连续挤压成形过程的温度场研究

在连续挤压成形过程中 ,摩擦力为驱动力 ,变形体和模具接触面上的摩擦功和塑性变形功不断转化为热能 ,使得变形体在塑性变形的同时 ,与模具及周围环境进行热交换 ,促使变形体和模具内的温度场不断发生变化 ,这种温度的变化对模具和变形体的性能又有强烈的影响。因此 ,对连续挤压成形过程中变形体和模具的温度场的准确预报和控制 ,将有助于连续挤压产品的内部质量和尺寸精度的提高。本文在分析连续挤压技术特点的基础上 ,采用刚粘塑性有限元模型 ,重点分析了连续挤压摩擦力学模型和热力耦合模型 ,组建了一个有关连续挤压的计算机仿真系统 ,对连续挤压的成形过程进行了计算机仿真 ,得出了有关连续挤压全过程的温度场。     

基于BP神经网络的铝型材挤压模具优化设计

采用三层BP神经网络建立挤压模具的数学模型,利用三维刚塑性有限元模拟获得神经网络的样本信号,对神经网络模型进行训练。利用神经网络函数逼近功能,以U形铝型材在挤压工作带出口处具有最均衡的轴向挤压速度为目标,最终对U形铝型材挤压模具合理模孔位置进行了优化设计,并采用计算机模拟仿真对优化结果进行验证,表明优化结果是有效的。     

椭圆异型挤压塑性成形及模腔映射优化

针对非轴对称金属异型挤压塑性流动及模腔研究的理论课题,借助于近代共形映射数学理论研究成果,利用法线收敛法,建立了映射函数解析方法。将三维金属异型材挤压塑性成形问题转化为二维轴对称成形问题,求解椭圆异型挤压金属塑性成形连续流动场和应变速度场的数学解析模型,并应用金属塑性成形理论,建立了精密挤压异型材优化模腔的数学模型,同时为精密快速地实现挤压模腔的CAD／CAM一体化目标提供了技术支持。     

连续挤压杆坯直径的工艺影响研究

针对坯料直径对铜扁线连续挤压的影响,采用刚粘塑性有限元模型,基于Deform-3D软件平台,进行三维有限元数值模拟,获得两种不同直径的坯料连续挤压扩展成形过程的金属流动规律、温度场、应力场、应变场以及挤压轮扭距。通过理论计算和对模拟结果的分析比较,初步确定了坯料直径和金属塑性变形的关系,为连续挤压工模具设计提供了理论依据。     

CONFORM连续挤压过程的有限元分析

为研究CONFORM连续挤压过程中金属的变形行为,本文构造了一个反映CONFORM连续挤压金属塑性变形力学机制的计算模型。采用刚粘塑性有限元方法对CONFORM连续挤压金属变形过程进行了数值模拟,得到了金属的流动规律以及相关力学场量的分布。     

光塑性在连续挤压成形研究中的若干关键技术

分析了光塑性和连续挤压技术的特点，总结了光塑性在连续挤压成形研究中的若干关键技术，重点研究了连续挤压过程的光塑性实验建模，光塑性材料的选取，试样制取过程中存在的问题，为今后本领域工作的开展指出可能涉及到的问题。     

剧烈塑变形对AZ31镁合金微观组织演化的影响

等截面通道角挤压(Equal channel angular Extrusion, ECAE)是制备无疏松孔洞大块超细晶材料的重要方法之一。论文通过刚塑性有限元法对ECAE进行三维数值仿真,采用单元点映射方法,结合三维模型转换进行了A,Ba,Bc和C多次挤压路线的有限元连续仿真,得出了圆形截面挤压试样等效应变分布及其变形均匀性规律,同时,给出了多次挤压不同挤压路线等截面通道角挤压晶粒细化机理。通过变换挤压路线可以改变挤压试样内部微观组织结构。随着挤压次数的增加,不同挤压路线对应挤压试样均得到有效细化,与其它挤压路线相比,路线Bc和C能够得到大角度晶界的等轴晶粒分布的挤压试样。同时,通过实验得到的各路线挤压试样对应的微观结构演化规律与模拟分析得到的应变分布规律一致。     

