模具外角和内角对等通道角挤压的影响的有限元分析

等通道角挤压(ECAE)工艺受模具外角和模具内角的影响较大,为此利用有限元分析方法对该工艺过程进行了模拟.结果表明:模具外角主要影响等效应变分布的均匀性,对等效应变值的大小影响不大;模具内角主要影响等效应变值的大小,对等效应变分布的均匀性影响较模具外角小;随着模具外角的逐渐增大,模具拐角变形区域逐渐变大,变形机理由纯剪切变形变为剪切变形和弯曲变形相结合的复合变形;随着模具内角的逐渐增大,模具拐角变形区域基本保持不变,变形机理由纯剪切变形变为弯曲变形;模具内角较模具外角对加载载荷的影响更为显著.     

工业纯铝等通道球形转角挤压数值模拟与实验研究

为提高传统ECAE工艺的挤压效率和变形效果,提出一种具有"球形分流"结构的新型等通道球形转角挤压工艺。采用DEFORM-3D有限元软件对工业纯铝ECAE-SC变形过程进行模拟,研究金属流动、挤压载荷、等效应变以及平均应力的分布及变化规律;在自行设计的ECAE-SC模具上成功实现工业纯铝室温单道次连续变形,对变形组织进行了EBSD分析和显微硬度测试。结果表明:ECAE-SC模具外角处球状圆弧的平滑过渡有效改善底部金属流动性,坯料经球形转角依次发生剪切、膨胀和挤压等3种不同形式的复合变形,挤压载荷表现出"急剧上升-缓慢增加-稳定变形"的变化趋势;1道次ECAE-SC变形后,坯料内部平均累积塑性应变高达3.07,沿长度方向形成1个近似平行四边形的稳定应变区,变形均匀性良好;工业纯铝坯料经室温1道次ECAE-SC变形后,外形完整、表面光滑、宏观无裂纹;材料内部形成大量细长的剪切变形带,晶粒破碎和细化现象明显,平均显微硬度大幅提高,由初始36.6 HV增加至58.7 HV。     

有限元分析等径角挤压中通道外角的影响

通道外角是等径角挤压过程中影响试样变形均匀性的重要因素.运用有限元模拟的方法研究了通道外角在等径角挤压过程中的影响.研究结果表明:随着通道外角的增大,材料的流动阻力降低,材料的剪切更加趋于均匀,致使试样的变形和等效应变分布都更加均匀.     

等通道转角挤压中摩擦影响的数值模拟

采用大型商用有限元软件ANSYS对等通道转角挤压(Equal Channel Angular Pressing, ECAP)过程进行数值模拟,得到了ECAP变形过程中的等效应变和等效应力分布规律,分析了摩擦对ECAP变形的影响.结果表明,当模具转角φ＝90°、ψ＝0°时,与无摩擦情况相比,摩擦的存在使与模具接触的试样底部金属发生较大的变形,使等效应变和等效应力分布不均;最大等效应变主要分布在试样的底部,最大等效应力主要分布在转角处且比无摩擦时的分布区域有所扩张.同时,无摩擦时,试样与模具外转角处产生"间隙";存在摩擦时,随着摩擦的增大这种"间隙"逐渐减小甚至会消失.     

基于Deform-3D不同背压等通道转角挤压的计算机仿真

通过Deform-3D有限元分析软件对不同背压辅助下7075铝合金的ECAE挤压过程进行了数值模拟,分析了转角处平均应力的分布。结果表明:随着背压的增加,挤压过程所需的变形力大幅增加,对挤压设备和模具的要求更高;随着材料在通道转角处所受的静水压力增加,材料的塑性变形程度提高,对晶粒的细化效果较好;由于材料在转角处的等效应变速率趋于集中,分布更均匀,因而塑性变形更接近理想的纯剪切变形;等效应变分布规律变化不大。     

AZ91D镁合金等径道角挤压制备半固态坯数值模拟

基于半固态坯采用等径道角挤压（ECAE）制备的应用背景，采用PRO／E建立了等径道角挤压的几何模型，通过压缩实验获取了AZ91D镁合金的高温应力应变曲线，采用有限元软件DEFORM-3D对ECAE挤压变形过程进行了模拟，分析了内外转角部位的应力（平均应力、最大主应力和等效应力）变化、应变分布情况等，以揭示等径道角挤压变形跟模具内转角半径的关系。结果表明，模具内转角半径不为零时，坯料挤压过程中，将有正虚力存在，并且内外转角应力变化不尽相同；应变分布不均匀，具有一定梯度；内转角部位，除了承受剪切，还受到压缩作用，外转角反之。     

数值模拟模具外角对2017铝合金ECAP变形的影响

采用刚塑性有限元法对2017铝合金等通道转角挤压(ECAP)进行热力耦合的数值模拟,分析了模具外角(0~50°)对ECAP过程中载荷、工件中等效应变及其均匀性和工件温度的影响。研究结果表明:随着模具外角增大,载荷峰值和等效应变迅速下降,然后下降幅度越来越小,降至30°左右均趋于稳定;而等效应变的均匀性则随着模具外角增大先提高后略有降低,在模具外角为20°时应变均匀性最好。随着模具外角增大,工件整体温度一直下降,降幅越来越小。     

