Effect of heat treatment for the gas atomized Mn-Al-C alloy powders on the magnetic properties of extruded magnets by powder-extrusion process

摘要

Mn-Al-C magnet has been produced by powder-extrusion process since 1989. It is known that rapidly solidified powder improves the magnetic properties of magnet. In this work, the possibilities to improve magnetic properties for powder-extrude Mn-Al-C-alloy were studied by using heat treated gas atomized powders. The effect of isothermal annealing at 973K for gas atomized powders on the magnetic properties after extrusion was investigated. The effect of homogenization at 1373K for gas atomized powders was also investigated. After these heat treatments r phase volume ratio in powder-extruded magnet was increased. In consequence, better saturation magnetization (4πIs (at O.8MA/m)) and residual magnetization (Br) were obtained. By annealing at 973K maximumenergy product ((BH)max) was improved since Br was increased with keeping the consistent intrinsic coercivity (iHc). By 1373K homogenization for gas atomized powders, Br was significantly increased while iHc was decreased, so that (BH)max was inferior to the one without heat treatment. This iHc decreasemay be caused by the grain coarsening of τ phase after extrusion, which was due to the coarsening of ε phase during 1373K homogenization heat treatment. As a result, it can be said that the increasing r phase volume ratio as well as keeping fine structure is important to improve magnetic properties of Mn-Al-C magnet.