Effect of Phosphating and Heat Treatment on Magnetic Properties of Fe-3.3Si-6.5Cr Soft Magnetic Composites

Fe-3.3Si-6.5Cr powders were first treated by phosphoric acid solution and then mixed with epoxy-modified silicone resin uniformly, forming insulation coating. The Fe-3.3Si-6.5Cr soft magnetic composites were prepared by compaction and annealing treatment of the coated Fe-3.3Si-6.5Cr powders. The microstructure and composition of Fe-3.3Si-6.5Cr powders were analyzed by scanning electron microscope coupled with energy-dispersive spectrometer, Fourier-transform infrared spectra, and X-ray photoelectron spectroscopy, respectively. The magnetic properties were determined by the LCR bridge tester and an auto testing system for magnetic materials (MATS-2010SA). Results show that both proper phosphating treatment and annealing at higher temperature can improve the permeability and reduce the core loss of the Fe-3.3Si-6.5Cr SMCs. When the concentration of phosphoric acid was 0.5 wt% and the heat treatment temperature reached 500 °C, the Fe-3.3Si-6.5Cr SMCs showed the optimized magnetic properties, including the permeability (μe) of 44.7 H/cm, the core loss (P) of 521.8 mW/cm3 at the saturated magnetic flux density of 50 mT, and the frequency of 100 kHz. The Fe-3.3Si-6.5Cr SMCs with distinguished magnetic properties provide great application prospect in various fields such as filter inductors, transformers, and sensors.