AZ91D镁合金在SO_2薄液膜下的电化学腐蚀行为

Electrochemical Corrosion Behavior of AZ91D Magnesium Alloy under Thin Electrolyte Layer Containing SO_2

利用自建厚度可控的大气腐蚀薄液膜电化学测试装置,通过分析极化曲线以及交流阻抗谱探讨了AZ91D镁合金在含SO2薄液膜下的腐蚀电化学行为,并观察了镁合金在薄液膜下的腐蚀形貌。结果表明:薄液膜厚度和SO2对镁合金阴、阳极化率都有影响;SO2的存在使阴、阳极化率降低,加速镁合金在薄液膜下的腐蚀;随着薄液膜的减薄,腐蚀加速,50μm下出现最大值,但在极薄液膜下腐蚀产物的形成阻碍O2的扩散,腐蚀减缓;极限扩散电流密度随薄液膜厚度的增大先增加后减小,薄液膜厚度小于50μm时,腐蚀产物的堆积使阳极过程受到抑制;镁合金在SO2薄液膜下的阻抗谱由一个高频容抗弧和一个低频扩散阻抗组成,表现为两个时间常数;在不同厚度SO2薄液膜下腐蚀倾向从大到小的顺序为50,20,200,300μm。

The self-built electrochemical measurement device for atmospheric corrosion, with a thin electrolyte layer thickness controlling set was utilized to investigate the electrochemical corrosion behavior of AZ91D magnesium alloy under thin electrolyte layer containing SO2 by means of polarization curve and electrochemical impedance spectrum. Furthermore the corrosion morphology was observed. Results show both the thickness of thin electrolyte layer and SOe affected the anodic/cathodic polarization slope. SOz addition reduced anodic/cathodic polarization slope, indicating the acceleration of corrosion for magnesium alloy. With the decrease of the thickness of thin electrolyte layer, the corrosion rate increased. The maximum value was found in 50 μm thickness. The formation of corrosion products under electrolyte layer with very thin thickness blocked the oxygen diffusion, leading to the slowing down of corrosion. The limited diffusion current density firstly increased and then decreased with the increase in the thickness of thin electrolyte layer. When the thickness of electrolyte layer was less than 50 μm, anodic process was inhibited because of pileup of corrosion products. The Nyquist curve consisted of high frequency capacity reactance arc and low frequency diffusion impedance, and showed two time constants. The order of corrosion tendency under electrolyte layer containing SO2 in different thickness was 50,20,200,300 fire.