JPS648448B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a precipitation type rare earth permanent magnet. A method for manufacturing a rare earth permanent magnet according to the present invention is shown in FIG. It has long been known that the magnetic performance of this magnet is affected by alloy composition, heat treatment, powder particle size and shape, molding method, etc., but now we have newly discovered that the macrostructure of the cast ingot can significantly change the magnetic performance. I found out what to do. Generally, when molten metal is poured from a crucible into a mold, it begins to solidify from the mold. This is explained by the fact that the energy barrier to stable nucleation of embryos (crystal buds) that come into contact with solid foreign matter is smaller than that of embryos that float in the melt without contact. Crystals formed on the casting wall grow into the molten metal while competing with neighboring crystals. The competitive growth region of crystals in the outermost layer of the ingot, as shown in FIG. 3, is called the chill crystal zone. Since crystals have anisotropy in growth rate, crystals whose direction of maximum growth rate is parallel to the direction of heat flow grow preferentially, suppressing the growth of adjacent crystals. During crystal growth, the closer the preferential orientation is to the heat flow, the longer the crystals survive, and other crystals are weeded out. As a result, the number of crystals decreases toward the inside of the ingot, forming columnar crystal zones. When the conditions are right, the columnar crystal bands collide and solidification is completed, but as shown in FIG. 3, equiaxed crystals are usually formed inside the columnar crystals. Although the origin of equiaxed crystals was not well known before, it is now known that crystals formed on the casting wall or on the cooled surface of the liquid become free crystals, and these free crystals form equiaxed crystals. (A. Ohno, T. Motegi, andH.
Soda: Trans. ISIJ11 (1971) 18). Magnets using Sm-Pr-Co-Cu alloys fall into the category of precipitation hardening type or two-phase separation type magnets.
This is because a different phase is precipitated in the matrix and magnetically hardened. This system of magnets was initially
It is an Sm-Co-Cu ternary alloy that has been widely developed since it was first made into a magnet with a composition mainly using Sm ₂ Co ₁₇ type crystals. When a part of Sm is replaced with Pr, it becomes possible to obtain a magnet with a high energy product because the Pr ₂ Co ₁₇ type has a higher saturation magnetization 4πIs than the Sm ₂ Co ₁₇ type. Also, from the viewpoint of securing rare earth metal resources, it is convenient because both Sm and Pr can be used. However, Sm
When a part of is replaced with Pr, 4πIs increases, but the value of the anisotropic magnetic field Ha decreases. If Ha decreases, coercive force iHc will also inevitably decrease. Therefore, one object of the present invention is to prevent the decrease in iHc caused by the addition of Pr by converting the ingot into columnar crystals. In this alloy, as mentioned above, it has become clear that among the chill crystal zone, columnar crystal zone, and equiaxed crystal zone, the columnar crystal zone is the most suitable for making into a magnet. Regarding chill crystals, between equiaxed chill crystals and columnar chill crystals, columnar chill crystals are superior.
An example will now be explained using a resin bonded rare earth cobalt magnet. This magnet is made from a magnetic alloy by the method shown in FIG. The manufacturing method is exactly the same,
When using equiaxed crystal alloys, columnar crystal alloys, and chill crystal alloys as magnets, the columnar crystal alloys are superior in all performances, such as saturation magnetization 4πIs, coercivity iHc, bHc, and hysteresis loop squareness. I found out that there was. On the contrary, equiaxed crystal alloys and equiaxed chill crystal alloys have the poorest performance. Columnar chill crystal alloys produce magnets with values intermediate between these. This is thought to be because the columnar crystal structure acts effectively when the alloy is heat treated (solution treatment and aging treatment). That is, it is thought that the columnar crystals promote uniform distribution of different phase precipitates precipitated in the matrix, thereby improving the squareness of the hysteresis. At the same time, it is thought that the crystal structure and morphology of precipitates also act to increase iHc, and therefore
iHc also improves. Regarding the production of this alloy, it is important to produce a good magnet by using columnar chill crystals in the chill crystal zone near the casting wall and columnar crystals in other parts. Since the amount of telluric crystal bands is small in the whole alloy, the most important thing in manufacturing is to prevent equiaxed crystal bands and increase the ratio of columnar crystal bands. The most effective composition formula using atomic ratios is Sm _1-x Pr _x (Co _1-u Cu _u ) _z (0<x<0.5 0<u<0.2 6.5≦z< 9.0) is an alloy represented by The reason for limiting the components and composition range will be explained below. In this alloy system and its composition range, Sm-
Co type is the basic type. Among them, Sm ₂ Co ₁₇ type crystals are the main type. Cu is added to obtain the coercive force of the Sm ₂ Co ₁₇ type alloy, and adding Cu improves iHc, but lowers 4πIs. Therefore, as a practical magnetic material, the value of u in the composition formula is
<0.2 is desirable. When the value of z is between 5z8.5, the Sm-Co alloy is similar to the SmCo type ₅ compound.
Separates into Sm ₂ Co ₁₇ type compounds. The value of 4πIs is
Sm ₂ Co ₁₇ type is more expensive. Therefore, in order to realize a high 4πIs, it is desirable that z be 6.5 or more. Also z
When is 9.0 or more, the Co phase increases and the squareness of the hysteresis loop deteriorates, which is preferable. In addition, the Pr ₂ Co ₁₇ type compound has a larger value of 4πIs than the Sm ₂ Co ₁₇ type compound, but the crystal magnetic anisotropy constant K ₁
is negative, and if the Pr ₂ Co ₁₇ type is used as is, a magnet using uniaxial anisotropy cannot be made. Therefore, by combining a Sm ₂ Co ₁₇ type compound with a large positive K ₁ and a Pr ₂ Co ₁₇ type compound with a large 4πIs to make a magnet, a magnet with a large saturation magnetization and a somewhat high coercive force can be obtained. This is an effective method for For this occasion
In the Sm _1-x Pr _x (Co _1-u Cu _u ) _z composition, x<0.5 is desirable for a practical material. If the value of x is larger than that, iHc becomes insufficient. As mentioned above, the performance of the ingot is improved by the macrostructure during casting, and the magnet manufacturing method that can best utilize this fact is the fine powder bonded magnet. This is because manufacturing the magnet requires the steps shown in Figure 1, so all heat treatment is done as an ingot, and after magnetic hardening,
Grind and bind with binder. Therefore, it can be magnetized in the ingot state, and in this respect it is no different from cast magnets. The purpose of binding with a binder is to align the crystals, improve moldability and reduce costs when making actual products, and the essence of magnetism is the same as that of cast magnets. For this reason, in the sintering method, the performance of the magnet is not affected by the metal structure of the ingot during casting, but in the case of fine powder bonded magnets, it is greatly affected. In other words, this can be used to improve the performance of fine powder bonded magnets. Hereinafter, the present invention will be explained in detail according to examples. Example 1 An alloy having the composition shown in Table 1 was melted in an argon gas atmosphere using a high frequency melting furnace. The cylindrical iron mold shown in FIG. 2 was used for casting.

