摘要：本次研究是针对纯铝在剧烈塑性变形下晶粒细化，形成层状结构的超细晶材料。研究采用的主要方法是ECAP和液氮冷轧相结合。最大的创新之处在于采用ECAP和液氮冷轧结合的方式，从而达到更进一步细化晶粒的目的。

本实验所选用质量分数为99.8827%工业纯铝作为原料，使用NYL-2000D型压力试验机和ECAP模具对样品进行Bc、A路线4、8次数的挤压。然后用热轧冷轧多用途轧机对ECAP后的试样进行压下量分别为50%、70%、80%的液氮冷轧。制备完样品之后，用线切割将样品加工成所需形状进行金相观察、EBSD分析和拉伸实验。以晶粒直径的变化为例，分析实验结果可以发现：与原始样品比较，Bc路线挤压4次且进行变形量为80%的试样d的晶粒直径与a相比，减小了67.8%；Bc路线挤压8次且进行变形量为80%的液氮冷轧的试样e的晶粒直径与a相比减小了72.9%。。从以上结果可以发现ECAP和轧制有效细化了晶粒，提高了纯铝的机械性能，使强度和硬度上升。

关键词  剧烈塑性变形  ECAP  液氮冷轧  片层  超细晶    

毕业设计说明书外文摘要

Title  Preparation of ultra-fine lamellar structure aluminum alloy  

Abstract：This study is aimed at grain refinement of pure aluminum with the help of severe plastic deformation , which can formation the ultra fine-grained materia with layered structure. The main method used in the study was the combination of ECAP and cryogenic rolling. The biggest innovation is the combination of ECAP and cryogenic rolling, so that we can achieve further refinement of the grain.

The raw materials used in this experiment are industrial pure aluminum, in which the mass fraction of aluminum is 99.8827%. With the help of NYL-2000D pressure tester and ECAP mold, samples were subjected to ECAP at room temperature. The sample with four passes and eight passes was deformed by route Bc and route A. Then the samples were subsequently cryogenic rolled along their extrusion direction to overall thickness reduction of 50%, 70% and 80%. After the samples were prepared, they were machined into the desired shape with wire cutting for observation with a metallographic microscope, EBSD analysis and tensile experiment. Taking the change of the grain diameter as an example, we can find that ECAP and rolling can effectively refine the grain and improve the mechanical properties of pure aluminum, which rises the strength and hardness.

Keywords  Severe plastic deformation  ECAP  cryogenic rolling  sheet  ultra fine-grained

目   次

1  引言1

1.1  剧烈塑性变形对金属铝及其合金的影响1

1.2  等通道转角挤压1

1.3  低温轧制对金属铝及其合金的影响3

 1.4  超细晶材料与片层结构4

1.5  电子背散射衍射(EBSD)5

2  实验方法6

2.1  实验材料与仪器6

2.2  ECAP（等通道转角挤压）7

2.3  液氮冷轧8

2.4  拉伸实验9

2.5  金相观察10

2.6  硬度测试10

2.7  拉伸试样断口扫描10

2.8  电子背散射衍射(EBSD)11

3  实验结果与讨论12

3.1  拉伸实验12

3.2  硬度测试14

 3.3  拉伸试样断口扫描与分析15

 3.4  电子背散射衍射数据分析18

 3.5  存在的一些不足21

 结论 23

致谢 24

参考文献25

1  引言

1.1  剧烈塑性变形对金属铝及其合金的影响

剧烈塑性变形是一种新兴的塑性变形方法，金属在剧烈塑性变形时产生较大的应变量；而传统的塑性变形难以实现应变量大于1的真应变。因而它能够有效细化晶粒，并且能够获得完整的大尺寸块体试样[1]。在变形过程中通过控制微观组织，可以获得不但具有较高强度而且具有较高塑性的材料。剧烈塑性变形是金属和合金晶粒细化的可靠方法。据报道，通过剧烈塑性变形（SPD）技术处理的超细晶粒金属和合金具有优异的机械性能，如强度高，硬度高，延展性好。剧烈塑性变形有许多的加工方法[2]，例如低温轧制，等通道转角挤压（ECAP），高压扭转（HPT），通过它们可以获得细小的晶粒。高应力下变形，以铝为例，会形成一个非常细的晶粒尺寸和相应的高位错密度。相比于初始材料，这些因素会使材料的屈服强度和拉伸强度显著增强。