JP2007284718A - Zn-Al ALLOY HOT-DIP PLATED STEEL SHEET SUPERIOR IN CORROSION RESISTANCE AND WORKABILITY, AND PRODUCTION METHOD THEREFOR - Google Patents

Zn-Al ALLOY HOT-DIP PLATED STEEL SHEET SUPERIOR IN CORROSION RESISTANCE AND WORKABILITY, AND PRODUCTION METHOD THEREFOR Download PDF

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JP2007284718A
JP2007284718A JP2006110961A JP2006110961A JP2007284718A JP 2007284718 A JP2007284718 A JP 2007284718A JP 2006110961 A JP2006110961 A JP 2006110961A JP 2006110961 A JP2006110961 A JP 2006110961A JP 2007284718 A JP2007284718 A JP 2007284718A
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Hideo Takamura
日出夫 高村
Hideo Ogishi
英夫 大岸
Hiroshi Ishikawa
博司 石川
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JFE Galvanizing and Coating Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a Zn-Al alloy hot-dip plated steel sheet superior in corrosion resistance, workability, further appearance after having been plated and spot weldability, and to provide a production method therefor. <P>SOLUTION: A plating bath has a composition adjusted so as to give the plated layer a composition, by average mass%, 25 to 70% Al, 0.5 to 5% Mg, 0.1 to 5% Si, 0.005×(Si%) to 0.05×(Si%)% Sr, or further 0.02 to 2% Cr, 0.02 to 2% Ni, and the balance Zn with unavoidable impurities. A method for forming the hot-dip plated Zn-Al alloy layer on the surface of a steel sheet comprises the steps of: dipping the steel sheet in the above plating bath; raising it up from the plating bath; and cooling it at a cooling rate of 10 to 100°C/s until the steel sheet reaches 350°C. The method may further comprises: temper-rolling the steel sheet at a rolling reduction of 0.5 to 5%; and overaging it at 150 to 350°C. Thereby produced Zn-Al alloy hot-dip plated steel acquires superior corrosion resistance, workability, further appearance after having been plated, and spot weldability. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、建築、建材、土木、家電等の分野で好適な、溶融Zn−Al系合金めっき鋼板に係り、とくに溶融Zn−Al系合金めっき鋼板の耐食性、加工性の改善に関する。   The present invention relates to a hot-dip Zn—Al-based alloy-plated steel sheet suitable for fields such as construction, building materials, civil engineering, and home appliances, and more particularly to improvement of corrosion resistance and workability of the hot-dip Zn-Al-based alloy-plated steel sheet.

従来から、自動車、建築、建材、土木、家電等の分野では、溶融Zn−Al系合金めっき鋼板が広く利用されてきた。なかでも、55%Al−Zn合金めっき鋼板(以下、ガルバリウム鋼板ともいう)で代表されるめっき層がAlを25〜75質量%含有する溶融Al−Zn合金めっき鋼板は、通常の溶融Znめっき鋼板に比べて耐食性が優れていることから、建築、建材、土木等の一部で用途が拡大している。しかし、ガルバリウム鋼板では、一般に、
(1)めっき層表面に、独特の6〜8角形のスパングル(花模様)が形成されるため、塗装を施しカラー鋼板とした場合、塗装面にスパングルが浮き上がり、塗装後の外観を損なう、
(2)めっき層が硬質なため、成形加工時にめっき層にクラックが発生しやすく、厳しい加工が施される部位ではめっき剥離が生じる場合がある、
(3)耐食性は、通常の溶融Znめっき鋼板に比べ優れているが、めっき層中のAlに起因して、腐食環境によっては、表面が局所的に黒灰色に変色する、いわゆる黒変現象が発生して、商品価値を著しく損なう場合がある、また、腐食環境によっては、切断端面部に赤錆が発生しやすく、さらに塗装した場合にエッジクリープと称する塗膜ふくれがはやく発生する場合がある、など耐食性に問題を残している、
(4)成形加工、曲げ加工等でめっき層にクラックが発生しやすいことから、この部分から赤錆が発生しやすく、加工部の耐食性も問題とされている、
(5)めっき層中のAl含有量が高いことに起因して、一般の冷延鋼板に比べてスポット溶接性が劣り、とくに通常の溶融Znめっき鋼板に比べ、スポット溶接時の適正溶接電流範囲が狭く、連続打点性が劣る、
等の問題が指摘されている。
Conventionally, molten Zn-Al alloy-plated steel sheets have been widely used in the fields of automobiles, construction, building materials, civil engineering, home appliances, and the like. Among them, a molten Al-Zn alloy-plated steel sheet in which a plating layer represented by a 55% Al-Zn alloy-plated steel sheet (hereinafter also referred to as a galbarium steel sheet) contains 25 to 75 mass% of Al is a normal molten Zn-plated steel sheet. Because of its superior corrosion resistance compared to, the use is expanding in some parts of construction, building materials, civil engineering, etc. However, with galvalume steel plates,
(1) Since a unique hexagonal octagonal spangle (flower pattern) is formed on the surface of the plating layer, when painted to make a color steel plate, the spangle floats on the painted surface and impairs the appearance after painting.
(2) Since the plating layer is hard, cracks are likely to occur in the plating layer during molding, and plating peeling may occur at sites where severe processing is performed.
(3) Corrosion resistance is superior to normal hot-dip Zn-plated steel sheets, but due to Al in the plating layer, depending on the corrosive environment, the so-called blackening phenomenon, in which the surface locally turns black-gray, The product value may be seriously impaired, and depending on the corrosive environment, red rust is likely to occur on the cut end face, and when it is further coated, a blister called edge creep may occur quickly. Leaving problems in corrosion resistance, etc.
(4) Since cracks are likely to occur in the plating layer during molding, bending, etc., red rust is likely to occur from this part, and the corrosion resistance of the processed part is also a problem.
(5) Due to the high Al content in the plating layer, spot weldability is inferior to that of ordinary cold-rolled steel sheets, and in particular, the appropriate welding current range during spot welding compared to ordinary hot-dip zinc-plated steel sheets. Is narrow and the continuous dotability is inferior,
Such problems have been pointed out.

このような問題に対し、例えば特許文献1には、Al:40〜70wt%、Si:0.5〜2.0wt%、残部Znからなる平均めっき皮膜組成を有し、めっき−鋼板界面に存在する合金層を除いた領域のめっき皮膜のSi濃度が1%以下で、平均めっき皮膜組成のSi濃度より低く、平均スパングル径が0.7mm以下である微小スパングルを有する溶融Zn−Al系合金めっき鋼板が開示されている。特許文献1に記載された溶融Zn−Al系合金めっき鋼板は、Si含有量を調整したAl−Zn合金溶融浴中で溶融めっき処理を行うことによりスパングルが微細化した溶融Zn−Al系合金めっき層が得られ、塗装後の外観むらが減少するとしている。   For such a problem, for example, Patent Document 1 discloses an alloy layer having an average plating film composition composed of Al: 40 to 70 wt%, Si: 0.5 to 2.0 wt%, and the balance Zn, and existing at the plating-steel sheet interface. Disclosed is a hot-dip Zn-Al alloy-plated steel sheet having fine spangles in which the Si concentration of the plating film in the region excluding 1 is 1% or less, lower than the Si concentration of the average plating film composition, and the average spangle diameter is 0.7 mm or less. ing. The hot-dip Zn-Al alloy-plated steel sheet described in Patent Document 1 is a hot-dip Zn-Al-based alloy plating in which spangles are refined by hot-dip plating in an Al-Zn alloy hot-water bath with an adjusted Si content. A layer is obtained, and the appearance irregularity after painting is reduced.

また、特許文献2には、Al:25〜70重量%、Si:0.5×Al重量%、残部Znからなるアルミニウム−亜鉛合金被覆された鉄基材製品を、約93℃〜427℃の温度に加熱し、この温度に所定時間保持し、ついで熱処理後に製品の熱硬化を防止する速度で周囲温度まで冷却する金属被覆鉄基材製品の製造方法が提案されている。特許文献2に記載された技術によれば、アルミ−亜鉛被覆の硬さを115HV以下とすることができ、高度に延性を有するものになるとしている。   Patent Document 2 discloses that an iron-base product coated with an aluminum-zinc alloy consisting of Al: 25 to 70 wt%, Si: 0.5 × Al wt%, and the balance Zn is set to a temperature of about 93 ° C. to 427 ° C. There has been proposed a method for producing a metal-coated iron base product that is heated and held at this temperature for a predetermined time and then cooled to ambient temperature at a rate that prevents the product from thermosetting after heat treatment. According to the technique described in Patent Document 2, the hardness of the aluminum-zinc coating can be made 115 HV or less, and is highly ductile.

また、特許文献3には、Zn−高Al合金めっきを施した鋼板のめっき面にブラスト処理し、次いでこのめっき鋼板に低温短時間の熱処理を行なう加工性に優れたZn−高Al合金めっき鋼板の製造方法が提案されている。特許文献3に記載された技術によれば、加工性が著しく改善されるとしている。
しかし、特許文献1、特許文献2、特許文献3に記載された技術では、いずれも20minから2.5hという長時間の熱処理を必要とし、生産性が極めて低いという問題がある。
Patent Document 3 discloses a Zn-high Al alloy-plated steel sheet excellent in workability in which a plated surface of a steel sheet plated with Zn-high Al alloy is blasted and then subjected to heat treatment at a low temperature in a short time. The manufacturing method of this is proposed. According to the technique described in Patent Document 3, the workability is remarkably improved.
However, the techniques described in Patent Document 1, Patent Document 2, and Patent Document 3 all require a long-time heat treatment of 20 min to 2.5 h, and have a problem that productivity is extremely low.

