JP3740112B2 - Method for improving corrosion resistance of zinc-based alloy-plated steel sheet - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、亜鉛系合金めっき鋼板の耐食性の改善方法に関し、詳しくは、亜鉛系合金めっき鋼板の加工部の耐食性を向上させる方法に関する。
【０００２】
【従来の技術】
鋼板の耐食性を向上させるために、鋼板表面に亜鉛系合金、例えば、Ｚｎ−Ａｌ系、Ｚｎ−Ａｌ−Mg系、Ｚｎ−Ａｌ−Ｍｇ−Ｓｉ系合金などを、電解法や溶融めっき金属への浸漬法などの方法によりめっきすることが広く行なわれている。
【０００３】
これらのめっき鋼板は、その優れた耐食性によって、自動車、建材など多くの部材として使用されている。特に、屋外において直接腐食環境に曝される建材などでは、Ｚｎ−Ａｌ−Ｓｉ系のやや硬質なめっき層を形成したものを使用することが多い。これらの用途として使用される場合、めっき鋼板は、切断、曲げ、張り出し、溶接などの加工が施される。
【０００４】
亜鉛系合金めっき層は、加工性には優れているものの、これらの加工によってめっき層に微小の亀裂が発生することは避けられない。
【０００５】
亜鉛系合金めっき層に亀裂が入ると、亀裂部分の隙間に沿ってめっき層の腐食が進行し、白錆が発生し、また、この腐食がめっき層を貫通して基板の鋼板に達すると、赤錆が発生し美観を損ねるのみならず、腐食がさらに進行し、鋼板自体の耐食性を劣化させる。このような亜鉛系合金めっき層の耐食性の劣化を防止するために、めっき層にさらに塗装を施したりして、めっき層の微小亀裂からの腐食の進行を防止したものがある。
【０００６】
ところで、溶接製品の溶接部の強度を向上させ、応力集中や、微小応力欠陥を抑制する応力パターンを形成するために超音波衝撃エネルギにより処理する方法が知られている（例えば、特許文献１参照）。
【０００７】
【特許文献１】
米国特許第６，１７１，４１５号明細書
【０００８】
【発明が解決しようとする課題】
このように、亜鉛系合金めっき層の上に防錆のための皮膜を形成する方法は、めっき処理した後の鋼板にほぼ全面にわたって塗装被覆されており、塗装被覆のためのコストがきわめて高いものとなる。さらに、この塗装被覆した亜鉛系合金めっき鋼板も、鋼板を所定の形状に加工した際にめっきに亀裂が入ると共に、塗装皮膜にも亀裂がはいることがあり、塗装皮膜の亀裂を通してめっき層、さらには基板の鋼板にまで腐食が進展する。従って、この塗装被覆した亜鉛系合金めっき鋼板でも、めっき鋼板の耐食性向上のための十分な対策とはなりえない。本発明は、亜鉛系合金めっき鋼板の加工によって生じるめっき層の亀裂の進展を効率的に防止し、亜鉛系合金めっき鋼板の耐食性を改善する方法を提供することを課題とする。
【０００９】
【課題を解決するための手段】
本発明は、上記の課題を解決するものであって、超音波で先端を振幅２０〜60μm、周波数１９ｋHｚ〜６０ｋHz、出力０．２〜３kwで振動させる工具を用いて亜鉛系合金めっき鋼板を打撃する超音波衝撃処理を、鋼板を加工した後の加工部に施すことによって、亜鉛系合金めっき層の表層を塑性変形させ、よって耐食性を改善するものである。その要旨とするところは、以下のとおりである。
【００１０】
（１）鋼板の表面に、質量％で亜鉛を３０％以上含有する亜鉛系合金めっきを施した鋼板において、該鋼板を加工した後に、該鋼板の加工部分に、超音波衝撃処理を施すことを特徴とする亜鉛系合金めっき鋼板の耐食性改善方法。
【００１１】
（２）亜鉛系合金めっき鋼板のめっき層が、５５％アルミニウム−亜鉛合金のめっき層であることを特徴とする（１）記載の亜鉛系合金めっき鋼板の耐食性改善方法。
【００１２】
（３）亜鉛系合金めっき鋼板のめっき層が、質量％で、１〜２０％のアルミニウム、０．５〜１０％のＭｇを含有する亜鉛系合金めっき層であることを特徴とする（１）記載の亜鉛系合金めっき鋼板の耐食性改善方法。
【００１３】
（４）さらに、亜鉛系合金めっき鋼板のめっき層が質量％で、Ｓｉ：０．０１〜１％を含有する亜鉛系合金めっき層であることを特徴とする（３）に記載の亜鉛系合金めっき鋼板の耐食性改善方法。
【００１４】
