Surface-treated magnesium alloy and preparation method thereof

Abstract

The invention relates to the technical field of surface treatment, and discloses a surface-treated magnesium alloy and a preparation method thereof. The magnesium alloy with the extremely low density is selected as the base body from the angle of light weight, graphene is added into the plasma electrolytic oxidation electrolyte to serve as a corrosion inhibitor, so that the discharge process, composition and structure of the plasma electrolytic oxidation film layer are changed, and the plasma electrolytic oxidation film layer is prepared on the surface of the base body; and the defects of multiple holes and multiple cracks of the plasma electrolytic oxidation film layer are optimized, so that the corrosion resistance of the magnesium alloy is improved. According to the magnesium alloy subjected to surface treatment, the application of the magnesium alloy in the fields of aerospace, 3C, national defense military industry, automobiles and the like can be further expanded, and compared with existing metal materials such as aluminum, nickel, titanium and stainless steel and alloys of the metal materials, the weight of products can be greatly reduced, and the magnesium alloy has excellent corrosion resistance.

Description

Technical Field

[0001] The present application relates to the field of surface treatment technology, and in particular to a surface-treated magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium and magnesium-lithium alloys have high specific strength and specific stiffness, as well as good shock absorption, thermal conductivity, electrical conductivity, electromagnetic shielding, mechanical processing performance and recycling performance. They have gradually become the most ideal and most promising materials in the fields of aerospace, aviation, automobiles, nuclear industry, and medical treatment, and are also known as "green materials of the 21st century." However, magnesium and lithium are chemically active, and their standard electrode potentials are relatively low. When in contact with other metals or in an electrolyte environment, they are easily oxidized as anodes, lose electrons and are corroded. And they are easy to react chemically with oxygen, moisture, etc. in the air. In the air, an oxide film will quickly form on the surface of magnesium and magnesium-lithium alloys, but this oxide film is usually loose and cannot effectively prevent further intrusion of oxygen and moisture, resulting in continuous corrosion inside the alloy.

[0003] Therefore, how to effectively and reasonably improve the corrosion resistance of magnesium and magnesium-lithium alloys has become one of the focuses of current research on the application of magnesium and magnesium-lithium alloys. Improving the corrosion resistance of magnesium and magnesium-lithium alloys can be carried out from two aspects: on the one hand, starting from the magnesium and magnesium-lithium alloys themselves, developing new magnesium and magnesium-lithium alloys with excellent performance; on the other hand, improving the corrosion resistance and wear resistance of magnesium and magnesium-lithium alloys through effective surface treatment. Numerous research results show that the corrosion resistance of magnesium and magnesium-lithium alloys can be improved by changing the chemical composition and organizational structure of magnesium and magnesium-lithium alloys, but the changes in the composition and organization of magnesium and magnesium-lithium alloys are generally accompanied by the addition of heavy rare earth elements, which makes the density of magnesium and magnesium-lithium alloys increase significantly, which reduces the advantages of the application of magnesium and magnesium-lithium alloys. Therefore, in order not to change the low density advantage of magnesium and magnesium-lithium alloys, the surface properties of magnesium and magnesium-lithium alloys can be changed through surface technology to improve their corrosion resistance. Summary of the invention

[0004] In view of this, the purpose of the present application is to provide a surface-treated magnesium alloy and a preparation method thereof, so that the corrosion resistance of the magnesium alloy is significantly improved.

[0005] In order to solve the above technical problems / achieve the above objectives or at least partially solve the above technical problems / achieve the above objectives, as a first aspect of the present application, a method for preparing a surface-treated magnesium alloy is provided, comprising:

[0006] S1. Pretreatment of magnesium alloy substrate;

[0007] S2. The magnesium alloy after the pretreatment is subjected to plasma electrolytic oxidation surface treatment using an electrolyte containing graphene to obtain the surface-treated magnesium alloy.

[0008] Optionally, the pre-treatment includes one or more of grinding, cleaning, degreasing, pickling and alkali washing.

[0009] Optionally, the electrolyte includes sodium silicate, sodium hydroxide and graphene; further optionally, the electrolyte includes 5-40 g / L sodium silicate, 5-50 / L sodium hydroxide and 0.1-5 g / L graphene. Further optionally, the electrolyte also includes one or more of potassium fluoride, sodium tetraborate and sodium citrate; optionally, the concentration of potassium fluoride is not higher than 10 g / L, the concentration of sodium tetraborate is not higher than 30 g / L, and the concentration of sodium citrate is not higher than 40 g / L.

