Published online by Cambridge University Press: 21 February 2011
When silicon killed steels are galvanized in a pure zinc bath at 450°C, the first Fe-Zn compound to precipitate is ξ-compound. If the silicon content is higher than 0.07 wt%, the reactivity of steel in the liquid leads to thick coating and is clearly due to a silicon super-saturated liquid layer near the substrate. In this case, anarchical growth of ξ-crystals is observed.
In order to validate the model proposed for this mechanism, zinc vapor deposition on different substrates has been used. In this case it was shown that the first intermetallic compound which precipitates is no more ξ-compound but the iron richest one: Γ. This result shows that the reactivity of the different steels facing the zinc vapor is the same. In fact, silicon present in the substrate can be totally dissolved in the Γ-phase according to the Fe-Zn-Si phase diagram at 450°C and Si does not play any more its role in preventing the formation of the ξ-compound.