The growth mechanism of CPED coating with zirconia sol addition on an Al-12Si alloy

A novel thermal-protective coating has been prepared by CPED process on Al-12%Si alloy with the ZrO2 sol addition. 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. It was confirmed that the sol particle adsorbed on the cathode surface at first, and then formed a thin zirconia gel layer, which can promote the cathode discharge. With ZrO2 sol addition, the cathode plasma discharge on the coating surface is more obvious than that without zirconia sol addition and the coating is more uniform and compact and the thickness of the coating increases. Compared with the electrolyte without ZrO2 sol addition, the crystalline degree of ceramic layer is higher in zirconia sol solution, which indicates that ZrO2 sol can promote the transition of coating from amorphous to crystalline. Under the high temperature of plasma discharge, gel particles entered the discharge channels and then were sintered into ZrO2 ceramic particles. ZrO2 combined with Al2O3 formed by barrier layer together to finally form the composite ceramic coating. With ZrO2 sol addition, the thermal insulation performance of the coating increases.