Electropolishing method for inconel substrates

Abstract

This application provides an electropolishing method for Invar alloy substrates, specifically tailored to the surface characteristics of Invar alloy substrates thinned by ferric chloride reduction. The method involves using the Invar alloy substrate to be treated as the anode and a pure lead plate as the cathode, simultaneously immersing both the anode and cathode in an electrolytic tank containing an electrolyte for electropolishing. The electrolyte comprises phosphoric acid, sulfuric acid, malic acid, ethylene glycol, sodium dodecylbenzenesulfonate, and deionized water in a volume ratio of 6:1:1:1:0.5:0.5. Electropolishing the Invar alloy substrate thinned by ferric chloride using the above electrolyte composition and ratio yields an Invar alloy substrate with excellent surface quality. After polishing, the surface gloss of the Invar alloy substrate is increased to ≥92 GU, exhibiting a uniform and bright mirror-like effect.

Description

Technical Field

[0001] This application relates to the field of precision surface treatment technology for metallic materials, and more specifically, to an electropolishing method for an Invar alloy substrate. Background Technology

[0002] Invar alloy (iron-nickel alloy) substrate has an extremely low coefficient of thermal expansion (≤1.5×10⁻⁶ at 20℃-100℃). -6 In the manufacture of precision structural components, thinning processes are necessary to achieve accurate dimensional control. Ferric chloride solution is a commonly used chemical thinning agent for Invar alloy substrates due to its stable thinning rate and high dimensional accuracy. However, there are significant technical challenges in the ferric chloride thinning process:

[0003] 1. Ferric chloride is a strong oxidizing etchant. After thinning, uneven corrosion pitting, micro-pits, and residual etching marks easily form on the surface of the tile alloy substrate, resulting in a surface roughness Ra as high as 0.8μm-1.5μm, and no obvious luster; 2. After thinning, residual Fe on the surface of the tile alloy substrate... 3+ Cl - Plasma can easily cause subsequent oxidation and discoloration, further deteriorating the surface appearance; 3. Existing general electropolishing processes are not optimized for the surface state after "thinning with ferric chloride". The electrolyte has poor compatibility with residual ions, which can easily lead to uneven polishing, grain boundary corrosion and other problems. It cannot effectively improve the gloss and may even damage the dimensional accuracy after thinning.

[0004] Therefore, there is an urgent need to develop a dedicated electropolishing method that adapts to the surface characteristics of Invar alloy substrates after ferric chloride thinning, so as to efficiently improve the surface gloss without affecting dimensional accuracy and meet the requirements of precision components. Summary of the Invention

[0005] This application provides an electropolishing method for Invar alloy substrates, a dedicated electropolishing method adapted to the surface characteristics of Invar alloy substrates thinned by ferric chloride. This method optimizes the electrolyte composition and its ratio to efficiently improve surface gloss without affecting dimensional accuracy, meeting the requirements for precision components. The technical solution of this application is as follows:

[0006] This application provides an electropolishing method for an Invar alloy substrate to improve the surface gloss of the Invar alloy substrate, including:

[0007] The Invar alloy substrate to be treated is used as the anode, and a pure lead plate is used as the cathode. The anode and the cathode are simultaneously immersed in an electrolytic cell containing electrolyte to electropolish the Invar alloy substrate to be treated.

[0008] The electrolyte comprises phosphoric acid, sulfuric acid, malic acid, ethylene glycol, sodium dodecylbenzenesulfonate, and deionized water, and is prepared in a volume ratio of phosphoric acid: sulfuric acid: malic acid: ethylene glycol: sodium dodecylbenzenesulfonate: deionized water = 6:1:1:1:0.5:0.5.

[0009] In one embodiment, during the electropolishing process: the energizing frequency between the anode and the cathode is 50 Hz, and the current density of the electrolyte in the electrolytic cell is 18 A / dm³. 2 -28A / dm 2 Electrolysis temperature 45℃-60℃, polishing time 6min-10min.

[0010] In one embodiment, the distance between the anode and the cathode is 50mm-150mm, and magnetic stirring is used during the electropolishing process to ensure uniform electrolyte concentration.

[0011] In one embodiment, before electropolishing the Invar alloy substrate to be processed, a pretreatment step is further included;

[0012] The preprocessing steps include:

[0013] S10a, using an alkaline slag removal solution to remove residual ferric chloride etching products from the surface of the Invar alloy substrate to be treated, wherein the ferric chloride etching products include: ferric hydroxide and chloride ions; the slag removal solution includes: sodium hydroxide with a concentration of 2%, the treatment temperature of the slag removal solution is 40℃~50℃, and the treatment time of the slag removal solution is 2min.

