JPH0680608B2 - Rare earth magnet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on an R ₂ T ₁₄ B system containing a rare earth metal (R), a transition metal (T), and boron (B) as a main component, represented by Nd / Fe / B system permanent magnets. The present invention relates to a method for manufacturing an intermetallic compound magnet, and particularly to improvement of magnet characteristics when a permanent magnet is manufactured by a powder metallurgy method.

The method of manufacturing the R / Fe / B magnet is roughly classified into two methods. One is a polymer composite type magnet manufactured by ultra-quenching a molten alloy and orienting crushed magnet powder in a magnetic field. One is a sintered magnet, which is manufactured by pulverizing an ingot of a magnet alloy obtained by melting, shaping it in a magnetic field, and then sintering it. The present invention relates to sintered magnets.

As a literature on sintered type magnets manufactured by powder metallurgy of R / Fe / B-based magnets, refer to Japanese Patent Application Laid-Open No. 59-46008 and the 35th research meeting material of the Japan Society for Applied Magnetics "Nd / Fe / B-based new magnets". (May 1984). These documents describe a method of using a melted and cast alloy ingot as a raw material, crushing and molding, and then sintering in an Ar atmosphere.

In general, the manufacturing process of the present magnet by the powder metallurgy method proceeds in the order of melting of raw material alloy, pulverization, orientation in a magnetic field, compression molding, sintering, and aging. Melting is usually performed in a vacuum such as an arc or a high frequency or in an inert atmosphere, and is cast to obtain a raw material ingot. Grinding is divided into coarse grinding and fine grinding,
Coarse crushing is performed with a jaw crusher, an iron pestle, a disc mill, a roll mill, or the like. The fine pulverization is performed with a ball mill, a vibration mill, a jet mill or the like. Magnetic field orientation and compression molding are typically performed simultaneously in a magnetic field using a mold. Sintering is performed in the range of 1000-1150 ° C in an inert atmosphere. Aging is performed at a temperature near 600 ° C.

The present inventor, as a result of repeating various experiments, in these steps, as an alloy raw material, not a usual melt-casting ingot, but a heat treatment of an alloy ribbon produced by quenching a melted alloy, It has been discovered that by using it as a raw material, a remarkable improvement in magnet characteristics is realized. This system magnet alloy is roughly divided into main phase (R ₂ T ₁₄ B), Brich phase, N dric
It is a composite alloy consisting of three types of h-phase. Further, it can be said that the alloy raw material ingot is in a state of unstable phase formation such as precipitation of Fe phase. In particular, precipitation of the Fe phase causes a marked deterioration in magnet characteristics. Also, the sinterability of the powder compact depends largely on the dispersibility of the Ndrich phase, and the one with poor dispersibility leads to an increase in the sintering temperature, and at the same time, ₁ H _c is significantly reduced, which is an industrial disadvantage. Become. The dispersibility of N drich in the conventional raw material ingot is not in a good state in the powder compact because the crystal grains forming the ingot are large.

Therefore, the present inventor has found that the magnet characteristics are remarkably improved by reducing the Fe phase in the alloy raw material and improving the dispersibility of the Ndrich phase. In order to satisfy both of these at the same time, the melted alloy is rapidly cooled to form a ribbon, which is then heat-treated to grow the main phase crystal grains, so that there is no Fe precipitate phase and the N drich phase An alloy raw material having high dispersibility can be obtained. The crystal grain size of the main phase in the alloy raw material is most preferably about 3 to 10 μm, and the suitable heat treatment temperature varies depending on the composition of the alloy, but if it is a neodymium-iron-boron system magnet composition, it is in the range of 600 to 1100 ° C. is there.

Next, examples will be described.

[Example 1] Nd with a purity of 98% (the rest other rare earth elements), ferroboron (B purity of about 20%) and electrolytic iron were used, and Nd was 32.0 wt%.
It was melted by high-frequency heating in an argon atmosphere so that B was 1.0 wt% and the balance was Fe, and was rapidly cooled by spraying on a rotating iron roll to obtain a quenched ribbon having a thickness of about 50 μm.

Next, this alloy ribbon was heat-treated at 900 ° C. for 1 hour in Ar atmosphere and then rapidly cooled.

On the other hand, for comparison, the same raw material was used and ingots having the same composition were melted by high frequency heating in an argon atmosphere. This is a normal manufacturing method.

