The activating process of Al-Sn alloys in alkaline solution is investigated by electrochemical measurements, and their structure and morphology are analyzed by X-ray diffraction(XRD) and scanning electron microscope(SEM). A vigorous potential fluctuation process which is composed of a great amount of V-shape potential barrancas is observed during the galvanostatic discharging process. When discharged at the stable potential platform of V-shape potential barrancas, a great amount of arc-shape protuberances exists on the surface of the anode. When discharged at the bottom of the V-shape potential barranca, a lot of micropores and micro cracks exist on the surface of the anode. An explanation for the potential fluctuation is proposed. Higher Sn content is necessary for the formation of micro cracks in the hydroxide film which is formed on the surface of the anode, which results from the mismatch in the size and structure between SnO32- ions and Al(OH)(3). The formation, propagation and convergence of the micro cracks and the rupture of the film all need a strong internal stress in the film, which relies on the thickness of the film. The thickness of the film depends on the discharging current density. (c) 2018 The Electrochemical Society.