Effect of silicon on interfacial reaction and morphology of hot-dip aluminizing
Hongjin Wang, Shunping Sun, Xiaoping Li, Jianhua Wang, Xuping Su
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.