JPH03295202A - Hot-worked magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain the title magnet having no cracks by facilitating the plastic working to be performed thereon, and to obtain uniform orientation to improve magnetic characteristics by a method wherein Al metal powder is mixed in magnetic powder, and a hot plastic working is conducted. CONSTITUTION:The alloy of composition, consisting of Nd 14.5 and FebalCo of 7.56, is arc-fused, it is jetted on a single roll rotating in an Ar atmosphere, and the flake-like thin pieces of indeterminate form are formed. Then, Al metal powder of 0.05 to 5wt.% is added to the crushed magnetic powder, and magnetic powder and the Al powder are mixed by V-type mixer so that they become uniform. The molded body, obtained by molding the above-mentioned mixed powder, is hot-pressed, and a high density molded body is obtained. Then, magnetic anisotropy is given by conducting a hot working of the magnet at 700 deg.C.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is an improvement of a warm-worked magnet, which is a permanent magnet consisting essentially of rare earth elements, transition metals, and boron, and which imparts magnetic anisotropy through warm working. In particular, the present invention relates to a permanent magnet that has improved workability, is free from cracks, has improved orientation, and has good magnetic properties by adding an appropriate amount of AI, and a method for manufacturing the same.

[Prior Art] Permanent magnets made essentially of rare earth elements, transition metals, and boron (hereinafter referred to as R-T-B permanent magnets) are attracting attention because they are inexpensive and have high magnetic properties. This is because this alloy system develops an intermetallic compound represented by R2Tl4B having a tetragonal crystal structure and having excellent magnetic properties. This intermetallic compound has an a-axis and a C-axis at room temperature.
The lattice constants of the axes are a=0.878 nm, c=1.
It is 218 nm.

Methods for manufacturing magnetically anisotropic magnets of this type are broadly divided into methods for manufacturing sintered magnets that follow conventional powder metallurgy and methods for manufacturing warm-worked magnets using a quenching method.

The first process is the R
- After crushing the T-B alloy, it is molded while being oriented in a magnetic field, and then subjected to sintering treatment and aging heat treatment to form a sintered magnet.

In the second process, for example, as described in JP-A-60-100402, a molten RTB alloy is rapidly cooled to form a quenched ribbon consisting of amorphous and microcrystalline materials at temperatures above 700°C. In this method, a compacted body densified by hot pressing or HIP at a temperature of 700° C. is further subjected to upsetting at a temperature of 700° C. or higher to obtain a warm-worked magnet with anisotropy in the direction of compression.

[Problems to be Solved by the Invention] The sintered magnet obtained by the first process has high magnetic properties with an energy product of 35 to 40 MG-Oe, but it requires the troublesome process of molding in a magnetic field. is essential and is restricted by the shape of the magnet.

On the other hand, according to the second process, it is possible to create magnetic anisotropy by applying warm plastic working, and magnetic anisotropy is closely correlated with the direction perpendicular to plastic flow (orientation of crystal grains). There is a relationship. The magnetic properties of this warm-processed magnet are 4
There are problems in that either an energy product of 0 MG-Oe or more is obtained or the magnetic properties vary widely due to non-uniform plastic flow. In addition, non-uniform deformation causes a large rack at the edge due to the bulge phenomenon (the edge deforms into a barrel shape) of the workpiece during plastic working. These are caused by friction between magnetic particles during warm working, which causes significant non-uniform deformation. This means that
This poses a major problem when trying to obtain a magnet as a product.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to easily plastically work an R-T-B type warm-worked magnet without cracking, and to obtain a uniform orientation. The purpose is to provide a product with good magnetic properties.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses the following technical means. That is, a molten R-T-B alloy (R is one or more rare earth elements including Y, T is a transition metal, and B is boron) is ultra-rapidly solidified to obtain a ribbon or flake. After pulverizing to obtain magnetic powder, 600°C to 800°C
Magnetic anisotropy is imparted by warm working at ℃, and the average crystal grain size of the anisotropic magnet after the final step is 0.02 to 0.5 μm.
This method of manufacturing a warm-worked magnet is characterized in that the magnetic powder is mixed with Al metal powder and metal chips.

In the method for manufacturing a warm-worked magnet of the present invention, it is desirable that the amount of Al added is set to 0.05 to 5 wt% based on the magnetic powder. If the amount added is less than 0.05 wt%, a sufficient addition effect will not be observed, and it may not be possible to make the plastic deformation of the warm-worked magnet uniform.
%, the amount of magnetic powder per unit volume may decrease and sufficient magnetic properties may not be obtained.

