JP4237326B2 - Method for producing aluminum alloy sheet excellent in formability and corrosion resistance - Google Patents
Method for producing aluminum alloy sheet excellent in formability and corrosion resistance Download PDFInfo
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【0001】
【発明の属する技術分野】
本発明は、成形性および耐食性に優れる、自動車ボディシ−ト等に好適なアルミニウム合金板の製造方法に関する。
【0002】
【従来の技術】
近年、自動車の燃費向上を目的とした車体軽量化の要望が高まっており、軽量化手段の一つとして自動車ボディシ−ト等へのアルミニウム合金板の使用が行われている。自動車のボディシート用材料としては、プレス成形性に優れるだけではなく、塗装焼付後の強度や、耐食性等に優れることが要求される。
現在使用されている自動車ボディシ−ト用アルミニウム合金としては、非熱処理型のAl−Mg系合金と、熱処理型のAl−Mg−Si系とが用いられている。
【0003】
Al−Mg系合金は、Mg含有量の増加とともに延性が向上することから、成形性に優れたアルミニウム合金として、我が国では自動車ボデイパネルに多用されている。しかしながら、Al−Mg系合金では、Al−Mg−Si系合金より成形性は優れているものの、プレス成形の際にストレッチャー−ストレイン模様が現れて表面品位を損なう場合があることや、塗装焼付時に軟化してしまい、耐デント性に劣るという問題点がある。
【0004】
一方、Al−Mg−Si系合金で本質的にストレッチャー−ストレイン模様はほとんど出現のしないことや、塗装焼付工程の熱処理を活用して降伏強度の上昇も図り得るという長所を有するが、Al−Mg系合金に比べて成形性に劣るという問題点があり、自動車ボディパネル用としては、その適用に限界があった。
このように自動車ボデイパネル用アルミニウム合金としては、プレス成形性に優れるとともに、プレス後の表面品位にも優れ、塗装焼付によって十分な強度がえられることが求められている。
【0005】
【発明が解決しようとする課題】
このような要求特性に対して、例えば特開平1−287244号公報では、時効硬化性を有するAl−Cu−Mg−Si系合金を芯材として、良好な成形性を有し、かつストレッチャー−ストレイン模様も問題のない純Alを皮材としたアルミニウム合金合わせ板が提案されており、プレス成形性と塗装焼付硬化性が両立されている。しかしながら、合わせ板では、製造コストが高くなるとともに、端面において異種金属接触腐食を起こす懸念がある。
本発明は、単板でプレス成形性に優れるとともに、塗装焼付によって十分な強度が得られ、かつ耐食性にも優れる自動車用アルミニウム合金板の製造方法を提供することを目的としたものである。
【0006】
【課題を解決するための手段】
本発明者らは、上記の目的を達成するために、先ずアルミニウム合金板の成形性に及ぼす材料因子について種々検討した結果、溶質原子が溶体化後室温近傍の温度で形成されるMg−Siクラスターとして存在すると、(TS−YS)値が高くなり、成形性に優れることを見出した。
しかし、このMg−Siクラスターは、塗装焼付時のG.P.ゾーンの析出を阻害し、塗装焼付け処理時には大きな強度上昇は期待できないが、合金成分および製造方法を特定することによって、塗装焼付により軟化してしまうAl−Mg系合金以上の十分な強度が得られることもわかった。
そしてこのMg−Siクラスターは通常の熱分析法の一つである示差走査熱分析法によって、その形成の有無を知ることができることがわかった。
【0007】
本発明は上記の知見に基づいて得られたもので、その要旨とするところは、
(1)mass%で、Mg:0.2〜1.1%、Si:0.6〜1.7%、Ti:0.15%以下、B:0.05%以下を含有し、残部がAlおよび不可避的不純物からなり、熱分析曲線がMg−Siクラスター溶解に相当する吸熱ピークを有する成形性および耐食性に優れたアルミニウム合金板の製造方法であって、前記成分組成からなるアルミニウム合金板を、冷間圧延後、450〜580℃の温度で溶体化処理を施した後に10℃/s以上の冷却速度で室温まで冷却し、室温で2日以上放置し、その後さらに50〜120℃の温度で1〜50時間の熱処理を行うことを特徴とする成形性および耐食性に優れたアルミニウム合金板の製造方法。
【0008】
(2)mass%で、Mn:0.4%以下、Fe:0.3%以下、Zn:1.0%以下のうち一種以上を、さらに含有することを特徴とする前記(1)に記載の成形性および耐食性に優れたアルミニウム合金板の製造方法である。
【0009】
【発明の実施の形態】
以下、本発明について詳細に説明する。
