A PROCESS FOR SEALABLES OF ALUMINUM ALLOYS USING A SILANE AND A PART BASED ON ALUMINUM OR AN ALUMINUM ALLOY OBTAINED BY THIS PROCESS

Abstract

The present invention relates to a part (1) made of aluminum or an aluminum alloy, comprising: - a body (10) made of aluminum or an aluminum alloy, - an inner layer (12) comprising aluminum oxide disposed on the body (10), - an intermediate layer (14) comprising chromium and zirconium, and - an outer layer (16) comprising an organosilicate, the intermediate layer (14) being disposed between the inner layer (12) and the outer layer (16). It also relates to a method for post-anodizing sealing of a body (10) made of aluminum or an aluminum alloy. Figure for the abstract: None

Description

Title of the invention: CLOSING METHOD ALUMINUM ALLOYS USING SILANE AND ALUMINUM-BASED PARTS OR ALUMINUM ALLOYS OBTAINED BY THIS PROCESS Technical field of the invention

[0001] The present invention falls within the scope of the search for new anti-corrosion protection solutions on aluminium alloys, particularly for aeronautical applications, with or without the application of a paint system. Technical background

[0002] Aluminum alloys are materials of choice for the transportation industry, and more specifically for the aerospace industry, due to their excellent mechanical properties-to-weight ratio and their relatively low manufacturing cost. However, depending on their environment, these alloys are susceptible to several types of localized corrosion, leading to the degradation of the part and potentially resulting in its removal or failure. Numerous strategies have been implemented to overcome this weakness, and among them, the formation or deposition of a protective layer on the surface of aluminum alloy parts is the most widely used. This is particularly true of the protective layers obtained by the anodizing process for aluminum alloy parts.Anodizing is an electrolytic process that replaces the natural oxide (native oxide), a few nanometers thick, which coats aluminum, with an oxide layer that can be several micrometers thick. The oxide layers produced by anodizing range in thickness from two to fifteen microns, providing long-term corrosion protection. Anodizing, also called anodic oxidation, involves forming a porous layer of aluminum oxides / hydroxides, known as the anodic layer, on the surface of the part. This is achieved by applying an electric current to the part immersed in an electrolytic bath containing a strong acidic electrolyte. The part itself acts as the anode in the electrolytic system. After a sealing treatment, the layer formed on the surface of the part enhances its corrosion resistance.Anodizing treatments are now commonly used in the aerospace industry, primarily to improve the corrosion resistance of parts, and therefore their lifespan, but also to facilitate the adhesion of organic coatings (paints). However, the anodizing process is directly impacted by European regulations (REACH). which, since September 2017, has prohibited (or restricted to authorization) the use of certain key components in surface treatments, in particular, hexavalent chromium. However, hexavalent chromium is present in the OAC type anodizing treatment (Chromic Anodic Oxidation as described, for example, in www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-chromique), but also in the usual surface preparation pretreatments, aimed at cleaning / stripping the surfaces of the parts before the anodizing treatment, and finally in the final so-called sealing treatments, the objective of which is to close the pores of the anodic layer formed during the anodizing treatment.

[0003] Various processes have therefore been proposed to replace the OAC and OAS (Sulfuric Anodic Oxidation) treatments clogged with hexavalent chromium, impacted by the European REACH regulation:

[0004] - the OAS NG (new generation sulfuric anodic oxidation as described for example in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfurique-version-5-2") was proposed to replace the OAS;

[0005] - OAST (sulfo-tartaric anodic oxidation as described, for example, in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfo-tartrique-oast-tartric-sulfuric-anodizing-tsa") has been proposed to replace OAC.

[0006] OAC can also be replaced by OAS NG FE (new generation thin thickness sulfuric anodic oxidation) which is an OAS NG type anodization whose anodization parameters (Voltage, Immersion Time) have been adapted to obtain an anodization layer whose thickness is between 2 and 7 pm.

[0007] Although current conventional anodizing solutions, such as OAS NG followed by hot water sealing, employ treatment ranges compatible with the European REACH regulation, they nevertheless remain unsatisfactory or only marginally effective in terms of corrosion protection on certain grades of so-called "difficult" aluminum alloys. Non-limiting examples of such "difficult" aluminum alloys include 2214, 2618A, and AU5NKZr. These alloys possess particular microstructures due to their chemical composition, which result in either casting-type defects or precipitates such as copper-, iron-, or nickel-rich intermetallics, etc. Thus, when the anodic layer forms on the surface of these alloys, layer defects may occur, leading to localized weaknesses susceptible to corrosion.

