Surface Modification of 7075 Al-Alloy with SiC-Doped Micro-Arc Oxidation Coatings

The surfaces of 7075 Al-alloy,an advanced oil drill-pipe material,were modified with the SiC-doped coatings synthesized by micro-arc oxidation(MAO).The influence of the SiC-doping on the microstructures,tribological properties and synthesis of MAO coating was investigated with X-ray diffraction,energy dispersive spectroscopy and scanning electron microscopy.The preliminary results show that the SiC-doping made the difference.For instance,as the SiC-content increased,the deposition-rate,thickness,surface-roughness and defect densities,including the micro-pores,pin-holes and sintered clusters,increased,because SiC-grains resulted in the increases of resistivity,MAO-voltage,number of large-sized discharge holes,followed by the formation of micro discharge-holes in cooling.Doping at a SiC-content of 4 g/L brought about stronger hardness enhancement of the thick MAO coatings,mainly comprising γ-Al₂O₃,α-Al₂O₃ and SiO₂ grains,possibly because of the micro arc oxidation of SiC grains.