Method for detecting a chemical conversion or passivation layer

Abstract

The present invention relates to a method for detecting the possible presence of a chemical conversion layer on a part, comprising at least the following steps: A) a step of contacting at least a portion of the part's surface with an oxidizing composition; B) a step of detecting any persistent stain at the point of contact as defined in step A). ​​Figure for the abstract: None

Description

Title of the invention: Method for detecting a chemical conversion or passivation layer Technical field of the invention

[0001] The present invention relates to the detection of a surface treatment, in particular the possible presence of a chemical conversion or passivation layer on a part, for example in aluminium (and its alloys), in magnesium (and its alloys), in steel bearing a metallic coating (cadmium plating, zinc-nickel, ...), particularly in the aeronautical industry. Technical background

[0002] For years, numerous studies in both the aerospace and non-aerospace industries have been conducted on methods for detecting the conversion layer (trivalent chromium). This need arises from the fact that the chemical conversion layer is colorless and barely visible, or even invisible, to the naked eye, whereas the need to confirm its presence during production or during post-application quality control is paramount for manufacturers and their customers.

[0003] Research work to detect conversion to trivalent chromium has focused on the following techniques.

[0004] Colorimetry:

[0005] In the context of surface colorimetry, we are only interested in reflected radiation, generally assuming that the object is opaque.

[0006] The device used is, for example, the Alumeter AL 100, which is in the form of a tablet connected to a probe. It is supplied with a standard for calibrating the device before each series of measurements.

[0007] However, prior to testing, a suitable environment is required for the use of the device. This requires optimal ambient conditions of 21°C ± 4° and 40% to 70% relative humidity, among others.

[0008] In addition, surface preparation is necessary to ensure a clean surface before detection and this technique should not be used under direct lamplight or sunlight.

[0009] And in order to be able to detect the color, it is essential to have a similar surface finish. The results obtained demonstrate that this method is not always functional, depending on the geometry of the part and the environment.

[0010] X-ray fluorescence:

[0011] XRF spectrometry is an analytical technique for obtaining qualitative and quantitative elemental analyses. The sample is bombarded by photons emitted from an X-ray tube, electrons from the inner shells of atoms are ejected. This is the absorption phase of the primary radiation. The atoms, ionized by their "missing" electron, are in an unstable state. The inner shells of these atoms reorganize to move towards a more stable state. Electrons from the outermost shells fill the unsaturated inner shells; this is the emission phase (secondary X-ray beam emitted). This electronic relaxation releases energy in the form of a characteristic photon (called Ka, K[3]) for each atom and for each transition of each atom. These photons can be detected by a counter, which identifies the atom based on its energy.

[0012] The technique is functional by exploiting the peak areas of the spectrogram, as these are representative of the concentrations of the elements present. This integration is very well achieved through computer processing. Furthermore, no special surface preparation is required for this analysis.

[0013] However, a minimum cost of €30,000 is required to purchase such a device. Furthermore, the device may not necessarily be able to access all areas of a part to detect chromium or zirconium (making it difficult to implement in machining / processing facilities). In addition, this type of device requires specific certification (related to X-rays).

[0014] Detection of Chromium III with reagent droplets:

[0015] Commercial reagents use a principle of detecting elements on the surface of the layer. This method requires the combination of at least two solutions which, after a few minutes of contact with the surface, change color to indicate the presence of the chemical layer.

[0016] However, this reaction causes the destruction of the conversion layer.

[0017] In addition, the mixture is unstable if made early before use, which may require a surplus test to be carried out.

[0018] The use of this methodology will result in a high scrap rate unless the part concerned is taken back for a new surface treatment in retouching.

[0019] The present invention aims to overcome the drawbacks of the aforementioned methods.

