阅读说明：本技术 一种铝合金表面处理方法 (Aluminum alloy surface treatment method ) 是由 赵园园 于 2021-08-21 设计创作，主要内容包括：本发明提供了一种铝合金表面处理方法,通过预处理氮化硅和多阶段可调变微弧氧化电压,有效的改善无机微纳米颗粒在微弧氧化膜中分布状况,使得无机微纳米颗粒有效的均匀分散于微弧氧化膜层内,显著提高铝合金氧化膜耐腐蚀性能和耐磨性能,尤其改善微弧氧化膜的稳定性,减低其波动性。(The invention provides an aluminum alloy surface treatment method, which effectively improves the distribution condition of inorganic micro-nano particles in a micro-arc oxidation film through silicon nitride pretreatment and multi-stage adjustable micro-arc oxidation voltage, so that the inorganic micro-nano particles are effectively and uniformly dispersed in the micro-arc oxidation film layer, the corrosion resistance and the wear resistance of the aluminum alloy oxidation film are obviously improved, particularly the stability of the micro-arc oxidation film is improved, and the volatility of the micro-arc oxidation film is reduced.)

1. The aluminum alloy surface treatment method is characterized by comprising the following steps:

(1) carrying out surface pretreatment on the aluminum alloy;

(2) preparing Si3N4 suspension and micro-arc oxidation electrolyte;

(3) taking aluminum alloy as an anode, performing segmented micro-arc oxidation treatment,

(4) the polishing treatment is carried out on the mixture,

the segmented micro-arc oxidation treatment process comprises the following steps:

stage I: bidirectional voltage, the forward voltage is 400V, the reverse voltage is 200V, the positive-negative duty ratio is 20%, the pulse number proportion is 1:1, and the time is 90s;

stage II: bidirectional voltage, forward voltage 500V, reverse voltage 150V, positive-negative duty ratio 10%, pulse number ratio 1:1 and time 60s are adopted;

stage III: adopting bidirectional voltage, wherein the forward voltage is 600V, the reverse voltage is 100V, the positive-negative duty ratio is 5%, the pulse number ratio is 1:1, the time is the time required by the current density to reach the peak value, and the current density range is 110-²；

In the IV stage, a unidirectional voltage of 400V is adopted, the time of the stage is 3-5min after a stable current is formed, and the density of the stable current is 15-18 mA/cm²。

2. The surface treatment method of claim 1, wherein the surface treatment comprises mechanical grinding, degreasing and acid treatment, wherein the degreasing is performed by using 12wt.% NaOH, 75 wt.%^oC immersion for 7min, acid wash with 25wt.% HNO₃Soaking for 1min, and washing with deionized water.

3. The surface treatment method of an aluminum alloy as set forth in claim 1, wherein Si is contained in said Si₃N₄The preparation method of the suspension comprises (1) taking Si with nanometer size of 20-60nm₃N₄2-4g of nano particles are placed in a three-neck flask, and 40 mL of 98 mass percent H is added₂SO₄And 20mL of 65 mass percent HNO₃Under stirring at 100^oC, carrying out reflux treatment for 6 h,

(2) ultracentrifugation washing at 8000-10000rpm for many times until the solution is neutral, and vacuum freeze drying;

(3) the dried Si3N4 was placed in deionized water,then adding AES surfactant at normal temperature, and stirring to obtain 2-4wt.% Si₃N₄Suspending an aqueous solution wherein the amount of AES surfactant is 1 wt.%.

4. The method for treating the surface of an aluminum alloy according to claim 1, wherein the micro-arc oxidation solution is a suspension aqueous solution of 9-10g/L sodium silicate, 3-4g/L sodium tungstate, 1-1.5g/L potassium hydroxide, 2-3g/L EDTA-2Na, and the balance of 2-4wt.% Si3N4, and HNO is used₃Adjusting pH =11 + -1, and the temperature of micro-arc oxidation is 20-25^oC, the stirring speed is 120-150 rpm.

5. The surface treatment method of an aluminum alloy according to claim 1, wherein the polishing is sanding polishing using 400#, 800#, 1200# and 2000# sandpaper in sequence.

Technical Field

The invention relates to an aluminum alloy surface treatment method, in particular to a method for treating aluminum alloy through micro-arc oxidation.

