A polishing electrolyte for connecting rod and a preparation method thereof

Abstract

A polishing electrolyte for connecting rod and a preparation method thereof belong to the technical field of metal surface treatment. The polishing electrolyte for connecting rod comprises the following components: phosphoric acid, sulfuric acid and a composite additive; wherein the composite additive comprises sodium polyphosphate, a compounded corrosion inhibitor, TiO2 particles and polyethylene glycol in a mass ratio of 1:4-6:1-2:1-2; the compounded corrosion inhibitor comprises thiourea, brominated cetylpyridine and sodium dodecylsulfate in a mass ratio of 1:1.5-2:1.5-2. The polishing electrolyte has excellent polishing effect and stability, and the connecting rod treated by electrolytic polishing with the polishing electrolyte has excellent corrosion resistance, surface flatness, bright color and other characteristics.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a polishing electrolyte for connecting rods and its preparation method. Background Technology

[0002] Electropolishing is an electrochemical machining process that utilizes the principle of anodic dissolution of microscopic protrusions on a metal surface under a specific electrolyte and appropriate current density. During electropolishing, a high-viscosity metal salt film (i.e., a viscous film) forms on the workpiece surface near the anode in the electrolyte. On the uneven anode metal surface, the viscosity, thickness, and density of the viscous film vary; the film layer on the protruding parts is thinner, has lower resistance, and a higher current density, thus accelerating the dissolution of the metal in the protruding parts. The protruding parts gradually flatten, ultimately achieving a smooth and even surface. Electropolishing selectively removes material at the microscopic level, making the metal surface smooth and bright, enhancing corrosion resistance, reducing surface roughness, and improving aesthetics. Therefore, it has been widely used in the field of metal surface treatment, especially in the surface treatment of precision parts.

[0003] Connecting rods consist of a connecting rod body, connecting rod big end cap, connecting rod small end bushing, connecting rod big end bearing, and connecting rod bolts (or screws). To ensure sufficient rigidity and strength while maintaining a lightweight structure, high-quality medium-carbon structural steel with a low carbon content is generally used. Electrolytic machining has been proposed to address the machining challenges of hot forging dies with high hardness, complex shapes, high surface quality requirements, and good demolding effects. Currently, although electrolytic polishing technology has significant advantages in improving the surface quality of connecting rods, existing polishing slurry systems still have obvious limitations, restricting their application in high-standard precision manufacturing. First, the three traditional categories of chemical electrolytic polishing slurries present significant environmental and safety issues: Nitric acid-containing systems release toxic "yellow fumes" such as nitrogen oxides during polishing, seriously endangering operator health and the environment; while hexavalent chromium in dichromate-containing systems, a recognized strong carcinogen, poses serious challenges for wastewater and waste residue treatment. Secondly, there are shortcomings in the process performance: Although the hydrogen peroxide-containing system is relatively environmentally friendly, its poor chemical stability and rapid decomposition result in poor reproducibility of polishing effects and low efficiency, making it difficult to meet the needs of large-scale production. Connecting rods treated with existing polishing electrolytes exhibit poor corrosion resistance, rough surfaces, and poor color gloss.

[0004] Patent application CN111020687A discloses an electrolytic polishing solution and method. This electrolytic polishing solution comprises, by weight, the following components: 50-55 parts sulfuric acid; 45-50 parts phosphoric acid; 1.5-2.2 parts glycerol; 0.07-1 part cyclohexamethylenetetramine; 2-3 parts trimethylolpentyl alcohol polyoxyethylene polyoxypropylene ether; and 1.5-2.2 parts brightener. Using this electrolytic polishing solution to replace traditional mechanical polishing reduces surface roughness, controls macroscopic unevenness of materials, increases surface gloss, and reduces the coefficient of friction. However, the long-term storage stability and long-term corrosion resistance of the treated workpiece still need further improvement. These shortcomings collectively highlight the urgent need for a new, efficient, and stable electrolytic polishing solution. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a polishing electrolyte for connecting rods and its preparation method. The polishing electrolyte possesses both excellent polishing effect and stability. Connecting rods treated with the polishing electrolyte provided by the present invention exhibit excellent corrosion resistance, smooth surface, and bright color.

