A green electrochemical polishing slurry and polishing method for additive manufacturing of stainless steel

Abstract

This invention discloses a green electrochemical polishing slurry and polishing method for additive manufacturing of stainless steel, belonging to the field of stainless steel surface treatment technology. The electrochemical polishing slurry comprises an acid, a polyol, glucose, sodium tungstate, and a corrosion inhibitor, wherein phosphoric acid is preferred, and polyaspartic acid is preferred. The polishing method includes surface pretreatment of the additively manufactured stainless steel workpiece, electrochemical polishing treatment, and post-polishing cleaning treatment. This invention utilizes the synergistic effect of sodium tungstate and polyaspartic acid to dynamically control the anodic dissolution interface during polishing, effectively suppressing over-polishing and pitting defects easily caused by the surface heterogeneity of additively manufactured stainless steel. Using the polishing slurry and method provided by this invention, the surface roughness of additively manufactured stainless steel can be significantly reduced, obtaining a bright and smooth high-quality surface. Furthermore, the polishing slurry is environmentally friendly and has significant industrial application value.

Description

Technical Field

[0001] This invention relates to the field of stainless steel surface treatment technology, and in particular to a green electrochemical polishing liquid and polishing method for additive manufacturing of stainless steel. Background Technology

[0002] In the process of advancing towards precision and complexity in high-end manufacturing, additive manufacturing technology, with its disruptive design freedom and excellent material compatibility, has become a core driving force for innovation in the manufacturing industry. As a key technology in this field, laser powder bed fusion technology has achieved high-precision manufacturing of complex components through a precise layer-by-layer deposition mechanism. However, due to the combined effects of challenges in dynamic energy density control, geometric constraints on printing angles, and anisotropic thermal conduction, defects such as surface powder adhesion, molten pool instability and spheroidization, and step effects inevitably occur during the forming process. This results in the surface quality of components failing to meet the stringent service standards of high-end fields such as aerospace and biomedicine, necessitating efficient post-processing for quality optimization.

[0003] In existing post-processing technologies, traditional shot peening and grinding are limited by processing paths and tool accessibility, making it difficult to meet the precision processing requirements of complex additive manufacturing components. Electrochemical polishing technology, with its unique advantages of low internal stress processing and no tool electrode wear, shows significant application potential in the field of metal surface treatment, especially suitable for the synergistic polishing and precision leveling of the inner and outer surfaces of materials. However, the sulfuric acid-phosphate based electrolyte system widely used in the electrochemical polishing of stainless steel currently generates sulfur-containing wastewater that is difficult to treat after use, increasing production costs and posing a serious threat to the ecological environment, which runs counter to the current industrial concepts of green manufacturing and sustainable development. Therefore, developing an electrolyte system that combines high-efficiency polishing performance with environmentally friendly characteristics, as well as a suitable polishing process, has become the key to breaking through the surface quality bottleneck of additively manufactured stainless steel components. Summary of the Invention

[0004] To address the problems existing in the prior art, the main objective of this invention is to propose an electrochemical polishing slurry and polishing method for additive manufacturing of stainless steel.

[0005] This invention provides a green electrochemical polishing slurry for additive manufacturing of stainless steel, comprising a base polishing slurry and sodium tungstate; the base polishing slurry is composed of an acid, a polyol, glucose, and a corrosion inhibitor.

[0006] Preferably, based on 100 parts by weight of the base polishing solution, it contains 40-60 parts by weight of acid, 30-50 parts by weight of polyol, 2-8 parts by weight of glucose and 2-8 parts by weight of corrosion inhibitor.

[0007] Preferably, the concentration of sodium tungstate in the electrochemical polishing solution is 10-20 g / L.

[0008] Preferably, the acid is selected from at least one of sulfuric acid, phosphoric acid, and nitric acid.

[0009] Preferably, the polyol is selected from at least one of ethanol, ethylene glycol, and propylene glycol.

[0010] Preferably, the corrosion inhibitor is selected from at least one of polyaspartic acid, tannic acid, and benzotriazole.

[0011] The present invention also provides an electrochemical polishing method for additive manufacturing stainless steel, comprising the following steps: first, performing surface pretreatment on the additive manufacturing stainless steel; then, using the above-mentioned electrochemical polishing liquid to perform electrochemical polishing treatment on the surface-pretreated additive manufacturing stainless steel; and finally, performing polishing and cleaning treatment on the electrochemically polished additive manufacturing stainless steel.

[0012] Preferably, the surface pretreatment includes: ultrasonically cleaning the additively manufactured stainless steel in acetone, rinsing it with water spray, and finally drying it.

