The Effect of Strain Localization on Galvanic Corrosion Pitting in AA7050

Abstract

Corrosion is the primary failure mechanism for sea-based structures, as it plays an important role in material degradation and structural integrity. The localized corrosion behavior is affected by the micromechanics and the electrochemistry of the material; however, there are very limited studies where both mechanisms are studied jointly, let alone relative to microstructural attributes, i.e., at the mesoscale. High-resolution strain maps are created on pre-loaded AA7050 in the transverse-short orientation via digital image correlation to identify strain accumulation with respect to the microstructure. Afterward, this material is subjected to a galvanic corrosion environment. In order to investigate the driving force for localized corrosion, the microstructure, the cathodic particles, the localized strain, and the evolution of surface topology caused by corrosion pitting are spatially characterized in the region of interest. The evolution of the corroded surface is tracked every 24 h throughout the 20 d of corrosion that the material was immersed in 0.6 M NaCl solution. Specifically, three representative sized cathodic particles are monitored throughout the corrosion study, to identify their evolution of pitting before and after the particles fallout from contact with the matrix. Finally, the relationship between strain and localized galvanic corrosion is quantitatively investigated using Gaussian process modeling to identify the underlying correlations. The results show that localized strains within ±3σ of the macroscopic residual strain do not affect the corrosion rate of the material; however, extreme values beyond that threshold associated with the cracking of the particle itself seem to heavily promote the growth of localized galvanic corrosion.