[0006] To achieve the above objectives, according to one aspect of the present invention, a polishing electrolyte for connecting rods is provided, comprising the following components: phosphoric acid, sulfuric acid, and a composite additive; wherein the composite additive comprises sodium polyphosphate, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol in a mass ratio of 1:4-6:1-2:1-2; and the compound corrosion inhibitor comprises thiourea, hexadecylpyridine bromide, and sodium dodecyl sulfonate in a mass ratio of 1:1.5-2:1.5-2.

[0007] In this invention, the volume ratio of phosphoric acid to sulfuric acid is (1.5-2):1. It can be understood that this volume ratio can be any specific value among 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, and 2:1, or any value within the range of (1.5-2):1. The inventors have discovered that controlling the volume ratio of phosphoric acid to sulfuric acid within the range described in this invention can improve both the stability of the polishing electrolyte and the gloss of the surface after polishing. If the phosphoric acid content is too low, the stability of the polishing electrolyte deteriorates; if the phosphoric acid content is too high, the polishing effect is poor, and the gloss of the surface after polishing deteriorates.

[0008] In this invention, the mass concentration of the composite additive is 10-15 g / L. It is understood that the mass concentration can be any specific value among 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, and 15 g / L, or any value within the range of 10-15 g / L. In this invention, the composite additive comprises sodium polyphosphate, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol in a mass ratio of 1:4-6:1-2:1-2. Preferably, the composite additive comprises sodium polyphosphate, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol in a mass ratio of 1:5:1.5:1.5. The inventors have found that when the mass ratio of each component in the composite additive of this invention is controlled within the above-mentioned range, the synergistic effect between the components is optimal, the polishing electrolyte has a suitable viscosity, a film layer easily forms on the connecting rod surface, the reaction rate during the chemical polishing process can be effectively controlled, the connecting rod surface can be dissolved uniformly and regularly, and the polishing effect of the polishing electrolyte is better.

[0009] In this invention, the TiO2 particles are rutile TiO2 particles. The particle size of the TiO2 particles in this invention is 20-30 nm. The inventors have discovered that the TiO2 particles of this type possess both suitable dielectric constant and hardness. Compared to other types of TiO2 particles and inorganic particles, they exhibit better dispersion performance in polishing electrolytes, resulting in superior polishing effects and low surface roughness after polishing.

[0010] In this invention, the polyethylene glycol includes one or more of polyethylene glycol 1000 and polyethylene glycol 2000. In this invention, the polyethylene glycol can better adjust the viscosity of the polishing electrolyte, which helps to form a film on the connecting rod surface, slowing down the chemical polishing reaction rate and thus making the polishing reaction process smoother and slower.

[0011] The specific compounds in the compound corrosion inhibitor described in this invention exhibit synergistic effects, which can synergistically improve adsorption stability, surface coverage, and alter the adsorption rate. On one hand, the thiourea molecule contains both hydrophobic and hydrophilic groups, enabling it to physically adsorb and form a dense protective film on the connecting rod surface, thereby reducing the concentration of H+ in the solution. + The sulfur atom in sodium dodecyl sulfonate is difficult to approach the connecting rod surface, thus reducing the corrosion rate of the connecting rod by phosphoric acid and sulfuric acid. On the other hand, the sulfur atom in sodium dodecyl sulfonate is conducive to nucleophilic attack and coordination reaction, and iron ions can form coordination bonds with the π electron cloud on the hexadecylpyridine heterocycle of bromide, resulting in chemisorption and thus improving the corrosion inhibition effect. Through the combined effect of physical adsorption and chemisorption, the compound corrosion inhibitor in this application has excellent corrosion inhibition effect.

