Electrochemical characterization and CFD simulation of erosion-corrosion of aluminum alloy in automotive coolant

Aluminum (Al) alloys have been commonly used in a variety of industry fields, including automotive industry. To date, Al alloys, most notably the 3000 series materials, have been broadly integrated into vehicular heat exchange systems, replacing more traditional materials like steels and copper alloys. However, Al is prone to corrosion, erosion and erosion-corrosion (E-C) in the automotive cooling system. A thorough investigation of E-C of Al materials is critically important in order to increase flow rates in heat exchange systems to realize higher performance by encroaching on E-C limits of the materials and also expanding the Al alloys to other applications and product design configurations.;Fluid hydrodynamics play an important role in Al E-C. The effect of fluid impact angle on Al E-C depends on the competitive combination of normal stress and shear stress caused by mechanical effect from fluid and sands. Furthermore, microelectrode technique was used to study the distribution of fluid flow field on the surface of Al specimen and its effect on Al E-C. It showed that, with the increase of the distance of microelectrodes from the center of the specimen, both the intensity of flow field and the shear stress on microelectrode increases, resulting in an enhanced corrosion rate of the electrode.;In this research, weight-loss and electrochemical corrosion measurements, surface characterization and computational fluid dynamics (CFD) simulation were combined to study erosion-corrosion (E-C) of 3003 Al alloy in ethylene glycol--water solution under conditions that were relevant to the automotive cooling system through a home-developed impingement jet system. The results demonstrated that Al alloy exhibited obvious E-C in the simulated automotive coolant solutions. Al E-C is dominated by erosion components, i.e., pure erosion and corrosion-enhanced erosion, which account for 92%--97% of the total E-C rate. Contribution from corrosion components, including pure corrosion and erosion-enhanced corrosion, is slight. With the increase of fluid flow velocity and sand concentration, the total E-C rate increases, which is attributed to the enhanced electrode activation upon fluid impingement. In particular, passivity of Al that develops in static solution cannot be maintained under fluid flow, where an activation mechanism dominates the corrosion process of Al. An increase of solution pH enhances the activity of Al due to dissolution of Al oxide film in alkaline environment.