[0010] Optionally, the operating parameters of the plasma electrolytic oxidation include:

[0011] The temperature is lower than 40° C., the plasma electrolytic oxidation time is 10 to 40 minutes, a constant voltage mode is adopted, the frequency is 500 to 1000 Hz, and the forward duty cycle is 12% to 20%.

[0012] Optionally, the preparation method further comprises cleaning and drying the magnesium alloy substrate after the plasma electrolytic oxidation surface treatment. Further optionally, it further comprises performing other surface treatments on the plasma electrolytic oxidation film; the other surface treatments comprise one or more of electroplating, chemical plating, anodizing, chemical conversion and coating.

[0013] As a second aspect of the present application, a magnesium alloy prepared by the preparation method described in the present application is provided.

[0014] From the perspective of lightweight, this application selects a magnesium alloy with extremely low density as the matrix, and adds graphene as a corrosion inhibitor to the plasma electrolytic oxidation electrolyte, thereby changing the discharge process, composition and structure of the plasma electrolytic oxidation film layer, preparing a plasma electrolytic oxidation film layer on the surface of the matrix, and optimizing the defects of the plasma electrolytic oxidation film layer with multiple pores and cracks, thereby improving the corrosion resistance of the magnesium alloy. The surface-treated magnesium alloy provided by this application can further expand its application in the fields of aerospace, 3C, national defense, military industry and automobiles. Compared with existing metal materials such as aluminum, nickel, titanium and stainless steel and their alloys, it can greatly reduce the weight of the product and has excellent corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The contact angle of the magnesium alloy plasma electrolytic oxide film prepared in Example 1 of the present application; (a) no graphene is added to the electrolyte, (b) graphene is added to the electrolyte;

[0016] Figure 2 The potentiodynamic polarization curves of the magnesium alloy plasma electrolytic oxidation film layer and the magnesium and magnesium-lithium alloy plasma electrolytic oxidation-polyaniline composite film layer prepared in Example 1 of the present application; LA91 represents a magnesium alloy that has not been surface treated, PEO represents a magnesium alloy that has been surface treated with an electrolyte without graphene addition, and PEO-Gr represents a magnesium alloy that has been surface treated with an electrolyte with graphene added. DETAILED DESCRIPTION

[0017] The present application discloses a surface-treated magnesium alloy and a preparation method thereof. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all deemed to be included in this application. The products, processes and applications described in this application have been described through preferred embodiments. Relevant personnel can obviously modify or appropriately change and combine the processes and applications described in this article without departing from the content, spirit and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0018] It should be noted that, in this article, if relational terms such as "first" and "second", "step 1" and "step 2", and "(1)" and "(2)" appear, they 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. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements. At the same time, the embodiments in this application and the features in the embodiments may be combined with each other without conflict.

[0019] Common surface treatment methods for magnesium and magnesium-lithium alloys include plasma electrolytic oxidation, anodizing, chemical plating / electroplating, organic coating, chemical conversion, etc. Among them, plasma electrolytic oxidation can form a film with a metal oxide as the main phase, controllable thickness and good bonding with the substrate on the surface of magnesium and magnesium-lithium alloys by adjusting the composition of the electrolyte and controlling the corresponding power supply mode and electrical parameters, which improves the corrosion resistance of the magnesium and magnesium-lithium alloy substrates to a certain extent. However, the surface of the plasma electrolytic oxidation film layer with hydrophilic properties has structural defects such as micropores and microcracks, and the shielding effect is poor. The protective effect on the magnesium and magnesium-lithium alloy substrates needs to be improved.

[0020] Based on the defects of the existing plasma electrolytic oxidation film layer, this application can reduce the problems of cracks, micropores and peeling of the film layer by adding graphene as a corrosion inhibitor in the electrolyte. Although graphene is widely used as an additive in coatings, there is no precedent or inspiration for using it as a corrosion inhibitor in plasma electrolytic oxidation electrolyte to participate in the formation of the film layer.

