JP3761180B2 - High-strength aluminum alloy forged material and forged products using the same - Google Patents

High-strength aluminum alloy forged material and forged products using the same Download PDF

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JP3761180B2
JP3761180B2 JP2003087130A JP2003087130A JP3761180B2 JP 3761180 B2 JP3761180 B2 JP 3761180B2 JP 2003087130 A JP2003087130 A JP 2003087130A JP 2003087130 A JP2003087130 A JP 2003087130A JP 3761180 B2 JP3761180 B2 JP 3761180B2
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aluminum alloy
mass
strength
forging
forged
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JP2004292892A (en
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佳也 稲垣
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Kobe Steel Ltd
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Kobe Steel Ltd
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Description

【0001】
【発明の属する技術分野】
本発明は、高強度アルミニウム合金鍛造材及びこれを用いて製造された鍛造製品に係り、特に、機械的強度と耐食性に優れた高強度アルミニウム合金鍛造材及びこれを用いて製造された鍛造製品に関する。
【0002】
【従来の技術】
従来、車両、船舶、あるいは航空機をはじめとする輸送機の構造部材には、軽量かつ機械的特性に優れたアルミニウム合金が多用され、その中で、成形性及び焼付硬化性等の面からJIS H 4001のAl−Mg−Si系の6000系合金が好適に用いられている。この6000系合金は、耐食性、特に応力腐食割れに対する耐性でも優れるとともに、Mg等の含有量が比較的少ないので、このスクラップを溶解して6000系合金の原料へ再生するリサイクル性にも優れた材料である。
【0003】
また、前記6000系合金が輸送機の構造部材に適用される際には、コスト削減や複雑な形状への加工性の点から、その鋳造材や鍛造材が用いられる。このうち、特に、高強度、高靱性等が要求される構造部材には、主に、前記6000系合金の鍛造材が適用される。
【0004】
近年、地球環境への負荷を軽減させるために、前記輸送機では、更なる軽量化及び耐食性の向上が図られている。それにともなって、その構造部材たるアルミニウム合金の鍛造材に対して、更なる薄肉化、ひいてはそれを実現させるための強度や靱性等の機械的特性の向上、及び耐食性の向上が要請されている。
【0005】
たとえば、アルミニウム合金組織の粒界上に存在するMg2SiやAl−Fe−Si−(Mn、Cr、Zr)系晶析出物の平均粒径を1.2μm以下とするとともに、これら晶析出物同士の平均間隔を3.0μm以上とし、なおかつ、該アルミニウム合金鍛造材をアノードとし、30℃で5%のNaCl水溶液中において、100μA/cm2で30分間直流電解後に測定されるアルミニウム合金鍛造材の自然電位の最低値を−1020mV以上になるにように構成することにより、アルミニウム合金鍛造材の耐食性を向上させる技術(耐食性に優れた高強度高靱性アルミニウム合金鍛造材)が提案されている(たとえば、特許文献1参照)。
【0006】
また、アルミニウム合金組織の粒界上に存在するMg2SiやAl−Fe−Si−(Mn、Cr、Zr)系晶析出物の平均粒径を1.2μm以下とするとともに、これら晶析出物同士の平均間隔を3.0μm以上とし、なおかつ、デンドライト2次アーム間隔(DAS)が30μm以下となるように鋳造することにより、アルミニウム合金鍛造材の耐食性、強度、及び靱性を向上させる技術(耐食性に優れた高強度高靱性アルミニウム合金鍛造材)が提案されている(たとえば、特許文献2参照)。
【0007】
さらに、アルミニウム合金組織中のMg2SiやAl−Fe−Si−(Mn、Cr、Zr)系晶析出物の合計の面積率を1.5%以下とすることにより、アルミニウム合金鍛造材の機械的特性を向上させる技術(高強度高靱性アルミニウム合金鍛造材)が提案されている(たとえば、特許文献3参照)。
【0008】
あるいは、アルミニウム合金の溶体化処理後のミクロ組織における再結晶粒の平均結晶粒径が45μm以下であり、Al−Fe系及びMg2Si晶析物の平均粒径を5μm以下とするとともに、これら晶析物間の平均間隔を20μm以上、なおかつ単位体積あたりの分散粒子の個数を1個/μm3以上とすることにより、アルミニウム合金鍛造素材の機械的特性を向上させる技術(プレス成形性及びヘム加工性に優れたアルミニウム合金板)が開示されている(たとえば、特許文献4参照)。
【0009】
【特許文献1】
特開2002−294382号公報(第2−11頁)
【特許文献2】
特開2001−107168号公報(第2−9頁)
【特許文献3】
特開2000−144296号公報(第2−10頁)
【特許文献4】
特開2000−144294号公報(第2−11頁)
【0010】
【発明が解決しようとする課題】
