JP4040787B2

JP4040787B2 - Aluminum alloy rolled plate with stable gray color after anodization and method for producing the same

Info

Publication number: JP4040787B2
Application number: JP07403299A
Authority: JP
Inventors: 宗太郎関田; 俊樹村松
Original assignee: Furukawa Sky Aluminum Corp
Current assignee: Furukawa Sky Aluminum Corp
Priority date: 1999-03-18
Filing date: 1999-03-18
Publication date: 2008-01-30
Anticipated expiration: 2019-03-18
Also published as: JP2000273563A

Description

【０００１】
【発明の属する技術分野】
この発明は陽極酸化処理を施して使用される用途のアルミニウム合金圧延板、特に建築内装材などの建材、あるいは器物、容器、各種電気機器・計測器の筐体、電気機械装置のパネル、装飾品などに使用されるアルミニウム合金圧延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】
一般に建材などに使用されるアルミニウム合金圧延板は、耐食性の観点から陽極酸化処理を施すのが通常である。またこのような用途では、美観のために陽極酸化処理後の色調として灰色系の色調が求められることが多い。そしてこのような要望を満たすため、通常の陽極酸化処理のままで灰色系の色調が得られるアルミニウム合金圧延板の製造方法として、既に特許第２５４４２３３号に示される「陽極酸化処理後の色調が青灰色のアルミニウム合金およびその製造方法」の発明が提案され、また特開平９−７１８３１号に示される「陽極酸化処理後の色調が黄みと赤みの少ないグレー色のアルミニウム合金板およびその製造方法」の発明が提案されている。
【０００３】
【発明が解決しようとする課題】
ところで建材の用途のうちでも、カーテンウォールやそのほかの外装材などにおいては、高い耐食性が求められるため、一般に２０μｍ程度と比較的厚く陽極酸化皮膜を形成することが行なわれているが、内装材などに使用する場合、外装材ほどには耐食性が要求されないため、外装材の場合の１／２程度、すなわち１０μｍ程度の陽極酸化皮膜厚みで充分とされている。しかるに、厚み２０μｍ程度の比較的厚い陽極酸化皮膜を形成する場合は、前記各提案の方法で得られたアルミニウム合金圧延板でも、通常の陽極酸化処理を適用することにより安定して灰色の色調の陽極酸化皮膜を得ることが可能であるが、前記各提案の方法により得られたアルミニウム合金圧延板に対して、通常の陽極酸化処理により厚み１０μｍ程度の薄い陽極酸化皮膜を生成させた場合、灰色の色調を得ることは困難であり、せいぜい淡い灰色（淡灰色）を呈するに過ぎない。このように耐食性の観点からは陽極酸化皮膜厚が１０μｍ程度で足りる内装材の場合も、安定した灰色の色調を得るにやむを得ず２０μｍ程度の厚い陽極酸化皮膜を生成させていたのが実情である。
【０００４】
また内装材の用途では、外装材などと比較して精細でかつより立体的なデザインが要求されることが多く、例えば陽極酸化処理の前工程として９０°曲げ以上の１００〜１８０°の苛酷な曲げ加工が必要とされることが多い。このように苛酷な曲げ加工が要求される用途に対して前記各提案の方法により得られたアルミニウム合金圧延板を適用した場合、強度が不足したり曲げ加工時に割れたり肌荒れが生じたりすることがある。また内装材の用途では、外装材などと比較して、外観品質についてもより高品質であることが求められることが多いが、前述の各提案の方法により得られたアルミニウム合金圧延板では、この点でも不充分であった。
【０００５】
すなわち、前記各提案の方法により得られたアルミニウム合金圧延板の場合、鋳塊加熱処理温度が低い領域では、比較的大きなＡｌ−Ｍｎ系針状析出物が不均一に析出し、それに起因して陽極酸化処理後の表面に筋目状の模様、すなわちいわゆる「筋目不良」と称される外観不良が生じたり、またＭｇ量が少ない領域では結晶粒が大きくなって曲げ加工時に肌荒れ不良を生じたり、中間焼鈍後の冷間圧延率の大小によっては強度と伸びのバランスが崩れて、強度不足が生じたり逆に苛酷な曲げ条件下での曲げ加工時に割れが生じたりすることがある。
【０００６】
そこで本発明者は、２０μｍ未満の例えば１０μｍ程度の薄い陽極酸化皮膜を生成した場合でも、陽極酸化皮膜の色調として安定に灰色を呈し、しかも筋目不良が生じにくく、さらには従来材と同等以上の強度で曲げ加工性を従来よりも格段に向上させたアルミニウム合金圧延板を製造する方法を特願平１０−０５０１３９に提案した。
しかしながらこの提案では、Ｓｉ含有量の規制が一部不適切だったため、また最終板における金属組織状態と陽極酸化処理後の色調の関係を完全に把握できていなかったため、量産を繰り返すと一部において、陽極酸化処理後の色調が変動するものもあった。
【０００７】
【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ため、本発明者は鋭意実験・研究を重ねた結果、合金の成分組成を適切に設定すると同時に、製造プロセス条件、特に鋳塊加熱条件、熱間圧延条件、中間焼鈍条件、最終冷間圧延条件を適切に選定して、最終板における金属組織状態を適切なものとすることにより、前述の課題を解決し得ることを見出し、この発明をなすに至った。
【０００８】
具体的には請求項１の発明の陽極酸化処理後の色調が灰色で安定なアルミニウム合金圧延板は、Ｍｎ１．３〜１．５％（重量％、以下同じ）、Ｍｇ０．４〜１．２％、Ｆｅ０．０５％を超え０．２％以下を含有し、Ｓｉ０．０５％未満に規制し、残部がＡｌおよび不可避的不純物よりなり、かつ、１μｍ未満の大きさのＡｌ−Ｍｎ−Ｓｉ系粒状析出物の析出がなく、１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物が１０００〜４０００個／０．２ｍｍ²の範囲内の密度で析出しており、しかも平均結晶粒径が８０μｍ以下で、耐力が９５Ｎ／ｍｍ²以上であることを特徴とする。
【０００９】
そして、請求項２の発明では、アルミニウム合金に、前記各成分のほか、さらに０．００３〜０．１５％のＴｉを単独でもしくは０．０００１〜０．０１％のＢと組合されて含有することを特徴とする。
【００１０】
さらに、請求項３の発明の陽極酸化処理後の色調が灰色で安定なアルミニウム合金圧延板の製造方法は、請求項１または請求項２記載の化学組成を有するＡｌ合金の鋳塊に、５８０〜６３０℃の範囲内の温度で１〜２４時間保持する加熱処理を施し、次いで前記加熱処理における処理温度以下で熱間圧延を開始して、その熱間圧延を３００℃以下で終了し、その後１〜５０℃／秒の昇温速度で４００〜６００℃の範囲内の温度に加熱して０〜１０分保持した後１〜５０℃／秒の冷却速度で冷却する中間焼鈍を施し、さらに２〜３０％の圧延率で冷間圧延を施し、これにより１μｍ未満の大きさのＡｌ−Ｍｎ−Ｓｉ系粒状析出物の析出がなく、１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物が１０００〜４０００個／０．２ｍｍ² の範囲内の密度で析出しており、しかも平均結晶粒径が８０μｍ以下で、耐力が９５Ｎ／ｍｍ² 以上であることを特徴とする。
【００１１】
さらにまた請求項４の発明は、請求項３に記載のアルミニウム合金圧延板の製造方法において、熱間圧延後、中間焼鈍の前に一次冷間圧延を施すことを特徴とするものである。
【００１２】
【発明の実施の形態】
先ずこの発明における成分組成の限定理由について説明する。
【００１３】
Ｍｎ：
