Neodymium-iron-boron permanent magnet potassium chloride zinc-iron alloy plating process

Abstract

The invention discloses a potassium chloride zinc-iron alloy plating process for a neodymium-iron-boron permanent magnet. A cyanide-free copper-zinc alloy plating layer, a zinc-iron alloy plating layer, a passive film and a graphene modified sealing layer are sequentially prepared on a neodymium-iron-boron substrate from inside to outside. According to the potassium chloride zinc-iron alloy plating process, 50-70 g / L of zinc chloride, 2-12 g / L of ferrous chloride tetrahydrate, 180-220 g / L of potassium chloride, 25-35 g / L of boric acid, 8-40 g / L of a coordination agent, 0.1-0.2 mL / L of a brightening agent and 20-30 mL / L of an auxiliary agent are adopted, the pH value of a plating solution is 4.5-5.6, the temperature of a plating bath is 15-30 DEG C, the cathode current density is 1-3 A / dm < 2 >, and the cathode movement is 3-5 m / min. A neodymium iron boron galvanized iron alloy sample piece passivated by trivalent chromium blue and white and sealed by the graphene modified sealing agent is free of white rust on the surface after being subjected to a neutral salt spray test for 400 h according to the GB / T 10125-2021 standard, and a plating layer has excellent corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of metal surface treatment, and in particular relates to a process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets. Background Art

[0002] Due to my country's rich reserves of rare earth metal ores and the accumulation and development of mining and processing technologies, my country has become the global production and market center 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 by powder metallurgy and have defects such as sintering pores. NdFeB alloys have a multi-phase structure, including the main phase Nd2Fe14B, Nd-rich phase (Nd4Fe) and B-rich phase (Nd1+εFe4B4), and the volume fractions of each phase are approximately 84%, 14% and 2%, respectively. The main phase Nd2Fe14B is a magnetic phase. Since the Nd-rich phase and the B-rich phase are very active and easily oxidized, and the electrochemical potentials of the phases are very different, electrochemical corrosion is very likely to occur. [1] .

[0003] The Nd-rich phase and B-rich phase of the sintered NdFeB matrix are highly chemically active, which brings some difficulties to its electroplating treatment. During the electroplating process, the acidic plating solution, alkaline plating solution and plating solution containing chloride that penetrate into the pores on the surface of NdFeB will corrode the NdFeB matrix and the coating. At present, the neutral citrate nickel plating process is usually used to prepare a pre-plated nickel layer on the surface of NdFeB, but this coating has a high magnetic shielding problem for NdFeB permanent magnet materials. [2] .

[0004] Neodymium iron boron permanent magnets are mainly made of zinc plating and nickel plating to prepare protective layers. Zinc plating has low costs and is used in low-end manufacturing, while nickel plating has higher costs and is used in mid- to high-end manufacturing.

[0005] It is generally believed that the zinc coating on the surface of NdFeB is an anodic coating, which has an electrochemical protective effect on the NdFeB matrix. However, in practical applications, it is found that pitting corrosion often occurs on the surface of NdFeB zinc-plated parts, that is, granular red corrosion products are generated on the surface of the zinc coating, while the zinc coating itself does not corrode, which means that the zinc coating does not have an effective electrochemical protective effect on the NdFeB matrix. The standard electrode potential of metal neodymium is -2.37V, and the standard electrode potential of metal zinc is -0.762V, the latter is 1.608V more positive than the former. The standard electrode potential of metal iron is -0.441V. According to the ratio of neodymium and iron in the Nd-rich phase, the average standard electrode potential of the mixture of neodymium and iron in the Nd-rich phase is -1.89V. It can be seen that the electrode potential of the Nd-rich phase with a mass fraction of 14% in the NdFeB matrix is ​​significantly negative than the electrode potential of the zinc coating. From this, we can draw the following conclusion: the zinc coating has no electrochemical protective effect on the Nd-rich phase. The previous view that the zinc coating has an electrochemical protective effect on the NdFeB matrix is ​​a technical prejudice. The existing technology directly coats zinc on the surface of NdFeB, and there is a technical defect that the zinc coating has no electrochemical protective effect on the Nd-rich phase in the matrix.

[0006] The hydroxy graphene modified sealant developed and applied in recent years has made great progress in improving the corrosion resistance of the coating. The prepared sealing layer has self-healing properties. [3] It is used to seal the zinc coating and zinc alloy coating that have been passivated with trivalent chromium, solving the problem that the trivalent chromium passivation film does not have self-repairing properties.

