Method for improving the bonding force of neodymium iron boron deposition layer based on reinforced ion exchange deposition technology

Abstract

The application provides a method for improving the bonding force of a neodymium iron boron deposition layer based on a reinforced ion exchange deposition technology, and belongs to the technical field of rare earth permanent magnet material preparation. The method comprises the following steps: neodymium iron boron magnet cleaning pretreatment, removing contaminants and metal oxides on the surface of the magnet; activating the neodymium iron boron magnet by acid corrosion to obtain a pretreated magnet with a rough surface; soaking the pretreated magnet in an electrolyte and connecting the magnet to a negative electrode; and performing ion exchange deposition on the surface of the magnet to be deposited by applying a pulse variable frequency electric field on the surface of the magnet to prepare a deposition layer; wherein, the surface of the magnet is first modified by micro-electrolysis, and then the ion exchange deposition is performed by applying a variable frequency electric field. In the initial stage, the surface of the magnet is continuously subjected to micro-electrolytic corrosion by a stable current to regulate the interface state and then realize surface modification, which is beneficial to the effective bonding of the deposition layer formed by the subsequent ion exchange deposition.

Description

Technical Field

[0001] This invention belongs to the technical field of rare earth permanent magnet material preparation, and specifically relates to a method for improving the bonding force of NdFeB deposition layers based on enhanced ion exchange deposition technology. Background Technology

[0002] Sintered neodymium iron boron (NdFeB) magnets, renowned for their superior magnetic properties, are widely used in aerospace, wind power generation, energy-saving appliances, electronics, and new energy vehicles. However, due to their unique multiphase structure and the differences in chemical properties between the phases, NdFeB rare-earth permanent magnets exhibit inherently insufficient corrosion resistance. In particular, the Nd-rich grain boundaries, which are prone to corrosion, preferentially undergo galvanic corrosion. The potential difference between the phases accelerates the corrosion and dissolution of the Nd-rich phase at the grain boundaries, causing the binding medium between the main phase grains inside the magnet to disappear, leading to the shedding of the main phase grains and even pulverization failure of the magnet. This increases the instability and safety risks of the material during service. Therefore, the application and development of NdFeB magnetic materials rely heavily on reliable corrosion protection technologies. Currently, the most common way to improve the corrosion resistance of NdFeB magnetic materials is to add an anti-corrosion deposition layer to their surface.

[0003] Currently, pulse electroplating is the main process for obtaining corrosion-resistant deposited layers on the surface of NdFeB magnets. It involves connecting a forward cathode pulse current and a reverse anode pulse current, repeating this process periodically. This method offers advantages such as reduced concentration polarization, high deposition efficiency, uniform and dense deposited layers with low porosity, high purity and smoothness, elimination of hydrogen embrittlement, good electrolyte dispersion, and excellent deep-plating capability. However, current coatings still suffer from poor adhesion. Coating adhesion is the most important indicator of electroplating performance; it refers to the bonding strength between the deposited layer and the base metal or intermediate deposited layer, i.e., the force required to peel the coating per unit surface area from the base metal or intermediate deposited layer.

[0004] Therefore, there is an urgent need for a method to improve the adhesion of coatings on the surface of NdFeB magnets. Summary of the Invention

[0005] Therefore, the present invention aims to provide a method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology, in order to solve at least one technical problem in the background art.

[0006] This invention is implemented as follows:

[0007] A method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology includes the following steps:

[0008] Neodymium iron boron magnet cleaning pretreatment removes contaminants and metal oxides from the magnet surface;

[0009] A pre-treated magnet with a rough surface is obtained by activating neodymium iron boron magnets through acid etching;

[0010] The pre-treated magnet is immersed in an electrolyte and connected to the negative electrode. A two-step process is used to prepare a deposition layer on the surface of the pre-treated magnet. The two-step process involves first applying surface micro-electrolytic corrosion and then performing ion exchange deposition under the action of a variable frequency electric field.

[0011] Preferably, the application of surface micro-electrolytic corrosion in the two-step treatment method involves the following operations:

[0012] Reverse current density 1-3 A / dm 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 30-60s.

