Preparation method for PVD (Physical Vapor Deposition) corrosion-resistant coating on surface of aluminum alloy

Abstract

The invention discloses a preparation method of a PVD (physical vapor deposition) corrosion-resistant coating on the surface of an aluminum alloy, and belongs to the technical field of corrosion-resistant coatings, the method comprises the following steps: pretreating and cleaning an aluminum alloy matrix, depositing a gradient functional layer by adopting a physical vapor deposition technology, and periodically pausing in the growth process of the gradient functional layer, switching to a reactive sputtering mode for in-situ deposition of an ultrathin oxide hole sealing layer to form a composite structure with alternate gradient layers and hole sealing layers; and then a self-healing outer layer containing corrosion inhibitor microcapsules and an outermost color layer or hydrophobic functional layer are deposited on the surface of the composite structure. Through collaborative integration of gradient component design, periodic in-situ deep hole sealing and a self-repairing function, coating microdefects are effectively blocked, the film-substrate binding force, the corrosion resistance and the damage tolerance are remarkably improved, the technological process is green and environmentally friendly, and the method is suitable for protection of aluminum alloy parts with the strict requirement for corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of anti-corrosion coating technology, specifically, it relates to a method for preparing a PVD-deposited corrosion-resistant coating on an aluminum alloy surface. Background Technology

[0002] Aluminum alloys, due to their lightweight, high strength, and excellent machinability, are widely used in aerospace, marine engineering, transportation, and consumer electronics. However, aluminum alloys are chemically reactive, especially in humid environments containing chloride ions, where they are highly susceptible to pitting corrosion and intergranular corrosion, severely impacting their structural safety and service life. Therefore, applying high-performance protective coatings to the surface of aluminum alloys has become a key technological approach to ensure their reliable service.

[0003] Traditionally, to improve the adhesion between aluminum alloys and protective coatings and enhance overall corrosion resistance, the industry commonly employs electroplating pretreatment processes, such as zinc immersion followed by copper or nickel plating, to form a dense metallic transition layer on the aluminum alloy surface. Subsequently, hard ceramic coatings such as nitrides and carbides are deposited on top using physical vapor deposition (PVD). While this composite process can partially meet protective requirements, it suffers from inherent drawbacks such as lengthy processes, high energy consumption, and severe environmental pollution caused by the use of electroplating solutions containing heavy metals. Therefore, developing green technologies that can directly deposit high-performance PVD coatings on aluminum alloy surfaces without complex electroplating pretreatment has become an important research direction in this field.

[0004] Currently, the core technological bottleneck in directly applying PVD coatings to aluminum alloy surfaces lies in the contradiction between coating structural defects and long-term corrosion protection. Firstly, conventional PVD coatings tend to form columnar crystalline structures during deposition, with obvious grain boundaries and micropores between the grains. These microscopic defects provide channels for the rapid diffusion of corrosive media, allowing them to reach the coating-substrate interface, inducing interfacial corrosion, and ultimately leading to coating blistering and peeling. Secondly, even with multilayer designs to improve performance, the physical interfaces between layers can themselves become weak points for stress concentration and corrosion propagation.

[0005] To overcome the aforementioned problems, numerous explorations have been undertaken in existing technologies. A common approach is to refine grains or promote the formation of amorphous phases by improving PVD process parameters or doping with specific elements, aiming to increase the density of the coating. However, these methods struggle to completely eliminate the intrinsic defect network at the nanoscale of the coating. Another approach is to design multilayer or gradient structures to disrupt the continuous growth of columnar crystals. While this can extend the corrosion path to some extent, the interlayer interfaces introduce new potential failure risks, and the sealing effect on existing micropores is limited. Furthermore, some studies have attempted to introduce oxide phases into PVD coatings to improve chemical stability. However, how to form a uniform, dense oxide sealing layer in situ within the PVD coating and with good adhesion to the gradient coating without significantly reducing deposition efficiency remains a technical challenge. Moreover, existing coating systems are essentially passive barriers. Once macroscopic damage occurs due to accidental scratches or fatigue, corrosion will rapidly occur and spread from the damaged area, leading to the failure of the overall protective function.

[0006] In summary, existing technological improvement approaches, whether optimizing a single coating composition or constructing a macroscopic multilayer structure with a clear interface, have failed to effectively solve the fundamental problem of in-situ and deep sealing of inherent micro-defects during PVD coating growth. They also lack effective means to integrate and coordinate the design and manufacturing of functions such as composition gradient enhancement, microstructure densification, and long-term service reliability assurance within a single process cycle. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a PVD-deposited corrosion-resistant coating on an aluminum alloy surface.

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows: A method for preparing a PVD-deposited corrosion-resistant coating on an aluminum alloy surface includes the following steps: (1) The aluminum alloy substrate is subjected to sandblasting, polishing, cleaning and vacuum drying to obtain a pretreated substrate; (2) The pretreated substrate is placed in a PVD furnace and subjected to glow discharge cleaning and plasma cleaning in sequence; (3) On the cleaned substrate surface, a functional layer with a continuous gradient composition change is deposited by using physical vapor deposition technology and periodically modulating the reactive gas flow rate and bias voltage; wherein the composition of the functional layer transitions continuously from the metallic state at the bottom to the nitride, oxide or carbide state at the surface. (4) During the deposition of the functional layer in step (3), after every 200 nm to 1000 nm of thickness, physical vapor deposition is paused, and reactive sputtering mode is switched to. In an oxygen-containing atmosphere, at least one of a silicon target, an aluminum target, or a titanium target is sputtered to deposit an oxide sealing layer with a thickness of 5 to 50 nm in situ; the oxide sealing layer is SiO2. x AlO x TiO x One or more of the following constitute a single layer, a mixed layer, or a nanolayer stack; (5) Repeat steps (3) and (4) until the total thickness of the functional layer reaches the predetermined value, thereby forming a composite structure consisting of alternating PVD gradient layers and PVD oxide sealing layers; (6) On the surface of the composite structure consisting of alternating PVD gradient layers and PVD oxide sealing layers, a self-healing outer layer containing microcapsules is deposited, wherein the microcapsules contain corrosion inhibitors. (7) Deposit a color layer or a hydrophobic functional layer on the surface of the self-healing outer layer.