纯铝等径角挤扭新工艺变形

等径角挤扭(ECAPT)是结合等径角挤压(ECAP)和挤扭(TE)两种典型的大塑性变形(SPD)工艺而产生的一种新型细晶材料制备技术。利用刚塑性有限元技术对纯铝1100ECAPT工艺变形特征进行模拟研究,获得了等效应变和等效应力的大小及分布规律,分析了挤压载荷随变形时间的变化规律及其对试样变形的影响。结果显示,在模具拐角和螺旋通道处,等效应变得到有效积累,最终呈层状分布,且相对较为均匀,应变分布均匀性也得到一定改善,等效应力在上述两处区域达到最大。采用纯铝进行室温3道次ECAPT实验,测量试样显微组织和力学性能的变化。结果表明,实验结果与模拟结果具有较好的一致性;晶粒得到了明显细化,屈服强度、抗拉强度与显微硬度等力学性能得到明显提高,但试样塑性略有降低。     

双向挤压与等通道复合变形模型的有限元分析

以AZ31镁合金为研究对象,对其进行了双向挤压与等通道复合变形模型的数值模拟计算,分析了模具转角对金属流动状态、等效应力、应变与挤压力的影响,并定量的分析了等效应变分布的不均匀程度。结果表明:AZ31镁合金经过双向挤压与等通道复合变形后发生了剧烈的塑性变形,应力主要集中在模具转角剪切区,且能有效的获得高的均匀等效应变值。     

ECAE法制备铜铝双金属复合棒材数值模拟与试验研究

利用Deform-3D有限元软件对铜铝双金属复合棒材室温4道次B_C路径ECAE变形过程进行模拟，研究了金属流动、挤压载荷、等效应变以及平均应力的分布及变化规律；并在自行设计的模具上进行了试验验证，成功制备出铜铝双金属复合棒材，对变形材料进行了物理网格试验及组织性能测试。结果表明，ECAE工艺下铜铝双金属复合棒材内部存在剧烈剪切变形区，复合坯料由不稳定变形逐渐过渡为均匀协调变形，材料内部处于理想的三向压应力状态，静水压力较高，界面处金属结合紧密。4道次ECAE挤压后，铜铝双金属复合坯料整体变形相对均匀，平均累积等效应变量为4.49。随着挤压道次的增加，载荷峰值不断增加，同时复合坯料内部显微硬度不断升高，但包覆层增幅大于芯部材料。     

Die structure optimization of equal channel angular extrusion for AZ31 magnesium alloy based on finite element method

Three-dimensional(3D)geometric models with different corner angles(90°and 120°)and with or without inner round fillets in the bottom die were designed.Some important process parameters were regarded as the calculation conditions used in DEFORMT M-3D software,such as stress—strain data of compression test for AZ31 magnesium,temperatures of die and billet,and friction coefficient.Influence of friction coefficient on deformation process was discussed.The results show that reasonable lubrication condition is im...     

面向应变均匀性和成形力的等径道角挤压模具结构参数优化

面向等径道角挤压成形应变均匀性和成形力,以3003铝合金为研究对象,采用有限元法分析不同模具外角、内角、内角半径挤压变形的等效应变均匀性和挤压成形力。研究结果表明:外角ψ对等效应变均匀性影响显著,而内角φ主要对挤压成形力影响较大,内角半径r对二者影响不明显。因此采用合理的模具结构参数,既可以提高应变均匀性,又能降低挤压成形力。基于正交试验分析得到了模具结构参数为:ψ=40°,φ=105°,r=1.5 mm,这为研究试样宏观塑性变形与细化晶粒微观组织演变规律、模具结构设计参数提供理论依据。     

Severe plastic deformation of commercially pure aluminum using novel equal channel angular expansion extrusion with spherical cavity

Equal channel angular expansion extrusion with spherical cavity (ECAEE-SC) was introduced as a novel severe plastic deformation (SPD) technique, which is capable of imposing large plastic strain and intrinsic back-pressure on the processed billet. The plastic deformation behaviors of commercially pure aluminum during ECAEE-SC process were investigated using finite element analysis DEFORM-3D simulation software. The material flow, the load history, the distribution of effective strain and mean stress in the billet were analyzed in comparison with conventional equal channel angular extrusion (ECAE) process. In addition, single-pass ECAEE-SC was experimentally conducted on commercially pure aluminum at room temperature for validation, and the evolution of microstructure and microhardness of as-processed material was discussed. It was shown that during the process, the material is in the ideal hydrostatic stress state and the load requirement for ECAEE-SC is much more than that for ECAE. After a single-pass ECAEE-SC, an average strain of 3.51 was accumulated in the billet with homogeneous distribution. Moreover, the microstructure was significantly refined and composed of equiaxed ultrafine grains with sub-micron size. Considerable improvement in the average microhardness of aluminum was also found, which was homogenized and increased from HV 36.61 to HV 70.20, denoting 91.75% improvement compared with that of the as-cast billet.     

