Processing-induced phase redistribution for enhanced self-corrosion control and discharge performance in Mg–Al–Mn anodes for Mg–air batteries

Abstract

Abstract The long-term performance of Mg–air anodes in chloride electrolytes is governed by the interplay of phase architecture, self-corrosion, discharge-product evolution, and anodic utilization. This study elucidates the processing-dependent influence of Al in Mg–0.25Mn–xAl anodes by comparing low- and high-Al alloys in the as-cast (AM20, AM90) and extruded (EXAM20, EXAM90) conditions in 3.5 wt. % NaCl. Microstructure, immersion corrosion, time-dependent PDP/EIS analysis, 24 h galvanostatic discharge at 10 mA $${\text{cm}}^{ - 2}$$ anodic efficiency, and post-discharge macroscopic/SEM morphology were correlated. In the as-cast state, increasing Al content refined the α-Mg grains but generated a continuous Al-rich/β $${\text{Mg}}_{17} {\text{Al}}_{12}$$ -phase network in AM90, promoting discharge activation while intensifying micro-galvanic self-corrosion and hydrogen evolution. Homogenization followed by extrusion disrupted this network and redistributed Al-rich and Al–Mn-rich particles within fine recrystallized α-Mg grains. Consequently, EXAM90 exhibited the lowest immersion corrosion rate and hydrogen evolution while maintaining the most negative average discharge potential (− 1.484 V vs. SCE). EXAM90 also delivered the highest anodic efficiency (51.0 ± 1.2%), indicating the most effective utilization of Mg during discharge. Post-discharge observations revealed persistent Mg $$\left( {{\text{OH}}} \right)_{2}$$ -rich deposits on the low-Al alloys, whereas EXAM90 exhibited discontinuous product coverage, open surface channels, and controlled removal of discharge products. These findings demonstrate that extrusion-induced phase redistribution partially decouples anodic activation from self-corrosion, enabling improved discharge performance and Mg utilization. This positions EXAM90 as a promising anode for long-life primary Mg–air batteries, especially in marine and backup power systems where sustained performance and material utilization are critical.