Cavitation Corrosion of Cast Al-Alloy in an Ethylene Glycol-Water Solution

Abstract

As a heat media, an ethylene glycol-water solution is widely used as a key component in a cooling liquid for the cooling systems of motors and electric equipment or devices. Therefore, cast Al alloy pumps are often used to circulate the ethylene glycol-water solution in the cooling systems. Thus, cast Al alloy are often subjected to cavitation corrosion. In this study, the cavitation behaviors of cast Al alloy in an ethylene glycol-water solution were studied using the ultrasonic cavitation corrosion apparatus which was made in accordance with ASTM G32. Then, the electrochemical kinetic of cavitation corrosion and the chemical structures of the corroded surface were investigated with EIS in conjunction with XPS analysis. The results showed that the synergistic effect between electrochemical corrosion and cavitation resulted in the increment of the cumulative weight loss of cast Al-alloy in an ethylene glycol-water solution with cavitation time. The calculation of the impacting efficient for cathodic and anodic processes demonstrated that the cavitation corrosion of cast Al-alloy was controlled by anodic process. In this case, the polarization resistance increased with cavitation time. In a stagnant ethylene glycol-water solution, EIS spectra of cast Al-alloy consisted of a deformed capacitance loop, but it had two time constants based on the Bode plot. Under cavitation, its EIS spectra consisted of a capacitance loop at high frequency zone and an inductive loop at a low frequency zone. It was indicated that the cavitation corrosion mechanism of cast Al alloy in an ethylene glycol-water solution under cavitation was changed obviously. Under cavitation, corroded morphology became rougher with cavitation time and many of pits and cracks existed after cavitation. At the same time, the volume of Al and Si compounds decreased, and that Si compound decreased much more compared with Al(OH)3. At the same time, the volume of OH- increased with cavitation time. This was shown that cavitation accelerated Si compound to peel off from the substrate, resulting in the changes of both the morphology and the chemical structures of surface film under cavitation. Finally, the cavitation corrosion model was proposed based on the above studies.