【作者】 王泽鑫；

【导师】 芦笙；

【作者基本信息】 江苏科技大学 ， 材料学， 2011， 硕士

【摘要】 微弧氧化技术是一项从传统阳极氧化基础上发展起来具有较好应用前景的表面处理技术。国内外对镁合金微弧氧化技术的研究主要集中在AZ系和AM系,对变形Mg-Zn-Zr系的研究很少,并且这些研究主要集中在单一的主成膜剂中。本课题以ZK60变形镁合金作为基体材料,在恒流微弧氧化模式下开发出了新型复合电解液工艺体系,并对微弧氧化膜层的组织和性能进行了分析,探讨了膜层形成机理。实验开展了以下几个方面的工作并取得了创新性成果:首先,将微弧氧化主成膜剂铝酸盐、磷酸盐和硅酸盐分别按一定比例两两混合,通过对膜层厚度、耐蚀性的分析测试,得出较优的复合电解液体系,即铝酸钠-磷酸钠体系,在此复合电解液体系下进行后续试验。其次,通过系列单变量实验分别研究了复合电解液中的各个组分浓度变化对镁合金微弧氧化过程电压、膜层厚度、微观形貌以及膜层耐腐蚀性能的影响规律,确定了电解液各组分浓度的最佳值,以此为基础,通过正交实验优化出最佳配方:即铝酸钠12.5g/L,磷酸钠5g/L,氢氧化钠3g/L,硼酸钠2g/L,柠檬酸钠3.6g/L。在优化的复合电解液配方下,通过系列单变量实验分别研究了电参数的各个变量对镁合金微弧氧化过程电压、膜层厚度、微观形貌以及膜层耐腐蚀性能的影响规律,确定出较优的电参数,并在此基础上进行正交优化实验,最后得到的最优电参数:即电流密度22A/dm²,频率500Hz,占空比38%,微弧氧化时间15min。通过SEM、XRD、EDS等手段对优化工艺下制备的微弧氧化膜层微观组织结构进行了分析,并探讨了微弧氧化的形成机理。结果表明:恒流方式下,膜层的生长过程主要经历了钝化膜生成阶段,微弧氧化快速生长阶段,以及微弧氧化电压微降阶段和微弧氧化细小火花放电阶段,最终形成表面较为致密的膜层。优化工艺参数下制备的微弧氧化膜层表面均匀致密,其中主要物相为尖晶石结构的MgAl₂O₄和方镁石结构的MgO。最后,通过电化学实验、硬度实验、摩擦磨损实验、划格实验和划痕实验等测试手段,测试了优化膜层的耐腐蚀性、硬度、耐磨性以及膜层结合力等性能,结果表明:优化后膜层与基体相比,耐蚀性大幅提高。膜层表面平整致密,有光泽,粗糙度较低。膜层的硬度为基体的7倍左右;且膜层具有较好的耐高温性和耐磨性。膜层与基体的结合力达到一级标准,通过划痕实验表明膜层与基体的临界结合力为13.85N。更多还原

【Abstract】 Micro-arc oxidation （MAO）, as a novel and unique surface treatment technique based on anodic oxidation, has been used for surface modification of many metals. At present, MAO researching of magnesium alloys mainly focus on AZ and AM alloys, but few about Mg-Zn-Zr alloys such as ZK60. In this paper, a new dual electrolyte system was developed under constant current micro-arc oxidation mode and the microstructure and composition of the coating were analyzed by modern surface analysis methods such as SEM, EDS, XRD. Some valuable researches about ZK60 have been carried out and some innovative results have been obtained.Firstly, Micro-arc oxidation （MAO） process was carried out in a dual electrolyte system of NaAlO₂-Na₃PO₄ and NaAlO₂-Na₂SiO₃ and Na₂SiO₃-Na₃PO₄ respectively. Test of weight loss was conducted at a 3.5%NaCl solution to assess the resistance to corrosion. The results reveal that the best dual electrolyte system is NaAlO₂-Na₃PO₄.Secondly, by means of single variable experiments, the effect of every element of the dual electrolyte system on voltage-time responses during MAO process and the coating characteristic was analyzed and discussed systematically. Combined with the orthogonal experiment an optimized dual electrolyte system was developed, which composes of 12.5g/L NaAlO2, 5g/L Na₃PO₄, 3g/L NaOH, 2g/L NaB4O7 and 3.6g/L C₆H₅Na₃O₇.The optimized electronic parameters are current density:20 A/dm²; power frequency: 500Hz; duty cycle ratio: 38%; oxidation time: 15min.The microstructural characteristics of coating were investigated by XRD and SEM coupled with EDS. Studies have shown that the optimized micro-arc oxidation coating growth process is mainly composed of the following stages: anodic oxidation stage, micro-arc oxidation stage, voltage droping stage and tiny spark discharge stage, The coating prepared with the optimized process parameters was characterized with compact, smooth, glossy, colorful and exquisite surface. The main phase of surface of Coating is MgAl₂O₄ and MgO phase.The optimized coating in the electrochemical experiments exhibited higher impedance value. In addition, The microhardness test results show that the coating’s microhardness is 726HV, the wear resistance test results show that friction coefficient of optimized MAO coating decreases with increasing of loads under the condition of dry sliding wear. The adhesion test results showed that the bonding between coating and substrate achieve the top 1 level of corresponding standard.更多还原