【発明の実施の形態】
本発明の方法は、亜鉛系合金めっき鋼板を加工して使用する構造製品、例えば、自動車の構造部材、電気製品用部材、建築部材などに広く適用されるものである。特に、曲げ加工、張り出し加工など、表面が厳しい引張加工を受けるものに有用である。このような構造製品部材の加工途上において、めっき鋼板が上記のような厳しい引張加工を受けると、めっき鋼板のめっき層の表面に微小な亀裂が発生する。この微小な亀裂が湿潤空気、水滴などが存在すると、亀裂部分とそれ以外の部分との間に電位差が生じて、亜鉛系合金めっき層の腐食が起こり、腐食生成物としての白錆（酸化亜鉛）が発生する。この腐食がさらに進行し亀裂がめっき層を貫通して下地の鋼板にまで達すると、鋼板が腐食し生成物として赤錆（酸化鉄）が発生する。このように加工によって形成されためっき表面の亀裂がめっき鋼板の耐食性を著しく低下させる。
【００１５】
従って、加工によって生じた亀裂を修復するか、亀裂の開口部が環境と接触しないように閉塞すれば腐食の進行を防止することができることがわかる。
【００１６】
このようなめっき層の亀裂の発生は、厳しい加工を受けた箇所が主であるため、少なくともこの箇所に対してめっき層の亀裂を修復し、或いは、その開口部が環境と接触しないように閉塞する処理を施せばよいことになる。
【００１７】
ところで、亀裂を修復ないしは、その開口部を閉塞する方法として、超音波衝撃処理を適用することに想到した。この処理は、超音波で先端のハンマー部を振幅２０〜５０μm、周波数１９〜６０ｋHz、出力０．２〜３kwで振動させる装置により金属表面を打撃してピーニングを行なうものであって、基本的にはハンマーピーニングと同じであるが、一回一回の打撃のエネルギーは小さいかわりに、1秒間に1万回を超える回数の打撃を加えることによって、金属に塑性変形を与えるものである。
【００１８】
この打撃処理により、めっき層の表層部を塑性変形させ、よって、亀裂の密着させて、これをなくし或いは、亀裂の開口部を閉塞することにより、亀裂への腐食物質の侵入を防ぐことができる。すなわち、図1（ａ）、図1（ｂ）は、鋼板１に亜鉛系合金めっき層２を有するめっき鋼板１の加工部に対して、超音波衝撃処理を施す場合の、（ａ）処理前と（ｂ）処理後のめっき層の性状変化を説明する断面模式図であるが、処理前にあっためっき層の亀裂４は、超音波衝撃処理により、亀裂が解消し、或いは小さくなり、或いは開口部が閉塞されたものとなっている。
【００１９】
これによって、めっき層の耐食性を向上させることが可能となる。
【００２０】
超音波衝撃処理は、1回の打撃エネルギーが小さいため、先端部のハンマー形状は、小型にすることができ、微小な部分や、狭隘な部分に対しても打撃処理を施すことができる。この点において、曲げや張り出しなどの加工を受けた部分にでも処理が適用可能となる。この場合でも、上述のように打撃回数を極めて多くできることから、十分な塑性変形を与えることができる。
【００２１】
また、この超音波衝撃処理は、金属表面に対して非常に多くの回数の打撃を与えているので、金属表面に対して従来のハンマーピーニングにはない効果をもあり、また、一回一回の打撃エネルギーショットは、ショットピーニングよりも大きいので、従来のショットピーニングにない効果もある。
【００２２】
すなわち、先ず、打撃の回数が多いことで、処理の均一性が得られる。ハンマーピーニングでも数パスを同一線上で実施すればある程度の均一性が得られるが、超音波衝撃処理の打撃サイクル数は、１９〜６０ｋHzであり、その得られる均一性はハンマーピーニングのそれとは全く異なるレベルにあり、処理スピードが０．５ｍ／分程度であれば、所要の金属表面のほとんどを均一にかつ欠陥を残すことなく仕上げることができる。
【００２３】
このとき、一回一回の打撃力は小さいために、打撃装置に生じる反動は殆どなく、ハンマーピーニング装置に比べて使用性、施工性の面で優れている。
【００２４】
めっき層の表層部を塑性変形させるために必要な変形のためのエネルギーはほぼ一定であるため、１サイクルの衝撃エネルギーを大きくして短時間に処理しても良いが、均一性を高めたい場合や、衝撃部位の位置をより精緻に制御し、過度な塑性変形を防止したい場合は、1サイクルの衝撃エネルギーを小さくし、二回以上の処理を同一箇所に対して行なうことが好ましい。
