Lightweight metal workpiece and method for producing a corrosion-resistant and glossy coating for a lightweight metal workpiece

Abstract

Lightweight metal workpiece with improved surface protection, including: a light metal alloy or matrix with an exposed surface, wherein the light metal alloy or matrix comprises at least one valve metal selected from the group consisting of aluminium, magnesium, titanium and mixtures thereof; a corrosion-resistant base layer (32) applied to at least one section of the exposed surface, the corrosion-resistant base layer comprising: a pretreatment layer (34), wherein the pretreatment layer (34) comprises an oxide layer formed on the exposed surface, and wherein the oxide layer is formed with a thickness of 5 µm to 20 µm; and a first primer coating (36) applied to the pretreatment layer (34), wherein the first primer coating (36) comprises at least one electrostatic coating and one powder material coating, and wherein the first primer coating (36) is applied with a thickness of 50 µm to 150 µm; a protective top layer (40) applied to at least one section of the corrosion-resistant base layer (32), the protective top layer (40) comprising: a second primer coating (42) applied over the first primer coating (36), wherein the second primer coating (42) comprises at least one electrostatic coating and one powder material coating, and wherein the second primer coating (42) is applied with a thickness of 50 µm to 150 µm; and wherein the electrostatic coating of the first primer coating and the second primer coating consists of fluoropolymers, acrylic, epoxy, polyester, polysiloxanes or polyvinylidene fluoride (PVDF), and wherein the powder material coating of the first primer coating and the second primer coating consists of polyester, polyurethane, polyester epoxy, straight-chain epoxy or acrylics, and a sputtered metallic film (44) applied to at least one section of the second primer coating (42) using a physical vapor deposition technique, wherein the sputtered metallic film (44) is applied with a thickness of 5 nm to 15 nm; and a clear lacquer layer (46) applied to at least one section of the metallic film (44), wherein the first clear lacquer layer (46) is applied with a thickness of 20 µm to 30 µm.

Description

CROSS-REFERENCE TO RELATED REGISTRATIONS

[0001] This application claims the benefit and priority of International Patent Application No. PCT / CN2014 / 074878, filed on April 8, 2014. The entire disclosure content of the above patent application is incorporated herein by reference. AREA

[0002] The present disclosure relates to coatings and methods for applying surface treatments for increased corrosion resistance of metals and alloys that are susceptible to corrosion. BACKGROUND

[0003] The background information provided herein is intended to provide a general context for the disclosure. The work of the currently named inventors, to the extent described in this background section, and any aspects of the description that cannot otherwise be considered prior art at the time of filing, are neither explicitly nor implicitly recognized as prior art with respect to the present technology.

[0004] Alloy wheels with a high magnesium or aluminum content are not uncommon on special-purpose and racing vehicles. However, the use of such alloy wheels in less expensive passenger cars has been limited to a few production sports cars. Galvanic corrosion, for example, is a design consideration for alloy wheels with a high magnesium content when fitted with steel or cast iron wheel hubs and brake components. These components can often be exposed to steam or wet conditions for much of their service life, unfortunately often including road salt, which accelerates galvanic corrosion reactions. Various coatings have been applied to light metal workpieces and substrates (including, for example, magnesium or aluminum), such as alloy wheels, to improve corrosion protection, but these have had many drawbacks. For example,Workpieces with only thin oxide layers have been used, but these are often brittle and prone to cracking. Workpieces with powder coating materials applied directly to oxide layers have shown poor adhesion. Workpieces incorporating chemical passivation techniques in combination with an oxide layer have been used, but these exhibited poor resistance to chipping. Furthermore, workpieces with a simple electrocoating applied over an oxide layer have also been used, although these can result in a product with poor scratch corrosion resistance and poor thermal shock resistance. According to other alternatives, wheels can be designed as two-component assemblies with inner and outer sections, the inner section galvanically isolating the outer section from the steel or cast iron wheel hub and brake components.However, such two-component arrangements may not always be desirable.

[0005] DE 102 33 120 A1 describes a decorative universal surface coating for semi-finished products (long profiles or products) made of, for example, metal, as well as its manufacturing process. The coating comprises several layers applied successively, i.e., a conversion coating is applied to the surface of a semi-finished product, followed by a leveling coat, then a layer acting as an adhesion promoter, then a metallic or metallic glossy tempering layer, and finally a topcoat.

[0006] EP 0 198 092 B1 describes a surface-treated magnesium or magnesium alloy, with an oxide film produced on the surface of the magnesium or magnesium alloy, a film of heat-curing resin produced on the oxide film and a conductive film produced on the film of heat-curing resin.

[0007] DE 197 02 566 C2 describes a process for the high-gloss coating of parts by applying a coating system. The process comprises the following steps: (a) application of a corrosion-inhibiting, smoothing base coat, (b) dusting of a high-gloss layer made of a metal, a metal alloy or a metal compound using a magnetron in a vacuum, and (c) application of a transparent, wear-resistant top coat made of a lacquer.

[0008] Therefore, there remains a need for improved surface treatments to enhance the corrosion resistance of light metals and alloys that are susceptible to corrosion. SUMMARY

[0009] This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope of protection or all of its features.

[0010] According to various aspects, the present teachings provide for a light metal workpiece with improved surface protection and a method for providing an improved surface coating on a metal or alloy substrate.

[0011] This problem is solved by the subject matter of the independent claims. Advantageous further developments and embodiments are the subject matter of the dependent claims. Further features, applications, and advantages of the invention will become apparent from the following description.

[0012] According to one aspect, the present teachings provide for a light metal workpiece with improved surface protection. The workpiece comprises a metal or alloy matrix, such as magnesium, with an exposed surface having a corrosion-resistant base layer applied to at least a portion of the exposed surface and a protective top layer applied to at least a portion of the corrosion-resistant base layer. The corrosion-resistant base layer may include a pretreatment layer and a first primer coating applied to at least a portion of the pretreatment layer.The protective topcoat can comprise a second primer coating applied to at least one section of the first primer coating, and a sputtered metallic film applied to at least one section of the second primer coating using a physical vapor deposition technique. A clear coat can be applied to at least one section of the metallic film.

