Influence of Electron Mediator on Microbiologically Influenced Corrosion Behavior of 2024 Aluminum Alloy

In microbiologically influenced corrosion (MIC) caused by sulfate-reducing bacteria (SRB), extracellular electron transfer (EET) between metals and microorganisms affects the metal corrosion process. In this work, the effect of the electron mediator riboflavin on the EET-MIC behavior of 2024 aluminum alloy (AA2024) was investigated by electrochemical methods, surface analysis techniques, focused ion beam, scanning electron microscopy, and x-ray photoelectron spectroscopy techniques. The results showed that the electron mediator was significantly able to accelerate SRB attack against AA2024. SRB utilized to consume H⁺ to accelerate its own metabolism and promoted the corrosion of AA2024, resulting in the formation of corrosion product AlOOH and Al(OH)₃. The addition of electron mediator riboflavin increased the electron transfer efficiency and affected the reaction rate constant to accelerate the corrosion rate of aluminum alloy. The addition of 10 ppm riboflavin led to denser corrosion product biofilms on the surface of the aluminum alloy, which accelerated the formation of NaAlO₂. Cl⁻ diffused into the film layer through the pores of the surface of the aluminum alloy and was adsorbed into the film layer to induce pitting corrosion on the surface of the aluminum alloy. A large amount of SRB was attached, which resulted in an increasing pit depth on the surface of the aluminum alloy. Riboflavin accelerated the electron transfer process from the surface of the aluminum alloy across the cell wall to the cytoplasm, which led to serious corrosion of the aluminum alloy. The distribution of SRB in biofilm and the longitudinal distribution of bacteria in the process of pitting corrosion showed that the addition of electron mediators increased the depth of pits in aluminum alloys. Bacteria in the pitting area gathered at the bottom of the biofilm, and the pits were rich in Ca, P, and other elements.