Abstract:The electrochemical behaviors and coupling behaviors of the Mg₂Si and Si phases with α(Al) were investigated, the corrosion morphologies of Al alloys containing Mg₂Si and Si particles were observed, and the corrosion mechanism associated with them in Al−Mg−Si alloys was advanced. The results show that Si particle is always cathodic to the alloy base, Mg₂Si is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Mg and the enrichment of Si make Mg₂Si transform to cathode from anode, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery at a later stage. As the mole ratio of Mg to Si in an Al−Mg−Si alloy is less than 1.73, it contains Mg₂Si and Si particles simultaneously in the grain boundary area, and corrosion initiates on the Mg₂Si surface and the precipitate-free zone (PFZ) at the adjacent periphery of Si particle. As corrosion time is extended, Si particle leads to severe anodic dissolution and corrosion of the PFZ at its adjacent periphery, expedites the polarity transformation between Mg₂Si and the PFZ and accelerates the corrosion of PFZ at the adjacent periphery of Mg₂Si particle.

Key words: Al−Mg−Si alloys; intergranular corrosion; corrosion mechanism; electrochemical behaviors; Mg₂Si; Si