Corrosion behavior of EN AC-AlSi10Mg in boiling coolant with various average flow temperatures

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 CO2 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 increasing engine temperature, 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 impact of increased coolant temperatures, along with stable and unstable boiling and changing flow conditions are discussed. The experimental results have been obtained with silicium, organic acid, and silicium/organic acid-based coolants in a special test device, mimicking the temperature and flow conditions in cooling cycles next to engine walls. An evaluation of the results is given on the basis of surface conditions (investigated by REM/EDX analyses and cross-sections), temperature gradients, and mass loss of the used specimens. Furthermore, the evaluation is also based on electrochemical measurements of the open circuit potential, which was recorded in the coolant flow. The obtained results provide information on damage relevant parameters and their interaction with coolant inducing corrosion on hot aluminum surfaces. In particular, the influence of boiling processes with complete coolant evaporation, as they can appear in common start-stop systems today, are investigated.