Electron microscopy of Mn-Al-C magnets

The microstructures of warm-extruded Mn-A1-C alloys with and without Ni addition have been characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with X-ray microanalysis. The existence of finely dispersed AI2O3particles in the extruded magnet is confirmed for the first time. Antiphase domain boundaries are not found, but some grains are disordered. Other microstructural features such as twins and dislocations are characterized and the origin of these features are discussed. The role of Ni in improving the magnetic properties is attributed to its influence on a) the deformation behavior of the material affecting the texture, b) the magnetic-exchange interaction between Mn atoms, and c) the degree of ordering of the τ phase.