JP4591986B2

JP4591986B2 - Aluminum alloy sheet for transportation-related structures with excellent paintability and press formability

Info

Publication number: JP4591986B2
Application number: JP2001153176A
Authority: JP
Inventors: 克己小山; 昭男新倉
Original assignee: Furukawa Sky Aluminum Corp
Current assignee: Furukawa Sky Aluminum Corp
Priority date: 2001-05-22
Filing date: 2001-05-22
Publication date: 2010-12-01
Anticipated expiration: 2021-05-22
Also published as: JP2002348629A

Description

【０００１】
【発明の属する技術分野】
本発明は、所要の強度を有し、かつ塗装性およびプレス成形性に優れた輸送関連構造体用アルミニウム合金板材に関する。
【０００２】
【従来の技術】
これまで、自動車などの構造体には、スチールが多用されてきたが、近年、自動車の環境に対する負荷が問題視され、それに応じて、所要強度が得られ、かつ軽量で燃費節減に有利なアルミニウム合金板材が注目されるようになった。
前記アルミニウム合金板材には、加工硬化型の５０００系（Ａｌ−Ｍｇ系）合金、塗装焼き付け時の熱で析出硬化する６０００系（Ａｌ−Ｍｇ−Ｓｉ系）合金、５０００系合金のＭｇ量を増やしＣｒなどを微量添加した新合金（特開平７−３１０１３６号公報）などが提案された。
【０００３】
【発明が解決しようとする課題】
しかし、輸送関連構造体は、一般に塗装して用いられるが、前記従来の合金板材は、いずれも曲げ加工部の塗膜が剥離し易く塗装性に劣り、プレス成形時には割れが生じ易いという問題があった。
【０００４】
このようなことから、本発明者等は、前記従来の合金板材が塗装性およびプレス成形性に劣る原因を調べ、従来の合金板材は結晶粒が粗大で結晶粒の方位差に起因して曲げ加工部に凹凸が顕著に現れるのが原因であることを突き止め、前記凹凸（以下、肌荒れと称す）は表層部の結晶粒径を適度に微細化することで改善し得ること、また前記プレス成形性はアルミニウム合金板材の結晶粒径を表層部より中央部で大きくすることで改善し得ることを見いだし、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、所要の強度を有し、かつ塗装性およびプレス成形性に優れた輸送関連構造体用アルミニウム合金板材を提供するにある。
【０００５】
【課題を解決するための手段】
請求項１記載の発明は、Ｓｉを０．０７〜０．１８mass％、Ｍｇを４．３５〜４．７５mass％、Ｃｕを０．０５〜０．１５mass％、Ｆｅを０．０７〜０．３５mass％、Ｍｎを０．２５〜０．４５mass％、Ｃｒを０．０２〜０．０５mass％、Ｔｉを０．００１〜０．１mass％含有し、Ｎａを０．０００５mass％以下、Ｃａを０．００１０mass％以下に規制し、残部がＡｌおよび不可避不純物からなるアルミニウム合金板材であって、その板厚方向に計測した平均結晶粒径が表層部で１０μｍ以下、中央部で表層部の１．２倍以上であることを特徴とする塗装性およびプレス成形性に優れた輸送関連構造体用アルミニウム合金板材である。
【０００６】
請求項２記載の発明は、アルミニウム合金板材の厚さが０．５〜５．５ｍｍであることを特徴とする請求項１記載の塗装性およびプレス成形性に優れた輸送関連構造体用アルミニウム合金板材である。
【０００７】
【発明の実施の形態】
以下に、本発明のアルミニウム合金板材（以下、適宜、板材と略記する。）の合金組成について説明する。
Ｍｇは、主にアルミニウムマトリックスに固溶して、板材の強度およびプレス成形性を向上させる。
その含有量が４．３５mass％未満では前記効果が十分に得られず、４．７５mass％を超えると圧延加工性が低下する。
【０００８】
Ｓｉは鋳造時にＦｅやＭｎなどと晶出物を生成し、この晶出物が再結晶核となって板材の結晶粒径を適度（１０μｍ以下）に微細化し、曲げ加工部の肌荒れを防止し、以て塗装性を改善する。
その含有量が０．０７mass％未満では前記結晶粒径を適度に微細化させる効果が十分に得られず、０．１８mass％を超えるとＳｉは固溶Ｍｇと反応して固溶Ｍｇを著しく減少させるため十分な強度およびプレス成形性が得られなくなる。
【０００９】
Ｃｕは固溶および析出して強度向上に寄与する。
その含有量が０．０５mass％未満では前記効果が十分に得られず、０．１５mass％を超えるとプレス成形性が低下する。
【００１０】
Ｆｅは前述のようにＳｉやＭｎなどと晶出物を生成して結晶粒径を適度に微細化する。
その含有量が０．０７mass％未満では前記効果が十分に得られず、０．３５mass％を超えると巨大な不溶性化合物が生成し、これが成形加工時に割れの起点となるためプレス成形性が低下する。
【００１１】
Ｍｎも前述のようにＳｉやＦｅなどと晶出物を生成して結晶粒径を適度に微細化し、また一部は固溶して強度向上に寄与する。
