A method for preparing special-shaped NdFeB magnets by vacuum superplastic forming process

Abstract

The present invention belongs to the technical field of rare earth magnetic materials and discloses a method for preparing special-shaped NdFeB magnets by a vacuum superplastic forming process. The method for preparing special-shaped NdFeB magnets by a vacuum superplastic forming process comprises: applying a mold release agent to the inside of a mold, then installing the treated NdFeB magnet in the mold, heating it to a certain temperature while evacuating it, and then performing superplastic forming; cooling the mold after superplastic forming, removing the cooled NdFeB magnet from the mold after cooling; and finely processing the cooled NdFeB magnet according to the external dimensions of the three-dimensional digital model processed parts. This method solves the problems of complicated procedures and high processing difficulty in existing special-shaped magnet preparation technologies. It also has higher magnetic properties than special-shaped magnets produced by bonding processes.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth magnetic materials, and in particular to a method for preparing a special-shaped NdFeB magnet through a vacuum superplastic forming process. Background Art

[0002] There are two main traditional methods for forming special-shaped NdFeB magnets. The first involves machining sintered NdFeB magnets, but this process is cumbersome and, due to the poor mechanical properties of sintered NdFeB magnets, can only produce simple magnets. The second method involves custom-molding special-shaped bonded NdFeB magnets. While this method can produce more complex special-shaped NdFeB magnets, the presence of the binder in bonded NdFeB magnets generally results in poor performance, making them unsuitable for high-performance and high-temperature applications. Superplasticity refers to the ability of a material to exhibit exceptionally high plasticity without significant necking under certain structural conditions, temperature, and strain rate conditions. The superplastic temperature of NdFeB is relatively high, generally between 700 and 1000°C. The superplastic deformation of NdFeB is primarily due to the adaptability of its crystal structure and the grain slip mechanism at high temperatures. At high temperatures, the crystal structure of NdFeB becomes looser and the activity of its grain boundaries increases, resulting in excellent plasticity. The superplasticity of NdFeB can be widely used in the preparation of complex-shaped and high-precision magnetic components, such as micromotors, sensors, audio equipment, and high-performance magnets. Superplasticity also provides a wider range of deformation methods and conditions for processing NdFeB, providing an important approach to improving the material's processing performance. However, superplastic deformation of NdFeB requires high temperatures and is susceptible to environmental factors such as oxidation. Therefore, in practical applications, it is important to carefully control the temperature and environmental conditions of superplastic deformation to ensure the performance and stability of the magnet. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing special-shaped NdFeB magnets by vacuum superplastic forming process, so as to solve the problems existing in the prior art.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing a special-shaped NdFeB magnet by a vacuum superplastic forming process, comprising the following steps:

[0006] Pre-treating the sintered NdFeB magnet to obtain a treated NdFeB magnet;

[0007] A release agent is applied to the inside of the mold, and the treated NdFeB magnet is installed in the mold. The mold is then heated to a certain temperature and vacuumed, and then superplastic forming is performed. After superplastic forming, the mold is cooled, and the cooled NdFeB magnet is removed from the mold.

[0008] The cooled NdFeB magnets are finely processed according to the external dimensions of the three-dimensional digital model processed parts.

[0009] Preferably, in the above method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming process, the pre-treatment process is:

[0010] The sintered NdFeB magnet is subjected to wire cutting to obtain a magnet plate, the surface of the magnet plate is degreased, and then water washing and acid washing are performed in sequence to remove impurities on the surface of the magnet plate.

[0011] Preferably, in the above method for preparing special-shaped NdFeB magnets by vacuum superplastic forming, the shape of the mold includes but is not limited to hemispherical, tile-shaped, and ring-shaped.

[0012] Preferably, in the above method for preparing special-shaped NdFeB magnets by vacuum superplastic forming, the heating temperature is 700-1000°C and the vacuum degree is 1×10 -3 ~1×10 -5 Pa.

[0013] Preferably, in the above method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming, the superplastic forming process:

[0014] At a strain rate of 1×10 -3 ~1×10 -4 / s for superplastic gas bulging, and when the stress reaches 1-20 MPa, pressure holding is performed for 30-60 min.

[0015] Preferably, in the above method for preparing special-shaped NdFeB magnets by vacuum superplastic forming, the cooling temperature is less than 100°C.

