Comparison of the corrosion behavior of die-upset and sintered NdFeB magnets

Corrosion rates for sintered NdFeB magnets are compared with NdFeB magnets prepared from melt spun material (hot pressed and die upset). Corrosion rat es were determined by standard electrochemical methods in 0.9 M Na2SO4, at pH 2.4 and 4.4. Autoclave tests correlated quite well with corrosion rates measured electrochemically in the more aggressive pH electrolyte. The more aggressive pH 2.4 electrolyte is more representative of the conditions occu rring in the autoclave tests. The hot pressed and die upset magnets exhibit significantly lower corrosion rates than sintered magnets. The reduction i n corrosion rate is probably due to smaller grain size and diminished amoun ts of Nd-rich material.