このように、アルミニウム合金鍛造材の高強度化を図るべく、アルミニウム合金中のSiの含有量を過剰とする、あるいはアルミニウム合金にCuのような高強度化に寄与する元素を添加すると、アルミニウム合金素材の強度や靱性等の機械的特性を一段と高めることが可能になるが、アルミニウム合金の鍛造材の組織における粒界腐食や応力腐食割れの感受性が顕著となって耐食性が低下するという問題が生じることとなって、機械的特性と耐食性とは互いに二律背反の関係にあるといえる。
【0011】
そこで、前記問題点を解決するために、本発明の目的は、前記のように機械的特性を向上させるべく、アルミニウム合金中のSiの含有量を過剰とした場合や、アルミニウム合金中にCuのような高強度化に寄与する元素を添加した場合でも粒界腐食や応力腐食割れが抑えられ、かつ、所望とする高強度化及び高靱性化が得られるアルミニウム合金鍛造材、及びこのアルミニウム合金鍛造材を用いて製造されたアルミニウム合金鍛造製品を提供することにある。
【0012】
【課題を解決するための手段】
前記目的を達成するために、本発明者らは、前記粒界腐食や応力腐食割れが抑えられる、優れた耐食性と、所望とする高強度化及び高靱性化とを両立させるべく、6000系合金に含有される元素の最適化について検討を行った。その結果、必須元素であるMg、Si、Mn及びTiの含有量を規制するとともにSiとMgの比率Si/Mgをさらに規制し、Cr及び/又はZrの元素を含むとともにこれらの含有量を規制し、さらに0.11μm以下の平均粒径の分散粒子が単位面積あたり13個/μm2以上存在するように規制することにより、前記目的を達成することが可能なことを見い出し、本発明を創作するに至った。
【0013】
(1)すなわち、本発明に係る高強度アルミニウム合金鍛造材は、必須含有元素として、Mgを0.6〜1.8質量%、Siを0.8〜1.8質量%、SiとMgの比率Si/Mgが1以上、Mnを0.1〜1.0質量%、Tiを0.01〜0.10質量%含有するとともに、選択的含有元素として、Crを0.05〜0.2質量%及び/又はZrを0.01〜0.2質量%含み、残部がAl及び不可避的不純物からなる組成からなり、さらに、0.11μm以下の平均粒径の分散粒子が単位面積あたり13個/μm2以上存在する構成とした。
【0014】
このように構成すれば、Mg、Si、Mn及びTiの含有量を規制するとともにSiとMgの比率Si/Mgをさらに規制し、Cr及び/又はZrを含むとともにこれらの含有量を規制したので、アルミニウム合金中のSiの含有量を過剰とした場合や、アルミニウム合金中にCuのような高強度化に寄与する元素を添加した場合でも粒界腐食や応力腐食割れが抑えられ、かつ、所望とする高強度化及び高靱性化が得られるアルミニウム合金鍛造材、及びこのアルミニウム合金鍛造材を用いて製造されたアルミニウム合金鍛造製品が具現される。
【0015】
(2)また、本発明は、高強度アルミニウム合金鍛造材において、さらにCuを0.2〜0.6質量%含有することが望ましい。
【0016】
このように構成すれば、前記高強度アルミニウム合金鍛造材において、高引張強度を実現し得るので、優れた機械的強度が具現される。
【0017】
(3)そして、本発明に係る高強度アルミニウム合金鍛造材は、前記高強度アルミニウム合金鍛造材を用いて鍛造した後に機械加工をして鍛造製品として製造される。
【0018】
このように構成すれば、粒界腐食や応力腐食割れが抑えられて優れた耐食性を備えるとともに、強度や靱性等が向上されたアルミニウム合金鍛造製品が具現される。
【0019】
【発明の実施の形態】
以下、本発明に係る実施の形態について詳細に説明する。
本発明に係る高強度アルミニウム合金鍛造材には、JIS H4000で規定される6000系合金が用いられる。具体的には、たとえば、JIS H4000で規定される6101合金、6003合金、6151合金、6061合金、6N01合金、6063合金等が挙げられる。
【0020】
そして、本発明に係る高強度アルミニウム合金鍛造材は、このような6000系合金を用いて従来公知の通常の製造方法にて製造される。すなわち、まず、本発明で規制する合金成分を有するアルミニウム合金を溶解した後、所定の冷却速度で冷却することにより、丸棒等の鍛造前の形態に鋳造し、鍛造素材とする。ここで、鋳造方法は、連続鋳造でも、半連続鋳造でも、どちらでも差し支えない。
【0021】
次に、前記鍛造素材に均質化熱処理を施す。本発明は、前記均質化熱処理の工程における温度及び時間について特に限定するものではないが、前記したアルミニウム合金の鍛造素材を製造する際に生じ易いアルミニウム合金成分の偏析を抑えて均質化するとともに、続いて行われる鍛造加工の効率性を確保する観点から、この工程温度を通常の条件範囲である温度480〜560℃で4〜8時間保持し、均質化熱処理を施す。
【0022】
引き続き、前記鍛造素材に鍛造加工を施すが、鍛造加工前に材料が、400〜480℃になるように調整する。これは、均質化熱処理後、一旦冷却を施した後に再度加熱しても良いし、均熱温度から直接この温度範囲まで冷却して、鍛造を開始しても良い。なお、数回に分けて鍛造をする(粗鍛造、中間鍛造、仕上げ鍛造等)場合には、適宜各鍛造間に材料を再加熱する工程を設けてもよい。
【0023】
そして、鍛造素材を所定の形状に鍛造加工した後は、溶体化焼入れ、そして析出時効処理(いわゆるT6処理)を施すことにより本発明に係る高強度アルミニウム合金鍛造材が得られる。
【0024】
つぎに、本発明に係る高強度アルミニウム合金鍛造材で、各種合金の含有量、分散粒子の平均結晶粒径の大きさと密度を数値限定した理由について説明する。
【0025】
(Mg:0.6〜1.8質量%)
Mgは、本発明に係る高強度アルミニウム合金鍛造材の強度を必要かつ充分に確保するために重要な元素である。すなわち、Mgの含有量が、0.6質量%未満であると所望の強度が得られず、また、1.8質量%より多くなると強度は高くなるものの耐食性が阻害される。このため、本発明にあっては、Mgの含有量を0.6〜1.8質量%とする。
【0026】