[0007] References: [1]. 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. [2]. Meng Chao, Wang Qun, Shi Meiwu, Preparation and properties of iron-nickel alloy magnetic shielding film [J], Safety and Electromagnetic Compatibility, 2015, 27(4): 58-61. [3]. Guo Chongwu, Lai Huanwen, Xia Liang, Study on the performance of graphene oxide in coating sealant [J], Electroplating and Finishing, 2021, 40(9): 696-700. Summary of the invention

[0008] In order to overcome the defect that the zinc coating prepared by direct zinc plating of NdFeB has no electrochemical protection effect on the Nd-rich phase in the NdFeB matrix, the present invention provides a process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets. In order to achieve the above purpose, the present invention adopts the following technical solutions: A process for plating potassium chloride zinc-iron alloy on NdFeB permanent magnets comprises the following steps: (1) Grinding, chamfering, degreasing, and pickling and activation of NdFeB workpieces; (2) After pretreatment of the NdFeB workpiece, a cyanide-free copper-zinc alloy coating is prepared by using a polymerized thiocyanate copper-zinc alloy plating process; (3) The NdFeB workpiece is polymerized with thiocyanate to plate a copper-zinc alloy, and then a potassium chloride zinc-iron alloy plating process is used to prepare a zinc-iron alloy coating; (4) The NdFeB workpiece is plated with zinc-iron alloy and then passivated to prepare a passivation film; (5) After the NdFeB workpiece is passivated, it is sealed to prepare a sealing layer; The potassium chloride zinc-iron alloy plating process includes the following components and process parameters: Zinc chloride 50-70g / L, ferrous chloride tetrahydrate 2-12g / L, potassium chloride 180-220g / L, boric acid 25-35g / L, complexing agent 8-40g / L, brightener 0.1-0.2mL / L, auxiliary agent 20-30mL / L, plating solution pH 4.5-5.6, plating tank temperature 15-30℃, cathode current density 1-3A / dm 2 , the cathode moves 3-5 m / min, a zinc plate with a mass fraction of ≥99.95% is used as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% mass fraction of ferrous chloride tetrahydrate solution is added to the plating tank to keep its concentration within the process range; The ligand comprises sodium glucose heptanoate and sodium sulfosalicylate, the mass ratio of sodium glucose heptanoate to sodium sulfosalicylate is 3:(1-3), and sodium glucose heptanoate and sodium sulfosalicylate are mixed according to the ratio and stirred evenly.

[0009] In some embodiments, the brightener comprises o-chlorobenzaldehyde and formic acid, the mass ratio of o-chlorobenzaldehyde to formic acid is 1:(0.8-1.2), and o-chlorobenzaldehyde and formic acid are mixed in the ratio and stirred until all the solids are dissolved; In some embodiments, the auxiliary agent includes three intermediates: a sulfonation product of a fatty alcohol polyoxyethylene ether with a model number of OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid. Calculated by weight, the sulfonation product of a fatty alcohol polyoxyethylene ether with a model number of OX-105 and aminosulfonic acid is 17 to 23 parts, sodium benzoate is 5 to 7 parts, nicotinic acid is 0.4 to 0.6 parts, and deionized water is 80 to 90 parts. The three intermediates are added to water according to the weight fractions and stirred until all the solids are dissolved.

[0010] In some embodiments, the polythiocyanate 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 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 angle code-named H59 is used as the anode, the brass angle 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 brightener comprises the following components in weight fractions: 6-10 parts of N,N'-di-n-propylethylenediamine, 1-2 parts of waterborne polyurethane resin, 8-12 parts of polyacrylamide with a molecular weight less than 8000, and 77-87 parts of deionized water.

[0011] In some embodiments, the pickling activation adopts a lactic acid pickling activation process: Lactic acid 40-80 mL / L, operating temperature 20-35°C, activation time 20-40 s.

[0012] In some of the embodiments, the passivation film is prepared by TRIROS 348 zinc iron blue-white passivation process: TRIROS 348 zinc iron blue-white passivator 135-175 mL / L, passivation solution pH 2.0-2.8, operating temperature 30-60°C, immersion time 30-60s, air stirring.

[0013] In some of the embodiments, the passivation film is prepared by TRIROS BP-885 trivalent chromium black passivation process: TRIROS BP-885A agent 40~80mL / L, TRIROS BP-885B agent 30~70mL / L, passivation temperature 20~30℃, passivation solution pH value 2.3~2.7, passivation time 40~120s, workpiece swing.

[0014] In some of the embodiments, the graphene-modified sealing layer is prepared using PRODICO 480 graphene-modified sealing agent: Dilute PRODICO 480 graphene modified sealer with water to 2.5-3.2 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 8-15 seconds. Drain after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure at 70-80°C for 20-35 minutes.

[0015] In some of the embodiments, the thickness of the cyanide-free copper-zinc alloy coating is 6-12 μm.

