Enhancing hard magnetic properties in Fe69.5-xNd7B21Nb2.5Zrx (x=0-3) bulk magnets by magnetic field heat treatment

Fe69.5-xNd7B21Nb2.5Zrx (x = 0-3) permanent magnets were produced by annealing bulk amorphous alloys. The intrinsic coercivity (H-cj) as well as maximum energy product ((BH)(max)) were enhanced significantly by Zr substitution in the Fe69.5-xNd7B21Nb2.5Zrx (x = 0-3) alloys, while the remanence (B-r) is reduced slightly. When x = 2, annealed magnets tend to display the optimal properties of H-cj = 513.92 kA/m, B-r = 0.57 T and (BH)(max) = 37.59 kJ/m(3). The effects of the magnetic field intensity on the distribution of elements, microstructures and hard magnetic properties in Fe67.5Nd7B21Nb2.5Zr2 magnets were investigated. The results of X-ray diffractometry, transmission electron microscope and atom probe tomography indicated that the magnetic field heat treatment can not only contribute to a uniformly distributed B element enriched region but also benefit the precipitation of alpha-Fe. After heat-treatment at 563 K x 1 T, H-cj, B-r and (BH)(max) experienced an increase from 513 kA/m to 583 kA/m, 0.57 T to 0.65 T and 37.59 kJ/m(3) to 50.05 kJ/m(3), respectively. Thus, the H-cj, B-r, and (BH)(max) are enhanced by 14%, 14% and 33%, respectively.