JP2004183035A

JP2004183035A - Aluminum alloy sheet for aluminum can barrel with screw

Info

Publication number: JP2004183035A
Application number: JP2002350348A
Authority: JP
Inventors: Hiroshi Yokoi; 洋横井; Seiichi Hirano; 清一平野
Original assignee: Sumitomo Light Metal Industries Ltd
Current assignee: Sumitomo Light Metal Industries Ltd
Priority date: 2002-12-02
Filing date: 2002-12-02
Publication date: 2004-07-02

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet having excellent neck workability and screwing workability in an aluminum can with a screw. <P>SOLUTION: The aluminum alloy sheet has a composition comprising, by weight, 0.25 to 0.40% Si, 0.35 to 0.50% Fe, 0.15 to 0.25% Cu, 0.7 to 1.3% Mn, 0.93 to 1.3% Mg, and ≤0.25% Zn, and the balance aluminum with inevitable impurities. The number of intermetallic compound grains of ≥1 μm observed from the sheet surface is ≥3,500 pieces/mm<SP>2</SP>. The 45° ear ratio in a formed cup drawn under the conditions meeting a blank diameter of 55 mm and a drawing ratio of 1.67 is ≤3%. Further, (the average value of 0 to 180° ear heights)-(the average value of 45° ear heights)≤0.3 mm is satisfied. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【技術分野】
本発明は，絞り，しごき加工で成形されるリシール機能のついたネジ付アルミ缶胴用アルミニウム合金板に関する。
【０００２】
【従来技術】
アルミ缶としては，従来から２ピース（蓋と胴）からなる２ピースアルミ缶が用いられてきた。この２ピースアルミ缶の胴部（以下，２ピースアルミ缶胴と称す）を製造するに当たっては，図１に示すように，素材となるアルミ缶胴用アルミニウム合金板（板材Ｓ０）に対し，ブランキング工程Ｓ１１を施してブランク材を打ち抜くと共に，カッピング工程Ｓ１２を施して大径のカップに成形する。次に，カップ絞り（ＤＲＡＷＩＮＧ）としごき（ＩＲＯＮＩＮＧ）を組み合わせたＤＩ成形工程Ｓ１３を施して，細長い円筒状カップを作製する。その後，開口部のトリミングを行うトリミング工程Ｓ１４および内・外面の塗装・印刷を行い，さらに開口部のネック加工を行うネッキング工程Ｓ１５と，蓋部と嵌合させるためのフランジ部を形成するフランジング工程Ｓ１６を施して２ピースアルミ缶胴が完成する。
【０００３】
一方，最近においては，缶デザインの多様化により，従来の２ピースアルミ缶とは異なる，ボトル形状の缶が誕生した。現在のところ，非特許文献１に示すように，ボトル形状には，口部がペットボトルと同サイズの「ニューボトル缶」と，口部が比較的大きい「ボトル缶」の２種類がある。両者共通の特徴はボトル形状とするための大きなネック部と，ネジキャップによるリシール性を得るためのネジ部とを有する点にある。
【０００４】
本明細書では両者を含めたボトル形状の缶を総称して「ネジ付アルミ缶」と称する。ニューボトル缶の製造方法は特許文献２〜特許文献４に，ボトル缶の製造方法は文献５に開示されているが，それらネジ付アルミ缶の胴部（以下，ネジ付アルミ缶胴と称す）の製造方法の主要部を図２，図３に示す。図２は，ボトル缶用の胴部の製造方法を示し，図３は，ニューボトル缶用の胴部の製造方法を示す。
【０００５】
両者の加工方法は異なるものの，従来の２ピースアルミ缶胴にない，大きなネック部を形成するための絞り加工，および絞り加工により形成された口部にネジ切り加工を行うことが特徴となっている。
即ち，両者の製造工程は，それぞれ図２，図３に示すごとく，アルミニウム合金板Ｓ０に対して，ブランキング工程Ｓ２１，Ｓ３１，カッピング工程Ｓ２２，Ｓ３２，ＤＩ成形工程Ｓ２３，Ｓ３３，トリミング工程Ｓ２４，Ｓ３４までは，従来の２ピースアルミ缶胴の製造工程とほぼ同様に行われる。その後は，ボトル缶用としては，カップの開口部側にネッキング工程Ｓ２５を施した後，ネジ切り工程Ｓ２６を施す。一方，ニューボトル缶用としては，カップの底部側にネッキング＋エンド部開口工程Ｓ３５，カップの開口部側にフランジング工程Ｓ３６，底部の巻き締め＋ネジ切り工程Ｓ３７が施される。
【０００６】
ここで，注目すべき点は，両ネジ付アルミ缶胴の製造方法では，ネッキングを行う工程Ｓ２５，Ｓ３５において，詳細な工程はそれぞれ異なるが，いずれも，２ピースアルミ缶胴にない，大きなネック部を形成するための絞り加工が施され，さらにその後のネジ切り工程Ｓ２６，Ｓ３６が施される点にある。
【０００７】
これらの加工は，従来の２ピースアルミ缶胴より過酷であるため，従来材ではしわや割れが発生しやすい不具合があった。この不具合を解決するために，特許文献６ではベーキング（印刷後の焼付け）後の耐力を２２０〜２５０Ｎ／ｍｍ^２とすること，さらに好ましくは４５°耳の耳率を２．５％以下にすることが開示されている。しかし，ネジ付アルミ缶胴の過酷な加工に絶えきれるアルミニウム合金板を得るには，更なる研究及び改良が必要であった。