[0013] Preferably, the parameters of the variable frequency electric field are: current density of 6-10 A / dm. 2 The operating frequency is 200-600Hz, and the duty cycle is 20-40%.

[0014] Preferably, the temperature for the two-step process is 45±5℃.

[0015] Preferably, the electrolyte is a nickel-based electrolyte; the nickel-based electrolyte contains at least the following components at concentrations: nickel sulfate 180-280 g / L; nickel chloride 20-40 g / L; boric acid 30-40 g / L; saccharin 0.6-1 g / L; 1,4-butynediol 0.2-0.5 g / L; coumarin 0.1-0.2 g / L; formaldehyde 0.1-0.2 g / L; sodium dodecyl sulfate 0.05-0.1 g / L.

[0016] Other corrosion-resistant electrolytes may also be used in this invention, such as epoxy resin electrolytes, zinc-based electrolytes, chromium-based electrolytes, or any other electrolytes permitted in the art for preparing coatings.

[0017] Preferably, the neodymium iron boron magnet cleaning pretreatment, which removes contaminants and metal oxides from the magnet surface, specifically includes:

[0018] The neodymium iron boron magnet was placed in an alkaline cleaning solution and cleaned at 65±5℃ to remove surface organic contaminants.

[0019] Clean the magnet to remove residual alkaline cleaning solution, then soak it in nitric acid to remove surface metal oxides and inorganic contaminants.

[0020] Preferably, the alkaline washing solution contains at least the following concentrations of components:

[0021] NaOH 5~10g / L;

[0022] Na2CO3 40~50g / L;

[0023] Na3PO4 40~60g / L;

[0024] OP-10 1~3g / L;

[0025] Sodium dodecyl sulfate 0.1–0.3 g / L.

[0026] Preferably, the acid corrosion activation step is as follows: first, the neodymium iron boron magnet is immersed in sulfuric acid; then, it is ultrasonically cleaned and dried with ethanol.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses an initial stable current to continuously perform micro-electrolytic corrosion on the magnet surface to regulate its interface state and thus achieve surface modification. This allows the magnet to change its original surface structure under the synergistic regulation of chemical and electrochemical effects, increase surface roughness, enhance the bonding force of the deposition layer, and improve the corrosion resistance of the deposition layer.

[0029] (2) Before deposition, the present invention uses alternating micro-electrolysis and electrodeposition on the NdFeB magnet to change the surface structure of the magnet while replacing some rare earth elements, thereby reducing the potential difference between the substrate and the deposition layer, reducing surface stress, enhancing the bonding force of the deposition layer, and improving the corrosion resistance of the deposition layer. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] A method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology, comprising the following steps:

[0032] S1. Neodymium iron boron magnet cleaning pretreatment to remove contaminants and metal oxides from the magnet surface;

[0033] First, the neodymium iron boron magnet is placed in an alkaline cleaning solution and cleaned at 65±5℃ for several minutes to remove surface organic contaminants. The alkaline cleaning solution contains at least: NaOH 5~10g / L; Na2CO3 40~50g / L; Na3PO4 40~60g / L; OP-10 1~3g / L; sodium dodecyl sulfate 0.1~0.3g / L.

[0034] Then, clean the magnet with deionized water to remove any residual alkaline cleaning solution;

[0035] Next, immerse the magnet in nitric acid (generally for no more than 1 minute), and then clean it with deionized water to remove metal oxides and inorganic contaminants from the surface.

[0036] The alkaline washing solution can be adjusted according to actual needs, and any cleaning solution permitted in this field can be used. The alkaline washing solution in the following examples comprises: NaOH 7.5 g / L; Na2CO3 45 g / L; Na3PO4 50 g / L; OP-10 2 g / L; sodium dodecyl sulfate 0.2 g / L.

[0037] S2. A pre-treated magnet with a rough surface is obtained by activating neodymium iron boron magnets through acid corrosion;

[0038] First, immerse the neodymium iron boron magnet in sulfuric acid for 5–30 seconds; then clean it with alcohol using ultrasound and dry it. Acid corrosion can create macroscopic roughness on the surface of the magnet.

