A trivalent chromium plating rare earth additive, a chromium plating solution and a chromium plating process

Abstract

The application discloses a trivalent chromium plating process, which comprises the following process parameters: chromium chloride hexahydrate 80-140 g / L, potassium chloride 90-160 g / L, ammonium chloride 90-160 g / L, ammonium bromide 16-30 g / L, ammonium formate 40-60 g / L, boric acid 45-65 g / L, rare earth additive 8-12 mL / L, walking agent 2-4 mL / L, accelerator 1-3 mL / L, plating solution pH value 2.5-3.2, plating bath temperature 25-35 DEG C, cathode current density 10-18 A / dm 2 2, inert anode is adopted, and moderate air stirring is adopted. The rare earth additive comprises lanthanum chloride heptahydrate 40-140 g / L and praseodymium chloride heptahydrate 0-130 g / L. The steel base is subjected to cyanide-free copper plating + bright nickel plating + trivalent chromium plating + rare earth electrolytic protection, neutral salt spray test is carried out according to GB / T 10125-2021 'Salt Spray Test of Artificial Atmosphere Corrosion Test', and the prepared sample surface is free of corrosion product generation. The technical scheme obviously improves the corrosion resistance of the trivalent chromium plating layer, and has a good market prospect.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a trivalent chromium plating rare earth additive, chromium plating solution, and chromium plating process. Background Technology

[0002] In the 21st century, trivalent chromium electroplating has developed rapidly, mainly used for decorative chromium plating. Sulfate trivalent chromium plating produces high-quality layers, but its deposition rate is slow, and thicker layers may exhibit a hazy appearance. [1] The initial setup cost of trivalent chloride chromium plating baths is less than 50% lower than that of sulfate systems, and the operating cost is also lower. Deposition rates are higher, but corrosion resistance is poor, and it is currently mainly used in the low-end domestic market. The problem of poor corrosion resistance in trivalent chloride chromium plating layers has not been solved. Without protective agent treatment, neutral salt spray tests generally do not exceed 72 hours, and some even fail to reach 48 hours. More seriously, the plating layer is prone to mold growth during the rainy season, posing a serious quality hazard. [2] .

[0003] Currently, trivalent chromium plating is generally required to undergo a neutral salt spray test for 72 hours without discoloration. [3] Traditional trivalent chloride chromium plating processes often fail to meet the technical requirements of the manufacturing industry.

[0004] During the trivalent chromium plating process, trivalent chromium ions can form hydroxy-bridged polymers. [4] The chromium plating rate decreases, and the plating solution shows signs of aging.

[0005] In the past, the industry typically used intermediates such as polyoxyethylene ether alkyl alcohols to formulate trivalent chromium plating additives. After polyoxyethylene ether alkyl alcohols decompose in the plating bath, they generate alkyl alcohols containing multiple carbon atoms. These alkyl alcohols form micelles in the plating solution, and when these micelles are adsorbed onto the trivalent chromium plating layer, mold spots will appear on the plating layer.

[0006] References: [1] Guo Chongwu, Lai Huanwen, Rapid plating process of trivalent chromium in sulfate system [J], Electroplating and Finishing, 2011, 30(3): 13-16. [2] Tu Zhenmi, Zheng Jian, Li Ning et al., Current status and development trend of trivalent chromium electroplating [J], Surface Technology, 2007, 36(5): 59-63+87. [3] Lai Huanwen, Guo Chongwu, New process of trivalent chromium electroplating in chloride system and its coating performance [J], Electroplating and Finishing, 2013, 32(1): 18-20. [4] Li Guohua, Lai Huanwen, Huang Qingan, Role of ligands in trivalent chromium plating solution [J], Materials Protection, 2005, 38(12): 44-46. Summary of the Invention

[0007] To address the poor performance of trivalent chromium plating processes using chloride systems, this invention provides a rare earth additive for trivalent chromium plating, a plating solution, and a plating process. To achieve the above objectives, this invention employs the following technical solution: A rare earth additive for trivalent chromium plating, wherein the rare earth additive contains 40-140 g / L lanthanum chloride heptahydrate and 0-130 g / L praseodymium chloride heptahydrate, based on the volume of the rare earth additive solution. During the trivalent chromium plating process, the lanthanum chloride and praseodymium chloride hydrolyze on the cathode surface to form a rare earth salt film, which increases the cathode polarization, makes the trivalent chromium plating layer denser, and improves the coverage of the plating solution. The lanthanum chloride and praseodymium chloride have a synergistic effect in increasing cathode polarization.

[0008] A trivalent chromium plating solution, comprising the following components, concentrations, and plating solution parameters: Chromium chloride hexahydrate 80-140 g / L, potassium chloride 90-160 g / L, ammonium chloride 90-160 g / L, ammonium bromide 16-30 g / L, ammonium formate 40-60 g / L, boric acid 45-65 g / L, rare earth additives 8-12 mL / L, leveling agent 2-4 mL / L, accelerator 1-3 mL / L, plating solution pH 2.5-3.2; The rare earth additives contain 40-140 g / L lanthanum chloride heptahydrate and 0-130 g / L praseodymium chloride heptahydrate; The leveling agent contains 30-90 g / L of vanadium oxysulfate and 100-160 g / L of ammonium formate by volume of the leveling agent solution. The ammonium formate is used as a complexing agent to dissolve vanadium oxysulfate in the leveling agent. The accelerator contains 10-40 g / L of acidic ethoxylated alcohol phosphate by volume of the accelerator solution, and the acidic ethoxylated alcohol phosphate is used to increase the deposition rate of trivalent chromium.

[0009] In some embodiments, the acidic ethoxylated alcohol phosphate is NORFOX PE-600.

[0010] The positioning agent is prepared using the following method: Add 4 / 5 of the required volume of pure water to the reaction vessel, add ammonium formate according to the leveling agent formula, stir until the ammonium formate dissolves, then add vanadium oxysulfate, stir until the leveling agent solution is clear, and then add pure water to the required volume.

[0011] In some embodiments, the preparation of the trivalent chromium plating solution includes the following steps: (1) Pour 2 / 3 volume of pure water into the plating tank, and add potassium chloride, ammonium chloride, ammonium bromide, ammonium formate and boric acid according to the plating solution formula requirements, and stir to dissolve the solids; (2) Add 10% hydrochloric acid to the plating bath to adjust the pH of the plating solution to 2.5-2.7 to avoid hydrolysis of trivalent chromium ions after the addition of chromium chloride; (3) Add chromium chloride hexahydrate to the plating tank according to the plating solution formula requirements and stir until the chromium chloride dissolves; (4) Heat the plating solution to 52-58°C and keep it warm for 3-6 hours to allow ammonium formate to form a complex with trivalent chromium ions.

[0012] (5) After the plating solution cools, add pure water to the specified volume of the plating tank; (6) Within 0.5~1.5A / dm 2 The plating solution is then electrolyzed for 60–180 minutes to remove harmful impurities. (7) Add rare earth additives, leveling agents and accelerators to the plating tank according to the plating solution formula requirements; (8) Adjust the pH of the plating solution to 2.5 to 3.2 with 10% hydrochloric acid or 10% ammonia.

[0013] A trivalent chromium plating process includes the following components and process parameters: Chromium chloride hexahydrate 80–140 g / L, potassium chloride 90–160 g / L, ammonium chloride 90–160 g / L, ammonium bromide 16–30 g / L, ammonium formate 40–60 g / L, boric acid 45–65 g / L, rare earth additives 8–12 mL / L, leveling agent 2–4 mL / L, accelerator 1–3 mL / L, plating bath pH 2.5–3.2, plating bath temperature 25–35℃, cathode current density 10–18 A / dm³ 2 An inert anode material is used as the anode, and medium air agitation is employed. The rare earth additives contain 40-140 g / L lanthanum chloride heptahydrate and 0-130 g / L praseodymium chloride heptahydrate.

