Time-dependent corrosion and layer formation reactions of EN ACAlSi10Mg in coolants for combustion engines under various boiling conditions

摘要

Even with an increasing share in electrical vehicles, the combustion engine can be assumed to be the main drive technology in automobiles over the next 20 years. Increasing demands to the engine, such as the reduction of CO_2 emissions and minimization of fuel consumption while maintaining performance, require new concepts regarding the motor design. Known examples like "downsizing" and "thermal management" are already being developed. Even start-stop systems which reduce fuel consumption while waiting at traffic lights or in traffic jams are increasingly used. These measures often result in an increase in temperature in the engine, which has to be balanced by the coolant. The increased thermal loading, associated with local boiling processes result in still unknown effects in terms of the formation of corrosion protective layers and coolant long-term stability. At this point, the reaction between materials and the respective coolant is of particular importance. In this report, the time dependent development of corrosion and the formation of reaction or inhibition layers along with stable and unstable boiling with complete coolant evaporation and changing flow conditions, as they can appear in common start-stop systems today, are discussed. The presented results are based on experiments with specimens made of aluminium alloy EN AC-AlSi10Mg in silicate and organic based coolants. An evaluation of the results is given on basis of mass loss and SEM analysis. Furthermore, cross sections and 3D-Microscope analysis were employed to demonstrate the dependency of the used test cycle with its implemented heat, rest, and vapour phases to the corrosion- and layer-formation process. The evaluation is also based on in-situ electrochemical measurements (open circuit potential and impedance spectroscopy), which were recorded directly in the coolant flow. The obtained results provide information on damage relevant parameters and their interaction with coolant inducing corrosion on hot aluminium surfaces.