Background

Micro Arc Oxidation (MAO), also known as Plasma oxidation (Plasma electrolytic)

oxidation, PEO), is a process of applying a metal (Ti, Al, Mg, Zr, Nb, Ta, etc.) to the surface

New technology for preparing ceramic coating in aqueous electrolyte environment by applying high voltage, simple method and raw coating

The long-term efficiency is high, and the prepared ceramic coating has excellent thermal, mechanical and other properties. Research shows that the ceramic film layer and the matrix are in metallurgical bonding mode, have good bonding strength, have a typical structure consisting of an inner compact layer and an outer loose porous layer, and generally have higher hardness, and the aluminum alloy micro-arc oxidation ceramic film layer is made of Al₂O₃The hardness of the material is 800-2000 HV as a main phase; the magnesium alloy micro-arc oxidation ceramic film layer takes MgO as a main phase, and the hardness can reach 300-600 HV; titanium alloy micro-arc oxidation ceramic film layer coated with TiO₂ When the ceramic film is a main phase, the hardness can reach 600-800 HV, and the wear resistance of the surface is obviously improved due to the improvement of the hardness of the ceramic film. But inherent in the ceramic film layerThe micro-arc discharge channel and the crack exist, so that the surface presents a loose porous structure and presents a higher friction coefficient under a dry friction working condition, in the tribology application process, the higher friction coefficient not only can accelerate the wear failure of the micro-arc discharge channel and but also can aggravate the wear of dual materials, and in the prior art, in order to improve the wear resistance of a micro-arc oxidation ceramic film layer, stable-phase micro-nano particles (SiO) with high hardness are usually directly added into the electrolyte₂， Cr₂0₃， ZrO₂， SiC， Si₃N₄TiC, etc.), the addition of particles improves the hardness of the composite coating, and the compactness is improved to a certain extent, so that the composite coating shows better abrasion resistance.

For example, CN 109868386A discloses a wear-resistant material, wherein particles of aluminum nitride, aluminum oxide, molybdenum disilicide and graphite powder are uniformly distributed in an aluminum alloy matrix, and a composite micro-arc oxidation layer is distributed on the surface of the aluminum alloy matrix, so that the hardness and wear resistance of the material are remarkably improved, and the friction reduction performance of the graphite powder can be improved. The composite micro-arc oxidation layer on the surface can effectively improve the wear resistance and corrosion resistance of the alloy surface.

For example, CN 106995931A discloses a preparation method of an aluminum alloy micro-arc oxidation composite ceramic layer, which is to pretreat an aluminum alloy substrate: grinding the aluminum alloy substrate, removing an oxide layer on the surface of the aluminum alloy substrate, polishing, removing grease on the surface of the aluminum alloy substrate, performing ultrasonic cleaning, and then drying; adding SiC nano-particles and polyethylene glycol into distilled water, and performing ultrasonic oscillation to disperse the SiC nano-particles to prepare SiC dispersion liquid; adding SiC dispersion liquid in the preparation process of the electrolyte to enable the concentration of SiC in the electrolyte to reach 2g/L, wherein the solvent of the electrolyte is distilled water; and c, carrying out micro-arc oxidation on the aluminum alloy matrix by using the electrolyte obtained in the step c, wherein the aluminum alloy matrix is used as an anode. Functional particles are tried to be sintered in the ceramic layer by a method of adding SiC nano particles into electrolyte, so that the ceramic layer is obviously improved in various performances, is more compact and has a smaller friction coefficient in a friction and wear process.

CN 112195491A is a preparation method of a SiC-Al2O3 coating based on micro-arc oxidation, the method comprises matrix pretreatment, solution preparation, composite ceramic coating preparation and ceramic layer post-treatment, and the method finally obtains a SiC-Al2O3 composite layer with an inner layer of an Al2O3 ceramic layer and an outer layer of a SiC ceramic layer, and the thickness of the composite layer is 30-400 mu m; wherein, the solution in the solution preparation adopts a deionized water solution taking KOH-Na2SiO3- (NaPO3)6-Na2WO4 as a main component and a mixed solution of an alkaline silica sol solution, water-soluble phenolic resin and nano SiC particles. According to the method, the two composite ceramic layers are prepared on the surface of the aluminum alloy workpiece by the one-step micro-arc oxidation process, so that the preparation efficiency is high, the production energy consumption is low, the preparation cost is low, and the preparation time is saved; meanwhile, the method does not need hole sealing treatment, the bonding strength between the ceramic layer and between the ceramic layer and the substrate is high, the compactness of the composite ceramic coating is good, and the overall wear resistance, corrosion resistance, heat insulation and ablation resistance of the aluminum alloy workpiece are excellent.