[0014] In some embodiments, the inert anode material is an inert graphite rod.

[0015] In some embodiments, the inert anode material is a titanium plate coated with a metal oxide.

[0016] In some embodiments, the area ratio of the anode to the cathode is 1:(1.5 to 2.5).

[0017] In some embodiments, when the trivalent chromium in the trivalent chromium plating solution generates hydroxy-bridged polymers, causing a decrease in the chromium plating rate, hydrochloric acid is added to the plating bath to acidify the plating solution, the pH of the plating solution is adjusted to 2, and the reaction is carried out for 2 hours. Then, ammonia is added to raise the pH to within the process range.

[0018] In some embodiments, a trivalent chromium plating layer is prepared on a bright nickel plating layer, a bright nickel-cobalt alloy plating layer, a bright nickel-copper alloy plating layer, or a bright nickel-iron alloy plating layer of the plated part using the aforementioned trivalent chromium plating process.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention discloses a trivalent chromium plating rare earth additive, chromium plating solution and chromium plating process, which uses lanthanum chloride and praseodymium chloride as trivalent chromium plating additives. By improving the cathodic polarization of the plating solution, the density of the trivalent chromium plating layer is increased, and the corrosion resistance of the plating layer is significantly improved. 2. The present invention discloses a trivalent chromium plating rare earth additive, chromium plating solution and chromium plating process, which uses lanthanum chloride and praseodymium chloride as trivalent chromium plating additives to improve the coverage of the plating solution. 3. The present invention discloses a trivalent chromium plating rare earth additive, chromium plating solution and chromium plating process, which uses acidic ethoxylated alcohol phosphate ester instead of traditional polyoxyethylene ether alkyl alcohol as additive, thus overcoming the problem that black spots easily appear on the trivalent chromium plating layer. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the coating structure of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the coating structure in Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the coating structure in Embodiment 3 of the present invention; Figure 4 This is a schematic diagram of the coating structure in Embodiment 4 of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0022] A trivalent chromium rare earth additive, chromium plating solution and electroplating process include: preparing trivalent chromium plating additive, preparing trivalent chromium plating solution, metal workpiece pretreatment, cyanide-free copper plating, bright nickel or nickel alloy plating, trivalent chromium plating and rare earth electrolytic protection.

[0023] 1. Preparation of trivalent chromium plating additives: 1) Preparation of rare earth additives: The rare earth additive comprises 40-140 g / L lanthanum chloride heptahydrate and 0-130 g / L praseodymium chloride heptahydrate. The rare earth additive is obtained by dissolving lanthanum chloride heptahydrate and praseodymium chloride heptahydrate in water according to the formulation requirements.

[0024] 2) Preparation of the positioning agent: The leveling agent comprises 30-90 g / L of vanadium oxysulfate and 100-160 g / L of ammonium formate. Add pure water to the reaction vessel to 4 / 5 of the required volume, then add ammonium formate according to the leveling agent formulation. Stir until the ammonium formate dissolves, then add vanadium oxysulfate and stir until the leveling agent solution becomes clear. Finally, add pure water to the required volume to obtain the leveling agent.

[0025] Tetravalent vanadium ions readily deposit on the cathode surface to form metallic vanadium nuclei. These newly formed vanadium nuclei can induce the electrodeposition of trivalent chromium ions to form a trivalent chromium plating layer. Therefore, vanadium oxysulfate functions as a leveling agent, increasing the coverage of the plating bath.

[0026] 3) Preparation of accelerator: The accelerator comprises 10-40 g / L of acidic ethoxylated phosphate. The accelerator is obtained by dissolving the acidic ethoxylated phosphate in water according to the accelerator formulation requirements.

[0027] Preferably, the accelerator is formulated using an acidic ethoxylated alcohol phosphate with product model NORFOX PE-600.

[0028] Acidic ethoxylated alcohol phosphates do not form micelles after decomposition in the plating bath, thus avoiding the problem of mold spots appearing on the trivalent chromium plating layer.

[0029] 2. Prepare trivalent chromium plating solution: 1) Pour 2 / 3 volume of pure water into the plating tank, and add potassium chloride, ammonium chloride, ammonium bromide, ammonium formate and boric acid according to the plating solution formula requirements, and stir to dissolve the solids; 2) Add 10% hydrochloric acid to the plating bath to adjust the pH of the plating solution to 2.5-2.7 to avoid hydrolysis of trivalent chromium ions after the addition of chromium chloride; 3) Add chromium chloride hexahydrate to the plating tank according to the plating solution formula, and stir until the chromium chloride dissolves; 4) Heat the plating solution to 52-58℃ and keep it at that temperature for 3-6 hours to allow ammonium formate to form a complex with trivalent chromium ions.

[0030] 5) After the plating solution cools, add pure water to the specified volume of the plating tank; 6) Within 0.5~1.5A / dm 2Electrolysis for 60–180 minutes removes harmful impurities from the plating solution; 7) Add rare earth additives, leveling agents, and accelerators to the plating tank according to the plating solution formula requirements; 8) Adjust the pH of the plating solution to 2.5-3.2 using 10% hydrochloric acid or 10% ammonia.

[0031] 3. Pre-treatment of steel parts: The steel parts are chemically degreased, derusted, electrolyzed, and activated according to the current pretreatment process.

[0032] 4. Cyanide-free copper plating: A cyanide-free copper plating layer is prepared using the existing cyanide-free copper plating process. Preferably, the thickness of the cyanide-free copper plating layer is 4–8 μm.

[0033] Preferably, the cyanide-free copper plating layer is prepared using the CB-101 polymeric thiocyanate copper plating process developed by Chaobang Chemical. Polymeric cuprous thiocyanate 18–24 g / L, polymeric sodium thiocyanate 130–170 g / L, sodium hydroxyethylidene diphosphonate 20–30 g / L, CB-101 copper plating brightener 8–12 mL / L, plating bath pH 12–13, plating bath temperature 30–40℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min. Oxygen-free electrolytic copper particles are used as the anode. The copper particles are loaded into a titanium anode basket. The area ratio of the anode to the cathode is >3:1. The anode moves at a speed of 3-5 m / min.

[0034] 5. Plating with bright nickel or bright nickel alloy: A bright nickel plating layer is prepared using the existing bright nickel plating process, preferably with a thickness of 8–15 μm.

[0035] Preferably, the bright nickel plating layer is prepared using the NINFEA 8002 high-leveling bright nickel plating process from Chaobang Chemical: Nickel sulfate hexahydrate 240–300 g / L, nickel chloride hexahydrate 45–70 g / L, boric acid 37–45 g / L, NINFEA 8002 main brightener 0.6–1 mL / L, NINFEA SC-263 softener 8–15 mL / L, NINFEA AS-250 auxiliary agent 1–4 mL / L, NINFEA NI-35 wetting agent 0.2–1 mL / L, plating bath pH 4–4.6, operating temperature 55–65℃, cathode current density 2–6 A / dm³ 2 Anode current density 1-3 A / dm 2 The system circulates and filters 5-8 times per hour, ensuring uniform air agitation.

[0036] A bright nickel-cobalt alloy coating is prepared using the existing bright nickel-cobalt alloy plating process. Preferably, the thickness of the bright nickel-cobalt alloy coating is 8–15 μm.

