POST-ANODIZING SEALANT FOR ALUMINUM AND ALUMINUM ALLOYS WITHOUT THE USE OF CHROME

Abstract

The invention relates to a post-anodization sealing process for aluminum or aluminum alloy without the use of chromium. The invention also relates to a surface treatment process for an aluminum or aluminum alloy part intended for use in the aerospace sector, comprising at least the following steps: i) subjecting said part to an anodization step; ii) treating the anodized part by a post-anodization sealing process according to the invention; and optionally iii) applying one or more coats of paint. The invention also relates to an aluminum or aluminum alloy part treated by a post-anodization sealing process according to the invention, optionally comprising one or more coats of paint. Figure 1

Description

Title of the invention: METHOD FOR POSSTANODIZING ALUMINUM AND ALUMINUM ALLOYS WITHOUT USING CHROME Technical field of the invention

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

[0002] In particular, the process of the invention makes it possible to obtain a coating having very high anti-corrosion properties on aluminium or aluminium alloys, without using chromium. Technical background

[0003] The technical background includes, in particular, documents US-A1-2002 / 117,236, US-A1-2006 / 191,599, US-B-6,663,700, US-A1-2016 / 047,057 and WO- Al-2013 / 117767.

[0004] 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 component degradation and potentially resulting in 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 the alloys is the most widely used. This is particularly true of the protective layers obtained through the anodizing process of aluminum alloys.

[0005] 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 up to several micrometers thick. The oxide layers produced by anodizing have a thickness ranging from two microns to about fifteen microns, in order to provide long-term corrosion protection. Anodizing, also called anodic oxidation, therefore consists of forming a porous layer of aluminum oxides / hydroxides, called the anodic layer, on the surface of the part by applying a current to the part immersed in an electrolytic bath containing a strong acid electrolyte. The part constitutes the anode of the electrolytic system. The layer thus formed on the surface of the part, after a sealing treatment, enhances the part's corrosion resistance. Anodizing treatments are Today, anodizing is 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 / a nodisation-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. .

[0006] 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: • OAS NG (new generation sulfuric anodic oxidation as described for example in www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfurique-version-5-2) has been proposed to replace OAS; • OAST (sulfo-tartaric anodic oxidation as described, for example, in www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfo-tartrique-oast-tartric-sulfuric-anodizing-tsa) has been proposed to replace OAC.

[0007] 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 whose thickness is between 2 and 7 pm.

[0008] 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 satisfactory in terms of corrosion protection on certain grades of so-called "difficult" aluminum alloys. Non-limiting examples of such "difficult" aluminum alloys include alloys 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 than intermetallics rich in copper or iron or nickel, etc. Thus, when the anodic layer forms on the surface of these alloys, layer defects may exist, leading to some local weaknesses susceptible to corrosion.

[0009] For these alloys, it is therefore necessary to optimize the anodizing ranges in order to improve anti-corrosion performance.

[0010] 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 affected 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. Despite the improved corrosion resistance provided by this process, there is a risk of long-term obsolescence of trivalent chromium.Indeed, the CrIU / Zr impregnation step, which is mandatory to allow the silicate sealing step to take place, may become obsolete (due to the chromium) in the future with the tightening of environmental regulations.

[0011] To prevent the long-term obsolescence of trivalent Cr and to be able to comply with future tightening of environmental regulations, it is necessary to optimize the sealing process of anodized aluminum or aluminum alloys, in particular by avoiding the use of chromium.

[0012] There is therefore a real need for a sealing process for aluminium or aluminium alloy, including so-called "difficult" anodized aluminium alloys, not using chromium.

