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

Abstract 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 Al 3 C 4 -Al 2 O 3 and Al 3 C 4 -Al 2 O 3 -ZrO 2 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 ZrO 2 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 ZrO 2 also increased the brittleness, resulting in a slightly higher wear rate than that of the ZrO 2 -free coating. The wear mechanisms of the Al 3 C 4 -Al 2 O 3 -ZrO 2 and ZrO 2 -free coatings were concluded to be fatigue failure and abrasive wear, respectively. Both coated samples exhibited improved corrosion resistance. The ZrO 2 introduced in the coating also decreased the corrosion current density to only 2.7% of that of the Al 3 C 4 -Al 2 O 3 coating and enhanced the capacitive loop and impedance.