JPS6159388B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in the manufacturing method of rare earth cobalt permanent magnets, and relates to a manufacturing method that performs a two-stage process of heating in a vacuum atmosphere and sintering in a reduced pressure argon gas atmosphere. Rare earth cobalt magnets have a higher
As permanent magnets with high coercive force and large energy product, their demand has particularly increased in recent years, and they are used in a wide variety of fields including the electronics industry. In order to maximize the magnetic properties of rare earth cobalt magnet alloys, the manufacturing method is most important, and each process must be strictly controlled. In other words, rare earth metals have an extremely strong affinity for oxygen, and are stronger than, for example, Mg, Al, and Si, which are effective deoxidizers in ordinary steelmaking. It has properties not found in magnetic materials. Therefore, when producing rare earth cobalt magnets, it is important to process them in an inert atmosphere, and in particular, a non-oxidizing atmosphere is most important during sintering, which is at a high temperature. Therefore, various studies have been made regarding the manufacturing method of rare earth cobalt-based magnet alloys. For example, JP-A-52-4421 proposes that it is effective to use a hydrogen-containing atmosphere during sintering.
In other words, the same publication compares the magnetic properties of samarium-cobalt magnets when sintered in an argon gas and hydrogen atmosphere at 760 Torr normal pressure, and found that the sintered density was higher when sintered in hydrogen. ,
Assuming that properties such as residual magnetic flux density (Br), coercive force (Hc), and energy product ((BH)max) improve, but only coercive force (Hci) decreases, the effectiveness of sintering in a hydrogen gas atmosphere is Says. However, hydrogen gas has the lowest density of all gases and has a very high diffusion rate, so it easily leaks to the outside from, for example, minute holes in a sintering furnace. Furthermore, the amount of heat generated when hydrogen is combusted is extremely large, and when it is mixed with air in a wide range of 4 to 75% by volume, a large explosion can occur from even the slightest ignition source, making it difficult to manufacture permanent magnets in a hydrogen atmosphere. requires extremely strict handling control. In view of the above-mentioned problems, the present invention aims to improve the characteristics of a sintered magnet alloy that is easy to handle and inexpensive.
Various studies have been conducted on the sintering atmosphere in which this can be achieved. That is, the present invention involves forming a rare earth cobalt magnet alloy powder made of cobalt containing a rare earth metal, the cobalt-copper alloy, the cobalt-iron-copper alloy, the cobalt-iron-nickel-copper alloy, etc. into a predetermined shape. Compress to make a molded body, and this molded body 1
Raise the temperature from room temperature to 800°C at a rate of 4 to 20°C/min in a vacuum atmosphere of ×10 ^-2 Torr or less,
This is a method for producing a rare earth cobalt-based permanent magnet, the gist of which is then sintering in a temperature range of 950 to 1250° C. in a reduced pressure argon gas atmosphere of 50 to 350 Torr. Next, the manufacturing method according to the present invention will be explained in detail. First, a rare earth cobalt magnet alloy powder consisting of cobalt containing a rare earth metal, the above cobalt-copper alloy, the above cobalt-iron-copper alloy, the above-mentioned cobalt-iron-nickel-copper alloy, etc., is mixed with an average particle size of 2 to 10
The powder is pulverized into a micron-sized powder, and a compression molded body of a predetermined shape is produced using a press machine in a magnetic field. Next, in order to promptly remove oxygen, water vapor, hydrogen gas, etc. adsorbed or occluded in the compression molded body and to maximize the effect of the subsequent sintering in a reduced pressure argon atmosphere, the following steps were carried out. Perform pre-processing such as That is, the temperature of the above molded body is raised from room temperature to 800°C, but at the same time as degassing treatment, it is slowly heated at a rate of 4 to 20°C/min in a vacuum atmosphere of 1 × 10 ^-2 Torr or less to prevent oxidation. and raise the temperature. The reason for limiting the heating rate is that if the heating rate is less than 4°C/min, it will take more than 3 hours to raise the temperature to 800°C, making it unsuitable for industrial production. This is because the molded body is oxidized, and if the temperature exceeds 20°C/min, the temperature rises too quickly and the adsorbed and occluded gases in the molded body cannot be sufficiently removed. This is because the effect of improving properties due to atmosphere sintering cannot be obtained. During this heating process, approximately 90% of the adsorbed and occluded gas in the molded body is released in the temperature range of 200 to 600°C, so the heating rate in this temperature range is set to 4 to 10°C/ It is preferable to carry out the degassing treatment while preventing oxidation by keeping the temperature in a high vacuum atmosphere of about 1×10 ⁻⁴ to ^{10 −5} Torr. Next, sintering is performed, but after the above degassing treatment,
The process of increasing the temperature beyond 800℃ to the temperature range of 950 to 1250℃ and the sintering process of maintaining a constant temperature in the above temperature range are in order to increase the density after sintering to near the theoretical density and improve the magnetic properties. Next, sintering is performed in an argon gas atmosphere at a reduced pressure of 50 to 350 Torr. In addition, the atmospheric pressure during the cooling process after the completion of sintering is not particularly specified, but in order to reduce the consumption of argon gas and reduce costs, it is recommended that
Cooling in an argon gas atmosphere at a reduced pressure of 350 Torr is preferred. Here, the reason for limiting the argon gas atmosphere pressure is that at a low pressure of less than 50 Torr, the components of the rare earth cobalt magnet alloy, especially the vapor pressure of the rare earth component, is as high as 20 to 30 Torr at 800°C or higher, so rare earth metals are prioritized. The final sintered body will have a composition different from the predetermined one, resulting in significant deterioration of magnetic properties, so the temperature should be 50 Torr or more.
In addition, when the pressure exceeds 350 Torr, as is clear from Figure 1, which shows the relationship between argon gas pressure and the obtained magnetic properties, sufficient improvement in density cannot be obtained, and in the end, excellent magnetic properties cannot be obtained. Since the characteristics cannot be obtained, the pressure should be 350 Torr or less. The reason for limiting the sintering temperature range is that the optimal sintering temperature range for rare earth cobalt magnet alloys varies depending on their constituent components and their composition ratios, but a sintering temperature of less than 950°C is sufficient for sintering. The sintering temperature is set at 950°C to 1250°C, since a high density cannot be obtained and the alloy melts at a sintering temperature exceeding 1250°C, and a sintered magnet body with good properties cannot be obtained. Examples according to the present invention will be shown below to clarify its effects. Example 1 A base alloy consisting of 33.8wt% Sm with a purity of 99.9% or more and 66.2wt% Co with a purity of 99.9% or more was produced by arc button melting. Similarly, Sm60wt
%, and an additive alloy consisting of 40wt% Co was prepared. Next, after coarsely crushing this base alloy and additive alloy, 50 gr of base alloy and 6 gr of additive alloy were prepared.
120 c.c. organic solvent, stainless steel ball
The mixture was placed in a ball mill with 500 gr and mixed and pulverized to obtain a fine powder of 2 to 10 μm. Next, add fine powder〓〓〓〓〓
A compression molded body was produced by press molding in a magnetic field of 10 KOe. Next, the molded body was heated to 700°C in a vacuum atmosphere of 1×10 ^-3 Torr at a heating rate of 10°C/min, and then heated at 1140°C for 1 hour in a reduced pressure argon gas atmosphere of 200 Torr. sintering and further furnace cooling treatment in the same atmosphere. after that,
Aging treatment was performed at 900°C for 5 hours to obtain a magnet according to the method of the present invention. In addition, as a comparative example, the above molded body was
In a normal pressure argon gas atmosphere, the temperature is raised with exactly the same heat pattern as the method of this invention described above.
A magnet was obtained by sintering, furnace cooling, and aging treatment. The magnetic properties of the obtained permanent magnet are shown in Table 1.
As is clear from Table 1, it can be seen that the rare earth cobalt based magnet produced by the method of the present invention has superior properties to the comparative example in which the magnet is sintered in an argon gas atmosphere at normal pressure.

