Deplating solution and deplating method for aluminum-manganese alloy

Abstract

The invention belongs to the technical field of metal surface treatment, and particularly relates to a deplating solution for aluminum-manganese alloy and a deplating method. The invention discloses a deplating solution for an aluminum-manganese alloy, which comprises the following components: 30-70g / L of sodium hydroxide; and 20 g / L-70 g / L of sodium citrate. According to the deplating solution for the aluminum-manganese alloy and the deplating method, sodium hydroxide is adopted as a core deplating component, a strong alkaline environment is provided to guarantee that the dissolution reaction of aluminum in an aluminum-manganese alloy coating is efficiently carried out, sodium citrate serves as a key complexing agent, citric acid radical ions dissociated by the sodium citrate are strong multidentate ligands, and therefore the deplating effect is good. According to the stripping solution, through the synergistic effect of the two core components, the technical problems that an existing single sodium hydroxide stripping solution is blocked in stripping and uneven in stripping, a base material is prone to being damaged and the like are solved in a targeted mode, and a reliable solution is provided for efficient and high-quality stripping of an aluminum-manganese alloy coating.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a stripping solution and stripping method for aluminum-manganese alloys. Background Technology

[0002] Aluminum-manganese alloys, with their excellent mechanical strength, corrosion resistance, and processing performance, are widely used in various fields such as electronics, automobiles, and aerospace. Especially in the consumer electronics sector, pure aluminum and aluminum-manganese alloy coatings are increasingly popular due to their ability to meet stringent corrosion resistance requirements and the ability to achieve diverse aesthetic results through anodizing. Currently, the main preparation processes for aluminum-manganese alloy coatings include PVD vacuum aluminum plating, ionic liquid aluminum plating, and high-temperature molten salt aluminum plating. Among these, ionic liquid aluminum plating, with its advantages of low cost, high deposition efficiency, and good coating density, is gradually becoming the mainstream plating method.

[0003] In the electroplating process of aluminum-manganese alloy coatings, factors such as fluctuations in process parameters and deviations in equipment precision inevitably lead to defective products with insufficient adhesion, uneven thickness, and surface defects. Simultaneously, in the barrel plating process, steel balls and other auxiliary materials added to ensure coating uniformity will also deposit an aluminum-manganese alloy coating on their surfaces after each electroplating cycle. If reuse is required, stripping is necessary. If the aluminum-manganese alloy coating on defective workpieces or auxiliary materials is not removed promptly, a dense oxide film will quickly form on the coating surface, significantly reducing the adhesion between the new coating and the substrate during subsequent electroplating, severely impacting product quality. Therefore, the stripping process is an indispensable and crucial step in the aluminum-manganese alloy coating production process.

[0004] In existing technologies, the stripping of aluminum-manganese alloy coatings mainly uses a single sodium hydroxide solution as the stripping solution. The core principle is to utilize the amphoteric properties of aluminum, causing it to react with sodium hydroxide to form water-soluble aluminates, thereby dissolving the coating. However, this traditional stripping technology has insurmountable technical drawbacks: during the stripping process, the aluminum in the aluminum-manganese alloy coating reacts violently with sodium hydroxide, generating sodium aluminate and releasing a large amount of hydrogen gas. The exothermic reaction causes a sharp rise in the system temperature. Furthermore, the manganese in the coating cannot dissolve in a single sodium hydroxide solution and remains in the solution as particulate oxides or hydroxyl oxides. These insoluble manganese compound particles become the "core framework" for stripping agglomeration. As the reaction continues, the concentration of sodium aluminate in the solution continuously increases, and the high temperature environment accelerates the hydrolysis of sodium aluminate, generating gel-like aluminum hydroxide. This aluminum hydroxide firmly bonds with the manganese compound particles, forming a dense and robust mixed deposition layer. This mixed deposit layer not only adheres to the workpiece surface, hindering the contact between the stripping solution and the remaining coating, resulting in incomplete and uneven stripping, but also causes wear or corrosion of the substrate, reducing the reusability of the workpiece and the substrate. At the same time, the clumping phenomenon leads to a decrease in the stability of the stripping solution system, shortens the service life of the stripping solution, and increases production costs. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a stripping solution and method for aluminum-manganese alloys. Sodium hydroxide is used as the core stripping component, providing a strongly alkaline environment to ensure efficient aluminum dissolution in the aluminum-manganese alloy coating. Sodium citrate serves as a key complexing agent, with its dissociated citrate ions being strong polydentate ligands. Through the synergistic effect of these two core components, this stripping solution effectively solves the technical problems of existing single-sodium hydroxide stripping solutions, such as stripping agglomeration, uneven stripping, and easy damage to the substrate. It provides a reliable solution for efficient and high-quality stripping of aluminum-manganese alloy coatings.

