれを４００〜５００℃の温度で溶体化処理を行い、これを５０℃／hr以上の冷却速度で室温まで冷却した後、９０〜１１０℃の温度で２〜１２時間の一段目の時効処理、さらに１２０〜１８０℃の温度で５〜２４時間二段目の時効処理を施して、材料の伸び／引張強さの比が０．０３０以上で、かつ断面組織がすべて繊維状組織か又は再結晶組織が表層部深さ３００μｍ以下として靱性と耐応力腐食割れ性に優れた材料とすることを特徴とするＡｌ−Ｚｎ−Ｍｇ系合金押出材の製造方法である。
【０００７】
【発明の実施の形態】
以下、本発明を詳細に説明する。
まず、請求項１の発明は、Ａｌ−Ｚｎ−Ｍｇ系合金押出材であるが、詳細は前記のごとく所定のＡｌ−Ｚｎ−Ｍｇ系合金押出材に成形加工を施し、これにＴ６処理を施した状態の材料である。
まず、本発明に係わるＡｌ−Ｚｎ−Ｍｇ系合金押出材の合金組成の限定理由について説明する。
Ｚｎは、機械的性質を向上させる効果がある。その添加量が４．００ｗｔ％未満では効果がなく、一方６．５０ｗｔ％を越えて添加すると耐応力腐食割れ性（以下耐ＳＣＣ性ともいう）、成形性及び押出加工性が劣化し、生産性も低下する。従って本発明ではＺｎの添加量を４．００〜６．５０ｗｔ％と限定した。
Ｍｇは、機械的性質を向上させる元素であるが、その添加量が０．５０ｗｔ％未満ではその効果が少なく、一方１．５０ｗｔ％を越えて添加すると耐応力腐食割れ性、成形性及び押出加工性が劣化し、生産性も低下する。従って本発明ではＭｇの添加量を０．５０〜１．５０ｗｔ％と限定した。
【０００８】
Ｃｕは、機械的性質を向上させるとともに、耐応力腐食割れ性を向上させる効果がある。その添加量が０．１０ｗｔ％未満ではその効果がなく、一方０．５０ｗｔ％を越えて添加すると耐食性に害を及ぼす。従って本発明ではＣｕ添加量を０．１０〜０．５０ｗｔ％と限定した。
Ｚｒは、合金中の再結晶粒の粗大化を抑制し、結晶粒を繊維状組織として組織の安定化を図ると共に曲げ加工、スウェ−ジング加工等の成形性を改善する効果がある。その添加量が０．１０ｗｔ％未満ではその効果が少なく、一方０．５０ｗｔ％を越えて添加すると粗大なＡｌ−Ｚｒ系金属間化合物が生成して靱性等を劣化させる。従って本発明ではＺｒの添加量を０．１０〜０．５０ｗｔ％と限定した。
【０００９】
ＭｎおよびＣｒは、その共存状態でアルミニウム素地中に微細に分散した繊維状組織の再結晶化を防止して組織を安定化し、曲げ加工、スウェ−ジング加工等の成形加工後の押出材の表面にオレンジピール状の肌荒れが発生することを防ぐ効果がある。その添加量がそれぞれ０．０５ｗｔ％未満ではその効果が少なく、逆にそれぞれ０．２０ｗｔ％を越えて添加するとその効果が飽和する一方で粗大な金属間化合物を生成したり、焼き入れ感受性が増大したりするほかに、強度及び押出加工性にも悪影響を及ぼす。従って本発明ではＭｎおよびＣｒの添加量をそれぞれ０．０５〜０．２０ｗｔ％と限定した。
また、Ｔｉ、Ｎｉ、Ｂ等の不純物についてはそれぞれが０．０５ｗｔ％以下、であれば本発明の効果に悪影響を及ぼさないので含有しても差し支えない。
【００１０】
次に、本材料は、焼鈍した材料について曲げ、スウェ−ジング等の成形加工を施し、更にＴ６処理を施した材料であるが、材料の伸び／引張強さの比が０．０３０以上と限定したのは、本材料は自動車用の成形部材例えばバンパー、二輪用のメインフレーム、スイングアーム等の構造部材を目的とするものであり、製品の性質上材料にねばり強さ、即ち靱性が必要であるからである。本発明においては、材料の伸び／引張強さの比をこの靱性特性の目安とした。
また、本発明において、材料の断面組織がすべて繊維状組織か又は再結晶組織が表層部深さ３００μｍ以下と限定したのは、前記の靱性特性と耐応力腐食割れ性を改善するためである。
なお、再結晶組織が表層部の深さ３００μ以下の場合は、後の表面加工（バフによる加工、ショットによる加工等）により除去できるので、最終製品では問題ない。
【００１１】
請求項２の発明は、成形加工性に優れたＡｌ−Ｚｎ−Ｍｇ系合金押出材の製造方法に関するものである。
前述のごとく、押出材は曲げ、スウェ−ジング等の成形加工が施されるが、本発明においては、特に熱間押出材の焼鈍後の冷却において、その冷却速度を非常に遅くすることにより、成形加工性を改善したものである。
また、請求項３の発明は、前記の成形加工後に、Ｔ６処理を施すもので、請求項１の発明に係わるＡｌ−Ｚｎ−Ｍｇ系合金押出材の製造方法に関するものである。
【００１２】
ところで、Ａｌ−Ｚｎ−Ｍｇ系合金押出材は一般に、均質化熱処理した鋳塊を熱間押出加工でプレス焼入れ又は別途溶体化処理をし、その後、人工時効処理する方法と熱間押出加工後に焼鈍処理をし、塑性加工を行った後、Ｔ６処理を施す方法で製造される。
本発明の製造方法は、本発明に係わるＡｌ合金を用いて、後者の製造の各段階での温度条件や処理時間条件を限定することにより、目的を達成するものである。
【００１３】
以下、請求項２及び３の製造方法の発明における各段階の製造条件について、詳細に説明する。