[0013] More preferably, the surface pretreatment includes: placing the additively manufactured stainless steel in acetone, ultrasonically cleaning it for 10-15 minutes at an ultrasonic frequency of 20-50kHz and an ultrasonic power of 200-300W to remove surface oil, then rinsing it with water spray 2-3 times, and finally drying it in a hot air stream at a temperature ≤50℃.

[0014] Preferably, the electrochemical polishing process includes: placing the pretreated additively manufactured stainless steel in the above-mentioned electrochemical polishing solution, using the additively manufactured stainless steel as the anode and a platinum sheet as the cathode, and performing electrochemical polishing.

[0015] Preferably, the electrochemical polishing conditions are as follows: electrochemical polishing voltage of 8-12V, electrochemical polishing temperature of 30-70℃, stirring speed of 500-1200rpm, electrochemical polishing time of 16-24min, and electrode distance of 8-12mm.

[0016] In a further description of the present invention, in the above-mentioned electrochemical polishing process, the pretreated additively manufactured stainless steel is placed in an electrochemical polishing solution, and under continuous stirring, the polishing solution forms a uniform liquid film on the surface of the additively manufactured stainless steel; a dual-electrode system is constructed with the additively manufactured stainless steel as the anode and a platinum sheet as the cathode, a DC voltage is applied, and the anode is driven to dissolve through an electrochemical reaction to complete the electrochemical polishing process.

[0017] Preferably, the post-polishing cleaning process includes: rinsing the electrochemically polished additively manufactured stainless steel with water, then ultrasonically cleaning it in ethanol or acetone, followed by rinsing with water spray, and finally drying it.

[0018] More preferably, the post-polishing cleaning process includes: first rinsing the electrochemically polished additively manufactured stainless steel with water to remove surface acid residue, then placing it in ethanol or acetone for ultrasonic cleaning at an ultrasonic frequency of 20-50kHz and an ultrasonic power of 200-300W for 5-10 minutes to remove residual polishing liquid and adhering products; then rinsing with water spray 2-3 times, and finally drying it in a hot air stream at a temperature ≤50℃.

[0019] Preferably, the additive manufacturing stainless steel material is 316L stainless steel.

[0020] Preferably, the additive manufacturing stainless steel material is 316L stainless steel formed by laser powder bed melting.

[0021] More preferably, the 316L stainless steel formed by laser powder bed melting is formed using an SLM-125 molding equipment with a substrate temperature of 80°C, a laser power of 195W, a scanning speed of 1083mm / s, a scanning spacing of 90μm, a powder layer thickness of 25μm, and a powder size of 15-53μm.

[0022] The beneficial effects of this invention are as follows: 1. Compared with existing technologies, this invention provides a green electrochemical polishing slurry and polishing method for additive manufacturing of stainless steel. It offers an efficient polishing solution for defects unique to the surface of additively manufactured stainless steel components, such as powder adhesion and molten pool boundaries. After polishing using the method provided by this invention, the workpiece surface is bright and smooth, and the surface roughness (Sa) is significantly reduced to below 1μm, fully meeting the stringent requirements for component surface quality in high-end industrial fields.

[0023] 2. Compared with existing technologies, the green electrochemical polishing solution of this invention is composed of acid, polyol, glucose, corrosion inhibitor, and sodium tungstate in a certain proportion. Phosphoric acid is preferred as the main acid, which can generate a viscous phosphate diffusion layer during anodic dissolution to achieve microscopic smoothing. The polyol acts as an organic thickener, increasing the viscosity of the system to enhance the diffusion layer control effect and improve surface wettability. Glucose acts as both a stabilizer and a brightener, also adjusting the viscosity of the electrochemical polishing solution and increasing the brightness of the polished sample. The synergistic use of sodium tungstate and corrosion inhibitor effectively prevents over-dissolution and over-polishing. When this green electrochemical polishing solution is applied to the electrochemical polishing of additively manufactured stainless steel, the synergistic mechanism between the components effectively suppresses over-polishing and pitting defects easily caused by the surface heterogeneity of additively manufactured stainless steel, significantly reducing the surface roughness and obtaining a bright, smooth, high-quality surface. Furthermore, the electrochemical polishing solution used in this invention preferably uses phosphoric acid as the main acid, avoiding the sulfur-containing wastewater treatment problems associated with traditional sulfuric acid-phosphoric acid systems, reducing environmental pollution at the source, and representing an environmentally friendly green polishing technology solution. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 These are schematic diagrams illustrating additive manufacturing of stainless steel in embodiments and comparative examples of the present invention; Figure 2 The images shown are scanning electron microscope (SEM) images and 3D morphology images of Examples 1-3 of this invention before electrochemical polishing. Figure 3 The images shown are scanning electron microscope (SEM) images and 3D morphology images of the electrochemically polished components in Examples 1-3 of this invention. Figure 4 Examples 1-3 of this invention show the changes in surface roughness before and after electrochemical polishing; Figure 5 These are confocal images and 3D morphology diagrams of Comparative Examples 1-3 after electrochemical polishing, as shown in this invention. Figure 6 These are confocal images and 3D morphology diagrams of Comparative Examples 4-6 after electrochemical polishing, as shown in this invention. Figure 7 These are confocal images and 3D morphology diagrams of the electrochemical polishing processes in Comparative Examples 7-9 of this invention. Figure 8 These are confocal images and 3D morphology diagrams of Comparative Examples 10-12 after electrochemical polishing, as shown in this invention. Figure 9 These are confocal images and 3D morphology diagrams of comparative examples 13-15 after electrochemical polishing, as shown in this invention. Figure 10 These are confocal images and 3D morphology diagrams of comparative examples 16-18 after electrochemical polishing, as shown in this invention. Figure 11 These are confocal images and 3D morphology diagrams of comparative examples 18-21 after electrochemical polishing, as shown in this invention.

