振动塑性加工及其在轻合金成形中的应用

振动塑性加工是将超声波等形式的振动施加在塑性成形的模具或坯料上,以达到提高坯料变形能力和加工质量等目的的一种塑性成形技术.回顾了振动塑性加工技术及其在铝、镁等轻合金塑性成形领域的理论研究和应用情况,探讨了利用该技术提高镁合金塑性成形性能与质量的可能性.     

轻合金电致塑性成形技术研究进展

轻合金室温难变形的特性在一定程度上限制了其广泛应用,而电致塑性成形技术在提高轻合金塑性、解决其成形性能差等方面具有较大优势。在传统金属材料电致塑性效应研究基础之上,综述了铝、镁、钛等典型轻合金电致塑性成形机理的研究进展,并对电致塑性成形工艺应用的研究情况进行了介绍。总结了轻合金电致塑性成形机理及应用研究的不足。     

新世纪中国塑性加工行业的发展与展望

进入新世纪以来,在航空、航天、汽车和装备制造等行业的国家重大需求的牵引下,中国塑性加工行业获得快速发展,取得举世瞩目的成绩。根据2000年以来塑性加工行业获得国家技术发明奖和科技进步奖的情况,讨论了汽车覆盖件成形、高性能轻量化构件成形和多工位挤压等塑性加工关键技术的创新与发展,介绍了中国研制的超大型液压成形机、超大型环轧机、360 MN垂直挤压机和120 MN铝合金板材拉伸机等"世界第一"的超大型装备,展望了新世纪塑性加工技术发展趋势,包括:超大尺寸复杂构件塑性成形技术、轻质耐高温材料高性能复杂构件塑性成形技术、非理想材料塑性本构模型与高精度数值模拟、智能化塑性加工装备及生产线。     

MB26镁合金的超塑性与超塑挤压研究

研究了MB26镁合金的超塑性,找到了该合金的最佳超塑性条件,分析了变形速率、温度等因素对该合金超塑性的影响。另外还对该合金的超塑性挤压作了实验研究。     

搅拌摩擦焊塑性金属流动基本模型

通过对搅拌摩擦焊接过程进行抽象和假设,建立了搅拌摩擦焊接过程中塑性金属流动的基本模型.文中定义了步长塑性层、步长空腔以及剥离侧和堆积侧等概念.提出了步长塑性层是塑性金属转移流动的基本单元,步长塑性层连续转移流入并填满步长空腔,塑性金属流动的一个周期结束同时下一个周期开始.分析了步长塑性层流动的驱动力以及阻力等因素.结果表明,若步长塑性层不能全部填满步长空腔,焊缝中会出现体积型缺陷的结论.步长塑性层在流入步长空腔的过程中,同时会掉头转向.     

材料超塑性研究的现状与发展

对20世纪90年代以来国内外超塑性的研究工作进行了介绍和评述.主要介绍了新的超塑材料的开发及超塑性的应用,概述了国内外超塑性研究的最新进展,并对超塑性研究的热点问题进行了评述,重点评述了用超塑成型方法制作大型铝合金汽车零件、用分子动力学模拟超塑变形中的晶界滑动、新材料和纳米材料的超塑性开发及超塑微成形的研究等国内外超塑性研究的新进展.展望了超塑性的发展趋势,指出应开发材料的低温或高速超塑性,重视超塑性流动过程的理论研究,进一步拓展超塑性的应用领域.     

铝基和钛基复合材料的塑性与超塑性

综述了近年来铝基和钛基复合材料的塑性和超塑性研究进展 ,分析了材料制备工艺和变形温度等参数对于复合材料的塑性和超塑性的影响规律 ,并展望了两种复合材料塑性和超塑性研究的发展方向。     

非理想材料塑性本构关系的研究现状及发展方向

介绍了金属材料塑性本构关系的研究与应用现状,阐述了塑性本构中屈服方程和塑性位势方程的物理含义及其相互关系,分析了现有塑性本构关系用于工程材料塑性变形分析时存在的主要问题,重点分析了实验数据应用导致的预测误差、屈服方程与塑性位势相关联假设条件所导致的不能同时反映屈服和流动的问题以及数学模型和本构关系基本结构方面存在的问题,讨论了发展非理想材料(各向异性材料、压力敏感材料等)塑性本构关系亟待解决的理论和实验难题,指出了非理想材料塑性本构关系的若干发展方向。突破经典塑性力学的理论体系、建立全新的"非关联"各向异性材料塑性本构关系理论体系,需要在理论模型、实验方法、数值仿真及工程应用等环节开展相关研究。     