[0016] In some of the embodiments, the thickness of the zinc-iron coating is 10-20 μm.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The potassium chloride zinc-iron alloy plating process of NdFeB permanent magnets of the present invention prepares a zinc-iron alloy coating on a cyanide-free copper-zinc alloy coating, and the zinc-iron alloy coating is an anodic coating. This coating structure can effectively prevent the corrosive medium from corroding the NdFeB substrate, thus overcoming the defect that direct zinc plating on the NdFeB substrate has no electrochemical protection effect on the Nd-rich phase. 2. The potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets of the present invention uses sodium glucose heptanoate and sodium sulfosalicylate as complexing agents. Sodium glucose heptanoate has a special complexing effect on ferrous ions, and sodium sulfosalicylate has a special complexing effect on ferric ions. No iron precipitate is generated during electroplating, and iron and zinc are co-deposited to form a good zinc-iron alloy coating, thereby overcoming the defect of instability of the traditional chloride zinc-iron alloy plating solution; 3. The potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets of the present invention has a pH value of 9-10 for the polythiocyanate copper-zinc alloy plating solution, which is weakly alkaline and does not contain chloride. The plating solution immersed in the pores on the surface of NdFeB has basically no residual corrosion problem, and at the same time overcomes the high magnetic shielding problem existing in the preparation of the citrate nickel plating layer on the surface of NdFeB; 4. The potassium chloride zinc-iron alloy plating process of NdFeB permanent magnets of the present invention has a self-repairing property for the sealing layer prepared by using a hydroxy graphene modified sealing agent on the zinc-iron alloy plating layer passivated by trivalent chromium, thus overcoming the defect that the trivalent chromium passivation film has no self-repairing property; 5. In the potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets of the present invention, the high pH of the polysulfate copper-zinc alloy plating solution is conducive to the dissolution of the anode; the polysulfate copper-zinc alloy plating process of the present invention adopts a large anode area and anode movement to promote the dissolution of the anode, thereby reducing the pH of the plating solution, overcoming the problem of residual corrosion of the NdFeB matrix caused by the high pH of the plating solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 It is a schematic diagram of the coating structure of Example 1, Example 2, Example 3 and Example 4 of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0020] A potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets comprises pre-treatment of NdFeB workpieces, and sequentially preparing a cyanide-free copper-zinc alloy plating layer, a zinc-iron alloy plating layer, a passivation film, and a sealing layer on a NdFeB substrate from inside to outside.

[0021] The existing pre-treatment process is used to grind, chamfer, degrease, and pickle and activate the NdFeB workpiece.

[0022] Preferably, the pickling activation adopts a lactic acid activation process: Lactic acid 40-80 mL / L, operating temperature 20-35°C, activation time 20-40 s.

[0023] After the NdFeB workpiece is pre-treated, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy plating layer.

[0024] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 6 to 12 μm.

[0025] Polymeric cuprous thiocyanate 14-20 g / L, polymeric zinc thiocyanate 12-18 g / L, polymeric sodium thiocyanate 140-180 g / L, copper-zinc alloy 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 to 5 m / min, a brass angle code-named H59 is used as the anode, the brass angle is placed in the titanium anode blue, the area ratio of the anode to the cathode is >3:1, and the anode moves 3 to 5 m / min.

[0026] Preferably, the copper-zinc alloy brightener comprises the following components in weight fractions: 6-10 parts of N,N'-di-n-propylethylenediamine, 1-2 parts of waterborne polyurethane resin, 8-12 parts of polyacrylamide with a molecular weight less than 8000, and 77-87 parts of deionized water.

[0027] After the NdFeB workpiece is polymerized with thiocyanate to plate copper-zinc alloy, the potassium chloride zinc-iron alloy plating process of the present invention is used to prepare a zinc-iron alloy coating.

[0028] Preferably, the zinc-iron alloy coating has a thickness of 10 to 20 μm.

[0029] Zinc chloride 50-70g / L, ferrous chloride tetrahydrate 2-12g / L, potassium chloride 180-220g / L, boric acid 25-35g / L, complexing agent 8-40g / L, brightener 0.1-0.2mL / L, auxiliary agent 20-30mL / L, plating solution pH 4.5-5.6, plating tank temperature 15-30℃, cathode current density 1-3A / dm 2 , the cathode moves 3 to 5 m / min, a zinc plate with a mass fraction of ≥99.95% is used as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% mass fraction of ferrous chloride tetrahydrate solution is added to the plating tank to keep its concentration within the process range.

[0030] Preferably, the ligand comprises sodium gluconate and sodium sulfosalicylate, the mass ratio of sodium gluconate to sodium sulfosalicylate is 3:(1-3), and sodium gluconate and sodium sulfosalicylate are mixed in the said ratio and stirred evenly.

[0031] Preferably, the brightener comprises o-chlorobenzaldehyde and formic acid, the mass ratio of o-chlorobenzaldehyde to formic acid is 1:(0.8-1.2), and o-chlorobenzaldehyde and formic acid are mixed in the said ratio and stirred until all the solids are dissolved.

[0032] Preferably, the auxiliary agent includes three intermediates: a sulfonation product of a fatty alcohol polyoxyethylene ether with a model number of OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid. Calculated by weight, the sulfonation product of a fatty alcohol polyoxyethylene ether with a model number of OX-105 and aminosulfonic acid is 17 to 23 parts, sodium benzoate is 5 to 7 parts, nicotinic acid is 0.4 to 0.6 parts, and deionized water is 80 to 90 parts. The three intermediates are added to water according to the weight fractions and stirred until all the solids are dissolved.

[0033] After the NdFeB workpiece is plated with zinc-iron alloy, the passivation film is prepared by the current zinc-iron alloy trivalent chromium passivation process.

[0034] Preferably, the passivation film is prepared by the TRIROS 348 zinc-iron blue-white passivation process developed by Chaobang Chemical: TRIROS 348 zinc iron blue-white passivator 135-175mL / L, passivation solution pH 2.0-2.8, operating temperature 30-60℃, immersion time 30-60s, air stirring.

[0035] Preferably, the passivation film is prepared by using the TRIROS BP-885 trivalent chromium black passivation process of Chaobang Chemical: TRIROS BP-885A agent 40~80mL / L, TRIROS BP-885B agent 30~70mL / L, passivation temperature 20~30℃, passivation solution pH value 2.3~2.7, passivation time 40~120s.