[0013] In particular, there is a real need for a post-anodizing sealing process such as the one described above, which provides good corrosion protection for aluminum or aluminum alloys, including so-called "difficult" aluminum alloys, while complying with the requirements of current and future REACH regulations. Summary of the invention

[0014] The present invention is specifically designed to meet these needs, in particular, in terms of corrosion resistance of aluminum alloys, especially the 2xxx, 6xxx and 7xxx series, cast aluminum alloys such as AS7G06, AS7G03, AS10G or AS9U3, aluminum alloys produced by processes such as additive manufacturing, and so-called difficult aluminum alloys, by providing a post-anodization sealing process for aluminum or aluminum alloy, comprising at least the following steps:

[0015] A) a step of impregnating the anodized aluminum or aluminum alloy, 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 di-, tri-, tetra-, or hepta-valent manganese salt selected from the group consisting of lithium permanganate (LiMnO4), sodium permanganate (NaMnO4), potassium permanganate (KMnO4), ammonium permanganate (NH4MnO4), manganese chloride (MnCl2(H2O)x, where the value of x is 0, 2, or 4),

[0016] or • a tungsten salt selected from the group consisting of lithium tungstate (Li2WO4), sodium tungstate (Na2WO4), potassium tungstate (K2WO4), calcium tungstate (CaWO4), zirconium tungstate (Zr(WO4)2), ammonium tungstate potassium tungstate ((NH4)ioH2(W2O7)6),

[0017] at a temperature between 20 and 80°C;

[0018] B) a sealing step carried out in an aqueous solution of deionized water having a conductivity less than or equal to 100 pS / cm containing between 1 and 500 g / L of an alkali metal silicate or alkaline earth metal silicate, at a temperature between 60 and 100°C;

[0019] C) a post-fouling rinsing step in deionized water having a conductivity less than or equal to 100 pS / cm and at a temperature between 15 and 75°C.

[0020] In the impregnation step A), the concentration of hexafluorozirconate salt is between 0.5 and 50 g / L. The concentration of manganese salt in this step is between 0.1 and 50 g / L.

[0021] Intermediate rinses, in particular with demineralized water, are preferably carried out

[0022] - between steps A) and B), and / or

[0023] - before and / or after the part has been treated by anodizing.

[0024] 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.

[0025] The post-anodization sealing process of the invention makes it possible to obtain a coating having 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.

[0026] The sealing process of the invention can be applied to various anodizings known to those skilled in the art, among which we can mention OAST, OAS NG FE, OAS NG.

[0027] It may or may not be followed by an application of paint.

[0028] The process of the invention demonstrates the possibility of using other types of chrome-free impregnation layers to deposit the silicate on the surface, such as, for example, a Mn / Zr impregnation.

[0029] Knowing that sulfuric anodizing consists of a layer of aluminum oxide, the inventors sought to know

[0030] a) if it were possible to deposit silicate on a chromium-free impregnation layer, for example a Mn / Zr impregnation layer instead of CrIU / Zr, and

[0031] b) if so, whether this deposition would improve the corrosion resistance of the chromium-free impregnation layer, for example a Mn / Zr impregnation layer, as is the case for a CrIU / Zr impregnation layer.

[0032] The invention also relates to a surface treatment method for an aluminum or aluminum alloy part intended for use in the aeronautical sector, comprising at least the following steps:

[0033] i) submitting said part to an anodizing step, possibly having previously undergone a surface preparation step (degreasing, then pickling);

[0034] ii) treatment of the anodized part by a post-anodizing sealing process according to the invention; and possibly

[0035] iii) application of one or more coat(s) of paint.

[0036] Another object of the invention is the use of a post-anodization sealing process according to the invention, in the surface treatment of aluminum or aluminum alloy parts intended for the aeronautical sector.

[0037] The invention also relates to an aluminum or aluminum alloy part treated by a post-anodizing sealing process according to the invention, possibly comprising one or more layers of paint and intended for the aeronautical sector. Brief description of the figures

[0038] Other features and advantages of the invention will become apparent during the course of the Read the detailed description that follows, for an understanding of which refer to the attached drawings in which:

[0039] [Fig.1] Fig.1 represents a theoretical diagram comparing the deposition of species on the anodizing layer (OA) by the sealing process described in FR3106838B1 and by the sealing process of the invention. Detailed description of the invention

[0040] The present invention is specifically aimed at meeting the needs of the prior art, in particular, in terms of corrosion resistance of aluminum alloys, especially of the 2xxx, 6xxx and 7xxx series, casting alloys, and aluminum alloys produced by processes such as additive manufacturing and so-called difficult aluminum alloys, by providing a post-anodization sealing process for aluminum or aluminum alloy, comprising at least the following steps:

