等通道转角挤压对铝青铜力学性能的影响

采用等通道转角挤压（ECAE）工艺对铝青铜(Cu 10%Al 4%Fe)进行热处理,研究了ECAE处理工艺中预热温度、挤压道次及退火处理对铝青铜外观形貌、微观组织及力学性能的影响.结果表明:在650 °C的预热温度下,铝青铜可以顺利通过ECAE挤压通道;随着ECAE挤压道次从1增至4,铝青铜的显微硬度、屈服强度及延伸率显著增加;经500 °C退火60 min处理后,铝青铜的力学性能最佳.     

400℃退火对ECAP形变Q235钢的强度和位错强化的影响

将经过淬火预处理和等通道转角挤压加工(ECAP)的Q235钢进行400℃退火.采用拉伸试验、X射线衍射(XRD)分析及描述强度-位错密度关系的Taylor公式,研究400℃退火对ECAP形变低碳钢的强度和位错强化的影响.拉伸试验表明:400℃退火使ECAP形变Q235钢强度降低,屈服强度从825 MPa下降到725 MPa,加工硬化能力和塑性显著提高.基于XRD分析和Taylor公式的定量计算说明,400℃退火对ECAP形变Q235钢的位错强化影响很小,实际强度的降低不是来自于位错强化的降低,而是来自于其他强化机制(晶界、亚晶界等)的降低.     

再结晶退火对荫罩带钢力学性能和微观组织的影响

针对我国宝钢、德国维克多尔和日本东洋三种荫罩带钢,分别在730、780、830℃进行退火试验,研究退火温度对荫罩带钢力学性能和微观组织的影响.通过金相分析和常温拉伸试验,对荫罩带钢微观组织和力学性能--屈服强度、屈服延伸率进行了对比和分析.结果表明,退火后荫罩带钢发生了再结晶和晶粒长大,退火温度对屈服延伸率无影响;退火温度越高,晶粒越粗大,屈服强度越小;宝钢一次冷轧荫罩带钢优于德国和日本二次冷轧荫罩带钢,再结晶退火温度在780℃比较合适.     

等径弯曲通道变形制备超细晶铝合金的组织性能

用等径弯曲通道变形(ECAP)的方法制备出超细晶铝合金材料,并研究了在不同道次条件下其显微组织的演化过程.研究表明,随着强烈塑性变形的增加,显微组织中开始形成大量晶粒尺寸小于1μm的位错胞组织,当其晶界取向差增大时,亚晶粒变为越来越细的板条状组织.当经过8道次ECAP变形后,晶粒尺寸由变形前的约50μm细化为约0.2μm.该超细晶铝合金材料在150℃的退火条件下,其晶粒尺寸稳定在0.2～0.3μm的范围内.在温度为500℃、应变速率为10-3s-1的拉伸实验中,该超细晶铝合金材料的最大延伸率高达370%,呈现出良好的超塑性.     

室温Φ=120°等径弯曲通道变形工业纯钛的力学性能

采用模角Φ=120°的模具,以BC方式(两次挤压道次之间试样绕纵轴沿同一方向转动90°进行下一道次挤压)在室温下成功实现了工业纯钛8道次等径弯曲通道变形(ECAP),对挤压过程中各道次试样的微观结构及性能进行了分析测试. 结果表明:工业纯钛经8道次ECAP变形后,抗拉强度由407 MPa升高到791 MPa;显微硬度由1 588 MPa升高到2 641 MPa;并保持良好的塑性,伸长率为19%.     

