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 bringing at least part of the surface of the part into contact with an oxidizing composition; B) a step of detecting a possible persistent stain at the location of the contact as defined in step A).

Description

[0001] DESCRIPTION

[0002] TITLE: Method for detecting a chemical conversion or passivation layer

[0003] Technical field of the invention

[0004] The present invention falls within the scope of detecting 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.

[0005] Technical background

[0006] Numerous studies in both the aerospace and non-aerospace industries have been conducted for years 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, while the need to confirm its presence during production or in post-application quality control is crucial for manufacturers and their customers.

[0007] Research efforts to detect conversion to trivalent chromium have focused on the following techniques.

[0008] Colorimetry:

[0009] In the context of surface colorimetry, we are only interested in reflected radiation, generally assuming that the object is opaque.

[0010] The device used is, for example, the Alumeter AL 100, which is a tablet connected to a probe. It comes with a standard for calibrating the device before each series of measurements.

[0011] However, prior to testing, a suitable environment is required for the device to function. This includes optimal ambient conditions of 21°C ± 4°C and 40% to 70% relative humidity, among other factors. Furthermore, surface preparation is necessary to ensure a clean surface before detection, and this technique should not be used under direct lamplight or sunlight.

[0012] In order to detect color, a similar surface finish is essential. The results obtained demonstrate that this method is not always effective, depending on the geometry of the part and the environment.

[0013] X-ray fluorescence:

[0014] XRF spectroscopy is an analytical technique used to obtain 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 then 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 within each atom. These photons can be detected by a counter, which identifies the atom based on its energy.

[0015] The technique is effective because it uses the peak areas of the spectrogram, as these areas represent the concentrations of the elements present. This integration is very efficient thanks to computer processing. Furthermore, no special surface preparation is required for this analysis.

[0016] However, a minimum cost of €30,000 is required to purchase the device. Furthermore, the device cannot necessarily 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). Detection of Chromium III with reagent drop(s):

[0017] 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.

[0018] However, this reaction causes the destruction of the conversion layer.

[0019] In addition, the mixture is unstable if made too early in the process, which may require a surplus test to be carried out.

[0020] Using this methodology will result in a high scrap rate unless the part in question is reworked for a new surface treatment.

[0021] The present invention aims to overcome the drawbacks of the aforementioned methods.

[0022] In particular, one objective of the present invention is to provide a detection method that is both:

[0023] - non-destructive to the conversion or passivation layer (therefore no rework is necessary);

[0024] - 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

[0025] - reliable (i.e., in particular, detection is possible regardless of the surface condition and / or the type of alloy).

[0026] Summary of the invention

[0027] 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:

[0028] A) a step of bringing at least part of the surface of the part into contact with an oxidizing composition;

[0029] B) a step for detecting any persistent stain at the point of contact as defined in step A). ​​Thus, in the process of the invention, the oxidizing composition reacts on the surface with the part, in particular 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 at oxidation state +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 or its associated properties (primarily corrosion resistance and layer resistivity). The appearance of the layer is therefore not altered, even temporarily.

[0030] 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.

[0031] Detailed description of the invention

[0032] One 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:

[0033] A) a step of bringing at least part of the surface of the part into contact with an oxidizing composition;

[0034] B) a step to detect any possible persistent stain at the point of contact as defined in step A).

[0035] According to a particular embodiment, 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: A) a step of bringing at least a part of the surface of the part into contact with an oxidizing composition;

[0036] B) a step for detecting any persistent stain at the point of contact as defined in step A); the oxidizing composition reacting on the surface of the part, but not reacting in the presence of a chemical preservation or passivation layer, the oxidizing composition:

[0037] - comprising a permanganate,

[0038] - comprising a copper salt, or

[0039] - 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 colouring compounds.

[0040] According to a particular embodiment, 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:

[0041] A) a step of bringing at least part of the surface of the part into contact with an oxidizing composition;

[0042] B) a step for detecting any persistent stain at the point of contact as defined in step A); the part being made of aluminum or an aluminum alloy, the oxidizing composition reacting on the surface with the aluminum or aluminum alloy of the part, but not reacting in the presence of a chemically sealed or passivated layer, the oxidizing composition:

[0043] - comprising a permanganate,

[0044] - comprising a copper salt, or

[0045] - 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 colorants. Step A) may optionally be followed, prior to step B), by a step in which excess oxidizing composition is removed. This may, for example, be carried out using a dry or moistened absorbent medium, such as a sponge or cloth.

