EP0488430B1 - Revêtement de conversion au cobalt, sans chromate - Google Patents

Revêtement de conversion au cobalt, sans chromate Download PDF

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Publication number
EP0488430B1
EP0488430B1 EP91202181A EP91202181A EP0488430B1 EP 0488430 B1 EP0488430 B1 EP 0488430B1 EP 91202181 A EP91202181 A EP 91202181A EP 91202181 A EP91202181 A EP 91202181A EP 0488430 B1 EP0488430 B1 EP 0488430B1
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European Patent Office
Prior art keywords
cobalt
solution
salt
substrate
conversion coating
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EP91202181A
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German (de)
English (en)
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EP0488430A2 (fr
EP0488430A3 (en
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Matthias P. Schriever
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Boeing Co
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Boeing Co
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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
    • C23C22/68—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 solutions with pH between 6 and 8
    • 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
    • C23C22/82—After-treatment
    • C23C22/83—Chemical after-treatment

Definitions

  • This environmental-quality invention is in the field of chemical conversion coatings formed on metal substrates, for example, on aluminum substrates. More particularly, one aspect of the invention is a new type of oxide coating (which I refer to as a "cobalt conversion coating") which is chemically formed on metal substrates.
  • the invention enhances the quality of the environment of mankind by contributing to the maintenance of air and water quality.
  • chemical conversion coatings are formed chemically by causing the surface of the metal to be "converted" into a tightly adherent coating, all or part of which consists of an oxidized form of the substrate metal.
  • Chemical conversion coatings can provide high corrosion resistance as well as strong bonding affinity for paint.
  • the industrial application of paint (organic finishes) to metals generally requires the use of a chemical conversion coating, particularly when the performance demands are high.
  • aluminum protects itself against corrosion by forming a natural oxide coating, the protection is not complete.
  • aluminum alloys particularly the high-copper 2000-series aluminum alloys, such as alloy 2024-T3, corrode much more rapidly than pure aluminum.
  • the first is by anodic oxidation (anodization) in which the aluminum component is immersed in a chemical bath, such as a chromic or sulfuric acid bath, and an electric current is passed through the aluminum component and the chemical bath.
  • a chemical bath such as a chromic or sulfuric acid bath
  • an electric current is passed through the aluminum component and the chemical bath.
  • the resulting conversion coating on the surface of the aluminum component offers resistance to corrosion and a bonding surface for organic finishes.
  • the second type of process is by chemically producing a conversion coating, which is commonly referred to as a chemical conversion coating, by subjecting the aluminum component to a chemical solution, such as a chromic acid solution, but without using an electric current in the process.
  • a chemical solution such as a chromic acid solution
  • the chemical solution may be applied by immersion application, by manual application, or by spray application.
  • the resulting conversion coating on the surface of the aluminum component offers resistance to corrosion and a bonding surface for organic finishes.
  • the present invention relates to this second type of process for producing chemical conversion coatings.
  • the chemical solution may be applied by immersion application, by various types of manual application, or by spray application.
  • chromic acid process for forming chemical conversion coatings on aluminum substrates is described in various embodiments in Ostrander et al. U.S. Patent 2,796,370 and Ostrander et al. U.S. Patent 2,796,371, in military process specification MIL-C-5541, and in Boeing Process Specification BAC 5719.
  • These chromic acid chemical conversion baths contain hexavalent chromium, fluorides, and cyanides, all of which present significant environmental as well as health and safety problems.
  • the constituents of a typical chromic acid conversion bath are as follows: CrO 3 - "chromic acid” (hexavalent chromium); NaF - sodium fluoride; KBF 4 - potassium tetrafluoroborate; K 2 ZrF 6 - potassium hexafluorozirconate; K 3 Fe(CN) 6 - potassium ferricyanide; and, HNO 3 - nitric acid (for pH control).
  • Chromic acid conversion films as formed on aluminum substrates, meet a 168 hours corrosion resistance criterion, but they primarily serve as a surface substrate for paint adhesion. Because of their relative thinness and low coating weights (430-1615 mg/m 2 (40-150 milligrams/ft 2 )), chromic acid conversion coatings do not cause a fatigue life reduction in the aluminum structure.
  • the process according to the invention for forming an oxide film cobalt conversion coating exhibiting corrosion resistance and paint adhesion properties on a metal substrate comprises the steps of:
  • the substrate may be aluminum or aluminum alloy, as well as magnesium and its alloys, Cd plated substrates and Zn plated substrates.
  • the cobalt-III hexanitrite complex may be present in the form of Me 3 [Co(NO 2 ) 6 ], wherein Me corresponds to Na, K or Li.
  • Another aspect of the invention is a chemical conversion coating solution for producing an oxide film cobalt conversion coating on a metal substrate, said solution comprising an aqueous solution of a soluble cobalt-III hexacoordinated complex in the form of a soluble cobalt-III hexanitrite complex, the concentration of said cobalt-III hexacoordinated complex being from 0.03 moles per liter (0.1 mole per gallon) of solution to the saturation limit of said cobalt-III hexacoordinated complex, said reaction solution is obtainable by reacting a cobalt-II salt with a metal nitrite salt, wherein the concentration of said cobalt-II salt is from 0.03 moles per liter (0.1 moles per gallon) of final solution to the saturation limit of the cobalt-II salt employed and the concentration of said metal nitrite salt is from 0.16 moles per liter (0.6 moles per gallon) of final solution, and an oxidizer to oxidize the cobalt-
  • the substrate may be aluminum or aluminum alloy, as well as magnesium and its alloys, Cd plated substrates, and Zn plated substrates.
  • the cobalt-III hexacoordinated complex may be present in the form of Me 3 [Co(NO 2 ) 6 ] wherein Me corresponds to Na, K, or Li.
