Deformation mechanism of highly textured Alnico magnets

Abstract

Deformed Alnico magnets were prepared by hot isostatic pressing (HIP) spherical powders and hot rolling (HR), and the hot-rolled magnets were solution-treated at 1250 ℃, magnetic heat treated at 835 ℃, and three-stage aged at 600 – 500 ℃, respectively. The results show that Alnico spherical powder comprises 77.5% α phase, 8.6% α1 phase, and 13.9% α2 phase. The HIP magnet has spinodal decomposed during the preparation, and HR improved α content. The magnet has spinodal decomposed thoroughly after magnetic heat treatment (MHT) and aging heat treatment (AHT), composed of 62.1% α1 phase with a B2 structure and 37.9% Fe2NiAl-type α2 phase with the L21 structure. Moreover, the HIP and HR magnet preferentially produces the< 100 > texture, which is also enhanced along the< 211 > directions. The preferred deformation of the α1 phase is carried out under the synergistic action of the α2 phase. The HIP deformation mechanism is that composition diffusion and structural transformation are carried out in different stages, resulting in four kinds of two-phase structures. The rolling deformation mechanism is that the grains parallel or nearly parallel to the rolling direction are directly rolled into lath-like ones, and four kinds of microstructures are formed in the grains. Compared to the HIP magnet, the MHT and AHT promote the formation of the fibrous structure, and the maximum aspect ratio of α1 phase reaches ∼35:1. The coercivity of the heat-treated magnet increased by 160.9%, and the remanence and magnetic energy product also increased simultaneously.