Surface treatment method for aluminum base member

Abstract

The present invention relates to a surface treatment method of a part made of aluminum or an aluminum alloy, comprising an anodization step and a step of closing with a silicate. The present invention also relates to the use of a surface treatment method according to the invention for the manufacture of aluminum and aluminum alloy parts, in particular for the aeronautical field.

Description

Technical Field

[0001] This invention is part of the search for new solutions to improve the resistance of aluminum or aluminum alloy components to bio-corrosion. Background Technology

[0002] Biocorrosion encompasses all corrosion phenomena caused directly or indirectly by microorganisms, particularly bacteria, through their metabolism. It is an electrochemical phenomenon involving the dissolution of metals, affecting all industries where microorganisms, especially bacteria, can thrive. Most metals and alloys are susceptible to biocorrosion: iron, steel, non-alloy or low-alloy steels, stainless steel, copper, aluminum, and their alloys. Biocorrosion is considered a serious problem in many industries, such as aerospace and automotive, and in oilfield and marine environments. The economic losses directly related to biocorrosion can reach billions of dollars annually. Therefore, preventing biocorrosion of metallic or metal alloy components has received considerable attention in recent decades.

[0003] One of the most common techniques for improving the resistance of metal or metal alloy components, especially aluminum or aluminum alloy components, to biocorrosion is anodizing. Anodizing is an electrolytic process that replaces the several nanometer-thick layer of natural oxides (native oxides) covering aluminum with a layer of oxide that can be several micrometers thick. The oxide layer produced by anodizing is about 10 μm thick, providing long-term corrosion protection. Depending on the requirements, the thickness of the anodic layer can also range from a few micrometers to 20-30 μm. Anodizing, also known as anodic oxidation, involves applying an electric current to a component immersed in an electrolytic cell containing a strongly acidic electrolyte, which acts as the anode of the electrolytic system. This process forms a porous aluminum oxide / hydroxide layer on the surface of the component, called the anodic layer. After sealing treatment, this layer formed on the surface of the component enhances its corrosion resistance. This sealed anodic layer can also serve as a support for the adhesion of coating systems.

[0004] Generally, the anodic layer formed by anodizing improves the corrosion resistance of components, but its high porosity makes it highly sensitive to corrosive environments. The porous structure cannot provide an effective barrier against invasive species such as microorganisms, which are the primary protective barrier layer. Therefore, proper sealing treatment can improve the biocorrosion resistance of the anodic layer.

[0005] Current anodizing surface treatments utilize standard commercially available products such as closed OAC (chromium anodizing), for example, TSA (tartrate-sulfuric acid anodizing) as described in https: / / www.a3ts.org / actualite / commissions-techniques / fiches-techniques-traitement-surface / anodisation-sulfo-tartrique-oast-tartric-sulfuric-anodizing-tsa / , and fine OAS (fine anodizing with sulfuric acid), for example, https: / / www.a3ts.org / actualite / commissions-te OAS (anodic sulfuric acid oxidation) described in chniques / fiches-techniques-traitement-surface / anodisation-sulfurique-version-5-2 / , BSAA (boric acid sulfuric acid oxidation) described in https: / / www.anoplate.com / finishes / boric-sulfuric-acid-anodize-bsaa / , and PSAA (phosphoric acid sulfuric acid oxidation) described in http: / / www.metroplating.co.uk / phosphoric-acid-anodising.php are not resistant to the media described above. To date, these surface treatments are not resistant to biocorrosion, for example, biocorrosion that may occur at low points in aircraft liquid storage tanks. Corrosive acidic environments, associated with the release of acidic substances by microorganisms in saline environments, can erode anodized aluminum. This is directly related to the instability of anodized products at pH < 4.

[0006] In addition, chromium anodizing (OAC) and sulfuric acid anodizing (OAS) methods used to protect aluminum alloys from corrosion are also affected by REACH regulations.

[0007] Another option to combat biocorrosion is to apply a coating to the outer surfaces of the equipment that come into contact with these critical areas of the reservoir. This will incur additional costs and cycle time.

[0008] Therefore, there is an urgent need for a surface treatment method that complies with REACH regulations to improve the resistance of aluminum or aluminum alloy parts to bio-corrosion. Summary of the Invention

[0009] The present invention aims to overcome the shortcomings of the above-mentioned anodizing methods for aluminum or aluminum alloy parts, especially in terms of the resistance of the treated parts to biocorrosion.

[0010] This invention aims to meet these needs, particularly regarding the resistance of the treated parts to biocorrosion, by providing a surface treatment method for aluminum or aluminum alloy parts, the method comprising at least the following steps:

[0011] A) Anodizing steps; and

[0012] B) The step of sealing the anode layer formed on the component after step A);

[0013] The process is carried out in an aqueous solution of deionized water containing 1-500 g / L of alkali metal or alkaline earth metal silicates at a temperature of 60℃-100℃. The resistivity is equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms.

