JP2004225157A

JP2004225157A - Highly corrosion-resistant coated steel plate having excellent sharpness

Info

Publication number: JP2004225157A
Application number: JP2003121686A
Authority: JP
Inventors: Kazuhiko Honda; 和彦本田; Hidetoshi Hatanaka; 英利畑中
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-11-27
Filing date: 2003-04-25
Publication date: 2004-08-12
Anticipated expiration: 2023-04-25
Also published as: JP3793522B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly corrosion-resistant coated steel plate having excellent sharpness. <P>SOLUTION: A galvannealed layer having the composition consisting of, by mass, 4-22% Al, 1-5% Mg, ≤ 0.1% Ti, and ≤ 0.5% Si as necessary, and the balance Zn with inevitable impurities is formed on the surface of a steel plate. The chemical conversion coating film of a chromate film or a phosphate film is formed as an intermediate layer, and an organic coating layer of 0.2-100 μm is formed as a top layer. A galvanized layer has a metal structure in which one or two or more kinds of [Al phase], [Zn<SB>2</SB>Mg phase], and [Zn phase] are mixed in a base metal of [three-element eutectic structure of Al/Zn/Zn<SB>2</SB>Mg], and Ti-Al intermetallic compounds are contained in one or two or more kinds of [Al phase], [Zn<SB>2</SB>Mg phase], and [Zn phase]. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、塗装鋼板に係わり、更に詳しくは優れた耐食性を有し、種々の用途、例えば、家電用や建材用鋼板として適用できる塗装鋼板に関するものである。
【０００２】
【従来の技術】
塗装金属板は、金属板を先に成形加工して複雑な形状物とした後に塗装を加える方式に比べ、塗装工程が合理化できる、品質が均一になる、塗料の消費量が節約される等の利点があることから、これまで多く使用されており、今後とも使用量は増加すると考えられる。
【０００３】
一般に塗装金属板は、冷延鋼板、亜鉛めっき系鋼板、その他の金属板に予め塗装をした後、任意の形状に成形加工して最終の用途に供するものであり、例えば、冷蔵庫、洗濯機、電子レンジなどの家電製品、自動販売機、事務機器、自動車、エアコン室外機などの金属製品に用いられている。
【０００４】
こうした塗装鋼板の耐食性を向上させることを目的として本発明者らは、塗装溶融Ｚｎ−Ａｌ−Ｍｇ−Ｓｉめっき鋼板を提案した（例えば、特許文献１参照）。また、本発明者らは、この溶融Ｚｎ−Ａｌ−Ｍｇ−Ｓｉめっき鋼板にＣａ、Ｂｅ、Ｔｉ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｒ、Ｍｎの１種または２種以上を添加することにより、更に耐食性が優れた塗装鋼板が得られることを明らかにした（例えば、特許文献２参照）。
【０００５】
また、溶融Ｚｎ−Ａｌ−Ｍｇめっき鋼板にＴｉ、Ｂ、Ｓｉを添加することにより表面外観が良好になることが知られている（例えば、特許文献３参照）。
【０００６】
【特許文献１】
特許第３１７９４４６号公報
【特許文献２】
特開２０００−６４０６１号公報
【特許文献３】
特開２００１−２９５０１５号公報
【０００７】
【発明が解決しようとする課題】
Ｚｎ−Ｍｇ−Ａｌの三元系合金は３質量％Ｍｇ−４質量％Ａｌ−９３質量％Ｚｎに三元共晶点を持ち、それよりＡｌ濃度が高い場合、初晶としてＡｌ相が晶出する。
【０００８】
溶融めっき時のめっき凝固速度が十分に確保されている場合、Ａｌ相が大きく成長しないうちにめっきが凝固するため表面平滑性は問題とならないが、めっき凝固速度が小さい場合、このＡｌ相が先に大きく成長することによってめっき表面に凸凹が形成され、表面平滑性が劣化するという問題点を有している。
【０００９】
このため、このような表面平滑性が低い鋼板で塗装鋼板を製造した場合、０．２〜１００μｍ程度の厚さの比較的薄い塗膜ではめっき表面の凸凹を完全には隠蔽できず、塗装鋼板の鮮映性が劣化するという問題点を有している。
【００１０】
しかし、前記特許文献１及び２に開示される技術では、塗装鋼板の鮮映性が劣化するという問題は考慮されていない。
【００１１】
また、前記特許文献３に開示される技術では、表面外観を劣化させるＺｎ_１１Ｍｇ_２相の生成・成長を抑制する目的としてＴｉとＢを添加しているが、表面平滑性や塗装後の鮮映性が劣化するという問題は考慮されておらず、金属間化合物についても言及されていない。
【００１２】
そこで、本発明は、上記問題点に鑑みなされたものであり、４質量％を超えるような高Ａｌ濃度の場合でも十分鮮映性が優れた高耐食性塗装鋼板を提供することを目的としている。
【００１３】
【課題を解決するための手段】
本発明者らは、鮮映性の優れた高耐食性塗装鋼板の開発について鋭意研究を重ねた結果、鋼板の表面に添加元素の添加量を最適化した亜鉛系めっきを形成した後に、クロメート処理もしくはりん酸塩処理の化成処理、塗装を行うことによって鮮映性の優れた高耐食性塗装鋼板を得られることを見いだした。
【００１４】
すなわち、本発明の要旨は以下のとおりである。
【００１５】
（１）鋼板の片面または両面に、Ａｌ：４〜１０質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．０１質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、中間層としてクロメート皮膜もしくはりん酸塩被膜の化成被膜を有し、上層として０．２〜１００μｍ厚の有機被膜層を有することを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００１６】
（２）鋼板の片面または両面に、Ａｌ：４〜２２質量％ろ、Ｍｇ：１〜５質量％、Ｔｉ：０．０１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、中間層としてクロメート皮膜もしくはりん酸塩被膜の化成被膜を有し、上層として０．２〜１００μｍ厚の有機被膜層を有することを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００１７】
（３）鋼板の片面または両面に、Ａｌ：４〜１０質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、中間層としてクロメート皮膜もしくはりん酸塩被膜の化成被膜を有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕及び〔Ｚｎ相〕の１種または２種以上が混在した金属組織を有し、且つ、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕及び〔Ｚｎ相〕の１種または２種以上の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００１８】
（４）鋼板の片面または両面に、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、中間層としてクロメート皮膜もしくはりん酸塩被膜の化成被膜を有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔Ｍｇ_２Ｓｉ相〕、〔Ａｌ相〕及び〔Ｚｎ_２Ｍｇ相〕が混在した金属組織を有し、且つ、〔Ａｌ相〕と〔Ｚｎ_２Ｍｇ相〕の１種または２種の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００１９】
（５）鋼板の片面または両面に、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、中間層としてクロメート皮膜もしくはりん酸塩被膜の化成被膜を有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔Ｍｇ_２Ｓｉ相〕、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕及び〔Ｚｎ相〕が混在した金属組織を有し、且つ、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕及び〔Ｚｎ相〕の１種または２種以上の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００２０】
（６）鋼板の片面または両面に、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下を含有し残部が亜鉛及び不可避的不純物よりなる亜鉛系めっき層を有し、中間層としてクロメート皮膜もしくはりん酸塩被膜の化成被膜を有し、上層として０．２〜１００μｍ厚の有機被膜層を有する塗装鋼板の亜鉛系めっき層が〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔Ｍｇ_２Ｓｉ相〕、〔Ａｌ相〕及び〔Ｚｎ相〕が混在した金属組織を有し、且つ、〔Ａｌ相〕と〔Ｚｎ相〕の１種または２種の中にＴｉ−Ａｌ系金属間化合物を含有することを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００２１】
（７）前記（３）乃至（６）のいずれかに記載のＴｉ−Ａｌ系金属間化合物が、ＴｉＡｌ_３であることを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００２２】
（８）前記（３）乃至（６）のいずれかに記載のＴｉ−Ａｌ系金属間化合物が、Ｔｉ（Ａｌ_１−ＸＳｉ_Ｘ）_３（但し、Ｘ＝０〜０．５である）であることを特徴とする鮮映性の優れた高耐食性塗装鋼板。
【００２３】
（９）めっき層中の〔Ａｌ相〕の中に含有されるＴｉ−Ａｌ系金属間化合物が、Ｚｎ−Ａｌの共析反応によって析出したＺｎ相中に存在することを特徴とする前記（３）乃至（８）のいずれかに記載の鮮映性の優れた高耐食性塗装鋼板。
【００２４】
（１０）めっき層中の〔Ａｌ相〕の樹枝状晶の大きさが５００μｍ以下であることを特徴とする前記（１）乃至（９）のいずれかに記載の鮮映性の優れた高耐食性塗装鋼板。
【００２５】
（１１）有機被膜が，熱硬化型の樹脂塗膜であることを特徴とする前記（１）乃至（１０）のいずれかに記載の鮮映性の優れた高耐食性塗装鋼板。
【００２６】
（１２）有機皮膜層が防錆顔料を含む下塗り層と着色された上塗り層からなる前記（１）乃至（１１）のいずれかに記載の鮮映性の優れた高耐食性塗装鋼板。
【００２７】
【発明の実施形態】
以下に本発明を詳細に説明する。
【００２８】
本発明において、塗装鋼板とは、鋼板上に亜鉛系めっき層とクロメート皮膜もしくはりん酸塩被膜の化成被膜、及び、有機皮膜からなる層を順次付与したものである。本発明の下地鋼板としては、熱延鋼板、冷延鋼板共に使用でき、鋼種もＡｌキルド鋼、Ｔｉ、Ｎｂ等を添加した極低炭素鋼板、及び、これらにＰ、Ｓｉ、Ｍｎ等の強化元素を添加した高強度鋼、ステンレス鋼等種々のものが適用できる。
【００２９】
下層の亜鉛系めっき層は、Ａｌ：４〜１０質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、残部がＺｎ及び不可避不純物からなるめっき層か、或いは、Ａｌ：４〜２２質量％、Ｍｇ：１〜５質量％、Ｔｉ：０．１質量％以下、Ｓｉ：０．５質量％以下、残部がＺｎ及び不可避不純物からなるめっき層である。
【００３０】
Ｚｎ−Ａｌ−Ｍｇ−Ｔｉ系めっき層においてＡｌの含有量を４〜１０質量％に限定した理由は、Ａｌの含有量が１０質量％を超えるとめっき密着性の低下が見られるため、Ｓｉを添加していないめっき層中のＡｌの含有量は１０質量％以下にする必要があるためである。また、４質量％未満では初晶としてＡｌ相が晶出しないため、平滑性低下の問題がないためである。
【００３１】
従って、本発明における高耐食性塗装鋼板においては、特にＡｌ濃度が１０質量％を超えるような高濃度の場合には、めっき密着性を確保するために、めっき層中にＳｉを添加することが必須である。
【００３２】
一方、Ｚｎ−Ａｌ−Ｍｇ−Ｔｉ−Ｓｉ系めっき層において、Ａｌの含有量を４〜２２質量％に限定した理由は、４質量％未満では初晶としてＡｌ相が晶出しないため、平滑性低下の問題がないためであり、２２質量％を超えると耐食性を向上させる効果が飽和するためである。
【００３３】
Ｓｉの含有量を０．５質量％以下（但し、０質量％を除く）に限定した理由は、Ｓｉは密着性を向上させる効果があるが、０．５質量％を超えると密着性を向上させる効果が飽和するからである。望ましくは０．００００１〜０．５質量％である、更に望ましくは０．０００１〜０．５質量％である。
【００３４】
Ｓｉの添加はＡｌの含有量が１０質量％を超えるめっき層には必須であるが、Ａｌの含有量が１０％以下のめっき層においてもめっき密着性向上に効果が大きいため、加工が厳しい部材に使用する等、高いめっき密着性を必要とする場合にはＳｉを添加することが有効である。また、Ｓｉ添加によりめっき層の凝固組織中に〔Ｍｇ_２Ｓｉ相〕が晶出する。この〔Ｍｇ_２Ｓｉ相〕は加工部耐食性向上に効果があるため、Ｓｉの添加量を多くし、めっき層の凝固組織中に〔Ｍｇ_２Ｓｉ相〕が混在した金属組織を作製することがより望ましい。
【００３５】
Ｍｇの含有量を１〜５質量％に限定した理由は、１質量％未満では耐食性を向上させる効果が不十分であるためであり、５質量％を超えるとめっき層が脆くなって密着性が低下するためである。
【００３６】
Ｔｉの含有量を０．１質量％以下（０質量％は除く）に限定した理由は、ＴｉはＴｉ−Ａｌ系金属間化合物を晶出させ、鮮映性を向上させる効果があるが、０．１質量％を超えるとめっき後の外観が粗雑になり、外観不良が発生する。また、Ｔｉ−Ａｌ系金属間化合物がめっき表面に濃化し表面平滑性を低下させる。望ましくは０．００００１〜０．１質量％である。更に望ましくは０．００００１〜０．０１質量％未満である。
【００３７】
本めっき層には、〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕の素地中に〔Ｚｎ相〕、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｍｇ_２Ｓｉ相〕、Ｔｉ−Ａｌ系金属間化合物の１つ以上を含む金属組織ができる。
【００３８】