[Table] The macrostructure of the cast ingot was as shown in Figure 3. A, B and C indicate the chill zone, columnar zone and equiaxed zone, respectively. B
The portions C and C were cut out from each ingot, and magnets were manufactured according to the manufacturing process for resin-bonded magnets shown in FIG. However, solution treatment is performed at a temperature between 1100 and 1200℃ for 24 hours, and aging is
The temperature was 800℃ for 24 hours. The magnet molding method is Manufacturing Method 1
I followed. The results are shown in FIG. As the Pr content increases, 4πIs increases and iHc decreases. However, it can be seen that for any composition, the columnar crystal zone has better magnetic performance than the equiaxed crystal zone. Example 2 In the same manner as in Example 1, the alloys shown in Table 2 were cast.

【table】

[Table] Cut out the columnar crystal part and the equiaxed crystal part, Example 1
A resin-bonded magnet was fabricated using the same method as in . The results are shown in Table 3.

[Table] Compared to columnar crystals, equiaxed crystals have 4πIs,
Not only are Br and iHc low, but the squareness Br/4πIs is also low. Therefore, due to the columnar crystals, Sm−Pr−
It was found that the magnetism of the Co-Cu alloy was greatly improved. In this way, fine powder bonded magnets using an alloy that increases saturation magnetization by adding Pr to the Sm-Co-Cu alloy and further improves coercive force and squareness through columnar crystallization have excellent magnetic performance, formability, and processability. It is superior in terms of performance and cost, and has great utility not only in the precision industry but in other industries as well.

[Brief explanation of drawings]

FIG. 1 shows the manufacturing process of a resin-bonded magnet. Figure 2 shows a round iron mold. Dimensions are in mm
It is. FIG. 3 shows the macrostructure of the ingot when it is cast into the mold shown in FIG. A
is a chill crystal zone, B is a columnar crystal zone, C is an equiaxed crystal zone, and D is a cross section of the side surface of the mold. Figure 4 shows Sm _1-x Pr _x
(Co _0.9 Cu _0.1 ) The magnetic properties of the resin-bonded magnet when x is changed in _8.3 are shown.

Claims (1)

[Claims] 1. A rare earth permanent magnet formed by kneading a binder into powder of an alloy mainly composed of Sm ₂ Co ₁₇ type crystals and molding the alloy, wherein the alloy has a composition using an atomic ratio of Sm _{1-x Pr _ _ _} A rare earth permanent magnet characterized by: