JP2004027253A

JP2004027253A - Aluminum alloy sheet for molding, and method of producing the same

Info

Publication number: JP2004027253A
Application number: JP2002181732A
Authority: JP
Inventors: Masamichi Aono; 青野　雅路; Akira Hibino; 日比野　旭; Toshiki Muramatsu; 村松　俊樹; Makoto Saga; 佐賀　誠; Takeshi Takada; 高田　健; Yuichi Sato; 佐藤　雄一
Original assignee: Nippon Steel Corp; Toyota Motor Corp; Furukawa Sky KK
Current assignee: Nippon Steel Corp; Toyota Motor Corp; Furukawa Sky KK
Priority date: 2002-06-21
Filing date: 2002-06-21
Publication date: 2004-01-29

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al alloy sheet for molding which has satisfactory hem bendability and high baking hardenability. <P>SOLUTION: The Al alloy sheet comprises 0.4-0.7% Mg and 0.8-1.2% Si, one or more of metals selected from 0.03-0.4% Mn, 0.01-0.4% Cr, 0.01-0.4% Zr, 0.01-0.4% V, 0.03-0.5% Fe, 0.005-0.2% Ti and 0.03-2.5% Zn, in which the content of Cu is controlled to ≤0.1%, and the balance substantially Al. In a region of 1/4 of the sheet thickness from the surface, cube orientation density is more than two fold of gross orientation density, and is four fold of that of a random sample. The Al alloy sheet has an electric conductivity of ≤54%IACS, and a mean crystal grain size of ≥4.5 in an ASTM number. Hot rolling is started at ≥370°C so as to obtain a sheet thickness of 1.0-8.0 mm and a finishing temperature of 180-350°C. Further, cooling is performed from the temperature range in the finishing of the hot rolling to ≤100°C at ≤100°C/min. Also, after cold rolling at a rolling ratio of ≥30%, solution treatment is performed under holding at ≥480°C for ≤5 min or without the holding, and cooling is performed to 50 to <150°C at ≥100°C/min. Then, stabilization treatment is performed within the above temperature range for ≥2 hr. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明が属する技術分野】
この発明は、自動車ボディシートやそのほか各種自動車部品、各種機械器具、家電製品やその部品等の素材として、成形加工および塗装焼付を施して使用されるＡｌ−Ｍｇ−Ｓｉ系のアルミニウム合金板およびその製造方法に関するものであり、成形性、特にヘム曲げ性が良好であるとともに、焼付硬化性が良好で塗装焼付後の強度が高い成形加工用アルミニウム合金板およびその製造方法に関するものである。
【０００２】
【従来の技術】
従来自動車のボディシートとしては、主として冷延鋼板を使用することが多かったが、最近では車体軽量化等の観点から、アルミニウム合金圧延板を使用することが多くなっている。ところで自動車のボディシートはプレス加工を施して使用するところから、成形加工性が優れていること、また成形加工時におけるリューダースマークが発生しないことが要求され、また外板としての接合のためにヘム曲げ加工を施して使用することが多いところから、成形性のうちでも特にヘム曲げ性が優れていることが要求され、そのほか高強度を有することも必須であり、特に塗装焼付を施すのが通常であるため、塗装焼付後に高強度が得られることが要求される。
【０００３】
従来このような自動車用ボディシート向けのアルミニウム合金としては、Ａｌ−Ｍｇ系合金のほか、時効性を有するＡｌ−Ｍｇ−Ｓｉ系合金が主として使用されている。この時効性Ａｌ−Ｍｇ−Ｓｉ系合金は、塗装焼付前の成形加工時においては比較的強度が低くて成形性が優れている一方、塗装焼付時の加熱によって時効されて塗装焼付後の強度が高くなる利点を有するほか、リューダースマークが発生しない等の利点を有する。
【０００４】
なお上述のような塗装焼付時における時効硬化を期待した時効性Ａｌ−Ｍｇ−Ｓｉ系合金板の製造方法としては、鋳塊を均質化熱処理した後、熱間圧延および冷間圧延を行なって所定の板厚とし、かつ必要に応じて熱間圧延と冷間圧延との間あるいは冷間圧延の中途において中間焼鈍を行ない、冷間圧延後に溶体化処理を行なって焼入れるのが通常である。
【０００５】
【発明が解決しようとする課題】
前述のような自動車用ボディシート向けの時効性Ａｌ−Ｍｇ−Ｓｉ系合金板についての従来の一般的な製造方法により得られた板では、最近の自動車用ボディシートに要求される特性を充分に満足させることは困難であった。
【０００６】
すなわち、最近ではコストの一層の低減や自動車車体の軽量化等のために、自動車用ボディシートについても従来よりさらに薄肉化することが強く要求されており、そのため薄肉でも充分な強度が得られるように、一層の高強度化が求められると同時に、成形性、特にヘム曲げ性の改善が強く要求されているが、これらの性能をバランスよく満足させる点については、従来の一般的な製造方法によって得られたＡｌ−Ｍｇ−Ｓｉ系合金板では不充分であった。特にヘム曲げ加工は、曲げ内径が１ｍｍ以下の１８０°曲げという過酷な曲げ加工であるため、良好なヘム曲げ性と強度とを両立させることが困難であるという問題があった。
