The effects of the pressing step on the microstructure and aging of NdFeB bonded magnets

The effects of the compaction step on the (micro)structural features and aging behavior of polymer coated NdFeB-based bonded magnets is reported. Due to the fracture of the material during pressing, it is estimated an increase of at least 14% in the particles' area which is not coated. Such uncoated surfaces, when exposed to the environment, reduce the magnetic performance of the magnets aged/cured in air by 19% in the conditions evaluated in this investigation. Furthermore, XRD results interpreted by Rietveld analyses show a lattice parameter change in the tetragonal structure of the hard magnetic phase after pressing. Such change varies as a function of the height of the compacted part and it is ascribed to macro-elastic stress arising from the pressure distribution in the magnet. An aging/curing step during 24 h is able to relief such macro-elastic stress.

A fractured NdFeB particle after pressing at 800 MPa whose exposed uncoated surfaces reduce the performance of NdFeB bonded magnets.Figure optionsDownload as PowerPoint slideHighlights
► Pressing affects microstructure and aging of NdFeB-based bonded magnets.
► Uncoated surfaces are exposed due to fragile fracture of the particles.
► Magnetic performance is reduced by 19% after aging in air.
► Pressing reduces Nd2Fe14B lattice parameter and causes macro elastic stress.
► An aging/curing step during 24 h is able to relief such macro-elastic stress.