[0036] After the NdFeB workpiece is passivated with trivalent chromium, the sealing layer is prepared using the current sealing process.

[0037] Preferably, the sealing layer is prepared using PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical: Dilute PRODICO 480 graphene modified sealer with water to 2.5-3.2 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 8-15 seconds. Drain after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After the plated parts are sealed, dry and cure at 70-80°C for 20-35 minutes. Example 1

[0038] like Figure 1 As shown, a potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets includes pre-treatment of a NdFeB substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a zinc-iron alloy coating 3, a trivalent chromium blue-white passivation film 4, and a graphene-modified sealing layer 5 on the pre-treated NdFeB substrate 1 from the inside to the outside.

[0039] 1. Pre-treatment: The NdFeB workpiece substrate 1 is subjected to the current pre-treatment process of "grinding and chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0040] The lactic acid activation adopts the following lactic acid activation process: lactic acid 60mL / L, operating temperature 28°C, activation time 30s.

[0041] 2. Copper-zinc alloy plating: After the NdFeB workpiece is pre-treated, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, and the coating thickness is 10 μm.

[0042] 1) Preparation of copper-zinc alloy brightener: Calculated by weight, 82 parts of deionized water were added to a reaction tank, and 8 parts of N,N'-di-n-propylethylenediamine, 1.5 parts of waterborne polyurethane resin, and 10 parts of polyacrylamide with model GRO-70 were added under stirring, and stirred evenly to obtain the copper-zinc alloy brightener.

[0043] 2) Plating: Polymeric cuprous thiocyanate 17g / L, polymeric zinc thiocyanate 15g / L, polymeric sodium thiocyanate 160g / L, copper-zinc alloy brightener 10mL / L, plating solution pH 9.5, plating tank temperature 40℃, cathode current density 1A / dm 2 , the cathode moves 4m / min, a brass angle code-named H59 is used as the anode, the brass angle is placed in the titanium anode blue, the area ratio of the anode to the cathode is >3:1, and the anode moves 4m / min.

[0044] 3. Galvanized iron alloy: After the NdFeB workpiece is plated with copper-zinc alloy, the potassium chloride zinc-iron alloy plating process of the present invention is used to prepare a zinc-iron alloy coating 3, and the coating thickness is 15 μm.

[0045] 1) Preparation of complexing agent: Sodium glucose heptanate and sodium sulfosalicylate are mixed in a mass ratio of 3:2 and stirred evenly to obtain the complexing agent.

[0046] 2) Prepare brightener: The brightener is obtained by mixing o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stirring until all the solids are dissolved.

[0047] 3) Preparation of auxiliary agents: Calculated by weight, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, 6 parts of sodium benzoate, 0.5 parts of nicotinic acid, and 85 parts of water. The sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid are added into water and stirred until all the solids are dissolved to obtain the auxiliary agent.

[0048] 4) Preparation of potassium chloride zinc-iron alloy plating solution: a) Add 70% water into the plating tank according to the volume of the plating solution, add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, adjust the pH of the plating solution to 5.4 with 10% by mass sodium hydroxide solution or 3% by mass hydrochloric acid, and add water to the specified volume; d) at 0.15A / dm 2 The electrolysis was carried out for 60 min at the current density.

[0049] 5) Plating: Zinc chloride 65g / L, ferrous chloride tetrahydrate 11g / L, potassium chloride 210g / L, boric acid 30g / L, complexing agent 37g / L, brightener 0.15mL / L, auxiliary agent 25mL / L, plating solution pH 5.4, plating tank temperature 25℃, cathode current density 2A / dm 2 , the cathode moves 4m / min, the anode is made of zinc plate with a mass fraction of ≥99.95%, and the area ratio of cathode to anode is 2:1; during production, 30% of ferrous chloride tetrahydrate solution is added to the plating tank to maintain its mass concentration at the required value.

[0050] 4. Passivation: After the NdFeB workpiece is plated with galvanized iron alloy, a trivalent chromium blue-white passivation film is prepared using the TRIROS 348 zinc-iron blue-white passivation process of Chaobang Chemical 4.

[0051] TRIROS 348 zinc iron blue-white passivator 150mL / L, passivation solution pH 2.4, operating temperature 45℃, immersion time 45s, air stirring.

[0052] The specific process is "film removal with sulfuric acid with a volume fraction of 0.2% → water washing → passivation → water washing → draining after leaving the tank".

[0053] 5. Closure: After the NdFeB workpiece is passivated, the graphene-modified sealing layer 5 is prepared using PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical.

[0054] Dilute PRODICO 480 graphene-modified sealer with water to 2.8 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 10 seconds, drain them after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure them at 75°C for 30 minutes.

[0055] Embodiment 2: like Figure 1 As shown, a potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets includes pre-treatment of a NdFeB substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a zinc-iron alloy coating 3, a trivalent chromium blue-white passivation film 4, and a graphene-modified sealing layer 5 on the pre-treated NdFeB substrate 1 from the inside to the outside.

