6061铝合金等通道挤压工艺数值模拟

采用有限元技术模拟6061铝合金在室温下等通道转角挤压(ECAP)过程,分析了模具圆心角、摩擦因数对ECAP过程的影响。结果表明,圆心角减小,试样等效应变值增大且较为均匀,但是挤压载荷增加;摩擦对载荷的影响明显。单道次挤压后,试样变形不均匀。     

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.     

摩擦条件对高强铝合金ECAP变形作用的有限元模拟

应用三维金属塑性成形模拟软件DEFORM-3D,对高强铝合金等通道转角挤压(ECAP)变形过程中摩擦力的作用进行了有限元模拟。计算模拟结果表明,挤压过程中载荷-位移曲线可分为快速增加、载荷稳定、快速增加、载荷稳定及快速下降5个阶段。摩擦系数越大,变形载荷越大;摩擦系数从0到0.3,最大载荷增加了2.1倍,所消耗的功增加了1.3倍,摩擦条件下,载荷一部分用于克服摩擦阻力,一部分用于材料变形,增大了能耗,同时减少了模具使用寿命。此外摩擦系数大,材料平均等效应变基本不变,而芯部应变不均匀程度增大。因此在等通道转角挤压的过程中,应保证挤压凹模内壁表面光洁、使用合适的润滑剂,以减小摩擦,减小载荷,从而改善晶粒细化及组织的均匀性效果。     

摩擦条件对高强铝合金单次ECAP作用的有限元模拟

对高强铝合金等通道转角挤压(ECAP)单次变形过程中摩擦力的作用进行了有限元模拟.结果表明,随着摩擦因数的增大,其变形载荷不断增大,所消耗的功也不断增大,心部应变不均匀程度增大,而材料平均等效应变保持基本不变.挤压过程中载荷-位移曲线可分快速增加、载荷稳定、快速增加、载荷稳定及快速下降5个阶段.当摩擦因数从0到0.30时,最大载荷提高了2.1倍,所消耗的功增加了1.3倍.因此在等通道转角挤压的过程中,应保证挤压凹模内壁表面光洁、使用合适的润滑剂,以减小摩擦和载荷,从而改善晶粒细化及组织的均匀性.     

ECAP中摩擦因数对7075铝合金变形及组织的影响

采用有限元软件DEFORM-3D对7075铝合金等通道角挤压(ECAP)过程进行数值模拟,分析了不同摩擦条件下载荷变化、变形行为以及等效应力应变分布情况,并利用7075铝合金动态再结晶模型对微观组织变化过程进行了预测。结果表明,随着摩擦因数增大,载荷峰值明显增大甚至成倍增长,且载荷值波动加剧,试样"端部效应"减弱,等效应力应变分布不均匀;试样中部稳定变形区晶粒随挤压道次增多而不断细化,试样与通道接触部位形成晶粒细小区,经过4道次挤压后,摩擦因数为0.4时稳定变形区的晶粒比摩擦因数为0.1时的细小。     

不同温度下AZ31镁合金等通道转角挤压工艺模拟分析

采用Deform-3D有限元软件,在挤压温度为250~400℃条件下,对AZ31镁合金等径角挤压工艺进行了数值模拟,主要分析塑形成型过程中的挤压载荷、等效应力和等效应变的变化规律。结果表明,AZ31镁合金塑形成型过程中挤压载荷分为3个阶段:无明显变形阶段、快速增长阶段和稳定变形阶段。挤压载荷随着挤压温度的增加显著下降,试样的等效应力分布不均,模具转角处等效应力较大,存在应力集中现象,等效应变逐渐增加,在转角剪切区最大。试样经过ECAP变形后,心部等效应变大,从内向外应变呈减小的趋势,试样上部等效应变较大,下部等效应变相对较小,组织均匀性较好。     

数值模拟模具内角对6082铝合金ECAP的影响

基于有限元分析,以6082铝合金为研究对象,采用DEFORM-3D分析了90~150°模具内角范围时等通道转角挤压(ECAP)过程中的载荷-行程曲线与应力及应变分布。结果表明,当模具内角为90°时,试样获得的等效应力和等效应变最大,塑性变形程度最强;随着模具内角增大,试样挤压过程中载荷值明显下降,试样中等效应力和等效应变减小,等效应变分布均匀性提高。     

摩擦系数对等通道转角挤压工艺影响的有限元分析及试验研究

采用ANSYS软件建立了等通道转角挤压有限元模型,对试样与模具接触面间不同摩擦系数条件下的等通道转角挤压过程进行了模拟,获得了摩擦应力、试样与模具内部应力的变化及分布规律。以AZ31镁合金为试验对象,进行了等通道转角挤压试验,将模拟分析结果与试验结果进行了对比。结果表明,等通道转角挤压过程中,试样与模具间的摩擦系数对摩擦应力、试样变形及弹性应力均有重要影响。随着试样与模具接触面摩擦系数的增加,试样与模具表面会产生较大摩擦应力,导致试样与模具内应力分布不均匀。摩擦应力、材料内部应力大小及分布区域随着摩擦系数的增加而增加。     

工业纯钛室温一道次ECAP加工后的组织和硬度

室温下,分别采用90°模具和120°模具对工业纯钛(CP-Ti)进行一道次等径弯曲通道变形(Equal ChannelAngular Pressing,简称ECAP),研究了其组织和硬度的变化情况.结果表明,工业纯钛经一道次ECAP变形后都形成板条状组织,硬度显著提高.90°模具挤压后试样上、下表面的硬度值稍低于试样中间的硬度值,而120°模具挤压后试样表面硬度分布较均匀.     

通道截面形状对纯钛室温ECAP变形影响的有限元分析

采用有限元软件Deform-3D对室温纯钛等径弯曲通道变形(ECAP)过程进行数值模拟,分析了不同等通道截面形状条件下载荷变化、变形行为以及等效应变分布情况。结果表明:不同截面形状试样随着通道截面圆角增大,端部效应有所增加,试样与出口通道上壁之间的缝隙增大;不同通道截面挤压的行程载荷曲线趋势一致,常用的方形截面(R=0 mm)ECAP挤压时载荷最大;ECAP挤压后,试样纵向上等效应变从中部向两端递减,竖直方向上等效应变从上到下逐渐下降;方形(R=0 mm)和圆形(R=10 mm)截面ECAP挤压的等效应变较高,特别是圆形截面ECAP挤压心部等效应变要高于外表,这有别于其他塑性变形形式。     

激光熔覆各向异性对Fe60合金磨损腐蚀性能的影响

目的 提高激光熔覆各向异性材料的抗磨损腐蚀性能。方法 以激光熔覆Fe60合金粉末为研究对象,选取与熔覆方向平行、倾斜45°以及垂直的3个工作表面进行磨损腐蚀测试,重点分析材料构筑方向对磨损腐蚀性能的影响机制。结果 通过对不同工作面摩擦系数、开路电位以及磨损体积的监测,发现与熔覆方向成45°的试样表面具有更好的摩擦稳定性、耐腐蚀性以及磨损抗性。原因在于,工作表面晶粒取向与晶界密度差异引起了试样表面变形抗力的不同。另外,与铸造试样进行对比得出,激光熔覆试样的磨损腐蚀抗性更加优越,主要与凝固过程中高冷却速率引起的组织细化有关。结论 对于激光熔覆各向异性材料,工作表面具有细化的微观组织结构、较高的晶界密度以及良好的变形抗力,有助于提高其磨损腐蚀抗性。     

半固态Al-6.6%Si合金的变形行为

分别对常规铸造Al 6.6%Si合金和电磁搅拌制备的半固态Al 6.6%Si合金试样进行了压缩实验 ,分析了它们的应力—应变关系和组织变化。结果表明 ,半固态Al 6.6%Si合金液固两相区压缩变形可分为触变流动初始阶段和稳定触变流动两个阶段。在触变流动初始化阶段 ,应力从零急剧增大到最大值 ,并在这个最大值上保持一段时间。在稳定触变流动阶段 ,随应变增加 ,应力缓慢下降 ,整个过程应力都大大低于常规铸造Al 6.6%Si合金压缩变形时应力。半固态合金在液固态两相区压缩变形后 ,其初生相微粒仍保持为球状 ,并且试样各处变形均匀。同时 ,对半固态合金变形中的初生相微粒簇现象和液固分离现象也进行了讨论。     

考虑摩擦和温升效应的Ti60合金流变曲线修正

采用Thermecmaster-Z型热加工模拟试验机对Ti60合金进行等温恒应变速率压缩实验,获得该合金在变形温度700～950℃,应变速率0.001～10s-1和真应变0.51条件下的流变曲线.通过考虑摩擦和温升效应对流动应力的影响,对Ti60合金实测流变曲线进行修正.结果表明,摩擦和温升效应对Ti60合金流动应力均...     

Friction Factor Evaluation Using Experimental and Finite Element Methods for Al-4%Cu Preforms

In this study, ring compression tests and finite element (FE) simulations have been utilized to evaluate the friction factor, m, under different lubricating conditions for powder metallurgical (P/M) Al-4%Cu preforms. A series of ring compression tests were carried out to obtain friction factor (m) for a number of lubricating conditions, including zinc stearate, graphite, molybdenum disulfide powder, and unlubricated condition. FE simulations were used to analyze materials deformation, densification, and geometric changes, and to derive the friction calibration curves. The friction factor has been determined for various initial relative densities and different lubricating conditions, and a proper lubricant for cold forging of P/M Al-4%Cu preforms is found. Studies show that the use of lubricants has reduced the friction. However, increase in the number of pores in the preforms leads to excessive friction. The FE simulation results demonstrate a shift in the neutral plane distance from the axis of ring specimen, which occurred due to variations in the frictional conditions and initial relative densities. The load requirement for deformation, effective stress, and effective strain induced, and bulging phenomena obtained by FE simulations have a good agreement with the experimental data.     