[0014] In one embodiment of the invention, the anodizing step A) is anodizing as described below, in which the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14°C-21°C and a concentration of 150-250 g / L, and a DC voltage is applied to the immersed component according to a voltage profile, the voltage profile comprising a voltage rise at a rate of less than 1 V / min until a voltage value of 5-13 V, referred to as a plateau, is reached.

[0015] Another embodiment of the present invention includes, after sealing step B), a post-sealing rinse (step B1) in deionized water at a temperature of 15°C-35°C with a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms.

[0016] Another embodiment of the invention includes, prior to the silicate sealing step (step B), an immersion step A1) of the component in an aqueous bath described below.

[0017] - In an aqueous bath containing trivalent chromium salts 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 (step A1-1);

[0018] Then optionally

[0019] - In an aqueous bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide (H2O2), ammonium fluoride (NH4F), potassium fluorozirconate (K2ZrF6), potassium permanganate (KMnO4), and sodium permanganate (NaMnO4) (step A1-2).

[0020] In another embodiment, after the silicate sealing according to step B), the surface treatment method further includes a final hydrothermal sealing (step C) in deionized water at a temperature of 97°C-100°C with a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms.

[0021] The surface treatment method of the present invention significantly improves the resistance of aluminum or aluminum alloy parts to bio-corrosion and meets the requirements of REACH regulations.

[0022] The method of the present invention is of great benefit to any type of industry seeking to improve the resistance of aluminum or aluminum alloy components to biocorrosion, such as the aerospace, automotive, and petroleum industries.

[0023] Another object of the present invention relates to a method for manufacturing aluminum or aluminum alloy components for use in the aerospace field, comprising:

[0024] (i) the step of surface treatment of the component by the method according to the invention, and optionally

[0025] (ii) The step of applying one or more layers of paint, varnish, dry lubricant or mastics.

[0026] Another object of the present invention is the use of the surface treatment method according to the invention for manufacturing aluminum or aluminum alloy parts for the aerospace field.

[0027] The invention also includes anodized aluminum or aluminum alloy components sealed by the surface treatment method of the invention, the components comprising one or more layers of paint, varnish, dry lubricant or filler, said components for use in the aerospace field. Attached Figure Description

[0028] Further features and advantages of the invention will become more apparent from the following detailed description, with reference to the accompanying drawings, in which:

[0029] Figure 1 shows an installation diagram for biocorrosion testing of components treated by the methods of the present invention and prior art methods, according to §4.7.19 of the MIL-C-27725B standard. Detailed Implementation

[0030] The object of this invention is to meet the needs of the prior art by providing a surface treatment method for aluminum or aluminum alloy parts, particularly regarding the resistance of the treated parts to biocorrosion. This method includes at least the following steps:

[0031] A) Anodizing step; and

[0032] B) The step of sealing the anode layer formed on the component after step A);

[0033] The process is carried out in an aqueous solution of deionized water containing 1-500 g / L of alkali metal or alkaline earth metal silicates at a temperature of 60℃-100℃. The resistivity is equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms.

[0034] According to a preferred embodiment of the present invention, the anodizing step A) is anodizing as described below, in which the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14°C-21°C and a concentration of 150-250 g / L, and

[0035] A DC voltage is applied to the submerged component according to a voltage distribution that includes a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached.

[0036] Once a voltage value known as a plateau is reached, the applied voltage is maintained at the plateau value for a sufficient period of time to obtain an anodic layer with a thickness between 2 and 7 μm on the surface of the component.

[0037] The voltage applied to the submerged component can be maintained at a plateau value for a period of 20-80 minutes.

[0038] The voltage value referred to as the platform can be 6-10V.

[0039] This anodizing is a fine OAS.

[0040] In the method of the present invention, the anodizing step A) can also be anodizing of the type TSA (sulfuric acid tartaric acid anodizing), OAS (sulfuric acid anodizing), PSAA (sulfuric acid phosphoric acid anodizing), BSAA (sulfuric acid boric acid anodizing) or OAC (chromium anodizing).

[0041] The method of the present invention is particularly applicable to aluminum and aluminum alloy parts obtained by additive manufacturing from different production modes, namely, aluminum and aluminum alloy parts selected from the group consisting of 2014, 2017A, 2024, 2214, 2219, 2618, AU5NKZr, 7175, 5052, 5086, 6061, 6063, 7010, 7020, 7050, 7050T7451, 7055T77, 7068, 7085T7651, 7075, 7175 and 7475, AS7G06, AS7G03, AS10G, AS9U3, AS7G06 and AS10G.

