JP4865174B2

JP4865174B2 - Manufacturing method of aluminum alloy sheet with excellent bending workability and drawability

Info

Publication number: JP4865174B2
Application number: JP2001301169A
Authority: JP
Inventors: 保史清水; 洋一郎戸次; 耕史大山; 克己飯島
Original assignee: Furukawa Sky Aluminum Corp
Current assignee: Furukawa Sky Aluminum Corp
Priority date: 2001-09-28
Filing date: 2001-09-28
Publication date: 2012-02-01
Anticipated expiration: 2021-09-28
Also published as: JP2003105473A

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車ボディシート、自動車部品、機械部品などに適した曲げ加工性および絞り成形性に優れたアルミニウム合金板の製造方法に関する。
【０００２】
【従来の技術】
自動車は、ボディシートなどのアルミ化が進んでおり、アウター材にはベークハード性（塗装焼付時の加熱で析出硬化する性質）に優れ、塗装焼付後に高強度となる６０００系（Ａｌ−Ｍｇ−Ｓｉ系）アルミニウム合金が多用され、インナー材には絞り成形性に優れた５０００系（Ａｌ−Ｍｇ系）アルミニウム合金が使用されている。
【０００３】
【発明が解決しようとする課題】
しかし、アウター材はインナー材とかしめて用いられるため曲げ加工性に優れることが要求されるが、６０００系アルミニウム合金板は曲げ加工性に劣り、特にベークハード性を高めるために高温で溶体化処理した材料は曲げ加工性が著しく劣るという問題があった。一方、リサイクル性向上を目的にインナー材も６０００系アルミニウム合金に統一する動きがあり、それに応じて６０００系アルミニウム合金の絞り成形性を向上させることが重要課題とされている。
【０００４】
このような状況を踏まえ、本発明者等は６０００系アルミニウム合金における曲げ加工性について検討し、時効処理時に結晶粒界近傍に無析出帯（ＰＦＺ）が形成され、このＰＦＺは低強度のため曲げ加工時に割れの起点になるが、その幅を狭くすれば無害化し得ることを知見し、また絞り成形性は、引張強さおよび加工硬化特性を高めることにより改善し得ることを知見し、さらに検討を進めて本発明を完成させるに至った。本発明の目的は、曲げ加工性および絞り成形性に優れたアルミニウム合金板の製造方法を提供することにある。
【０００５】
【課題を解決するための手段】
請求項１記載の発明は、必須元素としてＳｉ０．５〜１．３mass％、Ｍｇ０．２５〜１．０mass％を含み、Ｍｎ０．０３〜０．２mass％、Ｃｒ０．０２〜０．２mass％のうちの１種または２種を含み、Ｆｅ０．３mass％以下、Ｃｕ０．２mass％以下に規制したアルミニウム合金圧延板を走行させ、これに溶体化処理を４８０℃以上の温度で連続的に施し、次いで焼入処理を、４５０℃から３５０℃の温度範囲を２０℃／秒以上の速度で急冷し、かつ前記焼入処理における圧延板の温度勾配が下記（３）式を満足するように施すことを特徴とする曲げ加工性に優れたアルミニウム合金板の製造方法である。
１５００００（ｔ³ ／ｂ）≧Ｌ.........（３）
但しｔはアルミニウム合金板の厚さ（ｍｍ）の数値、ｂは幅（ｍｍ）の数値、Ｌは温度勾配（℃／ｍ）の数値で、急冷開始直前の温度Ｐ（℃）と急冷開始位置から走行方向に１ｍ離れた位置の温度Ｑ（℃）を１（ｍ）で除した数値（〔Ｐ−Ｑ〕／１）である。
【０００６】
【発明の実施の形態】
本発明において、ＭｇとＳｉはＭｇ₂ Ｓｉ化合物として析出してアルミニウム合金板の強度向上に寄与する。Ｓｉの含有量を０．５〜１．３mass％に規定する理由は、０．５mass％未満ではその効果が十分に得られず、１．３mass％を超えると粗大なＳｉ系化合物が析出して曲げ加工性が低下するためである。ＳｉをＭｇ₂ Ｓｉの化学量論的にバランスする組成から過剰に添加するとベークハード性が向上する。またＭｇの含有量を０．２５〜１．０mass％に規定する理由は、０．２５mass％未満ではその効果が十分に得られず、１．０mass％を超えるとＭｇ₂ Ｓｉ化合物が多量に析出して曲げ加工性が低下するためである。
【０００７】
本発明において、ＭｎまたはＣｒは結晶粒を微細化して曲げ加工性を高める。ＭｎまたはＣｒの含有量をそれぞれ０．０３〜０．２mass％、０．０２〜０．２mass％に規定する理由は、下限値未満ではいずれもその効果が十分に得られず、上限値を超えるといずれも粗大化合物が析出して曲げ加工性が低下するためである。
【０００８】
本発明において、Ｆｅを０．３mass％以下に規制する理由は、Ｆｅが０．３mass％を超えて含まれるとＦｅ系化合物が増加して曲げ加工性が低下するためである。またＣｕを０．２mass％以下に規制する理由は、Ｃｕが０．２mass％を超えて含まれるとＣｕ系化合物が結晶粒界に析出して曲げ加工性が低下し、また粒界が腐食し易くなり耐食性が低下するためである。
【０００９】
本発明者等は曲げ加工性について検討し、曲げ割れの起点となる無析出帯（ＰＦＺ）の幅を小さくすること、その幅は引張強さ、耐力、結晶粒径が影響することを知見し、この知見を基にさらに検討を進めて下記（１）式を導き出した。
Ｗ≦（５２５０−１５．３Ｔ＋８．６Ｙ）／ｄ .........（１）
但しＴはアルミニウム合金板を圧延方向に引張ったときの引張強さ（ＭＰａ）の数値、Ｙはそのときの０．２％耐力（ＭＰａ）の数値、ｄはアルミニウム合金板の圧延面における平均結晶粒径（μｍ）の数値、Ｗは無析出帯（ＰＦＺ）の平均幅（ｎｍ）の数値である。
【００１０】
以下に前記（１）式の導出過程を詳しく説明する。曲げ加工での割れは、曲げ歪みを付与したときのマトリックスの発生応力Ｕ（ＭＰａ）が粒界破壊強度Ｇ（ＭＰａ）を上回ると発生する。Ｕは耐力Ｙと曲げ歪みによる加工硬化の和であり、以下の式で表せることを見いだした。
Ｕ＝Ｙ＋２．３（Ｔ−Ｙ）、（但しＴは引張強さ、Ｙは耐力）。
即ち、高強度材ほど曲げ歪みを付与したときの発生応力が大きくなり曲げ性は低下する。一方、ＧはＰＦＺ幅Ｗ（ｎｍ）と粒径ｄ（μｍ）に依存し、Ｗおよびｄが小さいほどＧが上昇することが分かっている。つまり、高強度材でもＷおよびｄを小さくしてＧを大きくすることにより曲げ性の低下を防ぐことができる。そこで、ＷとＵの関係を種々調査し、Ｗ≦（−０．１９Ｕ＋１５０) ×３５／ｄの関係式が成り立つとき良好な曲げ性が得られることを見いだした。この関係式に前記Ｕ＝Ｙ＋２．３（Ｔ−Ｙ）を代入して（１）式を導き出した。
【００１１】
次に、本発明者等は、絞り成形性について検討し、絞り成形性は、引張強さ（Ｔ）を、降伏比〔Ｙ／Ｔ〕で補正したパラメータＴ〔Ｔ／Ｙ〕が大きいほど向上することを知見し、この知見を基に検討を進めて下記（２）式を導き出した。
（Ｔ² ／Ｙ）≧４３０.........（２）
但しＴはアルミニウム合金板を圧延方向に引張ったときの引張強さ（ＭＰａ）の数値、Ｙはそのときの０．２％耐力（ＭＰａ）の数値。
【００１２】
請求項１記載発明は、溶体化処理および焼入処理の各条件を規定して、曲げ加工性、絞り成形性および形状性（フラットネス）に優れたアルミニウム合金板を製造する方法である。
【００１３】
請求項１記載発明で、溶体化処理温度を４８０℃以上に規定する理由は、４８０℃未満ではＭｇ、Ｓｉが十分に固溶されず、良好なベークハード性が得られないためである。また焼入処理を４５０℃〜３５０℃の温度範囲を２０℃／秒以上の速度で急冷して行う理由は、前記温度範囲を前記速度で急冷すれば、Ｍｇ、Ｓｉの析出および過剰空孔の消滅が抑えられて十分なベークハード性が得られ、ＰＦＺの幅が十分狭くなって良好な曲げ加工性が得られ、また２０℃／秒以上の急冷を前記温度範囲に限れば、形状性の悪化も防げるためである。前記２０℃／秒以上の冷却速度は水冷またはミストスプレー冷却などにより実現可能である。
【００１４】
請求項１記載発明で、焼入処理時の板材の温度勾配Ｌを下記（３）式を満足するように小さく規定する理由は、下記（３）式を外れると材料が熱収縮する際に変形して形状性（フラットネス）が悪化するためである。
１５００００×（ｔ³ ／ｂ）≧Ｌ.........（３）
但しｔはアルミニウム合金板の厚さ（ｍｍ）の数値、ｂは幅（ｍｍ）の数値、Ｌは温度勾配（℃／ｍ）の数値で、急冷開始直前の温度Ｐ（℃）と急冷開始位置から走行方向に１ｍ離れた位置の温度Ｑ（℃）を１（ｍ）で除した数値（〔Ｐ−Ｑ〕／１）である。
【００１５】
前記急冷と小温度勾配とを両立させる方法としては、（１）溶体化処理温度から４５０℃付近までを徐冷しそこから急冷する方法がある。この方法は４５０℃付近から急冷するので、規定温度範囲の冷却速度を上げ易く温度勾配は小さく抑えられる。また（２）高速通板すれば、急冷しても温度勾配を低く抑えることができる。
【００１６】
【実施例】
以下に本発明を実施例により詳細に説明する。
（実施例１）表１に示す本発明規定組成のアルミニウム合金（Ｎｏ．ａ〜ｉ）を常法により厚さ５００ｍｍのインゴットに溶解鋳造し、このインゴットを５４０℃で６時間均質化処理し、次いで圧延開始温度５００℃、圧延終了温度４２０℃で厚さ２５ｍｍに熱間粗圧延し、引続きタンデム式熱間圧延機により厚さ２．５ｍｍに仕上圧延し、次いで冷間圧延して厚さ１ｍｍ、板幅１５００ｍｍのアルミニウム合金素板とし、この素板に５４０℃で溶体化処理を施し、次いで種々条件で焼入処理を施してアルミニウム合金板を製造した。
【００１７】
（比較例１）実施例１において、表１に示す本発明規定組成外のアルミニウム合金（Ｎｏ．ｊ〜ｑ）を用いた他は、実施例１と同じ方法によりアルミニウム合金板を製造した。
【００１８】
実施例１および比較例１で製造した各々のアルミニウム合金板について、（１）形状性、また製造後１０日間室温に放置したのちの、（２）機械的性質、（３）曲げ加工性、（４）絞り成形性を調べた。結果を表２、３に示す。表２、３には（５）ＰＦＺの最大幅Ｗおよび（６）結晶粒径ｂを併記した。（１）〜（６）の測定方法などを以下に記す。
（１）形状性（フラットネス）
溶体化処理後に連続焼鈍炉から製出されるアルミニウム合金板を目視観察し、表面が平坦で実用上問題ないものは形状性が良好（○）、表面が平坦でなく実用が困難と思われるものは不良（×）と判定した。
（２）機械的性質（引張強さＴ、０．２％耐力Ｙ）
各々のアルミニウム合金板からＪＩＳ５号試験片を切り出しインストロン型引張試験機を用いて測定した。引張速度は１０ｍｍ／分とした。
（３）曲げ加工性
各々のアルミニウム合金板から所定形状の試験片を切り出し、この試験片について１８０°の密着曲げを行い、割れおよび肌荒れが全く生じないものは極めて良好（◎）、肌荒れが生じたが軽微で実用上差し支えないものは曲げ加工性が良好（○）、肌荒れが明確に生じたものまたは割れが生じたものは不良（×）と判定した。
（４）絞り成形性
各々のアルミニウム合金板から直径８．５ｍｍφのブランクを切り出し、しわ押さえ力３０００ｋｇｆで円筒絞り試験を行い、破断に至るまでのポンチの押込み深さが８．５ｍｍ以上のものは絞り成形性が良好（○）、８．５ｍｍ未満のものは不良（×）と判定した。
（５）ＰＦＺ幅Ｗ
Ｔ６処理した試験片の粒界近傍を、ビームの入射方向を（１００）面に合わせて透過電子顕微鏡写真を１０万倍で２視野撮影し、１視野あたり５箇所のＰＦＺ幅を測定し、合計１０箇所の平均値をＰＦＺ幅Ｗとした。
（６）結晶粒径ｂ
各々のアルミニウム合金板の表面を研磨し、エッチングして組織観察し、ＪＩＳＨ０５０１（切断法）に準じて測定した。
【００１９】
【表１】

【００２０】
【表２】

【００２１】
【表３】

【００２２】
表２、３から明らかなように、本発明例のＮｏ．１〜９は、いずれも形状性、機械的性質、曲げ加工性、絞り成形性の全てが良好であり、総合的にみて優れる評価を得た。これに対し、比較例のＮｏ．１１、１３はそれぞれＭｇ、Ｓｉが少なかったためいずれも機械的性質が低下し、また引張強さが低かったため（２）式が満足されず絞り成形性が劣った。Ｎｏ．１０、１２、１４〜１７は、それぞれＭｇ、Ｓｉ、Ｍｎ、Ｃｒ、Ｆｅ、Ｃｕが多かったため、いずれも曲げ加工性が低下し、Ｎｏ．１７は耐食性も低下し、総合評価はいずれも劣った。
【００２３】
（実施例２）表１に示す本発明規定組成のアルミニウム合金（Ｎｏ．ａ）を用い、実施例１と同じ方法によりアルミニウム合金素板を製造し、この素板に５４０℃で溶体化処理し、次いで焼入処理を冷却速度および温度勾配を本発明規定条件内で施してアルミニウム合金板を製造した。アルミニウム合金素板の厚さおよび幅は種々に変化させた。
【００２４】
（比較例２）実施例２において、焼入処理での温度勾配を本発明規定条件外（（３）式を外れる条件）で変化させた他は、実施例２と同じ方法によりアルミニウム合金板を製造した。
【００２５】
実施例２および比較例２で製造した各々のアルミニウム合金板について（１）形状性、（２）機械的性質、（３）曲げ加工性、（４）絞り成形性、（５）ＰＦＺ幅Ｗ、（６）結晶粒径ｂを実施例１の場合と同じ方法により調べた。結果を表４、５に示す。
【００２６】
【表４】

【００２７】
【表5】

【００２８】
表４、５から明らかなように、本発明例のＮｏ．２１〜２４は、いずれも形状性、機械的性質、曲げ加工性、絞り成形性の全てが良好であり、総合的にみて優れる評価を得た。これに対し、比較例のＮｏ．２５〜２８はいずれも形状性が劣った。これは焼入処理時の温度勾配が大きく（３）式を満足しなかったためで、総合評価はいずれも劣るものとなった。
【００２９】
（実施例３）表１に示す本発明規定組成のアルミニウム合金（Ｎｏ．ａ）を用い、実施例１と同じ方法により厚さ１．０ｍｍ、幅１５００ｍｍのアルミニウム合金素板を製造し、この素板に本発明規定条件内で溶体化処理および焼入処理を施してアルミニウム合金板を製造した。
【００３０】
（比較例３）実施例３において、焼入処理での冷却速度を本発明規定条件外で変化させた他は、実施例３と同じ方法によりアルミニウム合金板を製造した。
【００３１】
実施例３および比較例３で製造した各々のアルミニウム合金板について（１）形状性、（２）機械的性質、（３）曲げ加工性、（４）絞り成形性、（５）ＰＦＺ幅Ｗ、（６）結晶粒径ｂを実施例１の場合と同じ方法により調べた。結果を表６、７に示す。
【００３２】
【表６】

【００３３】
【表７】

【００３４】
表６、７から明らかなように、本発明例のＮｏ．３１〜３５は、いずれも形状性、機械的性質、曲げ加工性、絞り成形性の全てが良好であり、総合的にみて優れる評価を得た。これに対し、比較例のＮｏ．３６〜４０は、いずれも曲げ加工性が劣った。これはＰＦＺの幅Ｗが大きく（１）式を満足しなかったためで、総合評価はいずれも劣るものとなった。
【００３５】
本発明例のＮｏ．１〜９、２１〜２４、３１〜３５からＪＩＳ５号試験片を切り出し、これに２％のストレッチを付与したのち、１７０℃で２０分間（塗装焼付相当条件）加熱し、前記加熱前後の０．２％耐力（ＭＰａ）をインストロン型引張試験機を用いて測定し、両者の差（ΔＹ）を求めた。その結果、ΔＹはいずれも９０ＭＰａ以上ありベークハード性に優れることが確認された。
【００３６】
【発明の効果】
以上に説明したように、本発明の製造方法によるアルミニウム合金板は、形状性、機械的性質、曲げ加工性、絞り加工性、ベークハード性などに優れ、自動車ボディシートのアウター材やインナー材などに好適であり、このアルミニウム合金板はアルミニウム合金素板に所定条件で溶体化処理および焼入処理を施すことにより容易に製造することができる。依って、工業上顕著な効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an aluminum alloy plate excellent in bending workability and drawability suitable for automobile body sheets, automobile parts, machine parts and the like.
[0002]
[Prior art]
Automobiles are being made of aluminium such as body sheets. Outer materials are excellent in bake hardness (property that precipitates and hardens when heated during paint baking), and high strength after paint baking (6000 series) (Al-Mg- Si-based) aluminum alloys are frequently used, and 5000-based (Al-Mg-based) aluminum alloys having excellent drawability are used as the inner material.
[0003]
[Problems to be solved by the invention]
However, since the outer material is caulked with the inner material, it is required to be excellent in bending workability. However, the 6000 series aluminum alloy plate is inferior in bending workability, and is particularly subjected to solution treatment at a high temperature in order to improve the bake hardness. There was a problem that the material was remarkably inferior in bending workability. On the other hand, there is a movement to unify the inner material into a 6000 series aluminum alloy for the purpose of improving recyclability, and accordingly, it is an important issue to improve the drawability of the 6000 series aluminum alloy.
[0004]
Based on this situation, the present inventors examined the bending workability of the 6000 series aluminum alloy and formed a precipitation-free zone (PFZ) in the vicinity of the grain boundary during the aging treatment, and this PFZ is bent because of its low strength. We know that cracks become the starting point of cracking during processing, but they can be made harmless if the width is narrowed, and we know that drawability can be improved by increasing tensile strength and work-hardening properties. This has led to the completion of the present invention. An object of the present invention is to provide a method for producing an aluminum alloy plate excellent in bending workability and drawability.
[0005]
[Means for Solving the Problems]
Invention of Claim 1 contains Si0.5-1.3mass%, Mg0.25-1.0mass% as an essential element, Of Mn0.03-0.2mass%, Cr0.02-0.2mass% An aluminum alloy rolled sheet containing one or two of these and controlled to Fe 0.3 mass% or less and Cu 0.2 mass% or less is run, and solution treatment is continuously performed at a temperature of 480 ° C. or higher, followed by firing. The quenching treatment is performed by rapidly cooling a temperature range of 450 ° C. to 350 ° C. at a rate of 20 ° C./second or more, and performing a temperature gradient of the rolled sheet in the quenching treatment so as to satisfy the following expression (3). It is the manufacturing method of the aluminum alloy plate excellent in bending workability.
150,000 (t ^{3 /} b) ≧ L ( ³ )
However, t is a numerical value of the thickness (mm) of the aluminum alloy plate, b is a numerical value of the width (mm), L is a numerical value of the temperature gradient (° C./m), and the temperature P (° C.) immediately before the start of the rapid cooling and the rapid cooling start position Is a numerical value ([PQ] / 1) obtained by dividing the temperature Q (° C.) at a position 1 m away from the vehicle by 1 (m).
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Oite this onset bright, Mg and Si contributes to improving the strength of the aluminum alloy plate was precipitated as Mg ₂ Si compound. The reason for prescribing the Si content to 0.5 to 1.3 mass% is that the effect cannot be sufficiently obtained if it is less than 0.5 mass%, and if it exceeds 1.3 mass%, a coarse Si compound is precipitated. This is because bending workability is lowered. If Si is added excessively from a composition that balances the stoichiometry of Mg ₂ Si, the bake hardness is improved. The reason for defining the content of Mg in 0.25～1.0Mass%, the effect is insufficient at less than 0.25 mass%, it exceeds 1.0 mass% Mg ₂ Si compound a large amount of precipitation This is because bending workability is lowered.
[0007]
In the present invention, Mn or Cr refines crystal grains and improves bending workability. The reason why the contents of Mn or Cr are specified to be 0.03 to 0.2 mass% and 0.02 to 0.2 mass%, respectively, is that the effect is not sufficiently obtained if the content is less than the lower limit value, and exceeds the upper limit value. In both cases, a coarse compound precipitates and bending workability decreases.
[0008]
In the present invention, the reason for restricting Fe to 0.3 mass% or less is that when Fe is contained in excess of 0.3 mass%, the Fe-based compound is increased and bending workability is lowered. Moreover, the reason for restricting Cu to 0.2 mass% or less is that when Cu is contained in excess of 0.2 mass%, a Cu-based compound is precipitated at the crystal grain boundary, the bending workability is lowered, and the grain boundary is corroded. This is because it becomes easy and the corrosion resistance decreases.
[0009]
The present inventors examined bending workability, and found that the width of the precipitation-free zone (PFZ), which is the starting point of bending cracks, was reduced, and that the tensile strength, proof stress, and crystal grain size affected the width. Based on this finding, further studies were made to derive the following formula (1).
W ≦ (5250-15.3T + 8.6Y) / d (1)
Where T is a numerical value of tensile strength (MPa) when the aluminum alloy sheet is pulled in the rolling direction, Y is a numerical value of 0.2% proof stress (MPa) at that time, and d is an average crystal on the rolled surface of the aluminum alloy sheet. The numerical value of the particle diameter (μm) and W is the numerical value of the average width (nm) of the precipitation-free zone (PFZ).
[0010]
Hereinafter, the derivation process of the equation (1) will be described in detail. Cracks in bending work occur when the generated stress U (MPa) of the matrix when bending strain is applied exceeds the grain boundary fracture strength G (MPa). U is the sum of yield strength Y and work hardening due to bending strain, and it was found that it can be expressed by the following equation.
U = Y + 2.3 (T−Y), where T is tensile strength and Y is yield strength.
That is, the higher the strength, the greater the stress generated when bending strain is applied, and the bendability decreases. On the other hand, G depends on the PFZ width W (nm) and the particle size d (μm), and it is known that G increases as W and d are smaller. That is, even in a high-strength material, a decrease in bendability can be prevented by decreasing W and d and increasing G. Therefore, various relationships between W and U were investigated, and it was found that good bendability can be obtained when the relational expression of W ≦ (−0.19U + 150) × 35 / d is satisfied. By substituting U = Y + 2.3 (T−Y) into this relational expression, the expression (1) was derived.
[0011]
Next, the present inventors examined the drawability, and the drawability improved as the parameter T [T / Y] obtained by correcting the tensile strength (T) with the yield ratio [Y / T] is larger. Based on this knowledge, the following formula (2) was derived.
(T ^{2 /} Y) ≧ 430 ... ( ² )
However, T is a numerical value of tensile strength (MPa) when an aluminum alloy sheet is pulled in the rolling direction, and Y is a numerical value of 0.2% proof stress (MPa) at that time.
[0012]
The invention according to claim 1 is a method for manufacturing an aluminum alloy plate excellent in bending workability, drawability and shape (flatness) by defining each condition of solution treatment and quenching treatment.
[0013]
In the first aspect of the invention, the reason why the solution treatment temperature is specified to be 480 ° C. or more is that Mg and Si are not sufficiently solid-solved at a temperature lower than 480 ° C., and good bake hardness cannot be obtained. The reason why the quenching treatment is performed by rapidly cooling the temperature range of 450 ° C. to 350 ° C. at a rate of 20 ° C./second or more is that if the temperature range is rapidly cooled at the rate, precipitation of Mg, Si and excess vacancies The disappearance is suppressed, sufficient bake hardness is obtained, the width of the PFZ is sufficiently narrowed to obtain good bending workability, and if rapid cooling of 20 ° C./second or more is limited to the above temperature range, the shape property is improved. This is to prevent deterioration. The cooling rate of 20 ° C./second or more can be realized by water cooling or mist spray cooling.
[0014]
In the first aspect of the invention, the reason why the temperature gradient L of the plate material at the time of quenching is specified to be small so as to satisfy the following equation (3) is that if the material deviates from the following equation (3), it is deformed when the material is thermally contracted. This is because the shape (flatness) deteriorates.
150,000 × (t ^{3 /} b) ≧ L ( ³ )
However, t is a numerical value of the thickness (mm) of the aluminum alloy plate, b is a numerical value of the width (mm), L is a numerical value of the temperature gradient (° C./m), and the temperature P (° C.) immediately before the start of the rapid cooling and the rapid cooling start position Is a numerical value ([PQ] / 1) obtained by dividing the temperature Q (° C.) at a position 1 m away from the vehicle by 1 (m).
[0015]
As a method for achieving both the rapid cooling and the small temperature gradient, there is (1) a method of gradually cooling from the solution treatment temperature to around 450 ° C. and then rapidly cooling from there. Since this method rapidly cools from around 450 ° C., it is easy to increase the cooling rate in the specified temperature range, and the temperature gradient can be kept small. Further, (2) if the plate is passed at high speed, the temperature gradient can be kept low even if it is rapidly cooled.
[0016]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
(Example 1) An aluminum alloy (No. ai) of the present invention composition shown in Table 1 was melt-cast into a 500 mm-thick ingot by a conventional method, and this ingot was homogenized at 540 ° C for 6 hours. Next, hot rough rolling to a thickness of 25 mm at a rolling start temperature of 500 ° C. and a rolling end temperature of 420 ° C., followed by finish rolling to a thickness of 2.5 mm by a tandem hot rolling mill, followed by cold rolling to a thickness of 1 mm An aluminum alloy base plate having a width of 1500 mm was formed, and the base plate was subjected to a solution treatment at 540 ° C., and then subjected to a quenching treatment under various conditions to produce an aluminum alloy plate.
[0017]
(Comparative example 1) In Example 1, the aluminum alloy plate was manufactured by the same method as Example 1 except having used the aluminum alloy (No.j-q) outside the composition prescribed in the present invention shown in Table 1.
[0018]
About each aluminum alloy plate manufactured in Example 1 and Comparative Example 1, (2) mechanical properties after being left at room temperature for 10 days after manufacturing, (3) bending workability, ( 4) The drawability was examined. The results are shown in Tables 2 and 3. Tables 2 and 3 also show (5) the maximum width W of PFZ and (6) the crystal grain size b. The measuring methods (1) to (6) are described below.
(1) Shape (flatness)
The aluminum alloy sheet produced from the continuous annealing furnace after the solution treatment is visually observed. If the surface is flat and there is no practical problem, the shape is good (○). It was determined to be defective (x).
(2) Mechanical properties (tensile strength T, 0.2% proof stress Y)
A JIS No. 5 test piece was cut out from each aluminum alloy plate and measured using an Instron type tensile tester. The tensile speed was 10 mm / min.
(3) Bending workability A test piece of a predetermined shape is cut out from each aluminum alloy plate, and the test piece is subjected to close contact bending at 180 °. If the test piece does not cause any cracks or rough skin, it is extremely good (◎). However, those that were minor and could be used practically were judged to have good bending workability (◯), and those that had rough skin or cracks were judged to be defective (x).
(4) Drawing formability Blanks with a diameter of 8.5 mmφ were cut out from each aluminum alloy plate, subjected to a cylindrical drawing test with a wrinkle holding force of 3000 kgf, Those having good drawability (◯) and less than 8.5 mm were determined to be defective (×).
(5) PFZ width W
The vicinity of the grain boundary of the T6-treated specimen is aligned with the (100) plane of the beam, two transmission electron micrographs are taken at a magnification of 100,000, and five PFZ widths are measured per field. The average value at 10 locations was defined as the PFZ width W.
(6) Crystal grain size b
The surface of each aluminum alloy plate was polished, etched, microstructured, and measured according to JIS H 0501 (cutting method).
[0019]
[Table 1]