[0039] S3. Immerse the pre-treated magnet in the electrolyte and connect it to the negative electrode. Prepare a deposition layer on the surface of the pre-treated magnet using a two-step process. The two-step process involves first applying surface micro-electrolytic corrosion and then performing ion exchange deposition under the action of a variable frequency electric field.

[0040] (1) Prepare the electrolyte

[0041] This invention can use any electrolyte capable of producing a corrosion-resistant coating, such as epoxy resin electrolyte, zinc-based electrolyte, chromium-based electrolyte, or any other electrolyte permitted in the art for preparing coatings. Considering cost and corrosion resistance, a nickel-based electrolyte is preferred in this invention.

[0042] Nickel-based electrolyte formulations include, but are not limited to, nickel sulfate 180–280 g / L, nickel chloride 20–40 g / L, boric acid 30–40 g / L, saccharin 0.6–1 g / L, 1,4-butynediol 0.2–0.5 g / L, coumarin 0.1–0.2 g / L, formaldehyde 0.1–0.2 g / L, and sodium dodecyl sulfate 0.05–0.1 g / L, prepared with deionized water. Reagents can also be added or component formulations adjusted based on the above nickel-based electrolyte to achieve deposition layers with different components. The nickel-based electrolyte formulation in the following examples is as follows: 230 g / L nickel sulfate, 30 g / L nickel chloride, 35 g / L boric acid, 0.8 g / L saccharin, 0.35 g / L 1,4-butynediol, 0.15 g / L coumarin, 0.15 g / L formaldehyde, and 0.07 g / L sodium dodecyl sulfate, prepared with deionized water.

[0043] Nickel sulfate and nickel chloride serve as the main salts, providing sufficient cations for the entire reaction. Boric acid, as an essential pH stabilizer in the electroplating process, maintains a stable electrolyte pH. Saccharin acts as a primary brightener in nickel plating, improving low-temperature areas, reducing metallic impurities, and lowering internal stress in the deposited layer, working synergistically with the main brightener to achieve a glossy finish. 1,4-Butynediol acts as a stabilizer and an promoter of adhesion and corrosion resistance. Coumarin reduces porosity in the deposited layer and increases brightness. Formaldehyde acts as a brightener, promoting a bright and fine deposited layer while reducing porosity. Sodium dodecyl sulfate acts as a wetting agent in the electrolyte, reducing the surface tension between the magnet and the electrolyte, thus improving the deposition effect.

[0044] (2) Surface micro-electrolysis

[0045] The pre-treated magnet after step S2 is placed in an electrolytic cell, electrolyte is introduced into the electrolytic cell, the pre-treated magnet is connected to the negative pole, the positive and negative poles are connected to the power supply, and the inside of the electrolytic cell is heated to 45±5℃.

[0046] In this invention, any positive electrode material permitted in the art can be used, such as an inert platinum sheet electrode, a graphite electrode, etc.; the following embodiments select a graphite sheet as the positive electrode;

[0047] Surface micro-electrolysis employs a relatively long and stable reverse pulse of current to continuously irradiate the magnet, further corroding it and thus modifying its surface. This enhances the adhesion of the subsequent ion exchange deposition layer. The process parameters are as follows: reverse current density 1-3 A / dm³. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 30-60s.

[0048] (3) Variable frequency electric field ion exchange deposition

[0049] Ion exchange deposition involves connecting a forward cathode pulse current and a reverse anode pulse current in a cyclical manner. During forward conduction, a large current promotes nucleation and growth, resulting in a dense, bright, and low-porosity deposition layer. During reverse conduction, a fixed small current is used to suppress excessively rapid grain growth, promote grain refinement, and etch sharp, coarse grains and potential defects on the cathode surface, improving the smoothness of the deposition layer.

[0050] To deposit a superior deposition layer, this step optimizes the pulse parameters, specifically: the pulse current density is 6-10 A / dm³. 2 The pulse operating frequency is 200-600Hz, and the pulse duty cycle is 20-40%; the total electrodeposition time for bidirectional pulses is 15-20 minutes.

