Multi billet extrusion technology for manufacturing bi-layered components

The development of the multi billet extrusion technology for manufacturing bi-layered aluminum based semi-products for heat radiators is the subject of this work. To obtain increased strength of the product, ultra fine grained ECAP billets were prepared and used during the extrusion. Appropriate deformation route to get desirable level of grain refinement and billet quality were identified by a series of experiments and numerical simulations performed with the implemented microstructure evolution model. Similar combination of experimental and numerical research was used within the paper for identification of dies geometry and process parameters during development of the multi billet extrusion technology.     

Through-process macro–micro finite element modeling of local loading forming of large-scale complex titanium alloy component for microstructure prediction

The intrinsic multi-heat unequal deformation behavior of the local loading forming requires a through-process macro–micro model to characterize the microstructure evolution during the forming process. In the present work, the phenomena and mechanisms of microstructural developments in local loading forming of titanium alloys are summarized. Mechanism-based unified material models, which characterize the through process microstructure evolution, are developed for integrated prediction of constitutive behavior and microstructure. A through-process macro–micro finite element model is established for the local loading forming of large scale complex titanium alloy component. The model can predict the microstructure evolution as well as macroscopic deformation in multi-step local loading forming process. Model predictions are in good agreement with experimental results. The microstructure evolution in local loading forming is investigated by the established finite element model. It is found that the thermo-mechanical processing route greatly affects the volume fraction of primary alpha but has little influence on the grain size in local loading forming     

A Study on the Recrystallization Behavior of Ni-Based Alloy G3 During Hot Deformation

An integrated microstructure evolution model of thermomechanical processing was developed in terms of dynamic recrystallization (DRX), post-dynamic recrystallization (PDRX) and grain growth. Hot compression tests were carried out on a Gleeble-1500 thermal simulator under different conditions to model DRX, PDRX and short-time grain growth during the post-deformation and cooling process. Furthermore, in combination with the established microstructure evolution models, an elastic–plastic finite element model was built using DEFORM-2D software to simulate the microstructure evolution during the hot extrusion process. The simulation result was compared with the microstructure of a hot-extruded pipe of alloy G3 manufactured in a factory. The simulation results agree well with the experimental ones, validating the accuracy of the established microstructure evolution model. Furthermore, the finite element simulation is an effective method for hot deformation analysis, which can provide theoretical guidance for the optimization manufacturing parameters.     

AZ31和AZ91镁合金等温挤压及挤压后的微观组织变化

通过等温挤压和金相观察,研究了AZ31和AZ91镁合金不同变形条件下的挤压性能和变形后的微观组织变化。结果表明,AZ31镁合金的挤压变形性能较好,而AZ91镁合金在挤压比为4∶1、挤压温度为400℃,以及在挤压比为9∶1、挤压温度为350℃和400℃时,挤压后的试件表面均出现了裂纹;AZ31镁合金的最佳成形温度为300℃～400℃,AZ91镁合金的最佳成形温度为300℃～350℃;镁合金在热挤压过程中发生了动态再结晶,挤压之后合金的晶粒显著细化。     

Microstructure Evolution and Deformation Behavior of AZ31 Magnesium Alloy During Alternate Forward Extrusion

The paper presents a new extrusion method,alternate forward extrusion,in which the punch was replaced with double-split structures so as to achieve the grain refinement for material near the interface of double-split structures.The results showed that the unique loading mode made metal flow sequence and behavior significantly changed during alternate forward extrusion.The additional shear deformation produced by the double-split punch structures resulted in a refining effect on the microstructure of the blank,which was then further refined during flow through the die orifice owing to shear deformation.Compared with the conventional extrusion,the recrystallization process in the alternate forward extrusion process produced grains that were smaller and more homogeneous in size.The recrystallization process was more abundant,and the dislocation density was significantly increased.It can be concluded that the alternate forward extrusion process could achieve fine-grained strengthening,which provided technical support and scientific guidance for the engineering application of magnesium alloy extrusion forming technology.     

