A room-temperature bleaching agent for magnesium alloys and its preparation method

Abstract

This application relates to chemical bleaching technology, disclosing a room-temperature bleaching agent for magnesium alloys and its preparation method, as well as a surface treatment method for magnesium alloys based on the room-temperature bleaching agent. Utilizing the oxidizing properties of hydrogen peroxide at a mild concentration, and introducing a composite complex-buffer system of sodium citrate and sodium dihydrogen phosphate, along with a synergistic corrosion inhibition network of sodium silicate and thiourea, supplemented by the interface modification effect of nano-silica, this achieves uniform removal and modification of uneven oxide films or corrosion products on the surface of magnesium alloys at room temperature. This room-temperature operation avoids the energy consumption and workpiece deformation problems of high-temperature processes, and overcomes the drawbacks of traditional strong oxidants or high-temperature bleaching that easily lead to over-corrosion of the magnesium matrix. The resulting surface is cleaner and more uniform, which is beneficial for subsequent coating or bonding, providing a safe, energy-saving, and environmentally friendly pretreatment solution for magnesium alloys.

Description

Technical Field

[0001] This application relates to the field of chemical reagent bleaching technology, and in particular to a magnesium alloy room temperature bleaching agent, a method for preparing the magnesium alloy room temperature bleaching agent, and a magnesium alloy surface treatment method based on the magnesium alloy room temperature bleaching agent. Background Technology

[0002] Magnesium alloys are widely used in aerospace, automotive manufacturing, electronic communications, and medical devices due to their low density, high specific strength, good electromagnetic shielding properties, and recyclability. However, magnesium alloys are chemically reactive and easily react with moisture and oxygen in the environment during processing or use, resulting in the formation of uneven oxide films or corrosion products on the surface, affecting their appearance and subsequent treatments (such as painting and bonding).

[0003] Traditional magnesium alloy surface treatments often employ methods such as chromate passivation, acid etching, or high-temperature chemical oxidation, but these processes have significant limitations: (1) Chromate process: Although it can form a dense passivation film, hexavalent chromium is highly toxic and poses a great threat to the environment and human health; (2) Acid etching: strong acids such as nitric acid and sulfuric acid are commonly used, which can easily lead to over-corrosion of the magnesium matrix, creating a risk of hydrogen embrittlement, and the acid mist pollutes the working environment; (3) High temperature treatment: high energy consumption, complex process, and easy to cause deformation of thin-walled or precision parts.

[0004] Furthermore, conventional bleaching or deoxidation treatments often rely on strong oxidants (such as potassium permanganate) or high temperatures (>50℃), which are not only inefficient but may also exacerbate magnesium alloy corrosion. Therefore, developing a safe, energy-saving, environmentally friendly bleaching agent specifically for magnesium alloys that can be operated at room temperature is of significant industrial importance.

[0005] The above content is only used to help understand the technical solution of this application and does not represent an admission that the above content is prior art. Summary of the Invention

[0006] The main objective of this application is to provide a magnesium alloy room temperature bleaching agent, a method for preparing the magnesium alloy room temperature bleaching agent, and a magnesium alloy surface treatment method based on the magnesium alloy room temperature bleaching agent, aiming to provide a safe, energy-saving, environmentally friendly magnesium alloy-specific bleaching agent that can be operated at room temperature.

[0007] To achieve the above objectives, this application provides a magnesium alloy room temperature bleaching agent, comprising the following components per liter of solution: 50-80 mL of hydrogen peroxide; 20-40g of sodium citrate; 10-20g of sodium dihydrogen phosphate; 5-15g of sodium silicate; 0.5~2g of thiourea; 30-50 mL of nano-silica sol; And the remaining deionized water.

[0008] Optionally, the component may further include 0.1 to 0.5 g of rare earth cerium salt.

[0009] Optionally, the rare earth cerium salt is at least one of cerium nitrate, cerium ammonium nitrate, and cerium chloride.

[0010] Optionally, the component may also include 1 to 3 mL of phytic acid.

[0011] Optionally, the nano-silica sol has a particle size of 10-50 nm and a solid content of 8-12 wt%.