【０００７】
また塗装焼付については、省エネルギおよび生産性の向上、さらには高温に曝されることが好ましくない樹脂等の材料との併用などの点から、従来よりも焼付温度を低温化し、また焼付時間も短時間化する傾向が強まっている。しかしながら従来の一般的な製法により得られた時効性Ａｌ−Ｍｇ−Ｓｉ系合金板の場合、低温・短時間の塗装焼付処理では、塗装焼付時の硬化（焼付硬化）が不足し、塗装焼付後に充分な高強度が得難くなる問題があった。
【０００８】
さらに、従来の一般的な製法により得られた時効性Ａｌ−Ｍｇ−Ｓｉ系合金板では、塗装焼付後に高強度を得るために焼付硬化性を高めようとすれば、素材の延性と曲げ加工性（特にヘム曲げ性）が低下しがちとなるという問題が生じる。
【０００９】
この発明は以上の事情を背景としてなされたもので、良好な成形加工性、特に良好なヘム曲げ加工性を有すると同時に、焼付硬化性が優れていて、塗装焼付時における強度上昇が大きい成形加工用アルミニウム合金板とその製造方法を提供することを目的とするものである。
【００１０】
なおこの明細書において、ヘム曲げ性が良好であるとは、圧延方向に対して一方向のみのヘム曲げ性だけではなく、全方向のヘム曲げ性が良好であることを意味する。
【００１１】
【課題を解決するための手段】
前述のような課題を解決するべく本発明者等が実験・検討を重ねた結果、ヘム曲げ性の向上には、材料の結晶粒径制御などのほか、特に金属組織における結晶方位の適切な制御が極めて重要であることを見出した。そして板製造プロセス条件、特に熱間圧延条件と、溶体化処理後の冷却条件および安定化処理条件を適切に規制して、結晶方位条件等を適切に調整することによって、前述の課題を一挙に解決し得ることを見出し、この発明をなすに至ったのである。
【００１２】
具体的には、請求項１の発明の成形加工用アルミニウム合金板は、Ｍｇ０．４〜０．７％、Ｓｉ０．８〜１．２％を含有し、かつＭｎ０．０３〜０．４％、Ｃｒ０．０１〜０．４％、Ｚｒ０．０１〜０．４％、Ｖ０．０１〜０．４％、Ｆｅ０．０３〜０．５％、Ｔｉ０．００５〜０．２％、Ｚｎ０．０３〜２．５％のうちから選ばれた１種または２種以上を含有し、さらにＣｕが０．１％以下に規制され、残部がＡｌおよび不可避的不純物よりなる合金を素材とし、板表面から板厚の１／４の深さまでの板表層領域において、結晶組織のキューブ方位密度が、圧延方向を軸としてキューブ方位と４５°の回転関係にあるゴス方位密度の２倍以上でありかつそのキューブ方位密度がランダム試料の４倍以上であり、さらに導電率が５４％ＩＡＣＳ以下で、かつ平均結晶粒径がＡＳＴＭナンバーで４．５以上であることを特徴とするものである。
【００１３】
さらに請求項２の発明の成形加工用アルミニウム合金板の製造方法は、請求項１に記載の成形加工用アルミニウム合金板を製造するにあたり、前記成分組成のアルミニウム合金鋳塊を溶体化処理後、熱間圧延を３７０℃以上で開始して、１．０〜８．０ｍｍの範囲内の板厚まで熱間圧延し、かつその熱間圧延において、上がり温度を１８０〜３５０℃の温度域内に制御するとともに、熱間圧延上がりの１８０〜３５０℃の温度域から１００℃以下の温度域までの冷却速度を１００℃／ｈｒ以下に制御し、その後冷間圧延を行なってから溶体化処理を施し、さらに安定化処理を行なうことを特徴とするものである。
【００１４】
また請求項３の発明の成形加工用アルミニウム合金板の製造方法は、請求項２に記載のアルミニウム合金板の製造方法において、熱間圧延後の冷間圧延を、３０％以上の圧延率で行い、得られた圧延板に対する溶体化処理を、４８０℃以上の温度で５分以内の保持もしくは保持なしの条件で行なってから１００℃／ｍｉｎ以上の平均冷却速度で５０℃以上１５０℃未満の温度域まで冷却し、続いてその温度域内で２時間以上の安定化処理を行なうことを特徴とするものである。
【００１５】
【発明の実施の形態】
先ずこの発明の成形加工用アルミニウム合金板における成分組成の限定理由について説明する。
【００１６】
Ｍｇ：
Ｍｇはこの発明で対象としている系の合金で基本となる合金元素であって、Ｓｉと共同して強度向上に寄与する。Ｍｇ量が０．４％未満では塗装焼付時に析出硬化によって強度向上に寄与するＧ．Ｐ．ゾーンの生成量が少なくなるため、充分な強度向上が図られず、一方０．７％を越えれば、粗大なＭｇ−Ｓｉ系の金属間化合物が生成され、成形性、特に曲げ加工性が低下するから、Ｍｇ量は０．４〜０．７％の範囲内とした。
【００１７】
Ｓｉ：
Ｓｉもこの発明の系の合金で基本となる合金元素であって、Ｍｇと共同して強度向上に寄与する。またＳｉは、鋳造時に金属Ｓｉの晶出物として生成され、その金属Ｓｉ粒子の周囲が加工によって変形されて、溶体化処理の際に再結晶核の生成サイトとなるため、再結晶組織の微細化にも寄与する。Ｓｉ量が０．８％未満では上記の効果が充分に得られず、一方１．２％を越えれば粗大なＳｉ粒子や粗大なＭｇ−Ｓｉ系の金属間化合物が生じて、曲げ加工性の低下を招く。したがってＳｉ量は０．８〜１．２％の範囲内とした。
【００１８】
Ｍｎ、Ｃｒ、Ｚｒ、Ｖ、Ｆｅ、Ｔｉ、Ｚｎ：
これらの元素は、強度向上や結晶粒微細化、あるいは時効性の向上や表面処理性の向上に有効であり、いずれか１種または２種以上を添加する。これらのうちＭｎ、Ｃｒ、Ｚｒ、Ｖは強度向上と結晶粒の微細化および組織の安定化に効果がある元素であり、Ｍｎの含有量が０．０３％未満、またＣｒ、Ｚｒ、Ｖの含有量がそれぞれ０．０１％未満では上記の効果が充分に得られず、一方Ｍｎ、Ｃｒ、Ｚｒ、Ｖの含有量がそれぞれ０．４％を越えれば、上記の効果が飽和するばかりでなく、多数の金属間化合物が生成されて、成形性、特にヘム曲げ性に悪影響を及ぼすおそれがあり、したがってＭｎは０．０３〜０．４％の範囲内、Ｃｒ、Ｚｒ、Ｖはいずれも０．０１〜０．４％の範囲内とした。またＴｉも強度向上と鋳塊組織の微細化に有効な元素であり、その含有量が０．００５％未満では充分な効果が得られず、一方０．２％を越えればＴｉ添加の効果が飽和するばかりでなく、粗大な晶出物が生じるおそれがあるから、Ｔｉ量は０．００５〜０．２％の範囲内とした。さらにＦｅも強度向上と結晶粒微細化に有効な元素であり、その含有量が０．０３％未満では充分な効果が得られず、一方０．５％を越えれば成形性が低下するおそれがあり、したがってＦｅ量は０．０３〜０．５％の範囲内とした。またＺｎは時効性向上を通じて強度向上に寄与するとともに表面処理性の向上に有効な元素であり、Ｚｎの添加量が０．０３％未満では上記の効果が充分に得られず、一方２．５％を越えれば成形性が低下するから、Ｚｎ量は０．０３〜２．５％の範囲内とした。
【００１９】
Ｃｕ：
Ｃｕは強度向上および成形性向上に有効な元素ではあるが、合金の耐食性（耐粒界腐食性、耐糸錆性）を劣化させる元素であり、特にＣｕ量が０．１％を越えればその傾向が顕著となるから、Ｃｕの含有量は０．１％未満に規制することとした。
【００２０】
以上の各元素のほかは、基本的にはＡｌおよび不可避的不純物とすれば良い。
【００２１】
なお前述のＭｎ、Ｃｒ、Ｚｒ、Ｖ、Ｔｉ、ＺｎおよびＦｅの含有量範囲は、それぞれ積極的に添加する場合の範囲として示したものであり、いずれも下限値より少ない量を不純物として含有する場合を排除するものではない。特に０．０３％未満のＦｅは、通常のアルミ地金を用いれば不可避的に含有されるのが通常である。
