Classifications

• • 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
• • 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
  • C23C22/57—Treatment of magnesium or alloys based thereon
• • 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
• • 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
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/30—Anodisation of magnesium or alloys based thereon
• • 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
  • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
  • C23C2222/10—Use of solutions containing trivalent chromium but free of hexavalent chromium

Definitions

• the present invention is in the field of surface treatment of light alloy parts made of aluminum, aluminum alloy, magnesium or magnesium alloy, in order to give them protection against corrosion. More particularly, it relates to a method of surface treatment of aluminum or magnesium parts or their respective alloys.
• parts made from aluminum alloy or magnesium alloy must undergo surface treatment operations, in order to increase their corrosion resistance. This is particularly the case for parts intended for use in the aeronautical industry, for which it is imposed stringent requirements, particularly in terms of performance test salt spray resistance.
• a first of these techniques is the chemical conversion treatment of the aluminum alloy.
• the most common of these processes known under the trade name "Alodine® 1200" from Henkel, carries out a chromating treatment. To this end, it uses a substance based on hexavalent chromium. If this process makes it possible to confer on the aluminum alloy a good resistance to corrosion, while ensuring a capacitance of electrical conduction of the part, by the formation on the part of a complex surface layer composed mainly of hydroxides
• chromium oxyhydroxides and aluminum it raises an environmental problem. Hexavalent chromium substances are toxic to living organisms.
• Another technique conventionally used to significantly improve the corrosion resistance of aluminum alloy parts involves an anodizing step, followed by one or more clogging steps, that is to say closing or closing existing porosities in the porous anodic layer created on the surface of the room by the anodizing step.
• clogging steps that is to say closing or closing existing porosities in the porous anodic layer created on the surface of the room by the anodizing step.
• the most commonly used to obtain a significant increase in corrosion resistance of the parts, in particular to meet the requirements of the aeronautical sector consists of chromic anodic oxidation, followed by hydrothermal clogging based on potassium dichromate. .
• this process thus uses a substance based on hexavalent chromium, which is dangerous for health.
• magnesium alloy parts there are also currently several surface treatment techniques to increase their corrosion resistance properties.
• One of these techniques is the chemical conversion treatment of the magnesium alloy.
• the most common of these methods known as etching, performs a chromating treatment. To this end, it uses a substance based on hexavalent chromium. If this process makes it possible to confer on the magnesium alloy a good resistance to corrosion, by forming a complex surface layer composed mainly of hydroxides, chromium oxyhydroxides and magnesium on the part, it nevertheless raises also, for the same reasons as expressed above, an environmental problem.
• the document US 2011/300390 describes a method of coating a metal substrate comprising successively immersing this substrate in an aqueous bath containing cerium ions, then in a bath containing a zirconium compound selected from zirconium nitrate and hexafluorozirconate, and a metal nitrate such as yttrium nitrate.
• the document US 2006/113007 discloses a method of coating a metal substrate comprising immersing the substrate in an aqueous composition containing two rare earth salts and an oxidizing compound.
• the present invention aims to remedy the disadvantages of the processes surface treatment of aluminum alloy or magnesium alloy parts in order to increase their resistance to corrosion, as proposed by the prior art, in particular to those described above, by proposing a such a process which does not use any substance that is toxic to living organisms, and in particular no hexavalent chromium, while at the same time having a performance, in terms of protection of the parts against oxidation, that is at least equivalent to the processes of the art prior art using substances based on hexavalent chromium.
• corrosion inhibitor means an element which, present in a low concentration in a coating formed on a part, slows or stops the corrosion process of the part in contact with a corrosive medium.
• a transition metal is here defined in a conventional manner in itself, as a metal of the block d of Mendeleyev's painting, with the exception of lutetium and lawrencium.
• the trivalent chromium salt may especially be a sulphate, a chloride, a nitrate, a fluoride, an acetate, etc.
• conventional trivalent chromium is understood to mean chromium in the +3 oxidation state.
• Hexavalent chromium means chromium in the +6 oxidation state.
• the second bath comprises, in addition to an oxidizing compound, a rare earth salt corrosion inhibitor.
• Rare earths are here defined conventionally in themselves, and include the fifteen lanthanides, scandium and yttrium.
• the rare earth salt corrosion inhibitor can be for example a salt of lanthanides such as cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, d holmium, erbium, thulium, ytterbium, lutetium; a scandium salt; or yttrium salt.
• This salt may especially be a sulphate, a chloride, a nitrate, a fluoride, an acetate, etc.
