Electrochemical Degradability of Al-20% Mg and Al-22% Si Alloys in an Acidic Environment in Relation with their Microstructure

The electrochemical degradability of Al-20% Mg and hypereutectic Al-22% Si industrial alloys was evaluated in an aggressive acidic environment, namely 1 M H2SO4, using potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) techniques. The microstructure and constituting phases of the surface alloys were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), coupled with Energy Dispersive X-ray Spectroscopy (EDX). It was found that the two alloys’ corrosion behavior mainly depends on their crystalline phases. The presence of the active intermetallic βAl3Mg2 phase in the Al alloy with high Mg content induced a preferential Mg dissolution, which caused a severe intergranular attack on this alloy by the corrosive solution. Meanwhile, the Al alloy containing high Si content, which presented the eutectic Al-Si phase, showed a uniform and weaker dissolution. It was also observed that a rise in temperature reduced the corrosion performance of the two studied alloys, as these corroded faster than pure aluminum.