阅读说明：本技术 一种钕铁硼磁体复合镀层及其制备方法 (Neodymium-iron-boron magnet composite coating and preparation method thereof ) 是由 李志强 刘艳 魏蕊 于 2020-12-25 设计创作，主要内容包括：本发明公开一种钕铁硼磁体的复合镀层及其制备方法。复合镀层至少包括两种镀层：第一镀层和第二镀层,其中所述第一镀层为含有镍、铜和锌中至少一种金属的镀层,所述第二镀层为锡镍锌三元合金镀层。本发明提供的用于钕铁硼磁体的复合镀层,可以进一步提高钕铁硼磁体产品的耐腐蚀性能、耐湿热性,镀层与磁体表面、镀层与镀层之间的结合力优异,且镀层并几乎不会影响磁体的磁性能。整体制备过程具有操作简易、维护方便,环保性强、生产效率高等优点。复合镀层的耐蚀性较好(SST可达到300h以上),耐湿热性能可达到3000h以上。(The invention discloses a composite coating of a neodymium iron boron magnet and a preparation method thereof. The composite coating at least comprises two coatings: the plating layer comprises a first plating layer and a second plating layer, wherein the first plating layer is a plating layer containing at least one metal of nickel, copper and zinc, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer. The composite coating for the neodymium iron boron magnet provided by the invention can further improve the corrosion resistance and the humidity resistance of a neodymium iron boron magnet product, the binding force between the coating and the surface of the magnet and between the coating and the coating is excellent, and the coating hardly influences the magnetic property of the magnet. The whole preparation process has the advantages of simple operation, convenient maintenance, strong environmental protection, high production efficiency and the like. The composite plating layer has good corrosion resistance (SST can reach more than 300 h), and the damp-heat resistance can reach more than 3000 h.)

1. The composite coating of the neodymium iron boron magnet is characterized by at least comprising a tin-nickel-zinc ternary alloy coating.

2. The composite coating of claim 1, wherein the composite coating is a tin-nickel-zinc ternary alloy coating. Preferably, the number of the tin-nickel-zinc ternary alloy coating layers is one, two or more. Preferably, the thickness of the single-layer tin-nickel-zinc ternary alloy coating is 2-25 μm.

Preferably, the composite coating comprises at least two coatings: the plating layer comprises a first plating layer and a second plating layer, wherein the first plating layer is a plating layer containing at least one metal of nickel, copper and zinc, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer.

Preferably, the first plating layer is at least one layer of an alloy plating layer of at least two metals of nickel, copper and zinc, or at least one layer of a single metal plating layer of nickel, copper or zinc.

Preferably, the thickness of the first plating layer is 2 to 20 μm.

Preferably, the thickness of the second plating layer is 2 to 25 μm.

3. The composite plating layer as claimed in claim 1 or 2, wherein the ternary tin-nickel-zinc alloy comprises, in mass%, 5 to 70 wt% of zinc, 10 to 35 wt% of nickel, and 15 to 70 wt% of tin.

4. A neodymium iron boron magnet, characterized in that it contains a composite coating according to any one of claims 1 to 3.

Preferably, the first plating layer is in contact with the neodymium iron boron magnet and the second plating layer is in contact with the first plating layer.

5. The method for preparing a composite coating layer of a neodymium-iron-boron magnet according to any one of claims 1 to 3, characterized by comprising the following steps: preparing a first plating layer on the surface of a neodymium iron boron magnet, and preparing a second plating layer on the surface of the first plating layer;

the first and second coating layers have the meaning as defined in claim 2 or 3.

6. The preparation method of claim 5, wherein the surface of the NdFeB magnet is pretreated before the first plating layer is prepared on the surface of the NdFeB magnet. For example, the pretreatment includes degreasing, derusting, and/or activating the surface of the ferroboron magnet.

7. The method according to claim 5 or 6, wherein the first and/or second coating is produced by electrodeposition, electroless plating or PVD, preferably electrodeposition.

Preferably, the Dk is in the range of 0.5-1.5A/dm when the first coating is prepared by electrodeposition²。

Preferably, the Dk is in the range of 0.4-2.0A/dm when the second coating is prepared by electrodeposition²。

8. The production method according to any one of claims 5 to 7, wherein the plating solution of the first plating layer is a plating solution containing at least one metal element of nickel, copper, and zinc, preferably a nickel plating solution, a nickel-plated copper alloy solution.

Preferably, the plating solution of the first plating layer contains main salt, an activating agent and optionally at least one of a conductive agent, a buffering agent, a cylinder opening agent, a leveling agent and a wetting agent.

Preferably, the main salt is selected from at least one of the sulfates of nickel, copper and zinc or their hydrated sulfates. Preferably, the content of the main salt in the plating solution of the first plating layer is 180-400 g/L.

Preferably, the activator is selected from chlorides, such as at least one of the hydrochlorides of sodium, potassium, nickel, copper and zinc or their hydrated hydrochlorides. Preferably, in the plating solution of the first plating layer, the content of the activating agent is 0.1-80 g/L.

Preferably, the conductive agent is selected from at least one of sulfuric acid, hydrochloride, and hydrochloride hydrate. Preferably, in the plating solution of the first plating layer, the concentration of the first conductive salt is 15 to 45 g/L.

