Influence of superimposed mechanical loading on the susceptibility of aluminium alloys to alcohalte corrosion in alcohol blended biofuels

As a contribution to climate protection and to attenuate the dependency on fossil fuels alcohol blended biofuels gain in importance for the energy supply in Europe. Investigations on aluminium alloys exposed to bioethanol blended fuels have revealed two principal types of corrosion which are strongly dependent on the water content, aqueous corrosion and alcoholate corrosion and the interaction with the passive layer. The latter type of corrosion is dominantly found in dry ethanol blended fuels at higher temperatures. It has been shown that temperature is a dominant factor influencing the probability of the occurrence of alcoholate corrosion [1]. Aberrant from static corrosion testing in the laboratory automotive components in contact with fuel at higher temperature such as pistons and cylinder liners moreover experience cyclic mechanical loading. It is yet unknown whether a temperature threshold under which no alcoholate corrosion is found in static and tempered immersion is lowered by cyclic mechanical loading. For this reason corrosion fatigue testing was performed on round fatigue specimens of the aluminium alloys Al99,5 and AlSi9Cu3 in dry E85 bioethanol blended fuel (ASTM C + 85 % ethanol) at elevated temperature. Testing was conducted at threshold temperature levels statistically verified by immersion tests based on the staircase method. The results of these investigations are presented in the present paper