High-performance Alnico magnets prepared by powder bed fusion

Fine-grained and anisotropic Alnico magnets were prepared by powder bed fusion using a laser beam. The asbuilt magnets were treated by solution treatment (ST) at 1250 C-degrees, magnetic heat treatment (MHT) at 835 C-degrees, and three-stage aging treatment (TSA) at 600 - 500 C-degrees, 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 similar to 1.5 mu m 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 mu m, and every grain exhibits a spinodal structure consisting of the FeCo-type alpha 1 phase and the Fe2NiAl-type alpha 2 phase as well as enhanced < 211 > orientation. The orientation relation between alpha 1 and alpha 2 mainly forms {(1)10}alpha(1)//{220}alpha(2), {200}alpha(1)//{400}alpha(2), and the atoms at the interface have a strong coherent matching. The spinodal structure in ST-MHT-TSA magnets mainly displays checkerboard-like. Both alpha 1 and alpha 2 phases exhibit a single domain structure; their interface is the magnetic domain wall. High alpha 1 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.