[0026] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0027] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

[0028] This invention provides a green electrochemical polishing slurry for additive manufacturing of stainless steel, comprising a base polishing slurry and sodium tungstate; the base polishing slurry is composed of an acid, a polyol, glucose, and a corrosion inhibitor.

[0029] Preferably, based on 100 parts by weight of the base polishing solution, it contains 40-60 parts by weight of acid, 30-50 parts by weight of polyol, 2-8 parts by weight of glucose and 2-8 parts by weight of corrosion inhibitor.

[0030] Preferably, the concentration of sodium tungstate in the electrochemical polishing solution is 10-20 g / L.

[0031] Specifically, the concentration of sodium tungstate in the electrochemical polishing solution can be any one of 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L, 20 g / L, or any combination thereof.

[0032] Preferably, the acid is selected from at least one of sulfuric acid, phosphoric acid, and nitric acid.

[0033] Preferably, the polyol is selected from at least one of ethanol, ethylene glycol, and propylene glycol.

[0034] Preferably, the corrosion inhibitor is selected from at least one of polyaspartic acid, tannic acid, and benzotriazole.

[0035] In the electrochemical polishing solution of this invention, acid serves as both an electrolyte and a dissolution driving force. Phosphoric acid is preferred in this invention because it provides the strong acidic environment and hydrogen ions necessary for electrochemical polishing. This is the basis for initiating and maintaining the metal dissolution process of the anode (additive manufacturing stainless steel). During the electrochemical polishing process, phosphoric acid can form a viscous phosphate diffusion layer on the anode surface, which is a key physicochemical barrier for achieving microscopic smoothing and brightening.

[0036] In the electrochemical polishing slurry of this invention, the polyol acts as a viscosity modifier and medium stabilizer. Its addition significantly increases the overall viscosity of the polishing slurry, which helps stabilize the phosphate diffusion layer formed by phosphoric acid during the polishing process, weakens the interference of solution convection on the dissolution process, and thus makes the removal of metal more uniform at the microscopic level. In addition, it can also improve the wettability of the polishing slurry on the surface of additively manufactured stainless steel, thereby improving the polishing effect.

[0037] In the electrochemical polishing slurry of this invention, glucose serves as a brightener and auxiliary stabilizer. The addition of glucose can further adjust the viscosity of the polishing slurry. During the electrochemical polishing process, its reducing properties and potential complexing effects help to obtain a brighter and smoother surface morphology, improving the visual and functional quality after polishing.

[0038] In this invention, the electrochemical polishing solution is composed of sodium tungstate, corrosion inhibitor polyaspartic acid, acid, polyol, and glucose, providing a strongly acidic, high-viscosity polishing environment. During the electrochemical polishing process, tungstate ions generated from the dissolution of sodium tungstate participate in the formation of a dense, tungsten-rich oxide film on the anode surface. This oxide film forms more rapidly in raised areas with higher current densities, dynamically inhibiting excessively rapid dissolution in these areas and thus macroscopically preventing the formation of a fish-scale-like over-polishing morphology. Simultaneously, polyaspartic acid, with its abundant polar groups, strongly adsorbs onto microscopic defects and grain boundaries on the surface of additively manufactured stainless steel, forming a physicochemical adsorption barrier layer that effectively inhibits the generation and propagation of pitting corrosion. When used synergistically, the inorganic oxide film constructed by sodium tungstate provides macroscopic leveling, while the organic adsorption layer formed by polyaspartic acid fills the protective gaps at microscopic defects. This inorganic-organic composite layer can adaptively respond to the inherent micro-inhomogeneities of additively manufactured stainless steel surfaces, enabling the electrochemical polishing process to remove surface unevenness while avoiding the generation of new defects. It effectively prevents over-dissolution and over-polishing, ultimately obtaining a high-quality additively manufactured stainless steel surface with high gloss, low roughness, and no over-polishing or pitting.

