Modeling of hot deformation behavior of the Nd-Fe-B permanent magnet and its application in forming of magnetic ring

Hot-deformed (HD) Nd-Fe-B magnet exhibits good magnetic and mechanical properties, which are dictated by the thermomechanical behavior of the feedstock during the hot deformation process. To enhance the HD magnet properties, the hot deformation behavior of the Nd-Fe-B material must be well understood and an accurate model of the process must be established and validated. In this work, the hot deformation behaviors of the Nd-Fe-B magnet were studied by experiments and simulations. Experiments were conducted using a thermomechanical simulator at the temperatures ranging from 740 to 820 °C and the strain rates between 0.001 and 0.05 s ^-1 . Results indicated that the flow stress was significantly affected by strain, temperature, and strain rate. Therefore, a modified constitutive model was developed to incorporate the effects of these three factors. The model achieved a correlation coefficient of 0.991, and further was implemented for the simulation of the forming processes. The simulated results matched the experimental ones very well. Furthermore, microstructural analysis and magnetic properties results showed the microstructure and magnetic properties were sensitive to temperature and strain rate, similar to the effective strain. Finally, the modified model was used to simulate the backward-extruded (BE) process for magnetic ring with high precision, verifying the applicability of the modified constitutive model. The method combining experiments, simulation and microstructural analysis provides an efficient tool for obtaining high-performance HD magnet and designing process routes in engineering.