Classifications

• • 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
  • C25D11/026—Anodisation with spark discharge
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/40—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates
  • C23C22/44—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates containing also fluorides or complex fluorides
• • 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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids
• • 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
  • C25D11/16—Pretreatment, e.g. desmutting
• • 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

Definitions

• the present invention is in the field of surface treatment of aluminum or magnesium alloy parts in order to protect them from corrosion.
• the present invention relates to a method of surface treatment of an aluminum or aluminum alloy or magnesium or magnesium alloy part using an aqueous composition for the surface treatment.
• the invention also relates to a part made of aluminum alloy or of magnesium alloy obtained by such a process.
• Aluminum or magnesium alloys are widely used in the aeronautical field for their low density and good mechanical properties. However, they must be protected by surface treatments to avoid corrosion.
• the parts to be treated are immersed, with an appropriate counter electrode, in a bath containing an electrolyte, in which an anode current is applied.
• a protective layer is then formed on the surface of the part, called an anode layer, which is composed mainly of oxides and hydroxides from the elements of the substrate, and in some cases elements from the electrolyte.
• the anodic layers alone are not sufficient to effectively protect the parts against corrosion, since they are generally porous, therefore sensitive to corrosion. They therefore need to be painted or sealed.
• the clogging treatments proposed for this purpose by the prior art, and implemented for many years, use potassium or sodium dichromate. Furthermore, in the case where an electrical conductivity is required for the part, the combination of anodization and clogging is replaced by a chemical conversion treatment. Currently, this treatment is most generally carried out by means of a solution based on chromium trioxide, for example by the solution sold under the name "Alodine 1200" by the company Henkel.
• the anticorrosion protection conferred by the conductive layer thus formed is less than that obtained by anodizing and then clogging, but it can also serve as a base for attachment to a paint.
• HTS hydrothermal clogging
• HWS hot water clogging
• the anodized part is immersed in boiling water or near its boiling point, generally at 98 ° C.
• the surface of the pores is then partially converted into aluminum hydroxides, in particular boehmite (AIOOH) and pseudoboehmite (AIO (OH)), which clog the pores and thus improve the corrosion resistance of the anodic layer.
• AIOOH boehmite
• AIO pseudoboehmite
• compositions based on trivalent chromium are capable of generating traces of hexavalent chromium in the layer formed on the part, in particular when they undergo aging under wet conditions, so that they too are liable to exhibit an environmental risk.
• the present invention aims to remedy the drawbacks of the solutions proposed by the prior art for the surface treatment of parts made of aluminum or magnesium alloy with a view to improving their resistance to corrosion, in particular the drawbacks set out above. , by proposing a process using a composition free of chromium and which makes it possible to replace solutions using chromium with equivalent performance in terms of corrosion resistance imparted to the treated part.
• Additional objectives of the invention are that the process is easy and quick to perform and uses little energy, and that the composition used by the process is free from any substance toxic to living organisms and the environment in general.
• the invention also aims to ensure that the capacity for resistance to corrosion of the treated part is durable over time, and that this treated part has self-healing properties of the defects formed in the coating present on its surface.
• a method of surface treatment of an aluminum or aluminum alloy or magnesium or magnesium alloy part in order to improve its resistance to corrosion.
• This method comprises a step of treatment by oxidation of the part, then a step of applying to the surface of the part, an aqueous liquid composition very suitable for use for the surface treatment of a metal part, especially aluminum or aluminum alloy or magnesium or magnesium alloy.
• This aqueous composition contains:
• composition is also free of chromium, in particular hexavalent chromium and trivalent chromium.
• chromium in particular hexavalent chromium and trivalent chromium.
• the composition is substantially free of chromium, that is to say that it does not contain chromium, or only in trace amounts.
• the composition does not contain hexavalent chromium, even in the trace state.
• trivalent chromium it is accepted within the scope of the invention that the composition may contain small amounts, for example less than 0.01% by weight.
• the surface treatment method comprises, prior to the step of applying to the surface of the part of the composition, a stage of treatment of the part by oxidation, in particular by micro-arc oxidation or even by anodic oxidation, also called anodization.
• the part treated by the method according to the invention also has a dense surface layer, and, when the treatment step is an anodization treatment step, the pores of the anodic layer which have been formed on its surface during the anodization are advantageously blocked.
• the step of applying the composition according to the invention to the surface of the part then clogs the anodic layer which has been formed during anodization.
• Anodization can be carried out according to any conventional method in itself.
• the anodization processes using chromium, in particular hexavalent chromium are preferably avoided in the context of the present invention, for obvious environmental safety reasons.