[0020] In particular, an objective of the present invention is to provide a detection method that is both: - non-destructive to the conversion or passivation layer (therefore no rework is necessary); - inexpensive and simple (the detection of the invisible conversion or passivation layer can, in particular, be carried out, after a first step, with the naked eye); and - reliable (i.e., in particular, detection is possible regardless of the surface condition and / or the type of alloy). Summary of the invention

[0021] The present invention is specifically designed to meet these needs by providing a method for detecting the possible presence of a chemical conversion or passivation layer on a part, comprising at least the following steps:

[0022] A) a step of bringing at least part of the surface of the part into contact with an oxidizing composition;

[0023] B) a step of detecting any possible persistent stain at the point of contact as defined in step A).

[0024] Thus, in the process of the invention, the oxidizing composition reacts on the surface with the aluminum or aluminum alloy (raw aluminum) of the part, leaving in particular a persistent detectable trace, notably a colored or contrasting detectable trace in the absence of a conversion or passivation layer, but does not react in the presence of a chemical conversion or passivation layer, particularly on aluminum or aluminum alloy (conversion-treated aluminum (chromium-based with an oxidation state of +3, or chromium VI, for example using Alodine 1500)). This is therefore a non-destructive strategy for conversion-treated or passivated parts. Indeed, the oxidizing composition, in addition to not coloring the conversion or passivation layer, does not degrade the layer and its associated properties (primarily corrosion resistance and layer resistivity).

[0025] The invention also relates to a detection method as described above, comprising, in addition, steps for detecting the possible presence of a chemical conversion or passivation layer on a part, at least one step C) for detecting the possible presence of an electrolytic conversion layer on said part. Detailed description of the invention

[0026] An object of the invention relates to a method for detecting the possible presence of a chemical conversion or passivation layer on a part, comprising at least the following steps:

[0027] A) a step of bringing at least part of the surface of the part into contact with an oxidizing composition;

[0028] B) a step of detecting any possible persistent stain at the point of contact as defined in step A).

[0029] Step A) may optionally be followed, prior to step B), by a step in which the excess oxidizing composition is removed. This may, for example, be carried out using a dry or moistened absorbent medium, for example using a sponge or cloth.

[0030] The part can be obtained by any technique well known to a person skilled in the art, for example by a process comprising a step of forging, rolling, casting, additive manufacturing, etc.

[0031] The part is in particular based on aluminium or an aluminium alloy, for example an alloy used in aeronautics. The aluminum alloy can be selected from the 2000, 5000, 6000 and 7000 series, in particular selected from the group consisting of 2014, 2017, 2024, 2214, 2219, 2618, AU5NKZr, 7175, 5052, 5086, 6061, 6063, 7010, 7020, 7050, 7050 T7451, 7055, 7068, 7085, 7075, 7175 and 7475, the aluminum alloys selected from the group consisting of AS7G06, AS7G03, AS10G and AS9U3, in particular the aluminum alloys (so-called difficult) selected from the group consisting of 2618A, 2214 and AU5NKZr.

[0032] The part may also be based on magnesium or a magnesium alloy.

[0033] The part may also be made of steel with a metallic coating, which may in particular be passivated by a colorless conversion coating, especially one based on CrIII, such as cadmium plating, zinc-nickel plating, ...

[0034] This can be a steel with a cathodic deposit of one metal (Cadmium for example) or several metals (Zn-Ni for example), which can potentially then be passivated by a conversion.

[0035] The part can also be made of cadmium-plated steel, or of steel bearing a zinc-nickel-based coating.

[0036] By "chemical conversion or passivation layer" is meant a layer comprising trivalent chromium (chromium III) or chromium VI, and / or zirconium (in particular zirconium IV).

[0037] According to a particular embodiment, the layer is a chemical conversion or passivation layer comprising trivalent chromium (chromium III) or chromium VI, and / or zirconium (in particular zirconium IV), on aluminium and / or its alloys, magnesium and / or its alloys, or steel bearing a metallic coating (cadmium plating, zinc-nickel, ...).