ＭｎはＡｌ−Ｍｎ系の金属間化合物析出物を生成して、陽極酸化処理後の色調を決定するために重要な元素である。すなわち、Ｍｎは鋳造時に鋳塊のマトリックス中に固溶し、その後の鋳塊加熱時にＡｌ−Ｍｎ系金属間化合物として析出し、この析出物が最終板まで残存し、陽極酸化処理後も皮膜中に残存して灰色の色調を呈するに寄与する。ここで、１０μｍ程度の厚みの陽極酸化皮膜においては、１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物の密度が１０００個／０．２ｍｍ² 未満では充分な灰色とならずに淡灰色となり、一方４０００個／０．２ｍｍ² を越えれば灰色が濃過ぎて濃灰色〜黒色となり、したがって安定した灰色の色調を得るためには、１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物の密度が１０００〜４０００個／０．２ｍｍ² の範囲内となることが必要である。そして、１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物の密度が１０００個／０．２ｍｍ² 未満となるのは合金中のＭｎ量が１．３％未満となる場合であり、一方その密度が４０００個／０．２ｍｍ² を越えるのは合金中のＭｎ量が１．５％を越える場合であり、したがって陽極酸化処理後の色調を安定した灰色とすべく１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物の密度を１０００〜４０００個／０．２ｍｍ² とするためには、Ｍｎ量を１．３〜１．５％の範囲内とする必要がある。
【００１４】
Ｍｇ：
Ｍｇは強度向上に寄与する元素である。Ｍｇ量が０．４％未満では曲げ加工性は良好であるが、充分な強度が得られず、一方１．２％を越えれば強度が高過ぎて曲げ加工性が不充分となる。したがってＭｇ量は０．４〜１．２％の範囲内とした。
【００１５】
Ｆｅ：Ｆｅは中間焼鈍時において再結晶粒を微細化する有益な作用を有する。この作用はＦｅ含有量０．０５ % を超えると発現する。その一方では鋳造時においてＡｌ−Ｍｎ−Ｆｅ系金属間化合物を生成させて鋳塊マトリックス中へのＭｎ固溶量を減少させ、これにより鋳塊加熱時のＡｌ−Ｍｎ系析出物の析出を妨げる有害な作用も有する。特にＦｅ量が０．２％を越えれば鋳塊加熱時におるＡｌ−Ｍｎ系析出物の析出が著しく減少し、１０μｍ程度の厚みの陽極酸化皮膜では灰色となりにくい。したがってＦｅ量は０．０５％を超え０．２％以下とした。
【００１６】
Ｓｉ：
Ｓｉも陽極酸化処理後の色調に影響を与える元素である。Ｓｉ量が０．０５％以上では１μｍ未満の大きさのＡｌ−Ｍｎ−Ｓｉ系粒状析出物がＳｉ量に比例して増加し、陽極酸化処理後の色調もＡｌ−Ｍｎ−Ｓｉ系粒状析出物の分布密度に比例して黄色味がかった灰色となってしまう。したがって陽極酸化処理後の色調変動を小さくするには１μｍ未満の大きさのＡｌ−Ｍｎ−Ｓｉ系粒状析出物を析出させないことが必要であり、そのためのＳｉ量は０．０５％未満である。
【００１７】
このほか一般にＡｌ合金の不可避的不純物としては、Ｃｒ，Ｃｕ，Ｚｎ，Ｚｒ，Ｖなどがあるが、このうちＣｒ，Ｃｕは陽極酸化処理後の色調にある程度影響を与えるから、少量に規制することが好ましい。すなわちＣｒは０．０５％を、Ｃｕは０．１％を越えれば、陽極酸化処理後の色調が黄色味がかるから、不純物としてのＣｒ量は０．０５％以下、Ｃｕ量は０．１％以下に規制することが好ましい。一方、Ｚｎ，Ｚｒ，Ｖはいずれも陽極酸化処理後の色調に本質的な影響を与えないが、Ｚｎが１．０％を越えれば耐食性が低下し、またＺｒおよびＶがそれぞれ０．３％を越えれば粗大金属間化合物が生成されて曲げ加工性が阻害されるから、不純物としてのＺｎ量は１．０％以下、Ｚｒ量およびＶ量はそれぞれ０．３％以下に規制することが好ましい。
【００１８】
さらに、一般にＡｌ合金においては、鋳塊組織の微細化のためにＴｉを単独で、あるいはＴｉをＢと組合せて添加する場合があるが、この発明の場合もこれらを添加しても良い。但し、Ｔｉ量が０．００３％未満では鋳塊組織微細化の効果が得られず、一方Ｔｉ量が０．１５％を越えればＴｉＡｌ３の粗大金属間化合物が生成されて曲げ加工性が阻害されるから、Ｔｉを添加する場合のＴｉ量は０．００３〜０．１５％の範囲内とする。またＴｉとともにＢを添加する場合のＢ量は、０．０００１％未満では鋳塊組織微細化の効果が得られず、一方０．０１％を越えれば粗大なＴｉＢ２が生成されて曲げ加工性が阻害されるから、Ｔｉと組合せてＢを添加する場合のＢ量は０．０００１〜０．０１％の範囲内とする。
【００１９】
またＭｇを含有する合金において溶湯酸化防止のためにＢｅを添加することがあるが、本発明においてもＢｅの添加は許容される。Ｂｅを添加する場合のＢｅ量は、０．０００１％未満では溶湯酸化防止の効果が得られず、一方０．０５％を越えてＢｅを添加しても上記効果は飽和するだけで経済的に無駄となるから、Ｂｅを添加する場合のＢｅ量は０．０００１〜０．０５％の範囲内とする。
【００２０】
さらにこの発明では、最終的に得られる最終板（陽極酸化処理前の板）について、その組織条件および特性値を規定しており、これらについて以下に説明する。
【００２１】
最終板においては、１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物の密度が１０００〜４０００個／０．２ｍｍ² の範囲内であることと、１μｍ未満の大きさのＡｌ−Ｍｎ−Ｓｉ系粒状析出物を析出させないことが必要であり、このように１〜８μｍの大きさのＡｌ−Ｍｎ系針状析出物の密度範囲の選定と、１μｍ未満の大きさのＡｌ−Ｍｎ−Ｓｉ系粒状析出物を析出させないことによって、前述のように１０μｍ程度の薄い膜厚の陽極酸化皮膜で灰色で安定な色調を得ることができる。ここで、最終板においては、１μｍ未満および８μｍを超える大きさのＡｌ−Ｍｎ系針状析出物は、この発明で規定する成分組成、鋳塊加熱処理条件の範囲内では実質的に存在しない。さらにＳｉ量が０．０５％以上では１μｍ未満のＡｌ−Ｍｎ−Ｓｉ系粒状析出物は存在するが、本発明では、Ｓｉ量を０．０５％未満に規制したのでＡｌ−Ｍｎ−Ｓｉ系粒状析出物は存在しない。
したがってこの発明では、特に大きさが１〜８μｍの範囲内のＡｌ−Ｍｎ系針状析出物の密度と１μｍ未満のＡｌ−Ｍｎ−Ｓｉ系粒状析出物を析出させないことを規定したのである。なおここでＡｌ−Ｍｎ系針状析出物の「大きさ」とは、その最大長さ方向の長さを意味し、Ａｌ−Ｍｎ−Ｓｉ系粒状析出物の「大きさ」とは最大直径を意味するものとする。
【００２２】
また最終板における平均結晶粒径は８０μｍ以下である必要がある。平均結晶粒径は曲げ加工時における肌荒れの発生に影響を与え、その値が小さいほど肌荒れが発生しにくくなる。そして特に平均結晶粒径を８０μｍ以下とすることによって、９０°曲げ以上の１００〜１８０°の苛酷な曲げ加工でも肌荒れの発生を確実に防止することができる。
【００２３】
さらに最終板における耐力は９５Ｎ／ｍｍ² 以上であることが必要である。すなわち耐力が９５Ｎ／ｍｍ² 以上であれば、従来並の強度となり、従来材と同様な用途に適用することが可能となるのである。
【００２４】
次にこの発明の製造方法における各プロセスについて説明する。
【００２５】
先ず前述のような成分組成のアルミニウム合金を鋳造して鋳塊を得る。この鋳造方法は特に限定されるものではなく、常法に従えば良いが、通常はＤＣ鋳造法（半連続鋳造法）が好ましい。
【００２６】
鋳塊に対しては加熱処理を施す。この鋳塊加熱処理は、最終板に対する陽極酸化処理によって灰色の色調を得るに必要なＡｌ−Ｍｎ系析出物を析出させるための処理である。この鋳塊加熱処理の温度が５８０℃未満では、最終板の状態で１〜８μｍ程度の大きさの針状析出物は分布も粗く不均一なため、陽極酸化処理後に筋目不良が生じるおそれがある。そして鋳塊加熱処理の温度が５８０℃以上となれば、１〜８μｍの針状析出物の分布が均一化されて筋目不良が生じにくくなる。さらに鋳塊加熱処理の温度が６３０℃を越えれば共晶融解が生じるおそれがある。したがって筋目不良の発生を防止するためには、鋳塊加熱処理温度を５８０〜６３０℃の範囲内とする必要がある。鋳塊加熱処理の保持温度は、１時間未満では充分にＡｌ−Ｍｎ系析出物が析出されず、一方２４時間を越えて長時間加熱保持しても、Ａｌ−Ｍｎ系析出物の析出は飽和状態となり、経済性を損なうだけである。したがって鋳塊加熱処理の加熱保持時間は１〜２４時間とした。ここで、１０μｍ程度の比較的薄い陽極酸化皮膜において安定した灰色を得るためには、既に述べたように最終板における１〜８μｍの大きさの針状析出物の分布密度が１０００〜４０００個／０．２ｍｍ² であることが必要であり、合金のＭｎ量を１．３〜１．５％としかつ上述のような条件の鋳塊加熱処理を施すことによって、Ａｌ−Ｍｎ系針状析出物の分布密度の要件を満たすことができる。
