Properties of thick ceramic composite coatings synthesized on an aluminium alloy by cathodic plasma electrolytic deposition

Cathodic plasma electrolytic deposition (CPED) was applied to efficiently produce a thick ceramic coating with superior wear and corrosion resistance on aluminium alloy. Ceramic composite coatings were synthesized in a glycerin-carbamide-based electrolyte with and without zirconium nitrate, and their phase components, morphologies and compositions were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). The tribological behaviour and electrochemical corrosion resistance were also evaluated. The results show that Al3C4-Al2O3 and Al3C4-Al2O3-ZrO2 coatings with thicknesses of 65 μm and 50 μm, respectively, were produced by DC-powered CPED in only 7 min. Relative to the uncoated alloy, both coated samples exhibited a much lower friction coefficient and wear rate. The ZrO2 incorporated in the coating enhanced the hardness of the coating and dramatically decreased the friction coefficient to 22% of that of the uncoated alloy. The incorporation of ZrO2 also increased the brittleness, resulting in a slightly higher wear rate than that of the ZrO2-free coating. The wear mechanisms of the Al3C4-Al2O3-ZrO2 and ZrO2-free coatings were concluded to be fatigue failure and abrasive wear, respectively. Both coated samples exhibited improved corrosion resistance. The ZrO2 introduced in the coating also decreased the corrosion current density to only 2.7% of that of the Al3C4-Al2O3 coating and enhanced the capacitive loop and impedance.