[0013] According to other aspects, the present teachings provide for a magnesium metal wheel with a magnesium metal matrix, exhibiting an exposed surface. A magnesium oxide ceramic layer can be formed on at least a portion of the exposed surface. A first primer coating can be applied to at least a portion of the magnesium oxide ceramic layer. A second primer coating can be applied to at least a portion of the first primer coating. A sputtered metallic film can be deposited onto at least a portion of the second primer coating using a physical vapor deposition technique. Then, a clear coat can be applied to at least a portion of the metallic film. According to certain aspects, the sputtered metallic film can be deposited with a thickness of approximately 5 nm to approximately 15 nm.According to various aspects, each of the first primer coating and the second primer coating includes at least one electrostatic coating and one powder material coating.

[0014] According to other aspects, the present teachings comprise a method for providing an improved surface coating on a metal or alloy substrate. The method includes providing a metal or alloy substrate with an exposed surface. A corrosion-resistant base layer can be formed on at least a portion of the exposed surface. The corrosion-resistant base layer can be formed by creating an oxide layer on the exposed surface of the substrate and applying a first primer coating to the oxide layer. A protective topcoat can be formed on the at least one portion of the corrosion-resistant base layer.The process for forming the protective topcoat can include applying a second primer coating to at least a section of the first primer coating and depositing a sputtered metallic film onto the second primer coating using a physical vapor deposition technique. The sputtered metallic film can be deposited with a thickness of approximately 5 nm to approximately 15 nm. The process can further include applying a clear coat over at least a section of the metallic film. According to various aspects, each of the first and second primer coatings comprises at least one electrostatic coating and one powder coating.

[0015] Depending on certain other aspects, the process may further include identifying corrosion-prone areas of the exposed surface before the corrosion-resistant base layer is formed on the exposed surface. The metal or alloy substrate is arranged on a support frame element. Thus, the process may include aligning one or more support regions of the support frame element with predetermined contact regions of the substrate, the predetermined contact regions being located outside the corrosion-prone areas. The corrosion-resistant base layer can then be formed on a section of the exposed surface. The oxide layer can be created on the exposed surface of the substrate by immersing the substrate in an electrolyte bath while it rests on the support elements of the support frame.The support frame element can be designed to serve as a conductive electrode, such as a working electrode / cathode.

[0016] Further applications and various methods for improving the corrosion protection of light metal workpieces and valve metals will become apparent from the description provided herein. The description and specific examples in this summary are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present teachings become more understandable through the detailed description and the accompanying drawings, whereby: Fig. 1 a front plan view of an exemplary wheel arrangement in accordance with various aspects of the present disclosure; Fig. 2 a cross-sectional view of the wheel arrangement along line 2-2 of Fig. 1 is; Fig. 3 is a simplified schematic representation illustrating various coatings which can be applied to a metal matrix in accordance with various aspects of the present disclosure; Fig. 4 A cross-sectional view of the wheel arrangement, viewed as that of Fig. 2, which also includes a tire as part of the wheel assembly; Fig. 5 a schematic view of a support frame for receiving a light alloy wheel assembly during a coating process such as a microarc oxidation technique, wherein the contact points with the wheel workpiece are arranged on the least corrosion-prone regions, in accordance with certain aspects of the present disclosure; Fig. 6 a side view of the support frame and the light alloy wheel arrangement in Fig. 5 is; Fig. 7 is a light alloy control arm which can be coated for improved corrosion protection in accordance with certain aspects of the present disclosure; and Fig. 8 is a light metal door leaf which can be coated for improved corrosion protection in accordance with certain aspects of the present disclosure.

[0018] Note that the figures shown herein are intended to serve as examples of the general characteristic features of the materials, processes, and devices among those of current technology for the purpose of describing certain aspects. These figures may not accurately represent the characteristic features of any particular aspect and are not necessarily intended to define or limit specific embodiments within the scope of protection of this technology. Furthermore, certain aspects may embody features from a combination of figures. DETAILED DESCRIPTION

[0019] The following description of the various embodiments is purely illustrative and is in no way intended to limit the disclosure, its application, or uses. As used herein, the phrase "at least one of A, B, and C" is to be interpreted as referring to a logic (A or B or C) that employs a non-exclusive logical "or." It should be noted that steps within a procedure may be performed in different orders without altering the principles of the present disclosure. The disclosure of domains includes the disclosure of all values ​​and further subdivided domains within the entire domain.

[0020] The headings (such as "Background" and "Summary") and subheadings used herein are intended only for the general organization of the topics within this disclosure and are not intended to limit the disclosure of the technology or any aspect thereof. The mention of several embodiments with specified features is not intended to preclude other embodiments with additional features or other embodiments incorporating different combinations of the specified features.

[0021] As used herein, the word "include" and its variants are not intended to be restrictive, so that the inclusion of items in a list does not imply the exclusion of other similar items that may also be expedient in the materials, compositions, devices, and processes of this technology. Likewise, the expressions "may" and "may under certain circumstances" and their variants are not intended to be restrictive, so that the statement that an embodiment may or may include certain elements or features does not exclude other embodiments of the present technology that do not include such elements or features.

[0022] Spatially related terms such as "inner," "outer," "below," "under," "lower," "above," "upper," "on," and their variants may be used herein to simplify descriptions and to describe the relationship of one element or feature to one or more other elements or features. Spatially related terms may include different orientations of the device in use or operation. As used herein, when a coating, layer, or material is "applied," "applied over," "formed thereon," "deposited thereon," etc., to another substrate or object, the added coating, layer, or material may be applied, formed, or deposited on the entire substrate or object or on at least a portion of the substrate or object.

[0023] The comprehensive teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of protection of the disclosure is not intended to be limited in this way, since further variations will become apparent to the skilled person after studying the patent description and the subsequent claims.

[0024] The present technology relates to generally improved surface coatings for light metal workpieces and valve metals. As used herein, the term "valve metal" refers to a metal or metal alloy that can self-coat with nanoporous oxide films. The resulting oxide layer formed on a valve metal can readily provide a degree of corrosion protection, as it creates a physical barrier between the metal and a corrosive environment. However, it may not be aesthetically pleasing and may not provide adequate corrosion resistance for light metal workpieces such as wheels.

[0025] Exemplary valve metals suitable for the present technology include aluminum, magnesium, titanium, zirconium, hafnium, chromium, cobalt, molybdenum, vanadium, tantalum, and mixtures and alloys thereof. As is known in the engineering field, valve metals can exhibit electrical rectification behavior in an electrolytic cell, and for a given applied current, they will withstand a higher potential when anodically charged than when cathodically charged. Depending on certain aspects, a workpiece may comprise a light or valve metal such as magnesium or aluminum. Depending on certain other aspects, the workpiece may comprise magnesium with alloys and matrix composites thereof. A magnesium matrix composite comprises a metal matrix (e.g., magnesium or a magnesium alloy) with a reinforcing phase or material dispersed therein.Suitable reinforcement materials include conventional reinforcement particles, powders, fibers, fiber crystals, and the like.

[0026] According to various aspects, the present teachings envision a light metal workpiece, such as a valve metal or metal alloy with improved surface protection. According to certain aspects, the light metal workpiece can be a component exposed to a corrosive environment. For example, the light metal workpiece can be a component of a vehicle, such as an automobile. With regard to Fig. 1. According to one aspect of the present disclosure, the light metal workpiece can be a wheel 10. According to certain variants, the light metal workpiece wheel 10 can be made of aluminum, magnesium, or an alloy. It should be noted that the technology of the present disclosure can generally be used with any wheel design or, as mentioned above, any other workpiece or component that can be conceived as being made of a valve metal, which may have an exposed surface that is subject to a corrosive environment. For illustrative purposes, the wheel 10 can generally be a unitary element or optionally be provided with a central section 12 coupled to an outer wheel section 14, as shown.The outer wheel section 14 can comprise a rim 16 and can also include one or more spokes 18 extending from the rim 16 in a generally radial direction towards the central wheel section 12. The wheel section 12 can include a central opening 20 suitable for a wheel cover (not shown) and can define one or more wheel bolt holes 22 suitable for mounting the wheel 10 on a vehicle.

[0027] Referring to Fig. 2, which shows a cross-sectional view of Fig. If the wheel 10 is located along line 2-2, it can have an inside 10a and an outside 10b. The inside 10a generally indicates the side of the wheel 10 facing the vehicle, and the outside 10b generally indicates the side of the wheel 10 facing away from the vehicle and visible when the wheel 10 is attached to the vehicle.

[0028] According to various aspects, the wheel 10 or other light metal workpiece comprises a metal or alloy matrix with an exposed surface. Fig. Figure 3 is a simplified schematic representation illustrating various coatings that can be applied to a section of, or the entire, exposed surface of, a metal matrix in accordance with various aspects of the present disclosure. The coatings and treatments discussed herein can be applied to the entire workpiece or selected sections thereof. For example, both the inner surface 10a and the outer surface 10b of a wheel can be subjected to methods of the present teachings that apply improved corrosion protection coatings; however, it may also be desirable to apply only a specific coating or layers to the visible outer surface 10b.

[0029] Reference number 30 of Fig. 3 generally indicates the material comprising a light metal, such as a metal matrix encompassing the light metal, which initially has an exposed metal surface 30a. The light metal workpiece with the exposed surface 30a can be subjected to various cleaning processes known in the technical field, including degreasing, descaling, neutralization, and similar washing processes. Depending on various aspects, a corrosion-resistant base layer 32 can be applied to the metal or metal matrix, followed by a protective and visually appealing top layer 40. As in Fig. As shown in Figure 3, a pretreatment layer 34 can be applied to or formed on the exposed surface 30a. The pretreatment layer 34 can, for example, be a corrosion-resistant oxide layer formed on the exposed surface 30a using a microarc oxidation or plasma electrolytic technique. A first primer coating 36 can be applied to the oxide-formed pretreatment layer 34 and can be designed to seal the pretreatment layer 34. Then, a second primer coating 42 can be applied to the first primer coating 36 as part of the protective topcoat 40. As explained in more detail below, the first primer coating 36 and the second primer coating 42 can comprise at least one electrostatic coating and one powder coating.A metallic film 44 can be applied to the second primer coating 42 to give a highly reflective, refined appearance. A clear coat 46 can then be applied over at least a section of the metallic film 44 (e.g., the outer surface 10b) as a final protective barrier. As is known in the engineering field, the clear coat 46 can comprise one or more coatings that impart a desired color / hue, sheen, and / or gloss to the workpiece.

[0030] As is well known in the technical field, micro-arc oxidation techniques (MAO), sometimes also referred to as plasma electrolytic oxidation (PEO), spark anodizing, discharge anodizing, or by other combinations of these terms, can involve the use of various electrolytes operating in an electrolytic cell to create a porous oxide layer or a porous ceramic oxide layer on the exposed surface of a metal matrix. For example, if the workpiece is aluminum, the oxide layer or ceramic oxide layer can be formed using MAO or PEO techniques to obtain a layer of aluminum oxide or an aluminum ceramic, the composition of which can vary depending on the electrolyte and other materials present.There are many patented and commercial variations of the MAO and PEO processes, including those described in U.S. Patents Nos. 3,293,158; 5,792,335; 6,365,028; 6,896,785; and U.S. Patent Application No. 13 / 262,779, published as U.S. Pub. Pat. App. No. 2012 / 003 1,765, all of which are incorporated herein by reference in their entirety. In one example, the MAO or PEO process can be carried out using a silicate-based electrolyte, which may include sodium silicate, potassium hydroxide, and potassium fluoride.

