EP1612294A1 - Bath and associated method for the conversion coating of articles made of aluminium and alloys thereof - Google Patents

Bath and associated method for the conversion coating of articles made of aluminium and alloys thereof Download PDF

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Publication number
EP1612294A1
EP1612294A1 EP05105831A EP05105831A EP1612294A1 EP 1612294 A1 EP1612294 A1 EP 1612294A1 EP 05105831 A EP05105831 A EP 05105831A EP 05105831 A EP05105831 A EP 05105831A EP 1612294 A1 EP1612294 A1 EP 1612294A1
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EP
European Patent Office
Prior art keywords
bath
acid
carrier
bath according
vary
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05105831A
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German (de)
English (en)
French (fr)
Inventor
Walter Dalla Barba
Fabio Vincenzi
Federico Vincenzi
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ITALTECNO Srl
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ITALTECNO Srl
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Publication date
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Publication of EP1612294A1 publication Critical patent/EP1612294A1/en
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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
    • C23C22/367—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 alkaline earth metal cations
    • 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
    • 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
    • C23C22/48—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 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/56—Treatment of aluminium or alloys based thereon

Definitions

  • the present invention relates to a bath for the conversion coating of articles made of aluminum and alloys thereof and to the associated method.
  • inorganic coatings obtained by conversion of the metallic material are known; i.e., said coatings are the result of the conversion (transformation caused by chemical reactions) of a surface layer, having a thickness on the order of 0.5-2 ⁇ m, of the unstable metallic material into a stable and corrosion-resistant layer.
  • Inorganic conversion coatings can be formed by means of chemical or electrochemical processes affecting the metallic material in suitable baths, the composition of which determines the nature of the resulting coating.
  • known inorganic conversion coatings include chromate-based ones, phosphochromate-based ones, and chromium-free ones.
  • the coating process substantially follows three stages: cleaning of the surface to be coated; conversion of the clean surface into a protective inorganic coating, respectively by chromating, phosphochromating, and in the absence of chromium; drying of the resulting coating.
  • cleaning the surface to be treated comprises generally a step for alkaline degreasing and a step for acid descaling (also termed “neutralization” or “activation” of the surface), each of which is followed by at least one wash.
  • Conversion occurs by applying a conversion bath to the clean surface; the application times and temperature and the qualitative and quantitative composition of the bath vary depending on the type of coating to be provided: chromate-based, phosphochromate-based, or chromium-free.
  • the bath can be applied by immersion or spraying.
  • washes in general, by a first wash with mains water and by a second wash with demineralized/deionized water.
  • the conversion coating obtained by chromating and phosphochromating has an amorphous structure and contains water of imbibition, which must be eliminated by subjecting the coated surface to slow drying at ambient temperature or at low temperatures (on the order of 70-80 °C), so as to avoid the formation of cracks.
  • the bath for chromium conversion is an aqueous solution of chromates (hexavalent chromium), acids, fluorides and optionally accelerating agents, with a pH that can vary between 1.5 and 2.5.
  • Reactions occur between the clean aluminum surface and the conversion bath which form a coating constituted by a layer that contains chromium chromates (Cr(OH) 2 HCrO 4 ) and optionally basic aluminum oxide (AlOOH) in addition to other compounds, which depend on the composition of the bath, such as for example, in the case of accelerated baths, chromium ferrocyanide (CrFe(CN) 6 ).
  • the coating obtained by chromating can be identified visually by its typical coloring, which varies from iridescent yellow to brownish yellow and is caused by the hexavalent state of the chromium present in the form of chromates.
  • the bath for phosphorus-chromium conversion is an aqueous solution of acid phosphates, acid and alkaline chromates, complexed and free fluorides, and optional accelerating agents.
  • Reactions occur between the clean aluminum surface and the conversion bath which lead to the formation of a coating constituted by a layer containing chromium phosphate (CrPO 4 ) and aluminum phosphate (AlPO 4 ).
  • the coating obtained by phosphochromating can be identified visually by the typical green coloring, caused by the trivalent state of the chromium, which is present in the form of phosphate.