[0021] In a first aspect of the present application, a method for preparing a surface-treated magnesium alloy is provided, comprising:

[0022] S1. Pretreatment of magnesium alloy substrate;

[0023] S2. The magnesium alloy after the pretreatment is subjected to plasma electrolytic oxidation surface treatment using an electrolyte containing graphene to obtain the surface-treated magnesium alloy.

[0024] In the present application, the magnesium alloy includes magnesium-lithium alloy.

[0025] On the one hand, graphene has a unique two-dimensional sheet structure, which can be doped into the film layer to form a physical barrier, blocking the diffusion of corrosive media such as oxygen, moisture and corrosive ions into the metal matrix, thereby slowing down the occurrence of corrosion; on the other hand, graphene has good chemical stability, is not easy to react chemically in most environments, and continues to play a barrier and protective role; on the other hand, the plasma electrolytic oxidation process is carried out in an ultrasonic or stirring state. Graphene itself has strong conductivity, which can change the conductivity of the electrolyte and affect the discharge process of the film layer, thereby changing the composition and structure of the film layer and reducing the porosity of the film layer. Fourthly, graphene itself is hydrophobic, and doping into the film layer can increase the contact angle of the plasma electrolytic oxidation film layer. Therefore, the corrosion resistance of the plasma electrolytic oxidation film layer of magnesium alloy can be significantly improved.

[0026] In certain embodiments of the present application, the pre-treatment includes one or more treatments of grinding, cleaning, degreasing, pickling, and alkali cleaning. In other embodiments of the present application, the grinding can be performed by selecting sandpaper of a series of meshes, for example, 180 mesh, 400 mesh, 800 mesh, and 1200 mesh SiC sandpaper is selected for step-by-step grinding, and the surface of the substrate is alternately polished in two vertical directions until the surface is smooth and flat. In other embodiments of the present application, the cleaning can be performed by ultrasonic cleaning, for example, ultrasonic cleaning with anhydrous ethanol, and then rinsing with deionized water. In other embodiments of the present application, the degreasing removes oil stains on the surface of the magnesium alloy by using a degreasing solution, and the degreasing solution includes 2-50 g / L sodium hydroxide, 0-30 g / L sodium silicate, 1-20 g / L sodium carbonate, 0-30 g / L sodium phosphate, and 0-10 g / L surfactant. In some other embodiments of the present application, the pickling is performed by using an acid solution to remove impurities and chemical oxide film on the surface of the magnesium alloy, and the acid solution includes 5 to 100 g / L of an organic acid and 0 to 50 g / L of sodium nitrate, and the organic acid is selected from at least one of glacial acetic acid, oxalic acid, citric acid, and tartaric acid, preferably glacial acetic acid or oxalic acid. In some other embodiments of the present application, the alkali washing uses an alkali solution to remove pickling residues on the surface of the magnesium alloy, and the alkali solution includes 5 to 20 g / L of sodium hydroxide, 0 to 10 g / L of sodium tripolyphosphate, and 0 to 1 g / L of sodium dodecyl sulfate.

[0027] In certain embodiments of the present application, the electrolyte containing graphene can be prepared as a graphene dispersion before mixing with other electrolyte components. Considering that graphene is insoluble in aqueous solution and has poor dispersibility in aqueous solution, the dispersion of graphene is achieved by adding a surfactant. The amount of surfactant added to the graphene dispersion is 0.1wt% to 3wt% (relative to the mass of graphene). In some other embodiments of the present application, the surfactant is selected from at least one of sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, polyvinyl pyrrolidone, and polyethylene glycol. The average radial size of the graphene is 0.5 to 10 μm, and the average thickness is 0.8 to 1.2 nm.

[0028] In certain embodiments of the present application, the electrolyte includes sodium silicate, sodium hydroxide and graphene; further optionally, the electrolyte includes 5-40 g / L sodium silicate, 5-50 / L sodium hydroxide and 0.1-5 g / L graphene. In other embodiments of the present application, the electrolyte also includes one or more of potassium fluoride, sodium tetraborate and sodium citrate;

[0029] Adding potassium fluoride can reduce the arc starting voltage, enhance the corrosion resistance of the film, improve the surface roughness of the film, increase the growth rate and thickness of the film, improve the microstructure of the film, optimize the surface morphology of the film, adjust the properties of the electrolyte, and adjust the pH value.