まず、本発明に係わるＡｌ合金鋳塊に均質化熱処理を施す。
均質化熱処理はＺｒ、Ｍｎ、Ｃｒ等の化合物を微細均一に分散させるために比較的高温で行う。ただし５２０℃を越える温度や２４時間を越えて処理すると、押出後の断面表層の再結晶を促進し、又は析出物が粗大化して押出性、焼入感受性等の特性が悪化する。一方、４２０℃未満や２時間未満の処理では均質化が不充分である。従って本発明において、均質化熱処理は４２０〜５２０℃×２〜２４時間の条件で行う。
【００１４】
次に鋳塊を押出温度まで再加熱して熱間押出加工を行う。
押出温度については、押出加工が困難な押出比の大きい薄肉の中空形材も加工できるように４３０〜５２０℃の高温で行う。従来の合金をこのような高温で押出加工すると、再結晶が進行し、粗大な再結晶粒が生成するため耐応力腐食割れ性が著しく低下し、また粗大な金属間化合物が生成するため、押出加工性、成形性、耐食性等が悪化する。しかしながら本発明に係わる組成の合金においては、Ｚｒ添加で再結晶粒のない繊維状組織とすること、ＭｎとＣｒを微細に分散させることにより再結晶の進行を抑制し、さらにＣｕ添加で耐ＳＣＣ性を大幅に向上させることにより、高温での押出加工を可能としている。
なお、押出温度が４３０℃未満では中空形材の押出が困難であり、５２０℃を越えると押出後の断面表層の再結晶を促進し、又は析出物が粗大化して押出性、焼入感受性等の特性が悪化する。従って押出温度は４３０〜５２０℃とする。
【００１５】
次に押出材に焼鈍処理を行う。
焼鈍処理は、固溶中の溶質元素を粗大に析出させると共に粗大な金属間化合物の生成による機械的性質及び硬度の低下により、焼鈍処理後の曲げ、スウェ−ジング、バルジ、据込み加工等の塑性加工が可能となる。ただし４２０℃を越える温度で焼鈍処理すると、再結晶を誘発すると共に焼入感受性が鈍感なために強度アップを促す。一方、３６０℃未満では焼鈍処理が不充分となる。
なお、焼鈍処理後の室温までの冷却は、冷却速度を３０℃／hr以下に抑える必要がある。なぜなら、冷却速度が３０℃／hrを越えると焼入感受性が鈍感なために充分な０材硬度を得るのが難しい。よって焼鈍処理条件は、３６０〜４２０℃の温度で焼鈍し、３０℃／hr以下の冷却速度で冷却する必要がある。
【００１６】
次に焼鈍処理後は、曲げ、スウェ−ジング、バルジ、据込み加工等の塑性加工を行う。塑性加工後は、通常の熱処理型合金のようにＴ６処理（溶体化処理と人工時効処理）を行い、機械的性質をアップする必要がある。
溶体化処理は、溶質元素をアルミニウム素地に充分に固溶させた過飽和固溶体を形成する必要がある。ただし、溶体化処理温度が５００℃を越えると共晶溶融（バーニング）を生じて、金属組織に欠陥を生じると共に機械的性質が低下する。一方、４００℃未満では溶体化が不充分である。なお、溶体化処理後の冷却速度は５０℃／hr以上で行う必要がある。なぜなら、５０℃／hr未満で冷却すると強度を付与するための充分な過飽和固溶体が得られず、さらに、押出材の全断面が再結晶するか又は表層部に粗大な再結晶を生じる。よって溶体化処理条件は４００〜５００℃の温度で行い、溶体化処理の冷却は５０℃／hr以上の冷却速度で行う必要がある。
【００１７】
次に、これらの材料は人工時効硬化処理を行う。
この人工時効処理は、溶体化処理で得られた過飽和固溶体を低温で加熱処理することにより析出物を微細に析出させるものである。
具体的には二段時効とし、一段目の時効でＭｇＺｎ2 の微細析出物を均一に分散させ、二段目の高温時効で粗大なＧＰゾーンあるいは中間相へと成長させる。一段目の人工時効は、析出物の粗大化を防ぎつつ、微細な析出物を十分に均一に分散析出させるために、９０〜１１０℃で２〜１２時間の条件で行う。
二段目の時効処理は、一段目より高温で行うが、１８０℃を越える温度で処理を行うとＭｇＺｎ2 が粗大に析出し、成形性、耐食性が劣化する。一方、１２０℃未満の温度で処理を行うとＧＰゾーンあるいは中間相への成長が不充分となり、強度が不足する。さらに生産性を考慮して、本発明においては二段目の時効処理は１２０〜１８０℃で５〜２４時間の条件で行う。
【００１８】
以上説明したように、本発明の製造方法によるＡｌ−Ｚｎ−Ｍｇ系合金押出材は、焼鈍処理後に塑性加工（曲げ、スウェ−ジング、バルジ、据込み加工等）を行い、続いてＴ６処理を施しても、材料の断面組織がすべて繊維状組織か又は
再結晶組織を表層部の深さ３００μ以下とすることができる。
なお、再結晶組織が表層部の深さ３００μ以下の場合は、後の表面加工（バフによる加工、ショットによる加工等）により除去できるので、最終製品では問題ない。
また、このような材料は、強度、靱性に優れ、耐応力腐食割れ性にも優れている。
【００１９】
【実施例】
次に本発明の実施例（本発明例）を、比較例、従来例と比較しながら、更に詳細に説明する。