[0051] Example 1

[0052] A method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology, using unmagnetized N40 commercial sintered NdFeB magnets as the prepared magnet, specifically includes the following steps:

[0053] 1. First, immerse the magnet in an alkaline cleaning solution at 65±5℃ and stir for 10 minutes to remove oil. The alkaline cleaning solution formula is: NaOH 7.5g / L; Na2CO3 45g / L; Na3PO4 50g / L; OP-10 2g / L; sodium dodecyl sulfate 0.2g / L. After cleaning and removing oil, rinse thoroughly with deionized water, then soak in a 6wt% HNO3 solution for 30 seconds, and finally rinse thoroughly with deionized water.

[0054] 2. Immerse the magnet in a 3wt% H2SO4 solution for 30 seconds, then ultrasonically clean it with anhydrous ethanol for 3 minutes to obtain the pretreated sintered NdFeB magnet.

[0055] 3. Place the pretreated sintered NdFeB magnet in a nickel-based electrolyte, with the magnet connected to the negative electrode and the graphite sheet used as the positive electrode. Control the electrolyte temperature at 45℃ and perform a two-step ion exchange deposition.

[0056] 3-1. Surface micro-electrolysis: Current density of 1 A / dm² when a reverse pulse is applied. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 60s.

[0057] 3-2. Variable frequency electric field ion exchange deposition: pulse current density is 10 A / dm³ 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the duty cycle is 30%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0058] 3-3 Finally, the nickel-plated sintered NdFeB magnets are sequentially cleaned in deionized water at 50°C and then ultrasonically cleaned in anhydrous ethanol.

[0059] The nickel-based electrolyte formula is as follows: 230 g / L nickel sulfate, 30 g / L nickel chloride, 35 g / L boric acid, 0.8 g / L saccharin, 0.35 g / L 1,4-butynediol, 0.15 g / L coumarin, 0.15 g / L formaldehyde, and 0.07 g / L sodium dodecyl sulfate, prepared with deionized water.

[0060] Example 2

[0061] This embodiment is a method for improving the bonding force of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the reverse pulse current density in step 3-1. The other parameters and conditions are the same as in Embodiment 1.

[0062] In this embodiment, 3-1, surface micro-electrolysis: the applied reverse pulse current density is 2A / dm. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 60s.

[0063] Example 3

[0064] This embodiment is a method for improving the bonding force of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the reverse pulse current density in step 3-1. The other parameters and conditions are the same as in Embodiment 1.

[0065] In this embodiment, 3-1, surface micro-electrolysis: the applied reverse pulse current density is 3A / dm. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 60s.

[0066] Example 4

[0067] This embodiment is a method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the reverse pulse processing time in step 3-1. The other parameters and conditions are the same as in Embodiment 1.

[0068] In this embodiment, 3-1, surface micro-electrolysis: the applied reverse pulse current density is 1 A / dm. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 30s.

[0069] Example 5

[0070] This embodiment is a method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the reverse pulse processing time in step 3-1. The other parameters and conditions are the same as in Embodiment 1.

[0071] In this embodiment, 3-1, surface micro-electrolysis: the applied reverse pulse current density is 1 A / dm. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 40s.

[0072] Example 6

[0073] This embodiment is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the reverse pulse processing time in step 3-1, while the other parameters and conditions are the same as in Embodiment 1.

[0074] In this embodiment, 3-1, surface micro-electrolysis: the applied reverse pulse current density is 1 A / dm. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 50s.

[0075] Example 7

[0076] This embodiment is a method for improving the bonding force of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the pulse current density in step 3-2, while the other parameters and conditions are the same as in Embodiment 1.

[0077] In this embodiment, 3-2, frequency conversion electric field ion exchange deposition: pulse current density is 6A / dm². 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the duty cycle is 30%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0078] Example 8

[0079] This embodiment is a method for improving the bonding force of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the pulse current density in step 3-2, while the other parameters and conditions are the same as in Embodiment 1.

