Investigations on the metallurgical features and magnetic properties of Nd16.8Fe75.7-xAlxB7.5 ,O⩽×⩽6

Alloys of nominal composition Nd_16.8Fe_75.7-xAl_xB_7.5, 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 (H_ci) and marginal reduction in remanence (B_r ) and Curie temperature (T_c) were observed in alloys with x=0.25 to 1.5. However, in alloys with x⩾3 a fall in H_ci , B_r and T_c 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