The finite element analysis of equal channel angular pressing (ECAP) considering the strain path dependence of the work hardening of metals

It is widely known that extreme grain refinement of metals can be attained through multiple passes of equal channel angular pressing (ECAP). Such processing can follow various strain paths, which correspond to different work hardening behaviors of the material being deformed. The available finite element analyses (FEA) of multiple pass ECAP do not consider this strain path effect, and employ a single stress–effective strain curve of the material for all passes. The present paper presents a FEA of a two pass ECAP processing of copper following route C. This processing route involves the shearing of the material in the same plane as in the first pass, but in a reversed shear direction. The experimental stress–strain curve of the material, considering this strain path change, was determined through reversed torsion at various strain levels associated with the strain heterogeneity in the material caused by the first ECAP pass. The consideration of the strain path effects changed the final strain distribution in the material and led to a lower punch force in the second pass, in comparison with the results from the analysis considering a single stress–strain curve for all passes.     

等通道转角挤压变形Mg-1.5Mn-0.3Ce镁合金的组织、织构与力学性能

采用等通道转角挤压(ECAP)工艺以Bc路径在623K温度下对Mg-1.5Mn-0.3Ce镁合金进行变形,观察显微组织与织构,测试了力学性能。显微组织分析表明,镁合金经ECAP变形晶粒尺寸明显得到细化,经6道次ECAP变形后晶粒尺寸由原轧制态的约26.1μm细化至约1.2μm,且细小的第二相粒子Mg12Ce弥散分布于晶内及晶界处;同时经ECAP变形后,原始轧制织构随变形道次的增加不断减小,并开始转变为ECAP织构,织构强度不断增强;力学性能结果表明,由于晶粒细化作用大于织构软化作用,前3道次ECAP变形镁合金强度随道次的增加不断提高,与Hall?Petch关系相符,在第3道次时其抗拉强度和屈服强度达到最大值,分别为272.2和263.7MPa;在4道次之后形成较强的非基面织构,镁合金强度下降,与Hall?Petch呈相悖关系。断口分析表明,轧制态与ECAP变形镁合金的断裂方式都是沿晶断裂,由于6道次变形镁合金晶粒细化,存在更多的韧窝并获得16.8%最大室温伸长率。     

单晶铜在ECAP过程中的织构转变和强化行为

由于优秀的导电性能,单晶铜已经在各个领域得到了广泛的应用。然而,较低的强度性能严重阻碍了其进一步的发展和使用。所以,使用ECAP技术对单晶铜进行强化,同时研究采用三个不同路径挤压时对材料性能的影响。使用电子背散射衍射和 X 射线衍射来对 6 道次 ECAP 变形过程中单晶铜的织构进行检测。模具的内角为 120°,挤压路径为 A、Bc、C。结果表明： 5 道次挤压后,A 路径,Bc路径和 C 路径的强度和延伸率分别为 405MPa 、30%,395 MPa、26.7%,385 MPa 、27.9%。6 道次挤压后,A 路径的织构为{112}<110>以及较弱的{110}<112>织构;Bc 路径为{001}<110>织构;而 C 路径的织构已经产生了分散。当采用 C 路径进行几道次的挤压后,首先在其极图中出现了双织构并存的情况,随后 A 路径极图中同样出现了双织构。而在 Bc 路径极图中,并没有其他的织构出现。在挤压过程中材料的导电性只有少量的下降,且全部在 98%IACS 以上。可以看出,在合适的应变量下,ECAP 可以使单晶铜强度明显提高而且导电性损失很小。同时,采用不同的挤压路径可以显著影响材料的性能,例如采用A路径挤压出的材料有最高的强度,C路径挤压出的材料有最好的导电性能。     