Preferably, the buffer is selected from H₃BO₃. Preferably, in the plating solution of the first plating layer, the content of the buffer is 30-60 g/L.

Preferably, the biscuit release agent is selected from one, two or more of sulfonamide, sulfimide, formaldehyde and polysulfide organic sulfonate. Preferably, in the plating solution of the first plating layer, the content of the cylinder opener is 2-9 ml/L.

Preferably, the leveling agent is selected from one or two of sodium perborate, 1, 4-butynediol and ethylene thiourea. Preferably, in the plating solution of the first plating layer, the content of the leveling agent is 0.1-1.5 ml/L.

Preferably, the wetting agent is selected from one, two or more of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate and OP emulsifier. Preferably, in the plating solution of the first plating layer, the content of the wetting agent is 0.5-5 ml/L.

Preferably, the pH value of the plating solution of the first plating layer is 3.5-5.0.

9. The production method according to any one of claims 5 to 8, wherein interlayer activation and water washing are required before the second plating layer is produced on the first plating layer.

Preferably, the activation and interlayer activation in the pretreatment are performed using an activation solution.

Preferably, the tin-nickel-zinc ternary alloy plating solution used for the second plating layer comprises the following components: the conductive tin sulfate comprises tin sulfate or sulfate hydrate thereof, nickel sulfate or sulfate hydrate thereof, zinc sulfate or sulfate hydrate thereof, a complexing agent, a conductive salt and a wetting agent.

Preferably, the sulfate of tin is SnSO₄. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of tin sulfate or sulfate hydrate thereof is 8-12 g/L.

Preferably, the sulfate hydrate of nickel is NiSO₄·6H₂And O. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of the sulfate of the nickel or the sulfate hydrate thereof is 10-20 g/L.

Preferably, the sulfate hydrate of zinc is ZnSO₄·7H₂And O. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of the sulfate of the nickel or the sulfate hydrate thereof is 40-80 g/L.

Preferably, the complexing agent is selected from C₆H₅Na₃O₇·2H₂O and C₄H₆O₆One or two of them. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of the complexing agent is 90-150 g/L.

Preferably, the conductive salt is selected from KCl and/or Na₂SO₄. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of the conductive salt is 5-10 g/L.

Preferably, the wetting agent is selected from one, two or more of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate and OP emulsifier. Preferably, the content of the wetting agent in the tin-nickel-zinc ternary alloy plating solution is 0.5-2 g/L.

Preferably, the pH value of the tin-nickel-zinc ternary alloy plating solution is 6.5-7.5.

Preferably, the preparation method further comprises: and after the second coating is prepared, washing and drying the neodymium iron boron magnet.

10. The method for producing a neodymium-iron-boron magnet according to claim 4, comprising the method for producing the composite plating layer according to any one of claims 5 to 9.

Technical Field

The invention belongs to the technical field of neodymium iron boron magnet corrosion prevention, and particularly relates to a neodymium iron boron magnet composite coating and a preparation method thereof.

Background

Based on the advantages of the neodymium iron boron, the neodymium iron boron is widely applied to industries such as information technology, automobiles, motors, wind power, hybrid electric vehicles and the like. The neodymium-iron-boron magnet is a product of powder metallurgy, because the electrode potentials of various neodymium-rich phases, boron-rich phases and main phases of the neodymium-iron-boron magnet are different, electrochemical corrosion is easily caused, neodymium is one of elements with high chemical activity, corrosion is easily caused, and poor corrosion resistance of the outer surface is one of the key defects of the neodymium-iron-boron magnet. Therefore, before application, the neodymium-iron-boron magnet must be surface-treated to prevent corrosion.

The surface treatment method of the general neodymium iron boron magnet comprises phosphorization, electrodeposition, electrophoresis, spraying, physical vapor deposition and the like. Conventional electrodeposition coatings include nickel, nickel-copper-nickel, zinc-nickel alloy-copper-nickel, and the like.

The nickel plating layer has high porosity, so the corrosion resistance can be improved only by increasing the thickness of the plating layer, but the nickel plating layer has too thick thickness, which not only influences the magnetic performance, but also highlights the corner effect, and seriously influences the product assembly.

Double-layer nickel plating, generally semi-bright nickel is a columnar structure, bright nickel is a layered structure, so the corrosion resistance of the double-layer nickel is better than that of single-layer nickel, but the problem of low corrosion resistance caused by high porosity of the nickel cannot be avoided.

The corrosion resistance of the product is improved due to the addition of copper with better compactness in the nickel-copper-nickel coating structure, but the improvement is limited, and the requirement of high corrosion resistance can not be met for the product with higher corrosion resistance requirement.

The zinc-nickel alloy in the zinc-nickel alloy-copper-nickel coating structure replaces semi-bright nickel in the nickel-copper-nickel coating structure, the influence on the magnetic property can be reduced, the bonding force with a substrate is far better than that of nickel and the substrate, but the zinc-nickel alloy is difficult to clean and easy to bring impurities to a copper plating solution, and the zinc is more active than the copper, so that the zinc-nickel alloy can be generated in the copper plating solutionZn²⁺Impurities affect the plating performance of copper, are complex to produce and maintain, and bring troubles to stable production.