【００２２】
また時効性Ａｌ−Ｍｇ−Ｓｉ系合金においては、高温時効促進元素あるいは室温時効抑制元素であるＡｇ、Ｉｎ、Ｃｄ、Ｂｅ、あるいはＳｎを微量添加することがあるが、この発明の場合も微量添加であればこれらの元素の添加も許容され、それぞれ０．３％以下であれば特に所期の目的を損なうことはない。
【００２３】
なおまた、一般のＡｌ合金においては、結晶粒微細化のために前述のＴｉと同時にＢを添加することもあり、この発明の場合もＴｉとともに５００ｐｐｍ以下のＢを添加することは許容される。
【００２４】
ここで、この発明の成形加工用アルミニウム合金板においては、合金の成分組成を前述のように調整するばかりではなく、平均結晶粒径および導電率を適切に調整する必要がある。
【００２５】
すなわち、結晶粒径はヘム曲げ性に影響を与え、平均結晶粒径がＡＳＴＭナンバーで４．５未満では、成形加工時に肌荒れが生じやすく、ヘム曲げ性も低下する。したがって平均結晶粒径をＡＳＴＭナンバーで４．５以上とする必要がある。
【００２６】
また合金板の導電率は、合金中のＭｇ、Ｓｉの固溶量の指標となり、塗装焼付け後の強度に関係する。導電率が５４％ＩＡＣＳを越える場合は、ＭｇおよびＳｉの固溶量が少なく、時効析出による硬化が充分に図られないため、塗装焼付け後に充分な高強度が得られなくなる。そこで導電率を５４％ＩＡＣＳ以下に規制することとした。なお導電率の下限は特に定めないが、通常はこの系の合金で導電率を４０％ＩＡＣＳ未満にしても、塗装焼付硬化性の効果は飽和し、また工業的に４０％ＩＡＣＳ未満を達成することは困難であり、したがって通常は４０〜５４％ＩＡＣＳの範囲内とすれば良い。
【００２７】
さらにこの発明の成形加工用アルミニウム合金板においては、合金の成分組成、平均結晶粒径、および導電率ばかりでなく、金属組織条件として、結晶方位密度の条件が極めて重要である。
【００２８】
すなわち本発明者等は、ヘム曲げ性と結晶方位密度との関係について慎重かつ詳細に実験・検討を重ねた結果、合金板の表面層、特に板表面から板厚の１／４の深さまでの領域における結晶のキューブ（Ｃｕｂｅ）方位密度がヘム曲げ性に大きな影響を与えることを見出した。そして、板表面から板厚の１／４の深さまでの板表層領域において、
Ａ：キューブ方位密度が、圧延方向を軸としてキューブ方位と４５°の回転関係にあるゴス方位密度の２倍以上であること、
Ｂ：キューブ方位密度が、ランダム試料の４倍以上であること、
の２条件を満たすことによって、確実かつ安定して優れたヘム曲げ性が得られることを見出し、そこでこれらの条件を規定した。
【００２９】
ここで、上記のＡ、Ｂの２条件が満たされない場合には、ヘム曲げ加工時に曲げ部位にすべり線が発達して、曲げ歪が集中しやすく、その歪が集中した箇所から割れが発達しやすくなってヘム曲げ性を低下させる。したがって結晶方位密度に関して前記２条件を満たすことがヘム曲げ性の安定した向上のために重要である。
【００３０】
なお前記Ｂの条件において、より一層良好なヘム曲げ性を確保するためには、板表面層部分のキューブ方位密度を、ランダム方位を有する試料の８倍以上とすることが望ましい。
【００３１】
次にこの発明の成形加工用アルミニウム合金板の製造方法、すなわち請求項２、請求項３で規定する製造方法について説明する。この製造方法は、請求項１に係る成形加工用アルミニウム合金板、すなわち前述の結晶方位密度条件Ａ、Ｂや平均結晶粒条件、導電率条件を満たすアルミニウム合金板を、確実かつ安定して得るためのものである。
【００３２】
製造方法としては、先ず前述のような成分組成の合金を常法に従って溶製し、ＤＣ鋳造法などによって鋳造する。得られた鋳塊に対しては、通常は均質化処理を行なってから熱間圧延を施して熱延板とし、さらに冷間圧延を行なって製品板厚とし、その後溶体化処理−冷却（焼入れ）を施した後、最終的に安定化処理を行なう。
【００３３】
ここで、鋳塊に対する均質化処理の加熱温度、加熱保持時間は特に限定しないが、通常は４８０℃以上で１〜２４時間程度の保持とすることが好ましい。また、均質化処理後、冷却せずにそのまま熱間圧延を開始しても良い。
【００３４】
熱間圧延は、結晶方位の制御に大きな影響を与えるから、最終板の結晶方位密度条件を前述のように調整して良好なヘム曲げ性を確保するためには、熱間圧延過程の諸条件を厳密に規制必要がある。すなわち、熱間圧延過程においては、熱延開始温度を３７０℃以上とし、熱延上りの板厚を１．０〜８．０ｍｍとして、熱間圧延上り温度を１８０〜３５０℃の温度域に制御し、さらに熱間圧延上りの１８０〜３５０℃の温度域から１００℃以下の温度域までの冷却過程の冷却速度を１００℃／ｈｒ以下とする必要がある。
【００３５】
ここで熱間圧延中においては、固溶元素が析出したり、回復・再結晶が繰り返されたりするため、熱間圧延の開始温度、終了温度、冷却速度を上述のように厳密にコントロールすることが、結晶方位の制御にとって極めて重要であり、上述のような熱間圧延条件を１つでも外せば、請求項１で規定する結晶方位密度条件を満たすことが困難となる。また熱間圧延開始温度を３７０℃以上とすることは、Ｍｇ、Ｓｉ元素の固溶量を確保して、請求項１で規定する導電率５４％以下の条件を確保するためにも不可欠である。また特に熱間圧延上りの１８０〜３５０℃の温度域から１００℃以下の温度域までの冷却速度が１００℃／ｈｒを越えれば、材料の回復・再結晶が著しく制御されてしまって、前述の結晶方位条件を満たすことが極めて困難となってしまう。なお平均冷却速度の下限は特に規定しないが、生産性を考慮して１℃／ｈｒ以上とするのが一般的である。また熱間圧延開始温度の上限も特に規定しないが、共晶融解等を考慮して、５９０℃以下とするのが通常である。
【００３６】
熱間圧延後には最終溶体化処理までの間に，３０％以上の圧延率での冷間圧延を行なう。このように圧延率３０％以上の冷間圧延によって、材料に歪エネルギーが蓄積されて、溶体化処理時に生成された結晶粒が微細になるばかりでなく、前述のキューブ方位密度を高め、最終的に良好なヘム曲げ性を得るためにも極めて有効となる。最終溶体化処理までの冷間圧延率が３０％未満では、溶体化処理後の結晶粒が粗大になると同時に、前述のキューブ方位密度条件を満たすことが困難となり、良好なヘム曲げ性が得られなくなる。なお溶体化処理までの間の冷間圧延率の上限は特に規定しないが、通常は９０％程度以下であれば良い。
【００３７】
上述のようにして冷間圧延により所要の製品板厚とした後、４８０℃以上の温度で５分以内の溶体化処理を行なう。この溶体化処理は、Ｍｇ_２Ｓｉ、単体Ｓｉ等をマトリックスに固溶させ、これにより焼付硬化性を付与して塗装焼付後の強度向上を図るために重要な工程である。またこの溶体化処理工程は、Ｍｇ_２Ｓｉ、単体Ｓｉ粒子等の固溶により、第２相粒子の分布密度を低下させ、ひいては延性と曲げ性の向上にも寄与し、さらには、材料の再結晶により全般的に良好な成形性を得るためにも必要な工程である。さらにこの溶体化処理は、再結晶により再結晶集合組織を形成して、請求項１で規定する結晶方位密度条件を満たす最終板を得るために不可欠な工程でもある。
【００３８】
