ALUMINUM ALLOY PART AND ASSOCIATED MANUFACTURING PROCESS

Abstract

The invention relates to a part (1) comprising: - a body (10) made of aluminum alloy, - a first layer (12) comprising aluminum oxide, arranged on the body (10), - an intermediate layer (14) comprising chromium, and - a second layer (16) comprising aluminum oxide, the intermediate layer (14) being arranged between the first layer (12) and the second layer (16). Figure 1

Description

Title of the invention: ALUMINUM ALLOY PART AND ASSOCIATED MANUFACTURING METHOD Technical field of the invention

[0001] The invention relates to the technical field of aluminum alloy parts, and in particular, parts that have undergone an anodic oxidation step. Specifically, the invention relates to parts that have undergone anodic oxidation, impregnation, and sealing steps.

[0002] The invention also relates to the field of manufacturing processes for aluminum alloy parts, including in particular anodic oxidation, impregnation and sealing steps. Technical background

[0003] In the aeronautical industry, it is common practice to use aluminum alloy parts. Indeed, aluminum alloys offer an excellent mechanical properties-to-weight ratio and their manufacturing cost is relatively low. However, depending on their environment, these parts are susceptible to several types of localized corrosion, leading to part degradation and potentially resulting in their removal or failure. To improve the corrosion resistance of titanium alloy parts, it is known to perform a surface treatment on the part.

[0004] The surface treatment typically includes a chromic anodic oxidation step of the part, which forms a surface aluminum oxide layer with a thickness between 2 µm and 15 µm. Since the aluminum oxide layer is porous, the anodic oxidation step is typically followed by a sealing step to fill the pores of the aluminum oxide layer. This improves the corrosion resistance of the part.

[0005] The anodic oxidation step is typically carried out by immersing the part in a chromic acid solution, and the sealing step is carried out by immersing the part in a solution containing hexavalent chromium. However, hexavalent chromium is a compound that is prohibited by new health and environmental standards.

[0006] In order to eliminate the need for hexavalent chromium, document FR-B1-3 106 838 proposes a surface treatment for an anodized aluminum alloy part comprising the steps of impregnating the part by immersing it in a solution comprising a hexafluorozirconate salt and a trivalent chromium salt, and of sealing the part by immersing it in a solution comprising a silicate. Thus, Each of the solutions for the impregnation and sealing stages uses alternatives to hexavalent chromium that comply with safety and environmental standards. The resulting part comprises an aluminum alloy body coated with a first layer of aluminum oxide, an intermediate layer of chromium, and a final layer of silicate.

[0007] The present invention proposes a new solution for providing a part that is corrosion-resistant while complying with safety and environmental standards. Summary of the invention

[0008] To this end, the invention proposes a part comprising:

[0009] - an aluminum alloy body,

[0010] - a first layer comprising aluminium oxide, arranged on the body,

[0011] - an intermediate layer comprising chromium, and

[0012] - a second layer comprising aluminum oxide, the intermediate layer being arranged between the first layer and the second layer.

[0013] The part according to the invention is therefore remarkable in that it has a second layer of aluminum oxide. This second layer of aluminum, rich in oxygen and aluminum, gives the part very good corrosion resistance properties. It has also been observed that this aluminum layer could give the part better paint adhesion.

[0014] Therefore, thanks to the invention, the part is corrosion resistant, has good paint adhesion properties and can be manufactured in accordance with health and environmental standards.

[0015] The invention may comprise one or more of the following features, taken individually or in combination with each other:

[0016] - the second layer has a thickness between 10 nm and 500 nm.

[0017] - a layer of paint arranged on the second layer.

[0018] The invention also relates to a method for manufacturing a part comprising the following chronological steps:

[0019] (a) supply of an aluminum alloy body,

[0020] (d) anodic oxidation of the body,

[0021] (e) impregnation of the body with an impregnation solution comprising a salt of trivalent chromium and an oxidizing compound, and

[0022] (f) sealing the body with a sealing solution comprising an aluminate.

[0023] According to the invention, the sealing step of the aluminum alloy part is carried out using a sealing solution comprising an aluminate. Indeed, it has been shown that an anodized aluminum alloy part impregnated with oxide A chromium / zirconium (CrIII / Zr) part, for example, sealed with an aluminate, exhibits good corrosion resistance, at least equivalent to a part sealed with a silicate. Furthermore, aluminate sealing improves paint adhesion to the part. It has also been observed that aluminate sealing improves the breakdown voltage of the process. The treatment is more resistant to electrical stresses.

[0024] Also, the process of the invention makes it possible to do without hexavalent chromium and is therefore compatible with safety and environmental standards.