[0038] According to a particular embodiment, the layer is a chemical conversion or passivation layer comprising trivalent chromium (chromium III), and / or zirconium (in particular zirconium IV), on aluminium and / or its alloys.

[0039] According to a particular embodiment, the layer is a chemical conversion or passivation layer comprising trivalent chromium (chromium III), on aluminium and / or its alloys, magnesium and / or its alloys, or steel bearing a metallic coating (cadmium plating, zinc-nickel, ...).

[0040] According to a particular embodiment, the layer is a chemical conversion or passivation layer comprising trivalent chromium (chromium III) and zirconium (in particular zirconium IV), on aluminium and / or its alloys, magnesium and / or its alloys, or steel bearing a metallic coating (cadmium plating, zinc-nickel, ...).

[0041] According to a particular embodiment, the layer is a chemical conversion or passivation layer comprising chromium VI, on aluminium and / or its alloys, magnesium and / or its alloys, or steel bearing a metallic coating (cadmium plating, zinc-nickel, ...).

[0042] According to a particular embodiment, the layer is a passivation layer comprising trivalent chromium (chromium III), on cadmium-plated steel.

[0043] The preparation of the chemical conversion layer to trivalent chromium or passivation is well known in itself.

[0044] Typically, the implementation conditions are provided with the technical data sheets by the manufacturers of the chemical conversion or passivation baths.

[0045] By way of non-limiting example, the chromating bath may be a bath marketed under the SurTec650 brand of SurTec or Lanthane 613.3 of Coventya.

[0046] By way of non-limiting example, the chemical conversion or passivation layer can be obtained on the part as follows: the bath is a SurTec 650 bath with 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 measured values ​​are as follows: concentration: 20.1%; pH: 3.9; temperature: 37.5°C in a 100 L (liter) tank. The part to be treated is manually agitated. After immersion in a chemical conversion or passivation bath, the part can be rinsed with demineralized water and dried. This could, for example, involve immersion rinsing followed by spray rinsing with demineralized water.

[0047] After carrying out the chemical conversion or passivation of the part in the chromating bath, a part is typically obtained having on at least one surface of the part a coating comprising chromium III, for example in the form of chromium oxide (Cr2O3) and / or chromium hydroxide (Cr(OH)3).

[0048] When the chromating bath contains zirconium, the coating includes zirconium, in particular in the form of zirconium oxide (ZrO2).

[0049] When the chromate bath includes chromium and also zirconium, the coating includes chromium III, for example in the form of chromium oxide (Cr2 O3) and / or chromium hydroxide (Cr(OH)3), and also zirconium, in particular in the form of zirconium oxide (ZrO2).

[0050] According to a particular embodiment, the chemical conversion or passivation layer is obtained by applying to the part a solution comprising a fluorinated compound, a corrosion-inhibiting metallic compound, said corrosion-inhibiting metallic compound being a trivalent chromium salt (chromium III).

[0051] Such a solution is described for example in patent FR2986806.

[0052] According to another particular embodiment, the chemical conversion layer or Passivation is achieved by applying the following to the part: - of a first solution comprising a fluorinated compound, a corrosion-inhibiting metallic compound, said corrosion-inhibiting metallic compound being a trivalent chromium salt (chromium III); - and optionally a second solution comprising an oxidizing compound, preferably hydrogen peroxide.

[0053] For example, the chemical conversion or passivation layer is obtained using the Socosurf TCS PACS product from the company Socomore, as described for example in patent FR 2 986 806. The chemical conversion or passivation layer can also be obtained using the Socosurf TCS product from the company Socomore, or the Socosurf TCS product and then the Socosurf PACS product, both from the company Socomore.

[0054] When the part is made of cadmium steel, the chromium III passivation layer is obtained for example using the product Finidip 128 CF, from the company MacDermid Enthone (Ex-Coventya).