New Methods for Severe Plastic Deformation Processing

Several new concepts for possible methods of severe plastic deformation (SPD) of bulk quantities of materials are presented. The first of these are variations of equal channel angular extrusion (ECAE) in which the conventional fixed die is replaced by rotating tools, for the inner die corner, the outer die corner, or both corners. Other methods share some characteristics of ECAE in that they use shearing strains to deform the material; these are reversed shear spinning and transverse rolling. Deformation sequences for a cylindrical or annular workpiece that deform the workpiece while eventually restoring the initial workpiece geometry can be performed by numerous processes. These techniques can be used to accumulate high strains by repeated deformation cycles. These methods offer possible alternatives to ECAE and high-pressure torsion, with potential benefits that include different and larger workpiece geometries, simplified tooling design, lower tooling loads, ease of lubrication, automated or reduced part handling, and, in some cases, potentially continuous operation. It is hoped that these suggestions will prompt new examination of alternative methods for SPD. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

纯铝粉末多孔材料等通道转角挤压数值模拟及实验

采用体积可压缩刚粘塑性有限元法,对纯铝粉末多孔烧结材料的等通道转角挤压过程进行数值模拟,获得了挤压过程试件内部变形场、静水应力场及相对密度场的分布。研究结果表明,等通道转角挤压对粉末多孔材料具有强烈的致密效果。分析认为,挤压过程所提供的高静水压力状态和大剪切变形,是孔隙得以有效焊合的关键。对纯铝粉末烧结材料进行的实验结果表明,试样经过一次挤压后,主要变形区组织剪切变形特征明显,内部的孔隙基本闭合,组织明显细化,材料的力学性能显著提高。     

Simulation of Aluminum Powder in Tube Compaction Using Equal Channel Angular Extrusion

Aluminum powder in tube compaction with a 25 mm front plug through equal channel angular extrusion (ECAE) at room temperature was modeled using the finite element analysis package ABAQUS. The Gurson model was used in modeling this process. 2-D simulations in a 90° angle die showed better consolidation of powder near the inner edge of the die than the outer edge after one pass of ECAE but almost full densification occurs after two passes. The effect of hydrostatic pressure on densification of the powder was investigated by using two plugs varying in length dimension. The results obtained from the simulations were also compared with experiments conducted to compact aluminum powder with mean particle diameter of 45 μm. Optical microscopy, microhardness test, and density measurements confirmed the simulations. The simulations were extended to powder compaction in a 60° and 120° angle die. It was found that one pass of ECAE is sufficient to consolidate the aluminum powder completely and uniformly in a 60° angle die, whereas the material is still porous in a 120° angle die.     

Equal channel angular extrusion of NiTi shape memory alloy tube

As a new attempt, equal channel angular extrusion (ECAE) of nickel–titanium shape memory alloy (NiTi SMA) tube was investigated by means of process experiment, finite element method (FEM) and microscopy. NiTi SMA tube with the steel core in it was inserted into the steel can during ECAE of NiTi SMA tube. Based on rigid-viscoplastic FEM, multiple coupled boundary conditions and multiple constitutive models were used for finite element simulation of ECAE of NiTi SMA tube, where the effective stress field, the effective strain field and the velocity field were obtained. Finite element simulation results are in good accordance with the experimental ones. Finite element simulation results reveal that the velocity field shows the minimum value in the corner of NiTi SMA tube, where severe shear deformation occurs. Microstructural observation results reveal that severe plastic deformation leads to a certain grain orientation as well as occurrence of substructures in the grain interior and dynamic recovery occurs during ECAE of NiTi SMA tube. ECAE of NiTi SMA tube provides a new approach to manufacturing ultrafine-grained NiTi SMA tube.     

不同工艺参数对大口径厚壁无缝钢管垂直挤压过程的影响

针对火电、核电设备使用的基础构件大口径厚壁无缝钢管,利用有限元模拟软件Deform-3D对钢管的垂直挤压过程进行数值模拟,通过改变挤压比、凹模锥角等参数对其等效应力、等效应变、温度场及载荷进行分析。结果表明:随着挤压的进行,坯料等效应力、等效应变及载荷都是先逐渐增加后趋于平稳;随着挤压比以及凹模锥角的变化,等效应力、等效应变及载荷也发生不同程度的变化;并且当挤压比为6、凹模锥角为30°时最有利于坯料的成形。     

往复挤压变形ZK60镁合金应变分布的有限元数值模拟

利用有限元法研究ZK60镁合金在多道次往复挤压过程中的应变分布。为优化往复挤压工艺,研究摩擦条件和模具结构尺寸对ZK60合金总等效塑性应变分布的影响。结果表明：ZK60合金试样经往复挤压后内应变分布不均匀。试样两个端部的应变量低于试样中间部位的应变量。工艺参数对应变分布的影响很大。试样和模具间的摩擦不利于试样内应变量的均匀分布,因而应尽量降低摩擦。为了提高应变量的均匀分布,应该使用较大的过渡圆角半径和较低的挤压角度。