JP3783995B2 - Magnesium alloy surface treatment method - Google Patents
Magnesium alloy surface treatment method Download PDFInfo
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- JP3783995B2 JP3783995B2 JP13199699A JP13199699A JP3783995B2 JP 3783995 B2 JP3783995 B2 JP 3783995B2 JP 13199699 A JP13199699 A JP 13199699A JP 13199699 A JP13199699 A JP 13199699A JP 3783995 B2 JP3783995 B2 JP 3783995B2
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
- C23C22/08—Orthophosphates
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
- C23C22/08—Orthophosphates
- C23C22/18—Orthophosphates containing manganese cations
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
- C23C22/36—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates
- C23C22/361—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates containing titanium, zirconium or hafnium compounds
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/40—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates
- C23C22/44—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates containing also fluorides or complex fluorides
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/78—Pretreatment of the material to be coated
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F1/00—Etching metallic material by chemical means
- C23F1/10—Etching compositions
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Description
【０００１】
【発明の属する技術分野】
本発明は、マグネシウム合金の表面に優れた耐食性、塗膜密着性、および低表面抵抗値を付与するための新規な表面処理方法に関するものである。本発明が特に効果的に適用される分野は、ダイキャスト法あるいはチクソモ−ルド法と呼ばれる鋳造法によって成型されたマグネシウム合金製品である。これらの方法で成型されたマグネシウム合金の表面には、鋳造時に使用される離型剤や合金成分であるアルミニウムや亜鉛が偏析しているのが一般で、表面処理にて清浄化しにくい表面になっている。本発明の表面処理方法はこれらの表面を清浄化し、優れた耐食性、塗膜密着性、および低表面抵抗値を付与するのに特に有効である。
【０００２】
【従来の技術】
マグネシウム合金は低比重で強靱、かつリサイクル性に優れるため、自動車や家電分野の製品に広く利用されている。しかし、マグネシウム合金は実用金属の中で最も活性で腐食しやすいため、一般に化成処理により耐食皮膜を形成させて使用している。自動車部品に用いる場合は主に耐食性と塗膜密着性が、また、ノ−トパソコンや携帯電話等の家電製品の筐体に用いる場合は耐食性、塗膜密着性とともにマグネシウム合金のもつ優れた電磁波シ−ルド性を損なわないように、表面処理後の表面抵抗値が低いことが要求される。
【０００３】
前記のごとく、これらのマグネシウム合金製品の多くはダイキャスト、あるいはチクソモ−ルド法と呼ばれる鋳造法によって成型されている。これらの鋳造法は、溶融あるいは半溶融状態のマグネシウム合金を高速、高圧で金型に注入して成型するものである。一般に鋳造に際し、鋳造毎に金型表面に水系あるいはエマルジョン系の離型剤を塗布しているが、このため成型後のマグネシウム合金製品の表面には離型剤が強固に付着している。この離型剤は溶融したマグネシウム合金の熱（約６６０℃）によって変質し、また、離型剤の一部は素材の内部まで巻き込まれているため、表面処理にて清浄化しにくい状態になっている。
【０００４】
一般に、ダイキャストおよびチクソモ−ルド法で使用されるマグネシウム合金には、鋳造性や機械的強度を上げるため合金成分としてアルミニウムや亜鉛が添加されている。最も一般的なマグネシウム合金であるＡＺ９１Ｄでは、合金成分としてアルミニウムが９％、亜鉛が１％添加されている。この様な合金成分を含む多元合金は、凝固速度によって合金成分の析出形態が異なるので、金型で急冷されたマグネシウム合金の最表層は、部位によって凝固速度が大きく異なることが多く、特に金型の注入口に相当する部位（ゲ−ト側）と注入口の反対側（オ−バ−フロ−側）では最表層の合金成分濃度と晶出形態は大きく異なっている。また、製品の形状や鋳造条件によっても最表層の状態は異なる。
【０００５】
前記のごとく、マグネシウム合金の表面処理において最も重要な点は、離型剤および合金の偏析層を含む最表層を除去し、化成処理工程の前にできる限り清浄な表面を形成することにある。清浄化が不十分だと均一な化成処理が施せず、優れた耐食性、塗膜密着性、および低表面抵抗値を発揮させることは難しい。
【０００６】
マグネシウム合金の表面処理方法としては、一般に以下のプロセスが適用されている。この中で、脱脂工程は機械油、切削油等の軽度な有機物汚れの除去を、酸エッチング工程では機械油、切削油等の軽度な有機物汚れとともに離型剤や合金偏析を含む最表層の除去を担っている。化成処理工程ではクロム酸クロメートやリン酸マンガン系の皮膜を形成させ、耐食性と塗膜密着性を付与している。機械油、切削油等の有機汚れの付着が少ない製品や、あらかじめショットブラストや機械的研磨を施した製品では、脱脂工程が省略されることもある。以下の工程１〜工程３を基に従来技術の問題点をまとめる。
【０００７】
工程１；脱脂→水洗→化成処理→水洗→純水洗→乾燥
工程２；脱脂→水洗→酸エッチング→水洗→化成処理→水洗→純水洗→乾燥
工程３；脱脂→水洗→酸エッチング→水洗→脱スマット→水洗→化成処理→水洗→純水洗→乾燥
【０００８】
前記工程で、脱脂は水酸化ナトリウムやリン酸ナトリウム等のアルカリビルダ−に界面活性剤を配合したもの、あるいは硫酸や硝酸、酒石酸等の酸に界面活性剤を配合したものが用いられる。酸エッチングは硫酸、硝酸、リン酸等の鉱酸またはクエン酸、シュウ酸、酒石酸等の有機酸が一般に使用されている。しかし、マグネシウム合金の表面に残存する離型剤と合金の偏析層を完全に除去する程度まで脱脂や酸エッチングを行うと、合金成分のスマットが表面に残存してしまう。これは、これらの工程でマグネシウムの素地が選択的にエッチングされるためで、スマットが残存した状態では化成処理しても緻密で均一な皮膜は形成されず、優れた性能は発揮できない。このため、前記の工程１，２ではスマットが発生しない程度の弱エッチングしか適用できず、離型剤および合金の偏析層を含む最表層を完全に除去することは難しい。