(Si:0.8〜1.8質量%)
Siは、アルミニウム合金中、Mgと共に人工時効処理により強度を付与するための元素である。このSiの含有量が0.8質量%以上であると、このアルミニウム合金鍛造材で所要の機械的特性が確保される。このSiの含有量が1.8質量%を超えると、後記する不可避的不純物の一つであるFe及び後記する必須含有元素の一つであるMnと共に、比較的サイズの大きなAl−Fe−Mn−Si系の金属間化合物が形成され、靭性・耐食性が低下する。従って、本発明に含まれるアルミニウム合金板中のSiの含有量は、0.8〜1.8質量%とする。
【0027】
(Si/Mg比:1以上)
Si及びMgは、Mg2Siの析出物を形成して強度を向上させる。Siは、Al−Mn−Si等の晶出物も形成するため、Si/Mg比が少ないとMg2Siが充分形成されず、強度の向上が図れないこととなる。従って、Si/Mg比は、1.0以上であることが必要であるが、Siが多すぎても強度の大幅な向上が望めず、一方で靭性が低下する等の弊害が生ずる可能性がある。従って、Si/Mg比の好ましい範囲は、1.1〜1.3である。
【0028】
(Mn:0.1〜1.0質量%)
Mnは、アルミニウム合金の強度向上及び組織微細化の役割を果たすものである。このMnの含有量が0.1質量%未満であると、強度不足となると共に組織が粗くなり、また、1.0質量%を超えると、引張強度・耐力は上るが、靭性・鍛造性が低下することとなる。このため、本発明にあっては、Mnの含有量を0.1〜1.0質量%とする。
【0029】
(Ti:0.01〜0.10質量%)
Tiは、鋳塊の結晶粒を微細化し、押出、圧延、鍛造時の加工性を向上させるために添加する元素である。しかし、Tiの0.01質量%未満の含有では、加工性向上の効果が得られない。一方、Tiを0.10質量%を超えて含有すると、粗大な晶出物を形成し、前記加工性を低下させる。従って、Tiの含有量は、0.01〜0.10質量%の範囲とすることが望ましい。
【0030】
また、本発明に係るアルミニウム合金鍛造材及びこれを用いた鍛造材は、機械的強度を、より充分に高めるために、Cr及び/又はZrを、以下の含有量で含有する。
【0031】
(Cr:0.05〜0.2質量%)
Crはアルミニウム合金中の結晶粒の大きさに寄与する元素である。すなわち、Crの含有量が、0.05質量%より少ないと、アルミニウム合金中で最大長が50μmを超えるような粗大な結晶粒が生成し易くなる。また、Cr含有量が、0.2%を超えると、溶解及び鋳造時に粗大な晶出物を生成しやすく、破壊の起点となり、靭性や疲労特性を低下させる原因となる。従って、本発明にあっては、Crを含有させる場合は、その含有量を0.05〜0.2質量%の範囲に規制する。
【0032】
(Zr:0.01〜0.2質量%)
Zrは、微細なAl−Zr系分散粒子を析出させ、結晶粒化や亜結晶粒化する効果が大きい。このZrの含有量が、0.01質量%未満であるとこれらの効果が期待できず、一方、0.2質量%を超えると、溶解及び鋳造時に粗大な晶出物を生成しやすく、破壊の起点となり、靭性や疲労特性を低下させる原因となる。従って、本発明にあっては、Zrを含有させる場合は、その含有量を0.01〜0.2質量%の範囲に規制する。
【0033】
(不可避的不純物)
本発明に係る高強度アルミニウム合金鍛造材に含まれる不可避的不純物としては、Zn、Fe等が挙げられる。本発明の効果を奏するためには、これらの不可避的不純物の含有量を各々0.1質量%以下及び0.3質量%以下に抑える必要がある。なお、本発明にあっては、このFeの含有量が少なければ少ないほど、粗大化したAl−Fe系晶出物の生成が少なくなるので好ましい。
【0034】
(分散粒子の平均結晶粒径が0.11μm以下の金属間化合物が13個/μm2以上)
本発明に係る高強度アルミニウム合金鍛造材で、分散粒子の平均粒径が0.11μmより大きな金属間化合物でその密度が13個/μm2よりも少ないと、最終製品の結晶粒が粗大になり、機械的性質・耐食性が低下する。前記高強度アルミニウム合金鍛造材の製造ロットの違いや形状の違いによる機械的特性等のバラツキを考慮すると、分散粒子の平均結晶粒径が0.11μm以下の金属間化合物が13個/μm2以上となることが好ましい。
【0035】
(Cu:0.2〜0.6質量%)
Cuは、本発明に係る高強度アルミニウム合金鍛造材の強度を向上させる元素である。このCuの含有量が、0.2質量%未満であると所望の強度が得られず、0.6質量%を超えると耐食性が阻害される。このため、本発明にあっては、Cuの含有量を0.2〜0.6質量%とする。
【0036】
ここで、本発明に係る高強度アルミニウム合金鍛造材から鍛造製品としてサスペンション部品を成形する工程の一つの実施例について説明する。まず、押出し加工、又は、鋳造により形成した丸棒材を所定の長さに切断した成形用素材を製造する。そして、鍛造前の予備加工として、前記成形用素材を加熱してロール成形を行い、成形用素材の外観形状をサスペンション部品の外観形状に近づけることが、歪が少なく寸法精度のよい鍛造製品に仕上げるためにより好ましい。次に、鍛造工程として、予備加工により成形した予備加工品にプレス加工を施す。このプレス加工は三段階に分けて行われ、最初のプレス加工である第一鍛造は、第一の金型により大まかな形状に成形する。次に、第一の金型よりも最終形状に近い形状を有する第二の金型を用いて第二鍛造を行う。そして、最終仕上げ金型により仕上げ鍛造を行い、発生したバリを除去した後、前記T6処理を施して、サスペンション部品の鍛造製品が完成する。
【0037】
(実施例)
以下、本発明の必要条件を満たす実施例を、本発明の必要条件を満足しない比較例と対比させながら、具体的に説明する。
【0038】
すなわち、表1に示す化学組成のアルミニウム合金鍛造材を用いて、本発明に係る実施の態様のアルミニウム合金の供試材による実施例(No.1〜8)と、本発明の要件を満足しないアルミニウム合金の供試材による比較例(No.9〜15)とを作製した。
【0039】
【表1】

Figure 0003761180
【0040】
次に、前記供試材の各々について、種々の評価試験を行った結果を表2に示すが、表2の番号は、表1の番号と対応しており、同じ番号の供試材は同一の化学組成を有する。
【0041】
【表2】
Figure 0003761180
【0042】
(分散粒子の測定方法)
鍛造終了後、鍛造材よりサンプリングを行い試験片を調製した。透過電子顕微鏡TEM(倍率×10000)で、前記試験片の任意の測定箇所10視野を観察し、画像解析装置により、分散粒子の粒径と数を算出し、その平均値を採用している。なお、前記分散粒子の粒径は、前記各視野で測定できる個々の前記分散粒子の最大長を分散粒子サイズとした。また、本発明における分散粒子とは、均質化熱処理時に形成され析される物であって、主としてAl−Mn系、Al−Cr系、Al−Zr系の分散粒子を意味する。
【0043】
(機械的特性)
アルミニウム合金鍛造材から複数個採取した試験片の引張強度(MPa)、耐力(MPa)、伸び(%)及びシャルピー衝撃値(J/cm2)等の機械的特性を測定し、その結果も表2に示す。
【0044】
(応力腐食割れ試験:SCC)
アルミニウム合金鍛造材から、各々の化学成分組成の試験片を採取し、応力腐食割れ試験を実施した。応力腐食割れ試験の条件は、JIS−H−8711(アルミニウム合金材料の応力腐食割れ試験方法)の規定に準拠し、交互漬せき法で、30日間行い、応力腐食割れ発生の有無を確認した。これらの結果を、応力腐食割れが発生している場合を「×」、発生していない場合を「○」として、表2に示す。
【0045】
表1の実施例(No.1〜8)は、本発明に係る実施の態様の実施例であり、これらはすべて本発明の化学成分組成の範囲内であり、表2を参照すると、何れも、分散粒子サイズが、0.11μm以下、かつ、分散粒子密度が13個/μm2以上である。また、機械的特性のうち引張強度及び耐力に関し、実施例は、何れも、比較例(No.9〜15)の該当する値を上回っており、さらに応力腐食割れに対する耐性が優れていることがわかる。また、実施例No.4,No.5,No.7及びNo.8は、これら以外の実施例と比較して、化学成分組成のうちCuをさらに含有しているので、表2を参照すると、引張強度がすべての実施例の中でも最も高い方に位置することがわかった。
【0046】
一方、比較例No.9は、化学成分組成が本発明の範囲内ではあるが、表2を参照すると、分散粒子のサイズが0.11μmを超えており、さらに分散粒子密度が10個/μm2以下(13個/μm2以下)となっているため、応力腐食割れが起こり易くまたシャルピー衝撃値も低いという欠点を有するものであった。また、No.11は、化学成分組成のうち選択的含有元素であるCr及びZrをともに含有せず、表2を参照すると、比較例No.9と同様に、分散粒子のサイズが0.11μmを超えており、さらに分散粒子密度が10個/μm2以下(13個/μm2以下)となっているため、応力腐食割れが起こり易いという欠点を有するものであった。
【0047】
比較例No.10とNo.12は、応力腐食割れに対する耐性は良好であったが、Si/Mg比が本発明の範囲の下限値未満であるため、引張強度と耐力が比較例の中でも最も低い方に位置する値であった。
【0048】
また、比較例No.13は、応力腐食割れに対する耐性は良好であったが、化学成分組成のうち、Si/Mg比が本発明の範囲の上限値を超えたため、伸びが比較例の中で最も低い方から2番目であり、機械的性質が好ましいものではなかった。
【0049】
比較例No.14及びNo.15は、化学成分組成の必須含有元素のうち、それぞれMn及びTiを含まないため、応力腐食割れが起こり易いという欠点を有するものであった。
【0050】
従って、これらのすべての比較例については、引張特性、耐力、伸び、シャルピー衝撃値、応力腐食割れ耐性に関し、充分満足できる結果を得られなかったことがわかる。ゆえに、これら比較例は、機械的特性及び耐食性など鍛造材としての信頼性の問題から使用することができず、また、本発明の構成要件の臨界的意義も理解できる。
【0051】
以上、本発明に係る実施例について具体的に説明したが、本発明はこのような実施例のみに限定されるものではなく、本発明の効果を奏する限りにおいて適宜変更することが可能である。
【0052】
【発明の効果】
以上説明したとおりに構成される本発明によれば、以下の効果が具現される。すなわち、本発明に係る請求項1によれば、Mg、Si、Mn及びTiの含有量を規制し、Si/Mgの比率を規制し、Cr及び/又はZrを含むとともにこれらの含有量を規制し、さらに、分散粒子の平均粒径及び単位面積の密度を規制したので、粒界腐食や応力腐食割れが抑えられ、かつ、所望とする高強度化及び高靱性化が得られるアルミニウム合金鍛造材を提供することができる。
【0053】
また、請求項2の発明によれば、前記アルミニウム合金鍛造材で、含有量を規制したCuを含むようにしたので応力腐食割れが抑えられ、かつ、所望とする高強度化が得られるアルミニウム合金鍛造材を提供することができる。
【0054】
そして、請求項3の発明によれば、前記高強度アルミニウム合金鍛造材を用いて製造されるので、粒界腐食や応力腐食割れが抑えられて優れた耐食性を備えるとともに、強度や靱性等が向上されたアルミニウム合金鍛造製品を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-strength aluminum alloy forged material and a forged product manufactured using the same, and more particularly to a high-strength aluminum alloy forged material excellent in mechanical strength and corrosion resistance and a forged product manufactured using the same. .
[0002]
[Prior art]
Conventionally, aluminum alloys that are lightweight and excellent in mechanical properties are frequently used for structural members of vehicles such as vehicles, ships, and airplanes. Among them, JIS H is used in terms of formability and bake hardenability. 4001 Al-Mg-Si 6000 series alloy is preferably used. This 6000 series alloy is excellent in corrosion resistance, particularly resistance to stress corrosion cracking, and has a relatively low content of Mg and the like, so that the material is also excellent in recyclability in which this scrap is melted and recycled to the raw material of the 6000 series alloy. It is.
[0003]
Further, when the 6000 series alloy is applied to a structural member of a transport aircraft, the cast material or the forged material is used from the viewpoint of cost reduction and workability to a complicated shape. Among these, the forged material of the 6000 series alloy is mainly applied to a structural member that particularly requires high strength and high toughness.
[0004]
In recent years, in order to reduce the load on the global environment, the transport aircraft has been further reduced in weight and improved in corrosion resistance. Accordingly, there is a demand for further thinning of the aluminum alloy forging material, which is a structural member, and further improvement of mechanical properties such as strength and toughness for realizing it, and improvement of corrosion resistance.
[0005]
For example, the average particle diameter of Mg 2 Si or Al—Fe—Si— (Mn, Cr, Zr) based crystal precipitates existing on the grain boundaries of the aluminum alloy structure is 1.2 μm or less, and these crystal precipitates Aluminum alloy forging material measured after DC electrolysis at 100 μA / cm 2 for 30 minutes in an aqueous 5% NaCl solution at 30 ° C. with an average interval of 3.0 μm or more as the anode and the aluminum alloy forging material as an anode A technology for improving the corrosion resistance of an aluminum alloy forged material (high strength and high toughness aluminum alloy forged material excellent in corrosion resistance) has been proposed by configuring the minimum value of the natural potential of -1020 mV or more ( For example, see Patent Document 1).
[0006]
The average grain size of Mg 2 Si and Al—Fe—Si— (Mn, Cr, Zr) based crystal precipitates present on the grain boundaries of the aluminum alloy structure is 1.2 μm or less, and these crystal precipitates Technology for improving the corrosion resistance, strength, and toughness of aluminum alloy forgings by casting so that the average distance between them is 3.0 μm or more, and the dendrite secondary arm distance (DAS) is 30 μm or less. High strength and high toughness aluminum alloy forging material) has been proposed (for example, see Patent Document 2).
[0007]
Furthermore, by making the total area ratio of Mg 2 Si and Al—Fe—Si— (Mn, Cr, Zr) -based crystal precipitates in the aluminum alloy structure 1.5% or less, the machine for aluminum alloy forgings A technique (high strength and high toughness aluminum alloy forged material) for improving the mechanical properties has been proposed (see, for example, Patent Document 3).
[0008]
Alternatively, the average crystal grain size of the recrystallized grains in the microstructure after the solution treatment of the aluminum alloy is 45 μm or less, and the average grain size of the Al—Fe-based and Mg 2 Si crystallized product is 5 μm or less. Technology for improving the mechanical properties of aluminum alloy forging materials (press formability and hem) by setting the average distance between crystallized materials to 20 μm or more and the number of dispersed particles per unit volume to 1 piece / μm 3 or more. An aluminum alloy plate excellent in workability is disclosed (for example, see Patent Document 4).
[0009]
[Patent Document 1]
JP 2002-294382 A (page 2-11)
[Patent Document 2]
JP 2001-107168 A (pages 2-9)
[Patent Document 3]
JP 2000-144296 A (page 2-10)
[Patent Document 4]
JP 2000-144294 A (page 2-11)
[0010]
[Problems to be solved by the invention]
In this way, in order to increase the strength of the aluminum alloy forging, if the content of Si in the aluminum alloy is excessive or an element that contributes to increasing the strength such as Cu is added to the aluminum alloy, the aluminum alloy Although mechanical properties such as strength and toughness of the material can be further enhanced, there is a problem that the corrosion resistance is lowered due to the remarkable sensitivity of intergranular corrosion and stress corrosion cracking in the structure of the forged aluminum alloy. In other words, it can be said that mechanical properties and corrosion resistance are in a trade-off relationship with each other.
[0011]
Therefore, in order to solve the above-mentioned problems, the object of the present invention is to improve the mechanical properties as described above when the Si content in the aluminum alloy is excessive, or when Cu is contained in the aluminum alloy. Aluminum alloy forging that can suppress intergranular corrosion and stress corrosion cracking even when an element that contributes to high strength is added, and can achieve the desired high strength and high toughness, and this aluminum alloy forging An object of the present invention is to provide an aluminum alloy forged product manufactured using a material.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have made a 6000 series alloy in order to achieve both excellent corrosion resistance capable of suppressing the intergranular corrosion and stress corrosion cracking, and desired high strength and high toughness. We investigated the optimization of elements contained in slag. As a result, the contents of the essential elements Mg, Si, Mn, and Ti are regulated, the ratio of Si to Mg, Si / Mg, is further regulated, and the contents of Cr and / or Zr are contained and regulated. In addition, it was found that the object can be achieved by regulating the dispersion particles having an average particle size of 0.11 μm or less to be 13 particles / μm 2 or more per unit area, and created the present invention. It came to do.
[0013]
(1) That is, the high-strength aluminum alloy forging according to the present invention includes, as essential elements, 0.6 to 1.8% by mass of Mg, 0.8 to 1.8% by mass of Si, and Si and Mg. The ratio Si / Mg is 1 or more, 0.1 to 1.0 mass% of Mn, 0.01 to 0.10 mass% of Ti, and 0.05 to 0.2 Cr as a selectively contained element. It is composed of 0.01% to 0.2% by mass of Zr and / or Zr, with the balance being composed of Al and inevitable impurities, and 13 dispersed particles having an average particle size of 0.11 μm or less per unit area / Μm 2 or more.
[0014]
With this configuration, the contents of Mg, Si, Mn, and Ti are regulated, and the Si / Mg ratio Si / Mg is further regulated, and the contents of Cr and / or Zr are regulated while these contents are regulated. Even when the Si content in the aluminum alloy is excessive, or when an element contributing to high strength such as Cu is added to the aluminum alloy, intergranular corrosion and stress corrosion cracking can be suppressed, and desired. An aluminum alloy forged material that can achieve high strength and high toughness, and an aluminum alloy forged product manufactured using the aluminum alloy forged material are realized.
[0015]
(2) Moreover, as for this invention, in a high intensity | strength aluminum alloy forging material, it is desirable to contain 0.2-0.6 mass% of Cu further.
[0016]
If comprised in this way, in the said high-strength aluminum alloy forging material, since high tensile strength can be implement | achieved, the outstanding mechanical strength is embodied.
[0017]
(3) The high-strength aluminum alloy forged material according to the present invention is manufactured as a forged product by forging using the high-strength aluminum alloy forged material and then machining.
[0018]
With such a configuration, an aluminum alloy forged product having excellent corrosion resistance while suppressing intergranular corrosion and stress corrosion cracking, and improved strength, toughness and the like is realized.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments according to the present invention will be described in detail.
As the high-strength aluminum alloy forging material according to the present invention, a 6000 series alloy defined by JIS H4000 is used. Specific examples include 6101 alloy, 6003 alloy, 6151 alloy, 6061 alloy, 6N01 alloy, 6063 alloy and the like specified by JIS H4000.
[0020]
And the high-strength aluminum alloy forging material which concerns on this invention is manufactured by a conventionally well-known normal manufacturing method using such a 6000 type alloy. That is, first, an aluminum alloy having an alloy component regulated in the present invention is melted and then cooled at a predetermined cooling rate, thereby casting into a form before forging such as a round bar to obtain a forging material. Here, the casting method may be either continuous casting or semi-continuous casting.
[0021]
Next, the forging material is subjected to a homogenizing heat treatment. The present invention is not particularly limited with respect to the temperature and time in the step of the homogenization heat treatment, and suppresses the segregation of the aluminum alloy components that are likely to occur when manufacturing the forging material of the aluminum alloy described above, and homogenizes. From the viewpoint of ensuring the efficiency of the subsequent forging process, this process temperature is maintained at a temperature of 480 to 560 ° C., which is a normal condition range, for 4 to 8 hours, and a homogenization heat treatment is performed.
[0022]
Subsequently, the forging material is forged, but the material is adjusted to 400 to 480 ° C. before forging. After homogenization heat treatment, this may be once cooled and then heated again, or may be cooled directly from the soaking temperature to this temperature range and forging may be started. In addition, when forging by dividing into several times (rough forging, intermediate forging, finish forging, etc.), a step of reheating the material may be appropriately provided between each forging.
[0023]
Then, after forging the forging material into a predetermined shape, a high-strength aluminum alloy forging according to the present invention is obtained by solution quenching and precipitation aging treatment (so-called T6 treatment).
[0024]
Next, in the high-strength aluminum alloy forging according to the present invention, the reason why the contents of various alloys and the size and density of the average crystal grain size of the dispersed particles are limited numerically will be described.
[0025]
(Mg: 0.6-1.8% by mass)
Mg is an important element for ensuring the necessary and sufficient strength of the high-strength aluminum alloy forging according to the present invention. That is, if the Mg content is less than 0.6% by mass, the desired strength cannot be obtained, and if it exceeds 1.8% by mass, the corrosion resistance is hindered although the strength increases. For this reason, in this invention, content of Mg shall be 0.6-1.8 mass%.
[0026]
(Si: 0.8-1.8% by mass)
Si is an element for imparting strength by artificial aging treatment together with Mg in an aluminum alloy. When the Si content is 0.8% by mass or more, the required mechanical properties are ensured by the aluminum alloy forging. When the content of Si exceeds 1.8% by mass, a relatively large Al—Fe—Mn together with Fe, which is one of the inevitable impurities described later, and Mn, which is one of the essential elements to be described later. -Si-based intermetallic compounds are formed, and toughness and corrosion resistance are reduced. Therefore, the content of Si in the aluminum alloy plate included in the present invention is set to 0.8 to 1.8% by mass.
[0027]
(Si / Mg ratio: 1 or more)
Si and Mg improve the strength by forming a precipitate of Mg 2 Si. Si is to crystallized substances also formed such Al-Mn-Si, and Mg 2 Si Si / Mg ratio is small is not sufficiently formed, so that the can not be improved strength. Therefore, the Si / Mg ratio needs to be 1.0 or more. However, even if there is too much Si, it is not possible to expect a significant improvement in strength, while there is a possibility that adverse effects such as a decrease in toughness may occur. is there. Therefore, the preferable range of Si / Mg ratio is 1.1 to 1.3.
[0028]
(Mn: 0.1 to 1.0% by mass)
Mn plays a role of improving the strength and refining of the structure of the aluminum alloy. When the Mn content is less than 0.1% by mass, the strength becomes insufficient and the structure becomes rough. When the Mn content exceeds 1.0% by mass, the tensile strength and proof stress increase, but the toughness and forgeability are improved. Will be reduced. For this reason, in this invention, content of Mn shall be 0.1-1.0 mass%.
[0029]
(Ti: 0.01-0.10% by mass)
Ti is an element added to refine crystal grains of an ingot and improve workability during extrusion, rolling, and forging. However, when the Ti content is less than 0.01% by mass, the effect of improving workability cannot be obtained. On the other hand, when Ti is contained exceeding 0.10 mass%, a coarse crystallized substance is formed and the workability is lowered. Therefore, the Ti content is desirably in the range of 0.01 to 0.10% by mass.
