New Insights About the Role of Sn‐Rich and Pb‐Rich Phases Over the Corrosion Mechanism of Low‐Tin Quaternary Bronze Alloys Under Sulfur‐Containing Conditions

The early corrosion process of a quaternary bronze alloy was studied using electrochemical polarization and chronoamperometry. The morphology and composition of the formed corrosion layers were characterized by Raman spectroscopy and SEM/EDS images. The results showed preferential corrosion of Pb‐rich and Sn‐rich phases. In Pb‐rich zones the corrosion process leads to the formation of mixed Pb and Cu sulfate compounds. Meanwhile Sn‐rich interdendritic regions corrode in Type I patina formation, leading to local decuprification and formation of a protective Sn oxide layer. SEM/EDS maps of corroded samples indicate that this process is driven by galvanic coupling between the Sn‐rich interdendritic phases and the Cu‐rich dendrite core, resulting in anodic zones within the interdendritic regions and cathodic activity at the dendrite core.