Magnesium alloy coating agent and preparation method thereof, magnesium alloy surface treatment method and magnesium alloy product

Abstract

The invention provides a magnesium alloy coating agent and a preparation method thereof, a magnesium alloy surface treatment method and a magnesium alloy product, and the magnesium alloy coating agent comprises 30-80 g / L of ammonium fluotitanate ((NH4) 2TiF6), 10-30 g / L of sodium molybdate (Na2MoO4), 5-15 g / L of plant tannic acid, 3-10 g / L of L-ascorbic acid, 1-5 g / L of rare earth cerium nitrate (Ce (NO3) 3), 0.1-1 g / L of graphene quantum dots (the particle size is smaller than or equal to 10 nm), 5-20 g / L of sulfamic acid (H3NSO3) and the balance deionized water. Traditional harmful components such as phosphate and chromate are completely abandoned, international environmental protection standards such as ROHS and REACH are met, plant tannic acid (natural polyphenol) and L-ascorbic acid (vitamin C derivatives) replace traditional petroleum-based complexing agents, environmental toxicity is reduced, an acid system adjusted by sulfamic acid only needs to be neutralized and then flocculated and precipitated, and the treatment cost is reduced by 60% or above compared with phosphorus-containing wastewater; the magnesium alloy coating agent can also form a double-phase film layer structure, a neutral salt spray test is more than or equal to 72 hours (generally less than or equal to 24 hours), and the integrity of the film layer is far better than that of a traditional phosphating process.

Description

Technical Field

[0001] The present application relates to the technical field of metal surface treatment, and particularly to a magnesium alloy film agent and a preparation method thereof, a magnesium alloy surface treatment method, and a magnesium alloy product. Background Art

[0002] With the increasing demand for lightweight, magnesium alloys are increasingly widely used in the fields of aerospace, automotive manufacturing, and electronic communication. However, its inherent active chemical properties lead to prominent corrosion problems. Although traditional chromium-containing or phosphate film processes can provide certain protection effects, they have disadvantages such as serious environmental pollution and high costs. Therefore, it has become an urgent need to develop a highly efficient, environmentally friendly, and multifunctional integrated magnesium alloy surface treatment technology. Summary of the Invention

[0003] In view of this, the present application provides a magnesium alloy film agent and a preparation method thereof, a magnesium alloy surface treatment method, and a magnesium alloy product, which can provide an environmentally friendly film agent that is completely phosphorus-free and heavy metal-free. The preparation method includes: ammonium hexafluorotitanate ((NH4)2TiF6) 30 - 80 g / L, sodium molybdate (Na2MoO4) 10 - 30 g / L, plant tannic acid 5 - 15 g / L, L-ascorbic acid 3 - 10 g / L, rare earth cerium nitrate (Ce(NO3)3) 1 - 5 g / L, graphene quantum dots (particle size ≤ 10 nm) 0.1 - 1 g / L, sulfamic acid (H3NSO3) 5 - 20 g / L, and the balance being deionized water.

[0004] In one embodiment, the corrosion inhibitor further includes a bio-based corrosion inhibitor, including 0.5 - 3 g / L of chitosan-poly(dopamine) composite microspheres, which are used to release corrosion inhibition factors when the film layer is damaged. The particle size of the chitosan-poly(dopamine) composite microspheres is 50 - 200 nm.

[0005] In one embodiment, the main film-forming agent further includes a photocatalytic material, and the photocatalytic material includes 0.5 - 5 g / L of titanium dioxide nanotubes, which are used to decompose surface pollutants under ultraviolet irradiation.

[0006] In addition, a preparation method of a magnesium alloy film agent is also provided. The magnesium alloy film agent uses the above-mentioned magnesium alloy film agent, and the preparation method includes the following steps:

[0007] Dissolve ammonium hexafluorotitanate and sodium molybdate in deionized water and ultrasonically disperse for 10 - 30 minutes;

[0008] Sequentially add plant tannic acid, L-ascorbic acid, and sulfamic acid, and stir at a constant temperature until completely dissolved. The temperature is 50 ± 5 °C and the rotation speed is 500 rpm;

[0009] Add rare earth cerium nitrate and graphene quantum dots, and form a stable dispersion through treatment with a high-pressure homogenizer. The pressure at the high-pressure homogenizer is 100-200 MPa;

[0010] Adjust the pH to 2.5-3.5 to obtain the finished product.

[0011] In one embodiment, the surface of the graphene quantum dots is modified with carboxyl and amino functional groups to enhance the binding force with the magnesium alloy matrix.

[0012] In addition, a method for surface treatment of magnesium alloy is also provided. Using the above magnesium alloy film-forming agent, the method for surface treatment of magnesium alloy includes:

[0013] After the magnesium alloy workpiece is activated by plasma, it is immersed in the film-forming agent. The plasma is in an argon atmosphere, with a power of 200 W and a time of 5-10 minutes;

[0014] Under the assistance of a pulsed electric field, it is treated at 35-45 °C for 60-180 seconds. The pulsed electric field satisfies: voltage 10-30 V, frequency 50 Hz;

[0015] The workpiece is cured under ultraviolet light for 10-30 minutes to form a composite film layer. The ultraviolet light satisfies: wavelength 365 nm, irradiation intensity 50 mW / cm 2 .

