A post-treatment method for improving the corrosion resistance of a chemical nickel plating layer in a plasma environment

Abstract

The present application relates to the technical field of corrosion-resistant coating, in particular to a post-treatment method for improving corrosion resistance of electroless nickel coating in plasma environment. The method comprises composite sol preparation, workpiece coating, plasma-assisted curing and subsequent heat treatment of inorganic-organic hybrid coating framework. The method makes the surface of electroless nickel workpiece form a firm inorganic-organic hybrid coating framework combined with the electroless nickel coating at low temperature by preparing composite sol and plasma-assisted curing, and in-situ immobilizes rare earth elements. The subsequent heat treatment promotes the further condensation of the inorganic-organic hybrid coating framework, realizes pore collapse and structure densification, thereby forming a final dense corrosion-resistant coating, and fixes the rare earth elements in the dense corrosion-resistant coating by chemical bonding. Thus, the risk of thermal stress and interface peeling caused by heat curing process is eliminated, and long-term, stable and reliable protection of the substrate under extremely harsh working conditions is realized.

Description

Technical Field

[0001] This invention relates to the field of corrosion-resistant coating technology, and more specifically, to a post-treatment method for improving the corrosion resistance of electroless nickel plating layers in a plasma environment. Background Technology

[0002] The corrosion resistance of nickel plating refers to the ability of nickel plating to resist corrosion damage from surrounding media (such as high temperature, plasma impact, acid and alkali solutions, atmospheric environment, etc.), which is mainly achieved through the chemical composition, structure and process control of the plating.

[0003] Traditional methods for improving the corrosion resistance of electroless nickel plating layers include:

[0004] The nickel-plated parts are immersed in a solution primarily composed of hexavalent chromium, forming a thin chromium-containing passivation film on the nickel layer surface. This film effectively isolates the nickel layer from moisture and oxygen in the atmosphere, providing good rust prevention in normal atmospheric environments.

[0005] Inorganic salt seals (such as silicates and molybdates) and organic coating seals (such as varnishes and thin-layer resins) seals, etc.

[0006] In addition, existing technologies also utilize organic polymers (such as epoxy resin and polyurethane) and silane films and rare earth conversion films to form superimposed corrosion-resistant coatings. The latter, combined with rare earth materials, improves the corrosion resistance of the coating and adds self-healing ability. However, in high-end equipment manufacturing fields, such as aerospace and semiconductor processing equipment, the chemical nickel plating layer on the surface of its core components often needs to be used for a long time under extreme and harsh conditions such as high temperature, strong plasma sputtering, and high frequency thermal cycling.

[0007] For electroless nickel-plated workpieces operating under extreme conditions such as high temperatures and plasma environments, traditional post-coating treatment techniques, especially conventional thermal curing processes, have limitations. These processes are prone to interfacial delamination between the plating layer and the substrate due to high-temperature thermal stress, and their surface-to-substrate curing method can easily introduce structural defects such as pinholes into the coating itself. This makes the coating vulnerable to sputtering erosion and accelerated decomposition failure under continuous plasma impact. Summary of the Invention

[0008] This invention provides a post-treatment method to improve the corrosion resistance of electroless nickel plating layers in plasma environments. By inducing deep cross-linking of the sol-gel under low-temperature conditions using high-energy active particles, a uniform and extremely dense ceramic-like hybrid structure is constructed, avoiding thermal stress damage. This strengthens the interfacial bonding between the coating and the substrate, eliminates structural defects caused by surface-to-interior curing, and firmly bonds rare earth elements to the network in a controllable active state. Ultimately, the nickel plating layer simultaneously achieves interfacial bonding stability, excellent bulk corrosion resistance, and continuous self-healing protection under extreme harsh environments such as high temperatures and plasma, thus solving the problems mentioned in the background art.

[0009] Traditional thermosetting technology, due to its high temperature and curing characteristics from the surface to the interior, can cause coating interface peeling and coating structure defects in extreme plasma environments, resulting in insufficient coating protection performance.

[0010] To achieve the above objectives, the post-treatment method for improving the corrosion resistance of electroless nickel plating in a plasma environment includes the following steps:

[0011] S1. Preparation of composite sol: Silane coupling agent, metal alkoxide, rare earth metal salt, solvent and water are mixed and hydrolyzed to prepare rare earth-doped composite sol.

