Method for applying a colored coating to an alloy

Abstract

In an example embodiment, a method of coloring an alloy is provided. The method includes anodizing a substrate in an anodizing bath comprising phosphoric acid at a constant temperature and a constant voltage for a first period of time to form an anodized layer comprising a barrier layer; reducing the constant voltage applied to the anodizing bath for a second period of time to change a thickness of the barrier layer and change a width of pores in the anodized layer; plating the substrate in a plating bath at a first current that increases over a third period of time according to a current profile of the plating bath; and plating the substrate in the plating bath at a second current for a fourth period of time.

Description

BACKGROUND

[0001] Various methods have been developed to coat light metal alloys with colored anodic films. In many cases, the exact coloring mechanism is not defined. However, it is generally understood that the total internal reflection between the transparent anodized reflective substrate and the inorganic deposit produces changes in brightness ) while the hue and tone , ) are produced by destructive interference between the incident and reflected light. In the case of organic coatings, the coloring is generally a direct result of the selected organic molecule.

[0002] In U.S. Patent 4,251,330 ('330 patent), a mechanism for strongly coloring anodized aluminum or aluminum alloys is disclosed. In this patent, the substrate is anodized to a thickness of 15 microns in a primarily sulfuric acid bath with direct current (DC). The pores are widened in a primarily phosphoric acid bath using primarily alternating current (AC) anodization. Coloring is provided by depositing a majority of the nickel from an acidic nickel sulfate, magnesium sulfate, and boric acid bath using AC. The various colors from violet to blue, to green are formed by destructive interference.

[0003] AC phosphoric acid anodization is considered beneficial due to the more uniform widening of the pores, while AC deposition results in differences in deposition in the improved (widened) pores versus the original narrow pores. The method disclosed in the '330 patent requires two baths to produce the pore structure necessary to color the surface, thus less controlled.

[0004] In addition, residual acid from the widening and deposition processes results in a clouding of the color which requires a further neutralization step.

[0005] Patent EP 018247981 discloses a direct coloring method using nickel sulfate in a sulfuric acid anodization structure using AC deposition.

[0006] U.S. Patent 5,064,512 discloses a method for dyeing a sulfuric acid anodized substrate using an organotin salt on a sulfuric acid anodized substrate using AC or AC superimposed DC coloring. This patent specifically addresses the need to stabilize the tin content of the bath and to increase the throwing power of the solution. This method requires the preparation of a complex tin containing coloring bath and close monitoring of the tin content to achieve the desired results.

[0007] Patent WO 01 / 18281 discloses a process for producing primarily black anodized coatings by anodizing an aluminum or aluminum alloy substrate in a sulfuric acid bath to produce an oxide layer 8-15 microns thick, modifying the pore structure in a primarily phosphoric acid bath using AC or DC anodization at a reduced voltage so that most of the pores become incapable of participating in the coloration process, and coloration of the anodized layer using an AC deposition scheme containing inorganic salts and UNICOL® improvements. This process is largely an improvement over the process disclosed in the '330 patent described above, but relies on a different pore modification method. In each of the above cases, the coloration is achieved by using a phosphoric acid method to improve the sulfuric acid anodization structure, followed by a portion of the coloration using an inorganic bath. SUMMARY

[0008] According to aspects shown herein, methods for coloring light metal alloys are provided. One disclosed feature of embodiments is a method comprising: anodizing a substrate in an anodization bath comprising phosphoric acid at a constant temperature and a constant voltage for a first period of time to form an anodized layer comprising a barrier layer; reducing the constant voltage applied to the anodization bath to change a thickness of the barrier layer and to change a width of pores in the anodized layer for a second period of time; plating the substrate in a plating bath at a first current that increases according to a current profile of the plating bath for a third period of time; and plating the substrate in the plating bath at a second current for a fourth period of time.

[0009] One disclosed feature of embodiments is a method comprising: anodizing an aluminum alloy substrate in an anodization bath comprising phosphoric acid at a constant temperature and a constant voltage for a first period of time to form an anodized layer 2 to 10 microns thick, the anodized layer comprising a barrier layer; reducing the constant voltage applied to the anodization bath to change (i) a thickness of the barrier layer located between the substrate and anodization pores and to change (ii) a width of pores in the anodized layer for a second period of time; plating the aluminum alloy substrate in a plating bath at a first current that increases according to a direct current (DC) plating current profile of the plating bath for a third period of time; plating the aluminum alloy substrate in the plating bath at a second current for a fourth period of time to partially fill pores in the anodized layer with metal nanorods; and sealing the pores of the anodized layer to form a sealing layer. In one embodiment, the step of sealing the pores leaves an air gap between the metal nanorods and the sealing layer.

[0010] One disclosed feature of an embodiment is a method comprising: pretreating an aluminum alloy substrate; activating the aluminum alloy substrate; anodizing the aluminum alloy substrate in an anodizing bath comprising phosphoric acid at a constant temperature and a constant voltage for a first period of time to form an anodized layer; reducing the constant voltage applied to the anodizing bath for a second period of time to change a thickness of the barrier layer and change a width of pores in the anodized layer; rinsing the aluminum alloy substrate to further reduce the thickness of the barrier layer; plating the aluminum alloy substrate in a plating bath via a plurality of plating stages to deposit colored metal nanorods into the pores of the anodized layer; and sealing the pores of the anodized layer while leaving an air gap over the metal nanorods. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 Flow chart illustrating an exemplary method for producing a thin colored coating;

[0012] Figure 2 Illustrating an exemplary sulfuric acid anodized substrate;

[0013] Figure 3 Illustrating an exemplary phosphoric acid anodized substrate of the disclosure;

[0014] Figure 4 Is a surface electron microscope (SEM) image of an exemplary phosphoric acid anodized structure of the disclosure;

[0015] Figure 5 Is a SEM image of an exemplary cross-section of an anodized colored substrate of the disclosure;

[0016] Figure 6 Is a SEM image of an exemplary close-up image of a cross-section;

[0017] Figure 7 Illustrating an exemplary ultraviolet imaging spectrometer (UVIS) spectrum of a colored hybrid coating on 6061 aluminum of the disclosure;

[0018] Figure 8 Illustrating an exemplary graph showing the relationship between anodization charge, plating amp-minutes, and color through the methods of the disclosure;

[0019] Figure 9 Illustrating a schematic of the color generation mechanism of the disclosure;

[0020] Figure 10 Illustrating an exemplary graph showing the relationship between the average roughness of a substrate of the disclosure and the gloss of a coating;

[0021] Figure 11Exemplary graphs showing the maximum achievable anodization layer thickness for several phosphoric acid concentrations of the present disclosure are illustrated; and

[0022] Figure 12 is a set of exemplary images and tables showing the effect of barrier thinning and temperature on the color of coatings of the present disclosure.

[0023] Figure 13 is a cross-sectional view of a coating according to one aspect of the present invention showing an air gap that preserves the surface color. DETAILED DESCRIPTION

[0024] The embodiments described herein provide methods of forming thin colored coatings on aluminum or light metal alloys. As described above, various methods have been developed to coat alloys. Anodized oxide films on aluminum (including aluminum alloys) can be colored using organic and inorganic colorants. Coloration typically occurs by depositing organic or inorganic materials in the pores when the anodized surface is immersed in a bath containing the appropriate inorganic salt or a combination of inorganic salt and organic molecules, using an alternating current between the anodized surface and a counter electrode.

[0025] Prior methods have a number of drawbacks or can be inefficient. The present disclosure provides methods that can anodize and color aluminum and other light metal surfaces using a two-step process involving phosphoric acid anodization and direct metal deposition. Thus, the methods of the present disclosure can be more efficient and more environmentally friendly due to the use of less energy, less volatile organic compounds, and less waste.

[0026] In one embodiment, the method can include one or more of the following steps: degreasing the alloy substrate; electropolishing the substrate; activating the surface; anodizing a 2-10 micron film on the substrate in an anodization bath comprising substantially phosphoric acid at a desired temperature and following a desired voltage-current profile; electrodepositing a metal into the anodized pores at a desired temperature and following a desired current profile; and sealing the pores with a transparent medium. The total average thickness of the hybrid coating can be about 2 to 15 microns.

