【作者】 陈博；

【导师】 李青；

【作者基本信息】 西南大学 ， 无机化学， 2009， 硕士

【摘要】 镁合金作为21世纪的绿色工程材料,不但具有良好的导电性、导热性、阻尼性、尺寸稳定性和电磁屏蔽性等性能,还具有很好的铸造和切削加工性能,因而在许多领域得到广泛的应用。但镁合金的化学稳定性差,在使用环境中容易发生氧化,特别是在酸性环境和含Cl^-,Br^-,SO₄^2-等离子的盐溶液中会发生严重的腐蚀,大大影响了其应用范围。因此对镁合金材料的表面防护技术研究具有十分重要的理论价值及实际意义。目前增强镁合金耐蚀性最有效、最简便的途径是对其进行表面涂层处理。涂层在基体和外界环境之间形成一个有效的屏障,以达到抑制和缓解镁合金材料腐蚀的目的。本文在综述了近年来压铸型镁合金材料腐蚀机理和防护处理研究的基础上,通过适当的前处理,再通过溶胶-凝胶法在镁合金表面制备耐蚀性良好的氧化物陶瓷涂层的方法对AZ91D镁合金进行表面防护研究。本论文的主要研究内容和结论如下:以醋酸锆为前驱物,无水乙醇为溶剂,添加适量的表面活性剂,采用溶胶-凝胶法在经锡酸盐转化前处理的AZ91D镁合金表面首次成功制备了ZrO₂陶瓷涂层。采用X射线衍射、扫描电镜表征了涂层的结构和形貌,通过动电位极化曲线测试和电化学阻抗测试探讨了ZrO₂陶瓷涂层的耐腐蚀性能。结果表明:（1）前驱物锆浓度为0.08mol·L^-1,溶剂与表面活性剂的体积比为8:2,中速搅拌回流6小时,得到稳定透明的溶胶;（2）通过研究得到的最佳涂层制备工艺在AZ91D镁合金表面制备了耐蚀性能良好的ZrO₂陶瓷涂层。锡酸盐转化膜的成分主要是MgSnO₃·H₂O,呈现晶态结构特征。ZrO₂溶胶,经过400℃下2小时热处理后形成了ZrO₂陶瓷涂层,其主要呈四方型晶态结构且其平均晶粒尺寸为10 nm。研究在AZ91D镁合金表面形成无毒致密、无污染的CeO₂陶瓷涂层来解决AZ91D镁合金的腐蚀问题。讨论了转化液组成、稀土铈转化膜形貌等因素的影响,得到了稀土铈转化液的最佳配方。采用金相显微镜（OM）、SEM、XRD、动电位极化曲线测试和电化学阻抗测试表征了转化膜和涂层成膜性及耐蚀性能。结果表明:CeO₂陶瓷涂层可有效地对AZ91D镁合金进行腐蚀保护。为了提高AZ91D镁合金的耐蚀性能,在已有的研究基础上,结合植酸转化工艺和溶胶-凝胶工艺的优点,在镁合金材料表面制备出Al₂O₃耐蚀性陶瓷涂层。采用热分析、红外测试、扫描电镜测试、X射线衍射、X射线能谱、接触角测试、动电位极化曲线测试、电化学阻抗测试等手段表征膜层的结构及性能。结果表明:（1）植酸转化膜主要由C、O、Mg、Al、P几种元素组成,这几种元素在膜层表面不同位置的重量百分含量大体一致,植酸转化膜在镁合金表面均匀分布。这为后续形成均匀的Al₂O₃陶瓷涂层打下了良好的基础;（2）当涂层的热处理温度达到280℃时,Al₂O₃涂层开始由非晶态向晶态转变。与经过120℃和280℃处理的Al₂O₃涂层相比,经380℃下热处理形成的Al₂O₃陶瓷涂层具有最佳的耐蚀性能。为在AZ91D镁合金表面制备耐蚀性能优异的防护层,在AZ91D镁合金表面实施具有一定功能梯度的涂层。先应用植酸转化工艺在AZ91D镁合金表面制备植酸转化膜,将其作中间过渡层,再应用溶胶-凝胶法,在植酸转化膜表面制备CeO₂陶瓷涂层。采用扫描电镜测试、X射线衍射、X射线能谱、接触角测试、动电位极化曲线测试、电化学阻抗测试等手段表征膜层的性能。结果表明:（1）CeO₂陶瓷涂层的最佳制备工艺参数为:旋涂速度为1000 rpm时,涂敷两层0.5 M CeO₂溶胶的试样,在280℃下热处理制得的CeO₂陶瓷涂层对镁合金具有最好的防护效能;（2）在CeO₂陶瓷涂层表面有明显裂纹处还是不明显裂纹的位置,其Mg、O、Ce元素的重量百分含量基本是一致的,P和Al元素消失。表明镁合金表面已完全被CeO₂陶瓷涂层均匀覆盖。涂层表面裂纹都是浅表性的,没有到达到植酸转化膜;（3）该具有一定功能梯度的涂层能大幅提高AZ91D镁合金的耐蚀性能。更多还原

