Morphological Change and Open-circuit Potential of Single Metastable Pit on AA1050 Aluminum in NaCl Solution

Abstract

The relationship between the change in the open-circuit potential (OCP) and the morphology of metastable pitting at Al–Fe–Si particles of AA1050 aluminum in 0.1 M NaCl was clarified. First, a metastable pit grew in the depth direction as the OCP decreased suddenly. Second, the pit started to grow on the Al surface, and the OCP remained low. Finally, the pit was repassivated with the reincrease of the OCP. In the early stage of OCP measurements of the electrode area of 1 cm 2 , the potential oscillations and values were found to be associated with the growth of many metastable pits rather than the initiation and repassivation of each metastable pit. The amplitude of the OCP oscillation decreased with time and disappeared. Then, the OCP decreased slowly and became constant. The transition from metastable to stable pitting was determined to occur gradually.