CN113430607A

CN113430607A - Fluoride-free electroplating process for neodymium magnet

Info

Publication number: CN113430607A
Application number: CN202110714797.1A
Authority: CN
Inventors: 李代文; 李政宇
Original assignee: Dongguan Hongyu Surface Treatment Technology Co ltd
Current assignee: Dongguan Hongyu Surface Treatment Technology Co ltd
Priority date: 2021-06-26
Filing date: 2021-06-26
Publication date: 2021-09-24

Abstract

The invention relates to a fluorine-free electroplating process for a neodymium magnet, which comprises a neodymium magnet electroplating pretreatment tin immersion process, wherein the neodymium magnet electroplating pretreatment tin immersion process comprises the steps of sequentially carrying outComprises the following steps: deoiling a neodymium iron boron magnet → derusting and brightening → washing → treating 45g/L oxalic acid solution by RT for 30-60S → washing → dipping tin → washing → activating by 5% tartaric acid → washing → removing the bottom plating of an electroplating bath; wherein in the step of tin immersion, the formula of the tin immersion liquid is stannous pyrophosphate Sn₂P₂O₇7g/L, potassium pyrok₄P₂O₇·3H₂O36g/L, Rochelle salt 5g/L, disodium hydrogen phosphate 10g/L, sodium acetate 5g/L, DS 0.05g/L, PEG 0.1.1 g/L, PEI1.5ml/L, oxygen removal stabilizer and benzenediol, wherein the temperature is 30-40 ℃. The neodymium magnet electroplating pretreatment tin immersion process achieves the effect of actual use requirements, combines cyanide-free combined alkali copper pre-electroplating or potassium chloride bottom electroplating with high complexing stability, and is reliable and practical; better social and economic benefits are obtained by changing a fluorine-containing electroplating process system with poor environmental protection; is beneficial to the development of the magnet electroplating industry.

Description

Fluoride-free electroplating process for neodymium magnet

Technical Field

The invention relates to the technical field of neodymium magnet electroplating, in particular to a fluorine-free electroplating process for a neodymium magnet.

Background

The NdFeB permanent magnetic material is called as 'King' because of the excellent magnetic property, has extremely high magnetic energy and coercive force, has the advantages of high energy density and the like, and has wide market prospect in modern industry and electronic technology.

The structure of the NdFeB magnet provides high coercive force and magnetic energy product for the magnet, but also becomes a root cause of poor corrosion resistance of the NdFeB magnet. The neodymium iron boron magnet is divided into a sintering type and a bonding type according to different manufacturing methods. Neodymium iron boron electroplating is generally used for sintering type, the volatilization of a binder solvent in the manufacturing process of a bonding type neodymium iron boron magnet is easy to form holes, and the holes and the binder cannot form a conductive loop, so that the electrochemical deposition of metal on the surface of a part is difficult to perform. The main problems of electroplating on the NdFeB magnet are that neodymium in the NdFeB magnet is very easy to oxidize, the binding force of a plating layer is reduced due to improper pretreatment, the NdFeB magnet is prepared by sintering powder, the surface is rough, a large number of pores exist, acid, alkali and electroplating solution can permeate in the electroplating process, and the corrosion of a substrate and the plating layer can be caused later; because the surface structure of the magnet is uneven, the porosity of the plating layer is increased during electroplating, and the protection performance of the plating layer is reduced.

NdFeB is more susceptible to corrosion, firstly because the rare earth Nd element is one of the most chemically active metal elements, and the standard potential is (Nd3+/Nd) — 2.431V; the second is related to the multiphase structure of the magnet and the difference of electrochemical potentials among phases. The results of the study show that corrosion of NdFeB magnets occurs mainly in high temperature, warm and electrochemical environments. In the environment of high-temperature drying, when the temperature is lowAt 150 ℃, the oxidation speed of the magnet is very slow, but at higher temperature, the Nd-rich phase reacts, 4Nd +3O₂→2Nd₂O₃. Primary phase Nd₂Fe₁₄B will decompose to form Fe and Nd₂O₃The magnet will further oxidize to produce Fe₂O₃In a hot and humid environment, the grain boundary Nd-rich phase in the NdFeB magnet reacts with water first: nd +3H₂O→3H+Nd(OH)₃. The atomic H generated by the reaction permeates into the grain boundary phase, so that the Nd-rich phase can further generate grain boundary corrosion, and the reaction formula is 3H + Nd → NdH₃. Wherein the volume of the grain boundary phase can expand and become larger due to the generation of NdH3, grain boundary stress is generated, and further the migration and the grain boundary damage of the main phase can be caused, and even the grain boundary phase can break to cause the pulverization and the failure of the magnet, in addition, under the relatively dry aerobic condition, the corrosion product film generated on the surface of the magnet is relatively dense, and the magnet can be prevented from further oxidation, under the humid environment condition, the hydroxide and other compounds containing hydrogen formed on the surface of the magnet can not have the protection capability any more, especially when the environment humidity is relatively overlarge, the surface of the magnet can be electrochemically corroded due to the existence of liquid water, therefore, the corrosion behavior influence of the humidity on the magnet is larger than the corrosion behavior influence of the temperature on the magnet, under the electrochemical environment, the electrochemical potentials of the phases of the magnet are different, and the Nd-rich phase and the B-rich phase are used as anodes, and corrosion can occur preferentially, the grain boundary corrosion is further accelerated by the characteristic of a small anode and a large cathode because the volume of the main phase as the cathode is relatively large.

In the processes of acid washing, activation, chemical plating, electroplating and the like, hydrogen is separated out from the surface of the magnet, wherein the Nd-rich phase reacts with the hydrogen as Nd +3H → NdH₃Causing grain boundary corrosion to occur, and the Nd-rich phase undergoes a hydrogen absorption reaction: nd + Hx → NdHx, and if the subsequent hydrogen desorption is incomplete, these desorbed residual hydrogen will also cause corrosion of the magnet.

