Effect of processing parameters on the structure and magnetic properties of Nd60Fe30Al10 alloy

Although rapidly solidified Nd-Fe-Al alloys exhibit hard magnetic properties they so far have not found any practical application, however, their study has great scientific meaning. Investigations of the Nd-Fe-Al alloys enable one to evaluate the effect of magnetic interactions, between nanoscale precipitates, having different structure and properties, on the macroscopically observed phenomena. The evolution of microstructure in the course of annealing is generally unclear. Most of the reported data were obtained for different materials, using various processing methods, which makes their comparison difficult. It was shown that different fabrication methods (melt spinning, suction casting) generate different properties. On the other hand, for the particular processing method the structure and magnetic properties are highly affected by the processing variables. In this study the samples fabricated by two methods were compared. Melt spinning, with the roll speed 5-30 m/s, and casting into moulds having bore diameters 1, 3, 6 and 12 mm were used. The alloy composition was kept constant Nd60Fe30Al10. Strong dependence of the magnetic properties on quenching rate was proved. Application of the appropriate processing variables for both the methods (roll speed or rode diameter) enables one to obtain comparable quenching rates and thus overall similar magnetic properties. However, for the cylindrical specimens different cooling rates for the surface and core produces a structural gradient, which leads to variation of the magnetic properties on the sample cross-section. The structural and property gradients were evaluated using SEM and magnetic measurements, respectively.