Neodymium-iron-boron trivalent chromium plating method with triple electrochemical protection effect and plating layer structure

Abstract

The invention discloses a neodymium-iron-boron trivalent chromium plating method with a triple electrochemical protection effect and a plating layer structure. The method comprises the step of sequentially preparing a cyanide-free copper-zinc alloy plating layer, a cyanide-free copper plating layer, a nickel-copper alloy plating layer, a semi-bright nickel plating layer, a nickel-cobalt alloy plating layer, a trivalent chromium plating layer and a rare earth electrolysis protection film on a neodymium-iron-boron substrate. According to the process for preparing the cyanide-free copper plating layer, 18-24 g / L of polycuprous thiocyanate, 130-170 g / L of polysodium thiocyanate, 20-30 g / L of sodium hydroxyethylidene diphosphonate and 8-12 mL / L of a copper plating brightener are adopted, the pH value of a plating solution is 12-13, the temperature of a plating tank is 30-40 DEG C, the cathode current density is 0.5-1.5 A / dm < 2 >, the cathode movement speed is 3-5 m / min, oxygen-free electrolytic copper particles serve as an anode, and the anode movement speed is 3-5 m / min. The surface of the prepared trivalent chromium-plated sample piece is not rusted after being subjected to a neutral salt spray test for 142 hours according to the GB / T 10125-2021 standard.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal surface treatment, and particularly relates to a method for trivalent chromium electroplating of neodymium iron boron with triple electrochemical protection and a coating structure. Background Art

[0002] China has become the production and market center of global neodymium iron boron permanent magnet materials, but the poor corrosion resistance of neodymium iron boron plated parts restricts the development of China's neodymium iron boron and related industries. The neodymium iron boron alloy has a multiphase structure, including the main phase Nd2Fe14B, Nd-rich phase (Nd4Fe), and B-rich phase (Nd1+εFe4B4). The volume fractions of each phase are approximately 84%, 14%, and 2% respectively, and the main phase Nd2Fe14B is the magnetic phase. Since the Nd-rich phase and B-rich phase are very active and easily oxidized, and the electrochemical potentials of each phase vary greatly, galvanic corrosion is likely to occur. [1] 。

[0003] During the electroplating process, acidic plating solutions, alkaline plating solutions, and plating solutions containing chlorides that penetrate into the pores on the surface of neodymium iron boron will corrode the neodymium iron boron substrate and the coating, which is called residual corrosion in the industry. Currently, a neutral citrate nickel plating process is usually used to prepare a pre-nickel plating layer on the surface of neodymium iron boron, but this coating has a high magnetic shielding problem for neodymium iron boron permanent magnet materials. [2] 。

[0004] In the mid- to high-end manufacturing industry, the neodymium iron boron permanent magnet is mainly prepared with a nickel plating process for the protective layer. The process is as follows: a citrate pre-nickel plating layer and a bright nickel plating layer are sequentially prepared on the neodymium iron boron substrate, or a citrate pre-nickel plating layer, a copper plating layer, and a bright nickel plating layer are sequentially prepared on the neodymium iron boron substrate. GB / T 34491–2017 "Surface Coatings on Sintered Neodymium Iron Boron" stipulates that the time for rusting to occur during the neutral salt spray test for nickel plating or nickel + copper + nickel coatings on the surface of neodymium iron boron is 48h, while the time for rusting to occur during the neutral salt spray test for nickel plating or nickel + copper + nickel coatings on the surface of other materials is much higher than this value.

[0005] In the application of neodymium iron boron electroplated parts, it is found that the corrosion that occurs on the plated parts is usually pitting corrosion. The corrosive medium penetrates through the coating to corrode the neodymium iron boron substrate, and granular red corrosion products appear on the surface of the coating, while the coating itself is not corroded. Therefore, to solve the corrosion resistance problem of neodymium iron boron plated parts, the key is to solve the electrochemical protection problem of the coating.

[0006] Functional multi-layer electroplating technology is very important for breaking through some problems faced in the electroplating field by integrating the coating structure. The multi-layer composite coating not only has a mechanical protection effect but also has good electrochemical protection function [3] and can meet the corrosion resistance requirements of various high-end products.

[0007] The nickel-cobalt alloy coating has many excellent physical, chemical, and mechanical properties, and its market share is increasing year by year. The nickel-cobalt alloy coating has higher corrosion resistance and wear resistance than the bright nickel coating, so it can be used as a protective and decorative coating in high-end manufacturing [4] .

[0008] Using trivalent chromium electroplating to replace hexavalent chromium electroplating has achieved good social and environmental benefits. In protective and decorative electroplating, the trivalent chromium electroplating process is used to prepare a surface coating on the bright nickel coating to improve the corrosion resistance, wear resistance, and anti-discoloration ability of the coating [5] .

[0009] References: [1]. Li Hongying, Hao Zhuangzhi, Liu Yuhui, et al., Research progress on the corrosion mechanism and surface protection technology of sintered NdFeB permanent magnetic materials [J], Mining and Metallurgical Engineering, 2016, 36(6): 118-124. [2]. Meng Chao, Wang Qun, Shi Meiwu, Preparation and properties of iron-nickel alloy magnetic shielding films [J], Safety and Electromagnetic Compatibility, 2015, 27(4): 58-61. [3]. Dai Pengmin, Guo Chongwu, A multi-layer nickel plating process suitable for aerospace aluminum alloy parts [J], Electroplating & Finishing, 2024, 43(4): 74-78. [4]. Zhu Longzhang, Zhang Qingyuan, Chen Yufei, et al., Electrodeposition of nickel-cobalt alloy coatings and their corrosion resistance [J], Materials Protection, 1997, 30(5): 4-6. [5]. Guo Chongwu, Lai Huanwen, A rapid trivalent chromium electroplating process in sulfate system [J], Electroplating & Finishing, 2011, 30(10): 13-16. Summary of the Invention

[0010] In order to solve the problems of high magnetic shielding and low corrosion resistance in direct nickel plating on the surface of neodymium iron boron, the present invention provides a neodymium iron boron trivalent chromium electroplating method and coating structure with triple electrochemical protection. To achieve the above purpose, the present invention adopts the following technical solutions: A neodymium iron boron trivalent chromium electroplating method with triple electrochemical protection, comprising the following steps: (1) Grind and chamfer the neodymium iron boron workpiece, degrease, and pickle and activate it; (2) After the pretreatment of the neodymium iron boron workpiece, use a weakly alkaline polymeric thiocyanate copper-zinc alloy plating process to prepare a cyanide-free copper-zinc alloy coating; (3) After the neodymium iron boron workpiece is plated with a polymeric thiocyanate copper-zinc alloy, use a polymeric thiocyanate copper plating process to prepare a cyanide-free copper coating; (4) After the neodymium iron boron workpiece is plated with a polymeric thiocyanate copper, use a nickel-copper alloy plating process to prepare a nickel-copper alloy coating; (5) After the neodymium iron boron workpiece is plated with a nickel-copper alloy, use a semi-bright nickel plating process to prepare a semi-bright nickel coating; (6) After the neodymium iron boron workpiece is plated with semi-bright nickel, a nickel-cobalt alloy plating process is used to prepare a nickel-cobalt alloy coating; (7) After the neodymium iron boron workpiece is plated with nickel-cobalt alloy, a trivalent chromium plating process is used to prepare a trivalent chromium plating layer; (8) After the neodymium iron boron workpiece is plated with trivalent chromium, a rare earth electrolytic protection process is used to prepare a rare earth electrolytic protection film; The copper plating process with polymeric thiocyanate includes the following components and process parameters: Copper(I) polymeric thiocyanate 18 - 24 g / L, sodium polymeric thiocyanate 130 - 170 g / L, 2-hydroxyethylidene-1,1-diphosphonic acid sodium salt 20 - 30 g / L, copper plating brightener 8 - 12 mL / L, pH value of the plating solution 12 - 13, plating bath temperature 30 - 40 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode movement 3 - 5 m / min, using oxygen-free electrolytic copper granules as the anode, loading the copper granules into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, anode movement 3 - 5 m / min; The copper plating brightener includes the following components by weight fraction: melamine 1 - 2 parts, waterborne polyurethane resin 10 - 20 parts, polyacrylamide with a molecular weight less than 8000 80 - 120 parts, cobalt acetate 40 - 60 parts, formic acid 390 - 430 parts, pure water 390 - 430 parts.