その含有量が０．２５mass％未満では前記効果が十分に得られず、０．４５mass％を超えるとＦｅの場合と同じ理由でプレス成形性が低下する。
【００１２】
Ｃｒは析出して結晶粒径を適度に微細化する効果を有する。
その含有量が０．０２mass％未満では前記効果が十分に得られず、０．０５mass％を超えると前記ＦｅやＭｎの場合と同じ理由でプレス成形性が低下する。
【００１３】
Ｔｉは鋳塊の凝固セルを微細化して圧延加工性を改善する。
その含有量が０．００１mass％未満では前記効果が十分に得られず、０．１mass％を超えると前記Ｆｅなどの場合と同じ理由でプレス成形性が低下する。
【００１４】
ＮａおよびＣａは結晶粒界に偏析して熱間圧延割れの原因になる。そのためＮａは０．０００５mass％以下に、Ｃａは０．００１mass％以下にそれぞれ規制する。
【００１５】
本発明において、板材の厚さ方向に計測した平均結晶粒径を表層部で１０μｍ以下に規定する理由は、表層部の平均結晶粒径が１０μｍを超えると曲げ加工部が肌荒れして、その部分の塗装性が低下するためである。
また板材中央部の平均結晶粒径を前記表層部の１．２倍以上に規定する理由は、前記表層部と中央部の結晶粒径の差によりプレス成形時の表層部と中央部の負荷応力差が緩和されてプレス成形性が改善されるためである。
なお、本発明において、表層部とは、図１に示すように、板材の厚さをｔとしたとき、表面から０．１ｔまでの部分を言い、中央部とは表面から０．４〜０．６ｔの部分を言う。
【００１６】
本発明の板材は、Ｓｉ、Ｆｅ、Ｍｎ、Ｃｒなどの元素が適量含有されているため、板材の厚さ方向の平均結晶粒径が適度（１０μｍ以下）に微細化される。
本発明では、前記板材中央部の平均結晶粒径を表層部より大きくするが、その方法は、例えば、表面の摩擦力が適度に調整された圧延ロールを用いて板厚方向に応力分布を生じさせつつ圧延する方法が挙げられる。
この場合、圧延ロール表面の摩擦力が大き過ぎると板材表面の品質が低下することがあるので注意を要する。
【００１７】
前記圧延ロール表面の摩擦力は、ロール表面粗度、クーラントの種類、圧延温度などにより制御する。
前記板材表層部と中央部で結晶粒径に差をつける方法は、板材の厚さが０．５〜５．５ｍｍにおいて最も良好に行える。
【００１８】
本発明では、Ｓｉ、Ｍｇ、Ｃｕ、Ｆｅ、Ｍｎ、Ｃｒ、Ｔｉを適量含有しているため、肌荒れが生じず、プレス成形性に優れ、所要強度が得られる。さらにＮａおよびＣａの量を低く規制するので圧延加工などの製造加工性に優れる。
【００１９】
本発明の板材の調質状態は、プレス成形性を重視する場合は熱間圧延板材または低転位密度の焼鈍板材が良く、強度を重視する場合は圧延率３０％以下の冷間圧延板材が良い。
【００２０】
本発明において、板材表面の酸化膜が厚すぎると、塗装の際に塗膜が剥離し易くなるので、酸化膜厚さは０．１μｍ以下が望ましい。特に本発明のように表層の結晶粒径が適度に微細な場合は、塗膜との界面に結晶配列が乱れた粒界が多く含まれるため剥離し易い。酸化膜を薄くする方法としては、酸またはアルカリ液でエッチングする方法が簡便で推奨される。但し、酸化膜が５ｎｍよりも薄くなるとプレス成形時に金型に凝着が生じたり、ハンドリング時に傷が付き易くなるので酸化膜の厚さは５ｎｍ以上が良い。
【００２１】
本発明の板材は、途中工程または最終工程で、テンションレベラーやロールレベラーによる矯正、或いは軽圧下圧延（スキンパス）などを行って平坦度を高めておくと、後のプレス成形などが良好に行えて望ましい。
【００２２】
【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を半連続鋳造法により鋳造し、製出鋳塊に面削および均質化処理を施し、次いでリバース式熱間粗圧延機により熱間圧延して厚さ３０ｍｍの熱延板とし、この熱延板を４スタンドのタンデム型熱間仕上圧延機により圧延して厚さ２ｍｍの板材の熱延コイルを製造した。
熱間仕上圧延機の最終スタンドで、圧下量、圧延温度、圧延速度、クーラント吐出量を調整して、前記板材（再結晶組織）の結晶粒径およびその分布を本発明で規定する範囲内で種々に変化させた。
【００２３】
（比較例１）
表１に示す本発明規定外組成のアルミニウム合金を用いた他は、実施例１と同じ方法により熱延コイルを製造した。
【００２４】
（比較例２）
表１に示した本発明規定組成のＮｏ．１の合金を用い、ロール表面の摩擦力および圧延温度を実施例１とは異なる条件で圧延して結晶粒径およびその分布を本発明規定外とした。その他は実施例１と同じ方法により熱延コイルを製造した。
【００２５】
実施例１および比較例１、２で製造した各々の熱延コイルから試験片をサンプリングして、平均結晶粒径、引張特性、絞り成形性（プレス成形性）、曲げ加工性を調べた。
結晶粒径は、板材を縦に切断し、切断面を研磨し、エッチングして、板材の一方の表層部から他方の表層部にかけて疑似ラインを引き、前記疑似ラインを横切る結晶粒界数を光学顕微鏡で測定し、その平均結晶粒径を表層部（表面から０．２ｍｍまでの外側部分）と中央部（表面から０．８〜１．２ｍｍの中央部分）について求めた。
引張特性は、ＪＩＳ５号引張試験片を作製し、これをＪＩＳＺ２２４１に準じて引張試験して調べた。絞り成形性は直径４０ｍｍの平頭パンチを用いた深絞り試験により調べた。曲げ加工性は、曲げ半径０ｔで１８０度曲げ加工し、曲げ加工部の表面を観察し肌荒れの有無で評価した。結果を表２に示す。
【００２６】
【表１】

