Evolution of microstructure and magnetic properties in Alnico 6 magnets under various processing conditions

This manuscript reports the magnetic properties of Alnico 6 magnets, with a focus on the superior performance achieved through directional solidification (DS), combined with magnetic field annealing. Four distinct magnet types were fabricated and compared; isotropic ribbons, isotropic bulk, anisotropic bulk (thermomagnetically annealed), and directionally solidified followed by thermomagnetically annealed. A clear improvement in the magnetic performance is observed in the DS variant, which exhibits the highest properties with a remanence (B_r) of 12.92 kG, an intrinsic coercivity (H_cj) of 790 Oe, and a maximum energy product ((BH)_max) of 5.51 MGOe at room temperature. These values represent a significant enhancement over the magnetic properties of the anisotropic magnet (B_r = 11.82 kG, H_cj = 634 Oe, (BH)_max = 3.89 MGOe). To elucidate the origin of these enhanced properties, a detailed microstructural analysis is conducted, correlating the improved magnetic performance with the orientation of the grain and spinodal structures, as well as the elemental distribution. The purity of the spinodal phases, and the formation mechanism of the spinodal phases are discussed. Furthermore, the service performance of the DS magnet is rigorously evaluated, demonstrating excellent thermal stability across a broad temperature range from 10 K to 800 K, albeit with a slight anomalous behavior at low temperature. This work underscores the critical role of microstructural alignment at multiple length scales in optimizing the magnetic performance of Alnico 6.