Abstract: The surfaces of 2A12-T4 alloy,an advanced structural material in auto and aerospace industries,were modified with coatings synthesized by micro arc oxidization(MAO) in BN-doped phosphate electrolyte.The influence of the BN particle-size on the microstructures and tribological behavior of MAO coatings was analyzed with X-ray diffraction,energy dispersive spectroscopy,scanning electron microscopy and mechanical probes.The preliminary results show that the BN particle-size had a major impact.Specifically,doping of 16.63 μm BN-particle(best grain-size available) increased the compactness and surface roughness,decreased the size and density of micro-pores and significantly improved the tribological properties,because the BN-particles induced melting-sintering of oxides in MAO reaction,resulting in filling of pores.For example,the BN-doping considerably decreased the friction coefficient and wear-rate.The adhesive wear accounted for the wear mechanism of the BN-doped MAO coatings.