Investigations on the metallurgical features and magnetic properties of Nd16.8Fe75.7-xAlxB7.5, 0 <= x <= 6

Alloys of nominal composition Nd16.8Fe75.7-x AlxB7.5, with x = 0.25, 0.5, 0 .75, 1.5, 3 and 6 were selected and powder metallurgically processed into s intered magnets. Significant improvement in intrinsic coercivity (H-ci) and marginal reduction in remanence (B-r) and Curie temperature (T-C) were obs erved in alloys with x = 0.25 to 1.5. However, in alloys with x greater tha n or equal to 3 a fall in H-ci, B-r and T-C was observed. All the alloys co ntain a multiphase microstructure with Nd2Fe14B (phi) as major phase and se condary phases including oxides. Al partly dissolves into the matrix phase and much of it goes for the formation of a separate phase (mu or delta), wh ich is distributed at the intergranular region with other secondary phases (Nd-rich and eta). The volume fraction of the intergranular phases increase s with Al concentration in the alloy. The decrease in the coercivity value at x greater than or equal to 3 at.% is attributed to the distribution of t hese intergranular phases and the magnetic character of mu and delta phases .