Controlling the magnetic properties of Fe-Si soft magnetic composites through annealing-mediated evolution of the coating layer

This work presents the fabrication of low-loss, high-permeability Fe-Si soft magnetic composites (SMCs) utilizing alumina-coated and subsequently annealed Fe-Si powder. Appropriate annealing preserves a uniform, dense, and continuous alumina insulating layer, enabling optimization of the magnetic properties through powder annealing. The optimal annealing duration for Fe-Si SMCs was identified as 180 min, yielding a minimum core loss of 259.1 mW/cm 3 and a peak permeability of 94.85 (measured at 50 mT/100 kHz). The observed reduction in hysteresis loss arises from the combined influence of grain growth and stress relaxation during the annealing process. A uniform insulating layer effectively restricts induced eddy currents to individual powder particles, thereby minimizing eddy current losses. However, prolonged annealing compromises the coating’s structural integrity, resulting in a decline in magnetic performance. This work introduces a systematic strategy for enhancing the overall magnetic properties of SMCs by precisely controlling the annealing time of the powders, establishing a distinct correlation between coating evolution and composite performance. These insights provide practical direction for the high-efficiency deployment of soft magnetic composites in high-frequency magnetic applications.