Magnesium alloy micro-arc oxidation process, magnesium alloy and application thereof

Abstract

The application relates to a magnesium alloy micro-arc oxidation process, a magnesium alloy and application thereof, and the process comprises the following steps: firstly, a magnesium alloy workpiece to be treated is pretreated and then placed into an electrolyte; the composition of the electrolyte comprises the following components: 5-10 g / L of sodium silicate, 10-15 g / L of potassium pyrophosphate, 1-3 g / L of sodium aluminate, 3-5 g / L of sodium hydroxide and 1-10 g / L of potassium fluorotitanate; then, the magnesium alloy workpiece is subjected to micro-arc oxidation treatment by using the electrolyte; during the micro-arc oxidation treatment, the pH value of the electrolyte is greater than 12, the treatment temperature is 25+ / -5 DEG C, the current density is 1-5 A / dm2, and the treatment time is 5-60 min; then, the electrolyte is subjected to component analysis according to a preset interval, and the concentration of each component of the electrolyte is adjusted according to the analysis result. The application solves the problems that the yield of magnesium alloy prepared by the current magnesium alloy micro-arc oxidation is low, the corrosion resistance is insufficient, and the magnesium alloy is difficult to be used in a cooling liquid corrosion environment for a long time.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to a micro-arc oxidation process for magnesium alloys, magnesium alloys, and their applications. Background Technology

[0002] Magnesium alloys, as a typical lightweight structural material, possess advantages such as low density, high specific strength, high specific stiffness, and good thermal conductivity, making them highly promising for lightweight automotive design and improving energy efficiency. With the rapid development of the new energy vehicle industry, the demand for lightweight and efficient heat dissipation in vehicles is constantly increasing, leading to a gradual expansion of the application scope of magnesium alloys in automotive components. Especially in the electric drive systems of new energy vehicles, magnesium alloys are increasingly being explored for use in key components such as internal cooling water channels to improve thermal management efficiency, reduce system weight, and optimize structural integration.

[0003] However, the cooling channels of electric drive systems are in direct contact with coolants containing complex chemical compositions for extended periods during actual use. These coolants typically include corrosion inhibitors, antifreeze agents, conductive ions, and various other complex chemical components. Simultaneously, the cooling channels operate under conditions of high temperature, high humidity, high pressure, and the coupled effects of complex electrochemical environments. Magnesium alloys themselves have high electrochemical activity, and prolonged exposure to these environments makes them highly susceptible to corrosion reactions, including pitting corrosion, crevice corrosion, and general corrosion. In severe cases, this can lead to thinning of the channel walls, seal failure, or a decrease in structural strength, thereby affecting the safety and reliability of the electric drive system. Therefore, improving the corrosion resistance of magnesium alloys in coolant environments has become a key technical issue in their engineering applications.

[0004] To improve the corrosion resistance of magnesium alloys, micro-arc oxidation (MAO) is commonly used to grow ceramic oxide films in situ on the surface of magnesium alloys. This process involves applying a high voltage to an electrolyte, causing dielectric breakdown and micro-arc discharge on the magnesium alloy surface. Under the high temperature of plasma, an oxide film layer composed of magnesium oxide and other composite ceramic phases is formed. The resulting film layer has high bonding strength with the substrate, significantly improving the corrosion resistance, wear resistance, and insulation properties of magnesium alloys. However, existing micro-arc oxidation processes generally suffer from the following problems: 1. The process parameter range is set too wide, and the control precision of key parameters such as voltage, current density, frequency and duty cycle is insufficient, resulting in large fluctuations in the discharge state, which leads to insufficient stability of the film formation process. Consequently, there are significant differences in film thickness, porosity and dense layer thickness between different batches of products.

[0005] 2. The electrolyte system and its composition ratio lack specific optimization for the corrosive environment of coolant, resulting in the rapid decay of the corrosion resistance of the prepared film under long-term high-temperature coolant immersion or circulating flushing environment, making it difficult to meet the durability standards of electric drive cooling water channels for new energy vehicles. Summary of the Invention

[0006] One objective of this invention is to provide a micro-arc oxidation process for magnesium alloys, addressing the problems of low yield and insufficient corrosion resistance in magnesium alloys produced by current micro-arc oxidation methods, which hinders their long-term use in corrosive coolant environments. A second objective is to provide a magnesium alloy with an in-situ grown oxide film. A third objective is to provide an application of a magnesium alloy with an in-situ grown oxide film in the cooling water channels of new energy vehicles.

[0007] To achieve the above objectives, the first aspect of this invention proposes a micro-arc oxidation process for magnesium alloys, the technical solution of which is as follows: A micro-arc oxidation process for magnesium alloys includes the following steps: S101. After pretreatment, the magnesium alloy workpiece to be processed is placed in an electrolyte; the electrolyte comprises 5-10 g / L sodium silicate; 10-15 g / L potassium pyrophosphate; 1-3 g / L sodium aluminate; 3-5 g / L sodium hydroxide; and 1-10 g / L potassium fluorotitanate. S102. The magnesium alloy workpiece is subjected to micro-arc oxidation treatment using the electrolyte; during the micro-arc oxidation treatment, the pH value of the electrolyte is greater than 12; the treatment temperature is 25±5℃; the current density is 1~5 A / dm²; and the treatment time is 5~60 min. S103. Perform component analysis on the electrolyte at preset intervals, and adjust the concentration of each component of the electrolyte according to the analysis results.

[0008] Furthermore, during the micro-arc oxidation process, the starting current of the power supply of the micro-arc oxidation equipment is set to 6A and the starting voltage is set to 120V. The voltage is then increased in stages, with the voltage increasing by 20V every 2 minutes until it reaches 300V.

[0009] Furthermore, in step S101, the pretreatment includes: sequentially performing organic solvent degreasing, chemical degreasing, activation, water washing, and alkaline etching on the magnesium alloy workpiece.

[0010] Furthermore, the organic solvent degreasing includes: using one or more of acetone, gasoline, and water-based cleaning agents to perform preliminary degreasing on the magnesium alloy workpiece.

[0011] Furthermore, the chemical degreasing includes: using a magnesium alloy degreasing agent to perform deep degreasing on the magnesium alloy workpiece after preliminary degreasing; wherein, during the chemical degreasing process, the concentration of the magnesium alloy degreasing agent is 80-100 g / L; the chemical degreasing temperature is 50±5℃; and the chemical degreasing time is 5-10 min.

