纯铜粉末包套挤扭成形致密的灰色预测与优化

以横截面扭转角α、螺旋角β、摩擦因子、挤压速度、初始相对密度为因子,建立正交试验设计方案,对纯铜粉末材料进行一道次包套扭挤数值模拟,以获得的平均等效塑性应变εm、平均最大损伤值δmax、平均相对密度ρm作为优化设计目标,运用追踪点法和灰色系统理论的灰色关联度优化工艺参数,使设计目标值达到等效应变最大、最大损伤值最小、相对密度最大。模拟验证结果表明,运用多目标优化参数进行挤扭成形能使纯铜粉末体变形材料迅速地形变累积,最大损伤值显著地减小,致密效率高,提高了材料综合质量。     

铝粉烧结材料等通道转角挤压组织性能演变

对不同路径和不同道次下铝粉烧结材料的等通道转角挤压工艺进行了试验研究,用光学显微镜、扫描电子显微镜和透射电镜分析了粉末烧结材料在不同工艺条件下的晶粒细化规律和致密行为,并测量了挤压后试样的密度和硬度等性能.结果表明,等通道转角挤压工艺对粉末烧结材料具有很强的致密效果和细化效果,可显著提高其力学性能.在单道次变形中,大剪切塑性变形和高静水压力状态是粉末烧结材料获得良好的致密效果的关键;在多道次变形中,变形量的累积和不同的剪切特征不断地改变内部的孔隙形状,使内部基体材料进一步致密.而晶粒的细化效果则取决于变形中的静水压力、变形量和剪切特征等关键因素.     

非致密喷射沉积耐热铝合金锭坯制备φ520/φ460 mm管材过程数值模拟

采用DEFORM通用有限元软件对喷射沉积耐热铝合金非致密锭坯制备φ520φ/460 mm管材过程数值模拟,分析了镦粗、充型、反挤压过程中致密度、应变场以及挤压力的变化情况.通过挤压力和致密度大小的比较,计算机模拟结果与实验结果基本相符.     

基于有限元不同大塑性变形应变特征对比研究及组织分析

目的 探究往复挤压工艺(CEC)与往复挤扭镦工艺(SETE)的变形特点,并研究单道次变形后的金属流动行为和应变分布特征。方法 以低活化钢为材料,对CEC和SETE等2种工艺下的变形过程进行有限元模拟分析,获得3个道次变形后的CLAM钢等效应变云图,同时,开展相关试验以验证有限元模拟的准确性。结果 往复挤压工艺(CEC)与往复挤扭镦工艺(SETE)均能实现多道次累积应变,其中SETE下的单道次累积应变量更大,其各道次等效应变分别比CEC下的等效应变高2.47、5.06、7.84。0.5道次变形后,SETE下的平均硬度值比CEC下的高6.1HV。结论 在CEC与SETE下进行各道次变形后,边缘等效应变都高于心部等效应变,且1道次变形后应变均匀性相差不大,但随着道次的增加,SETE下的应变分布更加均匀。0.5道次变形后,CEC与SETE下的边缘晶粒尺寸均较心部晶粒尺寸细小,且SETE下的晶粒细化程度更高。     

等径角挤扭工艺的研究

针对等径角挤压(ECAP)工艺和挤扭(TE)工艺中,材料变形不均匀,1道次变形获得的应变量不够大的缺点,将2种工艺有机结合,提出了等径角挤扭(ECAPT)工艺。利用UG和DEFORM-3D软件进行几何造型和有限元模拟,研究变形过程、应力应变分布和载荷变化,并用纯铝进行2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,ECAPT使组织产生更大的应变量,随着行程的增加,载荷增大,在TE通道平稳阶段达最大值,试样头部挤出TE通道后载荷降低;材料的宏观形貌同模拟结果一致,显微组织发生了明显细化,其中第1道次z面和第2道次y面细化效果明显;力学性能得以较大提高,屈服强度由43.31MPa提升至52.19MPa,抗拉强度由71.30MPa提升至130.38MPa。     

AZ31镁合金等通道转角挤压应变累积均匀性分析及组织性能研究

等通道转角挤压工艺(Equal Channel Angular Pressing,ECAP)是通过剧烈塑性变形改变微观组织结构生产超细晶粒材料的材料加工方法,工件变形的均匀性一直是ECAP 工艺过程中影响材料性能的主要原因之一.采用空间转换法实现了AZ31镁合金多道次ECAP挤压过程中有限元分析相关场量的准确传递,完成了四种不同挤压路径ECAP多道次挤压工艺的有限元模拟,获得了相应挤压件累积等效应变的分布规律.研究确定了经过四道次ECAP挤压以后等效应变累积最为均匀的挤压路径.通过微观组织观察和室温拉伸力学性能实验探讨了不同路径多道次ECAP挤压AZ31镁合金的组织性能变化规律.分析结果表明通过合适的变形路径可以获得细小而均匀的微观组织,当材料的应变累积均匀时,其力学性能也较好.     

新型大塑性变形复合挤扭过程数值模拟分析

针对挤扭(Twist Extrusion,TE)过程试样变形不均匀,结合挤扭和挤压工艺提出了复合挤扭(Composite Twist Extrusion,CTE)新型大塑性变形工艺。运用有限元分析法对纯铝在室温下进行数值模拟,获得了应力应变分布,载荷行程曲线,并对工艺进行改进消除了头部难变形区域。结果表明复合挤扭工艺可以有效地降低均匀系数,改进后的工艺可以获得变形均匀的试样。     

可压缩材料挤压过程有限元模拟

利用QFORM通用有限元软件对可压缩材料挤压过程进行了数值模拟，研究了初始相对密度对等效应变和挤压力、挤压比对致密速度和挤压力的影响，同时，通过对平面应变和轴对称各种挤压工况进行模拟分析，给出了两种状态单位挤压力间的关系。     

机械球磨Cu-15%Cr复合粉末的致密化工艺研究

探讨机械球磨Cu—15％Cr复合粉末经真空烧结后采用热静液挤压致密化的可能性．研究了机械球磨时间、烧结温度、保温时间和挤压温度等工艺参数对材料致密化的影响．结果表明，热静液挤压工艺可以有效的促进机械球磨复合粉末的致密，所获得的材料具有优异的组织性能．     

ECAP法制备细晶ZK60镁合金的微观组织与力学性能

利用等通道转角挤压法(ECAP)制备出了细晶ZK60合金,通过金相组织观察,拉伸性能测试,EBSD和透射电镜(TEM)研究了不同挤压温度和挤压道次对合金组织与性能的影响.结果表明:ZK60镁合金在210～240℃温度范围内进行ECAP挤压能获得较好的晶粒细化效果;在240℃进行ECAP挤压时,随着挤压道次的增加,合金晶...     

Influence of twist extrusion process on microstructure and mechanical properties of 6063 aluminum alloy

In this study, aluminum alloy 6063 was severely deformed by twist extrusion (TE) technique and its mechanical properties, before and after TE, was investigated using a die with the twist line slope of β = 30°. It was revealed that large strains imposed on the material by this advanced method of severe plastic deformation (SPD) led to a nano-scale ultra-fine microstructure and to an enhancement of the mechanical properties. The more passes of TE the finer grained microstructure was produced. Also with increasing the number of TE passes, yield strength, ultimate tensile strength and hardness increased, while after relative reduction of uniform elongation and elongation to failure by intermediate passes they remained almost unchanged. Therefore, both the strength and ductility of the material were improved when deformed by twist extrusion.     

