镁合金微弧氧化体系中四硼酸钠的作用机理研究

Effects of Sodium Tetraborate in the Electrolyte Systems on Micro-arc Oxidation of Magnesium Alloy

摘要:

利用扫描电镜、电化学工作站等分析手段，探讨了镁合金微弧氧化体系中四硼酸钠添加对膜层组织结构及耐蚀性的影响规律，分析了四硼酸钠在镁合金微弧氧化膜层形成及生长过程中的作用机理。研究发现：微弧放电发生前，（B4O7）2-与Mg离子结合于阳极表面形成难溶于水的偏硼酸镁；随着四硼酸钠含量的增加，沉积于阳极表面的偏硼酸镁结构由3g/L时的颗粒状逐步过渡到15g/L的网状结构；这些具有高阻抗特性的偏硼酸镁沉积层的形成为微弧放电过程的进行构建出了合适的电场条件；微弧放电发生后，沉积于阳极表面的偏硼酸镁通过提高等脉宽恒峰值电流条件下的放电电压而增强了单脉冲的放电强度，进而加快了微弧氧化膜层的生长速度。

Abstract:

The microstructure and corrosion resistance of ceramic coatings formed by micro-arc oxidation on magnesium alloys in electrolyte systems with different Na2B4O7 concentrations was investigated by scanning electron microscopy and electrochemical workstation respectively. The function of sodium tetraborate in the formation and growth process of micro-arc oxidation coatings was analyzed. The results showed that a compound of (B4O7) 2- and Mg2 on the anode surface was formed the water-insoluble material of Mg(BO2)2 before the occurrence of micro-arc discharge. As the concentrations of Na2B4O7 increased from 3g/L to 15g/L, the morphology of deposited layer transited from granular to net structure gradually. The formation of Mg(BO2)2 layer with a high impedance characteristic set up a suitable electric field condition for MAO process. After micro-arc discharge happened, Mg(BO2)2 on the anode surface by raising the discharge voltage enhanced the strength of single pulse discharge under constant pulse width and peak current, and then speed up the growth of micro-arc oxidation coatings.