  • the cobalt conversion solution may be prepared by a bath makeup sequence including the steps of: (a) dissolving a metal nitrite salt; (b) dissolving an accelerator such as NaI; (c) dissolving a cobalt-II salt; and (d) then adding an oxidizer such as H 2 O 2 .
  • the invention relates also to the obtained coated article exhibiting corrosion resistance and paint adhesion properties, the article including: (a) an aluminium or aluminium alloy substrate; and (b) a cobalt conversion coating formed on the substrate, the cobalt conversion coating including aluminum oxide Al 2 O 3 as the largest volume percent, and one or more cobalt oxides from the group consisting of CoO, Co 3 O 4 , and Co 2 O 3 , wherein the cobalt conversion coating has a thickness of 0.12 to 0.14 ⁇ m.
  • FIGS. 1-20 are photomicrographs (scanning electron microscope operated at 20 KV) of aluminum alloy 2024-T3 test panels with cobalt conversion coatings made by the invention.
  • FIGS. 1-16 show surface views and fracture views of unsealed cobalt conversion coatings.
  • the photomicrographs of FIGS. 1-16 reveal a highly porous surface oxide (unsealed cobalt conversion coatings) with a thickness range of about 0.12 to 0.14 micron (1200 to 1400 Angstroms).
  • FIGS. 1-4 show an unsealed cobalt conversion coating formed by a 20 minute immersion in a typical cobalt coating solution.
  • FIGS. 5-8 show an unsealed cobalt conversion coating formed by a 30 minute immersion in a typical cobalt coating solution.
  • FIGS. 9-12 show an unsealed cobalt conversion coating formed by a 50 minute immersion in a typical cobalt coating solution.
  • FIGS. 13-16 show an unsealed cobalt conversion coating formed by a 60 minute immersion in a typical cobalt coating solution. There were only minor differences in oxide coating thickness between these immersion times. This suggests that at any given bath operating temperature, the oxide structure becomes self limiting.
  • FIGS. 17-20 show surface views and fracture views of a sealed cobalt conversion coating.
  • FIG. 1 is a photomicrograph at X10,000 magnification of a test panel showing a cobalt conversion coating 130 of the invention.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 130.
  • the top of oxide coating 130 is porous and looks like a layer of chow mein noodles.
  • the porosity of oxide coating 130 gives excellent paint adhesion results.
  • This test panel was immersed in a cobalt conversion coating solution for 20 minutes.
  • the white bar is a length of 1 micron.
  • FIG. 2 is a photomicrograph at X50,000 magnification of the test panel of FIG. 1.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 130.
  • FIG. 2 is a close-up, at higher magnification, of a small area of FIG. 1.
  • the white bar is a length of 1 micron.
  • FIG. 3 is a photomicrograph at X10,000 magnification of a test panel showing a side view of a fractured cross section of a cobalt conversion coating 130 of the invention.
  • the fractured cross section of the aluminum substrate of the test panel is indicated by reference numeral 132.
  • This test panel was immersed in a coating bath for 20 minutes. To make the photomicrograph, the test panel was bent and broken off to expose a cross section of oxide coating 130.
  • the white bar is a length of 1 micron.
  • FIG. 4 is a photomicrograph at X50,000 magnification of the test panel of FIG. 3 showing a side view of a fractured cross section of cobalt conversion coating 130 of the invention.
  • FIG. 4 is a close-up, at higher magnification, of a small area of FIG. 3.
  • the aluminum substrate of the test panel is indicated by reference numeral 132.
  • the white bar is a length of 1 micron.
  • Oxide coating 130 has a vertical thickness of about 0.12-0.14 micron.
  • FIG. 5 is a photomicrograph at X10,000 magnification of another test panel showing another cobalt conversion coating 150 of the invention.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 150.
  • the top of oxide coating 150 is porous and looks like a layer of chow mein noodles.
  • This test panel was immersed in a cobalt conversion coating solution for 30 minutes.
  • the white bar is a length of 1 micron.
  • FIG. 6 is a photomicrograph at X50,000 magnification of the test panel of FIG. 5.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 150.
  • FIG. 6 is a close-up, at higher magnification, of a small area of FIG. 5.
  • the white bar is a length of 1 micron.
  • FIG. 7 is a photomicrograph at X10,000 magnification of a test panel showing a side view of a fractured cross section of cobalt conversion coating 150 of the invention.
  • the aluminum substrate of the test panel is indicated by reference numeral 152.
  • This test panel was immersed in a coating bath for 30 minutes. To make the photomicrograph, the test panel was bent and broken off to expose a cross section of oxide coating 150.
  • the white bar is a length of 1 micron.
  • FIG. 8 is a photomicrograph at X50,000 magnification of the test panel of FIG. 7 showing a side view of a fractured cross section of cobalt conversion coating 150 of the invention.
  • FIG. 8 is a close-up, at higher magnification, of a small area of FIG. 7.
  • the aluminum substrate of the test panel is indicated by reference numeral 152.
  • the white bar is a length of 1 micron.
  • Oxide coating 150 has a vertical thickness of about 0.12-0.14 micron.
  • FIG. 9 is a photomicrograph at X10,000 magnification of a test panel showing a cobalt conversion coating 190 of the invention.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 190.
  • the top of oxide coating 190 is porous and looks like a layer of chow mein noodles.
  • This test panel was immersed in a cobalt conversion coating solution for 50 minutes.
  • the oblong object indicated by reference numeral 192 is an impurity, believed to be a piece of oxidized material, on top of oxide coating 190.
  • the white bar is a length of 1 micron.
  • FIG. 10 is a photomicrograph at X50,000 magnification of the test panel of FIG. 9.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 190.
  • FIG. 10 is a close-up, at higher magnification, of a small area of FIG. 9.
  • the roundish object indicated by reference numeral 192a is an unidentified impurity on top of oxide coating 190.
  • the white bar is a length of 1 micron.
