Tdk Corporation

Akihiro Ohsawa

Yasushi Enokido

Kenichi Suzuki

Since the cross-sectional area of the plastic deforming portion of the extrusion die gradually decreases from the starting end portion toward the terminal end portion, the pressure applied to the molded body in hot deforming is not loosened, hence, the occurrence of cracks can be effectively suppressed.

Extrusion die for hot-deformed magnet and method for manufacturing hot-deformed magnet using same

A rare earth based permanent magnet formed by a sintered compact with an R-T-B based composition, wherein, R contains R1 and R2 as the necessity, R1 represents at least one rare earth element including Y and excluding Dy, Tb and Ho, and R2 represents at least one from the group made of Dy, Tb and Ho. Its main phase grains have a core-shell structure in which a core part and shell part coating the core part are contained. When the atom concentrations of R1 and R2 in the core part and the atom concentrations of R1 and R2 in the shell part are defined as &#x3b1;R1, &#x3b1;R2, &#x3b2;R1 and &#x3b2;R2, respectively, &#x3b1;R1&#x3c;&#x3b2;R1, &#x3b1;R2&#x3e;&#x3b2;R2, &#x3b1;R1&#x3c;&#x3b1;R2 and &#x3b2;R2&#x3c;&#x3b2;R1. Relative to all the main phase grains observed at the cross-section of the sintered compact, the ratio occupied by the main phase grain having the core-shell structure is 5% or more.

Rare earth based permanent magnet

A rare earth based permanent magnet has a sintered compact with R-T-B based composition. The compact has two kinds of main phase grains M1 and M2 having different concentration distributions of R including R1 and R2 respectively representing at least one rare earth element including Y and excluding Dy, Tb and Ho, and at least one from Ho, Dy and Tb. M1 and M2 have a core-shell structure containing a shell part coating a core part. In M1, when the R1 and R2 atom concentrations in the core and shell parts are defined as &#x3b1;R1, &#x3b1;R2, &#x3b2;R1 and &#x3b2;R2, respectively, &#x3b1;R1&#x3e;&#x3b2;R1, &#x3b1;R2&#x3c;&#x3b2;R2, &#x3b1;R1&#x3e;&#x3b1;R2 and &#x3b2;R1&#x3c;&#x3b2;R2. In M2, when the R1 and R2 atom concentrations in the core and shell parts are defined as &#x3b3;R1, &#x3b3;R2, &#x3b5;R1 and &#x3b5;R2, respectively, &#x3b3;R1&#x3c;&#x3b5;R1, &#x3b3;R2&#x3e;&#x3b5;R2, &#x3b3;R1&#x3c;&#x3b3;R2 and &#x3b5;R1&#x3e;&#x3b5;R2. Ratios occupied by the main phase grains having the core-shell structure are 5% or more, respectively.

The present invention provides a permanent magnet with both a high corrosion resistance and magnetic properties compared to the existing R-T-B based magnets. It is a R-T-B based sintered magnet (wherein, R includes Y (yttrium) and R1 as essential, R1 is at least one kind of rare earth elements except Y but includes Nd as essential, and T is at least one kind of transition metal element including Fe or the combination of Fe and Co as essential). By allowing the ratio of R1 to Y (R1:Y) in the R contained in the grain boundary phase to be 80:20&#x2dc;35:65 in terms of the calculated molar ratio of the grain boundary phase and adding Y to the raw materials of the R-T-B based magnet, Y segregates at the triple point, and corrosion of grain boundary phase is prevented by oxidized Y.

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Tokyo, Japan

Akihiro Ohsawa