[0056] 1. Pre-treatment: The NdFeB workpiece substrate 1 is subjected to the current pre-treatment process of "grinding and chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0057] The lactic acid activation adopts the following lactic acid activation process: 80 mL / L lactic acid, operating temperature 25° C., activation time 20 s.

[0058] 2. Copper-zinc alloy: After the NdFeB workpiece is pre-treated, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, and the coating thickness is 10 μm.

[0059] 1) Preparation of copper-zinc alloy brightener: Calculated by weight, 82 parts of deionized water were added to a reaction tank, and 8 parts of N,N'-di-n-propylethylenediamine, 1.5 parts of waterborne polyurethane resin, and 10 parts of IC-113 polyacrylamide were added under stirring, and stirred evenly to obtain the copper-zinc alloy brightener.

[0060] 2) Plating: Polymeric cuprous thiocyanate 20g / L, polymeric zinc thiocyanate 18g / L, polymeric sodium thiocyanate 180g / L, copper-zinc alloy brightener 10mL / L, plating solution pH 9, plating tank temperature 40℃, cathode current density 1A / dm 2 , the cathode moves 4m / min, a brass angle code-named H59 is used as the anode, the brass angle is placed in the titanium anode blue, the area ratio of the anode to the cathode is >3:1, and the anode moves 4m / min.

[0061] 3. Galvanized iron alloy: After the NdFeB workpiece is plated with copper-zinc alloy, the potassium chloride zinc-iron alloy plating process of the present invention is used to prepare a zinc-iron alloy coating 3, and the coating thickness is 15 μm.

[0062] 1) Preparation of complexing agent: Sodium glucose heptanate and sodium sulfosalicylate are mixed in a mass ratio of 3:2 and stirred evenly to obtain the complexing agent.

[0063] 2) Prepare brightener: The brightener is obtained by mixing o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stirring until all the solids are dissolved.

[0064] 3) Preparation of auxiliary agents: Calculated by weight, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, 6 parts of sodium benzoate, 0.5 parts of nicotinic acid, and 85 parts of water. The sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid are added into water and stirred until all the solids are dissolved to obtain the auxiliary agent.

[0065] 4) Preparation of potassium chloride zinc-iron alloy plating solution: a) Add 70% water into the plating tank according to the volume of the plating solution, add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, adjust the pH of the plating solution to 4.6 with 10% sodium hydroxide solution or 3% hydrochloric acid, and add water to the specified volume; d) at 0.15A / dm 2 The electrolysis was carried out for 60 min at the current density.

[0066] 5) Plating: Zinc chloride 70g / L, ferrous chloride tetrahydrate 12g / L, potassium chloride 220g / L, boric acid 25g / L, complexing agent 40g / L, brightener 0.15mL / L, auxiliary agent 25mL / L, plating solution pH 4.6, plating tank temperature 15℃, cathode current density 2A / dm 2 , the cathode moves 4m / min, a zinc plate with a mass fraction of ≥99.95% is used as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% mass fraction of ferrous chloride tetrahydrate solution is added to the plating tank to keep its concentration within the process range.

[0067] 4. Passivation: After the NdFeB workpiece is plated with galvanized iron alloy, a trivalent chromium blue-white passivation film is prepared using the TRIROS 348 zinc-iron blue-white passivation process of Chaobang Chemical 4.

[0068] TRIROS 348 zinc iron blue-white passivator 175mL / L, passivation solution pH 2.2, operating temperature 35℃, immersion time 45s, air stirring.

[0069] The specific process is "film removal with sulfuric acid with a volume fraction of 0.2% → water washing → passivation → water washing → draining after leaving the tank".

[0070] 5. Closure: After the NdFeB workpiece is passivated, the graphene-modified sealing layer 5 is prepared using PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical.

[0071] Dilute PRODICO 480 graphene-modified sealer with water to 2.8 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 10 seconds, drain them after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure them at 80°C for 20 minutes.

[0072] Embodiment 3: like Figure 1 As shown, a potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets includes pre-treatment of a NdFeB substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a zinc-iron alloy coating 3, a trivalent chromium black passivation film 4, and a graphene-modified sealing layer 5 on the pre-treated NdFeB substrate 1 from the inside to the outside.

[0073] 1. Pre-treatment: The NdFeB workpiece substrate 1 is subjected to the current pre-treatment process of "grinding and chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0074] The lactic acid activation adopts the following lactic acid activation process: lactic acid 40mL / L, operating temperature 35°C, activation time 40s.

[0075] 2. Copper-zinc alloy plating: After the NdFeB workpiece is pre-treated, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, and the coating thickness is 10 μm.

[0076] 1) Preparation of copper-zinc alloy brightener: Calculated by weight, 82 parts of deionized water were added to a reaction tank, and 8 parts of N,N'-di-n-propylethylenediamine, 1.5 parts of waterborne polyurethane resin, and 10 parts of IC-125 polyacrylamide were added under stirring, and stirred evenly to obtain the copper-zinc alloy brightener.

[0077] 2) Plating: Polymeric cuprous thiocyanate 14g / L, polymeric zinc thiocyanate 12g / L, polymeric sodium thiocyanate 140g / L, copper-zinc alloy brightener 10mL / L, plating solution pH 9.5, plating tank temperature 45°C, cathode current density 1A / dm 2 , the cathode moves 4m / min, a brass angle code-named H59 is used as the anode, the brass angle is placed in the titanium anode blue, the area ratio of the anode to the cathode is >3:1, and the anode moves 4m / min.

