A surface protection method for NdFeB magnets

Abstract

The present invention discloses a surface protection method for NdFeB magnets, comprising the following steps: step one, polishing the surface of the NdFeB magnet; step two, cutting the iron-based amorphous alloy strip according to the surface size of the NdFeB magnet to be protected; step three, laying the iron-based amorphous alloy strip prepared in step two on the upper and lower surfaces corresponding to the magnet; step four, welding the iron-based amorphous alloy strip and the NdFeB magnet together by using a spark plasma sintering method; step five, rotating the magnet, repeating steps three and four, welding the other four surfaces of the NdFeB magnet with the iron-based amorphous alloy strip. The surface protection method of the present invention is environmentally friendly, does not generate pollutants, is simple and convenient, and is suitable for large-scale promotion and application; the iron-based amorphous alloy strip has high magnetic permeability, and as a protective layer, it will not reduce the magnetic field strength of the NdFeB magnet, and its interior has good corrosion resistance due to the absence of grain boundaries; the iron-based amorphous alloy strip has high hardness, good toughness, and excellent wear resistance.

Description

Technical Field

[0001] The invention belongs to a surface protection method for rare earth permanent magnetic materials, in particular to a surface protection method for neodymium iron boron magnets. Background Art

[0002] Rare earth permanent magnet NdFeB material is the type of permanent magnet material with the highest magnetic energy product at present, and has been widely used in new energy vehicles, wind power generation, variable frequency air conditioners and other fields. my country has a unique advantage in rare earth resources. At present, the annual output of NdFeB magnets is nearly 200,000 tons, providing more than 90% of the global supply of NdFeB magnets.

[0003] Sintered NdFeB magnets are composed of a matrix phase and a rare earth-rich phase at the grain boundary. The rare earth-rich phase at the grain boundary has high chemical activity and poor corrosion resistance. In order to prevent sintered NdFeB magnets from being damaged and failing due to corrosion during use, the industry currently generally uses electroplating to protect the magnets by electroplating metal layers such as zinc, nickel, and chromium on the surface of the magnets.

[0004] However, electroplating is a highly polluting industry that is subject to key supervision by environmental protection departments. The electroplating process of sintered NdFeB magnets will inevitably have adverse effects on the environment. Moreover, in the coating metals of sintered NdFeB magnets, except for the nickel coating, the rest are non-magnetic metal coatings. Non-magnetic coatings will reduce the magnetic field strength of the magnet and are not conducive to the performance of magnetic properties. In addition, due to its low hardness, the metal coating is easy to wear during use. Summary of the invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a surface protection method for NdFeB magnets which does not reduce the magnetic field strength and has good corrosion resistance.

[0006] Technical solution: The surface protection method of a NdFeB magnet of the present invention comprises the following steps:

[0007] Step 1: Grind the surface of the NdFeB magnet clean;

[0008] Step 2, cutting the iron-based amorphous alloy strip according to the surface size of the NdFeB magnet to be protected;

[0009] Step 3, laying the iron-based amorphous alloy ribbon prepared in step 2 on the upper and lower surfaces corresponding to the magnet;

[0010] Step 4, welding the iron-based amorphous alloy strip and the NdFeB magnet together;

[0011] Step 5: rotate the magnet, repeat steps 3 and 4, and weld the other four surfaces of the NdFeB magnet to the iron-based amorphous alloy strip.

[0012] Furthermore, in step 1, the grinding is performed using SiC sandpapers of No. 400, No. 600 and No. 800 in sequence. The NdFeB magnet is a sintered NdFeB magnet with an average grain size of 3 to 10 μm.

[0013] Furthermore, in step 2, the iron-based amorphous alloy ribbon is made of any one of 1K101, 1K102, 1K103, 1K104, 1K105, 1K106, and 1K107. The thickness of the iron-based amorphous alloy ribbon is 25µm to 30µm.

