On the effect of thermal diffusion treatment on the hot-dipped Al-Si alloy coating on Fe-Cr-B cast steel

The periodic layered structures (PLSs) consisting of alternatively arranged Cr-Al-B MAB phase and FeAl3 were formed in-situ at the (Cr, Fe)2B/pure Al melt interface during hot dip aluminizing (HDA) of Fe-Cr-B cast steel. In the present investigation, HDA of a novel Fe-Cr-B cast steel was carried out in an Al-5.7 wt% Si alloy melt at 750 degrees C for 30 min. The HDA samples were given thermal diffusion treatment (TDT) at 750 degrees C. The microstructural evolution of the Al-Si coating during HDA and TDT were analyzed in details. Results showed that Si in Al melt had a great influence on the compositions of PLSs. During HDA, Si atoms in the melt partially replaced Al atoms in the Cr-Al-B MAB phase, and Si-rich phase were rich at the boundary of Cr-Al-B MAB phase. While, during TDT, the Si-rich phase dissolved into the adjacent FeAl3. The formation process of PLSs during TDT experienced the both transformation from the laminar structure formed in the initial stage to the graininess structure at last and from disordered to ordered arrangement.