また、特許文献4には、重量%で、Al :45〜70%、Mg:1〜5%、Si:1.5〜10%を含有し、残部がZnおよび不可避的不純物からなり、Al/Zn:0.89〜2.75を満たし、さらに所定形状を有する塊状MgSi相の含有率が0.1〜30容量%である溶融亜鉛合金めっき層を有する耐食性に優れたZn−Al−Mg−Si合金めっき鋼材が提案されている。特許文献4に記載されためっき鋼板は、一般的なガルバリウム鋼板のめっき層組成であるAl−Zn−Si系合金めっき層にMgを添加したものである。 Patent Document 4 contains Al: 45 to 70%, Mg: 1 to 5%, Si: 1.5 to 10% by weight, and the balance is composed of Zn and inevitable impurities, and Al / Zn: Proposed Zn-Al-Mg-Si alloy-plated steel material excellent in corrosion resistance having a hot-dip zinc alloy plating layer satisfying 0.89 to 2.75 and having a bulk Mg 2 Si phase content of 0.1 to 30% by volume Has been. The plated steel sheet described in Patent Document 4 is obtained by adding Mg to an Al—Zn—Si alloy plating layer that is a plating layer composition of a general galvalume steel sheet.

また、特許文献5には、Al:25〜75重量%、Mg:1.0〜5.0%、Si:(Al含有量に対して0.5重量%以上)、を含有し、残部は本質的に亜鉛からなる合金めっき層が形成された亜鉛−アルミニウム合金めっき層が提案されている。特許文献5に記載されためっき鋼板は、一般的なガルバリウム鋼板のめっき層組成であるAl−Zn−Si系合金めっき層にMgを添加したものである。   Patent Document 5 contains Al: 25 to 75% by weight, Mg: 1.0 to 5.0%, Si: (0.5% by weight or more based on the Al content), and the balance is essentially made of zinc. A zinc-aluminum alloy plating layer in which an alloy plating layer is formed has been proposed. The plated steel sheet described in Patent Document 5 is obtained by adding Mg to an Al—Zn—Si based alloy plating layer, which is a plating layer composition of a general galbarium steel sheet.

また、特許文献6には、質量%で、Al :25〜75%、Cr:0.05〜5%、Si:Al含有量の0.5〜10%、あるいはさらにMg:0.1〜5%を含有し、残部はZn及び不可避的不純物からなるめっき層を有する溶融Zn−Al−Cr合金めっき鋼材が提案されている。特許文献6に記載されためっき鋼板は、一般的なガルバリウム鋼板のめっき層組成であるAl−Zn−Si系合金めっき層にCr、あるいはMgを添加し、耐食性の向上を狙ったものである。
特開平11−36057号公報 特公昭61−28748号公報 特開平4−41657号公報 特開2001−115247号公報 特開2000−104153号公報 特開2002−356759号公報
Patent Document 6 contains, in mass%, Al: 25 to 75%, Cr: 0.05 to 5%, Si: Al content of 0.5 to 10%, or Mg: 0.1 to 5%, and the balance. Has proposed a hot-dip Zn-Al-Cr alloy-plated steel material having a plating layer made of Zn and inevitable impurities. The plated steel sheet described in Patent Document 6 aims to improve corrosion resistance by adding Cr or Mg to an Al—Zn—Si alloy plating layer, which is a plating layer composition of a general galbarium steel sheet.
Japanese Patent Laid-Open No. 11-36057 Japanese Patent Publication No.61-28748 Japanese Patent Laid-Open No. 4-41657 Japanese Patent Laid-Open No. 2001-115247 JP 2000-104153 A JP 2002-356759 A

本発明者らの調査によれば、特許文献4〜6に記載された技術で製造された溶融Zn−Al系合金めっき鋼板はいずれも、切断端面部や曲げ加工部の耐食性にばらつきがあり、また加工性も劣り、十分なめっき層品質を有する溶融Zn−Al系合金めっき鋼板であるとは言いがたいものであり、問題を残していた。
本発明は、上記した従来技術の問題を有利に解決し、耐食性および加工性に優れるうえ、さらにめっき外観、スポット溶接性にも優れた溶融Zn−Al系合金めっき鋼板およびその製造方法を提供することを目的とする。
According to the investigations of the present inventors, all of the molten Zn-Al alloy-plated steel sheets manufactured by the techniques described in Patent Documents 4 to 6 have variations in the corrosion resistance of the cut end face part and the bent part, Moreover, it is hard to say that it is a hot-dip Zn-Al alloy-plated steel sheet having poor workability and sufficient plating layer quality, leaving a problem.
The present invention advantageously solves the above-described problems of the prior art, and provides a hot-dip Zn-Al alloy-plated steel sheet having excellent corrosion resistance and workability, and also excellent in plating appearance and spot weldability, and a method for producing the same. For the purpose.

本発明者らは、上記した課題を達成するために最適な、めっき層構造およびめっき処理工程について鋭意考究した。その結果、めっき層組成を、一般的なガルバリウム鋼板のめっき層組成であるAl−Zn−Si系めっき層組成に加えてさらにSr、Mgを、あるいはさらにCr、Niを含有させためっき層組成にすることにより、耐食性、加工性に優れるうえ、さらに美麗なめっき外観、優れたスポット溶接性を兼備する溶融Zn−Al系合金めっき鋼板となることを知見した。また、上記した特性を有する溶融Zn−Al系合金めっき鋼板は、下地鋼板に、上記しためっき層組成となるようにめっき浴組成を調整しためっき浴に浸漬したのち、めっき浴から引き上げめっき層が凝固するまでのめっき処理後の鋼板冷却速度を適正範囲に調整し、あるいはさらに調質圧延および過時効処理を組合わせた工程を施すことにより、製造できることを知見した。   The present inventors diligently studied about a plating layer structure and a plating process that are optimal for achieving the above-described problems. As a result, in addition to the Al-Zn-Si plating layer composition which is a plating layer composition of a general galvanium steel sheet, the plating layer composition is further changed to a plating layer composition containing Sr, Mg, or Cr, Ni. As a result, it was found that a hot-dip Zn-Al alloy-plated steel sheet having excellent corrosion resistance and workability, as well as a beautiful plating appearance and excellent spot weldability was obtained. In addition, the hot-dip Zn-Al alloy-plated steel sheet having the above-mentioned properties is immersed in a plating bath whose plating bath composition is adjusted so as to have the above-described plating layer composition on the base steel plate, and then lifted from the plating bath to have a plating layer. It has been found that the steel plate can be manufactured by adjusting the cooling rate of the steel plate after the plating treatment until solidification to an appropriate range, or by applying a process combining temper rolling and overaging treatment.

本発明は、上記した知見に基づき、さらに検討を加えて完成されたものである。すなわち、本発明の要旨は次のとおりである。
(1)鋼板表面に、溶融Zn−Al系合金めっき層を有してなる溶融Zn−Al系合金めっき鋼板であって、前記溶融Zn−Al系合金めっき層が、質量%で、Al:25〜70%、Si:0.1〜5%、Mg:0.5〜5%、Sr:0.005×(Si%)〜0.05×(Si%)%(ここで、Si%:Si含有量(質量%))を含み、残部Znおよび不可避的不純物からなる組成を有する合金めっき層であることを特徴とする耐食性および加工性に優れた溶融Zn−Al系合金めっき鋼板。
The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) A hot-dip Zn-Al-based alloy-plated steel plate having a hot-dip Zn-Al-based alloy plating layer on the surface of the steel plate, wherein the hot-melt Zn-Al-based alloy plating layer has a mass% of Al: 25 -70%, Si: 0.1-5%, Mg: 0.5-5%, Sr: 0.005 × (Si%)-0.05 × (Si%)% (where Si%: Si content (mass%)) A hot-dip Zn-Al alloy-plated steel sheet excellent in corrosion resistance and workability, characterized in that it is an alloy plating layer having a composition comprising the balance Zn and inevitable impurities.

(2)(1)において、前記溶融Zn−Al系合金めっき層が、前記組成に加えてさらに、質量%で、Cr:0.02〜2%およびNi:0.02〜2%を含有することを特徴とする溶融Zn−Al系合金めっき鋼板。
(3)鋼板に、溶融Zn−Al系合金めっき浴に浸漬したのち、該溶融Zn−Al系合金めっき浴から引き上げて冷却し、鋼板表面に溶融Zn−Al系合金めっき層を形成するめっき処理工程を施して、溶融Zn−Al系合金めっき鋼板とするに当り、前記溶融Zn−Al系合金めっき浴を、前記溶融Zn−Al系合金めっき層が平均で、質量%で、Al:25〜70%、Mg:0.5〜5%、Si:0.1〜5%、Sr:0.005×(Si%)〜0.05×(Si%)%(ここで、Si%:Si含有量(質量%))を含有し、残部Znおよび不可避的不純物からなるめっき層組成を有するように、めっき浴組成を調整しためっき浴とし、該溶融Zn−Al系合金めっき浴から引き上げたのちの前記冷却を、前記溶融Zn−Al系合金めっき浴から引き上げてから350℃までの平均冷却速度が10〜100℃/sである冷却とすることを特徴とする耐食性および加工性に優れた溶融Zn−Al系合金めっき鋼板の製造方法。
(2) In (1), the molten Zn—Al-based alloy plating layer further contains Cr: 0.02 to 2% and Ni: 0.02 to 2% by mass% in addition to the composition. Hot-dip Zn-Al alloy-plated steel sheet.
(3) Plating treatment that forms a molten Zn-Al alloy plating layer on the surface of the steel sheet after being immersed in a molten Zn-Al alloy plating bath and then pulled up from the molten Zn-Al alloy plating bath and cooled. When the step is performed to obtain a molten Zn-Al alloy-plated steel sheet, the molten Zn-Al-based alloy plating bath has an average of the molten Zn-Al-based alloy plating layer in mass%, and Al: 25 to 70%, Mg: 0.5-5%, Si: 0.1-5%, Sr: 0.005 × (Si%)-0.05 × (Si%)% (where Si%: Si content (mass%)) The plating bath composition is adjusted to have a plating layer composition composed of the balance Zn and unavoidable impurities, and the cooling after pulling up from the molten Zn-Al alloy plating bath is performed by the molten Zn- Corrosion resistance characterized by cooling with an average cooling rate of 10-100 ° C / s up to 350 ° C after being pulled up from the Al-based alloy plating bath And method for producing excellent melt Zn-Al alloy coated steel sheet in workability.

