Titanium alloy nitric acid-free chemical polishing solution and preparation method thereof

Abstract

The application is suitable for the technical field of titanium alloy surface treatment, and provides a nitric acid-free chemical polishing solution for titanium alloy and a preparation method thereof. Each 1L of the polishing solution comprises the following components: 100-150g of ammonium hydrogen fluoride, 150-250g of 50% concentration hydrogen peroxide, 200-350g of 85% concentration phosphoric acid, 60-120g of modified ethylene glycol, 10-20g of a composite stabilizer, 5-10g of a modified corrosion inhibitor, and water as the balance; the modified ethylene glycol is ethylene glycol modified by silane coupling agent KH550, and the modified corrosion inhibitor is a modified product of thiourea grafted maleic anhydride; through modification of raw materials and synergy of components, the application can improve the surface treatment effect of titanium alloy, completely eliminate the generation of toxic nitrogen oxide gas, avoid the decomposition of hydrogen peroxide and the excessive corrosion of titanium alloy, and is suitable for efficient and environmentally-friendly polishing of titanium alloy parts with complex shapes.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy surface treatment technology, specifically to a nitric acid-free chemical polishing solution for titanium alloys and its preparation method. Background Technology

[0002] Titanium alloys are widely used in aerospace, medical equipment, and electronic products due to their high strength, strong corrosion resistance, and good biocompatibility. For titanium alloy parts requiring high precision and high surface quality, chemical polishing is a key process for obtaining high-gloss and high-smooth surfaces. Existing titanium alloy chemical polishing solutions all use nitric acid and fluorides as core components. During the polishing process, toxic brown-yellow gases such as NO and NO2 are generated, polluting the environment and harming the health of operators. They also increase the total nitrogen content in wastewater, resulting in high subsequent treatment costs.

[0003] Furthermore, in existing polishing solutions containing hydrogen peroxide, the hydrogen peroxide is prone to decomposition, leading to solution failure. Moreover, the lack of effective corrosion inhibition mechanisms easily causes excessive corrosion of titanium alloys, affecting the dimensional accuracy of parts. While mechanical polishing and electropolishing can achieve surface smoothing, they require specialized equipment and have poor adaptability to complex-shaped parts, making it difficult to meet diverse production needs.

[0004] Therefore, in view of the above situation, there is an urgent need to provide a nitric acid-free chemical polishing solution for titanium alloys and its preparation method to overcome the shortcomings in current practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a nitric acid-free chemical polishing solution for titanium alloys and its preparation method, effectively solving the problems in the background art mentioned above.

[0006] This invention is achieved by providing a nitric acid-free chemical polishing solution for titanium alloys, wherein each 1L of the polishing solution contains the following components:

[0007] Ammonium bifluoride 100-150g, 50% hydrogen peroxide 150-250g, 85% phosphoric acid 200-350g, modified ethylene glycol 60-120g, composite stabilizer 10-20g, modified corrosion inhibitor 5-10g, water as balance;

[0008] The modified ethylene glycol is ethylene glycol modified with silane coupling agent KH550, and the modified corrosion inhibitor is a modified product of thiourea grafted with maleic anhydride.

[0009] As a further aspect of the present invention: the preferred composition of each 1L of the polishing solution is:

[0010] 125g ammonium bifluoride, 200g 50% hydrogen peroxide, 280g 85% phosphoric acid, 80g modified ethylene glycol, 15g composite stabilizer, 7.5g modified corrosion inhibitor, with water as the balance.

[0011] As a further aspect of the present invention, the preparation steps of the modified ethylene glycol are as follows:

[0012] S301: Place ethylene glycol in a constant temperature reactor, purge the air inside the reactor with nitrogen 3-5 times, each purge lasting 5-8 minutes, and control the oxygen content inside the reactor to ≤0.5%;

[0013] S302: Heat ethylene glycol to 40-50℃ and keep it at that temperature for 10-15 minutes. Slowly add silane coupling agent KH550 at a rate of 3-5% of the mass of ethylene glycol, at a rate of 1-2 g / min.

[0014] S303: Adjust the stirring speed to 300-400 r / min and stir for 20-30 min under constant temperature conditions of 40-50℃;

[0015] S304: Keep warm and stand for 1 hour, cool naturally to room temperature, filter to remove insoluble impurities, and obtain modified ethylene glycol.