[0020]
[Table 2]

[0021]
[Table 3]

[0022]
As is apparent from Tables 2 and 3, No. of the present invention example. All of Nos. 1 to 9 were excellent in formability, mechanical properties, bending workability, and drawability, and were comprehensively evaluated. In contrast, No. of the comparative example. 11 and 13 were low in Mg and Si, respectively, so the mechanical properties were both lowered, and the tensile strength was low, so the formula (2) was not satisfied and the drawability was inferior. No. Nos. 10, 12, and 14 to 17 each had a large amount of Mg, Si, Mn, Cr, Fe, and Cu. No. 17 also deteriorated the corrosion resistance, and the overall evaluation was inferior.
[0023]
(Example 2) Using an aluminum alloy (No. a) of the present invention composition shown in Table 1, an aluminum alloy base plate was manufactured by the same method as in Example 1, and this base plate was subjected to solution treatment at 540 ° C. Then, a quenching process was performed with a cooling rate and a temperature gradient within the conditions specified in the present invention to produce an aluminum alloy plate. The thickness and width of the aluminum alloy base plate were variously changed.
[0024]
(Comparative Example 2) In Example 2, the aluminum alloy plate was prepared by the same method as in Example 2 except that the temperature gradient in the quenching process was changed outside the conditions specified in the present invention (conditions outside Formula (3)). Manufactured.
[0025]
About each aluminum alloy plate manufactured in Example 2 and Comparative Example 2, (1) shape, (2) mechanical properties, (3) bending workability, (4) drawability, (5) PFZ width W, (6) The crystal grain size b was examined by the same method as in Example 1. The results are shown in Tables 4 and 5.
[0026]
[Table 4]