  • FIG. 11 is a photomicrograph at X10,000 magnification of a test panel showing a side view of a fractured cross section of a cobalt conversion coating 190 of the invention.
  • the fractured cross section of the aluminum substrate of the test panel is indicated by reference numeral 194.
  • This test panel was immersed in a coating bath for 50 minutes. To make the photomicrograph, the test panel was bent and broken off to expose a cross section of oxide coating 190.
  • the white bar is a length of 1 micron.
  • FIG. 12 is a photomicrograph at X50,000 magnification of the test panel of FIG. 11 showing a side view of a fractured cross section of cobalt conversion coating 190 of the invention.
  • FIG. 12 is a close-up, at higher magnification, of a small area of FIG. 11.
  • the aluminum substrate of the test panel is indicated by reference numeral 194.
  • the white bar is a length of 1 micron.
  • Oxide coating 190 has a vertical thickness of about 0.12-0.14 micron.
  • FIG. 13 is a photomicrograph at X10,000 magnification of another test panel showing a cobalt conversion coating 230 of the invention.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 230.
  • the top of oxide coating 230 is porous and looks like a layer of chow mein noodles.
  • This test panel was immersed in a cobalt conversion coating solution for 60 minutes.
  • the white bar is a length of 1 micron.
  • FIG. 14 is a photomicrograph at X50,000 magnification of the test panel of FIG. 13.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of oxide coating 230.
  • FIG. 14 is a close-up, at higher magnification, of a small area of FIG. 13.
  • the white bar is a length of 1 micron.
  • FIG. 15 is a photomicrograph at X10,000 magnification of a test panel showing a side view of a fractured cross section of cobalt conversion coating 230 of the invention.
  • the aluminum substrate of the test panel is indicated by reference numeral 232.
  • This test panel was immersed in the coating bath for 60 minutes. To make the photomicrograph, the test panel was bent and broken off to expose a cross section of oxide coating 230.
  • the white bar is a length of 1 micron.
  • FIG. 16 is a photomicrograph at X50,000 magnification of the test panel of FIG. 15 showing a side view of a fractured cross section of cobalt conversion coating 230 of the invention.
  • FIG. 16 is a close-up, at higher magnification, of a small area of FIG. 15.
  • the white bar is a length of 1 micron.
  • Oxide coating 150 has a vertical thickness of about 0.12-0.14 micron.
  • FIG. 17 is a photomicrograph at X10,000 magnification of another test panel showing a sealed cobalt conversion coating 270 of the invention.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of sealed oxide coating 270.
  • This test panel was immersed in a sealing solution for 20 minutes.
  • Sealed oxide coating 270 is not as porous as an unsealed oxide coating, the pores of the oxide coating being partially filled by hydration as a result of immersion in a sealing solution.
  • the partial sealing of the oxide coating gives reduced paint adhesion results, but excellent corrosion resistance performance.
  • the whitish areas identified by reference numeral 274 are believed to be impurities from the sealing solution.
  • the white bar is a length of 1 micron.
  • FIG. 18 is a photomicrograph at X50,000 magnification of the test panel of FIG. 17.
  • the photomicrograph is a top view, from an elevated angle, of the upper surface of sealed oxide coating 270.
  • FIG. 18 is a close-up, at higher magnification, of a small area of FIG. 17.
  • Sealed oxide coating 270 is not as porous as an unsealed oxide coating, the pores of the oxide coating being partially filled by hydration as a result of immersion in a sealing solution.
  • the white bar is a length of 1 micron.
  • FIG. 19 is a photomicrograph at X10,000 magnification of a test panel showing a side view of a fractured cross section of sealed cobalt conversion coating 270 of the invention.
  • the aluminum substrate of the test panel is indicated by reference numeral 272. This test panel was immersed in the sealing bath for 20 minutes. To make the photomicrograph, the test panel was bent and broken off to expose a cross section of oxide coating 270.
  • the white bar is a length of 1 micron.
  • FIG. 20 is a photomicrograph at X50,000 magnification of the test panel of FIG. 19 showing a side view of a fractured cross section of sealed cobalt conversion coating 270 of the invention.
  • FIG. 20 is a close-up, at higher magnification, of a small area of FIG. 19.
  • the white bar is a length of 1 micron.
  • Sealed oxide coating 270 has a vertical thickness of about 0.12-0.14 micron.
  • the first class is a cobalt conversion coating consisting of an oxide structure in unsealed condition and suitable for use in service where paint adhesion is especially important.
  • the second class is a cobalt conversion coating consisting of an oxide structure in sealed condition and suitable for use in service where bare metal corrosion resistance performance is desired.
  • cobalt coordination complexes are formed where the portion of the complex which includes the ligand (the bracketed portion in equations (1)-(5)) is negatively charged, i.e., (8) [Co(NO 2 ) 6 ] 3- and the complete complex is (9) Me 3 [Co(NO 2 ) 6 ] where Me corresponds to Na, K, or Li (alkali metal ions).
  • This cobalt nitrite complex bath chemistry (equation (1)) has a distinct advantage over the previously described cobalt hexammine complex chemistry (equation (6)) in that pH control of the cobalt hexanitrite complex bath is not required.
  • cobalt-III hexanitrite complexes are capable of forming oxide structures on aluminum substrates.
  • the oxidizing ability of the cobalt-III hexanitrite complex is believed to be responsible for the formation of the observed oxide films (which I refer to as "cobalt conversion coatings") on aluminum substrates.
  • the formation of oxide structures has been confirmed by instrumental analysis (Auger analysis and electron microscopy) of the coating.
  • the photomicrographs in FIGS. 1-20 illustrate the appearance of the cobalt conversion coating of the invention.
  • cobalt salts and metal nitrite salts are operable for cobalt complexing.