As shown in fig. 1, the high-power microstructure of the sintered NdFeB magnet is schematically shown, and the composition and structure of the NdFeB magnet are comprehensively analyzed, so that the corrosion of the magnet is mainly from two aspects, namely chemical corrosion (namely oxidation) and electrochemical corrosion. In a damp hot corrosion environment, when water vapor is condensed into small droplets on the surface of the magnet, microcell corrosion occurs, so that the Nd-rich phase preferentially corrodes to generate corrosion pits. Meanwhile, the intergranular corrosion is further accelerated due to the different electrochemical potentials among the phases of the magnet.

The strong magnetism is protected by electroplating, the metal coating can be a metal or metal-based composite coating such as Ni, Zn, Al, Ni-P, Ni-Fe, Cu, Cr, TiN, ZrN, Ni-P, Ni-Co-P, Ni-Cu-P, and the like, and the surface of the magnet is coated by electroplating, chemical plating, physical vapor deposition or vacuum coating technology and the like. The electroplating surface treatment process has the advantages of low equipment requirement, easy meeting of process conditions, high film forming speed, low price, easy mass production and the like, and becomes the most main choice for surface protection of the NdFeB magnet. At present, the NdFeB magnet in China mainly adopts electroplated Ni and electroplated Zn. The Zn-plated layer is used as a sacrificial anode plating layer, and the corrosion resistance is greatly improved after the passivation of the main and auxiliary amino acid salts, and the production cost is low and the Zn-plated layer is widely adopted. Although the cost of Ni plating is higher than that of Zn plating, the Ni plating is more favored because of its better mechanical properties such as heat resistance, oxidation resistance, corrosion resistance, decorative property, bending resistance, compression resistance, impact resistance and the like. However, because the surface porosity of the magnet is high, in the pretreatment and electroplating processes before plating, the pretreatment liquid and the electroplating liquid penetrate into the micropores to form corrosive inclusion substances, so that the binding force between the magnet and the plating layer is poor, and the plating layer is often layered and foamed. Various Ni electroplating processes have been successfully developed in laboratories, but Ni-Cu-Ni multilayer coatings are most used in practical production. The porosity of the Ni-Cu-Ni plating layer is greatly reduced, and the high temperature resistance and the oxidation resistance of the plating layer are also greatly improved, so that the Ni-Cu-Ni plating layer is the most main protective plating layer at present.

The protection principle of the zinc plating and the nickel plating is different, and the zinc plating layer is still an anode plating layer relative to neodymium-iron-boron, so that the corrosion is mainly limited in the zinc plating layer, and the corrosion resistance of a zinc chromate conversion film directly influences the appearance and the corrosion resistance of the zinc plating layer; the nickel coating is relative to the neodymium-iron-boron matrix, because of the activity of neodymium and the anode acceleration action in the corrosion couple, the corrosion is rapidly intensified once the corrosion occurs, and the reduction of the pores of the coating is beneficial to improving the corrosion resistance of the coating.

Aiming at the corrosion characteristics of the galvanized layer and the nickel-plated layer, the galvanizing process mainly focuses on the development of a high-corrosion-resistance passivation process and the protection treatment of a passivation film. The more effective process is a zinc alloy electroplating process with extremely high corrosion resistance of a passive film, a white corrosion point begins to appear in more than 400 hours when the nickel content of a zinc-nickel alloy coating is 8-10%, red rust appears in more than 2000 hours, and the zinc-nickel alloy coating has extremely excellent corrosion resistance which is 3-5 times that of a zinc coating with the same thickness. Electroplating zinc or zinc-nickel alloy on the neodymium-iron-boron magnet, and selecting a potassium chloride micro-acid type electroplating process.

In recent years, in Japan, the electroplating treatment of neodymium-iron-boron has mostly adopted a multilayer structure, such as a copper/nickel/electroless nickel-phosphorus alloy in JP 0803768, a copper/nickel/copper/nickel four-layer structure in JP 0803762, and Pd-Ni/electroless nickel-phosphorus/nickel in JP 07272922. In the multi-layer nickel electroplating process, the potential difference between the bright nickel and the semi-bright nickel is kept at 150-170mV, so that the corrosion extension can be blocked on the semi-bright nickel, and the substrate can be protected.

The surface of the neodymium iron boron is loose, porous and rough, which not only brings great burden to the pre-plating treatment, but also mainly causes great limitation to the selection of the pre-plating (or direct plating) process, namely complex plating solutions (such as alkali copper, citric acid nickel plating, alkali zinc and the like) with good plating layer bonding force, good corrosion resistance and low current efficiency cannot be selected.

At present, neodymium iron boron can not be directly plated with copper, and can be plated with copper after nickel preplating is adopted, wherein the nickel preplating is generally a nickel immersion method or low-alkaline chemical complex nickel (closed) deposition. (nickel immersion: 70g/L of nickel acetate, 65g/L of boric acid and 170g/L of hydrofluoric acid, room temperature and 30s of time, and is used for immersion plating before nickel plating of neodymium iron boron) to form the nickel-copper-nickel combined plating layer of neodymium iron boron. Copper is commonly pyrophosphate, and because the equilibrium data of the electrode potential of the copper complex ion is too many times, the copper layer is only suitable to be thickened to reduce the porosity, and the nickel plating can be carried out by the conventional nickel sulfate.

The citric acid nickel plating is a complex type, and the low current efficiency causes difficulty in plating on the neodymium iron boron substrate. Research shows that the neodymium iron boron is pre-plated with neutral or alkalescent nickel plating, the corrosion to a substrate is small, the obtained plating layer is uniform and bright, the porosity is low, the bonding force and the corrosion resistance of the plating layer are better, and the process is an ideal neodymium iron boron pre-nickel plating process if the process is mature.

The acidic nickel plating solution is weakly acidic, is a simple salt plating solution, and is extremely easy to corrode parts if used for pre-plating neodymium iron boron. Especially, barrel plating can not be directly performed on the neodymium iron boron substrate, so that the selection of acidic nickel plating solution for pre-plating is inevitable. Thus, the selected acid nickel plating process is required to have a faster deposition rate so as to shorten the plating time on the surface of the part as much as possible and reduce the corrosion degree of the part. The sulfamate nickel plating has the advantages of high deposition speed, small plating stress and good dispersing capacity, so the sulfamate nickel plating process is suitable for neodymium iron boron preplating, and the process is advocated by the industry for a long time, but the sulfamate nickel plating has high cost and poor stability of the plating solution compared with the sulfate-low chloride type nickel plating process, so the sulfamate nickel plating process is not easily accepted by the neodymium iron boron electroplating industry.