From the above-mentioned several prior art patents, the following problems are evident: (1) it should be known to those skilled in the art that inorganic micro-nano particles are added to the micro-arc oxidation electrolyte, the dispersion stability of the micro-nano particles in the electrolyte can directly affect the film forming quality of the composite film, if the inorganic micro-nano particles have low water solubility and poor dispersion, the phenomena of non-uniform composition and thickness of the composite film can be easily caused, and the above patents generally adopt machines

Mechanical, ultrasonic and surface modification are used for improving the dispersion stability of the particles and improving the dispersibility of the inorganic nano particles, so that the particles can enter a ceramic film layer, but researches on how to obtain the highly dispersed inorganic micro-nano particles in detail are rare; (2) the size and concentration of the micro-nano particles directly influence the distribution condition of inorganic micro-nano particles in the micro-arc oxide film, if particles with smaller particle sizes are easy to appear at positions such as discharge channels and cracks, the particles with larger particle sizes only have higher content on the surface of the composite film layer, and the distribution condition of the inorganic particles directly influences the stability and the volatility of the composite micro-arc oxide film in each direction.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide an aluminum alloy surface treatment method, which can effectively improve the distribution condition of inorganic micro-nano particles in a micro-arc oxidation film through multi-stage adjustable micro-arc oxidation voltage, so that the inorganic micro-nano particles are effectively and uniformly dispersed in the micro-arc oxidation film layer, the corrosion resistance and the wear resistance of the aluminum alloy oxidation film are obviously improved, particularly the stability of the micro-arc oxidation film is improved, and the volatility of the micro-arc oxidation film is reduced.

An aluminum alloy surface treatment method comprises the following steps:

(1) carrying out surface pretreatment on the aluminum alloy;

(2) preparing Si3N4 suspension and micro-arc oxidation electrolyte;

(3) taking aluminum alloy as an anode, performing segmented micro-arc oxidation treatment,

(4) the polishing treatment is carried out on the mixture,

the segmented micro-arc oxidation treatment process comprises the following steps:

stage I: bidirectional voltage, the forward voltage is 400V, the reverse voltage is 200V, the positive-negative duty ratio is 20%, the pulse number proportion is 1:1, and the time is 90s;

stage II: bidirectional voltage, forward voltage 500V, reverse voltage 150V, positive-negative duty ratio 10%, pulse number ratio 1:1 and time 60s are adopted;

stage III: adopting bidirectional voltage, wherein the forward voltage is 600V, the reverse voltage is 100V, the positive-negative duty ratio is 5%, the pulse number ratio is 1:1, the time is the time required by the current density to reach the peak value, and the current density range is 110-²；

In the IV stage, a unidirectional voltage of 400V is adopted, the time of the stage is 3-5min after a stable current is formed, and the density of the stable current is 15-18 mA/cm²。

Further, the surface treatment includes mechanical polishing, degreasing and acid treatment, wherein the degreasing is performed by using 12wt.% NaOH, 75^oC immersion for 7min, acid wash with 25wt.% HNO₃Soaking for 1min, and washing with deionized water.

Further, said Si₃N₄Method for producing a suspensionTaking Si with the nanometer size of 20-60nm₃N₄2-4g of nano particles are placed in a three-neck flask, and 40 mL of 98 mass percent H is added₂SO₄And 20mL of 65 mass percent HNO₃Under stirring at 100^oC, refluxing for 6 h.

(2) Ultracentrifugation washing at 8000-one 1000rpm for many times until the solution is neutral, and vacuum freeze drying;

(3) placing the dried Si3N4 into deionized water, then adding AES surfactant at normal temperature, and stirring to obtain 2-4wt.% Si₃N₄Suspending an aqueous solution wherein the amount of AES surfactant is 1 wt.%.

Further, the micro-arc oxidation solution is prepared from 9-10g/L sodium silicate, 3-4g/L sodium tungstate, 1-1.5g/L potassium hydroxide, 2-3g/L LEDTA-2Na and the balance of 2-4wt.% Si3N4 suspension aqueous solution by using HNO₃Adjusting pH =11 + -1, and the temperature of micro-arc oxidation is 20-25^oC, the stirring speed is 120-150 rpm.

Further, the polishing is grinding and polishing by using 400#, 800#, 1200# and 2000# sandpaper in sequence.

