MECHANISMS OF PITTING INITIATION IN ALUMINIUM AND ITS ALLOYS.

In spite of extensive research on the pitting corrosion of aluminum and its alloys, the mechanism of pit initiation is not completely understood. Even though a perfect theory does not exist, sufficient evidence exists to suggest that pits initiate at a characteristic potential, the critical pitting potential, which is fairly reproducible in value. In the past, objections have been raised against its existence. A description is given of adsorption theories to explain the pitting mechanism. The induction time is defined as the initial period of time at the critical pitting potential during which the anodic current remains constant prior to the beginning of a continuous increase of current with time which reaches current values higher than the induction current by many orders of magnitude.