In patent document CN 103326005a, a tin-nickel-zinc ternary alloy soft porous material applied to a negative electrode of a lithium ion battery and a preparation method thereof are disclosed, wherein a tin-nickel-zinc ternary alloy is obtained on the surface of a soft porous conductive material, and then a relatively active metal is selectively corroded by corrosion, so as to obtain the porous material. However, the method cannot be directly applied to magnetic materials such as neodymium iron boron and the like, and iron and even neodymium in the neodymium iron boron magnet can be corroded in the process of selectively corroding the active metal, so that the structure of the magnet is damaged, and the corrosion resistance of the magnet is influenced. And the porous structure obtained by corroding the coating is extremely favorable for the storage capacity and the service life of the lithium ion battery, but for the neodymium iron boron magnet, the corrosion resistance of the magnet can be influenced, the integrity of the coating can be damaged, and the service life of the magnet can be influenced.

Patent document CN 102276245a discloses a nickel-zinc soft magnetic ferrite material and a preparation method thereof, wherein the main formula comprises iron oxide Fe in molar parts₂O₃45-50 mol%, 26-32 mol% of zinc oxide ZnO, 17-21 mol% of nickel protoxide NiO and 4-8 mol% of copper oxide CuO; meanwhile, in the main formula, 0.2-0.5 wt% of auxiliary material A and 0.1-0.2 wt% of auxiliary material B are added according to the weight percentage, wherein the auxiliary material A is Bi₂O₃、SiO₂、Ta₂O₅One or two of the auxiliary materials B is TiO₂、V₂O₅、Nb₂O₅One or more of them. The obtained nickel-zinc soft magnetic ferrite material has the characteristics of high frequency, high magnetic conductivity, high Bs and high TC.

Patent document CN107502929A discloses electroplating tin-nickel-zinc ternary alloy on the surface of stainless steel material, the obtained coating has bright and flat surface, good binding property with stainless steel matrix, small internal stress of coating, and good binding property with its outer continuous film layer, cardiac glycoside and aluminum isopropoxide synergistic effect can improve the anti-tarnishing ability of the film layer, polysilazane modified resin and filler etc. combined effect, so that the scratch resistance of the surface is significantly improved, and the application range of stainless steel shelf can be enlarged.

Disclosure of Invention

The invention provides a composite coating of a neodymium iron boron magnet, which at least comprises a tin-nickel-zinc ternary alloy coating.

According to the embodiment of the invention, the composite coating is a tin-nickel-zinc ternary alloy coating. For example, the number of layers of the tin-nickel-zinc ternary alloy plating layer may be one, two or more. Illustratively, the composite coating is a tin-nickel-zinc ternary alloy coating with one layer. For example, the thickness of the single layer tin-nickel-zinc ternary alloy coating is 2-25 μm, such as 4-20 μm, illustratively 2 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 45 μm, 20 μm.

According to an embodiment of the invention, the composite coating comprises at least two coatings: the plating layer comprises a first plating layer and a second plating layer, wherein the first plating layer is a plating layer containing at least one metal of nickel, copper and zinc, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer.

According to an embodiment of the invention, the first coating layer is at least one layer of an alloy coating of at least two metals of nickel, copper and zinc, or at least one layer of a single metal coating of nickel, copper or zinc, preferably at least one layer of a single metal coating of nickel, copper or zinc, or at least one layer of an alloy coating of nickel and copper; further preferred is at least one layer of a single metal plating of nickel or at least one layer of an alloy plating of nickel and copper.

According to an embodiment of the invention, the thickness of the first plating layer is 2-20 μm, preferably 4-10 μm, exemplarily 2 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 45 μm, 20 μm. If the first plating layer is too thin, the corrosion resistance of the magnet is not good, and if the first plating layer is too thick, the corner effect is large.

According to an embodiment of the invention, the thickness of the second plating layer is 2-25 μm, preferably 4-10 μm, exemplarily 2 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 15 μm, 20 μm, 25 μm.

According to the embodiment of the invention, in the tin-nickel-zinc ternary alloy, the zinc content is 5-70 wt%, the nickel content is 10-35 wt% and the tin content is 15-70 wt% in percentage by mass. For example, the zinc content is 30 to 65 wt%, the nickel content is 12 to 30 wt%, and the tin content is 20 to 50 wt% in mass%. Illustratively, in the tin-nickel-zinc ternary alloy, the zinc content is 55.97 wt%, the nickel content is 16.38 wt%, and the tin content is 27.65 wt% in percentage by mass.

According to an exemplary aspect of the invention, the composite coating comprises two coatings: the first plating layer is a nickel layer with the thickness of 10 mu m, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer with the thickness of 10 mu m;

or the first plating layer is a nickel layer with the thickness of 4 mu m, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer with the thickness of 4 mu m;

or the first plating layer is a nickel layer with the thickness of 2 mu m, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer with the thickness of 2 mu m;

or the first plating layer is a nickel layer with the thickness of 20 mu m, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer with the thickness of 25 mu m;

or the first plating layer contains a nickel layer with the thickness of 5 mu m and a copper layer with the thickness of 5 mu m, and the second plating layer is a tin-nickel-zinc ternary alloy plating layer with the thickness of 10 mu m.

According to an exemplary embodiment of the present invention, the composite coating is a tin-nickel-zinc ternary alloy coating with a thickness of 20 μm.