ここで、溶体化処理温度が４８０℃未満では、室温の経時変化の抑制には有利となると思われるが、Ｍｇ_２Ｓｉ、Ｓｉなどの固溶量が少なくなり、その結果充分な焼付硬化性が得られなくなるばかりでなく、延性と曲げ性も著しく悪化する。一方溶体化処理温度の上限は特に規定しないが、共晶融解の発生のおそれや再結晶粒粗大化等を考慮して、通常は５８０℃以下とすることが望ましい。また溶体化処理における保持時間が５分を越えれば、溶体化効果が飽和し、経済性を損なうばかりでなく、結晶粒の粗大化を招くおそれもあるから、溶体化処理の時間は５分以内とする。
【００３９】
溶体化処理後には、１００℃／ｍｉｎ以上の平均冷却速度で、５０〜１５０℃の温度域まで冷却（焼入れ）する。ここで、溶体化処理後の冷却速度が１００℃／ｍｉｎ未満では、冷却中にＭｇ_２Ｓｉあるいは単体Ｓｉが粒界に多量に析出してしまい、成形性、特にヘム曲げ性が低下すると同時に、焼付硬化性が低下して塗装焼付時の充分な強度向上が望めなくなる。
【００４０】
上述のように、４８０℃以上の温度で溶体化処理を行なって、１００℃／ｍｉｎ以上の平均冷却速度で５０〜１５０℃未満の温度域内まで冷却（焼入れ）した後には、５０℃より低い温度域まで温度降下しないうちに引続いてその温度域（５０〜１５０℃未満）内で２時間以上保持する安定化処理を行なう。ここで、溶体化処理後の冷却を５０〜１５０℃未満の温度域までとし、さらに５０℃より低い温度域まで温度降下しないうちに引続いて溶体化処理を行なう理由は次の通りである。
【００４１】
すなわち、溶体化処理後に１００℃／ｍｉｎ以上の冷却速度で５０℃未満の温度域（室温）に冷却した場合には、室温クラスターが生成される。この室温クラスターは強度に寄与するＧ．Ｐ．ゾーンに移行しにくいため、塗装焼付硬化性向上に不利となる。一方、溶体化処理後に１５０℃以上の温度域まで冷却してそのまま保持した場合には、高温クラスターあるいはＧ．Ｐ．ゾーンが生成され、塗装焼付硬化性については有利となるが、成形前の素材強度が高くなり過ぎて、ヘム曲げ性やその他の成形性が劣化するとともに、室温での経時変化が生じやすくなる。したがってヘム曲げ性、室温経時変化と塗装焼付硬化性とのバランスの観点から、上記の条件を満たす必要がある。
【００４２】
安定化処理は、前述のように溶体化処理後に５０〜１５０℃未満の温度域まで冷却してから、５０℃未満の温度域（室温）まで冷却することなく、５０〜１５０℃未満の範囲内の温度に保持して行なう。この安定化処理は、最終的にクラスターあるいはＧ．Ｐ．ゾーンの安定性を向上させ、板製造後の経時変化を抑制して、充分な焼付硬化性を確保するとともに、良好な成形加工性を得るために必要な工程であり、この安定化処理は、５０〜１５０℃未満の範囲内の温度に２時間以上保持の条件とする必要がある。安定化処理の温度が５０℃未満では上記の効果が充分に得られず、一方１５０℃を越えれば高温時効によって粒界析出の傾向が強くなり、成形性、特にヘム曲げ性が低下してしまう。また安定化処理における５０〜１５０℃未満の範囲内の温度に保たれる時間が２時間未満では、その後の室温での経時変化が速くなって成形性と焼付硬化性が悪くなる。なお安定化処理の加熱保持時間の上限は特に限定しないが、通常は経済性の観点から４８時間以下とすることが好ましい。なおまた、上述のような５０〜１５０℃未満の温度域での２時間以上の安定化処理は、必ずしも一定温度で２時間以上保持する必要はない。すなわち、要は５０℃以上１５０℃未満の範囲内の温度に２時間以上維持されれば良いから、例えば徐冷などによって５０〜１５０℃未満の温度域内で２時間以上経過させるようにしても良い。
【００４３】
以上のように、熱間圧延過程における諸条件を厳密に規制し、さらに溶体化処理前の冷間圧延率と、溶体化処理−冷却−安定化処理の条件を厳密に規制することによって、既に述べたような結晶方位密度条件および結晶粒径条件、導電率条件を満たし、成形性、特にヘム曲げ性が優れ、かつ塗装焼付硬化性が良好な時効性Ａｌ−Ｍｇ−Ｓｉ系アルミニウム合金板を得ることができる。
【００４４】
【実施例】
表１に示すこの発明成分組成範囲内の合金記号Ａ１〜Ａ５の合金、およびこの発明の成分組成範囲外の合金記号Ｂ１の合金について、それぞれ常法に従ってＤＣ鋳造法により鋳造し、得られた５５０ｍｍ厚の鋳塊に５３０℃×２時間の条件で均質化処理を施した後、５１０℃の温度で熱間圧延を開始し、熱間圧延終了後冷間圧延を施して、最終的に厚さ１ｍｍの圧延板とした。その他の熱間圧延、冷間圧延の諸条件を表２に示す。
【００４５】
次いで各冷間圧延板に対し、種々の溶体化処理を行なってから、１００℃／ｍｉｎ以上の冷却速度で所定の温度域まで冷却（焼入れ）して、引続き種々の条件の安定化処理を行なった。溶体化処理から安定化処理までの具体的な条件を表３に示す。
【００４６】
以上のようにして得られた板について、その金属組織状態、特に平均結晶粒径と、板表面層の結晶方位密度（キューブ方位密度およびゴス方位密度）および導電率を調べた。
【００４７】
なお平均結晶粒径は、偏光顕微鏡により倍率１００倍で撮った試料の結晶組織写真を、ＡＳＴＭナンバーと照合して、結晶粒の大きさが最も類似したもののナンバーを付した。
【００４８】
また結晶方位密度の測定は、厚さ１ｍｍ板をＮａＯＨ水溶液で表面から１００μｍエッチングしたものを測定サンプルとし、Ｘ線回折装置を用いて、シュルツ（Ｓｃｈｕｌｚ）反射法により、｛２００｝、｛２２０｝、｛１１１｝の不完全極点図を測定し、これらをもとに三次元結晶方位解析（ＯＤＦ）を行なった。なおこの明細書において言及している結晶方位密度は、すべて三次元結晶方位解析（ＯＤＦ）によるものである。ここで、｛１００｝＜００１＞の方位をキューブ方位あるいは立方体方位の理想方位とするが、工業用材料のキューブ方位としては上記の理想方位を中心に１５°までずれた結晶方位も含ませるのが通常であり、この実施例の場合もそれに従った。またゴス方位の理想方位は｛１１０｝＜００１＞であるが、工業用材料ではこの理想方位を中心に１５°までずれる結晶方位も含ませるのが通常であり、この実施例の場合もそれに従った。
【００４９】
さらに導電率は、渦電流式導電率測定装置を用い、銅、黄銅を基準試料として測定した。
【００５０】
これらの結果を表４に示す。
【００５１】
さらに前述のように得られた板を、室温に３ケ月間放置し、各板について、それぞれ２％ストレッチ後、１７０℃×２０分の塗装焼付処理を施した。塗装焼付前の各板の機械的特性（耐力、伸び）および成形性と、塗装焼付後の機械的特性（耐力）を調べた。その結果を表５に示す。
【００５２】
なお成形性評価としては、ヘム曲げ試験、球頭張出試験、絞り試験を行なったが、これらの試験条件、評価方法は次の通りである。
【００５３】
ヘム曲げ試験：
圧延方向に対し０°、４５°、９０°の３方向に曲げ試験片を採取し、それぞれ１５％ストレッチして、突き曲げを行い、突き曲げ後、０．５ｍｍ厚の中板を挿入して１８０°曲げを行ない、目視による割れ観察を行なって、全方向で割れの発生のないものを合格（○印）、１方向でも割れの発生のあるものを不合格（×印）とした。
【００５４】
張出試験：
板両面に成形フィルムを貼り付け、さらに潤滑油を塗布した後、１００ｍｍφの球頭ポンチを使って張出試験を実施し、球頭張出高さを調べた。
【００５５】
絞り試験：
潤滑油を塗布した後、５０ｍｍポンチ径を使って絞り試験を行ない、限界絞り比ＬＤＲを調べた。
【００５６】
【表１】

