Preparation method of zinc-aluminum-magnesium composite coating of high corrosion-resistant electric power fitting

Abstract

This invention discloses a method for preparing a zinc-aluminum-magnesium composite coating for high corrosion-resistant power fittings, specifically relating to the field of advanced non-ferrous metal materials technology. The method includes preparing a zinc-aluminum-magnesium passivation film using a plasma-ultrasound coupling process and collecting data. Based on this data, a ternary gradient control of zinc, aluminum, and magnesium is implemented, supplemented by low-frequency pulsed electric field to enhance bonding. Hot-dip galvanizing parameters are matched according to three types of parts of the fitting, and the entire process is weighted and scored, combined with corrosion resistance and lifespan data to adjust the process and complete the preparation. This invention prepares a zinc-aluminum-magnesium passivation film using a plasma-ultrasound coupling in-situ homogeneous passivation process, collects core parameters to construct a substrate-coating adaptation transition layer, and provides a benchmark for component control. Based on this, a ternary component gradient control of zinc, aluminum, and magnesium is implemented, supplemented by low-frequency pulsed electric field to enhance interfacial bonding. Differential hot-dip galvanizing parameters are matched according to the fitting's operating conditions, and the entire process is weighted and scored, combined with corrosion resistance and lifespan indicators for optimization, improving the coating's corrosion resistance and service stability.

Description

Technical Field

[0001] This invention relates to the field of advanced non-ferrous metal materials technology, and in particular to a method for preparing a zinc-aluminum-magnesium composite coating for highly corrosion-resistant power fittings. Background Technology

[0002] With the continuous expansion of my country's power transmission and distribution network construction and the constant improvement of power grid safety operation standards, the long-term service reliability and environmental tolerance of core metal components such as power fittings have become key factors restricting the stable operation of the power transmission and distribution system throughout its entire life cycle. Corrosion failure under complex outdoor working conditions is the most common failure mode of power fittings. Therefore, the research and development and upgrading of high-performance metal surface protection technology has always been a core necessity in the industry, and this technology direction belongs to the core research scope of advanced non-ferrous metal materials technology. This field focuses on the full-chain technology research of non-ferrous metal material performance optimization and engineering application, covering key technology branches such as non-ferrous metal alloy composition design and formulation, metal surface protective coating preparation, and multi-metal composite coating processing. It focuses on core directions such as the optimization of metal surface protective layer forming process, multi-metal coating raw material compatibility design, and metal component surface modification processing. Related technologies have been widely applied in scenarios such as power metal fitting protection treatment, industrial metal component surface processing, and large-scale preparation of alloy composite coatings, continuously improving the whole process implementation system of metal substrate surface treatment.

[0003] Among various technical solutions for surface protection of power fittings, zinc-aluminum-magnesium multi-element composite coatings have become the mainstream upgrade technology to replace traditional hot-dip galvanizing layers due to their strong corrosion resistance, excellent cathodic protection effect, and damage resistance. The preparation process of high corrosion-resistant zinc-aluminum-magnesium composite coatings, developed specifically for the service conditions of power fittings, has also become a key research and development area in this field. This process is a dedicated processing technology adapted to the long-term protection requirements of power fitting components. Its core aspects include pretreatment of the metal substrate surface, optimization of the zinc-aluminum-magnesium multi-element metal raw material ratio, rational arrangement of the hot-dip galvanizing process for the composite coating, and step-by-step processing of multiple metal coatings. By clearly defining the compatibility ratio specifications of zinc, aluminum, and magnesium raw materials, the entire process—from surface purification and cleaning of the workpiece, to precise setting of hot-dip galvanizing process parameters, and step-by-step application of the zinc-aluminum-magnesium composite coating—is completed sequentially, achieving stable preparation of a high corrosion-resistant composite coating on the surface of power fittings.

