Optimization of the Magnetic Properties of Hot Deformed Nd-Fe-B Magnets

We investigated the effects of density of Nd-Fe-B isotropic MQ2 counterparts and hot deformation parameters, including temperature and time, on the microstructure, (0 0 L) texture, and magnetic properties of anisotropic MQ3 magnets. A higher MQ2 density yields a more homogeneous density distribution throughout the MQ2 magnet. When the MQ2 density reaches 7.58 g/cm
³
, the grain size is as fine as 70 nm. After hot deformation, the length of the platelet-like grains in the MQ3 magnet can be as small as 300 nm when deformed at 780 °C for 120 s. An increase in the deformation time to 240 s gives more uniform MQ3 grain sizes throughout the magnet, resulting in higher values of remanent induction B
_r
= 13.8 kG, intrinsic coercivity
_i
H
_c
= 15.7 kOe, and maximum energy product (B·H)
_max
= 46.5 MG·Oe. Inhomogeneity in (0 0 L) texture and microstructure along the MQ3 thickness axis is inevitable after hot deformation. However, if 12.5% of the upper and lower surfaces of the MQ3 magnet, deformed at 780 °C for 120 s, are polished, outstanding magnetic properties can be achieved: B
_r
= 14.7 kG,
_i
H
_c
= 15.8 kOe, and (B·H)
_max
= 51.5 MG·Oe.