Trivalent chromium coating with amorphous-crystalline heterogeneous composite structure and preparation method of trivalent chromium coating

Abstract

The invention relates to the technical field of electrodeposition chromium plating layers, and provides a trivalent chromium plating layer with an amorphous-crystalline heterogeneous composite structure and a preparation method of the trivalent chromium plating layer. The preparation method of the trivalent chromium plating layer comprises the following steps that S1, a nucleating agent is added into a plating solution, and then the trivalent chromium plating layer is prepared on the surface of a metal matrix in an electro-deposition mode; and S2, the metal matrix deposited with the trivalent chromium plating layer is placed in an annealing furnace, the temperature is increased to 200-250 DEG C, heat preservation is conducted for 60-150 min, and then cooling is conducted. Through cooperative regulation and control of the organic nucleating agent and low-temperature annealing, crystal phases are uniformly distributed in an amorphous matrix in a granular form, and the crystallinity is stabilized at 10-50%. The amorphous phase guarantees good corrosion resistance, the granular crystal phase improves hardness and wear resistance, the problems that a traditional nano-particle nucleating agent is prone to agglomeration and large in performance fluctuation are solved, and the final coating can stably meet the comprehensive performance requirement for surface protection of mechanical parts.

Description

Technical Field

[0001] This invention relates to the field of electrodeposited chromium plating technology, and more particularly to a trivalent chromium plating with an amorphous-crystalline heterocomposite structure and its preparation method. Background Technology

[0002] In the field of surface protection for mechanical parts, many key components need to withstand load friction and corrosive media erosion for a long time. Their surface coatings need to have excellent comprehensive performance to ensure the reliability and life of the components, while also taking into account environmental protection and the feasibility of industrial production, so as to avoid component damage or environmental hazards due to protection failure, and meet the long-term stable operation requirements of mechanical equipment in multiple scenarios.

[0003] In electrodeposited chromium plating, hexavalent chromium plating was once widely used in surface protection due to its good hardness and wear resistance. However, its high toxicity and carcinogenicity cause serious environmental hazards, violating environmental protection principles and sustainable development requirements, and it has been gradually replaced by low-toxicity trivalent chromium plating. However, conventional trivalent chromium electrodeposited products are mostly pure amorphous structures, and the long-range disorder of atoms makes it difficult for their wear resistance to meet the requirements of heavy-duty operating conditions. Moreover, although the amorphous structure has a certain degree of corrosion resistance, it is still prone to protective failure in long-term complex media environments, and cannot provide durable and stable surface protection for components.

[0004] To improve the overall performance of trivalent chromium plating, existing technologies have explored various improvement paths: alloy electrodeposition, by introducing metallic elements into the plating to refine its structure, can improve performance to some extent, but it easily leads to a decrease in plating toughness, making it prone to breakage under impact; composite electrodeposition technology embeds nanoparticles into the plating to enhance wear resistance, but it significantly increases the brittleness of the plating, leading to a risk of cracking; while annealing to achieve complete crystallization of the trivalent chromium plating can improve the plating hardness, if the plating is completely crystallized, numerous grain boundaries will become channels for the invasion of corrosive media, resulting in a significant decrease in corrosion resistance. Furthermore, existing technologies for controlling the crystalline phase of trivalent chromium plating largely rely on a single annealing process, making it difficult to achieve a uniform granular distribution of the crystalline phase. This easily leads to crystalline phase agglomeration or the formation of continuous grain boundaries, resulting in poor plating performance stability and significant fluctuations, making it unsuitable for mass production requirements. Therefore, how to achieve uniform granular distribution of crystalline phases in trivalent chromium plating, while simultaneously ensuring the coating's hardness, wear resistance, and corrosion resistance, and taking into account environmental protection requirements and the convenience of industrial production, has become a pressing technical challenge in this field. Summary of the Invention

[0005] In view of this, the present invention proposes a trivalent chromium plating with an amorphous-crystalline heterogeneous composite structure having a granular distribution and its preparation method. By precisely controlling the microstructure of the plating, the crystallinity of 10%-50% and the crystalline phase being uniformly distributed in a granular form are achieved, which meets the comprehensive performance required for surface protection and achieves a synergistic improvement in hardness, wear resistance and corrosion resistance, while taking into account environmental protection and the feasibility of industrial production.