  • cobalt-II salts which are operable in water solution are: cobalt nitrate, Co(NO 3 ) 2 ⁇ 6H 2 O; cobalt chloride, CoCl 2 ⁇ 6H 2 O; cobaltous sulfate, CoSO 4 ; cobaltous acetate, Co(CH 3 COO) 2 ⁇ 4H 2 O; and cobaltous basic carbonate, 2CoCO 3 ⁇ Co(OH) 2 ⁇ H 2 O.
  • a nitrite salt such as NaNO 2 , KNO 2 , or LiNO 2 .
  • cobalt-II salts may be used if they possess a minimum solubility in water or in a water solution containing a metal nitrite salt.
  • the minimum solubility needed is 25 grams per 100 ml of water at 20°C (68°F) or 25 grams per 100 ml of water solution containing a metal nitrite salt at 20°C (68°F).
  • the preferred reactants are Co(NO 3 ) 2 ⁇ 6H 2 O and NaNO 2 , since cobalt nitrite complexes formed with potassium or lithium nitrite are of limited solubility and will eventually drop out of an aqueous solution.
  • a preferred chemical additive is an oxidizer, preferably hydrogen peroxide, H 2 O 2 .
  • the function of the oxidizer is to oxidize the cobalt-II ions in solution to cobalt-III ions. Care must be taken that an excess amount of chemical oxidizer is not used because an excess would have the undesired effect of oxidizing the nitrite ions in solution to nitrate ions.
  • the stream of air flowing into the tank functions as an oxidizer, so the presence of hydrogen peroxide is not essential for operability.
  • the hydrogen peroxide increases the rate of oxidation of the cobalt-II ions in solution to cobalt-III ions and therefore is useful for commercial practice of the invention in that the solution becomes operational in a shorter period of time.
  • reaction accelerator chemical such as sodium bromide (NaBr) or sodium iodide (NaI) may be added to the solution.
  • NaBr sodium bromide
  • NaI sodium iodide
  • the reaction accelerator was found to have the effect of accelerating the formation of the oxide conversion coatings on aluminum alloy substrates as compared to solutions of cobalt-III hexanitrite complexes which did not contain this additive. The presence of the accelerator is not essential for operability. The accelerator increases the rate of formation of the oxide conversion coatings on aluminum alloys and therefore is useful for commercial practice of the invention.
  • the preferred chemical reactants and additives are: Cobalt nitrate Co(N0 3 ) 2 ⁇ 6H 2 O Sodium nitrite NaNO 2 Hydrogen peroxide (oxidizer) H 2 O 2 Sodium iodide (accelerator) NaI
  • the concentration of dissolved cobalt-II salt used may be from about 0.03 moles per liter (0.1 moles per gallon) of final solution up to the saturation limit of the cobalt-II salt employed.
  • the concentration of dissolved metal nitrite salt may be from about 0.16 to 3.2 moles per liter (0.6 to 12 moles per gallon) of final solution.
  • the concentration of oxidizer, such as hydrogen peroxide may be from complete omission up to about 0.1 moles per liter (0.5 moles per gallon) of final solution. As stated above, an excess amount of hydrogen peroxide has undesired effects.
  • the concentration of accelerator salt, such as NaI, may be from complete omission up to the solubility limit of the accelerator in the solution.
  • the pH of the bath may be from about 7.0 to 7.2.
  • the temperature of the bath may be from about 20 °C (68°F) to 66°C (150°F); below 38°C (100°F coating formation is very slow; above 66°C (150°F) gradual decomposition of the cobalt-III hexanitrite complex occurs.
  • the immersion time may be from about 3 minutes to 60 minutes.
  • the cobalt conversion coating should be applied after all trimming and fabrication have been completed. Parts, where solution entrapment is possible, should not be subjected to immersion alkaline cleaning or immersion deoxidizing; manual cleaning and manual deoxidizing procedures should be used to obtain water break-free surfaces before applying cobalt conversion treatment.
  • a water break-free surface is a surface which maintains a continuous water film for a period of at least 30 seconds after having been sprayed or immersion rinsed in clean water at a temperature below 38°C (100°F).
  • Vapor degrease may be performed in accordance with Boeing Process Specification BAC 5408, emulsion clean in accordance with Boeing Process Specification BAC 5763, or solvent clean in accordance with Boeing Process Specification BAC 5750 if parts are greasy or oily. Parts with open faying surfaces or spot-welded joints where solution entrapment is possible should be immersed in cold water (or in hot and cold water) for 2 minutes after precleaning.
  • Alkaline clean and rinse may be performed in accordance with Boeing Process Specification BAC 5744 or Boeing Process Specification BAC 5749 except for parts with open faying surfaces or spot welded joints, in which case, rinsing should be for at least 10 minutes using agitation with multiple immersions (a minimum of four times) followed by manual spray rinsing as required to prevent solution entrapment.
  • Deoxidize and rinse may be performed in accordance with Boeing Process Specification BAC 5765 except for parts where solution entrapment is possible, which parts may be rinsed using the method described above under "Alkaline Cleaning". Castings may be deoxidized by either of the following methods:
  • Example 1 The formulation of Example 1, with a molar ratio of nitrite salt to cobalt salt of about 12 to 1, is useful for producing oxide coatings exhibiting high paint adhesion in unsealed condition.
  • Example 2 also having a molar ratio of nitrite salt to cobalt salt of about 12 to 1, is useful for producing oxide coatings possessing high paint adhesion properties in unsealed condition.
  • any 2-valent soluble cobalt salt may be reacted with any soluble nitrite salt to form 3-valent cobalt hexanitrite complexes.
  • this type of complexing is not restricted to nitrites only.
  • cyanide salts were used (i.e., sodium cyanide, NaCN) to form hexacyano complexes of the type shown below (10) Me 3 [Co(CN) 6 ] and have yielded satisfactory conversion coatings on aluminum alloys.
  • cyanide complexes will not be used because of environmental considerations.
