Investigation of phase evolution of Al–Si–Mg coating on hot dipped interstitial-free steel

Abstract

Evolution of different phases formed on interstitial free (IF) steel after hot dipping in Al–Si–Mg alloy melt at 700 ​°C for 0.5, 1, 3 and 6 ​min were examined in the present research. Notable findings from XRD studies include presence of Al3FeSi2 (τ4) Al2FeSi (τ3) phases along with elemental Si and Mg in the form of Mg2Si. Composition profiles revealed by EDS and GDOES studies has been in line with the XRD results. Interestingly, EPMA study established presence of Si as isolated islands across the coating and up to the intermetallic layer apart from its association with Mg in the form of Mg2Si. The microstructure across the cross-section revealed by the EBSD technique showed three distinct layers consisting of Al–Si top coat, θ-FeAl3 and a major η-Fe2Al5 phase layer adjoining the steel substrate. This study also revealed ternary Fe–Al–Si intermetallic Al3FeSi2 (τ4) and Al2FeSi (τ3) phases scattered in the intermetallic layer. Texture measurement from EBSD revealed the presence of strong γ-fiber for 3 ​min hot dipped aluminized samples. Grain boundary characteristics distribution (GBCD) results indicated that the volume fractions of high angle grain boundaries were gradually increased with the advancement of dipping time.

Keywords

• Hot dip Al–Mg–Si coating
• Intermetallics
• EBSD phase mapping
• Crystallographic texture
• γ –fiber