Effect of silicon on interfacial reaction and morphology of hot-dip aluminizing

Abstract

Interfacial reaction and morphology are investigated between pure iron sheet and aluminum alloy with different silicon additions in hot-dip aluminizing (HDA) at 700 °C. The width of intermetallic reaction layer hot-dipped in a pure aluminum bath is mainly governed by the diffusion controlled growth of the η-Al5Fe2 phase. Al atoms can diffuse rapidly in a preferred [001] direction, resulting in the continuous growth of η phase with a tongue-like morphology. The addition of Si 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 and lead to the structural vacancy obstruction. The investigation reveals that the diffusion of Si at the interface will control the phase transformation of θ phase with a low Si content to higher Si containing τ1-Al2Fe3Si3 and τ5-Al8Fe2Si phase. The continuous τ1-Al2Fe3Si3 phase layer will be formed as the segregation concentration of the Si atoms reach 5 at.% at the interface between Al alloy and θ phase. And the continuous τ5-Al8Fe2Si layer is observed in the reaction layer of Al-6Si and Al-10Si, which will reduce the growth rate of η phase as a diffusion barrier.

Keywords

• Hot-dip aluminizing
• Fe-Al interface reaction
• Coatings
• Intermetallic compound