[0014] S10b, the Invar alloy substrate to be treated after alkaline slag removal is neutralized and surface activated using a weak acid solution; wherein, the weak acid solution is an aqueous acetic acid solution with a volume concentration of 3%-5%, and the treatment is carried out at room temperature for 1-3 minutes;

[0015] S10c, the neutralized Invar alloy substrate is ultrasonically cleaned using multi-stage deionized water; wherein the ultrasonic frequency is 40 kHz, and the cleaning time for each stage is 3-5 minutes.

[0016] In one embodiment, after electropolishing the Invar alloy substrate to be treated, the method further includes a post-processing step.

[0017] S30a is initially rinsed with flowing deionized water, and then placed in deionized water with a resistivity ≥15 MΩ·cm for ultrasonic cleaning at a frequency of 40 kHz.

[0018] S30b, vacuum drying treatment, wherein the process conditions for vacuum drying treatment are: vacuum degree not higher than 1×10⁻⁶.-2 Pa, drying temperature is 60℃-80℃, drying time is 20 minutes-40 minutes.

[0019] In one embodiment, the thickness of the Invar alloy substrate to be treated is 0.6mm-1.2mm, and the gloss of the Invar alloy substrate to be treated after electropolishing is increased to greater than 90GU.

[0020] In one embodiment, the Invar alloy substrate to be treated is an Invar alloy thinned using a ferric chloride solution, wherein the nickel content in the Invar alloy is 35%-37%.

[0021] In one embodiment, the electropolishing method for the Invar alloy substrate further includes:

[0022] As the number of electropolishing cycles increases, the change in the specific gravity of phosphoric acid in the electrolyte is measured. Based on the change in the specific gravity of phosphoric acid, a pre-prepared concentrated mother liquor is added to restore the specific gravity of phosphoric acid to the initial set value.

[0023] In one embodiment, the method further includes: performing a phosphoric acid concentration titration analysis on the electrolyte.

[0024] The concentration of free phosphoric acid was accurately determined using acid-base titration.

[0025] If the free phosphoric acid concentration is lower than 15%-20% of the initial value, calculate and add pure phosphoric acid.

[0026] After adding the pure phosphoric acid, the mixture was stirred thoroughly, and the specific gravity of the phosphoric acid in the electrolyte was measured again.

[0027] In one embodiment, the method further includes: installing an acid-resistant pump and a filter element with a precision of 1-5 micrometers in the electrolytic cell for 24-hour continuous circulation filtration.

[0028] The solution provided in this application has the following beneficial effects:

[0029] 1. The electropolishing method for Invar alloy substrate provided in this application uses an electrolyte with a volume ratio of phosphoric acid: sulfuric acid: malic acid: ethylene glycol: sodium dodecylbenzenesulfonate: deionized water = 6:1:1:1:0.5:0.5. This composition and ratio, when used to electropolish Invar alloy substrate thinned with ferric chloride, significantly improves the gloss of the substrate. The surface gloss of the Invar alloy substrate is increased from matte (≤20 GU) to mirror gloss (≥92 GU, conforming to ASTM D523 standard), resulting in a uniformly bright mirror-like surface.

[0030] Electropolishing of the Invar alloy substrate thinned by ferric chloride using the above-mentioned electrolyte composition and ratio yields an Invar alloy substrate with excellent surface quality. The surface roughness Ra after polishing is ≤0.03μm, completely eliminating pitting and etching marks caused by ferric chloride thinning, and eliminating new defects such as grain boundary corrosion and pitting.

[0031] Electropolishing the Invar alloy substrate thinned by ferric chloride using the above-mentioned electrolyte composition and ratio ensures that the dimensions and properties of the Invar alloy substrate are not damaged. Electropolishing removes only 0.5μm-1μm of surface layer thickness, which does not affect the dimensional accuracy of the thinned Invar alloy (dimensional deviation ≤ ±0.005mm) and does not change the metallographic structure of the Invar36 alloy, with a low expansion performance retention rate of ≥99.5%.

[0032] The electropolishing treatment of Invar alloy substrates thinned with ferric chloride using the above-mentioned electrolyte composition and ratio demonstrates excellent process adaptability. The surface characteristics of the Invar alloy thinned with ferric chloride have been optimized, resulting in good electrolyte compatibility during electropolishing, making it suitable for precision components of different sizes and shapes.

[0033] Using the above-mentioned electrolyte composition and ratio for electropolishing the Invar alloy substrate thinned by ferric chloride is more environmentally friendly and sustainable. The electrolyte can be recycled 6-8 times (after replenishing the lost phosphoric acid and / or malic acid), and the chromium-free passivation process reduces environmental pressure and is suitable for industrial mass production.

