搅拌摩擦加工对AZ31镁合金微观组织和性能改性的研究

发布时间：2018-07-17 07:37

【摘要】：镁合金是目前能够实际应用的最轻的金属结构材料,具有比强度高、电磁屏蔽性强、阻尼性能好等优异的性能。然而由于具有密排六方的晶体结构,其对称性较低,其塑性加工性能较差,这也限制了镁合金更加广泛的应用。大量研究结果表明,晶粒细化能够同时提高镁合金的强度和塑性,对于改善镁合金的成形性能有着重要的作用。搅拌摩擦加工方式作为一种大塑性变形手段,能够起到有效细化镁合金晶粒组织的作用。本文较为系统的研究了AZ31镁合金搅拌摩擦加工过程的微观组织演变规律,以及该加工方式对室温力学性能的改性规律;并对搅拌摩擦加工后的板材进行了热轧实验;利用透射电镜、扫描电镜EBSD对轧制过程中的孪生、位错滑移以及动态再结晶行为进行了研究。研究结果表明,搅拌摩擦加工细化了原始的晶粒组织,使基面织构得以弱化,提高了材料的抗拉强度和塑性,但屈服强度有所降低。热轧实验结果显示,轧制过程应变较小的阶段,窄片状的?孪晶起主导作用,孪晶区域出现了局部动态再结晶现象;随着应变量的增加,晶界处开始发生动态再结晶,并逐渐演变称为细小再结晶晶粒包围原始基体的项链状组织形貌特征。与此同时,基体中出现了大量的亚晶组织,微观织构分析结果表明,晶界处的小角度亚晶组织遵循晶粒取向梯度变化规律,而再结晶晶粒的取向形成则不能用连续取向梯度变化解释。
[Abstract]:Magnesium alloy is the lightest metal structure material which can be used in practice at present. It has excellent properties such as high specific strength, strong electromagnetic shielding property, good damping property and so on. However, due to the low symmetry and poor plasticity of magnesium alloys with hexagonal crystal structure, the wider application of magnesium alloys is limited. A large number of results show that grain refinement can improve the strength and plasticity of magnesium alloys at the same time and play an important role in improving the formability of magnesium alloys. As a large plastic deformation method, friction stir processing can effectively refine the grain structure of magnesium alloy. In this paper, the evolution law of microstructure and the modification of mechanical properties at room temperature during friction stir processing of AZ31 magnesium alloy were studied systematically, and the hot rolling experiments were carried out on the plates after friction stir processing. The twinning, dislocation slip and dynamic recrystallization behavior during rolling were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (EBSD). The results show that friction stir processing refines the original grain structure, weakens the basic texture and improves the tensile strength and plasticity of the material, but the yield strength decreases. The results of the hot rolling experiment show that the strain of the rolling process is smaller, narrow flake? The local dynamic recrystallization occurred in the twin region, and the dynamic recrystallization began to occur at the grain boundary with the increase of the strain. It is called fine recrystallized grain surrounding the original matrix and the necklace-like microstructure is gradually evolved. At the same time, a large number of subcrystalline structures appear in the matrix. The results of microtexture analysis show that the sub-crystalline structure at grain boundaries follows the law of grain orientation gradient. However, the orientation formation of recrystallized grains cannot be explained by continuous orientation gradient.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22

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