冷加工塑性硬化对304不锈钢力学参数的影响

准确的材料力学参数是结构完整性分析与评价的重要基础,冷加工硬化现象会造成材料力学性能参数的改变,而受冷加工硬化作用力学性能发生变化的局部区域往往是需要进行结构完整性分析的关键部位。为获取不同冷加工硬化量下材料的力学性能,文中采用数值模拟和力学试验相结合的方法,以常用的金属材料304奥氏体不锈钢为研究对象,通过单轴拉伸试验获得了10%,20%,30%,40%等4种不同冷加工条件下的工程应力应变数据;利用线弹塑性硬化模型,结合ABAQUS软件建立了获取冷加工硬化后材料力学性能的数值模拟方法,分析了不同冷加工硬化量下304奥氏体不锈钢力学性能的变化规律。结果表明,线弹塑性硬化模型在一定范围内能够较好地反映304奥氏体不锈钢受冷加工硬化作用后的力学行为,随着冷加工硬化量的不断增大,304奥氏体不锈钢的屈服应力大幅度升高,同时,冷加工硬化对304奥氏体不锈钢折减系数的影响相对较小。提出的方法可以用于重要工程结构中关键部位的结构完整性分析。     

多道次ECAP的模具设计及实验研究

为了研究多道次等径角挤压(ECAP)工艺制备超细晶材料,以解决传统ECAP模具存在的飞边和装拆困难等问题,提出了一种对称分模自由套模具的设计方案。该方案是将凹模模芯设计成对称拼块式并通过凹模座进行预紧;凹模座内表面与凹模外表面均采用锥面的设计,当受到挤压时,凹模的闭合会愈来愈紧而不易产生飞边,拆卸时只需将模具倒扣反压即可轻松脱模。同时,基于虚拟设计技术优化了模具的结构和工艺参数,进行了ECAP制样及相关实验的研究。研究结果表明,模具设计方案有效防止飞边产生,实验效果较好。金相显微组织观察表明,随着挤压道次的增加,平均晶粒尺寸逐渐减小。显微硬度分析表明,随着挤压道次的增加,试样的硬度有大幅度的提高。     

ECAP挤压L2纯铝的微观组织演化规律

用等通道转角挤压对纯铝L2进行10道次挤压,结果表明：挤压1道次后,原来晶粒尺寸为1 mm的等轴晶沿剪切方向被拉长为条带状晶,在条带状晶粒之间出现被剪切破碎的细小亚晶粒.挤压2道次后,出现了少量等轴晶.挤压4道次后,晶粒取向性变得不太明显,小角度晶界的亚晶粒逐步向大角度晶界的等轴晶演化,晶粒细化到1 μm.随挤压道次的继续增加,晶粒大小不再变化,而形状向等轴状演化.挤压10道次后,合金组织由晶粒大小为1 μm的等轴晶组成.ECAP挤压中,纯剪切变形和应变量的双重作用导致晶粒细化.当晶粒尺寸小于临界尺寸时,剪切变形对晶粒的细化起主要作用;当达到临界尺寸后,应变量起主要作用,表现在使合金组织形貌向等轴晶转变.     

等通道转角挤压超细化合金组织性能的研究

等通道转角挤压技术是目前制备超细晶粒金属块材的最新研究领域之一.本实验采用了等通道转角挤压技术对3种商业铝合金以A、B、C等3种方式挤压,结果表明:3种挤压方式后的硬度与挤压道次的关系基本一致,即3~4次挤压后硬度趋于饱和;应用的负荷大小对ECAP期间剥落的可能性也被测量,以便改善挤压过程.X-射线衍射分析法显示挤压后这些铝合金出现亚微米级晶粒尺寸.本实验中,经不同方式等通道转角挤压(ECAP)铝合金组织结构变化有较大不同,晶粒得到明显细化.     

不同路径等通道转角挤压镁合金的结构与力学性能

为了研究等通道转角挤压时不同工艺路径对镁合金微观结构及性能的影响 ,采用模角φ =12 0°的模具 ,以A ,BA,BC,C四种工艺路径对AZ31镁合金进行了等通道转角挤压 ,分析测试了室温下挤压试样的微观结构及性能 .结果表明 ,相比于A ,BA,C路径挤压 ,BC 路径挤压容易实现较多的挤压道次和变形量 ;多道次挤压后 ,镁合金的晶粒得到显著细化 ,力学性能也显著改善 ,但不同路径的影响不同 .当挤压 12道次时 ,BC,BA 路径挤压试样的屈服强度显著下降 ,延伸率大幅度提高 ;A ,C路径挤压试样的屈服强度变化较小 ,延伸率的提高幅度也小 .     