  • Nickel sulfate NiS0 4 ⁇ 6H 2 0 (hexahydrate) 40.2 (152) gm (about 0.15 (0.58) moles) 38.0-42.0 (144-159) gm Ammonium nitrate, NH 4 NO 3 30.1 (114) gm (about 0.375 (1.42) moles) 27.7-32.0 (105-121) gm Manganese acetate, Mn(CH 3 COO) 2 ⁇ 4H 2 O 20 (76) gm (about 0.082 (0.31) moles) 18-22 (68-84) gm Operating temperature 85 ⁇ 3°C (185 ⁇ 5° F)
  • the immersion time in the sealing solution may be about 10-30 minutes, with 15 minutes being preferred.
  • the sealing solution is believed to seal the cobalt conversion coating by a hydration mechanism.
  • FIGS. 17-20, particularly FIG. 18, show a sealed cobalt conversion coating 270.
  • Other sealing solutions which may be employed are as follows:
  • Solutions 1-3 are not preferred because they lose their effectiveness over a period of time, whereas the solution in Example 4 has a long life.
  • a continuous operating temperature range of the cobalt conversion tank of 49-60°C (120-140°F) yields optimum results with respect to coating performance on aluminum alloy substrates.
  • Optimum paint adhesion is obtained when the tank is operated at or near 49°C (120°F), while optimum corrosion resistance performance is given at 60°C (140°F) in combination with the subsequent seal process.
  • Immersion times in the cobalt conversion tank have an effect on the oxide coating thickness as measured by the coating weight (in unsealed condition) ranging from 430 to 646 mg/m 2 (40 to 60 mg/ft 2 ).
  • An optimum immersion time for maximum paint adhesion is 15 minutes and for maximum corrosion resistance performance is 30 minutes.
  • Salt spray corrosion resistance of cobalt conversion coatings produced by the above processes varies over a wide range, depending on reactant selection, immersion times, and bath operating temperatures. Preferred results are obtained when the formulation of Example 1 is utilized at immersion times of 30 minutes. In this way, sealed oxide coatings have been produced with 168 hrs. of salt spray corrosion resistance when sealed with the seal solution as described herein and tested in accordance with ASTM B117.
  • Paint adhesion tests were conducted using aircraft paints qualified to Boeing Material Specification BMS 10-11 (a highly crosslinked epoxy primer) and BMS 10-60 (a highly crosslinked urethane topcoat).
  • BMS 10-11 a highly crosslinked epoxy primer
  • BMS 10-60 a highly crosslinked urethane topcoat
  • corrosion resistance and paint adhesion performance properties have an inverse relationship. In general, where corrosion resistance is at a maximum, paint adhesion is at a minimum, and vice versa.
  • the optional post-conversion step consisting of immersion into a heated solution (at 85 ⁇ 3°C (185 ⁇ 5°F)) of NiS0 4 /NH 4 NO 3 /Mn-acetate minimizes this problem by maintaining sufficient paint adhesion values while maintaining high corrosion resistance properties.
  • ESCA electron spectroscopy for chemical analysis (also known as XPS or X-ray photoelectron spectroscopy).)
  • the cobalt conversion coating consists of a mixture of oxides, namely, aluminum oxide, Al 2 O 3 , as the largest volume percent, and cobalt oxides, CoO, Co 3 O 4 , and Co 2 O 3 .
  • the term "largest volume percent” means that the volume of this oxide exceeds the volume of any other oxide which is present, but the term “largest volume percent” does not necessarily imply that the volume of this oxide is more than 50 volume percent.
  • the data further shows that in the lower portion of the oxide coating (that is, next to the aluminum substrate), the largest volume percent is Al 2 O 3 .
  • the middle portion of the oxide coating is a mixture of CoO, Co 3 O 4 , Co 2 O 3 , and Al 2 O 3 .
  • the data shows that in the top portion of the oxide coating, the largest volume percent is a mixture of Co 3 O 4 and Co 2 O 3 .
  • FIGS. 1-4 show a cobalt conversion coating 130 (in the unsealed condition) formed by a 20 minute immersion in a typical cobalt conversion coating solution.
  • FIGS. 5-8 show a cobalt conversion coating 150 (in the unsealed condition) formed by a 30 minute immersion in a typical cobalt conversion coating solution.
  • FIGS. 9-12 show a cobalt conversion coating 190 (in the unsealed condition) formed by a 50 minute immersion in a typical cobalt conversion coating solution.
  • FIGS. 1-4 show a cobalt conversion coating 130 (in the unsealed condition) formed by a 20 minute immersion in a typical cobalt conversion coating solution.
  • FIGS. 5-8 show a cobalt conversion coating 150 (in the unsealed condition) formed by a 30 minute immersion in a typical cobalt conversion coating solution.
  • FIGS. 9-12 show a cobalt conversion coating 190 (in the unsealed condition) formed by a 50 minute immersion in a typical cobalt
  • FIGS. 13-16 show a cobalt conversion coating 230 (in the unsealed condition) formed by a 60 minute immersion in a typical cobalt conversion coating solution. Comparing FIGS. 1-4, FIGS. 5-8, FIGS. 9-12, and FIGS. 13-16, there does not appear to be any significant structural difference between coating 130, coating 150, coating 190, and coating 230. This suggests that at any given bath operating temperature, the oxide coating becomes self limiting.
  • the top surface of the cobalt conversion coating as shown in FIGS. 1, 2, 5, 6, 9, 10, 13, and 14 is porous and bears a resemblance to chow mein noodles. This oxide structure provides appreciable surface area and porosity for good paint adhesion.
  • FIGS. 17-20 show sealed cobalt conversion coating 270.
  • the cobalt conversion coating was formed on the substrate and then the coating was partially sealed by immersion in a sealing solution.
  • FIG. 18 shows the partially sealed structure of coating 270.
