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。     

AZ31镁合金室温多道次压缩过程微观组织和织构演变的研究

对AZ31镁合金在室温进行多道次压缩变形,利用EBSD技术研究其微观组织和织构演变,分析孪晶在细化晶粒和调控织构方面发挥的作用。结果表明:多道次压缩过程中的组织和织构演变主要受{10孪生影响,道次应变量越大,织构变化越明显,每道次压缩后,利于拉伸孪生的晶粒取向发生孪生转到压缩轴附近,从而弱化初始基面织构,而退孪晶的发生则不利于细化晶粒和弱化织构。在多道次压缩过程中,孪生Schmid准则支配着变形中的{10与后续变形中产生的孪晶片层相互交叉,分割细化晶粒;道次变形量会影响多向变形过程每道次孪晶的激活量和孪晶片层的形貌,从而影响晶粒的细化程度。     

压缩对AZ31镁合金微观组织和力学性能的影响

对AZ31镁合金在室温下沿轧制板材不同方向进行多向压缩,研究了不同加载路径下AZ31镁合金的力学性能和微观组织演变。结果表明,沿不同方向3道次压缩时,样品表现出不同的力学行为,沿TD(横向)-RD(轧向)-ND(法向)路径压缩时,材料屈服强度随压缩道次增加而增大;沿ND-RD-TD路径压缩时,材料的屈服强度随压缩道次增加先减小后增大。每次压缩后,(0001)基面织构都转到压缩轴附近。TD样品的主要塑性变形机制为孪生,而ND样品的主要塑性变形机制为滑移。多向压缩产生的孪生可以分割细化晶粒,使镁合金强度提高。     

往复镦挤和热处理的稀土镁合金组织和性能变化

采用往复镦挤(RUE)工艺可以对合金进行剧烈塑性变形。应用降温RUE工艺对Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr(wt%)合金进行不同道次的变形和热处理,对比分析了其微观组织、织构及力学性能的演变。结果发现:随着变形道次的增加,合金粗大晶粒减少,动态再结晶晶粒数量分数升高,动态再结晶晶粒对原始晶粒的吞噬作用促进了晶粒的连续细化,组织均匀性大大改善。同时合金(0001)基面织构最大极密度值随着加工道次的增加显著下降,动态再结晶晶粒取向随机分布,促进了基面织构弱化。由于组织细化和织构减弱,合金的室温抗拉强度及屈服强度均明显升高,在3道次变形和热处理后材料的力学性能达到最高。     

降温往复镦粗-挤压变形对Mg-Gd-Y-Zn-Zr合金晶粒细化及织构变化的研究（英文）

在480℃降温至370℃条件下,采用循环镦-挤工艺对均匀化后的Mg-Gd-Y-Zn-Zr合金进行变形,对循环镦-挤变形过程中的合金微观组织和织构变化进行研究。结果表明,随着循环镦-挤变形道次的增加,晶粒尺寸逐渐减小。在变形6道次后,累积应变达到8.4,得到了平均晶粒尺寸为3.4μm的细小均匀的微观组织。晶粒细化是由非连续动态再结晶和连续动态再结晶复杂共同作用引起的。另外,变形过程中,原始粗大晶粒内的片层状长程有序相(LPSO)发生扭折变形产生扭折带,并在扭折带上发生动态再结晶,分割原始粗晶,起到晶粒细化作用。结果还表明,1道次镦-挤变形后,合金产生强的基面织构,随着变形道次的增加,织构强度有所减弱。织构弱化的原因是动态再结晶和加载力在轴向和径向交替变化共同作用。     

