Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface 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
  • 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
  • C23C22/73—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 characterised by the process
• • 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
  • 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
  • C25D11/18—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
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D13/00—Electrophoretic coating characterised by the process
  • C25D13/22—Servicing or operating apparatus or multistep processes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
• • 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

• This presentation relates to the protection, for example against corrosion, of a part comprising an aluminum-based alloy containing copper, in particular more than 0.5% by mass of copper.
• Aluminum-based alloys have the advantage of being light. However, they can be susceptible to corrosion. Also, it is known to protect parts made from aluminum-based alloys against corrosion by carrying out, for example, a chemical conversion of the surface of the part.
• This chemical conversion treatment was generally carried out by bringing the part into contact with a bath containing hexavalent chromium (or chromium VI or Cr VI).
• the bath can be made from a solution such as, for example, the solution commonly designated by the registered trademark Alodine® 1200S from Henkel.
• This chemical conversion treatment is a chromating treatment of the aluminum-based alloy during which the alloy is converted at the surface in order to precipitate therein in particular aluminum oxyhydroxides and aluminum chromates.
• This treatment makes it possible to produce a coating on the surface of the part which increases the resistance to corrosion of the part made of an aluminum-based alloy. Furthermore, this coating makes it possible to retain electrical conductivity of the coated zone and to allow easy and good quality adhesion of organic paints which are generally also based on hexavalent chromium.
• the chemical conversion is carried out over the entire part.
• a paint is then applied but in order to preserve areas of electrical continuity on the part, each of these areas is covered with a resist.
• This operation is usually performed manually, for example by applying a protective adhesive to the areas that you want to keep free of paint.
• Chromating bath solutions have been developed from trivalent chromium.
• the chromating treatment does not make it possible to guarantee sufficient corrosion resistance.
• This presentation relates to a process for protecting a part comprising an aluminum-based alloy whose copper content is greater than or equal to 0.5% by mass, the process comprising the following steps:
• the process for protecting aluminum-based alloy parts containing at least 0.5% by mass of copper makes it possible to obtain a treated part which is effectively protected in particular from corrosion by a coating comprising conductive zones ( areas having undergone chemical conversion - conductive protective layer) and non-conductive areas (areas bearing the non-conductive protective layer).
• the part then has, on the areas protected by the conductive protective layer, less than five pitting per dm 2 (square decimeter) after exposure to neutral salt spray for 168 hours, in accordance with the requirements of standard NF EN ISO 9227:2017 . It is understood that the non-conductive protective layer does not undergo the chemical conversion.
• the non-conductive protective layer is not altered or modified by the chemical conversion step. And, conversely, the non-conductive protective layer does not pollute the chemical conversion bath.
• the step of chemical conversion to trivalent chromium takes place only on the unprotected zones which have been previously pickled during the laser pickling step.
• the 2000 Series and part of the 7000 Series of aluminum-based alloys have a copper content greater than or equal to 0.5% by mass.
• the trivalent chromium chemical conversion step is known per se. Typically, the conditions of implementation are provided with the technical sheets by the manufacturers of the chemical conversion baths.
• the chromating bath may be a bath marketed under the SurTec650® or Lanthane 613.3® brand.
• the part After immersion in a chemical conversion bath, the part is rinsed with demineralised water and dried.
• demineralised water By way of non-limiting example, it can it is a rinsing by immersion followed by a rinsing by spraying with demineralised water.
• the drying step can be carried out at ambient temperature under compressed air and/or in an oven at a temperature less than or equal to 60° C. (degrees Celsius). It is understood that compressed air can be used at room temperature and then put the part in a study at a temperature less than or equal to 60°C until the part is dry.
• the surface roughness Ra is less than or equal to 1.7 ⁇ m, preferably less than or equal to 1.6 ⁇ m.
• the unprotected area may be cleaned.
• This step makes it possible to remove residues, for example in the form of powder, which may have been formed during the laser etching step.
• the cleaning of the unprotected zone can be carried out by mechanical brushing.
• the cleaning of the unprotected zone can be assisted by ultrasound.