【０００８】
【非特許文献１】
「飲料缶の新展開−機能と差別化をめざす−」ビバリッジジャパンＮｏ．２３７（２００１年第９号）
【特許文献２】
特開２００１−１１４２４５号公報
【特許文献３】
特開２００１−１５８４３６号公報
【特許文献４】
特開２００１−１６２３４４号公報
【特許文献５】
特開２０００−１９１００６号公報
【特許文献６】
特開２００２−２５６３６６号公報
【０００９】
【解決しようとする課題】
本発明は，上記従来の問題点に鑑みてなされたもので，ネジ付アルミ缶のネック加工およびネジ切り加工に優れたアルミニウム合金板を提供しようとするものである。
【００１０】
【課題の解決手段】
本発明は，重量比において，Ｓｉ：０．２５〜０．４０％，Ｆｅ：０．３５〜０．５０％，Ｃｕ：０．１５〜０．２５％，Ｍｎ：０．７〜１．３％，Ｍｇ：０．９３〜１．３％，Ｚｎ：≦０．２５％を含み，残部がアルミニウムと不可避的不純物からなる組成を有し，
板表面から観察される１μｍ以上の金属間化合物が３５００個／ｍｍ^２以上であり，
かつ，ブランク径が５５ｍｍ，絞り比が１．６７という条件で絞った成形カップにおける４５°耳率が３％以下であると共に，（０−１８０°耳高さの平均値）−（４５°耳高さの平均値）≦０．３ｍｍであることを特徴とするネジ付アルミ缶胴用アルミニウム合金板にある（請求項１）。
【００１１】
まず，本発明における各成分の限定範囲について説明する。
Ｓｉ：０．２５〜０．４０％，
Ｓｉは，Ｍｎ，Ｆｅとともに，しごき成形時の素材と工具の焼き付き防止に効果のあるα相化合物（Ａｌ−Ｍｎ−Ｆｅ−Ｓｉ系）形成に必要な成分である。また，この他にＡｌ−Ｍｎ−Ｓｉ相も形成し，Ｍｎの固溶量を低下させて，より均一な変形を促進する。したがって，ネック成形性の向上には，その量の最適化が重要である。Ｓｉ含有量は，０．２５％未満では不十分であり，望ましくは０．２８％以上であり，更に望ましくは０．３２％以上である。しかし，Ｓｉ含有量が０．４０％を越えて過剰に添加されると，Ｍｇ_２Ｓｉ相晶出物が形成されやすくなり，成形性が低下するとともに耐食性を損なう。
【００１２】
Ｆｅ：０．３５〜０．５０％，
Ｆｅは，Ｍｎとともに鋳造時にＡｌ_６（Ｍｎ，Ｆｅ）相，α相化合物（Ａｌ−Ｆｅ−Ｍｎ−Ｓｉ系），Ａｌ−Ｆｅ−Ｓｉ系の化合物を形成する。これは上述したようにしごき成形時に不可欠である。しかし，Ｆｅ添加量が０．５０％を越えると粗大な化合物を生じやすく，成形加工時に破断の起点となりうるので好ましくない。また，０．３５％未満では，均一変形に寄与する金属間化合物の形成が不十分であり，好ましくない。
【００１３】
Ｃｕ：０．１５〜０．２５％，
Ｃｕは，Ｍｇとともに低温熱処理などにより，Ａｌ−Ｍｇ−Ｃｕ系化合物を形成して強度を高め，塗装焼き付けなどの加熱による軟化を抑制する効果をもつ。Ｃｕ添加量が０．１５％未満であると上記効果が小さく，０．２５％を越えると成形加工時の加工硬化性が大きくなりすぎて成形性が低下し，また耐食性が低下し好ましくない。また，現行の国内の缶ボディ材には，Ｃｕが０．２０〜０．２５％含まれている材料が大半のため，リサイクルの観点からも，上記範囲の量のＣｕを添加した合金が好ましい。
【００１４】
Ｍｎ：０．７〜１．３％，
Ｍｎは，強度に寄与する主要元素であり，またα相化合物（Ａｌ−Ｍｎ−Ｆｅ−Ｓｉ系）の生成によるしごき加工時の焼き付き防止に効果のある成分である。Ｍｎ添加量が０．７％未満では上記効果が得られない。１．３％を越えると，Ｍｎ固溶量が増加し，ネック成形時に均一変形しにくくなり，好ましくない。
【００１５】
Ｍｇ：０．９３〜１．３％，
Ｍｇは，Ｍｎとともに強度を付与する不可欠な添加元素であり，固溶して合金を硬化する。Ｍｇ添加量が０．９３％未満では，強度が不十分であり，また後述の０−１８０°耳の抑制の観点からも所定の量以上の添加が好ましい。一方，酸化抑制しフローマークを出にくくするため，添加量は抑制した方が良いので，１．３％を越えて添加することは望ましくなく，望ましくは１．２％以下である。
【００１６】
Ｚｎ：≦０．２５％，
Ｚｎは，絞りおよびしごき加工性，ならびにネック・フランジ成形性の向上に効果がある。しかし，Ｚｎ添加量が１．０％を越えると耐食性を損なう傾向があり，コスト的にも不利となる。ここでは，現行のＡ３００４（Ａ３１０４）と同範囲である０．２５％以下とした。
【００１７】
また，本発明では，板表面から観察される１μｍ以上の金属間化合物が３５００個／ｍｍ^２以上である。これにより，ネック成形時にひずみが均一に入りやすく，成形性の優れた材料となる。望ましくは４０００個／ｍｍ^２以上がよい。一方，この１μｍ以上の金属間化合物が３５００個／ｍｍ^２未満の場合には，上記の成形性向上効果があまり得られない。
ここで，上記金属間化合物としては，例えば，Ａｌ_６（Ｍｎ，Ｆｅ），α相化合物（Ａｌ−Ｍｎ−Ｆｅ−Ｓｉ系）等がある。
【００１８】
また，本発明では，ブランク径が５５ｍｍ，絞り比が１．６７という条件で絞った成形カップにおける４５°耳率が３％以下であると共に，（０−１８０°耳高さの平均値）−（４５°耳高さの平均値）≦０．３ｍｍである。
ネジ付アルミ缶胴のネックを成形する際には，板材を何度も絞っていくので，耳率を小さくすることは重要である。このため，上記のごとく，ブランク径５５ｍｍの円板から絞り比１．６７で成形した絞りカップにおいて，耳率を３％以下にすること，かつ（０−１８０°耳高さの平均値）−（４５°耳高さの平均値）の値を０．３ｍｍ以下とする。好ましくは０．１５ｍｍ以下がよい。
【００１９】
また，製品の板厚が既存のアルミ缶用材料よりも厚くなっている場合には，熱間圧延上がりから冷間圧延上がりまでの冷間圧延の負荷を軽減することが一般的である。しかし，冷間圧延加工度が小さくなると，圧延集合組織の発達が不十分で，また熱間圧延上がりで形成されたＣｕｂｅ方位およびＣｕｂｅ方位から冷間圧延の過程で増加する圧延軸回りに回転したＲＤ−ｒｏｔａｔｅｄＣｕｂｅに起因する０−１８０°耳が多く残存しやすくなる。したがって，０−１８０°耳が大きく残らないように，化学成分および製造条件を規定する必要がある。化学成分として０−１８０°耳を抑制するために最も効果のある元素はＭｇであり，少なくとも０．９３％以上添加する必要がある。
