PROTECTING ANODIZED SURFACES DURING MANUFACTURING PROCESSES
1. A part, comprising:
- an anodic film on a metal substrate, the anodic film having a first section and a second section,wherein the first section is characterized as having a substantially fully sealed pore, andwherein the second section is characterized as having a partially sealed pore.
Treatments for anodic coatings that provide improved resistance to staining and cracking during various manufacturing processes are described. According to some embodiments, the methods include placing the anodic coatings in partially sealed states by sealing only the outermost portions of the anodic coatings, which protect the outer surfaces of the anodic coatings from contamination and staining. Inner portions of the anodic coatings are left unsealed, thereby making the anodic coatings more compliant and resistant to cracking when exposed to manufacturing processes, even those that involve exposure to high temperatures or high mechanical stress. Subsequent to the processing, another sealing process can be implemented to fully seal the anodic coatings so that they provide good corrosion and wear resistance.
- 1. A part, comprising:
an anodic film on a metal substrate, the anodic film having a first section and a second section, wherein the first section is characterized as having a substantially fully sealed pore, and wherein the second section is characterized as having a partially sealed pore.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- 11. A method of treating a part having an anodic film on a metal substrate, the method comprising:
partially sealing the anodic film; performing one or more manufacturing operations on the part; and substantially fully sealing at least a section of the anodic film.
- View Dependent Claims (12, 13, 14, 15, 16, 17)
- 18. A part, comprising:
an anodic film integrally bonded to a metal substrate at an interface and having an outer surface opposite the interface, wherein an outermost one micrometer of the anodic film is characterized as having a nickel concentration of at least 20 weight %, and an interior portion of the anodic film between the outermost one micrometer and the interface is characterized as having a nickel concentration of no more than about 1 weight %.
- View Dependent Claims (19, 20)
The described embodiments relate to anodic films and related processes. In particular embodiments, porous anodic films are treated with a partial sealing process that seals the outermost portions of the pores to resist contamination, while remaining portions of the pores are substantially unsealed to provide strain tolerance for further processing.
Fully sealed anodic films tend to craze or crack when exposed to high temperatures, such as those induced by laser marking or other thermal treatments during some manufacturing processes. This is due to differential thermal expansion between the anodic film and underlying metal substrate, compounded by the high stiffness of a sealed anodic film. Unsealed anodic films are generally less stiff, and are thus less susceptible to damage from thermal strain induced by such processes as heat treatments or laser marking. However, unsealed anodic films can be vulnerable to staining, discoloration or other cosmetic damage. What is needed, therefore, are methods of protecting anodized parts during manufacturing processes.
This paper describes various embodiments that relate to treatments for anodic films useful for implementing during production of consumer products, such as consumer electronic devices. According to some embodiments, the anodic films are treated with a partial sealing process to place the anodic films in a protected yet thermally compliant state.
According to one embodiment, a part is described. The part includes an anodic film on a metal substrate. The anodic film has a first section and a second section. The first section is characterized as having a substantially fully sealed pore, and the second section is characterized as having a partially sealed pore.
According to another embodiment, a method of treating a part having an anodic film on a metal substrate is described. The method includes partially sealing the anodic film. The method also includes performing one or more manufacturing operations on the part. The method further includes substantially fully sealing at least a section of the anodic film.
According to a further embodiment, a part is described. The part includes an anodic film integrally bonded to a metal substrate at an interface and having an outer surface opposite the interface. An outermost one micrometer of the anodic film is characterized as having a nickel concentration of at least 20 weight %, and an interior portion of the anodic film between the outermost one micrometer and the interface is characterized as having a nickel concentration of no more than about 5 weight %.
These and other embodiments will be described in detail below.
The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements.
Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims.
Methods described herein involve protecting surfaces of anodized parts during manufacturing processes. In some embodiments, the methods involve partially sealing the pores of an anodic film so as to protect the anodic film against staining and other cosmetic damage. Since most of the volume within the pores is left unsealed, the anodic film can retain the elasticity and resilience of an unsealed anodic film. Thus, the anodic film is less susceptible to cracking when put under mechanical or thermal stress. Furthermore, an anodic film in a partially sealed state can be subjected to a wider range of manufacturing processes compared to a fully sealed or unsealed anodic film without causing structural or cosmetic damage to the anodic film. After the manufacturing processes are complete, a full sealing process can be implemented to fully seal the pores.