[0025] The invention may comprise one or more of the following features, taken individually or in combination with each other:

[0026] - the sealing solution has a mass concentration of aluminate between 0.1 g / L and 10 g / L, preferably between 0.5 g / L and 5 g / L,

[0027] -1'aluminate is a sodium aluminate,

[0028] - in step (d), the body is immersed in a tank containing a solution of sulfuric anodic oxidation comprising sulfuric acid at a mass concentration between 150 g / L and 250 g / L, preferably 180 g / L,

[0029] - the impregnation solution has a temperature between 30°C and 50°C, preferably at 40°C,

[0030] - between steps (e) and (f), a post-impregnation step (e') of the body with a post-impregnation solution comprising hydrogen peroxide and a lanthanum salt,

[0031] - the oxidizing compound is a hexafluorozirconate salt,

[0032] — the sealing solution has a temperature between 50°C and 150°C, preferably between 80°C and 100°C,

[0033] — step (f) is carried out for a duration of between 5 min and 60 min, preferably between 10 and 20 minutes,

[0034] — step (d) is a sulfuric anodic oxidation,

[0035] — step (e) is carried out for a duration of between 5 min and 60 min, preferably between 10 min and 20 min. Brief description of the figures

[0036] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which:

[0037] [Fig.1] is a schematic cross-sectional representation of a part according to the invention;

[0038] [Fig.2] is a schematic representation of a process according to an embodiment of the invention. Detailed description of the invention

[0039] A part 1 according to an embodiment of the invention is illustrated in [Fig. 1]. Part 1 according to the invention comprises a body 10 made of aluminum alloy. The aluminum alloy is, for example, selected from the 2000 series such as alloys 2014, 2017, 2024, 2214, 2219, 2618, or the 6000 series such as alloys 6061, 6063, or the 7000 series such as alloys 7010, 7020, 7050, 7055, 7068, 7075, 7085, 7175, 7475. In another example, the aluminum alloy is a casting alloy of type AS7G06, AS7G03, AS10G, or AS9U3.

[0040] Part 1 further includes a first layer 12 arranged on the body 10. The first layer 12 comprises aluminum oxide. The first layer 12 has a thickness of between 2 µm and 30 µm, preferably between 5 µm and 25 µm. The first layer 12 is obtained by anodic oxidation of part 1.

[0041] Part 1 according to the invention further comprises an intermediate layer 14 comprising chromium. 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 by impregnating part 1 with a solution comprising a trivalent chromium salt and an oxidizing compound.

[0042] Part 1 according to the invention further comprises a second layer 16. The intermediate layer 14 is arranged between the first and second layers 12, 16. The second layer 16 comprises aluminum oxide 16. The second layer 16 has a thickness of between 10 nm and 500 nm, preferably 200 nm. The second layer 16 is obtained by sealing part 14 with an aluminate.

[0043] Preferably, part 1 further comprises a layer of paint 18. The layer of paint 18 is arranged on the second layer of aluminum oxide 16. The layer of paint 18 has a thickness of between 10 pm and 100 pm, preferably of 50 pm.

[0044] Part 1 according to the invention exhibits good corrosion resistance and good paint adhesion. Indeed, the combination of the intermediate layer 14 and the second layer 16 of aluminum oxide provides good corrosion resistance to part 1. Furthermore, the second layer 16 of aluminum oxide promotes the adhesion of the paint layer 18.

[0045] A manufacturing process for part 1 will now be described. The manufacturing process comprises the following chronological steps:

[0046] (a) supply of the body 10 in aluminium alloy,

[0047] (b) optionally, degreasing of body 10,

[0048] (c) optionally, stripping of body 10,

[0049] (d) anodic oxidation of body 10,

[0050] (e) impregnation of body 10 with an impregnation solution comprising a salt of hexafluorozirconate and a trivalent chromium salt,

[0051] (e') optionally, post impregnation of body 10,

[0052] (f) sealing the body 10 with a sealing solution comprising an aluminate,

[0053] (g) optionally, application of paint to body 10.

[0054] Where applicable, aqueous compositions / solutions are made up with water up to 100% of their volume.

[0055] The degreasing step (b) advantageously dissolves any grease that may be present on the surface of the body 10. The degreasing step can be carried out with an alkaline aqueous degreasing solution. The alkaline aqueous degreasing solution comprises, for example, SOSOCLEAN A3432 at a volume concentration, for example, of 11% (volume / volume). The temperature of the alkaline aqueous degreasing solution is, for example, between 30°C and 50°C, typically 45°C. The duration of step (b) is, for example, between 1 min and 30 min, typically 10 min. Step (b) can be carried out by immersion, spraying, or any other technique known to those skilled in the art.

