The Impact of Particle Size and Ratio on the Magnetic Properties of Soft Magnetic Composite Materials for Motors

The influence of iron phosphide powder with different particle sizes and ratios on the magnetic properties of soft magnetic composite materials for motors was studied. The results showed that the magnetic powder cores with larger particle sizes and narrower particle size distributions had poor flowability during the pressing process, resulting in more air gaps and higher eddy current losses at higher frequencies, leading to higher overall losses. The magnetic powder cores with smaller particle sizes and narrower particle size distributions had more non-magnetic gaps, lower permeability, lower density, and poorer magnetic properties. An appropriate particle size distribution could improve the flowability of the powder, facilitate the pressing of magnetic powder cores, increase the density, reduce coercivity, and consequently decrease hysteresis losses. However, excessive large particles in the powder with narrow particle size distributions would result in higher eddy current losses at high frequencies. To balance hysteresis losses and eddy current losses, and thus reduce overall losses, it is recommended to choose iron powder with a wide particle size distribution, a smaller proportion of large particles, and an average particle size around 100 μm. There are many factors influencing the magnetic properties of magnetic powder cores, and a single magnetic characteristic parameter is determined by multiple influencing factors. Therefore, iron powders with a suitable particle size distribution should be a candidate for soft magnetic composites.