Simple shear extrusion versus equal channel angular pressing:A comparative study on the microstructure and mechanical properties of an Mg alloy

Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD passes.Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation.The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DRX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were obtained.The compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes.ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE.This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion(ECAE)in semi-solid isothermal treatment was investigated.The results show that with increasing semi-solid isothermal treatment temperature,the α phase solid grain size of processed Mg-Al-Zn alloy by ECAE increases firstly due to coarsening of α phase solid grains,then decreases due to melting of α phase solid grains.With the increase of extrusion passes during ECAE,the α phase solid grain size in the following semi-solid isothermal treatment decreases.The α phase solid grain size of processed Mg-Al-Zn alloy by ECAE under route BC is the smallest,while the α phase solid grain size of processed material by ECAE under route A is the largest.The primary mechanism of spheroid formation depends on the melting of recrystallizing boundaries and diffusion of solute atoms in the semi-solid state.

Mechanical properties and damping capacities of magnesium alloys processed by equal channel angular extrusion(ECAE)

Equal channel angular extrusion (ECAE) was applied to commercial pure magnesium and AZ91D alloy. Microstructures of these magnesium alloys before and after ECAE process were observed by optical microscopy (OM). The ultimate tensile strength of pure magnesium and AZ91D alloy processed by ECAE is about 130 and 260MPa, respectively, and it is much higher than that of the as cast alloys. The elongation of them is increased from about 2% to 8%. The strain amplitude dependence damping capacities of these magnesium alloys were investigated by dynamic mechanical analyzer (DMA). ECAE process largely decreases the damping capacities of pure magnesium from 0.033 to about 0.012 (ε=1×10 -4), but does not show obvious influence on that of AZ91D alloy, which is about 0.0015.

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 important to plastic deformation.The change characteristics for distributions of effective stress and strain during an equal channel angular extrusion(ECAE)process with inner angle of 90°and without fillets at outer corner were described. Inhomogeneity index(C)was defined and deformation heterogeneity of ECAE was analyzed from the simulation and experiment results.The deformation homogeneity caused by fillets at outer corner increased compared with the die without fillets.The cumulated maximum strains decrease with increasing the fillets of outer corner in ECAE die and the inner corner angle.The analysis results show that better structures of ECAE die including appropriate outer corner fillet and the inner corner angle of 90°for the die can improve the strain and ensure plastic deformation homogenization to a certain extent.The required extrusion force drops with increasing the fillet made at outer corner in ECAE die.It is demonstrated that the prediction results are in good agreement with experiments and the theoretical calculation and the research conclusions in literatures.

Improvements in the microstructure and fatigue behavior of pure copper using equal channel angular extrusion

In this study, annealed pure copper was extruded using equal channel angular extrusion （ECAE） for a maximum of eight passes. The fatigue resistance of extruded specimens was evaluated for different passes and applied stresses using fatigue tests, fractography, and metallography. The mechanical properties of the extruded material were obtained at a tensile test velocity of 0.5 mm/min. It was found that the maximum increase in strength occurred after the 2nd pass. The total increase in ultimate strength after eight passes was 94%. The results of fatigue tests indicated that a significant improvement in fatigue life occurred after the 2nd pass. In subsequent passes, the fatigue life con-tinued to improve but at a considerably lower rate. The improved fatigue life was dependent on the number of passes and applied stresses. For low stresses （or high-cycle fatigue）, a maximum increase in fatigue resistance of approximately 500%was observed for the extruded material after eight passes, whereas a maximum fatigue resistance of 5000%was obtained for high-applied stresses （or low-cycle fatigue）. Optical microscopic examinations revealed grain refinements in the range of 32 to 4 μm. A maximum increase in impact energy absorption of 100%was achieved after eight passes. Consistent results were obtained from fractography and metallography examinations of the ex-truded material during fatigue tests.

Bonding interface zone of Mg-Gd-Y/Mg-Zn-Gd laminated composite fabricated by equal channel angular extrusion

In order to improve the mechanical properties and corrosion resistance of Mg alloys,the equal channel angular extrusion (ECAE)was employed to fabricate the Mg-5Gd-5Y/Mg-2Zn-1Gd(GW55/ZG21)laminated composites.After fabrication and annealing treatment,the microstructural evolution,phase constitution,microhardness,and bonding strength were investigated on the bonding interface zone of GW55/ZG21 laminated composites.The bonding interface zone of GW55/ZG21 laminated composites comprises a lot of Mg3(Y,Gd)2Zn3 particles along the bonding interface,some rod Mg24(Y,Gd)5 phases on GW55 side,and a precipitation free zone(PFZ)on ZG21 side.After annealing treatment,Mg3(Y,Gd)2Zn3 particles along the bonding interface increase, rod Mg24(Y,Gd)5 phases on GW55 side decrease,and PFZ is broadened.Meanwhile,the hardness on the bonding interface zone decreases and the bonding strength increases from 126 MPa to 162 MPa.

