EIS and potentiodynamic polarization studies on immiscible monotectic Al-In alloys

The electrochemical behavior of monotectic Al-In alloys is experimentally investigated. Electrochemical impedance spectroscopy (EIS), potentiodynamic anodic polarization techniques and an equivalent circuit analysis were used to evaluate the corrosion response in a stagnant and naturally aerated 0.5 M NaCl solution at 25 degrees C. It was found that a better galvanic protection can be provided for microstructures having indium droplets of larger diameters and larger interphase spacings. From five samples extracted along the length of a directionally solidified Al-In casting, that having smallest interphase spacing (lambda = 18 pm) and droplet diameter (d = 0.7 mu m) had its corrosion resistance significantly decreased (about 2 and 3 times in terms of the current density and polarization resistance) when compared with that of the sample having the coarsest microstructure (lambda = 60 mu m and d = 2.5 mu m). Such behavior is attributed to both localized strains between aluminum and indium boundaries and the corrosion potential of the indium particles. (C) 2013 Elsevier Ltd. All rights reserved.