Regarding the dispersibility of the inorganic nano-particles, the inorganic nano-particles selected by the invention are 20-60nm silicon nitride, and the surface of the silicon nitride has less hydrophilic groups, so that the surface of the silicon nitride needs to be subjected to hydrophilic modification treatment, and 2-4g of Si is added₃N₄2-4g of nano particles are placed in a three-neck flask, and 40 mL of 98 mass percent H is added₂SO₄And 20mL of 65 mass percent HNO₃Under stirring at 100^oC, refluxing for 6 h, forming acidic functional groups such as carboxyl, hydroxyl, aldehyde group and the like on the surfaces of inorganic particles after the silicon nitride is subjected to mixed acid treatment, performing centrifugal treatment by using filtration washing for a plurality of times to be neutral at 8000-10000rpm because the inorganic particles are nanoscale, performing vacuum freeze drying for preventing agglomeration due to high specific surface area of the nanoparticles, and performing vacuum freeze drying on the dried Si₃N₄Placing the mixture into deionized water, adding AES surfactant at normal temperature, and stirring to obtain 2-4wt.% of Si₃N₄Suspending an aqueous solution wherein the AES surfactant is present in an amount of 1wt.% when said Si is present₃N₄When the pH of the electrolyte is =10-12, the molecular Zeta potential of the electrolyte is-46.4 to-48.2 mV, namely the Si₃N₄The high-dispersion inorganic particle additive can be dispersed in electrolyte in a high-dispersion manner, namely, hydrophilic groups are introduced on the surface of silicon nitride through acidic modification, then the nonionic surfactant AES is added into the solution, although the electronegativity of inorganic particles can be obviously increased by theoretically adding an anionic surfactant, the AES has both ethoxy and sulfonic acid groups, namely, the high-dispersion inorganic particle additive has both anionic and nonionic surface activity characteristics and stronger alkali resistance, and is more suitable for being used as the surface activity additive of the high-dispersion inorganic particle additive.

Regarding the micro-arc oxidation process, the following processes are generally included: the first stage is as follows: generating a large amount of bubbles and generating micro-arc small points, wherein an oxide film is mainly generated in the process, the thickness of the oxide film has obvious nonuniformity, and the second stage is as follows: because the thickness of the oxide film has obvious nonuniformity, the oxide film breaks down relatively thin and weak micro areas in the oxide film at the same time under strong voltage, and because of the instantaneous high temperature of the breakdown part, fused and even gasified alumina and aluminum exist in the high area and then react with electrolyte to form alumina, the relatively thin and weak micro areas are caused to thicken, the current is continuously increased in the stage, and the third stage is carried out when the current is increased to a peak; and a third stage: because earlier stage is relatively thin, and weak micro-region thickens, under the forceful electric pressure, discharges and can shift to other relatively thin regions, through discharging many times, originally less gas pocket links to each other and forms great discharge gas pocket, and the quantity of gas pocket obviously increases, and thickness also obvious increase leads to the resistance to obviously increase, and the electric current obviously descends promptly, the fourth stage: only sporadic tiny sparks can be seen at the stage, and the current can not change obviously after long-time electrification, namely the current is stable.

Regarding the composite micro-arc oxidation process, the process is basically similar to the common micro-arc oxidation process, and the difference is only the participation of the nano particles, firstly, the inorganic nano particles are compounded through surface modification and surface activity, and the inorganic nano particles are electronegative in the micro-arc oxidation alkaline electrolyte, secondly, the negatively charged nano particles are adsorbed to the surface of the anode aluminum material under the action of an electric field, then an anode oxidation film is formed and the nano particles are captured in the first stage process, then the local melting is started in the second stage, in the process, the nano particles are randomly coated into the oxidation film, and then the third stage and the fourth stage are carried out. In short, the whole process is that inorganic particles are deposited on the surface of an anode by means of electronegativity, the inorganic particles are extruded on the surface of the anode by virtue of spark discharge, and then a random balance is formed, so that the inorganic particles, particularly the inorganic particles with extremely small nanometer sizes, are preferentially distributed in an electricity-proof pore passage and a crack position, and the distribution of the inorganic particles in the whole micro-arc oxidation film is non-uniform.

