The precipitation in annealing and its effect on permittivity of Fe–Si–Al powders

• As-milled Fe–Si–Al powders were annealed at various temperature.
• The change of morphology and microstructure of as-annealed Fe–Si–Al was examined.
• Complex permittivity decrease significantly after annealed over 400 °C and permeability increase as annealing temperature rises.
• The precipitation process in annealing and its effect on permittivity were analyzed.

SEM images show that some precipitates distributed on the surface of as-annealed Fe–Si–Al powders. Subsequent experimental results indicate that both morphology and microstructure of as-annealed Fe–Si–Al powders change with increasing annealing temperature. Meanwhile, dielectric properties analysis suggesting that both real part ε′ and imaginary part ε″ of the Fe–Si–Al powders decrease significantly after annealed at 450 °C or higher temperature. We assume that it’s the precipitates with low electrical conductivity developed on the surface of powders that increase the surface resistivity of as-annealed powders and leading to a lower imagine part of permittivity. The drop of real part ε′ ascribed to the weakened interfacial polarization which resulted from the decrease of structural defects such as grain boundaries and interfaces during annealing process.