ECAP变形对Mg-Y-Nd-Zr合金组织和性能的影响

利用等通道角变形(ECAP)方法,沿Bc路径在400℃温度下对稀土Mg-2Y-0.6Nd-0.6Zr合金进行不同道次的塑性变形,采用光学显微镜,X射线衍射仪和电子背散射衍射(EBSD)技术等分析了不同道次挤压之后合金的微观组织、晶粒尺寸、物相和织构的变化,采用硬度试验和拉伸试验研究了ECAP不同道次对合金力学性能的影响。结果表明:ECAP之后Mg-2Y-0.6Nd-0.6Zr合金晶粒得到明显细化,并且在4道次之后晶粒细化效果最佳,大部分晶粒已细化至0.45μm;在ECAP变形6道次后再结晶的晶粒开始长大,但晶粒组织在6道次的时候均匀性最好;Mg-2Y-0.6Nd-0.6Zr合金第二相体积分数较小,ECAP变形后有大量的第二相粒子Mg_2Y相从过饱和的基体中析出且多分布于晶界处,ECAP变形4道次后各相数量趋于稳定;Mg-2Y-0.6Nd-0.6Zr合金随着挤压道次的增加,小角度晶界所占比例减少,大角度晶界有所增加;同时,进行ECAP变形后,Mg-2Y-0.6Nd-0.6Zr合金织构的强度和取向都有所变化,织构强度在4道次时最弱,在随后的ECAP变形中又开始增强,在6道次时由倾斜织构转变成强基面织构,Schmind因子趋于0,力学性能结果表明晶粒的细化作用大于织构的软化作用和强化作用,随着ECAP道次的增加,Mg-2Y-0.6Nd-0.6Zr合金的力学性能有所提高,但是在ECAP变形4道次后提高幅度较小,抗拉强度由150 MPa提高到183 MPa,硬度也从54.8 HV0.1提高到了63.7 HV0.1,屈服强度也较ECAP变形之前提高了56%,基本上符合Hall-Petch关系;并且在6道次后,由于晶粒细化且均匀分布,室温伸长率提高到了26.7%。     

降温往复镦粗-挤压变形对Mg-Gd-Y-Zn-Zr合金晶粒细化及织构变化的研究

本文在480°C降温至370°C条件下,采用循环镦?挤工艺对均匀化后的Mg-Gd-Y-Zn-Zr合金进行变形,对循环镦?挤变形过程中的合金微观组织和织构变化进行研究。结果表明,随着循环镦?挤变形道次的增加,晶粒尺寸逐渐减小。在变形6道次后,累积应变达到 8.4,得到了平均晶粒尺寸为 3.4 μm 的细小均匀的微观组织。晶粒细化是由非连续动态再结晶和连续动态再结晶复杂共同作用引起的。另外,变形过程中,原始粗大晶粒内的片层状长程有序相(LPSO)发生扭折变形产生扭折带,并在扭着带处引起动态再结晶产生,分割原始粗晶,起到晶粒细化作用。结果还表明,一道次镦?挤变形后,合金产生强的基面织构,随着变形道次的增加,织构强度有所减弱。织构弱化的原因是动态再结晶和加载力在轴向和径向交替变化共同作用。     

ZK60镁合金异步降温轧制显微组织与力学性能的演变（英文）

将异步降温轧制应用于制造沿轧制方向具有弱基面织构的细晶ZK60镁合金板。结果表明,多道次降温轧制可以显著改善显微结构的均匀性,细化晶粒尺寸。同时,在轧制过程中逐渐形成沿横向的纤维织构。重要的是,沿轧向的剪切变形使基面的c轴向轧向旋转,削弱沿此方向的基面织构。受这种显微结构变化的影响,由于连续的晶粒细化和柱面滑移的增加,沿横向的屈服强度持续增加,而由于应变硬化能力的下降,均匀伸长率下降。相反,沿轧向的基面织构的持续减弱大大抵消晶粒细化所带来的强化效果,从而导致屈服强度的轻微下降。     

