Preparation of ceramic coatings on an Al–Si alloy by the incorporation of ZrO2 particles in microarc oxidation

Ceramic coatings containing ZrO2 were prepared on ADC12 aluminum alloys using microarc oxidation (MAO) in aqueous silicate solutions containing various amounts of ammonium metavanadate (NH4VO3) and 0.2 μm of solid ZrO2 powder. A bipolar rectangular pulse with a frequency of 1000 Hz was galvanostatically used in this study. The morphologies and friction coefficients of the MAO coatings were investigated using scanning electron microscopy and a CSM tribometer, respectively. The results indicated that NH4VO3 electrolytes facilitate the formation of a smooth dark oxide film on Al–Si alloy because of the existence of vanadium oxide, resulting in a favorable appearance but poor tribological behavior. The introduction of ZrO2 powder preserved the favorable and uniform dark appearance of the MAO coating on the ADC12 aluminum alloy. The uniform incorporation of monoclinic/tetragonal zirconia nanoparticles into MAO coating will reduce surface roughness and enhance hardness. These were beneficial to the tribological properties.