Ordering suppression and excellent ductility in soft-magnetic Fe-6.5 wt%Si sheet by Hf addition

Highlights: • Fe-6.5w.t.%Si-xHf alloy sheets were fabricated by warm-cold rolling. • A small Hf addition can enhance ductility without damaging soft magnetic property. • A great increase of fracture strain is observed from 5.2 ± 1.8 to 18.4 ± 2.5%. • HRTEM observation reveals suppression of FeSi brittle phase. • A mechanism based on precipitation-dependent atomic rearrangements is proposed. Fe-6.5 wt%Si alloy is superior to other materials in terms of its soft magnetic performance but its lack of ductility leads to poor workability and large restriction on shaping. It is quite challenging to improve ductile performance without sacrificing soft magnetic properties. In this work, an excellent ductile behavior is observed in the Fe-6.5 wt%Si alloy with a slight addition of Hf, together with low coercivity of 0.73 ± 0.005 Oe and low core loss P_1/10k of 13.4 ± 0.41 W/kg. The Hf-added Fe-6.5 wt%Si alloy exhibits an elongation to fracture of 18.4 ± 2.5% and an ultimate tensile strength of 906 ± 30 MPa, which are much higher than the corresponding values (5.2 ± 1.8% and 755 ± 63 MPa) of the Hf-free Fe-6.5 wt%Si alloy. X-ray diffraction analysis and high-resolution transmission electron microscopy observations reveal that Hf addition brings about formation of Hf-enriched Hf-Fe-Si precipitates with face-centered-cubic structure, which is found to play a significant role in effectively suppressing formation of Fe-Si ordered phase, and thus greatly improving ductility of the alloy. A mechanism based on precipitation-dependent atomic rearrangements is proposed to explain the desirable suppression of Fe-Si ordered phase.