剧烈塑性变形对AZ31镁合金微观组织演化的影响

等截面通道角挤压(equal channel angular extrusion,ECAE)是制备无疏松孔洞大块超细晶材料的重要方法之一。通过刚塑性有限元法对ECAE进行三维数值仿真,采用单元点映射方法,结合三维模型转换进行了A,Ba,Bc和C多次挤压路线的有限元连续仿真,得出了圆形截面挤压试样等效应变分布及其变形均匀性规律,同时,给出了多次挤压不同挤压路线等截面通道角挤压晶粒细化机理。通过变换挤压路线可以改变挤压试样内部微观组织结构。随着挤压次数的增加,不同挤压路线对应挤压试样均得到有效细化,与其它挤压路线相比,路线Bc和C能够得到大角度晶界的等轴晶粒分布的挤压试样。同时,通过实验得到的各路线挤压试样对应的微观结构演化规律与模拟分析得到的应变分布规律一致。     

连续挤压变形力学模型与接触应力分布规律

在连续挤压技术研究的基础上,通过观测挤压轮槽金属的变形形貌,提出了“五分区”的连续挤压变形过程描述模型,构成了连续挤压轮沟槽变形区系统、完整、准确的表征。根据各分区的变形特点,利用塑性力学理论得出接触应力的解析表达式,讨论连续挤压变形区接触应力的分布特点与规律。通过深入分析,得出了个分区关键参数的设计准则与确定方法,探讨了提高挤压力的措施,最后通过与实验结果的比较验证了其工程应用价值。     

铜包钢接触线坯连续包覆工艺优化设计

采用刚-粘塑性有限元法,建立了铜包钢连续包覆的三维热力耦合有限元模型,对变形过程进行了数值模拟。通过模拟,分析了芯线位置、挤压轮转速、导向模与凹模间隙等工艺参数对连续包覆过程的温度场、金属流动情况、挤压轮扭矩等的影响规律,得到了合理的工艺参数和优化的模具结构。     

Principles of ECAP–Conform as a continuous process for achieving grain refinement: Application to an aluminum alloy

Equal-channel angular pressing (ECAP) combined with the Conform process provides a solution for the continuous production of ultrafine-grained materials. Rods of a commercial Al-6061 alloy were processed by ECAP–Conform at room temperature for up to a total of four passes. Microstructural observations showed significant grain refinement but with elongated grains after four passes with average widths of ～150 nm and lengths of ～1.2 μm when viewed on the longitudinal planes. Microhardness measurements after a single pass revealed inhomogeneities both on the cross-sectional planes and along the rod. After processing through four passes there was reasonable homogeneity throughout the rod. Measurements of the shear strengths in two orthogonal directions perpendicular to the extrusion axis showed significant strengthening after ECAP–Conform and there was no evidence for any plastic anisotropy after processing through four passes.     

汽车空调器用铝合金盘管的开发

采用Conform连续挤压技术研制汽车空调器用铝合金盘管，获得生产汽车空调器用铝合金盘管的最新生产工艺。     

采用Conform连续挤压工艺生产D97—H113DQC5铝合金口琴管

D97－H112铝合金口琴管是制造管－带式汽车空调器所需的原材料,主要论述了采用Comform连续挤压工艺生产D97－H112DQC5铝合金琴管的生产工艺过程及熔炼、铸轧、退火、挤压等主要工艺参数。     

连续铸挤成形技术的发展及应用

连续铸挤技术(Castex)是连续挤压技术(Conform)的进一步发展,它将液态金属连续铸造与加工合为一体,实现液态金属直接加工成形,属短流程,高效节能的先进工艺。论述了连续铸挤技术的先进性及其发展现状,介绍了连续铸挤的设备结构、工艺以及其产品。并且总结了20年来东北大学对连续铸挤理论、工艺及设备研究与开发的成果,现已成功地设计与制造了DZJ-300、350、460、500、1100型等连续铸挤机,可连续铸挤铝及其合金的管、棒、线、型材,在国内得到应用。     

Microstructure and Properties of 7075Al Alloy Fabricated by Directly Combined of Spray Forming and Continuous Extrusion Forming under Different Atomization Gas Pressures