[0008] For these alloys, it is therefore necessary to optimize the anodizing ranges in order to improve anti-corrosion performance.

[0009] French patent FR 3106838B1 proposes a post-anodization sealing process for aluminum or aluminum alloys that improves the corrosion resistance of the part without using hexavalent chromium, which is impacted by the European REACH regulation. This process, which is also suitable for so-called "difficult" aluminum alloys, comprises an impregnation step of the aluminum or aluminum alloy in an aqueous bath containing a hexaflurozirconate salt and a trivalent chromium salt, followed by a sealing step carried out in an aqueous solution comprising an alkali metal silicate or an alkaline earth metal silicate, and optionally followed by the application of a paint.Despite the improved anti-corrosion performance provided by this process, there is a real need to further optimize current anodizing processes for aluminum or aluminum alloy parts, including so-called "difficult" aluminum alloys, in order to improve the anti-corrosion performance of these alloys and, where appropriate, the adhesion of paints, while complying with the requirements of the European REACH regulation.

[0010] The present invention aims to overcome the drawbacks of current anodizing processes for aluminum or aluminum alloy parts, including aluminum alloys that are considered "difficult" in terms of corrosion resistance, and allows for better paint adhesion, obtained using a robust process.

[0011] Furthermore, the present invention aims to provide a part made of aluminium or aluminium alloy whose corrosion resistance is improved while complying with the requirements of the European REACH regulation.

[0012] Furthermore, the present invention aims to provide an aluminum or aluminum alloy part with improved corrosion resistance and better paint adhesion, while having its other properties, in particular in terms of thermal resistance, fluid resistance, sealant adhesion, fatigue resistance, friction resistance, not altered or even improved compared to parts obtained by prior art processes. Summary of the invention

[0013] The present invention is specifically designed to meet these needs by providing a part (1) made of aluminum or an aluminum alloy, characterized in that it comprises:

[0014] - a body (10) made of aluminum or an aluminum alloy,

[0015] - an inner layer (12) comprising aluminum oxide disposed on the body (10),

[0016] - an intermediate layer (14) comprising chromium and zirconium, and

[0017] - an outer layer (16) comprising an organosilicate, the intermediate layer (14) being arranged between the inner layer (12) and the outer layer (16).

[0018] The invention also relates to a post-anodization sealing method for a body (10) made of aluminum or an aluminum alloy, comprising at least the following steps:

[0019] A) a step of impregnating the body (10) made of aluminum or an anodized aluminum alloy having an inner layer (12) comprising aluminum oxide, in an aqueous bath of demineralized water containing

[0020] - a hexafluorozirconate salt selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2 ZrF6), potassium hexafluorozirconate (K2ZrF6), and

[0021] - a trivalent chromium salt selected from the group consisting of CrF3,xH2O, CrCl3,xH 2O, Cr(NO3)3,xH2O, (CH3CO2)2Cr,xH2O, (CH3CO2)7Cr3(OH)2,xH2O, Cr2(SO4)3,xH2O, CrK(SO4)2,xH2O,

[0022] at a temperature between 20 and 80°C;

[0023] B) a sealing step carried out in an aqueous solution of deionized water having a conductivity less than or equal to 200 pS / cm containing a composition consisting of or comprising a silane and an alkali metal or alkaline earth metal silicate, at a temperature between 60 and 100°C;

[0024] in particular a sealing step carried out in an aqueous solution of deionized water having a conductivity less than or equal to 200 pS / cm containing between 1 and 200g / L of a composition consisting of or comprising a silane, in particular an organosilane, in particular a trialkoxy organosilane, and an alkali metal or alkaline earth metal silicate, at a temperature between 60 and 100°C;

[0025] C) a post-fouling rinsing step with deionized water having a conductivity less than or equal to 100 pS / cm and at a temperature between 15 and 75°C.

[0026] Intermediate rinses, in particular with demineralized water, may be carried out:

[0027] - between steps A) and B), and / or

[0028] - before and / or after the part has been treated by anodizing.

[0029] Since anodized coatings have a highly porous structure, when chemical and / or corrosion resistance is paramount, the anodized layer must be sealed. This involves transforming the aluminum oxide layer into an aluminum hydroxide complex where the pores are closed. Therefore, sealing, in addition to anodizing, is crucial for the quality of the anodized layer because: • the sealing of pores leads to an increase in corrosion resistance; • fouling is avoided; • The washing of dyes out of the pores is avoided.