航空航天紧固件用TC16钛合金在冷压缩过程中的组织演变

为了解钛合金在冷压缩过程中的变形机理和微观组织演变,使用Gleeble 3800热模拟试验机进行冷压缩试验。在冷压缩试验中,通过不同应变（0.2、0.4、0.6、0.8和1.0）和不同应变率（0.1、1.0和10.0 s^-1）,来研究应变和应变率对钛合金冷变形中微观组织演变的影响。结果表明,较大的真应变和较高的应变率容易使材料内部产生局部晶粒粗化和绝热剪切带。真应变应选择在0.2~0.6的范围内。1.0 s^-1的应变速率下,组织均匀且晶粒细小,适合冷变形。在冷变形过程中观察到的变形软化主要是由在较大的真应变和应变速率下产生的绝热温升和局部晶粒粗化引起的。     

The effect of strain path on the development of deformation structures in severely deformed aluminium alloys processed by ECAE

Equal channel angular extrusion (ECAE) has been used to investigate the formation of submicron grain structures in Al-alloys deformed to ultra-high plastic strains by different strain paths. The different strain paths were obtained by rotating billets through 0, 90, and 180° between each extrusion cycle. High resolution EBSD analysis has been employed to measure the boundary misorientations within the deformation structures. This has highlighted great differences in the evolution of the deformed state, as a function of the strain path, even after effective strains as high as 16. It has been demonstrated that the most effective method of forming a submicron grain structure by severe plastic deformation is to maintain a constant strain path. Processing routes involving a 180° rotation reverse the shear strain every second pass and this prevents the build up of significant numbers of new high angle boundaries. When a sample is processed with an alternate clockwise and anticlockwise 90° rotation, between each extrusion cycle the billet is deformed on two shear planes, each of which experiences half the total strain, compared to the single shear plane when there is no rotation. This reduces the rate of formation of high angle boundaries. With a constant clockwise 90° rotation the sample is also deformed on two alternate shear planes, but the total strain becomes redundant every fourth extrusion cycle. However, in this case each shear is reversed out of sequence after first deforming the billet on the alternate shear plane. This appears to be a much more effective means of forming new high angle boundaries than 180° rotation, where the shear strain is immediately reversed each alternate cycle, but is still less efficient than deformation with a constant strain path.     

Control of ultrafine microstructure by single-pass heavy deformation and cold forging of metal

A hot extrusion system with controlled cooling is investigated in this study. This system is used with the aim of manufacturing steel and other metal products with ultrafine microstructures by single-pass heavy deformation followed by controlled cooling. The continuous formation of bulk materials with the desired geometry and microstructure could be realized using the proposed system or by adding hot rolling stands after processing using the proposed system. Microstructure evolution during and after heavy single-pass deformation is examined through a series of experiments involving the hot extrusion of plain carbon steel followed by controlled cooling. The effects of severe plastic deformation on grain refinement and the mechanical properties of the formed products are discussed. It is clear that the use of the proposed system is helpful for the grain refinement of a cast microstructure. Also, ultrafine-grain steel with a grain diameter of 3 μm can be formed using the proposed system. Finally, the formability of the ultrafine-grain steel manufactured using the proposed system is examined by a cold-forging experiment.     

等通道转角挤压制备超细晶材料的最新研究进展

等通道转角挤压(Equal channel angular pressing,ECAP)方法是制备性能优异超细晶材料最常见的大塑性变形方法之一。模角、挤压路径、挤压道次、挤压温度和挤压速度等因素都会影响等通道转角挤压制备超细晶材料的性能;等通道转角挤压的模具也在不断地优化,如背压-等通道转角挤压(Back pressure ECAP,BP-ECAP)模具、可加热的模具以及在等通道转角挤压基础上形成的板材连续剪切技术等,这些新的模具可以改变ECAP变形过程中的组织均匀性。本文综述了等通道转角挤压制备超细晶材料的最新研究进展,并指出了几个需要深入研究的问题及方向。     

热挤压成形GH3625合金管材组织及裂纹形成机理

通过对比热挤压成形管材和爆裂管材的组织以及对爆裂管材裂纹和断口的分析,研究了热挤压成形GH3625合金管材的组织及裂纹形成机理。结果表明:爆裂管材与成形管材的组织均为等轴晶,但爆裂管材的开裂使晶界处的应力集中得以释放,其组织中并没有形成变形孪晶,在管材径向方向上也不存在晶粒尺寸不均匀的现象。挤压比过高导致管材在热挤压过程中绝热升温严重,使低熔点的Laves相熔化并扩散到周围基体中,是裂纹形成的根本原因。在模具出口处高拉应力的作用下,这些裂纹不断扩展最终连接在一起,导致管材的爆裂现象。由于断口表面冷却速率较高,组织通过奥氏体区的时间较短,再结晶形核核心多且晶粒长大过程受阻,使断口表面形成了一层十分细小的再结晶晶粒。     

