Influence of dipping conditions on intermetallic layer formation and electrochemical behaviour of aluminized steel

Aluminized steel is a promising material, since it combines the excellent mechanical properties and cost of steel, with the barrier properties of aluminum. It provides an alternative for galvanized steels. Aluminum coatings are already applied in industry despite limited knowledge on the intermetallic layers formed and the corresponding electrochemical behaviour of those layers. The structure, thickness and presence of different intermetallic layers are studied in this work. This is done by combining several electron microscopy techniques (performed at Ghent University). The electrochemical behavior of the various layers is also under examination by measuring local current densities in different electrolytes (scanning vibrating electrode technique performed at SURF group, Vrije Universiteit Brussel). In particular the effect of dipping temperature and silicon content in the aluminum bath on the layer structure and corrosion behavior of the coated steel is investigated. The results show that increasing the silicon content not only decreases the thickness of the intermetallic η phase and changes its morphology, but also drastically changes its orientation distribution (texture). This shows that silicon interferes with the growth mechanism of the η phase. The ability of aluminum coatings to protect the steel from cut edge corrosion is demonstrated only in a chloride-containing environment. Coatings with higher silicon contents perform better, as they have thinner intermetallic layers and hence reduced distance between the aluminum coating and the steel substrate.