连续等径角挤压及其成形过程的三维数值模拟

连续等径角挤压是一种制备大尺寸超细晶材料的新技术,它结合了等径角挤压和连续挤压技术的特点,解决了等径角挤压不能制备大尺寸超细晶材料的问题,该技术对超细晶材料的推广应用具有重要意义。利用DE-FORM3D软件对纯铜连续等径角挤压变形行为进行了数值模拟,分析了变形过程中材料的流动、应变和温度变化情况,并对不同变形速度、摩擦条件和模具结构下的变形过程进行了比较,为连续等径角挤压工艺提供了理论指导。     

等径弯曲通道变形制备超细晶铜的热稳定性

室温下采用等径弯曲通道变形(Equal Channel Angular Pressing,ECAP)C方式进行了纯铜(99.95%)12道次挤压变形。通过等温和等时退火,研究ECAP变形后铜的退火行为,并研究了等径弯曲通道变形和退火后纯铜的显微硬度和显微结构变化。分析了ECAP应变量、退火时间和退火温度对超细晶铜的再结晶行为、抗软化性能的影响。结果表明:ECAP变形后的超细晶铜在退火过程中,表现出不连续再结晶现象;ECAP降低了铜的热稳定性,变形道次越高再结晶温度越低。退火后稳态晶粒尺寸随变形道次的增加而细化,硬度值随变形道次的增加而增大,回归分析表明,晶粒尺寸与硬度之间的关系符合Hall-Petch公式。     

等径角挤压制备超细生物医用纯钛的静态力学性能和塑性（英文）

等径角挤压是制备超细晶和纳米晶材料最有效的工艺之一。由于工业纯钛具有极佳的生物相容性,因此它可用作生物植入体材料。然而,较低的静/动态强度是纯钛类材料的不足之处。利用等径角挤压工艺可消除此类缺陷。本文作者在室温和通道角为135°条件下进行3道次挤压得到2级工业纯钛试样(2级CP-Ti)。对经等径角挤压3道次的CP-Ti样品进行显微组织分析及拉伸、硬度、三点弯曲和夏比冲击等力学性能测试。样品的显微组织演变结果表明,经等径角挤压工艺后样品的粗晶组织转变成超细晶或纳米晶组织。此外,力学性能测试结果表明,等径角挤压工艺能显著提高工业纯钛的屈服强度、抗拉强度、弯曲强度、硬度和断裂韧度,因此用该工艺制得的钛可以作为金属合金的替代品用作生物医用材料。     

挤压件尺寸对等径角挤压成形工艺的影响

为了通过大塑性变形技术制备出满足工业需求的大尺寸块体超细晶材料,采用有限元法模拟了不同尺寸挤压件的1、2道次等径角挤压过程,得到了各挤压件的等效应变、等效应力和载荷曲线.分析得出:挤压件尺寸对等效应变的大小和分布以及等效应力的大小影响甚微;但随着挤压件尺寸的增大,等效应力和2道次等效应变的分布均匀性降低,挤压载荷增大.这表明:经过多道次等径角挤压的大尺寸挤压件可以获得晶粒分布均匀的大块体超细晶材料.     

等径角挤压获得超细晶铜的研究

采用等径角挤压技术成功地将纯铜组织超细化，并对其组织、硬度及组织稳定性演变过程进行了研究。结果表明：挤压10道次后，得到了均匀、细小的等轴晶，其平均晶粒尺寸为0．75p．m；等径角挤压后材料的硬度明显上升，挤压4道次后硬度趋于饱和；通过对等径角挤压后试样在不同温度退火时首次发现，可以通过控制再结晶的温度和时间进一步细化晶粒。     

等径角挤压晶粒细化技术对纯铝显微组织演变、力学性能和腐蚀行为的影响(英文)

在室温下,采用等径角挤压法加工纯铝样品10道次。研究等径角挤压道次数对加工样品显微组织演变、力学性能、变形均匀性和腐蚀行为的影响。所施加的应变导致晶粒尺寸明显减小,等径角挤压前,晶粒尺寸为390μm,经等径角挤压2、4和10道次后,晶粒尺寸分别减小至1.8、0.4和0.3μm。随着等径角挤压道次数的增加,显微硬度、变形均匀性和拉伸强度增大,而伸长率下降。浸泡试验、开路电势、Tafel极化、循环极化和恒电位测试表明,与铸态样品相比,在3.5%Na Cl溶液中,经等径角挤压样品的耐蚀性明显提高。增加挤压道次数能成功用来生产具有高错位角、高力学性能和耐蚀性的超细晶大块纯铝。     

等径角挤压制备超细晶CNTs/AZ31镁基复合材料研究

采用模角为90°的模具对退火处理后的AZ31镁基碳纳米管复合材料进行了等径角挤压实验.结果表明:AZ31镁基碳纳米管复合材料经过一道次的等通道角挤压后,复合材料中就有大量的超细晶粒出现.随着道次数增加,超细晶粒比例逐渐增多.四道次挤压后复合材料晶粒尺寸达到1～5μm,显微硬度得到显著提高.     