【００２５】
また、衝撃エネルギーによって生じる塑性変形の厚さは、衝撃装置の先端のハンマーの曲率半径Rとも関係しており、1サイクルの衝撃エネルギーが同じでも、Rが小さければ、１サイクルの衝撃で生じる塑性変形の厚さは大きくなり、Rが大きければその厚さは小さくなる。
【００２６】
また、ハンマーのＲが小さければ、１サイクルで処理される範囲が狭いので繰り返し処理が必要となり、またＲが大きければ、微小部分への衝撃制御が困難となることもある。従って、超音波打撃処理装置の先端のハンマーの形状は、処理対象とする鋼板の加工部の状況によって適宜選択する。
【００２７】
超音波衝撃処理を施すにあたっては、亜鉛系合金めっき鋼板の処理対象箇所すなわち、加工部の形状、加工度などの性状に応じて、超音波打撃処理に必要なハンマーの形状、１サイクルの打撃エネルギー、サイクル数、処理回数などの処理条件を、予備試験などにより、予め設定しておき、これに従って超音波衝撃処理を行なうことにより、加工部のめっき層を塑性変形させ、亀裂を修復ないしは閉塞して耐食性を向上させることが出来る。
【００２８】
加工部は、曲げ、張り出しなどに限らず、切断、絞りなど亜鉛系合金めっき層に亀裂を生ぜしめるような加工を加えた個所を含むものであり、少なくともこの加工部を含む周辺に施すことが好ましい。
【００２９】
なお、この超音波衝撃処理を施した表面は、塑性変形によって微小な凹凸が形成されることになるため、その表面光沢は若干変化する。これによって、処理されたかどうかを判定することができる。
【００３０】
なお、必要により、鋼板の加工部に超音波処理を施し、その後、加工部を含む鋼板の表面に塗装を行なっても良い。また、鋼板の加工部に塗装を施した後、超音波衝撃処理を施しても良い。
【００３１】
しかしながら、めっき鋼板の超音波衝撃処理を施した部分に対しては、この箇所にさらに亀裂を生ぜしめるような加工は行なわないことが好ましい。超音波処理を施した後に、この箇所のめっき層に亀裂を生ぜしめるような引張、曲げ張り出しなどの加工を行なうと、再び亀裂が発生したり、閉塞した開口部が再び開口することがあり、耐食性を向上させる効果が減殺されるからである。
本発明が対象とするめっき鋼板は、亜鉛を主体として合金元素を多量に含有する亜鉛系合金めっき鋼板である。合金元素を多量に含有させることで耐食性や溶接性などの性能が向上する一方で、合金元素の多量添加は金属間化合物を形成するなどしてめっき層の硬さを上げ、加工時のめっき割れを促進することが多いからである。具体的には、５５％アルミニウム−亜鉛めっき鋼板（ＪＩＳ Ｇ ３３２１）、Ｚｎ−１〜２０％Ａｌ−０．５〜１０％Ｍｇめっき鋼板、Ｚｎ−１〜２０％Ａｌ−０．５〜１０％Ｍｇ−０．０１〜１％Ｓｉめっき鋼板、が挙げられる。
【００３２】
めっき層がＺｎを３０％以上含有するものとするのは、Ｚｎ含有量が４０％未満ではめっき層の耐食性が不充分となるからである。
【００３３】
Ｚｎ−Ａｌ合金めっき鋼板において、Ａｌはめっきの耐食性を高める目的で添加され、５５％Ａｌ−Ｚｎめっき鋼板（ＪＩＳ Ｇ ３３２１）はその代表例としてよく知られている。めっき層中のＡｌ含有量が７０％を超えると湿潤環境での耐食性が低下する。
【００３４】
Ｚｎ−Ａｌ−Ｍｇ合金めっき鋼板において、ＡｌおよびＭｇは耐食性を高める目的で添加されるが、Ａｌ含有量が１％未満、Ｍｇ含有量が０．５％未満では耐食性向上効果が充分ではない。Ａｌ含有量が２０％を超えるか、Ｍｇ含有量が１０％を超えると、めっき層が脆くなりすぎて、超音波衝撃処理を施しても耐食性の改善効果が充分ではない。Ｍｇ含有量はより好ましくは５％を上限とする。
【００３５】
Ｚｎ−Ａｌ−Ｍｇ合金めっき鋼板には、必要に応じてさらに耐食性を向上させる目的で、Ｓｉを添加し得る。ＳｉはＺｎ−Ａｌ−Ｍｇ合金めっき鋼板の耐食性を一段と向上させる効果があるが、含有量が０．１％未満ではその効果が充分ではない。Ｓｉ含有量が１％を超えて添加することはめっきの外観を著しく損なうので、Ｓｉを添加する場合の上限含有量は１％とする。
【００３６】
