Mg-Gd-Y系合金微弧氧化层生长机制及耐蚀性研究

利用扫描电镜(SEM)、X射线衍射(XRD)等分析手段,研究Mg-11Gd-1Y-0.5Zn合金微弧氧化陶瓷层的生长规律,分析微弧氧化膜层相结构及不同生长阶段的耐蚀性。结果表明,在微弧氧化初期,膜层生长遵循直线规律,为典型的电化学极化控制的阳极沉积阶段;随处理时间的延长及膜层增厚,膜层生长符合抛物线规律,属微弧氧化阶段,较氧化初期相比,生长速率慢;在弧光放电阶段,抛物线斜率增大,疏松层增厚,生长速率有所提高。微弧氧化疏松层主要以MgSiO3为主,致密层以MgO为主;微弧氧化各阶段,膜层耐蚀性随氧化时间增长而提高,到弧光放电阶段,耐蚀性有所降低。在7～12min时,膜层具有较好的耐蚀性。

Growth Mechanism and Corrosion Resistance of Micro-arc Oxidized Coating of Mg-Gd-Y Alloy

A Mg-11Gd-1Y-0.5Zn(wt%) alloy was coated by different micro-arc oxidation (MAO) processes, and the coating structure and corrosion resistance of the alloy were studied by scanning electron microscopy (SEM), glancing angle X-ray diffraction (GAXRD) and various electrochemical methods. The micro-arc oxidation process used for the alloy consists of 3 stages, corresponding with different coating structures. In the initial stage, the coating thickness is linearly increased and controlled by electrochemical polarization. In the second stage, the coating is mainly inward growth and accords with parabolic regularity. In the third stage, the loose coating is formed and controlled by local arc light. The loose coating is mainly composed of MgSiO3 and the compact coating is mainly of MgO. From the stage of micro-arc oxidation to that of local arc light, the corrosion resistance of the coated alloy is firstly increased and then decreased. The satisfied corrosion resistance corresponds to the coating time ranging from 7 to12 min.