等径角挤压Al-4%Mg-0.3%Ce合金的拉伸及断裂行为

对Al-4％Mg-0．3％Ce合金进行了不同道次和路径的等径角挤压（ECAP）加工,对其所加工样品在室温下进行了10^-4～10^-1s^-1不同应变速率的拉伸试验及其断口观察,探讨了ECAP合金的室温拉伸及断裂行为,并与常规热挤压进行了对比分析。结果表明,ECAP合金表现出更高的室温屈服强度,经过不同道次和路径ECAP的合金的拉伸断裂方式为切断型,而常规热挤压合金的拉伸断裂方式则为正断型。     

等通道转角挤压对LA141镁锂合金显微组织及力学性能的影响

采用等通道转角挤压(ECAP)工艺在室温下对LA141镁锂合金进行了1～4道次挤压变形。对变形合金进行了物相分析、显微组织观察、扫描电镜分析以及室温拉伸试验,研究了ECAP挤压工艺对LA141镁锂合金显微组织及力学性能的影响。结果表明:随着ECAP挤压道次的增加,合金中粗大的晶粒在剪应力作用下沿挤压方向被拉长而形成带状组织,剪切带变得更加细小并趋于均匀分布;与原始态试样相比,挤压后试样的拉伸强度和伸长率均有不同程度的提高,挤压后拉伸断口呈韧窝状,随着挤压道次的增加,韧窝尺寸减小,韧窝数量增多,塑性增加。     

等通道转角挤压对铝硅合金的硅形态及力学性能的影响

采用等通道转角挤压工艺(ECAP)对两种铸造铝硅合金(ZL101和ZL102)进行不同道次的加工,研究晶粒细化及硅形态对合金力学性能的影响。结果表明:多道次ECAP能有效细化针状共晶硅相并改善其在铝基体中分布的均匀性,具有尺寸细小、分布弥散且棱角钝化共晶硅的铝硅合金具有更优的力学性能;铸态合金ECAP加工后强度和韧性均获提高,固溶+16道次ECAP加工后ZL102合金的伸长率和抗拉强度约为铸态的5.04倍和1.39倍;随挤压道次的增加,两种合金的断裂方式均由脆性断裂向韧性断裂转变;固溶后挤压可获得优良的强韧组合,满足制造行业需要。     

超细晶高性能Cu-0.6Cr合金的疲劳裂纹的产生与断裂

研究了经等径角挤压工艺(ECAP)制备的超细晶和粗晶Cu-0.6Cr合金的疲劳裂纹的产生和断裂,用扫描电镜观察表面和断口形貌.研究发现,粗晶Cu-0.6Cr合金的驻留滑移带非常杂乱,超细晶铜铬合金的剪切带沿着ECAP最后一道次剪切面发展,沿着ECAP最后一道次剪切面发展的剪切带在疲劳断裂初期和早期的裂纹增殖中起着决定性作用.ECAP挤压形变剪切面和沿平面界面的晶界剪切滑动是循环形变剪切带形成的主要机制.粗晶铜铬合金的断口呈塑性特征.而超细晶铜铬合金的断口则显示脆性特征.     

等通道转角挤压Mg-3.52Sn-3.32Al合金的组织与力学性能

采用等通道转角挤压（ECAP）Bc路径对固溶态Mg-3.52Sn-3.32Al合金分别挤压1、4和8道次。利用光学显微镜、扫描电子显微镜、透射电子显微镜和X射线衍射仪分析合金的组织和相组成,并测试了其室温拉伸力学性能。结果表明,经ECAP挤压后,固溶态合金组织中析出大量细小的Mg2Sn相和极少量的Mg17Al12相。随挤压道次增加,合金的综合力学性能先提高后降低。经4道次挤压后,合金的综合拉伸力学性能相对较佳,抗拉强度、伸长率和硬度分别达到250 MPa、20.5%和61.3 HV9.8,较未ECAP时分别提高43.7%、105%和26.9%。经ECAP挤压的合金室温拉伸断口均呈韧性断裂。等通道转角挤压Mg-3.52Sn-3.32Al合金的力学性能受晶粒尺寸、析出相以及组织织构的共同影响。     

ECAP对A390铝合金显微组织和拉伸性能的影响（英文）

研究等径角挤压(ECAP) A390铝合金的抗拉强度和伸长率,揭示其显微组织和拉伸性能之间的关系。采用光学显微镜(OM)、扫描电镜(SEM)和能谱仪(EDS)对样品的显微组织进行分析。力学性能测试结果表明,经过3道次挤压后,材料的极限抗拉强度(UTS)从铸态的142 MPa提高到275 MPa。与铸态样品相比,当ECAP道次增加到4时,材料的伸长率显著提高。研究发现,随着ECAP道次的增加,材料的强度和伸长率提高,这是因为颗粒的均匀分布、颗粒尺寸的减小和空位的消除,尤其是与原始硅颗粒相邻的空位的消除。断口分析结果表明,当ECAP的道次增加到4时,在合金中形成均匀的圆形韧窝,合金断裂机理由铸态时的脆性断裂转变为韧性断裂。     

