Method for sealing aluminum alloys using tungsten salts and aluminum-based or aluminum alloy-based parts obtained by this method

Abstract

The invention relates to an aluminum or aluminum alloy-based component (1) comprising a main body (10) made of aluminum or aluminum alloy, an inner layer (12) comprising aluminum oxide placed on the main body (10), an intermediate layer (14) comprising chromium and zirconium, and an outer layer (16) comprising tungsten oxide, 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 main body (10) made of aluminum or aluminum alloy.

Description

Technical Field

[0001] This invention is part of the search for new solutions for corrosion protection of aluminum alloys, particularly those used in aerospace applications, with or without the application of a coating system. Background Technology

[0002] Aluminum alloys are the preferred material for the transportation industry, especially the aerospace industry, due to their excellent mechanical properties / weight ratio and relatively low manufacturing cost. However, depending on the environment in which they are used, these alloys can be susceptible to several types of localized corrosion, leading to component degradation and potentially their removal or failure. Many strategies have been implemented to overcome this deficiency, among which forming or depositing a protective layer on the surface of aluminum alloy components is the most widely used. This is especially true of the protective layer obtained during the anodizing process of aluminum alloy components. Anodizing is an electrolytic process that replaces the several nanometer-thick layer of natural oxides (native oxides) covering aluminum with an oxide layer that can be several micrometers thick. The oxide layer produced by anodizing ranges in thickness from 2 micrometers to approximately 15 micrometers to provide long-term corrosion protection. Anodizing (also known as anodic oxidation) involves forming a porous aluminum oxide / hydroxide layer (called the anodic layer) on the surface of the component by applying an electric current to the component immersed in an electrolytic bath containing a strongly acidic electrolyte. This component forms the anode of the electrolytic system. The layer thus formed on the component surface can enhance the corrosion resistance of the component after a sealing treatment. Anodizing is now commonly used in the aerospace industry, primarily to improve the corrosion resistance of components, thereby extending their service life, and also to facilitate the adhesion of organic layers (coatings). However, anodizing methods are directly affected by European regulations (REACH), which, since September 2017, have prohibited (or restricted the authorization of) the use of certain critical elements in surface treatments, particularly hexavalent chromium. Hexavalent chromium is present in CAA-type anodizing (chromic acid anodizing, as described at www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-chromique), as well as in routine surface preparation pretreatments aimed at cleaning / stripping the surface of the component before anodizing, and finally in the final treatment (called sealing), which aims to seal the pores of the anodic layer formed during anodizing.

[0003] Different methods have been proposed as alternatives to CAA and SAA (sulfuric acid anodizing) treatments using hexavalent chromium seals, which are subject to the European regulation REACH. NGSAA (Next Generation Sulfuric Acid Anodizing, as described in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfurique-version-5-2") has been proposed as an alternative to SAA; TSA (tartaric acid-sulfuric acid anodizing, as described in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfo-tartrique-oast-tartric-sulfuric-anodizing-tsa") has been proposed as an alternative to CAA.

[0004] CAA can also be replaced by NGSAA-TL (Thin-Layer Next-Generation Sulfuric Acid Anodizing), which is an anodizing of the NGSAA type with its anodizing parameters (voltage, immersion time) adjusted to obtain an anodized layer with a thickness between 2 μm and 7 μm.

[0005] While current conventional anodizing solutions, such as NGSAA and subsequent hot water sealing, achieve a range of treatments compliant with European regulation REACH, they remain unsatisfactory, or unsatisfactory in terms of corrosion protection on certain grades of aluminum alloys referred to as "difficult." Non-limiting examples of aluminum alloys termed "difficult" include alloys 2214, 2618A, or AU5NKZr. These alloys possess specific microstructures due to their chemical composition, which makes them susceptible to casting defects or deposits, such as intermetallic compounds rich in copper, iron, or nickel. Therefore, when an anodizing layer forms on the surface of these alloys, these layer defects may be retained, leading to certain localized brittleness that makes them susceptible to corrosion.

