镁合金微弧氧化膜表面层与致密层界面组织的研究

Microstructure of boundary between surface layer and dense layer in micro-arc oxidation coating of magnesium alloys

研究镁合金微弧氧化膜的表面层与致密层界面处的组织形态。在磷酸盐碱性电解液(5～20g/LNaH2PO4,1～5g/LNaOH,5～8g/LKF,0.5～2g/LNa3C6H5O7,0.5～2g/LEDTA)中,以AZ91镁合金为基体制备出微弧氧化陶瓷薄膜,制备时采用恒电流控制模式,电流密度为10～30A/dm2。采用透射电镜(TEM)和扫描电镜(SEM)研究氧化薄膜界面及附近区域的微观结构。结果表明:微弧氧化膜的表面层靠近表面层与致密层界面处的组织以微晶和纳米晶为主,含有少量非晶态物质;微弧氧化膜的表面层与致密层界面处的组织以非晶态物质为主;微弧氧化膜的致密层靠近表面层与致密层界面处的组织为混晶组织,主要为MgO晶粒,少量为MgAlO4晶粒,并含有少量非晶态物质。

Microstructure of boundary between surface layer and dense layer of the ceramic coating formed on AZ91 magnesium alloy substrate by micro-arc oxidation（MAO） was studided. The coating was prepared in a phosphate alkaline electrolytic solution composed of 5-20 g/L of NaH2PO4, 1-5 g/L of NaOH, 5-8 g/L of KF, 0.5-2 g/L of Na3C6H5O7, and 0.5-2 g/L of EDTA, a constant current controlled AC power supply with a current density of 10-30 A/din2 was employed; and the microstructure of the coatings was characterized using transmission electron microscopy （TEM） and scanning electron microscopy （SEM）. It is found that the main constituent of the coating near the boundary in the surface layer is microcrystalline, nanocrystalline and a small amount of amorphous ; the microstructure on boundary area is amorphous mainly ; the constituent in the dense layer adjacent to the boundary is a mixed crystalline microstructure, and the main phase is identified by electron diffraction to be MgO, containing a small amount of MgA1O4 and some amorphous substance.