(4)(3)において、前記めっき処理工程に続いて、さらに圧下率:0.5〜5%の調質圧延を施す調質圧延工程と、ついで150〜350℃の温度範囲で過時効処理を施す過時効処理工程とを施すことを特徴とする溶融Zn−Al系合金めっき鋼板の製造方法。
(5)(3)または(4)において、前記めっき層組成に加えてさらに、質量%で、Cr:0.02〜2%およびNi:0.02〜2%を含有するめっき層組成とすることを特徴とする溶融Zn−Al系合金めっき鋼板の製造方法。
(4) In (3), subsequent to the plating treatment step, a temper rolling step for further temper rolling at a reduction ratio of 0.5 to 5%, and then an overaging treatment in a temperature range of 150 to 350 ° C. The manufacturing method of the hot-dip Zn-Al type alloy plating steel plate characterized by performing an overaging treatment process.
(5) In (3) or (4), in addition to the plating layer composition, the plating layer composition further contains, in mass%, Cr: 0.02 to 2% and Ni: 0.02 to 2%. A method for producing a hot-dip Zn-Al alloy-plated steel sheet.

本発明によれば、Zn−Al系合金めっき組成およびめっき後の冷却速度の調整により、耐食性および加工性に優れるうえ、さらにめっき外観、スポット溶接性にも優れた溶融Zn−Al系合金めっき鋼板を、安価にしかも安定して製造でき、産業上格段の効果を奏する。また、本発明によれば、めっき後の調質圧延、過時効処理によって、溶融Zn−Al系合金めっき鋼板の更なる加工性の向上と同時に、加工部の更なる耐食性の向上が実現できるという効果もある。   According to the present invention, by adjusting the Zn-Al alloy plating composition and the cooling rate after plating, the molten Zn-Al alloy-plated steel sheet has excellent corrosion resistance and workability as well as excellent plating appearance and spot weldability. Can be manufactured stably at a low cost, and has a remarkable industrial effect. In addition, according to the present invention, the temper rolling after plating and the overaging treatment can further improve the workability of the hot-dip Zn-Al alloy-plated steel sheet, and at the same time, further improve the corrosion resistance of the processed part. There is also an effect.

本発明の溶融Zn−Al系合金めっき鋼板(以下、単に本発明めっき鋼板ともいう)は、鋼板表面に、溶融Zn−Al系合金めっき層を形成してなる溶融Zn−Al系合金めっき鋼板である。本発明めっき鋼板のめっき層は、平均で、質量%で、Al:25〜70%、Si:0.1〜5%、Mg:0.5〜5%、Sr:0.005×(Si%)〜0.05×(Si%)%(ここで、Si%:Si含有量(質量%))を含み、あるいはさらにCr:0.02〜2%およびNi:0.02〜2%を含有し、残部Znおよび不可避的不純物からなる組成を有する合金めっき層である。   The hot-dip Zn-Al alloy-plated steel sheet of the present invention (hereinafter also simply referred to as the present invention-plated steel sheet) is a hot-dip Zn-Al-based alloy-plated steel sheet in which a hot-dip Zn-Al-based alloy plating layer is formed on the steel sheet surface. is there. The plating layer of the present plated steel sheet is, on average, mass%, Al: 25 to 70%, Si: 0.1 to 5%, Mg: 0.5 to 5%, Sr: 0.005 × (Si%) to 0.05 × (Si %) (Where Si%: Si content (mass%)), or Cr: 0.02 to 2% and Ni: 0.02 to 2%, and the balance consisting of Zn and inevitable impurities. It is an alloy plating layer.

なお、下地鋼板として使用する鋼板は、用途に応じて公知の鋼板から適宜選定すれば良く、とくに限定する必要はないが、例えば低炭素アルミキルド鋼、極低炭素鋼を用いることがめっき作業の観点から好ましい。
まず、本発明めっき鋼板のめっき層組成の限定理由について説明する。
めっき層のAl含有量が、25質量%未満では、Znがリッチとなりすぎ、めっき層の平面部耐食性が低下する。一方、Alを70質量%を超えて含有すると、Alリッチになり、儀性防食作用が低下するため端面耐食性が低下するとともに、めっき層が硬質化して加工性が低下する。このため、めっき層中のAlは25〜70質量%の範囲に限定した。
In addition, the steel plate used as the base steel plate may be appropriately selected from known steel plates depending on the application, and is not particularly limited. For example, low carbon aluminum killed steel or ultra low carbon steel may be used from the viewpoint of plating work. To preferred.
First, the reason for limiting the plating layer composition of the plated steel sheet of the present invention will be described.
If the Al content of the plating layer is less than 25% by mass, Zn becomes too rich, and the flat surface corrosion resistance of the plating layer decreases. On the other hand, when Al is contained in excess of 70% by mass, it becomes Al-rich and the anticorrosive action is lowered, so that the end face corrosion resistance is lowered and the plating layer is hardened and the workability is lowered. For this reason, Al in a plating layer was limited to the range of 25-70 mass%.

また、めっき層のSi含有量が、0.1質量%未満では、めっき層と鋼板との界面に形成される合金層が厚く形成され、めっき層の加工性が低下する。一方、5質量%を超えてSiを含有すると、Si結晶がインターデンドライト中で粗大化し加工性が低下するとともに、耐エッジクリープ性が低下する。このため、めっき層中のSiは0.1〜5質量%の範囲に限定した。   Moreover, if the Si content of the plating layer is less than 0.1% by mass, the alloy layer formed at the interface between the plating layer and the steel sheet is formed thick, and the workability of the plating layer is lowered. On the other hand, when Si is contained exceeding 5% by mass, the Si crystal becomes coarse in the interdendrite, and the workability is lowered and the edge creep resistance is lowered. For this reason, Si in a plating layer was limited to the range of 0.1-5 mass%.

本発明めっき鋼板のめっき層では、上記したAl、Siに加えて、Mg:0.5〜5質量%を含有する。
本発明ではMgは、スパングルサイズの調整を目的として、めっき層に含有させる。めっき層にMgを含有させることにより、スパングルが微細化し、未塗装でのめっき外観、さらには、塗装外観を美麗化することができる。スパングルサイズとめっき層中のMg含有量との関係を図1に示す。
In addition to Al and Si described above, the plating layer of the plated steel sheet of the present invention contains Mg: 0.5 to 5% by mass.
In the present invention, Mg is contained in the plating layer for the purpose of adjusting the spangle size. By containing Mg in the plating layer, spangles can be refined, and the appearance of plating without coating can be further improved. The relationship between the spangle size and the Mg content in the plating layer is shown in FIG.

図1から、めっき層中のMg含有量が増加するにしたがい、スパングルサイズが小さくなりスパングルの微細化が促進されることがわかる。スパングルは、めっき層中のMg含有量が0.5質量%以上で大きく微細化し、さらに3質量%以上で著しく微細化し、5質量%でほぼノースパングルとなる。なお、めっき層中のMg含有量が0.5質量%未満では、スパングルの微細化の程度が少なく、一方、5質量%を超えて含有すると、加工性が劣化する。このため、本発明では、めっき層中のMgを0.5〜5質量%に限定した。   From FIG. 1, it can be seen that as the Mg content in the plating layer increases, the spangle size is reduced and the refinement of the spangle is promoted. The spangle is greatly refined when the Mg content in the plating layer is 0.5% by mass or more, further remarkably refined when the content is 3% by mass or more, and becomes almost a North Pangle at 5% by mass. If the Mg content in the plating layer is less than 0.5% by mass, the degree of spangle miniaturization is small, whereas if it exceeds 5% by mass, the workability deteriorates. For this reason, in this invention, Mg in a plating layer was limited to 0.5-5 mass%.

なお、Mgは、硬い金属であり、めっき層全体(デンドライトおよびインターデントライト)にほぼ均一に分布している。このため、Mgの含有は加工性の観点からは不利になると考えられる。しかし、MgをSrと複合して含有すると、Mgの一部が優先的にSrと化合物を形成する。このため、加工時のめっき層のクラック発生が緩和され、加工性の低下が抑制されるものと推定される。5質量%を超えてめっき層中にMgを含有すると、Srが共存していても、フリーなMgが増加し、加工性が劣化する。   Note that Mg is a hard metal and is distributed almost uniformly over the entire plating layer (dendrite and interdentite). For this reason, inclusion of Mg is considered disadvantageous from the viewpoint of workability. However, when Mg is contained in combination with Sr, a part of Mg preferentially forms a compound with Sr. For this reason, it is estimated that the crack generation of the plating layer at the time of a process is relieve | moderated and the fall of workability is suppressed. When Mg is contained in the plating layer exceeding 5 mass%, free Mg increases even if Sr coexists, and workability deteriorates.