[0006] The technical solution of this invention is achieved as follows: On one hand, this invention provides a method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterocomposite structure, comprising the following steps: S1, a nucleating agent is added to the plating solution, and then a trivalent chromium plating layer is prepared on the surface of the metal substrate by electrodeposition. S2, the metal substrate with the deposited trivalent chromium plating layer is placed in an annealing furnace, heated to 200-250℃, held for 60-150 minutes and then cooled.

[0007] Specifically, the role of organic nucleating agents is to provide uniformly distributed heterogeneous nucleation sites for the crystalline phase through interfacial adsorption or metal ion complexation, thereby inducing the formation and dispersion of granular crystalline phases.

[0008] Low-temperature annealing (200-250℃) can avoid excessive grain growth or coating interface cracking. Combined with the inductive effect of organic nucleating agents, it can achieve precise control of the morphology and proportion of crystalline phase particles, while retaining the corrosion resistance advantages of amorphous phase.

[0009] Based on the above technical solutions, preferably, in step S1, the plating solution components include: chromium sulfate, formic acid, urea, sodium sulfate, boric acid, aluminum sulfate octadecahydrate, and SDS.

[0010] Based on the above technical solutions, the preferred concentrations of each component in the plating solution are: 0.3-0.8 mol / L chromium sulfate, 0.3-0.7 mol / L formic acid, 0.2-0.6 mol / L urea, 0.2-0.5 mol / L sodium sulfate, 0.3-0.6 mol / L boric acid, 0.1-0.2 mol / L aluminum sulfate octadechydrate, and 0.1-0.5 g / L SDS, with water as the solvent and a pH of 1.5-2.5.

[0011] Based on the above technical solutions, preferably, the nucleating agent is one or more of triethanolamine, citric acid and tartaric acid.

[0012] Based on the above technical solutions, preferably, the amount of nucleating agent used is 0.1-3 g / L.

[0013] Based on the above technical solution, preferably, in step S1, the current density during electrodeposition is 16-25 A / dm³. 2The deposition temperature is 30-40℃ and the deposition time is 30-100 min.

[0014] Based on the above technical solutions, preferably, in step S1, the cooling method is furnace cooling or air cooling.

[0015] Based on the above technical solutions, preferably, in step S2, the temperature is increased to 200-250℃ at a rate of 5-20℃ / min.

[0016] On the other hand, the present invention also provides a trivalent chromium plating layer with an amorphous-crystalline heterocomposite structure, which is prepared by the above-described preparation method.

[0017] Based on the above technical solutions, preferably, the crystallinity of the trivalent chromium plating layer is 10%-50%.

[0018] The trivalent chromium plating layer with an amorphous-crystalline heterocomposite structure and its preparation method of the present invention have the following advantages over the prior art: (1) This invention achieves uniform distribution of crystalline phase in a granular form in an amorphous matrix through the synergistic regulation of organic nucleating agent and low-temperature annealing, with crystallinity stable at 10%-50%. The amorphous phase ensures good corrosion resistance, while the granular crystalline phase improves hardness and wear resistance, solving the problems of easy agglomeration and large performance fluctuation of traditional nanoparticle nucleating agents. The final coating can stably meet the comprehensive performance requirements of surface protection for mechanical parts.

[0019] (2) Organic nucleating agents have advantages such as good dispersibility and high compatibility with plating solutions. Moreover, the present invention can achieve the target structure and performance by simply adding organic nucleating agents to the plating solution and single-step annealing. No complex equipment modification is required, which effectively simplifies the production process, reduces industrialization costs, and is more conducive to mass production applications.

[0020] (3) The preparation process of this invention uses a low-toxicity trivalent chromium system and an environmentally friendly organic nucleating agent, which has no risk of hexavalent chromium pollution and avoids the potential environmental hazards of nanoparticles. It meets the requirements of sustainable development and can be adapted to the surface protection scenarios of various parts in the field of mechanical manufacturing, with a wide range of applications. Attached Figure Description

[0021] 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 these drawings without creative effort.

[0022] Figure 1This is an electron microscope image of a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 25% prepared in Example 3 of the present invention. Figure 2 This is an electron microscope image of a trivalent chromium plating layer with an amorphous-crystalline heterostructure of 50% prepared in Example 5 of the present invention. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 This embodiment provides a method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure, including the following steps: S1, add 0.1 g / L of nucleating agent triethanolamine to the plating bath, and then prepare a trivalent chromium plating layer on the surface of the metal substrate by electrodeposition; The plating solution consists of: 0.5 mol / L chromium sulfate, 0.5 mol / L formic acid, 0.5 mol / L urea, 0.3 mol / L sodium sulfate, 0.5 mol / L boric acid, 0.15 mol / L aluminum sulfate octadecahydrate, and 0.3 g / L SDS. The solvent is water, and the pH is 2.