[0014] Furthermore, in step 4, the welding is spark plasma sintering welding, and the vacuum degree of spark plasma sintering welding is ≤1×10 -2 Pa, the applied pressure is 1~20Mpa, the sintering temperature range is 450~530℃, and the sintering time is 2~10min. When the sintering temperature is higher than 530℃, the iron-based amorphous alloy ribbon will crystallize and the protective effect will be reduced. When the sintering temperature is lower than 450℃, the grain boundary phase of the NdFeB magnet will not melt and welding cannot occur.

[0015] Protection principle: Iron-based amorphous alloy ribbon is a kind of soft magnetic material with the highest magnetic permeability at present. Using iron-based amorphous alloy ribbon as a protective layer can minimize the reduction of the magnetic field strength of the NdFeB magnet by the surface protective layer; the iron-based amorphous alloy ribbon is prepared by rapid quenching process, and the internal atoms maintain the disordered state of liquid state, there is no grain boundary, and intergranular corrosion will not occur. At the same time, the internal components of the amorphous alloy are evenly distributed, there is no component segregation, there is no potential difference between different parts, and electrochemical corrosion is not easy to occur. In addition, the high hardness and wear resistance of amorphous alloys also provide better mechanical protection for the surface of magnets than existing pure metal coatings.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0017] 1. The surface protection method is environmentally friendly, does not produce pollutants, is simple and convenient, and provides a new method for surface protection of NdFeB magnets. The promotion and application of this technology will not only improve the performance of NdFeB magnets, but also reduce the pollution of the traditional electroplating process to the environment.

[0018] 2. Iron-based amorphous alloy ribbon is currently the best soft magnetic material with high magnetic permeability. As a protective layer, the iron-based amorphous alloy ribbon will not reduce the magnetic field strength of the NdFeB magnet;

[0019] 3. Since there is no grain boundary inside the iron-based amorphous alloy ribbon and the composition is evenly distributed, its corrosion resistance is far better than the metal coating currently used in NdFeB magnets;

[0020] 4. The iron-based amorphous alloy strip has high hardness, good toughness and excellent wear resistance. Its mechanical protection effect on the surface of magnets is far better than traditional metal coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of the present invention;

[0022] Figure 2 It is a backscattered electron image at the welding interface 3 of the present invention. DETAILED DESCRIPTION

[0023] In the following embodiments, the welding device used is an existing one. The NdFeB magnet 1 is a commercial sintered NdFeB magnet 1 with an average grain size of 3 to 10 μm.

[0024] Example 1

[0025] like Figure 1 , a surface protection method for a NdFeB magnet 1, comprising the following steps:

[0026] Step 1: Select a commercial magnet blank with the grade N52, the size of which is 20×20×10mm. 3 , polish the surface of the NdFeB magnet 1 clean;

[0027] Step 2: Select a commercial iron-based amorphous alloy ribbon 2 with a grade of 1K101 and a thickness of 25 μm, and cut the iron-based amorphous alloy ribbon 2 into 20×20 mm pieces according to the surface size of the NdFeB magnet 1 to be protected. 2 2 sheets, 20×10mm 2 4 slices of thin slices;

[0028] Step 3: Prepare the 20×20 mm 2 The iron-based amorphous alloy thin strip 2 is laid on the upper and lower surfaces corresponding to the magnet;

[0029] Step 4: In 1×10 -2 Under a vacuum degree of 1.50 MPa, a uniaxial pressure of 20 MPa was applied, and the Fe-based amorphous alloy ribbon 2 and the NdFeB magnet 1 were welded together by spark plasma sintering technology. The sintering temperature was controlled at 450°C and the sintering time was 10 min.

[0030] Step 5: rotate the magnet, and repeat steps 3 and 4 to weld the other four surfaces of the NdFeB magnet 1 to the Fe-based amorphous alloy strips 2 of corresponding sizes.

