Annealing temperature effects on microstructure and magnetic properties of Fe-6.5wt. %Si alloy strips prepared by TSTRC process

Abstract

The Fe-6.5wt.%Si alloy exhibits remarkable soft magnetic characteristics, such as high magnetic permeability, low coercivity, high resistivity, and nearly zero magnetostriction. These attributes establish it as an ideal material for low-power, low-noise electric motors and transformers. This investigation aimed to assess the impact of annealing temperature (ranging from 800 to 1200 °C for 1 h) on the microstructure, texture, and magnetic properties of a 0.15 mm thick Fe-6.5wt.%Si alloy sheet, which was obtained by subjecting the strips produced through the top side-pouring twin-roll casting (TSTRC) process to multi-pass warm rolling in the temperature range of 600 ∼ 800 °C, avoiding hot rolling. Additionally, the recrystallization mechanism of the annealed sheet at 1100 °C for 1 h was explored. The findings indicate that enhancing the annealing temperature corresponded to a reduction in magnetic induction (B8 and B50) as well as iron losses (P10/50, P10/400, and P2/1000). The annealed sheet at 1200 °C for 1 h demonstrated the most favorable magnetic properties, displaying iron losses of 0.486 W/kg, 6.895 W/kg, and 1.232 W/kg for P10/50, P10/400, and P2/1000, respectively. These results illustrate excellent overall magnetic characteristics. The coercivity (Hc) of both B8 and B50 decreased as the annealing temperature increased in the hysteresis loop measurements. Specifically, for B8, it decreased from 62.84 A/m to 24.50 A/m, and for B50, it decreased from 78.10 A/m to 35.50 A/m. The average grain size of the samples gradually increased as the annealing temperature ranged from 800 to 1200 °C. The dominant texture observed was {111}, and the volume fraction of {111} texture increased while the volume fractions of {100} and {110} textures decreased. Upon annealing at 1100 °C for 8 s, the elongated and flattened deformed structures were mainly replaced by equiaxed grains, indicating the completion of the recrystallization process. However, there was a noticeable distinction in the coarsening degree of equiaxed grains based on their orientations. The presence of λ-oriented grains was less prominent, while α-oriented and γ-oriented grains were relatively more abundant. As the annealing time increased from 8 s to 1 h, there was a decrease in the presence of λ-oriented and α-oriented grains, while the presence of γ-oriented grains significantly increased.