Effects of different current densities on properties of MAO coatings embedded with and without α-Al2O3 nanoadditives

Abstract

Ceramic coatings have been synthesised on 6063 aluminium alloy by microarc oxidation (MAO) technique in the solution of NaAlO2 electrolyte with and without α-Al2O3 nanoadditive. Effects of different current densities on the properties of ceramic coatings have been studied in this paper. The phase composition and microstructure of the MAO coatings were investigated by X-ray diffraction and scanning electron microscopy analyses respectively. Microhardness, adhesion and wear resistance tests were also performed. X-ray diffraction shows that the ceramic coating prepared in NaAlO2 electrolyte with α-Al2O3 nanoadditive has better crystallisation in comparison with that prepared without α-Al2O3 nanoadditive. Scanning electron microscopy shows that the surface of the coating prepared with α-Al2O3 nanoadditive became denser and smoother and the number of pores decreased with increasing current density from 15 to 20 A dm−2. Mechanical property tests show that values of microhardness and adhesion of the ceramic coatings increase with increasing current density, while the samples prepared under the current density of 20 A dm−2 with α-Al2O3 nanoadditive have better wear resistance than the others, which is mainly attributed to its dense surface, high hardness and relatively low friction coefficient.