The invention also provides a neodymium iron boron magnet containing the composite coating. Preferably, the first plating layer is in contact with the neodymium iron boron magnet, and the second plating layer is in contact with the first plating layer.

The invention also provides a preparation method of the composite coating of the neodymium iron boron magnet, which comprises the following steps: preparing a first plating layer on the surface of the neodymium iron boron magnet, and preparing a second plating layer on the surface of the first plating layer;

the first and second plating layers have the meaning as described above.

According to the embodiment of the invention, the surface of the neodymium iron boron magnet is also subjected to pretreatment before the first plating layer is prepared on the surface of the neodymium iron boron magnet. For example, the pretreatment includes degreasing, derusting and/or activating the surface of the iron boron magnet, and after each process of degreasing, derusting and activating is completed, the neodymium iron boron magnet needs to be washed by water.

According to an embodiment of the present invention, the degreasing treatment may be performed on the surface of the ferroboron magnet using a degreasing liquid. For example, the degreasing fluid is non-foaming and non-phosphorus normal-temperature degreasing fluid. For another example, the time for the degreasing treatment is 60-200s, and preferably 100-150 s.

According to the embodiment of the invention, the rust removal can be performed by treating the surface of the degreased ferroboron magnet by using dilute nitric acid. For example, the dilute nitric acid has a concentration of 1 to 10% by volume, preferably 1 to 6% by volume. For example, the time of the rust removing treatment is 10 to 300s, preferably 30 to 200 s.

According to an embodiment of the present invention, the first and/or second coating layer may be prepared by methods known in the art, such as electrodeposition, electroless plating or PVD (physical vapor deposition) and the like, preferably electrodeposition.

Preferably, Dk (cathode current density) is in the range of 0.5-1.5A/dm for the electrodeposition preparation of the first coating layer²。

According to an embodiment of the present invention, the plating solution of the first plating layer is a plating solution containing at least one metal element of nickel, copper, and zinc, and preferably a nickel plating solution and a copper plating solution.

According to the embodiment of the invention, the plating solution of the first plating layer contains main salt, an activating agent and at least one of a conductive agent, a buffering agent, a cylinder opening agent, a leveling agent and a wetting agent which optionally contains or does not contain the main salt and the activating agent.

Wherein the main salt can be selected from at least one of sulfates of nickel, copper and zinc or hydrated sulfates thereof, such as NiSO₄·6H₂O。

Preferably, in the plating solution of the first plating layer, the content of the main salt is 180-400g/L, such as 320g/L, 350g/L, 380g/L, 400 g/L.

Wherein the activator may be selected from chlorides, such as at least one of the hydrochlorides of sodium, potassium, nickel, copper and zinc or their hydrated hydrochlorides, for example NiCl₂·6H₂And O. Preferably, the activator is contained in the plating solution of the first plating layer in an amount of 0.1 to 80g/L, for example, 40 to 70g/L,exemplary are 50g/L, 60 g/L.

Wherein the conductive agent may be selected from at least one of sulfuric acid, sulfate and hydrated sulfate, such as NaSO₄. For example, the concentration of the conductive agent in the plating solution of the first plating layer is 15 to 45 g/L.

Wherein the buffer may be selected from H₃BO₃. Preferably, the content of the buffer in the plating solution of the first plating layer is 30-60g/L, such as 40-50g/L, and exemplary 45 g/L.

Wherein, the cylinder opener can be selected from one, two or more of sulfamide, sulfimide, formaldehyde, polysulfide organic sulfonate and the like. Preferably, the content of the cylinder opener in the plating solution of the first plating layer is 2-9ml/L, such as 3ml/L, 4ml/L, 5ml/L, 6ml/L, 7ml/L, and 8 ml/L.

Wherein, the filling agent can be one or two selected from sodium perborate, 1, 4-butynediol, ethylene thiourea and the like. Preferably, the content of the leveling agent in the plating solution of the first plating layer is 0.1-1.5ml/L, for example, 0.5-1.0 ml/L.

Wherein, the wetting agent may be selected from one, two or more of sodium dodecylbenzene sulfonate, sodium dodecylsulfate, OP emulsifier, and the like. Preferably, the content of the wetting agent in the plating solution of the first plating layer is 0.5-5ml/L, such as 1-4ml/L, and is exemplarily 2ml/L and 3 ml/L.

Preferably, the plating solution of the first plating layer comprises the following components: 400g/L of main salt 300, 30-80g/L of activating agent, 30-60g/L of buffering agent, 2-9ml/L of cylinder opener agent, 0.1-1.5ml/L of filling agent and 0.5-5ml/L of wetting agent.

According to an embodiment of the invention, the pH of the bath of the first coating is 3.5-5.0, such as 3.5, 4.0, 4.5, 5.0.

Illustratively, the plating solution comprises the following components: main salt NiSO₄·6H₂O300-₂·6H₂O30-80 g/L, buffer H₃BO₃30-60g/L, 2-9ml/L of a jar opener, 0.1-1.5ml/L of a flatting agent and 0.5-5ml/L of a wetting agent. Preferably, the plating solutionThe pH value is 3.5-5.0.

According to an embodiment of the present invention, interlayer activation and water washing are required before the second plating layer is prepared on top of the first plating layer.