[0030] Adding sodium tetraborate can promote film formation, form a magnesium metaborate deposition layer, build a suitable electric field condition for micro-arc discharge, and help the subsequent oxide film formation; accelerate film growth; improve film quality, increase film density, and increase the bonding strength between the film and the substrate; adjust the pH value of the electrolyte;

[0031] Adding sodium citrate can improve the structure and performance of the membrane layer, make the membrane layer more uniform and dense, and reduce the pore size; enhance the corrosion resistance of the membrane layer, adjust the pH value of the electrolyte, and reduce the plasma electrolytic oxidation voltage;

[0032] Optionally, the concentration of potassium fluoride is not higher than 10 g / L, the concentration of sodium tetraborate is not higher than 30 g / L, and the concentration of sodium citrate is not higher than 40 g / L.

[0033] In certain embodiments of the present application, the present application also compensates for the defects of the existing plasma electrolytic oxidation film layer by optimizing the working parameters of the plasma electrolytic oxidation, and the working parameters of the plasma electrolytic oxidation include:

[0034] The temperature is lower than 40° C., the plasma electrolytic oxidation time is 10 to 40 minutes, a constant voltage mode is adopted, the frequency is 500 to 1000 Hz, and the forward duty cycle is 12% to 20%.

[0035] In the working parameters of plasma electrolytic oxidation in this application, the temperature setting has the following effects:

[0036] (1) Ensure the quality of the film layer: Too high a temperature will increase the dissolution effect of the alkaline electrolyte on the oxide film, causing the film thickness and hardness to decrease significantly, the film structure to become loose, and the performance to decrease. Moreover, when the solution temperature exceeds 40°C, the film formation rate will also decrease.

[0037] (2) Avoid film defects: If the temperature is too high, the solution is easy to splash, and the film is easy to be partially burned or punctured, resulting in defects, which affects the integrity and corrosion resistance of the film.

[0038] (3) Reduce energy consumption: The plasma electrolytic oxidation process itself generates a lot of heat. If the temperature is too high, more energy is required for the cooling system to control the temperature, which increases energy consumption and production costs.

[0039] (4) Prevent electrolyte deterioration: Higher temperatures may cause the components in the electrolyte to decompose, volatilize or chemically react, changing the composition and properties of the electrolyte, affecting the stability and repeatability of the plasma electrolytic oxidation reaction, and reducing the treatment effect.

[0040] (5) Ensure stable operation of the equipment: Excessively high temperatures can damage the plasma electrolytic oxidation equipment and affect its service life and stability. Controlling the temperature below 40°C helps protect the equipment and reduce the frequency of equipment failures.

[0041] The setting of plasma electrolytic oxidation time has the following effects:

[0042] (1) Ensure the performance of the film layer: Within this time range, the film layer can achieve good compactness, hardness, corrosion resistance and other properties. A film layer with a certain protective effect can be initially formed in about 10 minutes. As the time is extended to 40 minutes, the film layer continues to grow and improve, and the performance is further improved. If the time is too short, the film layer is too thin and cannot effectively play the protective role of plasma electrolytic oxidation; if the time is too long, the roughness of the film layer increases, cracks and other defects may appear, and it will also affect production efficiency.

[0043] (2) Control production costs: If the time is too short, a qualified film layer cannot be formed and needs to be reprocessed, which increases costs. If the time is too long, more electricity, electrolyte and other resources will be consumed, and the equipment operation time will be extended, resulting in increased equipment wear and tear and increased maintenance costs. At the same time, it will also reduce production efficiency, reduce output per unit time, and increase production costs.

[0044] (3) Adapt to the needs of different materials and workpieces: Different metal materials and their alloys, as well as workpieces of different shapes and sizes, require different film-forming times during plasma electrolytic oxidation. The time range of 10-40 minutes can meet the film-forming requirements of most materials and workpieces to a certain extent. By adjusting the time, various materials and workpieces can obtain oxide films with good performance.

[0045] (4) Meet the requirements of process stability: Within this time range, the chemical reactions and physical processes in the plasma electrolytic oxidation process are relatively stable and easy to control. It can ensure the uniformity and continuity of arc discharge, stabilize the growth process of the oxide film, and thus obtain a film layer with stable quality and consistent performance.

[0046] The setting of plasma electrolytic oxidation frequency has the following effects:

[0047] (1) Improve the quality of the film layer: In this frequency range, the number of discharges per unit time is more appropriate, which can make the surface of the film layer smoother and have lower porosity, and help to form a uniform and dense oxide film. At 500Hz, the self-corrosion potential is the most positive, there is a wider passivation zone, and the corrosion resistance is better.

