Evaluation of mechanical and magnetic properties of laser-DED Fe–Si alloy: element segregation and low-frequency AC performance

Fe-3 wt.% Si (Fe–3Si) gas atomised powder is used to fabricate laser-directed energy deposition (laser-DED) test specimens. The magnetic and mechanical properties of the as-built and three post-processed samples, including annealing and hot isostatic pressing (HIP), are evaluated in terms of the microstructure. The diffusion of silicon and the formation of Si-rich zones are observed when the material is annealed at 700 °C for 5 h, resulting in a dramatic reduction of the mechanical properties due to the formation of brittle precipitates. The best static soft magnetic properties combined with good mechanical properties are obtained by annealing at 1150 °C for 2 h, resulting in high magnetic saturation (2.02 T), low coercive field (89 A/m), high elongation (∼30 %) and high tensile strength (∼480 MPa). Additionally, the core loss of the as-built sample and the sample annealed at 1150 °C for 2 h is dissected and compared with that of the flat-rolled Fe–Si material. The as-built conditions provide better performance under low frequency AC conditions due to lower skin effect, giving a core loss of W15/50 = 28.5 W/kg, while maintaining good mechanical and magnetic properties. This work shows that further research into the additive manufacturing of low-frequency machines is needed to make this technology an effective option for the production of the future next-generation engines.