[0006] Therefore, for these alloys, it is necessary to optimize the anodizing range to improve corrosion resistance.

[0007] Patent FR 3106838B1 discloses a method for post-anodization sealing of aluminum or aluminum alloys that improves corrosion resistance of components without the use of hexavalent chromium, which is subject to the European REACH regulations. This method is also applicable to so-called “difficult” aluminum alloys and includes a step of immersing the aluminum or aluminum alloy in a water bath containing hexafluorozirconate and trivalent chromium salts, followed by a sealing step in an aqueous solution containing alkali metal or alkaline earth metal silicates, optionally followed by the application of a coating. While this method brings improvements in corrosion resistance, further optimization of current anodizing methods for aluminum or aluminum alloy components, including so-called “difficult” aluminum alloys, is needed to improve the corrosion resistance of these alloys while complying with the requirements of the European REACH regulations.

[0008] The purpose of this invention is to overcome the shortcomings of current methods for anodizing parts made of aluminum or aluminum alloys (including so-called "difficult" aluminum alloys) in terms of the corrosion resistance and good coating adhesion of the alloys.

[0009] Furthermore, the present invention aims to provide an aluminum or aluminum alloy component that has improved corrosion resistance while complying with the requirements of the European REACH regulations. Summary of the Invention

[0010] The present invention is configured to meet these requirements by providing an aluminum- or aluminum alloy-based component, characterized in that the component comprises: The main body is made of aluminum or aluminum alloy. An inner layer containing alumina is placed on the main body. An intermediate layer containing chromium and zirconium, and The outer layer contains tungsten oxide, and the middle layer is placed between the inner and outer layers.

[0011] This component may include one or more of the following features: The component includes a coating layer (18) placed on the outer layer; Aluminum alloys are selected from the 2000, 6000, and 7000 series; The aluminum alloy is selected from the group consisting of 2014, 2017, 2024, 2214, 2219, 2618, AU5NKZr, 7175, 5052, 5086, 6061, 6063, 7010, 7020, 7050, 7050 T7451, 7055, 7068, 7085, 7075, 7175 and 7475. The aluminum alloy is a cast aluminum alloy selected from the group consisting of AS7G06, AS7G03, AS10G and AS9U3. Aluminum alloys are so-called difficult aluminum alloys selected from the group consisting of 2618A, 2214, and AU5NKZr; The thickness of the outer layer is between 10 and 500 nm; The thickness of the coating layer is between 10 and 100 µm.

[0012] The present invention also relates to a method for sealing a body made of aluminum or aluminum alloy after anodizing, the method comprising at least the following steps: A) The step of impregnating anodized aluminum or aluminum alloy in a water bath containing demineralized water at a temperature between 20°C and 80°C. Hexafluorozirconate, wherein the hexafluorozirconate is selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), and potassium hexafluorozirconate (K2ZrF6), and The trivalent chromium salt is selected 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, and CrK(SO4)2,xH2O. B) A sealing step performed in an aqueous solution of deionized water containing 1 to 200 g / L, preferably 5 to 100 g / L, of alkali metal or alkaline earth metal silicates with a conductivity of less than or equal to 100 μS / cm at a temperature between 60°C and 100°C. C) A post-sealing rinsing step performed with deionized water having a conductivity of less than or equal to 100 µS / cm at a temperature between 15°C and 75°C.

[0013] The method may include one or more of the following features or steps: In impregnation step A), the concentration of hexafluorozirconate is between 0.5 and 50 g / L; In impregnation step A), the concentration of trivalent chromium salt is between 0.1 and 50 g / L; In step B), the alkali metal or alkaline earth metal tungstate is selected from lithium tungstate (Li₂WO₄), sodium tungstate (Na₂WO₄), potassium tungstate (K₂WO₄), calcium tungstate (CaWO₄), zirconium tungstate (Zr(WO₄)₂), and ammonium tungstate ((NH₄)₂). 10 The group composed of H2(W2O7)6; After step A) and before step B), the method includes the step of immersion in a bath of lanthanum salt and hydrogen peroxide.

