A copper-hardened permanent-magnet alloy consisting of cobalt, copper and at least one of the rare-earth metals (RE) with atomic number 57 - 71, is characterized by a coarse-grained matrix of the composition Re (Co.sub.1-y Cu.sub.y).sub.6+X, wherein 0.ltoreq.X.ltoreq.1 and 0.15<y<0.35.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a copper-hardened permanent-magnet alloy 
consisting of cobalt, copper and at least one of the rare earth metals 
(RE) having atomic numbers 57-71, and also to a method of producing such 
an alloy. This invention also relates to certain uses of this novel alloy. 
2. Description of the Prior Art 
In U.S. Pat. No. 3,560,200 (German Pat. No. 1,915,358) there is disclosed 
copper-hardened permanent-magnet alloys consisting of the components A 
(cobalt or iron), RE (at least one element from the group consisting of 
samarium, cerium, gadolinium, praseodymium, lanthanum, yttrium, neodymium 
and hafnium) and B (copper). In that reference, it is disclosed that 
hardening of the alloys with the nonmagnetic copper results in a 
considerable decrease in the wall movement of the magnetic domains, so 
that an increasing proportion of component B increases the coercive force. 
On the other hand, increasing the proportion of the magnetic component A 
(e.g., Co) improves the remanence of the alloy. However, in the 
above-mentioned patent the disclosed alloys, (Co, Cu).sub.x Sm or 
(Co,Cu).sub.x Ce, with x = 5, 5.5, 6.24, 6.75 and 8.5, exhibit high values 
of coercive force, H.sub.C, and remanence, B.sub.r, only for x = 5 and 
then only after heat treatment. For many applications it would be most 
desirable to have magnetic alloys from which permanent magnets could be 
produced having optimal magnetic properties without concomitant increase 
in cost. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide a copper-hardened 
permanent-magnet alloy which not only exhibits optimal magnetic properties 
but also is producible by an inexpensive process and, in addition, is 
easily fabricated into permanent magnets. 
This and other objects of the invention as will hereinafter be made clear 
by the ensuing discussion have been achieved by providing a 
copper-hardened permanent-magnet alloy which is a coarse-grained matrix of 
composition RE (Co.sub.1-y Cu.sub.y).sub.6+x, where 0.ltoreq.X.ltoreq.1, 
01.15&lt;y&lt;0.35 and RE represents at least one of the rare earth metals 
having atomic numbers 57-71.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Copper-hardened permanent-magnet alloys of the composition and structure of 
this invention exhibit surprisingly high values of coercive force and 
remanence. In particular Hc and Br values up to 20 KOe and 10 kg, 
respectively, and energy products of over 20 MGOe have been obtained in 
samarium-hardened alloys. This result is all the more surprising since 
German Pat. No. 1,915,358 and the publication of E. A. Nesbitt, R. H. 
Willens, R. C. Sherwood, E. Buchler and J. H. Wernick in Applied Physics 
Letters 12,361 (June 1968) indicate that only (Co, Cu).sub.5 Sm-alloys 
are permanent-magnet materials with good magnetic characteristics. 
Moreover, this is surprising since it is well known in the art that only 
the SmCo.sub.5 alloy, but not the SmCo.sub.6 or SmCo.sub.8.5 alloys, 
exhibits good magnetic properties. 
Furthermore, the alloys fabricated in accordance with this invention not 
only have superior magnetic properties but, in addition, are significantly 
lower in cost of raw materials than for conventional alloys on account of 
the relatively small proportion of expensive rare-earth metals required. 
The alloys of this invention are characterized by a coarse-grained matrix 
of a size of 1mm to 10cm in size, statistically distributed grains or an 
aligned solidified structure, each grain being a perfectly aligned 
permanent magnet. No significant improvements are made in the magnetic 
properties of the alloys by heat-treating them. 