[0016] As a further aspect of the present invention: the composite stabilizer is composed of ethanol and sodium benzoate mixed in a mass ratio of 3:1.

[0017] As a further aspect of the present invention, the preparation steps of the modified corrosion inhibitor are as follows:

[0018] S501: Dry thiourea and maleic anhydride separately until the moisture content is ≤0.3%, and put them into a reaction vessel equipped with a reflux condenser at a molar ratio of 1:0.8-1.2. Add anhydrous ethanol as a solvent, and the amount of solvent is 2-3 times the total mass of the reactants.

[0019] S502: Introduce nitrogen for protection, with a nitrogen flow rate of 0.5-1 L / min. Heat to 70-80℃, adjust the stirring speed to 400-500 r / min, and react for 2-3 hours. During this period, take samples every 30 minutes to check the reaction conversion rate. Stop the reaction when the conversion rate is ≥95%.

[0020] S503: Cool the reaction solution to 20-25℃, slowly add 1 / 2 volume of deionized water to the reaction solution, stir for 10 minutes, let stand and separate into layers, and remove the upper clear liquid.

[0021] S504: The lower layer product is recrystallized twice with anhydrous ethanol, with a crystallization temperature of 0-5℃ and a crystallization time of 8-12h each time;

[0022] S505: Place the crystallized product in a vacuum drying oven and dry it for 4-6 hours at 60-70℃ and a vacuum degree ≤-0.09MPa to obtain the modified corrosion inhibitor.

[0023] As a further aspect of the present invention: the working conditions of the polishing solution are as follows:

[0024] The temperature is 50-60℃, the polishing time is 2-4 minutes, and the titanium alloy parts are periodically oscillated during the polishing process.

[0025] As a further aspect of the present invention: the frequency of the periodic oscillation is 30-40 times / min, and the amplitude of a single oscillation is 5-8cm.

[0026] As a further aspect of the present invention: the purity of the ammonium bifluoride is ≥99.5%, the purity of the phosphoric acid is ≥85%, and the purity of the ethylene glycol is ≥99.0%.

[0027] This invention also provides a method for preparing the nitric acid-free chemical polishing solution for titanium alloys as described above, comprising the following steps:

[0028] S1: Weigh out ammonium bifluoride, 50% hydrogen peroxide, 85% phosphoric acid, modified ethylene glycol, composite stabilizer, modified corrosion inhibitor, and deionized water according to the specified proportions.

[0029] S2: Add deionized water to a reaction vessel equipped with a temperature control device and a stirring device, turn on the stirring, and slowly add ammonium bifluoride and phosphoric acid in sequence, with an interval of 10-15 minutes between each addition. Control the solution temperature at 30-40℃ during the addition process, and stir until the raw materials are completely dissolved.

[0030] S3: Turn off the heating device and allow it to cool naturally to 25-30℃. Add the composite stabilizer and modified corrosion inhibitor, adjust the stirring speed to 250-300 r / min, and stir for 15-20 min.

[0031] S4: Keep the stirring speed at 250-300 r / min and slowly add hydrogen peroxide dropwise at a rate of 5-10 mL / min. After the addition is complete, continue stirring for 10 min.

[0032] S5: Add modified ethylene glycol, adjust the stirring speed to 300-350 r / min, and continue stirring at 25-30℃ for 20-30 min;

[0033] S6: After stirring, let the solution stand and filter to remove mechanical impurities, and obtain a nitric acid-free chemical polishing solution for titanium alloy.

[0034] As a further aspect of the present invention: in S4, the hydrogen peroxide is added at a rate of 5-10 mL / min, and the solution temperature is controlled to not exceed 35°C during the dropwise addition process by a cooling device.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] This invention completely eliminates the nitric acid component in traditional polishing solutions, and no toxic gases such as nitrogen oxides are generated during the polishing process. This avoids environmental pollution and harm to the health of operators from the source, while reducing the total nitrogen load in wastewater and simplifying the subsequent wastewater treatment process, which is in line with the environmental protection development trend of green production.

[0037] This invention, through component synergistic design and raw material modification optimization, produces a bright and clean titanium alloy surface after polishing. It can effectively remove burrs and rough edges generated during machining, and the surface flatness and smoothness meet the requirements of high-precision parts. During the polishing process, the titanium alloy dissolution rate can be precisely controlled to avoid excessive corrosion and ensure the dimensional accuracy of the parts. It is suitable for processing titanium alloy parts with high requirements for surface quality and dimensional accuracy.

