Post-anodization sealing method of aluminum and aluminum alloys without using chromium

Abstract

The invention relates to a post-anodizing sealing method of aluminum or aluminum alloy without using chromium. The invention also relates to a method for treating the surface of a component made of aluminum or an aluminum alloy, intended for use in the aeronautical field, comprising at least the following steps: i) subjecting said component to an anodizing step; ii) treating the anodized part by means of a post-anodization sealing method according to the invention; and optionally iii) applying one or more layers of a coating. The invention also relates to a component made of aluminum or an aluminum alloy treated by the post-anodization sealing method according to the invention, optionally comprising one or more layers of a coating.

Description

Technical Field

[0001] The present invention is part of the search for new solutions for the corrosion protection of aluminum or aluminum alloys, in particular for aerospace applications, with or without the application of a coating system.

[0002] In particular, the method of the present invention is capable of obtaining a coating with very high corrosion resistance properties on aluminum or aluminum alloys without the use of chromium. Background Art

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

[0004] Aluminum alloys are the material of choice for the transport 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 affected by several types of local corrosion, leading to component degradation and possibly to their removal or failure. Many strategies have been implemented to overcome this drawback, among which the formation or deposition of a protective layer on the alloy surface is the most widely used. This is particularly true for the protective layers obtained by anodization methods of aluminum alloys.

[0005] Anodization is an electrolytic process that replaces the natural oxide (native oxide) of a few nanometers thick covering aluminum with an oxide layer of up to several micrometers. The thickness of the oxide layer produced by anodization ranges from 2 micrometers to about 15 micrometers to provide long-term corrosion protection. Anodization (also known as anodic oxidation) involves forming a porous aluminum oxide / hydroxide layer (referred to as the anodic layer) on the surface of a component by applying an electric current to the component immersed in an electrolytic bath containing a strong acid-type electrolyte, and the component constitutes the anode of the electrolytic system. The layer thus formed on the component surface can enhance the corrosion resistance of the component after sealing treatment. Anodization treatment is now commonly used in the aviation industry, mainly to improve the corrosion resistance of components, thereby increasing the service life of components, and also helps the adhesion of organic layers (coatings). However, the anodization method is directly affected by European regulations (REACH), and since September 2017, this regulation has prohibited (or restricted authorization) the use of certain key elements in surface treatment, especially hexavalent chromium. Hexavalent chromium is present in, for example, OAC-type anodization (chromic anodization) as described in www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-chromique, and also in the usual surface preparation pretreatment, the purpose of which is to clean / strip the surface of the component before anodization treatment, and finally in the final treatment (referred to as sealing), the purpose of which is to close the pores of the anodic layer formed during anodization treatment.

[0006] Different methods have been proposed to replace the OAC and OAS (anodic sulfuric acid oxidation) treatments sealed with hexavalent chromium, and the OAC and OAS treatments are affected by the European regulation REACH:

[0007] - OAS NG (New Generation Anodic Sulfuric Acid Oxidation, for example, as described in www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfurique-version-5-2) has been proposed as an alternative to OAS;

[0008] - OAST (anodic sulfo-tartaric acid oxidation, as described for example at www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfo-tartrique-oast-tartric-sulfuric-anodizing-tsa) has been proposed as an alternative to OAC.

[0009] OAC can also be replaced by OAS NG FE (New Generation Fine Thickness Sulfuric Anodic Oxidation), which is an anodization of the OAS NG type with adjusted anodization parameters (voltage, immersion time) to obtain an anodized layer with a thickness between 2 μm and 7 μm.

[0010] Although current conventional anodization solutions, such as OAS NG and subsequent hot water sealing, achieve a treatment range compatible with the European REACH regulation, they are still unsatisfactory or still unsatisfactory in terms of corrosion protection on certain grades of aluminum alloys called "difficult". Non-limiting examples of aluminum alloys called "difficult" include alloys 2214, 2618A or AU5NKZr. These alloys have a specific microstructure due to their chemical composition, which gives them casting defects or precipitates, such as intermetallic compounds rich in copper, iron or nickel. Therefore, when the anodic layer forms on the surface of these alloys, layer defects may remain, resulting in certain local brittleness that is prone to corrosion.