本発明者らは、上記の目的を達成するために、先ずアルミニウム合金板の成形性に及ぼす材料因子について種々検討した結果、合金板の(TS−YS)値(TS:引張強さ、YS:耐力)を高めると、プレス成形性が向上することを見出した。次に、ストレッチャー−ストレイン模様の発生もなく、また時効硬化性を有するAl−Mg−Si系合金において、プレス成形性に及ぼす溶質原子の存在状態、合金成分および製造条件の影響について鋭意検討した。
【0010】
さらに本検討の際には、良好な耐食性を付与するために強度および成形性に有効とされるCuは添加しないことを前提としている。
種々検討の結果、溶質原子が溶体化後室温近傍の温度で形成されるMg−Siクラスターとして存在すると、(TS−YS)値が高くなり、成形性に優れることを見出した。
また、一般的な塗装焼付け条件である180℃程度で30分間足らずの熱処理では、このMg−Siクラスターは安定に存在するために、溶質原子の過飽和固溶量を減少させ、G.P.ゾーンの析出を阻害してしまう。その結果、塗装焼付け処理時には大きな強度上昇は期待できないが、合金成分および製造方法を特定することによって、塗装焼付により軟化してしまうAl−Mg系合金以上の十分な強度が得られることもわかった。
【0011】
なお、このMg−Siクラスターは通常の熱分析法のである示差熱分析法(DTA)や示差走査熱分析法(DSC)によって、その形成の有無を知ることができる。発明者らは理学電機株式会社製示差走査熱量計DSC−8230Dを用いてMg−Siクラスター形成を評価した。本機器を用いて、昇温速度20℃/分で測定した場合の典型的な測定結果を図1に示す。Mg−Siクラスターが存在していれば、5〜30℃/分の昇温速度で測定した際、図1のような示差走査熱分析曲線において150〜250℃の温度範囲にてMg−Siクラスターの溶解に相当するピークLが認められる。熱の出入りのない温度域を基準にベースラインをひき、Lのピーク面積(熱量に相当)が概ね0.3cal/g以上あればピークが存在するとした。
【0012】
このように、示差走査熱分析法による測定結果において、Mg−Siクラスター溶解に相当する吸熱ピークの認められるAl−Mg−Si系合金は、成形性に優れ、さらに合金成分等を特定することで塗装焼付によりAl−Mg系合金以上の強度を得ることが可能であることがわかった。
また、示差走査熱分析法による測定結果においてMg−Siクラスター溶解に相当する吸熱ピークの認められるAl−Mg−Si系合金板の好適な成分系は以下の通りである。 主要な合金成分としてはMgとSiの成分関係をバランス組成よりもSi過剰とし、時効性に優れた成分系とする方が、溶体化処理後に成形性向上に有効なMg−Siクラスターを形成させる点で好ましい。
【0013】
本発明における好適な成分組成範囲の限定理由について説明する。
MgとSi:MgとSiは本発明の必須の基本成分であり、微細なMg−Siクラスターを形成して、高い成形性ならびに十分な塗装焼付硬化性を得るために含有させる。また成分範囲としては、バランス組成に対してSi過剰側である、Mg:0.2〜1.1mass%、Si:0.6〜1.7mass%の範囲とするのが好ましい。Siが0.6mass%未満でもまた成形性および塗装焼付硬化性が得られなくなってしまう。一方、Mgが過剰になり1.0mass%を越えて含有されるとバランス組成に近づき、成形性および塗装焼付け効果性が低下する。またMgが0.2mass%未満では、上記の特性が得にくくなる。
【0014】
本発明においては、さらに必要に応じて、Ti、B、Mn、Fe、Znのうち1種類以上を含有させてもよい。
TiとB:TiとBは微量添加により鋳塊の結晶粒を微細化してプレス成形性等を改善する効果を有するので、Tiの含有量は0.15mass%以下、Bの含有量は0.05mass%以下の範囲に規定するのが好ましい。それぞれの含有量がTi 0.15mass%、B 0.05mass%を超えると粗大な晶出物を形成し、成形性が劣化するので、それぞれ0.15mass%、0.05mass%を上限とするのが好ましい。
【0015】
Mn:Mnは強度を向上させるために、0.4mass%以下で含有させるとよい。その含有量が0.4mass%を超えると粗大晶出物が生成し、成形性を低下させるので0.4mass%を上限とするのが良い。
Fe:Feは強度向上効果は小さく、その含有量が0.3mass%を超えると粗大晶出物が生成し、成形性を低下させるので0.3mass%を上限とするのが好ましい。
【0016】
Zn:Znは強度を向上させるため、1.0mass%以下で含有させるとよい。その含有量が1.0mass%を超えると成形性を低下させるので1.0mass%を上限とするのが好ましい。
上記元素の他、通常のアルミニウム合金と同様、不可避的不純物が含有されるが、その量は本発明の効果を損なわない範囲であれば許容される。
【0017】
また、製造方法としては、溶体化処理後室温まで急冷してMgおよびSi溶質を過飽和に固溶させ、室温時効によりMg−Siクラスターを形成させる方法を基本とする。そして室温時効だけではMgおよびSi溶質の拡散が遅く短時間では十分な強度特性が得られない場合には、室温時効後に50〜120℃の温度範囲で引き続き熱処理を行うことが有効である。
【0018】