【００２７】
上述のような鋳塊加熱処理の後には、熱間圧延を施す。この熱間圧延は、鋳塊加熱温度以下の温度で開始し、再結晶温度以下で終了させる。この発明で用いている合金の場合、再結晶温度はほぼ３００℃であるから、熱間圧延終了温度は３００℃以下とする。熱間圧延終了温度が３００℃を越える場合、熱間圧延終了後の熱間圧延板に部分再結晶粒や粗大再結晶粒が残り、そのためその後の中間焼鈍で微細な均一再結晶組織が得難くなり、陽極酸化処理後の表面に結晶組織の不均一に起因する筋目不良が生じやすくなるから、熱間圧延は３００℃以下で終了させる必要がある。
【００２８】
熱間圧延終了後には、直ちに中間焼鈍を施しても良く、また必要に応じて冷間圧延（一次冷間圧延）を施してから中間焼鈍を行なっても良い。すなわち最終板の板幅方向および長さ方向の板厚精度が厳しく要求される場合などには、熱間圧延後に一次冷間圧延を施してから中間焼鈍を行なっても良く、このような中間焼鈍前の冷間圧延はこの発明の目的に対して本質的な影響は与えない。
【００２９】
熱間圧延後、あるいは熱間圧延および一次冷間圧延を施した後の中間焼鈍は、組織を微細かつ均一に再結晶させて、曲げ加工時の肌荒れ発生防止のために必要な工程である。この発明で規定する平均結晶粒径８０μｍ以下の微細再結晶粒組織を得るためには、急速昇温、急速冷却の条件で中間焼鈍を行なう必要がある。具体的には、昇温速度、冷却速度が１℃／秒未満では平均結晶粒径８０μｍ以下の微細再結晶粒組織を得ることが困難となり、曲げ加工時に肌荒れが生じやすくなるから、中間焼鈍後の昇温速度、冷却速度はともに１℃／秒以上とする必要がある。一方昇温速度および冷却速度がより高ければ平均結晶粒径が８０μｍ以下の微細再結晶粒組織を得ることは可能であるが、５０℃／秒を越えれば焼鈍時における板の変形が生じやすくなり、また量産規模での工業的な実施も困難となる。したがって中間焼鈍の昇温速度、冷却速度はともに１〜５０℃／秒の範囲内とした。なおこのような１〜５０℃／秒の急速昇温、急速冷却の中間焼鈍は、連続焼鈍炉によって行なうことができる。バッチ炉による焼鈍では、昇温速度、冷却速度がともに２０〜６０℃／ｈｒと極めて遅く、そのため平均結晶粒径が８０μｍ以下の微細再結晶粒組織が得られず、曲げ加工時に肌荒れが生じるおそれが高い。一方連続焼鈍による中間焼鈍は短時間加熱となるため、中間焼鈍温度が４００℃未満では充分に再結晶せず、６００℃を越えれば粗大再結晶粒が生じて曲げ加工性が阻害されるから、中間焼鈍温度は４００〜６００℃の範囲内とする。また４００〜６００℃の加熱温度での保持が１０分を越えれば生産性が低下するから、保持時間は１０分以下とする。なお保持を０分、すなわち保持なしとしても良いことはもちろんである。
【００３０】
中間焼鈍後には最終板厚とするために冷間圧延を行なう。この冷間圧延は強度向上のために必要な工程である。冷間圧延率が２％未満では最終板の耐力が９５Ｎ／ｍｍ² を下廻り、一方３０％を越えれば強度と曲げ加工性のバランスが崩れて、強度は高くなるものの曲げ加工性が低下し、いずれの場合もこの発明の目的を達成できない。したがって中間焼鈍後の冷間圧延率は２〜３０％の範囲内とする。
【００３１】
以上のようにして得られた冷間圧延後の最終板厚の圧延板を内装材等に用いるにあたっては、陽極酸化処理を施す。この陽極酸化処理の条件は特に限定されるものではないが、経済性等から最も一般的な硫酸電解浴を用いることが望ましい。具体的には、例えばＨ２ＳＯ４濃度が１０〜２５ｖｏｌ％程度の硫酸浴を用い、浴温１０〜３０℃程度、電流密度１．０〜２．５Ａ／ｄｍ² 程度の条件で陽極酸化処理を施せば良い。陽極酸化処理による皮膜厚は特に限定しないが、この発明の方法の場合、１０μｍ程度の薄い皮膜厚でも灰色で安定な色調が安定して得られることを大きな特徴としており、その意味から、２０μｍ未満の皮膜厚、特に６〜１５μｍの膜厚の場合にこの発明の効果を最大限に発揮することができる。
【００３２】
ここで、陽極酸化処理後の色調については、ハンターの色差式（ＪＩＳＺ８７３０参照）による明度指数Ｌとクロマティクネス指数ａ，ｂの値によって評価することができる。すなわち、明度指数のＬ値は高いほど白く、一方クロマティクネス指数は着色度についてのものであって、そのａ値は高いほど赤味が強く、ｂ値は高いほど黄味が強いことをあらわす。
【００３３】
そしてこの発明において、陽極酸化皮膜が１０μｍ程度の薄い膜厚でＬ値変動の小さい安定した灰色を有する色調とは、皮膜厚が６〜１５μｍの場合のＬ値が６０〜７７の範囲内であって、しかも皮膜厚を一定とした場合のＬ値の変動範囲が３以内、ａ値およびｂ値がいずれも−１〜＋１の範囲内の無彩色を目標としている。さらに詳細に各皮膜厚での色調のＬ値、ａ値、ｂ値の目標値を示せば、
皮膜厚６μｍの場合Ｌ値：７４〜７７、ａ値およびｂ値：−１〜＋１
皮膜厚９μｍの場合Ｌ値：７０〜７３、ａ値およびｂ値：−１〜＋１
皮膜厚１５μｍの場合Ｌ値：６０〜６３、ａ値およびｂ値：−１〜＋１
となる。そしてこの発明のアルミニウム合金圧延板に通常の硫酸浴による陽極酸化処理を施せば、上述のような目標値を容易に達成して、特にＬ値変動が小さく安定した灰色を呈する６〜１５μｍの厚みの陽極酸化皮膜を得ることができる。
【００３４】
【実施例】
表１に化学組成が示される合金符号Ａ〜Ｌの各合金の溶湯を常法に従って溶製し、ＤＣ鋳造法によって５５０ｍｍ×１２００ｍｍ×４０００ｍｍのスラブを鋳造した。得られた各スラブについて面削後、表２の製造条件番号１〜２０に示すような各条件で鋳塊加熱処理を施し、続いてその加熱温度以下の温度で熱間圧延を開始し、表２中に示す温度で熱間圧延を終了させ、板厚４ｍｍの熱延板とした。各熱延板に対し、製造条件番号１９，２０を除いた製造条件番号１〜１８の場合は板厚２．２ｍｍまで一次冷間圧延を施してから中間焼鈍を施した。製造条件番号１９，２０の場合は一次冷間圧延を行なわずに、熱延板に対し直接中間焼鈍を施した。中間焼鈍は、製造条件番号１〜１２，１４〜２０の場合は、昇温速度、冷却速度が１〜５０℃／秒の範囲内の連続焼鈍炉により５００℃で保持なしの条件で行ない、製造条件番号１３の場合は比較例として４００℃×２ｈｒのバッチ焼鈍を適用した。これらの中間焼鈍後、製造条件番号１〜１３，１６〜１８の場合は板厚２．０ｍｍまで冷間圧延を施して最終板とし、製造条件１５の場合は板厚１．３ｍｍまで冷間圧延を施して最終板とし、さらに製造条件番号１４の場合は冷間圧延を施さずに中間焼鈍のまま最終板とした。また製造条件番号１９の場合は中間焼鈍後３．６ｍｍまで、製造条件番号２０の場合は３．２ｍｍまで、それぞれ冷間圧延を施して最終板とした。
【００３５】
各最終板について、引張試験により耐力を測定し、また曲げ性について、曲げ加工の苛酷な条件の１３５°曲げ試験（先端半径０．１ｍｍＲ）により評価し、さらに結晶粒径について、表面の結晶粒を切断法により調べて平均結晶粒径を求めた。さらに、最大長さ１〜８μｍのＡｌ−Ｍｎ系針状析出物および１μｍ未満のＡｌ−Ｍｎ−Ｓｉ系粒状析出物の密度を、透過電子顕微鏡と光学顕微鏡とを併用して調べた。
【００３６】
さらに各最終板について、１０％ＮａＯＨ水溶液でエッチングし、水洗後硝酸でデスマット処理した後、次のような条件で陽極酸化処理を施した。すなわち、Ｈ２ＳＯ４濃度１５ｖｏｌ％の硫酸浴を用いて、浴温２０℃、電流密度１．５Ａ／ｄｍ² で陽極酸化処理を行ない、それぞれ９μｍの陽極酸化処理皮膜を生成させた。
【００３７】
各板の陽極酸化処理皮膜の表面色調について、スガ試験機製多光分光測色計ＭＳＣ−ＩＳ−２ＤＨを用い、色調はハンターの色差式による明度指数Ｌ、クロマティクネス指数ａ，ｂで評価し、筋目は目視にて評価した。これらの結果を表３に示す。なお表３中において、１３５°曲げの評価は、○印は割れなし（合格）、△印は肌荒れ発生（不合格）、×印は割れ発生（不合格）を示す。
【００３８】
【表１】

