JP2004197184A

JP2004197184A - Aluminum alloy for hole expansion, and method for manufacturing the same

Info

Publication number: JP2004197184A
Application number: JP2002368757A
Authority: JP
Inventors: Makoto Saga; 誠佐賀; Yuichi Sato; 雄一佐藤; Takeshi Takada; 健高田; Toshiyasu Ukiana; 俊康浮穴
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-12-19
Filing date: 2002-12-19
Publication date: 2004-07-15
Anticipated expiration: 2022-12-19
Also published as: JP3872753B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy for effectively improving the hole expansion performance without any special device, and a method for manufacturing the same. <P>SOLUTION: In an aluminum alloy plate having a punched hole by shearing, the hardening ratio within 1 mm from the surface of the punched hole is set to be ≤ 20%, where the hardening ratio (%)=(hardness of a portion of the punched hole - hardness of a base metal)×100/(hardness of the base metal), and the hardness of the portion of the punched hole is the hardness within 1 mm from the surface of the punched hole in a plate thickness cross section passing through the center of the punched hole. After working the punched hole at a temperature below 200°C, and before expanding the hole, at least a portion of 1 mm from the surface of the punched hole is heated to 200 to 600°C, and heat-treated for ≤ 2 hours. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車用ボディパネル、構造材料等に使用されるアルミニウム合金、特に剪断加工により形成した打ち抜き穴を有し、その後穴拡げ加工されるアルミニウム合金において、穴拡げ性に優れたアルミニウム合金及び製造方法に関する。
【０００２】
【従来の技術】
近年、自動車の車体を軽量化するために、ボディパネル及び構造材料にアルミニウム合金を適用する検討が進められている。自動車部材等の用途には、優れたプレス成形性が要求され、これまでに張出成形性及び深絞り成形性に優れたアルミニウム合金が開発されている。ところが実際の自動車部材には張出及び深絞りのような成形を行った後に、伸びフランジ加工及びバーリング加工等の穴拡げ加工が施される。特に、足廻り部品等の構造材料にアルミニウム合金を適用する際には、穴拡げ性の改善が重要な課題である。
【０００３】
一般に、金属材料の穴拡げ性を向上させるには、材料の局部延性を向上させるか、又は穴内表面を平滑化することが有効である。材料の延性は、温度の上昇とともに向上するため、高温で穴拡げ加工を施す方法が、特許文献１、特許文献２、特許文献３、特許文献４及び特許文献５に開示されている。しかし、このような方法は特別な加工設備が必要である。
【０００４】
また、穴内表面を平滑化するために、レーザーで穴加工を施す方法が特許文献６に、剪断加工によって形成した穴（以下、打抜き穴）を、さらに切削加工する方法が特許文献７に開示されている。しかし、アルミニウム合金にレーザーによる穴加工を施すと、穴内面近傍が凝固組織となるため局部延性が低下し、穴拡げ性の改善効果は小さいことが判明した。また、打抜き穴の内表面をさらに剪断加工して平滑化しても、穴拡げ性が大幅に改善しないという問題があった。
【０００５】
【特許文献１】
特開昭５９−２２５８１３号公報
【特許文献２】
特開昭６０−１２１０１８号公報
【特許文献３】
特開昭６０−１７７９１３号公報
【特許文献４】
特開昭６０−１７７９１４号公報
【特許文献５】
特開昭６３−１１５６１４号公報
【特許文献６】
特開平１０−２７７７６６号公報
【特許文献７】
特開平６−３９４５０号公報
【０００６】
【発明が解決しようとする課題】
本発明は、高温での穴拡げ加工のように特別な装置を必要とせず、レーザーによる穴加工又は打抜き後の剪断加工による穴内表面の平滑化よりも極めて効果的に穴拡げ性を改善した、アルミニウム合金及び製造方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明者は、剪断加工により打抜き穴を形成したアルミニウム合金の穴拡げ性を詳細に調査した。その結果、打抜き穴の板厚断面において、打抜き穴内表面より１ｍｍの範囲が加工硬化していることが穴拡げ性低下の原因であることを明らかにした。この知見から、少なくとも加工硬化している部分の塑性歪みを回復させる熱処理を施すことが穴拡げ性の向上に極めて有効であることを見出した。
【０００８】
本発明はこのような知見に基づいたものであり、その要旨は以下のとおりである。
【０００９】
（１）剪断加工による打抜き穴を有するアルミニウム合金において、打抜き穴内表面より１ｍｍの範囲内の硬化率が２０％以下であることを特徴とする穴拡げ加工用アルミニウム合金。
【００１０】
ただし、
硬化率（％）＝（打抜き穴加工部の硬さ−母材の硬さ）×１００／母材の硬さ
ここで、打抜き穴加工部の硬さは、打抜き穴の中心を通る板厚断面における打抜き穴内表面より１ｍｍ範囲内の硬さであり、母材及び打抜き穴加工部の硬さはビッカース硬さである。
【００１１】
（２）質量％で、
Ｍｇ：０．２〜６．０％、Ｓｉ：１．０％以下、
を含有し、
Ｆｅ：０．００１〜１．０％、Ｍｎ：０．０１〜２．０％、
Ｃｒ：０．００１〜１．０％、
の１種又は２種以上を含有し、残部Ａｌ及び不可避不純物からなることを特徴とする（１）記載の穴拡げ加工用アルミニウム合金。
【００１２】
（３）質量％で、
Ｍｇ：０．２〜１．５％、Ｓｉ：０．４〜２．０％、
を含有し、
Ｆｅ：０．００１〜１．０％、Ｍｎ：０．０１〜２．０％、
Ｃｒ：０．００１〜１．０％、
の１種又は２種以上を含有し、残部Ａｌ及び不可避不純物からなることを特徴とする（１）記載の穴拡げ加工用アルミニウム合金。
【００１３】
（４）質量％で、さらに、
Ｃｕ：０．０１〜１．０％、Ｚｎ：０．１〜２．０％、
Ｖ：０．０１〜０．５％、Ｚｒ：０．０１〜０．５％、
Ｔｉ：０．００１〜０．５％、Ｂ：０．０００１〜０．０５％
の１種又は２種以上を含有することを特徴とする（２）又は（３）に記載の穴拡げ加工用アルミニウム合金。
【００１４】
（５）２００℃未満で打抜き穴加工後、穴拡げ加工前に、少なくとも打抜き穴内表面より１ｍｍの範囲内を、２００〜６００℃に加熱し、２時間以下保持する熱処理を施すことを特徴とする（１）〜（４）のいずれか１項に記載の穴拡げ加工用アルミニウム合金の製造方法。
