Mechanistic investigation of thickness-controlled microstructure and magnetic performance in Sb-microalloyed ultra-thin Fe-6.5 %Si ribbons fabricated by planar flow casting

Planar flow casting (PFC) is recognized as a promising near-net-shape technology for fabricating Fe-6.5 %Si alloy ribbons. However, its application is constrained by poor melt wettability, insufficient cooling efficiency, and unstable thickness control. To address these challenges, this study introduces a synergistic strategy combining Sb-induced surface energy reduction with enhanced system cooling capacity, enabling the stable fabrication of ultra-thin Fe-6.5 %Si-0.1 %Sb ribbons with controlled thicknesses. Subsequent low-strain rolling and annealing were further employed to optimize magnetic performance. A systematic investigation was conducted to clarify the mechanisms linking processing conditions, microstructural evolution, and magnetic performance. Results reveal that ribbon thickness regulates the cooling rate, thereby governing grain growth, texture formation and B2/D03 ordered phases precipitation. Thicker ribbon exhibits a more favorable texture, resulting in higher magnetic induction. Based on loss separation theory and microstructural analysis, total iron loss in annealed ribbons is determined by the frequency-dependent interplay between hysteresis and eddy current losses, which are primarily governed by grain size and ribbon thickness, respectively. At medium frequencies where hysteresis loss dominates, total loss decreases monotonically with grain size. At high frequencies, thicker ribbons exhibit increased eddy current loss but reduced hysteresis loss due to larger grain size. Such a competitive mechanism leads to a non-monotonic variation in total iron loss. This work presents a research paradigm for planer flow casting of ultra-thin Fe-6.5 %Si ribbons and provides theoretical insights and useful references for the manufacture of other high-performance metallic foils.