JP2004225124A

JP2004225124A - Aluminum alloy having superior impact absorption characteristic and adequate hardenability and extrudability, and manufacturing method therefor

Info

Publication number: JP2004225124A
Application number: JP2003015594A
Authority: JP
Inventors: Masahiro Arashiro; 昌弘荒城; Hiroyuki Tanihata; 弘之谷畑
Original assignee: YKK AP Inc
Current assignee: YKK AP Inc
Priority date: 2003-01-24
Filing date: 2003-01-24
Publication date: 2004-08-12
Anticipated expiration: 2023-01-24
Also published as: JP4052641B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-Mg-Si aluminum alloy extrusion material which has high strength and shows superior impact absorption characteristic when compressed in the direction of an extruding axis. <P>SOLUTION: This aluminum alloy comprises 0.45-0.75% (mass%) Mg, 0.45-0.80% Si, 0.1-0.4% more Si than a balance quantity for the composition of Mg<SB>2</SB>Si, 0.15-0.40% Mn, 0-0.1% Cr and the balance Al with unavoidable impurities. This method for manufacturing the aluminum alloy extrusion material comprises homogenizing the billet of the aluminum alloy having the above composition for 2 to 48 hours at 500 to 600°C, extruding it and quenching the extruded material by air cooling. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明が属する分野】
本発明は、Ａｌ−Ｍｇ−Ｓｉ合金押出材からなり、圧縮応力がかかる衝突衝撃を受けたときにその衝撃荷重を吸収する作用を持つ衝撃吸収部材に関する。
【０００２】
【従来の技術】
従来から、例えば自動車のフレーム構造において、サイドメンバーやバンパーステイなどの衝撃吸収部材等の軽量化のためアルミニウム合金中空押出材の適用が検討されている。これらの衝撃吸収部材は自動車の衝突の際、押出軸方向に荷重をうけたとき圧壊割れを生じることなく蛇腹状に変形して、安定した高いエネルギー吸収を得ること、及び自動車フレーム構造材として必要な強度（耐力）を有することが要求される。
【０００３】
これまで、衝撃吸収部材として利用できるアルミ合金として、Ａｌ−Ｍｇ−Ｓｉ系アルニミウム合金押出材が多く提案されている。
そのような合金押出材の例としては、Ａｌ−Ｍｇ−Ｓｉ系合金を加熱後押出成形し、次いで１０００℃／分以上の平均冷却速度で空冷し、その後人工時効処理を施すもの（特許文献１〜３参照）、Ａｌ−Ｍｇ−Ｓｉ系合金を均質化熱処理した後、前記溶体化処理温度にて熱間直接押出法にて押し出すと同時に常温水を用いて焼入れを行い、次いで人工時効処理を施したもの（特許文献４参照）を挙げることができる。
【０００４】
上記公報にも記載されているように、Ａｌ−Ｍｇ−Ｓｉ系アルミニウム合金押出材を衝撃吸収部材に適用する場合、一般にオンラインによるプレス焼入れ又はオフラインによる溶体化・焼入れ処理を行った後、時効処理を施している。ここで時効処理を施すのは、押出材の強度を向上させ、かつ組織を安定化し使用中に自然時効が進行して圧壊割れ性が劣化するのを防止するためである。
【０００５】
水冷によるプレス焼入れは、押出後再加熱する溶体化・焼入れ処理とほぼ同等の特性が得られる利点があるが、押出材の断面形状や肉厚の差等に基づいて断面で冷却速度に差が生じ、冷却中に温度分布が不均一となって歪みが発生し、寸法精度が悪くかつ断面形状の薄肉化が難しくなり、また、そのような歪みの発生を防止しようとすれば、断面形状の自由度が小さくなるという問題がある。さらに、空冷に比べ高コストであるという問題がある。
【０００６】
一方、空冷による焼入れは、水冷によるプレス焼入れに比べ低コストであるという利点があるが、冷却速度に限りがあるため合金組成によっては高い強度（特に耐力）が得られず、高い強度が得られた場合でもエネルギー吸収や耐圧壊割れ性に劣るという問題があった。
【０００７】
上記の問題を改善したものとして、Ａｌ−Ｍｇ−Ｓｉ系アルミニウム合金を均熱処理した後押出加工を行い、押出直後の位置で空冷によるプレス焼入れを行い、次いでこの押出材に対し時効処理を施した押出合金材が提案されている（特許文献５参照）。
しかし、前記特許文献５記載の合金材は、組織が繊維状組織であるため、衝撃吸収特性、曲げ特性には優れているが、繊維状組織であるため材料特性の方向依存性が強いといった問題がある。また繊維状の組織を安定して得るためには押出時の加工歪量や加工発熱量を抑える必要があるため、高速での押出成形ができず生産性が悪い。上記内容から加工歪量が多くなる複雑形状や薄肉形材への対応が難しく、押出材の特徴が十分生かされない。
【０００８】
【特許文献１】
特開平６−２５７８３号公報
【特許文献２】
特開平７−５４０９０号公報
【特許文献３】
特開平７−１１８７８２号公報
【特許文献４】
特開平９−２５６０９６号公報
【特許文献５】
特開２０００−３４５２７０号公報
【０００９】
【発明が解決しようとする課題】
本発明は、Ａｌ−Ｍｇ−Ｓｉ系アルミニウム合金押出材において、寸法精度やコスト面で有利な空冷による焼入れを前提とし高強度でかつ押出軸方向に圧縮したときに優れた衝撃吸収特性を示す押出材を得ることを目的とする。
【００１０】