[0031] Example 2

[0032] A surface protection method for a NdFeB magnet 1 comprises the following steps:

[0033] Step 1: Select a commercial magnet blank with the grade N48, the size of which is 20×20×20mm. 3 , polish the surface of the NdFeB magnet 1 clean;

[0034] Step 2: Select a commercial iron-based amorphous alloy ribbon 2 with a grade of 1K102 and a thickness of 30 μm, and cut the iron-based amorphous alloy ribbon 2 into 20×20 mm pieces according to the surface size of the NdFeB magnet 1 to be protected. 2 6 slices of thin slices;

[0035] Step 3: Prepare the 20×20 mm 2 The iron-based amorphous alloy thin strip 2 is laid on the upper and lower surfaces corresponding to the magnet;

[0036] Step 4: In 5×10 -3 Under a vacuum degree of 1000 Pa, a uniaxial pressure of 1 MPa was applied, and the Fe-based amorphous alloy thin strip 2 and the NdFeB magnet 1 were welded together by spark plasma sintering technology, the sintering temperature was controlled at 530°C, and the sintering time was 2 min;

[0037] Step 5: rotate the magnet, and repeat steps 3 and 4 to weld the other four surfaces of the NdFeB magnet 1 to the Fe-based amorphous alloy strips 2 of corresponding sizes.

[0038] Example 3

[0039] A surface protection method for a NdFeB magnet 1 comprises the following steps:

[0040] Step 1: Select a commercial magnet blank with a grade of 45H. The size of the blank is 10×10×10mm. 3 , polish the surface of the NdFeB magnet 1 clean;

[0041] Step 2: Select a commercial iron-based amorphous alloy ribbon 2 with a grade of 1K103 and a thickness of 27 μm, and cut the iron-based amorphous alloy ribbon 2 into 10×10 mm pieces according to the surface size of the NdFeB magnet 1 to be protected. 2 6 slices of thin slices;

[0042] Step 3: Prepare the 10×10 mm 2 The iron-based amorphous alloy thin strip 2 is laid on the upper and lower surfaces corresponding to the magnet;

[0043] Step 4: In 8×10 -3 Under a vacuum degree of 1000 Pa, a uniaxial pressure of 10 MPa was applied, and the Fe-based amorphous alloy ribbon 2 and the NdFeB magnet 1 were welded together by spark plasma sintering technology, the sintering temperature was controlled at 475°C, and the sintering time was 7 minutes;

[0044] Step 5: rotate the magnet, and repeat steps 3 and 4 to weld the other four surfaces of the NdFeB magnet 1 to the Fe-based amorphous alloy strips 2 of corresponding sizes.

[0045] Example 4

[0046] A surface protection method for a NdFeB magnet 1 comprises the following steps:

[0047] Step 1: Select a commercial magnet blank with the grade of 42SH. The size of the blank is 15×15×10mm. 3 , polish the surface of the NdFeB magnet 1 clean;

[0048] Step 2: Select a commercial iron-based amorphous alloy ribbon 2 with a grade of 1K104 and a thickness of 29 µm, and cut the iron-based amorphous alloy ribbon 2 into 15×15 mm pieces according to the surface size of the NdFeB magnet 1 to be protected. 2 2 sheets of thin film, 15×10mm 2 4 slices of thin slices;

[0049] Step 3: Prepare the 15×15 mm 2 The iron-based amorphous alloy thin strip 2 is laid on the upper and lower surfaces corresponding to the magnet;

[0050] Step 4: In 6×10 -3 Under a vacuum degree of 1.5 MPa, a uniaxial pressure of 5 MPa was applied, and the Fe-based amorphous alloy thin strip 2 and the NdFeB magnet 1 were welded together by spark plasma sintering technology, the sintering temperature was controlled at 500°C, and the sintering time was 5 min;

[0051] Step 5: rotate the magnet, and repeat steps 3 and 4 to weld the other four surfaces of the NdFeB magnet 1 to the Fe-based amorphous alloy strips 2 of corresponding sizes.