[0039] The present invention also provides an electrochemical polishing method for additive manufacturing stainless steel, comprising the following steps: first, performing surface pretreatment on the additive manufacturing stainless steel; then, using the above-mentioned electrochemical polishing liquid to perform electrochemical polishing treatment on the surface-pretreated additive manufacturing stainless steel; and finally, performing polishing and cleaning treatment on the electrochemically polished additive manufacturing stainless steel.

[0040] Preferably, the surface pretreatment includes: ultrasonically cleaning the additively manufactured stainless steel in acetone, rinsing it with water spray, and finally drying it.

[0041] More preferably, the surface pretreatment includes: placing the additively manufactured stainless steel in acetone, ultrasonically cleaning it for 10-15 minutes at an ultrasonic frequency of 20-50kHz and an ultrasonic power of 200-300W to remove surface oil, then rinsing it with water spray 2-3 times, and finally drying it in a hot air stream at a temperature ≤50℃.

[0042] Preferably, the electrochemical polishing process includes: placing the pretreated additively manufactured stainless steel in the above-mentioned electrochemical polishing solution, using the additively manufactured stainless steel as the anode and a platinum sheet as the cathode, and performing electrochemical polishing.

[0043] Preferably, the electrochemical polishing conditions are as follows: electrochemical polishing voltage of 8-12V, electrochemical polishing temperature of 30-70℃, stirring speed of 500-1200rpm, electrochemical polishing time of 16-24min, and electrode distance of 8-12mm.

[0044] Specifically, the electrochemical polishing voltage can be any one or any two of 8V, 9V, 10V, 11V, and 12V; the electrochemical polishing temperature can be any one or any two of 30℃, 40℃, 50℃, 60℃, and 70℃; the stirring speed can be any one or any two of 500rpm, 800rpm, 1000rpm, and 1200rpm; the electrochemical polishing time can be any one or any two of 16min, 18min, 20min, 22min, and 24min; and the electrode distance can be any one or any two of 8mm, 9mm, 10mm, 11mm, and 12mm.

[0045] In a further description of the present invention, in the above-mentioned electrochemical polishing process, the pretreated additively manufactured stainless steel is placed in an electrochemical polishing solution, and under continuous stirring, the polishing solution forms a uniform liquid film on the surface of the additively manufactured stainless steel; a dual-electrode system is constructed with the additively manufactured stainless steel as the anode and a platinum sheet as the cathode, a DC voltage is applied, and the anode is driven to dissolve through an electrochemical reaction to complete the electrochemical polishing process.

[0046] Preferably, the post-polishing cleaning process includes: rinsing the electrochemically polished additively manufactured stainless steel with water, then ultrasonically cleaning it in ethanol or acetone, followed by rinsing with water spray, and finally drying it.

[0047] More preferably, the post-polishing cleaning process includes: first rinsing the electrochemically polished additively manufactured stainless steel with water to remove surface acid residue, then placing it in ethanol or acetone for ultrasonic cleaning at an ultrasonic frequency of 20-50kHz and an ultrasonic power of 200-300W for 5-10 minutes to remove residual polishing liquid and adhering products; then rinsing with water spray 2-3 times, and finally drying it in a hot air stream at a temperature ≤50℃.

[0048] Preferably, the additive manufacturing stainless steel material is 316L stainless steel.

[0049] Preferably, the additive manufacturing stainless steel material is 316L stainless steel formed by laser powder bed melting.

[0050] More preferably, the 316L stainless steel formed by laser powder bed melting is formed using an SLM-125 molding equipment with a substrate temperature of 80°C, a laser power of 195W, a scanning speed of 1083mm / s, a scanning spacing of 90μm, a powder layer thickness of 25μm, and a powder size of 15-53μm.

