Effect of Silicon on Interfacial Reaction and Morphology of Hot-Dip Aluminizing

Interfacial reaction and morphology are investigated between pure iron sheet and aluminum alloy with different silicon additions in hot-dip aluminizing at 700°C. The intermetallic reaction layer hot-dipped in a pure aluminum bath is mainly governed by the diffusion controlled growth of the η-Al 5 Fe 2 phase, which changes with time according to a parabola rule. Al atoms can diffuse rapidly in a preferred [001] direction, thereby causing the continuous growth of η phase with a tongue-like morphology. The thickness of the θ-Al 13 Fe 4 phase layer exhibits a slow linear growth with the increase of dipping time. Adding silicon into aluminum baths reduces the growth rate of the reaction layer and eliminates the rough interface. The effect of Si inhibiting the growth of η phase can be attributed to the segregation of Si atoms at the Fe/Al interface. The Si concentration segregation in θ and η phase hinders the rapid diffusion of Al atoms, resulting in the structural vacancy obstruction, which is responsible for the thickness reduction. The investigation reveals that the continuous τ 1 -Al 2 Fe 3 Si 3 ternary phase layer will be formed as the segregation concentration of the Si atoms reach 5 at.% at the interface between Al-4Si alloy and θ phase. The continuous τ 5 -Al 8 Fe 2 Si layer is observed in the reaction layer of Al-6Si and Al-10Si. The continuous Al-Fe-Si ternary phase layer can reduce the growth rate of η phase as a diffusion barrier. The diffusion of Si at the interface will control the phase transformation of θ phase with a low Si content to higher Si containing τ 1 and τ 5 phase