[0012] To achieve the above objectives, this application also provides a method for preparing a magnesium alloy room temperature bleaching agent, used to prepare the magnesium alloy room temperature bleaching agent as described above; the method for preparing the magnesium alloy room temperature bleaching agent includes the following steps: Step S1: In partially deionized water, add sodium citrate, sodium silicate, and sodium dihydrogen phosphate in sequence and stir until completely dissolved; then, under stirring, gradually add hydrogen peroxide; finally, add thiourea and continue stirring until the mixture is homogeneous to obtain the base solution. Step S2: After premixing the nano-silica sol with a portion of deionized water, add it dropwise to the base solution under stirring and mix thoroughly; Step S3: Use deionized water to bring the volume of the mixture obtained in step S2 to the target volume, stir evenly, seal and let it stand to mature, and obtain a magnesium alloy room temperature bleaching agent.

[0013] Optionally, after step S1, the method further includes: If the formulation contains rare earth cerium salts and / or phytic acid, then in step S2, the rare earth cerium salts and / or phytic acid are added to the base liquid and stirred until uniformly dissolved.

[0014] Optionally, in step S1, when adding hydrogen peroxide, the system temperature is controlled to not exceed 30°C.

[0015] Optionally, in step S3, the curing process is carried out under light-protected conditions, with a curing time of 12 to 48 hours and a temperature controlled at 20 to 25°C.

[0016] To achieve the above objectives, this application also provides a method for surface treatment of magnesium alloys based on a room-temperature magnesium alloy bleaching agent, wherein the room-temperature magnesium alloy bleaching agent is the same as described in any one of claims 1-5; the method for surface treatment of magnesium alloys includes the following steps: Pretreatment of magnesium alloy workpieces includes degreasing, oil removal and cleaning; Immerse the pretreated magnesium alloy workpiece in magnesium alloy room temperature bleaching agent for 3-10 minutes at room temperature. After bleaching, the workpiece is removed, cleaned, and dried to obtain a magnesium alloy workpiece with a uniform bright white oxide film on the surface.

[0017] The magnesium alloy room temperature bleaching agent, the preparation method of the magnesium alloy room temperature bleaching agent, and the magnesium alloy surface treatment method based on the magnesium alloy room temperature bleaching agent provided in this application utilize the oxidizing properties of hydrogen peroxide at a mild concentration, and introduce a composite complex-buffer system of sodium citrate and sodium dihydrogen phosphate, as well as a synergistic corrosion inhibition network of sodium silicate and thiourea, supplemented by the interface modification effect of nano silica. This achieves uniform removal and modification of uneven oxide film or corrosion products on the surface of magnesium alloy at room temperature.

[0018] This solution completely eliminates the use of highly toxic hexavalent chromium and strongly corrosive concentrated acids, thus removing significant environmental and health risks at the source. Room temperature operation avoids the energy consumption and workpiece deformation problems associated with high-temperature processes, and also overcomes the drawbacks of traditional strong oxidants or high-temperature bleaching that can easily lead to over-corrosion of the magnesium matrix. The resulting surface is cleaner and more uniform, which is beneficial for subsequent coating or bonding, providing a safe, energy-saving, and environmentally friendly pretreatment solution for magnesium alloys. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation steps of a room-temperature bleaching agent for magnesium alloys in one embodiment of this application.

[0020] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein 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 intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] Furthermore, descriptions using terms such as "first" and "second" in this application are for descriptive purposes only (e.g., to distinguish identical or similar features) and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, technical solutions from different embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If a combination of technical solutions is contradictory or impossible to implement, such a combination should be considered nonexistent and not within the scope of protection claimed in this application.

[0023] In one embodiment, a magnesium alloy room temperature bleaching agent is provided, comprising the following components per liter of solution: 50-80 mL of hydrogen peroxide; 20-40g of sodium citrate; 10-20g of sodium dihydrogen phosphate; 5-15g of sodium silicate; 0.5~2g of thiourea; 30-50 mL of nano-silica sol; And the remaining deionized water.

