西沙严酷海洋大气环境下AZ31镁合金的长周期腐蚀行为

通过现场暴露实验，研究了AZ31镁合金在西沙海洋大气环境下暴露4 a的长周期腐蚀行为.利用扫描电镜观察表面、截面的腐蚀产物以及去除腐蚀产物后的腐蚀形貌，并用能谱分析及X射线衍射仪对腐蚀产物的元素含量及相组成进行分析.研究结果表明，AZ31镁合金在西沙海洋大气环境下发生了较为严重的腐蚀，4 a内的平均腐蚀速度为11.95μm·a-1.Cl-和CO₂在镁合金的腐蚀过程中起着至关重要的作用.吸附液膜中的Cl-主要破坏镁合金的保护膜，使镁合金发生阳极溶解；而CO₂则会中和阴极反应产生的碱性离子并与Mg（OH）2发生反应生成含不同结晶水的Mg₅（CO₃）₄（OH）₂·xH₂O表层腐蚀产物.由于表层腐蚀产物阻挡了CO₂和Cl-向镁合金表面的传输，靠近基体处的腐蚀产物主要为Mg（OH）₂. 

Long-term corrosion behavior of AZ31 magnesium alloy in Xisha marine atmosphere

By field exposure test, atmospheric corrosion tests of AZ31 magnesium alloy were conducted in Xisha Islands for 4 a. The surface and cross-section morphologies of corrosion products as well as the corrosion morphologies of the alloy after removing corro-sion products were observed by scanning electron microscopy. Energy dispersive X-ray spectroscopy and X-ray diffraction analysis were used to obtain the element content and phase composition of corrosion products. The results indicate that the alloy undergoes severe corrosion. The average corrosion rate is 11.95μm·a-1. Cl- and CO₂ play important roles in the corrosion process. The Cl-—containing absorbed electrolyte layers will destroy the oxidation film and induce anodic dissolution of the alloy. While CO₂ dissolved in the absorbed electrolyte layers tends to neutralize the alkali formed in the cathodic area and reacts with Mg (OH) 2 to form Mg₅(CO₃)₄(OH)₂·xH₂O. The surface corrosion products restrict the transport of CO₂ and Cl- to the surface of the alloy, so the inner layer of corrosion products is mainly composed of Mg(OH) 2.