Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1990-02-02
1992-09-15
Lechert, Jr., Stephen J.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75244, 419 12, 419 29, 419 38, G22F 900
Patent
active
051474476
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns sintered magnets and a method for their production, said sintered magnets having exceedingly good anti-corrosion properties, and at the same time, magnetic properties which do not deteriorate with time. The magnets of the present invention are necessarily composed of a rare earth metal (hereafter indicated by R) component including at least one element chosen from the rare earth element group including yttrium; boron; as well as iron.
PRIOR ART
In recent years, Nd-B-Fe permanent magnets have been discovered which, in comparison with the previously known Sm-Co magnets, have improved magnetic properties, and moreover, do not necessarily include Sm and Co which are more valuable from the standpoint of resources. The manufacturing method for these Nd-B-Fe permanent magnets involves first of all melting starting materials, casting, pulverizing the thus obtained alloy ingot, then as is needed, press forming in the a magnetic field, and finally sintering.
However, with these Nd-B-Fe permanent magnets, while having improved magnetic properties, they are very liable to corrosion and also have the additional defect of severe deterioration with time of their magnetic properties.
In an attempt to solve these problems, in Japanese Patent Application No. 61-185910, a method for diffusion forming a thin zinc coating over the surface of an R-B-Fe permanent magnet, and in Japanese Patent Application No. 61-270308, a method in which the surface layer of an R-B-Fe permanent magnet is removed after which an aluminum coating layer is applied have been described.
For both of the previously stated prior art anti-corrosion methods for Nd-B-Fe permanent magnets, however, because some protective coating of zinc, aluminum, or the like must be deposited on the permanent magnet surface, in addition to the manufacturing processes for the magnet, and thus additional processes are necessary. Accordingly, the above described manufacturing methods are not only complicated, but also high cost. Furthermore, because the above anti-corrosion methods do nothing more than protect the outer portion of the permanent magnet from corrosion and the like, when the above mentioned protective coating layers exfolliate or crack, corrosion may penetrate inwards from such areas. Thus, internal corrosion is not prevented and the additional problem of deterioration of magnetic properties with such magnets also occurs.
SUMMARY OF THE INVENTION
For these reasons, in order to develop an R-B-Fe permanent magnet having superior corrosion resistant properties, the present inventors carried out research, the results of which showed that a manufacturing method for a sintered R-B-Fe magnet was possible in which first an R-B-Fe alloy powder which included at least one oxide powder chosen from the group including Al, Ga, Ni, Co, Mn, Cr, Ti, V, Nb, Y, Ho, Er, Tm, LuZr, as well as Eu oxides, plus an additive comprising a total of from 0.0005 to 3.0 weight % of at least one hydride powder chosen from the group including Zr, Ta, Ti, Nb, V, Hf, and Y hydrides were processed; pressing, sintering and carrying out heat treatment as necessary; whereby a sintered R-B-Fe magnet having improved anti-corrosion properties and no time decay of magnetic properties could be formed.
The present invention is based on the knowledge thus obtained, and the manufacturing method for an R-B-Fe sintered magnet of the present invention will be explained in detail in the following.
(1) An R-B-Fe alloy powder having a fixed composition is prepared. This R-B-Fe alloy powder is prepared by, for example, a method in which a molten alloy is cast into an ingot, then pulverized; a liquid atomization method; or a reduction-diffusion method in which a rare earth oxide is used, and the like.
The above mentioned R-B-Fe alloy powder is a mixture composed of at least one oxide powder chosen from the group including Al, Ga, Ni, Co, Mn, Cr, Ti, V, Nb, Y, Ho, Er, Tm, LuZr, as well as Eu oxides, plus an additive comprising a total of from 0.0005 to 3.0
REFERENCES:
patent: 4770702 (1988-09-01), Ishigaki et al.
patent: 4836868 (1989-06-01), Yajima et al.
Takeshita Takuo
Watanabe Muneaki
Lechert Jr. Stephen J.
Mitsubishi Materials Corporation
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