Recycling of NdFeB Magnets by Electrodischarge Sintering—Microstructure, Magnetic, and Mechanical Properties

In this work, we investigate the feasibility of recycling NdFeB magnets by means of electrodischarge sintering (EDS). We crushed, sintered, and hot-deformed NdFeB magnets in a jaw crusher, and the NdFeB fragments were further compacted to a round shape by EDS. The EDS technique is a fast and energy-saving compaction process for powders with sufficient electrical conductivity. The current is discharged from capacitors into a loose powder that has been precompacted by Cu punches into a ceramic die, thus resulting in fully dense magnets. In this study, we investigated the apparent density, particle size distribution, oxygen content, and morphology of the crushed powder. In addition, the microstructure, compressive strength, and the magnetic properties of the EDS-densified samples were examined. For all specimens, the energy product decreases with the increasing discharge energy during EDS processing and the increasing oxygen content of the initial powder. Furthermore, high apparent densities together with large particle sizes promote EDS densification of NdFeB magnets. The applied EDS parameters led to the formation of three different microstructures (insufficiently densified zone, fully densified zone, and remelted zone) along the cross section of the EDS-densified specimens. These volume fractions of the different microstructural constituents during the EDS process and the powder characteristics (oxygen content, morphology, etc.) determine the resulting mechanical and magnetic properties of the specimens.