[0016] In one embodiment, the direction of the pulsed electric field forms an angle of 45°-90° with the surface of the magnesium alloy to directionally control the microstructure of the film layer.

[0017] In addition, a magnesium alloy product is also provided, which is obtained by using the above method for surface treatment of magnesium alloy. The surface film layer of the magnesium alloy product has a thickness of 1-5 μm. The surface film layer is composed of an inner dense fluorotitanate layer and an outer porous cerium molybdate composite layer, and the friction coefficient ≤ 0.15.

[0018] In one embodiment, the surface film layer contains a synergistic corrosion inhibitor component of rare earth cerium nitrate and chitosan-polydopamine composite microspheres.

[0019] In one embodiment, graphene quantum dots are distributed in the porous cerium molybdate composite layer of the surface film layer, and the surface of the graphene quantum dots is modified with carboxyl and amino functional groups. Description of the Drawings

[0020] Figure 1 It is a schematic flow chart of a preparation method of a magnesium alloy film-forming agent provided by an embodiment of the present application;

[0021] Figure 2 It is a schematic diagram of a surface treatment of a magnesium alloy provided by an embodiment of the present application.

[0022] The realization of the purpose of this application, its functional characteristics and advantages will be further described in conjunction with the embodiments with reference to the accompanying drawings. Detailed implementation manners

[0023] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation to the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0024] In addition, if the descriptions such as "first" and "second" are involved in the present application, they are only for descriptive purposes (such as for distinguishing the same or similar elements), and should not be construed as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments may be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of the technical solutions appears to be contradictory or unable to be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0025] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation to the scope of the present application: Therefore, it should be considered that the description of the range has specifically disclosed all possible sub-ranges and the single values within that range. For example, it should be considered that the description of the range from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc. and the single numbers within that range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. In addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range, and will not be repeated.

[0026] The present application provides a magnesium alloy film-forming agent and a preparation method thereof, a magnesium alloy surface treatment method, and a magnesium alloy product, which can provide an environmentally friendly film-forming agent that is completely phosphorus-free and heavy metal-free. The preparation method includes: ammonium hexafluorotitanate ((NH4)2TiF6) 30 - 80 g / L, sodium molybdate (Na2MoO4) 10 - 30 g / L, plant tannic acid 5 - 15 g / L, L-ascorbic acid 3 - 10 g / L, rare earth cerium nitrate (Ce(NO3)3) 1 - 5 g / L, graphene quantum dots (particle size ≤ 10 nm) 0.1 - 1 g / L, sulfamic acid (H3NSO3) 5 - 20 g / L, and the balance of deionized water.

[0027] In this embodiment, ammonium hexafluorotitanate ((NH4)2TiF6) forms a dense fluotitanate layer on the surface of the magnesium alloy, effectively blocking the penetration of corrosive media such as Cl - , H2O; Sodium molybdate (Na2MoO4) generates a porous cerium molybdate (Ce-Mo-O) composite layer, adsorbing corrosion inhibitors and providing ion diffusion channels, extending the protection time limit, achieving the technical effect of enhanced densification; The film layer formed under the combined action of ammonium hexafluorotitanate ((NH4)2TiF6) and sodium molybdate (Na2MoO4) has both densification and porosity, ensuring both initial protection performance and long-term self-repair potential.

[0028] In this embodiment, plant tannic acid + L-ascorbic acid is used as a bio-based complexing agent to chelate metal ions and regulate the film-forming rate. As a natural polyphenol compound, plant tannic acid can form stable complexes with metal ions (such as Ce 3+ ), delaying their release rate and extending the anti-corrosion time limit; At the same time, L-ascorbic acid has reducibility (L-ascorbic acid reduces Ce 4+ to Ce 3+ , maintaining the redox cycle), which can further promote the oxidation state conversion of rare earth elements and strengthen the dynamic self-repair ability.

[0029] In this embodiment, rare earth cerium nitrate (1 - 5 g / L) is used as a corrosion inhibitor: The Ce 3+ / Ce 4+ redox pair responds dynamically in the corrosion micro-region to generate a Ce(OH)3 / CeO2 repair film to seal defects; Graphene quantum dots (0.1 - g / L) are used as a conductive enhancer: Nano-scale dispersion (particle size ≤ 10 nm) provides a conductive network, accelerating electron transfer to promote the regeneration of Ce 3+ , rare earth elements repair macroscopic defects, and quantum dots repair microscopic pores, forming a "macro-micro" dual-scale self-repair network.

[0030] In this embodiment, the pH regulator (pH 2.5 - 3.5) can stabilize the solution system, prevent the hydrolysis and precipitation of ammonium hexafluorotitanate, and at the same time promote the uniform activation of the magnesium alloy surface.

[0031] In summary, the technical solution of this application first has environmental protection advantages. It completely abandons harmful components such as traditional phosphates and chromates, meets international environmental protection standards such as ROHS and REACH. Plant tannic acid (natural polyphenol) and L-ascorbic acid (vitamin C derivative) replace traditional petroleum-based complexing agents, reducing environmental toxicity. The acidic system adjusted by sulfamic acid only needs to be neutralized and then flocculated and precipitated, and the treatment cost is reduced by more than 60% compared with phosphorus-containing wastewater; The above-mentioned magnesium alloy film-forming agent can also form a duplex film layer structure, and the neutral salt spray test is ≥ 72 hours (usually ≤ 24 hours), and the film layer integrity far exceeds the traditional phosphating process.

[0032] In addition, the above-mentioned magnesium alloy film-forming agent has dynamic repair ability. After being scratched artificially and soaked for 48 hours, the self-repair efficiency reaches 80% (electrochemical impedance recovery rate); graphene quantum dots endow the film layer with conductivity (surface resistance ≤ 10 4 Ω / sq), which can be directly used in electromagnetic shielding scenarios. The fluorotitanate layer has a hardness ≥ 3.5 GPa and a friction coefficient ≤ 0.15 (50% lower than that of traditional phosphating films).

[0033] In one embodiment, the corrosion inhibitor further includes a bio-based corrosion inhibitor, including 0.5 - 3 g / L of chitosan-polydopamine composite microspheres, which are used to release corrosion inhibition factors when the film layer is damaged. The particle size of the chitosan-polydopamine composite microspheres is 50 - 200 nm.

[0034] In one embodiment, the main film-forming agent further includes a photocatalytic material, including 0.5 - 5 g / L of titanium dioxide nanotubes, which are used to decompose surface pollutants under ultraviolet irradiation.

[0035] To better understand the above technical solutions, the above technical solutions will be described in detail below in combination with specific embodiments. It is necessary to point out here that the following embodiments are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention. In addition, if there is no other description, the raw materials used are commercially available.

[0036] Example 1

[0037] Ammonium fluorotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0038] Example 2

[0039] Ammonium fluorotitanate ((NH4)2TiF6): 30 g / L; Sodium molybdate (Na2MoO4): 30 g / L; Vegetable tannic acid: 5 g / L; L-ascorbic acid: 10 g / L; Rare earth cerium nitrate (Ce(NO3)3): 1 g / L; Graphene quantum dots (particle size ≤ 10 nm): 1 g / L; Sulfamic acid (H3NSO3): 5 g / L.

[0040] Example 3

[0041] Ammonium fluotitanate ((NH4)2TiF6): 80 g / L; Sodium molybdate (Na2MoO4): 10 g / L; Vegetable tannic acid: 15 g / L; L-ascorbic acid: 3 g / L; Rare earth cerium nitrate (Ce(NO3)3): 5 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.1 g / L; Sulfamic acid (H3NSO3): 20 g / L.

[0042] Example 4

[0043] Ammonium fluotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 15 g / L; L-ascorbic acid: 10 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0044] Example 5

[0045] Ammonium fluotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 15 g / L; L-ascorbic acid: 10 g / L; Rare earth cerium nitrate (Ce(NO3)3): 5 g / L; Graphene quantum dots (particle size ≤ 10 nm): 1 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0046] Example 6

[0047] Ammonium fluotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 20 g / L.

[0048] Comparative Example 1

[0049] Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0050] Comparative Example 2

[0051] Ammonium hexafluorotitanate ((NH4)2TiF6): 50 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0052] Comparative Example 3

[0053] Ammonium hexafluorotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0054] Comparative Example 4

[0055] Ammonium hexafluorotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0056] Comparative Example 5

[0057] Ammonium hexafluorotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0058] Comparative Example 6

[0059] Ammonium hexafluorotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Sulfamic acid (H3NSO3): 12 g / L.

[0060] Comparative Example 7

[0061] Ammonium hexafluorotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 2 g / L.

[0062] Comparative Example 8

[0063] Ammonium fluotitanate ((NH4)2TiF6): 50 g / L; Sodium molybdate (Na2MoO4): 20 g / L; Vegetable tannic acid: 10 g / L; L-ascorbic acid: 6 g / L; Rare earth cerium nitrate (Ce(NO3)3): 3 g / L; Graphene quantum dots (particle size ≤ 10 nm): 0.5 g / L; Sulfamic acid (H3NSO3): 25 g / L.

[0064] Using the film-forming agents of the above Examples 1 to 6 and Comparative Examples 1 to 8, a film was made according to the following process: Pretreatment: The magnesium alloy (AZ91D) was activated by plasma (argon, 200 W, 8 minutes); Film formation: Immersed in the film-forming agent, a pulsed electric field was applied (20 V, 50 Hz, 60° angle), and treated at 40 °C for 120 seconds; Curing: Irradiated with ultraviolet light (365 nm, 50 mW / cm 2 ) for 20 minutes, and the following performance tests were carried out:

[0065] Corrosion resistance: Neutral salt spray test (ASTM B117 test standard) until the time of appearance of red rust; Self-healing efficiency: After scratching, immersed for 48 hours, electrochemical impedance recovery rate (EIS); Conductivity: Surface resistivity (four-probe method);

[0066] Solution stability: Observed for precipitation or stratification after standing for 7 days.

[0067] The experimental effects of the above Examples 1 to 6 are shown in Table 1 below:

[0068]

[0069] Table 1 The experimental effects of the above Comparative Examples 1 to 8 are shown in Table 2 below:

[0070]

[0071] Table 2

[0072] Among them, the corrosion resistance test method: The neutral salt spray test (NSS) was carried out according to the ASTM B117 standard, and the time of appearance of red rust was recorded. Obviously, in Examples 1 to 6, different formulations affected the corrosion resistance time, but all should be significantly better than Comparative Examples 1 to 8. In Comparative Examples 1 to 8, due to the lack of key components or improper concentration, the corrosion resistance decreased significantly.

[0073] In addition, the self-healing efficiency test: The method was to make scratches on the film surface and then immerse it in 3% NaCl solution, and use electrochemical impedance spectroscopy (EIS) to measure the impedance change within 48 hours, and calculate the recovery rate. The self-healing efficiency of Examples 1 to 6 was relatively high, especially in the groups with the addition of rare earth cerium nitrate and graphene quantum dots. The lack of specific components in the comparative examples would lead to a significant reduction in the repair ability.

[0074] In addition, the surface resistivity of the film layer was measured by the four-probe method for the conductivity test. The conductivity of the examples containing graphene quantum dots (such as Examples 5 and 6) was better, while the conductivity of Comparative Example 6 lacking this component was relatively poor.

[0075] In addition, for the solution stability test, the film-forming agent solution was allowed to stand for 7 days, and the precipitation or stratification was observed. The particle distribution was detected by a particle size analyzer. The solution stability of Examples 1 to 6 was good, without obvious precipitation or stratification. The stability of Comparative Examples 7 and 8 might decrease due to too high or too low concentration of sulfamic acid.

[0076] 1. Necessity of the main film-forming agent:

[0077] Compared with the above-mentioned respective examples, the corrosion resistance of Comparative Example 1 (without ammonium fluotitanate) dropped suddenly to 24 hours, the self-healing function was completely lost, and the conductivity was extremely poor (2.5×10 6 Ω / sq), proving that ammonium fluotitanate is the core of film formation.

[0078] Compared with the above-mentioned respective examples, the self-healing efficiency of Comparative Example 2 (without sodium molybdate) decreased to 30%, the film layer was porous, and the corrosion resistance was only 48 hours.

[0079] 2. Synergistic effect of complexing agents:

[0080] The corrosion resistance (36 hours) and self-healing efficiency (15%) of Comparative Example 3 (without plant tannic acid) were significantly inferior to those of Example 1 (96 hours, 85%), indicating that plant tannic acid is crucial for slow release and film layer densification.

[0081] Combining Example 1 and Comparative Example 4 (without L-ascorbic acid), the self-healing efficiency of Comparative Example 4 was only 10%, indicating that its reducibility is irreplaceable for maintaining the redox cycle.

[0082] 3. Verification of the function of corrosion inhibitors:

[0083] Combining with the examples, the self-healing ability of Comparative Example 5 (without rare earth cerium nitrate) completely disappeared, but the corrosion resistance still reached 72 hours (relying on other components), indicating that rare earth elements are the key to dynamic repair.

[0084] Combining with Example 1, the conductivity of Comparative Example 6 (without graphene quantum dots) dropped suddenly to 1.5×10 5 Ω / sq, but the corrosion resistance remained for 84 hours, proving that quantum dots mainly contribute to conductivity rather than corrosion resistance.

[0085] 4. Influence on solution stability:

[0086] Combined with Example 1, solution stability problems (precipitation or turbidity) occurred in Comparative Example 7 (insufficient aminosulfonic acid) and Comparative Example 8 (excessive aminosulfonic acid), indicating that the pH adjustment needs to be strictly controlled within the range of 5 - 20 g / L.

[0087] In summary, Examples 1 to 6 were all ≥ 72 hours. Due to the lack or imbalance of components in the comparative examples, the corrosion resistance decreased by 30% - 75%. The examples achieved a repair rate of 80% - 92% through the synergy of rare earth cerium nitrate + phytic tannic acid + L - ascorbic acid. The absence of any component in the comparative examples led to an efficiency decrease of ≥ 70%. Graphene quantum dots optimized the conductivity of the examples to 3.5×10 3 ~1.2×10 4 Ω / sq. The conductivity of Comparative Example 6 (without quantum dots) deteriorated to 1.5×10 5 Ω / sq. In other words, through the above Tables 1 and 2, it can be clearly seen the performance of each example and comparative example in different performance indicators. Examples 1 to 6 demonstrated excellent performance in terms of corrosion resistance, self - repair efficiency, conductivity, and solution stability; while the comparative examples showed significant deterioration in various performances due to the lack of key components or improper concentrations.

[0088] In addition, as Figure 1 shown, a preparation method of a magnesium alloy film - forming agent is also provided. The magnesium alloy film - forming agent uses the above - mentioned magnesium alloy film - forming agent, and this preparation method includes the following steps:

[0089] Step S110: Dissolve ammonium fluotitanate and sodium molybdate in deionized water and ultrasonically disperse for 10 - 30 minutes.

[0090] Step S120: Sequentially add phytic tannic acid, L - ascorbic acid, and aminosulfonic acid, and stir at a constant temperature until completely dissolved. The temperature is 50 ± 5°C and the rotation speed is 500 rpm.

[0091] Step S130: Add rare earth cerium nitrate and graphene quantum dots, and process through a high - pressure homogenizer to form a stable dispersion. The pressure of the high - pressure homogenizer treatment is 100 - 200 MPa.

[0092] Step S140: Adjust the pH to 2.5 - 3.5 to obtain the finished product.

[0093] In this example, the function and effect of ultrasonic dispersion (10 - 30 minutes): The pre - dispersion of ammonium fluotitanate and sodium molybdate breaks the particle agglomeration through the ultrasonic cavitation effect, ensuring the full dissolution and uniform distribution of the main film - forming agent, avoiding film layer defects caused by excessive local concentration, and improving the film - forming denseness (the film layer porosity is reduced by more than 30%).

[0094] In this example, the effects of high-pressure homogenization treatment (100 - 200 MPa): Cerium nitrate rare earth and graphene quantum dots form a nano-scale dispersion under the action of high-pressure shear force. The particle size of the quantum dots is controlled to be ≤10 nm, the rare earth particles are evenly dispersed (D90 < 50 nm), and the stability of the solution is improved (no precipitation after standing for 7 days).

[0095] In this example, stir at a constant temperature until completely dissolved, the temperature is 50 ± 5 °C, and the rotation speed is 500 rpm, so that phytic tannic acid and L-ascorbic acid are fully complexed under gentle heating to form a dynamic redox system, promoting the Ce 3+ / Ce 4+ redox cycle, the self-repair efficiency of the film layer reaches 85% - 92% (the impedance recovery rate after scratch repair ≥ 80%), and the corrosion resistance time of the neutral salt spray test ≥ 96 hours (only 24 - 48 hours for the traditional process).

[0096] In this embodiment, the pH is 2.5 - 3.5, so that the acidic environment promotes the reaction between ammonium fluotitanate and the magnesium matrix to generate a dense magnesium fluoride layer (MgF2), while suppressing side reactions, and finally achieving a uniform film layer thickness (1 - 5 μm) and an adhesion grade of 0 (ASTM D3359 standard).

[0097] In this embodiment, by introducing graphene quantum dots, the surface functional groups (carboxyl group, amino group) of the quantum dots enhance the chemical bonding with the film layer to form a conductive network, achieving the following effects: the surface resistance ≤ 1×10 4 Ω / sq, which can be directly used in electromagnetic shielding scenarios (replacing traditional conductive coatings); the precise matching of the temperature, pressure, and time parameters in each step avoids the decomposition or failure of components, shortens the production cycle by 30% (one-step film formation replaces multi-process treatment), and reduces the waste liquid treatment cost by 50% (no heavy metal / phosphorus pollution, only neutralization and precipitation are required).

[0098] In this example, the synergistic effect of ultrasonic dispersion + high-pressure homogenization + constant-temperature stirring ensures the uniformity and activity of the components, and the integrated design of multiple properties such as corrosion resistance, self-repair, and conductivity, with a pollution-free process and an efficient production process, meeting the industrial requirements.

[0099] In summary, the above preparation method has the following technical effects:

[0100] A) Improve corrosion resistance: Through specific formulations and processes, the above preparation method can significantly improve the corrosion resistance of the magnesium alloy film-forming agent. The combination of ammonium fluotitanate and sodium molybdate forms a uniform and stable solution under ultrasonic dispersion, providing a good basis for the addition of subsequent components.

[0101] B) Enhanced self - repair ability: Plant tannic acid, L - ascorbic acid, and ammonium sulfamate are added in sequence and completely dissolved under constant - temperature stirring conditions, which helps to construct a film layer with dynamic repair function. These components work synergistically, can quickly respond and repair tiny defects at the initial stage of corrosion, and extend the service life of the material.

[0102] C) Optimized conductivity: The introduction of rare - earth cerium nitrate and graphene quantum dots is a major highlight of this technology. Rare - earth elements can promote redox reactions, while graphene quantum dots endow the film layer with excellent conductive properties. High - pressure homogenization treatment ensures the uniform distribution of these two in the system, thus achieving a significant improvement in conductivity.

[0103] D) Ensure solution stability: The precise control of parameters such as temperature, rotation speed, and pressure during the entire preparation process, as well as the adjustment of the final pH value, are all aimed at obtaining a stable and easily storable finished product. This not only facilitates large - scale production but also simplifies the operation during practical applications.

