JP3860939B2

JP3860939B2 - Al-Mn-Mg alloy plate for case forming and method for producing the same

Info

Publication number: JP3860939B2
Application number: JP31073199A
Authority: JP
Inventors: 義和鈴木; 正勝吉田
Original assignee: Furukawa Sky Aluminum Corp
Current assignee: Furukawa Sky Aluminum Corp
Priority date: 1999-11-01
Filing date: 1999-11-01
Publication date: 2006-12-20
Anticipated expiration: 2019-11-01
Also published as: JP2001131666A

Description

【０００１】
【発明の属する技術分野】
本発明は、角型Ｌｉイオン電池などのケース成形用に好適なＡｌ−Ｍｎ−Ｍｇ系合金板に関し、特に良好なレーザー溶接性を有することにより電池製造時のレーザー溶接における接合不良が無く、またケースの耐加熱フクレ性を向上することにより、自動車内放置等で想定される７０〜９０℃の加熱および内圧発生時にもケースの変形が少ない電池を得ることができ、電子機器用電池のケース素材として好適なアルミニウム合金板に係る。
【０００２】
【従来の技術】
電池ケース等のケース用プレス成形素材として、鉄系材料に代りＡｌ合金を用いることはケースの軽量化のために有利である。
特に、軽量化の要求により携帯電話等に搭載される角形の小型Ｌｉイオン二次電池ケースでは、アルミニウム合金板を素材とするものが実用化されている。この角型電池のケース用材としてＡｌ−Ｍｎ系合金、具体的には主に３００３合金（Ｍｎ：１．０〜１．５ｗｔ％、Ｍｇ：無添加）が用いられるのが通常である。
【０００３】
【発明が解決しようとする課題】
この角型電池ケースの肉厚としては現在、正面（最も面積の広い面）で０．５mm前後のものが用いられているが、さらに肉厚を減らしてケースの軽量化を進めることが求められており、そのため３００３合金より機械的強度が高い成形素材が用いられている。
【０００４】
これに対し、Ｍｇを添加したＡｌ−Ｍｎ−Ｍｇ合金、例えば３００４合金（Ｍｎ：１．０〜１．５ｗｔ％、Ｍｇ：０．８〜１．３ｗｔ％）は機械的強度の上で３００３合金より有利となる。
しかし、３００４合金のケースは蓋とのレーザー溶接の際に、溶接部に微小な亀裂が入る問題がありレーザー溶接性の点から用いられていないのが現状である。
【０００５】
また、電池ケースが加熱され内圧が発生した場合にフクレ変形が生じる問題があり、これは単に機械的強度を高くするだけでは解決せず、合せて耐クリープ性を向上させる必要がある。
たとえば、角形のＬｉイオン二次電池等が携帯電話等に搭載された場合、充電、放電の繰り返しによる発熱や、夏場の外気温の高い条件での自動車内放置状態を考えると、最高では７０〜９０℃の温度にさらされると推定される。
このような条件下に長時間置かれると、電池内部で反応が進み気泡等の発生により内圧が高まってケースにフクレ変形を生じる。このフクレ変形は特定部位への応力集中による塑性変形と、温度および内圧保持中に進行するクリープ変形により生じるものである。このフクレ変形量が過大になった際には、携帯電話等に組み込まれた電子部品を圧迫したり、電子部品外側のケースに変形等の不具合を生じ、また、ケースの蓋部分との溶接部分等に亀裂を生じ内容物の漏れにより構成する電子部品に不具合を生じる等の問題が生じる恐れがある。
従って、ケースを薄肉化するために、単に常温での機械的強度が高いだけでなく、加熱と内圧が作用する状態でのフクレに対する抵抗が大きい材料を用いることが必要となる。
【０００６】
本発明は、上記の技術課題を解消して、レーザー溶接性が良好で、温度上昇と内圧増加等によるケースフクレが少ないケース成形素材用Ａｌ−Ｍｎ−Ｍｇ系合金板を提供する事を目的とするものである。
【０００７】
【課題を解決するための手段】
本発明者は、レーザー溶接が良好で、かつケースが加熱と内圧によるフクレに対する抵抗（以下、耐加熱フクレ性）に優れるようなＡｌ−Ｍｎ−Ｍｇ系合金材料の必要条件や、その具体的な製造方法について種々検討し、本発明に至った。そして、Ｍｇの添加と共にＭｎ固溶量の制御を行い、レーザー溶接性を損わないＭｇ添加量にて十分にケースの耐加熱フクレ性を向上させることを可能としたのである。
具体的には、本発明のＡｌ−Ｍｎ合金板は、Ｍｎ０．８〜２％およびＭｇ０．２〜０．７５％を含み、不純物元素であるＳｉが０．０４〜０．２％に、Ｆｅが０．０４〜０．６％に制御され、残部他の不可避的不純物とＡｌからなる組成、あるいはさらにＣｕ０．０５〜０．２％、Ｃｒ０．０２〜０．２％およびＺｒ０．０２〜０．２％のうち１種以上を含む組成であり、かつ固溶Ｍｎ量が０．２％以上で、耐力が１７０〜２７０Ｎ／ｍｍ²の範囲にある。
その製造方法は、鋳塊を３２０〜４１０℃で０．５〜２０ｈ保持する予備加熱処理したのち、材料温度が４１０℃を越えないように制御して熱間圧延を行い、その後、圧下率３０〜７０％の最終冷間圧延を施すものであり、あるいは熱間圧延を行い、ついで１５％以上の圧下率の冷間圧延を施し、昇温速度５℃／ｓ以上で３８０〜５８０℃に加熱し、０〜２００ｓ保持して直ちに冷却速度５℃／ｓ以上で降温する条件で中間焼鈍を行い、その後、圧下率３０〜７０％の最終冷間圧延を施すものであり、さらには、最終冷間圧延後に昇温・冷却速度を１０〜１００℃／ｈとして１６０〜２１０℃で１〜１８ｈ、または昇温・冷却速度を５℃／ｓ以上として１８０〜２６０℃で０〜２００ｓの焼鈍を行うものである。
【０００８】
【発明の実施の形態】
まず合金成分について説明する。
【０００９】
Ｍｎは、主に固溶状態において機械的強度向上に寄与し、耐加熱フクレ性向上に寄与する添加元素である。これは、固溶したＭｎが加熱・内圧負荷時のクリープ変形に関る転位移動の抵抗として働くためである。Ｍｎ添加量０．８％未満ではこの効果が不足し、また機械的強度も低くなるため不適当である。Ｍｎ添加量２％を越えると粗大な晶出物が多くなり成形性が問題となるためケース成形用素材として不適当である。従ってＭｎは０．８〜２．０％とする。
なお、本発明の材料は固溶Ｍｎ量を０．２％以上であることを必要とする。これ以下であると、上述の固溶Ｍｎによる耐加熱フクレ性向上に対する効果が不十分となる。なお固溶Ｍｎ量を０．４％以上とするとさらに望ましい。この固溶Ｍｎ量は、図１のようなフェノール分析法により測定されるものである。
