A process for treating an aluminum or aluminum alloy part, a part obtained by implementing such a process, and an anodizing bath for implementing such a process

Abstract

A process (100) for treating a part (1) made of aluminum or aluminum alloy, the process comprising an anodizing step (102), the process being characterized in that the anodic bath (2) comprises a titanium salt, and characterized in that it further comprises, after the formation of the oxidation layer (10), a whitening step (103) which includes the precipitation of titanium as titanium oxide in the oxidation layer (10), so that the resulting oxidation layer (10) is white. Figure for the abbreviation: Figure 4

Description

Title of the invention: Method for treating an aluminum or aluminum alloy part, part obtained by implementing such a method, and anodizing bath for implementing such a method. SCOPE OF THE INVENTION

[0001] The present invention relates to the field of forming a protective anodic layer on a metal part, particularly aluminum. More specifically, the invention concerns a method for forming a white anodic layer on a part made of aluminum or aluminum alloy. technological BACKGROUND

[0002] The formation of an anodic layer on a metal part on an industrial scale has been known for about a century, in order to protect the part from corrosion and wear, to make it more durable, and / or to enhance its aesthetic appearance. The anodizing process, also called anodizing, is well known. It is based on redox reactions: in the presence of an electric current, the positive pole, called the anode, is oxidized while the negative pole, called the cathode, is reduced. Thus, by placing the metal part as an anode in an anodizing bath, and simultaneously placing a cathode in the same bath, an electric current flowing through the anodizing bath between the cathode and the anode causes oxidation of the surface of the metal part in contact with the bath. The anodic layer is then formed.

[0003] Anodizing is often used on parts made of so-called "light" metals such as aluminum and its alloys in order to improve their properties and broaden their fields of application. The fields of use of anodized aluminum are extremely varied, including, for example, aeronautics, jewelry, watchmaking, the food industry, automotive, construction, building, cosmetic product packaging, as well as smartphones, door and window frames, and garden fences.

[0004] The principle of anodizing aluminum parts is widely known: the aluminum part acts as the anode, a part, for example made of steel, acts as the cathode, and the redox reaction is as follows:

[0005] 4A1 + 3O2 -> 2A12O3

[0006] The aluminum oxide (Al₂O₃) layer that forms during the anodizing process naturally has a dark gray color. It is then known to apply a colored layer over the oxide layer, for example in the form of paint or of lacquer. This colored layer has the main drawback of not having the same resistance properties as the oxidation layer resulting from anodizing. The white color layer applied over the oxidation layer deteriorates more easily than the oxidation layer itself, revealing the dark gray color underneath. While this defect may be acceptable in certain sectors where products have a limited lifespan and / or use, such as cosmetic packaging, it limits the use of anodized aluminum in other areas like vehicle bodies or construction.

[0007] It is known to incorporate color pigments into the oxidation layer. More specifically, the oxidation layer comprises pores on its surface, into which color pigments are integrated.

[0008] US patent 2017 / 0121838 describes an example in which the pore size of the oxidation layer is increased by electrolytic treatment in an acid bath. Then, color particles are deposited into the pores. For example, the anodized part is immersed in a solution in which the pigments are suspended. The pigments then infuse into the pores. The part is then dried.

[0009] Achieving a white color for the oxidation layer of an anodized part is particularly difficult. Indeed, the white color is generally obtained by using light-reflecting particles. These particles can notably be titanium dioxide (TiO2), as in US2017 / 0121838.

[0010] One drawback is that the resulting color can be a shade of white tending towards gray or beige, unlike a layer of white paint or lacquer: it is unsatisfactory. This is because the added coloring particles enter the pores randomly. In particular, the penetration of reflective particles into the pores is not controlled. The dimensions of the pores and particles are on the order of nanometers, so some pores remain empty of coloring particles. The distribution of coloring particles on the surface of the part is therefore uneven, leaving uncolored areas visible. To the human eye, this lack of uniformity results in a shade of white that can be described as lacking purity.

