The Influence of Roughness on the Protective Layer Formation Induced by Marine Microorganisms on 5083 Aluminum Alloy

This study investigates the formation of a protective layer on a 5083 aluminum alloy surface induced by microorganisms from salt marsh. The influence of the initial surface roughness was examined to identify optimal conditions for maximum coverage and thickness of the protective layer. As two opposing effects are suspected, where high surface roughness enhances bacterial adhesion but reduces the resistance to abiotic corrosion, various degrees of roughness were tested. Using electrochemical experiments (OCP measurement, 1/Rp determination, and pitting sensitivity), SEM/TEM observation and EDX characterization, a compromise was found on the initial roughness to obtain a thick protective layer through good bacterial adhesion while minimizing abiotic corrosion. The optimal roughness, achieved through 240-grit grinding, facilitates a uniform distribution of microorganisms and the development of a dense, evenly thick protective layer that significantly enhances the alloy's resistance to pitting corrosion. The passivity domain doubled when comparing the electrochemical behavior of electrodes immersed in the presence of microbial activity to those immersed without it.