[0037] Preferably, the bright nickel-cobalt alloy coating is prepared using the NINFEA 310 bright nickel-cobalt alloy plating process from Chaobang Chemical Co., Ltd. Nickel sulfate hexahydrate 220–260 g / L, nickel chloride hexahydrate 50–70 g / L, cobalt sulfate heptahydrate 15–20 g / L, boric acid 40–50 g / L, NINFEA SC-230 auxiliary agent 12–20 mL / L, NINFEA 310 main brightener 0.5–1.5 mL / L, NINFEA 312 leveling agent 0.5–1.5 mL / L, NINFEA NI-35 wetting agent 0.5–1.5 mL / L, plating bath pH 4.0–4.5, plating bath temperature 55–60℃, cathode current density 2–6 A / dm³ 2 Uniform air mixing.

[0038] A bright nickel-copper alloy coating is prepared using the existing bright nickel-copper alloy plating process. Preferably, the thickness of the bright nickel-copper alloy coating is 8–15 μm.

[0039] Preferably, the bright nickel-copper alloy plating is prepared using the Nistar 6070 bright nickel-copper alloy plating process from Chaobang Chemical Co., Ltd. Nickel sulfate hexahydrate 180–220 g / L, copper sulfate pentahydrate 8–12 g / L, trisodium citrate 50–70 g / L, disodium hydroxyethylidene diphosphonate 20–30 g / L, boric acid 28–35 g / L, sodium chloride 5–8 g / L, NISTAR 6070 brightener 0.3–0.7 mL / L, NISTAR 6071 auxiliary agent 6–10 mL / L, NI-35 wetting agent 0.3–1.0 mL / L, plating bath pH 4.3–4.8, plating bath temperature 50–55℃, cathode current density 2.6–3.2 A / dm³ 2 The cathode moves at a speed of 3–5 m / min.

[0040] A bright nickel-iron alloy coating is prepared using the existing bright nickel-iron alloy plating process. Preferably, the thickness of the bright nickel-iron alloy coating is 8–15 μm.

[0041] Preferably, the bright nickel-iron alloy coating is prepared using Chaobang Chemical's EMFASI FN-35 bright nickel-iron alloy plating process: Nickel sulfate hexahydrate 220–260 g / L, nickel chloride hexahydrate 50–70 g / L, ferric sulfate heptahydrate 18–22 g / L, boric acid 45–55 g / L, EMFASI FN-35 Auxiliary 15–25 mL / L, EMFASI FN-35 Carrier Softener 15–25 mL / L, EMFASI FN-35 Bri Brightener 0.5–2 mL / L, EMFASI FN-35 STAB Stabilizer 10–15 g / L, NINFEA NI-28 Wetting Agent 1.0–3.0 mL / L, plating bath pH 2.8–3.2, plating bath temperature 50–60℃, cathode current density 2–6 A / dm³ 2 Uniform air mixing.

[0042] 6. Trivalent chromium plating: The trivalent chromium plating layer is prepared using the trivalent chromium plating process of the present invention. Preferably, the thickness of the trivalent chromium plating layer is 0.3 to 0.8 μm.

[0043] Chromium chloride hexahydrate 80–140 g / L, potassium chloride 90–160 g / L, ammonium chloride 90–160 g / L, ammonium bromide 16–30 g / L, ammonium formate 40–60 g / L, boric acid 45–65 g / L, rare earth additives 8–12 mL / L, leveling agent 2–4 mL / L, accelerator 1–3 mL / L, plating bath pH 2.5–3.2, plating bath temperature 25–35℃, cathode current density 10–18 A / dm³ 2 An inert anode material is used as the anode, and the area ratio of the anode to the cathode is 1:(1.5~2.5), with moderate air agitation.

[0044] Preferably, the inert anode material is an inert graphite rod.

[0045] Preferably, the inert anode material is a titanium plate coated with a metal oxide.

[0046] Formate ions are oxidized to carbon dioxide on the anode surface. Using a smaller anode area can reduce the amount of formate ions consumed during the electroplating process.

[0047] When the trivalent chromium in the trivalent chromium plating solution forms hydroxy-bridged polymers, causing a decrease in the chromium plating rate, hydrochloric acid is added to the plating bath to acidify the plating solution, the pH of the plating solution is adjusted to 2, and the reaction is carried out for 2 hours. Then, ammonia is added to raise the pH to the process range.

[0048] 7. Rare earth electrolysis protection: Rare earth electrolytic protective films were prepared using a rare earth electrolytic protection process developed by Chaobang Chemical. Cerium acetate 2–5 g / L, sodium molybdate 5–15 g / L, HEDP complexing agent 10–30 g / L, anhydrous sodium carbonate 100–150 g / L, electrolyte pH 11.5–12.5, cathode current density 0.5–1.5 A / dm³ 2 Operating at room temperature, using the plated part as the cathode and the titanium plate as the anode, electrolysis for 60–120 seconds.

[0049] 8. Drying: The plated parts are dried using a conventional drying process.

[0050] Example 1: A trivalent chromium rare earth additive, a chromium plating solution, and an electroplating process, comprising the preparation of a trivalent chromium plating additive, the preparation of a trivalent chromium plating solution, pretreatment of metal workpieces, cyanide-free copper plating, bright nickel plating, trivalent chromium plating, and rare earth electrolytic protection.

[0051] like Figure 1 As shown, a coating structure prepared by a trivalent chromium plating process includes a steel substrate 1a, and a cyanide-free copper plating 2a, a bright nickel plating layer 3a, a trivalent chromium plating layer 4a, and a rare earth electrolytic protective film 5a sequentially prepared from the inside to the outside on the steel substrate 1a.

[0052] 1. Preparation of trivalent chromium plating additives: 1) Preparation of rare earth additives: The rare earth additive comprises 90 g / L lanthanum chloride heptahydrate and 60 g / L praseodymium chloride heptahydrate. The rare earth additive is obtained by dissolving lanthanum chloride heptahydrate and praseodymium chloride heptahydrate in water according to the formulation requirements.

[0053] 2) Preparation of the positioning agent: The leveling agent comprises 60 g / L vanadyl sulfate and 130 g / L ammonium formate. Add pure water to the reaction vessel to 4 / 5 of the required volume, then add ammonium formate according to the leveling agent formulation. Stir until the ammonium formate dissolves, then add vanadyl sulfate and stir until the leveling agent solution is clear. Finally, add pure water to the required volume to obtain the leveling agent.

[0054] 3) Preparation of accelerator: The accelerator comprises 25 g / L of acidic ethoxylated phosphate ester NORFOX PE-600. The accelerator is obtained by dissolving the acidic ethoxylated phosphate ester NORFOX PE-600 in water according to the accelerator formulation requirements.

[0055] 2. Prepare trivalent chromium plating solution: 1) Pour 2 / 3 volume of pure water into the plating tank, and add potassium chloride, ammonium chloride, ammonium bromide, ammonium formate and boric acid according to the plating solution formula requirements, and stir to dissolve the solids; 2) Add 10% hydrochloric acid to the plating bath to adjust the pH of the plating solution to 2.6 to avoid hydrolysis of trivalent chromium ions after the addition of chromium chloride; 3) Add chromium chloride hexahydrate to the plating tank according to the plating solution formula, and stir until the chromium chloride dissolves; 4) Heat the plating solution to 55°C and keep it at that temperature for 4.5 hours to allow ammonium formate to form a complex with trivalent chromium ions.

[0056] 5) After the plating solution cools, add pure water to the specified volume of the plating tank; 6) At 1A / dm 2 Electrolysis for 120 minutes removes harmful impurities from the plating solution; 7) Add rare earth additives, leveling agents, and accelerators to the plating tank according to the plating solution formula requirements; 8) Adjust the pH of the plating solution to 2.8 using 10% hydrochloric acid or 10% ammonia.

[0057] 3. Pre-treatment of steel parts: According to the current pretreatment process, the steel workpiece substrate 1a is subjected to the following steps: "chemical degreasing → water washing → pickling and rust removal → water washing → alkaline cathodic electrolytic degreasing → water washing → alkaline anodic electrolytic degreasing → water washing → activation → water washing".