[0012] According to another aspect of the present invention, a method for preparing the above-described polishing electrolyte for connecting rods is also provided, the method comprising the following steps: (1) Preparation of compound corrosion inhibitor: Thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate are mixed in proportion and stirred evenly to obtain the compound corrosion inhibitor; (2) Preparation of composite additive: The composite corrosion inhibitor, sodium polyphosphate, TiO2 particles and polyethylene glycol are mixed in proportion and stirred evenly to obtain the composite additive; (3) Slowly add sulfuric acid to phosphoric acid while stirring, let it stand and cool to room temperature, add the composite additive, mix evenly, and obtain the polishing electrolyte for connecting rod.

[0013] In this invention, in step (1), the compound corrosion inhibitor is prepared by mixing thiourea, hexadecylpyridine bromide, and sodium dodecyl sulfonate in a certain proportion and stirring until uniform to obtain the compound corrosion inhibitor. Further, the stirring is carried out at room temperature.

[0014] In this invention, in step (2), the composite additive is prepared by mixing the composite corrosion inhibitor, sodium polyphosphate, TiO2 particles and polyethylene glycol in proportion and stirring evenly to obtain the composite additive.

[0015] In this invention, in step (3), sulfuric acid is slowly added to phosphoric acid under stirring, allowed to stand and cool to room temperature, the composite additive is added, and the mixture is homogeneous to obtain the polishing electrolyte for the connecting rod. In this invention, in step (3), the rate of adding sulfuric acid is 10-20 L / min. It can be understood that the rate can be any specific value among 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min, and 20 L / min, or any value within the range of 10-20 L / min.

[0016] In this invention, in step (3), the stirring speed is 100-200 r / min, and the stirring speed can be any specific value among 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, and 200 r / min, or any value within the range of 100-200 r / min.

[0017] According to another aspect of the present invention, the application of the above-described polishing electrolyte or the polishing electrolyte prepared according to the above method in a connecting rod is also provided.

[0018] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention creatively designs a polishing electrolyte. By using a composite additive with specific components and controlling the mass ratio of each component within a specific range, the synergistic effect between the components is optimal. The polishing electrolyte has a suitable viscosity, and a film layer is easily formed on the connecting rod surface. It can effectively control the reaction rate in the chemical polishing process, so that the connecting rod surface is uniformly and regularly dissolved, and the polishing effect of the polishing electrolyte is better.

[0019] (2) The specific compounds in the compound corrosion inhibitor described in this invention have a synergistic effect, which can synergistically improve adsorption stability, surface coverage, and change the adsorption rate. On the one hand, the thiourea molecule contains hydrophobic and hydrophilic groups, which can physically adsorb onto the metal surface to form a dense protective film, thereby reducing the H in the solution. + The sulfur atom in sodium dodecyl sulfonate is difficult to approach the connecting rod surface, thus reducing the corrosion rate of the connecting rod by phosphoric acid and sulfuric acid. On the other hand, the sulfur atom in sodium dodecyl sulfonate is conducive to nucleophilic attack and coordination reaction, and iron ions can form coordination bonds with the π electron cloud on the hexadecylpyridine heterocycle of bromide, resulting in chemisorption and thus improving the corrosion inhibition effect. Through the combined effect of physical adsorption and chemisorption, the composite corrosion inhibitor in this application exhibits excellent corrosion inhibition performance.

[0020] (3) The present invention also provides a method for preparing a polishing electrolyte for connecting rods, the method being simple and easy to operate and suitable for large-scale production. Detailed Implementation

[0021] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0022] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0023] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0024] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0025] This invention provides a polishing electrolyte for connecting rods, comprising the following components: phosphoric acid, sulfuric acid, and composite additives; wherein the composite additives comprise sodium polyphosphate, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol in a mass ratio of 1:4-6:1-2:1-2; and the compound corrosion inhibitor comprises thiourea, hexadecylpyridine bromide, and sodium dodecyl sulfonate in a mass ratio of 1:1.5-2:1.5-2.