A new process consisting of the spray forming and the continuous extrusion forming for manufacturing 7075Al alloy was proposed.The microstructure evolution,mechanical properties and the resistance to stress corrosion cracking of the alloy were studied.The results indicate that the spray forming process induces obviously grain refinement and greatly lower segregation microstructure.Besides,the Conform process produces finer grains and conduces to more uniform distribution of the precipitates of Al Cu and MgZn_2 phases.The fabricated alloy shows good comprehensive mechanical properties and superb performance of stress corrosion resistance.Moreover,a better combination of the mechanical properties and the resistance to stress corrosion cracking could then be obtained under a certain condition of atomization gas pressure of 0.19 MPa.The enhanced properties are attributed to the following factors,which include the grain refinement,the fine and homogeneous distribution of Al Cu and MgZn_2 phases,the high density of the extruded products,as well as the discontinuous distribution of the grain boundaries after retrogression and reaging(RRA)heat treatment.     

A comparison of the phenomenological theory of martensitic transformations with a model based on interfacial defects

Structural models of martensitic interfaces are those where the habit plane (HP) is comprised of coherent terraces reticulated by arrays of interfacial defects. Such interfaces are shown explicitly to exhibit no long-range displacements and to move in a glissile manner by lateral motion of disconnections along the interface. We quantify predictions of HP and orientation relationship (OR) between the parent and product crystals for such models in terms of a reference lattice in an approach called a topological model (TM). These crystallographic quantities for the TM are compared with those of the phenomenological theory of martensite crystallography (PTMC). For the case of transformations resembling α to β in Ti, but where lattice invariant deformation is suppressed, the two models agree when the interplanar spacings of the terraces in the two crystals are the same. However, although the OR’s according to the two approaches are very similar, the predicted HP’s differ systematically when the terrace plane spacings are varied. The differences arise because the PTMC interfaces are unrelaxed configurations that are invariant planes of the geometrical shape transformation, whereas TM interfaces are physically invariant planes as a transformation progresses.     

Rapid solidification of steel droplets with different carbon contents in drop tube

Rapid solidification is regarded as being an effective method to refine the microstructure and reduce or eliminate the segregation of alloying elements.In this study the microstructures of rapid solidified carbon steel droplets (cooled in silicone oil) with different C contents by drop tube processing were observed.The volumes of droplets were set to be 2 mm×2 mm×2 mm (TM) and 5 mm×5 mm×5 mm (FM).For most samples,the microstructures are nearly the same from the surface to the center region.The microstructures of the FM samples with higher C content are much finer than those of the TM samples,which is the opposite of the situation with the lower C content samples.The distribution of C along the diameter of each sample was detected.The segregation of C was observed in TM samples with higher C contents while not in FM samples.This is regarded as relating to recalescence and the diffusion of C atoms during the solidification process.     

Mechanics of continuous equal-channel angular extrusion

The paper discusses possible approaches for realization of continuous equal-channel angular extrusion (ECAE). A practical interest presents Conform ECAE (CECAE) converting an inlet channel into a friction press. Slip line solutions and plastic zones are analyzed for different cases of active and passive frictions. It is shown that CECAE provides lower extrusion pressure, higher effective strains and better approximation to simple shear deformation mode than ordinary ECAE. Specific distributions of plastic friction depending on a slip between material and roll are introduced for the beginning stage, steady CECAE and during slippage. The paper describes a few designs of CECAE. Optimization of the main characteristics is performed for the concept of CECAE with an additional coining roll.     

Internal friction and evolution of ultrafine-grained structure during annealing of Grade-4 titanium subjected to severe plastic deformation

Electron microscopy, X-ray diffraction, tensile tests, and measurements of internal friction (IF) have been used to study the transformation of the structure and properties of commercial Grade-4 titanium subjected to deformation using equal-channel angular pressing combined with the Conform process (ECAP-Conform), drawing, and subsequent annealing. It has been found that the ECAP-CONFORM with drawing leads to a decrease in the grain size of titanium to about 150 nm. During annealing at 400°C for 1 h, the growth of separate grains was observed; with an increase in the annealing temperature to 450°C or higher, the growth of grains in the whole volume of a specimen occurred. It has been shown that titanium in the ultrafine-grained (UFG) state is characterized by an internal-friction peak at temperatures of 450–500°C (under the selected measurement conditions), which results from the processes of recovery and recrystallization. During repeated heating, no such effect was observed. At higher temperatures, a thermally activated relaxation internal-friction peak was found, which appears to be a grain-boundary internal-friction peak.