[0058] 4. Cyanide-free copper plating: After pretreatment of the steel workpiece, a cyanide-free copper plating layer 2a was prepared using the CB-101 polymeric thiocyanate copper plating process developed by Chaobang Chemical. The thickness of the copper layer was 5μm.

[0059] Polymeric cuprous thiocyanate 21 g / L, polymeric sodium thiocyanate 150 g / L, sodium hydroxyethylidene diphosphonate 25 g / L, CB-101 copper plating brightener 10 mL / L, plating bath pH 12.5, plating bath temperature 35℃, cathode current density 1 A / dm³ 2 The cathode moves at a speed of 4 m / min. Oxygen-free electrolytic copper particles are used as the anode. The copper particles are loaded into a titanium anode basket. The area ratio of the anode to the cathode is 3.5:1. The anode moves at a speed of 4 m / min.

[0060] 5. Bright nickel plating: After cyanide-free copper plating, a bright nickel plating layer 3a was prepared using the NINFEA 8002 high-filling bright nickel plating process of Chaobang Chemical. The thickness of the plating layer was 13μm.

[0061] Nickel sulfate hexahydrate 270 g / L, nickel chloride hexahydrate 58 g / L, boric acid 40 g / L, NINFEA 8002 main brightener 0.8 mL / L, NINFEA SC-263 softener 12 mL / L, NINFEA AS-250 auxiliary agent 2.5 mL / L, NINFEA NI-35 wetting agent 0.6 mL / L, plating bath pH 4.3, operating temperature 60℃, cathode current density 4 A / dm³ 2 Anode current density 2A / dm 2 The system is circulated and filtered 6 times per hour, with uniform air agitation.

[0062] 6. Trivalent chromium plating: After plating bright nickel onto a steel workpiece, a trivalent chromium plating layer 4a is prepared using the trivalent chromium plating process of this invention, with a plating thickness of 0.6 μm.

[0063] The plating solution contained 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating bath was 2.8, the plating tank temperature was 30℃, and the cathode current density was 14 A / dm³. 2 A titanium plate with a metal oxide coating is used as the anode, with an anode-to-cathode area ratio of 1:2 and medium air agitation.

[0064] When the trivalent chromium in the trivalent chromium plating solution forms hydroxy-bridged polymers, causing a decrease in the chromium plating rate, hydrochloric acid is added to the plating bath to acidify the plating solution, the pH of the plating solution is adjusted to 2, and the reaction is carried out for 2 hours. Then, ammonia is added to raise the pH to the process range.

[0065] 7. Rare earth electrolysis protection: After trivalent chromium plating, steel workpieces are prepared with rare earth electrolytic protective film 5a using a rare earth electrolytic protection process developed by Chaobang Chemical.

[0066] Cerium acetate 3.5 g / L, sodium molybdate 10 g / L, HEDP complexing agent 20 g / L, anhydrous sodium carbonate 125 g / L, electrolyte pH 12, cathode current density 1 A / dm³ 2 Operating at room temperature, using the plated part as the cathode and the titanium plate as the anode, electrolyzing for 90 seconds.

[0067] 8. Drying: After rare earth electrolytic protection, steel workpieces are dried at 70℃ for 20 minutes.

[0068] Example 2: A trivalent chromium rare earth additive, a chromium plating solution, and an electroplating process, comprising the preparation of a trivalent chromium plating additive, the preparation of a trivalent chromium plating solution, pretreatment of metal workpieces, cyanide-free copper plating, plating of bright nickel-cobalt alloy, trivalent chromium plating, and rare earth electrolytic protection.

[0069] like Figure 2 As shown, a coating structure prepared by a trivalent chromium plating process includes a steel substrate 1b, and a cyanide-free copper plating 2b, a bright nickel-cobalt alloy plating layer 3b, a trivalent chromium plating layer 4b, and a rare earth electrolytic protective film 5b sequentially prepared from the inside to the outside on the steel substrate 1b.

[0070] 1. Preparation of trivalent chromium plating additives: 1) Preparation of rare earth additives: The rare earth additive comprises 40 g / L lanthanum chloride heptahydrate and 130 g / L praseodymium chloride heptahydrate. The rare earth additive is obtained by dissolving lanthanum chloride heptahydrate and praseodymium chloride heptahydrate in water according to the formulation requirements.

[0071] 2) Preparation of the positioning agent: The leveling agent comprises 50 g / L vanadium oxysulfate and 120 g / L ammonium formate. Add pure water to the reaction vessel to 4 / 5 of the required volume, then add ammonium formate according to the leveling agent formulation. Stir until the ammonium formate dissolves, then add vanadium oxysulfate and stir until the leveling agent solution becomes clear. Finally, add pure water to the required volume to obtain the leveling agent.

[0072] 3) Preparation of accelerator: The accelerator comprises 20 g / L of acidic ethoxylated phosphate ester NORFOX PE-600. The accelerator is obtained by dissolving the acidic ethoxylated phosphate ester NORFOX PE-600 in water according to the accelerator formulation requirements.

[0073] 2. Prepare trivalent chromium plating solution: 1) Pour 2 / 3 volume of pure water into the plating tank, and add potassium chloride, ammonium chloride, ammonium bromide, ammonium formate and boric acid according to the plating solution formula requirements, and stir to dissolve the solids; 2) Add 10% hydrochloric acid to the plating bath to adjust the pH of the plating solution to 2.6 to avoid hydrolysis of trivalent chromium ions after the addition of chromium chloride; 3) Add chromium chloride hexahydrate to the plating tank according to the plating solution formula, and stir until the chromium chloride dissolves; 4) Heat the plating solution to 58°C and keep it at that temperature for 3 hours to allow ammonium formate to form a complex with trivalent chromium ions.

[0074] 5) After the plating solution cools, add pure water to the specified volume of the plating tank; 6) At 1.5A / dm 2 Electrolysis for 60 minutes removes harmful impurities from the plating solution; 7) Add rare earth additives, leveling agents, and accelerators to the plating tank according to the plating solution formula requirements; 8) Adjust the pH of the plating solution to 3.2 using 10% hydrochloric acid or 10% ammonia.

[0075] 3. Pre-treatment of steel parts: According to the current pretreatment process, the steel workpiece substrate 1b is subjected to the following steps: "chemical degreasing → water washing → pickling and rust removal → water washing → alkaline cathodic electrolytic degreasing → water washing → alkaline anodic electrolytic degreasing → water washing → activation → water washing".

[0076] 4. Cyanide-free copper plating: After pretreatment of the steel workpiece, a cyanide-free copper plating layer 2b was prepared using the CB-101 polymeric thiocyanate copper plating process developed by Chaobang Chemical, with a plating thickness of 6μm.

[0077] Polymeric cuprous thiocyanate 24 g / L, polymeric sodium thiocyanate 170 g / L, sodium hydroxyethylidene diphosphonate 30 g / L, CB-101 copper plating brightener 10 mL / L, plating bath pH 12.2, plating bath temperature 30℃, cathode current density 1 A / dm³ 2 The cathode moves at a speed of 4 m / min. Oxygen-free electrolytic copper particles are used as the anode. The copper particles are loaded into a titanium anode basket. The area ratio of the anode to the cathode is 3.2:1. The anode moves at a speed of 4 m / min.

[0078] 5. Bright nickel-cobalt alloy plating: After cyanide-free copper plating, the steel workpiece was coated with a nickel-cobalt alloy 3b using the NINFEA 310 bright nickel-cobalt alloy plating process of Chaobang Chemical Co., Ltd., with a coating thickness of 12μm.

