Grain refinement and orientation of AZ31B magnesium alloy in hot flow forming under different thickness reductions

An analysis of the hot flow forming of Mg-3.0Al-l.0Zn-0.3Mn （AZ31B） alloy was conducted by experiments and numerical simulations. The effects of different thickness reductions on the microstructure and mechanical properties were investigated at a temperature of 693 K, a spindle speed of 800 rev/min and a feed ratio of 0.1 mm/rev. Thickness reductions have great influence on the uniformity of microstructure along the radial direction （RD） and the grain sizes become refined and uniform when the thickness reduction reaches 45%. The c-axes of most grains are approximately parallel to the RD, with a slight inclination towards the axial direction （AD）. The best mechanical properties with UTS of 280 MPa and YS of 175 MPa near the outer surface while 266 MPa and 153 MPa near the inner surface have been achieved due to grain refinement and texture. Moreover, the material flow behavior and stress/strain distributions for singlepass reductions were studied using the ABAQUS/Explicit software. The calculated results indicate that the materials mainly suffer from triaxial compressive stresses and undergo compressive plastic strain in RD and tensile strains in other directions. The higher stress and strain rate near the outer surface lead to more refined grains than that of other regions along the RD, whereas the orientation of the maximum principal compressive stress leads to a discrepancy of the grain orientations in RD.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Development of microstructural inhomogeneity in multi-pass flow forming of TA15 alloy cylindrical parts

Revealing the development of microstructural inhomogeneity in the multi-pass flow forming of titanium alloy components is of great significance to the microstructure control and property tailoring.To this end,the microstructural inhomogeneity of TA15 alloy spun cylindrical parts was analyzed based on the deformation history.The results indicate that the material underwent significant compressive strain in the normal direction(ND),tension strain in the rolling and circumferential directions(RD and CD),while tension strain in the CD is slightly small due to the limited material flow in this direction.These strain characteristics make the microstructure,especially the primary a(ap),present different morphologies in the different planes of the part.Meanwhile,the combined effects of inhomogeneous deformation and temperature distribution in the ND also cause the inhomogeneity of microstructure morphology and parameters in this direction.Quantitative analyses show that with the forming pass increasing,the aspect ratio of apincreases most in the normal-rolling plane,then in the normal-circumferential plane and least in the circumferential-rolling plane,whereas apcontent decreases in an opposite trend.Along the ND,the aspect ratio and content of apis relatively high in the outer and inner surface areas but lowest in the central area,and these inhomogeneous characteristics can be gradually diminished with the forming pass increasing.Furthermore,the variation of hardness inhomogeneity factor indicates that a four-pass forming with the total reduction ratio of 63%could obtain a homogenous microstructure along the ND of the TA15 alloy spun cylindrical part.

Analysis of anisotropy mechanism in the mechanical property of titanium alloy tube formed through hot flow forming

Anisotropy of mechanical property is an important feature influencing the service performance of titanium(Ti)alloy tube component.In this work,it is found that the hot flow formed Ti alloy tube exhibits higher yield strength along circumferential direction(CD),and larger elongation along rolling direction(RD),presenting significant anisotropy.Subsequently,the quantitative characteristics and underlying mechanism of the property anisotropy were revealed by analyzing the slip,damage and fracture behavior under the combined effects of the spun{0002}basal texture and fibrous microstructure for different loading directions.The results showed that the prismatic slip in primaryαgrain is the dominant deformation mechanism for both loading directions at the yielding stage.The prismatic slip is harder under CD loading,which makes CD loading present higher yield strength than RD loading.Additionally,the yield anisotropy can be quantified through the inverse ratio of the averaged Schmid Factor of the activated prismatic slip under different loading directions.As for the plasticity anisotropy,the harder and slower slip development under CD loading causes that the CD loading presents larger external force and normal stress on slip plane,thus leading to more significant cleavage fracture than RD loading.Moreover,the micro-crack path under RD loading is more tortuous than CD loading because the fibrous microstructure is elongated along RD,which may suppress the macro fracture under RD loading.These results suggest that weakening the texture and fibrous morphology of microstructure is critical to reduce the differences in slip,damage and fracture behavior along different directions,alleviate the property anisotropy and optimize the service performance of Ti alloy tube formed by hot flow forming.