• the non-conductive protective layer and the unprotected zone can be degreased with a solvent and/or an alkaline solution.
• This step makes it possible to degrease the part when the non-conductive protective layer and/or the unprotected zone show dirt of the “fingerprint” type which may result from successive manipulations of the part during the preceding steps.
• the degreasing step is not carried out using an acid solution.
• the solvent may be ethanol or methyl ethyl ketone (butanone-2, also called MEK in accordance with the acronym in English for Methyl Ethyl Ketone).
• the alkaline solution may be a solution marketed under the name Sococlean A3432.
• the laser stripping can be carried out by means of a YAG laser with a wavelength of 1064 nm at a frequency comprised between 10 and 200 kHz.
• a profile of the laser beam may be Gaussian-shaped or flat-topped.
• a flat-top laser beam profile is also called a "Top Hat”.
• the non-conductive protective layer can be deposited by anodic oxidation.
• the laser beam may have a fluence greater than or equal to 4 J/cm 2 .
• the laser beam may have a fluence less than or equal to 65 J/cm 2 , preferably less than or equal to 56 J/cm 2 .
• the non-conductive protective layer is deposited by anaphoresis.
• the laser beam may have a fluence greater than or equal to 4 J/cm 2 and the laser etching may comprise one to four passes.
• the laser beam may have a fluence less than or equal to 56 J/cm 2 and the laser etching may comprise one to four passes.
• the laser etching can be carried out with a laser beam recovery rate greater than or equal to 20% and less than or equal to 80%.
• the recovery rate can be in one or both directions of movement of the laser beam.
• the values in the two directions can be different from each other.
• the recovery rate may be equal to 50% in both directions.
• Figure 1 is a flowchart representing the steps of a method of protecting a part comprising an aluminum-based alloy.
• Figure 2 a partial schematic view in section and in perspective of a part with a non-conductive protective layer.
• Figure 3 is a partial schematic view in section and in perspective of the part of Figure 2 after laser etching.
• Figure 4 is a partial schematic view in section and in perspective of the part of Figure 3 after chemical conversion and drying.
• Figure 5 is a summary of micrographs of an unprotected area after laser stripping with the laser.
• Figure 1 shows a method 100 of protection, in particular against corrosion, of a part 12 comprising an aluminum-based alloy whose copper content is greater than or equal to 0.5% by mass.
• the method 100 includes a first step 102 of depositing a non-conductive protective layer 14 over the entire part 12, as shown in Figure 2.
• Figure 2 is a schematic partial sectional view of an element 10. It is therefore understood that the part 12 is completely covered by the non-conductive protective layer 14. A partial sectional view is shown in order to to see part 12 and the non-conductive protective layer 14.
• the deposition step 102 of the protective layer 14 can be carried out by anodic oxidation or by anaphoresis.
• Anodic oxidation is a process which makes it possible to form a porous layer of oxide on the outer surface of part 12 by immersing part 12 in an acid bath and applying an electric voltage between part 12 serving as anode and a counter-electrode.
• the acid bath can be a sulfuric acid bath.
• the step of depositing 102 the protective layer also includes the clogging of the porosity of the porous oxide layer by immersion in an impregnation and sealing bath to obtain the non-conductive protective layer 14. This process is a conventional process.
• Anaphoresis is a method for forming the non-conductive protective layer 14 by immersing the part 12 in an electrically charged paint bath, and which, under the effect of an electrical voltage applied between the part serving anode and a counter-electrode, is deposited on part 12. Once the deposit has reached the desired thickness, the deposit is polymerized at a temperature making it possible to fix the paint on part 12 and form the protective layer not driver 14.
• the method 100 includes a step 104 of laser etching by means of a laser beam of an area of the non-conductive protective layer 14 to form an unprotected area 16, as shown in Figure 3. It is understood that in the unprotected zone 16, the part 12 is exposed.
• the laser stripping 104 can be carried out by means of a YAG laser with a wavelength of 1064 nm at a frequency of between 10 and 200 kHz.
• the profile of the laser beam can be Gaussian or flat-topped.