[0004] Existing technologies employ fixed raw material ratios and a uniform hot-dip plating process, which cannot adapt to the diverse service conditions of different parts of power fittings. This easily leads to problems such as insufficient local corrosion resistance or compromised electrical connection performance, shortening the service life of the fittings. Simply performing routine substrate cleaning without adapting transition structures easily results in stress concentration at the substrate-plating interface, causing plating peeling. The fixed-ratio layered coating mode cannot finely control component distribution, resulting in high plating porosity, insufficient deformation resistance, and a lack of a full-process data linkage control mechanism, leading to large batch-to-batch fluctuations in plating performance and insufficient service stability. Summary of the Invention

[0005] The main objective of this invention is to provide a method for preparing a zinc-aluminum-magnesium composite coating for highly corrosion-resistant power fittings, which can effectively solve the problems mentioned above in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a zinc-aluminum-magnesium composite coating for highly corrosion-resistant power fittings includes the following steps: S1. The power fitting substrate is treated by plasma-ultrasonic coupling in-situ homogeneous passivation process to prepare zinc-aluminum-magnesium passivation film. Data on passivation film thickness, zinc-aluminum-magnesium composition ratio of passivation film, and substrate surface roughness are collected and output. S2. Based on the zinc-aluminum-magnesium component ratio of the passivation film output by S1, implement the gradient control of the zinc-aluminum-magnesium ternary component, apply a low-frequency pulse electric field simultaneously to implement component bonding, and collect and output the corresponding data of the final ternary component ratio gradient system, component interface bonding strength, and intermetallic compound bond ratio. S3. Divide the power fittings into three categories: exposed, connected and stressed parts. Based on the component ratio gradient system output by S2, implement coating and molding according to the hot-dip galvanizing process parameters matched to the parts, and collect and output the corresponding data of coating thickness, coating adhesion and coating porosity of each part. S4. Retrieve the core test data from S1 to S3 and implement weighted scoring. Combine the neutral salt spray corrosion resistance time and the predicted service life of the coating to implement process adjustments and complete the entire coating preparation process.

[0007] Preferably, in the plasma-ultrasound coupled in-situ homogeneous passivation process in S1, the particle size of zinc-aluminum-magnesium micro-nano particles is 50nm-100nm, the plasma discharge gap is 6mm, the volume ratio of argon to oxygen is 9:1, the ultrasonic power is 600W-900W, the ultrasonic frequency is 30kHz-50kHz, the system pressure is 0.1MPa-0.3MPa, the substrate surface roughness is 0μm-1.6μm, the passivation film thickness is 1μm-3μm, and the passivation film interface bonding force is 80MPa-200MPa.

[0008] Preferably, in step S1, two sets of plasma process parameters are set: the first set of plasma power is 1000W-1200W, and the action time is 60s-80s; the second set of plasma power is 800W-1000W, and the action time is 40s-60s; the ratio of ultrasonic power to plasma power is 0.75:1; the product of ultrasonic frequency and action time is 1500kHz·s; the passivation film preparation repeated coupling treatment time is 10s / time; and the upper limit of plasma power is adjusted to 1300W.

[0009] Preferably, in the zinc-aluminum-magnesium formulation directional bonding control process of S2, the zinc component accounts for 65%-85% by mass, the aluminum component accounts for 10%-25% by mass, the magnesium component accounts for 3%-8% by mass, the low-frequency pulse electric field strength is 50V / m-100V / m, the pulse frequency is 10Hz-20Hz, the argon atmosphere purity is 99.99%-99.999%, the ambient pressure is 0.05MPa-0.15MPa, the proportion of intermetallic compound bonds in the components is 70%-100%, and the component interfacial bonding strength is 120MPa-250MPa.

[0010] Preferably, in step S2, the composition gradient is controlled based on the proportion of zinc, aluminum and magnesium components in the passivation film. The proportion of zinc component decreases continuously from +15% to -5%, the proportion of aluminum component increases continuously from -5% to +10%, and the proportion of magnesium component increases continuously from -2% to +7%. The composition gradient change rate is simultaneously increased by increasing the electric field strength. The ratio of pulse frequency to ambient pressure is 100Hz / MPa, the upper limit of electric field strength is adjusted to 120V / m, and the composition gradient change rate is reduced by 20%.

[0011] Preferably, in the targeted gradient coating forming process of S3, the overall coating thickness is 80μm-120μm, the hot-dip coating temperature is 450℃-550℃, the coating growth rate is 5μm / min-15μm / min, the coating-substrate bonding force is 90MPa-200MPa, and the coating porosity is 0%-0.05%.

