Effect and controlling mechanism of vanadium on Fe–Al interface reaction in Al–Zn bath

Abstract

Abstract The influence of vanadium on Fe–Al interface reaction of steels during hot-dip process was investigated by immersing low carbon steel plates into six different Al and Al–Zn baths at 730 °C and 620 °C. The microstructure and phase constituent of the formed coatings were analyzed with SEM–EDS and XRD. The intermetallic layers formed on the steel plate surfaces in Al bath consist of Fe2Al5 and FeAl3 phases. As 0.05 wt.% V was added to the Al bath, the Fe2Al5 layer became thinner. Whereas the steel plates were immersed into 55%Al–Zn bath, a periodic laminar structure, containing FeAl3 and Al–Zn phases, formed. However, the periodic laminar structure disappeared and a continuous thin Fe2Al5 layer appeared as V was added into Galvalume bath, and the whole intermetallic layer consists of Fe2Al5, Fe2Al8Si and FeAl3 phases. The presence of 0.05 wt.% V in the bath promoted the formation of Fe2Al5 layer. As it covers the whole steel plate surface, it retards the further Fe–Al reaction in the bath, leading to a thin intermetallic layer. The influence of V on Fe–Al interface reaction was studied by means of Vienna Ab-initio Simulation Package (VASP) based on first-principles method. The exchange energy, bonding energy, charge density differences and electronic density of states of Fe2(Al,V3)5 and Fe(Al,V12)3 are analyzed. Both the experimental results and theoretical calculation results show that V could occupy the vacancies of Fe2Al5 lattice which could promote the nucleation of Fe2Al5, and therefore it suppresses the growth of Fe–Al phase.