[0034] 2. The electropolishing method for Invar alloy substrates provided in this application also clarifies the key process window for achieving optimal polishing results, ensuring efficient material removal while obtaining a high-gloss surface and avoiding over-corrosion, pitting, or insufficient polishing due to improper parameters. This key process window can guarantee the uniformity of electric field distribution and mass transfer throughout the polishing area, thereby obtaining a large-area, highly consistent polished surface.

[0035] 3. The electropolishing method for Invar alloy substrates provided in this application also includes pretreatment and posttreatment steps. The pretreatment thoroughly removes contaminants and oxide layers remaining from previous etching processes (such as ferric chloride etching), providing an absolutely clean and activated metal surface for electropolishing, which is a prerequisite for obtaining defect-free, high-gloss polishing results. The posttreatment effectively removes the viscous electrolyte adhering to the substrate after polishing and employs an oxygen-free, low-temperature drying method to prevent water stains, oxidation, or heat discoloration from forming on the obtained high-gloss surface in the final stage.

[0036] 4. The electropolishing method for Invar alloy substrate provided in this application also includes a dynamic monitoring and maintenance scheme for maintaining the long-term stability of the electrolyte (by adding pre-prepared concentrated mother liquor according to the change in the specific gravity of phosphoric acid to restore the specific gravity of phosphoric acid to the initial set value) and the consistency of polishing effect (by performing phosphoric acid concentration titration analysis on the electrolyte and adding more). This scheme is applicable to daily rapid maintenance and periodic fine calibration, and together constitutes a complete liquid tank management strategy.

[0037] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A schematic flowchart of an electropolishing method for an Invar alloy substrate provided in one embodiment of this application;

[0040] Figure 2 The image shows the effect after electropolishing of Invar alloy substrate using existing technology.

[0041] Figure 3 The image shows the effect of electropolishing the Invar alloy substrate using the method provided in Example 1 of this application.

[0042] Figure 4 The image shows the effect after electropolishing of Invar alloy substrate using existing technology.

[0043] Figure 5 This is a diagram showing the effect of electropolishing the Invar alloy substrate using the method provided in Example 2 of this application. Detailed Implementation

[0044] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0045] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0046] This application provides an electropolishing method for Invar alloy substrates to improve the surface gloss of Invar alloy substrates. The electropolishing formula and process in this application, specifically designed for Invar alloys, solves the problems of orange peel, pitting, or uneven gloss that easily occur on the surface in traditional polishing, and can significantly and stably improve the surface gloss.

[0047] In one embodiment, the electropolishing method for the Invar alloy substrate includes: S20, using the Invar alloy substrate to be treated as the anode and a pure lead plate as the cathode, immersing the anode and cathode simultaneously in an electrolytic cell containing an electrolyte to electropolish the Invar alloy substrate to be treated.

[0048] The electrolyte comprises phosphoric acid, sulfuric acid, malic acid, ethylene glycol, sodium dodecylbenzenesulfonate, and deionized water, in a volume ratio of phosphoric acid: sulfuric acid: malic acid: ethylene glycol: sodium dodecylbenzenesulfonate: deionized water = 6:1:1:1:0.5:0.5.

[0049] In this embodiment, the composition and ratio of the electrolyte used to enhance the surface gloss of the Invar alloy substrate are specifically adjusted. Phosphoric acid is the main component. Phosphoric acid is a moderately strong acid with high viscosity, capable of forming a viscous phosphate diffusion layer on the anode surface, enabling selective dissolution (preferential dissolution of microscopic protrusions) to obtain a smooth surface. Sulfuric acid is a strong acid, helping to increase the electrolyte conductivity, reduce the electrolytic cell voltage, improve polishing efficiency, and also aiding in the dissolution of certain oxides on the Invar alloy surface. Malic acid is an organic polyacid, acting as a complexing agent and corrosion inhibitor. It can form soluble complexes with nickel and iron ions, preventing localized supersaturation deposition of metal ions on the surface and thus preventing defects. Its corrosion inhibition also contributes to more uniform dissolution. Ethylene glycol is a high-boiling-point organic solvent with thickening and hygroscopic properties. It can regulate the electrolyte viscosity and surface tension, stabilize the anode diffusion layer, and prevent excessively rapid changes in electrolyte concentration due to water evaporation. Sodium dodecylbenzenesulfonate is an anionic surfactant. It reduces the surface tension of the electrolyte, enhances wettability to the substrate, and prevents hydrogen (generated at the cathode) bubbles from adhering to the anode surface, thus preventing polishing streaks or dark spots and resulting in a more uniform surface. Deionized water acts as a solvent, adjusting the overall concentration and conductivity.

[0050] The specific volume ratio of phosphoric acid: sulfuric acid: malic acid: ethylene glycol: sodium dodecylbenzenesulfonate: deionized water = 6:1:1:1:0.5:0.5 is the optimal ratio for balancing polishing efficiency, surface quality, diffusion layer stability, and cost. Deviating from this ratio may result in over-polishing, under-polishing, or surface defects.