[0012] Furthermore, the activation includes: placing the magnesium alloy workpiece in an activator with a concentration of 190-220 ml / L and immersing it at room temperature for 3-5 minutes.

[0013] Furthermore, the water washing includes: using ultrasound to wash the magnesium alloy workpiece at room temperature for 1-2 minutes.

[0014] Furthermore, the alkaline etching includes: treating with an alkaline etchant at a concentration of 190–220 ml / L for 1–2 min at 80±5℃.

[0015] Furthermore, after step S102, the process also includes: sealing and drying the magnesium alloy workpiece after micro-arc oxidation.

[0016] Furthermore, the sealing process includes: immersing the magnesium alloy workpiece in hot water for sealing; wherein, during the sealing process, the temperature of the hot water is 85±5℃; the immersion time is 20±5 min; and the conductivity of the hot water during the sealing process is less than 60 ms / cm.

[0017] Furthermore, the drying process includes: blowing the magnesium alloy workpiece dry with compressed air at a pressure of not less than 0.4 MPa; and then drying the magnesium alloy workpiece in a drying oven at 100±10℃ for 20±5 min.

[0018] Furthermore, the magnesium alloy workpiece, after being degreased with organic solvent, is clamped in a pre-reserved position in an aluminum or titanium fixture.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a micro-arc oxidation process for magnesium alloys, comprising: firstly, pre-treating the magnesium alloy workpiece to be processed and then immersing it in an electrolyte; the electrolyte comprises 5-10 g / L sodium silicate; 10-15 g / L potassium pyrophosphate; 1-3 g / L sodium aluminate; 3-5 g / L sodium hydroxide; and 1-10 g / L potassium fluorotitanate; then performing micro-arc oxidation treatment on the magnesium alloy workpiece using the electrolyte; during the micro-arc oxidation process, the pH value of the electrolyte is greater than 12; the processing temperature is 25±5℃; the current density is 1-5 A / dm²; and the processing time is 5-60 min; then, the composition of the electrolyte is analyzed at preset intervals, and the concentration of each component of the electrolyte is adjusted according to the analysis results.

[0020] By employing the technical solution of this invention, and through optimized design of the electrolyte components for the corrosive environment of the coolant, the electrolyte is compounded according to the proportions of each component to form a synergistic system encompassing "film formation-regulation-enhancement-pore sealing." Sodium silicate and sodium hydroxide provide the basic framework for the film layer and ensure the film formation environment, while potassium pyrophosphate, as the core regulator, achieves multiple functions of complexation, dispersion, and discharge optimization, ensuring uniform and defect-free film growth. Sodium aluminate and potassium fluorotitanate form a wear-resistant and corrosion-resistant composite ceramic phase in the film layer, while the synergistic effect of potassium pyrophosphate achieves uniform distribution and micropore sealing. The components work together to solve the problems of loose film formation, poor corrosion resistance, many film defects, and insufficient wear resistance in traditional magnesium alloy micro-arc oxidation electrolytes. Ultimately, a uniform, dense, strong, hard, corrosion-resistant, and wear-resistant ceramic film is formed on the magnesium alloy surface. It can still maintain excellent corrosion resistance under high-temperature coolant immersion and circulating flushing environments, and is fully adapted to the harsh working conditions of key components such as automotive magnesium alloy electric drive water channels.

[0021] Simultaneously, by combining a progressive voltage boosting control strategy with precise control of process parameters such as temperature and current density, the conductivity stability of the electrolyte is improved, violent discharge jumps are suppressed, and repeatability is improved, thereby obtaining a composite ceramic film structure with uniform thickness and good dense layer continuity, significantly improving batch consistency and long-term durability.

[0022] The second aspect of the present invention provides a magnesium alloy with an in-situ grown oxide film on its surface, which is prepared by the magnesium alloy micro-arc oxidation process provided in the first aspect of the present invention.

[0023] The third aspect of the present invention also provides an application of magnesium alloys with in-situ grown oxide films as provided in the second aspect of the present invention in cooling water channels of new energy vehicles.

[0024] The advantages of the magnesium alloy and the above-mentioned process compared to the prior art are the same, and will not be repeated here. Attached Figure Description

[0025] To more clearly illustrate the technical solution of this application, the drawings used in the description of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a process flow diagram of the micro-arc oxidation process for magnesium alloys according to an embodiment of this application; Figure 2 This is an appearance diagram of the magnesium alloy electrically driven waterway after micro-arc oxidation as described in Embodiment 2 of this application; Figure 3 Micrograph (50 μm) of the micro-arc oxidation layer of the magnesium alloy electric drive water channel described in Example 2 of this application; Figure 4 Micrograph of the metallographic structure (200 μm) of the micro-arc oxide layer of the magnesium alloy electric drive water channel described in Example 2 of this application. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] In related technologies, relatively mature micro-arc oxidation processes for magnesium alloys have been established. For example, various electrolyte formulations for silicate, aluminate, and composite systems have been invented, and the influence of different electrolyte systems on the film structure has been studied. However, current technical solutions mostly focus on optimizing single factors, such as adjusting only the electrolyte formulation or only locally optimizing process parameters, lacking an overall matching design for specific service environments. Especially in the actual application scenarios of cooling water channels for electric drives in new energy vehicles, magnesium alloy components are exposed to a coolant environment containing complex additives for a long time, coupled with high temperature, high humidity, and electrochemical coupling corrosion. The film not only needs to have initial corrosion resistance, but also needs to maintain structural stability and density under long-term cyclic scouring and temperature fluctuations. Simply relying on traditional silicate or aluminate systems or simply adjusting process parameters makes it difficult to simultaneously achieve discharge stability, pore structure controllability, and dense layer strengthening effect, thus failing to meet the reliability requirements of long-term service of cooling water channels.

[0029] Therefore, current designs do not adequately address the unique service conditions of electric drive cooling channels in new energy vehicles, which operate under high temperature, high humidity, and high electrochemical corrosion environments. Consequently, optimizing micro-arc oxidation process parameters and electrolyte systems to achieve controllable film structure, stable performance, high batch consistency, and significantly improved long-term corrosion resistance of magnesium alloys in complex coolant environments has become a pressing technical challenge in this field.