Microstructural evolution of a recycled aluminum alloy deformed by equal channel angular pressing process

The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing (ECAP) up to four passes was investigated using X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). Microhardness tests were performed to determine the associated changes in mechanical properties. An ultrafine-grained material has been obtained with a microstructure showing a mixture of highly strained crystallites. A high density of dislocations was achieved as a result of severe plastic deformation (SPD) through the die. Changes in mechanical behavior are also revealed after ECAP due to strain hardening. Thermal analysis and TEM micrographs obtained after annealing indicate the succession of the recovery, recrystallization, and grain growth phenomena. Moreover, the energy stored during ECAP may be related to the dislocation density introduced by SPD. We finally emphasize the role played by the precipitates in this alloy.     

基于位错演化理论的等径角挤压纳米微晶材料数值分析

研究材料微观组织的演化对应力、应变以及应变硬化等问题的影响,是实现等径角挤压成形技术的关键.以纯铝为例,基于位错演化模型,利用有限元分析方法对纯铝的等径角挤压变形行为进行了数值仿真,分析了挤压过程中材料应力、应变以及应变硬化的演化趋势及分布规律.结果表明:随着挤压道次增加,纯铝中等效应力逐渐增加,这导致材料中位错密度的增加;随着位错密度的增加,主应变最大值随后续挤压道次的增加呈增大趋势.因此,考虑等径角挤压过程中的位错演化等材料微观组织演化规律,对材料的实际挤压成形有指导作用.     

Influence of ECAP on the fatigue behavior of age-hardenable 2xxx aluminum alloy

The fatigue behavior under load control and the mechanical properties of commercial 2011 aluminum as an age-hardenable Al alloy was studied. To estimate the effects of the equal channel angular pressing (ECAP) process, solution heat treatments, and aging on the fatigue life, tests were conducted at four different stages:furnace cooling; furnace cooling plus one ECAP pass; solid solution heat treatment, quenching, one ECAP pass plus aging at peak age level; and the T6 condition. Only one pass was possible at room temperature because of the high strength of the material. The fracture surface morphology and microstructure after fatigue were evaluated by scanning electron microscopy (SEM). The experimental results revealed that the optimum fatigue life under load control, the tensile strength, and the Vickers hardness of the material were interdependent. The optimum fatigue life under load control was achieved by increasing the tensile strength and hardness of the material.     

Enhanced biodegradation behavior of ultra fine-grained ZE41A magnesium alloy in Hank's solution

The biodegradation behavior of an ultrafne-grained(UFG) magnesium alloy ZE41A containing rare-earth(RE),obtained through multi-pass of equal channel angular pressing(EACP),was investigated by electrochemical measurements in Hank’s solution.The highest value of charge transfer resistance was obtained in the electrochemical impedance spectroscopy plots of the ECAPed samples with the largest pressing pass,while a movement of corrosion potential toward noble direction and a decrement of corrosion current density were observed in the potentiodynamic polarization curves of the ECAPed samples with further pressing passes.These results indicated that ECAP could be an effcient way to reduce the biodegradation rate of the ZE41A alloy.     