• the anodization process is chosen in particular from the processes known to those skilled in the art of sulfo-tartaric, sulfo-boric anodization, etc.
• Particularly preferred in the context of the invention are the anodic oxidation methods of sulfuric type (OAS), in particular the methods making it possible to form on the part an anodic layer of thin thickness, typically between 3 and 7 ⁇ m, commonly designated by the terms of OAS fine.
• OAS sulfuric type
• An example of such a process is described in particular in patent document FR 2 986 807.
• the invention is not however limited to such a process and can also be applied, with the same success, to the sealing of thick anodic layers larger, for example until 25 pm. It also applies, with the same success, to the clogging of the layers formed on the surface of the substrates by the micro- bow.
• the treatment method according to the invention may comprise, before applying the composition according to the invention to the surface of the part, a step of rinsing the surface of the part, for example with water, and where appropriate a drying step, such steps being entirely optional.
• the step of applying said composition can be carried out according to any conventional method in itself for the skilled person. It is preferably carried out by immersing the part in a bath of the composition according to the invention.
• the temperature of the composition is preferably advantageously between 10 and 60 ° C, preferably between 15 and 30 ° C, and preferably between 18 and 25 ° C, in particular around 20 ° C, and more generally at room temperature.
• Such a characteristic proves to be particularly advantageous with regard to the energy expenditure necessary for the implementation of the method according to the invention, which are particularly low.
• the composition according to the invention is applied to the surface of the part for a time greater than or equal to 5 minutes, preferably between 5 and 60 minutes, and preferably between 5 and 20 minutes, in particular between 8 and 15 minutes. Again, such a characteristic turns out to be particularly advantageous from an economic point of view.
• the method according to the invention makes it possible to form on the part a surface layer having a particularly good, durable corrosion resistance and a good capacity for self-healing.
• the part treated by the method according to the invention also has a dense surface layer, and, when the treatment step is a step of treatment by anodization, the pores of the anodic layer which have been formed on its surface during anodization are advantageously blocked.
• the method comprises a preliminary stage of pretreatment of the part by chemical degreasing and / or chemical pickling, also called stage of surface preparation.
• Such a prior surface preparation step advantageously makes it possible to clean the surface of the part from its dirt, oxides, etc.
• Degreasing like stripping, can be carried out in any manner known to those skilled in the art.
• Degreasing can in particular be of the solvent or alkaline type. It is, for example, an alkaline degreasing, by soaking the part, for example for 20 minutes, in an aqueous bath of temperature of 60 ° C. for example, containing the products marketed under the names Turco® 4215 NCLT and Turco ® 4215 additive, pH 9, for example at the respective concentrations of 50 g / l and 10 g / l.
• the pickling can be both acidic and alkaline. This is, for example, an acid pickling, by soaking the part, for example for 5 minutes, in an aqueous bath at a temperature of 20 ° C. for example, containing the product sold under the name Turco® Smut Go NC, for example at a concentration of 19% by volume.
• Rinses in particular with demineralized water, and at room temperature, can be carried out between the different degreasing and pickling phases, and at the end of this preliminary stage of surface treatment.
• the step of applying the composition according to the invention to the surface of the part of the surface treatment process can be carried out directly after this preliminary pretreatment step. It then performs the chemical conversion of the aluminum alloy or the magnesium alloy, to form a surface layer resistant to corrosion on the part.
• the surface treatment method comprises a final step of rinsing the surface of the part, for example with water, and if necessary a step of drying this surface.
• the method according to the invention comprises, after the step of applying the composition according to the invention to the surface of the part, no other clogging step, in particular clogging with hot water.
• the method according to the invention comprises a step of applying an aqueous composition to the surface of the part, which can thus contain:
• fluorozirconate ions preferably, fluorozirconate ions, molybdate ions, lithium ions and permanganate ions.
• composition applied to the part by a method according to the invention is advantageously usable, with high performance, as well for a post-anodization or post-oxidation micro-arc clogging treatment.
• High corrosion protection performances are also obtained both on parts obtained by rolling and on parts obtained by machining.
• This composition after its application to the surface of a part to be treated, gives the latter a corrosion resistance capacity as good, or even better, than hot water clogging solutions or commercial solutions for clogging or chemical conversion based on trivalent chromium, which are proposed by the prior art.
• part surface self-healing properties For example, no corrosion pitting appears on scratched specimens treated with the composition according to the invention, after more than 800 hours of exposure to salt spray.
• the part treated by the method according to the invention exhibits very little corrosion pitting after more than 1000 hours exposure to salt spray; it also exhibits a corrosion current, determined by the method of potentiodynamic polarization curves, which is very low.