ここで、〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕とは、Ａｌ相と、Ｚｎ相と金属間化合物Ｚｎ_２Ｍｇ相との三元共晶組織であり、この三元共晶組織を形成しているＡｌ相は例えばＡｌ−Ｚｎ−Ｍｇの三元系平衡状態図における高温での「Ａｌ″相」（Ｚｎ相を固溶するＡｌ固溶体であり、少量のＭｇを含む）に相当するものである。この高温でのＡｌ相は常温では通常は微細なＡｌ相と微細なＺｎ相に分離して現れる。また、該三元共晶組織中のＺｎ相は少量のＡｌを固溶し、場合によっては更に少量のＭｇを固溶したＺｎ固溶体である。該三元共晶組織中のＺｎ_２Ｍｇ相は、Ｚｎ−Ｍｇの二元系平衡状態図のＺｎ：約８４重量％の付近に存在する金属間化合物相である。状態図で見る限りそれぞれの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられるがその量は通常の分析では明確に区別できないため、この３つの相からなる三元共晶組織を本明細書では〔Ａｌ／Ｚｎ／Ｚｎ_２Ｍｇの三元共晶組織〕と表す。
【００３９】
また、〔Ａｌ相〕とは、前記の三元共晶組織の素地中に明瞭な境界をもって島状に見える相であり、これは例えばＡｌ−Ｚｎ−Ｍｇの三元系平衡状態図における高温での「Ａｌ″相」（Ｚｎ相を固溶するＡｌ固溶体であり、少量のＭｇを含む）に相当するものである。この高温でのＡｌ″相はめっき浴のＡｌやＭｇ濃度に応じて固溶するＺｎ量やＭｇ量が相違する。この高温でのＡｌ″相は常温では通常は微細なＡｌ相と微細なＺｎ相に分離するが、常温で見られる島状の形状は高温でのＡｌ″相の形骸を留めたものであると見てよい。状態図で見る限りこの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられるが通常の分析では明確に区別できないため、この高温でのＡｌ″相に由来し、且つ、形状的にはＡｌ″相の形骸を留めている相を本明細書では〔Ａｌ相〕と呼ぶ。この〔Ａｌ相〕は前記の三元共晶組織を形成しているＡｌ相とは顕微鏡観察において明瞭に区別できる。
【００４０】
また、〔Ｚｎ相〕とは、前記の三元共晶組織の素地中に明瞭な境界をもって島状に見える相であり、実際には少量のＡｌさらには少量のＭｇを固溶していることもある。状態図で見る限りこの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられる。この〔Ｚｎ相〕は前記の三元共晶組織を形成しているＺｎ相とは顕微鏡観察において明瞭に区別できる。
【００４１】
また、〔Ｚｎ_２Ｍｇ相〕とは、前記の三元共晶組織の素地中に明瞭な境界をもって島状に見える相であり、実際には少量のＡｌを固溶していることもある。状態図で見る限りこの相にはＳｉ、Ｔｉが固溶していないか、固溶していても極微量であると考えられる。この〔Ｚｎ_２Ｍｇ相〕は前記の三元共晶組織を形成しているＺｎ_２Ｍｇ相とは顕微鏡観察において明瞭に区別できる。
【００４２】
また、〔Ｍｇ_２Ｓｉ相〕とは、めっき層の凝固組織中に明瞭な境界をもって島状に見える相である。状態図で見る限りＺｎ、Ａｌ、Ｔｉは固溶していないか、固溶していても極微量であると考えられる。この〔Ｍｇ_２Ｓｉ相〕はめっき中では顕微鏡観察において明瞭に区別できる。
【００４３】
また、Ｔｉ−Ａｌ系金属間化合物とは、めっき層の凝固組織中に明瞭な境界をもって島状に見える相である。状態図で見る限りＴｉＡｌ_３であると考えられるが、分析するとＳｉが観察されることから、Ｓｉを固溶したＴｉＡｌ_３またはＡｌの一部がＳｉに置き換わったＴｉ（Ａｌ_１−ＸＳｉ_Ｘ）_３（但し、Ｘ＝０〜０．５である）であると考えられる。
【００４４】
本発明の高耐食性塗装鋼板において、このＴｉ−Ａｌ系金属間化合物は、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｚｎ相〕の中に存在することを特徴とする。Ｔｉ−Ａｌ系金属間化合物の含有形態を〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｚｎ相〕の中に限定した理由は、それ以外の位置に存在するＴｉ−Ａｌ系金属間化合物では、鮮映性を向上させることができないためである。〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｚｎ相〕の中に存在するＴｉ−Ａｌ系金属間化合物が鮮映性を向上させる理由は、Ｔｉ−Ａｌ系金属間化合物が、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕，〔Ｚｎ相〕の核となることでこれらの結晶の晶出を促進させ、微細で多数の組織とするためであると考えられる。即ち、結晶が微細になるとめっき層表面の凹凸が抑制され、めっき表面が平滑になり、比較的薄い塗膜でもめっき表面の凸凹を隠蔽できるようになり、塗装鋼板の鮮映性が向上すると考えられる。
【００４５】
この効果は、特に〔Ａｌ相〕において顕著である。〔Ａｌ相〕の樹枝状晶の大きさを５００μｍ以下に制御することにより、表面が平滑になり、摩擦係数が低下する。望ましくは４００μｍ以下である。更に望ましくは３００μｍ以下である。
【００４６】
本発明者等が多数のめっき中の金属組織を調査した結果、大部分の金属組織の中から大きさ数μｍの金属間化合物が観察された。〔Ａｌ相〕中に存在する金属間化合物の一例を図１に示す。図１の（ａ）は、本発明における高耐食性塗装鋼板のめっき層の顕微鏡写真（倍率１０００倍）であり、該写真中の各組織の分布状態を図示したものが図１の（ｂ）である。この図からも判るように、本発明における高耐食性塗装鋼板のめっき層の顕微鏡写真によって明確に各組織を特定することができる。
【００４７】
図１の（ａ）ではＡｌ−Ｚｎ−Ｍｇの三元系平衡状態図における高温での「Ａｌ″相」に相当するものの中にＴｉ−Ａｌ系金属間化合物が観察される。この高温でのＡｌ″相は、Ａｌ−Ｚｎの二元系平衡状態図における２７７℃で起こる共析反応により、常温では通常は微細なＡｌ相と微細なＺｎ相に分離して現れる。ここで亜共析反応の場合、高温で晶出したＡｌ″相は、Ａｌ−Ｚｎ−Ｍｇの三元系平衡状態図における三元共晶温度からＺｎ相の析出を開始し、Ａｌ−Ｚｎの二元系平衡状態図における共析反応に相当する温度で残ったＡｌ″相が微細なＡｌ相と微細なＺｎ相の共析組織となる。
【００４８】
図２の（ａ）は、図１のＡｌ″相を拡大した顕微鏡写真（倍率３５００倍）であり、該写真中の各組織の分布状態を図示したものが図２の（ｂ）である。Ａｌ″相を詳細に観察すると、析出したＺｎ相がＡｌ″相の外側とＴｉ−Ａｌ系金属間化合物の周りに存在することが観察される。
【００４９】
本発明において金属間化合物の大きさは特に限定しないが、発明者らが観察したものは、大きさ１０μｍ以下であった。また、めっき組織中の金属間化合物の存在割合も特に限定しないが、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｚｎ相〕のどれかに１割以上存在することが望ましい。
【００５０】
本発明において、めっき鋼板の製造方法については特に限定するところはなく、通常の無酸化炉方式の溶融めっき法が適用できる。
【００５１】
金属間化合物の添加方法については特に限定するところはなく、金属間化合物の微粉末を浴中に混濁させる方法や、金属間化合物を浴に溶解させる方法等が適用できるが、無酸化炉方式の溶融めっき法を使用した連続ライン等で製造する場合、めっき浴中にＴｉを溶解させる方法が適当である。めっき浴中にＴｉを溶解させる方法としては、Ｔｉ−Ｚｎ系金属間化合物を添加する方法が低温、短時間で溶解可能なため効率的である。添加するＴｉ−Ｚｎ系金属間化合物としては、Ｚｎ_１５Ｔｉ、Ｚｎ_１０Ｔｉ、Ｚｎ_５Ｔｉ、Ｚｎ_３Ｔｉ、Ｚｎ_２Ｔｉ、ＺｎＴｉ等がある。こうした金属間化合物を単独或いはＺｎ、Ｚｎ−Ａｌ、Ｚｎ−Ａｌ−Ｍｇ合金中に混合させてめっき浴に添加すると、溶解したＴｉがめっき中にＴｉ−Ａｌ系金属間化合物として晶出し、表面平滑性と成形性を向上させる。
【００５２】
めっきの付着量については特に制約は設けないが、耐食性の観点から１０ｇ／ｍ^２以上、加工性の観点から３５０ｇ／ｍ^２以下で有ることが望ましい。
【００５３】
亜鉛めっき層中には、これ以外にＦｅ、Ｓｂ、Ｐｂ、Ｓｎを単独或いは複合で０．５質量％以内含有してもよい。また、Ｃａ、Ｂｅ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｒ、Ｍｎ、Ｐ、Ｂ、Ｎｂ、Ｂｉや３族元素を合計で０．５質量％以下含有しても本発明の効果を損なわず、その量によっては更に耐食性が改善される等好ましい場合もある。
【００５４】
次に、塗装鋼板の化成被膜としてはクロメート被膜もしくはりん酸塩被膜を用いる。化成被膜はめっき面と塗膜の間に位置し加工時の密着性、耐食性向上に寄与する。クロメートは３価クロム水和酸化物を主成分とする後水洗型の電解還元クロメート、３価クロムと６価クロム水和酸化物を主成分とする後水洗型のエッチングクロメート液を塗布し乾燥する無水洗型の塗布クロメート被膜を採用できる。付着量については特に制約は設けないが、耐食性の観点から５ｍｇ／ｍ^２以上、密着性の観点から１００ｍｇ／ｍ^２以下であることが望ましい。クロメート被膜は３価クロム／６価クロム比率の高い、水系潤滑塗料に溶解し難いものが望ましい。
【００５５】
りん酸塩被膜は亜鉛、鉄、ニッケル、マンガン、カルシウム等のリン酸塩で構成されるものである。付着量は、耐食性の観点から０．２ｇ／ｍ^２以上、密着性の観点から５．０ｇ／ｍ^２以下であることが望ましい。
【００５６】
次に塗装鋼板の上層の有機被膜としては、ポリエステル樹脂、アミノ樹脂、エポキシ樹脂、アクリル樹脂、ウレタン樹脂、フッ素樹脂等が例として挙げられ、特に限定されるものではないが、特に加工が厳しい製品に使用する場合、熱硬化型の樹脂塗膜が最も好ましい。熱硬化型の樹脂塗膜としては、エポキシポリエステル塗料、ポリエステル塗料、メラミンポリエステル塗料、ウレタンポリエステル塗料等のポリエステル系塗料や、アクリル塗料が挙げられる。
【００５７】
ポリエステル樹脂の酸成分の一部を脂肪酸に置き換えたアルキッド樹脂や、油で変性しないオイルフリーアルキッド樹脂に、メラミン樹脂やポリイソシアネート樹脂を硬化剤として併用したポリエステル系の塗料、及び各種架橋剤と組み合わせたアクリル塗料は、他の塗料に比べて加工性が良いため、厳しい加工の後にも塗膜に亀裂などが発生しないためである。
【００５８】
膜厚は、０．２〜１００μｍが適正である。膜厚を０．２μｍ以上とした理由は、膜厚が０．２μｍ未満では耐食性が確保できないためである。また、膜厚を１００μｍ以下とした理由は、膜厚が１００μｍを超えるとコスト面から不利になるためである。望ましくは、５０μｍ以下である。有機被膜層は、単層でも複層でもかまわない。
【００５９】
なお、本発明の方法に使用される有機被膜には、必要に応じ、可塑剤、酸化防止剤、熱安定剤、無機粒子、顔料、有機潤滑などの添加剤を配合される。
【００６０】
有機被覆層は公知の方法で下地処理層の上に塗装される。例えば、ロールコーター、カーテンコーター、静電塗装、スプレー塗装、浸漬塗装などである。その後、熱風、誘導加熱、近赤外、遠赤外、などの加熱によって乾燥・硬化される。有機被覆層の樹脂が電子線や紫外線で硬化するものであればこれらの照射によって硬化される。これらの併用であってもよい。
【００６１】
本発明の塗装鋼板で化成処理層と着色された有機層の間に、必要に応じて防錆顔料を添加した皮膜層を下塗り層として有することができる。この下塗り層は主に耐食性の向上を目的とするが、その他に成形加工性，耐薬品性なども考慮して設計される。下塗り層を構成する樹脂としては、一般に公知の樹脂、例えば、ポリエステル樹脂、ウレタン樹脂、アクリル樹脂、エポキシ樹脂、メラミン樹脂などをそのまま、或いは組み合わせて使用できる。防錆顔料としては一般に公知のもの、例えば、▲１▼リン酸亜鉛、リン酸鉄、リン酸アルミニウム、亜リン酸亜鉛、等のリン酸系防錆顔料、▲２▼モリブデン酸カルシウム、モリブデン酸アルミニウム、モリブデン酸バリウム、等のモリブデン酸系防錆顔料、▲３▼酸化バナジウムなどのバナジウム系防錆顔料、▲４▼カルシウムシリケートなどのシリケート系顔料、▲５▼ストロンチウムクロメート、ジンククロメート、カルシウムクロメート、カリウムクロメート、バリウムクロメートなどのクロメート系防錆顔料、▲６▼水分散シリカ、ヒュームドシリカ、等の微粒シリカなどを用いることができる。
【００６２】
防錆顔料の添加量は皮膜の固形分基準に１〜４０重量％がよい。１重量％より少ないと耐食性の改良が十分でなく、４０重量％を超えると加工性が低下して、加工時に有機被膜層の脱落が起こり、耐食性も劣るようになる。
【００６３】
防錆顔料を含む下塗り層の塗布は一般に公知の方法でできる。例えば、ロールコート、カーテンコート、エアースプレー、エアーレススプレー、浸漬、刷毛塗り、バーコートなどである。その後、熱風、誘導加熱、近赤外、遠赤外、などの加熱によって乾燥・硬化される。有機被覆層の樹脂が電子線や紫外線で硬化するものであればこれらの照射によって硬化される。これらの併用であってもよい。
【００６４】
【実施例】
以下、実施例により本発明を具体的に説明する。
【００６５】
（実施例１）
まず、厚さ０．８５ｍｍの冷延鋼板を準備し、これに４００〜６００℃で浴中の添加元素量を変化させためっき浴で３秒溶融めっきを行い、Ｎ_２ワイピングでめっき付着量を片面１４０ｇ／ｍ^２に調整し、冷却速度１０℃／ｓ以下で冷却した。得られためっき鋼板のめっき組成を表１に示す。また、めっき鋼板を断面からＳＥＭで観察し、めっき層の金属組織を観察した結果を同じく表１に示す。
【００６６】
Ｔｉ−Ａｌ系金属間化合物は、めっき鋼板を１０度傾斜で研磨した後、ＥＰＭＡで観察し、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｚｎ相〕の中に存在するものを観察した。
【００６７】
めっき層中の〔Ａｌ相〕の樹枝状晶の大きさは、めっき鋼板の表面をＣＭＡでマッピングし、得られたＡｌのマッピングを使用して樹脂状晶の長径を測定した。測定は、５×５ｃｍの範囲を行い、大きいものから順に５つの樹脂状晶の長径を測定し、その平均値を〔Ａｌ相〕の樹枝状晶の大きさとして使用した。
【００６８】
次に、このめっきを行った鋼板に表１に示す化成処理を行い、その上に、プライマーとしてエポキシポリエステル塗料をバーコーターで塗装し、熱風乾燥炉で焼き付けて膜厚を５μｍに調整した。トップコートは、ポリエステル塗料をバーコーターで塗装し、熱風乾燥炉で焼き付けて膜厚を２０μｍに調整した。クロメート処理は塗布型のクロメート処理液に浸漬した。クロメート皮膜の付着量はＣｒ換算量で５０ｍｇ／ｍ^２とした。りん酸塩処理は浸漬型のりん酸亜鉛処理を行った。りん酸亜鉛皮膜の付着量は１．５ｇ／ｍ^２とした。
【００６９】
以上の様にして作製した塗装鋼板を１５０×７０ｍｍに切断し、塗膜の上から地鉄に達するスクラッチを入れ、ＪＩＳＺ−２３７１に準ずる塩水噴霧試験を２０日間行った後テーピング試験を行い、スクラッチ部の塗膜剥離幅を調べた。耐食性は、塗膜剥離幅が４ｍｍ以下のものを合格、塗膜剥離幅が４ｍｍを超えたものを不合格とした。
【００７０】
鮮映性は携帯用鮮明度光沢度計（ＰＧＤ計）での鮮映性測定値（Ｇｄ値）を測定した。鮮映性は、Ｇｄ値が０．６以上のものを合格、Ｇｄ値が０．６未満のものを不合格とした。
【００７１】
評価結果を表１に示す。番号１６は、Ｔｉ−Ａｌ系金属間化合物を含有しないため、Ａｌ相が成長し、鮮映性が不合格となった。番号１７は、Ｔｉの含有量が多すぎたため、Ｔｉ−Ａｌ系金属間化合物が表面に濃化し、鮮映性が不合格となった。番号１８は、Ｍｇ、Ａｌ、Ｓｉ、Ｔｉが本発明の範囲外であるため、耐食性が不合格となった。これら以外はいずれも良好な鮮映性、耐食性を示した。
【００７２】
【表１】

