A galvanizing simulator with rapid spot cooling was used to obtain a well-characterized reaction times as short as 2 seconds in order to study the short-time microstructural development and kinetics of the galvanizing and galvannealing interfacial reaction layer. It was determined that the incubation and nucleation events of the interfacial layer formation were completed by the 2-second reaction time in all cases. For a 0.20 wt pct dissolved Al bath, FeAl 3 nucleates and grows during the initial stages of interfacial layer formation followed by Fe 2 Al 5 Zn X formation by diffusion-controlled transformation and growth. The final microstructure of the interfacial layer consisted of Fe 2 Al 5 Zn X in a two-layer arrangement comprising a fine-grained, compact lower layer with a coarser, noncompact upper layer. The Al content of the interfacial layer increased with reaction time and reaction temperature. Both of the Fe-Al phases formed exhibited a strong preferential crystallographic orientation with respect to the substrate surface. The evolution of the interfacial layer formed in a 0.13 wt pct dissolved Al bath was the result of competing processes. Fe-Al phases formed and grew during the reaction times explored, per the preceding mechanism. However, Fe-Zn phases also nucleated and grew during the reaction times explored via the process of inhibition breakdown, with these phases dominating the interfacial layer microstructures at longer reaction times. In this case, the Al content of the interfacial layer increased for all reaction times explored, but decreased with increasing reaction temperature, due to the more rapid initiation of inhibition breakdown. A model to describe the interfacial layer growth kinetics as a function of reaction time, bath temperature, and inhibition layer microstructure for the case of the 0.20 wt pct dissolved Al bath was proposed. It indicated that the development of microstructure of the interfacial layer had significant influence on the effective diffusion coefficient and growth rate of this layer.

Today the baths of galvanisation contain different chemical elements : zinc, but also aluminium, iron and chromium. To understand the formation of solid phases and the reactions that take place in the molten zinc bath, the zinc rich corner of the quaternary diagram Fe-Zn-Al-Cr has to be investigated. The base of this quaternary diagram is composed by three ternary diagrams : Fe-Al-Zn, Fe-Cr-Zn and AI-Cr-Zn, the two first were already known, but not the last one. The main purpose of this study is the exploration of the ternary diagram Al-Cr-Zn with different experiences : immersion of chromium in aluminium added zinc bath, PVD of zinc on a Al-Cr alloy, galvanizing procedure, mechanical alloying, evaporation of zinc. Each new ternary phase is characterized by EDS and XRD. This experimental results allows the optimization of this ternary diagram by the modelisation software Thermo-Calc.

The Fe-Cr-Zn system in relation with the galvanizing process in chromium-added zinc bathTaking into account new experimental measurements, the Fe -Zn -Cr ternary system is critically modified at 460°C. A continuous solid solution between f-FeZn 13 and CrZn 13 compounds is shown but is shared at 460°C by the stable CrZn 17 compound containing about 2 wt.% Fe. This ternary system is assessed with the CALPHAD method using the PARROT modulus of the Thermo-Calc software. The liquid and solid solution phases are modeled with Redlich -Kister -Muggianu equations. The intermetallic compounds f-(Fe,Cr)Zn 13 and CrZn 17 are treated as stoichiometric compounds in the binary systems. The experimental Fe and Cr solubilities at various temperatures modify the shape of the liquidus curve and are satisfying for industrial applications. A set of parameters consistent with most of the available experimental data on both phase diagram and solubility measurements is obtained by optimization. A comparison with previous experimental work is also presented and a reactional model between iron substrate and Zn -Cr bath is proposed. This optimization allows to interpret the growth of intermetallic layers and the formation of dross when galvanizing in Cr-added Zn bath.

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