Process for protecting an aluminum alloy part
Patent Information
- Authority / Receiving Office
- IL · IL
- Patent Type
- Patents
- Current Assignee / Owner
- SAFRAN ELECTRONICS & DEFENSE (FR)
- Filing Date
- 2021-11-25
- Publication Date
- 2026-07-01
AI Technical Summary
Aluminum-based alloys are susceptible to corrosion and existing corrosion protection methods using hexavalent chromium are prohibited by regulations, necessitating a new process that eliminates chromium hexavalent use, simplifies stages, reduces costs, and improves reliability.
A method involving anaphoresis for applying a non-conductive polymerized primer coat, laser stripping to expose specific areas, chemical conversion to trivalent chromium for conductive zones, drying, and applying a finishing paint, which eliminates the need for manual resist application and allows for effective corrosion protection while maintaining electrical continuity.
The method provides excellent corrosion resistance, with conductive zones showing less than five pits per dm² after 168 hours and non-conductive areas lasting over 3000 hours in neutral salt spray, while avoiding the use of hexavalent chromium and simplifying the process.
Smart Images
Figure 00000017_0000 
Figure 00000017_0001 
Figure 00000017_0002
Abstract
Description
METHOD FOR PROTECTING AN ALUMINUM-BASED ALLOY PART Technical field
[0001] This disclosure relates to the protection, for example against corrosion, of a part comprising an aluminum-based alloy. Prior art
[0002] Aluminum-based alloys have the advantage of being lightweight. However, they can be susceptible to corrosion. Therefore, it is known to protect parts made from aluminum-based alloys against corrosion by, for example, chemically converting the part's surface.
[0003] This chemical conversion treatment was generally carried out by placing the part in contact with a bath containing hexavalent chromium (or chromium VI or Cr VI). The bath can be produced from a solution such as 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 on the surface in order to precipitate aluminum oxyhydroxides and aluminum chromates in particular. This treatment produces a coating on the surface of the part that increases the corrosion resistance of the part made of aluminum-based alloy. Furthermore, this coating maintains the electrical conductivity of the coated area and allows easy and good quality adhesion of organic paints that are generally also based on hexavalent chromium.
[0004] Furthermore, in the process used, chemical conversion is carried out on the entire part. 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 generally carried out manually, for example by applying a protective adhesive to the areas that one wishes to keep free of paint.
[0005] However, under the REACH regulation (English acronym for "Registration, Evaluation, Authorisation and Restriction of Chemicals"), the use of hexavalent chromium has been banned.
[0006] There is therefore a need to develop new processes that eliminate the use of hexavent chrome and also simplify the process steps and / or reduce production costs while improving process reliability. Statement of the invention
[0007] This presentation aims to remedy at least part of these drawbacks.
[0008] This disclosure relates to a method of protecting a part comprising an aluminum-based alloy, the method comprising the following steps: - application of a layer of primer paint by anaphoresis over the entire part; - polymerization of the primer paint layer to form a non-conductive polymerized primer paint layer; - laser stripping by means of a laser beam of an area of the non-conductive polymerized primary paint layer to form an unpainted area; - chemical conversion to trivalent chromium of the unpainted area to form a conductive protective layer; - drying the room; - depositing a layer of finishing paint on at least part of the layer of non-conductive polymerized primary paint; - polymerization of the finishing paint layer.
[0009] The process for protecting aluminum-based alloy parts results in a treated part that is effectively protected, in particular, from corrosion by a coating comprising conductive areas (areas that have undergone chemical conversion - conductive protective layer) and non-conductive areas (areas bearing the non-conductive polymerized primer paint layer). In particular, the part has, on the areas protected by the conductive protective layer, less than five pits per dm 2 (square decimeter) after 168 and 144 hours of exposure to neutral salt spray, respectively for wrought and cast alloys, according to the requirements of standard NF EN ISO 9227:2017; on the areas protected by the non-conductive polymerized primer paint layer and / or the topcoat paint layer after polymerization, the part exhibits acceptable resistance after more than 3000 hours of exposure to neutral salt spray, according to the requirements of standard NF EN ISO 9227:2017. It is understood that the non-conductive polymerized primer paint layer does not undergo chemical conversion. The non-conductive polymerized primer paint layer is not altered or modified by the chemical conversion step. And, conversely, the non-conductive polymerized primer paint layer does not pollute the chemical conversion bath.Thus, the chemical conversion step to trivalent chromium only takes place on the unpainted areas, i.e. the areas not protected against corrosion by the non-conductive polymerized primer paint, which have been previously stripped during the laser stripping step. It is understood that the non-conductive polymerized primer paint layer is a non-conductive protective layer.