また、Mgは、めっき層の耐食性向上にも寄与する。Mgはめっき層全体に分布するとともに、めっき層表面部およびめっき層と鋼板との界面部にそれぞれ濃化する傾向を示す。このため、とくに、Crと共存した場合には、エッジクリープの進行が遅くなり、長期的な腐食抑制効果を助長すると考えられる。
本発明めっき鋼板のめっき層では、上記したAl、Si、Mgに加えてさらに、Sr を含有する。Sr はSi含有量と関連して含有し、Si含有量の0.5〜5質量%、すなわち0.005×(Si%)〜0.05×(Si%)質量%を含有する。ここで、Si%は質量%で表示したSi含有量を意味する。
Mg also contributes to improving the corrosion resistance of the plating layer. Mg is distributed throughout the plating layer and tends to be concentrated at the surface of the plating layer and at the interface between the plating layer and the steel sheet. For this reason, especially when coexisting with Cr, it is considered that the progress of edge creep is slowed and the long-term corrosion inhibiting effect is promoted.
The plated layer of the plated steel sheet of the present invention further contains Sr in addition to the above-described Al, Si, and Mg. Sr is contained in relation to the Si content, and contains 0.5 to 5% by mass of the Si content, that is, 0.005 × (Si%) to 0.05 × (Si%)% by mass. Here, Si% means the Si content expressed in mass%.

ガルバリウム鋼板のめっき層は、一般的にAlを含むデンドライトとZnを主としたインターデントライトを骨格としためっき層構造を有し、硬い針状のSi結晶およびSi化合物がインターデントライト中に濃化する。このため、加工性が低下する。本発明では、加工性を改善するために、めっき層にSrを含有させる。Sr含有量がSi含有量に対して一定の割合にあるとき、加工性が改善される。   The plating layer of galvalume steel sheet generally has a plating layer structure with a dendrite containing Al and an interdentite mainly composed of Zn, and hard needle-like Si crystals and Si compounds are concentrated in the interdentite. Turn into. For this reason, workability falls. In the present invention, in order to improve workability, the plating layer contains Sr. When the Sr content is at a certain ratio with respect to the Si content, workability is improved.

本発明では、めっき層にSrをSi含有量に対して一定の割合で含有させ、めっき層中の針状のSi結晶を球状の微細なSi結晶に変化させて、曲げ加工時にインターデンドライトからのクラック発生を抑制する。
Sr含有量が、0.005×(Si%)質量%未満では、上記した効果が認められない。一方、Srを0.05×(Si%)質量%を超えて含有すると、めっき層にSr−Si系の析出物が析出し、これに起因すると推定される筋状欠陥がめっき表面に発生してめっき外観を損なう。このため、Srは0.005×(Si%)〜0.05×(Si%)質量%の範囲に限定した。なお、好ましくは、0.01×(Si%)〜0.03×(Si%)質量%である。
In the present invention, Sr is contained in the plating layer at a certain ratio with respect to the Si content, and the needle-like Si crystal in the plating layer is changed to a spherical fine Si crystal, so that the Suppresses the generation of cracks.
When the Sr content is less than 0.005 × (Si%) mass%, the above-described effects are not observed. On the other hand, when Sr exceeds 0.05 × (Si%) mass%, Sr-Si-based precipitates are deposited on the plating layer, and the streak defects that are presumed to result from this occur on the plating surface. The appearance is damaged. For this reason, Sr was limited to the range of 0.005 × (Si%) to 0.05 × (Si%) mass%. In addition, Preferably, they are 0.01x (Si%)-0.03x (Si%) mass%.

ガルバリウム鋼板は、腐食環境によっては、黒変しやすく、また、加工部および切断端面部には赤錆が発生しやすい。さらに塗装したものは、エッジクリープと称するめっき層腐食による塗膜ふくれが発生しやすい。これらの問題を解消するため、本発明めっき鋼板のめっき層では、上記したAl、Si、Mg、Srに加えてさらに、Cr:0.02〜2質量%、Ni:0.02〜2質量%を、複合して含有することが好ましい。   The Galvalume steel plate is likely to turn black depending on the corrosive environment, and red rust is likely to occur in the processed part and the cut end face part. Further, the coated material is liable to cause blistering due to plating layer corrosion called edge creep. In order to solve these problems, in the plating layer of the plated steel sheet of the present invention, in addition to the above Al, Si, Mg, Sr, Cr: 0.02 to 2% by mass, Ni: 0.02 to 2% by mass are combined. It is preferable to contain.

めっき層中では、Crは、主として鋼板とめっき層界面近傍に、Niは、主としてめっき層表面に、濃化する傾向がある。図2に、本発明めっき鋼板について、めっき層表面から深さ方向に、グロー放電発光分光分析(GDS分析)によりめっき層中に含有する他の元素(Al、Zn、Si、Sr、Mg)と共に分析した、CrおよびNiの分布を、デプス分析結果の一例として示す。なお、めっき層組成は、Cr:0.1質量%、Ni:0.1質量%、Al:50質量%、Si:2.0質量%、Sr:0.033質量%、Mg:3質量%、残部Znである。図2から、Crは主として鋼板とめっき層界面近傍に濃化ピークが、Niは主としてめっき層表面に濃化ピークが認められる。   In the plating layer, Cr tends to concentrate mainly in the vicinity of the interface between the steel plate and the plating layer, and Ni mainly concentrates on the surface of the plating layer. Fig. 2 shows the plated steel sheet of the present invention, along with other elements (Al, Zn, Si, Sr, Mg) contained in the plating layer by glow discharge emission spectroscopic analysis (GDS analysis) in the depth direction from the surface of the plating layer. The analyzed distribution of Cr and Ni is shown as an example of the depth analysis result. The plating layer composition is Cr: 0.1% by mass, Ni: 0.1% by mass, Al: 50% by mass, Si: 2.0% by mass, Sr: 0.033% by mass, Mg: 3% by mass, and the balance Zn. From FIG. 2, Cr has a concentration peak mainly near the interface between the steel plate and the plating layer, and Ni has a concentration peak mainly on the surface of the plating layer.

黒変は、めっき層表面の酸化により、また、切断端面部の赤錆発生、エッジクリープは、鋼板端面とめっき層の腐食により発生する。したがって、めっき層と鋼板界面に濃化したCrは、切断端面部の錆発生の抑制に大きく寄与するものと推定でき、耐切断端面さび性、耐エッジクリープ性を改善する作用を有し、また、めっき層表面に濃化するNiは、黒変発生の抑制に大きく寄与するものと推定でき、耐黒変性を改善する作用を有する。   Blackening is caused by oxidation of the plating layer surface, red rust is generated at the cut end face portion, and edge creep is caused by corrosion of the steel plate end face and the plating layer. Therefore, it can be estimated that Cr concentrated at the interface between the plating layer and the steel sheet greatly contributes to the suppression of rust generation at the cut end face part, and has the effect of improving the cut end face rust resistance and edge creep resistance. Ni concentrated on the surface of the plating layer can be presumed to greatly contribute to the suppression of the occurrence of blackening, and has the effect of improving blackening resistance.

Cr含有量が0.02質量%未満では、切断端面の耐食性の改善が少なく、またNi含有量が0.02質量%未満では、耐黒変性の改善が少ない。一方、Cr、Niをそれぞれ2質量%を超えてめっき層中に含有させると、めっき浴にCr、Niを含有したドロスが多量に発生し、めっき時に鋼板にドロスが付着し、めっき外観が低下する。このため、Cr、Niをめっき層中に含有する場合には、Crは0.02〜2質量%、Niは0.02〜2質量%に限定することが好ましい。   When the Cr content is less than 0.02% by mass, the corrosion resistance of the cut end face is little improved, and when the Ni content is less than 0.02% by mass, the blackening resistance is hardly improved. On the other hand, if more than 2% by mass of Cr and Ni are contained in the plating layer, a large amount of dross containing Cr and Ni is generated in the plating bath, and the dross adheres to the steel sheet during plating, resulting in poor plating appearance. To do. For this reason, when Cr and Ni are contained in the plating layer, Cr is preferably limited to 0.02 to 2% by mass, and Ni is preferably limited to 0.02 to 2% by mass.