[0009] This invention provides a complete method for preparing PVD composite coatings that can be directly applied to aluminum alloy surfaces. It sequentially integrates three functional modules—gradient composition strengthening, periodic in-situ oxide sealing, and outer self-healing—within a single process cycle, generating a synergistic protective effect. Specifically, the gradient functional layer achieves a smooth transition of physical properties between the coating and the aluminum alloy substrate, significantly improving film-substrate adhesion and fundamentally solving the problem of easy coating peeling. The periodic embedding of a dense oxide sealing layer during gradient layer growth effectively breaks and physically blocks the inherent columnar grain boundaries and microporous defect network of the PVD coating, greatly extending the penetration path of corrosive media and thus significantly improving the intrinsic corrosion resistance of the coating. The outermost microcapsule-containing self-healing functional layer provides the coating with active repair capabilities against accidental mechanical damage, significantly improving the long-term service reliability of the coating under complex working conditions. This method eliminates traditional electroplating pretreatment, making the process green and environmentally friendly. Furthermore, through the synergy of the above multiple mechanisms, a protective coating with excellent comprehensive performance is ultimately obtained.

[0010] Furthermore, the modulation period of the gradient modulation functional layer in step (3) is 50~200 nm, with the reactive gas flow rate changing by 20~80% and the bias voltage changing by 10~50% within each period. By specifically defining the modulation period of the gradient modulation functional layer and the changes in reactive gas and bias voltage, this invention enables precise control over the coating composition and microstructure. This ensures the continuity and smoothness of the gradient transition, avoiding internal stress concentration or weak bonding interfaces caused by abrupt changes in composition, thereby further optimizing the mechanical load-bearing capacity and bonding stability of the coating, and providing a more solid and uniform substrate for the subsequent deposition of the sealing layer and self-healing layer.

[0011] Further, in step (4), the oxide sealing layer is SiO2. x / AlO x or TiO x / AlO x The nanolayers are stacked, with each sublayer having a thickness of 3–15 nm. This invention specifies the oxide sealing layer as SiO₂. x / AlO x or TiO x / AlO x The nanolayered structure leverages the synergistic advantages of the materials. AlO x It possesses excellent chemical inertness and insulation properties, while SiO2... x or TiO x This can further enhance the density and stability of the coating. This nanolayer design can introduce more interfaces to deflect and scatter the diffusion of corrosive media, and may refine the grains through interface effects, thereby achieving superior barrier properties and structural stability compared to a single oxide layer.

[0012] Further, in step (4), the volume ratio of oxygen flow rate to argon flow rate used in the reactive sputtering mode is 1:10 to 1:2, and the sputtering power density is 2~6 W / cm². This invention, by precisely limiting the oxygen-argon flow rate ratio and sputtering power density in reactive sputtering, can accurately control the stoichiometry, deposition rate, and film density of the oxide sealing layer. A suitable oxygen-argon ratio ensures the formation of an oxide with a near-complete stoichiometry and few defects, while an optimized power density ensures good adhesion and moderate internal stress in the film, preventing cracks or peeling of the sealing layer due to improper processing, thus ensuring the effective realization of its sealing function.

[0013] Furthermore, the shell material of the microcapsules described in step (6) is SiO2. xThe microcapsules, or polymers, have a particle size of 50-500 nm, and the corrosion inhibitor is at least one of cerium salts, molybdates, phosphates, or benzotriazoles. This invention ensures the stability and functionality of the microcapsules in the coating by limiting the shell material and particle size. A suitable shell material ensures good compatibility with the coating matrix, while the particle size range guarantees uniform dispersion in the coating without significantly disrupting its continuity. The selected cerium salts, molybdates, and other corrosion inhibitors are environmentally friendly and have highly efficient corrosion inhibition effects on aluminum alloys. Once released, they can quickly form a protective film at the damaged site, achieving efficient self-repair.

[0014] Furthermore, the self-healing outer layer described in step (6) is formed using plasma-enhanced chemical vapor deposition. The microcapsules are pre-dispersed on the substrate surface by electrostatic adsorption or gas flow carrier before deposition begins, and then embedded and grown in a silicon-containing precursor atmosphere as amorphous SiN. x or SiC x In this invention, a self-healing outer layer is formed using PECVD, and microcapsules are pre-dispersed and embedded into amorphous SiN. x or SiC x Within the matrix. This method ensures that the microcapsules are firmly encapsulated and uniformly distributed on the coating surface. The amorphous matrix itself is dense and chemically stable, providing robust protection for the microcapsules and contributing additional wear and corrosion resistance. This design ensures self-healing functionality without sacrificing the mechanical properties and durability of the outer coating.