【００２０】
ここで，上記４５°耳率，０−１８０°耳高さの平均値，および４５°耳高さの平均値の定義について説明する。なお，０°，４５°，１８０°等の角度は，いずれも圧延方向を０°とした場合に板面上において時計回り方向に角度をとった方向を意味する。また，耳高さおよび谷高さは，いずれも成形カップの底から上端までの高さをいう。
【００２１】
まず，４５°耳高さ＝Ａ，１３５°耳高さ＝Ｂ，２２５°耳高さ＝Ｃ，３１５°耳高さ＝Ｄ，４５°と１３５°の間の最小谷高さ＝Ｅ，１３５°と２２５°の間の最小谷高さ＝Ｆ，２２５°と３１５°の間の最小谷高さ＝Ｇ，３１５°と４５°の間の最小谷高さ＝Ｈ，と定義する。
また，０°耳高さ＝Ｉ，１８０°耳高さ＝Ｊと定義する。
【００２２】
＜４５°耳率＞
（４５°耳率）＝（Ｍ４５−Ｖ４５）／｛（Ｍ４５＋Ｖ４５）／２｝×１００（％），
ここで，Ｍ４５＝（Ａ＋Ｂ＋Ｃ＋Ｄ）／４，Ｖ４５＝（Ｅ＋Ｆ＋Ｇ＋Ｈ）／４
【００２３】
＜０−１８０°耳高さの平均値＞
（０−１８０°耳高さの平均値）＝（Ｉ＋Ｊ）／２
＜４５°耳高さの平均値＞
（４５°耳高さの平均値）＝（Ａ＋Ｂ＋Ｃ＋Ｄ）／４
【００２４】
【発明の実施の形態】
本発明のネジ付アルミ缶胴用アルミニウム合金板は，上記成分組成において，さらに，Ｔｉ：≦０．１０％を含むことが好ましい。
Ｔｉは，鋳造組織を微細化し，圧延加工性や再結晶特性を向上し，組織を均一化するので，最終硬質板の異方性を軽減し成形加工性を向上させるのに有効である。なお，鋳塊組織微細化剤としてＡｌ−Ｔｉ−Ｂ中間合金を添加する場合は，Ｂが含有されるが，Ｂは０．０２％以下の範囲で添加されるのが好ましい。
Ｔｉ添加量が０．０１％未満では上記効果が十分に得られず，Ｔｉ添加量が０．１０％を越える，あるいはＢ添加量が０．０２％を越えると粗大なＡｌ−ＴｉあるいはＴｉ−Ｂ化合物を形成し，割れやピンホールなどの重大欠陥を誘発するため好ましくない。
【００２５】
次に，上記ネジ付アルミ缶胴用アルミニウム合金板においては，ベーキング後の耐力がベーキング前の耐力より２０〜３０ＭＰａ低いことが好ましい（請求項２）。
ここでいうベーキングとは，ネジ付アルミ缶胴の製造工程の塗料焼き付け工程を想定して，未成形の上記アルミニウム合金板を温度２０５℃に１０分間保持する熱処理を加えることを意味する。そして，ベーキング前の耐力とは，上記アルミニウム合金板にベーキングを加える前に引張試験を行って得られた耐力値を意味し，一方，ベーキング後の耐力とは，上記アルミニウム合金板にベーキングを加えた後に引張試験を行って得られた耐力値を意味する。
【００２６】
そして，上記ベーキング前の耐力とベーキング後の耐力との差が，２０ＭＰａ未満では材料が硬く，ネック成形でしわが発生しやすい。３０ＭＰａを越えると，強度の低下が大きく，缶体としての強度を維持できないという問題がある。それ故，上記のごとく，ベーキング前後の耐力の差は２０〜３０ＭＰａが好ましい。
【００２７】
また，板表面に付着しているリオイル油の付着量が３０〜２５０ｍｇ／ｍ^２であることが好ましい（請求項３）。
ここでいうリオイル油とは，板製造の最終工程において板面上に塗布するオイルのことであり，キズ防止，耐食性付与，およびプレス加工時の潤滑の補助の役割を果たすものである。例えば，鉱油系，合成油系のものを用いることができる。また，リオイル油量は，上記アルミニウム合金板の片面当たりに換算した付着量である。上記リオイル油量が３０ｍｇ／ｍ^２未満では，成形時に潤滑不良が起こりやすく，一方，２５０ｍｇ／ｍ^２を越える場合には，潤滑過多により成形時に良好な面質を得ることができない。
【００２８】
また，上記ネジ付アルミ缶胴用アルミニウム合金板は，板厚が０．３〜０．４５ｍｍであることが好ましい（請求項４）。板厚が０．３ｍｍ未満では，所定の缶体強度が得られない。０．４５ｍｍを越える場合には，必要以上に板厚が厚すぎてコストアップになり好ましくない。
【００２９】
また，本発明のネジ付アルミ缶胴用アルミニウム合金板は，鋳造された鋳塊を均質化処理した後，熱間圧延し，さらに，中間焼鈍を行うことなく冷間圧延を行うことにより作製されていることが好ましい（請求項５）。これにより，上述した優れたネジ付アルミ缶胴用アルミニウム合金板を得ることができる。
以下に，各工程毎にさらに好ましい方法について説明する。
【００３０】
鋳造，均質化処理：
上述した成分範囲の合金を，通常の方法で溶解，鋳造した後，得られた鋳塊を，５８０℃以上，融点以下の温度で１時間以上均質化処理することが好ましい。また，Ａｌ_６（Ｍｎ，Ｆｅ）から，しごき成形時に焼き付き防止効果のあるα相化合物（Ａｌ−Ｍｎ−Ｆｅ−Ｓｉ系）の変態を十分に行うためにも，均質化処理はできるだけ高温，長時間行うのが好ましい。しかし，融点を越えた高温で加熱すると，鋳塊の一部が共晶融解を生じ，板表面の面質が悪化するので好ましくない。保持温度が５８０℃以上融点以下の範囲であれば保持時間は１時間でよく，２０時間よりも長く保持しても経済性において不利となる。
【００３１】
熱間圧延：
均質化処理後の熱間圧延は，好ましくは４５０〜５５０℃で開始する。５５０℃より高温では表面が酸化したり再結晶粒が粗大化して成形性が低下するなどの問題点を生じやすい。また，４５０℃より低温では圧延途中の再結晶が不十分となり製品の耳率（異方性）が悪化する傾向がある。硬質板の耳率は，熱間圧延終了時の再結晶集合組織と，それ以後に加えられる冷間圧延時の圧延集合組織に依存する。熱間圧延は圧延終了時の材料温度が２８０〜３５０℃になるように行うことが好ましい。３５０℃を越えると再結晶粒が粗大化し，２８０℃以下になると再結晶が不十分となり，いずれも耳率を悪化させるので好ましくない。
【００３２】
冷間圧延前あるいは途中の中間焼鈍：
中間焼鈍すると，溶質元素の固溶度を上げ，ネック成形性を低下させるので，好ましくない。従って，上記のごとく，中間焼鈍を行うことなく冷間圧延工程を行うことが好ましい。