【０００９】
前記工程３の例としては特開平６−２２０６６３号公報が開示されている。この公報には、酸エッチング工程で硫酸、リン酸、酒石酸等を用いて離型剤、合金の偏析層を含む最表層を完全に除去するまでエッチングし、エッチングで生じたスマットをエチレンジアミンテトラ酢酸をアルカリでｐＨ１２〜１３に調整した処理液で脱スマットを行う方法が開示されている。しかし、この方法では離型剤、合金の偏析層を含む最表層は除去できるが、化成処理前にこの方法で清浄な表面を形成すると、化成処理前の水洗工程で水酸化皮膜が形成する。この水酸化皮膜はポ−ラスな構造で、その後の化成処理工程にて緻密な化成皮膜の形成を阻害し、耐食性、塗膜密着性を劣化させる。
【００１０】
また、特開平２−２５４３０号公報には、めっきの前処理方法としてピロリン酸塩系の処理液でエッチングした後、フッ酸系の処理液で脱スマットする工程が開示されている。この方法では、脱スマット後にフッ化マグネシウムの薄膜が形成し、その後の水洗工程での水酸化皮膜の形成は抑制できる。しかし、この後に化成処理し塗装すると、塗膜密着性が悪く、また、化成処理後の表面抵抗値も高くなってしまう。また、フッ化物を含む処理液は人体や作業環境も良いとは言えない。
【００１１】
【発明が解決しようとする課題】
本発明は、従来のマグネシウム合金の表面処理方法における前記の問題を解決したものであり、マグネシウム合金の表面に優れた耐食性、塗膜密着性、および低表面抵抗値を有する化成皮膜を形成させる表面処理方法を得ることを目的とするものである。
【００１２】
【課題を解決するための手段】
本発明者らは、前記従来技術の抱える問題点を解決するための手段について、前記の工程３を基に鋭意検討した結果、マグネシウム合金の表面を酸でエッチングして離型剤を含む最表層を溶解除去する。次いで有機リン化合物をキレ−ト剤とするアルカリ液に接触させて酸エッチング工程にて表面に残存した合金成分のスマットを選択的に溶解し、同時にリン化合物の薄膜を形成させてその後の水洗工程での水酸化皮膜の成長を抑制し、化成処理をすると、前記課題を解決できることを新たに見いだして本発明を達成するに至った。
【００１３】
すなわち、本発明の第１のマグネシウム合金の表面処理方法は、マグネシウム合金の表面をｐＨ１〜５の酸エッチング液に接触させて該表面をエッチングし、次いで該マグネシウム合金を有機リン化合物を含有するｐＨ７〜１４のアルカリ性水溶液に接触させることを特徴とするものである。また、あらかじめマグネシウム合金の表面を脱脂し、機械油、切削油等の有機物汚れを除去した後に酸エッチングを行ったほうがより好ましい。この際の脱脂液は、界面活性剤を含むアルカリまたは酸を用い、アルカリではｐＨ９〜１４、酸ではｐＨ０〜６の液を用いることができる。
【００１４】
前記酸エッチング液は、グリコ−ル酸、クエン酸、酒石酸、リンゴ酸、シュウ酸、マロン酸、ギ酸、酢酸、乳酸、グルタ−ル酸、プロピオン酸、酪酸、安息香酸、およびフタル酸からなる群から選ばれる少なくとも１種のカルボン酸化合物を含有するのが好ましい。前記有機リン化合物は、ヒドロキシエタンジホスホン酸、アミノトリメチレンホスホン酸、エチレンジアミンテトラメチレンホスホン酸、ジエチレントリアミンペンタメチレンホスホン酸、ヒドロキシルイミノビスメチレンホスホン酸、およびヘキサメチレンジアミンテトラメチレンホスホン酸からなる群から選ばれる少なくとも１種が好ましい。前記脱スマット用水溶液は、さらにオルソリン酸、ピロリン酸、およびトリポリリン酸からなる群から選ばれる少なくとも１種の無機リン酸を含有してもよい。
【００１５】
本発明の第２のマグネシウム合金の表面処理方法は、前記請求項１〜７の何れか１項に記載の表面処理方法を適用した後、オルソリン酸とＺｎ、Ｆｅ、Ｍｎ、Ｍｇ、およびＣａからなる群から選ばれる少なくとも１種の金属イオンを含有するｐＨ２〜６の酸性水溶液に接触させることを特徴とするものである。
【００１６】
本発明の第３のマグネシウム合金の表面処理方法は、前記請求項１〜７の何れか１項に記載の表面処理方法を適用した後、フッ化水素酸、硅フッ化水素酸、ジルコンフッ化水素酸、およびチタンフッ化水素酸からなる群から選ばれる少なくとも１種のフッ素化合物と、Ｃｒ、Ｍｏ、Ｗ、Ｒｅ、およびＶからなる群から選ばれる少なくとも１種の金属酸素酸化合物とを含有するｐＨ２〜６の酸性水溶液に接触させるさせることを特徴とするものである。
【００１７】
【工程および処理液組成の説明】
本発明の酸エッチング工程では、離型剤、および合金の偏析層を含む最表層を完全に溶解除去する。酸としては特に限定はしないが、グリコ−ル酸、クエン酸、酒石酸、リンゴ酸、シュウ酸、マロン酸、ギ酸、酢酸、乳酸、グルタ−ル酸、プロピオン酸、酪酸、安息香酸およびフタル酸からなる群から選ばれる少なくとも１種のカルボン酸化合物が含まれている液を使用するのが好ましい。離型剤、および合金の偏析層を含む最表層は、製品形状や製品部位、鋳造条件によりその厚さが異なるが、一般には表面から５〜１０μｍまでの層である。このためエッチング条件は１０〜１５μｍを除去できるように設定する必要がある。エッチング量が５μｍを下回ると離型剤および合金の偏析層が残存し、耐食性や塗膜密着性の劣化、表面抵抗値の上昇等の問題が生じる。エッチング条件は濃度、温度、時間にて調整する。
【００１８】
酸エッチング工程では、離型剤、および合金の偏析層を含む最表層の除去と共に、機械油、切削油等の有機物汚れも除去できる。しかし、前記酸エッチング工程の前にあらかじめ脱脂した方が、酸エッチング液の老化がより抑えられ、より好ましい。脱脂液としては、有機物汚れを除去できるものであれば特に組成は限定しないが、界面活性剤を含むアルカリ、または酸を用いるのが好ましい。アルカリではアルカリ金属の水酸化物、リン酸塩、ケイ酸塩、炭酸塩等、酸では硫酸、硝酸、酒石酸等が用いられる。また、界面活性剤としてはノニオン系、アニオン系、カチオン系のいずれも使用できる。また、脱脂効率をあげるためにキレ−ト剤を配合してもよい。本脱脂液をマグネシウム合金に接触させる温度と時間は特に制限はないが、３５〜７０℃、２〜１０分の範囲で接触させるのが好ましい。
【００１９】
次に、前記酸エッチング後、十分に水洗し、次いで有機リン化合物のキレ−ト剤を配合したアルカリ液に接触させ、酸エッチング工程にて表面に残存した合金成分のスマットを選択的に溶解除去する。この様なキレ−ト剤としては、スマットの主成分が合金成分であるアルミニウム合金であるため、これを優先的にキレ−トするホスホン酸化合物が有効である。この様な化合物としては、ヒドロキシエタンジホスホン酸、アミノトリメチレンホスホン酸、エチレンジアミンテトラメチレンホスホン酸、ジエチレントリアミンペンタメチレンホスホン酸、ヒドロキシルイミノビスメチレンホスホン酸およびヘキサメチレンジアミンテトラメチレンホスホン酸からなる群から選ばれる少なくとも１種が使用できる。
【００２０】
なお、ホスホン酸化合物の配合量は特に限定はないが、５〜１００g/Lが好ましい。また、スマットを優先的に溶解させるには、マグネシウム素地の溶解を可能な限り抑え、さらに前記キレ−ト剤が最も効果的に作用するアルカリ領域が好ましく、水酸化物、リン酸塩および炭酸塩からなる群から選ばれる少なくとも１種のｐＨ調剤剤でｐＨを７〜１４に、より好ましくはｐＨ９〜１３に調整する必要がある。ｐＨをアルカリ側にすることによりマグネシウム素地の溶解が抑えられ、かわりに合金成分のスマットがキレ−ト剤により選択的に溶解除去される。また、本処理液にマグネシウム合金を接触させると、スマット除去と同時にリン化合物の薄膜が形成される。このリン化合物の薄膜は塗膜密着性や表面抵抗値に悪影響を及ぼすことなく次工程の水洗工程での水酸化皮膜の成長を抑えることができるため、緻密な化成皮膜を形成させるのに有効である。本処理液をマグネシウム合金に接触させる温度と時間は特に制限はないが、６０〜９０℃、１〜１０分の範囲で接触させるのが好ましい。
