Method for sealing aluminum alloys using a silane and aluminum-based or aluminum alloy-based part obtained by this method

Abstract

The present invention relates to a part (1) based on aluminum or on an aluminum alloy, comprising - a body (10) made of aluminum or of an aluminum alloy, - an inner layer (12) comprising aluminum oxide placed 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 placed between the inner layer (12) and the outer layer (16). The invention also relates to a method for post-anodization sealing of a body (10) made of aluminum or of an aluminum alloy.

Description

[0001] DESCRIPTION

[0002] TITLE: PROCESS FOR SEALABLES OF ALUMINUM ALLOYS USING A SILANE AND ALUMINUM-BASED PART OR PART MADE OF AN ALUMINUM ALLOY OBTAINED BY THIS PROCESS

[0003] Technical field of the invention

[0004] 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.

[0005] Technical background

[0006] Aluminum alloys are materials of choice for the transportation industry, and particularly for the aerospace industry, due to their excellent mechanical properties-to-weight ratio and relatively low manufacturing cost. However, depending on their environment, these alloys are susceptible to various types of localized corrosion, leading to component degradation and potentially resulting in removal or failure. Numerous strategies have been implemented to address 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 notably the case with the protective coatings obtained through the anodizing process.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, have prohibited (or restricted to authorization) the use of certain key components in surface treatments, in particular, hexavalent chromium. Hexavalent chromium is present in the OAC (Chromic Anodic Oxidation) type anodizing treatment, as described, for example, at www.a3ts.org / actualite / commissions- techniques / fiches-techniques-traitement-surface / anodisation-chromique), but also in the usual pretreatments of surface preparation, aimed at cleaning / stripping the surfaces of the parts before the anodizing treatment, and finally in the final treatments known as sealing, the objective of which is to close the pores of the anodic layer formed during the anodizing treatment.

[0007] 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:

[0008] - 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") has been proposed to replace OAS;

[0009] - 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.

[0010] OAC can also be replaced by OAS NG FE (new generation thin thickness sulfuric anodic oxidation) which is an OAS NG type anodizing whose anodizing parameters (Voltage, Immersion Time) have been adapted to obtain an anodized layer with a thickness of between 2 and 7 pm.

[0011] Although current conventional anodizing solutions, such as OAS NG followed by hot water sealing, employ treatment ranges compliant with European REACH regulations, they remain unsatisfactory or even inadequate in terms of corrosion protection on certain grades of so-called "difficult" aluminum alloys. Examples of such "difficult" aluminum alloys include 2214, 2618A, and AU5NKZr. These alloys possess unique microstructures due to their chemical composition, resulting in either casting-type defects or precipitates such as copper-, iron-, or nickel-rich intermetallics. Consequently, when the anodic layer forms on the surface of these alloys, layer defects may persist, leading to localized weaknesses susceptible to corrosion.

[0012] For these alloys, it is therefore necessary to optimize the anodizing ranges in order to improve anti-corrosion performance.

[0013] 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 containing an alkali metal silicate or an alkaline earth metal silicate, and optionally followed by the application of a paint.Despite the improved corrosion resistance offered 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 corrosion resistance of these alloys and, where applicable, paint adhesion, while complying with the requirements of the European REACH regulation. The present invention aims to overcome the drawbacks of current anodizing processes for aluminum or aluminum alloy parts, including so-called "difficult" aluminum alloys, in terms of the corrosion resistance of said alloys, and enables better paint adhesion, achieved using a robust process.

[0014] Furthermore, the present invention aims to provide an aluminum or aluminum alloy part with improved corrosion resistance while complying with the requirements of the European REACH regulation.

[0015] 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, particularly in terms of thermal resistance, fluid resistance, sealant adhesion, fatigue resistance, and friction resistance, unaltered or even improved compared to parts obtained by prior art processes.

[0016] Summary of the invention

[0017] 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:

[0018] - a body (10) made of aluminium or an aluminium alloy,

[0019] - an inner layer (12) comprising aluminium oxide disposed on the body (10),

[0020] - an intermediate layer (14) comprising chromium and zirconium, and

[0021] - an outer layer (16) comprising an organosilicate, the intermediate layer (14) being arranged between the inner layer (12) and the outer layer (16).

