Hot workability of melt-spun Nd-Fe-Co-B magnets

Abstract

Anisotropic Nd-Fe-B magnets are produced from melt-spun ribbons by hot working technique. The processing is facilitated by improved workability. In order to obtain a sound magnet, it is important to suppress the crack initiation and growth. An investigation was carried out to study the deformation mechanism of the alloy system and to improve workability by changes in alloy composition. Alloy ribbons with composition (Nd13.6−xRx) (Fe77.6−y Ty Co2.8)B6.0 [R=Ce, Dy; T=Al, Si, V, Cu, Ga, Zr, Nb, Mo, Sn; x= 0, 1, 2; y=0, 0.5, 1.0] were prepared by melt spinning and then hot pressed into fully dense compacts. These compacts were upset in a hot working simulator. Hot workability was evaluated by measuring the crack opening displacement on the surface at the half height of the upset specimen. The relationship between strain rate and flow stress was found to be expressed by the equation: ε̇ = Aσn exp( − Q/RT). Values of n and Q were obtained for quarternary composition (Nd-Fe-Co-B). The effects of strain and strain rate on magnetic properties were also studied for quarternary composition. Of the additive elements, cerium and silicon addition showed significant improvement in workability without loss of coercivity.