| The «Fe2Al5 → δ» and «δ → Fe2Al5» transformations occuring in industrial galvanizing baths were studied during this project, using synthetic Fe 2Al5 and FeZn10 binary intermetallics in bulk form.; The Fe2Al5 compound was produced by a «combustion synthesis/hot pressing» method, in a specially designed hot press at École Polytechnique de Montréal. The resulting intermetallic had the desired composition, very high homogeneity and a density which was close to the theoritical density of the stœchiometric compound. The vacuum annealing of a cold-pressed pellet of iron and zinc powders was used to synthesize the δ intermetallic. The FeZn10 compound produced this way was also homogeneous and of the required composition, but was also very porous.; Each of these compounds, in disc form, was rotated at several angular speeds and immersed in Zn(Al, Fe) alloys at 460°C to provoke the desired phase transformations. The experiments were successful, but as no replicas were made, the quantitative results of this study should only be considered to be preliminary.; The «Fe2Al5 → δ» rotating-disc transformation experiments revealed that this type of phase change occured by way of an interfacial mechanism, with a δ layer growing at the Fe 2Al5/liquid Zn (0,11 wt% Al, 0,0283 wt% Fe) alloy interface. The thickness of this layer increased with increasing immersion time, but the effect of the angular velocity of the Fe2Al5 disc could not be determined from the limited amount of data obtained during the experiments. The analysis of bath samples taken at regular intervals during this transformation showed that the «total» Fe content increased with time, while the «total» Al concentration remained constant (within experimental error limits). Furthermore, the iron mass transfer rate increased with increasing rotation velocity, which could mean that the hydrodynamic conditions influenced the «Fe2Al5 → δ» transformation kinetics to some extent.; The modeling of the «δ → Fe2Al5» transformation, for kinetics controlled by the diffusion of aluminum in the liquid alloy, have shown that the calculations are very sensitive to the chosen value of the particle-liquid slip-velocity and to the value of the Al diffusivity in the liquid alloy (which is not currently available). The model can be considered to be satisfactory until more precise diffusion and transformation data can be obtained. (Abstract shortened by UMI.)... |