【００１０】
Ｍｇは固溶強化により機械的強度向上に寄与し、固溶Ｍｎとともに耐加熱フクレ性を向上させる効果を持つ添加元素である。しかし、過度の添加によりレーザー溶接性を低下させるという問題もあり、他の成分とのバランスで適正な添加量の範囲が定められる。Ｍｇ添加量が０．２％未満であると、機械的強度および耐加熱フクレ性向上に対する効果が不十分である。一方、Ｍｇ添加量が０．７５％を超えると、レーザー溶接性の低下、具体的には溶接部のクラックが発生しやすいため不適当である。従って、Ｍｇ量は０．２〜０．７５％とする。
なお、Ｍｇの添加のみで耐加熱フクレ性を向上させるためには本発明範囲を超えたＭｇ添加量が必要となり、良好なレーザー溶接性との両立が困難となる。このため、本発明では固溶ＭｎとＭｇの両方の効果を利用することにより、良好なレーザー溶接性を損わないＭｇ添加量範囲内での耐加熱フクレ性向上が可能となった。
【００１１】
Ｓｉは、含有量が多いほどＭｎの析出を促進する作用がある。そこで０．２％を越えてＳｉを含有すると固溶Ｍｎが減少し、その結果固溶Ｍｎによるフクレ防止効果が阻害され耐加熱フクレ性が低下するため不適当である。なおＳｉは０．１２％以下とすればさらに望ましい。また、Ｓｉを０．０４％未満に低減することはこれ以上の特性向上に結びつかないにもかかわらず、高純度地金を必要とし高コストとなるので不適当である。
【００１２】
Ｆｅは０．６％を越えて添加されると、粗大な晶出物を生じ易くケース成形性に悪影響を及ぼすため不適当である。なおＦｅ添加量は０．４％以下であればさらに望ましい。Ｆｅを０．０４％未満に低減することはこれ以上の特性向上に結びつかないにもかかわらず、高純度地金を必要とし高コストとなるので不適当である。
【００１３】
Ｃｕ、Ｃｒ、Ｚｒは、耐加熱フクレ性の向上に効果のある添加元素である。Ｃｕを０．０５〜０．２％のＣｕを添加することにより、耐加熱フクレ性が向上するとともに機械的強度が向上する。ただしＣｕ量が規定より多いと、レーザー溶接製が低下するため不適当である。ＣｒおよびＺｒを０．０２〜０．２％添加する事で、耐加熱フクレ性が向上するとともに結晶粒の安定化がはかられ、諸特性のバラツキが低減する。ただし規定より多いと鋳造時に粗大晶出物が形成され、ケース成形性が悪くなるため不適当である。
【００１４】
このほか、アルミニウム合金の鋳造の際に一般的に添加されるＴｉ系あるいはＴｉ−Ｂ系の微細化剤に起因するＴｉは０．１％以下、Ｂは０．０３％以下の範囲で含んでもよい。
【００１５】
本発明のＡｌ−Ｍｎ−Ｍｇ合金板の耐力は、１７０〜２７０Ｎ／ｍｍ²の範囲に制御される必要がある。１７０Ｎ／ｍｍ²より低いと、成形されたケースに内圧がかかった時に単純に塑性変形でのフクレが生じやすいため不適当である。また、２７０Ｎ／ｍｍ²より高い耐力であると成形が困難であるため不適当である。
【００１６】
次に本発明材の製造方法について説明する。
【００１７】
鋳造は通常の半連続鋳造法（ＤＣ法）および板連続鋳造法（ＣＣ法）のいずれでも行うことができる。
諸特性の安定および量産性ではＤＣ材が有利であるが、高いＭｎ固溶量を容易に実現するにはＣＣ法を用いるのが有利である。
【００１８】
熱間圧延前の予備加熱処理は３２０〜４１０℃で０．５〜２０ｈ保持する条件で行う。この条件より高温になるかあるいは長時間加熱されると、Ｍｎの析出が過度に生じて、最終的にケースの耐加熱フクレ性が低下する。また、この範囲より低温あるいは短時間であると、熱間圧延が安定して行えないため不適当である。
また、熱間圧延中の材料温度は、４１０℃を越えないように制御する必要がある。これより高温になると過度にＭｎの析出が生じて、成形されたケースの耐加熱フクレ性が低下するので不適当である。なお熱間圧延では少なくとも５０％以上の圧下を加えることが望ましい。
【００１９】
本発明の製造法の一つとしては、熱間圧延の次に圧下率３０〜７０％の最終冷間圧延を施す。圧下率が３０％より低いと、機械的強さが不足し、初期の塑性変形により大きなフクレが起こってしまうため不適当である。一方７０％を越えると耐力などの機械的強度は高くなるが成形が困難となり、また多くの可動転位を組識中に含み最終的に成形された後のケースでも可動転位が多くなるため、クリープ変形が起こりやすくなるので不適当である。
【００２０】
また、本発明の別の製造方法としては、熱間圧延後に１５％以上の圧下率の冷間圧延を行ない、急速加熱冷却による中間焼鈍を施し、次に圧下率３５〜７０％の冷間圧延を施すものである。
中間焼鈍前の冷間圧延の圧下率は１５％より低いと中間焼鈍での再結晶が不安定となり不均一な組織となる恐れがある。
この中間焼鈍は、連続焼鈍ライン（ＣＡＬ）により実施することが望ましく、昇温５℃／ｓ以上で３８０〜５８０℃に加熱し、０〜２００ｓ保持して直ちに冷却速度５℃／ｓ以上で降温する条件で行う。ここで０ｓ保持とは、所定温度に到達後、直ちに冷却する条件である。この様な急速加熱冷却による焼鈍方法でないとＭｎの析出が生じ、Ｍｎ固溶量が低くなるので不適当である。
中間焼鈍後の最終冷間圧延での圧下率を３５〜７０％とする。これより低いと機械的強さが不足し、初期の塑性変形により大きなフクレが起こってしまうため不適当である。この圧下率が７０％を越えると、耐力などの機械的強度は高くなるがプレス成形が困難となり、また多くの可動転位を組識中に含み最終的に成形された後のケースでも可動転位が多くなるためクリープ変形が起こりやすくなるので不適当である。
【００２１】
本発明のケース用素材は、最終の冷間圧延のままで成形素材として使用することができるが、これに最終焼鈍を加えて用いることもできる。その場合、昇温速度１０〜１００℃／ｈ、焼鈍温度１６０〜２１０℃、保持時間１〜１８ｈの焼鈍条件が好適であるが、この条件はバッチ式の焼鈍装置で行うのに適している。また、昇温・冷却速度を５℃／ｓ以上として１８０〜２６０℃で０〜２００ｓの焼鈍を行う最終焼鈍条件も採用できるが、これは急速加熱および冷却が可能な連続焼鈍ライン（ＣＡＬ）により実施することができる。この最終焼鈍は、冷間圧延により生じた可動転位を低減する効果と、一部で固溶Ｍｎの転位近傍への偏析を起こしてクリープ変形時の転移移動への抵抗を増大させる効果を持ち、さらなる耐加熱フクレ性の向上を可能とするものである。
【００２２】
【実施例】
以下、本発明の実施例について説明する。
【００２３】
＜実施例１＞
通常のＤＣ法（半連続鋳造法）で表１に示す本発明範囲組成の合金を鋳造し、次に表２の製造条件で板厚０．８ｍｍの圧延板とした。
なお最終焼鈍の昇温、冷却は、発明例Ｇ−９が昇温１０℃／ｓ、冷却１０℃／ｓ、他は昇温５０℃／ｈ、冷却１５０℃／ｈの条件で行った。
【００２４】
【表１】

