A process for cadmium iron alloy plating of neodymium iron boron without cyanide suitable for aerospace applications

Abstract

This invention discloses a cyanide-free cadmium-iron alloy plating process for NdFeB substrates suitable for the aerospace field. The process involves sequentially preparing a sulfate zinc plating layer, a cyanide-free copper-zinc alloy plating layer, a cyanide-free cadmium-iron alloy plating layer, and a passivation layer on a NdFeB substrate from the inside out. The cyanide-free cadmium-iron alloy plating process is as follows: 25-35 g / L cadmium chloride, 4-6 g / L ferrous chloride tetrahydrate, 100-140 g / L potassium chloride, 100-140 g / L complexing agent, 1.5-2.5 mL / L leveling agent, 1.5-2.5 mL / L brightener, 25-30 mL / L auxiliary agent, 25-35 g / L stabilizer, pH of the plating bath 6-8, plating bath temperature 20-35℃, and cathode current density 0.5-1.5 A / dm³. 2 The cathode moved at a speed of 2–4 m / min. The prepared NdFeB-plated cadmium-iron alloy color passivated samples were subjected to an acetic acid spray test for 360 h according to GB / T 10125–2021 standard. No white rust was found on the surface, and the coating exhibited excellent corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a cyanide-free cadmium-iron alloy plating process for neodymium iron boron plating suitable for the aerospace field. Background Technology

[0002] my country possesses abundant rare earth metal reserves and has accumulated and developed advanced mining and processing technologies, making it a global center for the production and market of NdFeB permanent magnet materials. However, the poor corrosion resistance of NdFeB materials still restricts the development of NdFeB and related industries in my country. NdFeB permanent magnet materials are prepared using powder metallurgy, which results in defects such as sintering porosity. NdFeB alloys have a multiphase structure, including a main phase Nd₂Fe₁₄B, an Nd-rich phase (Nd₄Fe), and a B-rich phase (Nd₁+εFe₄B₄), with volume fractions of approximately 84%, 14%, and 2%, respectively. The main phase Nd₂Fe₁₄B is the magnetic phase. Because the Nd-rich and B-rich phases are highly reactive and easily oxidized, and because the electrochemical potentials of the phases differ significantly, electrochemical corrosion is highly likely to occur. [1] .

[0003] The porous surface of sintered NdFeB substrates and the high chemical reactivity of the material itself present challenges for electroplating. Direct electroplating of the base layer onto the surface of NdFeB workpieces using acidic, alkaline, or chloride-containing solutions presents residual corrosion problems due to the plating solution penetrating into the surface pores, leading to pitting corrosion and even localized coating detachment.

[0004] Current electroplating processes typically prepare protective layers on NdFeB surfaces, including zinc plating, nickel plating, copper + nickel + chromium composite plating, nickel + copper + nickel composite plating, nickel + tin composite plating, nickel + silver composite plating, nickel + gold composite plating, and electroplated nickel + chemical nickel composite plating. The most typical and effective methods are zinc plating and nickel plating, with nickel plating being the most widely used. [2] The GB / T 34491-2017 standard, "Sintered NdFeB Surface Coatings," stipulates that for nickel + copper + nickel composite coatings, the time to the start of corrosion under neutral salt spray testing according to GB / T 10125–2021, "Artificial Atmosphere Corrosion Test - Salt Spray Test," is 48 hours for barrel-plated coatings and 16 hours for rack-plated coatings. Clearly, the corrosion resistance of this coating structure is far from meeting the growing technical demands of my country's aerospace industry.

[0005] Citrate nickel plating solutions are neutral and have a very weak corrosive effect on NdFeB substrates. Currently, the NdFeB nickel plating processes reported in the literature generally use citrate nickel plating to prepare the base coating, followed by bright nickel plating to prepare the top coating. [3] The process of preparing protective and decorative coatings for NdFeB workpieces has the following two drawbacks: First, directly plating nickel onto the surface of NdFeB workpieces results in a high magnetic shielding effect. [4]First, it will significantly reduce the magnetic field strength of the NdFeB workpiece; second, directly plating nickel on the surface of the NdFeB workpiece results in a cathodic plating layer that provides no electrochemical protection to the NdFeB substrate. When the plating layer has pores or is damaged, galvanic corrosion will occur, destroying the NdFeB substrate.

[0006] Traditionally, hydrochloric acid, sulfuric acid, and nitric acid are used to remove oxides from the surface of NdFeB workpieces. [5] Production practice has shown that acid pickling with hydrochloric acid or sulfuric acid presents a problem of neodymium hydrogenation. During the pickling reaction, hydrogen generated penetrates into the NdFeB matrix, where hydrogen atoms slowly react with neodymium to form neodymium hydrides, causing the neodymium to transform into a powdery substance. While acid pickling with nitric acid can remove oxides from the NdFeB surface and avoid this hydrogenation problem, nitric acid has a passivating effect on the metal surface, affecting the adhesion between the substrate and the coating.

[0007] References: [1]. Yan Fenying, Zhao Chunying, Zhang Lin, Research progress on surface protection technology of NdFeB permanent magnet materials [J], Electroplating & Finishing, 2012, 34(8): 22-25. [2]. Li Hongying, Hao Zhuangzhi, Liu Yuhui et al., Research progress on corrosion mechanism and surface protection technology of sintered NdFeB permanent magnet materials [J], Mining and Metallurgical Engineering, 2016, 36(6): 118-124. [3]. Guangzhou Chaobang Chemical Co., Ltd., A coating structure of NdFeB nickel plating and rare earth electrolytic protection: 202222706008.2 [P], 2023-03-17. [4]. Meng Chao, Wang Qun, Shi Meiwu, Preparation and performance of iron-nickel alloy magnetic shielding film [J], Safety and Electromagnetic Compatibility, 2015, 27(4): 58-61. [5]. Zhao Qing, Du Nan, Xiao Jun, et al. Study on nickel plating process on NdFeB workpieces [J]. Materials Protection, 2003, 36(6): 32-33. Summary of the Invention

[0008] To address the issues of magnetic shielding and lack of electrochemical protection in direct nickel plating of NdFeB workpieces, this invention provides a cyanide-free cadmium-iron alloy plating process for NdFeB suitable for the aerospace field. To achieve the above objectives, this invention employs the following technical solution:

[0009] A cyanide-free cadmium-iron-boron plating process for neodymium iron boron alloys suitable for the aerospace field includes the following steps:

[0010] (1) Grinding, chamfering, degreasing, and activation of NdFeB workpieces;

[0011] (2) After the NdFeB workpiece is pretreated, a sulfate zinc plating layer is prepared using the current sulfate zinc plating process;

[0012] (3) After sulfate zinc plating, neodymium iron boron workpieces are coated with copper zinc alloy by polymer thiocyanate copper zinc alloy plating process to prepare cyanide-free copper zinc alloy coating;

[0013] (4) After cyanide-free copper-zinc alloy plating, cyanide-free cadmium-iron alloy plating is prepared using cyanide-free cadmium-iron alloy plating process.