[0030] In view of this, the main objective of this invention is to provide a micro-arc oxidation process that, through systematic analysis of the electrolyte system composition, electrochemical reaction behavior, and discharge evolution process, proposes a special electrolyte system composed of sodium silicate, potassium pyrophosphate, sodium aluminate, sodium hydroxide, and potassium fluorotitanate, and combines it with specific process parameters and an equal-interval voltage boosting control strategy. In this process, the electrolyte components are compounded in proportion to form a synergistic system encompassing film formation, regulation, enhancement, and pore sealing. Sodium silicate and sodium hydroxide provide the basic framework for the film layer and ensure the film formation environment; potassium pyrophosphate, as the core regulator, performs multiple functions including complexation, dispersion, and discharge optimization, ensuring uniform and defect-free film growth; sodium aluminate and potassium fluorotitanate form a wear-resistant and corrosion-resistant composite ceramic phase in the film layer, while the synergistic effect of potassium pyrophosphate achieves uniform distribution and micropore sealing. The components work synergistically to optimize film formation rate, porosity, and dense layer thickness, solving the problems of loose film formation, poor corrosion resistance, numerous defects, and insufficient wear resistance in traditional magnesium alloy micro-arc oxidation electrolytes. This results in a uniform, dense, strongly bonded, high-hardness, highly corrosion-resistant, and wear-resistant ceramic film on the magnesium alloy surface, perfectly suited to the demanding operating conditions of critical components such as automotive magnesium alloy electric drive water channels. Furthermore, by incorporating specific process parameters and an equal-interval voltage boosting control strategy based on the electrolyte, the stability of the micro-arc oxidation discharge process can be effectively improved, thereby reducing batch-to-batch differences in film thickness and structure, and decreasing the number of internal defects in the film.

[0031] Based on the above technical requirements, the technical solution of this application will be further described below with reference to specific embodiments.

[0032] In a first aspect, the present invention aims to provide a micro-arc oxidation process for magnesium alloys, comprising the following steps: S101. After pretreatment, the magnesium alloy workpiece to be treated is placed in the electrolyte. The electrolyte consists of sodium silicate 5-10 g / L; potassium pyrophosphate 10-15 g / L; sodium aluminate 1-3 g / L; sodium hydroxide 3-5 g / L; and potassium fluorotitanate 1-10 g / L.

[0033] In step S101, the micro-arc oxidation process provided in this embodiment is applicable to various types of magnesium alloy workpieces, or can be selected from magnesium-based alloy components containing a magnesium mass fraction greater than 1%. For example, vehicle parts such as electric drive system housings, cooling water channels, water pump housings, motor end covers, electronic control housings, heat dissipation module structural components, and lightweight support components can be selected as the magnesium alloy workpieces to be processed. Of course, the magnesium alloy workpieces to be processed can also be applied to other fields such as aircraft parts, electronic components, military components, and medical device components. Similarly, in addition to being applicable to the surface treatment of magnesium alloy workpieces, this embodiment of the invention can also be applied to the treatment of other metallic materials such as magnesium, aluminum alloys, and titanium alloys by adjusting the electrical parameters in other embodiments.

[0034] It is worth mentioning that the electrolyte of this invention is particularly suitable for processing magnesium alloys, especially for selecting cooling water channel components of electric drive systems in new energy vehicles as the magnesium alloy workpieces to be processed. Cooling water channels made of magnesium alloys are in long-term direct contact with coolant containing various additives during use, and are subjected to high temperature, high humidity, and electrochemical coupling corrosion environments, requiring high density, corrosion resistance, and long-term stability of the film layer. The specific electrolyte system provided in this application is designed specifically for magnesium alloy substrates, enabling the micro-arc oxidation film layer formed in situ on the surface of the magnesium alloy workpiece during micro-arc oxidation to have a high density ratio and low porosity, effectively inhibiting coolant penetration and electrochemical corrosion, thereby significantly improving the service life and reliability of the cooling water channel components.

[0035] Specifically, a pretreatment is performed on the magnesium alloy workpiece before micro-arc oxidation. This pretreatment removes surface oil, oxide film, and impurities from the magnesium alloy, providing stable initial interface conditions for subsequent micro-arc oxidation discharge, thereby improving the adhesion and consistency of the formed film. For example, the pretreatment includes at least one step: part acceptance, loading into the electrolytic cell, organic solvent degreasing, chemical degreasing, activation treatment, ultrasonic water washing, and alkaline etching. The pretreated magnesium alloy workpiece is placed in an electrolytic cell, and the components are added in proportion, stirred and dissolved, with the pH value controlled above 12. Simultaneously, a circulating cooling system is activated to facilitate the micro-arc oxidation film formation process.

[0036] A major improvement in this embodiment lies in the electrolyte system specifically designed for film formation on magnesium alloy workpieces. The following is a detailed description of the electrolyte provided in this embodiment during the micro-arc oxidation process: Sodium silicate and sodium hydroxide work synergistically as core film-forming and alkalinity-regulating components: Sodium silicate acts as the main film-forming agent. Under the high-temperature and high-pressure discharge environment of micro-arc oxidation, silicate ions combine with magnesium and oxygen ions to form a magnesium silicate ceramic phase, providing basic hardness and density to the film layer and serving as the skeleton component of the ceramic film. Sodium hydroxide acts as an alkalinity regulator, controlling the electrolyte pH above 12. This ensures that the magnesium alloy substrate surface is in an alkaline passivation state, preventing excessive corrosion of the substrate during micro-arc oxidation. It also provides a stable alkaline environment for the hydrolysis of sodium silicate and the dissociation of silicate ions, promoting the orderly growth of the magnesium silicate ceramic phase. The synergistic participation of sodium silicate and sodium hydroxide in the oxidation reaction not only constructs the ceramic skeleton of the film layer but also ensures the stability of the substrate during film formation, preventing corrosion voids at the film-substrate interface and enhancing film adhesion.

[0037] Potassium pyrophosphate participates in the complementary synergistic effect of the other four components: Potassium pyrophosphate is a key synergistic regulator in this electrolyte system, possessing four functions: complexation, dispersion, film formation aid, and optimized discharge characteristics. It is the core of achieving synergy among the components and improving the overall performance of the film. Its synergistic effect with other components runs through the entire film formation process, as described below: Synergistic complexation of potassium pyrophosphate and magnesium alloy substrate: Pyrophosphate ions can form stable magnesium pyrophosphate complexes with magnesium ions dissolved on the magnesium alloy surface, which can effectively inhibit excessive dissolution of the magnesium alloy substrate in the early stage of micro-arc oxidation and slow down local pitting corrosion. At the same time, the complex slowly dissociates around the discharge channel, providing a uniform magnesium ion source for film growth and avoiding loose film and pinhole defects caused by uneven substrate dissolution.