FE simulation and process analysis on forming of aluminum alloy multi-layer cylinder parts with flow control forming

The aluminum alloy parts used in airbag of car were studied with flow control forming(FCF) method, which was a good way to low forming force and better mechanical properties. The key technology of FCF was the design of control chamber to divide metal flow. So, the design method of FCF was analyzed and two type of control chamber were put forward. According to divisional principle, calculation model of forming force and approximate formula were given. Then forming process of aluminum alloy multi-layer cylinder parts was simulated. The effect of friction factor, die radius and punch velocity on metal flow and forming force was obtained. Finally, the experiment was preformed under the direction of theory and finite element(FE) simulation results. And the qualified parts were manufactured. The simulation data and experimental results show that the forming sequence of inner wall and outer wall, and then the force step, can be controlled by adjusting the process parameters. And the FCF technology proposed has very important application value in precision forging.

Formation Mechanisms and Geomorphic Evolution of the Erlian Mudflow Fans, Eastern Guide Basin of the Upper Reaches of Yellow River

Several argillaceous platforms lie along the Yellow River（YR） of the eastern Guide Basin, northeastern Tibetan Plateau, and their compositions, formation processes, and geomorphic evolution remain debated. Using field survey data, sample testing, and high-resolution remote sensing images, the evolution of the Erlian mudflow fans are analyzed. The data show significant differences between fans on either side of the YR. On the right bank, fans are dilute debris flows consisting of sand and gravel. On the left bank, fans are viscosity mudflows consisting of red clay. The composition and formation processes of the left bank platforms indicate a rainfall-induced pluvial landscape. Fan evolution can be divided into two stages： early-stage fans pre-date 16 ka B.P., and formed during the last deglaciation; late-stage fans post-date 8 ka B.P.. Both stages were induced by climate change. The data indicate that during the Last Glacial Maximum, the northeastern Tibetan Plateau experienced a cold and humid climate characterized by high rainfall. From 16–8 ka, the YR cut through the Erlian early mudflow fan, resulting in extensive erosion. Since 8 ka, the river channel has migrated south by at least 1.25 km, and late stage mudflow fan formation has occurred.

SEDIMENTARY MACRO-STRUCTURES AND FORMING MECHANISM OF DEBRIS FLOW

The discussion on sedimentary macro-structures and their forming mechanics of debris flow is based on thedata of present processes and ancient deposits of Dongchuan in Yunnan Province, Wudu in Gansu Province and Fuxin inLiaoning Province. Non-cohesive debris flow, which is 1. 3 -1. 7 t/m3 in density, follows hydraulic fluid and flow model. In the hydraulic fluid of flood, electrolytic water combines clay into pulp to transport solid debris. The sedimentary structures show fluid processes as stone-line structure, imbricated structure and stone supporting-sustructure. A part of non-cohesive debris flow with a density of 1. 7 -1. 9t/m3 follows granular model. Debris is in the action of friction, collision and dispersion which forces as debris moving upward to form reverse graded load. The sedimentary structures of granular flow show reverse graded bedding, reverse-normal graded bedding, imbricated verticalstructure and circling linear structure.Cohesive debris flow, which is 1. 9 - 2. 3 t/m3 in density, follows structural two phase flow (viscoplastic) model. The sedimentary structures of cohesive debris flow show reverse graded-chaotic structure,bottom mud-chaotic structure and outwedging structure.

Research on flow stress of spray formed 70Si30Al alloy under hot compression deformation

The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble- 1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the swain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.

汽车刹车泵体注塑模具优化设计

针对汽车刹车泵体在注塑成型过程中出现翘曲变形、收缩和缩痕的问题,采用Moldflow软件对3种浇注方案和2种冷却方案进行筛选,有效抑制了泵体注塑成型过程中缺陷的形成,提高了产品的精度和质量。

基于移动网格法的流动旋压快速仿真方法研究

目的针对筒形件流动旋压有限元仿真中因网格模型规模庞大而导致的计算极端耗时问题,提出一种基于移动网格法动态控制网格密度的高效仿真算法,并验证该算法的高效性与可靠性。方法移动网格法包括局部加密全六面体网格的动态重构与新旧网格间的数据传递两部分。针对平滑过渡的局部加密网格构造提出了维度分离弹簧比拟法以快速动态重构,并采用三次样条曲线来精确描述工件的几何形状以保证网格重构过程的一致性。在数据传递过程中,为避免冗长的邻域搜索步骤,采用自适应反距离加权插值算法提升传递效率。根据上述算法,设计编制了基于动力显式有限元求解器ABAQUS/Explicit的移动网格法插件,以实现快速仿真模型的连续计算。结果基于移动网格法插件,建立了单旋轮筒形件流动旋压的快速仿真模型。与全加密网格相比,采用移动网格法的仿真模型可在获得精确几何形状的同时提速2~4倍。结论所提出的算法可实现筒形件流动旋压的高效仿真,同时可结合并行计算进一步提高仿真效率。

