EBSD Study of Crystallographic Identification on Fe-Al-Si Intermetallic Phases in Aluminide Coatings on Mild Steels

Abstract

Mild steels were coated by hot-dipping in molten aluminum and aluminum-silicon baths at 700 °C for 180 seconds. Phase identification of the Fe-Al or Fe-Al-Si intermetallic compounds in the hot-dipped aluminide steel was carried out by using a combination of scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The results showed that the aluminide layer of the hot-dipped aluminum steel possessed a thicker intermetallic layer than that of the hot-dipped aluminum-silicon steel which was composed of minor monoclinic FeAl3 and major orthorhombic Fe2Al5. The intermetallic layer of the hot-dipped aluminum-silicon steel was composed of not only the same FeAl3 and Fe2Al5 phases in the hot-dipped aluminum steel but also Fe-Al-Si intermetallic compounds of hexagonal Al7Fe2Si and tetragonal (Al,Si)5Fe3.

A review on metallurgical features of hot-dip aluminized steel

“…One study on the formation of IMC formation with Al-10% Si alloy coating deserves special mention because it involved a short dipping time of 3 seconds [121]. It was observed that a distinct IMC layer of a few micron thicknesses could form at the interface with steel.…”

“…It can provide crystallographic information regardless of the content of the materials by analyzing generated Kikuchi patterns or electron-backscattered diffraction patterns (EBSPs). Cheng et al reported that the intermetallic layer of the coating consisted of a thin FeAl 3 layer and a thicker Fe 2 Al 5 layer [121]. EBSD provided a rapid phase identification of the ternary compounds based on composition and crystallography.…”

Raman Spectroscopic Analysis of the Reaction between Al-Si Coatings and Steel

“…In the case of the asreceived steel, for example, the dip-coating process is known to produce a layer of τ 5 at the steel interface. 4,8,10,43,44 This layer acts as a barrier between the Al-Si coating and the Fe in the substrate steel, thereby inhibiting further transformation of the Al-Si coating up to 580 °C. 4,45 Other compounds that have been identified as minority components after the hot-dipping process include τ 1 , τ 6 , η, and θ.…”

“…Raman microscopic mapping shows the emergence of intermetallic compounds at temperatures that are consistent with observations in previous studies. In the case of the as-received steel, for example, the dip-coating process is known to produce a layer of τ 5 at the steel interface. ,,,, This layer acts as a barrier between the Al-Si coating and the Fe in the substrate steel, thereby inhibiting further transformation of the Al-Si coating up to 580 °C. , Other compounds that have been identified as minority components after the hot-dipping process include τ 1 , τ 6 , η, and θ. ,,, Previous studies have reported that θ and η form at ca. 650 °C, τ 2 at 830 °C, AlFe at 882 °C, and τ 1 at 900 °C. , AlFe and Al 2 Fe 2 Si emerge at higher temperatures, around 900 °C. , Some EDS and electron back-scattering diffraction measurements suggest that Al-Si-coated steels heated to 900 °C contain mixtures of τ 1 , τ 2 , and ω (FeSi 2 ), while others show τ 1 , τ 5 , AlFe, Al 2 Fe, θ, and η. ,,,, Variations in the composition of the Al-Si-Fe layer may arise due to variations in heating time.…”

Influence of Pre-Tinning Process on Coating Morphology and Interface Structure of Low Carbon Steel Dipped in Molten 6061 Al Alloy

“…Many researchers from different points of view investigated the morphology and interface characteristics of the coating layer during hot-dip aluminizing techniques [6][7][8][9][10]. Generally, hot-dip aluminizing can be divided into two types, hot dipping in pure aluminum and hot dipping in aluminum alloys, based on the composition of the used molten baths [6].…”