[0024] In this embodiment, the components of the magnesium alloy room temperature bleaching agent, per liter of solution, include: The oxidizing component is a 30% (w / w) aqueous solution of hydrogen peroxide, added in an amount of 50-80 mL. This component acts as the main bleaching agent, providing a controllable oxidizing environment at room temperature to achieve modification of the oxide film on the magnesium alloy surface or decomposition of the coloring components.

[0025] The complexing stabilizing components include sodium citrate and sodium dihydrogen phosphate. Sodium citrate, added at a rate of 20-40g, primarily functions to complex metal ions (such as magnesium and iron ions) in the solution, inhibiting the formation of harmful precipitates and acting as a buffer to help maintain the relative stability of the working solution's pH. Sodium dihydrogen phosphate, added at a rate of 10-20g, provides phosphate ions, which can react with the magnesium alloy surface to form a protective phosphate conversion film, and also act as a pH buffer and dispersant, synergistically stabilizing the system.

[0026] The corrosion inhibitor and surface conditioning components include sodium silicate and thiourea. Sodium silicate, added at a rate of 5-15g, acts as an inorganic corrosion inhibitor, preferentially adsorbing or reacting on the magnesium alloy surface to form a silicate protective layer. This effectively inhibits excessive corrosion of the substrate by hydrogen peroxide and improves the uniformity of the treated surface. Thiourea, added at a rate of 0.5-2g, acts as an organic corrosion inhibitor and metal ion reducing agent, further inhibiting localized corrosion and reducing or complexing certain high-valence metal ions, preventing them from adversely affecting the bleaching process.

[0027] The nanofunctional component is nano-silica sol (calculated as SiO2, with a solid content typically of 10-30%), added in amounts of 30-50 mL. The nano-silica particles in this component can serve as physical adsorption and nucleation sites, uniformly distributed on the treated surface, which helps to refine the structure of the treated film, improve its density and uniformity, and impart specific functionalities to the surface.

[0028] The solvent and balance component is deionized water. The amount used is sufficient to replenish all the aforementioned components (and may also include rare earth cerium salts and / or phytic acid) to a total volume of 1 liter. Deionized water is used to dissolve the solid and liquid components, forming a homogeneous and stable solution system. Its high purity prevents impurity ions from interfering with the bleaching chemical reaction process.

[0029] The synergistic effect of the above components is that, under normal temperature (15~30°C) conditions, the bleaching agent can effectively treat magnesium alloy workpieces. Through a comprehensive mechanism of oxidation, complexation, corrosion inhibition and nanoparticle modification, it can achieve surface decolorization, whitening or pre-passivation, while controlling the corrosion of the substrate at a low level, providing a clean, uniform and moderately active surface state for subsequent surface treatment processes.

[0030] In one embodiment, the oxidizing properties of hydrogen peroxide at a mild concentration are utilized, and a composite complex-buffer system of sodium citrate and sodium dihydrogen phosphate is innovatively introduced, along with a synergistic corrosion inhibition network of sodium silicate and thiourea, supplemented by the interface modification effect of nano-silica. This achieves uniform removal and modification of uneven oxide film or corrosion products on the surface of magnesium alloy at room temperature (15-30°C).

[0031] This solution completely eliminates the use of highly toxic hexavalent chromium and strongly corrosive concentrated acids, thus removing significant environmental and health risks at the source. Room temperature operation avoids the energy consumption and workpiece deformation problems associated with high-temperature processes, and also overcomes the drawbacks of traditional strong oxidants or high-temperature bleaching that can easily lead to over-corrosion of the magnesium matrix. The resulting surface is cleaner and more uniform, which is beneficial for subsequent coating or bonding, providing a safe, energy-saving, and environmentally friendly pretreatment solution for magnesium alloys.

[0032] In one embodiment, based on the above embodiment, the component further includes 0.1~0.5g of rare earth cerium salt.

[0033] In this embodiment, the bleaching agent further comprises a rare earth cerium salt, added at a rate of 0.1-0.5 g per liter of solution. This rare earth cerium salt is introduced as a synergist, and its cerium ions (Ce...) 3+ / Ce 4+ It can undergo redox reactions on magnesium alloy surfaces, promoting the formation of denser and more stable composite oxide / conversion films, significantly enhancing the corrosion resistance of the treated surface, and providing a better adhesion substrate for subsequent organic coatings.