[0014] (5) After plating cadmium iron alloy onto neodymium iron boron workpieces, a passivation layer is prepared through post-treatment.

[0015] The cyanide-free cadmium-iron alloy plating process includes the following components and process parameters:

[0016] Cadmium chloride 25–35 g / L, ferrous chloride tetrahydrate 4–6 g / L, potassium chloride 100–140 g / L, complexing agent 100–140 g / L, leveling agent 1.5–2.5 mL / L, brightener 1.5–2.5 mL / L, auxiliary agent 25–30 mL / L, stabilizer 25–35 g / L, plating bath pH 6–8, plating tank temperature 20–35℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 2–4 m / min.

[0017] The leveling agent comprises 5-10 g / L of trithiotriazine, 30-60 g / L of organic amine epoxy derivative, and 5-10 g / L of sodium hydroxide;

[0018] The stabilizer includes sodium gluconate heptate and sodium succinate, with the mass ratio of sodium gluconate heptate to sodium succinate being 1:(2-3).

[0019] The ligand comprises triacetic acid, sulfosalicylic acid, and malic acid. The ligand is obtained by mixing the above components evenly. The mass ratio of triacetic acid, sulfosalicylic acid, and malic acid is 3:(1-2):(4-6).

[0020] The brightening agent comprises three components: A, B, and C. Component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt; component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde; and component C comprises any one or two of propynyl alcohol ethoxy ether, propynyl alcohol propoxy ether, N,N-diethylpropynylamine, N,N-diethylpropynylamine formate, and N,N-diethylpropynylamine sulfate. The concentrations are as follows: component A: 30–80 g / L; component B: 30–80 g / L; component C: 60–100 g / L; and isopropanol: 280–320 g / L.

[0021] The auxiliary agents include polyacrylamide with a molecular weight of less than 8000, sodium 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine with epichlorohydrin, and component D, which is consistent with component C in the brightener; wherein the polyacrylamide with a molecular weight of less than 8000 is 50-80 g / L, the condensate of ethylenediamine or dimethylpropylamine with epichlorohydrin is 20-50 g / L, the sodium 2-ethylhexyl sulfate is 30-80 g / L, and component D is 30-60 g / L.

[0022] In some embodiments, the polymeric thiocyanate copper-zinc alloy plating process includes the following components and process parameters:

[0023] Polymeric cuprous thiocyanate 18–24 g / L, polymeric zinc thiocyanate 9–13 g / L, polymeric sodium thiocyanate 130–170 g / L, copper-zinc alloy electroplating brightener 8–12 mL / L, plating bath pH 10–12, plating bath temperature 35–55℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, with the anode moving at a speed of 3-5 m / min. The copper-zinc alloy electroplating brightener includes the following components by weight: 60-100 parts of N,N'-di-n-propylethylenediamine, 10-20 parts of waterborne polyurethane resin, 80-120 parts of polyacrylamide with a molecular weight of less than 8000, and 770-870 parts of deionized water.

[0024] In some embodiments, the thickness of the cyanide-free cadmium iron coating is 8–24 μm.

[0025] In some embodiments, the thickness of the cyanide-free copper-zinc alloy coating is 6–10 μm.

[0026] In some embodiments, the activation is performed using a lactic acid activation process:

[0027] Lactic acid 40-80 mL / L, operating temperature 20-35℃, activation time 20-40 s.

[0028] In some embodiments, the sulfate zinc plating layer is prepared using a conventional sulfate zinc plating process: zinc sulfate heptahydrate 350–450 g / L, boric acid 25–35 g / L, ZL-94 brightener 14–18 mL / L, plating bath pH 5.0–5.8, plating bath temperature 15–45 °C, and cathode current density 1–4 A / dm³. 2 The cathode moves at a rate of 3–5 m / min.

[0029] In some embodiments, the thickness of the sulfate zinc plating layer is 10–20 μm.

[0030] In some embodiments, the passivation layer includes a hexavalent chromium colored passivation layer, a hexavalent chromium military green passivation layer, a hexavalent chromium black passivation layer, and a trivalent chromium blue-white passivation layer.

[0031] In some embodiments, the hexavalent chromium color passivation layer is prepared using the HC-5 low-chromium color passivation process: the volume concentration of the HC-5 high-protection low-chromium color passivating agent is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15 seconds, and weak air stirring or workpiece oscillation is used.

[0032] In some embodiments, the hexavalent chromium military green passivation layer is prepared using the OVG-31 military green passivation process: OVG-31 military green passivating agent 80-120 mL / L, passivation solution pH value 1.0-1.6, passivation temperature 20-30℃, passivation time 30-90 s, and air stirring or oscillating of the plated part.

[0033] In some embodiments, the hexavalent chromium black passivation layer is prepared using the BZ-71 cadmium plating black passivation process: 80-100 mL / L of BZ-71A cadmium plating black passivation agent, 80-100 mL / L of BZ-71B cadmium plating black passivation agent, pH value of passivation solution 1.1-1.5, passivation temperature 20-35°C, passivation time 15-40 s, and air stirring or oscillating of the plated part.

[0034] In some embodiments, the trivalent chromium blue-white passivation layer is prepared using the TRIROS TCP-185 trivalent chromium blue-white passivation process: 40-80 mL / L of TRIROS TCP-185 trivalent chromium blue-white passivating agent, pH value of passivation solution 1.8-2.5, passivation temperature 20-30°C, passivation time 20-40 s, and air stirring or oscillating of the plated part.

[0035] The preparation of a copper-zinc alloy coating on a zinc layer using a polymeric thiocyanate copper-zinc alloy plating process is similar to that using a cyanide copper plating process, resulting in good adhesion between the coatings. Over time, zinc atoms in the zinc layer diffuse into the copper-zinc alloy coating, and copper and zinc atoms in the copper-zinc alloy coating also diffuse into the zinc alloy coating, ultimately eliminating the obvious interface between the two coatings and further increasing the adhesion between them.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The present invention provides a cyanide-free cadmium-iron alloy plating process for neodymium iron boron in the aerospace field. The prepared cadmium-iron alloy coating has excellent corrosion resistance, overcoming the technical defect of poor corrosion resistance of existing protective layers for neodymium iron boron workpieces.

[0038] 2. The present invention provides a cyanide-free cadmium-plated iron alloy process for NdFeB in the aerospace field. It uses a sulfate zinc plating process to prepare a zinc plating layer on the surface of NdFeB workpieces, overcoming the high magnetic shielding problem of preparing a nickel plating layer on the surface of NdFeB workpieces using a citrate nickel plating process.

[0039] 3. The present invention provides a cyanide-free cadmium iron alloy plating process for NdFeB in the aerospace field. It uses a grinding method to remove the oxide scale on the surface of the NdFeB workpiece and a lactic acid activation method to remove the oxide film on the surface of the NdFeB workpiece. This overcomes the problem of hydrogenation of metal NdFeB caused by the pickling method of hydrochloric acid or sulfuric acid, and also overcomes the problem of passivation of the surface of NdFeB workpiece caused by the pickling method of nitric acid.

