The Effect of <i>Ralstonia pickettii</i> on Environmental Fatigue Crack Growth of 7xxx Series Aluminum Alloys

Abstract

As more industries and nations focus on environmental protection, the desire to develop non-toxic, sustainable coatings to protect against corrosion becomes a primary focus. One of the areas on the cutting edge of new coating development is the use of bacteria in corrosion prevention coatings. For many years the focus in the corrosion community was on microbial influenced corrosion with the assumption that all bacteria had negative consequences for corrosion and corrosion fatigue. More recently it has been documented that a variety of bacteria can protect against general surface corrosion. None of the work to date on bacteria preventing general corrosion has shown that the inhibitive effects could also be applied to corrosion fatigue. Researchers at the United States Air Force Academy discovered that a bacteria, Ralstonia pickettii, is capable of reducing the fatigue crack growth rate of AA7075-T651 and AA7475-T7351 in 0.06M NaCl to near that of chromate. In cycles to failure testing in 0.06M NaCl the sample life was extended approximately 5 to 6 times depending on the fatigue loading variables compared to samples in 0.06M NaCl without the bacteria. The mechanism behind the corrosion fatigue protection is being investigated in hopes that it could lead to the development of new coatings to reduce corrosion fatigue. The current theories behind how the bacteria slows corrosion fatigue crack propagation are (1) presence of a biofilm, (2) metal sequestration and replating on the crack surface, (3) desalination of the test solution, and (4) oxide layer development and repair.