[0034] Optionally, the rare earth cerium salt is at least one of cerium nitrate, cerium ammonium nitrate, and cerium chloride. The selection of these specific cerium salts is based on their good solubility and chemical stability in the aqueous solution system, as well as their ability to effectively release active cerium ions to participate in surface reactions during the treatment process.

[0035] In one embodiment, based on the above embodiment, the component further includes 1-3 mL of phytic acid.

[0036] In this embodiment, the bleaching agent also includes phytic acid, with an addition amount of 1-3 mL per liter of solution (based on a commercially available 50% (w / w) phytic acid aqueous solution). Phytic acid, as a multidentate chelating agent and corrosion inhibitor, has multiple phosphate groups in its molecule that strongly chelate metal ions in the solution, further stabilizing the working solution and inhibiting impurity precipitation. Simultaneously, it can form an adsorption layer or participate in film formation on the magnesium alloy surface, synergistically improving surface treatment quality and corrosion resistance.

[0037] In one embodiment, based on the above embodiment, the particle size of the nano-silica sol is 10~50nm and the solid content is 8~12wt% (weight percentage).

[0038] In this embodiment, the nanoparticles within the specific particle size range help to achieve stable dispersion in the solution and uniform adsorption on the treated surface, while the solid content range ensures the effective addition amount of the nanocomponents, which can significantly improve the film density and functionality, and avoid the decrease in solution stability or the increase in surface roughness due to particle agglomeration or excessive concentration.

[0039] In addition, a method for preparing a room-temperature bleaching agent for magnesium alloys is provided, for use in preparing the room-temperature bleaching agent for magnesium alloys described in the above embodiments; refer to Figure 1 The preparation methods of magnesium alloy room temperature bleaching agents include: Step S1: In partially deionized water, add sodium citrate, sodium silicate, and sodium dihydrogen phosphate in sequence and stir until completely dissolved; then, under stirring, gradually add hydrogen peroxide; finally, add thiourea and continue stirring until the mixture is homogeneous to obtain the base solution. Step S2: After premixing the nano-silica sol with a portion of deionized water, add it dropwise to the base solution under stirring and mix thoroughly; Step S3: Use deionized water to bring the volume of the mixture obtained in step S2 to the target volume, stir evenly, seal and let it stand to mature, and obtain a magnesium alloy room temperature bleaching agent.

[0040] Step S1 is used to prepare the base solution: In a preparation container, first measure 30% to 60% of the total amount of deionized water according to the formula. Under room temperature and continuous stirring, add the formula amounts of sodium citrate, sodium silicate, and sodium dihydrogen phosphate to the deionized water in sequence, maintaining stirring until all solid components are completely dissolved to form a clear or homogeneous solution. Then, while maintaining stirring, slowly and uniformly add the formula amount of hydrogen peroxide aqueous solution. Finally, add the formula amount of thiourea, and continue stirring for 5 to 15 minutes to ensure that all components are fully mixed and homogeneous, thus obtaining the base solution.

[0041] The designed order of component addition effectively buffers the drastic local pH changes that may occur upon the immediate addition of hydrogen peroxide, significantly reducing the ineffective decomposition rate of hydrogen peroxide under suboptimal pH conditions and improving its storage and usage stability. The final addition of thiourea prevents premature oxidation and loss due to contact with hydrogen peroxide.

[0042] Step S2 is used for functional component compounding: First, the formulated amount of nano-silica sol is pre-diluted and mixed with 10%~20% of deionized water in an auxiliary container to obtain diluted nano-sol. Then, under the condition of continuous stirring of the base liquid, the diluted nano-sol is slowly added to the base liquid by dropping or flowing in a thin stream. After the addition is completed, stirring is continued for 10~20 minutes to fully disperse and mix it evenly.

[0043] This stepwise dilution and controlled addition method can minimize the risk of nanoparticles agglomerating or settling due to sudden changes in concentration or environment, ensuring that they are uniformly and stably dispersed in the final working solution, thereby exerting their expected surface modification function.

