Formation sequence of Fe–Al intermetallic phases at interface between solid Fe and liquid Zn–6Al–3Mg alloy.

In the present study, we characterized the Fe–Al intermetallic phases formed in interstitial-free (IF) steel hot-dipped in a Zn–6Al–3Mg (wt.%) alloy melt at different temperatures (400, 460 and 500 °C) and dipping times (from 2 to 3600 s). Chemical composition analyses indicated Fe dissolution into the Zn alloy melt even after 2 s of dipping. Microstructural characterization revealed the initial formation of a continuous θ-Fe 4 Al 13 phase layer, followed by the local growth of η-Fe 2 Al 5 phase toward both steel and Zn alloy melt sides during the hot-dipping process. After long-term hot-dipping, further growth of the η phase was accompanied by significant dissolution of Fe into the Zn alloy melt, resulting in the loss of thickness of the IF steel sheets. Altogether, we rationalized the formation mechanism of Fe–Al intermetallic phases and their associated growth at the interface between solid Fe and liquid Zn alloy in terms of a Zn–Al–Mg–Fe quaternary phase diagram, calculated according to thermodynamic database available in the literature. • Fe–Al intermetallic phases formed in hot-dip Zn–6Al–3Mg alloy coating on steel sheets was characterized. • A continuous θ-Fe 4 Al 13 phase layer was initially formed, followed by the local growth of η-Fe 2 Al 5 phase. • The growth of the η phase was accompanied by significant dissolution of Fe into the Zn alloy melt. • The formation sequence of Fe–Al intermetallics was rationalized according to the calculated Zn–Al–Mg–Fe phase diagram. [ABSTRACT FROM AUTHOR]