Effect of Surface Etching on the Magnetic Properties and Grain-Boundary Dy-Diffusion in DyH2-Dip-Coated Sintered Nd-Fe-B Magnets

Abstract

We investigated the effect,4 of surface etching on the magnetic and microstructural properties of DyH2-dip-coated, sintered Nd-Fe-B magnets. When the magnets were dip-coated with DyH2 solution after their surfaces had been optimally etched in 1 wt% HNO3 for 50s, the Dy diffusion depth (similar to 450 mu m) improved compared with the values for unetched and DyH2-dip-coated etched magnets (similar to 350 mu m). In addition, the core-shell microstructure of the dip-coated magnet was well developed by the optimal etching process. As a result, the coercivity of the dip-coated magnet increased by 4.6%. The optimal surface state of the Nd-Fe-B sintered magnet showed minimal surface damage after it was homogeneously etched along the grain boundaries. In contrast, overetched magnets showed kinks on the demagnetization curves because of surface damage. The relationship between the change in the etched maghet gurface and the magnetic properties of dip-coated magnets was examined.