[0027] Figure 1 An exemplary method 100 for producing thin film colored coatings of the present disclosure is illustrated. In one embodiment, the method 100 can be performed by various equipment or tools in a processing facility under the control of a processor or controller.

[0028] At block 102, the method 100 begins. At block 104, the method 100 can pre-treat a substrate. In one embodiment, the substrate can include aluminum or any alloy of aluminum.

[0029] The pre-treatment can include degreasing the substrate in an alkaline bath, roughening the substrate in a solution of polyethylene glycol, sulfuric acid and hydrofluoric acid or other similar solution, and etching the substrate in a solution of nitric acid. An example of such a pre-treatment can be a commercial aluminum surface pre-treatment known as Probright AL. The solution that roughens the substrate can clean the substrate surface as it etches the substrate surface.

[0030] One example of a pre-treatment can include first treating the substrate by degreasing in a commercially available solution such as Activax, commercially available from MacDermid, Inc. The degreasing step can be followed by a rinse. Rinsing the substrate prior to anodization can have the effect of eliminating impurities on the surface that can cause defects in the thin anodization layer.

[0031] In one embodiment, the pre-treatment can include electropolishing the substrate in a bath selected from the group consisting of: 70-85% H3PO4, 2-4 HF, 6-9% H2SO4, and 5-20% glycerol. The electropolishing bath can be maintained at a temperature of 70 to 80 degrees Celsius (°C) at a voltage (V) of about 12V. The electropolishing bath can include a Pb counter electrode. The electropolishing step produces a substrate with a uniform surface having a low average roughness (Ra) that helps to achieve a lustrous colored coating. The electropolished substrate can then be rinsed in deionized water (DI) prior to the activation and anodization steps discussed below.

[0032] The average surface roughness Ra of an aluminum alloy substrate is directly related to the apparent gloss of a colored coating. In one embodiment, the Ra of the substrate prior to anodization can be 1.8 to 4 to achieve a matte surface. In one embodiment, the Ra can be about 2.

[0033] In one embodiment, the Ra of the substrate prior to anodization can be 0.4 to 1.8 to achieve a semi-gloss surface. In one embodiment, the Ra can be about 0.8 to 1.2.

[0034] In one embodiment, the Ra of the substrate prior to anodization can be 0 to 0.4 to achieve a gloss finish. In one embodiment, the Ra can be less than about 0.2.

[0035] At block 106, the method 100 can activate the substrate. The substrate can be activated prior to anodization. The activation step can provide some benefits on certain alloys. One example of an activation step can include activating the surface in a bath comprising 40 volume percent HN03 and 1-10 milliliter per liter (mL / L) HF. In one embodiment, 20 volume percent to 50 volume percent HN03 can also be used. The bath can be maintained at a temperature of 20 °C to 25 °C, the substrate is immersed and agitated about once per second for 20 to 40 seconds.

[0036] At block 108, the method 100 places the substrate in an anodization bath comprising phosphoric acid and an additive or solvent that supports the desired anodization voltage and thus determines the pore structure that dictates the resulting coating color. The bath can comprise phosphoric acid and sulfuric acid at least for an initial period of time to produce a thin anodization layer. In one embodiment, as shown in FIG. 1, the temperature, electrical parameters, and bath composition result in a thin-walled pore with a uniform high density distribution of 50 to 160 nanometers (nm) in diameter and are discussed in further detail below. Figure 5

[0037] The anodization bath contains primarily phosphoric acid along with small amounts of sulfuric acid and oxalic acid. The bath composition is selected from H3P04 (40-600 milliliter per liter (ml / l)), H2S04 (0-15 ml / l), and HOOCCOOH (1-10 grams per liter (g / L)). In one embodiment, the concentration of H3P04 can be about 150 ml / l, the concentration of H2S04 can be about 0.6 ml / l, the concentration of HOOCCOOH can be about 1 g / l, and the solvent is deionized water.

[0038] In some embodiments, other additives can be added to achieve the desired pore structure of the anodization layer. Examples of other additives can include small amounts of copper sulfate, chelating agents, and the like, which are discussed in further detail below.

[0039] ​For any given phosphoric acid concentration in the anodization bath, a maximum anodization thickness can be obtained due to the pore widening effect of phosphoric acid. In one embodiment, the maximum anodization thickness can be about 6 microns. While increasing the phosphoric acid concentration increases the conductivity of the anodization bath, and thus the current density for a fixed anodization voltage, the increased phosphoric acid concentration can also increase pore widening and film dissolution, resulting in the aforementioned limitation on the thickness of the anodized film. The addition of 0-15 weight percent (wt%) or about 10 wt% of a short chain alcohol has been shown to cool the growing pore structure and reduce the dissolution of the surface of the porous anodized structure by the anodization bath. The addition of 0-80 wt% or about 50 wt% of ethylene glycol can increase the viscosity of the electrolyte, thereby reducing the rate of pore widening at the expense of reducing the growth rate of the porous anodized film. A low volume of phosphoric acid can allow for a thicker anodized layer. This can improve the mechanical properties of the coating, but requires a longer anodization time due to the slower film growth.

[0040] The thickness and pore structure of the barrier layer has been shown to be a factor in determining the color of the coating, as described in the examples below. The thickness of the barrier layer is proportional to the anodization voltage. However, the pore width is also proportional to the anodization voltage. In many cases, the requirement for a thick barrier layer with narrow pores can play an important role in producing a functional colored coating. The addition of 10-50 wt% of polyethylene glycol or similar organic that increases the viscosity of the anodization solution has been shown to allow for higher anodization voltages, which form thicker barrier layers while keeping the pore size lower or smaller than previous methods. Replacing up to 50% of the H3PO4 with NaH2PO4 or LiH2PO4 reduces the acidity and thus the dissolution of the pore walls and barrier layer, allowing for higher voltages, thicker barrier layers, and narrower pore openings. The thicker barrier layers thus formed can be altered by thinning as described below to form the correct or desired color of the coating.

[0041] At block 110, the method 100 anodizes the substrate at a voltage and a temperature for a time to form a pore structure. For example, the substrate can be placed in an anodization bath. The anodization bath can be operated at a constant temperature of 5°C to 40°C or 27°C to 31°C. The temperature of the bath can be adjusted to form an optimal pore structure. In one embodiment, the temperature can be maintained within ±2°C. In one embodiment, the temperature can be maintained within ±1°C. In one embodiment, the temperature can be maintained within ±0.5°C.

[0042] In one embodiment, a constant voltage can be applied to the anodization bath. In one embodiment, the voltage can be 60V to 280V, and the maximum current density is 2 amperes per square decimeter (A / dm 2 ) to provide optimal pore distribution, density, and structure, as further described below.

[0043] In one embodiment, the initial voltage can be 60 to 80 volts, and the anodizing period can be 10 to 40 minutes. In another embodiment, the voltage can be about 65V, and the period can be about 20 minutes.

[0044] The thickness of the anodic film / layer in this disclosure can be formed or grown to be 2 to 10 micrometers. However, the thickness can also be 2 to 8 micrometers. In one embodiment, the thickness can be 4 to 5 micrometers. Anodizing for 20 minutes under the above conditions yields an anodic film approximately 6 micrometers thick. In one embodiment, pulsed DC anodizing can be employed. In one embodiment, the hue of the coating can depend on the thickness of the anodic layer (also referred to herein as a barrier layer), as described below. For an anodizing bath consisting of an acid or a mixture of acids, the structure of the anodic layer can be summarized as comprising a dense barrier layer closely adjacent to the alloy substrate, and a porous layer above the barrier layer, wherein the pores extend substantially vertically from the barrier layer to the surface. At block 112, method 100 may optionally vary the voltage and temperature of the anodic bath over additional time periods to form a fine structure. For example, the thickness of the barrier layer and the width of the pores can be varied (e.g., increasing the pore width while decreasing the barrier layer thickness, or decreasing the pore width while increasing the barrier layer thickness).

[0045] In one implementation scheme, such as Figure 5 As shown, the anodizing voltage can be reduced according to the voltage distribution to thin the barrier layer and increase light absorption, thereby darkening the color. As described below, the width of the anodizing aperture and the thickness of the barrier layer are generated as a function of the anodizing voltage and the solubility of the anodizing electrolyte. In one embodiment, the anodizing voltage decreases by 50% within 2 to 10 minutes, or in another embodiment within about 5 minutes, and anodizing continues.

[0046] In one embodiment, the anodizing voltage is similarly reduced by 50% over a period of 2 to 10 minutes, or over a period of about 5 minutes in another embodiment. Then, the anodizing voltage is reduced by another 50% over another period of 2 to 10 minutes, or over a period of about 5 minutes in another embodiment.

[0047] In one embodiment, the anodizing voltage is reduced from the initial voltage to 15% of the initial voltage over a time period of 2 to 20 minutes, 5 to 15 minutes, or 8 to 12 minutes. It will be apparent to those skilled in the art that different voltages and time periods can be used to further reduce the voltage to produce different pore structures.

[0048] At block 114, the method 100 optionally chemically rinses the substrate. For example, the substrate can be rinsed in a solution to further thin the barrier layer and prepare the substrate for plating with a colorizing metal. In one embodiment, the rinse can thin the barrier layer by partially dissolving the anodization seal. In one embodiment, the solution can be a bath comprising 0.5-5 mL / L HF.

[0049] The anodized substrate to be treated can be immersed in the rinse bath for about 30 seconds while being agitated about once per second. It will be apparent to those skilled in the art that other chemical baths and methods can be employed to chemically thin the barrier layer.

[0050] At block 116, the method 100 places the substrate in a bath comprising a metal sulfate or cyanide to plate and form metal nanorods at the bottom of the pores in compliance with a current profile. In one embodiment, nickel sulfate can be the metal source used to produce a colorized coating, hereinafter referred to as a colorizing metal. The colorizing metal can be plated into the pores of the anodized layer of the substrate in an electrodeposition bath in compliance with a plating current profile for a predetermined period of time. For example, a colorized electrodeposited coating can be applied to the anodized film from a bath selected from a range of possible baths. The electrical parameters associated with the metal colorizing deposition are controlled by a first plating phase and a second plating phase. The first plating phase can include a first plating current that can be applied for a first plating time period. The second plating phase can include a second plating current that can be applied for a second plating time period.

[0051] In alternative embodiments, the colorizing metal can be any pure metal including, but not limited to, silver, gold, copper, cobalt, tin; or a metal alloy including, but not limited to, zinc-nickel, nickel-phosphorus, cobalt-phosphorus, and the like.

[0052] In one embodiment, prior to plating, the substrate can be optionally immersed in a metal colorizing solution for a period of time of 0 to 6 minutes. In one embodiment, the substrate can be immersed for about 3 minutes. Immersing the substrate in the metal colorizing solution can allow the metal ions to fully diffuse into the pores and can allow any residual anodization solution to be rinsed from the pores.

[0053] In one embodiment, the plating process that forms metal nanorods at the bottom of the pores and colors the substrate can be performed in multiple phases. A first colorizing deposition phase can be performed for a first plating time period during which a first DC plating current profile is set to a percentage of a second plating current, where the second plating current is set to a percentage of a nominal plating current for the selected bath composition. The first plating current can be selected to be between 10% and 50% of the second plating current. In one embodiment, the first plating current can be selected to be about 33% of the second plating current.

[0054] The second plating current can be selected to be between 1% and 20% of the nominal plating current for the selected bath composition. In one embodiment, the second plating current can be selected to be about 10% of the nominal plating current for the selected bath composition. The first plating current profile can ensure that the colored metal nucleates at the bottom of the anodized porous structure. The nominal plating current can be defined by the technical data sheet (TDS) provided by the formulator for the plating bath.

[0055] For example, the DC plating current for the semi-bright nickel bath referred to herein can be between 2 and 4 A / dm 2 . In one embodiment, the nominal plating current for the baths described herein can be 3 A / dm 2 . The first current profile can be imposed such that the plating current is ramped up from 0 to the selected current in 2 to 8 minutes. In one embodiment, the substrate can be heated for 3 minutes.

[0056] The second plating time period can be sufficient to grow the metal nanorods to partially fill the anodized pores without reaching the top of any of the anodized pores. In one embodiment, the second plating time period depends on the thickness of the anodized film and the desired brightness, as further described below.

[0057] The sufficient time can be defined by the following function. In one embodiment, for an anodized layer of 6 microns, a time of 2 to 10 minutes can be sufficient to produce a black surface in a semi-bright nickel bath with a second plating current of 10% of the nominal plating current. The plating rate for this reduced current has been shown to be between 0.05 and 0.5 times the plating rate for the bath under normal operating conditions. Thus, the plating time period during which the plating current is applied can be approximated by the following equation (1):

[0058] Equation (1) ,

[0059] where 't' is the plating time period in minutes, 'd' is the thickness of the anodized layer in microns, the fill fraction is the average fill needed to produce the defined color (i.e., the length of the metal nanorod as a percentage of the anodized layer thickness), 'n' is the plating rate under normal bath operating conditions for the first electrodeposition bath in microns / minute, and the rate factor is 0.05 to 0.5 depending on the percentage reduction in current, the normal plating efficiency for the selected plating bath, and the variation in plating rate for that plating bath relative to current.

[0060] In one embodiment, pulsed DC or pulse / reverse pulse DC plating can be employed. The pulsed plating can produce uniform nanorod lengths by limiting hydrogen evolution and changing the metal nucleation at the bottom of the anodized pores.

[0061] In one embodiment, the first electrodeposited layer can be deposited from a semi-bright nickel bath (e.g., Chemipure / Niflow, commercially available from CMP India). In another embodiment, the first electrodeposited layer can be deposited from a copper bath. In another embodiment, the electrodeposited layer can be deposited from a simple nickel sulfate bath. In another embodiment, the first electrodeposited layer can be deposited from a zinc-nickel bath commercially available from Atotech Corporation. Here, the availability of zinc in the first electrodeposited layer can be beneficial to form a transparent sealing layer, as further described below. Other suitable metal layers can be selected by one skilled in the art.

[0062] At block 118, the method 100 seals the substrate following one of several methods. For example, the coating (e.g., a pigmented coating via metal plating described above) can be sealed. The coating can be sealed to ensure that the coating provides corrosion resistance while maintaining color. For most applications, a 6 micron coating has sufficient scratch resistance, but is not sufficiently corrosion resistant without the sealing step.

[0063] In one embodiment, the sealing step can completely close the pores, make the surface of the substrate water tight, and provide high corrosion resistance. Traditionally, anodization is sealed by immersing the plated, anodized, and pigmented substrate in boiling water or a nickel acetate bath. This method provides minimal corrosion resistance to coatings containing large pores produced in a primary phosphoric acid anodization bath. To ensure that the sealing does not interfere with the appearance of the coating, the sealing layer can be transparent and can provide a low refractive index space (air gap) above the metal nanorods. In addition to traditional sealing techniques, two sealing methods produce acceptable results.

[0064] In one embodiment, the desired air gap is maintained by plugging the anodization pores with transparent nanoparticles of a size that matches the pore width. In one embodiment, the transparent nanoparticles are polymethyl methacrylate (pMMA) nanoparticles, and an emulsion of pMMA in water or ethanol is applied to the pigmented surface. The inventors have found that applying a dilute solution to the surface successfully plugs the pores when the transparent nanoparticles are drawn into the pores by capillary action as the transparent nanoparticles dry in the solvent (water, ethanol, or other suitable solvent). In one embodiment, the color is preserved by plugging 60-100% of the pores. In a preferred embodiment, >90% of the pores are plugged. Figure 13A cross-section of a coating is shown according to one embodiment of the present application, where transparent pMMA nanoparticles 1301 block the anodized tube orifice 1302, allowing a transparent pDUDMA sealing layer (or similar transparent sealing layer) 1303 to cover and completely protect the coating surface, while maintaining an air gap in the hole 1302. This air gap is necessary to maintain the refractive index between the air and the hole wall 1305, which is responsible for the color of the surface as described below.

[0065] In one embodiment, transparent pMMA nanoparticles of appropriate size are formed from a bath containing 20-100 mL / L of methyl methacrylate (MMA) and 0.001-1 wt% of sodium dodecyl sulfate (SDS) relative to MMA (to control the number and size of micelles) into which MMA migrates. The inventors have found that controlling the size of the micelles into which MMA migrates controls the particle size. 0.5-2 wt% of sodium bicarbonate or other alkali bicarbonate is added to the MMA as a buffer to control the initiator kinetics and reduce the polydispersity index of the pMMA to ensure transparency. Ammonium persulfate (APS) is the initiator and is added at 0.4-2.5 wt% of monomer to polymerize the MMA. Sodium bisulfite or similar alkali sulfite is added as a reducing agent.

[0066] In alternative embodiments, any transparent nanoparticle can be used to block the orifice.

[0067] In one embodiment, the sealing method uses a SOL / GEL process. In the SOL / GEL process, an aluminum oxide SOL is created and applied to the surface. In one embodiment, such an aluminum oxide SOL is prepared with 0.025 M tri-sec-butyl aluminum (ATSB), 1.5 mL of absolute ethanol per gram of ATSB, hydrochloric acid (to adjust the pH), and the remainder of the solution is made up with water of appropriate purity. One skilled in the art will understand the steps to combine these reagents in the correct order and by the correct method. The SOL can be applied by soaking the article in the SOL, spraying the surface with 1 to 5 thin coats (3 thin coats in some embodiments), or using electrophoretic deposition to fill the holes. In one embodiment, the SOL can fill the holes with little to no impact on the colored surface. After filling the holes, the substrate is baked at a temperature of 100°C to 300°C (about 120°C in one embodiment) for a period of time of 10 minutes to 480 minutes (about 30 minutes in one embodiment) to convert the SOL to a SOL that seals the surface and provides a transparent outer appearance.

[0068] In one embodiment, the sealing method can use a surface polymerization coating. Here, the surface can be activated by heating to 100 to 300 °C (in one embodiment, about less than 200 °C) for a period of 0 minutes to 180 minutes (in one embodiment, about 30 minutes). Alternatively, the surface can be activated by dipping in a dilute solution of ZnO nanoparticles and drying before applying the monomer. The monomer is selected from the group consisting of precursors including, but not limited to, polyurethane dimethacrylate (PUDMA), methyl methacrylate (MMA), methyl acrylate (MA), butyl acrylate (BA), and butyl methacrylate (BMA). In one embodiment, PUDMA can be selected as the monomer. The monomer is applied to the surface by spin coating, spraying, or other method. The surface is irradiated with ultraviolet (UV) light at a wavelength of 200 nanometers (nm) to 400 nm (in one embodiment, about 254 nm) at an intensity of 500 microwatts per square centimeter (μW / cm 2 ) to 2000 μW / cm 2 (in one embodiment, about 1000 μW / cm 2 ) for 2 to 60 minutes (in one embodiment, about 10 minutes). The polymer is then cured at a temperature of 30 to 120 °C (in one embodiment, about 80 °C) for 1 to 12 hours (in one embodiment, about 2 hours). The result is a tough, optically transparent coating that is well bonded to the surface.

[0069] In another embodiment, the sealing layer can be an automotive clearcoat or an electrophoretic clearcoat. It will be apparent to those skilled in the art that many sealing methods can be employed, so long as the sealing material is optically transparent. At step 120, the method 100 ends.

[0070] Figure 2 An exemplary anodization layer / coating 204 is illustrated. The anodization layer 204 can be produced from a sulfuric acid bath and includes a barrier layer 203. The pore width 201 can depend on the bath temperature, composition, and anodization voltage. The pore depth 202 can depend on the anodization voltage and time. The thickness, shown by the dimension 205 of the barrier layer 203, can depend on the bath composition and anodization voltage. Direct coloring of such a surface can be difficult due to the relatively narrow pores (e.g., 7-15 nm in diameter) and the inter-pore distance.

[0071] Several methods have been developed to mitigate the direct coloring problem, with varying degrees of success. One such method, described in U.S. Patent 4,251,330 and subsequent patents, is commonly referred to as the Anolok II interference coloring process.

[0072] Here, a second phosphoric acid anodization process at low voltage is used to extend the lower end of the anodization pores, effectively closing off certain pores by the electrodeposition process. Metal is deposited in a subset of the pores, and color is produced by destructive interference between incident and reflected light. Light entering the empty pores is scattered by the metal filling adjacent pores and darkens the surface.

[0073] Another example, briefly described above, is disclosed by WO 01 / 18281 ('181 patent). The '181 patent uses a combination of low voltage DC and AC in a primarily phosphoric acid bath for pore expansion, resulting in a branched nanopore structure after a sulfuric acid bath. The pore structure is filled using modified AC electrodeposition from a bath containing a metal salt, typically nickel. Incident light is scattered by the metal, and the coating has a dark or black appearance.

[0074] Figure 3 A cross-section of an exemplary phosphoric acid anodized substrate 301 of the present disclosure is illustrated. In one embodiment, the substrate 301 can be anodized in a primarily phosphoric acid anodization bath, as described above. Unlike a sulfuric acid bath, anodization in a phosphoric acid bath results in much wider pores. An enlarged view of a single anodization pore 302 allows for easier understanding of certain aspects of the present invention. The pore opening 303 can have a bottom diameter (dp. bottom) 305 of 50 to 150 nm, depending on the anodization voltage (VA) and bath temperature. Phosphoric acid attacks Al203 more aggressively than sulfuric acid, which results in pore widening. The diameter at the surface (dp. surf) 304 is primarily a function of bath temperature and phosphoric acid concentration. In one embodiment, it has been found that the following relationships exist according to equations (2)-(5):

[0075] Equation (2): d p.底部 ∝ V A in nm;

[0076] Equation (3): in pores per pm 2 ;

[0077] Equation (4): in pores per pm 2 ;

[0078] Equation (5): d p.surf = 1.31 d p.底部

[0079] at a nominal bath operating temperature of 18 to 30 degrees Celsius and phosphoric acid concentration.

[0080] The widening of the aperture 302 is a significant advantage of using a phosphoric acid anodizing bath, as color is formed through the interference between incident light 311 and reflected light 312. The widening of aperture 302 provides a wider viewing angle, making the color appear more uniform. This is known as "flop" in commercial standards used for applying dyed and colored coatings.

[0081] It has been found that by making Figure 2 Thinning the barrier layer 203 as shown produces improved results. The thickness of the barrier layer 203 is proportional to the aperture width (dp. bottom), which is proportional to the anodizing voltage (VA). Therefore, to thin the barrier layer 203, a lower anodizing voltage can be used. The aperture width is proportional to the anodizing voltage. Therefore, halving the voltage will halve the width, for example, four apertures 307 can be formed at the bottom of a single aperture 302, and the thickness of the barrier layer 203 can be halved. Sub-apertures (e.g., apertures 307) can be formed in a short time, typically less than 10 minutes, or less than 5 minutes in some embodiments. A second halving of the anodizing voltage produces a total of 16 sub-apertures 308 and a very thin barrier layer of less than 25 nm. The thinning of the barrier layer 203 facilitates the deposition of the coloring metal 309.

[0082] Figure 9 A schematic diagram illustrating the color generation mechanism of this disclosure is provided. Figure 9 The main processes that affect hue and brightness through anodizing and overcoating according to this disclosure are explained.

[0083] In one embodiment, the coating includes a nanostructured substrate 901, a barrier layer 902, a hole 903, and a side hole 904 in the hole wall 905. Two light paths are described. Light path 920 corresponds to light entering the hole 903. Light path 920 can be directly absorbed by the nanostructured metal coating or reflected by the nanostructured metal coating. The reflected light can exit the hole 903 as shown by line 922 or be absorbed by the side hole 904 as shown by line 923. Absorption should be understood as a combination of total internal reflection and surface plasmonic effects. Light path 940 represents light that enters directly into the hole wall 905 or enters the side hole 904 and is refracted by the hole wall 905. The metal coating on the hole wall 905 acts as a light guide, directing the light through the trench to the substrate 901. The light is reflected / refracted by the boundary 942 of the film / substrate boundary and the film / nanostructured metal boundary. The trench between the nanostructured metal coating and the substrate 901 of the barrier layer 902 acts as a bandpass filter for light, with the peak allowed frequency depending on the thickness of the barrier layer 902. The light exiting the filter is transmitted through the hole wall 905 to the surface as shown by line 944. The relative refractive indices of the aluminum oxide film (905), the aluminum substrate (901), and the metal nanorods (942) and air in the hole (903) are responsible for the color. The inventors have determined that the air gap is important for minimizing light absorption (and thus black or dark color coatings). Another factor in the color is the size of the photonic crystal formed by the side holes (904) spaced in relation to the barrier layer thickness.

[0084] Without being bound by theory, it can be understood that two different mechanisms can affect the perceived color of the coating. Brightness can depend on the size of the holes and the light absorption in the holes. Hue can depend on the thickness and uniformity of the barrier layer.

[0085] Referring again to Figure 3 Some publications have suggested Figure 3 The horizontal holes 306 shown are due to copper in the aluminum alloy. However, when filled with nickel, the horizontal holes 306 can act as nanoparticles, absorbing light 313 by surface plasmonic absorption.

[0086] Many aluminum alloys naturally contain copper, for example 6061 aluminum contains 0.15% to 0.4% copper, while 6022 aluminum contains 0.01% to 0.11% copper. Variations in the amount of copper cause variations in the number of horizontal holes 306, and thus variations in the darkening of the coating. Adding 0-5% (or in one embodiment about 1%) copper sulfate to the anodizing bath can allow for overcoming the lack of copper in some alloys. Chelating agents such as ethylenediaminetetraacetic acid (EDTA) or similar chemicals can prevent copper from depositing onto the cathode plate.

[0087] Thus, the present disclosure clearly demonstrates the fundamental difference between a colored surface produced using sulfuric acid anodization of a surface and a colored surface produced by the present disclosure.

[0088] Figure 7 Example ultraviolet imaging spectrometer (UVIS) spectra of the colored hybrid coating on 6061 aluminum of the present disclosure are illustrated. The UVIS spectra were measured on a spectrophotometer UV2550 commercially available from Labomed Inc. Here, the samples were measured against a barium chloride reference. It is believed that the important factor of the nearly flat absorption spectrum is plasmonic absorption of the horizontal nanopores, as expected from the black coloration. The slightly higher absorption at 200 nm is a result of destructive interference from the ~100 nm pore width, where the reflection from the pore walls is significantly attenuated at this wavelength.

[0089] Examples

[0090] The following examples indicate specific operating conditions and illustrate the practice of the present disclosure. However, these examples should not be considered as limiting the scope of the present disclosure. The examples were chosen to specifically illustrate aspects of coloration of thin anodized aluminum surfaces.

[0091] Example 1 - Effect of Ra (average roughness) reducing pretreatment on hybrid anodized 6061 Al with electrodeposited SB-Ni

[0092] Eleven samples of a colored coating including a thin anodized layer in combination with a semi-bright nickel layer provided a deep black surface with varying degrees of gloss.

[0093] Each sample was a 2 centimeter (cm) x 2 cm 6061 aluminum coupon and was mechanically polished using several grades of wet sandpaper ranging from 400 grit to 1200 grit. The mechanical polishing was varied for the various samples.

[0094] Each sample was then immersed in a commercially available alkaline Prelude AC-100 bath at 70 °C for 8 minutes with slight air agitation to remove surface contamination. The samples were then rinsed in deionized water.

[0095] Samples requiring surface finishing to have very low average roughness (Ra) were then electropolished in a bath containing H3PO4, HF, H2SO4, and glycerol in a volume ratio of 70:2:8:20 for 0-4 minutes. The electropolishing bath was maintained at a temperature of 80 °C with a voltage of 12 V applied between the coupon and a Pb cathode to produce a surface with an average roughness (Ra) of 0.1 to 0.5. The average roughness Ra was measured for each sample.

[0096] The electropolished substrate was then rinsed in deionized water and immersed in 50 volume percent nitric acid at room temperature for 1 minute to condition the surface prior to activation.

[0097] The samples were anodized in an anodizing bath at 27°C for 10 minutes. The anodizing bath composition was 205 mL / L H3PO4, 0.6 mL / L H2SO4, and 1 g / L HOOCCOOH. Application at 2 A / dm 2 Constant current anodizing was performed. It is believed that constant current anodizing produces a more uniform anodized pore structure when the thin coating is colored. Under these conditions, the voltage rapidly rises to 58V and then slowly decreases to about 45V. The anodized layer is about 2.5 micrometers thick.

[0098] In the electrodeposition stage, semi-bright nickel was electroplated into the anodic holes. The bath was a commercial CheMiPure SB bath, purchased from CMT Pvt. Ltd., India. The plating time was 90 minutes, and the temperature was 60°C. Initially, the current was increased from 0 A / dm³ over a two-minute period. 2 Rising to 0.10 A / dm 2 Then it remained constant at 0.1 A / dm for 80 minutes. 2 This is compared to the selected bath's 2-4 A / dm³. 2 Compared to the nominal plating current, the semi-bright nickel filler has a thickness of 2.5 micrometers, and the anodized layer is approximately 1 micrometer.

[0099] The resulting coating is a uniform glossy black. Figure 10 This is an exemplary graph illustrating the relationship between the average surface roughness of the substrate and the gloss of the coating. Graph 1001 shows a fitted curve that illustrates the relationship between the initial average surface roughness of the substrate and the measured gloss (in gloss units (GU) of the colored coating). A GU of 100 is representative of a highly polished reference black sample, while GU 0 is a perfectly matte sample.

[0100] Example 2 - Effect of Ra pretreatment on hybrid anodized 6061 Al with electrodeposited SB-Ni

[0101] A color coating consisting of a thin anodized layer bonded to a semi-bright nickel layer forms a matte, deep black surface.

[0102] A 2 cm × 2 cm 6061 aluminum sample was mechanically polished using 400-grit wet sandpaper to achieve an average surface roughness of Ra 2.5.

[0103] The sample was then immersed in a commercially available alkaline Prelude AC-100 bath at 70°C for 8 minutes with gentle air agitation to remove surface contaminants. The sample was then rinsed in deionized water.

[0104] The substrate was then rinsed in deionized water and immersed in 50% nitric acid at room temperature for 1 minute before activation to condition the surface.

[0105] The sample was anodized in an anodizing bath at 27°C for 10 minutes. The anodizing bath composition was 205 mL / L H3PO4, 0.6 mL / L H2SO4, and 1 g / L HOOCCOOH. It was applied at 2 A / dm 2 Constant current anodizing is applied. It is believed that constant current anodizing produces a more uniform density of pores in the anodized structure when the thin coating is colored.

[0106] Under these conditions, the voltage rapidly increased to 58V and then slowly decreased to approximately 45V. The anodized layer was approximately 2.5 micrometers thick. During the electrodeposition stage, semi-bright nickel was electroplated into the anodized holes. The bath was a commercial CheMiPure SB bath, commercially available from CMT Pvt. Ltd., India. The plating time was 90 minutes, and the temperature was 60°C. Initially, the current was increased from 0 A / dm³ over a two-minute period. 2 Rising to 0.10 A / dm 2 Then it remained constant at 0.1 A / dm for 80 minutes. 2 This is compared with the selected bath's 2-4 A / dm 2 Compared to the nominal plating current, the thickness is approximately 1 micrometer.

