制备块体细晶材料的大塑性变形方法

利用大塑性变形技术(Severe Plastic Deformation,SPD)制备块体细晶材料近年来得到迅猛发展.他适用于不同金属、合金、金属间化合物等,使材料获得了优异的性能,因此受到了越来越多的关注.本文叙述了大塑性变形的常用方法及其工作原理,指出了目前大塑性变形法在制备块体细晶材料时存在的问题.     

高强高耐蚀镁合金材料制备获进展

正中国科学院金属研究所中科院核用材料与安全评价重点实验室研究员许道奎团队与南京工业大学教授信运昌课题组合作,在制备高强高耐蚀镁合金材料方面取得重要进展。据了解,镁合金的密度是钢铁的1/4、铝合金的2/3,是最轻的金属结构材料,但低的绝对强度和耐蚀性极大限制了其实际工程应用。通常采用的剧烈塑性变形(SPD)方法对镁合金强度的大幅提升较为有效,可制备出超细晶超高强镁合金。已有研究发现,具有密排六方结构的镁合金具有较差的冷变形能力,需在较高温度条件下进行SPD加工处理,极易造成晶粒长大,难以获得超细晶组织。更为严重的是,传统SPD制备的超细晶所形成非平衡晶界会显著降低镁合金的耐蚀性。     

镁合金大塑性变形轧制技术研究进展

镁合金大塑性变形轧制技术是一种高性能镁合金板材加工技术,介绍了大塑性变形(SPD)技术原理及新发展起来的几种大塑性变形轧制技术,并对大塑性变形轧制技术进行了展望.     

多模式超声振动等径角挤压超细晶纯铝成形机理研究

超细晶金属材料由于具有优异的力学性能,特别适合微小金属零件的塑性成形。大塑性变形法是制备超细晶金属材料的常用方法,等径角挤压法被认为是最具有发展前景的大塑性变形方法之一。传统等径角挤压需要通过多道次的应变量累积来获得超细晶材料,制备效率较低。将超声振动与等径角挤压过程相结合可以有效减小挤压成形载荷,提高等径角挤压制备超细晶的性能和效率。现有研究主要采用工具辅助超声振动模式,提出并研发基于工件辅助超声振动模式的等径角挤压成形工艺,并对不同超声振动模式1070纯铝等径角挤压成形机理进行对比研究,研究工具超声振动和工件超声振动两种不同振动方式对晶粒道次细化能力的影响规律。结果表明,随着超声功率的增大,工具超声振动和工件超声振动的超声软化效应逐渐增强,能更大幅度降低等径角挤压成形力,并提高晶粒道次细化能力。工件超声振动比工具超声振动更有利于吸收超声能量,从而能更有效提升超细晶金属的制备效率。     

压扭成形中优化摩擦条件的研究

大塑性变形工艺即在外力作用下通过特制模具,使常规粗晶材料内部发生大的塑性变形,从而达到细化晶粒、改善材料性能的目的。用此方法制备块体纳米材料的研究热点主要集中在等通道角挤压法和高压扭转法。本文主要就改进HPT工艺的摩擦接触条件进行讨论。     

镁合金板材温热变形机理及温热成形技术

镁合金温热成形工艺具有较好的应用前景,是实现轻量化的重要途径,但镁合金温热成形机理需要进一步深入研究。通过电子背散射衍射(Electron back scatter diffraction,EBSD)原位跟踪观测方法,针对100～230℃范围,对轧制镁合金板材在单向压缩和单向拉伸变形时的变形机理进行系统研究和定量分析。分析镁合金板材在不同条件下的力学性能、织构转变特点、孪晶与滑移系启动规律,揭示不同变形条件下镁合金板材的塑性变形机理。研究结果表明,镁合金板材在变形过程的力学性能变化、织构演化和晶粒取向变化在很大程度上取决于孪晶参与变形的比例。镁合金板材在170℃具有较高的塑性成形能力,该温度下的大量锥面滑移系启动有利于协调轧板在厚度方向的变形。根据已获得镁合金板材变形机理,为镁合金板件冲压成形工艺提出建议。提出镁合金板件温热成形工艺,开发若干典型镁合金板件产品。     

不同挤压态高硅含量Mg-9Al-6Si合金的压缩性能

对普通铸造制备的高硅含量Mg-9Al-6Si镁合金进行了均匀化处理,然后进行了1道次正挤压和8道次往复挤压,以探讨不同挤压工艺对其组织与压缩性能的影响.结果表明:正挤压对该镁合金中Mg2Si相的破碎、细化效果不明显,而往复挤压对Mg2Si相有很好的破碎、细化作用;Mg2Si相的细化可提高镁合金的压缩性能;合金往复挤压8...     

