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Influence of Si on the Growth Kinetics of Fe2Al5 during Reactive Diffusion between Fe and Al

Author: HanZuo
Tutor: YinFuCheng
School: Xiangtan University
Course: Materials Science
Keywords: Growth kinetics Al-Si Diffusion coefficients Hot-dip Activation energy
CLC: TG174.443
Type: Master's thesis
Year: 2009
Downloads: 51
Quote: 1
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Abstract


Hot-dip zinc was the common used technology for protecting the steels from corrosion. The zinc-aluminum alloy coating was the most widely used technology because of its good corrosion-resistence. The Galvalume deveoped by the Bethlehem Steel Corporation was the improving rapidly at present. The microstructures of galvalume hot-dip coatings were very complex. The Fe2Al5 adjacent to iron was of the most importance to the coating’s performance. And the silicon had a strong effect for the growth kinetic of the Fe2Al5. As a part of the system research, neglecting the zinc’s influence and the effect of silicon on the microstructures of the coating and the growth kinetics of the Fe2Al5 were investigated by the optical microscopy and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and wave dispersive X-ray spectroscopy (SEM-EDS, SEM-WDS).With the solid-state diffusion couples experiment, there was only Fe2Al5 phase in diffusion layer when the content of Si was 0, 0.5, 1.0 and 1.5 (in wt pct) and the interdiffusion coefficient D of Fe2Al5 was evaluated to be 3.46×10-15, 2.61×10-15, 1.28×10-15 and 0.86×10-15 m2/s. With the increasing of the content of silicon, the interdiffusion coefficient D reduced. When Si was added to 2.0 and 3.0 wt pct in Al, the first formed phase was Fe2Al5. In the later stage, theτ1/τ9 andτ5 phase was formed between Fe2Al5 and Al-Si boundary. Simultaneously, the growth rate of the compounds was accelerated. Because of some silicon exists as ternary compounds, the prohibiting ability to the growth of Fe2Al5 was evidently reduced.The hot-dip experiments were carried out. The thickness of Fe2Al5 layer became thinner as the content of silicon in aluminum bath increased. The growth kinetics of Fe2Al5 was parabolic. The activation energy of Fe2Al5 was evaluated to be 207, 186, 169, 168, 167 and 172 kJ/mol, when the content of silicon is 0, 0.5, 1.0, 1.5, 2.0 and 3.0 (in wt pct). It was clear that the activation energy of Fe2Al5 reduced when the content of silicon was less than 1.0wt% because of drastic reduction of frequency factor caused the the growth rate of the Fe2Al5 decreased. There was almost no changes in the activation energy of Fe2Al5 when the content of silicon was more than 1.0wt% When the content of silicon was largered than 1.0wt%, beacause frequency factor was no significant difference to the growth rate of the Fe2Al5. The intermetallic compounds were FeAl3 and Fe2Al5 when galvanized in the pure aluminum. Theτ1/τ9 phase was formed in the Fe2Al5 when galvanized in the Al-Si alloys. To be same as the solid diffusion, silicon in the bath improved the prohibiting ability to the growth of Fe2Al5. Because there was noτ5 phase, the prohibiting ability to the growth of Fe2Al5 was obviously intensified when the content of silicon was increased. The amount of silicon in the Fe2Al5 for both diffusion couple experiment and hot-dip experiment was found to be tardily increased with the silicon adding to the Al-Si alloys.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology > Metal complex layer of protection > Hot dip
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