In some cases, the methods involve using two separate sealing processes—a first sealing process to place the anodic film in a partially sealed state, and a second sealing process to place the anodic film in a fully sealed state. In some embodiments, the first sealing process is a hydrothermal process whereby only the outermost portion of the anodic film is hydrolyzed and sealed, leaving a bulk of the anodic film unsealed. In other embodiments, the first sealing process involves depositing a very thin layer of material, such as a silicate layer, to cover and protect an exterior surface of the anodic film, leaving a bulk of the anodic film unsealed. The second sealing process can involve a hydrothermal process that hydrolyzes and swells the oxide material of the anodic film to a point where the air within the pores is substantially fully replaced with a metal oxide hydroxide material. One or both of the first and second sealing processes can include use of an aqueous solution containing nickel acetate or other catalyst.
When in the partially sealed state, the anodized part can be subjected to one or more manufacturing processes without developing cracks. For example, laser marking or laser etching processes, which may conventionally cause portions of the anodic film near the laser marking or etching area to crack due to thermal stress, can be implemented without substantial cracking. Other thermal processes can include thermal or ultraviolet curing of polymer adhesives, tempering of alloy substrates, hot air-drying processes, and hot injection molding processes. The result can be a substantially crack-free, defect-free and cosmetically pleasing anodized part, suitable for any of a number of consumer products. For example, the methods can be used to form durable and cosmetically appealing finishes for housing of computers, portable electronic devices, wearable electronic devices, and electronic device accessories, such as those manufactured by Apple Inc., based in Cupertino, Calif.
As described herein, the terms oxide, anodic oxide, metal oxide, etc. can be used interchangeably and can refer to any suitable metal oxide materials, unless otherwise specified. Furthermore, the terms coating, layer, film, etc. can be used interchangeably and can refer to any suitable thin layer of material that, for example, covers a surface of a substrate, part, etc., unless otherwise specified. For example, an anodic oxide film can be referred to as an anodic film, anodic coating, anodic oxide coating, anodic oxide layer, metal oxide coating, oxide film, etc. Furthermore, an oxide formed by anodizing a metal substrate will generally be understood to consist of an oxide of the metal substrate. For example, an oxide formed by anodizing an aluminum or aluminum alloy substrate can form a corresponding aluminum oxide film, layer or coating.
These and other embodiments are discussed below with reference to
The methods described herein can be used to form durable and cosmetically appealing coatings for metallic surfaces of consumer products, such as consumer electronic devices shown in
During manufacturing, the anodized metal portions of devices 102, 104, 106 and 108 can be subjected to any of a number of subsequent thermal processes, such as laser marking processes, thermal cure cycles for adhesives and other polymeric components, or artificial aging of alloy substrates. As described in detail below, these thermal processes can cause small but visible cracks to form within the anodic oxide coatings. Described herein are manufacturing processes for reducing the occurrence of thermal cracking within anodic oxide coatings on devices such as devices 102, 104, 106 and 108.
As shown, the thermal process(es) can form cracks 206 within anodic film 204, which can be visible to a user and breaks the otherwise continuous exterior surface 205 of anodic film 204. Cracks 206 are formed due to differences in material of metal substrate 202 and anodic film 204. In particular, anodic film 204 comprises a metal oxide material while substrate 202 comprises metal. These two types of materials have different thermal expansion coefficients (a), which are measures of how much the materials expand when heated, and are generally measured as a fractional change in size per degree change in temperature at a constant pressure. In general, metal materials expand more when heated compared to metal oxide materials—and therefore metal materials generally have higher thermal expansion coefficients than those of metal oxide materials.
For example, aluminum alloys can have a thermal expansion coefficient of about 22-23 micro-strain per Kelvin, whereas corresponding aluminum oxides can have thermal expansion coefficient of about 5 to 6 micro-strain per Kelvin (i.e., almost 4 times smaller than that of an aluminum alloy). It should be noted that for films and layered materials, it can be useful to define thermal expansion in terms of in-plane thermal expansivity, which can be defined as the change in area (or length) per change in temperature. Thus, due to the differences in thermal expansion coefficients of metal versus metal oxides, metal substrate 202 will have a higher in-plane thermal expansivity than that of anodic film 204. That is, metal substrate 202 will thermally expand (lengthen) more than anodic film 204, causing stress to form within anodic film 204 near interface 203, and ultimately causing cracks 206 to form within anodic film 204 in order to release the stress.