[0011] The invention thus aims to provide a solution to the aforementioned disadvantages by proposing the production of an anodized part with a white surface color which is resistant to wear and corrosion and whose purity of white provides complete satisfaction. Summary of the invention

[0012] Thus, according to a first aspect, the invention relates to a treatment method of a part made of aluminum or aluminum alloy. The process includes an anodizing step which comprises: • the preparation of an anodizing bath and the placement of a cathode in the anodic bath; • immersion in the anodizing bath, at least in part, of said part as an anode; • the application of a voltage between the part and the cathode; • the formation of an oxidation layer on said part.

[0013] The anodic bath includes, in particular, a dissolved titanium salt such that the oxidation layer comprises titanium particles. Furthermore, the process further comprises, after the formation of the oxidation layer, a bleaching step which includes: • the preparation of a bleaching bath including a precipitating agent for titanium; • immersion at least partially in the bleaching bath of the part; • the precipitation of titanium as titanium oxide in at least part of the oxidation layer, so that the resulting oxidation layer is white in color.

[0014] Thus, the white color is initiated in the oxidation layer by the anodizing bath containing titanium, and the white color is obtained by precipitating the titanium as titanium oxide directly within the oxidation layer. The oxidation layer thus obtained exhibits a brilliant white color compared to the white color obtained by prior art processes based on bleaching the oxidation layer.

[0015] Depending on different aspects, it is possible to foresee one and / or the other of the characteristics below taken alone or in combination.

[0016] According to one embodiment, the bleaching step may include placing an anode in the bleaching bath and may further include applying a voltage between the anode and the part to achieve the precipitation of titanium into titanium oxide in the oxidation layer, the part acting as a cathode.

[0017] The precipitation of titanium to titanium oxide by applying a voltage notably protects the oxidation layer during titanium oxidation. Specifically, the release of hydrogen at the cathode during the reaction protects the oxidation layer. Furthermore, the immersion time in the bleaching bath is reduced compared to the absence of voltage. Finally, the quality of the oxidation layer is satisfactory. In particular, it is sufficiently resistant for applications in the building sector.

[0018] According to one embodiment, the titanium salt in the oxidation bath comprises a double titanium and potassium oxalate, which is readily available and cheap.

[0019] According to one embodiment, the precipitating agent of the bleach bath comprises soda, which is readily available and cheap.

[0020] According to one embodiment, the bleaching bath includes potassium bicarbonate to produce a buffering effect against the caustic soda on the part. The aluminum under the oxidation layer is thus protected from unwanted oxidation.

[0021] According to one embodiment, the process may include a final sealing step comprising immersing at least part of the part in an aqueous solution. The pores formed during the oxidation step are then closed, trapping the titanium oxide and ensuring the long-term durability of the oxidation layer.

[0022] According to one embodiment, the process may include an initial step of preparing the part to obtain a specific surface finish. The surface finish can influence the quality of the oxidation layer. By controlling the initial surface finish, the quality of the oxidation layer is also controlled.

[0023] According to a second aspect, the invention relates to a part made of aluminum or aluminum alloy obtained by implementing the manufacturing process as described above. The oxidation layer of the part then comprises titanium oxide, is white in color, and has a hardness between 300 and 450 HV (Vickers hardness).

[0024] According to a third aspect, the invention relates to an anodizing bath for implementing the process as presented below, which may include a titanium salt dissolved in an acidic solution and / or whose bath pH is between 1.8 and 2.2, ensuring an oxidation layer with high mechanical properties and good penetration of titanium into the oxidation layer. Brief description of the drawings

[0025] Embodiments of the invention will be described below with reference to the drawings, briefly described below:

[0026] [Fig.1] schematically represents the steps of a process for treating a part according to an embodiment of the invention, comprising a preparation step, an anodizing step, a whitening step and a sealing step.

[0027] [Fig.2] schematically represents an anodizing bath for carrying out the anodizing step of [Fig.1].

[0028] [Fig.3] is a diagram of a detailed view of a portion of the part treated at the level of the oxidation layer.

[0029] [Fig.4] schematically represents a bleaching bath for carrying out the bleaching step of [Fig.1].