【００３３】
冷間圧延：
冷間圧延は材料強度を向上させるために行う。冷間における総圧下量が６０％未満では十分な強度が得られず，また９０％より高いと，圧延集合組織が発達しすぎることにより４５°耳が高くなりすぎ，材料の歩留まりが悪化する。冷間の総圧下量は，強度と耳率の関係から，より好ましくは８０〜８８％が良い。
【００３４】
そして，上記の好ましい圧下量による冷間圧延まで終えることにより，材料の板表面には，１５μｍを越える化合物が存在せず，観察した板面の面積を１００％とした場合に１〜１５μｍの化合物の面積率が５．０％以上であり，この１〜１５μｍの化合物の面積全体を１００％とした場合に，α相化合物の面積率が５０％以上であり，且つＭｇ_２Ｓｉ相の面積率が１．０％以下である状態を得ることが好ましい。
【００３５】
１５μｍを越える化合物が存在すると，しごき成形およびネック成形後のフランジ成形時に割れの起点となる。１〜１５μｍの化合物は主に鋳造時に生成したＡｌ_６（Ｍｎ，Ｆｅ）相晶出物および均質化処理によってα相化したものであり，しごき成形時の焼き付き防止となる。この絶対量が５％未満ではその効果が少ない。さらに，このうち，α相化した化合物が５０％未満でも効果が少ない。Ｍｇ_２Ｓｉ相は，塗装焼き付け処理後の強度を維持するために必要なＭｇ固溶量の減少および耐食性に不利となるために，板表面における面積率で１．０％以下とすることが好ましい。
【００３６】
【実施例】
本例では，表１に示すごとく，本発明の実施例としての５種類のアルミニウム合金板（Ｅ１〜Ｅ５）と，比較例としての４種類のアルミニウム合金板（Ｃ１〜Ｃ４）を製造し，さらにこれらの特性を測定した。
まず，表１に示す成分を含有するアルミニウム合金鋳塊を半連続鋳造にて造塊し，表面を面削後，５８０℃の温度に１２時間保持する均質化処理を行い，直ちに熱間圧延を開始し，３５０℃の温度で終了し，３ｍｍ厚の熱間圧延板を得た。得られた熱間圧延板が常温になってから８７％の圧延率で０．４ｍｍ厚まで冷間圧延を行って，上記５種類の実施例（Ｅ１〜Ｅ５）および４種類の比較例（Ｃ１〜Ｃ４）の供試材を得た。
【００３７】
次に，すべての供試材に対し，板面における金属間化合物の観察，耳率の測定，ベーキング後の耐力低下の測定を行い，その特性を評価した。
板面における金属間化合物の観察は，供試材の表面を脱脂洗浄後，ＳＥＭ（走査型電子顕微鏡）の組成像で板表面を撮影して行った。そして，画像解析装置（（株）ニレコ製ルーゼクス５００）を用いて金属間化合物の分布密度およびその面積率を測定した。金属間化合物の大きさとしては，その直径を測定した。この場合，金属間化合物の直径は円相当直径，すなわち写真における金属間化合物の面積と同じ面積を有する円の直径として測定した。
判定は，１μｍ以上の金属間化合物が３５００個／ｍｍ^２以上の場合に合格，３５００個／ｍｍ^２未満の場合を不合格とした。
【００３８】
耳率の測定は，ダイス径３４ｍｍ，ポンチ径３３ｍｍ，ポンチ肩Ｒ１．５ｍｍの金型を用い，供試材ブランク径５５ｍｍ，絞り比１．６７の条件でカップ絞りを実施した。得られた絞りカップを用い，前述の式により，４５°耳率と，（０−１８０°耳高さの平均値）−（４５°耳高さの平均値）の値を求めた。
４５°耳率は，３％以下を合格，３％越えを不合格とした。また，（０−１８０°耳高さの平均値）−（４５°耳高さの平均値）は０．３ｍｍ以下を合格，０．３ｍｍ越えを不合格とした。
【００３９】
上記ベーキングの条件は，２０５℃の温度に１０分間保持する条件とした。そして，このベーキングを行っていない供試材とベーキングを完了した供試材をそれぞれＪＩＳ５号試験片に加工して，ＪＩＳＺ２２４１に準拠して引張試験をを行った。そして，ベーキング前の試験片の耐力値からベーキング後の試験片の耐力値を差し引いて耐力低下値として求めた。
そして，ベーキング後の耐力低下が２０〜３０ＭＰａの範囲内の場合には合格，これをはみ出した場合を不合格とした。
【００４０】
得られた結果を表２に示す。表２より知られるごとく，実施例Ｅ１〜Ｅ５は，すべての評価項目において合格となり，総合的に合格（○）の判定が得られた。一方，比較例Ｃ１〜Ｃ４は，少なくとも１つの評価項目において不合格となり，総合的にすべて不合格（×）の判定となった。
【００４１】
具体的には，比較例Ｃ１においては，Ｍｇ量が少ないため，４５°耳の形成が少なくなり，（０−１８０°耳高さの平均値）−（４５°耳高さの平均値）が大きくなった。
また，比較例Ｃ２においては，Ｓｉ量が多いため，ベーキングによる軟化量が多く，必要とする缶体強度が得られない。
また，比較例Ｃ３においては，Ｍｎ量が多く，Ｓｉ，Ｆｅ量が少ないため，晶出物は多くなるがＭｎ固溶量が多くベーキングによる軟化量が少なくなった。
また，比較例Ｃ４においては，Ｓｉ，Ｆｅ量が少ないため，晶出物が少ない。そのため，ベーキングによる軟化量が少なくなったと考えられる。
【００４２】
【表１】

【００４３】
【表２】

【図面の簡単な説明】
【図１】２ピースアルミ缶胴の製造工程を示す説明図。
【図２】ネジ付アルミ缶胴（ボトル缶）の胴部の製造工程を示す説明図。
【図３】ネジ付アルミ缶胴（ニューボトル缶）の胴部の製造工程を示す説明図。
【符号の説明】
Ｓ０．．．アルミニウム合金板，
Ｓ１１，Ｓ２１，Ｓ３１．．．ブランキング工程，
Ｓ１２，Ｓ２２，Ｓ３２．．．カッピング工程
Ｓ１３，Ｓ２３，Ｓ３３．．．ＤＩ成形工程，
Ｓ１４，Ｓ２４，Ｓ３４．．．トリミング工程，
Ｓ１５，Ｓ２５．．．ネッキング工程，
Ｓ１６，Ｓ３６．．．フランジング工程，
Ｓ２６，Ｓ３６．．．ネジ切り工程，
Ｓ３５．．．ネッキング＋エンド部開口工程，
Ｓ３７．．．底部の巻き締め＋ネジ切り工程，[0001]
【Technical field】
The present invention relates to an aluminum alloy plate for a screwed aluminum can body having a reseal function and formed by drawing and ironing.