表１に示す組成の本発明例（Ｎｏ．１〜４）、比較例（Ｎｏ．５〜７）、従来例（Ｎｏ．８〜１０）の合金をＤＣ鋳造によりφ２１９ｍｍの押出用鋳塊に鋳造し、均質化熱処理をそれぞれ表１に示す条件で行った。その後、表１に示す押出温度までそれぞれ再加熱し、中空形材（断面：巾６０ｍｍ×高さ６０ｍｍ×肉厚３．０ｍｍ）及びφ２０ｍｍの押出棒に押出加工した。押出後、表１に示す焼鈍処理条件で焼鈍し、その後表１に示す冷却速度で室温まで冷却して焼鈍材（０材）を作製した。焼鈍処理後の０材形材のみ、角管スウェ−ジングにより断面が巾４０ｍｍ×高さ４０ｍｍ×肉厚２．５ｍｍの角管に塑性加工した後、表１に示す溶体化処理条件（処理後の冷却速度を考慮）で、溶体化処理を行った。溶体化処理後は、表１に示す２段の人工時効処理を施して供試材を作製した。
【００２０】
【表１】
これらの供試材について、０材については機械的性質、スウェ−ジング加工性、据込加工性を評価し、Ｔ６材については機械的性質、金属組織、耐応力腐食割れ試験（塩水噴霧試験及びクロム酸促進試験）を評価した。
０材及びＴ６材の機械的性質は、ＪＩＳ５号引張試験片を押出長手方向から採取し、引張試験を行い、引張強さ、耐力、伸びにより評価した。
更にＴ６材については、伸び／引張強さの比を求めた。この値の高いものは材料にねばり強さがあり、靱性の有無の目安とした。
スウェ−ジング加工は、前述の通りに中空形材（断面が巾６０ｍｍ×高さ６０ｍｍ×肉厚３．０ｍｍの角管）から断面が巾４０ｍｍ×高さ４０ｍｍ×肉厚２．５ｍｍの角管に塑性加工を施し、加工後の表面状態を目視観察して評価した。
据込加工は、０材押出棒を使用し、φ２０ｍｍ×高さ５０ｍｍのブランクについて、冷間で据込加工して、割れ限界までの高さ方向の減少率を示した。
Ｔ６後の金属組織は、前記の角管のスウェ−ジング加工後にＴ６処理を施した材料について、表層部の断面ミクロ組織を観察した。
耐応力腐食割れ試験は、塩水噴霧試験及びクロム酸促進試験の２種類の試験で評価した。 塩水噴霧試験は、３．５％ＮａＣｌ溶液中に３点曲げ（耐力の９５％）で応力を負荷して１か月放置後に割れの有無を観察した。
クロム酸促進試験は、クロム酸沸騰溶液中に３点曲げ（耐力の９５％）で応力を負荷して１２ｈｒ保持後に割れの有無を観察した。
これらの各特性の試験結果を表２に示す。
【００２２】
【表２】
表２から明らかなように、本発明例Ｎｏ．１〜４は、比較例Ｎｏ．５〜７や従来例Ｎｏ．８〜１０に比べ、０材については、伸びが高いことに伴いスウェ−ジング加工や据込加工等の加工性が優れている。また、本発明例Ｎｏ．１〜４は、Ｔ６材についても、伸び／引張強さの比が高く材料の靱性に優れ、金属組織、耐応力腐食割れ性も著しく改善されているのが明瞭である。
【００２４】
【発明の効果】
以上詳述したごとく、従来のＡｌ−Ｚｎ−Ｍｇ系合金押出材は、塑性加工を施した後にＴ６処理を行うとその断面の全面もしくは大部分に再結晶を生じ、押出材表層部にオレンジピール等の欠陥を生じると共に、応力腐食割れを生じるため、塑性加工後のＴ６処理は行わないのが一般的で、Ｔ６処理した高強度材を得ることができなかったが、本発明により塑性加工後のＴ６処理が可能となった。
即ち本発明は、Ａｌ−Ｚｎ−Ｍｇ系合金押出材の０材での各種の塑性加工（曲げ、スウェ−ジング、バルジ、据込加工等）性に優れ、又このような加工材のＴ６処理材は高強度で靱性に優れ、金属組織及び耐応力腐食割れ性についても問題ないＡｌ−Ｚｎ−Ｍｇ系合金材が得られるもので工業上顕著な効果を奏するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention is an extruded material of Al-Zn-Mg based alloy which is excellent in workability with an annealed material (0 material), is a solution age-hardened material (T6 material) and is excellent in toughness and stress corrosion cracking resistance More specifically, molded parts for automobiles such as bumpers, two-wheel main frames, swing arms, etc. Al-Zn-Mg alloy extruded materials (extrusion) used for electrical and mechanical parts by cutting and forging, etc. And a manufacturing method thereof.
[0002]
[Prior art]