[0030] In the drawings, identical references designate identical or similar objects. DETAILED DESCRIPTION

[0031] Figure 1 shows an example of an embodiment of the process 100 for treating a part 1 made of aluminum or aluminum alloy. The part 1 may need to be treated over its entire outer surface or over one or more specific portions. The surface or portions of the surface of the part 1 to be treated form what is referred to hereafter as the exposed surface.

[0032] The process is characterized by producing an anodized oxidation layer that is white on at least part of the outer surface of the part. More precisely, the white color is provided by the oxidation layer, and not by the addition of another colored layer.

[0033] By "white" or "white color" we mean here what is commonly called white to the human eye, that is to say what is perceived visually by a human being as giving an impression of brightness without any other color of the light spectrum being dominant over the others.

[0034] The treatment process 100 may include, in particular, an initial preparation step 101 of the part 1 to be treated. The preparation step 10 aims to achieve a specific external surface finish of the part, determined in particular according to the desired final result for the part 1. For example, the preparation step 101 may include a degreasing operation, possibly followed by a satin or polishing operation.

[0035] Once the part 1 to be treated has been prepared, it is subjected to an anodizing step 102.

[0036] More specifically, the anodizing step 102 comprises the preparation of an anodic bath 2 in a container, for example an anodizing tank 3. A metal, for example in the form of a bar, is immersed at least partially in the bath 2 to constitute a cathode 4. The cathode 4 can be made of any material commonly used for anodizing aluminum and its alloys, such as aluminum, titanium, or lead. The cathode 4 can be added to the bath 2 in the tank 3, in one or more elements, or integrated into the tank. Preferably, the external surface area of ​​the cathode 4 is greater than or equal to twice the exposed surface area of ​​the part 1 to be treated. A system 5 for stirring and homogenizing bath 2 can also be placed in bath 2, in tank 3.This includes, for example, a system 5 for agitation and homogenization using pressurized air, or circulation with a Venturi system, incorporating continuous filtration. The filtration can, for example, be set below 5 µm (microns), which is sufficient to ensure effective filtration of the anodizing bath 2, guaranteeing high-quality anodizing. The particles that can... Any contaminants that might contaminate the anodizing bath 2 are thus continuously filtered, keeping the composition of the anodizing bath 2 clean, so that the quality of the anodizing is ensured throughout the anodizing step 102. A heating device 6 can be placed in the bath 2, in the tank 3. The heating device 6 maintains the bath 2 within a predetermined temperature range. For example, the heating device 6 can maintain the temperature of the bath 2 between 40°C and 60°C, plus or minus 1°C. The heating device 6 can, for example, include a heating element with a control system to maintain the bath 2 at a set temperature.

[0037] To perform the anodizing process, a current generator 7 is electrically connected to the cathode 4 and to the part 1 to be treated. More precisely, the negative terminal of the generator 7 is connected to the cathode 4, and the positive terminal is connected to the part 1 to be treated, which then acts as the anode. The generator 7 is typically a 0V to 120V DC generator, with sufficient power to apply a voltage adequate to initiate and sustain the redox reaction. Typically, the power depends on the exposed surface area of ​​the part 1 to be treated. For example, it is between 1.5A and 3A / dm² on the exposed surface area of ​​the part 1 to be treated.

[0038] The workpiece 1 to be treated is immersed in the anodizing bath 2. For example, it is suspended from a support 8 specially adapted for the anodizing step. The electrical connection between the workpiece 1 to be treated and the generator 7 can be made via the support 8, which is then made of an electrically conductive material. Such a support 8 is known. It is made, for example, of titanium.

[0039] Although in the example illustrated in the figures, only one part 1 is treated at a time, several parts can be treated simultaneously in the same bath 2 in the same tank 3.

[0040] The anodic bath 2 is typically acidic, with a pH maintained, for example, around 2. According to the invention, the anodic bath 2 comprises at least one titanium salt. This is, for example, a titanium potassium double oxalate. The titanium salt is added to the bath 2 and dissolves. The volume of the anodizing bath 2 is chosen according to the exposed surface area of ​​the part 1 to be treated. For example, it is chosen to be equal to 4 L / dm² (liters per square decimeter) of exposed surface area.