Additionally, it is surprising that in producing the copper-hardened 
permanent-magnet alloys by melting together the stoichiometrically weighed 
and mixed components--cobalt, copper and rare earth metal -- at about 
1400.degree. C and subsequently cooling the melt, the cooling rate has 
been found to have no significant influence on the magnetic properties of 
the alloys. 
All specimens of the copper-hardened permanent magnet alloys mentioned 
below were produced by melting together the elements cobalt, copper and 
samarium in an induction oven. The raw materials, 99.9% pure samarium, 
99.9% pure cobalt and oxygen-poor, 99.999% pure, electrolytic copper, 
coarsely pulverized, were placed in a boron nitride crucible, and melted 
in a high-purity argon atmosphere at a temperature of about 1400.degree. 
C. 
The frequency of 10 KHz brings the liquid into rotation and provides for a 
thorough mixing. After 3-5 minutes of standing at melting temperature, the 
heat is discontinued and the melt is hardened in situ. 
To obtain a material with coarse granular structure, the cooling speed 
should not be too rapid, especially in the temperature range between the 
beginning and end of the hardening step. At a cooling speed of 
50.degree./min in this temperature range (for the disclosed material, 
between 1300.degree. and 1200.degree. C), one obtains a 3-5 mm coarse 
granular composition, in which an almost totally aligned permanent magnet 
is produced in every grain. The melt was allowed to solidify in situ with 
a cooling rate less than 50.degree. C/min. The resulting material 
exhibited a matrix consisting of 3-5 mm grains, each of which was found to 
be almost a completely aligned permanent magnet. The crystallographic, and 
therewith also the magnetically preferred directions, of these grains were 
statistically distributed throughout the material. From the grains of this 
material, spherical, single-crystal samples of about 2 mm diameter were 
ground in a ball mill. The demagnetization curves of these spherical 
single crystals were obtained by means of a vibration magnetometer with a 
maximum field of 23 KOe. From these curves the coercive force Hc and the 
remanance Br were obtained. The compositions were determined by wet 
chemistry to an accuracy of 1%. The results of measurements on some of the 
alloys of the invention are given in the following table. 
__________________________________________________________________________ 
Composition (weight %) 
Coercive Force 
Remanence 
Alloy Sm Co Cu H.sub.c [kOe] 
Br [kG] 
__________________________________________________________________________ 
Sm.sub.0.143 Co.sub.0.657 Cu.sub.0.20 
29.46 
53.11 
17.43 
7.4 6.8 
[Sm(Co.sub.0.77 Cu.sub.0.23).sub.6 ] 
Sm.sub.0.143 Co.sub.0.607 Cu.sub.0.25 
29.36 
48.92 
21.72 
14.3 6.8 
[Sm(Co.sub.0.71 Cu.sub.0.29).sub.6 ] 
Sm.sub.0.143 Co.sub.0.557 Cu.sub.0.30 
29.27 
44.75 
25.98 
19.6 5.3 
[Sm(Co.sub.0.65 Cu.sub.0.35).sub.6 ] 
Sm.sub.0.14 Co.sub.0.64 Cu.sub.0.22 
28.94 
51.85 
19.22 
14.3 7.1 
[Sm(Co.sub.0.75 Cu.sub.0.25).sub.6.12 ] 
Sm.sub.0.135 Co.sub.0.645 Cu.sub.0.22 
28.08 
52.58 
19.34 
16 6.5 
[Sm(Co.sub.0.75 Cu.sub.0.25).sub.6.4 ] 
Sm.sub.0.13 Co.sub.0.65 Cu.sub.0.22 
27.21 
53.33 
19.46 
10.8 7.4 
[Sm(Co.sub.0.75 Cu.sub.0.25).sub.6.7 ] 
Sm.sub.0.125 Co.sub.0.75 Cu.sub.0.125 
26.49 
62.30 
11.20 
3.2 9.7 
[Sm(Co.sub.0.80 Cu.sub.0.14).sub.7 ] 
Sm.sub.0.128 Co.sub.0.73 Cu.sub.0.142 
26.95 
60.37 
12.68 
5.3 9.1 
[Sm(Co.sub.0.84 Cu.sub.0.16).sub.6.85 ] 
__________________________________________________________________________ 
In FIGS. 1 and 2 are plotted the coercive force and remanence of some of 
the samples in the alloy series Sm(Co.sub.0.75 Cu.sub.0.25).sub.6+X and 
Sm(Co.sub.1-y Cu.sub.y).sub.6. In the alloy series Sm(CO.sub.0.75 