【００２１】
前記の有機リン化合物を含むアルカリ液において、さらにオルソリン酸、ピロリン酸、およびトリポリリン酸からなる群から選ばれる少なくとも１種の無機リン酸を含有させると、マグネシウム合金の表面にさらに緻密なリン化合物の薄膜が形成される。実際の表面処理ラインにおいては水洗効率を上げるため、水洗時間を長くしたり温度を上げたりする場合があり、水酸化皮膜の成長がより促進され易いが、この様な場合、前記の無機リン酸の添加は有効である。なお、無機リン酸の配合量は特に制限はないが、０．１〜３０g/Lが好ましい。
【００２２】
前記脱スマット工程までで清浄かつある程度の耐食性を有する表面が得られるが、より高度な耐食性、および塗膜密着性を付与するために化成処理を行う。化成処理液としてはオルソリン酸とＺｎ、Ｆｅ、Ｍｎ、ＭｇおよびＣａからなる群から選ばれる少なくとも１種の金属イオンを含有するｐＨ２〜６の酸性液が使用できる。形成される皮膜はこれらの金属のリン酸塩が主成分である。皮膜の付着量は特に制限はないが、要求性能に応じて付着量を調整することが望ましい。付着量は処理液濃度、処理温度、処理時間で調整できる。前記、オルソリン酸、金属イオンの配合量も特に制限はないが、０．１〜５０g/Lが好ましい。
【００２３】
また、化成処理液としてはフッ化水素酸、硅フッ化水素酸、ジルコンフッ化水素酸およびチタンフッ化水素酸からなる群から選ばれる少なくとも１種のフッ素化合物と、Ｃｒ、Ｍｏ、Ｗ、ＲｅおよびＶからなる群から選ばれる少なくとも１種の金属酸素酸化合物をと含有するｐＨ２〜６の酸性水溶液も適用できる。前記同様に皮膜の付着量は特に制限はないが、要求性能に応じて付着量を調整することが望ましい。付着量は処理液濃度、処理温度、処理時間で調整できる。前記、フッ素化合物、金属酸素酸化合物の配合量も特に限定しないが、０．１〜５０g/Lが好ましい。
【００２４】
前記表面処理を施した後十分に水洗し、最後に純水洗し、乾燥する。乾燥条件は特に制限はない。また、この後、必要に応じて塗装を行っても良い。塗料は溶剤系、水系、いずれも適用可能である。
【００２５】
【実施例】
以下に本発明の表面処理方法に関し、いくつかの実施例を挙げ、その有効性を比較例と対比して示す。
（１）離型剤除去性の評価方法。
離型剤除去性は固体用全有機炭素計（島津製作所製ＴＯＣ５０００−Ａ／ＳＳＭ５０００−Ａ）を用い、試料表面の全有機炭素残留量を測定して評価した。試料を１０×３０ｍｍに切り出し、化成処理工程まで処理した後試料を乾燥させ、６００℃、１０分の条件で試料表面に残存した離型剤を燃焼させ、発生した二酸化炭素の赤外線吸光度により全有機炭素残留量を定量した。一般に全有機炭素残留量が低い程離型剤除去性に優れ、優れた耐食性、塗膜密着性、および低表面抵抗値が得られる。
【００２６】
（２）化成処理後の耐食性の評価方法。
化成処理した試料を５％塩化ナトリウム水溶液を用いた塩水噴霧試験法（ＪＩＳ Ｚ−２３７１）により２４時間試験を施した後、目視により腐食面積率を判定した。
◎：腐食面積率５％未満
○：腐食面積率５％以上１０％未満
△：腐食面積率１０％以上２０％未満
×：腐食面積率２０％以上
【００２７】
（３）塗装後の耐食性の評価方法。
塗装した試料で前記塩水噴霧試験を２４０時間実施し、クロスカットからの腐食によるフクレ幅を測定した。
【００２８】
（４）塗膜密着性の評価方法。
化成処理した試料にエポキシ系溶剤塗料（２コ−ト１ベ−ク、５０μｍ）をスプレ−塗装し、１５０℃、２０分乾燥した後、塗膜密着性を評価した。評価は引っ張り式塗膜付着力試験機（コ−テック製エルコメ−タ−）にて行った。エルコメ−タ−とは塗膜を強制的に剥離し、その時の密着力を測定するもので、一般にその値が高い方が塗膜密着性は良好である。
【００２９】
（５）表面抵抗値の評価方法。
表面抵抗値の評価は表面抵抗計（三菱化学製ロレスタＭＰ 型番ＭＣＰ−Ｔ３５０ ２点式プロ−ブＭＣＰ−ＴＰ０１にて測定）にて行った。
【００３０】
実施例１
［供試料］ＡＺ９１Ｄダイキャスト材、１００mm×１００mm×１mm
［処理工程］
脱脂→水洗→酸エッチング→水洗→脱スマット→水洗→化成→水洗→純水洗→乾燥→塗装→乾燥
実施例２
実施例１の工程で脱脂工程を省略して表面処理した。
［供試料］ 実施例１と同様。
［処理工程］ 脱脂工程の省略以外は実施例１と同様。
酸エッチング→水洗→脱スマット→水洗→化成→水洗→純水洗→乾燥→塗装→乾燥
実施例３
実施例１の工程で酸エッチング工程の有機酸の種類を変更して表面処理した。［供試料］ 実施例１と同様。
［処理工程］ 実施例１と同様。
実施例４
あらかじめショットブラストを施した実施例１の供試料を用い、脱脂工程を省略して表面処理した。
［供試料］ 実施例１と同様。
［処理工程］ 脱脂工程の省略以外は実施例１と同様。
酸エッチング→水洗→脱スマット→水洗→化成→水洗→純水洗→乾燥→塗装→
乾燥
実施例５
実施例１の工程で脱スマット工程のキレ−ト剤の種類を変更して表面処理した。［供試料］ 実施例１と同様。
［処理工程］ 実施例１と同様。
実施例６
実施例１の工程で水洗工程の時間を長くして表面処理した。
［供試料］ 実施例１と同様。
［処理工程］ 実施例１と同様。
［処理液組成および処理条件］
脱脂 ；実施例１と同様。
酸エッチング；実施例１と同様。
脱スマット ；実施例１と同様。
化成 ；実施例１と同様。
水洗 ；２５℃、５分、浸せき。
【００３６】
実施例７
実施例１の工程で脱スマット液にピロリン酸を添加し、化成処理を省略して表面処理した（脱スマット工程で形成されるリン化合物皮膜の性能確認）。
［供試料］ 実施例１と同様。
［処理工程］
脱脂→水洗→酸エッチング→水洗→脱スマット→水洗→水洗→純水洗→乾燥→
塗装→乾燥
比較例１
実施例１の工程で酸エッチング、脱スマットの各工程を省略して表面処理した。［供試料］ 実施例１と同様。
［処理工程］
脱脂→水洗→化成→水洗→純水洗→乾燥→塗装→乾燥
［処理液組成および処理条件］
脱脂 ；実施例１と同様。
化成 ；実施例１と同様。
水洗 ；実施例１と同様。
【００３８】
比較例２
実施例１の工程で酸エッチング工程でのエッチング時間を１／５にし、脱スマット工程を省略して表面処理した。
［供試料］ 実施例１と同様。
［処理工程］
脱脂→水洗→酸エッチング→水洗→化成→水洗→純水洗→乾燥→塗装→乾燥
比較例３
実施例１の工程で脱スマット工程のキレ−ト剤を変更して表面処理した（特開平６−２２０６６３号公報の追試験）。
［供試料］ 実施例１と同様。
［処理工程］ 実施例１と同様。
比較例４
特開平２−２５４３０号公報の追試験を行った。
［供試料］ 実施例１と同様。
［処理工程］
脱脂→水洗→化学エッチング→水洗→フッ化物処理→水洗→中和→水洗→化成
→水洗→純水洗→乾燥→塗装→乾燥
比較例５
実施例１の工程で脱スマット工程のキレ−ト剤なしで表面処理した。
［供試料］ 実施例１と同様。
［処理工程］ 実施例１と同様。
比較例６
比較例２で水洗時間を長くして表面処理した。
［供試料］ 実施例１と同様。
［処理工程］
脱脂→水洗→酸エッチング→水洗→化成→水洗→純水洗→乾燥→塗装
［処理液組成および処理条件］
アルカリ脱脂；比較例２と同様。
酸エッチング；比較例２と同様。
化成 ；比較例２と同様。
水洗 ；２５℃、５分、浸せき
【００４３】
【表１】
表１の結果から明らかなように、本発明を用いた実施例１〜７は比較例１〜６と比べ優れた離型剤除去性、耐食性、塗膜密着性、および低表面抵抗値を同時に有することがわかる。また、水洗時間を長くした実施例６においても性能の劣化は認められない。
【００４５】
【発明の効果】
