阅读说明：本技术 一种镁合金黑色微弧氧化膜纳米钝化剂及钝化的方法 (Magnesium alloy black micro-arc oxidation film nano passivator and passivation method ) 是由 汪超 于 2019-09-27 设计创作，主要内容包括：本发明公开了一种镁合金黑色微弧氧化膜纳米钝化剂,按照质量份包括如下组分：有机酸：1-15份,有机醇：1-20份,络合剂：1-10份,硅烷偶联剂：1-10份,氧化剂：1-10份,氧化石墨烯：1-10份,表面活性剂：0.5-2份,其中所述的有机酸包括冰乙酸和甲酸中的至少一种。该镁合金黑色微弧氧化纳米钝化剂,无磷无铬,无重金属,形成的钝化膜具有超强独立的耐腐蚀性能和与油漆涂料的紧密结合力。(The invention discloses a magnesium alloy black micro-arc oxidation film nano passivator which comprises the following components in parts by mass: organic acid: 1-15 parts, organic alcohol: 1-20 parts of complexing agent: 1-10 parts of a silane coupling agent: 1-10 parts of an oxidant: 1-10 parts of graphene oxide: 1-10 parts of surfactant: 0.5-2 parts, wherein the organic acid comprises at least one of glacial acetic acid and formic acid. The magnesium alloy black micro-arc oxidation nanometer passivator is phosphorus-free, chromium-free and heavy metal-free, and a formed passivation film has super-strong independent corrosion resistance and tight bonding force with paint coating.)

1. The magnesium alloy black micro-arc oxidation film nano passivator is characterized by comprising the following components in parts by weight: the passivator comprises the following components in parts by mass:

organic acid: 1-15 parts of (A) a stabilizer,

organic alcohol: 1-20 parts of (A) a stabilizer,

complexing agent: 1-10 parts of (A) a solvent,

Silane coupling agent: 1-10 parts of (A) a solvent,

Oxidizing agent: 1-10 parts of (A) a solvent,

Graphene: 1-10 parts of (A) a solvent,

surfactant (b): 0.5-2 parts.

2. The magnesium alloy black micro-arc oxidation film nano passivator of claim 1, characterized in that: the passivator comprises the following components in parts by mass:

Organic acid: 1-5 parts of (A) a stabilizer,

organic alcohol: 1-5 parts of (A) a stabilizer,

complexing agent: 1-5 parts of (A) a stabilizer,

silane coupling agent: 5-10 parts of (A) a water-soluble polymer,

Oxidizing agent: 1-5 parts of (A) a stabilizer,

graphene: 1-3 parts of (A) a solvent,

Surfactant (b): 0.5-1 part.

3. The magnesium alloy black micro-arc oxidation film nano passivator of claim 1, wherein the complexing agent comprises at least one of ethylene diamine tetraacetic acid, disodium ethylene diamine tetraacetic acid, sodium gluconate, sodium citrate and sodium hexametaphosphate.

4. the magnesium alloy black micro-arc oxidation film nano passivator of claim 1, wherein: wherein the organic acid comprises at least one of glacial acetic acid and formic acid; the organic alcohol comprises at least one of methanol, ethanol, propylene glycol, glycerol and ethylene glycol.

5. The magnesium alloy black micro-arc oxidation film nano passivator of claim 1, wherein: the silane coupling agent comprises at least one of vinyl triethoxy silicon, vinyl trimethoxy silane, propyl trimethoxy silane, amino propyl triethoxy silane and methyl acryloxy functional group silane.

6. The magnesium alloy black micro-arc oxidation film nano passivator of claim 1, wherein: the oxidant comprises at least one of hydrogen peroxide, potassium permanganate, sodium nitrate and sodium persulfate.

7. The magnesium alloy black micro-arc oxidation film nano passivator of claim 1, wherein: the graphene is single-layer graphene oxide or 2-10 layers of graphene oxide.

