A high-carbon-content hydrophobic corrosion-resistant trivalent chromium-carbon alloy plating layer and a low-temperature electroplating preparation method thereof

Abstract

This invention discloses a high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating and its low-temperature electroplating preparation method, relating to the field of metal electroplating technology. The method includes the following steps: substrate pretreatment, preparation of the electroplating solution, low-temperature circulating cooling system, electroplating reaction, formation of the Cr-C coating, and post-treatment. This invention can increase the carbon content, achieving a coating carbon content of over 40 at%; improve hydrophobicity, with a contact angle of 100–120°, optimally reaching over 114°; improve corrosion resistance, significantly reducing corrosion current; improve conductivity, forming a Cr-C conductive network; reduce surface resistivity; reduce coating cracking, with low-temperature growth reducing deposition stress; and comply with environmental regulations, being completely free of hexavalent chromium and meeting RoHS and REACH requirements.

Description

Technical Field

[0001] This invention relates to the field of metal electroplating technology, specifically to a high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating and its low-temperature electroplating preparation method. Background Technology

[0002] Chromium plating, due to its excellent wear resistance, high hardness, corrosion resistance, high temperature resistance, and good decorative effect, has long been widely used in mechanical parts, molds, automotive components, aerospace equipment, medical devices, and the electronics industry. Traditional chromium plating primarily uses hexavalent chromium electroplating, resulting in coatings with high hardness and wear resistance. However, hexavalent chromium compounds are highly oxidizing and toxic, and have been listed as carcinogens by the World Health Organization (WHO). Furthermore, the electroplating process easily generates chromium-containing fumes, posing serious harm to human health and the environment. Therefore, the EU RoHS directive and REACH regulations have strictly restricted the use of hexavalent chromium, leading the electroplating industry towards non-toxic and green manufacturing, and in recent years, it has been gradually replaced by trivalent chromium electroplating technology.

[0003] Trivalent chromium electroplating technology has gradually become one of the important technologies to replace traditional hexavalent chromium electroplating due to its advantages such as low toxicity, environmental friendliness, easy wastewater treatment, and compliance with international environmental regulations. However, trivalent chromium ions easily form a stable hydrated ionic structure in aqueous solution, and its reduction deposition efficiency is much lower than that of the hexavalent chromium system. Therefore, it is necessary to add organic chelating agents, conductive salts, and other functional additives to promote the deposition reaction of metallic chromium.

[0004] In the trivalent chromium electroplating process, organic chelating agents such as formic acid, ammonium formate, acetate, and oxalate are commonly used as coordination compounds. Studies have found that during the electroplating reaction, some carbon elements in these carbon-containing organic coordination agents co-deposit with chromium ions in the coating, forming a chromium-carbon (Cr-C) alloy coating with unique properties. Compared to traditional pure chromium coatings, Cr-C alloy coatings retain the high hardness and wear resistance of chromium, while also exhibiting better corrosion resistance, electrical conductivity, and thermal stability. Therefore, they have received significant attention from the materials engineering and surface treatment industries in recent years.

[0005] On the other hand, in recent years, hydrophobic surface materials have been widely used in medical devices, marine equipment, solar modules, electronic components, and corrosion protection engineering. Generally, hydrophobic surfaces are prepared using methods such as fluoride coatings, silane modification, or nanomaterial coatings. However, these methods are complex, costly, and the coatings are prone to failure due to wear. Therefore, if a Cr-C alloy coating with high hardness, high corrosion resistance, and hydrophobic properties could be directly formed using electroplating, it would have extremely high industrial application value.

[0006] However, most known Cr-C alloy coating processes are performed at room temperature or higher temperatures. Under these conditions, the reduction rate of chromium ions is faster, resulting in a higher chromium content in the coating, while the co-deposition efficiency of carbon is lower, leading to insufficient carbon content in the coating. Due to insufficient carbon content, the coating surface is prone to large internal stresses and microcracks, which in turn affect the corrosion resistance and service life of the coating. In addition, traditional Cr-C coatings often exhibit hydrophilic or weakly hydrophobic properties, with contact angles typically below 90°, making it difficult to meet the application requirements for self-cleaning, anti-fouling, anti-sticking, and special functional surfaces.

