Effect of coarse grains on magnetic properties of Nd-Fe-Co-B-Ga die-upset magnets

Coarse grains contained in Nd-FeCo-Ga-B hot-pressed and die-upset magnets are examined. Coarse grains contained in hot-pressed magnets are found to maintain their shapes during die upsetting and to increase deformation resistance B_r, H_k, and (BH)_max of die-upset magnets decrease with increase in the volume fraction of coarse grains. Equiaxed coarse grains nucleate and grow during melt spinning. Columnar coarse grains grow during hot pressing. It is shown that the volume fraction of coarse grains before die upsetting should be minimized to increase (BH)_max