[0026] In some embodiments, the volume ratio of phosphoric acid to sulfuric acid is (1.5-2):1.

[0027] In some embodiments, the mass concentration of the composite additive is 10-15 g / L.

[0028] In some embodiments, the TiO2 particles are rutile TiO2 particles.

[0029] In some embodiments, the polyethylene glycol includes one or more of polyethylene glycol 1000 and polyethylene glycol 2000.

[0030] In some embodiments, the TiO2 particles have a particle size of 20-30 nm.

[0031] According to another aspect of the present invention, a method for preparing the above-described polishing electrolyte for connecting rods is also provided, the method comprising the following steps: (1) Preparation of compound corrosion inhibitor: Thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate are mixed in proportion and stirred evenly to obtain the compound corrosion inhibitor; (2) Preparation of composite additive: The composite corrosion inhibitor, sodium polyphosphate, TiO2 particles and polyethylene glycol are mixed in proportion and stirred evenly to obtain the composite additive; (3) Slowly add sulfuric acid to phosphoric acid while stirring, let it stand and cool to room temperature, add the composite additive, mix evenly, and obtain the polishing electrolyte for connecting rod.

[0032] In some embodiments, in step (3), the rate at which sulfuric acid is added is 10-20 L / min.

[0033] In some embodiments, in step (3), the stirring speed is 100-200 r / min.

[0034] According to another aspect of the present invention, the application of the above-described polishing electrolyte or the polishing electrolyte prepared according to the above method in a connecting rod is also provided.

[0035] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0036] Example 1 is the best example.

[0037] The chemical additives used in the embodiments and comparative examples of this invention are all commercially available, and the specific information is as follows: Phosphoric acid: 85%, purchased from Aladdin Reagent Co., Ltd.; Sulfuric acid: 98%, purchased from Aladdin Reagent Co., Ltd.; Sodium polyphosphate: purchased from Aladdin Reagent Co., Ltd.; Rutile TiO2 particles: 20nm in diameter, purchased from Zhongke Keyou Co., Ltd.; Polyethylene glycol 1000, polyethylene glycol 2000, thiourea, hexadecylpyridine bromide, sodium dodecyl sulfonate: purchased from Aladdin Reagent Co., Ltd.

[0038] Example 1 The polishing electrolyte for connecting rods described in this embodiment comprises the following components: phosphoric acid, sulfuric acid, and composite additives; wherein, the composite additives comprise sodium polyphosphate in a mass ratio of 1:5:1.5:1.5, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol 1000; the compound corrosion inhibitor comprises thiourea, hexadecylpyridine bromide, and sodium dodecyl sulfonate in a mass ratio of 1:1.8:1.5; the volume ratio of phosphoric acid to sulfuric acid is 1.5:1; the mass concentration of the composite additives is 12 g / L; and the TiO2 particles are rutile TiO2 particles.

[0039] The method for preparing the polishing electrolyte described in this embodiment includes the following steps: (1) Preparation of compound corrosion inhibitor: Thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate are mixed in proportion and stirred evenly at room temperature to obtain the compound corrosion inhibitor; (2) Preparation of composite additive: The composite corrosion inhibitor, sodium polyphosphate, TiO2 particles and polyethylene glycol are mixed in proportion and stirred evenly to obtain the composite additive; (3) Slowly add 1L of sulfuric acid to 1.5L of phosphoric acid under stirring, let stand and cool to room temperature, add 30g of the composite additive, mix evenly, and obtain the polishing electrolyte for connecting rod; wherein the sulfuric acid is added at a rate of 15L / min and the stirring speed is 150r / min.