[0011] Therefore, for these alloys, it is necessary to optimize the anodization range to improve the corrosion resistance.

[0012] FR 3106838B1 provides a post-anodization sealing method for aluminum or aluminum alloys that can improve the corrosion resistance of components without using hexavalent chromium, which is affected by the European REACH regulation. This method is also applicable to so-called "difficult" aluminum alloys and includes the 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 silicate. Although improved corrosion resistance has been achieved by this method, there is a risk of long-term phasing out of trivalent Cr. In fact, the Cr III / Zr immersion step is a mandatory step that allows the silicate sealing step to be carried out, and as environmental regulations become more stringent, the Cr III / Zr immersion step may be phased out in the future (because of chromium).

[0013] To prevent the long-term phasing-out risk of trivalent Cr and to comply with future more stringent environmental regulations, it is necessary to optimize the method for sealing aluminum or anodized aluminum alloys, in particular by avoiding the use of chromium.

[0014] Therefore, there is indeed a need for a method for sealing aluminum or aluminum alloys without using chromium, which aluminum alloys include so-called "difficult" anodized aluminum alloys.

[0015] In particular, there is a need for a post-anodization sealing method as described above, which imparts good corrosion resistance to aluminum or aluminum alloys (including so-called "difficult" aluminum alloys), while meeting the requirements of current and future REACH regulations. Summary of the Invention

[0016] The object of the present invention is precisely to meet these needs by providing a post-anodization sealing method for aluminum or aluminum alloys, in particular with respect to the corrosion resistance of aluminum alloys, especially 2xxx, 6xxx, and 7xxx series aluminum alloys, aluminum casting alloys such as AS7G06, AS7G03, AS10G, or AS9U3, aluminum alloys produced by methods such as additive manufacturing, and so-called difficult aluminum alloys, said method comprising at least the following steps:

[0017] A) A step of immersing the anodized aluminum or aluminum alloy in a water bath of softened water at a temperature between 20 °C and 80 °C, said water bath containing

[0018] - hexafluorozirconate salts selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and

[0019] - divalent, trivalent, tetravalent, or heptavalent manganese salts 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,

[0020] Or

[0021] - hexafluorozirconate salts selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and

[0022] - tungsten salts 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 ((NH4) 10Groups composed of H2(W2O7)6);

[0023] B) A sealing step carried out in an aqueous solution of deionized water with a conductivity less than or equal to 100 μS / cm containing an alkali metal or alkaline earth metal silicate between 1 g / L and 500 g / L at a temperature between 60 °C and 100 °C;

[0024] C) A post-sealing rinsing step carried out in deionized water with a conductivity less than or equal to 100 μS / cm at a temperature between 15 °C and 75 °C.

[0025] In the impregnation step A), the concentration of hexafluorozirconate is between 0.5 g / L and 50 g / L. The concentration of manganese salt in this step is between 0.1 g / L and 50 g / L.

[0026] Preferably, an intermediate rinse is carried out, especially with softened water,

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

[0028] - before and / or after anodizing the component.

[0029] Since the anodized layer has a very porous structure, when chemical resistance and / or corrosion resistance are very important, the anodized layer must be sealed. This means transforming the aluminum oxide layer into an aluminum hydroxide complex in which the pores are closed. Therefore, in addition to anodizing, sealing is decisive for the quality of the anodized layer because:

[0030] - Sealing of the pores increases corrosion resistance;

[0031] - Scaling is avoided;

[0032] - Leaching of dyes from the pores is avoided.

[0033] The post-anodizing sealing method of the present invention can obtain a coating with very high corrosion resistance on so-called difficult aluminum alloys (such as 2618A and 2214) and on the most common aluminum alloys in the aviation field (such as 2024 or 7175).