さらに、Mg−Siクラスター形成温度域が約70℃以下であることから、溶体化後に室温以上70℃以下のMg−Siクラスター温度範囲に急冷し、その温度範囲にて時効する方法も有効である。まず、本発明はAl−Mg−Si系アルミニウム合金板において、優れたプレス成形性を有するために、示差走査熱分析曲線にMg−Siクラスターの溶解に相当するピークが認められるものとする。このピークの存在が、Mg−Siクラスターの存在を立証し、優れたプレス成形性が確保されるものである。
【0019】
次に本発明のアルミニウム合金板の好適な製造方法について詳しく説明する。
本発明のAl−Mg−Si系アルミニウム合金は、常法に従って鋳造、熱間および冷間圧延を施すが、Mg−Siクラスターを形成させて優れた成形性を得るためには、冷間圧延後、450〜580℃の範囲内の温度で溶体化処理を施して10℃/s以上の冷却速度で室温まで冷却することが有効である。上記工程の溶体化処理条件としては、450℃以下の温度では成形性向上ならびに塗装焼付硬化性確保(時効硬化)に寄与するMg、Si原子がAl母相中に十分に固溶せずに、第2相として析出してしまうために、成形性向上ならびに塗装焼付硬化性の確保が得られず、またヘム曲げ性を低下させてしまう。
【0020】
一方、溶体化温度が580℃を越えると、部分溶解が生じてしまう。そのために溶体化処理温度は450〜580℃の範囲内とした。また、上記の溶体化温度での保持については、溶質原子の固溶が十分に行われるのならば、保持なし(溶体化処理温度到達後、すぐに冷却)でも、ある程度の保持時間をとっともよい。 溶体化処理後の冷却速度を10℃/s未満にすると、冷却中に第2相が析出し、ヘム曲げ性が低下するとともに、Mg、Si過飽和固溶量が減少してしまい、成形性向上に有効なMg−Siクラスター形成量が少なくなるとともに、塗装焼付硬化能も低下してしまう。そのため、溶体化処理温度から室温までの冷却速度は10℃/s以上とした。
【0021】
第二に、冷間圧延後、450〜580℃の範囲内の温度で溶体化処理を施して10℃/s以上の冷却速度で室温まで冷却した後、室温で1日以上放置し、その後50〜120℃の温度範囲で1〜50時間の熱処理を施すことが、優れた成形性を得るために有効である。上記工程の溶体化処理温度および冷却速度条件の設定理由は前述した理由と同じである。溶体化後室温での放置時間が1日未満であると、成形性向上に寄与するMg−Siクラスターの形成量が少なくなってしまう。なお、溶体化後室温での放置時間の下限は、本発明の実施例の表3のNo.(4)、(6)及び(7)の2日に基づいて2日以上とした。
【0022】
また、1日以上の室温時効だけではMgおよびSi溶質の拡散が遅く、短期間では十分な強度特性が得られず、工業的な生産性の観点で問題が生じる場合がる。その場合には、室温時効後に50〜120℃の温度範囲で引き続き熱処理を行うことが有効である。本熱処理の範囲の規定理由としては、50℃未満、1時間未満の処理では、十分な強度上昇が得られず、120℃超、50時間超では逆に強度上昇が大きくなりすぎてしまうためである。
【0023】
第三に、冷間圧延後、450〜580℃の範囲内の温度で溶体化処理を施して10℃/s以上の冷却速度で室温以上70℃以下の温度まで冷却し、室温以上70℃以下の温度で1〜100時間の熱処理を行うことが、優れた成形性を得るために有効でる。
溶体化処理後に冷却する温度範囲の規定理由としては、70℃を越えるとMg−SiクラスターではなくGPゾーンが形成されてしまい、室温以下ではMg−Siクラスターは形成されるものの、MgおよびSiの拡散が遅くMg−Siクラスターの形成に長時間を要してしまうためである。ここでの室温とは、概ね25℃である。
【0024】
さらに、熱処理時間の規定理由としては、1時間未満ではMg−Siクラスター形成量が不十分であり、100時間以上では強度上昇が大きくなりすぎてしまうためである。
このようにして得られたアルミニウム合金板は、成形加工性に優れ、かつ塗装焼付後にも5000系合金と同等以上の十分な強度が得られる。したがってこのようなアルミニウム合金板は自動車のボディシ−ト用として好適である。
【0025】
【実施例】
以下、本発明を実施例で説明する。
(参考例1)
表1に示すような成分組成を有する合金を、通常の方法で溶解・鋳造、圧延して板厚1mmの板にした。そして上記圧延板に対して550℃で10秒保持の溶体化処理を施した後室温まで20℃/sの平均冷却速度で空冷して、アルミニウム合金板を製造した。製造後、10日間室温に放置した後に、理学電機(株)製示差走査熱量計DSC−8230Dを用いてMg−Siクラスター溶解ピークの有無を調べるとともに、引張特性、成形性(深絞り試験、球頭張出試験)を調査した。さらに塗装焼付硬化性を評価するために、プレスにより受ける加工に相当する2%の予ひずみを与えた後に塗装焼付処理に相当する170℃で20分の熱処理を行い、耐力を調査した。それらの調査結果を表2に示す。
【0026】
【表1】
【0027】
【表2】
【0028】
本発明は良好な成形性と、5000系合金と同等以上のほぼ十分な塗装焼付硬化性を有するアルミニウム合金板の提供を目的としていることから、合金板の成形性能として、限界絞り比:2.00以上、エリクセン値:10.2以上、塗装焼付硬化性としては塗装焼付け後の耐力:140MPa以上を目標とした。
【0029】