[0031] As is generally known in the technical field, the presence of micropores and / or cracks on the surface of MAO or PEO coatings can be considered potentially disadvantageous and represent a weakness with regard to corrosion. A higher pore density on the surface of MAO or PEO coatings increases the effective surface area and thus the tendency for a corrosive medium to be adsorbed and concentrated within these pores. However, the presence of a porous outer layer in MAO or PEO coatings can also be advantageous by significantly improving the mechanical interlocking effect, the bonding area, and the stress distribution, resulting in a higher bond strength.With regard to the potential susceptibility to corrosion due to the larger effective surface area and porosity, the pore density, the pore distribution, and the flexibility of the pore connections with the rest of the substrate can be important factors. According to various aspects of this disclosure, the corrosion-resistant base layer 32 (with the pretreatment oxide or ceramic layer 34) can be produced or formed such that it has a controlled and substantially uniform porosity of about 0.1 µm to about 5 µm, about 1 µm to about 3 µm, or about 0.1 µm to about 1 µm. The oxide layer 32 can be produced or formed such that it has a substantially uniform thickness of about 2 µm to about 30 µm, about 4 µm to about 25 µm, or about 5 µm to about 20 µm.

[0032] Regarding the aforementioned potential weakness of MAO or PEO coatings, a sealing coating is applied to the porous oxide or ceramic layer resulting from the MAO or PEO process. The present disclosure, as such, applies a first primer coating 36 over the oxide pretreatment layer 34. Depending on various aspects, the first primer coating 36 can be an electrostatic coating layer or an electrostatic layer applied to the oxide pretreatment layer 34 using an electrocoating technique (“E-coating” or electrophoretic coating), designed to seal the oxide pretreatment layer 34 and provide increased adhesion of optional additional layers applied thereon. As an alternative to the E-coating, the first primer coating 36 can comprise a powder material coating.Before applying the first primer coating 36, the workpiece can optionally be washed or immersed in deionized water.

[0033] In aspects where an E-coating is used as the first primer coating 36, it should be understood that there can be several pore-closing systems that can be used in conjunction with the MAO and PEO processes, and these can include a wide variety of polymers and resins, including but not limited to fluoropolymers, acrylics, epoxies, polyesters, polysiloxanes, and polyvinylidene fluoride (PVDF). These materials can be applied in the form of electrostatically sprayed coatings by electrophoretic deposition or using known dip or wet spraying techniques. In a currently preferred aspect, which can be used with magnesium workpieces such as magnesium or magnesium alloy wheels, an epoxy resin, e.g., EPOXY RESIN KATAPHORESIS COATING (EED-060M), commercially available from Unires or its affiliate Tianjin Youli Chemical Co., Ltd., Tianjin, China, can be used.In general, the first primer coating 36 will not contain a significant amount of a chemically active agent. Depending on various aspects, the E-coating treatment process can take approximately 0 to approximately 3 minutes using a voltage between approximately 160 V and approximately 220 V, and it can be cured at a temperature between approximately 160 °C and approximately 180 °C for a curing time of approximately 20 to approximately 30 minutes. According to various aspects, the first primer coating 36 can be an E-coating or a powder material coating applied with a substantially uniform thickness of about 1 µm to about 200 µm, or from about 50 µm to about 150 µm, or from about 70 µm to about 130 µm, or from about 80 µm to about 120 µm, and, according to various aspects, a thickness of about 100 µm.

[0034] If the first primer coating 36 comprises an electrostatically applied coating, the approaches adopted by the present teachings include that the first primer coating 36 is applied to the oxide pretreatment layer 34 within less than about 30 hours and preferably less than about 24 hours, less than about 20 hours or less than about 16 hours after the production or formation of the oxide or ceramic oxide pretreatment layer 34.

[0035] As mentioned above, the first primer coating 36 can be a powdered coating material. Powder coating materials suitable here as the first primer coating 36 can include thermoplastic or reactive polymers commonly used in the engineering field, which are typically solid at room temperature. Most powders are reactive, one-component systems that liquefy, flow, and then crosslink upon heat treatment. Common polymers that can be used as powder coating materials include polyester, polyurethane, polyester-epoxy (known as hybrid), straight-chain epoxy (thick-film epoxy), and acrylics.

[0036] As an example, the method for applying the powder coating may include electrostatically spraying a wet, black resin powder onto the oxide pretreatment layer of a heated substrate, the resin powder being supplied at a voltage of about 40 kV to about 50 kV or about 45 kV and a current of about 0.4 A to about 0.6 A or about 0.5 A. The methods of the present teachings further include curing and densifying each powder coating layer by placing the workpiece or substrate in a heated environment at a temperature of about 180 °C to about 200 °C or about 190 °C for a period of about 15 minutes to about 25 minutes or about 20 minutes.

[0037] As is well known in the technical field, a wide variety of materials and encapsulation processes are commercially available, employing diverse strategies to achieve varying degrees of durability and corrosion resistance. The approaches adopted in the present teachings include the application of a protective topcoat 40, which may involve applying a second primer coating 42 over the first primer coating 36. Depending on certain aspects, the entire process can be carried out in a single assembly line. Alternatively, the corrosion-resistant primer 32 can be applied in a first assembly, and the protective topcoat 40 can be applied in a second assembly.