[0048] (2) Accelerate the film formation speed: In the frequency range of 500-1000Hz, the discharge energy is large enough. As the frequency increases, the number of discharges per unit time increases, the number of parts of the surface that are broken down also increases, the film formation speed is accelerated, and the film thickness increases. When the pulse frequency is 1000Hz, the thickness of the plasma electrolytic oxide film can reach a maximum value.

[0049] (3) Improve process stability: This frequency range can make the arc discharge in the plasma electrolytic oxidation process more stable, avoiding the situation where the discharge is too violent or unstable, ensuring the repeatability and stability of the process, and is conducive to obtaining an oxide film layer with consistent performance.

[0050] (4) Considering both equipment and cost: From the perspective of equipment, the frequency of 500-1000Hz is relatively easy to achieve, and the requirements for power supply and other equipment are not too high. The burden on the equipment is small, and the equipment cost and energy consumption are also reduced. At the same time, this frequency range can achieve a good film-forming effect within a certain processing time, improve production efficiency, and reduce overall costs.

[0051] The setting of the plasma electrolytic oxidation duty cycle has the following effects:

[0052] (1) Ensure the quality of the film layer: Within this duty cycle range, the single pulse discharge time is moderate, which can enable the metal surface to obtain appropriate energy input, and help form a uniform and dense oxide film. It can ensure that the film layer has sufficient thickness to provide good protection performance, and will not cause burnout, large pores and other defects due to excessive discharge energy, thereby improving the hardness and corrosion resistance of the film layer.

[0053] (2) Improve process stability: The arc discharge in the plasma electrolytic oxidation process can be stabilized to avoid excessive or unstable discharge, thereby ensuring the repeatability and stability of the process and facilitating the acquisition of an oxide film with consistent performance.

[0054] (3) Optimizing film-forming efficiency: When the duty cycle is between 12% and 20%, the number of effective discharges and the discharge energy per unit time are relatively reasonable. While ensuring the quality of the film layer, a faster film-forming speed can be achieved, thereby improving production efficiency and reducing processing time and cost.

[0055] (4) Reduce energy consumption: Compared with a higher duty cycle, the energy consumption of the equipment under this duty cycle range is relatively low. On the basis of meeting the film formation requirements, the energy consumption is reduced, which meets the requirements of energy conservation and environmental protection.

[0056] In some embodiments of the present application, the preparation method further comprises cleaning and drying the magnesium alloy substrate after the plasma electrolytic oxidation surface treatment. In other embodiments of the present application, the magnesium alloy substrate is cleaned with anhydrous ethanol and deionized water in sequence, dried with hot air, and then placed in a vacuum drying oven and dried at 30 to 60°C for 5 to 20 minutes.

[0057] In certain embodiments of the present application, a composite film layer is used to further increase the corrosion resistance of the magnesium alloy, for example, other surface treatments are performed on the plasma electrolytic oxide film; the other surface treatments include one or more of electroplating, chemical plating, anodizing, chemical conversion and coating, so that the advantages of various surface treatment technologies can be fully utilized to effectively prevent the intrusion of corrosive media.

[0058] In the second aspect of the present application, by comparing with the film layer of the electrolyte without adding graphene and other corrosion inhibitors, the contact angle of the film layer on the surface of the magnesium alloy of the present application is significantly increased, and at the same time, the self-corrosion potential shifts positively and the self-corrosion current density decreases, indicating that the corrosion resistance of the magnesium alloy matrix prepared by the present application is significantly improved. Therefore, the present application also provides a magnesium alloy prepared by the preparation method described in the present application.

[0059] In each group of comparative experiments provided in this application, unless otherwise specified, other experimental conditions, materials, etc. are kept consistent except for the differences indicated in each group, so as to provide comparability. The experimental materials and reagents used in the examples can be obtained from commercial channels unless otherwise specified.

[0060] The following is a further description of a surface-treated magnesium alloy and a preparation method thereof provided in the present application.