[0038] The combination of the composite stabilizer and raw material modification process in this invention can effectively inhibit the decomposition of hydrogen peroxide, extend the effective service life of the polishing solution, and reduce the frequency of solution replacement. At the same time, the solution system is uniform and stable, and is not prone to stratification or precipitation. It can be reused multiple times, thereby improving the solution utilization rate.

[0039] The modified ethylene glycol of this invention is grafted with a silane coupling agent, which significantly improves its compatibility with other components and forms a more uniform viscous system, further enhancing the bright and smoothing effect. The modified corrosion inhibitor, after being treated by grafting, recrystallization and other processes, has improved purity and enhanced adsorption capacity to the titanium alloy surface, resulting in a better corrosion inhibition effect and comprehensive protection of the titanium alloy surface from excessive corrosion.

[0040] This invention requires no special or complex equipment and has good adaptability to titanium alloy parts with complex shapes and special structures, solving the problem of difficult processing of complex parts by mechanical polishing and electrolytic polishing; the polishing temperature is mild, the time is short, the energy consumption is low, and the production efficiency is high; the preparation process is easy to achieve industrial mass production through precise temperature control and raw material pretreatment.

[0041] The solution prepared by this invention has an extended service life and a simplified wastewater treatment process. At the same time, it reduces the scrap of parts caused by polishing defects and lowers production losses. All raw materials used are conventional chemical products, which are convenient to purchase and have a stable supply. This can effectively control production costs and has environmental, economic and practical benefits, with broad market application prospects. Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The present invention will be further explained below with reference to specific embodiments.

[0044] The present invention provides a nitric acid-free chemical polishing solution for titanium alloys. Each 1L of the polishing solution contains the following components: 100-150g ammonium bifluoride, 150-250g 50% hydrogen peroxide, 200-350g 85% phosphoric acid, 60-120g modified ethylene glycol, 10-20g composite stabilizer, 5-10g modified corrosion inhibitor, and water as the balance.

[0045] The modified ethylene glycol is ethylene glycol modified with silane coupling agent KH550, and the modified corrosion inhibitor is a modified product of thiourea grafted with maleic anhydride.

[0046] Through component synergistic design and raw material modification optimization, the polished titanium alloy surface is bright and clean, effectively removing burrs and rough edges generated during machining. The surface smoothness and finish meet the requirements of high-precision parts. The titanium alloy dissolution rate can be precisely controlled during polishing to avoid excessive corrosion and ensure dimensional accuracy, making it suitable for machining titanium alloy parts with high surface quality and dimensional accuracy requirements. The combination of composite stabilizers and raw material modification processes effectively inhibits hydrogen peroxide decomposition, extends the effective service life of the polishing solution, and reduces the frequency of solution replacement. Simultaneously, the solution system is homogeneous and stable, less prone to stratification and precipitation, and can be reused multiple times, improving solution utilization.

[0047] In one embodiment of the present invention, the preferred components of each 1L polishing solution are: 125g ammonium bifluoride, 200g 50% hydrogen peroxide, 280g 85% phosphoric acid, 80g modified ethylene glycol, 15g composite stabilizer, 7.5g modified corrosion inhibitor, and water as the balance.

[0048] In one embodiment of the present invention, the modified ethylene glycol is prepared by:

[0049] S301: Place ethylene glycol in a constant temperature reactor, purge the air inside the reactor with nitrogen 3-5 times, each purge lasting 5-8 minutes, and control the oxygen content inside the reactor to ≤0.5%;

[0050] S302: Heat ethylene glycol to 40-50℃ and keep it at that temperature for 10-15 minutes. Slowly add silane coupling agent KH550 at a rate of 3-5% of the mass of ethylene glycol, at a rate of 1-2 g / min.

[0051] S303: Adjust the stirring speed to 300-400 r / min and stir for 20-30 min under constant temperature conditions of 40-50℃;

[0052] S304: Keep warm and stand for 1 hour, cool naturally to room temperature, filter to remove insoluble impurities (filtration accuracy is 0.22μm) to obtain modified ethylene glycol.