[0038] Depending on various aspects, the second primer coating 42 can be an e-coating or a powder coating applied with a substantially uniform thickness of about 1 µm to about 200 µm, or about 50 µm to about 150 µm, or about 70 µm to about 130 µm, or about 80 µm to about 120 µm, or about 100 µm. Depending on certain aspects, the first primer coating 36 can be applied to the oxide pretreatment layer 34 with a first thickness, and the second primer coating 42 can be applied to the first primer coating 36 with a second thickness. The first thickness can be substantially equal to or less than the second thickness. The second primer coating 42 can be made of the same material as the first primer coating 36, or the material can be different from that of the first primer coating 36.Both primer coatings can be electrolytic coatings, both primer coatings can be powder coatings, or one of the primer coatings can be an electrolytic coating while the other is a powder coating. Furthermore, multiple layers of each coating can be applied. In cases where the first primer coating 36 is an electrolytic coating and the second primer coating 42 is a powder coating, it may be advantageous for the powder coating to have a thickness much greater than that of the electrolytic coating to provide increased corrosion protection. Thus, the approaches adopted by the present teachings may include applying the second layer or coating 42 with a thickness approximately 1.5 to approximately 10 times greater than the thickness of the first coating 36.Therefore, according to certain aspects, for example, a first primer coating 36 with a thickness of about 15 µm can be used with a second primer coating 42 with a thickness of about 25 µm to about 150 µm.

[0039] According to various aspects, the methods of the present teachings may include heating the workpiece or substrate, which has the first primer coating 36, to a temperature of about 80 °C to about 100 °C before applying the second primer coating 42.

[0040] According to a currently preferred approach, which can be used with magnesium workpieces that have a first epoxy primer coating, the second primer coating can be a powder coating containing primarily a high polyurethane content. For example, it can be a high-gloss TIGER DRYLAC® "wet black" powder coating 049 / 80036, commercially available from TIGER Coatings GmbH & Co, Austria.

[0041] A variety of deposition methods can be used to apply the metal compositions that form the metal layer or metal film 44 in the cover layer section 40. A preferred method for depositing the metal film 44 on the second primer coating 42 is one using sputtering techniques. Sputtering is an ion-assisted physical vapor deposition (PVD) technique for depositing the films by sputtering. This typically involves propelling a material from a "target," which is a source, onto a "substrate," such as the primer coating (e.g., the second primer coating 42) on a workpiece. Depending on certain aspects, physical vapor deposition can be atmospheric plasma-assisted or ion beam-assisted.

[0042] Preferred metals for the sputtered metal film 44 include those that impart a bright, metallic appearance, e.g., chromium (Cr) or compounds of Cr such as chromium nitride (CrN) and nickel (Ni) or compounds of Ni. As those skilled in the art can see, the metal film composition may also include mixtures of the metals mentioned above.

[0043] It is conceivable that various ion-assisted PVD devices can be used to apply the metal film 44. An exemplary device may comprise a deposition chamber and one or more electron guns for depositing the metal film. As is known in the technical field, the device can be operated in an ultra-high vacuum according to certain aspects. The substrate to be coated with the metal film can first be placed in a chamber, and the pressure is reduced. A first crucible in the chamber can contain the metal to be deposited. If a combination of metals is to be deposited, a second metal can be contained in a second crucible, which is deposited over the first layer, forming a second layer. Another available option is to deposit a combination of metals simultaneously.Metals can be deposited on the second primer coating 42 at a rate of approximately 0.10 nm / s to a thickness of more than approximately 1 nm and less than approximately 50 nm, which can be monitored by thickness monitoring devices as are known in the technical field. The metal film 44 can be deposited on the second primer coating 42 with an ultra-thin thickness of less than approximately 50 nm, optionally less than approximately 40 nm, or, depending on certain aspects, from approximately 25 nm to approximately 30 nm. Depending on certain aspects, it may be possible to apply a very thin layer, e.g., an ultra-thin layer on the order of approximately 1 nm to approximately 20 nm, from approximately 5 nm to approximately 15 nm, or approximately 10 nm, and still achieve good surface coverage, substantially uniform coverage, and good adhesion.Therefore, the use of PVD allows the metal film 44 to be deposited very evenly, smoothly and in a thin layer on the second primer coating 42 substrate.

[0044] Other suitable PVD methods may include magnetron sputtering, in which a target (the second primer coating 42) is bombarded with a sputter gun in an argon ion atmosphere while the substrate is charged. The sputter gun generates a plasma of metal particles and argon ions that are pulse-driven to coat the substrate. Still other methods for depositing the metal film 44 may include electron beam evaporation, in which the substrate is heated in a vacuum chamber (of about 10 -3 up to 10 -4 Torr or approximately 1.3 × 10 -1 Pa up to 1.3 × 10 -2Pa) is contained within, and a metal vaporization material is heated by a charged electron beam, causing it to vaporize and then condense on the target substrate. The metal film 44 can also be applied by electroplating (e.g., electrolytic deposition), electroless deposition / coating, or pulsed laser deposition. Depending on the material of the second primer coating, it is also conceivable that the metal film could be applied by electroplating (e.g., electrolytic deposition) or pulsed laser deposition.

[0045] According to certain aspects, the methods for providing an improved surface coating on a light metal or alloy substrate may include the process and treatment as discussed above, but they may further include specifically identifying corrosion-prone or corrosion-prone areas on the exposed substrate of the workpiece when it is used in operation and exposed to corrosive conditions. According to certain aspects of this disclosure, the methods for treating the light metal substrate may include designing a support structure with predetermined support regions that will be in contact with the substrate at predetermined contact points. Such a support structure design may be particularly advantageous for use during the oxide layer formation process (formation of the pretreatment layer 34) on the exposed surface of the substrate.Thus, the support structures can be designed such that the support regions correspond to the regions on the substrate that are at least susceptible to corrosion, where contact is made (at predetermined contact points or regions on the substrate). According to such a variant, the contact points or regions on the substrate may not have such a thick or complete coverage of the protective coatings, including the oxide pretreatment layer 34. This makes the potentially corrosion-prone contact regions on the substrate the least susceptible to corrosion.

