The microbiologically induced corrosion (MIC) behavior of open-cell aluminum foams (UNS A96101) was evaluated in sodium chloride solutions. Cast and heat treated UNS A96101 foams of relative densities in the 6–8% range and pore densities of 10, 20, and 40 pores per inch (PPI) were subjected to immersion tests under three different conditions. In one set of tests, coupons were subjected to immersion in simulated seawater (3.5 wt.% NaCl) under laboratory conditions in accordance with the ASTM G31-12a standard. Another set of experiments was performed by immersing foam test coupons in natural seawater off Terminal Island, Long Beach, California, for 7 and 14 days. An additional series of tests was conducted by immersing coupons in natural seawater aged in the laboratory. The surface of the foam coupons following each of the immersion tests was cleaned using an acid cleaning procedure that was developed expressly for quantifying foam corrosion. The microstructure and surface morphology were then characterized using scanning electron microscopy, coupled with energy dispersive spectroscopy. Microbial analysis of the natural seawater was also conducted.
Microbiologically induced corrosion (MIC), or biocorrosion, is an electrochemical process in which microorganisms contribute to the initiation, facilitation, or acceleration of corrosion.1 This form of corrosion is a prevalent issue in the marine industry due to the presence of microbes, and is an integral environmental factor for the evaluation of emerging metallic alloys used for near-coast applications.2
One of these emerging metallic alloys is open-cell aluminum foam. Open-cell aluminum foam exhibits a lightweight and porous structure as well as tailorable physical and mechanical properties due to their unique cell geometry.3 Commercially available 6000-series open-cell aluminum foams serve as a versatile solution to a variety of aerospace and marine needs. The most common fabrication method for this material is through an investment casting process, in which molten alloy is poured into a foam-shape mold imbedded in a compact pool of ceramic powders.4 As a consequence of investment casting, it has been observed that these foam materials have Al–Fe–Si intermetallics on the surface, subsequently leading to matrix-intermetallic interfacial attacks confirmed in localized corrosion studies.5,6 Recent studies on the corrosion behavior of open-cell aluminum 6101 foams have shown that their bulk counterparts exhibit lower mass loss in simulated seawater environments.7 Given the growing commercial expansion of aluminum foam, it is crucial to extend investigations of its corrosion behavior in more realistic marine environments, particularly taking into consideration the influence of MIC.