[0034] The sealing method of the present invention can be applied to various anodizings known to those skilled in the art, including OAST, OASNG FE, OAS NG.

[0035] A coating may or may not be applied after this method.

[0036] This method demonstrates the possibility of depositing silicates on the surface using other types of chromium-free impregnation layers, such as Mn / Zr impregnation.

[0037] It is known that sulfuric acid anodization consists of an aluminum oxide layer, and the inventors have tried to find out

[0038] a) whether it is possible to deposit silicate, such as a Mn / Zr impregnation layer instead of Cr, on a chromium-free impregnation layer, and III / Zr, and

[0039] b) if so, whether such deposition will improve the corrosion resistance of the chromium-free impregnation layer, such as the Mn / Zr impregnation layer, as is the case with the Cr III / Zr impregnation layer.

[0040] The present invention also relates to a method for treating the surface of a component made of aluminum or an aluminum alloy, which is intended for the aviation field, and the method at least comprises the following steps:

[0041] (i) subjecting the component to an anodization step, which may have previously undergone a surface preparation step (degreasing and then stripping);

[0042] (ii) treating the anodized component by a post-anodization sealing method according to the present invention; and optionally

[0043] (iii) applying one or more coating layers.

[0044] Another object of the present invention is the use of the post-anodization sealing method according to the present invention in the surface treatment of aluminum or aluminum alloy components, which are intended for the aviation field.

[0045] Another object of the present invention is an aluminum or aluminum alloy component treated by the post-anodization sealing method according to the present invention, which optionally includes one or more coating layers and is intended for the aviation field. Description of the Drawings

[0046] Further features and advantages of the present invention will become apparent from the following detailed description, with reference to the drawings for understanding the detailed description, in which:

[0047] Figure 1 A theoretical diagram showing the deposition of substances on an anodized layer (OA) by the sealing method described in FR3106838B1 and by the sealing method of the present invention is shown. Detailed Description

[0048] The present invention specifically aims to meet the needs of the prior art by providing a post-anodization sealing method for aluminum or aluminum alloys, especially in terms of the corrosion resistance of aluminum alloys, especially aluminum alloys in the 2xxx, 6xxx, and 7xxx series, casting alloys, and aluminum alloys produced by methods such as additive manufacturing and so-called difficult aluminum alloys, and the method at least comprises the following steps:

[0049] A) A step of immersing an anodized aluminum or aluminum alloy in a water bath of softened water at a temperature between 20 °C and 80 °C, said water bath containing

[0050] - hexafluorozirconate, said hexafluorozirconate being selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and

[0051] - divalent, trivalent, tetravalent or heptavalent manganese salt, said manganese salt being 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,

[0052] or

[0053] - hexafluorozirconate, said hexafluorozirconate being selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and

[0054] - tungstate, said tungstate being 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 ((NH4) 10 H2(W2O7)6);

[0055] B) A sealing step carried out in an aqueous solution of deionized water with a conductivity less than or equal to 100 μS / cm containing an alkali metal or alkaline earth metal silicate between 1 g / L and 500 g / L at a temperature between 60 °C and 100 °C;

[0056] C) A post - sealing rinsing step carried out in deionized water with a conductivity less than or equal to 100 μS / cm at a temperature between 15 °C and 75 °C.

[0057] The divalent, trivalent, tetravalent or heptavalent manganese salt can be, for example, one of the following commercial products: Bonderite M - ED160 / 161.

[0058] The tungstate can be, for example, one of the following commercial products: lithium tungstate (Li2WO4), sodium tungstate (Na2WO4), potassium tungstate (K2WO4), calcium tungstate (CaWO4), ammonium tungstate ((NH4) 10H2(W2O7)6) and zirconium tungstate (Zr(WO4)2) from Fisher Scientific.

[0059] The intermediate rinsing is preferably carried out at the following times, in particular the intermediate rinsing with softened water,

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

[0061] - before and / or after anodizing the component.