8. the magnesium alloy black micro-arc oxidation film nano passivator of claim 1, wherein: the surfactant comprises at least one of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, nonylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether.

9. the method for passivating by using the magnesium alloy black micro-arc oxidation film nano passivator according to any one of claims 1 to 8, wherein the method comprises the following steps: the method comprises the following steps:

S1, degreasing treatment: putting the magnesium alloy into a degreasing agent solution with the concentration of 50-100g/L, and controlling the temperature to be 50-80 ℃ to strip oil stains on the surface of the magnesium alloy;

S2, activation treatment: cleaning the degreased magnesium alloy by at least two times of a clean water tank, then putting the magnesium alloy into 10-15% of activating agent solution, and treating at normal temperature to uniformly corrode the surface of the magnesium alloy so that the surface of the magnesium alloy is completely uniform and black;

s3, acid surface conditioning: after ultrasonic cleaning for at least two times, the magnesium alloy after the activation treatment is placed in a solution of 20-30% of an acidic surface conditioner for normal-temperature treatment, black and grey on the surface of the magnesium alloy are uniformly removed, and the surface of the magnesium alloy is leveled and whitened;

s4, alkaline surface conditioner: cleaning the magnesium alloy subjected to acid surface conditioning for at least two times by using a clean water tank, then placing the magnesium alloy into a 10-15% solution of an alkaline surface conditioning agent, and treating at normal temperature to remove a black film which is difficult to remove by using the acid surface conditioning; neutralizing the acid surface-adjusted residual acid liquor, and further leveling the surface of the magnesium alloy;

s5, black micro-arc oxidation treatment: the magnesium alloy after alkaline surface conditioning treatment is rinsed by quick warm water and cold water and then is sent into a micro-arc oxidation tank for treatment, and the first stage is as follows: the frequency is 300-1500HZ, the duty ratio is 15-35%, and the current density is controlled to be 1-3A/DM²In the second stage, the frequency is 800-1800HZ, the duty ratio is 5-25%, and a layer of nano-scale uniform and highly corrosion-resistant micro-arc oxidation film is formed on the surface of the magnesium alloy;

s6, passivation treatment: rinsing the passivated magnesium alloy by using cold pure water, and quickly transferring the magnesium alloy into a ventilated oven with the temperature of 100-160 ℃ for drying;

s7, coating treatment: and (4) spraying paint or performing electrophoresis treatment on the magnesium alloy subjected to passivation treatment to obtain a final protective layer.

10. The method for passivating the magnesium alloy black micro-arc oxidation film nano passivator according to claim 9, wherein:

s1, degreasing treatment: the treatment time is 2-4 minutes;

S2, an activation treatment stage, wherein the normal temperature treatment time is 1-3 minutes;

S3, acid surface conditioning: the normal temperature treatment time is 3-5 minutes;

S4, alkaline surface conditioner: the normal temperature treatment time is 1-3 minutes;

s5, black micro-arc oxidation treatment: the first stage treatment time is 1-15 minutes, and the second stage treatment time is 10-15 minutes;

s6, passivation treatment: the drying time is 10-15 minutes.

Technical Field

the invention relates to the field of magnesium alloy surface treatment, in particular to a magnesium alloy black micro-arc oxidation film nano passivator and a passivation method.

Background

the magnesium alloy has the advantages of low density, high strength, impact resistance, good damping property and cutting processing property, and easy recycling, and is about 33% lighter than aluminum and 77% lighter than steel; magnesium alloy is applied to the automobile industry at home and abroad to reduce weight, save energy, reduce pollution and improve environment; meanwhile, the usage amount of magnesium alloy is increased in high-speed rail, airplane, aerospace, satellite, 3C products, building decoration materials, batteries and the like. However, magnesium is active in chemical property, is easy to oxidize in air, and rapidly generates a natural oxidation film, the corrosion resistance of the natural oxidation film is poor, so that the natural oxidation film has no protective effect at all, and the direct application of the natural oxidation film is greatly limited, therefore, the magnesium alloy can be effectively subjected to surface treatment, and the protective performance is enhanced to exert the excellent performance of the magnesium alloy.

