Effects of Si on the formation of intermetallic phases in alloying reaction between iron substrate and liquid Zn containing 0.2 wt% Al

The Fe-Zn and Fe-Al-based alloying phases are formed on galvanized/galvannealed steels which are extensively used as automobile bodies. This paper investigated the effects of Si on the formation of intermetallic phases in the alloying reaction between an iron substrate and liquid Zn containing 0.2 wt% Al and partitioning of Si between the phases. The addition of Si to the iron substrate was found to scarcely influence the formation and morphology of the Fe2Al5 intermetallic phase layer but to reduce the amount of the delta(1)-FeZn7-10 intermetallic phase layer at the substrate/liquid interface and to disperse the phase as grains in the Zn-0.2 wt% Al coating matrix. STEM-EDS analysis demonstrates that Si partitions less into the Fe2Al5 and the delta(1) phases than into the iron substrate. Enrichment of Si around an Si-depleted Fe-Zn intermetallic phase product was also observed in the beginning of the alloying reaction. The results obtained allow us to explain the effect of Si on the intermetallic phase formation in terms of a difficulty in nucleating the delta(1) phase at the substrate/liquid interface.