【Abstract】 Magnesium alloys, as the 21st green engineering material, present a wide range of applications due not only to their better electrical conductivity, high thermal conductivity, high dimensional stability and good electromagnetic shielding characteristics, but also their good cast ability and good welding ability. Unfortunately, it is prone to oxidation in common environments, especially in the acidic environments and in salt-water conditions containing Cl^-, Br^-SO₄^2- and so on, which leads to a severe erosion. Poor corrosion resistance is the obstruction to broaden applications of magnesium alloys. So it is very important to study the surface anti-corrosion technology of magnesium alloys.At present, surface coating treatment on the magnesium alloys is one of the most effective and simple ways. The coating employed between the substrate and the environment could offer an effective barrier to improve its corrosion resistance. In this thesis, anti-corrosion technologies of magnesium alloys were investigated. Based on corrosion mechanism and anticorrosion treatment of magnesium alloys, through some appropriate pre-treatment, and then the oxide ceramic coatings were prepared on the AZ91D magnesium alloy surface through sol-gel method. The main contents and conclusions in this paper are as follows:The ZrO₂ ceramic coatings were first successfully prepared on the stannate-coated AZ91D magnesium alloy surface by sol-gel method taken zirconium acetate as precursor, anhydrous ethanol as solvent and proper surfactant. The morphology and structure of the coatings were investigated by SEM and XRD. The potentiodynamic polarization curves and EIS were employed to characterize the anti-corrosion properties of the coatings. The results indicated that: （1） Transparent steady sol was achieved by keeping the concentration of zirconium at a range of 0.08 mol/L^-1 and the volume ratio of solvent and surfactant at 8:2; （2） Anti-corrosion ZrO₂ ceramic coatings were obtained on AZ91D magnesium alloy surface through the optimal technique parameters. The chemical conversion coating was mainly consisted of MgSnO₃·H₂O. The ZrO₂ sol sintered at 400℃for 2 h turned into nanocrystalline ZrO₂ ceramic coating. The ZrO₂ ceramic film was mainly composed of tetragonal phase ZrO₂ and the average grain size of crystalline ZrO₂ was 10 nm.The nonpoisonous, compact and friendly CeO₂ ceramic coatings had been successfully prepared on AZ91D magnesium alloy surface to improve its corrosion resistance. The effect factors on the preparation of cerium-based conversion coating such as the different composition of the reacted solution, surface morphology and so on were investigated. The optimal technique parameters of the reacted solution were filtrated. The preparation and anticorrosion properties of the conversion coatings and CeO₂ ceramic coatings on AZ91D magnesium alloy surface were analyzed by OM, SEM, XRD, EIS test and potentiodynamic polarisation curve test. The results showed that the corrosion resistance of AZ91D magnesium alloy was found to be greatly improved by means of this novel environmental-functionally CeO₂ ceramic coatings.To improve the corrosion resistance of AZ91D magnesium alloy, on the basis of quondam experiments, we successfully combined the advantage of phytic-acid conversion coating and sol-gel technology, a novel anti-corrosion sol-gel based A1₂O₃ ceramic coating was developed on the AZ91D magnesium alloy. The performance of the coatings were investigated by TG-DTA, FT-IR, SEM, XRD, EDS, Contact angles test, EIS test and potentiodynamic polarisation curve test. The results indicated that: （1） The phytic-acid chemical conversion coating was mainly composed of C, O, Mg, Al and P. The weight percents of C, O, Mg, Al and P were roughly in line on different places of the coating, indicating that the phytic acid conversion coating could be homogeneously formed on the magnesium alloy. This provided good conditions for the preparation of the follow-up homogeneous Al₂O₃ ceramic coating. （2） The Al₂O₃ gel begun to transformate from amorphous to crystalline phase when the sintering temperatures was 280℃. The Al₂O₃ sol-gel coated specimen sintered at 380℃had the best corrosion resistance properties as compared to the specimens sintered at 120℃and 280℃.A functional gradient coating was prepared on the AZ91D magnesium alloy surface to improve corrosion resistance of AZ91D magnesium alloy. The phytic acid conversion coating was employed as chemical pre-treatment and a barrier to environment before applying the sol-gel-based CeO₂ ceramic coating. The performance of the coatings were investigated by SEM, XRD, EDS, Contact angles test, EIS test and potentiodynamic polarisation curve test. The results indicated that: （1） The optimal technique parameters of the functional gradient coating were 0.5 M CeO₂ sol, two layers obtained for sol-gel spin-coating process with the speed of 1000 rpm on phytic-acid chemical-pretreated specimens and the sintered temperature was 280℃. （2） The weight percents of C,O, Ce were nearly equivalent no matter where cracks were seriously or the coatingss were relatively compact, P and Al disappeared in the functional gradient coating, which indicated that the magnesium alloy substrates were fully and homogeneously covered by the functional gradient coating. The uniformly distributed micro-cracks in the CeO₂ ceramic coating were lobed, didn’t reach the phytic acid conversion coating. （3） The anticorrosion properties of the AZ91D magnesium alloy were improved greatly by the functional gradient coating.更多还原