[0079] Nickel sulfate hexahydrate 240 g / L, nickel chloride hexahydrate 60 g / L, cobalt sulfate heptahydrate 18 g / L, boric acid 45 g / L, NINFEA SC-230 auxiliary agent 16 mL / L, NINFEA 310 brightener 1 mL / L, NINFEA 312 leveling agent 1 mL / L, NINFEANI-35 wetting agent 1 mL / L, plating bath pH 4.3, plating tank temperature 58℃, cathode current density 4 A / dm³ 2 Uniform air mixing.

[0080] 6. Trivalent chromium plating: After plating a steel workpiece with a bright nickel-cobalt alloy, a trivalent chromium plating layer 4b is prepared using the trivalent chromium plating process of this invention, with a plating thickness of 0.6 μm.

[0081] The plating solution contained 140 g / L chromium chloride hexahydrate, 90 g / L potassium chloride, 160 g / L ammonium chloride, 30 g / L ammonium bromide, 60 g / L ammonium formate, 50 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating solution was 3.2, the plating tank temperature was 25℃, and the cathode current density was 14 A / dm³. 2A titanium plate with a metal oxide coating is used as the anode, with an anode-to-cathode area ratio of 1:2.2 and moderate air agitation.

[0082] When the trivalent chromium in the trivalent chromium plating solution forms hydroxy-bridged polymers, causing a decrease in the chromium plating rate, hydrochloric acid is added to the plating bath to acidify the plating solution, the pH of the plating solution is adjusted to 2, and the reaction is carried out for 2 hours. Then, ammonia is added to raise the pH to the process range.

[0083] 7. Rare earth electrolysis protection: After trivalent chromium plating, steel workpieces are prepared with rare earth electrolytic protective film 5b using a rare earth electrolytic protection process developed by Chaobang Chemical.

[0084] The electrolyte composition is as follows: cerium acetate 5 g / L, sodium molybdate 15 g / L, HEDP complexing agent 30 g / L, anhydrous sodium carbonate 100 g / L, electrolyte pH 11.8, cathode current density 1 A / dm³. 2 Operating at room temperature, using the plated part as the cathode and the titanium plate as the anode, electrolysis for 60 seconds.

[0085] 8. Drying: After rare earth electrolytic protection, steel workpieces are dried at 75℃ for 15 minutes.

[0086] Example 3: A trivalent chromium rare earth additive, a chromium plating solution, and an electroplating process, comprising the preparation of a trivalent chromium plating additive, the preparation of a trivalent chromium plating solution, pretreatment of metal workpieces, cyanide-free copper plating, plating of bright nickel-copper alloy, trivalent chromium plating, and rare earth electrolytic protection.

[0087] like Figure 3 As shown, a coating structure prepared by a trivalent chromium plating process includes a steel substrate 1c, and a cyanide-free copper plating 2c, a bright nickel-copper alloy plating layer 3c, a trivalent chromium plating layer 4c, and a rare earth electrolytic protective film 5c sequentially prepared from the inside to the outside on the steel substrate 1c.

[0088] 1. Preparation of trivalent chromium plating additives: 1) Preparation of rare earth additives: The rare earth additive comprises 120 g / L lanthanum chloride heptahydrate and 30 g / L praseodymium chloride heptahydrate. The rare earth additive is obtained by dissolving lanthanum chloride heptahydrate and praseodymium chloride heptahydrate in water according to the formulation requirements.

[0089] 2) Preparation of the positioning agent: The leveling agent comprises 70 g / L vanadium oxysulfate and 150 g / L ammonium formate. Add pure water to the reaction vessel to 4 / 5 of the required volume, then add ammonium formate according to the leveling agent formulation. Stir until the ammonium formate dissolves, then add vanadium oxysulfate and stir until the leveling agent solution becomes clear. Finally, add pure water to the required volume to obtain the leveling agent.

[0090] 3) Preparation of accelerator: The accelerator comprises 40 g / L of acidic ethoxylated phosphate ester NORFOX PE-600. The accelerator is obtained by dissolving the acidic ethoxylated phosphate ester NORFOX PE-600 in water according to the accelerator formulation requirements.

[0091] 2. Prepare trivalent chromium plating solution: 1) Pour 2 / 3 volume of pure water into the plating tank, and add potassium chloride, ammonium chloride, ammonium bromide, ammonium formate and boric acid according to the plating solution formula requirements, and stir to dissolve the solids; 2) Add 10% hydrochloric acid to the plating bath to adjust the pH of the plating solution to 2.6 to avoid hydrolysis of trivalent chromium ions after the addition of chromium chloride; 3) Add chromium chloride hexahydrate to the plating tank according to the plating solution formula, and stir until the chromium chloride dissolves; 4) Heat the plating solution to 52°C and keep it at that temperature for 6 hours to allow ammonium formate to form a complex with trivalent chromium ions.

[0092] 5) After the plating solution cools, add pure water to the specified volume of the plating tank; 6) At 0.5A / dm 2 Electrolysis for 180 minutes removes harmful impurities from the plating solution; 7) Add rare earth additives, leveling agents, and accelerators to the plating tank according to the plating solution formula requirements; 8) Adjust the pH of the plating solution to 3 using 10% hydrochloric acid or 10% ammonia.

[0093] 3. Pre-treatment of steel parts: According to the current pretreatment process, the steel workpiece substrate 1c is subjected to the following steps: "chemical degreasing → water washing → acid pickling and rust removal → water washing → alkaline cathodic electrolytic degreasing → water washing → alkaline anodic electrolytic degreasing → water washing → activation → water washing".

[0094] 4. Cyanide-free copper plating: After pretreatment of the steel workpiece, a cyanide-free copper plating layer 2c was prepared using the CB-101 polymeric thiocyanate copper plating process developed by Chaobang Chemical, with a plating thickness of 7μm.

[0095] Polymeric cuprous thiocyanate 18 g / L, polymeric sodium thiocyanate 135 g / L, sodium hydroxyethylidene diphosphonate 22 g / L, CB-101 copper plating brightener 10 mL / L, plating bath pH 12.8, plating bath temperature 40℃, cathode current density 1 A / dm³ 2 The cathode moves at a speed of 4 m / min. Oxygen-free electrolytic copper particles are used as the anode. The copper particles are loaded into a titanium anode basket. The area ratio of the anode to the cathode is 4:1. The anode moves at a speed of 4 m / min.

[0096] 5. Bright nickel-copper alloy plating: After cyanide-free copper plating, steel workpieces were coated with a bright nickel-copper alloy 3c using Chaobang Chemical's Nistar 6070 bright nickel-copper alloy plating process. The thickness of the coating was 10μm.

[0097] Nickel sulfate hexahydrate 200 g / L, copper sulfate pentahydrate 10 g / L, trisodium citrate 60 g / L, disodium hydroxyethylidene diphosphonate 25 g / L, boric acid 32 g / L, sodium chloride 7 g / L, NISTAR 6070 brightener 0.5 mL / L, NISTAR 6071 auxiliary agent 8 mL / L, NI-35 wetting agent 0.6 mL / L, plating bath pH 4.5, plating tank temperature 53℃, cathode current density 2.8 A / dm³ 2 The cathode moves at a speed of 4 m / min.

[0098] 6. Trivalent chromium plating: After plating a steel workpiece with a nickel-copper alloy, a trivalent chromium plating layer 4c is prepared using the trivalent chromium plating process of the present invention. Preferably, the thickness of the trivalent chromium plating layer is 0.7 μm.

[0099] The plating solution contains 130 g / L chromium chloride hexahydrate, 150 g / L potassium chloride, 120 g / L ammonium chloride, 18 g / L ammonium bromide, 55 g / L ammonium formate, 60 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating solution is 3, the plating tank temperature is 25℃, and the cathode current density is 14 A / dm³. 2 An inert graphite rod is used as the anode, with an anode-to-cathode area ratio of 1:2.5, and moderate air agitation is employed.

