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Study on the initial electrodeposition behavior of aluminum on TiB2/A356 composite



The electrodeposition behavior of aluminum on TiB2/A356 composite from AlCl3–NaCl–KCl molten salt was studied in this paper. The surface morphology, microstructure, and phase composition of aluminum coating were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The phase composition of the composite was examined by X-ray diffraction technique. The polarization curves were measured and the corrosion current densities were obtained. The results indicated that the aluminum coating was preferentially electrodeposited on the surface of TiB2 and Si phases. This phenomenon could be largely attributed to the different surface energies of TiB2, Si, and Al phases. With the increasing of deposition time, a continuous, dense, and faceted aluminum coating was finally obtained. It was inferred that the growth of aluminum coating on the surface of the composite was mainly through two-dimensional spreading. However, three-dimensional growth could also be seen. The corrosion current density of the aluminum-coated TiB2/A356 composite (1 min) decreased by an order of magnitude as compared with that of TiB2/A356 composite, and was close to that of A356 alloy, and also in the same order of magnitude with that of pure aluminum. It is evident that, the coverage of TiB2 and Si phases by aluminum coating (1 min) can effectively improve the corrosion resistance of TiB2/A356 composite. In combination with SEM and EDS results, the behavior can be characterized as preferential electrodeposition.