[0053] In one embodiment of the present invention, the composite stabilizer is composed of ethanol and sodium benzoate mixed in a mass ratio of 3:1.

[0054] In one embodiment of the present invention, the modified corrosion inhibitor is prepared by:

[0055] S501: Dry thiourea and maleic anhydride separately until the moisture content is ≤0.3%, and put them into a reaction vessel equipped with a reflux condenser at a molar ratio of 1:0.8-1.2. Add anhydrous ethanol as a solvent, and the amount of solvent is 2-3 times the total mass of the reactants.

[0056] S502: Introduce nitrogen for protection, with a nitrogen flow rate of 0.5-1 L / min. Heat to 70-80℃, adjust the stirring speed to 400-500 r / min, and react for 2-3 hours. During this period, take samples every 30 minutes to check the reaction conversion rate. Stop the reaction when the conversion rate is ≥95%.

[0057] S503: Cool the reaction solution to 20-25℃, slowly add 1 / 2 volume of deionized water to the reaction solution, stir for 10 minutes, let stand and separate into layers, and remove the upper clear liquid.

[0058] S504: The lower layer product is recrystallized twice with anhydrous ethanol, with a crystallization temperature of 0-5℃ and a crystallization time of 8-12h each time;

[0059] S505: Place the crystallized product in a vacuum drying oven and dry it for 4-6 hours at 60-70℃ and a vacuum degree ≤-0.09MPa to obtain a modified corrosion inhibitor with a purity ≥99.0%.

[0060] Modified ethylene glycol, through grafting modification with silane coupling agents, exhibits significantly improved compatibility with other components, forming a more uniform viscous system and further enhancing the bright and smoothing effect. Modified corrosion inhibitors, after being processed by grafting, recrystallization, and other processes, have improved purity and enhanced adsorption capacity to the titanium alloy surface, resulting in superior corrosion inhibition and comprehensive protection of the titanium alloy surface from excessive corrosion.

[0061] In one embodiment of the present invention, the working conditions of the polishing solution are: temperature 50-60℃, polishing time 2-4 min, and periodic oscillation of the titanium alloy parts during the polishing process.

[0062] In one embodiment of the present invention, the frequency of the periodic oscillation is 30-40 times / min, and the amplitude of a single oscillation is 5-8cm.

[0063] In one embodiment of the present invention, the ammonium bifluoride has a purity of ≥99.5%, the phosphoric acid has a purity of ≥85%, and the ethylene glycol has a purity of ≥99.0%.

[0064] This invention also provides a method for preparing the nitric acid-free chemical polishing solution for titanium alloys as described above, characterized by the following steps: S1: Weigh ammonium bifluoride, 50% hydrogen peroxide, 85% phosphoric acid, modified ethylene glycol, composite stabilizer, modified corrosion inhibitor, and deionized water (conductivity ≤10μS / cm) in proportion.

[0065] S2: Add deionized water to a reaction vessel equipped with a temperature control device and a stirring device, turn on the stirring (200-250 r / min), and slowly add ammonium bifluoride and phosphoric acid in sequence, with an interval of 10-15 min between each addition. Control the solution temperature at 30-40℃ during the addition process, and stir until the raw materials are completely dissolved (dissolution judgment criteria: the solution is clear and transparent, with no visible particles, and no precipitate is formed after standing for 30 min).

[0066] S3: Turn off the heating device and allow it to cool naturally to 25-30℃. Add the composite stabilizer and modified corrosion inhibitor, adjust the stirring speed to 250-300 r / min, and stir for 15-20 min.

[0067] S4: Maintain a stirring speed of 250-300 r / min and slowly add hydrogen peroxide dropwise at a rate of 5-10 mL / min. During the dropwise addition, control the solution temperature to not exceed 35℃ using a cooling device. After the dropwise addition is complete, continue stirring for 10 min.

[0068] S5: Add modified ethylene glycol, adjust the stirring speed to 300-350 r / min, and continue stirring at 25-30℃ for 20-30 min;

[0069] S6: After stirring, let the solution stand and filter (filtration accuracy is 0.45μm) to remove mechanical impurities and obtain a nitric acid-free chemical polishing solution for titanium alloy.

[0070] In this embodiment, a nitric acid-free chemical polishing solution for titanium alloys is mainly used for chemical polishing of titanium alloys, and it includes the following steps:

[0071] Heat the above polishing solution to 50-60℃;

[0072] Clean the titanium alloy parts to be chemically polished by removing oil and cleaning them thoroughly.