前記の説明から明らかなように、本発明の方法でダイキャスト法あるいはチクソモ−ルド法によって成型されたマグネシウム合金を表面処理することにより、耐食性、塗膜密着性、および低表面抵抗値に優れた表面を形成することができる。本発明の表面処理方法では、離型剤、および合金の偏析層を含む最表層を完全に溶解除去し、かつ、水洗工程での水酸化皮膜の成長を抑制するため、製品形状や製品部位、鋳造条件等の影響を受けにくく、安定した性能を発揮させることができるので、利用価値が大きいものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel surface treatment method for imparting excellent corrosion resistance, coating film adhesion, and low surface resistance to the surface of a magnesium alloy. The field to which the present invention is particularly effectively applied is a magnesium alloy product formed by a casting method called a die casting method or a thixo mold method. The surface of magnesium alloy molded by these methods is generally segregated with mold release agents and alloy components such as aluminum and zinc, which are difficult to clean by surface treatment. ing. The surface treatment method of the present invention is particularly effective for cleaning these surfaces and imparting excellent corrosion resistance, coating film adhesion, and low surface resistance.
[0002]
[Prior art]
Magnesium alloys are widely used in products in the automobile and home appliance fields because of their low specific gravity, toughness, and excellent recyclability. However, since magnesium alloys are the most active and easy to corrode among practical metals, they are generally used by forming a corrosion-resistant film by chemical conversion treatment. When used for automobile parts, it mainly has corrosion resistance and coating film adhesion, and when used for housing of home appliances such as notebook PCs and mobile phones, it has excellent electromagnetic wave resistance with magnesium alloy as well as corrosion resistance and coating film adhesion. -The surface resistance after the surface treatment is required to be low so as not to impair the moldability.
[0003]
As described above, many of these magnesium alloy products are formed by a die casting or a casting method called a thixo mold method. In these casting methods, a molten or semi-molten magnesium alloy is injected into a mold at a high speed and a high pressure. In general, during casting, a water-based or emulsion-based release agent is applied to the mold surface every time the casting is performed. For this reason, the release agent adheres firmly to the surface of the magnesium alloy product after molding. This mold release agent is altered by the heat of the molten magnesium alloy (about 660 ° C.), and since part of the mold release agent is entrained to the inside of the material, it becomes difficult to clean by surface treatment. Yes.
[0004]
In general, aluminum and zinc are added as alloy components to magnesium alloys used in die casting and thixomold processes in order to improve castability and mechanical strength. In AZ91D, which is the most common magnesium alloy, 9% aluminum and 1% zinc are added as alloy components. Multi-component alloys containing such alloy components have different precipitation forms of the alloy components depending on the solidification rate. Therefore, the outermost layer of the magnesium alloy that has been rapidly cooled by the mold often varies greatly depending on the site. In the portion corresponding to the injection port (gate side) and the opposite side (overflow side) of the injection port, the alloy component concentration and the crystallization form of the outermost layer are greatly different. Further, the state of the outermost layer varies depending on the shape of the product and casting conditions.
