EP4256105A1

EP4256105A1 - Process for protecting an aluminum alloy part

Info

Publication number: EP4256105A1
Application number: EP21830452.5A
Authority: EP
Inventors: Mathieu LEROY; Marie SAVOYE; Coralie CHEVALLIER; Etienne NEMETH
Original assignee: Safran Electronics and Defense SAS
Current assignee: Safran Electronics and Defense SAS
Priority date: 2020-12-03
Filing date: 2021-11-25
Publication date: 2023-10-11
Also published as: WO2022117935A1; US20240009700A1; FR3117131A1; IL303282A; FR3117131B1; CN116583625A

Abstract

A process (100) for protecting a part comprising an aluminum-based alloy, the process comprising depositing (102) a primer paint layer by anaphoresis over the entire part, polymerizing (104) the primer paint layer in order to form a non-conductive polymerized primer paint layer, laser pickling (106), by means of a laser beam, an area of the non-conductive polymerized primer paint layer in order to form an unpainted area, trivalent chromium chemical conversion (108) of the unpainted area in order to form a conductive protective layer and drying (110) the part, depositing (112) a finishing paint layer on at least a portion of the non-conductive polymerized primer paint layer, and polymerizing (114) the finishing paint layer.

Description

METHOD FOR PROTECTING AN ALUMINUM-BASED ALLOY PART

Technical area

This presentation relates to the protection, for example against corrosion, of a part comprising an aluminum-based alloy.

Prior technique

[0002] 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.

[0004] Furthermore, in the method used, 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 carried out manually, for example by applying a protective adhesive to the areas that you want to keep free of paint. [0005] However, pursuant to the REACH regulation (English acronym for “Registration, Evaluation, Authorization and Restriction of Chemicals”), the use of hexavalent chromium has been prohibited.

[0006]There is therefore a need to develop new processes making it possible to dispense with the use of chromium hexavent and also to simplify the stages of the process and/or to reduce the production costs while improving the reliability of the process.

Disclosure of Invention

[0007] The present presentation aims to remedy these drawbacks at least in part.

This presentation relates to a method for protecting a part comprising an aluminum-based alloy, the method comprising the following steps:

- application of a coat of primary paint by anaphoresis over the entire part;

- Polymerization of the primary paint layer to form a non-conductive polymerized primary 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 of the part;

- depositing a coat of finishing paint on at least part of the non-conductive polymerized primer coat;

- polymerization of the finishing coat of paint.

[0009] The process for protecting aluminum-based alloy parts makes it possible to obtain a treated part which is effectively protected in particular from corrosion by a coating comprising conductive zones (zones having undergone the chemical conversion - conductive protective layer ) and non-conductive areas (areas bearing the non-conductive polymerized primer coat). In particular, the part 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 and 144 hours, respectively for wrought and foundry alloys, according to the requirements of standard NF EN ISO 9227:2017; on the areas protected by the non-conductive polymerized primer coat and/or the finish paint coat after polymerization, the part exhibits acceptable behavior after more than 3000 hours of exposure to neutral salt spray, according to the requirements of the standard EN ISO 9227:2017. It is understood that the non-conductive polymerized primary paint layer does not undergo the 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 primary paint layer does not pollute the chemical conversion bath. Thus, the chemical conversion step to trivalent chromium only takes place on the unpainted areas, that is to say the areas not protected against corrosion by the non-conductive polymerized primer paint, which were previously stripped during of the laser etching step. It is understood that the non-conductive polymerized primary paint layer is a non-conductive protective layer.

[0010] The areas undergoing the chemical conversion being stripped by laser stripping, the manual step of applying resists is no longer required for the application of the non-conductive polymerized primer paint.

[0011] Laser stripping makes it possible to expose the part for specific areas where it is desired to have conductive parts of the protection. It is understood that the number of unpainted areas is not limited to one. During the laser stripping step, the non-conductive polymerized primary paint layer is removed only in the areas where electrical continuity between the part and external elements is desired. In these unpainted areas, the part is therefore bare again.

