JPS648456B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a precipitation-type rare earth permanent magnet whose main components are rare earth elements and transition metals. 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 influenced by alloy composition, heat treatment, powder particle size and shape, binder type, molding method, etc. We found that the performance changed significantly. Magnets using Sm-Ce-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 series of magnets was initially made of Sm-Co-Cu ternary alloy, mainly
It has been widely developed since it was first made into a magnet with a composition using Sm ₂ Co ₁₇ type crystal. When part of Sm is replaced with cerium (Ce), saturation magnetization
4πIs is slightly higher (about 8%) in Ce ₂ Co ₁₇ type than in Sm ₂ Co ₁₇ type.
Although it is low, since the price of Ce is less than half that of Sm, it is possible to manufacture magnets with a high energy product and at a low price. Also, from the viewpoint of securing rare earth metal resources, it is advantageous because both Sm and Ce can be used. The anisotropic magnetic field of Sm ₂ Co ₁₇ type is
It is about 100 KOe at room temperature, while the Ce ₂ Co ₁₇ type has about 15 KOe under the same conditions. Therefore, Sm ₂ Co ₁₇ type
As part of Sm is replaced with Ce, the anisotropy field decreases, making it difficult to obtain a large coercive force iHc. Therefore, one objective of the present invention is to
The objective is to prevent the decrease in iHc caused by replacing Sm with Ce by converting the ingot into columnar crystals. Another purpose is to offset the slight decrease in 4πIs caused by replacing Sm with Ce by increasing 4πIs by crystallizing the ingot into columnar shapes. In this way, the cost of rare earth cobalt magnets, which are expensive as magnetic materials, can be reduced without reducing their performance. Next, we will discuss the solidification of metals and clarify why columnar crystal alloys have good performance. Generally, when molten metal is poured from a crucible into a mold, solidification begins at the casting walls. This is explained by the fact that the energy barrier for stable nucleation of embryos (crystal buds) that have come into contact with a solid foreign material is smaller than that of embryos that are floating in solution 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 preferred 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 as they move inside 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, and H.
Soda: Trans.ISIJ.11 (1971) 18). Even in this alloy, as mentioned above, chill crystal bands,
It has become clear that among the columnar crystal bands and equiaxed crystal bands, the columnar crystal band is the most suitable for making into magnets.
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.
If we make magnets using equiaxed crystal alloys, columnar crystal alloys, and chilled crystal alloys using exactly the same manufacturing method, we find that the columnar crystal alloys have the same characteristics as the saturation magnetization 4πIs, the coercive forces iHc, bHc, and the squareness of the hysteresis loop. It was found that the performance was excellent across the board. 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. In manufacturing 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 chill crystal bands is small in the overall alloy, the most important thing in manufacturing is to prevent equiaxed crystal bands and increase the ratio of columnar crystal bands. In addition, the composition that is expected to have the most effect due to columnar crystallization is the composition using the atomic ratio: Sm _1-x Ce _x (Co _1-u Cu _u ) _z (where 0<x< 0.5 0<u<0.2 6.5≦z<9.0). 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 when Cu is added, iHc
will improve. However, since 4πIs decreases, for practical magnetic materials, the value of u in the composition formula should be u<0.2
is desirable. When the value of z is 5z8.5, Sm
-Co alloy is separated into SmCo ₅ type compound and Sm ₂ Co ₁₇ type compound. 4πIs is about 20% higher for Sm ₂ Co ₁₇ type, so to realize a magnet with high 4πIs, z
6.5 is preferable. Moreover, when z is 9.0 or more, the Co phase increases and the squareness of the hysteresis curve deteriorates, which is not preferable. Furthermore, as mentioned above, Ce ₂ Co ₁₇ type compounds are more sensitive to anisotropic magnetic fields than Sm ₂ Co ₁₇ type compounds.
Since Ha is low and it is difficult to obtain a coercive force, and 4πIs is also slightly low, in order to realize a magnet with a high energy product, in the Sm _1-x Ce _x (CoCu) _z composition, x <
0.5 is preferable. As mentioned above, the magnetic performance of the ingot is improved by improving 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 FIG. 1, so the ingot is magnetically hardened by heat treatment, then crushed and bonded with a binder. Therefore, it can be made into a magnet in the ingot state. In this respect, it is no different from a cast magnet. The purpose of binding with a binder is to orient the crystals, improve formability and reduce costs when making actual products, and the essence of magnetism is the same as that of cast magnets. If a magnet is manufactured by a sintering method, the performance of the magnet will hardly be affected by the cast structure of the ingot due to the sintering process and recrystallization process during sintering. However, as mentioned above, the fine powder bonding method is greatly affected by the casting structure. Conversely, this fact can be used to improve the performance of fine powder bonded magnets by improving the casting structure. 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. Even if the Ce content is high, the 4πIs of the columnar crystal is not lower than that of the equiaxed crystal without Ce. Also, iHc is preferably a columnar crystal. Chill crystals are more 4πIs than columnar crystals.
The weight was about 0.2KG lower, and the iHc was the same. Example 2 In the same manner as in Example 1, the alloys shown in Table 2 were cast. Example 1: Cut out the columnar crystal part and the equiaxed crystal part.
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 ratio Br/4πIs is also low. Therefore, due to columnar crystals, Sm−Ce−
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 lowers cost by adding Ce to the Sm-Co-Cu alloy and improves coercive force and squareness through columnar crystallization have excellent magnetic performance, formability, workability, It is excellent in terms of cost and has benefits not only for the precision industry but also for other industries.

【table】

【table】 big.

[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 etc., 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 Ce _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 mixing a binder with powder of an alloy mainly composed of Sm ₂ Co ₁₇ type crystals and molding the mixture, wherein the alloy has a composition using an atomic ratio of Sm _1-x We used an alloy represented by Ce _x (Co _1-u Cu _u ) _z (0<x<0.5 0<u<0.2 6.5≦z<9.0) and whose macrostructure is mainly a columnar crystal structure. A rare earth permanent magnet characterized by: