Effects of Ag on the magnetic and mechanical properties of sintered NdFeB permanent magnets

This paper investigates the effects of Ag on the magnetic and mechanical properties of sintered NdFeB permanent magnets. The microstructure of the NdFeB permanent magnets was characterised using scanning electron microscopy (SEM)with energy dispersive X-ray spectroscopy (EDS)analysis. 0.1 wt% of Ag was added to the overall NdFeB composition to study the effects of Ag on the microstructural changes. The NdFeB and NdFeB + Ag magnets exhibit a two-phase structure with the main Nd₂Fe₁₄B phase and the Nd-rich grain boundary phase. It is found that Ag is enriched in the Nd-rich grain boundary phase and tends to alloy with the minor element, Cu. An enhanced coercivity (H_cj)is obtained in the NdFeB + Ag whilst the remanence (B_r)and maximum magnetic energy product ((BH)_max)decrease due to the addition of 0.1 wt% Ag. Impact resistance tests were carried out to examine the impact toughness of NdFeB and NdFeB + Ag magnets. It is shown that the magnets still exhibit a brittle fracture behaviour and no significant increase in the impact resistance of the NdFeB + Ag magnet is presented.