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In this paper, the magnetic ageing of a bulk forged non-annealed magnetic core, used in claw pole synchronous machine, is investigated. The study is carried out by characterizing the material properties of two groups of samples subjected to a thermal ageing at 180 °C that corresponds to the maximum operating temperature of the claw pole rotor. The investigated characteristics are the electrical conductivity, the magnetic properties, the material microstructure and the Vickers hardness. They were characterized along with the ageing time. The results show that, during the thermal ageing, the hysteresis losses and the Vickers hardness have been affected by the magnetic ageing, whereas the electric conductivity and the normal B-H curve have not been modified. The microstructure analyses showed that carbides precipitates were the main cause behind the magnetic ageing. Moreover, the comparison between the results of two groups of samples revealed the possibility that the magnetic ageing of the material could have started during the manufacturing process of the magnetic core.

16MnCr5 steel parts were additively manufactured by laser powder bed fusion in order to investigate the effect of microstructure on electromagnetic properties. As process parameters have a direct impact on the obtained microstructure, different conditions were used to manufacture samples on which magnetic and electrical tests were conducted. The obtained results were presented and discussed in terms of density, microstructure and electromagnetic properties. Finally, correlations have been demonstrated between the microstructure and the electromagnetic performances. Lower magnetic and electric properties were obtained with the higher porosity rates at low volume energy density. The microstructural effects were evidenced, through a decrease in magnetic properties with grain orientation, and an improvement with stress relief annealing.

In this work, we investigate in Fe-Si laminations the core-loss coefficients variation with the flux density within the loss statistical approach framework. We find that the dynamical core-loss coefficients can be linked with the differential permeability defined from the low frequency normal curve. We interpret these variations as the fingerprint of the domain-wall activity (i.e. all the processes involving domain-wall movements, nucleation and anihilation) during the magnetization process. We show that the classical loss variation can be qualitatively described by the macroscopic formulation of the skin-depth, but not quantitatively.

During the operation of Claw Pole (CP) machines, and for some operating loads, the magnetic core temperature can reach 180°C in some hot spots. As a consequence, the core electromagnetic properties may considerably change, impacting the machine performances. In such a case, a deep knowledge of the electromagnetic behavior as a function of the temperature is required. In this paper, we present a dedicated study of the CP rotor made from a forged magnetic steel. In fact, the CP magnetic properties heterogeneity and the claw shape made it necessary to extract specific samples that are characterized with a miniaturized Single Sheet Tester (SST). To that end, this work proposes a specific methodology to characterize the electromagnetic properties of the CP rotor material as a function of the temperature in order to better predict the machine electrical performances, especially regarding the iron losses.

Magneto-optical (MO) analysis is a powerful tool to reveal the magnetization processes in magnetic materials at all relevant scales. Because the magnetization processes involve the restructuration of the magnetic domain structure (domain-wall nucleation, annihilation, and propagation, etc.), MO studies are of prime importance to link the material microstructure to its basic macroscopic properties (e.g., magnetic losses) and then improve the knowledge of these properties and their modelling. In this work, we propose a MO investigation of the magnetic domain structure evolution under rotating magnetic field.

La roue polaire des alternateurs à griffes est une pièce magnétique massive issue d’un processus de fabrication impactant pour les propriétés magnétiques du matériau. L’une des pistes d’amélioration des performances des alternateurs est la maîtrise des paramètres du processus de fabrication pour en réduire l’impact. Ceci passe nécessairement par l’identification du lien entre les procédés et les propriétés microstructurales et mécaniques du matériau. Ensuite, ces propriétés sont à leur tour mises en lien, par le biais de caractérisations, avec les propriétés magnétiques du matériau.