[0042] As described, the voltage distribution applied to the component comprises an initial value of 0V, increasing at a rate of less than 1V / min, preferably 0.3V / min-0.7V / min, until a voltage value known as a plateau is reached, between 5-13V, preferably between 6-10V. The voltage applied to the component immersed in the aqueous bath is then maintained at the plateau value for an appropriate period to obtain an anode layer of aluminum oxide / aluminum hydroxide with a thickness of 2-7 μm, for example, about 3 μm, on the surface of the component.

[0043] According to one embodiment of the invention, the voltage applied to the submerged component is maintained at a plateau value for a period of 20-80 minutes, preferably 30-60 minutes.

[0044] Unwilling to be bound by any theory, the inventors unexpectedly discovered that during anodizing using the aforementioned preferred fine OAS anodizing method, the slower the voltage rise, the greater the resistance to biocorrosion of the anolyte layer formed on the component surface. Similarly, the lower the applied voltage, the higher the resistance to biocorrosion of the anolyte layer. These two parameters result in a less porous, denser, and therefore more biocorrosion-resistant layer.

[0045] In the anodizing step A) according to a preferred embodiment of the present invention, the sulfuric acid concentration in the aqueous bath is preferably between 160 g / L and 220 g / L, for example equal to 190 g / L.

[0046] In the anodizing step A) according to a preferred embodiment of the present invention, the temperature of the aqueous bath can be between 10-25°C, preferably between 14-21°C, for example 18°C.

[0047] In the method of the present invention, step B) follows directly or indirectly after the anodizing step A), and step B) is the step of sealing the anode layer formed on the component during step A). ​​As described above, the sealing in step B) is...

[0048] - The resistivity is equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms, and

[0049] - It is carried out in an aqueous solution of deionized water containing 1-500 g / L of alkali metal or alkaline earth metal silicates.

[0050] Alkali metal or alkaline earth metal silicates can be selected from the group consisting of lithium silicate, sodium silicate, potassium silicate, calcium silicate and magnesium silicate.

[0051] The quality of the water used in the enclosed aqueous bath is important because it affects the resistance to biocorrosion of the anodic layer formed on the component. Purer water, such as water with a resistivity equal to or greater than 10 MOhms, may provide better performance over time than water with a resistivity less than 10 MOhms. According to a preferred embodiment, deionized water is mounting water, i.e., the water used to fill the active aqueous bath during the installation / filling process, said water having a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, and more preferably equal to or greater than 10 MOhms.

[0052] In the sealing step B), the concentration of alkali metal or alkaline earth metal silicate in the solution is preferably between 15 and 40 g / L, for example 23 g / L.

[0053] The temperature of the sealing liquid in step B) can be between 60°C and 100°C, preferably between 97°C and 100°C, for example, 98°C.

[0054] The duration of the closing step B) is 1-40 minutes, preferably 15-25 minutes, for example 20 minutes.

[0055] In one embodiment of the invention, prior to the silicate sealing step (step B), the component may be immersed in an aqueous bath in step A1.

[0056] - In an aqueous bath containing trivalent chromium salts 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 (step A1-1);

[0057] Then optionally

[0058] - In an aqueous bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide (H2O2), ammonium fluoride (NH4F), potassium fluorozirconate (K2ZrF6), potassium permanganate (KMnO4), and sodium permanganate (NaMnO4) (step A1-2).

[0059] The trivalent chromium salt may be, for example, one of the following commercial products: Surtec 650 from SURTEC, Lanthane 613.3 from COVENTYA, TCS from SOCOMORE, or Bonderite MNT 65000 from HENKEL.

[0060] Oxidizing compounds can be, for example, SOCOMORE's PACS product.

[0061] In immersion step A1), steps A1-1) and A1-2) can be performed in the following order: perform step A1-1), then perform step A1-2). Immersion step A1) can also be a standalone step A1-1) without a subsequent step A1-2).

[0062] As described above in steps A1-1) and A1-2), the temperatures of the aqueous bath containing trivalent chromium salts and the aqueous bath containing oxidizing compounds are 20°C-80°C, preferably 20°C-60°C. These two aqueous bath temperatures can be the same or different.

[0063] In step A1), the immersion time for each aqueous bath can be the same or different. It can be 5-40 minutes, preferably 5-20 minutes.

[0064] The pH value of the aqueous bath containing trivalent chromium salts can be 3-4.5, preferably 3-4, for example 3.5.

[0065] The concentration of trivalent chromium salt in the aqueous bath is preferably between 0.5 and 500 g / L.

[0066] The pH value of an aqueous bath containing oxidizing compounds is 3-6.

[0067] The concentration of oxidizing compounds in the aqueous bath is preferably 0.1-500 g / L.