[0040] Example 2 The polishing electrolyte for connecting rods described in this embodiment comprises the following components: phosphoric acid, sulfuric acid, and composite additives; wherein, the composite additives comprise sodium polyphosphate, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol 2000 in a mass ratio of 1:4:1:1; the compound corrosion inhibitor comprises thiourea, hexadecylpyridine bromide, and sodium dodecyl sulfonate in a mass ratio of 1:1.5-2:1.5-2; the volume ratio of phosphoric acid to sulfuric acid is 2:1; the mass concentration of the composite additives is 10 g / L; and the TiO2 particles are rutile TiO2 particles.

[0041] The method for preparing the polishing electrolyte described in this embodiment includes the following steps: (1) Preparation of compound corrosion inhibitor: Thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate are mixed in proportion and stirred evenly at room temperature to obtain the compound corrosion inhibitor; (2) Preparation of composite additive: The composite corrosion inhibitor, sodium polyphosphate, TiO2 particles and polyethylene glycol are mixed in proportion and stirred evenly to obtain the composite additive; (3) Slowly add 1L of sulfuric acid to 2L of phosphoric acid under stirring, let stand and cool to room temperature, add 30g of the composite additive, mix evenly, and obtain the polishing electrolyte for connecting rod; wherein the sulfuric acid is added at a rate of 10L / min and the stirring speed is 100r / min.

[0042] Example 3 The polishing electrolyte for connecting rods described in this embodiment comprises the following components: phosphoric acid, sulfuric acid, and composite additives; wherein, the composite additives comprise sodium polyphosphate, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol 1000 in a mass ratio of 1:6:2:2; the compound corrosion inhibitor comprises thiourea, hexadecylpyridine bromide, and sodium dodecyl sulfonate in a mass ratio of 1:1.5-2:1.5-2; the volume ratio of phosphoric acid to sulfuric acid is 1.5:1; the mass concentration of the composite additives is 15 g / L; and the TiO2 particles are rutile TiO2 particles.

[0043] The method for preparing the polishing electrolyte described in this embodiment includes the following steps: (1) Preparation of compound corrosion inhibitor: Thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate are mixed in proportion and stirred evenly at room temperature to obtain the compound corrosion inhibitor; (2) Preparation of composite additive: The composite corrosion inhibitor, sodium polyphosphate, TiO2 particles and polyethylene glycol are mixed in proportion and stirred evenly to obtain the composite additive; (3) Slowly add 1L of sulfuric acid to 1.5L of phosphoric acid under stirring, let stand and cool to room temperature, add 37.5g of the composite additive, mix evenly, and obtain the polishing electrolyte for connecting rod; wherein the sulfuric acid is added at a rate of 20L / min and the stirring speed is 200r / min.

[0044] Comparative Example 1 The preparation method of the polishing electrolyte for the connecting rod in this comparative example is exactly the same as that in Example 1, except that the mass ratio of sodium polyphosphate, compound corrosion inhibitor, TiO2 particles and polyethylene glycol is 1:8:1.5:1.5.

[0045] Comparative Example 2 The preparation method of the polishing electrolyte for the connecting rod in this comparative example is exactly the same as that in Example 1, except that the mass ratio of sodium polyphosphate, compound corrosion inhibitor, TiO2 particles and polyethylene glycol is 1:3:1.5:1.5.

[0046] Comparative Example 3 The preparation method of the polishing electrolyte for the connecting rod in this comparative example is exactly the same as that in Example 1, except that the TiO2 particles are anatase TiO2 particles.

[0047] Comparative Example 4 The preparation method of the polishing electrolyte for the connecting rod in this comparative example is exactly the same as that in Example 1, except that the compound corrosion inhibitor includes thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate in a mass ratio of 1:3:1.5.

[0048] Comparative Example 5 The preparation method of the polishing electrolyte for the connecting rod in this comparative example is exactly the same as that in Example 1, except that the compound corrosion inhibitor includes thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate in a mass ratio of 1:1:1.5.

