Influence of Al addition on structure and magnetic properties of nanocrystalline Fe65Co15Si5Nb3Cu1B11-xAlx alloys

• A series of Al-contained Fe65Co15Si5Nb3Cu1B11-xAlx alloys were fabricated.
• Tx1 can be decreased to 388 °C with Al substituting for B.
• Both Tx2 and ΔTx are enhanced by Al-substitution in Fe65Co15Si5Nb3Cu1B11 alloy.
• Excellent magnetic softness at high-temperature was found in x = 3 alloy.

The microstructure and soft magnetic properties of amorphous and nanocrystalline Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys were investigated. Microstructure has been analyzed from XRD patterns and magnetic properties were mainly studied by the evolution of initial permeability (μi) from room temperature to 700 °C. It was found that adding a certain amount of Al in Fe65Co15Si5Nb3Cu1B11 alloy significantly decreases onset primary crystallization temperature Tx1 from 452 °C to 388 °C and increases the crystallized interval temperature ΔTx from 188 °C to 290 °C. However, with the Al adding, the Curie temperature of amorphous phase Tcam shows a decline tendency. After annealing at 550 °C, the alloy with x = 1 exhibited the maximum room-temperature μi, however, the most stable soft magnetic properties at elevated temperatures was found in the alloy with x = 3. Therefore, the (μi-T) curves of Fe65Co15Si5Nb3Cu1B8Al3 samples annealed at 520–580 °C were also investigated in detail.