Corrosion behaviour of AA1050 aluminium alloy in bioethanol blended gasoline environment

This work originates from a case study, where a fuel tank made of an Al-alloy (AA1050) exhibited significant corrosion phenomena when exposed to E27 biofuel (green gasoline with 27 % v/v bioethanol. The focus is on understanding corrosion mechanisms and operational parameters. Biofuel characterization using Fourier Transform Infrared Spectroscopy and Gas Chromatography-Mass Spectrometry, allowed to detect the presence of alcoholates, acetic acid, and water, which affect the alloy passivating layer. Samples were subjected to Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy, both pre- and post-corrosion, while the presence of surface oxides was evaluated through X-Ray Diffraction. Electrochemical analysis was employed to explore the corrosion phenomena under controlled laboratory conditions. Corrosion resistance improved with increasing concentrations of dissolved oxygen in the fuel, primarily due to the formation and stability of surface (hydro)oxide layer. Moreover, water contributed positively by facilitating the formation of a protective hydrous oxide layer on the aluminum alloy, whereas acetic acid had a detrimental effect, compromising both the oxide film and the alloy matrix. Immersion tests conducted in the absence of oxygen highlighted a different mechanism: without oxygen, soluble alkoxides formed with continuous attack of the alloy's surface. In this oxygen-deprived environment, the resulting corrosion products differed significantly, with no acetic acid formation observed. The generation of these products was closely tied to the test temperature. An immersion test conducted at 60 °C confirmed that, at temperatures below 80 °C, no signs of corrosion were detected. This research elucidated corrosion mechanisms and proposed mitigation strategies, to enhance the sustainability and reliability of biofuel applications within the automotive industry.