[0055] The preparation of the chemical conversion layer with chromium VI or passivation is also well known in itself.

[0056] For example, the chemical conversion layer to chromium VI or passivation is obtained using the product Alodine 1500, also known as BONDERITE® M-CR 1500 AERO, from the Henkel company.

[0057] Step A) may be preceded by a degreasing step of the part.

[0058] This degreasing can be carried out using an organic solvent, in particular acetone. This solvent can, for example, be applied to a cloth soaked (by said solvent).

[0059] This degreasing can also be carried out using an alkaline solution, in particular one with a pH between 9 and 14, preferably between 9.5 and 11. This alkaline solution is, for example, a commercial alkaline degreaser, in particular Chemetall OAKite NST alkaline degreaser. This alkaline solution can, for example, be applied with a cloth soaked (in said solvent) or by immersion.

[0060] By "oxidizing composition" is meant in particular a composition comprising a metal salt and / or a halogen salt, which is more oxidizing than aluminium (Al3+).

[0061] According to a particular embodiment, the oxidizing composition is such that it gives a colored conversion.

[0062] By "color conversion", it is understood in particular that at least one of the products of the reaction taking place when at least a part of the surface of the part is brought into contact with an oxidizing composition is colored.

[0063] According to a particular embodiment, the persistent stain is detected with the naked human eye.

[0064] According to another particular embodiment, the persistent stain is detected by spectral analysis, preferably using a colorimeter.

[0065] The oxidizing composition is in particular an aqueous composition, in particular an aqueous solution.

[0066] The pH of this oxidizing composition, in particular aqueous composition, in particular aqueous solution, is in particular between 2.5 and 10 and preferably between 3 or 3.2 and 8.

[0067] According to a particular embodiment, the oxidizing composition comprises a permanganate, preferably potassium permanganate (KMnO4).

[0068] According to another particular embodiment, the oxidizing composition comprises a copper salt, in particular a copper sulfate, a zinc salt, in particular a zinc sulfate, an iron salt, in particular an iron sulfate, or a mixture thereof.

[0069] According to a more particular embodiment, the oxidizing composition comprises a copper salt, in particular a copper sulfate, a zinc salt, in particular a zinc sulfate, an iron salt, in particular an iron sulfate, or a mixture thereof, which composition is acidic, in particular having a pH of about 3.

[0070] According to another particular embodiment, the oxidizing composition is an aqueous composition for the surface treatment of a metallic substrate, said composition containing metallic salts, excluding compounds based on hexavalent chromium, and one or more water-soluble coloring compounds.

[0071] The pH of said composition is between 3 and 5.

[0072] The dye(s) in question is - or are - capable of maintaining a color within the indicated pH range.

[0073] This composition makes it possible to form on metallic substrates, in particular aluminum or aluminum alloy, magnesium or magnesium alloy, or steel substrates, a colored surface coating which does not degrade a conversion or passivation layer already formed on the surface of the metal oxide.

[0074] The colorant (coloring compound), or the mixture of colorants, is notably present according to the invention in a concentration of between 0.1 and 2g / L. Such a concentration range is indicative.

[0075] The dye (coloring compound) is for example a fluorescent dye (with fluorescence properties, detectable by UV), such as in particular rhodamine B.

[0076] The detection composition according to the invention may further contain one or more conventional additives, for example surfactants, wetting agents, pH stabilizers, additional corrosion inhibitors, chelating / complexing agents, etc.

[0077] The viscosity of the detection composition according to the invention can be adjusted to obtain a gel.

[0078] The contact in step A) is carried out in particular for a period of time from 1 second to 20 minutes, preferably from 30 seconds to 10 minutes.