[0030] The post-anodization sealing process of the invention makes it possible to obtain a coating with very high anti-corrosion properties on so-called difficult aluminum alloys such as, for example, 2618A and 2214, but also on the most common aluminum alloys in the aeronautical field, such as 2024 or 7175 for example.

[0031] The sealing process of the invention can be applied to various anodizings known to those skilled in the art, among which we can mention OAC (Chromic Anodizing), OAD (Hard Anodizing), OAS (Sulfuric Anodizing), OAST (Sulfuric-Tartaric Anodizing), OAS NG FE (New Generation Thin Thick Sulfuric Anodizing), OAS NG (New Generation Sulfuric Anodizing), TSA (Tartaric sulfuric Anodizing).

[0032] The invention also relates to a method for manufacturing a part (1) based on aluminium or an aluminium alloy according to the invention, comprising at least the following steps:

[0033] i) subjecting a body (10) made of aluminium or an aluminium alloy to an anodising step, possibly having previously undergone a surface preparation step (degreasing, then pickling);

[0034] ii) treating the anodized body comprising an inner layer (12) by a post-anodizing sealing process according to the invention, to successively obtain an intermediate layer (14) comprising chromium and zirconium, and an outer layer (16) comprising an organosilicate; and possibly

[0035] iii) application of a layer of paint (18).

[0036] The invention further relates to a part according to the invention, optionally comprising a layer of paint and intended for the aeronautical sector. Brief description of the figures

[0037] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which:

[0038] [Fig. 1] schematically represents the steps to carry out a surface treatment of test specimens in aluminium alloys implementing the post-anodisation sealing process of the invention.

[0039] [Fig.2] represents examples of treatment range and operating conditions Tests were carried out. SOCOCLEAN A3432 from SOCOMORE is a degreaser compatible with aluminum and its alloys. SOCOSURF A1858-A1806 from SOCOMORE is a two-component bath used for deoxidizing or whitening aluminum and its alloys after degreasing or alkaline pickling. The SOCOSURF TCS bath from SOCOMORE impregnates the pores of the oxide layer obtained after OAS (ThinSAA) or TSA anodizing with Cr(III) and zirconium. SOCOSURF PACS is a 10% vol / vol aqueous bath from SOCOMORE. The porous layer is then sealed with an aqueous solution consisting of or containing a silane, particularly an organosilane, and an alkali metal or alkaline earth metal silicate (for example, 80 g / L of silicate).

[0040] [Fig.3] is a schematic cross-sectional representation of a part according to one of the embodiments of the invention. Detailed description of the invention

[0041] A first object of the invention relates to a part (1) made of aluminium or an aluminium alloy, characterized in that it comprises:

[0042] - a body (10) made of aluminum or an aluminum alloy,

[0043] - an inner layer (12) comprising aluminum oxide disposed on the body (10),

[0044] - an intermediate layer (14) comprising chromium and zirconium (CrIU / Zr), and

[0045] - an outer layer (16) comprising an organosilicate, the intermediate layer (14) being arranged between the inner layer (12) and the outer layer (16).

[0046] As indicated, the part (1) according to the invention comprises a body (10) made of aluminum or an aluminum alloy.

[0047] The aluminum alloy can be selected from the 2000, 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, aluminum casting alloys selected from the group consisting of AS7G06, AS7G03, AS10G and AS9U3, in particular aluminum alloys (so-called difficult) selected from the group consisting of 2618A, 2214 and AU5NKZr.

[0048] The part (1) comprises a body (10) on which an inner layer (12) is disposed. The layer (12) comprises aluminum oxide. The inner layer (12) has a thickness of between 2 and 30 µm, preferably between 5 and 25 µm. The inner layer (12) is obtained by anodic oxidation of the body (10) by one of the aforementioned anodizing processes known to those skilled in the art.

[0049] The part (1) according to the invention comprises an intermediate layer (14) comprising chromium and zirconium. The thickness of the intermediate layer (14) is between 1 µm and 10 µm, for example between 3 µm and 5 µm. The intermediate layer (14) is obtained after the impregnation step (A) of the body (10) comprising the inner layer (12) under the conditions described below.

