Effect of ECAE on Microstructure and Tribological Properties of Cu–10%Al–4%Fe Alloy

Equal channel angular extrusion (ECAE) process was carried out for a commercial aluminum bronze alloy (Cu–10%Al–4%Fe) produced by hotrolling at high temperature. The effect of ECAE on microstructure, mechanical, and tribological properties of the alloy was investigated. Experimental results showed that the grain size of the alloy decreased with the increase of the pass number of ECAE. After applying ECAE with six passes, the hardness and yield strength of the alloy increased from 118 kgf/mm² and 356 MPa to 165 kgf/mm² and 588 MPa, respectively. The friction coefficient and wear rate of the aluminum bronze alloy were largely reduced due to the improvement of mechanical properties after ECAE. The adhesive wear was the primary wear mechanism for the specimen without ECAE, while abrasive wear was dominant for the specimen with ECAE after six passes.     

Forgeability of ultra-fine grained aluminum alloy for bolt forming

In the present investigation, an equal channel angular extrusion (ECAE) was used to make bulk nanostructure of the commercially available aluminum alloy AA1050 at room temperature. In order to investigate the effect of the ECAE routes on formability, three different routes A, Bc, and C were applied up to three passes by employing a split die set-up, which required less extrusion load compared with the conventional dies. Formability of the conventional and ultra-fine grained specimens was measured by applying a compression test. Considering the formability obtained from the compression test, bolt forming sequences were developed into three stages and applied to manufacture a high strength bolt using a cylindrical ultra-fine grained specimen at room temperature. The effects of processing routes and number of passes in the ECAE on strength increase and its homogeneity in the manufactured bolts were investigated by the tension and microhardness test, respectively. According to this investigation, a novel approach to utilize the ECAE to manufacture high strength bolt using the conventional material is demonstrated. This approach can be extended to other manufacturing parts that require high strength and lesser weight at a competitive manufacturing cost.     

Quantitative analysis of microstructure refinement in ultrafine-grained strips of Al6063 fabricated using large strain extrusion machining

Abstract

In present research work, ultrafine-grained strips of Al-6063 alloy were fabricated using hybrid extrusion machining technique known as “large strain extrusion machining (LSEM).” Fabrication of strips was done using the customized HSS tools of different rake angles varying from 0° to 10° under different machining conditions. Microstructural and mechanical characterizations of these strips were done to ascertain the effect of different parameters on their properties. From the results of hardness measurement of strips, it was concluded that hardness of the strips increased by 34–97% of the base material as of the refinement of grain size occurred. Surface lay was improved by 30% with higher cutting velocity and rake angle. Crystallite size was found to decrease with increase in the rate of strain. The shear strain was increased as chip compression ratio increased and rake angle decreased. Fabrication ability of strips increased due to increase in strain hardening exponent and it may result in the large scope of their applications. Nano-hardness of the strips was found to be more than bulk alloy. These above said results showed that ultrafine strips fabricated using LSEM process can become a good choice for future material fabrication.     

聚四氟乙烯对聚丙烯复合材料等通道转角挤压加工性的影响

研究了聚四氟乙烯（PTFE）对聚丙烯（PP）共混物固态等通道转角挤压（ECAE）加工性及性能的影响.结果表明：在PP中加入少量（小于2%的质量分数）PTFE使PP共混物的摩擦因数从纯PP的0.32减小到0.28,ECAE加工挤出压力从纯PP的130 MPa降低到115 MPa;含有少量PTFE的PP共混物使ECAE加工挤出过程更容易,挤出更稳定,其挤出物呈现出较好的形变均匀性,因此,PTFE对PP共混物的固态ECAE加工具有较大的促进作用,少量PT-FE的加入对PP共混物的力学性能影响较小.     