In addition, the pre-plated dark nickel layer has high purity and does not contain surface active substances or other substances different from nickel, which can cause plating layer stress, and the pre-plated dark nickel layer is undoubtedly favorable for improving the plating layer bonding force. Therefore, under the condition that neodymium iron boron can not be preplated with copper, preplating with dark nickel is an ideal choice, and the comprehensive effect of the process is always good after the process is used for many years. Preplating semi-bright nickel may be slightly better than dark nickel; because it is more galvanic than the use of dark nickel, which is beneficial for faster deposition (encapsulation). The inventor does not suggest the use of pre-plated dark nickel or pre-plated semi-gloss nickel; the binding force is considered poor and difficult to guarantee.

In addition, the neodymium iron boron magnet can also be galvanized to be a coating; the zinc dipping process comprises the following steps: ZnSO₄ 30g/L， Na₄P₂O₇·10H₂O 120g/L，KF 7g/L，Na₂CO₃7g/L, 85 ℃, and the time is 50 s; other pre-plating dip plating types are as follows:

comparing the oxidation potential after immersion plating with the oxidation potential before immersion plating, the neodymium iron boron potential is positively shifted after surface unit treatment, thereby reducing the oxidation capacity of neodymium, reducing the oxidation degree of workpieces and improving the binding force of the plating layer. The immersion plating can obtain a complete and uniform immersion plating layer, the improvement of the binding force and corrosion resistance of an electroplated layer and the reduction of the porosity are both significant effects, the oxidation potential of the neodymium iron boron magnet after rust removal and water washing is about-0.4807V, and in addition; the Hunan Chengxiang has been published in the researches of 'NdFeB magnet pretreatment process, Ni-W-P electroplating gold-containing property and deplating process thereof': as shown in FIG. 2, the graph of the potential-time of the NdFeB magnet in 0.5mol/L oxalic acid pickling activation solution shows that the Nd on the surface of the NdFeB magnet after the oil removal by chemical alkaline cleaning₂O₃，Fe₂O₃In the presence of an equal oxidation film, the potential is-0.515V, and the following reaction occurs after oxalic acid complex film ion treatment: nd (neodymium)₂O₃+3H₂C₂O₄＝Nd₂(C₂O₄)₃↓+3H₂0；Fe₂O₃+3H₂C₂O₄＝Fe₂(C₂O₄)₃↓+3H ₂0； Nd+3H₂C₂O₄＝Nd₂(C₂O₄)₃↓+3H₂↑；Fe+3H₂C₂O₄＝Fe₂(C₂O₄)₃↓+3H₂↑。

From FIG. 2, the NdFeB magnet is at 0.5mol/L H₂C₂O₄Open circuit potential curves in solution it can be seen that when NdFeB magnets are immersed in oxalic acid pickling activation solution, dissolution of surface oxides causes the open circuit potential of the magnets to start to drop. When the dissolution and deposition reactions on the surface of the NdFeB magnet reach equilibrium, the open circuit potential is at oneAnd a stable value is reached within a period of time, so that the conclusion can be drawn that after the pretreatment of pickling and activating by oxalic acid, a layer of uniform and compact passivation film of Nd and Fe oxalate complexes can be formed on the surface of the NdFeB magnet, and the surface components and the potential of the sample are basically in a consistent state.

In summary, pretreatment is the most critical factor for ensuring good bonding force between the NdFeB magnet and the plating layer. Compared with the common pickling and activating pretreatment process, the oxalic acid pickling and activating process can weaken the corrosion of Nd-rich phase on the surface of the magnet and form a layer of compact and uniform passive film containing Nd and Fe oxalate complex on the surface of the magnet, can prevent the surface of a fresh magnet after pickling and activating from being secondarily oxidized in the subsequent cleaning process, can also prevent active neodymium on the surface of the magnet from further generating corrosion reaction in the subsequent steps, simultaneously, the oxalic acid pickling and activating pretreatment generates a rough surface to improve the mechanical gripping force between a coating and a matrix, microscopic cross section images and heat-cold cycle experiments can show that the binding force between the coating and the magnet is good, the NdFeB magnet can achieve the functions of pickling and activating after being treated by further oxalic acid pickling and activating solution, the flow of the pretreatment process is simplified, and the further oxalic acid pickling and activating has a certain time range, is convenient for operation and application.

Before the one-step oxalic acid pickling activation is found, a two-step activation method is often adopted, namely: derusting and activating, wherein the activating process comprises the following steps: at RT room temperature, 20-25g/L of sulfosalicylic acid and 10-15g/L of ammonium bifluoride, and the preferable derusting process comprises the following steps: 40ml/L nitric acid; 0.5g/L thiourea; the pH is 4-5; room temperature; 30-40 s.

The problems of the electroplating pretreatment of the NdFeB magnet are as follows: the pickling medium and the pickling conditions have great influence on the cleaning effect, and the common pickling solution formula before the surface of the NdFeB magnet is nitric acid and thiourea, the activating solution formula is ammonium bifluoride and sulfosalicylic acid, the thiourea belongs to an adsorptive corrosion inhibitor and is easily adsorbed on the surface of the NdFeB magnet and difficult to clean, and the thiourea is partially decomposed under the acidic condition to generate H₂S, the corrosion of the magnet is accelerated, and the hydrogen permeation phenomenon is generated; must be strictly controlledAcid cleaning time of nitric acid and thiourea, otherwise, the magnet is easy to over-corrode; the fluorine ions in the activating liquid are harmful to the environment and human body, and the absorption of excessive fluorine ions can cause symptoms of hypoadreno-function, hyperparathyroidism, tooth and human skeleton softening, sperm distortion and the like, thereby increasing the treatment cost of the waste liquid. Liqing et al proposed anhydrous PdCl₂the/EtOH solution replaces the commonly used activation solution (sulfosalicylic acid + ammonium bifluoride), however palladium is a noble metal element that limits its wide application.

