US 6,444,048 B1Granted

Alloy for use in preparation of R-T-B-based sintered magnet and process for preparing R-T-B-based sintered magnet

AssigneeShowa Denko K.K.

InventorsHiroshi Hasegawa, Yoichi Hirose

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Abstract

Processes for the preparation of a sintered alloy comprising R2Fe14B as a magnetic phase constituting a main phase include a binary alloy process wherein a main phase alloy having a lower R content than the above phase is mixed with a grain boundary phase alloy rich in R component and serving as a liquid phase in the sintering in order to prepare a mixture to be used as the starting material. The conventional main phase alloy has a structure comprising the R2Fe14B phase and, in addition, a large amount of an easily oxidizable lamella R-rich phase and a harmful dendrite α phase. On the other hand, the main phase alloy of the invention has a low dendrite a phase content and a low lamella R-rich phase and contains a lamella α Fe phase. This contributes to excellent oxidation resistance and improved properties of the magnet. The preparation of a sintered magnet by mixing the main phase alloy with the grain boundary phase alloy by the binary alloy method can reduce abnormal growth of crystal grains.

Claims8

Dependent claims

Main phase alloy used for producing an R—T—B sintered magnet, comprising R2T14B, where R is at least one selected from rare-earth elements including Y, T is Fe, part of which is replaceable with at least one of Co and Ni, and B is boron, part of which is replaceable with at least one of C and N, made by a two-alloy mixing method of mixing main phase alloy and boundary-phase alloy,

wherein said main phase alloy having a composition comprising 10 to 11.8 at % of a rare earth element consisting of 1 to 6 at % of Dy based on said main phase alloy and the balance at least one of Nd and Pr, 5.88 to 8.00 at % of B, and the balance of T;
wherein said main phase alloy having a structure consisting of a first region, a second region and a matrix of R2T14B phase other than the first region and the second region,
said first region having a dendritic α Fe phase dispersed in the matrix of R2T14B phase,
said second region having a lamellar α Fe phase dispersed in the matrix of R2T14B phase,
said first region having the dendritic α Fe phase occupying 0 to 10 vol % of the main phase alloy, and
said second region having the lamellar α Fe phase occupying not less than 5 vol % of the main phase alloy.

3 more elements

Dependencies are inferred from the claim text.