Permanent magnet alloy

Abstract

 A permanent magnet of R₂Co₁₇ type crystal structure consisting of, in percent by weight, at least one rare earth element within the range of 24 to 28, cobalt within the range of 48 to 53, copper within the range of 2 to 4.9, iron within the range of 18 to 30 and zirconium within the range of 1.7 to 3.0. By substituting zirconium for a portion of copper an optimum combination of coercive force and residual magnetization (saturation induction) may be achieved.

Description

[0001] The present invention relates to permanent magnets of R₂Co₁₇ type crystal structure.

[0002] It is known in the production of rare earth-cobalt permanent magnets (R-Co) that iron may be used to replace a significant portion of the cobalt when zirconium is added to the composition. It is also known that additions of copper may be made to compositions of this type. However, with a copper addition the residual magnetization (saturation induction) is decreased. Likewise as iron is increased there is a corresponding reduction in coercive force.

[0003] It is accordingly a primary object of the present invention to provide a permanent magnet alloy containing at least one rare earth element, preferably samarium, cobalt, iron and copper wherein an optimum combination of coercive force and residual magnetization is achieved.

[0004] A more specific object of the invention is to provide a permanent magnet alloy of this type wherein copper is reduced and replaced by a zirconium addition, whereby an optimum combination of coercive force and residual magnetization may be achieved.

[0005] The present invention provides a permanent magnet of R₂Co_l7 type crystal structure consisting of, in percent by weight, at least one rare earth element within the range of 24 to 28, cobalt within the range of 48 to 53, copper within the range of 2 to 4.9 to less than 5, iron within the range of 18 to 30 and zirconium within the range of 1.7 to 3.0.

[0006] Broadly in the practice of the invention the permanent magnet is of an alloy of the general formula R₂Co₁₇ wherein R is at least one rare earth component, preferably samarium, and the Co component is cobalt. The alloy, in weight percent, consists of at least one rare earth element, preferably samarium, within the range of 24 to 28, cobalt within the range of 48 to 53, copper within the range of 2 to 4.9, iron within the range of 18 to 30 and zirconium within the range 1.7 to 3.0. By maintaining copper at an amount less than 5% and adding zirconium within the above stated range, the adverse affect of copper with regard to residual magnetization is eliminated and thus an optimum combination of coercive force and residual magnetization is achieved.

[0007] As specific examples of the practice of the invention the following alloy compositions were employed:

[0008] The alloys were produced by induction melting and casting, whereupon they were then crushed and ball milled to a particle size within the range of 5 to 10 microns. The powder was then oriented in a magnetic field and samples thereof were both pressed by a pulsating magnetic field in combination with hot isostatic pressing and also by die pressing in a transverse magnetic field. Thereafter, the magnets were heat treated at 1200°C for 1 hour, cooled for 2 hours to 1150°C and held at this temperature for 5 hours, quenched, and then heated to 850°C and aged for 17 hours, cooled for 13 hours to 400°C, held at 400°_C for I hour to 10 hours, and then quenched.

[0009] Hysteresis loops were measured on these magnets and the results are set forth in TABLE I.

[0010] For the above alloy so processed TABLE II shows a comparison between ball milled powder and jet milled powder on the magnet properties of transversed die pressed blocks.

[0011] TABLE III shows that cold isostatic pressing produces higher remanence than the transverse die pressed blocks.

[0012] TABLE IV shows the effect of heat treatment on the magnetic properties of the tested magnets.

[0013] An alloy of the composition 26.0 samarium, 49.0 cobalt, 3.9 copper, 19.2 iron, 2.5 zirconium, closely similar in composition to Alloy B, was jet milled and die pressed with the applied field in the same direction as the pressing direction. These magnets were solution treated over a temperature range of 1080 to 1180°C for five hours and aged at different temperatures as indicated in TABLES V to VII.

[0014] This same alloy composition was jet milled and die pressed with the applied field perpendicular to the pressing direction. These magnets were solution heat treated at 1180 or 1150°C and aged at 850°C. The magnetic properties obtained are shown in TABLE VIII.

[0015] As may be seen from these specific examples, the desired combination of coercive force and residual magnetization may be obtained by continuous cooling after the aging treatment.

Claims

1. A permanent magnet of R₂Co₁₇ type crystal structure characterised in consisting of, in percent by weight, at least one rare earth element within the range of 24 to 28, cobalt within the range of 48 to 53, copper within the range of 2 to 4.9 to less than 5, iron within the range of 18 to 30 and zirconium within the range of 1.7 to 3.0.

2. A permanent magnet according to claim 1, characterised in that R is samarium.

3. A permanent magnet according to claims 1 and 2, characterised in that said magnet is aged and thereafter continuously cooled prior to quenching.