【課題を解決するための手段】
本発明者等は、上記課題を解決するために鋭意研究を重ねた結果、空冷による焼き入れによって良好な衝撃吸収特性と押出性が得られる最適な合金組成、熱処理条件を見出して、本発明を完成させたものであり、本発明は次の態様からなる。
【００１１】
（１）Ｍｇを０．４５％〜０．７５％（質量％、以下同じ）、Ｓｉを０．４５％〜０．８０％、Ｍｇ_２Ｓｉのバランス組成よりも過剰のＳｉを０．１０％〜０．４０％、Ｍｎを０．１５％〜０．４０％、Ｃｒを０〜０．１％の範囲で含有し、残部が不可避的不純物及びＡｌからなる組成を有し、その組織が実質的に繊維状組織を有しない組織であることを特徴とする衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金。
（２）前記アルミニウム合金の組成が、Ｍｇを０．４７〜０．５８％、Ｓｉを０．６０〜０．６８％、Ｍｇ_２Ｓｉのバランス組成よりも過剰のＳｉを０．２５〜０．４０％、Ｍｎを０．１５〜０．３０％、Ｃｒを０〜０．０５％の範囲で含有し、残部が不可避的不純物及びＡｌからなる組成であることを特徴とする上記（１）記載の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金。
【００１２】
（３）Ａｌ相にＭｇ_２Ｓｉが析出した組織をベースとしてＭｎまたは／及びＣｒ系化合物が該組織内に分散しており、さらにその化合物の周りには針状のＭｇ_２Ｓｉが析出しない母相領域をもつ組織を有することを特徴とする上記（１）または（２）記載の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金。
（４）前記Ｍｎまたは／及びＣｒ系化合物の断面積が０．００３μｍ^２以上であることを特徴とする上記（３）記載の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金。
（５）前記Ｍｎまたは／及びＣｒ系化合物の分布密度が０．２個／μｍ^２以上であることを特徴とする上記（３）または（４）記載の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金。
（６）耐力値が２２０ＭＰａ以上、伸び１０％以上であることを特徴とする上６記（１）〜（５）のいずれかに記載の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金。
【００１３】
（７）Ｍｇを０．４５％〜０．７５％、Ｓｉを０．４５％〜０．８０％、Ｍｇ_２Ｓｉのバランス組成よりも過剰のＳｉを０．１０％〜０．４０％、Ｍｎを０．１５％〜０．４０％、Ｃｒを０〜０．１％の範囲で含有し、残部が不可避的不純物及びＡｌからなる組成を有するアルミニウム合金のビレットを、５００℃〜６００℃の範囲で２〜４８時間均質化処理した後、押出成形し、空冷による焼入れを行うことを特徴とする、衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金の製造方法。
（８）Ｍｇを０．４５％〜０．７５％、Ｓｉを０．４５％〜０．８０％、Ｍｇ_２Ｓｉのバランス組成よりも過剰のＳｉを０．１０％〜０．４０％、Ｍｎを０．１５％〜０．４０％、Ｃｒを０〜０．１％の範囲で含有し、残部が不可避的不純物及びＡｌからなる組成を有するアルミニウム合金のビレットを、５７０℃〜６００℃の範囲で２〜１０時間均質化処理した後、押出成形し、空冷による焼入れを行い、その後最大強度もしくは過時効状態まで時効処理を行うことを特徴とする衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金の製造方法。
（９）前記アルミニウム合金のビレットの組成が、Ｍｇを０．４７〜０．５８％、Ｓｉを０．６０〜０．６８％、Ｍｇ_２Ｓｉのバランス組成よりも過剰のＳｉ量が０．２５〜０．４０％、Ｍｎを０．１５〜０．３０％、Ｃｒを０〜０．０５％の範囲で含有し、残部が不可避的不純物及びＡｌからなる組成であることを特徴とする上記（７）または（８）記載の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金の製造方法。
【００１４】
【発明の実施の形態】
本発明の合金は、上記したような組成及び組織とすることにより、本発明の目的を達成できるものである。
そこで、まず、本発明の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金を構成する各成分組成について説明する。
なお、本明細書では、「％」は「質量％」を意味する。
【００１５】
＜Ｍｇ＞：Ｍｇは本発明で対象としている系の合金で基本となる合金元素の一つであり、Ｓｉとともに化合物を形成して強度の向上に寄与する。Ｍｇ量が０．４５％未満では析出硬化によって強度の向上に寄与するＭｇ_２Ｓｉ量の生成量が少なくなるため、十分な強度が得られず、一方０．７５％を超えれば焼き入れ性が低下する上に押出加工性も低下することからＭｇは０．４５〜０．７５％とする。また、良好な強度と焼き入れ性とをバランスよく備えた衝撃吸収部材を得るためには、Ｍｇを０．４７％〜０．５８％とすることが好ましい。
【００１６】
＜Ｓｉ＞：Ｓｉも本発明の系の合金で基本となる合金元素であって、Ｍｇとともに化合物を形成して強度の向上に寄与する。Ｓｉが０．４５％未満では硬化に寄与するＭｇ_２Ｓｉ量の生成量が少なくなるため十分な強度が得られず、一方０．８０％を超えると、押出加工性や曲げ加工性を低下させる。従って、Ｓｉ量は０．４５〜０．８０％とする。また、良好な強度と焼き入れ性とをバランスよく備えた衝撃吸収部材を得るためには、Ｓｉを０．６０〜０．６８％とすることが好ましい。
【００１７】
＜Ｍｇ_２Ｓｉ＞：ＭｇとＳｉとは結合して析出し合金強度を向上させる。自動車フレーム構造材への使用を想定した場合、Ｔ５処理で必要な強度（耐力）を得るためにはＭｇ＋Ｓｉ量で最低１．０％程度必要となる。しかし焼入れ性を考慮した場合Ｍｇ_２Ｓｉ量が多くなると焼き入れ性が悪くなり、Ｍｇ量が多くなると押出性が悪くなる。従ってＭｇ＋Ｓｉ量は１．０〜１．３％の範囲がよい。一方Ｍｇ_２Ｓｉバランス組成に過剰に添加したＳｉはＭｇ量を多くした材料に比べ焼入れ性を阻害する影響が小さく、材料強度を高くすることができる。但し過剰Ｓｉ量が多すぎると焼き入れ性が悪くなる。適正な過剰Ｓｉ量としては０．１０％〜０．４０％が好ましく、良好な押出性と焼き入れ性とをバランスよく備えた衝撃吸収部材を得るためには０．２５％〜０．４０％とすることがより好ましい。
【００１８】