[0107] The resulting coating is black. Figure 4 This is a scanning electron microscope (SEM) image 401 of an exemplary phosphoric acid anodized structure of this disclosure. SEM image 401 shows an unsealed colored coating on a 6061 aluminum substrate according to one embodiment of this disclosure. Here, the anodizing voltage is approximately 58V, and the pore density calculated from a 1-micron square 402 is 60 / μm. 2 Furthermore, the average pore width is 80 nm (invisible). The widening effect of the pores at the surface can be clearly seen from the 100 nm square 403 with a pore width of approximately 105 nm.

[0108] Figure 5 This is an exemplary cross-sectional SEM image of an anodized colored substrate of the present disclosure. Figure 6 This is an SEM image of an exemplary close-up image of a cross-section of an anodized colored substrate according to the present disclosure. Figure 5 and Figure 6 In the process, the anodized coloring substrate is on 6061 aluminum.

[0109] Figure 5 An aluminum substrate 501 is shown. Figure 5Example 4 - How horizontal holes connect to the main holes in frame 502 at a density of about 1 per 100 nm for a 4% copper content. There are no horizontal holes at the surface closest to the surface, and hole widening occurs at the surface due to anodizing bath dissolution. The resulting coating is shown in inset image 503, which has the following (L , a , b ) characteristics (CIELAB) (7.1, -1.0, 0.5).

[0110] Figure 6 An aluminum substrate 601 is shown. In frame 602, the periodic filling of holes with nickel can be clearly seen. Figure 6

[0111] Example 3 - Relationship between anodizing time and plated metal deposition time in forming surface color

[0112] Approximately 32 substrates of 6061-T6 aluminum were prepared for this example. Each sample was 3 cm x 5 cm and prepared identically.

[0113] Each sample was then immersed in a commercially available alkaline Prelude AC-100 bath at 70°C for 10 minutes with slight air agitation to remove surface contamination. The samples were immersed in 50% nitric acid to decontaminate the surface. The samples were rinsed in deionized water between each step.

[0114] The main anodizing bath composition was H3PO4 205 mL / L, H2SO4 0.6 mL / L, and HOOCCOOH 1 g / L. The counter electrode was a titanium mesh, and vigorous air agitation was used to refresh the anodizing electrolyte at the example surface. The anodizing bath was placed in a water bath, and the temperature of the solution was maintained at 24 ± 1 °C to 36 ± 1 °C depending on the bath composition and color desired.

[0115] The bath composition was changed to support higher anodizing voltages. For voltages of 90 to 120 V, the H2SO4 was removed and a 75-80% ethanol solution was used instead of deionized water. From 120 to 150 V, ethylene glycol was used instead of deionized water as the solvent. > 150 V, 50% H3PO4 and 50% NaH2PO4 were used instead of H3PO4.

[0116] Constant voltage DC anodization was used, with the voltage limited to 60-280 V. In addition, the maximum current was limited to 2.0 A / dm 2 ​Eight samples were anodized under each voltage condition. Anodizing was performed in multiple time intervals ranging from approximately 15 to 25 minutes. The time interval was determined by the total charge passed, which was calculated for each treated sample based on records of voltage and current measured during the anodizing time interval. For each voltage, the charge passed through the eight samples remained constant. Immediately after anodizing, the samples were rinsed in deionized water and then immersed in a metal deposition solution.

[0117] In the electrodeposition stage, semi-bright nickel was electroplated into the anodized holes. The bath was a commercial CheMiPure SB bath, purchased from CMT Pvt. Ltd., India. The bath was maintained at 60°C and air agitation was used to ensure uniform deposition. Initially, the current was increased from 0 A / dm³ over a two-minute period. 2 Increased to 0.1 A / dm 2 Then, it remained constant at 0.1 A / dm over different time periods. 2 ,like Figure 8 As shown, and discussed in further detail below.

[0118] The coated sample was rinsed in deionized water and carefully dried. Color measurement was then performed by imaging the sample against a white background and calculating the L, a, b color coordinates of the sample using ImageJ 1.52 software.

[0119] Analyze sample data to develop a model of the color generation mechanism. Figure 8 An exemplary graph illustrating the relationship between voltage (60-280V), plating ampere-minutes (2-10 ampere-minutes), and color is shown in the methods of this disclosure. Figure 8 The graph in the figure shows the representative colors of the samples in spectrum for each anodizing voltage and nickel electrodeposition time. In each case, the color for a given anodizing voltage follows a spectrum from silver / gray to a specific color (depending on the anodizing voltage) to metallic color (depending on the plated metal).

[0120] It should be understood that several methods can contribute to coating color. The above discussion... Figure 6 A cross-section of a partially filled array of anodized holes is shown. Low deposition ampere-min / dm of the coloring metal. 2 (< 2 amperes per minute / dm) 2 This is independent of the anodic charge passed through, resulting in little or no metal deposition (i.e., very short metal nanorods). Figure 8 (as in strip 802). Here, light will be primarily reflected by the substrate, and this will cause the transparency of the blocking layer to be colored down to the silver-gray appearance of the underlying aluminum alloy (e.g., as shown in strip 802). Figure 9 (as determined by the base 901 in the middle).

[0121] For narrow anodized pores (e.g., low anodization voltage), as more metal deposition amperes-minutes are applied, the substrate is quickly shielded by the nanostructured metal 942, as shown in Figure 9 The resulting color formed is primarily dependent on the light absorption of the shiny metal deposition (e.g., the side pores 923 shown in Figure 9 Both the light entering the pores (e.g., light path 920) and the light entering the anodized layer that is reflected by the substrate (e.g., light path 940) contribute to the light absorption. This results in a black or gray band as shown in bar 803 in Figure 8 However, higher anodization voltages can form wider pores, while correspondingly facilitating metal deposition, which results in a dense metal layer at the bottom of the pores. Here, the coating color is dominated by a combination of the light absorption within the pores as described previously and the blue spectrum of colors formed by the selective absorption of light passing through the barrier layers (e.g., the barrier layer 902 shown in Figure 9 ) and the light spectrum of the metal deposition. As the anodization voltage increases, the pores become wider and for each anodization voltage, the dominant color formed is purple (bar 803 in Figure 8 ), dark blue (bar 804-806 in Figure 8 ), green (bar 807-808 in Figure 8 ), yellow (bar 809 in Figure 8 ), orange (bar 811-812 in Figure 8 ), and red (bar 813 in Figure 8 ). As the pores become wider, the range of metal deposition amperes-minutes increases during which the color is perceptible.

[0122] As the metal deposition amperes-minutes increase, the average pore filling also increases. At high amperes-minutes, the metal color dominates (as shown in bar 801 in Figure 8 However, due to changes in the nucleation process, a periodic range of filling occurs (e.g., as shown in the images shown in Figure 5 Three color generation mechanisms compete to produce the perceived coating color. First, the depth of the deposited metal controls the amount of light absorption. Here, as shown in the images in Figure 5 The filling of the side pores presents additional light absorbance through plasmonic effects.

[0123] Second, the light then passes through the light pipe in a manner determined by the geometry and length of the light pipe (e.g., by Figure 9The frequency selectivity of this light pipe is proportional to its length, which depends on the depth of the metal in the hole, the hole diameter, and the thickness of the anodized film barrier. Those skilled in the art will recognize that there are multiple effective lengths of the light pipe depending on the angle of incidence and the associated reflections; thus, there are transmission and absorption spectra.

[0124] Finally, light is reflected directly from the metal surface, where the distance between the metal surface and the top of the hole creates either destructive or constructive interference depending on the path length and the wavelength of the light, as shown by the light paths shown by lines 940 in FIG. 9. Figure 9

[0125] The distribution of wavelengths exiting the coating produces the perceived color of the coating, and the total absorption of the incident light within the structure causes the resulting color to darken or lose brightness, in the extreme case, the coating tends toward black. Narrower holes and thus narrower sidewalls are more constrained light paths, which leads to greater control over the color of the coating. This can lead to a wider band of metal deposition over which a single color can be perceived.