[0078] 3. Galvanized iron alloy: After the NdFeB workpiece is plated with copper-zinc alloy, the potassium chloride zinc-iron alloy plating process of the present invention is used to prepare a zinc-iron alloy coating 3, and the coating thickness is 15 μm.

[0079] 1) Preparation of complexing agent: Sodium glucose heptanate and sodium sulfosalicylate are mixed in a mass ratio of 3:2 and stirred evenly to obtain the complexing agent.

[0080] 2) Prepare brightener: The brightener is obtained by mixing o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stirring until all the solids are dissolved.

[0081] 3) Preparation of auxiliary agents: Calculated by weight, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, 6 parts of sodium benzoate, 0.5 parts of nicotinic acid, and 85 parts of water. The sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid are added into water and stirred until all the solids are dissolved to obtain the auxiliary agent.

[0082] 4) Preparation of potassium chloride zinc-iron alloy plating solution: The potassium chloride zinc-iron alloy plating solution is prepared as follows: a) Add 70% water into the plating tank according to the volume of the plating solution, add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, adjust the pH of the plating solution to 4.8 with 10% by mass sodium hydroxide solution or 3% by mass hydrochloric acid, and add water to the specified volume; d) at 0.15A / dm 2 The electrolysis was carried out for 60 min at the current density.

[0083] 5) Plating: Zinc chloride 50g / L, ferrous chloride tetrahydrate 8g / L, potassium chloride 180g / L, boric acid 30g / L, complexing agent 28g / L, brightener 0.15mL / L, auxiliary agent 25mL / L, plating solution pH 4.8, plating tank temperature 25℃, cathode current density 2A / dm 2 , the cathode moves 4m / min, a zinc plate with a mass fraction of ≥99.95% is used as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% mass fraction of ferrous chloride tetrahydrate solution is added to the plating tank to keep its concentration within the process range.

[0084] 4. Passivation: After the NdFeB workpiece is plated with galvanized iron alloy, a trivalent chromium black passivation film is prepared using the TRIROS BP-885 trivalent chromium black passivation process of Chaobang Chemical 4.

[0085] TRIROS BP-885A agent 60mL / L, TRIROS BP-885B agent 50mL / L, passivation temperature 25℃, passivation solution pH 2.5, passivation time 80s.

[0086] The specific process is "lightening with 1% volume fraction nitric acid → water washing → passivation → water washing → draining after leaving the tank".

[0087] 5. Closure: After the NdFeB workpiece is passivated, the graphene-modified sealing layer 5 is prepared using PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical.

[0088] Dilute PRODICO 480 graphene-modified sealer with water to 2.8 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 10 seconds, drain them after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure them at 70°C for 35 minutes.

[0089] Embodiment 4: like Figure 1 As shown, a potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets includes pre-treatment of a NdFeB substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a zinc-iron alloy coating 3, a trivalent chromium black passivation film 4, and a graphene-modified sealing layer 5 on the pre-treated NdFeB substrate 1 from the inside to the outside.

[0090] 1. Pre-treatment: The NdFeB workpiece substrate 1 is subjected to the current pre-treatment process of "grinding and chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0091] The lactic acid activation adopts the following lactic acid activation process: lactic acid 70mL / L, operating temperature 33°C, activation time 25s.

[0092] 2. Copper-zinc alloy plating: After the NdFeB workpiece is pre-treated, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, and the coating thickness is 10 μm.

[0093] 1) Preparation of copper-zinc alloy brightener: Calculated by weight, 82 parts of deionized water were added to a reaction tank, and 8 parts of N,N'-di-n-propylethylenediamine, 1.5 parts of waterborne polyurethane resin, and 10 parts of IC-213 polyacrylamide were added under stirring, and stirred evenly to obtain the brightener.

[0094] 2) Plating: Polymeric cuprous thiocyanate 18g / L, polymeric zinc thiocyanate 17g / L, polymeric sodium thiocyanate 175g / L, copper-zinc alloy brightener 10mL / L, plating solution pH 9.2, plating tank temperature 38°C, cathode current density 1A / dm 2 , the cathode moves 4m / min, a brass angle code-named H59 is used as the anode, the brass angle is placed in the titanium anode blue, the area ratio of the anode to the cathode is >3:1, and the anode moves 4m / min.

[0095] 3. Galvanized iron alloy: After the NdFeB workpiece is plated with copper-zinc alloy, the potassium chloride zinc-iron alloy plating process of the present invention is used to prepare a zinc-iron alloy coating 3, and the coating thickness is 15 μm.

[0096] 1) Preparation of complexing agent: Sodium glucose heptanate and sodium sulfosalicylate are mixed in a mass ratio of 3:2 and stirred evenly to obtain the complexing agent.

[0097] 2) Prepare brightener: The brightener is obtained by mixing o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stirring until all the solids are dissolved.