[0068] According to another embodiment of the invention, the method further includes a final hydrothermal sealing after silicate sealing according to step B), referred to as step C). The final hydrothermal sealing C) is carried out in deionized water at a temperature T > 96°C, for example, a temperature of 97°C-100°C, with a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, and more preferably equal to or greater than 10 MOhms.

[0069] In the final hydrothermal sealing (C), the component is immersed in deionized water with an advantageous resistivity of 10 MOhms or higher. The immersion time in this step can be 10-30 minutes, preferably 15-25 minutes.

[0070] According to one embodiment of the present invention, the surface treatment method for aluminum or aluminum alloy parts according to the present invention includes the following steps:

[0071] A) Anodizing step, in which the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14℃-21℃ and a concentration of 150-250 g / L, and

[0072] A DC voltage is applied to the submerged component according to a voltage distribution comprising a voltage rise at a rate of less than 1 V / min until a voltage value of 5-13 V, referred to as a plateau, is reached; and

[0073] B) The step of sealing the anode layer formed on the component after step A).

[0074] The process is carried out in an aqueous solution of deionized water containing 1-500 g / L of alkali metal or alkaline earth metal silicates at a temperature of 60℃-100℃. The resistivity is equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms.

[0075] According to another embodiment of the present invention, the surface treatment method for aluminum or aluminum alloy parts according to the present invention includes the following steps:

[0076] A) Anodizing step, in which the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14℃-21℃ and a concentration of 150-250 g / L, and

[0077] A DC voltage is applied to the submerged component according to a voltage distribution comprising a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached.

[0078] A1) The immersion step of the component in the following aqueous liquid bath.

[0079] - In an aqueous bath containing trivalent chromium salts 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 (step A1-1);

[0080] Then

[0081] - In an aqueous bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide (H2O2), ammonium fluoride (NH4F), potassium fluorozirconate (K2ZrF6), potassium permanganate (KMnO4), and sodium permanganate (NaMnO4) (step A1-2); and

[0082] B) A sealing step, wherein the sealing step is carried out in an aqueous solution of deionized water at a temperature of 60°C-100°C, a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms, and containing 1-500 g / L of alkali metal or alkaline earth metal silicates.

[0083] According to another embodiment of the present invention, the surface treatment method for aluminum or aluminum alloy parts according to the present invention includes the following steps:

[0084] A) Anodizing step, in which the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14℃-21℃ and a concentration of 150-250g / L.

[0085] A DC voltage is applied to the submerged component according to a voltage distribution that includes a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached.

[0086] A1) The immersion step of the component in the following aqueous liquid bath.

[0087] - In an aqueous bath containing trivalent chromium salts 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 (step A1-1);

[0088] Then

[0089] -In an aqueous liquid bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide (H2O2), ammonium fluoride (NH4F), potassium fluorozirconate (K2ZrF6), potassium permanganate (KMnO4), and sodium permanganate (NaMnO4) (step A1-2));

[0090] B) A sealing step, wherein the sealing step is carried out in an aqueous solution of deionized water at a temperature of 60°C-100°C, a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms, and containing 1-500 g / L of alkali metal or alkaline earth metal silicates; and

[0091] C) The final hydrothermal sealing is carried out in deionized water at a temperature of 97℃-100℃ with a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, and more preferably equal to or greater than 10 MOhms.

[0092] According to another embodiment of the present invention, the surface treatment method for aluminum or aluminum alloy parts according to the present invention includes the following steps:

[0093] A) Anodizing step, in which the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14℃-21℃ and a concentration of 150-250 g / L, and

[0094] A DC voltage is applied to the submerged component according to a voltage distribution comprising a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached.

[0095] A1) The immersion step of the component in the following aqueous liquid bath.

[0096] - In an aqueous bath containing trivalent chromium salts 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 (step A1-1); and

[0097] B) The sealing step is carried out in an aqueous solution of deionized water at a temperature of 60°C-100°C, a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms, and containing 1-500 g / L of alkali metal or alkaline earth metal silicates.

[0098] In another embodiment of the present invention, the surface treatment method for aluminum or aluminum alloy parts according to the present invention includes the following steps:

[0099] A) Anodizing step, in which the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14℃-21℃ and a concentration of 150-250 g / L, and

[0100] A DC voltage is applied to the submerged component according to a voltage distribution comprising a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached.

[0101] Im) At the end of step A), the step of immersing the anodized component in an organic or inorganic dye bath, and then optionally...

[0102] A1) The immersion step of the component in the following aqueous liquid bath.