(実施例)
表1の発明合金5の1mm厚の圧延板に対して、550℃で10秒保持の溶体化処理を施した後に冷却速度を制御して室温まで空冷した。空冷後、室温放置の後に、引き続き熱処理を行った。溶体化後の平均冷却速度、空冷から熱処理までの放置時間、室温放置後の熱処理条件を表3に示す。
このようにして製造したアルミニウム合金板に対して、参考例1で行ったものと同様な調査を実施した。その調査結果を表4に示す。製造条件(1)は冷却速度が小さすぎて十分な過飽和固溶体が得られなかったため、製造条件(3)は溶体化後の室温での放置が不十分であったのに、Mg−Siクラスターの形成が認められず、良好な成形性が得られなかったものである。また製造条件(5)は熱処理が不十分であったために初期強度が低く、塗装焼付後の耐力が不足してしまい、製造条件(8)は熱処理による強度上昇が大きすぎて、成形性が劣化してしまった。このように、本発明内の製造条件で処理を行ったものは上述の比較例の製造条件に対して、成形性に優れるとともに、十分な塗装焼付硬化量も備わっていることがわかる。
【0030】
【表3】
【0031】
【表4】
【0032】
(参考例2)
表1の発明合金5の1mm厚の圧延板に対して、550℃で10秒保持の溶体化処理を施した後に20℃/sの平均冷却速度である温度まで空冷した。空冷後、引き続き熱処理を行った。溶体化後の空冷温度および引き続き行う熱処理の条件を表5に示す。このようにして製造したアルミニウム合金板に対して、参考例1で行ったものと同様な調査を実施した。その調査結果を表6に示す。
【0033】
【表5】
【0034】
【表6】
【0035】
【発明の効果】
本発明によれば、成形性に優れるとともに、十分な塗装焼付硬化性を有しており、成形性および焼付後の耐デント性が必要とされる自動車ボディ用などに好適なアルミニウム合金板が提供できるので、自動車重量の軽量化に大いに寄与できる。したがって、本発明の産業上の価値は極めて高いといえる。
【図面の簡単な説明】
【図1】Al−Mg−Si系合金の示差走査熱分析曲線の一例を示した図である。
【符号の説明】
K クラスターの析出に相当するピーク
L クラスターの溶解に相当するピーク
P GPゾーンの析出に相当するピーク
T GPゾーンの溶解に相当するピーク
Q 中間相の析出に相当するピーク[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an aluminum alloy plate that is excellent in formability and corrosion resistance and is suitable for automobile body sheets and the like.
[0002]
[Prior art]
In recent years, there has been an increasing demand for weight reduction of automobile bodies for the purpose of improving the fuel efficiency of automobiles, and aluminum alloy plates are used for automobile body sheets and the like as one of weight reduction means. As a body sheet material for automobiles, it is required not only to be excellent in press formability but also to be excellent in strength after baking and corrosion resistance.
Non-heat-treatable Al—Mg alloys and heat-treatable Al—Mg—Si alloys are used as aluminum alloys for automobile body sheets that are currently used.
[0003]
Al-Mg alloys are frequently used in automobile body panels in Japan as aluminum alloys having excellent formability because ductility improves as the Mg content increases. However, although Al-Mg-based alloys have better formability than Al-Mg-Si-based alloys, stretcher-strain patterns may appear during press molding, which may impair surface quality, and paint baking There is a problem that it is sometimes softened and has poor dent resistance.