[0041] A) a step of impregnating the aluminum or the anodized aluminum alloy 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 di-, tri-, tetra-, or hepta-valent manganese salt selected from the group consisting of lithium permanganate (LiMnO4), sodium permanganate (NaMnO4), potassium permanganate (KMnO4), ammonium permanganate (NH4MnO4), manganese chloride (MnCl2(H2O)x, where the value of x is 0, 2 or 4),

[0042] or • a tungsten salt chosen from the group consisting of lithium tungstate (Li2WO4), sodium tungstate (Na2WO4), potassium tungstate (K2WO4), calcium tungstate (CaW04), zirconium tungstate (Zr(WO4)2), ammonium tungstate potassium tungstate ((NH4)ioH2(W207)6),

[0043] at a temperature between 20 and 80°C;

[0044] B) a sealing step carried out in an aqueous solution of deionized water having a conductivity less than or equal to 100 pS / cm containing between 1 and 500 g / L of an alkali metal silicate or alkaline earth metal silicate, at a temperature between 60 and 100°C;

[0045] C) a post-fouling rinsing step in deionized water having a conductivity less than or equal to 100 pS / cm and at a temperature between 15 and 75°C.

[0046] The di-, tri-, tetra-, or hepta-valent manganese salt may be, for example, one of the following commercial products: Bonderite M-ED160 / 161.

[0047] The tungstate salt may be, for example, one of the following commercial products: lithium tungstate (Li2WO4), sodium tungstate (Na2WO4), potassium tungstate (K2WO4), calcium tungstate (CaWO4), ammonium tungstate potassium tungstate ((NH4)i0H2(W2O7)6) from the Sigma Aldrich brand of Merck, and zirconium tungstate (Zr(WO4)2) from Fisher Scientific.

[0048] Intermediate rinses, in particular with demineralized water, are preferably carried out

[0049] - between steps A) and B), and / or

[0050] - before and / or after the part has been treated by anodizing.

[0051] 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 2xxx, 6xxx and 7xxx series, previously anodized by different processes, for example, by the OAST (sulfo-tartaric anodic oxidation), OAS NG FE (new generation thin thickness sulfuric anodic oxidation) or OAS NG (new generation sulfuric anodic oxidation) processes.

[0052] 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.

[0053] Thus, the post-anodization sealing process of the invention makes it possible to obtain a coating having very high anti-corrosion properties on the aluminum alloys of the 2xxx, 6xxx and 7xxx series and the difficult aluminum alloys, but also on the most common aluminum alloys in the aeronautical field, such as 2024 and 7175 and the so-called "difficult" aluminum alloys such as 2618A and 2214.

[0054] The process of the invention is particularly suitable for aluminum and aluminum alloy parts of the 2xxx, 6xxx and 7xxx 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 of type AS7G06, AS7G03, AS10G and AS9U3, aluminum alloys produced by processes such as additive manufacturing.

[0055] 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. The concentration of di-, tri-, tetra-, or hepta-valent manganese salt, or tungstate salt in this step is between 0.1 and 50 g / L, for example equal to 1 g / L.

[0056] The bath temperature in step A) can be between 20 and 80°C, preferably between 20 and 60°C, more preferably between 35 and 60°C, by example between 35 and 45°C.

[0057] 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.

[0058] 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.

[0059] The impregnation step A) is followed by a step B) which is a sealing step. 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.

[0060] The temperature of the aqueous solution in step B) is preferably between 80 and 100°C, for example between 80 and 98°C.

[0061] The alkali metal or alkaline earth metal silicate may be selected from the group consisting of lithium silicate, sodium silicate, potassium silicate, calcium silicate and magnesium silicate.

[0062] 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.

[0063] The duration of the sealing step B) is between 1 and 40 minutes, preferably between 5 and 35 minutes, for example between 5 and 30 minutes.

[0064] The pH of the sealing solution is between 9 and 12, preferably between 10 and 11.5 minutes, for example between 10.5 and 11.4.

[0065] 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.

[0066] Post-clogging rinsing is preferably carried out at a temperature between 10 and 75°C, for example between 15 and 60°C.

[0067] 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.

[0068] 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.