Therefore, whether the electroplating process is used for preventing infection or not can be realized, a high-quality neodymium iron boron electroplating process can be developed by adopting no fluorine-containing substance as far as possible and combining the advantages of classic 'derusting' and 'activating and uniformly passivating' of an oxalic acid film.

In addition, vacuum ion plating is to deposit an Al or TiN film on the surface of NdFeB by vacuum evaporation or vacuum arc ion plating, and has the advantages of strong film adhesion, high deposition speed, wide platable materials and the like. However, the ion plating equipment has large investment, low productivity, difficult plating of parts with irregular shapes and high production cost, and the method is only limited to laboratory research and is not applied to industrial production at present.

Disclosure of Invention

In order to solve the defects of the prior art, the invention provides a fluorine-free electroplating process for neodymium magnets.

In order to achieve the purpose, the technical scheme provided by the invention is as follows: a fluorine-free electroplating process of a neodymium magnet comprises a neodymium magnet electroplating pretreatment tin immersion process, wherein the neodymium magnet electroplating pretreatment tin immersion process comprises the following steps of: deoiling a neodymium iron boron magnet → derusting and brightening → washing → treating 45g/L oxalic acid solution by RT for 30-60S → washing → dipping tin → washing → activating by 5% tartaric acid → washing → removing the bottom plating of an electroplating bath; wherein in the step of tin immersion, the formula of the tin immersion liquid is stannous pyrophosphate Sn₂P₂O₇7g/L, potassium pyrok₄P₂O₇·3H₂O36g/L, Rochelle salt 5g/L, disodium hydrogen phosphate 10g/L, sodium acetate 5g/L, DS (jar opener) 0.05g/L, PEG (polyethylene glycol) 0.1g/L, PEI (polyethyleneimine) 1.5ml/L, and oxygen-removing stabilityThe temperature of the agent and the benzenediol is 30-40 ℃.

In the technical scheme, in the step of deoiling the neodymium iron boron magnet, 70g/L of trisodium phosphate, 50g/L of sodium carbonate, 5g/L, OP-10 g/L of sodium hydroxide and 0.5g/L of emulsifier (dodecyl phenol polyoxyethylene ether) and 30-40g/L of citric acid in the formula of deoiling liquid are completely deoiled on the surface of the neodymium iron boron magnet at the temperature of 65 ℃ and the pH of 10.5; or alkaline chemical oil removal process is adopted, and the concentration of NaOH in the deoiled liquid is 6g/L, Na₂C0₃Has a concentration of 50g/L, Na₃PO₄The concentration of the uranium dodecyl sulfate is 70g/L, the concentration of the uranium dodecyl sulfate is 0.5g/L, the pH value is adjusted to 9-9.5 by formic acid, the temperature is 65-70 ℃, and auxiliary oil removal is carried out by ultrasonic waves.

In the technical scheme, in the step of derusting and brightening: the formula of the pickling solution is 30-40mL/L of nitric acid and O.5g/L of thiourea, the pH value is 4-5 (adjusted by ammonia water), the temperature is room temperature, and the rust removal light-emitting time is 30-40S; pickling until the surface of the part is uniform, fine and glossy silvery white; among them, hydrochloric acid cannot be used.

In the technical scheme, the copper plating process after tin immersion treatment is also included, the copper plating process after tin immersion treatment is a citric acid-tartaric acid copper plating process, and the formula of the electroplating solution of the citric acid-tartaric acid copper plating process comprises 31.25g/L of copper sulfate, 40g/L of potassium carbonate, 30g/L of citric acid, 110g/L of sodium citrate, 40g/L, PEG (M.W.6000) of rochelle salt, 0.08g/L of polyethylene glycol and polyethyleneimine (CH)₂CH₂NH)_n0.1g/L of 2-mercaptobenzimidazole 1.2mg/L, PPS (sodium 3- (1-pyridyl) propanesulfonate// pyridylpropanesulfonic acid inner salt) 0.5-1 g/L, pH 9-10.5, and temperature 45-50 ℃.

In the technical scheme, the method also comprises a process for plating potassium zinc chloride after tin immersion treatment, and the formula of the used plating solution is KCl 180-₂ 65-75g/L、H₃BO₃25-35g/L, 14-18ml/L of additive and 4-5 PH; dk is 0.45-0.8A/dm²。

The neodymium magnet pretreatment tin immersion process has the advantages that the structure is reasonable, the design is novel, the practicability is high, the neodymium magnet pretreatment tin immersion process achieves the effect of strict actual use requirements, and the neodymium magnet pretreatment immersion before electroplatingThe tin process has the advantages that the fluoride treatment is avoided in the nickel immersion and zinc immersion processes (the nickel immersion process is 70g/L of nickel acetate, 65g/L of boric acid and 170g/L of hydrofluoric acid, the temperature is room temperature, the time is 30s// the zinc immersion process is ZnSO)₄ 30g/L，Na₄P₂O₇·10H₂O 120g/L，KF 7g/L，Na₂CO₃7g/L, 85 ℃, time 50 s); and the dip galvanizing process uses the operation in the temperature range of room temperature to 40 ℃, and has obvious advantages of energy consumption and environmental protection. The tin concentration can be maintained by a titration analysis method, and the method can be conveniently popularized; the method combines the cyanide-free combination of alkali copper pre-electroplating or potassium chloride bottom electroplating with high complexing stability, and is reliable and practical; the fluorine-containing electroplating process system which is not good in environmental protection at present can be changed, better social and economic benefits can be obtained, product lines can be enriched, and the coating thickness of the original fluorine-containing electroplating system can be properly reduced. Designing a better formula and a better process path for reasonable tin immersion; the method is suitable for the development and the adjustment opportunity of the prior magnet barrel plating, and is beneficial to the development of the magnet electroplating industry.

Drawings

FIG. 1 is a schematic view of a sintered NdFeB high-magnification microstructure.

FIG. 2 is a graph of the potential versus time of an NdFeB magnet in a 0.5mol/L oxalic acid pickling activation solution.

Detailed Description

The following describes specific embodiments of the present invention.