[0014] Intermediate rinsing, especially intermediate rinsing with demineralized water, can be performed at the following times: Between steps A) and B), and / or Before and / or after the parts are anodized.

[0015] Because anodized layers have a highly porous structure, they must be sealed when chemical resistance and / or corrosion resistance are critical. This means transforming the aluminum oxide layer into an aluminum hydroxide composite, in which the pores are closed. Therefore, in addition to anodizing, sealing is crucial to the quality of the anodized layer because: Sealing the hole increases corrosion resistance; Avoided scaling; This prevents the dye from leaching out of the holes.

[0016] The post-anodization sealing method of the present invention can produce coatings with very high corrosion resistance on aluminum alloys known as difficult to work (such as 2618A and 2214) as well as on aluminum alloys most commonly used in the aerospace field (such as 2024 or 7175).

[0017] The sealing method of the present invention can be applied to various anodizing processes known to those skilled in the art, including CAA (chromic acid anodizing), HA (hard anodizing), SAA (sulfuric acid anodizing), TSA (tartaric acid-sulfuric acid anodizing), as well as NGSAA-TL (thin-layer next-generation sulfuric acid anodizing), NGSAA (next-generation sulfuric acid anodizing), and TSA (tartaric acid-sulfuric acid anodizing).

[0018] The present invention also relates to a method for manufacturing aluminum- or aluminum alloy-based components according to the present invention, the method comprising at least the following steps: i) Anodizing the body made of aluminum or aluminum alloy, which may have previously undergone surface preparation steps (degreasing, then stripping). ii) Treating the anodized body, including the inner layer, by the post-anodization sealing method according to the invention to sequentially obtain an intermediate layer containing chromium and zirconium and an outer layer containing tungsten oxide; and optionally iii) Apply a coating layer.

[0019] The present invention also relates to a component according to the invention, which may include a coating layer and is intended for use in the aerospace field. Attached Figure Description

[0020] Further features and advantages of the invention will become apparent from the following detailed description, with reference to the accompanying drawings for understanding, in which: [ Figure 1 The diagram schematically illustrates the steps of surface treatment of aluminum alloy samples 2618 T6 and 2024 using the post-anodization sealing method of the present invention.

[0021] [ Figure 2 The symbol indicates the treatment range and operating conditions of the test performed. SOCOMORE's SOCOCLEAN A3432 is a degreaser compatible with aluminum and its alloys. SOCOMORE's SOCOSURF A1858-A1806 is a two-component bath for deoxidizing or bleaching aluminum and its alloys after degreasing or alkaline stripping. SOCOMORE's SOCOSURF TCS bath impregnates the pores of the oxide layer obtained after OAS (anodic sulfuric acid oxidation) anodizing with Cr(III) and zirconium. Finally, the porous layer is sealed with an aqueous sodium tungstate solution.

[0022] [ Figure 3 [Illustrated cross-sectional view of a component according to one embodiment of the present invention.] Detailed Implementation

[0023] The first object of the present invention relates to a component (1) based on aluminum or an aluminum alloy, characterized in that the component comprises: The main body (10) is made of aluminum or aluminum alloy. An inner layer (12) containing aluminum oxide is placed on the main body (10). Contains chromium and zirconium (Cr III The intermediate layer (14) of / Zr) and An outer layer (16) containing tungsten oxide is placed between an inner layer (12) and an outer layer (16).

[0024] As indicated, the component (1) according to the invention comprises a body (10) made of aluminum or an aluminum alloy.

[0025] Aluminum alloys can be selected from the 2000, 6000 and 7000 series.

[0026] Aluminum alloys can be selected from the following groups: 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 so-called difficult aluminum alloys selected from the group consisting of 2618A, 2214 and AU5NKZr.