【００５７】
【表２】

【００５８】
【表３】

【００５９】
【表４】

【００６０】
【表５】

【００６１】
製造番号１〜４は、いずれも合金の成分組成がこの発明で規定する範囲内でかつ製造条件もこの発明で規定する条件を満たしたものであるが、これらの場合は、塗装焼付前の伸びおよび球頭張出高さが充分に高く、かつ絞り成形性を表すＬＤＲ値も充分に高くて、一般的な成形性が優れるばかりでなく、ヘム曲げ性も優れており、また焼付硬化性が高くて塗装焼付時に充分な焼付硬化性を示した。
【００６２】
これに対し製造番号５は、合金の成分組成はこの発明範囲内であるが、製造条件がこの発明で規定する条件を満たさなかったものであり、この場合は成形性、特にヘム曲げ性が劣り、また塗装焼付後の強度も不充分であった。さらに製造番号６は、成分組成がこの発明で規定する範囲を外れた合金を用いかつ製造条件もこの発明で規定する条件を満たさなかったものであり、この場合には塗装焼付後の強度は高いが、ヘム曲げ性が劣っていた。
【００６３】
【発明の効果】
この発明によれば、成形性、特にヘム曲げ性が優れており、しかも塗装焼付硬化性が良好で塗装焼付後の強度が高い成形加工用アルミニウム合金板を得ることができ、したがって自動車用ボディシートなど、成形加工特にヘム曲げ加工と塗装焼付を施して使用されるアルミニウム合金板に最適である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an Al-Mg-Si-based aluminum alloy sheet used as a material for an automobile body sheet and other various automobile parts, various machine tools, home electric appliances and parts thereof, which is used after being subjected to molding and baking. The present invention relates to a manufacturing method, an aluminum alloy sheet for forming which has good formability, particularly hem bending property, good baking hardenability, and high strength after baking, and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, cold rolled steel sheets have been mainly used as body sheets for automobiles, but recently, rolled aluminum alloy sheets have been increasingly used from the viewpoint of reducing the weight of a vehicle body. By the way, since the body sheet of an automobile is used after being subjected to press working, it is required that it be excellent in formability, and that no Rudersmark be generated during the forming process. Since it is often used after being subjected to hem bending, it is required that the hem bendability is particularly excellent among the moldability, and it is also essential that it has high strength. Since it is normal, it is required that high strength be obtained after baking.
[0003]
Conventionally, as such aluminum alloys for body sheets for automobiles, Al-Mg-Si alloys having aging properties have been mainly used in addition to Al-Mg alloys. This aging Al-Mg-Si based alloy has relatively low strength and excellent formability during molding before baking, while aging by heating during baking causes the strength after baking to be low. In addition to the advantage of increasing the height, there are advantages such as that no Rudersmark is generated.
[0004]
In addition, as a method of manufacturing an aging Al-Mg-Si based alloy sheet which is expected to undergo age hardening at the time of coating baking as described above, after a homogenizing heat treatment of an ingot, hot rolling and cold rolling are performed. Usually, intermediate annealing is performed between hot rolling and cold rolling or during cold rolling as needed, and a solution treatment is performed after cold rolling to quench.
[0005]
[Problems to be solved by the invention]
The plate obtained by the conventional general production method for the aging Al-Mg-Si alloy sheet for the automobile body sheet as described above sufficiently satisfies the characteristics required for the recent automobile body sheet. It was difficult to satisfy.
[0006]
That is, recently, in order to further reduce costs and reduce the weight of an automobile body, it has been strongly required that the body sheet of an automobile be made thinner than before, so that sufficient strength can be obtained even with a thin wall. In addition, at the same time as higher strength is required, improvement of moldability, especially hem bendability is strongly demanded, but in terms of satisfying these performances in a well-balanced manner, the conventional general manufacturing method The obtained Al-Mg-Si alloy plate was insufficient. In particular, hem bending is a severe bending process in which the bending inner diameter is 180 ° or less with a bending inner diameter of 1 mm or less, and thus has a problem that it is difficult to achieve both good hem bending properties and strength.
[0007]
Regarding paint baking, the baking temperature has been lowered and the baking time has been reduced from the viewpoint of saving energy and improving productivity, and further using together with materials such as resins that are not preferably exposed to high temperatures. The tendency to shorten the time is increasing. However, in the case of the aging Al-Mg-Si alloy plate obtained by the conventional general manufacturing method, the curing at the time of low-temperature and short-time coating baking (baking hardening) is insufficient. There was a problem that it was difficult to obtain a sufficiently high strength.
[0008]
Furthermore, in the case of an aging Al-Mg-Si alloy plate obtained by a conventional general manufacturing method, if the baking hardenability is to be enhanced to obtain high strength after coating baking, the ductility and bending workability of the material are increased. (Especially, the hem bending property) tends to decrease.
[0009]
The present invention has been made in view of the above circumstances, and has good formability, particularly good hem bending workability, and also has excellent bake hardenability and a large increase in strength at the time of paint baking. It is an object of the present invention to provide an aluminum alloy sheet for use and a method for producing the same.
[0010]
In this specification, good hem bendability means good hem bendability not only in one direction with respect to the rolling direction but also in all directions.
[0011]
[Means for Solving the Problems]
As a result of repeated experiments and studies conducted by the present inventors to solve the above-mentioned problems, in addition to controlling the crystal grain size of the material, in addition to controlling the crystal orientation of the metal structure, it is necessary to appropriately control the crystal orientation in the metal structure. Is extremely important. By properly regulating the sheet manufacturing process conditions, in particular, the hot rolling conditions, the cooling conditions after the solution treatment and the stabilization treatment conditions, and appropriately adjusting the crystal orientation conditions and the like, the above-mentioned problems can be solved at once. They have found that they can be solved, and have accomplished the present invention.
[0012]
Specifically, the aluminum alloy sheet for forming according to the first aspect of the present invention contains 0.4 to 0.7% of Mg, 0.8 to 1.2% of Si, and 0.03 to 0.4% of Mn. Cr 0.01 to 0.4%, Zr 0.01 to 0.4%, V 0.01 to 0.4%, Fe 0.03 to 0.5%, Ti 0.005 to 0.2%, Zn 0.03 to 2 0.5% or less, Cu is regulated to 0.1% or less, and the balance is made of an alloy consisting of Al and unavoidable impurities. In the plate surface region up to 1/4 of the depth, the cube orientation density of the crystal structure is at least twice the Goss orientation density having a 45 ° rotational relationship with the cube orientation about the rolling direction, and the cube orientation density Is more than 4 times that of the random sample, and the conductivity is 54% IAC. Hereinafter, and an average crystal grain size is characterized in that at least 4.5 in ASTM number.
[0013]
Further, in the method for producing an aluminum alloy sheet for forming according to the first aspect of the present invention, in producing the aluminum alloy sheet for forming according to the first aspect, the aluminum alloy ingot having the component composition is subjected to a solution treatment, followed by heat treatment. Hot rolling is started at 370 ° C. or higher, hot rolling is performed to a sheet thickness in a range of 1.0 to 8.0 mm, and in the hot rolling, the rising temperature is controlled within a temperature range of 180 to 350 ° C. At the same time, the cooling rate from the temperature range of 180 to 350 ° C. after hot rolling to a temperature range of 100 ° C. or less is controlled to 100 ° C./hr or less, and then cold rolling is performed, and then a solution treatment is performed. It is characterized by performing stabilization processing.
[0014]
According to a third aspect of the present invention, in the method for manufacturing an aluminum alloy sheet according to the second aspect, the cold rolling after the hot rolling is performed at a rolling rate of 30% or more. And performing a solution treatment on the obtained rolled sheet at a temperature of 480 ° C. or more under conditions of holding or no holding for 5 minutes or less, and then at an average cooling rate of 100 ° C./min or more and a temperature of 50 ° C. or more and less than 150 ° C. It is characterized in that it is cooled down to a temperature range, and then a stabilization process is performed for 2 hours or more in the temperature range.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reasons for limiting the component composition in the aluminum alloy sheet for forming according to the present invention will be described.
[0016]
Mg:
Mg is a basic alloy element in the alloy of the system targeted in the present invention, and contributes to improvement in strength in cooperation with Si. If the Mg content is less than 0.4%, G. contributes to the improvement of the strength by precipitation hardening at the time of coating baking. P. Since the generation amount of the zone is small, sufficient strength cannot be improved. On the other hand, if it exceeds 0.7%, a coarse Mg-Si based intermetallic compound is generated, and the formability, particularly the bending workability, is reduced. Therefore, the amount of Mg was set in the range of 0.4 to 0.7%.
[0017]
Si:
Si is also a basic alloying element in the alloy of the present invention, and contributes to improvement of strength in cooperation with Mg. Further, Si is generated as a crystal of metal Si at the time of casting, and the periphery of the metal Si particles is deformed by processing and becomes a generation site of a recrystallization nucleus during solution treatment. It also contributes to the development. If the Si content is less than 0.8%, the above effects cannot be sufficiently obtained, while if it exceeds 1.2%, coarse Si particles and coarse Mg-Si-based intermetallic compounds are generated, and bending workability is increased. Causes a decline. Therefore, the amount of Si is set in the range of 0.8 to 1.2%.
[0018]
Mn, Cr, Zr, V, Fe, Ti, Zn:
These elements are effective for improving the strength, refining the crystal grains, or improving the aging property and the surface treatment property, and one or more of these elements are added. Of these, Mn, Cr, Zr, and V are elements that are effective in improving strength, refining crystal grains, and stabilizing the structure. The Mn content is less than 0.03%. When the contents are less than 0.01%, the above effects cannot be sufficiently obtained. On the other hand, when the contents of Mn, Cr, Zr, and V each exceed 0.4%, not only the above effects are saturated, but also , A large number of intermetallic compounds may be formed, which may adversely affect the formability, especially the hem bendability, so that Mn is in the range of 0.03 to 0.4% and Cr, Zr, and V are all 0. 0.01 to 0.4%. Ti is also an element effective for improving the strength and refining the ingot structure. When the content is less than 0.005%, a sufficient effect cannot be obtained. On the other hand, when the content exceeds 0.2%, the effect of Ti addition is not obtained. The Ti content is set in the range of 0.005 to 0.2% because not only saturation but also a large crystallized substance may be generated. Further, Fe is also an element effective for improving the strength and refining the crystal grains. If its content is less than 0.03%, a sufficient effect cannot be obtained, while if it exceeds 0.5%, the formability may be reduced. Therefore, the amount of Fe was set in the range of 0.03 to 0.5%. Zn is an element that contributes to the improvement of the strength through the improvement of the aging property and is effective for the improvement of the surface treatment property. When the addition amount of Zn is less than 0.03%, the above effect cannot be sufficiently obtained. %, The formability decreases, so the Zn content was set in the range of 0.03 to 2.5%.
[0019]
Cu:
Cu is an element effective for improving strength and formability, but is an element that deteriorates the corrosion resistance (intergranular corrosion resistance and thread rust resistance) of the alloy, and particularly when the Cu content exceeds 0.1%. Since the tendency becomes remarkable, the content of Cu is limited to less than 0.1%.
[0020]
In addition to the above elements, Al and unavoidable impurities may be basically used.
[0021]
The content ranges of Mn, Cr, Zr, V, Ti, Zn, and Fe described above are shown as ranges in the case where they are positively added, and each of them contains an amount less than the lower limit as an impurity. It does not exclude the case. In particular, Fe of less than 0.03% is usually contained inevitably when ordinary aluminum ingots are used.
[0022]
Further, in the aging Al-Mg-Si alloy, a small amount of Ag, In, Cd, Be, or Sn, which is a high-temperature aging accelerating element or a room-temperature aging suppressing element, may be added. In this case, the addition of these elements is permissible. If the content of each element is 0.3% or less, the intended purpose is not particularly impaired.
[0023]
In addition, in a general Al alloy, B may be added simultaneously with the above-mentioned Ti in order to refine the crystal grains. In the case of the present invention, addition of 500 ppm or less of B together with Ti is permitted.
[0024]
Here, in the aluminum alloy sheet for forming according to the present invention, it is necessary not only to adjust the component composition of the alloy as described above, but also to appropriately adjust the average crystal grain size and the conductivity.
[0025]
That is, the crystal grain size affects the hem bendability. If the average crystal grain size is less than 4.5 in ASTM number, the surface is easily roughened at the time of molding, and the hem bendability also decreases. Therefore, the average crystal grain size needs to be 4.5 or more in ASTM number.
[0026]
The conductivity of the alloy plate is an index of the amount of solid solution of Mg and Si in the alloy, and is related to the strength after baking. When the conductivity exceeds 54% IACS, the solid solution amount of Mg and Si is small and hardening by aging precipitation is not sufficiently achieved, so that sufficient high strength cannot be obtained after baking. Therefore, the electric conductivity is restricted to 54% IACS or less. Although the lower limit of the electric conductivity is not particularly defined, usually, even if the electric conductivity of the alloy of this type is less than 40% IACS, the effect of the coating baking hardenability is saturated, and industrially less than 40% IACS is achieved. It is difficult to do so, so it is usually sufficient to be in the range of 40-54% IACS.
[0027]
Furthermore, in the aluminum alloy sheet for forming according to the present invention, not only the component composition of the alloy, the average crystal grain size, and the electrical conductivity, but also the condition of the crystal orientation density is extremely important as the metallographic structure condition.
[0028]
That is, the present inventors have conducted careful and detailed experiments and studies on the relationship between the hem bendability and the crystal orientation density, and as a result, have found that the surface layer of the alloy sheet, particularly from the sheet surface to a depth of 1/4 of the sheet thickness, is reduced. It has been found that the Cube orientation density of the crystal in the region has a significant effect on the hem bendability. And, in the plate surface layer region from the plate surface to a depth of 1/4 of the plate thickness,
A: Cube azimuth density is twice or more of Goss azimuth density which has a 45 ° rotational relationship with the cube azimuth around the rolling direction,
B: Cube orientation density is 4 times or more of the random sample,
It has been found that by satisfying the two conditions, excellent hem bending properties can be surely and stably obtained, and these conditions are defined.
[0029]
Here, when the above two conditions A and B are not satisfied, a slip line develops at the bent portion during the hem bending process, bending strain tends to concentrate, and cracks develop from the portion where the strain is concentrated. And the hem bendability decreases. Therefore, it is important for the crystal orientation density to satisfy the above two conditions in order to stably improve the hem bending property.
[0030]
In order to ensure even better hem bendability under the above condition B, it is desirable that the cube orientation density of the plate surface layer is at least eight times that of a sample having a random orientation.
[0031]
Next, the method of manufacturing the aluminum alloy sheet for forming according to the present invention, that is, the manufacturing method defined in claims 2 and 3 will be described. This manufacturing method is intended to reliably and stably obtain an aluminum alloy sheet for forming according to claim 1, that is, an aluminum alloy sheet that satisfies the crystal orientation density conditions A and B, the average crystal grain condition, and the conductivity condition. belongs to.
[0032]
As a manufacturing method, first, an alloy having the above-described composition is melted according to a conventional method, and is cast by a DC casting method or the like. The obtained ingot is usually subjected to a homogenization treatment, followed by hot rolling to form a hot-rolled sheet, further cold-rolled to a product sheet thickness, and then a solution treatment-cooling (quenching) ), A stabilization process is finally performed.
[0033]
Here, the heating temperature and the heating holding time of the homogenization treatment for the ingot are not particularly limited, but it is usually preferable to hold the ingot at 480 ° C. or higher for about 1 to 24 hours. After the homogenization treatment, hot rolling may be started without cooling.
[0034]
Since hot rolling greatly affects the control of the crystal orientation, various conditions of the hot rolling process are required to adjust the crystal orientation density condition of the final sheet as described above to secure a good hem bending property. Need to be strictly regulated. That is, in the hot rolling process, the hot rolling starting temperature is set to 370 ° C. or more, the hot-rolled sheet thickness is set to 1.0 to 8.0 mm, and the hot-rolling rising temperature is controlled to a temperature range of 180 to 350 ° C. Further, the cooling rate in the cooling process from the temperature range of 180 to 350 ° C. after the hot rolling to the temperature range of 100 ° C. or less needs to be 100 ° C./hr or less.
[0035]
Here, during hot rolling, since solid solution elements precipitate or recovery / recrystallization is repeated, the starting temperature, end temperature, and cooling rate of hot rolling must be strictly controlled as described above. However, it is extremely important for controlling the crystal orientation, and it is difficult to satisfy the crystal orientation density condition defined in claim 1 if at least one of the above hot rolling conditions is removed. In addition, setting the hot rolling start temperature to 370 ° C. or more is indispensable for securing the solid solution amount of the Mg and Si elements and securing the condition of the conductivity of 54% or less as defined in claim 1. . In particular, if the cooling rate from the temperature range of 180 to 350 ° C. after the hot rolling to the temperature range of 100 ° C. or less exceeds 100 ° C./hr, the recovery and recrystallization of the material is significantly controlled, and It becomes extremely difficult to satisfy the crystal orientation condition. Although the lower limit of the average cooling rate is not particularly defined, it is generally 1 ° C./hr or more in consideration of productivity. Although the upper limit of the hot rolling start temperature is not particularly specified, it is usually set to 590 ° C. or less in consideration of eutectic melting and the like.
[0036]
After hot rolling, cold rolling is performed at a rolling reduction of 30% or more before the final solution treatment. As described above, by the cold rolling at a rolling ratio of 30% or more, strain energy is accumulated in the material, and not only the crystal grains generated during the solution treatment become fine, but also the above-described cube orientation density is increased, and the final crystal orientation density is increased. This is extremely effective in obtaining a good hem bending property. If the cold rolling reduction until the final solution treatment is less than 30%, the crystal grains after the solution treatment become coarse, and at the same time, it becomes difficult to satisfy the above-mentioned cube orientation density condition, and good heme bending property is obtained. Disappears. The upper limit of the cold rolling reduction until the solution treatment is not particularly limited, but usually may be about 90% or less.
[0037]