A computational study of die geometry and processing conditions effects on equal channel angular extrusion of a polymer

Equal channel angular extrusion (ECAE) is an efficient process to obtain enhanced microstructures via super-plastic deformation. In view of its optimisation, it is of prime importance to assess the relationships between processing conditions and material flow. More precisely, detailed knowledge of the plastic strain distribution in the extruded material in relation to the ECAE processing variables is required. The key parameters of the ECAE process are primarily die geometry, ram speed, extrusion temperature, use of back-pressure, number of extrusion sequences and processing route (e.g. rotation of the sample between successive passes). A numerical investigation was achieved to check out the influence of these parameters on the homogeneity of plastic strain distribution in the case of a conventional thermoplastic polymer. Material parameters of a phenomenological elastic viscoplastic model were deduced from compressive deformation tests at different temperatures and strain rates on high-density polyethylene (HDPE). Recommendations on tool geometry and processing conditions can then be provided, according to the numerical results.It was found that optimum ECAE die geometry is strongly material dependent. The application of a back-pressure significantly contributes to reduce the corner gap and consequently promotes the homogeneity of the plastic strain field. A slight sensitivity of plastic strain to ram speed and friction conditions was pointed out. The extrusion temperature strongly influences the magnitude of the plastic strain and has a slight effect on its homogeneity. The number of passes has a significant effect on the magnitude of the plastic strain but has a negligible influence beyond a certain temperature. The extruded material reaches a stationary strain state after few passes. The homogeneity of the plastic strain field is strongly affected by the processing route.     

镁合金等径角挤压的研究与进展

对等径角挤压工艺的基本原理及其工艺参数在挤压过程中对镁合金显微组织、力学性能的影响,等径角挤压过程中镁合金的晶粒细化机理、变形机理及其微观结构、力学性能等的演变规律作了综述,并对等径角挤压镁合金超塑性研究现状和镁合金等径角挤压发展趋势作了介绍.     

铝合金轴固定件热挤压成形的有限体积法模拟研究

由于变形剧烈，复杂铝型材挤压成形有限元模拟会因网格不断重划分而精度欠佳。文中基于可以有效避免网格重划分难题的有限体积法，对铝合金门轴固定产品的热挤压过程进行数值模拟，详细分析挤压成形中各个阶段金属流动情况以及应力、应变、温度、速度等场量的分布变化情况。棒料进人模口至完全流出工作带这段时间是型材挤压最为困难的阶段，材料在工作带处的应力、应变最大，温度最高，因而对模具工作带处造成的磨损也最为严重。进人到最终稳定挤压阶段时挤压方向金属流速计算值与理论挤出速度吻合很好。模拟结果表明所用有限体积法是有效的，可以为铝型材挤压的模具设计与工艺参数的选择提供理论指导。     

Damage and failure characterization of 7075 aluminum alloy hot stamping

7000 series high strength aluminum alloys are increasingly used in manufacturing automobile body parts to meet the more stringent demands for automobile lightweight. Hot stamping of 7000 series high strength aluminum alloys is a complex thermal-mechanical coupling process and precise simulation is needed to predict material fracture. To obtain damage model of 7075 aluminum alloy in hot stamping, five different stress triaxiality specimens were designed. The fracture strain, critical strain and average stress triaxiality of different specimens were obtained by the hybrid finite element simulation and experiment (FE-EXP) method. GISSMO model of 7075 aluminum alloy at 400 °C was established. Compared with the experimental results of U-shaped part hot stamping under different lubrication conditions, the calibrated GISSMO model was demonstrated to predict the damage behavior of 7075 aluminum alloy during high temperature deformation accurately.

     

阻流块对薄壁空心铝型材挤压过程材料流速的影响

采用基于任意拉格朗日—欧拉(Arbitrary Largrang-Euler,ALE)算法的HyperXtrude软件模拟带有细小特征的薄壁空心铝型材挤压过程,以模孔出口处材料流速均方差作为衡量其均匀性的指标,通过设计一系列阻流块有效控制材料流速及型材变形。研究阻流块对流速均匀性的影响规律,提出阻流块设计的一般原则。结果表明,阻流块的截面形状对流速控制起着关键作用,应保证阻流块截面形状合理,再调整阻流块高度及其到模孔的距离,可有效控制材料流速及型材的变形,获得形状和尺寸符合要求的型材。在阻流块高度的一定范围内,增加其高度可增加型材整个截面上材料流速的均匀性,但阻流块的宽度对平衡材料流速作用不大。     

有限体积法在三维非稳态铝合金挤压过程模拟中的应用

研究基于Euler网格的有限体积法(Finite volume method,FVM)模拟三维大变形非稳态铝型材挤压过程的基本理论和关键技术,应用C语言编制程序求解速度场、温度场等物理场量,并利用运动界面追踪技术--流体体积(Volume of fluid,VOF)方法捕捉材料流动前沿.采用"移动的网格"处理计算区域边界的移动问题,实现对真实物理过程的数值模拟,并将模拟结果与比较成熟的商品化有限元软件DEFORM-3D的模拟结果进行对比,表明所建立的有限体积法模拟模型有效、可靠.结果对比表明,FvM模型的模拟结果更符合实际,证明有限体积法比有限元法更适合大变形挤压过程模拟.     