[0012] Preferably, in step S3, the process parameters are matched according to the location: for exposed locations, the zinc content is 55%-65%, the aluminum content is 20%-25%, and the magnesium content is 15%-20%, with a growth rate of 5μm / min-8μm / min and a hot-dip galvanizing temperature of 500℃-550℃; for connecting locations, the zinc content is 70%-75%, the aluminum content is 15%-20%, and the magnesium content is 5%-10%, with a growth rate of 8μm / min-12μm / min and a hot-dip galvanizing temperature of 470℃-500℃; for stress-bearing locations, the zinc content is 75%-80%, the aluminum content is 10%-15%, and the magnesium content is 3%-5%, with a growth rate of 10μm / min-15μm / min and a hot-dip galvanizing temperature of 450℃-470℃. The remaining coating thickness is reduced simultaneously with the growth rate, and the thickness of repeated coating is 5μm-10μm / time. The hot-dip galvanizing temperature is increased by 20℃.

[0013] Preferably, in the S4 full-link closed-loop verification process, the weighting coefficients for passivation film adhesion, component bonding strength, and coating adhesion are 0.2, 0.3, and 0.5, respectively; the synergistic compatibility score is 100-200 points; the neutral salt spray corrosion resistance time is 3000-5000 hours; the predicted service life of the coating is 15-30 years; the upper limit of parameters in a single link is increased by 10%; and the upper limit of core parameters throughout the entire process is simultaneously increased by 10%.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a plasma-ultrasonic coupled in-situ homogeneous passivation process to treat the substrate of power fittings, preparing a zinc-aluminum-magnesium homogeneous passivation film. Simultaneously, core parameters are collected to construct a suitable transition layer between the substrate and the coating, providing a data benchmark for component control. Based on the passivation film composition, a ternary component gradient control of zinc, aluminum, and magnesium is implemented, supplemented by a low-frequency pulsed electric field to enhance interfacial bonding, reduce internal stress in the coating, and improve interfacial density. Differentiated hot-dip plating parameters are matched to different service locations of the fittings to achieve precise adaptation of coating performance to operating conditions. Weighted scoring of core data throughout the entire process, combined with dynamic adjustment of corrosion resistance time and lifespan prediction values, constructs a closed-loop control system to improve coating corrosion resistance and service stability. Detailed Implementation

[0015] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0016] A method for preparing a zinc-aluminum-magnesium composite coating for highly corrosion-resistant power fittings includes the following steps: S1. The power fitting substrate is treated by plasma-ultrasonic coupling in-situ homogeneous passivation process to prepare zinc-aluminum-magnesium passivation film. Data on passivation film thickness, zinc-aluminum-magnesium composition ratio of passivation film, and substrate surface roughness are collected and output. S2. Based on the zinc-aluminum-magnesium component ratio of the passivation film output by S1, implement the gradient control of the zinc-aluminum-magnesium ternary component, apply a low-frequency pulse electric field simultaneously to implement component bonding, and collect and output the corresponding data of the final ternary component ratio gradient system, component interface bonding strength, and intermetallic compound bond ratio. S3. Divide the power fittings into three categories: exposed, connected and stressed parts. Based on the component ratio gradient system output by S2, implement coating and molding according to the hot-dip galvanizing process parameters matched to the parts, and collect and output the corresponding data of coating thickness, coating adhesion and coating porosity of each part. S4. Retrieve the core test data from S1 to S3 and implement weighted scoring. Combine the neutral salt spray corrosion resistance time and the predicted service life of the coating to implement process adjustments and complete the entire coating preparation process.

[0017] In the plasma-ultrasound coupled in-situ homogeneous passivation process in S1, the particle size of zinc-aluminum-magnesium micro-nano particles is 50nm-100nm, the plasma discharge gap is 6mm, the volume ratio of argon to oxygen is 9:1, the ultrasonic power is 600W-900W, the ultrasonic frequency is 30kHz-50kHz, the system pressure is 0.1MPa-0.3MPa, the substrate surface roughness is 0μm-1.6μm, the passivation film thickness is 1μm-3μm, and the passivation film interface adhesion is 80MPa-200MPa.

