Abstract:The corrosion and electrochemical behaviors of 7A09 Al-Zn-Mg-Cu alloy were investigated in 3.5% NaCl (mass fraction) solution using complementary techniques such as scanning electron microscopy (SEM), metallographic microscopy and electrochemical measurements. The results show that both pitting corrosion from or around the intermetallic particles and intergranular corrosion are observed after the immersion test due to the inhomogeneous nature of the microstructure of the 7A09 alloy. The preferential dissolution of the anodic Cu-depleted zone along grain boundaries is believed to be the possible cause of intergranular corrosion. The passivation and depassivation of this alloy show significant dependence of immersion time, owing to the formation and dissolution of various passive films on the sample surfaces. Furthermore, the corrosion process and corrosion mechanism were also analyzed.

Key words: 7A09 Al-Zn-Mg-Cu alloy; intergranular corrosion; intermetallic particles; electrochemical impedance spectroscopy; polarization