[0103] - In an aqueous bath containing trivalent chromium salts 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 (step A1-1);

[0104] Then

[0105] - In an aqueous bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide (H2O2), ammonium fluoride (NH4F), potassium fluorozirconate (K2ZrF6), potassium permanganate (KMnO4), and sodium permanganate (NaMnO4) (step A1-2); and then optionally

[0106] B) The sealing step is carried out in an aqueous solution of deionized water at a temperature of 60°C-100°C, a resistivity equal to or greater than 0.01 MOhms, preferably equal to or greater than 0.1 MOhms, more preferably equal to or greater than 10 MOhms, and containing 1-500 g / L of alkali metal or alkaline earth metal silicates.

[0107] Step Im) can be performed using any technique known to those skilled in the art. For example, it can be performed in a dye bath suitable for surface treatment, available from sources such as Clariant. For instance, the organic dye Sanodal Blue (from Clariant) at a concentration of 3 g / L can be mentioned, in which 2 g / L of sodium acetate must be added, at a pH of 5-6, at a temperature of 40°C-65°C, preferably equal to 50°C, for a duration of 5-35 minutes, preferably equal to 20 minutes. The active ingredient of the organic dye is anthraquinone molecules.

[0108] In all embodiments, before the component is subjected to the surface treatment method of the present invention, and therefore before the anodizing step A), the component may be surface prepared by degreasing and / or pickling to remove grease, dirt and oxides present on its surface.

[0109] The preliminary steps of this surface preparation may include one or more of the following operations:

[0110] Solvent degreasing to dissolve grease on the surface of the parts. This operation can be performed by soaking, spraying, or any other method known to those skilled in the art;

[0111] - Alkaline degreasing to dissolve grease on the surface of the parts. This operation can be performed by soaking, spraying, or any other technique known to those skilled in the art;

[0112] - Alkaline pickling to dissolve oxides that naturally form on the surface of the component. This operation can be performed by immersion, spraying, or any other technique known to those skilled in the art. At the end of this operation, the component is covered with a powdery layer formed by the oxidation products of intermetallic compounds, which must be removed by a pickling step;

[0113] Pickling is used to dissolve oxides that naturally form on the surface of the component and / or oxide layers that form on the surface of the component during an alkaline pickling step. This operation can be performed by immersion, spraying, or any other technique known to those skilled in the art.

[0114] For example, these steps are described in detail in application WO 2013 / 117759.

[0115] Intermediate rinsing, especially with softened water, is preferably performed between the aforementioned consecutive steps and before passing through the anodized parts.

[0116] The surface treatment method of the present invention significantly improves the resistance of aluminum or aluminum alloy parts to bio-corrosion and meets the requirements of REACH regulations.

[0117] The method of this invention is of great benefit to any type of industry seeking to improve the resistance of aluminum or aluminum alloy components to biocorrosion, such as the aerospace, automotive, and petroleum industries.

[0118] Another object of the present invention relates to a method for manufacturing aluminum or aluminum alloy components for use in the aerospace field, comprising:

[0119] (i) the step of surface treatment of the component by the method of the present invention, and optionally

[0120] (ii) The step of applying one or more layers of paint, varnish, dry lubricant or filler.

[0121] The application of one or more layers of paint, varnish, dry lubricant, or filler can be performed by any method known to those skilled in the art. Furthermore, those skilled in the art will know how to select paints, varnishes, dry lubricants, and fillers suitable for the aerospace field.

[0122] Another object of the present invention is the use of the surface treatment method according to the invention for manufacturing aluminum or aluminum alloy parts for the aerospace field.

[0123] The invention also includes anodized aluminum or aluminum alloy components sealed by the surface treatment method of the invention, the components comprising one or more layers of paint, varnish, dry lubricant or filler, said components being used in the aerospace field.

[0124] Example

[0125] Example 1

[0126] Surface treatment methods for aluminum alloy parts

[0127] The method described below is used to process a rolled 2024T3 aluminum alloy part on one of two surfaces with dimensions of 120×60×2mm.

[0128] First, perform the surface preparation steps for the components in sequence:

[0129] - Alkaline degreasing: Immerse the parts in an ALUMAL CLEAN 101 (purchased from COVENTYA) liquid bath at 60°C for 20 minutes.

[0130] - Rinse with tap water or softened water;

[0131] - Pickling: Immerse the parts in a solution of ALUMAL DEOX411 (purchased from COVENTYA);

[0132] Rinse with tap water or softened water.

[0133] The pickled and rinsed parts are then subjected to the anodizing method according to the invention. During the anodizing process, the parts are immersed in an aqueous bath containing sulfuric acid at a concentration of 160 g / L to 220 g / L, for example, equal to 190 g / L. This aqueous bath is transported and maintained at 18°C. A DC voltage is applied to the immersed parts according to the following voltage distribution: the voltage increases from 0V at a rate of 0.4V / min until a voltage value of 6V, referred to as the plateau, is reached. The voltage is maintained at this plateau value for 50 minutes. An anodic layer with a thickness of 2-4 μm is formed on the surface of the parts.

