Thin Fe-Si-Al alloy sheet fabricated by Al gradient diffusion through PVD for excellent high-frequency magnetic properties

In recent years, research on environmentally friendly methods to reduce energy loss of high-frequency trans-formers has gained momentum. In this study, an Fe-Si-Al alloy sheet with excellent magnetic properties at high frequencies was fabricated by an environment-friendly method involving Al diffusion through physical vapor deposition for high-frequency transformer applications. To improve the magnetic properties of the alloy, the effects of Al diffusion patterns and frequency on the magnetic properties of the Fe-Si alloy sheet were theo-retically and experimentally investigated. Up to 12-& mu;m-thick Al was deposited via physical sputtering on a 0.2 -mm Fe-Si alloy sheet, which was subsequently annealed for 10-90 min under 10-4 Torr without changing the grain size and texture or forming an intermetallic phase. At 50 Hz, the eddy current loss reached a minimum, when the Al diffusion into the surface and interior was uniform with a deviation of approximately 10 %. In contrast, the high-frequency (above 400 Hz) eddy current loss was minimized, when more than 70 % of the total Al was concentrated on the surface to a depth of 1/4 area. Tension effect occurred owing to the difference be-tween the thermal expansion coefficients of the surface Al-diffused part and the that in the interior. This tension effect minimized the eddy current loss by reducing the domain width. The core loss of our specimen at 20 kHz (8.36 W/kg) was approximately 15 % superior to that of a commercial Si steel sheet of the same thickness. These results indicate the potential of the proposed method in high-frequency transformer eco-technology.