[0015] Furthermore, the physical vapor deposition technique described in step (3) is high-power pulsed magnetron sputtering, with a pulse frequency of 100~1000 Hz, a pulse width of 50~200 μs, and a peak power density of 0.5~2 kW / cm². This invention specifies the use of high-power pulsed magnetron sputtering to deposit the gradient functional layer. High-power pulsed magnetron sputtering can generate high-density, high-ionization plasma, significantly increasing the energy and activity of the deposited particles. This is beneficial for obtaining a gradient functional layer with finer grains, a denser structure, and stronger adhesion to the substrate, laying an excellent mechanical foundation for the entire coating system and further reducing the intrinsic defects of the coating itself.

[0016] Furthermore, the total thickness of the functional layer described in step (3) is 1~5 μm. This invention limits the total thickness of the gradient functional layer to the range of 1 to 5 μm, balancing coating performance with preparation cost and efficiency. Insufficient thickness may lead to insufficient protective capability; excessive thickness may increase internal stress accumulation, increasing the risk of cracking, and resulting in excessively long deposition time. This thickness range ensures excellent adhesion, hardness, and sufficient length of the corrosive medium diffusion barrier while maintaining the economy and feasibility of the process.

[0017] Further, in step (1), the surface roughness Ra after polishing is ≤0.1μm, and the vacuum drying is carried out at 80~120℃ and vacuum degree ≤5 Pa; in step (2), the glow discharge cleaning uses a mixture of argon and oxygen, wherein the volume ratio of oxygen is 1~10%, and the chamber pressure during cleaning is 0.5~2.0 Pa. This invention specifically optimizes the key parameters of pretreatment and glow discharge cleaning conditions. The extremely low surface roughness Ra≤0.1 μm provides an ideal interface for good bonding at the atomic scale; vacuum drying thoroughly removes surface adsorbed water; glow discharge cleaning using argon containing an appropriate amount of oxygen combines the physical cleaning effect of argon ion sputtering with the chemical cleaning and activation effect of oxygen plasma, which can more effectively remove surface contaminants and weak boundary layers, greatly activate the workpiece surface, and thus provide an ultra-clean and highly active substrate for subsequent coating deposition, which is a key prerequisite for obtaining ultra-high adhesion.

[0018] The present invention also provides a corrosion-resistant coating for aluminum alloy surfaces prepared by the method described above, wherein the coating has an electrochemical impedance of not less than 5 × 10⁻⁶ in a 3.5% NaCl solution. 7 The coating exhibits a corrosion resistance of Ω·cm² and a neutral salt spray test tolerance time of no less than 360 h. These quantitative indicators far exceed those of conventional PVD coatings and existing technologies, providing direct and compelling evidence of the combined effects of gradient strengthening, in-situ deep sealing, and self-healing mechanisms integrated in this invention. This clearly demonstrates that the coating product possesses superior long-term corrosion resistance and service reliability, meeting the application requirements under harsh conditions such as marine environments and high salt spray, thus exhibiting clear market competitiveness and application value.

[0019] Compared with the prior art, the present invention has the following beneficial effects: I. This invention creatively integrates gradient composition enhancement, periodic in-situ sealing, and active self-healing into a single process cycle. By depositing a gradient functional layer with continuously transitioning compositions, internal stress is effectively alleviated and the film-substrate adhesion is greatly enhanced. Through the periodic embedding of ultra-thin, dense oxide sealing layers during gradient layer growth, the inherent columnar grain boundaries and microporous defect network of the PVD coating are fundamentally physically blocked and filled, significantly extending the diffusion path of corrosive media. The outermost self-healing functional layer, embedded with microcapsules, endows the coating with the ability to actively repair accidental mechanical damage. The synergistic effect of these multiple mechanisms achieves long-lasting, active protection exceeding that of conventional coatings.

[0020] Second, this invention abandons the traditional macroscopic multilayer structure that relies on clear physical interfaces, and instead adopts a composite structure design of alternating "gradient layers + in-situ sealing layers". This design not only avoids stress concentration and weak points at the interface through dual gradients in composition and structure, but more importantly, the dense oxide layer introduced periodically at the nanoscale can effectively interrupt and seal the continuous growth channels of columnar crystals, achieving in-situ and efficient sealing of deep microscopic defects in the coating. Combined with high-power pulsed magnetron sputtering and other technologies to refine the grains, a coating body with fewer defects, low internal stress, dense structure and strong bonding is finally obtained, effectively overcoming the bottleneck of the prior art where it is difficult to achieve both protective performance and coating structural defects.

[0021] Third, the method provided by this invention eliminates the need for traditional electroplating pretreatment processes such as zinc immersion and copper plating, avoiding heavy metal pollution and lengthy processing procedures, making it an environmentally friendly green manufacturing technology. The entire coating system can be completed sequentially by adjusting process parameters in the same PVD equipment, resulting in a compact process and high production efficiency. The prepared coating not only possesses excellent corrosion resistance, but the outermost layer can also be deposited with a color layer or a hydrophobic functional layer as needed to meet aesthetic or special functional requirements. This method provides a high-performance, high-reliability, and easily industrialized surface protection solution for high-end aluminum alloy components in aerospace, marine engineering, and other fields, exhibiting significant market competitiveness and application value. Detailed Implementation

[0022] The specific embodiments are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise specified, the raw materials and reagents used in the examples are commercially available.

[0023] The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the invention without departing from the spirit and scope of the invention, and all such modifications and substitutions should be covered within the scope of the claims of the invention.

[0024] Example 1 A method for preparing a PVD-deposited corrosion-resistant coating on an aluminum alloy surface includes the following steps: Example 1 1. Substrate preparation A piece of aluminum alloy sheet with grade 6061 was used as the base material, with dimensions of 100 mm × 100 mm × 5 mm and a weight of approximately 1.35 kg.