[0012] S2. Workpiece coating: After cleaning and activating the workpiece that has undergone electroless nickel plating, the composite sol prepared in step S1 is coated on the surface of the nickel plating layer to form a wet film.

[0013] S3. Plasma-assisted curing: The workpiece coated with a wet film is placed in a low-temperature plasma environment and subjected to plasma treatment in a mixed atmosphere of inert gas and oxygen to crosslink and cure the wet film, forming a dense corrosion-resistant coating on the surface of the nickel plating layer.

[0014] S4. Heat-treat the inorganic-organic hybrid coating skeleton at a temperature of 180-250℃ for 0.5-2 hours.

[0015] In the above technical solution, in S1, it should be further explained that the silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and methyltrimethoxysilane; the metal alkoxide is selected from at least one of tetraethyl orthosilicate, methyl orthosilicate, and aluminum isopropoxide; the rare earth metal salt is selected from at least one of cerium nitrate, cerium chloride, and cerium acetate; the solvent is anhydrous ethanol; wherein in the composite sol prepared in S1, the molar ratio of rare earth element to silicon element is (0.08-0.15):1; the specific preparation method of the composite sol in S1 is as follows: the mixture of γ-aminopropyltriethoxysilane and methyltrimethoxysilane as the basic network forming agent, tetraethyl orthosilicate as the inorganic precursor, and cerium nitrate as the dopant source are dissolved together in a mixture of anhydrous ethanol and deionized water. In the solvent, the pH of the reaction system is adjusted to the range of 2.5 to 4.0 by adding acid dropwise, and the system temperature is maintained between 20°C and 35°C with continuous stirring. First, the above-mentioned silane coupling agent, tetraethyl orthosilicate and cerium nitrate are fully hydrolyzed to generate active intermediates containing silanol groups and cerium ions. Then, under closed conditions, the mixture is aged for 12 to 36 hours, so that these active intermediates form a three-dimensional network structure mainly composed of Si-O-Si and Si-O-Ce covalent bonds through condensation reaction. Finally, a structurally uniform and stable composite sol is obtained, in which the molar ratio of rare earth cerium to silicon is precisely controlled in the range of 0.08 to 0.15:1 to ensure that rare earth elements are uniformly bonded in the sol network at an optimized concentration.

[0016] In step S2, it should be noted that when coating the composite sol prepared in step S1 onto the nickel-plated surface of the workpiece, one of the following coating methods should be used: dip coating, spin coating, or spray coating. Taking spin coating as an example, the coating process is as follows: First, the workpiece that has completed electroless nickel plating is subjected to ultrasonic cleaning with an alkaline solution and immersion in an acidic activator to thoroughly remove oil and oxides from the surface of the nickel plating layer and enhance surface activity. Then, the composite sol prepared in step S1 is coated onto the activated nickel-plated surface by spin coating. By precisely controlling the spin coater speed within the range of 2000 to 4000 rpm and maintaining it for 10 to 30 seconds, the sol is evenly spread under centrifugal force, thereby forming a uniform and defect-free wet film, laying the foundation for the subsequent curing process.

[0017] In S3, it should be further explained that during plasma treatment, the low-temperature plasma environment of the workpiece is generated by an inductively coupled plasma source; the inert gas is argon, and the volume ratio of oxygen to argon is 1:(8-15); in addition, the plasma treatment power is 200~400W, and the temperature of the workpiece is controlled below 60℃ during the treatment process; the plasma-assisted curing process is specifically as follows: the workpiece coated with wet film is placed in a low-temperature plasma environment generated by an inductively coupled plasma source, and a plasma treatment power of 200 to 400W is applied in a mixed gas atmosphere composed of oxygen and argon with a volume ratio of 1:(8-15). During this process, the workpiece temperature is always controlled below 60℃ by an external cooling system. By utilizing the interaction between highly active particles in the plasma and the wet film components, the sol network is further cross-linked and condensed to achieve stable doping of rare earth elements, and finally a dense, strongly adherent, and corrosion-resistant composite coating is formed on the surface of the nickel plating layer.