新型镁合金大变形技术的研究与验证

研究了一种正挤压与等通道挤压相结合的新的Extrusion-Shearing(ES)变形方法。应用有限元法对ES变形过程进行了计算机模拟,表明ES技术可以大大提高累积应变和动态再结晶晶粒的体积分数。在Gleeble1500热模拟机上安装ES成形模具,对ES成形挤出的棒料进行微观组织观察,并对热模拟的数据进行处理。结果表明,ES成形可以细化晶粒并提高成形的均匀性。计算机模拟和热模拟实验表明,ES成形是一种新型的镁合金大塑性变形方法,可以有效细化晶粒、提高组织的均匀性     

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。     

基于有限元法的铝合金四通阀多向加载成形过程中的变形特征分析(英文)

采用数值模拟方法,研究7075铝合金四通阀体类零件在多向加载成形条件下成形过程中的材料变形特征。结果表明:四通阀多向加载成形过程中存在正挤、反挤、正挤和侧挤复合、反挤和侧挤复合等4种变形模式。在不同成形阶段,表现出的变形模式依赖于加载路径。一般在变形初期会发生正挤或反挤的变形行为;在变形中期以反挤变形模式为主;在变形终期一般会发生反挤、正挤和侧挤复合变形模式。为提高型腔填充稳定性和减少成形缺陷,在变形初期和中期,应增加侧挤变形行为;在变形终期应减少或避免正挤变形行为。     

Superplastic deformation mechanisms of high Nb containing TiAl alloy with (α2 + γ) microstructure

In this paper, superplastic deformation behaviour of a high Nb containing TiAl alloy with fine (α₂ + γ) microstructure, Ti–43.5Al–8Nb–0.2W–0.2B (at.%), has been examined and studied by means of hot tension from 850 °C to 1050 °C under an initial strain rate of 10⁻⁴ s⁻¹. The mechanical behaviour and microstructure evolution have been characterized and analyzed. Besides, to gain insight into deformation mechanisms, the texture evolution during deformation at ordinary (non-superplastic) and superplastic conditions has been systematically studied. The results showed that, the alloy exhibited impressive superplastic elongation at 1000 °C with a strain-rate sensitivity exponent (m) of about 0.5 and an apparent activation energy (Q_app) value of about 390 kJ/mol. The microstructural characterization showed that, when the alloy was deformed at ordinary condition (850 °C), severe grain refinement occurred and the fraction of low-angle grain boundary notably increased. Meanwhile, the textures were characterized by <100> and <111> double-fiber components parallel to the tensile direction. All these observations suggested a dislocation slip and twinning mechanism. However, if deformed at the superplastic condition (1000 °C), it was found that the microstructure was fairly stable in terms of grain size, morphology and grain boundary characteristics during tension, but a continuous weakening of the initial <110> fiber texture (resulted from canned-forging) was observed. This was believed to be an indication of grain boundary sliding mechanism. Moreover, the deformation texture (<100> + <111>)—though is very weak—was simultaneously appeared. According to a detailed discussion on the deformation kinetics and microstructure evolution, it was believed that the slip/twinning-accommodated grain boundary sliding was responsible for superplastic deformation and the dislocation climb inside of γ grains was the rate-controlling step.     

TA15合金大型筋板件等温局部加载晶粒尺寸演化研究

随着航空工业的迅速发展,大飞机和新一代军机的研制,钛合金大型筋板件的应用日益广泛,等温局部加载技术为该类构件的成形提供了新的途径。然而,等温局部加载成形是一个多因素耦合作用下的复杂成形过程,工艺参数控制不当将产生粗晶、组织不均匀等缺陷。为此,文章采用内变量法,建立了TA15合金高温变形微观组织演化物理模型,并与有限元软件DEFORM 3D结合对TA15合金筋板件等温局部加载成形过程等轴α相晶粒尺寸演化进行数值模拟。结果表明,锻件先加载区、后加载区及变形过渡区晶粒尺寸基本一致;随着温度的升高,锻件等轴α相晶粒尺寸平均值,呈先减小,后增加的趋势;锻件等轴α相平均晶粒尺寸随模具运动速度增加,先快速减小,后趋于平缓,较大的模具运动速度易造成组织不均匀性增加;采用只局部加载的加载方式,可以获得比采用先局部后整体的加载方式,更均匀细小的组织。     

