短切碳纤维/AZ91D镁合金复合材料高温变形动态再结晶行为

在变形温度为340~400℃、应变速率为0.001~0.1 s^-1、最大真应变为0.7的条件下,采用等温压缩实验研究了短切碳纤维（CF_s）/AZ91D复合材料和AZ91D镁合金的动态再结晶行为。结果表明：CF_s/AZ91D复合材料和AZ91D镁合金在高温压缩过程中均发生了显著的动态再结晶;CF_s极大地促进了AZ91D基体的动态再结晶过程,减小了动态再结晶临界应变并细化了再结晶晶粒组织;AZ91D镁合金动态再结晶体积分数随应变量增加表现为典型的"S"型变化曲线,而CF_s/AZ91D复合材料则呈现出快速增长-缓慢增长-趋于平稳的非线性变化规律。根据实验结果分别建立了CF_s/AZ91D复合材料和AZ91D镁合金的动态再结晶临界应变模型和动力学模型,在此基础上分析了二者高温变形动态再结晶行为的差异。     

SiCW/ AZ91 镁基复合材料及AZ91镁合金的高温变形行为

利用Gleeble-1500 对SiC_W/ AZ91 复合材料和AZ91 镁合金在温度为423～723 K、应变速率为0.002～0.25s-1 、最大应变量为60 %的条件下进行高温压缩变形行为的研究。测试了其真应力-应变曲线, 观察了变形后的显微组织。结果表明: 晶须的转动和折断导致复合材料的应变软化现象较合金明显; 复合材料和合金的应变速率敏感指数(m) 和表观激活能(Q) 均随温度的升高而增大; 晶须的加入细化了晶粒, 使复合材料的m 值比合金高; 同时晶须的加入也限制了位错交滑移和晶界的迁移, 因此复合材料的Q 值比合金高; 压缩变形过程中, 合金和复合材料发生了动态回复和动态再结晶。      

漂珠/AZ91D镁合金复合材料的高温压缩变形行为

采用搅拌铸造法制备了漂珠(FAC)/AZ91D镁合金复合材料。研究了该复合材料的高温压缩变形行为,分析了压缩变形温度和应变率对FAC/AZ91D镁合金复合材料压缩变形行为的影响规律,并计算了其热变形激活能。结果表明:FAC/AZ91D镁合金复合材料的高温压缩真应力-真应变曲线分为4个阶段:弹性变形、加工硬化、峰值应力和稳态流变阶段。相同应变率下,FAC/AZ91D镁合金复合材料的峰值应力和稳态流变应力随压缩变形温度的升高而降低;相同压缩变形温度下,流变应力随应变率增大而升高。在相同应变率或相同压缩变形温度下,FAC/AZ91D镁合金复合材料的热变形激活能随压缩应变率或压缩变形温度的升高而增大,其热压缩行为可以用双曲正弦函数形式的Arrhenius关系来描述。压缩变形温度与应变率对FAC/AZ91D镁合金复合材料的高温压缩组织均有重要影响。提高压缩变形温度或增大应变率,均可加速动态再结晶的进程。     

SiCw/AZ91复合材料及AZ91镁合金的高温压缩变形的研究

利用GPL-1500热模拟试验机对SiCw/AZ91复合材料和AZ91镁合金在不同温度及不同应变速率条件下进行高温压缩试验。根据压缩的真应力-应变曲线计算出合金和复合材料的应变速率敏感指数（m)和表观激活能（Q）。结合金的m值。另外，复合材料和镁合金的表观激活能也随温度和应变速率的改变而发生变化。表明在不同条件下压缩时，复合材料和镁合金的高温压缩变形机制也发生变化。     

搅拌铸造法制备短碳纤维/AZ91复合材料的组织与性能

采用搅拌铸造法制备了不同体积分数（10vol%、15vol%、20vol%）的短碳纤维增强镁基（CF_s/AZ91）复合材料,并选取了三个挤压比和两个挤压温度对其进行热挤压变形,采用光学显微镜（OM）、SEM和TEM对CF_s/AZ91复合材料的显微组织进行了观察,并测试其室温力学性能及阻尼性能。研究结果表明,热挤压能够有效降低CF_s/AZ91复合材料气孔率;在热挤压过程中,纤维沿挤压方向定向排列,同时基体发生动态再结晶。随着挤压温度及挤压比的增大,晶粒呈现等轴状,组织更加均匀。CF_s/AZ91复合材料经过挤压后,其力学性能得到提高,屈服强度和抗拉强度随挤压比和CF_s体积分数的增大而增大,然而CF_s纤维在热挤压后发生明显断裂,限制了挤压态复合材料强度的进一步提升。低温低挤压比条件下,CF_s/AZ91复合材料具有较好的阻尼性能,随着挤压比及挤压温度的升高,CF_s/AZ91复合材料室温及高温阻尼性能均有所降低。      