[0025] During electrodeposition, the current density was 20 A / dm³. 2 The deposition temperature was 35℃ and the deposition time was 65 min.

[0026] S2, the metal substrate with the deposited trivalent chromium plating layer is placed in an annealing furnace, heated to 250°C at a rate of 5°C / min, held at that temperature for 60 minutes, and then cooled with the furnace.

[0027] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 30% was prepared. The plating layer had a hardness of 936 HV, a coefficient of friction of 0.48, and a corrosion rate of 3.65 × 10⁻⁶. -2 mm / a. The methods for detecting the friction coefficient and corrosion rate are as follows: Friction coefficient: Tribological properties were characterized using a tribological testing machine (Retc MT-5000, USA), with Al2O3 balls of 6 mm diameter used as the grinding pair. The friction test was conducted under a constant normal load of 5 N for 1800 s, with a sliding frequency of 1 Hz, a sliding speed of 2 cm / s, and a stroke length of 10 mm.

[0028] Corrosion rate (3.5 wt% HCl solution): The potentiodynamic polarization curves were measured using a CHI660E electrochemical instrument employing a conventional three-electrode system, including a platinum sheet (1 cm²). 2 The electrode used was a counter electrode, a saturated calomel electrode (SCE, 3M KCl) was used as a reference electrode, and the sample (exposed area: 1 cm²) was used as the reference electrode. 2 The sample was used as the working electrode. Before measurement, the sample was immersed in the electrolyte for 60 min to obtain a stable open-circuit potential (OCP). Potentiodynamic polarization measurements were performed in the range of -0.5 to 0.5 V relative to the open-circuit potential (OCP) at a scan rate of 1 mV·s. -1 .

[0029] Example 2 Compared with Example 1, this embodiment adds 1.5 g / L of nucleating agent triethanolamine to the plating solution, and the rest are the same as in Example 1.

[0030] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 40% was prepared. The plating layer had a hardness of 954 HV, a coefficient of friction of 0.50, and a corrosion rate of 3.27 × 10⁻⁶. -2 mm / a.

[0031] Example 3 Compared with Example 1, this embodiment adds 3g / L of nucleating agent triethanolamine to the plating solution, and the rest are the same as in Example 1.

[0032] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 25% was prepared. Figure 1 As shown. At this point, the coating hardness is 880 HV, the coefficient of friction is 0.53, and the corrosion rate is 3.05 × 10⁻⁶. -2 mm / a.

[0033] Example 4 Compared with Example 2, the heat preservation time in this embodiment is 150 minutes, and the rest of the contents are the same as in Example 2.

[0034] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 45% was prepared. The plating layer had a hardness of 980 HV, a coefficient of friction of 0.54, and a corrosion rate of 3.11 × 10⁻⁶. -2 mm / a.

[0035] Example 5 Compared with Example 2, the heat preservation time in this embodiment is 100 minutes, and the rest of the contents are the same as in Example 2.

[0036] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 50% was prepared. Figure 2As shown. At this time, the hardness of the coating is 1000 HV, the coefficient of friction is 0.44, and the corrosion rate is 4.92 × 10⁻⁶. -2 mm / a.

[0037] Example 6 Compared with Example 2, this embodiment is heated to 220°C, and the rest of the contents are the same as Example 2.

[0038] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 30% was prepared. The plating layer had a hardness of 915 HV, a coefficient of friction of 0.50, and a corrosion rate of 3.21 × 10⁻⁶. -2 mm / a.

[0039] Example 7 Compared with Example 2, this embodiment is heated to 200°C, and the rest of the contents are the same as Example 2.

[0040] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 30% was prepared. The plating layer had a hardness of 927 HV, a coefficient of friction of 0.55, and a corrosion rate of 3.14 × 10⁻⁶. -2 mm / a.

[0041] Example 8 Compared with Example 1, the heating rate in this embodiment is 10°C, and the rest of the contents are the same as in Example 1.

[0042] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 25% was prepared. The plating layer had a hardness of 915 HV, a coefficient of friction of 0.52, and a corrosion rate of 3.48 × 10⁻⁶. -2 mm / a.

[0043] Example 9 Compared with Example 1, the heating rate in this embodiment is 20°C, and the rest of the contents are the same as in Example 1.

[0044] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 20% was prepared. The plating layer had a hardness of 885 HV, a coefficient of friction of 0.54, and a corrosion rate of 3.35 × 10⁻⁶. -2 mm / a.