[0046] The part can be obtained by any technique well known to a person skilled in the art, for example by a process including a step of forging, rolling, casting, additive manufacturing, etc.

[0047] The part is made primarily of aluminum or an aluminum 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.

[0048] The part can also be made of magnesium or a magnesium alloy.

[0049] The part can also be made of steel with a metallic coating, which can be passivated by a colorless conversion coating, particularly one based on Grill, such as cadmium plating, zinc-nickel plating, etc.

[0050] It 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.

[0051] The part can also be made of cadmium-plated steel, or steel with a zinc-nickel coating.

[0052] By "chemical conversion or passivation layer" we mean a layer comprising trivalent chromium (chromium III) or chromium VI, and / or zirconium (in particular zirconium IV).

[0053] 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, ...).

[0054] 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.

[0055] 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, ...).

[0056] 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, ...).

[0057] 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, ...).

[0058] In one particular embodiment, the coating is a passivation layer comprising trivalent chromium (chromium III) on cadmium-plated steel. The preparation of the trivalent chromium chemical conversion or passivation layer is well known in itself.

[0059] Typically, implementation conditions are provided with technical data sheets by the manufacturers of chemical conversion or passivation baths.

[0060] As a non-limiting example, the chromate bath may be a bath marketed under the SurTec650 brand of SurTec or Lanthane 613.3 of Coventya.

[0061] As a non-limiting example, the chemical conversion or passivation layer can be applied to 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 bath temperature 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 the 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.

[0062] After 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 (C^Os) and / or chromium hydroxide (Cr(OH)3).

[0063] When the chromate bath contains zirconium, the coating includes zirconium, particularly in the form of zirconium oxide (ZrC₂). When the chromate bath contains chromium and also zirconium, the coating includes chromium(III), for example in the form of chromium oxide (C₂O₃) and / or chromium hydroxide (Cr(OH)₃), and also zirconium, particularly in the form of zirconium oxide (ZrC₂).

[0064] 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).

[0065] Such a solution is described, for example, in patent FR2986806.

[0066] According to another particular embodiment, the chemical conversion or passivation layer is obtained by application to the part:

[0067] - 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);

[0068] - and optionally a second solution comprising an oxidizing compound, preferably hydrogen peroxide. For example, the chemical conversion or passivation layer is obtained using the Socosurf TCS PACS product from 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 Socomore, or the Socosurf TCS product followed by the Socosurf PACS product, both from Socomore.

[0069] 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).

[0070] The preparation of the chemical conversion layer with chromium VI or passivation is also well known in itself.

[0071] 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.

[0072] Step A) may be preceded by a degreasing step of the part.

[0073] This degreasing can be carried out using an organic solvent, such as acetone. This solvent can, for example, be applied with a cloth soaked in the solvent.

[0074] This degreasing can also be carried out using an alkaline solution, specifically one with a pH between 9 and 14, preferably between 9.5 and 11. This alkaline solution could be, for example, a commercial alkaline degreaser, such as Chemetall OAKite NST. This alkaline solution can be applied, for example, with a cloth soaked in the solvent or by immersion.

[0075] The term "oxidizing composition" refers, in particular, to a composition containing a metal salt and / or a halogen salt, which is more oxidizing than aluminum (Al 3+ ).

[0076] According to a particular embodiment, the oxidizing composition is such that it produces a colored conversion. By "colored conversion," it is understood, in particular, that at least one of the products of the reaction occurring when at least a part of the surface of the workpiece is brought into contact with an oxidizing composition is colored.

[0077] According to a particular embodiment, the persistent spot is detected with the naked human eye.

[0078] According to another particular embodiment, the persistent stain is detected by spectral analysis, preferably using a colorimeter.

[0079] The oxidizing composition is notably an aqueous composition, in particular an aqueous solution.

[0080] 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.

[0081] According to a particular embodiment, the oxidizing composition is a liquid composition.

[0082] According to a particular embodiment, the oxidizing composition comprises a permanganate, preferably potassium permanganate (KMnC).

[0083] According to a particular embodiment, the oxidizing composition consists of a solvent, in particular water, and a permanganate, preferably potassium permanganate (KMnCU).

[0084] 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.

[0085] 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.