[0079] According to a more particular embodiment, the oxidizing composition comprises a permanganate, preferably potassium permanganate (KMnO4), and:

[0080] Step A) is preceded by a degreasing step of the part, in particular using an organic solvent, or using an alkaline solution, in particular having a pH between 9 and 14, preferably between 9.5 and 11, by immersion;

[0081] and / or

[0082] the contact in step A) is carried out for a period of 8, 10 or 12 minutes to 20 minutes, in particular from 12 minutes to 20 minutes, for example about 8, 10, or 12 minutes.

[0083] According to another more particular embodiment, the oxidizing composition comprises a copper salt, in particular a copper sulfate, a zinc salt, in particular a zinc sulfate, an iron salt, in particular an iron sulfate, or a mixture thereof, which composition is acidic, having in particular a pH of about 3, and

[0084] step A) is preceded by a degreasing step of the part;

[0085] and / or

[0086] the contact in step A) is carried out for a period of 5 or 10 minutes to 20 minutes, for example about 5 or 10 minutes.

[0087] According to another more particular embodiment, the oxidizing composition comprises an aqueous composition for the surface treatment of a metallic substrate, said composition containing metallic salts, excluding hexavalent chromium-based compounds, and one or more water-soluble coloring compounds, and

[0088] step A) is preceded by a degreasing step of the part;

[0089] and / or

[0090] the contact in step A) is carried out for a period of 4, 5 or 6 minutes to 20 minutes, in particular from 4, 5, or 6 minutes to 10 minutes, for example about 4, 5, or 6 minutes.

[0091] The detection method according to the invention may also include, in addition to the steps of detecting the possible presence of a chemical conversion or passivation layer on a first surface of a part, at least one step C) of detecting the possible presence of an electrolytic conversion layer on a second surface of said part.

[0092] According to a particular embodiment, step C) is carried out before steps A) and B).

[0093] The electrolytic conversion layer is typically obtained by anodizing. This anodizing process is well known to those skilled in the art.

[0094] This electrolytic conversion layer is generally barely visible, or even invisible, to the naked eye.

[0095] Step C) can in particular be carried out by checking the electrical insulation.

[0096] In particular, step C) is carried out by using a diode bridge multimeter at two points (two electrodes) in the area supposedly bearing the electrolytic conversion layer, by the absence of electric current flow. EXAMPLES

[0097] Example 1: Detection method according to the invention

[0098] In this example, an aqueous solution of KMnO4 at 0.02M is used as the oxidizing composition. This solution is applied in the form of drops onto the surface to be tested.

[0099] Tests have shown in particular that after prior degreasing (alkaline degreasing by immersion in Chemetall OAKite NST alkaline degreaser or degreasing with acetone applied with a soaked cloth), raw (untreated, i.e. without conversion coating) aluminum alloy parts (for example 2024 T3 or 6061 T6) were visibly marked with the solution, whereas the corresponding treated parts (i.e. with conversion coating) were not marked, after 8, 10 or 12 minutes of contact, in particular 12 minutes.

[0100] Example 2: Another example of a detection method according to the invention

[0101] In this example, an aqueous composition is used as an oxidizing composition for the surface treatment of a metallic substrate, said composition containing metallic salts, excluding hexavalent chromium-based compounds, and one or more water-soluble coloring compounds.

[0102] This solution is applied in the form of drops onto the surface to be tested.

[0103] Tests have shown in particular that after prior degreasing (for example, alkaline degreasing applied with a cloth soaked in Chemetall OAKite NST alkaline degreaser, alkaline degreasing by immersion in Chemetall alkaline degreaser OAKite NST or acetone degreasing applied with a soaked cloth), raw (untreated, i.e. without conversion coating) aluminum alloy parts (e.g. 2024 T3 or 6061 T6) were visibly marked with the solution, while corresponding treated parts (i.e. with conversion coating) were not marked, for example after 4, 5 or 6 minutes of contact.

[0104] Example 3: Another example of a detection method according to the invention

[0105] In this example, a 20 g / L CuSO4 solution is used as the oxidizing agent. For the preparation, 4 g of CuSO4 were weighed and dissolved in 200 mL of distilled water. The pH of this solution was adjusted to 3, for example, using a 0.02 M sulfuric acid (H2SO4) solution.

