Imaging with a high-speed camera at a resolution of 10-20 mu m has been used for the direct observation of the anodic dissolution of aluminium alloys containing Sn and Ga. The imaging allows confirmation that hydrogen bubble evolution occurs from the Sn inclusions within rounded pits during both open circuit corrosion and anodic dissolution. Using microelectrodes with only a few Sn inclusions in their surface, it is shown that the evolution of H-2 is not continuous and may be correlated with a potential oscillations between -1.50V (where H-2 evolution occurs) and significantly less negative potentials (where not H-2 is evolved). It is proposed that this potential shift is associated with pH changes resulting from H-2 evolution itself (C) 2009 Elsevier Ltd. All rights reserved.