Synergistic Effect of Second Phase and Grain Size on Electrochemical Discharge Performance of Extruded Mg–9Al–xIn Alloys as Anodes for Mg–Air Battery

The extruded Mg–9Al– x In alloys are systematically studied as the potential anode material for primary Mg–air batteries. In this study, the effect of grain size and second phase particles on electrochemical behavior and discharge performance of Mg–Al–In alloys with In content ranging from 0 to 1.0 wt% is investigated through microstructure characterization, electrochemical measurements, and half‐cell discharge tests. The results of this study indicate that the grain size of the alloy is remarkably refined to a range between 7.60 and 2.23 μm, and the distribution of the β‐Mg 17 Al 12 phase can be effectively modified after the In element is added to the extruded Mg–9Al alloy. In addition, as the content of the In element increases, the area fraction of the second phase decreases while the size increases. The Mg–9Al–0.5In alloy is shown to have the highest discharge potential (−1.63 V) and the most negative corrosion potential (−1.51 V) among the studied alloys. In addition, the anode efficiency and power density of the Mg–9Al–0.5In alloy reaches 78.2% and 76.8 mW cm −2 , respectively. The excellent discharge performance of the alloy is attributed to fine grain size, large area fraction, and dispersed micron‐sized precipitates and loose corrosion products. Consequently, these results reveal that Mg–9Al–0.5In alloy can serve as a promising anode material for Mg–air batteries.