Electrochemical corrosion performance of eutectic Al-Si automotive alloy in 0.1 M and 0.2 M NaCl solution

Abstract

Corrosion behavior of eutectic Al-Si automotive alloy is investigated in different strengths of 0.1 M and 0.2 M NaCl solution at room temperature. Alloy with Si as trace impurity is also considered for the comparison of the property. The study is done by electrochemical method, using potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) techniques. The alloy surfaces are characterized by both optical microscopy and scanning electron microscopy. The results indicate that Si addition improves the corrosion performance of the Al-Si automotive alloy and this improvement is more pronounced in higher corrosive environments. The corrosion rate along with current density (Icorr) of trace Si added alloy showed higher value than that of higher Si added alloy. The corrosion potential (Ecorr) and open circuit potential (OCP) of higher Si added alloy are shifted to the more noble direction. The cause behind this, the higher amount of Mg2Si precipitates in higher Si added alloys tends to form oxides like SiO2 and MgO which protects the surfaces from further corrosion. Microscopic images confirm that the polishing scratches on the surfaces of the alloys are not visible after corrosion. The SEM images also confirm that the corroded surfaces seem to have pit formations which are lower in higher Si added alloys due to formation of a protective layer of oxides. The higher corrosion performance is observed for higher Si added alloys especially in higher strength of corrosive environment.