JPH07105289B2 - Rare earth permanent magnet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is a method for producing a rare earth permanent magnet, and in particular, a high iHc can be obtained with a small amount of an additive, and a decrease in Br due to an additive element can be minimized. , (BH) max, and a method for manufacturing a rare earth permanent magnet.

(Prior Art and Problems) Among rare earth permanent magnets, Nd-Fe-B magnets have attracted much attention in recent years due to their high magnetic properties, and are particularly powerful magnets for energy saving and device miniaturization. Large demand is expected in the field of motors that require

However, the magnet of this system has a large temperature coefficient and has a drawback that the magnetic characteristics are deteriorated at high temperature. When the temperature rises during operation of the motor and the temperature rises to 100 ° C to 150 ° C, the magnetic characteristics decrease greatly. However, there is a need for a magnet that can maintain good magnetic properties.

In the Nd-Fe-B system magnet, the temperature change of the residual magnetization (Br) is -0.
13% / ℃, coercive force (iHc) temperature change is -0.6% /
The temperature change of iHc is the most serious problem. The change of −0.6% / ° C. means that iHc becomes about half when the temperature is raised from room temperature to 100 ° C., for example. Therefore, conventionally, the operating temperature range of Nd magnets has been limited to 50 ° C to 70 ° C at the maximum.

There are two methods to improve the temperature change of iHc, one of which is to use heavy rare earth elements such as Dy and Tb, light metal elements such as Al, Nb and V, and transition metals as has been conventionally done. It is to use the added alloy (JP-A-59-89401,
The other one is to change the mechanism of coercive force generation to, for example, a two-phase separation type, but this method has not been successful yet.

The former method achieves a high iHc at room temperature by using an additive element, and provides a sufficient iHc for practical use even if the temperature rises and the iHc decreases. However, Al, Nb, and V are nonmagnetic elements, and the addition of Br causes the proportion thereof to be proportional to or more than that of Br. Heavy rare earth elements such as Dy and Tb
Since the magnetic moments are antiparallel to those of transition metals,
The decrease of Br is large above l, Nb, and V. For this reason, in the conventional high coercive force type Nd magnet alloy, Br was always much lower than that of the ternary Nd-Fe-B magnet.

The coercive force mechanism of Nd magnet is a nucleation growth type (J.Appl.Phy
s. 55, 1984 P2083). This is because the crystal grain boundaries are very smooth and clean, so even if a magnetic field is applied in the direction opposite to the magnetization, it is difficult for reverse magnetic domain buds to occur, but since the domain wall is strongly pinned in a narrow region near the grain boundaries. It is said that.

Recently, electron microscopy of Hiraga and Sagawa (Japa
n., J.Appl.Phys. 24, 1985 L30), in Nd magnet has become the surface of the Nd ₂ Fe ₁₄ B crystal grains structure as wrapped is magnetically soft thin bcc phase, moreover It became clear that the boundary between the two was very clean and undistorted.
From this fact, it is considered that a large coercive force is generated because the domain wall is pinned to the magnetically soft bcc phase of the outermost layer. It is considered that heavy rare earth elements, Al, Nd, etc. increase iHc because they increase the anisotropic magnetic field of the 2: 14: 1 compound and affect the morphology near the grain boundaries.

Based on such knowledge, the present inventor has reached the present invention by realizing that it is necessary to control only the vicinity of the crystal grain boundary in order to improve the coercive force.

(Structure of the Invention) The present invention relates to a method for manufacturing a rare earth magnet, which comprises 25 to 35% by weight of RI (RI is one or more light rare earth elements consisting of Ce, Nd, Pr and Sm, provided that Of the light rare earth elements
RI-B in which Nd and / or Pr is 50% or more), 0.7 to 1.5% B, and the balance is MI (MI is Fe or Fe and Co)
-95 to 97 parts by weight of MI-based alloy composition and 30 to 8 by weight percentage
6% R II (R II is one or more heavy rare earth elements consisting of Tb, Dy, Ho, Er and Tm, provided that Tb, Dy and / or Ho of the heavy rare earth elements are 50% or more) 70 to 14% is M II (M
II is Al), and an alloy powder consisting of 5 to 3 parts by weight of the R II-M II alloy composition is molded and sintered, and the rare earth permanent magnet is R II. −M II
The alloy composition relates to a rare earth permanent magnet composed of a Laves phase of DyAl ₂ .