Anodic film 204 is much more susceptible to cracking after anodic film 204 is sealed using a sealing process. A sealing process generally involves exposing anodic film 204 to a hot aqueous solution to hydrolyze the metal oxide material of anodic film 204, thereby filling in the pores with a corresponding metal oxide hydroxide. This rigidifies anodic film 204 and constrains the expansion of anodic film 204 during a subsequent thermal process. In general, cracks 206 cannot be repaired using conventional sealing processes since they are too large. For example, in some instances, these cracks 206 are at least 1000 nanometers wide across or greater.
It should also be noted that cracks 206 can also be formed by non-thermal processes. For example, anodic film 204 can be vulnerable to mechanical stresses brought on by, for example, fixtures used to support or position anodized part 200 during any of a number of manufacturing operations.
Methods described herein can be implemented to avoid formation of such cracks during the manufacturing process.
The composition of the metal oxide material of walls 408 will depend, in part, on the composition of metal substrate 402. In some applications, metal substrate 402 is composed of an aluminum alloy, thereby resulting in anodic film 404 composed of an aluminum oxide (Al2O3) material. Thickness 405 of anodic film 404 can depend on design requirements of particular applications. For example, thickness 405 of between about 5 and 15 micrometers may be suitable for housings for consumer electronic in some cases.
In some embodiments, a colorant (not shown), such as a dye, pigment or metal material, is deposited within pores 406 to impart a desired color to anodic film 404. Any suitable colorant can be used. In some embodiments, the colorant is a dye that adheres to internal surfaces of walls 408, while in some embodiments, the colorant is a metal that is electrodeposited deep within pores 406 (including at terminal ends 410 of pores 406 near interface 403). In some applications, a combination of dyes, pigments, and/or metals is deposited within pores 406.
After anodizing (and after an optional coloring process), anodic film 404 can be highly vulnerable to staining and cosmetic damage because it can have a mesoporous structure (with about 10-11 pores 406 per square centimeter, of about 20 nanometer in diameter 407, of good wettability and very high aspect ratio). Typically, a hydrothermal seal is conducted prior to any further material processing, surface finishing operations, or other types of handling, in order to prevent contaminants from entering and getting trapped within pores 406, and resulting in visible defects. In general, hydrothermal sealing involves hydrating the metal oxide material of walls 408 to a corresponding metal oxide hydroxide. For example, an amorphous alumina (Al2O3) can be converted to Boehmite (aluminum oxide hydroxide). This hydrolysis causes walls 408 to swell and close the open volume of pores 406. However, fully sealing pores 406 can cause anodic film 404 to have a highly rigid structure that is resistant to deformation when stress is applied, such as the thermal stress associated with certain manufacturing processes described above.
Thus, instead of fully sealing anodic film 404, at
The extent to which the hydrolysis through the thickness of anodic film 404 will occur depends directly on the exposure time to the hot sealing solution (or steam). In addition, the hot aqueous solution may include a catalyst, such as nickel acetate, which can increase the speed of hydrolysis. In particular embodiments, anodized part 400 is immersed in a hot nickel acetate aqueous solution having a temperature of at least 70 degrees Celsius (typically between 85 and 90 degrees Celsius) for a period of time ranging between about 5 seconds and 3 minutes. In some embodiments, an exposure time period of no more than one minute is found to provide good results. This is compared to the one to two minutes per micrometer exposure time used in conventional sealing (e.g., 15 minutes to one hour long conventional hydrothermal sealing process). In some embodiments, the partial sealing results in seared exterior portion 418 constituting less than about one micrometer of the entire thickness (i.e., from exterior surface 412 to interface 403) of anodic film 404.
Once the partial sealing process is complete, anodized part 400 can be from the hot aqueous solution to stop hydrolysis. In some cases, a drying process can be implemented in order to remove aqueous solution trapped within pores 406. The resultant anodic film 404 can include metal oxide hydroxide 414 having a distinctive inverse cup-shaped structure 422 near exterior surface 412.
While in this partially sealed state, top portions of pores 406 are closed such that contaminants cannot enter the pores 406, thereby making the exterior surface 412 resistant to staining from absorbing dirt or oil. Therefore, anodized part 400 can be transferred between manufacturing stations without incurring contaminant related defects. Nevertheless, anodic film 404 remains almost as compliant and strain tolerant as it was prior to partial sealing. Thus, anodized part 400 can undergo any of a number of mechanically or thermally intensive manufacturing processes without crazing or cracking. It should be noted that even though metal oxide hydroxide 414 sufficiently seals exterior portion 418 to prevent contaminants such as dirt and oil from entering interior portion 420 of pores 406, metal oxide hydroxide 414 at exterior portion 418 can still permeable to aqueous solution so that a subsequent hot aqueous sealing process can fully seal pores 406.