[0011] In some embodiments, the copper plating brightener is prepared as follows: Calculated by weight parts, add 390 - 430 parts of formic acid into a reaction tank, add 1 - 2 parts of melamine with stirring, stir until the solid substances are dissolved, then add 10 - 20 parts of waterborne polyurethane resin, 80 - 120 parts of polyacrylamide with a molecular weight less than 8000, 40 - 60 parts of cobalt acetate, and 390 - 430 parts of pure water, stir until the solid substances are dissolved to obtain the copper plating brightener.

[0012] In some embodiments, the weakly alkaline copper-zinc alloy plating process with polymeric thiocyanate includes the following components and process parameters: Copper(I) polymeric thiocyanate 14 - 20 g / L, zinc(I) polymeric thiocyanate 12 - 18 g / L, sodium polymeric thiocyanate 140 - 180 g / L, copper-zinc alloy plating brightener 8 - 12 mL / L, pH value of the plating solution 9 - 10, plating bath temperature 35 - 45 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode movement 3 - 5 m / min, using brass granules coded as H59 as the anode, loading the brass granules into a titanium anode blue, the area ratio of the anode to the cathode > 3:1, anode movement 3 - 5 m / min; The described brightener for copper-zinc alloy plating comprises the following components in parts 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 less than 8000, and 770-870 parts of pure water.

[0013] In some embodiments, the nickel-copper alloy coating is prepared by the Nistar 6070 process for plating bright nickel-copper alloy: Nickel sulfate hexahydrate 180-220 g / L, copper sulfate pentahydrate 8-12 g / L, trisodium citrate 50-70 g / L, disodium hydroxylethylidene 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, pH value of the plating solution 4.3-4.8, plating bath temperature 50-55 °C, cathode current density 2.6-3.2 A / dm 2 , cathode movement 3-5 m / min.

[0014] In some embodiments, the semi-bright nickel coating is prepared by the NINFEA SM-700 process for plating semi-bright nickel: Nickel sulfate hexahydrate 240-300 g / L, nickel chloride hexahydrate 40-50 g / L, boric acid 40-50 g / L, NINFEA SM-700A auxiliary agent 2-5 mL / L, NINFEA SM-700B main brightener 0.3-0.8 mL / L, NINFEA SM-700C stabilizer 0.3-0.8 mL / L, NINFEA NI-27 wetting agent 1-3 mL / L, pH value of the plating solution 3.8-4.4, plating bath temperature 50-65 °C, cathode current density 3-5 A / dm 2 , cathode movement 5-6 m / min.

[0015] In some embodiments, the nickel-cobalt alloy coating is prepared by the NINFEA 310 process for plating bright nickel-cobalt alloy: 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 8-12 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, pH value of the plating solution 4.0-4.5, plating bath temperature 55-60 °C, cathode current density 2-6 A / dm 2 , with uniform air agitation.

[0016] In some of these embodiments, the trivalent chromium electroplated coating is prepared by the Trich-9551 sulfate trivalent chromium electroplating process: Trich-9551 M starter 8 - 12 mL / L, Trich-9551 B supplement 260 - 300 mL / L, Trich-9551 CS conductive salt 260 - 300 g / L, where the mass concentration of trivalent chromium is 12 - 18 g / L, the mass concentration of boric acid is 65 - 75 g / L, the pH value of the plating solution is 3.4 - 3.8, the plating bath temperature is 50 - 55 °C, and the cathode current density is 8 - 15 A / dm 2 , with gentle air agitation or cathode movement.

[0017] In some of these embodiments, the trivalent chromium electroplated layer is prepared by the Trich-6561 chloride trivalent chromium electroplating process: Trich-6561 starting salt 400 - 450 g / L, Trich-6563 complexing agent 65 - 85 mL / L, Trich-6564 stabilizer 1 - 2 mL / L, Trich-6565 wetting agent 1 - 3 mL / L, where the mass concentration of trivalent chromium is 23 - 25 g / L, the mass concentration of boric acid is 55 - 60 g / L, the pH value of the plating solution is 2.5 - 3.0, the operating temperature is 25 - 32 °C, and the cathode current density is 8 - 16 A / dm 2 , with medium air agitation.

[0018] In some of these embodiments, the rare earth electrolytic protective film is prepared by the rare earth electrolytic protection process: Cerium acetate 1 - 5 g / L, sodium molybdate 5 - 15 g / L, HEDP complexing agent 5 - 30 g / L, anhydrous sodium carbonate 100 - 150 g / L, the pH value of the electrolyte is 11.5 - 12.5, the cathode current density is 0.5 - 1.5 A / dm 2 , operating at room temperature, using the workpiece as the cathode and a titanium plate as the anode, and electrolyzing for 60 - 120 s.

[0019] A coating structure prepared by a neodymium iron boron trivalent chromium electroplating method with triple electrochemical protection functions, the coating structure includes a neodymium iron boron substrate, and a cyanide-free copper-zinc alloy coating, a cyanide-free copper coating, a nickel-copper alloy coating, a semi-bright nickel coating, a nickel-cobalt alloy coating, a trivalent chromium electroplated coating, and a rare earth electrolytic protective film sequentially prepared on the neodymium iron boron substrate.

[0020] In some of these embodiments, the thickness of the cyanide-free copper-zinc alloy coating is 4 - 8 μm.

[0021] In some of these embodiments, the thickness of the cyanide-free copper coating is 4 - 8 μm.

[0022] In some of these embodiments, the thickness of the nickel - copper alloy coating is 5 - 15 μm.

[0023] In some of these embodiments, the thickness of the semi - bright nickel coating is 5 - 15 μm.

[0024] In some of these embodiments, the thickness of the nickel - cobalt alloy coating is 3 - 7 μm.

[0025] In some of these embodiments, the thickness of the trivalent chromium electroplated chromium layer is 0.3 - 0.6 μm.

[0026] This technical solution uses a weakly alkaline polymer thiocyanate copper - zinc alloy electroplating process to prepare the bottom coating. The pH of the plating solution is 3 - 7, and the plating solution does not contain chlorides. There is basically no residual corrosion problem for the plating solution immersed in the pores on the surface of neodymium - iron - boron. Nickel - copper alloy is plated on the copper plating layer. The nickel - copper alloy coating is anodic. Semi - bright nickel is plated on the copper - nickel alloy coating. The semi - bright nickel coating is anodic. Nickel - cobalt alloy is plated on the semi - bright nickel coating. The nickel - cobalt alloy coating is also anodic. This coating structure can effectively prevent the corrosion medium from eroding towards the substrate direction.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. The neodymium - iron - boron trivalent chromium electroplating method and coating structure with triple electrochemical protection effects of the present invention use a weakly alkaline cyanide - free copper - zinc alloy electroplating process to prepare the bottom coating on the surface of neodymium - iron - boron, overcoming the high magnetic shielding problem existing in directly electroplating nickel on the surface of neodymium - iron - boron; 2. The neodymium - iron - boron trivalent chromium electroplating method and coating structure with triple electrochemical protection effects of the present invention use a weakly alkaline cyanide - free copper - zinc alloy electroplating process to prepare the bottom coating on the surface of neodymium - iron - boron, overcoming the residual corrosion problem existing in neodymium - iron - boron electroplating; 3. The neodymium - iron - boron trivalent chromium electroplating method and coating structure with triple electrochemical protection effects of the present invention, the prepared composite coating structure has triple electrochemical protection effects, overcoming the defect that directly preparing a nickel coating on the surface of neodymium - iron - boron does not have electrochemical protection effects, and significantly improving the corrosion resistance of the coating; 4. The neodymium - iron - boron trivalent chromium electroplating method and coating structure with triple electrochemical protection effects of the present invention, the polymer thiocyanate copper plating solution has good throwing power. Polymer thiocyanate copper plating is carried out on the cyanide - free copper - zinc alloy coating, which can completely seal the pores on the surface of neodymium - iron - boron. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not constitute an improper limitation to the present invention. In the drawings, Figure 1It is a schematic diagram of the coating structure of Embodiment 1, Embodiment 2, Embodiment 3 and Embodiment 4 of the present invention. Detailed implementation manners

[0029] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Here, the schematic embodiments and descriptions of the present invention are used to explain the present invention, but not to limit the present invention.