[0051] The configuration of Invar alloy as the anode and pure lead plate as the cathode is extremely stable in strong acid environments, corrosion resistant, and can provide a uniform cathode reaction (mainly hydrogen evolution) for a long time, ensuring stable current during the anode polishing process.

[0052] In this embodiment, the electropolishing treatment of the Invar alloy substrate thinned by ferric chloride using the above-mentioned electrolyte composition and ratio can significantly improve the gloss of the Invar alloy substrate. Subsequent embodiments (Examples 1 and 2 and related figures) clearly show that the surface gloss of the Invar 36 alloy after ferric chloride thinning is improved from matte (≤20GU) to mirror gloss (≥92GU, conforming to ASTM D523 standard), and the surface of the Invar alloy substrate exhibits a uniform and bright mirror effect.

[0053] Electropolishing of the Invar alloy substrate thinned by ferric chloride using the above-mentioned electrolyte composition and ratio yields an Invar alloy substrate with excellent surface quality. The surface roughness Ra after polishing is ≤0.03μm, completely eliminating pitting and etching marks caused by ferric chloride thinning, and eliminating new defects such as grain boundary corrosion and pitting.

[0054] Electropolishing the Invar alloy substrate thinned by ferric chloride using the above-mentioned electrolyte composition and ratio ensures that the dimensions and properties of the Invar alloy substrate are not damaged. Electropolishing removes only 0.5μm-1μm of surface layer thickness, which does not affect the dimensional accuracy of the thinned Invar alloy (dimensional deviation ≤ ±0.005mm) and does not change the metallographic structure of the Invar36 alloy, with a low expansion performance retention rate of ≥99.5%.

[0055] The electropolishing treatment of Invar alloy substrates thinned with ferric chloride using the above-mentioned electrolyte composition and ratio demonstrates excellent process adaptability. The surface characteristics of the Invar alloy thinned with ferric chloride have been optimized, resulting in good electrolyte compatibility during electropolishing, making it suitable for precision components of different sizes and shapes.

[0056] Using the above-mentioned electrolyte composition and ratio for electropolishing the Invar alloy substrate thinned by ferric chloride is more environmentally friendly and sustainable. The electrolyte can be recycled 6-8 times (after replenishing the lost phosphoric acid and / or malic acid), and the chromium-free passivation process reduces environmental pressure and is suitable for industrial mass production.

[0057] In one embodiment, during the electropolishing process, the use of industrial frequency AC power between the anode and cathode for electropolishing, with a specific process selection of 50Hz (which may refer to rectified pulsating DC or specific AC power), helps to break up any passivation film that may form on the anode surface and promotes a more uniform dissolution process.

[0058] During the electropolishing process, the current density of the electrolyte in the electrolytic cell is 18 A / dm³. 2 -28A / dm 2 This involves electropolishing the Invar alloy substrate thinned with ferric chloride using the aforementioned electrolyte composition and ratio. A specific electrolyte corresponds to a specific current density range. Too low a current density results in weak polishing, while too high a current density can easily cause pitting or "boiling," damaging the surface of the Invar alloy substrate.

[0059] During electropolishing, the electrolysis temperature is maintained within the range of 45℃-60℃. The electrolysis temperature affects the electrolyte viscosity, ion mobility, and reaction rate. This temperature range ensures the electrolyte has suitable activity and fluidity, facilitating the formation of the diffusion layer and heat dissipation.

[0060] During electropolishing, the polishing time is set to 6-10 minutes. The polishing time is matched with the above-mentioned current density and temperature range to ensure sufficient material removal to achieve a smooth finish, without causing excessive edge corrosion or inefficiency due to excessive time.

[0061] In this embodiment, the key process window for achieving the best polishing effect is defined to ensure that a high-gloss surface is obtained while efficiently removing material, and to avoid over-corrosion, pitting, or insufficient polishing caused by improper parameters.

[0062] In one embodiment, the optimal distance between the anode and cathode during electropolishing is set to 50mm-150mm. Too small a distance can lead to uneven current distribution and short-circuit risks. Too large a distance increases the electrolytic cell voltage, energy consumption, and edge effects may be more pronounced. During electropolishing, magnetic stirring forces convection to ensure uniform electrolyte composition and temperature, promptly removing dissolved products and heat near the anode and preventing polishing defects caused by excessively high local concentrations or temperatures.

[0063] In this embodiment, the uniformity of electric field distribution and mass transfer throughout the polishing area is ensured, thereby obtaining a large-area polished surface with extremely high consistency.

[0064] In one embodiment, before electropolishing the Invar alloy substrate to be treated, a pretreatment step is further included. The pretreatment step includes:

[0065] S10a: An alkaline descaling solution is used to remove residual ferric chloride etching products from the surface of the Invar alloy substrate to be treated. These ferric chloride etching products include ferric hydroxide and chloride ions. The descaling solution consists of 2% sodium hydroxide, and the treatment temperature is 40℃~50℃ for 2 minutes. This step specifically removes the residual ferric hydroxide colloidal precipitate and adsorbed chloride ions after ferric chloride etching. Chloride ions, if introduced into the polishing tank / electrolytic tank, can easily cause pitting corrosion. The aforementioned descaling solution provides mild alkaline conditions, effectively dissolving hydroxides and saponifying any potential organic contaminants without damaging the Invar alloy substrate. This step neutralizes residual alkaline agents and slightly activates the surface, providing a uniform substrate for electropolishing.

[0066] S10b involves neutralizing and surface-activating the Invar alloy substrate after alkaline slag removal using a weak acid solution. The weak acid solution is a 3%-5% (v / v) aqueous acetic acid solution, treated at room temperature for 1-3 minutes. This step serves to neutralize and activate the substrate. The weak acid solution neutralizes residual alkali and lightly etches the surface, removing a very thin oxide layer and exposing fresh, active metal lattice, increasing surface energy and allowing for a more uniform initiation of the subsequent polishing reaction. The 3%-5% (v / v) aqueous acetic acid solution, treated at room temperature for 1-3 minutes, provides a sufficient weak acid environment for neutralization and activation, with low corrosiveness and good controllability.

[0067] S10c involves ultrasonic cleaning of the neutralized Invar alloy substrate using multi-stage deionized water. The ultrasonic frequency is 40kHz, and each stage lasts 3-5 minutes. This step achieves multi-stage ultrasonic cleaning, thoroughly removing all chemical residues and particles from the previous two steps. Multi-stage deionized water prevents cross-contamination and progressively increases cleanliness. The 40kHz ultrasonic frequency and 3-5 minute cleaning time per stage utilize cavitation to physically remove adhering substances, providing excellent cleaning results, especially in tiny crevices. In this step, after slag removal and neutralization, ultrasonic cleaning with deionized water ensures no residual chemicals or ions remain on the surface, preventing any impact on electropolishing results.

[0068] In this embodiment, a systematic pretreatment process is used to thoroughly remove contaminants and oxide layers remaining from previous etching processes (such as ferric chloride etching), providing an absolutely clean and activated metal surface for electropolishing. This is a prerequisite for obtaining defect-free, high-gloss polishing results.

[0069] In one embodiment, after electropolishing the Invar alloy substrate to be treated, a post-processing step is further included.

[0070] S30a is initially rinsed with flowing deionized water, followed by ultrasonic cleaning at a frequency of 40 kHz in deionized water with a resistivity ≥15 MΩ·cm. In this step, rinsing and ultrasonic cleaning thoroughly remove residual electrolyte. If components such as phosphoric acid are not removed, they will form white stains after drying. Using high-resistivity deionized water and ultrasonic cleaning ensures cleaning purity and effectiveness. In this step, first flowing deionized water, then ultrasonic cleaning, thoroughly removes residual electrolyte from the surface.

[0071] S30b, vacuum drying treatment, the process conditions for vacuum drying treatment are: vacuum degree not higher than 1×10 -2 The drying temperature is 60℃-80℃, and the drying time is 20-40 minutes. This step involves rapid moisture removal under low oxygen and low temperature conditions. The high vacuum level (≤1×10⁻⁶) in this step... -2 The vacuum drying process significantly reduces oxygen partial pressure, preventing oxidation and darkening of the activated metal surface after polishing. The low drying temperature of 60℃-80℃ in this step avoids thermal stress or microstructural changes in the Invar alloy due to excessively high temperatures, while also saving energy. Vacuum drying in this step prevents surface dust adhesion caused by hot air drying, ensuring long-lasting gloss.

[0072] In this embodiment, the viscous electrolyte adhering to the substrate after polishing is effectively removed, and an oxygen-free, low-temperature drying method is used to prevent water stains, oxidation, or heat discoloration from occurring on the obtained high-gloss surface in the final stage.

[0073] In one embodiment, the thickness of the Invar alloy substrate to be treated is 0.6 mm to 1.2 mm, making the electropolishing method for the Invar alloy substrate of this application applicable to improving the surface gloss of various types of precision components such as metal photomasks and photovoltaic grids. The gloss of the Invar alloy substrate after electropolishing is improved to greater than 90 GU, providing an objective and measurable quality indicator (GU is a unit of gloss), which is significantly better than untreated or conventionally treated surfaces, demonstrating the excellent leveling and brightening capabilities of this method.

