碳纳米管增强镁基复合材料的组织性能及变形行为研究

发布时间：2018-02-02 16:58

  本文关键词： 镁合金 碳纳米管 复合材料 伸长率 热压缩 动态再结晶　出处：《湖南大学》2015年硕士论文　论文类型：学位论文

【摘要】：金属镁及其合金具有一系列优异的性能,是一种极具前途的轻质金属结构材料。近年来,随着各行业的不断发展,对镁合金材料的性能提出了越来越苛刻的要求,并相继发展了高强镁合金、阻燃镁合金和耐热镁合金等高性能镁合金。与此同时,很多领域要求材料兼顾强度、塑性、耐热及耐蚀等多方面的综合性能。因此,研制和开发具有优异综合性能的新型镁合金及其复合材料具有重要意义。本文以进一步改善镁合金的综合性能为目标,选择具有较佳综合性能的Mg-Mn-Ce-Zn四元合金为基体,用搅拌铸造法制备碳纳米管(CNTs)增强镁基复合材料。采用金相观察、电子能谱、断口扫描、透射电镜、差热分析及电化学分析和热模拟等手段,较系统地研究了复合材料的微观组织、力学性能、耐蚀性能及热变形行为,并对复合材料的强韧化机理、耐蚀机理、断裂机制及热变形过程中的组织变化规律进行了探讨和分析。首先,研究了CNTs/Mg-1.3Mn-1.0Ce-4.0Zn复合材料的显微组织、力学性能、时效行为及耐蚀性能。对显微组织和力学性能的研究发现,添加CNTs后基体合金的晶粒组织得以细化,晶粒形貌及第二相的分布特征发生改变,铸态晶粒组织逐渐由等轴状转变为树枝状,晶内第二相的数量增加。随着CNTs添加量的增大,复合材料的室温强度和伸长率均呈先增大后减小的趋势。当CNTs添加量为0.5%时,复合材料的性能最佳,其铸态下的室温抗拉强度和断后伸长率分别达212.2MPa和21.1%,与基体合金相比分别增加了8.5%和37.5%。对时效行为的研究表明,添加CNTs后基体合金的峰值时效硬度提高,并且达到峰值时效硬度所需的时间缩短。电化学极化曲线结果显示,添加CNTs后基体合金的自腐蚀电位升高、电流密度降低,其耐蚀性能得到改善。其次,在Gleeble-3500热模拟试验机上对0.5%CNTs/Mg-1.3Mn-1.0Ce-4.0Zn复合材料进行了热压缩实验。对复合材料热变形行为的研究发现,变形温度和应变速率是影响其流变应力的关键因素,该材料在热变形过程中的流变应力模型可以用含Z(Zener-Hollomon)参数的双曲正弦方程表示,其中应变硬化指数n值和变形激活能Q值分别为9.23和207.19kJ/mol。对不同热变形条件下复合材料微观组织的研究表明,变形温度和应变速率对复合材料的热变形组织形貌及晶粒尺寸均具有重要影响。在较低温度(200～250℃)下压缩时,形变组织以纤维组织和孪晶为主,孪晶之间的交错程度随应变速率的增大而增强；在较高温度(300-400℃)下压缩时发生连续动态再结晶,再结晶程度随应变速率的增大而加剧,晶粒尺寸随应变速率的增大而减小,当变形温度为400℃和初始应变速率为10s-1时,复合材料具有细小均匀的动态再结晶晶粒组织。
[Abstract]:Metal magnesium and its alloys have a series of excellent properties, and they are a kind of light metal structural materials with great prospect. In recent years, with the development of various industries. High strength magnesium alloys, flame retardant magnesium alloys and heat resistant magnesium alloys have been developed. At the same time, the strength of materials is required in many fields. Plastic, heat and corrosion resistance and other aspects of the comprehensive properties. It is of great significance to develop new magnesium alloys and their composites with excellent comprehensive properties. This paper aims to further improve the comprehensive properties of magnesium alloys. Carbon nanotubes (CNTs) reinforced magnesium matrix composites were prepared by agitation casting with Mg-Mn-Ce-Zn quaternary alloy with better comprehensive properties. Metallographic observation and electron spectroscopy were used. The microstructure, mechanical properties, corrosion resistance and thermal deformation behavior of the composites were systematically studied by means of fracture scanning, transmission electron microscopy, differential thermal analysis, electrochemical analysis and thermal simulation. The strengthening and toughening mechanism, corrosion resistance mechanism, fracture mechanism and microstructure change during hot deformation of the composites were discussed and analyzed. The microstructure, mechanical properties, aging behavior and corrosion resistance of CNTs/Mg-1.3Mn-1.0Ce-4.0Zn composites were studied. After the addition of CNTs, the grain structure of the matrix alloy was refined, the grain morphology and the distribution of the second phase changed, and the as-cast grain structure gradually changed from equiaxed to dendritic. With the increase of CNTs content, the room temperature strength and elongation of the composites increased first and then decreased. When the content of CNTs was 0.5%. The tensile strength at room temperature and the elongation after break of the composites were 212.2 MPA and 21.1% respectively. Compared with the base alloy, the aging behavior of the alloy increased by 8.5% and 37.5, respectively. The results show that the peak aging hardness of the matrix alloy increases with the addition of CNTs. The electrochemical polarization curve showed that the corrosion potential of the matrix alloy increased, the current density decreased, and the corrosion resistance was improved after the addition of CNTs. The thermal compression experiments of 0.5 CNTs / Mg-1.3 Mn-1.0Ce-4.0 Zn composites were carried out on a Gleeble-3500 thermal simulator. The study of formalism found. Deformation temperature and strain rate are the key factors affecting the flow stress. The rheological stress model of the material during hot deformation can be expressed by the hyperbolic sinusoidal equation with ZAZener-Hollomon parameters. The strain hardening exponent n and the deformation activation energy Q are 9.23 and 207.19kJ / mol, respectively. The deformation temperature and strain rate have an important effect on the morphology and grain size of the composites. When the deformation temperature is 200 ~ 250 鈩，

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