[0051] Example 1 An electrochemical polishing method for additive manufacturing of stainless steel includes the following steps: First, immerse the 316L stainless steel workpiece with a printing angle of 45° in anhydrous acetone, and then... (The sentence is incomplete and requires more context to translate accurately.) 2 The surface to be treated was subjected to 50 mL of anhydrous acetone and ultrasonic cleaning for 10 min at an ultrasonic frequency of 40 kHz and an ultrasonic power of 270 W to remove surface oil. Then, it was rinsed three times with water spray and finally dried in a hot air stream at a temperature of 50℃ to obtain the pretreated stainless steel workpiece. The pretreated stainless steel workpiece was then placed in an electrochemical polishing solution. The workpiece dimensions were 10mm × 10mm × 2mm, and the volume of the electrochemical polishing solution was 100mL. Using the stainless steel workpiece as the anode and a platinum sheet as the cathode, electrochemical polishing was performed for 20 minutes at a temperature of 50℃, an electrode distance of 10mm, a voltage of 10V, and a stirring speed of 800rpm to obtain the electrochemically polished stainless steel workpiece. The electrochemical polishing solution consisted of a base polishing solution and sodium tungstate. Based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution consisted of the following components: 40 parts by mass of ethylene glycol, 50 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid. The concentration of sodium tungstate in the electrochemical polishing solution was 14g / L. Finally, the additively manufactured stainless steel after electrochemical polishing is first rinsed with water to remove surface acid residue, and then placed in anhydrous acetone, per 1 cm 2 The surface to be treated was subjected to 50 mL of anhydrous acetone and ultrasonic cleaning for 10 min at an ultrasonic frequency of 40 kHz and an ultrasonic power of 270 W to remove residual polishing liquid and adhering products; then rinsed with water three times and finally dried in a hot air stream at a temperature of 50 °C.

[0052] The surface morphology of the stainless steel workpiece before polishing in this embodiment is as follows: Figure 2 As shown in (a), the surface morphology of the polished stainless steel workpiece is as follows: Figure 3 As shown in (a); the surface roughness change of the stainless steel workpiece before and after electrochemical polishing is as follows: Figure 4 As shown.

[0053] Example 2 This embodiment provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation in Embodiment 1, except that a 316L stainless steel workpiece with a printing angle of 60° is used.

[0054] The surface morphology of the stainless steel workpiece before polishing in this embodiment is as follows: Figure 2 As shown in (b), the surface morphology of the polished stainless steel workpiece is as follows: Figure 3 As shown in (b); the surface roughness change of the stainless steel workpiece before and after electrochemical polishing is as follows: Figure 4 As shown.

[0055] Example 3 This embodiment provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation in Embodiment 1, except that a 316L stainless steel workpiece with a printing angle of 90° is used.

[0056] The surface morphology of the stainless steel workpiece before polishing in this embodiment is as follows: Figure 2 As shown in (c), the surface morphology of the polished stainless steel workpiece is as follows: Figure 3 As shown in (c); the surface roughness change of the stainless steel workpiece before and after electrochemical polishing is as follows: Figure 4 As shown.

[0057] Comparative Example 1 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 40 parts by mass of ethylene glycol and 60 parts by mass of phosphoric acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0058] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 5 As shown in (a), the surface exhibits a fish-scale morphology, indicating over-polishing, with a roughness Sa of 5.4 μm.

[0059] Comparative Example 2 This comparative example provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation of Example 1, except that: 316L stainless steel with a printing angle of 60° is used; the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 40 parts by mass of ethylene glycol and 60 parts by mass of phosphoric acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0060] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 5 As shown in (b), the surface exhibits a fish-scale morphology, indicating over-polishing, with a roughness Sa of 4.0 μm.

[0061] Comparative Example 3 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: 316L stainless steel with a printing angle of 90° is used, and the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 40 parts by mass of ethylene glycol and 60 parts by mass of phosphoric acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0062] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 5 As shown in (c), the surface exhibits a fish-scale morphology, indicating over-polishing, with a roughness Sa of 4.1 μm.

[0063] Comparative Example 4 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 40 parts by mass of ethylene glycol, 50 parts by mass of phosphoric acid, and 10 parts by mass of glucose; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0064] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 6 As shown in (a).

[0065] Comparative Example 5 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: 316L stainless steel with a printing angle of 60° is used; the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 40 parts by mass of ethylene glycol, 50 parts by mass of phosphoric acid, and 10 parts by mass of glucose; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0066] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 6 As shown in (b).

[0067] Comparative Example 6 This comparative example provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation of Example 1, except that: 316L stainless steel with a printing angle of 90° is used; the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 40 parts by mass of ethylene glycol, 50 parts by mass of phosphoric acid, and 10 parts by mass of glucose; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0068] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 6 As shown in (c).

[0069] Comparative Example 7 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 35 parts by mass of ethylene glycol, 60 parts by mass of phosphoric acid, and 5 parts by mass of glucose; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0070] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 7 As shown in (a).

[0071] Comparative Example 8 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: 316L stainless steel with a printing angle of 60° is used, and the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 35 parts by mass of ethylene glycol, 60 parts by mass of phosphoric acid, and 5 parts by mass of glucose; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0072] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 7 As shown in (b).