[0061] Embodiment 1:

[0062] 1) Substrate pretreatment

[0063] ① Mechanical polishing: LA103Z magnesium-lithium alloy was used as the substrate, and SiC sandpapers of 180 mesh, 400 mesh, 800 mesh, and 1200 mesh were used to polish the surface step by step until it was smooth and flat. After polishing, anhydrous ethanol was ultrasonicated for 5 minutes and then rinsed with deionized water;

[0064] ② Degreasing: Place the mechanically polished LA103Z magnesium-lithium alloy sample in a mixed solution of 30 g / L sodium hydroxide, 5 g / L sodium silicate, 5 g / L sodium carbonate and 20 g / L sodium phosphate, completely immerse it, and soak it at 80°C for 10 minutes. Take it out and rinse it with deionized water.

[0065] ③ Pickling: Place the degreased LA103Z magnesium-lithium alloy sample in a mixed solution of 10 g / L glacial acetic acid and 5 g / L citric acid, completely immerse it, soak it at 40 °C for 40 s, take it out and rinse it with deionized water.

[0066] ④ Alkali washing: Place the acid-washed LA103Z magnesium-lithium alloy sample in a mixed solution of 10 g / L sodium hydroxide, 5 g / L sodium tripolyphosphate and 0.5 g / L sodium dodecyl sulfate, soak at 60 °C for 50 s, and take out and rinse with deionized water.

[0067] 2) Preparation of graphene dispersion

[0068] 1 g of graphene (with an average radial dimension of 0.5 to 10 μm and an average thickness of 0.8 to 1.2 nm) and 0.03 g of sodium dodecylbenzene sulfonate were added into 1 L of deionized water and ultrasonically dispersed for 5 h to obtain a graphene dispersion.

[0069] 3) Plasma electrolytic oxidation surface treatment

[0070] The pre-treated LA103Z magnesium-lithium alloy is connected to the anode of the plasma electrolytic oxidation power supply and completely immersed in the plasma electrolytic oxidation electrolyte. The electrolyte is a mixed solution of 20g / L sodium silicate, 10 / L sodium hydroxide, 10g / L sodium tetraborate and 2g / L potassium fluoride. The constant voltage mode is adopted, the frequency is set to 500Hz, and the forward duty cycle is 15%. The electrolyte temperature is set to 15°C, the plasma electrolytic oxidation time is 15min, and then it is taken out and rinsed with deionized water and placed in a vacuum drying oven at 50°C for 10min to obtain a magnesium and magnesium-lithium alloy plasma electrolytic oxidation film layer (without graphene) (PEO); then the prepared graphene dispersion is added to the originally prepared electrolyte to make the graphene concentration 0.1-5g / L, and the above process parameters are kept consistent to obtain a LA103Z magnesium-lithium alloy plasma electrolytic oxidation film layer (with graphene added) (PEO-Gr).

[0071] See also Figure 1 It can be seen that the contact angle of the LA103Z magnesium-lithium alloy plasma electrolytic oxidation film prepared in this embodiment changes after graphene is added to the electrolyte. When graphene is not added to the electrolyte, the contact angle of the film is about 37.6°, while the contact angle of the film prepared after adding graphene to the electrolyte is about 65.8°, and the contact angle is significantly increased and white. This shows that graphene doping into the film can increase the contact angle of the plasma electrolytic oxidation film. Therefore, the corrosion resistance of the film is significantly improved.

[0072] Table 1 Potentiodynamic polarization curve fitting data

[0073]

[0074] See also Figure 2 As shown in Table 1, compared with the magnesium-lithium alloy substrate LA103Z, the magnesium-lithium alloy plasma electrolytic oxidation film layer (without graphene) (PEO) and the magnesium-lithium alloy plasma electrolytic oxidation film layer (with graphene) (PEO-Gr) prepared in this embodiment have a positive shift in self-corrosion potential and a reduced self-corrosion current density, indicating that the plasma electrolytic oxidation surface treatment technology can improve the corrosion resistance of the substrate. In addition, the film layer prepared after adding graphene to the electrolyte has a positive shift in self-corrosion potential of 0.186V compared to the film layer prepared without adding graphene, and the self-corrosion current density is reduced by one order of magnitude, and the polarization resistance is increased by one order of magnitude, which indicates that adding graphene to the electrolyte can enhance the corrosion resistance of the film layer.

