Abstract
The phase formation, crystal structure, crystallographic texture, microstructure and magnetic properties of Alnico-8 alloys with varying Co and Nb content have been investigated and presented. Alnico-8 alloys were fabricated by induction melting and casting techniques. Magnetic properties in the alloys were induced by optimized thermomagnetic treatment and subsequent aging. The 37.9Fe-32Co-14Ni-7.5Al-3.1Cu-5.5Ti alloy exhibits coercivity of 110kA/m, remanence of 0.66T and energy product of 31.2kJ/m3. The addition of 35wt% Co in conjunction with 1.5wt%Nb to 37.9Fe-14Ni-7.5Al-3.1Cu-5.5Ti alloys led to increase the magnetic properties, especially coercivity. The enhancement of the coercivity is attributed to ideal shape anisotropy and optimum mass fraction of ferromagnetic Fe-Co rich particles, which are 25–30nm in diameter and 300–350nm in length. The 33.4Fe-35Co-14Ni-7.5Al-5.5Ti-3.1Cu-1.5Nb alloy yields the optimum magnetic properties of coercivity of 141.4kA/m, remanence of 0.83T and energy product of 42.4kJ/m3. The good magnetic properties in the studied alloys are attributed to the nanostructured microstructure comprising textured Fe-Co-Nb rich α1 phase and Al-Ni-Cu rich α2 phase.
•Synthesize of Alnico-8 magnets by casting and thermomagnetic treatment.•High coercivity up to 148.3kA/m can be obtained with Alnico magnets.•Properties are affected by intrinsic properties of spinodal phases and thermal cycle.•Magnet exhibits properties as: Hc=141.4kA/m, Br=0.83T and (BH)max =42.4kJ/m3.