• the cerium salts which may be in the +4 oxidation state, and preferably in the +3 oxidation state, in particular in the nitrate form, are particularly preferred in the context of the invention, as are lanthanum salts.
• the chromium-based substances in a +3 oxidation state, as well as the cerium salts and the lanthanum salts, are in particular advantageously not harmful to the environment or health.
• Such a process advantageously makes it possible to form on the surface of the part a layer of oxides / hydroxides containing metal derived from the metal salt present in the first bath, trivalent chromium, and the rare earth from the rare earth salt present in the second bath, for example cerium or lanthanum.
• This layer has excellent corrosion resistance properties and thus effectively protects the part against corrosion.
• the succession of the immersion steps in each of the first bath and the second bath, each inducing a chemical conversion of the material on the surface of the part makes it possible to obtain a synergistic effect, which leads, unexpectedly, to properties of resistance to corrosion of the room much greater than those obtained by immersion in one of these baths, or in two successive baths, the second containing only an oxidizing compound, or only a rare earth salt corrosion inhibitor.
• the conversion layer obtained on the surface of the part also advantageously makes it possible to provide electrical conduction, and it also constitutes a good hanging base for paint systems used in particular in the aeronautical sector.
• the adhesion of conventional paint systems to the surface layer formed on the part by the process according to the invention is in particular as good as that obtained for the parts treated by the processes of the prior art using hexavalent chromium .
• one or more rinsing steps of the workpiece are carried out between immersion in the first bath and immersion in the second bath.
• the oxidizing compound in the one and the other of the first bath and the second bath, can be of any type known in itself for the chemical conversion baths of aluminum or magnesium or their respective alloys. Compounds having no adverse effect on the environment are particularly preferred in the context of the invention.
• the first bath it is within the scope of the present invention any compound capable of activating the surface of the part by dissolving the natural passivation layer and the substrate, causing a local increase in the pH and consequently the precipitation in the form of oxides / hydroxides of the active compounds, i.e., trivalent chromium, and the metal constituting the part.
• the oxidizing compounds are fluoride-based substances, such as ammonium fluoride or potassium fluoride zirconate K 2 ZrF 6 , permanganate, such as potassium permanganate, dihydrogen peroxide H 2 O 2 .
• the concentration of oxidizing compound in the first bath may especially be between 0.1 and 50 g / l.
• the trivalent chromium salt and the oxidizing compound present in the first bath may be constituted by two different compounds, or by a single compound capable of ensuring by itself the two functions of inhibition of corrosion and oxidation, by for example, trivalent chromium fluoride CrF 3 .
• the oxidizing compound is chosen to be able to oxidize the surface of the part, thus causing its own simultaneous reduction, with, again, local increase in pH and precipitation of rare earth oxides / hydroxides / trivalent chromium / metal constituting the piece.
• the oxidizing compounds are fluoride-based substances, such as ammonium fluoride or potassium fluoride zirconate K 2 ZrF 6 , permanganate, such as potassium permanganate, dihydrogen peroxide H 2 O 2 .
• the invention also satisfies the following characteristics, implemented separately or in each of their technically operating combinations.
• the trivalent chromium salt can be brought in any conventional form in itself for chemical conversion treatments of metal substrate, especially in the form of fluoride, chloride, nitrate, acetate, acetate hydroxide, sulfate, potassium sulfate, etc., trivalent chromium, for example CrF 3 , xH 2 O, CrCl 3 , xH 2 O, Cr (NO 3 ) 3 , xH 2 O, (CH 3 CO 2 ) 2 Cr, xH 2 O, (CH 3 CO 2 ) 7 Cr 3 (OH) 2 , xH 2 O, Cr 2 (SO 4 ) 3 , xH 2 O, CrK (SO 4 ) 2 , xH 2 O, etc.
• trivalent chromium for example CrF 3 , xH 2 O, CrCl 3 , xH 2 O, Cr (NO 3 ) 3 , xH 2 O, (CH 3 CO 2 ) 2 Cr, xH 2 O, (CH
• the trivalent chromium salt present in the first bath is selected from fluorides and sulphates. These are, for example, chromium trifluoride CrF 3 , potassium chromium sulphate CrK (SO 4 ) 2 , or chromium sulphate Cr 2 (SO 4 ) 3 .
• the concentration of trivalent chromium salt in the first bath is preferably between 0.5 and 50 g / l, preferably between 1 and 20 g / l.
• the cerium or lanthanum that may be present in the second bath preferably have a +3 oxidation state.