the magnesium alloy micro-arc oxidation technology is a protection technology which develops rapidly in the last two decades: the ceramic film is mainly applied to magnesium, aluminum and titanium, can grow in situ on the surface of metal, and has comprehensive performance superior to that of anodic oxidation and chromate treatment; then, through various hole sealing means, the surface of the magnesium alloy achieves excellent performance: at present, with the coming of the 5G era, the requirements for light weight of intelligent equipment, wearable equipment, communication equipment and the like are increasingly severe; the magnesium alloy micro-arc oxidation technology is beginning to be applied to notebook computer housings in a large quantity: the film layer after micro-arc oxidation is taken as a delicate notebook shell and is finally protected in a spraying mode; the salt spray resistance of the surface of the final shell is also important, and besides the coating material, the performance of the nanometer passivator is also important.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a magnesium alloy black micro-arc oxidation film nano passivator and a passivation process thereof, so as to improve the corrosion resistance of the salt mist in a bare package of the magnesium alloy and the binding force performance of the salt mist and the coating.

The technical problem to be solved by the invention is to provide the magnesium alloy black micro-arc oxidation film nano passivator and the passivation process thereof, which do not contain phosphorus, chromium, ammonia nitrogen, heavy metals and the like, meet the environmental protection requirement of liquid medicine discharge and are environment-friendly.

in order to solve the technical problem, the invention provides a magnesium alloy black micro-arc oxidation film nano passivator which comprises the following components in parts by mass:

organic acid: 1-15 parts of (A) a stabilizer,

Organic alcohol: 1-20 parts of (A) a stabilizer,

Complexing agent: 1-10 parts of (A) a solvent,

silane coupling agent: 1-10 parts of (A) a solvent,

Oxidizing agent: 1-10 parts of

Graphene: 1-10 parts of (A) a solvent,

Surfactant (b): 0.5-2 parts.

the passivating agent comprises the following components in parts by mass:

Organic acid: 1-5 parts of (A) a stabilizer,

Organic alcohol: 1-5 parts of (A) a stabilizer,

complexing agent: 1-5 parts of (A) a stabilizer,

silane coupling agent: 5-10 parts of (A) a water-soluble polymer,

oxidizing agent: 1-5 parts of (A) a stabilizer,

graphene: 1-3 parts of (A) a solvent,

Surfactant (b): 0.5-1 part.

wherein, the complexing agent comprises at least one of EDTA, EDTA disodium, sodium gluconate, sodium citrate and sodium hexametaphosphate.

wherein the organic alcohol is at least one of methanol, ethanol, propylene glycol, glycerol and ethylene glycol; the organic acid comprises at least one of glacial acetic acid and formic acid.

Wherein the silane coupling agent is at least one of vinyl triethoxy silicon, vinyl trimethoxy silane, propyl trimethoxy silane, amino propyl triethoxy silane and methyl acryloyl oxygen functional group silane.

wherein the oxidant is at least one of hydrogen peroxide, potassium permanganate, sodium nitrate and sodium persulfate.

Preferably, the graphene is a single layer of graphene oxide or 2-10 layers of graphene oxide.

