The role of surface oxides on annealed high-strength steels in hot-dip galvanizing

Oxidized alloying elements on the surface of annealed advanced high-strength steels deteriorate zinc wetting during hot-dip galvanizing. The present work describes reactions taking place during immersion of a steel strip in a zinc bath and gives new insight in changes of the surface oxides during hot-dipping. By using different advanced analysis techniques a direct proof for the occurrence of an aluminothermic reduction of Mn-oxides by Al dissolved in the zinc bath is shown. Furthermore, the morphology – rather than the chemical composition – of the surface oxides is crucial for obtaining a satisfactory galvanizability, mandatory for efficient corrosion prevention.

► Reactions proceeding between the liquid zinc and steel surface oxides during hot-dip galvanizing were investigated.
► Surface oxides change during immersion in the zinc bath, improving galvanizability.
► The changes of oxides in the zinc bath were characterized by SEM, TEM and XPS.
► A direct proof for the occurrence of an aluminothermic reduction of MnO is shown for the first time.
► The morphology of surface oxides is most essential for a satisfying galvanizability.