[0056] Step (c) of pickling advantageously dissolves any oxides that may have formed on the surface of the body 10. The pickling step can be carried out with an alkaline aqueous pickling solution. The alkaline aqueous pickling solution comprises, for example, a mixture of SOCOSURF A1858 at a volume concentration, for example, of 42% and SOCOSURF A1806 at a volume concentration, for example, of 10% (volume / volume). The temperature of the alkaline aqueous pickling solution is, for example, between 30°C and 100°C, typically 50°C. The duration of step (c) is, for example, between 1 min and 30 min, typically 10 min. Step (c) can be carried out by immersion, spraying, or any other technique known to those skilled in the art.

[0057] Step (d) according to the invention creates the first layer 12 of aluminum oxide. After this step, the first layer of aluminum oxide 12 is porous. The anodic oxidation is advantageously a sulfuric acid anodic oxidation. During this step, the body 10 is immersed in a tank containing a sulfuric acid anodic oxidation solution comprising sulfuric acid at a mass concentration of between 150 g / L and 250 g / L, preferably 180 g / L.

[0058] The solution is, in particular, an aqueous solution. Preferably, the sulfuric acid anodic oxidation solution is at a temperature between 10°C and 20°C, typically 18°C. The tank also includes an anode connected to the body 10. The anode and the body 10 are typically connected to a current generator. The body 10 is subjected to a current density of between 1 A / dm² and 5 A / dm², typically 2 A / dm². Body 10 is subjected to a DC voltage, for example, between 10 V and 30 V, typically between 15 V and 20 V. The duration of step (d) is, for example, between 10 min and 120 min, for example, 60 min.

[0059] The impregnation step (e) is advantageously carried out by immersing the body 10 in the impregnation solution. The impregnation solution is an aqueous solution. According to the invention, the impregnation solution comprises a trivalent chromium salt and an oxidizing compound. In the present invention, trivalent chromium is understood, in a known manner, to mean chromium in the +3 oxidation state.

[0060] Trivalent chromium salt can be in the form of trivalent chromium fluoride, chloride, nitrate, acetate, acetate hydroxide, sulfate, potassium sulfate, etc., for example CrF3,xH2O, CrCl3,xH2O, Cr(NO3)3,xH2O, (CH3CO2)2Cr,xH2O, (CH3CO2)7Cr3(OH)2,xH2O, Cr2(SO4)3,xH2O, CrK(SO4)2,xH2O.

[0061] The oxidizing compound according to the invention is preferably a hexafluorozirconate salt. For example, it is chosen from the group consisting of ammonium hexafluorozirconate ((NH4)2ZrF6), sodium hexafluorozirconate (Na2ZrF6), potassium hexafluorozirconate (K2ZrF6).

[0062] Advantageously, the impregnation solution has a mass concentration of trivalent chromium salt between 0.5 g / L and 50 g / L and a mass concentration of oxidizing compound between 0.5 g / L and 50 g / L.

[0063] Advantageously, the impregnation solution has a temperature between 30°C and 50°C, preferably 40°C.

[0064] Advantageously, the duration of step (e) is between 5 min and 60 min, preferably between 10 min and 20 min.

[0065] Preferably, the impregnation solution comprises SOCOSURF TCS at a volume concentration of 34% (volume / volume).

[0066] Preferably, step (e') is carried out with a post-impregnation solution. Step (e') is carried out, for example, by immersing the body 10 in the post-impregnation solution. The post-impregnation solution is an aqueous solution comprising, for example, hydrogen peroxide and a lanthanum salt. The lanthanum salt is, for example, lanthanum carbonate (La2(CO3)3).

[0067] Preferably, the impregnation solution comprises SOCOSURF PACS at a volume concentration of 10% (v / v). The temperature of the impregnation solution is, for example, between 15°C and 30°C, typically 25°C. The duration of step (e') is, for example, between 2 min and 30 min, typically 5 min.

[0068] Steps (e) and possibly (e') allow the intermediate layer 14 to be formed and the pores of the aluminum oxide layer formed in step (d) to be filled.

[0069] According to the invention, in step (f), the sealing solution is an aqueous solution comprising an aluminate. The aluminate is, for example, sodium aluminate (NaAlO2), potassium aluminate (KaAlO2), or lithium aluminate (LiAlO2). Preferably, the aluminate is sodium aluminate (NaAlO2). The mass concentration of aluminate is between 0.1 g / L and 10 g / L, preferably between 0.5 g / L and 5 g / L. Preferably, the sealing solution has a temperature between 50°C and 150°C, preferably between 80°C and 100°C. Preferably, the duration of this step is between 5 min and 60 min, preferably between 10 min and 20 min. The sealing step allows the formation of the second layer 16.