＜Ｍｎ＞：Ｍｎはビレットの均質化処理においてＡｌ、Ｓｉと結合し、Ａｌ−Ｍｎ−Ｓｉ系の化合物をつくり、この化合物の分散によって材料の粒内変形を促進し衝撃吸収特性を向上させる効果がある。添加量が０．１５％未満では粒内変形を促進させる効果が小さく、０．４０％を超えると焼き入れ性が鋭くなりすぎ、空冷による焼き入れでは焼きが入らず必要な強度が得られなかったり、粗大な化合物を形成しこの化合物相が微小な破壊の起点として働くため、成形性を低下させると共に圧壊性も低下させてしまう。従って、Ｍｎ量は０．１５〜０．４０％、より好ましくは０．１５〜０．３０％とした。
【００１９】
＜Ｃｒ＞：Ｃｒは必要に応じて添加される成分であり、Ｍｎと同じく結晶粒を微細化、安定化するとともに強度を上昇させる。またＣｒはＭｎ同様Ａｌ−Ｃｒ−Ｓｉ系などの化合物が結晶粒内に分散して析出するために粒内変形が促進されるので衝撃吸収性が向上する。しかしＣｒは焼き入れ性に及ぼす影響が大きく、Ｃｒが０．１％を超えると材料の焼き入れ性が悪くなり、空冷による焼き入れでは十分な強度が得られない。よってＣｒを添加する量は０％〜０．１％、より好ましくは０％〜０．０５％の範囲である。
Ｍｎ及びＣｒの添加量は粒内変形を促進させるＭｎ、Ｃｒ系化合物の析出量に影響するため、上記のＭｎ、Ｃｒの組成範囲を限定した理由と同様の理由により、Ｍｎ＋Ｃｒの添加量は０．２〜０．３％の範囲で含有するのが好ましい。
【００２０】
＜不可避不純物＞：不可避不純物のうちＦｅはアルミニウム地金に最も多く含まれる不純物であり、０．３５％を超えて合金中に存在すると製造時に粗大な金属間化合物を晶出し、合金の機械的性質を損なう。従って、Ｆｅの含有量は０．３５％以下に規制する。望ましくは０．３０％以下でありさらに０．２５％以下が望ましい。またアルミニウム合金を鋳造する際には地金、添加元素の中間合金等様々な経路より不純物が混入する。混入する元素は様々であるが、Ｆｅ以外の不純物は単体で０．０５％以下、総量で０．１５％以下であれば合金の特性にほとんど影響を及ぼさない。従ってこれらの不純物は単体で０．０５％以下、総量で０．１５％以下とする。なお、不純物のうち、Ｔｉについては鋳造材の組織を微細化する効果があり添加される場合がある。このＴｉの含有量は単体で０．１％以下とする。
【００２１】
次に、本発明の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金における組織について説明する。
＜ミクロ組織＞：本発明のアルミニウム合金の組織を図１、図２に示す。図１（ａ）は組織を示す図であり、図１（ｂ）はその模式図である。図２はＡｌ相の粒界部分を含めて示した模式図である。図１、２に示すように、Ａｌ相に針状のＭｇ_２Ｓｉ（１）が析出した組織をベースとしてＭｎ、Ｃｒ系化合物（２）が材料の結晶粒内に均一に分散しており、さらにその化合物の周りに上記針状のＭｇ_２Ｓｉ組織が析出しない母相領域（３）をもつ組織であることを特徴とする。さらに図２に示すように、Ａｌ相の粒界においても実質的に上記針状のＭｇ_２Ｓｉ組織が析出しない母相領域［ＰＦＺ幅］（４）を有している。このような組織を有していることで、粒内に変形を吸収する領域を造りだし、粒内変形を促進させている。これにより、変形応力が分散し衝撃吸収特性（圧壊特性）や曲げ特性に優れた材料となる。すなわち、応力が加えられたときには、Ｍｎ、Ｃｒ系化合物（２）の界面が破壊の起点となり、破壊挙動が従来の粒界破断から粒内破断（５）へと変化する。
【００２２】
＜Ｍｎ、Ｃｒ系化合物の分散密度＞：本合金では均質化処理でＭｎ、Ｃｒ系の化合物を結晶粒内に分散させることにより衝撃吸収特性を向上させており、その分散状態は材料の焼入れ性や衝撃吸収特性に大きな影響を与える。材料中に存在する断面積０．００３μｍ^２以上のＭｎ、Ｃｒ系化合物の分布密度が０．２個／μｍ^２より少ないと十分な衝撃吸収特性が得られず１．０個／μｍ^２を超えると焼き入れ性が鋭くなりすぎる。焼き入れ性と衝撃吸収特性を良好に保つためＭｎ、Ｃｒ系化合物の分布密度が０．２個／μｍ^２以上好ましくは０．３〜０．８個／μｍ^２とする。
【００２３】
次に、本発明の衝撃吸収特性に優れ、かつ良好な焼入れ性と押出性を有するアルミニウム合金における製造方法について詳細に説明する。
【００２４】
＜均質化処理＞：本合金では均質化処理で析出するＭｎ、Ｃｒ系化合物の分散状態により、衝撃吸収特性、焼き入れ性を制御している。Ｍｎ、Ｃｒ系化合物は均質化処理温度により析出量が決まり、処理時間、昇温速度により分散状態が決定される。処理温度が高すぎると析出量が減少し衝撃吸収特性が悪化する。処理時間が短かすぎたり昇温速度が遅すぎたりすると焼入れ性が悪化する。本合金において良好な衝撃吸収特性と、焼入れ性が得られる均質化処理条件としては、昇温速度３〜５℃／分、処理温度５００〜６００℃、好ましくは５７０〜６００℃、処理時間２〜４８時間、時間効率を考えた場合、好ましくは２〜１０時間の範囲がよい。
【００２５】
＜押出加工＞
押出加工は通常熱間において行われ、加工熱を利用して溶体化を兼ねる。本発明においては必要十分な材料強度を得るために押出直後の形材温度は５４０℃以上になることが望ましい。また、押出時に材料内に繊維状の組織が残存しているとその後異常粒成長が起きて、材料内での特性が大きく変化する場合がある。そのため材料内の組織は全面等軸再結晶粒組織か、もしくは押出方向にやや伸びた伸長粒組織であることが望ましい。また、押出後の熱処理で十分な強度を得るためには押出後の形材の冷却速度を６０℃／分以上にすることが望ましい。
【００２６】
＜熱処理＞
本発明合金において形材の衝撃吸収特性（エネルギー吸収量）は材料の耐力値によって変化する。また、割れ性は耐力値、引張り強度いずれかが高くなると悪くなる傾向があり、耐力値／引張り強度比は大きい（１に近い）方が効率的にエネルギーを吸収できる。耐力値／引張り強度比を大きくするには、時効最高強度前のいわゆる亜時効状態よりも、ピーク時効、過時効状態が適している。ここで時効温度が低いと、強度は高くなるがピーク時効状態まで時間がかかりすぎ、時効温度が高すぎると十分な強度が得られないという問題がある。本発明合金において、望ましい時効熱処理温度は生産性を考慮すると、１８０〜２１０℃の範囲である。
【００２７】
本合金では、自動車用構造部材として必要な強度、衝撃吸収特性を有し、かつ均質化処理時間を極力短くすることを目的に材料組成の最適化を行っており、押出後の組織が安定な等軸粒、もしくは伸長粒組織であることから押出速度を早くすることが可能である。また複雑形状の形材や押出比５０を超える形材にも対応できるという生産性に優れた材料である。
【００２８】
【実施例】
以下、本発明の実施例について比較例と比較して説明する。表１に本実験で用いたアルミニウム鋳塊の合金組成を示す。
【００２９】
【表１】