[0005]
As described above, the most important point in the surface treatment of the magnesium alloy is to remove the outermost layer including the release agent and the segregation layer of the alloy and form a surface as clean as possible before the chemical conversion treatment step. If the cleaning is insufficient, uniform chemical conversion treatment cannot be performed, and it is difficult to exhibit excellent corrosion resistance, coating film adhesion, and low surface resistance.
[0006]
As a surface treatment method for magnesium alloy, the following processes are generally applied. In this process, the degreasing process removes mild organic dirt such as machine oil and cutting oil, and the acid etching process removes the outermost layer including mold release agent and alloy segregation together with mild organic dirt such as machine oil and cutting oil. Is responsible. In the chemical conversion treatment step, a chromate chromate or manganese phosphate-based film is formed to provide corrosion resistance and coating film adhesion. The degreasing process may be omitted in products with less organic dirt such as machine oil and cutting oil, or products that have been subjected to shot blasting and mechanical polishing in advance. The problems of the prior art are summarized based on the following steps 1 to 3.
[0007]
Step 1: Degreasing → Washing → Chemical conversion treatment → Washing → Pure water washing → Drying process 2; Degreasing → Washing → Acid etching → Washing → Chemification treatment → Washing → Pure water washing → Drying process 3; Degreasing → Washing → Acid etching → Water washing → Desalting Smut → Washing → Chemical conversion treatment → Washing → Pure water washing → Drying [0008]
In the above step, degreasing is performed by blending a surfactant with an alkali builder such as sodium hydroxide or sodium phosphate, or blending a surfactant with an acid such as sulfuric acid, nitric acid or tartaric acid. In acid etching, mineral acids such as sulfuric acid, nitric acid and phosphoric acid or organic acids such as citric acid, oxalic acid and tartaric acid are generally used. However, if degreasing or acid etching is performed to such an extent that the release agent remaining on the surface of the magnesium alloy and the segregation layer of the alloy are completely removed, the smut of the alloy component remains on the surface. This is because the magnesium substrate is selectively etched in these steps, and in the state where the smut remains, even if chemical conversion is performed, a dense and uniform film is not formed, and excellent performance cannot be exhibited. For this reason, only weak etching that does not generate smut can be applied in steps 1 and 2 described above, and it is difficult to completely remove the outermost layer including the release agent and the segregation layer of the alloy.
[0009]
As an example of the step 3, JP-A-6-220663 is disclosed. In this publication, etching is carried out using sulfuric acid, phosphoric acid, tartaric acid or the like in the acid etching process until the outermost layer including the segregation layer of the release agent and the alloy is completely removed, and the smut generated by the etching is changed to ethylenediaminetetraacetic acid. A method of desmutting with a treatment liquid adjusted to pH 12-13 with an alkali is disclosed. However, this method can remove the outermost layer including the mold release agent and the segregation layer of the alloy, but if a clean surface is formed by this method before the chemical conversion treatment, a hydroxide film is formed in the water washing step before the chemical conversion treatment. This hydroxide film has a porous structure, which inhibits the formation of a dense chemical film in the subsequent chemical conversion treatment step, and deteriorates the corrosion resistance and coating film adhesion.
[0010]
JP-A-2-25430 discloses a process of etching with a pyrophosphate processing solution and then desmutting with a hydrofluoric acid processing solution as a pretreatment method for plating. In this method, a thin film of magnesium fluoride is formed after desmutting, and the formation of a hydroxide film in the subsequent water washing step can be suppressed. However, if a chemical conversion treatment is applied after this, coating film adhesion is poor, and the surface resistance value after the chemical conversion treatment also becomes high. Moreover, it cannot be said that the treatment liquid containing fluoride has a good human body and working environment.
[0011]
[Problems to be solved by the invention]
The present invention solves the above-described problems in the conventional magnesium alloy surface treatment method, and forms a chemical conversion film having excellent corrosion resistance, coating adhesion, and low surface resistance on the surface of the magnesium alloy. The object is to obtain a processing method.
[0012]
[Means for Solving the Problems]
As a result of intensive investigations on the means for solving the problems of the prior art based on the above-mentioned step 3, the inventors of the present invention etched the surface of the magnesium alloy with an acid and included a release agent. Is dissolved and removed. Next, the organophosphorus compound is brought into contact with an alkaline solution containing a chelating agent to selectively dissolve the smut of the alloy component remaining on the surface in the acid etching process, and at the same time, a thin film of the phosphorus compound is formed, followed by a water washing process. The present inventors achieved the present invention by newly finding that the above-mentioned problems can be solved by suppressing the growth of the hydroxide film and performing chemical conversion treatment.
[0013]
That is, in the first magnesium alloy surface treatment method of the present invention, the surface of the magnesium alloy is contacted with an acid etching solution having a pH of 1 to 5 to etch the surface, and then the magnesium alloy is pH 7 containing an organophosphorus compound. It is made to contact with -14 alkaline aqueous solution. It is more preferable to degrease the surface of the magnesium alloy in advance to remove organic contaminants such as machine oil and cutting oil and then perform acid etching. As the degreasing solution, an alkali or acid containing a surfactant is used, and a solution having a pH of 9 to 14 for an alkali and a pH of 0 to 6 for an acid can be used.
[0014]
The acid etching solution is composed of glycolic acid, citric acid, tartaric acid, malic acid, oxalic acid, malonic acid, formic acid, acetic acid, lactic acid, glutaric acid, propionic acid, butyric acid, benzoic acid, and phthalic acid It is preferable to contain at least one carboxylic acid compound selected from: The organophosphorus compound is selected from the group consisting of hydroxyethanediphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, hydroxyliminobismethylenephosphonic acid, and hexamethylenediaminetetramethylenephosphonic acid. At least one selected from the above is preferred. The desmutting aqueous solution may further contain at least one inorganic phosphoric acid selected from the group consisting of orthophosphoric acid, pyrophosphoric acid, and tripolyphosphoric acid.
[0015]
The surface treatment method of the second magnesium alloy according to the present invention is based on orthophosphoric acid and Zn, Fe, Mn, Mg, and Ca after applying the surface treatment method according to any one of claims 1 to 7. It is made to contact the acidic aqueous solution of pH 2-6 containing the at least 1 sort (s) of metal ion chosen from the group which consists of.