[0012] The step of chemical conversion to trivalent chromium is known per se. Typically, the conditions of implementation are provided with the technical sheets by the manufacturers of the chemical conversion baths.

[0013] By way of non-limiting example, the chromating bath can be a bath marketed under the SurTec650® or Lanthane 613.3® brand.

[0014] After immersion in a chemical conversion and/or anaphoresis bath, the part is rinsed with demineralised 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 (degree 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.

[0016] The finishing coat of paint is for example applied to areas of the part to improve the fluid and UV resistance of the covered areas.

[0017] By way of non-limiting example, the finishing paint can be a paint based on polyurethane and/or acrylic (example: Interthane 870/990 from the International supplier).

[0018] By way of non-limiting example, the finishing coat of paint can be applied by spraying using a pneumatic gun.

[0019] By way of non-limiting example,

[0020] In some embodiments, after laser stripping, the unpainted area may be cleaned.

[0021] 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.

[0022] In certain embodiments, the cleaning of the unpainted area can be carried out by mechanical brushing.

[0023] In some embodiments, the cleaning of the unpainted area may be assisted by ultrasound.

[0024] In certain embodiments, before the chemical conversion, the polymerized non-conductive primer paint layer and the unpainted area can be degreased with a solvent and/or an alkaline solution.

[0025] This step makes it possible to degrease the part when the non-conductive polymerized primer paint layer and/or the unpainted zone show dirt of the “fingerprint” type which may result from successive manipulations of the part during the preceding steps.

It is understood that the degreasing step is not carried out using an acid solution.

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 primary 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 p.m.

[0030] In certain embodiments, 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.

[0031] In some embodiments, a profile of the laser beam may be Gaussian-shaped or flat-topped.

[0032] A flat-top laser beam profile is also called a "Top Hat".

In some embodiments, 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.

In some embodiments, 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.

[0035] In certain embodiments, the laser etching can be carried out with a laser beam recovery rate greater than or equal to [0036] 20% and less than or equal to 80%.

It is understood that 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.

By way of non-limiting example, the recovery rate may be equal to 50% in both directions.

Brief description of the drawings

Other characteristics and advantages of the object of this presentation will emerge from the following description of embodiments, given by way of non-limiting examples, with reference to the appended figures.

[0040] [Fig. 1] Figure 1 is a flowchart representing the steps of a method of protecting a part comprising an aluminum-based alloy. [0041] [Fig. 2] Figure 2 a partial schematic view in section and in perspective of a part with a layer of non-conductive polymerized primer paint.

[0042] [Fig. 3] Figure 3 is a partial schematic view in section and in perspective of the part of Figure 2 after laser etching.

[0043] [Fig. 4] Figure 4 is a partial schematic view in section and in perspective of the part of Figure 3 after chemical conversion and drying.

[0044] [Fig. 5] Figure 5 is a partial schematic view in section and in perspective of the part of Figure 4 after deposition of the finishing paint layer.

In all of the figures, the elements in common are identified by identical reference numerals.

detailed description

[0046] Figure 1 shows a method 100 of protection, in particular against corrosion, of a part 12 comprising an aluminum-based alloy.

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 polymerization step 104 of the primer paint layer to obtain a non-conductive polymerized primer paint layer 14 over the entire part 12, as shown in Figure 2.

Note that Figure 2 is a schematic view in partial section of an element 10. It is therefore understood that the part 12 is completely covered by the non-conductive polymerized primary paint layer 14. A partial view is shown in section to see part 12 and the non-conductive polymerized primer coat 14.

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 an anode and a counter-electrode, is deposited on part 12. Once the deposit has reached the thickness desired, the deposit is polymerized at a temperature making it possible to fix the paint on the part 12 and form the non-conductive polymerized primary paint layer 14. By way of non-limiting example, mention may be made of the Aerocron 2200 electrodeposited paint system.

When part 12 is completely coated with the non-conductive polymerized primary paint layer 14, part 12 is protected in particular against corrosion. However, this protective layer is non-conductive.

The method 100 includes a laser stripping step 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 Figure 3. understands that in the unpainted area 16, part 12 is exposed.