[0006] Therefore, the first objective of this invention is to provide a stripping solution for aluminum-manganese alloys.

[0007] The second objective of this invention is to provide a method for stripping plating from aluminum-manganese alloys.

[0008] To achieve the first objective of this invention, the technical solution of this invention provides a stripping solution for aluminum-manganese alloys, comprising: sodium hydroxide, 30g / L-70g / L; sodium citrate, 20g / L-70g / L.

[0009] Compared with existing technologies, the technical effects achieved by this solution are as follows: the alkaline environment of sodium hydroxide provides the reaction basis for coating dissolution, while the complexing and dispersing effects of sodium citrate prevent uneven local reactions. The synergistic effect of these two within a limited concentration range ensures a uniform and controllable coating dissolution rate, avoiding localized coating residue or excessive corrosion. After stripping, the workpiece surface is free of residual coating, pitting, and scratches, significantly improving surface quality. It is particularly suitable for precision electronic components, steel balls requiring high surface precision, and other workpieces, ensuring adhesion for subsequent reuse or re-plating. The sodium hydroxide concentration in the stripping solution is limited to 30g / L-70g / L, a concentration range that provides sufficient OH... - Ions, satisfying the reaction requirements of aluminum and sodium hydroxide in aluminum-manganese alloy coatings, 2Al + 2OH- - +2H₂O=2AlO₂ -+3H2 ensures efficient dissolution of the coating while avoiding excessively vigorous reactions, exothermic runaway, and excessive corrosion of the substrate caused by excessive concentration. Sodium citrate, as a strong multidentate complexing agent, can fully dissociate citrate ions at a concentration of 20g / L-70g / L. On the one hand, it can form a stable and soluble complex with manganese ions that are insoluble in sodium hydroxide during the stripping process, completely eliminating the agglomerated skeleton, i.e., manganese oxide / hydroxy oxide particles. On the other hand, it can complex with aluminum ions generated by the hydrolysis of sodium aluminate, inhibiting the formation rate and quantity of aluminum hydroxide gel and reducing the source of binding material. At the same time, sufficient citrate ions can adsorb small particles in the solution, forming a protective film to prevent agglomeration. It avoids agglomeration from both chemical complexation and physical dispersion, ensuring continuous and sufficient contact between the stripping solution and the coating, and ensuring the continuous stripping reaction. Moreover, the stripping solution system is stable and environmentally friendly, suitable for industrial applications.

[0010] In one technical solution of the present invention, the stripping solution for aluminum-manganese alloy further includes: sodium potassium tartrate, 5 g / L-20 g / L; and a surfactant, 0.1 g / L-1 g / L; wherein the surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and fatty alcohol polyoxyethylene ether.