Improving significantly the failure strain and work hardening response of LPSO-strengthened Mg-Y-Zn-Al alloy via hot extrusion speed control

The effect of hot extrusion speed on the microstructure and mechanical properties of MgY_1.06Zn_0.76Al_0.42 (at%) alloy strengthened by the novel long-period stacking ordered (LPSO) phase was systematically investigated. Increase in the speed of extrusion accelerated dynamic recrystallization of α-Mg via particle-stimulated nucleation and grain growth in the alloy. The intensive recrystallization and grain growth events weakened the conventional basal texture and Hall-Petch strengthening in the alloy which led to significant improvement in its failure strain from 4.9% to 19.6%. The critical strengthening contribution from LPSO phase known for attributing high strength to the alloy was observed to be greatly undermined by the parallel competition from texture weakening and the adverse Hall-Petch effect when the alloy was extruded at higher speed. Absence of work hardening interestingly observed in the alloy extruded at lower speed was discussed in terms of its ultra-fine grained microstructure which promoted the condition of steady-state defect density in the alloy; where dislocation annihilation balances out the generation of new dislocations during plastic deformation. One approach to improve work hardening response of the alloy to prevent unstable deformation and abrupt failure in service is to increase the grain diameter in the alloy by judiciously increasing the extrusion speed.     

35CrMo钢动态再结晶过程数值模拟与试验研究

以热物理模拟试验研究为基础,得出35CrMo钢发生动态再结晶时的数学模型。采用热一力耦合的弹塑性有限元法对35CrMo结构钢在热变形过程进行了数值模拟。变形的不均匀性导致动态再结晶进行的不等时性,动态再结晶的发生初始于大变形区,随着应变的增加,逐渐向粘着区和自由变形区延伸。同时预测热变形过程的形变量、形变速率和形变温度对再结晶微观组织演变的影响。在一定温度下,再结晶晶粒尺寸的大小与应变速率呈反方向变化,随着变形的进行,试样内的晶粒尺寸趋于细化和均匀化。在一定应变速率下,随着形变温度的降低,再结晶晶粒尺寸趋于细化,导致了锻件的综合性能提高。为了观察显微组织演化过程,对模拟结果进行了金相法验证,模拟结果与实验结果比较吻合,模拟的结果是合理的。     

Microstructure evolution model based on deformation mechanism of titanium alloy in hot forming

The microstructure evolution in hot forming will affect the mechanical properties of the formed product. However, the microstructure is sensitive to the process variables in deformation process of metals and alloys. A microstructure evolution model of a titanium alloy in hot forming, which included dislocation density rate and primary a phase grain size, was presented according to the deformation mechanism and driving forces, in which the effect of the dislocation density rate on the grain growth was studied firstly. Applying the model to the high temperature deformation process of a TC6 alloy with deformation temperature of 1 133 - 1 223 K, strain rate of 0.01 -50 s^-1 and height reduction of 30%, 40% and 50%, the material constants in the present model were calculated by the genetic algorithm（GA） based objective optimization techniques. The calculated results of a TC6 alloy are in good agreement with the experimental ones.     

激光焊接头超塑变形组织表征

采用高温拉伸研究激光焊接头超塑性变形行为,分析了焊缝及热影响区在超塑性变形过程中的显微组织演变规律,并提出采用等轴化系数来表征焊缝组织的等轴化进程,采用平均晶粒尺寸来表征热影响区组织的转变程度.结果表明,随着变形的进行,等轴化系数逐渐升高;在相同变形量时,变形温度升高或初始应变速率降低均有利于等轴化系数上升,促进焊缝超塑性变形的进行.随着变形的进行,热影响区平均晶粒尺寸逐渐升高;在相同变形量时,变形温度升高或初始应变速率降低均有利于平均晶粒尺寸上升,促进焊缝超塑性变形的进行.     

镍基合金大锻件成形过程流变行为与晶粒尺寸预测

基于IN718合金热态成形过程中流动应力软化特征,采用动态再结晶软化本构模型来描述锻造过程中变形-传热-微观组织演变的相互作用。借助DEFORM-3D二次开发,将本构模型和微观演变模型进行耦合,模拟预测了IN718合金在多道次锻造过程中流变行为与晶粒尺寸演变,为大锻件锻造热力参数的合理制定与控制提供了依据。