[0038] Synergistic film-forming effect of potassium pyrophosphate and sodium silicate: The dispersing effect of pyrophosphate ions can effectively prevent silicate ions from agglomerating in the electrolyte, ensuring that silicate ions are uniformly distributed on the magnesium alloy surface. Together with the magnesium pyrophosphate complex, they participate in the construction of the ceramic film, making the magnesium silicate ceramic phase uniformly dispersed in the film, greatly improving the density and uniformity of the film. At the same time, the presence of potassium pyrophosphate can reduce the crystal grain size of the magnesium silicate ceramic phase, making the microstructure of the film finer and reducing the generation of microcracks.

[0039] Synergistic effect of potassium pyrophosphate and potassium fluorotitanate at the interface: Potassium pyrophosphate can promote the adsorption of titanium fluoride complex ions from potassium fluorotitanate onto the magnesium alloy surface, guide the enrichment of titanium elements at the discharge channels of the film, and form a dense titanium-based ceramic phase (such as titanium oxide and fluorotitanate) together with fluoride ions, sealing the micropores formed by the discharge channels and achieving the self-sealing effect of the film; at the same time, the complexation effect of pyrophosphate can prevent titanium ions from precipitating in the electrolyte, ensuring that titanium elements continue to participate in film formation, and improving the corrosion resistance and hardness of the film.

[0040] Optimizing micro-arc discharge characteristics: Potassium pyrophosphate can regulate the conductivity and ion migration rate of the electrolyte, transforming the discharge during the micro-arc oxidation process from "localized concentrated large discharge" to "uniform small discharge throughout the entire area". This avoids defects such as electrical burns and localized ablation of the film caused by concentrated discharge, ensuring a smooth film surface. At the same time, uniform discharge allows the ceramic film to grow more fully in situ on the magnesium alloy surface, improving the metallurgical bonding between the film and the substrate.

[0041] Sodium aluminate and potassium fluorotitanate work together to enhance wear and corrosion resistance: Sodium aluminate dissociates into aluminate ions in alkaline electrolyte, forming an alumina ceramic phase during micro-arc oxidation discharge. The high hardness of alumina significantly improves the wear resistance of the film, while the alumina phase fills the gaps in the magnesium silicate ceramic phase, further increasing the film density. Potassium fluorotitanate dissociates into titanium fluoride complex ions, forming a titanium-based ceramic phase in the discharge region. This phase possesses both high hardness and excellent chemical corrosion resistance, resisting the intrusion of corrosive media such as coolant and salt spray. Simultaneously, fluoride ions form a passivation layer on the magnesium alloy surface, inhibiting electrochemical corrosion of the substrate. The two work synergistically: the alumina phase enhances the wear resistance of the film, while the titanium-based ceramic phase strengthens its corrosion resistance, forming a dual-reinforcement system of "wear resistance + corrosion resistance." Both phases can intercalate with magnesium silicate ceramics to construct a dense composite ceramic film, avoiding performance shortcomings caused by uneven distribution of a single reinforcing phase.

[0042] S102. Micro-arc oxidation treatment of magnesium alloy workpieces is performed using an electrolyte. During the micro-arc oxidation treatment, the pH value of the electrolyte is greater than 12; the treatment temperature is 25±5℃; the current density is 1~5 A / dm²; and the treatment time is 5~60 min.

[0043] In step S102, during the micro-arc oxidation treatment, the magnesium alloy workpiece to be treated can be connected to the positive terminal of the power supply as the anode via a conductive hanger. A stainless steel plate is placed inside the electrolytic cell as the cathode and connected to the negative terminal of the power supply, with the distance between the anode and cathode controlled at a certain level. The electrolyte prepared in step S101 is added to the electrolytic cell, and the circulation and cooling systems are started to stabilize the electrolyte temperature at 25±5℃, with the pH value checked to be greater than 12. The power supply is started, with the initial voltage set to 120V and the initial current to 6A, forming an initial oxide film layer on the anode surface. As the voltage gradually increases to the breakdown voltage, a micro-arc discharge phenomenon occurs on the anode surface, forming a localized high-temperature plasma channel. Under the action of the plasma, the magnesium alloy matrix and electrolyte components undergo a high-temperature reaction and rapid quenching, forming an oxide film layer structure containing MgO and a composite ceramic phase. During the discharge process, the current density is controlled at 1–5 A / dm², and the voltage is gradually increased by 20 V every 2 minutes until it reaches 300 V. This allows the discharge to gradually shift from localized concentration to uniform distribution, forming an outer porous layer and an inner dense layer structure. The entire treatment time is controlled within 5–60 minutes, during which the electrolyte temperature, current changes, and discharge status are continuously monitored. After treatment, the voltage is gradually reduced, the power supply is disconnected, the workpiece is removed, and it is washed with water.

[0044] S103. Perform component analysis on the electrolyte at preset intervals, and adjust the concentration of each component in the electrolyte based on the analysis results. In this embodiment, component analysis can be performed periodically (e.g., every 3 days) once or multiple times, including but not limited to pH analysis, conductivity analysis, analysis of each ion concentration, and Mg content analysis. 2+ Content analysis, etc. Based on the analysis results, the corresponding components can be replenished according to the loss of each component, and the electrolyte can be partially replaced when necessary. Therefore, through periodic component analysis and adjustment, the electrolyte is always maintained within a specific concentration window, preventing conductivity fluctuations, thereby reducing batch differences and improving membrane consistency.

[0045] Thus, by optimizing the electrolyte components for the corrosive environment of the coolant, and compounding the electrolyte according to the proportions of each component, a synergistic system of "film formation-regulation-enhancement-sealing" is formed. Sodium silicate and sodium hydroxide provide the basic framework for the film layer and ensure the film formation environment, while potassium pyrophosphate, as the core regulator, achieves multiple functions of complexation, dispersion, and discharge optimization, ensuring uniform and defect-free film growth. Sodium aluminate and potassium fluorotitanate form a wear-resistant and corrosion-resistant composite ceramic phase in the film layer, while achieving uniform distribution and micropore sealing through the synergistic effect of potassium pyrophosphate. The synergistic effect of each component solves the problems of loose film formation, poor corrosion resistance, many film defects, and insufficient wear resistance in traditional magnesium alloy micro-arc oxidation electrolytes. Ultimately, a uniform, dense, strongly bonded, high-hardness, excellent corrosion resistance, and good wear resistance ceramic film layer is formed on the magnesium alloy surface. It can still maintain excellent corrosion resistance under high-temperature coolant immersion and circulating flushing environments, fully meeting the harsh operating conditions of key components such as automotive magnesium alloy electric drive water channels.

