The effect of dry and wet milling on microstructure and properties of bonded NdFeB magnets

Abstract

The preparation of NdFeB has been conducted in a dry and wet milling condition using a planetary ball mill (PBM) for ½, 1, 2, 3, 4, and 5 hours. The dry and wet milling was performed in an argon gas and toluent, respectively with ball and powder ratio of 10:1. The milled powder was dried in the vacuum condition of 11 mBar at the temperature of 60°C for 10 hours. 5wt.%Celuna (WE-518) was used as binder, mixed with magnetic powder and anisotropically pressed at 25 kgf/cm2. Curing process was conducted in a vacuum chamber of 11 mBar at temperature of 180°C for 1 hour. The particle diameter and the true density of NdFeB powder were measured by using PSA and Pycnometer, respectively. The morphology and phase composition were characterized using SEM and XRD, respectively. The obtained results show that the optimum milling time of NdFeB powder is 3 hours using wet milling method. The results also concluded that the powder true density of 7.79 g/cm3, the bulk density of 5.98 g/cm3 and the mean particle diameter of 9.59 μm can be achieved. The SEM image confirmed that the milling process has an effect in reducing the particles size. But the milling process lead to a damage in the crystal structure of the material, resulting in decreasing the magnetic flux density. The half hour dry milling is capable to produce a maximum magnetic flux density of 1816 Gauss.