• the fluorozirconate ions in which a zirconium atom is in complexed form with fluorine atoms, would participate in forming, on the surface of the part, a hydrated layer of Al-Zr-OF which would increase the character hydrophilic from the workpiece surface and activate it.
• the molybdate ions which have a reducible hexavalent anion which forms an insoluble oxide, would have within this surface layer an action of inhibiting corrosion.
• the lithium ions would participate in the formation of a lithium aluminate salt (LiH (AI02) 2.5H20), which would plug the pores in the surface layer of the part.
• Permanganate ions for their part, would have a self-healing effect by leaching of Mn 7+ , transport by the composition and reduction in insoluble form of manganese at the level of the defects present in the surface layer, to form clogging intermetallic precipitates therein. .
• composition applied to said part by the method according to the invention comprises one or more, preferably all, of the following characteristics:
• a concentration of hexafluorozirconate ions between 3.5 and 22 g / l, preferably between 3.5 and 9 g / l;
• a concentration of molybdate ions between 1.5 and 7 g / l, preferably between 3.5 and 7 g / l;
• a concentration of lithium ions of between 0.2 and 1 g / l, preferably of between 0.4 and 1 g / l;
• composition applied to said part by the process according to the invention may also contain cerium ions, preferably at the degree of oxidation +3. Such a characteristic further increases the anticorrosion performance of the treated part, in particular by the formation of precipitates of cerium oxides and hydroxides on the cathode sites of the metal surface, due to a strong local increase in pH.
• composition applied to said part by the method according to the invention may in particular comprise a concentration of cerium ions of between 0.01 and 0.2 g / l, preferably between 0.05 and 0.2 g / l.
• composition applied to said part by the process according to the invention also preferably contains nitrate ions.
• nitrate ions which advantageously play an oxidizing role in said composition, thus further improving the anticorrosion performance of the treated part, can for example be brought into the composition in the form of a salt, for example a lithium salt and / or cerium salt.
• all of the ions contained in the composition applied to said part by the method according to the invention can be added in the form of one or more water-soluble salts.
• the cations in particular of lithium and / or cerium, can for example be provided in the form of sulfate, persulfate, chloride, nitrate, fluoride, acetate, carbonate, etc., or any of their mixtures.
• they are provided in the form of nitrate, in particular lithium nitrate and / or cerium nitrate.
• composition applied to said part by the process according to the invention preferably contains lithium nitrate UNO3 and / or cerium nitrate, in particular cerium with an oxidation state of +3, Ce (N03) 3.
• the anions in particular of fluorozirconate, molybdate and / or permanganate, can for example be provided in the composition in the form of one or more salts of one or more alkali metals, for example in the form of a potassium or sodium salt , or their mixture.
• composition applied to said part by the process according to the invention can, for example, contain one or more of the following salts:
• composition applied to said part by the method according to the invention may for example comprise at least one, preferably several, and preferably all, of the following characteristics:
• molybdate salt for example sodium molybdate Na2Mo04, 2H2O;
• cerium salt for example nitrate of cerium Ce (N03) 3, 6H2O.
• composition applied to said part by the method according to the invention contains one of the following combinations of constituents:
• - fluorozirconate ions preferably hexafluorozirconate ions, in particular in the form of potassium salt
• molybdate ions especially in the form of the sodium salt
• lithium ions in particular in the form of lithium nitrate. It can for example essentially contain these constituents, in solution in water;
• - fluorozirconate ions preferably hexafluorozirconate ions, in particular in the form of potassium salt
• molybdate ions especially in the form of the sodium salt
• lithium ions in particular in the form of lithium nitrate
• cerium ions in particular in the form of cerium nitrate. It can for example essentially contain these constituents, in solution in water;
• - fluorozirconate ions preferably hexafluorozirconate ions, in particular in the form of potassium salt
• molybdate ions especially in the form of the sodium salt
• permanganate ions in particular in the form of potassium salt. It can for example essentially contain these constituents, in solution in water;
• - fluorozirconate ions preferably hexafluorozirconate ions, in particular in the form of potassium salt
• molybdate ions especially in the form of the sodium salt
• permanganate ions in particular in the form of potassium salt
• cerium ions in particular in the form of a cerium salt. It can for example essentially contain these constituents, in solution in water.
• a composition applied to said part by the process according to the invention preferably contains, in solution in water:
• fluorozirconate salt for example potassium hexafluorozirconate
• molybdate salt for example sodium molybdate
• lithium salt for example lithium nitrate
• permanganate salt for example potassium permanganate
• cerium salt for example cerium nitrate.