[0016]
The third magnesium alloy surface treatment method of the present invention is the hydrofluoric acid, hydrofluoric acid, zircon hydrogen fluoride after applying the surface treatment method according to any one of claims 1 to 7. PH 2 containing at least one fluorine compound selected from the group consisting of an acid and titanium hydrofluoric acid, and at least one metal oxyacid compound selected from the group consisting of Cr, Mo, W, Re, and V It is made to contact the acidic aqueous solution of -6.
[0017]
[Description of process and treatment liquid composition]
In the acid etching process of the present invention, the outermost layer including the release agent and the segregation layer of the alloy is completely dissolved and removed. Although it does not specifically limit as an acid, From glycolic acid, citric acid, tartaric acid, malic acid, oxalic acid, malonic acid, formic acid, acetic acid, lactic acid, glutaric acid, propionic acid, butyric acid, benzoic acid, and phthalic acid It is preferable to use a liquid containing at least one carboxylic acid compound selected from the group consisting of: Although the thickness of the outermost layer including the release agent and the segregation layer of the alloy varies depending on the product shape, product site, and casting conditions, it is generally a layer from the surface to 5 to 10 μm. For this reason, it is necessary to set etching conditions so that 10-15 micrometers can be removed. When the etching amount is less than 5 μm, the segregation layer of the release agent and the alloy remains, and problems such as deterioration of corrosion resistance, coating film adhesion, and increase in surface resistance value occur. Etching conditions are adjusted by concentration, temperature, and time.
[0018]
In the acid etching step, organic contaminants such as machine oil and cutting oil can be removed together with the removal of the outermost layer including the release agent and the segregation layer of the alloy. However, it is more preferable to degrease in advance before the acid etching step because aging of the acid etching solution is further suppressed. The composition of the degreasing liquid is not particularly limited as long as it can remove organic dirt, but an alkali containing a surfactant or an acid is preferably used. Alkali metal hydroxides, phosphates, silicates, carbonates, etc. are used for alkalis, and sulfuric acid, nitric acid, tartaric acid, etc. are used for acids. As the surfactant, any of nonionic, anionic and cationic types can be used. Further, a chelating agent may be blended in order to increase the degreasing efficiency. The temperature and time for contacting the degreasing solution with the magnesium alloy are not particularly limited, but it is preferably contacted in the range of 35 to 70 ° C. and 2 to 10 minutes.
[0019]
Next, after the acid etching, the substrate is thoroughly washed with water, and then contacted with an alkaline solution containing an organophosphorus compound chelating agent to selectively dissolve and remove the alloy component smut remaining on the surface in the acid etching step. To do. As such a chelating agent, since the main component of the smut is an aluminum alloy which is an alloy component, a phosphonic acid compound preferentially chelating it is effective. Such a compound is selected from the group consisting of hydroxyethanediphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, hydroxyliminobismethylenephosphonic acid and hexamethylenediaminetetramethylenephosphonic acid. At least one of the above can be used.
[0020]
The amount of the phosphonic acid compound is not particularly limited, but is preferably 5 to 100 g / L. Further, in order to preferentially dissolve the smut, it is preferable to suppress the dissolution of the magnesium base as much as possible, and the alkali region in which the chelating agent works most effectively is preferable, and hydroxides, phosphates and carbonates. It is necessary to adjust the pH to 7 to 14, more preferably to pH 9 to 13, with at least one pH preparation selected from the group consisting of: By setting the pH to the alkali side, dissolution of the magnesium base is suppressed, and instead the smut of the alloy component is selectively dissolved and removed by the chelating agent. Further, when a magnesium alloy is brought into contact with the treatment liquid, a thin film of a phosphorus compound is formed simultaneously with the removal of smut. This thin film of phosphorus compound is effective in forming a dense chemical conversion film because it can suppress the growth of the hydroxide film in the subsequent water washing step without adversely affecting the coating adhesion and surface resistance. is there. The temperature and time for contacting the treatment liquid with the magnesium alloy are not particularly limited, but it is preferable to contact the treatment liquid at 60 to 90 ° C. for 1 to 10 minutes.
[0021]
In the alkaline solution containing the organophosphorus compound, when at least one inorganic phosphoric acid selected from the group consisting of orthophosphoric acid, pyrophosphoric acid, and tripolyphosphoric acid is further contained, the surface of the magnesium alloy has a more dense phosphorus compound. A thin film is formed. In an actual surface treatment line, in order to increase the water washing efficiency, the water washing time may be increased or the temperature may be raised, and the growth of the hydroxide film is more easily promoted. The addition of is effective. In addition, the compounding quantity of inorganic phosphoric acid does not have a restriction | limiting in particular, However, 0.1-30 g / L is preferable.
[0022]
A clean surface having a certain degree of corrosion resistance can be obtained up to the desmutting step, but a chemical conversion treatment is performed in order to provide higher corrosion resistance and coating film adhesion. As the chemical conversion treatment solution, an acidic solution having a pH of 2 to 6 containing orthophosphoric acid and at least one metal ion selected from the group consisting of Zn, Fe, Mn, Mg and Ca can be used. The formed film is mainly composed of phosphates of these metals. Although there is no restriction | limiting in particular in the adhesion amount of a film | membrane, it is desirable to adjust the adhesion amount according to a required performance. The amount of adhesion can be adjusted by the treatment liquid concentration, treatment temperature, and treatment time. The blending amounts of orthophosphoric acid and metal ions are not particularly limited, but are preferably 0.1 to 50 g / L.
[0023]
Further, as the chemical conversion treatment liquid, at least one fluorine compound selected from the group consisting of hydrofluoric acid, hydrofluoric acid, zircon hydrofluoric acid and titanium hydrofluoric acid, and Cr, Mo, W, Re and V An acidic aqueous solution having a pH of 2 to 6 and containing at least one metal oxyacid compound selected from the group consisting of: Similar to the above, the amount of the coating is not particularly limited, but it is desirable to adjust the amount of coating according to the required performance. The amount of adhesion can be adjusted by the treatment liquid concentration, treatment temperature, and treatment time. The blending amounts of the fluorine compound and the metal oxyacid compound are not particularly limited, but are preferably 0.1 to 50 g / L.
[0024]
After the surface treatment, it is thoroughly washed with water, finally washed with pure water, and dried. There is no particular limitation on the drying conditions. Moreover, you may perform coating after this as needed. Both solvent-based and water-based paints can be applied.
[0025]
【Example】
Hereinafter, several examples will be given and the effectiveness of the surface treatment method of the present invention will be shown in comparison with comparative examples.
(1) Evaluation method of release agent removability.