Preferably, the surfactant comprises at least one of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, nonylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether.

the invention also discloses a passivation method by applying the magnesium alloy black micro-arc oxidation film nano passivator, which comprises the following steps:

S1, degreasing treatment: putting the magnesium alloy into a degreasing agent solution with the concentration of 50-100g/L, and controlling the temperature to be 50-80 ℃ to strip oil stains on the surface of the magnesium alloy;

s2, activation treatment: cleaning the degreased magnesium alloy by at least two times of a clean water tank, then putting the magnesium alloy into 10-15% (limited range) of an activating agent solution, and treating at normal temperature to uniformly corrode the surface of the magnesium alloy so that the surface of the magnesium alloy is completely uniform and black;

s3, acid surface conditioning: after ultrasonic cleaning for at least two times, the magnesium alloy after the activation treatment is placed in a solution of 20-30% (limited range) of an acidic surface conditioner for normal-temperature treatment, black and grey on the surface of the magnesium alloy are uniformly removed, and the surface of the magnesium alloy is leveled and whitened;

S4, alkaline surface conditioner: cleaning the magnesium alloy subjected to acid surface conditioning for at least two times by using a clean water tank, then placing the magnesium alloy into a 10-15% solution of an alkaline surface conditioning agent, and treating at normal temperature to remove a black film which is difficult to remove by using the acid surface conditioning; neutralizing the acid surface-adjusted residual acid liquor, and further leveling the surface of the magnesium alloy;

S5, black micro-arc oxidation treatment: the magnesium alloy after alkaline surface conditioning treatment is rinsed by quick warm water and cold water and then is sent into a micro-arc oxidation tank for treatment, and the first stage is as follows: the frequency is 300-1500HZ, the duty ratio is 15-35%, and the current density is controlled to be 1-3A/DM²in the second stage, the frequency is 800-1800HZ, the duty ratio is 5-25%, and a layer of nano-scale uniform and highly corrosion-resistant micro-arc oxidation film is formed on the surface of the magnesium alloy;

s6, passivation treatment: rinsing the passivated magnesium alloy by using cold pure water, and quickly transferring the magnesium alloy into a ventilated oven with the temperature of 100-160 ℃ for drying;

S7, coating treatment: and (4) spraying paint or performing electrophoresis treatment on the magnesium alloy subjected to passivation treatment to obtain a final protective layer.

s1, degreasing treatment: the treatment time is 2-4 minutes;

S2, an activation treatment stage, wherein the normal temperature treatment time is 1-3 minutes;

s3, acid surface conditioning: the normal temperature treatment time is 3-5 minutes;

S4, alkaline surface conditioner: the normal temperature treatment time is 1-3 minutes;

s5, black micro-arc oxidation treatment: the first stage treatment time is 1-15 minutes, and the second stage treatment time is 10-15 minutes;

s6, passivation treatment: the drying time is 10-15 minutes.

The embodiment of the invention has the following beneficial effects:

the invention discloses a magnesium alloy black micro-arc oxidation film nano passivator and a passivation process thereof, compared with the existing magnesium alloy passivation process, the passivation process utilizes the compounding of a silane coupling agent and graphene to form a nano-scale protective film, and utilizes graphene atomic-level particles to permeate into micropores and gaps which can not be permeated by the conventional process; meanwhile, the silane film is fused with the graphene lamellar structure, so that the surface layer of the black micro-arc oxidation film of the magnesium alloy is better covered, the salt spray resistance is improved, and the binding force with the coating is improved; the traditional process, no matter which passivating agent, can not solve the problem that the exposed salt spray test stability of the black micro-arc oxidation film of the magnesium alloy exceeds 2hours and the boiling test after the paint spraying: or the salt spray test can be carried out, and the skin can be peeled off after the water boiling after the paint spraying; or the salt spray test cannot be passed, and the water boiling after the paint spraying can pass through the salt spray test reluctantly.

drawings

FIG. 1 is a schematic diagram of a hole sealing effect of a magnesium alloy micro-arc oxidation film by a traditional process;

FIG. 2 is a schematic view of the effect of the process of the present invention.

Detailed Description

The invention discloses a magnesium alloy black micro-arc oxidation film nano passivator which comprises the following components in parts by mass: organic acid: 1-15 parts, organic alcohol: 1-20 parts of complexing agent: 1-10 parts of a silane coupling agent: 1-10 parts of an oxidant: 1-10 parts of graphene oxide: 1-10 parts of surfactant: 0.5-2 parts.