[0030] A neodymium-iron-boron trivalent chromium electroplating method and coating structure with triple electrochemical protection functions include pre-treatment of neodymium-iron-boron workpieces, and sequentially preparing a cyanide-free copper-zinc alloy coating, a cyanide-free copper coating, a nickel-copper alloy coating, a semi-bright nickel coating, a nickel-cobalt alloy coating, a trivalent chromium electroplating coating, and a rare earth electrolytic protective film on the neodymium-iron-boron substrate from the inside to the outside.

[0031] The neodymium-iron-boron workpieces are ground and chamfered, degreased, and pickled and activated by using the current pre-treatment process.

[0032] Preferably, the pickling and activation adopts a lactic acid activation process: Lactic acid 40 - 80 mL / L, operating temperature 20 - 35 °C, activation time 20 - 40 s.

[0033] After the pre-treatment of the neodymium-iron-boron workpieces, a cyanide-free copper-zinc alloy coating is prepared by using the weak alkaline polymeric thiocyanate copper-zinc alloy electroplating process of the present invention.

[0034] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 4 - 8 μm.

[0035] Cuprous polymeric thiocyanate 14 - 20 g / L, zinc polymeric thiocyanate 12 - 18 g / L, sodium polymeric thiocyanate 140 - 180 g / L, copper-zinc alloy electroplating brightener 8 - 12 mL / L, pH value of the plating solution 9 - 10, plating bath temperature 35 - 45 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode movement 3 - 5 m / min, using brass grains coded as H59 as the anode, loading the brass grains into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, anode movement 3 - 5 m / min.

[0036] Preferably, the copper-zinc alloy electroplating brightener includes the following components in weight fractions: N,N'-di-n-propylethylenediamine 60 - 100 parts, waterborne polyurethane resin 10 - 20 parts, polyacrylamide with a molecular weight less than 8000 80 - 120 parts, pure water 770 - 870 parts.

[0037] After the neodymium-iron-boron workpieces are electroplated with the cyanide-free copper-zinc alloy by polymeric thiocyanate, a cyanide-free copper coating is prepared by using the polymeric thiocyanate copper electroplating process of the present invention.

[0038] Preferably, the thickness of the cyanide-free copper coating is 4 - 8 μm.

[0039] Preferably, the polymeric thiocyanate copper plating process comprises the following components and process parameters: cuprous polymeric thiocyanate 18 - 24 g / L, sodium polymeric thiocyanate 130 - 170 g / L, sodium 1 - hydroxyethylidene-1,1-diphosphonate 20 - 30 g / L, copper plating brightener 8 - 12 mL / L, pH value of the plating solution 12 - 13, plating bath temperature 30 - 40 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode moving speed 3 - 5 m / min, using oxygen-free electrolytic copper grains as the anode, loading the copper grains into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, anode moving speed 3 - 5 m / min; Preferably, the copper plating brightener comprises the following components by weight fraction: melamine 1 - 2 parts, waterborne polyurethane resin 10 - 20 parts, polyacrylamide with a molecular weight less than 8000 80 - 120 parts, cobalt acetate 40 - 60 parts, formic acid 390 - 430 parts, pure water 390 - 430 parts.

[0040] Preferably, the copper plating brightener is prepared by the following method: Calculated by weight parts, add 390 - 430 parts of formic acid into a reaction tank, add 1 - 2 parts of melamine under stirring, stir until the solid substances are dissolved, then add 10 - 20 parts of waterborne polyurethane resin, 80 - 120 parts of polyacrylamide with a molecular weight less than 8000, 40 - 60 parts of cobalt acetate, and 390 - 430 parts of pure water, stir until the solid substances are dissolved to obtain the copper plating brightener.

[0041] After the neodymium iron boron workpiece is plated with copper by polymeric thiocyanate, a nickel-copper alloy coating is prepared by the current nickel-copper alloy plating process.

[0042] Preferably, the thickness of the nickel-copper alloy coating is 5 - 15 μm.

[0043] Preferably, the nickel-copper alloy coating is prepared by the Nistar 6070 bright nickel-copper alloy plating process of Superbond Chemical Industry: nickel sulfate hexahydrate 180 - 220 g / L, copper sulfate pentahydrate 8 - 12 g / L, trisodium citrate 50 - 70 g / L, disodium 1-hydroxyethylidene-1,1-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, pH value of the plating solution 4.3 - 4.8, plating bath temperature 50 - 55 °C, cathode current density 2.6 - 3.2 A / dm 2 , cathode moving speed 3 - 5 m / min.

[0044] After the neodymium iron boron workpiece is plated with nickel - copper alloy, the semi - bright nickel plating layer is prepared by using the current semi - bright nickel plating process.

[0045] Preferably, the thickness of the semi - bright nickel plating layer is 5 - 15 μm.

[0046] Preferably, the semi - bright nickel plating layer is prepared by using the NINFEA SM - 700 semi - bright nickel plating process of Superbond Chemical Industry: Nickel sulfate hexahydrate 240 - 300 g / L, nickel chloride hexahydrate 40 - 50 g / L, boric acid 40 - 50 g / L, NINFEA SM - 700A auxiliary agent 2 - 5 mL / L, NINFEA SM - 700B main brightening agent 0.3 - 0.8 mL / L, NINFEA SM - 700C stabilizer 0.3 - 0.8 mL / L, NINFEA NI - 27 wetting agent 1 - 3 mL / L, pH value of the plating solution 3.8 - 4.4, plating bath temperature 50 - 65 °C, cathode current density 3 - 5 A / dm 2 , cathode movement 5 - 6 m / min.

[0047] After the neodymium iron boron workpiece is plated with semi - bright nickel, the nickel - cobalt alloy plating layer is prepared by using the current nickel - cobalt alloy plating process.

[0048] Preferably, the thickness of the nickel - cobalt alloy plating layer is 3 - 7 μm.

[0049] Preferably, the nickel - cobalt alloy plating layer is prepared by using the NINFEA 310 bright nickel - cobalt alloy plating process of Superbond Chemical Industry: 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 8 - 12 mL / L, NINFEA 310 main brightening agent 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, pH value of the plating solution 4.0 - 4.5, plating bath temperature 55 - 60 °C, cathode current density 2 - 6 A / dm 2 , with uniform air agitation.

[0050] After the neodymium iron boron workpiece is plated with nickel - cobalt alloy, the trivalent chromium plating layer is prepared by using the current trivalent chromium plating process.

[0051] Preferably, the thickness of the trivalent chromium plating layer is 0.3 - 0.6 μm.

[0052] Preferably, the trivalent chromium plating layer is prepared by using the Trich - 9551 sulfate trivalent chromium plating process of Superbond Chemical Industry: Trich-9551 start-up agent 8 - 12 mL / L, Trich-9551 B replenisher 260 - 300 mL / L, Trich-9551 CS conductive salt 260 - 300 g / L, where the mass concentration of trivalent chromium is 12 - 18 g / L, the mass concentration of boric acid is 65 - 75 g / L, the pH value of the plating solution is 3.4 - 3.8, the plating bath temperature is 50 - 55 °C, and the cathode current density is 8 - 15 A / dm 2 , with gentle air agitation or cathode movement.

[0053] Preferably, the trivalent chromium electroplated layer is prepared by the Trich-6561 chloride trivalent chromium electroplating process of Superbond Chemical Industry: Trich-6561 start-up salt 400 - 450 g / L, Trich-6563 complexing agent 65 - 85 mL / L, Trich-6564 stabilizer 1 - 2 mL / L, Trich-6565 wetting agent 1 - 3 mL / L, where the mass concentration of trivalent chromium is 23 - 25 g / L, the mass concentration of boric acid is 55 - 60 g / L, the pH value of the plating solution is 2.5 - 3.0, the operating temperature is 25 - 32 °C, and the cathode current density is 8 - 16 A / dm 2 , with medium air agitation.

[0054] After trivalent chromium electroplating of the neodymium iron boron workpiece, a rare earth electrolytic protective film is prepared by the rare earth electrolytic protection process developed by Superbond Chemical Industry.

[0055] Preferably, the rare earth electrolytic protective film is prepared by the following rare earth electrolytic protection process: Cerium acetate 1 - 5 g / L, sodium molybdate 5 - 15 g / L, HEDP complexing agent 5 - 30 g / L, anhydrous sodium carbonate 100 - 150 g / L, the pH value of the electrolyte is 11.5 - 12.5, and the cathode current density is 0.5 - 1.5 A / dm 2 , operating at room temperature, using the workpiece as the cathode and a titanium plate as the anode, and electrolyzing for 60 - 120 s.

[0056] After electrolytic protection of the neodymium iron boron workpiece, it is dried by a conventional process.

[0057] Example 1: As Figure 1 shown, a neodymium iron boron trivalent chromium electroplating method and coating structure with triple electrochemical protection functions includes pretreatment of the neodymium iron boron substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a cyanide-free copper coating 3, a nickel-copper alloy coating 4, a semi-bright nickel coating 5, a nickel-cobalt alloy coating 6, a trivalent chromium electroplated layer 7, and a rare earth electrolytic protective film 8 from the inside to the outside on the pretreated neodymium iron boron substrate 1.

[0058] 1. Pretreatment: The matrix 1 of the neodymium iron boron workpiece is processed by the current pretreatment process as "grinding and chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0059] The lactic acid activation adopts the following lactic acid activation process: 60 mL / L of lactic acid, operating temperature of 28 °C, and activation time of 30 s.

[0060] 2. Copper-zinc alloy plating: After the pretreatment of the neodymium iron boron workpiece, a cyanide-free copper-zinc alloy coating 2 is prepared by the polymerized thiocyanate copper-zinc alloy plating process of the present invention, and the coating thickness is 6 μm.

[0061] 1) Preparation of copper-zinc alloy brightener: Calculated by weight, 820 parts of pure water are added to the reaction tank, and 80 parts of N,N'-dipropylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of polyacrylamide of model GRO-70 are added under stirring, and the obtained copper-zinc alloy brightener is stirred evenly.

[0062] 2) Plating: Copper(I) thiocyanate polymer 17 g / L, zinc(I) thiocyanate polymer 15 g / L, sodium thiocyanate polymer 160 g / L, copper-zinc alloy brightener 10 mL / L, pH of the plating solution is 9.5, temperature of the plating bath is 40 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min, brass grains of code H59 are used as the anode, the brass grains are loaded into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, and the anode moving speed is 4 m / min.

[0063] 3. Copper plating: After the neodymium iron boron workpiece is plated with copper-zinc alloy by polymerized thiocyanate, a cyanide-free copper plating layer 3 is prepared by the polymerized thiocyanate copper plating process of the present invention, and the coating thickness is 6 μm.

[0064] 1) Preparation of copper plating brightener: Calculated by weight, 410 parts of formic acid are added to the reaction tank, 1.5 parts of melamine are added under stirring, and stirred until the solid substances are dissolved, then 15 parts of waterborne polyurethane resin, 100 parts of polyacrylamide of model GRO-70, 50 parts of cobalt acetate, and 410 parts of pure water are added, and stirred until the solid substances are dissolved to obtain the copper plating brightener.

[0065] 2) Plating: Copper(I) thiocyanate polymer 18 g / L, sodium thiocyanate polymer 130 g / L, 2-hydroxyethylidene diphosphonic acid sodium salt 20 g / L, copper plating brightener 10 mL / L, pH of the plating solution is 13, temperature of the plating bath is 40 °C, cathode current density is 1 A / dm 2, the cathode moves at 4 m / min. Use oxygen-free electrolytic copper pellets as the anode, load the copper pellets into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, and the anode moves at 4 m / min.

[0066] 4. Nickel-Copper Alloy Plating: After the neodymium iron boron workpiece is plated with polymerized thiocyanate copper, use the Nistar 6070 bright nickel-copper alloy plating process of Superbond Chemical Industry to prepare the nickel-copper alloy coating 4, and the coating thickness is 8 μm.

[0067] Nickel sulfate hexahydrate 180 g / L, copper sulfate pentahydrate 8 g / L, trisodium citrate 50 g / L, sodium dihydrogen ethylenediamine tetraacetate 20 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 0.7 mL / L, the pH of the plating solution is 4.3, the plating bath temperature is 55 °C, and the cathode current density is 2.8 A / dm 2 , the cathode moves at 4 m / min.

[0068] 5. Semi-bright Nickel Plating: After the neodymium iron boron workpiece is plated with nickel-copper alloy, use the NINFEA SM-700 semi-bright nickel plating process of Superbond Chemical Industry to prepare the semi-bright nickel coating 5, and the coating thickness is 8 μm.

[0069] Nickel sulfate hexahydrate 240 g / L, nickel chloride hexahydrate 40 g / L, boric acid 45 g / L, NINFEA SM-700A auxiliary agent 4 mL / L, NINFEA SM-700B main brightener 0.5 mL / L, NINFEA SM-700C stabilizer 0.5 mL / L, NINFEA NI-27 wetting agent 2 mL / L, the pH of the plating solution is 3.8, the plating bath temperature is 65 °C, and the cathode current density is 4 A / dm 2 , the cathode moves at 6 m / min.

[0070] 6. Nickel-Cobalt Alloy Plating: After the neodymium iron boron workpiece is plated with semi-bright nickel, use the NINFEA 310 bright nickel-cobalt alloy plating process of Superbond Chemical Industry to prepare the nickel-cobalt alloy coating 6, and the coating thickness is 5 μm.

[0071] Nickel sulfate hexahydrate 220 g / L, nickel chloride hexahydrate 50 g / L, cobalt sulfate heptahydrate 15 g / L, boric acid 45 g / L, NINFEA SC-230 auxiliary agent 10 mL / L, NINFEA 310 main brightener 1 mL / L, NINFEA 312 leveling agent 1 mL / L, NINFEA NI-35 wetting agent 1 mL / L, the pH of the plating solution is 4.0, the plating bath temperature is 60 °C, and the cathode current density is 4 A / dm 2 , with uniform air agitation.

[0072] 7. Trivalent chromium electroplating: After the neodymium iron boron workpiece is plated with nickel cobalt alloy, the trivalent chromium electroplating layer 7 is prepared by using the Trich-9551 sulfate trivalent chromium electroplating process of Superbond Chemical Industry, and the thickness of the electroplating layer is 0.5 μm.