[0022] 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:

[0023] A) an impregnation step of the body (10) made of aluminium or an anodized aluminium alloy having an inner layer (12) comprising aluminium oxide, in an aqueous bath of demineralized water containing - a hexafluorozirconate salt selected from the group consisting of ammonium hexafluorozirconate ((NH₄ZrFe), sodium hexafluorozirconate (Na₂ZrFe), potassium hexafluorozirconate (K₂ZrFe), and

[0024] - a trivalent chromium salt chosen from the group consisting of CrF3,xH2O, CrCl3,xH2O, Cr(NO3)3,xH2O, (CHsCO^Cr.x , (CH3CO2)7Cr3(OH)2,xH2O, Cr2(SO4)3,xH2O, CrK(SO4)2,xH2O, at a temperature between 20 and 80°C;

[0025] 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; 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;

[0026] C) a post-clogging 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.

[0027] Intermediate rinses, particularly with demineralized water, can be carried out:

[0028] - between steps A) and B), and / or

[0029] - before and / or after the part has been treated by anodizing.

[0030] Because anodized coatings have a highly porous structure, when chemical and / or corrosion resistance is critical, 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:

[0031] • Sealing the pores leads to increased corrosion resistance; • Fouling is prevented;

[0032] • The washing of dyes out of the pores is avoided.

[0033] 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.

[0034] 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 (Sulforic-Tartaric Anodizing), OAS NG FE (New Generation Thin Thick Sulfuric Anodizing), OAS NG (New Generation Sulfuric Anodizing), TSA (Tartaric sulfuric Anodizing).

[0035] 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: i) subjecting a body (10) made of aluminium or an aluminium alloy to an anodizing step, having optionally 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 the invention, 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).

[0036] The invention also relates to a part according to the invention, possibly comprising a layer of paint and intended for the aeronautical sector.

[0037] Brief description of the figures

[0038] Other features and advantages of the invention will become apparent during the reading of the detailed description which follows, for the understanding of which reference will be made to the attached drawings in which: [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] shows examples of treatment ranges and the operating conditions of the tests performed. SOCOCLEAN A3432 from SOCOMORE is a degreaser compatible with aluminum and its alloys. SOCOSURF A1858-A1806 from SOCOMORE is a two-component bath for deoxidizing or bleaching 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 sealing of the porous layer is finally carried out with an aqueous solution, consisting of or comprising a silane, in particular an organosilane, and an alkali metal or alkaline earth metal silicate (for example at 80g / L in silicate).

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

[0041] Detailed description of the invention

[0042] A first object of the invention relates to a part (1) made of aluminium or an aluminium alloy, characterized in that it comprises:

[0043] - a body (10) made of aluminium or an aluminium alloy,

[0044] - an inner layer (12) comprising aluminium oxide disposed on the body (10),

[0045] - an intermediate layer (14) comprising chromium and zirconium (Cr IH / Zr), and

[0046] - an outer layer (16) comprising an organosilicate, the intermediate layer (14) being arranged between the inner layer (12) and the outer layer (16).

[0047] As indicated, the part (1) according to the invention comprises a body (10) made of aluminum or an aluminum alloy. The aluminum alloy can be selected from the 2000, 6000, and 7000 series, specifically 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; and in particular, aluminum alloys (so-called difficult alloys) selected from the group consisting of 2618A and 2214. and AU5NKZr.

[0048] The part (1) comprises a body (10) on which an inner layer (12) is deposited. 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) using 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 deposited 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 (Cr IH / Zr) and the outer layer (16) comprising an organosilicate, provides good corrosion resistance to the part (1). In addition, 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) an impregnation step of the anodized aluminum or 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 (Na2ZrFe), potassium hexafluorozirconate (ZrFe), and

[0056] - a trivalent chromium salt chosen from the group consisting of CrF3,xH2O, CrCl3,xH2O, Cr(NO3)3,xH2O, (CH3CO2)2Cr,xH2O, (CH3CO2)7Cr3(OH)2,xH2O, Cr2(SO4)3,xH2O, CrK(SO4)2,xH2O, at a temperature between 20 and 80°C;

[0057] B) a sealing step carried out in an aqueous solution of deionized water having a conductivity of 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; in particular a sealing step carried out in an aqueous solution of deionized water having a conductivity of 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; C) a post-sealing rinsing step with deionized water having a conductivity of less than or equal to 100 pS / cm and at a temperature between 15 and 75°C.