[0106] This solution is applied in the form of drops onto the surface to be tested.

[0107] Tests have shown in particular that after prior degreasing (for example alkaline degreasing applied with a cloth soaked in Chemetall OAKite NST alkaline degreaser, alkaline degreasing by immersion in Chemetall OAKite NST alkaline degreaser or degreasing with acetone applied with a soaked cloth), raw (untreated, i.e. without conversion coating) aluminum alloy parts (for example 2024 T3 or 6061 T6) were visibly marked with the solution, whereas the corresponding treated parts (i.e. with conversion coating) were not marked, for example after 5 or 10 minutes of contact.

Claims

Demands

1. A method for detecting the possible presence of a chemical conversion or passivation layer on a part, comprising at least the following steps: A) a step of contacting at least a part of the surface of the part with an oxidizing composition; B) a step of detecting any persistent stain at the point of contact as defined in step A).

2. A method according to claim 1, wherein the part is made of aluminum or an aluminum alloy, magnesium or a magnesium alloy, or steel bearing a metallic coating, for example cadmium plating or zinc-nickel plating, the aluminum alloy being in particular selected from the 2000, 5000, 6000 and 7000 series, in particular selected from the group consisting of 2014, 2017, 2024, 2214, 2219, 2618, AU5NKZr, 7175, 5052, 5086, 6061, 6063, 7010, 7020, 7050, 7050 T7451, 7055, 7068, 7085, 7075, 7175 and 7475, the aluminum alloys selected from the group consisting of AS7G06, AS7G03, AS10G and AS9U3.

3. A method according to claim 1 or 2, wherein the chemical conversion or passivation layer is obtained by applying to the part a solution comprising a fluorinated compound, a corrosion-inhibiting metallic compound, said corrosion-inhibiting metallic compound being a trivalent chromium salt (chromium III).

4. A method according to claim 1 or 2, wherein the chemical conversion or passivation layer is obtained by applying to the part: - a first solution comprising a fluorinated compound, a corrosion-inhibiting metallic compound, said corrosion-inhibiting metallic compound being a trivalent chromium salt (chromium III); - then optionally a second solution comprising an oxidizing compound, preferably hydrogen peroxide.

5. A method according to any one of the preceding claims, wherein step A) is preceded by a step of degreasing the part.

6. A method according to any one of the preceding claims, wherein the persistent stain is detected with the naked human eye, or by spectral analysis, preferably using a colorimeter.

7. A process according to any one of the preceding claims, wherein the oxidizing composition is an aqueous composition, in particular an aqueous solution, having a pH in particular between 2.5 and 10 and preferably between 3 or 3.2 and 8.

8. A process according to any one of the preceding claims, wherein the oxidizing composition comprises a permanganate, preferably potassium permanganate (KMnO4).

9. A process according to any one of the preceding claims, wherein the oxidizing composition comprises a copper salt, in particular a copper sulfate, a zinc salt, in particular a zinc sulfate, an iron salt, in particular an iron sulfate, or a mixture thereof.

10. A process according to any one of the preceding claims, wherein the oxidizing composition is an aqueous composition for the surface treatment of a metallic substrate, said composition containing metallic salts, excluding hexavalent chromium compounds, and one or more water-soluble coloring compounds.

11. A method according to claim 10, wherein the coloring compound is a fluorescent dye.

12. A method according to any one of the preceding claims, wherein the contact in step A) is carried out in particular for a duration of from 1 second to 20 minutes, preferably from 30 seconds to 10 minutes.

13. A method according to any one of the preceding claims, which includes, in addition to the steps of detecting the possible presence of a chemical conversion or passivation layer on a part, at least one step C) of detecting the possible presence of an electrolytic conversion layer on said part, in particular by checking the electrical insulation.