【００１５】
（６）加熱炉内で熱処理することを特徴とする（５）記載の穴拡げ加工用アルミニウム合金の製造方法。
【００１６】
（７）誘導加熱により熱処理することを特徴とする（５）記載の穴拡げ加工用アルミニウム合金の製造方法。
【００１７】
（８）２００〜６００℃に加熱した高温体を接触させることを特徴とする（５）記載の穴拡げ加工用アルミニウム合金の製造方法。
【００１８】
（９）バーナーで加熱することを特徴とする（５）記載の穴拡げ加工用アルミニウム合金の製造方法。
【００１９】
【発明の実施の形態】
本発明者は、アルミニウム合金板を剪断加工して打抜き穴を形成した後、穴広げ性が低下する原因を明らかにするため、以下の検討を行った。まず、３．５ｍｍ厚の５０５２アルミニウム合金より９０ｍｍ角の試験片を切り出し、１０ｍｍφのポンチと１０．２〜１１．０ｍｍφのダイスを用いてクリアランスを変化させ、プレス加工機によって剪断加工により打抜き穴を室温で形成した。打抜き穴径の測定は、拡大鏡を用いて穴径を１０倍に拡大して行った。クリアランスは、ダイス直径とポンチ直径との差を２で除し、さらに板厚で除した百分率である。
【００２０】
打抜き穴の内面は、剪断加工の際のポンチの入側が金属光沢を呈する剪断面であり、出側が光沢のない破断面である。打抜き穴内面の圧延方向２箇所及び圧延方向に直交する幅方向２箇所の４箇所において、板厚方向の剪断面の長さを測定し、板厚で除した百分率として剪断面比率を算出し、さらに４箇所の平均値を求めた。剪断面の長さは、ノギスを用いて側定した。なお比較材として、ボール盤によって１０ｍｍφの穴を切削加工により形成した試験片を作製した。
【００２１】
これらの試験片を用いて、６０°の円錐ポンチを用いて穴拡げ加工を施した後、試験前と同様に穴径を測定した。この測定値から穴拡げ試験前の穴径を減じて、これを試験前の穴径で除した百分率として、穴拡げ率を算出した。その結果、比較材の穴拡げ率は約１３０％であり、これに対して剪断加工により打抜き穴を形成した材料の穴拡げ率は約４０％と大幅に低下することがわかった。また、剪断加工により打抜き穴を形成した材料の穴拡げ率は剪断面比率に依らずほぼ同等であることがわかった。このことから、打抜き穴加工により穴拡げ率が低下する原因は従来知見と異なり、打抜き穴内表面の性状よりも、剪断加工による加工硬化の影響の方が大きいという知見を得た。
【００２２】
そこで、打抜き穴内表面近傍の板厚断面の加工硬化を以下のようにして確認した。まず試験片は、打抜き穴加工後、打抜き穴の中心を通った圧延方向に切断し、切断面である板厚断面を鏡面研磨して作製した。この打抜き穴内表面より０．１〜２ｍｍの範囲のビッカース硬さを、板表面より０．１ｍｍ、板厚中心部及び板表面より１／４板厚の位置で、０．１ｍｍ間隔で測定した。同様の測定を２〜５枚の試料を用いて行い、それぞれ同じ位置での測定値の平均値を算出し、打抜き穴加工部の硬さとした。なお、ビッカース硬さ試験は、ＪＩＳＺ２２４４に準じて、硬さ記号ＨＶ０．０１に対応する、試験力０．０９８７Ｎで行った。打抜き穴加工を行っていない試験片のビッカース硬さを同様にして測定し、母材の硬さとした。この測定値から硬化率を、
硬化率（％）＝（打抜き穴加工部の硬さ−母材の硬さ）×１００／母材
として求めた。
【００２３】
その結果、打抜き穴内表面より０．１ｍｍの部位では、硬化率は５０〜８０％であり、打抜き穴内表面より離れるに従って硬化率は低下して、打抜き穴内表面より１ｍｍの位置での硬化率はほぼ０％になることがわかった。
【００２４】
打抜き穴内表面より１ｍｍの範囲が加工硬化していることから、塑性歪みを熱処理によって回復させて穴拡げ性の向上を試みた。上述の試験と同条件で打抜き穴加工して穴径を測定し、３５０℃で２時間保持する熱処理を加熱炉内にて施し、室温まで空冷した。穴拡げ試験を上述の試験と同条件で行い、穴拡げ率を評価した。
【００２５】
その結果、打抜き穴性状の指標である剪断面比率の影響は小さく、熱処理によって穴拡げ率が大幅に向上し、切削加工材と同等になることを確認した。これは、（１）アルミニウム合金の穴拡げ性は、打抜き穴内表面の剪断面比率とともに低下し、（２）アルミニウム合金は、局部変形能が小さく、穴拡げ率は著しく低いため、（３）剪断加工により打抜き穴を形成した場合、穴拡げ率を向上させることは困難である、という従来知見を覆すものである。本発明者は、このようにして、室温で剪断加工し、打抜き穴を形成したアルミニウム合金の穴拡げ率を著しく改善させることに成功した。
【００２６】
以下、本発明について詳細に説明する。
本発明では、剪断加工によって打抜き穴内表面近傍に生じた加工硬化が、穴拡げ性低下の原因であることから、加工硬化が生じている打抜き穴内表面より１ｍｍの範囲の硬化率を限定する。
【００２７】
硬化率が２０％を超えると穴拡げ性が低下するため、２０％以下を上限とする。下限は低いほど良く、母材とほぼ同等である場合には０％となる。なお、５０００系アルミニウム合金において、冷間加工歪みが残留している場合、熱処理によって歪みが回復し、母材よりも硬さが低下することがある。また６０００系アルミニウム合金において、Ｔ５及びＴ６処理を施した場合、析出硬化により強度が大きくなっているため、熱処理の条件によっては、析出物が固溶して強化能を失い、母材よりも硬さが低下することがある。例えば、Ｔ５及びＴ６処理を施した６０００系アルミニウム合金に、４９０〜５５０℃で０〜６０ｓの熱処理を施すと、析出物が溶解してＭｇ及びＳｉが固溶するため、熱処理を施した部分の硬さは、母材よりも低下する。このような場合、硬化率の下限は−３０％程度である。
【００２８】
硬化率の測定は以下のようにして行うことができる。まず試験片は、打抜き穴加工後、打抜き穴の中心を通った圧延方向に切断し、切断面である板厚断面を鏡面研磨して作製する。この試験片の打抜き穴内表面より０．１〜２ｍｍの範囲のビッカース硬さを、板表面より０．１ｍｍ、板厚中心部及び板表面より１／４板厚の位置で、０．１ｍｍ間隔で測定する。このようにして、それぞれの測定位置においてビッカース硬さ測定し、この測定値を打抜き穴加工部の硬さとして、それぞれの測定位置における硬化率を求める。
【００２９】
なお、ビッカース硬さ試験は、ＪＩＳＺ２２４４に準じて行えば良いが、試験力が０．９８０７よりも大きいとビッカースくぼみが大きいため、測定の間隔を０．１ｍｍとすることが難しくなる。したがって、ビッカース硬さ試験は、試験力を０．０９８０７〜０．９８０７の範囲で行うことが好ましい。
【００３０】
打抜き穴加工を行っていない試験片のビッカース硬さを同様にして測定し、母材の硬さとする。母材の硬さの測定は、打抜き穴加工部の硬さを測定した試験片を用いて、打抜き穴内表面より２０ｍｍ以上離れた位置で測定しても良い。母材の硬さは、３点以上の測定値の平均値とすることが好ましい。
【００３１】
この打抜き穴内表面から０．１ｍｍ間隔で測定したビッカース硬さの、それぞれの測定値と母材の硬さの測定値から硬化率を、
硬化率（％）＝（打抜き穴加工部の硬さ−母材の硬さ）×１００／母材の硬さ
として求める。打抜き穴内表面から離れた位置での硬化率は低下するが、内抜き穴内表面から１ｍｍ以内の各位置において測定した硬化率が全て２０％以下であることが必要である。
【００３２】
なお、硬さの測定は複数の試験片を用いて測定することが好ましい。試料の採取方向は、圧延方向でも良いが、圧延方向と直交する幅方向及び４５°方向において行っても良い。また、複数の試料にから試験片を採取する場合は、方向に依らず、測定した打抜き穴内表面からの距離に対応するそれぞれの位置で測定したビッカース硬の平均値を算出することが好ましい。
【００３３】
次に本発明のアルミニウム合金の成分について説明する。
【００３４】
本発明は、自動車の足廻り部品等の構造材料に好適な、穴拡げ性に優れたアルミニウム合金である。この用途には強度、成形性及び耐食性に優れたＡｌ−Ｍｇ系の５０００系合金とＡｌ−Ｍｇ−Ｓｉ系の６０００系合金の適用が好ましい。これらの合金において、Ｍｇ量及びＳｉ量の規定は必須であり、Ｆｅ、Ｍｎ及びＣｒは１種又は２種以上を含有するものである。