A new generalized upper-bound solution for the ECAE process

A new generalized upper-bound solution for the equal-channel angular extrusion (ECAE) process is presented in this paper. Using mathematical definition of Bezier curves, a streamline was formulated to define a generalized deforming region. Based on this deforming region, a kinematically admissible velocity field was obtained from which upper-bound solutions were computed. By changing the parameters defining the Bezier-shaped streamline which in turn defines the deforming region, the optimization of the upper-bound solution was carried out. Equal-channel angular extrusion through a 90° bend was considered. Using the formulation presented in here, it was possible to predict the shape of the dead metal zone and its variation with frictional conditions. Unlike previous work in which a fixed circular shape had been assumed for the dead metal zone, in this paper, a generalized shaped Bezier curve was used. The optimum value of the extrusion pressure for ECAE was obtained and compared with both experimental and theoretical data from previous works. It was concluded that the present solution gave an improvement over all previous works and the authors’ results were closer to experimental data.     

An approximate analysis for studying the plane strain deformation of strain rate sensitive materials

The paper presents a numerical method for analyzing the plane strain deformation of rate sensitive materials. A rate of energy functional is introduced which is thought to take adequate account of the strain rate sensitivity of the material. In the numerical technique the functional is minimized with respect to a kinematically admissible velocity field and used in a discretized form in a finite element analysis.To serve as an illustration the frictionless, plane-strain, side extrusion process was considered. To simulate actual side extrusion processes friction was incorporated into the analysis by assuming a constant fraction, α, of the current shear stress of the material.Data were available from some preliminary experiments on the side extrusion of a superplastic tin-lead alloy. The theoretically predicted forming pressure, taking α = 0·3, showed reasonably good agreement with the experimental values.     

Process responses and resultant joint properties of friction stir welding of dissimilar 5083 and 6061aluminum alloys

The effects of combinations of dissimilar aluminum alloys during Friction stir welding (FSW) on the process response and resultant joint properties are experimentally investigated using two dissimilar automotive structural aluminum alloys. Depending on the materials on the advancing and retreating sides of the tool travel direction during FSW, four different material combinations are considered. FSW joints without macroscopic defects are successfully fabricated for the four different material combinations. The optical microscopy results show that the macroscopic material mixing behaviors of the two dissimilar material combinations during FSW are somewhat different from each other, even though the process responses during joining are not much different. The results of the quasi-static tensile tests and EBSD analysis demonstrate that the mechanical behaviors and orientation changes of the joint during tensile deformation are affected by the material locations with respect to the tool travel direction during FSW.

     

A lightweight design approach for an EMU carbody using a material selection method and size optimization

This study proposes a weight reduction design approach for urban transit carbody using a material selection method and size optimization. First, the material selection method, which uses specific stiffness and strength indices to predict the weight reduction rate, is set up when the materials of the under-frame and roof structure are substituted. The CFRP was chosen as the best weight reduction material in terms of the material selection method but was not appropriate for application to an urban transit carbody as a thin panel because of out-of-plane deformation. Therefore, we applied CFRP-AL honeycomb sandwich composites to the under-frame and roof structures, and the size optimization method was subsequently applied to derive a lightweight composite hybrid carbody design. Finally, the proposed approach was applied to an urban transit carbody, i.e., a Korean electrical multiple units carbody made of aluminum extrusion profiles. The weight of the optimized composite hybrid carbody design was 29.0% lighter than that of the original K-EMU. The resulting composite hybrid carbody design satisfied the design guidelines of the Performance test standard for K-EMU according to the corresponding FE simulations.