[0027] The component (1) includes a body (10) and an inner layer (12) placed on the body. The layer (12) comprises aluminum oxide. The thickness of the inner layer (12) is between 2 and 30 µm, preferably between 5 µm and 25 µm. The inner layer (12) is obtained by anodizing the body (10) using one of the anodizing methods known to those skilled in the art as described above.

[0028] The component (1) according to the invention comprises an intermediate layer (14) containing 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 at the end of an impregnation step (A) under the following conditions of the body (10) including the inner layer (12).

[0029] The component (1) according to the invention further includes an outer layer (16). An intermediate layer (14) is disposed between the inner layer (12) and the outer layer (16). The outer layer (16) comprises tungsten oxide. The thickness of the outer layer (16) is between 10 and 500 nm, preferably 200 nm. The outer layer (16) is obtained at the end of the sealing step (B) under the following conditions, comprising the body (10) comprising the inner layer (12) and the intermediate layer (14) in sequence.

[0030] In one embodiment of the invention, component (1) further includes a coating layer (18). The coating layer (18) is disposed on an outer layer (16) comprising tungsten oxide. The thickness of the coating layer 18 is between 10 µm and 100 µm, preferably 50 µm. Figure 3 The diagram shows a component (1) according to this embodiment of the invention. If several coating layers are applied, the total thickness of these layers is between 10 and 100 µm, preferably 50 µm.

[0031] The component (1) according to the invention has good corrosion resistance and good paint adhesion. It contains chromium and zirconium (Cr). III The combination of the intermediate layer (14) of / Zr and the outer layer (16) containing tungsten oxide gives the component (1) good corrosion resistance. In addition, the outer layer 16 improves the adhesion of the coating layer (18).

[0032] This invention relates to a method for sealing a body (10) made of aluminum or an aluminum alloy after anodizing, the method comprising at least the following steps: A) The step of impregnating anodized aluminum or aluminum alloy in a water bath containing demineralized water at a temperature between 20°C and 80°C. Hexafluorozirconate, wherein the hexafluorozirconate is selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), and potassium hexafluorozirconate (K2ZrF6), and The trivalent chromium salt is selected 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, and CrK(SO4)2,xH2O. B) A sealing step performed in an aqueous solution of deionized water containing 1 to 200 g / L, preferably 5 to 100 g / L, of alkali metal or alkaline earth metal silicates with a conductivity of less than or equal to 100 μS / cm at a temperature between 60°C and 100°C. C) A post-sealing rinsing step performed with deionized water having a conductivity of less than or equal to 100 µS / cm at a temperature between 15°C and 75°C.

[0033] The deposition of tungstate on CrIII / Zr-impregnated anodized surfaces improves the corrosion resistance of aluminum or aluminum alloy parts and the adhesion of coatings to the parts.

[0034] In addition, due to its relative hardness, tungstates can affect other properties of aluminum or aluminum alloy parts, such as friction and surface hardness.

[0035] As already noted, intermediate rinsing, especially intermediate rinsing with demineralized water, can be performed at the following times: Between steps A) and B), and / or Before and / or after the parts are anodized.

[0036] The optimized sealing method of the present invention is applicable to any type of aluminum alloy, including so-called “difficult” alloys, particularly the 2000, 6000 and 7000 series aluminum alloys, which have previously been anodized by various methods, including CAA, HA, SAA, TSA, NGSAA-TL, NGSAA, and TSA.

[0037] Furthermore, the post-anodization sealing method of the present invention is compatible with the requirements of the European REACH regulation and produces good corrosion protection on aluminum alloys known as "difficult" (e.g., 2618A, 2214, and AU5NKZr). This method may or may not be followed by the application of a coating.

[0038] Therefore, the post-anodization sealing method of the present invention can achieve coatings (outer layer (16)) with very high corrosion resistance on 2000, 6000 and 7000 series aluminum alloys and “difficult” aluminum alloys (such as 2618A and 2214), as well as on aluminum alloys most commonly used in the aerospace industry (such as 2024 and 7175).

[0039] In impregnation step A), the concentration of hexafluorozirconate 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.