【００３９】
【表２】

【００４０】
【表３】

【００４１】
以下にこれらの個々の結果について説明する。
【００４２】
製造条件番号１，４，５，１６〜２０の各材料は、いずれも成分組成および製造プロセスの両者がこの発明で規定する条件を満たす発明例であり、表３に示すように耐力は９５Ｎ／ｍｍ² 以上の従来材と同等以上の強度を示し、一方曲げ性については、苛酷な１３５°曲げ試験でも割れや肌荒れが発生せず、しかも９μｍと薄い陽極酸化処理皮膜でも灰色で安定した色調が得られる優れた材料となっていることが明らかである。
【００４３】
一方製造条件番号２，３，６〜１０の材料は、いずれもこの発明で規定する製造プロセス条件は満たしているが、成分組成条件を満たさない比較例である。このうち製造条件番号２はＭｎ量がこの発明で規定する成分範囲よりも低い合金Ｂを用い、製造条件番号３はＭｎ量がこの発明で規定する成分範囲よりも高い合金Ｃを用いたものであり、前者の場合はＭｎ量が少ないため１〜８μｍのＡｌ−Ｍｎ系針状析出物の密度が低過ぎてＬ値が目標範囲を上廻ってしまい、後者の場合はＭｎ量が多いため１〜８μｍのＡｌ−Ｍｎ系針状析出物の密度が高過ぎてＬ値が目標範囲を下廻ってしまった。一方製造条件番号６はＭｇ量がこの発明で規定する成分範囲よりも低い合金Ｆを用い、製造条件番号７はＭｇ量がこの発明で規定する成分範囲よりも高い合金Ｇを用いたものであり、前者の場合はＭｇ量が少ないため耐力が９５Ｎ／ｍｍ² 以下の低強度となり、後者の場合はＭｇ量が多いため耐力が高過ぎて曲げ加工性が低下してしまった。さらに製造条件番号８はＦｅ量がこの発明で規定する成分範囲よりも高い合金Ｈを用い、製造条件番号９および１０はＳｉ量がこの発明で規定する成分範囲よりも高い合金ＩおよびＪを用いたものであり、前者の場合はＦｅ量が多いためＡｌ−Ｍｎ−Ｆｅ系金属間化合物が増加して１〜８μｍのＡｌ−Ｍｎ系針状析出物の密度が低くなって、Ｌ値が目標範囲を上廻ってしまい、後者の場合はＳｉ量が多いため１μｍ未満の大きさのＡｌ−Ｍｎ−Ｓｉ系粒状析出物が析出してｂ値が上りＬ値が目標範囲を下廻ってしまった。
【００４４】
一方製造条件番号１１〜１５はこの発明で規定する成分組成条件を満たした合金（製造条件番号１３のみ合金Ｄ、他は合金Ａ）を用いてはいるが、製造プロセス条件がこの発明で規定する条件から外れた比較例である。このうち製造条件番号１１は鋳塊加熱温度が低過ぎて、１〜８μｍのＡｌ−Ｍｎ系針状析出物が不均一に分布してその密度が低下したため、Ｌ値が目標範囲を上廻り、筋目不良が発生した。また製造条件番号１２は熱間圧延終了温度が高過ぎて熱間圧延終了時に部分再結晶が生じ、それが中間焼鈍の再結晶粒にも影響して混粒組織となってしまい、筋目不良が発生した。さらに製造条件番号１３は中間焼鈍をバッチ炉で行なったため、再結晶粒が粗大化して曲げ加工時に肌荒れが発生した。そしてまた製造条件番号１４は中間焼鈍後に冷間圧延を行なわなかったため耐力が９５Ｎ／ｍｍ² 以下の低強度となってしまった。一方製造条件番号１５は冷間圧延率が高過ぎて高耐力となったため、曲げ加工で割れてしまった。
【００４５】
【発明の効果】
前述の実施例からも明らかなように、この発明の製造方法によれば、特に曲げ加工性が良好であって強度も耐力９５Ｎ／ｍｍ² 以上と従来材なみで、しかも１０μｍ程度の薄い陽極酸化皮膜でもＬ値変動の小さい安定した灰色を呈するアルミニウム合金圧延板を得ることができる。そしてこの発明により得られたアルミニウム合金圧延板を陽極酸化処理を施した灰色の建材、特に内装材や、そのほか器物、各種電気機器・計測器の筐体やパネル、装飾品等に使用すれば、厳しい曲げ加工の施工デザインでも可能となり、かつ薄い陽極酸化皮膜でＬ値変動が小さく安定した灰色を呈するところから、陽極酸化処理コストの低減も可能となる。[0001]
BACKGROUND OF THE INVENTION
This invention relates to an aluminum alloy rolled sheet for use in an anodizing treatment, in particular, building materials such as building interior materials, containers, containers, housings of various electric devices and measuring instruments, panels of electromechanical devices, ornaments The present invention relates to a rolled aluminum alloy sheet used for the above and a method for producing the same.
[0002]
[Prior art]
Generally, an aluminum alloy rolled sheet generally used for building materials is subjected to anodizing treatment from the viewpoint of corrosion resistance. Further, in such applications, for the sake of beauty, a gray color tone is often required as the color tone after the anodizing treatment. In order to satisfy such a demand, as a manufacturing method of an aluminum alloy rolled sheet that can obtain a gray color tone with a normal anodizing treatment, a color tone after anodizing treatment is already shown in Japanese Patent No. 2544233. "A Gray Aluminum Alloy and a Method for Producing the Same" have been proposed, and "Aluminum Alloy Plate of Gray Color with Less Yellowness and Redness after Anodizing Treatment and Method for Producing the Same" disclosed in JP-A-9-71831 The invention has been proposed.
[0003]
[Problems to be solved by the invention]
By the way, among building materials, curtain walls and other exterior materials are required to have high corrosion resistance. Therefore, it is generally performed to form an anodic oxide film with a relatively large thickness of about 20 μm. In the case of use in the case, the corrosion resistance is not required as much as that of the exterior material, and therefore, an anodic oxide film thickness of about 1/2 of the exterior material, that is, about 10 μm is sufficient. However, in the case of forming a relatively thick anodic oxide film having a thickness of about 20 μm, the aluminum alloy rolled plate obtained by the above-described methods can be stably gray-colored by applying a normal anodizing treatment. An anodized film can be obtained, but when a thin anodized film having a thickness of about 10 μm is formed on a rolled aluminum alloy plate obtained by the above-described methods by a normal anodizing process, a gray color is obtained. It is difficult to obtain the color tone, and it is only light gray (light gray). Thus, from the viewpoint of corrosion resistance, even in the case of an interior material in which an anodized film thickness of about 10 μm is sufficient, it is unavoidable that a thick anodized film of about 20 μm is inevitably produced in order to obtain a stable gray color tone.
[0004]
Further, in the use of the interior material, a finer and more three-dimensional design is often required as compared with the exterior material or the like. For example, as a pre-process of the anodizing treatment, a severe 100 to 180 ° of 90 ° bending or more is required. Bending is often required. When the aluminum alloy rolled sheet obtained by the above proposed methods is applied to applications that require severe bending as described above, the strength may be insufficient, or cracking or roughening may occur during bending. is there. In addition, in the use of interior materials, the appearance quality is often required to be higher than that of exterior materials, etc., but in the aluminum alloy rolled plate obtained by the above-mentioned proposed methods, The point was also insufficient.
[0005]
That is, in the case of the aluminum alloy rolled sheet obtained by each of the proposed methods, relatively large Al-Mn needle-like precipitates are deposited non-uniformly in the region where the ingot heat treatment temperature is low. The surface after anodization treatment has a streak-like pattern, that is, a poor appearance called a so-called `` stitching defect '', and in a region where the amount of Mg is small, the crystal grains become large, resulting in a rough skin defect during bending, Depending on the size of the cold rolling rate after the intermediate annealing, the balance between strength and elongation may be lost, resulting in insufficient strength or conversely cracking during bending under severe bending conditions.
[0006]
Therefore, even when a thin anodic oxide film having a thickness of less than 20 μm, for example, about 10 μm, is produced, the present inventor stably exhibits gray as the color tone of the anodic oxide film, is less likely to cause streaking, and is equal to or higher than that of conventional materials Japanese Patent Application No. 10-050139 has proposed a method of manufacturing a rolled aluminum alloy sheet having strength and bending workability that is significantly improved.
However, in this proposal, the regulation of the Si content was partially inappropriate, and because the relationship between the metallographic state of the final plate and the color tone after anodization could not be completely understood, In some cases, the color tone after anodizing treatment fluctuated.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventor has conducted extensive experiments and researches. As a result, the alloy composition is set appropriately, and at the same time, manufacturing process conditions, particularly ingot heating conditions, hot rolling conditions, intermediate The inventors have found that the above-mentioned problems can be solved by appropriately selecting the annealing conditions and the final cold rolling conditions and making the metallographic state of the final plate appropriate, and have reached the present invention.
[0008]
Specifically, the stable aluminum alloy rolled sheet having a gray color tone after the anodizing treatment according to the invention of claim 1 has a Mn of 1.3 to 1.5% (% by weight, the same applies hereinafter), and Mg of 0.4 to 1.2. %, FeOver 0.05%Containing 0.2% or less, regulated to less than 0.05% of Si, the balance is made of Al and inevitable impurities, and there is no precipitation of Al-Mn-Si-based granular precipitates having a size of less than 1 μm, 1000 to 4000 pieces of Al-Mn-based acicular precipitates having a size of 1 to 8 μm / 0.2 mm²The average crystal grain size is 80 μm or less and the proof stress is 95 N / mm.²It is the above.
