New developments in soft magnetic materials alternative to Fe-Si alloys and their magnetic characterization techniques

Electrical machines designers have shown in the last decade an increasing interest towards new materials that could represent a valid alternative to those commonly adopted in the realization of magnetic circuits. It is the case of parts or components realized with magnetic powders in place of laminated steels. The main advantages concern the reduction of eddy current losses, and consequently minor iron losses at medium-high frequencies. The focus of the paper is about the realization of magnetic circuits by means of the powder metallurgy technique, adopting the so called “Soft Magnetic Composites”, or SMC, opening to the possibility of realizing by compression complex shapes otherwise impossible to be even considered. The impact of these new materials and their increasing adoption in the electrical machines scenario, has put in evidence the necessity of analyzing their realization process and providing the characterization of the obtained SMCs. Figure 1 highlights the difference between magnetic flux direction in laminated steel and SMC materials: the magnetic flux path has the same behavior in all directions (3D) for SMCs. Moreover, the eddy currents are only restricted to particle dimensions. SMCs materials have some drawbacks, mainly related to mechanical strength. Nevertheless, the promising use of SMC materials in several applications, brings to the necessity to a comprehensive characterization. The paper will first of all face the problem of describing the influence of the production process parameters, starting from the selection of the possible and more suitable binders, their percentage, the mold pressure, the curing temperature. Then the attention will move on the analysis of all the tests required to get a complete information of the obtained material. In particular, the characterization regards the magnetic behavior and the energetic performance, together with measurements of the conductivity, and the evaluation of the mechanical characteristics.