[0050] The part (1) according to the invention also comprises an outer layer (16). The intermediate layer (14) is disposed between the inner (12) and outer (16) layers. The outer layer (16) comprises an organosilicate. The outer layer (16) has a thickness of between 10 and 500 nm, preferably 200 nm. The outer layer (16) is obtained at the end of the sealing step (B) of the body (10) comprising successively an inner layer (12) and an intermediate layer (14) under the conditions described below.

[0051] According to one embodiment of the invention, the part (1) further comprises a paint layer (18). The paint layer (18) is disposed on the outer layer (16) comprising an organosilicate. The paint layer (18) has a thickness of between 10 µm and 100 µm, preferably 50 µm. A part (1) according to this embodiment of the invention is illustrated in [Fig. 3]. In the case where several paint layers are deposited, the total thickness of the layers is between 10 and 100 µm, preferably 50 µm.

[0052] The part (1) according to the invention exhibits good corrosion resistance and good paint adhesion. Indeed, the combination of the intermediate layer (14) comprising chromium and zirconium (CrUI / Zr) and the outer layer (16) comprising an organosilicate, confers good corrosion resistance to the part (1). Furthermore, the outer layer 16 promotes the adhesion of the paint layer (18).

[0053] The present invention relates to a post-anodization sealing method for a body (10) made of aluminum or an aluminum alloy, comprising at least the following steps:

[0054] A) a step of impregnating the aluminum or the anodized aluminum alloy in an aqueous bath of demineralized water containing

[0055] - a hexafluorozirconate salt selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2 ZrF6), potassium hexafluorozirconate (K2ZrF6), and

[0056] - a trivalent chromium salt selected from the group consisting of CrF3,xH2O, CrCl3,xH 2O, Cr(NO3)3,xH2O, (CH3CO2)2Cr,xH2O, (CH3CO2)7Cr3(OH)2,xH2O, Cr2(SO4)3,xH2O, CrK(SO4)2,xH2O,

[0057] at a temperature between 20 and 80°C;

[0058] B) a sealing step carried out in an aqueous solution of deionized water having a conductivity less than or equal to 200 pS / cm containing a composition consisting of or comprising a silane and an alkali metal or alkaline earth metal silicate, at a temperature between 60 and 100°C;

[0059] in particular a sealing step carried out in an aqueous solution of deionized water having a conductivity less than or equal to 200 pS / cm containing between 1 and 200 g / L of a composition consisting of or comprising a silane, in particular an organosilane, in particular a trialkoxy organosilane, and an alkali metal or alkaline earth metal silicate, at a temperature between 60 and 100°C;

[0060] C) a post-fouling rinsing step with deionized water having a conductivity less than or equal to 100 pS / cm and at a temperature between 15 and 75°C.

[0061] The deposition of the organosilicate on the surface of an anodizing impregnated with CrlIFZr makes it possible to improve the resistance of the aluminum or aluminum alloy part to corrosion as well as the adhesion of the paint to said part.

[0062] As already indicated, intermediate rinses, in particular with demineralized water, can be carried out

[0063] - between steps A) and B), and / or

[0064] - before and / or after the part has been treated by anodizing.

[0065] The optimized sealing process of the invention can be suitable for all types of aluminium alloys including so-called "difficult" alloys, in particular aluminium alloys of the 2000, 6000 and 7000 series, previously anodized by various processes including OAC, OAD, OAS, OAST, OAS NG FE, OAS NG, TSA.

[0066] Furthermore, the post-anodizing sealing process of the invention is compatible with the requirements associated with the European REACH regulation and provides good corrosion protection on so-called "difficult" aluminum alloys (for example, 2618A, 2214 and AU5NKZr). This process may or may not be followed by a painting application.

[0067] Thus, the post-anodization sealing process of the invention makes it possible to obtain a coating (outer layer (16)) having very high anti-corrosion properties on the 2000, 6000 and 7000 series aluminium alloys and difficult aluminium alloys such as 2618A and 2214, but also on the most common aluminium alloys in the aeronautical field, such as 2024 and 7175.

[0068] In the impregnation step A), the concentration of hexafluorozirconate salt is between 0.5 and 50 g / L. The concentration of trivalent chromium salt in this step is between 0.1 and 50 g / L.

[0069] The trivalent chromium salt may be, for example, one of the following commercial products: Surtec 650 from the company SURTEC, Lanthane 613.3 from the company COVENTYA, TCS from the company SOCOMORE.

[0070] In the impregnation step A), the concentration of hexafluorozirconate salt is between 0.5 and 50 g / L, for example equal to 2 g / L.