[0040] Trivalent chromium salts can be one of the following commercial products, for example: Surtec 650 from SURTEC, Lanthane 613.3 from COVENTYA, and TCS from SOCOMORE.

[0041] In impregnation step A), the concentration of hexafluorozirconate is between 0.5 g / L and 50 g / L, for example, equal to 2 g / L.

[0042] The temperature of the bath in step A) can be between 20 and 80°C. In 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.

[0043] In step A), the pH of the bath is between 3 and 5, preferably between 3.5 and 4.5, for example between 3.7 and 4.2.

[0044] The duration of soaking in the bath in step A) is between 1 and 40 minutes, preferably between 5 and 30 minutes, for example between 5 and 20 minutes.

[0045] After step A) and before step B), the method of the present invention may optionally include a step of immersion in a bath of lanthanum salt and hydrogen peroxide. This immersion step is well known to those skilled in the art and is used to enhance the corrosion resistance of the body (10).

[0046] In step B), the alkali metal or alkaline earth metal tungstate is selected from lithium tungstate (Li₂WO₄), sodium tungstate (Na₂WO₄), potassium tungstate (K₂WO₄), calcium tungstate (CaWO₄), zirconium tungstate (Zr(WO₄)₂), and ammonium tungstate ((NH₄)₂). 10 The group consists of H2(W2O7)6.

[0047] Alkali metal or alkaline earth metal tungstates can be one of the following commercial products, for example: lithium tungstate (Li₂WO₄), sodium tungstate (Na₂WO₄), potassium tungstate (K₂WO₄), calcium tungstate (CaWO₄), zirconium tungstate (Zr(WO₄)₂), and ammonium tungstate ((NH₄)₂) from Merck's Sigma-Aldrich brand. 10 H2(W2O7)6); and zirconium tungstate (Zr(WO4)2) from Fisher Scientific.

[0048] The sealing in step B) is carried out in an aqueous solution of deionized water with a conductivity of less than or equal to 100 μS / cm, preferably between 1 and 100 μS / cm, for example between 1 and 50 μS / cm.

[0049] The concentration of alkali metal or alkaline earth metal silicate in sealing step B) is preferably between 1 and 50 g / L, for example between 5 and 50 g / L.

[0050] 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 80 and 98°C.

[0051] The longer the sealing step B) lasts, the more tungstate will be placed. The duration of sealing step B) is between 1 and 40 minutes, preferably between 5 and 35 minutes, for example, between 5 and 30 minutes.

[0052] The pH of the sealing solution is less than 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.

[0053] After sealing comes the rinsing step C). The rinsing step C) is carried out in deionized water with a conductivity of less than or equal to 100 μS / cm, preferably between 1 μS / cm and 100 μS / cm, more preferably between 10 μS / cm and 100 μS / cm, for example between 10 μS / cm and 50 μS / cm.

[0054] The rinsing after sealing is preferably carried out at a temperature between 10°C and 75°C, for example, between 15°C and 60°C.

[0055] In step C), the pH of the water is between 4.5 and 8.5, preferably between 5 and 8, for example between 5.5 and 7.5.

[0056] The duration of rinsing after sealing is between 10 seconds and 10 minutes, preferably between 10 seconds and 5 minutes, for example between 30 seconds and 2 minutes.

[0057] Surprisingly, it was found that the combination of the steps described below—impregnation A), sealing B), and post-sealing rinsing C)—is essential for ensuring good corrosion resistance of aluminum or aluminum alloys.

[0058] In addition, in order to obtain the desired corrosion resistance and properties of aluminum or aluminum alloys, alkali metal or alkaline earth metal tungstates must be applied after impregnation step A).

[0059] Intermediate rinsing, especially intermediate rinsing with demineralized water, can be performed between the steps described above.

[0060] Prior to the anodizing step of the aluminum or aluminum alloy body (10), the body may undergo a surface preparation step by degreasing and / or stripping to remove grease, dirt and oxides present on its surface.