等通道挤压对AZ80镁合金的组织和织构的影响

研究了AZ80镁合金在300℃下经A路径等通道挤压后显微组织和织构的演变规律,揭示了该应变路径下织构特征形成的内在机制,并讨论了ECAP对第二相析出的影响。结果表明:材料经ECAP后最终获得3~4μm的等轴晶,并显著促进了粒状Mg17Al12相的连续析出,但增加挤压道次晶粒细化效果减弱,粒子粗化;挤压初始可获得基面法线向挤压方向偏转的倾斜织构与基面织构共存的织构特征,在剪切面倾斜度效应和通道间隙的影响下,随着挤压道次的增加,倾斜织构的偏转程度减小,最终获得单一的基面织构。     

Microstructure,Texture and Mechanical Properties of Titanium Grade 2 Processed by ECAP (Route C)

In the present work the properties of titanium grade 2 after ECAP processing with original route and regimes (route C, channel angle \(\varPhi\)?=?120°, deformation temperature 300 °C, number of passes up to 8) were examined. Texture development and microstructure parameters after ECAP processing and after recrystallization were determined using electron back scatter diffraction and analysed. A significant increase of the mechanical strength accompanied by some increase of ductility was observed in the deformed samples. The kernel average misorientation and average grain orientation spread were strongly increased after deformation, which confirms the material refinement and fragmentation. The proportion of low angle boundaries increased after four ECAP passes, but after four consecutive passes high angle grain boundaries became predominant. No deformation twins were observed after four and eight ECAP passes. The material recrystallized after deformation retained a fine grain microstructure. The textures of deformed and recrystallized samples were determined. It was found that texture after 8 passes is more homogeneous that that after 4 passes, which partly explains higher ductility of this first sample.     

Structure and mechanical behaviour of interstitial-free steel processed by equal-channel angular pressing

The influence of the number of passes in equal channel angular pressing (ECAP) following route B_C on microstructure and mechanical properties of interstitial-free steel was investigated by means of tensile tests and X-ray texture and diffraction profile analysis. A significant improvement of the mechanical properties was found with increasing the number of ECAP passes. After 8 passes, beside the high strength considerable ductility was observed and at 300 °C the ductility was the same as for the initial sample but with a two-times larger strength. The high strength measured at room temperature was only slightly reduced during annealing at temperatures up to 500 °C.     

Effects of die angle on microstructures and mechanical properties of AZ31 magnesium alloy processed by equal channel angular pressing

1　INTRODUCTIONMagnesiumalloysarethelightestmetallicstruc turalmaterialsandhencetheyprovidegreatpotentialintheweightsavingofautomotiveandaerospacecomponents ,materialhandlingequipment ,portabletoolsandevensportinggoods[1,2 ] .Duetotheirhexago nalclose packed (HCP)crystalstructure ,magnesiumalloysperform poorformabilityandlimitedductilityatroomtemperature ,thustheirproductsaremainlyfabricatedbycasting ,inparticular ,die casting ,andtheapplicationsofwroughtmagnesiumalloysarelim ited .Nowit…     

Q235钢C方式等径弯曲通道变形及组织研究

在室温下对Q235钢成功进行了C方式11道次等径弯曲通道，等效应变约高达11，获得了亚微晶铁索体组织。组织观察表明，第1道次组织细化效果最显著，随后道次的主要作用是增加晶粒的位相差，使大角度晶界的比例随变形道次增加而增加。在本实验条件下，由于珠光体组织中的渗碳体表现出较强的塑性变形能力，使得珠光体组织具有与铁素体类似的宏观塑性变形行为，并且在等效应变约高达11的情况下，珠光体组织中未发现微观裂纹。     

Recrystallization of high-purity aluminium during equal channel angular pressing

Aluminium with 5N purity were deformed at room temperature by equal channel angular pressing following Route A up to three passes. The microstructure and the crystallographic texture were investigated by orientation imaging microscopy and electron backscatter diffraction, respectively. The microstructure showed complete recrystallization after the first ECAP pass onwards. The grain size decreased slightly with increasing number of passes. The corresponding texture consisted of an oblique cube component. The oblate grains and the cube texture were rotated anticlockwise about the transverse direction. The inclination of grains with respect to the direction of ECAP was dependent on the distance from the top of the billet and changed from pass to pass. The mechanism of formation of the microstructure and texture is discussed in the light of the physical phenomena involved.     