[0062] The optimized sealing method of the present invention is applicable to any type of aluminum alloy, including alloys known as "difficult", in particular aluminum alloys of the 2xxx, 6xxx and 7xxx series, which have been anodized previously by various methods, such as by OAST (sulfotartaric acid anodizing), OAS NG FE (new generation fine thickness sulfuric acid anodizing) or OAS NG (new generation sulfuric acid anodizing) methods.

[0063] Furthermore, the post-anodization sealing method of the present invention is compatible with the requirements related to the European regulation REACH and provides good corrosion protection on aluminum alloys known as "difficult" (such as 2618A, 2214 and AU5NKZr). A coating may or may not be applied after this method.

[0064] Therefore, the post-anodization sealing method of the present invention is capable of obtaining coatings with very high corrosion resistance on aluminum alloys of the 2xxx, 6xxx and 7xxx series, on difficult aluminum alloys, but also on aluminum alloys most common in the aviation field (such as 2024 and 7175) and on difficult aluminum alloys (such as 2618A and 2214).

[0065] The method of the present invention is particularly applicable to aluminum and aluminum alloy components 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, 7050T7451, 7055, 7068, 7085, 7075, 7175 and 7475, aluminum casting alloys of the AS7G06, AS7G03, AS10G and AS9U3 types, and aluminum alloys produced by methods such as additive manufacturing.

[0066] In the impregnation step A), the hexafluorozirconate concentration is between 0.5 g / L and 50 g / L, for example equal to 2 g / L. In this step, the concentration of divalent, trivalent, tetravalent or heptavalent manganese salts or tungstates is between 0.1 g / L and 50 g / L, for example equal to 1 g / L.

[0067] The temperature of the bath in step A) can be between 20 °C and 80 °C, preferably between 20 °C and 60 °C, more preferably between 35 °C and 60 °C, for example between 35 °C 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 impregnation 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.

[0070] After the impregnation step A), a sealing step B) is carried out. The sealing in step B) is carried out in an aqueous solution of deionized water with a conductivity less than or equal to 200 μS / cm, preferably between 1 and 100 μS / cm, for example between 1 and 50 μS / cm.

[0071] The temperature of the aqueous solution in step B) is preferably between 80 °C and 100 °C, for example between 80 °C and 98 °C.

[0072] The alkali metal or alkaline earth metal silicate can be selected from the group consisting of lithium silicate, sodium silicate, potassium silicate, calcium silicate and magnesium silicate.

[0073] In the sealing step B), the concentration of the alkali metal or alkaline earth metal silicate in the solution is preferably between 1 g / L and 500 g / L, for example between 5 g / L and 100 g / L.

[0074] 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.

[0075] The pH of the sealing solution is between 9 and 12, preferably between 10 and 11.5, for example between 10.5 and 11.4.

[0076] After sealing, there is a rinsing step C), and the rinsing step C) is carried out in deionized water with a conductivity 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.

[0077] 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.

[0078] 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.

[0079] The duration of the post-sealing rinse is between 10 seconds and 10 minutes, preferably between 10 seconds and 5 minutes, for example between 30 seconds and 2 minutes.

[0080] It has been very unexpectedly found that the combination of the impregnation + sealing + post-sealing rinse steps as described below is essential for ensuring good corrosion resistance of aluminum or aluminum alloys.

[0081] An intermediate rinse, especially with softened water, can be carried out between the above steps.

[0082] Sealing with boiling water has the advantage of not using harmful substances and can significantly improve the corrosion resistance of the anodic layer when properly controlled: the sealing must be carried out in softened water with a minimum temperature exceeding 75 °C, preferably exceeding 90 °C, more preferably exceeding or equal to 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 levels (e.g., Ca 2+ , Cu 2+ , Fe 2+ , F - , Cl - , SiO3 - , PO4 3- ). Silicates, phosphates and chloride ions have a particularly harmful effect. The treatment time is about 2.5 min / μm (close to the anodizing time). This operation is a partial hot hydration of alumina, and alumina crystallizes into boehmite ).