[0018] In S1, two sets of plasma process parameters are set. The first set of plasma power is 1000W-1200W, and the action time is 60s-80s. The second set of plasma power is 800W-1000W, and the action time is 40s-60s. The ratio of ultrasonic power to plasma power is 0.75:1. The product of ultrasonic frequency and action time is 1500kHz·s. The repeat coupling treatment time for passivation film preparation is 10s / time. The upper limit of plasma power is adjusted to 1300W.

[0019] In the S2 zinc-aluminum-magnesium formulation directional bonding control process, the zinc component accounts for 65%-85% by mass, the aluminum component accounts for 10%-25% by mass, and the magnesium component accounts for 3%-8% by mass. The low-frequency pulse electric field strength is 50V / m-100V / m, the pulse frequency is 10Hz-20Hz, the argon atmosphere purity is 99.99%-99.999%, the ambient pressure is 0.05MPa-0.15MPa, the proportion of intermetallic compound bonds in the components is 70%-100%, and the component interfacial bonding strength is 120MPa-250MPa.

[0020] In S2, the composition gradient is controlled based on the proportion of zinc, aluminum and magnesium components in the passivation film. The proportion of zinc component is continuously decreased from +15% to -5%, the proportion of aluminum component is continuously increased from -5% to +10%, and the proportion of magnesium component is continuously increased from -2% to +7%. The composition gradient change rate is increased in tandem with the electric field strength. The ratio of pulse frequency to ambient pressure is 100Hz / MPa, the upper limit of electric field strength is adjusted to 120V / m, and the composition gradient change rate is reduced by 20%.

[0021] In the targeted gradient coating forming process of S3, the overall coating thickness is 80μm-120μm, the hot-dip coating temperature is 450℃-550℃, the coating growth rate is 5μm / min-15μm / min, the coating-substrate bonding force is 90MPa-200MPa, and the coating porosity is 0%-0.05%.

[0022] In S3, process parameters are matched according to the parts. For exposed parts, the zinc content is 55%-65%, the aluminum content is 20%-25%, and the magnesium content is 15%-20%, with a growth rate of 5μm / min-8μm / min and a hot-dip galvanizing temperature of 500℃-550℃. For connecting parts, the zinc content is 70%-75%, the aluminum content is 15%-20%, and the magnesium content is 5%-10%, with a growth rate of 8μm / min-12μm / min and a hot-dip galvanizing temperature of 470℃-500℃. For stress-bearing parts, the zinc content is 75%-80%, the aluminum content is 10%-15%, and the magnesium content is 3%-5%, with a growth rate of 10μm / min-15μm / min and a hot-dip galvanizing temperature of 450℃-470℃. The remaining coating thickness is reduced simultaneously with the growth rate. The thickness of repeated coating is 5μm-10μm / time, and the hot-dip galvanizing temperature is increased by 20℃.

[0023] In the S4 full-link closed-loop verification process, the weighting coefficients for passivation film adhesion, component bonding strength, and coating adhesion are 0.2, 0.3, and 0.5, respectively. The synergistic compatibility score is 100-200 points, the neutral salt spray corrosion resistance time is 3000-5000 hours, the predicted service life of the coating is 15-30 years, the upper limit of parameters in a single link is increased by 10%, and the upper limit of core parameters in the entire process is simultaneously increased by 10%.