[0061] The preliminary steps of this surface preparation may include one or more of the following operations: Solvent degreasing is used to dissolve grease on the surface of aluminum or aluminum alloys. This operation can be achieved by soaking, spraying, or any other method known to those skilled in the art; Alkaline degreasing is used to dissolve grease on the surface of aluminum or aluminum alloys. This operation can be achieved by soaking, spraying, or any other technique known to those skilled in the art. Alkaline stripping is used to allow the oxides formed on the surface of the aluminum or aluminum alloy to dissolve naturally. This operation can be achieved by immersion, spraying, or any other method known to those skilled in the art. At the end of this operation, the aluminum or aluminum alloy is covered with a powdery layer of intermetallic compound oxide products, which must be removed by an acid stripping step. Acid stripping is used to dissolve naturally occurring oxides on the surface of aluminum or aluminum alloys and / or oxide layers formed on the surface of the component during an alkaline stripping step. This operation can be achieved by immersion, spraying, or any other method known to those skilled in the art.

[0062] The preliminary steps of surface preparation (10) for removing grease, dirt and oxides present on the surface of the body (10) by degreasing and / or peeling can be carried out, for example, under the conditions described in application WO 2013 / 117759.

[0063] Intermediate rinsing, particularly intermediate rinsing with demineralized water, is preferably performed between the aforementioned consecutive steps and before passing through the anodizing components.

[0064] Prior to applying the sealing method of the present invention, the body (10) made of aluminum or aluminum alloy, which may have undergone surface preparation steps of degreasing and / or peeling by one or more of the above operations, is anodized. Any type of anodizing on aluminum known to those skilled in the art can be used.

[0065] Various alternatives have been proposed to the use of hexavalent chromium-sealed CAA and SAA (sulfuric acid anodizing) treatments, which are subject to the European REACH regulations: NGSAA (Next Generation Sulfuric Acid Anodizing, as described in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfurique-version-5-2") has been proposed as an alternative to SAA; TSA (tartaric acid-sulfuric acid anodizing, as described in "a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfo-tartrique-oast-tartric-sulfuric-anodizing-tsa") has been proposed as an alternative to CAA. NGSAA-TL: Thin-Layer Next-Generation Sulfuric Acid Anodizing, an NGSAA anodizing method in which anodizing parameters (voltage, immersion time) have been tuned to obtain anodized layers with thicknesses between 2 and 7 µm.

[0066] For the purposes of this invention, TSA, NGSAA-TL, and NGSAA anodizing methods are preferred.

[0067] The surface treatment method of the present invention significantly improves the corrosion resistance of aluminum or aluminum alloy parts and complies with the requirements of the European REACH regulation.

[0068] Furthermore, the method of the present invention provides better conditions for coating adhesion. In addition, due to its chemical properties, tungstates may cause surface functionalization, such as increased surface hardness or improved tribological properties.

[0069] The present invention also relates to a method for manufacturing an aluminum- or aluminum alloy-based component (1) according to the present invention, the method comprising at least the following steps: i) Anodizing the body (10) made of aluminum or aluminum alloy, which may have previously undergone surface preparation steps (degreasing, then stripping). ii) The anodized body comprising the inner layer (12) is treated by the anodized-sealing method according to the invention to sequentially obtain an intermediate layer comprising chromium and zirconium and an outer layer comprising tungsten oxide; and optionally iii) Apply a coating layer (18).

[0070] The present invention also relates to a component according to the invention, which may include a coating layer and is intended for use in the aerospace field.

[0071] Example Example 1: Surface treatment methods for aluminum alloy parts The following method is used to process rolled aluminum alloy 2618 T6, 7175 T73 and aluminum alloy 2024 T351 parts with dimensions of 120x60x2mm that are machined on one of two sides.

