ALLIAGE D'AIMANT PERMANENT

PERMANENT MAGNET ALLOY

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A permanent magnet alloy consisting essentially of, in
weight percent, 1 to 10 dysprosium, 20 to 37 neodymium, with the
total dysprosium and neodymium content being within the range of
30 to 38, 0.8 to 1.33 boron and balance iron. This alloy is
characterized by high resistance to demagnetization at elevated
temperatures with the alloy content being of relatively low cost.
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Revendications

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
1. A permanent magnet alloy having good coercive force
at elevated temperature consisting essentially of in weight
percent 1 to 10 dysprosium, 30 to 37 neodymium, with the
total dysprosium and neodymium content being within the
range of 31 to 38, 0.8 to 1.33. boron and balance iron.

Description

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Permanent magnet alloys used in the production of
permanent magnets for use in electric motors, and particularly
electric motors used in househol~ appliances and the like, are
required to have good resistance to demagnetization at elevated
temperatures ~or efficient motor operation. The temperatures
involved in these motor applications are typically within the rang~
of 125 to 150C. To achieve high resistance to demagnetization
good remanence (Br) and coercive force (HCi) values are required
within this temperature range. It is further desired in
applications such as permanent magnets used in electric motors for
household and appliance applications that the alloy of the magnet
be relatively low cost.
It is known that permanent magnet alloys of neodymium,
iron, boron have remanence values sufficiently high for the purpos~
and these are relatively inexpensive alloys; however, at the
typical service temperatures of 125 to 150C magnets of these
alloys are characterized by a loss of coercive force to below the
level suitable for the purpose. Coercive force is known to be
increased by increasing the crystal anisotropy or the anisotropy
field (HA),
It is accordingly a primary object of the present
invention to provide a low-cost permanent magnet alloy that may be
used in the manufacture of magnets having high resistance to
demagnetization at elevated temperatures within the range of 125
to 150C.
-~ A more specific object of the invention is to provide a
; permanent rnagnet alloy of low cost having a ~ood combination of
both remanence and coercive force within the temperature range of
125 to 150C which increase in coercive force is achieved by an
improved crystal anisotropy without decreasing remanence to below
acceptable levels,




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These and other objects of the invention, as well as a
more complete understanding thereof, may be obtained from the
following description, specific examples and drawing.
The single FIGURE of the drawing is a graph illustrating
the effect of the dysprosium content of a magnet alloy on the
coercive force.
The permanent Magnet alloy of the invention consists
essentially or in weight percent 1 to 10 dysprosium, 20 to 37
neodymium, with the total dysprosium and neodymium content being
within the range of 30 to 38, 0.8 to 1.33 boron and balance iron.
Preferably the dysprosium content is 2.5 to 6.5% and more
preferred within the range of 3 to 6%. It is known generally that
coercive force (HCi) is increased by increases in the crystal
anisotropy (HA). It has been discovered, in accordance with the
present inventivn, that generally with magnet alloys of iron and
boron with a neodymium content of approximately 33% the HA in kilo
oersteds is 150; with similar alloys having dysprosium as the rare
earth element the HA values in kilo oersteds are approximately 314.
It may be seen, therefore, that by the use of dysprosium in rare
earth, iron, boron alloys the crystal anisotropy is improved to in
turn increase the coercive force. In addition, however, it has
been determined that the use of dysprosium in alloys of this type
decreases remanence (Br)~ -
The following specific examples of the invention show
with neodymium, iron, boron magnets the temperature effect on ioss
of coercive force. Also, the examples demonstrate that coercive
.orce in ma~net alloys of this type are increased by the addition
of dsyprosium as a rare earth element. They also show that
increased dysprosium above the limits of the invention decreases
remanence values to below acceptable levels. Consequently, it is

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critical with regard to achieving a combination of good remanence
and coercive force within the required temperature range of 125 to
150C to have the rare earth ele~ent content of the alloy comprise
a combination of dysprosium and neodymium.
An alloy of Nd (33%) B (1%) Fe (66%) in weight percent
was melted, crushed to about 1 to 10 micron particle size. The
fine powder was oriented in a magnètic field and pressed. The
pressed part was sintered over a temperature range of 1000C -
1100C and cooled. The sintered rQagnet had the intrinsic coercive
force at the indicated temperatures in Table I.
TABLE I
INTP~INSIC COERCIVE FORCE VARIATION WITH
TE~PERATURE FOR AN ALLOY CONTAINING NO DY
TemperatureIntrinsic Coercive
(C) Force (Oe)
10,500
62 6,130
94 3,900
142 2,550
The remanence of the magnet varied from 12,100 Gauss ~o 10,738
Gauss from 20 to 145C. The loss of intrinsic coercive force to
below 6,000 ~ersted at 94C makes this magnet not applicable for
motors.
Dysprosium was added to NdFeB alloy maintaining the
total rare earth content as 35.6% and 37.1%. Tables II and III
list the magnetic properties of the magnets.

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TABLE II
INTRIi~SIC COERCIVE FORCE AND RE~ANENCE FOR
ALLOYS OF NdDyFeB WITH A TOTAL Dy+Nd = 35.6%
AT ROOM TEMPERATURE
Wt. % B Hc
Dy (G~ _ (Oe~
1.8~ 11,200 9,600
2.97 11,650 15,830
4.10 11,700 18,800
~.21 11,560 >20,000
6.32 11,000 >20,000
. 6.88 11,000 >20,000
7.44 11,200 >20,000

TABLE III
Dy + ;Id = 37.1%
Wt. ','c Br ~ci
Dy (G) (Oe)
1.74 12,380 13,020
2.7~ 11,750 17,000
3.83 11,330 19,300
4.87 10,800 >20,000
5.92 11,300 >20,000
6.43 10,700 >20,000
As can be seen from Tables II and III and ~IG. 1 adding
dysprosium increases the coercive force rapidly at room
ternperature. The temperature dependence of the coercive force of
a 3% Dy containing alloy and 6% Dy containing alloy is given in
Table IV.

TABLE IV
COERCIVE FORCE DEPENDENCE ON TEMPERATURE
OF 3% ~1~ 6% Dy CO~TAINING MAGI~ET
3C/o Dy Containin~ Magnet
5TernperatureIntrinsic Coercive Force
(C) (Oe) _
16,100
69 11,100
87 9,500
140 5,200
6~b Dy Containing Magnet
20,000
78 15,900
106 12,750
147 8,400
As can be seen from Table IV, dysprosium addition in
combination with neodymium permits utilization of these magnets
at elevated temperatures. Increasing the dysprosiuM further
results in a decrease in Br which makes the magnets not have
enough flux at the required tempèrature for the intended
applications. Table V shows the magnetic properties of a 10~o Dy
containing magnet.
TABLE V
10% Dy CO~TAINING MAGNET
Br ~ci
(G)__ (OE)
g,goo >26,000




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