Production and corrosion resistance of NdFeBZr magnets with an improved response to thermal variations during sintering

This study describes an attempt to produce NdFeB magnets that are insensitive to the sintering temperature. It was found that addition of Zr to NdFeB magnets significantly augmented the thermal stability of this magnetic material during sintering at high temperature even at industrial scale. The best sintered magnets were produced by jet-milling the powder (to achieve an average 3.4 mu m particle size), and then aligned, pressed and sintered under argon at 1100 degrees C for 3 h followed by appropriate heat treatment. The magnetic properties of the resulting magnets were: (BH)(m)=403.8 kJ m(-3) ( +/- 4.7 kJ m(-3)), B-r = 1430 mT ( +/- 9 mT) and H-i(c) = 907 kA m(-1) ( +/- 12 kA m(-1)). Large grain growth, in excess of 100 mm in the Zr-free magnets, was observed during sintering at 1100 degrees C. This did not occur in the presence of Zr. These observations imply that the sensitivity of this class of magnets to high sintering temperatures is greatly reduced by Zr addition. Corrosion resistance of NdFeB was therefore significantly improved by the addition of small amounts of Zr. (C) 2010 Elsevier B.V. All rights reserved.