[0011] Compared with existing technologies, the technical effects achieved by this solution are as follows: Potassium sodium tartrate, as an auxiliary complexing agent, can form a synergistic complexing system with sodium citrate. The tartrate ions released from potassium sodium tartrate can further form stable multi-component complexes with manganese and aluminum ions. Compared with sodium citrate alone, this significantly improves the complexing capacity and stability for metal ions. Simultaneously, tartrate ions can further inhibit the hydrolysis of sodium aluminate, reducing the formation of aluminum hydroxide gel. Working together with sodium citrate, it chemically blocks the formation of mixed deposition layers. Its concentration is limited to 5g / L-20g / L, and it can act as a reaction promoter to prevent excessively vigorous reactions. The surfactant reduces interfacial tension, ensuring uniform stripping. It significantly reduces the interfacial tension between the stripping solution and the workpiece surface, improving the wetting performance of the stripping solution on the coating surface. Even if there are tiny gaps or depressions on the workpiece surface, the stripping solution can quickly penetrate and fully contact the surface, avoiding incomplete stripping and coating residue problems caused by insufficient local wetting. Furthermore, the surfactant can… This process promotes the rapid removal of hydrogen gas generated during stripping from the workpiece surface, preventing "gas resistance" caused by bubble adhesion. It ensures consistent dissolution rates of the plating layer across all areas of the workpiece, resulting in a smooth, uniform surface free of defects such as pitting and color differences. The surfactant molecules possess an amphiphilic structure, and at concentrations of 0.1 g / L to 1 g / L, they form a stable colloidal dispersion system in the stripping solution, further enhancing the dispersion effect on minute particles. They adsorb onto the surface of incompletely complexed microparticles, forming a double-layer protective film, increasing interparticle repulsion, and preventing particle aggregation and sedimentation. This synergistic effect with the dispersing action of sodium citrate and potassium sodium tartrate ensures the stripping solution remains clear and uniform throughout long-term use, free from turbidity and sedimentation, extending its service life and reducing waste liquid replacement frequency and production costs. Potassium sodium tartrate exhibits excellent compatibility with sodium hydroxide and sodium citrate in alkaline systems, with no adverse reactions. The selected surfactants are all commonly used industrial products, exhibiting strong alkali resistance and stable performance in stripping solutions with high pH values, without decomposition or failure. This composite component system can be used for batch stripping of plating materials such as steel balls, as well as for stripping of workpieces with high surface quality requirements such as electronic components and automotive precision parts. It can also achieve efficient stripping under mild process conditions of room temperature and mechanical tumbling, without the need for additional equipment parameter adjustments. It has strong process adaptability and is easy to promote and apply in industrial applications.

[0012] In one embodiment of the present invention, the pH value of the stripping solution is 10-12.

[0013] Compared with existing technologies, the technical advantages achieved by this solution are: the pH value of the stripping solution is limited to an alkaline range of 10-12, which preserves both aluminum and OH groups. -The alkaline environment required for the ionic reaction ensures the orderly progress of the core reaction for coating dissolution; it also avoids the problems of excessively vigorous reactions and exothermic runaway under strongly alkaline conditions. A strongly alkaline environment accelerates the hydrolysis of sodium aluminate to form aluminum hydroxide gel and exacerbates the aggregation of manganese compound particles. An alkaline system with a pH of 10-12 significantly slows down the hydrolysis rate of sodium aluminate, reduces the generation of gel-like binders, and reduces the tendency of manganese compound particles to aggregate, thus inhibiting agglomeration from the reaction environment perspective. Sodium citrate, as the core complexing agent, has an ability to complex manganese and aluminum ions that is closely related to the solution pH. At a pH range of 10-12, the dissociation state of citrate ions is optimal, allowing them to fully form stable and soluble complexes with manganese ions. If the pH is too low, the citrate ions are insufficiently dissociated, reducing the complexing ability and failing to effectively capture metal ions, easily leading to agglomeration recurrence. If the pH is too high, it will destroy the stability of the complex and even cause it to decompose, losing its agglomeration inhibition effect. An alkaline system with a pH of 10-12 can significantly reduce OH-. - The erosion rate of ions on the substrate, combined with the corrosion inhibition effect of sodium citrate, can effectively protect the surface condition of the substrate. After stripping, the substrate has no corrosion spots or dimensional deviations, and the stripping solution system is stable, making the coating dissolution rate more gentle and controllable, optimizing the uniformity of stripping, and improving the surface quality of the workpiece.