[0016] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention provides a new technology for preparing special-shaped NdFeB magnets using a vacuum superplastic forming process. During the vacuum superplastic forming process, the growth of magnet grains is small, and superplasticity is achieved through mechanisms such as grain boundary sliding and diffusion creep, which retains the performance of the original magnet to the maximum extent, while obtaining good plasticity that cannot be achieved by sintered magnets. Due to its high density and uniform microstructure, superplastic formed magnets can withstand higher operating temperatures (usually above 200°C) and can still maintain stable magnetic properties at high temperatures. However, bonded magnets have a significant impact on magnet performance due to the presence of binders, resulting in poor thermal stability, an operating temperature usually not exceeding 150°C, and a significant decrease in magnetic properties at high temperatures. At the same time, it solves the problems of complicated procedures and high processing difficulty in existing special-shaped magnet preparation technologies. At the same time, it also has higher magnetic properties than special-shaped magnets made by bonding processes. DETAILED DESCRIPTION

[0018] The present invention provides a method for preparing a special-shaped NdFeB magnet by a vacuum superplastic forming process, comprising the following steps:

[0019] Pre-treating the sintered NdFeB magnet to obtain a treated NdFeB magnet;

[0020] A release agent is applied to the inside of the mold, and the treated NdFeB magnet is installed in the mold. The mold is then heated to a certain temperature and vacuumed, and then superplastic forming is performed. After superplastic forming, the mold is cooled, and the cooled NdFeB magnet is removed from the mold.

[0021] The cooled NdFeB magnets are finely processed according to the external dimensions of the three-dimensional digital model processed parts.

[0022] In the present invention, the pre-treatment process is:

[0023] Wire cutting is performed on the sintered NdFeB magnet to obtain a magnet plate, the surface of the magnet plate is degreased, and then water washing and acid washing are performed in sequence to remove impurities on the surface of the magnet plate;

[0024] The grain size of the magnet plate is preferably less than 10 μm. The superplasticity of NdFeB material is closely related to its microstructure (especially grain size). To achieve superplasticity, the grain size of NdFeB material needs to be kept below 10 microns, as smaller grains enhance grain boundary sliding and reduce the risk of fracture.

[0025] The thickness of the magnet plate is preferably 3 to 5 mm, more preferably 3.5 to 4.5 mm, and even more preferably 4 mm.

[0026] In the present invention, the shape of the mold includes but is not limited to hemispherical, tile-shaped, and ring-shaped.

[0027] In the present invention, the release agent is preferably molybdenum disulfide.

[0028] In the present invention, the heating temperature is preferably 700-1000°C, more preferably 750-950°C, and more preferably 800-900°C; the vacuum degree is preferably 1×10 -3 ~1×10 -5 Pa, more preferably 1×10 -3 ~1×10 -4 Pa, more preferably 1×10 -4 Pa.

[0029] In this invention, temperature is a key factor in the material's superplasticity. In NdFeB materials, superplasticity typically begins only after heating to above 700°C. This is because at high temperatures, the activation energy of mechanisms like grain boundary sliding and diffusion decreases, accelerating atomic and grain boundary motion and making the material more susceptible to deformation.

[0030] In the present invention, the superplastic forming process:

[0031] At a strain rate of 1×10 -3 ~1×10 -4 / s for superplastic gas bulging, and when the stress reaches 1-20 MPa, the pressure is maintained for 30-60 minutes;

[0032] The strain rate is preferably 1×10 -3 ~1×10 -4 / s, more preferably 1×10 -3 / s;

[0033] When the stress reaches a pressure of 1 to 20 MPa, the pressure is maintained, preferably 10 to 20 MPa, and more preferably 15 to 20 MPa;

[0034] The pressure holding time is preferably 30 to 60 minutes, more preferably 30 to 45 minutes, and even more preferably 30 to 40 minutes.

[0035] In the present invention, strain rate is another important parameter in superplastic forming. The superplasticity of NdFeB materials usually only appears at a relatively low strain rate, usually around 10 -3 ~10 -4 / s. Too high a strain rate will prevent the material from adjusting through grain boundary sliding and diffusion in time, leading to brittle fracture; while too low a strain rate may cause excessive creep of the material, leading to failure.

[0036] In the present invention, the cooling temperature is preferably <100°C, more preferably 40-80°C, and even more preferably 50-60°C.