In the present invention, the average crystal grain size is fine as a characteristic of the magnet produced by the ultra-quenching method. It is difficult to industrially stably obtain ultrafine crystals with an average crystal grain size of less than 0.02 μm using current technology;
If it exceeds this, the coercive force iHc decreases, which is not preferable.

In addition, the temperature at which plastic working is performed is 60oC to SOO
C is preferred, and most preferably 670 to 800C.

In other words, at temperatures below 600°C, the R-rich liquid phase, which is important for plastic deformation, does not occur at the grain boundaries inside the flakes, making it impossible to impart magnetic anisotropy to the magnet, and the deformation resistance during processing is high, leading to cracking. also occur in large numbers. At temperatures above 600°C, R
Magnetic anisotropy becomes possible only when a rich liquid phase is generated.

Also, since the melting point of Al is 670°C, the processing temperature is 670°C.
At temperatures above 70°C, the molten A existing at the flake interface
The lubricating effect of l improves the non-uniform plastic flow, thereby significantly improving the orientation of crystal grains, resulting in good magnetic properties, as well as lower deformation resistance and improved workability.

Here, the degree of orientation of crystal grains can be measured by XN1 diffraction. That is, first, the X-ray diffraction intensity of each diffraction surface is measured using a diffractometer on an isotropic sample, then a sample cut from an anisotropic warm-processed magnet is measured, and the diffraction intensity is measured on an isotropic sample. Standardize by the strength of the sample. The normalized values are plotted with respect to the angle that each diffraction plane makes with the zero plane, approximated by a Gaussian distribution, and the crystal orientation can be evaluated based on the angular dispersion.

The angular dispersion in conventional warm worked magnets is 3 on the magnet surface.
However, in the present invention, this angular dispersion is less than 30 degrees, good crystal orientation is obtained, and high magnetic properties are achieved. It became possible to do so.

Furthermore, at temperatures above 800°C, rapid crystal grain growth occurs, causing the average crystal grain size of the magnet to exceed 0.5 μm, the coercive force to drop rapidly, and many cracks to occur, resulting in poor magnetic properties. It is unfavorable from both the viewpoint of workability.

[Function] In the magnet according to the present invention configured as described above, since the magnetic powder is mixed with Al metal powder and warm plastic working is performed, the molten Al acts as a lubricant, and therefore the plasticity is reduced. The flow is improved, resulting in uniform plastic deformation, improving the magnetic properties of the magnet and improving workability.

[Example code] The present invention will be specifically explained below using Examples.

(Example 1) N d 14.5 Fe bal Co 7.568
An alloy having a composition of 6 was produced by arc melting. This alloy was jetted onto a single roll rotating at a circumferential speed of 30 m/sec in an Ar atmosphere to produce irregular flake-like flakes with a thickness of about 30 μm. As a result of X-ray diffraction, it was found to be a mixture of amorphous and crystalline materials. Next, magnetic powder was prepared by pulverizing the flakes to a size of 500 μm or less. This magnetic powder was mixed with 0.5 wt% of Al metal powder (invention) and with no additive (comparative example), using a V-type mixer so that the magnetic powder and Al powder were uniform. mixed with. These mixed powders were molded under a pressure of 6 tons/Cm.
2, the density is about 5.7g/cc and the diameter is 28.
A molded body with a height of 46 mm and a height of 46 mm was produced.

The obtained molded body was hot pressed at 700°C and 2 tons/cm2, and the diameter was 30 mm with a high density of about 7.6 g/cc.
A molded body with a height of 30 mm and a height of 30 mm was obtained.

Further, the magnet was subjected to warm working at 700'C to a working rate (height reduction rate before upsetting and after upsetting) of 75% to impart magnetic anisotropy.

When a sample cut from this magnet was analyzed by EP-IA, it was found that Al was contained in the Nd-rich grain boundary phase.

In addition, a measurement sample was cut out from the processed magnet and the magnetic properties and angular dispersion values indicating crystal orientation were measured. Table 1 shows the magnetic properties and angular dispersion values. Here, the smaller the angular dispersion value, the higher the degree of crystal orientation.

As is clear from Table 1, the addition of Al improves the plastic fluidity during warm working and improves crystal orientation.
It can be seen that the magnetic properties are significantly improved.