[0070] Advantageously, in step (g), the paint is applied mechanically, for example using a spray gun, or manually using a brush.

[0071] The impregnation and sealing steps make it possible to fill the pores of the aluminum oxide layer 12 and to strengthen the corrosion resistance of part 1. Since the sealing step is carried out with an aluminate, the corrosion resistance of part 1 is improved and the paint adhesion is improved. Examples

[0072] Example 1: corrosion tests

[0073] Parts made of 2618 T6 aluminum alloy and parts made of 2024 T3 aluminum alloy were subjected to degreasing, pickling, sulfuric anodizing, impregnation and post-impregnation steps according to the conditions set out in Table 1. Then, various sealing steps were carried out according to the conditions set out in Table 2, including an aluminate sealing 1 according to the invention, a silicate sealing 2 according to the prior art and a water sealing 3 according to the prior art.

[0074] [Tables 1] Degreasing, Stripping, Anodizing, Impregnation, Post-impregnation. Aqueous solution: SOSOCL EAN A3432 at a volume concentration of 11%, SOSOCU RF A1858 at a volume concentration of 42%, and SOSOCURF A1806 at a volume concentration of 10%. Sulfuric acid at a mass concentration of 180 g / L, SOCOSU RF TCS at a volume concentration of 34%, SOCOSU RF PACS at a volume concentration of 10%. Temperature: 45°C, 50°C, 18°C, 40°C, 25°C. Processing time: 10 min, 10 min, 20 min, 10 min, 5 min. Voltage: 17 V.

[0075] [Tables2] Clogging 1 Clogging 2 Clogging 3 Composition of the aqueous solution: NaAlO2 at a mass concentration of 0.5-5 g / L, SuperSeal 2S at a mass concentration of 20-80 g / L, Deionized water. Solution temperature: 80°C-100°C, 80°C-100°C, 100°C. Treatment time: 10 min-20 min, 10 min-20 min, 10 min-20 min.

[0076] The parts were then subjected to a salt spray resistance test in accordance with standard NF EN ISO 9227. The results are shown in Table 3.

[0077] [Tables3] Neutral salt spray after 500h (Number of punctures (average over 3 pieces)) 2618 T6 2024 T3 Clogging 1 0 0 Clogging 2 1 <1 Clogging 3 >2 -

[0078] It is observed that sealing methods 1 and 2 increase the corrosion resistance of the parts compared to sealing method 3. Silicate and aluminate sealing therefore improve the corrosion resistance of aluminum alloy parts. Aluminate sealing thus gives the part good corrosion properties at least equivalent to silicate sealing.

[0079] Example 2: Extreme surface analysis

[0080] The parts that underwent sealing step 1 and sealing step 2 were subjected to X-ray photoelectron spectrometric analyses (XPS).

[0081] The results are presented in Table 4.

[0082] [Tables4] CO Al Si Zr N Na s F Ca Clogging 1 23.7 55.4 17.0 1.0 0.3 0.5 1.0 0.1 0.9 0.2 Clogging 2 33.2 47.2 - 19.4 - 0.1 - - - 0.1

[0083] Elemental analysis of the extreme surface of the parts to a thickness of 50 nm demonstrates the presence of aluminum oxide (presence of aluminum and oxygen). This surface layer of aluminum oxide promotes the corrosion resistance of the part, as demonstrated in Example 1, compared to water clogging and paint adhesion.

Claims

Demands

1. A method for manufacturing a part (1) comprising the following chronological steps: (a) supplying a body (10) of aluminum alloy, (d) anodic oxidation of the body (10), (e) impregnation of the body (10) with an impregnation solution comprising a trivalent chromium salt and an oxidizing compound, and (f) sealing the body (10) with a sealing solution comprising an aluminate.

2. A process according to the preceding claim, characterized in that the sealing solution has a mass concentration of aluminate between 0.1 g / L and 10 g / L, preferably between 0.5 g / L and 5 g / L.

3. A method according to any one of claims 1 to 2, wherein the aluminate is sodium aluminate.

4. A method according to any one of claims 1 to 3, characterized in that in step (d), the body (10) is immersed in a tank comprising a sulfuric anodic oxidation solution comprising sulfuric acid with a mass concentration between 150 g / L and 250 g / L, preferably 180 g / L.

5. A method according to any one of claims 1 to 4, wherein the impregnation solution has a temperature between 30°C and 50°C, preferably 40°C.

6. A method according to any one of claims 1 to 5, further comprising, between steps (e) and (f), a post-impregnation step (e') of the body (10) with a post-impregnation solution comprising hydrogen peroxide and a lanthanum salt.

7. A process according to any one of claims 1 to 6, characterized in that the oxidizing compound is a hexafluorozirconate salt.

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