Spatially Tuned Properties in a Bulk Fe-Co Soft Magnetic Alloy via Transverse Induction Annealing and Feasibility Study for Motor Applications

Electric vehicle adoption has seen a dramatic upward trend in the last decade. Maximal efficiency of electric motor technology for maximum range, achieved by minimizing losses experienced by motor stator and rotor, is limited by a trade-off with high strength, as necessary to withstand torque experienced during operation. Spatial tailoring of magnetic and mechanical properties for optimized magnetic performance while retaining sufficient mechanical strength is a desirable pathway toward improved performance. Here, radiofrequency transverse induction annealing is demonstrated as a novel pathway to continuous spatial variation in microstructure of bulk crystalline soft magnetic alloys, providing a novel processing route to spatially tuned properties. Via local control of grain size, magnetic and mechanical properties may be separately prioritized as functions of position, enabling optimized stator laminations with reduced losses while retaining requisite mechanical strength. Experiment and finite element modeling demonstrate that a cylindrical induction coil can impose significant microstructure and property variation in a Fe-Co bulk crystalline soft magnetic alloy. A basic feasibility study follows, examining improved performance of a motor containing a stator with radial variation in coercivity. Results indicate future potential for co-optimization of spatial thermal processing of magnetic laminations with motor designs for unprecedented performance. A novel technique, transverse induction annealing, is shown to generate inhomogeneous heating within a single lamination of soft magnetic alloy, resulting in continuous spatial variations in microstructure on the cm scale. This enables spatial optimization of power magnetic components such as electric motor laminations, mitigating trade-offs in mechanical and magnetic performance.image (c) 2023 WILEY-VCH GmbH