[0073] Comparative Example 9 The difference from Example 1 is that, This comparative example provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation of Example 1, except that: 316L stainless steel with a printing angle of 90° is used; the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 35 parts by mass of ethylene glycol, 60 parts by mass of phosphoric acid, and 5 parts by mass of glucose; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0074] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 7 As shown in (c).

[0075] Comparative Example 10 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 80 parts by mass of ethylene glycol, 10 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0076] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 8 As shown in (a).

[0077] Comparative Example 11 This comparative example provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation of Example 1, except that: 316L stainless steel with a printing angle of 60° is used; the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 80 parts by mass of ethylene glycol, 10 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0078] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 8 As shown in (b).

[0079] Comparative Example 12 This comparative example provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation of Example 1, except that: 316L stainless steel with a printing angle of 90° is used; the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 80 parts by mass of ethylene glycol, 10 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0080] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 8 As shown in (c).

[0081] Comparative Example 13 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0082] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 9 As shown in (a).

[0083] Comparative Example 14 The difference from Example 1 is that, The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: 316L stainless steel with a printing angle of 60° is used, and the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0084] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 9 As shown in (b).

[0085] Comparative Example 15 This comparative example provides an electrochemical polishing method for additive manufacturing of stainless steel, which is basically the same as the operation of Example 1, except that: 316L stainless steel with a printing angle of 90° is used; the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0086] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 9 As shown in (c).

[0087] Comparative Example 16 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 8 g / L.

[0088] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 10 As shown in (a).

[0089] Comparative Example 17 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid; the concentration of sodium tungstate in the electrochemical polishing solution is 22 g / L.

[0090] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 10 As shown in (b).

[0091] Comparative Example 18 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that the electrochemical polishing liquid is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of polyaspartic acid, based on a total mass of 100 parts by mass of the electrochemical polishing liquid.

[0092] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 10 As shown in (c).

[0093] Comparative Example 19 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, and 10 parts by mass of glucose; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0094] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 11 As shown in (a).

[0095] Comparative Example 20 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of thiourea; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0096] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 11 As shown in (b).

[0097] Comparative Example 21 The electrochemical polishing method for additive manufacturing of stainless steel provided in this comparative example is basically the same as that in Example 1, except that: the electrochemical polishing solution is composed of a base polishing solution and sodium tungstate; based on a total mass of 100 parts by mass of the base polishing solution, the base polishing solution is composed of the following components: 10 parts by mass of ethylene glycol, 80 parts by mass of phosphoric acid, 5 parts by mass of glucose, and 5 parts by mass of hexamethylenetetramine; the concentration of sodium tungstate in the electrochemical polishing solution is 14 g / L.

[0098] The surface morphology of the polished stainless steel workpiece in this comparative example is as follows: Figure 11 As shown in (c).

[0099] It should be noted that the study on the electrochemical polishing characteristics of the 316L stainless steel workpiece formed by laser powder bed melting in this invention is based on typical angle models of 45°, 60° and 90°. Figure 1 This is a schematic diagram of the printing process. The printing angle described is merely an illustrative example. The electrochemical polishing liquid and polishing method proposed in this invention are applicable to the polishing of stainless steel surfaces at any angle in additive manufacturing, including but not limited to 45° inclined surfaces, 60° slope surfaces, and 90° vertical surfaces, and have wide engineering applicability.

[0100] Figure 2 The images shown are scanning electron microscope (SEM) images and 3D morphology images of Examples 1-3 before electrochemical polishing. Figure 2 It can be seen that before electrochemical polishing, the stainless steel surface in Examples 1-3 all showed defects such as unmelted powder, adhered powder, and surface protrusions. Among them, Example 1 ( Figure 2 (a) is 45°, and a large number of protrusions and powder clusters appear on the surface. Example 2 ( Figure 2 (b) is 60°, and partially molten powder appears on the surface, Example 3 ( Figure 2 (c) shows a large amount of unmelted powder on the 90° side.

[0101] Figure 3 The images shown are scanning electron microscope (SEM) images and 3D morphology images of the electrochemically polished components in Examples 1-3. Figure 3 As can be seen, after electrochemical polishing in Examples 1-3, the stainless steel surface is smooth and flat with minimal undulations. Defects such as adhering powder and protrusions on the surfaces of the three types of stainless steel (45°, 60°, and 90°) were successfully removed, resulting in a smooth surface.

[0102] Figure 4 The surface roughness changes before and after electrochemical polishing in Examples 1-3 are represented by the following data: Figure 4 It can be seen that after electrochemical polishing, the surface roughness of Examples 1-3 was reduced to below 1μm, meeting the requirements for industrial use (≤1μm).

