Microstructures and Magnetic Properties of Rapidly Solidified MnAl Alloys Modified with Indium

A ternary Mn-Al-In alloy with the nominal composition Mn53Al44In3 were prepared by rapid solidification followed by heat treatment. Doping in MnAl alloys can improve the stability of the tau-phase when the annealing temperature is lower than 600 ?. The decomposition of tau-phase started after annealing at 500 ? for 30 min and almost completed after annealing at 650 ? for 30 min. It was found that most of the In-rich phases in as-spun alloys are generally distributed on the grain boundary of magnetic tau-MnAl. After annealing, the small ball-shaped beta-phase particles were precipitated on the surface of tau-MnAl grains. The average particle size of beta-phase increased sharply from about 73 nm to about 830 nm with the increasing annealing time from 10 to 30 min at 550 ?. The optimal magnetic properties of M-s = 105.7 emu/g and H-c = 1.094 kOe were obtained in the ribbons after annealing at 550 ? for 10 min. The highest value of the H-c was 4.261 kOe achieved in the Mn53Al44In3 ribbons after annealing at 650 ? for 30 min. However, the high coercivity was obtained at an expense of low saturation magnetization.