Basic study for plastic deformation of rapidly quenched Nd-Fe-Co-Ga-B magnets at elevated temperature

In order to optimize hot-working conditions of rapidly quenched Nd-Fe-Co-Ga-B magnets, the behavior of plastic deformation at elevated temperatures has been studied. Compressive and tensile tests were performed with various hot-working parameters. From compression tests, a strain-rate sensitivity factor and a strain hardening factor at 700°C of 0.4 and 0.3, respectively, were obtained. From tensile tests, the tensile strength and elongation at 700°C were determined to be 1.0~1.8 kgf/mm² and 6~12%, respectively. Based on these data, computer simulation of the die upsetting process was performed by rigid plastic FEM (finite-element method) calculation. It was found that, to suppress the occurrence of peripheral cracks and improve magnetic properties, low strain rates are necessary. Computer calculation of the stress distribution can explain the mechanism of peripheral crack initiation in the die upsetting process