【００３０】
これらの鋳塊に対して表２中に示した条件で均質化処理を行い、その後４５０℃まで加熱したビレットを押出速度２０〜２８ｍ／分の条件で押出加工し、続いてファンによる強制空冷を行い、表２に示す時効処理を行い角パイプ（形材断面、縦×横×厚＝５０ｍｍ×５０ｍｍ×２．５ｍｍ、コーナ部Ｒ＝０．３、長さ＝３００ｍｍ）を作製した。
【００３１】
【表２】

【００３２】
上記のようにして得られた材料について透過型電子顕微鏡により組織観察を行ったところ、以下のような組織が得られた。
【００３３】
（実施例品）
Ａｌ相に針状のＭｇ_２Ｓｉが析出した組織をベースとしてＭｎＣｒ系化合物が材料の結晶粒内に分散しており、さらにその化合物の周りに上記針状のＭｇ_２Ｓｉ組織が析出しない母相領域をもち、さらにＡｌ相の結晶粒界において針状のＭｇ_２Ｓｉ組織が析出しない母相領域を持った組織であった。
【００３４】
（比較例品）
実施例品と似たような組織を有しているが、Ｍｎ、Ｃｒ系化合物が析出しない組織であったり、また析出していても不均一に析出している組織であったり、また針状のＭｇ_２Ｓｉが不均一に析出している組織であった。
【００３５】
次にこれらの供試材からＪＩＳ５号試験片を採取し、０．２％耐力値、破断伸びを測定した。材料の焼入れ性については、押出後の形材の冷却速度の差（６０℃／分〜１００℃／分）による焼き戻し後材料強度の差から判断し、耐力値の最大値と最小値の差が１０ＭＰａ以内のものを○、１５ＭＰａ以内のものを△と評価した。割れ性については、軸圧壊試験により蛇腹状に変形したときに開口割れがないものを○とし、亀裂の発生の多いものは△、開口割れが発生したものについては×と評価した。総合評価は材料強度、焼入れ性、割れ性、均質化処理条件などを総合評価し、衝撃吸収部材として量産に適している場合を◎、製造は可能だが◎より特性が多少劣る点があるものを○と評価した。
【００３６】
表２に示したように、実施例１から４は焼入れ性、割れ性ともに良好で、０．２％耐力も２２０ＭＰａを超えており、衝撃吸収部材としての特性に優れる。実施例５、６は１〜４に比べ焼入れ性、割れ性に劣る点があるが衝撃吸収部材としての特性を十分に持つ。比較例１は規定よりＭｎを多く含み焼入れ性に劣る。比較例２から４はＭｎ、Ｃｒを含まない合金であり、割れ性に劣る。比較例５はＭｎ量が規定より少なく割れ性に劣る。比較例６はＣｒを規定より多く含むため焼入れ性に劣った材料である。
【００３７】
【発明の効果】
本発明の合金材料は、良好な軸圧壊特性を有する形材を強制空冷により作製することが可能であり、また焼入れ性に優れ材料特性が安定であること、高い押出速度、押出比の形材が作製可能であることから、複雑中空断面を持つフロントサイドメンバー、バンパーサポートなどの自動車用構造部材を製造するのに好適な材料である。
【図面の簡単な説明】
【図１】本発明のアルミニウム合金の組織を示す図である。
【図２】本発明のアルミニウム合金の、粒界領域を含めた組織を示す模式図である。
【符号の説明】
１母相に針状のＭｇ_２Ｓｉが析出した組織
２Ｍｎ、Ｃｒ系化合物
３針状のＭｇ_２Ｓｉ組織が析出しない母相領域
４針状のＭｇ_２Ｓｉ組織が析出しない母相領域
５粒内破断[0001]
[Field of the Invention]
The present invention relates to an impact-absorbing member made of an extruded Al-Mg-Si alloy and having an action of absorbing an impact load when subjected to a collision impact under compressive stress.
[0002]
[Prior art]
Conventionally, for example, in a frame structure of an automobile, application of an aluminum alloy hollow extruded material to reduce the weight of an impact absorbing member such as a side member or a bumper stay has been studied. These shock absorbing members are required to obtain a stable and high energy absorption by deforming in a bellows shape without generating crushing cracks when subjected to a load in the direction of the extrusion axis in the event of an automobile collision, and as a structural material for automobile frames. High strength (proof stress) is required.
[0003]
Heretofore, as an aluminum alloy that can be used as a shock absorbing member, many extruded Al-Mg-Si aluminum alloys have been proposed.
As an example of such an alloy extruded material, an Al-Mg-Si based alloy is extruded after heating, then air-cooled at an average cooling rate of 1000 ° C / min or more, and then subjected to artificial aging treatment (Patent Document 1). ~ 3), after homogenizing heat treatment of the Al-Mg-Si alloy, extruded by the hot direct extrusion method at the solution treatment temperature, and at the same time, quenched using room temperature water, and then subjected to artificial aging treatment. (See Patent Document 4).
[0004]
As described in the above publication, when an Al-Mg-Si-based aluminum alloy extruded material is applied to an impact absorbing member, generally, quenching treatment is performed after online press hardening or offline solution heat treatment. Has been given. Here, the aging treatment is performed to improve the strength of the extruded material, stabilize the structure, and prevent the natural aging from progressing during use to prevent the crush cracking property from deteriorating.
[0005]
Press quenching by water cooling has the advantage that almost the same characteristics as solution heat treatment after quenching after extrusion are obtained.However, there is a difference in cooling rate in the cross-section based on the cross-sectional shape and thickness difference of the extruded material. During cooling, the temperature distribution becomes non-uniform during cooling, causing distortion, which makes it difficult to reduce the dimensional accuracy and the thickness of the cross-sectional shape. There is a problem that the degree of freedom is reduced. Further, there is a problem that the cost is higher than air cooling.
[0006]
On the other hand, quenching by air cooling has the advantage of lower cost than press quenching by water cooling, but high strength (particularly proof stress) cannot be obtained depending on the alloy composition due to the limited cooling rate, and high strength can be obtained. In this case, there is a problem that energy absorption and pressure cracking resistance are poor.
[0007]
As a solution to the above problem, an Al-Mg-Si-based aluminum alloy was subjected to soaking treatment after being soaked, subjected to press quenching by air cooling immediately after extrusion, and then subjected to aging treatment for the extruded material. An extruded alloy material has been proposed (see Patent Document 5).
However, the alloy material described in Patent Document 5 is excellent in shock absorption characteristics and bending characteristics because the structure is a fibrous structure, but has a problem that the material characteristics are strongly direction-dependent because the structure is a fibrous structure. There is. In addition, in order to obtain a fibrous structure stably, it is necessary to suppress the amount of processing distortion and the amount of heat generated during extrusion, so that extrusion molding at a high speed cannot be performed and productivity is poor. From the above description, it is difficult to cope with a complicated shape or a thin-walled material having a large processing strain, and the characteristics of the extruded material cannot be fully utilized.
[0008]
[Patent Document 1]
JP-A-6-25783 [Patent Document 2]
JP-A-7-54090 [Patent Document 3]
Japanese Patent Application Laid-Open No. 7-118782 [Patent Document 4]
Japanese Patent Application Laid-Open No. 9-256096 [Patent Document 5]
JP 2000-345270 A
[Problems to be solved by the invention]
The present invention relates to an extruded Al-Mg-Si based aluminum alloy which has high strength and excellent shock absorbing properties when compressed in the extrusion axis direction, assuming quenching by air cooling which is advantageous in terms of dimensional accuracy and cost. The purpose is to obtain the material.
[0010]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found an optimum alloy composition and a heat treatment condition under which good shock absorption properties and extrudability can be obtained by quenching by air cooling, and the present invention. The present invention has been completed, and the present invention has the following aspects.
[0011]
(1) 0.45% to 0.75% (mass%, the same applies hereinafter) of Mg, 0.45% to 0.80% of Si, and 0.10% of excess Si than the balance composition of Mg ₂ Si ０．４0.40%, Mn 0.15% 〜0.40%, Cr 0０〜0.1%, with the balance consisting of unavoidable impurities and Al. An aluminum alloy having excellent shock absorbing properties and excellent quenchability and extrudability, characterized in that the aluminum alloy has no specific fibrous structure.
(2) Composition of the aluminum alloy, the Mg from 0.47 to 0.58%, the Si from .60 to .68%, the excess of Si than balanced composition of _Mg 2 Si 0.25-0. The composition described in (1) above, wherein the composition contains 40%, Mn in the range of 0.15 to 0.30%, and Cr in the range of 0 to 0.05%, with the balance being unavoidable impurities and Al. Aluminum alloy with excellent shock absorbing properties and good hardenability and extrudability.