The 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 profile of the laser beam can be Gaussian or flat-topped.

As shown in Figure 3, the part 12, the non-conductive polymerized primary paint layer 14 has been removed in one area, has an unpainted area 16. It is understood that the number of unpainted areas 16 n ' 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 primary paint layer 14.

The method 100 includes a step 108 of chemical conversion to trivalent chromium of the unpainted area 16 to form a conductive protective layer 18, as shown in Figure 4.

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 does not takes place only on the unpainted areas 16 which have been 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.

The method 100 includes 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 (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 includes a step 112 of depositing a layer of finishing paint on at least a portion of the non-conductive polymerized primary paint layer.

The method 100 includes a step 114 of polymerization of the finish paint layer to form a layer of polymerized finish paint 20 on the layer of non-conductive polymerized primer paint 18, as shown schematically in Figure 5.

The polymerized finishing paint layer 20 may not cover all of the non-conductive polymerized primer paint layer 18, as shown schematically in Figure 5.

The method 100 can also include a cleaning step 116 of the unpainted area 16 after the laser stripping step 106.

[0063] When the unpainted area or areas 16 are covered with a light dusting 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 of the laser etching step 106.

The cleaning 116 of the unpainted area 16 can be carried out by mechanical brushing.

The cleaning 116 of the unpainted area 16 can be assisted by ultrasound.

The method 100 may also include a degreasing step 118 of the non-conductive polymerized primary paint layer 14 and of the unpainted area 16 after the laser stripping step 106.

The degreasing step 118 may or may not be carried out 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.

This step makes it possible to degrease the part when the layer of non-conductive polymerized primer paint 14 and/or the unpainted zone 16 show dirt of the "fingerprint" type which may result from successive manipulations of the part during previous steps.

It is understood that the degreasing step 118 is not carried out using an acid solution.

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

By way of non-limiting example, the alkaline solution may be a solution marketed under the name Sococlean A3432.

Although this presentation has been described with reference to a specific embodiment, it is obvious that various modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. Further, individual features of the various embodiments discussed may be combined in additional embodiments. Accordingly, the description and the drawings should be considered in an illustrative rather than restrictive sense.

Claims

[Claim 1] Method (100) for protecting a part (12) comprising an aluminum-based alloy, the method (100) comprising the following steps:

- Deposition (102) of a layer of primary paint by anaphoresis over the entire part;

- polymerization (104) of the primary paint layer to form a non-conductive polymerized primary paint layer (14);

- laser stripping (106) by means of a laser beam of an area of the polymerized non-conductive primer 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 layer of finishing paint on at least part of the layer of non-conductive polymerized primer paint (14);

- Polymerization (114) of the finishing coat of paint.

[Claim 2] A method (100) according to claim 1, wherein after the laser etching (106), the unpainted area (16) is cleaned (116).

[Claim 3] A method (100) according to claim 2, wherein the cleaning (116) of the unpainted area (16) is accomplished by mechanical brushing.

[Claim 4] A method (100) according to claim 2, wherein the cleaning (116) of the unpainted area (16) is assisted by ultrasound.

[Claim 5] A method (100) according to any one of claims 1 to 4, wherein prior to the chemical conversion (108), the non-conductive polymerized primer coat (14) and the unpainted area (16) are degreased (118) with a solvent and/or an alkaline solution.

[Claim 6] Method (100) according to any one of Claims 1 to 5, in which the layer of polymerized non-conductive primer paint (14) has 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.

[Claim 7] Method (100) according to any one of claims 1 to 6, in which the laser etching (106) is carried out by means of a YAG laser of wavelength 1064 nm at a frequency comprised between 10 and 200kHz.

[Claim 8] A method (100) according to any of claims 1 to 7, wherein the profile of the laser beam is Gaussian or flat-topped.

[Claim 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/cm ² and the laser etching comprises four passes. [Claim 10] Method (100) according to any one of claims 1 to 9, in which the laser stripping (100) is carried out with a recovery rate of the laser beam greater than or equal to 20% and less than or equal to 80% .