[0010] Since the areas undergoing chemical conversion are stripped by laser etching, the manual step of applying resists is no longer required for the application of the non-conductive polymerized primer paint.
[0011] Laser stripping allows the part to be exposed in specific areas where conductive parts of the protection are desired. It is understood that the number of unpainted areas is not limited to one. During the laser stripping step, the non-conductive polymerized primer paint layer is removed only in areas where electrical continuity between the part and external elements is desired. In these unpainted areas, the part is therefore exposed again.
[0012] The chemical conversion step to trivalent chromium is known per se. Typically, the implementation conditions are provided with the technical data sheets by the manufacturers of the chemical conversion baths.
[0013] By way of non-limiting example, the chromating bath may be a bath marketed under the brand name SurTec650® or Lanthane 613.3®.
[0014] After immersion in a chemical conversion and / or anaphoresis bath, the part is rinsed with demineralized water and dried.
[0015] By way of non-limiting example, the drying step 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 (degrees Celsius). It is understood that compressed air can be used at room temperature and then the part can be placed in a study at a temperature less than or equal to 60°C until the part dries.
[0016] The finishing coat of paint is, for example, applied to areas of the part to improve the resistance to fluids and UV rays of the covered areas.
[0017] By way of non-limiting example, the finishing paint may be a polyurethane and / or acrylic-based paint (example: Interthane 870 / 990 from the supplier International).
[0018] As a non-limiting example, the finishing coat of paint can be applied by projection using a pneumatic gun.
[0019] By way of non-limiting example,
[0020] In some embodiments, after laser etching, the unpainted area may be cleaned.
[0021] This step allows the removal of residues, for example in the form of powder, which may have formed during the laser stripping step.
[0022] In some embodiments, cleaning of the unpainted area may be accomplished by mechanical brushing.
[0023] In some embodiments, cleaning of the unpainted area may be ultrasonically assisted.
[0024] In some embodiments, prior to chemical conversion, the non-conductive cured primer paint layer and the unpainted area may be degreased with a solvent and / or an alkaline solution.
[0025] This step allows the part to be degreased when the non-conductive polymerized primary paint layer and / or the unpainted area show “fingerprint” type dirt which may be the result of successive handling of the part during the previous steps.
[0026] It is understood that the degreasing step is not carried out using an acid solution.
[0027] By way of non-limiting example, 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).
[0028] By way of non-limiting example, the alkaline solution may be a solution marketed under the name Sococlean A3432.
[0029] In some embodiments, the non-conductive polymerized primer paint layer may have a thickness greater than or equal to 10 μm, preferably greater than or equal to 15 μm and less than or equal to 40 μm, preferably less than or equal to 30 μm.
[0030] In some embodiments, the laser etching may be performed using a 1064 nm wavelength YAG laser at a frequency of between 10 and 200 kHz.
[0031] In some embodiments, a profile of the laser beam may be Gaussian or flat-topped.
[0032] A flat-topped laser beam profile is also called a "Top Hat" in English.
[0033] In some embodiments, the laser beam may have a fluence greater than or equal to 4 J / cm 2 and laser stripping can include one to four passes.
[0034] In some embodiments, the laser beam may have a fluence less than or equal to 56 J / cm 2 and laser stripping can include one to four passes.
[0035] In some embodiments, the laser stripping may be performed with a laser beam coverage rate greater than or equal to
[0036] 20% and less than or equal to 80%.
[0037] It is understood that the coverage rate can be in one or both directions of laser beam travel. The values in the two directions can be different from each other.
[0038] As a non-limiting example, the recovery rate may be equal to 50% in both directions. Brief description of the drawings
[0039] Other characteristics and advantages of the subject of the present disclosure will emerge from the following description of embodiments, given as non-limiting examples, with reference to the appended figures.