According to an embodiment of the present invention, the activation in the pretreatment and the interlayer activation may be performed using an activation solution. Preferably, the activating solution contains 1-5% of acid, 0.5-1.5g/L of corrosion inhibitor and 0.5-1.5g/L of surfactant by mass concentration; preferably, the acid is citric acid, the corrosion inhibitor is thiourea, and the surfactant is sodium dodecyl benzene sulfonate. Illustratively, the activating solution contains 3.5% by mass of citric acid, 1g/L of thiourea and 1g/L of sodium dodecyl benzene sulfonate.

Preferably, the time of the activation treatment in the pretreatment and the time of the interlayer activation treatment are the same or different, for example, 5 to 15 seconds each.

According to the embodiment of the invention, the tin-nickel-zinc ternary alloy plating solution used for the second plating layer comprises the following components: the conductive tin sulfate comprises tin sulfate or sulfate hydrate thereof, nickel sulfate or sulfate hydrate thereof, zinc sulfate or sulfate hydrate thereof, a complexing agent, a conductive salt and a wetting agent.

Wherein the sulfate of tin may be SnSO₄. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of tin sulfate or sulfate hydrate thereof is 8-12g/L, such as 8g/L, 9g/L, 10g/L, 11g/L and 12 g/L.

Wherein the sulfate hydrate of nickel may be NiSO₄·6H₂And O. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of the sulfate of nickel or the sulfate hydrate thereof is 10-20g/L, such as 10g/L, 12g/L, 14g/L, 15g/L, 18g/L and 20 g/L.

Wherein the sulfate hydrate of zinc may be ZnSO₄·7H₂And O. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of the sulfate of nickel or the sulfate hydrate thereof is 40-80g/L, such as 40g/L, 50g/L, 60g/L, 70g/L and 80 g/L.

Wherein the complexing agent may be selected from C₆H₅Na₃O₇·2H₂O and C₄H₆O₆One or two of (tartaric acid). Preferably, the content of the complexing agent in the tin-nickel-zinc ternary alloy plating solution is 90-150g/L, preferably 100-140g/L, and exemplarily 100g/L, 110g/L, 120g/L, 125g/L, 130g/L and 140 g/L.

Wherein the conductive salt can be selected from KCl and/or Na₂SO₄. Preferably, in the tin-nickel-zinc ternary alloy plating solution, the content of the conductive salt is 5-10g/L, such as 5g/L, 6g/L, 7g/L, 8g/L, 9g/L and 10 g/L.

Wherein the wetting agent is selected from one, two or more of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and OP emulsifier. Preferably, the content of the wetting agent in the tin-nickel-zinc ternary alloy plating solution is 0.5-2g/L, such as 1g/L, 1.5g/L and 2 g/L.

According to an embodiment of the invention, the pH of the tin-nickel-zinc ternary alloy plating solution is 6.5 to 7.5, for example 6.5, 6.6, 6.8, 7.0, 7.2, 7.5.

Preferably, the tin-nickel-zinc ternary alloy plating solution contains the following components: SnSO₄ 8-12g/L，NiSO₄·6H₂O 10-20g/L，ZnSO₄·7H₂40-80g/L of O, 90-150g/L of complexing agent, 5-10g/L of conductive salt and 0.5-2g/L of wetting agent.

According to an embodiment of the invention, the Dk ranges from 0.4 to 2.0A/dm when the second coating is prepared by electrodeposition²。

According to an embodiment of the invention, the water wash is at least one rinse or ultrasonic water wash.

According to an embodiment of the invention, the preparation method further comprises: and after the second coating is prepared, washing and drying the neodymium iron boron magnet.

The invention also provides a preparation method of the neodymium iron boron magnet containing the composite coating, which comprises the preparation method of the composite coating.

The invention has the beneficial effects that:

the composite coating for the neodymium iron boron magnet provided by the invention can further improve the corrosion resistance and the humidity resistance of a neodymium iron boron magnet product, the binding force between the coating and the surface of the magnet and between the coating and the coating is excellent, and the coating hardly influences the magnetic property of the magnet. The whole preparation process has the advantages of simple operation, convenient maintenance, strong environmental protection, high production efficiency and the like.

The obtained composite plating layer has good corrosion resistance, the SST can reach more than 300h, and the damp-heat resistance can reach more than 3000 h.

Drawings

Fig. 1 is a surface electron microscope photograph of the nickel-tin-nickel-zinc composite plating layer prepared in example 1.

FIG. 2 is the surface energy spectrum of the ternary alloy of Sn-Ni-Zn in the composite coating of example 1.

Detailed Description

The technical solution of the present invention will be further described in detail with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

Unless otherwise indicated, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.

The following examples and comparative examples all use a 20mm × 10mm × 4mm square neodymium iron boron product, the electrodeposition is performed in a barrel plating manner, and the pretreatment process of the neodymium iron boron product before electrodeposition is as follows:

step one, degreasing: degreasing the neodymium iron boron product by adopting a non-foaming and non-phosphorus normal-temperature degreasing liquid for 120 s;

step two, washing twice with water;

thirdly, derusting: carrying out rust removal treatment on the degreased product by using dilute nitric acid with the volume concentration of 5%, wherein the treatment time is 40 s;

fourthly, after rust removal is finished, ultrasonic water washing and water washing are carried out on the product;

fifthly, activation: after the fourth step is finished, activating the derusted neodymium iron boron product by using an activating solution, wherein the activating solution consists of 3.5 wt% of citric acid, 1g/L of thiourea and 1g/L of sodium dodecyl benzene sulfonate, and the activating time is 12 s;

and sixthly, washing twice to obtain the pretreated neodymium iron boron product.

