Large Deformation And Properties Of Induction Heat Treatment ARB Regulation And Ultrafine-grained Copper Organizational Structure

In present thesis, structure evolution process of copper was regulated by Asymmetrical Accumulative Rolling Bonding(AARB) and heat treatment. By means of AARB and heat treatment technology searching, analysis of copper microstructure in different conditions, analysis and theoretical calculation of the twins and grain boundaries, calculation of texture in deformed and recrystallized process, testing of copper in every process condition, the deformation and grain refinement mechanism of copper deformed by AARB, ultrafine twins and recrystallization mechanism of copper, evolution of deformed and recrystallized texture to twin orientation, mechanical properties and electrical conductivity of copper were researched by experimental and theoretical analysis. The mainly results could be concluded as follows.1. The evolution of the structure and grain boundary structure of copper deformed by AARB were studied. The process of grain refinement was obtained.The copper with big grains was obtained by AARB when the equivalent strain(ε) was less than1.6, bands shaped like "S" were formed with the action of shear stress. The crisscrossed dislocation walls in "S" band refined the "S" band to smaller dislocation cells. Based on the slipping of grain boundaries and the slipping of crystal in grains, low-angle boundaries were produced in most of the big grains.As copper deformed by AARB with the equivalent strain(ε) within2.4and4.0,"S" bands can’t be obtained, and about2-3subgrains were obtained in most of deformed grains. With the effect of plastic deformation and gathering of dislocation walls, one sub-grain was divided to two grains. Deformed grains were refined to0.5μm, and distribution of piling up of dislocations was uneven.2. Ultrafine copper was treated by recrystallization annealing when ε was4.8, and the microstructure and twins was observed, the results were as follows:Recovering of deformed grains was observed first of all in the recrystallization annealing of copper deformed by AARB with ε was4.8, in this stage, cliping and compensation of dislocations in deformed grains had happened. The dislocations were lined up in subgrain boundaries, and neat subgrain structure was obtained. Along with the recrystallization annealing time, nucleation and growth happened during recrystallization. Due to the orientation gradient in subgrains in recovering stage, the subgrains occured aggregation and coarsening to nucleation. At last, the grains grown to adjacent grain boundaries approached. In that stage, low-angle boundaries decreased and high-angle boundaries increased with which migrated to the dislocation area of high density.The original annealing twin nucleation was observed at grain boundary when recrystallization annealing for20minutes. Along with the annealing time, when the partial dislocation inside the subgrain boundary swept forward in the very subgrain cell structure, the annealing twin nucleation grown to the grain inside, and two of twin boundaries were produced. Finally annealing for35～40minutes, a plenty of ultrafine twins were obtained.The low-Σ CSL grain boundries were broken crushed by AARB shearing deformation. According Σ3remotication model, the Σ3-Σ9-Σ3grain boundaries bonding formed with the growth of recrystallization nucleation and the migration of high-angle grain boundaries.3. The evolution of texture of copper deformed by AARB with different s and recrystallization annealing for different times were observed, and the results showed as follows:Annealing texture was obtained in copper after homogenizing annealing, and which disappeared in AARB deformation followed. The deformed texture was complex. But there was mainly shear texture ({001}<110>) whose density increased with the rise of ef fective strain s. The feeblish cube texture({001}<100>) was obtained after relief annealing in every twice passes.Great changes had happened in copper during recrystallization. The shear texture was the only remained deformed texture, and whose density decreased with extension of annealing time. The new texture was obtained in recrystallization, in which texture {221}<114> was twin orientation, a mirror reflection of shear texture from AARB deformation along twinning plane{111}.4. The micro hardness,tesile properties, fatigue properties and electrical conductivity of copper under different conditions were determined and the change of properties was analyzed.During the course of AARB, the strength of copper increases with the rise ofε, but its elongation rate decreases. Ultrafine copper with good properties could be obtained when recrystallized annealing at240℃for40minutes.During the course of AARB, the fatigue life of copper increases with the rise of ε; and it achieved the maximum at three passes deformed by AARB. Recrystallization annealing ultrafine copper achieved the maximum at240℃for40minutes, and its tensile strength got the maximum.Electrical conductivity decreased with the rise of equivalent strain. During the recrystallization annealing, electrical conductivity of ultrafine copper increased with the annealing time extension. Ultral-fine annealing twins formed during recrystallization annealing increased the electrical conductivity of ultra-fine grain copper.Ultra-fine grain copper possessing uniform structure, high strength and ductility, good electrical conductivity has been prepared by AARB and recrystallization annealing. Ultrafine-twin copper obtained by AARB was proposed firstly. This could provide new research contents to controling the stucture of ultrafine materials, and also provide a new method for preparing ultrafine-twin copper with block size. By means of regulating deformation by AARB and recrystallization annealing, preparation of ultrafine-twin copper and its structure and texture had not been reported yet, but this work was researched here, in the meantime, the mechanism of grain refinement and recrystallization twins formation were analyzed and discussed too.