[0052] Table 1 shows the corrosion resistance tests of Example 1, Example 2, Example 3, Example 4 and four commercially available electroplated nickel NdFeB magnets 1N52 (Comparative Example 1), N48 (Comparative Example 2), 45H (Comparative Example 3), and 42SH (Comparative Example 4) in the neutral salt spray test, wet heat test, and pressure vessel test. The corrosion resistance is compared by comparing the time to start corrosion.

[0053] The neutral salt spray test is carried out in accordance with the provisions of GB / T 10125, using a 24h continuous spray test.

[0054] For the wet heat test, the sample was placed in a constant temperature and humidity test chamber, the temperature was raised to 80°C, and the temperature was kept constant for 30 minutes. The sample was sprayed with distilled water or deionized water with pH 7 for humidification, and the relative humidity was controlled at 90%±3%.

[0055] For the pressure vessel test, the sample is placed in a pressure vessel filled with distilled water or deionized water at pH=7, and the temperature is raised to 120°C so that the steam pressure is 0.20MPa~0.24MPa, and the temperature is maintained at a constant pressure.

[0056] At the same time, Table 1 also records the time when each embodiment of the present invention and each comparative example show obvious corrosion in the corresponding corrosive environment. The obvious corrosion refers to the phenomenon of rust, bubbles, cracks, shedding, powdering, etc. on the surface of the magnet. It can be seen from Table 1 that the time when the protective layer of the NdFeB magnet 1 prepared by the method of the present invention shows corrosion in different corrosion test environments is more than twice that of the corresponding comparative example. It can be seen that the method of the present invention can effectively improve the corrosion resistance of the NdFeB magnet 1.

[0057] Table 1 Time for obvious corrosion to occur in Examples and Comparative Examples (unit: hours)

[0058]

[0059] like Figure 2 It can be seen from the backscattered electron image of Example 1 that the iron-based amorphous alloy strip 2 and the sintered NdFeB magnet 1 are welded together by the discharge plasma sintering technology under pressure through the process of the present invention, and the interface 3 is well welded. The low melting point grain boundary phase on one side of the NdFeB magnet 1 at the interface 3 penetrates into the interface 3 under the action of capillary force, which has an effective welding effect on the NdFeB magnet 1 and the iron-based amorphous alloy strip 2.

Claims

1. A surface protection method for NdFeB magnets, It is characterized in that The following steps are involved: Step 1: Grind the surface of the NdFeB magnet (1) cleanly; Step 2: cutting the iron-based amorphous alloy ribbon (2) according to the surface size of the NdFeB magnet (1) to be protected; the iron-based amorphous alloy ribbon (2) is made of any one of the materials 1K101, 1K102, 1K103, 1K104, 1K105, 1K106, and 1K107; Step 3, laying the iron-based amorphous alloy thin strip (2) prepared in step 2 on the upper and lower surfaces corresponding to the magnet; Step 4, welding the iron-based amorphous alloy strip (2) and the NdFeB magnet (1) together; Step 5, rotating the magnet, repeating steps 3 and 4, and welding the other four surfaces of the NdFeB magnet (1) to the Fe-based amorphous alloy strip (2); In the step 1, the NdFeB magnet (1) is a sintered NdFeB magnet having an average grain size of 3 to 10 μm; In the step 4, the welding is spark plasma sintering welding, and the vacuum degree of the spark plasma sintering welding is ≤1×10 - 2 Pa, applied pressure is 1~20Mpa, sintering temperature range is 450~530℃, sintering time is 2~10min; In the step 2, the thickness of the iron-based amorphous alloy thin strip (2) is 25 µm to 30 µm and is prepared by a rapid quenching process.

2. A surface protection method for NdFeB magnets according to claim 1, Features: In the step 1, the grinding is performed using SiC sandpapers of No. 400, No. 600 and No. 800 in sequence.

Images