等径弯曲通道变形力的研究

本文利用上界定理计算等径弯曲通道变形 (ECAP)的挤压力 ,为ECAP的模具设计、挤压力的计算提供了一种可行的方法     

带背压等径角挤压挤压力上限解析

等径角挤压过程中施加背压,可以有效地改善材料微观组织和力学性能。运用上限理论推导出了带背压等径角挤压的挤压力解析式,结合实验进行验证,分析了背压作用的影响因素及背压效果,为等径角挤压的工艺优化、背压施加方式、模具设计及设备选择,提供了可行的方法。     

等通道转角挤压Al-Cu合金的冲击性能

对铸态Al-0.63%Cu和Al-3.9%Cu(质量分数)合金进行等通道转角挤压处理,研究了Al-Cu合金冲击性能的变化.结果表明,等通道转角挤压增强了Al-0.63%Cu合金的冲击性能;而对于Al-3.9%Cu合金,虽然晶粒细化和第二相的弥散分布使其强度增加,但较多的第二相θ(Al2Cu)未提高其冲击性能.该合金的冲击吸收功与其静力韧度有关.     

等径角挤压过程的计算机模拟

等径角挤压可以在不改变材料横截面的情况下使其反复产生严重的塑性变形,从而降低材料的晶粒尺寸,是制备块体超细晶材料的新工艺。该文采用DEFORM程序对等径角挤压过程进行了模拟,分析了挤压过程中材料的应力、应变、挤压力等的变化及其分布,为今后的研究打下了基础。     

等径角挤压法制备块体超细晶材料的研究现状及展望

对块体超细晶材料的研究是近年来的一大热点.大塑性变形法（Sever Plastic Deformation,SPD）之一的等径角挤压（Eaqual channel angular pressing ,ECAP）法,可以在室温或不太高的温度下,将材料的晶粒由几微米至几十微米细化至200nm～400nm,材料的性能得到提高,并且ECAP法有着相对简单的制备工艺及较好的细化效果.本文介绍了ECAP处理对提高材料的强度、疲劳寿命、超塑性等的贡献以及影响ECAP工艺的因素,分析了ECAP目前存在的问题,并对ECAP的应用前景进行了展望.     

Investigations on workability of commercial purity aluminum processed by equal channel angular pressing

Equal channel angular pressing (ECAP) is an important process for producing ultra fine grains in bulk metallic materials by means of severe plastic deformation. Workability of metals and alloys is an important parameter as it influences the fracture resistance of the material and the ease of subsequent forming by conventional techniques. In this study, the effect of various passes and processing routes of ECAP on the workability of commercially pure aluminum has been investigated. Aluminum specimens were subjected to ECAP using 90° angle ECAP die. ECAP was carried out using two processing routes for up to three passes. Microstructure characterization and mechanical property measurements were carried out. Workability was determined by means of upsetting tests on hexagonal collar specimens machined from specimens processed by ECAP. A Cockcroft fracture criterion was used to evaluate experimental results. It is observed that processing to two passes through Route C results in enhanced mechanical properties with only a slight decrease in workability.     

等通道转角挤压制备超细晶材料的最新研究进展

等通道转角挤压(Equal channel angular pressing,ECAP)方法是制备性能优异超细晶材料最常见的大塑性变形方法之一。模角、挤压路径、挤压道次、挤压温度和挤压速度等因素都会影响等通道转角挤压制备超细晶材料的性能;等通道转角挤压的模具也在不断地优化,如背压-等通道转角挤压(Back pressure ECAP,BP-ECAP)模具、可加热的模具以及在等通道转角挤压基础上形成的板材连续剪切技术等,这些新的模具可以改变ECAP变形过程中的组织均匀性。本文综述了等通道转角挤压制备超细晶材料的最新研究进展,并指出了几个需要深入研究的问题及方向。     

Monte-carlo modeling of grain growth in Zr equal channel angular pressed and recrystallized

Grain boundary character distribution in equal-channel-angular pressed Zr was studied. Using a die design of 90°/20° and an operation temperature of 350°C. The initial grain size of 20 μm was reduced to about 270 nm with 4 passes via route B_c. The grain growth kinetics of the recrystallized state was obtained by experiment and Monte-Carlo computer simulation, respectively, which showed good agreement. Based on kinetics and morphological characteristics, it was concluded that the grain coarsening mechanism was governed by normal grain growth. No sign of abnormal grain growth was detected either in the experiment or in simulation despite taking into consideration anisotropy in grain boundary energy as well as its mobility. This indicates that grain boundaries produced by severely deformed Zr are stable against explosive coarsening. The evolution characteristics of the microstructure in the present ECA pressed and recrystallized Zr differed from those of cold rolled Ti in that the grain boundary misorientation distribution and texture were rather stable during grain growth. Jointly Appointed by the Center for Advanced Aerospace Materials This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