[0046] Fig. 4 is, for example, another view of the wheel arrangement in the Fig. 1 and Fig. 2, but also includes a tire 50, which is arranged around the wheel assembly along the rim 16 of the outer wheel section 14 of the wheel 10. The exposed surfaces of the light alloy wheel 10 exhibit different susceptibility to corrosion and are in Fig. 4 are therefore designated with other contours. The first surface regions 60 on the exposed surface or substrate of the wheel 10 exhibit the highest susceptibility to corrosion, as they are exposed to an external corrosive environment on the outside 10b and also have galvanic contact with dissimilar metals in other components in the wheel assembly 10. For example, the wheel bolt holes 22 may have wheel fastening nuts (not shown) made of dissimilar metals, such as steel, in direct contact with the substrate. The combination of the strongest exposure to corrosive substances and the galvanic contact makes the first surface regions the most corrosion-prone regions on the workpiece substrate of the wheel 10.

[0047] The second surface regions 62 are also susceptible to corrosion, but are located on the inner side 10a and thus along the better protected rear side of the wheel 10. Furthermore, there is less galvanic contact exposure along these second surface regions 62. Therefore, the second surface regions 62 exhibit a lower susceptibility to corrosion than the first surface regions 60.

[0048] Finally, the wheel 10 defines a third surface region 64, which is / are defined along the rim 16 of the outer wheel section 14 where the tire 50 is located. The third surface region 64 is / are the least corrosion-prone region(s) on the wheel 10, as it has / have reduced exposure to the external environment and is / are thus protected from corrosive substances and also experiences little or no galvanic contact. Thus, the third surface regions 64 of the wheel 10 exhibit the lowest degree of susceptibility to corrosion compared with the first surface regions 60 and the second surface regions 62.

[0049] During the formation process, particularly during MAO and / or PEO processing techniques, the workpiece is mounted on an electrically conductive support frame and then exposed to an electrolyte (e.g., by placing or immersing the support frame and the workpiece in an electrolyte bath). An electrical potential or current is generated, which flows from the electrically conductive support frame to the workpiece to facilitate the formation of the pretreatment layer 34 in the electrolyte bath. However, the deposited oxide or other formed layers may be thinner or absent in regions where physical contact is established between the frame and the workpiece, because the contact point is not exposed to as much electrolyte and also forms part of the electrical conduction path between the workpiece and the frame (which acts as an electrode during the process).

[0050] Thus, the methods for providing an improved surface coating on a light metal or alloy substrate, according to certain aspects, include selecting one or more regions of the workpiece substrate as contact points with the support frame, wherein the contact points have a lower risk of exposure to corrosive substances or galvanic conditions during operation or use. Thus, in the example of the wheel assembly, 10 of Fig. 4. The areas on the exposed substrate of the workpiece that are particularly susceptible to or prone to corrosion are the first surface regions 60 and the second surface regions 62. A support frame can therefore be specially designed to have predetermined support regions that will come into contact or engage with the predetermined contact points on the substrate. Here, the predetermined contact points can be located in the third surface regions 64, which have the lowest degree of susceptibility to corrosion and galvanic contact compared with the first surface regions 60 and the second surface regions 62. It should be noted that, according to certain variants, the predetermined contact points on the substrate or the workpiece can be selected to be located in regions with medium levels of corrosion susceptibility, e.g.,the second surface regions 62, whereby the extent of exposure to corrosive substances or galvanic conditions (with metals of different galvanic potential) of these second surface regions 62 can be minimized. However, the regions with the highest risk of corrosion susceptibility (the first surface regions 60) are not selected as contact points when designing the support structure.

[0051] In the Fig. 5 and Fig. Figure 6 shows an exemplary and simplified tooling system for illustration. Such a tool can, for example, include a support frame 70, which can be used in a process to create an improved surface coating on a light metal or alloy substrate. The tool for an MAO process includes a conductor track to supply electricity through one or more support points for holding the workpiece (e.g., in an electrolyte). In the Fig. 5 and Fig. 6 is the light metal or alloy workpiece with a substrate to be protected, the wheel 10. The support frame 70 has a conductive body 72 attached to extension elements 74 and a lower support platform 76. The extension elements 74 can be used to position the support frame 70 within an electrolyte bath 80. A plurality of support regions 78 are arranged on the lower support platform 76 to establish contact with and engage the wheel 10. According to certain variants, the support frame 70 defines a plurality of support regions 78, and the workpiece substrate (wheel 10) is placed on the support frame 70 by aligning the support regions 78 with predetermined contact regions of the substrate (wheel 10).More specifically, the support regions 78 are designed to create contact points corresponding to the third surface regions 64 (the least corrosion-prone regions) on the rim 16 of the outer wheel section 14 of the wheel 10. According to certain variants, the wheel 10 is a magnesium wheel, and the predetermined contact regions are located on the outer rim 16 of the magnesium wheel.

[0052] The support frame 70 with the wheel 10 mounted on it can be immersed in the electrolyte bath 80 or brought into contact with it in another way. According to certain variants, the support frame 70 is an independent component that can be removed from the electrolyte bath 80, as shown in the Fig. 5 and Fig. Figure 6 shows that, according to other variants, the support frame 70 is integral with a structure containing the electrolyte bath (not shown). The support frame 70 can be made of an electrically conductive material and thus serve as a working electrode when a potential is applied (while it is in contact with the electrolyte and the workpiece). The support frame 70 can, for example, serve as a conductive cathode during at least one of a microarc oxidation process and a plasma electrolytic oxidation process. The arrows in the Fig. 5 and Fig. Figure 6 shows the path of the electricity through the workpiece wheel 10.

