Evolution of corrosion in cast Al alloy in antifreeze radiator coolant

Corrosion is an important issue for cast Al alloy in an engine cooling system, but how the microstructural features affect the coolant-related corrosion behaviour is not well understood. In this research, the evolution of corrosion in an ISO 2379 cast Al alloy was studied in an antifreeze radiator coolant under heat-rejecting conditions. Extensive analyses of microstructures and corroded surfaces were carried out using an optical microscope, scanning electron microscope equipped with energy dispersive spectroscopy and X-ray diffractometer. Intergranular cavitation corrosion was observed to occur at interfaces between α-Al matrix and intermetallics (Al 2 Cu and Al 5 FeSi) or to a less degree at interfaces between α-Al matrix and Si phase. The large area fraction of the cathodic phases (Al 2 Cu, Al 5 FeSi and Si) led to the galvanic coupling between them and the adjacent anodic α-Al matrix. The heat-rejecting condition in antifreeze radiator coolant was favourable condition to cavitation process while severe crevice corrosion was predominant at oxygen-depleted regions in the heat-transfer corrosion cell.