Effect of pulse frequency on growth kinetics of ceramic coatings formed on 2090 Al–Li alloy

Abstract

Ceramic coatings of Al₂O₃ were prepared on a 2090 Al–Li alloy using a pulsating microarc oxidation (MAO) method in NaOH–Na₂SiO₃ aqueous solution. A two-stage regulating regime was used during the MAO process, initially at a constant current density of 5 A dm⁻² and then at a constant voltage of 450 V. The effects of pulse frequency on coating growth kinetics, microstructure features and tensile properties were investigated. The growth rates of the coatings are enhanced with an increase in pulse frequency from 300 to 900 Hz at a constant current density. A high pulse frequency beyond 600 Hz significantly promotes nonlinear growth, which corresponds to the two-stage regulating regime. Owing to the influence of pulse frequency on coating growth rate and surface roughness, the tensile properties of a 2090 Al–Li alloy slightly decrease with increasing coating thickness. Thus, a high pulse frequency indirectly influences the tensile properties of a 2090 Al–Li alloy with ceramic coatings.