基于INTERNET的超塑性数据库系统

介绍了首个基于国际互联网INTERNET的超塑性数据库，包括超塑性简介、超塑性材料、超塑性文献、超塑性专家、单位等，为广大的超塑成形工作者提供服务。     

现代汽车板材的有铆钉塑性连接及其核心技术探讨

近些年,很多轻质材料如铝合金、镁合金等在现代汽车板材上得到了广泛应用。有铆钉塑性连接在轻质材料的连接上具有巨大优势。本文首先介绍了现代汽车板材有铆钉塑性连接方式及其机制,并对有铆钉塑性连接和点焊等连接方式进行了对比。分析了现代汽车板材有铆钉塑性连接的关键技术。有铆钉塑性连接的关键技术包括铆钉形状、塑性变形程度、板材表面状况、塑性变形速率和加热处理。     

Toward a quantitative understanding of mechanical behavior of nanocrystalline metals

Focusing on nanocrystalline (nc) pure face-centered cubic metals, where systematic experimental data are available, this paper presents a brief overview of the recent progress made in improving mechanical properties of nc materials, and in quantitatively and mechanistically understanding the underlying mechanisms. The mechanical properties reviewed include strength, ductility, strain rate and temperature dependence, fatigue and tribological properties. The highlighted examples include recent experimental studies in obtaining both high strength and considerable ductility, the compromise between enhanced fatigue limit and reduced crack growth resistance, the stress-assisted dynamic grain growth during deformation, and the relation between rate sensitivity and possible deformation mechanisms. The recent advances in obtaining quantitative and mechanics-based models, developed in line with the related transmission electron microscopy and relevant molecular dynamics observations, are discussed with particular attention to mechanistic models of partial/perfect-dislocation or deformation-twin-mediated deformation processes interacting with grain boundaries, constitutive modeling and simulations of grain size distribution and dynamic grain growth, and physically motivated crystal plasticity modeling of pure Cu with nanoscale growth twins. Sustained research efforts have established a group of nanocrystalline and nanostructured metals that exhibit a combination of high strength and considerable ductility in tension. Accompanying the gradually deepening understanding of the deformation mechanisms and their relative importance, quantitative and mechanisms-based constitutive models that can realistically capture experimentally measured and grain-size-dependent stress–strain behavior, strain-rate sensitivity and even ductility limit are becoming available. Some outstanding issues and future opportunities are listed and discussed.     

Mechanical behavior of nanocrystalline metals and alloys

Nanocrystalline metals and alloys, with average and range of grain sizes typically smaller than 100 nm, have been the subject of considerable research in recent years. Such interest has been spurred by progress in the processing of materials and by advances in computational materials science. It has also been kindled by the recognition that these materials possess some appealing mechanical properties, such as high strength, increased resistance to tribological and environmentally-assisted damage, increasing strength and/or ductility with increasing strain rate, and potential for enhanced superplastic deformation at lower temperatures and faster strain rates. From a scientific standpoint, advances in nanomechanical probes capable of measuring forces and displacements at resolutions of fractions of a picoNewton and nanometer, respectively, and developments in structural characterization have provided unprecedented opportunities to probe the mechanisms underlying mechanical response. In this paper, we present an overview of the mechanical properties of nanocrystalline metals and alloys with the objective of assessing recent advances in the experimental and computational studies of deformation, damage evolution, fracture and fatigue, and highlighting opportunities for further research.     

Microstructure and Mechanical Properties of Cold Metal Transfer Welding Similar and Dissimilar Aluminum Alloys

Integrating structures made from aluminum alloys in automotive industry requires a large amount of joining. As a consequence, the properties of the joints have a significant influence on the overall performance of the whole structure.Robot cold metal transfer welding is a relatively new joining technique and has been used in this work to join 6082-T4 and5182-O aluminum alloy sheets by using ER5356 and ER4043 filler metals. Microstructure characterization was performed by optical microscopy and energy dispersive X-ray spectroscopy, and the mechanical properties were measured by tensile and hardness tests. A correlation is made between welding variables, mechanical properties and the microstructure of welded joints. Results indicate that robot cold metal transfer welding provides good joint efficiency with high welding speed, good tensile strength, and ductility. Owing to the low heat input of robot cold metal transfer welding process, the heat affected zone microstructure was quite similar to base metals, and weld metal microstructure was the controlling factor of joint efficiency. The best performing were the 5182/5182 joints welded with ER5356 and these had mechanical property coefficients of 100%, 98%, and 85% for yield strength, ultimate tensile strength, and elongation, respectively.     

Observations of grain boundary impurities in nanocrystalline Al and their influence on microstructural stability and mechanical behaviour

The exceptional properties of nanocrystalline materials lend themselves to a wide range of structural and functional applications. There is recent evidence to suggest that grain boundary impurities may have a dramatic effect on the stability, strength and ductility of nanocrystalline metals and alloys. In this study, transmission electron microscopy and atom probe tomography were used to characterize specimens deposited at different base pressures, thus providing a direct comparison of impurity content with microstructural stability and mechanical behaviour. Atom probe measurements provide clear experimental evidence of grain boundary segregation of oxygen in samples deposited at higher base pressures. It is proposed that these oxygen atoms pin the boundaries, preventing stress-assisted grain growth and resulting in increased strength and loss in ductility. This study provides the first direct experimental evidence that boundary impurities play a critical role in determining the microstructural stability and deformation behaviour of nanocrystalline metals.     

