Micro Arc Oxidation of Al-4Si, Al-4Mn and Al-4Mg Binary Alloys

Binary synthetic aluminum alloys Al-M (M = Mg, Mn, Si) containing 4 at.% alloying elements as substrate materials were prepared under controlled vacuum/argon atmosphere. The substrates were coated by micro arc oxidation (MAO) method for 120 minutes in aqueous alkaline electrolyte using the same electrical parameters. The phase constituents, chemical composition, surface roughness and the microstructure of the coatings were characterized by XRD, profilometry and SEM-EDS. The average coating thicknesses are 127 μm, 91 μm and 78 μm on Al-4Mn, Al-4Mg and Al-4Si alloys, respectively. All MAO coatings were composed of mullite (3Al₂O₃·2SiO₂) and γ-Al₂O₃ phases. In addition to these phases, α-Al₂O₃ phase, in the form of precipitates, was detected in coatings on Al-4Mn and Al-4Mg alloys. The presence of Si, Mn and Mg was detected in the coatings, depending of the chemical content of the substrate alloys.