Abstract

MURTHY, H. C. Ananda; SANAULLA, P. F.  and  RAJU, V. Bheema. Influence of Chlorides, Nitrate and Sulphate Media on Corrosion Behaviour of TiO₂ Particulate Reinforced Al-6061 Composites. Port. Electrochim. Acta [online]. 2010, vol.28, n.5, pp.309-320. ISSN 0872-1904.

The corrosion behaviour of Al 6061-TiO₂ particulate composites in chloride, nitrate, sulphate and acidic media has been studied in the present investigation. The unreinforced matrix, and the composites containing 2, 4  and 6 weight percent of TiO₂ particulates were prepared by liquid metallurgy route using the vortex technique. Their corrosion behaviour was evaluated by weight loss, potentiodynamic polarisation, scanning electron micrograpaph (SEM) and energy dispersive X-ray analysis (EDXA) methods. The studies show that corrosion current density (I_Corr) and the corrosion rate were highest in the case of corrodent 0.1 N HCl. The rate of corrosion of both the matrix alloy and the composites decreased with increase in time of exposure in acid medium, possibly due to the formation of a passive oxide layer. Corrosion current (I_Corr), corrosion potential (E_Corr) and pitting potential (E_Pit) were obtained from potentiodynamic polarisation studies. In all the media, the I_Corr values of unreinforced matrix alloy and composites were found to increase as the TiO₂ content increased from 0% to 6%, which could be attributed to the microgalvanic coupling between the reinforcement or conducting interfacial products and the matrix alloy. Insulator TiO₂ particulates are perceived to act as inert material and degrade the integrity of the protective oxide layer on the Al matrix alloy. The presence of reinforcement in the matrix increases cathode to anode ratio in the composites, resulting in the formation of pits during localised corrosion. Moreover, the pitting effect was more pronounced in the presence of aggressive Cl^- ions compared to mild NO₃^- and SO₄^2- ions. SEM and EDX analysis of samples in chloride media showed the presence of large pits and completely deteriorated surface, complementing weight loss and polarisation studies.

Keywords : Al6061 MMCs; TiO₂ particulates; SEM; EDXS; interfacial products.

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