Comparison and process study of hot-pressed and hot-deformed Nd-Fe-B magnets prepared by amorphous and nanocrystalline powders

Abstract

Hot-pressed and hot-deformed Nd-Fe-B magnets are generally made from rapidly quenched powder after crystallization treatment. In this work, the amorphous melt-spun ribbons are also employed directly as the precursor. The amorphous and crystallized powders with the composition of Nd28.47Pr0.56FebalB0.97Co3.63Al0.13Nb0.56Zr0.44 were employed for fabricating hot-pressed and hot-deformed magnets. The influences of processing parameters on the microstructure and magnetic properties have been investigated. For the hot-pressed magnets produced from both crystallized and amorphous powders, the grain pre-orientation and magnetic properties including coercivity, remanence and maximum energy product increase with the increasing temperature, pressure and holding time in the ranges of 650–800 °C, 300–600 MPa and 30–150 min, respectively. The hard magnetic properties of the hot-pressed magnets obtained from amorphous powder are slightly higher than those from crystalline powder due to the smaller grain size of the former. The magnetic properties of hot-deformed magnets are mainly determined by the deformation temperature and not influenced by the state of the powder and hot-pressed precursors. The hot-pressed magnets and hot deformed magnets with different microstructures exhibit different magnetization mechanisms. The optimal hot-deformation temperature is found to be 750 °C for obtaining a high maximum energy product of 39 MGOe. The present results suggest that the rapidly quenched amorphous powder can be used to not only directly prepare hot-pressed magnets with higher magnetic properties, but also to reduce the process step for hot-deformed Nd-Fe-B magnets.