工艺路线对等径角挤压变形均匀性的影响

等径角挤压被认为是制备块体超细晶材料最有前景的工艺方法之一.采用刚塑性有限元法分析了不同路线多道次等径角挤压后的等效应变分布.结果表明:一道次等径角挤压后坯料中间主要变形区下部坯料的等效应变较低.A路线多道次挤压后,变形更加不均匀,上下表面的等效应变差值增大;C路线挤压后等效应变分布呈上下表面小,中间较高的分布特征,且随挤压次数的增加,中心和上下表面的等效应变差异增大.B_c路线多次挤压后的等效应变分布较均匀,等效应变较高的区域应变相差较小且所占区域较大.模拟结果对于等径角挤压工艺的制定可起到指导作用.     

采用双通道等径侧面挤压法提高AA5083铝合金力学性能（英文）

采用双通道等径侧面挤压剧烈塑性变形工艺提高AA5083铝合金的力学性能。采用多组实验研究路径类型(A和B路径)和挤压道次对材料力学性能的影响。挤压道次为6道次,挤压温度范围为573~473 K,采用金相、硬度测试和拉伸测试研究这些工艺参数的影响。硬度测试表明经6道次挤压后,硬度提高了64%,且分布均匀。屈服强度和抗拉强度分别提高了107%和46%。这是由于晶粒的剧烈剪切变形和变形温度降低导致的晶粒细化。TEM结果表明,经DECLE 6道次变形后,合金的平均晶粒尺寸从退火态的100μm减小至200 nm。对比研究了路径A和B的实验结果,并得到一些重要结论。     

等径弯曲通道变形制备高性能Cu-Cr合金的组织性能

用两种方式等径弯曲通道变形(equal-channel angular pressing,简称ECAP)制备了的具有等轴晶组织的超细晶Cu-0.4Cr合金,晶粒尺寸为500nm。研究了不同挤压方式、不同挤压道次合金的组织和性能的变化。探讨了不同退火温度对5～8道次材料导电率和硬度的影响。结果表明,经ECAP挤压后的Cu-0.4Cr合金具有很好的综合性能,拉伸强度可达565MPa;硬度和导电率分别为225 HV和66.4%IACS;723K退火1h后材料的导电率和硬度可达80.3%IACS和210.9HV;软化温度可达723K。     

Static mechanical properties and ductility of biomedical ultrafine-grained commercially pure titanium produced by ECAP process

Equal channel angular pressing (ECAP) is one of the most effective processes to produce ultra-fine grain (UFG) and nanocrystalline (NC) materials. Because the commercially pure titanium exhibits excellent biocompatibility properties, it has a significant potential to be utilized as an implant material. The low static and dynamic strengths of the pure titanium are one of the weaknesses of this material. This defect can be removed by applying the ECAP process on the pure titanium. In this work, the commercially pure titanium Grade 2 (CP-Ti of Grade 2) was pressed at room temperature by the ECAP process via a channel angle of 135° for 3 passes. The microstructural analysis and mechanical tests such as tensile test, hardness test, three-point bending test and Charpy impact test were all carried out on the ECAPed CP-Ti through 3 passes. The microstructural evolution reveals that by applying the ECAP process, coarse grain (CG) structure develops to UFG/NC structure. Moreover, the results of the mechanical tests show that the process significantly increases the yield and ultimate tensile strengths, bending strength, hardness and fracture toughness of the commercially pure titanium so that it can be used as a replacement for metallic alloys used as biomaterials.     

Plastic deformation mechanism of ultra-fine-grained AA6063 processed by equal-channel angular pressing

Equal-channel angular pressing (ECAP) is an established method to produce ultra-fine-grained (UFG) materials with extraordinary mechanical properties. However, different methods to characterize the complex microstructure give contradictory results. Therefore an ECAP-processed UFG aluminum alloy AA6063 was characterized by various electron-microscopy-based methods such as backscattered electron contrast, electron backscatter diffraction, transmission electron microscopy and low-voltage scanning transmission electron microscopy. Only a skilful combination of all methods reveals the complete information about the microstructure which is needed to understand the results of the mechanical testing by nanoindentation, tensile tests and strain-rate jump test. The main difference is the amount of low-angle grain boundaries and high-angle grain boundaries which determine hardness, tensile and yield strength and strain-rate sensitivity of ECAP materials produced by different numbers of passes and routes. This is explained by the interaction of dislocations with the different grain boundaries.     