[0004]
On the other hand, the Al-Mg-Si alloy has the advantage that essentially no stretcher-strain pattern appears and the yield strength can be increased by utilizing the heat treatment in the paint baking process. There is a problem that the formability is inferior to that of an Mg-based alloy, and there is a limit to its application as an automobile body panel.
As described above, an aluminum alloy for an automobile body panel is required to have excellent press formability, excellent surface quality after pressing, and sufficient strength by baking.
[0005]
[Problems to be solved by the invention]
With respect to such required characteristics, for example, in Japanese Patent Laid-Open No. 1-287244, an Al—Cu—Mg—Si alloy having age-hardening properties is used as a core material, and it has good formability and is a stretcher. There has been proposed an aluminum alloy laminated plate made of pure Al, which has no problem with the strain pattern, and has both press formability and paint bake hardenability. However, with the laminated plate, there is a concern that the manufacturing cost is increased, and contact with different metals is caused at the end face.
The object of the present invention is to provide a method for producing an aluminum alloy sheet for automobiles which is excellent in press formability with a single plate, has sufficient strength obtained by paint baking, and has excellent corrosion resistance.
[0006]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors first studied various material factors affecting the formability of an aluminum alloy plate. As a result, Mg-Si clusters formed by solute atoms at a temperature close to room temperature after solutionization. As a result, it was found that the (TS-YS) value was high and the moldability was excellent.
However, this Mg-Si cluster is a G.I. P. Although the precipitation of the zone is hindered and no significant increase in strength can be expected during the paint baking process, by specifying the alloy components and the manufacturing method, sufficient strength can be obtained over Al-Mg alloys that soften by paint baking. I also understood that.
It was found that the presence or absence of this Mg-Si cluster can be determined by differential scanning calorimetry, which is one of the usual thermal analyses.
[0007]
The present invention was obtained based on the above findings, and the gist thereof is as follows:
(1) In mass%, Mg: 0.2-1.1%, Si: 0.6-1.7% , Ti: 0.15% or less, B: 0.05% or less , the balance being A method for producing an aluminum alloy plate comprising Al and unavoidable impurities and having an endothermic peak corresponding to Mg-Si cluster dissolution in a thermal analysis curve and excellent in formability and corrosion resistance. After cold rolling, solution treatment is performed at a temperature of 450 to 580 ° C., then cooled to room temperature at a cooling rate of 10 ° C./s or more, and left at room temperature for 2 days or more, and then further at a temperature of 50 to 120 ° C. The manufacturing method of the aluminum alloy plate excellent in the moldability and corrosion resistance characterized by performing heat processing for 1 to 50 hours.
[0008]
(2) The above-mentioned ( 1 ), further comprising at least one of mass% , Mn: 0.4% or less, Fe: 0.3% or less, Zn: 1.0% or less. This is a method for producing an aluminum alloy sheet having excellent formability and corrosion resistance.
[ 0009 ]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
In order to achieve the above object, the present inventors first studied various material factors affecting the formability of an aluminum alloy plate. As a result, the (TS-YS) value (TS: tensile strength, YS: It has been found that the press formability is improved when the yield strength is increased. Next, in the Al-Mg-Si based alloy having no stretcher-strain pattern and age-hardening properties, the present inventors studied diligently about the influence of the existence state of solute atoms, alloy components and production conditions on press formability. .
[ 0010 ]
Further, in the present study, it is assumed that Cu, which is effective for strength and formability, is not added in order to impart good corrosion resistance.
As a result of various studies, it has been found that when solute atoms exist as Mg—Si clusters formed at a temperature near room temperature after solution formation, the (TS-YS) value increases and the moldability is excellent.
Further, in the heat treatment of about 180 ° C., which is a general paint baking condition, for less than 30 minutes, since this Mg—Si cluster exists stably, the amount of supersaturated solid solution of solute atoms is reduced. P. This will inhibit zone deposition. As a result, it was not possible to expect a significant increase in strength during the paint baking process, but it was also found that by specifying the alloy components and the manufacturing method, a sufficient strength higher than that of an Al-Mg alloy that is softened by paint baking can be obtained. .
[ 0011 ]
In addition, this Mg-Si cluster can know the presence or absence of the formation by the differential thermal analysis method (DTA) and the differential scanning thermal analysis method (DSC) which are the usual thermal analysis methods. The inventors evaluated the formation of Mg—Si clusters using a differential scanning calorimeter DSC-8230D manufactured by Rigaku Corporation. FIG. 1 shows a typical measurement result when measured at a temperature elevation rate of 20 ° C./min using this device. If Mg—Si clusters are present, the Mg—Si clusters are measured in the temperature range of 150 to 250 ° C. in the differential scanning calorimetry curve as shown in FIG. 1 when measured at a heating rate of 5 to 30 ° C./min. A peak L corresponding to dissolution of is observed. A baseline was drawn based on a temperature range where heat did not enter and exit, and a peak was present if the L peak area (corresponding to the amount of heat) was approximately 0.3 cal / g or more.
