Optimizing magnetic performance of Fe–50Ni alloy for electric motor cores through LPBF: A study of as-built and heat-treated scenarios

Abstract

This study aims to identify the optimal combination of process variables for laser powder bed fusion (LPBF) of electric motor (EM) cores using Fe–50Ni alloy. A thorough analysis of mechanical and magnetic properties, with a focus on its dynamic magnetic performance within 50–500 Hz frequency range, is presented. Optimized process parameters yielded relative densities above 99%. In the as-built condition, high hardness (twice that of conventionally processed alloy) and high ductility (>30% at rupture) were achieved. The as-built samples demonstrated magnetic properties below the requirements, but significant improvement was observed in the semi-static magnetic properties after heat treatment, with acceptable coercivity (44 A/m) and maximum permeability (∼104) attributed to a notable reduction in geometrically necessary dislocations (GNDs) density. Heat treatment did not significantly reduce the total loss at high flux densities or elevated testing frequencies because the energy loss in the as-built microstructure is lower than what is expected due to the activation of more domain walls resulting in a homogeneous distribution of eddy currents. The superior semi-static performance of the optimum sample is related to its texture, which was more oriented toward the easy axis of magnetization in this alloy (<111> direction). This research demonstrates the LPBF process's potential for manufacturing electric motor soft cores, providing acceptable surface integrity, roughness levels, and desired coercivity and permeability. However, the high total loss, specifically at elevated frequencies, highlights the need for additional capabilities of LPBF, such as fabricating multi-materials, to mitigate energy losses without resorting solely to heat treatment.