[0041] When the generator 7 is switched on, an oxidation layer 10 forms on the exposed surface of the workpiece 1 being treated, which is immersed in the anodizing bath 2. In this case, it is a layer 10 of aluminum oxide, also called alumina. Beneath the oxidation layer 10, the material is unaffected by the redox reaction, forming a base layer 11 of aluminum or aluminum alloy. Generally, the thickness of the oxidation layer 10 formed is on the order of microns, while the thickness of the base layer 11 is arbitrary, generally greater than that of the oxidation layer 10, and for example on the order of millimeters. The thickness of the oxidation layer 10 depends however on the parameters applied to the anodizing step according to the desired result, and in particular on the duration of the anodizing step and the electrical power applied: the longer the duration and / or the higher the electrical power applied, the greater the thickness of the oxidation layer 10.

[0042] The oxidation layer 10 comprises pores 12 open to the environment outside the part 1. The width of the pores 12 is typically between a few tens of nanometers and a few hundred nanometers. For example, it is between 20 nm and 800 nm. The pores 12 appear during the anodizing step, and titanium particles 13 in the form of dissolved salt penetrate the pores 12 and thus become integrated into the oxidation layer 10. More specifically, liquid anodic bath 2 penetrates the pores 12, transporting the particles into the pores 12 during the anodizing step 102.

[0043] Titanium salt, particularly when in the form of titanium potassium oxalate, is initially white. Once placed in the anodizing bath 2, it becomes clear and colorless. When the generator 7 is switched on and applies a voltage to the anodizing bath 2, the titanium salt turns brown. Once the voltage is switched off, the salt becomes colorless and clear again.

[0044] Therefore, at the end of the anodizing step 102, the color of the exposed surface of the visible part 1 is that of the oxidation layer 10, i.e. the dark grey of the aluminium oxide.

[0045] The process 100 then includes a step 103, called the bleaching step, of the oxidation layer 10 resulting from the anodizing step 102. The principle of the bleaching step 103 is to precipitate the titanium particles in the pores 12 of the oxidation layer 10 as titanium oxide, in order to "reveal" the white color. The bleaching step 103 is carried out immediately after the anodizing step 102, without any drying time for the part between the two steps so that the pores 12 do not become clogged and remain open to the environment outside the part 1. Thus, after the anodizing step 102, the part 1 can be drained for a few minutes above the anodizing bath 2 and then rinsed, for example, with demineralized water. Rinsing allows the residues of the anodizing bath 2 to be cleaned from the surface of part 1, except for the inside of pores 12. Then, without waiting for drying, part 1 is transferred to bleaching step 103.

[0046] The bleaching step 103 more specifically comprises the preparation of a bleaching bath 20 in a suitable container, such as a tank 21. The bleaching bath 20 includes, in particular, a precipitating agent, in order to precipitate the titanium to titanium oxide and obtain the white color

[0047] According to one embodiment, the bleaching step 103 is carried out under applied voltage in the bleaching bath 20. Thus, an anode 22 is immersed, at least partially, in the bleaching bath 20. The anode 22 is formed, as previously described for the cathode 4 of the anodizing step 102, from any suitable material, such as stainless steel, titanium, or lead. The anode 22 may be inserted into the bath 20 in the tank 21, in one or more elements, or integrated into the tank 21. A heating device 23 may be placed in the bath 20, in the tank 21, to maintain the bleaching bath 20 within a specified temperature range, for example, a range between 15°C and 35°C, and more specifically between 18°C ​​and 25°C. the temperature can be set and maintained around a setpoint thanks to a control system;

[0048] A current generator 24 is electrically connected to the anode 22 and to the workpiece 1 to be treated. More precisely, the positive terminal of the generator 24 is connected to the anode 22, and the negative terminal is connected to the workpiece 1, which then acts as the cathode. The generator 24 is, for example, identical to the generator 7 of the anodizing step 102.