[0044] Step S3 is used for volume adjustment and aging: the mixture obtained in step S2 is transferred to the final preparation container, and the remaining deionized water is added quantitatively to precisely adjust the total volume to the final target volume (per liter), and stirring is continued for 10-20 minutes to ensure the overall homogeneity of the solution. Afterwards, the prepared bleaching agent solution is sealed and allowed to stand and age at room temperature (15-30℃) for 6-24 hours to obtain the finished magnesium alloy room temperature bleaching agent.

[0045] This preparation method can be performed at room temperature, has low energy consumption, and requires simple equipment. The final S3 step allows the components to reach sufficient interaction equilibrium at the molecular / ionic level, which helps to form a more stable colloidal or solution system, thus exhibiting more stable and efficient treatment results during use.

[0046] In one embodiment, based on the above embodiment, after step S1, the method further includes: If the formulation contains rare earth cerium salts and / or phytic acid, then in step S2, the rare earth cerium salts and / or phytic acid are added to the base liquid and stirred until uniformly dissolved.

[0047] In this embodiment, when the bleaching agent formulation contains rare earth cerium salts and / or phytic acid, in step S2, the formulated amount of rare earth cerium salts and / or phytic acid is first added directly to the base solution prepared in step S1, and stirred at room temperature for 5 to 10 minutes until the rare earth cerium salts and / or phytic acid are completely dissolved and uniformly mixed with the base solution. Then, following the original procedure of step S2, the pre-diluted nano-silica sol is added to this mixed base solution containing additives for subsequent dispersion, volume adjustment, and aging operations. This sequence ensures that the rare earth cerium salts and / or phytic acid are fully dissolved and pre-reacted in the base solution first, avoiding aggregation or failure that may result from direct interaction with the nano-sol.

[0048] In one embodiment, based on the above embodiment, in step S1, when hydrogen peroxide is added, the system temperature is controlled to not exceed 30°C.

[0049] In this embodiment, during step S1, when hydrogen peroxide is gradually added, the temperature of the entire reaction system must be controlled to ensure that the temperature does not exceed 30°C by controlling the feeding rate, employing cooling measures, or managing the ambient temperature. This temperature control aims to suppress the accelerated decomposition of hydrogen peroxide that may occur at higher temperatures, thereby ensuring the effective concentration of the oxidant, improving the stability of the working fluid, and reducing the risk of process reproducibility issues caused by temperature fluctuations.

[0050] In one embodiment, based on the above embodiment, the curing process is carried out under light-protected conditions, with a curing time of 12 to 48 hours and a temperature controlled at 20 to 25°C.

[0051] In this embodiment, in step S3, the curing process must be carried out under light-protected conditions, with the curing time controlled between 12 and 48 hours, and the curing ambient temperature controlled between 20 and 25°C. The light-protected conditions aim to prevent photosensitive components such as hydrogen peroxide from decomposing under light. This curing temperature and time range provides sufficient and stable interaction conditions for each component (especially nano-silica particles, complexes, and additive ions), ensuring that the physicochemical state of the solution system reaches equilibrium and stability, thereby obtaining a finished bleaching agent with uniform performance and stable storage.

[0052] In one embodiment, based on the above embodiments, the magnesium alloy room temperature bleaching agent is the magnesium alloy room temperature bleaching agent as described in the above embodiments; the magnesium alloy surface treatment method includes the following steps: Pretreatment of magnesium alloy workpieces includes degreasing, oil removal and cleaning; Immerse the pretreated magnesium alloy workpiece in magnesium alloy room temperature bleaching agent for 3-10 minutes at room temperature. After bleaching, the workpiece is removed, cleaned, and dried to obtain a magnesium alloy workpiece with a uniform bright white oxide film on the surface.

[0053] In this embodiment, the magnesium alloy workpiece undergoes cleaning and activation pretreatment, including but not limited to chemical degreasing with alkaline or neutral degreasing agents to remove surface oil stains, followed by descaling treatment using physical or chemical methods (such as pickling or mechanical polishing), and finally thorough cleaning with deionized water or tap water to remove residual chemical reagents and impurities from the workpiece surface, thereby obtaining a clean and activated magnesium alloy surface.