Uniformity and continuity of effective strain in AZ91D processed by multi-pass equal channel angular extrusion

AZ91D magnesium alloy was processed by equal channel angular extrusion(ECAE).The influence of extrusion temperature,extrusion pass and extrusion route on the ultimate strength of the extruded billet was analyzed.The process of multi-pass extrusion was simulated with the method of finite element analysis,and the continuity and uniformity of effective strain in multi-pass extrusion were investigated.The results show that extrusion pass plays the most important role in improving the ultimate strength of AZ91D magnesium alloy,the extrusion route is the second,and the extrusion temperature is the last.From the numerical simulation,there exists the continuity of the accumulated deformation in multi-pass extrusion and the effective strain increases linearly.The tendency of the strain uniformity is different in multi-pass extrusion with extrusion routes.The results of experiment agree with those of numerical simulation.

Deformation temperature and postdeformation annealing effects on severely deformed TiNi alloy by equal channel angular extrusion

Micron TiNi alloy blocks were fabricated at high temperature by equal channel angular extrusion （ECAE） using hotforged Ti-50.3at%Ni alloy as the raw material and the effects of deformation temperature and postdeformation annealing on the severely deformed TiNi alloy by ECAE were investigated. The results show that the TiNi alloy processed by ECAE undergoes severe plastic deformation, and lowering the deformation temperature and increasing the number of extrusions contribute to grain refinement. When the annealing temperature is below 873 K, static recovery is the main restoration process; when the temperature rises to 973 K, static recrystallization occurs. It is found that fine particles are precipitated when the TiNi alloy processed by ECAE is annealed at 773 K.

Effect of friction on equal channel angular extrusion process

The influence of the friction between deformed material and die wall during equal channel angular extrusion (ECAE) was studied. Because of the special design of the extrusion die, the direction of the frictional force has been altered and the distribution of the strain field has been uniformed. The results of the finite element analysis(FEA) indicate that the homogeneity of the finial deformation has been greatly enhanced with this method provided. The ratio of maximum strain to minimum strain along the width is reduced from 6.39 to 1.03. Along the billet length, the strain homogeneity region increases more obviously and the strain is uniformed more greatly than that of common extrusion. The lubrication before extrusion reduces greatly or even it is ignored, which has a great significance for the industrial application of ECAE.

Effect of Equal Channel Angular Extrusion on the Microstructures and Properties of Two Extruded Al-Mg-Si Alloys

The effect of equal channel angular extrusion （ECAE） on the microstructure of two Al-Mg-Si extrusion alloys was investigated by high resolution electron backscattered diffraction （EBSD） using a field emission gun scanning electron microscope （FEG-SEM） and a transmission electron microscope （TEM）. Two contrasting alloys： a dilute alloy, based on alloy 6061 and a concentrated alloy, based on alloy 6069 were employed for this research. It has been found that prior ECAE to extrusion promotes high angle grain boundaries （HAGBs） in the extrusions, and the increase in HAGBs ratio is due to the large shear deformation involved in the process of ECAE. Tensile testing results show that a further ageing treatment strengthens the alloys after extrusion and the ECAE processed extrusions are more ductile than conventional extrusions.

Super-Elasticity Characteristics of TiNi Alloy Processed by Equal Channel Angular Extrusion

A Ni-rich TiNi alloy was processed by Equal Channel Angular Extrusion (ECAE) at 500℃. After four passes ECAE treatment, microstructure of the alloy was refined but slightly inhomogeneous, to sub-micron scale, approximately 0.5～0.6 μm. Comparing with the solution-treated TiNi specimen, the martensitic transformations start (Ms) and peak temperatures (Mp) of TiNi specimens processed by ECAE were dramatically lowered. After ECAE treatment, the R-phase transformation was stimulated and separated from martensitic transformation, but occurred within a larger temperature range. Super-elasticity characteristics of TiNi alloy were tested by tensile loading and unloading cycles. The results revealed that at a tensile strain of 6% or smaller, TiNi alloy processed by four passes ECAE showed better super-elasticity, with less residual strain retained, than solution-treated sample. After tensile strain exceeded 6%, up to 8%, the maximum recoverable strain of TiNi alloy ECAE treated was decreased. Microstructure evolution and its effect on phase transformations and super-elasticity characteristics were discussed.