[0018] In S4, the inorganic-organic hybrid coating skeleton is treated with heat treatment parameters of 180-250℃ and holding time of 0.5-2 hours, which further condenses the inorganic-organic hybrid coating skeleton, realizes pore collapse and structural densification, thereby forming a final dense corrosion-resistant coating, and fixes rare earth elements in the dense corrosion-resistant coating through chemical bonding.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] By preparing a composite sol and using plasma-assisted curing, an inorganic-organic hybrid coating framework is formed on the surface of a chemically plated nickel workpiece under low-temperature conditions, which is firmly bonded to the nickel plating layer, and rare earth elements are fixed in situ. Subsequent heat treatment promotes further condensation of the inorganic-organic hybrid coating framework, realizing pore collapse and structural densification, thereby forming a final dense corrosion-resistant coating, and fixing the rare earth elements within the dense corrosion-resistant coating through chemical bonding. This eliminates the risks of thermal stress and interface delamination caused by the thermosetting process, and its highly uniform and dense bulk structure can more effectively block and resist the long-term erosion and penetrating corrosion of high temperature and plasma. Ultimately, long-term, stable and reliable protection of the substrate is achieved under extremely harsh working conditions. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the post-treatment steps for improving the corrosion resistance of electroless nickel plating in a plasma environment according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Current thermosetting technologies, due to their high temperature and surface-to-depth curing characteristics, can cause interfacial peeling and structural defects in the coating under extreme plasma environments, leading to insufficient coating protection. This invention provides a post-treatment method to improve the corrosion resistance of electroless nickel plating layers in plasma environments, such as... Figure 1 As shown, it includes the following steps:

[0024] S1. Preparation of composite sol: Silane coupling agent, metal alkoxide, rare earth metal salt, solvent and water are mixed and hydrolyzed to prepare rare earth-doped composite sol.

[0025] S2. Workpiece coating: After cleaning and activating the workpiece that has undergone electroless nickel plating, the composite sol prepared in step S1 is coated on the surface of the nickel plating layer to form a wet film.

[0026] S3. Plasma-assisted curing: The workpiece coated with wet film is placed in a low-temperature plasma environment. In the mixed atmosphere of inert gas and oxygen, plasma treatment is carried out. Through the high-activity energy field of plasma treatment, the wet film is cross-linked at low temperature to form an inorganic-organic hybrid coating skeleton that is firmly bonded to the nickel plating layer.

[0027] Simultaneously, rare earth metal salts are decomposed, and rare earth elements are in situ immobilized in the inorganic-organic hybrid coating skeleton in the form of rare earth oxides and ionic states.

[0028] S4. The inorganic-organic hybrid coating skeleton is heat-treated at a temperature of 180-250℃ for 0.5-2 hours. This heat treatment promotes further condensation of the inorganic-organic hybrid coating skeleton, leading to pore collapse and structural densification, thus forming a final dense, corrosion-resistant coating. Rare earth elements are then chemically bonded within this dense, corrosion-resistant coating. The mechanism by which rare earth elements are in situ immobilized in the inorganic-organic hybrid coating skeleton in S3, in the form of rare earth oxides and ions, is explained in detail below:

[0029] The high-energy particles and active groups generated during plasma treatment partially disrupt the coordination bonds or ionic dipole interactions between rare earth ions and the siloxane skeleton in the inorganic-organic hybrid coating framework. This results in the rare earth ions being in a weakly bonded metastable state within the inorganic-organic hybrid coating framework. This state is thermodynamically unstable but is frozen under the kinetic conditions of a intact coating. Once the coating develops microcracks due to external forces, the newly exposed surface at the crack tip and the changes in the local chemical environment provide these metastable rare earth ions with energy-driven forces and migration channels, enabling them to spontaneously diffuse towards the damaged area and recoordinate and aggregate, forming a protective barrier.

[0030] Example 1:

[0031] This embodiment provides a post-treatment method to improve the corrosion resistance of electroless nickel plating on aluminum alloy surfaces in a plasma environment.

[0032] Matrix pretreatment:

[0033] A 100mm × 50mm × 2mm 6061 aluminum alloy sample was used as the substrate. The following treatments were performed sequentially: alkaline degreasing (60℃, 5wt% NaOH solution, 10 minutes), water rinsing, acid pickling and brightening (room temperature, 5vol% HNO3 solution, 30 seconds), water rinsing, and a second water rinsing. Subsequently, a commercial electroless nickel plating solution was used at 85℃ for 60 minutes to obtain an electroless nickel plating layer with a thickness of 12±2μm. After plating, the sample was rinsed with water and dried with nitrogen for later use.