[0074] In one embodiment, the Invar alloy substrate to be treated is an Invar alloy thinned using a ferric chloride solution, wherein the nickel content in the Invar alloy is 35%-37%. This clarifies that the electropolishing method for the Invar alloy substrate of this application is particularly suitable for substrates with specific compositions (standard Invar alloy composition) that have been treated by a specific etching process (ferric chloride), demonstrating the compatibility and specificity of the method with upstream processes.

[0075] In one embodiment, the electropolishing method for Invar alloy substrate further includes: measuring the change in specific gravity of phosphoric acid in the electrolyte as the number of electropolishing cycles increases, and replenishing a pre-prepared concentrated mother liquor according to the change in phosphoric acid specific gravity to restore the specific gravity of phosphoric acid to the initial set value. Phosphoric acid is the main consumable component, and its specific gravity change can directly reflect the overall change in electrolyte concentration. By replenishing a pre-prepared concentrated phosphoric acid solution with the same composition, the main components of the electrolyte are quickly restored to the optimal ratio.

[0076] In one embodiment, the electropolishing method for the Invar alloy substrate further includes: performing a phosphoric acid concentration titration analysis on the electrolyte, specifically including: accurately determining the free phosphoric acid concentration using an acid-base titration method. If the free phosphoric acid concentration is lower than 15%-20% of the initial value, pure phosphoric acid is calculated and added. After adding pure phosphoric acid, the electrolyte is thoroughly stirred, and the specific gravity of phosphoric acid in the electrolyte after addition is remeasured.

[0077] In this step, acid-base titration is used to determine the free phosphoric acid content, allowing for more precise analysis of the consumption of the key active ingredient (free phosphoric acid). When the concentration falls below 15%-20% of the initial value, pure phosphoric acid is added, establishing a scientifically designed maintenance trigger point to prevent performance degradation. Furthermore, the titration method is correlated with the specific gravity method to establish dual calibration, resulting in more accurate maintenance.

[0078] This embodiment and the previous embodiment provide a dynamic monitoring and maintenance scheme to maintain the long-term stability of the electrolyte (by adding pre-prepared concentrated mother liquor according to the change in the specific gravity of phosphoric acid to restore the specific gravity of phosphoric acid to the initial set value) and the consistency of polishing effect (by performing phosphoric acid concentration titration analysis on the electrolyte and adding more). It can be applied to daily rapid maintenance and periodic fine calibration, together forming a complete liquid tank management strategy.

[0079] In one embodiment, the electropolishing method for Invar alloy substrates further includes: installing an acid-resistant pump and a filter element with a precision of 1-5 microns in the electrolytic cell, and performing continuous 24-hour circulation filtration. The acid-resistant pump circulation in this step enables forced flow and filtration of the electrolyte. The 1-5 micron precision filter element effectively traps most of the tiny particles harmful to surface quality. 24-hour continuous circulation filtration maintains cleanliness even during non-production periods, ensuring the polishing solution is always clean and facilitating zero-defect production.

[0080] In this embodiment, physical filtration is used to continuously remove metallic flocs, insoluble particles, and other mechanical impurities generated by anodic dissolution in the electrolyte. This fundamentally prevents these impurities from adhering to the workpiece surface and causing scratches or uneven gloss. It is a key equipment guarantee for ensuring the long-term and stable production of high-quality products.

[0081] Example 1:

[0082] The Invar alloy substrate to be processed is selected from thin Invar36 alloy sheet (reduced to a thickness of 1.0 mm by ferric chloride). Specifically, Invar36 alloy is an iron-nickel alloy containing 36% nickel.

[0083] The state of the Invar alloy substrate to be processed: Invar 36 alloy sheet (150mm × 150mm × 1.0mm), after being thinned by ferric chloride solution (30% by mass), as follows: Figure 2 The surface shown is dark gray with obvious pitting, gloss level 18 GU, and roughness Ra = 1.2 μm.

[0084] The method used in the embodiments of this application is as follows:

[0085] (1) Pre-processing steps:

[0086] S10a uses an alkaline slag-removing solution to remove residual ferric chloride etching products from the surface of the Invar alloy substrate to be treated. The ferric chloride etching products include ferric hydroxide and chloride ions. The slag-removing solution consists of 2% sodium hydroxide, the treatment temperature is 45℃, and the treatment time is 2 minutes.

[0087] S10b involves neutralizing and surface-activating the Invar alloy substrate after alkaline slag removal treatment with a weak acid solution. The weak acid solution is a 3.5% (v / v) aqueous acetic acid solution, and the treatment is performed at room temperature for 2 minutes.

[0088] S10c employs multi-stage deionized water to ultrasonically clean the neutralized Invar alloy substrate. The ultrasonic frequency is 40kHz, and each stage of cleaning lasts 4 minutes.

