Characterization of micro-arc oxidation coatings on aluminum drillpipes at different current density

Micro-arc oxidation coatings were fabricated on 7E04 aluminum drillpipes materials in Na2SiO3-NaOH electrolyte system containing 3.0 g/L SiC particles at different current density (1, 5, 10, 15 and 20 A/dm2). The oxidation voltage, coating thickness, surface morphologies, surface micro-hardness, phase composition and potentiodynamic polarization curves of the MAO coatings were investigated. The results showed that the oxidation voltage increased and the coatings thickened with the increment of current density. The coating surface morphologies got coarser gradually which led to the reduction of the surface micro-hardness. The phase composition of the coatings consisted of SiO2 because of the oxidation of SiC particles and the corrosion resistance of the coatings increased slightly.