One thermally intensive manufacturing process can include a laser marking process, where a laser is used to form a visibly apparent mark, such as a logo or lettering, on a surface of part 400. For example, a laser beam can be directed at exterior surface 412 and tuned to have a wavelength and a power density that locally heats metal substrate 402 at interface 403 between metal substrate 402 and anodic film 404. The heating locally melts the metal substrate 402 at the interface 403, which can cause local changes in the physical structure of the interface 403 (e.g., changes in roughness, changes in optical reflectivity, etc.), thereby resulting in a visible mark (not shown). In some applications, the laser mark is visibly darker (e.g., black or dark grey) in comparison to surrounding unmarked portions of anodic film 404, while in other applications the laser mark is visibly lighter (e.g., white or light grey) in comparison to unmarked portions. This process can be useful in that an indelible mark can be made on part 400 without significantly interrupting exterior surface 412. One of the consequences of laser marking is localized heating and expansion of metal substrate 402 and anodic film 404 near interface 403. In conventionally fully sealed anodic films, this can cause differential expansion of a metal substrate and an anodic film that result in cracks within the anodic film, as described above. Since pores 406 are only partially sealed, anodic film 404 is allowed to expand and contract at higher temperatures without cracking.
Another thermally intensive operation can include metal alloy heat treatments of metal substrate 402. For example, a post-anodizing heat treatment can be used to diffuse interfacially enriched alloying elements (e.g., zinc) away from interface 403. On some types of aluminum alloys that include relatively large concentrations of zinc, this heat treatment can overcome susceptibility to interfacial adhesion failures and may also be used to change the color of anodized part 400, or to change the temper of metal substrate (e.g., to age-harden an alloy that was anodized in a O, W or T4 temper state). Such post-anodizing heat treatments may be performed on anodized part 400 while in a partially sealed state to help prevent damage to anodic film 404. Details of suitable post-anodizing substrate heat treatments are described in U.S. Pat. No. 9,359,686, issued on Jun. 7, 2016, which is incorporated herein by reference in its entirety.
Other thermally intensive processes can include some drying processes that remove moisture from anodic film 404, bake out processes where hydrogen is removed from anodized part 400, shrink wrapping processes where anodized part 400 is heated during shrink wrapping with a polymer material, molding processes where heated molten material is molded onto surfaces of anodized part 400, thermal cycles for curing adhesives, lacquers, or certain sealing compounds applied to surfaces of anodized part 400, or any other suitable thermal operations.
Some manufacturing process can induce high mechanical strain on anodized part 400. For example, anodized part 400 can be handled by a robot, secured in a fixture, or undergo mild bending for a shaping operation. Some applications involve lapping or polishing of surfaces of anodized part 400. These types of high mechanical stress operations can dent, scratch, or crack a fully sealed anodic film. However, if anodic film 404 is only partially sealed, it will be in a more elastic and resilient state, and will therefore be able to tolerate these types of operations without damage better than a fully sealed anodic film.
It should be noted that a partially sealed anodic film could be accomplished using techniques other than hydrothermal sealing. For example, instead of, or in addition to, a hydrothermal sealing process, a very thin (e.g., less than one micrometer in thickness) silicate layer (not shown) can be applied on exterior surface 412 such that the openings of pores 406 are effectively sealed off while leaving a majority of the volume of pores 406 filled with air and/or colorant. Thus, the silicate layer can prevent contaminants from entering pores 406 while leaving the majority of anodic film 404 stress-tolerant, similar to partial hydrothermal sealing described above. In some manufacturing lines, however, a hydrothermal partial sealing process may be preferable over a silicate partial sealing process since equipment for a hydrothermal sealing process may be more readily accessible and simpler to implement.
After one or more manufacturing processes are performed, at
As described above, approximately one minute per micrometer of anodic film 404 thicknesses is generally used to provide a complete seal. However, a previous thermal process may affect the amount of time necessary to fully seal anodic film 404. For example, after exposing anodized part 400 to a thermal adhesive curing process, it may be necessary to expose anodized part 400 to a longer full sealing process compared to an anodized part that had not undergone such an adhesive curing process.