[0089] (2) Electropolishing process:

[0090] S20, the Invar alloy substrate to be treated is used as the anode and the pure lead plate is used as the cathode. The anode and the cathode are simultaneously immersed in an electrolytic cell containing electrolyte to electropolish the Invar alloy substrate to be treated.

[0091] The electrolyte comprises: phosphoric acid, sulfuric acid, malic acid, ethylene glycol, sodium dodecylbenzenesulfonate, and deionized water, and is prepared in a volume ratio of phosphoric acid: sulfuric acid: malic acid: ethylene glycol: sodium dodecylbenzenesulfonate: deionized water = 6:1:1:1:0.5:0.5.

[0092] The energizing frequency between the anode and the cathode is 50 Hz, and the current density of the electrolyte in the electrolytic cell is 20 A / dm³. 2 Electrolysis temperature 50℃, polishing time 6-10 minutes.

[0093] (3) Post-processing steps:

[0094] S30a is initially rinsed with flowing deionized water, and then subjected to ultrasonic cleaning at a frequency of 40kHz in deionized water with a resistivity of 35MΩ·cm.

[0095] S30b, vacuum drying treatment, the process conditions for vacuum drying treatment are: vacuum degree not higher than 1×10 -2 Pa, drying temperature is 65℃, drying time is 25 minutes.

[0096] The treatment results of the Invar alloy substrate in Example 1 are as follows: Figure 3 As shown, the surface of the Invar alloy substrate to be treated exhibits a mirror-like gloss with a gloss level of 95 GU, Ra = 0.02 μm, and a dimensional deviation of ±0.003 mm. Its coefficient of thermal expansion is 1.3 × 10⁻⁶ under conditions of 20℃-100℃. -6 / ℃ (consistent with the substrate, which is an Invar36 alloy that has not been thinned with ferric chloride), no oxidation discoloration was observed after 300h of salt spray testing.

[0097] Example 2:

[0098] The Invar alloy substrate to be processed is selected from precision Invar36 alloy structural parts (thinned to a thickness of 0.8 mm with ferric chloride).

[0099] The state of the Invar alloy substrate to be processed: Invar 36 alloy precision structural parts (with complex curved surfaces, thickness 0.8mm), after thinning with ferric chloride, as follows: Figure 4 The surface shown has localized etching marks, a gloss level of 22 GU, and Ra = 1.0 μm.

[0100] The method used in the embodiments of this application is as follows:

[0101] (1) Pre-processing steps:

[0102] S10a uses an alkaline slag-removing solution to remove residual ferric chloride etching products from the surface of the Invar alloy substrate to be treated. The ferric chloride etching products include ferric hydroxide and chloride ions. The slag-removing solution consists of 2% sodium hydroxide, the treatment temperature is 48℃, and the treatment time is 2 minutes.

[0103] S10b involves neutralizing and surface-activating the Invar alloy substrate after alkaline slag removal treatment with a weak acid solution. The weak acid solution is a 4% (v / v) aqueous acetic acid solution, and the treatment is performed at room temperature for 2 minutes.

[0104] S10c employs multi-stage deionized water to ultrasonically clean the neutralized Invar alloy substrate. The ultrasonic frequency is 40kHz, and each stage of cleaning lasts 4 minutes.

[0105] (2) Electropolishing process:

[0106] S20, the Invar alloy substrate to be treated is used as the anode and the pure lead plate is used as the cathode. The anode and the cathode are simultaneously immersed in an electrolytic cell containing electrolyte to electropolish the Invar alloy substrate to be treated.

[0107] The electrolyte comprises: phosphoric acid, sulfuric acid, malic acid, ethylene glycol, sodium dodecylbenzenesulfonate, and deionized water, and is prepared in a volume ratio of phosphoric acid: sulfuric acid: malic acid: ethylene glycol: sodium dodecylbenzenesulfonate: deionized water = 6:1:1:1:0.5:0.5.

[0108] The energizing frequency between the anode and the cathode is 50 Hz, and the current density of the electrolyte in the electrolytic cell is 25 A / dm³. 2 Electrolysis temperature 50℃, polishing time 8 minutes.

[0109] (3) Post-processing steps:

[0110] S30a is initially rinsed with flowing deionized water, and then subjected to ultrasonic cleaning at a frequency of 40 kHz in deionized water with a resistivity of 40 MΩ·cm.

[0111] S30b, vacuum drying treatment, the process conditions for vacuum drying treatment are: vacuum degree not higher than 1×10 -2 Pa, drying temperature is 68℃, drying time is 30 minutes.

[0112] The treatment results of the Invar alloy substrate in Example 2 are as follows: Figure 5As shown, the surface gloss of the Invar alloy substrate to be treated is 93 GU, Ra=0.03μm, the complex curved surface is polished uniformly, there is no local darkening, the dimensional accuracy meets the design requirements, and the corrosion resistance is improved by 40%.