[0025] 2. Pretreatment (1) Sandblasting is performed on the aluminum alloy substrate using white corundum sand with a particle size of 120 mesh and a sandblasting pressure of 0.4 MPa until the surface is uniformly rough. (2) The substrate after sandblasting is mechanically polished using diamond polishing paste, so that the surface roughness Ra reaches 0.08 μm; (3) Place the polished substrate in acetone and anhydrous ethanol in sequence, and ultrasonically clean each for 15 minutes. Then rinse with deionized water and dry with nitrogen. (4) Place the cleaned substrate into a vacuum oven and dry it for 60 minutes at a temperature of 100 °C and a vacuum of 3 Pa to obtain the pretreated substrate.

[0026] 3. PVD deposition The pretreated substrate is loaded onto the workpiece holder of a multi-target high-power pulsed magnetron sputtering PVD furnace. The workpiece holder is connected to a bias power supply and a rotation mechanism. The following steps are performed sequentially: (1) Glow discharge cleaning and plasma cleaning: Evacuate the chamber until the background pressure is below 5.0 × 10⁻⁶. -3 Pa, introduce a mixture of argon and oxygen, with oxygen accounting for 5% by volume, adjust the gas flow rate to stabilize the chamber pressure at 1.0 Pa, turn on the bias power supply, apply a -800 V DC bias voltage for glow discharge cleaning for 20 minutes, then switch to pulse bias mode for plasma cleaning for 10 minutes. (2) A composite structure with alternating deposition gradient functional layers and oxide sealing layers: First, functional layer deposition was performed: a high-power pulsed magnetron sputtering power supply was turned on, using a pure titanium target measuring 500 mm long × 100 mm wide and weighing approximately 15 kg. The pulse frequency was set to 500 Hz, the pulse width to 100 μs, and the peak power density to 1.2 kW / cm². Argon gas was introduced as the working gas at a flow rate of 200 sccm; nitrogen gas was simultaneously introduced as the reactant gas. The nitrogen flow rate and the pulsed bias voltage applied to the substrate were periodically modulated under computer program control to deposit a gradient functional layer. The modulation period was set to 100 nm. Within each cycle, the nitrogen flow rate linearly increased from an initial 20 sccm to 80 sccm (a 60% variation), and the bias voltage linearly changed from -50 V to -100 V (a 50% variation). This process caused the deposited coating composition to continuously transition from a titanium-rich metallic state at the bottom to a TiN ceramic state on the surface.

[0027] Then, the sealing layer deposition is performed: whenever the gradient functional layer reaches a thickness of 500 nm, the sputtering of the titanium target is paused and the nitrogen gas is turned off. Switch to reactive sputtering mode and turn on the power to the pure silicon target. Argon and oxygen are introduced, with the volume ratio of oxygen flow rate to argon flow rate controlled at 1:5, for example, 20 sccm of oxygen and 100 sccm of argon. The sputtering power density is set to 4 W / cm². A 20 nm thick SiO₂ layer is deposited in situ on the substrate. x Sealing layer.

[0028] (3) Repeat the above cycle of depositing 500 nm of functional layer plus 20 nm of sealing layer.

[0029] (4) A total of 5 cycles were performed to achieve a total thickness of 2.6 μm for the functional layer, which is 5 times 500 nm plus 5 times 20 nm equals 2.6 μm, forming a PVD gradient TiN layer and a PVD SiO layer. x A composite structure consisting of alternating sealing layers.

[0030] (5) Deposition of self-healing outer layer: First, microcapsules were prepared: SiO2-based microcapsules were prepared using the sol-gel method. Tetraethyl orthosilicate was hydrolyzed and condensed under alkaline conditions. Sodium molybdate was added as a corrosion inhibitor during the reaction, forming a suspension of SiO2 microcapsules coated with sodium molybdate. After centrifugation, washing, and drying, a powder was obtained. The average particle size of the microcapsules was 200 nm.

[0031] Then, coating deposition is performed: the composite substrate is removed from the PVD furnace. Microcapsule powder is uniformly sprayed onto the substrate surface via an airflow carrier. Subsequently, the substrate is reloaded into the plasma-enhanced chemical vapor deposition chamber. A mixture of silane and ammonia is introduced as a precursor. Plasma is generated under radio frequency power excitation for deposition. During this process, microcapsules are embedded within the continuously growing amorphous SiN. x Within the matrix, a self-healing outer layer containing microcapsules is formed with a thickness of approximately 800 nm.

[0032] (6) Deposition of color layer: On the self-healing outer layer, a zirconium nitride color layer with a thickness of about 100 nm is deposited using magnetron sputtering technology, which presents a golden yellow color.

[0033] Example 2 A method for preparing a PVD-deposited corrosion-resistant coating on an aluminum alloy surface includes the following steps: 1. Substrate preparation A piece of aluminum alloy forging with grade 7075 was used as the base, with dimensions of 150 mm × 50 mm × 10 mm and a weight of approximately 2.0 kg.

[0034] 2. Pretreatment (1) The aluminum alloy substrate is sandblasted using brown corundum sand with a particle size of 100 mesh and a sandblasting pressure of 0.5 MPa. (2) The substrate after sandblasting is mechanically polished to achieve a surface roughness Ra of 0.05 μm; (3) Place the polished substrate in gasoline and ethanol for ultrasonic cleaning for 20 minutes each, rinse with deionized water, and dry with nitrogen. (4) Place the cleaned substrate into a vacuum oven and dry it for 90 minutes at a temperature of 120 °C and a vacuum of 2 Pa to obtain the pretreated substrate.

