Corrosion behavior of 7A09 aluminum alloy exposed to propylene glycol coolant at different conditions

Abstract

Aluminum alloys possess high strength and hardness, making them widely utilized in cooling systems. However, prolonged use can result in corrosion failure. To address the corrosion failure of 7A09 aluminum alloy in propylene glycol coolant, this study systematically investigates the synergistic effects of temperature (50–80 ℃), pH value (4–9), and Cl^- concentration (30–90 mg/L) on the corrosion behavior of the aluminum alloy. A comprehensive approach was employed, integrating corrosion testing, electrochemical polarization curve measurements, surface morphology characterization via scanning electron microscopy, and surface composition analysis using X-ray photoelectron spectroscopy (XPS). The results showed that increasing temperature promotes the thermal oxidation of propylene glycol, resulting in the generation of organic acids and an exponential increase in the corrosion rate (I_corr reached 3040 nA cm⁻² at 80 ℃). Elevated Cl^- concentration significantly enhances the sensitivity of the passivation film pitting, with the corrosion current density rising by 24.3 times under 90 mg/L compared to the 30 mg/L conditions. A strongly acidic environment with pH= 4 induces acidic dissolution of the oxide film, whereas, under near-neutral conditions (pH=6–8), the aluminum passivation film synergizes with the Al₂O₃ oxide film to effectively reduce the corrosion rate. XPS analysis further confirmed that Cl^- attacks the C-O bond in propylene glycol molecules, leading to the formation of C-Cl compounds, which compromises the integrity of the protective film and accelerates localized pitting processes.