[0113] The core technical solution of this application includes a pretreatment to remove ferric chloride residue, an electropolishing core step to improve gloss using a special electrolyte and process parameters, and a post-treatment to stabilize gloss. Specifically, the pretreatment removes ferric chloride residue and surface defects. The electropolishing core step, using a special electrolyte and process parameters, significantly improves the gloss of the Invar alloy substrate while reducing its surface roughness.

[0114] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0115] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An electropolishing method adapted to Invar alloy substrates thinned with ferric chloride, used to improve the surface gloss of the Invar alloy substrates thinned with ferric chloride, characterized in that, include: The Invar alloy substrate to be treated is used as the anode, and a pure lead plate is used as the cathode. The anode and the cathode are simultaneously immersed in an electrolytic cell containing electrolyte to electropolish the Invar alloy substrate to be treated. The electrolyte comprises phosphoric acid, sulfuric acid, malic acid, ethylene glycol, sodium dodecylbenzenesulfonate, and deionized water, and is prepared in a volume ratio of phosphoric acid: sulfuric acid: malic acid: ethylene glycol: sodium dodecylbenzenesulfonate: deionized water = 6:1:1:1:0.5:0.

5.

2. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 1, characterized in that, During the electropolishing process: the energizing frequency between the anode and the cathode is 50 Hz, and the current density of the electrolyte in the electrolytic cell is 18 A / dm³. 2 -28A / dm 2 Electrolysis temperature 45℃-60℃, polishing time 6min-10min.

3. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 1, characterized in that, The distance between the anode and the cathode is 50mm-150mm. During the electropolishing process, magnetic stirring is used to ensure uniform electrolyte concentration.

4. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 1, characterized in that, Before electropolishing the Invar alloy substrate to be processed, a pretreatment step is also included; The preprocessing steps include: S10a, using an alkaline slag removal solution to remove residual ferric chloride etching products from the surface of the Invar alloy substrate to be treated, wherein the ferric chloride etching products include: ferric hydroxide and chloride ions; the slag removal solution includes: sodium hydroxide with a concentration of 2%, the treatment temperature of the slag removal solution is 40℃~50℃, and the treatment time of the slag removal solution is 2min. S10b, the Invar alloy substrate to be treated after alkaline slag removal is neutralized and surface activated using a weak acid solution; wherein, the weak acid solution is an aqueous acetic acid solution with a volume concentration of 3%-5%, and the treatment is carried out at room temperature for 1-3 minutes; S10c, the neutralized Invar alloy substrate is ultrasonically cleaned using multi-stage deionized water; wherein the ultrasonic frequency is 40 kHz, and the cleaning time for each stage is 3-5 minutes.

5. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 1, characterized in that, After electropolishing the Invar alloy substrate to be treated, the process further includes a post-processing step. S30a is initially rinsed with flowing deionized water, and then placed in deionized water with a resistivity ≥15 MΩ·cm for ultrasonic cleaning at a frequency of 40 kHz. S30b, vacuum drying treatment, wherein the process conditions for vacuum drying treatment are: vacuum degree not higher than 1×10⁻⁶. -2 Pa, drying temperature is 60℃-80℃, drying time is 20 minutes-40 minutes.

6. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 1, characterized in that, The thickness of the Invar alloy substrate to be treated is 0.6mm-1.2mm, and the gloss of the Invar alloy substrate to be treated after electropolishing is increased to greater than 90GU.

7. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 6, characterized in that, The nickel content in this Invar alloy is between 35% and 37%.

8. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 1, characterized in that, Also includes: As the number of electropolishing cycles increases, the change in the specific gravity of phosphoric acid in the electrolyte is measured. Based on the change in the specific gravity of phosphoric acid, a pre-prepared concentrated mother liquor is added to restore the specific gravity of phosphoric acid to the initial set value.

9. The electropolishing method for Invar alloy substrates thinned with ferric chloride according to claim 1, characterized in that, Also includes: The electrolyte was analyzed by phosphoric acid concentration titration: The concentration of free phosphoric acid was accurately determined using acid-base titration. If the free phosphoric acid concentration is lower than 15%-20% of the initial value, calculate and add pure phosphoric acid. After adding the pure phosphoric acid, the mixture was stirred thoroughly, and the specific gravity of the phosphoric acid in the electrolyte was measured again.

10. The electropolishing method for an Invar alloy substrate thinned with ferric chloride according to claim 8 or 9, characterized in that, Also includes: An acid-resistant pump and a filter element with a precision of 1-5 micrometers are installed in the electrolytic cell for continuous 24-hour circulation filtration.

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