Microbiologically Influenced Corrosion of AA 6061 with Bacillus Species in an Environment Containing an Organic Nitrogen Source

Microbiologically influenced corrosion (MIC) is closely associated with the metabolism of microorganisms, and organic nitrogen sources (ONS) are some of the key nutrients for bacterial metabolism. However, the influence of the amount of ONS on MIC and the corresponding mechanisms involved are still elusive. In this study, the MIC behavior of aluminum alloy 6061 in aqueous media with different amounts of ONS was investigated. Microbial activity and metabolism, which influenced the environment, were analyzed by optical density, pH, and NH₄⁺ ion concentration. Pitting corrosion was analyzed by scanning electronic microscopy and electrochemical impedance spectroscopy. Bacillus aerius inhibited the development of pitting corrosion in aluminum alloy 6061 because of the NH₄⁺ and NH₃·H₂O in their metabolites, which provided a pH buffering effect that suppressed the autocatalysis alkalinization around intermetallic inclusions. The inhibitory effect was positively correlated with microbial activity. Therefore, a higher concentration of ONS contributed to the inhibition of pitting corrosion because ONS was beneficial to the propagation and proliferation of bacteria.