The thickness of the plating layers in the following examples and comparative examples refers to the thickness of the center point of the composite plating layer.

Wherein, the SST experimental test conditions are as follows: and at the temperature of 35 ℃, the concentration of the NaCl aqueous solution is 50g/L +/-5 g/L, the pH value is between 6.5 and 7.2, salt mist is deposited on the composite plating neodymium iron boron product to be detected in a spraying mode, and the time in the table 1 is the time when the plating layer begins to rust.

The testing conditions of the damp-heat experiment are that the composite coating neodymium-iron-boron product is placed in a closed environment with the temperature of 85 ℃ and the humidity of 85% RH, and the corrosion condition of the coating is observed. The wet heat result time in table 1 is the time when the coating starts to rust.

Example 1

Preparing a composite coating on the surface of the pretreated neodymium iron boron product, wherein the preparation process comprises the following steps:

step one, electrodepositing nickel on the surface of the pretreated neodymium iron boron product: the nickel plating solution comprises NiSO₄·6H₂O 350g/L，NiCl₂·6H₂O 50g/L，H₃BO₃45g/L, 5ml/L of sulfamide, 1ml/L of 1, 4-butynediol and 2ml/L of sodium dodecyl sulfate;

dk (cathode current density) is in the range of 1.0-1.2A/dm²；

Secondly, washing the neodymium iron boron product with the nickel layer plated on the surface twice after the nickel plating;

thirdly, interlayer activation: after the second step of water washing is finished, carrying out interlayer activation on the nickel-plated neodymium iron boron product, wherein the interlayer activation is the same as the activation process in the pretreatment;

step four, after the step three is finished, washing the product twice;

fifthly, electrodepositing the ternary alloy of tin, nickel and zinc: the composition of the plating solution is SnSO₄ 8g/L，NiSO₄·6H₂O 13g/L，ZnSO₄·7H₂O 70g/L，C₆H₅Na₃O₇·2H₂O 125g/L，C₄H₆O₆26g/L, KCl 9g/L and sodium dodecyl sulfate 1 g/L;

dk (cathode current density) is in the range of 1.0-1.2A/dm²；

Sixthly, after the fifth step is finished, washing the neodymium iron boron product with the tin-nickel-zinc ternary alloy layer plated on the nickel layer twice;

seventhly, drying;

and step eight, drying to obtain the neodymium iron boron product with the nickel-tin-nickel-zinc composite coating.

Examples 1 to 1

Through the preparation process in the embodiment 1, the total thickness of the obtained nickel-tin-nickel-zinc composite plating layer is 20 μm, wherein the thickness of the nickel layer is 10 μm, and the thickness of the tin-nickel-zinc ternary alloy layer is 10 μm. Wherein the current densities of the nickel layer and the tin-nickel-zinc layer are both 1.0-1.2A/dm²The electrodeposition time of the nickel layer is 60min, and the electrodeposition time of the tin-nickel-zinc layer is 55 min.

As shown in figure 1, the surface of the nickel-tin-nickel-zinc composite coating is flat and compact.

As shown in fig. 2, in the tin-nickel-zinc ternary alloy layer, the content of Ni element was 16.38 wt%, the content of Zn element was 55.97 wt%, and the content of Sn element was 27.65 wt%.

Examples 1 to 2

Through the preparation process in the embodiment 1, the total thickness of the obtained nickel-tin-nickel-zinc composite plating layer is 8 μm, wherein the thickness of the nickel layer is 4 μm, and the thickness of the tin-nickel-zinc ternary alloy layer is 4 μm. Wherein the current densities of the nickel layer and the tin-nickel-zinc layer are both 1.0-1.2A/dm²The electrodeposition time of the nickel layer is 25min, and the electrodeposition time of the tin-nickel-zinc layer is 20 min.

Examples 1 to 3

Through the preparation process in the embodiment 1, the total thickness of the obtained nickel-tin-nickel-zinc composite plating layer is 4 μm, wherein the thickness of the nickel layer is 2 μm, and the thickness of the tin-nickel-zinc ternary alloy layer is 2 μm. Wherein the current densities of the nickel layer and the tin-nickel-zinc layer are both 1.0-1.2A/dm²The electrodeposition time of the nickel layer is 10min, and the electrodeposition time of the tin-nickel-zinc layer is 10min。

Examples 1 to 4

Through the preparation process in the embodiment 1, the total thickness of the obtained nickel-tin-nickel-zinc composite plating layer is 45 μm, wherein the thickness of the nickel layer is 20 μm, and the thickness of the tin-nickel-zinc ternary alloy layer is 25 μm. Wherein the current densities of the nickel layer and the tin-nickel-zinc layer are both 1.0-1.2A/dm²The electrodeposition time of the nickel layer is 120min, and the electrodeposition time of the tin-nickel-zinc layer is 135 min.