【００２５】
【表２】

【００２６】
できあがった圧延板についてＭｎ固溶量と耐力を測定した。
また圧延板を多段のプレス成形により図２に示すケース厚さ８ｍｍ、幅３０ｍｍで角がＲ１．５ｍｍの断面を持ち、高さ４５ｍｍで肉厚０．４５ｍｍの角型ケースとした。実用化されている肉厚約０．５ｍｍのものに対して、これは１０％程度薄肉化した試験である。
次に０．８ｍｍの圧延板をケースの肉厚と同じの板厚０．４５ｍｍまで冷間圧延加工した板を突合わせて、１回当りの照射エネルギー５Ｊ、パルス数２０Ｈｚ、ビーム径０．６ｍｍ、４００ｍｍ／ｍｉｎの速度で溶接長２００ｍｍのレーザー溶接を同一材に対して６回行い、工業顕微鏡にて溶接部での微小な割れの発生の有無を確認するレーザー溶接性試験を行った。割れの有無により、○：割れ無し、×：割れ有り、××：割れ顕著と評価した。
また、電池が加熱されて電池内容物の反応により内圧が生じた場合を模して、成形したケースを８５℃で保持しながら、図３の概略図の装置で２ｋｇ／ｃｍ²の内圧をかけ２４ｈ保持する加熱内圧フクレ試験を同一材について３回行い、フクレ量（ケース厚さの増加）を平均値で評価した。その結果を表３に示す。
【００２７】
【表３】

【００２８】
表に示されるように、発明例のものはすべて問題なくケース成形できた。またレーザー溶接においても割れの発生が無くレーザー溶接性に優れており、またフクレも小さく、本発明のＡｌ−Ｍｎ−Ｍｇ系合金板を素材とした角形ケースは、耐加熱フクレ性に優れ、この材料のレーザー溶接性が良好であることが明らかである。
これに対して、比較例はいずれかの特性が劣っている。
ＮＧ１はＭｎ量が本発明の範囲以下の合金を用いたものであり、このためＭｎ固溶量も少なく、その結果、耐力が低くフクレも大きくなってしまっている。
ＮＧ２はＭｎ量が本発明の範囲以上の合金を用いたものであり、鋳造時に鋳塊の一部に割れが発生して圧延板の製造ができなかった。
ＮＧ３はＭｇ量が本発明の範囲以下の合金を用いたものであり、耐力がやや低くまたフクレが多くなってしまっている。
ＮＧ４はＭｇ量が本発明の範囲以上に多量に含まれているものであり、耐力、耐加熱フクレ性は充分であるもののレーザー溶接性が悪くなっている。
ＮＧ５はＭｇ量が本発明の範囲以上に多量に含まれているものであり、耐力は充分であるものの強度が強くなりすぎてケース成形時に一部に割れが発生した。またレーザー溶接性が悪くなっている。割れの発生していないケースに対してフクレ試験を行った結果、耐加熱フクレ性は良好であった。
ＮＧ６はＦｅ、Ｓｉ量が本発明の規定を越えた合金を用いたものであり、粗大晶出物が形成されており、このためケース成形時に粗大晶出物を起点として局部割れを生じたものがあった。割れの無い成形ケースを選びフクレ試験を実施したところＭｎ固溶量が低いため、フクレ量が大きくなっている。
ＮＧ７はＣｕを本発明の範囲以上に多量に添加したものであり、耐力、耐加熱フクレ性は充分であるものの、レーザー溶接性が悪くなっている。
ＮＧ８はＣｒ、Ｚｒを本発明の範囲以上に多量に添加したものであり、粗大晶出物が形成されているためケース成形時に局部割れが生じて健全なケースが得られず、フクレ試験が実施できなかった。
ＮＧ９は本発明の規定を満たす合金成分であるが、最終冷間圧延率が低い製造方法を用いたものであり、このため耐力が低く、フクレ量が大きなものとなってしまっている。
ＮＧ１０は本発明の規定を満たす合金成分であるが、熱間予備加熱条件が本発明の規定より高温で行い、熱間圧延中の最高材温も高すぎたため、Ｍｎ固溶量が減少し、このためフクレ量が大きなものとなってしまっている。
ＮＧ１１は本発明の規定を満たす合金成分であるが、最終冷間圧延率が本発明の規定より大きな製造条件であり、そのため耐力が大きくなりすぎ、ケース成形時に割れが発生してしまい、フクレ試験ができなかった。
【００２９】
＜実施例２＞
表１のｂ、ｃの合金についてＣＣ法（連続鋳造圧延法）で板厚６ｍｍの板状の鋳造材を作製し、これを表４の条件で０．８ｍｍの圧延板とした。
これを実施例１の場合と同様に成形し試験を実施した。さらに、実施例１と同様にレーザー溶接性を調べた。その結果を表５に示す。
【００３０】
【表４】

【００３１】
【表５】

【００３２】
表４より、本発明例のＡｌ−Ｍｎ−Ｍｇ系合金板を素材とした場合、レーザー溶接性に優れているとともに、角形ケースの耐加熱フクレ性が優れることわかる。ＤＣ鋳造法（半連続鋳造法）による実施例１と比較すると、同一合金を用いてもＭｎ固溶量が多くなっており、これによりフクレ量がさらに小さなものとなっており、より耐加熱フクレ性に優れていることがわかる。
これに対して比較例のＮＧ１４、ＮＧ１５は合金成分は本発明の範囲内であるものの、熱延予備加熱条件が本発明の範囲から外れており熱間圧延中の材料温度も本発明の範囲から外れているため、Ｍｎ固溶量が少なくなっており、また耐力が低く、レーザー溶接性は良好であるもののフクレ量が大きくなってしまっている。
【００３３】
【発明の効果】
本発明のＡｌ−Ｍｎ−Ｍｇ系合金は、固溶ＭｎとＭｇの両方の効果を利用することにより、レーザー溶接性を損わなず、かつケースの耐加熱フクレ性向上を可能としたものである。
これにより、電池製造時の蓋材とのレーザー溶接による接合に支障がなく、またケースの肉厚を薄くしても自動車内放置等で想定される７０〜９０℃の加熱および内圧発生時にもフクレ変形を抑えられケースの変形が少ないことから、本発明にかかる合金板は軽量・安全が要求される電子機器用角型Ｌｉイオン電池のケース素材として好適である。特に小型軽量の角形Ｌｉイオン電池のケース素材として有用性が高い。
【図面の簡単な説明】
【図１】固溶Ｍｎ量の分析方法を示すフローチャートである。
【図２】実施例で成形したケースの高さ方向に垂直な断面の形状を示す模式図である。
【図３】実施例で行ったフクレ試験を示す断面図である。
【符号の説明】
１電池ケース
２固定治具
３シリコンゴムシール
４シリコンゴム[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an Al-Mn-Mg alloy plate suitable for forming a case such as a prismatic Li-ion battery, and has particularly good laser weldability, so that there is no bonding failure in laser welding during battery production. By improving the heat resistance of the case, it is possible to obtain a battery with less deformation of the case even when heating and internal pressure are generated at 70 to 90 ° C., which is assumed when left in an automobile, etc. It relates to a suitable aluminum alloy plate.
[0002]
[Prior art]
It is advantageous to reduce the weight of the case by using an Al alloy instead of the iron-based material as a press forming material for a case such as a battery case.
In particular, a prismatic small Li-ion secondary battery case mounted on a mobile phone or the like due to a demand for weight reduction has been put into practical use using an aluminum alloy plate as a material. In general, an Al—Mn alloy, specifically, a 3003 alloy (Mn: 1.0 to 1.5 wt%, Mg: no additive) is usually used as a case material for the rectangular battery.
[0003]
[Problems to be solved by the invention]
The thickness of this square battery case is currently around 0.5mm at the front (the surface with the widest area), but it is required to further reduce the thickness and reduce the case weight. Therefore, a molding material having higher mechanical strength than 3003 alloy is used.
[0004]
On the other hand, an Al—Mn—Mg alloy to which Mg is added, for example, a 3004 alloy (Mn: 1.0 to 1.5 wt%, Mg: 0.8 to 1.3 wt%) is a 3003 alloy in terms of mechanical strength. More advantageous.
However, the case of 3004 alloy is not used from the viewpoint of laser weldability because there is a problem that a minute crack is formed in the welded part during laser welding with the lid.
[0005]
In addition, there is a problem that blister deformation occurs when the battery case is heated and internal pressure is generated. This cannot be solved simply by increasing the mechanical strength, and it is necessary to improve the creep resistance.
For example, when a square Li-ion secondary battery or the like is mounted on a mobile phone or the like, considering the heat generation due to repeated charging and discharging and the state of being left in a car under high outdoor temperature conditions in summer, the maximum is 70 to It is estimated to be exposed to a temperature of 90 ° C.
When placed under such conditions for a long time, the reaction proceeds inside the battery, the internal pressure increases due to the generation of bubbles and the like, and the case is deformed. This blister deformation is caused by plastic deformation due to stress concentration at a specific site and creep deformation that proceeds while maintaining temperature and internal pressure. When the amount of deformation is excessive, the electronic parts built into the mobile phone or the like are compressed, the case outside the electronic parts is deformed, or the welded part with the lid part of the case There is a risk that problems such as cracks occur in the electronic parts and the like due to leakage of the contents may cause problems.
Therefore, in order to reduce the thickness of the case, it is necessary to use a material that not only has a high mechanical strength at normal temperature but also has a large resistance to blistering in a state where heating and internal pressure are applied.
[0006]
An object of the present invention is to provide an Al—Mn—Mg-based alloy plate for case molding material that solves the above technical problems, has good laser weldability, and has less case swelling due to temperature rise and internal pressure increase. Is.
[0007]
[Means for Solving the Problems]
The inventor of the present invention provides necessary conditions for an Al—Mn—Mg-based alloy material that is excellent in laser welding and has excellent resistance to blistering due to heating and internal pressure (hereinafter referred to as “heat-resistant blistering resistance”), and specific examples thereof. Various investigations were made on the production method, and the present invention was achieved. Then, the amount of Mn solid solution is controlled together with the addition of Mg, and the heat resistance of the case can be sufficiently improved with the addition amount of Mg that does not impair the laser weldability.
Specifically, the Al—Mn alloy sheet of the present invention contains Mn 0.8 to 2% and Mg 0.2 to 0.75%, and the impurity element Si is 0.04 to 0.2%, Fe Is controlled to 0.04 to 0.6%, the balance is composed of other inevitable impurities and Al, or Cu 0.05 to 0.2%, Cr 0.02 to 0.2% and Zr 0.02 to 0 The composition contains 1 or more of 2%, the solid solution Mn content is 0.2% or more, and the proof stress is in the range of 170 to 270 N / mm ² .
In the production method, the ingot is preheated at 320 to 410 ° C. for 0.5 to 20 hours, hot rolling is performed so that the material temperature does not exceed 410 ° C., and then the reduction rate is 30 ~ 70% final cold rolling is performed, or hot rolling is performed, then cold rolling is performed at a reduction rate of 15% or more, and heated to 380 to 580 ° C at a temperature rising rate of 5 ° C / s or more. Then, intermediate annealing is performed under the condition that the temperature is kept at 0 to 200 s and immediately cooled at a cooling rate of 5 ° C./s or higher, and then final cold rolling with a reduction rate of 30 to 70% is performed. After hot rolling, annealing is performed at 160 to 210 ° C. for 1 to 18 hours at a heating / cooling rate of 10 to 100 ° C./h, or at 180 to 260 ° C. for 0 to 200 s at a heating / cooling rate of 5 ° C./s or more. Is.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
First, the alloy components will be described.
[0009]
Mn is an additive element that contributes to improvement in mechanical strength mainly in a solid solution state and contributes to improvement in resistance to heat swell. This is because the dissolved Mn acts as a resistance to dislocation movement related to creep deformation during heating and internal pressure loading. If the amount of Mn added is less than 0.8%, this effect is insufficient, and the mechanical strength is lowered, which is inappropriate. If the amount of Mn added exceeds 2%, coarse crystallized substances increase and the moldability becomes a problem, so that it is unsuitable as a case molding material. Accordingly, Mn is set to 0.8 to 2.0%.
In addition, the material of this invention requires that the amount of solute Mn is 0.2% or more. If it is less than this, the effect of the above-mentioned solid solution Mn for improving the resistance to heat swell will be insufficient. It is more preferable that the amount of dissolved Mn is 0.4% or more. This amount of solute Mn is measured by a phenol analysis method as shown in FIG.
[0010]
Mg is an additive element that contributes to improving the mechanical strength by solid solution strengthening and has the effect of improving the resistance to heat swell together with the solid solution Mn. However, there is also a problem that laser weldability is lowered by excessive addition, and an appropriate range of addition amount is determined in balance with other components. If the added amount of Mg is less than 0.2%, the effect for improving the mechanical strength and the resistance to heat swell is insufficient. On the other hand, if the amount of Mg exceeds 0.75%, laser weldability is lowered, specifically, cracks in the welded portion are likely to occur, which is inappropriate. Therefore, the Mg amount is set to 0.2 to 0.75%.