[0103] Figure 5For comparative examples 1-3, the confocal images and 3D morphology images after electrochemical polishing are provided by... Figure 5 It is known that when the base polishing solution in the electrochemical polishing slurry consists of ethylene glycol and phosphoric acid, after 20 minutes of polishing at printing angles of 45°, 60°, and 90° on 316L stainless steel workpieces, confocal microscopy revealed typical over-polishing defects on their surfaces. These defects included regularly arranged fish-scale-like protrusions in localized areas and pitting corrosion in some areas. Analysis indicates that this phenomenon stems from a dual effect caused by the increased proportion of phosphoric acid: firstly, high-concentration phosphoric acid significantly increases the difference in current density distribution on the workpiece surface, leading to uneven metal dissolution rates in different areas; secondly, the large number of bubbles generated during polishing are difficult to escape in the high-viscosity electrolyte, forming a bubble film covering the surface, further exacerbating localized dissolution inhomogeneity, and ultimately leading to surface morphology deterioration.

[0104] Figure 6 To illustrate the confocal images and 3D morphology diagrams after electrochemical polishing in Comparative Examples 4-6, the images were created by... Figure 6 It was found that when sodium tungstate and polyaspartic acid were lacking in the polishing solution, the stainless steel surface exhibited significant uneven polishing and numerous pitting corrosion. Analysis indicated that this was due to the lack of synergistic regulation from sodium tungstate and polyaspartic acid, which prevented the formation of an effective composite protective layer on the anode surface. This resulted in uncontrolled dissolution rates in highly active areas of the additively manufactured stainless steel surface, leading to excessive local dissolution and pitting corrosion, while insufficient dissolution in less active areas ultimately resulted in uneven surface polishing.

[0105] Figure 7 The images shown are confocal images and 3D morphology diagrams of Comparative Examples 7-9 after electrochemical polishing. Comparative Examples 7-9 have a higher phosphoric acid content and a lower ethylene glycol content in their polishing solutions, and no polyaspartic acid corrosion inhibitor was added. Figure 7 It is evident that the stainless steel surface exhibits localized protrusions and depressions, resulting in poor leveling. This may be due to excessively high phosphoric acid content leading to rapid dissolution, insufficient ethylene glycol content resulting in inadequate viscosity, and a lack of adsorption protection from polyaspartic acid, all of which exacerbate selective dissolution and make it difficult to obtain a smooth and even surface.

[0106] Figure 8 The confocal images and 3D morphology diagrams after electrochemical polishing of Comparative Example 10-12 are produced by... Figure 8 It can be seen that a small amount of undissolved powder remains on the stainless steel surface, and the original protruding structure has not been significantly eliminated. This is mainly because as the ethylene glycol content increases, the solution viscosity increases accordingly, making it easier to adhere to the sample surface, thereby reducing the dissolution rate.

[0107] Figure 9 For comparative examples 13-15, the confocal images and 3D morphology images after electrochemical polishing are provided by... Figure 9It can be seen that there is obvious over-polishing on the stainless steel surface. Although the adhering powder is removed, the surface protrusions are not eliminated but increased, and significant pitting corrosion appears. This is because the phosphoric acid concentration in the polishing solution is too high, which leads to excessive corrosion of the stainless steel surface.

[0108] Figure 10 For comparative examples 16-18, the confocal images and 3D morphology images after electrochemical polishing are provided by... Figure 10 It is evident that when the amount of sodium tungstate added deviates from the preferred range of this invention or is absent, the stainless steel surface still exhibits obvious local protrusions, depressions, and uneven dissolution. The surface roughness of Comparative Examples 16-18 are 6.2 μm, 6.0 μm, and 6.7 μm, respectively, significantly higher than that of the Example samples (where surface roughness is reduced to below 1 μm). This indicates that when the sodium tungstate content is too low, it is difficult to form an effective interface control effect and cannot sufficiently inhibit the rapid dissolution of local active areas; when the sodium tungstate content is too high, it may affect the uniformity of the anodic dissolution process, leading to a decrease in surface leveling effect. Therefore, sodium tungstate needs to be controlled within a suitable concentration range to synergistically inhibit over-polishing and pitting defects with the corrosion inhibitor.

