Effects of Al Contents on Magnetic Properties in Non-Oriented Electrical Steels

Abstract

The addition of aluminum (Al) to electrical leads great advantages on enhancing core loss without cold-workability sacrifice. The improvements on core loss by Al addition is concentrated on eddy current loss. However the effect of Al on the magnetic properties of electrical steels has not been studied in detail. Therefore present work attempts to investigate the effect of Al addition on magnetic properties in Fe-Al and Fe-Si-Al based non-oriented electrical steels. In addition, correlation between magnetic properties, magnetic domain structure and metallurgical structure was investigated in Fe-Al alloys. For understanding the effects on Al on non-oriented electrical steels, the effects of Al content on microstructure, texture, magnetic flux density, permeability, core loss and magnetic domain structure of Fe-Al and Fe-Si-Al alloys were measured or observed. Average grain size decreased as Al content increased, but Al contents had no severe effects on texture. Magnetic flux density and permeability decreased as Al content increased, while ratio of flux density to saturation magnetic flux density was constant. Total core loss was separated into hysteresis loss, eddy-current loss and anomalous loss. As Al increased, hysteresis loss increased, but eddy current loss and anomalous loss decreased. Comparing the each loss in Fe-Al and Fe-Si-Al alloys which have similar electrical resistivity shows increased hysteresis loss while decreased in anomalous loss in Fe-Si-Al alloys. Present study also treats the effect of Al contents on iron, especially focused on the correlation between magnetic properties, magnetic domain structure and its motion under external magnetizing force. Kerr microscopy was used for observing demagnetized magnetic domain structure and its domain wall motion under external magnetizing force, 300 A/m at 0.1Hz. Separated core loss, especially hysteresis and anomalous loss, behavior of Fe-Al alloys were understood by magnetic domain structure and its motion. In high Al contents, complexity of demagnetized state causes higher hysteresis loss. Saturation of anomalous loss at Al contents over 6.54 wt.% is due to the pinning of magnetic domain wall motion by 90o walls.