A phase stability map of metallic magnesium powder, exposed to environmental conditions for 12 months (Mg-12M) and subjected to different high-energy ball-milling speeds and milling times, was constructed. Mg-12M-160 [1/2MgO-1/3Mg(OH)(2)-1/6 hydromagnesite] and Mg-12M-640 [1/4MgO-5/8Mg(OH)(2)-1/8hydromagnesite] composites were obtained changing the milling conditions. The correlation among the accumulated energy (Delta E-accum), the impact energy (Delta E-hit), and the phase stability under different high-energy ball-milling conditions were generated. The Mg-12M-160 composite had a hydrogen storage capacity of 0.63 wt% at -196 degrees C and 8.3 bar, although further hydrogen adsorption at higher pressures is expected. Structural defects play a significant role in the adsorption capacity. A representation of the possible absorption mechanism is proposed. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.