The effect of small addition of tin and indium on the corrosion behavior of aluminium in chloride solution

The corrosion behavior of Al, Al–In, Al–Sn and Al–Sn–In alloys in 2 M NaCl solution has been studied by using potentiodynamic polarization, open circuit potential and impedance measurements as well as volumetric determination of evolved hydrogen. Polarization measurements indicated that the alloying elements considerably change the electrochemical behavior of aluminium. Changes are especially pronounced in the anodic branch of the polarization curve, and manifest in significant shift of the corrosion and the pitting potentials in the negative direction, reducing the passive potential region, and increasing the current output already at low anodic overpotentials. The open circuit corrosion process of tested samples was monitored through the period of 17 days. It was established that the dissolution of Al and its alloys is mainly accompanied by the cathodic reaction of hydrogen evolution, with In inhibits the cathodic reaction of hydrogen evolution, while Sn catalyzes the same one. The impedance measurement performed also during the 17 days of corrosion test, provided a continuous monitoring of the parameters, which characterize the properties of the surface and their changes as corrosion occurs. Different equivalent circuits were employed to account for the electrochemical processes taking place at different stages of corrosion.