  • the chromium-free conversion bath is an aqueous solution of fluorides together with titanium or zirconium; reactions occur between the clean aluminum surface and the conversion bath which lead to the formation of a coating constituted by a layer containing aluminum oxide (Al 2 O 3 ) and aluminum fluorotitanium (AlOF ⁇ TiO 2 , AlOF TiOF 2 ).
  • wastewater of chromating and phosphochromating conversion processes contain hexavalent chromium, in addition to fluorides and ferrocyanides (if used as accelerating agents), which are highly pollutant; this wastewater, before being released, must be subjected to long and complex treatments, the cost of which affects substantially the overall process cost.
  • Chromium-free and titanium- or zirconium-based inorganic conversion coatings instead have the drawback of being substantially colorless, and this, differently from chromating treatments (which are brownish-yellow) and phosphochromating treatments (which are green), on the one hand prevents the operators assigned to the corresponding process from checking visually the actual execution of the process or of the quality of the coating obtained thereby (continuity, uniformity, etc) and on the other hand forces the execution of periodic chemical tests, which are in themselves less effective.
  • conversion systems can be installed in-line, for example, with systems for the subsequent painting of aluminum parts; in this case, parts that are not coated or are coated incompletely and unevenly may reach the painting step.
  • chromium-free processes for inorganic conversion coating consists of the fact that they have a reduced yield with respect to chromating and phosphochromating processes and depend to a greater extent on the initial steps for cleaning the surfaces to be treated, which accordingly must be performed with greater care and monitoring.
  • a conversion coating process is also known from Italian Industrial Patent Application No. M02003A185, in the name of this same Applicant, which uses a chromium-free bath substantially constituted by a manganese carrier, preferably potassium permanganate (KMnO 4 ), in an aqueous solution at an alkaline pH.
  • a chromium-free bath substantially constituted by a manganese carrier, preferably potassium permanganate (KMnO 4 ), in an aqueous solution at an alkaline pH.
  • the basicity of the bath that is used does not allow to introduce in the solution salts of zirconium and/or titanium, which as is known assist the conversion process and increase the corrosion resistance of the resulting coating.
  • the aim of the present invention is to eliminate the drawbacks noted above, by providing a bath for the conversion coating of articles made of aluminum and alloys thereof, which allows to obtain uniform protective coatings having high resistance to corrosion and can be used in currently existing plants without requiring particular structural adaptations thereof and does not entail the execution of additional preliminary treatments.
  • an object of the present invention is to provide a bath that is not toxic or noxious to the health of the operators assigned to the corresponding process, does not pollute the environment, and allows operators to perform a straightforward and complete visual check of the effectiveness of the treatment performed on all the processed articles.
  • Another object of the present invention is to provide a method for conversion coating of articles made of aluminum and alloys thereof that can be performed simply and effectively by using known plants and technologies, has a high yield and has wastewater that can be treated easily at low costs.
  • Another object of the present invention is to provide a structure that is simple, relatively easy to provide in practice, safe in use, effective in operation, and has a relatively low cost.
  • a bath for the conversion coating of articles made of aluminum and alloys thereof which comprises at least one manganese (Mn) carrier, characterized in that said manganese (Mn) carrier is in a aqueous solution with a pH that is not basic and therefore is neutral or acid.
  • the bath according to the invention comprises a manganese carrier in an aqueous solution with acid pH.
  • the manganese carrier is preferably constituted by potassium permanganate (KMnO 4 ) and is present in quantities which can vary between 1 and 10 g/l (liter of bath), preferably 5 g/l.
  • the acidity of the bath corresponds to pH values comprised between 2 and 4, preferably substantially equal to 2.6.
  • the manganese carrier has a protective effect, since it reacts with the surface of the article to be treated, "converting" it into a protective coating, and a coloring effect on said coating.
  • the bath can contain at least one titanium (Ti) carrier and/or at least one zirconium (Zr) carrier, which increase the corrosion resistance of the resulting coating.
  • Ti titanium
  • Zr zirconium
  • the titanium carrier is preferably constituted by fluorotitanic acid (H 2 TiF 6 ) and is comprised in quantities variable between 0.2 and 2 g/l (liter of bath).
