Improving hydrogen storage performance of Mg-based alloy through microstructure optimization

Abstract

Different fast forging processes are used for microstructure optimization in an attempt to improve hydrogen storage in Mg-based composites obtained from a mixture of Mg-22 wt% Ni powders. First, fast forging is employed at room temperature to change the amount of structural defects, produce fine grains and modify crystallographic textures. The effects of such microstructure modifications (including the exact nature of phases) on the H-storage behavior are investigated. A Mg {0001} basal fiber texture develops upon fast cold forging, which facilitates the initial activation of hydrogenation while, owing to the high stability of the MgH2 hydride, the kinetics of desorption remains rather slow. Second, to promote hydrogen desorption, forging is conducted at elevated temperature to form Mg2Ni phase. Interestingly, for this sample, faster desorption is recorded while slower absorption kinetics is obtained due to the occurrence of dynamic recrystallization inducing weaker texture and lower amount of structural defects. Third, annealing followed by cold forging is used to produce a microstructure consisting of fragmented Mg2Ni lamellae embedded in a textured Mg-matrix. Using this third approach, both hydrogen absorption and desorption kinetics are found to be markedly improved.