JPS648446B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a fine powder bonded rare earth permanent magnet. FIG. 2 shows a method for manufacturing a rare earth permanent magnet according to the present invention. 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. 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 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. Competitive growth region A of crystals in the outermost layer of the ingot as shown in Figure 1
is called the chill 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 as it goes inside the ingot, and columnar crystal zones B are formed. When the conditions are right, the columnar crystal bands collide and solidification is completed, but as shown in FIG. 1, equiaxed crystals C are usually formed inside the columnar crystals B. Regarding the origin of equiaxed crystals,
Although it was not well known before, it is now clear that crystals formed on the casting wall or on the cooled surface of the molten metal are liberated and become free crystals, and these free crystals form equiaxed crystal bodies. . (A. Ohno, T.
Motegi and H.Soda: Trans.ISIJ.11 (1971)
18). A magnet using a quinary alloy of Sm-Co-Cu-Fe-Si is called a precipitation hardening type or a two-phase separation type magnet. This is because a different phase is precipitated in the matrix and magnetically hardened. of this alloy
Using a cast magnetic alloy with a quinary composition of Sm-Co-Cu-Fe-Si, we conducted various experiments on the three types of structures mentioned above. It became clear that columnar crystal bands were the most suitable for making into magnets. An example will now be explained using a resin bonded rare earth cobalt magnet. This magnet is made from a magnetic alloy using the method shown in FIG. When we use exactly the same manufacturing method to make magnets from equiaxed crystal alloy, columnar crystal alloy, and chill crystal alloy, we find that the columnar crystal alloy has a saturation magnetization of 4πIs and a coercive force.
It was found that all performances were excellent, including iHc, bHc, and the squareness of the hysteresis loop. 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 uniformity in the 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. Therefore, in order to obtain a good magnet, it is important to produce a good magnet by forming the chill crystals near the casting wall of this alloy into columnar chill crystals and forming the other parts into columnar crystals. 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, in terms of composition, the effect of columnar crystallization was most pronounced when the Sm content was
The composition had a crystal structure of 21 to 28 wt% Sm ₂ Co ₁₇ type. If Sm is less than 21% or more than 28%, a phase different from the Sm ₂ Co ₁₇ type will appear, resulting in a significant decrease in performance. Hereinafter, the effects of columnar crystals will be explained according to examples. Example 1 Using a high frequency melting furnace, 1 kg of an alloy having the composition of Alloy 1 in Table 1 was melted in an alumina crucible, and the melt was put into an iron mold with a wall thickness of 10 mm as shown in Figure 3.
It was cast at a water temperature of 1550℃. At that time, it took the form of the organization shown in Figure 1. Figure 1 shows the structure when the ingot is cut at the center. Among these parts, the chill crystal structure is A, the columnar crystal structure is B,
And let C be the equiaxed crystal structure. In this example, ingots were cut from cast ingots A, B, and C of Alloy 1, and the ingots were heated between 1130 and 1180°C.

[Table] Compact treatment was performed at the optimum temperature, followed by aging treatment at 800°C and magnetic hardening. After crushing it into a powder with an average particle size of 10μ, an organic binder is added.
It was mixed with 1.6wt%. The kneaded mixture was press-formed in a magnetic field, and the resin in the molded body was cured by applying appropriate heat (curing process) to complete a magnet. The relationship between magnetic performance and alloy structure is shown in FIGS. 4 and 5. Figure 4 shows the relationship between coercive force iHc and aging time at 800°C.
The symbol C indicates a chill crystal structure, a columnar crystal structure, and an equiaxed crystal structure, respectively. FIG. 5 shows the relationship between saturation magnetization Ms and aging time. As can be seen from FIGS. 4 and 5, higher magnetic performance was obtained in the columnar crystal structure than in other parts. Example 2 Alloys 2 and 3 shown in Table 1 were melted in the same manner as in Example 1, and cast at casting temperatures of 1400°C and 1700°C. In order to obtain columnar crystals, it is first necessary to form stable solidification nuclei on the casting wall and prevent the crystals from being released from the casting wall. However, if the pouring temperature is high, crystals may be released from the casting wall in the early stage of solidification. Even if there are crystals that do, it is possible to dissolve and eliminate them, making it easy to form columnar crystals. Observing the structures of ingots at different casting temperatures, we find that for both Alloys 2 and 3, those with low casting temperatures (1400°C) are almost entirely equiaxed crystals, while those with high casting temperatures (1700°C) are almost entirely equiaxed. The crystals were columnar. For Alloys 2 and 3, each ingot was subjected to compaction treatment at optimal conditions between 1130 and 1180°C, followed by aging treatment at 800°C for 24 hours. Then, a resin-bonded magnet was manufactured in the same manner as in Example 1. The results are shown in Tables 2 and 3. Table 2 shows the results for Alloy 2, and Table 3 shows the results for Alloy 3.

【table】

[Table] As can be seen from Tables 2 and 3, alloys 2 and 3
It can also be said that ingots with columnar crystals and cast at a high temperature have better magnetic performance. As explained above, by utilizing the columnar crystal structure, the magnetic performance of Sm ₂ Co ₁₇ type magnets can be improved compared to conventional magnets, making it possible to manufacture high-performance magnets. The high-energy product magnet of the present invention has a wide range of industrial uses, such as motors for electronic watches, small speakers, and motors.

[Brief explanation of drawings]

FIG. 1 is a cross-section of an ingot cast into a mold, taken along the center of the mold. A, B, and C represent chill crystals, columnar crystals, and equiaxed crystals, respectively. D
is the cross section of the mold. FIG. 2 shows the manufacturing process of the resin-bonded magnet. Figure 3 shows an iron mold. All walls are 10mm thick. The unit of length is mm. FIG. 4 shows the magnetic performance of magnets obtained from ingots of chill crystal A, columnar crystal B, and equiaxed crystal C, and shows the relationship between aging time and coercive force (iHc). Figure 5 shows the fourth
This figure shows the relationship between aging time and saturation magnetization (Ms) for a magnet similar to the one shown in the figure.

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, in which the alloy is composed of Sm, Co, Cu, Fe, and Si, and the Sm content is 21-28 in ratio
% range, and is characterized by using an alloy whose macrostructure is mainly a columnar crystal structure.