Comparative example 1

The total thickness of the nickel-tin-nickel-zinc plating layer obtained by the process treatment in the embodiment 1 is 3 μm, wherein the thickness of the nickel layer is 1.5 μm, and the thickness of the tin-nickel-zinc ternary alloy is 1.5 μm. Wherein the current densities of the nickel layer and the tin-nickel-zinc layer are both 1.0-1.2A/dm²The electrodeposition time of the nickel layer is 9min, and the electrodeposition time of the tin-nickel-zinc layer is 8 min.

Example 2

Preparing a composite coating on the surface of the pretreated neodymium iron boron product, wherein the preparation process comprises the following steps:

step one, electrodepositing nickel on the surface of the pretreated neodymium iron boron product: the nickel plating solution comprises NiSO₄·6H₂O 350g/L，NiCl₂·6H₂O 50g/L，H₃BO₃45g/L, 5ml/L of sulfamide, 1ml/L of 1, 4-butynediol and 2ml/L of sodium dodecyl sulfate;

dk (cathode current density) is in the range of 1.0-1.2A/dm²；

Secondly, washing the neodymium iron boron product with the nickel layer plated on the surface twice after the nickel plating;

thirdly, interlayer activation: after the second step of water washing is finished, carrying out interlayer activation on the nickel-plated neodymium iron boron product, wherein the interlayer activation is the same as the activation process in the pretreatment;

step four, after the step three is finished, washing the product twice;

fifthly, electrodepositing copper by adopting a conventional method, wherein the main salt is CuSO₄·5H₂O。

Dk (cathode current density) is in the range of 1.2-1.5A/dm²；

Sixthly, after the fifth step is finished, washing the neodymium iron boron product sequentially plated with the nickel layer and the copper layer twice;

seventhly, interlayer activation: after the sixth step of water washing is finished, interlayer activation is carried out on the nickel-plated neodymium iron boron product, and the activation process in the pretreatment is the same as that in the step of water washing;

eighthly, washing twice after interlayer activation;

and ninthly, electrodepositing the tin-nickel-zinc ternary alloy: the plating solution consists of SnSO₄ 8g/L，NiSO₄·6H₂O 13g/L，ZnSO₄·7H₂O 70g/L，C₆H₅Na₃O₇·2H₂O 125g/L，C₄H₆O₆26g/L, KCl 9g/L and sodium dodecyl sulfate 1 g/L;

dk (cathode current density) is in the range of 1.2-1.5A/dm²；

Step ten, after the step ninth, washing the neodymium iron boron product sequentially plated with the ternary alloy layers of the nickel layer, the copper layer and the tin-nickel-zinc layer twice;

step eleven, drying;

and step eleven, drying to obtain the neodymium iron boron product with the nickel-copper-tin-nickel-zinc composite coating.

The composite plated nd-fe-b products obtained in examples 1-1 to 1-4, example 2 and comparative example 1 were subjected to corrosion resistance and wet heat resistance tests, and the test results are shown in table 1.

TABLE 1

The results in table 1 show that the corner effect and the salt spray resistance and damp-heat resistance of the different coating thicknesses in examples 1-1 to 1-4 and comparative example 1 are different, and the thinner the coating is, the worse the salt spray resistance and damp-heat resistance is, and the thicker the coating is, the larger the corner effect is. The combination of properties is best for the products of examples 1-1 and 2.

The results in Table 1 show that the corner effect, the salt spray resistance and the damp-heat resistance are equivalent to each other for the same film thickness in the case of comparing the example 1-1 with the example 2.

Example 3

Preparing a composite coating on the surface of the pretreated neodymium iron boron product, wherein the preparation process comprises the following steps:

step one, electrodepositing a tin-nickel-zinc ternary alloy on the surface of the pretreated neodymium iron boron product: the composition of the plating solution is SnSO₄ 8g/L，NiSO₄·6H₂O 13g/L，ZnSO₄·7H₂O 70g/L，C₆H₅Na₃O₇·2H₂O 125g/L，C₄H₆O₆26g/L, KCl 9g/L and sodium dodecyl sulfate 1 g/L;

dk (cathode current density) is in the range of 1.0-1.2A/dm²The electrodeposition time was 110 min.

Step two, after the step five is finished, washing the product with the tin-nickel-zinc ternary alloy layer plated on the neodymium iron boron twice;

thirdly, drying;

and fourthly, drying to obtain the neodymium iron boron product with the tin-nickel-zinc composite coating, wherein the thickness of the coating is 20 microns.

Comparative example 2

Plating a nickel layer on the surface of the pretreated neodymium iron boron product, wherein the treatment process is as follows:

step one, electrodepositing nickel on the surface of the pretreated neodymium iron boron product: the nickel plating solution consists of NiSO₄·6H₂O 350g/L，NiCl₂·6H₂O 50g/L，H₃BO₃45g/L, 5ml/L of sulfamide, 1ml/L of 1, 4-butynediol and 2ml/L of sodium dodecyl sulfate;

dk (cathode current density) is in the range of 1.0-1.2A/dm²；

Secondly, washing the neodymium iron boron product with the nickel layer plated on the surface twice after the nickel plating;

thirdly, drying;

and fourthly, drying to obtain the neodymium iron boron product with the surface plated with the nickel layer, wherein the thickness of the plating layer is 20 microns.