等通道转角挤压Mg-3.52Sn-3.32Al合金的组织与力学性能（英文）

采用等通道转角挤压(ECAP)Bc路径对固溶态Mg-3.52Sn-3.32Al合金分别挤压1、4和8道次。利用光学显微镜、扫描电子显微镜、透射电子显微镜和X射线衍射仪分析合金的组织和相组成,并测试了其室温拉伸性能。结果表明,经ECAP挤压后,固溶态合金组织中析出大量细小的Mg2Sn相和极少量的Mg17Al12相。随挤压道次增加,合金的综合力学性能先提高后降低。经4道次挤压后,合金的综合拉伸性能相对较佳,抗拉强度、伸长率和硬度HV9.8分别达到250 MPa、20.5%和613 MPa,较未ECAP时分别提高43.7%、105%和26.9%。经ECAP挤压的合金室温拉伸断口均呈韧性断裂。等通道转角挤压Mg-3.52Sn-3.32Al合金的力学性能受晶粒尺寸、析出相以及组织织构的共同影响。     

等径角挤压工艺对固溶状态CuCrZr合金性能的影响

研究了等径角挤压工艺(ECAP)对固溶态CuCrZr合金性能的影响.结果表明,随着挤压道次的增加,合金的硬度迅速上升,导电率略有下降.时效前经ECAP处理可以加速时效初期第二相的析出,使合金的性能以较快的幅度上升.ECAP六道次试样400℃时效1 h,导电率和硬度分别为81.1%IACS和200 HV30.     

ECAP挤压对5083铝合金组织与力学性能的影响

研究了5083铝合金等通道转角挤压(ECAP)的室温拉伸性能.结果表明:5083铝合金经100℃、16道次ECAP挤压后,晶粒明显细化且第二相均匀弥散分布,合金的强度提高至480MPa;200℃、16道次ECAP挤压后,合金强度有所下降(约380MPa),但塑性显著改善(伸长率16％以上);降低ECAP挤压温度、增加挤压道次可获得更高的挤压硬化和细晶强化效果,在100℃ECAP挤压和200℃退火同样可提高该合金的抗拉强度和塑性变形能力.     

挤压速度对等通道转角挤压6061铝合金力学性能的影响

用自行设计的内角90°,外角30°的等通道转角挤压模具对6061铝合金进行了室温挤压,分析了不同挤压速度对其力学性能的影响。利用金相显微镜和扫描电镜(SEM)观察了金相组织和拉伸断口的形貌特征。结果表明:6061铝合金的断裂特征是韧性断裂,在3道次ECAP变形过程中,随着变形道次增加,6061铝合金的显微硬度和抗拉强度增大。当挤压速度达到35 mm/min时,合金的强度和硬度是最好的。     

等通道转角挤压变形Mg-1.5Mn-0.3Ce镁合金的组织、织构与力学性能

采用等通道转角挤压(ECAP)工艺以Bc路径在623K温度下对Mg-1.5Mn-0.3Ce镁合金进行变形,观察显微组织与织构,测试了力学性能。显微组织分析表明,镁合金经ECAP变形晶粒尺寸明显得到细化,经6道次ECAP变形后晶粒尺寸由原轧制态的约26.1μm细化至约1.2μm,且细小的第二相粒子Mg12Ce弥散分布于晶内及晶界处;同时经ECAP变形后,原始轧制织构随变形道次的增加不断减小,并开始转变为ECAP织构,织构强度不断增强;力学性能结果表明,由于晶粒细化作用大于织构软化作用,前3道次ECAP变形镁合金强度随道次的增加不断提高,与Hall?Petch关系相符,在第3道次时其抗拉强度和屈服强度达到最大值,分别为272.2和263.7MPa;在4道次之后形成较强的非基面织构,镁合金强度下降,与Hall?Petch呈相悖关系。断口分析表明,轧制态与ECAP变形镁合金的断裂方式都是沿晶断裂,由于6道次变形镁合金晶粒细化,存在更多的韧窝并获得16.8%最大室温伸长率。     

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。     

Microstructures, strengthening mechanisms and fracture behavior of Cu-Ag alloys processed by high-pressure torsion

Disks of a eutectic Cu-Ag alloy were processed by high-pressure torsion (HPT) up to 20 revolutions to reveal the microstructural evolution and mechanical properties. Both the Cu and Ag phases were thinned continuously with increasing numbers of revolutions. After 20 revolutions, the alternating Cu and Ag phases were significantly refined and became fibrous with dimensions as thin as 5 nm. The strain hardening behavior of the Cu-Ag alloy was characterized after different numbers of HPT revolutions, and a saturation microhardness was attained. It is shown that the tensile fracture mode changed from necking to fully brittle shearing with increasing numbers of revolutions, and some shear offsets with sizes of ∼5-20 μm were observed on the fracture surfaces. Based on the abnormal saturation microhardness value of the eutectic alloy, the strengthening mechanisms of various Cu-Ag alloys are discussed.     