[0037] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0038] Example 1

[0039] Wire cutting is performed on N40 NdFeB to obtain magnet plates with a thickness of 3 to 5 mm, and the grain size of the magnet plates is less than 10 μm. The surface of the magnet plates is degreased, and then ultrasonically washed and acid-washed in sequence to remove surface impurities to obtain the treated magnet plates;

[0040] A layer of molybdenum disulfide release agent was applied to the inside of the hemispherical mold, and the treated magnet plate was installed in the hemispherical mold. The mold was placed in a vacuum superplastic forming device, heated to 800 ° C, and vacuumed to 1 × 10 -4 Pa, and then start the air pressure control system of the vacuum superplastic forming equipment, according to the strain rate of 1×10 -4 / s process parameters for superplastic gas pressure bulging, when the stress reaches 10MPa, the pressure is maintained, and the superplastic forming is completed after 40 minutes of pressure maintenance. The gas pressure is unloaded and the mold is cooled to below 100℃. After cooling, the NdFeB magnet is taken out.

[0041] The cooled NdFeB magnets are finely processed according to the external dimensions of the three-dimensional digital model processed parts.

[0042] Example 2

[0043] Wire cutting is performed on N40 NdFeB to obtain magnet plates with a thickness of 3 to 5 mm, and the grain size of the magnet plates is less than 10 μm. The surface of the magnet plates is degreased, and then ultrasonically washed and acid-washed in sequence to remove surface impurities to obtain the treated magnet plates;

[0044] A layer of molybdenum disulfide release agent was applied to the inside of the hemispherical mold, and the treated magnet plate was installed in the hemispherical mold. The mold was placed in a vacuum superplastic forming equipment, heated to 900 ° C, and vacuumed to 1 × 10 -3 Pa, and then start the air pressure control system of the vacuum superplastic forming equipment, according to the strain rate of 1×10 -3 / s process parameters for superplastic gas pressure bulging, when the pressure reaches 10MPa, the pressure is maintained, and the superplastic forming is completed after the pressure is maintained for 30 minutes. The gas pressure is unloaded, and the mold is cooled to below 100℃. After cooling, the NdFeB magnet is taken out;

[0045] The cooled NdFeB magnets are finely processed according to the external dimensions of the three-dimensional digital model processed parts.

[0046] Comparative Example 1

[0047] preparing a mold for a hemispherical bonded magnet model;

[0048] Ball milling N40 NdFeB magnets to obtain NdFeB magnetic powder; mixing the NdFeB magnetic powder with epoxy resin to obtain mixed rubber magnetic powder; wherein the mass fraction of the epoxy resin is 2.5wt%;

[0049] The mixed rubber magnetic powder is oriented and pressed in a bonded hemispherical model mold, and cured at 150° C. for 1.5 hours to obtain a bonded hemispherical magnet.

[0050] The magnetic properties of the magnets prepared in Examples 1 and 2 and Comparative Example 1 are shown in Table 1.

[0051] Table 1 Magnetic properties of the magnets in Examples 1, 2 and Comparative Example 1

[0052] Coercive force (kA / m) Remanence (T) <![CDATA[Magnetic energy product (kJ / m 3 )]]> Example 1 893 1.27 304 Example 2 874 1.26 297 Comparative Example 1 415 0.42 113

[0053] In summary, the magnetic properties of the special-shaped magnets prepared by the method of the present invention are superior to those of conventional bonded special-shaped magnets. Furthermore, the method of the present invention fills the gap in the traditional mechanical processing that cannot produce complex structure special-shaped sintered magnets.

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing special-shaped NdFeB magnets by vacuum superplastic forming process, characterized in that: The following steps are involved: Pre-treating the sintered NdFeB magnet to obtain a treated NdFeB magnet; A release agent is applied to the inside of the mold, and the treated NdFeB magnet is installed in the mold. The mold is then heated to a certain temperature and vacuumed, and then superplastic forming is performed. After superplastic forming, the mold is cooled, and the cooled NdFeB magnet is removed from the mold. Finely process the cooled NdFeB magnets according to the dimensions of the three-dimensional digital model parts; The pre-treatment process is as follows: Wire cutting is performed on the sintered NdFeB magnet to obtain a magnet plate, the surface of the magnet plate is degreased, and then water washing and acid washing are performed in sequence to remove impurities on the surface of the magnet plate; The superplastic forming process: At a strain rate of 1×10 -3 ~1×10 -4 / s for superplastic gas bulging, and when the stress reaches 10~20MPa, pressure is maintained for 30~60min.

2. The method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming according to claim 1, wherein: The shape of the mold includes but is not limited to hemispherical, tile-shaped, and ring-shaped.

3. The method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming according to claim 2, wherein: The heating temperature is 700-1000°C and the vacuum degree is 1×10 -3 ~1×10 -5 Pa.

4. The method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming according to claim 3, wherein: The cooling temperature is less than 100°C.