[0030]
Moreover, the aluminum alloy forging material and the forging material using the same according to the present invention contain Cr and / or Zr in the following contents in order to sufficiently increase the mechanical strength.
[0031]
(Cr: 0.05 to 0.2% by mass)
Cr is an element that contributes to the size of crystal grains in the aluminum alloy. That is, when the Cr content is less than 0.05% by mass, coarse crystal grains having a maximum length exceeding 50 μm are easily generated in the aluminum alloy. On the other hand, if the Cr content exceeds 0.2%, a coarse crystallized product is likely to be generated during melting and casting, which becomes a starting point of fracture and causes toughness and fatigue characteristics to be reduced. Therefore, in the present invention, when Cr is contained, the content is restricted to a range of 0.05 to 0.2 mass%.
[0032]
(Zr: 0.01 to 0.2% by mass)
Zr has a great effect of precipitating fine Al—Zr-based dispersed particles to crystallize or subcrystallize. If the Zr content is less than 0.01% by mass, these effects cannot be expected. On the other hand, if the Zr content exceeds 0.2% by mass, a coarse crystallized product is likely to be generated during melting and casting, and destruction occurs. It becomes a starting point of this and causes toughness and fatigue characteristics to deteriorate. Therefore, in the present invention, when Zr is contained, the content is restricted to a range of 0.01 to 0.2% by mass.
[0033]
(Inevitable impurities)
Examples of inevitable impurities contained in the high-strength aluminum alloy forging material according to the present invention include Zn and Fe. In order to achieve the effects of the present invention, it is necessary to suppress the contents of these inevitable impurities to 0.1% by mass or less and 0.3% by mass or less, respectively. In the present invention, the smaller the Fe content, the smaller the generation of coarse Al-Fe crystallized products.
[0034]
(The number of intermetallic compounds having an average crystal grain size of dispersed particles of 0.11 μm or less is 13 / μm 2 or more)
When the average particle size of dispersed particles is an intermetallic compound larger than 0.11 μm and the density is less than 13 particles / μm 2 in the high-strength aluminum alloy forging according to the present invention, the crystal grains of the final product become coarse. , Mechanical properties and corrosion resistance decrease. Taking into account variations in mechanical properties due to differences in production lots and shapes of the high-strength aluminum alloy forgings, the number of intermetallic compounds having an average crystal grain size of dispersed particles of 0.11 μm or less is 13 / μm 2 or more. It is preferable that
[0035]
(Cu: 0.2-0.6% by mass)
Cu is an element that improves the strength of the high-strength aluminum alloy forging according to the present invention. If the Cu content is less than 0.2% by mass, the desired strength cannot be obtained, and if it exceeds 0.6% by mass, the corrosion resistance is inhibited. For this reason, in this invention, content of Cu shall be 0.2-0.6 mass%.
[0036]
Here, an embodiment of a process for forming a suspension part as a forged product from the high-strength aluminum alloy forged material according to the present invention will be described. First, a molding material is manufactured by cutting a round bar formed by extrusion or casting into a predetermined length. Then, as a preliminary process before forging, the molding material is heated to perform roll forming, and the appearance shape of the molding material is brought close to the appearance shape of the suspension part, thereby finishing the forged product with less distortion and good dimensional accuracy. Therefore, it is more preferable. Next, as a forging process, a pre-processed product formed by pre-processing is pressed. This press work is performed in three stages, and the first forging, which is the first press work, is formed into a rough shape by the first die. Next, second forging is performed using a second mold having a shape closer to the final shape than the first mold. Then, forging is performed by a final finishing die and the generated burrs are removed, and then the T6 treatment is performed to complete a forged product of a suspension part.
[0037]
(Example)
Hereinafter, specific examples that satisfy the requirements of the present invention will be described in detail in comparison with comparative examples that do not satisfy the requirements of the present invention.
[0038]
That is, using the aluminum alloy forging material having the chemical composition shown in Table 1, the examples (Nos. 1 to 8) of the aluminum alloy test material according to the embodiment of the present invention and the requirements of the present invention are not satisfied. The comparative example (No. 9-15) by the test material of aluminum alloy was produced.
[0039]
[Table 1]
Figure 0003761180
[0040]
Next, the results of various evaluation tests performed on each of the test materials are shown in Table 2. The numbers in Table 2 correspond to the numbers in Table 1, and the test materials with the same numbers are the same. The chemical composition is
[0041]
[Table 2]
Figure 0003761180
[0042]
(Measurement method of dispersed particles)
After completion of forging, sampling was performed from the forged material to prepare a test piece. The transmission specimen is observed with a transmission electron microscope TEM (magnification × 10000) at 10 arbitrary measurement points of the test piece, the particle size and number of dispersed particles are calculated by an image analyzer, and the average value is adopted. In addition, as for the particle diameter of the dispersed particles, the maximum length of the individual dispersed particles that can be measured in each field of view was defined as the dispersed particle size. Also, the dispersed particles in the present invention, there is to be output is formed during homogenizing heat treatment analysis, mainly Al-Mn-based, Al-Cr-based, meaning dispersed particles of Al-Zr system.
[0043]
(Mechanical properties)
The mechanical properties such as tensile strength (MPa), yield strength (MPa), elongation (%), Charpy impact value (J / cm 2 ), etc. of test pieces taken from aluminum alloy forgings were measured. It is shown in 2.