【００２７】
【表２】

【００２８】
表２から明らかなように、本発明例のＮｏ．１〜４はいずれも引張特性および絞り成形性が優れた。
これに対し、比較例のＮｏ．５はＭｇが少ないため、Ｎｏ．７はＣｕが少ないためいずれも強度が低く、Ｎｏ．９はＳｉおよびＦｅが少ないため表層の平均結晶粒径が大きくなり、曲げ加工部に肌荒れが生じた。Ｎｏ．５は絞り成形性も劣った。Ｎｏ．１１はＭｎが多いため、絞り成形性が低下した。Ｎｏ．６、８、１０はそれぞれＭｇ、Ｃｕ、Ｍｎが多いため、圧延加工で割れが多発した。Ｎｏ．１２、１３は表層部の結晶粒径が大きいため曲げ加工部に肌荒れが生じて塗装性が劣った。さらにＮｏ．１３は表層部と中央部の結晶粒径が同等なため、絞り成形性が劣った。Ｎｏ．１４は表層部の結晶粒径が小さいため肌荒れは生じなかったが、表層部と中央部の結晶粒径が同じため、絞り成形性が劣った。
【００２９】
前記実施例１の本発明例の板材は、熱間圧延時に割れが生じたりせず、いずれも製造加工性に優れた。また塩水噴霧試験を行ったが、いずれも良好な耐食性を示した。
【００３０】
【発明の効果】
本発明のアルミニウム合金板材は、Ｓｉ、Ｍｇ、Ｃｕ、Ｆｅ、Ｍｎ、Ｃｒ、Ｔｉを適量含有し、ＮａおよびＣａの量を低く抑えたので、構造体に必要な強度を有し、製造加工時に割れなどが生じず、また表層部の結晶粒径が適度に微細化されるため曲げ加工部に肌荒れが生じずに塗装性に優れ、さらに中央部の結晶粒径が表層部より大きいので表層部と中央部の負荷応力差が緩和されてプレス成形性にも優れる。従って、自動車などの輸送関連構造体に用いて有用であり工業上顕著な効果を奏する。
【図面の簡単な説明】
【図１】本発明のアルミニウム合金板材における表層部と中央部の説明図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aluminum alloy sheet material for transportation-related structures having a required strength and excellent paintability and press formability.
[0002]
[Prior art]
Up to now, steel has been used extensively in automobiles and other structures, but in recent years the burden on the environment of automobiles has been regarded as a problem, and accordingly, the required strength can be obtained, and it is lightweight and advantageous for fuel economy. Alloy plate materials have been attracting attention.
The aluminum alloy plate material includes a work hardening type 5000 (Al-Mg) alloy, a 6000 (Al-Mg-Si) alloy that precipitates and hardens with heat during paint baking, and an increased amount of Mg in the 5000 alloy. A new alloy (Japanese Patent Laid-Open No. 7-310136) to which a small amount of Cr or the like is added has been proposed.
[0003]
[Problems to be solved by the invention]
However, the transport-related structures are generally used after being painted, but all of the conventional alloy sheet materials have a problem that the coating film of the bent portion is easy to peel off and the paintability is inferior, and cracks are likely to occur during press molding. there were.
[0004]
For this reason, the present inventors investigated the cause of the above-described conventional alloy plate material being inferior in paintability and press formability, and the conventional alloy plate material has coarse crystal grains and is bent due to the difference in crystal grain orientation. Ascertaining that unevenness appears in the processed part is the cause, the unevenness (hereinafter referred to as rough skin) can be improved by appropriately miniaturizing the crystal grain size of the surface layer part, and the press molding It has been found that the crystallinity of the aluminum alloy plate can be improved by increasing the crystal grain size of the aluminum alloy sheet at the center portion rather than the surface layer portion, and further studies have been made to complete the present invention. An object of the present invention is to provide an aluminum alloy sheet for a transport-related structure having a required strength and excellent paintability and press formability.
[0005]
[Means for Solving the Problems]
The invention described in claim 1 is that Si is 0.07 to 0.18 mass%, Mg is 4.35 to 4.75 mass%, Cu is 0.05 to 0.15 mass%, and Fe is 0.07 to 0.35 mass%. %, Mn 0.25 to 0.45 mass%, Cr 0.02 to 0.05 mass%, Ti 0.001 to 0.1 mass%, Na 0.0005 mass% or less, Ca 0.0010 mass %, And the balance is an aluminum alloy plate made of Al and inevitable impurities, and the average crystal grain size measured in the thickness direction is 10 μm or less at the surface layer portion, and 1.2 times or more of the surface layer portion at the center portion It is an aluminum alloy sheet material for transport-related structures excellent in paintability and press formability.
[0006]
The invention according to claim 2 is characterized in that the aluminum alloy sheet has a thickness of 0.5 to 5.5 mm. The aluminum alloy for transport-related structures having excellent paintability and press formability according to claim 1 It is a board material.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Below, the alloy composition of the aluminum alloy sheet material of the present invention (hereinafter, abbreviated as a sheet material as appropriate) will be described.
Mg is mainly dissolved in the aluminum matrix to improve the strength and press formability of the plate material.
If the content is less than 4.35 mass%, the above effect cannot be obtained sufficiently, and if it exceeds 4.75 mass%, the rolling processability is lowered.
[0008]
Si produces crystallized substances such as Fe and Mn at the time of casting, and these crystallized substances become recrystallization nuclei to refine the crystal grain size of the plate material to an appropriate level (less than 10 μm), thereby preventing roughening of the bent part. Thus, paintability is improved.
If the content is less than 0.07 mass%, the effect of appropriately refining the crystal grain size cannot be obtained sufficiently, and if it exceeds 0.18 mass%, Si reacts with solid solution Mg to significantly reduce solid solution Mg. Therefore, sufficient strength and press formability cannot be obtained.
[0009]
Cu dissolves and precipitates and contributes to strength improvement.
If the content is less than 0.05 mass%, the above effect cannot be obtained sufficiently, and if it exceeds 0.15 mass%, the press formability decreases.
[0010]
As described above, Fe forms a crystallized product such as Si and Mn to appropriately refine the crystal grain size.
If the content is less than 0.07 mass%, the above effect cannot be obtained sufficiently, and if it exceeds 0.35 mass%, a huge insoluble compound is formed, which becomes a starting point of cracking during molding processing, so that press formability is lowered. .
[0011]
As described above, Mn also forms crystallized substances such as Si and Fe to appropriately refine the crystal grain size, and partly dissolves and contributes to strength improvement.
If the content is less than 0.25 mass%, the above effect cannot be obtained sufficiently, and if it exceeds 0.45 mass%, the press formability deteriorates for the same reason as in the case of Fe.
[0012]
Cr has the effect of precipitating and appropriately reducing the crystal grain size.
If the content is less than 0.02 mass%, the above effect cannot be obtained sufficiently, and if it exceeds 0.05 mass%, the press formability deteriorates for the same reason as in the case of Fe or Mn.
[0013]
Ti refines the ingot solidification cell to improve rolling processability.
If the content is less than 0.001 mass%, the above effect cannot be obtained sufficiently, and if it exceeds 0.1 mass%, the press formability deteriorates for the same reason as in the case of Fe or the like.
[0014]
Na and Ca segregate at the grain boundaries and cause hot rolling cracks. Therefore, Na is regulated to 0.0005 mass% or less, and Ca is regulated to 0.001 mass% or less.
[0015]
In the present invention, the reason why the average crystal grain size measured in the thickness direction of the plate material is defined as 10 μm or less in the surface layer part is that when the average crystal grain size of the surface layer part exceeds 10 μm, the bent part becomes rough, and the part This is because the paintability of the resin deteriorates.
The reason why the average crystal grain size in the central part of the plate material is specified to be 1.2 times or more that of the surface layer part is that the load stress in the surface layer part and the central part during press molding is due to the difference in crystal grain size between the surface layer part and the central part This is because the difference is relaxed and the press formability is improved.
In the present invention, as shown in FIG. 1, the surface layer portion means a portion from the surface to 0.1 t when the thickness of the plate material is t, and the central portion is 0.4 to 0 from the surface. .6t part.
[0016]
Since the plate material of the present invention contains an appropriate amount of elements such as Si, Fe, Mn, and Cr, the average crystal grain size in the thickness direction of the plate material is appropriately refined (10 μm or less).
In the present invention, the average crystal grain size of the central portion of the plate material is made larger than that of the surface layer portion, but the method produces stress distribution in the plate thickness direction using, for example, a rolling roll whose surface frictional force is appropriately adjusted. And rolling while rolling.
In this case, if the frictional force on the surface of the rolling roll is too large, the quality of the plate material surface may be deteriorated, so care must be taken.
[0017]
The frictional force on the surface of the rolling roll is controlled by roll surface roughness, coolant type, rolling temperature, and the like.
The method of making a difference in crystal grain size between the surface layer portion and the central portion of the plate material can be best performed when the thickness of the plate material is 0.5 to 5.5 mm.