Cu.sub.0.25).sub.6+X the remanence remains almost constant over the range 
0.ltoreq.X.ltoreq.1 because of the fixed proportion of Co, while the 
coercive force which is relatively low at the ends of this range, climbs 
to surprisingly high values in the middle of it. By varying the copper 
content in this alloy series the magnetic properties can be improved 
further still. This is apparent from FIG. 2 in which the coercive force 
and remanence of the alloy series Sm(Co.sub.1-y Cu.sub.Y).sub.6 are 
plotted as functions of the copper content y. As can be seen, the 
remanence decreases as the copper content goes up since the copper atom in 
contrast to cobalt has no magnetic moment. On the other hand, the coercive 
force rises very steeply between y = 0.15 and y = 0.35. A material in 
which both the coervice force and the remanence are high in value, as in 
the range y = 0.2 to y = 0.3 in FIG. 2 for the alloy of this invention is 
especially suitable for magents. 
The energy product of almost all samples lay above 9 MGOe and reached a 
maximum of about 20 MGOe in the alloy Sm(CO.sub.0.84 CU.sub.0.16).sub.6.85 
In FIG. 3 using the alloy Sm(Co.sub.0.78 Cu.sub.0.22).sub.6 as an example, 
there is shown the dependence of the magnetic properties on the annealing 
temperature T after about a 2-hour heat treatment. It is seen that after 
heat treatment at 450.degree. C there is a slight improvement in the 
coercive force. The coercive force also improves somewhat at 650.degree. 
C, but at this temperature the alloy dissociates after several hours into 
a mixture of two phases. 
Besides samarium any other rare-earth metals having atomic numbers from 57 
to 71 can be used separately or in combination, e.g., Ce-mischmetal, as 
components of the alloys of this invention. 
Two paths can be followed in producing arbitrarily large magnets from the 
coarse-grained permanent-magnet material of this invention obtained from 
the melt: (1) production of large single crystals by solidification 
alignment; or (2) pulverization of the coarse-grained materials followed 
by aligning, pressing and sintering of the powder. Through regulated 
solidification, either large single crystals are extracted, or in a 
powder-metallurgical method, sufficiently large magnetic bodies are 
prepared. By the powder-metallurgical method, the coarse grained material 
is first ground. In order to achieve a high density and also a small 
oxygen content in the ground material, a medium grain size of 4-20 m is 
advantageous. The best magnets are obtained at a grain size of 5 m. For 
magnetic alignment of the silicon formed powders which are drawn off, a 
magnetic field is necessary which is at least larger than the coercive 
field of the materials. In the disclosed process, in each case, a magnetic 
field of 40 KOe is used. The aligned powder will finally be compressed to 
a pressure of 6000 atm at about 60% of the theoretical density. The 
sinter-forming temperature must also be selected so that the density of 
the finished sintered magnets are 98% of the theoretical density. In the 
disclosed materials, the necessary sinter-forming temperature is between 
1140.degree. C and 1100.degree. C, whereby the sinter-forming temperature 
is a function of the chemical composition of the materials. In the latter 
powder-metallurgical method of fabricating magnets, the alloy of this 
invention offers a distinct advantage in that the particle size of the 
powder obtained by grinding in a mill is not critical. This occurs because 
the magnetic properties of the materials of the invention are produced by 
dispersion hardening, and cannot thereafter be changed by domain formation 
and domain-boundary motions. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.