The inhibition of MnO on Fe2Al5Znx growth and associated three-dimensional nested phase distribution in the galvanized coating of high-Al low-Si dual phase steel

Abstract

Continuous hot-dip galvanizing is an important process for dual phase (DP) steel and other advanced high-strength steels (AHSSs). During this process, the formation of a Fe-Al inhibition layer and the selective oxidation of alloying elements will change the interfacial layer structure, and affect the galvanized coating structure. So far, the interfacial layer structure and its relationship with galvanized coating in high-Al low-Si DP steel are still unclear. In this paper, the interfacial layer and galvanized coating of hot-dip galvanized high-Al low-Si DP steel were characterized by electron microscopy. The results showed that there exists abundant nano-size MnO phases and Fe2Al5Znx phases inside the interfacial layer, and the galvanized coating consists of Fe3Zn10 nanophases and η-Zn phase. The competitive relationship between those interfacial phases strongly affects the phase distribution inside the galvanized coating adjacent to the interfacial layer. The MnO phases in the interfacial layer hinder the nucleation and growth of Fe2Al5Znx phases. As a result, the inhibition of the Fe-Zn reaction is weakened and the final galvanized coating exhibited a three-dimensional nested distribution of coexistence of Fe3Zn10 nanophases and η-Zn phase.