Texture evolution during semicontinuous equal-channel angular extrusion process of interstitial-free steel

Semicontinuous equal-channel angular extrusion（ SC-ECAE） is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specimens in the conventional ECAE,driving forces are applied to dies in SC-EACE. The deformation of interstitial-free（ IF） steel w as performed at room temperature,and individual specimens w ere repeatedly processed at various passes. An overall grain size of 0. 55 μm w as achieved after 10 passes. During SC-ECAE,the main textures of IF steel included { 111} ,{ 110} ,{ 112} ,{ 110} ,and { 110} At an early stage,increasing dislocations induce new textures and increase intensity. When the deformation continues,low-angle boundaries are formed betw een dislocation cell bands,w hich cause some dislocation cell bands to change their orientation,and therefore,the intensity of the textures begins to decrease. After more passes,the intensity of textures continues to decrease w ith high-angle boundaries,and the sub-grains in dislocation cell bands continuously increase. The present study reports the evolution of textures during deformation; these w ere examined and characterized using high-resolution electron backscattered diffraction（ EBSD） in a field emission scanning electron microscope. The mechanisms of texture evolution are discussed.

Deformation Behavior and Microstructure Evolution during Equal Channel Angular Pressing of Pure Aluminum

The deformation behavior of equal channel angular pressing(ECAP)was discussed by using plasticity method.The node mapping method is employed to realize the analysis of multi-pass ECAP by using three-dimensional FEM methods for pure aluminum.The single-pass ECAP is a non-uniform shear deformation process in the cross-section of the workpiece.The uniform deformation processing routes are obtained during multi-pass ECAP process.In addition,the density of dislocations and defects of crystal lattice are also largely changed for different processing routes.The grain microstructure is gradually refined with the increase of the pressing passes.The grains and their distribution obtained by route Bc are more useful for producing the material with high angle grain boundaries.The grain microstructure of the cross section of the pressed material decreases with the increase of strain,and some grains exhibit transformed grain boundary(PTB)fringes.The dislocation density in the grain decreases,and the grain boundary presents equiaxed distribution.

上偏心距对等通道球形转角挤压影响的有限元分析

等通道球形转角挤压(Equal Channel Angular Extrusion With Spherical Cavity,ECAE-SC)是集耦合剪切应变和正应变于一体的新型复合大塑性变形工艺,具有复合、连续、高效变形等优点。偏心距作为该工艺模具结构的重要参数之一,对金属的成形过程和变形行为有着重要影响。本文以塑性性能较好的工业纯铝作为研究对象,利用DEFORM-3D有限元软件对不同上偏心距条件下的ECAE-SC单道次室温变形行为进行有限元模拟,分析了挤压载荷、金属流动、等效应变、平均应力等场量的分布及变化规律。结果表明,上偏心距对挤压载荷变化趋势的影响不大,稳定变形阶段下坯料的最大挤压载荷约为3.15 kN。随着上偏心距的增加,金属的流动性得到显著提高,填充效果更好。当上偏心距增大时,坯料可获得较大的应变累积和良好的变形均匀性。同时,坯料保持高静水压力状态的时间更长,这对于提高材料塑性变形能力,获得理想的晶粒细化效果十分有利。本文模拟条件下,当上偏心距为2.5mm时,坯料整体成形效果最好。

Warm Deformation of Low Carbon Steel Using Forward Extrusion-Equal Channel Angular Pressing Technique

A combination of extrusion and equal channel angular pressing （ECAP） was used to deform a plain low carbon steel. This process consists of two successive deformations by extrusion and ECAP in a single die （Ex-ECAP）. Cylindrical samples were heated to predefined temperatures （650 and 850 ℃） and then pressed through a die channel with crosshead speed of 10 mm/s. Microstructure and resultant mechanical properties of processed material were studied. The results showed that pressing temperature has a significant effect on the resultant microstructure. While at 650 ℃, the cold worked structure with elongated ferrite grains were obtained, and at 850 ℃ the microstructure consisted of elongated ferrite grains and very fine grains at their boundaries as a consequence of continuous dynamic recrystallization （CDRX） of ferrite phase. Also at 850 ℃, a particular microstructure consisted of cold worked ferrite and static recrystallized grains on shear bands was obtained.