[0002]
[Prior art]
As the aluminum can, a two-piece aluminum can consisting of two pieces (lid and body) has been used. In manufacturing the body of the two-piece aluminum can (hereinafter, referred to as a two-piece aluminum can body), as shown in FIG. A blank material is punched out by performing a ranking step S11, and a cup having a large diameter is formed by performing a cupping step S12. Next, a DI forming step S13 in which cup drawing (DRAWING) and ironing (IRONING) are combined is performed to produce an elongated cylindrical cup. Thereafter, a trimming step S14 for trimming the opening, a coating / printing of the inner and outer surfaces, and a necking step S15 for necking the opening, and flanging for forming a flange for fitting with the lid. By performing step S16, a two-piece aluminum can body is completed.
[0003]
On the other hand, recently, with the diversification of can designs, bottle-shaped cans, which are different from conventional two-piece aluminum cans, have been born. At present, as shown in Non-Patent Document 1, there are two types of bottle shapes, a "new bottle can" having the same size as a plastic bottle and a "bottle can" having a relatively large mouth. A feature common to both is that it has a large neck portion for forming a bottle shape and a screw portion for obtaining resealability with a screw cap.
[0004]
In the present specification, a bottle-shaped can including both of them is generically referred to as a "screwed aluminum can". Patent Literature 2 to Patent Literature 4 disclose a method for manufacturing a new bottle can and Patent Literature 5 disclose a method for manufacturing a bottle can. 2 and 3 show a main part of the manufacturing method of the present invention. FIG. 2 shows a method for producing a body for a bottle can, and FIG. 3 shows a method for producing a body for a new bottle can.
[0005]
Although the two processing methods are different, they are characterized by the draw processing to form a large neck part, which is not in the conventional two-piece aluminum can body, and the threading processing at the mouth formed by the draw processing. I have.
That is, as shown in FIG. 2 and FIG. 3, respectively, the manufacturing steps of the two are performed on the aluminum alloy plate S0 by blanking steps S21, S31, cupping steps S22, S32, DI forming steps S23, S33, trimming step S24, The process up to S34 is performed in substantially the same manner as the conventional manufacturing process of a two-piece aluminum can body. Thereafter, for a bottle can, a necking step S25 is performed on the opening side of the cup, and then a thread cutting step S26 is performed. On the other hand, for a new bottle, a necking + end opening step S35 on the bottom side of the cup, a flanging step S36 on the opening side of the cup, and a bottom tightening + thread cutting step S37 are performed.
[0006]
Here, it should be noted that in the method of manufacturing the double-threaded aluminum can body, detailed steps are different in the steps S25 and S35 of performing necking, but none of the two-piece aluminum can body has a large neck. The point is that drawing processing for forming a portion is performed, and further subsequent threading steps S26 and S36 are performed.
[0007]
Since these processes are more severe than the conventional two-piece aluminum can body, the conventional material has a problem that wrinkles and cracks are easily generated. In order to solve this problem, in Patent Document 6, the proof stress after baking (baking after printing) is set to 220 to 250 N / mm ^2, and more preferably, the ear ratio of the 45 ° ear is set to 2.5% or less. It is disclosed. However, further research and improvement were needed to obtain an aluminum alloy plate that could be used for severe processing of a screwed aluminum can body.
[0008]
[Non-patent document 1]
"New Development of Beverage Can-Aiming for Function and Differentiation-" Beverage Japan No. 237 (No. 9, 2001)
[Patent Document 2]
Japanese Patent Application Laid-Open No. 2001-114245 [Patent Document 3]
JP 2001-158436 A [Patent Document 4]
JP 2001-162344 A [Patent Document 5]
Japanese Patent Application Laid-Open No. 2000-191006 [Patent Document 6]
JP 2002-256366 A
[Problem to be solved]
The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide an aluminum alloy plate excellent in necking and threading of an aluminum can with a screw.
[0010]
[Means for solving the problem]
In the present invention, in terms of weight ratio, Si: 0.25 to 0.40%, Fe: 0.35 to 0.50%, Cu: 0.15 to 0.25%, Mn: 0.7 to 1.3. %, Mg: 0.93 to 1.3%, Zn: ≤0.25%, the balance being composed of aluminum and unavoidable impurities,
The number of intermetallic compounds of 1 μm or more observed from the plate surface is 3500 / mm ² or more,
In addition, the 45 ° ear ratio of the formed cup squeezed under the conditions of a blank diameter of 55 mm and a drawing ratio of 1.67 is 3% or less, and (0-180 ° ear height average) − (45 ° ear height). (Average value of height) ≦ 0.3 mm.