异步轧制AZ31镁合金板材的组织和晶粒取向

主要对异步轧制AZ31镁合金板材的显微组织和晶粒取向进行了研究,以探讨提高镁合金板材塑性变形能力的途径。结果表明:由于异步轧制时板材的变形量比常规轧制时的大,其动态再结晶进行得比较完全,因此异步轧制有利于AZ31镁合金板材晶粒的细化与均匀化;并且改变异步轧制的工艺条件,能够在一定程度上改善镁合金板材中的(0002)基面织构取向,使织构得到软化,从而提高镁合金的塑性变形能力。     

等通道转角挤压技术及其工程应用研究

等通道转角挤压技术（ECAP）是一种目前最有工程应用潜力的大塑性变形（SPD）细晶材料制备技术，具有材料组织细化效果好、加工材料尺寸大等优点。阐述了ECAP处理对材料性能的影响，主要包括材料强韧性能的提高、超塑性的获得以及材料疲劳性能和功能特性的改善。在此基础上，探讨了近年来ECAP技术在工业化应用方面的研究进展，如各种大尺寸材料加工的试验研究、连续化生产和提高加工效率的解决方案等，同时指出了目前研究中存在的不足之处和需要解决的主要问题。     

镁合金塑性变形机制及动态再结晶研究进展

综述镁及镁合金在室温下塑性变形机制和高温下动态再结晶行为,总结镁合金塑性变形机制和动态再结晶的研究进展。结果表明:工艺参数、加工工艺、合金元素等均能影响镁合金的塑性成形过程,孪生能有效促进非基面滑移,动态再结晶作为一种重要的晶粒细化机制能有效启动晶界处的棱柱面滑移,提高镁合金的塑性。指出优化工艺参数,研发新型工艺,细化晶粒尺寸是变形镁合金发展的重要方向。     

Finite element analysis of planar twist channel angular extrusion (PTCAE) as a novel severe plastic deformation method

A new severe plastic deformation (SPD) method based on equal channel angular pressing (ECAP) is introduced for producing ultrafine grains in bulk alloys, entitled as “Planar twist channel angular extrusion (PTCAE)”. In PTCAE method, there is additional angle, α, (plus φ and ψ angles in ECAP method) which represents angle associated with the lateral reversal arc of curvature in deformation zone. Three dimensional finite element method (FEM) simulations of both ECAP and PTCAE processes were performed in order to investigate the plastic deformation state of processed samples and, moreover, the effect of different die geometry (in terms of variation of planar twist angle) on plastic strain distribution and magnitude. Results revealed that PTCAE process related with ECAP process can impose higher strain values in different shear planes simultaneously in one deformation zone. Therefore, PTCAE can produce UFG or nanostructured materials better than ECAP method which has simpler design and significantly higher efficiency compared with other new SPD processes.     

累积轧合法的研究现状及存在的问题

累积轧合法是一种深度塑性变形方法,它是通过累积的轧制过程达到金属材料发生强烈塑性变形的目的,可以显著细化金属材料的晶粒尺寸,对材料的微观组织和性能都产生很大的影响。对累积轧合法的工艺作了介绍,并对其目前的研究现状和存在问题作了分析。     

多目标质量的粉末包套等通道挤扭成形致密工艺参数优化

剧烈塑性变形法—挤扭以剪切塑变为主变形方式,成形工艺复杂,影响因素很多,难以精确地建立工艺参数与成形质量之间的关系;选取优化合理的工艺参数匹配是材料尤其是粉末材料成形无破裂、塑性好、致密化程度高等成形质量的关键。以等通道横截面扭转角、螺旋角、摩擦因子、挤压速度、初始相对密度为自变量,正交试验为设计方案,对纯铝粉末烧结材料进行一道次包套等通道扭挤数值模拟,获得以等效塑性应变、静水压力、最大损伤值、相对密度数据,通过层次分析法计算多质量目标的权重,运用追踪点法和灰色系统理论的灰色关联度优化工艺参数,使设计目标值达到等效应变最大、静水压力最大、最大损伤值最小、相对密度最大。模拟和试验结果表明,运用多目标优化组合参数进行等通道挤扭成形能使纯铝粉末体材料迅速地形变累积,静水压力提高,损伤值显著地减小,致密效率高,晶粒明显细化,提高了材料综合质量。     

高强铝合金热塑性变形本构关系研究现状及发展趋势

高强铝合金热成形工艺条件下的变形行为表征,需要在考虑温度、应变速率及应变影响的基础上结合微观演化行为建立热塑性本构关系。总结了高强铝合金热塑性变形本构关系相关研究成果。研究结果表明：广泛应用的唯象本构模型通过修正模型参数可以充分耦合应变、温度及应变速率作用,并准确地预测不同变形条件下的流动应力,然而缺乏对变形机制的明确解释,使得唯象本构模型对试验温度、应变速率变化范围较大以及试验条件范围外的变形行为预测精度难以得到保证;基于物理意义的本构模型能够模拟位错密度、晶粒尺寸及动态再结晶等微观演化过程,对流动应力进行精确计算,展现了强大的宏微观变形预测能力,是高强铝合金热塑性变形本构关系的研究趋势。     

