Abstract:The role of Mg 2 Si in the electrochemical behavior of Al-Si-Mg aluminum alloys has been studied using four experimental aluminum alloys with variations in the Si/Mg molar ratio (A1-0.12, A2-0.49, A3-0.89, A4-1.05), in neutral aerated 0.1M NaCl solutions. Accordingly, the corrosion potential in open circuit (E oc ) and polarization resistance (Rp) were measured. Results show that the augment in Si/Mg molar ratio increases the presence of Mg 2 Si intermetallic phase. During immersion tests in neutral aerated chloride solutions the anodic activity of the Mg 2 Si intermetallic decreased rapidly, as indicated by a fast ennoblement of open circuit potential. After the immersion period (7 days), higher Rp values for alloys A3 and A4 (21 and 26 K cm 2 , respectively) as compared to those for alloys A1 and A2 (5 and 10 K cm 2 , respectively), suggest a greater corrosion resistance in Cl -containing environments for alloys A3 and A4.

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Cyclic polarization measurements were carried out for Al-10%Si- X%Mg (X: 3%, 6% and 9.5%) alloys in borate solutions with and without additions of 50 mM NaCl. The voltammetric response exhibited some features of oxide film growth consistent with the high field conduction model. However, higher currents and distortions in the voltammetric wave shape compared to those for pure Al were ascribed to a possible incorporation of alloying elements in the oxide film, rendering it more defective, and to the strong electrochemical activity of Mg2Si particles