[0049] Part 1 is immersed in the bleaching bath 20. For example, it is suspended from a support 25 specially adapted for the bleaching step 103. The electrical connection between the part 1 to be treated and the generator 24 can be made via the support 25, which is then made of an electrically conductive material. Such a support 25 is known. It is made, for example, of titanium. According to one embodiment, the support 25 of the bleaching step 103 is combined with the support 8 of the anodizing step 102, the part 1 being immediately transferred from the anodizing tank 3 to the bleaching tank 21 with its support 8, 25, by any suitable transfer system, for example, using a hoist. We must avoid detaching part 1 from its support between step 102 of anodizing and step 103 of bleaching, in order to maintain the point of contact between the support 8, 25 and part 1.Indeed, since the alumina layer is an electrical insulator, moving the contact point to another part of part 1, and therefore onto the alumina layer formed, would prevent current from passing from the bath to part 1 during the bleaching step. Applying a voltage to induce precipitation makes it possible, in particular, to reduce the immersion time of part 1 in the bleaching bath 20 required to precipitate the titanium.

[0050] The bleaching bath 20 is alkaline, with a pH greater than 10, for example between 11 and 12. The bleaching bath 20 includes a titanium bleaching agent, that is, a chemical species capable of causing titanium to precipitate in the pores 12 of the oxidation layer 10. For example, the bleaching agent is caustic soda, or sodium hydroxide (NaOH).

[0051] According to one embodiment, the bleaching bath 20 includes a pad to protect part 1 from the aggressiveness of the sodium hydroxide. Indeed, the sodium hydroxide reacts naturally with aluminum, and therefore potentially with the base layer 11 beneath the oxidation layer 10, which can result in the oxidation layer 10, obtained in anodizing step 102, detaching from the base layer 11. The buffer is, for example, potassium bicarbonate.

[0052] The part 1 to be treated, on its support 25, is immersed in the bleaching bath 20. The generator 24 is switched on to pass a current between the anode 22 and the part 1. The hydrogen released at the cathode, i.e., at the part 1, by the reduction reaction, protects the part 1 from oxidation. At the anode 22, the oxidation that takes place has no impact on the part 1. The applied voltage also has the effect of widening the pores 12, facilitating contact between the titanium particles 13 and the sodium hydroxide.

[0053] The sodium hydroxide solution comes into contact with the titanium particles 13 in the pores 12 of the oxidation layer 10. Without describing the underlying theory, the applicant assumes that the following phenomena are involved. The sodium hydroxide solution is composed of sodium (Na+) and hydroxide (OH-) ions, which readily separate in the bleaching bath 20. The titanium particles then react with the hydroxide ions to precipitate as titanium dioxide (TiO2). Without being bound by any particular theory, the precipitation reaction can be expressed as follows:

[0054] Ti + 2OH -> TiO2 + H2

[0055] Titanium oxide forms directly in the pores 12 of the oxidation layer 10 of the part and therefore gives the white color to the oxidation layer 10.

[0056] This bleaching step preserves the properties of the oxidation layer 10 as obtained after the anodizing step 102. In particular, the hardness of the white oxidation layer 10, obtained after the bleaching step 103, is, for example, between 300 and 450 HV (Vickers hardness) and more precisely, for example, between 350 and 400 HV.

[0057] After the bleaching step 103, the part 1 to be treated can undergo a sealing step 104 by immersion in an aqueous solution. More specifically, after the bleaching step 103, the part 1 can be drained over the bleaching bath 20 for a few seconds, then rinsed, for example, with water. The part 1 is then immersed in a sealing bath to hydrate the oxidation layer 10. The addition of water closes the pores 12 of the oxidation layer 10 and permanently traps the white titanium oxide particles.

[0058] The adhesion of the oxidation layer 10 to the aluminum after the bleaching step 103 is similar to that of the oxidation layer immediately after the anodizing step 102, and is in any case superior to the adhesion of a paint, varnish, or lacquer layer applied to an anodized aluminum part. Adhesion can be measured by any known coating adhesion test. Such tests are called coating adhesion tests. For example, a test by scraping, according to standard e.g. ASTM D2197, or by a pull-off test, according to standard e.g. ASTM D4541. Another known adhesion test is called the cross-cut test. This test involves scoring a sample of part 1, on the oxidation layer 10, using a tool that penetrates the oxidation layer 10 at a right angle, down to the unoxidized aluminum layer. Pressure-sensitive adhesive tape is applied to the score and smoothed down. The tape is then removed at an angle close to 180°. Such a test and the apparatus used conform, for example, to ISO 2409:2020.