等通道转角挤压对L2工业纯铝力学性能的影响

利用等通道转角挤压(ECAP)技术挤压工业纯铝L2，探讨了挤压次数对其力学性能的影响。结果表明，随挤压次数的增加，L2的抗拉强度和硬度得到显著提高，抗拉强度可提高95％，硬度提高70％。挤压1次后，其伸长率由40％下降至15％，此后伸长率基本保持稳定。     

Effect of soft Bi particles on grain refinement during severe plastic deformation

Two aluminum alloys, Al–8Zn and Al–6Bi–8Zn were subjected to equal channel angular pressing (ECAP) up to 5 passes at room temperature. The microstructural evolution and the grain refinement behavior of these alloys were systematically studied by electron backscatter diffraction (EBSD). After 5 passes of ECAP, ultrafine grained microstructures formed in both alloys. However, the grain structure in the Al–6Bi–8Zn alloy is much finer than that of Al–8Zn alloy, showing that the soft Bi particles have a strong influence on enhancing the grain refinement during ECAP. The strengths of the ECAP-processed materials were measured by hardness test and it showed that after 5 passes of ECAP, the hardness of the Al–6Bi–8Zn alloy was higher than that of the Al–8Zn alloy. The effects of soft Bi particles on the deformation behavior during ECAP and the final strength of the Al–6Bi–8Zn alloy were discussed.     

Finite Element Analysis of the Deformation Distribution During Multi-Pass Rotary-Die ECAP

Rotary-die equal channel angular pressing (RD-ECAP) is a specially designed continuous processing technique to prepare bulk ultrafine-grained/nanostructure (UFG/NS) materials. In this article, an Al-7wt.% Si-0.35wt.% Mg alloy was processed by up to four RD-ECAP passes. The deformation behavior was studied by experiments and FEM simulation, including the observation of the scribed deformation patterns, the macrostructures, the simulated flow lines feature, and the equivalent stain distribution after different RD-ECAP passes. The results show that the shear deformation can accumulate effectively all over the entire billet via multi-pass RD-ECAP. The observed zigzag shape metal flow is formed after three ECAP passes, and the structure homogeneity can be achieved by RD-ECAP with more processing passes.     

等通道转角挤压制备超细晶Mg15Al双相合金组织与性能

对高铝双相合金Mg15Al在553K以Bc路线进行了不同道次的等通道挤压(ECAP),获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm～200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32.04%,抗拉强度σb从150MPa提高到269.3MPa,延伸率δ由0.05%提高到7.4%;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。     

等通道转角挤压Al-Mg2Si合金的组织与性能研究

研究Al-Mg2Si合金经250℃等通道转角挤压后的微观组织与力学性能。维氏硬度及拉伸力学性能测试结果表明:经4道次ECAP挤压后,Al-Mg2Si合金的硬度、抗拉强度和延伸率均显著提高;8道次挤压后合金的塑性进一步提高,但其硬度和抗拉强度却有所下降。扫描电子显微镜和透射电子显微镜分析表明:经ECAP挤压后,原汉字状或骨骼状Mg2Si相显著碎化,且挤压道次越多,Mg2Si相的破碎效果越明显,合金组织也不断细化。对合金经较多道次挤压后硬度及抗拉强度反而有所下降的原因进行了分析。     

Improving corrosion resistance of Al‐11mass%Si alloy through a large number of ECAP passes

Ultrafine‐grained (UFG) Al‐11mass%Si alloy, processed by multi‐pass equal‐channel angular pressing (ECAP) at 573 K, was investigated on corrosion behavior in 0.6 M NaCl solution. Potentiodynamic polarization tests and scanning electron microscopy observation showed that a large number of ECAP passes resulted in lower corrosion current density, more positive corrosion potential, and rather smooth corroded surface with shallow corrosion pits. The uniform distribution of fine secondary‐phase particles on UFG Al matrix weakened the susceptibility to pitting corrosion while inhibited general microgalvanic reactions. The present results indicate that grain refinement of aluminum matrix to the UFG state and uniform redistribution of broken particles (including eutectic silicon and secondary phases), via severe plastic deformation at elevated temperature undergoing dynamic recrystallization, can significantly improve the corrosion resistance of Al alloys, besides the known exceptional mechanical advantages. The simple and effective ECAP procedure makes UFG Al alloys more attractive for high strength structural application in corrosive environment.