Electrochemical Impedance Spectroscopy and Potentiodynamic Polarization Studies Affected by the Microstructure Array of a Monotectic Al-Pb Alloy in a NaCl Solution

In this study, electrochemical impedance spectroscopy (EIS) plots and potentiodynamic polarization curves of tests carried out with monotectic Al-Pb alloy samples in a 0.5 Molar sodium chloride (NaCl) solution at 25°C are evaluated. It is shown that for a microstructure characterized by immiscible Pb droplets disseminated into an Al matrix, the microstructural array and segregation pattern are the corrosion driving forces. Microstructures characterized by Pb droplets of higher diameter and more homogeneously distributed into the Al-matrix, typical of positions close to the casting surface, have lower corrosion resistance. This has been attributed to a higher anode/cathode area that characterizes such microstructures and that, as a consequence, induces a higher number of galvanic couples that are formed between the Pb droplets and the Al matrix.