[0035] 3. PVD deposition The pretreated matrix is ​​loaded into the PVD furnace.

[0036] (1) Glow discharge cleaning and plasma cleaning: The chamber background pressure is lower than 4.0 × 10 -3 Pa. Introduce a mixture of argon and oxygen, with oxygen comprising 1% by volume, and adjust the chamber pressure to 2.0 Pa. Apply a -700 V DC bias for glow discharge cleaning for 25 minutes, followed by a pulsed bias plasma cleaning for 15 minutes.

[0037] (2) A composite structure with alternating deposition gradient functional layers and oxide sealing layers: First, functional layer deposition was performed: a high-power pulsed magnetron sputtering power supply was turned on, using a pure chromium target weighing approximately 18 kg. The pulse frequency was set to 100 Hz, the pulse width to 200 μs, and the peak power density to 0.8 kW / cm². The working gas argon flow rate was 180 sccm, and the reactant gas was a mixture of acetylene and nitrogen. The modulation period was set to 50 nm. Within each period, the total reactant gas flow rate linearly increased from 25 sccm to 45 sccm, a variation of 44%, and the bias voltage linearly changed from -30 V to -45 V, a variation of 33%. The deposited coating composition transitioned from a chromium-rich metallic state at the bottom to a CrN and CrC mixed ceramic state on the surface.

[0038] Then, the sealing layer deposition was performed: whenever the gradient functional layer reached a thickness of 200 nm, chromium target sputtering was paused and the reactive gas was turned off. The system was switched to reactive sputtering mode, and aluminum and titanium targets were simultaneously activated for co-sputtering. Argon and oxygen were introduced, with the oxygen flow rate to argon flow rate volume ratio controlled at 1:2, for example, 50 sccm for oxygen and 100 sccm for argon. The total sputtering power density was set to 6 W / cm². A 50 nm thick mixed oxide sealing layer, mainly composed of AlO₂, was deposited in situ on the substrate. x and TiO x A mixture.

[0039] (3) Repeat the above cycle of depositing 200 nm of functional layer plus 50 nm of sealing layer.

[0040] (4) A total of 4 cycles are performed to make the total thickness of the functional layer reach 1.0 μm, that is, 4 times 200 nm plus 4 times 50 nm equals 1.0 μm, forming a composite structure.

[0041] (5) Deposition of self-healing outer layer: First, microcapsules were prepared: using polyurea as the shell material, microcapsules were prepared by interfacial polymerization, with the core material being a mixture of benzotriazole and disodium hydrogen phosphate. The prepared microcapsules had an average particle size of 500 nm.

[0042] Then, coating deposition is performed: the microcapsule powder is attached to the surface of the composite structure substrate by electrostatic adsorption. Subsequently, plasma-enhanced chemical vapor deposition is used, introducing a mixed gas of silane and methane to deposit amorphous SiC. x The matrix into which microcapsules are embedded forms a self-healing outer layer with a thickness of approximately 1 μm.

[0043] (6) Deposition of hydrophobic functional layer: A commercial fluorinated silane hydrophobic coating with a thickness of about 2 μm is deposited on the self-healing outer layer by spraying.

[0044] Example 3 A method for preparing a PVD-deposited corrosion-resistant coating on an aluminum alloy surface includes the following steps: 1. Substrate preparation A piece of aluminum alloy profile with grade 2024 was used as the base material, with dimensions of 80 mm × 80 mm × 3 mm and a weight of approximately 0.52 kg.

[0045] 2. Pretreatment (1) The aluminum alloy substrate is sandblasted using glass beads with a particle size of 150 mesh and a sandblasting pressure of 0.3 MPa. (2) The substrate after sandblasting is mechanically polished to achieve a surface roughness Ra of 0.10 μm; (3) The polished substrate is immersed in alkaline cleaning solution and acidic activation solution for 5 minutes each, then ultrasonically cleaned with deionized water and dried with nitrogen. (4) Place the cleaned substrate into a vacuum oven and dry it for 120 minutes at a temperature of 80 ℃ and a vacuum degree of 5 Pa to obtain the pretreated substrate.

[0046] 3. PVD deposition The pretreated matrix is ​​loaded into the PVD furnace.

[0047] (1) Glow discharge cleaning and plasma cleaning: The chamber background pressure is lower than 6.0 × 10 -3 Pa, introduce a mixture of argon and oxygen, with oxygen accounting for 10% by volume, adjust the chamber pressure to 0.5 Pa, apply a -900 V DC bias for glow discharge cleaning for 15 minutes, followed by pulse bias plasma cleaning for 8 minutes; (2) A composite structure with alternating deposition gradient functional layers and oxide sealing layers: First, functional layer deposition was performed: a high-power pulsed magnetron sputtering power supply was turned on, using a pure aluminum target weighing approximately 12 kg. The pulse frequency was set to 1000 Hz, the pulse width to 50 μs, and the peak power density to 2.0 kW / cm². The working gas argon flow rate was 250 sccm, and the reactant gas was oxygen. The modulation period was set to 200 nm. Within each period, the oxygen flow rate linearly increased from 10 sccm to 18 sccm (80% variation), and the bias voltage linearly changed from -40 V to -60 V (33% variation). The deposited coating composition transitioned from an aluminum metallic state at the bottom to an Al₂O₃ ceramic state on the surface.

