Method for treating a part made of aluminum or aluminum alloy, part obtained by implementing such a method, and anodizing bath for implementing such a method

Abstract

Method (100) for treating a part (1) made of aluminum or aluminum alloy, the method comprising an anodizing step (102), the method 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 bleaching step (103) which comprises the precipitation of titanium into titanium oxide in the oxidation layer (10), so that the oxidation layer (10) obtained is white in color. Figure for abstract: figure 4

Description

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

[0001] The present invention relates to the field of forming a protective anodic layer on a metal part, in particular made of aluminum. More specifically, the invention relates to 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 increase its aesthetic appearance. The anodizing process, also called anodizing, is well known. It is based on oxidation-reduction reactions: in the presence of a current, the positive pole, called the anode, oxidizes while the negative pole, called the cathode, is reduced. Thus, by placing the metal part as an anode in a so-called anodizing bath, and at the same time placing a cathode in this same bath, a current passing through the anodizing bath between the cathode and the anode causes the 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 so-called "light" metal parts such as aluminum and its alloys in order to improve its properties and expand its areas of application. The areas of use of anodized aluminum are extremely varied, since they include for example aeronautics, jewelry, watchmaking, the food industry, the automobile industry, construction, building, packaging of cosmetic products, or even smartphones, door frames and garden fences.

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

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

[0006] The layer of aluminum oxide (A12O3) that forms during the anodizing process naturally has a dark gray color. It is then known to apply a layer of color on the oxidation layer, for example in the form of paint or lacquer. The main drawback of this colored layer is that it does not have the same resistance properties as the oxidation layer resulting from anodization. The white colored layer applied to the oxidation layer therefore deteriorates more easily than the oxidation layer, revealing the dark gray color underneath. While this defect can be accepted in certain areas where products have a limited lifespan and / or use, for example for cosmetic packaging, it limits the use of anodized aluminum in other areas such as vehicle bodywork 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] Document US2017 / 0121838 describes an example in which the pore size of the oxidation layer is increased by electrolytic treatment in an acid bath. Then, coloring particles are deposited in 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] The white color for the oxidation layer of an anodized part is particularly difficult to obtain. Indeed, the white color is generally obtained by using light-reflecting particles to give the white color. These particles can in particular be titanium oxide (TiO2) as in US2017 / 0121838.

[0010] A disadvantage is that the color thus obtained can be a shade of white tending towards gray or beige, unlike a layer of paint or white lacquer: it is not satisfactory. Indeed, the coloring particles introduced enter the pores randomly. In particular, the penetration of the reflective particles into the pores is not controlled. The dimensions of the pores and particles are of the order of a nanometer, so some pores remain empty of coloring particles. The distribution of the coloring particles on the surface of the part is therefore non-uniform, leaving uncolored portions visible. On the scale of the human eye, this lack of uniformity results in a shade of white which can be described as lacking purity.

[0011] The invention thus aims to provide a solution to the aforementioned drawbacks 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 includes: • 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 comprises in particular a dissolved titanium salt so that the oxidation layer comprises titanium particles. In addition, the method further comprises, after the formation of the oxidation layer, a bleaching step which comprises: • the preparation of a bleaching bath comprising a precipitation agent for titanium; • immersion at least partially in the bleaching bath of the part; • the precipitation of titanium into 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 which comprises titanium, and the white color is obtained by carrying out the precipitation of titanium into titanium oxide directly in the oxidation layer. The oxidation layer thus obtained has a bright white color compared to the white color obtained by the methods of the prior art based on the bleaching of the oxidation layer.

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

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

[0017] The precipitation of titanium into titanium oxide by the application of a voltage makes it possible in particular to protect the oxidation layer during the oxidation of the titanium. Indeed, in particular, the release of hydrogen at the cathode during the reaction protects the oxidation layer. In addition, 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 application in the field of buildings.