[0100] When the trivalent chromium in the trivalent chromium plating solution forms hydroxy-bridged polymers, causing a decrease in the chromium plating rate, hydrochloric acid is added to the plating bath to acidify the plating solution, the pH of the plating solution is adjusted to 2, and the reaction is carried out for 2 hours. Then, ammonia is added to raise the pH to the process range.

[0101] 7. Rare earth electrolysis protection: After trivalent chromium plating, steel workpieces are prepared with rare earth electrolytic protective film 5c using the rare earth electrolytic protection process developed by Chaobang Chemical.

[0102] The electrolyte composition is as follows: cerium acetate 4 g / L, sodium molybdate 12 g / L, HEDP complexing agent 25 g / L, anhydrous sodium carbonate 120 g / L, electrolyte pH 12.2, cathode current density 1 A / dm³. 2 Operating at room temperature, using the plated part as the cathode and a titanium plate as the anode, electrolyzing for 75 seconds.

[0103] 8. Drying: After rare earth electrolytic protection, steel workpieces are dried at 80℃ for 10 minutes.

[0104] Example 4: A trivalent chromium rare earth additive, a chromium plating solution, and an electroplating process, comprising the preparation of a trivalent chromium plating additive, the preparation of a trivalent chromium plating solution, pretreatment of metal workpieces, cyanide-free copper plating, plating of bright nickel-iron alloy, trivalent chromium plating, and rare earth electrolytic protection.

[0105] like Figure 4 As shown, a coating structure prepared by a trivalent chromium plating process includes a steel substrate 1d, and cyanide-free copper plating 2d, a bright nickel-iron alloy plating layer 3d, a trivalent chromium plating layer 4d, and a rare earth electrolytic protective film 5d sequentially prepared from the inside to the outside on the steel substrate 1d.

[0106] 1. Preparation of trivalent chromium plating additives: 1) Preparation of rare earth additives: The rare earth additive comprises 60 g / L lanthanum chloride heptahydrate and 110 g / L praseodymium chloride heptahydrate. The rare earth additive is obtained by dissolving lanthanum chloride heptahydrate and praseodymium chloride heptahydrate in water according to the formulation requirements.

[0107] 2) Preparation of the positioning agent: The leveling agent comprises 80 g / L vanadyl sulfate and 140 g / L ammonium formate. Add pure water to the reaction vessel to 4 / 5 of the required volume, then add ammonium formate according to the leveling agent formulation. Stir until the ammonium formate dissolves, then add vanadyl sulfate and stir until the leveling agent solution is clear. Finally, add pure water to the required volume to obtain the leveling agent.

[0108] 3) Preparation of accelerator: The accelerator comprises 35 g / L of acidic ethoxylated phosphate ester NORFOX PE-600. The accelerator is obtained by dissolving the acidic ethoxylated phosphate ester NORFOX PE-600 in water according to the accelerator formulation requirements.

[0109] 2. Prepare trivalent chromium plating solution: 1) Pour 2 / 3 volume of pure water into the plating tank, and add potassium chloride, ammonium chloride, ammonium bromide, ammonium formate and boric acid according to the plating solution formula requirements, and stir to dissolve the solids; 2) Add 10% hydrochloric acid to the plating bath to adjust the pH of the plating solution to 26 to avoid hydrolysis of trivalent chromium ions after the addition of chromium chloride; 3) Add chromium chloride hexahydrate to the plating tank according to the plating solution formula, and stir until the chromium chloride dissolves; 4) Heat the plating solution to 56°C and keep it at that temperature for 4 hours to allow ammonium formate to form a complex with trivalent chromium ions.

[0110] 5) After the plating solution cools, add pure water to the specified volume of the plating tank; 6) At 1.2A / dm 2Electrolysis for 90 minutes removes harmful impurities from the plating solution; 7) Add rare earth additives, leveling agents, and accelerators to the plating tank according to the plating solution formula requirements; 8) Adjust the pH of the plating solution to 2.6 using 10% hydrochloric acid or 10% ammonia.

[0111] 3. Pre-treatment of steel parts: According to the current pretreatment process, the steel workpiece substrate is subjected to the following steps: "chemical degreasing → water washing → acid pickling for rust removal → water washing → alkaline cathodic electrolytic degreasing → water washing → alkaline anodic electrolytic degreasing → water washing → activation → water washing".

[0112] 4. Cyanide-free copper plating: After pretreatment of steel parts, a cyanide-free copper plating layer with a thickness of 8μm was prepared using the CB-101 polymeric thiocyanate copper plating process developed by Chaobang Chemical.

[0113] Polymeric cuprous thiocyanate 19 g / L, polymeric sodium thiocyanate 140 g / L, sodium hydroxyethylidene diphosphonate 20 g / L, CB-101 copper plating brightener 10 mL / L, plating bath pH 12.8, plating bath temperature 40℃, cathode current density 1 A / dm³ 2 The cathode moves at a speed of 4 m / min. Oxygen-free electrolytic copper particles are used as the anode. The copper particles are loaded into a titanium anode basket. The area ratio of the anode to the cathode is 3.8:1. The anode moves at a speed of 4 m / min.

[0114] 5. Bright nickel-iron alloy plating: After cyanide-free copper plating, steel workpieces were coated with a bright nickel-iron alloy using Chaobang Chemical's EMFASI FN-35 process to prepare a 3-day bright nickel-iron alloy coating with a thickness of 12μm.

[0115] Nickel sulfate hexahydrate 240 g / L, nickel chloride hexahydrate 60 g / L, ferric sulfate heptahydrate 20 g / L, boric acid 50 g / L, EMFASI FN-35 Auxiliary 20 mL / L, EMFASI FN-35 Carrier Softener 20 mL / L, EMFASI FN-35 Bri Brightener 1.5 mL / L, EMFASI FN-35 STAB Stabilizer 12 g / L, NINFEA NI-28 Wetting Agent 2 mL / L, plating bath pH 3, plating bath temperature 55℃, cathode current density 4 A / dm³ 2 Uniform air mixing.

[0116] 6. Trivalent chromium plating: After plating a steel workpiece with nickel-iron alloy, a trivalent chromium plating layer of 4d is prepared using the trivalent chromium plating process of the present invention, with a plating thickness of 0.7μm.

[0117] The plating solution contained 90 g / L chromium chloride hexahydrate, 90 g / L potassium chloride, 140 g / L ammonium chloride, 20 g / L ammonium bromide, 45 g / L ammonium formate, 50 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating solution was 2.6, the plating tank temperature was 32℃, and the cathode current density was 14 A / dm³. 2 An inert graphite rod is used as the anode, with an anode-to-cathode area ratio of 1:1.8, and moderate air agitation is employed.

[0118] When the trivalent chromium in the trivalent chromium plating solution forms hydroxy-bridged polymers, causing a decrease in the chromium plating rate, hydrochloric acid is added to the plating bath to acidify the plating solution, the pH of the plating solution is adjusted to 2, and the reaction is carried out for 2 hours. Then, ammonia is added to raise the pH to the process range.

[0119] 7. Rare earth electrolysis protection: After trivalent chromium plating, steel workpieces are treated with rare earth electrolytic protection film prepared by Chaobang Chemical using a rare earth electrolytic protection process developed by Chaobang Chemical for 5 days.

[0120] Cerium acetate 3 g / L, sodium molybdate 8 g / L, HEDP complexing agent 18 g / L, anhydrous sodium carbonate 150 g / L, electrolyte pH 12.5, cathode current density 1 A / dm³ 2 Operating at room temperature, using the plated part as the cathode and the titanium plate as the anode, electrolysis for 120 seconds.