[0007] Studies show that lowering the electroplating temperature can effectively alter the reaction kinetics between chromium ions and organic coordinating agents, making it easier for carbon elements to participate in the co-deposition reaction and increasing the carbon content in the Cr-C coating. Simultaneously, the high-carbon-content Cr-C coating can form unique micro-nano surface structures, thereby improving surface contact angle and hydrophobic properties. However, a technology currently lacking that can stably control the plating bath temperature, effectively increase the carbon content, and simultaneously obtain trivalent chromium-carbon alloy coatings with high corrosion resistance and high hydrophobicity is still lacking.

[0008] Currently, trivalent chromium electroplating mainly utilizes organic carboxylic acid chelating agents to form a stable plating solution. During the electroplating reaction, carbon elements co-deposit with metallic chromium to form a Cr-C alloy coating. This type of coating has advantages such as high corrosion resistance, high hardness, and good electrical conductivity. However, current trivalent chromium Cr-C coatings still have problems such as difficulty in controlling the carbon content of the coating, insufficient hydrophobicity, numerous coating cracks, and unstable corrosion resistance. Specifically:

[0009] (a) Low carbon content in the coating

[0010] Trivalent chromium electroplating is generally performed at 20–40°C. At high temperatures, the reduction rate of chromium ions is too rapid, resulting in an increase in the chromium content of the plating layer and a decrease in the carbon content.

[0011] (ii) Insufficient hydrophobicity

[0012] Traditional Cr-C coatings typically have a contact angle of less than 90°, making them unable to achieve a self-cleaning effect.

[0013] (III) Coating cracking problem

[0014] After increasing the coating thickness:

[0015] It is prone to cracking due to internal stress, which reduces its corrosion resistance.

[0016] (iv) It is difficult to achieve both electrical conductivity and corrosion resistance.

[0017] Increasing the chromium content can increase hardness, but it will reduce the carbon content, affecting corrosion resistance and electrical conductivity.

[0018] (v) Lack of low temperature control mechanism

[0019] Currently, there is no complete technical solution for improving the carbon content and hydrophobic properties of Cr-C coatings using low temperatures. Summary of the Invention

[0020] The purpose of this invention is to provide a high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating and its low-temperature electroplating preparation method, which solves the problems that still exist in the preparation of trivalent chromium coatings at low temperatures, such as difficulty in controlling the carbon content of the coating, insufficient hydrophobicity, numerous coating cracks, and unstable corrosion resistance.

[0021] To achieve the above objectives, the present invention provides the following technical solution:

[0022] A high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating, wherein the carbon content of the coating is 20-50 at%, and the contact angle is 100-120°.

[0023] Furthermore, the carbon content in the coating is 35-45 at%, and the contact angle is not less than 114°.

[0024] This invention also provides the following technical solutions:

[0025] A low-temperature electroplating solution for a high-carbon-content, hydrophobic, corrosion-resistant trivalent chromium-carbon alloy coating, the solution comprising a main salt, a chelating agent, a conductive salt, and a surfactant.

[0026] Main salt: 0.1–0.5 M chromium chloride;

[0027] Chelating agent: one or any combination of ammonium formate, sodium formate, oxalate, and acetate, totaling 3M;

[0028] Conductive salt: one or any combination of ammonium chloride, sodium chloride, and ammonium sulfate, totaling 1M;

[0029] Surfactant: Succinate sulfonate, 0.01-0.5 wt%, to improve coating uniformity.

[0030] This invention also provides the following technical solutions:

[0031] A high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating and its low-temperature electroplating preparation method include the following steps: substrate pretreatment, preparation of electroplating solution, low-temperature circulating cooling system, electroplating reaction, formation of Cr-C coating, and post-treatment.