【００３５】
５０００系合金におけるＭｇ及びＳｉの効果並びに含有量の範囲について説明する。
【００３６】
Ｍｇ：Ｍｇは固溶強化により強度を向上させ、さらに成形性及び加工性も向上させる元素であるが、０．２％未満ではその効果が不十分であるため、０．２％以上をＭｇ量の下限とする。一方、Ｍｇを６．０％を超えて添加すると、熱間加工性が大幅に劣化し、また耐応力腐食割れ性も著しく低下するため、Ｍｇ量の上限を６．０％とする。なお、製造性、加工性及び耐応力腐食割れ性の点から好ましいＭｇ量の範囲は０．５〜５．５％であり、最適範囲は１．５〜３．５％の範囲である。
【００３７】
Ｓｉ：Ｓｉは不純物であり、１．０％を超えて過剰に含有すると、粗大な晶出物及び析出物を生じて延性が低下するため、Ｓｉ量の上限を１．０％とした。なお、好ましい上限は、０．２％以下である。Ｓｉ量の下限は規定しないが、通常、不純物として０．０１％以上を含有する。
【００３８】
次ぎに６０００系合金におけるＭｇ及びＳｉの効果並びに含有量の範囲について説明する。
【００３９】
Ｍｇ：ＭｇはＳｉと複合添加することにより、Ｍｇ−Ｓｉ系の微細な析出物を生じて強度及びプレス成形性を向上させる元素であるが、Ｍｇ量が０．２％未満ではその効果が不十分である。一方、１．５％超のＭｇを添加すると粗大な晶出物及び析出物を形成し、延性が低下する。従って、Ｍｇ量の範囲を０．２〜１．５％の範囲とする。さらに、強度、プレス成形性及び延性が良好な、好ましいＭｇ量の範囲は、０．３〜１．０％である。
【００４０】
Ｓｉ：ＳｉもＭｇとの複合添加により、強度及びプレス成形性を向上させる元素であるが、その効果はＳｉ量が０．４％未満では不十分である。一方、２．０％超のＳｉ量を添加すると、粗大な晶出物及び析出物を生じて延性が低下する。従って、Ｓｉ量を０．４〜２．０％の範囲とする。さらに、強度及び延性が良好な好ましいＳｉ量の範囲は、０．５〜１．５％である。
【００４１】
５０００系及び６０００系合金における、Ｆｅ、Ｍｎ及びＣｒの効果並びに含有量の範囲について説明する。
【００４２】
Ｆｅ：Ｆｅは組織を微細化する元素であるが、その効果は０．００１％未満では不十分であるため、Ｆｅ量の下限を０．００１％以上とする。一方、Ｆｅ量が１．０％を超えると粗大な晶出物及び析出物を生じて延性が低下するため１．０％以下をＦｅ量の上限とする。さらに、組織の微細化と微細析出物の生成の抑制による穴拡げ性の向上を両立するための好ましいＦｅ量の範囲は０．０１〜０．２％であり、最適範囲は０．０１〜０．１％である。
【００４３】
Ｍｎ：Ｍｎは組織を微細化する元素であるが、その効果は０．０１％未満では不十分であり、２．０％を超えると粗大な晶出物及び析出物を生じて延性が低下するため。従って、Ｍｎ量の範囲を０．０１〜２．０％の範囲とする。さらに、微細な析出物の生成を抑制して穴拡げ性を向上するための好ましいＭｎ量の範囲は０．０１〜０．１％であり、最適範囲は０．０１〜０．０７％である。
【００４４】
Ｃｒ：Ｃｒも組織を微細化する元素であるが、その効果は０．００１％未満では不十分であるり、１．０％を超えると粗大な晶出物及び析出物を生じて延性が低下する。従って、Ｃｒ量の範囲を０．０００１〜１．０％の範囲とする。さらに、組織の微細化と微細析出物の生成の抑制による穴拡げ性の向上を両立するための好ましいＣｒ量の範囲は０．０１〜０．１％であり、最適範囲は０．０１〜０．０５％である。
【００４５】
さらに、必要に応じてＣｕ、Ｚｎ、Ｖ、Ｚｒ、Ｔｉ及びＢの１種又は２種以上を含有しても良い。
【００４６】
Ｃｕ：Ｃｕは固溶強化により板材、押出形材ともに加工性を向上させる元素であるが、０．０１％未満ではその効果が小さく、１．０％を超えて添加すると耐食性、応力腐食割れ性が低下する。従って、０．０１〜１％の添加が好ましい。さらに好ましい範囲は、０．１〜０．８％であり、最適範囲は０．２〜０．７％である。
【００４７】
Ｚｎ：Ｚｎは、強度向上により成形性を向上させる効果を有する。その効果は０．１％未満では小さく、２．０％を超えて過剰に添加すると逆に成形性が低下する。従って、０．１〜２．０％の添加が好ましい。
【００４８】
Ｖ：Ｖは、組織を微細化する元素であるが、その効果は０．０１％未満では効果が小さく、０．５％を超えると粗大な晶出物及び析出物を生じて延性が低下する。従って、０．０１〜０．５％の添加が好ましい。
【００４９】
Ｚｒ：Ｚｒは、組織を微細化する元素であるが、その効果は０．０１％未満では不十分であり、０．５％を超えると粗大な晶出物及び析出物を生じて延性が低下する。従って、０．０１〜０．５％の添加が好ましい。
【００５０】
Ｔｉ：Ｔｉは、凝固組織を微細化する元素であるが、その効果は０．００１％未満では小さく、０．５％を超えると粗大な晶出物及び析出物を生じて延性が低下する。従って、０．００１〜０．５％の添加が好ましい。
【００５１】
Ｂ：Ｂは、組織を微細化する元素であるが、その効果は０．０００１％未満では小さく、０．０５％を超えると粗大な晶出物及び析出物を生じて延性が低下する。従って、０．０００１〜０．０５％の添加が好ましい。
【００５２】
次に製造方法について説明する。
【００５３】
穴拡げ加工前の素材は板材、押出形材ともに、常法の製造方法でよい。剪断加工による打抜き穴の形成は、作業性から２００℃未満で行うものとする。また、アルミニウム合金板を液体窒素に浸漬し、−１９６℃以上で行っても良いが、室温が好ましい。
【００５４】
本発明において重要な製造方法は剪断加工後の熱処理であり、これによって打抜き穴内表面近傍の加工硬化の原因である塑性歪みを回復させる。従って、加工硬化している、少なくとも打抜き穴内表面より１ｍｍの範囲の部位を熱処理することが必要である。加熱温度は２００℃より低いと塑性歪みが回復しないため、２００℃以上を下限とする。一方、６００℃を超えると結晶粒径が粗大化して穴拡げ性が低下するため６００℃以下を上限とする。なお、熱処理温度の好ましい範囲は、３００〜５７０℃であり、最適範囲は、３５０〜５５０℃である。保持時間は、加熱温度に到達後、直ちに冷却しても良い。一方、２時間を超えて保持しても効果が飽和するため、２時間を上限とする。
【００５５】
なお、６０００系合金は、４９０〜５５０℃で０〜６０ｓの熱処理を施し、Ｍｇ₂Ｓｉを固溶させることが好ましい。この後、強度を上昇させるために、１５０〜２００℃で、２０分〜２時間の熱処理を施しても良い、
この熱処理は、加熱炉内で行っても良い。この場合には打ち抜き穴周辺だけではなく、アルミニウム合金全体が熱処理を受けることになる。５０００系合金の場合は、穴拡げ加工前に受けた加工歪も回復するために、二次加工性も向上させることができる。一方６０００系合金の場合、熱処理により析出物の存在状態が変化して強度が低下することがある。そこで、強度が必要とされる場合には打ち抜き穴周辺のみの部分的な加熱とする方が望ましい。
【００５６】
加熱炉内での熱処理は、昇温に時間を要するため、電磁コイルによる高周波加熱などの誘導加熱によって行っても良い。また、特別な設備を必要とせず、熱処理を行うために２００〜６００℃に加熱した高温体を接触させることでも良い。また、部分的な加熱で良いため、作業効率の点からバーナーで加熱しても良い。
【００５７】
【実施例】
表１に示す合金組成からなる３．５ｍｍ厚のアルミニウム合金板を以下の方法により作製した。Ａ、Ｂ及びＣは５０００系合金であり、鋳造後、熱延、冷延により板厚を３．５ｍｍとし、３５０〜４００℃で２時間保持する熱処理を施し、調質はＯ材とした。Ｄ、Ｅ及びＦは６０００系合金であり、熱間押出により板厚を３．５ｍｍとし、Ｄ及びＥは５３０℃に昇温し、保持せずにそのまま水冷し、さらに１７０〜１８０℃で８時間の熱処理を施してＴ６材としＦは押出し後１７０〜１８０℃で８時間の熱処理を施してＴ５材とした。
【００５８】
【表１】

