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• Co20 wt.% Al powder was milled for 30 h. • A complete structural transformation was evidenced annealing at 600 °C. • Cubic spinel with a = 8.066 Å of ZnAl 2 O 4 prototype was formed. • A fibrous mesoporous morphology was developed on CoAl after annealing. Ball milling (BM) of elemental Co and Al was conducted for 30 h (h). This process has altered the original morphologies of both elemental Co and Al powders. Spherical Al powder particles has changed into a smooth pancake-shape while the original irregular-shaped Co agglomerates became disintegrated ultrafine particles. BM of the Co20 wt.% Al powder mixture after 30 h yielded thin irregular-shaped particles. XRD analysis revealed a partial structural transformation after BM and further structural change upon annealing the powder at 600 °C, as confirmed by the SEM images. The formation of the cubic spinel superstructure with lattice parameter a = 8.066 Å (ZnAl 2 O 4 prototype) and Fd-3 m # 227 space group was realized. By means of LEO 1525 field-emission scanning electron microscope (FE-SEM), a fibrous mesoporous structure was revealed on the milled powder after annealing the Co-Al mixture at 600 °C. The EDS analysis confirmed a minor N impurity on the annealed powder. [ABSTRACT FROM AUTHOR]