[0040] 4. The present invention provides a cyanide-free cadmium iron alloy plating process for NdFeB in the aerospace field. The pH of the sulfate zinc plating solution is 5-5.8, which is very weakly acidic. Sulfate has no corrosive effect on the NdFeB substrate. Therefore, the use of sulfate zinc plating process to prepare the bottom coating can effectively seal the pores on the surface of the NdFeB workpiece, and there is no residual corrosion problem on the NdFeB workpiece substrate.

[0041] 5. The NdFeB cyanide-free cadmium-iron alloy plating process of the present invention, applicable to the aerospace field, uses a polymeric thiocyanate copper-zinc alloy plating process to prepare a copper-zinc alloy coating on the zinc layer, and the two coatings can form a good bonding force.

[0042] 6. The present invention provides a cyanide-free cadmium-iron alloy plating process for NdFeB in the aerospace field. A cyanide-free cadmium-iron alloy plating layer is prepared on a copper-zinc alloy plating layer. The cadmium-iron alloy plating layer is an anodic plating layer relative to the copper-zinc alloy plating layer, which can effectively prevent the corrosion medium from eroding towards the substrate, overcoming the defect of direct nickel plating on the surface of NdFeB workpieces without electrochemical protection. Attached Figure Description

[0043] 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:

[0044] Figure 1 These are schematic diagrams of the coating structures in Embodiments 1, 2, 3 and 4 of the present invention. Detailed Implementation

[0045] 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.

[0046] A process for cyanide-free cadmium-iron alloy plating of neodymium iron boron (NdFeB) for the aerospace field includes pretreatment of NdFeB workpieces and sequential preparation of a sulfate zinc plating layer, a cyanide-free copper-zinc alloy plating layer, a cyanide-free cadmium-iron alloy plating layer, and a passivation layer on a NdFeB substrate from the inside out.

[0047] The neodymium iron boron workpiece is ground, chamfered, degreased, and activated.

[0048] Preferably, the activation is performed using a lactic acid activation process:

[0049] Lactic acid 40-80 mL / L, operating temperature 20-35℃, activation time 20-40 s.

[0050] After pretreatment, the NdFeB workpiece is coated with a sulfate zinc layer using the current sulfate zinc plating process.

[0051] Preferably, the thickness of the sulfate zinc plating layer is 10–20 μm.

[0052] Preferably, the sulfate zinc plating layer is prepared using the ZL-94 sulfate zinc plating process of Tianjin Feige Group United Chemical Plant:

[0053] Zinc sulfate heptahydrate 350–450 g / L, boric acid 25–35 g / L, ZL-94 brightener 14–18 mL / L, plating bath pH 5.0–5.8, plating bath temperature 15–45℃, cathode current density 1–4 A / dm³ 2 The cathode moves at a rate of 3–5 m / min.

[0054] The specific process is: "Zinc plating → water washing → film removal with 0.5% sulfuric acid → water washing".

[0055] After zinc plating, the neodymium iron boron workpiece is coated with a cyanide-free copper-zinc alloy using the polymeric thiocyanate copper-zinc alloy plating process of the present invention.

[0056] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 6–10 μm.

[0057] Polymeric cuprous thiocyanate 18–24 g / L, polymeric zinc thiocyanate 9–13 g / L, polymeric sodium thiocyanate 130–170 g / L, copper-zinc alloy electroplating brightener 8–12 mL / L, plating bath pH 10–12, plating bath temperature 35–55℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, which moves at a speed of 3-5 m / min.

[0058] Preferably, the copper-zinc alloy electroplating brightener comprises the following components in weight fractions: 60-100 parts of N,N'-di-n-propylethylenediamine, 10-20 parts of waterborne polyurethane resin, 80-120 parts of polyacrylamide with a molecular weight less than 8000, and 770-870 parts of deionized water.

[0059] Preferably, the copper-zinc alloy electroplating brightener is prepared as follows: 770-870 parts by weight of deionized water are added to a reaction vessel, and 60-100 parts of N,N'-di-n-propylethylenediamine, 10-20 parts of waterborne polyurethane resin, and 80-120 parts of polyacrylamide with a molecular weight less than 8000 are added while stirring. The mixture is stirred evenly to obtain the brightener.

[0060] Preferably, the polyacrylamide with a molecular weight of less than 8000 includes any one or two of the following: polyacrylamide of type GRO-70, polyacrylamide of type IC-113, polyacrylamide of type IC-125, and polyacrylamide of type IC-213.

[0061] After plating NdFeB workpieces with copper-zinc alloy, a cyanide-free cadmium-iron alloy coating is prepared using the cyanide-free cadmium-iron alloy plating process of this invention.

[0062] Preferably, the thickness of the cyanide-free cadmium iron alloy coating is 8–24 μm.

[0063] Cadmium chloride 25–35 g / L, ferrous chloride tetrahydrate 4–6 g / L, potassium chloride 100–140 g / L, complexing agent 100–140 g / L, leveling agent 1.5–2.5 mL / L, brightener 1.5–2.5 mL / L, auxiliary agent 25–30 mL / L, stabilizer 25–35 g / L, plating bath pH 6–8, plating tank temperature 20–35℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 2–4 m / min.

[0064] Preferably, the leveling agent comprises 5-10 g / L of trithiotriazine, 30-60 g / L of organic amine epoxy derivative, and 5-10 g / L of sodium hydroxide.

[0065] Preferably, the stabilizer includes sodium gluconate and sodium hydrogen succinate, wherein the mass ratio of sodium gluconate to sodium hydrogen succinate is 1:(2-3).

[0066] Preferably, the ligand comprises triacetic acid, sulfosalicylic acid, and malic acid, and the ligand is obtained by mixing the above components evenly; the mass ratio of triacetic acid, sulfosalicylic acid, and malic acid is 3:(1-2):(4-6).

[0067] Preferably, the brightening agent comprises three components: A, B, and C. Component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt; component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde; and component C comprises any one or two of propynyl alcohol ethoxy ether, propynyl alcohol propoxy ether, N,N-diethylpropynylamine, N,N-diethylpropynylamine formate, and N,N-diethylpropynylamine sulfate. The concentrations are as follows: component A: 30–80 g / L; component B: 30–80 g / L; component C: 60–100 g / L; and isopropanol: 280–100 g / L.

[0068] Preferably, the auxiliary agent includes polyacrylamide with a molecular weight of less than 8000, sodium 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, wherein component D is consistent with component C in the brightener; wherein the polyacrylamide with a molecular weight of less than 8000 is 50-80 g / L, the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin is 20-50 g / L, the sodium 2-ethylhexyl sulfate is 30-80 g / L, and component D is 30-60 g / L.

[0069] After plating cadmium-iron alloy onto NdFeB workpieces, a passivation layer is prepared using the current cadmium plating post-treatment process. Preferably, the passivation layer includes a hexavalent chromium colored passivation layer, a hexavalent chromium military green passivation layer, a hexavalent chromium black passivation layer, and a trivalent chromium blue-white passivation layer.