[0046] Simultaneously, by combining a progressive voltage boosting control strategy with precise control of process parameters such as temperature and current density, the conductivity stability of the electrolyte is improved, violent discharge jumps are suppressed, and repeatability is improved, thereby obtaining a composite ceramic film structure with uniform thickness and good dense layer continuity, significantly improving batch consistency and long-term durability.

[0047] As a specific explanation of step S101 in this embodiment, the pretreatment includes: organic solvent cleaning and degreasing, mounting parts, degreasing with a degreasing agent, activation, ultrasonic water washing, and alkaline etching. This embodiment, through a multi-stage pretreatment process involving organic solvent degreasing, chemical degreasing, activation, water washing, and alkaline etching, can progressively remove organic contaminants, oxide films, and processing stress layers from the workpiece surface, forming a uniform micro-coarsening structure on the substrate surface. This makes the surface resistance distribution and breakdown voltage distribution of the magnesium alloy more consistent, thereby significantly improving the discharge uniformity and film formation stability of the micro-arc oxidation process, avoiding localized ablation, and improving film adhesion and batch consistency.

[0048] Magnesium alloy cooling channels are characterized by complex internal cavities, long and narrow flow channels, and a tendency to accumulate oil and residual processing fluid. This embodiment utilizes a two-stage degreasing process combined with multiple pretreatment steps to thoroughly remove oil from blind holes, ensuring uniform film formation within the internal cavity and improving resistance to coolant corrosion. Therefore, it is particularly suitable for the pretreatment of magnesium alloy cooling channels in environments with circulating coolant.

[0049] Preferably, organic solvent degreasing is performed: Acetone, gasoline, or other organic solvents, or water-based cleaners conforming to HB 5226 standard, are used for preliminary degreasing of the parts. Magnesium alloy workpieces can be soaked, sprayed, or wiped using organic solvents or water-based cleaners for 1–10 minutes at room temperature. This preliminary degreasing dissolves and removes lubricating oil, rust-preventive oil, and residual machining grease from the workpiece surface, creating a continuous water film that provides a clean surface for subsequent chemical degreasing and micro-arc oxidation treatments.

[0050] Preferably, after degreasing with organic solvent, an aluminum or titanium fixture is used to clamp the magnesium alloy workpiece in a conductive position specified in the process design or with a process allowance.

[0051] Preferably, chemical degreasing: use magnesium alloy degreasing agent 530 with a concentration of 80-100g / L, and perform secondary degreasing at a temperature of 50±5℃ for 5-10 minutes. If the product surface contains metal shavings or heavy oil stains after degreasing, wipe it clean with organic solvents such as alcohol. The water film on the degreased parts must be continuous within 30 seconds. For some special products with severe oil stains on the surface, the soaking time can be increased.

[0052] Preferably, activation is performed by immersing the magnesium alloy workpiece in activator M1 at a concentration of 190-220 ml / L at room temperature for 3-5 minutes. The magnesium alloy workpiece, after secondary degreasing, is placed in the activator M1 solution and immersed at room temperature. This selectively dissolves the original oxide film on the workpiece surface, reduces surface resistance, and increases substrate activity, resulting in a more uniform breakdown voltage distribution on the workpiece surface and thus improving the stability of the subsequent micro-arc oxidation film formation process.

[0053] Preferably, ultrasonic water washing: The activated magnesium alloy workpiece is ultrasonically washed at room temperature for 1-2 minutes. The residual activator and reaction byproducts adhering to the workpiece surface are removed by ultrasonic cavitation, ensuring the uniformity of the reaction in the subsequent alkaline etching and micro-arc oxidation processes.

[0054] Preferably, alkaline etching involves immersing the magnesium alloy workpiece, after ultrasonic water washing, in an alkaline etching agent 920 solution with a concentration of 190–220 ml / L, and subjecting it to an alkaline etching process at 80±5℃ for 1–2 minutes. This alkaline etching treatment achieves controllable and uniform micro-dissolution of the workpiece surface, forming a uniform micro-coarsening structure on the magnesium alloy surface. This results in a more uniform surface electric field distribution, reduces local discharge concentration, and improves the stability and adhesion strength of the micro-arc oxidation film.

[0055] In the specific implementation process, after step S102, the process further includes: performing a hot water sealing treatment on the magnesium alloy workpiece after micro-arc oxidation. The sealing liquid penetrates into the pores of the micro-arc oxidation film and undergoes a hydration or deposition reaction, reducing the film porosity and improving the film's density and corrosion resistance. Subsequently, a drying process is performed to remove residual moisture and sealing liquid, preventing water vapor retention or localized corrosion during subsequent storage or service.

[0056] Preferably, hot water sealing: hot water at a temperature of 85±5℃ is used for hot water immersion sealing. During the sealing process, the hot water should remain clear and transparent with a conductivity of less than 60 ms / cm, and the sealing time should be controlled at 20±5 min.

[0057] Preferably, the drying process involves using compressed air at a pressure greater than or equal to 0.4 MPa to blow away impurities and residual liquid from the blind holes of the product; the drying is carried out in a tank-type drying oven at a temperature of 100±10℃ for a time of 20±5 min.

[0058] The following description, in conjunction with the above embodiments and accompanying drawings, provides a detailed explanation of a specific technical solution of the present invention.

[0059] like Figure 1 As shown, Figure 1 A process flow diagram of the magnesium alloy micro-arc oxidation process of this embodiment is shown. This embodiment provides a magnesium alloy micro-arc oxidation process, including the following steps: organic solvent degreasing, parts mounting, degreasing, activation, ultrasonic water washing, alkaline etching, micro-arc oxidation, hot water sealing and drying, and finally unmounting to complete the process. First, the parts are inspected before processing. The surface quality of the parts should meet the requirements of HB 5034, and the sharp edges and corners of the parts should be rounded with a radius not less than 0.5 mm.

[0060] The specific implementation process of the micro-arc oxidation process is as follows: S1. Organic solvent degreasing: Use organic solvents such as acetone and gasoline, or water-based cleaners that meet the HB 5226 standard to degrease the parts.

[0061] S2. Part mounting: Use aluminum or titanium fixtures to clamp the parts in conductive positions specified in the process design or with process allowance.