The segmented micro-arc oxidation treatment process comprises the following steps:

stage I: bidirectional voltage, the forward voltage is 400V, the reverse voltage is 200V, the positive-negative duty ratio is 20%, the pulse number proportion is 1:1, and the time is 90s;

stage II: bidirectional voltage, forward voltage 500V, reverse voltage 150V, positive-negative duty ratio 10%, pulse number ratio 1:1 and time 60s are adopted;

stage III: adopting bidirectional voltage, wherein the forward voltage is 600V, the reverse voltage is 100V, the positive-negative duty ratio is 5%, the pulse number ratio is 1:1, the time is the time required by the current density to reach the peak value, and the current density range is 110-²；

In the IV stage, a unidirectional voltage of 400V is adopted, the time of the stage is 3-5min after a stable current is formed, and the density of the stable current is 15-18 mA/cm²。

The method comprises the steps of increasing forward voltage and reducing reverse voltage in a segmented manner, effectively and uniformly dispersing the adsorption uniformity of inorganic particles with negative electricity on the surface of an anode, mainly adjusting the first stage and the second stage of micro-arc oxidation, wherein the third stage and the fourth stage mainly increase the thickness of micro-arc oxidation, so that the micro-arc oxidation process is a common micro-arc oxidation process without adjustment, in addition, obvious loose porous layers can be formed in the third stage and the fourth stage, the porous layers are not beneficial to improving the corrosion resistance and the wear resistance of aluminum alloy, the porous layers are completely generated in a disordered manner, so that the stability of the aluminum alloy in each direction is not beneficial to improving the physicochemical stability of the aluminum alloy, the physical and chemical stability of the aluminum alloy is reduced, the porous layers are removed by polishing means, the polishing is sequentially polished by 400#, 800#, 1200# and 2000# abrasive paper, the loose layers of the ceramic film layers are removed by a polishing treatment technology, and the exposed dense layers show higher corrosion resistance, Hardness and lower roughness.

The beneficial technical effects are as follows:

(1) by acid washing reflux and surfactant treatment, the dispersibility of silicon nitride in aqueous solution is effectively improved while oxides or impurities on the surface of the silicon nitride are removed, and the Zeta negative potential of the silicon nitride is effectively reduced when the silicon nitride is dispersed in alkaline electrolyte, so that a high-dispersion silicon nitride suspension is obtained, and the high-dispersion state is favorable for the distribution of the silicon nitride in composite micro-arc oxidation.

(2) The micro-arc oxidation voltage can be adjusted in multiple stages, the distribution condition of inorganic micro-nano particles in the micro-arc oxidation film is effectively improved, the inorganic micro-nano particles are effectively and uniformly dispersed in the micro-arc oxidation film layer, the corrosion resistance and the wear resistance of the aluminum alloy oxidation film are obviously improved, the stability of the micro-arc oxidation film is especially improved, and the volatility of the micro-arc oxidation film is reduced.

Drawings

FIG. 1 is a scanning transmission diagram of the micro-arc oxide film obtained in comparative example 1.

FIG. 2 is a scanning transmission diagram of the micro-arc oxide film obtained in example 2 of the present invention.

FIG. 3 is a scanning transmission elemental nitrogen analysis chart of the micro-arc oxide films obtained in example 2 of the present invention and comparative example 1.

FIG. 4 is a graph showing the change of the segmented voltage micro-arc oxidation time-roughness Ra of the present invention.

Detailed Description

Example 1

An aluminum alloy surface treatment method comprises the following steps:

(1) carrying out surface pretreatment on the aluminum alloy; surface treatments include mechanical sanding, degreasing, and acid treatment, wherein degreasing is with 12wt.% NaOH, 75^oC immersion for 7min, acid wash with 25wt.% HNO₃Soaking for 1min, and washing with deionized water.

(2) Preparation of Si3N4 suspension and micro-arc oxidation electrolyte:

said Si₃N₄The preparation method of the suspension comprises the following steps:

(a) taking Si with the nanometer size of 20-60nm₃N₄2g of nano particles are placed in a three-neck flask, and 40 mL of H with the mass fraction of 98 percent is added₂SO₄And 20mL of 65 mass percent HNO₃Under stirring at 100^oC, refluxing for 6 h.

(b) Ultracentrifugation washing at 8000rpm for several times until the solution is neutral, and vacuum freeze drying.

(c) Placing the dried Si3N4 into deionized water, then adding AES surfactant at normal temperature, and stirring to obtain 2wt.% Si₃N₄Suspending an aqueous solution wherein the amount of AES surfactant is 1 wt.%.

The micro-arc oxidation electrolyte is prepared from 9g/L sodium silicate, 3g/L sodium tungstate, 1g/L potassium hydroxide, 2g/L LEDTA-2Na and 2wt.% of Si3N4 in balance by suspending aqueous solution and using HNO₃pH =11 was adjusted.

(3) Taking aluminum alloy as an anode, and performing segmented micro-arc oxidation treatment:

wherein the segmented micro-arc oxidation treatment process is as follows, and the temperature in the micro-arc oxidation process is 20^oAnd C, stirring at the rotating speed of 120 rpm.

Stage I: bidirectional voltage, forward voltage 400V, reverse voltage 200V, positive-negative duty ratio 20%, pulse number ratio 1:1 and time 90s are adopted.

Stage II: bidirectional voltage, forward voltage 500V, reverse voltage 150V, positive-negative duty ratio 10%, pulse number ratio 1:1 and time 60s are adopted.

Stage III: bidirectional voltage, namely, forward voltage 600V, reverse voltage 100V, positive-negative duty ratio 5%, pulse number ratio 1:1 and time required for the current density to reach the peak value are adopted.

And in the IV stage, unidirectional voltage is adopted, the voltage is 400V, and the time of the stage is 3-5min after the stable current is formed.

(4) The polishing treatment is carried out on the mixture,

the polishing is grinding and polishing by using 400#, 800#, 1200# and 2000# sandpaper in sequence.

Example 2

An aluminum alloy surface treatment method comprises the following steps:

(1) carrying out surface pretreatment on the aluminum alloy; surface treatments include mechanical sanding, degreasing, and acid treatment, wherein degreasing is with 12wt.% NaOH, 75^oC immersion for 7min, acid wash with 25wt.% HNO₃Soaking for 1min, and washing with deionized water.

(2) Preparation of Si3N4 suspension and micro-arc oxidation electrolyte:

said Si₃N₄The preparation method of the suspension comprises the following steps:

(a) taking Si with the nanometer size of 20-60nm₃N₄3g of nano particles are placed in a three-neck flask, and 40 mL of H with the mass fraction of 98 percent is added₂SO₄And 20mL of 65 mass percent HNO₃Under stirring at 100^oC, refluxing for 6 h.

(b) The mixture was washed to neutrality by ultracentrifugation at 9000rpm several times and freeze-dried in vacuo.

(c) Placing the dried Si3N4 in deionized water, adding AES surfactant at normal temperature, and stirring to obtain 3wt.% Si₃N₄Suspending an aqueous solution wherein the amount of AES surfactant is 1 wt.%.

The micro-arc oxidation electrolyte is prepared from 9.5g/L sodium silicate, 3.5g/L sodium tungstate, 1.25g/L potassium hydroxide, 2.5g/L LEDTA-2Na and 3wt.% of Si3N4 in balance by using HNO (HNO)₃pH =11 was adjusted.

(3) Taking aluminum alloy as an anode, and performing segmented micro-arc oxidation treatment:

wherein the segmented micro-arc oxidation treatment process is as follows, and the temperature in the micro-arc oxidation process is 23^oAnd C, stirring at the rotating speed of 135 rpm.

Stage I: bidirectional voltage, forward voltage 400V, reverse voltage 200V, positive-negative duty ratio 20%, pulse number ratio 1:1 and time 90s are adopted.

Stage II: bidirectional voltage, forward voltage 500V, reverse voltage 150V, positive-negative duty ratio 10%, pulse number ratio 1:1 and time 60s are adopted.

Stage III: adopting bidirectional voltage, wherein the forward voltage is 600V, the reverse voltage is 100V, the positive-negative duty ratio is 5%, the pulse number ratio is 1:1, the time is the time required by the current density to reach the peak value, the time for the peak current density to appear is 52s after multiple tests, and the peak current value to reach is 123mA/cm²。

In the IV stage, a unidirectional voltage is adopted, the voltage is 400V, the time of the stage is 3-5min after the stable current is formed, the time of forming the stable current is 13.5min, and the density of the stable current is 16.4 mA/cm²。

(4) The polishing treatment is carried out on the mixture,

the polishing is grinding and polishing by using 400#, 800#, 1200# and 2000# sandpaper in sequence.

Example 3

An aluminum alloy surface treatment method comprises the following steps:

(1) carrying out surface pretreatment on the aluminum alloy; surface treatments include mechanical sanding, degreasing, and acid treatment, wherein degreasing is with 12wt.% NaOH, 75^oC immersion for 7min, acid wash with 25wt.% HNO₃Soaking for 1min, and washing with deionized water.

(2) Preparation of Si3N4 suspension and micro-arc oxidation electrolyte:

said Si₃N₄The preparation method of the suspension comprises the following steps:

(a) taking Si with the nanometer size of 20-60nm₃N₄4g of nano particles are placed in a three-neck flask, and 40 mL of H with the mass fraction of 98 percent is added₂SO₄And 20mL massFraction of 65% HNO₃Under stirring at 100^oC, refluxing for 6 h.