粉煤灰漂珠粒径对粉煤灰漂珠/AZ91D镁合金复合材料阻尼性能的影响

通过搅拌铸造法向半固态AZ91D镁合金中添加粉煤灰漂珠（FAC）制备了FAC/AZ91D镁合金复合材料,研究了FAC粒径对该复合材料阻尼性能的影响。结果表明:FAC/AZ91D镁合金复合材料的阻尼性能明显优于基体材料,在FAC含量相同时,FAC的粒径越大,其阻尼性能越好。室温下FAC对提高FAC/AZ91D镁合金复合材料的阻尼性能起重要作用,FAC附近的基体产生了高密度的位错,形成了塑性区。室温下FAC粒径越大,在其附近产生的塑性区越大,阻尼性能越好。随温度的升高,FAC/AZ91D镁合金复合材料的阻尼性能迅速提高。位错、晶界以及FAC和基体之间的界面运动是提高阻尼性能的关键。      

真空热压烧结制备10vol%TiC/Cu-Al_2O_3复合材料及热变形行为研究

在VDBF-250真空热压烧结炉中,采用真空热压烧结工艺制备了10%(体积分数)TiC/Cu-Al2O3复合材料。利用Gleeble-1500热力模拟实验机,在温度为450~850℃、应变速率为0.001~1s-1、真应变量0.7的条件下,对10%(体积分数)TiC/Cu-Al2O3复合材料高温塑性变形过程中的动态再结晶行为及其热加工图进行研究和分析。结果表明,该材料烧结态致密度为98.53%,显微硬度为158 HV,导电率为48.7%IACS;材料的高温流变应力-应变曲线主要以动态再结晶软化机制为特征,峰值应力随变形温度的降低或应变速率的升高而增加,属于温度和应变速率敏感材料;同时,利用10%(体积分数)TiC/Cu-Al2O3复合材料DMM加工图分析了其变形机制和失稳机制,并最终确定了热加工工艺参数选取范围为变形温度750~850℃,应变速率0.01~0.1s-1。     

Mg_2Si/AZ91D复合材料阻尼性能

以AZ91D镁合金为基体,采用搅熔铸造法将球磨后的粉煤灰漂珠颗粒加入到熔融态基体中,设置球磨漂珠质量分数(2%、6%和10%)和搅拌时间(3min和6min),成功制备了Mg2Si/AZ91D复合材料。采用金相分析、XRD分析和动态机械热分析等方法研究了铸态和固溶态Mg2Si/AZ91D复合材料的显微组织、成分及阻尼性能。研究表明:与AZ91D镁合金相比,加入球磨漂珠颗粒后制备的Mg2Si/AZ91D复合材料中生成了Mg2Si相,而且随着漂珠质量分数的增加,Mg2Si相呈现不规则形状,固溶后Mg2Si相呈现均匀块状。随着漂珠质量分数的增加,Mg2Si/AZ91D复合材料的阻尼性能越好,搅拌时间6min制备的复合材料阻尼性能高于搅拌时间3min制备的复合材料的阻尼性能,并且固溶态的阻尼性能优于铸态。在室温下,Mg2Si/AZ91D复合材料阻尼性能可用位错理论来解释。     

等通道角挤压AZ91D镁合金热压缩变形行为

在应变速率为0.005~1 s~(-1)、温度200~275℃条件下,利用Instron-5500热模拟机,对经过等通道角挤压(Equal Channel Angular Extrusion,ECAE)后的AZ91D镁合金的高温压缩特性进行了研究,得到了ECAE-ed态AZ91D镁合金真实应力-应变曲线,分析了挤压温度、应变速率等对其的影响,得出本构方程的一系列常量,建立了ECAE-ed态AZ91D镁合金在高温压缩中的本构方程关系式,并与铸态AZ91D镁合金进行了对比。结果表明:热压缩过程中,ECAE-ed态AZ91D镁合金与铸态一样,流动应力随温度的升高而降低,随应变速率的升高而升高;流动应力也可以用双曲正弦函数来描述,且双曲正弦值随Zener-Hollomon参数的自然对数的升高呈线性升高;两者同为正应变速率敏感材料,但ECAE-ed态AZ91D镁合金要比铸态应变速率敏感性小,其指数从铸态的m=0.14下降为0.096,变形激活能从182.65 kJ/mol上升为227.14 kJ/mol。研究结果对AZ91D镁合金进一步塑性成形和应用具有指导意义。     

