Corrosion behaviour and discharge properties of extruded Mg-Zn-Ca anodes for primary Mg-air batteries

The corrosion behaviour and discharge performance of extruded Mg-xZn-1Ca (x = 0, 2, 5, 8) alloys, used as anodes for primary Mg-air batteries, were investigated by hydrogen evolution immersion, electrochemical and battery tests. The results show that the grain size first decreases and then increases with the increase Zn content. The type of the second phases changes from Mg2Ca to Ca2Mg6Zn3 and Ca2Mg5Zn13, and the percentage of the second phases increases. Among the four alloys, the ZX21 (Mg-2Zn-1Ca) alloy has the best corrosion and discharge performances, mainly uniform corrosion. The local corrosion of the other three alloys is mainly galvanic corrosion. At 10 mA cm−2, the anode efficiency, discharge capacity and discharge energy of the ZX21 alloy are 57.97%, 1244 mAhg−1 and 1493 mWhg−1, respectively. The improvement of the discharge performance of the ZX21 alloy is mainly due to the enrichment of Zn in the Mg2Ca phase, which reduces the potential difference between the matrix and Mg2Ca. It improves the corrosion performance of the alloy. In addition, the influence of the chunk effect diminished due to grain refinement.