【作者】 高会会；

【导师】 吴松全；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2008， 硕士

【摘要】 本文采用微弧氧化单脉冲直流电源,在AZ91D镁合金上制备了含氧化锆相的陶瓷膜层,研究了电解液浓度和电参数对陶瓷膜及其耐蚀性的影响规律,分析了陶瓷膜的生长特点,测试了陶瓷膜与碳纤维等异种材料偶接的电偶腐蚀性能。利用X射线衍射分析(XRD)、X射线散射能谱(EDS)分析及扫描电子显微镜(SEM)分析技术研究了陶瓷膜的组成及形貌;涡流测厚仪测定陶瓷膜的厚度,电化学分析技术研究了陶瓷膜的耐腐蚀性能。XRD和EDS结果表明:通过微弧氧化技术在AZ91D镁合金表面制备的陶瓷膜层中引进了锆、镁元素,锆相对含量较高,且大多以晶相存在于陶瓷膜层中;而镁的含量相对较低。SEM研究表明:在单脉冲条件下,随着电解液浓度的提高,膜层变粗糙;电流密度越大,膜层越粗糙,表面裂纹越多;低电源频率下的膜层比较平整,裂纹少,较致密。陶瓷膜的结构是典型的双层结构,由内层致密阻挡层和外层多孔疏松层组成。膜层生长前期双层结构不明显,生长后期膜层向基体内部发展,以及电解液反应沉积的加快,使阻挡层和疏松层的厚度都增大,膜层的双层结构明显。陶瓷膜的结构对膜层的耐蚀性有很大的影响。Na5P3O10浓度的增加,陶瓷膜厚度先减小后增加,膜层耐蚀性呈相反规律,当Na5P3O10浓度为3g·L-1时膜层的耐全面腐蚀性能最好;而随K2ZrF6浓度的提高,膜层厚度随之增加,膜层变致密,耐蚀性提高。电流密度增加使陶瓷膜厚度增加,但是膜层表面裂纹变大,耐蚀性下降;低电源频率下,膜层较薄,但表面裂纹少,有利于陶瓷膜耐蚀性的提高。电源频率为100Hz时的膜层耐蚀性最好。经微弧氧化处理后,陶瓷膜的电偶腐蚀电流密度减小,电偶腐蚀性能比镁合金基体的提高。在两种偶接材料中,虽然与M40碳纤维偶接的热力学腐蚀倾向大,但电偶腐蚀电流密度较小,在13μA·cm-2左右。与LY12铝合金偶接的电偶腐蚀电流密度很大,达到80μA·cm-2,陶瓷膜破坏严重,LY12铝合金也有一定程度的腐蚀,陶瓷膜不能与LY12铝合金接触使用。更多还原

【Abstract】 Ceramic coatings including ZrO2 were prepared on surface of AZ91D magnesium alloy by micro-arc oxidation (MAO) with single-polar anode pulse MPO power source. The thickness, composition, structure and galvanic corrosion property of the coatings were investigated.The composition and microstructures of the ceramic coatings were characterized by X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). The thickness and corrosion resistance of the coatings were evaluated by eddy current thickness meter, and electrochemical instrument respectively.The results of EDS and XRD analyses revealed that the zirconium and magnesium were brought into the ceramic coatings prepared on the surface of AZ91D magnesium alloy by micro-arc oxidation (MAO) with different electric parameters and electrolyte. Zirconium is crystalline in the coating. The results of SEM showed that the coating became cruder as the concentration of electrolyte increasing. The coating prepared by low current density and low frequency is of flatness, crackles, and compactness. The ceramic coating was representatively double-layer structure. It included compact barrier layer and pores layer. The double-layer structure was unconspicuous in early period. In the later period of MAO, the growth of the coating developed towards to Mg substrate direction. The thickness of barrier layer and pores layer increased rapidly. The ceramic coating appeared double-layer structure obviously.The corrosion resistance of ceramic coating was greatly affected by the structure of coating. The study showed that the thickness of the ceramic coatings first decreased and later increased with the Na5P3O10 concentration increasing, but the corrosion resistance of coatings changed contrary. As the K2ZrF6 concentration increasing, the coating was thicker and much more compact, the corrosion resistance of coating enhanced. With the current density increasing, the crackle of the coating was larger, and the corrosion resistance of coatings became worse. The low frequency could help enhancing the corrosion resistance of coatings.Comparing with the mg alloy substrate, the galvanic corrosion current of ceramic coating was lower, the property of galvanic corrosion enhanced. Between two coupled materials, the corrosion tendency of coating coupled with M40 carbon fiber was larger, but the corrosion current was lower, so the ceramic coating could couple with M40 carbon fiber in practical application. Coupling with LY12Al alloy, the galvanic corrosion current was greatly high, and the destruction of coating was serious. Ceramic coating was impossible to couple with LY12Al alloy in practical application.更多还原