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The corrosion behaviour of commercially used aluminium engine block and piston were investigated in 0.1M NaCl solution at room temperatures. The study was done by electrochemical method, using Tafel polarization and electrochemical impedance spectroscopy (EIS) techniques. The surface was characterized by optical microscope and scanning electron microscope (SEM). The results indicated differences in the charge transfer resistance of engine block and piston alloys. The current density (Icorr) of engine block material showed higher value than that of piston material. The corrosion potential (Ecorr) and pitting corrosion potential (Epit) of piston material were shifted to the more noble direction. In aluminium piston alloy there seems to be uniform surface pits formations which are in fewer amounts as compared to those in engine block alloy. The corrosion performance of aluminium piston alloy was found to be higher than that of aluminium engine block due to the presence of Ni and lower percentage of Fe in aluminium piston alloy.

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In the present work, the corrosion behavior of aluminium alloy engine block in 3.5% NaCl solution was studied. The work was carried out using conventional gravimetric measurements and complemented by scanning electron microscopy (SEM) and X-ray analyzer (EDX) investigations. The results obtained indicate that the main process the alloy undergoes, under the medium of exposure studied, is related to localized corrosion that takes place as a consequence of the process of alkalinization around the cathodic precipitates existing in the alloy. The alloy suffers a process of corrosion localized to the area surrounding the precipitates of the Al (Si, Mg) and Al-Mg, which resulted in hemispherical pits. This identification was confirmed by SEM and EDX analysis. No evidence was found of the formation of crystallographic pitting for exposure times up to 54 days. Gravimetric analysis confirmed that with varying exposure periods the weight loss of the alloy increases and the corrosion rate decreases with time.

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