[0024] Example 1, Preparation steps: S1. Plasma-ultrasound coupled in-situ homogeneous passivation: Zinc-aluminum-magnesium micro / nano particles with a diameter of 80 nm, plasma discharge gap of 6 mm, argon to oxygen mixing volume ratio of 9:1, ultrasonic power of 750 W, frequency of 40 kHz, system pressure of 0.2 MPa, substrate surface roughness of 0.8 μm, passivation film thickness of 2 μm, and interfacial bonding force of 140 MPa. The first group of plasma power was 1100 W for 70 s, the second group of power was 900 W for 50 s, the ratio of ultrasonic power to plasma power was 0.75:1, the product of ultrasonic frequency and treatment time was 1500 kHz·s, the coupling treatment was repeated 10 s / time, and the upper limit of plasma power was 1300 W. S2, Zinc-Aluminum-Magnesium Ternary Component Gradient Regulation + Low-Frequency Pulsed Electric Field Bonding: Zinc 75%, Aluminum 18%, Magnesium 7%, Low-Frequency Pulsed Electric Field Strength 75V / m, Frequency 15Hz, Argon Purity 99.995%, Ambient Pressure 0.1MPa, Intermetallic Compound Bond Ratio 85%, Interfacial Bond Strength 180MPa. Based on the passivation film composition, the zinc percentage decreases by +10% to -3%, the aluminum percentage increases by -3% to +7%, and the magnesium percentage increases by -1% to +5%, with an upper limit of electric field strength of 120V / m, reducing the component gradient change rate by 20%. S3. Hot-dip coating in sections: Total coating thickness 100μm, hot-dip coating temperature 500℃, growth rate 10μm / min, coating adhesion 145MPa, porosity 0.02%. Exposed parts: zinc 60%, aluminum 22%, magnesium 18%, growth rate 6μm / min, temperature 520℃; Connecting parts: zinc 72%, aluminum 17%, magnesium 7%, growth rate 10μm / min, temperature 480℃; Stress-bearing parts: zinc 77%, aluminum 12%, magnesium 4%, growth rate 12μm / min, temperature 460℃; Repeat coating 8μm / time, temperature increase 20℃. S4. Full-link closed-loop verification: passivation film adhesion, component bonding strength, and coating adhesion weighting coefficients are 0.2, 0.3, and 0.5, respectively; synergistic compatibility score is 150 points; neutral salt spray corrosion resistance is 4000h; coating service life is 22 years; and the upper limit of core parameters in the entire process is increased by 10%.

[0025] Example 2, Preparation steps: S1. Passivation process optimization: Zinc-aluminum-magnesium micro / nano particles with a diameter of 50 nm, ultrasonic power of 900 W, frequency of 50 kHz, and system pressure of 0.3 MPa; passivation film thickness of 3 μm, and interfacial adhesion of 200 MPa. The first group of plasma power was 1200 W for 80 s, and the second group of plasma power was 1000 W for 60 s; the remaining coupling parameters were the same as in Example 1.

[0026] The closed-loop verification of S2, S3, and S4 is exactly the same as in Example 1.

[0027] Example 3, Preparation steps: S1 is exactly the same as Example 1; S2. Composition and Electric Field Optimization: Zinc 85%, Aluminum 12%, Magnesium 3%; Low-frequency pulsed electric field strength 120V / m, frequency 20Hz, ambient pressure 0.15MPa. Based on the passivation film composition, the zinc percentage decreased by +15% to -5%, the aluminum percentage increased by -5% to +10%, and the magnesium percentage increased by -2% to +7%; other bonding parameters were the same as in Example 1. S3 and S4 are exactly the same as in Example 1.

[0028] Example 4, Preparation steps: S1 and S2 are exactly the same as in Example 1; S3. Coating process optimization: Total coating thickness 120μm, growth rate of exposed parts 5μm / min, temperature 550℃, growth rate of connecting parts 12μm / min, temperature 500℃, growth rate of stressed parts 15μm / min, temperature 470℃, repeated coating 10μm / time, other bonding force and porosity parameters are the same as in Example 1. The S4 closed-loop verification is exactly the same as in Example 1.

[0029] Comparative Example 1, Preparation Steps: S1. The plasma-ultrasonic coupling in-situ homogeneous passivation process is cancelled and replaced by conventional chemical passivation. The passivation film thickness and composition cannot be precisely controlled. The parameters S2, S3, and S4 are the same as in Example 1.

[0030] Comparative Example 2, Preparation Steps: S1, S3, and S4 are the same as in Example 1; S2. The low-frequency pulse electric field component bonding process is eliminated, and the zinc, aluminum and magnesium components are only physically mixed without intermetallic compound bonding reinforcement.

[0031] Comparative Example 3, Preparation Steps: S1, S2, and S4 are the same as in Example 1; S3. Exposed / connected / stressed parts use a uniform component ratio, hot-dip galvanizing temperature, and growth rate, without targeted gradient molding.

[0032] Comparative Example 4, Preparation Steps: S1, S2, and S3 are the same as in Example 1; S4. Weighted scoring, salt spray calibration, and process adjustments are cancelled; core parameters are fixed and not optimized.