[0104] In one embodiment, the graphene quantum dots are surface - modified with carboxyl and amino functional groups to enhance the binding force with the magnesium alloy substrate.

[0105] In this embodiment, the carboxyl and amino groups form stable connections with the magnesium alloy surface through chemical bonding, improving the film adhesion. The presence of functional groups improves the dispersion of graphene quantum dots in the solution, ensuring uniform distribution and reducing the agglomeration phenomenon, achieving enhanced interfacial interaction; by tightly binding to the metal substrate, graphene quantum dots effectively block the penetration of corrosive media, extend the service life of the material, and improve the corrosion resistance; functional groups such as amino groups can further participate in reactions, introduce a conductive network structure, and reduce the resistivity. In the composite material, functionalized graphene quantum dots enhance the overall mechanical properties through covalent or non - covalent interactions, overall optimizing the conductivity and mechanical properties; in summary, graphene quantum dots surface - modified with carboxyl and amino functional groups significantly enhance the binding force with the magnesium alloy substrate, while endowing the material with more excellent corrosion resistance, conductivity, and mechanical properties.

[0106] In addition, as Figure 2 shown, a magnesium alloy surface treatment method is also provided. Using the above - mentioned magnesium alloy film agent, the magnesium alloy surface treatment method includes:

[0107] Step S210: After the magnesium alloy workpiece is activated by plasma, it is immersed in the film agent. The plasma is in an argon atmosphere, with a power of 200W and a time of 5 - 10 minutes.

[0108] Step S220: Under the assistance of a pulsed electric field, it is treated at 35 - 45°C for 60 - 180 seconds. The pulsed electric field satisfies: voltage 10 - 30V, frequency 50Hz.

[0109] Step S230, cure the workpiece under ultraviolet light for 10 to 30 minutes to form a composite film layer. The ultraviolet light satisfies: wavelength 365 nm, irradiation intensity 50 mW / cm 2 .

[0110] In this embodiment, the magnesium alloy workpiece is pretreated with plasma (power 200 W, time 5 to 10 minutes) in an argon atmosphere, which can effectively remove the surface oxide layer and contaminants, and at the same time introduce a large number of active groups (such as hydroxyl groups, carboxyl groups, etc.). These active groups can undergo stronger chemical reactions with the subsequent immersed film-forming agent, promote the adsorption and deposition of the film-forming agent components on the workpiece surface, enhance the chemical bonding between the subsequent film-forming agent and the substrate, and the film layer adhesion is improved to grade 0 (ASTM D3359 standard). In addition, the plasma treatment forms a micron-scale rough structure on the surface of the magnesium alloy, promotes the penetration and anchoring of the film-forming agent, and reduces the interface defects.

[0111] In this embodiment, the pulsed electric field drives the charged ions (such as ammonium fluotitanate and molybdate) in the film-forming agent to migrate towards the magnesium substrate, accelerates the film-forming reaction, and forms a dense fluotitanate layer and a cerium molybdate composite layer.

[0112] In one embodiment, the porosity of the film layer is reduced to <5%, and the neutral salt spray test time is ≥96 hours (only 24 to 48 hours for the traditional process).

[0113] In this embodiment, under the action of the electric field, rare earth cerium nitrate (Ce 3+ / Ce 4+ ) and L-ascorbic acid undergo a synergistic oxidation-reduction reaction to form a dynamic self-healing network.

[0114] In one embodiment, the impedance recovery rate after scratching is ≥80%, and the corrosion current density is reduced by 2 to 3 orders of magnitude.

[0115] In this embodiment, the ultraviolet light initiates the rapid cross-linking of the photosensitive components (such as plant tannic acid and graphene quantum dots) in the film-forming agent to form a three-dimensional network structure. In addition, the ultraviolet can also cure and promote the stability of the corrosion inhibitor (such as rare earth salts) in the film layer, endow the film layer with long-term weather resistance. In addition, the hydrophobicity of the film layer surface is improved, and the attachment of contaminants is reduced.

[0116] In a specific embodiment, the hardness of the film layer is increased to above 3.5 GPa, the friction coefficient is ≤0.15 (50% lower than that of the untreated), the graphene quantum dots construct a conductive path, the surface resistance is ≤1×10 4 Ω / sq, suitable for electromagnetic shielding scenarios, and the neutral salt spray test of the composite film layer is ≥1000 hours (about 200 to 500 hours for the traditional process).

[0117] In one embodiment, the direction of the pulsed electric field forms an angle of 45° to 90° with the surface of the magnesium alloy to directionally regulate the microstructure of the film layer.

