Changing process from ζ· Fe-Zn phase to Al-Fe intermetallic compounds in molten Zn-5mass%Al alloy bath

摘要

As a purpose to investigate the changing process from Fe-Zn intermetallic compounds (IMCs) toAl-Fe IMCs in a molten Zn-5mass%AI alloy, this study has been carried out by immersing thegalvanized steel sheet withΓ, Γ', δ andζ Fe-Zn phases as a coating layer in a Zn-5mass%Al bath at 450°C.ζ·Fe-Zn phase changed to particle products mainly consisted of Zn-containingAl{sub}5Fe{sub}2 and the melt with less Al concentration than the Zn-5mass%Al bath at anextremely high rate. This change was found to be occurred under the two steps reaction; (1) ζFe-Zn+ Al(L)→ Al-Fe-Zn amorphous phase +Zn(L), (2) Al-Fe-Zn amorphous phase→Al{sub}5Fe{sub}2+Zn(L). At the first step, the Al-Fe-Zn amorphous phase was formed around the grain boundaries ofζ Fe-Zn phase in contact with the Zn-5mass%Al melt and then nuclei of Al{sub}5Fe{sub}2 were formed in this amorphous phase. It is consideredthat Zn concentration at an area of the amorphous phase surrounded Al{sub}5Fe{sub}2 is increased with the growth of Al{sub}5Fe{sub}2. As a result, the area surrounded Al{sub}5Fe{sub}2 becomes a liquid state and Al{sub}5Fe{sub}2 changed fromζ Fe-Zn phaseexists as a particle in the Zn-rich melt. The Al-Fe-Zn amorphous phase is considered to be a quasi-equilibrium phase which has a wide range ofconcentration for Al (l5~60at%), Fe (l0~25at%) and Zn (l5~75at%).