本願発明におけるＺｎ系合金めっきにおいては、耐食性、めっき密着性、成形性などを改善する目的で、めっき層中にさらにＰｂ，Ｓｂ，Ｃ，Ｐ，Ｆｅ，Ｓｎ，Ｍｎ，Ｎｉ，Ｃｒ，Ｃｏ，Ｃｕ，Ｃａ，Ｌｉ，Ｔｉ，Ｂ、希土類元素の１種または２種以上を総和で２５％以下含有させることができる。あるいは不純物として上記の元素を混入したＺｎめっきであっても、支障を来すことはない。また、Ｓ，Ａｓ等の元素、酸化物、炭化物、硫化物等の化合物を分散させためっきとすることもできる。
【００３７】
本願発明が対象とするめっき鋼板の下地鋼板の成分は特に限定されるものではなく、必要な強度、加工性、成形性などに応じて適切な成分を選択することができる。
【００３８】
さらに、本発明に適用される鋼板は通常のプロセスで製造される冷延鋼板、熱延鋼板のいずれであってもその効果は充分に発揮されるものであり、鋼板の履歴によって効果が大きく変化するものでもない。
【００３９】
当然のことながら、本発明が対象とするめっき鋼板上に、各種の処理を付加して施すことも勿論可能であり、例えば、潤滑性向上処理、樹脂塗布処理、溶接性向上処理、りん酸塩処理、りん酸塩処理性を向上させるための処理、等を施したとしても、本願発明の範囲を逸脱するものではなく、付加して必要とする特性に応じて、各種の処理を施しても本願発明の効果は何ら変わるところはない。
【００４０】
本発明が対象とするめっき鋼板の強度としては、引張強度が３００Ｎ／mm2未満の普通鋼あるいは超深絞り用鋼板から、３００Ｎ／mm2以上の高強度鋼（３００，３４０，４００，４４０，５９０，７８０，９８０，１１８０，１４５０Ｎ／mm2級など）などの広範囲にわたるものである。
【００４１】
なお、亜鉛系合金めっき鋼板の製造方法は、特に限定するものではないが、鋼板を上記の亜鉛系合金の溶融めっき浴に浸漬してめっきすることが一般的である。
【００４２】
【実施例】
亜鉛系合金めっきを施した板厚１．０ｍｍの亜鉛系合金めっき鋼板から曲げ試験片（１．０ｍｍ（板厚）×２０ｍｍ（幅）×１００ｍｍ（長さ））を採取し、めっき面が曲げの外側となるようにして曲げを施した。曲げは、ＪＩＳ Ｇ ３３２１に準拠した。次いで、本発明の例においては、この試験片の曲げ面に、半径が１．５ｍｍのハンマーを備えた超音波打撃装置により、振幅３０μｍ、周波数３０ｋＨｚにて０．５ｍ／minの速度で、超音波衝撃処理を行なった。また、比較例として、曲げ面に、ショット粒径７ｍｍ、ショット速度１０ｍ／ｓで、２分間のショットピーニングを施したもの、および曲げ状態のまま(無処理)のものを準備し、これらの試験片について大気中での曝露試験を行なった。
【００４３】
その結果を表1に示す。
【００４４】
表1から判るように、ショットピーニングを施した比較例１，２では３５日で白錆が、１２０日で赤錆が認められ、特に処理を施さなかった比較例２，３では、３０〜４０日で白錆が、１００〜１３０日で赤錆が認められた。これに対して、本発明の試験片には、長期間白錆、赤錆が発生せず、超音波衝撃処理により耐食性が向上しているのがわかる。
【００４５】
【表１】
【発明の効果】
本発明の方法によれば、亜鉛系合金めっき鋼板の加工部に発生する耐食性の劣化を抑制することができるので、亜鉛めっき鋼板を使用した構造製品の耐久性を向上させることができる。本発明の方法は、ハンマーピーニング装置などに比して使用性に優れた超音波打撃装置を使用するので、加工部という限られた箇所、微小な箇所、狭隘な箇所に対して適用でき、構造製品の耐食性を向上させるための処理として効率的であり、経済的にも優れた方法である。
【図面の簡単な説明】
【図１】本発明の方法による亜鉛系合金めっき鋼板の加工部の性状変化を説明する断面模式図であり、（ａ）は、超音波衝撃処理前、（ｂ）は、超音波衝撃処理後の亀裂の性状を示す。
【符号の説明】
１…亜鉛系合金めっき鋼板
２…鋼板
３…亜鉛系合金めっき層
４…亀裂[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for improving the corrosion resistance of a zinc-based alloy plated steel sheet, and more particularly to a method for improving the corrosion resistance of a processed part of a zinc-based alloy plated steel sheet.