上記した成分以外のめっき層の残部は、Znおよび不可避的不純物である。
上記したようなめっき層組成を有することにより、従来のガルバリウム鋼板に比べて、耐食性および加工性に優れるうえ、めっき外観にも優れた溶融Zn−Al系合金めっき鋼板とすることができる。
また、本発明めっき鋼板は、スポット溶接性にも優れためっき鋼板となる。一般的に、溶融Znめっき鋼板および溶融Zn−Al系合金めっき鋼板は、冷延鋼板に比べ、低融点めっき層のため、スポット溶接性が劣る。とくに、ガルバリウム鋼板は、溶融Znめっき鋼板より適正溶接範囲が狭いと言われている。これは、めっき層中のAl含有量が多いため、電極の消耗が速いことによると考えられる。本発明めっき鋼板は、めっき層中にAl、Siに加えて、Sr、Mg、あるいはさらにCr、Niを含有しており、めっき層の融点が上昇し、電極へのAl酸化物の付着が防止され、スポット溶接時の電極の損傷が抑制されて、スポット溶接性、とくに連続打点性が向上するものと考えられる。
The balance of the plating layer other than the above components is Zn and inevitable impurities.
By having such a plating layer composition as described above, it is possible to obtain a hot-dip Zn-Al alloy-plated steel sheet that is excellent in corrosion resistance and workability as well as in the appearance of plating as compared with a conventional galbarium steel sheet.
Moreover, this invention plated steel plate turns into a plated steel plate excellent also in spot weldability. Generally, a hot-dip Zn-plated steel sheet and a hot-dip Zn-Al-based alloy-plated steel sheet are inferior in spot weldability because of a low melting point plating layer as compared with a cold-rolled steel sheet. In particular, it is said that the galvalume steel sheet has a narrower appropriate welding range than the hot-dip Zn-plated steel sheet. This is thought to be due to the fact that the electrode is consumed quickly because of the high Al content in the plating layer. The plated steel sheet of the present invention contains Sr, Mg, or even Cr, Ni in addition to Al and Si in the plating layer, which increases the melting point of the plating layer and prevents adhesion of Al oxide to the electrode. Thus, it is considered that the damage of the electrode during spot welding is suppressed, and the spot weldability, particularly the continuous spotting property is improved.

次に、本発明の溶融Zn−Al系合金めっき鋼板の好ましい製造方法について説明する。
本発明で、下地鋼板として使用する鋼板は、用途に応じ公知の鋼板から適宜選定すれば良く、特に限定する必要はないが、例えば低炭素アルミキルド鋼、極低炭素鋼を用いることが、めっき作業の観点から好ましい。
本発明では、これらの鋼板を下地鋼板として、鋼板に、溶融Zn−Al系合金めっき浴に浸漬したのち、該溶融Zn−Al系合金めっき浴から引き上げて冷却し、鋼板表面に溶融Zn−Al系合金めっき層を形成するめっき処理工程を施して、溶融Zn−Al系合金めっき鋼板とする。
Next, the preferable manufacturing method of the hot dip Zn-Al system alloy plating steel plate of the present invention is explained.
In the present invention, the steel sheet used as the base steel sheet may be appropriately selected from known steel sheets depending on the application, and is not particularly limited. For example, a low carbon aluminum killed steel or an extremely low carbon steel may be used for the plating operation. From the viewpoint of
In the present invention, these steel plates are used as base steel plates, immersed in a steel plate in a molten Zn-Al alloy plating bath, then cooled by pulling up from the molten Zn-Al alloy plating bath, and molten Zn-Al on the steel plate surface. A plating treatment step for forming a base alloy plating layer is performed to obtain a hot-dip Zn-Al alloy plated steel sheet.

使用する溶融Zn−Al系合金めっき浴は、形成される溶融Zn−Al系合金めっき層組成と実質的に同一のめっき浴組成に調整することが好ましい。なお、形成される溶融Zn−Al系合金めっき層は、平均で、質量%で、Al:25〜70%、Mg:0.5〜5%、Si:0.1〜5%、Sr:0.005×(Si%)〜0.05×(Si%)%を含み、あるいはさらにCr:0.02〜2%、Ni:0.02〜2%を含有し、残部Znおよび不可避的不純物からなる組成のめっき層である。なお、使用するめっき浴の浴温は、580〜630℃の範囲の温度に調節することが好ましい。   It is preferable to adjust the hot-dip Zn-Al alloy plating bath used to a plating bath composition substantially the same as the hot-dip Zn-Al alloy plating layer composition to be formed. In addition, the hot-dip Zn-Al alloy plating layer to be formed has an average mass% of Al: 25 to 70%, Mg: 0.5 to 5%, Si: 0.1 to 5%, Sr: 0.005 × (Si% ) To 0.05 × (Si%)%, or further containing Cr: 0.02 to 2% and Ni: 0.02 to 2%, and a plating layer having a composition composed of the balance Zn and inevitable impurities. The bath temperature of the plating bath used is preferably adjusted to a temperature in the range of 580 to 630 ° C.

鋼板を溶融Zn−Al系合金めっき浴に浸漬したのち、溶融Zn−Al系合金めっき浴から引き上げて冷却し、表面のめっき層の凝固を完成させるが、めっき浴から引き上げたのちの冷却は、めっき浴から引き上げてから350℃までの平均冷却速度を10〜100℃/sとすることが好ましい。平均冷却速度が10℃/s未満では,めっき層と鋼板との界面に形成される合金層の厚みを、所定範囲内の厚みに調整することが困難となり、一方、100℃/sを超えて大きくなると、インターデンドライト部へのSrの濃化が抑制され、針状のSi結晶を含む合金層が厚く成長し、加工性が低下する。このようなことから、めっき浴から引き上げてから350℃までの平均冷却速度を10〜100℃/sに限定することが好ましい。なお、350℃以下はとくに冷却速度を既定する必要はない。   After the steel sheet is immersed in a molten Zn-Al alloy plating bath, it is pulled up from the molten Zn-Al alloy plating bath and cooled to complete the solidification of the surface plating layer. It is preferable that the average cooling rate up to 350 ° C. after pulling up from the plating bath is 10 to 100 ° C./s. If the average cooling rate is less than 10 ° C / s, it becomes difficult to adjust the thickness of the alloy layer formed at the interface between the plating layer and the steel sheet to a thickness within a predetermined range, while it exceeds 100 ° C / s. When it becomes larger, the concentration of Sr in the interdendrite portion is suppressed, and an alloy layer containing needle-like Si crystals grows thick, resulting in a decrease in workability. For this reason, it is preferable to limit the average cooling rate up to 350 ° C. after pulling up from the plating bath to 10 to 100 ° C./s. Note that it is not necessary to set the cooling rate below 350 ° C.

また、本発明では、更なる加工性向上および加工部の更なる耐食性向上のために、上記しためっき処理工程に引続いて、調質圧延工程および過時効処理工程を順次施すことが好ましい。めっき処理工程に引続いて、調質圧延工程および過時効処理工程を施すことにより、めっき層中のデンドライト部のα−Al(Zn)相の軟質化を図ることができ、これによりめっき層全体が軟質化してめっき鋼板の加工性を向上させることができる。   In the present invention, in order to further improve the workability and further improve the corrosion resistance of the processed portion, it is preferable to sequentially perform the temper rolling process and the overaging process process following the plating process described above. Subsequent to the plating treatment step, the temper rolling step and the overaging treatment step can be performed to soften the α-Al (Zn) phase of the dendrite part in the plating layer, thereby making the entire plating layer Can be softened to improve the workability of the plated steel sheet.

調質圧延工程は、圧下率:0.5〜5%の調質圧延を施す工程とすることが好ましい。調質圧延を施し、めっき層中のα−Al(Zn)相に適正量の転位を導入する。これにより、次工程の過時効処理の処理時間を短縮することができる。圧下率が0.5%未満では、導入される転位量が不十分で、調質圧延工程と過時効処理工程の組み合わせによる効果が期待できない。一方、圧下率が5%を超えても、過時効処理時間の短縮効果が飽和する。このようなことから、調質圧延の圧下率は0.5〜5%の範囲に限定することが好ましい。   The temper rolling step is preferably a step of temper rolling with a rolling reduction of 0.5 to 5%. Temper rolling is performed, and an appropriate amount of dislocations is introduced into the α-Al (Zn) phase in the plating layer. Thereby, the processing time of the overaging process of the next process can be shortened. When the rolling reduction is less than 0.5%, the amount of dislocation introduced is insufficient, and the effect of the combination of the temper rolling process and the overaging process cannot be expected. On the other hand, even if the rolling reduction exceeds 5%, the effect of shortening the overaging treatment time is saturated. For this reason, it is preferable to limit the rolling reduction of temper rolling to a range of 0.5 to 5%.

過時効処理工程は、150〜350℃の温度範囲で過時効処理を施す工程とすることが好ましい。過時効処理を施すことにより、めっき層中のα−Al(Zn)相に過飽和に固溶されているZnの析出を図る。過時効処理の温度が150℃未満では、GPゾーンの形成によって却って時効硬化し、加工性が劣化する。一方、350℃を超えて高くなると、硬いAl2.45Zn(六方晶R3m)が形成されて硬化し、加工性が劣化する。このため、過時効処理の温度は150〜350℃の範囲の温度に限定することが好ましい。なお、より好ましくは170〜250℃である。また、過時効処理の時間は20s〜20minとすることがより好ましい。 The overaging treatment step is preferably a step of performing overaging treatment in a temperature range of 150 to 350 ° C. By applying an overaging treatment, precipitation of Zn that is supersaturated in the α-Al (Zn) phase in the plating layer is attempted. If the temperature of the overaging treatment is less than 150 ° C., the age hardening is caused by the formation of the GP zone, and the workability deteriorates. On the other hand, when the temperature exceeds 350 ° C., hard Al 2.45 Zn (hexagonal R3m) is formed and hardened, and the workability deteriorates. For this reason, it is preferable to limit the temperature of an overaging process to the temperature of the range of 150-350 degreeC. In addition, More preferably, it is 170-250 degreeC. The overaging treatment time is more preferably 20 s to 20 minutes.