(Example 2) Al metal powder was added to magnetic powder having the same alloy composition as in Example 1 at 0 wt %, 0.03 wt %, and 0.0 wt %. 05wt%
, O,1wt%, 1,0wt%, 3,0wt%, 5.0
The powder was added in eight steps of wt% and 8.0 wt%, and the magnetic powder and Al powder were mixed uniformly using a type mixer. These mixed powders are molded under a pressure of 6 tons/c.
M2 is molded with a density of approximately 5.7 g/cc and a diameter of 28. A molded body having a mmt height of 46 mm was produced. The obtained molded body was hot pressed at 700° C. and 2 tons/cm 2 to obtain a molded body having a high density of about 7.6 g/cc and a diameter of 30 mm and a height of 30 mm.

Furthermore, the magnet is warm-processed at 700°C to a processing rate of 75% (height reduction rate before and after upsetting) to impart magnetic anisotropy, and a measurement sample is cut out from the processed magnet and magnetically The angular dispersion value, which indicates the properties and crystal orientation, was measured. Table 2 shows the measurement results of magnetic properties and angular dispersion values.

(Left below) Table 2 1.0 12.0 18.7
34.1 213.0 12.0
18.9 34.0 215, O11,
919,033,421 8, Ol 10.5 18.5 25.0
24 Table 2 shows that there is no change in the magnetic properties when the amount of Al added is less than 0.05 wt%, but when the amount added is 0.05 to
At 5 wt%, 4π1r was particularly improved and good magnetic properties were obtained, and the effect of Al addition was recognized. In addition, when the amount added exceeds 5 wt%, the proportion of the magnetic alloy responsible for the magnetic properties per unit volume decreases, so the 4πI
r decreased significantly.

(Example 3) Using the same warm processing method as in Example 1, the upsetting processing temperatures were set to 550°C, 600°C, 700°C, 800°C, and 850°C.
The upsetting process was performed by changing the temperature in 5 steps. ``The relationship between deformation resistance during machining and machining rate was calculated from recording paper, and the summarized results are shown in Table 3. Here, the magnets in which cracks occurred during machining are marked with an X, and the others are marked with an X. is the deformation resistance (ton/cm2) at a processing rate of 30%.

Table 3 Processing temperature (°C) 0 580 × 600 '2.03 700. 1.13 750 1, 10 50 × Al addition amount (w°C%) 0.5 1.0 3. O X In this case, the deformation resistance was quite large and cracks occurred in the magnet. On the other hand, even at 850°C, the deformation resistance increased significantly and many cracks occurred in the magnet.

Therefore, the warm processing according to the present invention ranges from about 00°C to about 80°C.
0°C is preferred.

[Effects of the Invention] According to the present invention, it is possible to obtain an anisotropic magnet in which the formability, which has conventionally been insufficient in warm-worked magnets, is improved, and at the same time, the magnetic properties are significantly improved.

Claims (4)

[Claims] (1) An R-T-B alloy whose main component is a transition metal T, a rare earth element R including yttrium, and boron B, and has an average crystal grain size of 0.02 to 0.02 or more with magnetic anisotropy.
In a warm-worked magnet with fine crystal grains of 0.5 μm, the grain boundary phase is composed of an R (rare earth element) rich phase containing Al, and the magnetic anisotropy is suitable for warm or hot plastic working. A warm-processed magnet characterized by being given by. (2) An R-T-B alloy containing the transition metal T as a main component, a rare earth element R including yttrium, and boron B, and having an average crystal grain size of 0.02 to 0.02 or more with magnetic anisotropy.
A warm worked magnet having fine crystal grains of 0.5 μm, characterized in that the angular dispersion of the crystal orientation from the C axis of the crystal as determined by X-ray diffraction is less than 30 degrees at the magnet surface. . (3) A molten R-T-B alloy containing transition metal T as a main component, rare earth element R including yttrium, and boron B is rapidly solidified to obtain a thin body or powder, which is then warm-processed. In a method for manufacturing a warm-worked magnet that imparts magnetic anisotropy through processing, 0.05 to 5 wt% of Al metal powder and metal chips are mixed and dispersed in magnetic powder, and warm plastic working is performed to create anisotropy. A method for manufacturing a warm-processed magnet, characterized by imparting the following properties. (4) The method for manufacturing a warm-worked magnet according to claim 2, wherein the warm-work is performed at a temperature of 600°C to 800°C.