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.     

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。     

Diffusional bonds in laminated composites produced by ECAP

The microstructure, diffusional and mechanical bonding behavior and microhardness distribution of laminated composites fabricated by ECAP process were investigated. Al-Cu and Cu-Ni laminated composites were produced by ECAP process up to 4 passes at room temperature and high temperature (300 °C). The results of microstructure characterization by SEM and shear strength test revealed that the joints between the layers of 4-pass ECAPed samples were considerably stronger than those of 1-pass ECAPed samples due to tolerating higher values of plastic deformations during ECAP. Furthermore, shear strength data showed that increasing ECAP temperature caused a notable increase in shear strength of the specimens. The reason lies in the formation of diffusional joint between the interface of both Al/Cu and Cu/Ni layers at high temperature. The shear bonding strength of ECAPed Cu/Ni/Cu composite at high temperature was remarkably higher than that of ECAPed Cu/Al/Cu composite.     

In situ thermomechanical processing to avoid grain boundary precipitation and strength-ductility loss of age hardening alloys

To avoid grain boundary (GB) precipitation during aging, a new strategy of in situ thermomechanical processing for age hardening alloys was proposed. Specifically, high-density nanoscale precipitates were introduced into ultrafine grain (UFG) interiors of 7075Al alloy by equal-channel-angular (ECAP) processing at 250 °C for 8 passes, thus avoiding GB precipitation. Tensile test results indicated that the UFG 7075Al alloy exhibits superior mechanical properties (yield strength of 350 MPa, ultimate tensile strength of 500 MPa, uniform elongation of 18% and tensile ductility of 19%) compared with the UFG 1050Al counterpart (yield strength of 170 MPa, ultimate tensile strength of 180 MPa, uniform elongation of 2.5% and tensile ductility of 7%). Fracture surface morphology studies revealed numerous homogeneous micro shear bands in necking shrinkage areas of both UFG 7075Al and 1050Al alloys, which are controlled by cooperative GB sliding. Moreover, the introduction of nanoscale precipitates in UFG 7075Al matrix weakened the tendency of shear fracture, resulting in a higher tensile ductility and more homogeneous deformation. Different from the GB precipitation during postmortem aging, in situ thermomechanical treatment dynamically formed GBs after precipitation, thus avoiding precipitation on GBs.     

Effect of equal-channel angular pressing routes on high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy

The effect of equal-channel angular pressing (ECAP) route on the high-strain-rate deformation behavior of ultra-fine-grained aluminum alloy was investigated. The 8-pass ECAPed specimens deformed via three different routes consisted of ultra-fine grains 0.5 μm in size, and contained a considerable amount of second-phase particles, which were fragmented and distributed in the matrix. In the torsion tests, the maximum shear stress significantly increased with increasing number of ECAP passes, while the maximum shear stress and fracture shear strain were lowest in the specimen deformed via route A among the three 8-pass ECAPed specimens. Observation of the deformed area beneath the fractured surface revealed the adiabatic shear bands of 100 μm in width in the specimen deformed via route A, which minimized the maximum shear stress and fracture shear strain, whereas they were hardly formed in the specimens deformed via route B or C. The formation of adiabatic shear bands was explained in terms of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.     

体外浸泡纯钛的表面腐蚀和ECAP的影响

采用在Ringer模拟体液静态体外浸泡的方法,研究工业纯钛试片经过一定时间的浸泡后的失重和表面形貌的变化。采用等通道径角挤压(ECAP)方法处理工业纯钛并与粗晶纯钛进行对比,对ECAP处理的TA9和粗晶TA9也做了对比。结果表明:纯钛在400℃ECAP处理后的微观组织形成具有明显方向性的板条状组织,ECAP纯钛表面沉积的Na Cl晶体数量大于粗晶Ti,TA9也表现出相似结果。纯钛的腐蚀机制是一种受到电偶腐蚀控制的均匀腐蚀,细晶组织导致电偶的数量增加。     

Microstructure and corrosion behaviour of Mg–2Gd–1Y–1Zn–0·2Zr (at-%) alloy processed by equal channel angular pressing

Significant grain refinement was achieved in a new Mg–2Gd–1Y–1Zn–0·2Zr (at-%) alloy through multipass equal channel angular pressing (ECAP) at 623 K. Corrosion behaviours of the ECAPed alloy were investigated by hydrogen evolution and electrochemical measurement in NaCl solution at room temperature. The results showed that a large number of intergranular phases were stretched and gradually broken above four ECAP passes, but the fine grained α-Mg phase was much easier to grow after 12 ECAP passes for dynamic recrystallisation. The corrosion resistance of the ECAPed Mg alloy in a fine grained state considerably increases, compared with that in the as cast state. After four ECAP passes, the corrosion potential, the pitting potential and the resistance value achieved ?1·55 V, ?1·39 V and 2·08 KΩ respectively. However, excessive ECAP passes reduced the corrosion resistance of the fine grained Mg alloy, due to grain coarsening and the gradual loss of barrier effect of intergranular phases.