[0069] It has been found, quite unexpectedly, that the combination of the steps of impregnation + sealing + post-sealing rinsing, as described below, is essential to guarantee good anti-corrosion performance of aluminum or aluminum alloy.

[0070] Intermediate rinses, in particular with demineralized water, can be carried out between the steps described above.

[0071] Boiling water sealing, which has the advantage of not using harmful substances and significantly improves the corrosion resistance of anodized layers when properly controlled: sealing must be carried out in demineralized water with a minimum temperature above 75°C, preferably above 90°C, more preferably at or above 96°C, and a pH between 5.5 and 6.5. The quality of the water used is important for the success of the operation, as certain impurities are known to be harmful even at very low concentrations (for example, Ca2+, Cu2+, Fe2+, F, Cl, SiO3, PO43). In particular, a particularly harmful effect of silicate, phosphate, and chloride ions will be observed. The treatment time is approximately 2.5 min / pm (close to the anodizing time). This operation is a partial thermohydration of alumina which crystallizes into monohydrated alumina (Bôhmite).

[0072] Before subjecting the aluminium or aluminium alloy to the anodizing step, the aluminium or aluminium alloy 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.

[0073] 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 immersion, 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 oxides naturally formed on the surface of 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 a person in the trade.

[0074] The preliminary step of surface preparation of the aluminium or 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.

[0075] Intermediate rinses, in particular with demineralized water, are preferably carried out between the successive steps above, and before the treatment of the part by anodizing.

[0076] Before applying the sealing process of the invention, the aluminum or 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. Examples include • OAS: Sulfuric Anodic Oxidation (Clogging based on Chromium VI, a process impacted by the European REACH regulation), • OAC: Chromic Anodic Oxidation (Based on Chromium VI, a process impacted by the European REACH regulation), • OAST: SulfoTartaric Anodic Oxidation, • OAST: SulfoTartaric Anodic Oxidation, • OAS NG FE: New Generation Thin Sulfuric Anodic Oxidation, • OAS NG: New Generation Sulfuric Anodic Oxidation.

[0077] In the context of the present invention, the OAST LC, OAS NG FE, OAS NG anodizing processes are preferred.

[0078] The surface treatment process of the invention substantially improves the corrosion resistance properties of metal or metal alloy parts, in particular aluminum or aluminum alloy parts, and complies with the requirements of the European REACH regulation.

[0079] The process of the invention is of great interest in any type of industry where it is sought to improve the corrosion resistance properties of metal or metal alloy parts, in particular aluminum or aluminum alloy parts, such as in aeronautics, automotive, petroleum industry etc.

[0080] The method according to the invention may comprise one or more of the following features and / or steps, taken individually or in combination with each other:

[0081] - the aluminum alloy is an aluminum alloy of the 2xxx, 6xxx and 7xxx series, in particular chosen 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 type AS7G06, AS7G03, AS10G and AS9U3, aluminum alloys produced by processes such as additive manufacturing;

[0082] - in the impregnation step A), the concentration of hexafluorozirconate salt is between 0.5 and 50 g / L;

[0083] - in the impregnation step A), the concentration of di-, tri-, tetra- manganese salt, or hepta-valent, or in tungstate is between 0.1 and 50 g / L;

[0084] - the alkali metal silicate or alkaline earth metal silicate is chosen from the group consisting of lithium silicate, sodium silicate, potassium silicate, calcium silicate and magnesium silicate;

[0085] - the concentration of alkali metal silicate or alkaline earth metal in the the solution concentration is between 5 and 100 g / L;

[0086] - the rinsing step C) is carried out in deionized water having a conductivity between 1 and 100 pS / cm.

[0087] The process of the invention makes it possible to obtain corrosion resistance similar to chromated anodizing without the use of chromium. It provides an innovative sealing solution for anodizing aluminum alloys, thus meeting the specifications for corrosion resistance and paint adhesion without using chromium.

[0088] The invention also relates to a surface treatment method for an aluminum or aluminum alloy part intended for use in the aeronautical sector, comprising at least the following steps:

[0089] i) submitting said part to an anodizing step, possibly having previously undergone a surface preparation step (degreasing, then pickling);

[0090] ii) treatment of the anodized part by a post-anodizing sealing process according to the invention; and possibly

[0091] iii) application of one or more coat(s) of paint.

