Structurally-layered soft magnetic Fe-Si components with surface insulation prepared by shell-shaping selective laser melting

Highlights: • Shell-shaping selective laser melting has been introduced. • Structurally-layered Fe-6.5 wt%Si soft magnetic components have been fabricated. • High-temperature heat treatment greatly improves magnetic properties. • Stators for novel axial flux motor have been demonstrated. Recently, selective laser melting (SLM) of soft magnetic components (SMCs) has attracted great interest due to its high accuracy in three-dimensional shaping of hard-to-form high performance alloys (e.g. Fe-6.5 wt%Si), which are being highly pursued for the realization of small and lightweight next-generation electric motors. However, SLMed SMCs with internal insulation have never been successfully demonstrated because there are no suitable insulation materials to withstand extremely-high-temperature laser processing. Here we introduce a novel shell-shaping selective laser melting (SS-SLM) process and demonstrate highly-dense (relative density > 98%) structurally-layered Fe-6.5 wt% SMCs with surface insulation. In particular, high-temperature heat treatment induced grain growth and dramatically enhanced magnetic properties, including coercivity of 34.6 A/m, permeability of 7393, and saturation magnetization of 1.68 T. Furthermore, a sol-gel-based process yielded a uniform and dense SiO₂ insulation layer on the shell surface, which effectively confines eddy current only in the shell. Remarkably, core loss of 52.5 W/kg (at 1 kHz, B_m = 1 T) was observed with definable minimum sheet thickness of 0.2 mm. Finally, we demonstrate structurally-layered SMCs (stators for novel axial-flux motors) with surface insulation, which eventually can be used to realize a three-dimensionally optimized magnetic path and considerably increased power density with high efficiency.