[0070] Preferably, the hexavalent chromium colored passivation layer is prepared using the HC-5 low-chromium colored passivation process: the volume concentration of the HC-5 high-protection low-chromium colored passivation agent is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15 seconds, and weak air stirring or workpiece oscillation is used.

[0071] Preferably, the hexavalent chromium military green passivation layer is prepared using the OVG-31 military green passivation process: 80-120 mL / L of OVG-31 military green passivating agent, pH value of passivation solution 1.0-1.6, passivation temperature 20-30℃, passivation time 30-90 s, and air stirring or oscillating of the plated part.

[0072] Preferably, the hexavalent chromium black passivation layer is prepared using the BZ-71 cadmium plating black passivation process: 80-100 mL / L of BZ-71A cadmium plating black passivation agent, 80-100 mL / L of BZ-71B cadmium plating black passivation agent, pH value of passivation solution 1.1-1.5, passivation temperature 20-35℃, passivation time 15-40 s, and air stirring or oscillating of the plated part.

[0073] Preferably, the trivalent chromium blue-white passivation layer is prepared using the TRIROS TCP-185 trivalent chromium blue-white passivation process: 40-80 mL / L of TRIROS TCP-185 trivalent chromium blue-white passivating agent, pH value of passivation solution 1.8-2.5, passivation temperature 20-30℃, passivation time 20-40 s, and air stirring or oscillating of the plated part.

[0074] After passivation, NdFeB workpieces are dried using conventional drying processes.

[0075] Example 1:

[0076] like Figure 1 As shown, a process for cyanide-free cadmium-iron alloy plating of neodymium iron boron suitable for the aerospace field includes: pretreatment of neodymium iron boron substrate 1, and sequential preparation of sulfate zinc plating layer 2, cyanide-free copper-zinc alloy plating layer 3, cyanide-free cadmium-iron alloy plating layer 4, and hexavalent chromium color passivation layer 5 on the pretreated neodymium iron boron substrate 1 from the inside out.

[0077] 1. Pre-processing:

[0078] The NdFeB workpiece substrate 1 is subjected to the following process: "grinding and chamfering → water washing → weak alkaline ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0079] The lactic acid activation process is as follows: lactic acid 60 mL / L, operating temperature 28℃, activation time 30 s.

[0080] 2. Sulfate zinc plating:

[0081] After pretreatment, the NdFeB workpiece was prepared with sulfate zinc plating layer 2 using the ZL-94 sulfate zinc plating process of Tianjin Feige Group United Chemical Plant. The thickness of the zinc plating layer was 15μm.

[0082] Zinc sulfate heptahydrate 400 g / L, boric acid 30 g / L, ZL-94 brightener 16 mL / L, plating bath pH 5.4, plating tank temperature 30℃, cathode current density 2 A / dm³ 2 The cathode moves at a speed of 4 m / min.

[0083] The specific process is: "Zinc plating → water washing → film removal with 0.5% sulfuric acid → water washing".

[0084] 3. Copper-zinc alloy plating:

[0085] After zinc plating, the neodymium iron boron workpiece is prepared with a cyanide-free copper-zinc alloy coating 3 using the polymeric thiocyanate copper-zinc alloy plating process of the present invention. The thickness of the copper-zinc alloy coating is 8 μm.

[0086] 1) Preparation of copper-zinc alloy electroplating brightener:

[0087] By weight, 820 parts of deionized water were added to a reaction vessel, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of GRO-70 polyacrylamide were added under stirring. The mixture was stirred until homogeneous to obtain the brightener.

[0088] 2) Plating:

[0089] Polymeric cuprous thiocyanate 21 g / L, polymeric zinc thiocyanate 11 g / L, polymeric sodium thiocyanate 150 g / L, copper-zinc alloy electroplating brightener 10 mL / L, plating bath pH 10.5, plating bath temperature 45℃, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, which moves at a speed of 4 m / min.

[0090] 4. Cadmium-plated iron alloy:

[0091] After the neodymium iron boron workpiece is plated with copper-zinc alloy, a cyanide-free cadmium iron alloy coating 4 is prepared using the cyanide-free cadmium iron alloy plating process of the present invention. The thickness of the cadmium iron alloy coating is 12μm.

[0092] 1) Preparation of leveling agent:

[0093] The leveling agent comprises 7.5 g / L of trithiotriazine, 45 g / L of an organic amine epoxy derivative (product model GDX) sold by Sefik New Materials Co., Ltd., and 7.5 g / L of sodium hydroxide. Sodium hydroxide is dissolved in water according to the formulation requirements, then trithiotriazine is added and stirred until dissolved. The organic amine epoxy derivative is then added, and water is added to the required volume to obtain the leveling agent.

[0094] 2) Preparation of stabilizers:

[0095] The stabilizer comprises sodium glucono-heptanate and sodium bisuccinate, with a mass ratio of sodium glucono-heptanate to sodium bisuccinate of 1:2.5. Sodium glucono-heptanate and sodium bisuccinate are mixed together according to the formulation requirements and stirred until homogeneous to obtain the stabilizer.

[0096] 3) Preparation of the complexing agent:

[0097] The complexing agent comprises triacetic acid, sulfosalicylic acid, and malic acid, with a mass ratio of 3:1.5:5. The triacetic acid, sulfosalicylic acid, and malic acid are mixed together according to the formulation ratio and stirred until homogeneous to obtain the complexing agent.

[0098] 4) Preparation of brightening agent:

[0099] The brightener comprises three components: A, B, and C. Component A includes α-vinyl-N-propanesulfonic acid pyridine inner salt; component B includes any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde; and component C includes any one or two of propynyl alcohol ethoxy ether, propynyl alcohol propoxy ether, N,N-diethylpropynylamine, N,N-diethylpropynylamine formate, and N,N-diethylpropynylamine sulfate. 30 kg of isopropanol is added to 40 kg of water and mixed thoroughly. Then, 5.5 kg of component A, 4 kg of component B, and 8 kg of component C are added and stirred until dissolved. Water is then added to a final volume of 100 L to obtain the brightener.

[0100] 5) Preparation of auxiliary agents:

[0101] The auxiliary agent includes polyacrylamide with a molecular weight of less than 8000, sodium 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, which is the same as component C in the brightener; add 6.5 kg of polyacrylamide with a molecular weight of less than 8000, 3.5 kg of the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 5.5 kg of sodium 2-ethylhexyl sulfate, and 4.5 kg of component D to 70 kg of water, stir to dissolve, and add water to 100 L to obtain the auxiliary agent.

[0102] 6) Plating:

[0103] Cadmium chloride 30 g / L, ferrous chloride tetrahydrate 5 g / L, potassium chloride 120 g / L, complexing agent 120 g / L, leveling agent 2.0 mL / L, brightener 2.0 mL / L, auxiliary agent 27 mL / L, stabilizer 30 g / L, plating solution pH 7, plating tank temperature 28℃, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 3 m / min.

