Electrochemical behavior of Al 356 metallic foams in choride media

Aluminium metallic foams are part of a new family of materials called cellular metals CM, which have a porous structure that give them an excellent combination of physical, chemical and mechanical properties. In our work we used the 356 Al alloy for the manufacture of metallic foams from NaCl Soluble Preform Infiltration method. Despite the potential application of these foams, their performance may be affected by corrosion caused by salt remnant that could be inside of the foams due to poor washing practices. To study the electrochemical behavior of the 356 Al alloy in NaCl, polarization curves and electrochemical impedance spectroscopy were performed in rotating disk electrode RDE, and in porous rotating disk electrode PRDE made from aluminium foams. The results showed that cathodic reaction of oxygen reduction is the crucial stage of the process of dissolution of the material for both electrodes. In the corrosion process there is also an effect of oxygen transport, which limits the overall process of corrosion of the material. In addition it was found that due to the large surface area of the foams, the cathodic limiting current is much greater than for a solid electrode, thereby obtaining a dissimilar behavior to that described by Levich. The behavior of the porous electrode was quite similar to that found by Bomi Nam and coworkers in their work, where the limiting current reaches a highest value at very high electrode rotation speed. Nyquist plots were performed at -20 mV vs OCP to avoid the scatter in the curves that is typical in curves obtain at OCP values. The pitting potential of the aluminium at these conditions coincides with the corrosion potential, making impossible the system to get stable.