[0002]
[Prior art]
In order to improve the corrosion resistance of the steel sheet, a zinc-based alloy, for example, a Zn-Al-based, Zn-Al-Mg-based, Zn-Al-Mg-Si-based alloy, or the like is applied to the surface of the steel sheet to an electrolytic method or a hot dipped metal. Plating by a method such as an immersion method is widely performed.
[0003]
These plated steel sheets are used as many members such as automobiles and building materials because of their excellent corrosion resistance. In particular, building materials that are directly exposed to a corrosive environment outdoors often use a Zn-Al-Si-based somewhat hard plating layer. When used as these applications, the plated steel sheet is subjected to processing such as cutting, bending, overhanging and welding.
[0004]
Although the zinc-based alloy plating layer is excellent in workability, it is inevitable that micro cracks are generated in the plating layer by these processes.
[0005]
When cracks occur in the zinc-based alloy plating layer, corrosion of the plating layer proceeds along the gaps in the crack part, white rust occurs, and when this corrosion penetrates the plating layer and reaches the steel plate of the substrate, Not only does red rust occur and the appearance is impaired, but corrosion further progresses and the corrosion resistance of the steel sheet itself is deteriorated. In order to prevent such deterioration of the corrosion resistance of the zinc-based alloy plating layer, there is one in which the plating layer is further coated to prevent the progress of corrosion from the microcracks of the plating layer.
[0006]
By the way, a method of processing with ultrasonic impact energy is known in order to improve the strength of a welded part of a welded product and form a stress pattern that suppresses stress concentration and minute stress defects (see, for example, Patent Document 1). ).
[0007]
[Patent Document 1]
US Pat. No. 6,171,415
[Problems to be solved by the invention]
As described above, the method of forming a coating for rust prevention on the zinc-based alloy plating layer is that the coated steel sheet is almost entirely coated and the cost for coating is extremely high. It becomes. In addition, this coated zinc-based alloy-plated steel sheet also has cracks in the plating when the steel sheet is processed into a predetermined shape, and the coating film may also have cracks. Furthermore, corrosion progresses to the steel plate of the substrate. Therefore, even this coated zinc-based alloy plated steel sheet cannot be a sufficient measure for improving the corrosion resistance of the plated steel sheet. This invention makes it a subject to provide the method of preventing the progress of the crack of the plating layer produced by processing of a zinc-based alloy plating steel plate, and improving the corrosion resistance of a zinc-based alloy plating steel plate.
[0009]
[Means for Solving the Problems]
The present invention solves the above-described problem, and hits a zinc-based alloy plated steel sheet using a tool that vibrates the tip with an ultrasonic wave with an amplitude of 20 to 60 μm, a frequency of 19 kHz to 60 kHz, and an output of 0.2 to 3 kw. By applying ultrasonic shock treatment to the processed part after processing the steel sheet, the surface layer of the zinc-based alloy plating layer is plastically deformed, thereby improving the corrosion resistance. The gist is as follows.
[0010]
(1) In a steel sheet having a zinc-based alloy plating containing 30% or more of zinc by mass% on the surface of the steel sheet, after processing the steel sheet, subjecting the processed part of the steel sheet to ultrasonic shock treatment. A method for improving the corrosion resistance of a zinc-based alloy-plated steel sheet.
[0011]
(2) The method for improving corrosion resistance of a zinc-based alloy plated steel sheet according to (1), wherein the plating layer of the zinc-based alloy plated steel sheet is a 55% aluminum-zinc alloy plating layer.
