Effects of different current densities on properties of MAO coatings embedded with and without α -Al 2 O 3 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.