After the desired product thickness is obtained by cold rolling as described above, a solution treatment is performed at a temperature of 480 ° C. or more for 5 minutes or less. This solution treatment is performed using Mg ₂ This is an important step for dissolving Si, elemental Si, or the like in the matrix, thereby imparting bake hardenability and improving the strength after baking. Also, this solution treatment step is performed by using Mg ₂ The solid solution of Si, single Si particles, etc., lowers the distribution density of the second phase particles, thereby contributing to the improvement of ductility and bendability, and further improving the overall good formability by recrystallization of the material. This is a necessary step to obtain. Further, this solution treatment is also an indispensable step for forming a recrystallized texture by recrystallization and obtaining a final plate satisfying the crystal orientation density condition defined in claim 1.
[0038]
Here, if the solution treatment temperature is lower than 480 ° C., it seems to be advantageous for suppressing the temporal change of room temperature. ₂ The amount of solid solution of Si, Si and the like is reduced, and as a result, not only sufficient bake hardenability is not obtained, but also ductility and bendability are remarkably deteriorated. On the other hand, the upper limit of the solution treatment temperature is not particularly limited, but is usually preferably 580 ° C. or less in consideration of the possibility of eutectic melting and coarsening of recrystallized grains. Further, if the holding time in the solution treatment exceeds 5 minutes, the solution treatment effect is saturated, not only impairing the economic efficiency but also possibly causing the crystal grains to become coarse. Therefore, the time for the solution treatment is within 5 minutes. And
[0039]
After the solution treatment, it is cooled (quenched) to a temperature range of 50 to 150 ° C. at an average cooling rate of 100 ° C./min or more. Here, if the cooling rate after the solution treatment is less than 100 ° C./min, ₂ A large amount of Si or Si is precipitated at the grain boundary, and the moldability, particularly the hem bending property, is reduced, and the bake hardenability is reduced, so that it is not possible to expect a sufficient improvement in the strength at the time of paint baking.
[0040]
As described above, after the solution treatment is performed at a temperature of 480 ° C. or more and cooled (quenched) to a temperature range of 50 to less than 150 ° C. at an average cooling rate of 100 ° C./min or more, a temperature lower than 50 ° C. Before the temperature drops to the temperature range, a stabilization process is performed in which the temperature is kept within the temperature range (less than 50 to 150 ° C.) for 2 hours or more. Here, the reason why the cooling after the solution treatment is performed to a temperature range of 50 to less than 150 ° C. and the solution treatment is continuously performed before the temperature is lowered to a temperature range lower than 50 ° C. is as follows.
[0041]
That is, when cooled to a temperature range of less than 50 ° C. (room temperature) at a cooling rate of 100 ° C./min or more after the solution treatment, a room temperature cluster is generated. This room temperature cluster contributes to the strength of G. P. Since it is difficult to move to the zone, it is disadvantageous for improving the paint baking hardenability. On the other hand, when the solution is cooled to a temperature range of 150 ° C. or more and kept as it is after the solution treatment, the high temperature cluster or G.C. P. Zones are formed, and the baking hardenability is advantageous, but the material strength before molding becomes too high, and the hem bending property and other moldability deteriorate, and the temporal change at room temperature is apt to occur. Therefore, it is necessary to satisfy the above conditions from the viewpoint of the balance between the hem bending property, the aging change at room temperature and the paint baking hardenability.
[0042]
As described above, the stabilization treatment is performed after cooling to a temperature range of 50 to less than 150 ° C. after the solution treatment, and without cooling to a temperature range of less than 50 ° C. (room temperature). The temperature is maintained at This stabilization processing is finally performed by the cluster or G.E. P. Improving the stability of the zone, suppressing changes over time after the manufacture of the plate, ensuring sufficient bake hardenability, is a necessary step to obtain good moldability, this stabilization process, It is necessary to maintain the temperature within a range of 50 to less than 150 ° C. for 2 hours or more. If the temperature of the stabilization treatment is lower than 50 ° C., the above effects cannot be sufficiently obtained. On the other hand, if the temperature exceeds 150 ° C., the tendency of grain boundary precipitation is increased due to high-temperature aging, and the formability, particularly the hem bending property, decreases. . If the time during which the temperature is kept within the range of 50 to less than 150 ° C. in the stabilization treatment is less than 2 hours, the subsequent change with time at room temperature becomes faster, and the moldability and the bake hardenability deteriorate. The upper limit of the heating holding time of the stabilization treatment is not particularly limited, but is usually preferably 48 hours or less from the viewpoint of economy. In addition, the stabilization process for two hours or more in the temperature range of 50 to less than 150 ° C. as described above does not necessarily need to be maintained at a constant temperature for two hours or more. That is, since it is only necessary to maintain the temperature within the range of 50 ° C. or more and less than 150 ° C. for 2 hours or more, the temperature may be allowed to elapse in the temperature range of 50 to less than 150 ° C. for 2 hours or more by, for example, slow cooling. .
[0043]
As described above, by strictly regulating the conditions in the hot rolling process, and further strictly regulating the cold rolling ratio before the solution treatment and the conditions of the solution treatment-cooling-stabilization treatment, An aging Al-Mg-Si-based aluminum alloy plate that satisfies the crystal orientation density condition, crystal grain size condition, and conductivity condition as described above, has excellent moldability, particularly excellent hem bending property, and has good paint bake hardenability. Obtainable.
[0044]
【Example】
The alloys of the alloy symbols A1 to A5 within the composition range of the present invention and the alloy symbols B1 out of the composition range of the invention shown in Table 1 were each cast by a DC casting method according to a conventional method to obtain 550 mm. After subjecting the thick ingot to homogenization at 530 ° C. × 2 hours, hot rolling is started at a temperature of 510 ° C., and after completion of hot rolling, cold rolling is performed. It was a rolled plate of 1 mm. Table 2 shows other hot rolling and cold rolling conditions.
[0045]
Next, each of the cold-rolled sheets is subjected to various solution treatments, then cooled (quenched) to a predetermined temperature range at a cooling rate of 100 ° C./min or more, and subsequently subjected to stabilization treatments under various conditions. Was. Table 3 shows specific conditions from the solution treatment to the stabilization treatment.
[0046]
With respect to the plate obtained as described above, its metallographic structure, in particular, the average crystal grain size, the crystal orientation density (cube orientation density and Goss orientation density) of the plate surface layer, and electrical conductivity were examined.
[0047]
The average crystal grain size was determined by comparing the crystal structure photograph of the sample taken at a magnification of 100 times with a polarizing microscope with the ASTM number and assigning the number of the crystal grain having the most similar size.
[0048]
The crystal orientation density was measured by etching a 1-mm-thick plate with an aqueous solution of NaOH by 100 μm from the surface as a measurement sample, and using an X-ray diffractometer by the Schulz reflection method, {200}, {220}. , {111} were measured, and a three-dimensional crystal orientation analysis (ODF) was performed based on these. All the crystal orientation densities referred to in this specification are based on three-dimensional crystal orientation analysis (ODF). Here, the orientation of {100} <001> is an ideal orientation of a cube orientation or a cubic orientation, and the cube orientation of an industrial material includes a crystal orientation shifted from the ideal orientation by 15 °. Is normal, and this example was followed. The ideal Goss orientation is {110} <001>. However, industrial materials usually include a crystal orientation that deviates from the ideal orientation by up to 15 °. Was.
[0049]
Further, the conductivity was measured using an eddy current conductivity measuring device, using copper and brass as reference samples.
[0050]
Table 4 shows the results.
[0051]
Further, the boards obtained as described above were allowed to stand at room temperature for 3 months. Each board was stretched by 2% and then subjected to a paint baking treatment at 170 ° C. for 20 minutes. The mechanical properties (proof stress, elongation) and formability of each plate before paint baking and the mechanical properties (proof stress) after paint baking were examined. Table 5 shows the results.
[0052]
As the evaluation of formability, a hem bending test, a ball head overhang test, and a drawing test were performed. The test conditions and evaluation method are as follows.
[0053]
Hem bending test:
Bending test specimens were sampled in three directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, stretched by 15% each, and pierced. After piercing, a 0.5 mm thick middle plate was inserted. After bending by 180 ° and visually observing cracks, those having no cracks in all directions were accepted (marked with ○), and those having cracks in one direction were rejected (marked with x).
[0054]
Overhang test:
After sticking a molded film on both sides of the plate and further applying lubricating oil, an overhang test was performed using a 100 mmφ ball-head punch to check the ball-head protrusion height.
[0055]
Aperture test:
After applying the lubricating oil, a drawing test was performed using a 50 mm punch diameter to check the limit drawing ratio LDR.
[0056]
[Table 1]