A fluorine-free electroplating process of a neodymium magnet comprises a neodymium magnet electroplating pretreatment tin immersion process, wherein the neodymium magnet electroplating pretreatment tin immersion process comprises the following steps of: deoiling a neodymium iron boron magnet → derusting and brightening → washing → treating 45g/L oxalic acid solution by RT for 30-60S → washing → dipping tin → washing → activating by 5% tartaric acid → washing → removing the bottom plating of an electroplating bath; in the step of deoiling the neodymium iron boron magnet, 70g/L of trisodium phosphate, 50g/L of sodium carbonate, 5g/L, OP-10 of sodium hydroxide, 0.5g/L of emulsifier and 30-40g/L of citric acid in the formula of deoiling liquid are completely deoiled on the surface of the neodymium iron boron magnet at the temperature of 65 ℃ and the pH value of 10.5; or alkaline chemical oil removal process is adopted, and the concentration of NaOH in the deoiled liquid is 6g/L, Na₂C0₃Has a concentration of 50g/L, Na₃PO₄The concentration of the uranium dodecyl sulfate is 70g/L, the concentration of the uranium dodecyl sulfate is 0.5g/L, the pH value is adjusted to 9-9.5 by formic acid, the temperature is 65-70 ℃, and auxiliary oil removal is carried out by ultrasonic waves.

In the rust removal and light extraction step: the formula of the pickling solution is 30-40mL/L of nitric acid and O.5g/L of thiourea, the pH value is 4-5 (adjusted by ammonia water), the temperature is room temperature, and the rust removal light-emitting time is 30-40S; pickling until the surface of the part is uniform, fine and glossy silvery white; wherein, thiourea in the formula plays a role in corrosion inhibition, and the PH value between ammonia water is because the ammonia water has a certain complexing effect on neodymium, so that the oxidation of the neodymium can be prevented; hydrochloric acid cannot be used because chlorine in hydrochloric acid reacts strongly with neodymium, causing corrosion to the magnet substrate.

In the step of immersion tin, often [ P ]₂O₇ ^4-]/[CO²⁺(or Ni)²⁺)+Sn²⁺]1 is added to (3.0-4.5). Taking the tin immersion liquid by 4 times, wherein the formula of the tin immersion liquid is stannous pyrophosphate Sn₂P₂O₇7g/L, potassium pyrok₄P₂O₇·3H₂36g/L of O, 5g/L of Rochelle salt, 10g/L of disodium hydrogen phosphate, 5g/L, DS 0.05.05 g/L, PEG 0.1.1 g/L, PEI 1.5.5 ml/L of sodium acetate, an oxygen removal stabilizer and p- (or m-) dihydroxybenzene, wherein the temperature is 30-40 ℃. The dihydroxybenzene is an antioxidant, the stable constant of the complex of the rochelle salt and the tin is almost the same as the stable constant equivalent of the stannous pyrophosphate, and the integral equilibrium potential is not influenced.

The process of tin immersion before neodymium magnet electroplating has the advantages that fluoride-containing treatment (fluorine influences post-electroplating liquid/fluorine is harmful to environment and human bodies) is needed in nickel immersion and zinc immersion processes can be avoided; and the low-temperature operation is used, the energy consumption and the environmental protection advantage are obvious, the tin concentration can be maintained by a titration analysis method, the popularization is convenient, and the potential of the 4-valent tin immersion electrode is as follows: [ Sn (OH)₆]^2-+2e-＝HSn0^2-+H ₂0+30H^--0.93；HSn0^2-+H₂O+2e-＝Sn+30H^--0.909; compared with the Nd-Fe-B magnet, the magnet is about-0.515V.

And (3) performing a technical analysis and a potential analysis: tin equilibrium acidity-0.1375V; co²⁺、Ni²⁺Formed complex [ Sn (P) ]₂O₇)₂]^6-、 [Co(P₂O₇)₂]^6-And [ Ni (P) ]₂O₇)₂]^6-Respectively, are 10^-7.2And 10^-8And 10^-7.4(ii) a At room temperature [ Sn (P) ]₂O₇)₂]^6-the/Sn equilibrium potential is-0.367V; equilibrium potential-0.382V at 40 ℃. The complexation degree is zinc pyrophosphate (1:2) complexation stability constant is 10(11 power exponent); (1:1) 10 (power of 8.7). The zinc pyrophosphate/zinc equilibrium potential is-0.76V. 3g/L of tin and 20g/L of free potassium pyrophosphate; the temperature was 40 ℃. Equilibrium potential-0.353V. 100 g potassium, 40 deg.C is balance potential-0.40V. 1.5 parts of tin; free potassium salt 40; the temperature was 40 ℃ and the equilibrium potential was-0.384V.

Since the oxidation potential before tin immersion of NdFeB magnet is (refer to the above mentioned) -0.4807V or-0.515V, [ Sn (P)₂O₇)₂]^6-the/Sn solution is reduced by the neodymium iron boron magnet with the oxidation potential of (-0.4807V or-0.515V) when the oxidation potential of the solution is-0.353V. I.e. a (wicking) reaction occurs which leaches the tin crystal metal layer.

The electroplating of the bottom layer after tin immersion of the neodymium iron boron magnet can be a cyanide-free non-coke copper process or a potassium chloride PH4-5 process, so that the available electroplating processes are enriched, and the processes (such as a potassium zinc chloride-nickel plating-silver (gold) replacing process; a copper-thickened coke copper-double-layer nickel process and the like) can be reasonably planned again; expanding the current route of nickel, copper and nickel and zinc dipping-zinc: the nickel-copper-nickel and zinc-immersion process line has unique plating seed formed by electroplating (such as nickel-immersion and zinc-immersion, fluorine-containing nickel closed chemical plating), non-broad-spectrum hardware electroplating seed plating, and small application range. By the invention, neodymium iron boron magnet electroplating is pushed into a broad-spectrum hardware electroplating (era) direction.