[0104] 5. Hexavalent chromium color passivation:

[0105] After plating cadmium-iron alloy onto NdFeB workpieces, a hexavalent chromium color passivation layer is prepared using Chaobang Chemical's HC-5 low-chromium color passivation process.

[0106] The volume concentration of HC-5 high-protection low-chromium colored passivating agent is 3%, the passivation temperature is 28℃, the pH of the passivation solution is 1.6, the passivation time is 8s, and the workpiece is oscillating.

[0107] The specific process is as follows: "Brightening with 1.5% nitric acid by volume → water washing → passivation → water washing → draining after removal from the tank → blowing away residual water on the surface of the plated parts with high-pressure air".

[0108] 6. Drying:

[0109] After passivation, the neodymium iron boron workpiece is dried at 60°C for 10 minutes.

[0110] Example 2:

[0111] like Figure 1 As shown, a process for cyanide-free cadmium-iron alloy plating of neodymium iron boron suitable for the aerospace field includes: pretreatment of neodymium iron boron substrate 1, and sequential preparation of sulfate zinc plating layer 2, cyanide-free copper-zinc alloy plating layer 3, cyanide-free cadmium-iron alloy plating layer 4, and hexavalent chromium military green passivation layer 5 on the pretreated neodymium iron boron substrate 1 from the inside out.

[0112] The NdFeB workpiece substrate 1 is subjected to the following process: "grinding and chamfering → water washing → weak alkaline ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0113] The lactic acid activation process is as follows: lactic acid 60 mL / L, operating temperature 20℃, activation time 30 s.

[0114] 2. Sulfate zinc plating:

[0115] After pretreatment, the NdFeB workpiece was prepared with sulfate zinc plating layer 2 using the ZL-94 sulfate zinc plating process of Tianjin Feige Group United Chemical Plant. The thickness of the zinc plating layer was 15μm.

[0116] Zinc sulfate heptahydrate 450 g / L, boric acid 35 g / L, ZL-94 brightener 16 mL / L, plating bath pH 5.2, plating tank temperature 30℃, cathode current density 3 A / dm³ 2 The cathode moves at a speed of 4 m / min.

[0117] The specific process is: "Zinc plating → water washing → film removal with 0.5% sulfuric acid → water washing".

[0118] 3. Copper-zinc alloy plating:

[0119] After zinc plating, the neodymium iron boron workpiece is prepared with a cyanide-free copper-zinc alloy coating 3 using the polymeric thiocyanate copper-zinc alloy plating process of the present invention. The thickness of the copper-zinc alloy coating is 8 μm.

[0120] 1) Preparation of copper-zinc alloy electroplating brightener:

[0121] By weight, 820 parts of deionized water were added to a reaction vessel, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of IC-113 polyacrylamide were added under stirring. The mixture was stirred until homogeneous to obtain the brightener.

[0122] 2) Plating:

[0123] Polymeric cuprous thiocyanate 24 g / L, polymeric zinc thiocyanate 13 g / L, polymeric sodium thiocyanate 170 g / L, copper-zinc alloy electroplating brightener 10 mL / L, plating bath pH 10, plating bath temperature 45℃, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, which moves at a speed of 4 m / min.

[0124] 4. Cadmium-plated iron alloy:

[0125] After the neodymium iron boron workpiece is plated with copper-zinc alloy, a cyanide-free cadmium iron alloy coating 4 is prepared using the cyanide-free cadmium iron alloy plating process of the present invention. The thickness of the cadmium iron alloy coating is 12μm.

[0126] 1) Preparation of leveling agent:

[0127] The leveling agent comprises 7.5 g / L of trithiotriazine, 45 g / L of an organic amine epoxy derivative (product model GDX) sold by Sefik New Materials Co., Ltd., and 7.5 g / L of sodium hydroxide. Sodium hydroxide is dissolved in water according to the formulation requirements, then trithiotriazine is added and stirred until dissolved. The organic amine epoxy derivative is then added, and water is added to the required volume to obtain the leveling agent.

[0128] 2) Preparation of stabilizers:

[0129] The stabilizer comprises sodium glucono-heptanate and sodium bisuccinate, with a mass ratio of sodium glucono-heptanate to sodium bisuccinate of 1:2.5. Sodium glucono-heptanate and sodium bisuccinate are mixed together according to the formulation requirements and stirred until homogeneous to obtain the stabilizer.

[0130] 3) Preparation of the complexing agent:

[0131] The complexing agent comprises triacetic acid, sulfosalicylic acid, and malic acid, with a mass ratio of 3:1.5:5. The triacetic acid, sulfosalicylic acid, and malic acid are mixed together according to the formulation ratio and stirred until homogeneous to obtain the complexing agent.

[0132] 4) Preparation of brightening agent:

[0133] The brightener comprises three components: A, B, and C. Component A includes α-vinyl-N-propanesulfonic acid pyridine inner salt; component B includes any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde; and component C includes any one or two of propynyl alcohol ethoxy ether, propynyl alcohol propoxy ether, N,N-diethylpropynylamine, N,N-diethylpropynylamine formate, and N,N-diethylpropynylamine sulfate. 30 kg of isopropanol is added to 40 kg of water and mixed thoroughly. Then, 5.5 kg of component A, 4 kg of component B, and 8 kg of component C are added and stirred until dissolved. Water is then added to a final volume of 100 L to obtain the brightener.

[0134] 5) Preparation of auxiliary agents:

[0135] The auxiliary agent includes polyacrylamide with a molecular weight of less than 8000, sodium 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, which is the same as component C in the brightener; add 6.5 kg of polyacrylamide with a molecular weight of less than 8000, 3.5 kg of the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 5.5 kg of sodium 2-ethylhexyl sulfate, and 4.5 kg of component D to 70 kg of water, stir to dissolve, and add water to 100 L to obtain the auxiliary agent.

[0136] 6) Plating:

[0137] The plating solution contains 28 g / L cadmium chloride, 4.7 g / L ferrous chloride tetrahydrate, 135 g / L potassium chloride, 125 g / L complexing agent, 2.0 mL / L leveling agent, 2.0 mL / L brightener, 28 mL / L auxiliary agent, and 28 g / L stabilizer. The pH of the plating solution is 6.5, the plating tank temperature is 32℃, and the cathode current density is 1.0 A / dm³. 2 The cathode moves at a speed of 3 m / min.

[0138] 5. Hexavalent chromium military green passivation:

[0139] After plating cadmium-iron alloy onto neodymium iron boron workpieces, a military green passivation layer 5 was prepared using Chaobang Chemical's OVG-31 military green passivation process.

[0140] OVG-31 military green passivating agent 100mL / L, passivation solution pH 1.3, passivation temperature 25℃, passivation time 60s, oscillating plated parts.

[0141] The specific process is as follows: "Brightening with 1.5% nitric acid by volume → water washing → passivation → water washing → draining after removal from the tank → blowing away residual water on the surface of the plated parts with high-pressure air".