[0048] Then, perform the sealing layer deposition: whenever the gradient functional layer thickness reaches 1000 nm, pause aluminum target sputtering and shut off oxygen. Switch to reactive sputtering mode and turn on the silicon target. Introduce argon and oxygen, controlling the volume ratio of oxygen flow rate to argon flow rate to be 1:10, for example, 10 sccm of oxygen and 100 sccm of argon. Set the sputtering power density to 2 W / cm². Deposit a layer of SiO₂ in situ on the substrate. x With AlO x The nano-layered sealing layer is specifically operated by first depositing a 5 nm layer of SiO₂. x Sublayer, then deposit 10nm of AlO x Sublayer, this is a stacked unit. This unit is repeated twice to form a nanolayered sealing layer with a total thickness of 30 nm. AlO₂ is included. x The sublayer is achieved by co-sputtering a small amount of aluminum target.

[0049] (3) Repeat the above cycle of depositing a 1000 nm functional layer plus a 30 nm nanolayer sealing layer.

[0050] (4) A total of 3 cycles are performed to make the total thickness of the functional layer reach 3.09 μm, that is, 3 times 1000 nm plus 3 times 30 nm equals 3.09 μm, forming a composite structure.

[0051] (5) Deposition of self-healing outer layer: First, microcapsules were prepared: microcapsules with a polymer-SiO2 composite as the shell material and cerium nitrate as the core material were prepared using a layer-by-layer self-assembly method. The average particle size of the microcapsules was 50 nm.

[0052] Then, coating deposition was performed: the microcapsule dispersion was coated onto the surface of the composite structure substrate and dried. Subsequently, plasma-enhanced chemical vapor deposition was used, with silane and ammonia gas introduced, to deposit amorphous SiN. x The matrix forms a self-healing outer layer with a thickness of approximately 500 nm.

[0053] (6) Deposition of color layer: On the self-healing outer layer, an arc ion plating technique is used to deposit a TiAlN coating with a thickness of about 150nm, which appears as blue-gray.

[0054] Comparative Example 1: PVD gradient coating without periodic oxide sealing layer This comparative example aims to verify the necessity of periodically embedding oxide sealing layers in gradient functional layers.

[0055] Preparation method: The only difference from Example 1 is that the periodic sealing layer deposition and cyclic operation in steps (4) and (5) are omitted. Specifically, after performing the same glow discharge cleaning and plasma cleaning as in Example 1, only gradient TiN functional layers are continuously deposited without any pause or mode switching until the total thickness reaches 2.5 μm (close to the total thickness of the functional layer in Example 1). Subsequently, the self-healing outer layer and color layer are deposited according to the same steps (6) and (7) as in Example 1.

[0056] Comparative Example 2: Replacing the gradient + sealing composite structure with a traditional clear interface multi-layer structure. This comparative example aims to verify the advantages of the composite structure of "gradient transition + in-situ sealing" over the traditional macroscopic multilayer structure.

[0057] Preparation method: The difference from Example 1 lies in steps (3) to (5). Gradient modulation and periodic sealing are not performed. Specifically: First, a 0.5 μm thick pure titanium metal bonding layer is deposited; then a 0.5 μm thick TiN layer is deposited; this “metal layer / ceramic layer” cycle is repeated twice to form a Ti / TiN multilayer structure with a total of 5 layers and a total thickness of about 2.5 μm. The composition between each layer changes abruptly, and there are clear interfaces. Subsequently, the outer layer is deposited according to steps (6) and (7) exactly the same as in Example 1.

[0058] Comparative Example 3: Using a single thick SiO2 layer as the sealing layer This comparative example aims to verify the difference in effectiveness between periodic, ultrathin in-situ sealing and single thick-layer surface sealing.

[0059] Preparation method: The difference from Example 1 lies in steps (4) and (5). Periodic embedding is not used. Specifically, a gradient TiN functional layer with a total thickness of 2.5 μm is first deposited continuously according to the parameters of Example 1. Then, the reactive sputtering mode is switched, and a SiO2 layer with a thickness of 100 nm is deposited at one time as a surface sealing layer under the same process parameters. Subsequently, the outer layer is deposited according to the same steps (6) and (7) as in Example 1.

[0060] Comparative Example 4: Coating system without self-healing outer layer This comparative example aims to verify the effect of self-healing function on improving the long-term reliability and damage tolerance of the coating.

[0061] Preparation method: The difference from Example 1 is that step (6) is completely omitted. After completing the deposition of the composite structure (total thickness 2.6 μm) with alternating gradient layers and sealing layers, the color layer of Example 1 is directly deposited on its surface.

[0062] Comparative Example 5: Replacing high-power pulsed magnetron sputtering with conventional DC magnetron sputtering This comparative example aims to verify the effect of high-power pulsed magnetron sputtering technology on improving the density and bonding strength of gradient functional layers.

[0063] Preparation method: The only difference from Example 1 is that in step (3), when depositing the gradient functional layer, conventional DC magnetron sputtering technology is used instead of high-power pulsed magnetron sputtering. All other parameters, such as the target material, gas, and gradient modulation program, are consistent with those in Example 1. The subsequent sealing layer and outer layer deposition process are the same as in Example 1.

[0064] Comparative Example 6: Corrosion inhibitors containing heavy metal chromates were used. This comparative example aims to highlight the green advantages of the environmentally friendly inhibitors used in this invention from an environmental perspective.

[0065] Preparation method: The only difference from Example 1 is that in step (5) when preparing microcapsules, sodium chromate is used as a corrosion inhibitor instead of sodium molybdate. The remaining process steps are exactly the same as in Example 1.