Microstructure and texture evolution during equal channel angular extrusion of interstitial-free steel: Effects of die angle and processing route

Die angle (Φ) and processing route are two important factors that greatly impact microstructure and texture developments during equal channel angular extrusion (ECAE). In this study, the microstructure and texture evolution in interstitial-free steel during ECAE using a Φ = 120° die are investigated for up to four passes via three routes (A, B_C and C). Finite element simulations and polycrystal modeling using the Taylor and viscoplastic self-consistent models are conducted to help understand deformation behavior and texture formation. Transmission electron microscopy results reveal remarkable microstructural differences between various observation planes for each billet. The effects of Φ and processing route are discussed by comparing the current results with those for the same material processed via the same routes but using a Φ = 90° die. The efficiency of grain refinement is found to be only mildly dependent on Φ and processing route. The textures can be completely characterized by predefined ideal fibers, regardless of processing route and pass number. With the exception of even-numbered passes in route C, textures developed after the same route and pass number, but different Φ can be approximately related by a rotation about the axis normal to the flow plane and the rotation angle is half of the Φ difference.     

等通道转角挤压对L2工业纯铝力学性能的影响

利用等通道转角挤压(ECAP)技术挤压工业纯铝L2，探讨了挤压次数对其力学性能的影响。结果表明，随挤压次数的增加，L2的抗拉强度和硬度得到显著提高，抗拉强度可提高95％，硬度提高70％。挤压1次后，其伸长率由40％下降至15％，此后伸长率基本保持稳定。     

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。     

Microstructure evolution and mechanical behavior of AZ31 Mg alloy processed by equal-channel angular pressing

AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP, in placing of planes and become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane (0001).     

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。     

Microstructure and texture gradient in copper deformed by equal channel angular pressing

The aim of this paper was to examine the gradient in the microstructure and texture that develops during equal channel angular pressing (ECAP). Copper of 4N purity was subjected to ECAP deformation at room temperature by using three passes of Route A. The local microstructure and texture were investigated by orientation imaging microscopy and high-energy synchrotron radiation, respectively. The refined microstructure consists of elongated grains inclined in the direction of extrusion. The texture is characterized by typical shear components of face-centred cubic metals which deviate from their ideal positions. Inclination of the grain long axis and the texture components with respect to the extrusion direction depend on the distance from the top of the extruded bar and change from pass to pass. The texture gradient is modelled with the flow line model using the viscoplastic self-consistent polycrystal approach. Microstructure formation and reasons for the texture gradient are discussed.     

Mechanical properties at room temperature of an Al-Zn-Mg-Cu alloy processed by equal channel angular pressing

Tensile tests were conducted to evaluate the influence of equal-channel angular pressing (ECAP) on the mechanical properties at room temperature of overaged Al 7075-O alloy. ECAP processing was performed using route B_C at different temperatures and number of passes, i.e. different processing severity conditions. The maximum load (F_max) recorded during the last pass of each ECAP path considered in this study is a very good estimation of the processing severity. The mechanical properties were studied in terms of the balance between tensile strength and ductility. In the processed Al 7075-O alloy, the grain size was reduced down to ∼150 nm. Consequently, tensile testing at room temperature revealed a significant increase in the maximum tensile strength after ECAP with respect to the as start material. In the present study, as the processing severity increases with the number of ECAP passes or with the decrease in processing temperature, there is a consistent trend of increment in ultimate tensile strength with minor decrease in uniform plastic elongation respect to the first ECAP pass at room temperature. This is in contrast to the behaviour after more severe plastic deformation conditions, where an increase in strength together with a strong decrease in elongation would be expected.     