[0059] Application example

[0060] Currently, in the building sector, white surfaces are desirable because white reflects sunlight and thus limits the heating of buildings. However, the joinery and facades of buildings (skyscrapers) are made of aluminum, and the application of white lacquer or paint to these structures deteriorates rapidly due to corrosion.

[0061] The following example relates to a part 1 intended in particular for the building.

[0062] According to one example, the part to be treated is considered to be an alloy part The AL1050 aluminum part, with an external surface area of ​​0.01 m² (square meter), corresponds to the exposed surface on which a white oxidation layer is to be formed. Part 1 is rectangular in shape, measuring 20 x 20 x 75 mm (millimeters).

[0063] Preparation step 101 includes degreasing in a degreasing bath containing a degreasing agent, for example, "Anoclean 665 FP Industrie" at a concentration of 50 g / l (grams per liter). The temperature of the degreasing bath is set between 35°C and 40°C. Gentle mechanical agitation is applied to the degreasing bath. Part 1 is immersed in the degreasing bath for 5 to 10 minutes. Then, part 1 is removed from the degreasing bath and rinsed under running water.

[0064] If necessary, part 1, once removed from the degreasing bath, is subjected to a satin finishing and / or polishing operation by being immersed successively in appropriate baths.

[0065] The next anodizing step 102 aims to form an oxidation layer with a thickness between 15 µm and 25 µm. The anodizing bath 2 has a volume of 4 L (liters). The anodizing bath has the following composition and parameters: • Titanium and Potassium double oxalate: 30 to 60 g / L (grams per liter) • Boric acid: 7 to 10 g / L • Citric Acid: 1 to 2 g / L • Oxalic acid: 1 to 2 g / L • Bath temperature: 50 to 60 °C • pH = 1.8 to 2.2

[0066] Once the part is immersed in the anodizing bath 2, the treatment is carried out at a substantially constant current of 2 A / dm² (Amps per square decimeter). By working with a constant current, the oxide layer is allowed to form progressively. The growth of the oxidation layer 10 and the size of the pores 12 are then more homogeneous, resulting in an oxidation layer 10 of satisfactory whiteness and offering scratch resistance suitable for a building application. As an example, the parameters recorded during the treatment are shown below. summarized in the table below: [Table 1] Duration (minutes) Voltage (Volts) Current (Amps) Temperature (Celsius) 0 0 2 50 5 25 2 52 10 47 2 52 15 52 2 52 20 60 2 52 30 65 2 52 40 71 2 52 60 76 2 52 80 100 2 52 90 115 2 53

[0067] After 90 minutes of treatment, the oxidation layer 10, i.e. alumina, formed on the surface of part 1 is 22 pm. The pores of the oxidation layer 10 have a width of 50 nm to 300 nm.

[0068] Part 1 is drained over the anodizing bath 2, then double-rinsed with demineralized water. Part 1 is then transferred to the bleaching bath 20 to undergo bleaching step 103.

[0069] According to the example, the composition of the bleaching bath 20 and its parameters are as follows: Sodium hydroxide: 5 to 10 g / L Potassium bicarbonate: 30 to 35 g / L Bath temperature: 20 to 25 °C • Voltage: 2 to 3 V • pH = 11 to 12

[0070] A voltage of 3V is applied for 10 to 20 seconds, then reduced to 2V for 10 to 12 minutes.

[0071] Part 1 is then removed from the bleaching bath 20, drained over the bleaching bath 20 for a few seconds, and then rinsed in a raw water bath. The raw water rinse may be followed by a double rinse in demineralized water for 5 minutes.