[0014] In one technical solution of the present invention, the stripping solution for aluminum-manganese alloy further includes: a corrosion inhibitor of 1g / L-5g / L, wherein the corrosion inhibitor is at least one of benzotriazole, mercaptobenzothiazole, and hexamethylenetetramine.

[0015] Compared with existing technologies, the technical effects achieved by this solution are as follows: benzotriazole, mercaptobenzothiazole, and hexamethylenetetramine all exhibit excellent alkali resistance and remain stable in the alkaline environment of the stripping solution of this invention, without decomposition, failure, or the generation of harmful impurities. Furthermore, the corrosion inhibitors selected in this invention do not react with core stripping components such as sodium hydroxide and sodium citrate, nor do they hinder the reaction between aluminum and OH groups. - The dissolution reaction of ions and the complexation effect of sodium citrate on metal ions ensure that the coating removal efficiency is not affected while ensuring the safety of the substrate. The concentration of 1g / L-5g / L can form a synergistic and stable system with the components of the stripping solution. It will not cause the solution to become turbid or separate due to excessive corrosion inhibitor, nor will it affect the protective effect due to insufficient concentration. It ensures that the stripping solution remains uniform and stable during long-term use and extends the service life of the stripping solution.

[0016] In one embodiment of the present invention, the stripping solution for aluminum-manganese alloys further includes: a complexing agent of 2 g / L-8 g / L, wherein the complexing agent is at least one of disodium ethylenediaminetetraacetate and sodium gluconate.

[0017] Compared with existing technologies, the technical effects achieved by this solution are as follows: The complexing agent, by forming soluble complexes with metal ions, can reduce the activation energy of the stripping reaction and moderately accelerate the dissolution rate of the aluminum-manganese alloy coating. Disodium ethylenediaminetetraacetate (EDTA) is a strong chelating agent that can form multi-component chelates with higher stability constants with manganese and aluminum ions, while sodium gluconate has good complexing selectivity for metal ions. Both can supplement the complexing capacity of sodium citrate, ensuring that the manganese and aluminum ions generated during the stripping process are fully captured. The synergistic effect of sodium hydroxide on stripping and sodium citrate on complexing results in a more efficient coating dissolution process with a uniform and controllable dissolution rate. Simultaneously, the addition of the complexing agent avoids reaction rate differences caused by localized metal ion accumulation, ensuring uniform dissolution of the coating in all areas of the workpiece surface. A concentration of 2 g / L-8 g / L ensures that metal ions in the stripping solution remain dissolved, maintaining a homogeneous and clear system over a long period, reducing the loss of solution components due to precipitation.

[0018] To achieve the second objective of this invention, the technical solution of this invention provides a method for stripping aluminum-manganese alloy plating, using any of the above-mentioned technical solutions for stripping aluminum-manganese alloy plating, comprising the following steps: S100, workpiece pretreatment, in which the aluminum-manganese alloy plating workpiece to be stripped is sequentially cleaned and dried; S200, stripping treatment, in which the pretreated workpiece is placed in a perforated mesh basket, and the mesh basket is placed in the stripping solution for stripping treatment; S300, post-treatment, in which the stripped workpiece is taken out and sequentially cleaned and dried to obtain the stripped aluminum-manganese alloy workpiece.

[0019] Compared with existing technologies, the technical effects achieved by this solution are as follows: Pre-treatment of the workpiece by sequential cleaning and drying before stripping effectively removes impurities such as oil, dust, and oxide scale from the workpiece surface. If these impurities are not removed, they will form an isolation layer during stripping, hindering direct contact between the stripping solution and the aluminum-manganese alloy coating, leading to incomplete stripping and coating residue. This pre-treatment ensures a clean and contaminant coating surface, providing a uniform contact interface for the stripping reaction, allowing the stripping solution to fully interact with the coating, ensuring complete dissolution of the coating, and avoiding stripping failure caused by impurities. Placing the workpiece in a perforated mesh basket for stripping ensures that the stripping solution quickly penetrates and surrounds the workpiece, preventing... The design eliminates dead zones in the liquid flow caused by workpiece stacking, ensuring that each workpiece is in a dynamic flow environment of the stripping solution. This guarantees consistent contact probability and contact time between different areas of the workpiece surface and the stripping solution, avoiding differences in coating dissolution rates due to uneven contact. This results in uniform stripping of the entire workpiece, with no local thickness differences or residues on the surface after stripping. The perforated basket facilitates operation and workpiece protection, and allows for easy overall transfer and flipping during stripping, reducing direct friction between workpieces and improving the ease of operation and production efficiency of the stripping process. The cleaning and drying treatment after stripping thoroughly removes residual stripping solution, complexes, and trace impurities from the workpiece surface, restoring it to a clean and dry state and ensuring its reliability for subsequent use or reprocessing.