[0080] In this embodiment, 3-2, frequency conversion electric field ion exchange deposition: pulse current density is 8A / dm². 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the duty cycle is 30%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0081] Example 9

[0082] This embodiment is a method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the pulse operating frequency in step 3-2, while the other parameters and conditions are the same as in Embodiment 1.

[0083] In this embodiment, 3-2, frequency conversion electric field ion exchange deposition: pulse current density is 10A / dm². 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 200Hz, and the duty cycle is 30%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0084] Example 10

[0085] This embodiment is a method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the pulse operating frequency in step 3-2, while the other parameters and conditions are the same as in Embodiment 1.

[0086] In this embodiment, 3-2, frequency conversion electric field ion exchange deposition: pulse current density is 10A / dm². 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 600Hz, and the duty cycle is 30%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0087] Example 11

[0088] This embodiment is a method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the pulse duty cycle in step 3-2, while the other parameters and conditions are the same as in Embodiment 1.

[0089] In this embodiment, 3-2, frequency conversion electric field ion exchange deposition: pulse current density is 10A / dm². 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the pulse duty cycle is 20%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0090] Example 12

[0091] This embodiment is a method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology. The difference between this embodiment and Embodiment 1 is the pulse duty cycle in step 3-2, while the other parameters and conditions are the same as in Embodiment 1.

[0092] In this embodiment, 3-2, frequency conversion electric field ion exchange deposition: pulse current density is 10A / dm². 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the pulse duty cycle is 40%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0093] Comparative Example 1

[0094] This comparative example is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this example and Example 1 is the reverse pulse processing time in step 3-1, while the other parameters and conditions are the same as in Example 1.

[0095] Comparative Example 3-1: Surface Micro-electrolysis: Current density of 4 A / dm² under reverse pulse application 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 60s.

[0096] Comparative Example 2

[0097] The method of this comparative example differs from that of Example 1 in that step 3-1 is omitted and ion exchange deposition is performed directly. The remaining parameters and conditions are the same as those of Example 1.

[0098] Comparative Example 3

[0099] The method of this comparative example differs from that of Example 1 in step 3-1, while the remaining parameters and conditions are the same as those of Example 1.

[0100] Comparative Example 3-1, Forward Pulse Electrodeposition: The applied forward pulse current density is 6 A / dm². 2 The forward conduction time is 1ms, the forward cutoff time is 1ms, and the processing time is 60s.

[0101] Comparative Example 4

[0102] The method of this comparative example differs from that of Example 1 in step 3-1, while the remaining parameters and conditions are the same as those of Example 1.

[0103] In this embodiment, 3-1, forward pulse electrodeposition: the applied forward pulse current density is 6 A / dm². 2 The forward conduction time is 1ms, the forward cutoff time is 1ms, and the processing time is 90s.

[0104] Comparative Example 5

[0105] This comparative example is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this example and Example 1 is the reverse pulse processing time in step 3-1, while the other parameters and conditions are the same as in Example 1.

[0106] Comparative Example 3-1, Surface Micro-electrolysis: Current density of 1 A / dm² applied by a reverse pulse. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 10s.

[0107] Comparative Example 6

[0108] This comparative example is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this example and Example 1 is the reverse pulse processing time in step 3-1, while the other parameters and conditions are the same as in Example 1.

[0109] Comparative Example 3-1, Surface Micro-electrolysis: Current density of 1 A / dm² applied by a reverse pulse. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 70s.

[0110] Comparative Example 7

[0111] This comparative example is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this example and Example 1 is the pulse current density in step 3-2, while the other parameters and conditions are the same as in Example 1.

[0112] Comparative Example 3-2: Variable frequency electric field ion exchange deposition: pulse current density 11 A / dm³ 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the duty cycle is 30%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0113] Comparative Example 8

[0114] This comparative example is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this example and Example 1 is the pulse operating frequency in step 3-2, while the other parameters and conditions are the same as in Example 1.

[0115] Comparative Example 3-2: Variable frequency electric field ion exchange deposition: pulse current density 10 A / dm³ 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 650Hz, and the duty cycle is 30%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0116] Comparative Example 9

[0117] This comparative example is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this example and Example 1 is the pulse duty cycle in step 3-2, while the other parameters and conditions are the same as in Example 1.

