【作者】 陈海红；

【导师】 胡治流；

【作者基本信息】 广西大学 ， 材料加工工程， 2008， 硕士

【摘要】 等径角挤压(ECAP)是一种利用纯剪切变形实现材料晶粒细化的大塑性变形加工方法,是目前获得块状超细晶材料的重要方法之一,已引起了国内外材料界的极大关注。到目前为止,用ECAP法制备出的主要为φ10mm左右的小尺寸试样材料,由于制备尺寸的限制,使得ECAP技术在工业上的推广应用大大受阻。本文利用自行设计的ECAP模具,在室温下对φ30mm的大尺寸纯铝棒材进行了四道次挤压试验,对ECAP变形过程中挤压力的变化规律、组织演变规律、挤压后材料的力学性能、变形的均匀性及其影响因素等进行了研究,并对ECAP变形过程中纯铝的细化机理和等径角挤压法的产业化问题进行了探讨。结果表明:含残余试样等径角挤压载荷随位移的变化可分为快速增加、快速下降、缓慢增加、缓慢下降和载荷值有所回升等五个阶段;采用等径角挤压技术,可以显著改善工业纯铝的力学性能。按照Bc路径,经四次ECAP挤压后,纯铝的晶粒尺寸由原来的40～50μm细化到5μm左右;用金相显微镜对纯铝微观结构的观测分析表明,在纯铝的ECAP变形过程中,模具转角处的剪切变形作用,应变量的大量累积以及由此引入的一系列位错运动是其晶粒细化的主要原因。用硬度法对ECAP变形的均匀性分析表明,在等径角挤压过程中,试样头部和尾部的变形极不均匀,试样顶部与中部区域的变形相近,试样底部的变形与试样顶部和中心的差异较大;残余试样的存在,对新试样起到了反向挤压力的作用,使新试样内部的变形及其应力分布更为均匀。更多还原

【Abstract】 Equal Channel Angular Pressing (ECAP) is one kind of severe plastic deformation method, which can refine grain size by introducing the simple shear deformation into the workpice and has been proved to be an effective method for obtaining various bulk ultrafine-grained materials. It has been attracting more and more attention in material field. At present, ECAP technique is mainly used to process sample of small-size about 10mm in diameter. Due to the limitation of fabrication size, its application in industries has been greatly impeded.In this paper, the large-size pure aluminum samples of 30mm in diameter were pressed at room temperature by 4 passes with ECAP dies self-designed. The change law of extrusion force and the microstructure evolution during ECAP were investigated. The mechanical properties of pure aluminum after ECAP, the uniformity of deformation and its influencing factors were also researched. Further more, the grain refining mechanism of pure aluminum during ECAP and the industrialization of ECAP were discussed.The results show that the load required to drive the deformation varies with the increasing displacement, according to the following five steps when there exists residual sample: rapid increase, rapid decrease, slow increase, slow decrease and load rising slightly. And the mechanical properties of pure aluminum are greatly improved by ECAP process. After 4 passes of ECAP in route Bc, the grain size of pure aluminum has been refined from 40-50μm to about 5μm. It is found that the shearing deformation, the large cumulative of strain and dislocation movements are the main causes for grain refining during ECAP. Hardness method research results show that the deformations of sample in head and tail are extremely inhomogeneous, the deformation at the top is similar to that in the middle, and the deformation at the bottom is very different with the top and the middle. In addition, residual sample plays a role of backward extrusion during ECAP, and makes the deformation and strain distribution more uniform.更多还原