JPS5819405A - Manufacture of mn-al-c magnet - Google Patents

Abstract

PURPOSE:To inexpensively obtain an Mn-Al-C magnet of high performance in a high yield by cold molding powder of an Mn-Al-C material having a prescribed composition, sintering the molded body in an evacuated atmosphere under a specified partial pressure of gaseous CO, and subjecting the sintered body to solubilizing heat treatment. CONSTITUTION:A magnet material consisting of 70wt% Mn, 29.5wt% Al and 0.5wt% c is cast, pulverized, and cold molded into a prescribed shape. The molded body is sintered at a prescribed temp. in an evacuated atmosphere under 1-100 Torr partial pressure of gaseous CO. The sintered body is subjected to solubilizing heat treatment in a cooling stage. By this method a lightweight powerful sintered Mn-Al-C magnet having maximum energy product about 2 times that of isotropic ferrite can be manufactured easily.

Description

[Detailed Description of the Invention] Mn-Al-C magnets are materials that do not use CO, which is a rare resource, and are therefore highly economical. They are also lightweight and have large magnetic energy per weight, making them ideal for high-performance magnet-applied equipment. It is suitable for improving performance, reducing weight and thickness, 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 HRc 50 to 5.
5, it is still 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, it has been extremely difficult to produce Mn-A/-C based materials using conventional powder metallurgy methods. Because M
n-Al! -C-based materials are hard and brittle as mentioned above, making them difficult to mold, and Mn and AI have extremely high bonding strength with oxygen! This is because the main component is easily oxidized during heating, so 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. In addition, a method of adding a low melting point element and sintering (Japanese Patent Application Laid-open No. C855-100944
No.) has been proposed, but its magnetic properties were not sufficient.

In this way, conventional powder metallurgy methods can produce high-performance sintered seeds -Aj7
-C magnets were difficult to manufacture.

The present invention is capable of sintering magnets with higher performance than conventional sintering using hydrogen, ammonia decomposition gas (AX gas), or vacuum atmosphere by sintering in a reduced pressure atmosphere with a CO gas partial pressure of 1-100 Torr. This is what we discovered.

Mn-A/-C alloys are ground and AI! oxides formed on the powder surface, these oxides could not be reduced and removed during sintering in the conventional atmosphere, and it was inevitable that the remaining oxides would impair the magnetic properties. The oxide of Mn is mainly MnO, and the dissociation pressure of this oxide is expressed as △G0=91950-17.4T in the formula MnO8Mn+-〇x
When the maximum heating temperature is 1jlO'C,
10-″19 or more □.

It became impossible to decompose using normal vacuum.

On the other hand, the method of reducing MnO with carbon is MnO-
1-C: Mn 10C0 ΔG0 = 65250-88J5T Therefore, unless the heating temperature is 1428℃ or higher, M
It is not possible to reduce nO, and at this temperature -Al-
The C alloy turned into a melt and could not be sintered. However, in the method of the present invention, the CO of the above reaction
By setting the gas to, for example, l -40 Torr, that is, by setting PC8 = 0.0018 to 0.05, the free energy change ΔG1 ΔG = 65250-88.85T + RT/nP
c.

The temperature can be lowered to 993-1200'C. On the other hand, in this thermodynamic calculation, it seems that significantly lowering the CO gas partial pressure makes the reduction reaction more likely to occur, but in reality, C in Mn -A/-C is consumed, and the optimal composition It is undesirable that it deviates from the range. Furthermore, even if the 00 partial pressure (Pco) is higher than the theoretical partial pressure, sintering may proceed well because the oxygen partial pressure in the atmospheric gas is low (oxidation of the Mn-Aj-C alloy is suppressed). It seems that it is for the purpose of being treated.

As a result of experiments, good sintering was possible when the PCO was 1 to 100 Torr.

When the sintering temperature is equal to or higher than the peritectic temperature, rapid sintering with a liquid phase is possible, and a sintered body with few residual pores can be obtained.

However, since the difference between the peritectic temperature and the melting temperature is small, it is necessary to use a sintering furnace with good temperature accuracy.