In recent years, extruded profiles have a hollow shape with a complicated cross-sectional shape due to the needs of the industry, and it has become the mainstream to perform forming processes (plastic processing) such as bending, swaging, pipe expansion, and bulging.
The extruded bar is also subjected to secondary processing such as cutting and cold forging to obtain a predetermined shape, and then subjected to heat treatment, that is, age hardening after solution treatment (hereinafter referred to as T6 material).
Therefore, the characteristic required for the Al alloy material is that the extruded material is excellent in various workability. Therefore, it is necessary to use a material softened by annealing after extrusion (hereinafter referred to as 0 material). However, in a conventional alloy of Al-Zn-Mg type which is a heat treatment type alloy, if T6 treatment is performed after plasticizing the softened extruded material, recrystallization occurs on the whole or most of the cross section, and the extrusion In addition to causing defects such as orange peel in the surface layer of the material and causing stress corrosion cracking, it is common not to perform T6 treatment after plastic working, and T6 treatment after molding is excellent in strength and toughness, and A material excellent in stress corrosion cracking property could not be obtained.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-described problems, and specifically, various plastic workings (bending, swaging, bulging, upsetting processing) using zero material of an Al—Zn—Mg alloy extruded material. Etc.) and finding an Al-Zn-Mg alloy extruded material with improved strength and toughness, metal structure and stress corrosion cracking resistance of the T6 treated material, and a method for producing the same. is there.
[0004]
[Means for Solving the Problems]
In the present invention, as a result of intensive studies in view of the above situation, the workability is improved by examining the alloy components and the 0-material annealing treatment conditions after extrusion, and further, the extruded material after T6 treatment by examining the T6 treatment conditions after machining. Improved strength and toughness, structure and stress corrosion cracking resistance.
That is, the invention of claim 1 for solving the above-mentioned problem is Zn 4.00 to 6.50 wt%, Mg 0.50 to 1.50 wt%, Cu 0.10 to 0.50 wt%, Zr 0.10 to 0.50 wt. %, Mn 0.05 to 0.20 wt%, Cr 0.05 to 0.20 wt%, and the balance is an Al alloy extruded material formed of Al and inevitable impurities, and is T6 treated, The material has an excellent toughness and stress corrosion cracking resistance in which the ratio of elongation / tensile strength of the material is 0.030 or more and the cross-sectional structure is all a fibrous structure or the recrystallized structure has a surface layer depth of 300 μm or less. An Al—Zn—Mg alloy extruded material .
[0005]
The invention of claim 2 is Zn 4.00 to 6.50 wt%, Mg 0.50 to 1.50 wt%, Cu 0.10 to 0.50 wt%, Zr 0.10 to 0.50 wt%, Mn 0.05 to 0.20 wt% %, Cr 0.05 to 0.20 wt%, and the remainder of the Al alloy ingot consisting of Al and inevitable impurities is subjected to a homogenization heat treatment at a temperature of 420 to 520 ° C. for 2 to 24 hours. Extrusion is performed at a temperature of 520 ° C., and then this is annealed at a temperature of 360 to 420 ° C., and this is cooled to room temperature at a cooling rate of 30 ° C./hr or less, and a material excellent in moldability This is a method for producing an extruded Al—Zn—Mg alloy .
[0006]
The invention of claim 3 is Zn 4.00 to 6.50 wt%, Mg 0.50 to 1.50 wt%, Cu 0.10 to 0.50 wt%, Zr 0.10 to 0.50 wt%, Mn 0.05 to 0.20 wt% %, Cr 0.05 to 0.20 wt%, and the remainder of the Al alloy ingot consisting of Al and inevitable impurities is subjected to a homogenization heat treatment at a temperature of 420 to 520 ° C. for 2 to 24 hours. perform extrusion at a temperature of 520 ° C., this was subject to annealing at a temperature of 360 to 420 ° C. next, this was cooled to room temperature in less than a cooling rate 30 ° C. / hr, facilities strained molded thereto Subsequently, this was subjected to a solution treatment at a temperature of 400 to 500 ° C., cooled to room temperature at a cooling rate of 50 ° C./hr or higher, and then at the first stage for 2 to 12 hours at a temperature of 90 to 110 ° C. Aging treatment, further 120-180 ℃ 5 to 24 hours at a second aging treatment, the material elongation / tensile strength ratio is 0.030 or more, and the cross-sectional structure is all a fibrous structure or the recrystallized structure is the surface layer depth. This is a method for producing an Al—Zn—Mg alloy extruded material characterized in that the material has excellent toughness and stress corrosion cracking resistance of 300 μm or less.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
First, the invention of claim 1 is an Al—Zn—Mg alloy extruded material. As described in detail above, a predetermined Al—Zn—Mg alloy extruded material is subjected to a forming process and subjected to T6 treatment. It is the material of the state.
First, the reasons for limiting the alloy composition of the Al—Zn—Mg alloy extruded material according to the present invention will be described.
Zn has the effect of improving mechanical properties. If the amount added is less than 4.00 wt%, there is no effect, while if it exceeds 6.50 wt%, stress corrosion cracking resistance (hereinafter also referred to as SCC resistance), moldability and extrusion processability deteriorate, and productivity is increased. Also decreases. Therefore, in the present invention, the addition amount of Zn is limited to 4.00 to 6.50 wt%.
Mg is an element that improves mechanical properties, but its effect is small when its addition amount is less than 0.50 wt%, while stress corrosion cracking resistance, formability and extrusion processing when it is added in excess of 1.50 wt%. Deteriorates and productivity also decreases. Therefore, in the present invention, the amount of Mg added is limited to 0.50 to 1.50 wt%.
[0008]
Cu has the effect of improving mechanical properties and improving stress corrosion cracking resistance. If the addition amount is less than 0.10 wt%, the effect is not obtained. On the other hand, if the addition amount exceeds 0.50 wt%, the corrosion resistance is adversely affected. Therefore, in the present invention, the amount of Cu added is limited to 0.10 to 0.50 wt%.