Severely deformed copper by equal channel angular pressing

Mechanical and microstructural analysis of equal channel angular pressed copper was experimentally investigated. The results showed that the hardness distribution uniformity was rapidly decreased after the first pass and gradually improved at the following passes. Also, the bottom region of the pressed material experienced lower Vickers hardness magnitude irrespective of pass number. Furthermore, the addition of 0.1% magnesium to the pure copper had a considerable effect on the distribution uniformity. In addition, the material fracture mode changed from ductile to brittle by the alteration of the dimples to cleavage planes mechanism. Moreover, the formability index was dramatically reduced after the first pass and slowly improved at the succeeding passes. Eventually, ECAP process led to the increment of low angle grain boundaries and the decrease of high angle grain boundaries at the initial passes and vice versa at the subsequent ones.     

多道次等径角轧制对AZ31镁板组织性能的影响

对AZ31镁合金进行多道次等径角轧制,并分析其微观组织、宏观织构和室温力学性能.结果表明,随着轧制道次的增加,板材的晶粒组织出现交替细化与粗化的现象,并直接影响板材后续退火组织的大小和均匀性.由于累积剪切变形的作用,等径角轧制后板材的基面织构明显弱化.七道次等径角轧制后基面极轴出现沿轧向分离,板材屈服强度降低约54%,而伸长率提高约43%.基面织构弱化和晶粒细化是等径角轧制板材塑性提高的主要原因.     

Forming of magnesium alloy microtubes in the fabrication of biodegradable stents

Magnesium alloys have, in recent years, been recognized as highly promising biodegradable materials, especially for vascular stent applications. Forming of magnesium alloys into high-precision thin-wall tubes has however presented a technological barrier in the fabrication of vascular stents, because of the poor workability of magnesium at room temperature. In the present study, the forming processes, i.e., hot indirect extrusion and multi-pass cold drawing were used to fabricate seamless microtubes of a magnesium alloy. The magnesium alloy ZM21 was selected as a representative biomaterial for biodegradable stent applications. Microtubes with an outside diameter of 2.9 mm and a wall thickness of 0.2 mm were successfully produced at the fourth pass of cold drawing without inter-pass annealing. Dimensional evaluation showed that multipass cold drawing was effective in correcting dimensional non-uniformity arising from hot indirect extrusion. Examinations of the microstructures of microtubes revealed the generation of a large number of twins as a result of accumulated work hardening at the third and fourth passes of cold drawing, corresponding to the significantly raised forming forces. The work demonstrated the viability of the forming process route selected for the fabrication of biodegradable magnesium alloy microtubes.     

Dependence of mechanical behavior on grain size of metastable Ti–Nb–O titanium alloy

Cold-rolled metastable β-type Ti–38Nb-0.2O alloy was subjected to annealing treatment to obtain different precipitates and grain sizes. The influence of annealing on microstructure and mechanical properties was investigated. The alloy annealed at 673 ?K or 773 ?K exhibited a single-stage yielding with high strength and low uniform elongation, due to the residual work hardening and the precipitation of ω or α phases. The alloy annealed at above 873 ?K exhibited an obvious double yielding behavior resulting from the stress-induced martensitic transformation. The grain growth kinetics of single β phase alloy is sensitive to temperature, and it is suggested that the existence of oxygen decreases the grain growth exponent and increases the required activation energy for grain growth. The critical stress for slip decreased monotonously with the increase of grain size, following the classic Hall-Petch relationship. However, the critical stress for martensitic transformation decreased to a minimum and then increased again, as the grain size increased. The results are worth for design of the heat-treatment parameters of the Ti–38Nb-0.2O alloy for engineering applications.     

Microstructure,mechanical properties and wear resistance of an Al–Mg–Si alloy produced by equal channel angular pressing

Microstructure, mechanical properties and wear resistance in an ultrafine-grained Al–Mg–Si alloy fabricated utilizing a combination of equal channel angular pressing(ECAP) and dynamic aging were investigated in this paper. The results indicated that the grain size of the ECAP alloy was significantly refined, i.e., to ～239 nm after three ECAP passes. Meanwhile, the yield and tensile strength of the ECAPed material reached 340 MPa and445 MPa, respectively, while maintaining a significant uniform e...