【００７３】
（実施例２）
まず、厚さ０．８５ｍｍの冷延鋼板を準備し、これに４００〜６００℃で浴中の添加元素量を変化させためっき浴で３秒溶融めっきを行い、Ｎ_２ワイピングでめっき付着量を片面に調整し、冷却速度１０℃／ｓ以下で冷却した。得られためっき鋼板のめっき組成を表２に示す。また、めっき鋼板を断面からＳＥＭで観察し、めっき層の金属組織を観察した結果を同じく表２に示す。
【００７４】
Ｔｉ−Ａｌ系金属間化合物は、めっき鋼板を１０度傾斜で研磨した後、ＥＰＭＡで観察し、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｚｎ相〕の中に存在するものを観察した。
【００７５】
めっき層中の〔Ａｌ相〕の樹枝状晶の大きさは、めっき鋼板の表面をＣＭＡでマッピングし、得られたＡｌのマッピングを使用して樹脂状晶の長径を測定した。測定は、５×５ｃｍの範囲を行い、大きいものから順に５つの樹脂状晶の長径を測定し、その平均値を〔Ａｌ相〕の樹枝状晶の大きさとして使用した。
【００７６】
次に、このめっきを行った鋼板を塗布型のクロメート処理液に浸漬して、クロメート処理を行った。クロメート皮膜の付着量はＣｒ換算量で５０ｍｇ／ｍ^２とした。
【００７７】
塗装は、エポキシポリエステル塗料、ポリエステル塗料、メラミンポリエステル塗料、ウレタンポリエステル塗料、アクリル塗料をそれぞれバーコーターで塗装し、熱風乾燥炉で焼き付けて表２に示す膜厚に調整した。
【００７８】
鮮映性は携帯用鮮明度光沢度計（ＰＧＤ計）での鮮映性測定値（Ｇｄ値）を測定した。鮮映性は、Ｇｄ値が０．６以上のものを合格、Ｇｄ値が０．６未満のものを不合格とした。
【００７９】
耐食性は、ＪＩＳＢ−７７２９に準ずるエリクセン試験機を使用して７ｍｍ押し出した加工部をＪＩＳＺ−２３７１に準ずる塩水噴霧試験で７２ｈｒ試験し、白錆が発生しなかったものを合格、白錆が発生したものを不合格とした。
【００８０】
評価結果を表２に示す。番号３０は、塗膜厚が本発明の範囲外であるため、耐食性が不合格となった。これら以外はいずれも良好な鮮映性、耐食性を示した。
【００８１】
【表２】