[0121] 8. Drying: After rare earth electrolytic protection, steel workpieces are dried at 65℃ for 25 minutes.

[0122] Experimental Example 1: 1) Preparation of trivalent chromium plating additives: Rare earth additives: Lanthanum chloride heptahydrate 65g / L, Praseodymium chloride heptahydrate 65g / L.

[0123] Leveling agent: contains 60g / L vanadium oxysulfate and 130g / L ammonium formate.

[0124] Accelerator: 25g / L of acidic ethoxylated alcohol phosphate, product model NORFOX PE-600.

[0125] 2) Trivalent chromium plating process: The plating solution contained 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating bath was 2.8, the plating tank temperature was 30℃, and the cathode current density was 14 A / dm³. 2 A titanium plate with a metal oxide coating is used as the anode, with an anode-to-cathode area ratio of 1:2 and medium air agitation.

[0126] Following the process flow and coating thickness requirements of Example 1, trivalent chromium-plated samples on a steel substrate were prepared. A neutral salt spray test was conducted for 136 hours according to GB / T10125–2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". No white rust was observed on the sample surface. This is 89% higher than the industry requirement of 72 hours, indicating that the prepared coating exhibits excellent corrosion resistance.

[0127] Experimental Example 2: 1) Preparation of trivalent chromium plating additives: Rare earth additives: 130g / L lanthanum chloride heptahydrate, without praseodymium chloride heptahydrate.

[0128] Leveling agent: contains 60g / L vanadium oxysulfate and 130g / L ammonium formate.

[0129] Accelerator: 25g / L of acidic ethoxylated alcohol phosphate, product model NORFOX PE-600.

[0130] 2) Trivalent chromium plating process: The plating solution contained 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating bath was 2.8, the plating tank temperature was 30℃, and the cathode current density was 14 A / dm³. 2 A titanium plate with a metal oxide coating is used as the anode, with an anode-to-cathode area ratio of 1:2 and medium air agitation.

[0131] Following the process flow and coating thickness requirements of Example 1, trivalent chromium-plated samples on a steel substrate were prepared. A neutral salt spray test was conducted for 120 hours according to GB / T10125–2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". No white rust was observed on the sample surface. Compared to Example 1, using lanthanum chloride heptahydrate as a rare earth additive alone reduced the neutral salt spray test time by 16 hours.

[0132] Experimental Example 3: 1) Preparation of trivalent chromium plating additives: Rare earth additives: 130g / L praseodymium chloride heptahydrate, lanthanum chloride heptahydrate not added.

[0133] Leveling agent: contains 60g / L vanadium oxysulfate and 130g / L ammonium formate.

[0134] Accelerator: 25g / L of acidic ethoxylated alcohol phosphate, product model NORFOX PE-600.

[0135] 2) Trivalent chromium plating process: The plating solution contained 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating bath was 2.8, the plating tank temperature was 30℃, and the cathode current density was 14 A / dm³. 2 A titanium plate with a metal oxide coating is used as the anode, with an anode-to-cathode area ratio of 1:2 and medium air agitation.

[0136] Following the process flow and coating thickness requirements of Example 1, trivalent chromium-plated samples on a steel substrate were prepared. A neutral salt spray test was conducted for 120 hours according to GB / T10125–2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test," and no white rust was observed on the sample surface. Compared to Example 1, using praseodymium chloride heptahydrate alone as a rare earth additive reduced the neutral salt spray test time by 16 hours.

[0137] The experimental data from Examples 1, 2, and 3 show that lanthanum chloride and praseodymium chloride have a synergistic effect on improving the salt spray resistance of trivalent chromium plating.

[0138] Experimental Example 4: 1) Preparation of trivalent chromium plating additives: Leveling agent: contains 60g / L vanadium oxysulfate and 130g / L ammonium formate.

[0139] Accelerator: 25g / L of acidic ethoxylated alcohol phosphate, product model NORFOX PE-600.

[0140] 2) Trivalent chromium plating process: The plating solution contained 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 3 mL / L leveling agent, 2 mL / L accelerator, a pH of 2.8, a plating bath temperature of 30℃, and a cathode current density of 14 A / dm³. 2 A titanium plate with a metal oxide coating is used as the anode, with an anode-to-cathode area ratio of 1:2 and medium air agitation.

[0141] Trivalent chromium-plated samples on a steel substrate were prepared according to the process flow and coating thickness requirements of Example 1. A neutral salt spray test was conducted for 96 hours according to GB / T10125–2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test," and no white rust was observed on the sample surface. Compared to Example 1, in Example 4, the neutral salt spray test time for the plated parts was reduced by 40 hours when no rare earth additives were added to the plating solution. Compared to Example 2 or Example 3, the neutral salt spray test time for the plated parts was reduced by 24 hours.

[0142] Tests have shown that adding rare earth additives to trivalent chromium plating solution significantly improves the salt spray resistance of trivalent chromium plating layers.

[0143] Experimental Example 5: 1) Preparation of trivalent chromium plating additives: Rare earth additives: Lanthanum chloride heptahydrate 65g / L, Praseodymium chloride heptahydrate 65g / L.

[0144] Leveling agent: contains 60g / L vanadium oxysulfate and 130g / L ammonium formate.

[0145] Accelerator: 25g / L of acidic ethoxylated alcohol phosphate, product model NORFOX PE-600.

[0146] 2) Trivalent chromium plating solution: The plating solution contains 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating solution is 2.8, and the plating bath temperature is 28℃.

[0147] 3) Hull flume experiment A 267 mL Hull cell experiment was conducted. Trivalent chromium was plated onto a bright nickel-plated sample. A current of 7 A was applied for 3 min, and the chromium plating layer covered up to 93 mm from the cathode.

[0148] The thickness of the trivalent chromium plating layer was measured using a DJH-D electrolytic thickness gauge, and the deposition rate was calculated. The current density values ​​at corresponding points on the test piece were calculated using the Watson method. The results are listed in Table 1.

[0149] Table 1 shows the deposition rate of trivalent chromium plating according to the present invention. Experiments show that the trivalent chromium plating solution of the present invention has high coverage and high deposition rate.

[0150] Experimental Example 6: 1) Preparation of trivalent chromium plating additives: Leveling agent: contains 60g / L vanadium oxysulfate and 130g / L ammonium formate.

[0151] Accelerator: 25g / L of acidic ethoxylated alcohol phosphate, product model NORFOX PE-600.

[0152] 2) Trivalent chromium plating solution: The plating solution contains 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 3 mL / L leveling agent, 2 mL / L accelerator, pH 2.8, and a plating bath temperature of 28℃. No rare earth additives are added to the plating solution.

[0153] 3) Hull flume experiment A 267 mL Hull cell experiment was conducted. Trivalent chromium was plated onto a bright nickel-plated sample. A current of 7 A was applied for 3 min, and the chromium plating layer covered up to 78 mm from the cathode.

[0154] A comparison of Experiment 5 and Experiment 6 shows that adding rare earth additives to trivalent chromium plating solution can significantly improve the coverage of the plating solution.

[0155] Experimental Example 7: 1) Preparation of trivalent chromium plating additives: Rare earth additives: Lanthanum chloride heptahydrate 65g / L, Praseodymium chloride heptahydrate 65g / L.

[0156] Leveling agent: contains 60g / L vanadium oxysulfate and 130g / L ammonium formate.

[0157] Accelerator: Sodium ethylhexyl sulfate 25g / L.

[0158] 2) Trivalent chromium plating solution: The plating solution contains 110 g / L chromium chloride hexahydrate, 125 g / L potassium chloride, 125 g / L ammonium chloride, 21 g / L ammonium bromide, 50 g / L ammonium formate, 60 g / L boric acid, 10 mL / L rare earth additives, 3 mL / L leveling agent, and 2 mL / L accelerator. The pH of the plating solution is 2.8, and the plating bath temperature is 28℃.