[0071] The temperature of the bath in step A) can be between 20 and 80°C. According to one embodiment, the temperature of the bath in step A) is between 20 and 60°C. According to another embodiment of the invention, the temperature of the bath in step A) is between 35 and 45°C.

[0072] The pH of the bath in step A) is between 3 and 5, preferably between 3.5 and 4.5, for example between 3.7 and 4.2.

[0073] The duration of the impregnation, in the bath at step A) is between 1 and 40 minutes, preferably between 5 and 30 minutes, for example between 5 and 20 minutes.

[0074] After step A) and before step B), the process of the invention may optionally include an immersion step in a lanthanum salt and hydrogen peroxide bath. This immersion step is well known to those skilled in the art for enhancing the corrosion resistance properties of the body (10).

[0075] The sealing of step B) is carried out in an aqueous solution of deionized water having a conductivity less than or equal to 200 pS / cm, preferably between 1 and 100 pS / cm, for example between 1 and 50 pS / cm.

[0076] The silane as defined in step B) is in particular an organosilane, in particular a trialkoxy organosilane, for example a trimethoxy organosilane.

[0077] Silane is for example 3-(2,3-epoxypropoxy)propyl]trimethoxysilane.

[0078] The alkali metal silicate or alkaline earth metal silicate may be selected from the group consisting of lithium silicate, sodium silicate, potassium silicate, calcium silicate, magnesium silicate, lithium polysilicate, sodium polysilicate, potassium polysilicate, calcium polysilicate, and magnesium polysilicate, the silicate being in particular lithium silicate or lithium polysilicate.

[0079] The concentration of silane in the clogging step B) is preferably between 1 and 50 g / L, for example between 5 and 50 g / L.

[0080] The silane content can be adjusted, in particular with respect to the silicate content of alkali metal or alkaline earth metal, in particular according to the desired organosilicate content in the part of the invention.

[0081] In the sealing step B), the concentration of alkali metal silicate or alkaline earth metal in the solution is preferably between 1 and 500g / L, for example between 5 and 100 g / L.

[0082] In one embodiment of the invention, the temperature of the aqueous solution in step B) is between 80 and 100°C. In another embodiment of the invention, the temperature of the aqueous solution in step B) is between 96°C and 100°C, for example equal to 98°C.

[0083] The longer the duration of the sealing step B), the more organosilicate will be deposited. The duration of the sealing step B) is in particular between 1 and 40 minutes, preferably between 5 and 35 minutes, for example between 5 and 30 minutes, in particular 10 minutes.

[0084] The pH of the sealing solution is in particular less than 12, in particular from 9 to 12, for example between 7 and 11.5. In one embodiment of the invention the pH of the sealing solution is between 8 and 9.

[0085] The sealing is followed by a rinsing step C) in deionized water having a conductivity less than or equal to 100 pS / cm, preferably between 1 and 100 pS / cm, more preferably between 10 and 100 pS / cm, for example between 10 and 50 pS / cm.

[0086] Post-clogging rinsing is preferably carried out at a temperature between 10 and 75°C, for example between 15 and 60°C.

[0087] The pH of the water in step C) is between 4.5 and 8.5, preferably between 5 and 8, for example between 5.5 and 7.5.

[0088] The duration of the post-clogging rinse is between 10 seconds and 10 minutes, preferably between 10 seconds and 5 minutes, for example between 30 seconds and 2 minutes.

[0089] It has been found, quite unexpectedly, that the combination of the steps, impregnation A) + sealing B) + post-sealing rinsing C), as described below, is essential to guarantee good anti-corrosion performance of aluminum or aluminum alloy.

[0090] Furthermore, the application of the composition consisting of or comprising a silane, in particular an organosilane, and an alkali metal or alkaline earth metal silicate, must necessarily be carried out after the impregnation step A), in order to obtain the desired anti-corrosion properties and performance of the aluminium or aluminium alloy.

[0091] Intermediate rinses, in particular with demineralized water, can be carried out between the steps described above.

[0092] Before subjecting the body (10) made of aluminum or an aluminum alloy to the anodizing step, said body may be subjected to a surface preparation step by degreasing and / or pickling in order to remove grease, dirt and oxides present on its surface.

