R-t-b rare earth sintered magnet, alloy for r-t-b rare earth sintered magnet, and method of manufacturing the same

An alloy for an R-T-B rare earth sintered magnet comprising R which represents a rare earth element;

• T which represents a transition metal essentially containing Fe;
• a metal element M which represents Al and/or Ga;
• B;
• Cu;
• and inevitable impurities;
• wherein the R-T-B rare earth sintered magnet contains 13.4 to 17 at % of R, 4.5 to 5.5 at % of B, 0.1 to 2.0 at % of M and T as the balance;
• wherein a main phase composed of R2Fe14B and a grain boundary phase including a larger amount of R than the main phase are included;
• and
• wherein a distance between adjacent grain boundary phases is 1.5 μm to 2.8 μm.

A method of manufacturing an alloy for an R-T-B rare earth sintered magnet, comprising:

• a casting step of producing a cast alloy using a strip cast method including supplying a molten alloy to a cooling roll and solidifying the molten alloy;
• wherein the molten alloy contains R which represents a rare earth element, T which represents a transition metal essentially containing Fe, a metal element M which represents Al and/or Ga, B, Cu, and inevitable impurities;
• wherein the molten alloy contains 13.4 to 17 at % of R, 4.5 to 5.5 at % of B, 0.1 to 2.0 at % of M, and T as the balance;
• and
• wherein in the casting step, the cast alloy is removed from the cooling roll at 400° C. to 600° C. to obtain the cast alloy having an average thickness of 0.15 mm to 0.27 mm.