Growth of Fe<sub>2</sub>Al<sub>5</sub> Phase on Pure Iron Hot-Dipped in Al–Mg–Si Alloy Melt with Fe in Solution

Abstract

We have examined the growth and morphology of the Fe–Al alloy layer (Fe2Al5-η and FeAl3-θ phases) on pure Fe sheets hot-dipped at 750°C in an Al-8.2Mg-4.8Si–Fe (wt.%) and Al–Fe alloy melts which are saturated with Fe where the effect of Fe dissolution from the solid Fe can be eliminated. In both the Al–Mg–Si–Fe and Al–Fe melts, the total thickness of Fe sheets increased during the dipping, indicating that the diffusion of Al from the melt side is dominant in the growth of the Fe–Al alloy layer. The growth rate constant of the η phase layer in the both melts was close to 0.5 while the growth rate in the Al–Mg–Si–Fe alloy melt was approximately one order of magnitude slower than that in the Al-Fe melt. The θ phase layer appeared continuous in the Al–Mg–Si–Fe alloy melt, whereas the layer was discontinuous in the Al–Fe melt. The sluggish growth of the η phase layer in the Al–Mg–Si–Fe alloy melt is discussed.