[0027]
[Table 5]

[0028]
As is apparent from Tables 4 and 5, No. of the present invention example. All of Nos. 21 to 24 were excellent in shape, mechanical properties, bending workability, and drawability, and were excellent overall. In contrast, No. of the comparative example. Any of 25-28 was inferior in shape. This was because the temperature gradient during the quenching treatment was large and the expression (3) was not satisfied, and the overall evaluation was inferior.
[0029]
(Example 3) An aluminum alloy base plate having a thickness of 1.0 mm and a width of 1500 mm was manufactured by the same method as Example 1 using an aluminum alloy (No. a) of the present invention composition shown in Table 1. An aluminum alloy plate was manufactured by subjecting the plate to solution treatment and quenching treatment within the conditions specified in the present invention.
[0030]
(Comparative Example 3) An aluminum alloy plate was manufactured in the same manner as in Example 3, except that the cooling rate in the quenching process was changed outside the conditions specified in the present invention.
[0031]
About each aluminum alloy plate manufactured in Example 3 and Comparative Example 3, (1) shape, (2) mechanical properties, (3) bending workability, (4) drawability, (5) PFZ width W, (6) The crystal grain size b was examined by the same method as in Example 1. The results are shown in Tables 6 and 7.
[0032]
[Table 6]

[0033]
[Table 7]

[0034]
As is apparent from Tables 6 and 7, No. Nos. 31 to 35 were all excellent in formability, mechanical properties, bending workability, and drawability, and obtained an overall excellent evaluation. In contrast, No. of the comparative example. 36 to 40 were all inferior in bending workability. This is because the width W of the PFZ is large and does not satisfy the expression (1), and the overall evaluation is inferior.
[0035]
No. of the example of the present invention. A JIS No. 5 test piece was cut out from 1-9, 21-24, 31-35, and 2% stretch was applied thereto, and then heated at 170 ° C. for 20 minutes (equivalent condition for paint baking). 2% yield strength (MPa) was measured using an Instron type tensile tester, and the difference (ΔY) between the two was determined. As a result, ΔY was 90 MPa or more, and it was confirmed that the bake hardness was excellent.
[0036]
【Effect of the invention】
As described above, the aluminum alloy plate according to the production method of the present invention is excellent in formability, mechanical properties, bending workability, drawing workability, bake hardness, and the like, such as an outer material and an inner material of an automobile body sheet. This aluminum alloy plate can be easily manufactured by subjecting an aluminum alloy base plate to solution treatment and quenching treatment under predetermined conditions. Therefore, there is an industrially significant effect.

Claims

Including Si 0.5-1.3 mass%, Mg0.25-1.0 mass% as essential elements, including one or two of Mn0.03-0.2 mass%, Cr0.02-0.2 mass% An aluminum alloy rolled sheet regulated to Fe 0.3 mass% or less and Cu 0.2 mass% or less is run, and solution treatment is continuously performed at a temperature of 480 ° C. or higher, followed by quenching treatment from 450 ° C. to 350 ° C. Excellent bending workability, characterized in that the temperature range of ℃ is rapidly cooled at a rate of 20 ℃ / second or more, and the temperature gradient of the rolled sheet in the quenching treatment is applied so as to satisfy the following formula (3) A method for producing an aluminum alloy plate.
150,000 (t ^{3 /} b) ≧ L ( ³ )
However, t is a numerical value of the thickness (mm) of the aluminum alloy plate, b is a numerical value of the width (mm), L is a numerical value of the temperature gradient (° C./m), and the temperature P (° C.) immediately before the start of the rapid cooling and the rapid cooling start position Is a numerical value ([PQ] / 1) obtained by dividing the temperature Q (° C.) at a position 1 m away from the vehicle by 1 (m).