Role of Al and Mg alloying elements on corrosion behavior of zinc alloy-coated steel substrates in 0.1 M NaCl solution

The corrosion behavior and corrosion products of three zinc alloy-coated steel substrates with different Al and Mg contents such as hot-dip galvanized steel (HDG), Zn-Al-coated steel (ZA), and Zn-Al-Mg-coated steel (ZM) substrates were investigated during 168 h of immersion in 0.1 M NaCl solution. The characteristics and morphology of corrosion products on all the substrates formed during exposure to electrolyte solution were observed by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. Their electrochemical behavior was investigated by open-circuit potential, polarization curves, and electrochemical impedance spectroscopy. The addition of Al and Mg alloying elements affected the corrosion mechanism as well as the anticorrosion properties. The main crystalline corrosion products on the HDG surface were simonkolleite and zincite, while the ZnAl hydrotalcite was identified as the main corrosion product on ZA and ZM surfaces. The corrosion resistance of ZA and ZM substrates was improved compared to the HDG substrate due to the enhanced adhesion of the corrosion product layer.