[0142] 6. Drying:

[0143] After passivation, the neodymium iron boron workpiece is dried at 60°C for 10 minutes.

[0144] Example 3:

[0145] like Figure 1 As shown, a process for cyanide-free cadmium-iron alloy plating of neodymium iron boron suitable for the aerospace field includes: pretreatment of neodymium iron boron substrate 1, and sequential preparation of sulfate zinc plating layer 2, cyanide-free copper-zinc alloy plating layer 3, cyanide-free cadmium-iron alloy plating layer 4, and hexavalent chromium black passivation layer 5 on the pretreated neodymium iron boron substrate 1 from the inside out.

[0146] 1. Pre-processing:

[0147] The NdFeB workpiece substrate 1 is subjected to the following process: "grinding and chamfering → water washing → weak alkaline ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0148] The lactic acid activation process is as follows: lactic acid 40 mL / L, operating temperature 35℃, activation time 40 s.

[0149] 2. Sulfate zinc plating:

[0150] After pretreatment, the NdFeB workpiece was prepared with sulfate zinc plating layer 2 using the ZL-94 sulfate zinc plating process of Tianjin Feige Group United Chemical Plant. The thickness of the zinc plating layer was 15μm.

[0151] Zinc sulfate heptahydrate 350 g / L, boric acid 25 g / L, ZL-94 brightener 16 mL / L, plating bath pH 5.6, plating tank temperature 45℃, cathode current density 2 A / dm³ 2 The cathode moves at a speed of 4 m / min.

[0152] The specific process is: "Zinc plating → water washing → film removal with 0.5% sulfuric acid → water washing".

[0153] 3. Copper-zinc alloy plating:

[0154] After zinc plating, the neodymium iron boron workpiece is prepared with a cyanide-free copper-zinc alloy coating 3 using the polymeric thiocyanate copper-zinc alloy plating process of the present invention. The thickness of the copper-zinc alloy coating is 8 μm.

[0155] 1) Preparation of copper-zinc alloy electroplating brightener:

[0156] By weight, 820 parts of deionized water were added to a reaction vessel, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of IC-125 polyacrylamide were added under stirring. The mixture was stirred until homogeneous to obtain the brightener.

[0157] 2) Plating:

[0158] Polymeric cuprous thiocyanate 18 g / L, polymeric zinc thiocyanate 9 g / L, polymeric sodium thiocyanate 130 g / L, copper-zinc alloy electroplating brightener 10 mL / L, plating bath pH 11.5, plating bath temperature 55℃, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, which moves at a speed of 4 m / min.

[0159] 4. Cadmium-plated iron alloy:

[0160] After the neodymium iron boron workpiece is plated with copper-zinc alloy, a cyanide-free cadmium iron alloy coating 4 is prepared using the cyanide-free cadmium iron alloy plating process of the present invention. The thickness of the cadmium iron alloy coating is 12μm.

[0161] 1) Preparation of leveling agent:

[0162] The leveling agent comprises 7.5 g / L of trithiotriazine, 45 g / L of an organic amine epoxy derivative (product model GDX) sold by Sefik New Materials Co., Ltd., and 7.5 g / L of sodium hydroxide. Sodium hydroxide is dissolved in water according to the formulation requirements, then trithiotriazine is added and stirred until dissolved. The organic amine epoxy derivative is then added, and water is added to the required volume to obtain the leveling agent.

[0163] 2) Preparation of stabilizers:

[0164] The stabilizer comprises sodium glucono-heptanate and sodium bisuccinate, with a mass ratio of sodium glucono-heptanate to sodium bisuccinate of 1:2.5. Sodium glucono-heptanate and sodium bisuccinate are mixed together according to the formulation requirements and stirred until homogeneous to obtain the stabilizer.

[0165] 3) Preparation of the complexing agent:

[0166] The complexing agent comprises triacetic acid, sulfosalicylic acid, and malic acid, with a mass ratio of 3:1.5:5. The triacetic acid, sulfosalicylic acid, and malic acid are mixed together according to the formulation ratio and stirred until homogeneous to obtain the complexing agent.

[0167] 4) Preparation of brightening agent:

[0168] The brightener comprises three components: A, B, and C. Component A includes α-vinyl-N-propanesulfonic acid pyridine inner salt; component B includes any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde; and component C includes any one or two of propynyl alcohol ethoxy ether, propynyl alcohol propoxy ether, N,N-diethylpropynylamine, N,N-diethylpropynylamine formate, and N,N-diethylpropynylamine sulfate. 30 kg of isopropanol is added to 40 kg of water and mixed thoroughly. Then, 5.5 kg of component A, 4 kg of component B, and 8 kg of component C are added and stirred until dissolved. Water is then added to a final volume of 100 L to obtain the brightener.

[0169] 5) Preparation of auxiliary agents:

[0170] The auxiliary agent includes polyacrylamide with a molecular weight of less than 8000, sodium 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, which is the same as component C in the brightener; add 6.5 kg of polyacrylamide with a molecular weight of less than 8000, 3.5 kg of the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 5.5 kg of sodium 2-ethylhexyl sulfate, and 4.5 kg of component D to 70 kg of water, stir to dissolve, and add water to 100 L to obtain the auxiliary agent.

[0171] 6) Plating:

[0172] The plating solution contains 35 g / L cadmium chloride, 6 g / L ferrous chloride tetrahydrate, 140 g / L potassium chloride, 140 g / L complexing agent, 2.0 mL / L leveling agent, 2.0 mL / L brightener, 28 mL / L auxiliary agent, and 35 g / L stabilizer. The pH of the plating solution is 7.5, the plating tank temperature is 20℃, and the cathode current density is 1.0 A / dm³. 2 The cathode moves at a speed of 3 m / min.

[0173] 5. Hexavalent chromium black passivation:

[0174] After cadmium-iron-boron workpieces are plated with cadmium-iron alloy, a hexavalent chromium black passivation layer is prepared using Chaobang Chemical's BZ-71 cadmium plating black passivation process.

[0175] BZ-71A cadmium plating black passivating agent 90mL / L, BZ-71B cadmium plating black passivating agent 90mL / L, passivation solution pH 1.3, passivation temperature 25℃, passivation time 28s, oscillating plated parts.

[0176] The specific process is as follows: "Brightening with 1.5% nitric acid by volume → water washing → passivation → water washing → draining after removal from the tank → blowing away residual water on the surface of the plated parts with high-pressure air".

[0177] 6. Drying:

[0178] After passivation, the neodymium iron boron workpiece is dried at 60°C for 10 minutes.

[0179] Example 4:

[0180] like Figure 1 As shown, a process for cyanide-free cadmium-iron alloy plating of neodymium iron boron suitable for the aerospace field includes: pretreatment of neodymium iron boron substrate 1, and sequential preparation of sulfate zinc plating layer 2, cyanide-free copper-zinc alloy plating layer 3, cyanide-free cadmium-iron alloy plating layer 4, and trivalent chromium blue-white passivation layer 5 on the pretreated neodymium iron boron substrate 1 from the inside out.

[0181] 1. Pre-processing:

[0182] The NdFeB workpiece substrate 1 is subjected to the following process: "grinding and chamfering → water washing → weak alkaline ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0183] The lactic acid activation process is as follows: lactic acid 70 mL / L, operating temperature 25℃, activation time 25 s.

[0184] 2. Sulfate zinc plating:

[0185] After pretreatment, the NdFeB workpiece was prepared with sulfate zinc plating layer 2 using the ZL-94 sulfate zinc plating process of Tianjin Feige Group United Chemical Plant. The thickness of the zinc plating layer was 15μm.

[0186] Zinc sulfate heptahydrate 430 g / L, boric acid 32 g / L, ZL-94 brightener 16 mL / L, plating bath pH 5.6, plating tank temperature 30℃, cathode current density 2 A / dm³ 2 The cathode moves at a speed of 4 m / min.

[0187] The specific process is: "Zinc plating → water washing → film removal with 0.5% sulfuric acid → water washing".

[0188] 3. Copper-zinc alloy plating:

[0189] After zinc plating, the neodymium iron boron workpiece is prepared with a cyanide-free copper-zinc alloy coating 3 using the polymeric thiocyanate copper-zinc alloy plating process of the present invention. The thickness of the copper-zinc alloy coating is 8 μm.

[0190] 1) Preparation of copper-zinc alloy electroplating brightener:

[0191] By weight, 820 parts of deionized water were added to a reaction vessel, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of IC-213 polyacrylamide were added under stirring. The mixture was stirred until homogeneous to obtain the brightener.

[0192] 2) Plating:

[0193] Polymeric cuprous thiocyanate 23 g / L, polymeric zinc thiocyanate 12 g / L, polymeric sodium thiocyanate 165 g / L, copper-zinc alloy electroplating brightener 10 mL / L, plating bath pH 11.8, plating bath temperature 40℃, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, which moves at a speed of 4 m / min.

[0194] 4. Cadmium-plated iron alloy:

[0195] After the neodymium iron boron workpiece is plated with copper-zinc alloy, a cyanide-free cadmium iron alloy coating 4 is prepared using the cyanide-free cadmium iron alloy plating process of the present invention. The thickness of the cadmium iron alloy coating is 12μm.

[0196] 1) Preparation of leveling agent:

[0197] The leveling agent comprises 7.5 g / L of trithiotriazine, 45 g / L of an organic amine epoxy derivative (product model GDX) sold by Sefik New Materials Co., Ltd., and 7.5 g / L of sodium hydroxide. Sodium hydroxide is dissolved in water according to the formulation requirements, then trithiotriazine is added and stirred until dissolved. The organic amine epoxy derivative is then added, and water is added to the required volume to obtain the leveling agent.

[0198] 2) Preparation of stabilizers:

[0199] The stabilizer comprises sodium glucono-heptanate and sodium bisuccinate, with a mass ratio of sodium glucono-heptanate to sodium bisuccinate of 1:2.5. Sodium glucono-heptanate and sodium bisuccinate are mixed together according to the formulation requirements and stirred until homogeneous to obtain the stabilizer.

[0200] 3) Preparation of the complexing agent:

[0201] The complexing agent comprises triacetic acid, sulfosalicylic acid, and malic acid, with a mass ratio of 3:1.5:5. The triacetic acid, sulfosalicylic acid, and malic acid are mixed together according to the formulation ratio and stirred until homogeneous to obtain the complexing agent.

[0202] 4) Preparation of brightening agent:

[0203] The brightener comprises three components: A, B, and C. Component A includes α-vinyl-N-propanesulfonic acid pyridine inner salt; component B includes any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde; and component C includes any one or two of propynyl alcohol ethoxy ether, propynyl alcohol propoxy ether, N,N-diethylpropynylamine, N,N-diethylpropynylamine formate, and N,N-diethylpropynylamine sulfate. 30 kg of isopropanol is added to 40 kg of water and mixed thoroughly. Then, 5.5 kg of component A, 4 kg of component B, and 8 kg of component C are added and stirred until dissolved. Water is then added to a final volume of 100 L to obtain the brightener.

[0204] 5) Preparation of auxiliary agents:

[0205] The auxiliary agent includes polyacrylamide with a molecular weight of less than 8000, sodium 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, which is the same as component C in the brightener; add 6.5 kg of polyacrylamide with a molecular weight of less than 8000, 3.5 kg of the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 5.5 kg of sodium 2-ethylhexyl sulfate, and 4.5 kg of component D to 70 kg of water, stir to dissolve, and add water to 100 L to obtain the auxiliary agent.

[0206] 6) Plating:

[0207] Cadmium chloride 25 g / L, ferrous chloride tetrahydrate 4 g / L, potassium chloride 140 g / L, complexing agent 100 g / L, leveling agent 2.0 mL / L, brightener 2.0 mL / L, auxiliary agent 28 mL / L, stabilizer 25 g / L, plating solution pH 8, plating tank temperature 30℃, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 3 m / min.

[0208] 5. Trivalent chromium blue-white passivation:

[0209] After plating cadmium-iron alloy onto NdFeB workpieces, a trivalent chromium blue-white passivation layer was prepared using the TRIROS TCP-185 trivalent chromium blue-white passivation process from Chaobang Chemical Co., Ltd.

[0210] TRIROS TCP-185 trivalent chromium blue-white passivating agent 60mL / L, passivation solution pH 2.2, passivation temperature 25℃, passivation time 30s, oscillating plated parts.

[0211] The specific process is as follows: "Brightening with 1.5% nitric acid by volume → water washing → passivation → water washing → draining after removal from the tank → blowing away residual water on the surface of the plated parts with high-pressure air".

[0212] 6. Drying:

[0213] After passivation, the neodymium iron boron workpiece is dried at 60°C for 10 minutes.

[0214] Experimental Example 1:

[0215] Acetic acid salt spray tests were conducted according to GB / T 10125–2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The NdFeB-plated cadmium-iron alloy hexavalent chromium color passivated sample prepared in Example 1 showed no white rust on the surface after 360 hours. The NdFeB-plated cadmium-iron alloy hexavalent chromium military green passivated sample prepared in Example 2 showed no white rust on the surface after 380 hours. The NdFeB-plated cadmium-iron alloy hexavalent chromium black passivated sample prepared in Example 3 showed no white rust on the surface after 328 hours. The NdFeB-plated cadmium-iron alloy trivalent chromium blue-white passivated sample prepared in Example 4 showed no white rust on the surface after 96 hours. The prepared coatings exhibit excellent corrosion resistance.

[0216] Experimental Example 2:

[0217] The neodymium iron boron cadmium-plated iron alloy samples prepared in Examples 1, 2, 3, and 4 were tested for coating adhesion according to GB / T 5270–2005 "Review of Test Methods for Adhesion Strength of Electrodeposited and Chemically Deposited Metallic Coatings on Metal Substrates". The samples were heated to 250°C in a heating furnace and held for 30 minutes. After being removed, they were immediately placed in room temperature water to cool. No blistering or peeling of the coating occurred, and the coating adhesion met the standard requirements.