[Table] Example 2 Sm17.1wt% and Pr16.0wt% with purity 99.9%,
Base alloy consisting of Co66.9wt%, with purity 99.9%
An alloy for addition consisting of 60 wt% Sm and 40 wt% Co was produced in the same manner as in Example 1, and then coarsely ground. Then, 50 gr of base alloy and 6 gr of additive alloy were blended, and a compression molded body was produced in the same manner as in Example 1. This molded body was heated at a rate of 10°C/min to 700°C in a vacuum atmosphere of 1 × 10 ^-3 Torr,
Subsequently, sintering was performed at 1090℃ for 1 hour in a reduced pressure argon gas atmosphere of 200Torr, followed by furnace cooling, and further aging treatment at 900℃ for 5 hours.
A permanent magnet was obtained by the method of this invention. Further, as a comparative example, a magnet was produced using a sintering atmosphere of 760 Torr normal pressure argon gas atmosphere and a heat pattern under the same conditions as in the method of this invention described above. The magnetic properties of the obtained permanent magnet are shown in Table 2.

[Table] Example 3 Sm27.0wt% with purity of 99.9% or more, Co43.9wt% with purity of 99.8% or more, Fe13.2wt%, Ni8.0wt%,
An alloy consisting of 7.9wt% Cu was radiofrequency melted in an argon gas atmosphere and coarsely ground in an iron mortar. The coarsely ground powder was ground into a fine powder of 2 to 10 μm by ball milling in an organic solvent. This fine powder
A compression molded body was produced by press molding in a magnetic field of 12 KOe. Next, the molded body was heated to 800°C at a rate of 10°C/min in a vacuum atmosphere of 1 × 10 ^-3 Torr, and then heated to 800°C at a rate of 10°C/min at normal pressure (760Torr) and 560Torr.
360Torr, 260Torr, 200Torr, 60Torr, 0.1Torr
In seven types of reduced pressure argon gas atmospheres,
Sintering was performed at 1200°C for 2 hours, followed by rapid cooling. Then, it was aged at 800℃ for 4 hours.
The characteristics of the obtained magnet were measured, and the relationship between the argon gas atmosphere pressure and the magnet characteristics is shown in FIG. Table 3 shows the case of the argon gas atmosphere pressure of 200 Torr, which is the method of this invention, and the case of the comparative example.
It shows the magnetic properties of the magnet at 760Torr.

[Table] As is clear from the above results, the method of this invention, in which the molded body is first heated to 800°C in a vacuum atmosphere and then sintered in a reduced pressure argon gas atmosphere, is effective in improving density. in,
Accordingly, the magnetic properties are improved, and an excellent rare earth cobalt magnet can be manufactured. 〓〓〓〓〓

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the argon gas pressure in the sintering atmosphere and the magnetic properties of the obtained magnet. 〓〓〓〓〓

Claims (1)

[Claims] 1 Compression molding of rare earth cobalt magnet alloy powder is performed, and the molding is heated from room temperature to 800°C for 4 to 20 minutes in a vacuum atmosphere of 1×10 ^-2 Torr or less.
1. A method for producing a rare earth cobalt permanent magnet, which comprises raising the temperature at a rate of 0.degree. C./min, and then performing sintering at a temperature range of 950 to 1250.degree. C. in a reduced pressure argon gas atmosphere of 50 to 350 Torr.