(b) And (4) ultracentrifuging and washing the mixture at 10000rpm for multiple times until the mixture is neutral, and performing vacuum freeze drying.

(c) Putting the dried Si3N4 into deionized water, adding AES surfactant at normal temperature, and stirring to obtain 4wt.% Si₃N₄Suspending an aqueous solution wherein the amount of AES surfactant is 1 wt.%.

The micro-arc oxidation electrolyte is prepared from 10g/L sodium silicate, 4g/L sodium tungstate, 1.5g/L potassium hydroxide, 3g/L LEDTA-2Na and the balance of 4wt.% Si3N4 suspension aqueous solution by using HNO₃pH =11 ± 1. (3) Taking aluminum alloy as an anode, and performing segmented micro-arc oxidation treatment:

wherein the segmented micro-arc oxidation treatment process is as follows, and the temperature in the micro-arc oxidation process is 25 DEG^oAnd C, stirring at the rotating speed of 150 rpm.

Stage I: bidirectional voltage, forward voltage 400V, reverse voltage 200V, positive-negative duty ratio 20%, pulse number ratio 1:1 and time 90s are adopted.

Stage II: bidirectional voltage, forward voltage 500V, reverse voltage 150V, positive-negative duty ratio 10%, pulse number ratio 1:1 and time 60s are adopted.

Stage III: adopting bidirectional voltage, wherein the forward voltage is 600V, the reverse voltage is 100V, the positive-negative duty ratio is 5%, the pulse number ratio is 1:1, the time is the time required by the current density to reach the peak value, and the current density range is 110-²。

In the IV stage, a unidirectional voltage of 400V is adopted, the time of the stage is 3-5min after a stable current is formed, and the density of the stable current is 15-18 mA/cm²。

(4) The polishing treatment is carried out on the mixture,

the polishing is grinding and polishing by using 400#, 800#, 1200# and 2000# sandpaper in sequence.

Comparative example 1

An aluminum alloy surface treatment method comprises the following steps:

(1) carrying out surface pretreatment on the aluminum alloy; surface treatmentIncluding mechanical sanding, degreasing and acid treatment, wherein the degreasing is with 12wt.% NaOH, 75^oC immersion for 7min, acid wash with 25wt.% HNO₃Soaking for 1min, and washing with deionized water.

(2) Preparing micro-arc oxidation electrolyte:

(3) taking aluminum alloy as an anode, and performing micro-arc oxidation treatment: the micro-arc oxidation electrolyte is prepared from 9.5g/L sodium silicate, 3.5g/L sodium tungstate, 1.25g/L potassium hydroxide and 2.5g/L EDTA-2Na, and the balance is 3wt.% Si3N4 suspension aqueous solution, wherein the preparation method of the 3wt.% Si3N4 suspension aqueous solution is completely consistent with that of example 2, and HNO is used₃The pH is adjusted to be =11, the voltage is 600V bidirectional voltage, the positive-negative direction duty ratio is 10%, the pulse number ratio is 1:1, and the time is consistent with the total micro-arc oxidation time duration of the embodiment 2.

(4) The polishing treatment is carried out on the mixture,

the polishing is grinding and polishing by using 400#, 800#, 1200# and 2000# sandpaper in sequence.

Comparative example 2

An aluminum alloy surface treatment method comprises the following steps:

(1) carrying out surface pretreatment on the aluminum alloy; surface treatments include mechanical sanding, degreasing, and acid treatment, wherein degreasing is with 12wt.% NaOH, 75^oC immersion for 7min, acid wash with 25wt.% HNO₃Soaking for 1min, and washing with deionized water.

(2) Preparation of Si3N4 suspension and micro-arc oxidation electrolyte:

said Si₃N₄The preparation method of the suspension comprises taking Si with nanometer size of 20-60nm₃N₄3g of nanoparticles, directly placed in an aqueous solution.

The micro-arc oxidation electrolyte is prepared from 9.5g/L sodium silicate, 3.5g/L sodium tungstate, 1.25g/L potassium hydroxide, 2.5g/L LEDTA-2Na and 3wt.% of Si3N4 in balance by using HNO (HNO)₃pH =11 was adjusted.