[0062] S3. Degreasing and oil removal: Use magnesium alloy degreasing agent 530 with a concentration of 80-100g / L to remove oil at a temperature of 50±5℃ for 5-10 minutes. If the product surface contains metal shavings or heavy oil stains after degreasing, wipe it clean with organic solvents such as alcohol. The water film on the degreased parts must be continuous within 30 seconds. For some special products with severe oil stains on the surface, the soaking time can be increased.

[0063] S4. Activation: Use activator M1 with a concentration of 190-220 ml / L to soak and activate at room temperature for 3-5 minutes. S5. Ultrasonic water washing: After activation, perform ultrasonic water washing at room temperature for 1-2 minutes. S6. Alkali etching: Use alkaline etch 920 with a concentration of 190-220 ml / L and carry out the alkaline etching process for 1-2 minutes at a temperature of 80±5℃. S7. Micro-arc oxidation: Micro-arc oxidation is performed using an electrolyte with the following components: sodium silicate 5-10 g / L, potassium pyrophosphate 10-15 g / L, sodium aluminate 1-3 g / L, sodium hydroxide 3-5 g / L, and potassium fluorotitanate 1-10 g / L. Among the key parameters in the micro-arc oxidation process, the pH value must be greater than 12, the temperature must be controlled at 25±5℃, and the current density must be controlled at 1-5 A / dm³. 2 The time should be controlled between 5-60 minutes. During the micro-arc oxidation process, the initial current of the equipment power supply should be 6A and the initial voltage should be 120V. If the product is small, it should be manually adjusted to a voltage stabilization method, increasing the voltage by 20V every 2 minutes until it reaches 300V. The electrolyte in the micro-arc oxidation tank needs to be analyzed and adjusted regularly, once every 3 days.

[0064] S8. Hot water sealing: Use hot water at a temperature of 85±5℃ for hot water immersion sealing. During the sealing process, the hot water should remain clear and transparent with a conductivity of less than 60ms / cm. The sealing time should be controlled at 20±5min.

[0065] S9. Drying: Use compressed air of ≥0.4MPa to blow away impurities and residual liquid from the blind holes of the product; use a tank-type drying box for drying, with a drying temperature of 100±10℃ and a drying time of 20±5min.

[0066] S10. Finally, after the product is dried, hang it up and test it.

[0067] Maintenance: When the machine has not been used for a long time during holidays, it should be tested and adjusted according to the pre-start analysis before normal production can begin. The degreasing, pickling, alkaline etching, passivation, and sealing tanks should be replaced every 2 months. The micro-arc oxidation tank solution should be replaced weekly, and the water washing tank solution should be replaced weekly, or the replacement frequency can be appropriately reduced according to the actual production situation.

[0068] In summary, by constructing a uniform discharge interface through multi-stage pretreatment, optimizing the film structure using a composite electrolyte system containing potassium pyrophosphate, stabilizing the discharge process through a gradual voltage ramp control method, and further reducing film porosity through hot water sealing, the film thickness consistency, bonding strength, and coolant corrosion resistance are significantly improved, reducing batch-to-batch quality fluctuations and meeting the durability requirements of new energy vehicle electric drive cooling water channels under long-term high temperature, high humidity, and electrochemical corrosion environments.

[0069] To enable those skilled in the art to more clearly understand the present invention, the magnesium alloy micro-arc oxidation process of the present invention will now be described in detail through the following embodiments.

[0070] Example 1: A micro-arc oxidation process for magnesium alloys includes the following steps: S11. Use acetone to degrease the magnesium alloy electric drive water channel (hereinafter referred to as the part).

[0071] S12. Use aluminum fixtures to clamp the parts in conductive positions specified in the process design or with process allowances.

[0072] S13. Use magnesium alloy degreasing agent 530 with a concentration of 80g / L to remove oil at a temperature of 50±5℃ for 5 minutes.

[0073] S14. Use activator M1 with a concentration of 190 ml / L to perform immersion activation at room temperature for 3 minutes.

[0074] S15. After activation, perform ultrasonic water washing at room temperature for 1 minute.

[0075] S16. Use alkaline etching solution 920 with a concentration of 190 ml / L and perform an alkaline etching process at a temperature of 80 ± 5 °C for 1 minute.

[0076] S17. Prepare the electrolyte, comprising: sodium silicate 5 g / L; potassium pyrophosphate 10 g / L; sodium aluminate 1 g / L; sodium hydroxide 3 g / L; and potassium fluorotitanate 1 g / L. Immerse the parts in the electrolyte, maintaining the temperature at 25±5℃ and the current density at 1 A / dm³. 2 The time is controlled within 5 minutes. The initial current of the electro-oxidation equipment is 6A, and the initial voltage is 120V. The voltage increases by 20V every 2 minutes until it reaches 300V.

[0077] S18. Use hot water at a temperature of 85±5℃ for hot water immersion sealing. During the sealing process, the hot water should remain clear and transparent with a conductivity of less than 60 mS / cm. The sealing time should be controlled at 20±5 min. S19. Use compressed air of ≥0.4MPa to blow away impurities and residual liquid from the blind holes of the product; use a tank-type drying oven to dry the product at a temperature of 100±10℃ for a time of 20±5min.

[0078] Example 2: A micro-arc oxidation process for magnesium alloys includes the following steps: S21. Use acetone to degrease the magnesium alloy electric drive water channel (hereinafter referred to as the part).

[0079] S22. Use aluminum fixtures to clamp the parts in conductive positions specified in the process design or with process allowances.

[0080] S23. Use magnesium alloy degreasing agent 530 with a concentration of 100g / L to remove oil at a temperature of 50±5℃ for 10min.

[0081] S24. Use activator M1 with a concentration of 220 ml / L and soak and activate at room temperature for 5 minutes.

[0082] S25. After activation, perform ultrasonic water washing at room temperature for 2 minutes.

[0083] S26. Use alkaline etching solution 920 with a concentration of 220 ml / L and perform an alkaline etching process at a temperature of 80 ± 5 °C for 2 minutes.

[0084] S27. Prepare the electrolyte, comprising: sodium silicate 10 g / L; potassium pyrophosphate 15 g / L; sodium aluminate 3 g / L; sodium hydroxide 5 g / L; and potassium fluorotitanate 10 g / L. Immerse the parts in the electrolyte, maintaining the temperature at 25±5℃ and the current density at 5A / dm³. 2 The time is controlled at 60 minutes. The initial current of the electro-oxidation equipment is 6A, and the initial voltage is 120V. The voltage increases by 20V every 2 minutes until it reaches 300V.