Explaining this in detail below, the present invention does not use the one in which the coercive force-increasing element is previously weighed and dissolved as in the prior art, and the additive element is uniformly dispersed in the ingot. In this method, the Nd-Fe-B alloy and the Al alloy, which is an element for increasing the coercive force, are separately prepared, finely pulverized, and simultaneously mixed (hereinafter referred to as a two-alloy method). In the conventional method of adding an element during melting and uniformly distributing it in the alloy, a large amount of the element had to be added in order to affect the vicinity of the grain boundary. In the method, the additive element was created separately from the matrix phase and mixed in the powder state, so Nd ₂ -Fe ₁₄
-Diffuses into the B matrix phase from the surface, but does not diffuse to the center of the crystal grain. Therefore, in the present invention, the concentration of the additive near the grain boundary is high, and there is almost no heterogeneous state in the central portion. Therefore, a small amount of the additive produces an effect of greatly affecting the anisotropic magnetic field and morphology only in the vicinity of the grain boundary, and this point was actually confirmed by an X-ray microanalyzer. In addition, iH
Since the effect of increasing c was great, the decrease of Br was small, and the maximum energy product (BH) max was high.

The RI-B-MI based alloy composition used in the present invention is composed of 25 to 35% by weight of RI, 0.7 to 1.5% of B, and the balance of MI. Ce, N
One or more kinds of light rare earth elements such as d, Pr, and Sm, and 50% or more of the light rare earth elements are Nd and / or Pr.

Also, another alloy composition used here, R II-M
II-based alloy composition 30-80% R II and 70-14% by weight
% M II (M II is Al), and this R II is one or more of the heavy rare earth elements consisting of Tb, Dy, Ho, Er, and Tm. Of which 50% or more is composed of Tb, Dy and / or Ho.

The method for producing a rare earth permanent magnet of the present invention is the RI-B-MI.
The alloy powder consisting of the system alloy composition and the R II-M II system alloy composition may be molded and sintered. These two alloy compositions have the purity of each alloy of 99.0% or more. The components may be weighed and then mixed, and an ingot obtained by melting these components in a high frequency furnace may be used.

The RI-B-MI based alloy composition and the R II-M II based alloy composition are mixed in a weight percentage of the RI-B-MI based alloy composition.
95 to 97 parts by weight and 3 to 5 parts by weight of the R II-M II alloy composition may be used, but the ratio of the R II-M II alloy in the present invention is 3 parts by weight.
The reason for limiting the range to 5 parts by weight is that if less than 3 parts by weight
This is because the iHc increasing effect is small, and if it exceeds 5 parts by weight, B
This is because the decrease of r is large. Also added R II-M II
The reason for limiting the composition of the alloy is that when the content of R II is 30% by weight or less, the alloy becomes viscous and becomes difficult to grind, and when the content of R II is 86% by weight or more, the oxidation of the alloy becomes remarkable. The heavy rare earth element is used for R II because the heavy rare earth R II ₂ -Fe ₁₄ -B compound has a larger anisotropic magnetic field than the Nd ₂ -Fe ₁₄ -B compound and has an effect of increasing coercive force. The reason why M II is Al is that it has an effect of increasing coercive force even if it is a single element.
This is because the synergistic effect of both can be expected by using the II alloy. Incidentally, the Laves phase of DyAl ₂ was particularly selected as this R II-M II alloy because it is particularly brittle and easily crushed among various R II-M II alloys and the powder is difficult to oxidize, and the addition effect is Is large. The reason why Fe is replaced with Co is that the reversible temperature coefficient is improved because the Curie point can be raised.