[0134] As a comparative example, the same parts that had undergone the same surface preparation operations were anodized using conventional chromium anodizing (OAC) and fine sulfuric acid anodizing (fine OAS) methods. The operating conditions for these anodizing processes are shown in Table 1.

[0135] Table 1

[0136]

[0137] The thickness of the anode layer formed on the component is measured by eddy current according to ISO 2360 standard.

[0138] Then, the anodized component according to the invention is rinsed once or multiple times, preferably with softened water, followed by a sealing operation according to the invention under the conditions and sequence shown below:

[0139] Steps A1.1) and A1.2): The components are sequentially immersed in an aqueous bath at 40°C containing 29% v / v of trivalent chromium salt (potassium trivalent chromium sulfate, chemical formula KCr(SO4)2) and pH 3.9 for 20 minutes, then...

[0140] Immerse in an aqueous liquid bath at 25°C containing 7% v / v H2O2 and with a pH of 4.2 for 5 minutes.

[0141] Step B): After the first two operations are completed, the components are sealed by immersing them in an aqueous solution of deionized installation water containing 23 g / L sodium silicate at a temperature of 98°C and a resistivity of 10 MOhms for 20 minutes.

[0142] Between each closed step, rinse with softened water at a temperature of approximately 20°C for 1 minute.

[0143] In comparison, parts anodized using conventional OAC and fine OAS methods also undergo one or more conventional sealing operations, according to the conditions shown in Table 2, such as heat sealing with hexavalent chromium salts (for OAC), or hydrothermal heat sealing with prior pre-sealing (or immersion) with trivalent chromium salts in an oxidizing bath.

[0144] Table 2

[0145]

[0146] Resistance to biological corrosion

[0147] After these sealing operations are completed, a sealed anodic layer is obtained on each treated component. Following treatment, the components undergo immersion testing in a medium representing biocorrosion, following the protocol in §4.7.19 of standard MIL-27725B. A schematic diagram of the installation for biocorrosion testing of different components, according to §4.7.19 of standard MIL-27725B, is shown in Figure 1.

[0148] The results were evaluated by visual inspection after removing the component from the medium to mark any possible signs of degradation caused by the medium (lower phase) treatment and / or erosion of the substrate. The testing was conducted based on comparisons with past treatments (OAC) and more recent prior art alternatives (compliant with REACH). Visually observed degradation could be confirmed by measuring the ohmic resistivity of the layer; when the ohmic resistivity was not infinite, it highlighted that the layer would continue to deteriorate until the substrate was fully degraded.

[0149] Method for measuring resistance using an ohmmeter:

[0150] A multimeter can be used to measure resistance. However, it must be used in ohmmeter mode.

[0151] Using a multimeter in ohmmeter mode:

[0152] Terminal selection: COM terminal and terminal with Ω symbol.

[0153] Connection: Connect the multimeter directly to two points on the area where the test sample is in contact with the lower part of the two-phase medium.

[0154] Scale range (size): Select the largest scale range and then decrease it until the smallest scale range above the measured value is found.

[0155] Table 3 summarizes the relationship between the test results of the resistance to biocorrosion of different surface treatments and the number of days of immersion in a two-phase medium.

[0156] Table 3

[0157]

[0158] Pitting corrosion is localized corrosion that forms irregularly shaped cavities on the surface of aluminum alloy components. It occurs when the aluminum alloy components come into contact with aqueous solutions containing halide ions, most commonly chloride ions. Based on the results shown in Table 3, it is clear that the surface treatment according to the present invention at least doubles the performance in biocorrosion testing compared to conventional surface treatments.

[0159] The performance observed on a component treated according to the invention is equivalent to the performance obtained on a painted component (e.g., by anion electrophoresis) subjected to the same test.

[0160] Example 2

[0161] Voltage rise rate in fine OAS anodizing process

[0162] Twelve samples were degreased and pickled under the same conditions as in Example 1. They were then anodized with different voltage rise times (5 minutes and 15 minutes) and different plateau voltages (6, 10, and 13 volts, for 50, 40, and 30 minutes, respectively). These samples were then sequentially immersed in the aqueous baths of steps A1-1 and A1-2 under the same conditions as described in Example 1. Samples 1, 3, 6, 7, 9, and 11 were then immersed in a final hydrothermally closed aqueous bath of deionized water at 98°C with a resistivity equal to or greater than 10 MOHms for 30 minutes (as described in step C above).

[0163] Samples 2, 4, 5, 8, 10, and 12 were sealed and then rinsed and rinsed under the same conditions as described in Example 1 (Step B).

[0164] The thickness of the enclosed anode layer was measured using eddy current according to ISO 2360 standard. The conditions and thickness measurement results of these layers are shown in Table 4.