[0083] Before subjecting aluminum or an aluminum alloy to the anodizing step, the aluminum or aluminum alloy can be subjected to a surface preparation step by degreasing and / or stripping to remove grease, dirt and oxides from its surface.

[0084] This preliminary step of surface preparation can include one or more of the following operations:

[0085] - Solvent degreasing to dissolve the grease on the surface of the aluminum or aluminum alloy. This operation can be achieved by immersion, spraying or any other method known to those skilled in the art;

[0086] - Alkaline degreasing to dissolve the grease on the surface of the aluminum or aluminum alloy. This operation can be achieved by immersion, spraying or any other technique known to those skilled in the art;

[0087] - Alkaline stripping to dissolve the oxides naturally formed on the surface of aluminum or aluminum alloy. 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 oxidation products of intermetallic compounds, and this powdery layer of oxidation products must be removed by an acid stripping step;

[0088] - Acid stripping to dissolve the oxides naturally formed on the surface of aluminum or aluminum alloy and / or the oxide layer formed on the surface of the component during the alkaline stripping step. This operation can be achieved by immersion, spraying or any other method known to those skilled in the art.

[0089] The preliminary step of surface preparation of aluminum or aluminum alloy by degreasing and / or stripping to remove the grease, dirt and oxides present on the surface of aluminum or aluminum alloy can be carried out under the conditions described, for example, in application WO 2013 / 117759.

[0090] Intermediate rinsing, especially with softened water, is preferably carried out between the above consecutive steps and before anodizing the component.

[0091] Before applying the sealing method of the present invention, the aluminum or aluminum alloy that may have undergone the surface preparation step of degreasing and / or stripping 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. In this regard, mention can be made of:

[0092] - OAS: Anodic sulfuric acid oxidation (sealing based on chromium VI, a method affected by the European REACH regulation),

[0093] - OAC: Chromium anodic oxidation (based on chromium VI, a method affected by the European REACH regulation),

[0094] - OAST: Sulfotartaric acid anodic oxidation,

[0095] - OAST: Sulfotartaric acid anodic oxidation,

[0096] - OAS NG FE: New generation anodic sulfuric acid oxidation fine thickness,

[0097] - OAS NG: New generation anodic sulfuric acid oxidation.

[0098] In the context of the present invention, the OAST LC, OAS NG FE, and OAS NG anodizing methods are preferred.

[0099] The surface treatment method of the present invention significantly improves the corrosion resistance of metal or metal alloy components, especially aluminum or aluminum alloy components, and meets the requirements of the European regulation REACH.

[0100] The method of the present invention is of great interest in any type of industry seeking to improve the corrosion resistance of metal or metal alloy components, particularly aluminum or aluminum alloy components, such as in the aerospace, automotive, oil industry, etc.

[0101] The method according to the present invention may include one or more of the following features and / or steps taken alone or in combination with each other:

[0102] - The aluminum alloy is an aluminum alloy of the 2xxx, 6xxx, and 7xxx series, particularly selected from the group consisting of 2014, 2017, 2024, 2214, 2219, 2618, AU5NKZr, 7175, 5052, 5086, 6061, 6063, 7010, 7020, 7050, 7050T7451, 7055, 7068, 7085, 7075, 7175, and 7475, aluminum casting alloys of the AS7G06, AS7G03, AS10G, and AS9U3 types, and aluminum alloys produced by methods such as additive manufacturing;

[0103] - In the impregnation step A), the concentration of hexafluorozirconate is between 0.5 g / L and 50 g / L;

[0104] - In the impregnation step A), the concentration of divalent, trivalent, tetravalent, or heptavalent manganese salts or tungstates is between 0.1 g / L and 50 g / L;

[0105] - The alkali metal or alkaline earth metal silicate can be selected from the group consisting of lithium silicate, sodium silicate, potassium silicate, calcium silicate, and magnesium silicate;

[0106] - The concentration of the alkali metal or alkaline earth metal silicate in the solution is between 5 g / L and 100 g / L;

[0107] - The rinsing step C) is carried out in deionized water with a conductivity between 1 μS / cm and 100 μS / cm.

