Abstract
A cast Al12Si system piston alloy was treated by a modified plasma electrolytic oxidation (PEO) process with different zirconia sol additions in sodium silicate electrolyte. The microstructure characteristics and formation mechanism of the coating were investigated by SEM, TEM, EDS, XRD, fourier transform infrared spectrometer (FTIR) and laser particle size analyzer. Compared with the conventional electrolyte, the coating formed in the PEO with zirconia sol addition has more uniform morphology, less micropores and the faster growth rate. It was confirmed that the sol particle adsorbed on the substrate surface at first, and then formed a thin zirconia gel layer, which can restrain the effect of Si phase on plasma discharge and Al2O3 formation. At the high temperature of plasma discharge, the gel particles entered the discharge channels and then were sintered into ZrO2 ceramic particles. As a result, a tri-phase composite ceramic coating, Al2O3ZrO2 together with small amount SiO2, was formed on the substrate alloy.
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