2015 Volume 80 Issue 1 Pages 1-6
Microstructure of NdFeB ternary alloy for magnet has a strong influence on pulverization, orientation in magnetic field and sintering in the production process, therefore magnetic properties of NdFeB sintered magnets strongly depend on microstructure of starting alloy. So it is very important to optimize the microstructure of starting alloy. In this study the mechanism of microstructure formation by strip casting method was investigated. Nd14.65Febal.B6.11 compounds were prepared by vacuum induction furnace in Ar atmosphere and casted onto φ150 mm water cooled roll. Thickness of obtained strip were 200-500 μm, each batch of compounds was around 2 kg. Effects of 1) surface conditions of copper roll, 2) surface velocity of roll and 3) roll materials with different thermal conductivity on microstructure of strip were investigated.
Through this study, following results were found, 1) grain size was able to be controlled by the nucleation site depending on surface conditions and the thermal conductivity of roll material, 2) dendrite size was controlled by the growth rate of solid phase and the relaxation of solute condensing around solid-liquid interface due to traveling of solid phase in puddle. Based on the obtained results, nucleation of solid phase in strip cast samples was also discussed.