Characterization of microstructure in high strength Mg_(96)Y_3Zn_1 alloy processed by extrusion and equal channel angular pressing

The Mg96Y3Zn1 alloy processed by extrusion and equal channel angular pressing （ECAP） was investigated. It was found that the Mg96Y3Zn1 alloy processed by extrusion and ECAP obtained ultrafine grains and exhibited excellent mechanical properties. After ECAP, the average grain size of Mg96Y3Zn1 alloy was refined to about 400 nm. The highest strengths with yield strength of 381.45 MPa and ultimate tensile strength of 438.33 MPa were obtained after 2 passes at 623 K. The high strength of Mg96Y3Zn1 alloy was due to the strengthening by the grain refinement, the long period stacking （LPS） structure, solid solution, fine Mg24Y5 particles, and nano-scale precipitates. It was found that the elongation was decreased with pass number increasing. It was because that the cracks were preferentially initiated and propagated in the interior of X-phase during the tensile test.

Finite Element Analysis of Die Geometry and Process Conditions Effects on Equal Channel Angular Extrusion for β-Titanium Alloy

The finite element analysis was applied to evaluate the respective influences of die geometry and process conditions on plastic strain distribution for β-titanium (Ti-13V11Cr3Al) alloy during the equal channel angular extrusion (ECAE). It was found that optimum equal channel angular extrusion die geometry is strongly material dependent. Optimal strain homogeneity in the Ti-13V11Cr3Al alloy may be achieved at r (inner radius)=5 mm, R (outer radius)=3 mm. The equivalent plastic strain increases with increasing friction coefficient. And the better homogeneity of the equivalent plastic strain distribution can be achieved when friction coefficient value is lower. The faster the ram speed is, the lower the homogeneity of the equivalent plastic strain distribution is and the influence is slight. The back-pressure does not help to improve the plastic strain homogeneity, and the increasing temperature has a slightly favourable effect on the plastic strain homogeneity between 400 and 600 ℃.

Microstructure and Mechanical Properties of Semi-continuous Equal-channel Angular Extruded Interstitial-free Steel

An innovative method called semi-continuous equal channel angular extrusion （SC-ECAE） has been devel- oped to produce ullrafine grained steel by inducing severe plastic deformation. In contrast to the external forces that are exerted on specimens in traditional ECAE, the driving forces are applied on the dies in the novel SC EACE process. Commercial interslitial-free steel sheets with width of 160 mm and tbickness of 2 mm were processed re peatedly to various passes at room temperature using this method. The microstructural evolution was characterized using high-resolution electron backscatter diffraction （EBSD）, and the mechanical properties were investigated by tensile testing. The EBSD images indicated that the fraction of high angle boundaries （HABs） began to increase gradually after four passes; after six passes, elongated HAB structures with nearly submicron-scale average spacings were formed. The tensile testing results showed that strengthening was accompanied by a decrease in tensile ductili- ly, but no significant anisotropy was observed. After 10 passes, a final HAB fraction of about 90% and an overall grain size of 0.55 μm, yield strength of 638.7 MPa, an ultimate tensile strength （UTS） of 710.3 MPa, and a totfd elongation of 12.0 % were obtained.

大塑性变形制备细晶材料的研究、开发与展望

系统介绍了大塑性变形(SPD)细化晶粒的条件和目的,综述了4种主要的大塑性变形工艺的基本原理、特点和应用,剖析了细晶材料的强度和超塑性特征,展示了大塑性变形制备细晶材料的诱人前景和发展方向。

纯铝等径角挤扭新工艺数值模拟及实验研究

为了改进等径角挤压法(ECAE)的不足,结合扭挤(TE)工艺的特点,提出了等径角挤扭(ECAE-T)新工艺。采用有限元模拟软件DEFORM-3D对上述三种工艺的变形特征进行模拟研究,重点分析了ECAE-T工艺对制件应变应力大小和分布的影响。模拟结果显示:与ECAE和TE相比,ECAE-T工艺存在两个大塑性变形区,能累积更大的剪切塑性变形量。采用自行设计的模具,在室温下进行了纯铝ECAE和ECAE-T实验研究,实验结果表明:模拟过程与实验基本一致,与ECAE相比,ECAE-T工艺一道次后的组织更加狭长、细小。由模拟结果和实验结果可知,ECAE-T工艺是更加优异的大塑性变形法。