[0126] Table 1 shows the color (RGB) and color change (ΔΕ) produced on the surface for several anodization voltages and temperatures, higher temperatures in any bath formulation increase the porosity of the anodization and darken the color.

[0127] Table 1:

[0128]

[0129] Example 4 - Relationship between phosphoric acid concentration and maximum anodization thickness

[0130] Fifteen 6061-T6 aluminum substrates were prepared identically.

[0131] Each sample was then immersed in a commercially available alkaline Prelude AC-100 bath for 10 minutes at 70 °C with slight air agitation to remove surface contamination. The samples were immersed in 50% nitric acid to decontaminate the surface. The samples were rinsed in deionized water between each step.

[0132] The anodization bath composition was H3PO4 (100 ml / l to 210 ml / l depending on the sample), H2SO4 (0.6 mL / L), and HOOCCOOH (1 g / L) in each case. The counter electrode was a titanium mesh, and vigorous air agitation was used to refresh the anodization bath electrolyte at the example surface. The anodization bath was placed in a water bath, and the temperature of the solution was maintained at 25 ± 1 °C.

[0133] ​DC anodization using a constant voltage, where the voltage was limited to 60 V. In addition, the maximum current was limited to 2.0 A / dm 2 Anodization was performed for multiple time periods ranging from about 20 minutes to 120 minutes. The time period was determined by the total charge passed, which was calculated for each treated sample from the record of the voltage and current measured during the anodization time period.

[0134] Each sample was rinsed in deionized water and thoroughly dried. The samples were cross-sectioned and mounted as metallographic specimens, and the anodized film thickness was measured.

[0135] Figure 11 An exemplary graph showing the maximum achievable anodized layer thickness for several phosphoric acid concentrations of the present disclosure is illustrated. Graph 1101 shows the relationship between the maximum achievable anodized film thickness versus the concentration of phosphoric acid in the bath. As previously described, thick films provide improved coating mechanical properties at the expense of the time to produce the film and the transparency of the colored coating.

[0136] Example 5 - Effect of barrier layer thinning and anodizing bath temperature on dark gray colored coatings

[0137] Five 6022-T4 aluminum substrates were prepared identically.

[0138] Each sample was then immersed in a commercially available alkaline Prelude AC-100 bath at 70 °C for 10 minutes with slight air agitation to remove surface contamination. The samples were rinsed in Probright Al TM The alkaline cleaner was immersed at room temperature for 2 minutes. The samples were then decontaminated in 50% nitric acid at room temperature for 90 seconds. The samples were electropolished in a bath containing H3PO4, HF, H2SO4, and glycerol in a volume ratio selected from the following ranges: 70-85: 2-4: 6-9: 5-20. The electropolishing bath was maintained at a temperature of 65 degrees Celsius (°C), a voltage (V) of 12 V, and a Pb counter electrode for a time period of 0 to 8 minutes. The samples were rinsed in deionized water between each step.

[0139] The anodizing bath composition was H3PO4 (150 ml / l to 250 ml / l depending on the sample), H2SO4 (0.6 mL / L), and HOOCCOOH (1 g / L) in each case. The counter electrode was a titanium mesh, and vigorous air agitation was used to refresh the anodizing bath electrolyte at the example surface. The anodizing bath was placed in a water bath, and ice was used to maintain the temperature of the anodizing bath such that the temperature varied between 27 to 33 ± 3 °C depending on the sample.

[0140] DC anodization using a constant voltage, where the voltage was limited to 60 V. In addition, the maximum current was limited to 2.0 A / dm 2Anodization was performed for 20 minutes and various barrier thinning time periods were applied to each sample, for a total of 10 to 12 minutes of reduced anodization voltage at 30 V and / or 15 V. After anodization, the samples were rinsed in deionized water and immediately placed in the electroplating bath.

[0141] The samples were placed in a Chemipure / Niflow semi-bright nickel plating bath commercially available from CMP India. The bath was maintained at 60 °C and the anodes were nickel shavings in a bagged titanium mesh basket. The samples were initially soaked for 3 minutes to allow the nickel ions to penetrate the pores. The plating current was raised from 0 to 0.1 A / dm 2 for a period of 2 minutes, after which the current was held at 0.1 A / dm 2 for another 10 minutes, after which the current was increased to 0.3 A / dm 2 The samples were then rinsed and dried.

[0142] Figure 12 is a set of exemplary images and tables showing the effect of barrier thinning and temperature on the color of the coating of the present disclosure. Figure 12 The resulting samples 1201-1205, color distribution, and anodization temperature are shown. The anodization bath temperature has little effect on the pore size and barrier thickness, but has a large effect on the overall dissolution rate of the anodized layer in the phosphoric acid bath. The level and extent of barrier thinning also controls how much of the visible light spectrum is filtered out of the light reflected from the coating. This gives rise to a change in color, where in Figure 12 all five samples 1201-1205 appear dark gray, but samples 1201, 1202, and 1205 contain a blue tint; sample 1203 contains a red tint; and sample 1204 shows an orange-yellow tint. Table 1206 provides various processing parameters for each of samples 1201-1205.

[0143] Example 6 - Effect of Copper on Color

[0144] Three 6061-T6 aluminum substrates and three 6022-T4 aluminum substrates were prepared identically.

[0145] Each sample was immersed in a commercially available alkaline Prelude AC-100 bath at 70 °C for 10 minutes with slight air agitation to remove surface contamination. The samples were immersed in 50% nitric acid to decontaminate the surface. The samples were rinsed in deionized water between each step.

[0146] The anodic bath composition in each case was H3PO4 (30 mL / L to 300 mL / L, depending on the sample), H2SO4 (0.6 mL / L), and HOOCCOOH (1 g / L). The counter electrode was a titanium mesh, and vigorous air agitation was used to refresh the anodic electrolyte at the exemplary surface. The anodic bath was placed in a water bath, and the temperature of the solution was maintained at 25 ± 1°C.

[0147] Constant voltage DC anodizing was used, with the voltage limited to 60-100 V, depending on the 6061 / 6022 comparison pair samples. Furthermore, the maximum current was limited to 2.0 A / dm². 2 Anodizing is performed in multiple time intervals ranging from approximately 20 minutes to 120 minutes. The time interval is determined by the total charge passed through, which is calculated for each treated sample based on records of voltage and current measured during the anodizing time interval.

[0148] Each sample was rinsed in deionized water and thoroughly dried. The samples were then cross-sectioned and mounted in resin using metallographic preparation. The pore size of the anodic film and the side pores causing cross-flow were examined. Figure 12 The occurrence, size, and frequency of 1204.

[0149] As shown in Table 1 below, for the same anodizing voltage and passing charge, the 6061 sample has larger and more side holes compared to the 6022 sample; however, the 6022 aluminum alloy sample has a wider pore size. The volume of the formed side holes is roughly proportional to the copper content of the alloy, while the variation in the main pore volume is related to the volume of the side holes.

[0150] The measured brightness for the 6022 and 6061 aluminum alloy samples were 45.4 and 25.8, respectively. The change in brightness directly corresponds to the change in the side hole diameter, the light absorption assumed by side hole 923, and the light absorption caused by… Figure 12 The optical path represented by line 920 shown is as described above.

[0151] Table 2:

[0152]

[0153] Example 7 - Effects of Hole Pluging and Sealing

[0154] As described above, ten 100 × 25 mm 6061 aluminum substrates were anodized and colored to produce a dark gray surface. The samples were either unsealed and sealed with DUDMA only, or plugged with pMMA nanopores (to maintain air gaps) and then sealed with DUDMA.

[0155] For DUDMA sealing, a solution of ZnO nanoparticles in deionized water was applied to the surface and dried to act as a surface initiator and to maintain the clarity of the pDUDMA coating. The surface was then immersed three times in 80 volume % pure DUDMA monomer diluted with tetrahydrofuran (THF) and a controlled evaporation organic (such as acetone or ethyl acetate). The sample was exposed to strong UV light with a primary wavelength of 365 nm while being heated to 75 ± 5 °C. After 30 minutes, the DUDMA polymerized into a transparent coating.