等径角挤压工艺的无网格数值模拟研究

等径角挤压(Equal Channel Angular Pressing,ECAP)工艺,是一种通过材料的剧烈塑性变形,获得大块超细晶材料的有效方法。采用无网格伽辽金法对等径角挤压工艺进行了数值模拟研究,分析了挤压过程中材料的流动规律,研究了模具圆心角、挤压件与模具间的摩擦状况对ECAP挤压效果的影响。随着模具圆心角的减小,挤压件的等效应变增大并且变得更加均匀,但是模具圆心角越小,挤压载荷越大,严重影响模具的使用寿命;摩擦状况对挤压件的等效应变的影响较小,对挤压载荷影响显著。无网格模拟分析结果与实验结果吻合良好。     

Physical modeling of equal channel angular pressing using plasticine

We report here the results of our physical modeling study of the equal channel angular pressing process using two-colour constituent plasticine workpieces in a metallic die. The workpieces, usually called billets, are made up of discs as well as spherical balls. They are deformed repeatedly with and without changing the orientation between successive passes. Both square and round dies with inner channel intersection angle of 90° are used. The flow patterns are revealed by sectioning the billet after a requisite number of passes. Thorough mixing of the two constituents with a drastic reduction in the section size of each constituent of the plasticine workpiece was observed after 15 passes. The initial shape of the constituents of the billet does not affect the final flow pattern of the microstructure. Material accumulation of the two colour constituents of plasticine was observed in some regions of the billet along the central region at a low and intermediate number of passes.     

Multiple-stage transformation behavior of Ti49.2Ni50.8 alloy with different initial microstructure processed by equal channel angular pressing

Multiple-stage transformation of Ti_49.2Ni_50.8 alloy processed by equal channel angular pressing (ECAP) was investigated as a function of pass number and aging treatment before ECAP. When the pass number is no more than four passes, three stage transformation, namely A→R, R₁→M₁ and R₂→M₂, occurs in the as-ECAP processed alloy initially aged at 450 °C for 60 min. Only the A→R→M forward transformation occurs provided that the aging duration was decreased/increased to 10/600min. The transformation sequence was discussed based on the microstructure evolution of as-ECAP processed alloy with different initial microstructure and pass number.     

等通道转角挤压Mg-3.52Sn-3.32Al合金的组织与力学性能

采用等通道转角挤压（ECAP）Bc路径对固溶态Mg-3.52Sn-3.32Al合金分别挤压1、4和8道次。利用光学显微镜、扫描电子显微镜、透射电子显微镜和X射线衍射仪分析合金的组织和相组成,并测试了其室温拉伸力学性能。结果表明,经ECAP挤压后,固溶态合金组织中析出大量细小的Mg2Sn相和极少量的Mg17Al12相。随挤压道次增加,合金的综合力学性能先提高后降低。经4道次挤压后,合金的综合拉伸力学性能相对较佳,抗拉强度、伸长率和硬度分别达到250 MPa、20.5%和61.3 HV9.8,较未ECAP时分别提高43.7%、105%和26.9%。经ECAP挤压的合金室温拉伸断口均呈韧性断裂。等通道转角挤压Mg-3.52Sn-3.32Al合金的力学性能受晶粒尺寸、析出相以及组织织构的共同影响。     

Finite element simulations of deformation behavior in equal channel angular pressing using a rotated die

A new die design for equal channel angular pressing (ECAP) of square cross-section billet was proposed by a 45 rotation of the inlet and outlet channels around the channel axes. ECAP utilizing the rotated and conventional dies was simulated in three dimensions using the finite element method. Conditions with different material properties and friction coefficients were studied. The billet deformation behavior was evaluated in terms of the spatial distribution of equivalent plastic strain, plastic deformation zone and load history. The results show that the rotated die appears to produce billets with a smaller deformation inhomogeneity over the entire crosssection and a greater average of equivalent plastic strain at the cost of a slightly larger working load. The billet deformation enters into a steady state earlier in the case of the rotated die than the conventional die under the condition of a relatively large friction coefficient.     

Microstructure evolution of TA15 titanium alloy subjected to equal channel angular pressing and subsequent annealing at various temperatures

TA15 titanium alloy was successfully processed for the first time by equal channel angular pressing (ECAP) in the temperature range of 900-1000 °C and annealed in a wide temperature interval from 650 to 800 °C. The investigation was achieved by light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM) on the microstructure evolution of TA15 alloy subjected to ECAP and subsequent annealing after ECAP. In the present work, equal channel angular pressing (ECAP) was taken as the effective method to acquire severe plastic deformation (SPD). The studies we have performed show that grains have been obviously refined and well globularized after ECAP. When TA15 alloy was pressed at the temperatures of α + β phase region equiaxed microstructure was created. There was an increase in the equilibrium grain size with increasing pressing temperature, while a decrease in the volume fraction of equiaxed α phase. TEM microstructural images illustrate that an amount of deformation twins emerged while pressing TA15 below α-β transformation temperature (T_β), which led to the continued plastic deformation through the restarting of many slip bands. Severe coarsening took place in β grains during ECAP at the temperature above T_β. A larger number of well globularized and more homogeneous equiaxed α phase of TA15 alloy annealed after ECAP has been attained. Furthermore, with annealing at the optimum temperature, grains have not grown significantly.     