SiCp/AZ91D镁基纳米复合材料的室温拉伸行为及塑性变形机理

为得到高强度和高塑性的镁基复合材料,通过高能超声分散法和金属型重力铸造工艺制备了SiC纳米颗粒分散均匀的SiCp/AZ91D镁基纳米复合材料,并进行T4固溶热处理和室温拉伸。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)对试样拉伸后的显微组织和塑性变形机理进行观察与研究。结果表明:T4态SiCp/AZ91D镁基纳米复合材料室温下抗拉强度达到296 MPa,伸长率达到17.3%。经室温拉伸变形后复合材料基体微观组织中出现了大量的孪晶和滑移,孪生和滑移是复合材料塑形变形的主要机制。在室温拉伸过程中,α-Mg基体中SiC纳米颗粒周围形成高应变场,高应变场内形成大量位错和堆垛层错,这些位错和堆垛层错在拉伸应变的作用下演变成大量的滑移带和孪晶,这是SiCp/AZ91D镁基纳米复合材料在室温下具有高塑性的微观塑性变形机理。     

新型铝奥氏体耐热合金的高温塑性变形行为和热力工性能

新型含铝奥氏体耐热合金(AFA)进行压缩热模拟试验,使用OM和EBSD等手段研究了这种合金在950~1150℃和0.01~5 s^-1条件下的微观组织演变、建立了基于动态材料模型热加工图、分析了变形参数对合金加工性能的影响并按照不同区域组织变形的特征构建了合金的热变形机理图。结果表明：新型AFA合金的高温流变应力受到变形温度和应变速率的显著影响。在变形温度为950~1150℃和应变速率为0.18~10 s^-1条件下,这种合金易发生流变失稳。在变形温度为1050~1120℃、应变速率0.01~0.1 s^-1和变形温度1120~1150℃、应变速率10^-0.5~10^-1.5 s^-1这两个区间,这种合金发生完全动态再结晶行为且其再结晶晶粒均匀细小,功率耗散因子η达到峰值45%。新型AFA合金的热加工艺,应该优先选择再结晶区域。     

18.5%Cr高Mn型节镍双相不锈钢大变形热压缩的组织和再结晶行为

使用热模拟试验机在1123~1423 K/0.01~10 s^-1变形条件下对18.5%对Cr高Mn节镍型双相不锈钢进行了变形量为70%的大变形热压缩,研究其在热变形过程中两相的亚结构特征和软化机理。结果表明,在0.01~0.1 s^-1/1123~1223 K范围的热压缩软化以铁素体相的再结晶为主,而在0.1 s^-1/1323~1423 K和10 s^-1/1223 K范围的热压缩软化以奥氏体相的再结晶为主。在变形温度为1223 K、应变速率由0.01 s^-1增大到10 s^-1的条件下铁素体相内的位错缠结向胞状结构演化并出现位错线,奥氏体相内的亚结构则转变为细小的再结晶晶粒。应变速率为0.1 s^-1、变形温度由1123 K提高到1323 K时铁素体相内的位错增加,变形晶粒向胞状组织演化而奥氏体相内的位错减少,由回复组织转变为再结晶组织。根据热变形方程计算出表观应力指数n=7.13,热变形激活能Q=514.29 kJ/mol,并建立了Z参数关系本构方程。根据加工硬化率得到再结晶临界条件,并确定了Z参数与再结晶临界条件的关系。对热加工图的分析结果表明,随着变形量的增大失稳区逐渐减小,最佳加工区域为1348~1423 K/1~10 s^-1,功率耗散系数大于0.4。     

Compressive Creep Behavior of TiC/AZ91D Magnesium-matrix Composites with Interpenetrating Networks

The 42.1 vol. pct TiC/AZ91D magnesium-matrix composites with interpenetrating networks were fabricated by in-situ reactive infiltration process. The compressive creep behavior of as-synthesized composites was investigated at temperature ranging from 673 to 723 K under loads of 95-108 MPa. For a comparative purpose,the creep behavior of the monolithic matrix alloy AZ91D was also conducted under loads of 15-55 MPa at 548-598 K. The creep mechanisms were theoretically analyzed based on the power-law relation. The results showed that the creep rates of both TiC/AZ91D composites and AZ91D alloy increase with increasing the temperature and load. The TiC/AZ91D composites possess superior creep resistance as compared with the AZ91D alloy. At deformation temperature below 573 K, the stress exponent n of AZ91D alloy approaches theoretical value of 5, which suggests that the creep process is controlled by dislocation climb. At 598 K, the stress exponentof AZ91D is close to 3, in which viscous non-basal slip deformation plays a key role in the process of creep deformation. However, the case differs from that of AZ91D alloy when the stress exponent n of TiC/AZ91D composites exceeds 9, which shows that there exists threshold stress in the creep process of the composites, similar to other types of composites. The average activation energies for the creep of the AZ91D alloy and TiC/AZ91D composites were calculated to be 144 and 152 k J/mol, respectively. The existence of threshold stress in the creep process of the composites leads to an increase in activation energy for creep.     