[0156] MMA nanoparticles were prepared in advance to seal the openings of the porous anodized coating. 180 mL of deionized water was added to a 300 mL conical flask with 0.070 g of potassium bicarbonate (KHCO3), 0.024 g of ammonium persulfate (APS), and 0.029 g of sodium dodecyl sulfate (SDS) with magnetic stirring at 600 rpm. The solution was heated to 75 °C with 5 mL of methyl methacrylate (MMA) monomer added to the flask, followed by 0.0070 g of sodium bisulfite (NaHSO3). The flask was loosely sealed with a plug and the temperature was monitored over 3 hours. The solution was then immersed in an ice bath to rapidly cool to room temperature.

[0157] Thermogravimetric analysis showed 90% conversion of MMA monomer to PMMA nanoparticles. Dynamic light scattering showed an average particle size of 110 nm with a polydispersity index of 0.02.

[0158] Color change AE was measured by taking pictures of the samples in a light box, processing the images with ImageJ software, and determining the difference in color in RGB and the average color between samples.

[0159]

[0160] As shown in Table 2, the sealed samples provided an 8-fold improvement in corrosion performance, but the apparent color was noticeably different. This difference was more pronounced for the lighter samples with AE > 20. The sample with nanoparticle pore sealing and pDUDMA sealing had a 20-fold improvement in corrosion resistance, as well as an imperceptible color change.

[0161] Corrosion performance was measured by neutral salt spray testing per standard B117. The samples were rinsed dry and analyzed for corrosion each day. The time to first corrosion was recorded.

[0162] Table 3:

[0163]

[0164] It is to be understood that the variations and other features and functions described above, or those described in the following detailed description, can be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements can be subsequently made by others and such alternatives, modifications, variations or improvements are also intended to be encompassed by the described embodiments.

Claims

1. A method for forming a colored coating on an alloy by plasma absorption, comprising the following steps: (a) During a first time period, the substrate is anodized in an anodizing bath containing phosphoric acid at a constant temperature and constant voltage to form an anodized layer having pores and side pores, wherein the anodized layer includes a barrier layer. (b) During a second time period, the constant voltage applied to the anodizing bath is reduced to change the thickness of the barrier layer and the width of the pores in the anodizing layer; (c) The substrate is plated in the plating bath under a first current that increases during a third time period according to the current distribution of the plating bath; as well as (d) During a fourth time period, the substrate is deposited in the plating bath under a second current to at least partially fill the pores of the anodized layer with metal nanorods; as well as (e) Apply a sealing layer to the pores of the anodized layer and form an air gap between the metal nanorod and the sealing layer.

2. The method of claim 1, wherein the substrate comprises an aluminum alloy.

3. The method of claim 1, wherein in step (a), the anodizing bath further comprises copper sulfate and a chelating agent.

4. The method of claim 1, wherein in step (a), the constant temperature is a temperature between 20 degrees Celsius and 40 degrees Celsius.

5. The method of claim 1, wherein in step (a), the constant voltage is a voltage of 60 volts to 280 volts and the maximum current density is 2 amperes per square decimeter.

6. The method of claim 1, wherein in step (b), the constant voltage is reduced by 50%, and the second time period comprises 2 to 10 minutes, and then the constant voltage is reduced by another 50% in another time period of 2 to 10 minutes.

7. The method of claim 1, wherein in step (b), the voltage applied to the anodizing bath is reduced, (i) the thickness of the barrier layer is reduced, and (ii) the width of the aperture in the anodizing layer is increased.

8. The method of claim 1, wherein the barrier layer is located between the substrate and the pore in the anodized layer.

9. A method for forming a plasma-colored coating, the method comprising the steps of: (a) Anodizing an aluminum alloy substrate in an anodizing bath containing phosphoric acid at a constant temperature and constant voltage during a first time period to form an anodized layer of 2 to 10 micrometers thickness, wherein the anodized layer includes pores and side pores, and wherein the anodized layer includes a barrier layer. (b) During a second time period, the constant voltage applied to the anodizing bath is reduced to change the thickness of the barrier layer and the width of the pores in the anodizing layer; (c) The aluminum alloy substrate is plated in the plating bath under a first current that increases during a third time period according to the DC plating current distribution of the plating bath; (d) During a fourth time period, the aluminum alloy substrate is plated in the plating bath under a second current to at least partially fill the pores in the anodized layer with metal nanorods and generate a plasma effect; as well as (e) Seal the pores of the anodized layer, resulting in the formation of an air gap between the pores and the sealing layer.

10. The method of claim 9, wherein in step (a), the anodizing bath comprises 50 to 600 ml / L of phosphoric acid, 1 to 15 ml / L of sulfuric acid, and 1 to 10 g / L of oxalic acid.

11. The method of claim 9, wherein in step (a), the anodizing bath comprises 1 to 5 weight percent of copper sulfate and ethylenediaminetetraacetic acid (EDTA).

12. The method of claim 9, wherein in step (c), the plating bath comprises a nominal plating current of 2 amperes per decimeter (A / dm²). 2 Up to 4 A / dm 2 Semi-bright nickel bath.

13. The method of claim 12, wherein in step (d), the second current is 1% to 20% of the nominal plating current of the plating bath.

14. The method of claim 12 or 13, wherein the first current is 10% to 50% of the second current.

15. The method of claim 9, wherein the barrier layer is located between the substrate and the pore in the anodized layer.

16. A method for forming a colored coating on an alloy, comprising the following steps: (a) Optionally pretreat the aluminum alloy substrate; (b) Activate the aluminum alloy substrate; (c) The aluminum alloy substrate is anodized in an anodizing bath containing phosphoric acid at a constant temperature and constant voltage during a first time period to form an anodized layer having pores and side pores, wherein the anodized layer includes a barrier layer. (d) During a second time period, reduce the constant voltage applied to the anodizing bath to change the thickness of the barrier layer and the width of the pores in the anodizing layer; (e) Rinse the aluminum alloy substrate to further reduce the thickness of the barrier layer; (f) The aluminum alloy substrate is plated in a plating bath through multiple plating stages to deposit colored metal into the pores of the anodized layer; as well as (g) Seal the hole in the anodized layer, resulting in an air gap between the hole and the sealing layer.

17. The method of claim 16, wherein the preprocessing step (a) comprises: The aluminum alloy substrate is degreased in an alkaline bath; The aluminum alloy substrate is roughened in a solution of phosphoric acid, polyethylene glycol, sulfuric acid, and hydrofluoric acid. as well as The aluminum alloy substrate is etched in a nitric acid solution.

18. The method of claim 17, wherein the average roughness (Ra) of the aluminum alloy substrate is 0.4 to 1.

8.

19. The method of claim 16, wherein in step (f), the plurality of plating stages include: A first plating stage in which a first current is applied, increasing within a third time period according to the current distribution of the plating bath; as well as The second plating stage involves applying a constant second current during the fourth time period.

20. The method of claim 16, wherein the barrier layer is located between the substrate and the pore of the anodized layer.

21. The method of claim 16, wherein in step (g), the air gap between the pore and the sealing layer is maintained by nanoparticles configured to seal the pore.

22. A coating structure obtained by the method of any one of claims 1 to 8, comprising: Metal substrate; An anodized layer including a barrier layer is present on the metal substrate layer; The anodized layer has a plurality of spaced holes extending through the anodized layer toward the barrier layer; as well as The pores in the anodic layer are at least partially filled by metal nanorods.

23. The coating structure of claim 22, wherein the width of the hole is narrower at the end near the barrier layer and wider at the other end of the hole.

24. The coating structure of claim 22, wherein a sealing layer is present on the anodized layer.

25. The coating structure of claim 24, wherein the sealing layer seals the pores passing through the anodized layer.

26. The coating structure of claim 24, wherein an air gap exists between the metal nanorod and the sealing layer.

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