[0049] Comparative Example 6 The preparation method of the polishing electrolyte for the connecting rod in this comparative example is exactly the same as that in Example 1, except that the compound corrosion inhibitor includes thiourea, hexadecyltrimethylammonium bromide and sodium dodecyl sulfonate in a mass ratio of 1:1.8:1.5.

[0050] Comparative Example 7 The preparation method of the polishing electrolyte for the connecting rod in this comparative example is exactly the same as that in Example 1, except that the volume ratio of phosphoric acid to sulfuric acid is 3:1.

[0051] Application examples After the connecting rod was subjected to 80s of ultrasonic cleaning with a degreasing agent and 80s of ultrasonic cleaning with clean water, it was placed in the polishing electrolyte, with the connecting rod as the anode and the copper plate as the cathode, at a temperature of 40°C and an A / dm².2 Electropolishing was performed for 200 seconds at a current density, followed by ultrasonic cleaning with ethanol solution and drying.

[0052] Performance testing The connecting rods obtained by electropolishing with the polishing electrolytes obtained in Examples 1-3 and Comparative Examples 1-7 were subjected to performance tests according to the following method, and the specific results are shown in Table 1.

[0053] (1) Initial surface roughness: Five test points were randomly selected on the surface of the connecting rod after electropolishing treatment. The surface roughness of the five test points was tested using a roughness tester. The average roughness test value of the five test points was then used as the final result.

[0054] (2) Surface roughness after 10 polishing cycles: The 304 connecting rod samples were continuously polished and electrolyzed 10 times using the polishing electrolytes obtained in Examples 1-3 and Comparative Examples 1-7. Then, 5 test points were randomly selected on the surface of the connecting rod after 10 chemical polishing cycles. The surface roughness of the 5 test points was tested using a roughness meter. The average roughness test value of the 5 test points was then taken as the final result.

[0055] (3) Surface appearance: Observed by the naked eye.

[0056] (4) Gloss: Tested using an X-Rite SP64 spectrophotometer (X-Rite, USA).

[0057] (5) Corrosion resistance: The connecting rods obtained by electropolishing with the polishing electrolytes obtained in Examples 1-3 and Comparative Examples 1-7 were used as working electrodes and Tafel curve tests were performed in 1 mol / L H2SO4 solution at 25°C. The corrosion resistance of the connecting rods after polishing and electropolishing was judged based on the magnitude of corrosion potential and corrosion current.

[0058] Table 1 Performance data of Examples 1-3 and Comparative Examples 1-7 .

[0059] As shown in Table 1, the connecting rods obtained after electropolishing treatment with the polishing electrolytes described in Examples 1-3 have a bright and smooth surface with high gloss, a high corrosion potential, and a low corrosion current, indicating good corrosion resistance. The surface roughness decreases after 10 polishing cycles, indicating that the polishing performance of the electrolyte remains good even after multiple polishing cycles, demonstrating stable performance and reusability. Comparing Example 1 with Comparative Examples 1 and 2, the proportion of the compound corrosion inhibitor in the composite additives in Comparative Examples 1 and 2 is either too high or too low, leading to reduced surface gloss and smoothness of the connecting rods after electropolishing treatment, decreased surface corrosion resistance, and reduced stability of the polishing electrolyte. Comparing Example 1 with Comparative Example 3, the use of anatase TiO2 particles in Comparative Example 3 results in poorer polishing performance of the polishing electrolyte. Comparing Example 1 with Comparative Examples 4 and 5, the proportion of hexadecylpyridine bromide in the compound corrosion inhibitors in Comparative Examples 4 and 5 is either too high or too low, resulting in poorer polishing performance of the obtained polishing electrolytes. A comparison of Example 1 and Comparative Example 6 shows that the use of hexadecyltrimethylammonium bromide instead of hexadecylpyridine bromide in Comparative Example 6 resulted in a poorer polishing effect, indicating a synergistic effect among the three components in the compound corrosion inhibitor of this application. A comparison of Example 1 and Comparative Example 7 shows that the different volume ratios of phosphoric acid and sulfuric acid in Comparative Example 7 resulted in a poor polishing effect of the polishing electrolyte, leading to a decrease in surface gloss after polishing.

