Effects of electrolyte composition and electrical parameter on alumina coatings by cathodic micro-arc electrodeposition on titanium

Alumina coatings on titanium substrate were prepared by cathodic micro-arc electrodeposition. Effects of electrolyte composition, discharge voltage and time on morphologies, phase compositions and growth rates of the coatings were studied. Results show that the coatings are composed of α-Al₂O₃ and γ-Al₂O₃. With the increasing of Al(NO₃)₃ content in the electrolyte, both α-Al₂O₃ content and growth rates of the coatings first increase and then decrease. The Al(NO₃)₃ content of 0.2 mol/1 is the optimal one, which is decided by its conductivity. The arc-striking is greatly influenced by volume ratios of ethanol to water and the excessive water in the electrolyte is disadvantageous to cathodic micro-arc electrodeposition because of the high solvent effect. With the raising of voltage, the growth rate of the coatings increases and α-Al₂O₃ content increases as well. The α-Al₂O₃ content reaches 76% when the voltage is 400 V. The growth rates of the coatings are also fast firstly and then slow with prolonging the discharge time. The thickness of the coatings is up to 100 μm when treated for 120 min.