AZ31镁合金板材双向循环弯曲的孪晶组织及织构

采用等温双向循环弯曲工艺(bidirectional cyclic bending technology,BCBT)改善了AZ31镁合金板材的微观组织、织构和力学性能。循环弯曲变形能够产生压缩变形与拉伸变形的交替变化,使镁合金材料发生压缩变形→孪晶组织形成→发生动态再结晶→孪晶消失→晶粒细化的组织演变过程,形成分布均匀的细小的晶粒组织,改善了镁合金材料性能。AZ31镁合金板材在变形温度为483 K时经过3个道次的等温双向循环弯曲变形后,基面织构得到明显弱化,织构强度由原始9.59降低到变形后3.54,平均晶粒尺寸为12.2μm。在变形温度443 K,经过1个道次变形后,AZ31镁合金板材的抗拉强度为325 MPa,屈服强度为225 MPa。与原始坯料力能参数相比,抗拉强度提高了19%,屈服强度提高了28%。当变形温度483 K循环变形3道次时,材料的伸长率为17.1%,比原始材料提高了42%。     

等通道角挤压制备超细晶纯Ti的腐蚀性能研究

通过等通道角挤压(ECAP)的方法制备了超细晶纯Ti,利用EBSD技术研究了2～4道次样品晶粒尺寸、基面织构强度和大小角度晶界的变化规律。同时,采用动电位极化和EIS的方法研究不同晶粒尺寸样品的耐模拟海水腐蚀性能。结果表明:经过2道次ECAP,原始粗晶纯Ti的晶粒尺寸和基面织构强度减小,小角度晶界分数急剧增加。随着挤压道次的增加,纯Ti的晶粒尺寸继续减小,基面织构强度先增大后减少,小角度晶界分数逐渐降低。相比于原始粗晶纯Ti,所有ECAP制备的超细晶纯Ti的腐蚀电流密度和腐蚀速率明显降低,极化电阻增大,表现出更加优异的耐海水腐蚀性能。另一方面,随着ECAP道次的增加,纯Ti的耐海水腐蚀性能并不是呈单调增加的关系,3道次试样的耐腐蚀性能最优,这主要归因于晶粒尺寸、基面织构和晶界特征分布的耦合影响,其中基面织构强度的影响占据主导地位。     

Dynamic recrystallization and texture development during hot deformation of magnesium alloy AZ31

The dynamic recrystallization(DRX) and texture development, taking place during hot deformation of magnesium alloy AZ31 with a strong wire texture, were studied in compression at 673 K (0.73 Tm). Two kinds of samples were machined parallelly to the extruded and transverse directions of Mg alloy rods. New fine grains are evolved at original grain boundaries corrugated at low strains and develop rapidly in the medium range of strain, finally leading to a roughly full evolution of equiaxial fine grains. Kink bands are evolved at grain boundaries corrugated and also frequently in grain interiors at low strains. The boundary misorientations of kink band increase rapidly with increasing strain and approach a saturation value in high strain. The average size of the regions fragmented by kink band is almost the same as that of new grains evolved in high strain. These characteristics of new grain evolution process are not changed by the orientation of the samples, while the flow behaviors clearly depend on it. It is concluded that new grain evolution can be controlled by a deformation-induced continuous reaction, i.e. continuous dynamic recrystallization(DRX). The latter is discussed by comparing with conventional, i.e. discontinuous DRX.     

120°模具室温ECAP制备工业纯钛的热压缩变形行为

在Gleeble-1500热模拟机上对室温120°模具等径弯曲通道变形(ECAP)制备的平均晶粒尺寸为200nm的工业纯钛(CP-Ti)进行等温变速压缩实验,研究超细晶(UFG)工业纯钛在变形温度为298～673K和应变速率为10-3～100s-1条件下的流变行为。利用透射电子显微镜分析超细晶工业纯钛在不同变形条件下的组织演化规律。结果表明:流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳;峰值应力随温度的升高而减小,随应变速率的增大而增大;随变形温度的升高和应变速率的降低,应变速率敏感性指数m增加,晶粒粗化,亚晶尺寸增大,再结晶晶粒数量逐渐增加;超细晶工业纯钛热压缩变形的主要软化机制随变形温度的升高和应变速率的降低由动态回复逐步转变为动态再结晶。     