The release agent removability was evaluated by measuring the total organic carbon residue on the sample surface using a total organic carbon meter for solids (TOC5000-A / SSM5000-A manufactured by Shimadzu Corporation). The sample is cut into 10 × 30 mm, processed to the chemical conversion treatment step, the sample is dried, the release agent remaining on the sample surface is burned at 600 ° C. for 10 minutes, and the total organicity is determined by the infrared absorbance of the generated carbon dioxide. The amount of carbon residue was quantified. Generally, the lower the total amount of organic carbon, the better the release agent removability, and the better the corrosion resistance, coating film adhesion, and low surface resistance.
[0026]
(2) Evaluation method of corrosion resistance after chemical conversion treatment.
The sample subjected to chemical conversion treatment was subjected to a test for 24 hours by a salt spray test method (JIS Z-2371) using a 5% sodium chloride aqueous solution, and then the corrosion area ratio was visually determined.
◎: Corrosion area ratio less than 5% ○: Corrosion area ratio 5% or more and less than 10% △: Corrosion area ratio 10% or more and less than 20% ×: Corrosion area ratio 20% or more
(3) Evaluation method of corrosion resistance after painting.
The salt spray test was conducted for 240 hours on the coated sample, and the swelling width due to corrosion from the crosscut was measured.
[0028]
(4) Evaluation method of coating film adhesion.
The sample subjected to chemical conversion treatment was spray-coated with an epoxy solvent paint (2-coat, 1-bake, 50 μm), dried at 150 ° C. for 20 minutes, and then evaluated for coating film adhesion. Evaluation was carried out with a tensile coating film adhesion tester (Cormech Elko-Meter). The elcometer is forcibly peeling the coating film and measuring the adhesion force at that time. Generally, the higher the value, the better the coating film adhesion.
[0029]
(5) Evaluation method of surface resistance value.
The surface resistance value was evaluated with a surface resistance meter (measured with a Loresta MP, model number MCP-T350 2-point probe MCP-TP01 manufactured by Mitsubishi Chemical).
[0030]
Example 1
[Sample] AZ91D die-cast material, 100 mm x 100 mm x 1 mm
[Processing process]
Degreasing → Washing → Acid etching → Washing → Desmutting → Washing → Chemical conversion → Washing → Pure water washing → Drying → Painting → Drying
Example 2
The surface treatment was performed by omitting the degreasing step in the step of Example 1.
[Samples] Same as Example 1.
[Processing step] The same as in Example 1 except that the degreasing step is omitted.
Acid etching → Washing → Desmutting → Washing → Chemical conversion → Washing → Pure water washing → Drying → Painting → Drying
Example 3
In the process of Example 1, the type of the organic acid in the acid etching process was changed to perform surface treatment. [Samples] Same as Example 1.
[Processing step] Same as Example 1.
Example 4
Using the sample of Example 1 that had been subjected to shot blasting in advance, the surface treatment was performed by omitting the degreasing step.
[Samples] Same as Example 1.
[Processing step] The same as in Example 1 except that the degreasing step is omitted.
Acid etching → Washing → Desmutting → Washing → Chemical conversion → Washing → Pure water washing → Drying → Painting →
Dry
Example 5
The surface treatment was carried out by changing the type of chelating agent in the desmutting step in the step of Example 1. [Samples] Same as Example 1.
[Processing step] Same as Example 1.
Example 6
In the process of Example 1, the surface treatment was performed by extending the time of the water washing process.
[Samples] Same as Example 1.
[Processing step] Same as Example 1.
[Processing liquid composition and processing conditions]
Degreasing: as in Example 1.
Acid etching; similar to Example 1.
Desmutting as in Example 1.
Chemical formation: as in Example 1.
Wash with water; Soak at 25 ° C. for 5 minutes.
[0036]
Example 7
In the step of Example 1, pyrophosphoric acid was added to the desmutting solution and the surface treatment was performed by omitting the chemical conversion treatment (performance confirmation of the phosphorus compound film formed in the desmutting step).
[Samples] Same as Example 1.
[Processing process]
Degreasing → Washing → Acid etching → Washing → Desmutting → Washing → Washing → Pure water washing → Drying →
Painting → drying
Comparative Example 1
In the step of Example 1, each of the steps of acid etching and desmutting was omitted to perform surface treatment. [Samples] Same as Example 1.
[Processing process]
Degreasing → Washing → Chemical conversion → Washing → Pure water washing → Drying → Painting → Drying [Processing liquid composition and processing conditions]
Degreasing: as in Example 1.
Chemical formation: as in Example 1.
Washing with water: As in Example 1.
[0038]
Comparative Example 2
In the process of Example 1, the etching time in the acid etching process was set to 1/5, and the desmutting process was omitted to perform surface treatment.
[Samples] Same as Example 1.
[Processing process]
Degreasing → Washing → Acid etching → Washing → Chemical conversion → Washing → Pure water washing → Drying → Painting → Drying
Comparative Example 3
The surface treatment was carried out by changing the chelating agent in the desmutting step in the step of Example 1 (additional test in JP-A-6-220663).
[Samples] Same as Example 1.
[Processing step] Same as Example 1.
Comparative Example 4
The follow-up test of JP-A-2-25430 was conducted.
[Samples] Same as Example 1.
[Processing process]
Degreasing → Water washing → Chemical etching → Water washing → Fluoride treatment → Water washing → Neutralization → Water washing → Chemical conversion → Water washing → Pure water washing → Drying → Painting → Drying
Comparative Example 5
The surface treatment was carried out in the step of Example 1 without the smutting agent in the desmutting step.
[Samples] Same as Example 1.
[Processing step] Same as Example 1.
Comparative Example 6
In Comparative Example 2, the surface was treated with a long washing time.
[Samples] Same as Example 1.
[Processing process]
Degreasing → Washing → Acid etching → Washing → Chemical conversion → Washing → Pure water washing → Drying → Painting [Composition of processing solution and processing conditions]
Alkaline degreasing; similar to Comparative Example 2.
Acid etching; similar to Comparative Example 2.
Chemical conversion: Same as Comparative Example 2.
Washing with water; immersion at 25 ° C. for 5 minutes
[Table 1]
As is clear from the results in Table 1, Examples 1 to 7 using the present invention have excellent release agent removability, corrosion resistance, coating film adhesion, and low surface resistance values simultaneously as compared with Comparative Examples 1 to 6. You can see that In Example 6 in which the washing time was increased, no performance deterioration was observed.
[0045]
【The invention's effect】
As is apparent from the above description, the magnesium alloy formed by the die casting method or thixomold method according to the method of the present invention is surface-treated to provide excellent corrosion resistance, coating film adhesion, and low surface resistance. A surface can be formed. In the surface treatment method of the present invention, the outermost layer including the mold release agent and the segregation layer of the alloy is completely dissolved and removed, and the growth of the hydroxide film in the water washing step is suppressed. Since it is difficult to be influenced by casting conditions and can exhibit stable performance, the utility value is great.
