纯镁和Mg−14Li合金耐蚀性与表面膜的对比

Comparison on corrosion resistance and surface film of pure Mg and Mg−14Li alloy

采用析氢实验、失重实验、电化学实验、原位电化学拉曼光谱实验以及显微组织观察(光学与扫描电子显微镜)等实验方法,对比研究密排六方结构(HCP)的纯镁和体心立方结构(BCC)的二元Mg−14Li合金(质量分数,%)在0.1 mol/L NaCl溶液中的腐蚀行为与表面膜结构。实验结果表明:纯镁的耐蚀性优于Mg−14Li合金的,并且两种材料表面膜的保护功能均随着浸泡时间(16 h内)的延长而提高。通过扫描电子显微形貌分析,发现不同于纯镁表面形成的较薄且呈片状的Mg(OH)2膜层,Mg−14Li合金表面形成较厚且呈交织针状含有Li2CO3的膜层;然而,两种材料的表面膜均在高的阳极过电位下发生破损。因此,两种材料的不同腐蚀抗性可归功于在其表面形成不同的保护膜。

To study different corrosion resistances and surface film types of hexagonal close-packed(HCP)pure Mg and body-centered cubic(BCC)Mg−14wt.%Li alloy in 0.1 mol/L NaCl,a series of experiments were conducted,including hydrogen evolution,mass loss,in-situ electrochemical testing combined with Raman spectroscopy and microstructural observation.The results indicate that the corrosion resistance of pure Mg is superior to that of Mg−14Li,and the protective function of the surface films on both magnesium systems is elevated within 16 h of immersion in 0.1 mol/L NaCl.An articulated,thick,and needle-like surface film containing Li2CO3 on Mg−14Li,different from the typically thin,flaky Mg(OH)2 film on pure Mg,is confirmed via scanning electron microscopy(SEM).However,both surface films can be broken down at a high anodic over-potential.Thus,different corrosion resistances of the two Mg systems are ascribed to various protective films forming on their surfaces.