[0045] Example 10 This embodiment provides a method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure, including the following steps: S1, add 0.1 g / L of nucleating agent citric acid to the plating bath, and then prepare a trivalent chromium plating layer on the surface of the metal substrate by electrodeposition; The plating solution consists of: 0.3 mol / L chromium sulfate, 0.3 mol / L formic acid, 0.2 mol / L urea, 0.2 mol / L sodium sulfate, 0.3 mol / L boric acid, 0.1 mol / L aluminum sulfate octadecahydrate, and 0.1 g / L SDS. The solvent is water, and the pH is 1.5.

[0046] During electrodeposition, the current density was 16 A / dm³. 2 The deposition temperature was 40℃ and the deposition time was 65 min.

[0047] S2, the metal substrate with the deposited trivalent chromium plating layer is placed in an annealing furnace, heated to 250°C at a rate of 5°C / min, held at that temperature for 60 minutes, and then cooled with the furnace.

[0048] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 30% was prepared. The plating layer had a hardness of 925 HV, a coefficient of friction of 0.55, and a corrosion rate of 2.65 × 10⁻⁶. -2 mm / a.

[0049] Example 11 This embodiment provides a method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure, including the following steps: S1, add 0.1 g / L of nucleating agent citric acid to the plating bath, and then prepare a trivalent chromium plating layer on the surface of the metal substrate by electrodeposition; The plating solution consists of: 0.8 mol / L chromium sulfate, 0.7 mol / L formic acid, 0.6 mol / L urea, 0.5 mol / L sodium sulfate, 0.6 mol / L boric acid, 0.2 mol / L aluminum sulfate octadechydrate, and 0.5 g / L SDS. The solvent is water, and the pH is 2.5.

[0050] During electrodeposition, the current density is 25 A / dm³. 2 The deposition temperature was 30℃ and the deposition time was 65 min.

[0051] S2, the metal substrate with the deposited trivalent chromium plating layer is placed in an annealing furnace, heated to 250°C at a rate of 5°C / min, held at that temperature for 60 minutes, and then cooled with the furnace.

[0052] In this embodiment, a trivalent chromium plating layer with an amorphous-crystalline heterostructure and a crystallinity of 45% was prepared. The plating layer had a hardness of 995 HV, a coefficient of friction of 0.46, and a corrosion rate of 3.02 × 10⁻⁶. -2 mm / a.

[0053] Comparative Example 1 Compared with Example 1, no nucleating agent was added to the plating solution in this comparative example, but the rest of the contents are the same as in Example 1.

[0054] This comparative example yielded a trivalent chromium coating with an amorphous-crystalline heterostructure and a crystallinity of 5%. The coating exhibited a hardness of 770 HV, a coefficient of friction of 0.66, and a corrosion rate of 4.45 × 10⁻⁶. -2 mm / a. Due to the absence of a nucleating agent in this comparative example, the crystallinity is low, resulting in poor overall performance of the coating.

[0055] Comparative Example 2 Compared with Example 1, this comparative example has 5 g / L of nucleating agent triethanolamine (excess) added to the plating solution, and the rest is the same as in Example 1.

[0056] This comparative example yielded a trivalent chromium coating with an amorphous-crystalline heterocomposite structure and a crystallinity of 50%. The coating exhibited a hardness of 900 HV, a coefficient of friction of 0.75, and a corrosion rate of 2.21 × 10⁻⁶. -1 mm / a. Due to the excessive nucleating agent in this comparative example, although the crystallinity was about 50%, there was obvious uneven grain distribution and some abnormal grain growth, resulting in poor wear resistance.

[0057] Comparative Example 3 Compared with Example 1, the heat preservation time in this comparative example is 10 min, and the rest of the contents are the same as in Example 1.

[0058] This comparative example yielded a trivalent chromium coating with an amorphous-crystalline heterocomposite structure and a crystallinity of 5%. The coating exhibited a hardness of 710 HV, a coefficient of friction of 0.54, and a corrosion rate of 9.58 × 10⁻⁶. -2 mm / a. However, in this comparative example, the annealing holding time was too short. Even though the coating had reached the crystallization temperature, it failed to undergo sufficient crystallization transformation. In addition, the surface of the deposited chromium coating already contained many chromium nodules. The short holding time was insufficient to allow the nodules to completely diffuse and disappear, resulting in the presence of loosely arranged atomic regions within the nodules. The combined effect of these factors ultimately led to a high corrosion rate for the coating at this point. Furthermore, the low crystallinity prevented the coating from meeting the required wear resistance and hardness standards.