As a possible implementation mode, the magnesium alloy black micro-arc oxidation film nano passivator comprises the following components in parts by mass: organic acid: 1-5 parts of organic alcohol: 1-5 parts of complexing agent: 1-5 parts of a silane coupling agent: 5-10 parts of an oxidant: 1-5 parts, graphene: 1-3 parts of a surfactant: 0.5-1 part.

wherein the organic acid comprises at least one of glacial acetic acid and formic acid.

Specifically, the complexing agent comprises at least one of Ethylene Diamine Tetraacetic Acid (EDTA), disodium ethylene diamine tetraacetic acid (EDTA disodium), sodium gluconate, sodium citrate, and sodium hexametaphosphate.

Specifically, the organic alcohol includes at least one of methanol, ethanol, propylene glycol, glycerol, ethylene glycol, and the like.

specifically, the silane coupling agent comprises at least one of vinyl triethoxy silicon, vinyl trimethoxy silane, propyl trimethoxy silane, amino propyl triethoxy silane and methyl acryloxy functional group silane.

Specifically, the oxidant comprises at least one of hydrogen peroxide, potassium permanganate, sodium nitrate and sodium persulfate.

specifically, the graphene is a single layer of graphene oxide or 2-10 layers of graphene oxide.

specifically, the surfactant comprises at least one of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, nonylphenol polyoxyethylene ether and fatty alcohol polyoxyethylene ether.

the invention discloses a magnesium alloy black micro-arc oxidation film nanometer passivator and a passivation process thereof (the natural color micro-arc oxidation film is also suitable for the product, the process considers the particularity of the components of the natural color micro-arc oxidation film, is different from the industry standard of the black micro-arc oxidation film, and the invention is not limited); meanwhile, the silane film is fused with the graphene lamellar structure, so that the surface layer of the black micro-arc oxidation film of the magnesium alloy is better covered, the salt spray resistance is improved, and the binding force with the coating is improved; the traditional process has no passivation process aiming at the magnesium alloy micro-arc oxidation film, the traditional passivation process can only passivate on the exposed metal layer of the magnesium alloy to form a passivation layer with antioxidant protection, but no matter which passivating agent is, the problems that the exposed salt spray test of the black micro-arc oxidation film of the magnesium alloy is stable for more than 2hours and the boiling test after paint spraying can not be simultaneously solved: or the salt spray test can be carried out, and the skin can be peeled off after the water boiling after the paint spraying; or the salt spray test cannot be carried out, and the water boiling after the paint spraying can pass reluctantly; the traditional process only has a hole sealing process for a magnesium alloy micro-arc oxidation film, and the details are shown in figure 1; the magnesium alloy black micro-arc oxidation film after hole sealing can not solve the problems that the independent neutral salt fog of the magnesium alloy black micro-arc oxidation film is stable for 2hours and the water boiling test is carried out after the paint spraying. The invention has the passivation function of the traditional passivator, forms an anti-oxidation protective layer on the basis of the micro-arc oxidation film, has the hole sealing function of the traditional micro-arc oxidation film hole sealing agent, fills the micropores of the micro-arc oxidation film to a certain extent, and is shown in figure 2 in detail; meanwhile, the bonding force with paint and coating finally is not influenced, and the black micro-arc oxidation surface of the magnesium alloy is tightly protected.

