Cracking of soft magnetic FeSi to reduce eddy current losses in stator cores

To enable use of additively manufactured (AM) soft magnetic material in electric machines, large bulk cross-sections must be avoided as they allow large eddy currents, reducing efficiency. Fe-6.5 wt%Si is an excellent soft magnetic material, but is brittle. In this study we exploit this inherent characteristic of the material to develop crack networks within the AM material to inhibit parasitic eddy currents. By manipulating the laser parameters and scan strategy to purposefully induce cracking, the effective resistivity of the material can be increased to 206 µΩ·cm, 250% of the materials’ already high resistivity of 82 µΩ·cm. Crack density is shown to increase with decreasing scan speed, and calculated electrical tortuosity shown to correlate with effective resistivity. Different scan strategies are shown to alter the orientation of the cracks, demonstrating that the crack orientation could be controlled in relation to the magnetic flux, providing high electrical resistance in the plane of the eddy currents, whilst maintaining magnetic properties. This method yields losses of 2.2 W/kg at 1 T, 50 Hz, similar to methods using air gaps, but with a much higher stacking factor of > 97%, outperforming other methods used in AM of soft magnetic material, showing promise for manufacturing stators of complex electric machines.