  • the zirconium carrier is preferably constituted by fluorozirconic acid (H 2 ZrF 6 ) and is present in quantities that can vary between 0.1 and 1 g/l (liter of bath).
  • fluorotitanic acid and/or the fluorozirconic acid are absent or are present in small quantities, close to the minimum values of the ranges described above, it is possible to introduce conveniently in the bath at least one fluoride carrier acid.
  • the fluoride carrier acid is preferably constituted by hydrofluoric acid (HF) and is present in quantities comprised between 0.1 and 0.6 g/l.
  • HF hydrofluoric acid
  • the water used for the bath is preferably demineralized water or softened mains water.
  • the method 1 comprises a step 2 for cleaning the surface of the article made of aluminum or alloy thereof to be treated, a step 3 for converting a layer of the surface thus cleaned into a protective coating, and a step 4 for drying the resulting protective coating.
  • the present description does not describe in detail the cleaning step 2 and the drying step 4 and the corresponding plants, since they are similar to the ones used in known technologies for conversion coating of aluminum (chromating, phosphochromating, chromium-free).
  • the cleaning step 2 consists substantially of an alkaline degreasing 5, followed by a wash 6, and by an acid descaling 7 (neutralization or activation), followed by one or more washes 8; it is designed to remove from the surface to be treated all the pollutant particles, including the oxides that naturally coat aluminum.
  • the conversion step 3 comprises the application 9, to the surface cleaned in the preceding step, of a bath which contains a manganese (Mn) carrier in an aqueous solution having a non-basic and preferably acid pH, as described above.
  • a bath which contains a manganese (Mn) carrier in an aqueous solution having a non-basic and preferably acid pH, as described above.
  • the application 9 which can be performed with the known immersion or spray techniques, not shown, occurs at a temperature that can vary between 15 and 40 °C, preferably 20 °C, for a time that can vary between 30 seconds and 5 minutes, preferably 2 minutes.
  • a conversion coating i.e., produced by the transformation of a surface layer of aluminum
  • a conversion coating i.e., produced by the transformation of a surface layer of aluminum
  • the coating has a thickness which can vary between 0.5 and 2 ⁇ m, has an amorphous structure and a gold yellow/brown coloring.
  • the surfaces coated with the conversion coating are subjected to at least one wash 10 with mains water or preferably demineralized water, optionally containing traces of hydrogen peroxide, and preferably to at least one wash 11 with demineralized water, similar to the washes used in known chromating, phosphochromating and chromium-free coating technologies.
  • a bath for the inorganic conversion coating of aluminum and alloys thereof is prepared which is constituted by an acid aqueous solution (pH 2.6) which contains:
  • the bath is applied to a clean surface of an article made of aluminum or alloy thereof at a temperature of 20 °C and for 2 minutes.
  • a bath for the inorganic conversion coating of aluminum and alloys thereof is prepared which is constituted by an acid aqueous solution (pH 2.6) which contains:
  • the bath is applied to a clean surface of an article made of aluminum or alloy thereof at a temperature of 20 °C and for 2 minutes.
  • a bath for the inorganic conversion coating of aluminum and alloys thereof is prepared which is constituted by an acid aqueous solution (pH 2.6) which contains:
  • the bath is applied to a clean surface of an article made of aluminum or alloy thereof at a temperature of 20 °C and for 2 minutes.
  • a bath for the inorganic conversion coating of aluminum and alloys thereof is prepared which is constituted by an acid aqueous solution (pH 2.6) which contains:
  • the bath is applied to a clean surface of an article made of aluminum or alloy thereof at a temperature of 20 °C and for 2 minutes.
  • the bath according to the invention in fact allows to obtain a compact and uniform conversion coating on the surface of the treated articles, which by being colored (gold yellow/brown) allows operators to perform an immediate visual check of the actual execution of the coating process and/or of the quality of the resulting coating (continuity, uniformity, defects, etc).
  • the bath is not toxic, does not harm the health of the operators and does not pollute the environment.
  • the conversion coating obtained with the bath according to the invention protects aluminum or alloys thereof against corrosion and can act as a foundation for the subsequent application of paints or varnishes.
  • the method according to the invention can be performed with technologies and plants that are already known in the field, has a good yield and produces wastewater that has a reduced environmental impact with respect to wastewater produced with traditional chromium-based baths and can be treated simply and at lower cost.