Effect of friction-induced deformation and oxidation on the structure and microhardness of surface aluminum and silumin layers

Metallography, electron microscopy, and X-ray diffraction have been used to investigate structural transformations that take place in a 10-μm-thick surface layer in aluminum and Al–17% Si alloy under conditions of sliding friction and subsequent oxidation at 100 and 200°C for 1 h. Friction-induced deformation has been carried out at room temperature in air and at–196°C in liquid nitrogen by reciprocating sliding of a cylindrical indenter made of cubic boron nitride at a rate of 0.014 m/s and a load of 98 N. It is shown that deformation under these conditions forms nanocrystalline structures in the surface layer in aluminum and Al–17% Si alloy and increases their microhardness by a factor of 1.8–3.5. A high contact deformation and a high affinity of oxygen to aluminum and silicon cause the formation of anomalously supersaturated solid solutions of oxygen in aluminum and silicon in the surface layer of the alloy during friction. Oxidation at 100°C (1 h) of the deformed Al–17% Si alloy increases its microhardness due to the decomposition of anomalously supersaturated solid solutions of oxygen in aluminum and silicon and the formation of their oxides.     

Mg-Ti旋转摩擦焊过程的摩擦产热及原子扩散行为(英文)

利用新型物理模拟装置进行Mg-Ti旋转摩擦焊过程产热机理及原子扩散行为的研究,该装置包含高速摄像、红外热成像及力学传感器系统。结果表明,摩擦焊过程中,摩擦因数经历两个稳态阶段的变化。第一个稳态阶段为库伦摩擦,以磨蚀为主要形式;第二个稳态阶段为粘着摩擦,以塑性流动为主要形式。另外,随着旋转转速及轴向压力的提高,轴向位移、摩擦温度及摩擦系数的增加率也随之明显提高。Mg-Ti摩擦焊过程存在原子的快速扩散现象,该过程中由摩擦大变形激活的扩散系数大约是热激活扩散系数的105倍。     

Interface friction and deformation kinematics in metal compression with sticking friction

Friction at the die-metal interface results in nonuniform deformation in metal compression. With sticking friction, the plastic flow mechanism becomes extremely complex, and the force and energy requirements are higher compared to frictional compression. Earlier research, which had some limitations, enables evaluation of the forming load in metal compression involving sticking friction. In the present article, critical analysis has been made regarding frictional behavior at the real contact areas to propose a more realistic estimation of frictional constraints. For this purpose, available inferences in specific areas of metal forming, concerning fundamental concepts of friction and the influence of interface shear stress, bulk deformation, etc., on frictional behavior, have been used and modified as required. Also, a rational deformation kinematics has been proposed, assuming velocity discontinuity at every point within the flow field. The proposed estimation of friction and plastic flow kinematics yields results in line with the published experimental findings and the corresponding slip-line field solutions.     

纳米尺度单晶锗各向异性摩擦磨损性能试验研究

利用纳米压痕仪和原子力显微镜,分别对单晶锗Ge(100)、Ge(110)、Ge(111)3种晶向的表面进行纳米尺度下的摩擦磨损试验。在较大载荷的条件下,3种不同晶面取向的单晶锗磨损情况均呈现沟槽形式,沟槽两侧出现明显的碎屑堆积现象。在划痕试验过程中,单晶锗的磨损性能受晶面取向影响较小;单晶锗的摩擦力随着滑动速度的增加而增加。而且,随着滑动速度的增大,晶体表面出现严重的磨损-沟槽损伤,沟槽两侧碎屑堆积的体积也越来越大,沟槽的深度也逐渐增大;单晶锗在较低载荷下,摩擦力基本保持稳定,但随着载荷的增大,单晶锗的摩擦力呈非线性增长,载荷增大一定值时,晶体表面发生明显的由塑性变形向脆性破坏转变的脆塑转变过渡过程,导致单晶锗表面发生脆性剥离,形成沟槽两侧碎屑堆积。     

120°模具室温ECAP制备工业纯钛的压缩变形本构关系

在Gleeble-1500热模拟机上对120°模具室温Bc方式ECAP变形8道次制备的平均晶粒尺寸约为200 nm的工业纯钛进行等温变速压缩实验,研究超细晶工业纯钛在变形温度为298~673 K和应变速率为1×10-4~1×100s-1条件下的流变应力行为。结果表明:变形温度和应变速率均对流变应力具有显著影响,峰值应力随变形温度的升高和应变速率的降低而降低;流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳,呈现稳态流变特征。采用双曲正弦模型确定了超细晶工业纯钛的变形激活能Q=104.46 kJ/mol和应力指数n=23,建立了相应的变形本构关系。     

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.