Corrosion behaviour of the Al-2.1–Mg-1.8–Si alloy in chloride solution

Abstract

The corrosion behaviours of Al–Mg–Si alloys were studied in different $\hbox {Cl}^{-}$ concentrations by means of scanning electron microscopy, transmission electron microscopy and electrochemical experiments. The results show that the corrosion behaviours of Al–Mg–Si alloys are closely related to the $\hbox {Cl}^{-}$ concentration. With an increase in $\hbox {Cl}^{-}$ concentration, the corrosion rate increases sharply by facilitating the process of chemical and electrochemical reactions. In 2.0 wt.% NaCl solution, slight pitting corrosion occurred around the MgSi phase, but corrosion trenching was not found around the Fe–Mn–Si phase. In 3.5 wt.% NaCl solution, the alloy appeared localized corrosion dominated by intergranular corrosion attack. In 5.0 wt.% NaCl solution, the alloy presented serious overall corrosion, and the passivation platform of the polarization was not obvious. Furthermore, an appropriate corrosion mechanism according to polarization and electrochemical impedance spectroscopy was proposed for the Al–Mg–Si alloy in NaCl solution. In addition, the corrosion rate influenced by different $\hbox {Cl}^{-}$ concentrations was discussed in detail.