【００５９】
これらのアルミニウム合金より９０ｍｍ角の試験片を切り出し、１０ｍｍφのポンチと１１．０ｍｍφのダイスを用いてプレス加工機によって室温で打抜き穴加工した。これらの試験片に表２に示す条件で熱処理を施した。熱処理は、熱電対を装着した試験片を用いて、加熱炉、誘導加熱、バーナー加熱、高温体接触の条件による温度変化を調査して、最高温度での保持時間が表２に示す条件になるように調整して行った。熱処理後の試験片の打抜き穴内表面より０．１ｍｍのビッカース硬さを、板厚中心部及び板表面より１／４板厚の位置で測定した。ビッカース硬さ試験はＪＩＳＺ２２４４に準じて、試験力０．０９８７Ｎで行った。なお、打抜き穴加工を行っていない試験片のビッカース硬さを同様にして測定し、母材の硬さとし、硬化率を算出した。
【００６０】
さらに、６０°の円錐ポンチを用いて穴拡げ加工を施し、穴拡げ試験前後の穴径の変化から穴拡げ率を算出した結果を表２に示す。表２に示すように、本発明の熱処理を施すことにより、優れた穴拡げ性が得られることがわかる。
【００６１】
【表２】

【００６２】
【発明の効果】
本発明によれば、アルミニウム合金の穴拡げ性の向上により、高穴拡げ性打ち抜き穴を有するアルミニウム合金板及びその高穴広げ性打ち抜き穴の加工方法を提供することができ、アルミニウム合金の自動車への適用が工業的に容易になるなど、産業上有用な顕著な効果を奏する。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an aluminum alloy used for an automobile body panel, a structural material, and the like, in particular, an aluminum alloy having a punched hole formed by shearing, and an aluminum alloy having a hole expanding property, It relates to a manufacturing method.
[0002]
[Prior art]
In recent years, in order to reduce the weight of an automobile body, studies have been made to apply an aluminum alloy to a body panel and a structural material. For applications such as automotive parts, excellent press formability is required, and aluminum alloys excellent in stretch formability and deep draw formability have been developed so far. However, after forming such as overhanging and deep drawing, an actual automobile member is subjected to hole expanding processing such as stretch flange processing and burring processing. In particular, when an aluminum alloy is applied to a structural material such as a suspension component, improvement of hole expandability is an important issue.
[0003]
Generally, in order to improve the hole expandability of a metal material, it is effective to improve the local ductility of the material or to smooth the inner surface of the hole. Since the ductility of a material increases with an increase in temperature, methods for performing hole expansion at a high temperature are disclosed in Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, and Patent Literature 5. However, such a method requires special processing equipment.
[0004]
In addition, Patent Document 6 discloses a method of forming a hole with a laser in order to smooth the inner surface of the hole, and Patent Document 7 discloses a method of further cutting a hole formed by shearing (hereinafter, punched hole). ing. However, it has been found that when laser drilling is performed on an aluminum alloy, the vicinity of the inner surface of the hole becomes a solidified structure, so that local ductility is reduced and the effect of improving hole expandability is small. In addition, there is a problem that even if the inner surface of the punched hole is further subjected to shearing to smooth it, the hole expandability is not significantly improved.
[0005]
[Patent Document 1]
JP-A-59-225813 [Patent Document 2]
Japanese Patent Application Laid-Open No. Sho 60-12018 [Patent Document 3]
JP-A-60-177913 [Patent Document 4]
JP-A-60-177914 [Patent Document 5]
JP-A-63-115614 [Patent Document 6]
JP-A-10-277766 [Patent Document 7]
JP-A-6-39450
[Problems to be solved by the invention]
The present invention does not require special equipment like hole expanding at high temperature, improved the hole expandability much more effectively than laser drilling or smoothing the inner surface of the hole by shearing after punching, An object of the present invention is to provide an aluminum alloy and a manufacturing method.
[0007]
[Means for Solving the Problems]
The present inventors have investigated in detail the hole expandability of an aluminum alloy having a punched hole formed by shearing. As a result, it has been clarified that the work hardening in a section of 1 mm from the inner surface of the punched hole in the thickness cross section of the punched hole is the cause of the deterioration of the hole expandability. From this finding, it has been found that heat treatment for recovering at least the plastic strain of the work-hardened portion is extremely effective in improving hole expandability.
[0008]
The present invention is based on such knowledge, and the gist is as follows.
[0009]
(1) An aluminum alloy having a hole punched by shearing, wherein a hardening rate within 1 mm from the inner surface of the hole is not more than 20%.
[0010]
However,
Hardening rate (%) = (hardness of punched hole processed part−hardness of base material) × 100 / hardness of base material Here, the hardness of the punched hole processed part is the thickness cross section passing through the center of the punched hole. The hardness in the range of 1 mm from the inner surface of the punched hole in Example 1 is Vickers hardness.
[0011]
(2) In mass%,
Mg: 0.2-6.0%, Si: 1.0% or less,
Containing
Fe: 0.001 to 1.0%, Mn: 0.01 to 2.0%,
Cr: 0.001 to 1.0%,
(1) The aluminum alloy for hole enlarging according to (1), comprising at least one of the following, and the balance being Al and unavoidable impurities.
[0012]
(3) In mass%,
Mg: 0.2-1.5%, Si: 0.4-2.0%,
Containing
Fe: 0.001 to 1.0%, Mn: 0.01 to 2.0%,
Cr: 0.001 to 1.0%,
(1) The aluminum alloy for hole enlarging according to (1), comprising at least one of the following, and the balance being Al and unavoidable impurities.
[0013]
(4) In mass%,
Cu: 0.01 to 1.0%, Zn: 0.1 to 2.0%,
V: 0.01-0.5%, Zr: 0.01-0.5%,
Ti: 0.001 to 0.5%, B: 0.0001 to 0.05%
The aluminum alloy for hole enlarging according to (2) or (3), comprising one or more of the following.
[0014]
(5) After punching at a temperature of less than 200 ° C., before the hole expanding, at least 1 mm from the inner surface of the punched hole is heated to 200 to 600 ° C. and heat-treated for 2 hours or less. The method for producing an aluminum alloy for hole enlarging according to any one of (1) to (4).
[0015]
(6) The method for producing an aluminum alloy for hole enlarging according to (5), wherein the heat treatment is performed in a heating furnace.
[0016]
(7) The method for producing an aluminum alloy for hole enlarging according to (5), wherein the heat treatment is performed by induction heating.
[0017]
(8) The method for producing an aluminum alloy for hole enlarging according to (5), wherein a high-temperature body heated to 200 to 600 ° C. is brought into contact.
[0018]
(9) The method for producing an aluminum alloy for hole enlarging according to (5), wherein the aluminum alloy is heated by a burner.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
The inventors of the present invention have conducted the following studies in order to clarify the cause of the decrease in hole expanding properties after forming a punched hole by shearing an aluminum alloy plate. First, a 90 mm square test piece was cut out from a 3.52 mm thick 5052 aluminum alloy, the clearance was changed using a 10 mm φ punch and a 10.2 to 11.0 mm φ die, and a punched hole was formed by shearing with a press machine. Formed at room temperature. The measurement of the punched hole diameter was performed by magnifying the hole diameter ten times using a magnifying glass. The clearance is a percentage obtained by dividing the difference between the die diameter and the punch diameter by 2 and dividing by the plate thickness.
[0020]
The inner surface of the punched hole has a sheared surface with a metallic luster on the entrance side of the punch during the shearing process, and has a dull fracture surface on the exit side. At four locations in the rolling direction at two locations in the punched hole inner surface and at two locations in the width direction orthogonal to the rolling direction, the shear surface length in the thickness direction was measured, and the shear surface ratio was calculated as a percentage divided by the thickness, Further, the average value of four places was obtained. The length of the shear surface was determined using calipers. As a comparative material, a test piece having a hole of 10 mmφ formed by cutting with a drilling machine was manufactured.
[0021]
Using these test pieces, a hole was expanded using a 60 ° conical punch, and the hole diameter was measured in the same manner as before the test. The hole diameter before the hole expansion test was subtracted from the measured values, and the hole expansion ratio was calculated as a percentage obtained by dividing the difference by the hole diameter before the test. As a result, it was found that the hole expansion rate of the comparative material was about 130%, whereas the hole expansion rate of the material in which the punched holes were formed by shearing was significantly reduced to about 40%. It was also found that the hole expansion ratio of the material in which the punched hole was formed by the shearing process was almost the same regardless of the shear surface ratio. From this, it was found that the cause of the reduction in the hole expansion rate due to the punching hole processing was different from the conventional knowledge, and that the effect of the work hardening due to the shearing processing was greater than the properties of the inner surface of the punched hole.
