Stuttgart, March 1996
Just like other materials, metals are prone to attack from micro-organisms such as fungi, bacteria and algae, whose metabolic products can cause surface growth and corrosion. Daimler-Benz researchers are now investigating the processes governing microbial corrosion on aluminium alloy aircraft parts. Depending on the route, aircraft load and flight conditions, the micro-organisms are, "in the field", exposed to continuously varying conditions. As their reference conditions in the laboratory, the Daimler-Benz researchers therefore take the "worst-case scenario" as a basis for reaching conclusions of general validity.Corrosion specimens taken from different points on the metal contain chiefly bacteria, but also yeasts and fungi. In the course of categorising the individual micro-organisms and their contribution to the corrosion of aluminium alloys, the Daimler-Benz researchers have found that certain groups of micro-organism - bacteria that produce lactic acid, and a number of mould fungi - cause particularly high levels of corrosion damage. This knowledge helps them to develop more carefully targeted remedies against corrosion.
Aluminium surfaces exposed to air spontaneously develop a thin layer of oxide. This passivates the metal and protects it to a certain extent against external factors like corrosion. However, although the metal is then protected against mild acids and alkalis, bacteria can produce acids which are powerful enough to penetrate this protective layer and produce tiny surface holes, thus providing a foothold for further corrosion.
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© 1996 Daimler-Benz