compared with the prior magnesium alloy micro-arc oxidation film sealing process (no passivation process is available in the market), the passivation process has the advantages that a silane coupling agent and graphene oxide are utilized to form a reticular lamellar protective film on the surface of the magnesium alloy black micro-arc oxidation film under the weak acid condition, other metal ions in a complexing agent complexing solution are used for preventing interference and passivation, organic alcohol is added to promote effective components to permeate into gaps of the reticular protective film to enhance the protective film, meanwhile, the effective components are promoted to rapidly fill the gaps of the magnesium alloy black micro-arc oxidation film, and finally, the adhesive force of a magnesium alloy black micro-arc oxidation film passivation layer is improved; the proper oxidant is preferably selected, so that the long-acting structural performance of the graphene oxide can be maintained, the combination of the graphene oxide in the film forming process is promoted, the magnesium alloy black micro-arc oxidation film is more compact, and the surface corrosion resistance and the binding force of the coating are improved; the traditional hole sealing treatment process comprises the following steps: hydrated hole sealing, organic hole sealing, silicate hole sealing, electrochemical deposition hole sealing, alkali heat hole sealing, sol-gel hole sealing and the like.

The hydrated hole sealing is simple, but the temperature is high, the energy consumption is large, and the hydrated hole sealing can not completely fill the magnesium alloy micro-arc oxidation film, so the hole sealing effect is not ideal; in addition, due to factors of water quality and pH value, the glossiness and the like of the black micro-arc oxidation film of the magnesium alloy are easily influenced; hole sealing of organic matters: the common material is a surface modification reagent, and an organic layer is coated on the surface of the magnesium alloy after micro-arc oxidation, so that the corrosion resistance and the aesthetic property of the magnesium alloy are improved; the materials mainly comprise paraffin, resins, silanes and olefine acids; the organic hole sealing method comprises the treatment methods of dipping, spraying, brushing or electrophoretic deposition, and the sealing is realized through the physical adsorption effectthe pore agent flows to fill the pores, but the bonding force of the coating and the substrate is poor, which is the most important factor of the defects of the hole sealing scheme; sealing holes with silicate: the basic principle is silicate and magnesium alloy micro-arc oxidation film such as Mg (OH)₂with Na₂SiO₃Reaction to produce MgSiO₃precipitation, CO in air₂the remaining silicate also forms SiO₂Thereby sealing the aperture; the practical effect is not good because magnesium hydroxide is alkali which is difficult to dissolve in water, silicate reacts with strong alkali only in a liquid environment, and CO in air₂the requirement of reaction cannot be met, so the hole sealing effect cannot be good; corrosion resistance and binding force with the coating are not good; electrochemical deposition: at present, hydroxyapatite is mainly used, the reaction time is too long, and the effect is not good; alkali heat sealing: the magnesium alloy micro-arc oxidation film layer is soaked in a sodium bicarbonate solution, a light magnesium carbonate layer can be formed on the surface, a light magnesium carbonate matrix is a hexagonal prism crystal, the corrosion resistance of the magnesium alloy is improved, but the layer is not compact enough, and the binding force is weak; the sol-gel sealing has complex process, difficult entry of large particle particles into film holes, unsatisfactory sealing and poor corrosion resistance.

Therefore, a reasonable passivation or hole sealing technology is sought, the corrosion resistance of the magnesium alloy black micro-arc oxidation film and the binding force with the coating are solved, and the method is an important reason for the vigorous application and development of the magnesium alloy black micro-arc oxidation technology. The invention has the advantages of environment-friendly material selection, no heavy metal, no phosphorus and ammonia nitrogen, no pollution to water, no health threat to operators and accordance with the requirements of environment-friendly and green production.

the invention also discloses a passivation method by applying the magnesium alloy black micro-arc oxidation film passivator, which comprises the following steps:

S1, degreasing treatment: putting the magnesium alloy into a degreasing agent solution with the concentration of 50-100g/L, controlling the temperature to be 50-80 ℃, treating for 2-4min, and stripping oil stains on the surface of the magnesium alloy;

S2, activation treatment: cleaning the degreased magnesium alloy by at least two times of a clean water tank, then putting the magnesium alloy into 10-15% of activating agent solution, and treating for 1-3min at normal temperature to uniformly corrode the surface of the magnesium alloy so that the surface of the magnesium alloy is completely uniform and black;

s3, acid surface conditioning: after ultrasonic cleaning for at least two times, the magnesium alloy after the activation treatment is placed in a solution of 20-30% of an acidic surface conditioner, and the treatment time at normal temperature is as follows: uniformly removing black and gray on the surface of the magnesium alloy, leveling and whitening the surface of the magnesium alloy for 3-5 min;

