Discharge and corrosion behavior of Mg-2Zn-Mn-xY alloys as the anode for Mg-air battery

The microstructure, corrosion resistance and discharge properties of as-extruded Mg-2Zn-1Mn-xY (ZM21-xY, x = 0, 2, 3, 4 wt%) alloys are systematically studied. With the increase in Y/Zn ratio, the extruded ZM21 alloy gradually precipitate of W phase (Mg3Y2Zn3) and the long-period stacking ordered phase (LPSO phase, Mg12YZn). Compared with the Y-free ZM21 alloy, the addition of Y generally reduces the corrosion resistance of the alloy, which is mainly due to the galvanic corrosion of the second phase (W phases and LPSO phases) and the Mg matrix. However, with the further increase in Y, the corrosion resistance of the alloy is gradually increased mainly due to the phase distribution characteristics. The addition of the Y element effectively improves the discharge performance of the ZM21 alloy and when Y/Zn = 2:1, the ZM21-xY (x = 2, 3, 4 wt%) has the best corrosion resistance in the three alloys. The as-extruded ZM21-3Y alloy has a discharge voltage of 1.475 V and an anode utilization rate of 54% at the current density of 1 mA/cm(2). Especially under the current density of 10 mA/cm2, it still has a discharge voltage of 1.26 V and an anode utilization rate of 43%. The improved discharge performance is systematically discussed from the perspectives of the precipitation distribution, the surface characteristics and cracking effect of the discharge products in details.