[0053] According to other variations, the methods of the present disclosure create an improved corrosion protection surface coating on a metal or alloy substrate such as any of those discussed above, wherein the substrate is a control arm suspension component, as in Fig. Figure 7 shows that motor vehicles with steerable wheels have wheel axles mounted on pivot elements which are held between an upper and a lower wishbone (also known as a triangular wishbone or triangular control arm). An exemplary such wishbone 90 is attached to a body or frame member of a vehicle by means of mounting brackets (not shown) that receive fastening bolts through them. Thus, a wishbone 90 has a plurality of connection points with other adjacent assemblies. For example, one type of connection point is located where fastening bolts (not shown) pass through a plurality of bushings 92 at a lateral end 94 of the wishbone 90 to provide the ability to pivot the wishbone 90 (e.g., on the vehicle body or frame member).Another connection point is located at a distal end 96, opposite the lateral end 94, and is used to connect to a pivot element (not shown) via a joint 98 for holding and supporting a wheel. The control arm 90 can be made of a light metal or a metal alloy such as magnesium. The bushings 92 and the joint 98 are thus connection points in contact with other metals and therefore different galvanic potentials, which define fourth surface regions 97 that are at higher risk of corrosion. Furthermore, a lower side 99 of the control arm 90 may be exposed to an external environment and thus to corrosive substances.

[0054] According to such a variant, a support frame can therefore be specially designed to have predetermined support regions that are in contact with or engage with the predetermined bearing points on the control arm substrate. Here, the predetermined bearing points can be any regions outside the connection points that correspond to the fourth surface regions 97 or the lower side 99 of the control arm 90.

[0055] According to other variations, the methods of the present disclosure create an improved corrosion-resistant surface coating on a metal or alloy substrate such as any of those discussed above, wherein the substrate is a component in a lightweight automotive door assembly 100. Referring to Fig.Figure 8 shows an inner door leaf 102 before various fittings and other assemblies are installed on the door casing to form the door assembly. The door leaf 102 can be made of a light metal such as magnesium, aluminum, or alloys thereof. The door leaf 102 includes an inner region 104 that defines a lower section 106 connected to a front hinge post 110. The door leaf 102 can also have an inner beltline 112 and, optionally, an outer beltline 114. A mirror bracket 116 can be connected to the inner beltline 112.

[0056] A rear pillar 120 is arranged on a second side of the inner door leaf 102, opposite the front hinge pillar 110, where a locking bracket (not shown) may be located. A side impact guard 130 extends between the front hinge pillar 110 and the rear pillar 120. The side impact guard 130 may be made of a different metal than the inner door leaf 102 (e.g., steel) and is attached or mounted to it, for example, by means of fasteners 132. Thus, fifth surface regions 140 are defined where the door leaf 102 may come into contact with other metal components, which therefore have a higher risk of galvanic reaction and corrosion, e.g., where the door leaf 102 is in contact with the side impact guard 130.

[0057] Sixth surface regions 142 are shown along the lower section 106 of the door leaf 102, and regions corresponding to the inner belt line 112 and the outer belt line 114 are shown, where the door leaf may be exposed to corrosive conditions. Thus, for methods of forming a protective coating over the door, a support frame can be specially designed to have predetermined support regions that will contact or engage with predetermined bearing points on the door leaf substrate. Here, the predetermined bearing points can be those on the door leaf 102 that are located outside either the fifth surface regions 140 or the sixth surface regions 142. Thus, the improved surface coating is formed on the least corrosion-prone regions of the door leaf 102.

[0058] As experts will recognize, the present methods can be used to improve corrosion protection for a variety of light metal components, and are not limited to the exemplary embodiments described above.

[0059] Thus, according to certain other aspects, the present teachings comprise a method for providing an improved surface coating on a metal or alloy substrate of a workpiece. The method includes providing a metal or alloy substrate with an exposed surface. Such a method may include identifying corrosion-prone areas of the exposed substrate. The metal or alloy substrate is arranged on a support frame element. The method may therefore include aligning one or more support regions of the support frame element with predetermined contact regions of the substrate, wherein the predetermined contact regions are located outside the corrosion-prone areas (thus avoiding contact of the support element of the support frame element with the corrosion-prone areas of the substrate).A corrosion-resistant base layer can be formed on at least a portion of the exposed surface. This base layer can be formed by creating an oxide layer on the exposed surface of the substrate and applying a first primer coating to the oxide layer. Alternatively, the oxide layer can be created on the exposed surface of the substrate by immersing the substrate in an electrolyte bath while it rests on the support elements of the frame. Creating the oxide layer on the exposed surface of the substrate can utilize at least one microarc oxidation process and one plasma electrolytic oxidation process. The frame can be configured to serve as a conductive electrode, such as a working electrode / cathode, during at least one microarc oxidation process and one plasma electrolytic oxidation process.

[0060] In certain variants, the support frame element is an independent component that can be removed from the electrolyte bath. In other variants, the support frame element is integral with a structure containing the electrolyte bath. The substrate may include a magnesium wheel, and the predetermined contact regions are located on an outer rim or other area of ​​low corrosion resistance on the magnesium wheel. In certain other variants, the substrate includes a magnesium wishbone suspension component, and the predetermined contact regions are located outside the wishbone connection points or the lower / floor surface. In still other variants, the substrate includes a magnesium door component, and the predetermined contact regions are located outside the upper and lower edges of the door and the connection points with the impact protection or other metal components in the door assembly.

[0061] The protective coating is formed in accordance with the embodiments and methods described above. Thus, the protective topcoat is formed on at least a section of the corrosion-resistant base coat. The method for forming the protective topcoat may include applying a second primer coating to at least a section of the first primer coating and depositing a sputtered metallic film onto the second primer coating using a physical vapor deposition technique. The sputtered metallic film can be deposited with a thickness of approximately 5 nm to approximately 15 nm. The method may further include applying a clear coat over at least a section of the metallic film.According to various aspects, each of the first primer coating and the second primer coating includes at least one electrostatic coating and one powder material coating.

[0062] It should be understood that the present technology is neither dependent on nor limited to any particular type of material or manufacturing process, and the materials and processes can be modified as desired based on the intended results. It has been shown that the light metals and alloys coated with the improved surface protection coatings disclosed herein exhibit superior adhesion properties, resistance to chipping, thermal shock resistance, and minimal scratch corrosion.