[0011]
First, the limited range of each component in the present invention will be described.
Si: 0.25 to 0.40%,
Si, together with Mn and Fe, is a component necessary for forming an α-phase compound (Al—Mn—Fe—Si) that is effective in preventing seizure of the material and the tool during ironing. In addition, an Al-Mn-Si phase is also formed to reduce the solid solution amount of Mn and promote more uniform deformation. Therefore, optimization of the amount is important for improving the neck formability. If the Si content is less than 0.25%, it is insufficient, preferably 0.28% or more, and more preferably 0.32% or more. However, if the Si content exceeds 0.40% and is excessively added, a Mg ₂ Si phase crystallized substance is easily formed, and the moldability is reduced and the corrosion resistance is impaired.
[0012]
Fe: 0.35 to 0.50%,
Fe forms an Al ₆ (Mn, Fe) phase, an α-phase compound (Al—Fe—Mn—Si type), and an Al—Fe—Si type compound during casting together with Mn. This is essential during ironing as described above. However, if the added amount of Fe exceeds 0.50%, a coarse compound is apt to be generated, which may be a starting point of breakage during molding, which is not preferable. If it is less than 0.35%, the formation of intermetallic compounds contributing to uniform deformation is insufficient, which is not preferable.
[0013]
Cu: 0.15 to 0.25%,
Cu forms an Al-Mg-Cu-based compound together with Mg by low-temperature heat treatment or the like, thereby increasing the strength and suppressing softening due to heating such as paint baking. If the added amount of Cu is less than 0.15%, the above effect is small, and if it exceeds 0.25%, the work hardenability at the time of forming becomes too large, the formability is lowered, and the corrosion resistance is lowered, which is not preferable. In addition, most of the current domestic can body materials contain Cu in an amount of 0.20 to 0.25%. Therefore, from the viewpoint of recycling, an alloy containing Cu in the above range is preferable from the viewpoint of recycling. .
[0014]
Mn: 0.7-1.3%,
Mn is a main element that contributes to strength and is a component that is effective in preventing seizure during ironing due to generation of an α-phase compound (Al-Mn-Fe-Si system). If the amount of Mn is less than 0.7%, the above effects cannot be obtained. If it exceeds 1.3%, the amount of Mn solid solution increases, and it becomes difficult to uniformly deform during neck forming, which is not preferable.
[0015]
Mg: 0.93 to 1.3%,
Mg is an indispensable additive element that imparts strength together with Mn, and solidifies to harden the alloy. If the added amount of Mg is less than 0.93%, the strength is insufficient, and the addition of a predetermined amount or more is also preferable from the viewpoint of suppressing the 0-180 ° ear described below. On the other hand, in order to suppress oxidation and make it difficult to generate flow marks, it is better to suppress the amount of addition. Therefore, it is not desirable to add more than 1.3%, and preferably 1.2% or less.
[0016]
Zn: ≦ 0.25%,
Zn is effective in improving drawability and ironing workability and neck / flange formability. However, if the amount of Zn exceeds 1.0%, corrosion resistance tends to be impaired, which is disadvantageous in terms of cost. Here, it is set to 0.25% or less, which is the same range as the current A3004 (A3104).
[0017]
In the present invention, the number of intermetallic compounds of 1 μm or more observed from the plate surface is 3500 / mm ² or more. This makes it easy for the strain to enter uniformly during neck forming, resulting in a material having excellent formability. Desirably, the number is 4000 pieces / mm ² or more. On the other hand, when the number of intermetallic compounds having a size of 1 μm or more is less than 3500 / mm ² , the above-described effect of improving the formability is not obtained much.
Here, examples of the above-mentioned intermetallic compound include Al ₆ (Mn, Fe), α-phase compound (Al-Mn-Fe-Si type), and the like.
[0018]
In the present invention, the 45 ° ear ratio of the molded cup squeezed under the conditions of a blank diameter of 55 mm and a drawing ratio of 1.67 is 3% or less, and (an average value of 0-180 ° ear height) − (Average value of 45 ° ear height) ≦ 0.3 mm.
When forming the neck of a threaded aluminum can body, it is important to reduce the ear ratio because the plate material is repeatedly squeezed. For this reason, as described above, in a draw cup formed from a disk having a blank diameter of 55 mm at a draw ratio of 1.67, the ear ratio is set to 3% or less, and (the average value of 0 to 180 ° ear height). (Average value of 45 ° ear height) is set to 0.3 mm or less. Preferably, it is 0.15 mm or less.
[0019]
When the thickness of the product is thicker than the existing aluminum can material, it is common to reduce the load of cold rolling from hot rolling to cold rolling. However, when the degree of cold rolling was reduced, the development of the rolling texture was insufficient, and the steel roll rotated around the rolling axis, which increased during the cold rolling process from the Cube orientation formed by hot rolling and the Cube orientation. Many 0-180 ° ears caused by the RD-rotated Cube are likely to remain. Therefore, it is necessary to define the chemical composition and the manufacturing conditions so that the 0-180 ° ear does not remain large. The most effective element for suppressing the 0-180 ° ear as a chemical component is Mg, and it is necessary to add at least 0.93% or more.
[0020]
Here, the definitions of the 45 ° ear ratio, the average value of the 0-180 ° ear height, and the average value of the 45 ° ear height will be described. Note that angles such as 0 °, 45 °, and 180 ° mean directions that are angled clockwise on the plate surface when the rolling direction is 0 °. In addition, the ear height and the valley height refer to the height from the bottom to the top of the molding cup.
[0021]
First, 45 ° ear height = A, 135 ° ear height = B, 225 ° ear height = C, 315 ° ear height = D, minimum valley height between 45 ° and 135 ° = E, 135 Define the minimum valley height between ° and 225 ° = F, the minimum valley height between 225 ° and 315 ° = G, and the minimum valley height between 315 ° and 45 ° = H.
Also, 0 ° ear height = I and 180 ° ear height = J are defined.
[0022]
<45 ° ear rate>
(45 ° ear ratio) = (M45−V45) / {(M45 + V45) / 2} × 100 (%),
Here, M45 = (A + B + C + D) / 4, V45 = (E + F + G + H) / 4
[0023]
<Average of 0-180 ° ear height>
(Average of 0-180 ° ear height) = (I + J) / 2
<Average of 45 ° ear height>
(Average value of 45 ° ear height) = (A + B + C + D) / 4
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
It is preferable that the aluminum alloy sheet for a screwed aluminum can body of the present invention further includes Ti: ≤ 0.10% in the above composition.
