Towards manufacturing of Nd-Fe-B magnets by continuous rotary swaging of cast alloy
For the first time, Nd-Fe-B permanent magnets are manufactured by rotary swaging. Nd-Fe-B alloys were heated and deformed by a rotary swaging process with different stress states, degrees of deformation and feed speeds. As a result, the rotary swaged Nd-Fe-B samples were successfully magnetically hardened, which is confirmed by the measurements of magnetic properties with a vibrating sample magnetometer and a pulsed field magnetometer. Microstructures observation by SEM-BSE-EBSD before and after swaging confirmed the drastic grain refinement during the process. The reduction of grain size is attributed to the fracture of grains. The cohesion of the samples is maintained, because the cracks between the fractured grains were immediately filled with the liquid Nd-rich phase. The best swaged sample with a maximum energy product of 8.75 MGOe has a remanence of µ0Mr = 0.75 T and a coercivity of µ0H = 1.05 T. The rotary swaging process enables a continuous manufacturing of Nd-Fe-B permanent magnets directly from castings, which has the potential to be more productive and thus cost-effective in comparison with the conventional powder metallurgical production or hot deformation techniques.