[ 0012 ]
Thus, in the measurement results by differential scanning calorimetry, an Al—Mg—Si alloy with an endothermic peak corresponding to Mg—Si cluster dissolution is excellent in formability and further by specifying the alloy components and the like. It has been found that it is possible to obtain a strength higher than that of an Al—Mg alloy by painting and baking.
Moreover, the suitable component system of the Al-Mg-Si type alloy plate by which the endothermic peak equivalent to Mg-Si cluster melt | dissolution is recognized in the measurement result by a differential scanning calorimetry is as follows. As the main alloy component, the component relationship between Mg and Si is more Si than the balance composition, and the component system having excellent aging properties forms Mg-Si clusters that are effective in improving formability after solution treatment. This is preferable.
[ 0013 ]
The reason for limiting the preferred component composition range in the present invention will be described.
Mg and Si: Mg and Si are essential components of the present invention, and are included in order to form fine Mg-Si clusters and obtain high moldability and sufficient paint bake hardenability. Moreover, as a component range, it is preferable to set it as the range of Mg: 0.2-1.1mass% and Si: 0.6-1.7mass% which are Si excess sides with respect to a balance composition. Even if Si is less than 0.6 mass%, moldability and paint bake hardenability cannot be obtained. On the other hand, if Mg is excessive and contained in excess of 1.0 mass%, the composition approaches the balance composition, and the formability and paint baking effect deteriorate. If Mg is less than 0.2 mass%, it is difficult to obtain the above characteristics.
[ 0014 ]
In the present invention, if necessary, one or more of Ti, B, Mn, Fe, and Zn may be contained.
Ti and B: Ti and B have the effect of improving the press formability and the like by refining the crystal grains of the ingot by adding a small amount, so the Ti content is 0.15 mass% or less, and the B content is 0.00. It is preferable to prescribe | regulate in the range of 05 mass% or less. If each content exceeds 0.15 mass% Ti and 0.05 mass% B, a coarse crystallized product is formed and the formability deteriorates. Therefore, the upper limit is 0.15 mass% and 0.05 mass%, respectively. Is preferred.
[ 0015 ]
Mn: Mn is preferably contained at 0.4 mass% or less in order to improve the strength. If the content exceeds 0.4 mass%, a coarse crystallized product is generated and the moldability is lowered, so 0.4 mass% is preferably set as the upper limit.
Fe: Fe has a small strength improvement effect, and if its content exceeds 0.3 mass%, a coarse crystallized product is generated and the moldability is lowered. Therefore, it is preferable to set 0.3 mass% as the upper limit.
[ 0016 ]
Zn: Zn is preferably contained at 1.0 mass% or less in order to improve the strength. If the content exceeds 1.0 mass%, the moldability is deteriorated, so 1.0 mass% is preferable as the upper limit.
In addition to the above elements, inevitable impurities are contained as in the case of ordinary aluminum alloys, but the amount thereof is permissible as long as the effects of the present invention are not impaired.
[ 0017 ]
The manufacturing method is basically a method in which Mg and Si solutes are supersaturated by rapid cooling to room temperature after solution treatment, and Mg—Si clusters are formed by aging at room temperature. If the Mg and Si solute diffusion is slow due to room temperature aging alone and sufficient strength characteristics cannot be obtained in a short time, it is effective to continue the heat treatment in the temperature range of 50 to 120 ° C. after aging at room temperature.
[ 0018 ]
Furthermore, since the Mg-Si cluster formation temperature range is about 70 ° C. or lower, a method of rapidly cooling to a Mg-Si cluster temperature range from room temperature to 70 ° C. after solutionization and aging in that temperature range is also effective. . First, since the present invention has excellent press formability in an Al—Mg—Si based aluminum alloy plate, a peak corresponding to dissolution of Mg—Si clusters is recognized in the differential scanning calorimetry curve. The presence of this peak proves the presence of Mg—Si clusters, and ensures excellent press formability.
[ 0019 ]
Next, the suitable manufacturing method of the aluminum alloy plate of this invention is demonstrated in detail.