• composition applied to said part by the process according to the invention essentially contains the five constituents listed above.
• the expression “essentially contains” means the fact that the composition contains only these components, or that it also contains other components, but only in trace amounts, in non-operating amounts , that is to say having no effect on the aluminum or magnesium alloy constituting the treated part or on the surface layer formed on the surface of the latter, prior to the application of the composition according to the invention. invention on this surface, by anodization or other oxidation, or during this application.
• composition applied to said part by the method according to the invention is substantially free from one or more, and preferably all, of the following components:
• the composition applied to said part by the process according to the invention does not substantially contain, apart from the fluorozirconate ions, other ions containing fluorine.
• it is substantially free of any substance capable of releasing fluoride ions in the composition, for example ammonium fluoride, tetrafluoroboric acid, etc.
• composition is free of the compound, or that it contains it only in trace amounts, in amounts which are ineffective for the intended application.
• the pH of the composition applied to said part by the process according to the invention is preferably between 3 and 7, preferably between 4 and 6.5, and preferably between approximately 5 and approximately 6.
• a method of surface treatment of a part made of aluminum or aluminum alloy or of magnesium or magnesium alloy comprises a step of applying to the surface of said part an aqueous composition essentially comprising one or more fluorozirconate salt (s) and one or more molybdate salt (s).
• Another aspect of the invention relates to an aluminum or aluminum alloy or magnesium or magnesium alloy part obtained by a surface treatment process according to the invention.
• This part is coated with a surface layer having a particularly high resistance to corrosion as well as self-healing properties.
• This surface layer contains aluminum or magnesium; as well as zirconium, fluorine and molybdenum; and as well as lithium and / or manganese. It may also contain cerium.
• This surface layer is dense and contains uniformly ordered spheroidal aggregates.
• the pores of the layer anodic which has been formed by anodization are further advantageously closed.
• the step of applying the composition according to the invention to the surface of the part increases the thickness of the anode layer by approximately 0.1 to 2 ⁇ m, depending on the exact composition used.
• FIG. 1 shows photographs of laminated (a /) and machined (b /) specimens respectively, made of aluminum alloy, anodized and sealed according to the invention with an aqueous composition containing fluorozirconate, molybdate, lithium ions, permanganate and cerium (C4), after 750 h of exposure to salt spray;
• FIG. 2 shows analysis micrographs by scanning electron microscopy of anodized and clogged aluminum alloy test pieces in accordance with the invention, a / by an aqueous composition containing fluorozirconate, molybdate and lithium (C1) ions, b / by an aqueous composition containing fluorozirconate, molybdate, lithium and permanganate ions (C2), c / by an aqueous composition containing fluorozirconate, molybdate, lithium and cerium (C3) ions, d / by an aqueous composition containing fluorozirconate ions , molybdate, lithium, permanganate and cerium (C4); in this figure, for each test tube, the image obtained in backscattered electron mode is shown on the left and the image in secondary electronic mode on the right;
• FIG. 3 shows a photograph of a laminated test piece of aluminum alloy, anodized and sealed according to the invention with an aqueous composition containing fluorozirconate, molybdate, lithium, permanganate and cerium ions, and marked according to an X pattern by a touch of Van Laar:
• FIG. 4 shows scanning electron microscopy micrographs of anodized and clogged aluminum alloy specimens, and marked in an X pattern by a Van Laar point, before exposure to salt spray (a / ), and after 816 h of exposure to salt spray, respectively after clogging with an aqueous composition applied by the process according to the invention containing fluorozirconate, molybdate, lithium, permanganate and cerium (b /) ions and after clogging by an aqueous composition containing only fluorozirconate ions (c / and d /, at different magnifications).
• AA2024 aluminum alloy test pieces (of the following composition: 1.2 to 1.8% Mg, 0.3 to 0.9% Mn, max. 0.5% Fe, 3.8 to 4.9% Cu , max 0.25% Zn, max 0.1% Cr, max 0.15% Ti, Al for the remaining%), laminated or machined, dimensions 25x100x3 mm (for microstructural characterizations) and 150x80x3 mm ( for the salt spray tests) were treated by the process in accordance with the present invention according to the following operating conditions.
• the test pieces were first subjected to surface preparation steps. To this end, they have been successively soaked in the following baths:
• Turco® 4215 NCLT 50 50 g / l
• Turco® 4215 additive pH 9 10 g / l
• test pieces were then subjected to an anodic sulfuric oxidation treatment, conventionally in itself, according to the following parameters:
• test pieces were then subjected to a sealing treatment in accordance with the present invention. For this, they were immersed in the following aqueous composition:
• the pH of this composition is 6.
