As a purpose to investigate the changing process from Fe-Zn intermetallic compounds (IMCs) to Al-Fe IMCs in a molten Zn-5mass%Al alloy, this study has been carried out by immersing the galvanized steel sheet with Γ. Γ'. δ and ζ 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-containing Al
5Fe
2 and the melt with less Al concentration than the Zn-5mass%Al bath at an extremely high rate. This change was found to be occurred under the two steps reaction; (1) ζ·Fe-Zn+Al(L)→ Al-Fe-Zn amorphous phase + Zn (L), (2) Al-Fe-Zn amorphous phase →Al
5Fe
2 + Zn(L). At the first step, the Al-Fe-Zn amorphous phase was formed around the grain boundaries of ζ·Fe-Zn phase in contact with the Zn-5mass%Al melt and then nuclei of Al
5Fe
2 were formed in this amorphous phase. It is considered that Zn concentration at an area of the amorphous phase surrounded Al
5Fe
2 is increased with the growth of Al
5Fe
2. As a result, the area surrounded Al
5Fe
2 becomes a liquid state and Al
5Fe
2 changed from ζ·Fe-Zn phase exists 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 of concentration for Al (1560 at%), Fe (1025 at%) and Zn (1575 at%).
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