低温等通道转角挤压中定向凝固纯铜的组织及性能演变

采用光学显微镜(OM)和XRD技术对干冰冷却后的定向凝固纯铜(99.99%)经等通道转角挤压(ECAP)时的微观组织演变规律进行研究,并测试了ECAP后定向凝固纯铜的硬度及导电性能。结果表明,定向凝固纯铜在低温下经A和C路径变形后易于形成取向一致的纤维组织,并且保持(111)面的择优取向特征,而经Bc路径变形后,柱状晶破碎,形成均匀的等轴晶,且各晶面逐渐趋于随机取向;经过1道次变形后,各路径硬度大幅增加,约为原来的1.8倍,在随后的挤压中,硬度增加缓慢,经4道次ECAP后,Bc路径的硬度有所下降;在低应变下,晶粒取向的一致性使得导电率增加;随着应变的增加,晶格畸变使得电子发生散射,使导电率略有降低。     

Agglomerate breakdown in fine alumina powder by multiple extrusion

Repeated extrusion through dies of various diameters and die entry angles was used to determine the rate of agglomerate breakdown in a paste consisting of a fine alumina powder, carbon black and a binder of hydroxyl propyl methyl cellulose in water. It was found that three extrusion passes were enough to break up all but 0.4% of the agglomerates. Dies with orifices of approximately 1 mm diameter and die entry angles of 45 to 90 (where the elongational strain and the deformation rates were highest) were the most efficient for disrupting and dispersing agglomerates and distributing the moisture evenly. This process of deagglomeration was studied by monitoring the load required to extrude and moisture distribution during five repeated extrusion passes of each test paste. The density, agglomerate area fraction and agglomerate circularity of dried extradates were quantified and plotted.     

等通道挤压AZ80镁合金的析出行为和性能

研究了AZ80镁合金经300℃等通道挤压(ECAP)后的组织、织构与力学性能的演变规律以及第二相析出行为的影响。结果表明:ECAP显著促进了粒状连续析出,可有效节省后续热处理时间。A路径多道次挤压最终获得基面织构;Bc路径挤压后形成基面近似平行于剪切面的织构;第二相析出对ECAP织构特征的形成没有显著影响。用该工艺可获得较高的延伸率(13%-19%),但是抗拉强度过低(300 MPa),综合机械性能不理想。可通过抑制挤压前的未溶粗大粒子的析出、减少挤压道次和降低挤压温度等措施优化AZ80的析出控制。     

Strength and pore morphology of porous aluminum and porous copper with directional pores deformed by equal channel angular extrusion

Porous aluminum with a porosity of 17.6% and porous copper with a porosity of 39.7% (the pores of both aluminum and copper were cylindrical and oriented in one direction) were deformed by equal channel angular extrusion using a 150° die with sequential 180° rotations (route C), and the mechanical strength and pore morphology after the extrusions were investigated. In the case of porous aluminum with low porosity, the pores were collapsed by the extrusions that were both parallel and perpendicular to the orientation direction of the pores. In contrast, the porosity of porous copper decreased slightly after extrusions that were parallel to the orientation direction of the pores, and the pores thus remained even after four extrusions. The yield strength after the second extrusion was 7.3 times greater than it was before the extrusion, even though there was a decrease in porosity of only 8%. On the other hand, almost all the pores of the porous copper collapsed after the fourth extrusion, when the extrusion direction was perpendicular to the orientation direction of the pores. Thus, the yield stress cannot be enhanced without being accompanied by progressive densification.     

Analytical modeling of material flow in equal channel angular extrusion (ECAE)

We provide analytical forms for the plastic deformation and velocity gradients associated with a single pass of equal channel angular extrusion (ECAE). Three cases of plastic deformation are considered: ideal simple shear, a plastic deformation zone (PDZ) in the shape of a central fan of angle β_m, and a two-part PDZ consisting of a central fan in the ‘upper’ region and a low intensity shear deformation in the ‘lower’ region. The analysis for simple shear considers a general die angle Φ, whereas the other two cases only consider Φ=90°. The tensors for deformation and velocity gradients completely describe the deformation, such as the directions and magnitudes of material stretching and rotations. From this analysis, one can calculate deformation and texture evolution. Texture evolution during flow through the central fan zone involves continuous rotation of the texture components causing the texture developed at the end of the extrusion to be rotated relative to the ideal simple shear case. The analysis of the two-part zone suggests inhomogeneity in texture evolution, in which features of the initial texture are retained and rotated in the lower region, while they are nearly erased in the upper region. These analytical flow patterns for a single pass can be repeatedly applied for any number of passes of any ECAE route.     