摩擦系数对四对轮CR-ECA大应变技术的影响

集成传统轧制(conventional rolling)和等通道转角变形(equal channel angular deforma-tion)的新型大应变技术(CR-ECA大应变技术),是一种实现材料连续塑性大变形的有效手段。利用三维有限元分析软件Deform_3D对4对轮CR-ECA大应变技术进行了仿真计算。研究了4对轧制轮在不同摩擦系数下对工件应变、轧制轮扭矩及出口速度的影响。结果表明:摩擦系数是一个重要的技术参数;工件内部应变大小随着摩擦系数的变化而变化;随着摩擦系数的逐渐增大,轧制轮总扭矩逐渐增加,驱动性能提高;出口速度呈逐渐增大趋势,生产效率逐渐提高。     

Tribological properties of the AZ91D magnesium alloy hardened with silicon carbide and by severe plastic deformation

Results of investigation of the tribological contact characteristics of R18 tool steel in interface with AZ91D magnesium alloy hardened with SiC disperse powder filler and by severe plastic deformation (SPD)—specifically, equal-channel angular pressing (ECAP)—are presented. It is established that introduction of the SiC powder filler into the magnesium alloy increases the friction coefficient and reduces the wear rate. The size and volume of the powder filler particles, the normal load, and the relative sliding velocity influence these tribological characteristics. SPD of the original material leads to reduction of the molecular component of the friction coefficient.     

Investigation of deformation and collapse mechanism for magnesium tube in axial crushing test

This paper demonstrates the quasi-static axial compression and high-speed axial compression tests of extruded magnesium alloy circular tubes for evaluating the crash and fracture behavior of mg parts. To capture the buckling and fracture behavior of Mg tube during the axial compression tests, FE simulation adopts different types of flow curves depending on the deformation mode such as tension and compression with LS-DYNA software. The Mg tube undergoes compressive plastic strain prior to buckling while according to the model based on Hill yield criterion only bulging along the radial direction is predicted. Due to the tension-compression asymmetry of Mg alloys, diameter of Mg tube expands largely at the initial plastic strain before having bulging or folding while only a bulging mode typical for materials with cubic crystal structure can be predicted. Simulation results such as punch load and deformation mode are compared with experimental results in the axial crushing test with AZ61 alloy.     

Comparison of radiation-induced segregation in ultrafine-grained and conventional 316 austenitic stainless steels

Due to a high number density of grain boundaries acting as point defect sinks, ultrafine-grained materials are expected to be more resistant to irradiation damage. In this context, ultrafine-grained 316 austenitic stainless steel samples have been fabricated by high pressure torsion. Their behavior under ion irradiation has been studied using atom probe tomography. Results are compared with those obtained in an ion irradiated conventional coarse-grained steel. The comparison shows that the effects of irradiation are limited and that intragranular and intergranular features are smaller in the ultrafine-grained alloy. Using cluster dynamic modeling, results are interpreted by a higher annihilation of point defects at grain boundaries in the ultrafine-grained steel.     

Mg97Zn1Y2镁合金的高温磨损行为

对Mg97Zn1Y2合金的室温磨损行为已有研究,但是缺乏高温磨损研究,探究该合金高温磨损行为是非常必要的。采用MG-2000型销-盘磨损试验机对Mg97Zn1Y2合金进行磨损试验,试验温度范围为20~200℃,加载范围为20~320 N,探究不同温度以及载荷对Mg97Zn1Y2合金磨损行为的影响。根据试验数据绘制不同温度下的磨损率曲线;应用SEM观察磨损表面形貌,应用EDS分析磨损表面的化学成分,划分磨损区间。结果表明：随着温度的升高,Mg97Zn1Y2合金的磨损率随载荷的增加而上升得更加显著,磨损行为可以分为轻微磨损和严重磨损两个阶段：轻微磨损阶段的磨损机制为：磨粒磨损、剥层磨损、氧化磨损;严重磨损阶段为严重的塑性变形和表面熔化。绘制了磨损机制转变图,划分该合金的安全工作区间,为该合金在高温下的摩擦学应用提供有益参考。     

Creation of ultrafine-grained surfaces by large strain extrusion machining (LSEM)

Large strain extrusion machining (LSEM) is examined as a route for achieving controlled microstructure refinement at freshly generated surfaces in a single pass of the machining tool. It is shown that the extrusion ratio λ of LSEM, which is the ratio of the thickness of the chip to that of the preset depth of cut, controls the extent of the ultrafine-grained (UFG) zone. Microstructure analysis was performed using orientation imaging microscopy (OIM) and mechanical testing using nanoindentation was used to characterize the UFG microstructure beneath the freshly generated surfaces. The mechanics of deformation in LSEM were examined using infrared thermography and modeled. The present research demonstrates LSEM as a novel platform for tailoring surficial microstructures and controlling their spatial extents in fabricated components.