The Al—Mg—Si based aluminum alloy of the present invention is cast, hot and cold rolled in accordance with a conventional method, but in order to form an Mg—Si cluster and obtain excellent formability, It is effective to apply a solution treatment at a temperature in the range of 450 to 580 ° C. and cool to room temperature at a cooling rate of 10 ° C./s or more. As a solution treatment condition in the above process, Mg and Si atoms contributing to improvement of formability and ensuring bake hardenability (age hardening) at a temperature of 450 ° C. or lower are not sufficiently dissolved in the Al matrix. Since it precipitates as a 2nd phase, improvement of a moldability and ensuring of coating bake hardenability are not acquired, and heme bendability will be reduced.
[ 0020 ]
On the other hand, when the solution temperature exceeds 580 ° C., partial dissolution occurs. Therefore, the solution treatment temperature was set within the range of 450 to 580 ° C. In addition, with respect to holding at the above-mentioned solution temperature, if the solute atoms are sufficiently dissolved, even if there is no holding (cooling immediately after reaching the solution treatment temperature), a certain holding time will be obtained. Good. When the cooling rate after solution treatment is less than 10 ° C./s, the second phase is precipitated during cooling, and the hem bendability is reduced, and the Mg and Si supersaturated solid solution amounts are reduced, thereby improving the formability. As a result, the effective amount of Mg—Si cluster formation decreases and the paint bake hardenability also decreases. Therefore, the cooling rate from the solution treatment temperature to room temperature was set to 10 ° C./s or more.
[ 0021 ]
Secondly, after cold rolling, solution treatment is performed at a temperature in the range of 450 to 580 ° C., the solution is cooled to room temperature at a cooling rate of 10 ° C./s or more, and left at room temperature for one day or more. It is effective to perform heat treatment for 1 to 50 hours in a temperature range of ˜120 ° C. in order to obtain excellent moldability. The reasons for setting the solution treatment temperature and the cooling rate condition in the above process are the same as described above. If the standing time at room temperature after solution treatment is less than one day, the amount of Mg-Si clusters that contribute to improving the formability will be reduced. In addition, the lower limit of the standing time at room temperature after solution treatment is No. in Table 3 of the examples of the present invention. Based on the two days of (4), (6) and (7), it was set to 2 days or more.
[ 0022 ]
Moreover, the diffusion of Mg and Si solutes is slow only by aging at room temperature for 1 day or more, and sufficient strength characteristics cannot be obtained in a short period of time, which may cause problems in terms of industrial productivity. In that case, it is effective to continue the heat treatment in the temperature range of 50 to 120 ° C. after aging at room temperature. The reason for the definition of the range of this heat treatment is that a sufficient strength increase cannot be obtained with a treatment of less than 50 ° C. for less than 1 hour, and a strength increase is excessively greater than 120 ° C. for more than 50 hours. is there.
[ 0023 ]
Third, after cold rolling, solution treatment is performed at a temperature in the range of 450 to 580 ° C., and the solution is cooled to a temperature of room temperature to 70 ° C. at a cooling rate of 10 ° C./s or more. It is effective to perform heat treatment at a temperature of 1 to 100 hours for obtaining excellent moldability.
The reason for defining the temperature range for cooling after the solution treatment is that when it exceeds 70 ° C., a GP zone is formed instead of an Mg—Si cluster, and an Mg—Si cluster is formed below room temperature, but Mg and Si This is because the diffusion is slow and it takes a long time to form the Mg—Si cluster. The room temperature here is approximately 25 ° C.
[ 0024 ]
Furthermore, the reason for prescribing the heat treatment time is that the Mg—Si cluster formation amount is insufficient if it is less than 1 hour, and the increase in strength becomes too large if it is 100 hours or more.
The aluminum alloy sheet thus obtained is excellent in formability and can provide sufficient strength equal to or higher than that of a 5000 series alloy even after paint baking. Accordingly, such an aluminum alloy plate is suitable for use in automobile body sheets.
[ 0025 ]
【Example】
Hereinafter, the present invention will be described with reference to examples.
( Reference Example 1 )
An alloy having a component composition as shown in Table 1 was melted, cast and rolled by a usual method to obtain a plate having a thickness of 1 mm. Then, the above-mentioned rolled plate was subjected to a solution treatment that was held at 550 ° C. for 10 seconds, and then air-cooled to room temperature at an average cooling rate of 20 ° C./s to produce an aluminum alloy plate. After the production, after standing at room temperature for 10 days, the differential scanning calorimeter DSC-8230D manufactured by Rigaku Denki Co., Ltd. was used to check for the presence of Mg-Si cluster dissolution peaks, as well as tensile properties and formability (deep drawing test, ball The head overhang test) was investigated. Further, in order to evaluate the bake hardenability, after applying a pre-strain of 2% corresponding to the processing received by the press, a heat treatment was performed at 170 ° C. corresponding to the paint baking process for 20 minutes, and the proof stress was investigated. The survey results are shown in Table 2.