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

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

[0020] According to one embodiment, the bleaching bath comprises potassium bicarbonate to produce a buffer effect with respect to the soda on the part. The aluminum under the oxidation layer is thus protected from unwanted oxidation.

[0021] According to one embodiment, the method may comprise 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 resistance over time of the oxidation layer.

[0022] According to one embodiment, the method may comprise an initial step of preparing the part to obtain a determined surface condition. The surface condition may influence the quality of the oxidation layer. By controlling the initial surface condition, 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 method as presented above. The oxidation layer of the part then comprises titanium oxide, is white in color, and has a hardness of between 300 and 450 HV (Vickers hardness).

[0024] According to a third aspect, the invention relates to an anodizing bath for implementing the method as presented below, which may comprise a titanium salt dissolved in an acid solution and / or the pH of the bath of which is between 1.8 and 2.2, ensuring an oxidation layer with high mechanical properties and good penetration of the 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.l] schematically represents the steps of a method for treating a part according to an embodiment of the invention, comprising a preparation step, an anodizing step, a bleaching step and a sealing step.

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

[0028] [Fig.3] is a diagram of a detail 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.l].

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

[0031] In [Fig.l], an example of an embodiment of the method 100 for treating a part 1 made of aluminum or aluminum alloy to be treated is shown. The part 1 may have to be treated on the entire exterior surface or on one or more specific portions. The surface or surface portions of the part 1 to be treated form what is called in the following the exposed surface.

[0032] The method has the particularity of producing an oxidation layer obtained by anodization which has a white color, on at least part of the external surface of the part. More precisely, the white color is provided by the oxidation layer, and not by the addition of another color layer.

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

[0034] The treatment method 100 may comprise in particular an initial step 101 of preparing the part 1 to be treated. The purpose of the preparation step 10 is to achieve an external surface condition of the part determined in particular as a function of the final result sought for the part 1. For example, the preparation step 101 may comprise a degreasing operation, possibly followed by a satin or glossing 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 in part in the bath 2 in order to constitute a cathode 4. The cathode 4 can be made of any material usually used for the anodizing of 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 be integrated into the tank. Preferably, the external surface of the cathode 4 is greater than or equal to twice the exposed surface of the part 1 to be treated. A system 5 for stirring and homogenizing the bath 2 can also be placed in the bath 2, in the tank 3.This is for example a system 5 of agitation and homogenization by pressurized air, or by circulation with Venturi system, including a continuous filtration. The filtration can for example be set lower than 5pm (microns) which is sufficient to ensure an effective filtration of the anodizing bath 2 guaranteeing a high quality anodizing. The particles can . come to pollute 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 determined temperature range. For example, the heating device 6 can maintain the temperature of the bath 2 between 40°C (degrees Celsius) and 60°C, plus or minus 1°C. The heating device 6 can for example comprise a heating resistor with a servo to maintain the bath 2 at a set temperature.

[0037] In order to carry out the anodization, a current generator 7 is electrically connected to the cathode 4 and to the part 1 to be treated. More precisely, the negative pole of the generator 7 is connected to the cathode 4, and the positive pole is connected to the part 1 to be treated, which then acts as an anode. The generator 7 is typically a direct current generator of 0V to 120V (Volts), with adequate power to apply a sufficient voltage to initiate and maintain the oxidation-reduction reaction. Typically, the power depends on the exposed surface of the part 1 to be treated. It is for example between 1.5A (Amperes) and 3A / dm2 on the exposed surface of the part 1 to be treated.

[0038] The part 1 to be treated is immersed in the anodizing bath 2. For example, it is attached to a support 8 specially adapted for the anodizing step. The electrical connection between the part 1 to be treated and the generator 7 can be made via the support 8, then made of 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, a single 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 which is maintained for example around 2. According to the invention, the anodic bath 2 comprises at least one titanium salt. This is for example a double oxalate of titanium and potassium. The titanium salt is added to the bath 2 and is dissolved. The volume of the anodizing bath 2 is chosen according to the exposed surface of the part 1 to be treated. For example, it is chosen to be equal to 4L / dm2 (liters per square decimeter) of exposed surface.