上記した工程で製造された溶融Zn−Al系合金めっき鋼板は、厳しい成形加工、厳しい絞り加工等を施してもクラックの生成がほとんどなく、加工性が更に向上し、結果的に加工部の更なる耐食性向上が可能となる。
以下、実施例に基づいて、さらに本発明について詳細に説明する。
The hot-dip Zn-Al alloy-plated steel sheet manufactured in the above-described process has almost no cracks even when subjected to severe forming or severe drawing, and the workability is further improved. It becomes possible to improve the corrosion resistance.
Hereinafter, based on an Example, this invention is demonstrated further in detail.

Alキルド鋼板(未焼鈍:板厚0.8mm×板幅1500mm)を下地鋼板として、下地鋼板に、連続式溶融Zn−Al系合金めっき鋼板製造設備を用いて、溶融Zn−Al系合金めっき浴に浸漬したのち、溶融Zn−Al系合金めっき浴から引き上げて冷却し、鋼板表面に溶融Zn−Al系合金めっき層を形成するめっき処理工程を施し、溶融Zn−Al系合金めっき鋼板とした。
使用した溶融Zn−Al系合金めっき浴は、めっき層の平均組成が表1に示す組成となるように、めっき浴組成を調整し、浴温を表1に示す温度とするめっき浴とした。また、めっき浴から引き上げてのちの冷却は、めっき浴から引き上げてから350℃までの平均冷却速度が表1に示す冷却速度となるように調整した。なお、冷却速度の調整は、エアーによった。また、めっき付着量は片面当り65〜85g/m2とした。
Using an Al-killed steel plate (unannealed: plate thickness 0.8mm × plate width 1500mm) as the base steel plate, using the continuous hot-dip Zn-Al alloy-plated steel plate manufacturing equipment as the base steel plate, After the immersion, the steel sheet was pulled out of the molten Zn—Al alloy plating bath and cooled, and a plating treatment step for forming a molten Zn—Al alloy alloy plating layer on the steel sheet surface was performed to obtain a molten Zn—Al alloy alloy plated steel sheet.
The used molten Zn—Al-based alloy plating bath was a plating bath in which the plating bath composition was adjusted so that the average composition of the plating layer was the composition shown in Table 1, and the bath temperature was the temperature shown in Table 1. Further, the cooling after lifting from the plating bath was adjusted so that the average cooling rate up to 350 ° C. after the lifting from the plating bath was the cooling rate shown in Table 1. The cooling rate was adjusted by air. Moreover, the plating adhesion amount was 65 to 85 g / m 2 per side.

得られためっき鋼板の一部を用いて、それらめっき鋼板にさらに、表1に示す条件で調質圧延を行う調質圧延工程および表1に示す条件で過時効処理を行う過時効処理工程を順次施した。なお、過時効処理は、連続焼鈍炉又はバッチ式の焼鈍炉を使用した。
得られためっき鋼板について、めっき外観、めっき層組織、めっき層硬さ、加工性、耐黒変性、加工部耐食性、耐切断端面さび性、耐エッジクリープ性、スポット溶接性を調査した。調査方法は次のとおりである。
Using a part of the obtained plated steel sheet, a temper rolling process for performing temper rolling on the plated steel sheet under the conditions shown in Table 1 and an overaging treatment process for performing overaging treatment on the conditions shown in Table 1 Sequentially applied. In addition, the overaging process used the continuous annealing furnace or the batch-type annealing furnace.
The obtained plated steel sheet was examined for plating appearance, plating layer structure, plating layer hardness, workability, blackening resistance, processed portion corrosion resistance, cut end surface rust resistance, edge creep resistance, and spot weldability. The survey method is as follows.

(1)めっき外観
得られた各めっき鋼板について、一定面積内の不めっきおよびドロス付着等の表面欠陥の有無を目視で観察し、5段階で評価した。評価:5は表面欠陥が無い場合、評価:4は表面欠陥が1点、評価:3は表面欠陥が1〜3点、評価:2は表面欠陥が4〜6点、評価:1は表面欠陥が7点以上存在する場合とした。
(1) Plating appearance About each obtained plated steel plate, the presence or absence of surface defects, such as non-plating and dross adhesion within a fixed area, was visually observed and evaluated in five stages. Evaluation: 5 indicates no surface defect, Evaluation: 4 indicates 1 surface defect, Evaluation: 3 indicates 1 to 3 surface defects, Evaluation: 2 indicates 4 to 6 surface defects, Evaluation: 1 indicates surface defects 7 or more points.

また、得られた各めっき鋼板について、実体顕微鏡を用いて表面スパングル形態を撮影(10倍)し、一定の測定面積(70×100mm)内のスパングル核の数を測定し、下記式
スパングル平均面積=(測定面積)/(スパングル核数)=π(d/2)2
(ここでd:スパングルの円相当径、π:円周率)
を用いて、スパングルの平均面積を求めて、スパングルの円相当径dを算出し、これをスパングル平均径として、5段階で評価した。評価:5は、スパングル平均径が0mm、評価:4は、スパングル平均径が0.1〜0.5mm、評価:3は、スパングル平均径が0.6〜1.0mm、評価:2は、スパングル平均径が1.1〜2.0mm、評価:1は、スパングル平均径が2.1mm以上、の場合とした。なお、表面欠陥評価が評価:4以上、スパングルが評価:3以上であれば、めっき外観が良好であると評価する。
Also, for each plated steel sheet obtained, the surface spangle form was photographed (10x) using a stereomicroscope, and the number of spangle nuclei within a certain measurement area (70 x 100 mm) was measured. = (Measurement area) / (Number of spangle nuclei) = π (d / 2) 2
(Where d: equivalent circle diameter of spangle, π: pi)
Was used to determine the average area of spangles, and the equivalent circle diameter d of spangles was calculated, which was evaluated in five stages as the spangle average diameter. Evaluation: 5 has a spangle average diameter of 0 mm, Evaluation: 4 has a spangle average diameter of 0.1-0.5 mm, Evaluation: 3 has a spangle average diameter of 0.6-1.0 mm, and Evaluation: 2 has a spangle average diameter of 1.1- 2.0 mm, evaluation: 1 was the case where the spangle average diameter was 2.1 mm or more. In addition, if surface defect evaluation is evaluation: 4 or more and spangle is evaluation: 3 or more, it will evaluate that plating external appearance is favorable.

(2)めっき層組織
得られた各めっき鋼板から試験片(組織観察用)を採取し、走査型電子顕微鏡を用いて、めっき層インターデンドライト部のSi結晶の形状を観察し、Si結晶の球状化状況を5段階で評価した。評価:5は、球状化率が100%、評価:4は、球状化率が99〜80%、評価:3は、球状化率が79〜60%、評価:2は、球状化率が59〜40%、評価:1は、球状化率が39%以下、の場合とした。なお、球状化率は、全Si結晶個数に対する球状化したSi結晶個数の割合(%)をいうものとする。なお、評価:3以上であればめっき層組成が良好であると評価した。
(2) Plating layer structure A specimen (for structure observation) is collected from each of the obtained plated steel sheets, and the shape of the Si crystal in the plating layer interdrite portion is observed using a scanning electron microscope, and the spherical shape of the Si crystal The status of conversion was evaluated in five stages. Evaluation: 5 is 100% spheroidization rate, evaluation: 4 is 99-80% spheroidization rate, evaluation: 3 is 79-60% spheroidization rate, evaluation: 2 is 59 spheroidization rate -40%, evaluation: 1 was made when the spheroidization rate was 39% or less. The spheroidization rate refers to the ratio (%) of the number of spheroidized Si crystals to the total number of Si crystals. In addition, if the evaluation was 3 or more, it was evaluated that the plating layer composition was good.

(3)めっき層硬さ
得られた各めっき鋼板から試験片(硬さ測定用)を採取し、めっき層断面で、マイクロビッカース硬度計を用いて、めっき層デンドライト部のα−Al相の硬さHV0.025を測定した。硬さ測定は、JIS Z 2244 の規定に準拠して、荷重24.5mN(2.5gf)で行った。
(4)加工性
得られた各めっき鋼板から試験片(大きさ:板厚0.8×幅50×長さ50mm)を採取し、試験片に対し180°(0T)曲げ加工を施したのち、曲げ部について反射電子像を10倍で撮影し、その部分をスキャンして画像解析によりその領域に現れる亀裂部の面積を測定し、曲げ加工部全面積に対する亀裂面積率を算出して、加工性を5段階で評価した。評価:5は、亀裂面積率が5%以下、評価:4は、亀裂面積率が5%超え10%以下、評価:3は、亀裂面積率が10%超え30%以下、評価:2は、亀裂面積率が35%以上、評価:1は、剥離発生、の場合とした。なお、評価:4以上を加工性良好と評価した。
(3) Hardness of plating layer A specimen (for hardness measurement) is collected from each of the obtained plated steel sheets, and the hardness of the α-Al phase of the plating layer dendrite part is measured with a micro Vickers hardness meter in the cross section of the plating layer. HV0.025 was measured. Hardness measurement was performed at a load of 24.5 mN (2.5 gf) in accordance with the provisions of JIS Z 2244.
(4) Workability A test piece (size: thickness 0.8 x width 50 x length 50 mm) is sampled from each of the obtained plated steel sheets, subjected to 180 ° (0T) bending, and then bent. Take a backscattered electron image at a magnification of 10 times, scan the area, measure the area of the crack that appears in the area by image analysis, calculate the crack area ratio relative to the total area of the bent part, and workability Evaluation was made in 5 stages. Evaluation: 5 has a crack area ratio of 5% or less, Evaluation: 4 has a crack area ratio of 5% to 10%, Evaluation: 3 has a crack area ratio of 10% to 30%, Evaluation: 2 The crack area ratio was 35% or more, and evaluation: 1 was the case where peeling occurred. In addition, evaluation: 4 or more was evaluated as favorable workability.

