Effect of mechanical milling and heat treatment on the structure and magnetic properties of gas atomized Mn-Al alloy powders

Ferromagnetic Mn-Al alloy powders were fabricated by mechanical milling and heat treatment with gas-atomized powders. Different processes, i.e., heat treatment before ball milling and ball milling before heat treatment, result in different microstructures and magnetic properties of the powders. It was found that H_c increased and M_r decreased with the size reduction regardless of the sequence of heat treatment and ball milling. However, tendency of the change in H_c and M_r depended on the sequence. Further annealing of the powders ball-milled after heat treatment resulted in slight decrease of H_c and large increase of M_r. The magnetic properties, M_r = 41.2 emu/g, H_c = 3.1 kOe, were obtained from the powders ball-milled for 5 h after heat treatment at 650 °C for 20 min, and subsequent annealing at 280 °C for 20 min.