Localized alkaline corrosion of alloy AA5083 in neutral 3.5% NaCl solution

The corrosion process of the alloy AA5083 in an aerated solution of NaCl at 3.5% has been studied. The results obtained indicate that the main process that this alloy undergoes, under the conditions of exposure studied, is related to localized corrosion that takes place as a consequence of the process of alkalinization around the cathodic precipitates existing in the alloy. The pitting formed presents a hemispherical morphology that is clearly different from crystallographic pitting. The formation of crystallographic pitting has not been observed, even in samples submitted to tests of very long duration. In order to obtain the formation of crystallographic pitting, it is necessary to polarize the alloy at the nucleation potential of pitting and. in addition, the density of the current must be above a critical value. Only when the layer of oxide is eliminated does the formation of crystallographic pitting take place by simple exposure in an aerated solution of NaCl at 3.5%. (C) 2001 Elsevier Science Ltd. All rights reserved.