On the other hand, when performing in-phase sintering below the peritectic temperature, there is a drawback that the sintering time is long; It has the characteristic that even when using a sintering furnace, a sintered body that does not lose its shape or melt can be obtained.

Furthermore, another feature of the present invention is that solution heat treatment is continuously performed in the ε phase region in the same furnace during cooling after sintering, which eliminates the long time required in conventional manufacturing methods such as casting. Solution heat treatment time and effort can be eliminated.

Since the sintering temperature is set in the ε phase region, homogeneous solution treatment proceeds almost simultaneously, and the solution treatment can be easily performed by controlling the cooling rate after sintering.

The present invention provides a new method for manufacturing Mn-Aj'-C magnets by powder metallurgy, and this method is applicable to Mn7
0% by weight, AI! 29.5% by weight, C005% by weight
It is effective when applied to alloys of 1 to 3, but it is also effective even if the composition ratio is varied within the range that can be changed by normal manufacturing methods.

Furthermore, Ni, Tt sB, Ge, etc. may be added to this alloy system in order to further improve magnetic properties and workability, but the manufacturing method according to the present invention can be applied to any of these alloy systems. was useful.

Next, an example will be explained.

Example 1゜70wt, % Mn-29.5wt, 96A/-0.5
After casting an alloy with a composition of wt, % C, a powder of 1,100 mesh was obtained by crushing. This powder was pulverized using a cold isostatic press machine. 80H at a pressure of fl t/arl
It was molded into a cylinder of Jtx100. This molded body was heated at 1210°C in a reduced pressure atmosphere with a CO gas partial pressure of 8 ()-Torr.
After sintering for 15 minutes, the temperature was once held at 1050°C for 80 minutes, and then forced cooling was performed at a rate of 10°C/min or more. 550 left
The specific gravity of the sintered body obtained by tempering at ℃ is 464 J'/cc
and the maximum energy product (BH) max, is 2
．． It was IMG・Oe.

Example 2゜A molded body obtained in the same manner as in Example 1 was heated to a CO gas partial pressure of 1
Controlled cooling was performed after sintering at 1160° C. for 4 hours in a reduced pressure atmosphere of 0 Torr. The obtained sintered body has a specific gravity of 451 J'
Maximum energy product (BH) max at /cc.

was 1.7MG・Oe.

Example 8 After casting an alloy with the same composition as in Example 1, the low-oxygen powder was pulverized in a non-oxidizing atmosphere while being cooled with liquid nitrogen to form a molded body in the same manner as in Example 1. Sintering was performed at 1210° C. for 15 minutes in a reduced pressure atmosphere with a gas partial pressure of 10 Torr. During the cooling process, the temperature was held at 1050° C. for 30 minutes to homogenize it, and then controlled cooling at a rate of 15° C./min was carried out to substantially perform solution treatment.

The obtained sintered body had a specific gravity of 4687'/cc and a maximum energy product (BH) max of 2.5 MG·Oe.

As is clear from the above results, by the method of the present invention,
A powerful magnet with a maximum energy product nearly twice that of isotropic ferrite was obtained by powder metallurgy.
This makes it possible to manufacture complex-shaped magnetic parts such as uneven cylinders and hollow pipes at low cost with a high material yield, which has high industrial value.

Claims (1)

[Claims] (1) Mn 70% by weight, AI! 29.5% by weight
, C005% by weight is melted and cast, pulverized into powder, cold-formed into a predetermined shape, sintered in a reduced pressure atmosphere with a CO gas partial pressure of 1 = 100 Torr, and then melted into a solution during cooling. A method for manufacturing a Mn-A/-C magnet, which comprises performing chemical heat treatment. (2. In claim (1), Mn-Aj is characterized in that the sintering temperature is equal to or higher than the peritectic reaction temperature.
'-C-based magnet manufacturing method. (3) In claim (1), Mn-A/- is characterized in that the sintering temperature is below the peritectic reaction temperature.
Manufacturing method of C-based magnet.