[0054] The pretreated and drained magnesium alloy workpiece is completely immersed in a working tank containing the magnesium alloy room temperature bleach. Under normal temperature (15~30℃) conditions without external heating, the immersion treatment lasts for 3 to 10 minutes to allow the bleach to react chemically with the magnesium alloy surface.

[0055] After bleaching, remove the workpiece from the bleaching agent and immediately rinse it thoroughly with running deionized water or tap water to completely remove any residual bleach and its reaction byproducts from the workpiece surface. Then, dry the workpiece using methods such as compressed air drying, hot air drying, or air drying at room temperature to obtain a magnesium alloy workpiece with a uniform, dense, bright white oxide or conversion film on its surface.

[0056] In one embodiment, based on the above embodiments, to make the objectives, technical solutions, and advantages of the present invention clearer, preferred embodiments are provided below to further describe the present invention in detail. It should be understood that the preferred embodiments described herein are for illustrative purposes only and are not intended to limit the present invention.

[0057] (1) Example 1 The formula for a room-temperature bleaching agent for magnesium alloys, based on the preparation of 1L of solution, is as follows: Hydrogen peroxide (30%): 60 mL; Sodium citrate: 30g; Sodium silicate: 10g; Sodium dihydrogen phosphate: 15g; Thiourea: 1g; Nano silica sol (particle size 20~30nm, solid content 10wt%): 40mL; Deionized water: Add the remainder to a total of 1L.

[0058] Its preparation method is as follows: In a plastic container containing approximately 500 mL of deionized water, weighed sodium citrate, sodium silicate, and sodium dihydrogen phosphate are added sequentially at room temperature, and mechanically stirred until the solids are completely dissolved. In the above solution, under continuous stirring and temperature monitoring (controlled by an ice-water bath), 60 mL of hydrogen peroxide is slowly added dropwise, ensuring the mixing temperature does not exceed 30°C. Then, thiourea is added to the mixed solution, and stirring continues until completely dissolved, yielding a homogeneous base solution.

[0059] In a separate container, mix 40 mL of nano-silica sol with 100 mL of deionized water and pre-dilute until homogeneous. While stirring, slowly add the pre-diluted nano-silica sol dropwise to the base solution, stirring until homogeneous. Transfer the resulting mixture to a 1 L volumetric flask, dilute to the mark with deionized water, and stir until homogeneous. Pour the prepared bleaching solution into a brown reagent bottle, seal it, and allow it to stand at 25°C in the dark for 24 hours to mature, thus obtaining the magnesium alloy room-temperature bleaching agent.

[0060] (2) Example 2 The formula for a room-temperature bleaching agent for magnesium alloys, based on the preparation of 1L of solution, is as follows: Hydrogen peroxide (30%): 75 mL; Sodium citrate: 25g; Sodium silicate: 8g; Sodium dihydrogen phosphate: 12g; Thiourea: 1.5g; Cerium ammonium nitrate: 0.3g; Nano silica sol (particle size 10~20nm, solid content 12wt%): 35mL; Deionized water: Add the remainder to a total of 1L.

[0061] The preparation method is basically the same as in Example 1, except that: after obtaining the base solution, cerium ammonium nitrate is added to the base solution and stirred until completely dissolved. Subsequent steps are the same as in Example 1.

[0062] (3) Example 3 The formula for a room-temperature bleaching agent for magnesium alloys, based on the preparation of 1L of solution, is as follows: Hydrogen peroxide (30%): 50 mL; Sodium citrate: 35g; Sodium silicate: 12g; Sodium dihydrogen phosphate: 18g; Thiourea: 0.8g; Phytic acid: 2 mL; Nano silica sol (particle size 40-50nm, solid content 8wt%): 45mL; Deionized water: Add the remainder to a total of 1L.

[0063] The preparation method is basically the same as in Example 1, except that: after obtaining the base solution, phytic acid is added to the base solution and stirred evenly. Subsequent steps are the same as in Example 1.