基于模流平衡的U型材挤出口模结构优化

应用Polyflow软件分别建立了U型件模型、带内外气体辅助层厚度不同的U型件模型和U型件开口有倾角的模型。针对传统挤出、不同内外层辅助气体厚度、不同开口倾角下3种情况进行了数值模拟计算,并用Origin软件对部分结果进行了分析。研究发现,使用气体辅助技术比型腔结构优化更有利于模流平衡;当内外气体辅助层厚度不同时,内层气体层厚度偏大、外层气体层偏薄时,更有利于抑制U型件开口收缩的变形;而对口模开口臂倾斜角度的修正更有利于减小或调整U型件开口收缩的变形。

沉浸理论视域下短视频知识采纳意愿的形成机制研究——基于“挑战—技能平衡”特征的对比分析

[目的/意义]知识类短视频是当前信息用户广泛使用的信息资源。本文旨在从沉浸体验视角探索用户在观看知识类短视频时的采纳意愿形成机制。[研究设计/方法]以沉浸理论和信息采纳模型为基础,采用对照实验、问卷调查法收集数据,通过PLS-SEM模型分析知识采纳行为的形成机制。[结论/发现]沉浸体验对感知有用性和知识采纳意愿具有积极影响,并负向调节视频质量对感知有用性的正向影响、正向调节感知有用性对知识采纳意愿的正向影响。用户在高技能、高沉浸状态下,知识采纳同时受感觉体验和知识内容路径影响;在高挑战状态下,只受知识内容路径影响。[创新/价值]将沉浸理论引入知识采纳研究,提出了短视频知识采纳意愿形成模型,发现了沉浸体验、知识采纳和图像认知之间的复杂关联。

不同边界工况下受电弓区域流场结构及气动噪声特性对比分析

为研究流场结构对受电弓气动噪声的影响,运用分离涡模拟方法和FW-H方程对高速受电弓区域流场结构和气动声场进行数值计算,对比分析平面和车体凹腔2种边界工况下流场特性、涡旋结构以及气动噪声特性的变化差异,为局部结构的气动声学优化以及仿真预测提供参考。结果表明:边界形式对局部流动具有明显的调制作用,速度场、涡量场均发生较显著的变化,相比于平面边界工况,车体凹腔边界工况下涡旋尺度增大,流动结构变得更为“有序”;车体凹腔边界工况下受电弓表面声压级相对较低,且气动噪声能量主要分布集中在500 Hz内的低频段;不同边界工况下Lamb矢量散度分布特征显示,气动声源的类型未发生变化,且车体凹腔边界工况下气动声源强度相对较弱;2种边界工况下的螺旋度分布差异意味着边界形式对流场的调制影响湍流能量的输运过程以及气动噪声能量的转化效率。

基于CRCLA的形式化描述与退火遗传映射算法

为解决密码算法映射到粗粒度可重构密码逻辑阵列(CRCLA)过程的描述困难问题,提出一种数据流图节点与划分后节点簇的描述形式,并以一种坐标序列描述形式精确显示CRCLA中资源的占用情况;针对密码算法映射到CRCLA上性能不高及编译时间过长的问题,提出一种能快速收敛到全局最优解的退火遗传算法,从初始温度、降温系数等方面对退火算法进行改进,增加遗传算法的筛选、交叉与变异流程。实验结果表明,编译时间与性能平均降低了30.6%与13.4%,验证了算法的高能效映射。

花键毂内花键轴向增量挤压成形特征

轴向增量挤压成形工艺为重卡用花键毂长内花键的高效、高性能成形制造提供一条可行途径。为了进一步优化控制内花键轴向增量挤压成形工艺,采用数值方法分析了采用三段挤压冲头的轴向增量挤压成形特征。根据内花键齿形成形情况、材料流动、应力应变分布,可将成形齿形区分为切入区、校形区、退出区和完全成形区,这些区域内的材料位移、等效应力、等效应变在不同成形阶段分布特征类似,只是部分区域轴向长度在不同成形阶段有所不同。成形过程中塑性变形主要发生在切入区,材料主要流动方向是径向和轴向;从切入区到完全成形区,应变逐渐增加至基本保持不变。

