AZ91D镁合金微弧氧化陶瓷膜的制备及其性能研究

【作者】 肖湘；

【导师】 石西昌；

【作者基本信息】 中南大学 ， 冶金物理化学， 2009， 硕士

【摘要】 镁合金具有密度小、比强度和比刚度高、减震性好、电磁屏蔽性好等特性,具有广泛的应用前景。然而镁合金较差的抗腐蚀能力是制约其发展的主要因素。为了提高镁合金的防腐性能,必须对其表面进行改性。本论文选取AZ91D镁合金为研究对象,采用脉冲电源,在合金表面进行微弧氧化,并对微弧氧化陶瓷膜的制备及其性能进行了详细研究。本文首先选择出了适合于AZ91D镁合金表面微弧氧化的电解液组成。研究结果发现在铝酸盐体系或硅酸盐体系中能够得到性能良好的微弧氧化膜,其中铝酸盐体系中偏铝酸钠为主成膜剂,氢氧化钠为辅助成膜剂,蒙脱石、EDTA、阿拉伯树胶为性能改善剂;硅酸盐体系中硅酸钠为主成膜剂,氢氧化钠为辅助成膜剂,蒙脱石、EDTA、阿拉伯树胶为性能改善剂。对铝酸盐体系的组成进行了优化实验,选出铝酸盐体系主盐组成:偏铝酸钠30g/L,氢氧化钠20g/L。在此基础上,通过单因素和正交实验系统研究了各添加剂对微弧氧化膜层的影响,获得了较佳的添加剂组成为:蒙脱石3g/L、5%阿拉伯树胶50mL/L。采用单因素和正交实验对采用铝酸盐体系的微弧氧化工艺条件进行了优化研究,获得了较佳的工艺成膜条件为:氧化时间为30min、终止电压为180V、脉冲周期为20ms、占空比为50%。研究了硅酸盐体系各配方的组成,得到最优的主盐组成为:硅酸钠30g/L,氢氧化钠20g/L。通过正交实验系统研究了各添加剂对微弧氧化膜层的影响,获得了较佳的添加剂组成:蒙脱石4g/L、EDTA2g/L、5%阿拉伯树胶50mL/L。在硅酸盐体系的最佳组成条件下,对最佳工艺条件进行了研究,获得了最佳的工艺成膜条件为:氧化时间为30min、终止电压为200V、周期为30ms、占空比为40%。借助SEM,EDS、XRD,电化学腐蚀等方法,对最优实验条件下制备陶瓷层的形貌、成分、相组成和耐蚀性等性能进行了测试分析。SEM实验结果表明陶瓷膜表面比较光滑致密,但还是有少量的微孔存在,陶瓷膜纵向断面由内部致密层和外部疏松层组成,致密层组织致密,与基体结合紧密,属于冶金结合;疏松层组织有一些微孔。EDS结果表明电解液中所含的组分参与了微弧氧化成膜反应,电解液中一些原子进入微弧氧化膜层,使得可以通过改变电解液成分、浓度等参数来调整膜层的相组成,这有利于膜层的进一步改性。XRD实验结果表明在铝酸盐体系中,微弧氧化膜层主要由Mg、MgO、MgAl₂O₄和Al₁₂Mg₁₇等组成;在硅酸盐体系中,微弧氧化膜层主要由MgO、Mg₂SiO₄和SiO₂等组成。电化学腐蚀实验结果和浸泡实验结果表明微弧氧化处理后所得膜层显著提高了基体镁合金的耐腐蚀能力。通过两种电解液和工艺参数所形成的微弧氧化陶瓷膜的性能对比研究表明:与硅酸盐体系相比,铝酸盐体系中微弧氧化处理后的膜层具有更优良的耐蚀性。更多还原

【Abstract】 Magnesium alloys have an extensive application foreground because of their low density, high specific strength, high specific stiffness, good shock absorption and good electro-magnetic shielding etc. However magnesium alloys have a poor corrosion resistance that hinders their development. In order to improve the anti-corrosion properties, the surface must be modified. In this paper, AZ91D magnesium alloys had been selected for the study and a pulse power was used. The alloy was treated on the surface by micro-arc oxidation（MAO） process, and ceramic coating was prepared and the performance was studied in details.We initially selected some chemicals for the electrolyte solution which were suitable for MAO on AZ91D Magnesium alloy surface. The result showed that a good MAO film can be performed on AZ91D alloy surface in the aluminate system or silicate system. In aluminate system, NaAlO₂ is the main substance and NaOH is auxiliary into the film. Montmorillonite, EDTA and Arab resin play the role of performance improvement in aluminate system. Na₂SiO₃ is the main substance and NaOH is the auxiliary into the film, and montmorillonite, EDTA, Arab resin play the role of performance improvement in silicate system.The composition of the aluminate system was optimized in the thesis. The optimized main components were: NaAlO₂ was 30g/L, NaOH was 20g/L. On this basis, though a single factor experiment and an orthogonal experiment, the additives of aluminate system on the impact of MAO film were obtained as follows: Montmorillonite was 3g/L, 5%Arab resin was 50mL/L. By a single factor experiment and an orthogonal experiment, the conditions of MAO process were obtained as follows: Oxidation time was 30min, the termination voltage was 180V, pulse period was 20ms and occupy-empty ratio was 50%.The optimized composition of the silicate system was studied. The main components of silicate system were selected: Na₂SiO₃ was 30g/L, NaOH was 20g/L. The additives in the solution of MAO were studied by an orthogonal experiment. The optimized composition of additives are obtained as follows: Montmorillonite was 4g/L, EDTA was 2g/ L and 5% Arab resin was 50mL/L. The conditions of MAO process in silicate solution were obtained as follows: Oxidation time was 30min, the termination voltage was 200V, pulse period was 30ms and occupy-empty ratio was 40%.It was analyzed that morphology, composition, phase composition and corrosion resistance properties of the MAO ceramic layer that was formed in the optimal experimental conditions by SEM, EDS, XRD, electrochemical corrosion and so on. SEM results showed the surface of ceramic coating was relatively smooth and dense, but still existed some small micro-porous. Vertical cross-section of ceramic membrane showed it was composed of an outer loosed layer and an inner compact layer. Owing to the metallurgical bonding, the inner layer had good interfacial connection with the substrate. EDS results showed that the components contained in electrolyte were involved in the MAO film by MAO process. By changing the electrolyte composition, concentration and other parameters, we can adjust the phase composition, which is conducive to the further modification of the film. XRD results showed that in aluminate system, MAO coating are mainly composed of Mg, MgO, MgAl₂O₄, Al₁₂Mg₁₇ and so on. While in silicate systems, MAO coating are mainly composed of MgO, Mg₂SiO₄, SiO₂ and so on. According to results of the electrochemical experiments and the corrosion immersion test, we found the corrosion resistance of MAO film was significantly increased compared with the substance of magnesium alloy. The corrosion resistance of MAO film on AZ91D magnesium alloy surface formed in aluminate solution was better than in silicate solution.更多还原