[0012]
(3) The plated layer of the zinc-based alloy plated steel sheet is a zinc-based alloy plated layer containing 1 to 20% aluminum and 0.5 to 10% Mg in mass% (1). The method for improving corrosion resistance of the described zinc-based alloy-plated steel sheet.
[0013]
(4) Further, the zinc-based alloy plated steel sheet according to (3), wherein the zinc-based alloy-plated steel sheet is a zinc-based alloy plated layer containing Si: 0.01 to 1% by mass%. A method for improving the corrosion resistance of plated steel sheets.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention can be widely applied to structural products such as automobile structural members, electrical product members, building members, and the like that are obtained by processing zinc-based alloy plated steel sheets. In particular, it is useful for those that undergo severe tensile processing such as bending and overhanging. In the course of processing such a structural product member, when the plated steel sheet is subjected to the severe tension processing as described above, minute cracks are generated on the surface of the plated layer of the plated steel sheet. When this minute crack exists in the presence of wet air, water droplets, etc., a potential difference occurs between the cracked part and the other part, corrosion of the zinc alloy plating layer occurs, and white rust (zinc oxide as a corrosion product) ) Occurs. When this corrosion further progresses and the crack penetrates the plating layer and reaches the underlying steel plate, the steel plate is corroded and red rust (iron oxide) is generated as a product. Thus, the crack of the plating surface formed by processing significantly reduces the corrosion resistance of the plated steel sheet.
[0015]
Therefore, it can be seen that the progress of corrosion can be prevented by repairing the crack generated by the processing or by closing the crack so that the opening of the crack does not come into contact with the environment.
[0016]
The occurrence of such cracks in the plating layer is mainly caused by severe processing, so at least the cracks in the plating layer are repaired at this point, or the opening is closed so as not to contact the environment. It is only necessary to perform the process to do.
[0017]
By the way, it came to the idea to apply ultrasonic impact treatment as a method of repairing cracks or closing the openings. This process is to peen by hammering the metal surface with a device that vibrates ultrasonically the tip of the hammer with an amplitude of 20-50 μm, a frequency of 19-60 kHz, and an output of 0.2-3 kw. Is the same as hammer peening, but gives a plastic deformation to the metal by applying more than 10,000 shots per second, instead of the energy of one shot being small.
[0018]
By this striking treatment, the surface layer portion of the plating layer is plastically deformed, so that cracks are brought into close contact with each other to eliminate or block the opening of the cracks, thereby preventing the entry of corrosive substances into the cracks. . That is, FIG. 1A and FIG. 1B show the case in which ultrasonic impact treatment is performed on the processed portion of the plated
[0019]
Thereby, the corrosion resistance of the plating layer can be improved.
[0020]
Since the impact energy per ultrasonic shock is small, the hammer shape at the tip can be reduced in size, and the impact processing can be performed even on a minute part or a narrow part. In this respect, the processing can be applied to a portion subjected to processing such as bending or overhanging. Even in this case, since the number of hits can be extremely increased as described above, sufficient plastic deformation can be provided.
[0021]
In addition, since this ultrasonic impact treatment has hit the metal surface a very large number of times, it has an effect that the conventional hammer peening does not have on the metal surface. Since the hit energy shot is larger than the shot peening, there is an effect not found in the conventional shot peening.
[0022]
That is, first, the uniformity of processing can be obtained because the number of hits is large. Even with hammer peening, if a few passes are performed on the same line, a certain degree of uniformity can be obtained, but the number of striking cycles of ultrasonic impact treatment is 19-60 kHz, and the obtained uniformity is completely different from that of hammer peening. If the processing speed is about 0.5 m / min, most of the required metal surface can be finished uniformly and without leaving any defects.
[0023]
At this time, since the impact force per time is small, there is almost no reaction that occurs in the impact device, which is superior in terms of usability and workability compared to the hammer peening device.
[0024]
Since the energy required for plastic deformation of the surface layer of the plating layer is almost constant, the impact energy of one cycle can be increased and processed in a short time. In addition, when it is desired to control the position of the impact site more precisely and prevent excessive plastic deformation, it is preferable to reduce the impact energy of one cycle and perform the treatment twice or more on the same location.
[0025]
The thickness of the plastic deformation caused by the impact energy is also related to the radius of curvature R of the hammer at the tip of the impact device. Even if the impact energy of one cycle is the same, if R is small, the plasticity generated by the impact of one cycle The thickness of the deformation increases, and if R is large, the thickness decreases.