S4, alkaline surface conditioner: after the magnesium alloy with the acid surface conditioning is cleaned by at least two times of water tanks, the magnesium alloy is placed in 10-15% of alkaline surface conditioning agent solution, and the magnesium alloy is treated for the following time at normal temperature: removing black membrane difficult to remove in acid surface conditioning for 1-3 min; neutralizing the acid surface-adjusted residual acid liquor, and further leveling the surface of the magnesium alloy;

s5, black micro-arc oxidation treatment: the magnesium alloy after alkaline surface conditioning treatment is rinsed by quick warm water and cold water and then is sent into a micro-arc oxidation tank for treatment, and the first stage is as follows: frequency: 300-1500HZ, duty ratio 15-35%, 1-3A/dm²1-15 min; second stage, frequency: 800-1800HZ, duty cycle: 5-25%, 10-15 min; a layer of nano-scale uniform and high-corrosion-resistant micro-arc oxidation film is formed on the surface of the magnesium alloy;

S6, passivation treatment: rinsing the passivated magnesium alloy with cold pure water, quickly transferring to a ventilated oven with the temperature of 100-160 ℃, and drying for 10-15 min;

s7, coating treatment: and (4) spraying paint or performing electrophoresis treatment on the magnesium alloy subjected to passivation treatment to obtain a final protective layer.

Among them, S1, degreasing treatment: putting the magnesium alloy into a degreasing agent solution with the concentration of 50g/L, controlling the temperature to be between 50 and 80 ℃, treating for 2 to 4min, and stripping oil stains on the surface of the magnesium alloy;

s2, activation treatment: cleaning the degreased magnesium alloy by at least two times of a clean water tank, then putting the magnesium alloy into 10-15% of activating agent solution, and treating for 1-3min at normal temperature to uniformly corrode the surface of the magnesium alloy so that the surface of the magnesium alloy is completely uniform and black;

s3, acid surface conditioning: after ultrasonic cleaning for at least two times, the magnesium alloy after the activation treatment is placed in a solution of 20-30% of an acidic surface conditioner, and the treatment time at normal temperature is as follows: uniformly removing black and gray on the surface of the magnesium alloy, leveling and whitening the surface of the magnesium alloy for 3-5 min;

s4, alkaline surface conditioner: after the magnesium alloy with the acid surface conditioning is cleaned by at least two times of water tanks, the magnesium alloy is placed in 10-15% of alkaline surface conditioning agent solution, and the magnesium alloy is treated for the following time at normal temperature: removing black membrane difficult to remove in acid surface conditioning for 1-3 min; neutralizing the acid surface-adjusted residual acid liquor, and further leveling the surface of the magnesium alloy;

s5, black micro-arc oxidation treatment: the magnesium alloy after alkaline surface conditioning treatment is rinsed by quick warm water and cold water and then is sent into a micro-arc oxidation tank for treatment, and the first stage is as follows: frequency: 600HZ, duty cycle 30%, 2A/dm²2 min; second stage, frequency: 1500HZ, duty cycle: 20%, 10-15 min; a layer of nano-scale uniform and high-corrosion-resistant micro-arc oxidation film is formed on the surface of the magnesium alloy;

S6, passivation treatment: rinsing the passivated magnesium alloy with cold pure water, quickly transferring to a ventilated oven with the temperature of 100-160 ℃, and drying for 10-15 min;

s7, coating treatment: and (4) spraying paint or performing electrophoresis treatment on the magnesium alloy subjected to passivation treatment to obtain a final protective layer.

the present invention will be further described with reference to specific embodiments so as to clearly understand the technical idea of the present invention.