ORIGINAL PAPER Characterization of passivity and pitting corrosion of 3003 aluminum alloy in ethylene glycol–water solutions Y. Liu • Y. F. Cheng Received: 5 February 2010 / Accepted: 18 September 2010 / Published online: 22 September 2010 Ó Springer Science+Business Media B.V. 2010 Abstract In this work, the passivity and pitting corro- sion behavior of 3003 aluminum (Al) alloy in ethylene glycol–water solutions was investigated using various electrochemical measurements, Mott–Schottky analysis and surface analysis techniques. Results demonstrate that the passive film formed on Al alloy contains both Al oxide and Al alcohol, showing an n-type semiconductor in nature. There is an enhanced corrosion resistance of the Al-alcohol film, which is resistant to adsorption of chloride ions. The pitting corrosion of 3003 Al alloy occurs in the solutions containing a low concentration of ethylene glycol only, where the formed film is dominated by Al oxide. Chloride ions attack and replace the oxygen vacancies in the film, resulting in a local detachment of the film from the Al alloy. A galvanic effect exists between Al alloy sub- strate and the adjacent second phase particles. Pits form when Al alloy substrate is dissolved away and the second phase particles drop off from the substrate. Keywords Passivity  Pitting corrosion  Aluminum alloy  Ethylene glycol 1 Introduction Aluminum (Al) alloys, due to their favorable strength- to-weight property, high thermal conductivity, and excel- lent formability, have been widely used in automobile heat exchange system, replacing traditional materials like stainless steels and copper alloys [1, 2]. However, Al alloys are prone to experience corrosion and pitting corrosion in automotive cooling system, which generally contains eth- ylene glycol as anti-freezer [3–5]. It has been acknowledged [6–9] that the corrosion resistance of Al alloys depends on the formation of a layer of passive film on their surface in the environments. A significant number of works have been performed to characterize the passive films formed under various con- ditions [10–18]. For example, Bockris and coworkers [10, 11] found a two-layer structure of passive film formed on Al alloy in sodium borate solution. While the outer layer is a mixture of Al 2 O 3 and Al(OH) 3 , the inner layer is composed of Al 2 O 3 and AlOOH. Furthermore, the structure of the passive film on Al alloy is dependent on the forming solution. It was found [6] that passive film formed in a borate and tartaric acid solution is thin, dense, and coher- ent, whereas that formed in sulfuric and phosphoric acids shows a thick, porous, and crystalline layer. With respects to the semiconducting property of the passive film formed on Al alloys, there have existed controversial results. Fer- nandes et al. [12] reported that the passive film formed on 2024 Al alloy in a sulphuric–boric bath shows an n-type semiconducting behavior, while Levine et al. [13] deter- mined that the passive film on 2024 Al alloy is a p-type semiconductor. Liu et al. [19] demonstrated that passive films formed on 3003 Al alloy in air and in Na 2 SO 4 solu- tions in the absence and presence of chloride ions show an n-type semiconductor in nature. To date, research in passivity and corrosion of Al alloy in automotive coolant, i.e., ethylene glycol–water solu- tions, has been in its infancy. Cheng’s group [20–25] studied systematically the flow-assisted corrosion and erosion-corrosion of 3003 Al alloy in aqueous ethylene glycol solutions. It was proposed that the passive film formed on the Al alloy contains primarily Al-alcohol film, Y. Liu  Y. F. Cheng (&) Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada e-mail: fcheng@ucalgary.ca 123 J Appl Electrochem (2011) 41:151–159 DOI 10.1007/s10800-010-0215-6