In the fully sealed state, anodic film 404 provides high corrosion resistance and wear resistance to metal substrate 402, and thus functions as a highly protective finish during the service life of part 400. The mass loss of a substantially fully sealed anodic film 404 is generally about 15 mg/dm2, passing in accordance with ISO 7599-1983(E) standards. One of the ways to characterize whether anodic film 404 has been fully sealed is by measuring the admittance of anodic film 404—i.e., how easily an electric current can flow through anodic film 404. An admittance measurement can also be referred to as an electrical impedance measurement. In general, the more fully sealed anodic film 404 is, the lower the admittance measurement. A fully sealed anodic film 404 having a thickness below about 15 micrometers can have an admittance measurement of less than about 25 micro Siemens (μS). In particular embodiments, an admittance measurement of about 14 μS or less is desirable. In comparison, partially sealed anodic film 404 (
In some embodiments, the aqueous solution used to partially seal anodic film 404 (
If a sealing solution includes a catalyst, the resultant anodic film 404 can incorporate readily detectable amounts of the catalyst within the metal oxide hydroxide 414 material. Thus, if the sealing solution for the partial sealing process includes nickel acetate, the resultant metal oxide hydroxide 414 within exterior portion 418 will have trace amounts of nickel. And if the sealing solution for the full sealing process does not include nickel acetate, the resultant metal oxide hydroxide 414 within interior portion 420 will be substantially free of nickel (i.e., no nickel or very low concentrations). Put another way, exterior portion 418 will include a higher concentration of nickel (e.g., between about 20% weight and 35% weight) compared to interior portion 420 (e.g., <1 weight %). A chemical analysis through the thickness (from interface 403 to exterior surface 412) can thus indicate a very high nickel concentration at exterior portion 418 (e.g., top one micrometer of anodic film 404) with a sharp decline of nickel concentration once past exterior portion 418. A graph showing this nickel concentration distribution is described in detail below with reference to
After the partial sealing process, component 619 is coupled to surface 612 of anodic film 604, thereby blocking entry to pores 607 within second section 617. In some embodiments, component 619 is made of a polymer material that is adhered onto surface 612 of anodic film 604 using a thermal process. In some embodiments, component 619 is a thermosetting type adhesive cured by exposure to heat or light (e.g., ultraviolet light). The type of adhesive and the temperature required to cure the adhesive can vary. For example, some adhesives require exposure to temperatures of about 80 to 100 degrees Celsius, or more. The adhesive is not limited to thermosetting type adhesives. That is, the adhesive can include any suitable synthetic or natural adhesives. In some embodiments, the adhesive includes at least one of elastomer, thermoplastic, emulsion, or thermosetting type adhesives. In particular embodiments, the adhesive includes at least one of epoxy, polyurethane, cyanoacrylate, acrylic, or other suitable polymer adhesive. In some embodiments, multiple layers of adhesive are used. In some applications, the adhesive is non-electrically conducive, while in other applications the adhesive is electrically conductive (e.g., includes electrically conductive material). In some applications, the adhesive includes an optically clear adhesive, which may be used to bond optically transparent structures (e.g., display covers) to an anodized metal housing.
In some applications, component 619 is a polymer that has been molded onto surface 612 by hot injection molding, which can induce both thermal and mechanical strain on anodic film 604. Component 619 can have any suitable shape and size. For example, component can correspond to a very thin part having a thickness of around a few micrometers, or a larger polymer piece having a thickness of several millimeters or centimeters. Since the process for coupling component 619 to surface 612 is performed while anodic film 604 is in a partially sealed state, the risk of thermally or mechanically induced cracking of anodic film 604 is greatly reduced. Thus, anodic film 604 can remain craze-free.
Subsequent to applying component 619, anodized part 600 is exposed to a full hydrothermal sealing process, whereby hot aqueous solution or steam enters pores 606 of first section 615, thereby swelling walls 608 and filling substantially all of the remaining volume of pores 606 with metal oxide hydroxide 614 material. Component 619 prevents entry of the hot aqueous solution or steam from entering pores 607 of second section 617. Thus pores 607 remain only partially sealed, with metal oxide hydroxide 614 material having an inverse cup-shaped structure 622 near surface 612, and a discontinuous metal oxide hydroxide structure (i.e., voids 616) within interior portion 620 of pores 607.
One way to detect whether the partial sealing techniques described herein have been used in the manufacture of an anodized part is by taking cross section images of surface portions of the anodized part. For example, transmission electron microscopy (TEM) images may show a visual contrast between pores 606 that are substantially fully filled with metal oxide hydroxide 614 versus pores 607 having voids 616. That is, the presence of voids 616 within pores 607 of second section 617 can be indicative of implementation of a partial sealing process, and that the above-described benefits of having anodic film 604 in a partially sealed state were exploited in order to implement a thermally or mechanically intensive manufacturing process.