[0012]
(3) A Mn or / and Cr-based compound is dispersed in the structure based on a structure in which Mg ₂ Si is precipitated in the Al phase, and a needle-shaped Mg ₂ Si is not deposited around the compound. An aluminum alloy having an excellent shock absorbing property as described in (1) or (2) above and having good hardenability and extrudability, characterized by having a structure having a phase region.
(4) Aluminum having excellent shock absorbing properties and good hardenability and extrudability according to (3), wherein the Mn or / and Cr-based compound has a cross-sectional area of 0.003 μm ² or more. alloy.
(5) The shock-absorbing property as described in (3) or (4) above, wherein the distribution density of the Mn or / and Cr-based compound is 0.2 / μm ² or more, and good quenching. Aluminum alloy with extrudability and extrudability.
(6) excellent in shock absorption properties as described in any one of the above (1) to (5), wherein the proof stress value is 220 MPa or more and the elongation is 10% or more, and good hardenability and extrudability. An aluminum alloy having
[0013]
(7) 0.45% to 0.75% of Mg, 0.45% to 0.80% of Si, 0.10% to 0.40% of excess Si than the balance composition of Mg ₂ Si, Mn Of aluminum alloy containing 0.15% to 0.40%, Cr in the range of 0 to 0.1%, and having the balance of unavoidable impurities and Al in the range of 500 ° C to 600 ° C. A method for producing an aluminum alloy having excellent shock absorption properties and excellent quenchability and extrudability, which is characterized by extruding and then quenching by air cooling after homogenizing treatment for 2 to 48 hours.
(8) 0.45% to 0.75% of Mg, 0.45% to 0.80% of Si, 0.10% to 0.40% of excess Si than the balance composition of Mg ₂ Si, Mn Of aluminum alloy containing 0.15% to 0.40%, Cr in the range of 0 to 0.1%, and having the balance of unavoidable impurities and Al in the range of 570 ° C to 600 ° C. After 2 to 10 hours of homogenization treatment, extrusion molding, quenching by air cooling, and then aging treatment to the maximum strength or overaged state, excellent in shock absorption characteristics, and good hardenability A method for producing an extrudable aluminum alloy.
(9) The composition of the billet of the aluminum alloy is 0.47 to 0.58% of Mg, 0.60 to 0.68% of Si, and the excess Si content is 0.25 or more than the balance composition of Mg ₂ Si. (0.40%), Mn (0.15 to 0.30%), Cr (0 to 0.05%), the balance being unavoidable impurities and Al. 7) or a method for producing an aluminum alloy having excellent shock absorption properties as described in (8) and having good hardenability and extrudability.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The alloy of the present invention can achieve the object of the present invention by having the above composition and structure.
Therefore, first, each component composition constituting the aluminum alloy having excellent shock absorbing properties of the present invention and having good hardenability and extrudability will be described.
In this specification, “%” means “% by mass”.
[0015]
<Mg>: Mg is one of the basic alloying elements in the alloy of the system targeted in the present invention, and forms a compound together with Si to contribute to improvement in strength. If the amount of Mg is less than 0.45%, the amount of Mg ₂ Si generated which contributes to the improvement in strength due to precipitation hardening decreases, so that sufficient strength cannot be obtained. The content of Mg is set to 0.45 to 0.75% because the processability decreases and the extrusion processability also decreases. Further, in order to obtain a shock absorbing member having a good balance between good strength and hardenability, it is preferable to set Mg to 0.47% to 0.58%.
[0016]
<Si>: Si is also a basic alloy element in the alloy of the present invention, and forms a compound with Mg to contribute to improvement in strength. If the content of Si is less than 0.45%, the amount of Mg ₂ Si that contributes to hardening is reduced, so that sufficient strength cannot be obtained. On the other hand, if the content exceeds 0.80%, the extrudability and bendability deteriorate. . Therefore, the amount of Si is set to 0.45 to 0.80%. Further, in order to obtain a shock absorbing member having a good balance between good strength and hardenability, Si is preferably set to 0.60 to 0.68%.
[0017]
<Mg ₂ Si>: Mg and Si combine and precipitate to improve the alloy strength. Assuming use in an automobile frame structural material, at least about 1.0% of the amount of Mg + Si is required in order to obtain the required strength (proof stress) in the T5 treatment. However, when the quenching property is considered, the quenching property deteriorates when the amount of Mg ₂ Si increases, and the extrudability deteriorates when the Mg amount increases. Therefore, the amount of Mg + Si is preferably in the range of 1.0 to 1.3%. On the other hand, Si excessively added to the Mg ₂ Si balance composition has a smaller effect of impairing the hardenability as compared with a material having a large Mg content, and can increase the material strength. However, if the amount of excess Si is too large, hardenability deteriorates. The appropriate excess Si amount is preferably 0.10% to 0.40%, and 0.25% to 0.40% to obtain an impact absorbing member having a good balance between good extrudability and hardenability. Is more preferable.
[0018]
<Mn>: Mn combines with Al and Si in the billet homogenization treatment to form an Al-Mn-Si-based compound, and the effect of dispersing the compound promotes intragranular deformation of the material to improve the shock absorption characteristics. There is. If the addition amount is less than 0.15%, the effect of promoting intragranular deformation is small, and if it exceeds 0.40%, the hardenability becomes too sharp, and the quenching by air cooling does not cause quenching and the required strength cannot be obtained. Alternatively, a coarse compound is formed, and this compound phase acts as a starting point of minute destruction, so that the moldability and the crushability are reduced. Therefore, the Mn content is set to 0.15 to 0.40%, more preferably 0.15 to 0.30%.
[0019]
<Cr>: Cr is a component that is added as necessary and, like Mn, refines and stabilizes crystal grains and increases strength. In addition, as for Mn, a compound such as an Al-Cr-Si-based compound is dispersed and precipitated in crystal grains like Mn, so that intragranular deformation is promoted, so that shock absorption is improved. However, Cr has a large effect on hardenability, and if Cr exceeds 0.1%, the hardenability of the material deteriorates, and sufficient strength cannot be obtained by hardening by air cooling. Therefore, the amount of Cr added is in the range of 0% to 0.1%, more preferably 0% to 0.05%.
Since the addition amount of Mn and Cr affects the precipitation amount of Mn and Cr-based compounds that promote intragranular deformation, the addition amount of Mn + Cr is 0 for the same reason that the composition range of Mn and Cr is limited. The content is preferably in the range of 0.2 to 0.3%.
