Mg-Li-Ca表面气相扩散法制备氢氧化镁/硬脂酸复合涂层的耐蚀性能

Corrosion resistance of a magnesium hydroxide/stearic acid composite coating fabricated by vapor diffusion method on Mg-Li-Ca alloy

采用气相扩散法,在Mg-1Li-1Ca镁合金表面制备氢氧化镁/硬脂酸复合涂层,以提高镁合金的耐蚀性能。利用高分辨扫描电子显微镜(SEM)、傅里叶红外光谱仪(FTIR)、X射线衍射仪(XRD)对涂层的表面形貌和化学成分进行表征;通过电化学实验和腐蚀浸泡实验研究复合涂层的耐蚀性能,探讨复合涂层成膜机理和耐蚀机理。结果表明:Mg-1Li-1Ca合金表面氢氧化镁涂层呈紧密排列的花瓣状多孔结构,硬脂酸涂层未明显地改变氢氧化镁涂层形貌;因其具有较低的表面能,表现出良好的疏水性,有效地阻止了腐蚀介质进入涂层内部,增强了涂层的屏蔽作用;氢氧化镁/硬脂酸复合涂层的腐蚀电流密度(1.45×10–7A/cm2)比Mg-1Li-1Ca合金基体腐蚀电流密度(2.70×10–5A/cm2)降低了两个数量级。交流阻抗值表明,此复合涂层的电荷转移电阻约为基体的200倍。说明此复合涂层有效地提高了镁合金的耐蚀性能。

A composite coating of magnesium hydroxide/stearic acid on surface of Mg-1 Li-1 Ca alloy was prepared using vapor diffusion method to improve the corrosion resistance. The surface morphology and chemical composition of the films were characterized by high resolution scanning electron microscopy(HRSEM), Fourier transform infrared spectrometer(FTIR) and X-ray diffraction analysis(XRD). Electrochemical experiments and immersion test were conducted to study corrosion resistance of the obtained composite coating.The formation and degradation mechanisms of the composite coating were proposed.The results show that the magnesium hydroxide coating has a petal-like structure and is well-adhered to the surface of Mg-1 Li-1 Ca alloy.The stearic acid coating does not change the petal-like structure of the magnesium hydroxide coating. However, the stearic acid can effectively prevent the aggressive medium penetrating into the internal coating due to its low surface energy and good hydrophobicity.The corrosion current density of the magnesium hydroxide/stearic acid(Mg(OH) 2/SA) composite coating(1.45 × 10–7 A/cm2) is decreased by two orders of magnitude compared to that of the Mg-1 Li-1 Ca alloy substrate(2.70 × 10–5 A/cm2), leading to the enhanced corrosion resistance of magnesium alloy.