Tailoring the magnetic properties and microstructure of Alnico 8 magnets by various Ti contents and processing conditions

Shape anisotropy, developed as a result of spinodal decomposition (SD) is the basis for the hysteresis behavior of Alnico magnets. The SD process is sensitive to processing conditions and constituent elements. In this paper, the development of spinodal structure and its effects on magnetic properties and serviceability of Alnico 8 alloys are investigated. The Ti-content is varied between 2.5 and 7.5 wt%. The magnets are fabricated by conventional casting, homogenization, magnetic field annealing and tempering treatments. The magnetic properties of intrinsic coercivity, H_cj = 30 kA/m, remanence, B_r = 0.53 T and maximum energy density, (BH)_max = 6.03 kJ/m³ for 2.5 wt% Ti are increased to H_cj = 150 kA/m, B_r = 0.0.88 T and (BH)_max = 29.3 kJ/m³ for 6.5 wt% Ti alloy. These magnetic properties are 100% reversible up to 800 K. Furthermore, an alloy with 5.5 wt% Ti is directionally solidified and magnetic properties of B_r = 1.01 T and (BH)_max = 58.9 kJ/m³ are obtained. The evolution of mosaic nano structure, the mechanism of magnetic hardening and the interactions of various phases have been investigated.