Microstructure and properties of a MAO/PA/MoS2 composite coating formed on 6063 aluminum alloy by micro arc oxidation

Abstract

Different self-sealing and lubricating composite coatings were produced on 6063 Al alloy using micro arc oxidation (MAO) with MoS2 and/or phytic acid (PA) incorporated into the base electrolyte. The tribological properties and electrochemical corrosion behavior of the coatings were detailed investigated in this paper. The results showed that the coefficient of frictional (CoF) of MAO/MoS2 coating decreased 29.6 % compared to that of the pure MAO coating due to the excellent self-lubricating of MoS2. Meanwhile, the CoF of MAO/PA/MoS2 coating reduced 39.5 % attributed to a thicker and more compact coating obtained by the addition of PA as an intermediate chelating agent besides the self-lubricating effect of MoS2 particles. The pores were sealed by MoS2 during MAO process due to the electrodeposition effect which resulted in a positive shifting of the corrosion potential. However, the improvement of corrosion resistance for the MAO/MoS2 coating was limited as the intrinsic defects in MoS2 lattice preferred to form micro galvanic cell. The corrosion current density of the MAO/PA/MoS2 coating was three orders of magnitude lower than that of pure MAO coating. The thin PA layer produced at the substrate/coating interface of the MAO/PA/MoS2 coating can act as a barrier to suppress the galvanic corrosion, inducing the best corrosion resistance of the coating.