[0098] 3) Preparation of auxiliary agents: Calculated by weight, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, 6 parts of sodium benzoate, 0.5 parts of nicotinic acid, and 85 parts of water. The sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid are added into water and stirred until all the solids are dissolved to obtain the auxiliary agent.

[0099] 4) Preparation of potassium chloride zinc-iron alloy plating solution: a) Add 70% water into the plating tank according to the volume of the plating solution, add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, adjust the pH of the plating solution to 5.6 with 10% sodium hydroxide solution or 3% hydrochloric acid, and add water to the specified volume; d) At 0.1A / dm 2 The electrolysis was carried out for 90 min at the current density.

[0100] 5) Plating: Zinc chloride 65g / L, ferrous chloride tetrahydrate 11g / L, potassium chloride 210g / L, boric acid 28g / L, complexing agent 36g / L, brightener 0.15mL / L, auxiliary agent 25mL / L, plating solution pH 5.6, plating tank temperature 22℃, cathode current density 2A / dm 2 , the cathode moves 4m / min, a zinc plate with a mass fraction of ≥99.95% is used as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% mass fraction of ferrous chloride tetrahydrate solution is added to the plating tank to keep its concentration within the process range.

[0101] 4. Passivation: After the NdFeB workpiece is plated with galvanized iron alloy, a trivalent chromium black passivation film is prepared using the TRIROS BP-885 trivalent chromium black passivation process of Chaobang Chemical 4.

[0102] TRIROS BP-885A agent 70mL / L, TRIROS BP-885B agent 60mL / L, passivation temperature 20℃, passivation solution pH 2.6, passivation time 65s.

[0103] The specific process is "lightening with 1% volume fraction nitric acid → water washing → passivation → water washing → draining after leaving the tank".

[0104] 5. Closure: After the NdFeB workpiece is passivated, the graphene-modified sealing layer 5 is prepared using PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical.

[0105] Dilute PRODICO 480 graphene-modified sealer with water to 2.8 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 10 seconds, drain them after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure them at 77°C for 25 minutes.

[0106] Embodiment 4: like Figure 1As shown, a potassium chloride zinc-iron alloy plating process for NdFeB permanent magnets includes pre-treatment of a NdFeB substrate 1, and sequentially preparing a cyanide-free copper-zinc alloy coating 2, a zinc-iron alloy coating 3, a trivalent chromium black passivation film 4, and a graphene-modified sealing layer 5 on the pre-treated NdFeB substrate 1 from the inside to the outside.

[0107] 1. Pre-treatment: The NdFeB workpiece substrate 1 is subjected to the current pre-treatment process of "grinding and chamfering → water washing → chemical degreasing → water washing → ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0108] The lactic acid activation adopts the following lactic acid activation process: lactic acid 70mL / L, operating temperature 33°C, activation time 25s.

[0109] 2. Copper-zinc alloy plating: After the NdFeB workpiece is pre-treated, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, and the coating thickness is 10 μm.

[0110] 1) Preparation of copper-zinc alloy brightener: Calculated by weight, 82 parts of deionized water were added to a reaction tank, and 8 parts of N,N'-di-n-propylethylenediamine, 1.5 parts of waterborne polyurethane resin, and 10 parts of IC-213 polyacrylamide were added under stirring, and stirred evenly to obtain the brightener.

[0111] 2) Plating: Polymeric cuprous thiocyanate 18g / L, polymeric zinc thiocyanate 17g / L, polymeric sodium thiocyanate 175g / L, copper-zinc alloy brightener 10mL / L, plating solution pH 9.2, plating tank temperature 38°C, cathode current density 1A / dm 2 , the cathode moves 4m / min, a brass angle code-named H59 is used as the anode, the brass angle is placed in the titanium anode blue, the area ratio of the anode to the cathode is >3:1, and the anode moves 4m / min.

[0112] 3. Galvanized iron alloy: After the NdFeB workpiece is plated with copper-zinc alloy, the potassium chloride zinc-iron alloy plating process of the present invention is used to prepare a zinc-iron alloy coating 3, and the coating thickness is 15 μm.

[0113] 1) Preparation of complexing agent: Sodium glucose heptanate and sodium sulfosalicylate are mixed in a mass ratio of 3:2 and stirred evenly to obtain the complexing agent.

[0114] 2) Prepare brightener: The brightener is obtained by mixing o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stirring until all the solids are dissolved.

[0115] 3) Preparation of auxiliary agents: Calculated by weight, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, 6 parts of sodium benzoate, 0.5 parts of nicotinic acid, and 85 parts of water. The sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid are added into water and stirred until all the solids are dissolved to obtain the auxiliary agent.

[0116] 4) Preparation of potassium chloride zinc-iron alloy plating solution: a) Add 70% water into the plating tank according to the volume of the plating solution, add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, adjust the pH of the plating solution to 5.6 with 10% sodium hydroxide solution or 3% hydrochloric acid, and add water to the specified volume; d) At 0.1A / dm 2 The electrolysis was carried out for 90 min at the current density.

[0117] 5) Plating: Zinc chloride 65g / L, ferrous chloride tetrahydrate 11g / L, potassium chloride 210g / L, boric acid 28g / L, complexing agent 36g / L, brightener 0.15mL / L, auxiliary agent 25mL / L, plating solution pH 5.6, plating tank temperature 22℃, cathode current density 2A / dm 2 , the cathode moves 4m / min, a zinc plate with a mass fraction of ≥99.95% is used as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% mass fraction of ferrous chloride tetrahydrate solution is added to the plating tank to keep its concentration within the process range.