[0034] Preparation of composite sol:

[0035] In a 500 mL beaker, 160 mL of anhydrous ethanol and 40 mL of deionized water were added sequentially as a mixed solvent. 10 g of γ-aminopropyltriethoxysilane and 10 g of methyltrimethoxysilane were added to the solvent. In this embodiment, tetraethyl orthosilicate is preferred as the metal alkoxide. Then, 20 g of tetraethyl orthosilicate was added, and the mixture was magnetically stirred for 10 minutes.

[0036] In this embodiment, cerium nitrate is preferably used as the rare earth metal salt. 3.06 g of cerium nitrate (controlling the molar ratio of cerium to silicon to be 0.1:1) was weighed and added to the above solution, and stirred until completely dissolved. The pH of the system was adjusted to 3.0 using dilute nitric acid, and the solution was placed in a 25°C constant temperature water bath and continuously stirred magnetically for 4 hours. The resulting solution was sealed and aged at 25°C for 24 hours to obtain a homogeneous rare earth-doped composite sol.

[0037] Coating and curing:

[0038] In this embodiment, spin coating is preferred. The prepared electroless nickel-aluminum alloy sample is fixed in a spin coater. Approximately 3 mL of composite sol is added, and the sample is first rotated at 500 rpm for 10 seconds to spread the sol, followed by rotation at 3000 rpm for 20 seconds to form a uniform wet film. The sample is then transferred to a plasma vacuum chamber. After evacuation, a mixture of oxygen and argon gas with a volume ratio of 1:10 is introduced to maintain a working pressure of 20 Pa. The inductively coupled plasma source is activated and treated at 300 W for 5 minutes, during which the sample temperature is controlled to be below 50°C using back cooling. The plasma-treated sample is then placed in a muffle furnace and heated to 200°C at a rate of 3°C / min in an air atmosphere, and held at that temperature for 1 hour. The sample is then cooled to room temperature in the furnace to obtain a sample with a corrosion-resistant composite coating on its surface.

[0039] Example 2:

[0040] This embodiment provides a post-treatment method to improve the corrosion resistance of electroless nickel plating on magnesium alloy surfaces in a plasma environment.

[0041] Matrix pretreatment:

[0042] An AZ31B magnesium alloy sample measuring 100mm × 50mm × 2mm was taken. The following treatments were performed sequentially: alkaline degreasing (60℃, 5wt% NaOH solution, 10 minutes), water washing, acid pickling activation, water washing, and a second water washing; the acid pickling activation step involved immersion in a phosphate solution containing corrosion inhibitor for 60 seconds at room temperature. A dedicated magnesium alloy electroless nickel plating solution was used for plating at 85℃ for 60 minutes to obtain an electroless nickel plating layer with a thickness of 10±2μm. After plating, the sample was washed with water and dried with nitrogen for later use.

[0043] The preparation method of the composite sol is the same as in Example 1.

[0044] Coating and curing:

[0045] The coating and plasma curing steps are the same as in Example 1, except that the plasma-treated sample is placed in a muffle furnace and heated to 180°C at a rate of 2°C / min in an air atmosphere and held at that temperature for 1.5 hours; the sample is then cooled to room temperature in the furnace to obtain the final sample.

[0046] Example 3:

[0047] This embodiment provides a post-treatment method to improve the corrosion resistance of electroless nickel plating on copper alloy surfaces in a plasma environment.

[0048] Matrix pretreatment:

[0049] Take an H62 brass sample with dimensions of 100mm×50mm×2mm. Perform the following treatments in sequence: alkaline degreasing (60℃, 5wt% NaOH solution, 10 minutes), water washing, acid pickling activation (room temperature, 10vol% H2SO4 solution, 30 seconds), water washing, and a second water washing.

[0050] A commercial electroless nickel plating solution was used to plate the nickel at 85°C for 60 minutes to obtain an electroless nickel plating layer with a thickness of 13±2μm. After plating, the plating layer was rinsed with water and dried with nitrogen gas for later use.

[0051] The preparation method of the composite sol is the same as in Example 1.