[0092] Another object of the invention is the use of a post-anodization sealing process according to the invention, in the surface treatment of aluminum or aluminum alloy parts intended for the aeronautical sector.

[0093] The invention also relates to an aluminum or aluminum alloy part treated by a post-anodizing sealing process according to the invention, possibly comprising one or more layers of paint and intended for the aeronautical sector.

[0094] Anodizing treatment followed by painting: some aeronautical parts undergo a painting treatment after anodizing to enhance corrosion protection. The invention is compatible with various painting systems.

[0095] Other advantages and features of the invention will become apparent from the examples given below, which are given by way of illustration. EXAMPLES Example 1:

[0096] Post-anodization sealing process for aluminum alloy parts

[0097] Aluminum alloy 2618 T6 parts with dimensions of 120x100x5 mm are processed according to the methods described below.

[0098] Surface preparation steps for the part are first carried out successively: - alkaline degreasing, by soaking the part in a SOCOCLEAN A3431 solution at 11% by volume, at a temperature of 45°C, for 10 minutes; - rinse with tap water or demineralized water; - acid pickling by immersing the part in a SOCOSURF mixture A1858 at 42% by volume and SOCOSURF A1806 at 10% by volume at a temperature of 50°C for 10 minutes; - Rinse with tap water or demineralized water.

[0099] The pickled and rinsed parts are then subjected to a new generation sulfuric anodizing process (standard thickness or thin thickness (FE)).

[0100] The operating parameters for anodizing are indicated in Table 1 below.

[0101] [Tables 1] OAS NG Bath composition H2SO4: 150-220 g / L Bath temperature 16-20°C Layer thickness formed (pm) 8-15 pm

[0102] The anodized parts according to the invention are then subjected to the sealing process according to the invention under the conditions and in the order indicated below in: - step A): an impregnation step of said parts, successively, in an aqueous bath of BONDERITE M-ED 160 / 161 (15g / L ED160 and 18g / L ED161) at a temperature of 40°C for 10 minutes and at a pH of 3.9, then - step B): sealing by immersion of the parts in an aqueous solution of deionized water having a conductivity of less than 100 pS / cm with 80g / L of a sodium silicate, a temperature of 100°C and for 10 minutes; - step C): a post-clogging rinse by immersing the parts after the three previous clogging operations in deionized water having a conductivity of less than 100 pS / cm, at a temperature of 20°C for 1 minute.

[0103] Between each step a rinse with demineralized water is carried out.

[0104] These conditions are indicated in [Table 2].

[0105] [Tables2] Impregnation, Clogging, Post-clogging rinsing, Bath composition: BONDERITE M-ED 160 / 161, 15g / LED160, 18g / LED161, Deionized water (conductivity <100 pS / cm) + sodium silicate 80 g / L, Deionized water (conductivity <100 pS / cm), Bath temperature: 35 to 45°C, 98°C, 20°C, Bath pH: 3.7 - 4.2, 10.5-11.4, 5.5-7.5, Treatment time: 5 to 20 min, 5 to 30 min, 10s to 2 min

[0106] Corrosion resistance results evaluated on anodized alloys sealed by conventional sealing methods and by the process of the invention:

[0107] By way of comparison, aluminum alloy parts anodized according to the method shown in [Table 1] are then subjected to one or more sealing operations such as hydrothermal sealing (Mn / Zr + Water) according to methods known to those skilled in the art and compared to parts anodized and sealed by the process of the invention (Mn / Zr + Silicate). The parts thus treated are subjected to a salt spray (SB) resistance test conforming to standard NF EN ISO 9227. The number of pits at 500h of salt spray (SB) is reported in Table 3 below.

[0108] [Tables3] Alloy Configuration 500h BS OASfine+Mn / Zr+Si (according to the invention) 2618 2 / 9 / 2 OASfine+Mn / Zr+H2O 2618 50+ / 40+ / 50+ OASfine + W / Zr + water 2024 General Corrosion OASfine +W / Zr + Si 2024 5 / 4

[0109] The anodizing treatment followed by silicate-based sealing according to the invention achieves significantly better anti-corrosion performance than hydrothermal sealing. In light of these results, the positive impact of silicates is evident and allows for interesting results approaching those of chromate impregnation. Extreme Surface Analysis (XPS)

[0110] X-ray photoelectron spectrometric analyses (XPS) were performed on a THERMO K-alpha+ instrument with a monochromatized Al Kalpha source. Processing software: Advantage.

