Method for preparing special-shaped neodymium-iron-boron magnet by means of vacuum superplastic forming process

Abstract

The present invention relates to the technical field of rare earth magnetic materials. Disclosed is a method for preparing a special-shaped neodymium-iron-boron magnet by means of a vacuum superplastic forming process. The method for preparing a special-shaped neodymium-iron-boron magnet by means of a vacuum superplastic forming process comprises: coating the inside of a mold with a release agent, then mounting a treated neodymium-iron-boron magnet in the mold, heating to a certain temperature while performing vacuumizing, and then performing superplastic forming; after the superplastic forming is completed, cooling the mold, and after the cooling is completed, taking out the cooled neodymium-iron-boron magnet from the mold; and performing fine treatment on the cooled neodymium-iron-boron magnet on the basis of the appearance size of a part processed by a three-dimensional digital model. The method solves the problems of cumbersome procedures and high processing difficulty in existing special-shaped magnet preparation techniques. In addition, compared with a special-shaped magnet prepared by a bonding process, the special-shaped magnet also has higher magnetic properties.

Description

Method for preparing special-shaped neodymium-iron-boron magnet by vacuum superplastic forming process TECHNICAL FIELD

[0001] The present application relates to the technical field of rare earth magnetic materials, and particularly relates to a method for preparing a special-shaped neodymium-iron-boron magnet by a vacuum superplastic forming process. BACKGROUND

[0002] In the forming process of the special-shaped neodymium-iron-boron magnet, the traditional method mainly includes two kinds. One is to mechanically process the sintered neodymium-iron-boron magnet, but the processing procedure is complicated, and the mechanical performance of the sintered neodymium-iron-boron magnet is poor, so that only simple-shaped magnets can be processed by mechanical processing. The other is to customize the special-shaped bonded neodymium-iron-boron magnet by a mold, and although this method can form a relatively complex special-shaped neodymium-iron-boron magnet, the performance of the bonded neodymium-iron-boron magnet is generally poor due to the existence of the bonding agent, and the bonded neodymium-iron-boron magnet cannot be applied to high-performance and high-temperature use requirements. Superplasticity refers to the ability of a material to exhibit unusually high plasticity without obvious necking under certain organizational conditions and at a certain temperature and strain rate. The superplastic temperature point of neodymium-iron-boron is relatively high, generally between 700-1000 DEG C. The superplastic deformation of neodymium-iron-boron is mainly based on the adjustability of its crystal structure and the grain sliding mechanism at high temperature. At high temperature, the neodymium-iron-boron crystal structure becomes looser, and the grain boundary activity is enhanced, so that it has good plasticity. The superplasticity of neodymium-iron-boron material can be widely applied to the preparation of complex-shaped and high-precision magnetic elements, such as micro-motors, sensors, sound devices and high-performance magnets. At the same time, superplasticity also provides more deformation modes and condition choices for processing neodymium-iron-boron, and provides an important way to improve the processing performance of the material. However, the superplastic deformation of neodymium-iron-boron requires high temperature conditions, and is easily affected by environmental factors such as oxidation. Therefore, in practical application, the temperature and environmental conditions of the superplastic deformation need to be controlled to ensure the performance and stability of the magnet. SUMMARY

[0003] The present application aims to provide a method for preparing a special-shaped neodymium-iron-boron magnet by a vacuum superplastic forming process to solve the problems in the prior art.

[0004] In order to achieve the above-mentioned application purpose, the present application provides the following technical scheme:

[0005] The present application provides a method for preparing a special-shaped neodymium-iron-boron magnet by a vacuum superplastic forming process, which comprises the following steps:

[0006] The sintered neodymium-iron-boron magnet is pretreated to obtain a treated neodymium-iron-boron magnet;

[0007] Coating release agent inside the mold, installing the treated Nd-Fe-B magnet in the mold, then heating to a certain temperature while vacuumizing, then superplastic forming; after the superplastic forming, cooling the mold, and taking out the cooled Nd-Fe-B magnet in the mold after the cooling;

[0008] According to the shape size of the machined part, the cooled Nd-Fe-B magnet is finely processed.

[0009] Preferably, in the method for preparing the special-shaped Nd-Fe-B magnet by the vacuum superplastic forming process, the pre-treatment process is as follows:

[0010] Wire cutting the sintered Nd-Fe-B magnet to obtain a magnet plate, removing oil on the surface of the magnet plate, then sequentially washing and pickling the magnet plate to remove impurities on the surface of the magnet plate.

[0011] Preferably, in the method for preparing the special-shaped Nd-Fe-B magnet by the 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 method for preparing the special-shaped Nd-Fe-B magnet by the vacuum superplastic forming process, the heating temperature is 700-1000℃, and the vacuum degree is 1x10 -3 ~1x10 -5 Pa.