【００８２】
（実施例３）
まず、厚さ０．８５ｍｍの冷延鋼板を準備し、これに５２０℃で浴中の添加元素量を変化させためっき浴で３秒溶融めっきを行い、Ｎ_２ワイピングでめっき付着量を片面１４０ｇ／ｍ^２に調整し、冷却速度１０℃／ｓ以下で冷却した。得られためっき鋼板のめっき組成を表３に示す。また、めっき鋼板を断面からＳＥＭで観察し、めっき層の金属組織を観察した結果を同じく表３に示す。
【００８３】
Ｔｉ−Ａｌ系金属間化合物は、めっき鋼板を１０度傾斜で研磨した後、ＥＰＭＡで観察し、〔Ａｌ相〕、〔Ｚｎ_２Ｍｇ相〕、〔Ｚｎ相〕の中に存在するものを観察した。また、〔Ａｌ相〕の中に存在するＴｉ−Ａｌ系金属間化合物については、ＥＰＭＡで観察し、Ｚｎ−Ａｌの共析反応によって析出したＺｎ相中への存在有無を観察した。更にＴｉ−Ａｌ系金属間化合物のＥＰＭＡ観察を行い、Ｔｉ−Ａｌ系金属間化合物のＳｉ含有有無を観察した。
【００８４】
次に、このめっきを行った鋼板にＣｒ換算量で付着量５０ｍｇ／ｍ^２のクロメート処理を行い、その上に、プライマーとしてエポキシポリエステル塗料をバーコーターで塗装し、熱風乾燥炉で焼き付けて膜厚を５μｍに調整した。トップコートは、ポリエステル塗料をバーコーターで塗装し、熱風乾燥炉で焼き付けて膜厚を２０μｍに調整した。クロメート処理は塗布型のクロメート処理液に浸漬した。
【００８５】
密着性は、デュポン衝撃試験後の塗装めっき鋼板に粘着テープを貼り、その後引き剥がし、めっき及び塗膜が剥離しなかった場合を○、めっきまたは塗膜の剥離が１０％未満の場合を△、めっきまたは塗膜が１０％以上剥離した場合を×とした。デュポン試験は先端に１／２インチの丸みを持つ撃ち型を使用し、１ｋｇの重りを１ｍの高さから落下させて行った。
【００８６】
加工後耐食性の評価は、１Ｔ折り曲げ加工（原板を１枚はさんだ状態で１８０°の折り曲げ加工）を施したサンプルの折り曲げ部について、ＣＣＴ１２０サイクル後の赤錆発生状況を以下に示す評点づけで判定した。ＣＣＴは、ＳＳＴ２ｈｒ→乾燥４ｈｒ→湿潤２ｈｒを１サイクルとした。評点は３以上を合格とした。５：５％未満
４：５％以上１０％未満
３：１０％以上２０％未満
２：２０％以上３０％未満
１：３０％以上
【００８７】
評価結果を表３に示す。番号２はＡｌ、Ｓｉの添加量が本発明の範囲外であるため密着性が不合格となった。これら以外はいずれも、密着性、加工後耐食性が良好な結果となった。特にＳｉを添加しためっき鋼板は良好な密着性と加工後耐食性を示した。
【００８８】
【表３】