Ti is effective in reducing the anisotropy of the final hard plate and improving the formability since it refines the cast structure, improves the rolling workability and recrystallization characteristics, and makes the structure uniform. When an Al-Ti-B intermediate alloy is added as an ingot structure refining agent, B is contained, but B is preferably added in a range of 0.02% or less.
If the Ti content is less than 0.01%, the above effect cannot be sufficiently obtained. If the Ti content exceeds 0.10% or the B content exceeds 0.02%, coarse Al-Ti or Ti- It is not preferable because it forms a B compound and induces serious defects such as cracks and pinholes.
[0025]
Next, in the above-mentioned aluminum alloy plate for an aluminum body with a screw, the proof stress after baking is preferably lower by 20 to 30 MPa than the proof stress before baking (claim 2).
The term "baking" as used herein means that a heat treatment for holding the unformed aluminum alloy plate at a temperature of 205 ° C. for 10 minutes is performed assuming a paint baking process in the manufacturing process of the aluminum can body with screws. The proof stress before baking means the proof stress value obtained by conducting a tensile test before baking the aluminum alloy plate, while the proof stress after baking refers to the proof stress after baking the aluminum alloy plate. After the tensile test.
[0026]
If the difference between the proof stress before baking and the proof stress after baking is less than 20 MPa, the material is hard and wrinkles are likely to occur in neck forming. If it exceeds 30 MPa, there is a problem that the strength is greatly reduced and the strength as a can cannot be maintained. Therefore, as described above, the difference in proof stress before and after baking is preferably 20 to 30 MPa.
[0027]
Further, it is preferable that the amount of re-oil oil adhering to the plate surface is 30 to 250 mg / m ² (Claim 3).
Here, the re-oil oil is oil applied to the plate surface in the final step of plate manufacturing, and plays a role in preventing scratches, imparting corrosion resistance, and assisting lubrication during press working. For example, a mineral oil type or a synthetic oil type can be used. Further, the amount of re-oil oil is the amount of adhesion converted to one side of the aluminum alloy plate. If the re-oil oil amount is less than 30 mg / m ² , poor lubrication tends to occur during molding, while if it exceeds 250 mg / m ² , good surface quality cannot be obtained during molding due to excessive lubrication.
[0028]
Preferably, the thickness of the aluminum alloy plate for a screwed aluminum can body is 0.3 to 0.45 mm. If the plate thickness is less than 0.3 mm, a predetermined strength of the can cannot be obtained. If the thickness exceeds 0.45 mm, the thickness is unnecessarily large and the cost increases, which is not preferable.
[0029]
The aluminum alloy sheet for a screwed aluminum can body of the present invention is manufactured by homogenizing a cast ingot, hot rolling, and then cold rolling without intermediate annealing. (Claim 5). Thereby, the above-mentioned excellent aluminum alloy plate for a screwed aluminum can body can be obtained.
Hereinafter, a more preferable method for each step will be described.
[0030]
Casting and homogenization processing:
After melting and casting the alloy in the above-described component range by an ordinary method, it is preferable to homogenize the obtained ingot at a temperature of 580 ° C. or more and the melting point or less for one hour or more. Further, in order to sufficiently transform α ₆ (Mn, Fe) into an α-phase compound (Al—Mn—Fe—Si-based) having an anti-seizure effect during ironing, the homogenization treatment should be performed at a temperature as high as possible and as long as possible. It is preferable to perform for a time. However, heating at a high temperature exceeding the melting point is not preferable because eutectic melting occurs in a part of the ingot and the surface quality of the sheet surface deteriorates. If the holding temperature is in the range of 580 ° C. or higher and the melting point or lower, the holding time may be one hour, and holding for longer than 20 hours is disadvantageous in terms of economy.
[0031]
Hot rolling:
Hot rolling after the homogenization treatment preferably starts at 450-550 ° C. If the temperature is higher than 550 ° C., problems such as oxidization of the surface and coarsening of recrystallized grains and deterioration of moldability are likely to occur. On the other hand, if the temperature is lower than 450 ° C., recrystallization during rolling is insufficient, and the ear ratio (anisotropic) of the product tends to deteriorate. The ear ratio of the hard plate depends on the recrystallization texture at the end of hot rolling and the rolling texture at the time of cold rolling added thereafter. Hot rolling is preferably performed such that the material temperature at the end of rolling is 280 to 350 ° C. If the temperature exceeds 350 ° C., the recrystallized grains become coarse, and if the temperature is lower than 280 ° C., the recrystallization becomes insufficient.
[0032]
Intermediate annealing before or during cold rolling:
Intermediate annealing is not preferable because it increases the solid solubility of the solute element and lowers the neck formability. Therefore, as described above, it is preferable to perform the cold rolling step without performing the intermediate annealing.
[0033]
Cold rolling:
Cold rolling is performed to improve material strength. If the total rolling reduction in the cold is less than 60%, sufficient strength cannot be obtained, and if it is higher than 90%, the rolled texture will develop too much and the 45 ° ear will be too high, and the material yield will deteriorate. The total reduction amount in the cold is more preferably 80 to 88% from the relationship between strength and ear ratio.
[0034]
Then, by completing the above-mentioned cold rolling with the preferred rolling reduction, no compound exceeding 15 μm is present on the sheet surface of the material, and when the observed area of the sheet surface is 100%, the compound of 1 to 15 μm is obtained. Is not less than 5.0%, and the area ratio of the α-phase compound is not less than 50% and the area ratio of the Mg ₂ Si phase when the entire area of the compound of 1 to 15 μm is 100%. Is preferably 1.0% or less.
[0035]
If a compound exceeding 15 μm is present, it becomes a starting point of cracking during flange forming after ironing and neck forming. The compound having a size of 1 to 15 μm is mainly an Al ₆ (Mn, Fe) phase crystallized substance produced at the time of casting and an α phase formed by a homogenization treatment, and prevents seizure during ironing. If the absolute amount is less than 5%, the effect is small. Further, among them, the effect is small even if the α-phased compound is less than 50%. The Mg ₂ Si phase is preferably not more than 1.0% in area ratio on the plate surface because the Mg solid solution amount required for maintaining the strength after the paint baking treatment is reduced and the corrosion resistance is disadvantageous. .