After tin immersion, the system of non-cyanide citric acid and tartaric acid with similar potential of balance electrode can be directly pre-plated for copper plating. Reports indicate that: the water solution of potassium sodium tartrate is used to dissolve acid, floating rust and passive film remained in surface pores due to acid cleaning on the surface, so as to obtain a cleaner surface, and the activated surface can directly deposit a bottom copper layer with good combination in a complex copper plating tank or a chemical copper plating tank without water washing. To be safe; the technical proposal adopts 5 percent tartaric acid to treat the tin-dipped layer.

Reports indicate that: the magnet hole sealing agent is prepared from oxyacid salt solution with PH 8-12 containing metal ions of copper group, zinc group and intermediate VIII subgroup (metal ions of IB, IIB and VIIB groups-nickel, palladium, platinum, ruthenium, iron, cobalt and manganese).

And (4) performing a technical analysis: the oxidation potential before tin immersion of the NdFeB magnet is (refer to the above mentioned) -0.4807V or-0.515V. The stability constant of the cupric citrate complex ion is the power exponent 10(19) grade under the alkaline environment, the stability constant of the cupric tartrate complex ion is the power exponent 10(20) grade, the calculated estimation value of the equilibrium potential of the cupric complex ion is-0.2618V (measured by the power exponent 19 times) at room temperature, and the calculated estimation value of the equilibrium potential of the cupric tartrate complex ion is-0.323V at 50 ℃, so the oxidation potential difference of the cupric citrate complex ion and the neodymium iron boron magnet before tin immersion is not large. However, for the purpose of bonding force, the charging operation is preferably carried out electrically. at-0.2618V and more negative potentials, the deposited tin cannot displace copper; the charging referred to herein is to avoid the interfacial oxidation potential- -copper substitution- -after oxalic acid treatment. Since the deposited film is thin, the interface after oxalic acid treatment needs to be considered. (tin is not oxidized in the air at normal temperature and becomes tin dioxide under strong heat-so that after chemical tin deposition, the tin can be directly connected into citric acid and tartaric acid complex alkaline copper plating and electroplating.)

The copper plating process after tin immersion treatment is a citric acid-tartaric acid copper plating process (barrel plating), and the formula of the electroplating solution of the citric acid-tartaric acid copper plating process comprises 31.25g/L of copper sulfate, 40g/L of potassium carbonate, 30g/L of citric acid, 110g/L of sodium citrate, 40g/L, PEG (M.W.6000) of rochelle salt, 0.08g/L of polyethylene glycol and polyethyleneimine (CH)₂CH₂NH)_n0.1g/L, 1.2mg/L, PPS 0.5.5-1 g/L of 2-thio-benzimidazole, 9-10.5 PH, 45-50 ℃.

After the pickling process, the proper oxalic acid assisted complex film passivation process, the tin immersion process, the citric acid-tartaric acid alkaline copper plating process and the subsequent electroplating process (such as copper-thickened pyrocopper-double-layer nickel, copper-common watt semi-gloss nickel-bright nickel-subsequent silver (gold/imitation gold/hard bright silver)/tin cobalt black, copper-thickened pyrocopper-imitation gold/silver replacement and the like) are reasonably planned again, so that the product line is enriched and enlarged.

Also comprises a potassium zinc chloride plating process (barrel plating) after the tin immersion treatment, and the formula of the used plating solution is KCl 180-₂ 65-75g/L、H₃BO₃25-35g/L, 14-18ml/L additive, and 4-5 PH; dk is 0.45-0.8A/dm². The potassium chloride zinc plating can not generate replacement zinc deposition, and the binding force is guaranteed. But attention is paid to the acidic environment + chloride attack. The combined pretreatment of acid pickling process under the condition of PH4-5, proper oxalic acid assisted complex film passivation uniformity and tin dipping is adopted, the combined pretreatment adapts to the environment of acid environment and chloride ion attack, the bonding force is ensured, and therefore the traditional high-temperature zinc (fluoride) dipping and potassium chloride zinc plating process can be replaced, and considerable economic and social benefits are obtained. (of course: potassium chloride zincate nickel alloys are equivalent to potassium chloride zincate; suitable for use in the tin immersion post-treatment of the present invention. after this text, any reference to potassium chloride zincate also includes potassium chloride zincate nickel alloys.)

After the pickling process, the proper oxalic acid assisted complex film passivation, the tin immersion and the potassium zinc chloride electroplating are carried out, the subsequent electroplating process (such as a potassium zinc chloride-nickel plating-silver replacing (gold plating/gold imitation) process, a potassium zinc chloride-double-layer nickel-gold imitation process, a potassium zinc chloride (with a certain thickness of 5 microns), an alkaline zinc nickel alloy plating-passivation and the like) can be reasonably planned again. The silver-substituting process is suitable for barrel plating precision film thickness processing, and is a WCS white tin copper alloy process, the gold-imitating process can be a traditional cyanide-containing process, and the gold-plating process can be a hard gold process and comprises a hard bright silver process. Entering into a wide combination mode plating.

And (3) experimental verification: 1) after different pretreatment processes, potassium zinc chloride is electroplated for comparison (shown in the following table);

wherein, in the rust removing process: 40ml/L of nitric acid and 0.5g/L of thiourea (ammonia and sulfuric acid are used for pH adjustment). In the process of activating No. 1, sulfosalicylic acid is 20-25g/L, NH₄10-15g/L of HF; room temperature; 30-40S. Oxalic acid vein relaxing H₂C₂0₄45 g/L; room temperature; 50-60S. Binding force (Cold-Heat cycle test), Hot-Cold cycleThe ring method (according to the American ASTNB571 standard and the national standard GB/T13913-1992) detects the binding force of a coating and a magnet so as to determine the optimal oxalic acid pickling activation process. The specific operation is that the NdFeB magnet electroplated with the NiWP alloy is directly placed into a muffle furnace at a high temperature of 220 ℃, is taken out after heat preservation is carried out for 1h, is immediately immersed into cold water as a hot-cold cycle, and is used for observing whether the surface of a sample has the phenomena of bubbling, peeling or falling off, and the maximum cycle frequency without the defects of cracking, peeling and the like is used as the thermal shock resistance index of the sample.