[0026]
In addition, if the hammer R is small, the processing range in one cycle is narrow, so that repeated processing is necessary. If R is large, it may be difficult to control the impact on a minute part. Therefore, the shape of the hammer at the tip of the ultrasonic hitting apparatus is appropriately selected depending on the situation of the processed portion of the steel plate to be processed.
[0027]
When applying the ultrasonic impact treatment, the shape of the hammer required for the ultrasonic impact treatment, the energy of one cycle of impact, depending on the properties of the zinc-based alloy-plated steel sheet, that is, the shape of the machined part, the degree of work, etc. The processing conditions such as the number of cycles and the number of treatments are set in advance by preliminary tests, etc., and ultrasonic impact treatment is carried out in accordance with this, thereby plastically deforming the plated layer of the processed part and repairing or closing the cracks. Corrosion resistance can be improved.
[0028]
The processed part is not limited to bending, overhanging, etc., and includes a part where a process that causes a crack in the zinc-based alloy plating layer, such as cutting and drawing, is performed, and at least the periphery including the processed part is applied. preferable.
[0029]
Since the surface subjected to the ultrasonic impact treatment has minute irregularities formed by plastic deformation, the surface gloss slightly changes. This makes it possible to determine whether the processing has been performed.
[0030]
If necessary, the processed portion of the steel plate may be subjected to ultrasonic treatment, and then the surface of the steel plate including the processed portion may be coated. Moreover, after applying the coating to the processed portion of the steel plate, ultrasonic impact treatment may be applied.
[0031]
However, it is preferable not to perform processing that causes further cracks in the portion of the plated steel sheet that has been subjected to ultrasonic impact treatment. After performing ultrasonic treatment, if processing such as tension and bending overhang that causes cracks in the plating layer at this location, cracking may occur again, or the closed opening may reopen, This is because the effect of improving the corrosion resistance is diminished.
The plated steel sheet targeted by the present invention is a zinc-based alloy plated steel sheet mainly containing zinc and containing a large amount of alloy elements. Addition of a large amount of alloy elements improves performance such as corrosion resistance and weldability, while addition of a large amount of alloy elements increases the hardness of the plating layer by forming intermetallic compounds, etc. It is because it often promotes. Specifically, 55% aluminum-galvanized steel sheet (JIS G 3321), Zn-1-20% Al-0.5-10% Mg-plated steel sheet, Zn-1-20% Al-0.5-10% Mg-0.01 to 1% Si plated steel sheet.
[0032]
The reason why the plating layer contains 30% or more of Zn is that when the Zn content is less than 40%, the corrosion resistance of the plating layer becomes insufficient.
[0033]
In a Zn—Al alloy plated steel sheet, Al is added for the purpose of enhancing the corrosion resistance of plating, and 55% Al—Zn plated steel sheet (JIS G 3321) is well known as a representative example. When the Al content in the plating layer exceeds 70%, the corrosion resistance in a wet environment is lowered.
[0034]
In the Zn-Al-Mg alloy-plated steel sheet, Al and Mg are added for the purpose of enhancing the corrosion resistance. However, if the Al content is less than 1% and the Mg content is less than 0.5%, the corrosion resistance improving effect is not sufficient. When the Al content exceeds 20% or the Mg content exceeds 10%, the plating layer becomes too brittle, and the effect of improving the corrosion resistance is not sufficient even when subjected to ultrasonic impact treatment. More preferably, the upper limit of Mg content is 5%.
[0035]
Si can be added to the Zn-Al-Mg alloy-plated steel sheet as necessary for the purpose of further improving the corrosion resistance. Si has the effect of further improving the corrosion resistance of the Zn—Al—Mg alloy-plated steel sheet, but the effect is not sufficient when the content is less than 0.1%. If the Si content exceeds 1%, the appearance of the plating is remarkably impaired, so the upper limit content when adding Si is 1%.
[0036]
In the Zn-based alloy plating in the present invention, Pb, Sb, C, P, Fe, Sn, Mn, Ni, Cr, Co, and the like are further added to the plating layer for the purpose of improving corrosion resistance, plating adhesion, formability, and the like. One or more of Cu, Ca, Li, Ti, B and rare earth elements can be contained in a total of 25% or less. Or even if it is Zn plating which mixed said element as an impurity, it will not cause trouble. Moreover, it can also be set as the plating which disperse | distributed compounds, such as elements, such as S and As, an oxide, a carbide | carbonized_material, sulfide.