[0075] Embodiment 2:

[0076] 1) Substrate pretreatment

[0077] In this step, the substrate is MB15 magnesium alloy; the implementation process is the same as step 1 in Example 1;

[0078] 2) Preparation of graphene dispersion

[0079] 1 g of graphene (with an average radial size of 0.5 to 10 μm and an average thickness of 0.8 to 1.2 nm) and 0.03 g of polyvinyl pyrrolidone were added into 1 L of deionized water and ultrasonically dispersed for 5 h to obtain a graphene dispersion.

[0080] 3) Plasma electrolytic oxidation surface treatment

[0081] This step is the same as step 3 in Example 1.

[0082] In the contact angle test, the results were consistent with those in Example 1. When graphene was not added to the electrolyte, the contact angle of the film was small, while the contact angle of the film prepared after adding graphene to the electrolyte increased significantly and was white. This shows that graphene doping into the film can increase the contact angle of the plasma electrolytic oxidation film. Therefore, the corrosion resistance of the film is significantly improved.

[0083] In the results of the potentiodynamic polarization curve, compared with the MB15 magnesium alloy, the self-corrosion potential of the magnesium alloy plasma electrolytic oxide film layer (without graphene added) (PEO) and the magnesium alloy plasma electrolytic oxide film layer (with graphene added) (PEO-Gr) prepared in this embodiment shifted positively, and the self-corrosion current density decreased, indicating that the plasma electrolytic oxidation surface treatment technology can improve the corrosion resistance of the substrate.

[0084] Embodiment 3:

[0085] 1) Substrate pretreatment

[0086] This step is the same as step 1 in Example 1;

[0087] 2) Preparation of graphene dispersion

[0088] 1 g of graphene (with an average radial dimension of 0.5 to 10 μm and an average thickness of 0.8 to 1.2 nm) and 0.03 g of sodium dodecylbenzene sulfonate were added into 1 L of deionized water and ultrasonically dispersed for 5 h to obtain a graphene dispersion.

[0089] 3) Plasma electrolytic oxidation surface treatment

[0090] The pre-treated LA103Z magnesium-lithium alloy was connected to the anode of the plasma electrolytic oxidation power supply and completely immersed in the plasma electrolytic oxidation electrolyte. The electrolyte was a mixed solution of 10g / L sodium silicate, 5g / L sodium hydroxide, 10g / L sodium tetraborate and 10g / L sodium citrate. The constant voltage mode was adopted, the frequency was set to 500Hz, and the forward duty cycle was 15%. The electrolyte temperature was set to 15°C, the plasma electrolytic oxidation time was 15min, and then it was taken out and rinsed with deionized water and placed in a vacuum drying oven at 50°C for 10min to obtain the LA103Z magnesium-lithium alloy plasma electrolytic oxidation film layer (without graphene added); then the prepared graphene dispersion was added to the originally prepared electrolyte, and the above process parameters were kept consistent to obtain the LA103Z magnesium-lithium alloy plasma electrolytic oxidation film layer (with graphene added).

[0091] In the contact angle test, the results were consistent with those in Example 1. When graphene was not added to the electrolyte, the contact angle of the film was small, while the contact angle of the film prepared after adding graphene to the electrolyte increased significantly and was white. This shows that graphene doping into the film can increase the contact angle of the plasma electrolytic oxidation film. Therefore, the corrosion resistance of the film is significantly improved.

[0092] In the results of the potentiodynamic polarization curve, compared with the LA103Z magnesium-lithium alloy, the self-corrosion potential of the magnesium alloy plasma electrolytic oxide film layer (without graphene added) (PEO) and the magnesium alloy plasma electrolytic oxide film layer (with graphene added) (PEO-Gr) prepared in this embodiment shifted positively, and the self-corrosion current density decreased, indicating that the plasma electrolytic oxidation surface treatment technology can improve the corrosion resistance of the substrate.

[0093] Embodiment 4:

[0094] 1) Substrate pretreatment

[0095] This step is the same as step 1 in Example 1;

[0096] 2) Preparation of graphene dispersion

[0097] 1 g of graphene (with an average radial size of 0.5 to 10 μm and an average thickness of 0.8 to 1.2 nm), 0.01 g of sodium dodecylbenzene sulfonate and 0.01 g of polyethylene glycol were added into 1 L of deionized water and ultrasonically dispersed for 5 h to obtain a graphene dispersion.

[0098] 3) Plasma electrolytic oxidation surface treatment

[0099] This step is the same as step 3 in Example 3.