等通道转角挤压对生物Mg-Zn-Ca合金显微组织与腐蚀行为的影响

旨在探讨等通道转角挤压(equal-channel-angular-pressed,ECAP)对生物医用Mg-3Zn-0.2Ca合金的显微组织以及腐蚀行为的影响。对铸态Mg-3Zn-0.2Ca合金进行了1,2,4道次的剪切挤压变形。采用光学显微组织观察、X射线反射法、电化学等手段研究了挤压道次对镁合金显微组织、织构以及腐蚀行为的影响,也特别关注了ECAP对试样的不同截面方向的显微组织演变以及模拟体液(simulatedbodyfluid,SBF)电化学腐蚀行为的影响。结果表明:ECAP变形后铸态Mg-3Zn-0.2Ca镁合金晶粒逐渐细化,变形后镁合金呈现出与挤压方向呈一定角度的002面剪切织构;随着挤压道次增加,合金的耐蚀性先增加后降低。等通道转角挤压对合金耐蚀性的影响是晶粒尺寸、晶体缺陷和织构变化的综合效果;ECAP变形后合金不同截面方向呈现不同的耐蚀性,垂直于挤压方向截面的耐蚀性优于另2个方向截面的耐蚀性。     

Structural state and superplasticity of an aluminum-lithium alloy subjected to equal-channel-angular pressing

The structural-phase state of rods processed by different regimes of equal-channel angular pressing (ECAP) has been studied. A microcrystalline structure has been shown to be formed during the pressing process. A dislocation substructure and subgrains are formed in the grains. In the rods subjected to ten ECAP passes at 370°C, a uniform structural state is formed in the entire bulk material. The mechanical behavior of rods processed by ECAP has been investigated. Temperature and strain-rate conditions that are necessary to obtain the maximum deformation to fracture have been determined for the specimens of each structural state. It was established that the maximum deformation to fracture corresponds to the rods subjected to ten ECAP passes at 370°C. It corresponds to the deformation rate equal to 10^?2 s^?1 at 370°C. The maximum degree of deformation was ～1900%. The plasticity of the specimens with the smallest grain size proved to be low.     

Inhomogeneity Through Warm Equal Channel Angular Pressing

In this study, the hardness inhomogeneity of billets during multi-passes of equal channel angular pressing (ECAP) at elevated temperatures is investigated and the effect of large strain deformation during ECAP on the hardness inhomogeneity characteristics due to dynamic aging of aluminum 6061 under a variety of temperatures and ram speed was studied by TEM and hardness measurements. The hardness results showed that the hardness distribution is more homogenous after four passes using the pressing route B_c. However, when the deformation temperature was considered, performing ECAP at 100 °C may provide the most homogeneous microstructure after multi-pressing as long as the total number of pressing passes is four. This indicates that a lower temperature (in the range of warm working) is favorable for achieving an ultrafine-grained/nanomaterial with a more homogenous microstructure. In order to quantify the inhomogeneity in the cross section of the as-pressed sample, an inhomogeneity index has been defined. The results show an increase in the hardness in the first pass with significant inhomogeneous deformation and a transition toward a more homogeneous structure with subsequent passes.     

工业纯钛在120°模具中的多道次ECAP室温变形组织与性能

在室温,采用通道夹角为120°的变形模具对工业纯钛(Commemial Pure Titanium,CP-Ti)以Bc方式实施四道次ECAP(EqualChannel Angular Pressing)挤压变形,成功获得表面光滑无裂纹的变形试样.文中主要研究了工业纯钛在室温下进行ECAP多道次变形的组织结构演变,并测试了变形试样的力学性能.微观结构显示工业纯钛在室温下进行多道次ECAP变形时,只在前两道次产生了大量的变形孪晶,且随道次增加变形孪晶逐渐消失.最终获得的试样晶粒平均尺寸由最初的约28μm细化到约250 nm,试样断裂强度和显微硬度分别提高到773和2486 MPa,而试样仍保持较好的延伸率(可达16.8%).