[0037]
The component of the base steel plate of the plated steel plate targeted by the present invention is not particularly limited, and an appropriate component can be selected according to required strength, workability, formability, and the like.
[0038]
Furthermore, the steel plate applied to the present invention is sufficiently effective whether it is a cold-rolled steel plate or a hot-rolled steel plate manufactured by a normal process, and the effect varies greatly depending on the history of the steel plate. It's not something to do.
[0039]
Of course, it is of course possible to add various treatments to the plated steel sheet to which the present invention is applied, for example, lubricity improvement treatment, resin coating treatment, weldability improvement treatment, phosphate Even if the treatment, the treatment for improving the phosphate treatment property, etc. are performed, it does not depart from the scope of the present invention, and various treatments may be performed depending on the required properties. The effect of the present invention is not changed at all.
[0040]
As the strength of the plated steel sheet targeted by the present invention, a high strength steel (300, 340, 400, 440, 300, 340, 400, 440, 300N / mm 2 or more from ordinary steel or ultra deep drawing steel having a tensile strength of less than 300 N / mm 2 is used. 590, 780, 980, 1180, 1450 N / mm 2 grade).
[0041]
In addition, although the manufacturing method of a zinc-based alloy plated steel plate is not specifically limited, it is common to plate by immersing a steel plate in the hot-dipping bath of said zinc-based alloy.
[0042]
【Example】
A bending test piece (1.0 mm (plate thickness) x 20 mm (width) x 100 mm (length)) is taken from a zinc-based alloy-plated steel sheet with a thickness of 1.0 mm that has been plated with zinc-based alloy, and the plated surface is bent. Bending was performed so as to be on the outside. The bending was in accordance with JIS G 3321. Next, in the example of the present invention, an ultrasonic impacting device provided with a hammer having a radius of 1.5 mm is applied to the bending surface of the test piece at a speed of 0.5 m / min at an amplitude of 30 μm and a frequency of 30 kHz. Sonic shock treatment was performed. In addition, as comparative examples, a bent surface having a shot particle size of 7 mm, a shot speed of 10 m / s and subjected to shot peening for 2 minutes and a bent state (no treatment) are prepared, and these tests are performed. The piece was subjected to an exposure test in the air.
[0043]
The results are shown in Table 1.
[0044]
As can be seen from Table 1, in Comparative Examples 1 and 2 subjected to shot peening, white rust was observed in 35 days, red rust was observed in 120 days, and in Comparative Examples 2 and 3 where no treatment was performed, 30 to 40 days. And white rust was observed in 100 to 130 days. On the other hand, the test piece of the present invention does not generate white rust and red rust for a long time, and it can be seen that the corrosion resistance is improved by ultrasonic impact treatment.
[0045]
[Table 1]
【The invention's effect】
According to the method of the present invention, it is possible to suppress deterioration of the corrosion resistance generated in the processed portion of the zinc-based alloy plated steel sheet, and therefore it is possible to improve the durability of the structural product using the galvanized steel sheet. Since the method of the present invention uses an ultrasonic impacting device that is superior in usability compared to a hammer peening device, etc., it can be applied to a limited part, a minute part, a narrow part as a processing part, and a structure It is an efficient and economical method for improving the corrosion resistance of products.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic cross-sectional view illustrating changes in properties of a processed part of a zinc-based alloy plated steel sheet according to the method of the present invention, where (a) is before ultrasonic impact treatment, and (b) is after ultrasonic impact treatment. The properties of cracks are shown.
[Explanation of symbols]
DESCRIPTION OF
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| JP6025147B2 (en) * | 2013-05-29 | 2016-11-16 | 日新製鋼株式会社 | Processing method for Zn-based plated parts |
| WO2016027293A1 (en) * | 2014-08-22 | 2016-02-25 | 日新製鋼株式会社 | Method for processing galvanized component |
| CN110512156A (en) * | 2019-08-12 | 2019-11-29 | 江苏大学 | A kind of aluminium alloy based composites Nano surface treatment method |
| CN112575276A (en) * | 2020-12-03 | 2021-03-30 | 攀钢集团研究院有限公司 | Hot-dip zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing and preparation method thereof |
| KR102620034B1 (en) * | 2021-12-03 | 2024-01-03 | 닛폰세이테츠 가부시키가이샤 | Zn-based plated steel sheet |
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| US6171415B1 (en) * | 1998-09-03 | 2001-01-09 | Uit, Llc | Ultrasonic impact methods for treatment of welded structures |
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