[0073] Trich-9551 M bath starter: 10 mL / L, Trich-9551 B supplement: 280 mL / L, Trich-9551 CS conductive salt: 280 g / L, where the mass concentration of trivalent chromium is 15 g / L, the mass concentration of boric acid is 70 g / L, the pH of the plating solution is 3.6, the temperature of the plating bath is 53 °C, and the cathode current density is 12 A / dm 2 , and the cathode moves at 2 m / min.

[0074] 8. Electrolytic protection: After the trivalent chromium electroplating of the neodymium iron boron workpiece, the rare earth electrolytic protection film 8 is prepared by using the rare earth electrolytic protection process developed by Superbond Chemical Industry.

[0075] Cerium acetate: 2 g / L, sodium molybdate: 5 g / L, HEDP complexing agent: 10 g / L, anhydrous sodium carbonate: 150 g / L, the pH of the electrolyte is 12, the cathode current density is 1 A / dm 2 , operating at room temperature, using the workpiece as the cathode and a titanium plate as the anode, and electrolyzing for 120 s.

[0076] 9. Drying: After the electrolytic protection of the neodymium iron boron workpiece, it is dried by a conventional process.

[0077] Example 2: As Figure 1 shown, a method for trivalent chromium electroplating of neodymium iron boron with triple electrochemical protection and the coating structure include pretreatment of the neodymium iron boron substrate 1, and sequentially preparing a cyanide-free copper zinc alloy coating 2, a cyanide-free copper coating 3, a nickel copper alloy coating 4, a semi-bright nickel coating 5, a nickel cobalt alloy coating 6, a trivalent chromium electroplating layer 7, and a rare earth electrolytic protection film 8 from the inside to the outside on the pretreated neodymium iron boron substrate 1.

[0078] 1. Pretreatment: The neodymium iron boron workpiece substrate 1 is pretreated by the current pretreatment process of "grinding chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0079] The lactic acid activation adopts the following lactic acid activation process: lactic acid 80 mL / L, operating temperature 25 °C, activation time 20 s.

[0080] 2. Copper zinc alloy plating: After the pretreatment of the neodymium iron boron workpiece, the cyanide-free copper zinc alloy coating 2 is prepared by using the polymerized thiocyanate copper zinc alloy plating process of the present invention, and the thickness of the coating is 6 μm.

[0081] 1) Preparation of brightener for copper-zinc alloy plating: Calculated by weight parts, add 820 parts of pure water into the reaction tank, and add 80 parts of N,N'-dipropylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of polyacrylamide with the model of IC-113 under stirring, and stir evenly to obtain the brightener for copper-zinc alloy plating.

[0082] 2) Plating: Copper thiocyanate polymer 20g / L, zinc thiocyanate polymer 18g / L, sodium thiocyanate polymer 180g / L, brightener for copper-zinc alloy plating 10mL / L, pH of the plating solution is 9, temperature of the plating bath is 40°C, cathode current density is 1A / dm 2 , cathode moving speed is 4m / min, use brass grains with the code of H59 as the anode, load the brass grains into the titanium anode basket, the area ratio of the anode to the cathode > 3:1, anode moving speed is 4m / min.

[0083] 3. Copper plating: After the neodymium iron boron workpiece is plated with copper-zinc alloy of thiocyanate polymer, use the copper plating process of thiocyanate polymer of the present invention to prepare a cyanide-free copper plating layer 3, and the coating thickness is 6μm.

[0084] 1) Preparation of copper plating brightener: Calculated by weight parts, add 410 parts of formic acid into the reaction tank, add 1.5 parts of melamine under stirring, stir until the solid substances are dissolved, then add 15 parts of waterborne polyurethane resin, 100 parts of polyacrylamide with the model of IC-113, 50 parts of cobalt acetate, and 410 parts of pure water, and stir until the solid substances are dissolved to obtain the copper plating brightener.

[0085] 2) Plating: Copper thiocyanate polymer 20g / L, sodium thiocyanate polymer 145g / L, hydroxyethylidene diphosphonic acid sodium 23g / L, copper plating brightener 10mL / L, pH of the plating solution is 12.7, temperature of the plating bath is 33°C, cathode current density is 1A / dm 2 , cathode moving speed is 4m / min, use oxygen-free electrolytic copper grains as the anode, load the copper grains into the titanium anode basket, the area ratio of the anode to the cathode > 3:1, anode moving speed is 4m / min.

[0086] 4. Nickel-copper alloy plating: After the neodymium iron boron workpiece is plated with copper of thiocyanate polymer, use the Nistar 6070 bright nickel-copper alloy plating process of Superbond Chemical Industry to prepare a nickel-copper alloy coating 4, and the coating thickness is 8μm.

[0087] Nickel sulfate hexahydrate 195 g / L, copper sulfate pentahydrate 9.5 g / L, trisodium citrate 57 g / L, sodium dihydrogen ethylenediamine tetraacetate 23 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 0.7 mL / L, pH of the plating solution is 4.5, bath temperature 54 °C, cathode current density 2.8 A / dm 2 , cathode moving speed 4 m / min.

[0088] 5. Plating semi-bright nickel: After the NdFeB workpiece is plated with nickel-copper alloy, a semi-bright nickel coating 5 is prepared by using the NINFEA SM-700 semi-bright nickel plating process of Chaobang Chemical Industry, and the coating thickness is 8 μm.

[0089] Nickel sulfate hexahydrate 260 g / L, nickel chloride hexahydrate 43 g / L, boric acid 45 g / L, NINFEA SM-700A auxiliary agent 3 mL / L, NINFEA SM-700B main brightener 0.5 mL / L, NINFEA SM-700C stabilizer 0.5 mL / L, NINFEA NI-27 wetting agent 2 mL / L, pH of the plating solution is 4.0, bath temperature 60 °C, cathode current density 4 A / dm 2 , cathode moving speed 6 m / min.

[0090] 6. Plating nickel-cobalt alloy: After the NdFeB workpiece is plated with semi-bright nickel, a nickel-cobalt alloy coating 6 is prepared by using the NINFEA 310 bright nickel-cobalt alloy plating process of Chaobang Chemical Industry, and the coating thickness is 5 μm.

[0091] Nickel sulfate hexahydrate 235 g / L, nickel chloride hexahydrate 57 g / L, cobalt sulfate heptahydrate 17 g / L, boric acid 45 g / L, NINFEA SC-230 auxiliary agent 10 mL / L, NINFEA 310 main brightener 1 mL / L, NINFEA 312 leveling agent 1 mL / L, NINFEA NI-35 wetting agent 1 mL / L, pH of the plating solution is 4.2, bath temperature 58 °C, cathode current density 4 A / dm 2 , with uniform air agitation.

[0092] 7. Chromium plating with trivalent chromium: After the NdFeB workpiece is plated with nickel-cobalt alloy, a trivalent chromium plating layer 7 is prepared by using the Trich-9551 sulfate trivalent chromium plating process of Chaobang Chemical Industry, and the coating thickness is 0.5 μm.

[0093] Trich-9551 M starting solution: 12 mL / L, Trich-9551 B supplement: 280 mL / L, Trich-9551 CS conductive salt: 280 g / L, where the mass concentration of trivalent chromium is 18 g / L, the mass concentration of boric acid is 75 g / L, the pH of the plating solution is 3.6, the plating bath temperature is 50 °C, and the cathode current density is 12 A / dm 2 , with gentle air stirring.

[0094] 8. Electrolytic protection: After trivalent chromium plating of the neodymium iron boron workpiece, a rare earth electrolytic protection film 8 is prepared by using the rare earth electrolytic protection process developed by Chaobang Chemical Industry.

[0095] Cerium acetate: 3 g / L, sodium molybdate: 10 g / L, HEDP complexing agent: 20 g / L, anhydrous sodium carbonate: 130 g / L, the pH of the electrolyte is 12, and the cathode current density is 1 A / dm 2 , operating at room temperature, using the workpiece as the cathode and a titanium plate as the anode, and electrolyzing for 100 s.