等径弯曲通道变形制备超细晶铜的热稳定性

室温下采用等径弯曲通道变形(Equal Channel Angular Pressing,ECAP)C方式进行了纯铜(99.95%)12道次挤压变形。通过等温和等时退火,研究ECAP变形后铜的退火行为,并研究了等径弯曲通道变形和退火后纯铜的显微硬度和显微结构变化。分析了ECAP应变量、退火时间和退火温度对超细晶铜的再结晶行为、抗软化性能的影响。结果表明:ECAP变形后的超细晶铜在退火过程中,表现出不连续再结晶现象;ECAP降低了铜的热稳定性,变形道次越高再结晶温度越低。退火后稳态晶粒尺寸随变形道次的增加而细化,硬度值随变形道次的增加而增大,回归分析表明,晶粒尺寸与硬度之间的关系符合Hall-Petch公式。     

等径角挤压处理后的Mg-Gd-Y-Zr合金的微观组织和力学性能

研究等径角挤压过程中材料的微观组织和织构演变以及对其力学性能的影响。结果表明：挤压4道次后的微观组织是不均匀的,即在此过程中形成了粗晶区和细晶区2个区域。颗粒诱发的再结晶机制导致晶粒细化,在4道次后形成了更加随机的织构。与挤压前的原始材料相比较,经等径角挤压处理的材料虽然强度没有增加,但是塑性有了显著的提高。用织构改变和第二相颗粒解释了合金塑性的变化。     

Deformed texture of copper processed by equal channel angular pressing via different angle routes

The commercially pure copper with dimension of 80 mm×20 mm×4 mm was used for equal channel angular pressing （ECAP）, of which their outward appearance coordinate is corresponded with that of rolling deformation modes. Cold-deformed texture was investigated. The results show that the texture character in pure copper processed by ECAP is related with intersection angle （Ф） of the die channel. When Ф is 90° and the sample is extruded for one pass, its texture consists of α and β orientation lines including mainly C, B, S and Goss components, moreover a little rotated cube is found. When Ф is 135°, as extrusion pass increases, the weak texture forms on the scope of deviation from rotated cube （ψ=0°, θ=0°, Ф=45°＋15°） and develops to the ψ=45° fiber mainly including rotated cube. When Ф is 120°, the texture is ψ=45° fiber mainly including rotated cube that is maintained constant as extrusion pass increases.     

等通道转角挤压过程塑性变形行为的研究

等通道转角挤压工艺是一种利用纯剪切变形获得块状超细晶材料的新技术,本文采用坐标网格法进行实验,获得了力一行程曲线和试样网格的变化,并应用Deform-3D有限元软件数值模拟了5052铝合金挤压塑性变形过程,将挤压后的实验结果同模拟结果进行比较,两者吻合较好,以此为基础,分析了挤压变形力和等效应变的分布规律,探讨了塑性变形的行为.     

Effects of die geometry on variation of the deformation rate in equal channel angular pressing

The deformation behavior within the deformation zone of a workpiece during equal channel angular pressing (ECAP) was investigated using the finite element method. The effects of die geometry on the variations of normal and shear deformations were studied with a deformation rate tensor (D). The zero dilatation line, at which the normal components (D₁₁ and D₂₂) of the deformation rate tensor (D) are zero, in the die coincided with the line of intersection of the two die channels irrespective of die geometry such as curvature angle (Ψ) and oblique angle (Φ), while the maximum shear line, at which the shear components (D₁₂ and D₂₁) of the deformation rate tensor (D) have maximum value, is dependant on the die geometry     

连续ECAP技术制备超细晶铝

探讨一种连续等通道角挤压(ECAP)新技术,实现了纯铝的无限长度连续大变形,制备出具有超细晶结构的金属材料。组织和性能检测表明:在连续ECAP变形一道次后,在晶粒内部形成了直径为650~900 nm且内部基本无位错的亚晶,但部分大晶粒内部仍存在高密度的位错网,材料硬度提高了87%;经过4道次连续ECAP变形后,亚晶并未进一步细化,但亚晶界趋于平直、清晰,且亚晶内部基本未见位错组织,材料硬度提高也不显著;与传统ECAP相比,连续ECAP工艺由于具有较高的变形区温度,促进了晶内位错的反应即动态回复过程,较早形成了平直清晰的亚晶结构,同时伴随每道次变形过程的动态回复也降低了最后晶格中累积的能量,使变形两道次后的组织和性能变化不显著。