Abstract
The demand for advanced Al-based alloys with tailored structural and magnetic properties has intensified for applications requiring a high thermal stability and performance under challenging conditions. This study investigated the phase evolution, magnetic properties, thermal stability, and microstructural changes in the Al-based alloys Al(82)Fe(16)Nb(2) and Al(82)Fe(14)Nb(2)Mn(2), synthesized via mechanical alloying (MA), using stearic acid as a process control agent. The X-ray diffraction results indicated that Al(82)Fe(16)Nb(2) achieved a β-phase solid solution with 13-14 nm crystallite sizes after 5 h of milling, reaching an amorphous state after 10 h. In contrast, Al(82)Fe(14)Nb(2)Mn(2) formed a partially amorphous structure within 10 h, with enhanced stability with additional milling. Magnetic measurements indicated that both alloys possessed soft magnetic behavior under shorter milling times (1-5 h) and transitioned to hard magnetic behavior as amorphization progressed. This phenomenon was associated with a decrease in saturation magnetization (M(s)) and an increase in coercivity (H(c)) due to structural disorder and residual stresses. Thermal stability analyses on 10 h milled samples conducted via differential scanning calorimetry showed exothermic peaks between 300 and 800 °C, corresponding to phase transformations upon heating. Post-annealing analyses at 550 °C demonstrated the presence of phases including Al, β-phase solid solutions, Al₁(3)Fe₄, and residual amorphous regions. At 600 °C, the Al(3)Nb phase emerged as the β-phase, and the amorphous content decreased, while annealing at 700 °C fully decomposed the amorphous phases into stable crystalline forms. Microstructural analyses demonstrated a consistent reduction in and homogenization of particle sizes, with particles decreasing to 1-3 μm in diameter after 10 h. Altogether, these findings highlight MA's effectiveness in tuning the microstructure and magnetic properties of Al-Fe-Nb (Mn) alloys, making these materials suitable for applications requiring a high thermal stability and tailored magnetic responses.