  • Sealed oxide coating 270 is not as porous as an unsealed oxide coating, the pores of the oxide coating being partially filled by hydration as a result of immersion in a sealing solution. The partial sealing of the oxide coating gives reduced paint adhesion results, but excellent corrosion resistance performance.

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Chemically Coating (AREA)

Claims (39)

  1. Procédé pour former un revêtement de conversion au cobalt de film d'oxyde présentant des propriétés de résistance à la corrosion et d'adhérence de la peinture sur un substrat de métal, ledit procédé comprenant les étapes consistant :
    (a) à fournir une solution de conversion au cobalt formant un film d'oxyde comprenant une solution de réaction aqueuse comprenant un complexe hexacoordiné de cobalt-III soluble dans la forme d'un complexe d'hexanitrite de cobalt-III soluble, la concentration dudit complexe hexacoordiné de cobalt-III étant de 0,03 mol/l (0,1mol/gal) de solution jusqu'à la limite de saturation dudit complexe hexacoordiné de cobalt-III; et
    (b) à mettre en contact ledit substrat de métal avec ladite solution pendant une durée suffisante pour oxyder la surface dudit substrat, ledit revêtement de conversion au cobalt de film d'oxyde est par là formé, communiquant par là une résistance à la corrosion et une adhérence de la peinture audit substrat.
  2. Procédé selon la revendication 1, dans lequel ledit complexe hexacoordiné de cobalt-III est présent dans la forme de Me3[Co(NO2)6], où Me est un ou plusieurs éléments choisis parmi Na, K et Li.
  3. Procédé selon la revendication 1 ou 2, dans lequel ladite solution de conversion au cobalt a un pH de 7,0 à 7,2.
  4. Procédé selon les revendications 1-3, dans lequel ladite solution de conversion au cobalt a une température de 20°C (68°F) à 66°C (150°F).
  5. Procédé selon les revendications 1-4, dans lequel ledit substrat est mis en contact avec ladite solution de conversion au cobalt sur une durée de 3 minutes à 60 minutes.
  6. Procédé selon les revendications 1-5, dans lequel ledit substrat est du magnésium, un alliage de magnésium, un substrat plaqué au Cd ou un substrat plaqué au Zn.
  7. Procédé selon les revendications 1-6, dans lequel ledit substrat est de l'aluminium ou un alliage d'aluminium.
  8. Procédé selon les revendications 1-7, dans lequel ladite solution de conversion au cobalt comprend une solution aqueuse préparée en faisant réagir un sel de cobalt-II avec un sel de nitrite de métal, dans laquelle la concentration dudit sel de cobalt II est de 0,03 mol/l (0,1 mol/gal) de solution finale jusqu'à la limite de saturation du sel de cobalt-II utilisé et la concentration dudit sel de nitrite de métal est de 0,16 à 3,2 mol/l (0,6 à 12 mol/gal) de solution finale.
  9. Procédé selon la revendication 8, dans lequel ledit sel de cobalt II est CoX2, ou X2 est un ou plusieurs composés choisis parmi (NO3)2, Cl2, (CH3COO)2 (acétate), SO4, Br2, (CN)2, (SCN)2, ou Co3.
  10. Procédé selon la revendication 8 ou 9, dans lequel ledit sel de nitrite de métal est MeNO2, où Me est un ou plusieurs éléments choisis parmi Na, K ou Li.
  11. Procédé selon les revendications 8 -10, dans lequel on ajoute un oxydant à ladite solution de conversion au cobalt pour oxyder les ions de cobalt-II en solution en ions de cobalt-III.
  12. Procédé selon la revendication 11, dans lequel ledit oxydant est le peroxyde d'hydrogène, H2O2.
  13. Procédé selon la revendication 12, dans lequel on ajoute à ladite solution de conversion au cobalt du peroxyde d'hydrogène, H2O2, dans la quantité de 0,08 à 0,13 molli (0,3 à 0,5 mol/gal) de solution finale.
  14. Procédé selon les revendications 8-13, dans lequel on ajoute à ladite solution de conversion au cobalt un accélérateur de réaction, choisi parmi l'iodure de sodium, NaI, et le bromure de sodium, NaBr, pour accélérer la formation dudit revêtement de conversion au cobalt sur ledit substrat.
  15. Procédé selon la revendication 14, dans lequel on ajoute à ladite solution de conversion au cobalt de l'iodure de sodium, NaI, dans la quantité de 22 à 26 g/l (83 à 99 g/gal) de solution finale.
  16. Procédé selon les revendications 8-15, dans lequel on prépare ladite solution de conversion au cobalt par une séquence de préparation de bain comprenant:
    (a) l'addition et la dissolution dudit sel de nitrite de métal,
    (b) l'addition et la dissolution subséquentes d'un accélérateur de réaction;
    (c) l'addition et la dissolution subséquentes dudit sel de cobalt-II;
    (d) l'addition subséquente d'un oxydant à la solution.
  17. Procédé selon les revendications 8-16, dans lequel on prépare ladite solution en faisant réagir ledit sel de cobalt-II avec ledit sel de nitrite de métal, dans lequel le rapport molaire dudit sel de nitrite de métal au sel de cobalt est d'environ 6 à 1 à 14 à 1.
  18. Procédé selon les revendications 8-17, comprenant l'étape supplémentaire de mise en contact dudit substrat revêtu avec une solution aqueuse d'étanchéité comprenant du sulfate de nickel, NiSO4.6H2O, du nitrate d'ammonium, NH4NO3, et de l'acétate de manganèse Mn(CH3COO)2.4H2O.
  19. Procédé selon les revendications 1-18, dans lequel on fournit une solution de conversion au cobalt comprenant une solution aqueuse préparée en faisant réagir du nitrate de cobalt, CO(NO3)2.6H2O, avec du nitrite de sodium, NaNO2, dans laquelle la concentration dudit nitrate de cobalt est de 20 à 25g/l (75 à 95 g/gal) de solution finale et la concentration dudit nitrite de sodium est de 60 à 65 g/l (227 à 246 g/gal) de solution finale.