【００８９】
【発明の効果】
以上述べてきたように、本発明により、高Ａｌ濃度の場合でも十分鮮映性が優れた高耐食性塗装鋼板を製造することが可能となり、工業上極めて優れた効果を奏することができる。
【図面の簡単な説明】
【図１】めっき鋼板のめっき層の「Ａｌ″相」中に存在する金属間化合物の一例を示す図で、（ａ）はめっき層の顕微鏡写真（倍率１０００倍）であり、（ｂ）は該写真中の各組織の分布状態を示す図である。
【図２】（ａ）は「Ａｌ″相」を拡大した顕微鏡写真（倍率３５００倍）であり、（ｂ）は各組織の分布状態を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a coated steel sheet, and more particularly to a coated steel sheet having excellent corrosion resistance and applicable to various uses, for example, a steel sheet for home appliances and building materials.
[0002]
[Prior art]
Painted metal plate can streamline the coating process, make the quality uniform, save paint consumption, etc., compared with the method of forming a metal plate first to form a complicated shape and then painting. Because of its advantages, it has been widely used and its usage is expected to increase in the future.
[0003]
In general, a coated metal plate is a cold-rolled steel plate, a galvanized steel plate, or a pre-painted metal plate, and then formed into an arbitrary shape and provided for final use.For example, a refrigerator, a washing machine, It is used for home appliances such as microwave ovens, metal products such as vending machines, office equipment, automobiles, and air conditioner outdoor units.
[0004]
The present inventors have proposed a coated hot-dip Zn-Al-Mg-Si plated steel sheet for the purpose of improving the corrosion resistance of such a coated steel sheet (for example, see Patent Document 1). In addition, the present inventors further added one or more of Ca, Be, Ti, Cu, Ni, Co, Cr, and Mn to the hot-dip Zn-Al-Mg-Si plated steel sheet to further increase the corrosion resistance. (See, for example, Patent Document 2).
[0005]
It is known that the surface appearance is improved by adding Ti, B, and Si to a hot-dip Zn-Al-Mg plated steel sheet (for example, see Patent Document 3).
[0006]
[Patent Document 1]
Japanese Patent No. 3179446 [Patent Document 2]
JP 2000-64061 A [Patent Document 3]
JP 2001-295015 A
[Problems to be solved by the invention]
The ternary alloy of Zn-Mg-Al has a ternary eutectic point in 3% by mass Mg-4% by mass Al-93% by mass Zn, and when the Al concentration is higher than that, an Al phase is crystallized as a primary crystal. I do.
[0008]
If the plating solidification rate during hot-dip plating is sufficiently ensured, the plating will solidify before the Al phase grows significantly, so surface smoothness will not be a problem. As a result, unevenness is formed on the plating surface due to large growth, and the surface smoothness is deteriorated.
[0009]
Therefore, when a coated steel sheet is manufactured using such a steel sheet having a low surface smoothness, the unevenness of the plating surface cannot be completely hidden with a relatively thin coating film having a thickness of about 0.2 to 100 μm. Has a problem that the sharpness of the image is deteriorated.
[0010]
However, the techniques disclosed in Patent Documents 1 and 2 do not consider the problem that the sharpness of a coated steel sheet deteriorates.
[0011]
In the technique disclosed in Patent Document 3, Ti and B are added for the purpose of suppressing the generation and growth of the Zn ₁₁ Mg ₂ phase that deteriorates the surface appearance, but the surface smoothness and the freshness after painting are added. No consideration is given to the problem that the image quality deteriorates, and no mention is made of intermetallic compounds.
[0012]
Then, this invention was made | formed in view of the said problem, and an object of this invention is to provide the highly corrosion-resistant coating steel plate which was excellent in the sharpness sufficiently even in the case of high Al concentration exceeding 4 mass%.
[0013]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on the development of a highly corrosion-resistant coated steel sheet having excellent clarity, and as a result, after forming a zinc-based plating in which the amount of the added element is optimized on the surface of the steel sheet, chromate treatment or It has been found that a high corrosion-resistant coated steel sheet having excellent clarity can be obtained by performing a chemical conversion treatment of phosphate treatment and coating.
[0014]
That is, the gist of the present invention is as follows.
[0015]
(1) One or both surfaces of a steel sheet, a zinc-based plating layer containing 4 to 10% by mass of Al, 1 to 5% by mass of Mg, and 0.01% by mass or less of Ti, with the balance being zinc and unavoidable impurities. Characterized by having a chromate film or a phosphate conversion film as an intermediate layer, and an organic film layer having a thickness of 0.2 to 100 μm as an upper layer, and having excellent clarity and high corrosion resistance. .
[0016]
(2) One or both sides of the steel sheet contains 4 to 22% by mass of Al, 1 to 5% by mass of Mg, 0.01% by mass or less of Ti, 0.5% by mass or less of Si, and the balance of zinc And a zinc-based plating layer made of unavoidable impurities, a conversion coating of a chromate film or a phosphate film as an intermediate layer, and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer. High corrosion resistance coated steel sheet with excellent clarity.
[0017]
(3) A zinc-based plating layer containing 4 to 10% by mass of Al, 1 to 5% by mass of Mg, and 0.1% by mass or less of Ti on one or both surfaces of a steel sheet, with the balance being zinc and unavoidable impurities. A zinc-based plating layer of a coated steel sheet having a chromate film or a phosphate conversion film as an intermediate layer and an organic film layer having a thickness of 0.2 to 100 μm as an upper layer is [Al / Zn / Zn ₂ A metal structure in which one or two or more of [Al phase], [Zn ₂ Mg phase] and [Zn phase] are mixed in a base material of [ternary eutectic structure of Mg], and [Al phase] , [Zn ₂ Mg phase] and one or more of [Zn phase] containing a Ti-Al-based intermetallic compound, a highly corrosion-resistant coated steel sheet having excellent clarity.
[0018]
(4) One or both sides of the steel sheet contains 4 to 22% by mass of Al, 1 to 5% by mass of Mg, 0.1% by mass or less of Ti, 0.5% by mass or less of Si, and the balance is zinc and Zinc plating of a coated steel sheet having a zinc-based plating layer composed of unavoidable impurities, having a chromate film or a phosphate conversion film as an intermediate layer, and having an organic film layer having a thickness of 0.2 to 100 μm as an upper layer. The layer has a metal structure in which [Mg ₂ Si phase], [Al phase] and [Zn ₂ Mg phase] are mixed in a base material of [Al / Zn / Zn ₂ Mg ternary eutectic structure], and A highly corrosion-resistant coated steel sheet having excellent clarity, characterized in that one or two of [Al phase] and [Zn ₂ Mg phase] contain a Ti-Al-based intermetallic compound.
[0019]
(5) One or both surfaces of the steel sheet contains 4 to 22% by mass of Al, 1 to 5% by mass of Mg, 0.1% by mass or less of Ti, 0.5% by mass or less of Si, and the balance is zinc and Zinc plating of a coated steel sheet having a zinc-based plating layer composed of unavoidable impurities, having a chromate film or a phosphate conversion film as an intermediate layer, and having an organic film layer having a thickness of 0.2 to 100 μm as an upper layer. A metal structure in which [Mg ₂ Si phase], [Al phase], [Zn ₂ Mg phase] and [Zn phase] are mixed in a base material whose layer is [Al / Zn / Zn ₂ Mg ternary eutectic structure] A sharpness, characterized by containing a Ti-Al intermetallic compound in one or more of [Al phase], [Zn ₂ Mg phase] and [Zn phase] Excellent corrosion-resistant coated steel sheet.
[0020]
(6) One or both surfaces of the steel sheet contains Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and Zinc plating of a coated steel sheet having a zinc-based plating layer composed of unavoidable impurities, having a chromate film or a phosphate conversion film as an intermediate layer, and having an organic film layer having a thickness of 0.2 to 100 μm as an upper layer. The layer has a metal structure in which [Mg ₂ Si phase], [Al phase] and [Zn phase] are mixed in a base material of [Al / Zn / Zn ₂ Mg ternary eutectic structure], and [Al A highly corrosion-resistant coated steel sheet having excellent clarity, characterized in that one or two of [Phase] and [Zn phase] contain a Ti-Al-based intermetallic compound.
[0021]
(7) the (3) to TiAl-based intermetallic compound according to any one of (6), image clarity superior high corrosion resistance coated steel sheet, which is a TiAl _3.
[0022]
(8) The Ti-Al-based intermetallic compound according to any one of (3) to (6) is Ti (Al _1-X Si _X ) ₃ (where X = 0 to 0.5). Highly corrosion-resistant coated steel sheet with excellent clarity, characterized by
[0023]
(9) The method according to (3), wherein the Ti-Al-based intermetallic compound contained in the [Al phase] in the plating layer is present in the Zn phase precipitated by a Zn-Al eutectoid reaction. The highly corrosion-resistant coated steel sheet according to any one of (1) to (8), which has excellent clarity.
[0024]
(10) The high corrosion resistance with excellent sharpness described in any one of (1) to (9), wherein the size of the dendrites of the [Al phase] in the plating layer is 500 μm or less. Painted steel plate.
[0025]
(11) The highly corrosion-resistant coated steel sheet according to any one of (1) to (10), wherein the organic coating is a thermosetting resin coating.
[0026]
(12) The highly corrosion-resistant coated steel sheet according to any one of (1) to (11), wherein the organic coating layer comprises an undercoat layer containing a rust-preventive pigment and a colored overcoat layer.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0028]
In the present invention, the coated steel sheet is a steel sheet in which a zinc-based plating layer and a chemical conversion coating such as a chromate coating or a phosphate coating and an organic coating are sequentially applied. As the base steel sheet of the present invention, both hot-rolled steel sheets and cold-rolled steel sheets can be used, and the type of steel is an ultra-low carbon steel sheet added with Al-killed steel, Ti, Nb, etc. Various materials, such as high-strength steel and stainless steel to which is added, can be applied.
[0029]
The lower zinc-based plating layer is a plating layer composed of Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, with the balance being Zn and unavoidable impurities, or Al: 4%. ~ 22% by mass, Mg: 1 ~ 5% by mass, Ti: 0.1% by mass or less, Si: 0.5% by mass or less, with the balance being Zn and unavoidable impurities.
[0030]
The reason for limiting the content of Al in the Zn-Al-Mg-Ti-based plating layer to 4 to 10% by mass is that when the content of Al exceeds 10% by mass, a decrease in plating adhesion is observed. This is because the Al content in the plating layer not added needs to be 10% by mass or less. Also, when the content is less than 4% by mass, the Al phase does not crystallize as a primary crystal, and thus there is no problem of a decrease in smoothness.
[0031]
Therefore, in the highly corrosion-resistant coated steel sheet of the present invention, especially when the Al concentration is higher than 10% by mass, it is essential to add Si to the plating layer in order to secure plating adhesion. It is.
[0032]
On the other hand, the reason for limiting the Al content to 4 to 22% by mass in the Zn—Al—Mg—Ti—Si-based plating layer is that if the content is less than 4% by mass, the Al phase does not crystallize as primary crystals, so This is because there is no problem of reduction, and when it exceeds 22% by mass, the effect of improving corrosion resistance is saturated.
[0033]
The reason that the content of Si is limited to 0.5% by mass or less (excluding 0% by mass) is that Si has an effect of improving the adhesion, but if it exceeds 0.5% by mass, the adhesion is improved. This is because the effect of saturating becomes saturated. It is preferably 0.00001 to 0.5% by mass, and more preferably 0.0001 to 0.5% by mass.
[0034]
The addition of Si is indispensable for a plating layer having an Al content of more than 10% by mass. However, even for a plating layer having an Al content of 10% or less, the effect of improving the plating adhesion is great, so that a member that is strictly processed. When high plating adhesion is required, for example, when Si is used, it is effective to add Si. [Mg ₂ Si phase] crystallizes in the solidification structure of the plating layer due to the addition of Si. Since this [Mg ₂ Si phase] is effective in improving the corrosion resistance of the processed portion, it is more preferable to increase the amount of added Si to produce a metal structure in which [Mg ₂ Si phase] is mixed in the solidified structure of the plating layer. desirable.
[0035]
The reason why the content of Mg is limited to 1 to 5% by mass is that if it is less than 1% by mass, the effect of improving the corrosion resistance is insufficient. If it exceeds 5% by mass, the plating layer becomes brittle and the adhesion becomes poor. It is because it decreases.
[0036]
The reason for limiting the content of Ti to 0.1% by mass or less (excluding 0% by mass) is that Ti has an effect of crystallizing a Ti-Al-based intermetallic compound and improving sharpness, If it exceeds 0.1% by mass, the appearance after plating becomes coarse and poor appearance occurs. Further, the Ti-Al-based intermetallic compound concentrates on the plating surface and lowers the surface smoothness. Desirably, it is 0.00001 to 0.1% by mass. More preferably, the content is 0.00001 to less than 0.01% by mass.
[0037]
In this plating layer, [Zn phase], [Al phase], [Zn ₂ Mg phase], [Mg ₂ Si phase], and Ti in a base material of [ternary eutectic structure of Al / Zn / Zn ₂ Mg] -A metal structure containing one or more of the Al-based intermetallic compounds is formed.
[0038]
Here, the “ternary eutectic structure of Al / Zn / Zn ₂ Mg” is a ternary eutectic structure of an Al phase, a Zn phase, and an intermetallic compound Zn ₂ Mg phase. The Al phase forming the structure is, for example, an “Al ″ phase” (a solid solution of the Zn phase, containing a small amount of Mg) at a high temperature in the ternary equilibrium diagram of Al—Zn—Mg. It is equivalent. The Al phase at this high temperature usually appears at room temperature as being separated into a fine Al phase and a fine Zn phase. Further, the Zn phase in the ternary eutectic structure is a Zn solid solution in which a small amount of Al is dissolved in a solid solution, and in some cases, a small amount of Mg is further dissolved. Zn 2 _Mg phase of the ternary eutectic structure in the, Zn of Zn-Mg binary equilibrium state diagram of: is an intermetallic compound phase present in the vicinity of about 84 wt%. According to the phase diagram, it is considered that Si and Ti do not form a solid solution in each phase, or even if they do form a solid solution, they are considered to be extremely small. However, the amounts cannot be clearly distinguished by ordinary analysis. In the present specification, a ternary eutectic structure composed of two phases is referred to as [ternary eutectic structure of Al / Zn / Zn ₂ Mg].
[0039]
Further, the [Al phase] is a phase that looks like an island with a clear boundary in the matrix of the ternary eutectic structure. This is, for example, a high temperature in the ternary system diagram of Al-Zn-Mg. (Al solid solution that dissolves Zn phase and contains a small amount of Mg). The Al "phase at this high temperature differs in the amount of solid solution Zn and Mg depending on the Al and Mg concentrations in the plating bath. The Al" phase at this high temperature usually has a fine Al phase and a fine Zn phase at room temperature. Although it separates into phases, the island-like shape seen at room temperature may be regarded as retaining the form of the Al ″ phase at high temperature. From the phase diagram, Si and Ti are dissolved in this phase. It is considered that it is not present, or even if it forms a solid solution, it is considered to be a very small amount. However, it cannot be clearly distinguished by ordinary analysis. In the present specification, the phase retaining the term “Al phase” is clearly distinguishable from the Al phase forming the ternary eutectic structure by microscopic observation.
[0040]
The [Zn phase] is a phase that looks like an island with a clear boundary in the matrix of the above ternary eutectic structure, and actually has a small amount of Al and a small amount of Mg dissolved therein. There is also. From the phase diagram, it is considered that Si and Ti are not dissolved in this phase, or even if they are dissolved, they are minimal. This [Zn phase] can be clearly distinguished from the Zn phase forming the ternary eutectic structure by microscopic observation.
[0041]
The [Zn ₂ Mg phase] is a phase that looks like an island with a clear boundary in the ternary eutectic structure, and may actually dissolve a small amount of Al. From the phase diagram, it is considered that Si and Ti are not dissolved in this phase, or even if they are dissolved, they are minimal. This [Zn ₂ Mg phase] can be clearly distinguished from the Zn ₂ Mg phase forming the ternary eutectic structure by microscopic observation.
[0042]
The “Mg ₂ Si phase” is a phase that looks like an island with a clear boundary in the solidification structure of the plating layer. From the state diagram, it is considered that Zn, Al, and Ti do not form a solid solution, or even if they do form a solid solution, they are in a very small amount. This [Mg ₂ Si phase] can be clearly distinguished by microscopic observation during plating.
[0043]
The Ti-Al intermetallic compound is a phase that looks like an island with a clear boundary in the solidification structure of the plating layer. Are considered to be TiAl ₃ As far as in a state diagram, since Si and analyzed is observed, _Ti some TiAl ₃ or Al which dissolves the Si is replaced by _{_{Si (Al 1-X Si X}} ) ₃ (where X = 0 to 0.5).
[0044]
In the highly corrosion-resistant coated steel sheet of the present invention, the Ti-Al-based intermetallic compound is present in [Al phase], [Zn ₂ Mg phase], and [Zn phase]. The content form of the Ti-Al system intermetallic compound [Al phase], [Zn 2 _Mg phase], reasons for limiting in a [Zn phase], in Ti-Al system intermetallic compound present in the other positions This is because the sharpness cannot be improved. [Al phase], _[Zn 2 Mg phase], why Ti-Al system intermetallic compound present in the [Zn phase] is to improve the image clarity, Ti-Al system intermetallic compound is [Al phase It is considered that the crystallization of these crystals is promoted by forming nuclei of [Zn ₂ Mg phase] and [Zn phase] to form a fine and large number of structures. That is, it is considered that when the crystal becomes finer, the unevenness of the plating layer surface is suppressed, the plating surface becomes smooth, and the unevenness of the plating surface can be concealed even with a relatively thin coating film, and the sharpness of the coated steel plate is improved. Can be
[0045]
This effect is particularly remarkable in the [Al phase]. By controlling the size of the [Al phase] dendrites to 500 μm or less, the surface becomes smooth and the friction coefficient decreases. Desirably, it is 400 μm or less. More preferably, it is 300 μm or less.
[0046]
As a result of investigating the metal structures in many platings by the present inventors, an intermetallic compound having a size of several μm was observed from most of the metal structures. FIG. 1 shows an example of the intermetallic compound present in the [Al phase]. FIG. 1A is a photomicrograph (1000-fold magnification) of a plated layer of a highly corrosion-resistant coated steel sheet according to the present invention, and FIG. 1B shows the distribution of each structure in the photo. is there. As can be seen from this figure, each structure can be clearly identified from the micrograph of the plating layer of the highly corrosion-resistant coated steel sheet according to the present invention.
[0047]
In FIG. 1A, a Ti-Al-based intermetallic compound is observed in a ternary equilibrium diagram of Al-Zn-Mg corresponding to the "Al" phase at a high temperature. The Al ″ phase at this high temperature usually appears as a fine Al phase and a fine Zn phase at room temperature due to the eutectoid reaction occurring at 277 ° C. in the Al-Zn binary equilibrium diagram. In the case of the hypoeutectoid reaction, the Al ″ phase crystallized at a high temperature starts precipitation of the Zn phase from the ternary eutectic temperature in the ternary equilibrium diagram of Al—Zn—Mg, and the binary phase of Al—Zn The Al ″ phase remaining at a temperature corresponding to the eutectoid reaction in the system equilibrium diagram becomes an eutectoid structure of a fine Al phase and a fine Zn phase.
[0048]
FIG. 2A is a micrograph (magnification: 3500 times) of the Al ″ phase in FIG. 1 enlarged, and FIG. 2B shows the distribution state of each tissue in the photograph. When the Al ″ phase is observed in detail, it is observed that the precipitated Zn phase exists outside the Al ″ phase and around the Ti—Al-based intermetallic compound.
[0049]
In the present invention, the size of the intermetallic compound is not particularly limited, but the size observed by the inventors was 10 μm or less. Also, the proportion of the intermetallic compound in the plating structure is not particularly limited, but it is desirable that at least 10% of the intermetallic compound be present in any of the [Al phase], [Zn ₂ Mg phase], and [Zn phase].
[0050]
In the present invention, the method for producing the plated steel sheet is not particularly limited, and a normal hot-dip galvanizing method can be applied.
[0051]
There is no particular limitation on the method of adding the intermetallic compound, and a method of turbidizing the fine powder of the intermetallic compound in the bath, a method of dissolving the intermetallic compound in the bath, and the like can be applied. When manufacturing in a continuous line or the like using a hot-dip plating method, a method in which Ti is dissolved in a plating bath is appropriate. As a method of dissolving Ti in a plating bath, a method of adding a Ti—Zn-based intermetallic compound is efficient because it can be dissolved at a low temperature in a short time. The Ti-Zn-based intermetallic compound _{_{_{_{added, Zn 15 Ti, Zn 10 Ti}}}} , Zn 5 Ti, Zn 3 Ti, Zn 2 Ti, there is ZnTi like. When such an intermetallic compound is used alone or mixed in a Zn, Zn-Al or Zn-Al-Mg alloy and added to a plating bath, the dissolved Ti crystallizes out as a Ti-Al-based intermetallic compound during plating, and the surface becomes smooth. Improves formability and moldability.
[0052]
Although there is no particular limitation on the amount of plating, it is preferable that the amount is 10 g / m ² or more from the viewpoint of corrosion resistance and 350 g / m ² or less from the viewpoint of workability.
[0053]
The zinc plating layer may further contain Fe, Sb, Pb, and Sn singly or in a composite within 0.5% by mass. In addition, even if Ca, Be, Cu, Ni, Co, Cr, Mn, P, B, Nb, Bi or a Group 3 element is contained in a total amount of 0.5% by mass or less, the effect of the present invention is not impaired. Depending on the case, it may be preferable that the corrosion resistance is further improved.
[0054]
Next, a chromate film or a phosphate film is used as a chemical conversion film on the coated steel sheet. The chemical conversion film is located between the plating surface and the coating film and contributes to the improvement of adhesion and corrosion resistance during processing. The chromate is a post-wash type electrolytic reduction chromate containing trivalent chromium hydrated oxide as a main component, and a post-wash type etch chromate liquid containing trivalent chromium and hexavalent chromium hydrated oxide as a main component is applied and dried. An anhydrous washing type coated chromate film can be adopted. There is no particular limitation on the amount of adhesion, but it is preferably 5 mg / m ² or more from the viewpoint of corrosion resistance and 100 mg / m ² or less from the viewpoint of adhesion. It is desirable that the chromate film has a high trivalent chromium / hexavalent chromium ratio and is hardly dissolved in a water-based lubricating paint.
[0055]
The phosphate coating is composed of a phosphate such as zinc, iron, nickel, manganese, calcium and the like. The amount of adhesion is desirably 0.2 g / m ² or more from the viewpoint of corrosion resistance and 5.0 g / m ² or less from the viewpoint of adhesion.
[0056]
Next, examples of the organic coating of the upper layer of the coated steel sheet include polyester resin, amino resin, epoxy resin, acrylic resin, urethane resin, fluororesin, etc., and are not particularly limited. When used, a thermosetting resin coating is most preferred. Examples of the thermosetting resin coating film include polyester paints such as epoxy polyester paints, polyester paints, melamine polyester paints, urethane polyester paints, and acrylic paints.
[0057]
Combined with alkyd resin in which part of the acid component of polyester resin is replaced with fatty acid, oil-free alkyd resin not modified with oil, polyester-based paint using melamine resin or polyisocyanate resin as curing agent, and various crosslinking agents This is because the acrylic paint has better workability than other paints, so that cracks and the like do not occur in the coating film even after severe processing.
[0058]
The appropriate film thickness is 0.2 to 100 μm. The reason for setting the film thickness to 0.2 μm or more is that if the film thickness is less than 0.2 μm, corrosion resistance cannot be ensured. The reason for setting the film thickness to 100 μm or less is that if the film thickness exceeds 100 μm, it is disadvantageous from the viewpoint of cost. Desirably, it is 50 μm or less. The organic coating layer may be a single layer or multiple layers.
[0059]
The organic coating used in the method of the present invention may contain additives such as a plasticizer, an antioxidant, a heat stabilizer, inorganic particles, a pigment, and an organic lubricant, if necessary.
[0060]
The organic coating layer is applied on the base treatment layer by a known method. For example, a roll coater, a curtain coater, an electrostatic coating, a spray coating, a dip coating, and the like. Thereafter, drying and curing are performed by heating with hot air, induction heating, near-infrared radiation, far-infrared radiation, or the like. If the resin of the organic coating layer can be cured by electron beams or ultraviolet rays, it is cured by these irradiations. These may be used in combination.
[0061]
In the coated steel sheet of the present invention, a coating layer to which a rust preventive pigment is added as necessary may be provided as an undercoat layer between the chemical conversion treatment layer and the colored organic layer. This undercoat layer is designed mainly for the purpose of improving corrosion resistance, but is also designed in consideration of moldability, chemical resistance and the like. As the resin constituting the undercoat layer, generally known resins, for example, polyester resins, urethane resins, acrylic resins, epoxy resins, melamine resins and the like can be used as they are or in combination. As rust preventive pigments, generally known ones, for example, (1) phosphoric acid rust preventive pigments such as zinc phosphate, iron phosphate, aluminum phosphate, zinc phosphite, etc .; (2) calcium molybdate, molybdate Molybdate anticorrosive pigments such as aluminum and barium molybdate; (3) vanadium anticorrosive pigments such as vanadium oxide; (4) silicate pigments such as calcium silicate; (5) strontium chromate, zinc chromate and calcium chromate And chromate-based rust preventive pigments such as potassium chromate and barium chromate; and (6) finely divided silica such as water-dispersed silica and fumed silica.
[0062]
The amount of the rust preventive pigment to be added is preferably 1 to 40% by weight based on the solid content of the film. If the amount is less than 1% by weight, the corrosion resistance is not sufficiently improved, and if it exceeds 40% by weight, the processability is reduced, and the organic coating layer falls off during processing, resulting in poor corrosion resistance.
[0063]
The undercoat layer containing the rust-preventive pigment can be applied by a generally known method. For example, roll coating, curtain coating, air spray, airless spray, dipping, brush coating, bar coating, and the like. Thereafter, drying and curing are performed by heating with hot air, induction heating, near-infrared radiation, far-infrared radiation, or the like. If the resin of the organic coating layer can be cured by electron beams or ultraviolet rays, it is cured by these irradiations. These may be used in combination.
[0064]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
[0065]
(Example 1)
First, prepare the cold-rolled steel plate having a thickness of 0.85 mm, this for 3 seconds dip plating in a plating bath was varied amount of additive element in the bath at 400 to 600 ° C., the coating weight in N ₂ wiping It was adjusted to 140 g / m ² on one side and cooled at a cooling rate of 10 ° C./s or less. Table 1 shows the plating composition of the resulting plated steel sheet. Table 1 also shows the results of observing the plated steel sheet from the cross section by SEM and observing the metallographic structure of the plated layer.
[0066]
Ti-Al-based intermetallic compounds were observed by EPMA after polishing a plated steel plate at an inclination of 10 degrees, and those present in [Al phase], [Zn ₂ Mg phase], and [Zn phase] were observed. .
[0067]
The size of the dendrites of the [Al phase] in the plating layer was determined by mapping the surface of the plated steel sheet with CMA and measuring the major axis of the resinous crystal using the obtained Al mapping. The measurement was performed in a range of 5 × 5 cm, and the major axes of five resinous crystals were measured in order from the largest, and the average value was used as the size of the dendrites of the [Al phase].
[0068]
Next, the plated steel sheet was subjected to a chemical conversion treatment shown in Table 1, and an epoxy polyester paint was applied thereon as a primer with a bar coater and baked in a hot-air drying furnace to adjust the film thickness to 5 μm. For the top coat, a polyester coating was applied with a bar coater and baked in a hot-air drying oven to adjust the film thickness to 20 μm. The chromate treatment was immersed in a coating type chromate treatment solution. The attached amount of the chromate film was 50 mg / m ^{2 in} terms of Cr. For the phosphate treatment, an immersion type zinc phosphate treatment was performed. The adhesion amount of the zinc phosphate film was 1.5 g / m ² .
[0069]
The coated steel sheet prepared as described above was cut into 150 × 70 mm, a scratch reaching the ground iron was placed on the coating film, a salt spray test according to JIS Z-2371 was performed for 20 days, and then a taping test was performed. The peeling width of the coating film at the scratch portion was examined. As for the corrosion resistance, those having a coating film peeling width of 4 mm or less were passed, and those having a coating film peeling width of more than 4 mm were rejected.
[0070]
The sharpness was measured by a sharpness measurement value (Gd value) with a portable sharpness gloss meter (PGD meter). Regarding the sharpness, those having a Gd value of 0.6 or more were accepted, and those having a Gd value of less than 0.6 were unacceptable.
[0071]
Table 1 shows the evaluation results. In No. 16, since no Ti-Al-based intermetallic compound was contained, the Al phase grew and the sharpness was rejected. In No. 17, the Ti-Al intermetallic compound was concentrated on the surface because the content of Ti was too large, and the sharpness was rejected. In No. 18, the corrosion resistance was rejected because Mg, Al, Si, and Ti were out of the range of the present invention. Other than these, all showed good sharpness and corrosion resistance.
[0072]
[Table 1]