[0108] The method of the present invention can achieve corrosion resistance similar to chromate anodization without the use of chromium. This method provides an innovative sealing solution for anodized aluminum alloys, meeting the corrosion resistance and paint adhesion specifications without the use of chromium.

[0109] The present invention also relates to a method for surface treating an aluminum or aluminum alloy component intended for the aerospace field, the method comprising at least the following steps:

[0110] (i) Subjecting the component to an anodization step, the component may have previously undergone a surface preparation step (degreasing, then stripping);

[0111] (ii) Treating the anodized component by the post - anodization sealing method according to the present invention; and optionally

[0112] (iii) Applying one or more layers of coating.

[0113] Another object of the present invention is the use of the post - anodization sealing method according to the present invention in the surface treatment of aluminum or aluminum alloy components intended for the aviation field.

[0114] Another object of the present invention is an aluminum or aluminum alloy component treated by the post - anodization sealing method according to the present invention, said aluminum or aluminum alloy component possibly including one or more layers of coating and intended for the aviation field.

[0115] After anodization, applying a coating: Some aviation components have a coating treatment after anodization to enhance corrosion protection. The present invention is compatible with various coating systems.

[0116] Other advantages and features of the present invention will become apparent from the embodiments given below by way of example.

[0117] Examples

[0118] Example 1

[0119] Post - anodization sealing method for aluminum alloy components

[0120] An aluminum alloy 2618T6 component with dimensions of 120×100×5 mm is treated using the method described below.

[0121] First, the surface preparation steps of the component are sequentially implemented:

[0122] - Alkaline degreasing, immersing the component in a 11% by volume SOCOCLEAN A3431 solution at a temperature of 45 °C for 10 minutes;

[0123] - Rinsing with tap water or softened water;

[0124] - Acid stripping, immersing the component in a mixture of 42% by volume SOCOSURF A1858 and 10% by volume SOCOSURF A1806 at a temperature of 50 °C for 10 minutes;

[0125] - Rinsing with tap water or softened water.

[0126] Then, the stripped and rinsed component is subjected to a new - generation sulfuric acid anodization method (standard thickness or thin thickness (FE)).

[0127] The operating parameters of the anodization are given in Table 1 below.

[0128] [Table 1]

[0129] OAS NG Bath components <![CDATA[H2SO4: 150 - 220 g / L]]> Bath temperature 16℃-20℃ Thickness of the formed layer (μm) 8 - 15μm

[0130] The anodized component according to the invention is then subjected to the sealing method according to the invention under the conditions and sequence indicated below:

[0131] - Step A): a step of immersing the part, wherein the part is immersed in a water bath of BONDERITE M-ED 160 / 161 (15 g / L ED160 and 18 g / L ED161) at a temperature of 40°C and a pH of 3.9 for 10 minutes, and then

[0132] - Step B): Sealing, immersing the component in an aqueous solution of deionized water with a conductivity of less than 100 μS / cm and 80 g / L of sodium silicate at a temperature of 100° C. for 10 minutes;

[0133] - Step C): Post-sealing rinsing, after three previous sealing operations, immerse the component in deionized water with a conductivity of less than 100 μS / cm at a temperature of 20° C. for 1 minute.

[0134] Rinse with demineralized water between each step.

[0135] These conditions are shown in [Table 2].

[0136] [Table 2]

[0137]

[0138] Corrosion resistance evaluated for anodized alloys sealed by conventional sealing methods and by the method of the present invention Results:

[0139] As a comparison, the aluminum alloy parts anodized using the method shown in [Table 1] were subjected to one or more sealing operations, such as hydrothermal sealing (Mn / Zr+water), using methods known to those skilled in the art and compared with parts anodized and sealed using the method of the present invention (Mn / Zr+silicate). The parts treated in this way were subjected to a salt spray test (BS) according to standard NF ENISO 9227. The bite counts after 500 hours of salt spray (BS) are shown in Table 3 below.

