单道次ECAP纯铝织构演变的有限元模拟

利用晶体塑性有限元(Crystal Plasticity Finite Element,简称CPFE)子程序和ABAQUS商业软件对多晶体纯铝等径弯曲通道(Equal Channel Angular Pressing,简称ECAP)变形进行了细观三维计算机模拟,获得多晶体纯铝在ECAP变形后各晶粒的取向分布数据,并据此得到晶粒取向的ODF图及极图.通过对结果的分析,初始晶粒取向随机分布的多晶体纯铝在ECAP单道次变形后,靠近模具内角的试样和靠近模具外角的试样由于形变的方式不同而形成了不同的织构形态,靠近模具内角的试样形成剪切织构,靠近模具外角的试样形成扭转织构.因此多晶纯铝在通道夹角Ф=90°、外圆角Ψ=20°模具中的ECAP变形并不是通过理想的纯剪切变形实现的.     

ECAP变形与材料组织性能控制的研究

等径弯曲通道变形(ECAP)是制备超细晶材料的新工艺,其基本原理是将试样放入横截面形状完全相同、并成一定角度的弯曲通道中,试样在压力作用下通过通道时,在通道弯曲处产生一定量均匀的纯剪切变形,最终获得很高的变形量,使材料组织发生明显细化.详细介绍了ECAP变形工艺路线对晶粒细化的影响,以及ECAP变形制备超细晶材料的显微组织特征及其力学性能.     

ECAPT 过程中 TE 工艺对 ECAP 变形规律的影响

通过对纯铝等径角挤压(ECAP)和等径角挤扭(ECAPT)变形行为的数值模拟,获得了材料在不同工艺下的应变和损伤情况.结果表明,在ECAPT工艺中试样通过ECAP通道后能获得比单独的ECAP更高的应变累积,应变累积量随TE通道螺旋角β的增大而增大,同时试样内部的应变分布也得到改善,试样在受到TE工艺的背压后材料表面受到剪切破坏的可能性也明显降低.     

ECAP制备半硬磁2J4合金的磁性能研究

开发了用等径弯曲通道变形(ECAP)制备半硬磁2J4合金.研究结果表明:2J4合金的磁性能随着ECAP变形道次的增加而逐渐增大,在第3道次变形时,其磁性能增加速度最快.ECAP变形与冷轧类似,都形成极其相似的带状织构,提高了合金的各向异性常数.由于ECAP方式使晶粒细化,达到或接近单畴结构,使得2J4合金的磁性能优于冷轧条件下的磁性能.     

二次变形对等径弯曲通道变形的工业纯钛性能的影响

通过大塑性变形可以得到超细晶,从而获得有特殊性能的材料.对于工业纯钛以及一些难变形材料,等径弯曲通道变形(ECAP)是获得超细晶的一种最有潜力的方法,但由于ECAP模具的限制,获得的坯料形状和尺寸与所要求的半成品还有一定距离.     

挤压速度对工业纯钛室温ECAP变形孪晶的影响

在室温采用通道夹角为Φ=120°的模具,以不同挤压速度实现工业纯钛的单道次等径弯曲通道变形(ECAP),利用光学显微镜(OM)观察了变形前后的组织形貌特征,分析了不同挤压速度对显微组织的影响。结果表明:在单道次ECAP变形过程中,孪晶变形是主要的变形机制,且随着变形速率(即挤压速度)的增大,孪晶变细,孪晶的密度显著增大。     

ECAP变形道次对珠光体钢中渗碳体球化的影响

成功地实现了珠光体钢65Mn的等径弯曲通道变形(ECAP),并研究在650℃不同ECAP变形道次的条件下渗碳体球化的演化过程.结果表明,渗碳体在ECAP热变形过程中表现出明显的加速球化特征.第一道次ECAP热变形后,片状的渗碳体演化为细小碎块的聚集体;第二道次热变形后,渗碳体实质上已破碎,呈现出颗粒状和球化渗碳体的主要形貌特征;第五道次ECAP热变形后,进一步演化为超细的球状渗碳体均匀分布于超细晶铁素体基体的组织.     

珠光体组织的等径弯曲通道变形

具有全珠光体组织的65Mn钢在650℃以C方式等径弯曲通道变形(ECAP)后,珠光体组织中的渗碳体片层以周期性的弯曲变形、周期性的剪切变形、剪切断裂等形式协调ECAP的强烈塑性变形.渗碳体表现出很强的塑性变形能力,在其内部导入了大量的晶体缺陷,为渗碳体的球化打下了能量基础.变形五道次后,片层状的珠光体组织演变成了超细的渗碳体颗粒均匀分布于铁素体基体的组织.铁素体基体为均匀的等轴晶,平均晶粒大小为～0.3 μm.渗碳体的球化可能以两种机制进行:破碎渗碳体片的非均匀长大(Ostwald熟化)和细小球状渗碳体颗粒的形核长大.     

钛及钛合金ECAP变形研究进展

综述了等径变曲通道变形(Equal channel angular pressing,ECAP)技术制备超细晶(Ultra fine grain,UFG)钛及钛合金的研究进展。总结了模具参数、变形工艺参数对钛及钛合金ECAP变形及组织的影响,以期通过制定合理的变形工艺制备出组织均匀、性能优良的超细晶钛及钛合金,同时汇总了钛及钛合金ECAP变形组织变形机理、演变机理、ECAP变形组织稳定性及超细晶材料性能(超塑性、疲劳强度、耐腐蚀性等)的研究进展,最后指出ECAP制备超细晶钛及钛合金的研究方向。     

等径弯曲通道变形织构的研究进展

综述了等径弯曲通道变形制备FCC、BCC、HCP金属材料中织构的研究进展。介绍了ECAP变形织构的主要研究方法——蚀坑法、X射线衍射法、中子多晶体衍射法和电子背散射衍射法,论述了挤压路径、挤压道次、挤压温度、模具夹角、形变孪晶、初始织构等对ECAP变形过程织构演变及形成机理的影响,并对基于物理过程的织构演化模型(全约束Taylor多晶体模型和粘塑性自洽多晶体模型)进行评价,同时进一步指出织构演化研究的重要性及发展趋势。     

A modification on ECAP process by incorporating torsional deformation

In the present study, integration of equal channel angular pressing (ECAP), as a well known severe plastic deformation (SPD) technique, and torsion deformation, is studied by using three dimensional finite element analysis. This process is to be named as torsional-equal channel angular pressing (T-ECAP). In this modification a part of the exit channel in the ECAP die is rotating around its axis, to impose extra shear strains to the samples. To study deformation behavior in the T-ECAP process, three-dimensional finite element analysis (FEA) was carried out by using the elasto-plastic finite element analysis ABAQUS/Explicit Simulation. To investigate the validity of the simulation results, experimental studies were furthermore performed on commercially pure aluminum (AA 1050). Vickers hardness test was used to determine the distribution of hardness on both normal and longitudinal sections of the deformed samples with respect to the exit channel of the die. The hardness test results showed more uniform distribution of hardness in both sections of the T-ECAP processed samples regarding the ones produced by ECAP process. The load requirement comparison for performing both processes showed lower value for the T-ECAP with respect to the ECAP process. The simulation results for the strain values showed higher magnitude and more uniform distribution for the T-ECAP with respect to the ECAP process.     

纯铝粉末等径角挤压固结模拟及实验研究

目的研究纯铝粉末在等径角挤压(ECAP)工艺下的固结行为。方法采用Deform软件对铝粉的ECAP工艺进行热力耦合有限元模拟分析,研究粉末致密情况、静水压力情况以及温度场分布情况等,剖析铝粉的固结行为。通过铝粉的ECAP实验对粉末的固结质量进行综合评定。结果有限元模拟表明,ECAP剪切转角处静水压力最大,温度最高,相对密度接近0.97,接近完全致密材料,为粉末固结提供了必要前提。实验结果表明,在200℃条件下,可以通过ECAP工艺将铝粉固结成为块体材料。结论 ECAP变形过程能够在较低的温度条件下实现粉末的固结行为。     

Comparison of deformation and microstructural evolution between equal channel angular pressing and forward extrusion using the dislocation cell mechanism-based finite element method

In order to compare plastic deformation and microstructural evolution behavior deformation between equal channel angular pressing (ECAP) and forward extrusion (FE) processes, finite element analyses in associated with the mechanism of dislocation glide and cell formation have been employed. It was found from the simulation results that the ECAP process is superior to the FE process, in terms of strength, grain refinement and deformation homogeneity as well as repeatability due to the equal channels of entry and exit.     

等通道挤压工艺的有限元模拟研究进展

利用有限元法可以模拟ECAP工艺。综述了近年ECAP工艺的FEM研究成果,主要包括模具结构、摩擦、工艺条件几个因素的模拟分析。分析表明,优化磨具结构以及选取适当的工艺条件(如增加道次、选取C路径)可以减小死区、增加变形均匀性,摩擦对均匀性与死区的影响比较复杂。最后介绍了一些新型ECAP工艺的FEM研究进展。     

镁合金双通道转角挤压有限元分析

基于有限元分析软件建立了双通道转角挤压模型,对AZ91镁合金挤压变形过程进行了模拟,并对挤压变形过程、等效应变、挤压力等模拟结果进行了分析。模拟结果表明:双通道转角挤压所需要的挤压力要大于传统的等通道转角挤压,通道夹角越大,挤压所需要的挤压力越小;双通道转角挤压获得的总的应变更大。     

Finite element analysis of the effect of the inner corner angle in equal channel angular pressing

The inner corner angle (ICA) is one of the major factors affecting deformation homogeneity in workpieces during equal channel angular pressing (ECAP). In this study, the effect of the ICA on the plastic deformation behavior in ECAP was investigated using the finite element method. A round ICA induces highly inhomogeneous deformation in the head, tail, top and bottom regions of the workpiece due to increasing compressive and decreasing shear deformation components. It was found that a round inner corner with an angle up to 9° is acceptable in finite element simulations for reproducing a sharp inner corner. These results can serve as a design guide for processing and dies of ECAP.     

Analyses of route Bc equal channel angular pressing and post-equal channel angular pressing behavior by the finite element method

Equal channel angular pressing (ECAP) process provides an efficient procedure for achieving ultrafine grained microstructures with excellent mechanical properties in metallic materials. In this article, a simulation scheme for predicting the mechanical behavior during and after ECAP was proposed. The proposed scheme was applied for interstitial-free (IF) steels, which are widely used for the automobile body applications. Plastic deformation behavior during several passes of ECAP in route Bc, including such aspect as deformed geometry, corner gap, forming load and strain uniformity, was predicted. Tensile testing responses of the ECAP-processed IF steel, including strain hardening, onset of necking, and post-necking behavior, were analyzed using the finite element method and compared with the experimental results. The predicted tensile curves, ultimate tensile strength, and elongation varying with the number of ECAP passes were in good agreement with experimental results. The computational scheme developed was demonstrated to successfully predict not only the plastic deformation behavior during ECAP but also the mechanical properties of the ECAP-processed material.     

摩擦力在ECAP成形时作用的有限元模拟

应用有限元方法对一种全新的可应用于板料的等通道角挤压(ECAP)方法中摩擦力的作用进行了有限元模拟.计算模拟结果表明,不同于常规的等通道角挤压中摩擦力的负面影响,在板料等通道角挤压方法中一定的摩擦力和尺寸精确的模具结构却是保证此类等通道角挤压正常进行的关键.     

Deformation behavior of consecutive workpieces in equal channel angular pressing of solid dies

In this study, consecutive workpiece equal channel angular pressing (ECAP) in solid-dies, where the second workpiece is successively deformed without splitting and reassembling the die after the first workpiece processing, is employed to reduce the processing time in ECAP. The plastic deformation behavior of the two workpieces was investigated in terms of strain homogeneity, load, and defects using the finite element method (FEM). The experimental deformations of the consecutive workpiece during ECAP were compared with the FEM results, and it was found that the deformation was more heterogeneous in the second workpiece when compared with the first workpiece. The primary reason behind these findings is that the deformed geometry of the second workpiece was a back slant type and the first deformed workpiece provided back pressure to the second workpiece. Furthermore, the folding defect was less pronounced in the second workpiece because of the back slant head shape. Despite the less homogeneity in strain, the ECAP of the consecutive workpieces is an effective process for less defective materials and increases process efficiency.     

Plastic deformation characteristics of cross-equal channel angular pressing

For the first time, the plastic deformation characteristics of cross-equal channel pressing (cross-ECAP), a modified equal channel angular pressing, using a cross-shaped channel instead of a conventional l-shaped channel, was analyzed by using finite element analysis. The deformation in the cross-ECAP is more complicated and the strain induced is much more severe than that in the conventional ECAP. However, the plastic strain is localized in the central linear region of the workpiece and very small strain is developed in the edge regions, which is in good agreement with experimental results in the literature showing nonuniformity in microstructure and hardness distribution. The load requirements of cross-ECAP are much higher in comparison to conventional ECAP and T-ECAP processes.