(5)耐黒変性
得られた各めっき鋼板から試験片(大きさ:板厚0.8×幅50×長さ70mm)を採取し、各試験片同士をそれぞれ積層して、湿潤雰囲気(相対湿度:95%以上、温度:49℃)下に10日間放置する試験(黒変試験)を行ったのち、JIS Z 8722の規定に準拠して色差計で試験片表面のL値(明度)を測定し、黒変試験前後の試験片表面のL値(明度)の変化ΔL(=(黒変試験前のL値)−(黒変試験後のL値))を求め、耐黒変性を5段階で評価した。評価:5はΔLが0、評価:4はΔLが1〜3、評価:3はΔLが4〜8、評価:2はΔLが9〜12、評価:1はΔLが13以上、の場合とした。なお、評価:4以上を耐黒変性良好と評価した。
(5) Blackening resistance Test specimens (size: thickness 0.8 x width 50 x length 70 mm) were sampled from each of the obtained plated steel sheets, and the test specimens were laminated with each other to obtain a humid atmosphere (relative humidity: After a test (blackening test) that is allowed to stand for 10 days under a temperature of 95% or more and a temperature of 49 ° C, the L value (brightness) of the test piece surface is measured with a color difference meter in accordance with the provisions of JIS Z 8722. A change ΔL (= (L value before the blackening test) − (L value after the blackening test)) of the L value (brightness) on the surface of the test piece before and after the blackening test is obtained, and blackening resistance is determined in five stages. evaluated. Evaluation: 5 is ΔL is 0, Evaluation: 4 is ΔL is 1 to 3, Evaluation: 3 is ΔL is 4 to 8, Evaluation: 2 is ΔL is 9 to 12, Evaluation: 1 is ΔL is 13 or more did. In addition, evaluation: 4 or more was evaluated as favorable blackening-proof property.

(6)加工部耐食性
得られた各めっき鋼板から試験片(大きさ:板厚0.8×幅70×長さ150mm)を採取し、曲げ加工(密着曲げ:OT)を施したのち、試験片の上下左右の端面をテープでシールして、JIS K 5621の規定に準拠した複合促進試験(JIS CCT)を実施した。JIS CCT試験の条件は、塩水(5%NaCl)噴霧0.5h→湿潤(温度:30℃、相対湿度RH:95%)1.5h→乾燥(温度:50℃、相対湿度RH:20%)2h→乾燥(温度:30℃、相対湿度RH:20%)2hを1サイクルとして、このサイクルを2000サイクルまで行った。
(6) Corrosion resistance of machined parts Samples (size: thickness 0.8 x width 70 x length 150 mm) were collected from each plated steel sheet and subjected to bending (adhesion bending: OT). A composite accelerated test (JIS CCT) in accordance with JIS K 5621 was conducted by sealing the top, bottom, left and right end faces with tape. JIS CCT test conditions are: salt water (5% NaCl) spray 0.5h → wet (temperature: 30 ° C, relative humidity RH: 95%) 1.5h → dry (temperature: 50 ° C, relative humidity RH: 20%) 2h → Drying (temperature: 30 ° C., relative humidity RH: 20%) 2 h was one cycle, and this cycle was repeated up to 2000 cycles.

試験後、曲げ加工部について曲げ加工部の両端面シール部(5mm×2)を除く部分の面積(2×60mm)に対する赤さび発生面積率を目視観察して測定し、加工部耐食性を5段階で評価した。評価:5は、赤さび発生面積率が5%以下、評価:4は、赤さび発生面積率が6〜15%、評価:3は、赤さび発生面積率が16〜30%、評価:2は、赤さび発生面積率が31〜50%、評価:1は、赤さび発生面積率が51%以上、の場合とした。なお、評価:3以上を加工部耐食性良好と評価した。   After the test, the bent portion is measured by visually observing and measuring the red rust generation area ratio for the area (2 × 60mm) of the bent portion excluding both end seals (5mm × 2). evaluated. Evaluation: 5 is a red rust generation area rate of 5% or less, Evaluation: 4 is a red rust generation area rate of 6-15%, Evaluation: 3 is a red rust generation area rate of 16-30%, Evaluation: 2 is a red rust The generation area ratio is 31 to 50%, and evaluation 1 is the case where the red rust generation area ratio is 51% or more. In addition, evaluation: 3 or more was evaluated that the process part corrosion resistance was favorable.

(7)耐切断端面さび性
得られた各めっき鋼板から試験片(大きさ:板厚0.8×幅50×長さ50mm)を切断により採取し、下バリの状態で、切断端面部を重ねて固定し、切断端面部を上にしてJIS K 5621の規定に準拠した複合促進試験(JIS CCT)を実施した。JIS CCTの条件は、塩水(5%NaCl)噴霧0.5h→湿潤(温度:30℃、相対湿度RH:95%)1.5h→乾燥(温度:50℃、相対湿度RH:20%)2h→乾燥(温度:30℃、相対湿度RH:20%)2hを1サイクルとして、このサイクルを2000サイクルまで行った。
(7) Cut end face rust resistance Test pieces (size: plate thickness 0.8 x width 50 x length 50 mm) were cut from each of the obtained plated steel sheets, and the cut end faces were stacked in the state of lower burrs. The composite acceleration test (JIS CCT) was performed in accordance with the provisions of JIS K 5621 with the cut end face portion fixed. JIS CCT conditions: salt water (5% NaCl) spray 0.5 h → wet (temperature: 30 ° C, relative humidity RH: 95%) 1.5 h → dry (temperature: 50 ° C, relative humidity RH: 20%) 2 h → dry (Temperature: 30 ° C., relative humidity RH: 20%) 2 h was set as one cycle, and this cycle was repeated up to 2000 cycles.

試験後、切断端面部の面積(0.8×50mm)に対する赤さび発生面積率を目視観察して測定し、耐切断端面さび性を5段階で評価した。評価:5は、赤さび発生面積率が5%以下、評価:4は、赤さび発生面積率が6〜15%、評価:3は、赤さび発生面積率が16〜30%、評価:2は、赤さび発生面積率が31〜50%、評価:1は、赤さび発生面積率が51%以上、の場合とした。なお、評価:4以上を耐切断端面さび性良好と評価した。   After the test, the red rust generation area ratio with respect to the area (0.8 × 50 mm) of the cut end face portion was visually observed and measured, and the cut end face rust resistance was evaluated in five stages. Evaluation: 5 is a red rust generation area rate of 5% or less, Evaluation: 4 is a red rust generation area rate of 6-15%, Evaluation: 3 is a red rust generation area rate of 16-30%, Evaluation: 2 is a red rust The generation area ratio is 31 to 50%, and evaluation 1 is the case where the red rust generation area ratio is 51% or more. In addition, evaluation: 4 or more was evaluated as cutting | disconnection end surface rust resistance favorable.

(8)耐エッジクリープ性
得られた各めっき鋼板に、エポキシ系プライマーを乾燥塗膜厚さが5μmとなるように塗布したのち、220℃で30s間焼付け、さらにポリエステル系樹脂を乾燥膜厚が約20μmとなるように塗布し、200℃で30s間焼付けて、塗装鋼板とした。これら塗装鋼板から、切断機で、四面を切断して試験片(大きさ:板厚0.8×幅70×長さ150mm)を採取し、下バリの状態でJIS K 5621の規定に準拠した複合促進試験(JIS CCT)を実施した。なお、試験片の四端面のうち、幅方向端面はシールし、長さ方向端面にはシールを施すことなく、試験した。
(8) Edge creep resistance An epoxy primer was applied to each plated steel sheet so that the dry coating thickness was 5 μm, then baked at 220 ° C. for 30 seconds, and the polyester resin had a dry film thickness. It was applied to a thickness of about 20 μm and baked at 200 ° C. for 30 s to obtain a coated steel plate. From these coated steel plates, a test piece (size: thickness 0.8 x width 70 x length 150 mm) is sampled by cutting with a cutting machine, and composite acceleration in accordance with the provisions of JIS K 5621 in the state of lower burrs A test (JIS CCT) was conducted. Of the four end faces of the test piece, the end face in the width direction was sealed and the end face in the length direction was tested without sealing.

JIS CCTの条件は、塩水(5%NaCl)噴霧0.5h→湿潤(温度:30℃、相対湿度RH:95%)1.5h→乾燥(温度:50℃、相対湿度RH:20%)2h→乾燥(温度:30℃、相対湿度RH:20%)2hを1サイクルとして、このサイクルを2000サイクルまで行った。
試験後、試験片のシールなし端面におけるエッジクリープ幅(端面からのふくれ幅)を測定し、耐エッジクリープ性を5段階で評価した。評価:5はふくれ幅が0、評価:4はふくれ幅が1mm以下、評価:3はふくれ幅が1mm超え5mm以下、評価:2はふくれ幅が5mm超え10mm以下、評価:1はふくれ幅が10mm超え、の場合とした。なお、評価:4以上を耐エッジクリープ性良好と評価した。
JIS CCT conditions: salt water (5% NaCl) spray 0.5 h → wet (temperature: 30 ° C, relative humidity RH: 95%) 1.5 h → dry (temperature: 50 ° C, relative humidity RH: 20%) 2 h → dry (Temperature: 30 ° C., relative humidity RH: 20%) 2 h was set as one cycle, and this cycle was repeated up to 2000 cycles.
After the test, the edge creep width (bulge width from the end face) on the end face without seal of the test piece was measured, and the edge creep resistance was evaluated in five stages. Evaluation: 5 has a blister width of 0, Evaluation: 4 has a blister width of 1 mm or less, Evaluation: 3 has a blister width of 1 mm to 5 mm, Evaluation: 2 has a blister width of 5 mm to 10 mm, Evaluation: 1 has a blister width In case of exceeding 10 mm. Evaluation: 4 or more was evaluated as good edge creep resistance.