[0093] This preliminary surface preparation step may include one or more of the following operations: - Solvent degreasing, to dissolve greases present on the surface of the aluminum or aluminum alloy. This operation can be carried out by soaking, spraying, or any other method known to those skilled in the art; - Alkaline degreasing, to dissolve greases present on the surface of aluminum or aluminum alloy. This operation can be carried out by soaking, spraying, or any other technique known to those skilled in the art; - Alkaline pickling, to dissolve the oxides naturally formed on the surface of the aluminum or aluminum alloy. This operation can be carried out by immersion, spraying, or any other technique known to those skilled in the art. At the end of this operation, the aluminum or aluminum alloy is covered with a powdery layer formed from oxidation products of intermetallic compounds, which must be removed by an acid pickling step; - Acid pickling, to dissolve the oxides naturally formed on the surface of the aluminum or aluminum alloy, and / or the oxidation layer formed on the surface of the part during the alkaline pickling step. This operation can be carried out by immersion, spraying, or any other technique known to those skilled in the art.

[0094] The preliminary step of surface preparation of the body (10) made of aluminium or an aluminium alloy by degreasing and / or pickling to remove grease, dirt and oxides present on its surface can be carried out under the conditions described, for example, in application WO 2013 / 117759.

[0095] Intermediate rinses, in particular with demineralized water, are preferably carried out between the successive steps above, and before the part is treated by anodizing.

[0096] Before applying the sealing process of the invention, the body (10) made of aluminum or an aluminum alloy, possibly subjected to a surface preparation step by degreasing and / or pickling by one or more of the operations described above, is anodized. Any type of anodizing on aluminum known to those skilled in the art may be suitable.

[0097] Various processes have been proposed to replace the OAC and OAS (Sulfuric Anodic Oxidation) treatments clogged with hexavalent chromium, impacted by the European REACH regulation:

[0098] - the OAS NG (New Generation Sulfuric Anodic Oxidation as described for example in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfurique-version-5-2") was proposed to replace the OAS;

[0099] - OAST (Sulfotartric Anodic Oxidation as described, for example, in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfo-tartrique-oast-tartric-sulfuric-anodizing-tsa") has been proposed to replace 1'0AC; and

[0100] - OAS NG FE: New Generation Fine E Sulfuric Anodic Oxidation thickness, which is an OAS NG type anodizing whose anodizing parameters (Voltage, Immersion Time) have been adapted to obtain an anodizing layer with a thickness between 2 and 7 pm.

[0101] In the context of the present invention, the OAST, OAS NG FE, OAS NG anodizing processes are preferred.

[0102] The surface treatment process of the invention significantly improves the corrosion resistance properties of aluminum or aluminum alloy parts and complies with the requirements of the European REACH regulation.

[0103] Furthermore, the process of the invention allows for better conditions with regard to paint adhesion.

[0104] The invention also relates to a method for manufacturing a part (1) based on aluminium or an aluminium alloy according to the invention, comprising at least the following steps:

[0105] i) subjecting a body (10) made of aluminium or an aluminium alloy to an anodising step, possibly having previously undergone a surface preparation step (degreasing, then pickling);

[0106] ii) treating the anodized body comprising an inner layer (12) by a post-anodizing sealing process according to the invention, to successively obtain an intermediate layer (14) comprising chromium and zirconium, and an outer layer (16) comprising organosilicate; and possibly

[0107] iii) application of a layer of paint (18).

[0108] The invention further relates to a part according to the invention, optionally comprising a layer of paint and intended for the aeronautical sector. EXAMPLES

[0109] Example 1: Method according to the invention for surface treatment of an aluminum alloy part

[0110] Aluminum alloy parts 2024 T3 / T351, 2214 T6, 2618 T6, 7050 T7351, or 7175 T7351, rolled and machined on one of the two faces with dimensions 120x60x2 mm are treated according to the process described below.

[0111] Surface preparation steps for the part are first carried out successively: - alkaline degreasing, by immersing the part in a bath of SOCOCLEAN A3432 at 11% vol / vol (from the company SOCOMORE) at a temperature of 45°C, for 10 minutes; - rinse with tap water or demineralized water; - acid pickling, by immersing the part in a solution of SOCOSURF A1858 at 42% vol / vol - A1806 at 10% vol / vol (from the company SOCOMORE) at a temperature of 50°C, for 10 minutes; - Rinse with tap water or demineralized water.

[0112] The pickled and rinsed parts are then subjected to an anodizing process known to those skilled in the art, during which the parts are immersed in an aqueous bath containing sulfuric acid at a concentration between 160 g / L and 220 g / L, for example, 180 g / L. This bath is heated and maintained at a temperature of 18°C. A direct current voltage is applied to the immersed parts according to the following voltage profile: increasing from 0 V at a rate of 0.4 V / min until reaching a plateau voltage of 6 V. The voltage is maintained at the plateau value for 50 minutes. An anodic layer 4 to 7 µm thick forms on the surface of the parts.