[0059] Comparative Example 4 Compared with Example 1, the heat preservation time in this comparative example is 180 min, and the rest of the contents are the same as in Example 1.

[0060] This comparative example yielded a trivalent chromium coating with an amorphous-crystalline heterocomposite structure and a crystallinity of 50%. The coating exhibited a hardness of 950 HV, a coefficient of friction of 0.57, and a corrosion rate of 7.92 × 10⁻⁶. -2 mm / a. However, under these conditions, the heat preservation time is too long, which leads to excessive growth (coarsening) of grains in the coating, ultimately resulting in a decrease in corrosion resistance.

[0061] Comparative Example 5 Compared with Example 1, the annealing temperature of this comparative example is 150°C, and the rest of the contents are the same as those of Example 1.

[0062] This comparative example yielded a completely amorphous trivalent chromium coating. The coating exhibited a hardness of 700 HV, a coefficient of friction of 0.67, and a corrosion rate of 9.46 × 10⁻⁶. -2 mm / a. The annealing temperature is significantly low, far below the critical crystallization temperature of trivalent chromium plating, preventing the plating from undergoing a crystallization transformation and maintaining its amorphous state. Furthermore, at low temperatures, the chromium nodules on the surface of the deposited plating are difficult to diffuse effectively, preserving their internal porous structure. The amorphous plating itself has weak chemical stability, and the combined effect of the porous defects from the chromium nodules ultimately results in poor corrosion resistance. Moreover, the non-crystallized plating has low hardness and a high coefficient of friction, failing to meet usage standards.

[0063] Comparative Example 6 Compared with Example 1, the annealing temperature of this comparative example is 300°C, and the rest of the contents are the same as those of Example 1.

[0064] This comparative example yielded a trivalent chromium coating with an amorphous-crystalline heterostructure and a crystallinity of 90%. The coating exhibited a hardness of 1090 HV, a coefficient of friction of 0.51, and a corrosion rate of 4.50 × 10⁻⁶. -1 mm / a. The high annealing temperature in this process leads to high crystallinity of the coating and the appearance of network cracks on the coating surface, ultimately resulting in a significant decrease in corrosion resistance.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure, characterized in that, Includes the following steps: S1, a nucleating agent is added to the plating solution, and then a trivalent chromium plating layer is prepared on the surface of the metal substrate by electrodeposition. S2, the metal substrate with the deposited trivalent chromium plating layer is placed in an annealing furnace, heated to 200-250℃, held for 60-150 minutes and then cooled.

2. The method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure as described in claim 1, characterized in that, In step S1, the plating solution components include: chromium sulfate, formic acid, urea, sodium sulfate, boric acid, aluminum sulfate octadecahydrate, and SDS.

3. The method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure as described in claim 2, characterized in that, In step S1, the concentrations of each component in the plating solution are: 0.3-0.8 mol / L chromium sulfate, 0.3-0.7 mol / L formic acid, 0.2-0.6 mol / L urea, 0.2-0.5 mol / L sodium sulfate, 0.3-0.6 mol / L boric acid, 0.1-0.2 mol / L aluminum sulfate octadechydrate, and 0.1-0.5 g / L SDS. The solvent is water, and the pH is 1.5-2.

5.

4. The method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure as described in claim 1, characterized in that, The nucleating agent is one or more of triethanolamine, citric acid, and tartaric acid.

5. The method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure as described in claim 4, characterized in that, The amount of nucleating agent used is 0.1-3 g / L.

6. The method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure as described in claim 1, characterized in that, In step S1, the current density during electrodeposition is 16-25 A / dm³. 2 The deposition temperature is 30-40℃ and the deposition time is 30-100 min.

7. The method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure as described in claim 1, characterized in that, In step S1, the cooling method is furnace cooling or air cooling.

8. The method for preparing a trivalent chromium plating layer with an amorphous-crystalline heterostructure as described in claim 1, characterized in that, In step S2, the temperature is increased to 200-250℃ at a rate of 5-20℃ / min.

9. A trivalent chromium plating layer having an amorphous-crystalline heterogeneous composite structure, characterized in that: It is prepared by the preparation method according to any one of claims 1-8.

10. A trivalent chromium plating layer with an amorphous-crystalline heterogeneous composite structure as described in claim 9, characterized in that: The crystallinity of the trivalent chromium plating is 10%-50%.

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