Growth of Fe2Al5 Phase on Pure Iron Hot-Dipped in Al-Mg-Si Alloy Melt with Fe in Solution

We have examined the growth and morphology of the Fe Al alloy layer (Fe2Al5-eta and FeAl3-theta phases) on pure Fe sheets hot-dipped at 750 degrees 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 eta 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 theta 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 n phase layer in the Al-Mg-Si-Fe alloy melt is discussed.