Effect of Al Content on the Microstructure of Hot-Depped Zinc Coating on Hot Stamping Steel

Abstract

Different galvanized coatings on hot stamping steel was obtained by using hot dip galvanizing simulation experiment device dipping in zinc baths with four different Al contents. The effect of Al content on the microstructure of galvanized was investigated using SEM/EDS and glow discharge optical emission spectrometer(GDOES).The results show that press-hardened steel has good reactive wetting in different Al content zinc bath. The Al content(mass fraction) in zinc bath has a significant influence on coating/steel interface composition, morphology and light property. Enrichment of Mn, Si elements occurred in the steel surface during bright annealing process, and the Mn-Si oxides react(redox reaction) with Al in zinc bath. For 0.11% dissolved Al bath, continuous ζ phases formed at the coating/steel interface. For 0.17% dissolved Al bath, the coating/steel interface consist of ζ phases and Fe- Al phases. A continuous Fe2 Al5 inhibition layer achieved in baths with Al content 0.25% and 0.43%, and the morphology of interface layer became coarser when Al content in zinc bath was 0.25%. In addition, with the increase of Al content in zinc bath, the light property of zinc coatings gradually became worse.