[0073] Place the cleaned product into the above chemical polishing solution for polishing. During the process, gently agitate the workpiece to ensure even polishing. The immersion time is 2-4 minutes, which completes the polishing process of the titanium alloy.

[0074] Ammonium bifluoride and hydrogen peroxide work synergistically to achieve corrosion leveling; phosphoric acid reacts to form a viscous diffusion layer containing titanium salts, utilizing the thickness difference of the diffusion layer at uneven surfaces to achieve a leveling effect that rapidly dissolves protrusions and protects depressions; modified ethylene glycol improves the viscosity and gloss of the solution, and its modified structure allows for more uniform adsorption onto the titanium alloy surface; composite stabilizers inhibit the decomposition of hydrogen peroxide, extending the solution's service life; modified corrosion inhibitors enhance their bonding force with the titanium alloy surface through grafting structures, forming a dense protective film to prevent excessive corrosion; complexing agents form stable complexes with titanium ions, preventing titanium ion precipitation and ensuring consistent polishing of the solution. The synergistic effect of all components achieves environmentally friendly and efficient polishing. Example 1:

[0075] A nitric acid-free chemical polishing solution for titanium alloys, each 1L contains: 100g ammonium bifluoride, 250g 50% hydrogen peroxide, 350g 85% phosphoric acid, 120g modified ethylene glycol, 20g composite stabilizer, 10g modified corrosion inhibitor, with water as the balance.

[0076] Preparation method:

[0077] S1: Weigh out the above components, and the conductivity of deionized water is ≤10μS / cm;

[0078] S2: Add the remaining deionized water to the reaction vessel, turn on the stirrer (220 r / min), add ammonium fluoride first, stir for 10 min and then add phosphoric acid, control the solution temperature at 35℃, stir until the raw materials are completely dissolved (the solution is clear and transparent, with no visible particles, and no precipitate after standing for 30 min).

[0079] S3: Allow the temperature to cool naturally to 28℃, add the composite stabilizer and modified corrosion inhibitor, adjust the stirring speed to 280r / min, and stir for 18min;

[0080] S4: Maintain a rotation speed of 280 r / min and add hydrogen peroxide dropwise at a rate of 8 mL / min. Control the temperature to not exceed 35°C using a cooling device. Stir for 10 min after the addition is complete.

[0081] S5: Add modified ethylene glycol, adjust the speed to 320 r / min, and stir at 28℃ for 25 min;

[0082] S6: After standing, filter with a 0.45μm filter membrane. After standing for 24 hours, if there is no stratification or precipitation, the polishing solution is obtained.

[0083] Polishing process: Heat the solution to 50°C, clean the titanium alloy parts by removing oil, immerse them in the solution, and polish for 2 minutes by oscillating at a frequency of 35 times / min. Example 2:

[0084] A nitric acid-free chemical polishing solution for titanium alloys, each 1L contains: 150g ammonium bifluoride, 150g 50% hydrogen peroxide, 200g 85% phosphoric acid, 60g modified ethylene glycol, 10g composite stabilizer, 5g modified corrosion inhibitor, with water as the balance.

[0085] Preparation method:

[0086] S1: Weigh out the above components, and the conductivity of deionized water is ≤10μS / cm;

[0087] S2: Add the remaining deionized water to the reaction vessel, turn on the stirrer (200 r / min), add ammonium bifluoride first, stir for 15 min and then add phosphoric acid, control the solution temperature at 30℃, and stir until the raw materials are completely dissolved;

[0088] S3: Allow the temperature to cool naturally to 25°C, add the composite stabilizer and modified corrosion inhibitor, and adjust the stirring speed to 250 r / min;

[0089] S4: Keep the rotation speed at 250 r / min, add hydrogen peroxide dropwise at a rate of 5 mL / min, control the temperature not to exceed 35℃, and stir for 10 min after the addition is complete;

[0090] S5: Add modified ethylene glycol, adjust the speed to 300 r / min, and stir at 25℃ for 20 min;

[0091] S6: After standing, filter with a 0.45μm filter membrane. After standing for 24 hours, if there is no stratification or precipitation, the polishing solution is obtained.

