JPS5819409A - Manufacture of isotropic mn-al-c magnet - Google Patents

Abstract

PURPOSE:To obtain a high density isotropic Mn-Al-C magnet of high performance by sintering a molded body of Mn-Al-C powder having a prescribed composition in an evacuated atmosphere under a specified partial pressure of gaseous CO and by subjecting the sintered body to hot hydrostatic pressure molding and soln. heat treatment. CONSTITUTION:A magnet material consisting of 70wt% Mn, 29.5% Al and 0.5% C is cast, pulsverized, and cold molded into a prescribed shape. The molded body is sintered in an evacuated atmosphere under 1-100Torr partial pressure of gaseous CO. The sintered body is subjected to hot hydrostatic pressure molding at about 1,000-1,100 deg.C to increase the density, and soln. heat treatment is carried out in a cooling stage. By this method a sintered isotropic Mn- Al-C magnet comparable to a refined material in magnetic characteristics can be manufactured simply.

Description

DETAILED DESCRIPTION OF THE INVENTION Mn-Aj! -C-based magnets are materials that do not use CO, which is a rare resource, and are therefore highly economical. They are also lightweight and have a large amount of magnetic energy per unit weight, making them useful for improving the performance, weight, and thickness of magnet-applied equipment. It is suitable and has been actively developed for practical use.

This material has excellent machinability when compared to other magnet materials such as alnico alloys, but its hardness is HRc50-55.
Because of its high surface area, it is also a difficult material to cut, and the efficiency of turning and drilling is extremely poor, which poses a problem in practical use.

Powder metallurgy may be used as one of the methods for manufacturing magnetic components that are difficult to cut.

However, Mn-fi-12-
It has been extremely difficult to produce C-based materials. This is because, as mentioned above, Mn-A-no-C materials are hard and brittle, making it difficult to mold them, and because the main components are Mn and M, which have extremely high bonding strength with oxygen, they easily oxidize during heating. This is because sintering hardly progresses. For this reason, for example, a method was proposed in which the sintering atmosphere was made of high-purity hydrogen, but this method had no significant effect and could not be used as a magnet because a sintered body with sufficient density could not be obtained. Also, a method of adding a low melting point element and sintering (Japanese Patent Application Laid-Open No. 55-100
No. 944) has been proposed, but its magnetic properties were not sufficient.

As described above, it has been difficult to manufacture high-performance sintered Mn-A No. 0 magnets using conventional powder metallurgy methods.

The present invention is based on the discovery that it is possible to sinter a magnet with higher performance than vacuum recapture sintering with a CO gas partial pressure of 1-1'00 Torr, and furthermore, this sintered body can be sintered by hot isostatic pressing. It is isotropically densified and has almost no pores, so it has performance comparable to that of ingot lumber. We have discovered a method to obtain magnetic materials.

A method of obtaining a dense molded body without voids or voids by hot isostatic pressing (hereinafter referred to as 1 (abbreviated as IP)) a sintered body has already been widely put into practical use.

However, it has conventionally been impossible to densify Mn-A/C-based materials by applying HIP.

This is because sintered bodies made using conventional powder metallurgy have a high porosity and more continuous pores than independent pores. This is because the pores are easily penetrated, no pressure from the surroundings that would crush the pores acts, and no volume change occurs due to plastic deformation. Of course, there is also a method of sealing such a sintered body in an airtight container and HIPing it, but it is meaningless for this material because it significantly impairs economic efficiency.

However, according to the sintering method of the present invention, a good sintered body with almost no continuous pores, low porosity, and low oxide content can be obtained, so HIP treatment can be easily performed. became possible.

First, sintering in reduced pressure Co gas will be explained.

In Mn-fiJ-C alloys, Mn and M oxides are formed on the powder surface, so these oxides cannot be reduced and removed during sintering in a conventional atmosphere, and the remaining oxides become magnetic. It was inevitable that the characteristics would be lost. The oxide of Mn is mainly MnO, and the dissociation pressure of this oxide is ΔG0 = 91950-17.4T in the formula MnO'+10g, so when the maximum heating temperature is 1200°C, IQ
-19 or more, and it was impossible to decompose it under normal vacuum.