[0096] 9. Drying: After electrolytic protection of the neodymium iron boron workpiece, it is dried by a conventional process.

[0097] Example 3: As Figure 1 shown, a method for trivalent chromium plating of neodymium iron boron with triple electrochemical protection and the coating structure include pretreatment of the neodymium iron boron substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a cyanide-free copper coating 3, a nickel-copper alloy coating 4, a semi-bright nickel coating 5, a nickel-cobalt alloy coating 6, a trivalent chromium plating layer 7, and a rare earth electrolytic protection film 8 from the inside to the outside on the pretreated neodymium iron boron substrate 1.

[0098] 1. Pretreatment: The neodymium iron boron workpiece substrate 1 is subjected to "grinding chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing" using the current pretreatment process.

[0099] The lactic acid activation adopts the following lactic acid activation process: lactic acid 40 mL / L, operating temperature 35 °C, activation time 40 s.

[0100] 2. Copper-zinc alloy plating: After pretreatment of the neodymium iron boron workpiece, a cyanide-free copper-zinc alloy coating 2 is prepared by using the polymer thiocyanate copper-zinc alloy plating process of the present invention, and the coating thickness is 6 μm.

[0101] 1) Preparation of copper-zinc alloy brightener: By weight parts, 820 parts of pure water are added into a reaction tank, and 80 parts of N,N'-dipropylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of polyacrylamide of model IC-125 are added under stirring. After stirring evenly, the copper-zinc alloy brightener is obtained.

[0102] 2) Plating: Copper thiocyanate polymer 14 g / L, zinc thiocyanate polymer 12 g / L, sodium thiocyanate polymer 140 g / L, copper-zinc alloy brightener 10 mL / L, pH of the plating solution is 9.5, temperature of the plating bath is 45 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min, brass grains of code H59 are used as the anode, the brass grains are loaded into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, and the anode moving speed is 4 m / min.

[0103] 3. Copper plating: After the neodymium iron boron workpiece is plated with copper-zinc alloy by polymerized thiocyanate, a cyanide-free copper plating layer 3 is prepared by using the polymerized thiocyanate copper plating process of the present invention, and the coating thickness is 6 μm.

[0104] 1) Preparation of copper plating brightener: By weight parts, 410 parts of formic acid are added into a reaction tank, and 1.5 parts of melamine are added under stirring. Stir until the solid substances are dissolved, then 15 parts of waterborne polyurethane resin, polyacrylamide of model IC-125, 50 parts of cobalt acetate, and 410 parts of pure water are added. Stir until the solid substances are dissolved to obtain the copper plating brightener.

[0105] 2) Plating: Copper thiocyanate polymer 22 g / L, sodium thiocyanate polymer 155 g / L, hydroxyethylidene diphosphonic acid sodium 27 g / L, copper plating brightener 10 mL / L, pH of the plating solution is 12.3, temperature of the plating bath is 33 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min, oxygen-free electrolytic copper grains are used as the anode, the copper grains are loaded into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, and the anode moving speed is 4 m / min.

[0106] 4. Nickel-copper alloy plating: After the neodymium iron boron workpiece is plated with copper by polymerized thiocyanate, a nickel-copper alloy coating 4 is prepared by using the Nistar 6070 bright nickel-copper alloy plating process of Superbond Chemical Industry, and the coating thickness is 8 μm.

[0107] Nickel sulfate hexahydrate 210 g / L, copper sulfate pentahydrate 11 g / L, trisodium citrate 63 g / L, disodium hydroxylethylidene diphosphonate 27 g / L, boric acid 30 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 0.7 mL / L, pH of the plating solution is 4.6, plating bath temperature is 52 °C, cathode current density is 2.6 A / dm 2 , and the cathode moves at 4 m / min.

[0108] 5. Plating semi-bright nickel: After the NdFeB workpiece is plated with nickel-copper alloy, a semi-bright nickel coating 5 is prepared by using the NINFEA SM-700 semi-bright nickel plating process of Chaobang Chemical Industry, and the coating thickness is 8 μm.

[0109] Nickel sulfate hexahydrate 280 g / L, nickel chloride hexahydrate 47 g / L, boric acid 42 g / L, NINFEA SM-700A auxiliary agent 3.5 mL / L, NINFEA SM-700B main brightener 0.5 mL / L, NINFEA SM-700C stabilizer 0.5 mL / L, NINFEA NI-27 wetting agent 2 mL / L, pH of the plating solution is 4.2, plating bath temperature is 54 °C, cathode current density is 4 A / dm 2 , and the cathode moves at 6 m / min.

[0110] 6. Plating nickel-cobalt alloy: After the NdFeB workpiece is plated with semi-bright nickel, a nickel-cobalt alloy coating 6 is prepared by using the NINFEA 310 bright nickel-cobalt alloy plating process of Chaobang Chemical Industry, and the coating thickness is 5 μm.

[0111] Nickel sulfate hexahydrate 250 g / L, nickel chloride hexahydrate 65 g / L, cobalt sulfate heptahydrate 18 g / L, boric acid 42 g / L, NINFEA SC-230 auxiliary agent 10 mL / L, NINFEA 310 main brightener 1 mL / L, NINFEA 312 leveling agent 1 mL / L, NINFEA NI-35 wetting agent 1 mL / L, pH of the plating solution is 4.3, plating bath temperature is 53 °C, cathode current density is 4 A / dm 2 , with uniform air agitation.

[0112] 7. Trivalent chromium electroplating: After the NdFeB workpiece is plated with nickel-cobalt alloy, a trivalent chromium electroplated coating 7 is prepared by using the Trich-6561 chloride trivalent chromium electroplating process of Chaobang Chemical Industry, and the coating thickness is 0.5 μm.

[0113] Trich-6561 starting bath salt: 425 g / L, Trich-6563 complexing agent: 75 mL / L, Trich-6564 stabilizer: 3 mL / L, Trich-6565 wetting agent: 2 mL / L, where the mass concentration of trivalent chromium is 24 g / L, the mass concentration of boric acid is 58 g / L, the pH of the plating solution is 2.8, the operating temperature is 28 °C, and the cathode current density is 14 A / dm 2 , with medium air agitation.

[0114] 8. Electrolytic protection: After trivalent chromium electroplating of the neodymium iron boron workpiece, a rare earth electrolytic protection film 8 is prepared by using the rare earth electrolytic protection process developed by Chaobang Chemical Industry.

[0115] Cerium acetate: 4 g / L, sodium molybdate: 12 g / L, HEDP complexing agent: 26 g / L, anhydrous sodium carbonate: 110 g / L, the pH of the electrolyte is 12, and the cathode current density is 1 A / dm 2 , operating at room temperature, using the workpiece as the cathode and a titanium plate as the anode, and electrolyzing for 80 s.

[0116] 9. Drying: After electrolytic protection of the neodymium iron boron workpiece, it is dried by a conventional process.

[0117] Example 4: As Figure 1 shown, a neodymium iron boron trivalent chromium electroplating method and coating structure with triple electrochemical protection functions includes pretreatment of the neodymium iron boron substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a cyanide-free copper coating 3, a nickel-copper alloy coating 4, a semi-bright nickel coating 5, a nickel-cobalt alloy coating 6, a trivalent chromium electroplating coating 7, and a rare earth electrolytic protection film 8 from the inside to the outside on the pretreated neodymium iron boron substrate 1.

[0118] 1. Pretreatment: The neodymium iron boron workpiece substrate 1 is subjected to "grinding chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing" by using the current pretreatment process.

[0119] The lactic acid activation adopts the following lactic acid activation process: lactic acid 70 mL / L, operating temperature 33 °C, activation time 25 s.

[0120] 2. Copper-zinc alloy plating: After pretreatment of the neodymium iron boron workpiece, a cyanide-free copper-zinc alloy coating 2 is prepared by using the polymer thiocyanate copper-zinc alloy plating process of the present invention, and the coating thickness is 6 μm.