[0111] The surface of a sample that has undergone Mn / Zr+Si sealed anodization (named 2618-T652-047-104 in Table 4 below).

[0112] [Tables4] Sample CO Al Si Zr N Na s F Ca 2618-T652-047-104 33.2 47.2 - 19.4 - 0.1 - - - 0.1

[0113] As shown by the elemental analysis of the extreme surface (50 nm surface area), an enrichment in silicon in oxidized form (presence of oxygen) is detectable. This confirms the presence of silicate on the surface.

[0114] The deposition of silicate on the surface of an anodized Mn / Zr impregnated coating improves the corrosion resistance of a chrome-free anodized coating.

[0115] The invention proves the possibility of depositing silicate on an impregnation other than CrIU / Zr, thus making it possible to achieve interesting corrosion performance without the use of chromium.

Claims

Demands

1. A method for post-anodizing sealing of aluminum or aluminum alloy, comprising at least the following steps: A) a step of impregnating the anodized aluminum or aluminum alloy 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 di-, tri-, tetra-, or hepta-valent manganese salt selected from the group consisting of lithium permanganate (LiMnO4), sodium permanganate (NaMnO4), potassium permanganate (KMnO4), ammonium permanganate (NH4MnO4), manganese chloride (MnCl2(H2O)x), where the value of x is 0, 2 or 4, Or • a hexafluorozirconate salt selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and • a tungsten salt chosen from the group consisting of lithium tungstate (Li2WO4), sodium tungstate (Na2WO4), potassium tungstate (K2WO4), calcium tungstate (CaWO 4), zirconium tungstate (Zr(WO4)2), ammonium tungstate potassium tungstate ((NH4)ioH2(W207)6), 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 100 pS / cm containing between 1 and 500 g / L of an alkali metal silicate or alkaline earth metal silicate, at a temperature between 60 and 100°C; C) a post-fouling rinsing step in deionized water having a conductivity less than or equal to 100 pS / cm and at a temperature between 15 and 75°C.

2. A process according to claim 1, characterized in that the aluminum alloy is an aluminum alloy of the 2xxx, 6xxx, and 7xxx 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 of type AS7G06, AS7G03, AS10G, and AS9U3, aluminum alloys produced by processes such as additive manufacturing

3. A process according to any one of claims 1 or 2, characterized in that in the impregnation step A), the concentration of hexafluorozirconate salt is between 0.5 and 50 g / L.

4. A process according to any one of claims 1 to 3, characterized in that in the impregnation step A), the concentration of di-, tri-, tetra-, or hepta-valent manganese salt, or tungstate salt, is between 0.1 and 50 g / L.

5. A method according to any one of claims 1 to 4, characterized in that the sealing of step B) is carried out in an aqueous solution of deionized water having a conductivity between 1 and 100 pS / cm.

6. A method according to any one of claims 1 to 5, 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 and magnesium silicate.

7. A process according to any one of claims 1 to 6, characterized in that the concentration of alkali metal silicate or alkaline earth metal in the solution is between 5 and 100 g / L.

8. A method according to any one of claims 1 to 7, characterized in that the rinsing step C) is carried out in deionized water having a conductivity between 1 and 100 pS / cm.

9. A surface treatment method for an aluminum or aluminum alloy part intended for use in the aeronautical sector comprising at least the following steps: i) subjecting said part to an anodizing step, having optionally undergone a surface preparation step (degreasing, then pickling); ii) treating the anodized part by a post-anodizing sealing process according to any one of claims 1 to 8; and optionally iii) applying one or more coats of paint.

10. Use of a post-anodization sealing process according to any one of claims 1 to 8, in the surface treatment of aluminum or aluminum alloy parts intended for the aeronautical sector.

11. Part made of aluminium or aluminium alloy treated by a post-anodisation sealing process according to any one of claims 1 to 8, optionally comprising one or more layers of paint, intended for the aeronautical sector.

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