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
EP05105831A 2004-07-02 2005-06-29 Bath and associated method for the conversion coating of articles made of aluminium and alloys thereof Withdrawn EP1612294A1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
ITMO20040169 ITMO20040169A1 (it) 2004-07-02 2004-07-02 'bagno per il rivestimento di conversione di manufatti in allluminio e sue leghe e relativo procedimenti'.

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EP1612294A1 true EP1612294A1 (en) 2006-01-04

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1978130A1 (en) * 2007-03-29 2008-10-08 Tokai Rubber Industries, Ltd. Rubber member including aluminum-based metal component, and production method for the same
EP2100986A1 (en) * 2008-03-04 2009-09-16 Mazda Motor Corporation Chemical conversion treatment agent and surface-treated metal material
CN112126920A (zh) * 2020-09-25 2020-12-25 合肥朗逸表面处理有限公司 一种适用于辊筒涂覆工艺的无铬转换剂及其制备方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH136060A (de) * 1928-02-21 1929-10-31 Sprenger Patentverwertung Otto Verfahren zur Herstellung von Überzügen auf Metallen.
DE4031710A1 (de) * 1990-10-06 1992-04-09 Henkel Kgaa Korrosionsschutzmittel fuer aluminiumoberflaechen und verfahren zur herstellung von korrosionsschutzschichten auf aluminium
WO1999060186A1 (en) * 1998-05-20 1999-11-25 Henkel Corporation Composition and process for treating surfaces of light metals and their alloys
EP1447460A1 (en) * 2003-02-17 2004-08-18 Nippon Paint Co., Ltd. Rust prevention coating agent and method of rust-proofing
EP1571237A1 (en) * 2002-12-13 2005-09-07 Nihon Parkerizing Co., Ltd. Treating fluid for surface treatment of metal and method for surface treatment

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH136060A (de) * 1928-02-21 1929-10-31 Sprenger Patentverwertung Otto Verfahren zur Herstellung von Überzügen auf Metallen.
DE4031710A1 (de) * 1990-10-06 1992-04-09 Henkel Kgaa Korrosionsschutzmittel fuer aluminiumoberflaechen und verfahren zur herstellung von korrosionsschutzschichten auf aluminium
WO1999060186A1 (en) * 1998-05-20 1999-11-25 Henkel Corporation Composition and process for treating surfaces of light metals and their alloys
EP1571237A1 (en) * 2002-12-13 2005-09-07 Nihon Parkerizing Co., Ltd. Treating fluid for surface treatment of metal and method for surface treatment
EP1447460A1 (en) * 2003-02-17 2004-08-18 Nippon Paint Co., Ltd. Rust prevention coating agent and method of rust-proofing

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1978130A1 (en) * 2007-03-29 2008-10-08 Tokai Rubber Industries, Ltd. Rubber member including aluminum-based metal component, and production method for the same
EP2100986A1 (en) * 2008-03-04 2009-09-16 Mazda Motor Corporation Chemical conversion treatment agent and surface-treated metal material
CN112126920A (zh) * 2020-09-25 2020-12-25 合肥朗逸表面处理有限公司 一种适用于辊筒涂覆工艺的无铬转换剂及其制备方法

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Publication number Publication date
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