[0009]
And in invention of Claim 2, in addition to said each component, 0.003-0.15% Ti is contained in aluminum alloy individually or in combination with 0.0001-0.01% B in aluminum alloy. It is characterized by that.
[0010]
Furthermore, the method for producing a stable aluminum alloy rolled plate having a gray color tone after anodizing according to the invention of claim 3 is applied to an ingot of Al alloy having the chemical composition according to claim 1 or claim 2 at 580 to A heat treatment is performed at a temperature in the range of 630 ° C. for 1 to 24 hours, then hot rolling is started at a temperature equal to or lower than the processing temperature in the heat treatment, and the hot rolling is terminated at 300 ° C. or lower. Heat to a temperature in the range of 400 to 600 ° C. at a temperature increase rate of ˜50 ° C./second, hold for 0 to 10 minutes, and then perform intermediate annealing to cool at a cooling rate of 1 to 50 ° C./second, Cold rolling is performed at a rolling rate of 30%, whereby there is no precipitation of Al—Mn—Si based granular precipitates having a size of less than 1 μm, and Al—Mn based acicular precipitates having a size of 1 to 8 μm. 1000-4000 pieces / 0.2mm²  The average crystal grain size is 80 μm or less and the proof stress is 95 N / mm.²  It is the above.
[0011]
Furthermore, the invention of claim 4 is characterized in that in the method for producing an aluminum alloy rolled sheet according to claim 3, primary cold rolling is performed after hot rolling and before intermediate annealing.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
First, the reasons for limiting the component composition in the present invention will be described.
[0013]
Mn:
Mn is an important element for determining the color tone after anodizing treatment by generating an Al—Mn-based intermetallic compound precipitate. That is, Mn dissolves in the ingot matrix during casting, and precipitates as an Al-Mn intermetallic compound during subsequent ingot heating, and this precipitate remains up to the final plate and remains in the coating even after anodizing. It contributes to remaining a gray color tone. Here, in the anodic oxide film having a thickness of about 10 μm, the density of Al—Mn needle-like precipitates having a size of 1 to 8 μm is 1000 / 0.2 mm.²  If it is less than, it will not be sufficiently gray but light gray, while 4000 pieces / 0.2 mm²  In order to obtain a stable gray color tone, the density of Al-Mn needle-like precipitates having a size of 1 to 8 μm is 1000 to 4000/0. .2mm²  It is necessary to be within the range. The density of Al-Mn needle-like precipitates having a size of 1 to 8 μm is 1000 / 0.2 mm.²  When the amount of Mn in the alloy is less than 1.3%, the density is 4000 pieces / 0.2 mm.²  In the case where the amount of Mn in the alloy exceeds 1.5%, the Al-Mn needle-like precipitates having a size of 1 to 8 μm are required to make the color tone after anodizing stable gray. Density is 1000-4000 pieces / 0.2mm²  In order to achieve this, the amount of Mn needs to be in the range of 1.3 to 1.5%.
[0014]
Mg:
Mg is an element contributing to strength improvement. If the Mg content is less than 0.4%, the bending workability is good, but sufficient strength cannot be obtained. On the other hand, if it exceeds 1.2%, the strength is too high and bending workability becomes insufficient. Therefore, the Mg content is set in the range of 0.4 to 1.2%.
[0015]
Fe: Fe has a beneficial effect to refine recrystallized grains during intermediate annealing. This action has an Fe content of 0.05. % It expresses when exceeding.On the other hand, an Al-Mn-Fe intermetallic compound is produced during casting to reduce the amount of Mn solid solution in the ingot matrix, thereby preventing the precipitation of Al-Mn based precipitates during ingot heating. It also has harmful effects. In particular, if the amount of Fe exceeds 0.2%, precipitation of Al—Mn-based precipitates during heating of the ingot is significantly reduced, and an anodized film having a thickness of about 10 μm is unlikely to become gray. Therefore, the amount of Fe isOver 0.05%It was set to 0.2% or less.
[0016]
Si:
Si is also an element that affects the color tone after anodizing. When the amount of Si is 0.05% or more, Al-Mn-Si-based granular precipitates having a size of less than 1 μm increase in proportion to the Si amount, and the color tone after anodizing is also Al-Mn-Si-based granular precipitates. It becomes yellowish gray in proportion to the distribution density of. Therefore, in order to reduce the color tone variation after the anodizing treatment, it is necessary not to deposit Al—Mn—Si granular precipitates having a size of less than 1 μm, and the Si content for that purpose is less than 0.05%.
[0017]
In addition, there are generally inevitable impurities of Al alloys such as Cr, Cu, Zn, Zr, and V. Among these, Cr and Cu have some influence on the color tone after anodizing treatment, so they should be limited to a small amount. Is preferred. That is, if the Cr content exceeds 0.05% and the Cu content exceeds 0.1%, the color tone after the anodizing treatment becomes yellowish, so the Cr content as an impurity is 0.05% or less and the Cu content is 0.1%. It is preferable to regulate to the following. On the other hand, none of Zn, Zr, and V has an essential influence on the color tone after the anodizing treatment, but if Zn exceeds 1.0%, the corrosion resistance is lowered, and Zr and V are each 0.3%. If it exceeds 1, a coarse intermetallic compound is generated and bending workability is hindered. Therefore, it is preferable that the amount of Zn as an impurity is controlled to 1.0% or less, and the amount of Zr and the amount of V are each controlled to 0.3% or less. .
[0018]
Further, in general, in an Al alloy, Ti may be added alone or Ti in combination with B for refining the ingot structure. However, in the present invention, these may be added. However, if the Ti content is less than 0.003%, the effect of refining the ingot structure cannot be obtained. On the other hand, if the Ti content exceeds 0.15%, a coarse intermetallic compound of TiAl3 is generated and bending workability is hindered. Therefore, the amount of Ti in the case of adding Ti is within the range of 0.003 to 0.15%. If the amount of B in addition to Ti is less than 0.0001%, the effect of refining the ingot structure cannot be obtained. On the other hand, if it exceeds 0.01%, coarse TiB2 is produced and bending workability is improved. Therefore, the amount of B in the case of adding B in combination with Ti is set in the range of 0.0001 to 0.01%.
[0019]
Further, Be may be added to prevent oxidation of the molten metal in an alloy containing Mg, but the addition of Be is allowed also in the present invention. When the amount of Be is less than 0.0001%, the effect of preventing molten metal oxidation cannot be obtained. On the other hand, if the amount of Be exceeds 0.05%, the above effect is only saturated and economical. Since it becomes useless, the amount of Be when adding Be is set to be within a range of 0.0001 to 0.05%.
[0020]
Furthermore, in the present invention, the final conditions (the board before anodizing treatment) of the final plate are defined with respect to the structural conditions and characteristic values, which will be described below.