[0013] Preferably, in the method for preparing the special-shaped Nd-Fe-B magnet by the vacuum superplastic forming process, the superplastic forming process is as follows:

[0014] According to the strain rate 1x10 -3 ~1x10 -4 / s, superplastic gas pressure expansion is performed, pressure maintaining is performed when the stress reaches 1-20MPa pressure, and the pressure maintaining time is 30-60min.

[0015] Preferably, in the method for preparing the special-shaped Nd-Fe-B magnet by the vacuum superplastic forming process, the cooling temperature is <100℃.

[0016] According to the above technical solution, compared with the prior art, the present application has the following beneficial effects:

[0017] The application provides a novel technology for preparing a special-shaped neodymium-iron-boron magnet by a vacuum superplastic forming process, the grain growth of the magnet in the vacuum superplastic forming process is small, the superplasticity is realized through mechanisms such as grain boundary sliding and diffusion creep, the performance of the original magnet is maximally reserved, and good plasticity that cannot be realized by a sintered magnet is obtained. The superplastic forming magnet can withstand a higher working temperature (usually above 200 DEG C) due to high density and uniform microstructure, and can still maintain stable magnetic performance at high temperature. The bonded magnet has poor thermal stability due to the existence of a bonding agent, and the working temperature is usually not more than 150 DEG C, and the magnetic performance will obviously decrease at high temperature. Meanwhile, the problem of complicated process and high processing difficulty in the preparation technology of the existing special-shaped magnet is solved. Meanwhile, the special-shaped magnet prepared by the bonded process has higher magnetic performance. DETAILED DESCRIPTION

[0018] The application provides a method for preparing a special-shaped neodymium-iron-boron magnet by a vacuum superplastic forming process, comprising the following steps:

[0019] Pre-treating a sintered neodymium-iron-boron magnet to obtain a treated neodymium-iron-boron magnet;

[0020] Coating a release agent in a mold, installing the treated neodymium-iron-boron magnet in the mold, then heating to a certain temperature and performing vacuumizing, then performing superplastic forming, cooling the mold after the superplastic forming is completed, and taking out the cooled neodymium-iron-boron magnet in the mold after cooling is completed;

[0021] Performing fine treatment on the cooled neodymium-iron-boron magnet according to the outer shape size of the part processed by a three-dimensional model.

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

[0023] Linear cutting the sintered neodymium-iron-boron magnet to obtain a magnet plate, removing oil from the surface of the magnet plate, and then sequentially performing water washing and acid washing to remove impurities on the surface of the magnet plate;

[0024] The grain size of the magnet plate is preferably <10 mu m; the superplasticity of the neodymium-iron-boron material is closely related to the microstructure (especially the grain size). In order to realize superplasticity, the grain size of the neodymium-iron-boron 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 3-5 mm, further preferably 3.5-4.5 mm, and more preferably 4 mm.

[0026] In the application, the shape of the mold includes but is not limited to a hemispherical shape, a tile shape and a ring shape.

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

[0028] In this invention, the heating temperature is preferably 700–1000°C, more preferably 750–950°C, and even more preferably 800–900°C; the vacuum degree is preferably 1×10⁻⁶. -3 ~1×10 -5 Pa, more preferably 1×10 -3 ~1×10 -4 Pa, more preferably 1×10 Pa -4 Pa.

[0029] In this invention, temperature is a key factor in the superplasticity of the material. In NdFeB materials, heating to above 700°C is typically required for the material to begin exhibiting superplasticity. This is because at high temperatures, the activation energy of mechanisms such as grain boundary slip and diffusion decreases, atomic and grain boundary movement accelerates, and the material becomes more easily deformable.

[0030] In this invention, the superplastic forming process is as follows:

[0031] According to a strain rate of 1×10 -3 ~1×10 -4 Superplastic pneumatic bulging is performed at a pressure of 1–20 MPa, and the pressure is held 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 1-20 MPa, pressure is maintained, more preferably 10-20 MPa, and even more preferably 15-20 MPa;

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

[0035] In this invention, strain rate is another important parameter in superplastic forming. The superplasticity of NdFeB materials typically only manifests at relatively low strain rates, usually around 10. -3 ~10 -4 / s. Excessively high strain rates can prevent materials from adjusting through grain boundary slip and diffusion, leading to brittle fracture; while excessively low strain rates may cause excessive creep, resulting in failure.

[0036] In this 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 application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of them. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0038] Embodiment 1

[0039] The N40 neodymium-iron-boron is wire cut to obtain a magnet plate with a thickness of 3-5 mm, the grain size of the magnet plate is <10 μm, the surface of the magnet plate is deoiled, and then the ultrasonic machine is used to sequentially perform water washing and acid washing to remove the impurities on the surface, thereby obtaining the treated magnet plate;

[0040] A layer of molybdenum disulfide release agent is coated inside the semi-spherical mold, the treated magnet plate is installed in the semi-spherical mold, the mold is placed in the vacuum superplastic forming equipment, the temperature is raised to 800 ℃, and at the same time, the vacuum is extracted to 1×10 -4 Pa, then the gas pressure control system of the vacuum superplastic forming equipment is started, the superplastic gas pressure expansion is performed according to the process parameters of a strain rate of 1×10 -4 / s, the pressure maintaining state is performed when the stress reaches 10 MPa, the superplastic forming is completed after pressure maintaining for 40 min, the gas pressure is unloaded, the mold is cooled to below 100 ℃, and the neodymium-iron-boron magnet is taken out after the cooling is completed;

[0041] The neodymium-iron-boron magnet after cooling is finely processed according to the outer shape size of the three-dimensional numerical model.