  20. Procédé selon la revendication 19, dans lequel on prépare ladite solution de conversion au cobalt par une séquence de préparation de bain comprenant :
    (a) l'addition et la dissolution dudit nitrite de sodium,
    (b) l'addition et la dissolution subséquentes d'iodure de sodium, NaI;
    (c) l'addition et la dissolution dudit nitrate de cobalt; et
    (d) l'addition subséquente dudit peroxyde d'hydrogène, H2O2, à la solution.
  21. Procédé selon la revendication 19 ou 20, dans lequel ladite solution de conversion au cobalt a une température de 49 ± 3°C (120±5°F).
  22. Procédé selon les revendications 19-21, dans lequel ledit substrat est mis en contact avec ladite solution de conversion au cobalt pendant une durée de 15 min à 30 min.
  23. Solution de revêtement de conversion chimique pour produire un revêtement de conversion au cobalt de film d'oxyde sur un substrat de métal, ladite solution comprenant une solution de réaction aqueuse d'un complexe hexacoordiné de cobalt III soluble dans la forme d'un complexe d'hexanitrite de cobalt III soluble, la concentration dudit complexe hexacoordiné de cobalt III étant de 0,03 mol/l (0,1 mol/gal) de solution jusqu'à la limite de saturation dudit comple hexacoordiné de cobalt III, ladite solution de réaction peut être obtenue en faisant réagir un sel de cobalt II avec un sel de nitrite de métal, dans laquelle la concentration dudit sel de cobalt II est de 0,03 mol/l (0,1 mol/gal) de solution finale, jusqu'à la limite de saturation du sel de cobalt II utilisé et la concentration dudit sel de nitrite de métal est de 0,16 mol/l (0,6 mol/gal) de solution finale, et un oxydant pour oxyder les ions de cobalt II en ions de cobalt m et un accélérateur de réaction, choisi parmi l'iodure de sodium, NaI, ou le bromure de sodium NaBr, pour accélérer la formation dudit revêtement de conversion au cobalt sur ledit substrat.
  24. Solution selon la revendication 23, dans laquelle ledit complexe hexacoordiné de cobalt III est présent dans la forme de Me3[Co(NO2)6], où Me est un ou plusieurs éléments choisis parmi Na, K et Li.
  25. Solution selon la revendication 23 ou 24, dans laquelle ledit sel de cobalt II est CoX2, où X2 est un ou plusieurs composés choisis parmi (NO3)2, Cl2, (CH3COO)2 (acétate), SO4, Br2, (CN)2 (SCN)2, ou CO3.
  26. Solution selon la revendication 23 ou 25, dans laquelle ledit sel de nitrite de métal est MeNO2, où Me est un ou plusieurs éléments choisis parmi Na, K et Li
  27. Solution selon les revendications 23-26, dans laquelle ledit oxydant est le peroxyde d'hydrogène, H2O2.
  28. Solution selon les revendications 23-27, dans laquelle ladite solution de conversion au cobalt est préparée par une séquence de préparation de bain comprenant les étapes consistant :
    (a) à ajouter et à dissoudre ledit sel de nitrite de métal;
    (b) à ajouter et à dissoudre ensuite ledit accélérateur de réaction;
    (c) à ajouter et à dissoudre ensuite ledit sel de cobalt II; et
    (d) à ajouter ensuite ledit oxydant à la solution.
  29. Solution selon les revendications 23-28, dans laquelle on prépare ladite solution en faisant réagir ledit sel de cobalt II avec ledit sel de nitrite de métal, dans laquelle le rapport molaire du sel de nitrite au sel de cobalt est de 6 à 1 à 14 à 1.
  30. Solution selon les revendications 23-29, dans laquelle ladite solution a un pH de 7,0 à 7,2.
  31. Solution selon les revendications 23-30, dans laquelle ladite solution a une température de 20°C (68°F) à 66°C (150°F).
  32. Solution selon les revendications 23-31, dans laquelle ledit substrat est du magnésium, un alliage de magnésium, un substrat plaqué au Cd ou un substrat plaqué au Zn.
  33. Solution selon les revendications 23-32, dans laquelle ledit substrat est de l'aluminium ou un alliage d'aluminium.
  34. Solution selon les revendications 25-33, dans laquelle ledit complexe d'hexanitrite de cobalt III est le complexe d'hexanitrite de cobalt III et de sodium, ledit sel de cobalt II est le nitrate de cobalt II, ledit sel de nitrite de métal est le nitrite de sodium et ladite solution a une température de 49 ± 3°C (120 ± 5°F).
  35. Article revêtu obtenu dans un procédé selon les revendications 1-22 ou en utilisant la solution des revendications 23-34, le revêtement a par là une épaisseur de 0,12 à 0,14 µm.
  36. Article revêtu selon la revendication 35 présentant des propriétés de résistance à la corrosion et d'adhérence de la peinture, ledit article comprenant :
    (a) un substrat en aluminium ou en alliage d'aluminium; et
    (b) un revêtement de conversion au cobalt formé sur ledit substrat, ledit revêtement de conversion au cobalt comprenant de l'oxyde d'aluminium Al2O3 comme le pourcentage volumique le plus grand et un ou plusieurs oxydes de cobalt parmi CoO, Co3O4 et Co2O3,
    dans lequel ledit revêtement de conversion au cobalt a une épaisseur de 0,12 à 0,14 µm.
  37. Article selon la revendication 36, dans lequel
    (a) dans la partie dudit revêtement de conversion au cobalt adjacente audit substrat, le pourcentage volumique le plus grand dudit revêtement consiste essentiellement en Al2O3;
    (b) dans la partie du haut dudit revêtement de conversion au cobalt le pourcentage volumique le plus grand dudit revêtement consiste essentiellement en un mélange de Co3O4 et de Co2O3; et
    (c) dans la partie dudit revêtement de conversion au cobalt entre les deux, ledit revêtement consiste essentiellement en un mélange de CoO, de Co3O4, de Co2O3 et d'Al2O3.