[0066] The performance of Examples 1-3 and Comparative Examples 1-6 was compared and tested using the following methods: I. Electrochemical Impedance Spectroscopy 1. Test objective: To evaluate the barrier performance and protective durability of the coating in corrosive electrolytes. The higher the impedance value, the stronger the coating's ability to resist the penetration of corrosive media.

[0067] 2. Testing standards: Refer to ASTM G106, "Standard Practice for Performing Electrochemical Impedance Measurements," and related electrochemical testing specifications.

[0068] 3. Testing equipment: electrochemical workstation (equipped with a three-electrode system), electrolytic cell, and data acquisition and analysis software.

[0069] 4. Sample preparation: Cut the coating sample into a test area of ​​about 1 cm². The non-test area is strictly sealed with corrosion-resistant insulating adhesive (such as epoxy resin), exposing only the coating surface.

[0070] 5. Test conditions: (1) Electrolyte: 3.5 wt.% sodium chloride aqueous solution, simulating seawater environment.

[0071] (2) Temperature: Room temperature (25 ± 2 ℃).

[0072] (3) Three-electrode system: Working electrode: The coating sample to be tested.

[0073] Reference electrode: saturated calomel electrode.

[0074] Counter electrode: platinum sheet or graphite electrode.

[0075] 6. Testing steps: (1) Immerse the sample in the electrolyte and let it stand for 30 minutes to reach a stable open circuit potential; (2) Apply a sinusoidal perturbation signal with an amplitude of 10 mV at an open circuit potential; (3) In the frequency range, which is usually 10 5 Hz to 10 -2 The impedance response is measured by scanning within a Hz range. (4) The obtained impedance spectrum data is fitted using an equivalent circuit model to extract key parameters such as coating resistance. The report usually takes the impedance modulus in the low frequency region (such as 0.01 Hz) as the indicator for evaluating the protective performance of the coating.

[0076] II. Neutral Salt Spray Test 1. Test objective: To accelerate the evaluation of the corrosion resistance and failure time of coatings in a salt spray and humid environment, this is a widely recognized accelerated corrosion test method.

[0077] 2. Testing Standard: Follow ASTM B117, "Standard Operating Procedures for Salt Spray Testing".

[0078] 3. Testing equipment: Programmable constant temperature salt spray test chamber.

[0079] 4. Sample preparation: The edges of the sample should be properly protected. Make a scratch on the test surface using a hard scriber, penetrating the coating to the substrate (if scratch corrosion performance needs to be evaluated).

[0080] 5. Test conditions: (1) Salt solution: 5 ± 1 wt.% sodium chloride aqueous solution, pH adjusted to 6.5-7.2 (when collected at 35℃).

[0081] (2) Temperature inside the chamber: 35 ± 2 ℃.

[0082] (3) Settlement rate: per 80cm 2 Within the horizontal collection area, 1.0~2.0 mL / hour.

[0083] (4) Spraying method: continuous spraying.

[0084] 6. Testing Procedures and Judgment: (1) Place the sample in the test chamber at an angle of 15°-30° to the vertical direction.

[0085] (2) Start continuous spraying and record the start time.

[0086] (3) Regularly observe (e.g., every 24 hours) the surface condition of the sample. The inspection items include: the width and spread of corrosion products at the scratches, and whether there are signs of corrosion such as blistering, rust spots, and peeling in the unscratched areas.

[0087] (4) Termination criteria: Record the time (in hours) at which red rust (substrate corrosion) first appears or the coating shows large-area blistering and peeling, as the "tolerance time". This experiment uses the appearance of the first corrosion point as the main criterion.

[0088] III. Scratch Test for Bond Strength 1. Test objective: To quantitatively evaluate the bonding strength (adhesion) between the coating and the substrate.

[0089] 2. Test standard: Refer to ASTM C1624, "Standard test method for determining the adhesion of ceramic coatings by scratch test".

[0090] 3. Testing equipment: Scratch tester equipped with acoustic emission sensor and optical microscope.

[0091] 4. Sample preparation: The coating surface must be clean and flat.

[0092] 5. Test steps: (1) Use a diamond indenter (usually a Rockwell C type with a tip radius of 200 μm) to scratch the coating surface.

[0093] (2) While the indenter moves at a constant speed along the sample surface, it bears a vertical load that increases linearly or stepwise.

[0094] (3) Load range: Usually start from the initial load (e.g., 1 N) and gradually increase until the coating fails completely (e.g., 100 N).

[0095] (4) Monitoring: Real-time monitoring of acoustic emission signals, friction signals and optical images during the scratching process.

[0096] 6. Result determination: Critical load: By comprehensively analyzing the abrupt change points of acoustic emission signals, the inflection points of friction force curves, and optical / electron microscopy observations of scratch morphology, the load value corresponding to the first failure of the coating (such as the onset of cracks or peeling) is determined and denoted as Lc1 (first failure). The load corresponding to the complete peeling of the coating and exposure of the substrate is denoted as Lc2 (complete failure). Lc1 is usually used as the main evaluation index of coating adhesion in the report, and the unit is Newton.

[0097] The test data is shown in the table below: Analysis of the table data shows that the electrochemical impedances of Examples 1, 2, and 3 reached 8.7 × 10⁻⁶. 7 Ω·cm², 5.5×10 7 Ω·cm² and 6.3×10 7 The resistance to neutral salt spray tests exceeded 380 hours (Ω·cm²), and the critical load for bonding strength was also higher than 60 N. This performance benchmark significantly surpassed all comparative examples with design flaws. In particular, Comparative Example 1, due to the complete absence of a periodic oxide sealing layer, showed a two-order-of-magnitude decrease in impedance and salt spray lifetime compared to the examples. The traditional multilayer structure used in Comparative Example 2 and the single thick sealing layer design used in Comparative Example 3 also performed far worse than the examples. This directly proves that the composite structure of alternating growth of gradient functional layers and periodic in-situ sealing layers is the core to solving the intrinsic defects of the coating and achieving performance breakthroughs.