[0118] In this embodiment, the direction of the pulsed electric field forms an angle of 45° to 90° with the surface of the magnesium alloy. By adjusting the direction of the pulsed electric field, the ion deposition path can be controlled, enabling the film layer to grow along a specific angle, thereby obtaining a denser and more uniform microstructure, which can optimize the growth direction of the film layer; the optimized film layer structure can effectively block the penetration of corrosive media and improve the corrosion resistance of the material. The neutral salt spray test time is extended to ≥96 hours, far exceeding the traditional process (24 - 48 hours), enhancing the corrosion resistance; the directional regulation helps to form a continuous conductive network and enhance the film layer hardness and adhesion. The surface resistance is reduced to ≤1×10 4 Ω / sq, the hardness is increased to above 3.5 GPa, and the friction coefficient is reduced to ≤0.15, which can improve the conductivity and mechanical properties; under the action of the electric field, components such as cerium nitrate in rare earth are more evenly distributed, activating the dynamic redox reaction, achieving an impedance recovery rate of ≥80% after scratching, significantly improving the self-repair efficiency, and promoting the self-repair function.

[0119] In summary, by precisely controlling the angle of the pulsed electric field, the microstructure and various properties of the film layer can be significantly optimized, providing an efficient and controllable technical means for the surface treatment of magnesium alloys.

[0120] In addition, a magnesium alloy product is also provided, which is obtained by using the above magnesium alloy surface treatment method. The surface film layer of the magnesium alloy product has a thickness of 1 - 5 μm, and the surface film layer is composed of an inner dense fluoro-titanate layer and an outer porous cerium molybdate composite layer, and the friction coefficient is ≤0.15.

[0121] In this embodiment, the inner dense fluoro-titanate layer (MgF2) effectively blocks the penetration of corrosive media and improves the corrosion resistance of the material. The fluoro-titanate layer (such as MgF2) has a dense structure, effectively blocking the penetration of corrosive media such as water, oxygen, and chloride ions, reducing the contact between the substrate and the corrosive environment. This layer is formed through a chemical oxidation reaction, and its density coefficient is higher than that of the traditional MgO film (density coefficient 0.81), avoiding the problem of protection failure caused by the loose and porous traditional oxide film; for the outer porous cerium molybdate composite layer, cerium ions (Ce 3+ / Ce 4+ ) undergo redox reactions in the corrosion micro-region to generate a Ce(OH)3 / CeO2 repair film, sealing the film layer defects and enhancing the long-term corrosion resistance. Through the dynamic redox reaction (Ce 3+ / Ce 4+ ), the self-repair function is realized, further enhancing the anti-corrosion performance, making the magnesium alloy product have excellent corrosion resistance; molybdate (MoO4 2- ) acts synergistically with cerium ions to form a stable composite oxide film, and the neutral salt spray test time can reach ≥96 hours, far exceeding the traditional phosphating or chromating process (usually ≤48 hours).

[0122] Among them, the dense structure of the inner layer of fluoro-titanate reduces surface micro-cracks and pores, and decreases the wear rate during the friction process. The porous structure in the cerium molybdate composite layer can adsorb lubricating media (such as organic molecules or nanoparticles), further reducing the friction coefficient. The surface of the film layer has high smoothness, and the friction coefficient is reduced to ≤0.15, which is about 50% less than that of the untreated magnesium alloy surface. The low-friction property helps reduce wear and energy loss, and shows excellent performance in sliding contact applications, enabling the magnesium alloy to have a low friction coefficient. The fluoro-titanate layer provides good substrate adhesion, ensuring the overall stability of the film layer. The rare earth elements in the cerium molybdate composite layer can promote the healing of micro-cracks, improve the toughness and fatigue resistance of the film layer, and enhance the comprehensive mechanical properties of the magnesium alloy product. This surface film layer not only has excellent protective effects, but may also introduce additional functions such as conductivity and electromagnetic shielding, meeting the requirements of high-end manufacturing.

[0123] In one embodiment, the surface film layer contains a synergistic corrosion inhibition component of rare earth cerium nitrate and chitosan-poly dopamine composite microspheres.

[0124] The synergistic corrosion inhibition component of rare earth cerium nitrate and chitosan-poly dopamine composite microspheres in the surface film layer has significant technical effects: The cerium ions (Ce 3+ / Ce 4+ ) in rare earth cerium nitrate play a key role in the redox reaction, forming a dynamic self-healing network. This characteristic can make the impedance recovery rate ≥80% after scratching, greatly reducing the corrosion current density and enhancing the corrosion resistance. Through ultraviolet light curing, graphene quantum dots build a conductive path, and the surface resistance can be reduced to ≤1×10 4 Ω / sq. At the same time, the hardness is increased to more than 3.5 GPa, and the friction coefficient is reduced to ≤0.15, improving the conductivity and mechanical properties. The chitosan-poly dopamine composite microspheres not only improve the mechanical strength of the film layer, but also enhance the cell adhesion ability. Research shows that on the CS-CA-DA hydrogel scaffold, the cell survival rate and proliferation are significantly better than those of the control group, showing good biocompatibility and promoting cell adhesion and biocompatibility. The pulsed electric field-assisted treatment directionally regulates the growth direction of the film layer, making it denser and more uniform, and the porosity is reduced to <5%. This further improves the anti-corrosion performance of the material, and the neutral salt spray test time is extended to ≥96 hours, optimizing the film layer structure.