These alloy raw materials were roughly pulverized and then finely pulverized with a ball mill to an average particle size of about 3 μm. This fine crush
Molding was performed in a magnetic field of 10 KOe at a pressure of 1 ton / cm ² . This compact was held at 1080 ° C. in vacuum for 1 hour and then in Ar for 1 hour for sintering. Then, it was gradually cooled to 300 ° C. at a cooling rate of 100 ° C./hr or less and then rapidly cooled. This sintered body was aged at 550 ° C. for 1 hour. The measurement results of the magnet characteristics are shown in the table.

When the alloy raw material obtained by heat-treating the quenched ribbon which is the method of the present invention is used, Br, ₁ H _c and (BH) max show remarkably high values. It was also confirmed that the sinterability was improved by changing the sintering temperature.

Example 2 Using the quenched ribbon produced in Example 1, 600 ° C., 7
It heat-processed at 00 degreeC, 800 degreeC, 900 degreeC, 1000 degreeC, 1100 degreeC, and 1200 degreeC in Ar atmosphere for 1 hour.

Next, the cross section of the heat-treated alloy ribbon was polished and observed with an optical microscope. As a result, Ndric in the main phase (R ₂ T ₁₄ B) was observed.
The h phase was dispersed, and the grain size of them grew with the increase of the heat treatment temperature, and the dispersity of the Ndrich phase was obviously decreased in the 1200 ℃ heat treatment data. The average crystal grain size of the main phase in these heat-treated alloy ribbons is shown in FIG. 1 as Ic.

Next, in the same manner as in Example 1, fine pulverization, magnetic field molding, sintering, and heat treatment were performed to measure the magnet characteristics. As a result,
Through FIG.

Compared with the comparative example of the ingot alloy raw material shown in Example 1,
The magnet characteristics clearly show a high maximum energy product (BH) max in the heat treatment temperature range of 700 ℃ to 1100 ℃.

At a heat treatment temperature of 700 ° C. or less, the magnetic field orientation of crystal grains becomes insufficient, and the residual magnetic flux density Br of the sintered body decreases,
On the other hand, above 1200 ° C, the dispersion of Ndrich particles decreases, the sinterability decreases, and the squareness of the demagnetization curve decreases.
A high maximum energy product cannot be obtained due to the reduction of Hc and residual magnetic flux density Br.

Although only the Nd / Fe / B-based magnets are described in the above examples, the present invention heat-treats the alloy quenched ribbon to grow the main phase (R ₂ T ₁₄ B) crystal particles, and the alloy. It is used as a raw material and obtains magnet characteristics higher than those of ordinary manufacturing methods. Therefore, not only a single component of Nd / Fe / B but also a rare earth element such as Ce, Pr, Dy, Gd, Ho, Tb and Y or
It is obvious that the present invention can also be applied to Nd / Fe / B system magnet alloys containing transition metals such as Co and Ni.

The present invention has been described in detail above. In a method for producing an R ₂ T ₁₄ B-based magnet by a powder metallurgy method, a quenched ribbon of an alloy is heat-treated and then used as an alloy raw material to significantly increase the magnet characteristics. Can be realized,
The present invention is very useful industrially.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the relationship between the heat treatment temperature of the alloy ribbon and the average grain size Ic of the main phase (Nd ₂ Fe ₁₄ B phase) in the alloy ribbon in Example 2. FIG. 2 shows the relationship between the heat treatment temperature of the alloy ribbon and the maximum energy product (BH) max of the sintered magnet in Example 2. FIG. 3 shows the relationship between the heat treatment temperature of the alloy ribbon and the residual magnetic flux density Br of the sintered magnet in Example 2. FIG. 4 shows the relationship between the heat treatment temperature of the alloy ribbon and the coercive force ₁ H _c of the sintered magnet in Example 2.

Claims (1)

[Claims] 1. R ₂ T ₁₄ containing Nd, Fe and B as main components.
B-based magnet (where R is yttrium and a rare earth element,
T represents a transition metal. ) By a powder metallurgy method, the quenched ribbon of the alloy is heat treated at 700 to 1100 ° C. so that the crystal grain size of the R ₂ T ₁₄ B phase becomes 3 to 10 μm, and then crushed, molded and sintered. , A method for manufacturing a rare earth magnet characterized by aging.