[0072] First, perform the surface preparation steps for the components in sequence: Alkaline degreasing was performed by immersing the parts in a bath of 11% vol / vol SOCOCLEAN A3432 (from SOCOMORE) at 45°C for 10 minutes. Rinse with tap water or demineralized water; Acid stripping was performed by immersing the parts in a solution of SOCOSURF 42% vol / vol A1858-10% vol / vol A1806 (from SOCOMORE) at 50°C for 10 minutes. Rinse with tap water or demineralized water.

[0073] Then, the stripped and rinsed components are subjected to anodizing methods known to those skilled in the art, during which the components are immersed in a water bath containing sulfuric acid at a concentration between 160 g / L and 220 g / L, for example, 180 g / L. This bath is conducted at and maintained at 18°C. A DC voltage is applied to the immersed components according to the following voltage profile: the voltage increases from 0V at a rate of 0.4V / min until a voltage value of 6V, referred to as a plateau, is reached. The voltage is maintained at the plateau value for 50 minutes. An anodic layer with a thickness of 4 to 7 µm is formed on the surface of the components.

[0074] According to standard ISO2360, the thickness of the anode layer formed on the component is measured by eddy current.

[0075] Then, the anodized components are rinsed once or multiple times, preferably with demineralized water, and then the impregnation and sealing operations according to the invention are performed under the following conditions and in the following order: Step A): The step of immersing the component involves sequentially immersing it in a 34% vol / vol SOCOSURF TCS (from SOCOMORE) water bath at 40°C and pH 3.9 for 10 minutes, and then immersing it in a 10% vol / vol SOCOSURF PACS (from SOCOMORE) water bath at 25°C and pH between 4.5 and 5.5 for 5 minutes. Step B): Sealing, by immersing the parts at the end of impregnation step A) in a 20 g / L sodium tungstate aqueous solution at a temperature of 98°C and a pH less than 12, for example, pH 8 to 9, for 10 minutes, then... Step C): After sealing, rinse by immersing the operated components in deionized water with a conductivity of less than 100 µS / cm at 20°C for 1 minute.

[0076] Rinse with demineralized water between each step.

[0077] The resistance to corrosion of anodized alloys sealed by conventional sealing methods and by the sealing method of the present invention was evaluated. Corrosive results: For comparison, aluminum alloy parts anodized using the methods described above were sealed using methods known to those skilled in the art (WO2021 / 152241, for silicate sealing), such as hydrothermal sealing (CrIII / Zr + water) and silicate sealing (CrIII / Zr + silicate), and compared with parts sealed using the method of the present invention (CrIII / Zr + sodium tungstate). Parts treated in this manner were subjected to a salt spray test (BS) according to standard NF EN ISO 9227. The number of pits after 500 hours of salt spray (BS) is shown in Table 1 below.

[0078] [Table 1]

[0079] Two conclusions can be drawn from the results: 1- Comparing the configuration of Reference 2 with other configurations, it is clear that, in terms of the number of pits per sample, tungstate and silicate sealing improves the corrosion resistance of the anodized layer.

[0080] 2- Comparing Reference 1 with the tungstate configuration, in terms of the number of pits per sample, the corrosion resistance of the anodized tungstate seal is comparable to that of the silicate seal layer.

[0081] Therefore, the tungstate-based seal according to the present invention, after anodizing, achieves better corrosion resistance than the hydrothermal seal and is comparable to the corrosion resistance of the silicate-based seal described in WO2021 / 152241.

[0082] Extreme surface analysis (XPS and EDX) X-ray photoelectron spectroscopy (XPS) was performed on a Thermo K-alpha+ instrument equipped with the monochromatic Al Kalpha source processing software Advantage.

[0083] X-ray photoelectron spectroscopy (XPS) analysis was performed on the surface of the following samples: The surface of the sample that has been sealed and anodized with CrIII / Zr+tungstate (referred to as 109-NaW in Table 2 below); The surface of the sample that has been sealed and anodized with CrIII / Zr+H2O (referred to as 110-HWS in the table below); So that, compared with another type of seal, there is a reference with tungstate present on the surface.

[0084] [Table 2]

[0085] Al(III)* and Cr(III)* refer to these elements existing in the form of oxides or hydroxides.