(3) Taking aluminum alloy as an anode, and performing micro-arc oxidation treatment: the micro-arc oxidation electrolyte consists of 9.5g/L sodium silicate, 3.5g/L sodium tungstate, 1.25g/L potassium hydroxide, 2.5g/L LEDTA-2Na and the balance of 3wt.% Si3N4 suspension water solution and HNO₃The pH is adjusted to be =11, the voltage is 600V bidirectional voltage, the positive-negative direction duty ratio is 10%, the pulse number ratio is 1:1, and the time is consistent with the total micro-arc oxidation time duration of the embodiment 2.

(4) The polishing treatment is carried out on the mixture,

the polishing is grinding and polishing by using 400#, 800#, 1200# and 2000# sandpaper in sequence.

Comparative example 2 an aqueous solution was prepared using commercial silicon nitride, and the rest was similar to comparative example 1.

After the surface treatment, the surface roughness Ra =0.1 of the aluminum material adopted by the invention is about 1.7-1.8 after the micro-arc oxidation, and after the polishing treatment, the roughness is reduced to about 0.3, as shown in figure 4, in addition, as can be seen from figures 1 and 2, compared with the prior art, the micro-arc oxidation film subjected to the segmental micro-arc oxidation treatment is more compact, and the corresponding corrosion resistance is better.

The test was performed on the samples prepared in example 2 and comparative examples 1-2.

The aluminum alloy substrate is stripped by an electrochemical method mainly based on that the corrosion resistance of a micro-arc oxidation film is strong, the corrosion resistance of the aluminum material is weak, the aluminum material is slowly corroded by the electrochemical method, the pH =6-6.5 of the electrolyte is controlled at any time, the aluminum material can be effectively stripped, only the micro-arc oxidation film is left, the micro-arc oxidation film is cut into 1 cm-1 cm sheets, the corrosion current density and the corrosion voltage density are respectively tested, the number of the tests is 15, wherein the corrosion voltage of the substrate and the corrosion voltage of comparative example 1, comparative example 2 and example 2 are respectively-1.36V, -0.78V, -0.97V and-0.72V, and the corrosion current is respectively 10.51 mu Acm^-2、0.48μAcm^-2、5.35μAcm^-2、0.38μAcm^-2It can be clearly seen that the corrosion current of comparative example 1 and example 2 is significantly higher than that of comparative example 2, mainly because the silicon nitride of comparative example 2 obviously floats on the surface of the aqueous solution, and therefore, cannot participate in micro-arc oxidation, i.e., effective composite micro-arc oxidation deposition cannot be realized, similar to simple micro-arc oxidation treatment of aluminum alloy. The corrosion current difference between comparative example 1 and example 2 was not obtained, and as shown in the following table, some of the current densities were almost the same, namely, the micro-arc oxidation pair by the step voltageThe corrosivity has a positive effect, but is not obvious, but from the average deviation, the dispersion of the silicon nitride in the micro-arc oxidation film can be effectively improved through the step voltage treatment, namely, the average deviation is very low, namely, the uniformity of each direction is better, in addition, the average deviation of the comparative example 2 is also higher than that of the comparative example 1, the main reason is that the silicon nitride in the comparative example 2 hardly participates in the micro-arc oxidation reaction, namely, the uniformity of each direction is relatively higher, and the distribution degree of the silicon nitride obviously influences the uniformity of each direction of the micro-arc oxidation film due to the participation of the silicon nitride in the comparative example 1, namely, the pretreated silicon nitride and the step micro-arc oxidation treatment of the invention improve the corrosion resistance of the aluminum alloy and simultaneously further improve the uniformity and stability of the corrosion resistance of the micro-arc oxidation film of the aluminum alloy.

In order to further verify the influence of the sectional voltage on the distribution of silicon nitride in the micro-arc oxidation film, the N element is analyzed, and since the micro-arc oxidation solution contains the silicon element, the silicon element is not suitable for being used for evaluating the distribution of the silicon nitride, while the nitrogen element is mainly derived from the silicon nitride and EDTA-2Na, and the EDTA-2Na in the micro-arc oxidation film is very little, so that the distribution state of the silicon nitride in the micro-arc oxidation film can be effectively represented by using the energy spectrum of the nitrogen element, as shown in FIG. 3, the graph on FIG. 3 is the graph of the embodiment 2 of the invention, it can be clearly seen that, in the micro-arc oxidation film, the distribution of the whole N element is very uniform, in contrast, the graph (comparative example 1) under FIG. 3 does not undergo the sectional voltage micro-arc oxidation, wherein the distribution of the nitrogen element is obviously nonuniform, and the nitrogen elements which are closer to the aluminum material are fewer and the nitrogen elements which are farther from the aluminum material are more, and the left and the right are not uniformly distributed.