[0092] Polishing process: Heat the solution to 60℃, clean the titanium alloy parts by removing oil, immerse them in the solution, and polish for 4 minutes by oscillating at a frequency of 30 times / min. Example 3:

[0093] A nitric acid-free chemical polishing solution for titanium alloys contains, per 1L: 125g ammonium bifluoride, 200g 50% hydrogen peroxide, 280g 85% phosphoric acid, 80g modified ethylene glycol, 15g composite stabilizer, 7.5g modified corrosion inhibitor, with water as the balance.

[0094] Preparation method:

[0095] S1: Weigh out the above components, and the conductivity of deionized water is ≤10μS / cm;

[0096] S2: Add the remaining deionized water to the reaction vessel, turn on the stirrer (250 r / min), add ammonium bifluoride first, stir for 12 min and then add phosphoric acid, control the solution temperature at 38℃, and stir until the raw materials are completely dissolved;

[0097] S3: Allow the temperature to cool naturally to 30℃, add the composite stabilizer and modified corrosion inhibitor, and adjust the stirring speed to 300r / min;

[0098] S4: Keep the rotation speed at 300 r / min, add hydrogen peroxide dropwise at a rate of 10 mL / min, control the temperature not to exceed 35℃, and stir for 10 min after the addition is complete;

[0099] S5: Add modified ethylene glycol, adjust the speed to 350 r / min, and stir at 30℃ for 30 min;

[0100] S6: After standing, filter with a 0.45μm filter membrane. After standing for 24 hours, if there is no stratification or precipitation, the polishing solution is obtained.

[0101] Polishing process: Heat the solution to 55℃, clean the titanium alloy parts by removing oil, immerse them in the solution, and polish for 3 minutes by oscillating at a frequency of 40 times / min.

[0102] Comparative Example 1

[0103] The difference from Example 3 is that unmodified ethylene glycol was used instead of modified ethylene glycol, no modified corrosion inhibitor was used, and ethanol was used as a stabilizer.

[0104] Comparative Example 2

[0105] The difference from Example 3 is that 200 g / L nitric acid was added, the composite stabilizer and modified corrosion inhibitor were removed, and no filtration step was performed during the preparation process.

[0106] Performance testing

[0107] The performance of the polishing solutions and polished titanium alloy parts of Examples 1-3 and Comparative Examples 1-2 was tested, and the results are shown in Table 1:

[0108] Table 1 Performance Test Results

[0109]

[0110] The test results show that the polishing solutions of Examples 1-3 of the present invention do not produce toxic gases, and the total nitrogen content of the wastewater is significantly lower than that of the traditional nitric acid system (Comparative Example 2).

[0111] After polishing, the titanium alloy surface has low roughness and high gloss, and excellent corrosion inhibition efficiency and polishing pass rate.

[0112] The solution has a long effective service life and does not exhibit excessive corrosion.

[0113] Comparative Example 1 showed a significant decrease in surface quality and corrosion inhibition efficiency due to the lack of raw material modification, composite stabilizers, and precise process control.

[0114] Although Comparative Example 2 has better gloss, it produces toxic gases, has a high total nitrogen content in wastewater, and exhibits moderate to excessive corrosion, which does not meet environmental protection and precision requirements.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nitric acid-free chemical polishing solution for titanium alloys, characterized in that, Each 1L of the polishing solution contains the following components: Ammonium bifluoride 100-150g, 50% hydrogen peroxide 150-250g, 85% phosphoric acid 200-350g, modified ethylene glycol 60-120g, composite stabilizer 10-20g, modified corrosion inhibitor 5-10g, water as balance; The modified ethylene glycol is ethylene glycol modified with silane coupling agent KH550, and the modified corrosion inhibitor is a modified product of thiourea grafted with maleic anhydride. The composite stabilizer is composed of ethanol and sodium benzoate mixed in a mass ratio of 3:

1.

2. The nitric acid-free chemical polishing solution for titanium alloys according to claim 1, characterized in that, The preferred composition of each 1L of the polishing solution is: 125g ammonium bifluoride, 200g 50% hydrogen peroxide, 280g 85% phosphoric acid, 80g modified ethylene glycol, 15g composite stabilizer, 7.5g modified corrosion inhibitor, with water as the balance.