[0040] [Fig. 1] Figure 1 is a flowchart representing the steps of a method for protecting a part comprising an aluminum-based alloy.
[0041] [Fig. 2] Figure 2 is a partial schematic sectional and perspective view of a part with a non-conductive polymerized primer paint layer.
[0042] [Fig. 3] Figure 3 is a partial schematic sectional and perspective view of the part of Figure 2 after laser etching.
[0043] [Fig. 4] Figure 4 is a partial schematic sectional and perspective view of the part of Figure 3 after chemical conversion and drying.
[0044] [Fig. 5] Figure 5 is a partial schematic sectional and perspective view of the part of Figure 4 after the finishing coat of paint has been applied.
[0045] Throughout the figures, common elements are identified by identical numerical references. Detailed description
[0046] Figure 1 represents a method 100 for protection, in particular against corrosion, of a part 12 comprising an aluminum-based alloy.
[0047] The method 100 comprises a first step 102 of depositing a layer of primary paint by anaphoresis over the entire part 12. The step of depositing the layer of primary paint by anaphoresis is followed by a step 104 of polymerization of the layer of primary paint to obtain a layer of non-conductive polymerized primary paint 14 over the entire part 12, as shown in FIG. 2.
[0048] It will be noted that Figure 2 is a schematic view in partial section of an element 10. It is therefore understood that the part 12 is entirely covered by the layer of non-conductive polymerized primary paint 14. A partial view in section has been shown in order to see the part 12 and the layer of non-conductive polymerized primary paint 14.
[0049] The deposition step 102 of the protective layer 14 is carried out by anaphoresis.
[0050] Anaphoresis is a process for forming the non-conductive polymerized primary paint layer 14 by immersing the part 12 in a bath of electrically charged paint, and which, under the effect of an electrical voltage applied between the part serving as anode and a counter-electrode, is deposited on the part 12. Once the deposit has reached the thickness desired, the deposit is polymerized at a temperature allowing the paint to be fixed on the part 12 and the non-conductive polymerized primary paint layer 14 to be formed. By way of non-limiting example, the Aerocron 2200 electrodeposited paint system may be cited.
[0051] When the part 12 is entirely coated with the non-conductive polymerized primer paint layer 14, the part 12 is protected in particular against corrosion. However, this protective layer is non-conductive.
[0052] The method 100 comprises a step of laser stripping 106 using a laser beam of an area of the non-conductive polymerized primary paint layer 14 to form an unpainted area 16, as shown in FIG. 3. It is understood that in the unpainted area 16, the part 12 is exposed.
[0053] Laser stripping 106 can be carried out using a YAG laser with a wavelength of 1064 nm at a frequency of between 10 and 200 kHz.
[0054] The laser beam profile can be Gaussian or flat-topped.
[0055] As shown in Figure 3, the part 12, from which the non-conductive polymerized primer paint layer 14 has been removed in one area, has an unpainted area 16. It is understood that the number of unpainted areas 16 is not limited to one. Figure 3 being a schematic figure, the unpainted area 16 is shown as having the shape of a square. It is understood that this shape is not limiting and that the unpainted area 16 can have any shape. The shape of the unpainted area 16 is defined by the passage of the laser beam over the non-conductive polymerized primer paint layer 14.
[0056] The method 100 comprises a step of chemical conversion 108 to trivalent chromium of the unpainted area 16 to form a conductive protective layer 18, as shown in FIG. 4.
[0057] As shown schematically in Figure 4, the non-conductive polymerized primary paint layer 14 is not altered or modified by the chemical conversion step 108. Thus, the chemical conversion step 106 to trivalent chromium only takes place on the unpainted areas 16 which were previously stripped during the laser stripping step 106 and the formation of the conductive protective layer 18 is formed only at the location of the unpainted areas 16.
[0058] The method 100 comprises a drying step 110. By way of non-limiting example, the drying step 110 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 (degrees Celsius). It is understood that compressed air can be used at room temperature and then the part 12 can be placed in a study at a temperature less than or equal to 60°C until the part 12 is dried.