The RI-B-MI-based alloy composition and the RII-MII-based alloy composition are made into rare earth permanent magnets by mixing these alloy powders, molding and then sintering. 20 ingots of alloy composition with a disc mill
After coarsely pulverizing into a mesh under, weighing and mixing, finely pulverizing with a jet mill or the like, and then orienting in a magnetic field, it is preferable to obtain a compact by press molding or the like.

This sintering may be carried out by, for example, sintering the compact at 1,050 ° C. for 1 hour in Ar gas. The sintered body is then heat-treated at about 550 ° C. for 1 hour and then rapidly cooled by using an inert gas. The rare earth permanent magnet can be obtained.

(Effect of the Invention) The method for producing a rare earth permanent magnet according to the present invention is characterized by the two-alloy method in which two kinds of alloy powders having different compositions are mixed, shaped and sintered as described above. High iHc can be obtained with a small amount of additive, and the decrease of Br due to the additive element, which has been inevitable in the past, can be minimized, and (BH) ma
x can be improved. Further, since the R II-M II alloy is brittle, it is easy to be powdered, and it is possible to obtain the effect that the oxidation during fine pulverization can be reduced as compared with the rare earth metal which is not alloyed.

(Example) Next, the Example of this invention and a comparative example are given.

Example 1, Comparative Examples 1 to 3 Nd having a purity of 99.4%, Fe having a purity of 99.5%, and B having a purity of 99.5% were weighed so as to be 34% Nd, 64.9% Fe, and 1.1% B by weight, and sample I was used. And

Separately, Dy with a purity of 99.4% and Al with a purity of 99.9% were
Sample II was weighed to be 5.1 wt% Dy and 24.9 wt% Al.
And

Each was separately melted in a high frequency furnace to prepare an ingot. The ingots were separately crushed to 20 mesh under by a disc mill, and the obtained coarse powders were weighed and mixed in four weight ratios, and the average particle diameter was measured by a jet mill with N ₂ gas.
Finely pulverized to 3.0 μm. This powder was orientated in a magnetic field of 10 KOe, press-molded at a pressure of 1.5 t / cm ² into 4 compacts,
Sintering was performed in Ar gas at 1,050 ° C. for 1 hour. This sintered body was heat-treated at 550 ° C. for 1 hour and then rapidly cooled with an inert gas. The results of measuring the magnetic properties of the sintered body are shown in Table 1.

It can be seen that iHc rapidly increases depending on the amount of the Dy-Al-added alloy added, but Comparative Example 1 is the case where Sample II is not added, and Comparative Examples 2 and 3 are those in which Sample II is less than 3%. Is.

Example 2 Samples I and II were adjusted to the respective amounts shown by weight percentage in Table 2 and then the same treatment as in Example 1 was performed to obtain each sintered body. The results of measuring the magnetic properties of this sintered body are shown in Table 2.

Claims (2)

[Claims] 1. RI of 25 to 35% by weight percentage (RI is Ce, N
One or more light rare earth elements consisting of d, Pr and Sm, provided that Nd and / or Pr of the light rare earth elements are 50% or more), B of 0.7 to 1.5%, and the balance MI (MI is Fe or Fe and
95 to 97 parts by weight of the RI-B-MI alloy composition which is Co),
30% to 86% by weight of R II (R II is Tb, Dy, Ho, Er,
One or more heavy rare earth elements consisting of Tm, provided that Tb, Dy and / or Ho of the heavy rare earth elements are 50% or more) and 70
Alloy powder consisting of 5 to 3 parts by weight of an R II-M II alloy composition in which -14% is M II (M II is Al) is molded and sintered. Production method. _2. The method for producing a rare earth permanent magnet according to claim 1, wherein the R II-M II alloy composition comprises a Laves phase of DyAl ₂ .