[0073]
(Example 2)
First, prepare the cold-rolled steel plate having a thickness of 0.85 mm, this for 3 seconds dip plating in a plating bath was varied amount of additive element in the bath at 400 to 600 ° C., the coating weight in N ₂ wiping It was adjusted to one side and cooled at a cooling rate of 10 ° C./s or less. Table 2 shows the plating composition of the obtained plated steel sheet. Table 2 also shows the results of observing the plated steel sheet from the cross section by SEM and observing the metal structure of the plated layer.
[0074]
Ti-Al-based intermetallic compounds were observed by EPMA after polishing a plated steel plate at an inclination of 10 degrees, and those present in [Al phase], [Zn ₂ Mg phase], and [Zn phase] were observed. .
[0075]
The size of the dendrites of the [Al phase] in the plating layer was determined by mapping the surface of the plated steel sheet with CMA and measuring the major axis of the resinous crystal using the obtained Al mapping. The measurement was performed in a range of 5 × 5 cm, and the major axes of five resinous crystals were measured in order from the largest, and the average value was used as the size of the dendrites of the [Al phase].
[0076]
Next, the plated steel sheet was immersed in a coating type chromate treatment solution to perform a chromate treatment. The attached amount of the chromate film was 50 mg / m ^{2 in} terms of Cr.
[0077]
The coating was performed by coating each with an epoxy polyester paint, a polyester paint, a melamine polyester paint, a urethane polyester paint, and an acrylic paint with a bar coater and baking in a hot air drying oven to adjust the film thickness as shown in Table 2.
[0078]
The sharpness was measured by a sharpness measurement value (Gd value) with a portable sharpness gloss meter (PGD meter). Regarding the sharpness, those having a Gd value of 0.6 or more were accepted, and those having a Gd value of less than 0.6 were unacceptable.
[0079]
The corrosion resistance of the processed part extruded 7 mm using an Erichsen tester according to JIS B-7729 was tested for 72 hours in a salt spray test according to JIS Z-2371. Those that occurred were rejected.
[0080]
Table 2 shows the evaluation results. In No. 30, the corrosion resistance was rejected because the coating thickness was outside the range of the present invention. Other than these, all showed good sharpness and corrosion resistance.
[0081]
[Table 2]