• the part 12, whose non-conductive protective layer 14 has been removed in one area has an unprotected area 16. It is understood that the number of unprotected areas 16 is not limited to one.
• Figure 3 being a schematic figure, the unprotected area 16 is shown as having the shape of a square. It is understood that this shape is not limiting and that the unprotected zone 16 can have any shape.
• the shape of the unprotected area 16 is defined by the passage of the laser beam over the non-conductive protective layer 14.
• the method 100 includes a step 106 of chemical conversion to trivalent chromium of the unprotected area 16 to form a conductive protective layer 18, as shown in Figure 4.
• the non-conductive protective layer 14 is not altered or modified by the step of chemical conversion 106.
• the chemical conversion step 106 to trivalent chromium only takes place on the unprotected areas 16 which have been previously etched during the laser etching step 104 and the formation of the conductive protective layer 18 forms only at the location of unprotected areas 16.
• the method 100 includes a drying step 108.
• the drying step 108 can be carried out at room temperature under compressed air and/or in an oven at a temperature less than or equal to 60 °C (degree Celsius). It is understood that compressed air can be used at room temperature and then put part 12 in a study at a temperature less than or equal to 60°C until part 12 is dry.
• the method 100 may also include a cleaning step 110 of the unprotected area 16 after the laser stripping step 104.
• unprotected area or areas 16 are covered with a light dusting due to laser etching, it is advantageous to clean the unprotected areas 16 to remove these residues, for example in the form of powder, which may have been formed during of the laser etching step 104.
• the cleaning 110 of the unprotected area 16 can be carried out by mechanical brushing.
• the cleaning 110 of the unprotected area 16 can be assisted by ultrasound.
• the method 100 may also include a degreasing step 112 of the non-conductive protective layer 14 and of the unprotected area 16 after the laser etching step 104.
• the degreasing step 112 may or may not be carried out after the cleaning step 110.
• the part 12 and the non-conductive protective layer 14 can be degreased 112 with a solvent and/or an alkaline solution.
• This step makes it possible to degrease the part when the non-conductive protective layer 14 and/or the unprotected zone 16 show dirt of the "fingerprint" type which may result from successive manipulations of the part during the previous steps. . It is understood that the degreasing step 112 is not carried out using an acid solution.
• the solvent can be ethanol or methyl ethyl ketone (butanone-2, also called MEK in accordance with the acronym in English for Methyl Ethyl Ketone
• the alkaline solution may be a solution marketed under the name Sococlean A3432.
• An alloy based on aluminum 2024 (machined T351) is used.
• the mass composition of this alloy is 0.046% silicon (Si), 0.077% iron (Fe), 4.4389% copper (Cu), 0.621% manganese (Mn), 1.416% magnesium (Mg), 0.002 % Chromium (Cr), 0.039% Zinc (Zn), 0.0310% Titanium (Ti), 0.0007% Boron (B), 0.0013% Zirconium (Zr), 0.0027% lead (Pb), 0.0044 nickel (Ni), 0.055% tin (Sn), 0.0076% vanadium (V), the remainder consisting of aluminum and any impurities.
• An alloy based on aluminum 7175 (machined T351) is used.
• the mass composition of this alloy is 0.041% silicon (Si), 0.083% iron (Fe), 1.773% copper (Cu), 0.001% manganese (Mn), 2.490% magnesium (Mg), 0.197% chromium (Cr), 5.784% zinc (Zn), 0.0384% titanium (Ti), 0.0009% boron (B), 0.0037% zirconium (Zr), 0.0016% lead ( Pb), 0.0054 nickel (Ni), 0.0024% tin (Sn), 0.0076% vanadium (V), the remainder consisting of aluminum and any impurities.
• Test specimens having dimensions of 150 mm ⁇ 100 mm ⁇ 6 mm were produced in each alloy (Example 1 and Example 2).
• a non-conductive protective layer 14 was deposited on all the specimens by anodic oxidation in a bath of sulfuric acid and sealing of the porosity by immersion in an impregnation/sealing bath.
• the layer of non-conductive protection 14 can have a thickness of between 4 and 20 ⁇ m.
