High-performance Alnico magnets prepared by powder bed fusion

Abstract

Fine-grained and anisotropic Alnico magnets were prepared by powder bed fusion using a laser beam. The as-built magnets were treated by solution treatment (ST) at 1250 °C, magnetic heat treatment (MHT) at 835 °C, and three-stage aging treatment (TSA) at 600 − 500 °C, respectively. The phase transition, microstructure evolution, and magnetic characteristics of the magnets were investigated. The findings demonstrate that as-built magnets are composed of equiaxed grains with a fine grain size of ∼1.5 µm and exhibit crystalline and magnetic anisotropy. After ST-MHT-TSA treatment, the magnets are composed of equiaxed grains with an average grain size of 12.1 − 15.5 µm, and every grain exhibits a spinodal structure consisting of the FeCo-type α1 phase and the Fe2NiAl-type α2 phase as well as enhanced < 211 > orientation. The orientation relation between α1 and α2 mainly forms {110}α1//{220}α2, {200}α1//{400}α2, and the atoms at the interface have a strong coherent matching. The spinodal structure in ST-MHT-TSA magnets mainly displays checkerboard-like. Both α1 and α2 phases exhibit a single domain structure; their interface is the magnetic domain wall. High α1 aspect ratio and anisotropy give Alnico magnet exceptional magnetic performance with Hc= 1363.1 Oe, Br= 9.0 kGs, and (BH)max= 6.2 MGOe. Furthermore, micro-magnetic simulations were used to disclose how some defect structures in the micro-regions affect the magnetic properties.