[0058] The deposition of organosilicate on the surface of an anodized surface impregnated with Crill / Zr improves the corrosion resistance of the aluminum or aluminum alloy part as well as the adhesion of the paint to said part.

[0059] As already mentioned, intermediate rinses, particularly with demineralized water, can be carried out

[0060] - between steps A) and B), and / or

[0061] - before and / or after the part has been treated by anodizing.

[0062] The optimized sealing process of the invention can be suitable for all types of aluminum alloys including so-called "difficult" alloys, in particular aluminum alloys of the 2000, 6000 and 7000 series, previously anodized by various processes including OAC, OAD, OAS, OAST, OAS NG FE, OAS NG, TSA.

[0063] Furthermore, the post-anodization sealing process of the invention is compatible with the requirements of the European REACH regulation and provides good corrosion protection on so-called "difficult" aluminum alloys (e.g., 2618A, 2214, and AU5NKZr). This process may or may not be followed by a painting application.

[0064] 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.

[0065] 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.

[0066] The trivalent chromium salt can be, for example, one of the following commercial products: Surtec 650 from SURTEC, Lanthane 613.3 from COVENTYA, or TCS from SOCOMORE. In the impregnation step A), the concentration of the hexafluorozirconate salt is between 0.5 and 50 g / L, for example, 2 g / L.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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).

[0071] 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.

[0072] The silane as defined in step B) is in particular an organosilane, especially a trimethoxy organosilane, for example a trimethoxy organosilane. The silane is for example 3-(2,3-epoxypropoxy)propyl]trimethoxysilane.

[0073] The alkali metal silicate or alkaline earth metal silicate may be chosen 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.

[0074] The silane concentration in the sealing step B) is preferably between 1 and 50 g / L, for example between 5 and 50 g / L. The silane content may be adjusted, in particular with respect to the alkali metal or alkaline earth metal silicate content, especially according to the desired organosilicate content in the part of the invention.

[0075] 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.

[0076] 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.

[0077] The longer the duration of the sealing step B), the more organosilicate will be deposited. The duration of the sealing step B is specifically between

[0078] 1 and 40 minutes, preferably between 5 and 35 minutes, for example between 5 and 30 minutes, in particular 10 minutes.

[0079] 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.

[0080] 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.

[0081] Post-clogging rinsing is preferably carried out at a temperature between 10 and 75°C, for example between 15 and 60°C.

[0082] 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.

[0083] 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.

[0084] It was discovered, quite unexpectedly, that the combination of the steps (impregnation A) + sealing B) + post-sealing rinsing C), as described below, is essential to guarantee good corrosion protection performance of the aluminum or aluminum alloy. Furthermore, the application of the composition consisting of or comprising a silane, particularly an organosilane, and an alkali metal or alkaline earth metal silicate, must be carried out after the impregnation step (A) in order to obtain the desired corrosion protection properties and performance of the aluminum or aluminum alloy.

[0085] Intermediate rinses, particularly with demineralized water, can be carried out between the steps described above.

[0086] Before submitting 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.

[0087] This preliminary surface preparation step may include one or more of the following operations:

[0088] - Solvent degreasing, to dissolve greases present on the surface of the aluminum or aluminum alloy. This operation can be carried out by immersion, spraying, or any other method known to those skilled in the art;

[0089] - 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;

[0090] - 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;

[0091] - Acid pickling, to dissolve 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. The preliminary step of surface preparation of the body (10) made of aluminum or an aluminum 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.

[0092] Intermediate rinses, particularly with demineralized water, are preferably carried out between the successive steps above, and before the part is treated by anodizing.

[0093] 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 is suitable.

