[en] Research highlights: → Calcium hydride + magnesium-aluminum borides as candidates for hydrogen storage. → Long time ball milling improves hydrogen sorption kinetics of the CaH₂+MgB₂ system. → Coexistence of MgB₂ and AlB₂ does not improve hydrogen sorption performances. → Total substitution of MgB₂ with AlB₂ improves the system kinetics and reversibility. → Below 400 deg. C almost the full hydrogen capacity of the CaH₂ + AlB₂ system is reached. - Abstract: Among the borohydrides proposed for solid state hydrogen storage, Ca(BH₄)₂ is particularly interesting because of its favourable thermodynamics and relatively cheap price. Composite systems, where other species are present in addition to the borohydride, show some advantages in hydrogen sorption properties with respect to the borohydrides alone, despite a reduction of the theoretical storage capacity. We have investigated the milling time influence on the sorption properties of the CaH₂ + MgB₂ system from which Ca(BH₄)₂ and MgH₂ can be synthesized by hydrogen absorption process. Manometric and calorimetric measurements showed better kinetics for long time milled samples. We found that the total substitution of MgB₂ with AlB₂ in the starting material can improve the sorption properties significantly, while the co-existence of both magnesium and aluminum borides in the starting mixture did not cause any improvement. Rietveld refinements of the X-ray powder diffraction spectra were used to confirm the hypothesized reactions.