[0020]
<Inevitable impurities>: Among the inevitable impurities, Fe is the impurity contained most in aluminum ingots. If it exceeds 0.35% in the alloy, coarse intermetallic compounds are crystallized at the time of production, and the mechanical properties of the alloy are reduced. Impair the nature. Therefore, the content of Fe is restricted to 0.35% or less. It is desirably 0.30% or less, more desirably 0.25% or less. Further, when casting an aluminum alloy, impurities are mixed from various routes such as a base metal and an intermediate alloy of an additive element. There are various elements to be mixed, but impurities other than Fe alone have 0.05% or less, and if the total amount is 0.15% or less, it hardly affects the properties of the alloy. Therefore, these impurities are set to 0.05% or less in a simple substance and 0.15% or less in total. Of the impurities, Ti may be added because it has the effect of refining the structure of the cast material. The content of Ti alone is set to 0.1% or less.
[0021]
Next, the structure of the aluminum alloy according to the present invention, which has excellent shock absorption properties and has good hardenability and extrudability, will be described.
<Microstructure> The structure of the aluminum alloy of the present invention is shown in FIGS. FIG. 1A is a diagram showing a tissue, and FIG. 1B is a schematic diagram thereof. FIG. 2 is a schematic diagram including the grain boundaries of the Al phase. As shown in FIGS. 1 and 2, Mn and Cr-based compounds (2) are uniformly dispersed in the crystal grains of the material based on the structure in which acicular Mg ₂ Si (1) is precipitated in the Al phase. Further, the structure is characterized by having a matrix phase (3) around which the acicular Mg ₂ Si structure does not precipitate. Further, as shown in FIG. 2, even at the grain boundary of the Al phase, there is a matrix phase [PFZ width] (4) in which the acicular Mg ₂ Si structure is not substantially precipitated. By having such a structure, a region for absorbing the deformation is created in the grain, and the intragranular deformation is promoted. Thereby, the deformation stress is dispersed, and the material is excellent in shock absorption characteristics (crush characteristics) and bending characteristics. That is, when a stress is applied, the interface between the Mn and Cr-based compounds (2) becomes the starting point of the fracture, and the fracture behavior changes from the conventional intergranular fracture to the intragranular fracture (5).
[0022]
<Dispersion density of Mn and Cr-based compounds>: In this alloy, the Mn and Cr-based compounds are dispersed in the crystal grains by homogenization treatment to improve the impact absorption characteristics. And shock absorption characteristics. If the distribution density of the Mn and Cr compounds having a cross-sectional area of 0.003 μm ² or more in the material is less than 0.2 / μm ² , sufficient impact absorption characteristics cannot be obtained and the density exceeds 1.0 / μm ² . And the hardenability becomes too sharp. In order to maintain good hardenability and shock absorption characteristics, the distribution density of Mn and Cr-based compounds is 0.2 / μm ² or more, preferably 0.3 to 0.8 / μm ² .
[0023]
Next, the method for producing an aluminum alloy of the present invention which has excellent shock absorbing properties and has good hardenability and extrudability will be described in detail.
[0024]
<Homogenization treatment>: In the present alloy, the impact absorption characteristics and hardenability are controlled by the dispersion state of Mn and Cr compounds precipitated in the homogenization treatment. The precipitation amount of the Mn and Cr-based compounds is determined by the homogenization treatment temperature, and the dispersion state is determined by the treatment time and the heating rate. If the treatment temperature is too high, the amount of precipitation decreases and the shock absorption characteristics deteriorate. If the treatment time is too short or the rate of temperature rise is too slow, the hardenability deteriorates. The homogenization treatment conditions under which good shock absorption characteristics and hardenability are obtained in the present alloy are as follows: a heating rate of 3 to 5 ° C / min, a treatment temperature of 500 to 600 ° C, preferably 570 to 600 ° C, and a treatment time of 2 to 2. When considering the time efficiency of 48 hours, the range is preferably 2 to 10 hours.
[0025]
<Extrusion processing>
Extrusion processing is usually performed at a hot temperature, and also serves as a solution using the processing heat. In the present invention, in order to obtain necessary and sufficient material strength, it is desirable that the temperature of the section immediately after extrusion is 540 ° C. or higher. Further, if a fibrous structure remains in the material at the time of extrusion, abnormal grain growth may occur thereafter, and the characteristics in the material may change significantly. Therefore, the structure in the material is desirably an equiaxed recrystallized grain structure over the entire surface or an elongated grain structure slightly elongated in the extrusion direction. Further, in order to obtain sufficient strength by heat treatment after extrusion, it is desirable to set the cooling rate of the extruded profile to 60 ° C./min or more.
[0026]
<Heat treatment>
In the alloy of the present invention, the impact absorption characteristics (energy absorption amount) of the profile change depending on the proof stress value of the material. In addition, the cracking property tends to deteriorate when either the proof stress or the tensile strength increases, and the larger the proof stress / tensile strength ratio (closer to 1), the more efficiently energy can be absorbed. In order to increase the proof stress / tensile strength ratio, the peak aging and overaging conditions are more suitable than the so-called sub-aging condition before the maximum aging strength. Here, if the aging temperature is low, the strength increases, but it takes too much time to reach the peak aging state, and if the aging temperature is too high, sufficient strength cannot be obtained. In the alloy of the present invention, a desirable aging heat treatment temperature is in a range of 180 to 210 ° C. in consideration of productivity.
[0027]
This alloy has the strength and shock absorption properties required for structural members for automobiles, and the material composition is optimized for the purpose of minimizing the homogenization time, and the structure after extrusion is stable. The extrusion speed can be increased because of the equiaxed grain or elongated grain structure. In addition, it is a material excellent in productivity, capable of coping with a shape having a complicated shape and a shape having an extrusion ratio of more than 50.
[0028]
【Example】
Hereinafter, examples of the present invention will be described in comparison with comparative examples. Table 1 shows the alloy composition of the aluminum ingot used in this experiment.
[0029]
[Table 1]