[0022]
Then, work hardening of the plate thickness section near the inner surface of the punched hole was confirmed as follows. First, a test piece was prepared by punching a hole, cutting it in the rolling direction passing through the center of the punched hole, and mirror-polishing the cross section of the plate thickness. The Vickers hardness in the range of 0.1 to 2 mm from the inner surface of the punched hole was measured at 0.1 mm intervals at a position 0.1 mm from the plate surface, at the center of the plate thickness and at a position 1/4 plate thickness from the plate surface. The same measurement was performed using 2 to 5 samples, and the average value of the measured values at the same position was calculated to determine the hardness of the punched hole processed portion. The Vickers hardness test was performed at a test force of 0.0987 N corresponding to a hardness symbol of HV0.01 in accordance with JIS Z 2244. The Vickers hardness of a test piece that had not been subjected to punching was measured in the same manner to determine the hardness of the base material. From this measurement the cure rate is
Hardening rate (%) = (hardness of punched hole processed portion−hardness of base material) × 100 / base material.
[0023]
As a result, at a portion 0.1 mm from the inner surface of the punched hole, the curing rate is 50 to 80%, and the curing rate decreases as the distance from the inner surface of the punched hole increases, and the curing rate at a position 1 mm from the inner surface of the punched hole is substantially reduced. It turned out to be 0%.
[0024]
Since the range of 1 mm was hardened from the inner surface of the punched hole, plastic strain was recovered by heat treatment to improve hole expandability. Punching was performed under the same conditions as in the above-described test, and the hole diameter was measured. Heat treatment was performed at 350 ° C. for 2 hours in a heating furnace, followed by air cooling to room temperature. The hole expansion test was performed under the same conditions as the above-mentioned test, and the hole expansion ratio was evaluated.
[0025]
As a result, it was confirmed that the influence of the shear surface ratio, which is an index of the punched hole properties, was small, and that the heat treatment significantly improved the hole expansion rate and became equivalent to that of the cut material. This is because (1) the hole expandability of the aluminum alloy decreases with the shear surface ratio of the inner surface of the punched hole, and (2) the aluminum alloy has a small local deformability and the hole expansion ratio is extremely low. This reverses the conventional knowledge that it is difficult to improve the hole expansion rate when a punched hole is formed by processing. The present inventor has thus succeeded in remarkably improving the hole expansion ratio of the aluminum alloy having the punched holes formed by the shearing at room temperature.
[0026]
Hereinafter, the present invention will be described in detail.
In the present invention, since the work hardening generated in the vicinity of the inner surface of the punched hole due to the shearing process is a cause of the deterioration of the hole expandability, the hardening rate in a range of 1 mm from the inner surface of the punched hole where the work hardening occurs is limited.
[0027]
If the curing rate exceeds 20%, the hole expandability is reduced, so the upper limit is 20% or less. The lower limit is better as it is lower, and becomes 0% when it is almost equal to the base material. In the case of a 5000 series aluminum alloy, when cold working strain remains, the strain may be recovered by heat treatment and the hardness may be lower than that of the base metal. In addition, when the T5 and T6 treatments are applied to the 6000 series aluminum alloy, the strength increases due to precipitation hardening. Therefore, depending on the conditions of the heat treatment, the precipitates form a solid solution, lose the strengthening ability, and are harder than the base metal. May decrease. For example, when a 6000 series aluminum alloy subjected to T5 and T6 treatments is subjected to a heat treatment at 490 to 550 ° C. for 0 to 60 s, the precipitates are dissolved to dissolve Mg and Si, so that the heat treated part The hardness is lower than that of the base material. In such a case, the lower limit of the curing rate is about -30%.
[0028]
The measurement of the curing rate can be performed as follows. First, a test piece is prepared by punching a hole, cutting it in the rolling direction passing through the center of the punched hole, and mirror-polishing the cross section of the plate thickness. Vickers hardness in the range of 0.1 to 2 mm from the inner surface of the punched hole of this test piece was 0.1 mm from the plate surface, 1/4 plate thickness from the plate thickness center and the plate surface, at 0.1 mm intervals. Measure. In this way, Vickers hardness is measured at each measurement position, and the measured value is used as the hardness of the punched hole processing portion to determine the cure rate at each measurement position.
[0029]
The Vickers hardness test may be performed according to JIS Z 2244. However, if the test force is larger than 0.9807, the Vickers depression is large, so that it is difficult to set the measurement interval to 0.1 mm. Therefore, the Vickers hardness test is preferably performed with a test force in the range of 0.09807 to 0.9807.
[0030]
The Vickers hardness of a test piece that has not been subjected to punching is measured in the same manner, and the measured value is defined as the hardness of the base material. The hardness of the base metal may be measured at a position 20 mm or more away from the inner surface of the punched hole using a test piece having the hardness of the punched hole processed portion measured. The hardness of the base material is preferably an average value of three or more measured values.
[0031]
From the measured values of the Vickers hardness measured at 0.1 mm intervals from the inner surface of the punched hole and the measured values of the hardness of the base material,
Hardening rate (%) = (hardness of punched hole processed portion−hardness of base material) × 100 / hardness of base material. Although the curing rate at a position distant from the inner surface of the punched hole decreases, it is necessary that the curing rate measured at each position within 1 mm from the inner surface of the inner hole is 20% or less.
[0032]
The hardness is preferably measured using a plurality of test pieces. The sampling direction of the sample may be the rolling direction, but may be the width direction and the 45 ° direction orthogonal to the rolling direction. In the case of collecting test pieces from a plurality of samples, it is preferable to calculate the average value of Vickers hardness measured at each position corresponding to the measured distance from the inner surface of the punched hole, regardless of the direction.
[0033]
Next, the components of the aluminum alloy of the present invention will be described.
[0034]
The present invention is an aluminum alloy which is suitable for structural materials such as undercarriage parts of automobiles and has excellent hole expanding properties. For this purpose, it is preferable to use an Al-Mg-based 5000-based alloy and an Al-Mg-Si-based 6000-based alloy which are excellent in strength, formability and corrosion resistance. In these alloys, the definition of the amount of Mg and the amount of Si is essential, and Fe, Mn, and Cr contain one or more kinds.
[0035]
The effect of Mg and Si in the 5000 series alloy and the range of the content will be described.
[0036]
Mg: Mg is an element that enhances strength by solid solution strengthening and further improves formability and workability. However, if the content is less than 0.2%, the effect is insufficient, so that 0.2% or more of the Mg content Lower limit. On the other hand, if Mg is added in excess of 6.0%, the hot workability is significantly deteriorated, and the stress corrosion cracking resistance is also significantly reduced. Therefore, the upper limit of the amount of Mg is set to 6.0%. The preferable range of the Mg content is 0.5 to 5.5% from the viewpoint of manufacturability, workability, and stress corrosion cracking resistance, and the optimum range is 1.5 to 3.5%.