[0052] Coating and curing:

[0053] The coating and plasma curing steps are the same as in Example 1, except that the plasma-treated sample is placed in a muffle furnace and heated to 220°C at 3°C / min in an air atmosphere and held at that temperature for 1 hour; the sample is then cooled to room temperature in the furnace to obtain the final sample.

[0054] Comparative Example 1:

[0055] Aluminum alloy, magnesium alloy, and copper alloy specimens, having undergone the same pretreatment and electroless nickel plating process as in Examples 1, 2, and 3, were taken without any subsequent sol-gel coating and curing treatment. These samples were labeled Comparative Example 1-Al, Comparative Example 1-Mg, and Comparative Example 1-Cu, respectively, serving as blank control groups.

[0056] Comparative Example 2:

[0057] The difference between this comparative example and Example 1 is that rare earth metal salts are not added when preparing the composite sol, while other components and preparation processes remain exactly the same as the second step of Example 1.

[0058] Using this rare-earth-free sol, electroless nickel plating layers on three different substrates were coated and cured according to the third step of Example 1. The resulting samples were labeled as Comparative Example 2-Al, Comparative Example 2-Mg, and Comparative Example 2-Cu, respectively.

[0059] Comparative Example 3:

[0060] The difference between this comparative example and Example 1 is that, after preparing the composite sol and completing the coating as in Example 1, the plasma-assisted curing step was omitted, and the sample with the wet film was directly placed into a muffle furnace for the same heat treatment as in Example 1. The resulting samples were labeled as Comparative Example 3-Al, Comparative Example 3-Mg, and Comparative Example 3-Cu, respectively.

[0061] Comparative Example 4:

[0062] The difference between this comparative example and Example 1 is that, after coating, pure high-purity argon gas was used instead of the oxygen-argon mixture in the plasma treatment step; other process parameters were exactly the same as in step three of Example 1. The resulting samples were labeled as Comparative Example 4-Al, Comparative Example 4-Mg, and Comparative Example 4-Cu, respectively.

[0063] Comparative Example 5:

[0064] This comparative example demonstrates the commercially viable chromate passivation treatment of three substrates after electroless nickel plating. The specific process involved immersing the substrates in a 40 g / L sodium dichromate solution (pH adjusted to 3.0 with dilute sulfuric acid) at 50°C for 5 minutes, followed by rinsing with deionized water and drying. The resulting samples were labeled Comparative Example 5-Al, Comparative Example 5-Mg, and Comparative Example 5-Cu, respectively.

[0065] Comparative Example 6:

[0066] This comparative example aims to demonstrate that the specific combination of γ-aminopropyltriethoxysilane and methyltrimethoxysilane used in this invention can produce a synergistic effect and achieve better performance compared to a single silane system.

[0067] 1. When preparing the composite sol, only 20g of γ-aminopropyltriethoxysilane was used, without adding methyltrimethoxysilane or tetraethyl orthosilicate. The amount of rare earth cerium nitrate added (3.06g) and other preparation steps were the same as in Example 1.

[0068] Using the above solution, the surface of the electroless nickel plating layer on the aluminum alloy was treated according to the process of Example 1, and the resulting sample was marked as Comparative Example 6-A1.

[0069] 2. When preparing the composite sol, only 20g of methyltrimethoxysilane was used, without adding γ-aminopropyltriethoxysilane and tetraethyl orthosilicate. The amount of rare earth cerium nitrate added (3.06g) and other preparation steps were the same as in Example 1.

[0070] Using the above solution, the surface of the electroless nickel plating layer on the aluminum alloy was treated according to the process of Example 1, and the resulting sample was marked as Comparative Example 6-A2.

[0071] 3. When preparing the composite sol, do not add tetraethyl orthosilicate, and keep the amounts of γ-aminopropyltriethoxysilane (10g) and methyltrimethoxysilane (10g) and the addition of rare earth elements unchanged.

[0072] Using the above solution, the surface of the electroless nickel plating layer on the aluminum alloy was treated according to the process of Example 1, and the resulting sample was marked as Comparative Example 6-A3.

[0073] Comparative Example 7:

[0074] This comparative example aims to demonstrate that "plasma-assisted curing" and "heat treatment" in this invention are two indispensable steps with a fixed sequence, and their combined action produces a synergistic effect.