[0042] Embodiment 2

[0043] The N40 neodymium-iron-boron is wire cut to obtain a magnet plate with a thickness of 3-5 mm, the grain size of the magnet plate is <10 μm, the surface of the magnet plate is deoiled, and then the ultrasonic machine is used to sequentially perform water washing and acid washing to remove the impurities on the surface, thereby obtaining the treated magnet plate;

[0044] A layer of molybdenum disulfide release agent is coated inside the semi-spherical mold, the treated magnet plate is installed in the semi-spherical mold, the mold is placed in the vacuum superplastic forming equipment, the temperature is raised to 900 ℃, and at the same time, the vacuum is extracted to 1×10 -3 Pa, then the gas pressure control system of the vacuum superplastic forming equipment is started, the superplastic gas pressure expansion is performed according to the process parameters of a strain rate of 1×10 -3 / s, the pressure maintaining state is performed when the stress reaches 10 MPa, the superplastic forming is completed after pressure maintaining for 30 min, the gas pressure is unloaded, the mold is cooled to below 100 ℃, and the neodymium-iron-boron magnet is taken out after the cooling is completed;

[0045] The fine processing of the neodymium-iron-boron magnet after cooling is performed according to the shape size of the three-dimensional model.

[0046] Comparative Example 1

[0047] Preparation of the mold for the bonded magnet semi-spherical model;

[0048] The N40 neodymium-iron-boron magnet is ball milled to obtain neodymium-iron-boron magnetic powder; the neodymium-iron-boron magnetic powder is mixed with epoxy resin to obtain mixed adhesive magnetic powder; the mass fraction of the epoxy resin is 2.5wt%.

[0049] The mixed adhesive magnetic powder is oriented and pressed in the bonded semi-spherical model mold, and is cured at 150℃ for 1.5h to obtain the bonded semi-spherical magnet.

[0050] The magnetic property results of the magnets prepared in Example 1, 2 and Comparative Example 1 are shown in Table 1.

[0051] Table 1 Magnetic property results of the magnets in Example 1, 2 and Comparative Example 1

[0052] In summary, the magnetic properties of the special-shaped magnet prepared by the method of the present application are better than those of the conventional bonded special-shaped magnet. Moreover, the method of the present application fills the gap that the conventional mechanical processing cannot prepare complex structure special-shaped sintered magnets.

[0053] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the scope of protection of the present application.

Claims

1. A method of producing a shaped neodymium-iron-boron magnet by a vacuum superplastic forming process, characterized in that, The method comprises the following steps: Pre-treating sintered neodymium-iron-boron magnets to obtain treated neodymium-iron-boron magnets; Coating a release agent inside a mold, mounting the treated neodymium-iron-boron magnets in the mold, then heating to a certain temperature while performing vacuum extraction, and then performing superplastic forming; after the superplastic forming is completed, cooling the mold, and after the cooling is completed, taking out the cooled neodymium-iron-boron magnets from the mold; Performing fine processing on the cooled neodymium-iron-boron magnets according to the outer dimensions of the parts processed by three-dimensional models.

2. The method of claim 1, wherein the method is characterized by: The pre-treatment process is as follows: Wire cutting the sintered neodymium-iron-boron magnets to obtain magnet plates, removing oil from the surface of the magnet plates, and then sequentially performing water washing and acid pickling to remove impurities on the surface of the magnet plates.

3. The method of making a shaped neodymium-iron-boron magnet by a vacuum superplastic forming process according to claim 2, wherein, The shape of the mold includes but is not limited to hemispherical, tile-shaped, and ring-shaped.

4. The method of making a shaped neodymium-iron-boron magnet by a vacuum superplastic forming process according to claim 3, wherein, The heating temperature is 700-1000℃, and the vacuum degree is 1x10 -3 ~1x10 -5 Pa.

5. The method of producing a shaped neodymium-iron-boron magnet by a vacuum superplastic forming process according to claim 3 or 4, characterized in that, The superplastic forming process is as follows: Superplastic gas pressure bulging was performed at a strain rate of 1 x 10 -3 ~1 x 10 -4 / s, pressure holding was performed at a stress of 1 to 20 MPa, and the pressure holding time was 30 to 60 minutes.

6. The method of making a shaped neodymium-iron-boron magnet by a vacuum superplastic forming process according to claim 5, wherein, The cooling temperature is <100℃.

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