     

分流组合模挤压过程数值模拟及模具应力分析

采用有限体积数值模拟方法研究分流组合模中焊合室的深度对铝型材挤压过程的影响,分别采用21mm、26mm和31mm三种焊合室深度对挤压过程进行了模拟,得到了应力、应变、挤压力等各种物理场量的变化规律,并采用有限元法对模具受力及变形情况进行了分析。研究结果表明,焊合室深度对载荷影响不大,但焊合室深度为26mm时质点流速最均匀。模具变形分析结果表明,随着焊合室深度增加,模芯变形程度增大,对应力分布来说,存在一个最佳的焊合室深度。从型材产品质量和模芯变形量综合考虑,应合理设计焊合室深度。     

Die optimization design and experimental study of a large wallboard aluminum alloy profile used for high-speed train

The extrusion die plays a crucial role in the quality control of aluminum alloy profile production. But in practice, the design of extrusion die is mainly dependent on the experience and intuition of die designers; thus, many times of modifications and experiments should be undergone until an acceptable product is gained. In this paper, the extrusion process of a large wallboard aluminum alloy profile used for high-speed train was simulated by means of HyperXtrude software, and the flow behavior of material and deformation mechanism in the die cavity were investigated. With the simulation results of the initial die design scheme, a nonuniform velocity distribution in cross-section of the extrudate was observed. For optimizing the die design scheme, two optimal schemes (adoption of double-step welding chamber and introduction of baffle plate) were proposed. Through optimization, the velocity differences in the extrudate for optimal schemes are decreased from 39.9 to 12.2 and 10.8 mm/s, respectively. Thus, the uniformity of velocity distribution was improved in optimal schemes. The extrusion die design methods for large wallboard profiles were summarized and proposed, including the design methods of baffle plate and double-step welding chamber. Through trial production, a sound wallboard aluminum profile with good geometric shape and high dimensional accuracy was gained. Additionally, the mechanical properties of the extrudate were examined by means of experimental method. It is found that the test results stratified the practical engineering requirements.     

高强铝合金构件控制塑性成形技术在装备轻量化中的应用

车辆传动、行动构件数量多,且服役条件恶劣,要求有高的强韧性和疲劳寿命,现有铝材及制造技术无法满足。本文研究了变形参数对超高强铝合金构件性能的影响,发明了逐次控制变形方法和径向扩、收多次挤压控制金属流线方向新工艺,给出了相应的工艺规范,解决了构件疲劳寿命低的难题,实现了装备轻量化。     

Evaluation of a pyramid die extrusion for a hollow aluminum profile using FE simulation

The pyramid die extrusion for a hollow aluminum profile was analyzed to investigate the potential of such innovative dies. For this purpose, the pyramid and conventional porthole dies were respectively designed for a given hollow aluminum profile. And the extrusion process was comprehensively studied by performing different types of finite element simulation, such as the analysis of steady state, transient state and billet skin tracking. The effects of pyramid angle on the evaluation parameters of extrusion, such as extrusion load, material flow, exit temperature, length of transverse weld, quality of longitudinal weld, back end defect and die stress were overall analyzed and compared with the conventional porthole die. Through this study, the advantages and shortcomings of pyramid die were well concluded, which should be important information for die designers and makers.

     

铝型材挤压成型数值模拟及优化设计

应用有限元法,通过对AA6063铝合金方管挤出过程进行数值模拟,优化了分流组合模的工作带,以模孔出口处型材挤出速度的流速均方差为目标,使模孔出口处型材挤出速度均匀;同时通过对影响型材焊合品质的3个重要工艺参数:挤压速度、模具预热温度和坯料预热温度进行正交试验,以焊合面上的压力大小作为评定型材焊合品质好坏的标准,获得了AA6063铝型材挤压的最佳工艺参数组合。     

Effects of manufacturing process and surface treatments on mechanical properties of PLA/SCF composites using extrusion printing

Short carbon fiber (SCF) reinforced polylactic acid (PLA) composites were fabricated by extrusion printing, and the effects of process parameters and surface treatments on the mechanical properties of composites were studied. Based on the rheological properties of composites and the extrusion process simulation, pure PLA specimens and PLA/SCF specimens were manufactured under different printing parameters. Three kinds of surface treatment were adopted to improve the mechanical properties. The experimental results show that SCF can effectively improve the tensile strength and bending strength, but the compressive strength decreased. The specimen had the best mechanical properties when the layer height was 0.1 mm and the nozzle diameter was 0.6 mm. The mechanical properties can be further improved by coupling agent coating method, and the compressive strength was even higher than that of pure PLA specimen. The research in this paper can provide a reference for the fabrication of thermoplastic composites with excellent mechanical properties by extrusion printing.