[0100] In the contact angle test, the results were consistent with those in Example 1. When graphene was not added to the electrolyte, the contact angle of the film was small, while the contact angle of the film prepared after adding graphene to the electrolyte increased significantly and was white. This shows that graphene doping into the film can increase the contact angle of the plasma electrolytic oxidation film. Therefore, the corrosion resistance of the film is significantly improved.

[0101] In the results of the potentiodynamic polarization curve, compared with the LA103Z magnesium-lithium alloy, the self-corrosion potential of the magnesium alloy plasma electrolytic oxide film layer (without graphene added) (PEO) and the magnesium alloy plasma electrolytic oxide film layer (with graphene added) (PEO-Gr) prepared in this embodiment shifted positively, and the self-corrosion current density decreased, indicating that the plasma electrolytic oxidation surface treatment technology can improve the corrosion resistance of the substrate.

[0102] Embodiment 5:

[0103] 1) Substrate pretreatment

[0104] This step is the same as step 1 in Example 1;

[0105] 2) Preparation of graphene dispersion

[0106] 0.5 g of graphene (with an average radial dimension of 0.5 to 10 μm and an average thickness of 0.8 to 1.2 nm) and 0.01 g of hexadecyltrimethylammonium bromide were added into 1 L of deionized water and ultrasonically dispersed for 5 h to obtain a graphene dispersion.

[0107] 3) Plasma electrolytic oxidation surface treatment

[0108] This step is the same as step 3 in Example 3.

[0109] In the contact angle test, the results were consistent with those in Example 1. When graphene was not added to the electrolyte, the contact angle of the film was small, while the contact angle of the film prepared after adding graphene to the electrolyte increased significantly and was white. This shows that graphene doping into the film can increase the contact angle of the plasma electrolytic oxidation film. Therefore, the corrosion resistance of the film is significantly improved.

[0110] In the results of the potentiodynamic polarization curve, compared with the LA103Z magnesium-lithium alloy, the self-corrosion potential of the magnesium alloy plasma electrolytic oxide film layer (without graphene added) (PEO) and the magnesium alloy plasma electrolytic oxide film layer (with graphene added) (PEO-Gr) prepared in this embodiment shifted positively, and the self-corrosion current density decreased, indicating that the plasma electrolytic oxidation surface treatment technology can improve the corrosion resistance of the substrate.

[0111] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing a surface-treated magnesium alloy, characterized in that: include: S1. Pretreatment of magnesium alloy substrate; S2. The magnesium alloy after the pretreatment is subjected to plasma electrolytic oxidation surface treatment using an electrolyte containing graphene to obtain the surface-treated magnesium alloy.

2. The preparation method according to claim 1, characterized in that: The pre-treatment includes one or more treatments of grinding, cleaning, degreasing, pickling and alkali cleaning.

3. The preparation method according to claim 1, characterized in that: The electrolyte includes sodium silicate, sodium hydroxide and graphene.

4. The preparation method according to claim 3, characterized in that: The electrolyte comprises 5-40 g / L of sodium silicate, 5-50 g / L of sodium hydroxide and 0.1-5 g / L of graphene.

5. The preparation method according to claim 3, characterized in that: The electrolyte also includes one or more of potassium fluoride, sodium tetraborate and sodium citrate.

6. The preparation method according to claim 5, characterized in that: The concentration of potassium fluoride is not higher than 10 g / L, the concentration of sodium tetraborate is not higher than 30 g / L, and the concentration of sodium citrate is not higher than 40 g / L.

7. The preparation method according to claim 1, characterized in that: The operating parameters of the plasma electrolytic oxidation include: The temperature is lower than 40° C., the plasma electrolytic oxidation time is 10 to 40 minutes, a constant voltage mode is adopted, the frequency is 500 to 1000 Hz, and the forward duty cycle is 12% to 20%.

8. The preparation method according to any one of claims 1 to 9, characterized in that: The method also includes cleaning and drying the magnesium alloy substrate after the plasma electrolytic oxidation surface treatment.

9. The preparation method according to claim 8, characterized in that: It also includes performing other surface treatments on the plasma electrolytic oxide film; the other surface treatments include one or more of electroplating, chemical plating, anodizing, chemical conversion and coating.

10. The magnesium alloy prepared by the preparation method according to any one of claims 1 to 9.

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