新型Al-Zn-Mg-Sc-Er-Zr合金的热变形行为EI北大核心CSCD

采用Gleeble-3800热模拟机研究Al-8.9Zn-1.3Mg-0.1Sc-0.1Er-0.1Zr铝合金的热变形行为,构建温度380~440℃、应变速率0.01~10 s^(-1)区间内合金的热加工图,使用X射线衍射(XRD)、选区电子衍射(SAED)与能谱(EDS)对合金中存在的物相进行分析,并使用金相显微镜(OM)和透射电子显微镜(TEM)观察合金热变形后的微观组织。结果表明:合金的最佳热加工工艺参数区间为:400℃相似文献   

锻态TB6钛合金β相区压缩变形行为和动态再结晶

使用圆柱形试样在Thermecmaster-Z型热模拟试验机上进行锻态TB6钛合金β相区的热压缩实验(变形温度950~1100℃,应变速率0.001~1 s^-1),研究了合金的高温压缩变形和动态再结晶行为。结果表明,这种合金在β相区的变形激活能为246.7 kJ/mol,其热变形机制是动态再结晶,动态再结晶新晶粒的主要形核机制是弓弯形核。当应变速率为0.01~0.1 s^-1、变形温度为<1000℃时动态再结晶的发展比较充分,变形组织明显细化;当变形温度高于1000℃、应变速率低于0.001 s^-1时,动态再结晶的晶粒明显粗化。在动态再结晶的晶粒尺寸D与Z参数之间存在着相关性,其函数关系为D=6.44×10²·Z^-0.1628。     

Modeling high-temperature tensile deformation behavior of AZ31B magnesium alloy considering strain effects

The hot tensile deformation behaviors of AZ31B magnesium alloy are investigated over wide ranges of forming temperature and strain rate. Considering the effects of strain on material constants, a comprehensive constitutive model is applied to describe the relationships of flow stress, strain rate and forming temperature for AZ31B magnesium alloy. The results show that: (1) The effects of forming temperature and strain rate on the flow behaviors of AZ31B magnesium alloy are significant. The true stress–true strain curves exhibit a peak stress at small strains, after which the flow stress decreases until large strain, showing an obvious dynamic softening behavior. A considerable strain hardening stage with a uniform macroscopic deformation appears under the temperatures of 523 and 573 K. The strain hardening exponent (n) increases with the increase of strain rate or the decrease of forming temperature. There are not obvious strain-hardening stages when the forming temperature is relatively high, which indicates that the dynamic recrystallization (DRX) occurs under the high forming temperature, and the balance of strain hardening and DRX softening is easy to obtain. (2) The predicted stress–strain values by the established model well agree with experimental results, which confirm that the established constitutive equation can give an accurate and precise estimate of the flow stress for AZ31B magnesium alloy.     

Hot deformation behavior and processing map development of AZ110 alloy with and without addition of La-rich Mish Metal

In order to compare the workability of AZ110 alloy with and without addition of La-rich Mish Metal(MM), hot compression tests were performed on a Gleeble-3500 D thermo-mechanical simulator at the deformation temperature range of 473-623 K and strain rate range of 0.001-1 s-1. The flow stress, constitutive relation, DRX kinetic model, processing map and microstructure characterization of the alloys were investigated. The results show that the flow stress is very sensitive to deformation temperature and strain rate, and the peak stress of AZ110 LC(LC = La-rich MM) alloy is higher than that of AZ110 alloy.The hot deformation behavior of the alloys can be accurately predicted by the constitutive relations. The derived constitutive equations show that the calculated activation energy Q and stress exponent n for AZ110 alloy are higher than the calculated values of AZ110 LC alloy. The analysis of DRX kinetic models show that the development of DRX in AZ110 LC alloy is earlier than AZ110 alloy at the same deformation condition. The processing maps show that the workability of AZ110 LC alloy is significantly more excellent than AZ110 alloy and the microstructures are in good agreement with the calculated results.The AZ110 LC alloys can obtain complete DRX microstructure at high strain rate due to its higher stored energy and weak basal texture.