• test pieces were directly, that is to say without rinsing, exposed to salt spray for 750 or 1176 h, at a temperature between 15 and 25 ° C, according to the conditions in accordance with the standard.
• test pieces were subjected to clogging by means of the trivalent chromium-based process sold under the name SurTec® 650.
• test pieces were then sealed using the compositions applied by a process according to the invention and described in Table 2 (C1 to C4).
• the sealing conditions were 15 min at room temperature (i.e. around 21 ° C).
• test pieces were rinsed with water and dried at 60 ° C for 10 min.
• the thickness of the layer that has been formed on their surface is shown in Table 2 below.
• test pieces were subjected to the following tests.
• the technique used to characterize the behavior of the treated specimens with respect to corrosion is that of polarization curves.
• the anode and cathode curves were obtained on different samples for each of the clogging compositions studied.
• the medium was a 0.1 M NaCl solution in water, pH 5.67.
• the measurements were carried out at 25 ° C.
• the anodic and potentiodynamic polarization curves cathodic were obtained by a Gamry potentiostat / galvanostat, with a potential scanning speed of 0.5 mV / s.
• the recording of the potentiodynamic curves was carried out from the potential of the open circuit (E ocp ), measured in the absence of external current both in the anodic and cathodic directions. Individual samples were used for each potentiodynamic curve recorded.
• the open circuit potential of the samples studied was established by direct measurement of the "Eocp-t" function with respect to the same reference electrode after immersion in the 0.1 M NaCl solution up to 15 min.
• the values of the corrosion current i ⁇ rr were determined by Tafel extrapolation of the linear region of the anodic polarization curves at the corrosion potential.
• SSC stands for the standard silver electrode
• E ⁇ rr stands for the corrosion potential
• i ⁇ rr stands for the corrosion current.
• SEM Scanning electron microscopy
• EDX energy dispersive x-ray spectroscopy
• the morphology, structure and surface composition of the clogged specimens were examined by scanning electron microscopy (SEM) using a JEOL JSM 6390 electron microscope (Japan) equipped with an ultra-high resolution scanning system. (ASID-3D), under the conditions of secondary electronic image (SEI), and backscattered electrons (BEI).
• SEM scanning electron microscopy
• ASID-3D JEOL JSM 6390 electron microscope
• SEI secondary electronic image
• BEI backscattered electrons
• the electron microscope was equipped with an Oxford Instruments INCA x-sight energy dispersing spectrometer, which allows X-ray analyzes by EDX microprobe of the samples studied at a fixed point.
• nd indicates an element present but of quantity not determined
• FIG. 2 shows the micrographs obtained by SEM for the test specimens treated with the compositions applied by the method according to the invention C1 (in a /), C2 (in b /), C3 (in c /) and C4 (in d /).
• test tube treated with composition C1 (a /) is characterized by a dense surface layer with a symmetrically ordered spheroidal structure. Integral analysis from a "large" surface established the presence of zirconium, fluorine and molybdenum.
• composition C2 (b /) is covered with a dense surface layer. It also contains uniform spheroidal agglomerates containing in particular zirconium, fluorine, manganese and molybdenum.
• test tube treated with composition C3 (c /) is also covered with a dense layer of spheroidal agglomerates of two orders of different size, and of different chemical composition.
• the integral EDX analysis of a "large" surface has notably established the presence of zirconium, fluorine and molybdenum.
• the surface morphology is also a dense surface layer containing spheroidal agglomerates, and containing in particular zirconium, fluorine, manganese and molybdenum.
• Laminated test pieces of aluminum alloy AA2024, of dimensions 150 ⁇ 80 ⁇ 3 mm were treated by the process in accordance with the present invention described in example 1 above, but with the aqueous composition according to the following invention: - K 2 ZrF 6 12 g / l
• the pH of this composition is 5.82 (measured at 19.9 ° C).
• the treatment conditions with this composition are as follows: 19 ° C, 15 min.
• test pieces are marked, according to an X pattern, in accordance with standard ISO 17872, by means of a Van Laar point in tungsten carbonate.
• the marks are made in depth, so as to completely penetrate the surface layer, until reaching the basic metal alloy constituting the test piece.
• FIG. 4 shows, in a /, an analysis micrograph by scanning electron microscopy of a marked area.
• marked test tubes are also produced after anodization and clogging treatment using an aqueous composition containing only K 2 ZrF6 at a concentration of 12 g / l.
• the specimens thus marked are subjected to a salt spray exposure test for 816 h, at a temperature between 15 and 25 ° C, according to the conditions in accordance with standard NF EN ISO 9227.

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