• the cerium or lanthanum salt can be brought in any form, in particular chloride, fluoride, nitrate, sulfate, acetate, etc., of cerium, for example CeCl 3 , xH 2 O, CeF 3 , xH 2 O, Ce ( NO 3 ) 3 , xH 2 O, Ce 2 (SO 4 ) 3 , xH 2 O, Ce (CH 3 CO 2 ) 3 , xH 2 O, etc.
• lanthanum for example LaCl 3 , xH 2 O, LaF 3 , xH 2 O, La (NO 3 ) 3 , xH 2 O, La 2 (SO 4 ) 3 , xH 2 O, La (CH 3 CO 2 ) 3 , xH 2 O, etc.
• the rare earth salt present in the second bath is cerium nitrate Ce (NO 3 ) 3 or lanthanum nitrate La (NO 3 ) 3 .
• the concentration of rare earth salt, in particular of cerium or lanthanum salt, in the second bath is between 0 and 50 g / l, preferably between 1 and 10 g / l, for example equal to 5 g / l.
• a particularly preferred composition for the second bath uses dihydrogen peroxide H 2 O 2 as an oxidizing compound, and corresponds to one of the following compositions: Ce (NO 3 ) 3 , 6H 2 O or (NO 3 ) 3 , 6H 2 O, at a concentration of between 0.1 and 50 g / l, preferably between 1 and 10 g / l, preferably equal to 5 g / l, and H 2 O 2 , solution at 35% v / v, at a concentration of between 5 and 500 ml / l, preferably between 5 and 200 ml / l, more preferably between 10 and 100 ml / l, preferably equal to 50 ml / l.
• the oxidizing compound chosen for the second bath is hydrogen peroxide H 2 O 2
• the latter is incorporated in the form of an aqueous solution, for example at 35% v / v or 30% v / v. v, to obtain a concentration in the bath of between 5 and 500 ml / l, preferably between 5 and 200 ml / l, more preferably between 10 and 100 ml / l, and preferably equal to 50 ml / l.
• the part is subjected to an anodization treatment step prior to immersion in the first bath and the second bath.
• the invention is then also expressed in terms of post-anodization clogging process.
• the prior stage of anodization treatment can be carried out according to any known method in itself. Preferably, it does not use any substance based on hexavalent chromium.
• anodizations of the sulfuric anodization type diluted or not, such as standard Anodic Sulfuric Oxidation (so-called standard OAS), dilute Anodic Sulfuric Oxidation (so-called dilute OAS), oxidation Anodic Sulfo-Tartric (OAST), Sulfo-Boric Anodic Oxidation (OASB), etc.
• standard OAS Anodic Sulfuric Oxidation
• dilute OAS dilute Anodic Sulfuric Oxidation
• OFAST oxidation Anodic Sulfo-Tartric
• the part is subjected to a degreasing and / or stripping step prior to immersion of the first bath and the second bath, so as to eliminate grease, dirt and oxides present on its surface.
• this surface preparation step part degreasing and / or pickling is advantageously carried out before the anodization.
• Interleaved rinses are preferably carried out between the successive steps above, and before immersion of the piece in the first bath.
• the invention is expressed in terms of the chemical conversion process of aluminum or one of its alloys, or magnesium or one of its alloys.
• Parts made of 2024 T3 aluminum alloy laminated, dimensions 120x80x2 mm, are treated as follows.
• the parts are then subjected to successive immersions in the next aqueous bath, and in respectively one of the following second aqueous baths.
• the first bath based on trivalent chromium, named Bath 1, corresponds to the composition: CrK (SO 4 ) 2 , 6H 2 O at 2 g / L + K 2 ZrF 6 at 5 g / L, in water.
• the immersion time in this first bath is equal to 10 min.
• the second aqueous bath corresponds to one of the compositions indicated in Table 1 below.
• Three of these baths comprising an oxidizing compound and a rare earth salt, respectively of cerium (baths D1 and D2) or of lanthanum (bath D3) are in accordance with the present invention, and two of them, Comp.1 and Comp.2, are comparative examples.
• the temperature of each of these baths is the ambient temperature, ie a temperature of between 18 and 25 ° C.
• the immersion time in each of these second baths is equal to 5 min.
• Parts are also treated, after surface preparation, by immersion only in the bath 1 described above.
• identical pieces, having undergone identical surface preparation are processed by the following prior art chemical conversion processes: Alodine® 1200 (Henkel) (using chromium) hexavalent), SurTec® 650 (SurTec) (using trivalent chromium), and Lanthan® VS 613.3 (Coventya) (using trivalent chromium).