[0121] 1) Preparation of copper-zinc alloy brightener: Calculated by weight parts, 820 parts of pure water are added into a reaction tank, and 80 parts of N,N'-dipropylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of polyacrylamide of model IC-213 are added under stirring. After stirring evenly, the copper-zinc alloy brightener is obtained.

[0122] 2) Plating: Copper(I) thiocyanate 18 g / L, zinc(I) thiocyanate 17 g / L, sodium thiocyanate 175 g / L, copper-zinc alloy brightener 10 mL / L, pH of the plating solution is 9.2, temperature of the plating bath is 38 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min, brass grains of code H59 are used as the anode, the brass grains are loaded into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, and the anode moving speed is 4 m / min.

[0123] 3. Copper plating: After the neodymium iron boron workpiece is plated with copper-zinc alloy by thiocyanate, a cyanide-free copper plating layer 3 is prepared by using the copper plating process of the present invention, and the coating thickness is 6 μm.

[0124] 1) Preparation of copper plating brightener: Calculated by weight parts, 410 parts of formic acid are added into a reaction tank, and 1.5 parts of melamine are added under stirring. Stir until the solid substances are dissolved, then 15 parts of waterborne polyurethane resin, polyacrylamide of model IC-213, 50 parts of cobalt acetate, and 410 parts of pure water are added, and stir until the solid substances are dissolved to obtain the copper plating brightener.

[0125] 2) Plating: Copper(I) thiocyanate 24 g / L, sodium thiocyanate 170 g / L, 1-hydroxyethylidene-1,1-diphosphonic acid sodium salt 30 g / L, copper plating brightener 10 mL / L, pH of the plating solution is 12, temperature of the plating bath is 30 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min, oxygen-free electrolytic copper grains are used as the anode, the copper grains are loaded into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, and the anode moving speed is 4 m / min.

[0126] 4. Nickel-copper alloy plating: After the neodymium iron boron workpiece is plated with copper by thiocyanate, a nickel-copper alloy coating 4 is prepared by using the Nistar 6070 bright nickel-copper alloy plating process of Superbond Chemical Industry, and the coating thickness is 8 μm.

[0127] Nickel sulfate hexahydrate 220 g / L, copper sulfate pentahydrate 12 g / L, trisodium citrate 70 g / L, sodium dihydrogen ethylenediamine tetraacetate 30 g / L, boric acid 28 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 0.7 mL / L, pH of the plating solution is 4.8, plating bath temperature is 50 °C, cathode current density is 2.8 A / dm 2 , and the cathode moves at 4 m / min.

[0128] 5. Plating semi-bright nickel: After the NdFeB workpiece is plated with nickel-copper alloy, a semi-bright nickel coating 5 is prepared by using the NINFEA SM-700 semi-bright nickel plating process of Superbond Chemical Industry, and the coating thickness is 8 μm.

[0129] Nickel sulfate hexahydrate 300 g / L, nickel chloride hexahydrate 50 g / L, boric acid 40 g / L, NINFEA SM-700A auxiliary agent 4 mL / L, NINFEA SM-700B main brightener 0.5 mL / L, NINFEA SM-700C stabilizer 0.5 mL / L, NINFEA NI-27 wetting agent 2 mL / L, pH of the plating solution is 4.4, plating bath temperature is 50 °C, cathode current density is 4 A / dm 2 , and the cathode moves at 6 m / min.

[0130] 6. Plating nickel-cobalt alloy: After the NdFeB workpiece is plated with semi-bright nickel, a nickel-cobalt alloy coating 6 is prepared by using the NINFEA 310 bright nickel-cobalt alloy plating process of Superbond Chemical Industry, and the coating thickness is 5 μm.

[0131] Nickel sulfate hexahydrate 260 g / L, nickel chloride hexahydrate 70 g / L, cobalt sulfate heptahydrate 20 g / L, boric acid 40 g / L, NINFEA SC-230 auxiliary agent 10 mL / L, NINFEA 310 main brightener 1 mL / L, NINFEA 312 leveling agent 1 mL / L, NINFEA NI-35 wetting agent 1 mL / L, pH of the plating solution is 4.5, plating bath temperature is 55 °C, cathode current density is 4 A / dm 2 , with uniform air agitation.

[0132] 7. Chromium plating with trivalent chromium: After the NdFeB workpiece is plated with nickel-cobalt alloy, a trivalent chromium plating layer 7 is prepared by using the Trich-6561 chloride trivalent chromium plating process of Superbond Chemical Industry, and the coating thickness is 0.5 μm.

[0133] Trich-6561 starting bath salt: 450 g / L, Trich-6563 complexing agent: 85 mL / L, Trich-6564 stabilizer: 3 mL / L, Trich-6565 wetting agent: 2 mL / L, where the mass concentration of trivalent chromium is 25 g / L, the mass concentration of boric acid is 60 g / L, the pH of the plating solution is 2.6, the operating temperature is 30 °C, and the cathode current density is 14 A / dm 2 , with moderate air agitation.

[0134] 8. Electrolytic protection: After trivalent chromium electroplating of NdFeB workpieces, a rare earth electrolytic protection process developed by Chaobang Chemical Industry is used to prepare a rare earth electrolytic protection film.

[0135] Cerium acetate: 5 g / L, sodium molybdate: 15 g / L, HEDP complexing agent: 30 g / L, anhydrous sodium carbonate: 100 g / L, the pH of the electrolyte is 12, and the cathode current density is 1 A / dm 2 , operating at room temperature, using the workpiece as the cathode and a titanium plate as the anode, and electrolyzing for 70 s.

[0136] 9. Drying: After electrolytic protection of NdFeB workpieces, they are dried using a conventional process.

[0137] Test example 1: According to GB / T 10125–2021 "Artificial atmosphere corrosion test - Salt spray test" for neutral salt spray test, the surfaces of the NdFeB trivalent chromium electroplated samples prepared in Example 1, Example 2, Example 3, and Example 4 showed no rust after 142 h. The neutral salt spray test time is 3 times the rust appearance time of 48 h in the neutral salt spray test for the Ni+Cu+Ni coating on the surface of NdFeB specified in GB / T 34491–2017 "Surface coatings on sintered NdFeB".

[0138] Test example 2: According to GB / T 5270–2005 "Review of test methods for adhesion of metallic coatings on metallic substrates - Electrodeposited and chemically deposited coatings" to test the coating adhesion, the NdFeB samples electroplated with trivalent chromium prepared in Example 1, Example 2, Example 3, and Example 4 were heated in a heating furnace to 250 °C and held for 30 min, then immediately taken out and cooled in water at room temperature. The coating did not show blistering or peeling, and the coating adhesion met the standard requirements.

[0139] Test example 3: The damp heat, steady state test was carried out in accordance with GB / T 2423.3-2016 "Basic environmental testing procedures for electric and electronic products - Test Ca: Damp heat, steady state". The neodymium iron boron trivalent chromium electroplated samples prepared in Example 1, Example 2, Example 3 and Example 4 were tested for 240 h under the conditions of a temperature of 40 °C and a relative humidity of 93%. There was no visible change in the appearance of the coating, meeting the requirements of the standard GB / T34491–2017 "Surface coatings for sintered neodymium iron boron".

[0140] The technical solutions provided by the embodiments of the present invention have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the embodiments of the present invention. The descriptions of the above embodiments are only applicable to helping understand the principles of the embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these are also regarded as falling within the protection scope of the present invention.

Claims

1. A method for NdFeB trivalent chromium plating with triple electrochemical protection, characterized in that: The following steps are involved: (1) Grinding, chamfering, degreasing, and pickling and activation of NdFeB workpieces; (2) After the NdFeB workpiece is pre-treated, a cyanide-free copper-zinc alloy coating is prepared by a weakly alkaline polymerized thiocyanate copper-zinc alloy plating process; (3) After the NdFeB workpiece is polymerized with thiocyanate to plate copper-zinc alloy, a cyanide-free copper plating layer is prepared using a polymerized thiocyanate copper plating process; (4) preparing a nickel-copper alloy coating by using a nickel-copper alloy plating process after the NdFeB workpiece is polymerized with thiocyanate and copper-plated; (5) After the NdFeB workpiece is plated with nickel-copper alloy, a semi-bright nickel plating process is used to prepare a semi-bright nickel coating; (6) After the NdFeB workpiece is plated with semi-bright nickel, a nickel-cobalt alloy plating process is used to prepare a nickel-cobalt alloy coating; (7) After the NdFeB workpiece is plated with nickel-cobalt alloy, a trivalent chromium plating layer is prepared by a trivalent chromium plating process; (8) After the NdFeB workpiece is trivalent chromium-plated, a rare earth electrolytic protection film is prepared by a rare earth electrolytic protection process; The polymerized thiocyanate copper plating process includes the following components and process parameters: Polymeric cuprous thiocyanate 18-24 g / L, polymeric sodium thiocyanate 130-170 g / L, sodium hydroxyethylidene diphosphonate 20-30 g / L, copper plating brightener 8-12 mL / L, plating solution pH 12-13, plating tank temperature 30-40 °C, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 3-5 m / min, oxygen-free electrolytic copper particles are used as anodes, the copper particles are placed in a titanium anode basket, the area ratio of anode to cathode is >3:1, and the anode moves 3-5 m / min; The copper plating brightener comprises the following components in weight fractions: 1-2 parts of melamine, 10-20 parts of waterborne polyurethane resin, 80-120 parts of polyacrylamide with a molecular weight less than 8000, 40-60 parts of cobalt acetate, 390-430 parts of formic acid and 390-430 parts of pure water.

2. The NdFeB trivalent chromium plating method with triple electrochemical protection according to claim 1, characterized in that: The copper plating brightener is prepared as follows: Calculated by weight, 390 to 430 parts of formic acid are added to a reaction tank, 1 to 2 parts of melamine are added under stirring, and the mixture is stirred until the solid matter is dissolved. Then, 10 to 20 parts of waterborne polyurethane resin, 80 to 120 parts of polyacrylamide with a molecular weight less than 8000, 40 to 60 parts of cobalt acetate, and 390 to 430 parts of pure water are added, and the mixture is stirred until the solid matter is dissolved to obtain the copper plating brightener.

3. The NdFeB trivalent chromium plating method with triple electrochemical protection according to claim 1, characterized in that: The weakly alkaline polymerized thiocyanate copper-zinc alloy plating process includes the following components and process parameters: Polymeric cuprous thiocyanate 14-20 g / L, polymeric zinc thiocyanate 12-18 g / L, polymeric sodium thiocyanate 140-180 g / L, copper-zinc alloy plating brightener 8-12 mL / L, plating solution pH 9-10, plating tank temperature 35-45 ° C, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 3-5 m / min, a brass pellet with code name H59 is used as the anode, the brass pellet is placed in the titanium anode blue, the area ratio of the anode to the cathode is >3:1, and the anode moves 3-5 m / min; The copper-zinc alloy plating 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 pure water.

4. The NdFeB trivalent chromium plating method with triple electrochemical protection according to claim 1, characterized in that: The nickel-copper alloy coating is prepared by using Nistar 6070 bright nickel-copper alloy plating process: 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 solution pH 4.3-4.8, plating tank temperature 50-55 ° C, cathode current density 2.6-3.2 A / dm 2 , the cathode moves 3 to 5 m / min.

5. The NdFeB trivalent chromium plating method with triple electrochemical protection according to claim 1, characterized in that: The semi-bright nickel plating layer is prepared by NINFEA SM-700 semi-bright nickel plating process: Nickel sulfate hexahydrate 240-300g / L, nickel chloride hexahydrate 40-50g / L, boric acid 40-50g / L, NINFEA SM-700A auxiliary agent 2-5mL / L, NINFEA SM-700B main light agent 0.3-0.8mL / L, NINFEA SM-700C stabilizer 0.3-0.8mL / L, NINFEA NI-27 wetting agent 1-3mL / L, plating solution pH 3.8-4.4, plating tank temperature 50-65℃, cathode current density 3-5A / dm 2 , the cathode moves 5 to 6 m / min.

6. The NdFeB trivalent chromium plating method with triple electrochemical protection according to claim 1, characterized in that: The nickel-cobalt alloy coating is prepared by NINFEA 310 bright nickel-cobalt alloy plating process: 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 8-12 mL / L, NINFEA 310 main light agent 0.5-1.5 mL / L, NINFEA312 leveling agent 0.5-1.5 mL / L, NINFEA NI-35 wetting agent 0.5-1.5 mL / L, plating solution pH 4.0-4.5, plating tank temperature 55-60 ° C, cathode current density 2-6 A / dm 2 , uniform air stirring.

7. The NdFeB trivalent chromium plating method with triple electrochemical protection according to claim 1, characterized in that: The trivalent chromium plating layer is prepared by Trich-9551 sulfate trivalent chromium plating process: Trich-9551 M cylinder opener 8-12mL / L, Trich-9551 B supplement 260-300mL / L, Trich-9551 CS conductive salt 260-300g / L, wherein the mass concentration of trivalent chromium is 12-18g / L, the mass concentration of boric acid is 65-75g / L, the pH value of the plating solution is 3.4-3.8, the plating tank temperature is 50-55°C, and the cathode current density is 8-15A / dm 2 , slight air agitation or cathode movement; The trivalent chromium plating layer is prepared by Trich-6561 chloride trivalent chromium plating process: Trich-6561 aeration salt 400-450 g / L, Trich-6563 complexing agent 65-85 mL / L, Trich-6564 stabilizer 1-2 mL / L, Trich-6565 wetting agent 1-3 mL / L, wherein the mass concentration of trivalent chromium is 23-25 ​​g / L, the mass concentration of boric acid is 55-60 g / L, the pH value of the plating solution is 2.5-3.0, the operating temperature is 25-32 ° C, and the cathode current density is 8-16 A / dm 2 , medium air agitation.

8. The NdFeB trivalent chromium plating method with triple electrochemical protection according to claim 1, characterized in that: The rare earth electrolytic protection film is prepared by a rare earth electrolytic protection process: Cerium acetate 1-5g / L, sodium molybdate 5-15g / L, HEDP complexing agent 5-30g / L, anhydrous sodium carbonate 100-150g / L, electrolyte pH 11.5-12.5, cathode current density 0.5-1.5A / dm 2 , operate at room temperature, use the plated part as cathode and the titanium plate as anode, and electrolyze for 60 to 120 seconds.

9. A coating structure prepared by a NdFeB trivalent chromium plating method with triple electrochemical protection, characterized in that: The coating structure comprises a neodymium iron boron substrate, and a cyanide-free copper-zinc alloy coating, a cyanide-free copper coating, a nickel-copper alloy coating, a semi-bright nickel coating, a nickel-cobalt alloy coating, a trivalent chromium coating, and a rare earth electrolytic protective film which are sequentially prepared on the neodymium iron boron substrate.

10. The coating structure prepared by the NdFeB trivalent chromium plating method with triple electrochemical protection as claimed in claim 9, characterized in that: The thickness of the cyanide-free copper-zinc alloy plating layer is 4 to 8 μm, the thickness of the cyanide-free copper plating layer is 4 to 8 μm, the thickness of the nickel-copper alloy plating layer is 5 to 15 μm, the thickness of the semi-bright nickel plating layer is 5 to 15 μm, the thickness of the nickel-cobalt alloy plating layer is 3 to 7 μm, and the thickness of the trivalent chromium plating layer is 0.3 to 0.6 μm.

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