Influence of microbial activity on Aluminium Alloys in marine medium: natural vs artificial seawater

摘要

Corrosion in marine environments plays a key role in the viability of marine project, constituting a serious challenge for industrial initiative. The aggressiveness of seawater, due to the inorganic and, with more emphasis, organic compounds, has a crucial effect on the life-cycle of offshore structures. In this context, microbial activity is an important issue to take into account when dealing with metallic structures exposed to seawater. Thanks to remarkable properties like low weight, easy workability and recyclability, aluminium is currently the second most used metal in the world1. More specifically, the aluminium-magnesium alloy of the 5XXX series is commonly used in shipbuilding industry. A previous Joint Industry Project on corrosion protection for Al built ships , involving a 2-year natural exposure of AA5083 in splash and immersion zones, showed different corrosion behaviour between samples depending on the exposure zones and the biofouling presence. The results suggest that biochemical and microbial effects influenced the corrosion/protection process. The objective of the present study is to assess the influence of microbial activity on AA5O83 behaviour at the first stage of marine exposure. The experimental work included one-month immersion tests carried out in natural seawater (Genoa marine station) and in abiotic conditions (artificial seawater according ASTM Dl 141-90 standard). The open circuit potentials were measured all along the immersion duration. Surface and cross-section of samples were evaluated using scanning electron microscopy with energy dispersive spectroscopy. The results are discussed in terms of surface/interface evolution and corrosion mechanisms in presence or absence of microorganisms in the medium. European Aluminium, "Aluminium Innovation Hub", May 2016 M. J. F. Marques et al, in proceedings of Eurocorr, Estoril, Portugal, 1-5 Sept. (2013)