[0030]
These ingots were homogenized under the conditions shown in Table 2, and then the billet heated to 450 ° C. was extruded at an extrusion speed of 20 to 28 m / min, followed by forced air cooling by a fan. Then, an aging treatment shown in Table 2 was performed to produce a square pipe (profile section, length x width x thickness = 50 mm x 50 mm x 2.5 mm, corner R = 0.3, length = 300 mm).
[0031]
[Table 2]

[0032]
When the structure of the material obtained as described above was observed with a transmission electron microscope, the following structure was obtained.
[0033]
(Example product)
A matrix in which a MnCr-based compound is dispersed in crystal grains of a material based on a structure in which acicular Mg ₂ Si is precipitated in an Al phase, and the acicular Mg ₂ Si structure is not precipitated around the compound. The structure had a region and further had a matrix region in which no acicular Mg ₂ Si structure was precipitated at the crystal grain boundary of the Al phase.
[0034]
(Comparative product)
It has a structure similar to that of the example product, but a structure in which Mn and Cr-based compounds do not precipitate, or a structure in which even if it precipitates, it is a non-uniform precipitate, or a needle-like structure. Of Mg ₂ Si was unevenly precipitated.
[0035]
Next, JIS No. 5 test pieces were collected from these test materials, and the 0.2% proof stress value and the elongation at break were measured. The hardenability of the material is judged from the difference in the strength of the material after tempering due to the difference in the cooling rate of the extruded profile (60 ° C./min to 100 ° C./min), and the difference between the maximum value and the minimum value of the proof stress value. Was evaluated as ○ when it was within 10 MPa, and Δ when it was within 15 MPa. Regarding the cracking property, a sample having no opening cracks when deformed in a bellows shape by an axial crush test was evaluated as ○, a sample having many cracks was evaluated as Δ, and a sample having an opening crack was evaluated as ×. Comprehensive evaluation is based on comprehensive evaluation of material strength, hardenability, cracking properties, homogenization processing conditions, etc., ◎ when it is suitable for mass production as an impact absorbing member, O was evaluated.
[0036]
As shown in Table 2, Examples 1 to 4 have good hardenability and cracking properties, and have a 0.2% proof stress exceeding 220 MPa, and are excellent in properties as a shock absorbing member. Examples 5 and 6 are inferior in hardenability and cracking properties as compared with 1-4, but have sufficient properties as a shock absorbing member. Comparative Example 1 contains more Mn than specified and is inferior in hardenability. Comparative Examples 2 to 4 are alloys containing neither Mn nor Cr, and are inferior in cracking properties. In Comparative Example 5, the amount of Mn was less than the specified value and the cracking property was poor. Comparative Example 6 is a material that is inferior in hardenability because it contains more Cr than specified.
[0037]
【The invention's effect】
The alloy material of the present invention can produce a profile having good axial crushing properties by forced air cooling, and has excellent quenching properties, stable material properties, a high extrusion speed, and a high extrusion ratio. Is a material suitable for manufacturing structural members for automobiles such as front side members and bumper supports having a complicated hollow cross section.
[Brief description of the drawings]
FIG. 1 is a view showing a structure of an aluminum alloy of the present invention.
FIG. 2 is a schematic diagram showing a structure including a grain boundary region of the aluminum alloy of the present invention.
[Explanation of symbols]
1 tissue 2 Mn _{to Mg} 2 Si in the needle in the matrix is precipitated, Cr compound 3 needle-like _Mg 2 Si tissue matrix region 4 needle-like _Mg 2 Si organizations that do not precipitate does not precipitate the matrix phase region 5 grains Inner break