[0032] S1. Substrate pretreatment: Degreasing treatment, immerse the substrate in acetone for 2 minutes; Alkali washing treatment, immerse the degreased substrate in 30g / L NaOH solution for 30 seconds; Acid washing treatment, immerse the alkali-washed substrate in 10-20% HCl solution for 10 seconds to 1 minute; DI water cleaning treatment, use high-purity water to remove ionic residues, soluble impurities and particulate matter from the surface of the substrate after acid washing.

[0033] S2. Prepare the electroplating solution: Prepare a plating solution containing 0.2M chromium chloride, 3M chelating agent, 1M conductive salt, and 0.01-0.5wt% additives.

[0034] S3. Low-temperature circulating cooling system: The temperature of the plating solution is controlled within the range of -5 to 10℃ using refrigeration equipment;

[0035] S4. Electroplating reaction: Place the substrate after DI water cleaning into the plating solution, apply current, current density: 10~30A / dm², time: 10~60 minutes;

[0036] S5. Formation of a Cr-C coating: thickness 5–30 μm, carbon content 35–45 at%;

[0037] S6. Post-treatment: The substrate after electroplating reaction is washed again with DI water, and then dried with hot air to obtain the finished product.

[0038] The beneficial effects of this invention are as follows:

[0039] (1) Increase carbon content

[0040] The carbon content of the coating can reach over 40 at%.

[0041] (2) Improve hydrophobicity

[0042] Contact angle: 100-120°, optimal up to 114° or higher.

[0043] (3) Improve corrosion resistance

[0044] The corrosion current was significantly reduced.

[0045] (4) Improve electrical conductivity

[0046] Cr-C conductive network is formed, reducing surface resistivity.

[0047] (5) Reduce coating cracks

[0048] Low-temperature growth reduces deposition stress.

[0049] (6) Complies with environmental protection standards

[0050] It contains no hexavalent chromium and complies with RoHS and REACH requirements.

[0051] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the Cr-C coating formation mechanism of the present invention.

[0053] Figure 2 This is a graph showing the relationship between carbon content at different temperatures according to the present invention.

[0054] Figure 3 This is a diagram showing the contact angle relationship of the present invention at different temperatures.

[0055] Figure 4 This is a flowchart of the entire invention. Detailed Implementation

[0056] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0058] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0059] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0060] Please see Figure 1 A preferred embodiment of this application shows a high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating, wherein the carbon content in the coating is 20-50 at%, and the contact angle is 100-120°.

[0061] Furthermore, the carbon content in the coating is 35–45 at%, and the contact angle is not less than 114°.

[0062] This invention also provides the following technical solutions:

[0063] A low-temperature electroplating solution for a high-carbon-content, hydrophobic, corrosion-resistant trivalent chromium-carbon alloy coating, comprising a main salt, a chelating agent, a conductive salt, and a surfactant.

[0064] Main salt: 0.1–0.5 M chromium chloride;

[0065] Chelating agent: one or any combination of ammonium formate, sodium formate, oxalate, and acetate, totaling 3M;

[0066] Conductive salt: one or any combination of ammonium chloride, sodium chloride, and ammonium sulfate, totaling 1M;

[0067] Surfactant: Succinate sulfonate, 0.01-0.5 wt%, to improve coating uniformity.

[0068] This invention also provides the following technical solutions:

[0069] A high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating and its low-temperature electroplating preparation method include the following steps: substrate pretreatment, preparation of electroplating solution, low-temperature circulating cooling system, electroplating reaction, formation of Cr-C coating, and post-treatment.

[0070] S1. Substrate pretreatment: Degreasing treatment, immerse the substrate in acetone for 2 minutes; Alkali washing treatment, immerse the degreased substrate in 30g / L NaOH solution for 30 seconds; Acid washing treatment, immerse the alkali-washed substrate in 10-20% HCl solution for 10 seconds to 1 minute; DI water cleaning treatment, use high-purity water to remove ionic residues, soluble impurities and particulate matter from the surface of the substrate after acid washing.

[0071] S2. Prepare the electroplating solution: Prepare a plating solution containing 0.2M chromium chloride, 3M chelating agent, 1M conductive salt, and 0.01-0.5wt% additives.