[ 0026 ]
[Table 1]
[ 0027 ]
[Table 2]
[ 0028 ]
The present invention aims to provide an aluminum alloy plate having good formability and almost sufficient paint bake hardenability equivalent to or higher than that of a 5000 series alloy. 00 or more, Erichsen value: 10.2 or more, and the bake hardenability was set to have a proof stress after paint baking: 140 MPa or more .
[ 0029 ]
( Example)
A 1 mm thick rolled sheet of invention alloy 5 in Table 1 was subjected to a solution treatment that was held at 550 ° C. for 10 seconds, and then cooled to room temperature by controlling the cooling rate. After air cooling and standing at room temperature, heat treatment was subsequently performed. Table 3 shows the average cooling rate after solution treatment, the standing time from air cooling to heat treatment, and the heat treatment conditions after standing at room temperature.
The same investigation as that performed in Reference Example 1 was performed on the aluminum alloy plate thus manufactured. The survey results are shown in Table 4. In production condition (1), the cooling rate was too low to obtain a sufficient supersaturated solid solution. Therefore, although production condition (3) was not allowed to stand at room temperature after solution formation, No formation was observed and good moldability was not obtained. In addition, the initial strength is low due to insufficient heat treatment in the production condition (5), and the proof stress after baking is insufficient. In the production condition (8), the increase in strength due to the heat treatment is too large and the formability is deteriorated. have done. Thus, it can be seen that those treated under the production conditions in the present invention are excellent in moldability and have a sufficient amount of paint bake and harden with respect to the production conditions of the above-mentioned comparative example.
[ 0030 ]
[Table 3]
[ 0031 ]
[Table 4]
[ 0032 ]
( Reference Example 2 )
A 1 mm-thick rolled sheet of invention alloy 5 in Table 1 was subjected to a solution treatment that was held at 550 ° C. for 10 seconds, and then air-cooled to a temperature that was an average cooling rate of 20 ° C./s. After air cooling, heat treatment was subsequently performed. Table 5 shows the air cooling temperature after solution treatment and the conditions for the subsequent heat treatment. The same investigation as that performed in Reference Example 1 was performed on the aluminum alloy plate thus manufactured. The survey results are shown in Table 6.
[ 0033 ]
[Table 5]
[ 0034 ]
[Table 6]
[ 0035 ]
【The invention's effect】
According to the present invention, there is provided an aluminum alloy plate that is excellent in formability and has sufficient paint bake hardenability, and is suitable for automobile bodies that require formability and dent resistance after baking. This can greatly contribute to reducing the weight of the automobile. Therefore, it can be said that the industrial value of the present invention is extremely high.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a differential scanning calorimetry curve of an Al—Mg—Si alloy.
[Explanation of symbols]
K peak corresponding to cluster precipitation L peak corresponding to dissolution of cluster P peak corresponding to precipitation of GP zone T peak corresponding to dissolution of GP zone peak Q peak corresponding to precipitation of intermediate phase
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JP4117243B2 (en) * | 2003-11-10 | 2008-07-16 | 株式会社神戸製鋼所 | Aluminum alloy sheet with excellent bake hardenability |
JP5329746B2 (en) * | 2006-07-13 | 2013-10-30 | 株式会社神戸製鋼所 | Aluminum alloy sheet for warm forming |
JP5059423B2 (en) | 2007-01-18 | 2012-10-24 | 株式会社神戸製鋼所 | Aluminum alloy plate |
JP6227222B2 (en) * | 2012-02-16 | 2017-11-08 | 株式会社神戸製鋼所 | Aluminum alloy sheet with excellent bake hardenability |
WO2015133004A1 (en) * | 2014-03-06 | 2015-09-11 | 古河電気工業株式会社 | Aluminum alloy wire, aluminum alloy strand wire, coated electric wire, wire harness, process for producing aluminum alloy wire, and method for examining aluminum alloy wire |
JP6190307B2 (en) | 2014-03-31 | 2017-08-30 | 株式会社神戸製鋼所 | Aluminum alloy sheet with excellent formability and bake hardenability |
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JPS6289852A (en) * | 1985-09-24 | 1987-04-24 | Kobe Steel Ltd | Manufacture of aluminum alloy plate having superior burning hardenability |
JPS62177143A (en) * | 1986-01-30 | 1987-08-04 | Kobe Steel Ltd | Aluminum alloy sheet excellent in formability and baking hardening and its production |
JP2681396B2 (en) * | 1989-08-29 | 1997-11-26 | 日本軽金属株式会社 | Manufacturing method of aluminum alloy sheet for forming with excellent corrosion resistance |
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JPH10259464A (en) * | 1997-03-19 | 1998-09-29 | Mitsubishi Alum Co Ltd | Production of aluminum alloy sheet for forming |
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