[0165] Table 4

[0166]

[0167] The resistance to biocorrosion was then tested under the same conditions and controls as in Example 1. Tests were performed after immersion for 14 and 17 days. The results are shown in Table 5.

[0168] After 17 days of immersion, test results showed that when sealed in an aqueous bath containing silicates according to the invention, the appearance of the samples remained unchanged or showed very slight discoloration. Conversely, widespread corrosion was observed when the samples anodized at 13 and 10 volts were hydrothermally sealed. This effect was significantly less pronounced for samples 1 and 3 anodized at 6 volts. It is also noted that for the silicate-sealed samples anodized at 6 and 10 volts, a 15-minute voltage increase provided better results than a 5-minute voltage increase.

[0169] Therefore, it can be inferred from these results that a slower voltage rise (15 minutes is better than 5 minutes) and a plateau voltage preferably equal to 10 volts or 6 volts, along with the silicate sealing according to the invention, provide the best results for the bio-corrosion resistance simulation test.

[0170] Table 5

[0171]

Claims

1. A surface treatment method for aluminum or aluminum alloy parts used in the aerospace field, comprising at least the following steps: A) Anodizing step; and B) The step of sealing the anode layer formed on the component after step A); The sealing is carried out in an aqueous solution of deionized water at a temperature of 97℃-100℃, a resistivity equal to or greater than 10 MOhms, and containing 15-40 g / L of alkali metal or alkaline earth metal silicates.

2. The method according to claim 1, characterized in that, The anodizing step A) is anodizing as follows: during this anodizing process, the component is immersed in an aqueous liquid bath containing sulfuric acid at a temperature of 14℃-21℃ and a concentration of 150-250g / L, and A DC voltage is applied to the submerged component according to a voltage distribution that includes a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached.

3. The method according to claim 1, characterized in that, The anodizing step A) is an anodizing of the following types: sulfuric acid tartaric acid anodizing, sulfuric acid anodizing, sulfuric acid phosphoric acid anodizing, sulfuric acid boric acid anodizing, or chromium anodizing.

4. The method according to claim 1, characterized in that, The aluminum alloy is selected from the group consisting of 2014, 2017A, 2024, 2214, 2219, 2618, AU5NKZr, 7175, 5052, 5086, 6061, 6063, 7010, 7020, 7050, 7050 T7451, 7055 T77, 7068, 7085 T7651, 7075, 7175 and 7475, AS7G06, AS7G03, AS10G, AS9U3, AS7G06 and AS10G obtained by additive manufacturing.

5. The method according to claim 1, 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.

6. The method according to claim 2, characterized in that, A voltage is applied to the component immersed in the aqueous bath and then held at the plateau value for a sufficient time to obtain an anodic layer with a thickness between 2 and 7 μm on the surface of the component.

7. The method according to claim 2, characterized in that, The voltage applied to the submerged component is maintained at the plateau value for a period of 20-80 minutes.

8. The method according to claim 2, characterized in that, The voltage value referred to as the platform is 6-10V.

9. The method according to any one of claims 1 to 8, characterized in that, The sealing step B) is followed by a post-sealing rinsing step B1), which is carried out in deionized water at a temperature of 15°C-35°C and a resistivity equal to or greater than 0.01 MOhms.

10. The method according to claim 9, characterized in that, The resistivity of the deionized water in the post-sealing rinsing step B1) is equal to or greater than 0.1 MOhms.

11. The method according to claim 10, characterized in that, The resistivity of the deionized water in the post-sealing rinsing step B1) is equal to or greater than 10 MOhms.

12. The method according to any one of claims 1-8, characterized in that, Prior to the sealing step B), the surface treatment method includes an immersion step A1 of the component in an aqueous bath. - In an aqueous bath containing trivalent chromium salts 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, it is represented as step A1-1). Then optionally - In an aqueous liquid bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide, ammonium fluoride, potassium fluorozirconate, potassium permanganate, and sodium permanganate, denoted as step A1-2).

13. The method according to claim 12, characterized in that, The temperature of the aqueous bath containing trivalent chromium salt in step A1-1) and the temperature of the aqueous bath containing oxidizing compound in step A1-2) are 20℃-80℃.

14. The method according to claim 13, characterized in that, The temperature of the aqueous bath containing trivalent chromium salt in step A1-1) and the temperature of the aqueous bath containing oxidizing compound in step A1-2) are 20℃-60℃.

15. The method according to any one of claims 1 to 8, characterized in that, The method further includes a final hydrothermal sealing, referred to as step C), which is carried out in deionized water at a temperature of 97°C-100°C and a resistivity equal to or greater than 0.01 MOhms, and step C) is carried out after the silicate sealing according to step B).

16. The method according to claim 15, characterized in that, In step C), the resistivity of the deionized water is equal to or greater than 0.1 MOhms.