[0033] Experimental procedure: A comprehensive performance verification test of the zinc-aluminum-magnesium composite coating for high corrosion-resistant power fittings was conducted. This test focused on the outdoor service conditions of transmission lines and used zinc-aluminum-magnesium composite coated power fitting samples prepared from four sets of optimized processes and four sets of comparative examples lacking core process steps as test objects. Five parallel samples were prepared for each set, and the average test data was taken to eliminate errors. Through systematic testing of six core performance indicators, the technical advancement of the preparation method and the necessity of the core process steps of this invention were verified. Simultaneously, the optimal process parameter scheme was selected, providing sufficient experimental data support for the scope of protection of the claims.

[0034] Sample preparation: Zinc-aluminum-magnesium composite coating samples were prepared on 316L stainless steel power fitting substrates according to the process schemes of Examples 1-4 and Comparative Examples 1-4. The sample size was uniformly 150mm×75mm×5mm, and 5 parallel samples were prepared for each group.

[0035] Neutral salt spray test: According to GB / T10125-2021 standard, a 5% sodium chloride solution with a pH value of 6.5-7.2 and a test temperature of 35℃ is used. Continuous spraying is performed, and the time it takes for the coating to first show red rust is recorded.

[0036] Coating adhesion / interfacial bonding strength test: According to GB / T5270-2005 standard, the universal testing machine pull-out method is used for testing, with a tensile rate of 1mm / min. The maximum load when the coating peels off is recorded and converted into bonding strength.

[0037] Coating porosity test: According to GB / T6461-2002 standard, the iron filter paper method is used, with a test area of ​​10 cm². 2 The color development time was 10 minutes. The number of pore points was counted and the porosity was calculated.

[0038] Synergistic compatibility score: The weighted total score is calculated based on the weighting coefficients set in claim 8 (passivation film adhesion 0.2, component bonding strength 0.3, coating adhesion 0.5), with a maximum score of 100 for each individual performance item.

[0039] Service life prediction: Based on neutral salt spray accelerated corrosion data and combined with the acceleration ratio fitting of outdoor atmospheric corrosion environment, the service life of the coating under normal outdoor power transmission conditions is predicted.

[0040] The following is a table of experimental results: According to the table above, the overall coating performance of all embodiments is significantly better than that of the comparative examples. Among them, Example 4 is the optimal solution, with the highest neutral salt spray corrosion resistance time, synergistic compatibility score, and coating service life. The coating adhesion, porosity, and interfacial bonding strength are also at the industry-leading level. Its performance advantage stems from the targeted optimization of the S3 part-specific coating parameters based on the standard process of this invention, which accurately matches the service conditions of the three types of parts of the power fittings: exposed, connected, and stressed. Differentiated control of component ratio, hot-dip coating temperature, and coating growth rate achieves the best balance between coating density, interfacial adhesion, and corrosion resistance. Example 2 has improved the passivation film quality due to the optimization of the S1 plasma-ultrasonic coupling passivation process, resulting in slightly lower performance. The comparative examples, lacking the core passivation, electric field bonding, part-specific coating, or closed-loop verification processes of this invention, show a significant decrease in coating corrosion resistance, bonding strength, and density, failing to meet the long-term outdoor service requirements of high corrosion-resistant power fittings.

[0041] 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 illustrative of the principles of 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 this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a zinc-aluminum-magnesium composite coating of high corrosion-resistant electric power hardware, characterized in that, Includes the following steps: S1. The power fitting substrate is treated by plasma-ultrasonic coupling in-situ homogeneous passivation process to prepare zinc-aluminum-magnesium passivation film. Data on passivation film thickness, zinc-aluminum-magnesium composition ratio of passivation film, and substrate surface roughness are collected and output. S2. Based on the zinc-aluminum-magnesium component ratio of the passivation film output by S1, implement the gradient control of the zinc-aluminum-magnesium ternary component, apply a low-frequency pulse electric field simultaneously to implement component bonding, and collect and output the corresponding data of the final ternary component ratio gradient system, component interface bonding strength, and intermetallic compound bond ratio. S3. Divide the power fittings into three categories: exposed, connected and stressed parts. Based on the component ratio gradient system output by S2, implement coating and molding according to the hot-dip galvanizing process parameters matched to the parts, and collect and output the corresponding data of coating thickness, coating adhesion and coating porosity of each part. S4. Retrieve the core test data from S1 to S3 and implement weighted scoring. Combine the neutral salt spray corrosion resistance time and the predicted service life of the coating to implement process adjustments and complete the entire coating preparation process.