In addition, in order to improve the heat-resistant blistering property only by adding Mg, the amount of Mg added exceeding the range of the present invention is required, and it becomes difficult to achieve both good laser weldability. For this reason, in the present invention, by utilizing the effects of both the solid solution Mn and Mg, it has become possible to improve the resistance to heating blistering within the range of Mg addition without impairing the good laser weldability.
[0011]
Si has the effect of promoting the precipitation of Mn as the content increases. Therefore, if Si is contained in an amount exceeding 0.2%, the solid solution Mn is decreased, and as a result, the effect of preventing the swelling caused by the solid solution Mn is hindered, and the resistance to heat swelling is lowered. Si is more preferably 0.12% or less. Further, it is not appropriate to reduce Si to less than 0.04% because a high-purity bullion is required and the cost is increased although it does not lead to further improvement in characteristics.
[0012]
If Fe is added in an amount exceeding 0.6%, coarse crystallized products are liable to be produced, and the case moldability is adversely affected. It is more desirable if the amount of Fe added is 0.4% or less. It is not appropriate to reduce Fe to less than 0.04% because it requires high-purity bullion even though it does not lead to further improvement in characteristics.
[0013]
Cu, Cr, and Zr are additive elements that are effective in improving the resistance to thermal blistering. By adding 0.05 to 0.2% of Cu, the resistance to heat swelling is improved and the mechanical strength is improved. However, if the amount of Cu is more than specified, it is not appropriate because the laser welding is reduced. By adding 0.02 to 0.2% of Cr and Zr, the resistance to heating swelling is improved, the crystal grains are stabilized, and variations in various characteristics are reduced. However, if it exceeds the specified range, coarse crystals are formed at the time of casting, and the case moldability deteriorates.
[0014]
In addition, Ti caused by a Ti-based or Ti-B-based refining agent generally added during casting of an aluminum alloy may be contained in a range of 0.1% or less, and B may be contained in a range of 0.03% or less. Good.
[0015]
The yield strength of the Al—Mn—Mg alloy sheet of the present invention needs to be controlled in the range of 170 to 270 N / mm ² . If it is lower than 170 N / mm ^2, it is unsuitable because blistering due to plastic deformation is likely to occur when internal pressure is applied to the molded case. Further, if the proof stress is higher than 270 N / mm ^2, it is not suitable because molding is difficult.
[0016]
Next, the manufacturing method of this invention material is demonstrated.
[0017]
Casting can be performed by either a normal semi-continuous casting method (DC method) or a plate continuous casting method (CC method).
The DC material is advantageous in terms of stability of various properties and mass productivity, but it is advantageous to use the CC method in order to easily realize a high Mn solid solution amount.
[0018]
The preheating treatment before hot rolling is performed under the condition of holding at 320 to 410 ° C. for 0.5 to 20 hours. When the temperature is higher than this condition or when heating is performed for a long time, precipitation of Mn occurs excessively, and finally the heat resistance of the case is lowered. Further, if the temperature is lower than this range or shorter, the hot rolling cannot be stably performed, which is inappropriate.
Further, the material temperature during hot rolling needs to be controlled so as not to exceed 410 ° C. If the temperature is higher than this, Mn precipitates excessively, and the heat-resistant swelling resistance of the molded case is lowered. In hot rolling, it is desirable to apply a reduction of at least 50%.
[0019]
As one of the production methods of the present invention, the final cold rolling at a reduction rate of 30 to 70% is performed after the hot rolling. If the rolling reduction is lower than 30%, the mechanical strength is insufficient, and large blisters occur due to initial plastic deformation, which is inappropriate. On the other hand, if it exceeds 70%, mechanical strength such as proof stress becomes high, but molding becomes difficult, and many movable dislocations are included in the structure, and the number of movable dislocations also increases in the case after final molding. This is inappropriate because deformation tends to occur.
[0020]
As another production method of the present invention, after hot rolling, cold rolling at a reduction rate of 15% or more is performed, intermediate annealing is performed by rapid heating and cooling, and then cold rolling at a reduction rate of 35 to 70%. Is to be applied.
If the rolling reduction ratio of the cold rolling before the intermediate annealing is lower than 15%, the recrystallization in the intermediate annealing becomes unstable and there is a fear that the structure becomes uneven.
This intermediate annealing is desirably performed by a continuous annealing line (CAL), heated to 380 to 580 ° C. at a temperature increase of 5 ° C./s or more, held for 0 to 200 s, and immediately cooled at a cooling rate of 5 ° C./s or more. To be performed under the following conditions. Here, holding for 0 s is a condition for cooling immediately after reaching a predetermined temperature. If annealing is not performed by such rapid heating and cooling, Mn precipitates and the amount of Mn solid solution decreases, which is inappropriate.
The rolling reduction in the final cold rolling after the intermediate annealing is set to 35 to 70%. If it is lower than this, the mechanical strength is insufficient, and large blisters occur due to initial plastic deformation, which is inappropriate. When the rolling reduction exceeds 70%, mechanical strength such as proof stress is increased, but press molding becomes difficult. In addition, the movable dislocations are formed even in the case after the final molding including many movable dislocations in the assembly. Since it increases, creep deformation is likely to occur.
[0021]
The case material of the present invention can be used as a forming material as it is in the final cold rolling, but it can also be used after final annealing. In that case, annealing conditions of a temperature rising rate of 10 to 100 ° C./h, an annealing temperature of 160 to 210 ° C., and a holding time of 1 to 18 h are suitable, but these conditions are suitable for performing in a batch type annealing apparatus. Moreover, the final annealing conditions for annealing at 0 to 200 s at 180 to 260 ° C. with a temperature rise / cooling rate of 5 ° C./s or more can be adopted, but this is achieved by a continuous annealing line (CAL) capable of rapid heating and cooling. Can be implemented. This final annealing has the effect of reducing the mobile dislocations caused by cold rolling and the effect of increasing the resistance to transition movement during creep deformation by causing segregation in the vicinity of dislocations in part of the solid solution Mn, It is possible to further improve the resistance to thermal blistering.
[0022]
【Example】
Examples of the present invention will be described below.
[0023]
<Example 1>
An alloy having a composition in the range of the present invention shown in Table 1 was cast by a normal DC method (semi-continuous casting method), and then a rolled plate having a thickness of 0.8 mm was manufactured under the manufacturing conditions shown in Table 2.
The temperature increase and cooling of the final annealing were performed under the conditions of Invention Example G-9 with a temperature increase of 10 ° C./s and cooling of 10 ° C./s, and others with a temperature increase of 50 ° C./h and cooling of 150 ° C./h.
[0024]
[Table 1]

