Corrosion behavior of hot‐dip Al–Zn coating doped with Si, RE, and Mg during exposure to sodium chloride containing environments

Abstract

The corrosion behavior of hot‐dip Al–Zn–Si, Al–Zn–Si–RE, and Al–Zn–Si–RE–Mg coatings was investigated by neutral salt spray test and electrochemical measurements. The obtained results indicate that the elements of RE and Mg can reduce the defects and create a finer microstructure. Al–Zn–Si alloy coating was corroded with red rust after 168 h of salt spray corrosion experiment, while Al–Zn–Si–RE and Al–Zn–Si–RE–Mg coatings had better corrosion resistance where only a small amount of red rust appeared after 360 h. The products of corrosion formed on the surface of three coatings consisted mainly of Al‐rich phase and gibbsite Al2O3 · nH2O. Zinc was acting sacrificially in the process of corrosion and aluminum dissolved to form stable corrosion products. Al–Zn–Si–RE–Mg coating with finer microstructure buffered the pH at the cathodic sites and hindered formation of zinc oxide and thereby inhibited oxygen reduction, which improved its ability to resist corrosion. Moreover, different electrochemical impedance spectroscopy and equivalent circuits of three coatings were considered during an initial immersion in a solution of sodium chloride.