[0037]
Si: Si is an impurity, and if it is contained in excess of 1.0%, coarse crystals and precipitates are formed to lower ductility. Therefore, the upper limit of the amount of Si is set to 1.0%. Note that a preferable upper limit is 0.2% or less. Although the lower limit of the amount of Si is not specified, it usually contains 0.01% or more as an impurity.
[0038]
Next, the effects of Mg and Si in the 6000 series alloy and the range of the contents will be described.
[0039]
Mg: Mg is an element that improves the strength and press formability by forming a Mg-Si based fine precipitate when added in combination with Si, but its effect is not sufficient when the amount of Mg is less than 0.2%. It is enough. On the other hand, if more than 1.5% of Mg is added, coarse crystals and precipitates are formed, and the ductility decreases. Therefore, the range of the amount of Mg is set to the range of 0.2 to 1.5%. Further, the preferable range of the amount of Mg in which the strength, press formability and ductility are good is 0.3 to 1.0%.
[0040]
Si: Si is also an element that improves the strength and press formability by adding composite with Mg, but its effect is insufficient when the Si content is less than 0.4%. On the other hand, if more than 2.0% of Si is added, coarse crystals and precipitates are formed and ductility is reduced. Therefore, the amount of Si is set in the range of 0.4 to 2.0%. Further, the preferable range of the amount of Si having good strength and ductility is 0.5 to 1.5%.
[0041]
The effects of Fe, Mn, and Cr and the range of the contents in the 5000 series and 6000 series alloys will be described.
[0042]
Fe: Fe is an element for refining the structure, but its effect is insufficient if less than 0.001%. Therefore, the lower limit of the amount of Fe is set to 0.001% or more. On the other hand, if the amount of Fe exceeds 1.0%, coarse crystals and precipitates are generated and ductility is reduced. Therefore, the upper limit of the amount of Fe is 1.0% or less. Further, the preferable range of the amount of Fe for satisfying both the refinement of the structure and the improvement of the hole expandability by suppressing the generation of fine precipitates is 0.01 to 0.2%, and the optimum range is 0.01 to 0%. 0.1%.
[0043]
Mn: Mn is an element for refining the structure, but its effect is insufficient if it is less than 0.01%, and if it exceeds 2.0%, coarse crystals and precipitates are generated, and ductility is reduced. For. Therefore, the range of the amount of Mn is set to the range of 0.01 to 2.0%. Furthermore, the preferable range of the amount of Mn for suppressing the generation of fine precipitates and improving the hole expandability is 0.01 to 0.1%, and the optimum range is 0.01 to 0.07%. .
[0044]
Cr: Cr is also an element for refining the structure, but its effect is insufficient if it is less than 0.001%, and if it exceeds 1.0%, coarse crystals and precipitates are formed to lower the ductility. I do. Therefore, the range of the Cr content is set to the range of 0.0001 to 1.0%. Further, the preferable range of the amount of Cr for achieving both the refinement of the structure and the improvement of the hole expandability by suppressing the generation of fine precipitates is 0.01 to 0.1%, and the optimum range is 0.01 to 0%. 0.05%.
[0045]
Further, if necessary, one or more of Cu, Zn, V, Zr, Ti and B may be contained.
[0046]
Cu: Cu is an element that improves the workability of both sheet material and extruded shape material by solid solution strengthening, but its effect is small when it is less than 0.01%, and corrosion resistance and stress corrosion cracking resistance when it is added more than 1.0%. Decreases. Therefore, addition of 0.01 to 1% is preferable. A more preferred range is 0.1 to 0.8%, and an optimal range is 0.2 to 0.7%.
[0047]
Zn: Zn has the effect of improving formability by improving strength. The effect is small when it is less than 0.1%, and when it is added in excess of 2.0%, on the contrary, the formability decreases. Therefore, addition of 0.1 to 2.0% is preferable.
[0048]
V: V is an element for refining the structure, but the effect is small when the effect is less than 0.01%, and when it exceeds 0.5%, coarse crystals and precipitates are generated, and ductility is reduced. . Therefore, addition of 0.01 to 0.5% is preferable.
[0049]
Zr: Zr is an element for refining the structure, but its effect is insufficient if it is less than 0.01%, and if it exceeds 0.5%, coarse crystals and precipitates are formed to lower ductility. I do. Therefore, addition of 0.01 to 0.5% is preferable.
[0050]
Ti: Ti is an element that refines the solidification structure, but its effect is small when it is less than 0.001%, and when it exceeds 0.5%, coarse crystals and precipitates are generated, and ductility is reduced. Therefore, addition of 0.001 to 0.5% is preferable.
[0051]
B: B is an element for refining the structure, but its effect is small when it is less than 0.0001%, and when it exceeds 0.05%, coarse crystals and precipitates are generated to lower ductility. Therefore, the addition of 0.0001 to 0.05% is preferable.
[0052]
Next, a manufacturing method will be described.
[0053]
The material before the hole expansion processing may be a conventional manufacturing method for both the plate material and the extruded shape material. The formation of the punched hole by the shearing process is performed at less than 200 ° C. from the viewpoint of workability. Further, the aluminum alloy plate may be immersed in liquid nitrogen and may be heated at -196 ° C or higher, but preferably at room temperature.
[0054]
An important manufacturing method in the present invention is heat treatment after shearing, thereby recovering plastic strain which causes work hardening near the inner surface of the punched hole. Therefore, it is necessary to heat-treat at least a part of the work-hardened part within a range of 1 mm from the inner surface of the punched hole. If the heating temperature is lower than 200 ° C., the plastic strain does not recover, so the lower limit is 200 ° C. or higher. On the other hand, if the temperature exceeds 600 ° C., the crystal grain size becomes coarse and the hole expandability decreases. In addition, the preferable range of the heat treatment temperature is 300 to 570 ° C, and the optimal range is 350 to 550 ° C. The holding time may be cooling immediately after reaching the heating temperature. On the other hand, the effect is saturated even if it is maintained for more than 2 hours, so the upper limit is 2 hours.
[0055]
It is preferable that the 6000 series alloy is subjected to a heat treatment at 490 to 550 ° C. for 0 to 60 s to dissolve Mg ₂ Si. Thereafter, in order to increase the strength, heat treatment may be performed at 150 to 200 ° C. for 20 minutes to 2 hours.
This heat treatment may be performed in a heating furnace. In this case, not only the periphery of the punched hole but also the entire aluminum alloy is subjected to the heat treatment. In the case of a 5000 series alloy, since the processing strain received before the hole expansion processing is also recovered, the secondary workability can be improved. On the other hand, in the case of a 6000 series alloy, the heat treatment may change the existing state of the precipitates and reduce the strength. Therefore, when strength is required, it is preferable to perform partial heating only around the punched hole.
[0056]
The heat treatment in the heating furnace may be performed by induction heating such as high-frequency heating using an electromagnetic coil since it takes time to raise the temperature. In addition, a high-temperature body heated to 200 to 600 ° C. for performing heat treatment may be contacted without requiring special equipment. Since partial heating is sufficient, heating may be performed with a burner from the viewpoint of working efficiency.
[0057]
【Example】
A 3.5 mm-thick aluminum alloy plate having the alloy composition shown in Table 1 was produced by the following method. A, B, and C are 5000 series alloys. After casting, heat treatment was performed by hot rolling and cold rolling to a plate thickness of 3.5 mm and holding at 350 to 400 ° C. for 2 hours. D, E and F are 6000 series alloys. The thickness is 3.5 mm by hot extrusion. D and E are heated to 530 ° C., and are directly cooled with water without holding. After a heat treatment for a time, a T6 material was obtained, and after extruding F, a heat treatment was performed at 170 to 180 ° C. for 8 hours to obtain a T5 material.
[0058]
[Table 1]