[0072] S3. Low-temperature circulating cooling system: The temperature of the plating solution is controlled within the range of -5 to 10℃ using refrigeration equipment;

[0073] S4. Electroplating reaction: Place the substrate after DI water cleaning into the plating solution, apply current, current density: 10~30A / dm², time: 10~60 minutes;

[0074] S5. Formation of a Cr-C coating: thickness 5–30 μm, carbon content 35–45 at%;

[0075] S6. Post-treatment: The substrate after electroplating reaction is washed again with DI water, and then dried with hot air to obtain the finished product.

[0076] Figure 1 In the diagram, 1 is the electroplating tank; 2 is the anode plate; 3 is the cathode hanger; 4 is the substrate; 5 is the low-temperature circulating cooling system; 6 is the temperature sensor; 7 is the motion device; 8 is the DC power supply; and 9 is the cooling unit.

[0077] The hydrophobic Cr-C surface formation mechanism is achieved by forming a hydrophobic surface through a high-carbon-content micro-nano rough structure.

[0078] High corrosion resistant Cr-C coating

[0079] The composite structure of Cr, Cr2O3, Cr(OH)3, and Cr-C is used to enhance corrosion resistance.

[0080] In summary, this invention provides a high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating and its low-temperature electroplating preparation method. This method can increase the carbon content, with the coating carbon content reaching over 40 at%; improve hydrophobicity, with a contact angle of 100–120°, optimally reaching over 114°; improve corrosion resistance, significantly reducing corrosion current; improve conductivity, forming a Cr-C conductive network; reduce surface resistivity; reduce coating cracking, with low-temperature growth reducing deposition stress; and comply with environmental regulations, being completely free of hexavalent chromium and meeting RoHS and REACH requirements.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-carbon-content, hydrophobic, corrosion-resistant trivalent chromium-carbon alloy coating, characterized in that, The coating has a carbon content of 20–50 at%, and a contact angle of 100–120°.

2. The high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating as described in claim 1, characterized in that, The carbon content in the coating is 35-45 at%, and the contact angle is not less than 114°.

3. A plating solution for low-temperature electroplating of a high-carbon-content, hydrophobic, corrosion-resistant trivalent chromium-carbon alloy coating, characterized in that... The plating solution includes a main salt, a chelating agent, a conductive salt, and a surfactant. Main salt: 0.1–0.5 M chromium chloride; Chelating agent: one or any combination of ammonium formate, sodium formate, oxalate, and acetate, totaling 3M; Conductive salt: one or any combination of ammonium chloride, sodium chloride, and ammonium sulfate, totaling 1M; Surfactant: Succinate sulfonate, 0.01-0.5 wt%.

4. A high-carbon-content hydrophobic and corrosion-resistant trivalent chromium-carbon alloy coating and its low-temperature electroplating preparation method, characterized in that, The process includes the following steps: substrate pretreatment, preparation of electroplating solution, low-temperature circulating cooling system, electroplating reaction, formation of Cr-C coating, and post-treatment. S1. Substrate pretreatment: Degreasing treatment, immerse the substrate in acetone for 2 minutes; Alkali washing treatment, immerse the degreased substrate in 30g / L NaOH solution for 30 seconds; Acid washing treatment, immerse the alkali-washed substrate in 10-20% HCl solution for 10 seconds to 1 minute; DI water cleaning treatment, use high-purity water to remove ionic residues, soluble impurities and particulate matter from the surface of the substrate after acid washing. S2. Prepare the electroplating solution: Prepare a plating solution containing 0.2M chromium chloride, 3M chelating agent, 1M conductive salt, and 0.01-0.5wt% additives. S3. Low-temperature circulating cooling system: The temperature of the plating solution is controlled within the range of -5 to 10℃ using refrigeration equipment; S4. Electroplating reaction: Place the substrate after DI water cleaning into the plating solution, apply current, current density: 10~30A / dm², time: 10~60 minutes; S5. Formation of a Cr-C coating: thickness 5–30 μm, carbon content 35–45 at%; S6. Post-treatment: The substrate after electroplating reaction is washed again with DI water, and then dried with hot air to obtain the finished product.

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