2) Carrying out magnet tin immersion, cyanide-free combined alkali copper pre-electroplating, neutral nickel electroplating and bright nickel electroplating tests;

the pretreatment is carried out by adopting the process No. 4 in the experiment 1), and then the pretreatment is carried out at 50 ℃, and Dk is 0.3-0.5A/dm²Barrel plating cyanide-free combined alkali copper plating copper layer 2 microns; barrel plating nickel in a neutral nickel plating bath for 0.8-1.25 microns: na (Na)₃C₆H₅O₇·2H₂O 150-180g/L， H₃BO₃ 35g/L，NiSO₄·6H₂O 120g/L，NiCl₂·6H₂O12 g/L, pH 7.0, Dk 0.25-0.55A/dm²At 50 ℃; barrel plating followed by thickening with nickel 2 microns.

As a result: the coating passes the test of the cold-hot cycle test and is qualified.

3) Performing magnet tin immersion, cyanide-free combined alkali copper pre-electroplating, neutral nickel electroplating and copper sulfate thickening test;

carrying out pretreatment by adopting the process No. 4 in the experiment 1), and then carrying out barrel plating on a cyanide-free combined alkali copper plated layer by 1.5 microns at 50 ℃ and Dk of 0.3-0.45A/dm 2; barrel plating nickel in a neutral nickel plating bath for 0.8-1.25 microns; the acid copper was then plated with 5 microns of copper.

4) Magnet tin immersion, cyanide-free combined alkali copper pre-electroplating, semi-bright nickel electroplating and bright nickel electroplating test 1 #;

carrying out pretreatment by adopting the process No. 4 in the experiment 1), and then carrying out barrel plating on a cyanide-free combined alkali copper plating layer by 0.5-0.6 micron at 50 ℃ and Dk of 0.3-0.5A/dm 2; nickel is barrel-plated in a matte nickel (PH 4.2-4.4) plating bath for 0.5-0.8 micron; and then plated with bright nickel 0.5 micron.

5) Magnet tin immersion, cyanide-free combined alkali copper pre-electroplating, semi-bright nickel electroplating and bright nickel electroplating test 2 #;

carrying out pretreatment by adopting the process No. 4 in the experiment 1), and then carrying out barrel plating on a cyanide-free combined alkali copper plating layer by 0.8-1.0 micron at 50 ℃ and Dk of 0.3-0.5A/dm 2; barrel plating semi-gloss nickel in a matte nickel (PH 4.2-4.4) plating bath for 2.5-3 microns; and plating bright nickel 1-1.5 microns.

As a result: the coating passes the test of the cold-hot cycle test and is qualified; NSS salt fog Pass 72 hrs.

6) Carrying out magnet tin immersion, cyanide-free combined alkali copper pre-electroplating, bright nickel electroplating and electroplating gun gray tin-cobalt alloy test;

carrying out pretreatment by adopting the process No. 4 in the experiment 1), and then carrying out barrel plating on a cyanide-free combined alkali copper plating layer by 0.5-0.6 micron at 50 ℃ and Dk of 0.3-0.45A/dm 2; bright nickel of 1.5-2 microns; rolling a tin cobalt gun to 0.4 micron, treating the gold and silver protective solution and drying.

It is then recommended to perform electroless nickel-P alloy plating (without fluorine).

7) Because the chemical nickel plating used for sealing the hole of the neodymium iron boron magnet at present contains a fluorine formula and the chemical nickel plating temperature of the positive plating is very high, the requirements on equipment, time, clean production and the like are limited, and the chemical nickel plating test is not described in the invention. It is stated that electroless nickel-P alloy plating (without fluorine) may be performed after the electroplated nickel layer (neutral nickel and other electroplated nickel: including nickel sulfamate plating) is obtained. The method comprises the following steps: the nickel plating layer + [ (sealing treatment before electroless plating) - -, can be omitted]+ fluorine-free chemical nickel plating. Sealing treatment before non-fluorinated nickel plating is preferably carried out by a nickel soaking method (nickel soaking: 70g/L of nickel acetate, 65g/L of boric acid and 170g/L of hydrofluoric acid at room temperature for 30s) or by using low-phosphorus, low-temperature and low-concentration weak alkaline chemical nickel plating for sealing. Formulation 1 of the blocking treatment: nickel sulfate (NiSO)₄·7H₂O)10-20 g/L; sodium hypophosphite (NaH)₂PO₂·H₂O)

10-15 g/L; sodium citrate (Na)₃C₆H₅O₇)25-30 g/L; lactic acid (C)₃H₆O₃)5-10 g/L; 1-2.5g/L of sodium fluoride (NaF); lead acetate (pb (CH)₃COO)₂·3H₂O)0.001 g/L; pH 7.5-8; the temperature is 40-50 ℃; the deposition speed is 3-5 μm/h.

Formulation 2 for sealing treatment Nickel fluoride (NiF)₂·4H₂O)30-40 g/L; fluoroboric acid (HBF)₄)50-60 g/L; 25-45g/L of free hydrofluoric acid (HF); the temperature was room temperature.

Electroless Nickel-Bright type Nickel chloride (NiCl)₂·6H₂O)25-35 g/L; sodium hypophosphite (NaH)₂PO₂·H₂O)15-20 g/L; sodium Hydroxyacetate (C)₂H₃NaO₃)5-10 g/L; butynediol (HOH)₃CC≡CCH₃OH)0.1-0.3 g/L; pH4.2-4.8; the temperature is 90+5 ℃.

The neodymium magnet electroplating pretreatment tin immersion process has a reasonable structure, a novel design and strong practicability, and is obtained by the tests 1-6, so that the neodymium magnet electroplating pretreatment tin immersion process achieves the effect of actual use requirements (rigor); the neodymium magnet electroplating pretreatment tin immersion process has the advantages that the problems that nickel immersion and zinc immersion processes need to be treated by fluoride and clean production is considered can be avoided, the tin immersion process is operated at room temperature to low temperature, the energy consumption and environmental protection advantages are possessed, the tin concentration can be maintained by a titration analysis method, and the tin immersion process can be conveniently popularized; the combination of the method and the system is reliable and practical by combining the cyanide-free combination of alkali copper pre-electroplating (system electroplating) or potassium chloride bottom electroplating (system electroplating) with high complexing stability; ensure binding force (tactical analysis match); better social and economic benefits are obtained by changing a fluorine-containing electroplating process system with poor environmental protection; product lines can be enriched, the thickness of a plating layer under an original fluorine-containing electroplating system can be properly reduced according to the 'anticorrosion theory' of electroplating coating protection on the surface of neodymium iron boron, and a better formula and a process path for reasonable tin immersion are designed; the method is suitable for the development and the adjustment opportunity of the prior magnet barrel plating, advances with time, and is beneficial to the development of the magnet electroplating industry.