[0021]
In the final plate, the density of Al-Mn acicular precipitates having a size of 1 to 8 μm is 1000 to 4000 / 0.2 mm.²  It is necessary that the Al—Mn—Si granular precipitates having a size of less than 1 μm are not deposited, and thus Al—Mn acicular precipitates having a size of 1 to 8 μm are required. As described above, a gray and stable color tone is obtained with an anodic oxide film having a thin film thickness of about 10 μm as described above, by selecting a density range of 2 μm and not depositing Al—Mn—Si granular precipitates having a size of less than 1 μm. be able to. Here, in the final plate, Al—Mn-based acicular precipitates having a size of less than 1 μm and more than 8 μm are substantially absent within the range of the component composition and ingot heat treatment conditions defined in the present invention. Furthermore, when the Si content is 0.05% or more, there are Al-Mn-Si-based granular precipitates of less than 1 μm. However, in the present invention, since the Si content is restricted to less than 0.05%, Al-Mn-Si-based granular precipitates are present. There are no deposits.
Therefore, in the present invention, the density of the Al—Mn-based acicular precipitates having a size in the range of 1 to 8 μm and that the Al—Mn—Si granular precipitates of less than 1 μm are not deposited are specified. Here, “size” of the Al—Mn-based acicular precipitate means the length in the maximum length direction, and “size” of the Al—Mn—Si-based granular precipitate means the maximum diameter. Shall mean.
[0022]
The average crystal grain size in the final plate needs to be 80 μm or less. The average crystal grain size affects the occurrence of rough skin during bending, and the smaller the value, the less likely the rough skin is to occur. In particular, by setting the average crystal grain size to 80 μm or less, it is possible to reliably prevent the occurrence of rough skin even in severe bending at 100 to 180 ° of 90 ° bending or more.
[0023]
Furthermore, the yield strength of the final plate is 95 N / mm²  That is necessary. That is, the yield strength is 95 N / mm²  If it is above, it will become the intensity | strength equivalent to the past, and it will become possible to apply to the use similar to a conventional material.
[0024]
Next, each process in the manufacturing method of the present invention will be described.
[0025]
First, an ingot is obtained by casting an aluminum alloy having the composition described above. This casting method is not particularly limited, and may follow a conventional method, but a DC casting method (semi-continuous casting method) is usually preferable.
[0026]
Heat treatment is applied to the ingot. This ingot heat treatment is a treatment for depositing Al—Mn-based precipitates necessary for obtaining a gray color tone by anodizing the final plate. When the temperature of the ingot heat treatment is less than 580 ° C., the needle-like precipitates having a size of about 1 to 8 μm in the final plate state have a rough and uneven distribution, and thus there is a possibility that a line defect may occur after the anodizing treatment. . And if the temperature of an ingot heat processing will be 580 degreeC or more, the distribution of a 1-8 micrometers acicular precipitate will become uniform, and it will become difficult to produce a mesh defect. Furthermore, if the temperature of the ingot heat treatment exceeds 630 ° C., eutectic melting may occur. Therefore, in order to prevent the occurrence of line defects, the ingot heat treatment temperature needs to be in the range of 580 to 630 ° C. When the holding temperature of the ingot heat treatment is less than 1 hour, Al—Mn-based precipitates are not sufficiently precipitated. On the other hand, even when heated for more than 24 hours, the precipitation of Al—Mn-based precipitates is saturated. It will be in a state and it will only damage the economy. Therefore, the heating and holding time of the ingot heat treatment is set to 1 to 24 hours. Here, in order to obtain a stable gray color in a relatively thin anodic oxide film of about 10 μm, the distribution density of acicular precipitates having a size of 1 to 8 μm in the final plate is 1000 to 4000 / 0.2mm²  It is necessary that the Mn content of the alloy is 1.3 to 1.5% and the ingot heat treatment is performed under the conditions as described above, the distribution density of the Al—Mn-based acicular precipitates is reduced. Can meet the requirements.
[0027]
After the ingot heat treatment as described above, hot rolling is performed. This hot rolling starts at a temperature below the ingot heating temperature and ends at a temperature below the recrystallization temperature. In the case of the alloy used in this invention, the recrystallization temperature is approximately 300 ° C., so the hot rolling end temperature is set to 300 ° C. or less. When the hot rolling finish temperature exceeds 300 ° C., partially recrystallized grains and coarse recrystallized grains remain on the hot rolled plate after the hot rolling is finished, so that it is difficult to obtain a fine uniform recrystallized structure by subsequent intermediate annealing. Therefore, since it becomes easy to produce a line defect due to non-uniform crystal structure on the surface after the anodizing treatment, it is necessary to terminate the hot rolling at 300 ° C. or less.
[0028]
After the hot rolling is finished, intermediate annealing may be performed immediately, and if necessary, cold annealing (primary cold rolling) may be performed and then intermediate annealing may be performed. In other words, when the thickness accuracy in the width direction and the length direction of the final plate is strictly required, intermediate annealing may be performed after primary cold rolling after hot rolling. The previous cold rolling has no substantial effect on the object of the invention.
[0029]
Intermediate annealing after hot rolling or after hot rolling and primary cold rolling is a process necessary for preventing the occurrence of rough skin during bending by recrystallizing the structure finely and uniformly. In order to obtain a fine recrystallized grain structure having an average crystal grain size of 80 μm or less as defined in the present invention, it is necessary to perform intermediate annealing under conditions of rapid heating and rapid cooling. Specifically, when the heating rate and cooling rate are less than 1 ° C./second, it becomes difficult to obtain a fine recrystallized grain structure having an average crystal grain size of 80 μm or less, and rough skin is likely to occur during bending. Both the heating rate and cooling rate must be 1 ° C./second or more. On the other hand, if the heating rate and cooling rate are higher, it is possible to obtain a fine recrystallized grain structure with an average crystal grain size of 80 μm or less, but if it exceeds 50 ° C./second, deformation of the plate during annealing tends to occur. Also, industrial implementation on a mass production scale becomes difficult. Therefore, the temperature raising rate and cooling rate of the intermediate annealing are both in the range of 1 to 50 ° C./second. In addition, such rapid annealing at 1 to 50 ° C./second and intermediate annealing for rapid cooling can be performed by a continuous annealing furnace. In annealing with a batch furnace, the heating rate and cooling rate are both extremely slow, 20 to 60 ° C./hr. Therefore, a fine recrystallized grain structure with an average crystal grain size of 80 μm or less cannot be obtained, and rough skin may occur during bending. Is expensive. On the other hand, since the intermediate annealing by continuous annealing is heating for a short time, if the intermediate annealing temperature is less than 400 ° C, it will not recrystallize sufficiently, and if it exceeds 600 ° C, coarse recrystallized grains will be produced and the bending workability will be hindered. The intermediate annealing temperature is in the range of 400 to 600 ° C. Moreover, since productivity will fall if holding | maintenance with the heating temperature of 400-600 degreeC exceeds 10 minutes, holding time shall be 10 minutes or less. It goes without saying that the holding may be 0 minutes, that is, no holding.