[0018]
In the present invention, since appropriate amounts of Si, Mg, Cu, Fe, Mn, Cr, and Ti are contained, rough skin does not occur, the press formability is excellent, and the required strength is obtained. Furthermore, since the amount of Na and Ca is regulated to be low, it is excellent in manufacturing processability such as rolling.
[0019]
The tempered state of the plate material of the present invention is preferably a hot rolled plate material or a low dislocation density annealed plate material when emphasizing press formability, and a cold rolled sheet material with a rolling rate of 30% or less when emphasizing strength. .
[0020]
In the present invention, if the oxide film on the surface of the plate material is too thick, the coating film is easily peeled off during coating, so the oxide film thickness is preferably 0.1 μm or less. In particular, when the crystal grain size of the surface layer is moderately fine as in the present invention, it is easy to peel off because there are many grain boundaries with disordered crystal arrangement at the interface with the coating film. As a method of thinning the oxide film, a method of etching with an acid or alkali solution is simple and recommended. However, if the oxide film is thinner than 5 nm, adhesion to the mold is likely to occur during press molding or scratches are likely to occur during handling, so the thickness of the oxide film is preferably 5 nm or more.
[0021]
If the flatness of the plate material of the present invention is improved by performing tension leveler or roll leveler correction, or light rolling (skin pass) in the middle or final step, the subsequent press molding can be performed satisfactorily. desirable.
[0022]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
Example 1
The aluminum alloy having the composition defined in the present invention shown in Table 1 is cast by a semi-continuous casting method, the produced ingot is subjected to chamfering and homogenizing treatment, and then hot rolled by a reverse hot roughing mill to obtain a thickness A 30 mm hot-rolled sheet was used, and the hot-rolled sheet was rolled by a 4-stand tandem hot finish rolling mill to produce a hot-rolled coil having a thickness of 2 mm.
In the final stand of the hot finishing mill, the reduction amount, rolling temperature, rolling speed, coolant discharge amount are adjusted, and the crystal grain size and distribution of the plate material (recrystallized structure) are within the range specified in the present invention. Various changes were made.
[0023]
(Comparative Example 1)
A hot rolled coil was manufactured by the same method as in Example 1 except that an aluminum alloy having a composition outside the scope of the present invention shown in Table 1 was used.
[0024]
(Comparative Example 2)
No. of the composition prescribed in the present invention shown in Table 1. Using the alloy No. 1, the roll surface friction force and rolling temperature were rolled under conditions different from those in Example 1, and the crystal grain size and its distribution were out of the scope of the present invention. Other than that, a hot-rolled coil was manufactured in the same manner as in Example 1.
[0025]
Samples were sampled from the hot rolled coils produced in Example 1 and Comparative Examples 1 and 2, and the average crystal grain size, tensile properties, drawability (press formability), and bending workability were examined.
The crystal grain size is obtained by cutting a plate material vertically, polishing the cut surface, etching, drawing a pseudo line from one surface layer portion of the plate material to the other surface layer portion, and optically measuring the number of crystal grain boundaries crossing the pseudo line. It measured with the microscope and the average crystal grain diameter was calculated | required about the surface layer part (outer part from the surface to 0.2 mm) and the center part (center part of 0.8-1.2 mm from the surface).
The tensile properties were examined by preparing a JIS No. 5 tensile test piece and performing a tensile test according to JIS Z 2241. The drawability was examined by a deep drawing test using a flat head punch having a diameter of 40 mm. The bending workability was evaluated by the presence or absence of rough skin by bending 180 degrees with a bending radius of 0 t, observing the surface of the bent portion. The results are shown in Table 2.
[0026]
[Table 1]

