Enhancement mechanism of low alloying (Mn, Al) and plastic deformation for hydrogen storage kinetics of Mg alloy

The sluggish kinetics are a momentous hurdle for the application of Mg-based hydrogen storage alloys. To improve the kinetics, Mg-xMn-0.5Al alloys (x = 0, 0.5, 1, 2) were fabricated by combining low alloying strategy and plastic deformation. The results demonstrate that both low alloying and plastic deformation enhance the kinetic properties of hydrogen adsorption and desorption. The resulting Mg-2Mn-0.5Al alloy after plastic deformation can absorb ca. 5 wt% hydrogen within 3 min at 623 K, and the dehydrogenation activation energy (ca. 125 kJ/mol) is substantially reduced versus Mg (ca. 166 kJ/mol). The co-addition of Mn and Al can introduce more second phases, and the pinning effect of Al8Mn5 and α-Mn on grain boundaries can promote grain refinement and dislocation proliferation. The increase of grain boundaries, phase interfaces and dislocations accelerates the H atoms diffusion, benefitting the hydrogen absorption. Plastic deformation generates plenty of nanoscaled Al8Mn5 particles, which can serve as additional heterogeneous nucleation sites of Mg during dehydrogenation. Low alloying of Mn and Al combined with plastic deformation is a low-cost and effective way to improve the hydrogen storage kinetics of Mg-based alloys.