[0085] S28. Use hot water at a temperature of 85±5℃ for hot water immersion sealing. During the sealing process, the hot water should remain clear and transparent with a conductivity of less than 60 mS / cm. The sealing time should be controlled at 20±5 min. S29. Use compressed air of ≥0.4MPa to blow away impurities and residual liquid from the blind holes of the product; use a tank-type drying oven to dry the product at a temperature of 100±10℃ for a time of 20±5min.

[0086] Example 3: Unlike Example 2, the electrolyte composition includes 6 g / L sodium silicate; 11 g / L potassium pyrophosphate; 1.5 g / L sodium aluminate; 3.5 g / L sodium hydroxide; and 2 g / L potassium fluorotitanate.

[0087] Example 4: Unlike Example 2, the electrolyte composition includes 7 g / L sodium silicate; 12 g / L potassium pyrophosphate; 2 g / L sodium aluminate; 4 g / L sodium hydroxide; and 4 g / L potassium fluorotitanate.

[0088] Example 5: Unlike Example 2, the electrolyte composition includes 8 g / L sodium silicate; 13 g / L potassium pyrophosphate; 2.5 g / L sodium aluminate; 4.5 g / L sodium hydroxide; and 6 g / L potassium fluorotitanate.

[0089] Example 6: Unlike Example 2, the electrolyte composition includes 9 g / L sodium silicate; 14 g / L potassium pyrophosphate; 3 g / L sodium aluminate; 5 g / L sodium hydroxide; and 8 g / L potassium fluorotitanate.

[0090] Example 7: Unlike Example 2, in the micro-arc oxidation process, the pH value was controlled at 12 and the current density was controlled at 2 A / dm³. 2 The time should be controlled within 20 minutes.

[0091] Example 8: Unlike Example 2, in the micro-arc oxidation process, the pH value was controlled at 12 and the current density was controlled at 3 A / dm³. 2 The time should be controlled within 30 minutes.

[0092] Example 9: Unlike Example 2, in the micro-arc oxidation process, the pH value was controlled at 12 and the current density was controlled at 4 A / dm³. 2 The time should be controlled within 50 minutes.

[0093] Example 10: Unlike Example 2, the magnesium alloy parts were replaced with aluminum alloy parts.

[0094] Example 11: Unlike Example 2, potassium pyrophosphate was not added to the electrolyte components.

[0095] Example 12: Unlike Example 2, potassium fluorotitanate was not added to the electrolyte components.

[0096] Example 13: Unlike Example 1, the acetone degreasing step in S11 is omitted.

[0097] Example 14: Unlike Example 1, the degreasing step in S13 is omitted.

[0098] Example 15: Unlike Example 1, the activation step in S14 is omitted.

[0099] Example 16: Unlike Example 1, the ultrasonic water washing step in S15 is omitted.

[0100] Example 17: Unlike Example 1, the alkaline etching step in S16 is omitted.

[0101] Example 18: Unlike Example 1, the closing step in S18 is omitted.

[0102] Example 19: Unlike Example 1, the drying step in S19 is omitted.

[0103] Example 20: Unlike Example 1, the order of the activation step in S14 and the alkaline etching step in S16 is replaced.

[0104] Finally, the magnesium alloy workpieces with micro-arc oxide films prepared in Examples 1-20 were hung up, and twenty products were tested respectively. The tests specifically included the following: 1. Visual Inspection: The parts were visually inspected under natural diffused light or non-reflective light. A 3-5x magnifying glass could be used if necessary. The micro-arc oxidation films of the eleven products corresponding to Examples 1-10 and Example 19 were observed to be continuous and uniform, without defects such as cracks, localized peeling, electrical burns, or loose adhesion. Three products showed fixture marks and slight traces of sealed liquid flow, but these were acceptable. Due to differences in the base metal chemical composition, film thickness, process parameters, and surface condition of the twenty products, they exhibited different colors and glosses.

[0105] 2. Film thickness detection: The film thickness of the product prepared in each embodiment was measured according to GB / T4957 method for measuring the thickness of non-conductive coating on non-magnetic metal substrate. The thickness of the micro-arc oxidation film of the product was controlled within 10-40μm. The specific micro-arc oxidation film thickness was determined according to actual needs.

[0106] 3. Salt spray resistance: Tested according to GB / T 10125 "Artificial Atmosphere Corrosion Salt Spray Test", the obtained magnesium alloy micro-arc oxide film did not show corrosion or peeling after 1000h of neutral salt spray test. Except for the magnesium alloy micro-arc oxide film layer after sealing treatment in Example 18, which did not show corrosion or peeling after 336h of acidic salt spray test, a few products showed slight discoloration and local darkening.

[0107] 4. Resistance to filiform corrosion: The test was conducted according to GB / T 13452.4 "Resistance to filiform corrosion of coatings on steel surfaces with paints and varnishes". After 240 hours of testing, the average length of corrosion filiforms near the scratches on the magnesium alloy micro-arc oxide film did not exceed 3 mm.

[0108] 5. Resistance to coolant corrosion: Tested according to SH / T 0085 "Determination of corrosion of engine coolant (glassware method) - Coolant test method", after 1500h of test, the corrosion rate of the obtained magnesium alloy micro-arc oxide film is less than 0.0223mm / y.

[0109] 6. Resistance to damp heat: Tested according to GJB150.9 "Laboratory Environmental Test Methods for Military Equipment Part 9: Damp Heat Test", after 1000h of damp heat test, no corrosion or peeling was observed in the obtained magnesium alloy micro-arc oxide film.

[0110] 7. Antifungal properties: According to GJB150.9 "Laboratory Environmental Test Methods for Military Equipment Part 10: Antifungal Test", after 28 days of antifungal testing, the antifungal properties of the obtained magnesium alloy micro-arc oxide films are all greater than level 1.

[0111] 8. Hardness: The hardness of the products was tested according to GB / T4340.1 "Metallic materials Vickers hardness test - Part 1: Test method". Among the products with hardness requirements, the hardness of the magnesium alloy micro-arc oxide film layer met the requirements and was greater than 800 HV.

[0112] 9. Abrasion resistance: In accordance with HB 5057-1993 "Quality Inspection of Hard Anodized Films on Aluminum and Aluminum Alloys". The product is tested after the conveyor layer is removed. For products with abrasion resistance requirements, the abrasion loss of the magnesium alloy micro-arc oxide film is less than 20mg.