[0030]
After intermediate annealing, cold rolling is performed to obtain the final thickness. This cold rolling is a process necessary for improving the strength. If the cold rolling rate is less than 2%, the yield strength of the final sheet is 95 N / mm.²  On the other hand, if it exceeds 30%, the balance between strength and bending workability is lost, and although the strength is increased, the bending workability is lowered. In either case, the object of the present invention cannot be achieved. Therefore, the cold rolling rate after the intermediate annealing is in the range of 2 to 30%.
[0031]
When the rolled sheet having the final thickness after cold rolling obtained as described above is used as an interior material or the like, an anodizing treatment is performed. The conditions for this anodizing treatment are not particularly limited, but it is desirable to use the most common sulfuric acid electrolytic bath in view of economy and the like. Specifically, for example, a sulfuric acid bath having a H 2 SO 4 concentration of about 10 to 25 vol% is used, the bath temperature is about 10 to 30 ° C., and the current density is 1.0 to 2.5 A / dm.²  What is necessary is just to perform an anodizing process on the conditions of a grade. The film thickness by anodizing treatment is not particularly limited, but in the case of the method of the present invention, it is a major feature that a gray and stable color tone can be stably obtained even with a thin film thickness of about 10 μm, and in that sense, it is less than 20 μm. The effect of the present invention can be exhibited to the maximum when the film thickness is 6 to 15 μm.
[0032]
Here, the color tone after the anodizing treatment can be evaluated by the value of the brightness index L and the chromaticness indices a and b according to Hunter's color difference formula (see JIS Z8730). That is, the higher the L value of the brightness index, the whiter the color index, while the chromaticness index relates to the degree of coloring. The higher the a value, the stronger the redness, and the higher the b value, the stronger the yellowness.
[0033]
In the present invention, the anodic oxide film having a thin film thickness of about 10 μm and having a stable gray color having a small L value fluctuation is an L value in the range of 60 to 77 when the film thickness is 6 to 15 μm. In addition, when the film thickness is constant, the variation range of the L value is within 3, and the a value and the b value are both within the range of −1 to +1. In more detail, if the target values of the L value, a value, and b value of the color tone at each film thickness are shown,
When the film thickness is 6 μm L value: 74 to 77, a value and b value: −1 to +1
When the film thickness is 9 μm L value: 70 to 73, a value and b value: −1 to +1
When the film thickness is 15 μm L value: 60 to 63, a value and b value: −1 to +1
It becomes. If the aluminum alloy rolled sheet according to the present invention is subjected to an anodizing treatment with a normal sulfuric acid bath, the target value as described above can be easily achieved, and the thickness of 6 to 15 μm which exhibits a stable gray color with a particularly small L value fluctuation. An anodic oxide film can be obtained.
[0034]
【Example】
Molten metal of each of the alloy codes A to L whose chemical compositions are shown in Table 1 was melted in accordance with a conventional method, and a slab of 550 mm × 1200 mm × 4000 mm was cast by a DC casting method. After chamfering each obtained slab, ingot heating treatment was performed under each condition as shown in production condition numbers 1 to 20 in Table 2, and then hot rolling was started at a temperature equal to or lower than the heating temperature. The hot rolling was finished at the temperature shown in 2 to obtain a hot-rolled sheet having a thickness of 4 mm. In the case of production condition numbers 1 to 18 excluding the production condition numbers 19 and 20 for each hot-rolled sheet, primary cold rolling was performed to a plate thickness of 2.2 mm, followed by intermediate annealing. In the case of manufacturing condition numbers 19 and 20, intermediate annealing was performed directly on the hot-rolled sheet without performing primary cold rolling. In the case of production condition Nos. 1-12 and 14-20, the intermediate annealing is performed under the conditions of no holding at 500 ° C. in a continuous annealing furnace having a temperature rising rate and a cooling rate in the range of 1-50 ° C./second. In the case of Condition No. 13, 400 ° C. × 2 hr batch annealing was applied as a comparative example. After these intermediate annealings, in the case of manufacturing condition numbers 1 to 13, 16 to 18, cold rolling is performed to a plate thickness of 2.0 mm to obtain a final plate, and in the case of manufacturing condition 15, cold rolling is performed to a plate thickness of 1.3 mm. In the case of production condition number 14, the final plate was made without being subjected to cold rolling and subjected to intermediate annealing. Further, in the case of manufacturing condition number 19, cold rolling was performed up to 3.6 mm after intermediate annealing, and in the case of manufacturing condition number 20 to 3.2 mm, respectively, to obtain a final plate.
[0035]
For each final plate, the yield strength was measured by a tensile test, and the bendability was evaluated by a 135 ° bending test (tip radius 0.1 mmR) under severe bending conditions. Was examined by a cutting method to determine an average crystal grain size. Furthermore, the density of the Al—Mn-based acicular precipitate having a maximum length of 1 to 8 μm and the Al—Mn—Si-based granular precipitate having a length of less than 1 μm was examined using a transmission electron microscope and an optical microscope in combination.
[0036]
Further, each final plate was etched with a 10% NaOH aqueous solution, washed with water, desmutted with nitric acid, and then anodized under the following conditions. That is, using a sulfuric acid bath having a H2 SO4 concentration of 15 vol%, a bath temperature of 20 ° C., and a current density of 1.5 A / dm.²  And anodizing treatment was performed to produce 9 μm anodizing films.
[0037]
About the surface color tone of the anodized film of each plate, Suga Test Instruments multi-light spectrophotometric colorimeter MSC-IS-2DH is used, and the color tone is evaluated by the brightness index L, chromaticness index a, b by Hunter's color difference formula, The streak was visually evaluated. These results are shown in Table 3. In Table 3, in the evaluation of 135 ° bending, ○ mark indicates no cracking (pass), Δ mark indicates occurrence of rough skin (failure), and X mark indicates crack generation (failure).
[0038]
[Table 1]