A statistical model for predicting the mechanical properties of nanostructured metals with bimodal grain size distribution

A statistical analysis is employed to investigate the mechanical performance of nanostructured metals with bimodal grain size distribution. The contributions of microcracks in the plastic deformation are accounted for in the mechanism-based plastic model used to describe the strength and ductility of the bimodal metals. The strain-based Weibull probability distribution function and percolation analysis of microcracked solids are applied to predict the failure behavior of the bimodal metals. The numerical results show that the proposed model can describe the mechanical properties of the bimodal metals, including yield strength, strain hardening and uniform elongation. These predictions agree well with the experimental results. The stochastic approaches adopted in the proposed model successfully capture the failure behavior of bimodal coppers that are sensitive to grain size and the volume fraction of coarse grains in addition to the corresponding threshold for percolation. These results will benefit the optimization of both strength and ductility by controlling constituent fractions and the size of the microstructures in materials.     

纳米晶Ni疲劳行为的实验研究

系统研究了纳米晶Ni与粗晶Ni的疲劳行为. 通过疲劳实验获得了这2种材料的疲劳应力--寿命曲线, 并采用AFM对纳米晶Ni样品表面进行观察以研究其裂纹萌生的微观机制, 利用纳米压痕仪对疲劳实验前后样品的力学性能和显微组织变化进行了研究. 结果表明, 纳米晶Ni具有比粗晶Ni更高的疲劳极限. AFM观察表明,纳米晶疲劳后样品表面出现平均尺寸为73 nm的胞状起伏, 疲劳后样品的晶粒尺寸未发生明显改变. 压痕硬度结果表明, 疲劳过程材料的力学性能也未发生明显变化.     

Molecular dynamics simulation of intrinsic and extrinsic mechanical properties of amorphous metals

Mechanical response of amorphous metal Ni₄₀Zr₆₀ under applied tensile loading is investigated using large-scale atomistic simulations. To obtain intrinsic properties, homogeneous samples with atomically smooth surface are used while samples with deliberately introduced surface notches of varying depths and root radii are used to test extrinsic effects. It is found that the notch-free samples show strength close to the theoretical fracture strength and extremely large ductility. Apparent strain hardening and strain rate sensitivity are also observed in these studies. It is argued that the free volume generation and localized shear displacement are responsible for the mechanical properties. Therefore, the presence of surface imperfections can greatly reduce the strength and ductility. The results suggest that to retain and improve the intrinsic mechanical properties of amorphous metals, surface treatment may be needed, which has been practiced in oxide glass industry for centuries but received little attention in metallic glass community.     

A STUDY ON AGING TREATMENTS FOR ALLOY 2195

1.IntroductionTherecentlydevelopedAl-CuLi-Mg-AgWeldaliteRalloys(e.g.2O95,2195,2O94)aregreatlyattractivet0designersforhighstrengthandf0rgingapplications[1-3l.Theseal-loyshavepr0misingcombinedpr0perties0fstrengthandductilityafternaturalagingandartifitialagingwith0rwith0utpriordeformation[4-6l-Theartificialagedmicrostructurewasrep0rtedt0c0ntainpred0minantT1phases(Al2CuLi)withamin0rpresenceofO'(AlzCu)orS'(AlzCuMg)phases[3-6].In2O95alloys,loweringtheagingtemperaturere-sultedinreducedsubgra…     

激光快速成形Ti-6Al-4V合金力学性能

采用实验研究的方法，对激光快速成形Ti-6Al-4V合金的力学性能进行了探讨。结果发现：和锻造件相比，激光快速成形沉积态Ti-6Al-4V合金的拉伸性能具有高强低塑特点和更显著的各向异性；成形试样的组织、氧含量和冶金缺陷都将影响到拉伸性能，其中组织的影响最显著，其次为氧含量和熔合不良缺陷：对于氧含量符合GJBGJB2921-1997标准的激光快速成形Ti-6Al-4V合金，经固溶时效热处理后所获得的网篮组织综合性能最好，不论是强度指标还是塑性指标都高于锻件标准。     

高铝锌合金的铸态组织和机械性能关系分析

本文通过对比分析新研制的高塑韧性高强度锌合金和ZA27合金的显微组织,观察和分析了试样断口处显微组织的变化,研究了锌合金机械性能和显微组织间的关系,探讨了新研制合金塑韧性好的组织原因。