[0113] The thickness of the anodic layer formed on the part is measured by eddy current according to ISO2360 standard.

[0114] The anodized parts are then subjected to one or more rinses, preferably with demineralized water, followed by impregnation and sealing operations according to the invention under the conditions and in the order indicated below: - Step A): an impregnation step of said parts, successively, in an aqueous bath of SOCOSURF TCS at 34% vol / vol (from the company SOCOMORE), at a temperature of 40°C for 10 minutes and at a pH of 3.9, and an aqueous bath of SOCOSURF PACS at 10% vol / vol (from the company SOCOMORE) at a temperature of 25°C for 5 minutes at a pH between 4.5 and 5.5, then - Step B): Sealing by immersion of the parts after impregnation step A) in an aqueous solution of deionized water having a conductivity of 10 pS / cm containing 80 g / L of a composition consisting of or comprising a silane, in particular an organosilane, especially a trialkoxy organosilane, and an alkali metal silicate or a metal alkaline earth, at a temperature of 98°C for 20 minutes, the pH being in particular between 9 and 12, in particular between 10 and 11; - step C): a post-clogging rinse by immersing the parts after these operations in deionized water having a conductivity of less than 100 pS / cm, at a temperature of 20°C for 1 minute.

[0115] Between each step, a rinse with demineralized water is carried out.

[0116] Example 2: Corrosion resistance results evaluated on anodized alloys and sealed by conventional sealing methods and by the sealing method of the invention:

[0117] For comparison purposes, aluminum alloy parts anodized with chromic acid or anodized and then subjected to hydrothermal sealing operations (TSA+TCS+PACS + hot water sealing) according to methods known to those skilled in the art, were compared to parts sealed by the process of the invention (with OAS (ThinSAA) anodizing or TSA + silane sealing).

[0118] The parts thus treated are subjected to a salt spray (BS) resistance test in accordance with standard NF EN ISO 9227. The number of pits at 500h of salt spray (BS) is reported in Table 1 below.

[0119] [Tables 1] Configuration Alloy 500h BS ThinSAA (according to the invention) 2618 0 / 0 / 0 7175 0 / 1 / 0 TSA (according to the invention) 2618 0 / 0 / 0 7175 0 / 0 / 0 Water sealing (reference 1 not part of the invention) 2618 9 / 10 / 10 7175 11 / 8 / 6 7 / 4 / 5 Part obtained by chromic acid anodizing (reference 2 not part of the invention) 2618 3 / 5 / 7 1 / 2 / 1 7175 8 / 1 / 1 5 / 2 / 4

[0120] In view of these results, it can be concluded that the parts and corresponding processes according to the invention increase corrosion resistance performance compared to the prior art treatment by chromic acid anodizing), but also compared to the standard aeronautical treatment used in the industry (water sealing).

[0121] Parts made of 2024, 2214, or 7050 aluminum alloy treated according to the invention have also shown excellent corrosion resistance. Example 3#: Paint adhesion tests

[0122] Paint adhesion tests (3 paints containing CrVI inhibitors, 2 paints containing Cr-free inhibitors) were performed on parts treated by a sealing process according to the invention (with OAS (ThinSAA) anodizing and silane sealing). The painted parts were characterized after immersion in various aggressive fluids (water, Skydrol). The adhesion rating for this type of test according to ISO 2409 ranges from 0 (no degradation) to 5 (total degradation).

[0123] [Tables2] Dry Paint After immersion in water (2 weeks at room temperature 20+5 °C) Skydrol (2 weeks at 70°C) Paint 1 (CrVI-based) 0 0 0 Paint 2 (CrVI-based) 0 0 0 Paint 3 (CrVI-based) 0 0 0 Paint 4 (Cr-free) 0 0 0 Paint 5 (Cr-free) 0 0 0

[0124] The overall results show very good adhesion of all the paints tested on the parts of the invention.

[0125] Example 4: Study of corrosion resistance after exposure to heat

[0126] Thermal resistance tests were carried out on parts of the invention (with OAS anodization (ThinSAA) + sealing with silane). These parts were exposed to a salt spray (BS) for 3 hours at 180°C and compared to a reference outside the invention.