• the laser beam is a YAG laser with a wavelength of 1064 nm at a frequency between 1 and 120 kHz, of the TruMark 6130 type. that is to say that the base alloy of each specimen was exposed on an area of one square decimetre.
• the coverage rate is defined by considering the diameter of the laser spot and the coverage rate in one direction is defined as being equal to (1 - L/d) where L is the distance between the center of two adjacent laser spots in the given direction and the diameter of the laser spot.
• L is the distance between the center of two adjacent laser spots in the given direction and the diameter of the laser spot.
• an overlap rate of 50% is representative of a distance between the center of two spots equal to half the diameter of the laser spot.
• Tx is the overlap rate in the x direction and Ty is the overlap rate in the y direction, the y direction being perpendicular to the x direction. In these examples, Tx and Ty are equal. Tx might be different from Ty.
• the surface roughness Ra (arithmetic mean deviation) was measured on the unprotected areas.
• the surface roughness Ra is equal to 0.8 ⁇ m for tests 1 and 3, 0.7 ⁇ m for tests 2 and 4 and 1.0 ⁇ m for test 5.
• the surface roughness Ra is equal to 1.2 ⁇ m for test 1, 0.6 ⁇ m for tests 2 and 3, 0.55 ⁇ m for test 4 and 0.8 ⁇ m for test 5
• the surface roughness Ra (arithmetic mean deviation) is measured according to the requirements of the ISO 25178 standard with an optical roughness meter.
• Figure 5 shows micrographs at the same magnification of the unprotected area 16 of test specimens from the tests carried out with the laser II.
• the specimens are cleaned, for example by brushing.
• the brushing step makes it possible to improve the resistance to corrosion after chemical conversion.
• the specimens are degreased with a cloth soaked in methylethyl ketone.
• the bath is a bath of SurTec 650 having a theoretical concentration of 20% by volume of Surtec 650 in distilled water.
• the theoretical pH of the bath is between 3.7 and 4 and the theoretical temperature of the bath is 37.5°C.
• the test specimens undergo manual agitation.
• the specimens are rinsed by immersion in the bath for 1 minute in order to wet the surface in order to modify the surface tension of the specimen.
• the specimen is then rinsed with water before the actual chromating step.
• the specimens are then immersed for 4 minutes in the bath to carry out the step of chemical conversion to trivalent chromium of the unprotected zones 16 and to form a conductive protective layer 18.
• the test specimens are then rinsed by immersion in water for 1 minute and by sprinkling with water for 1 minute.
• the surface roughness Ra (arithmetic mean deviation) and the surface roughness Rz (maximum height) were measured on the conductive protection zones 18.
• the surface roughness Ra (arithmetic mean deviation) and the surface roughness Rz (maximum height) are measured according to the requirements of the ISO 25178 standard with an optical roughness meter. The results are shown in Table 2.
• the salt spray test is carried out according to the requirements of the ISO 9227:2017 standard. The test conditions are listed below. The test is carried out in an ERICHSEN salt spray corrosion test chamber of reference CORROTHERM 610e 1000L.
• the sodium chloride salt (NaCI) used is 99% pure. Distilled water has an electrical conductivity of less than 10 pS/cm (micro Siemens per centimeter).
• the saline solution has a concentration of 50 g/L (gram per litre), the temperature in the chamber throughout the test is between 34.6°C and 35.3°C and the temperature of the humidifier is 50°C.
• the spray pressure is between 0.93 and 0.96 bar
• the average recovery rate of the solution in the collectors is between 1.26 and 1.36 mL/h (milliliter per hour)
• the density of the solution collected in the collectors is between 1.031 and 1.035
• the pH of the solution collected in the collectors is 6.5.
• the duration of the salt spray test is 168 hours maximum with a minimum of 72 hours.
• Test specimens are removed from the enclosure after 72 hours and 168 hours and are observed visually to identify the defects. All the specimens tested show, on the areas protected by the conductive protective layer, less than five pitting per dm 2 after exposure to neutral salt spray for 168 hours, in accordance with the requirements of standard NF EN ISO 9227:2017.

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