Distinctive localized corrosion behavior of β-Mg2Si and α-Al(Fe,Mn)Si phases in a 6082 alloy

Abstract

6xxx series (Al–Mg–Si) alloys are generally known to be greatly susceptible to localized corrosion, which is closely related to the presence of coarse intermetallic compounds (IMCs). In this work, the localized corrosion behaviour of two representative IMCs, namely β-Mg2Si and α-Al(Fe,Mn)Si, were investigated in a 6082 alloy (Al–Mg–Si–Mn-based). For the β-Mg2Si phase, a rapid de-alloying process is primarily observed. Subsequently, their surface will transform to the electric insulating SiO2 layer, which tends to suppress the further corrosion in its periphery. However, it is found that the α-Al(Fe,Mn)Si phase surprisingly tends to be a potentially effective cathode to promote the initiation of stable localized corrosion, which is contrast with its outstanding corrosion-resistance. Careful examinations reveal that such abnormal corrosion behaviour of α-Al(Fe,Mn)Si is most likely to be relevant to the surface aggregation of Cu impurities, which is clarified by a large number of Cu-rich nanoparticles on its surfaces.

Keywords

• Al-Mg-Si alloy
• Localized corrosion
• Intermetallic compounds
• De-alloying