[0041] When the generator 7 is switched on, an oxidation layer 10 is formed on the exposed surface of the part 1 to be treated which is immersed in the anodizing bath 2. In this case, it is a layer 10 of aluminum oxide, also called alumina. Under the oxidation layer 10, the material is not affected by the redox reaction, forming a base layer 11 of aluminum or aluminum alloy. In general, the thickness of the oxidation layer 10 formed is of the order of microns, while the thickness of the base layer 11 is any, in general greater than that of the oxidation layer 10, and for example of 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 towards 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 20nm (nanometers) and 800nm. The pores 12 appear during the anodization step, and particles 13 of titanium in the form of dissolved salt penetrate into the pores 12, and are therefore integrated into the oxidation layer 10. More precisely, liquid anodic bath 2 penetrates into the pores 12, transporting the particles into the pores 12 during the anodization step 102.

[0043] The titanium salt, particularly when in the form of double oxalate of titanium and potassium, 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 takes on a brownish-brown color. Once the voltage is switched off, the salt becomes colorless and clear again.

[0044] Consequently, 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 gray of the aluminum oxide.

[0045] The method 100 then comprises a step 103 called bleaching of the oxidation layer 10 resulting from the anodizing step 102. The principle of the bleaching step 103 is to precipitate titanium oxide from the titanium particles in the pores 12 of the oxidation layer 10, 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 blocked and remain open to the environment outside the part 1. Thus, the part 1 after the anodizing step 102 can be drained for a few minutes above the anodizing bath 2 and then rinsed, for example with demineralized water. Rinsing allows the remains of the anodizing bath 2 to be cleaned from the surface of the part 1, with the exception of the interior of the pores 12. Then, without waiting for drying, the part 1 is transferred to the 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 comprises in particular a precipitation agent, in order to precipitate the titanium into titanium oxide and obtain the white color.

[0047] According to one embodiment, the bleaching step 103 is carried out under a voltage applied 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 for the cathode 4 of the anodizing step 102 in any suitable material, such as stainless steel, titanium or lead. The anode 22 can be added to the bath 20 in the tank 21, in one or more elements, or be integrated into the tank 21. A heating device 23 can be placed in the bath 20, in the tank 21, in order to maintain the bleaching bath 20 in a determined temperature range, for example a range between 15°C and 35°C, and more precisely between 18°C ​​and 25°C. the temperature can be adjusted and maintained around a set point using a servo system;

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

[0049] The part 1 is immersed in the bleaching bath 20. For example, it is attached to 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, 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 merged 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. It is necessary to avoid detaching part 1 from its support between the anodizing step 102 and the bleaching step 103, in order to maintain the point of contact between the support 8, 25 and part 1.Indeed, the alumina layer being an electrical insulator, the displacement of the contact point onto another part of the part 1 and therefore onto the alumina layer formed, would prevent the current from passing from the bath to the part 1 in the bleaching step. The application of a voltage to carry out the precipitation makes it possible in particular to reduce the duration of immersion of the part 1 in the bleaching bath 20 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 comprises a bleaching agent for titanium, that is to say a chemical species capable of precipitating the titanium in the pores 12 of the oxidation layer 10. For example, the bleaching agent is soda, or sodium hydroxide (NaOH).

[0051] According to one embodiment, the bleaching bath 20 comprises a buffer in order to protect the part 1 from the aggressiveness of the soda. Indeed, the soda reacts naturally with the aluminum, and therefore potentially with the base layer 11 under the oxidation layer 10, which may result in the oxidation layer 10 obtained in the anodization step 102 being detached 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, in order to cause a current to flow between the anode 22 and the part 1. The hydrogen released at the cathode, that is to say at the part 1, by the reduction reaction, protects the part 1 from oxidation. At the anode 22, the oxidation which 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 soda.