[0075] 1. After preparing the composite sol according to Example 1 and completing the coating, only a plasma treatment step was performed, without subsequent final heat treatment. The sample was then removed and placed at room temperature, and the resulting sample was labeled Comparative Example 7-B1.

[0076] 2. After preparing the composite sol according to Example 1 and completing the coating, it was first heat-treated (200°C, held for 1 hour), and after cooling, it was then plasma-treated. The resulting sample was labeled as Comparative Example 7-B2.

[0077] Experiment Example 1: Corrosion Resistance and Basic Mechanical Properties Test

[0078] First, the methods used for performance testing in this experimental example will be explained:

[0079] Neutral salt spray test (NSS): Performed according to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". Record the time (in hours) when the first red rust appears on the sample surface; the longer the time, the better the corrosion resistance.

[0080] Coating adhesion: Evaluated according to GB / T 9286-2021 "Paints and Varnishes Cross-cut Test". The grades range from grade 0 (best, the cut edge is completely smooth and no cells are peeled off) to grade 5 (worst, the peeling area is greater than 65%).

[0081] Electrochemical impedance spectroscopy (EIS): Tests were performed using an electrochemical workstation in a 3.5 wt% sodium chloride solution at open-circuit potential, with a frequency range of 100 kHz to 10 mHz and a perturbation signal amplitude of 10 mV. The report uses impedance modulus values ​​in the low-frequency region (0.01 Hz) for comparison (unit: Ω·cm). 2 The larger the value, the better the barrier protection performance of the coating.

[0082] Experimental subjects: All samples from Examples 1 to 3 and Comparative Examples 1 to 7 were systematically tested.

[0083] Table 1: Test Results of Corrosion Resistance and Basic Mechanical Properties

[0084]

[0085] Experimental Results: As shown in Table 1, the samples provided in Examples 1 to 3 of this invention exhibited excellent corrosion resistance and adhesion on three different substrates: aluminum alloy, magnesium alloy, and copper alloy. Their neutral salt spray test times exceeded 1000 hours, 850 hours, and 950 hours, respectively, and their low-frequency impedance modulus all reached 10. 8 Ω·cm 2 The excellent level of both the quantity and adhesion grade (both are grade 0) fully demonstrates that the technical solution of this invention can construct protective coatings with excellent barrier performance and bonding strength on different metal substrates.

[0086] In contrast, the Comparative Example 1 series samples, which underwent no post-treatment, exhibited poor corrosion resistance, with neutral salt spray test times ranging from 72 to 150 hours and low-frequency impedance modulus below 3.0 × 10⁻⁶. 5 Ω·cm 2 This clearly demonstrates the necessity of post-processing in this invention.

[0087] In the comparison of key technical features, the performance indicators of the comparative example series (lacking rare earth doping), the comparative example series (eliminating the plasma treatment step), and the comparative example series (using pure argon plasma) were all inferior to the corresponding examples. In particular, the neutral salt spray test time and the low-frequency impedance modulus decreased significantly. This confirms that rare earth doping and plasma treatment under an oxygen-argon mixed atmosphere are indispensable key steps to achieve high-performance coatings.

[0088] Furthermore, compared to the conventional chromate-treated Comparative Example 5 series, the embodiments of the present invention demonstrate advantages in corrosion resistance and adhesion, highlighting the technological advancement and environmental friendliness of Examples 1 to 3.

[0089] Furthermore, the results of Comparative Example 6 show that the performance of sol systems using a single silane component or lacking inorganic reinforcing components is significantly inferior to the composite silane system used in this invention, proving that the synergistic compatibility of specific components is crucial for improving the overall performance of the coating.

[0090] In the comparative example series 7, samples with incomplete or reversed curing steps exhibited poor performance, particularly with adhesion grades as low as 3-4. This strongly demonstrates that the sequential and synergistic nature of the "plasma pretreatment" and "subsequent heat treatment" curing processes plays a decisive role in forming a dense, stable, and highly adhesive hybrid coating structure. In summary, the above systematic performance comparison fully verifies the superior technical effectiveness and advancements of the post-treatment method provided by this invention in improving the corrosion resistance of electroless nickel plating layers.