Comparative example 3

Plating a nickel-nickel layer on the surface of the pretreated neodymium iron boron product, and the process is as follows:

step one, electrodepositing nickel on the surface of the pretreated neodymium iron boron product: the nickel plating solution consists of NiSO₄·6H₂O 350g/L，NiCl₂·6H₂O 50g/L，H₃BO₃45g/L, 5ml/L of sulfamide, 1ml/L of 1, 4-butynediol and 2ml/L of sodium dodecyl sulfate;

dk (cathode current density) is in the range of 1.0-1.2A/dm²；

Secondly, washing the neodymium iron boron product with the nickel layer plated on the surface twice after the nickel plating;

thirdly, carrying out secondary nickel electrodeposition, and carrying out the same operation as the first step;

fourthly, after the secondary nickel plating is finished, washing the neodymium iron boron product with the nickel-nickel layer plated on the surface twice;

fifthly, drying;

and sixthly, drying to obtain the neodymium iron boron product with the surface plated with the nickel-nickel layer, wherein the total thickness of the plating layer is 20 mu m.

Comparative example 4

Plating a nickel-copper-nickel layer on the surface of the pretreated neodymium iron boron product, wherein the process is as follows:

step one, electrodepositing nickel on the surface of the pretreated neodymium iron boron product: the nickel plating solution consists of NiSO₄·6H₂O 350g/L，NiCl₂·6H₂O 50g/L，H₃BO₃45g/L, 5ml/L of sulfamide, 1ml/L of 1, 4-butynediol and 2ml/L of sodium dodecyl sulfate;

dk (cathode current density) is in the range of 1.0-1.2A/dm²；

Secondly, washing the neodymium iron boron product with the nickel layer plated on the surface twice after the nickel plating;

thirdly, after the second step of water washing is finished, carrying out interlayer activation on the nickel-plated neodymium iron boron product, wherein the interlayer activation is the same as the activation process in the pretreatment;

step four, after the step three is finished, washing the product twice;

fifthly, electrodepositing copper: the composition of the copper plating solution was the same as in example 2;

sixthly, washing the product plated with the nickel-copper layer twice;

seventhly, performing interlayer activation on the product plated with the nickel-copper layer after washing, wherein the activation treatment is the same as the third step;

eighthly, washing the product twice after the seventh step;

step nine, electrodepositing nickel again: the operation is the same as the first step;

step ten, after the nickel plating is finished, washing the neodymium iron boron product with the surface plated with nickel-copper-nickel twice;

step eleven, drying;

and step eleven, drying to obtain the neodymium iron boron product with the surface plated with nickel-copper-nickel, wherein the total thickness of the plating layer is 20 microns.

Comparative example 5

Plating a zinc-nickel-copper-nickel layer on the surface of the pretreated neodymium iron boron product, wherein the process is as follows:

firstly, performing conventional electrodeposition of zinc on the surface of the pretreated neodymium iron boron product, wherein the main salt is ZnSO₄·7H₂O。

Dk (cathode current density) is in the range of 1.2-1.5A/dm²；

Secondly, washing the neodymium iron boron product with the zinc layer plated on the surface twice after the zinc plating is finished;

thirdly, emitting light;

fourthly, washing the product twice after finishing the light extraction;

fifthly, electrodepositing zinc-nickel alloy on the neodymium iron boron product with the surface plated with the zinc layer, wherein the zinc-nickel alloy plating solution is alkaline and consists of zinc²⁺Nickel, nickel²⁺Sodium hydroxide, complexing agent and additive;

dk (cathode current density) is in the range of 3.5-4.0A/dm²；

Sixthly, washing the neodymium iron boron product with the surface plated with zinc-zinc nickel twice after the zinc-nickel plating is finished;

seventhly, interlayer activation: after the sixth step of washing, carrying out interlayer activation on the zinc-nickel-neodymium-iron-boron plated product, wherein the interlayer activation is the same as the activation process in the pretreatment;

eighthly, washing the product twice after the seventh step;

step nine, electrodepositing copper on the neodymium iron boron product with the surface plated with the zinc-zinc nickel layer, wherein the operation of copper plating is the same as the fifth step in the embodiment 2;

step ten, after the copper plating is finished, washing the zinc-nickel-copper plated neodymium iron boron product twice;

step ten, interlayer activation: after the tenth step of water washing is finished, carrying out interlayer activation on the zinc-nickel-copper plated neodymium iron boron product, wherein the interlayer activation is the same as the activation process in the pretreatment;

step ten, after step seven, washing the product twice;

step ten, electrodepositing nickel on the zinc-nickel-copper plated neodymium iron boron product, wherein the operation of nickel plating is the same as the first step in the embodiment 1;

fourteenth, washing the product twice after the thirteenth step;

fifteenth, drying;

sixthly, drying to obtain the neodymium iron boron product with the surface plated with the zinc-nickel-copper-nickel layer, wherein the total thickness of the plating layer is 20 microns.

TABLE 2

Wherein the thickness of the plating layer is the total thickness; the binding force is the shearing force tested by a mechanical testing machine, and the binding force between the coating and the substrate and between the coating layers meets the requirements.

The results in Table 2 show that the corrosion resistance of example 1-1 is better than that of example 3, the salt spray resistance and the wet heat resistance of the plating layers of examples 1-1 and 3 are obviously better than those of each comparative example, and the influence on the magnetic flux is smaller than that of the comparative example.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.