120°模具室温ECAP制备工业纯钛的压缩变形本构关系

在Gleeble-1500热模拟机上对120°模具室温Bc方式ECAP变形8道次制备的平均晶粒尺寸约为200 nm的工业纯钛进行等温变速压缩实验,研究超细晶工业纯钛在变形温度为298~673 K和应变速率为1×10-4~1×100s-1条件下的流变应力行为。结果表明:变形温度和应变速率均对流变应力具有显著影响,峰值应力随变形温度的升高和应变速率的降低而降低;流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳,呈现稳态流变特征。采用双曲正弦模型确定了超细晶工业纯钛的变形激活能Q=104.46 kJ/mol和应力指数n=23,建立了相应的变形本构关系。     

Effects of dynamic recrystallization in extruded and compressed AZ31 magnesium alloy

Commercial AZ31 billets were extruded to round rods at three extrusion velocities of 0.8~m/min, 1.4 m/min and 2.2 m/min, at 643 K, 673 K and 703 K, respectively. The microstructure and texture evolution at different conditions were investigated by optical microscopy (OM) and electron backscattered diffraction (EBSD) techniques. The average grain size is reduced significantly after the hot extrusion, and the microstructure is obviously inhomogeneous due to dynamic recrystallization, which is confirmed by uni-axial compression experiments at elevated temperatures with different strain rates. The uni-axial compression leads to a fibre texture, and {1120}<0110> texture is the major texture in extruded rods due to non-basal slip. As the extrusion temperature is elevated, the main texture becomes weak and other texture components appear.     

Microstructural evolution,flow stress and constitutive modeling of Al−1.88Mg−0.18Sc−0.084Er alloy during hot compression

To explore the hot compression behavior and microstructural evolution, fine-grained Al?1.88Mg?0.18Sc? 0.084Er (wt.%) aluminum alloy wires were fabricated with Castex (continuous casting?extrusion) and ECAP-Conform, and their hot compression behavior was investigated at temperatures of 673?793 K and strain rates of 0.001?10 s^?1; the microstructures were characterized by optical microscope, X-ray diffractometer, transmission electron microscope, and electron backscattered diffractometer, and the flow stresses were obtained by thermal compression simulator. Microstructural evolution and flow curves reveal that dynamic recovery is the dominant softening mechanism. Continuous dynamic recrystallization followed by dynamic grain growth takes place at a temperature of 773 K and a strain rate of 0.001 s^?1; the yielding drop phenomenon was discovered. Hyperbolic sine constitutive equation incorporating dislocation variables was presented, and a power law constitutive equation was established. The stress exponent is 3.262, and the activation energy for deformation is 154.465 kJ/mol, indicating that dislocation viscous glide is the dominant deformation mechanism.     

Dynamic recrystallization behavior of AZ61 magnesium alloy

An AZ61 alloy was subjected to hot compression at temperatures ranging from 523 K to 673 K, with strain rates of 0. 001 - 1 s^-1. Flow softening occurs at all temperatures and strain rates. There are peak and plateau stresses on flow curves. The initiation and evolution of dynamic recrystallization（DRX） were studied by the flow softening mechanism based on the flow curves and microstructural observations. A linear relationship was established between the logarithmic value of the critical strain for DRX initiation（lnεc） and the logarithmic value of the Zener-Hollomon parameter （lnZ）. The volume fraction of DRX grain （φd） is formulated as a function of the process parameters including strain rate, temperature, and strain. The calculated values of φd agree well with the values extracted from the flow curves. The size of DRX grain（d） was also formulated as a function of the Zener- Hollomon parameter. This study suggests that DRX behavior of AZ61 can be predicated from plastic process parameters.     