[0086] Elemental analysis of the extreme surface (50 nm surface) revealed enrichment of tungsten in its oxidized form (presence of oxygen): W = 7.19 and O = 74.47. This confirms the presence of silicates on the surface.

[0087] The deposition of tungstate on Cr(III) / Zr impregnated anodized surfaces improves the corrosion resistance of chromium-free anodization.

[0088] Coating adhesion test Coating adhesion tests were performed on components treated with the sealing method according to the invention. The coated components were characterized after immersion in various corrosive liquids (water, Skydrol). According to ISO 2409, the adhesion grades for this type of test range from 0 (no degradation) to 5 (complete degradation).

[0089] Overall results indicate that the coatings that passed the tungstate sealing test have very good adhesion.

Claims

1. A component (1) based on aluminum or an aluminum alloy, characterized in that, The component includes: The main body (10) is made of aluminum or aluminum alloy. An inner layer (12) containing aluminum oxide is placed on the main body (10). An intermediate layer containing chromium and zirconium (14), and The outer layer (16) contains tungsten oxide, and the intermediate layer (14) is placed between the inner layer (12) and the outer layer (16).

2. The component according to claim 1, characterized in that, The component includes a coating layer (18) placed on the outer layer (16).

3. The component according to claim 1 or 2, characterized in that, The aluminum alloy is: Choose from aluminum alloys in 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, or Select cast aluminum alloys from the group consisting of AS7G06, AS7G03, AS10G, and AS9U3, or The so-called difficult aluminum alloys are selected from the group consisting of 2618A, 2214 and AU5NKZr.

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

5. The component according to any one of claims 2 and 3, characterized in that, The thickness of the coating layer (18) is between 10 and 100 µm.

6. A method for sealing a body (10) made of aluminum or an aluminum alloy after anodizing, the method comprising at least the following steps: A) The step of impregnating the anodized body (10) made of aluminum or aluminum alloy in a water bath containing demineralized water at a temperature between 20°C and 80°C, the body comprising an inner layer (12) containing alumina, the water bath containing Hexafluorozirconate, wherein the hexafluorozirconate is selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), and potassium hexafluorozirconate (K2ZrF6), and The trivalent chromium salt is selected 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, and CrK(SO4)2,xH2O. B) A sealing step performed in an aqueous solution of deionized water containing alkali metal or alkaline earth metal silicates with a conductivity of less than or equal to 100 μS / cm at a temperature between 60°C and 100°C. C) A post-sealing rinsing step performed with deionized water having a conductivity of less than or equal to 100 µS / cm at a temperature between 15°C and 75°C.

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

8. The method according to claim 6 or 7, characterized in that, In the impregnation step A), the concentration of trivalent chromium salt is between 0.1 and 50 g / L.

9. The method according to any one of claims 6 to 8, characterized in that, The alkali metal or alkaline earth metal tungstate in step B) is selected from lithium tungstate (Li₂WO₄), sodium tungstate (Na₂WO₄), potassium tungstate (K₂WO₄), calcium tungstate (CaWO₄), zirconium tungstate (Zr(WO₄)₂), and ammonium tungstate ((NH₄)₂). 10 The group consists of H2(W2O7)6.

10. The method according to any one of claims 6 to 9, characterized in that, After step A) and before step B), the method includes the step of immersion in a bath of lanthanum salt and hydrogen peroxide.

11. A method for manufacturing an aluminum- or aluminum alloy-based component (1) according to any one of claims 1 to 5, the method comprising at least the following steps: i) Anodizing the body (10) made of aluminum or aluminum alloy, which may have previously undergone surface preparation steps (degreasing, then peeling). ii) The anodized body comprising the inner layer (12) is treated by the post-anodization sealing method according to any one of claims 6 to 9 to sequentially obtain an intermediate layer (14) comprising chromium and zirconium and an outer layer (16) comprising tungsten oxide; and optionally iii) Apply a coating layer (18).

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