The lifetime assessment of hot-dip 5% Al–Zn coatings in chloride environments

Batch-type hot-dip zinc and 5% Al–Zn coatings were investigated for comparison of their corrosion resistance, electrochemical behavior and microstructures. The 5% Al–Zn coatings possess prominent electrochemical passivation behavior. Intermetallics formed mainly between iron, aluminum and zinc adhering to the substrate were identified with energy-dispersive X-ray analysis and are believed to be responsible for the passivation phenomena observed in the electrochemical polarization. The 5% Al–Zn coatings exhibit much better corrosion resistance than the conventional hot-dip galvanizing steels under salt spray tests. Although the corrosion potential of both coatings increases toward the noble potential as the immersion time increases, 5% Al–Zn coatings are always nobler than hot-dip zinc coatings.