[0057]
[Table 2]

[0058]
[Table 3]

[0059]
[Table 4]

[0060]
[Table 5]

[0061]
Production Nos. 1 to 4 are those in which the component composition of the alloy is within the range specified in the present invention and the manufacturing conditions also satisfy the conditions specified in the present invention. In addition, the ball head overhang height is sufficiently high, and the LDR value representing draw formability is sufficiently high, so that not only the general formability is excellent, but also the hem bending property is excellent, and the bake hardenability is high. It was high and showed sufficient bake hardenability when baking paint.
[0062]
On the other hand, in production number 5, the composition of the alloy is within the range of the present invention, but the production conditions did not satisfy the conditions specified in the present invention. In this case, the formability, particularly the hem bending property, was poor. Also, the strength after baking was insufficient. Further, in Production No. 6, an alloy having a component composition outside the range specified in the present invention was used, and the manufacturing conditions did not satisfy the conditions specified in the present invention. In this case, the strength after baking was high. However, the hem bending property was inferior.
[0063]
【The invention's effect】
According to the present invention, it is possible to obtain an aluminum alloy sheet for forming which is excellent in formability, particularly hem bending property, has good paint baking hardenability, and has high strength after paint baking. It is most suitable for aluminum alloy plate used after forming process, especially hem bending process and paint baking.

Claims

Mg 0.4-0.7% (mass%, the same applies hereinafter), Si 0.8-1.2%, Mn 0.03-0.4%, Cr 0.01-0.4%, Zr 0.01 Or 0.4%, V 0.01 to 0.4%, Fe 0.03 to 0.5%, Ti 0.005 to 0.2%, Zn 0.03 to 2.5%. It is made of an alloy containing two or more kinds, and further, Cu is regulated to 0.1% or less, and the balance is made of Al and unavoidable impurities, and in a plate surface layer region from the plate surface to a depth of 1/4 of the plate thickness. The cube orientation density of the crystal structure is at least twice the Goss orientation density which is in a 45 ° rotational relationship with the cube orientation about the rolling direction, and the cube orientation density is at least four times that of the random sample. Rate is 54% IACS or less and average grain size is ASTM Characterized in that at least 4.5 in members, heme bendability and bake hardenability excellent in molding an aluminum alloy plate.

In manufacturing the aluminum alloy sheet for forming according to claim 1,
After solution treatment of the aluminum alloy ingot having the above-mentioned composition, hot rolling is started at 370 ° C. or higher, hot-rolled to a thickness of 1.0 to 8.0 mm, and hot-rolled. In the above, while controlling the rise temperature within the temperature range of 180-350 ℃, the cooling rate from the temperature range of 180-350 ℃ of hot rolling to the temperature range of 100 ℃ or less is controlled to 100 ℃ / hr or less, A method for producing an aluminum alloy sheet for forming and processing having excellent hem bending property and bake hardenability, wherein cold rolling is performed, then solution treatment is performed, and further stabilization processing is performed.

The method for producing an aluminum alloy sheet according to claim 2, wherein the cold rolling after the hot rolling is performed at a rolling ratio of 30% or more, and the solution treatment for the obtained rolled sheet is performed at a temperature of 480 ° C or more. After holding under the condition of holding or not holding for 5 minutes or less, cooling at an average cooling rate of 100 ° C./min or more to a temperature range of 50 ° C. or more and less than 150 ° C., and then stabilizing treatment in the temperature range for 2 hours or more A method for producing an aluminum alloy sheet for forming and processing having excellent hem bending property and bake hardenability.