[0091] Experiment Example 2: Environmental Adaptability Verification

[0092] First, the methods used for performance testing in this experimental example will be explained:

[0093] Thermal shock test: Following a modification of GB / T 1735-2009, the sample was cyclically subjected to two environments: -40℃ (holding temperature for 30 minutes) and +120℃ (holding temperature for 30 minutes). The coating surface was inspected after each cycle. The number of cycles at which the coating first exhibited failure phenomena such as blistering, cracking, or peeling was recorded. A higher number of cycles indicates better thermal stability, cohesion, and adhesion to the substrate.

[0094] Experimental subjects: Example 1, Example 2, Example 3, Comparative Example 2-A1, Comparative Example 3-A1, Comparative Example 5-A1, Comparative Example 6-A3 and Comparative Example 7-B2.

[0095] Table 2: Environmental adaptability (thermal shock test) test results

[0096]

[0097] Experimental Results: According to the test data in Table 2, the samples of Examples 1 to 3 of this invention showed no signs of failure after more than 50 extreme thermal cycles, demonstrating excellent thermal stability. In contrast, the thermal shock resistance of all comparative samples decreased significantly: Comparative Example 2-Al, which lacked rare earth doping, failed after 15 cycles, proving the key role of rare earth elements in improving coating toughness; Comparative Example 3-Al, which eliminated the plasma curing step, could only withstand 8 cycles, indicating the indispensability of plasma treatment for forming a highly cross-linked coating structure; even Comparative Example 5-Al (25 cycles), representing conventional technology, performed worse than this invention; In particular, Comparative Example 6-A3 (lacking inorganic reinforcing components) and Comparative Example 7-B2 (curing steps reversed) failed after only 12 and 5 cycles, respectively, which strongly demonstrates the crucial synergistic effect of the complete composite sol formulation and specific process sequence in achieving excellent durability.

[0098] Experiment Example 3: Plasma Environment Simulation Tolerance Test

[0099] Experimental Objective: This experiment aims to simulate strong plasma conditions, quantitatively evaluate the ability of the electroless nickel plating layer post-treated by the present invention to resist plasma sputtering, erosion and performance degradation, and verify the technical advantages and necessity of the process of the present invention in extreme environments by comparing it with a series of comparative examples.

[0100] Test sample:

[0101] Representative samples were selected from the prepared examples and comparative examples for testing, as follows:

[0102] Test group: Example 1, Example 2, Example 3.

[0103] Control groups: Comparative Example 1-Al, Comparative Example 2-Al, Comparative Example 3-Al, Comparative Example 4-Al, Comparative Example 5-Al.

[0104] Test method: Plasma irradiation experiment

[0105] Test equipment: Inductively coupled plasma (ICP) etching system.

[0106] Environmental parameters:

[0107] Working gas: Ar / O2 mixed gas (volume ratio 10:1).

[0108] Cavity pressure: 2.0 Pa.

[0109] Plasma power: 500W.

[0110] Sample stage temperature: 80±5°C.

[0111] Irradiation time: 120 minutes.

[0112] Performance evaluation methods:

[0113] Following the plasma irradiation experiment, the samples underwent the following tests:

[0114] 1. Surface morphology analysis: The microstructure of the sample surface was observed using a scanning electron microscope (SEM).

[0115] 2. Sputter resistance assessment: Measure the mass of the sample before and after irradiation, and calculate the sputtering rate.

[0116] Sputtering rate = (mass loss × 10) 9 ) / (exposed area × irradiation time).

[0117] 3. Corrosion resistance degradation assessment: Electrochemical impedance spectroscopy (EIS) was performed on the irradiated samples immediately, and the low-frequency impedance modulus in 3.5wt% NaCl solution was recorded.

[0118] Table 3: Results of Plasma Irradiation Experiment

[0119]

[0120] Experimental Results: As shown in Table 3, Examples 1 to 3 exhibited excellent and consistent performance on aluminum alloy, magnesium alloy, and copper alloy substrates. The sputtering rates of the three examples were relatively low, specifically ranging from 14.9 to 16.8 ng / (cm³). 2 (·min), compared to 205.3 ng / (cm) of the untreated comparative example 1-Al. 2 The concentration of ·min was greatly reduced, proving that the composite coating can effectively resist the physical sputtering and erosion of high-energy particles.