[0059] The method 100 comprises a step 112 of depositing a layer of finishing paint on at least a portion of the layer of non-conductive polymerized primary paint.
[0060] The method 100 comprises a step 114 of polymerizing the topcoat paint layer to form a polymerized topcoat paint layer 20 on the non-conductive polymerized primer paint layer 18, as shown schematically in FIG. 5.
[0061] The polymerized topcoat paint layer 20 may not cover the entire non-conductive polymerized primer paint layer 18, as schematically shown in FIG. 5.
[0062] The method 100 may also comprise a step 116 of cleaning the unpainted area 16 after the laser stripping step 106.
[0063] When the unpainted area(s) 16 are covered with a light powdering due to laser stripping, it is advantageous to clean the unpainted areas 16 to remove these residues, for example in the form of powder, which may have been formed during the laser stripping step 106.
[0064] Cleaning 116 of the unpainted area 16 can be carried out by mechanical brushing.
[0065] The cleaning 116 of the unpainted area 16 may be assisted by ultrasound.
[0066] The method 100 may also comprise a step 118 of degreasing the non-conductive polymerized primary paint layer 14 and the unpainted area 16 after the laser stripping step 106.
[0067] The degreasing step 118 may or may not be performed after the cleaning step 116.
[0068] Thus, before the chemical conversion 108, the part 12 and the non-conductive polymerized primary paint layer 14 can be degreased 118 with a solvent and / or an alkaline solution.
[0069] This step allows the part to be degreased when the non-conductive polymerized primary paint layer 14 and / or the unpainted area 16 have “fingerprint” type dirt which may result from successive handling of the part during the previous steps.
[0070] It is understood that the degreasing step 118 is not carried out using an acid solution.
[0071] By way of non-limiting example, 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
[0072] By way of non-limiting example, the alkaline solution may be a solution marketed under the name Sococlean A3432.
[0073] Although the present disclosure has been described with reference to a specific exemplary embodiment, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments recited may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.
Claims
DEMANDS
1. A method (100) for protecting a part (12) comprising an aluminum-based alloy, the method (100) comprising the following steps: - deposition (102) of a primer coat by anaphoresis over the entire piece; - polymerization (104) of the primer paint layer to form a non-conductive polymerized primer paint layer (14); - laser stripping (106) using a laser beam of an area of the non-conductive polymerized primary paint layer (14) to form an unpainted area (16); - chemical conversion (108) to trivalent chromium of the unpainted area (16) to form a conductive protective layer (18); - drying (110) of the part; - deposition (112) of a topcoat of paint on at least part of the non-conductive polymerized primer coat (14); - polymerization (114) of the topcoat paint layer.
2. Method (100) according to claim 1, wherein, after laser stripping (106), the unpainted area (16) is cleaned (116).
3. A method (100) according to claim 2, wherein the cleaning (116) of the unpainted area (16) is carried out by mechanical brushing.
4. A method (100) according to claim 2, wherein the cleaning (116) of the unpainted area (16) is assisted by ultrasound.
5. A method (100) according to any one of claims 1 to 4, wherein, prior to chemical conversion (108), the non-conductive polymerized primer paint layer (14) and the unpainted area (16) are degreased (118) with a solvent and / or an alkaline solution.
6. A method (100) according to any one of claims 1 to 5, wherein the non-conductive polymerized primer paint layer (14) has a thickness greater than or equal to 10 pm, preferably greater than or equal to 15 pm and less than or equal to 40 pm, preferably less than or equal to 30 pm.
7. Method (100) according to any one of claims 1 to 6, wherein the laser stripping (106) is carried out using a YAG laser with a wavelength of 1064 nm at a frequency between 10 and 200 kHz.
8. Method (100) according to any one of claims 1 to 7, wherein the laser beam profile is Gaussian in shape or flat-topped.
9. A method (100) according to any one of claims 1 to 8, wherein the laser beam has a fluence greater than or equal to 4 J / cm² 2and the laser stripping includes a four-pass process.
10. A method (100) according to any one of claims 1 to 9, wherein the laser stripping (100) is carried out with a laser beam recovery rate greater than or equal to 20% and less than or equal to 80%.