Effect of Dew Point on Galvanizability in 4 Mass% Al Added Low Density Steel

Abstract

Hot dip galvanizing experiments were conducted on low density steel to investigate its galvanizability. The panels were annealed at 815°C for 150 s, and the dew point of the annealing atmosphere was varied from −40°C to +10°C. The surface morphologies of the coating and the substrate before dipping and after coating removal were demonstrated by SEM equipped with EDS. The cross sections prepared by common metallographic method and FIB were characterized by SEM and TEM respectively. It is found that the dew point of the annealing atmosphere has a great effect on the galvanizability of 4 mass% aluminium added low density steel. With the dew point increasing, the external Al oxidation converts into internal Al oxidation and an iron particle layer forms on the outmost surface of the matrix. The Al in the zinc bath mainly reacts with the iron particles to form Fe–Al–Zn inhibition layer at the interface of coating/matrix, resulting in both good wettability and strong coating adhesion of high aluminum low density steel sheet.