[0118] Comparative Example 3-2: Variable frequency electric field ion exchange deposition: pulse current density 10 A / dm³ 2The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the duty cycle is 15%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0119] Comparative Example 10

[0120] This comparative example is based on a method to improve the adhesion of NdFeB deposited layers using enhanced ion exchange deposition technology. The difference between this example and Example 1 is the pulse duty cycle in step 3-2, while the other parameters and conditions are the same as in Example 1.

[0121] Comparative Example 3-2: Variable frequency electric field ion exchange deposition: pulse current density 10 A / dm³ 2 The forward conduction time is 0.5ms, the forward cutoff time is 0.5ms, the pulse operating frequency is 400Hz, and the duty cycle is 45%; the reverse current density is 2A / dm³. 2 The reverse conduction time is 0.2ms, the reverse shutdown time is 0.5ms, and the processing time is 15min.

[0122] The neodymium iron boron magnets prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were tested, including the charge transfer resistance R. ct Corrosion potential E corr Corrosion current density I corr The corrosion inhibition efficiency and bonding strength were compared, with untreated sintered NdFeB magnets without deposits serving as a control group. The results are shown in Table 1.

[0123] Table 1. Performance comparison of deposition layers in various embodiments and comparative examples.

[0124]

[0125] As shown in Table 1, pulsed electrodeposition significantly enhances the corrosion resistance of the deposited layer. However, only by applying a surface micro-electrolysis current before ion exchange deposition can the bonding force of the NdFeB deposited layer be strengthened.

[0126] As can be seen from Examples 1 to 3, under the same deposition time, the adhesion of the deposited layer increases with the increase of the surface micro-electrolysis current density, but the charge transfer resistance R... ct Corrosion potential E corr Corrosion current density I corr Both corrosion inhibition efficiency and corrosion inhibition efficiency decreased slightly; when the surface micro-electrolysis current density increased to 3A / dm 2 The above is as shown in Comparative Example 1, 4A / dm 2The reduced adhesion of the deposited layer is due to excessive corrosion of the intergranular phases of the matrix magnetic material caused by excessive current density, leading to instability of the magnet surface structure; therefore, the initial surface micro-electrolysis current density was set to 1-3 A / dm³. 2 .

[0127] Comparative Example 2 directly used conventional ion exchange deposition, and the adhesion of its deposited layer was 13 MPa, which was far lower than the effect of surface micro-electrolysis applied in Example 1.

[0128] As can be seen from Comparative Examples 3 and 4, applying a positive pulse current before ion exchange deposition does not enhance the bonding force; on the contrary, it weakens the bonding force of the deposited layer. This is because the bonding effect of the nickel layer deposited by simply applying a positive current on a flat substrate is weaker than that on a surface treated with micro-electrolysis.

[0129] As can be seen from Comparative Example 5, if the surface micro-electrolysis application time is too short, although it can increase the adhesion of the deposited layer, the effect is not good.

[0130] As can be seen from Comparative Example 6, if the surface micro-electrolysis application time is too long, the adhesion of the deposited layer, the charge transfer resistance Rct, the corrosion potential Ecorr, the corrosion current density Icorr, and the corrosion inhibition efficiency all decrease slightly compared to Example 1. This is because the excessively long current application time also causes the magnet surface to show an unstable trend.

[0131] The neodymium iron boron magnets prepared in Examples 1, 7 to 12, and Comparative Examples 7 to 10 were tested, including the charge transfer resistance R. ct Corrosion potential E corr Corrosion current density I corr The corrosion inhibition efficiency and bonding strength were compared, with untreated sintered NdFeB magnets without deposits serving as a control group. The results are shown in Table 2.