[0127] [Tables3] BS Alloy Configuration at 500H, after 3H at 180°C Part (according to the invention) 2024 0 / 0 / 0 Part obtained by chromic acid anodizing (reference outside the scope of the invention) 2024 30 / 30 / 30

[0128] The results obtained with the parts of the invention show an improvement in corrosion resistance after exposure to high temperatures compared to the old treatment.

Claims

Demands

1. Part (1) based on aluminium or an aluminium alloy, characterized in that it comprises: - a body (10) of aluminium or an aluminium alloy, - an inner layer (12) comprising aluminium oxide disposed on the body (10), - an intermediate layer (14) comprising chromium and zirconium, and - an outer layer (16) comprising an organosilicate, the intermediate layer (14) being disposed between the inner layer (12) and the outer layer (16).

2. Part according to claim 1, characterized in that it comprises a layer of paint (18) disposed on the outer layer (16).

3. A part according to claim 1 or 2, characterized in that the aluminum alloy is: - an aluminum alloy of the 2000, 6000, and 7000 series, in particular selected from the group consisting of 2014, 2017, 2024, 2214, 2219, 2618, 7175, 6061, 6063, 7010, 7020, 7050, 7050T7451, 7055, 7068, 7085, 7075, 7175, and 7475, or selected from the group consisting of AU5NKZr, 5052, and 5086, in particular an aluminum alloy selected from the group consisting of 2618A, 2214, and AU5NKZr, or - a aluminum casting alloy selected from the group consisting of AS7G06, AS7G03, AS10G and AS9U3.

4. Part according to any one of claims 1 to 3, characterized in that the outer layer (16) has a thickness between 10 and 500 nm.

5. Part according to any one of claims 2 and 3, characterized in that the paint layer (18) has a thickness between 10 and 100 pm.

6. A method for post-anodizing sealing of an aluminum or aluminum alloy body (10), comprising at least the following steps: A) an impregnation step of the anodized aluminum or aluminum alloy body (10) having an internal layer (12) comprising aluminum oxide, in an aqueous bath of demineralized water containing - a hexafluorozirconate salt selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and - a trivalent chromium salt selected from the group consisting of CrF3,xH2O, CrCl3,xH2O, Cr(NO3)3,xH2O, (CH3CO2)2Cr,xH2O, (CH3CO2)7 Cr3(OH)2,xH2O, Cr2(SO4)3,xH2O, CrK(SO4)2,xH2O, at a temperature between 20 and 80°C; B) a sealing step carried out in an aqueous solution of deionized water having a conductivity less than or equal to 200 pS / cm containing a composition consisting of or comprising a silane and an alkali metal or alkaline earth metal silicate, at a temperature between 60 and 100°C; C) a post-sealing rinsing step with deionized water having a conductivity less than or equal to 100 pS / cm and at a temperature between 15 and 75°C.

7. A process according to claim 6, characterized in that in the impregnation step A), the concentration of hexafluorozirconate salt is between 0.5 and 50 g / L.

8. A process according to any one of claims 6 or 7, characterized in that in the impregnation step A), the concentration of trivalent chromium salt in this step is between 0.1 and 50 g / L.

9. A process according to any one of claims 6 to 8, characterized in that the silane is an organosilane, in particular a trialkoxy organosilane, for example 3-(2,3-epoxypropoxy)propyl]trimethoxysilane.

10. A method according to any one of claims 6 to 9, characterized in that the alkali metal or alkaline earth metal silicate is selected from the group consisting of lithium silicate, sodium silicate, potassium silicate, calcium silicate, magnesium silicate, lithium polysilicate, sodium polysilicate, potassium polysilicate, calcium polysilicate, and magnesium polysilicate, the silicate being in particular lithium silicate or lithium polysilicate.

11. A process according to any one of claims 6 to 10, characterized in that after step A) and before step B), the process comprises an immersion step in a lanthanum salt and hydrogen peroxide bath.

12. A method for manufacturing a part (1) based on aluminium or an aluminium alloy according to any one of claims 1 to 5, comprising at least the following steps: i) subjecting a body (10) made of aluminium or an aluminium alloy to an anodizing step, optionally having previously undergone a surface preparation step (degreasing, then pickling); ii) treating the anodized body having an inner layer (12) by a post-anodizing sealing process according to any one of claims 6 to 9, to successively obtain an intermediate layer (14) comprising chromium and zirconium, and an outer layer (16) comprising an organosilicate; and optionally iii) application of a paint layer (18).

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