Al-Si hypoeutectic alloys produced by casting are mostly used in the automotive industry, especially for engine blocks. They have the advantage of low weight associated with low coefficient of thermal expansion and excellent mechanical properties. The corrosion resistance of these alloys in coastal area, particularly in seawater environment is not well known. In this investigation, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation have been used to evaluate the corrosion resistance of Cu free and 0.5wt% Cu content Al-6Si-0.5Mg alloy in simulated seawater environment. The 0.5wt% Cu addition to the Al-6Si-0.5Mg alloy showed that Cu decreased susceptibility to electrochemical corrosion compared to the Cu free Al-6Si-0.5Mg alloy. The magnitude of open circuit potential (OCP), corrosion potential (Ecorr) and pitting corrosion potential (Epit) of Al-6Si-0.5Mg alloy in simulated seawater were shifted to the more noble direction due to 0.5wt% Cu addition and thermal modification.
The purpose of this paper is to understand the effect of 2Cu+2Ni addition on electrochemical corrosion behavior of thermal treated Al-6Si-0.5Mg alloy in 0.1M NaCl solution. The corrosion of the thermal treated samples was characterized by electrochemical potentiodynamic polarization technique consisting of linear polarization method using the fit Tafel plot and electrochemical impedance spectroscopy (EIS) techniques. Generally, from the linear polarization, the corrosion rate decreases at thermal treated Al-6Si-0.5Mg-2Cu-2Ni alloy (Alloy-2). The corrosion behavior of the Alloy-2 in the 0.1M NaCl solution showed better resistance than the Alloy-1. The EIS test results also showed that the changing of charge transfer resistance (Rct) is significant with the combined addition of 2Cu+2Ni to Al-6Si-0.5Mg alloy. The magnitude of the noble shift in the open circuit potential (OCP), corrosion potential (Ecorr) and pitting corrosion potential (Epit) increased with the addition of 2Cu+2Ni to Al-6Si-0.5Mg alloy.