The invention is based on the fact that the electroplating scheme which is more suitable for the strong neodymium magnet is discussed from the technical system, and comprises a plurality of module contents: 1) a surface pretreatment scheme suitable for the strong neodymium magnet and an optimized tin immersion process and flow. 2) The invention relates to an old strong neodymium magnet nickel copper nickel scheme, a nickel plus nickel scheme and a fluorine-free electroplating process and flow optimized after tin immersion. The nickel-soaking and fluorine-containing sealing nickel liquid of the old scheme contains fluorine; zinc impregnation is also inadequate (because of fluorine-containing; and high temperature). 3) The strong neodymium magnet galvanizing proposal and the extension optimization proposal electroplating process and flow. Provides an optimized scheme of strong neodymium magnet zinc plating, nickel plating and extension continuous silver (substitute) plating and even hard gold plating and a zinc base plating layer zinc-nickel alloy-converted electroplating process scheme. The tin immersion process (non-electrodeposition) and the cyanide-free non-pyrophosphate alkali copper plating process// the tin immersion process (non-electrodeposition) and the potassium chloride process are carried out by the invention; the two processes are arranged, so that the system reliability (the binding force is ensured) and the environmental protection (compared with the current fluorine scheme) of the strong neodymium magnet electroplated layer can be achieved, and certain economic and social benefits are obtained.

The invention particularly provides (1) a neodymium magnet electroplating pretreatment tin immersion process; (2) a cyanide-free non-pyrophosphate alkali copper plating process (a copper plating process after tin immersion treatment); (3) copper plating process after tin immersion treatment and conversion of semi-gloss nickel (expansion and direct) to fluorine-free chemical nickel plating process; (4) tin immersion (non-electrodeposition) and potassium chloride electroplating (and spreading). The electroplating theory of the strong neodymium magnet system is clearly combed by the method, and the electroplating scheme line and the products of the strong neodymium magnet are enriched by the scheme of the invention, and the method is a fluorine-free product line with reliability and environmental protection advantages, thereby obtaining environmental protection, economic benefit and social benefit.

The technical scope of the present invention is not limited to the above embodiments, and any modifications, equivalent variations and modifications made to the above embodiments according to the technical spirit of the present invention still fall within the technical scope of the present invention.

Claims

1. The fluorine-free electroplating process of the neodymium magnet is characterized by comprising a neodymium magnet electroplating pretreatment tin immersion process, wherein the neodymium magnet electroplating pretreatment tin immersion process comprises the following steps in sequence: deoiling a neodymium iron boron magnet → derusting and brightening → washing → treating 45g/L oxalic acid solution by RT for 30-60S → washing → dipping tin → washing → activating by 5% tartaric acid → washing → removing the bottom plating of an electroplating bath; wherein, in the step of tin immersion, the formula of the tin immersion liquid is pyrophosphoric acidTin (Sn)₂P₂O₇7g/L, potassium pyrok₄P₂O₇·3H₂O36g/L, Rochelle salt 5g/L, disodium hydrogen phosphate 10g/L, sodium acetate 5g/L, DS 0.05.05 g/L, PEG 0.1.1 g/L, PEI 1.5.5 ml/L, oxygen-removing stabilizer, and benzenediol at 30-40 deg.C.

2. A process for non-fluorine electroplating of neodymium magnet according to claim 1, wherein in the step of degreasing neodymium magnet, 70g/L trisodium phosphate, 50g/L sodium carbonate, 5g/L, OP-10 sodium hydroxide, 0.5g/L emulsifier, 30-40g/L citric acid are added to the degreasing fluid, and the oil on the surface of neodymium magnet is removed at 65 ℃ and pH 10.5; or alkaline chemical oil removal process is adopted, and the concentration of NaOH in the deoiled liquid is 6g/L, Na₂C0₃Has a concentration of 50g/L, Na₃PO₄The concentration of the uranium dodecyl sulfate is 70g/L, the concentration of the uranium dodecyl sulfate is 0.5g/L, the pH value is adjusted to 9-9.5 by formic acid, the temperature is 65-70 ℃, and auxiliary oil removal is carried out by ultrasonic waves.

3. A neodymium magnet fluorine-free electroplating process according to claim 2, wherein in the rust removing and brightening step: the formula of the pickling solution is 30-40mL/L of nitric acid and O.5g/L of thiourea, the pH value is 4-5 (adjusted by ammonia water), the temperature is room temperature, and the rust removal light-emitting time is 30-40S; pickling until the surface of the part is uniform, fine and glossy silvery white; among them, hydrochloric acid cannot be used.

4. The fluorine-free electroplating process for neodymium magnets according to claim 1, further comprising a copper plating process after tin immersion treatment, wherein the copper plating process after tin immersion treatment is a citric acid-tartaric acid copper plating process, and the formula of the electroplating solution of the citric acid-tartaric acid copper plating process comprises 31.25g/L copper sulfate, 40g/L potassium carbonate, 30g/L citric acid, 110g/L sodium citrate, 40g/L, PEG (M.W.6000) polyethylene glycol 0.08g/L Rochelle salt, and polyethyleneimine (CH)₂CH₂NH)_n0.1g/L, 1.2mg/L, PPS 0.5.5-1 g/L of 2-sulfenyl benzimidazole, 9-10.5 PH, 45-50 ℃.

5. The fluorine-free electroplating process for neodymium magnets according to claim 1, further comprising a process of plating zinc potassium chloride after tin immersion treatment, wherein the formula of the plating solution used is KCl 180-₂ 65-75g/L、H₃BO₃25-35g/L, 14-18ml/L of additive and 4-5 PH; dk is 0.45-0.8A/dm²。