Phase and morphology evolution study of ball milled Mg–Co hydrogen storage alloys

•Mg–Co alloys synthesized by ball milling may absorb hydrogen at 258 K.•Phase and morphology evolution process up to 400 h was investigated in detail.•Relationship between hydrogen storage property and structure was clarified.

Ball milled Mg–Co alloys with body-centered cubic structure (BCC) may absorb hydrogen at 258 K with a hydrogen capacity around 3 mass%. The phase and morphology evolution process of Mg50Co50 alloys ball milled for 0.5 h–400 h was studied by X-ray diffraction and scanning electron microscope. The formation mechanism of the Mg50Co50 alloys was clarified. Mg50Co50 alloys ball milled for various durations were found to present different hydrogen storage properties which could result from the phase and morphology difference in these samples.