【作者】 王辛；

【导师】 胡连喜；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2013， 博士

【摘要】 镁合金材料由于其比强度高、比刚度大、易于回收利用等一系列的优点而在航空、航天、汽车、电子工业等领域得到了广泛的应用。超细晶材料具有优异的物理、化学和力学性能，已经成为材料科学领域研究开发的重点和热点之一。基于镁合金材料和超细晶材料的特点，本文提出一种有效制备块体超细晶AZ31镁合金材料的工艺方法，主要工艺流程为：纳米晶AZ31镁合金粉末—冷压—真空热压—包套挤压等，其中获取纳米晶AZ31镁合金粉末、寻找真空热压和包套挤压最佳工艺参数是制备超细晶AZ31镁合金材料的关键环节。此外，超细晶AZ31镁合金材料的室温力学行为与高温力学行为显著不同于常规AZ31镁合金材料，因而，建立超细晶AZ31镁合金材料力学行为模型具有重要理论意义和指导意义。研究了纳米晶AZ31镁合金粉末的粒度、形貌、微观特征和组织热稳定性，探讨了纳米晶AZ31镁合金粉末的晶粒长大行为，计算得出晶粒长大动力学常数n值、k值和晶粒长大激活能G值，为后续的真空热压、包套挤压、轧制工艺提供理论依据；其次利用黄培元双对数压制方程研究了纳米晶AZ31镁合金粉末的压制特性，指导纳米晶AZ31镁合金粉末的冷压制实验；再次，采用数值模拟和试验研究相结合的方法探讨了工艺参数对真空热压和包套挤压过程的影响规律，最终确定制备超细晶AZ31镁合金材料的最佳工艺参数，从而获得性能优异的全致密超细晶AZ31镁合金材料。研究了超细晶AZ31镁合金材料的组织热稳定性、晶粒长大动力学和晶粒长大机制，确定了超细晶AZ31镁合金材料的最佳热加工温度；探讨了晶粒尺寸对超细晶AZ31镁合金材料组织和力学性能的影响规律，研究结果表明超细晶AZ31镁合金材料的晶粒尺寸对抗拉强度、屈服强度及硬度有着显著的影响，并且对于超细晶AZ31镁合金材料来说，其屈服强度与晶粒尺寸之间依然很好地符合Hall-Petch关系。研究了超细晶AZ31镁合金材料的力学行为与变形机制，室温条件下采用包套挤压获得的超细晶AZ31镁合金棒材，其抗拉强度为382MPa，屈服强度为278MPa；而轧制态超细晶AZ31镁合金板材抗拉强度为435MPa，屈服强度为330MPa，并且抗拉强度和屈服强度都随着应变速率的增加而增加，表明超细晶AZ31镁合金材料为正应变速率敏感性材料。采用Gleeble-3500热力模拟试验机上进行高温拉伸试验，研究了变形温度为190°C-250°C、应变速率为5×10^-4s^-1-5×10^-3s^-1时，超细晶AZ31镁合金材料热拉伸塑性变形时的力学行为与变化规律。分析了超细晶AZ31镁合金材料热拉伸变形时流变应力与变形程度、应变速率以及变形温度三者之间的函数关系，计算了应力指数和变形激活能，确定了高温热变形时的材料常数，建立了超细晶AZ31镁合金材料高温塑性变形时流变应力与应变之间的本构方程数学模型，为合理制定超细晶AZ31镁合金材料热加工工艺提供理论依据和参考，同时探讨了超细晶AZ31镁合金材料的超塑性变形机制。更多还原

【Abstract】 Magnesium alloys have been widely used in areas such as aerospace, automotive,electronics due to their high strength, stifness, easier to recycle and a series of advantages.Block magnesium alloy materials with ultra-fine grained microstructure have excellentphysical, chemical and mechanical properties, which is one of the research hot spots inmaterial area. This paper proposes an efective way to prepare block ultra-fine magnesiumalloy and the main technological process: nanocrystalline powder-cold pressing-vacuumhot pressing-extrusion-rolling. Extrusion and rolling are the key points to prepare ultra-fine grained materials. In addition, the mechanical behaviors of ultra-fine grained AZ31magnesium alloy are significantly diferent from conventional materials at room temper-ature and high temperature. It is very important to establish the model of mechanicalbehavior of ultra-fine grained materials.Research on grain degrees, morphology, microstructure and hot stability of nanocrys-talline AZ31magnesium alloy powder. The grain sizes increase with annealing tempera-ture and annealing time increasing. Discussion has been done on grain growth behavior ofnanocrystalline AZ31magnesium alloy powder. The grain growth index n and activationenergy G have been calculated, which shows as the basic work for the following vacuumhot pressing, extrusion and rolling. Studying on cold compactability of nano-grain mag-nesium alloy powder by Huang Peiyun compaction equation as experiment instruction ofcold pressing, hot pressing and extrusion, ultimately determined for nanocrystalline mag-nesium alloy powder preparation method of ultra fine-grained AZ31magnesium alloymaterials, optimizing the process parameters, to compact ultra fine-grained AZ31magne-sium alloy materials.Research on microstructure stability of ultra-fine AZ31magnesium alloy to deter-mine the optimum temperature of hot working process. Discussion on the efect of dif-ferent grain size on microstructure and properties and the results show the grain sizes ofAZ31magnesium alloy significantly efect the yield strength and the hardness. For theultra-fine grained AZ31magnesium alloy, its yield strength and grain size are still goodto meet traditional of Hall-Petch relationship.Research on mechanical behavior and deformation mechanism of ultra-fine magne-sium alloy. Preparation of ultra-fine grained AZ31magnesium alloy rod by extrusion at diferent temperature and its tensile strength at room temperature is382MPa, yieldstrength is278MPa. Rolled ultra-fine grained AZ31magnesium alloy sheet shows tensilestrength at room temperature is435MPa and yield strength is330MPa. Ultra-fine grainedAZ31magnesium alloy is strain rate sensitivity material for yield strength increasing withthe strain rate increasing.Gleeble-3500drawing simulation testing machine is taken to study on mechanicalbehavior of ultra-fine AZ31magnesium alloy at high temperature. An Analysis on hotflow stress with the deformation degree, tensile deformation strain rate and deformationtemperature have been done. Establishing the constitutive equations of flow stress, strainand Zener-Hollomon parameters to determine the material constants of thermal deforma-tion. Proposing reasonable thermal processing technology reference for hot working ofultra-fine grained AZ31magnesium alloy. Discussion on superplastic deformation mech-anisms of AZ31magnesium alloy materials and the establishment of appropriate models.更多还原