Microwave Absorbing Properties of MnAl Alloy Powder

Mn55Al45 alloy powder was prepared by the combined use of arc melting, high energy ball milling and tempering heat treatment process. The phase structure and the microstructure of the alloy powder were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and then their microwave absorbing properties were tested by a vector network analyzer. The results show that an increase of phases for Al2Mn3 and Al11Mn14 are accompanied by the increased milling time; the resonant frequency and the absorption peaks of ɛ″ and μ″ shift towards lower frequency region simultaneously. A better result of electromagnetic properties is brought to the alloy powder when the ball milling time is set to 18 h in first attempt. While the ball milling time is increased to 24 h during later experiment, the minimum reflectivity value reaches to −28 dB at a frequency of 16 GHz. The Al2Mn3 phase increases with an artificial increase of tempering temperature. The Mn55Al45 alloy powder ball milled for 18 h and tempered at 400 °C exhibits preferably comprehensive microwave absorbing properties in the range of 6∼8 GHz. The minimum reflectivity value and absorption peak frequency at the coating thickness of 2.0 mm are −26.4 dB, 17 GHz, respectively.