[0036]
【Example】
In this example, as shown in Table 1, five types of aluminum alloy plates (E1 to E5) as examples of the present invention and four types of aluminum alloy plates (C1 to C4) as comparative examples were manufactured. These properties were measured.
First, an aluminum alloy ingot containing the components shown in Table 1 was formed by semi-continuous casting, the surface was ground, and a homogenization treatment was performed at a temperature of 580 ° C. for 12 hours. Starting and ending at a temperature of 350 ° C., a 3 mm thick hot rolled sheet was obtained. After the obtained hot-rolled sheet was at room temperature, cold rolling was performed at a rolling reduction of 87% to a thickness of 0.4 mm, and the above-described five examples (E1 to E5) and four comparative examples (C1 To C4) were obtained.
[0037]
Next, the intermetallic compounds were observed on the plate surface, the ear ratio was measured, and the decrease in proof stress after baking was measured for all the test materials, and the characteristics were evaluated.
Observation of the intermetallic compound on the plate surface was performed by degreasing and cleaning the surface of the test material and then photographing the plate surface with a composition image of a scanning electron microscope (SEM). Then, the distribution density of the intermetallic compound and the area ratio thereof were measured using an image analyzer (Lurex 500 manufactured by Nireco Corporation). The diameter of the intermetallic compound was measured. In this case, the diameter of the intermetallic compound was measured as a circle equivalent diameter, that is, the diameter of a circle having the same area as the area of the intermetallic compound in the photograph.
Judgment was made when the intermetallic compound having a particle size of 1 μm or more was 3500 particles / mm ² or more, and was rejected when it was less than 3500 particles / mm ² .
[0038]
The ear ratio was measured by using a die having a die diameter of 34 mm, a punch diameter of 33 mm, and a punch shoulder R of 1.5 mm, and performing cup drawing under the conditions of a test material blank diameter of 55 mm and a drawing ratio of 1.67. Using the obtained aperture cup, the values of 45 ° ear ratio and (average value of 0-180 ° ear height) − (average value of 45 ° ear height) were determined by the above-described equations.
As for the 45 ° ear ratio, 3% or less was regarded as acceptable, and exceeding 3% was regarded as unacceptable. The average value of (0-180 ° ear height) − (the average value of 45 ° ear height) was 0.3 mm or less, and 0.3 mm or less was rejected.
[0039]
The baking was performed at a temperature of 205 ° C. for 10 minutes. The unbaked test material and the baked test material were each processed into JIS No. 5 test pieces, and a tensile test was performed in accordance with JIS Z2241. Then, the proof stress value of the test piece after baking was subtracted from the proof stress value of the test piece before baking to obtain a yield strength reduction value.
And, when the reduction in proof stress after baking was in the range of 20 to 30 MPa, the test was passed, and when it exceeded the range, the test was rejected.
[0040]
Table 2 shows the obtained results. As can be seen from Table 2, Examples E1 to E5 passed all of the evaluation items, and a comprehensive pass (○) was obtained. On the other hand, Comparative Examples C1 to C4 failed in at least one of the evaluation items, and all of them were judged as failed (x).
[0041]
Specifically, in Comparative Example C1, since the amount of Mg is small, the formation of 45 ° ears is reduced, and the average value of (0-180 ° ear height) − (the average value of 45 ° ear height) is obtained. It has grown.
In Comparative Example C2, since the amount of Si was large, the amount of softening due to baking was large, and the required strength of the can was not obtained.
In Comparative Example C3, since the amount of Mn was large and the amounts of Si and Fe were small, the amount of crystallized matter was large, but the amount of Mn solid solution was large and the amount of softening by baking was small.
Further, in Comparative Example C4, since the amounts of Si and Fe were small, the amount of crystallized substances was small. Therefore, it is considered that the amount of softening due to baking was reduced.
[0042]
[Table 1]

[0043]
[Table 2]

[Brief description of the drawings]
FIG. 1 is an explanatory view showing a manufacturing process of a two-piece aluminum can body.
FIG. 2 is an explanatory view showing a manufacturing process of a body portion of a screwed aluminum can body (bottle can).
FIG. 3 is an explanatory view showing a manufacturing process of a body portion of a screwed aluminum can body (new bottle can).
[Explanation of symbols]
S0. . . Aluminum alloy plate,
S11, S21, S31. . . Blanking process,
S12, S22, S32. . . Cupping steps S13, S23, S33. . . DI molding process,
S14, S24, S34. . . Trimming process,
S15, S25. . . Necking process,
S16, S36. . . Flanging process,
S26, S36. . . Thread cutting process,
S35. . . Necking + end opening process,
S37. . . Bottom winding + thread cutting process,

Claims

In weight ratio, Si: 0.25 to 0.40%, Fe: 0.35 to 0.50%, Cu: 0.15 to 0.25%, Mn: 0.7 to 1.3%, Mg: 0.93 to 1.3%, Zn: ≤0.25%, the balance being composed of aluminum and unavoidable impurities,
The number of intermetallic compounds of 1 μm or more observed from the plate surface is 3500 / mm ² or more,
In addition, the 45 ° ear ratio of the formed cup squeezed under the conditions of a blank diameter of 55 mm and a drawing ratio of 1.67 is 3% or less, and (0-180 ° ear height average) − (45 ° ear An aluminum alloy plate for a screwed aluminum can body, characterized by satisfying (average height) ≦ 0.3 mm.

2. The aluminum alloy plate for a screwed aluminum can body according to claim 1, wherein the proof stress after baking is lower than the proof stress before baking by 20 to 30 MPa.

3. The aluminum alloy plate for a screwed aluminum can body according to claim 1, wherein the amount of re-oil oil adhering to the plate surface is 30 to 250 mg / m < ² >.

The aluminum alloy plate for a screwed aluminum can body according to any one of claims 1 to 3, wherein the plate thickness is 0.3 to 0.45 mm.

The method according to any one of claims 1 to 4, wherein the cast ingot is manufactured by homogenizing, then hot rolling, and further cold rolling without intermediate annealing. Features Aluminum alloy plate for aluminum can body with screw.