[0044]
(Stress corrosion cracking test: SCC)
From the aluminum alloy forging material, specimens of each chemical composition were collected and subjected to a stress corrosion cracking test. The conditions for the stress corrosion cracking test were in accordance with the provisions of JIS-H-8711 (a method for stress corrosion cracking of aluminum alloy materials), and the alternate dipping method was performed for 30 days to confirm the presence or absence of the occurrence of stress corrosion cracking. These results are shown in Table 2 with “x” when stress corrosion cracking occurs and “◯” when no stress corrosion cracking occurs.
[0045]
Examples (Nos. 1 to 8) in Table 1 are examples of the embodiment according to the present invention, and these are all within the range of the chemical component composition of the present invention. The dispersed particle size is 0.11 μm or less, and the dispersed particle density is 13 particles / μm 2 or more. Moreover, regarding the tensile strength and the proof stress among the mechanical properties, all of the examples exceed the corresponding values of the comparative examples (No. 9 to 15), and further, the resistance to stress corrosion cracking is excellent. Recognize. In addition, Example No. 4, no. 5, no. 7 and no. 8 contains Cu in the chemical component composition as compared with the other examples, so that referring to Table 2, the tensile strength may be located at the highest of all the examples. all right.
[0046]
On the other hand, Comparative Example No. No. 9 has a chemical composition within the scope of the present invention, but referring to Table 2, the size of the dispersed particles exceeds 0.11 μm, and the dispersed particle density is 10 particles / μm 2 or less (13 particles / since that is the [mu] m 2 or less), and had a disadvantage tends also Charpy impact value is low occur stress corrosion cracking. No. 11 does not contain both Cr and Zr, which are selectively contained elements of the chemical component composition. As in 9, the size of the dispersed particles exceeds 0.11 μm and the density of the dispersed particles is 10 particles / μm 2 or less (13 particles / μm 2 or less), so stress corrosion cracking is likely to occur. It had a drawback.
[0047]
Comparative Example No. 10 and no. No. 12 had good resistance to stress corrosion cracking, but the Si / Mg ratio was less than the lower limit of the range of the present invention, so that the tensile strength and proof stress were the lowest values among the comparative examples. It was.
[0048]
Comparative Example No. No. 13 had good resistance to stress corrosion cracking, but among the chemical composition, since the Si / Mg ratio exceeded the upper limit of the range of the present invention, the elongation was second from the lowest in the comparative examples. And mechanical properties were not favorable.
[0049]
Comparative Example No. 14 and no. No. 15 has a defect that stress corrosion cracking is likely to occur because it does not contain Mn and Ti among the essential elements of the chemical component composition.
[0050]
Therefore, it can be seen that for all these comparative examples, sufficiently satisfactory results were not obtained with respect to tensile properties, yield strength, elongation, Charpy impact value, and stress corrosion cracking resistance. Therefore, these comparative examples cannot be used from the problem of reliability as a forging material such as mechanical characteristics and corrosion resistance, and the critical significance of the constituent elements of the present invention can be understood.
[0051]
The embodiment according to the present invention has been specifically described above, but the present invention is not limited to such an embodiment, and can be appropriately changed as long as the effects of the present invention are exhibited.
[0052]
【The invention's effect】
According to the present invention configured as described above, the following effects are realized. That is, according to claim 1 of the present invention, the contents of Mg, Si, Mn and Ti are regulated, the ratio of Si / Mg is regulated, and Cr and / or Zr is contained and the contents are regulated. Furthermore, since the average particle size and density of the unit area of the dispersed particles are regulated, the forged aluminum alloy can suppress intergranular corrosion and stress corrosion cracking, and can achieve desired high strength and high toughness. Can be provided.
[0053]
Further, according to the invention of claim 2, since the aluminum alloy forging is made to contain Cu whose content is regulated, stress corrosion cracking can be suppressed and desired high strength can be obtained. Forging material can be provided.
[0054]
And according to invention of Claim 3, since it manufactures using the said high intensity | strength aluminum alloy forging material, while providing intergranular corrosion and stress corrosion cracking and having excellent corrosion resistance, strength, toughness, etc. are improved. Forged aluminum alloy products can be provided.

Claims (3)

必須含有元素として、Mgを0.6〜1.8質量%、Siを0.8〜1.8質量%、SiとMgの比率Si/Mgが1以上、Mnを0.1〜1.0質量%、Tiを0.01〜0.10質量%含有するとともに、
選択的含有元素として、Crを0.05〜0.2質量%及び/又はZrを0.01〜0.2質量%含み、
残部がAl及び不可避的不純物からなる組成からなり、さらに、
0.11μm以下の平均粒径の分散粒子が単位面積あたり13個/μm2以上存在することを特徴とする高強度アルミニウム合金鍛造材。
As essential elements, Mg is 0.6 to 1.8% by mass, Si is 0.8 to 1.8% by mass, Si / Mg ratio Si / Mg is 1 or more, and Mn is 0.1 to 1.0. While containing 0.01% to 0.10% by mass of Ti and Ti,
As a selectively contained element, 0.05 to 0.2% by mass of Cr and / or 0.01 to 0.2% by mass of Zr,
The balance is composed of Al and inevitable impurities, and
A high-strength aluminum alloy forging material, wherein dispersed particles having an average particle diameter of 0.11 μm or less are present at 13 particles / μm 2 or more per unit area.
Cuを0.2〜0.6質量%含有することを特徴とする請求項1に記載の高強度アルミニウム合金鍛造材。The high-strength aluminum alloy forged material according to claim 1, containing 0.2 to 0.6 mass% of Cu. 請求項1又は請求項2に記載の高強度アルミニウム合金鍛造材を用いて鍛造した後に機械加工をして製造された鍛造製品。A forged product produced by forging using the high-strength aluminum alloy forged material according to claim 1 or 2 and machining.
JP2003087130A 2003-03-27 2003-03-27 High-strength aluminum alloy forged material and forged products using the same Expired - Fee Related JP3761180B2 (en)

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