[0086] According to another particular embodiment, the oxidizing composition consists of a solvent, in particular water, a copper salt, in particular copper sulfate, a zinc salt, in particular zinc sulfate, an iron salt, in particular iron sulfate, or a mixture thereof. According to a more particular embodiment, the oxidizing composition consists of a solvent, in particular water, a copper salt, in particular copper sulfate, a zinc salt, in particular zinc sulfate, an iron salt, in particular iron sulfate, or a mixture thereof, which composition is acidic, having in particular a pH of about 3.

[0087] 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.

[0088] The pH of said composition is between 3 and 5.

[0089] The dye(s) in question is - or are - capable of maintaining a color within the indicated pH range.

[0090] This composition allows the formation on metallic substrates, in particular aluminum or aluminum alloy, magnesium or magnesium alloy, or steel substrates, of a colored surface coating which does not degrade a conversion or passivation layer already formed on the surface of the metal oxide.

[0091] The colorant (coloring compound), or 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.

[0092] The dye (coloring compound) is for example a fluorescent dye (with fluorescence properties, detectable under UV), such as rhodamine B.

[0093] 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.

[0094] The viscosity of the detection composition according to the invention can be adjusted to obtain a gel.

[0095] The contact in step A) is carried out for a period of time ranging from 1 second to 20 minutes, preferably from 30 seconds to 10 minutes. According to a more particular embodiment, the oxidizing composition comprises a permanganate, preferably potassium permanganate (KMnC₄), and: 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; and / or the contact in step A) is carried out for a period of time ranging from 8, 10 or 12 minutes to 20 minutes, in particular from 12 minutes to 20 minutes, for example approximately 8, 10, or 12 minutes.

[0096] 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, in particular having a pH of about 3, and step A) is preceded by a degreasing step of the part; and / or 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.

[0097] 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 compounds based on hexavalent chromium, and one or more water-soluble coloring compounds, and step A) is preceded by a degreasing step of the part; and / or 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.

[0098] 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.

[0099] According to a particular embodiment, step C) is carried out before steps A) and B).

[0100] The electrolytic conversion layer is typically obtained by anodizing. This anodizing process is well known to those skilled in the art.

[0101] This electrolytic conversion layer is generally barely visible, or even invisible, to the naked eye.

[0102] Step C) can notably be carried out by checking the electrical insulation.

[0103] In particular, step C) is carried out by using a diode bridge multimeter at two points (two electrodes) of the area supposedly carrying the electrolytic conversion layer, by the absence of electric current flow.

[0104] EXAMPLES

[0105] Example 1: Detection method according to the invention

[0106] 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.

[0107] Tests have shown 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 (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, after 8, 10 or 12 minutes of contact, especially 12 minutes.

[0108] Example 2: Another example of a detection method according to the invention 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 compounds based on hexavalent chromium, and one or more water-soluble coloring compounds.

[0109] This solution is applied in the form of drops onto the surface to be tested.

[0110] Tests have shown that after prior degreasing (e.g., alkaline degreasing applied with a cloth soaked in Chemetall OAKite NST alkaline degreaser, alkaline immersion degreasing with Chemetall OAKite NST alkaline degreaser, or acetone degreasing applied with a soaked cloth), raw (untreated, i.e., without a conversion coating) aluminum alloy parts (e.g., 2024 T3 or 6061 T6) were visibly marked with the solution, whereas the corresponding treated parts (i.e., with a conversion coating) were not marked, for example, after 4, 5, or 6 minutes of contact.

[0111] Example 3: Another example of a detection method according to the invention

[0112] 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.

[0113] This solution is applied in the form of drops onto the surface to be tested.

[0114] Tests have shown that after prior degreasing (e.g. alkaline degreasing applied with a cloth soaked in Chemetall OAKite NST alkaline degreaser, alkaline immersion degreasing with Chemetall OAKite NST alkaline degreaser 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, whereas 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 bringing at least part of the surface of the part into contact with an oxidizing composition; B) a step for detecting any persistent stain at the point of contact as defined in step A); the part being made of aluminum or an aluminum alloy, the oxidizing composition reacting on the surface with the aluminum or aluminum alloy of the part, but not reacting in the presence of a chemically sealed or passivated layer, the oxidizing composition: - comprising a permanganate, - comprising a copper salt, or - 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 colouring compounds.

2. A method according to claim 1, wherein the aluminum alloy is 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 application 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.

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 (KMnC).

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 method 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 process 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, comprising, 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.