  38. Article selon la revendication 37, dans lequel le haut dudit revêtement de conversion au cobalt (150,190,230) est poreux et a l'apparence de nouilles chow mein à un agrandissement de 10 000.
  39. Article selon les revendications 37-38, dans lequel ledit revêtement de conversion au cobalt est étanche.
EP91202181A 1990-11-30 1991-08-27 Revêtement de conversion au cobalt, sans chromate Expired - Lifetime EP0488430B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US62113290A 1990-11-30 1990-11-30
US621132 1990-11-30

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EP0488430A2 EP0488430A2 (fr) 1992-06-03
EP0488430A3 EP0488430A3 (en) 1992-12-16
EP0488430B1 true EP0488430B1 (fr) 1997-06-11

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JP (1) JP3194607B2 (fr)
AT (1) ATE154401T1 (fr)
AU (1) AU650494B2 (fr)
BR (1) BR9105184A (fr)
CA (1) CA2056159C (fr)
DE (1) DE69126507T2 (fr)
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GR (1) GR3024046T3 (fr)
HK (1) HK1006861A1 (fr)
MX (1) MX9102254A (fr)
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CA2087473C (fr) * 1990-05-17 2001-10-16 Matthias P. Schriever Revetement d'oxyde non chrome pour substrats d'aluminium
US5551994A (en) * 1990-05-17 1996-09-03 The Boeing Company Non-chromated oxide coating for aluminum substrates
US5298092A (en) * 1990-05-17 1994-03-29 The Boeing Company Non-chromated oxide coating for aluminum substrates
US5472524A (en) * 1990-05-17 1995-12-05 The Boeing Company Non-chromated cobalt conversion coating method and coated articles
US5468307A (en) * 1990-05-17 1995-11-21 Schriever; Matthias P. Non-chromated oxide coating for aluminum substrates
ATE173513T1 (de) * 1991-07-19 1998-12-15 Boeing Co Nicht-chromatierte oxidüberzüge für aluminiumsubstrate
CN1138873C (zh) * 1992-06-25 2004-02-18 波音公司 在金属基体上形成钴转化膜层的方法，钴转化镀膜液及其用途
WO1995008008A1 (fr) 1993-09-13 1995-03-23 Commonwealth Scientific And Industrial Research Organisation Traitement de metaux par une solution de nettoyage contenant des ions acides de terres rares
AUPM621194A0 (en) * 1994-06-10 1994-07-07 Commonwealth Scientific And Industrial Research Organisation Conversion coating and process for its formation
PL320138A1 (en) 1994-11-11 1997-09-15 Commw Scient Ind Res Org Method of and solution for obtaining a conversive coating on metal surface
GB9617416D0 (en) * 1996-08-20 1996-10-02 Minnesota Mining & Mfg Thermal bleaching of infrared dyes
FR2752851B1 (fr) * 1996-09-02 1998-11-13 Cfpi Ind Bain et procede de phosphatation de substrats metalliques, concentre pour la preparation de ce bain et substrats metalliques traites a l'aide de ces bain et procede
US5873953A (en) * 1996-12-26 1999-02-23 The Boeing Company Non-chromated oxide coating for aluminum substrates
ZA983867B (en) * 1997-05-16 1998-11-13 Henkel Corp Lithium and vanadium containing sealing composition and process therewith
US6315823B1 (en) 1998-05-15 2001-11-13 Henkel Corporation Lithium and vanadium containing sealing composition and process therewith
US6432225B1 (en) * 1999-11-02 2002-08-13 The Boeing Company Non-chromated oxide coating for aluminum substrates
AUPQ633300A0 (en) 2000-03-20 2000-04-15 Commonwealth Scientific And Industrial Research Organisation Process and solution for providing a conversion coating on a metallic surface ii
AUPQ633200A0 (en) 2000-03-20 2000-04-15 Commonwealth Scientific And Industrial Research Organisation Process and solution for providing a conversion coating on a metallic surface I
WO2003060019A1 (fr) 2002-01-04 2003-07-24 University Of Dayton Pigments anticorrosion non toxiques a base de cobalt
US7294211B2 (en) * 2002-01-04 2007-11-13 University Of Dayton Non-toxic corrosion-protection conversion coats based on cobalt
US7235142B2 (en) 2002-01-04 2007-06-26 University Of Dayton Non-toxic corrosion-protection rinses and seals based on cobalt
US6818313B2 (en) 2002-07-24 2004-11-16 University Of Dayton Corrosion-inhibiting coating
US20040011252A1 (en) 2003-01-13 2004-01-22 Sturgill Jeffrey A. Non-toxic corrosion-protection pigments based on manganese
JP4934984B2 (ja) * 2005-03-31 2012-05-23 大日本印刷株式会社 金属酸化物膜の製造方法

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ATE154401T1 (de) 1997-06-15
AU8822591A (en) 1992-06-04
JP3194607B2 (ja) 2001-07-30
EP0488430A2 (fr) 1992-06-03
JPH059745A (ja) 1993-01-19
ES2104655T3 (es) 1997-10-16
CA2056159A1 (fr) 1992-05-31
DE69126507T2 (de) 1997-09-25
BR9105184A (pt) 1992-07-21
MX9102254A (es) 1992-06-01
CA2056159C (fr) 2001-07-03
NZ240779A (en) 1994-11-25
GR3024046T3 (en) 1997-10-31
DK0488430T3 (da) 1998-01-05
AU650494B2 (en) 1994-06-23
HK1006861A1 (en) 1999-03-19
EP0488430A3 (en) 1992-12-16
DE69126507D1 (de) 1997-07-17

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