Claims (7)
キレート可能なホスホン酸化合物を含有するｐＨ７〜１４のアルカリ性水溶液に接触させる第２処理を施し、その後更に、
オルソリン酸と、Ｚｎ、Ｆｅ、Ｍｎ、ＭｇおよびＣａからなる群から選ばれる少なくとも１種の金属イオンとを含有するｐＨ２〜６の酸性水溶液に接触させることを特徴とするマグネシウム合金の表面処理方法。 The magnesium alloy casting is subjected to a first treatment in which the surface is brought into contact with an acidic aqueous solution having a pH of 1 to 5 and etched , and then,
Applying a second treatment in contact with an alkaline aqueous solution having a pH of 7 to 14 containing a chelatable phosphonic acid compound;
A magnesium alloy surface treatment method comprising contacting an orthophosphoric acid with an acidic aqueous solution having a pH of 2 to 6 containing at least one metal ion selected from the group consisting of Zn, Fe, Mn, Mg and Ca.
キレート可能なホスホン酸化合物を含有するｐＨ７〜１４のアルカリ性水溶液に接触させる第２処理を施し、その後更に、Applying a second treatment in contact with an alkaline aqueous solution having a pH of 7 to 14 containing a chelatable phosphonic acid compound;
フッ化水素酸、硅フッ化水素酸、ジルコンフッ化水素酸およびチタンフッ化水素酸からなる群から選ばれる少なくとも１種のフッ素化合物と、Ｃｒ、Ｍｏ、Ｗ、ＲｅおよびＶの酸素酸からなる群から選ばれる少なくとも１種の金属酸素酸化合物とを含有するｐＨ２〜６の酸性水溶液に接触させることを特徴とするマグネシウム合金の表面処理方法。At least one fluorine compound selected from the group consisting of hydrofluoric acid, fluorohydrofluoric acid, zircon hydrofluoric acid and titanium hydrofluoric acid, and a group consisting of oxygen acids of Cr, Mo, W, Re and V A magnesium alloy surface treatment method comprising contacting with an acidic aqueous solution having a pH of 2 to 6 containing at least one selected metal oxyacid compound.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
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| JP13199699A JP3783995B2 (en) | 1999-05-12 | 1999-05-12 | Magnesium alloy surface treatment method |
| CN00118832A CN1288073A (en) | 1999-05-12 | 2000-05-10 | Surface treatment method for magnesium alloy |
| AU47968/00A AU4796800A (en) | 1999-05-12 | 2000-05-12 | Process for the surface treatment of magnesium alloys |
| PCT/US2000/006715 WO2000070123A1 (en) | 1999-05-12 | 2000-05-12 | Process for the surface treatment of magnesium alloys |
| KR1020000025305A KR20000077242A (en) | 1999-05-12 | 2000-05-12 | Surface treatment method of magnesium alloy |
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| JP13199699A JP3783995B2 (en) | 1999-05-12 | 1999-05-12 | Magnesium alloy surface treatment method |
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| JP3783995B2 true JP3783995B2 (en) | 2006-06-07 |
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| KR20180083433A (en) | 2015-12-25 | 2018-07-20 | 니혼 파커라이징 가부시키가이샤 | A surface modifier, a coated magnesium or magnesium alloy material, and a method for producing them |
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| KR101894488B1 (en) * | 2017-04-20 | 2018-09-05 | 최경수 | Method for treating the high gloss of magnesium alloy by chemical treatment |
| CN107245709A (en) * | 2017-06-06 | 2017-10-13 | 山东大学 | A kind of steel surface aqueous phase is self-assembled into film liquid and preparation method and application |
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| US3134702A (en) * | 1960-08-17 | 1964-05-26 | Dow Chemical Co | Chemical milling of magnesium metal and magnesium alloys |
| US3837803A (en) * | 1972-07-11 | 1974-09-24 | Betz Laboratories | Orthophosphate corrosion inhibitors and their use |
| NO145409C (en) * | 1979-12-07 | 1982-03-17 | Norsk Hydro As | PROCEDURE FOR METAL COATING OF MG ARTICLES |
| JPS59205488A (en) * | 1983-05-04 | 1984-11-21 | Nippon Light Metal Co Ltd | Surface treatment of aluminum alloy material |
| US5052421A (en) * | 1988-07-19 | 1991-10-01 | Henkel Corporation | Treatment of aluminum with non-chrome cleaner/deoxidizer system followed by conversion coating |
| JP3325366B2 (en) * | 1993-10-29 | 2002-09-17 | 日本パーカライジング株式会社 | Chemical conversion treatment liquid composition for magnesium-containing metal, chemical conversion treatment method, and chemical conversion-treated material |
| US5669980A (en) * | 1995-03-24 | 1997-09-23 | Atotech Usa, Inc. | Aluminum desmut composition and process |
| US5622569A (en) * | 1995-06-02 | 1997-04-22 | Aluminum Company Of America | Aluminum rigid container sheet cleaner and cleaning method |
| JPH108264A (en) * | 1996-06-21 | 1998-01-13 | Furukawa Electric Co Ltd:The | Production of magnesium-containing aluminum alloy |
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1999
- 1999-05-12 JP JP13199699A patent/JP3783995B2/en not_active Expired - Fee Related
-
2000
- 2000-05-10 CN CN00118832A patent/CN1288073A/en active Pending
- 2000-05-12 KR KR1020000025305A patent/KR20000077242A/en not_active Application Discontinuation
- 2000-05-12 AU AU47968/00A patent/AU4796800A/en not_active Abandoned
- 2000-05-12 WO PCT/US2000/006715 patent/WO2000070123A1/en not_active Application Discontinuation
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20180083433A (en) | 2015-12-25 | 2018-07-20 | 니혼 파커라이징 가부시키가이샤 | A surface modifier, a coated magnesium or magnesium alloy material, and a method for producing them |
| KR20190141029A (en) | 2015-12-25 | 2019-12-20 | 니혼 파커라이징 가부시키가이샤 | Surface-conditioning agent, as well as magnesium member or magnesium alloy material with film, and manufacturing method therefor |
| US11725287B2 (en) | 2015-12-25 | 2023-08-15 | Nihon Parkerizing Co., Ltd. | Method for manufacturing a magnesium material or magnesium alloy material with a coating |
Also Published As
| Publication number | Publication date |
|---|---|
| KR20000077242A (en) | 2000-12-26 |
| CN1288073A (en) | 2001-03-21 |
| AU4796800A (en) | 2000-12-05 |
| JP2000328261A (en) | 2000-11-28 |
| WO2000070123A1 (en) | 2000-11-23 |
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