12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

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 theta-Fe4Al13 phase layer, followed by the local growth of eta-Fe2Al5 phase toward both steel and Zn alloy melt sides during the hot-dipping process. After long-term hot-dipping, further growth of the eta 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 in hot-dip galvanaizing process using the Zn–Al–Mg alloy melts in terms of a Zn–Al–Mg–Fe quaternary phase diagram calculated. The thermodynamic caluculations assessed the formation sequence of Fe–Al intermetallic phases in various hot-dip Zn–Al–Mg alloy galvanized steels.