[0132] Table 2 Performance comparison of deposition layers in various embodiments and comparative examples

[0133]

[0134] Combining Tables 1 and 2, it can be seen from Examples 1, 7, and 8 that as the frequency conversion electric field current density increases, the adhesion of the deposited layer decreases slightly, but the charge transfer resistance R... ct Corrosion potential E corr Corrosion current density I corr Both corrosion inhibition efficiency and corrosion inhibition efficiency are improved to a certain extent; when the pulse current density increases to 10A / dm 2 The above, as shown in Comparative Example 7, is 11A / dm 2 The performance of the deposited layers deteriorates because excessively high current densities are not conducive to the formation of dense deposits; therefore, the preferred forward pulse current density is 6-10 A / dm³.2 .

[0135] As can be seen from Examples 1, 9 to 10, the performance of the deposited layer is optimal at 400 Hz as the positive pulse frequency increases. When the pulse frequency density increases to above 600 Hz, such as 650 Hz as shown in Comparative Example 8, the performance of the deposited layer begins to decline because the high frequency of the variable frequency electric field is not conducive to the formation of the deposited layer. Therefore, the preferred positive pulse frequency is 200-600 Hz.

[0136] As can be seen from Examples 1, 11 to 12 and Comparative Examples 9 to 10, different positive pulse duty cycles affect the corrosion resistance of NdFeB magnet deposits. When the positive pulse duty cycle is 20 to 40%, the impedance of the deposit increases and the corrosion resistance is better. As the duty cycle continues to increase, the performance of the deposit decreases significantly.

[0137] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology, characterized in that, The method includes the following steps: Neodymium iron boron magnet cleaning pretreatment removes contaminants and metal oxides from the magnet surface; A pre-treated magnet with a rough surface is obtained by activating neodymium iron boron magnets through acid etching; The pre-treated magnet is immersed in an electrolyte and connected to the negative electrode. A two-step process, combining surface micro-electrolytic corrosion and ion exchange deposition, is used to prepare a deposition layer on the surface of the pre-treated magnet. First, surface micro-electrolytic corrosion is applied to strengthen the magnet surface, and then a variable frequency electric field is applied to enhance ion exchange deposition. The surface micro-electrolytic etching in the two-step process is performed as follows: reverse current density 1-3 A / dm 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 30-60 seconds. The variable frequency electric field parameters are: forward current density of 6-10 A / dm. 2 The forward operating frequency is 200-600Hz, and the duty cycle is 20-40%; the reverse current density is 1-3 A / dm³. 2 The reverse conduction time is 1ms, the reverse cutoff time is 1ms, and the processing time is 30-60s.

2. The method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology according to claim 1, characterized in that, The temperature for the two-step process is 45±5℃.

3. The method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology according to claim 1, characterized in that, The electrolyte is a nickel-based electrolyte; The nickel-based electrolyte contains at least the following components at concentrations: Nickel sulfate 180~280 g / L; Nickel chloride 20~40 g / L; Boric acid 30~40g / L; Saccharin 0.6~1 g / L; 1,4-Butynediol 0.2~0.5 g / L; Coumarin 0.1~0.2 g / L; Formaldehyde 0.1~0.2 g / L; Sodium dodecyl sulfate 0.05~0.1g / L.

4. The method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology according to claim 1, characterized in that, The neodymium iron boron magnet cleaning pretreatment removes contaminants and metal oxides from the magnet surface, specifically including: The neodymium iron boron magnet was placed in an alkaline cleaning solution and cleaned at 65±5℃ to remove surface organic contaminants. Clean the magnet to remove residual alkaline cleaning solution, then soak it in nitric acid to remove surface metal oxides and inorganic contaminants.

5. The method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology according to claim 4, characterized in that, The alkaline washing solution contains at least the following components at concentrations: NaOH 5~10g / L; Na2CO3 40~50g / L; Na3PO4 40~60g / L; OP-10 1~3g / L; Sodium dodecyl sulfate 0.1~0.3 g / L.

6. The method for improving the adhesion of NdFeB deposited layers based on enhanced ion exchange deposition technology according to claim 1, characterized in that, The acid corrosion activation steps are as follows: first, the neodymium iron boron magnet is immersed in sulfuric acid; then, it is ultrasonically cleaned and dried with ethanol.

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