Comprehensive Study of τ-Phase Mn-Al-C Magnets: Corrosion Resistance, Structural Integrity, and Magnetic Properties.

This study investigates the chemical, physical, and magnetic properties of Mn-Al-C type magnets, focusing on their corrosion resistance. The hot compaction process is used for densification, producing isotropic magnets. Microstructural analysis reveals undesirable features, such as phase decomposition and deformation. Although these consolidated magnets do not have ideal microstructural and magnetic properties, they would serve as a good basis for corrosion experiments and provide a relative comparison of the effect on the magnetic properties. Voltammetry measurements compare the corrosion behavior of consolidated magnets and bulk cast material, revealing a potential difference of about 400 mV. The higher potential in bulk material likely results from reduced porosity and secondary phases. The formation of the β-phase is observed during the hot compaction process. The structural analysis of the corroded samples shows no substantial phase change up to 4 weeks of exposure under different conditions. The magnetic characterization of the corroded samples also shows no significant differences compared with the initial hot densified state. Microstructural analysis of the hot-compacted τ-phase Mn-Al-C magnets shows noticeable surface pitting and increased roughness under alkaline conditions, but no evidence of selective corrosion is observed. These results suggest that Mn-Al-C alloys are promising candidates for applications in which corrosion resistance is critical.