Effects of annealing condition and Al content on novel Fe73.5Si13.5B9Cu1Nba-xAlx alloys

The annealing condition, AI content, and field amplitude dependences of the complex permeability for Nb-poor Finemet type alloys, Fe73.5Si13.5B9Cu1Nba-xAlx （x = 0, 0.5, 1.5, 2.0, and 3.0）, were investigated using an impedance analyzer and X-ray diffraction. The results show that different AI contents lead to different optimum annealing conditions, and the A1 content exerts a distinct effect on microstructure thus resulting in a variety of real permeability value. For the samples annealed at 793 K for 0.5 h, the real permeability increases with an increase in A1 content when the AI content is below 2.0 at.%; as for those annealed at 793 K for 1 h and at 813 K for 0.5 h, an overall increase in real permeability can be obtained compared to those annealed at 793 K for 0.5 h. The permeability under different field amplitudes is also studied and it is found that the relaxation frequency in the lower frequency region tends to moving toward a higher frequency with an increase in field amplitude. All these might be because of the role of Nb in the annealing process and the solubility of AI in the amorphous matrix and nanocrystallized crystallites.