In wetting experiments using the sessile droplet method, deoxidation of aluminium by vaporisation of aluminium oxides, allows the equilibrium contact angle to be reached. Then, preferential etching of the alumina substrate at the gas-solid-liquid triple line occurs. The origine of this erosion phenomenon is explained by oxygen bulk diffusion from the interface Al/Al2O3 towards the liquid surface and then vaporisation under vacuum. Calculations are performed in order to evaluate the shape and depth of this groove.