[0064] (4) Example 4 The formula for a room-temperature bleaching agent for magnesium alloys, based on the preparation of 1L of solution, is as follows: Hydrogen peroxide (30%): 70 mL; Sodium citrate: 28g; Sodium silicate: 9g; Sodium dihydrogen phosphate: 14g; Thiourea: 1.2g; Cerium chloride: 0.2g; Phytic acid: 1.5 mL; Nano silica sol (particle size 30~40nm, solid content 10wt%): 50mL; Deionized water: Add the remainder to a total of 1L.

[0065] The preparation method is basically the same as in Example 1, except that after obtaining the base solution, cerium chloride and phytic acid are added to the base solution in sequence and stirred until the cerium chloride is completely dissolved and mixed evenly. Subsequent steps are the same as in Example 1.

[0066] (5) Comparative Example 1 A conventional chromate-containing magnesium alloy bleaching agent is provided, the formulation of which is as follows based on the preparation of 1L of solution: Sodium dichromate: 40g; Nitric acid (65%): 15 mL; Deionized water: Add the remainder to a total of 1L.

[0067] (6) Comparative Example 2 A bleaching agent without nano-silica sol is provided, the formulation of which is as follows based on the preparation of 1L of solution: Hydrogen peroxide (30%): 60 mL; Sodium citrate: 30g; Sodium silicate: 10g; Sodium dihydrogen phosphate: 15g; Thiourea: 1g; Deionized water: Add the remainder to a total of 1L.

[0068] The steps related to nano-silica were omitted during preparation, and the rest were the same as in Example 1.

[0069] (7) Comparative Example 3 A bleaching agent that does not contain thiourea is provided, the formulation of which is as follows based on the preparation of 1L of solution: Hydrogen peroxide (30%): 60 mL; Sodium citrate: 30g; Sodium silicate: 10g; Sodium dihydrogen phosphate: 15g; Nano silica sol (same as Example 1): 40 mL; Deionized water: Add the remainder to a total of 1L.

[0070] The step of adding thiourea is omitted during preparation; the rest is the same as in Example 1.

[0071] Application examples and performance tests are as follows: Magnesium alloy sheet with grade AZ31B was selected as the workpiece to be processed, and the following steps were performed in sequence: Pretreatment: Immerse the workpiece in alkaline degreasing solution (50g / L NaOH, 60℃) for 5 minutes to degrease, then rinse it with deionized water; then immerse it in pickling solution (10% HNO3, room temperature) for 30 seconds to activate, rinse it thoroughly with deionized water, and dry it with nitrogen.

[0072] Bleaching treatment: Immerse the pretreated workpieces in the bleaching agents prepared in Examples 1-4 and Comparative Examples 1-3 respectively, and soak them at room temperature of 25°C for 6 minutes.

[0073] Post-processing: Remove the workpiece, rinse it with plenty of deionized water, and then dry it for 10 minutes.

[0074] The processed workpieces were subjected to the following performance tests, including: Membrane appearance: Visually observe the color, uniformity, and gloss of the membrane.

[0075] Film thickness: Measured using an eddy current thickness gauge.

[0076] Corrosion resistance (salt spray test): Refer to GB / T 10125-2012 standard to conduct a neutral salt spray test (NSS) and record the time when the first rust spot appears on the workpiece surface.

[0077] Solution stability: After storing the prepared bleach at 25°C in the dark for 7 days, observe whether there is obvious precipitation or stratification, and test whether the appearance effect of the bleach on new workpieces is consistent with that of the fresh solution.

[0078] The test results are recorded in Table (1) below: Table (1): Results analysis: As can be seen from the comparison between Example 1 and Comparative Example 2, the uniformity, whiteness and corrosion resistance of the film are significantly improved after the addition of nano silica sol, proving that it plays a key role in filling, reinforcing and improving the density of the film.

[0079] As can be seen from the comparison between Example 1 and Comparative Example 3, thiourea is crucial as a stabilizer. In the absence of thiourea, hydrogen peroxide decomposes rapidly in solutions containing metal ions, leading to solution failure and uneven corrosion of the treated workpiece surface.

[0080] A comparison of Examples 2 and 4 with Example 1 shows that adding rare earth cerium salts (such as cerium ammonium nitrate and cerium chloride) can further improve the density and corrosion resistance of the oxide film and extend the time to first rust in the salt spray test. The addition of phytic acid can give the film a certain matte effect and synergistically improve corrosion resistance.