Zr has an effect of suppressing the coarsening of recrystallized grains in the alloy, stabilizing the structure by using the crystal grains as a fibrous structure, and improving formability such as bending and swaging. If the addition amount is less than 0.10 wt%, the effect is small, while if it exceeds 0.50 wt%, a coarse Al—Zr intermetallic compound is generated and the toughness is deteriorated. Therefore, in the present invention, the amount of Zr added is limited to 0.10 to 0.50 wt%.
[0009]
Mn and Cr stabilize the structure by preventing recrystallization of the fibrous structure finely dispersed in the aluminum substrate in the coexistence state, and the surface of the extruded material after forming processing such as bending and swaging Has the effect of preventing the occurrence of orange peel-like rough skin. If the added amount is less than 0.05 wt%, the effect is small. Conversely, if the added amount exceeds 0.20 wt%, the effect is saturated while a coarse intermetallic compound is formed, and the quenching sensitivity is increased. In addition, the strength and extrusion processability are also adversely affected. Therefore, in the present invention, the addition amounts of Mn and Cr are limited to 0.05 to 0.20 wt%, respectively.
Further, impurities such as Ti, Ni, and B may be contained because they do not adversely affect the effects of the present invention as long as each is 0.05 wt% or less.
[0010]
Next, this material is a material obtained by subjecting the annealed material to bending, swaging and the like, and further subjected to T6 treatment, but the material elongation / tensile strength ratio is limited to 0.030 or more. This material is intended for structural members such as molded parts for automobiles such as bumpers, mainframes for motorcycles, swing arms, etc., and due to the nature of the product, the material requires stickiness, that is, toughness. Because. In the present invention, the ratio of the elongation / tensile strength of the material was used as a measure of this toughness characteristic.
In the present invention, the reason why the cross-sectional structure of the material is all the fibrous structure or the recrystallized structure is limited to the surface layer depth of 300 μm or less is to improve the toughness characteristics and the stress corrosion cracking resistance.
If the recrystallized structure has a surface layer depth of 300 μm or less, it can be removed by subsequent surface processing (processing by buffing, processing by shots, etc.), so there is no problem in the final product.
[0011]
Invention of Claim 2 is related with the manufacturing method of the Al-Zn-Mg type alloy extrusion material excellent in forming workability.
As described above, the extruded material is subjected to molding processing such as bending and swaging, but in the present invention, particularly in the cooling after annealing of the hot extruded material, the cooling rate is made very slow, It has improved moldability.
A third aspect of the invention relates to a method for producing an extruded Al-Zn-Mg alloy according to the first aspect of the invention, in which a T6 treatment is performed after the forming process.
[0012]
By the way, Al-Zn-Mg alloy extruded material is generally a method of subjecting an ingot that has been subjected to homogenization heat treatment to press quenching or separate solution treatment by hot extrusion, followed by artificial aging treatment and annealing after hot extrusion. After processing and plastic working, it is manufactured by a method of performing T6 processing.
The production method of the present invention achieves the object by using the Al alloy according to the present invention and limiting temperature conditions and processing time conditions in each stage of the latter production.
[0013]
Hereinafter, the manufacturing conditions at each stage in the invention of the manufacturing method of claims 2 and 3 will be described in detail.
First, the Al alloy ingot according to the present invention is subjected to a homogenization heat treatment.
The homogenization heat treatment is performed at a relatively high temperature in order to finely and uniformly disperse compounds such as Zr, Mn, and Cr. However, if the treatment is performed at a temperature exceeding 520 ° C. or exceeding 24 hours, the recrystallization of the cross-sectional surface layer after extrusion is promoted, or the precipitates are coarsened to deteriorate the properties such as extrudability and quenching sensitivity. On the other hand, homogenization is insufficient in the treatment at less than 420 ° C. or less than 2 hours. Therefore, in this invention, the homogenization heat processing is performed on the conditions of 420-520 degreeC x 2-24 hours.
[0014]
Next, the ingot is reheated to the extrusion temperature and hot extrusion is performed.
About extrusion temperature, it carries out at high temperature of 430-520 degreeC so that a thin-walled hollow shape material with a large extrusion ratio which is difficult to extrude can be processed. When a conventional alloy is extruded at such a high temperature, recrystallization proceeds and coarse recrystallized grains are produced, so that the stress corrosion cracking resistance is remarkably lowered, and a coarse intermetallic compound is produced. Processability, moldability, corrosion resistance, etc. deteriorate. However, in an alloy having a composition according to the present invention, a fibrous structure without recrystallized grains can be formed by adding Zr, and the progress of recrystallization can be suppressed by finely dispersing Mn and Cr. By greatly improving the properties, extrusion at high temperatures is possible.