[0113] like Figures 2-4 As shown, Figure 2 This is an image showing the appearance of the magnesium alloy electrically driven waterway after micro-arc oxidation in Example 2; Figure 3 and Figure 4 The images show the metallographic structure of the magnesium alloy electrically driven waterway after micro-arc oxidation using the process described in Example 2, observed at 50 μm and 200 μm. Figures 2-4As can be seen, the micro-arc oxidation film prepared using the micro-arc oxidation process provided in Example 2 exhibits excellent quality. The micro-arc oxidation film is continuous and uniform, without obvious defects such as cracks, peeling, or electrical burns; and the film thickness is controllable and can be adjusted according to production needs. The obtained product showed no corrosion or peeling in a 1000-hour neutral salt spray test, a 336-hour acidic salt spray test after sealing treatment, and a 1000-hour damp heat test. Its resistance to filamentous corrosion was greater than 240 hours, and its resistance to coolant corrosion was greater than 1500 hours, demonstrating excellent corrosion resistance. After a 28-day mold test, the antibacterial grade was greater than 1, indicating good environmental tolerance. The magnesium alloy micro-arc oxidation film of the obtained product has a hardness of over 800 HV, meeting the requirements for high-strength use, and exhibits good wear resistance with a wear amount of less than 20 mg, complying with relevant standards.

[0114] Therefore, the above experiments demonstrate that the magnesium alloy micro-arc oxidation film prepared using the magnesium alloy micro-arc oxidation process provided by this invention can meet the production requirements in terms of appearance and film thickness. Furthermore, the prepared product exhibits excellent performance in terms of salt spray resistance, damp heat resistance, mildew resistance, hardness, and wear resistance. Applying the prepared product to the water channels of magnesium alloy electric drives can effectively improve the corrosion resistance of the water channels and prevent the water channels from being corroded by coolant.

[0115] Correspondingly, in a second aspect, the present invention provides a magnesium alloy with an in-situ grown oxide film on its surface, prepared by the magnesium alloy micro-arc oxidation process provided in the first aspect of the present invention.

[0116] Correspondingly, in a third aspect, the present invention also provides an application of magnesium alloys with in-situ grown oxide films as described above in cooling water channels of new energy vehicles.

[0117] For the magnesium alloy examples described above, since they are basically similar to the magnesium alloy micro-arc oxidation process examples, the description is relatively simple. For relevant details, please refer to the description of the magnesium alloy micro-arc oxidation process examples.

[0118] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0119] It should also be noted that, in this document, the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations, nor should they be construed as indicating or implying relative importance. Moreover, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device.

Claims

1. A micro-arc oxidation process for magnesium alloys, characterized in that: Includes the following steps: S101. After pretreatment, the magnesium alloy workpiece to be processed is placed in an electrolyte; the electrolyte comprises 5-10 g / L sodium silicate; 10-15 g / L potassium pyrophosphate; 1-3 g / L sodium aluminate; 3-5 g / L sodium hydroxide; and 1-10 g / L potassium fluorotitanate. S102. The magnesium alloy workpiece is subjected to micro-arc oxidation treatment using the electrolyte; during the micro-arc oxidation treatment, the pH value of the electrolyte is greater than 12; the treatment temperature is 25±5℃; the current density is 1~5 A / dm²; and the treatment time is 5~60 min. S103. Perform component analysis on the electrolyte at preset intervals, and adjust the concentration of each component of the electrolyte according to the analysis results.

2. The micro-arc oxidation process for magnesium alloys according to claim 1, characterized in that: During the micro-arc oxidation process, the starting current of the power supply of the micro-arc oxidation equipment is set to 6 A and the starting voltage is set to 120 V. The voltage is increased in stages, with the voltage increasing by 20 V every 2 minutes until it reaches 300 V.

3. The micro-arc oxidation process for magnesium alloys according to claim 1, characterized in that: In step S101, the pretreatment includes: sequentially performing organic solvent degreasing, chemical degreasing, activation, water washing, and alkaline etching on the magnesium alloy workpiece.

4. The micro-arc oxidation process for magnesium alloys according to claim 3, characterized in that: The organic solvent degreasing includes: using one or more of acetone, gasoline and water-based cleaning agents to perform preliminary degreasing on the magnesium alloy workpiece.

5. The micro-arc oxidation process for magnesium alloys according to claim 4, characterized in that: The chemical degreasing includes: using a magnesium alloy degreasing agent to perform deep degreasing on the magnesium alloy workpiece after preliminary degreasing; wherein, during the chemical degreasing process, the concentration of the magnesium alloy degreasing agent is 80-100 g / L; the chemical degreasing temperature is 50±5℃; and the chemical degreasing time is 5-10 min.

6. The micro-arc oxidation process for magnesium alloys according to claim 3, characterized in that: The activation process includes immersing the magnesium alloy workpiece in an activator with a concentration of 190–220 ml / L at room temperature for 3–5 minutes.

7. The micro-arc oxidation process for magnesium alloys according to claim 3, characterized in that: The water washing includes: washing the magnesium alloy workpiece with ultrasonic waves at room temperature for 1-2 minutes.

8. The micro-arc oxidation process for magnesium alloys according to claim 3, characterized in that: The alkaline etching process involves treating the sample with an alkaline etchant at a concentration of 190–220 ml / L at 80±5℃ for 1–2 minutes.

9. A micro-arc oxidation process for magnesium alloys according to any one of claims 1-8, characterized in that: Step S102 is followed by: sealing and drying the magnesium alloy workpiece after micro-arc oxidation.

10. The micro-arc oxidation process for magnesium alloys according to claim 9, characterized in that: The sealing process includes: immersing the magnesium alloy workpiece in hot water for sealing; wherein, during the sealing process, the temperature of the hot water is 85±5℃; the immersion time is 20±5 min; and the conductivity of the hot water during the sealing process is less than 60 ms / cm.

11. The micro-arc oxidation process for magnesium alloys according to claim 9, characterized in that: The drying process includes: blowing the magnesium alloy workpiece dry with compressed air at a pressure of not less than 0.4 MPa; and then drying the magnesium alloy workpiece in a drying oven at 100±10℃ for 20±5 min.

12. The micro-arc oxidation process for magnesium alloys according to claim 3, characterized in that: The magnesium alloy workpiece, after being degreased with organic solvent, is clamped in the reserved position of an aluminum or titanium fixture.

13. A magnesium alloy with an in-situ grown oxide film on its surface, characterized in that, It is prepared by the micro-arc oxidation process of magnesium alloy as described in any one of claims 1 to 12.

14. The application of a magnesium alloy with an in-situ grown oxide film as described in claim 13 in the cooling water channel of a new energy vehicle.

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