18.7Cr-1.0Ni-5.8Mn-0.2N节Ni型双相不锈钢的大变形热压缩软化行为

在1123~1423 K、0.1~10 s^-1条件下对18.7Cr-1.0Ni-5.8Mn-0.2N节Ni型双相不锈钢进行70%大变形量热压缩研究。利用OM、SEM和EBSD分析热变形组织。结果表明,铁素体动态再结晶(DRX)主要发生在1123 K较低变形温度,随应变速率增大,晶粒细化程度增加,晶粒不均匀程度减小。应变速率对铁素体DRX影响较大,而奥氏体DRX对变形温度更加敏感。在1223 K、10 s^-1条件下,铁素体相发生了以小角度晶界(LAGB)向大角度晶界(HAGB)转变的连续动态再结晶(CDRX),而在1323 K、0.1 s^-1条件下,奥氏体相以不连续动态再结晶(DDRX)为主。低应变速率条件下升高温度易诱发DDRX,而在高应变速率条件下易发生CDRX。在高温低应变条件下,奥氏体相晶粒取向主要为(001)和(111)再结晶织构,而铁素体相在(001)和(111)织构之间存在竞争关系。拟合获得临界应力(应变)并确定了其与峰值应力(应变)的关系。随着应变增加,热加工失稳区缩小,且稳定区逐渐向高温高应变速率方向移动,1323~1423 K、0.01~6.05 s^-1的热参数条件最适合热加工。     

AZ31B镁合金板材中晶界滑移的晶体塑性仿真

建立一种耦合滑移、动态再结晶以及晶界滑移的晶体塑性模型以仿真镁合金的高温变形行为及织构演化.首先,通过实验测量单轴拉伸、压缩后的织构以及显微组织演化,研究AZ31B镁合金在300°C的变形机制.结果发现,动态再结晶在应变小于0.2时起到细化晶粒的作用,之后晶界滑移在变形过程中起显著作用.此外,建立晶界滑移模型来评估由晶...     

Temperature dependence of microstructure and texture in cold drawn aluminum wire

The effect of strain and drawing temperature on the evolution of microstructure and fiber textures of aluminum wires drawn at room temperature and cryogenic temperature was investigated by TEM and EBSD observations. The results show that low angle boundaries frequency increases and high angle boundaries frequency decreases with strain increasing when the strain is low. At high strain, most of grain and dislocation boundaries are parallel to the drawn direction and low angle boundaries frequency decreases and high angle boundaries frequency increases with strain increasing. The decrease of deformation temperature leads to microstructure finer and low angle boundaries frequency increasing. Texture analysis indicates that volume fraction of complex texture component decreases with strain increasing and a mixture of 〈111〉 and 〈100〉 fiber texture forms at high strain. 〈111〉 is stable at low strains but 〈100〉 becomes stable at high strain. The decrease of temperature can enhance the stability of 〈111〉 orientation at high strain.     

Effect of Initial Grain Size on the Hot Deformation Behavior and Microstructural Evolution of Pure Copper

The influences of initial grain size (IGS) with 20 µm and 50 µm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623-1073 K and strain rate range of 0.001-0.1 s^-1. The effects of critical stress and corresponding critical strain were studied based on the internal and external processing parameters. The critical stress and strain decreased with increasing temperature and decreasing strain rate. The investigation results of the microstructure and true strain-stress diagrams showed that dynamic recovery, dynamic recrystallization (DRX), and twinning mechanisms were caused during the hot deformation of pure copper. Microstructure evolution indicated some DRXed fine-grain took place around grain boundary of hot deformed samples with IGS of 20 µm whereas DRXed fine-grain took place in interior grains for samples with larger IGS. The results also showed that grain growth is also dependent on IGS as the grain growth rate for samples with the larger IGS is greater than the smaller IGS. The critical strain rate and the temperature were obtained at 0.01 s^-1 and 973 K, respectively, for the sudden change in the grain growth rate. Also, twinning highly depended on IGS which almost did not happen in fine grain size while the volume fraction of twinning increased with increasing grain size.