[0059]
Test pieces of 90 mm square were cut out of these aluminum alloys, and punched at room temperature by a press machine using a 10 mmφ punch and a 11.0 mmφ die. These test pieces were heat-treated under the conditions shown in Table 2. In the heat treatment, using a test piece equipped with a thermocouple, the temperature change due to the conditions of the heating furnace, the induction heating, the burner heating, and the contact with the high-temperature body is investigated. Was adjusted as follows. The Vickers hardness of 0.1 mm from the inner surface of the punched hole of the test piece after the heat treatment was measured at the center of the plate thickness and at a position of 1/4 plate thickness from the plate surface. The Vickers hardness test was performed at a test force of 0.0987 N according to JIS Z 2244. In addition, the Vickers hardness of the test piece which was not punched was measured in the same manner, and the hardness was calculated as the hardness of the base material.
[0060]
Further, Table 2 shows the results of performing hole expansion using a 60 ° conical punch and calculating the hole expansion ratio from the change in the hole diameter before and after the hole expansion test. As shown in Table 2, it can be seen that by performing the heat treatment of the present invention, excellent hole expandability can be obtained.
[0061]
[Table 2]

[0062]
【The invention's effect】
According to the present invention, by improving the hole expandability of an aluminum alloy, it is possible to provide an aluminum alloy plate having a high hole expandability punched hole and a method of processing the high hole expandability punched hole, and to an aluminum alloy automobile. It has an industrially useful and remarkable effect, for example, its application is industrially easy.