It is difficult to extrude a hollow shape when the extrusion temperature is less than 430 ° C., and when it exceeds 520 ° C., the recrystallization of the cross-sectional surface layer after the extrusion is promoted, or the precipitate becomes coarse and extrudability, quenching sensitivity, etc. The characteristics of deteriorate. Accordingly, the extrusion temperature is 430 to 520 ° C.
[0015]
Next, the extruded material is annealed.
Annealing treatment precipitates solute elements in solid solution coarsely and decreases mechanical properties and hardness due to the formation of coarse intermetallic compounds, so that bending, swaging, bulging, upsetting, etc. after annealing treatment are performed. Plastic working becomes possible. However, if annealing is performed at a temperature exceeding 420 ° C., recrystallization is induced and the quenching sensitivity is insensitive, so that the strength is increased. On the other hand, if it is less than 360 degreeC, an annealing process will become inadequate.
In addition, the cooling to room temperature after annealing treatment needs to suppress a cooling rate to 30 degrees C / hr or less. This is because when the cooling rate exceeds 30 ° C./hr, the quenching sensitivity is insensitive, and it is difficult to obtain a sufficient 0 material hardness. Therefore, annealing treatment conditions are required to be annealed at a temperature of 360 to 420 ° C. and cooled at a cooling rate of 30 ° C./hr or less.
[0016]
Next, after the annealing treatment, plastic working such as bending, swaging, bulging, and upsetting is performed. After plastic working, it is necessary to improve mechanical properties by performing T6 treatment (solution treatment and artificial aging treatment) like ordinary heat-treatable alloys.
The solution treatment needs to form a supersaturated solid solution in which a solute element is sufficiently dissolved in an aluminum substrate. However, if the solution treatment temperature exceeds 500 ° C., eutectic melting (burning) occurs, and defects occur in the metal structure and the mechanical properties deteriorate. On the other hand, when the temperature is lower than 400 ° C., solution formation is insufficient. In addition, it is necessary to perform the cooling rate after solution treatment at 50 degreeC / hr or more. This is because, when cooled at less than 50 ° C./hr, a sufficient supersaturated solid solution for imparting strength cannot be obtained, and the entire cross section of the extruded material is recrystallized or coarse recrystallization occurs in the surface layer portion. Accordingly, the solution treatment conditions are 400 to 500 ° C., and the solution treatment needs to be cooled at a cooling rate of 50 ° C./hr or more.
[0017]
Next, these materials are subjected to artificial age hardening.
In this artificial aging treatment, the supersaturated solid solution obtained by the solution treatment is heat-treated at a low temperature to precipitate the precipitate finely.
Specifically, the second stage aging is used, and the fine precipitates of MgZn 2 are uniformly dispersed by the first stage aging, and grown into a coarse GP zone or an intermediate phase by the second stage high temperature aging. The first stage of artificial aging is performed at 90 to 110 ° C. for 2 to 12 hours in order to disperse and precipitate the fine precipitates sufficiently uniformly while preventing the precipitates from becoming coarse.
The second stage aging treatment is performed at a higher temperature than the first stage, but if the treatment is performed at a temperature exceeding 180 ° C., MgZn 2 precipitates coarsely, and the formability and corrosion resistance deteriorate. On the other hand, when the treatment is performed at a temperature of less than 120 ° C., the growth to the GP zone or the intermediate phase becomes insufficient, and the strength is insufficient. Furthermore, considering productivity, in the present invention, the second stage aging treatment is performed at 120 to 180 ° C. for 5 to 24 hours.
[0018]
As described above, the Al—Zn—Mg alloy extruded material according to the manufacturing method of the present invention is subjected to plastic working (bending, swaging, bulging, upsetting, etc.) after annealing, and subsequently subjected to T6 treatment. Even if applied, the cross-sectional structure of the material can be all fibrous structure or the recrystallized structure can have a surface layer depth of 300 μm or less.
If the recrystallized structure has a surface layer depth of 300 μm or less, it can be removed by subsequent surface processing (processing by buffing, processing by shots, etc.), so there is no problem in the final product.
Moreover, such a material is excellent in strength and toughness, and is also excellent in stress corrosion cracking resistance.
[0019]
【Example】
Next, examples of the present invention (examples of the present invention) will be described in more detail while comparing with comparative examples and conventional examples.