[0118] 4. Passivation: After the NdFeB workpiece is plated with galvanized iron alloy, a trivalent chromium black passivation film is prepared using the TRIROS BP-885 trivalent chromium black passivation process of Chaobang Chemical 4.

[0119] TRIROS BP-885A agent 70mL / L, TRIROS BP-885B agent 60mL / L, passivation temperature 20℃, passivation solution pH 2.6, passivation time 65s.

[0120] The specific process is "lightening with 1% volume fraction nitric acid → water washing → passivation → water washing → draining after leaving the tank".

[0121] 5. Closure: After the NdFeB workpiece is passivated, the graphene-modified sealing layer 5 is prepared using PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical.

[0122] Dilute PRODICO 480 graphene-modified sealer with water to 2.8 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 10 seconds, drain them after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure them at 77°C for 25 minutes.

Claims

1. A process for plating potassium chloride zinc-iron alloy on NdFeB permanent magnets, characterized in that: The following steps are involved: (1) Grinding, chamfering, degreasing, and pickling and activation of NdFeB workpieces; (2) After pretreatment of the NdFeB workpiece, a cyanide-free copper-zinc alloy coating is prepared by using a polymerized thiocyanate copper-zinc alloy plating process; (3) The NdFeB workpiece is polymerized with thiocyanate to plate a copper-zinc alloy, and then a potassium chloride zinc-iron alloy plating process is used to prepare a zinc-iron alloy coating; (4) The NdFeB workpiece is plated with zinc-iron alloy and then passivated to prepare a passivation film; (5) After the NdFeB workpiece is passivated, it is sealed to prepare a sealing layer; The potassium chloride zinc-iron alloy plating process includes the following components and process parameters: Zinc chloride 50-70g / L, ferrous chloride tetrahydrate 2-12g / L, potassium chloride 180-220g / L, boric acid 25-35g / L, complexing agent 8-40g / L, brightener 0.1-0.2mL / L, auxiliary agent 20-30mL / L, plating solution pH 4.5-5.6, plating tank temperature 15-30℃, cathode current density 1-3A / dm 2 , the cathode moves 3-5 m / min, a zinc plate with a mass fraction of ≥99.95% is used as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% mass fraction of ferrous chloride tetrahydrate solution is added to the plating tank to keep its concentration within the process range; The ligand comprises sodium glucose heptanoate and sodium sulfosalicylate, the mass ratio of sodium glucose heptanoate to sodium sulfosalicylate is 3:(1-3), and sodium glucose heptanoate and sodium sulfosalicylate are mixed according to the ratio and stirred evenly.

2. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The brightener comprises o-chlorobenzaldehyde and formic acid, the mass ratio of o-chlorobenzaldehyde to formic acid is 1:(0.8-1.2), and o-chlorobenzaldehyde and formic acid are mixed according to the ratio and stirred until all solids are dissolved.

3. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The auxiliary agent comprises three intermediates, namely, a sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid. Calculated by weight, the sulfonation product of fatty alcohol polyoxyethylene ether with model OX-105 and aminosulfonic acid comprises 17 to 23 parts, sodium benzoate comprises 5 to 7 parts, nicotinic acid comprises 0.4 to 0.6 parts, and deionized water comprises 80 to 90 parts. The three intermediates are added into water according to the weight fractions and stirred until all the solids are dissolved.

4. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The polythiocyanate 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 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 angle code-named H59 is used as the anode, the brass angle 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 brightener comprises the following components in weight fractions: 6-10 parts of N,N'-di-n-propylethylenediamine, 1-2 parts of waterborne polyurethane resin, 8-12 parts of polyacrylamide with a molecular weight less than 8000, and 77-87 parts of deionized water.

5. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The pickling activation adopts lactic acid pickling activation process: Lactic acid 40-80 mL / L, operating temperature 20-35°C, activation time 20-40 s.

6. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The passivation film is prepared by TRIROS 348 zinc iron blue-white passivation process: TRIROS 348 zinc iron blue-white passivator 135-175 mL / L, passivation solution pH 2.0-2.8, operating temperature 30-60°C, immersion time 30-60s, air stirring.

7. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The passivation film is prepared by TRIROS BP-885 trivalent chromium black passivation process: TRIROS BP-885A agent 40~80mL / L, TRIROS BP-885B agent 30~70mL / L, passivation temperature 20~30℃, passivation solution pH value 2.3~2.7, passivation time 40~120s, workpiece swing.

8. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The graphene-modified sealing layer is prepared using PRODICO 480 graphene-modified sealing agent: Dilute PRODICO 480 graphene modified sealer with water to 2.5-3.2 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 8-15 seconds. Drain after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure at 70-80°C for 20-35 minutes.

9. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The thickness of the cyanide-free copper-zinc alloy coating is 6 to 12 μm.

10. The process for potassium chloride zinc-iron alloy plating of NdFeB permanent magnets according to claim 1, characterized in that: The thickness of the zinc-iron alloy coating is 10-20 μm.

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