[0072] Part 1 is then transferred to the sealing bath for sealing step 104. The composition and parameters of the sealing bath are as follows: • Demineralized water • Neutral sodium silicates: 1 to 2 cc / 1 (cubic centimeter per liter) • Bath temperature: 95 to 100 °C • pH = 6 to 8

[0073] The resulting part 1 has on its surface a layer of aluminum oxide 15 to 30 µm thick, for example between 17 and 25 µm, and for example even 22 µm, exhibiting good adhesion to the base aluminum, good hardness, and a satisfactory white color. The longevity of the white color is ensured as long as the oxide layer 10 of part 1 is maintained.

[0074] A pull-off test according to ISO 2409:2020 demonstrated a particularly high resistance of the oxidation layer 10 obtained. More specifically, a grid was scored with a utility knife on the oxidation layer 10, over an area of ​​approximately 10 mm x 10 mm. The grid is approximately 3 x 3 mm, i.e., a grid of nine 3 mm squares. The result was a complete absence of pull-off, achieving classification 0, i.e., 100% adhesion of the oxidation layer 10 to the aluminum layer.

[0075] The applications of the part 1 thus obtained are very numerous and cover all the usual applications of anodized aluminum or aluminum alloy parts. The white color imparted to part 1 broadens the applications to more demanding fields for parts, such as aerospace, automotive, and construction.

[0076] The process 100 for treating part 1 involves the use of successive baths in which part 1 is immersed: the treatment process 100 ensures homogeneous treatment over the entire external surface of part 1, even in the case of complex shapes. Furthermore, throughout the implementation of the treatment process 100, part 1 can be suspended from a single support 8, 25 which is transferred with part 1 into the successive baths, for example, using hoists. The process 100 is therefore suitable for implementation on an industrial scale.

[0077] As the titanium particles penetrate the pores 12 of the anodizing layer 10 by being transported by the anodizing bath 2, the distribution of the titanium oxide particles on the surface of the part 1 is more uniform than in the prior art, giving a perception of a purer white color.

Claims

Claims

1. Method (100) for treating a part (1) made of aluminum or aluminum alloy, the method comprising an anodizing step (102) which comprises: • The preparation of an anodizing bath (2) and the placement in the anodic bath (2) of a cathode (4); • The immersion in the anodizing bath (2) at least in part of said part (1) as an anode; • The application of a voltage between the part (1) and cathode (4); • The formation of an oxidation layer (10) on said part (1), The method being characterized in that the anodic bath (2) comprises a dissolved titanium salt so that the oxidation layer (10) comprises titanium particles (13), and characterized in that it further comprises, after the formation of the oxidation layer (10), a bleaching step (103) which comprises: • The preparation of a bleaching bath (20) comprising a precipitation agent for titanium;• immersion at least in part in the bleaching bath (20) of the part(l); • precipitation of the titanium into titanium oxide in at least part of the oxidation layer (10), so that the oxidation layer (10) obtained is white in color.;

2. The method (100) of claim 1, wherein the bleaching step comprises placing an anode (22) in the bleaching bath (20) and comprises applying a voltage between the anode (22) and the part (1) to effect precipitation of the titanium into titanium oxide in the oxidation layer (10), the part (1) acting as a cathode.

3. A method (100) according to claim 1 or claim 2, wherein the titanium salt in the oxidation bath (2) comprises a double oxalate of titanium and potassium.

4. A method (100) according to any preceding claim, wherein the precipitating agent of the bleaching bath (20) includes soda.

5. Method according to the preceding claim, in which the bleaching bath (20) comprises potassium bicarbonate to produce a buffering effect against the soda on the part (1).

6. Method (100) according to any one of the preceding claims, comprising a final sealing step (104) comprising immersing at least part of the part in an aqueous solution.

7. Method (100) according to any one of the preceding claims, comprising an initial step (101) of preparing the part (1) to obtain a determined surface condition.

8. Part (1) made of aluminum or aluminum alloy obtained by implementing the manufacturing method (100) according to any one of the preceding claims, characterized in that the oxidation layer (10) of the part (1) comprises titanium oxide, is white in color, and has a hardness of between 300 and 450 HV.

9. Anodizing bath (2) for carrying out the method according to any one of claims 1 to 7, comprising a titanium salt dissolved in an acid solution.

10. Anodizing bath (2) according to the preceding claim, in which the pH of the bath is between 1.8 and 2.2.

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