[0159] 3) Hull flume experiment A 267 mL Hull cell experiment was conducted, in which trivalent chromium was plated onto a bright nickel-plated sample, and a current of 7 A was applied for 3 minutes.

[0160] The thickness of the trivalent chromium plating layer was measured using a DJH-D electrolytic thickness gauge, and the deposition rate was calculated. The current density values ​​at corresponding points on the test piece were calculated using the Watson method. The results are listed in Table 2.

[0161] Table 2. Deposition rates of trivalent chromium plating in comparative experiments. A comparison of Experiment 7 and Experiment 5 shows that replacing the acidic ethoxylated alcohol phosphate of NORFOX PE-600 of this invention with sodium ethylhexyl sulfate significantly reduces the deposition rate of trivalent chromium plating.

[0162] Experimental Example 8: The steel-based trivalent chromium plating samples prepared in Examples 1, 2, 3, and 4 were tested for 500 hours at 40°C and 93% relative humidity according to GB / T 2423.3–2016 "Basic Environmental Testing Procedures for Electrical and Electronic Products - Test Ca: Constant Damp Heat Test Method". The coatings showed no visible changes, which is far higher than the industry requirement of no change in the coating after 168 hours of constant damp heat testing.

[0163] Experimental Example 9: The steel-based trivalent chromium-plated samples prepared in Examples 1, 2, 3 and 4 were subjected to a mold test for 28 days according to GJB150.9A—2009 "Metasetest Methods for Laboratory Environment of Military Equipment - Part 10: Mold Test". No mold spots appeared on the surface of the samples, which met the environmental test requirements.

[0164] Experimental Example 10: The steel substrate trivalent chromium plating samples prepared in Examples 1, 2, 3 and 4 were tested for adhesion strength using the thermal shock test method according to GB / T 5270-2024 "Review of Test Methods for Adhesion Strength of Electrodeposition and Chemical Deposition of Metallic Coatings on Metallic Substrates". The samples were heated to 300°C in a heating furnace and held for 60 minutes. They were then removed and rapidly cooled in water at room temperature. No blistering or peeling of the plating was observed, indicating good adhesion.

[0165] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. It should be noted that, for those skilled in the art, based on the principles and concepts of the embodiments of the present invention, several modifications and improvements can be made in specific implementation methods and application scope, and these should all fall within the protection scope of the present invention.

Claims

1. A rare earth additive for trivalent chromium plating, characterized in that: The rare earth additive contains 40-140 g / L lanthanum chloride heptahydrate and 0-130 g / L praseodymium chloride heptahydrate, based on the volume of the rare earth additive solution. During the trivalent chromium plating process, the lanthanum chloride and praseodymium chloride hydrolyze on the cathode surface to form a rare earth salt film, which increases the cathode polarization, makes the trivalent chromium plating layer denser, and improves the coverage of the plating solution. The lanthanum chloride and praseodymium chloride have a synergistic effect in increasing cathode polarization.

2. A trivalent chromium plating solution, characterized in that, Includes the following components, concentrations, and plating solution parameters: Chromium chloride hexahydrate 80-140 g / L, potassium chloride 90-160 g / L, ammonium chloride 90-160 g / L, ammonium bromide 16-30 g / L, ammonium formate 40-60 g / L, boric acid 45-65 g / L, rare earth additives 8-12 mL / L, leveling agent 2-4 mL / L, accelerator 1-3 mL / L, plating solution pH 2.5-3.2; The rare earth additive contains 40-140 g / L lanthanum chloride heptahydrate and 0-130 g / L praseodymium chloride heptahydrate, based on the volume of the rare earth additive solution. The leveling agent contains 30-90 g / L of vanadium oxysulfate and 100-160 g / L of ammonium formate by volume of the leveling agent solution. The ammonium formate is used as a complexing agent to dissolve vanadium oxysulfate in the leveling agent. The accelerator contains 10-40 g / L of acidic ethoxylated alcohol phosphate by volume of the accelerator solution, and the acidic ethoxylated alcohol phosphate is used to increase the deposition rate of trivalent chromium.

3. The trivalent chromium plating solution according to claim 2, characterized in that: The acidic ethoxylated alcohol phosphate ester mentioned is the product model NORFOX PE-600.

4. The trivalent chromium plating solution according to claim 2, characterized in that, The positioning agent is prepared using the following method: Add 4 / 5 of the required volume of pure water to the reaction vessel, add ammonium formate according to the leveling agent formula, stir until the ammonium formate dissolves, then add vanadium oxysulfate, stir until the leveling agent solution is clear, and then add pure water to the required volume.

5. The trivalent chromium plating solution according to claim 2, characterized in that, The preparation of the trivalent chromium plating solution includes the following steps: (1) Pour 2 / 3 volume of pure water into the plating tank, and add potassium chloride, ammonium chloride, ammonium bromide, ammonium formate and boric acid according to the plating solution formula requirements, and stir to dissolve the solids; (2) Add 10% hydrochloric acid to the plating bath to adjust the pH of the plating solution to 2.5-2.7 to avoid hydrolysis of trivalent chromium ions after the addition of chromium chloride; (3) Add chromium chloride hexahydrate to the plating tank according to the plating solution formula requirements and stir until the chromium chloride dissolves; (4) Heat the plating solution to 52-58℃ and keep it at that temperature for 3-6 hours to allow ammonium formate to form a complex with trivalent chromium ions; (5) After the plating solution cools, add pure water to the specified volume of the plating tank; (6) Within 0.5~1.5A / dm 2 The plating solution is then electrolyzed for 60–180 minutes to remove harmful impurities. (7) Add rare earth additives, leveling agents and accelerators to the plating tank according to the plating solution formula requirements; (8) Adjust the pH of the plating solution to 2.5 to 3.2 with 10% hydrochloric acid or 10% ammonia.

6. A trivalent chromium plating process, characterized in that, Includes the following components and process parameters: Chromium chloride hexahydrate 80–140 g / L, potassium chloride 90–160 g / L, ammonium chloride 90–160 g / L, ammonium bromide 16–30 g / L, ammonium formate 40–60 g / L, boric acid 45–65 g / L, rare earth additives 8–12 mL / L, leveling agent 2–4 mL / L, accelerator 1–3 mL / L, plating bath pH 2.5–3.2, plating bath temperature 25–35℃, cathode current density 10–18 A / dm³ 2 An inert anode material is used as the anode, and medium air agitation is employed. The rare earth additives contain 40-140 g / L lanthanum chloride heptahydrate and 0-130 g / L praseodymium chloride heptahydrate.

7. The trivalent chromium plating process according to claim 6, characterized in that: The inert anode material is an inert graphite rod or a titanium plate coated with a metal oxide.

8. The trivalent chromium plating process according to claim 6, characterized in that: The area ratio of the anode to the cathode is 1:(1.5~2.5).

9. The trivalent chromium plating process according to claim 6, characterized in that: When the trivalent chromium in the trivalent chromium plating solution forms hydroxy-bridged polymers, causing a decrease in the chromium plating rate, hydrochloric acid is added to the plating bath to acidify the plating solution, the pH of the plating solution is adjusted to 2, and the reaction is carried out for 2 hours. Then, ammonia is added to raise the pH to the process range.

10. The trivalent chromium plating process according to claim 6, characterized in that: A trivalent chromium plating layer is prepared on a bright nickel plating layer, a bright nickel-cobalt alloy plating layer, a bright nickel-copper alloy plating layer, or a bright nickel-iron alloy plating layer using the aforementioned trivalent chromium plating process.

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