Another way to detect the presence of voids 616 within pores 607 is by taking admittance (electrical impedance) measurements of second section 617. In practice, this could be accomplished by removing component 619 (and second component 621, if present) from surface 612 of anodic film 604. In this way, surface 612 at second section 617 can be re-exposed for electrodes to be placed thereon for electrical impedance measurements to be taken. These measurements can be compared to those taken at first section 615. As described above, a fully sealed anodic film (first section 615) will have a much lower admittance measurement than a partially sealed anodic film (second section 617). In some cases, second section 617, which is laterally adjacent to first section 615, is characterized as having an admittance measurement that is at least ten times that of first section 615. In particular embodiments, first section 615 has an admittance measurement of about 25 μS or less. In some embodiments, second section 617 has an admittance measurement greater than about 250 μS.
As described above, a colorant, such as a dye, pigment or metal material, can be deposited within that anodic film prior to implementing the partial sealing operation in order to impart a desired color to the anodic film.
As shown, both anodic films A and B have relatively high concentrations of nickel within their exterior portions (e.g., corresponding to an outermost 1 micrometer). In some embodiments, the exterior portion of anodic film B is characterized as having a nickel concentration of at least 20% weight). In anodic film A, the nickel concentration declines only gradually toward the interface with the underlying metal substrate, with still significant concentrations of nickel disposed within its interior portion between the exterior portion and the interface. In contrast, the concentration of nickel in anodic film B declines sharply once past its exterior portion (e.g., outermost 1 micrometer), the interior portion having a nickel concentration of no more than about 1 weight %. The graph of
As described above, the partial sealing process is not limited to a hydrothermal sealing process, and may instead involve depositing a thin layer of sealing material.
Sealing layer 821 should be sufficiently thick to seal the open mouths of pores 806 at exterior surface 812 so as to prevent contaminants from entering pores 806 during one or more manufacturing processes, but may also need to be thin enough to allow solution to enter pores 806 during a subsequent hydrothermal process. In some embodiments, sealing layer 821 is deposited to a thickness ranging between about 0.05 micrometers and about 1 micrometer. In the partially sealed state, anodized part 800 can be subjected to one or more manufacturing processes, such as one or more of the thermally and/or mechanically intensive operations described above. Since the bulk of pores 806 are filled with air, anodic film 404 is more compliant and able to withstand higher thermal and mechanical strain compared to a fully sealed anodic film.
At 904, the anodic film is partially sealed such that exterior portions of the pores are sufficiently sealed to prevent contaminants from entering the pores during a subsequent manufacturing process. Interior portions of the pores can have air filled voids such that the anodic film is more resistant to cracking when placed under thermal and mechanical strain. In some embodiments, the partial sealing process involves a hydrothermal sealing process, whereby the exterior portions of the pore wall are hydrated and swelled closed. In some embodiments, the partial sealing process involves depositing a very thin sealing layer (e.g., silicate layer) on an exterior surface of the anodic film.
While in the partial sealed state, at 906 one or more thermally and/or mechanically intensive operations are performed on the anodized part. The one or more operations can include, but are not limited to, laser marking, thermal or ultraviolet curing of polymer adhesives, artificial ageing or tempering of alloy substrates, high air-drying processes, molten polymer injection molding, and anodic film polishing or lapping. In general, the anodic film in the partially sealed state can tolerate higher temperatures and more mechanical strain without cracking compared to a fully sealed anodic film. In some embodiments, one or more components (e.g., adhesive layers) are adhered to one or more sections of the anodic film prior to a subsequent full sealing process.
At 908, at least one section of the anodic film is fully sealed using, for example, a hydrothermal sealing process that fully closes voids within the pores. When in the fully sealed state, spaces within the anodic film are filled with metal oxide hydroxide material such a that water cannot easily pass through the anodic film to reach the underlying metal substrate. In this way, the fully sealed anodic film provides a good corrosion barrier to the metal substrate.
In embodiments where one or more components (e.g., adhesive layers) are adhered to the anodic film, the section(s) of the anodic film covered by the component(s) can be shielded from exposure to the sealing solution. Thus, these section(s) can remain in the partially sealed state. These partially sealed sections of the anodic film can be detected using one or more of the techniques described above.
The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.