The alloys of the present invention examples (Nos. 1 to 4), comparative examples (Nos. 5 to 7), and conventional examples (Nos. 8 to 10) having the compositions shown in Table 1 were cast into an ingot for extrusion with a diameter of 219 mm by DC casting. Then, the homogenization heat treatment was performed under the conditions shown in Table 1, respectively. Then, it reheated to the extrusion temperature shown in Table 1, respectively, and extruded into a hollow shape (cross section: width 60 mm × height 60 mm × wall thickness 3.0 mm) and an extrusion rod of φ20 mm. After the extrusion, annealing was performed under the annealing treatment conditions shown in Table 1, and then cooled to room temperature at the cooling rate shown in Table 1 to prepare an annealed material (0 material). Only the 0-shaped material after the annealing treatment was plastically processed into a square tube having a cross section of 40 mm in width, 40 mm in height, and 2.5 mm in thickness by square tube swaging, and then subjected to the solution treatment conditions shown in Table 1 (after treatment) In consideration of the cooling rate, the solution treatment was performed. After the solution treatment, a two-stage artificial aging treatment shown in Table 1 was performed to prepare a test material.
[0020]
[Table 1]
Regarding these test materials, the mechanical properties, swaging workability and upsetting workability were evaluated for the 0 material, and the mechanical properties, metal structure, stress corrosion cracking test (salt water spray test and The chromic acid acceleration test) was evaluated.
The mechanical properties of the 0 material and the T6 material were evaluated based on tensile strength, proof stress, and elongation by taking a JIS No. 5 tensile test piece from the longitudinal direction of extrusion and conducting a tensile test.
Further, for the T6 material, the ratio of elongation / tensile strength was determined. A material having a high value has a stickiness to the material, and was used as a measure of toughness.
As described above, the swaging process is a square tube having a cross section of width 40 mm × height 40 mm × thickness 2.5 mm from a hollow shape (cross section 60 mm wide × 60 mm high × 3.0 mm thick square tube). The surface state after processing was visually observed and evaluated.
The upsetting process was performed using a 0-material extrusion rod, and a blank of φ20 mm × height 50 mm was cold set up to show a reduction rate in the height direction up to the crack limit.
As for the metallographic structure after T6, the cross-sectional microstructure of the surface layer portion was observed for the material subjected to the T6 treatment after the swaging of the square tube.
The stress corrosion cracking test was evaluated by two types of tests, a salt spray test and a chromic acid acceleration test. In the salt spray test, stress was applied to a 3.5% NaCl solution by three-point bending (95% of yield strength), and the presence or absence of cracks was observed after standing for 1 month.
In the chromic acid accelerated test, stress was applied to the chromic acid boiling solution by three-point bending (95% of yield strength), and the presence or absence of cracks was observed after holding for 12 hours.
Table 2 shows the test results of each of these characteristics.
[0022]
[Table 2]
As is apparent from Table 2, Example No. of the present invention. 1-4 are comparative example No.1. 5-7 and conventional example No. Compared to 8-10, the 0 material is superior in workability such as swaging and upsetting due to its high elongation. In addition, Invention Example No. Nos. 1 to 4 clearly show that the T6 material also has a high elongation / tensile strength ratio and excellent material toughness, and the metal structure and stress corrosion cracking resistance are remarkably improved.
[0024]
【The invention's effect】
As described above in detail, the conventional Al—Zn—Mg alloy extruded material is recrystallized over the entire surface or most of its cross section when subjected to T6 treatment after plastic working, and orange peel is formed on the surface layer of the extruded material. In general, the T6 treatment after the plastic working is not performed, and a high-strength material subjected to the T6 treatment cannot be obtained. T6 processing became possible.
That is, the present invention is excellent in various plastic processing (bending, swaging, bulging, upsetting, etc.) with zero material of Al-Zn-Mg alloy extruded material, and T6 treatment of such processed material. The material provides an Al—Zn—Mg alloy material that has high strength and excellent toughness, and that has no problem with respect to the metal structure and stress corrosion cracking resistance.
Claims (3)
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| JP18709796A JP3681822B2 (en) | 1996-07-17 | 1996-07-17 | Al-Zn-Mg alloy extruded material and method for producing the same |
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| JP18709796A JP3681822B2 (en) | 1996-07-17 | 1996-07-17 | Al-Zn-Mg alloy extruded material and method for producing the same |
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1996
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| Publication number | Publication date |
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| JPH1030147A (en) | 1998-02-03 |
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