Impact of Pulsed Laser Irradiation, Scribing and Ablation on 2-D Scalar and Vector Magnetic Losses and General Properties of Grain-Oriented Electrical Steels

Abstract

Increasing the efficiency of electrical machines is a global objective. One way to contribute to its fulfilment is to reduce iron losses of soft magnetic materials within their magnetic circuits (stator, rotor, core, …). Improvement of soft magnetic material properties, especially Grain-Oriented Electrical Steels (GOES) based on iron and 3% silicon, is possible using surface laser treatments through the magnetic domain refinement technic and introduction of favorable stress [1-2]. These improvements are classically obtained for unidirectional excitation fields parallel to the rolling direction, the pronounced easy magnetic axis of GOES. However, in appliances such as rotating electrical machines, the flux lines are not always parallel to this preferred configuration (ex: in the teeth) and can also rotate (ex: in the yoke). In the literature, papers address the development of the expression and measurements of 2-D-magnetic properties [3], but the behavior of laser treated GOES under rotational and parallel to transverse direction fields remains slightly explored [4] and can be investigated further. Indeed, advanced pulsed laser technologies have been proven to improve magnetic [5-6] and magneto-mechanical [7] properties significantly under unidirectional field along the rolling direction. They include irradiation and scribing processes but also a new laser process called ablation with ultra-short laser pulses [5]. Therefore, in this research work, the effects of pulsed laser irradiation, scribing and ablation on GOES under transverse and rotational fields are presented. The objective is to optimize the vector behavior of GOES. The study focuses on power losses and B-H curves. The considered material is a laboratory grade of 0,28mm thickness with a CARLITE coating of 3-4µm thickness. The experimental plan includes 6 laser sets of parameters. The selection was made to enable comparisons between the types of laser processes (irradiation, scribing or ablation) and regarding the power loss reductions in the rolling direction. The main configurations were based on reference [5] in which the study was conducted with unidirectional excitation field parallel to the rolling direction on 150x150mm2 samples. In the present work, power losses have been measured in both rolling and transverse directions with a Single Sheet Tester (SST) and in rotational field with a Rotational Power loss Tester (RPT). An accuracy study will be detailed in the extended paper. So as to avoid any sample dispersion, measurements were carried out systematically on the same samples before and after laser treatment with the same setups (SST for 150x150mm2 samples and RPT for 60x60mm2 samples). The rotational power losses were obtained by considering the average of Clock-Wise (CW) and Counter-Clock-Wise (CCW) measurements and compared to the sum of unidirectional power losses. Thanks to loss model and B-H curve representation, while separating each direction but also the static and dynamic contributions, the impact of various laser parameters will be analyzed separately on scalar and vector magnetic properties as a function of working conditions. Additionally, all samples have been observed at each step (before and after laser treatment) with a Magneto-Optic Indicator Film technic (MOIF), which is very adapted for GOES’s magnetic domains observations. This will be illustrated in the final paper. Both macroscopic and microscopic analysis will be helpful to understand the reasons for opposite or simultaneous improvements in case of unidirectional or rotational fields. Concerning RPT measurements, rotational power losses reductions are reported for several laser sets of parameters (to be compared) and for several Polarization/Frequency couples as shown in figures 1 and 2. By using the pre-selected laser treatments, magnetic properties have been improved with iron losses reduction rate up to -12% at 50Hz&1T and up to -7% at 500Hz&0.5T in comparison with non-laser treated material for one of the selected sets of parameters. Further measurements will be carried out by the authors by improving the laser parameters (laser power and patterns), which might enhance the actual results and reduce even more significantly power losses. In the extended paper, measurement results (SST, RPT) will be presented with more details. Comparisons and discussions about the impact of considered laser treatments on GOES measured in both unidirectional and rotational fields on magnetic properties will be proposed as well. Acknowledgments: This work was supported by JEUMONT Electric and was carried out with the help of financing from the Association Nationale Recherche Technologie (ANRT). It was carried out in parallel with the ESSIAL project, which the authors would like to thank. The ESSIAL project is funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 766437. The authors would also like to thank the Aperam-Brazil company for having supplied the samples. **