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

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

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

[0056] This bleaching step makes it possible to preserve the properties of the oxidation layer 10 as they are 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 precisely, after the bleaching step 103, the part 1 can be drained above 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 makes it possible to close the pores 12 of the oxidation layer 10 and to permanently trap 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 just after the anodizing step 102, and is in any case superior to the adhesion of a layer of paint, varnish or lacquer applied to an anodized aluminum part. The adhesion can be measured by any known test for testing the adhesion of a coating layer. Such tests are called coating adhesion tests. This is, for example, a test by scratching, according to the standard for example ASTM D2197, or a tear-off test, according to the standard for example ASTM D4541. Another known adhesion test is called a crosshatch test. Such a test consists of crosshatching a sample of part 1, on the oxidation layer 10, using a tool penetrating the oxidation layer 10 at a right angle, down to the unoxidized aluminum layer. A pressure-sensitive adhesive tape is applied to the crosshatch and smoothed. The adhesive tape is then removed at an angle close to 180°. Such a test and the apparatus used are for example in accordance with the standard ISO 2409:2020.

[0059] Example of application

[0060] Currently, in the building industry, it is desirable to have white surfaces because white reflects the sun's rays and thus limits the heating of buildings. However, the woodwork and facades of buildings (skyscrapers) are made of aluminum, and the application of a white lacquer or paint on these structures quickly deteriorates due to the phenomenon of corrosion.

[0061] The following example concerns 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. of AL1050 aluminum, with an external surface area of ​​0.01m2 (square meter), which corresponds to the exposed surface, on which a white oxidation layer is to be formed. Part 1 is rectangular in shape, with dimensions of 20x20x75mm (millimeters).

[0063] Preparation step 101 comprises degreasing in a degreasing bath comprising a degreasing product, for example the product “Anoclean 665 FP Industrie” at a concentration of 50g / l (grams per liter). The temperature of the degreasing bath is set between 35°C and 40°C. Light mechanical agitation is put in place in 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 is rinsed with running water.

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

[0065] The following anodizing step 102 aims to form an oxidation layer with a thickness between 15 μm and 25 μm. The anodizing bath 2 is 4L (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 with a substantially constant intensity of 2A / dm2 (Ampere per square decimeter). By working with a constant intensity, the oxide layer is allowed to form gradually. The growth of the oxidation layer 10 and the size of the pores 12 are then more homogeneous, which leads to obtaining an oxidation layer 10 of a satisfactory white color and offering scratch resistance suitable for application to buildings. As an example, the parameters recorded during treatment are summarized in the table below: [Tables 1] Time (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 the part 1 is 22 μm. The pores of the oxidation layer 10 have a width of 50 nm to 300 nm.

[0068] Part 1 is drained above anodizing bath 2, then doubly rinsed with demineralized water. Part 1 is then transferred to 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: Soda: 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] The part 1 is then removed from the bleaching bath 20, drained above the bleaching bath 20 for a few seconds, then rinsed in a raw water bath. The raw water rinsing may be followed by a double rinsing in demineralized water for 5 minutes.

[0072] Part 1 is then transferred to the sealing bath for sealing step 104. The composition of the sealing bath and its parameters 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 part 1 obtained has on its surface a layer of aluminum oxide 15 to 30 pm thick, for example between 17 and 25 pm, and for example still 22 pm, having 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 oxidation layer 10 of the part 1 is maintained.

[0074] A peel test according to ISO2409:2020 demonstrated a particularly high resistance of the obtained oxidation layer 10. More precisely, a grid was traced with a cutter on the oxidation layer 10 using a cutter, over an area of ​​approximately 10mm x 10mm (millimeters). The grid is approximately 3 x 3mm, i.e. a grid of nine squares of 3mm on each side. The result was a completely absent peel, reaching classification 0, i.e. 100% resistance of the oxidation layer 10 on 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 given to the part 1 broadens the applications to more restrictive fields for the parts, such as aeronautics, automobiles and buildings.

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

[0077] As the titanium particles penetrate into 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 with respect to 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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