Effect of Al content on magnetic domains of {100} grains in electrical steels

•Magnetic domains of Fe-Al electrical steels were observed by Kerr microscopy.•The correlation between magnetic domains and magnetic properties was discussed.•Magnetic domain size of {100} grains decreased as Al contents increased.•The changes of magnetic properties may be caused by pinning of 90° walls. Magnetic domains of {100} grains in electrical steels with 1.85 ≤ Al ≤ 6.54 wt% were observed by magneto-optic Kerr microscopy. The characteristics and motion of magnetic domains were correlated with hysteresis loss, anomalous loss and permeability. As Al contents increased, domain wall energy decreased, so the magnetic domain size of {100} grains decreased. In steel with Al 6.54 wt%, 90° domain walls appeared, so the complexity of domain structures increased. Addition of Al caused increase in hysteresis loss. Anomalous loss decreased until Al 4.68 wt%, then saturated, despite high resistivity and small domain size. External magnetizing force H→ required to induce maximum permeability µmax increased drastically at Al 6.54 wt%. These changes of magnetic properties may be caused by pinning of 90° walls during magnetization. As domain size decreased to form closure domains, the complexity of reorganization of magnetic domains increased, and they were interrupted by pinning 90° walls.