[0063] The preceding description of the embodiments was provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but may be interchangeable and used in a selected embodiment, even if not specifically shown or described. These may also be modified in various ways. Such variations are not to be considered a deviation from the disclosure, and all such modifications are intended to be included within the scope of protection of the disclosure.

Claims

[1] Light metal workpiece with improved surface protection, comprising: a light metal alloy or matrix having an exposed surface, the light metal alloy or matrix comprising at least one valve metal selected from the group consisting of aluminum, magnesium, titanium, and mixtures thereof; a corrosion-resistant base layer (32) applied to at least a portion of the exposed surface, the corrosion-resistant base layer comprising: a pretreatment layer (34), wherein the pretreatment layer (34) comprises an oxide layer formed on the exposed surface, and wherein the oxide layer is formed with a thickness of 5 µm to 20 µm; and a first primer coating (36) applied to the pretreatment layer (34), wherein the first primer coating (36) comprises at least one of an electrostatic coating and a powder material coating, and wherein the first primer coating (36) is applied to a thickness of 50 µm to 150 µm; a protective cover layer (40) applied to the at least a portion of the corrosion-resistant base layer (32), the protective cover layer (40) comprising: a second primer coating (42) applied to the first primer coating (36), wherein the second primer coating (42) comprises at least one of an electrostatic coating and a powder material coating, and wherein the second primer coating (42) is applied to a thickness of 50 µm to 150 µm; and wherein the electrostatic coating of the first primer coating and the second primer coating consists of fluoropolymers, acrylic, epoxy, polyester, polysiloxanes or polyvinylidene fluoride (PVDF), and wherein the powder material coating of the first primer coating and the second primer coating consists of polyester, polyurethane, polyester epoxy, straight-chain epoxy or acrylics, and a sputtered metallic film (44) deposited on at least a portion of the second primer coating (42) using a physical vapor deposition technique, the sputtered metallic film (44) being deposited to a thickness of 5 nm to 15 nm; and a clear coat layer (46) applied to at least a portion of the metallic film (44), wherein the first clear coat layer (46) is applied to a thickness of 20 µm to 30 µm. [2] A light metal workpiece according to claim 1, which is a magnesium metal wheel comprising: a magnesium metal matrix having the exposed surface; a magnesium oxide ceramic layer formed as the corrosion-resistant base layer (32) on at least a portion of the exposed surface, the oxide layer being formed to a thickness of 5 µm to 20 µm; the first primer coating (36) applied to at least a portion of the magnesium oxide ceramic layer, wherein the first primer coating (36) is applied to a thickness of 50 µm to 150 µm; and the second primer coating (42) applied to at least a portion of the first primer coating (36), the second primer coating (42) being applied to a thickness of 50 µm to 150 µm; the sputtered metallic film (44) deposited using a physical vapor deposition technique on at least a portion of the second primer coating (42), wherein the sputtered metallic film (44) is applied to a thickness of 5 nm to 15 nm; and the clear coat layer (46) applied to at least a portion of the metallic film (44), wherein the first clear coat layer (46) is applied to a thickness of 20 µm to 30 µm. [3] A method of providing an improved surface coating on a metal or alloy substrate, the method comprising: a corrosion-resistant base layer (32) is formed on at least a portion of an exposed surface of a light metal or alloy substrate comprising at least one valve metal selected from the group consisting of aluminum, magnesium, titanium, and mixtures thereof, comprising: an oxide layer (34) on the exposed surface of the substrate, which comprises immersing the substrate in an electrolyte bath and placing the substrate on a support frame element, the oxide layer being formed with a thickness of 5 µm to 20 µm; and a first primer coating (36) is applied to the oxide layer, wherein the first primer coating (36) comprises at least one of an electrostatic coating and a powder material coating, wherein the first primer coating (36) is applied to a thickness of 50 µm to 150 µm, wherein the electrostatic coating is applied using an electrocoating technique, and wherein the powder material coating is electrostatically applied to the oxide layer; a protective cover layer (40) is formed on the at least a portion of the base layer (32), comprising: a second primer coating (42) is applied to the first primer coating (36), wherein the second primer coating (42) comprises at least one of an electrostatic coating and a powder material coating, and wherein the second primer coating (42) is applied to a thickness of 50 µm to 150 µm, wherein the electrostatic coating is applied using an electrocoating technique, and wherein the powder material coating is applied electrostatically to the first primer coating (36); and wherein the electrostatic coating of the first primer coating and the second primer coating consists of fluoropolymers, acrylic, epoxy, polyester, polysiloxanes or polyvinylidene fluoride (PVDF), and wherein the powder material coating of the first primer coating and the second primer coating consists of polyester, polyurethane, polyester epoxy, straight-chain epoxy or acrylics, and a sputtered metallic film (44) is deposited on the second primer coating (42) using a physical vapor deposition technique, the sputtered metallic film (44) being applied with a thickness of 5 nm to 15 nm; and a clear coat layer (46) is applied to at least a portion of the sputtered metallic film (44), wherein the first clear coat layer (46) is applied with a thickness of 20 µm to 30 µm. [4] The method of claim 3, wherein depositing the substrate is performed on the configured support frame member that serves as a conductive cathode during at least one of the micro-arc oxidation process and the plasma electrolytic oxidation process. [5] The method of claim 3, further comprising identifying the corrosion-prone areas of the exposed surface, wherein the support frame member defines a plurality of support regions, and depositing the substrate on the support frame member comprises aligning the support regions with predetermined contact regions of the substrate while avoiding contact with the corrosion-prone areas. [6] The method of claim 5, wherein the substrate is a magnesium wheel, and wherein the predetermined contact regions are disposed on an outer hub of the magnesium wheel. [7] The method of claim 5, wherein the substrate comprises a magnesium component, as a control arm suspension component or a door component.

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