[0109] Figure 11 To illustrate the surface morphology of Comparative Examples 19-21 after electrochemical polishing, by... Figure 11 It is evident that when polyaspartic acid is lacking in the polishing slurry, or when other conventional corrosion inhibitors such as thiourea and hexamethylenetetramine are used to replace polyaspartic acid, although some adhered powder and protrusions on the stainless steel surface are removed, many local residual protrusions, pits, and groove-like dissolution traces still remain. The surface roughness of Comparative Examples 19-21 is 4.2 μm, 4.5 μm, and 4.8 μm, respectively, indicating relatively high surface roughness and failing to achieve the desired polishing effect. This demonstrates that polyaspartic acid is irreplaceable in the polishing slurry system of this invention; it can form an effective synergistic effect with sodium tungstate, while other conventional corrosion inhibitors cannot achieve the same technical effect. Only by using polyaspartic acid as a corrosion inhibitor can the localized excessive dissolution of highly active areas on the surface of additively manufactured stainless steel be better suppressed, thus improving polishing uniformity.

[0110] In summary, the present invention employs an electrochemical polishing slurry with a specific composition to electrochemically polish additively manufactured stainless steel, achieving a good polishing effect and successfully reducing the surface roughness of stainless steel workpieces to meet industrial application requirements, namely, a surface roughness ≤1μm.

[0111] In summary, this invention addresses the unique surface defects of additively manufactured stainless steel components, such as powder adhesion and molten pool boundaries, by providing a green electrochemical polishing slurry and polishing method for additively manufactured stainless steel. The green electrochemical polishing slurry of this invention is composed of acid, polyol, glucose, corrosion inhibitor, and sodium tungstate in a specific ratio. When applied to the electrochemical polishing of additively manufactured stainless steel, the synergistic mechanism among the components effectively suppresses over-polishing and pitting defects easily caused by the surface heterogeneity of additively manufactured stainless steel, significantly reducing the surface roughness and obtaining a bright, smooth, high-quality surface. After polishing, the workpiece surface is bright and smooth, with the surface roughness (Sa) significantly reduced to below 1 μm, fully meeting the stringent surface quality requirements of high-end industrial fields. Furthermore, the electrochemical polishing slurry used in this invention preferably uses phosphoric acid as the main acid, avoiding the sulfur-containing wastewater treatment problems associated with traditional sulfuric acid-phosphoric acid systems, thus possessing environmentally friendly characteristics and significant industrial application value in the field of additively manufactured stainless steel surface treatment.

[0112] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A green electrochemical polishing slurry for additive manufacturing of stainless steel, characterized in that, It contains a base polishing slurry and sodium tungstate; the base polishing slurry is composed of acid, polyol, glucose and corrosion inhibitor.

2. The green electrochemical polishing slurry for additive manufacturing of stainless steel according to claim 1, characterized in that, Based on 100 parts by weight of the base polishing solution, it contains 40-60 parts by weight of acid, 30-50 parts by weight of polyol, 2-8 parts by weight of glucose and 2-8 parts by weight of corrosion inhibitor.

3. The green electrochemical polishing slurry for additive manufacturing of stainless steel according to claim 1, characterized in that, The concentration of sodium tungstate in the electrochemical polishing solution is 10-20 g / L.

4. The green electrochemical polishing slurry for additive manufacturing of stainless steel according to claim 1 or 2, characterized in that, The acid is selected from at least one of sulfuric acid, phosphoric acid, and nitric acid.

5. The green electrochemical polishing slurry for additive manufacturing of stainless steel according to claim 1 or 2, characterized in that, The polyol is selected from at least one of ethanol, ethylene glycol, and propylene glycol.

6. The green electrochemical polishing slurry for additive manufacturing of stainless steel according to claim 1 or 2, characterized in that, The corrosion inhibitor is selected from at least one of polyaspartic acid, tannic acid, and benzotriazole.

7. An electrochemical polishing method for additive manufacturing of stainless steel, characterized in that, Includes the following steps: First, the additively manufactured stainless steel is pretreated on the surface. Then, the pretreated additively manufactured stainless steel is electrochemically polished using the electrochemical polishing liquid according to any one of claims 1-6. Finally, the electrochemically polished additively manufactured stainless steel is cleaned after polishing.

8. The method according to claim 7, characterized in that, The surface pretreatment includes: ultrasonic cleaning of the additively manufactured stainless steel in acetone, followed by rinsing with water spray, and finally drying.

9. The method according to claim 7, characterized in that, The electrochemical polishing conditions are as follows: electrochemical polishing voltage is 8-12V, electrochemical polishing temperature is 30℃-70℃, stirring speed is 500rpm-1200rpm, electrochemical polishing time is 16min-24min, and electrode distance is 8mm-12mm.

10. The method according to claim 7, characterized in that, The post-polishing cleaning process includes: rinsing the electrochemically polished additively manufactured stainless steel with water, then ultrasonically cleaning it in ethanol or acetone, followed by rinsing with water spray, and finally drying it.

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