Claims

An aluminum alloy having a punched hole formed by shearing, wherein a hardening rate within a range of 1 mm from the inner surface of the punched hole is not more than 20%.
However,
Hardening rate (%) = (hardness of punched hole processed part−hardness of base metal) × 100 / hardness of base material Here, the hardness of the punched hole processed part is the thickness cross section passing through the center of the punched hole. The hardness in the range of 1 mm from the inner surface of the punched hole in Example 1 is Vickers hardness.

In mass%,
Mg: 0.2-6.0%,
Si: 1.0% or less,
Containing
Fe: 0.001 to 1.0%,
Mn: 0.01 to 2.0%,
Cr: 0.001 to 1.0%
The aluminum alloy for hole enlarging according to claim 1, comprising one or more of the following, and the balance being Al and unavoidable impurities.

In mass%,
Mg: 0.2-1.5%,
Si: 0.4 to 2.0%,
Containing
Fe: 0.001 to 1.0%,
Mn: 0.01 to 2.0%,
Cr: 0.001 to 1.0%
The aluminum alloy for hole enlarging according to claim 1, comprising one or more of the following, and the balance being Al and unavoidable impurities.

Mass%,
Cu: 0.01 to 1.0%,
Zn: 0.1 to 2.0%,
V: 0.01 to 0.5%,
Zr: 0.01-0.5%,
Ti: 0.001 to 0.5%,
B: 0.0001 to 0.05%
The aluminum alloy for hole enlarging according to claim 2 or 3, comprising one or more of the following.

2. A heat treatment for heating at least 1 mm from the inner surface of the punched hole to 200 to 600 [deg.] C. and holding for 2 hours or less after punching at 200 [deg.] C. and before hole expanding. 5. The method for producing an aluminum alloy for hole enlarging according to any one of items 4 to 4.

The method for producing an aluminum alloy for hole enlarging according to claim 5, wherein heat treatment is performed in a heating furnace.

The method for producing an aluminum alloy for hole enlarging according to claim 5, wherein the heat treatment is performed by induction heating.

The method for producing an aluminum alloy for hole expanding according to claim 5, wherein a high-temperature body heated to 200 to 600 ° C is brought into contact with the aluminum alloy.

The method for producing an aluminum alloy for hole enlarging according to claim 5, wherein the aluminum alloy is heated by a burner.