[0027]
[Table 2]

[0028]
As is apparent from Table 2, the No. of the present invention example. 1-4 were excellent in tensile properties and drawability.
In contrast, No. of the comparative example. No. 5 has less Mg, so No. 7 is low in strength because there is little Cu. In No. 9, since the amount of Si and Fe was small, the average crystal grain size of the surface layer was large, and roughening occurred in the bent portion. No. No. 5 was also inferior in drawability. No. Since No. 11 had a large amount of Mn, the drawability decreased. No. Since 6, 8, and 10 each had a large amount of Mg, Cu, and Mn, cracks frequently occurred during rolling. No. In Nos. 12 and 13, since the crystal grain size of the surface layer portion was large, the bent portion was rough and the paintability was inferior. Furthermore, no. No. 13 was inferior in drawability because the crystal grain size of the surface layer portion and the central portion were equal. No. In No. 14, the crystal grain size of the surface layer portion was small, so no roughening occurred.
[0029]
The plate material of the inventive example of Example 1 was not cracked during hot rolling, and all were excellent in manufacturing processability. In addition, a salt spray test was performed, and all showed good corrosion resistance.
[0030]
【The invention's effect】
The aluminum alloy plate material of the present invention contains appropriate amounts of Si, Mg, Cu, Fe, Mn, Cr, and Ti, and has low strength of Na and Ca. No cracking, etc., and the crystal grain size of the surface layer portion is appropriately refined, so that the surface of the bent portion is excellent in paintability without rough skin, and the crystal grain size in the central portion is larger than the surface layer portion. And the load stress difference in the central part is alleviated and the press formability is excellent. Therefore, it is useful for transportation-related structures such as automobiles and has an industrially significant effect.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a surface layer portion and a central portion in an aluminum alloy sheet material of the present invention.

Claims

0.07 to 0.18 mass% for Si, 4.35 to 4.75 mass% for Mg, 0.05 to 0.15 mass% for Cu, 0.07 to 0.35 mass% for Fe, and 0.25 to Mn 0.45 mass%, Cr is contained in 0.02 to 0.05 mass%, Ti is contained in 0.001 to 0.1 mass%, Na is regulated to 0.0005 mass% or less, Ca is regulated to 0.0010 mass% or less, and the balance is An aluminum alloy plate made of Al and inevitable impurities, the average crystal grain size measured in the thickness direction of the surface layer portion being 10 μm or less, and the center portion being 1.2 times or more of the surface layer portion Aluminum alloy sheet for transport-related structures that excels in pressability and press formability.

The aluminum alloy sheet for transport-related structures excellent in paintability and press formability according to claim 1, wherein the thickness of the aluminum alloy sheet is 0.5 to 5.5 mm.