Corrosion evolution and behaviour of Al–2.1Mg–1.6Si alloy in chloride media

Owing to the importance of finding better methods and technologies for protecting against corrosion of aluminium alloys, research into the electrochemical characteristics of the corrosion is an ongoing concern. In this paper, the corrosion behaviour of Al–Mg–Si alloys in 3.5 wt% NaCl solution was investigated using multiple methods, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), potentiodynamic polarisation measurement and electrochemical impedance spectroscopy (EIS). The results suggest that corrosion begins with dealloying of Mg, followed by conversion of MgSi particles into Al–Fe–Mn–Si particles. The corrosion rate increased until it reached a peak and then decreased. The increase in the corrosion rate may be attributed to an increased electrochemical driving force, which is produced by anodic dissolution between the matrix and residual MgSi particles. Additionally, the thin re-deposited layer of inert elements also plays an important role in accelerating the anodic process of the corrosion pit. The passivated corrosion pit and narrowed intergranular corrosion (IGC) pathway cause the area of active dissolution to decrease, thus reducing the corrosion rate.