[0140] [Table 3]

[0141]

[0142] A silicate based seal according to the invention after anodizing provides much better corrosion resistance than hydrothermal sealing.In view of these results, a positive influence of silicate is detected and gives interesting results close to chromate impregnation.

[0143] Extreme surface analysis (XPS)

[0144] X-ray photoelectron spectroscopy (XPS) analysis was performed on a Thermo K-alpha+ instrument with monochromatized Al Kalpha source processing software: advantages.

[0145] The surface of the anodized sample sealed with Mn / Zr + Si (named 2618-T652-047-104 in Table 4 below).

[0146] [Table 4]

[0147] Samples C O Al Si Zr N Na S F Ca 2618-T652-047-104 33.2 47.2 - 19.4 - 0.1 - - - 0.1

[0148] As shown by the elemental analysis of the extreme surface (50 nm surface), enrichment of silicon in the oxidized form (presence of oxygen) was detected. This confirmed the presence of silicate on the surface.

[0149] Depositing silicate on the Mn / Zr-impregnated anodized surface can improve the corrosion resistance of the chromium-free anodization.

[0150] The present invention demonstrates that it is possible to deposit silicate on impregnants other than Cr III / Zr, thus obtaining good corrosion performance without using chromium.

Claims

1. An anodizing post - sealing method for aluminum or aluminum alloy, comprising at least the following steps: A) A step of immersing the anodized aluminum or aluminum alloy in a water bath of softened water at a temperature between 20 °C and 80 °C, said water bath containing: - hexafluorozirconate, said hexafluorozirconate selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and - divalent, trivalent, tetravalent or heptavalent manganese salts, said manganese salts being 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 - hexafluorozirconate, said hexafluorozirconate selected from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6), and - Tungsten salts, the tungsten salts 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 ((NH4) 10 H2(W2O7)6); B) A sealing step carried out in an aqueous solution of deionized water with a conductivity less than or equal to 100 μS / cm and containing 1 g / L to 500 g / L of alkali metal or alkaline earth metal silicate at a temperature between 60 °C and 100 °C; C) A post - sealing rinsing step carried out in deionized water with a conductivity less than or equal to 100 μS / cm and at a temperature between 15 °C and 75 °C.

2. The method according to claim 1, characterized in that, The aluminum alloy is an aluminum alloy of 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, 7050T7451, 7055, 7068, 7085, 7075, 7175, and 7475, aluminum casting alloys of AS7G06, AS7G03, AS10G, and AS9U3 types, and aluminum alloys produced by methods such as additive manufacturing.

3. The method according to claim 1 or 2, characterized in that, In the immersion step A), the concentration of hexafluorozirconate is between 0.5 g / L and 50 g / L.

4. The method according to any one of claims 1 to 3, characterized in that In the immersion step A), the concentration of the divalent, trivalent, tetravalent, or heptavalent manganese salt or tungstate is between 0.1 g / L and 50 g / L.

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

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

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

9. A method for treating the surface of a component made of aluminum or aluminum alloy, said component intended for the aviation field, said method comprising at least the following steps: i) Subjecting the component to an anodizing step, which may have previously undergone a surface preparation step (degreasing, then stripping); ii) Treating the anodized component by the anodizing post - sealing method according to any one of claims 1 to 8; and optionally iii) Applying one or more layers of coating.

10. Use of the anodizing post - sealing method according to any one of claims 1 to 8 in the surface treatment of aluminum or aluminum alloy components intended for the aviation field.

11. An aluminum or aluminum alloy component treated by the post-anodization sealing method according to any one of claims 1 to 8, said aluminum or aluminum alloy component optionally comprising one or more layers of coating and intended for use in the aviation sector.

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