Speaker
Dominique Thierry
(French Corrosion Institute)
Description
Zinc and zinc-based alloys are the most important coating materials for corrosion protection of steel. The coatings are deposited by either electroplating or hot-dip galvanizing. Many research and development activities are still ongoing regarding the application of Zn and Zn-alloy coatings. In the last two decades, it turned out that zinc-magnesium (Zn-Mg) and zinc-magnesium-aluminum (ZM) show improved corrosion stability when compared to traditional zinc coatings. However, there is a strong interest to investigate alloying elements in addition to magnesium and aluminum and to evaluate their potential to enhance the corrosion protection provided by zinc, Zn-Mg, Zn-Al and Zn-Al-Mg coatings. In this work Zn-3Al-2Mg, Zn-3Al-2Mg-0.4Ti and Zn-3Al-2Mg-0.5Si coated steel have been produced using a Rhesca galvanizing simulator. Line produced hot dip galvanized steel made of zinc and ZM were also included in the study.
The corrosion behavior of the samples has been analyzed in the laboratory using the Scanning Kelvin probe. From the results it is shown that the addition of Si is beneficial to the corrosion stability of the coating. The samples were also exposed to 2 years exposure at a marine site in Brest (France). The corrosive attack initiates in the eutectics and propagates down to the steel substrate during exposure in marine atmosphere. Corrosion products or the interface substrate/corrosion products containing some silicon formed on Zn-3Al-2Mg-0.5Si were more stable than on Zn-3Al-2Mg. Less carbonates were formed on Zn-3Al-2Mg-0.5Si that could be related to a decrease in the cathodic activity and consequently to a better corrosion behavior
Keywords
ZM coated steel, corrosion, SKP, atmospheric corrosion
Author
Dominique Thierry
(French Corrosion Institute)
Co-authors
Mrs
Anne Le Gac
(French corrosion institute)
Dr
Goodwin Frank
(ILZRO)
Dr
Nathalie Le Bozec
(French corrosion institute)