[0020] In one technical solution of the present invention, in S200, the temperature of the stripping process is 25℃-40℃, and the frequency of mechanical tumbling in the stripping process is 3min / time-5min / time.

[0021] Compared with existing technologies, the technical effects achieved by this solution are as follows: the stripping temperature is limited to a mild range of 25℃-40℃, avoiding adverse consequences caused by high temperatures, such as accelerating the hydrolysis of sodium aluminate to generate a large amount of aluminum hydroxide gel and aggravating the agglomeration of manganese compound particles. Controlling the stripping temperature reduces the generation of gel-like adhesive substances, while maintaining the complexing activity of complexing agents such as sodium citrate. The frequency of mechanical tumbling is adapted, and regular tumbling can continuously change the posture of the workpiece in the basket, breaking the "gas resistance" formed by hydrogen bubbles attached to the workpiece surface and enhancing the uniformity of contact between the stripping solution and the coating. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be discussed below. Obviously, the technical solutions described in conjunction with the accompanying drawings are only some embodiments of the present invention. For those skilled in the art, other embodiments and their accompanying drawings can be obtained based on the embodiments shown in these drawings without creative effort.

[0023] Figure 1This is a schematic diagram of the state of the steel ball after deplating in Embodiment 1 of the present invention.

[0024] Figure 2 This is a schematic diagram of the state of the steel ball after deplating in Comparative Example 1 of the present invention. Detailed Implementation

[0025] The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments described in 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.

[0026]

Example 1

[0027]

Example 2

[0028]

Example 3

[0029]

Example 4

[0030]

Example 5

[0031]

Example 6

[0032]

Example 7

[0033]

Example 8

[0034]

Example 9

[0035]

Example 10

[0036] Comparative Example 1 The comparative stripping method is described in Example 1, except that in step S200, the stripping solution is only 50 g / L sodium hydroxide.

[0037] Comparative Example 2 The comparative method for stripping plating is described in Example 1, except that in step S200, the concentration of sodium citrate in the stripping solution is 10 g / L.

[0038] Comparative Example 3 The comparative stripping method is described in Example 1, except that in step S200, the pH value of the stripping solution is 9.

[0039] Table 1

[0040] Test description: Agglomeration phenomenon is measured by the proportion of the mass of the deposited layer in the solution after stripping and the mass of the deposited layer attached to the workpiece surface to the total mass of the workpiece; the substrate corrosion rate is calculated by weighing method (mass loss after corrosion / initial mass × 100%); the adhesion of re-electroplating is tested by pull-out method; the coating uniformity is grade 1 as the best (no obvious thickness difference) and grade 4 as the worst (local missing plating or thickness difference exceeding 0.5μm).

[0041] Reference Figure 1 and Figure 2 As shown, Figure 1 The stripped steel balls obtained by the stripping method of Embodiment 1 of the present invention are completely dispersed. Figure 2 The steel balls obtained by the existing deplating method in Comparative Example 1 exhibited a clumped morphology after deplating.

