【作者】 刘辉；

【导师】 周志敏；

【作者基本信息】 东北大学 ， 材料物理与化学， 2014， 硕士

【摘要】 众所周知,金属材料的诸多性能与其晶粒大小有着密切的联系,由Hall-Petch公式可知,晶粒尺寸越小,材料的强度、硬度就越高。虽然传统的变形方式如轧制、拉拔等可以使晶粒得以细化,但很难细化至亚微米级以下,各类大塑性变形方法虽然可以得到亚微米级以下晶粒尺寸的材料,但其工艺过程复杂,条件苛刻,且很难得到较大尺寸材料及进行大批量的生产。为了解决这些问题,本文利用自主研发的步进式挤压轧制装置对纯铜板材的变形行为及晶粒尺寸变化情况进行了探索研究,研究晶粒超细化的方法及细晶材料大规模生产的可行性。选用厚度为2.020mm、纯度为99.90%的T2工业纯铜板材作为原料,通过有限元分析,模拟了一些关键的实验参数,如步进长度、推进速度以及施加润滑的部位等,对后续实验进行了有预见性的指导,最终确定步进长度为20mm,推进速度为10mm/s,仅试样内表面施加润滑。本文共设置了1、2、4、6和8道次步进式挤轧变形实验,设备通道内角φ≈94°,外角Ψ≈5°,之后对变形试样进行热处理研究,为了减少工作量而又可以全面考察各种因素的影响,采用正交实验方案：挤轧变形道次四个水平分别为1道次、2道次、4道次、8道次；热处理温度四个水平分别为200℃、230℃、260℃、300℃;保温时间四个水平分别为10min、15min、20min、30min。每组试样热处理后,都对其进行水冷。经过4道次挤轧变形,试样横截面的平均晶粒尺寸由均匀化退火态的28.32μm细化至4.49μm,晶粒尺寸减小了约84.1%。通过正交实验分析找出适合该材料的最佳热处理方式,得出最佳处理工艺为：8道次、退火温度230℃、保温时间10min,得到的样品平均晶粒尺寸约为3.79μm。正交实验第14组的样品硬度值是初始退火态的1.81倍。研究发现：随着挤轧变形道次的增加,晶粒尺寸不断减小；合理的热处理工艺可以有效改善纯铜的微观组织。本文的变形方法对晶粒细化有较大作用,通过8道次步进式挤轧变形后,晶粒尺寸不再发生明显的细化,晶粒尺寸稳定在3-6μm之间。本文工作对于大尺寸超细晶材料的连续生产技术的研发具有很大参考价值。更多还原

【Abstract】 As is well known, many propertiese of metal materials is closely related to its grain size. According to Hall-Petch’s formula, the smaller the grain size, the higher the strength and the hardness. While conventional methods such as deformation rolling, drawing and others can refine grains, but it is difficult to refine to submicron grade. Though many kinds of plastic deformation methods can obtain the materials of submicron grain size, its complicated process and scale production difficulties making it difficult to preparation larger sizes of materials and mass production.To solve these problems, in this paper, an independent designed step by step extrusion-rolling deformation equipment was adopted, deformation behavior and grain size variation of pure copper plate was studied, the feasibility of grain refinement and fine grain materials of mass production was also explored. T2 copper plates was choosen as raw material. Its thickness is 2.020 mm and its purity is 99.90%. By the finite element simulation, the stepping length, advance speed, where should be lubricated and so on were explored. The results of the finite element simulation can be seen as the predictive guidance. The final step length is 20mm, the advancing speed is 10mm/s.In this paper, a series of 1,2,4,6 and 8 passes step by step extrusion-rolling deformation experiment were employed. The die channel interior angle φ≈94° and the outer corner Ψ≈5°. After that, the samples were heat treated and the process was researched. In order to reduce the workload yet to fully examine the influence of various factors, Orthogonal experiment design scheme were utilized:Four levels of extrusion deformation pass are respectively one-pass, two-passes, four-passes, eight-passes; Four levels of the heat treatment temperature are respectively 200℃,230℃,260℃,300℃; Four levels of holding time are respectively 10min,15min,20min,30min. After heat treatment, the specimens of each group were quenched by using water.After 4 passes deformation,the average grain size of the specimens’ cross section by homogenization annealing state of 28.32μm is refined to 4.49μm, the grain size is reduced by about 84.1%. Through the analysis of orthogonal test, the best heat treatment for the materials is found:eight-passes, annealing temperature is 230 ℃, holding time is 10min. The average grain size of the obtained samples is about 3.79μm. Hardness of the fourteenth orthogonal experiment samples is 1.81 times that of the initial annealing state. The results suggest that: With the deformation passes increasing, the grain size decreases; Reasonable heat treatment process can effectively ameliorate the microstructure of pure copper.It can be seen that, in this paper, the refinement of grain size is no longer obvious after 8 passes step by step extrusion-rolling deformation. The grain size steady in range of 3-6 μm. This study have great reference value for the continuous production of large size ultrafine grained materials.更多还原