[0082]
(Example 3)
First, the thickness to prepare a cold-rolled steel sheet of 0.85 mm, for 3 seconds dip plating in a plating bath was varied amount of additive element in the bath at 520 ° C. to, one surface 140g of the coating weight in N ₂ wiping / M ² and cooled at a cooling rate of 10 ° C./s or less. Table 3 shows the plating composition of the resulting plated steel sheet. Table 3 also shows the results of observing the plated steel sheet from the cross section by SEM and observing the metal structure of the plated layer.
[0083]
Ti-Al-based intermetallic compounds were observed by EPMA after polishing a plated steel plate at an inclination of 10 degrees, and those present in [Al phase], [Zn ₂ Mg phase], and [Zn phase] were observed. . The Ti-Al intermetallic compound present in the [Al phase] was observed by EPMA, and the presence or absence in the Zn phase precipitated by the eutectoid reaction of Zn-Al was observed. Further, an EPMA observation of the Ti-Al-based intermetallic compound was performed, and the presence or absence of Si in the Ti-Al-based intermetallic compound was observed.
[0084]
Next, the plated steel sheet is subjected to chromate treatment with an adhesion amount of 50 mg / m ^{2 in} terms of Cr, and then an epoxy polyester paint is applied as a primer with a bar coater and baked in a hot air drying oven to obtain a film thickness. Was adjusted to 5 μm. For the top coat, a polyester coating was applied with a bar coater and baked in a hot-air drying oven to adjust the film thickness to 20 μm. The chromate treatment was immersed in a coating type chromate treatment solution.
[0085]
Adhesion was measured by applying an adhesive tape to the coated steel sheet after the DuPont impact test and then peeling it off. The case where the plating or the coating film was peeled by 10% or more was evaluated as x. The Dupont test was performed by using a shooting type having a radius of 1/2 inch at the tip and dropping a 1 kg weight from a height of 1 m.
[0086]
The evaluation of corrosion resistance after processing was performed on the bent portion of a sample subjected to 1T bending processing (a bending process of 180 ° with one original sheet sandwiched between them), and a red rust occurrence state after 120 cycles of CCT was evaluated according to the following rating. . In the CCT, one cycle was defined as SST 2 hr → dry 4 hr → wet 2 hr. A score of 3 or more was accepted. 5: Less than 5% 4: 5% to less than 10% 3: 10% to less than 20% 2: 20% to less than 30% 1: 30% or more
Table 3 shows the evaluation results. In the case of No. 2, the adhesion was rejected because the addition amounts of Al and Si were outside the range of the present invention. In all cases other than these, good results were obtained in adhesion and post-processing corrosion resistance. In particular, the plated steel sheet to which Si was added showed good adhesion and corrosion resistance after processing.
[0088]
[Table 3]