[0042] According to the test results in the table above, the aluminum and aluminum-manganese alloy coating stripping methods provided in Examples 1-10 can all achieve stripping without agglomeration or with low agglomeration. The complete stripping time is 18-45 minutes, the substrate corrosion rate is ≤0.5%, the re-electroplating adhesion is ≥2.7MPa, the coating uniformity reaches level 1, and the overall performance is excellent. Examples 1, 2, and 3 all showed no agglomeration, with substrate corrosion rates controlled below 0.5%, and complete stripping time of 25-45 minutes. The stripping method of this invention can stably achieve agglomeration-free stripping, while also achieving both stripping efficiency and substrate protection. Examples 4-10 further optimized the stripping performance by adding auxiliary components such as potassium sodium tartrate, surfactants, corrosion inhibitors, and complexing agents to the core components. In particular, Example 10, using a fully compounded system, achieved a complete stripping time of only 18 minutes, 40% shorter than Example 1, with a re-electroplating adhesion of 3.5 MPa, and no agglomeration or substrate corrosion. This demonstrates the synergistic complexing effect of the auxiliary complexing agent and the core complexing agent, the wetting and dispersing effect of the surfactant, and the substrate protection effect of the corrosion inhibitor, achieving the optimal balance between stripping efficiency, stripping quality, and substrate safety.

[0043] Comparative Example 1 showed severe agglomeration in 85% of the substrate, with a corrosion rate of 8% and a re-electroplating adhesion of only 1.2 MPa, proving that sodium citrate is the core key to solving the agglomeration problem and protecting the substrate. Comparative Example 2 still showed agglomeration in 30% of the substrate, and the stripping time was extended to 55 minutes, indicating that the sodium citrate concentration was insufficient to fully complex metal ions, and the agglomeration inhibition effect was significantly reduced. Comparative Example 3 showed milder agglomeration, but the stripping time was extended to 48 minutes, proving that the pH value limit of 10-12 is an important condition to ensure complexation efficiency and stripping rate.

[0044] In summary, by limiting the core components, concentration, and pH range of the stripping solution, and combining it with a mechanical tumbling process, this invention can flexibly combine auxiliary components to form a multi-compound system, achieving efficient and non-caking stripping of aluminum and aluminum-manganese alloy coatings, while effectively protecting the substrate and ensuring the reusability of the workpiece. This represents a significant improvement in performance compared to existing single sodium hydroxide stripping technology.

[0045] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims, not by the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0046] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A stripping solution for aluminum-manganese alloys, characterized in that, include: Sodium hydroxide, 30g / L-70g / L; Sodium citrate, 20g / L-70g / L.

2. The stripping solution for aluminum-manganese alloys according to claim 1, characterized in that, Also includes: Potassium sodium tartrate, 5 g / L-20 g / L; Surfactants, 0.1 g / L - 1 g / L; The surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and fatty alcohol polyoxyethylene ether.

3. The stripping solution for aluminum-manganese alloys according to claim 1, characterized in that, The pH value of the stripping solution is 10-12.

4. The stripping solution for aluminum-manganese alloys according to claim 1, characterized in that, It also includes a corrosion inhibitor of 1g / L-5g / L, wherein the corrosion inhibitor is at least one of benzotriazole, mercaptobenzothiazole, and hexamethylenetetramine.

5. The stripping solution for aluminum-manganese alloys according to claim 1, characterized in that, It also includes a complexing agent of 2 g / L-8 g / L, wherein the complexing agent is at least one of disodium ethylenediaminetetraacetate and sodium gluconate.

6. A method for stripping aluminum-manganese alloy plating, using the stripping solution for aluminum-manganese alloy as described in any one of claims 1-5, characterized in that, Includes the following steps: S100. Pre-treatment of workpieces: Clean and dry the aluminum-manganese alloy coated workpieces to be de-plated in sequence. S200, Stripping treatment: Place the pretreated workpiece in a perforated mesh basket, place the mesh basket in the stripping solution, and perform stripping treatment. S300, post-processing: The workpiece after stripping is taken out and then cleaned and dried to obtain stripped aluminum-manganese alloy workpiece.

7. The aluminum-manganese alloy stripping method according to claim 6, characterized in that, In S200, the temperature for stripping is 25℃-40℃, and the frequency of mechanical tumbling during stripping is 3min / time to 5min / time.

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