Electron microscopy investigation of AlMg6 aluminum alloy surface defects caused by microorganisms extracted in space stations

摘要

The surfaces of AMg6 (aluminum-magnesium) alloy samples that have passed accelerated biocorrosion tests have been investigated in a Quanta-3D scanning electron microscope. The alloy samples have been treated with the Ulocladium botrytis Preuss fungus, which is an active destructive fungus and was previously extracted on surfaces of the International Space Station. Biocorrosion pits 2-10 μm in diameter, cavities the depths of which can reach 70-250 μm depth, and spots of modified color are found to be the most typical defects. The surfaces of large cavities consist of faceted cubic particles that are formed when the acid products of fungus metabolism interact with the alloy surface. The particles have an average size of 30 μm, which is close to the size of alloy grains. The microstructure of a biocorrosion layer has been investigated in a Quanta-3D microscope with the use of a focused Ga~+ ion beam. The samples of 12-μm-wide transverse slices are obtained near large cavities and investigated in a Tecnai G_(23)0ST transmission electron microscope. The X-ray microanalysis of the defective layer has revealed the high concentration of oxygen in this layer. Obtained images indicate that the corrosion cavity surface has a complex porous structure.