Mechanical Properties of Stochastically Cracked Soft Magnetic Material

Abstract

Processing of soft magnetic materials with additive manufacturing has shown capability to deliver good magnetic properties and increased silicon content of Fe-6.5 wt%Si, however methods must be used to reduce the eddy currents in large bulk cross-sections in components created by additive manufacturing. Geometrical design has been shown to do this effectively, however stochastically cracked parts show similar magnetic performance with a large increase in stacking factor. To enable their use in electrical machines the mechanical properties of this material must be understood. Therefore, this study uses uniaxial tensile testing to understand the mechanical performance. The ultimate tensile strength of the material in the as-built condition was 17.9 MPa (σ = 4.5 MPa), which was improved by 40% to 25.5 MPa (σ = 5.7 MPa) by infiltrating the cracks with a low viscosity resin. This brings the material strength to more than three standard deviations from the required strength of 7 MPa to be used in a specific axial flux machine. The material exhibited an elongation to failure of 8-10%, showing that the suppression of ordered phases by high cooling rates has improved the ductility of the material. Hence, the stochastically cracked parts have sufficient properties to be used in the 3D magnetic circuits of electrical machines.

Keywords: Laser Powder Bed Fusion, Cracking, Soft-Magnetic Material, Mechanical characterisation, FeSi