[0060] Therefore, this invention creatively designs a polishing electrolyte. By using a composite additive with specific components and controlling the mass ratio of each component within a specific range, the synergistic effect between the components is optimal. The polishing electrolyte has a suitable viscosity, easily forming a film layer on the connecting rod surface, effectively controlling the reaction rate during the chemical polishing process, and ensuring uniform and regular dissolution on the connecting rod surface, resulting in a better polishing effect. The specific compounds in the compound corrosion inhibitor described in this invention have a synergistic effect, which can synergistically improve adsorption stability, coverage, and change the adsorption rate. On the one hand, the thiourea molecule contains both hydrophobic and hydrophilic groups, which can physically adsorb onto the metal surface to form a dense protective film, thereby reducing the H+ in the solution. + The sulfur atom in sodium dodecyl sulfonate is difficult to approach the connecting rod surface, thus reducing the corrosion rate of the connecting rod by phosphoric acid and sulfuric acid. On the other hand, the sulfur atom in sodium dodecyl sulfonate is conducive to nucleophilic attack and coordination reaction. Iron ions can form coordination bonds with the π electron cloud on the hexadecylpyridine heterocycle of bromide, resulting in chemisorption and thus achieving a good corrosion inhibition effect. The combined effect of physical adsorption and chemisorption makes the composite corrosion inhibitor in this application have excellent corrosion inhibition effect.

[0061] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A polishing electrolyte for connecting rods, characterized in that, It is composed of the following components: phosphoric acid, sulfuric acid, and composite additives; wherein, the composite additives are sodium polyphosphate in a mass ratio of 1:5:1.5:1.5, a compound corrosion inhibitor, TiO2 particles, and polyethylene glycol; the compound corrosion inhibitors are thiourea, hexadecylpyridine bromide, and sodium dodecyl sulfonate in a mass ratio of 1:1.8:1.5; the TiO2 particles are rutile TiO2 particles; and the particle size of the TiO2 particles is 20-30 nm. The volume ratio of phosphoric acid to sulfuric acid is (1.5-2):1; the concentration of phosphoric acid is 85%, and the concentration of sulfuric acid is 98%. The mass concentration of the composite additive is 10-15 g / L.

2. The polishing electrolyte for connecting rods according to claim 1, characterized in that, The polyethylene glycol includes one or more of polyethylene glycol 1000 and polyethylene glycol 2000.

3. A method for preparing a polishing electrolyte for connecting rods according to any one of claims 1-2, characterized in that, The method includes the following steps: (1) Preparation of compound corrosion inhibitor: Thiourea, hexadecylpyridine bromide and sodium dodecyl sulfonate are mixed in proportion and stirred evenly to obtain the compound corrosion inhibitor; (2) Preparation of composite additive: The composite corrosion inhibitor, sodium polyphosphate, TiO2 particles and polyethylene glycol are mixed in proportion and stirred evenly to obtain the composite additive; (3) Slowly add sulfuric acid to phosphoric acid while stirring, let it stand and cool to room temperature, add the composite additive, mix evenly, and obtain the polishing electrolyte for connecting rod.

4. The method for preparing a polishing electrolyte for connecting rods according to claim 3, characterized in that, In step (3), the sulfuric acid is added at a rate of 10-20 L / min.

5. The method for preparing a polishing electrolyte for connecting rods according to claim 3, characterized in that, In step (3), the stirring speed is 100-200 r / min.

6. The application of the polishing electrolyte according to any one of claims 1-2 or the polishing electrolyte prepared by the method according to any one of claims 3-5 in a connecting rod.