3. The nitric acid-free chemical polishing solution for titanium alloys according to claim 1, characterized in that, The preparation steps of the modified ethylene glycol are as follows: S301: Place ethylene glycol in a constant temperature reactor, purge the air inside the reactor with nitrogen 3-5 times, each purge lasting 5-8 minutes, and control the oxygen content inside the reactor to ≤0.5%; S302: Heat ethylene glycol to 40-50℃ and keep it at that temperature for 10-15 minutes. Slowly add silane coupling agent KH550 at a rate of 3-5% of the mass of ethylene glycol, at a rate of 1-2 g / min. S303: Adjust the stirring speed to 300-400 r / min and stir for 20-30 min under constant temperature conditions of 40-50℃; S304: Keep warm and stand for 1 hour, cool naturally to room temperature, filter to remove insoluble impurities, and obtain modified ethylene glycol.

4. The nitric acid-free chemical polishing solution for titanium alloys according to claim 1, characterized in that, The preparation steps of the modified corrosion inhibitor are as follows: S501: Dry thiourea and maleic anhydride separately until the moisture content is ≤0.3%, and put them into a reaction vessel equipped with a reflux condenser at a molar ratio of 1:0.8-1.

2. Add anhydrous ethanol as a solvent, and the amount of solvent is 2-3 times the total mass of the reactants. S502: Introduce nitrogen for protection, with a nitrogen flow rate of 0.5-1 L / min. Heat to 70-80℃, adjust the stirring speed to 400-500 r / min, and react for 2-3 hours. During this period, take samples every 30 minutes to check the reaction conversion rate. Stop the reaction when the conversion rate is ≥95%. S503: Cool the reaction solution to 20-25℃, slowly add 1 / 2 volume of deionized water to the reaction solution, stir for 10 minutes, let stand and separate into layers, and remove the upper clear liquid. S504: The lower layer product is recrystallized twice with anhydrous ethanol, with a crystallization temperature of 0-5℃ and a crystallization time of 8-12h each time. S505: Place the crystallized product in a vacuum drying oven and dry it for 4-6 hours at 60-70℃ and a vacuum degree ≤-0.09MPa to obtain the modified corrosion inhibitor.

5. The nitric acid-free chemical polishing solution for titanium alloys according to claim 1, characterized in that, The working conditions of the polishing solution are as follows: The temperature is 50-60℃, the polishing time is 2-4 minutes, and the titanium alloy parts are periodically oscillated during the polishing process.

6. The nitric acid-free chemical polishing solution for titanium alloys according to claim 5, characterized in that, The frequency of the periodic oscillation is 30-40 times / min, and the amplitude of a single oscillation is 5-8cm.

7. The nitric acid-free chemical polishing solution for titanium alloys according to claim 1, characterized in that, The purity of the ammonium bifluoride is ≥99.5%, the purity of the phosphoric acid is ≥85%, and the purity of the ethylene glycol is ≥99.0%.

8. A method for preparing a nitric acid-free chemical polishing solution for titanium alloys as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Weigh out ammonium bifluoride, 50% hydrogen peroxide, 85% phosphoric acid, modified ethylene glycol, composite stabilizer, modified corrosion inhibitor, and deionized water according to the specified proportions. S2: Add deionized water to a reaction vessel equipped with a temperature control device and a stirring device, turn on the stirring, and slowly add ammonium bifluoride and phosphoric acid in sequence, with an interval of 10-15 minutes between each addition. Control the solution temperature at 30-40℃ during the addition process, and stir until the raw materials are completely dissolved. S3: Turn off the heating device and allow it to cool naturally to 25-30℃. Add the composite stabilizer and modified corrosion inhibitor, adjust the stirring speed to 250-300 r / min, and stir for 15-20 min. S4: Keep the stirring speed at 250-300 r / min and slowly add hydrogen peroxide dropwise at a rate of 5-10 mL / min. After the addition is complete, continue stirring for 10 min. S5: Add modified ethylene glycol, adjust the stirring speed to 300-350 r / min, and continue stirring at 25-30℃ for 20-30 min; S6: After stirring, let the solution stand and filter to remove mechanical impurities, and obtain a nitric acid-free chemical polishing solution for titanium alloy.

9. The preparation method according to claim 8, characterized in that, In S4, the hydrogen peroxide is added at a rate of 5-10 mL / min, and the solution temperature is controlled to not exceed 35°C during the dropwise addition process using a cooling device.

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