[0081] All preferred embodiments (1-4) of the present invention operate at room temperature, require no heating, have low energy consumption, and have short processing time (3-10 minutes) and high efficiency.

[0082] The bleaching agent of this invention does not contain heavy metals such as chromium and manganese, and uses hydrogen peroxide as an oxidant, making it environmentally friendly and safe. It also has good solution stability and meets the requirements of modern clean production.

[0083] In summary, the magnesium alloy room temperature bleaching agent and its preparation and application method provided by the present invention can quickly form a uniform, bright, and corrosion-resistant oxide film on the surface of magnesium alloys at room temperature, and has the advantages of high efficiency, environmental protection, simple operation, and stable solution.

[0084] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0085] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural changes made based on the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A magnesium alloy room temperature bleaching agent, characterized in that, Per liter of solution, it includes the following components: 50-80 mL of hydrogen peroxide; 20-40g of sodium citrate; 10-20g of sodium dihydrogen phosphate; 5-15g of sodium silicate; 0.5~2g of thiourea; 30-50 mL of nano-silica sol; And the remaining deionized water.

2. The magnesium alloy room temperature bleaching agent as described in claim 1, characterized in that, The components also include 0.1 to 0.5 g of rare earth cerium salts.

3. The magnesium alloy room temperature bleaching agent as described in claim 2, characterized in that, The rare earth cerium salt is at least one of cerium nitrate, cerium ammonium nitrate, and cerium chloride.

4. The magnesium alloy room temperature bleaching agent as described in claim 1, characterized in that, The components also include 1-3 mL of phytic acid.

5. The magnesium alloy room temperature bleaching agent as described in claim 1, characterized in that, The nano-silica sol has a particle size of 10-50 nm and a solid content of 8-12 wt%.

6. A method for preparing a room-temperature bleaching agent for magnesium alloys, characterized in that, A method for preparing a room-temperature bleaching agent for magnesium alloys as described in any one of claims 1-5; the method for preparing the room-temperature bleaching agent for magnesium alloys includes the following steps: Step S1: In partially deionized water, add sodium citrate, sodium silicate, and sodium dihydrogen phosphate in sequence and stir until completely dissolved; then, under stirring, gradually add hydrogen peroxide; finally, add thiourea and continue stirring until the mixture is homogeneous to obtain the base solution. Step S2: After premixing the nano-silica sol with a portion of deionized water, add it dropwise to the base solution under stirring and mix thoroughly; Step S3: Use deionized water to bring the volume of the mixture obtained in step S2 to the target volume, stir evenly, seal and let it stand to mature, and obtain a magnesium alloy room temperature bleaching agent.

7. The method for preparing the magnesium alloy room temperature bleaching agent as described in claim 6, characterized in that, After step S1, the method further includes: If the formulation contains rare earth cerium salts and / or phytic acid, then in step S2, the rare earth cerium salts and / or phytic acid are added to the base liquid and stirred until uniformly dissolved.

8. The method for preparing the magnesium alloy room temperature bleaching agent as described in claim 6, characterized in that, In step S1, when hydrogen peroxide is added, the system temperature is controlled to not exceed 30°C.

9. The preparation method according to claim 6, characterized in that, In step S3, the curing process is carried out under light-protected conditions, with a curing time of 12 to 48 hours and a temperature controlled at 20 to 25°C.

10. A method for surface treatment of magnesium alloys based on a room-temperature bleaching agent, characterized in that, The magnesium alloy room temperature bleaching agent is the magnesium alloy room temperature bleaching agent as described in any one of claims 1-5; the magnesium alloy surface treatment method includes the following steps: Pretreatment of magnesium alloy workpieces includes degreasing, oil removal and cleaning; Immerse the pretreated magnesium alloy workpiece in magnesium alloy room temperature bleaching agent for 3-10 minutes at room temperature. After bleaching, the workpiece is removed, cleaned, and dried to obtain a magnesium alloy workpiece with a uniform bright white oxide film on the surface.

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