2. The method according to claim 1, wherein the method is characterized by: In the plasma-ultrasound coupled in-situ homogeneous passivation process in S1, the particle size of zinc-aluminum-magnesium micro-nano particles is 50nm-100nm, the plasma discharge gap is 6mm, the volume ratio of argon to oxygen is 9:1, the ultrasonic power is 600W-900W, the ultrasonic frequency is 30kHz-50kHz, the system pressure is 0.1MPa-0.3MPa, the substrate surface roughness is 0μm-1.6μm, the passivation film thickness is 1μm-3μm, and the passivation film interface bonding force is 80MPa-200MPa.

3. The method according to claim 1, wherein the method is characterized by: In S1, two sets of plasma process parameters are set. The first set of plasma power is 1000W-1200W and the action time is 60s-80s. The second set of plasma power is 800W-1000W and the action time is 40s-60s. The ratio of ultrasonic power to plasma power is 0.75:

1. The product of ultrasonic frequency and action time is 1500kHz·s. The repeat coupling treatment time for passivation film preparation is 10s / time. The upper limit of plasma power is adjusted to 1300W.

4. The method according to claim 1, wherein the method is characterized by: In the zinc-aluminum-magnesium formulation directional bonding control process of S2, the zinc component accounts for 65%-85% by mass, the aluminum component accounts for 10%-25% by mass, the magnesium component accounts for 3%-8% by mass, the low-frequency pulse electric field strength is 50V / m-100V / m, the pulse frequency is 10Hz-20Hz, the argon atmosphere purity is 99.99%-99.999%, the ambient pressure is 0.05MPa-0.15MPa, the proportion of intermetallic compound bonds in the components is 70%-100%, and the component interfacial bonding strength is 120MPa-250MPa.

5. The method of claim 1, wherein the method is characterized by: In S2, the composition gradient is controlled based on the proportion of zinc, aluminum and magnesium components in the passivation film. The proportion of zinc component decreases continuously from +15% to -5%, the proportion of aluminum component increases continuously from -5% to +10%, and the proportion of magnesium component increases continuously from -2% to +7%. The composition gradient change rate is increased simultaneously with the electric field strength. The ratio of pulse frequency to ambient pressure is 100Hz / MPa, the upper limit of electric field strength is adjusted to 120V / m, and the composition gradient change rate is reduced by 20%.

6. The method of claim 1, wherein the method is characterized by: In the targeted gradient coating forming process of S3, the overall coating thickness is 80μm-120μm, the hot-dip coating temperature is 450℃-550℃, the coating growth rate is 5μm / min-15μm / min, the coating-substrate bonding force is 90MPa-200MPa, and the coating porosity is 0%-0.05%.

7. The method according to claim 1, wherein the method is characterized by: In S3, process parameters are matched according to the parts: for exposed parts, the zinc content is 55%-65%, the aluminum content is 20%-25%, and the magnesium content is 15%-20%, with a growth rate of 5μm / min-8μm / min and a hot-dip galvanizing temperature of 500℃-550℃; for connecting parts, the zinc content is 70%-75%, the aluminum content is 15%-20%, and the magnesium content is 5%-10%, with a growth rate of 8μm / min-12μm / min and a hot-dip galvanizing temperature of 470℃-500℃; for stress-bearing parts, the zinc content is 75%-80%, the aluminum content is 10%-15%, and the magnesium content is 3%-5%, with a growth rate of 10μm / min-15μm / min and a hot-dip galvanizing temperature of 450℃-470℃. The remaining coating thickness is reduced simultaneously with the growth rate, and the thickness of repeated coating is 5μm-10μm / time. The hot-dip galvanizing temperature is increased by 20℃.

8. The method according to claim 1, wherein the method is characterized by: In the S4 full-link closed-loop verification process, the weighting coefficients for passivation film adhesion, component bonding strength, and coating adhesion are 0.2, 0.3, and 0.5, respectively. The synergistic compatibility score is 100-200 points, the neutral salt spray corrosion resistance time is 3000-5000 hours, the predicted service life of the coating is 15-30 years, the upper limit of parameters in a single link is increased by 10%, and the upper limit of core parameters in the entire process is simultaneously increased by 10%.

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