[0094] 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:

[0095] - 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") has been proposed to replace OAS;

[0096] - OAST (Oxydation Anodique SulfoTartrique 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; and

[0097] - OAS NG FE: New Generation Thin Sulfuric Anodic Oxidation, which is an OAS NG type anodizing whose anodizing parameters (Voltage, Immersion Time) have been adapted to obtain an anodized layer with a thickness between 2 and 7 pm.

[0098] Within the framework of the present invention, the OAST, OAS NG FE, OAS NG anodizing processes are preferred.

[0099] 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. Furthermore, the process of the invention provides better conditions for paint adhesion.

[0100] 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: i) subjecting a body (10) made of aluminium or an aluminium alloy to an anodizing step, having optionally 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 the invention, to successively obtain an intermediate layer (14) comprising chromium and zirconium, and an outer layer (16) comprising organosilicate; and optionally iii) application of a paint layer (18).

[0101] The invention also relates to a part according to the invention, possibly comprising a layer of paint and intended for the aeronautical sector.

[0102] EXAMPLES

[0103] Example 1: Method according to the invention for surface treatment of an aluminum alloy part

[0104] 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 of 120x60x2 mm are treated according to the process described below.

[0105] The surface preparation steps for the part are first carried out successively:

[0106] - 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;

[0107] - rinse with tap water or demineralized water;

[0108] - Acid pickling, by immersing the part in a solution of SOCOSURF A1858 at 42% vol / vol - A1806 at 10% vol / vol (from SOCOMORE) at a temperature of 50°C for 10 minutes; rinsing with tap water or demineralized water. 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 0V at a rate of 0.4 V / min until reaching a plateau voltage of 6V. 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.

[0109] The thickness of the anodic layer formed on the part is measured by eddy current according to the ISO2360 standard.

[0110] 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:

[0111] - 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

[0112] - step B): sealing by immersion of the parts at the end of the 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, in particular a trialkoxy organosilane, and an alkali metal or alkaline earth metal silicate, at a temperature of 98°C for 20 minutes, the pH being in particular between 9 and 12, in particular between 10 and 11;

[0113] - 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.

[0114] Between each step, a rinse with demineralized water is performed. Example 2: Corrosion resistance results evaluated on anodized alloys sealed by conventional sealing processes and by the sealing process of the invention:

[0115] 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).

[0116] The parts thus treated are subjected to a salt spray (BS) resistance test in accordance with the NF EN ISO 9227 standard. The number of pits at 500h of salt spray (BS) is reported in table 1 below.

[0117] [Table 1]

[0118] 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).

[0119] Parts made of 2024, 2214, or 7050 aluminum alloy treated according to the invention also demonstrated excellent corrosion resistance. Example 3: Paint adhesion tests

[0120] Paint adhesion tests (3 paints containing CrVI inhibitors, 2 paints containing Cr-free inhibitors) were performed on parts treated with 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).

[0121] [Table 2]

[0122] The overall results show very good adhesion of all the paints tested on the parts of the invention.

[0123] Example 4: Study of corrosion resistance after exposure to heat

[0124] Thermal resistance tests were carried out on parts of the invention (with OAS (ThinSAA) anodizing + silane sealing). These parts were exposed to salt spray (BS) for 3 hours at 180°C and compared to a reference outside the invention.

[0125] [Table 3] 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) made of aluminium or an aluminium alloy, characterized in that it comprises: - a body (10) made 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 arranged 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. Part according to claim 1 or 2, characterized in that the aluminum alloy is - an aluminum alloy from 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, 7050 T7451, 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 - an aluminium foundry 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 post-anodization sealing process for a body (10) made of aluminum or an aluminum alloy, comprising at least the following steps: A) a step of impregnating the body (10) made of aluminum or an aluminum alloy, anodized and comprising an inner 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 (Na2ZrFe), potassium hexafluorozirconate (K2ZrFe), and - a trivalent chromium salt chosen from the group consisting of CrF3,xH2O, CrCl3,xH2O, Cr(NO3)3,xH2O, (CH3CO2)2Cr,xH2O, (CH3CO2)7Cr3(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-clogging 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. 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 process 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, having optionally 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) applying a paint layer (18).

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