17. The method according to claim 16, characterized in that, In step C), the resistivity of the deionized water is equal to or greater than 10 MOhms.

18. The method according to claim 12, characterized in that, The surface treatment method includes, in the immersion step A1), the concentration of trivalent chromium salt in the aqueous bath in step A1-1) is 0.5-500 g / L, and the concentration of oxidizing compound in the aqueous bath in step A1-2) is 0.1-500 g / L.

19. The method according to any one of claims 1 to 8, comprising the following steps: A) Anodizing step, during which the component is immersed in an aqueous bath containing sulfuric acid at a temperature of 14°C-21°C and a concentration of 150-250 g / L. A DC voltage is applied to the submerged component according to a voltage distribution comprising a voltage rise at a rate less than 1 V / min until a voltage value of 5-13 V, referred to as a plateau, is reached; and B) The step of sealing the anode layer formed on the component after step A). The sealing is carried out in an aqueous solution of deionized water at a temperature of 97℃-100℃, a resistivity equal to or greater than 10 MOhms, and containing 15-40 g / L of alkali metal or alkaline earth metal silicates.

20. The method according to any one of claims 1 to 8, comprising the following steps: A) Anodizing step, during which the component is immersed in an aqueous bath containing sulfuric acid at a temperature of 14°C-21°C and a concentration of 150-250 g / L. A DC voltage is applied to the submerged component according to a voltage distribution that includes a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached. A1) The immersion step of the component in the following aqueous liquid bath. - In an aqueous bath containing trivalent chromium salts 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, it is represented as step A1-1). Then - In an aqueous bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide, ammonium fluoride, potassium fluorozirconate, potassium permanganate, and sodium permanganate (represented as step A1-2), and B) The sealing step is carried out in an aqueous solution of deionized water at a temperature of 97°C-100°C, a resistivity equal to or greater than 10 MOhms, and containing 15-40 g / L of alkali metal or alkaline earth metal silicates.

21. The method according to any one of claims 1 to 8, comprising the following steps: A) Anodizing step, during which the component is immersed in an aqueous bath containing sulfuric acid at a temperature of 14°C-21°C and a concentration of 150-250 g / L. A DC voltage is applied to the submerged component according to a voltage distribution that includes a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached. A1) The immersion step of the component in the following aqueous liquid bath. - In an aqueous bath containing trivalent chromium salts 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, it is represented as step A1-1). Then -In an aqueous bath containing an oxidizing compound selected from the group consisting of hydrogen peroxide, ammonium fluoride, potassium fluorozirconate, potassium permanganate, and sodium permanganate, denoted as step A1-2). B) A sealing step, wherein the sealing step is carried out in an aqueous solution of deionized water at a temperature of 97°C-100°C, a resistivity equal to or greater than 10 MOhms, and containing 15-40 g / L of alkali metal or alkaline earth metal silicates; and C) The final hydrothermal sealing is carried out in deionized water at a temperature of 97℃-100℃ with a resistivity equal to or greater than 0.01 MOhms.

22. The method according to claim 21, characterized in that, The resistivity of the deionized water in the final hydrothermal seal (C) is equal to or greater than 0.1 MOhms.

23. The method according to claim 22, characterized in that, The resistivity of the deionized water in the final hydrothermal seal (C) is equal to or greater than 10 MOhms.

24. The method according to any one of claims 1 to 8, comprising the following steps: A) Anodizing step, during which the component is immersed in an aqueous bath containing sulfuric acid at a temperature of 14°C-21°C and a concentration of 150-250 g / L. A DC voltage is applied to the submerged component according to a voltage distribution that includes a voltage rise at a rate of less than 1V / min until a voltage value of 5-13V, referred to as a plateau, is reached. A1) The immersion step of the component in the following aqueous liquid bath. -In an aqueous bath containing trivalent chromium salts 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, denoted as step A1-1), and B) A sealing step, wherein the sealing step is carried out in an aqueous solution of deionized water at a temperature of 97°C-100°C, a resistivity equal to or greater than 10 Ohms, and containing 15-40 g / L of alkali metal or alkaline earth metal silicates.

25. The method of claim 20, prior to step A1), includes step Im of immersing the anodized component in an organic or inorganic dye bath.

26. A method for manufacturing aluminum or aluminum alloy components for use in the aerospace field, comprising: (i) the step of surface treating the component by the method of any one of claims 1 to 25, and optionally... (ii) The step of applying one or more layers of paint, varnish, dry lubricant or filler.

27. The surface treatment method according to any one of claims 1 to 25 is used for manufacturing aluminum or aluminum alloy parts for the aerospace field.

28. An anodized aluminum or aluminum alloy component sealed by any of the surface treatment methods of claims 1 to 25, comprising one or more layers of paint, varnish, dry lubricant or filler, said component being used in the aerospace field.

Images