Investigations on the metallurgical features and magnetic properties of Nd<inf>16.8</inf>Fe<inf>75.7-x</inf>Al<inf>x</inf>B<inf>7.5</inf>, 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 sintered magnets. Significant improvement in intrinsic coercivity (Hci) and marginal reduction in remanence (Br) and Curie temperature (TC) were observed in alloys with x = 0.25 to 1.5. However, in alloys with x ≥ 3 a fall in Hci, Br and TC was observed. All the alloys contain a multiphase microstructure with Nd2Fe14B (φ) as major phase and secondary phases including oxides. Al partly dissolves into the matrix phase and much of it goes for the formation of a separate phase (μ or δ), which is distributed at the intergranular region with other secondary phases (Nd-rich and η). The volume fraction of the intergranular phases increases with Al concentration in the alloy. The decrease in the coercivity value at x ≥ 3 at.% is attributed to the distribution of these intergranular phases and the magnetic character of μ and δ phases.