[0025]
[Table 2]

[0026]
The Mn solid solution amount and the proof stress were measured for the finished rolled sheet.
Further, the rolled plate was formed into a square case having a case thickness of 8 mm, a width of 30 mm, a corner of R1.5 mm, a height of 45 mm and a wall thickness of 0.45 mm as shown in FIG. This is a test in which the wall thickness is about 0.5 mm, which has been put to practical use, which is about 10% thinner.
Next, a 0.8 mm rolled plate was cold-rolled to a thickness of 0.45 mm, which is the same as the case thickness, and the irradiation energy per pulse was 5 J, the number of pulses was 20 Hz, and the beam diameter was 0.6 mm. Laser welding with a welding length of 200 mm was performed six times on the same material at a speed of 400 mm / min, and a laser weldability test was performed to confirm the presence or absence of microcracking in the welded portion with an industrial microscope. Depending on the presence or absence of cracks, it was evaluated that ◯: no crack, X: cracked, XX: crack remarkable.
Further, imitating the case where the battery is heated and the internal pressure is generated by the reaction of the battery contents, the internal pressure of 2 kg / cm ² is applied with the apparatus of the schematic diagram of FIG. 3 while holding the molded case at 85 ° C. The heating internal pressure swelling test for 24 hours was performed on the same material three times, and the amount of swelling (increase in case thickness) was evaluated as an average value. The results are shown in Table 3.
[0027]
[Table 3]

[0028]
As shown in the table, all of the inventive examples could be molded without any problems. In laser welding, there is no generation of cracks and laser weldability is excellent, and the swelling is small, and the square case made of the Al-Mn-Mg alloy plate of the present invention has excellent resistance to heat swelling. It is clear that the laser weldability of the material is good.
On the other hand, the comparative example is inferior in any of the characteristics.
NG1 uses an alloy whose Mn content is less than or equal to the range of the present invention. For this reason, the Mn solid solution amount is small, and as a result, the yield strength is low and the blistering is large.
NG2 uses an alloy having an Mn content equal to or greater than the range of the present invention, and cracks occurred in a part of the ingot during casting, and a rolled sheet could not be produced.
NG3 uses an alloy having an Mg amount equal to or less than the range of the present invention, and has a slightly low yield strength and a large amount of swelling.
NG4 contains a large amount of Mg in excess of the range of the present invention, and although the proof stress and heat proof resistance are sufficient, the laser weldability is poor.
NG5 contains a large amount of Mg exceeding the range of the present invention, and although the proof stress is sufficient, the strength is too strong and some cracks occur during case molding. In addition, laser weldability is deteriorated. As a result of performing a blister test on a case in which no crack occurred, the heat blister resistance was good.
NG6 uses an alloy whose Fe and Si content exceeds the provisions of the present invention, and a coarse crystallized product is formed. For this reason, local cracking occurred starting from the coarse crystallized product when forming the case. was there. When a mold case without cracks was selected and the blister test was performed, the amount of blister was large because the Mn solid solution amount was low.
NG7 is obtained by adding a large amount of Cu beyond the range of the present invention, and although the proof stress and the heat proof resistance are sufficient, the laser weldability is deteriorated.
NG8 is made by adding a large amount of Cr and Zr beyond the scope of the present invention. Since coarse crystals are formed, local cracking occurs during case molding, and a healthy case cannot be obtained, and a blister test is performed. could not.
NG9 is an alloy component that satisfies the provisions of the present invention, but uses a manufacturing method with a low final cold rolling rate, and therefore has a low yield strength and a large blister amount.
NG10 is an alloy component that satisfies the provisions of the present invention, but the hot preheating conditions are higher than the provisions of the present invention, and the maximum material temperature during hot rolling is too high, so the Mn solid solution amount decreases, For this reason, the amount of swelling is large.
NG11 is an alloy component that satisfies the provisions of the present invention, but the final cold rolling rate is a production condition larger than the provisions of the present invention, so that the proof stress becomes too large and cracks occur during case molding, and a blister test. I could not.
[0029]
<Example 2>
For the alloys b and c in Table 1, a plate-shaped cast material having a plate thickness of 6 mm was produced by the CC method (continuous casting and rolling method), and this was used as a 0.8 mm rolled plate under the conditions of Table 4.
This was molded in the same manner as in Example 1 and tested. Further, laser weldability was examined in the same manner as in Example 1. The results are shown in Table 5.
[0030]
[Table 4]

[0031]
[Table 5]

[0032]
From Table 4, it can be seen that when the Al—Mn—Mg alloy plate of the present invention is used as a raw material, it is excellent in laser weldability and excellent in heat resistance of the square case. Compared with Example 1 by the DC casting method (semi-continuous casting method), even when the same alloy is used, the amount of Mn solid solution is increased, and the amount of blistering is further reduced. It turns out that it is excellent in property.
On the other hand, although NG14 and NG15 of the comparative examples have alloy components within the scope of the present invention, the hot rolling preheating conditions are out of the scope of the present invention, and the material temperature during hot rolling is also within the scope of the present invention. Since it is off, the Mn solid solution amount is small, the yield strength is low, and the laser weldability is good, but the blister amount is large.
[0033]
【The invention's effect】
The Al—Mn—Mg-based alloy of the present invention makes it possible to improve the heat-swelling resistance of the case without impairing the laser weldability by utilizing the effects of both the solid solution Mn and Mg. .
As a result, there is no hindrance to joining by laser welding with the lid during battery production, and even when the case thickness is reduced, it is expected to be heated even at 70 to 90 ° C. and when internal pressure is generated when it is left in a car. Since the deformation is suppressed and the case is less deformed, the alloy plate according to the present invention is suitable as a case material for a prismatic Li-ion battery for electronic equipment that is required to be lightweight and safe. In particular, it is highly useful as a case material for small and light prismatic Li-ion batteries.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method for analyzing the amount of dissolved Mn.
FIG. 2 is a schematic view showing a cross-sectional shape perpendicular to the height direction of a case molded in an example.
FIG. 3 is a cross-sectional view showing a swelling test performed in Examples.
[Explanation of symbols]
1 Battery case 2 Fixing jig 3 Silicon rubber seal 4 Silicon rubber

Claims

Including Mn 0.8-2.0% and Mg 0.2-0.75%, the impurity element Si is controlled to 0.04-0.2%, Fe is controlled to 0.04-0.6%, The composition consisting of the remainder other inevitable impurities and Al, the solid solution Mn amount is 0.2% or more, and the proof stress is in the range of 170 to 270 N / mm ² , the laser weldability is good, An Al-Mn-Mg alloy plate for battery case molding material that has excellent heat resistance.

Including Mn 0.8-2.0% and Mg 0.2-0.75%, the impurity element Si is controlled to 0.04-0.2%, Fe is controlled to 0.04-0.6%, A composition comprising one or more of Cu 0.05 to 0.2%, Cr 0.02 to 0.2%, and Zr 0.02 to 0.2%, and the remainder consisting of other inevitable impurities and Al. Al-Mn- for battery case molding materials with good laser weldability and excellent resistance to thermal blistering, characterized in that the amount is 0.2% or more and the proof stress is in the range of 170 to 270 N / mm ² Mg alloy plate.

The ingot of the aluminum alloy composition according to claim 1 or 2 is subjected to a preheating treatment for holding at 320 to 410 ° C for 0.5 to 20 hours, and then hot rolling is performed while controlling the material temperature not to exceed 410 ° C. Then, the final cold rolling with a rolling reduction of 30 to 70% is performed. The laser weldability according to claim 1 or 2, and the Al-Mn for battery case molding material having excellent heat swell resistance. -Manufacturing method of Mg type alloy plate.

The ingot of the aluminum alloy composition according to claim 1 or 2 is subjected to a preheating treatment for holding at 320 to 410 ° C for 0.5 to 20 hours, and then hot rolling is performed while controlling the material temperature not to exceed 410 ° C. Then, cold rolling at a reduction rate of 15% or more is performed, heated to 380 to 580 ° C. at a heating rate of 5 ° C./s or more, maintained for 0 to 200 s, and immediately cooled at a cooling rate of 5 ° C./s or more. An intermediate annealing is performed, followed by a final cold rolling with a rolling reduction of 30 to 70%. The battery case molding with good laser weldability and excellent resistance to heat bulges according to claim 1 or 2 The manufacturing method of the Al-Mn-Mg type alloy plate for raw materials.

In addition to the production methods of claims 3 and 4, good laser weldability characterized by annealing at 160-210 ° C. for 1-18 h at a temperature increase rate of 10-100 ° C./h after the final cold rolling And the manufacturing method of the Al-Mn-Mg type | system | group alloy plate for battery case shaping | molding materials excellent in the heat-resistant blistering resistance.

In addition to the manufacturing method of Claim 3 and 4, the laser weldability characterized by performing 0 to 200 s annealing at 180-260 degreeC by making temperature increase and cooling rate into 5 degree-C / s or more after final cold rolling. A method for producing an Al—Mn—Mg alloy plate for a battery case molding material, which is good and has excellent resistance to thermal blistering.