[0039]
[Table 2]

[0040]
[Table 3]

[0041]
These individual results are described below.
[0042]
Each material of production condition numbers 1, 4, 5, 16 to 20 is an example of the invention in which both the component composition and the production process satisfy the conditions defined in the present invention. As shown in Table 3, the yield strength is 95 N / mm²  The strength is equivalent to or better than that of the above conventional materials. On the other hand, with regard to bendability, cracks and rough skin do not occur even in severe 135 ° bending tests, and a gray and stable color tone can be obtained even with a thin anodized film of 9 μm. It is clear that it is an excellent material.
[0043]
On the other hand, the materials of production condition numbers 2, 3, 6 to 10 are comparative examples that satisfy the production process conditions specified in the present invention but do not satisfy the component composition conditions. Among them, production condition number 2 uses an alloy B whose Mn amount is lower than the component range defined in the present invention, and production condition number 3 uses an alloy C whose Mn amount is higher than the component range defined in the present invention. In the former case, since the amount of Mn is small, the density of Al-Mn needle-like precipitates of 1 to 8 μm is too low and the L value exceeds the target range, and in the latter case, the amount of Mn is large. The density of ˜8 μm Al—Mn needle-like precipitates was too high, and the L value was below the target range. On the other hand, production condition number 6 uses an alloy F whose Mg amount is lower than the component range defined in the present invention, and production condition number 7 uses an alloy G whose Mg amount is higher than the component range defined in the present invention. In the former case, the proof stress is 95 N / mm because the Mg content is small.²  In the latter case, the yield strength was too high and the bending workability was lowered. Further, production condition number 8 uses an alloy H in which the Fe amount is higher than the component range defined in the present invention, and production condition numbers 9 and 10 use alloys I and J in which the Si amount is higher than the component range defined in the present invention. In the former case, since the amount of Fe is large, the Al—Mn—Fe intermetallic compound increases, the density of the Al—Mn needle-like precipitates of 1 to 8 μm decreases, and the L value is the target. In the latter case, since the amount of Si was large, an Al—Mn—Si granular precipitate having a size of less than 1 μm was deposited, the b value increased, and the L value fell below the target range.
[0044]
On the other hand, although manufacturing condition numbers 11 to 15 use an alloy that satisfies the component composition conditions specified in the present invention (only manufacturing condition number 13 is alloy D, and the other is alloy A), the manufacturing process conditions are specified in the present invention. This is a comparative example that deviates from the conditions. Among them, production condition number 11 is that the ingot heating temperature is too low, and the Al-Mn needle-like precipitates of 1 to 8 μm are unevenly distributed and the density thereof is lowered, so the L value exceeds the target range, A streak defect occurred. Production condition number 12 has a hot rolling end temperature that is too high, and partial recrystallization occurs at the end of hot rolling, which affects the recrystallized grains in the intermediate annealing to form a mixed grain structure. Occurred. Furthermore, in production condition No. 13, intermediate annealing was performed in a batch furnace, so that the recrystallized grains became coarse and rough skin was generated during bending. In addition, since the production condition number 14 was not cold-rolled after the intermediate annealing, the proof stress was 95 N / mm.²  It became the following low strength. On the other hand, production condition number 15 was cracked by bending because the cold rolling rate was too high and the yield strength was high.
[0045]
【The invention's effect】
As is clear from the above-described embodiments, according to the manufacturing method of the present invention, the bending workability is particularly good and the strength is 95 N / mm.²  As described above, a rolled aluminum alloy sheet exhibiting a stable gray color with a small L-value fluctuation can be obtained even with a thin anodized film of about 10 μm as in the conventional material. And if the aluminum alloy rolled sheet obtained by this invention is used for gray building materials that have been anodized, especially interior materials, other objects, housings and panels of various electrical equipment and measuring instruments, decorative items, etc. It is possible even with a severe bending work design, and since the thin anodized film exhibits a stable gray with a small L value variation, it is possible to reduce the anodizing treatment cost.

Claims

Mn 1.3-1.5% (weight%, the same shall apply hereinafter), Mg 0.4-1.2%, Fe 0.05% and 0.2% or less are contained, and Si is regulated to less than 0.05% , The balance consists of Al and unavoidable impurities, and there is no precipitation of Al-Mn-Si-based granular precipitates having a size of less than 1 μm, and Al-Mn-based acicular precipitates having a size of 1 to 8 μm. are precipitated in a density in the range of 4,000 /0.2Mm ^2, moreover the average crystal grain size of 80μm or less, and wherein the yield strength is 95N / mm ² or more, the color tone after the anodic oxidation treatment Gray and stable aluminum alloy rolled plate.

Further, 0.003 to 0.15% Ti is contained alone or in combination with 0.0001 to 0.01% B, and the color tone after anodizing treatment is gray. And stable aluminum alloy rolled plate.

The ingot of the Al alloy having the chemical composition according to claim 1 or 2 is subjected to heat treatment for 1 to 24 hours at a temperature within a range of 580 to 630 ° C, and then at a temperature equal to or lower than the treatment temperature in the heat treatment. Hot rolling is started, the hot rolling is finished at 300 ° C. or lower, and then heated to a temperature in the range of 400 to 600 ° C. at a heating rate of 1 to 50 ° C./second and held for 0 to 10 minutes. After that, it is subjected to intermediate annealing that is cooled at a cooling rate of 1 to 50 ° C./second, and further cold-rolled at a rolling rate of 2 to 30%, whereby an Al—Mn—Si based granular precipitate having a size of less than 1 μm. 1-8 μm Al-Mn needle-like precipitates are deposited at a density in the range of 1000 to 4000 / 0.2 mm ² , and the average crystal grain size is 80 μm or less. The proof stress is 95 N / mm ² or more. A method for producing a rolled aluminum alloy plate that is stable in gray color after anodizing.

The method for producing a rolled aluminum alloy sheet having a stable gray color tone after anodizing according to claim 3, wherein the first cold rolling is performed after the hot rolling and before the intermediate annealing.