[0121] After 120 minutes of continuous plasma irradiation, the low-frequency impedance modulus of all sample examples remained stable at 10. 8 Ω·cm 2 The high level indicates that its protective performance has only slightly degraded and the protective effect is fully preserved, which is superior to all comparative samples (impedance values ​​at 10). 4 Up to 10 7 Ω·cm 2 Within the range).

[0122] Furthermore, the degradation of the performance of the comparative example 2-Al confirms that cerium doping is crucial for improving the density and stability of the coating.

[0123] The presence of numerous defects on the surface of 3-Al in the comparative example demonstrates that this step is irreplaceable for forming a complete reinforced network structure.

[0124] The performance degradation of the comparative example 4-Al highlights the role of the oxygen-argon mixed atmosphere in constructing a better surface chemical structure.

[0125] The performance of the embodiments of the present invention is comprehensive and superior to that of the traditional chromate passivation process (Comparative Example 5-Al), demonstrating its superiority as an environmentally friendly high-performance alternative technology.

[0126] In summary, this invention, through a synergistic process of specific sol formulation design and plasma-assisted curing combined with heat treatment, successfully constructs a composite coating with superior resistance to plasma erosion and long-term protective stability on electroless nickel plating layers of various metal substrates, effectively improving the corrosion resistance of electroless nickel plating layers in plasma environments.

[0127] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A post-treatment method for improving the corrosion resistance of electroless nickel plating layers in a plasma environment, characterized in that, Includes the following steps: S1. Preparation of composite sol: Silane coupling agent, tetraethyl orthosilicate, rare earth metal salt, solvent and water are mixed and hydrolyzed to prepare rare earth-doped composite sol. S2. Workpiece coating: After cleaning and activating the workpiece that has undergone electroless nickel plating, the composite sol prepared in step S1 is coated on the surface of the nickel plating layer to form a wet film. S3. Plasma-assisted curing: The workpiece coated with wet film is placed in a low-temperature plasma environment. In the mixed atmosphere of inert gas and oxygen, plasma treatment is carried out. Through the high-activity energy field of plasma treatment, the wet film is cross-linked at low temperature to form an inorganic-organic hybrid coating skeleton that is firmly bonded to the nickel plating layer. Simultaneously, rare earth metal salts are decomposed, and rare earth elements are in situ immobilized in the inorganic-organic hybrid coating skeleton in the form of rare earth oxides and ionic states. S4. The inorganic-organic hybrid coating skeleton is subjected to heat treatment at a temperature of 180-250℃ and a holding time of 0.5-2 hours. The heat treatment promotes further condensation of the inorganic-organic hybrid coating skeleton, realizes pore collapse and structural densification, thereby forming a final dense corrosion-resistant coating, and fixes rare earth elements in the corrosion-resistant coating through chemical bonding. In S1, the rare earth metal salt is selected from at least one of cerium nitrate, cerium chloride, and cerium acetate; In S3, the inert gas is argon, and the volume ratio of oxygen to argon is 1:(8-15).

2. The post-treatment method for improving the corrosion resistance of electroless nickel plating in a plasma environment according to claim 1, characterized in that: In S1, the silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and methyltrimethoxysilane.

3. The post-treatment method for improving the corrosion resistance of electroless nickel plating in a plasma environment according to claim 1, characterized in that: In the composite sol prepared by S1, the molar ratio of rare earth elements to silicon elements is (0.08-0.15):

1.

4. The post-treatment method for improving the corrosion resistance of electroless nickel plating in a plasma environment according to claim 1, characterized in that: In step S2, the coating method is selected from dip coating, spin coating, and spray coating.

5. The post-treatment method for improving the corrosion resistance of electroless nickel plating in a plasma environment according to claim 1, characterized in that: In S3, the low-temperature plasma environment is generated by an inductively coupled plasma source.

6. The post-treatment method for improving the corrosion resistance of electroless nickel plating in a plasma environment according to claim 1, characterized in that: In S3, the power of plasma treatment is 200~400W, and the temperature of the workpiece is controlled below 60℃ during the treatment process.

7. The post-treatment method for improving the corrosion resistance of electroless nickel plating in a plasma environment according to claim 1, characterized in that: In step S1, the solvent is anhydrous ethanol.

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