Claims

0.45% to 0.75% of Mg (mass%, the same applies hereinafter), 0.45% to 0.80% of Si, and 0.10% to 0.2% of excess Si than the balance composition of Mg ₂ Si. 40%, 0.15% to 0.40% of Mn, 0 to 0.1% of Cr, the balance being unavoidable impurities and Al, and the structure is substantially fiber An aluminum alloy having an excellent shock absorbing property and a good quenchability and extrudability, characterized in that the aluminum alloy has no texture.

When the composition of the aluminum alloy is 0.47 to 0.58% of Mg, 0.60 to 0.68% of Si, and 0.25 to 0.40% of Si in excess of the balance composition of Mg ₂ Si, 2. The shock absorbing characteristic according to claim 1, wherein Mn is contained in a range of 0.15 to 0.30%, Cr is contained in a range of 0 to 0.05%, and the balance is composed of unavoidable impurities and Al. Aluminum alloy with excellent hardenability and extrudability.

Based on the structure in which Mg ₂ Si is precipitated in the Al phase, a Mn or / and Cr-based compound is dispersed in the structure, and a matrix region in which acicular Mg ₂ Si is not precipitated around the compound is further formed. 3. The aluminum alloy according to claim 1, wherein the aluminum alloy has an excellent shock absorbing property and good hardenability and extrudability.

4. The aluminum alloy according to claim 3, wherein the Mn or / and Cr-based compound has a cross-sectional area of 0.003 [mu] m < ² > or more.

5. The shock absorbing property according to claim 3 or 4, wherein the distribution density of the Mn or / and Cr-based compound is 0.2 / μm ² or more, and the hardening property and the extrudability are good. Aluminum alloy.

The aluminum alloy having excellent impact absorption properties and good hardenability and extrudability according to any one of claims 1 to 5, wherein a proof stress value is 220 MPa or more and an elongation is 10% or more.

0.45% to 0.75% of Mg (mass%, the same applies hereinafter), 0.45% to 0.80% of Si, and 0.10% to 0.2% of excess Si than the balance composition of Mg ₂ Si. A billet of an aluminum alloy containing 40%, 0.15% to 0.40% of Mn, and 0 to 0.1% of Cr, and having a balance of unavoidable impurities and Al at 500 ° C. Manufacture of an aluminum alloy having excellent shock absorption properties and good quenchability and extrudability, characterized by extruding and quenching by air cooling after homogenization treatment in the range of 600 ° C. for 2 to 48 hours. Method.

0.45% to 0.75% of Mg (mass%, the same applies hereinafter), 0.45% to 0.80% of Si, and 0.10% to 0.2% of excess Si than the balance composition of Mg ₂ Si. A billet of an aluminum alloy containing 40%, Mn in a range of 0.15% to 0.40%, and Cr in a range of 0 to 0.1%, and having a balance of unavoidable impurities and Al at 570 ° C. Excellent impact absorption characteristics, characterized by extruding, quenching by air cooling, and then aging to the maximum strength or overaged state after homogenizing treatment at 600 ° C for 2 to 10 hours. A method for producing an aluminum alloy having excellent hardenability and extrudability.

The composition of the billet of the aluminum alloy is 0.47 to 0.58% of Mg, 0.60 to 0.68% of Si, and the amount of Si in excess of the balance composition of Mg ₂ Si is 0.25 to 0. 9. A composition containing 40%, Mn in the range of 0.15 to 0.30%, and Cr in the range of 0 to 0.05%, with the balance being unavoidable impurities and Al. A method for producing an aluminum alloy having excellent shock absorption properties as described and having good hardenability and extrudability.