脉冲电流对6061T6铝合金流动摩擦挤压成形微观组织的影响

通过在流动摩擦挤压成形过程中施加脉冲电流,研究了脉冲电流对6061T6铝合金流动摩擦挤压成形性能的影响,同时,借助EBSD和TEM研究了脉冲电流对变形区材料组织演变的影响规律。结果表明:脉冲电流降低了材料的变形抗力,提高了材料的流动性,在下行速度0.6 mm·min^(-1)、转速950 r·min^(-1)以及下压量3 mm条件下,施加3800 A的脉冲电流可使6061T6铝合金的流动摩擦挤压成形高度从15 mm提高到20 mm。脉冲电流的施加促进了变形过程中再结晶的发生,细化了不同变形区的组织,并提高了变形区大角度晶界的比例;流动摩擦挤压成形后材料内部存在大量的线性位错、网状位错以及由位错攀移形成的位错墙;施加脉冲电流后,材料在搅拌力和挤压力的复合作用下发生大塑性变形,晶粒破碎,形成大量的纳米晶。

构网型分布式电源渗透率高的微电网潮流计算及优化控制

随着微电网(microgrid,MG)中构网型分布式电源(distributed generator,DG)渗透率的提高,传统的潮流计算和优化方法不再适用。基于下垂控制的数学模型,改进传统牛顿拉夫逊法;应用虚拟阻抗松弛DG的无功与电压约束,改进下垂控制;应用改进粒子群优化算法,得到使网损最小的MG优化潮流;通过仿真和实验,验证了该方法的有效性。该文有助于指导构网型DG渗透率高的末端电网或MG的规划与控制。

某拦河闸坝枢纽鱼道工程水力学特性试验研究

某闸坝枢纽作为天然河道上的永久性水工建筑物,其修建将对原河道天然水生生态环境连续性产生阻隔,影响鱼类洄游繁殖。为保障鱼类洄游成效,需要在枢纽上修建鱼道。针对鱼道设计方案能否满足水力学条件的问题,进行了不同水位组合条件下鱼道的整体水力特性和鱼道进出口数量与布置的研究。采用比尺为1∶16的物理模型试验方法,验证鱼道设计方案的合理性。结果表明,在推荐的鱼道布置和进口段采取补水措施下,各项水力指标均能满足规范和设计要求;当鱼道进口主流流速较小时,需要采用进口段补水措施满足诱鱼设计要求。

喷头流道结构参数对高黏度含能材料直写成型3D打印挤出过程稳定性影响

为了研究直写成型技术(DIW)中挤出系统的喷头流道结构参数(锥角角度、出口直径、成型段长度)对含能材料挤出过程的流体流动影响,研究建立了基于Polyfow Extrusion模块的高黏度含能材料挤出模型,并采用直写成型3D打印工况的挤出实验对其进行了验证。研究通过所建立的模型分析了锥角角度范围90°~130°,出口直径0.75~2 mm以及成型段长度5~20 mm对高黏度含能材料挤出过程的影响。结果表明:采用Polyflow Extrusion模块可以较准确地模拟复合含能材料的流动行为,同时发现锥角为100°、喷头出口直径为1.5~1.75 mm时挤出成型过程相对稳定、挤出膨胀较小,且成型段的增长会在增大所需入口压强的同时减小出口膨胀效应。

柔性Flow-Shop调度的遗传算法优化

柔性Flow-shop调度问题(Flexible Flow-shop Scheduling Problem,FFSP)是一般Flow-shop调度问题的推广,由于在某些工序上存在并行机器,所以比一般的Flow-shop调度问题更复杂。为了有效地解决柔性Flow-shop调度问题,用遗传算法求解,给出了一种改进的编码方法,能够保证个体的合法性;并根据编码方法提出了矩阵解码方法。最后以某汽车发动机厂金加工车间的生产调度实例进行仿真,通过比较表明了算法的有效性。

质子交换膜燃料电池金属双极板流道结构及制造工艺

金属双极板因具有强度高、导电性和传热能力好、能量损失小、密封性好等优势,且加工方便、加工成本低、可制造超薄厚度及高体积比功率等特性,逐渐成为双极板材料的首选,而流道结构设计和制造工艺是影响金属双极板成形质量和工作性能的关键。对比了金属双极板常用传统流道结构与新型流道结构,分析了结构变化对燃料电池性能的影响;梳理了金属双极板的冲压成形、液压成形、软膜成形、辊轧成形、电磁成形、特种成形等塑性成形工艺技术及成形装备;最后对金属双极板的流道结构设计与制造工艺进行了展望。