[0089]
【The invention's effect】
As described above, according to the present invention, it is possible to manufacture a highly corrosion-resistant coated steel sheet having sufficiently excellent sharpness even in the case of a high Al concentration, and it is possible to achieve industrially excellent effects.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an intermetallic compound present in an “Al” phase of a plating layer of a plated steel sheet, where (a) is a micrograph (× 1000) of the plating layer, and (b) is a photograph. It is a figure which shows the distribution state of each tissue in the photograph.
FIG. 2 (a) is a micrograph (magnification: 3500 times) of an enlarged “Al ″ phase”, and FIG. 2 (b) is a diagram showing the distribution of each tissue.

Claims

One side or both sides of the steel sheet has a zinc-based plating layer containing Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.01% by mass or less, with the balance being zinc and unavoidable impurities. A highly corrosion-resistant coated steel sheet having excellent clarity, characterized in that it has a conversion coating of a chromate coating or a phosphate coating as an intermediate layer and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer.

One or both sides of the steel sheet contain Al: 4 to 22% by mass, Mg: 1 to 5% by mass, Ti: 0.01% by mass or less, Si: 0.5% by mass or less, with the balance being zinc and inevitable. A sharpness property comprising a zinc-based plating layer made of impurities, a chromate film or a phosphate conversion film as an intermediate layer, and an organic film layer having a thickness of 0.2 to 100 μm as an upper layer. Excellent corrosion-resistant coated steel sheet.

One side or both sides of the steel sheet has a zinc-based plating layer containing Al: 4 to 10% by mass, Mg: 1 to 5% by mass, Ti: 0.1% by mass or less, with the balance being zinc and unavoidable impurities. A zinc-based plating layer of a coated steel sheet having a conversion coating of a chromate film or a phosphate film as an intermediate layer and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer [Al / Zn / Zn ₂ Mg 3 [Eutectic structure], a metal structure in which one or more of [Al phase], [Zn ₂ Mg phase] and [Zn phase] are mixed, and [Al phase], [Zn [ ₂ ] A highly corrosion-resistant coated steel sheet having excellent clarity, characterized in that one or more of the [Mg phase] and the [Zn phase] contain a Ti-Al-based intermetallic compound.

One or both sides of a steel sheet contains 4 to 22% by mass of Al, 1 to 5% by mass of Mg, 0.1% by mass or less of Ti, 0.5% by mass or less of Si, and the balance is zinc and inevitable impurities. A zinc-based plating layer of a coated steel sheet having a zinc-based plating layer consisting of a chromate coating or a phosphate conversion coating as an intermediate layer, and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer [ Al / Zn / Zn ₂ Mg ternary eutectic structure has a metal structure in which [Mg ₂ Si phase], [Al phase] and [Zn ₂ Mg phase] are mixed in the matrix, and [Al phase ] and [Zn 1 or two or sharpness of excellent high corrosion resistance coated steel sheet characterized by containing the Ti-Al system intermetallic compound in the 2 _Mg phase].

One or both sides of a steel sheet contains 4 to 22% by mass of Al, 1 to 5% by mass of Mg, 0.1% by mass or less of Ti, 0.5% by mass or less of Si, and the balance is zinc and inevitable impurities. A zinc-based plating layer of a coated steel sheet having a zinc-based plating layer consisting of a chromate coating or a phosphate conversion coating as an intermediate layer, and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer [ A metal structure in which [Mg ₂ Si phase], [Al phase], [Zn ₂ Mg phase] and [Zn phase] are mixed in a matrix of Al / Zn / Zn ₂ Mg ternary eutectic structure, In addition, one or more of [Al phase], [Zn ₂ Mg phase] and [Zn phase] contain a Ti-Al based intermetallic compound, and are excellent in sharpness. Corrosion resistant painted steel plate.

One or both sides of a steel sheet contains 4 to 22% by mass of Al, 1 to 5% by mass of Mg, 0.1% by mass or less of Ti, 0.5% by mass or less of Si, and the balance is zinc and inevitable impurities. A zinc-based plating layer of a coated steel sheet having a zinc-based plating layer consisting of a chromate coating or a phosphate conversion coating as an intermediate layer, and an organic coating layer having a thickness of 0.2 to 100 μm as an upper layer [ Al / Zn / Zn ₂ Mg ternary eutectic structure has a metal structure in which [Mg ₂ Si phase], [Al phase] and [Zn phase] are mixed in a matrix, and A highly corrosion-resistant coated steel sheet having excellent clarity, characterized in that one or two kinds of [Zn phase] contain a Ti-Al-based intermetallic compound.

TiAl-based intermetallic compound according to any one of claims 3 to 6, distinctness of excellent high corrosion resistance coated steel sheet, which is a TiAl _3.

Ti-Al system intermetallic compound according to any one of claims 3 to _6, characterized in that a _{_{Ti (Al 1-X Si X}} ) 3 ( provided that X = 0 to 0.5) High corrosion resistance coated steel sheet with excellent clarity.

The Ti-Al-based intermetallic compound contained in the [Al phase] in the plating layer is present in a Zn phase precipitated by a Zn-Al eutectoid reaction. A highly corrosion-resistant coated steel sheet having excellent clarity according to any of the above.

The highly corrosion-resistant coated steel sheet according to any one of claims 1 to 9, wherein dendrites of [Al phase] in the plating layer have a size of 500 µm or less.

The highly corrosion-resistant coated steel sheet according to any one of claims 1 to 10, wherein the organic coating is a thermosetting resin coating.

The highly corrosion-resistant coated steel sheet according to any one of claims 1 to 11, wherein the organic coating layer comprises an undercoat layer containing a rust preventive pigment and a colored overcoat layer.