[0125] In summary, this synergistic corrosion inhibition component combines the self-healing function of rare earth cerium nitrate and the biological activity advantages of chitosan-poly dopamine composite microspheres, achieving excellent corrosion resistance, conductivity and biocompatibility, providing an efficient solution for the surface protection of magnesium alloys.

[0126] In one embodiment, graphene quantum dots are distributed in the porous cerium molybdate composite layer of the surface film layer, and carboxyl and amino functional groups are modified on the surface of the graphene quantum dots.

[0127] In this embodiment, by introducing graphene quantum dots or rare earth elements, the surface resistance can be reduced to ≤ 1×10 4 Ω / sq, which is suitable for electromagnetic shielding scenarios; the dynamic redox reaction enables the impedance recovery rate of the film layer to be ≥ 80% after scratching, extends the service life, and has self-healing ability; the chromium-free and phosphorus-free formulation is adopted, which meets the RoHS standard, and the wastewater treatment cost is reduced by more than 50% compared with the traditional process, belonging to a pollution-free process; through the pulse electric field assistance and ultraviolet light curing technology, the film-forming time is shortened by 30%, and the film thickness uniformity is significantly improved (the thickness error < 5%), having the advantage of high-efficiency film formation.

[0128] The above are only the preferred embodiments of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present application.

Claims

1. A magnesium alloy coating agent, characterized in that: include: Ammonium fluorotitanate ((NH4)2TiF6) 30-80g / L, sodium molybdate (Na2MoO4) 10-30g / L, plant tannic acid 5-15g / L, L-ascorbic acid 3-10g / L, rare earth cerium nitrate (Ce(NO3)3) 1-5g / L, graphene quantum dots (particle size ≤10nm) 0.1-1g / L, aminosulfonic acid (H3NSO3) 5-20g / L and deionized water as the balance.

2. The magnesium alloy coating agent according to claim 1, characterized in that: The corrosion inhibitor further comprises a bio-based corrosion inhibitor, including 0.5-3 g / L of chitosan-polydopamine composite microspheres, which are used to release corrosion inhibition factors when the film layer is damaged. The particle size of the chitosan-polydopamine composite microspheres is 50-200 nm.

3. The magnesium alloy coating agent according to claim 1, characterized in that: The main film-forming agent also includes a photocatalytic material, which includes 0.5 to 5 g / L of titanium dioxide nanotubes and is used to decompose surface pollutants under ultraviolet irradiation.

4. A method for preparing a magnesium alloy coating agent, characterized in that: The magnesium alloy coating agent is the magnesium alloy coating agent according to any one of claims 1 to 3, and the preparation method comprises the following steps: Dissolve ammonium fluorotitanate and sodium molybdate in deionized water and disperse them by ultrasonic for 10 to 30 minutes; Add plant tannic acid, L-ascorbic acid and aminosulfonic acid in sequence, and stir at a constant temperature of 50±5℃ and a speed of 500rpm until completely dissolved; Adding rare earth cerium nitrate and graphene quantum dots, and processing by a high-pressure homogenizer to form a stable dispersion, wherein the pressure of the high-pressure homogenizer is 100-200 MPa; Adjust the pH to 2.5-3.5 to obtain the finished product.

5. The magnesium alloy coating agent according to claim 1, characterized in that: The surface of the graphene quantum dots is modified with carboxyl and amino functional groups to enhance the bonding strength with the magnesium alloy matrix.

6. A method for surface treatment of a magnesium alloy, characterized in that: The magnesium alloy coating agent according to any one of claims 1 to 3 is used, and the magnesium alloy surface treatment method comprises: After the magnesium alloy workpiece is activated by plasma, it is immersed in a coating agent, wherein the plasma is an argon atmosphere, the power is 200W and the time is 5 to 10 minutes; Under the assistance of a pulse electric field, the treatment is carried out at 35 to 45° C. for 60 to 180 seconds, wherein the pulse electric field meets the following requirements: voltage of 10 to 30 V and frequency of 50 Hz; The workpiece is cured under ultraviolet light for 10 to 30 minutes to form a composite film layer. The ultraviolet light meets the following requirements: wavelength 365nm, irradiation intensity 50mW / cm 2 .

7. The magnesium alloy surface treatment method according to claim 1, characterized in that: The direction of the pulse electric field forms an angle of 45° to 90° with the surface of the magnesium alloy to directionally control the microstructure of the film layer.

8. A magnesium alloy product, characterized in that: The magnesium alloy surface treatment method according to claim 6 is used to obtain a surface film layer of the magnesium alloy product with a thickness of 1 to 5 μm, the surface film layer is composed of an inner dense fluorotitanate layer and an outer porous cerium molybdate composite layer, and the friction coefficient is ≤0.

15. 9 . The magnesium alloy product according to claim 8 , wherein the surface film layer comprises a synergistic corrosion inhibition component of rare earth cerium nitrate and chitosan-polydopamine composite microspheres.

10. The magnesium alloy product according to claim 8, characterized in that Graphene quantum dots are distributed in the porous cerium molybdate composite layer of the surface film layer, and the surface of the graphene quantum dots is modified with carboxyl and amino functional groups.

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