• An adhesion test of conventional paint systems on the conversion layer formed on the part, on the one hand by a process according to the invention above, comprising immersing the piece in the bath 1 and then in the Bath 2 designated D1 (cerium salt), and secondly by the method of the prior art Alodine® 1200, is carried out as follows.
• Two paint systems are tested: a water-based epoxy system (P60 + F70) and a solvent-based polyurethane system (PAC33 + PU66).
• the tests are carried out according to the ISO 2409 standard, for dry adhesion, after drying of the paint system, and for wet adhesion: after drying of the paint system, the samples are immersed in demineralized water for 14 hours. days and then dried before undergoing the adhesion test according to the standard.
• adhesion of the paint systems is comparable to that obtained for the parts treated by the Alodine® 1200 prior art process.
• the parts treated by the process according to the invention comprising immersing the part in the bath 1 and then in the bath 2 designated D1 (cerium salt), are subjected to an electrical conductivity test in accordance with the standard MIL- DTL-81760B, which measures the resistivity of the layer / substrate / layer system.
• Alodine® 1200 layer As comparative examples, are also subjected to the same test parts treated by the commercial chemical conversion method proposed by the prior art Alodine® 1200, as described in Table 2 above ("Alodine® 1200 layer”). thick), as well as parts treated by the same Alodine® 1200 chemical conversion process, but including immersion in the treatment bath for only 30 seconds (“Alodine® 1200 thin layer”).
• the thick layer of Alodine® 1200 is recommended when good properties of corrosion resistance are sought, to the detriment of electrical conduction properties.
• the thin layer of Alodine® 1200 is recommended when good electrical conduction properties are sought, with, however, a reduction in the anti-corrosion performance of the treatment by half.
• the method according to the invention thus makes it possible to form on the part a layer advantageously combining corrosion protection performance superior to those obtained by the method of the prior art Alodine® 1200 thick layer, and good electrical conductivity.
• Example 1 Aluminum parts similar to those used for Example 1 are subjected to the prior surface preparation steps described in Example 1.
• the temperature is the temperature ambient, and the immersion time in Bath 2 is 5 min.
• Example 1 Aluminum parts similar to those used for Example 1 are subjected to the prior surface preparation steps described in Example 1.
• Each piece is then subjected to immersion in the bath 2 according to the invention D1 described above, at room temperature, for 5 min.
• the part is then subjected to successive immersions in the first and second aqueous baths.
• the first bath based on trivalent chromium, named Bain 1, corresponds to the composition: CrK (SO 4 ) 2 , 6H 2 O at 2 g / L + K 2 ZrF 6 at 5 g / L, in water.
• the immersion time in this first bath is equal to 10 min.
• the second bath based on cerium, named Bath 2
• Bath 2 has the following composition: Ce (NO 3 ) 3 , 6H 2 O at 5 g / L; H 2 O 2 , 35% v / v solution, 50 mL / L, in water.
• Its pH is set at 3, and its temperature is the ambient temperature, ie a temperature between 18 and 25 ° C approximately.
• the immersion time in this second bath is equal to 5 min.
• Parts 2024T3 laminated aluminum alloy 120x80x2 mm dimensions are treated by anodizing, then clogging, according to the methods below.
• anodizing step three different anodizing methods, namely the diluted OAS, the OAST and the OASB, are used, to obtain on the surface of the pieces an anodic layer with a thickness of 2 to 5 ⁇ m.
• the operating parameters for dilute OAS, OAST and OASB are shown in Table 12 below. ⁇ u> Table 12 ⁇ / u> - Operating Parameters Used for the Different Anodizing Steps Diluted OAS OAST OASB Composition of the bath H 2 SO 4 : 62 g / L H 2 SO 4 : 40 g / L H 2 SO 4 : 45 g / L C 4 H 6 O 6 : 80 g / L H 3 BO 3 : 8 g / L Bath temperature (° C) 22 37 27 Tension cycle 14 V - 24 min 14 V - 25 min 15 V - 23 min
• the parts obtained are subjected to a sealing step, either of the hydrothermal type, or of the hydrothermal type with nickel salts, or according to the process according to the invention used in the conditions indicated in Example 1 above, concerning the immersion in Bath 1 and Bath 2.
• the present invention achieves the objectives it has set for itself.
• it provides a method of surface treatment of aluminum or aluminum alloy parts, or magnesium or magnesium alloy, which, without using hexavalent chromium, provides performance in terms of protection of the piece against corrosion which are superior to those obtained by the processes of the prior art.

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