Modulation of Soft Magnetic Properties in Fe-Based Amorphous and Nanocrystalline Alloys for Power Transformers: A Review

Fe-based amorphous and nanocrystalline alloys are essential core materials for high-efficiency distribution transformers, high-frequency transformers, and power electronic transformers, owing to their high saturation magnetic flux density (Bs), low coercivity (Hc), low core loss, and excellent high-frequency response. This review summarizes recent progress in the modulation of soft magnetic properties, covering composition design, heat treatments, structural engineering, and transformer applications. For compositional design, a central issue is how to achieve high Bs while retaining sufficient Glass-forming ability (GFA), and appropriate additions of metalloid and transition-metal elements provide an effective route to this balance. Conventional isothermal, stress, magnetic-field, and rapid annealing processes enable structural relaxation, nanocrystallization, and anisotropy modulation. Ultrafine nanocrystals, amorphous/nanocrystalline transitional structures, and gradient and multilayer structures further improve overall performance through grain refinement, interface engineering, and domain optimization. Key engineering challenges include continuous ribbon casting, heat-treatment uniformity, winding-induced residual stress, and practical operating conditions. Future advances require the integration of in situ characterization, multiscale modeling, and machine learning, alongside advances in continuous heat treatment and low-stress manufacturing, to facilitate wider application in transformers.