Abstract
The superior corrosion resistance of hot dip galvanized steel (HDG) alloyed with addition of Al and Mg compared to conventional zinc coating has been shown in numerous atmospheric conditions including accelerated tests and natural exposures. Despite significant work in understanding the mechanisms of corrosion of Zn-Al-Mg coatings, there are still gaps of knowledge such as, on the exact interactions between the complex microstructure of theses coatings and their corrosion properties.The present study focuses on the microstructure of Zn-Al-Mg coated steel on the initiation and propagation of atmospheric corrosion. The results are compared to conventional HDG (Zn-0.2Al) and Galfan (Zn-5Al). Zn-Al-Mg produced with various microstructures differing in the grain size were investigated in different laboratory exposure conditions including different levels of humidity, chloride concentration and temperature. In addition to mass loss data, the surface pH was measured using wide range pH indicator in agar-agar gel. The corrosion products were analyzed by FTIR spectroscopy and X-Ray diffraction.It is shown that finer microstructure resulted in lower corrosion rates. This was connected to anode/cathode ratio and the formation of a stable corrosion products at the surface.
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