The effect of additional elements on the magnetic properties of hot-rolled NdFeB alloys

The magnetic properties of hot-rolled Nd₁₆Fe_bal.B₆M_1.5 (M = Cu, Ga and Al) and Nd₁₆Fe₇₆B_5.5Ga_1.5Al₁ alloys were investigated, in order to study the role of additive elements in improving the magnetic properties in the NdFeB system. It is found that the original grain size of Cu, Ga or GaAl added alloys is much finer than that of the ternary and Al added alloys. But the grain size is almost identical for all the alloys after hot-rolling at 1000°C with 90% reduction in thickness. The coercivity of hot-rolled alloys with Cu, Ga or GaAl addition is not improved as was expected, because Nd-rich liquid phase in these alloys is very easily squeezed out during high-reduction-ratio rolling. Less quantity and nonuniform distribution of Nd-rich phase between distributed grains are believed to be the main reasons to depress the effect on the grain boundary smoothing. This effect is not the same as those observed in the PrFeB system. The highest magnetic properties achieved in this study are B_r = 10 kG, _iH_c = 8.2 kOe, (BH)_max = 18.5 MGOe for the Nd₁₆Fe_76.5B₆Al _1.5 alloy.