Passivation of corroding surfaces in aluminum etch pits and tunnels was investigated by step reductions and cathodic pulses in applied etching current. Morphology study shows that, in the early stage of passivation, the corroding surface consisted of recessed patches, which are actively dissolving surface, and flat passive area. These active patches are found within the potential range between the potential of zero charge (E[subscript]PZC) and the repassivation potential, and the actively corroding area increases with potential, from zero near E[subscript]PZC to the entire surface at the repassivation potential. A mathematical model describing the progress of passivation was developed and compared to experimental measurements. The calculation indicated that patchwise passivation takes place in times less than 100 [mu]s and the fractional active area is a function of potential below the repassivation potential. It thus suggests that the patches are islands of specifically adsorbed chloride ions, so that the passivation is controlled by desorption of these ions. For cathodic current pulses, the effect of pulse time and current pulse ratio on passivation and pit nucleation was investigated through the morphological study of actively dissolving tunnel tip surface and accompanying potential transients.