Influence of processing parameters on the microstructure and magnetic properties of additively manufactured FeSi6.7 soft magnetic components
High-silicon soft magnetic steels like FeSi6.5 offer potential to increase the efficiency of energy conversion systems like generators and electric motors. This is due to their higher permeability and electric resistivity when compared to conventional electric sheet materials with 3-4 wt% silicon. However, the increased Si content also leads to an increase in brittleness, which makes them unfeasible for electric sheet production in most cases. Therefore, advanced manufacturing methods become necessary to create components of this material. One potential route are laser based additive manufacturing technologies like selective laser melting (SLM) or laser powder bed fusion (L-PBF).
However many factors can affect the final magnetic properties of such an additively manufactured soft magnetic material. This already begins with the production method, composition and purity of the powder being used. During the AM process the applied laser parameters, scanning strategies as well as the build platform temperature influence grain structure and the degree of defects like porosity or cracks. If these microstructural differences cannot be equalized by heat treating steps, they also have direct impact on the final magnetic properties.
Iron silicon alloys made from different powder materials with a Si content of 6.7 wt% were additively manufactured by selective laser melting (SLM). The influence of different processing parameters on the microstructure and defects is evaluated by microscopic methods. The correlating magnetic properties are measured in as-built condition as well as after a heat treatment at 1150°C for 1 h. For finished toroidal samples made from pre-alloyed powder, the final magnetic properties were in a range from 16 to 37 A/m for coercivity HC, while the maximum permeability µmax varied from 10.000 to 32.000 depending on the selected processing parameters.