On the other hand, the method of reducing MnO with carbon is MnO+
Since C':: Mn + C0 ΔG0 = 65250-38.857, MnO cannot be reduced unless the heating temperature is 1428°C or higher, and at this temperature Mn -
The AJ-C alloy turned into a melt and could not be sintered. However, in the method of the present invention, by reducing the pressure of the CO gas in the above reaction, that is, P. . =7
60'' = 760, it was found that a good sintered body could be obtained by lowering the equilibrium reaction temperature to below the melting point.The partial pressure of CO gas was l Tor.
When the temperature is lower than r, the atmosphere becomes similar to a high vacuum atmosphere, and although based on simple thermodynamic calculations it seems that the reduction reaction is more likely to occur, in reality, the C in the Mn-A no C is consumed, and the optimum condition is reached. This is undesirable as it deviates from the composition range. That is, it has been found that supplying an appropriate amount of C from the atmosphere is a condition for obtaining a good sintered body. On the other hand, we have also found that even if Pco is higher than the theoretical partial pressure at which MnO can be reduced at that temperature, sufficient sintering can be achieved by using a low-oxygen powder. The reason for this is that the oxygen partial pressure in the atmospheric gas is low (M
This seems to be because oxidation of the n-A-jl-C alloy is suppressed.

Experimental results P. Good sintering was possible when 0 was 1 to 100 Torr.

A requirement of the present invention is to produce a high-performance Mn-A)-〇-based magnet sintered body by densifying the sintered body thus obtained by HIP.

The temperature of HIP treatment is 1000~1, which has low high temperature deformation resistance.
It was discovered that by heating the material to 100°C, not only the effect of densification can be obtained in a relatively short period of time, but also solution treatment is performed at the same time, and solution treatment can be completed simply by controlling the cooling rate. .

Although HIP treatment is possible even in the above temperature range, for example,
At 00°C, it takes an extremely long time to achieve the densification effect, and at higher temperatures, the heat treatment becomes complicated due to solution treatment, which is not preferred. By HIPing in the above temperature range, it is possible to manufacture in a short time.

Next, an example will be explained.

Example 1゜70wt%Mn 29.5wt% All 0
After casting an alloy with a composition of 15 wt% C, it is crushed to
A powder of 0.00 mesh was obtained. This powder was molded into 30 mm diameter x 1 at a pressure of 1.6 t/crn2 using a cold isostatic press machine.
It was molded into a cylinder of a 00 whale. This molded body is heated to a CO gas partial pressure of 3
After sintering at 1210° C. for 180 minutes in a reduced pressure atmosphere of 0 Torr, HIP treatment was performed at 1080° C. for 2 hours in Ar gas at 1600 atm.

The obtained sintered body has a specific gravity of 496 g/cc and a maximum energy product (BH) Max indicating magnetic force of 3.1 MGOe.
Met.

Example 2 A sintered body obtained in the same manner as Example 1 was heated at 119σC for 3
10 minutes after HIP treatment in Ar gas at 1600 atm.
Solution treatment was continuously performed by rapid cooling to 50°C and further cooling with diameter control for 1 hour. The obtained sintered body had a specific gravity of 495 g/cc and a maximum energy product of &OMG Oe.

As explained above, by the method of the present invention, an isotropic Mn-A No. It has become possible to manufacture products with complex shapes with a high material yield without cutting.

Claims (1)

[Claims] (1) Mn 70% by weight, IU 29.5% by weight, C0
, 5% by weight of magnet material was melted and cast, pulverized into powder, cold-opened into a predetermined shape, and then CO gas partial pressure 1-1.
1. A method for producing a cuboidal Mn-A No. 0 magnet, which comprises sintering in a reduced pressure atmosphere of 0.00 Torr, densifying it by hot isostatic pressing, and then subjecting it to solution heat treatment. (2. In claim (1), 1000 to
A method for producing an isotropic Mn-AA-C magnet, characterized by performing hot isostatic pressing at 1100°C and solution treatment at the same time.