A crystal plasticity finite element analysis of cross-grain deformation heterogeneity in equal channel angular extrusion and its implications for texture evolution

A crystal plasticity finite element (CPFE) method was applied to evaluate cross-grain deformation heterogeneity and its implication on texture evolution during equal channel angular extrusion (ECAE) of pure copper. The simulations were conducted for one to four passes of ECAE via route C, assuming simple shear in each pass at the macroscopic level. Analyses of the stress and strain distributions reveal considerable deformation heterogeneities across individual grains in the polycrystal. The grain interactions are found to be remarkable after even-numbered passes and they partly contribute to the retained shear textures. The CPFE model captures very well the experimental textures after odd-numbered passes; however, it is not able to model the measured textures subsequent to even-numbered passes, and the results are only slightly improved as compared to a visco-plasticity self-consistent polycrystal model. These results suggest that dedicated considerations of deformation heterogeneities at both the macro- and meso-levels are necessary in modeling texture evolution during severe plastic deformation.     

Twist-channel angular pressing: effect of the strain path on grain refinement and mechanical properties of copper

Substructural characteristics of Cu (99.97%) were examined after the Twist channel angular pressing (TCAP) process carried out at ambient temperature. Grain refinement efficiency and resulting thermal stability were evaluated after three passes with respect to utilization of various strain paths. Results were obtained using light microscopy and X-ray diffraction methods; Mechanical properties of extruded materials were also tested. Thermal stability was studied after application of three annealing cycles. Based on the findings, Bc route is the most efficient strain path with respect to the grain refinement; higher speed of extrusion (10 mm/s) corresponds with suppression of the static recrystallization. Measured strength, obtained after three passes (route A), achieved values around 440 MPa homogeneously along the cross section of the extruded material. Homogeneity of deformation was also confirmed by micro-hardness tests. The grain size, determined after three passes, averaged out 1.2 μm. Application of TCAP (three passes) brought markedly homogeneous deformation throughout the processed sample in comparison with classical ECAP process.     

The microstructure,tensile, and shear deformation behavior of an AZ31 magnesium alloy after extrusion and equal channel angular pressing

The shear punch testing (SPT) technique and the uniaxial tension tests were employed to evaluate the mechanical properties of the equal channel angularly pressed (ECAPed) AZ31 magnesium alloy. After extruding, the material was ECAPed for 1, 2, and 4 passes using route B_C. The grain structure of the material was refined from 20.2 to 1.6 μm after 4 passes of ECAP at 200 °C. The 4 pass ECAPed alloy showed lower yield stress and higher ductility as compared to the as-extruded condition, indicating that texture softening has overcome the strengthening effects of grain refinement. The same trends in strength and ductility were also observed in shear punch testing. Similar shear strength and ductility values of the samples taken perpendicular to the extrusion direction (ED) and normal direction (ND) after 4 passes of ECAP indicated that {0 0 0 2} basal planes were inclined (∼45°) to the extrusion axis. The shear punch testing technique was found to be a useful method for verifying directional mechanical properties of the miniature samples of the ECAPed magnesium alloys.     

网眼多孔陶瓷浸渍成型工艺的研究

采用一种具有三维网状结构和连通气孔的氨酯海绵作为骨架来制备网眼多孔陶瓷．采用一种亲水憎水平衡值（ＨＬＢ）＞１２的表面活性剂溶液对海绵体孔筋表面进行改性处理,改善了海绵与水基浆料之间的粘附性,增加了浆料涂覆量．研究了浆料固含量、有机泡沫体网眼大小、对辊间距和挤压次数对浆量涂覆量及结构均匀性的影响．结果表明：浆料固含量和对辊间距是影响涂覆量及结构均匀性的最主要因素．还发现网眼烧结体的相对密度与相对对辊间距具有很好的线性关系,这为预测和优化材料的渗透率及机械强度提供了一定的依据．