Revealing the mechanism of grain refinement's effect on the discharge performance of AZ31 magnesium anode under different pulse currents

Abstract

Magnesium-air batteries possess high theoretical energy density, but their anode discharge performance is limited by microstructure. This study investigates the regulatory mechanism of microstructure on discharge performance by controlling effective pulse currents (120–240 A). The results show that the AZ31 magnesium alloy treated by 120 A pulse current exhibits excellent discharge performance at various discharge current densities. The discharge voltages was 1.077 V at current densities of 10 mA·cm⁻², respectively, with corresponding anode efficiencies of 58.9 %. This is primarily due to the formation of a uniformly distributed fine-grained structure (average grain size of 5.82 μm) compared to other pulse currents. The fine-grained structure provides more grain boundary dissolution channels, and the uniform grain distribution significantly mitigates the “chunk effect”. Although the alloy treated with 120 A pulse current has a relatively high β-Mg₁₇Al₁₂ phase content and a preferred (0001) grain orientation, which are disadvantageous, its uniform fine-grained structure effectively counteracts these adverse effects. This study confirms that grain size is the primary factor in regulating the discharge performance of magnesium anodes, providing a theoretical basis and technical pathway for designing high-performance magnesium-air battery anodes.