Hot-compacted Fe–Si soft magnetic composite with low loss at low frequency

The Fe-5.5wt%Si soft magnetic composites (SMCs) with outstanding magnetic properties at low frequency are prepared by hot compaction combined with H3PO4 passivation. The influences of H3PO4 dosage and hot compaction on microstructures and magnetic properties of the SMCs were investigated in detail. Compared with cold compaction, air gaps in the hot-compacted SMCs can be significantly reduced, leading to remarkable improvement of the core’s density and maximum permeability. With the H3PO4 dosage decreasing, both the density and the maximum permeability increase. This results in the improvement of the hysteresis loss, but causes the deterioration of the eddy current loss, which makes the total loss increase after an initial decrease with the H3PO4 dosage. The hot-compacted SMC treated with 1.2 wt% H3PO4 is found to possess lower loss than Somaloy® 110i 5P of Höganäs and higher permeability than cold-compacted SMCs. This work might provide novel reference for designing soft magnetic composites with good magnetic properties in low frequency range.