(9)スポット溶接性
得られた各めっき鋼板から、試験片(大きさ:板厚0.8×幅40×長さ100mm)を採取し、下記スポット溶接条件で連続打点して、スポット溶接継手を作製した。
溶接条件は次のとおりとした。
・初期加圧時間:45サイクル、通電時間:45サイクル、保持時間:45サイクル
・溶接電流:7.5 kA、加圧力:140kgf(1.3kN)
・電極:JIS C 9304−1999に規定されるDR(Dome Radius)型電極チップ(先端曲率半径:18mm、先端径:8mm)
得られた各スポット溶接継手について、JIS Z 3136の規定に準拠して引張剪断試験を実施し、引張剪断荷重を求め、引張剪断荷重がJIS Z 3140に規定するJIS A級(使用した母板強度、板厚から2.7kN)以下となる連続打点数からスポット溶接性を5段階で評価した。評価:5は、連続打点数が1000打点以上、評価:4は、連続打点数が1000打点未満800打点以上、評価:3は、連続打点数が800打点未満600打点以上、評価:2は、連続打点数が600打点未満400打点以上、評価:1は、連続打点数が400打点未満、の場合とした。なお、評価:4以上をスポット溶接性良好と評価した。
(9) Spot weldability From each of the obtained plated steel sheets, specimens (size: thickness 0.8 x width 40 x length 100 mm) are sampled and continuously spotted under the following spot welding conditions to produce spot welded joints. did.
The welding conditions were as follows.
・ Initial pressurization time: 45 cycles, energization time: 45 cycles, holding time: 45 cycles ・ Welding current: 7.5 kA, applied pressure: 140 kgf (1.3 kN)
・ Electrode: DR (Dome Radius) type electrode tip specified in JIS C 9304-1999 (tip radius of curvature: 18 mm, tip diameter: 8 mm)
For each spot welded joint obtained, a tensile shear test was performed in accordance with the provisions of JIS Z 3136 to determine the tensile shear load. The spot weldability was evaluated in five stages from the number of consecutive hit points, which was 2.7 kN or less from the plate thickness. Evaluation: 5 is the number of continuous hits of 1000 or more, Evaluation: 4 is the number of continuous hits of less than 1000, 800 or more, Evaluation: 3 is the number of continuous hits of less than 800, 600 or more, Evaluation: 2 The number of continuous hits is less than 600 and 400 or more. Evaluation: 1 is the case where the number of continuous hits is less than 400. In addition, evaluation: 4 or more was evaluated as favorable spot weldability.

得られた結果を表2に示す。   The obtained results are shown in Table 2.

Figure 2007284718
Figure 2007284718

Figure 2007284718
Figure 2007284718

本発明例はいずれも、良好なめっき外観を示し、さらに優れた加工性、優れた耐黒変性、優れた加工部耐食性、優れた耐切断端面さび性、優れた耐エッジクリープ性、優れたスポット溶接性を兼備する溶融Zn−Al系合金めっき鋼板となっている。一方、本発明の範囲を外れる比較例は、加工性、耐食性(耐黒変性、加工部耐食性、耐切断端面さび性、耐エッジクリープ性)のいずれかあるいは全てが低下している。また、めっき外観、スポット溶接性も低下している。   Each of the examples of the present invention shows a good plating appearance, and further has excellent workability, excellent blackening resistance, excellent corrosion resistance of processed parts, excellent cutting edge rust resistance, excellent edge creep resistance, and excellent spots. It is a hot-dip Zn-Al alloy-plated steel sheet that also has weldability. On the other hand, in comparative examples that are outside the scope of the present invention, any or all of workability and corrosion resistance (blackening resistance, processed part corrosion resistance, cut end surface rust resistance, edge creep resistance) are reduced. Moreover, the plating appearance and spot weldability are also reduced.

スパングルサイズに及ぼすめっき層中のMg含有量の影響を示すグラフである。It is a graph which shows the influence of Mg content in a plating layer on spangle size. GDS分析による、めっき層中に含有される各元素の深さ方向分布状況の一例を示すデプス分析結果である。It is a depth analysis result which shows an example of the depth direction distribution condition of each element contained in a plating layer by GDS analysis.

Claims (5)

鋼板表面に、溶融Zn−Al系合金めっき層を有してなる溶融Zn−Al系合金めっき鋼板であって、前記溶融Zn−Al系合金めっき層が、質量%で、Al:25〜70%、Si:0.1〜5%、Mg:0.5〜5%、Sr:0.005×(Si%)〜0.05×(Si%)%(ここで、Si%:Si含有量(質量%))を含み、残部Znおよび不可避的不純物からなる組成を有する合金めっき層であることを特徴とする耐食性および加工性に優れた溶融Zn−Al系合金めっき鋼板。   A hot-dip Zn-Al alloy-plated steel plate having a hot-dip Zn-Al alloy plating layer on the surface of the steel plate, wherein the hot-melt Zn-Al alloy plating layer has a mass% of Al: 25 to 70%. , Si: 0.1 to 5%, Mg: 0.5 to 5%, Sr: 0.005 × (Si%) to 0.05 × (Si%)% (where Si%: Si content (mass%)), the balance A hot-dip Zn-Al alloy-plated steel sheet excellent in corrosion resistance and workability, characterized by being an alloy plating layer having a composition comprising Zn and inevitable impurities. 前記溶融Zn−Al系合金めっき層が、前記組成に加えてさらに、質量%で、Cr:0.02〜2%およびNi:0.02〜2%を含有することを特徴とする請求項1に記載の溶融Zn−Al系合金めっき鋼板。   2. The molten alloy according to claim 1, wherein the molten Zn—Al-based alloy plating layer further contains Cr: 0.02 to 2% and Ni: 0.02 to 2% by mass% in addition to the composition. Zn-Al alloy plated steel sheet. 鋼板に、溶融Zn−Al系合金めっき浴に浸漬したのち、該溶融Zn−Al系合金めっき浴から引き上げて冷却し、鋼板表面に溶融Zn−Al系合金めっき層を形成するめっき処理工程を施して、溶融Zn−Al系合金めっき鋼板とするに当り、前記溶融Zn−Al系合金めっき浴を、前記溶融Zn−Al系合金めっき層が平均で、質量%で、Al:25〜70%、Mg:0.5〜5%、Si:0.1〜5%、Sr:0.005×(Si%)〜0.05×(Si%)%(ここで、Si%:Si含有量(質量%))を含有し、残部Znおよび不可避的不純物からなるめっき層組成を有するように、めっき浴組成を調整しためっき浴とし、該溶融Zn−Al系合金めっき浴から引き上げたのちの前記冷却を、前記溶融Zn−Al系合金めっき浴から引き上げてから350℃までの平均冷却速度が10〜100℃/sである冷却とすることを特徴とする耐食性および加工性に優れた溶融Zn−Al系合金めっき鋼板の製造方法。   After the steel sheet is immersed in a molten Zn-Al alloy plating bath, the steel sheet is pulled out from the molten Zn-Al alloy plating bath and cooled, and a plating treatment process is performed to form a molten Zn-Al alloy plating layer on the steel sheet surface. In order to obtain a molten Zn-Al alloy-plated steel sheet, the molten Zn-Al-based alloy plating bath has an average of the molten Zn-Al-based alloy plating layer in mass%, Al: 25 to 70%, Mg: 0.5 to 5%, Si: 0.1 to 5%, Sr: 0.005 × (Si%) to 0.05 × (Si%)% (where Si%: Si content (mass%)), the balance The plating bath composition is adjusted so as to have a plating layer composition composed of Zn and inevitable impurities, and the cooling after pulling up from the molten Zn-Al alloy plating bath is performed by the molten Zn-Al alloy. Corrosion resistance characterized by cooling with an average cooling rate from 10 to 100 ° C / s up to 350 ° C after pulling up from the plating bath Method for producing excellent melt Zn-Al alloy coated steel sheet in workability. 前記めっき処理工程に続いて、さらに圧下率:0.5〜5%の調質圧延を施す調質圧延工程と、ついで150〜350℃の温度範囲で過時効処理を施す過時効処理工程とを施すことを特徴とする請求項3に記載の溶融Zn−Al系合金めっき鋼板の製造方法。   Subsequent to the plating treatment step, a temper rolling step of temper rolling at a rolling reduction of 0.5 to 5% and an overaging treatment step of applying an overaging treatment in a temperature range of 150 to 350 ° C. 4. The method for producing a hot-dip Zn—Al-based alloy-plated steel sheet according to claim 3. 前記めっき層組成に加えてさらに、質量%で、Cr:0.02〜2%およびNi:0.02〜2%を含有するめっき層組成とすることを特徴とする請求項3または4に記載の溶融Zn−Al系合金めっき鋼板の製造方法。   The molten Zn- according to claim 3 or 4, further comprising a plating layer composition containing Cr: 0.02 to 2% and Ni: 0.02 to 2% by mass% in addition to the plating layer composition. A method for producing Al alloy-plated steel sheets.
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