[0218] Experimental Example 3:

[0219] The neodymium iron boron cadmium-plated iron alloy samples prepared in Examples 1, 2, 3, and 4 were tested for 360 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". No visible changes were observed in the coating, which meets the industry's technical requirements.

[0220] Experimental Example 4:

[0221] The neodymium iron boron cadmium-plated iron alloy samples prepared in Examples 1, 2, 3, and 4 were subjected to a mold test for 28 days in accordance with GJB150.9A–2009 "Metasequoia Test Methods for Military Equipment Laboratory Environment - Part 10: Mold Test". No mold grew on the surface of the samples, which met the environmental test requirements.

[0222] 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 those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these are also considered to fall within the protection scope of the present invention.

Claims

1. A cyanide-free cadmium-plating process for neodymium iron boron cadmium alloy suitable for the aerospace field, characterized in that, Includes the following steps: (1) Grinding, chamfering, degreasing, and activation of NdFeB workpieces; (2) After the NdFeB workpiece is pretreated, a sulfate zinc plating layer is prepared using the current sulfate zinc plating process; (3) After sulfate zinc plating, neodymium iron boron workpieces are coated with copper zinc alloy by polymer thiocyanate copper zinc alloy plating process to prepare cyanide-free copper zinc alloy coating; (4) After cyanide-free copper-zinc alloy plating, cyanide-free cadmium-iron alloy plating is prepared using cyanide-free cadmium-iron alloy plating process. (5) After plating cadmium iron alloy onto neodymium iron boron workpieces, a passivation layer is prepared through post-treatment. The cyanide-free cadmium-iron alloy plating process includes the following components and process parameters: Cadmium chloride 25–35 g / L, ferrous chloride tetrahydrate 4–6 g / L, potassium chloride 100–140 g / L, complexing agent 100–140 g / L, leveling agent 1.5–2.5 mL / L, brightener 1.5–2.5 mL / L, auxiliary agent 25–30 mL / L, stabilizer 25–35 g / L, plating bath pH 6–8, plating tank temperature 20–35℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 2–4 m / min. The leveling agent comprises 5-10 g / L of trithiotriazine, 30-60 g / L of organic amine epoxy derivative, and 5-10 g / L of sodium hydroxide; The stabilizer includes sodium gluconate heptate and sodium succinate, with the mass ratio of sodium gluconate heptate to sodium succinate being 1:(2-3). The ligand comprises triacetic acid, sulfosalicylic acid, and malic acid. The ligand is obtained by mixing the above components evenly. The mass ratio of triacetic acid, sulfosalicylic acid, and malic acid is 3:(1-2):(4-6). The brightening agent comprises three components: A, B, and C. Component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt; component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde; and component C comprises any one or two of propynyl alcohol ethoxy ether, propynyl alcohol propoxy ether, N,N-diethylpropynylamine, N,N-diethylpropynylamine formate, and N,N-diethylpropynylamine sulfate. The concentrations are as follows: component A: 30–80 g / L; component B: 30–80 g / L; component C: 60–100 g / L; and isopropanol: 280–320 g / L. The auxiliary agents include polyacrylamide with a molecular weight of less than 8000, sodium 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine with epichlorohydrin, and component D, which is consistent with component C in the brightener; wherein the polyacrylamide with a molecular weight of less than 8000 is 50-80 g / L, the condensate of ethylenediamine or dimethylpropylamine with epichlorohydrin is 20-50 g / L, the sodium 2-ethylhexyl sulfate is 30-80 g / L, and component D is 30-60 g / L.

2. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 1, characterized in that, The aforementioned polymeric thiocyanate copper-zinc alloy plating process includes the following components and process parameters: Polymeric cuprous thiocyanate 18–24 g / L, polymeric zinc thiocyanate 9–13 g / L, polymeric sodium thiocyanate 130–170 g / L, copper-zinc alloy electroplating brightener 8–12 mL / L, plating bath pH 10–12, plating bath temperature 35–55℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, with the anode moving at a speed of 3-5 m / min. The copper-zinc alloy electroplating brightener includes the following components by weight: 60-100 parts of N,N'-di-n-propylethylenediamine, 10-20 parts of waterborne polyurethane resin, 80-120 parts of polyacrylamide with a molecular weight of less than 8000, and 770-870 parts of deionized water.

3. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 1, characterized in that: The thickness of the cyanide-free cadmium iron coating is 8–24 μm.

4. The neodymium iron boron cyanide-free cadmium iron alloy plating process applicable to the aerospace field as described in claim 1, characterized in that: The thickness of the cyanide-free copper-zinc alloy coating is 6–10 μm.

5. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 1, characterized in that, The activation process employs lactic acid activation. Lactic acid 40-80 mL / L, operating temperature 20-35℃, activation time 20-40 s.

6. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 1, characterized in that, The sulfate zinc plating layer is prepared using the current sulfate zinc plating process: Zinc sulfate heptahydrate 350–450 g / L, boric acid 25–35 g / L, ZL-94 brightener 14–18 mL / L, plating bath pH 5.0–5.8, plating bath temperature 15–45℃, cathode current density 1–4 A / dm³ 2 The cathode moves at a rate of 3–5 m / min.

7. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 1 or 6, characterized in that: The thickness of the sulfate zinc plating layer is 10–20 μm.

8. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 1, characterized in that: The passivation layer includes a hexavalent chromium colored passivation layer, a hexavalent chromium military green passivation layer, a hexavalent chromium black passivation layer, and a trivalent chromium blue-white passivation layer.

9. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 8, characterized in that: The hexavalent chromium colored passivation layer is prepared using the HC-5 low-chromium colored passivation process: the volume concentration of the HC-5 high-protection low-chromium colored passivating agent is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15 seconds, and the process involves weak air stirring or workpiece oscillation. The hexavalent chromium military green passivation layer is prepared using the OVG-31 military green passivation process: OVG-31 military green passivating agent 80-120mL / L, passivation solution pH value 1.0-1.6, passivation temperature 20-30℃, passivation time 30-90s, and air stirring or oscillating of the plated part. The hexavalent chromium black passivation layer is prepared using the BZ-71 cadmium plating black passivation process: BZ-71A cadmium plating black passivation agent 80-100 mL / L, BZ-71B cadmium plating black passivation agent 80-100 mL / L, passivation solution pH value 1.1-1.5, passivation temperature 20-35℃, passivation time 15-40 s, and the plated part is agitated with air or oscillated.

10. The neodymium iron boron cyanide-free cadmium iron alloy plating process for the aerospace field as described in claim 8, characterized in that, The trivalent chromium blue-white passivation layer is prepared using the TRIROS TCP-185 trivalent chromium blue-white passivation process: 40-80 mL / L of TRIROS TCP-185 trivalent chromium blue-white passivating agent, pH value of passivation solution 1.8-2.5, passivation temperature 20-30℃, passivation time 20-40 s, and air stirring or oscillating of the plated part.

Images