[0098] The introduction of a self-healing outer layer significantly improves the long-term reliability of the coating system. Comparative Example 4, in its undamaged state, exhibits similar impedance and adhesion data to Example 1; however, it rapidly fails after being scratched. This precisely demonstrates that the active repair capability provided by the self-healing function is crucial for resisting accidental mechanical damage. The addition of this functional layer, without substantially weakening the coating's intrinsic barrier performance and adhesion strength, endows the coating with intelligent damage response characteristics, thereby greatly extending its service life under complex operating conditions.

[0099] Furthermore, the optimized process and selection of environmentally friendly materials further enhance the overall value of this solution. Comparative Example 5, using a conventional DC magnetron sputtering process, showed a significant decline in all performance indicators, confirming the crucial role of high-power pulsed magnetron sputtering technology in obtaining a high-density, strongly bonded substrate. While Comparative Example 6 achieved similar protective performance to the examples, it relied on environmentally toxic chromate inhibitors. This highlights the advantages of this invention, which uses environmentally friendly corrosion inhibitors such as molybdates and cerium salts, ensuring top-tier technical performance while possessing green manufacturing advantages and sustainable development potential.

[0100] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a PVD-deposited corrosion-resistant coating on an aluminum alloy surface, characterized in that, Includes the following steps: (1) The aluminum alloy substrate is subjected to sandblasting, polishing, cleaning and vacuum drying to obtain a pretreated substrate; (2) The pretreated substrate is placed in a PVD furnace and subjected to glow discharge cleaning and plasma cleaning in sequence; (3) On the cleaned substrate surface, a functional layer with a continuous gradient composition change is deposited by using physical vapor deposition technology and periodically modulating the reactive gas flow rate and bias voltage; wherein the composition of the functional layer transitions continuously from the metallic state at the bottom to the nitride, oxide or carbide state at the surface. (4) During the deposition of the functional layer in step (3), after every 200 nm to 1000 nm of thickness, physical vapor deposition is paused, and reactive sputtering mode is switched to. In an oxygen-containing atmosphere, at least one of a silicon target, an aluminum target, or a titanium target is sputtered to deposit an oxide sealing layer with a thickness of 5 to 50 nm in situ; the oxide sealing layer is SiO2. x AlO x TiO x One or more of the following constitute a single layer, a mixed layer, or a nanolayer stack; (5) Repeat steps (3) and (4) until the total thickness of the functional layer reaches the predetermined value, thereby forming a composite structure consisting of alternating PVD gradient layers and PVD oxide sealing layers; (6) On the surface of the composite structure consisting of alternating PVD gradient layers and PVD oxide sealing layers, a self-healing outer layer containing microcapsules is deposited, wherein the microcapsules contain corrosion inhibitors. (7) Deposit a color layer or a hydrophobic functional layer on the surface of the self-healing outer layer.

2. The preparation method according to claim 1, characterized in that: The modulation period of the gradient modulation functional layer in step (3) is 50~200 nm, the change range of the reactant gas flow rate is 20~80% and the change range of the bias voltage is 10~50% in each period.

3. The preparation method according to claim 1, characterized in that: In step (4), the oxide sealing layer is SiO2. x / AlO x or TiO x / AlO x Nanolayers, wherein the thickness of each sublayer is 3~15 nm.

4. The preparation method according to claim 1, characterized in that: In step (4), the volume ratio of oxygen flow rate to argon flow rate used in the reactive sputtering mode is 1:10 to 1:2, and the sputtering power density is 2~6 W / cm².

5. The preparation method according to claim 1, characterized in that: The shell material of the microcapsules mentioned in step (6) is SiO2. x The polymer or the capsule has a particle size of 50-500 nm, and the corrosion inhibitor is at least one of cerium salt, molybdate, phosphate or benzotriazole.

6. The preparation method according to claim 1, characterized in that: The self-healing outer layer described in step (6) is formed using plasma-enhanced chemical vapor deposition. The microcapsules are pre-dispersed on the substrate surface by electrostatic adsorption or gas flow carrier before deposition begins, and then embedded and grown in a silicon-containing precursor atmosphere as amorphous SiN. x or SiC x In the layer.

7. The preparation method according to claim 1, characterized in that: The physical vapor deposition technique described in step (3) is high-power pulsed magnetron sputtering with a pulse frequency of 100~1000 Hz, a pulse width of 50~200μs, and a peak power density of 0.5~2kW / cm².

8. The preparation method according to claim 1, characterized in that: The total thickness of the functional layer in step (3) is 1~5μm.

9. The preparation method according to claim 1, characterized in that: The surface roughness Ra ≤ 0.1 μm after polishing in step (1) is carried out at 80~120℃ and vacuum degree ≤ 5 Pa. The glow discharge cleaning in step (2) uses a mixture of argon and oxygen, wherein the volume ratio of oxygen is 1~10%, and the chamber pressure is 0.5~2.0 Pa during cleaning.

10. A corrosion-resistant coating on an aluminum alloy surface prepared by the method of claim 1, characterized in that: The coating exhibits an electrochemical impedance of not less than 5 × 10⁻⁶ in a 3.5% NaCl solution. 7 Ω·cm², the tolerance time for neutral salt spray test is not less than 360 h.

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