Method for preparing special-shaped neodymium-iron-boron magnet through vacuum superplastic forming process

Abstract

The invention belongs to the technical field of rare earth magnetic materials, and discloses a method for preparing a special-shaped neodymium iron boron magnet through a vacuum superplastic forming process. The method for preparing the special-shaped neodymium-iron-boron magnet through the vacuum superplastic forming process comprises the steps that the interior of a mold is coated with a release agent, then the treated neodymium-iron-boron magnet is installed in the mold, vacuumizing is carried out while the neodymium-iron-boron magnet is heated to a certain temperature, and then superplastic forming is carried out; after superplastic forming is finished, the mold is cooled, and after cooling is finished, the cooled neodymium-iron-boron magnet is taken out of the mold; and performing fine treatment on the cooled neodymium-iron-boron magnet according to the boundary dimension of the three-dimensional digital-analog processing part. The method solves the problems that in an existing special-shaped magnet preparation technology, procedures are tedious, and the machining difficulty is high. And meanwhile, compared with a special-shaped magnet prepared by a bonding process, the special-shaped magnet prepared by the invention has higher magnetic performance.

Description

Technical Field

[0001] The 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] In the forming process of special-shaped NdFeB magnets, the traditional methods are mainly divided into two types. One is to mechanically process sintered NdFeB magnets, but the processing procedures are cumbersome, and due to the poor mechanical properties of sintered NdFeB magnets, only simple-shaped magnets can be processed by mechanical processing. The second is to customize special-shaped bonded NdFeB magnets through molds. Although this method can complete the forming of more complex special-shaped NdFeB magnets, the performance of bonded NdFeB magnets is generally poor due to the presence of binders in bonded NdFeB magnets, and they cannot be applied to high-performance and high-temperature use requirements. Superplasticity refers to the ability of a material to exhibit abnormally high plasticity without obvious necking under certain organizational conditions and certain temperature and strain rate conditions. The superplastic temperature point of NdFeB is relatively high, generally between 700 and 1000°C. The superplastic deformation of NdFeB is mainly based on the adjustability of its crystal structure and the grain slip mechanism at high temperature. At high temperatures, the crystal structure of NdFeB becomes looser and the activity of grain boundaries is enhanced, which gives it good plasticity. The superplasticity of NdFeB materials can be widely used in the preparation of complex shapes and high-precision magnetic components, such as micromotors, sensors, sound equipment, and high-performance magnets. At the same time, superplasticity also provides more deformation modes and conditions for processing NdFeB, providing an important way to improve the processing performance of materials. However, the superplastic deformation of NdFeB requires high temperature conditions and is easily affected by environmental factors such as oxidation. Therefore, in practical applications, it is necessary to pay attention to controlling 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 a special-shaped NdFeB magnet by a 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 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 inside the mold, the treated NdFeB magnet is installed in the mold, and then the mold is heated to a certain temperature and vacuumed, and then superplastic forming is performed; after superplastic forming, the mold is cooled, and after cooling, the cooled NdFeB magnet is taken out of 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 the impurities on the surface of the magnet plate are removed by water washing and acid washing in sequence.

[0011] Preferably, in the above method for preparing special-shaped NdFeB magnets by vacuum superplastic forming process, 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 a special-shaped NdFeB magnet by vacuum superplastic forming process, 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 process, 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 1-20MPa, pressure is maintained for 30-60min.

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

[0016] It can be seen from the above technical solution 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 magnet grain growth 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 a binder, and have poor thermal stability. The operating temperature usually does not exceed 150°C, and the magnetic properties will drop significantly at high temperatures. At the same time, it solves the problems of complicated procedures and high processing difficulty in the existing special-shaped magnet preparation technology. 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 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 inside the mold, the treated NdFeB magnet is installed in the mold, and then the mold is heated to a certain temperature and vacuumed, and then superplastic forming is performed; after superplastic forming, the mold is cooled, and after cooling, the cooled NdFeB magnet is taken out of 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] Performing wire cutting on the sintered NdFeB magnet to obtain a magnet plate, degreasing the surface of the magnet plate, and then sequentially washing with water and pickling to remove impurities on the surface of the magnet plate;

[0024] The grain size of the magnet plate is preferably <10 μm; the superplasticity of NdFeB material is closely related to its microstructure (especially grain size). In order to achieve superplasticity, the grain size of NdFeB material needs to be kept below 10 microns, because smaller grains can enhance the effect of 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 to 1000°C, more preferably 750 to 950°C, and more preferably 800 to 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 the present invention, temperature is a key factor in the superplasticity of materials. In NdFeB materials, it is usually necessary to heat to above 700°C before the material begins to exhibit superplasticity. This is because at high temperatures, the activation energy of mechanisms such as grain boundary sliding and diffusion is reduced, the movement of atoms and grain boundaries is accelerated, and the material becomes easier to deform.

[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 1-20MPa, the pressure is maintained for 30-60min;

[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 min, more preferably 30 to 45 min, and even more preferably 30 to 40 min.

[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 cause the material to have no time to adjust through grain boundary sliding and diffusion, which will lead 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 technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] Wire cutting is performed on N40 NdFeB to obtain a magnet plate with a thickness of 3 to 5 mm, and the grain size of the magnet plate is less than 10 μm. The surface of the magnet plate is degreased, and then an ultrasonic machine is used to sequentially perform water washing and acid washing to remove surface impurities to obtain a treated magnet plate;

[0040] A layer of molybdenum disulfide release agent was applied inside the hemispherical mold, the treated magnet sheet was installed in the hemispherical mold, the mold was placed in a vacuum superplastic forming device, the temperature was raised to 800°C, and the vacuum was simultaneously drawn 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 a magnet plate with a thickness of 3 to 5 mm, and the grain size of the magnet plate is less than 10 μm. The surface of the magnet plate is degreased, and then an ultrasonic machine is used to sequentially perform water washing and acid washing to remove surface impurities to obtain a treated magnet plate;

[0044] A layer of molybdenum disulfide release agent was applied inside the hemispherical mold, the treated magnet sheet was installed in the hemispherical mold, the mold was placed in a vacuum superplastic forming device, the temperature was raised to 900°C, and the vacuum was simultaneously drawn 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 30 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;

[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 the conventional bonded special-shaped magnets, and the method of the present invention fills the gap that conventional machining cannot prepare special-shaped sintered magnets with complex structures.

[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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a special-shaped NdFeB magnet 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 inside the mold, the treated NdFeB magnet is installed in the mold, and then the mold is heated to a certain temperature and vacuumed, and then superplastic forming is performed; after superplastic forming, the mold is cooled, and after cooling, the cooled NdFeB magnet is taken out of the mold; The cooled NdFeB magnets are finely processed according to the external dimensions of the three-dimensional digital model processed parts.

2. The method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming process according to claim 1, characterized in that: The pre-treatment process is as follows: The sintered NdFeB magnet is subjected to wire cutting to obtain a magnet plate, the surface of the magnet plate is degreased, and then the impurities on the surface of the magnet plate are removed by water washing and acid washing in sequence.

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

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

5. The method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming process according to claim 3 or 4, characterized in that: 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 1-20MPa, pressure is maintained for 30-60min.

6. The method for preparing a special-shaped NdFeB magnet by vacuum superplastic forming process according to claim 5, characterized in that: The cooling temperature is less than 100°C.